Cellulose nanofiber powder dispersant and production method therefor

Abstract

To provide a cellulose nanofiber powder dispersant capable of dispersing fillers (individual particles) in a solvent in water or oil.SOLUTION: This cellulose nanofiber powder dispersant comprises 75-90 wt.% of cellulose nanofibers, 7-12 wt.% of ethylene glycol, 0.2-0.5 wt.% of an acrylic acid copolymer, 0.4-0.8 wt.% of water-soluble sorbitan, 0.6-1.0 wt.% of a higher fatty acid, and 0.4-0.8 wt.% of an alkylammonium salt.SELECTED DRAWING: Figure 2B

Description

Technical Field

[0001] The present invention relates to a cellulose nanofiber powder dispersant and a method for producing the same. In particular, the present invention relates to a cellulose nanofiber powder dispersant having an excellent dispersing effect on various fillers such as micro-sized plant fibers, synthetic fibers, inorganic and organic pigments, carbon, calcium carbonate, and glass fibers, regardless of whether they are in water or oil, and a method for producing such a cellulose nanofiber powder dispersant.

Background Art

[0002] Cellulose nanofiber (also known as "Cellulose Nano Fiber", hereinafter sometimes simply referred to as "CNF") is a next-generation material derived from plants, and it is said that it can obtain five times the strength with one-fifth of the weight of steel. By utilizing cellulose nanofibers in automobiles, home appliances, etc., the effect of weight reduction can be obtained, energy efficiency can be improved, and a great contribution to countermeasures against global warming can be expected. For the social implementation of CNF, the Ministry of Economy, Trade and Industry and the Ministry of Agriculture, Forestry and Fisheries are implementing model projects in various fields such as automobiles, home appliances, housing and building materials as a collaborative project, and promoting the evaluation and verification of CO 2 reduction effects and the demonstration of solutions to related problems.

[0003]

[0004] Furthermore, in recent years, cellulose nanofibers have begun to be widely used in aqueous paints and the like, and have also begun to be used in cosmetics and foods incorporating properties such as moisture retention. In addition, since cellulose nanofibers have a lower specific gravity than glass, metal, and carbon, and their nano-sized fiber length can be expected to improve functions such as enhancing the strength of resins, they can be an ideal material to be added to resin materials as a reinforcing material.

[0005] Cellulose nanofibers are generally sold and provided in the form of a dispersion (such as a slurry or sol) dispersed in a dispersion medium such as water at a solid content of about 1 to 10% by weight, and are usually used in various applications as an industrial material or an additive material for foods and cosmetics as the cellulose nanofiber dispersion at a predetermined concentration as it is. On the other hand, for compounding with materials such as hydrophobic resins and rubbers, water removal is required. Currently, there are several methods for removing water from a dispersion in which cellulose nanofibers are dispersed in water, and typically, precipitation methods, centrifugation methods, filtration methods, spray drying methods, freeze drying methods, etc. can be mentioned.

[0006] For example, Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2022-028316) discloses a container for freeze-drying cellulose nanofibers, which includes a main body portion for storing a brine solution therein and a jacket covering the outer periphery of the main body portion to which a heat medium is supplied, and the main body portion is characterized in that the brine solution can be cooled by supplying the heat medium to the jacket. According to Patent Document 2, it is possible to provide a container capable of freezing a cellulose nanofiber dispersion while suppressing aggregation of cellulose nanofibers.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] By the way, regarding cellulose nanofiber powder, which is a dried product of cellulose nanofibers, sufficient studies have not been made so far on using it as a dispersant. According to the findings of the present inventor, cellulose nanofiber powder having an appropriate composition can be applied amphoterically in water and oil, and in some cases, dispersion performance exceeding the critical micelle concentration of existing surfactants can be achieved.

[0009] The present invention has been completed based on the above findings, and in one embodiment, an object is to provide a cellulose nanofiber powder dispersant capable of dispersing fillers (individual particles) in solvents in water and oil. In another embodiment of the present invention, an object is to provide a method for producing such a cellulose nanofiber powder dispersant.

Means for Solving the Problems

[0010] As a result of intensive studies by the present inventor, it has been discovered that the above problems can be solved by a method different from the prior art. That is, by producing a cellulose nanofiber powder dispersant containing specific components, the cellulose nanofiber powder dispersant can exhibit a good effect of dispersing fillers in solvents both in water and in oil. The present invention has been completed based on this finding and is exemplified below.

[0011] [1] A cellulose nanofiber powder dispersant, containing 75 to 90% by weight of cellulose nanofibers, 7 to 12% by weight of ethylene glycol, 0.2 to 0.5% by weight of an acrylic acid copolymer, 0.4 to 0.8% by weight of water-soluble sorbitan, 0.6 to 1.0% by weight of a higher fatty acid, and 0.4 to 0.8% by weight of an alkylammonium salt. [2] The cellulose nanofiber powder dispersant according to [1], wherein the average fiber length of the cellulose nanofiber powder is in the range of 0.1 μm to 3.0 μm. [3] The cellulose nanofiber powder dispersant according to [1] or [2], wherein the average fiber diameter of the cellulose nanofiber powder is in the range of 0.5 nm to 10 nm. [4] A method for producing a cellulose nanofiber powder dispersant, comprising: Step A of preparing a cellulose nanofiber dispersion, and Step B of supplying the cellulose nanofiber dispersion to a two-roll mill and rotating the two-roll mill to dry the cellulose nanofiber dispersion to obtain a cellulose nanofiber powder. including The cellulose nanofiber dispersion is prepared to contain 75 to 90% by weight of cellulose nanofibers, 7 to 12% by weight of ethylene glycol, 0.2 to 0.5% by weight of an acrylic acid copolymer, 0.4 to 0.8% by weight of a water-soluble sorbitan, 0.6 to 1.0% by weight of a higher fatty acid, and 0.4 to 0.8% by weight of an alkylammonium salt in terms of solid content. [5] The method according to [4], wherein in step B, the surface temperature of the two-roll mill is heated to 95°C to 130°C.

