JP7079563B2 - Method for manufacturing cellulose nanofiber molded product - Google Patents

Description

The present invention relates to a method for producing a cellulose nanofiber molded product.

In recent years, nanotechnology has been attracting attention for the purpose of refining substances to the nanometer level and obtaining new physical properties different from the conventional properties of substances. Cellulose nanofibers (hereinafter, may be abbreviated as "CNF") produced from pulp, which is a cellulosic raw material, by chemical treatment, pulverization treatment, etc., are excellent in strength, elasticity, thermal stability, and the like. This CNF molded product is expected to be used for various purposes as a high-strength material derived from biomass.

CNF is usually obtained by refining pulp or the like in an aqueous dispersion state. Therefore, when trying to obtain a molded product of CNF from a slurry (aqueous dispersion) of CNF, it is necessary to dehydrate the slurry and mold it. As a method for dehydrating the CNF slurry to obtain a CNF molded product, a method of applying a load to the CNF-containing slurry filled in the mold and heating and / or reducing the pressure has been proposed (Japanese Patent Laid-Open No. 2016-94683). See Gazette).

Japanese Unexamined Patent Publication No. 2016-94683

However, the method of Patent Document 1 concentrates the CNF slurry by heating and / or reducing the pressure, and it is not economical to heat and / or reduce the pressure from the initial stage as a method for removing a large amount of water. Therefore, it is preferable to perform dehydration by mechanically pressurizing, but if simply mechanically pressurizing and dehydrating, CNF will flow out together with water. If CNF flows out during dehydration, it is not possible to obtain a molded product having the density, thickness, etc. as designed. In addition, if CNF leaks, it will lead to an increase in production costs.

The present invention has been made based on the above circumstances, and an object of the present invention is to provide a method for producing a cellulose nanofiber molded product capable of efficiently dehydrating while suppressing the outflow of cellulose nanofibers. To provide.

The invention made to solve the above problems includes a step of dehydrating a slurry containing cellulose nanofibers via a mesh-like member, wherein the slurry has a longer fiber length or a larger fiber diameter than the cellulose nanofibers. This is a method for producing a cellulose nanofiber molded body containing a fiber capable of hydrogen-bonding with the cellulose nanofiber.

In the production method, by adding a fiber having a longer fiber length or a larger fiber diameter than the CNF and capable of hydrogen bonding with the CNF to the slurry, the fiber surface and the CNF interact with each other, and the fiber surface and the CNF interact with each other. Since this large fiber does not easily pass through the mesh-like member, the outflow of CNF can be suppressed. Therefore, in the manufacturing method, the outflow of CNF is suppressed even if dehydration is performed at a relatively high pressure, and efficient dehydration can be performed.

It is preferable that the fiber is pulp. Like CNF, pulp contains cellulose as a main component and has a high affinity with CNF. Therefore, by using pulp as the fiber, the outflow of CNF can be suppressed more effectively. Further, by adding pulp, the pulp becomes a core material, and a molded product having excellent strength may be obtained.

It is preferable that the pulp is unbeaten pulp. By using unbeaten pulp as the pulp, the dehydration efficiency can be further improved.

The content of cellulose nanofibers in the solid content of the slurry is preferably 50% by mass or more. According to the production method, even when the CNF content is high and the raw material is likely to flow out during dehydration, the outflow of the raw material CNF is suppressed and the cellulose has a desired size and the like. A nanofiber molded product can be obtained. In addition, since each CNF has high strength, high elasticity, and nano size, increasing the content of such CNF increases the number of hydrogen bond points per unit volume, resulting in strength. It is possible to obtain a molded body having excellent properties such as.

The content of the fiber in the solid content of the slurry is preferably 0.1% by mass or more and 70% by mass or less. By setting the pulp content in the above range, the ability to suppress the outflow of CNF can be further enhanced and the dehydration efficiency can be further enhanced.

