High solids carboxymethylcellulose solution

Abstract

The present invention relates to a method for producing a carboxymethyl cellulose (CMC) solution, the method comprising the following steps: a) obtaining an aqueous solution containing at least one low molecular weight CMC having a weight average molecular weight of less than 30 kDa; and b) dissolving at least one high molecular weight CMC having a weight average molecular weight of at least 30 kDa in the solution of step a), wherein at least one high molecular weight CMC is added as a solid (preferably as a powder) to the solution of step a), wherein the amounts of the low molecular weight CMC and the high molecular weight CMC added in steps a) and b) respectively are such that the total amount of CMC in the solution is at least 18% by weight (relative to the total weight of the CMC solution).

Description

[Technical Field]

[0001] The present invention relates to a high-solids content carboxymethylcellulose solution and a method for preparing the same. [Background technology]

[0002] Cellulose ethers, such as carboxymethylcellulose (CMC), are typically supplied to end users in powder form. However, since cellulose ethers are usually required in aqueous solution form, the powder generally needs to be dissolved in water before use. Dissolving powder in water can be cost-ineffective for end users. If cellulose ethers could be supplied in a pre-dissolved, high-solids-content form, it would provide these end users with a more cost-competitive and sustainable alternative.

[0003] Due to its ability to impart rheological properties, improve water retention, enhance the efficiency of fluorescent whitening agents, and provide strength, CMC is a popular additive, particularly in the paper and cardboard industry for coating, sizing, and base web manufacturing. In paper and cardboard coating processes, CMC is added to coating makedown compositions as a pre-dissolved solution (typically containing 6-12% by weight of CMC), which usually includes inorganic pigments, organic binders, and additives such as dispersants, fluorescent whitening agents, crosslinking agents, lubricants, and dyes. CMC can also be used as or to produce surface treatment materials, such as barrier materials. Barrier materials containing CMC can provide oil and grease resistance, oxygen resistance, or both. Common film coating techniques used to form barrier layers in film form include sizing presses, weighing sizing presses, and various coating techniques. For each of these techniques, the viscosity and / or solids content of the polymer solution used plays a crucial role. While we do not wish to be bound by any theory, a uniform barrier layer is thought to result from a sufficiently high coat weight, good film retention, or both. These properties can be more easily obtained by fabricating the barrier material with a higher concentration of CMC solution. Higher concentrations of CMC in solution are often achieved by decomposing the CMC using various techniques. However, in these techniques, the molecular weight of CMC typically decreases very rapidly, so the resulting barrier layer does not have very good film retention, does not penetrate the base web, and therefore does not provide the required barrier properties.

[0004] Existing pre-dissolved CMC solutions with low solids concentrations generally do not allow for the formulation of coating compositions with high solids content, typically limiting the amount of cellulose ether that can be used in coating compositions required for paper coatings. While these problems can be solved by dry addition of cellulose ether to high-solids pigment slurries, the factory needs to have a handling system for the powder, sufficient manpower to add the powder by hand, or a mixing system that can provide sufficient shear force to disperse the powder throughout the solution.

[0005] Typically, it is difficult to obtain cellulose ether solution solids higher than 15% by weight, especially CMC solutions, without negatively impacting the pumpability of the cellulose ether solution and maintaining performance. This is particularly true for high molecular weight cellulose ethers, as they generally produce more viscous solutions. The low shear viscosity limit for good pumpability with frequently used centrifugal pumps is considered to be about 5000 mPas (measured with a Brookfield RV 100) at a typical process (pumping) temperature of about 25–60°C. High concentrations of high Mw cellulose ether solutions tend to have viscosities far exceeding these operating requirements, which significantly lowers the upper limit concentration of high Mw cellulose ether solutions.

[0006] Therefore, obtaining a high-solids cellulose ether solution that contains an increased amount of high-molecular-weight cellulose ether (for improved performance) while maintaining low shear and low viscosity (for improved processability) is not a simple task.

[0007] Solutions for providing stable concentrated aqueous CMC suspensions have been previously proposed. For example, U.S. Patent No. 4,883,537 describes a reduced viscosity CMC solution containing at least 33% by weight of potassium carbonate. However, the high concentration of potassium carbonate required may limit the usefulness of these solutions in applications, making these compositions less attractive / undesirable for high CMC solids applications.

[0008] International Publication No. 2009 / 061821 discloses a method for producing a low viscosity cellulose ether composition using a combination of ultra-low molecular weight cellulose ether and a plasticizer.

[0009] International Publication No. 2013 / 057132 discloses methods for increasing the solid content of CMC in low-viscosity compositions. These methods have been found to enable increasing the solid content of CMC solutions to up to approximately 24% by weight while maintaining the pumpability of the solution. However, in practice, these levels could only be achieved with low molecular weight cellulose ethers, which provided limited performance as coating thickeners or barriers. Furthermore, CMC solutions prepared according to the methods of International Publication No. 2013 / 057132 required the solution to have a pH of 7.5–11, which has been found to reduce the shelf life of the CMC solution if it contains impurities.

[0010] U.S. Patent No. 5080717 discloses aqueous fluid suspensions of polysaccharide mixtures in paper coating compositions. These suspensions required stabilizers (e.g., xanthan gums). The suspensions can be problematic because they tend to settle into suspended solids (e.g., forming aggregates, resulting in a heterogeneous product with unevenly distributed suspended solids). This can also negatively affect the application characteristics of the aforementioned suspensions (e.g., uneven distribution of the active substance), so the products of U.S. Patent No. 5080717 still need to be dissolved before use. Solutions, on the other hand, do not face this problem (i.e., the solute is uniformly distributed in a homogeneous aqueous phase). Therefore, cellulose ether solutions are much easier to handle and produce more consistent results when used in the aforementioned applications.