Advantages of the Invention

[0012] According to one embodiment of the present invention, it is possible to provide a cellulose nanofiber powder dispersant capable of dispersing fillers (individual particles) in solvents in water or oil. According to another embodiment of the present invention, it is possible to provide a method for producing such a cellulose nanofiber powder dispersant.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2A

Figure 2B

Mode for Carrying Out the Invention

[0014] Next, embodiments of the present invention will be described in detail with reference to the drawings. It should be understood that the present invention is not limited to the following embodiments, and modifications and improvements in design can be appropriately made based on the ordinary knowledge of those skilled in the art without departing from the gist of the present invention.

[0015] (1. Raw material of cellulose nanofiber) Cellulose nanofiber is obtained by finely pulverizing cellulose, which is the main component of plant fibers, into a nano size, and the main raw material is wood pulp (raw material for paper). It is mainly used for reinforcing resin materials and preventing shrinkage of resins at low temperatures. In the present invention, the raw material of cellulose nanofiber is not particularly limited.

[0016] Since cellulose nanofiber is usually a plant-derived material, it is in a slurry state dispersed in water at the stage of being taken out from plants. The solid content is usually 1 to 10% by weight. For example, when producing a dispersant as a powder from a cellulose nanofiber dispersion, it is necessary to first remove only the water from the cellulose nanofiber aqueous dispersion dispersed in water to take out the cellulose nanofiber alone. Also, it is assumed that the cellulose nanofiber alone is taken out again from a redispersion liquid in which the cellulose nanofiber alone is redispersed in water or a dispersion medium other than water. Therefore, in the present invention, the dispersion medium in the cellulose nanofiber dispersion is not limited to water. However, preferably, the dispersion medium in the cellulose nanofiber dispersion is water.

[0017] Incidentally, as described above, the solid content in the cellulose nanofiber dispersion is usually 1 to 10% by weight, but it may be further diluted to less than 1% by weight. Therefore, the cellulose nanofiber dispersion can also be preliminarily dried. The method of preliminary drying is not particularly limited, and any of the conventional methods can be adopted. The cellulose nanofiber dispersion can be preliminarily dried to a maximum solid content of 12% by weight, for example, and then the drying method of the present invention described below can be carried out.

[0018] As described below, when the cellulose nanofiber dispersion is dried under specific conditions, cellulose nanofiber powder can be obtained. It is preferable that the average fiber length of the cellulose nanofiber powder is 0.1 μm or more. Thereby, the effect of dispersion stability can be expected. From this viewpoint, it is more preferable that the average fiber length of the cellulose nanofiber powder is 0.2 μm or more, still more preferably 0.3 μm or more, and still more preferably 0.5 μm or more. If the average fiber length of the cellulose nanofiber powder is 0.1 μm or more, it has a high aspect ratio with respect to the average fiber diameter.

[0019] Also, it is preferable that the average fiber length of the cellulose nanofiber powder is 3.0 μm or less. Thereby, it is possible to suppress the cellulose nanofiber powder from rounding into a spherical shape during processing. From this viewpoint, it is more preferable that the average fiber length of the cellulose nanofiber powder is 2.5 μm or less, still more preferably 1.5 μm or less, and still more preferably 1.0 μm or less.

[0020] Incidentally, the average fiber length of the cellulose nanofiber powder means the D50 (median diameter) measured according to the laser diffraction / scattering method of JIS Z8825:2022 for the fibers of the cellulose nanofiber powder.

[0021] The average fiber diameter of the cellulose nanofiber powder is preferably 0.5 nm or more. Thereby, the effect of dispersion stability can be expected. From this viewpoint, the average fiber diameter of the cellulose nanofiber powder is more preferably 0.7 nm or more, even more preferably 1 nm or more, and even more preferably 3 nm or more.

[0022] Also, the average fiber diameter of the cellulose nanofiber powder is preferably 10 nm or less. If the cellulose nanofiber powder becomes too thick, the aspect ratio decreases, and the interparticle distance may not be maintained as a steric hindrance. From this viewpoint, the average fiber diameter of the cellulose nanofiber powder is more preferably 8 nm or less, even more preferably 7 nm or less, and even more preferably 5 nm or less.

[0023] Note that the average fiber diameter of the cellulose nanofiber powder means the average particle diameter measured according to the dynamic light scattering method of JIS Z8828:2019 for the fibers of the cellulose nanofiber powder.

[0024] (2. Cellulose Nanofiber Powder) Hereinafter, the utility value and superiority of the cellulose nanofiber powder of the present invention as a dispersant will be described.

[0025] Conventionally, in order to disperse fillers (individual particles) in solvents such as water and oil, surfactants suitable for hydrophilic and hydrophobic solvents are used. When seeking separation prevention and stability rather than particle dispersion, amphoteric surfactants are used as effective filler dispersants in mechanically emulsified mixed media of water and oil. Amphoteric surfactants dissolved in water have the property of being more likely to aggregate and arrange on the interface (surface) rather than existing separately as individual molecules when the concentration is low. As the concentration of amphoteric surfactant in water is increased, the water surface is covered with surfactant molecules, and in water, numerous surfactant molecules gather together, forming micelles with the hydrophilic group side facing the water side. If micelles are formed in the state of the critical micelle concentration, hydrophobic fillers can be incorporated into the micelles, enabling dispersion in water.

