Mixed suspension

Abstract

DEPCT65 This mixed suspension contains (1) a dispersant, (2) nanofibers. Cellulose and (3) fillers -----------------------------------------------------------

Description

mixed liquid

[0001] The present invention relates to a mixed liquid containing cellulose nanofibers and a filler.

[0002] Nanotechnology, the art of freely controlling matter at the nanometer scale, or the atomic and molecular scale, is expected to lead to the creation of a variety of convenient new materials and devices. One example is cellulose nanofiber, obtained by finely disintegrating plant fibers. Because these cellulose nanofibers are highly crystalline, have a low coefficient of thermal expansion, a high modulus of elasticity, and a high aspect ratio, they are expected to be effective as additives that impart strength and shape stabilization. Furthermore, in a dispersed state, they possess viscosity properties such as pseudoplasticity and thixotropy, making them promising additives for thickening and other applications.

[0003] Various developments and researches have been conducted on cellulose nanofibers. For example, Patent Document 1 discloses fine cellulose fibers (cellulose nanofibers) having a number-average fiber diameter of 2 to 150 nm, in which carboxyl groups have been introduced into some of the hydroxyl groups of cellulose.

[0004] These cellulose nanofibers have functions such as imparting strength and shape stability, and because they have properties such as high viscosity at low shear rates and low viscosity at high shear rates, they are used as high-performance thickeners in a variety of fields, including food, pharmaceuticals and cosmetics, daily necessities, civil engineering and building materials, paper, paints and inks, and other industrial materials. In these fields, mixed liquids containing fillers are sometimes used, and it has been found that adding cellulose nanofibers as a thickener improves the dispersion stability of the fillers.

[0005] Japanese Patent Application Laid-Open No. 2008-1728

[0006] However, there has been a demand for a mixed liquid containing cellulose nanofibers that has even better filler dispersion stability.

[0007] Therefore, an object of the present invention is to provide a mixed liquid containing cellulose nanofibers that has excellent dispersion stability of the filler.

[0008] The present invention provides the following [1] to [8]. [1] A mixed liquid containing the following (1) to (3): (1) a dispersant; (2) a cellulose nanofiber; and (3) a filler. [2] The mixed liquid according to [1], wherein the dispersant is an anionic polymer compound. [3] The mixed liquid according to [2], wherein the anionic polymer compound is a polymer compound having a carboxy group or a polymer compound having a phosphate group. [4] The mixed liquid according to [1] to [3], wherein the cellulose nanofiber is anion-modified cellulose nanofiber. [5] The mixed liquid according to [4], wherein the anion-modified cellulose nanofiber is oxidized cellulose nanofiber. [6] The mixed liquid according to [5], wherein the carboxy group amount of the oxidized cellulose nanofiber is 0.4 to 1.0 mmol / g. [7] The mixed liquid according to [1] to [6], wherein the cellulose nanofiber is added in an amount of 0.1 mass% or more. [8] The mixed solution according to any one of [1] to [7], wherein the water separation rate after standing for 72 hours is less than 1%.

[0009] According to the present invention, a mixed liquid containing cellulose nanofibers that has excellent filler dispersion stability can be provided.

[0010] The mixed liquid of the present invention is characterized by containing (1) a dispersant, (2) cellulose nanofibers, and (3) a filler.

[0011] (1) Dispersant The dispersant can be used without any particular limitation as long as it achieves the effects of the present invention. For example, any low-molecular-weight or high-molecular-weight compound, such as a carboxylic acid-based, urethane-based, acrylic resin-based, polyether-based, polyester-based, or fatty acid-based compound, can be used. It is preferable to select a compound that provides good dispersibility, taking into consideration the properties of the filler and cellulose nanofibers to be incorporated into the mixed solution of the present invention. Since cellulose nanofibers contain many hydroxyl groups, dispersibility may be impaired if the dispersant contains many hydrophobic groups. Furthermore, any type of anionic, cationic, or nonionic dispersant can be used. One type of dispersant may be used alone, or two or more types may be mixed and used. The dispersant used in the present invention does not include the cellulose nanofibers described in (2).

[0012] When an anionic polymer compound is used as the dispersant, a polymer compound having functional groups such as a carboxy group, a sulfonic acid group, a phosphate group, or a sulfate ester group can be used, and when used at a pH higher than the pKa (acid dissociation constant) of the respective functional group, the anionic group is formed, allowing the mixture to be prepared without causing aggregation of the anionic cellulose nanofiber dispersion. The functional group can be selected appropriately depending on the pH of the mixture to be prepared and the required basicity.

[0013] Examples of polymeric compounds having a carboxy group include polycarboxylic acid, carboxymethyl cellulose, and alginic acid. Examples of polycarboxylic acids include polyacrylic acid, sodium polyacrylate, styrene-maleic anhydride copolymers, and olefin-maleic anhydride copolymers. When a polymeric compound having a carboxy group is used as a dispersant, the carboxy group may be in the form of a metal salt or an ammonium salt. When the mixed liquid of the present invention is used in an application requiring water resistance, the ammonium salt type can be appropriately selected.

[0014] Examples of polymer compounds having a phosphate group include polyoxyethylene alkyl ether phosphate, polyoxyethylene phenyl ether phosphate, and alkyl phosphate ester.

[0015] Examples of polyether compounds include pluronic polyethers, polyether dialkyl esters, polyether dialkyl ethers, polyether epoxy modified products, and polyether amines. For example, by changing the ratio of polyoxyethylene or polyoxypropylene, the balance between hydrophilicity and hydrophobicity can be adjusted. Examples of urethane compounds include urethane association compounds. For example, by adding polyester chains or polyether chains as side chains to a polyurethane main skeleton, compatibility and steric hindrance stability can be adjusted. Examples of fatty acid compounds include aliphatic alcohol sulfates, aliphatic amines, and aliphatic esters.

