High-solid carboxymethyl cellulose 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-solid carboxymethyl cellulose solution and a method for preparing the same.

Background Art

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

[0003] Due to its ability to impart rheological properties, improve water retention, enhance the efficiency of optical brighteners, and provide strength, CMC is a widely used additive, particularly in the paper and board industries for coating, sizing, and base web manufacturing. In the paper and board coating process, CMC is added to the coating make-down composition as a pre-dissolved solution (typically having 6 - 12 wt% CMC), which usually contains inorganic pigments, organic binders, and additives such as dispersants, optical brighteners, cross-linking agents, lubricants, and dyes. CMC can also be used as, or to make, a surface treatment material, such as a barrier material. The barrier material containing CMC can provide oil and grease resistance, oxygen resistance, or both. Common film coating techniques used to form a film-shaped barrier layer include size press, metered size press, and various coating techniques. For each of these techniques, the viscosity and / or solids content of the polymer solution used play an important role. Without wishing to be bound by any theory, a uniform barrier layer is thought to result from a sufficiently high coat weight, good film holding power, or both. These properties can be more easily obtained by making the barrier material with a higher concentration of CMC solution. A higher concentration of CMC in the solution is often achieved by using various techniques to break down CMC. However, with these techniques, the molecular weight of CMC typically decreases very rapidly, so the resulting barrier layer does not have very good film holding power, does not penetrate the base web, and thus does not provide the required barrier properties.

[0004] Existing solutions of pre-dissolved CMC with low solids concentrations generally do not allow for the formulation of coating compositions with high solids contents and typically limit the amount of cellulose ether that can be used in coating compositions required for paper coating. Solving these problems by dry addition of cellulose ether to high solids pigment slurries is possible, but factories need to have a handling system for the powder, sufficient manpower to add the powder by hand, or a mixing system that can impart sufficient shear force to disperse the powder throughout the solution.

[0005] Typically, it is difficult to obtain cellulose ether solution solids above 15 wt%, especially CMC solutions, without adversely affecting the pumpability of the cellulose ether solution and while maintaining performance. This is particularly true for high molecular weight cellulose ethers as they generally result in more viscous solutions. The low shear viscosity limit for good pumpability by frequently used centrifugal pumps is thought to be about 5000 mPas (measured with a Brookfield RV 100) at typical process (pump) temperatures of about 25 - 60 °C. High concentration high Mw cellulose ether solutions tend to have viscosities far exceeding these operating requirements, thus significantly reducing the upper concentration limit of high Mw cellulose ether solutions.

[0006] Therefore, obtaining high solids cellulose ether solutions containing increased amounts of high molecular weight cellulose ethers while maintaining low viscosity at low shear (for improved processability) and high viscosity at high shear (for improved performance) is not an easy 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 CMC solution with reduced viscosity containing at least 33 wt% potassium carbonate. However, the required high concentration of potassium carbonate may limit the usefulness of these solutions in applications, making these compositions less attractive / desirable for high CMC solids applications.

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

[0009] International Publication No. WO 2013 / 057132 discloses a method for increasing the solids content of CMC in a low-viscosity composition. These methods have been found to be capable of increasing the solids content of the CMC solution up to about 24 wt% maximum while maintaining the pumpability of the solution. However, in practice, these levels could only be achieved with low molecular weight cellulose ethers that provide limited performance as coating thickeners or as barriers. Further, CMC solutions prepared according to the method of International Publication No. WO 2013 / 057132 require the solution to have a pH of 7.5 - 11, which has been found to reduce the shelf life of the CMC solution when the CMC solution contains impurities.

[0010] U.S. Patent No. 5,080,717 discloses an aqueous fluid suspension of a polysaccharide mixture in a paper coating composition. These suspensions required stabilizers (e.g., xanthan gums). The suspensions can be problematic because they tend to settle out of suspension solids (e.g., form aggregates, resulting in a non-uniform product with non-uniform distribution of suspended solids). This can also have an adverse effect on the application properties of the aforementioned suspensions (e.g., non-uniform application of the active substance), so the products of U.S. Patent No. 5,080,717 still need to be dissolved before use. In contrast, solutions do not face this problem (i.e., the solute is uniformly distributed within a homogeneous aqueous phase). Thus, 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 a method for preparing a low-viscosity carboxymethyl cellulose solution with an increased amount of high molecular weight carboxymethyl cellulose. If CMC could be supplied in a ready-made solution having a high solids content, especially a high solids content of high molecular weight CMC, it would be a more cost-effective and sustainable alternative for end-users, while at the same time providing an improved product.