[0026] However, inorganic pigments surface-treated with aluminum, silica, etc., or carbon used for high-concentration purposes, etc., have strong intermolecular attraction, so large aggregates are formed before being incorporated into micelles in water. The same thing happens in oil. Therefore, there is a limit to the dispersibility with only surfactants, and the current situation is that it must be used in combination with mechanical dispersion.

[0027] On the other hand, cellulose nanofiber powder has a more flexible and larger aspect ratio fiber shape than carbon nanotubes, fine particle nanocarbon, and nanosilica. When diffused into a network structure, it has high retention stability as a steric hindrance for other fillers, so it has great potential for use as a dispersant.

[0028] Here, for example, a dispersion such as an aqueous solution of cellulose nanofibers at 1 to 8% by weight also has the role of diffusing in water and dispersing other fillers. In recent years, the aqueous solution of cellulose nanofibers has sometimes been used as a dispersant for fillers in paints and coating agents. It is also used in the cosmetic field, and an effect of improving the uniformity of particle diffusion of water-soluble moisturizing materials has been recognized. Thus, several methods of using an aqueous solution of cellulose nanofibers as a dispersant have been established. This is because cellulose nanofibers are very slender nanofibers, are structurally hydrophilic, and their hydrophilicity and nano-sized diffusion ability can utilize the strong interfacial entropy of the aqueous solution of cellulose nanofibers as a dispersing ability. Therefore, cellulose nanofiber powder is expected to have better dispersibility than surfactants as a dispersant.

[0029] However, in the conventional technology, the realization of this dispersion is limited to an aqueous solution of cellulose nanofibers, and since hydrophobic substances can only be dispersed in water, the scope of application is limited. Therefore, it is conceivable to dry the aqueous solution of cellulose nanofibers and use it as a powder. However, simply drying the cellulose nanofiber dispersion alone makes it difficult to return to the state of the original dispersion even in water, let alone in oil, and it has the problem that it cannot serve as a dispersant for other fillers.

[0030] Therefore, the present invention has succeeded in obtaining cellulose nanofiber powder that is excellent in dispersion stability and dispersion retention after diffusion in a solvent among nano materials, regardless of whether the solvent is water or oil, by dispersing the cellulose nanofibers themselves under either water or oil media and obtaining a dried body. Such cellulose nanofiber powder as a dispersant can be used as a dispersant for various fillers such as micro-sized plant fibers, synthetic fibers, inorganic and organic pigments, carbon, calcium carbonate, and glass fibers. In some preferred embodiments of the present invention, the cellulose nanofiber powder dispersant has the advantage that it can be used in a region beyond the limits of the prior art as micelles for dispersing fillers.

[0031] In one embodiment of the present invention, the cellulose nanofiber powder dispersant contains 75 to 90% by weight of cellulose nanofibers, 7 to 12% by weight of ethylene glycol, 0.2 to 0.5% by weight of an acrylic acid copolymer, 0.4 to 0.8% by weight of water-soluble sorbitan, 0.6 to 1.0% by weight of a higher fatty acid, and 0.4 to 0.8% by weight of an alkylammonium salt.

[0032] When the amount of cellulose nanofibers is less than 75% by weight, the dispersion effect of the dispersant with cellulose nanofibers as the core weakens. From this perspective, the amount of cellulose nanofibers is 75% by weight or more, preferably 78% by weight or more, more preferably 80% by weight or more, even more preferably 82% by weight or more, and even more preferably 85% by weight or more. On the other hand, when the amount of cellulose nanofibers exceeds 90% by weight, the effects of other components weaken, so the dispersion effect of the dispersant decreases. From this perspective, the amount of cellulose nanofibers is 90% by weight or less, preferably 89% by weight or less, and more preferably 88% by weight or less.

[0033] Ethylene glycol has the function of a water-soluble solvent, has a high binding force with other chemical substances, and is also used as a heat stabilizer. Although no chemical bond occurs between cellulose nanofibers, ethylene glycol has a high adsorptivity to plant-based fibers and has a wetting effect on cellulose nanofibers.

[0034] The addition amount of ethylene glycol is added so as to be 7 to 12% by weight based on the total weight of the cellulose nanofiber powder dispersant. When the addition amount of ethylene glycol is less than 7% by weight, its effect cannot be fully exerted. From this perspective, the addition amount of ethylene glycol is preferably 8% by weight or more, more preferably 9% by weight or more. On the other hand, when the addition amount of ethylene glycol exceeds 12% by weight, it becomes sticky and the processability deteriorates. From this perspective, the addition amount of ethylene glycol is preferably 11% by weight or less, more preferably 10% by weight or less. Note that ethylene glycol is usually added in the state of an aqueous solution, but it may also be added as a single substance.

[0035] The acrylic acid copolymer has a function of accelerating the volatilization time of water, and in particular, in the case of a fibrous filler, it has an effect of suppressing the unraveling from the fiber bundle and suppressing the formation of ball-like aggregates. As specific examples of the acrylic acid copolymer, for example, acrylic acid-styrene copolymer, acrylic acid-methacrylic acid copolymer, acrylic acid-vinyl acetate copolymer, and acrylic acid-ethylene copolymer can be preferably used. Since these acrylic acid copolymers commonly have the above effects, they can be used interchangeably.

[0036] The addition amount of the acrylic acid copolymer is added so as to be 0.2 to 0.5% by weight based on the total weight of the cellulose nanofiber powder dispersant. When the addition amount of the acrylic acid copolymer is less than 0.2% by weight, its effect cannot be fully exerted. From this perspective, the addition amount of ethylene glycol is preferably 0.3% by weight or more. On the other hand, when the addition amount of the acrylic acid copolymer exceeds 0.5% by weight, its effect reaches a plateau. From this perspective, the addition amount of ethylene glycol is preferably 0.4% by weight or less. Note that the acrylic acid copolymer is usually added in the state of an aqueous solution, but it may also be added as a single substance.