[0016] The amount of dispersant added to the mixed solution of the present invention is sufficient to disperse the filler sufficiently, and is preferably 0.01 to 25 parts by mass, more preferably 0.1 to 10 parts by mass, per 100 parts by mass of the filler.

[0017] (2) Cellulose Nanofibers In the present invention, cellulose nanofibers (CNFs) are fine fibers with a fiber diameter of approximately 3 to 500 nm, which are obtained by pulp or other cellulose raw materials being refined to the nanometer level. The average fiber diameter and average fiber length of cellulose nanofibers can be obtained by averaging the fiber diameters and fiber lengths obtained from the observation of each fiber using an atomic force microscope (AFM) or a transmission electron microscope (TEM). Cellulose nanofibers can be obtained by applying mechanical force to pulp to refine it, or by defibrating modified cellulose obtained by chemical modification, such as anion-modified cellulose (carboxylated cellulose (also called oxidized cellulose), carboxymethylated cellulose, cellulose with phosphate ester groups introduced, etc.) or cation-modified cellulose. The average fiber length and average fiber diameter of the fine fibers can be adjusted by oxidation treatment or defibration treatment.

[0018] The average aspect ratio of the cellulose nanofibers used in the present invention is usually 50 or more. There is no particular upper limit, but it is usually 1000 or less, more preferably 700 or less, and even more preferably 500 or less. The average aspect ratio can be calculated using the following formula: Aspect ratio = average fiber length / average fiber diameter

[0019] <Cellulose Raw Material> The origin of the cellulose raw material that is the raw material for cellulose nanofibers is not particularly limited, and examples include plants (e.g., wood, bamboo, hemp, jute, kenaf, agricultural waste, cloth, pulp (e.g., unbleached softwood kraft pulp (NUKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), bleached hardwood kraft pulp (LBKP), bleached kraft pulp (BKP), unbleached softwood sulfite pulp (NUSP), bleached softwood sulfite pulp (NBSP), thermomechanical pulp (TMP), recycled pulp, waste paper, etc.), animals (e.g., ascidians), algae, microorganisms (e.g., acetic acid bacteria (Acetobacter)), microbial products, etc. The cellulose raw material may be any one of these or a combination of two or more types, but is preferably a cellulose raw material (e.g., cellulose fiber) derived from a plant or microorganism, and more preferably a cellulose raw material (e.g., cellulose fiber) derived from a plant.

[0020] The number average fiber diameter of the cellulose raw material is not particularly limited, but is about 30 to 60 μm in the case of softwood kraft pulp, which is a common pulp, and about 10 to 30 μm in the case of hardwood kraft pulp. In the case of other pulps, those that have undergone general refinement have a diameter of about 50 μm. For example, when chips or the like that are refined into pieces several centimeters in size are subjected to mechanical processing using a disintegrator such as a refiner or beater, and it is preferable to adjust the diameter to about 50 μm.

[0021] <Chemical Modification> In the present invention, the modified cellulose may be anionically modified or cationically modified, and it is preferable to use a modified cellulose that allows for good filler dispersion in accordance with the types of filler and dispersant to be blended in the mixed liquid of the present invention. For example, when an anionic polymer compound is used as a dispersant, it is preferable to select anionically modified cellulose nanofiber from the viewpoint of easily obtaining a synergistic effect for suppressing filler aggregation.

[0022] Examples of functional groups introduced by anionic modification include a carboxy group, a carboxymethyl group, a sulfone group, a phosphate ester group, and a nitro group. Of these, the carboxy group, the carboxymethyl group, and the phosphate ester group are preferred, and the carboxy group is more preferred.

[0023] (Carboxylation) When carboxylated (oxidized) cellulose is used as the modified cellulose in the present invention, the carboxylated cellulose (also referred to as oxidized cellulose) can be obtained by carboxylating (oxidizing) the above-mentioned cellulose raw material using a known method. During carboxylation, the amount of carboxy groups is preferably adjusted to 0.2 to 1.55 mmol / g, and more preferably 0.4 to 1.0 mmol / g, based on the bone-dry mass of the anion-modified cellulose nanofibers. If the amount of carboxy groups is too low, a large amount of energy is required for defibration to obtain a highly transparent and uniform nanofiber dispersion. Highly transparent nanofiber dispersions contain little residual coarse material, such as undefibrated fibers, and therefore do not impair the appearance of the mixture. Furthermore, if the amount of carboxy groups is too high, there are concerns about a decrease in the viscosity of the nanofiber dispersion due to fiber degradation caused by the reaction of an excessive amount of oxidizing chemicals, and a decrease in viscosity retention due to stirring. Although the relationship between the amount of carboxyl groups and viscosity retention is not entirely clear, it is presumed that if modified pulp with a low degree of modification is sufficiently defibrated, areas with hydroxyl groups that have not been chemically surface-treated will be exposed, which will not only reduce the surface charge of the oxidized CNF but also make it easier for the oxidized CNF to form hydrogen bonds with each other, thereby maintaining viscosity at low shear.

[0024] An example of a method for measuring the amount of carboxy groups is described below. 60 mL of a 0.5% by mass slurry (aqueous dispersion) of oxidized cellulose is prepared, and after adding 0.1 M aqueous hydrochloric acid to adjust the pH to 2.5, 0.05 N aqueous sodium hydroxide is added dropwise and the electrical conductivity is measured until the pH reaches 11. The amount of carboxy groups can be calculated using the following formula from the amount of sodium hydroxide (a) consumed in the neutralization stage of a weak acid, where the change in electrical conductivity is gradual: Amount of carboxy groups [mmol / g oxidized cellulose] = a [mL] × 0.05 / mass of oxidized cellulose [g]

[0025] An example of a carboxylation (oxidation) method is a method in which a cellulose raw material is oxidized in water using an oxidizing agent in the presence of an N-oxyl compound and a compound selected from the group consisting of bromides, iodides, or a mixture thereof. This oxidation reaction selectively oxidizes the primary hydroxyl group at the C6 position of the glucopyranose ring on the surface of the cellulose, leaving aldehyde groups and carboxy groups (-COOH) or carboxylate groups (-COO － The concentration of cellulose during the reaction is not particularly limited, but is preferably 5% by mass or less.

