JP6861972B2 - Manufacturing method of dried cellulose nanofibers - Google Patents

Description

The present disclosure relates to a method for producing dried cellulose nanofibers and a method for improving the redispersibility of dried cellulose nanofibers.

Cellulose nanofibers (CNFs) are plant-derived fibers that have been refined to a fiber diameter of about several nm to several hundred nm. CNF has various features such as low environmental load, light weight, high strength, high gas barrier property, small size deformation due to heat, high specific surface area, high permeability, and high viscosity in water. Therefore, CNF is expected to be used not only in automobile parts and food packaging materials, but also in a wide range of fields such as foods, pharmaceuticals and cosmetics.

CNF is usually produced as a low concentration aqueous dispersion (wet state). However, in the case of an aqueous dispersion, there are problems such as high transfer and storage costs and contamination by bacteria. Therefore, a method of drying CNF has been proposed (for example, Patent Document 1 and the like).

WO2015 / 107995

The dried CNF is usually used after being redispersed in a dispersion medium such as water. In performing this redispersion, there may be a problem that the CNF is not sufficiently redispersed. In particular, among the dried CNFs, there is a problem that the redispersibility of the dried anion-modified CNFs, particularly the 2,2,6,6-tetramethylpiperidin-1-oxyradine (TEMPO) oxidized CNFs is low. Therefore, there is a need for a new method capable of drying CNF while maintaining sufficient redispersibility.

The present disclosure, in one aspect, provides a method for producing a dry CNF with improved redispersibility and a method capable of improving the redispersibility of CNF.

In one aspect of the present disclosure, an anion-modified cellulose nanofiber and a redispersibility improver are mixed to obtain an aqueous suspension of the anion-modified cellulose nanofiber, and the aqueous suspension is dried to dry cellulose. The redispersibility improver, which comprises obtaining nanofibers, relates to a method for producing dried cellulose nanofibers, which is a water-soluble nonionic surfactant.

The present disclosure includes, in one embodiment, mixing an anion-modified cellulose nanofiber and a redispersibility improver to obtain an aqueous suspension of the anion-modified cellulose nanofiber, and drying the aqueous suspension. The redispersibility improving agent relates to a method for improving the redispersibility of cellulose nanofibers, which is a water-soluble nonionic surfactant.

The present disclosure relates, in one aspect, to a redispersibility improver containing a water-soluble nonionic surfactant, which is an agent for improving or improving the redispersibility of dried cellulose nanofibers in an aqueous dispersion medium.

The present disclosure relates to, in one aspect, a dry composition comprising anion-modified cellulose nanofibers and a redispersibility improver, wherein the redispersibility improver comprises a water-soluble nonionic surfactant.

According to the present disclosure, it is possible to provide a method for producing a dry CNF having improved redispersibility and a method capable of improving the redispersibility of CNF. According to the present disclosure, it is possible to preferably provide a method for producing dried TEMPO-oxidized CNF having improved redispersibility and a method capable of improving the redispersibility of dried TEMPO-oxidized CNF. Further, according to the present disclosure, it is possible to provide a method for producing a dry carboxymethyl (CM) -modified CNF having improved dispersibility during redispersion and a method capable of improving the dispersibility of the dried CM-modified CNF during redispersion. Further, according to the present disclosure, it is possible to provide a method for producing a dry phosphate-esterified CNF having improved dispersibility during redispersion and a method capable of improving the dispersibility of the dry phosphate-esterified CNF during redispersion.

In the present disclosure, the redispersibility of the obtained dried CNF is improved by drying an aqueous suspension in which an anion-modified CNF and a water-soluble nonionic surfactant are mixed, and the obtained dried CNF is dispersed in water or the like. It is based on the finding that a redispersion of dried CNF with improved dispersibility can be obtained by contact with the medium.

The present disclosure is based on the finding that a water-soluble nonionic surfactant can be used as a redispersibility improver when redispersing dry CNF.

As the "improvement or improvement of redispersibility" in the present disclosure, in one or more embodiments, a dispersion obtained by mixing the dried CNF obtained by the method for producing the dried CNF of the present disclosure with a dispersion medium ( Alternatively, the suspension) is obtained by mixing the dried product obtained by drying the anion-modified CNF in a state of being dispersed in water (wet state) as it is (without adding a drug) and a dispersion medium. It means that the turbidity is low or the amount of undispersed CNF pieces or gelled products is smaller than that of the dispersion liquid (or suspension). According to the dry CNF obtained by the method for producing a dry CNF of the present disclosure, in one or more embodiments, when redispersed in a dispersion medium such as water, the CNF is at a level close to microfibril units or microfibril units. It can be separated and redistributed.

[Anion-denatured CNF]
In the present disclosure, the "anion-modified CNF" refers to cellulose nanofibers obtained by chemically treating cellulose, and more specifically, the fiber surface is made into nanofibers by defibrating a chemically treated cellulose fiber. Fine fibers (nanofibers). The anion-modified CNF in the present disclosure, in one or more embodiments, has a charge on the surface of the cellulose fibers by chemical treatment. The anion-modified CNF in the present disclosure does not include naturally occurring cellulose nanofibers such as bacterial cellulose produced from bacteria in one or more embodiments.

Examples of the chemical treatment include carboxymethyl (CM) treatment, carboxylation (oxidation) treatment, phosphoric acid esterification treatment, and the like in one or more embodiments.

[Carboxymethyl (CM) conversion]
Examples of the method for carboxymethylating the cellulose raw material or the defibrated cellulose fiber include a method in which cellulose as a bottoming raw material is marcelled and then etherified. A solvent is usually used in the carboxymethylation reaction. Examples of the solvent include water, alcohol (eg, lower alcohol) and a mixed solvent thereof. Specific examples of the lower alcohol include methanol, ethanol, n-propyl alcohol, isopropyl alcohol, n-butanol, isobutanol, and tertiary butanol. The lower limit of the mixing ratio of the lower alcohol in the mixed solvent is usually 60% by weight or more, and the upper limit is usually 95% by weight or less, preferably 60% by weight to 95% by weight. The amount of the solvent is usually 3 times by weight or more with respect to the cellulose raw material or the defibrated cellulose fiber. The upper limit of the amount of the solvent is not particularly limited, but is usually 20 times by weight or less with respect to the cellulose raw material or the defibrated cellulose fiber. Therefore, the amount of the solvent is preferably 3 to 20 times by weight with respect to the cellulose raw material or the defibrated cellulose fiber.

