JP7195732B2 - Block for producing cellulose nanofiber resin composite and method for producing block for producing cellulose nanofiber resin composite - Google Patents

Description

The present invention provides a composite composition of unmodified cellulose nanofibers and a water-soluble or water-dispersible synthetic resin, in which an unmodified cellulose nanofiber resin composite can be produced by a relatively simple operation and stored and transported. It relates to a method for producing a nanofiber resin composite composition that can reduce production costs including distribution costs such as.

Nanofibers derived from natural resources such as wood pulp and chitin, such as cellulose nanofibers, are usually supplied in the form of a dispersion using an aqueous solvent as a medium. A film with high gas barrier properties can be obtained by coating using an aqueous solvent dispersion in which nanofibers are uniformly dispersed in an aqueous medium, preparing the coating film, and drying it. In addition, when a nanofiber resin composite composition in which nanofibers are dispersed in a water-soluble resin is used and subjected to cross-linking treatment after coating, shrinkage is small due to the effect of adding nanofibers, and strength, heat resistance, durability and Coating films and moldings with high gas barrier properties can be obtained.

The characteristic values such as the strength and durability of the coating film are affected by the amount of nanofibers added to the water-soluble resin. commonly known.

In Patent Document 1, an anionic dispersant is added to unmodified cellulose nanofibers, an aqueous dispersion composed of cellulose nanofibers and an anionic dispersant is prepared by mechanical fibrillation, and freeze-dried. A manufacturing method for obtaining powdered cellulose nanofibers for manufacturing compositions is disclosed.

In Patent Document 2, a fine cellulose nanofiber-dispersed aqueous solution is stored in a metallic bottomed cylindrical metal container, left to stand in an atmosphere of -20 to 0 ° C., and the dispersion is poured from the bottom to the top. A basic method of obtaining a porous body is disclosed in which the pressure is reduced to 10 Pa to sublimate the water after freezing the material. In this case, by setting the concentration of the microcellulose fibers to 1.0% by weight or less, a porous body having a high porosity of 99% or more can be obtained.

Patent Document 3 discloses a method of freeze-drying an aqueous slurry of microcellulose fibers to produce a porous body.

Japanese Patent No. 6189559 Japanese Patent No. 5988121 Japanese Patent No. 5691131

In Patent Document 1, powdery cellulose nanofibers for manufacturing a composition are produced by fibrillating an aqueous solvent dispersion obtained by adding an anionic dispersant and an aqueous solvent to unmodified cellulose nanofibers, followed by freeze-drying. It is a powder with a bulk density in the range of 0.09 to 0.2 g/cm ³ . When the powder is mixed or kneaded with a non-water-soluble solid-phase thermoplastic resin, thermosetting resin, or resin such as rubber using a melt-kneading device such as a twin-screw kneading extruder, mixing A fine powder is used as a form advantageous for excellent handling in the kneading step and high dispersion in the resin.

However, fine powders of unmodified cellulose nanofibers are very likely to be charged with static electricity and therefore easily adhere to containers and the like.
For this reason, for example, when kneading with a resin using a twin-screw extruder, if resin pellets or resin powder and the powder are premixed using a mixer, the mixture is charged with static electricity, and only the powder in the mixture tends to adhere to the walls of mixers and extruders, and to the walls of containers for collecting powders. This phenomenon is remarkable in the material supply hopper of the twin-screw extruder. When the mixture is put into the material hopper, the powdered resin component is first supplied to the screw part, and the unmodified cellulose nanofiber freeze-dried powder is obtained. Most of it adheres to the hopper wall surface and tends to remain. Therefore, there has been a problem that the composition of the cellulose nanofiber resin composition obtained by kneading varies or becomes inaccurate.

In addition, powders with low bulk density tend to float up the fine powder components contained in them when they are handled, such as when transferring containers, and the fine powders that float up lead to contamination of the work site and adverse effects on the health of workers. It is necessary to invest in equipment such as local exhaust ventilation at the manufacturing plant. In addition, once the fine powder rises up, it cannot be recovered, and not only is it likely to cause loss as a raw material for production, but also the space efficiency in the process of storage and transportation deteriorates, so the logistics cost as a raw material for production is reduced. The problem is that it tends to lead to an increase.
In addition, when the powder is melt-kneaded with a solid thermoplastic resin, thermosetting resin, or rubber, finely powdered cellulose nanofibers can be expected to be highly dispersed in the molten resin. The cellulose nanofibers that make up the are small in diameter and have a large aspect ratio, so the specific surface area is large. As a result, the kneading torque increases, and the maximum amount of cellulose nanofibers to be added to the molten resin is about 10% by weight, and it is difficult to increase the amount beyond this.

