JP7598184B1 - Cellulose nanofiber powder and its manufacturing method - Google Patents

Abstract

The present invention provides a cellulose nanofiber powder with high diffusivity that is suitable for pelletizing resin masterbatches.
[Solution] The cellulose nanofiber powder contains 75 to 90 weight % cellulose nanofiber, 10 to 20 weight % polyethylene glycol, 0.05 to 2.0 weight % ester-type dialkylammonium salt, 0.8 to 2.0 weight % silicone oil, and 0.2 to 0.8 weight % carnauba wax.
[Selected Figure] Figure 1

Description

The present invention relates to a cellulose nanofiber powder and a method for producing the same. In particular, the present invention relates to a cellulose nanofiber powder with high diffusivity that is suitable for pelletizing a resin master batch, and a method for producing such a cellulose nanofiber powder.

Cellulose nanofiber (also known as "Cellulose Nano Fiber"; hereafter, simply referred to as "CNF") is a next-generation plant-derived material that is said to be five times stronger than steel with one-fifth the weight. The use of cellulose nanofiber in automobiles, home appliances, etc. is expected to reduce weight, improve energy efficiency, and make a significant contribution to global warming countermeasures. Toward the social implementation of CNF, the Ministry of Economy, Trade and Industry and the Ministry of Agriculture, Forestry and Fisheries are carrying out model projects in various fields, such as automobiles, home appliances, and housing/building materials, as a collaborative project, and are promoting the evaluation and verification of the _CO2 reduction effects and demonstration of solutions to related issues.

As one application example of cellulose nanofibers, Patent Document 1 (JP 2022-044861) discloses a hot melt adhesive containing cellulose nanofiber fibers, which comprises a resin that melts in the range of 70°C to 160°C and cellulose nanofiber fiber powder. It is disclosed that such a hot melt adhesive can instantly solidify the bonded area, has excellent adhesive properties even at low temperatures, and can firmly hold the bonded surface.

JP 2022-044861 A

When adding CNF to resin products, the use of masterbatches containing CNF has been increasing in recent years. Since it is inconvenient to handle fine powders, there is an increasing demand for pelletizing masterbatches. In this case, it is possible to use a powder made by drying a water-dispersed slurry containing 1-8% by weight of CNF solids. However, dried CNF powder remains hydrophobic and hygroscopic. If CNF is hydrophobic, it will not diffuse well into the resin when directly added to a resin product compound or when combined with resins to make a masterbatch. Furthermore, it will absorb moisture even in the input equipment such as a hopper feeder before processing, causing aggregation in the molten resin and making problems.

The typical method for manufacturing CNF master batches is to mix CNF powder with dispersants and additives, knead them into resin, and then produce pellets. However, if the CNF master batch itself has been treated to be water repellent, it is not hygroscopic and CNF is expected to disperse. However, if the CNF itself has not been treated to make it diffusible, fine fiber aggregates are often scattered within the resin matrix of the master batch. Therefore, when a CNF master batch manufactured in this way is added to a resin matrix compound during product molding, the CNF will aggregate again and not diffuse, often affecting the product with poor dispersion and other issues.

When the masterbatch is melted into the resin compound, the fine fiber aggregates do not break apart, but instead turn into larger fiber aggregates within the resin of the compound. This is because when the compound is molded into a product, the emphasis is always on productivity, and the product is kneaded with mild shear forces and produced at a high output. Unlike the process of making a masterbatch, which involves kneading with strong shear forces, there is no molding process that disperses the small fiber aggregates remaining in the masterbatch.

The present invention was completed in consideration of the above problems, and in one embodiment, it is an object of the present invention to provide a cellulose nanofiber powder with high diffusivity that is suitable for pelletizing resin masterbatches. In another embodiment, it is an object of the present invention to provide a method for producing such a cellulose nanofiber powder.

After extensive research, the inventors have found that the above problems can be solved by modifying the CNF. That is, in order to reliably diffuse the CNF of the masterbatch into the molten resin during molding of the resin compound, a CNF filler that is less prone to absorbing moisture, less likely to form fiber aggregates, and easily loosens is required before the masterbatch is made. Therefore, by making the CNF hydrophobic, the hygroscopicity and tendency to easily form hydroxyl groups of the CNF added to the masterbatch are suppressed, so that the CNF is less likely to aggregate within the resin matrix during masterbatch processing, and furthermore, the masterbatch is well diffused even when melted in the base compound of the product.