Mercerization is usually carried out by mixing a cellulose raw material or a defibrated cellulose fiber with a mercerizing agent. Examples of the mercerizing agent include alkali metals hydroxide (eg, sodium hydroxide, potassium hydroxide).

The lower limit of the amount of the mercerizing agent used is usually 0.5 times or more per anhydrous glucose residue of the cellulose raw material or the defibrated cellulose fiber. The upper limit is usually 20 times or less. Therefore, the amount of the mercerizing agent used is preferably 0.5 to 20 times mol per anhydrous glucose residue of the cellulose raw material or the defibrated cellulose fiber.

The lower limit of the reaction temperature for mercerization is usually 0 ° C. or higher, preferably 10 ° C. or higher. The upper limit is usually 70 ° C. or lower, preferably 60 ° C. or lower. Therefore, the reaction temperature for mercerization is usually 0 ° C. to 70 ° C., preferably 10 ° C. to 60 ° C.

The lower limit of the reaction time for mercerization is usually 15 minutes or longer, preferably 30 minutes or longer. The lower limit is usually 8 hours or less, preferably 7 hours or less. Therefore, the reaction time for mercerization is usually 15 minutes to 8 hours, preferably 30 minutes to 7 hours.

The etherification reaction is usually carried out by adding a carboxymethylating agent to the reaction system after mercerization. Examples of the carboxymethylating agent include sodium monochloroacetate.

The lower limit of the amount of the carboxymethylating agent added per glucose residue of the cellulose raw material or the defibrated cellulose fiber is usually 0.05 times or more. The upper limit is usually 10.0 times mol or less. Therefore, the amount of the carboxymethylating agent added is usually 0.05 times to 10.0 times mol per glucose residue of the cellulose raw material or the defibrated cellulose fiber. The lower limit of the etherification reaction temperature is usually 30 ° C. or higher, preferably 40 ° C. or higher. The upper limit is usually 90 ° C. or lower, preferably 80 ° C. or lower. Therefore, the reaction temperature for etherification is usually 30 ° C. to 90 ° C., preferably 40 ° C. to 80 ° C.

The lower limit of the reaction time for etherification is usually 30 minutes or more, preferably 1 hour or more. The upper limit is usually 10 hours or less, preferably 4 hours or less. Therefore, the reaction time for etherification is usually 30 minutes to 10 hours, preferably 1 to 4 hours.

As a method for measuring the degree of carboxymethyl substitution per glucose unit of the carboxymethylated cellulose fiber or the carboxymethylated cellulose nanofiber, for example, it can be obtained by the following method. That is, 1) Approximately 2.0 g of carboxymethylated cellulose fiber or carboxymethylated cellulose nanofiber (absolutely dried) is precisely weighed and placed in an Erlenmeyer flask with a 300 mL stopper. 2) Add 100 mL of a nitrate methanol solution obtained by adding 100 mL of special grade concentrated nitric acid to 1000 mL of methanol, and shake for 3 hours to convert carboxymethyl cellulose salt (CM cellulose salt: for example Na-CMC) into H-CM cellulose. (H-CMC). 3) Weigh 1.5 to 2.0 g of H-CM-modified cellulose (absolutely dry) and place it in an Erlenmeyer flask with a 300 mL stopper. 4) Wet H-CM-modified cellulose with 15 mL of 80% methanol, add 100 mL of 0.1 N NaOH, and shake at room temperature for 3 hours. 5) Using phenolphthalein as an indicator, back titrate excess NaOH with _{0.1 N H 2} SO _4. 6) Calculate the degree of carboxymethyl substitution (DS) by the following formula:
A = [(100 x F'-(0.1 N H ₂ SO ₄ ) (mL) x F) x 0.1] / (absolute dry mass (g) of H-CM-formed cellulose)
DS = 0.162 × A / (1-0.058 × A)
A: 1N NaOH amount (mL) required to neutralize 1 g of H-CM-formed cellulose
F': 0.1N NaOH factor F: 0.1N H ₂ SO ₄ factor

In the present disclosure, "carboxymethylated cellulose", which is a kind of modified cellulose used for preparing modified CNF, means that at least a part of the fibrous shape is maintained even when dispersed in water. Therefore, it is distinguished from carboxymethyl cellulose (CMC), which is a kind of water-soluble polymer described later. When the aqueous dispersion of "carboxymethylated cellulose" is observed with an electron microscope, a fibrous substance can be observed. On the other hand, even when the aqueous dispersion of carboxymethyl cellulose, which is a kind of water-soluble polymer, is observed, no fibrous substance is observed. Further, in "carboxymethylated cellulose", the peak of cellulose type I crystal can be observed when measured by X-ray diffraction, but in the water-soluble polymer carboxymethyl cellulose, cellulose type I crystal is not observed.

[Carboxylation]
In the present disclosure, when carboxylated (oxidized) cellulose is used as the modified cellulose, carboxylated cellulose (also referred to as oxidized cellulose) can be obtained by carboxylating (oxidizing) the above-mentioned cellulose raw material by a known method. .. Although not particularly limited, in the case of carboxylation, the amount of carboxyl groups should be adjusted to 0.6 mmol / g to 2.0 mmol / g with respect to the absolute dry mass of the anion-modified CNF. Is preferable, and it is more preferable to adjust the concentration to 1.0 mmol / g to 2.0 mmol / g.

As an example of the carboxylation (oxidation) method, 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 bromide, iodide or a mixture thereof. The method can be mentioned. By this oxidation reaction, the primary hydroxyl group at the C6 position of the glucopyranose ring on the surface of cellulose is selectively oxidized, and the cellulose fiber having an aldehyde group and a carboxyl group (-COOH) or a carboxylate group (-COO-) on the surface. Can be obtained. The concentration of cellulose during the reaction is not particularly limited, but is preferably 5% by mass or less.

The N-oxyl compound is a compound capable of generating a nitroxy radical. As the N-oxyl compound, any compound can be used as long as it is a compound that promotes the desired oxidation reaction. For example, 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO) and its derivative (for example, 4-hydroxy TEMPO) can be mentioned.