Patent Document 2 discloses a production method for obtaining a porous body by freeze-drying an aqueous dispersion of microcellulose fibers. The concentration of the microcellulose fibers is set to 1.0 wt% or less, and the dispersion liquid stored in a bottomed cylindrical metal container is frozen from the bottom to the top in a below-freezing atmosphere of -20 to 0 ° C. to obtain a porous body. is being produced.
In addition, since the porous body according to the invention has a porosity of 99% or more, the bulk density is as small as 0.013 to 0.02 g/cm ³ , and therefore the porous body is fragile and collapses during handling. Since it is easy to use, it is not only disadvantageous as an industrial material, but also the storage cost and transportation cost of the porous body are high.
The porous body has a porosity of about 99% and is intended for use as an adsorbent, heat insulating material, or sound absorbing material, and is not a composite of microcellulose fibers and resin.

The porous body composed of microcellulose fibers disclosed in Patent Document 3 has an apparent density (synonymous with bulk density) of 0.005 to 0.11 g/cm ³ . In addition to fragility during handling, there are problems with storage and transportation costs. In addition, when the aqueous slurry containing the microcellulose fibers in this document is freeze-dried to form a porous body, the respective microcellulose fibers are strongly bonded by hydrogen bonds derived from the hydroxyl groups present on their surfaces. There is a problem that it is difficult to re-dissolve in an aqueous solvent.

An object of the present invention is to obtain a block for producing a cellulose nanofiber resin composite containing unmodified cellulose nanofibers and a polymer dispersant, and to provide a method for producing the same.

The present invention provides a method for producing a nanofiber resin composite composition and a nanofiber resin composite composition of [1] to [6] below.
[1] A block for producing a cellulose nanofiber resin composite, containing unmodified cellulose nanofibers in which cellulose-derived hydroxyl groups have not been modified, and a polymer dispersant.
[2] The block for producing a cellulose nanofiber resin composite according to [1], wherein the block has a bulk density of 0.22 g/cm ³ or more.
[3] The aqueous solvent dispersion containing the unmodified cellulose nanofibers and the polymer dispersant contains 0.01 to 25 parts by weight of the polymer dispersant per 100 parts by weight of the solid content of the unmodified cellulose nanofibers. The block for producing a cellulose nanofiber resin composite according to [1] and [2], which contains a part.
[4] A first step of preparing an unmodified cellulose nanofiber dispersion by mixing the unmodified cellulose nanofibers, a polymer dispersant, and a solvent, followed by mechanical fibrillation; A method for producing a block for producing a cellulose nanofiber resin composite according to [1] to [3], including a second step of removing the solvent from the fiber dispersion.
[5] The method for producing a block for producing a cellulose nanofiber resin composite according to [4], wherein the second step is freeze-drying.
[6] The production of a cellulose nanofiber resin composite according to [4] and [5], wherein the second step is freeze-drying while pressing the liquid surface of the unmodified cellulose nanofiber solvent dispersion. method of manufacturing blocks for

According to the present invention, a block for producing a cellulose nanofiber resin composite that can easily produce a cellulose nanofiber resin composite without the powder components floating up or adhering to the wall surface of the production apparatus or the wall surface of the collection container. can be obtained.

In the present invention, a nanofiber dispersion obtained by mixing nanofibers, a water-soluble dispersant, and an aqueous solvent in one step under mechanical fibrillation treatment is freeze-dried to obtain a bulk density of 0.22 g/cm ³ . A block for producing a cellulose nanofiber water-soluble resin composite can be produced by using the dried nanofibers as described above.
The block is added to an aqueous solvent solution of a water-soluble resin and stirred/mixed to obtain a water-soluble resin of cellulose nanofibers in which the unmodified cellulose nanofibers are uniformly and highly dispersed in the aqueous solvent solution of the water-soluble resin. A dispersion can be made. In the dispersion, the unmodified cellulose nanofibers are stably and uniformly dispersed without sedimentation or aggregation over time.

Here, a block is a three-dimensional object having a certain three-dimensional shape that can be visually recognized with the naked eye. Examples thereof include cuboids, spheres, and plate-like objects, and there are no particular limitations as long as they are three-dimensional objects having a certain three-dimensional shape. In the case of a rectangular parallelepiped, it is preferably a three-dimensional object whose length, width, and height are 3 to 600 mm, 3 to 600 mm, and 3 to 600 mm, respectively, from the viewpoint of moldability and ease of handling. It includes a rectangular parallelepiped whose width x height is 50 mm x 50 mm x 10 mm, respectively.

As the cellulose nanofibers used in the present invention, unmodified cellulose nanofibers in which the hydroxyl groups present on the fiber surface have not been oxidized or modified can be suitably used. Modified cellulose nanofibers are usually commercially available as aqueous dispersions using water as a dispersion medium and having a solid content of, for example, about 10% by weight. The dispersion contains aggregates of nanofibers due to hydrogen bonds originating from hydroxyl groups on the surfaces of unmodified cellulose nanofibers.