The present invention has been completed based on the above findings, and is exemplified below.
[Aspect 1]
A cellulose nanofiber powder comprising:
A cellulose nanofiber powder comprising 75 to 90% by weight of cellulose nanofibers, 10 to 20% by weight of polyethylene glycol, 0.05 to 2.0% by weight of an ester-type dialkylammonium salt, 0.8 to 2.0% by weight of silicone oil, and 0.2 to 0.8% by weight of carnauba wax.
[Aspect 2]
The cellulose nanofiber powder according to claim 1, wherein the average fiber length of the cellulose nanofibers is within the range of 0.1 μm to 3.0 μm.
[Aspect 3]
The cellulose nanofiber powder according to aspect 1 or 2, wherein the average fiber diameter of the cellulose nanofibers is within the range of 0.5 nm to 10 nm.
[Aspect 4]
A method for producing cellulose nanofiber powder, comprising:
a first process of supplying a cellulose nanofiber dispersion to a two-roll mill and rotating the two-roll mill to dry the cellulose nanofiber dispersion and obtain dried cellulose nanofibers;
A second process includes mixing the dried cellulose nanofibers with a melt containing silicone oil and carnauba wax to obtain a cellulose nanofiber powder;
The cellulose nanofiber dispersion is prepared so as to contain 75 to 90% by weight of cellulose nanofibers, 10 to 20% by weight of polyethylene glycol, 0.05 to 2.0% by weight of an ester-type dialkylammonium salt, and 10 to 20% by weight of isopropyl alcohol, based on the total weight of the cellulose nanofiber powder;
The melt is prepared to contain 0.8 to 2.0% by weight of silicone oil and 0.2 to 0.8% by weight of carnauba wax based on the total weight of the cellulose nanofiber powder.
[Aspect 5]
5. The method of claim 4, wherein the first treatment comprises heating the surface temperature of the two-roll mill to 100° C. to 120° C.

According to one embodiment of the present invention, it is possible to provide a cellulose nanofiber powder having high diffusivity and suitable for pelletizing a resin masterbatch. According to another embodiment of the present invention, it is possible to provide a method for producing such a cellulose nanofiber powder.

FIG. 2 is a schematic diagram for explaining the structure and operation principle of a two-roll mill in one embodiment of the present invention.

Next, an embodiment of the present invention will be described in detail. It should be understood that the present invention is not limited to the following embodiment, and that appropriate design changes, improvements, etc. may be made based on the ordinary knowledge of a person skilled in the art without departing from the spirit of the present invention.

(1. Raw materials for cellulose nanofiber)
Cellulose nanofibers are made by finely grinding cellulose, the main component of plant fibers, to nano size, and the main raw material is wood pulp (the raw material of paper). They are used primarily to reinforce resin materials and to prevent the shrinkage of resins at low temperatures. In the present invention, the raw material of the cellulose nanofibers is not particularly limited.

Since cellulose nanofibers are usually plant-derived materials, they are in the form of a slurry dispersed in water when extracted from the plant. The solid content is usually 1 to 8% by weight. For example, when producing a dispersant as a powder from a cellulose nanofiber dispersion, it is first necessary to remove only the water from the cellulose nanofiber aqueous dispersion dispersed in water and extract the cellulose nanofibers alone. It is also conceivable that the cellulose nanofibers alone are redispersed in water or a dispersion medium other than water, and then the cellulose nanofibers alone are extracted again from the redispersion. Therefore, in the present invention, the dispersion medium in the cellulose nanofiber dispersion is not limited to water. However, the dispersion medium in the cellulose nanofiber dispersion is preferably water.

As mentioned above, the solid content of the cellulose nanofiber dispersion is usually 1 to 8% by weight, but it may be further diluted to less than 1% by weight. Therefore, the cellulose nanofiber dispersion can be pre-dried before the above pretreatment. There are no particular limitations on the pre-drying method, and any conventional method can be used. The cellulose nanofiber dispersion can be pre-dried, for example, to a maximum solid content of 12% by weight, and then the drying method of the present invention described below can be carried out.