In the pressurizing step, it is preferable to increase the pressing force stepwise or continuously while dehydrating the slurry. Since the slurry of CNF has thixotropic property and the fluidity increases with pressurization, the fluidity of the slurry increases when a strong pressure is applied, and the outflow of CNF tends to occur easily. Therefore, by gradually increasing the pressing force while dehydrating the slurry in this way, dehydration can be performed while suppressing the fluidity, so that the outflow of CNF can be further suppressed.

Here, the "cellulose nanofiber" refers to a fine cellulose fiber obtained by defibrating a plant raw material such as pulp and having a fiber width of nano size (1 nm or more and 1000 nm or less).

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a method for producing a cellulose nanofiber molded product capable of efficiently dehydrating while suppressing the outflow of cellulose nanofibers.

It is explanatory drawing which shows the apparatus used in the manufacturing method of the cellulose nanofiber which concerns on one Embodiment of this invention.

Hereinafter, a method for manufacturing a CNF molded article according to an embodiment of the present invention will be described in detail with reference to the drawings as appropriate.

The method for producing a CNF molded product includes a step of dehydrating a slurry containing CNF via a mesh-like member. FIG. 1 is a schematic explanatory view showing a state of an example of the dehydration step. First, the apparatus, raw materials, and the like used in the manufacturing method will be described with reference to FIG.

(Equipment, raw materials, etc.)
The formwork 11 of FIG. 1 has a rectangular parallelepiped inner surface shape. Further, the formwork 11 is a frame without a bottom. The material of the formwork 11 is not particularly limited, and examples thereof include metal, resin, and wood, but metal is preferable from the viewpoint of durability against high pressure and the like.

The formwork 11 is placed, for example, on a horizontal table (not shown) having a flat upper surface. The table on which the formwork 11 is placed is not particularly limited as long as it has a strength that can withstand the pressure during the dehydration process, and a general metal, wooden, resin, or the like may be used. can. Further, at least the upper surface side of this table may be mesh-like, mesh-like, porous-like, or the like so that drainage can be efficiently performed.

Paper 13 is laid on the bottom of the formwork 11 (that is, the upper surface of the table (not shown) in the formwork 11). The paper 13 is not particularly limited to Japanese paper, Western paper, paperboard and the like, and known papers can be used. Further, the paper 13 may be one sheet or two or more sheets may be laminated.

The lower limit of the thickness of the paper 13 is, for example, 0.05 mm, preferably 0.1 mm. By setting the thickness of the paper 13 to the above lower limit or more, more sufficient cushioning property can be ensured, and the CNF outflow suppressing function by alleviating the sudden pressure increase in the dehydration step can be enhanced. On the other hand, the upper limit of this thickness is, for example, 2 mm. The thickness of the paper 13 means the thickness of the entire plurality of sheets in the laminated state when a plurality of sheets of paper are laminated and used.

Further, by laying the paper 13, the moisture in the filled slurry 15 described later is transferred to the paper 13 through the mesh sheet 14, so that the dehydration efficiency can be improved. When the thickness of the paper 13 is at least the above upper limit, the amount of water transferred to the paper 13 returns to the molded product after the pressure is released, so that the efficiency of dehydration is lowered. From the viewpoint of both cushioning and dehydration, the paper 13 preferably has a low density. Further, from the viewpoint of dehydration, it is preferable that the paper 13 has a low size. From this point of view, filter paper can be preferably used as the paper 13.

A mesh-like sheet 14, which is an example of a mesh-like member, is laminated on the upper surface of the paper 13. The material of the mesh-like sheet 14 is not particularly limited, and may be metal, resin, or other fibrous material. That is, the mesh-like sheet 14 may be a wire mesh, a plastic wire, a filter cloth (woven cloth, non-woven fabric, etc.) or the like. The shape of the mesh of the mesh-like sheet 14 is not particularly limited, and may be any of plain weave, twill weave, twill weave, twill weave and the like.