[0026] An N-oxyl compound refers to a compound capable of generating a nitroxy radical. Any compound can be used as the N-oxyl compound as long as it promotes the target oxidation reaction. Examples include 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) and its derivatives (e.g., 4-hydroxyTEMPO).

[0027] The amount of the N-oxyl compound used is not particularly limited, as long as it is a catalytic amount that can oxidize the raw material cellulose. For example, the amount is preferably 0.01 to 10 mmol, more preferably 0.01 to 1 mmol, and even more preferably 0.05 to 0.5 mmol, per 1 g of bone-dry cellulose. The amount is preferably about 0.1 to 4 mmol / L relative to the reaction system.

[0028] Bromides are compounds containing bromine, examples of which include alkali metal bromides that can dissociate and ionize in water. Iodides are compounds containing iodine, examples of which include alkali metal iodides. The amount of bromide or iodide used can be selected within a range that can promote the oxidation reaction. The total amount of bromide and iodide is, for example, preferably 0.1 to 100 mmol, more preferably 0.1 to 10 mmol, and even more preferably 0.5 to 5 mmol, per 1 g of bone-dry cellulose.

[0029] Known oxidizing agents can be used, such as halogens, hypohalous acids, halous acids, perhalogen acids or their salts, halogen oxides, and peroxides. Among these, sodium hypochlorite is preferred because it is inexpensive and has a low environmental impact. The amount of oxidizing agent used is, for example, preferably 0.5 to 500 mmol, more preferably 0.5 to 50 mmol, even more preferably 1 to 25 mmol, and most preferably 3 to 10 mmol, per 1 g of bone-dry cellulose. Furthermore, for example, 1 to 40 mol is preferred per 1 mol of the N-oxyl compound.

[0030] The oxidation of cellulose can proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature is preferably 4 to 40°C, or may be room temperature, about 15 to 30°C. As the reaction proceeds, carboxyl groups are generated in the cellulose, causing a decrease in the pH of the reaction solution. To efficiently proceed with the oxidation reaction, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution at about 8 to 12, preferably about 10 to 11. Water is preferred as the reaction medium because it is easy to handle and is less likely to cause side reactions.

[0031] The reaction time in the oxidation reaction can be appropriately set depending on the degree of progress of the oxidation, and is usually from 0.5 to 6 hours, for example, from about 0.5 to 4 hours.

[0032] The oxidation reaction may also be carried out in two stages. For example, the oxidized cellulose obtained by filtration after the completion of the first-stage reaction can be oxidized again under the same or different reaction conditions, thereby enabling efficient oxidation without reaction inhibition by sodium chloride produced as a by-product in the first-stage reaction.

[0033] Another example of a carboxylation (oxidation) method is a method in which cellulose raw materials are oxidized by contacting them with an ozone-containing gas. This oxidation reaction oxidizes at least the hydroxyl groups at positions 2 and 6 of the glucopyranose ring, and decomposes the cellulose chain. The ozone concentration in the ozone-containing gas is 50 to 250 g / m. ３ It is preferable that the density is 50 to 220 g / m ３ It is more preferable that the ozone addition amount relative to the cellulose raw material is preferably 0.1 to 30 parts by mass, and more preferably 5 to 30 parts by mass, based on 100 parts by mass of the solids content of the cellulose raw material. The ozone treatment temperature is preferably 0 to 50°C, and more preferably 20 to 50°C. The ozone treatment time is not particularly limited, but is approximately 1 to 360 minutes, and preferably approximately 30 to 360 minutes. When the ozone treatment conditions are within these ranges, excessive oxidation and decomposition of cellulose can be prevented, resulting in a good yield of oxidized cellulose. After the ozone treatment, a further oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used in the further oxidation treatment is not particularly limited, but examples include chlorine-based compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfuric acid, and peracetic acid. For example, the further oxidation treatment can be performed by dissolving these oxidizing agents in water or a polar organic solvent such as alcohol to prepare an oxidizing agent solution, and then immersing the cellulose raw material in the solution.

[0034] The amount of carboxy groups in the oxidized cellulose can be adjusted by controlling the reaction conditions, such as the amount of oxidizing agent added and the reaction time.

[0035] (Carboxymethylation) When carboxymethylated cellulose is used as the modified cellulose in the present invention, the carboxymethylated cellulose may be obtained by carboxymethylating the above-mentioned cellulose raw material using a known method, or a commercially available product may be used. In either case, the carboxymethyl group substitution degree per anhydroglucose unit of the cellulose is preferably 0.01 to 0.50. An example of a method for producing such carboxymethylated cellulose is the following. Cellulose is used as the starting material, and 3 to 20 times by mass of water and / or a lower alcohol, specifically water, methanol, ethanol, N-propyl alcohol, isopropyl alcohol, N-butanol, isobutanol, tertiary butanol, etc., is used as the solvent, or a mixture of two or more of these. When a lower alcohol is mixed, the mixing ratio of the lower alcohol is 60 to 95% by mass. As the mercerizing agent, 0.5 to 20 times the molar amount of an alkali metal hydroxide, specifically sodium hydroxide or potassium hydroxide, is used per anhydroglucose residue of the starting material. The starting material, solvent, and mercerizing agent are mixed and subjected to mercerization treatment at a reaction temperature of 0 to 70°C, preferably 10 to 60°C, for a reaction time of 15 minutes to 8 hours, preferably 30 minutes to 7 hours. Thereafter, a carboxymethylating agent is added at 0.05 to 10.0 times the moles per glucose residue, and an etherification reaction is carried out at a reaction temperature of 30 to 90°C, preferably 40 to 80°C, for a reaction time of 30 minutes to 10 hours, preferably 1 hour to 4 hours.