As described below, cellulose nanofiber powder is obtained by drying the cellulose nanofiber dispersion under specific conditions. The average fiber length of the cellulose nanofiber powder is preferably 0.1 μm or more. This is expected to have a dispersion stability effect. From this perspective, the average fiber length of the cellulose nanofiber powder is more preferably 0.2 μm or more, even more preferably 0.3 μm or more, and even 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 relative to the average fiber diameter.

It is also preferable that the average fiber length of the cellulose nanofiber powder is 3.0 μm or less. This prevents the cellulose nanofibers from curling into a spherical shape during processing. From this perspective, it is more preferable that the average fiber length of the cellulose nanofiber powder is 2.5 μm or less, even more preferable that it is 1.5 μm or less, and even more preferable that it is 1.0 μm or less.

The average fiber length of the cellulose nanofiber powder refers to the D50 (median diameter) of the fibers in the cellulose nanofiber powder measured according to the laser diffraction/scattering method of JIS Z8825:2022.

It is preferable that the average fiber diameter of the cellulose nanofiber powder is 0.5 nm or more. This is expected to have a dispersion stability effect. From this perspective, it is more preferable that the average fiber diameter of the cellulose nanofiber powder is 0.7 nm or more, even more preferable that it is 1 nm or more, and even more preferable that it is 3 nm or more.

It is also preferable that the average fiber diameter of the cellulose nanofiber powder is 10 nm or less. If the cellulose nanofibers are too thick, the aspect ratio decreases, and steric hindrance may occur, making it impossible to maintain the interparticle distance. From this perspective, it is more preferable that the average fiber diameter of the cellulose nanofiber powder is 8 nm or less, even more preferable that it is 7 nm or less, and even more preferable that it is 5 nm or less.

The average fiber diameter of the cellulose nanofiber powder refers to the average particle diameter of the fibers in the cellulose nanofiber powder measured according to the dynamic light scattering method of JIS Z8828:2019.

(2. Hydrophobization of Cellulose Nanofibers)
In order to obtain the diffusibility of CNF, it is necessary that the dried fiber aggregates are easily loosened. For this purpose, the inventor came up with the idea of applying the fiber softening effect of laundry softener. When water is removed from CNF slurry, fiber aggregates are always formed and are scattered as strong aggregates. Therefore, as a first treatment, a dry powder that is flexible and easy to loosen without strong aggregates is prepared by approaching the formulation of a softener. Furthermore, as a second treatment, the CNF is moistened with silicone to prevent moisture absorption during storage and to impart diffusibility and heat resistance from the beginning of resin kneading. By treating CNF in such two stages, it is possible to finish it into a granular powder that is easy to loosen in molten resin, has good diffusibility, and has an ideal resin matrix without aggregates.

(2-1. First Processing)
In the first process, the cellulose nanofiber dispersion is supplied to a two-roll mill, and the two-roll mill is rotated to dry the cellulose nanofiber dispersion and obtain dried cellulose nanofibers. The raw materials used for the cellulose nanofiber dispersion are as follows:

Cellulose nanofiber (CNF)
Cellulose nanofibers are the main raw material of cellulose nanofiber powder, and are usually dispersed in water in a slurry having a solid content of 1 to 8% by weight. In addition, any treatment can be applied to the CNF as long as it does not impair the effects of the present invention. For example, carboxymethyl CNF (CM-CNF), TEMPO-oxidized CNF, mechanically dispersed CNF, etc. can be suitably used.

If the amount of cellulose nanofibers is less than 0.2% by weight relative to the total weight of the cellulose nanofiber dispersion, workability will be poor. From this perspective, the amount of cellulose nanofibers in the cellulose nanofiber dispersion is preferably 0.3% by weight or more, more preferably 0.5% by weight or more, even more preferably 0.7% by weight or more, even more preferably 1.0% by weight or more, and even more preferably 1.5% by weight or more. On the other hand, if the amount of cellulose nanofibers exceeds 12% by weight, processing will become difficult. From this perspective, the amount of cellulose nanofibers in the cellulose nanofiber dispersion is preferably 10% by weight or less, more preferably 9% by weight or less, and even more preferably 8% by weight or less.