[0011] There is still a need for methods to prepare low-viscosity carboxymethylcellulose solutions with increased amounts of high molecular weight carboxymethylcellulose. If CMC could be supplied in ready-made solutions with high solids content, particularly high solids content of high molecular weight CMC, it would provide an improved product while offering a more cost-effective and sustainable alternative for end-users. [Overview of the project]

[0012] The inventors have developed a simple but highly effective method for preparing a carboxymethylcellulose (CMC) solution that satisfies this need. Therefore, in a first aspect, the present disclosure provides a method for producing a high-solids-content, low-viscosity CMC solution, the method comprising the following steps: a) A step of obtaining an aqueous solution containing at least one low molecular weight CMC having a weight-average molecular weight of less than 30 kDa, b) A step of dissolving at least one high molecular weight CMC having a weight-average molecular weight of at least 30 kDa in the solution of step a), wherein the at least one high molecular weight CMC is added to the solution of step a) as a solid (preferably as a powder). The present invention relates to a method comprising, wherein the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and b), respectively, are such that the total amount of CMC in the solution is at least 18% by weight, preferably at least 20% by weight, preferably at least 25% by weight, preferably at least 28% by weight, and most preferably at least 30% by weight (in all cases, the weight percentage is a relative amount to the total weight of the CMC solution). In a further optional step, the CMC content (by weight) can be adjusted to a desired value by adding water to the CMC solution.

[0013] A surprising finding was that by adding high molecular weight CMC as a solid, preferably in powder form, to an aqueous solution of low molecular weight CMC in step a), the total amount of high molecular weight CMC in the solution could be significantly increased without the need for stabilizers and, unexpectedly, while maintaining a low viscosity solution (≤5000 mPas). This novel method of combining two different CMCs results in a higher total solids content of the CMC, while also providing a significantly improved rheological profile for such a high solids CMC solution compared to CMC solutions produced by conventional methods.

[0014] High molecular weight CMC in solid form, preferably in powder form, may contain a considerable amount of residual moisture (e.g., hydration water or similar) when in solid form. Solid (preferably in powder form) high molecular weight CMC has a total moisture content of less than 60% by weight, preferably less than 50% by weight, and more preferably less than 40% by weight (relative to the total weight of the solid high molecular weight CMC).

[0015] The solid (preferably in powder form) high molecular weight CMC used in the above method is preferably substantially dry (i.e., subjected to a drying step before use in step b). As used herein, the “substantially dry” solid (preferably in powder form) high molecular weight CMC has a total moisture content of 15% by weight or less, preferably 10% by weight or less (in either case, the weight percent is relative to the total weight of the substantially dry solid—preferably in powder form—high molecular weight CMC).

[0016] The weight-average molecular weight of at least one low molecular weight CMC is preferably less than 20 kDa, more preferably less than 15 kDa.

[0017] The weight-average molecular weight of at least one high molecular weight CMC may be at least 40 kDa, at least 50 kDa, at least 75 kDa, or at least 100 kDa.

[0018] The "weight-average molecular weight" used in this specification was determined using a Malvern Omnisec gel permeation chromatography system equipped with a multi-detector module and a Viscotek ALS6000Mx2 (13 μm, 300 * 8.0 mm) column. The column temperature was 35 °C. The eluent used was an aqueous 0.1 M sodium nitrate solution containing 10% (V / V) methanol at a flow rate of 0.8 ml / min. The single sample injection volume was 100 μl, and the sample concentration was 1 mg / ml. The molar mass was determined as the average of three injections from each separate sample vial. The measurement was calibrated using a pullulan standard (Mw 113 kDa, PDI 1.13, Polymer Standards Service). The data was processed with Omnisec 5-software.

[0019] To avoid misunderstanding, the total amount of CMC in the CMC solution is the weight percentage of CMC in the solution (i.e., the weight % of CMC relative to the total weight of the CMC solution). The total amount of CMC in the CMC solution can be easily determined and easily controlled by those skilled in the art using routine techniques.

[0020] Preferably, the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and b) respectively are such that the total amount of CMC in the CMC solution is at least 20% by weight, preferably at least 25% by weight, preferably at least 28% by weight, most preferably at least 30% by weight, for example 30 - 40% by weight (in each case, the % by weight is the relative amount with respect to the total weight of the CMC solution). In a preferred embodiment, the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and b) respectively are such that the total amount of CMC in the CMC solution is about 18 - 50% by weight, preferably about 20 - 50% by weight, more preferably about 20 - 40% by weight, more preferably about 30 - 40% by weight (all are relative amounts with respect to the total weight of the CMC solution).

[0021] Preferably, the amounts of the low molecular weight CMC and the high molecular weight CMC added in steps a) and b) respectively are such that the total amount of the low molecular weight CMC in the final solution is at least about 15% by weight, preferably at least about 18% by weight, more preferably at least about 20% by weight, and the total amount of the high molecular weight CMC in the final solution is at least 5% by weight, more preferably at least about 8% by weight, more preferably at least about 10% by weight, more preferably at least about 15% by weight (both are relative amounts to the total weight of the CMC solution).

[0022] Preferably, the weight ratio of the low molecular weight CMC to the high molecular weight CMC in the CMC solution (low Mw: high Mw) is from about 3:7 to 9:1, preferably from about 1:2 to 5:1, more preferably from about 1:2 to 4:1, and most preferably from about 1:1 to 4:1.

[0023] In a preferred embodiment, the total amount of CMC in the CMC solution is 20 - 50% by weight, the amount of the low molecular weight CMC is about 15 - 45% by weight, and the amount of the high molecular weight CMC is about 5 - 35% by weight (in each case, the % by weight is a relative amount to the total weight of the CMC solution). In another preferred embodiment, the total amount of CMC in the CMC solution is 20 - 40% by weight, the amount of the low molecular weight CMC is about 15 - 35% by weight, and the amount of the high molecular weight CMC is about 5 - 25% by weight (in each case, the % by weight is a relative amount to the total weight of the CMC solution).

[0024] Preferably, the weight average molecular weight of the low molecular weight CMC is less than 20 kDa, and the weight average molecular weight of the high molecular weight CMC is more than 30 kDa. Preferably, the weight average molecular weight of the low molecular weight CMC is less than 15 kDa, and the weight average molecular weight of the high molecular weight CMC is more than 30 kDa.