[0037] Water-soluble sorbitan has a long shelf life in emulsions, a high surface activity effect on the filler surface, and little viscosity change with temperature even at low temperatures. It also has the effect of suppressing the swelling of pulp and cellulose nanofibers. At the same time, even if the filler dries, if water-soluble sorbitan adheres, it also has the effect of being easily soluble in water.

[0038] The addition amount of water-soluble sorbitan is added to be 0.4 to 0.8% by weight based on the total weight of the cellulose nanofiber powder dispersant. If the addition amount of water-soluble sorbitan is less than 0.4% by weight, its effect cannot be fully exerted. From this perspective, the addition amount of water-soluble sorbitan is preferably 0.5% by weight or more. On the other hand, if the addition amount of water-soluble sorbitan exceeds 0.8% by weight, its effect will plateau. From this perspective, the addition amount of water-soluble sorbitan is preferably 0.7% by weight or less. Note that water-soluble sorbitan is usually added in an aqueous solution state, but it may also be added as a single substance.

[0039] Higher fatty acids melt during the treatment with the two-roll mill described below, producing an effect similar to wax. That is, the dried cellulose nanofibers have better peelability from the roll plating surface or the roll metal surface and peel off naturally. In this specification, higher fatty acids refer to fatty acids having 10 to 25 carbon atoms, which can be saturated or unsaturated, and can be linear, branched, or otherwise shaped.

[0040] The addition amount of higher fatty acids is added to be 0.6 to 1.0% by weight based on the total weight of the cellulose nanofiber powder dispersant. If the addition amount of higher fatty acids is less than 0.6% by weight, its effect cannot be fully exerted. From this perspective, the addition amount of higher fatty acids is preferably 0.7% by weight or more. On the other hand, if the addition amount of higher fatty acids exceeds 1.0% by weight, its effect will plateau. From this perspective, the addition amount of higher fatty acids is preferably 0.9% by weight or less. Note that higher fatty acids are usually added in an aqueous solution state, but they may also be added as a single substance.

[0041] Alkylammonium salts have the effect of preventing the aggregation of cellulose nanofibers during the process of water reduction during drying.

[0042] Examples of alkylammonium salts include, but are not limited to, distearyldimethylammonium chloride, behenyltrimethylammonium chloride, stearyltrimethylammonium chloride, cetyltrimethylammonium chloride, lauryltrimethylammonium chloride, benzalkonium chloride, etc. These are usually added in an aqueous solution state. Alkylammonium salts have the effect of preventing the aggregation of cellulose nanofibers during the process of water reduction.

[0043] The addition amount of the alkylammonium salt is added so as to be 0.4 to 0.8% by weight based on the total weight of the cellulose nanofiber powder dispersant. If the addition amount of the alkylammonium salt is less than 0.4% by weight, its effect cannot be fully exerted. From this perspective, the addition amount of the alkylammonium salt is preferably 0.5% by weight or more, more preferably 0.6% by weight or more. On the other hand, if the addition amount of the alkylammonium salt exceeds 0.8% by weight, its effect reaches a plateau. From this perspective, the addition amount of the alkylammonium salt is preferably 0.7% by weight or less. Note that the alkylammonium salt is usually added in an aqueous solution state, but it may also be added as a single substance.

[0044] In a preferred embodiment of the present invention, during the production of the cellulose nanofiber powder dispersant, it is preferable to add the above-mentioned higher fatty acid and alkylammonium salt as a mixture with isopropyl alcohol (IPA). As an example, among higher fatty acids, the general chemical formula of carboxylic acid is R-COOH (R represents the substituent of carboxylic acid), and the chemical formula of isopropyl alcohol is C 3 H 8 O. When representing the mixture of the two by a reaction formula, R-COOH + C 3 H 8 O → R-COOC 3 H 7 +H 2It becomes O. That is, the higher fatty acid reacts with isopropyl alcohol to form a fatty acid ester (R-COOC 3 H 7 ) and water (H 2 O). As a result, the fatty acid ester compensates for the heat resistance and wetting promotion of the fiber, and isopropyl alcohol contains the generated water, lowering the boiling point of the water in the slurry medium and accelerating the time of vaporization. By accelerating the removal of moisture, the adsorptivity of other chemical substances to the cellulose nanofiber increases.

[0045] In addition, when the cellulose nanofiber dispersion is dried, the isopropyl alcohol disappears due to evaporation or the like. Therefore, in some embodiments of the present invention, the cellulose nanofiber powder dispersant does not contain isopropyl alcohol.

[0046] In one embodiment of the present invention, the cellulose nanofiber powder dispersant of the present invention can be obtained by adding each of the above additives to the cellulose nanofiber dispersion and drying it. For mixing, it is preferable to stir. In stirring, it is desirable that the cellulose nanofibers are kneaded so as to form a helix while maintaining the orientation in the liquid or sol. The method and apparatus for stirring are not particularly limited, but a super mixer (manufactured by Kawata Co., Ltd.), a Henschel mixer (manufactured by Nippon Coke Industry Co., Ltd.), a high-speed mixer (manufactured by Earth Technica Co., Ltd.), etc. can be preferably used.

[0047] (3. Method for producing cellulose nanofiber powder dispersant) The manufacturing method of the cellulose nanofiber powder dispersant of the present invention includes step A of preparing a cellulose nanofiber dispersion liquid, and step B of supplying the cellulose nanofiber dispersion liquid to a two-roll mill and rotating the two-roll mill to dry the cellulose nanofiber dispersion liquid and obtain cellulose nanofiber powder. The cellulose nanofiber dispersion liquid is prepared to contain 75 to 90% by weight of cellulose nanofibers, 7 to 12% by weight of ethylene glycol, 0.2 to 0.5% by weight of an acrylic acid copolymer, 0.4 to 0.8% by weight of water-soluble sorbitan, 0.6 to 1.0% by weight of a higher fatty acid, and 0.4 to 0.8% by weight of an alkyl ammonium salt in terms of solid content.