SUMMARY OF THE INVENTION

[0012] The inventors have developed a simple yet highly effective method for preparing a carboxymethyl cellulose (CMC) solution that meets this need. Thus, in a first aspect, the present disclosure is a method for producing a high solids, low viscosity CMC solution, the method comprising 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) 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 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, preferably at least 20% by weight, preferably at least 25% by weight, preferably at least 28% by weight, most preferably at least 30% by weight (in each case, % by weight is the relative amount with respect to the total weight of the CMC solution). In a further optional step, the CMC content (% by weight) can be adjusted to the desired value by adding water to the CMC solution.

[0013] The surprising finding was that by adding high molecular weight CMC as a solid, preferably a powder, 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 to use a stabilizer and, unexpectedly, while maintaining a low viscosity solution (≤5000 mPas). This new approach of combining two different CMCs results in a higher total solids content of CMC while also providing a much improved rheology profile of such high solids CMC solutions compared to CMC solutions produced via conventional methods.

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

[0015] The solid (preferably powder form) high molecular weight CMC used in the above method is preferably substantially dry (i.e., subjected to a drying process prior to use in step b). As used herein, "substantially dry" solid (preferably powder form) high molecular weight CMC has a total moisture content of 15% by weight or less, preferably 10% by weight or less (in each case, the % by weight is relative to the total weight of the substantially dry solid - preferably 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 can be at least 40 kDa, can be 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 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 with respect 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 about 3:7 to 9:1, preferably about 1:2 to 5:1, more preferably about 1:2 to 4:1, and most preferably about 1:1 to 4:1.

[0023] In a preferred embodiment, the total amount of CMC in the CMC solution is 20 to 50% by weight, the amount of the low molecular weight CMC is about 15 to 45% by weight, and the amount of the high molecular weight CMC is about 5 to 35% by weight (in each case, the % by weight is a relative amount with respect to the total weight of the CMC solution). In another preferred embodiment, the total amount of CMC in the CMC solution is 20 to 40% by weight, the amount of the low molecular weight CMC is about 15 to 35% by weight, and the amount of the high molecular weight CMC is about 5 to 25% by weight (in each case, the % by weight is a relative amount with respect 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 greater 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 greater 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] CMC having a molecular weight according to the above preferred embodiments is well known in the art. Many suitable CMCs are commercially available. Any suitable method for obtaining such CMC can be used in combination 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 the solid high Mw CMC in the low Mw CMC solution. In this regard, the high Mw CMC preferably has an anionic degree of substitution (''DS A '' in the range of about 0.4 to about 1.5. The solubility of the high Mw CMC in the low Mw CMC is optimal when the high Mw CMC has a DS A within this range. ''Anionic degree of substitution'' or ''DSA The term "DS" means the average number of substituted ring sites of the β-anhydroglucose ring of the cellulose derivative, where the substituent is anionic (in this example, a carboxymethyl group). Since there are three hydroxyl groups on each anhydroglucose ring of cellulose available for substitution, the maximum value of DS A is 3.0.

[0030] Low Mw CMC is also preferred when it has an anionic substitution degree in the range of about 0.4 to about 1.5 (the "DS" A .

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

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

[0033] Thus, in a 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; 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 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). comprising wherein the amounts of the low molecular weight CMC and the high molecular weight CMC added in steps a) and b) are such that the total amount of CMC in the solution is about 20 to 50% by weight, and 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 amount of the low molecular weight CMC in the final solution is at least 15% by weight, and the amount of the high molecular weight CMC in the final solution is at least 5% by weight (in each case, % by weight is the relative amount with respect to the total weight of the CMC solution).

[0034] 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 carboxymethylcellulose (CMC) having a weight average molecular weight of less than 30 kDa; 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 the at least one substantially dry high molecular weight CMC is added to the solution of step a) as a (preferably substantially dry) solid (preferably in powder form). comprising, wherein the amounts of the low molecular weight CMC and the high molecular weight CMC added in steps a) and b) are such that the total amount of CMC in the solution is about 20 to 50% by weight, and 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 amount of the low molecular weight CMC in the final solution is at least 15% by weight, and the amount of the high molecular weight CMC in the final solution is at least 5% by weight (in each case, % by weight is the relative amount with respect to the total weight of the CMC solution), and wherein the weight ratio of the low molecular weight CMC to the high molecular weight CMC in the final solution is about 3:7 to 9:1, preferably about 1:2 to 5:1, more preferably about 1:2 to 4:1, and most preferably about 1:1 to 4:1.

