High solids content carboxymethyl cellulose solutions

Abstract

The invention relates to a method for producing a carboxymethyl cellulose (CMC) solution, 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; 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 the at least one high molecular weight CMC is added in solid form, preferably in powder form, to the solution of step a) wherein the amounts of low molecular weight CMC and high molecular weight CMC respectively added in steps a) and b) 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

[0001] The invention relates to a high-solid content carboxymethyl cellulose solution and a preparation method thereof. Background Art

[0002] Cellulose ethers such as carboxymethyl cellulose (CMC) are usually supplied to end users in powder form. However, in practice, cellulose ethers are usually required in aqueous solution form, so it is usually necessary to dissolve the powder in water before use. Dissolving the powder in water may not be cost-effective for the end user. If the cellulose ethers could be supplied in a pre-dissolved, high solids content form, this would provide a cost-competitive and more sustainable alternative for these end users.

[0003] CMC is a popular additive in the paper and paperboard industry, especially for coating, sizing and base web manufacturing, because it can impart rheology, improve water retention, increase the efficiency of fluorescent brighteners and provide strength. In the paper and paperboard coating process, CMC is added to the coating preparation composition (makedown composition) in the form of a pre-dissolved solution (usually with 6 to 12% by weight of CMC), which usually contains inorganic pigments, organic binders and additives such as dispersants, fluorescent brighteners, crosslinking agents, lubricants and dyes. CMC can also be used as a surface treatment agent or for preparing surface treatment agents, such as barrier materials. Barrier materials containing CMC can provide grease resistance, oxidation resistance or both properties. Common film coating techniques for forming barrier layers in film shape include sizing press, metered sizing press and various coating techniques. For each of these techniques, the viscosity and / or solid content of the polymer solution used play an important role. Although not wishing to be bound by any theory, it is believed that a uniform barrier layer is produced by a sufficiently high coating weight, good film hold-out, or both. These properties can be more easily achieved by using a more concentrated CMC solution to prepare the barrier material. Higher concentrations of CMC in solution are often achieved by downgrading the CMC using various techniques. However, using these techniques, the molecular weight of the CMC is often dramatically reduced, so that the resulting barrier layer does not have very good retention and penetrates into the base web, thus failing to provide the desired barrier properties.

[0004] The low solids concentration of existing solutions of pre-dissolved CMC often does not allow for the formulation of high solids coating compositions and often limits the amount of cellulose ether that can be used in the coating composition required for paper coating. While dry addition of cellulose ether to high solids pigment slurries can address these issues, it requires a powder handling system in the plant, sufficient manpower to manually add the powder, or a mixing system that can impart sufficient shear to disperse the powder throughout the solution.

[0005] Generally speaking, it is a challenge to obtain cellulose ether solutions (especially CMC solutions) with solid contents above 15 wt% without negatively affecting the pumpability of the cellulose ether solution and with good retention. This is especially true for high molecular weight cellulose ethers, which generally produce more viscous solutions. At typical process (pumping) temperatures of about 25-60° C., the low shear viscosity limit for good pumping using conventional centrifugal pumps is believed to be about 5000 mPas (measured with a Brookfield RV 100). This significantly reduces the upper concentration limit for high molecular weight cellulose ether solutions, as higher concentrations of high molecular weight cellulose ether solutions often have viscosities that exceed the requirements of these operations.

[0006] Therefore, obtaining high solids cellulose ether solutions containing increased amounts of high molecular weight cellulose ethers (to improve properties) while also maintaining low viscosity under low shear (to improve processability) is not a simple task.

[0007] Early solutions have been proposed to provide stable concentrated aqueous CMC suspensions. For example, U.S. Pat. No. 4,883,537 describes a reduced viscosity aqueous CMC solution containing at least 33% by weight potassium carbonate. However, the required high concentration of potassium carbonate may limit the practicality of these solutions and make these compositions less attractive in high CMC solids content applications.

[0008] WO 2009 / 061821 discloses a process for producing low viscosity cellulose ether compositions using a combination of very low molecular weight cellulose ethers and a plasticizer.

[0009] WO 2013 / 057132 discloses methods for increasing the solids content of CMC in low viscosity compositions. It was found that these methods allow the solids content of CMC solutions to be increased up to about 24% by weight while maintaining the pumpability of the solution. However, in practice, these levels can only be achieved with low molecular weight cellulose ethers, which limits performance as coating thickeners or barriers. In addition, CMC solutions prepared according to the methods of WO 2013 / 057132 require a solution pH of 7.5-11, which can shorten the shelf life of the CMC solution if it contains impurities.