[0025] Preferably, the weight-average molecular weight of the low molecular weight CMC is less than 30 kDa, and the weight-average molecular weight of the high molecular weight CMC is greater than 50 kDa. Preferably, the weight-average molecular weight of the low molecular weight CMC is less than 30 kDa, and the weight-average molecular weight of the high molecular weight CMC is greater than 75 kDa. Preferably, the weight-average molecular weight of the low molecular weight CMC is less than 30 kDa, and the weight-average molecular weight of the high molecular weight CMC is greater than 100 kDa.

[0026] Preferably, the weight-average molecular weight of the low molecular weight CMC is less than 20 kDa, and the weight-average molecular weight of the high molecular weight CMC is greater than 50 kDa. Preferably, the weight-average molecular weight of the low molecular weight CMC is less than 20 kDa, and the weight-average molecular weight of the high molecular weight CMC is greater than 75 kDa. Preferably, the weight-average molecular weight of the low molecular weight CMC is less than 20 kDa, and the weight-average molecular weight of the high molecular weight CMC is greater than 100 kDa.

[0027] Preferably, the weight-average molecular weight of the low molecular weight CMC is less than 15 kDa, and the weight-average molecular weight of the high molecular weight CMC is greater than 50 kDa. Preferably, the weight-average molecular weight of the low molecular weight CMC is less than 15 kDa, and the weight-average molecular weight of the high molecular weight CMC is greater than 75 kDa. Preferably, the weight-average molecular weight of the low molecular weight CMC is less than 15 kDa, and the weight-average molecular weight of the high molecular weight CMC is greater than 100 kDa.

[0028] CMCs having molecular weights according to the preferred embodiments described above are well known in the art. Many suitable CMCs are commercially available. Any suitable method for obtaining such CMCs can be used in conjunction with the above-described method for producing a high solids content CMC solution.

[0029] The degree of substitution of CMC can also affect the solubility of solid high-Mw CMC in low-Mw CMC solutions. In this regard, high-Mw CMC preferably has an anionic substitution degree in the range of about 0.4 to about 1.5 ("DS"). A The solubility of high Mw CMC in low Mw CMC is such that high Mw CMC is within this range of DS. A It is ideal when it has "anion substitution degree" or "DSA The term "1" refers to the average number of substituted ring sites on the β-glucose anhydride ring of a cellulose derivative, where the substituent is anionic (carboxymethyl group in this example). Since there are three hydroxyl groups on each glucose anhydride ring of cellulose available for substitution, DS A The maximum value is 3.0.

[0030] Low Mw CMC also has an anion substitution degree in the range of approximately 0.4 to approximately 1.5 ("DS A It is preferable when it has the following characteristics.

[0031] Therefore, in preferred embodiments, the low molecular weight CMC has a weight-average molecular weight of less than 30 kDa, preferably less than 20 kDa, and more preferably less than 15 kDa, while the high molecular weight CMC has a weight-average molecular weight of about 0.4 to about 1.5 DS A and has a weight-average molecular weight of at least 30 kDa, more preferably 50 kDa, more preferably at least 75 kDa, and more preferably at least 100 kDa.

[0032] In a more preferred embodiment, the low molecular weight CMC is approximately 0.4 to approximately 1.5 DS A The high molecular weight CMC has a weight-average molecular weight of less than 30 kDa, preferably less than 20 kDa, and more preferably less than 15 kDa, and the DS is about 0.4 to about 1.5. A and has a weight-average molecular weight of at least 30 kDa, more preferably 50 kDa, more preferably at least 75 kDa, and more preferably at least 100 kDa.

[0033] Therefore, in a preferred embodiment, a method for producing a high solids content, low viscosity CMC solution involves the following steps: a) A step of obtaining an aqueous solution containing at least one low molecular weight carboxymethylcellulose (CMC) having a weight-average molecular weight of less than 30 kDa, b) A step of dissolving at least one high molecular weight CMC having a weight-average molecular weight of at least 30 kDa in the solution of step a), wherein the at least one high molecular weight CMC is added to the solution of step a) as a solid (preferably substantially dry) (preferably in powder form). Includes, Here, the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and b) are such that the total amount of CMC in the solution is approximately 20-50% by weight, and the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and b) respectively are such that the amount of low molecular weight CMC in the final solution is at least 15% by weight, and the amount of high molecular weight CMC in the final solution is at least 5% by weight (in all cases, the weight percentage is relative to the total weight of the CMC solution).

[0034] In a more preferred embodiment, a method for producing a high solids content, low viscosity CMC solution involves the following steps: a) A step of obtaining an aqueous solution containing at least one low molecular weight carboxymethylcellulose (CMC) having a weight-average molecular weight of less than 30 kDa, b) A step of dissolving at least one high molecular weight CMC having a weight-average molecular weight of at least 30 kDa in the solution of step a), wherein at least one substantially dry high molecular weight CMC is added to the solution of step a) as a solid (preferably substantially dry) (preferably in powder form). The mixture includes the following, where the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and b) are such that the total amount of CMC in the solution is about 20-50% by weight, where the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and b) respectively are such that the amount of low molecular weight CMC in the final solution is at least 15% by weight, and the amount of high molecular weight CMC in the final solution is at least 5% by weight (in all cases, the weight percentage is relative to the total weight of the CMC solution), where the weight ratio of low molecular weight CMC to high molecular weight CMC in the final solution is about 3:7-9:1, preferably about 1:2-5:1, more preferably about 1:2-4:1, and most preferably about 1:1-4:1.

[0035] In a more preferred embodiment, a method for producing a high solids, low viscosity CMC solution comprises the following steps: a) obtaining an aqueous solution comprising at least one low molecular weight carboxymethylcellulose (CMC) having a weight average molecular weight of less than 30 kDa and a DS of from about 0.4 to about 1.5 A and b) dissolving at least one high molecular weight CMC having a weight average molecular weight of at least 30 kDa and a DS of from about 0.4 to about 1.5 A in the solution of step a), wherein the at least one high molecular weight CMC is added to the solution of step a) as a (preferably substantially dry) solid (preferably in powder form) and wherein the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and b) are such that the total amount of CMC in the solution is from about 20 to 50% by weight, and the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and b) respectively are such that the amount of low molecular weight CMC in the final solution is at least 15% by weight and the amount of high molecular weight CMC in the final solution is at least 5% by weight (in each case, % by weight is relative to the total weight of the CMC solution), and where the weight ratio of low molecular weight CMC to high molecular weight CMC in the final solution is from about 3:7 to 9:1, preferably from about 1:2 to 5:1, more preferably from about 1:2 to 4:1, and most preferably from about 1:1 to 4:1.