[0036] In this specification, "carboxymethylated cellulose," a type of modified cellulose used in preparing cellulose nanofibers, refers to cellulose that maintains at least a portion of its fibrous shape when dispersed in water. Therefore, it is distinguished from carboxymethyl cellulose, a type of water-soluble polymer exemplified as a dispersant in this specification. When an aqueous dispersion of "carboxymethylated cellulose" is observed under an electron microscope, a fibrous substance can be observed. On the other hand, when an aqueous dispersion of carboxymethyl cellulose, a type of water-soluble polymer, is observed, no fibrous substance can be observed. Furthermore, when "carboxymethylated cellulose" is measured by X-ray diffraction, a peak of cellulose type I crystals can be observed, but cellulose type I crystals are not observed in the water-soluble polymer carboxymethyl cellulose.

[0037] (Phosphate esterification) Phosphate-esterified cellulose can be used as the chemically modified cellulose. The cellulose can be obtained by mixing a powder or an aqueous solution of phosphoric acid compound A with the above-mentioned cellulose raw material, or by adding an aqueous solution of phosphoric acid compound A to a slurry of the cellulose raw material.

[0038] Examples of the phosphoric acid compound A include phosphoric acid, polyphosphoric acid, phosphorous acid, phosphonic acid, polyphosphonic acid, and esters thereof. These may be in the form of a salt. Among these, compounds having a phosphoric acid group are preferred because they are low cost, easy to handle, and can be used to introduce phosphate groups into the cellulose of the pulp fibers, thereby improving defibration efficiency. Examples of compounds having a phosphoric acid group include phosphoric acid, sodium dihydrogen phosphate, disodium hydrogen phosphate, trisodium phosphate, sodium pyrophosphate, sodium metaphosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, tripotassium phosphate, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, and ammonium metaphosphate. These compounds can be used alone or in combination of two or more. Among these compounds, phosphoric acid, sodium salts of phosphoric acid, potassium salts of phosphoric acid, and ammonium salts of phosphoric acid are more preferred from the viewpoints of high efficiency of introducing phosphate groups, ease of defibration in the defibration step described below, and ease of industrial application. Sodium dihydrogen phosphate and disodium hydrogen phosphate are particularly preferred. In addition, it is preferable to use the phosphoric acid compound A as an aqueous solution, since this increases the uniformity of the reaction and the efficiency of introducing the phosphoric acid group. The pH of the aqueous solution of phosphoric acid compound A is preferably 7 or less, since this increases the efficiency of introducing the phosphoric acid group, but from the viewpoint of suppressing hydrolysis of the pulp fiber, a pH of 3 to 7 is preferred.

[0039] The following method can be mentioned as an example of a method for producing phosphated cellulose. A phosphoric acid compound A is added to a dispersion of a cellulose raw material having a solids concentration of 0.1 to 10% by mass while stirring, to introduce phosphate groups into the cellulose. When the cellulose raw material is taken as 100 parts by mass, the amount of phosphoric acid compound A added is preferably 0.2 to 500 parts by mass, and more preferably 1 to 400 parts by mass, in terms of the amount of phosphorus element. If the proportion of phosphoric acid compound A is equal to or greater than the lower limit, the yield of fine fibrous cellulose can be further improved. However, if the proportion exceeds the upper limit, the effect of improving the yield plateaus, which is not preferable from a cost perspective.

[0040] In this case, in addition to the cellulose raw material and phosphoric acid compound A, a powder or aqueous solution of compound B may be mixed. Compound B is not particularly limited, but a basic nitrogen-containing compound is preferred. "Basic" here is defined as an aqueous solution exhibiting a pink to red color in the presence of a phenolphthalein indicator, or a pH of the aqueous solution greater than 7. The basic nitrogen-containing compound used in the present invention is not particularly limited as long as it achieves the effects of the present invention, but a compound having an amino group is preferred. Examples include, but are not limited to, urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, and hexamethylenediamine. Among these, urea is preferred due to its low cost and ease of handling. The amount of compound B added is preferably 2 to 1,000 parts by mass, more preferably 100 to 700 parts by mass, per 100 parts by mass of the solid content of the cellulose raw material. The reaction temperature is preferably 0 to 95°C, more preferably 30 to 90°C. The reaction time is not particularly limited, but is about 1 to 600 minutes, and more preferably 30 to 480 minutes. When the esterification reaction conditions are within these ranges, it is possible to prevent the cellulose from being excessively esterified and becoming more soluble, resulting in a good yield of phosphated cellulose. After dehydrating the resulting phosphated cellulose suspension, it is preferably heat-treated at 100 to 170°C in order to suppress cellulose hydrolysis. Furthermore, it is preferable to heat the suspension at 130°C or lower, preferably 110°C or lower, while it contains water, and then, after removing the water, to heat the suspension at 100 to 170°C.

[0041] The degree of phosphate substitution per glucose unit of the phosphated cellulose is preferably 0.001 to 0.40. Introducing phosphate group substituents into cellulose causes electrical repulsion between cellulose molecules. Therefore, cellulose with phosphate groups introduced can be easily nano-fibrillated. Note that if the degree of phosphate substitution per glucose unit is less than 0.001, sufficient nano-fibrillation cannot be achieved. On the other hand, if the degree of phosphate substitution per glucose unit is greater than 0.40, the cellulose may swell or dissolve, making it impossible to obtain nanofibers. To ensure efficient fibrillation, the phosphated cellulose raw material obtained above is preferably boiled and then washed with cold water.

[0042] (Cationization) The chemically modified cellulose can be cellulose obtained by further cationizing the carboxylated cellulose. The cationically modified cellulose can be obtained by reacting the carboxylated cellulose raw material with a cationizing agent such as glycidyltrimethylammonium chloride, 3-chloro-2-hydroxypropyltrialkylammonium halide or its halohydrin form, and an alkali metal hydroxide catalyst (sodium hydroxide, potassium hydroxide, etc.) in the presence of water or an alcohol having 1 to 4 carbon atoms.