[0010] No. 5,080,717, U.S. Patent discloses an aqueous fluid suspension of a polysaccharide mixture in a paper coating composition. These suspensions require a stabilizer (e.g., xanthan gum). Problems may arise with the suspension because suspended solids are easily precipitated (e.g., forming aggregates, thus causing an uneven product in which the suspended solids are unevenly distributed). This in turn may have a negative impact on the application properties of the suspension (e.g., the active substance is unevenly applied), so the product of No. 5,080,717, U.S. Patent still needs to be dissolved before use. On the other hand, the solution is not affected by this problem (i.e., the solute is evenly distributed in a uniform aqueous phase). Therefore, when used in the above-mentioned application, the cellulose ether solution is easier to handle and produces a more consistent result.

[0011] There remains a need for a method of preparing a low viscosity carboxymethyl cellulose solution having an increased amount of high molecular weight carboxymethyl cellulose. If CMC could be provided as a ready-to-use solution having a high solids content, particularly a high solids content with high molecular weight CMC, this would provide an improved product while also being a more cost effective and sustainable alternative for the end user. DETAILED DESCRIPTION

[0012] The present inventors have developed a simple but efficient method for preparing a carboxymethyl cellulose (CMC) solution that meets this need. Therefore, in a first aspect, the present disclosure relates to a method for producing a high solids, low viscosity CMC solution, the method comprising the following steps:

[0013] a) obtaining an aqueous solution comprising at least one low molecular weight CMC having a weight average molecular weight of less than 30 kDa; and

[0014] 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) in solid form, preferably in powder form,

[0015] The amount of low molecular weight CMC and high molecular weight CMC added in steps a) and b), respectively, is such that the total amount of CMC in the solution is at least 18 wt %, preferably at least 20 wt %, preferably at least 25 wt %, preferably at least 28 wt %, and most preferably at least 30 wt % (in each case, wt % relative to the total weight of the CMC solution). In another optional step, the CMC content (wt %) in the final solution can be adjusted by adding water to the CMC solution.

[0016] An unexpected discovery is that by adding high molecular weight CMC in solid form (preferably in powder form) to the aqueous solution of low molecular weight CMC of step a), the total amount of high molecular weight CMC in the solution can be significantly increased without the need to use stabilizers, while unexpectedly maintaining a low viscosity of the solution (≤5000 mPas). This new method of combining these two different CMCs results in a higher total solids content of CMC relative to CMC solutions produced by conventional methods, while providing greatly improved rheological properties for this high solids content CMC solution.

[0017] The high molecular weight CMC in solid form (preferably powder form) may contain a large amount of residual moisture (e.g., hydration water or the like) in solid form. Preferably, the total water content of the solid (preferably powder form) high molecular weight CMC is less than 60 wt%, preferably less than 50 wt%, and more preferably less than 40 wt% (relative to the total weight of the solid high molecular weight CMC).

[0018] The solid (preferably in powder form) high molecular weight CMC used in the above process is preferably substantially dry (i.e., has been subjected to a drying step before it is used in step b)). As used herein, the "substantially dry" solid (preferably in powder form) high molecular weight CMC has a total water content of 15 wt. % or less, preferably 10 wt. % or less (in each case, the wt. % is relative to the total weight of the substantially dry solid (preferably in powder form) high molecular weight CMC).

[0019] The weight average molecular weight of the at least one low molecular weight CMC is preferably less than 20 kDa, more preferably less than 15 kDa.

[0020] The at least one high molecular weight CMC may have a weight average molecular weight of at least 40 kDa, and may be at least 50 kDa, 75 kDa, or 100 kDa.

[0021] "Weight average molecular weight" used herein is determined using a Malvern Omnisec gel permeation chromatography system with a multi-detector module and a Viscotek ALS6000Mx2 (13 μm, 300*8.0 mm) column. The column temperature is 35 ° C. The eluent used is a 0.1M sodium nitrate aqueous solution containing 10% (V / V) methanol, and the flow rate is 0.8 ml / min. The single sample injection volume is 100 μl, and the sample concentration is 1 mg / ml. Molar mass is determined as the average value of three (3) injections from separate sample vials. The measurement results are calibrated using pullulan standards (Mw 113 kDa, PDI 1.13, Polymer Standards Service). Data are processed by Omnisec 5 software.

[0022] For the avoidance of doubt, the total amount of CMC in the CMC solution is the weight percent 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 readily determined and readily controlled by those skilled in the art using routine skills.

[0023] Preferably, the amount of low molecular weight CMC and high molecular weight CMC added in steps a) and b), respectively, is such that the total amount of CMC in the CMC solution is at least 20 wt%, preferably at least 25 wt%, preferably at least 28 wt% and most preferably at least 30 wt%, such as about 30-40 wt% (in each case, the wt% is relative to the total weight of the CMC solution). In a preferred embodiment, the amount of low molecular weight CMC and high molecular weight CMC added in steps a) and b), respectively, is such that the total amount of CMC in the CMC solution is about 18 to 50 wt%, preferably about 20 to 50 wt%, more preferably about 20 to 40 wt% and more preferably about 30 to 40 wt% (each relative to the total weight of the CMC solution).