[0036] Preferably, the at least one high molecular weight CMC is added to the solution of step a) as a (preferably substantially dry) solid (preferably in powder form) at a temperature of from about 20°C to 70°C, preferably from about 25°C to 65°C, preferably from about 25°C to 60°C (i.e., the solution of step a) is adjusted to a temperature of from about 20°C to 70°C, preferably from about 25°C to 65°C, preferably from about 25°C to 60°C before the high molecular weight CMC is added). Thus, in a further preferred embodiment, a method for producing a high solids, low viscosity CMC solution comprises the following steps: a) obtaining an aqueous solution comprising at least one low molecular weight CMC having a weight average molecular weight of less than 30 kDa b) A step to adjust the temperature of the solution from step a) to approximately 20°C to approximately 70°C, c) A step of dissolving at least one high molecular weight CMC having a weight-average molecular weight of at least 30 kDa in the solution of step b), wherein the at least one high molecular weight CMC is added to the solution of step b) as a solid (preferably substantially dry) (preferably in powder form). Includes, Here, the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and c) are such that the total amount of CMC in the solution is at least 18% by weight (relative to the total weight of the CMC solution).

[0037] In a more preferred embodiment, a method for producing a high solids content, low viscosity CMC solution involves the following steps: a) Weight-average molecular weight less than 30 kDa and optionally DS with a molecular weight of approximately 0.4 to 1.5 A A step of obtaining an aqueous solution containing at least one low molecular weight carboxymethylcellulose (CMC) having the following characteristics: b) A step to adjust the temperature of the solution from step a) to approximately 25°C to 65°C, c) A weight-average molecular weight of at least 30 kDa and optionally a DS of approximately 0.4 to 1.5 A A step of dissolving at least one high molecular weight CMC having in the solution of step b), wherein the at least one high molecular weight CMC is added to the solution of step b) as a solid (preferably substantially dry) (preferably in powder form). and Here, the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and c) are such that the total amount of CMC in the solution is about 20-50% by weight, and the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and b) respectively are such that the amount of low molecular weight CMC in the final solution is at least 15% by weight, and the amount of high molecular weight CMC in the final solution is at least 5% by weight (in all cases, the weight percentage is relative to the total weight of the CMC solution), and the weight ratio of low molecular weight CMC to high molecular weight CMC in the final solution is optionally about 3:7-9:1, preferably about 1:2-5:1, more preferably about 1:2-4:1, and most preferably about 1:1-4:1.

[0038] This disclosure, of course, also relates to CMC solutions produced by the methods and preferred embodiments thereof described above. As described above, these CMC solutions are characterized by having unexpectedly beneficial rheological properties (particularly surprisingly low viscosity) for such solutions, while containing a large amount (wt%) of CMC. In this regard, in a second aspect, this disclosure relates to a high solids content, low viscosity CMC solution, a) Water and, b) At least one low molecular weight CMC having a weight-average molecular weight of less than 30 kDa, c) At least one high molecular weight CMC having a weight-average molecular weight of at least 30 kDa and Includes, Here, the total amount of CMC in the solution is at least 18% by weight (relative to the total weight of the CMC solution), and the CMC solution has a viscosity of 5000 mPas or less (Brookfield RV, 100 rpm, 40°C, spindle 6).

[0039] In a preferred embodiment, the CMC solution is a) Water and, b) At least one low molecular weight CMC having a weight-average molecular weight of less than 30 kDa, c) At least one high molecular weight CMC having a weight-average molecular weight of at least 30 kDa and Includes, Here, the total amount of CMC in the solution is at least 20% by weight, the amount of low molecular weight CMC in the final solution is at least 15% by weight, and the amount of high molecular weight CMC in the final solution is at least 5% by weight (in all cases, the weight percentage is relative to the total weight of the CMC solution), and the CMC solution has a viscosity of 5000 mPas or less (Brookfield RV, 100 rpm, 40°C, spindle 6).

[0040] In another preferred embodiment, the CMC solution is a) Water and, b) At least one low molecular weight CMC having a weight-average molecular weight of less than 30 kDa, c) At least one high molecular weight CMC having a weight-average molecular weight of at least 30 kDa and Includes, Here, the total amount of CMC in the solution is about 20-40% by weight, the amount of low molecular weight CMC in the final solution is at least 15% by weight, and the amount of high molecular weight CMC in the final solution is at least 5% by weight (in all cases, the weight percentage is relative to the total weight of the CMC solution), the weight ratio of low molecular weight CMC to high molecular weight CMC in the final solution is about 3:7-9:1, preferably about 1:2-5:1, more preferably about 1:2-4:1, and most preferably about 1:1-4:1, and the CMC solution has a viscosity of 5000 mPas or less (Brookfield RV, 100 rpm, 40°C, spindle 6).

[0041] In another preferred embodiment, the CMC solution is a) Water and, b) Weight-average molecular weight less than 30 kDa and DS of 0.4 to approximately 1.5 kDa A A low molecular weight CMC having at least one such CMC, c) Weight-average molecular weight of at least 30 kDa and DS of 0.4 to approximately 1.5. A A high molecular weight CMC having at least one such CMC Includes, Here, the total amount of CMC in the solution is about 20-50% by weight, the amount of low molecular weight CMC in the final solution is at least 15% by weight, and the amount of high molecular weight CMC in the final solution is at least 5% by weight (in either case, the weight percentage is relative to the total weight of the CMC solution), the weight ratio of low molecular weight CMC to high molecular weight CMC in the final solution is about 3:7-9:1, preferably about 1:2-5:1, more preferably about 1:2-4:1, and most preferably about 1:1-4:1, and the CMC solution has a viscosity of 5000 mPas or less (Brookfield RV, 100 rpm, 40°C, spindle 6).

[0042] Preferably, the CMC solution contains at least 40% by weight of water. In this regard, the CMC solution may contain about 40% to 82% by weight of water, preferably about 50% to 80% by weight, and more preferably about 60% to 70% by weight (in any case, the weight percentage is relative to the total weight of the CMC solution).