[0035] In a more preferred embodiment, a method for producing a high solids content, low viscosity CMC solution comprises the following steps: a) obtaining an aqueous solution comprising at least one low molecular weight carboxymethyl cellulose (CMC) having a weight average molecular weight of less than 30 kDa and a DS of 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 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); wherein the amounts of the low molecular weight CMC and the high molecular weight CMC added in steps a) and b) are such that the total amount of CMC in the solution is about 20 to 50% by weight, 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 amount of the low molecular weight CMC in the final solution is at least 15% by weight, and the amount of the high molecular weight CMC in the final solution is at least 5% by weight (in each case, the % by weight is the relative amount with respect to the total weight of the CMC solution), and the weight ratio of the low molecular weight CMC to the high molecular weight CMC in the final solution is about 3:7 to 9:1, preferably about 1:2 to 5:1, more preferably about 1:2 to 4:1, and most preferably 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 about 20°C to 70°C, preferably about 25°C to 65°C, preferably about 25°C to 60°C (i.e., the solution of step a) is adjusted to a temperature of preferably about 20°C to 70°C, preferably about 25°C to 65°C, preferably about 25°C to 60°C before adding the high molecular weight CMC). Thus, in a further preferred embodiment, a method for producing a high solids content, 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) adjusting the temperature of the solution in step a) to about 20°C to about 70°C; c) 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 at least one high molecular weight CMC is added to the solution of step b) as a (preferably substantially dry) solid (preferably in powder form); comprising wherein the amounts of the low molecular weight CMC and the 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 (based on the total weight of the CMC solution).

[0037] 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 carboxymethyl cellulose (CMC) having a weight average molecular weight of less than 30 kDa and optionally a DS of about 0.4 to about 1.5; A b) adjusting the temperature of the solution of step a) to about 25°C to 65°C; c) dissolving at least one high molecular weight CMC having a weight average molecular weight of at least 30 kDa and optionally a DS of about 0.4 to about 1.5 in the solution of step b), wherein at least one high molecular weight CMC is added to the solution of step b) as a (preferably substantially dry) solid (preferably in powder form). c) dissolving at least one high molecular weight CMC having a weight average molecular weight of at least 30 kDa and optionally a DS of about 0.4 to about 1.5 in the solution of step b), wherein at least one high molecular weight CMC is added to the solution of step b) as a (preferably substantially dry) solid (preferably in powder form). A comprising wherein the amounts of the low molecular weight CMC and the 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 (based on the total weight of the CMC solution). wherein 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 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, weight % is relative to the total weight of the CMC solution), wherein the weight ratio of low molecular weight CMC to high molecular weight CMC in the final solution is optionally about 3:7 to 9:1, preferably about 1:2 to 5:1, more preferably about 1:2 to 4:1, and most preferably about 1:1 to 4:1.

[0038] The present disclosure also relates to CMC solutions produced by the above-mentioned method and its preferred embodiments. As explained above, these CMC solutions are characterized by containing a large amount (wt%) of CMC, while having unexpectedly beneficial rheological properties for such solutions (in particular, surprisingly low viscosity). In this regard, in a second aspect, the present disclosure provides a high solids, low viscosity CMC solution, a) water; 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; Including, Wherein the total amount of CMC in the solution is at least 18% by weight (based on the total weight of the CMC solution), and where 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; 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; Including, Here, the total amount of CMC in the solution is at least 20% 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 each case, % by weight is the relative amount with respect to the total weight of the CMC solution), and here, 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 a) water and b) at least one low molecular weight CMC having a weight average molecular weight of less than 30 kDa, and c) at least one high molecular weight CMC having a weight average molecular weight of at least 30 kDa and here, the total amount of CMC in the solution is about 20 to 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 each case, % by weight is the relative amount with respect to the total weight of the CMC solution), and here, the weight ratio of the low molecular weight CMC to the high molecular weight CMC in the final solution is about 3:7 to 9:1, preferably about 1:2 to 5:1, more preferably about 1:2 to 4:1, and most preferably about 1:1 to 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 a) water and b) 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 and c) at least one high molecular weight CMC having a weight average molecular weight of at least 30 kDa and a DS of 0.4 to about 1.5 A and includes Here, the total amount of CMC in the solution is about 20 to 50% 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 both cases, % by weight is the relative amount with respect 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 to 9:1, preferably about 1:2 to 5:1, more preferably about 1:2 to 4:1, and most preferably about 1:1 to 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, preferably about 50% to 80% by weight, and more preferably about 60% to about 70% by weight of water (in both cases, % by weight is the relative amount with respect to the total weight of the CMC solution).