[0024] 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 low molecular weight CMC in the final solution is at least about 15 wt %, preferably at least about 18 wt %, more preferably at least about 20 wt %, and the total amount of high molecular weight CMC in the final solution is at least 5 wt %, more preferably at least about 8 wt %, more preferably at least about 10 wt %, more preferably at least about 15 wt % (each relative to the total weight of the CMC solution).

[0025] Preferably, the weight ratio of low molecular weight CMC to 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.

[0026] In a preferred embodiment, the total amount of CMC in the CMC solution is 20 to 50% by weight, the amount of low molecular weight CMC is about 15 to 45% by weight, and the amount of high molecular weight CMC is about 5 to 35% by weight (in each case, the weight % is relative 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 low molecular weight CMC is about 15 to 35% by weight, and the amount of high molecular weight CMC is about 5 to 25% by weight (in each case, the weight % is relative to the total weight of the CMC solution).

[0027] 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.

[0028] Preferably, the weight average molecular weight of low molecular weight CMC is less than 30 kDa and the weight average molecular weight of high molecular weight CMC is greater than 50 kDa. Preferably, the weight average molecular weight of low molecular weight CMC is less than 30 kDa and the weight average molecular weight of high molecular weight CMC is greater than 75 kDa. Preferably, the weight average molecular weight of low molecular weight CMC is less than 30 kDa and the weight average molecular weight of high molecular weight CMC is greater than 100 kDa.

[0029] Preferably, the weight average molecular weight of low molecular weight CMC is less than 20 kDa and the weight average molecular weight of high molecular weight CMC is greater than 50 kDa. Preferably, the weight average molecular weight of low molecular weight CMC is less than 20 kDa and the weight average molecular weight of high molecular weight CMC is greater than 75 kDa. Preferably, the weight average molecular weight of low molecular weight CMC is less than 20 kDa and the weight average molecular weight of high molecular weight CMC is greater than 100 kDa.

[0030] Preferably, the weight average molecular weight of low molecular weight CMC is less than 15 kDa and the weight average molecular weight of high molecular weight CMC is greater than 50 kDa. Preferably, the weight average molecular weight of low molecular weight CMC is less than 15 kDa and the weight average molecular weight of high molecular weight CMC is greater than 75 kDa. Preferably, the weight average molecular weight of low molecular weight CMC is less than 15 kDa and the weight average molecular weight of high molecular weight CMC is greater than 100 kDa.

[0031] CMC with molecular weights in accordance with 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 combination with the above-described method for producing a high solids content CMC solution.

[0032] The degree of substitution of CMC also affects the solubility of solid high Mw CMC in low Mw CMC solution. In this regard, the degree of substitution (“DS”) of high Mw CMC can be A ”) is preferably in the range of about 0.4 to about 1.5. If the DS of the high Mw CMC A Within this range, the solubility of the high Mw CMC in the low Mw CMC is optimal. A ” refers to the average number of substituted ring sites on the β-anhydroglucose ring of the cellulose derivative, where the substituent is anionic (in this case, a carboxymethyl group). Since each anhydroglucose ring of cellulose has three hydroxyl groups available for substitution, DS A The maximum value is 3.0.

[0033] If the anionic substitution degree (“DS A ”) in the range of about 0.4 to about 1.5 is also preferred.

[0034] Therefore, in a preferred embodiment, the weight average molecular weight of the low molecular weight CMC is less than 30 kDa, preferably less than 20 kDa, more preferably less than 15 kDa, and the DS of the high molecular weight CMC is less than 10 kDa. A The molecular weight is from about 0.4 to about 1.5 and the weight average molecular weight is at least 30 kDa, preferably 50 kDa, more preferably at least 75 kDa, more preferably at least 100 kDa.

[0035] In a more preferred embodiment, the DS of the low molecular weight CMC is A The DS of high molecular weight CMC is about 0.4 to about 1.5 and the weight average molecular weight is less than 30 kDa, preferably less than 20 kDa, more preferably less than 15 kDa. A The molecular weight is from about 0.4 to about 1.5 and the weight average molecular weight is at least 30 kDa, preferably 50 kDa, more preferably at least 75 kDa, and more preferably at least 100 kDa.