The amount of the N-oxyl compound used is not particularly limited as long as it is a catalytic amount capable of oxidizing cellulose as a raw material. For example, 0.01 mmol to 10 mmol is preferable, 0.01 mmol to 1 mmol is more preferable, and 0.05 mmol to 0.5 mmol is further preferable with respect to 1 g of cellulose that has been completely dried. Further, it is preferably about 0.1 mmol to 4 mmol / L with respect to the reaction system.

The bromide is a compound containing bromine, and examples thereof include alkali metals bromide that can be dissociated and ionized in water. Further, the iodide is a compound containing iodine, and an example thereof includes an alkali metal iodide. The amount of bromide or iodide used can be selected within a range in which the oxidation reaction can be promoted. The total amount of bromide and iodide is, for example, preferably 0.1 mmol to 100 mmol, more preferably 0.1 mmol to 10 mmol, still more preferably 0.5 mmol to 5 mmol, based on 1 g of dry cellulose.

As the oxidizing agent, known ones can be used, and for example, halogens, hypochlorous acids, hypochlorous acids, perhalogenic acids or salts thereof, halogen oxides, peroxides and the like can be used. Of these, sodium hypochlorite, which is inexpensive and has a low environmental impact, is preferable. As the amount of the oxidizing agent used, for example, 0.5 mmol to 500 mmol is preferable, 0.5 mmol to 50 mmol is more preferable, 1 mmol to 25 mmol is more preferable, and 3 mmol to 10 mmol is most preferable with respect to 1 g of cellulose which is absolutely dry. Further, for example, 1 mmol to 40 mol is preferable with respect to 1 mol of the N-oxyl compound.

Carboxylation (oxidation) of cellulose allows the reaction to proceed efficiently even under relatively mild conditions. Therefore, the reaction temperature is preferably 4 ° C. to 40 ° C., and may be room temperature of about 15 ° C. to 30 ° C. As the reaction progresses, carboxyl groups are generated in the cellulose, so that the pH of the reaction solution is lowered. In order to allow the oxidation reaction to proceed efficiently, it is preferable to add an alkaline solution such as an aqueous sodium hydroxide solution to maintain the pH of the reaction solution at 8 to 12, preferably about 10 to 11. Water is preferable as the reaction medium because it is easy to handle and side reactions are unlikely to occur.

The reaction time in the oxidation reaction can be appropriately set according to the degree of progress of oxidation, and is usually about 0.5 hour to 6 hours, for example, about 0.5 hour to 4 hours.

Further, the oxidation reaction may be carried out in two steps. For example, by oxidizing the oxidized cellulose obtained by filtration after the completion of the first-stage reaction again under the same or different reaction conditions, the efficiency is not affected by the reaction inhibition by the salt produced as a by-product in the first-stage reaction. Can be oxidized well.

As another example of the carboxylation (oxidation) method, there is a method of oxidizing by contacting a gas containing ozone with a cellulose raw material. By this oxidation reaction, the hydroxyl groups at at least the 2nd and 6th positions of the glucopyranose ring are oxidized, and the cellulose chain is decomposed. Ozone concentration in the ozone containing gas is preferably ^{50g / m 3 ~250g / m 3} , more preferably ^{50g / m 3 ~220g / m 3} . The amount of ozone added to the cellulose raw material is preferably 0.1 part by mass to 30 parts by mass, and more preferably 5 parts by mass to 30 parts by mass, when the solid content of the cellulose raw material is 100 parts by mass. .. The ozone treatment temperature is preferably 0 ° C to 50 ° C, more preferably 20 ° C to 50 ° C. The ozone treatment time is not particularly limited, but is about 1 minute to 360 minutes, preferably about 30 minutes to 360 minutes. When the ozone treatment conditions are within these ranges, it is possible to prevent the cellulose from being excessively oxidized and decomposed, and the yield of the oxidized cellulose becomes good. After the ozone treatment, the additional oxidation treatment may be performed using an oxidizing agent. The oxidizing agent used for the additional oxidation treatment is not particularly limited, and examples thereof include chlorine compounds such as chlorine dioxide and sodium chlorite, oxygen, hydrogen peroxide, persulfate, and peracetic acid. For example, the additional oxidation treatment can be performed by dissolving these oxidizing agents in a polar organic solvent such as water or alcohol to prepare an oxidizing agent solution, and immersing the cellulose raw material in the solution.

The amount of the carboxyl group of cellulose oxide can be adjusted by controlling the reaction conditions such as the amount of the oxidizing agent added and the reaction time described above.

[Phosphate esterification]
As the modified cellulose, phosphoric acid esterified cellulose can be used. The cellulose is obtained by a method of mixing a powder or an aqueous solution of a phosphoric acid compound A with a cellulose raw material, or a method of adding an aqueous solution of a phosphoric acid compound A to a slurry of a cellulose raw material.

Examples of the phosphoric acid-based compound A include phosphoric acid, polyphosphoric acid, phosphorous acid, phosphonic acid, polyphosphonic acid, and esters thereof. These may be in the form of salts. Among these, a compound having a phosphoric acid group is preferable because it is low in cost, easy to handle, and a phosphoric acid group can be introduced into the cellulose of the pulp fiber to improve the defibration efficiency. 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, and phosphorus. Examples thereof include tripotassium acid, potassium pyrophosphate, potassium metaphosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, triammonium phosphate, ammonium pyrophosphate, ammonium metaphosphate and the like. These can be used alone or in combination of two or more. Of these, from the viewpoints of high efficiency of introducing phosphoric acid groups, easy defibration in the following defibration steps, and easy industrial application, phosphoric acid, sodium phosphate of phosphoric acid, potassium salt of phosphoric acid, and phosphoric acid Ammonium salt is more preferred. In particular, sodium dihydrogen phosphate and disodium hydrogen phosphate are preferable. Further, the phosphoric acid-based compound A is preferably used as an aqueous solution because the uniformity of the reaction is enhanced and the efficiency of introducing the phosphoric acid group is increased. The pH of the aqueous solution of the phosphoric acid-based compound A is preferably 7 or less because the efficiency of introducing the phosphoric acid group is high, but is preferably 3 to 7 from the viewpoint of suppressing the hydrolysis of pulp fibers.