To the unmodified cellulose nanofibers containing such aggregates, for example, 5% by weight of a water-soluble dispersant and 95% by weight of water as an aqueous solvent are added to the solid content of the unmodified cellulose nanofibers, and the medialess dispersion described later is performed. By treating with a machine, the aggregates are loosened and the dispersant is uniformly ion-bonded to the hydroxyl groups on the surface of the unmodified cellulose nanofibers (A) to prepare a nanofiber dispersion. The dispersion is freeze-dried while being pressed to obtain a block for producing a cellulose nanofiber water-soluble resin composite having a bulk density of 0.22 g/cm ³ or more.

According to the present invention, a nanofiber resin composite composition having a high concentration of nanofibers can be prepared by a simple operation. The block for producing a cellulose nanofiber water-soluble resin composite used in the present invention is prepared by drying an aqueous medium dispersion containing nanofibers and a dispersant, and the block has a bulk density of 0.22 g/cm ³ or more. As a result, the binding of the unmodified cellulose nanofibers becomes stronger, and the fine powder components do not separate and rise up, making handling easier. Furthermore, the block becomes compact, and distribution costs for storage and transportation can be suppressed.

<Unmodified cellulose nanofiber>
Unmodified cellulose nanofibers are not chemically treated (different from chemical fibrillation), and the cellulose-derived hydroxyl groups in the molecular chains and/or at the ends of the molecular chains have not been hydrophobically modified, or functional groups other than hydroxyl groups have not been modified. cellulose nanofibers that are not blocked with In the present invention, the unmodified cellulose nanofiber is a fibrous substance obtained by disentangling a cellulose raw material such as plant-derived pulp by mechanical defibration described below. For the cellulose raw material, for example, a plurality of surface hydroxyl groups within one cellulose nanofiber form hydrogen bonds, and a hydroxyl group on the surface of one cellulose nanofiber and a hydroxyl group on the surface of another cellulose nanofiber form hydrogen. It may contain aggregates by forming bonds. This aggregate can be easily loosened by mechanical defibration treatment or the like.

Although the fiber diameter, fiber length and aspect ratio of the unmodified cellulose nanofiber are not particularly limited, the fiber diameter is preferably 500 nm or less, more preferably 300 nm or less, and still more preferably 250 nm or less, and the fiber length is preferably 10 to 100 nm. It is 1,000 μm, more preferably 100 to 500 μm, and the aspect ratio (fiber length/fiber diameter) is 1,000 to 15,000, preferably 2,000 to 10,000. The fiber diameter and fiber length here are obtained by measuring the fiber diameter and fiber length of an arbitrary number (for example, 20) of unmodified cellulose nanofibers by electron microscopic observation, and calculating the arithmetic mean value of the obtained measured values. .

As in the nanofiber dispersion (A) of the present invention, when the unmodified cellulose nanofibers and the dispersant described later are allowed to coexist in an aqueous system, at least part of the hydroxyl groups on the surface of the unmodified cellulose nanofibers and at least one Some dispersants may react with each other to form these ionic bonds. Such an ionic bond is considered to have the function of maintaining the dispersion stability of unmodified cellulose nanofibers at a high level over a long period of time, for example.

In the present invention, the unmodified cellulose nanofibers are preferably used in the form of an aqueous dispersion from the viewpoint of the dispersibility of the unmodified cellulose nanofibers in (C) the nanofiber resin composite composition. The content of the unmodified cellulose nanofibers in the aqueous dispersion is not particularly limited, but depends on the fiber diameter of the unmodified cellulose nanofibers, preferably 0.01 to 30% by weight of the total amount of the aqueous dispersion, more preferably It is 1 to 25% by weight of the total amount of the aqueous dispersion.

The elastic modulus and strength of unmodified cellulose nanofibers composed of extended chain crystals reach 140 GPa and 3 GPa, respectively, which are equal to typical high-strength fibers and aramid fibers and higher than glass fibers. Moreover, the coefficient of linear thermal expansion is 1.0×10 ⁻⁷ /° C., which is as small as quartz glass.

The cellulose raw material used for the production of unmodified cellulose nanofibers is preferably used as an aqueous dispersion. The shape of the cellulose raw material is, for example, any shape such as fibrous or granular. Microfibrillated cellulose from which lignin and hemicellulose are removed is preferable as the cellulose raw material. Alternatively, commercially available cellulose may be used. When the microfibrillated cellulose is treated with a medialess dispersing machine, which will be described later, the microfibrillated cellulose becomes thinner due to unraveling of hydrogen bonds derived from hydroxyl groups present on the fiber surface while maintaining the length of the fiber.