[0048] In step A of preparing the cellulose nanofiber dispersion liquid, since the types and amounts of the components of the cellulose nanofiber dispersion liquid are as described above, they will be omitted here.

[0049] After step A, the cellulose nanofiber dispersion liquid is supplied to a two-roll mill and the two-roll mill is rotated, whereby the cellulose nanofiber dispersion liquid is removed and concentrated and dried cellulose nanofiber powder is obtained (step B).

[0050] By supplying the cellulose nanofiber dispersion liquid to the middle part of the two-roll mill, the cellulose nanofiber dispersion liquid is bitten into the roll gap (nip) (Figure 1). As a characteristic of the two-roll mill, before entering the nip, the input raw material rotates in the same direction as the roll in the roll bank above the roll gap. At this time, the cellulose nanofibers are in a state of maintaining orientation, and the fibers enter the nip side by side in the same direction when entering the nip. Thereby, while giving the cellulose nanofibers orientation, shear occurs in the nip. Due to the self-heating caused by shear and the heating temperature of the two-roll mill, the raw material with a lowered boiling point easily vaporizes, shortening the drying time. The roll gap (clearance) is not particularly limited, but in the case of this embodiment, it is preferably 0.3 to 1.5 mm.

[0051] The greater the rotation ratio (i.e., the difference in rotational speeds) between the front roll and the rear roll in the two-roll mill, the faster the speed at which it bites into the nip. On the other hand, if the rotation ratio between the front roll and the rear roll is too large, the shear caused by the rotation ratio becomes small, and the time for water to vaporize becomes short. Therefore, the rotation ratio is preferably set to 1 to 3. Also, when there is no rotation ratio, the cellulose nanofiber dispersion cannot be made to bite into the nip and tends to stay on the roll bank.

[0052] Due to self-heating at the nip and heat transfer from the heated two-roll mill, under the action of the intermolecular attraction and thermal energy of water molecules, water molecules in the liquid state attract each other and interact with other nearby molecules. Under extremely high temperatures, water molecules obtain sufficient energy to overcome the intermolecular attraction with the fibers, and water and alcohol instantaneously transfer from the liquid state to the gaseous state. As described above, since the cellulose nanofibers enter the nip while maintaining their orientation, they encounter vaporization by steam explosion in the same direction, with little random stress on the cellulose nanofibers, enabling drying in a state close to their original form (where the double helix structure is hardly loosened).

[0053] Here, as kneaders other than the two-roll mill, a pressure kneader, a Banbury, and an extruder can be considered. However, since these result in random kneading, even if water instantaneously vaporizes, the cellulose nanofibers tend to entangle with each other and form lumps. Also, in conventional freeze-drying, drying ovens, spray drying, etc., there is no means to impart orientation to the cellulose nanofibers, and since drying is carried out over time, the double helix structure loosens and lumps are likely to occur. Therefore, the treatment using two rolls has advantages that cannot be obtained by conventional techniques. Note that the two-roll mill only needs to be able to knead the raw material between two rolls as a device, and it may have a third or more rolls.

[0054] Also, if the surface temperature of the two-roll mill is too high, there is a risk that the cellulose nanofibers will deteriorate, and when powdered, the surface will harden and it will be difficult to form fine particles. Therefore, it is preferably 130°C or lower, and more preferably 120°C or lower. Accordingly, in one embodiment of the present invention, the surface temperature of the two-roll mill is 95°C to 130°C.

[0055] As a result of the treatment with the above two-roll mill, cellulose nanofiber powder is obtained. When obtaining cellulose nanofiber powder, typically the following appearance and properties are obtained. · Shape: Plate-like flakes with a size of 1 mm to 5 mm and a thickness of 0.5 mm or less. · Color tone: Milky white with a transparent feeling. · Although it has a certain hardness, it can easily become fine powder with a fingertip. No special grinding treatment is required. · There is no burning or partial discoloration. · Almost no scattering into the air occurs even during weighing and packaging.

[0056] And, since fatty acids and amphoteric surfactants adhere to the surface of the cellulose nanofiber powder from which the moisture has disappeared, it is difficult to burn and char. Especially due to the adhesion of higher fatty acids or higher fatty acid amides, the heat resistance is high. Furthermore, in the two-roll mill, the supply of raw materials and the recovery of the cellulose nanofiber powder dispersant as a dried product can be continuously performed, so the advantage of high productivity can be obtained.

Examples

[0057] Examples of the present invention are shown below together with comparative examples. These examples are provided to better understand the present invention and its advantages, and are not intended to limit the invention.

[0058] (Production process of cellulose nanofiber powder dispersant) As the "hydrophilic dispersant" described in Table 1 below, ethylene glycol, acrylic acid copolymer, and water-soluble sorbitan were placed in one container and mixed with a dissolver stirrer at room temperature and 700 rpm for 10 minutes. Also, as the "IPA diluent fatty acid" described in Table 1, IPA (isopropyl alcohol), higher fatty acid, and alkyl ammonium salt were placed in one container and mixed with a dissolver stirrer at 700 rpm for 10 minutes at room temperature. The mixtures of the "hydrophilic dispersant" and the "IPA diluent fatty acid" were each stirred and mixed at 1500 rpm for 5 minutes using a Henschel mixer (high-speed type) manufactured by Nippon Coke & Engineering Co., Ltd. to perform mechanical emulsification treatment. This mixed mixture was in a liquid state, and an aqueous solution of cellulose nanofibers with a solid content of 8% by weight was added thereto, and the mixture was mixed with a dissolver stirrer at room temperature and 500 rpm for 5 minutes. The addition amounts of the respective components are as shown in Table 1.