[0043] The degree of cationic substitution per glucose unit is preferably 0.02 to 0.50. Introducing cationic substituents into cellulose causes electrical repulsion between cellulose molecules. Therefore, cellulose with cationic substituents introduced can be easily nano-fibrillated. If the degree of cationic substitution per glucose unit is less than 0.02, sufficient nano-fibrillation cannot be achieved. On the other hand, if the degree of cationic substitution per glucose unit is greater than 0.50, the cellulose may swell or dissolve, making it impossible to obtain nanofibers. To achieve efficient fibrillation, it is preferable to wash the cationically modified cellulose raw material obtained above. The degree of cationic substitution can be adjusted by the amount of cationizing agent added to the reaction and the composition ratio of water or alcohol with 1 to 4 carbon atoms.

[0044] In the present invention, when the anionically modified cellulose obtained by anionically modifying a cellulose raw material is in a salt form, the type of salt form does not matter, but it is preferable to select a salt such as sodium or ammonium that has good defibration and dispersibility.

[0045] <Defibrillation> In the present invention, the defibration device is not particularly limited, but it is preferable to apply a strong shear force to the aqueous dispersion using a device such as a high-speed rotation device, a colloid mill device, a high-pressure device, a roll mill device, or an ultrasonic device. In particular, for efficient defibration, it is preferable to use a wet high-pressure or ultra-high-pressure homogenizer that can apply a pressure of 50 MPa or more to the aqueous dispersion and a strong shear force. The pressure is more preferably 100 MPa or more, and even more preferably 140 MPa or more. Furthermore, prior to the defibration and dispersion treatment with the high-pressure homogenizer, the CNF can be subjected to a pre-treatment, if necessary, using a known mixing, stirring, emulsifying, or dispersing device such as a high-speed shear mixer. The number of treatments (passes) with the defibration device may be one or two or more times, with two or more being preferred.

[0046] In the dispersion treatment, the modified cellulose is usually dispersed in a solvent. The solvent is not particularly limited as long as it can disperse the modified cellulose, and examples thereof include water, organic solvents (e.g., hydrophilic organic solvents such as methanol), and mixtures thereof. Since the cellulose raw material is hydrophilic, the solvent is preferably water.

[0047] The solids concentration of the modified cellulose in the dispersion is usually 0.1% by mass or more, preferably 0.2% by mass or more, and more preferably 0.3% by mass or more. This ensures an appropriate amount of liquid relative to the amount of cellulose fiber raw material, which is efficient. The upper limit is usually 10% by mass or less, preferably 6% by mass or less. This allows fluidity to be maintained.

[0048] Prior to the defibration treatment or dispersion treatment, a pretreatment may be carried out as necessary. The pretreatment may be carried out using a mixing, stirring, emulsifying, or dispersing device such as a high-speed shear mixer.

[0049] When the modified cellulose nanofibers obtained through the defibration step are in the salt form, they may be used as they are, or may be converted into the acid form by acid treatment using a mineral acid, a method using a cation exchange resin, etc. Furthermore, they may be made hydrophobic by a method using a cationic additive.

[0050] The cellulose nanofibers used in the present invention may contain a modifier. For example, in the case of anion-modified cellulose nanofibers, nitrogen-containing compounds, phosphorus-containing compounds, onium ions, or the like may be bonded to the anionic groups on the surface of the cellulose nanofibers to change properties such as polarity, thereby adjusting the affinity for solvents and the dispersibility of fillers.

[0051] In the present invention, if an acid form is present in the anion-modified cellulose nanofiber obtained by defibrating anion-modified cellulose, the dispersibility of the filler may be deteriorated. Therefore, a basic compound such as sodium hydroxide or ammonium may be added as appropriate to convert it to a salt form.

[0052] When the mixed liquid of the present invention is used for a paint or the like, and water resistance is required for the coating film obtained after applying and drying the mixed liquid, it is preferable to use, for example, ammonium salt-type anion-modified cellulose nanofibers, because the ammonia volatilizes during drying, converting the nanofiber to an acid form and making the coating film water-resistant.

[0053]

[0054] The added amount of cellulose nanofibers to the mixed solution of the present invention has the advantage that the greater the amount added, the greater the effect of preventing filler sedimentation, but if the amount is too much, the mixed solution becomes significantly thicker and difficult to handle. From this perspective, the solids concentration of CNF in the mixed solution is preferably 0.01 to 5 mass%, and more preferably 0.1 to 0.5 mass%.

[0055] (3) Filler The filler used in the present invention may be either an inorganic filler or an organic filler, and may be in any shape, such as particulate, flat, or fibrous.

[0056] Inorganic fillers include calcium carbonate (light calcium carbonate, heavy calcium carbonate), magnesium carbonate, barium carbonate, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, clay (kaolin, calcined kaolin, delaminated kaolin), talc, mica, zinc oxide, zinc stearate, titanium dioxide, silica produced from sodium silicate and mineral acid (white carbon, silica / calcium carbonate complex, silica / titanium dioxide complex), white clay, bentonite, diatomaceous earth, calcium sulfate, inorganic compounds such as zeolite, metals or alloys such as aluminum, aluminum oxide, copper, zinc, iron, nickel, and tin, inorganic fillers recycled from ash obtained during the deinking process, and inorganic fillers formed as complexes with silica or calcium carbonate during the regeneration process. As calcium carbonate-silica composites, amorphous silica such as white carbon may be used in combination with calcium carbonate and / or light calcium carbonate-silica composites.

[0057] Examples of organic fillers include urea-formaldehyde resin, polystyrene resin, phenolic resin, microhollow particles, acrylamide composites, wood-derived substances (microfibers, microfibril fibers, powdered kenaf), modified insolubilized starch, and ungelatinized starch.