In addition, it is necessary to adjust the amount and concentration of the cellulose nanofiber dispersion so that the amount of cellulose nanofiber in the finished cellulose nanofiber powder is 75 to 90% by weight. If the amount of cellulose nanofiber is less than 75% by weight, the reinforcing effect of the cellulose nanofiber as a filler is weakened. From this perspective, the amount of cellulose nanofiber in the cellulose nanofiber powder is preferably 76% by weight or more, more preferably 77% by weight or more, even more preferably 78% by weight or more, even more preferably 79% by weight or more, and even more preferably 80% by weight or more. On the other hand, if the amount of cellulose nanofiber exceeds 90% by weight, the effect of other components is weakened, and the diffusion effect is reduced. From this perspective, the amount of cellulose nanofiber in the cellulose nanofiber powder is preferably 88% by weight or less, more preferably 86% by weight or less, and even more preferably 84% by weight or less.

Polyethylene glycol Polyethylene glycol is hydrophilic and highly compatible with water, so it dissolves easily in water. Polyethylene glycol has high adsorption to plant fibers, so by mixing it with CNF slurry, it is easy to impregnate the fibers in the slurry.

The amount of polyethylene glycol added is 10-20% by weight based on the total weight of the finished cellulose nanofiber powder. If the amount of polyethylene glycol added is less than 10% by weight, the effect cannot be fully exerted. From this viewpoint, the amount of polyethylene glycol added is preferably 12% by weight or more, more preferably 14% by weight or more. On the other hand, if the amount of polyethylene glycol added exceeds 20% by weight, the product becomes sticky and the processability becomes poor. From this viewpoint, the amount of polyethylene glycol added is preferably 19% by weight or less, more preferably 18% by weight or less. Note that polyethylene glycol is usually added in the form of an aqueous solution, but it may be added as a single substance.

As alkyl ammonium salts belonging to quaternary ammonium salts, which are also used in ester-type dialkyl ammonium salt softeners, there are ester-type dialkyl ammonium salts and amide-type alkyl amine salts. Ester-type dialkyl ammonium salts increase the flexibility of fibers, but have poor water absorption, such as not absorbing sweat. On the other hand, amide-type alkyl amine salts are poor in flexibility but have water absorption, and are considered to be suitable for washing underwear and other items that come into direct contact with the skin. In the present invention, ester-type dialkyl ammonium salts, which are highly hydrophobic, are selected. When ester-type dialkyl ammonium salts are combined with polyethylene glycol, there is an advantage that although no chemical bond is formed, extreme liquid interlayer separation does not occur.

When ester-type dialkylammonium salt is mixed into the CNF slurry, the ester-type dialkylammonium salt penetrates the fibers in the CNF slurry and is adsorbed onto the fibers. As a result, the ester-type dialkylammonium salt acts as a lubricant between the fiber bundles, eliminating friction and making them less likely to tangle, and even if the fibers are aggregates, they become soft. The ester-type dialkylammonium salt also imparts flexibility and antistatic properties to the fibers.

The amount of ester-type dialkylammonium salt added is 0.05 to 2.0% by weight based on the total weight of the finished cellulose nanofiber powder. If the amount of ester-type dialkylammonium salt added is less than 0.05% by weight, the effect cannot be fully exerted. From this viewpoint, the amount of ester-type dialkylammonium salt added is preferably 0.5% by weight or more, more preferably 1.0% by weight or more. On the other hand, if the amount of ester-type dialkylammonium salt added exceeds 2.0% by weight, the effect will plateau. From this viewpoint, the amount of ester-type dialkylammonium salt added is preferably 1.5% by weight or less. The ester-type dialkylammonium salt is usually added in the form of an aqueous solution, but it may be added as a single substance.

Isopropyl alcohol (IPA)
IPA lowers the boiling point of the water in the slurry solvent and promotes evaporation. This accelerates the removal of water, which increases the adsorption of other chemicals to the cellulose nanofibers. Note that IPA disappears during the first process due to evaporation, so it does not remain in the second process.

The amount of IPA added is 10-20% by weight based on the total weight of the finished cellulose nanofiber powder. If the amount of IPA added is less than 10% by weight, the effect will not be fully achieved. From this perspective, the amount of IPA added is preferably 12% by weight or more. On the other hand, if the amount of IPA added exceeds 20% by weight, the effect will plateau. From this perspective, the amount of IPA added is preferably 17% by weight or less. However, as mentioned above, it should be noted that IPA disappears due to evaporation during the first treatment, and is not contained in the finished cellulose nanofiber powder. Note that IPA is usually added in the form of an aqueous solution, but it may also be added alone.