[0059]

Table 1

[0060] For the "acrylic acid copolymer", BYK-199BF manufactured by BYK (main component: acrylic acid-methacrylic acid copolymer) was used. For the "water-soluble sorbitan", Leodol TW-L120 manufactured by Kao Corporation (content composition: polyoxyethylene sorbitan monolaurate) was used. For the "higher fatty acid", a mixture of BYK-109 (high molecular weight alkylol amino amide) and BYK-9077 (polyglycol polyester-modified polyalkyleneimine) manufactured by BYK at a ratio of 1:1 (main component: chemical formula C 10 H 20 O 2 ) was used. For the "alkyl ammonium salt", BYK-9076 manufactured by BYK (solution of 50 to 60% by mass of alkyl ammonium salt of high molecular weight copolymer) was used.

[0061] Regarding the "hydrophilic dispersant", the mixing of the acrylic acid copolymer, methacrylic acid copolymer, and ethylene glycol was carried out with the acrylic acid copolymer (C 3 H 4 O 2) n , methacrylic acid copolymer (C 5 H 8 O 2 ) n When dissolved and mixed with ethylene glycol C 2 H 6 O 2 in a solvent, (C 3 H 4 O 2 ) m + (C 5 H 8 O 2 ) n + C 2 H 6 O 2 → (C 3 H 4 O 2 ) m (C 5 H 8 O 2 ) n (C 2 H 6 O 2 ) mixture is formed. This supports the diffusion of the filler in water.

[0062] For "IPA diluent fatty acid", (C 3 H 4 O 2 ) m (C 5 H 8 O 2 ) n (C 2 H 6 O 2 ) + C 3 H 8 O(IPA) → (C 3 H 4 O 2 ) m (C 5 H 8 O 2 ) n (C 2 H 6 O 2 )(C 3 H 8 O). By this reaction, isopropyl alcohol participates in the mixing reaction and binds to the copolymer. Note that higher fatty acid C 10 H20 O 2 and the alkylammonium salt NR 4 + is dissolved, so R 4 N+C 3 H 7 O - +C 10 H 20 O 2 →R 4 N+C 3 H 7 OC 10 H 19 O 2 +H is generated. This is a mixture in which the alkyl part is substituted with an ester group and supports filler wetting in oil.

[0063] Since both the "hydrophilic dispersant" and the "IPA-diluted fatty acid" adhere to and wet the cellulose nanofibers, if they are made into an emulsified state by high-speed stirring before being added to the aqueous solution of cellulose nanofibers, the mixed additives can be diffused in the aqueous solution with stability without aggregating the cellulose nanofibers. The resulting final mixture is a highly viscous paste.

[0064] The above mixture was put into a two-roll mill (roll diameter: 8 inches. Surface treatment: bright plating. Nip clearance: 0.5 mm.) manufactured by Yasuda Seiki Seisakusho Co., Ltd. The input amount was 300 g. The surface temperature of the roll was heated to 120 °C. Next, the two-roll mill was operated so that the rotational speed of the front roll was 7 rpm and the rotational speed of the rear roll was 6 rpm, and a sample of the dried product was collected after 3 rotations of the front roll. The time required for drying was within 30 seconds. Figure 2A is a photograph showing the state in which the cellulose nanofiber dispersion was dried by the two-roll mill. Figure 2B is a photograph showing that the cellulose nanofiber powder dispersant was obtained by the two-roll mill.

[0065] Regarding the amount of each composition in the dry cellulose nanofiber powder dispersant, the entire composition was confirmed for gas chromatograph mass using a GC-MS series manufactured by Shimadzu Corporation. By burning in a ceramic crucible of Buehler Co., Ltd., the temperature was sequentially increased to remove carbides, and the residue was confirmed for peak elements using an FTIR of the IRA1S series manufactured by Shimadzu Corporation. The water-soluble portion was analyzed by mass spectrometry using a high-performance liquid chromatography of the Nexera series manufactured by Shimadzu Corporation. From the results of these analyses, the mass of each component was calculated. The results are shown in Table 1.

[0066] (Test 1: Verification of the dispersibility of carbon black) In order to investigate the influence of the above cellulose nanofiber powder dispersant on the dispersion of carbon black pigment in water and oil, the following tests were conducted. Mitsubishi Carbon Black #30 was used as the carbon black pigment.

[0067] Specifically, for oil, assuming a hydrophobic paint, phthalic acid ester (DOP), vinyl chloride resin (degree of polymerization 800), carbon black pigment, and the above dry product (cellulose nanofiber powder dispersant) were simultaneously added, stirred with a Three One motor stirrer for 5 minutes, and passed through a three-roll (6-inch roll mill manufactured by Inoue Manufacturing Co., Ltd.) once for dispersion treatment. The test was conducted by changing the addition amount of the cellulose nanofiber powder dispersant as shown in Table 2.

[0068] For water, assuming an aqueous paint, carbon black pigment, water-soluble acrylic resin ("Nicazole" manufactured by Nippon Carbide Industries Co., Ltd.), and the above dry product were simultaneously added, stirred with a Three One motor stirrer for 5 minutes, and passed through a three-roll (6-inch roll mill manufactured by Inoue Manufacturing Co., Ltd.) once for dispersion treatment. The test was conducted by changing the addition amount of the cellulose nanofiber powder dispersant as shown in Table 3.

[0069] For the dispersion liquid after dispersion treatment, the pigment particle residue (the number of particles with a particle size (maximum dimension) of 5 μm or more) was counted using a double-groove grindometer (0 - 100 μm gauge) manufactured by Taiyu Kikai Co., Ltd., and further, the numerical values of the viscosity reduction during dispersion and the thixotropic thickening due to re-aggregation were read using a B-type viscometer BM type (specimen temperature 25°C, No. 4 rotor, 6 rpm) manufactured by Toki Sangyo Co., Ltd., and the dispersibility was compared. The results are shown in Table 2 and Table 3.