[0043] The CMC solution produced by the method described above may also contain, but is not limited to, plasticizers such as sorbitol, glycerol, mannitol, and / or xylitol. The plasticizer may be present in any suitable amount, for example, 1 to 50% by weight (relative to the total weight of the CMC solution). The high-solids CMC solution may also contain further additives conventionally used in barrier coating applications, such as crosslinking agents and pigments.

[0044] High-solids CMC solutions preferably have a pH of about 4.5 to about 7.5. An unexpected finding is that CMC solutions can be produced at this pH range by the described method, which generally improves the shelf life of the solution, regardless of the presence of impurities in the solution.

[0045] In a third aspect, the disclosure relates to the use of the above-mentioned high-solids-content CMC solution as a surface treatment agent for paper and paperboard substrates, for example, as a barrier coating.

[0046] In a fourth aspect, the disclosure relates to a method for treating the surface of a paper or paperboard substrate, comprising the step of applying the above-mentioned high-solids CMC solution to the surface of the paper or paperboard substrate.

[0047] In a fifth aspect, the Disclosure relates to a surface-treated paper or cardboard substrate that can be obtained by the method of the fourth aspect of the Disclosure.

[0048] In a sixth aspect, the disclosure relates to the use of the above-mentioned high-solids CMC solution as a co-binding agent and / or thickener. The present specification includes the following embodiments. Section 1. A method for producing a carboxymethylcellulose (CMC) solution, the method comprising the following steps: a) A step of obtaining an aqueous solution containing at least one low molecular weight CMC having a weight-average molecular weight of less than 30 kDa, b) A step of dissolving at least one high molecular weight CMC having a weight-average molecular weight of at least 30 kDa in the solution of step a), wherein the at least one high molecular weight CMC is added to the solution of step a) as a solid. A method comprising, wherein the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and b) respectively are such that the total amount of CMC in the final solution is at least 18% by weight (relative to the total weight of the CMC solution). Section 2. The method according to claim 1, wherein the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and b) respectively are such that the total amount of CMC in the solution is at least 20% by weight. Section 3. The method according to item 2, wherein the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and b) respectively are such that the total amount of low molecular weight CMC in the final solution is at least about 15% by weight, and the total amount of high molecular weight CMC in the final solution is at least 5% by weight (in either case, the weight percentage is a relative amount to the total weight of the CMC solution). Section 4. The method according to any one of claims 1 to 3, wherein the weight ratio (low Mw:high Mw) of the low molecular weight CMC to the high molecular weight CMC in the CMC solution is approximately 3:7 to 9:1. Section 5. The method according to any one of claims 1 to 4, wherein the weight-average molecular weight of the low molecular weight CMC is less than 20 kDa, and the weight-average molecular weight of the high molecular weight CMC is greater than 30 kDa. Section 6. The aforementioned low molecular weight CMC has an anionic substitution degree of approximately 0.4 to approximately 1.5 (DS A ) has a high molecular weight CMC with an anionic substitution degree of about 0.4 to about 1.5 (DS A The method according to any one of items 1 to 5, having ) Section 7. A carboxymethylcellulose (CMC) solution, a) Water and, b) At least one low molecular weight CMC having a weight-average molecular weight of less than 30 kDa, c) At least one high molecular weight CMC having a weight-average molecular weight of at least 30 kDa and Includes, Here, the total amount of CMC in the solution is at least 18% by weight (relative to the total weight of the CMC solution), and the CMC solution is a CMC solution having a viscosity of 5000 mPas or less (Brookfield RV, 100 rpm, 40°C, spindle 6). Section 8. The CMC solution according to item 7, wherein the total amount of CMC in the solution is at least 20% by weight, where the amount of low molecular weight CMC in the solution is at least 15% by weight, and the amount of high molecular weight CMC in the solution is at least 5% by weight (in either case, the weight percentage is relative to the total weight of the CMC solution). Section 9. The CMC solution according to claim 7 or 8, wherein the CMC solution further comprises at least one plasticizer. Section 10. The CMC solution according to any one of claims 7 to 9, wherein the CMC solution has a pH of about 4.5 to about 7.5. Section 11. Use of a high-solids-content CMC solution as described in any one of items 7 to 10 as a surface treatment agent for paper and cardboard substrates. Section 12. A method for treating the surface of a paper or paperboard substrate, comprising the step of applying the CMC solution described in any one of paragraphs 7 to 10 to the surface of the paper or paperboard substrate. Section 13. A surface-treated paper or cardboard substrate that can be obtained by the method described in item 12. Section 14. Use of a high solids content CMC solution as described in any one of items 7 to 10 as a co-binding agent and / or thickener. [Examples]

[0049] The following embodiments provide detailed methods for carrying out the present invention. These embodiments are essentially illustrative and not limiting.

[0050] Example 1 As mentioned above, the conventional method for preparing a mixture of two different cellulose ethers is to prepare a solution of each cellulose ether and then mix the two in the required amounts to obtain the desired ratio of cellulose ethers. However, as mentioned above, there is a limit to the amount of high-Mw cellulose ether that can be dissolved before the resulting solution can no longer be properly handled (i.e., it can no longer be pumped). This limits the maximum total solids content that can be achieved for a solution containing high-Mw cellulose ether, and then hinders the ability to achieve the desired barrier properties of the coating.

[0051] To illustrate this problem, we selected two CMCs: CMC1-Mw < 30kDa ("LMw CMC") CMC2-Mw > 200kDa ("HMw CMC")

[0052] For solutions containing only CMC1, it was found that the maximum total solids content achievable is approximately 35% by weight.

[0053] However, for solutions containing only CMC2, the maximum total solids content achievable was found to be approximately 5% by weight (limited by high Mw, >200 kDa; the 5% by weight solution had a viscosity of >20,000 mPas at 25°C).

[0054] To increase the total solids content of a solution containing CMC2, the inventors aimed to produce a solution with a CMC1 to CMC2 solids content ratio of 80:20. This was achieved by mixing 229 grams of CMC1 solution with 400 grams of CMC2 solution to obtain the desired solids ratio. It was found that the total CMC content achievable with an 80:20 weight ratio (CMC1:CMC2) using conventional methods (mixed solution) is approximately 16% by weight.