In one embodiment of the present invention, the above-mentioned additives are added to an aqueous dispersion of cellulose nanofibers and then dried to obtain a cellulose nanofiber dispersion of the first treatment. Stirring is preferable for mixing. In the pretreatment stirring, it is desirable to knead the cellulose nanofibers in a spiral manner while maintaining their orientation in the liquid or sol. The stirring method and device are not particularly limited, but a Super Mixer (manufactured by Kawata Co., Ltd.), a Henschel Mixer (manufactured by Nippon Coke and Engineering Co., Ltd.), a high-speed mixer (manufactured by Earth Technica Co., Ltd.), etc. can be suitably used.

The cellulose nanofiber dispersion is fed to the middle of the two-roll mill, so that it penetrates into the gap between the rolls (nip) (Figure 1). A characteristic of the two-roll mill is that before entering the nip, the raw material rotates in the same direction as the rolls in the roll bank above the gap between the rolls. At this time, the cellulose nanofibers maintain their orientation, and when they enter the nip, the fibers enter lined up in the same direction. This causes shear shear in the nip while maintaining the orientation of the cellulose nanofibers. The raw material, whose boiling point has been lowered by self-heating due to shear shear and the heating temperature of the two-roll mill, is easily vaporized, and the drying time is shortened. There are no particular limitations on the distance between the rolls (clearance), but in this embodiment, it is preferable to set it to 0.3 to 1.5 mm.

The greater the rotation ratio (i.e., the difference in rotation speed) between the front and rear rolls in a two-roll mill, the faster the penetration into the nip. On the other hand, if the rotation ratio between the front and rear rolls is too large, the shear generated by the rotation ratio becomes small and the time it takes for the water to evaporate becomes short, so it is preferable to set the rotation ratio to 1 to 3. Furthermore, if there is no rotation ratio, the aqueous dispersion of cellulose nanofibers cannot penetrate the nip and tends to remain on the roll bank.

The self-heating in the nip and the heat transfer from the heated two-roll mill cause the water molecules to attract each other in liquid form and interact with other nearby molecules due to the intermolecular attraction and thermal energy of the water molecules. Under the sudden high temperature, the water molecules gain enough energy to overcome the intermolecular attraction with the fibers, and the water and alcohol instantly transition from liquid to gas. As mentioned above, the cellulose nanofibers enter the nip while retaining their orientation, so they undergo vaporization by steam explosion in the same direction, and there is little random stress on the cellulose nanofibers, allowing them to dry in a state close to their original form (a state in which the double helix structure is almost unraveled).

Here, other kneading machines that can be considered besides the two-roll mill include a pressure kneader, Banbury, and extruder. However, because these knead randomly, even if the water evaporates instantly, the cellulose nanofibers tend to entangle and form lumps. Furthermore, conventional techniques such as freeze drying, drying ovens, and spray drying do not provide a means for imparting orientation to the cellulose nanofibers, and because they take a long time to dry, the double helix structure tends to loosen and lumps tend to form. Therefore, processing using a two-roll mill has advantages that cannot be obtained with conventional techniques. Note that the two-roll mill may be any device that can knead the raw materials between the two rolls, and may have a third or subsequent roll.

In addition, the desired drying effect can be obtained if the surface temperature of the two-roll mill is 100°C or higher, but if the surface temperature of the two-roll mill is too high, there is a risk that the cellulose nanofibers will be altered, and the surface will harden during powderization, making it difficult to create fine particles, so it is preferable to keep the surface temperature at 120°C or lower, and more preferably at 115°C or lower. Therefore, in one embodiment of the present invention, the surface temperature of the two-roll mill is 100°C to 120°C, and preferably 105°C to 110°C.