[0058] The fillers may be used singly or in combination of two or more.

[0059] If necessary, the mixed solution of the present invention may contain additives such as preservatives, surfactants such as surface conditioners, binder resins, waterproofing agents, thickeners, etc.

[0060] In the present invention, the effect of cellulose nanofibers in preventing filler sedimentation is improved by adding a small amount of dispersant to the mixed solution. In particular, the larger the particle size and the higher the aspect ratio of filler, the larger the aggregates that form when aggregated, and the higher the sedimentation tendency, so the more likely the effect of adding a dispersant is to be seen.

[0061] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0062] <Syneresis Rate> 50 mL of the mixed liquid obtained in the Examples and Comparative Examples was poured into a 50 mL measuring cylinder conforming to JIS R 3505, and after leaving it to stand for 72 hours, the amount of liquid in the transparent portion at the top of the mixed liquid in the measuring cylinder was visually read. The syneresis rate was then calculated using the following formula. The results are shown in Table 1. Syneresis rate (%): (amount of liquid in the transparent portion (mL) / total amount of mixed liquid (mL)) x 100

[0063] <Uniformity of particle size and particle size distribution> The remaining 50 mL of the mixed solution obtained in the Examples and Comparative Examples was left to stand for 3 days, and then a sample was collected from the bottom of the container. The obtained sample was measured for volume average particle size (D10, D50, D90) using a laser diffraction particle size distribution analyzer (Mastersizer 3000, manufactured by Malvern Instruments). D10 is the particle size that includes 10% of the particles, calculated from the minimum value, in the particle size distribution based on the volume average particle size. D50 is the particle size that includes 50% of the particles, calculated from the minimum value, and D90 is the particle size that includes 90% of the particles, calculated from the minimum value. In this measurement, ion-exchanged water was used as the dispersion solvent, and circulation was performed by a pump without using ultrasound.

[0064] Furthermore, the uniformity of particle size distribution was measured using the same equipment and the same samples as in the measurement of particle size. The uniformity of particle size distribution is expressed by the following formula:

[0065] where di is the particle size of each fraction, d50 is the median of the particle size distribution, and Vi is the volume of each fraction. Uniformity is a measure of the absolute deviation from the median of the particle size distribution, and is preferably 1 or less. The obtained results of particle size and uniformity of particle size distribution are shown in Table 1.

[0066] <Transparency> In this specification, transparency refers to the transmittance of light with a wavelength of 660 nm when oxidized CNF is dispersed in water at a solid content of 1% (w / v). The transparency of the oxidized CNF obtained in the Production Examples was determined by preparing a CNF dispersion (solid content 1% (w / v), dispersion medium: water) and measuring the transmittance of 660 nm light using a UV-VIS spectrophotometer UV-1800 (manufactured by Shimadzu Corporation) and a square cell with an optical path length of 10 mm.

[0067] <Stability test> 210 g of the 1.0 wt% oxidized cellulose nanofiber aqueous dispersion obtained in Production Example was weighed into a 600 mL plastic container, and deionized water was added to the dispersion to a concentration of 0.7%, followed by stirring (1000 rpm, 5 minutes) to obtain 300 g of a 0.7 wt% oxidized CNF aqueous dispersion. Immediately after adjusting the concentration, the Brookfield viscosity was measured using a Brookfield viscometer at 6 rpm for 1 minute (viscosity before stirring).

[0068] After measuring the Brookfield viscosity, 300 g of the oxidized CNF aqueous dispersion was stirred for 30 minutes (1000 rpm, 23°C) using a disper. Immediately after 30 minutes of stirring, the Brookfield viscosity was measured using a Brookfield viscometer at 6 rpm for 1 minute (viscosity after stirring).

[0069] The viscosity retention rate can be calculated by the following formula: Viscosity retention rate (%) = (viscosity after stirring / viscosity before stirring) x 100

[0070] <Production Example 1> 5.00 g (bone-dry) of bleached, unbeaten kraft pulp derived from softwood (brightness 85%) was added to 500 mL of an aqueous solution containing 20 mg (0.025 mmol per 1 g of bone-dry cellulose) of TEMPO (Sigma-Aldrich) and 514 mg (1.0 mmol per 1 g of bone-dry cellulose) of sodium bromide, and the mixture was stirred until the pulp was uniformly dispersed. An aqueous solution of sodium hypochlorite was added to the reaction system so that the sodium hypochlorite concentration was 2.2 mmol / g, thereby initiating the oxidation reaction. During the reaction, the pH of the system decreased, but was adjusted to pH 10 by sequential addition of 3 M aqueous sodium hydroxide. The reaction was terminated when the sodium hypochlorite was consumed and the pH of the system no longer changed. The reaction mixture was filtered through a glass filter to separate the pulp, which was then thoroughly washed with water to obtain oxidized pulp (carboxylated cellulose). The pulp yield was 93%, the oxidation reaction took 60 minutes, and the carboxyl group content (hereinafter sometimes referred to as "modification degree") was 0.75 mmol / g. This was adjusted to 1.0% (w / v) with water and defibrated using a high-pressure homogenizer until the transparency was sufficiently high, yielding an aqueous dispersion of oxidized cellulose nanofibers with a transparency of 88%. The average fiber diameter was 4 nm and the aspect ratio was 280. A stability test was conducted on this aqueous dispersion of oxidized CNF, and the B-type viscosity values ​​before and after stirring were obtained. The viscosity retention rate at this time was 50%.