[0036] Therefore, in a preferred embodiment, the method for producing a high solids, low viscosity CMC solution comprises the following steps:

[0037] 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

[0038] 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) in (preferably substantially dry) solid form (preferably in powder form),

[0039] 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 about 20 to 50 wt %, 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 wt % and the amount of high molecular weight CMC in the final solution is at least 5 wt % (in each case, wt % relative to the total weight of the CMC solution).

[0040] In a further preferred embodiment, the method for producing a high solids, low viscosity CMC solution comprises the following steps:

[0041] 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

[0042] 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) in (preferably substantially dry) solid form (preferably in powder form),

[0043] 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 about 20 to 50 wt %, 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 wt % and the amount of high molecular weight CMC in the final solution is at least 5 wt % (in each case, wt % relative to the total weight of the CMC solution), and wherein 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.

[0044] In a further preferred embodiment, the method for producing a high solids, low viscosity CMC solution comprises the following steps:

[0045] a) obtaining a compound comprising at least one compound having a weight average molecular weight of less than 30 kDa and a DS A An aqueous solution of low molecular weight carboxymethyl cellulose (CMC) at about 0.4 to about 1.5; and

[0046] b) at least one oligonucleotide having a molecular weight of at least 30 kDa and a DS A A high molecular weight CMC of about 0.4 to about 1.5 is dissolved in the solution of step a), wherein the at least one high molecular weight CMC is added to the solution of step a) in a (preferably substantially dry) solid form (preferably in a powder form),

[0047] 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 about 20 to 50 wt %, and the amount of low molecular weight CMC in the final solution is at least 15 wt % and the amount of high molecular weight CMC in the final solution is at least 5 wt % (in each case, wt % relative to the total weight of the CMC solution), and wherein 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.

[0048] Preferably, the at least one high molecular weight CMC is added to the solution of step a) in (preferably substantially dry) solid form (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 temperature of the solution of step a) is preferably adjusted to about 20°C to 70°C, preferably about 25-65°C, preferably about 25-60°C before adding the high molecular weight CMC). Therefore, in a further preferred embodiment, the method for producing a high solid, low viscosity CMC solution comprises the following steps:

[0049] a) obtaining an aqueous solution comprising at least one low molecular weight CMC having a weight average molecular weight of less than 30 kDa;

[0050] b) adjusting the temperature of the solution of step a) to about 20°C to about 70°C, and

[0051] 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 the at least one high molecular weight CMC is added to the solution of step b) in (preferably substantially dry) solid form (preferably in powder form),

[0052] 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 wt % (relative to the total weight of the CMC solution).

[0053] In a further preferred embodiment, the method for producing a high solids, low viscosity CMC solution comprises the following steps:

[0054] a) obtaining a polyol comprising at least one polyol with a weight average molecular weight of less than 30 kDa and optionally DS A An aqueous solution of low molecular weight carboxymethyl cellulose (CMC) of about 0.4 to about 1.5,

[0055] b) adjusting the temperature of the solution of step a) to about 25°C to 65°C, and

[0056] c) at least one having a weight average molecular weight of at least 30 kDa and optionally DS A A high molecular weight CMC of about 0.4 to about 1.5 is dissolved in the solution of step b), wherein the at least one high molecular weight CMC is added to the solution of step b) in a (preferably substantially dry) solid form (preferably in a powder form),

[0057] wherein the amounts of low molecular weight CMC and high molecular weight CMC added in steps a) and c) respectively are such that the total amount of CMC in the solution is about 20 to 50 wt %, 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 wt % and the amount of high molecular weight CMC in the final solution is at least 5 wt % (in each case, wt % relative to the total weight of the CMC solution), and 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.

[0058] Of course, the present disclosure also relates to CMC solutions produced by the above-mentioned method and its preferred embodiments. As mentioned above, these CMC solutions are characterized in that they contain a large amount (weight %) of CMC, while having unexpected beneficial rheological properties (especially unexpectedly low viscosity) of such solutions. In this regard, the second aspect of the present disclosure is related to a high solids, low viscosity CMC solution, which comprises:

[0059] a) water;

[0060] b) at least one low molecular weight CMC having a weight average molecular weight of less than 30 kDa; and

[0061] c) at least one high molecular weight CMC having a weight average molecular weight of at least 30 kDa,

[0062] The total amount of CMC in the solution is at least 18 wt % (relative to the total weight of the CMC solution), and the viscosity of the CMC solution is 5000 mPas or less (Brookfield RV, 100 rpm, 40° C., spindle No. 6).

[0063] In a preferred embodiment, the CMC solution comprises:

[0064] a) water;

[0065] b) at least one low molecular weight CMC having a weight average molecular weight of less than 30 kDa; and

[0066] c) at least one high molecular weight CMC having a weight average molecular weight of at least 30 kDa,

[0067] wherein the total amount of CMC in the solution is at least 20 wt. %, wherein the amount of low molecular weight CMC in the final solution is at least 15 wt. % and the amount of high molecular weight CMC in the final solution is at least 5 wt. % (in each case, the wt. % relative to the total weight of the CMC solution), and wherein the viscosity of the CMC solution is 5000 mPas or less (Brookfield RV, 100 rpm, 40° C., spindle 6).