<Polymer dispersant>
The dispersant is a water-soluble dispersant, preferably a water-soluble dispersant capable of ion bonding with functional groups such as hydroxyl groups possessed on the surface of unmodified cellulose nanofibers, and more preferably a water-soluble dispersant possessed on the surface of unmodified cellulose nanofibers. A dispersant capable of forming an ionic bond with a functional group such as a hydroxyl group and capable of enhancing the dispersibility and dispersion stability of the unmodified cellulose nanofibers in the resin composite composition of the present invention by means of electrostatic repulsion or the like. be. The dispersant is not particularly limited as long as it is water-soluble as described above, but an anionic dispersant can be preferably used. Examples of anionic dispersants include compounds having at least one functional group selected from phosphoric acid groups, —COOH groups, —SO ₃ H groups, their metal ester groups, and imidazoline groups, acryloyloxyethyl and phosphorylcholine (co)polymers. Among these, acryloyloxyethylphosphorylcholine (co)polymers are biocompatible and can be preferably used as the dispersant in the present invention. A water-soluble dispersant can be used individually by 1 type or in combination of 2 or more types.

As the anionic dispersant used in the present invention, a (meth)acryloyloxyethylphosphorylcholine (co)polymer having a phosphorylcholine group having a biocompatible phospholipid-like structure may be used. The (meth)acryloyloxyethylphosphorylcholine (co)polymer can increase the dispersion stability of each component in the nanofiber resin composite obtained by the present invention, particularly the dispersion stability of the nanofibers, and is biocompatible, for example. and can be suitably used as a dispersant when the nanocellulose composite of the present invention is used for medical applications, food applications, and the like. Here, (meth)acryloyloxyethylphosphorylcholine includes methacryloyloxyethylphosphorylcholine and acryloyloxyethylphosphorylcholine. These are manufactured according to a conventional method. For example, 2-bromoethylphosphoryl dichloride, 2-hydroxyethylphosphoryl dichloride and 2-hydroxyethyl methacrylate are reacted to give 2-methacryloyloxyethyl-2'-bromoethyl phosphate, which is further treated with trimethylamine in methanol solution. can be obtained by reacting with

In the present invention, a commercially available (meth)acryloyloxyethylphosphorylcholine (co)polymer may be used. Specific examples of commercially available products include Lipidure HM and Lipidure BL (both trade names, polymethacryloyloxyethylphosphorylcholine). ), Lipidure PMB (trade name, methacryloyloxyethylphosphorylcholine/butyl methacrylate copolymer), Lipidure NR (trade name, methacryloyloxyethylphosphorylcholine/stearyl methacrylate copolymer), and the like. All of these are manufactured by NOF Corporation.

<Aqueous solvent>
Examples of aqueous solvents include water, monohydric or polyhydric alcohols (monohydric alcohols include, for example, lower alcohols having 1 to 4 carbon atoms), amides, ketones, and ketoalcohols. , cyclic ethers, glycols, lower alkyl ethers of polyhydric alcohols, polyalkylene glycols, glycerin, N-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, glycerin, Ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol , 1,2,6-hexanetriol, trimethylolpropane, pentaerythritol and other polyols, diethylene glycol monobutyl ether, tetraethylene glycol monomethyl ether and other polyhydric alcohol alkyl ethers, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether polyhydric alcohol aryl ethers and polyhydric alcohol aralkyl ethers such as 2-pyrrolidone, N-methyl-2-pyrrolidone, lactams such as ε-caprolactam, 1,3-dimethylimidazolidinone acetone, N-methyl-2 -pyrrolidone, m-butyrolactone, polyoxyalkylene adduct of glycerin, propylene glycol monomethyl ether acetate, dimethyl sulfoxide, diacetone alcohol, dimethylformamide, propylene glycol monomethyl ether and the like. A water-soluble solvent can be used individually by 1 type or in combination of 2 or more types.

As water, pure water such as ion-exchanged water, ultrafiltrated water, reverse osmosis water, distilled water, or ultrapure water can be used. In addition, it is preferable to use water sterilized by ultraviolet irradiation or addition of hydrogen peroxide, since the generation of mold or bacteria during long-term storage can be prevented.

<Medialess Disperser>
The unmodified cellulose nanofiber aqueous solvent dispersion of the present invention is obtained by supplying a cellulose nanofiber raw material, a dispersant, and a dispersion medium to a mechanical defibration means, and mechanically fibrillating the cellulose nanofiber raw material. Aggregation due to hydrogen bonding is broken down to promote formation of nanofibers, and by bonding with a dispersant, the ion repulsive force of the dispersant can stabilize dispersibility for a long period of time.
By this operation, even when the dispersion is in a freeze-dried solid state, the unmodified cellulose nanofiber structure can be maintained in which the aggregates are loosened.