[0071] <Production Example 2> 5.00 g (bone-dry) of bleached, unbeaten kraft pulp derived from softwood (brightness 85%) was added to 500 mL of an aqueous solution containing 39 mg (0.05 mmol per 1 g of bone-dry cellulose) of TEMPO (Sigma-Aldrich) and 514 mg (1.0 mmol per 1 g of bone-dry cellulose) of sodium bromide, and the mixture was stirred until the pulp was uniformly dispersed. An aqueous solution of sodium hypochlorite was added to the reaction system so that the sodium hypochlorite concentration was 6.0 mmol / g, thereby initiating the oxidation reaction. During the reaction, the pH of the system decreased, but was adjusted to pH 10 by sequential addition of 3 M aqueous sodium hydroxide. The reaction was terminated when the sodium hypochlorite was consumed and the pH of the system no longer changed. The reaction mixture was filtered through a glass filter to separate the pulp, which was then thoroughly washed with water to obtain oxidized pulp (carboxylated cellulose). The pulp yield was 90%, the oxidation reaction took 90 minutes, and the carboxyl group content was 1.51 mmol / g. This was adjusted to 1.0% (w / v) with water and defibrated using a high-pressure homogenizer to obtain an aqueous dispersion of oxidized cellulose nanofibers with a transparency of 95.0%. The average fiber diameter was 3 nm and the aspect ratio was 250. A stability test was conducted on this aqueous dispersion of oxidized CNF, and the B-type viscosity values ​​before and after stirring were obtained. The viscosity retention rate at this time was 39%.

[0072] <Production Example 3> 5.00 g (bone-dry) of bleached, unbeaten kraft pulp derived from softwood (brightness 85%) was added to 500 mL of an aqueous solution containing 20 mg (0.025 mmol per 1 g of bone-dry cellulose) of TEMPO (Sigma-Aldrich) and 514 mg (1.0 mmol per 1 g of bone-dry cellulose) of sodium bromide, and the mixture was stirred until the pulp was uniformly dispersed. An aqueous solution of sodium hypochlorite was added to the reaction system so that the sodium hypochlorite concentration was 1.3 mmol / g, thereby initiating the oxidation reaction. During the reaction, the pH of the system decreased, but 3 M aqueous sodium hydroxide was gradually added to adjust the pH to 10. The reaction was terminated when the sodium hypochlorite was consumed and the pH of the system no longer changed. The reaction mixture was filtered through a glass filter to separate the pulp, which was then thoroughly washed with water to obtain oxidized pulp (carboxylated cellulose). The pulp yield was 99%, the oxidation reaction took 50 minutes, and the carboxyl group content was 0.42 mmol / g. This was adjusted to 1.0% (w / v) with water and defibrated using a high-pressure homogenizer until the transparency was sufficiently high, yielding an aqueous dispersion of oxidized cellulose nanofibers with a transparency of 75.2%. The average fiber diameter was 4 nm and the aspect ratio was 380. A stability test was conducted on this aqueous dispersion of oxidized CNF, and the B-type viscosity values ​​before and after stirring were obtained. The viscosity retention rate at this time was 88%.

[0073] Example 1 An aqueous dispersion of oxidized cellulose nanofibers obtained in Production Example 1 above was prepared at 0.2% by mass (equivalent to CNF solids), and while stirring at 3000 rpm with a homomixer, a polycarboxylic acid (trade name: Aron T-50, manufactured by Toa Gosei Co., Ltd.) was added as a dispersant to a concentration of 0.1% by mass in terms of solids, followed by the addition of 10% by mass of kaolin (trade name: Barisurf HX, manufactured by Imerys Pharmaceuticals) as a filler and water to prepare 100 mL of a mixed solution. The resulting mixed solution was measured for water syneresis rate, particle size, and particle size uniformity.

[0074] Examples 2-6, 8-9, and 12-16 Mixed liquids were prepared in the same manner as in Example 1, except that the amount of carboxyl groups and addition concentration of the oxidized cellulose nanofiber aqueous dispersion, the type and addition concentration of the dispersant, and the type of filler were changed as shown in Table 1. The resulting mixed liquids were measured for water syneresis rate, particle size, and particle size uniformity.

[0075] Example 7: The oxidized pulp obtained in Production Example 1 was adjusted to pH 2.4 with hydrochloric acid and then washed twice with ion-exchanged water. Subsequently, 3.2 g of polyetheramine (JEFFAMINE® M1000) was added to 4 g of oxidized pulp solids, and the weight was adjusted to 400 g with ion-exchanged water. The mixture was then defibrated using a high-pressure homogenizer in the same manner as in Production Example 1, yielding an aqueous dispersion of oxidized cellulose nanofibers with a transparency of 90%. The average fiber diameter was 4 nm and the aspect ratio was 275. A stability test was conducted on this aqueous dispersion of oxidized CNF, and the B-type viscosity values ​​before and after stirring were obtained. The viscosity retention rate at this time was 52%. To this oxidized cellulose nanofiber dispersion, 10% by mass of kaolin (product name: Barisurf HX, manufactured by Imerys) as a filler and water were added in the same manner as in Example 1, to prepare 100 mL of a mixed solution. The resulting mixture was measured for water separation rate, particle size, and particle size uniformity.

[0076] Example 10 100 mL of a mixed liquid was prepared in the same manner as in Example 1, except for using the aqueous dispersion of oxidized cellulose nanofibers obtained in Production Example 2. The resulting mixed liquid was measured for water syneresis rate, particle size, and particle size uniformity.

[0077] Example 11 100 mL of a mixed liquid was prepared in the same manner as in Example 1, except for using the aqueous dispersion of oxidized cellulose nanofibers obtained in Production Example 3. The resulting mixed liquid was measured for water syneresis rate, particle size, and particle size uniformity.

[0078] Comparative Examples 1 to 5 Mixed liquids were prepared in the same manner as in Example 1, without adding a dispersant, and by changing the concentration of oxidized cellulose nanofibers and the type and concentration of filler added as shown in Table 1. The resulting mixed liquids were measured for water syneresis rate, particle size, and particle size uniformity.

[0079] Comparative Examples 6 to 11 Mixed liquids were prepared in the same manner as in Example 1, without adding cellulose nanofibers, and by changing the type and concentration of the dispersant, and the type and concentration of the filler as shown in Table 1. The resulting mixed liquids were measured for water syneresis rate, particle size, and particle size uniformity.