[0068] In another preferred embodiment, the CMC solution comprises:

[0069] a) water;

[0070] b) at least one low molecular weight CMC having a weight average molecular weight of less than 30 kDa; and

[0071] c) at least one high molecular weight CMC having a weight average molecular weight of at least 30 kDa,

[0072] wherein the total amount of CMC in the solution is about 20 to 40 wt. %, wherein the amount of low molecular weight CMC in the final solution is at least 15 wt. % and the amount of high molecular weight CMC in the final solution is at least 5 wt. % (in each case, the wt. % 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 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, wherein the viscosity of the CMC solution is 5000 mPas or less (Brookfield RV, 100 rpm, 40° C., spindle 6).

[0073] In another preferred embodiment, the CMC solution comprises:

[0074] a) water;

[0075] b) at least one weight average molecular weight less than 30 kDa and DS A A low molecular weight CMC of 0.4 to about 1.5; and

[0076] c) at least one compound having a weight average molecular weight of at least 30 kDa and a DS A High molecular weight CMC from 0.4 to about 1.5,

[0077] wherein the total amount of CMC in the solution is about 20 to 50 wt. %, wherein the amount of low molecular weight CMC in the final solution is at least 15 wt. % and the amount of high molecular weight CMC in the final solution is at least 5 wt. % (in each case, the wt. % 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 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, wherein the viscosity of the CMC solution is 5000 mPas or less (Brookfield RV, 100 rpm, 40° C., spindle 6).

[0078] 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, more preferably about 60% to about 70% by weight of water (in each case, the weight % is relative to the total weight of the CMC solution).

[0079] The CMC solution produced by the above method may also contain a plasticizer, such as but not limited to sorbitol, glycerol, mannitol and / or xylitol. The plasticizer may be present in any suitable amount, such as 1-50 wt % (relative to the total weight of the CMC solution). The high solids CMC solution may also contain other additives conventionally used in barrier coating applications, such as crosslinking agents, pigments, etc.

[0080] The pH of the high solids CMC solution is preferably from about 4.5 to about 7.5. An unexpected discovery is that a CMC solution having a pH in this range can be produced by the process, which generally extends the shelf life of the solution regardless of the presence of impurities in the solution.

[0081] In a third aspect, the present disclosure relates to the use of a high solids CMC solution as described above as a surface treatment agent (eg, a barrier coating) for paper and paperboard substrates.

[0082] In a fourth aspect, the present disclosure is directed to a method of treating the surface of a paper or paperboard substrate, comprising applying a high solids CMC solution as described above to the surface of the paper or paperboard substrate.

[0083] In a fifth aspect, the present disclosure relates to a surface treated paper or paperboard substrate obtained by the method of the fourth aspect of the present disclosure.

[0084] In a sixth aspect, the present disclosure relates to the use of a high solids content CMC solution as described above as a supplementary binder and / or thickener.

[0085] Example

[0086] The following examples provide detailed methods for practicing the present invention. These working examples are illustrative in nature and are not intended to limit the present invention.

[0087] Example 1

[0088] 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 cellulose ethers in the desired amounts to obtain the desired ratio of cellulose ethers. However, as mentioned above, there is a limit to the amount of high molecular weight cellulose ether that can be dissolved, after which the resulting solution is no longer suitable for processing (i.e., not pumpable). This limits the maximum total solids content that can be achieved with a solution containing a high Mw cellulose ether, which in turn hinders the ability to achieve the desired barrier properties of the coating.

[0089] To illustrate this problem, two CMCs were chosen:

[0090] CMC1–Mw<30kDa (“LMw CMC”)

[0091] CMC2–Mw>200kDa (“HMw CMC”).

[0092] For solutions containing only CMC1, the maximum total solids content achievable was found to be about 35 wt%.

[0093] However, for solutions with CMC2 alone, the maximum achievable total solids content was found to be about 5 wt% (limited by the high molecular weight of >200 kDa; the viscosity of a 5 wt% solution at 25°C is >20000 mPas).

[0094] In order to increase the total solid content of the solution containing CMC2, the inventors aimed to produce a solution in which the solid content ratio of CMC1 to CMC2 was 80:20. This was achieved by mixing 229 grams of CMC1 solution with 400 grams of CMC2 solution to achieve the desired solid content ratio. It was found that the total CMC content of the 80:20 weight ratio (CMC1:CMC2) that can be achieved by conventional methods (mixing the solutions) is about 16 weight %.