[0055] However, it was possible to produce a CMC solution with approximately twice the total CMC content (30% by weight) by first preparing a solution of approximately 25.5% low Mw CMC (i.e., no maximum solids content was required), and then mixing the required amount (22 grams) of high Mw CMC in a substantially dry powder form (8% by weight moisture content) into the low Mw CMC solution (at 600 rpm and 60°C) to produce the desired 80:20 ratio. [Table 1]

[0056] This demonstrates the substantial improvement provided by this method, not only by substantially increasing the total amount of CMC, but also by substantially increasing the total amount of high molecular weight CMC in the CMC solution.

[0057] The CMC solution according to the present invention is particularly suitable as a thickening agent for paper and cardboard coatings.

[0058] Example 2 Further research was conducted to determine whether the relative concentration of high-Mw CMC could be increased further while maintaining the excellent rheological properties of the solution.

[0059] In this regard, a second set of CMC was tested: CMC3-Mw < 15kDa ("LMw CMC") CMC4-Mw>30~40kDa (“HMw CMC”)

[0060] It was found that, with respect to these CMCs, it is again possible to produce CMC solutions with a high total solids content by following the method disclosed herein. Notably, it was possible to increase the weight ratio of low Mw CMC to high Mw CMC to 1:1 while maintaining a high total amount of CMC and an excellent rheological profile. To achieve this, a 25.5% solution of low Mw CMC (196 g; 49.98 g dry low Mw CMC) was mixed with the required amount of high Mw CMC (approximately 54 g; 49.68 g dry high Mw-CMC) in a substantially dry form (8% moisture content) (60°C, 600 rpm) to obtain the desired 1:1 ratio. The resulting CMC solution was diluted with water to adjust the final CMC content to 25% by weight. [Table 2]

[0061] The inventors found that using other known processes (including the solution mixing process described in Example 1), it was not possible to produce equivalent solutions with such high concentrations of high Mw CMC and low viscosity. Conventional methods (see Example 1) achieved a maximum total CMC content of 17.8% by weight (1:1 ratio, low Mw:high Mw).

[0062] Therefore, the inventors have developed a method for producing a CMC solution containing a level of HMw CMC that has been unattainable to the best of their knowledge, while possessing rheological properties suitable for paper / cardboard coating and barrier applications.

[0063] In summary, the inventors have developed an improved method for preparing a CMC solution in which the total amount of CMC is substantially increased, particularly with respect to high Mw CMCs, while maintaining excellent rheological properties.

[0064] While at least one exemplary embodiment has been presented in the above detailed description, it should be understood that a vast number of variations exist. It should also be understood that one or more exemplary embodiments are merely examples and are not intended in any way to limit the scope, applicability, or configuration of the invention. Rather, the above detailed description provides a convenient guide for carrying out the exemplary embodiments intended herein. It should be understood that various modifications can be made to the function and form of the elements described in the exemplary embodiments without departing from the scope of the invention as set forth in the appended claims.