[0080] The details of the dispersants and fillers used in the examples and comparative examples are as follows: (Dispersant) Product name: Aron T-50, sodium polyacrylate, solid content 43%, manufactured by Toagosei Co., Ltd.

[0081] Name: Polycarboxylic acid A, solids content 36.0% Polycarboxylic acid A was produced by the following method: A glass reaction vessel equipped with a thermometer, a stirrer, a reflux device, a nitrogen inlet tube, and a dropping device was charged with 148 parts of water and 94 parts (5 mol%) of polyethylene glycol polypropylene glycol monoallyl ether (average number of added moles of ethylene oxide: 37, average number of added moles of propylene oxide: 3, random addition of ethylene oxide and propylene oxide), the atmosphere in the reaction vessel was replaced with nitrogen with stirring, and the temperature was raised to 80°C in a nitrogen atmosphere. Thereafter, an aqueous monomer solution containing 35 parts (40 mol%) of methacrylic acid, 5 parts (7 mol%) of acrylic acid, 63 parts (5 mol%) of methoxypolyethylene glycol methacrylate (average number of moles of ethylene oxide added: 25), 60 parts (43 mol%) of hydroxypropyl acrylate, 8 parts of 3-mercaptopropionic acid, and 165 parts of water, and a mixed solution of 3 parts of ammonium persulfate and 47 parts of water were continuously added dropwise over two hours to a reaction vessel maintained at 80°C. The mixture was then allowed to react for one hour while the temperature was maintained at 100°C, yielding an aqueous solution of copolymer (polycarboxylic acid A).

[0082] ・Product name: Aron A30SL, ammonium polyacrylate, solids content 40%, manufactured by Toa Gosei Co., Ltd. ・Product name: Aron A-6114, carboxylic acid copolymer (ammonium salt), solids content 40%, manufactured by Toa Gosei Co., Ltd. ・Product name: FS600LC, carboxymethyl cellulose, powder form, manufactured by Nippon Paper Industries Co., Ltd. ・Product name: JEFFAMINE (registered trademark) M1000, polyether amine, manufactured by Huntsman Chemical Industries, Ltd. ・Product name: Disparlon AQ-330, polyether phosphate ester, active ingredient 100%, manufactured by Kusumoto Chemicals Co., Ltd. ・Product name: Demol EP, polymeric polycarboxylic acid, solids content 25%, manufactured by Kao Corporation

[0083] (Fillers) Product name: Barisurf HX, kaolin, particle size %: 64 (<2 μm), manufactured by Imerys Minerals Japan Co., Ltd. Product name: Callite KT, calcium carbonate, primary particle size: 300 nm (observed under an electron microscope), manufactured by Shiraishi Kogyo Co., Ltd. Product name: A-21S, mica, volume average particle size: 23 μm, aspect ratio: 70, manufactured by Yamaguchi Mica Co., Ltd. Product name: A-11, mica, volume average particle size: 3 μm, manufactured by Yamaguchi Mica Co., Ltd. Product name: B-82, mica, volume average particle size: 180 μm, aspect ratio: 100, manufactured by Yamaguchi Mica Co., Ltd.

[0084]

[0085] As can be seen from Table 1, the mixed liquid containing (1) a dispersant, (2) cellulose nanofibers, and (3) a filler had a low syneresis rate, excellent filler dispersion stability, and excellent particle size distribution uniformity (Examples 1 to 16).

[0086] On the other hand, when (2) cellulose nanofibers and (3) filler were contained but (1) dispersant was not contained, the syneresis rate value was high, resulting in poor filler dispersion stability, and differences in particle size measurement results were observed compared to the Examples (Comparative Examples 1 to 5). Specifically, when kaolin and mica were used as fillers, the uniformity value of the particle size distribution was high, and uniformity was deteriorated. In Comparative Example 5, which used large-particle-size B-82 as mica, the particle size D10 value was large. When calcium carbonate was used as the filler, the particle size D10 and D50 values ​​were large.

[0087] Furthermore, when (2) cellulose nanofibers were not contained but (1) a dispersant and (3) a filler were contained, the water syneresis rate was high, and the dispersion stability of the filler was poor (Comparative Examples 6 to 11).

[0088] From the above results, it is thought that fine cellulose nanofibers penetrate into the filler and inhibit the settling of the filler. In the case of anion-modified cellulose nanofibers, it is thought that they not only have this settling prevention effect but also function to some extent as an anionic dispersant.

[0089] However, even in the presence of cellulose nanofibers, if a filler that tends to aggregate in water is used, the anionic dispersant function of the cellulose nanofibers alone is insufficient to prevent the filler from aggregating, and aggregation occurs. The aggregated filler is prone to settling, and it is thought that syneresis occurs even in the presence of cellulose nanofibers. Using cellulose nanofibers in combination with a dispersant can suppress filler agglomeration and prevent settling.

Claims

DEPCT651. Mixed suspensions incorporating (1) to (3) of the following: (1) dispersant; (2) nanocellulose fibers; and (3) filler.

2. Mixed suspensions in accordance with claim 1 in which the dispersant is an anionic polymer compound.

3. Mixed suspensions in accordance with claim 2 in which the anionic polymer compound is a carboxylic polymer or a phosphated polymer.

4. Any one of the mixed suspensions in accordance with claims 1 to 3 in which nanocellulose fibers are 5. A mixed suspension under claim 4 in which the anionically modified nanocellulose fibers are oxidized nanocellulose fibers.

6. A mixed suspension under claim 5 in which the oxidized nanocellulose fibers contain 0.4 to 1.0 mmol / g of carboxylated groups.

7. Any one of the mixed suspensions under claims 1 to 6 in which the amount of nanocellulose fibers added results in a concentration of 0.1% by mass or more. 8.Suspension mixtures under any one of the claims 1 through 7 where the water separation rate after settling for 72 hours is less than 1%-----------------------------------------------------------;.