As the lower limit of the number of meshes of the mesh-shaped sheet 14, 100 mesh is preferable, and 200 mesh is more preferable. By setting it to the above lower limit or more, it is possible to suppress the outflow of CNF at the time of filling before pressurization. Further, even if it is equal to or more than the above lower limit, if the number of stitches is large, the speed of pressurizing stepwise becomes slow, so that 200 mesh or more is more efficient. On the other hand, as the upper limit of the number of stitches, 500 mesh is preferable, and 400 mesh is more preferable. By setting it to the above upper limit or less, sufficient opening can be ensured and the efficiency of dehydration can be improved. However, even if it is less than the upper limit, dehydration becomes slow and it becomes difficult to perform stepwise pressurization control, so 400 mesh or less is more preferable.

The lower limit of the wire diameter of the mesh sheet 14 is preferably 25 μm, more preferably 30 μm. On the other hand, the upper limit of the wire diameter is preferably 100 μm, more preferably 50 μm. By setting the wire diameter of the mesh-shaped sheet 14 to the above lower limit or more, it is possible to secure an appropriately small opening size, and it is possible to further suppress the outflow of CNF in the dehydration step. On the other hand, by setting the wire diameter of the mesh-shaped sheet 14 to be equal to or less than the above upper limit, it is possible to prevent the opening size from becoming too small and perform more efficient dehydration.

As described above, the CNF slurry 15 is filled in the mold 11 in which the paper 13 and the mesh sheet 14 are sequentially laminated on the bottom. The slurry 15 contains a CNF, a fiber having a longer fiber length or a larger fiber diameter than the CNF and hydrogen-bondable to the CNF, and water as a dispersion medium, and may further contain other components.

CNF can usually be obtained by defibrating a plant raw material (fiber raw material) by a known method. The raw material of this CNF is not particularly limited as long as it is a plant raw material, but pulp is preferable.

Examples of the pulp used as a raw material for CNF include broadleaf bleached kraft pulp (LBKP), hardwood bleached kraft pulp (LUKP) and other broadleaf kraft pulp (LKP), softwood bleached kraft pulp (NBKP), and softwood unbleached kraft pulp (NUKP). ) And other softwood craft pulp (NKP) and other chemical pulp;
Stone Grand Pulp (SGP), Pressurized Stone Grand Pulp (PGW), Refiner Grand Pulp (RGP), Chemi Grand Pulp (CGP), Thermo Grand Pulp (TGP), Grand Pulp (GP), Thermo Mechanical Pulp (TMP), Mechanical pulp such as Chemi-Thermo Mechanical Pulp (CTMP), Bleached Thermo-Mechanical Pulp (BTMP);
Used paper pulp manufactured from used tea paper, kraft envelope used paper, magazine used paper, newspaper used paper, leaflet used paper, office used paper, cardboard used paper, upper white used paper, Kent used paper, imitation used paper, ground ticket used paper, sashimi used paper, etc.;
Examples thereof include deinked pulp (DIP) obtained by deinking used paper pulp. These may be used alone or in combination of a plurality of types as long as the effects of the present invention are not impaired.

Among these, as the pulp used as a raw material for CNF, chemical pulp is preferable, and LKP and NKP are more preferable, from the viewpoint that a high-strength molded product can be obtained.

The method for producing CNF is not particularly limited as long as the effect of the present invention is not impaired, and a known method can be used. For example, the pulp in a water-dispersed state may be subjected to defibration by mechanical treatment, or may be subjected to chemical treatment such as enzyme treatment, acid treatment, TEMPO-catalyzed oxidation, and phosphorylation, and then subjected to defibration. ..

Examples of the defibration method by mechanical treatment include a grinder method in which pulp is ground between rotating grindstones, a counter-collision method using a high-pressure homogenizer, and a crushing method using a ball mill, a roll mill, a cutter mill, and the like.