[0070]

Table 2

[0071]

Table 3

[0072] As can be seen from Table 2 and Table 3, in oil, with respect to the weight of the carbon black pigment, the addition amount of the cellulose nanofiber powder dispersant is preferably 2 - 8%, and most effective at 3 - 5%. In water, with respect to the weight of the carbon black pigment, the addition amount of the cellulose nanofiber powder dispersant is preferably 2 - 8%, and most effective at 3 - 5%. Therefore, for the carbon black pigment, in both aqueous and oily systems, the addition amount of the cellulose nanofiber powder dispersant shows a dispersion effect at almost the same amount.

[0073] (Test 2: Verification of the Dispersibility of Titanium Dioxide Inorganic Pigment) In order to investigate the influence of the above cellulose nanofiber powder dispersant on the dispersion of titanium dioxide inorganic pigment in water and oil, the following test was conducted. As the titanium dioxide inorganic pigment, CR-60 titanium dioxide manufactured by Ishihara Sangyo Co., Ltd. was used.

[0074] Specifically, for the oil-based paint, assuming a hydrophobic paint, dioctyl phthalate (DOP), vinyl chloride resin (degree of polymerization 800), titanium dioxide inorganic pigment, and the above-mentioned dried product (cellulose nanofiber powder dispersant) were simultaneously added, stirred with a three-one motor stirrer for 5 minutes, passed through a three-roll (6-inch roll mill manufactured by Inoue Seisakusho Co., Ltd.) once, and dispersion treatment was performed. Tests were conducted by varying the addition amount of the cellulose nanofiber powder dispersant as shown in Table 4.

[0075] For the water-based paint, assuming an aqueous paint, titanium dioxide inorganic pigment and the above-mentioned dried product were simultaneously added to water, stirred with a three-one motor stirrer for 5 minutes, passed through a three-roll (6-inch roll mill manufactured by Inoue Seisakusho Co., Ltd.) once, and dispersion treatment was performed. Tests were conducted by varying the addition amount of the cellulose nanofiber powder dispersant as shown in Table 5.

[0076] For the dispersion liquid after dispersion treatment, the pigment particle residue (the number of particles with a particle size (maximum dimension) of 5 μm or more) was counted using a double-groove grindometer (0 - 100 μm gauge) manufactured by Taiyu Kikai Co., Ltd., and further, the numerical values of the reduction in viscosity during dispersion and the thixotropic thickening due to re-aggregation were read using a B-type viscometer BM type (specimen temperature 25 °C, No. 4 rotor, 6 rpm) manufactured by Toki Sangyo Co., Ltd., and the dispersibility was compared. The results are shown in Table 4 and Table 5.

[0077]

Table 4

[0078]

Table 5

[0079] As can be seen from Tables 4 and 5, in oil, the addition amount of the cellulose nanofiber powder dispersant is preferably 3 to 9%, and most effective at 4 to 6% based on the weight of the titanium dioxide inorganic pigment. In water, the addition amount of the cellulose nanofiber powder dispersant is preferably 3 to 9%, and most effective at 4 to 6% based on the weight of the titanium dioxide inorganic pigment. Therefore, for the titanium dioxide inorganic pigment, the addition amount of the cellulose nanofiber powder dispersant shows a dispersion effect at almost the same amount in both aqueous and oily media.

[0080] (Test 3: Verification of the dispersibility of the mixed pigment) In order to investigate the influence of the above cellulose nanofiber powder dispersant on the dispersion of carbon black pigment and titanium dioxide inorganic pigment in water and oil, the following tests were conducted. Mitsubishi Carbon Black #30 was used as the carbon black pigment, and CR-60 titanium dioxide manufactured by Ishihara Sangyo Co., Ltd. was used as the titanium dioxide inorganic pigment.

[0081] Specifically, for oil, assuming a hydrophobic paint, dioctyl phthalate (DOP), vinyl chloride resin (degree of polymerization 800), carbon black pigment, titanium dioxide inorganic pigment, and cellulose nanofiber powder dispersant were simultaneously added, stirred with a three-one motor stirrer for 5 minutes, and passed through a three-roll (6-inch roll mill manufactured by Inoue Seisakusho Co., Ltd.) once for dispersion treatment. Here, the composition of the cellulose nanofiber powder dispersant was changed as shown in Table 6, and the dry product was manufactured by the above process.

[0082] For water, assuming an aqueous paint, carbon black pigment, titanium dioxide inorganic pigment, and the above dry product were simultaneously added to water, stirred with a three-one motor stirrer for 5 minutes, and passed through a three-roll (6-inch roll mill manufactured by Inoue Seisakusho Co., Ltd.) once for dispersion treatment. Here, the composition of the cellulose nanofiber powder dispersant was changed as shown in Table 7, and the dry product was manufactured by the above process.

[0083] For the dispersion liquid after dispersion treatment, the pigment particle residue (the number of particles with a particle diameter (maximum dimension) of 5 μm or more) was counted using a double-groove grindometer (0 - 100 μm gauge) manufactured by Taiyu Kikai Co., Ltd., and further, the numerical values of thixotropic thickening due to low viscosity reduction and re-aggregation during dispersion were read using a B-type viscometer BM type (specimen temperature 25°C, No. 4 rotor, 6 rpm) manufactured by Toki Sangyo Co., Ltd., and the dispersibility was compared. The results are shown in Table 6 and Table 7.