(2-2. Second Processing)
In the second process, the dried cellulose nanofibers are mixed with a melt containing silicone oil and carnauba wax to obtain the finished cellulose nanofiber powder. The raw materials used in the second process are as follows:

Silicone oil Silicone oil forms a coating on fibers, imparts water repellency, and greatly reduces the coefficient of friction between fibers. On the other hand, silicone oil does not impair the ease of disintegration of fiber aggregates. In addition, since the main skeleton of silicone oil is a siloxane bond (Si-O-Si), the bond energy between atoms is large, and it can impart weather resistance and heat resistance. The melting point of silicone oil is about 90°C, and although its heat resistance depends on the combination with resin, it is not easily altered even when melted and processed with resin at around 280°C. Silicone oil gives water repellency to the finished CNF powder, so it has the advantage of being less likely to absorb moisture even during storage and processing.

The amount of silicone oil added is 0.8 to 2.0% by weight based on the total weight of the finished cellulose nanofiber powder. If the amount of silicone oil added is less than 0.8% by weight, the effect cannot be fully exerted. From this perspective, the amount of silicone oil added is preferably 1.0% by weight or more. On the other hand, if the amount of silicone oil added exceeds 2.0% by weight, the effect will plateau. From this perspective, the amount of silicone oil added is preferably 1.5% by weight or less.

In addition, from the viewpoint of improving the flexibility of CNF fibers, it is possible to use a low-viscosity oil-type silicone base material to which silicone containing a metal catalyst such as tin has been added.

Carnauba wax Carnauba wax contains hydrophobic aliphatic esters and hydrophilic hydroxycarboxylic acids. Silicone oil can be heated to a temperature above the melting point of carnauba wax (e.g. 88°C), and then carnauba wax can be added and mixed. Carnauba wax has the lowest melting point of all raw materials (usually 80°C to 86°C), so it has the effect of triggering the initial stage of CNF diffusion into the resin. It can also be added to a wide range of resins, is less likely to bleed, and has the same moisture absorption prevention properties as silicone.

The amount of carnauba wax added is 0.2 to 0.8% by weight based on the total weight of the cellulose nanofiber powder. If the amount of carnauba wax added is less than 0.2% by weight, the effect cannot be fully exerted. From this perspective, the amount of carnauba wax added is preferably 0.3% by weight or more. On the other hand, if the amount of carnauba wax added exceeds 0.8% by weight, the effect will plateau. From this perspective, the amount of carnauba wax added is preferably 0.7% by weight or less.

In addition, before mixing the dried cellulose nanofibers with the molten material containing silicone oil and carnauba wax, it is preferable to further stir the dried cellulose nanofibers with a stirrer or the like and dry them using processing heat.

The CNF powder obtained by the above method has high diffusibility in molten resin and is less likely to form agglomerates.

(3. Cellulose nanofiber powder)
In another aspect, the present invention provides a CNF powder comprising 75 to 90% by weight of cellulose nanofibers, 10 to 20% by weight of polyethylene glycol, 0.05 to 2.0% by weight of an ester-type dialkylammonium salt, 0.8 to 2.0% by weight of silicone oil, and 0.2 to 0.8% by weight of carnauba wax.

The manufacturing method of CNF powder and detailed explanation of each component have been described above, so they will not be repeated here.

The following examples of the present invention are provided to aid in the understanding of the present invention and its advantages, and are not intended to limit the invention.

(raw materials)
The raw materials used in each test example are as follows.
CNF: 8% by weight aqueous solution of mechanically dispersed CNF, manufactured by Sappi Corporation IPA: General-purpose isopropyl alcohol manufactured by ENEOS Corporation Polyethylene glycol: PEG-300 (liquid low molecular weight polyethylene glycol) manufactured by Sanyo Chemical Industries, Ltd.
Ester-type dialkyl ammonium salt: Catiogen (registered trademark) ES-O manufactured by Daiichi Kogyo Seiyaku Co., Ltd.
Silicone oil A: KF-96ADF (low viscosity oil type silicone) manufactured by Shin-Etsu Chemical Co., Ltd.
Silicone oil B: Shin-Etsu Chemical Co., Ltd. KM-2002-T-2 (a silicone fabric softener containing a tin catalyst)
Carnauba wax: Carnauba wax No. 1 (melting point approx. 82°C) manufactured by Kato Yoko Co., Ltd.