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

[0044] The high solids CMC solution preferably has a pH of about 4.5 to about 7.5. The unexpected finding is that a CMC solution can be produced at a pH in this range by the described method, thereby generally improving the shelf life of the solution regardless of the presence of impurities in the solution.

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

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

[0047] In a fifth aspect, the present disclosure relates to a surface-treated paper or paperboard substrate obtainable by the method of the fourth aspect of the present disclosure.

[0048] In a sixth aspect, the present disclosure relates to the use of the above-described high solids CMC solution as a co-binder and / or thickener.

Examples

[0049] The following examples provide detailed methods for practicing the invention. These examples are illustrative in nature and not limiting.

[0050] Example 1 As described 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 required ratio of cellulose ethers. However, as described 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 processed properly (i.e., it can no longer be pumped). This limits the total maximum solids content that can be achieved for a solution containing high Mw cellulose ether and in turn hinders the ability to achieve the desired barrier properties of the coating.

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

[0052] For a solution of CMC1 only, it was found that the maximum total solids achievable was approximately 35 wt%.

[0053] However, for the solution of CMC2 alone, it was found that the maximum total solids achievable was about 5 wt% (limited by high Mw, >200 kDa; the 5 wt% solution had a viscosity of >20000 mPas at 25°C).

[0054] To increase the total solids content of the solution containing CMC2, the inventors aimed to produce a solution in which the solids content ratio of CMC1 to CMC2 was 80:20. This was achieved by mixing 229 grams of the solution of CMC1 and 400 grams of the solution of CMC2 to obtain the desired solids ratio. It was found that the total CMC content achievable at a weight ratio of 80:20 (CMC1:CMC2) by the conventional method (mixed solution) was about 16 wt%.

[0055] However, it was possible to produce a CMC solution with a total CMC content of about twice (30 wt%) by first preparing an approximately 25.5% solution of low Mw CMC (i.e., maximum solids were not required), and then mixing the required amount (22 grams) of high Mw CMC in a substantially dry powder form (8 wt% 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 in that it not only substantially increases the total amount of CMC, but also substantially increases 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 thickener for paper and paperboard coatings.

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

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

[0060] For these CMCs, it was found that, according to the method disclosed herein, it was again possible to produce CMC solutions having a high total solids content. It should be noted that 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 rheology profile. To achieve this, a 25.5% solution of low Mw CMC (196 grams; 49.98 g dry low Mw CMC) was mixed with the required amount of high Mw CMC (about 54 grams; 49.68 g dry high Mw - CMC) in a substantially dry form (moisture content 8%) (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 wt%.

Table 2

[0061] The inventors were unable to produce equivalent solutions having such a high concentration of high Mw CMC and low viscosity when using other known processes (including the solution mixing process described in Example 1). With the conventional method (see Example 1), a maximum total CMC content of 17.8 wt% was reached (1:1 ratio, low Mw:high Mw).

[0062] Therefore, the inventors have developed a method for producing a CMC solution containing HMw CMC at a level that, to the best of their knowledge, has not been achievable heretofore while having rheological properties suitable for paper / board coating and barrier applications.

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

[0064] Although at least one exemplary embodiment has been presented in the foregoing detailed description, it should be understood that there are a vast number of variations. It should also be understood that one or more exemplary embodiments are merely examples and are not intended to limit in any way the scope, applicability, or configuration of the present invention. Rather, the foregoing detailed description provides those skilled in the art with a convenient guide for implementing the exemplary embodiments contemplated herein. It should be understood that various changes can be made to the functions and forms of the elements described in the exemplary embodiments without departing from the scope of the present invention as set forth in the appended claims.