[0084]

Table 6

[0085]

Table 7

[0086] As can be seen from Table 6, in oil, when the higher fatty acid and alkylammonium salt of the cellulose nanofiber powder dispersant are reduced, the dispersibility deteriorates proportionally. Also, as can be seen from Table 7, in water, when the acrylic acid copolymer and water-soluble sorbitan of the cellulose nanofiber powder dispersant are reduced, the dispersibility deteriorates proportionally. Therefore, in the difference between aqueous and oily solvents, when the amount of the composition adjusted to the solvent is reduced, the dispersion effect in each solvent decreases. From this, it can be understood that in order to be applicable to amphoteric solvents, it is necessary to matrix components suitable for aqueous and oily solvents respectively with cellulose nanofibers as the skeleton.

[0087] (Test 4: Comparison of the dispersibility of the present invention and commercially available surfactants) Next, the difference in the dispersibility between the cellulose nanofiber powder dispersant of the present invention and commercially available surfactants was compared.

[0088] First, a nonionic phosphate ester was selected as the surfactant. A phosphate ester is a compound in which a hydrocarbon chain and a phosphate group are bonded, has characteristics as a surfactant, and is used for filler dispersion by interaction at the interface of an oily liquid or solid. As the dispersant, maleic anhydride of the carboxylic acid type was selected. These components were stirred for 5 minutes with a Three One motor stirrer and passed through a three-roll (6-inch roll mill manufactured by Inoue Seisakusho Co., Ltd.) once for dispersion treatment. Tests were conducted by changing the addition amounts of the respective components as shown in Table 8.

[0089] For the dispersion liquid after the dispersion treatment, the pigment particle residue (the number of particles with a particle size (maximum dimension) of 5 μm or more) was counted with a double-groove grindometer (0 - 100 μm gauge) manufactured by Taiyu Kikai Co., Ltd., and further, the numerical values of the viscosity reduction during dispersion and the thixotropic thickening due to re-aggregation were read with a B-type viscometer BM type (specimen temperature 25°C, No. 4 rotor, 6 rpm) manufactured by Toki Sangyo Co., Ltd. to compare the dispersibility. The results are shown in Table 8.

[0090]

Table 8

[0091] As can be seen from Table 8, when the cellulose nanofiber powder dispersant (dispersant CNF powder) of the present invention was used, there were no problems with either dispersibility or viscosity stability, and it was good. On the other hand, although the phosphate ester was dispersible, the initial viscosity was very high and a large torque (ampere) was generated during pigment mixing. Maleic anhydride can be sufficiently used in commercially available paints for dispersion and viscosity, but after 1 hour, some separation of carbon and titanium dioxide was observed and color separation occurred.

[0092] Next, a polyoxyethylene alkyl ether, which is nonionic and has the highest stability in an aqueous solvent as a surfactant, was selected, and a polymer-based polyvinyl alcohol, which is also widely used in water-based gravure printing as a dispersant, was selected, and a comparative test was conducted. These components were stirred for 5 minutes with a Three One motor stirrer and passed once through a three-roll (6-inch roll mill manufactured by Inoue Seisakusho Co., Ltd.) for dispersion treatment. Tests were conducted by varying the addition amounts of the respective components as shown in Table 9.

[0093] For the dispersion liquid after the dispersion treatment, the pigment particle residue (the number of particles with a particle size (maximum dimension) of 5 μm or more) was counted with a double-groove grindometer (0 to 100 μm gauge) manufactured by Taiyu Kikai Co., Ltd., and further, the numerical values of the viscosity reduction during dispersion and the thixotropic thickening due to reaggregation were read with a B-type viscometer BM type (specimen temperature 25°C, No. 4 rotor, 6 rpm) manufactured by Toki Sangyo Co., Ltd. to compare the dispersibility. The results are shown in Table 9.

[0094]

Table 9

[0095] As can be seen from Table 9, when the cellulose nanofiber powder dispersant (dispersant CNF powder) of the present invention was used, the dispersibility and the stability of the viscosity were good without any problems. On the other hand, polyoxyethylene alkyl ether had good dispersion, but the viscosity was slightly higher than that of the cellulose nanofiber powder dispersant. Regarding polyvinyl alcohol, the addition amount had not reached the level at which the effect could be obtained, and it could not be dispersed.

Claims

1. A cellulose nanofiber powder dispersant, comprising: 75 to 90% by weight of cellulose nanofibers, 7 to 12% by weight of ethylene glycol, 0.2 to 0.5% by weight of an acrylic acid copolymer, 0.4 to 0.8% by weight of water-soluble sorbitan, 0.6 to 1.0% by weight of a higher fatty acid, and 0.4 to 0.8% by weight of an alkyl ammonium salt.

2. The cellulose nanofiber powder dispersant according to claim 1, wherein the average fiber length of the cellulose nanofiber powder is in the range of 0.1 μm to 3.0 μm.

3. The cellulose nanofiber powder dispersant according to claim 1 or 2, wherein the average fiber diameter of the cellulose nanofiber powder is in the range of 0.5 nm to 10 nm.

4. A method for producing a cellulose nanofiber powder dispersant, comprising: Step A of preparing a cellulose nanofiber dispersion, and Step B of supplying the cellulose nanofiber dispersion to a two-roll mill and rotating the two-roll mill to dry the cellulose nanofiber dispersion to obtain a cellulose nanofiber powder. The method includes: The cellulose nanofiber dispersion is prepared to contain 75 to 90% by weight of cellulose nanofibers, 7 to 12% by weight of ethylene glycol, 0.2 to 0.5% by weight of an acrylic acid copolymer, 0.4 to 0.8% by weight of water-soluble sorbitan, 0.6 to 1.0% by weight of a higher fatty acid, and 0.4 to 0.8% by weight of an alkyl ammonium salt in terms of solid content.

5. The method according to claim 4, wherein in step B, heating the surface temperature of the two-roll mill to 95°C to 130°C is included.

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