The following method can be mentioned as an example of the method for producing phosphoric acid esterified cellulose. A phosphoric acid-based compound A is added to a dispersion of a cellulose raw material having a solid content concentration of 0.1% by mass to 10% by mass with stirring to introduce a phosphoric acid group into the cellulose. When the cellulose raw material is 100 parts by mass, the amount of the phosphoric acid compound A added is preferably 0.2 parts by mass to 500 parts by mass, and is preferably 1 part by mass to 400 parts by mass. Is more preferable. When the ratio of the phosphoric acid compound A is at least the above lower limit value, the yield of the fine fibrous cellulose can be further improved. However, if the upper limit is exceeded, the effect of improving the yield will reach a plateau, which is not preferable from the viewpoint of cost.

At this time, in addition to the cellulose raw material and the phosphoric acid-based compound A, powders or aqueous solutions of other compounds B may be mixed. Compound B is not particularly limited, but a nitrogen-containing compound exhibiting basicity is preferable. "Basic" here is defined as the aqueous solution exhibiting a pink to red color in the presence of a phenolphthalein indicator, or the pH of the aqueous solution being greater than 7. The basic nitrogen-containing compound used in the present disclosure is not particularly limited as long as the effects of the present disclosure are exhibited, but a compound having an amino group is preferable. For example, urea, methylamine, ethylamine, trimethylamine, triethylamine, monoethanolamine, diethanolamine, triethanolamine, pyridine, ethylenediamine, hexamethylenediamine and the like can be mentioned, but are not particularly limited. Of these, urea, which is low in cost and easy to handle, is preferable. The amount of compound B added is preferably 2 parts by mass to 1000 parts by mass, more preferably 100 parts by mass to 700 parts by mass, based on 100 parts by mass of the solid content of the cellulose raw material. The reaction temperature is preferably 0 ° C. to 95 ° C., more preferably 30 ° C. to 90 ° C. The reaction time is not particularly limited, but is about 1 minute to 600 minutes, more preferably 30 minutes to 480 minutes. When the conditions of the phosphoric acid esterification reaction are within these ranges, it is possible to prevent the cellulose from being excessively phosphorylated and easily dissolved, and the yield of the phosphoric acid esterified cellulose becomes good. After dehydrating the obtained phosphoric acid esterified cellulose suspension, it is preferable to heat-treat it at 100 ° C. to 170 ° C. from the viewpoint of suppressing hydrolysis of cellulose. Further, it is preferable to heat at 130 ° C. or lower, preferably 110 ° C. or lower while water is contained in the heat treatment, remove the water, and then heat-treat at 100 ° C. to 170 ° C.

The degree of phosphoric acid group substitution per glucose unit of the phosphoric acid esterified cellulose is preferably 0.001 to 0.40. By introducing a phosphate group substituent into cellulose, the celluloses are electrically repelled from each other. Therefore, the cellulose into which a phosphoric acid group has been introduced can be easily nano-defibrated. If the degree of phosphate group substitution per glucose unit is less than 0.001, nano-defibration cannot be sufficiently performed. On the other hand, if the degree of phosphate substitution per glucose unit is greater than 0.40, it swells or dissolves and may not be obtained as nanofibers. In order to efficiently perform defibration, it is preferable that the phosphoric acid esterified cellulosic raw material obtained above is washed by boiling and then washing with cold water.

[Defibration]
In the present disclosure, the device for defibrating is not particularly limited, but a strong shearing force is applied to the aqueous dispersion of modified cellulose by using a device such as a high-speed rotary type, a colloid mill type, a high-pressure type, a roll mill type, or an ultrasonic type. It is preferable to apply. In particular, in order to efficiently defibrate, it is preferable to use a wet high-pressure or ultra-high pressure homogenizer capable of applying a pressure of 50 MPa or more to the aqueous dispersion and applying a strong shearing force. The pressure is more preferably 100 MPa or more, still more preferably 140 MPa or more. In addition, prior to the defibration / dispersion treatment with a high-pressure homogenizer, the above-mentioned modified cellulose may be pretreated, if necessary, using a known mixing, stirring, emulsifying, and dispersing device such as a high-speed shear mixer. It is possible. The number of treatments (passes) in the defibrator may be once, twice or more, and preferably twice or more.

In the dispersion treatment of the modified cellulose, 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, an organic solvent (for example, a hydrophilic organic solvent such as methanol), and a mixed solvent thereof. Since it is used in foods, the solvent is preferably water.

The solid content concentration of the modified cellulose in the dispersion is usually 0.1% by weight or more, preferably 0.2% by weight or more, and more preferably 0.3% by weight or more. As a result, the amount of liquid becomes appropriate with respect to the amount of the cellulose fiber raw material, which is efficient. The upper limit is usually 10% by weight or less, preferably 6% by weight or less. This makes it possible to maintain liquidity.

In the present disclosure, the fiber width of the anion-modified CNF is about 1 nm to 500 nm or 2 nm to 100 nm, preferably 1 nm or more and less than 20 nm, 2 nm or more and 15 nm or less, or 3 nm or more and 5 nm or less in one or more embodiments. .. The average aspect ratio of the anion-modified CNF is usually 100 or more. The upper limit of the average aspect ratio is not particularly limited, but is usually 1000 or less. The average aspect ratio can be calculated by the following formula:
Average aspect ratio = average fiber length / average fiber diameter

Examples of the cellulose raw material include plant materials, animal materials, algae and the like in one or more embodiments. Plant materials include, in one or more embodiments, wood, bamboo, hemp, jute, kenaf, cloth, pulp, recycled pulp, recycled paper and the like. Examples of the pulp include kraft pulp (KP), sulfate pulp (SP), dissolved sulfite pulp (DSP), dissolved kraft pulp (DKP), powdered cellulose, microcrystalline cellulose powder and the like in one or more embodiments. Examples of the animal material include sea squirts and the like in one or more embodiments. The anion-modified CNF in the present disclosure does not include bacterial cellulose produced from bacteria in one or more embodiments and cellulose derived thereto.

[Manufacturing method of dried CNF]
In one embodiment, the present disclosure comprises mixing an anion-modified CNF and a redispersibility improver to obtain an aqueous suspension of an anion-modified CNF, and drying the aqueous suspension to obtain a dried CNF. The present invention relates to a method for producing a dry CNF including the present disclosure method for producing a dry CNF. According to the method for producing a dry CNF of the present disclosure, in one or more embodiments, a film-like dry CNF and / or a powder-like dry CNF having sufficient redispersibility can be obtained. The method for producing a dry CNF of the present disclosure can be preferably used for TEMPO-oxidized CNF among anion-modified CNFs in one or more embodiments. According to the method for producing dried CNF of the present disclosure, the redispersibility of the dried product (dried CNF) of TEMPO-oxidized CNF can be improved or improved in one or more embodiments.