[0095] However, a CMC solution having about twice the total CMC content (30 wt%) can be prepared by first preparing a low Mw CMC solution of about 25.5% (i.e., no maximum solids content is required) and then mixing (at 600 rpm and 60° C.) the required amount (22 grams) of high Mw CMC in substantially dry powder form (8 wt% moisture content) into the low molecular weight CMC solution to achieve the desired 80:20 ratio:

[0096] Table 1

[0097]

[0098] This indicates that the present method brings about significant improvements in the following aspects: not only the total amount of CMC is significantly increased, but also the total amount of high molecular weight CMC in the CMC solution is significantly increased.

[0099] The CMC solutions of the present invention are particularly suitable for use as thickeners for paper and paperboard coatings.

[0100] Example 2

[0101] 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.

[0102] In this regard, a second group of CMCs was tested:

[0103] CMC3–Mw<15kDa (“LMw CMC”)

[0104] CMC4–Mw>30-40kDa (“HMw CMC”).

[0105] For these CMCs, it was found that following the methods disclosed herein could again produce CMC solutions with high total solids contents. Notably, the weight ratio of low Mw CMC to high Mw CMC could be increased to 1:1 while maintaining a high total CMC content and excellent rheological properties. To achieve this, a 25.5% low Mw CMC solution (196 grams; 49.98 g dry low Mw CMC) was mixed (60°C, 600 rpm) with the required amount of high Mw CMC (approximately 54 grams; 49.68 g dry high molecular weight CMC) in essentially dry form (8% moisture content) to achieve the desired 1:1 ratio. The resulting CMC solution was adjusted to a final 25 wt% CMC content by dilution with water:

[0106] Table 2

[0107] The present invention Weight ratio of CMC3 to CMC4 1:1 CMC content of final solution (wt%) 25 High Hw CMC content of final solution (wt%) 12.5 Viscosity (mPas; Brookfield RV, No. 6 rotor, 100 rpm, 40°C) 3400

[0108] The inventors were unable to prepare an equivalent solution having such a high concentration of high Mw CMC and low viscosity using other known processes (including the solution mixing process given in Example 1); the maximum total CMC content achieved by the conventional method (see Example 1) was 17.8 wt% (the ratio of low Mw CMC to high Mw CMC was 1:1).

[0109] Accordingly, the present inventors have now developed a process for producing CMC solutions which, to the present inventors' knowledge, have previously unattainable high molecular weight CMC levels while having rheological properties which render them suitable for use in paper / paperboard coating and barrier applications.

[0110] In summary, the present inventors have developed an improved method for preparing CMC solutions having a significantly increased total amount of CMC, particularly high molecular weight CMC, while maintaining excellent rheological properties.

[0111] Although at least one exemplary embodiment has been proposed in the foregoing detailed description, it should be appreciated that there are a large number of variations. It should also be appreciated that exemplary embodiments or exemplary embodiments are merely examples and are not intended to limit the scope, applicability or configuration of the present invention in any way. On the contrary, the foregoing detailed description will provide a convenient roadmap for those skilled in the art to implement the exemplary embodiments contemplated herein. It should be understood that various changes may be made to the functions and arrangements of the elements described in the exemplary embodiments without departing from the scope of the present invention described in the appended claims.

[0112] The present disclosure can be further described by the following aspects.

[0113] Aspect 1. A method for producing a high solid, low viscosity carboxymethyl cellulose (CMC) solution, the method comprising the following steps:

[0114] a) obtaining an aqueous solution comprising at least one low molecular weight CMC having a weight average molecular weight of less than 30 kDa; and

[0115] 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) in solid form, preferably in powder form,

[0116] 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 wt % (relative to the total weight of the CMC solution).

[0117] Aspect 2. The process of aspect 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 wt. %, preferably at least 25 wt. %, preferably at least 28 wt. % and most preferably at least 30 wt. % (in each case, wt. % relative to the total weight of the CMC solution).

[0118] Aspect 3. The method of aspect 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 about 18 to 50 wt%.

[0119] Aspect 4. The method of any one of aspects 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 about 20 to 40 wt%.

[0120] Aspect 5. The method of any of Aspects 1-4, 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 wt %, and the total amount of high molecular weight CMC in the final solution is at least 5 wt % (in each case, wt % relative to the total weight of the CMC solution).

[0121] Aspect 6. The method of any one of Aspects 1-5, wherein the total amount of CMC in the CMC solution is 20 to 50 wt %, the amount of low molecular weight CMC is about 15 to 45 wt %, and the amount of high molecular weight CMC is about 5 to 35 wt % (in each case, weight % is relative to the total weight of the CMC solution).