The pulp used as a raw material for CNF may be subjected to preliminary beating before defibration. The pre-beating (mechanical pretreatment) is not particularly limited, and a known method can be used. As an example of a specific method, for example, a method using a refiner can be mentioned.

Further, the pulp which is the raw material of CNF may be chemically pretreated before defibration. Examples of this chemical pretreatment include a hydrolysis treatment using an acid such as sulfuric acid, an enzyme or the like, and an oxidation treatment using an oxidizing agent such as ozone. By performing the defibration treatment after the chemical pretreatment in this way, CNF can be efficiently obtained. Further, as a pretreatment, a treatment such as oxidation using a TEMPO catalyst or the like or phosphoric acid esterification may be performed.

The water retention level of CNF is, for example, 250% or more and 500% or less. Since dehydration is inefficient for CNF having such a high degree of water retention, there is a great advantage in using the production method capable of effectively dehydrating. The water retention rate (%) of CNF is JAPAN TAPPI No. Measured according to 26.

The CNF preferably has a single peak in the pseudo-particle size distribution curve measured by laser diffraction in an aqueous dispersion. As described above, the CNF having one peak has been sufficiently miniaturized, can exhibit good physical properties as a CNF, and can further increase the strength of the obtained molded body. The particle size (mode) of the CNF that becomes the single peak is preferably, for example, 5 μm or more and 50 μm or less. When the CNF has the above size, various characteristics peculiar to the CNF can be exhibited better. The "pseudo particle size distribution curve" means a curve showing a volume-based particle size distribution measured using a particle size distribution measuring device (for example, a particle size distribution measuring device "LA-960S" manufactured by HORIBA, Ltd.).

The content of CNF in the slurry 15 to be subjected to the dehydration step is preferably more than 0.8% by mass, more preferably 1% by mass or more, still more preferably 1.5% by mass or more. By setting the CNF content in the slurry to more than 0.8% by mass, the outflow of CNF in the dehydration step can be more sufficiently suppressed. In addition, the time required for the dehydration step can be shortened. Further, when the CNF content is 0.8% by mass or less, the fluidity is high even without pressurization, and CNF may flow out from the mesh-like sheet during filling, but the content should be more than 0.8% by mass. Therefore, such an inconvenience can be eliminated. On the other hand, the upper limit of the CNF content is, for example, 10% by mass, 5% by mass, 4% by mass, or 3% by mass. By setting the CNF content in the slurry 15 to the above upper limit or less, good fluidity can be ensured and the filling property into the mold 11 can be improved. Further, by setting the CNF content to the above upper limit or less, unevenness in thickness and density can be suppressed, and a highly uniform molded product can be obtained.

The lower limit of the content of CNF in the solid content of the slurry 15 may be, for example, 30% by mass, preferably 50% by mass, 70% by mass, or 90% by mass. , 95% by mass, or 99% by mass. By setting the content of CNF in the solid content in the slurry 15 to the above lower limit or more, the content ratio of CNF in the obtained molded product can be increased, and the strength of the obtained molded product can be increased. On the other hand, the upper limit of the content of CNF may be 99.9% by mass, 90% by mass, 70% by mass, or 50% by mass.

The slurry 15 further contains fibers having a longer fiber length or a larger fiber diameter than the CNF and capable of hydrogen bonding with the CNF. By containing such fibers in the slurry 15, the surface of the fibers and the CNF interact with each other, and the outflow of the CNF can be suppressed. Therefore, the outflow of CNF is suppressed, and efficient dehydration can be performed.

Examples of such fibers include pulp, cotton fiber, silk fiber, hemp, wool, animal hair, rayon fiber, cupra fiber and the like, but pulp is preferable. Like CNF, pulp contains cellulose as a main component and has a high affinity with CNF. Therefore, by using pulp as the fiber, the outflow of CNF can be suppressed more effectively. Further, by adding pulp, the pulp becomes a core material, and a molded product having excellent strength may be obtained. The fiber diameter of the pulp is usually more than 1 μm, preferably 10 μm or more.