In addition, the method for producing dried CNF of the present disclosure can be used for CM-ized CNF in one or more embodiments. According to the method for producing a dried CNF of the present disclosure, in one or more embodiments, the dispersibility of the dried product (dried CNF) of the CMized CNF at the time of redispersion can be improved or improved.
In addition, the method for producing dried CNF of the present disclosure can be used for phosphate esterified CNF in one or more embodiments. According to the method for producing a dried CNF of the present disclosure, in one or more embodiments, the dispersibility of the dried product (dried CNF) of the phosphate esterified CNF at the time of redispersion can be improved or improved.

According to the method for producing a dried CNF of the present disclosure, it is possible to obtain a dried CNF with improved redispersibility in one or more embodiments. The resulting dried CNF may have sufficient redispersibility in one or more embodiments without particular limitation. “Having sufficient redispersibility” means that, in one or more embodiments, it has redispersibility in an aqueous dispersion medium at a level comparable to or comparable to that of an anion-modified CNF suspension before drying. Can be mentioned. The resulting dried CNF, in one or more embodiments, can be used in various chemical supplies, foods, cosmetics, pharmaceuticals, beverages, reinforcing materials (including paper-related), heat insulating materials, automobile parts, paints, pesticides, construction, batteries, households. It can be used for miscellaneous goods, water treatment, cleaning agents, etc.

In the present disclosure, the "water-soluble nonionic surfactant" is a nonionic substance that dissolves in a transparent or cloudy state when mixed with water at 25 ° C. at a concentration of 1% or 5% in one or more embodiments. Refers to a surfactant.

The HLB of the water-soluble nonionic surfactant is, in one or more embodiments, 10 or more, 12 or more, 14 or more or 16 or more, or 19.5 or less. In the present disclosure, "HLB (hydrophilic lipophilic balance)" can be calculated using the Griffin formula in one or more embodiments. Further, as the HLB, the value described in the catalog or the like of the manufacturer of the surfactant can also be used.

The molecular weight of the water-soluble nonionic surfactant is 200 or more, 500 or more or 1000 or more, or 5000 or less, 4000 or less or 3000 or less in one or more embodiments.

As the water-soluble nonionic surfactant, in one or more embodiments, polyoxyethylene fatty acid ester, polyoxyethylene alkylamine, polyoxyethylene alkyl ether, sucrose fatty acid ester, polyoxyethylene alkyl phenyl ether, polyoxy. Examples thereof include ethylene polyoxypropylene alkylamine, polyoxyethylene polyoxypropylene alkyl ether, and ethylene oxide adduct of sorbitan fatty acid ester.

The method for producing a dry CNF of the present disclosure comprises mixing a wet anion-modified CNF (dispersed in water) with a water-soluble nonionic surfactant in one or more embodiments. This makes it possible to obtain an aqueous suspension containing an anion-modified CNF and a water-soluble nonionic surfactant.

The blending ratio of the water-soluble nonionic surfactant to the anion-modified CNF (absolute dry solid content, 100 parts by mass) is 5 parts by mass or more, 5 parts by mass to 500 parts by mass, and 5 parts by mass in one or more embodiments. ~ 400 parts by mass to 5 parts by mass to 300 parts by mass or 10 parts by mass to 200 parts by mass, and more preferably 30 parts by mass to 350 parts by mass or 30 parts by mass to 150 parts by mass.

When the anion-modified CNF is a carboxylated CNF such as TEMPO oxide CNF, the blending ratio of the water-soluble nonionic surfactant to the anion-modified CNF (absolute dry solid content, 100 parts by mass) is, in one or more embodiments. 5 parts by mass or more, 5 parts by mass to 500 parts by mass, 5 parts by mass to 400 parts by mass, 5 parts by mass to 300 parts by mass or 10 parts by mass to 200 parts by mass, preferably 30 parts by mass to 250 parts by mass or 45 parts by mass. It is a mass part to 150 parts by mass.

When the anion-modified CNF is a CM-modified CNF, the blending ratio of the water-soluble nonionic surfactant to the anion-modified CNF (absolute dry solid content, 100 parts by mass) is 5 parts by mass or more in one or more embodiments. It is 10 parts by mass to 500 parts by mass or 30 parts by mass to 400 parts by mass, preferably 50 parts by mass to 350 parts by mass or 75 parts by mass to 350 parts by mass.

When the anion-modified CNF is a phosphate-esterified CNF, the blending ratio of the water-soluble nonionic surfactant to the anion-modified CNF (absolute dry solid content, 100 parts by mass) is 5 parts by mass in one or more embodiments. 5 parts by mass to 500 parts by mass, 5 parts by mass to 400 parts by mass, 5 parts by mass to 300 parts by mass or 10 parts by mass to 200 parts by mass, preferably 30 parts by mass to 250 parts by mass or 45 parts by mass. It is 150 parts by mass.

The method for producing a dry CNF of the present disclosure comprises, in one or more embodiments, drying an aqueous suspension containing an anion-modified CNF and a nonionic surfactant. The aqueous suspension may, in one or more embodiments, form a thin film and be dried or spray dried. Thereby, a dry film and / or a dry powder containing an anion-modified CNF and a nonionic surfactant can be obtained.

In the present disclosure, the method for drying the aqueous suspension is not particularly limited, and examples thereof include spray drying, air drying, hot air drying, vacuum drying, and squeezing in one or more embodiments.

In the dried CNF obtained by the method for producing a dried CNF of the present disclosure, in one or more embodiments, 0.1 g of the dried CNF finely divided to about 1 to 2 mm is added to 5 g of distilled water, and a point mixer is used for about 1 minute. After stirring, the mixture is left at room temperature for about 24 hours, and then stirred again with a point mixer for about 1 minute, and has at least redispersibility at a level comparable to or comparable to that of CNF before drying.

The dried CNF obtained by the method for producing a dried CNF of the present disclosure may be a dried product, and may be in the form of a film in one or more embodiments from the viewpoint of further improving the dispersibility in the dispersion medium to be redispersed. It may be present or it may be in powder form.