Examples of mechanical defibration means include grinders, kneaders, bead mills, high-pressure homogenizers, underwater counter-collisions, high-speed rotary dispersers, beadless dispersers, and high-speed stirring medialess dispersers. Agitation type medialess dispersers are most preferred.
A high-speed agitating medialess dispersing machine means a dispersing machine that does not substantially use dispersing media (for example, beads, sand (sand), balls, etc.) but utilizes shearing force for dispersing treatment.

The high-speed agitating medialess disperser produces a highly pure nanofiber dispersion with less impurities such as beads and grinder disk abrasion dust.

Examples of the medialess dispersing machine include, but are not limited to, DR-PILOT2000, ULTRA-TURRAX series, Dispax-Reactor series (all trade names, manufactured by IKA), T.I. K. Homomixer, T. K. Pipeline Homomixer (both trade names, manufactured by Primix Co., Ltd.), High Shear Mixer (both trade names, manufactured by Silverson), Milder, Cavitron (both trade names, manufactured by Pacific Machinery Co., Ltd.), Clearmix (trade name, manufactured by M Technic Co., Ltd.), Homomixer, Pipeline Mixer (trade name, manufactured by Mizuho Kogyo Co., Ltd.), Jet Paster (trade name, manufactured by Nihon Spindle Mfg. Co., Ltd.), Apex Disper ZERO (trade name, manufactured by Hiroshima Metal & Machinery Co., Ltd.).

Among these, as the medialess disperser, a disperser equipped with a rotor and a stator is preferable. As an example of such a high-speed stirring medialess disperser, Apex Disperser ZERO manufactured by Hiroshima Metal & Machinery Co., Ltd. is mentioned. This disperser includes a stator and a rotor that rotates inside the stator, and a gap is formed between the stator and the rotor. By rotating the rotor and passing the liquid mixture between the stator and rotor, shear force can be applied. The distance between the stator and rotor is the shear clearance.

Further, the disperser is not limited to the one described above, and for example, a disperser in which a stator and a rotor are installed in multiple stages may be used.

As the medialess dispersing machine of the present invention, it is preferable to use an in-line circulation type one in which the mixed liquid circulates in the dispersing machine from the viewpoint of uniform treatment.

The shear rate in the medialess disperser exceeds 900,000 [1/sec]. When the shear rate is 900,000 [1/sec] or less, cellulose is not defibrated.

The shear rate is preferably 2,000,000 [1/sec] or less, preferably 1,500,000 [1/sec] or less, and more preferably 1,200,000 [1/sec] or less.

The shear clearance is appropriately set according to the shear rate, the viscosity of the mixture of the above components, and the like. From the viewpoint of further improving dispersibility in water, it is preferably 100 µm or more, more preferably 150 µm or more, and even more preferably 200 µm or more. In addition, even if the viscosity of the mixed liquid of the above components is high, the clearance is preferably 5 mm or less, more preferably 4 mm or less, from the viewpoint of ensuring high dispersibility while maintaining the rotation speed of the disperser within an appropriate range. 3 mm or less is more preferable.

Furthermore, the rotational peripheral speed of the medialess dispersing machine is appropriately set according to the above shear rate. /s or more is more preferable. In addition, from the viewpoint of obtaining the optimum cellulose nanofiber diameter, the rotational peripheral speed is preferably 50 m/s or less, more preferably 40 m/s or less, and even more preferably 35 m/s or less. The rotating peripheral speed is the peripheral speed of the tip portion of the rotor.

Thus, the dispersion of unmodified cellulose nanofibers of the present invention can be obtained by treating a dispersion containing cellulose and a dispersing agent one to several times using a high-speed stirring medialess dispersing machine as described above. can be manufactured by

The unmodified cellulose nanofibers obtained by the method of the present invention have an average fiber diameter of about 10 to 300 nm, preferably about 10 to 200 nm, most preferably about 10 to 150 nm. Since the unmodified cellulose nanofibers of the present invention have a large fiber length/fiber width (aspect ratio) and a good dispersion state, it is possible to obtain a coating film in which the nanofibers are entangled like a nonwoven fabric while maintaining strength. It is easy and can be suitably used as various coating materials.

<Freeze-drying>
An appropriate means for removing the dispersion medium from the unmodified cellulose nanofiber dispersion is selected according to the type of the dispersion medium. drying method. Spray-drying is carried out by ejecting the dispersion from a nozzle to form fine droplets and then heating and drying the droplets in convection air. In particular, when natural drying or heat drying is used, it is preferable from the viewpoint of drying efficiency to mold the mixture into a film or sheet by casting (casting) or the like, and then dry the molded product. .