As the pulp, LKP and NKP are preferable. It is also preferable to use pulp, which is a raw material of CNF, as the fiber. For example, it is preferable to use a combination of CNF and LKP made of LKP as a raw material, or a combination of CNF and NKP made of NKP as a raw material. By using the pulp which is the raw material of CNF in this way, the affinity between CNF and pulp is further enhanced, and the outflow of CNF can be further suppressed. However, the raw material pulp of CNF and the pulp mixed with CNF may be different types.

The pulp may be unbeaten pulp or beaten pulp. By using unbeaten pulp, dehydration efficiency can be improved. On the other hand, by using the beaten pulp, the CNF is easily entangled, the outflow of the CNF can be further suppressed, and the strength of the molded product obtained by increasing the hydrogen bond points can be increased.

The lower limit of the content of the fiber in the solid content of the slurry 15 is preferably 0.1% by mass, more preferably 1% by mass, still more preferably 3% by mass. By setting the content of the fiber to the above lower limit or more, the function of suppressing the outflow of CNF can be enhanced and the dehydration efficiency can be enhanced. On the other hand, the upper limit of this content is, for example, 70% by mass, preferably 50% by mass, more preferably 30% by mass, and may be 10% by mass. By setting the content of the fiber to the above upper limit or less, the strength of the obtained molded product can be increased.

The slurry 15 may further contain CNF and solids other than the above fibers as long as the effects of the present invention are not affected. However, the upper limit of the content of the other solid content in the solid content of the slurry 15 is preferably 10% by mass, more preferably 3% by mass, still more preferably 1% by mass. When the content of other solids is not more than the above upper limit, the strength, thermal stability, etc. of the obtained molded product can be enhanced.

A plate-shaped lid 16 is laminated on the slurry 15 filled in the mold 11. The length and width of the lid 16 are substantially the same as or one size smaller than the inner dimensions of the mold 11. The slurry 15 is substantially sealed in a space composed of a lid 16, a formwork 11, and a table (not shown) on which the formwork 11 is placed. That is, it is the outer surface shape of the molded body from which the upper surface of the table and the inner surface shapes of the mold 11 and the lid 16 can be obtained.

The material of the lid 16 is not particularly limited, and examples thereof include metal, resin, and wood, but metal is preferable from the viewpoint of durability against high pressure and the like. The material of the lid 16 may be the same as or different from the material of the mold 11.

(Preparation process)
The manufacturing method may have a preparatory step of preparing the state of FIG. 1 before performing the dehydration step. This preparatory step is a step of laminating the paper 13 and the mesh sheet 14 in order on the bottom of the mold 11 placed on the table so as to be in the state of FIG. 1, and filling the slurry 15 on the paper 13 and the mesh sheet 14 in order. .. Further, the lid 16 is arranged on the slurry 15 after filling. As will be described later, if dehydration starts at the stage where the slurry 15 is filled, the lid 16 does not have to be placed on the slurry 15 at this timing.

Further, the production method may have a slurry preparation step containing CNF as a preparatory step, or may have a mixing step of CNF and the fiber.

(Dehydration process)
Hereinafter, the procedure of the dehydration process will be described in detail. In this dehydration step, it is preferable to increase the pressing force on the slurry 15 stepwise or continuously. In this dehydration step, the water in the slurry 15 flows out from the bottom (lower side in FIG. 1) of the mold 11 via the mesh sheet 14 and the paper 13.

The dehydration step preferably first has an initial step of pressurizing at 2.5 kPa or less. When a pressure exceeding 2.5 kPa is initially applied, CNF tends to flow out through the mesh sheet 14. If the mesh-like sheet 14 having a fine opening is used, the outflow of CNF can be suppressed even if a pressure exceeding 2.5 kPa is applied at the initial stage, but in this case, the overall dehydration efficiency may be lowered. The pressurization in this initial step may be substantially 0 kPa or atmospheric pressure. Further, the pressure may be applied only by the weight of the lid body 16. For example, when water flows out through the mesh sheet 14 (when dehydration starts) when the CNF 15 is charged (filled) into the mold 11 via the paper 13 and the mesh sheet 14, in this state. After leaving it for a while, the lid 16 can be placed on the slurry 15 when the outflow of water has subsided.