[Dry CNF]
The present disclosure relates, in one aspect, to a dry CNF containing a water-soluble nonionic surfactant and an anion-modified CNF (the dry CNF of the present disclosure). The dried CNF of the present disclosure can be obtained in one or more embodiments by the method of producing the dried CNF of the present disclosure. The dried CNF of the present disclosure contains an anion-modified CNF as a main component in one or more embodiments without particular limitation. The dried CNF of the present disclosure may be in the form of a film or in the form of powder in one or more embodiments.

[Manufacturing method of CNF redispersion]
The present disclosure relates, in one aspect, to a method for producing a CNF redispersion (method for producing a CNF redispersion of the present disclosure). The method for producing a CNF redispersion of the present disclosure is to obtain an aqueous suspension containing an anion-modified CNF and a redispersibility improver, to dry the aqueous suspension, in one or more embodiments. And redispersing the resulting dried product in a dispersion medium. The method for producing a CNF redispersion solution of the present disclosure comprises, in one or more embodiments, redispersing the dry CNF obtained by the method for producing a dry CNF of the present disclosure in a dispersion medium. According to the method for producing a CNF redispersion of the present disclosure, in one or more embodiments, the CNF redispersion has a level of dispersibility comparable to or comparable to that of a non-drying CNF aqueous suspension or aqueous dispersion. You can get things. The redispersion may be a liquid or a gel in one or more embodiments.

Examples of the dispersion medium include an aqueous dispersion medium such as water in one or more embodiments. The dispersion medium may contain various polymers other than CNF in one or more embodiments.

[CNF redispersibility improvement method]
As described above, the redispersibility of the obtained dried CNF can be improved or improved by drying the anion-modified CNF together with the redispersibility improving agent. Thus, in other embodiments, the present disclosure comprises mixing an anion-modified CNF with a redispersibility improver to obtain an aqueous suspension of anion-modified cellulose nanofibers and drying the aqueous suspension. The present invention relates to a method for improving the redispersibility of CNF including. According to the method for improving CNF redispersibility of the present disclosure, in one or more embodiments, the redispersibility of dried products of TEMPO-oxidized CNF, CM-modified CNF and phosphate-esterified CNF is further improved among anion-modified CNFs. Can be improved. The redispersibility improver and the compounding ratio are the same as the method for producing the dried CNF of the present disclosure.

In one or more embodiments, the aqueous suspension may contain a third component other than the anion-modified CNF and the redispersibility improver upon redispersion. The third component, in one or more embodiments, includes water-soluble polymers and the like.

Drying of the aqueous suspension can be carried out in one or more embodiments in the same manner as in the method for producing dried CNFs of the present disclosure.

[Redispersibility improver]
The present disclosure relates to a redispersibility improver (the redispersibility improver of the present disclosure) for improving or improving the redispersibility of dried cellulose nanofibers in an aqueous dispersion medium in another aspect. The redispersibility improver of the present disclosure includes a water-soluble nonionic surfactant. The redispersibility improver of the present disclosure can be used in one or more embodiments in the production of dried cellulose nanofibers with improved or improved redispersibility in an aqueous dispersion medium. The water-soluble nonionic surfactant is as described above.

[Dry composition]
The present disclosure is, in one embodiment, a dry composition containing anion-modified cellulose nanofibers and a redispersibility improver, wherein the redispersibility improver contains a water-soluble nonionic surfactant (the present invention). Also referred to as the disclosed dry composition).

The proportion of the redispersibility improver in the dry composition of the present disclosure is 5% by mass or more, 5 to 500% by mass, 5 to 5% by mass with respect to the anion-modified CNF (absolute dry solid content) in one or more embodiments. It is 400% by mass, 5 to 300% by mass, or 20 to 300% by mass, 10 to 200% by mass or 20 to 300% by mass, preferably 30 to 350% by mass or 30 to 150% by mass.

When the anion-modified CNF is TEMPO oxide CNF, the proportion of the redispersibility improver in the dry composition of the present disclosure is 5 mass by weight with respect to TEMPO oxide CNF (absolute dry solid content) in one or more embodiments. % Or more, 5% by mass to 500% by mass, 5% by mass to 400% by mass, 5% by mass to 300% by mass or 10% by mass to 200% by mass, preferably 30% by mass to 250% by mass or 45% by mass. ~ 150% by mass.

When the anion-modified CNF is a CM-modified CNF, the ratio of the redispersibility improver in the dry composition of the present disclosure is 5 mass by mass with respect to the CM-modified CNF (absolute dry solid content) in one or more embodiments. % Or more, 10% by mass to 500% by mass, or 30% by mass to 400% by mass, preferably 50% by mass to 350% by mass or 75% by mass to 350% by mass.

When the anion-modified CNF is a phosphate-esterified CNF, the proportion of the redispersibility improver in the dry composition of the present disclosure is, in one or more embodiments, relative to the phosphate-esterified CNF (absolute dry solids). 5% by mass or more, 5% by mass to 500% by mass, 5% by mass to 400% by mass, 5% by mass to 300% by mass, or 10% by mass to 200% by mass, preferably 30% by mass to 250% by mass. Alternatively, it is 45% by mass to 150% by mass.

The dry composition of the present disclosure may contain a third component other than the anion-modified CNF and the redispersibility improver in one or more embodiments. The third component, in one or more embodiments, includes water-soluble polymers and the like.

The dry composition of the present disclosure may be in the form of a film, solid or powder in one or more embodiments. The film thickness of the dry composition of the present disclosure is 50 μm or more or 100 μm or more, or 1000 μm or less or 300 μm or less in one or more embodiments.

The drying composition of the present disclosure may be produced in one or more embodiments by mixing an anion-modified CNF, a redispersibility improver, and, if necessary, the third component, and drying the mixture. Alternatively, it may be produced by mixing the dried CNF of the present disclosure with the third component and drying it.