[0065] The present disclosure can be further described by the following aspects. Aspect 1. A method for producing a high solids, low viscosity carboxymethyl cellulose (CMC) solution, the method comprising 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) 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), the step of adding at least one high molecular weight CMC 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). Aspect 2. The method according to Aspect 1, 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 20% by weight, preferably at least 25% by weight, preferably at least 28% by weight, most preferably at least 30% by weight (in each case, the % by weight is the relative amount with respect to the total weight of the CMC solution). Aspect 3. The method according to aspect 1 or 2, 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 CMC solution is about 18 to 50% by weight. Aspect 4. The method according to any one of aspects 1 to 3, 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 CMC solution is about 20 to 40% by weight. Aspect 5. The method according to any one of aspects 1 to 4, 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 the low molecular weight CMC in the final solution is at least about 15% by weight and the total amount of the high molecular weight CMC in the final solution is at least 5% by weight (in both cases, the % by weight is the relative amount with respect to the total weight of the CMC solution). Aspect 6. The method according to any one of aspects 1 to 5, wherein the total amount of CMC in the CMC solution is 20 to 50% by weight, the amount of the low molecular weight CMC is about 15 to 45% by weight, and the amount of the high molecular weight CMC is about 5 to 35% by weight (in both cases, the % by weight is the relative amount with respect to the total weight of the CMC solution). Aspect 7. The method according to any one of aspects 1 to 6, wherein the weight ratio of the low molecular weight CMC to the high molecular weight CMC (low Mw: high Mw) in the CMC solution is about 3:7 to 9:1. Aspect 8. The method according to any one of aspects 1 to 7, wherein the total amount of CMC in the CMC solution is 20 to 40% by weight, the amount of the low molecular weight CMC is about 15 to 35% by weight, and the amount of the high molecular weight CMC is about 5 to 25% by weight (in both cases, the % by weight is the relative amount with respect to the total weight of the CMC solution). Aspect 9. The method according to any one of aspects 1 to 8, wherein the weight ratio of the low molecular weight CMC to the high molecular weight CMC (low Mw: high Mw) in the CMC solution is about 1:2 to 5:1. Aspect 10. The method according to any one of aspects 1 to 9, wherein the weight ratio of the low molecular weight CMC to the high molecular weight CMC (low Mw: high Mw) in the CMC solution is about 1:1 to 4:1. Aspect 11. The method according to any one of aspects 1 to 10, wherein the solid high molecular weight CMC is in powder form. Aspect 12. The method according to any one of Aspects 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 the substantially dry solid high molecular weight CMC). Aspect 13. The method according to any one of Aspects 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. Aspect 14. The method according to any one of Aspects 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. Aspect 15. The method according to any one of Aspects 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. Aspect 16. The method according to any one of Aspects 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. Aspect 17. The method according to any one of Aspects 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. Aspect 18. The method according to any one of Aspects 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. Aspect 19. The method according to any one of Aspects 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. Aspect 20. The method according to any one of Aspects 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. Aspect 21. The method according to any one of Aspects 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. Aspect 22. The method according to any one of Aspects 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. Aspect 23. The method according to any one of Aspects 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. Aspect 24. The method according to any one of Aspects 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 about 50 kDa. Aspect 25. The method according to any one of Aspects 1 to 24, wherein the high molecular weight CMC has an anionic substitution degree (DS A ) of about 0.4 to about 1.5. Aspect 26. The method according to any one of Aspects 1 to 25, wherein the low molecular weight CMC has an anionic substitution degree (DS A ) of about 0.4 to about 1.5. Aspect 27. The method according to any one of Aspects 1 to 26, wherein the low molecular weight CMC has an anionic substitution degree (DS A ) of about 0.4 to about 1.5, and the high molecular weight CMC has an anionic substitution degree (DS A ) of about 0.4 to about 1.5. Aspect 28. The method according to any one of Aspects 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. Aspect 29. The method according to any one of Aspects 1 to 28, wherein the aqueous solution in step a) is adjusted to a temperature of about 25 to 60 °C before step b). Aspect 30. The method according to any one of Aspects 1 to 29, wherein the CMC solution further contains a plasticizer. Aspect 31. The method according to any one of Aspects 1 to 30, wherein the pH of the CMC solution is about 4.5 to about 7.5. Aspect 32. A CMC solution obtainable by the method according to any one of Aspects 1 to 31. Aspect 33. A CMC solution, comprising: 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 comprising wherein the total amount of CMC in the solution is at least 18% by weight (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). Aspect 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, and c) at least one high molecular weight CMC having a weight average molecular weight of at least 30 kDa comprising wherein the total amount of CMC in the solution is at least 20% by weight, wherein 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 each case, the % by weight is the relative amount with respect 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), the CMC solution according to aspect 33. Aspect 35. The total amount of CMC in the solution is about 20 - 40% by weight, wherein 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, the % by weight is the relative amount with respect to the total weight of the CMC solution), the CMC solution according to aspect 33 or 34. Aspect 36. The weight ratio of low molecular weight CMC to high molecular weight CMC in the final solution is about 3:7 to 9:1, the CMC solution according to any one of aspects 33 to 35. Aspect 37. The weight ratio of low molecular weight CMC to high molecular weight CMC in the final solution is about 1:2 to 5:1, the CMC solution according to any one of aspects 33 to 36. Aspect 38. The weight ratio of low molecular weight CMC to high molecular weight CMC in the final solution is about 1:2 to 4:1, the CMC solution according to any one of aspects 33 to 37. Aspect 39. The CMC solution according to any one of Aspects 33 to 38, wherein the weight ratio of the low molecular weight CMC to the high molecular weight CMC in the final solution is about 1:1 to 4:1. Aspect 40. The CMC solution according to any one of Aspects 33 to 39, wherein at least one low molecular weight CMC has a weight average molecular weight of less than 30 kDa and a DS of 0.4 to about 1.5 A Aspect 41. The CMC solution according to any one of Aspects 33 to 39, wherein 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 Aspect 42. The CMC solution according to any one of Aspects 33 to 41, wherein at least one high molecular weight cellulose CMC has a weight average molecular weight of more than 30 kDa and a DS of 0.4 to about 1.5 A Aspect 43. The CMC solution according to any one of Aspects 33 to 42, wherein at least one high molecular weight cellulose CMC has a weight average molecular weight of more than 30 kDa to a maximum of about 50 kDa and a DS of 0.4 to about 1.5 A Aspect 44. The CMC solution according to any one of Aspects 33 to 43, wherein the CMC solution contains at least 40% by weight of water. Aspect 45. The CMC solution according to any one of Aspects 33 to 44, wherein the CMC solution further contains at least one plasticizer. Aspect 46. The CMC solution according to Aspect 45, wherein the plasticizer is selected from sorbitol, glycerol, mannitol, and / or xylitol. Aspect 47. The CMC solution according to any one of Aspects 44 to 46, wherein the CMC solution has a pH of about 4.5 to about 7.5. Aspect 48. Use of the high solids CMC solution according to any one of Aspects 33 to 47 as a surface treatment agent for paper and paperboard substrates. Aspect 49. Use of the high solids CMC solution according to any one of Aspects 33 to 47 as a barrier coating for paper and paperboard substrates. ​​​​Aspect 50. 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 Aspects 33 to 47 to the surface of the paper or paperboard substrate. Aspect 51. A surface-treated paper or paperboard substrate obtainable by the method of Aspect 50. Aspect 52. Use of the high solids CMC solution according to any one of Aspects 33 to 47 as a co-binder and / or thickener.