[0122] Aspect 7. The method of any one of aspects 1-6, wherein the weight ratio of low molecular weight CMC to high molecular weight CMC in the CMC solution (low Mw:high Mw) is about 3:7 to 9:1.

[0123] Aspect 8. The method of any one of Aspects 1-7, wherein the total amount of CMC in the CMC solution is 20 to 40 wt %, the amount of low molecular weight CMC is about 15 to 35 wt %, and the amount of high molecular weight CMC is about 5 to 25 wt % (in each case, weight % is relative to the total weight of the CMC solution).

[0124] Aspect 9. The method of any one of aspects 1-8, wherein the weight ratio of low molecular weight CMC to high molecular weight CMC in the CMC solution (low Mw:high Mw) is about 1:2 to 5:1.

[0125] Aspect 10. The method of any one of aspects 1-9, wherein the weight ratio of low molecular weight CMC to high molecular weight CMC in the CMC solution (low Mw:high Mw) is about 1:1 to 4:1.

[0126] Aspect 11. The method of any one of aspects 1 to 10, wherein the solid high molecular weight CMC is in the form of a powder.

[0127] Aspect 12. The method of any of Aspects 1-11, wherein the solid high molecular weight CMC is a substantially dry solid having a total water content of 15 wt% or less (relative to the total weight of the substantially dry solid high molecular weight CMC).

[0128] Aspect 13. The method of any of aspects 1-12, 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.

[0129] Aspect 14. The method of any of aspects 1-12, 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.

[0130] Aspect 15. The method of any of aspects 1-12, 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.

[0131] Aspect 16. The method of any of aspects 1-12, 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.

[0132] Aspect 17. The method of any of aspects 1-12, 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.

[0133] Aspect 18. The method of any of aspects 1-12, 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.

[0134] Aspect 19. The method of any of aspects 1-12, 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.

[0135] Aspect 20. The method of any of Aspects 1-12, 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.

[0136] Aspect 21. The method of any of Aspects 1-12, 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.

[0137] Aspect 22. The method of any of Aspects 1-12, 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.

[0138] Aspect 23. The method of any of aspects 1-12, 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.

[0139] Aspect 24. The method of any of Aspects 1-12, 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 up to about 50 kDa.

[0140] Aspect 25. The method of any one of aspects 1 to 24, wherein the anionic degree of substitution (DS A ) is from about 0.4 to about 1.5.

[0141] Aspect 26. The method of any one of aspects 1 to 25, wherein the anionic degree of substitution (DS A ) is from about 0.4 to about 1.5.

[0142] Aspect 27. The method of any one of aspects 1 to 26, wherein the anionic degree of substitution (DS A ) is from about 0.4 to about 1.5 and wherein the anionic substitution degree (DS A ) is from about 0.4 to about 1.5.

[0143] Aspect 28. The method of any one of Aspects 24-27, wherein the weight average molecular weight of the high molecular weight CMC is greater than 30 kDa and wherein the weight average molecular weight of the low molecular weight CMC is less than 20 kDa.

[0144] Aspect 29. The method of any one of aspects 1 to 28, wherein the temperature of the aqueous solution of step a) is adjusted to about 25-60° C. before step b).

[0145] Aspect 30. The method of any one of aspects 1-29, wherein the CMC solution further comprises a plasticizer.

[0146] Aspect 31. The method of any one of aspects 1-30, wherein the pH of the CMC solution is from about 4.5 to about 7.5.

[0147] Aspect 32. A CMC solution obtained by the method of any one of aspects 1-31.

[0148] Aspect 33. A CMC solution comprising:

[0149] a) water;

[0150] b) at least one low molecular weight CMC having a weight average molecular weight of less than 30 kDa; and

[0151] c) at least one high molecular weight CMC having a weight average molecular weight of at least 30 kDa,

[0152] The total amount of CMC in the solution is at least 18 wt % (relative to the total weight of the CMC solution), and the viscosity of the CMC solution is 5000 mPas or less (Brookfield RV, 100 rpm, 40° C., No. 6 spindle).

[0153] Aspect 34. The CMC solution of Aspect 33, wherein the CMC solution comprises:

[0154] a) water;

[0155] b) at least one low molecular weight CMC having a weight average molecular weight of less than 30 kDa; and

[0156] c) at least one high molecular weight CMC having a weight average molecular weight of at least 30 kDa,

[0157] wherein the total amount of CMC in the solution is at least 20 wt. %, wherein the amount of low molecular weight CMC in the solution is at least 15 wt. % and the amount of high molecular weight CMC in the solution is at least 5 wt. % (in each case, the wt. % relative to the total weight of the CMC solution), and wherein the viscosity of the CMC solution is 5000 mPas or less (Brookfield RV, 100 rpm, 40° C., spindle 6).