The present disclosure further relates to one or more embodiments below.
[1] The present invention comprises mixing an anion-modified CNF and a redispersibility improver to obtain an aqueous suspension of the anion-modified CNF, and drying the aqueous suspension to obtain a dried CNF.
The redispersibility improver is a water-soluble nonionic surfactant, a method for producing a dry CNF [2] The anion-modified CNF is a carboxylated CNF, a CM-modified CNF, or a phosphate-esterified cellulose nanofiber. [1] The method for producing dried CNF according to the above.
[3] The present invention comprises mixing an anion-modified CNF and a redispersibility improver to obtain an aqueous suspension of the anion-modified CNF, and drying the aqueous suspension.
The method for improving the redispersibility of CNF, wherein the redispersibility improving agent is a water-soluble nonionic surfactant.
[4] The method for improving redispersibility according to [3], wherein the anion-modified CNF is a carboxylated CNF, a CM-modified CNF, or a phosphate-esterified CNF.
[5] An agent for improving or improving the redispersibility of dried CNF in an aqueous dispersion medium, which is a redispersibility improving agent containing a water-soluble nonionic surfactant.
[6] A dry composition containing an anion-modified CNF and a redispersibility improving agent.
A dry composition in which the redispersibility improver contains a water-soluble nonionic surfactant.
[7] The composition according to [6], wherein the anion-modified CNF is a carboxylated CNF, a CM-modified CNF, or a phosphate-esterified CNF.

Hereinafter, the present disclosure will be further described with reference to Examples and Comparative Examples. However, this disclosure is not construed as limited to the following examples.

[Manufacture of carboxylated cellulose nanofibers (anion-modified CNF1)]
5.00 g (absolutely dry) of bleached unbeaten kraft pulp (whiteness 85%) derived from coniferous trees, 39 mg (0.05 mmol per 1 g of absolute dry cellulose) of TEMPO (Sigma Aldrich) and 514 mg of sodium bromide (absolutely dry). It was added to 500 ml of an aqueous solution in which 1.0 mmol) was dissolved in 1 g of cellulose, and the mixture was stirred until the pulp was uniformly dispersed. An aqueous sodium hypochlorite solution was added to the reaction system so that the sodium hypochlorite content was 5.5 mmol / g, and the oxidation reaction was started at room temperature. Although the pH in the system decreased during the reaction, a 3M aqueous sodium hydroxide solution was sequentially added to adjust the pH to 10. The reaction was terminated when sodium hypochlorite was consumed and the pH in the system did not change.
The mixture after the reaction was filtered through a glass filter to separate the pulp, and the pulp was thoroughly washed with water to obtain oxidized pulp (carboxylated cellulose). The pulp yield at this time was 90%, the time required for the oxidation reaction was 90 minutes, and the amount of carboxyl groups was 1.6 mmol / g. This was adjusted to a pulp solid content of 1.1% (w / v) with water and treated three times with an ultra-high pressure homogenizer (20 ° C., 150 MPa) to obtain a carboxylated cellulose nanofiber (hereinafter referred to as T-CNF). An aqueous dispersion was obtained. The average fiber diameter was 3 nm and the aspect ratio was 250.

[Manufacture of carboxymethylated cellulose nanofibers (anion-modified CNF2)]
In a stirrer capable of mixing pulp, 200 g of softwood bleached kraft pulp (manufactured by Nippon Paper Co., Ltd.) by dry mass and 111 g of sodium hydroxide by dry mass (2.25 times mol per anhydrous glucose residue of the base material). ) Was added, and water was added so that the pulp solid content was 20% (w / v). Then, after stirring at 30 ° C. for 30 minutes, 216 g (active ingredient equivalent, 1.5-fold molar amount per glucose residue of pulp) was added. After stirring for 30 minutes, the temperature was raised to 70 ° C. and the mixture was stirred for 1 hour. Then, the reaction product was taken out, neutralized and washed to obtain a carboxymethylated pulp having a carboxymethyl substitution degree of 0.25 per glucose unit. This is made into a pulp solid content of 1.2% (w / v) with water, and defibrated by treating with a high-pressure homogenizer at a pressure of 20 ° C. and 150 MPa five times to defibrate the carboxymethylated cellulose nanofiber (hereinafter referred to as CM-CNF). ) Was obtained. The average fiber diameter was 12 nm and the aspect ratio was 130.

[Manufacture of Phosphate Esterified Cellulose Nanofiber (Anion-Modified CNF3)]
6.75 g of sodium dihydrogen phosphate dihydrate and 4.83 g of disodium hydrogen phosphate are dissolved in 19.62 g of water to obtain an aqueous solution of a phosphoric acid compound (hereinafter referred to as "phosphorylation reagent"). It was. Water is added to unbleached softwood kraft pulp (NUKP, water content 80%, Canadian standard drainage degree (CSF) 580 ml measured according to JIS P8121) so that the pulp solid content is 4% (w / v). It was. Then, using a double disc refiner, the irregular CSF (plain weave 80 mesh, conforming to JIS P8121 except that the pulp sampling amount was 0.3 g) was beaten until it became 200 ml and the average length fiber length became 0.66 mm. The cellulose suspension thus obtained was diluted to a pulp solid content of 0.3% (w / v), and a pulp sheet (thickness 200 μm) having a water content of 90% and a solid content (absolute dry mass) of 3 g was obtained by a papermaking method. It was. This pulp sheet is immersed in 31.2 g of the phosphorylation reagent (80 parts by mass as the amount of phosphorus element with respect to 100 parts by mass of dried pulp) and heated in a blower dryer (Yamato Scientific Co., Ltd. DKM400) at 105 ° C. for 1 hour. Further, heat treatment was performed at 150 ° C. for 1 hour to introduce a phosphoric acid group into the cellulose fibers. Next, 500 ml of ion-exchanged water was added to the pulp sheet in which a phosphate group was introduced into the cellulose fibers, and the pulp sheet was stirred and washed, and then dehydrated. The dehydrated sheet was diluted with 300 ml of ion-exchanged water, and 5 ml of a 1N aqueous sodium hydroxide solution was added little by little with stirring to obtain a cellulose suspension having a pH of 12 to 13. Then, this cellulose suspension was dehydrated, and 500 ml of ion-exchanged water was added for washing. This dehydration washing was repeated twice more. Ion-exchanged water was added to the sheet obtained after washing and dehydration, and the mixture was stirred to obtain a 0.5% by mass cellulose suspension. This cellulose suspension is defibrated for 30 minutes under the condition of 21500 rpm using a defibration treatment device (Clearmix-2.2S manufactured by M-Technique) to defibrate cellulose (phosphate ester). Esterified cellulose nanofiber) suspension was obtained. When the cellulose contained in the defibrated cellulose suspension was observed with a transmission electron microscope, it was confirmed that fine fibrous cellulose having a width of 4 nm was contained. In addition, it was confirmed by X-ray diffraction that cellulose maintained cellulose type I crystals. Infrared absorption spectrum measurement by FT-IR ^{showed absorption based on phosphate groups at 1230 cm -1 to} 1290 cm ^-1 , confirming the addition of phosphate groups. The amount of phosphoric acid group introduced at this time was 2.1 mmol / g per 1 g (mass) of fine fibrous cellulose.