(1. Test Examples 1 to 4)
First, in the first treatment, each raw material was weighed according to the composition described in Table 1, and mixed for 5 minutes at 400 rpm with a mixer (Henschel mixer manufactured by Nippon Coke & Engineering Co., Ltd.). The mixed raw materials were dried using a thermal mixing two-roll mill (8-inch roll mill manufactured by Inoue Seisakusho Co., Ltd.) that has a high moisture evaporation rate and shear shear. The roll surface temperature was 105 to 110 ° C, the front and rear rotation speeds were front:rear = 7:10, and the roll clearance was 0.5 to 0.7 mm. At this time, it is desirable to sequentially place the raw materials on the rolls, and the raw materials are inserted into the gaps while repeatedly rotating on their own in the roll bank. After 3 to 4 revolutions of the rolls, the raw materials naturally peeled off. The peeled off material became semi-wet scale flakes. If the water was completely evaporated and dried by the rolls, hard fiber aggregates would also be mixed in, making it difficult to loosen the whole when silicone oil was added in the next process, so this was the end point. The flakes peeled off from the roll were checked for their flexibility when touched with the hand and for their tendency to crumble. Test Example 1 had a suitable flexibility and tendency to crumble, making it suitable for subsequent processing. Test Examples 2 to 4 were not suitable for subsequent processing because one of the components was not added (see comments in Table 1).

(2. Test Examples 5 to 10)
Next, the first and second treatments were carried out according to the formulation in Table 2. The conditions of the first treatment were the same as those of Test Examples 1 to 4. In the second treatment, a jacket oil heating mixer with a pulverizing blade (FM mixer manufactured by Nippon Coke Engineering Co., Ltd.) was used as the agitator. The flakes produced in the first treatment were added, the jacket temperature was set to 110°C, and stirring was started at 600 rpm. At this time, an exhaust blower with an air filter was operated to discharge the water vapor coming out of the raw material. Stirring was continued until the moisture content reached about 5% by weight, and then the mixture was temporarily stopped. At this time, the material was in a fine powder state. Next, the jacket temperature was set to 110°C, the stirring speed was increased to 800 rpm, and stirring was continued again, and silicone oil containing carnauba wax was added while stirring.

If the additive is added while stirring is stopped, lumps of the additive will form, so it is preferable to add the additive while stirring. After five minutes of stirring, there were no more water droplets in the mixer tank, and a clean vortex was formed with reduced powder scattering. Stirring was stopped after about seven minutes, leaving the finished CNF powder.

(Evaluation of Diffusivity)
To confirm the diffusion state visually, the molten resin was wrapped around an open thermal mixing triple roll to make a roll bank, and the CNF powder was directly added to the roll bank to confirm the state of the particles diffusing onto the roll surface. The results are shown in Table 2.

Claims (5)

A cellulose nanofiber powder comprising:
A cellulose nanofiber powder comprising, relative to the total weight of the cellulose nanofiber powder , 75 to 88 % by weight of cellulose nanofibers, 10 to 20% by weight of polyethylene glycol, 0.05 to 2.0% by weight of an ester-type dialkylammonium salt, 0.8 to 2.0% by weight of silicone oil, and 0.2 to 0.8% by weight of carnauba wax. The cellulose nanofiber powder according to claim 1, wherein the average fiber length of the cellulose nanofibers is within the range of 0.1 μm to 3.0 μm. The cellulose nanofiber powder according to claim 1 or 2, wherein the average fiber diameter of the cellulose nanofibers is within the range of 0.5 nm to 10 nm. A method for producing cellulose nanofiber powder, comprising:
a first process of supplying a cellulose nanofiber dispersion to a two-roll mill and rotating the two-roll mill to dry the cellulose nanofiber dispersion and obtain dried cellulose nanofibers;
A second process includes mixing the dried cellulose nanofibers with a melt containing silicone oil and carnauba wax to obtain a cellulose nanofiber powder;
The cellulose nanofiber dispersion is prepared to contain 75 to 88 % by weight of cellulose nanofibers, 10 to 20% by weight of polyethylene glycol, 0.05 to 2.0% by weight of an ester-type dialkylammonium salt, and 10 to 20% by weight of isopropyl alcohol, based on the total weight of the cellulose nanofiber powder after the second treatment;
The method, wherein the melt is prepared to contain 0.8 to 2.0% by weight of silicone oil and 0.2 to 0.8% by weight of carnauba wax, based on the total weight of the cellulose nanofiber powder after the second treatment . The method according to claim 4, wherein the first process includes heating the surface temperature of the two-roll mill to 100°C to 120°C.