Claims

1. A method for producing a carboxymethyl cellulose (CMC) solution, the method comprising 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) 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; 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 final solution is at least 18% by weight (based on the total weight of the CMC solution).

2. The method according to claim 1, 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 20% by weight.

3. The method according to claim 2, 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 the low molecular weight CMC in the final solution is at least about 15% by weight and the total amount of the high molecular weight CMC in the final solution is at least 5% by weight (in each case, % by weight is the relative amount based on the total weight of the CMC solution).

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 from about 3:7 to 9:

1.

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.

6. The low molecular weight CMC has an anionic substitution degree (DS) of about 0.4 to about 1.5 Ａ ) and the high molecular weight CMC has an anionic substitution degree (DS) of about 0.4 to about 1.5 Ａ ) The method according to any one of claims 1 to 5.

7. A carboxymethyl cellulose (CMC) solution comprising: a) water; 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; wherein the total amount of CMC in the solution is at least 18% by weight (based on 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).

8. ​ The total amount of CMC in the solution is at least 20% by weight, where the amount of the low molecular weight CMC in the solution is at least 15% by weight, and where the amount of the high molecular weight CMC in the solution is at least 5% by weight (in each case, % by weight is the relative amount with respect to the total weight of the CMC solution), the CMC solution according to claim 7.

9. The CMC solution according to claim 7 or 8, wherein the CMC solution further comprises at least one plasticizer.

10. The CMC solution according to any one of claims 7 to 9, wherein the CMC solution has a pH of from about 4.5 to about 7.

5.

11. Use of the high solids CMC solution according to any one of claims 7 to 10 as a surface treatment agent for paper and paperboard 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 the paper or paperboard substrate.

13. A surface-treated paper or paperboard substrate obtainable by the method according to claim 12.

14. Use of the high solids CMC solution according to any one of claims 7 to 10 as a co-binder and / or thickener.

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