(Example 1)
Using the agents shown in Table 1, the production of dried anion-modified CNF (dried CNF) and the redispersibility of the dried CNF were evaluated. As the anion-modified CNF, an anion-modified CNF1 (T-CNF, average fiber width: 3 nm, aspect ratio: 250) was used.

[Manufacturing of dried CNF]
The agents shown in Table 1 were added as powders to a 1% (w / v) aqueous suspension of anion-modified CNF1. The drug was added in an amount (parts by mass) shown in Table 1 with respect to 100 parts by mass of CNF. The agents used in the examples in Table 1 were all water-soluble because they dissolved in a transparent or cloudy state when mixed with water at 25 ° C. at a concentration of 1% or 5%.
The drug was added in an equivalent amount to the CNF solid content in the suspension. Then, the mixture was stirred and mixed with a stirrer or a point mixer until it became transparent. The obtained liquid was applied on a Teflon ™ plate or a Teflon ™ dish and dried with warm air at 60 ° C. to 105 ° C. to obtain a film-like dry CNF.
In the blank, the same procedure as above was carried out except that no drug was added.

[Redispersion of dried CNF]
The film-shaped dried CNF was finely divided by hand to about 1 mm to 2 mm, and 0.1 g was weighed into a test tube. After adding 5 g of distilled water and stirring with a point mixer for about 1 minute, the mixture was left at room temperature for about 24 hours. This was stirred again with a point mixer for about 1 minute to obtain an aqueous dispersion or an aqueous suspension in which the anion-modified CNF was redispersed (solid content concentration 2% (w / v)).

[Evaluation of redispersibility]
The redispersibility of the aqueous dispersion or suspension in the test tube was visually evaluated. The evaluation was performed based on the following evaluation criteria. The results are shown in Table 1 below.
<Evaluation criteria>
A: Undispersed CNF pieces are not completely observed B: Fine undispersed CNF pieces are observed in a very small amount C: CNFs are not dispersed at all

As shown in Table 1, in none of the comparative examples dried with anionic, cationic and amphoteric agents, the obtained dried CNF could not be dispersed. On the other hand, in the examples dried with a water-soluble nonionic surfactant, it was confirmed that the obtained dried CNF could be dispersed and the redispersibility was improved.
In addition, undispersed CNF was confirmed in the blanks and comparative examples. On the other hand, in the test tubes of the examples, almost no undispersed CNF precipitate or undispersed gel-like substance was confirmed. Among them, in the test tube whose redispersibility evaluation was A, no undispersed CNF precipitate or undispersed gel-like substance was confirmed. In addition, all of the nonionic agents used in the examples showed high solubility in water.

[Evaluation of refilming and gelation]
The aqueous dispersion evaluated as A or B in the evaluation of redispersibility in Table 1 was evaluated for refilming and gelation.
The refilming was carried out by weighing about 2 g of the aqueous dispersion (redispersion) on a Teflon (trademark) plate and sufficiently drying it with warm air at 70 ° C to 80 ° C. Gelation was performed by adding a few drops of a 20% calcium chloride solution into a test tube containing an aqueous dispersion (redispersion).
As a result, both films and gels were formed. That is, it was suggested that the physical characteristics of the dried CNF obtained by the production method of the present disclosure are not significantly different from those of the untreated (before the drying treatment) anion-modified CNF.

(Example 2)
Production of dried CNF and production of dried CNF as in Example 1 except that anion-modified CNF2 (CM-CNF, average fiber width: 12 nm, aspect ratio: 130 or more) was used as the anion-modified CNF using the agents shown in Table 2. The redispersibility was evaluated. The results are shown in Table 2.

As shown in Table 2, it was confirmed that the obtained dried CNF could be dispersed and the redispersibility was further improved by drying the CM-ized CNF together with the water-soluble nonionic surfactant.

Claims (4)

Includes mixing anion-modified cellulose nanofibers with a redispersibility improver to obtain an aqueous suspension of anion-modified cellulose nanofibers, and drying the aqueous suspension to obtain dried cellulose nanofibers.
The cellulose nanofibers are anion-modified cellulose nanofibers selected from the group consisting of carboxylated cellulose nanofibers, carboxymethylated cellulose nanofibers and phosphoric acid esterified cellulose nanofibers.
The redispersibility improver is a water-soluble nonionic surfactant.
A method for producing dried cellulose nanofibers for redispersion in an aqueous dispersion medium. Including mixing the anion-modified cellulose nanofibers with a redispersibility improver to obtain an aqueous suspension of the anion-modified cellulose nanofibers and drying the aqueous suspension.
The anion-modified cellulose nanofibers are anion-modified cellulose nanofibers selected from the group consisting of carboxylated cellulose nanofibers, carboxymethylated cellulose nanofibers and phosphoric acid esterified cellulose nanofibers.
The redispersibility improver is a water-soluble nonionic surfactant.
A method for improving the redispersibility of anion-modified cellulose nanofibers in an aqueous dispersion medium. An agent for improving or improving the redispersibility of dried cellulose nanofibers in an aqueous dispersion medium, which comprises a water-soluble nonionic surfactant.
The dried cellulose nanofiber is an anion-modified cellulose nanofiber selected from the group consisting of carboxylated cellulose nanofiber, carboxymethylated cellulose nanofiber and phosphoric acid esterified cellulose nanofiber, and is a redispersibility improver. A dry composition obtained by the production method according to claim 1 for redispersion in an aqueous dispersion medium containing anion-modified cellulose nanofibers and a redispersibility improving agent.
The anion-modified cellulose nanofibers are anion-modified cellulose nanofibers selected from the group consisting of carboxylated cellulose nanofibers, carboxymethylated cellulose nanofibers and phosphoric acid esterified cellulose nanofibers.
A composition in which the redispersibility improver contains a water-soluble nonionic surfactant.