[0065] This disclosure can be further described by the following aspects. Embodiment 1. A method for producing a high-solids-content, low-viscosity carboxymethylcellulose (CMC) solution, the method comprising the following steps: a) A step of obtaining an aqueous solution containing at least one low molecular weight CMC having a weight-average molecular weight of less than 30 kDa, b) A step of dissolving at least one high molecular weight CMC having a weight-average molecular weight of at least 30 kDa in the solution of step a), wherein the at least one high molecular weight CMC is added to the solution of step a) as a solid (preferably as a powder). A method comprising, wherein the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and b) respectively are such that the total amount of CMC in the solution is at least 18% by weight (relative to the total weight of the CMC solution). Embodiment 2. The method according to Embodiment 1, wherein the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and b) respectively are such that the total amount of CMC in the solution is at least 20% by weight, preferably at least 25% by weight, preferably at least 28% by weight, and most preferably at least 30% by weight (in all cases, the weight percentage is a relative amount to the total weight of the CMC solution). Embodiment 3. The method according to Embodiment 1 or 2, wherein the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and b) respectively are such that the total amount of CMC in the CMC solution is approximately 18-50% by weight. Embodiment 4. The method according to any one of Embodiments 1 to 3, wherein the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and b) respectively are such that the total amount of CMC in the CMC solution is approximately 20 to 40% by weight. Embodiment 5. The method according to any one of Embodiments 1 to 4, wherein the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and b) respectively are such that the total amount of low molecular weight CMC in the final solution is at least about 15% by weight, and the total amount of high molecular weight CMC in the final solution is at least 5% by weight (in either case, the weight percentage is a relative amount to the total weight of the CMC solution). Embodiment 6. The method according to any one of Embodiments 1 to 5, wherein the total amount of CMC in the CMC solution is 20 to 50% by weight, the amount of low molecular weight CMC is approximately 15 to 45% by weight, and the amount of high molecular weight CMC is approximately 5 to 35% by weight (in all cases, the weight percentage is a relative amount to the total weight of the CMC solution). Embodiment 7. The method according to any one of Embodiments 1 to 6, wherein the weight ratio (low Mw:high Mw) of low molecular weight CMC to high molecular weight CMC in the CMC solution is approximately 3:7 to 9:1. Embodiment 8. The method according to any one of Embodiments 1 to 7, wherein the total amount of CMC in the CMC solution is 20 to 40% by weight, the amount of low molecular weight CMC is approximately 15 to 35% by weight, and the amount of high molecular weight CMC is approximately 5 to 25% by weight (in all cases, the weight percentage is a relative amount to the total weight of the CMC solution). Embodiment 9. The method according to any one of Embodiments 1 to 8, wherein the weight ratio (low Mw:high Mw) of low molecular weight CMC to high molecular weight CMC in the CMC solution is approximately 1:2 to 5:1. Embodiment 10. The method according to any one of Embodiments 1 to 9, wherein the weight ratio (low Mw:high Mw) of low molecular weight CMC to high molecular weight CMC in the CMC solution is approximately 1:1 to 4:1. Embodiment 11. The method according to any one of Embodiments 1 to 10, wherein the solid high molecular weight CMC is in powder form. Embodiment 12. The method according to any one of Embodiments 1 to 11, wherein the solid high molecular weight CMC is a substantially dry solid having a total water content of 15% by weight or less (relative to the total weight of substantially dry solid high molecular weight CMC). Embodiment 13. The method according to any one of Embodiments 1 to 12, wherein the weight-average molecular weight of the low molecular weight CMC is less than 20 kDa and the weight-average molecular weight of the high molecular weight CMC is greater than 30 kDa. Embodiment 14. The method according to any one of Embodiments 1 to 12, wherein the weight-average molecular weight of the low molecular weight CMC is less than 15 kDa and the weight-average molecular weight of the high molecular weight CMC is greater than 30 kDa. Embodiment 15. The method according to any one of Embodiments 1 to 12, wherein the weight-average molecular weight of the low molecular weight CMC is less than 30 kDa and the weight-average molecular weight of the high molecular weight CMC is greater than 50 kDa. Embodiment 16. Any one of Embodiments 1 to 12, wherein the weight-average molecular weight of the low molecular weight CMC is less than 30 kDa and the weight-average molecular weight of the high molecular weight CMC is greater than 75 kDa. Embodiment 17. The method according to any one of Embodiments 1 to 12, wherein the weight-average molecular weight of the low molecular weight CMC is less than 30 kDa and the weight-average molecular weight of the high molecular weight CMC is greater than 100 kDa. Embodiment 18. The method according to any one of Embodiments 1 to 12, wherein the weight-average molecular weight of the low molecular weight CMC is less than 20 kDa and the weight-average molecular weight of the high molecular weight CMC is greater than 50 kDa. Embodiment 19. Any one of Embodiments 1 to 12, wherein the weight-average molecular weight of the low molecular weight CMC is less than 20 kDa and the weight-average molecular weight of the high molecular weight CMC is greater than 75 kDa. Embodiment 20. The method according to any one of Embodiments 1 to 12, wherein the weight-average molecular weight of the low molecular weight CMC is less than 20 kDa and the weight-average molecular weight of the high molecular weight CMC is greater than 100 kDa. Embodiment 21. The method according to any one of Embodiments 1 to 12, wherein the weight-average molecular weight of the low molecular weight CMC is less than 15 kDa and the weight-average molecular weight of the high molecular weight CMC is greater than 50 kDa. Embodiment 22. The method according to any one of Embodiments 1 to 12, wherein the weight-average molecular weight of the low molecular weight CMC is less than 15 kDa and the weight-average molecular weight of the high molecular weight CMC is greater than 75 kDa. Embodiment 23. Any one of Embodiments 1 to 12, wherein the weight-average molecular weight of the low molecular weight CMC is less than 15 kDa and the weight-average molecular weight of the high molecular weight CMC is greater than 100 kDa. Embodiment 24. Any one of Embodiments 1 to 12, wherein the weight-average molecular weight of the low molecular weight CMC is less than 15 kDa and the weight-average molecular weight of the high molecular weight CMC is >30 to approximately 50 kDa. Embodiment 25. High molecular weight CMC with an anionic substitution degree of approximately 0.4 to approximately 1.5 (DS A The method according to any one of embodiments 1 to 24, having ) Appearance 26. Low molecular weight CMC with an anionic substitution degree of approximately 0.4 to approximately 1.5 (DS A The method according to any one of embodiments 1 to 25, having ) Appearance 27. Low molecular weight CMC with an anionic substitution degree of approximately 0.4 to approximately 1.5 (DS A ) has a high molecular weight CMC with an anionic substitution degree of approximately 0.4 to approximately 1.5 (DS A The method according to any one of embodiments 1 to 26, having ) Embodiment 28. The method according to any one of Embodiments 24 to 27, wherein the high molecular weight CMC has a weight-average molecular weight greater than 30 kDa and the low molecular weight CMC has a weight-average molecular weight less than 20 kDa. Embodiment 29. The method according to any one of Embodiments 1 to 28, wherein the aqueous solution of step a) is adjusted to a temperature of approximately 25 to 60°C before step b). Embodiment 30. The method according to any one of Embodiments 1 to 29, wherein the CMC solution further comprises a plasticizer. Embodiment 31. The method according to any one of Embodiments 1 to 30, wherein the pH of the CMC solution is approximately 4.5 to approximately 7.5. Embodiment 32. A CMC solution that can be obtained by the method described in any one of Embodiments 1 to 31. Embodiment 33. A CMC solution, a) Water and, b) At least one low molecular weight CMC having a weight-average molecular weight of less than 30 kDa, c) At least one high molecular weight CMC having a weight-average molecular weight of at least 30 kDa and Includes, Here, the total amount of CMC in the solution is at least 18% by weight (relative to the total weight of the CMC solution), and the CMC solution has a viscosity of 5000 mPas or less (Brookfield RV, 100 rpm, 40°C, spindle 6). Appearance 34. The CMC solution is a) Water and, b) At least one low molecular weight CMC having a weight-average molecular weight of less than 30 kDa, c) At least one high molecular weight CMC having a weight-average molecular weight of at least 30 kDa and Includes, The CMC solution according to embodiment 33, wherein the total amount of CMC in the solution is at least 20% by weight, the amount of low molecular weight CMC in the solution is at least 15% by weight, and the amount of high molecular weight CMC in the solution is at least 5% by weight (in all cases, the weight percentage is relative to the total weight of the CMC solution), and wherein the CMC solution has a viscosity of 5000 mPas or less (Brookfield RV, 100 rpm, 40°C, spindle 6). Embodiment 35. A CMC solution according to Embodiment 33 or 34, wherein the total amount of CMC in the solution is about 20-40% by weight, where the amount of low molecular weight CMC in the final solution is at least 15% by weight, and the amount of high molecular weight CMC in the final solution is at least 5% by weight (in either case, the weight percentage is a relative amount to the total weight of the CMC solution). Embodiment 36. A CMC solution according to any one of Embodiments 33 to 35, wherein the weight ratio of low molecular weight CMC to high molecular weight CMC in the final solution is approximately 3:7 to 9:1. Embodiment 37. A CMC solution according to any one of Embodiments 33 to 36, wherein the weight ratio of low molecular weight CMC to high molecular weight CMC in the final solution is approximately 1:2 to 5:1. Embodiment 38. A CMC solution according to any one of Embodiments 33 to 37, wherein the weight ratio of low molecular weight CMC to high molecular weight CMC in the final solution is approximately 1:2 to 4:1. Embodiment 39. A CMC solution according to any one of Embodiments 33 to 38, wherein the weight ratio of low molecular weight CMC to high molecular weight CMC in the final solution is approximately 1:1 to 4:1. Embodiment 40. At least one low molecular weight CMC having a weight-average molecular weight of less than 30 kDa and a DS of 0.4 to about 1.5 A A CMC solution according to any one of embodiments 33 to 39, having the following characteristics. Embodiment 41. At least one low molecular weight CMC has a weight-average molecular weight of less than 15 kDa and a DS of 0.4 to about 1.5. A A CMC solution according to any one of embodiments 33 to 39, having the following characteristics. Embodiment 42. At least one high molecular weight cellulose CMC has a weight-average molecular weight greater than 30 kDa and a DS of 0.4 to about 1.5. A A CMC solution according to any one of embodiments 33 to 41, having the following characteristics. Embodiment 43. At least one high molecular weight cellulose CMC has a weight-average molecular weight of over 30 kDa to a maximum of approximately 50 kDa and a DS of 0.4 to approximately 1.5. A A CMC solution according to any one of embodiments 33 to 42, having the following characteristics. Embodiment 44. The CMC solution according to any one of Embodiments 33 to 43, wherein the CMC solution contains at least 40% by weight of water. Embodiment 45. The CMC solution according to any one of Embodiments 33 to 44, wherein the CMC solution further comprises at least one plasticizer. Embodiment 46. The CMC solution according to Embodiment 45, wherein the plasticizer is selected from sorbitol, glycerol, mannitol, and / or xylitol. Embodiment 47. A CMC solution according to any one of Embodiments 44 to 46, wherein the CMC solution has a pH of approximately 4.5 to approximately 7.5. Embodiment 48. Use of the high-solids-content CMC solution according to any one of Embodiments 33 to 47 as a surface treatment agent for paper and cardboard substrates. Embodiment 49. Use of the high-solids-content CMC solution according to any one of Embodiments 33 to 47 as a barrier coating for paper and cardboard substrates. Embodiment 50. A method for treating the surface of a paper or paperboard substrate, comprising the step of applying the CMC solution described in any one of Embodiments 33 to 47 to the surface of a paper or paperboard substrate. Embodiment 51. A surface-treated paper or cardboard substrate that can be obtained by the method of Embodiment 50. Embodiment 52. Use of the high solids content CMC solution according to any one of Embodiments 33 to 47 as a co-binding agent and / or thickening agent.