Furthermore, as a drying means, the quality of the dried product obtained is less deteriorated, and the dried product becomes a solid form with a low bulk density, and is easy and simple to handle in the subsequent dissolution step in a water-soluble resin. For some reasons, freeze-drying is preferred.

Here, freeze-drying is a method of drying by freezing the dispersion and then reducing the pressure to sublimate the dispersion medium. The method of freezing the dispersion in freeze-drying is not particularly limited. There are other methods of freezing. A preferred method is to freeze the dispersion by placing it in a refrigerant. The freezing temperature of the dispersion must be lower than the freezing point of the dispersion medium in the dispersion, preferably -50°C or lower, more preferably -80°C or lower.

Freeze-drying requires sublimation of the dispersion medium in the frozen dispersion under reduced pressure. The pressure during decompression is preferably 100 Pa or less, more preferably 10 Pa or less. If the pressure exceeds 100 Pa, the dispersion medium in the frozen dispersion may melt. Although the temperature of the reduced-pressure atmosphere is not particularly limited, it is preferably about 20° C. from the viewpoint of the balance between the sublimation rate and the prevention of decomposition of the dispersion.

Freeze-drying in the present invention is preferably performed, for example, by the following procedure.
In freeze-drying, the container for storing the unmodified cellulose nanofiber dispersion is desirably made of non-metallic material with low thermal conductivity. By using a non-metallic storage container with low thermal conductivity, local rapid cooling of the region where the undenatured cellulose nanofiber dispersion is in contact with the container wall surface can be avoided and the freezing rate can be suppressed. It is possible to uniformize the dispersion of the density and the higher-order structure of the frozen dispersion.
The nonmetallic container is not particularly limited, and examples thereof include plastics such as polytetrafluoroethylene, glass, rubber, and wood. Above all, if the thermal conductivity is 1.0 w/m·k or less, rapid cooling of the nanofiber dispersion can be avoided, which is preferable. Among them, plastics, glass, and the like, which are excellent in water resistance and lightness, can be preferably used.
If variations in density occur inside the dried unmodified cellulose nanofibers, a local difference in density occurs in the resulting block for producing a cellulose nanofiber water-soluble resin composite, and the block is used to improve the water-solubility of cellulose nanofibers. It causes variation in composition when producing a resin composite.

It is preferable to install a pressing member having a size slightly smaller than the opening of the container on the liquid surface of the nanofiber dispersion stored in the nonmetallic container. The pressing member has an appropriate density (approximately 1.5 g/cm ³ as a guideline) so that it does not sink below the liquid surface of the nanofiber dispersion and can be maintained above the liquid surface. It is preferable to have The material of the pressing member is not particularly limited, but plastics such as phenolic resin, wood, and the like can be suitably used, for example. Among them, a hard plastic such as a cotton canvas laminate (density: 1.4 g/cm ³ ) impregnated with phenol resin is preferable. Further, the pressing member is not particularly limited as long as it has a shape that can be accommodated in the opening of the container. Among these, a circular or rectangular flat plate shape is particularly preferable in terms of ease of handling and ease of weight adjustment.

The pressing member may be provided with a large number of through holes having a diameter of 1 mm or less penetrating the upper and lower surfaces. The through-holes can increase the efficiency of sublimation of the aqueous solvent during freeze-drying.
Since the pressing member is held on the liquid surface of the nanofiber dispersion, even when the liquid surface of the dispersion drops as it dries, the pressing member is held above the liquid surface following changes in the height of the liquid surface. Therefore, it is possible to prevent the bulk density of the dried nanofibers produced after freeze-drying from becoming too small, and to make the block for producing a cellulose nanofiber water-soluble resin composite compact. The resulting block for producing a cellulose nanofiber water-soluble resin composite preferably has a bulk density of 0.22 g/cm ³ or more.

The shape of the non-metallic container for storing the nanofiber dispersion is not particularly limited, and any shape such as bottomed columnar shape or prismatic shape can be selected. The height in the direction from the bottom surface of the container to the opening is desirably a dimension that allows the container to be accommodated inside a freeze-drying apparatus to be described later. Furthermore, it is preferable that the inner side surface of the container is perpendicular to the liquid surface of the stored dispersion liquid, in order not to hinder the pressing member from following changes in the liquid surface of the dispersion liquid.

Freeze-drying in the present invention is preferably carried out by the following means.
First, a nanofiber dispersion is cast and stored in a nonmetallic container, and a pressing member is placed on the liquid surface of the dispersion. The non-metallic container is placed inside a freeze-drying apparatus and dried under reduced pressure of 100 Pa or less at room temperature until the liquid surface of the dispersion liquid is lowered to about one-half of its original height. After that, the drying chamber of the freeze-drying device is once returned to normal pressure, frozen at −80° C. or less, and then dried under reduced pressure at 10 Pa or less to obtain the cellulose nanofiber water-soluble resin composite having the bulk density. Obtain a crafting block.
In the block for producing a cellulose nanofiber water-soluble resin composite, aggregates due to hydrogen bonding derived from the hydroxyl groups of cellulose nanofibers contained in the raw material for cellulose nanofibers are treated with the medialess disperser to reduce the diameter of the nanofibers. is fibrillated to 10 to 200 nm, and at least part of the hydroxyl groups on the surface of the nanofibers are ionically bonded to the dispersant.