[0158] Aspect 35. The CMC solution of Aspect 33 or 34, wherein the total amount of CMC in the solution is about 20 to 40 wt %, wherein the amount of low molecular weight CMC in the final solution is at least 15 wt % and the amount of high molecular weight CMC in the final solution is at least 5 wt % (in each case, wt % relative to the total weight of the CMC solution).

[0159] Aspect 36. The CMC solution of any one of Aspects 33-35, wherein the weight ratio of low molecular weight CMC to high molecular weight CMC in the final solution is about 3:7 to 9:1.

[0160] Aspect 37. The CMC solution of any one of Aspects 33-36, wherein the weight ratio of low molecular weight CMC to high molecular weight CMC in the final solution is about 1:2 to 5:1.

[0161] Aspect 38. The CMC solution of any one of Aspects 33-37, wherein the weight ratio of low molecular weight CMC to high molecular weight CMC in the final solution is about 1:2 to 4:1.

[0162] Aspect 39. The CMC solution of any one of Aspects 33-38, wherein the weight ratio of low molecular weight CMC to high molecular weight CMC in the final solution is about 1:1 to 4:1.

[0163] Aspect 40. The CMC solution of any one of Aspects 33-39, wherein the at least one low molecular weight CMC has a weight average molecular weight of less than 30 kDa and a DS A From 0.4 to about 1.5.

[0164] Aspect 41. The CMC solution of any one of Aspects 33-39, wherein the at least one low molecular weight CMC has a weight average molecular weight of less than 15 kDa and a DS A From 0.4 to about 1.5.

[0165] Aspect 42. The CMC solution of any one of Aspects 33-41, wherein the at least one high molecular weight CMC has a weight average molecular weight greater than 30 kDa and a DS A From 0.4 to about 1.5.

[0166] Aspect 43. The CMC solution of any of Aspects 33-42, wherein the at least one high molecular weight CMC has a weight average molecular weight of greater than 30 kDa up to about 50 kDa and a DS A From 0.4 to about 1.5.

[0167] Aspect 44. The CMC solution of any one of Aspects 33-43, wherein the CMC solution contains at least 40 wt% water.

[0168] Aspect 45. The CMC solution of any one of Aspects 33-44, wherein the CMC solution further comprises at least one plasticizer.

[0169] Aspect 46. The CMC solution of Aspect 45, wherein the plasticizer is selected from sorbitol, glycerol, mannitol and / or xylitol.

[0170] Aspect 47. The CMC solution of any one of Aspects 44-46, wherein the pH of the CMC solution is from about 4.5 to about 7.5.

[0171] Aspect 48. Use of the high solids CMC solution of any one of Aspects 33-47 as a surface treatment agent for paper and paperboard substrates.

[0172] Aspect 49. Use of the high solids CMC solution of any one of Aspects 33-47 as a barrier coating for paper and paperboard substrates.

[0173] Aspect 50. A method for treating the surface of a paper and paperboard substrate, comprising applying the CMC solution according to any one of aspects 33-47 to the surface of the paper and paperboard substrate.

[0174] Aspect 51. A surface treated paper and paperboard substrate obtained by the method of Aspect 50.

[0175] Aspect 52. Use of the high solids CMC solution of any one of Aspects 33 to 47 as an auxiliary binder and / or thickener.

Claims

1. A method for producing a high solid, 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; 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 the at least one high molecular weight CMC is added to the solution of step a) in solid form, 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 wt %, relative to the total weight of the CMC solution.

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

3. The process 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 about 15% by weight and the total amount of high molecular weight CMC in the final solution is at least 5% by weight, the % by weight being in each case relative to the total weight of the CMC solution.

4. The method according to any one of claims 1 to 3, wherein the weight ratio of low molecular weight CMC to high molecular weight CMC in the CMC solution (low Mw:high Mw) is from about 3:7 to about 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 method according to any one of claims 1 to 5, wherein the anionic degree of substitution (DS A ) is from about 0.4 to about 1.5 and wherein the anionic substitution degree (DS A ) is from about 0.4 to about 1.

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; and 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 wt %, relative to the total weight of the CMC solution, and wherein the viscosity of the CMC solution is 5000 mPas or less (Brookfield RV, 100 rpm, 40° C., spindle No. 6).

8. The CMC solution according to claim 7, 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 wherein the amount of high molecular weight CMC in the solution is at least 5% by weight, the weight % being in each case relative to the total weight of the CMC solution.

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

10. The CMC solution of any one of claims 7-9, wherein the pH of the CMC solution is about 4.5 to about 7.

5.

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

12. A method for treating the surface of a paper or paperboard substrate, comprising 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 process according to claim 12.

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

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