Claims

1. A method for producing a carboxymethylcellulose (CMC) solution, the method comprising the following steps: a) A step of obtaining an aqueous solution containing at least one low molecular weight CMC having a weight-average molecular weight of less than 30 kDa, b) A step of dissolving at least one high molecular weight CMC having a weight-average molecular weight of at least 30 kDa in the aqueous solution of step a), wherein the at least one high molecular weight CMC is added to the aqueous solution of step a) as a solid. A method comprising, wherein the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and b) respectively are such that the total amount of CMC in the final solution is at least 18% by weight (relative to the total weight of the CMC solution).

2. The method according to claim 1, wherein the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and b) respectively are such that the total amount of CMC in the final solution is at least 20% by weight (relative to the total weight of the CMC solution).

3. The method according to claim 2, wherein the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and b) respectively are such that the total amount of low molecular weight CMC in the final solution is at least 15% by weight, and the total amount of high molecular weight CMC in the final solution is at least 5% by weight (in either case, the weight percentage is a relative amount to the total weight of the CMC solution).

4. The method according to claim 1, wherein the weight ratio (low Mw:high Mw) of the low molecular weight CMC to the high molecular weight CMC in the CMC solution is 3:7 to 9:

1.

5. The method according to claim 1, wherein the weight-average molecular weight of the low molecular weight CMC is less than 20 kDa, and the weight-average molecular weight of the high molecular weight CMC is greater than 30 kDa.

6. The low molecular weight CMC has an anionic substitution degree of 0.4 to 1.5 (DS Ａ ) and the high molecular weight CMC has an anionic substitution degree (DS) of 0.4 to 1.5 Ａ The method according to claim 1, having ).

7. A carboxymethylcellulose (CMC) solution, a) Water and, b) At least one low molecular weight CMC having a weight-average molecular weight of less than 30 kDa, c) At least one high molecular weight CMC having a weight-average molecular weight of at least 30 kDa and Includes, Here, the total amount of CMC in the CMC solution is at least 18% by weight (relative to the total weight of the CMC solution), and the CMC solution is a CMC solution having a viscosity of 5000 mPas or less (Brookfield RV, 100 rpm, 40°C, spindle 6).

8. The CMC solution according to claim 7, wherein the total amount of CMC in the CMC solution is at least 20% by weight, where the amount of low molecular weight CMC in the CMC solution is at least 15% by weight, and the amount of high molecular weight CMC in the CMC solution is at least 5% by weight (in all cases, the weight percentage is a relative amount to the total weight of the CMC solution).

9. The CMC solution according to claim 7, further comprising at least one plasticizer.

10. The CMC solution according to claim 7, wherein the CMC solution has a pH of 4.5 to 7.

5.

11. Use of the CMC solution according to any one of claims 7 to 10 as a surface treatment agent for paper and cardboard substrates.

12. A method for treating the surface of a paper or paperboard substrate, comprising the step of applying the CMC solution according to any one of claims 7 to 10 to the surface of a paper or paperboard substrate.

13. A method for producing a surface-treated paper or paperboard substrate, comprising the step of applying the CMC solution according to any one of claims 7 to 10 to the surface of a paper or paperboard substrate.

14. Use of the CMC solution according to any one of claims 7 to 10 as a co-binding agent and / or thickening agent.

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