Therefore, when the block for producing a cellulose nanofiber water-soluble resin composite is added to an aqueous solvent solution of a water-soluble resin or an aqueous solvent, it can be added without using a medialess dispersing machine, for example, using a tabletop propeller stirring device. By stirring and mixing, a nanofiber resin composite composition that is easily redispersed in an aqueous solvent solution of a water-soluble resin can be obtained. Furthermore, the dried nanofibers can be similarly redispersed in an aqueous solvent solution of a water-soluble resin instead of an aqueous solvent.

<Other additives>
In addition, in the present invention, antioxidants such as hindered phenols, phosphate esters and phosphites, heat stabilizers, and triazines are added to the extent that the desired properties of the resulting (C) nanofiber resin composite composition are not impaired. weather resistance-imparting agents such as chemical compounds, stabilizers such as weather resistance-imparting agents, plasticizers, antistatic agents, flame retardants, glass fibers, glass beads, metal powders, silica, inorganic layered compounds such as talc and mica, etc. Inorganic or organic fillers, pigments, coloring agents such as dyes, lubricants, water repellents, anti-blocking agents, flexibility improving agents, leveling agents, antifoaming agents, metal soaps, organic silanes, organic metal compounds, etc. can be done. These additives may be mixed during the production of the nanofiber dispersion (A) described above, and may be added and mixed at the stage of producing the nanofiber resin composite composition (C) obtained below. may

Among these additives, antioxidants and preservatives are preferred. Examples of antioxidants include phenol antioxidants, sulfur antioxidants, amine antioxidants, and the like. Among these, phenolic antioxidants are particularly preferred. The blending amount of the antioxidant is usually 0.1 to 10% by weight based on the total solid content of the nanofibers and the crosslinkable resin or the total solid content of the nanofibers, the crosslinkable resin and the dispersant. It is preferably 0.2 to 5% by weight.
Preferable examples of antiseptics include phenol, sodium omadine, sodium benzoate, and benzimidazole compounds.

The block for producing a cellulose nanofiber water-soluble resin composite of the present invention can be easily mixed and stirred with an aqueous solvent solution of a water-soluble resin by a simple operation to produce a cellulose nanofiber water-soluble resin composite. can. The cellulose nanofiber water-soluble resin composite can be suitably used for various coatings such as gas barrier coatings, impact-resistant coatings, adhesive coatings, vibration-absorbing coatings, molded articles, and the like.

In addition, the block for producing a cellulose nanofiber water-soluble resin composite of the present invention can be used not only by stirring and mixing in an estimated manner using a tumorous resin, but also by melting with a non-water-soluble solid thermoplastic resin or thermosetting resin. It can also be used publicly for kneading.

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples. The details of each component, apparatus, etc. used in the examples are as follows.

[Cellulose nanofiber]
As cellulose nanofibers, unmodified cellulose nanofibers (trade name: Celish KY100S, manufactured by Daicel Finechem Co., Ltd., average fiber diameter 180 nm, solid content 25% aqueous dispersion) were used. (Hereinafter, it may be referred to as unmodified CNF.)
[Dispersant]
A biocompatible polymethacryloyloxyethylphosphorylcholine (trade name: Lipidure BL, manufactured by NOF Corporation) was used as a water-soluble polymer dispersant.
[High-speed stirring type medialess disperser]
Apex Disperser ZERO (trade name, manufactured by Hiroshima Metal & Machinery Co., Ltd.) was used.

(Example 1)
The amounts of the components used in the form of aqueous solutions or aqueous dispersions are shown below in terms of solid content, which of course contain water.
200 g of unmodified cellulose nanofiber aqueous dispersion (Celish, KY100S) in terms of solid content, 10 g of polymer dispersant (Lipidure BL, 5% by weight based on CNF solid content), 200 g of purified water, and high-speed medialess dispersion machine (Apex Disperser ZERO) at the same time, set the clearance of the shearing part to 1 mm, the rotation peripheral speed of the rotor to 45 m / sec, perform fibrillation treatment for 10 minutes five times, the volume is about 1000 ml, and the solid content is A 20% by weight cloudy liquid nanofiber dispersion of the present invention was obtained. (A) When the average diameter of the unmodified cellulose nanofibers in the nanofiber dispersion (A) was observed by FE-SEM, it was in the range of 1 to 200 nm.

After that, the nanofiber dispersion is transferred to a polytetrafluoroethylene (PTFE) beaker (cylindrical shape with an inner diameter of φ100 mm and a height of 80 mm with a bottom, thermal conductivity: 0.23 W/m·k). A pressure member made of a cotton canvas laminate of phenolic resin having approximately the same shape and a diameter about 5 mm smaller (thickness 5 mm, many evenly pierced holes with a diameter of φ 1 mm) is placed on the liquid surface of the nanofiber dispersion. did. The container is placed in the chamber of a freeze dryer (FD-1, manufactured by Tokyo Rika Kikai Co., Ltd.), and the pressure is reduced to 90 Pa at room temperature, and the liquid level drops to about half or less of the original height. dried under reduced pressure. The initial liquid level of the nanofiber dispersion was 130 mm from the bottom, and the liquid level after drying under reduced pressure was 62 mm from the bottom.
After that, the chamber is once returned to normal pressure, the dispersion is frozen at −80° C. or less, and then dried under reduced pressure at normal temperature and 10 Pa or less for 24 hours to obtain cylindrical nanofibers having a diameter of about 98 mm and a height of about 25 mm. A dry product was obtained. This nanofiber resin composite was cut into 5 cubes having a side of about 20 mm using a utility knife, and the bulk density of each was determined. The bulk density ranged from 0.23 to 0.27 g/cm ³ . The bulk density was determined by dividing the weight of the dried nanofibers by the external dimensions.
The dried cellulose nanofibers cut above are slid under their own weight on a flat plate made of PTFE and a flat plate made of stainless steel (both 300 × 300 × 2 mm) set at an inclination angle of 45 degrees, and the dried cellulose nanofibers are applied to the surface of each flat plate. was observed visually. Table 1 shows the results.

(Example 2)
In Example 1, except that the container used for freeze-drying was changed from PTFE to stainless steel (SUS304), the same operation as in Example 1 was performed to prepare a cylindrical cellulose nanofiber dried body, and the same evaluation was performed. did The dry solid bulk density in this case was between 0.22 and 0.25 g/cm ³ . Table 1 shows the results.

(Comparative example 1)
A columnar dried cellulose nanofiber was produced in the same manner as in Example 1, except that freeze-drying was performed without installing a pressing member, and the same evaluation was performed. The dry solid bulk density in this case was between 0.14 and 0.20 g/cm ³ . Table 1 shows the results.

(Comparative example 2)
In Example 1, the container used for freeze-drying was changed from PTFE to stainless steel (SUS304), and freeze-drying was performed without installing a pressing member. The obtained dried solid had a sparse, almost columnar shape, but was fragile and easily crumbled by external force. The bulk density of the dry matter was in the range of 0.11-0.17 g/cm ³ . Table 1 shows the results of the same evaluation as in Example 1.

<Effect of Example>
As shown in Table 1, according to the present invention, it is possible to produce a dried cellulose nanofiber having a bulk specific gravity of 0.22 g/cm ³ or more, which is resistant to crumbling and contains little powder component.
The cellulose nanofiber storage container used for freeze-drying was made of stainless steel, which has high thermal conductivity. Met. If the container is made of PTFE, variation in bulk density of the dried product is reduced, which is preferable.

Claims (4)

A block for producing a cellulose nanofiber resin composite, comprising an unmodified cellulose nanofiber in which cellulose-derived hydroxyl groups are not modified, and a polymer dispersant, wherein the block has a bulk density of 0.22 g/cm ³ or more. A block for producing a cellulose nanofiber resin composite. The polymeric dispersant is a compound having at least one functional group selected from a phosphoric acid group, a —COOH group, a —SO ₃ H group, a metal ester group thereof, and an imidazoline group, acryloyloxyethylphosphorylcholine (co- ) The block for producing a cellulose nanofiber resin composite according to claim 1, which is at least one selected from polymers. The composition of the aqueous solvent dispersion containing the unmodified cellulose nanofibers and the polymer dispersant is such that the solid content of the unmodified cellulose nanofibers is 100 parts by weight, and the polymer dispersant is 0.01 to 25 parts by weight. The block for producing a cellulose nanofiber resin composite according to claim 1 or 2, which is a part. A first step of preparing an unmodified cellulose nanofiber dispersion by mixing the unmodified cellulose nanofibers, a polymer dispersant, and a solvent, followed by mechanical fibrillation, and the unmodified cellulose nanofiber dispersion. a second step of removing the solvent from
The method for producing a cellulose nanofiber resin composite according to any one of claims 1 to 3, wherein the second step is freeze-drying while pressing the liquid surface of the unmodified cellulose nanofiber solvent dispersion. Block manufacturing method.