It is preferable to increase the pressing force after dehydration has progressed to some extent by the pressurization in the initial step. The method for controlling the pressing force is not particularly limited, and may be controlled by a known press machine, or may be performed by placing a weight on the lid body 16. Further, the pressing force may be increased according to the progress of dehydration (dehydration amount), or the relationship between the composition of the slurry 15 and the pressing force may be stored in a database and the pressing force may be controlled according to the time. good.

In the dehydration step, it is preferable to increase the pressing force in this way and pressurize at 20 MPa or more, more preferably 30 MPa or more, still more preferably 40 MPa or more as the final step. By going through this final step, a sufficiently dehydrated CNF molded product can be obtained. The upper limit of the pressing force in this final step can be, for example, 200 MPa, or 100 MPa.

(Post-process)
After the dehydration step, further dehydration may be performed. Examples of further dehydration include a method of taking out the obtained molded product (dehydrated slurry 15) from the mold 11 and pressing it with a press while heating, a method of drying with a dryer, and the like. Among these, the method of pressing while heating is preferable. This makes it possible to further increase the density and strength of the CNF molded product.

(Advantages, etc.)
According to the production method, in addition to the CNF, a fiber having a longer fiber length or a larger fiber diameter than the CNF and capable of hydrogen-bonding to the CNF is added to the slurry in this way to obtain the fiber surface. It can interact with CNF and suppress the outflow of CNF. Therefore, in the manufacturing method, the outflow of CNF is suppressed even if dehydration is performed at a relatively high pressure, and efficient dehydration can be performed.

Further, by increasing the pressing force while dehydrating in the dehydration step, the initial pressure is very weak, so that the slurry is maintained at a high viscosity and the outflow of CNF can be suppressed. As dehydration progresses, the concentration of the slurry increases and the fluidity decreases, so it becomes difficult for CNF to flow out even if the pressure is increased to some extent. Dehydration can be performed. When the pressing force is increased stepwise, the number of steps is not particularly limited, and may be two or more steps. The upper limit of the number of stages is not particularly limited, and control may be performed in 100 stages, in 10 stages, or in 3 stages. Further, when the pressing force is continuously increased, it is not necessary to increase the pressing force at a constant ratio, and there may be a time when the pressing force is held at a constant pressing force.

By filling the mold 11 with the slurry and performing dehydration as in the present embodiment, it is possible to easily perform molding into a desired shape together with dehydration. In the present embodiment, a rectangular parallelepiped molded product can be obtained.

Further, as in the present embodiment, since the paper 13 is laminated on the outside of the mesh-shaped sheet 14 (under the mesh-shaped sheet 14), the cushioning property when the pressure is changed is enhanced, and the pressure changes suddenly. Is relaxed. As a result, the pressure can be gradually increased, so that the outflow of CNF can be further suppressed. Further, since the water content in the slurry 15 is transferred to the paper through the mesh sheet 14, the dehydration efficiency can be improved. The outside of the mesh-like sheet 14 (mesh-like member) is the side where the water in the slurry 15 flows out in the mesh-like sheet 14 (mesh-like member), and the slurry 15 of the mesh-like sheet 14 (mesh-like member) is formed. The side opposite to the contacting side.

(Other embodiments)
The present invention is not limited to the above embodiment, and can be implemented in various modifications and improvements in addition to the above embodiment. For example, the mesh-like member is not limited to the sheet shape, and at least a part of the formwork may be a mesh-like member, or the lid may be a mesh-like member. Further, unlike FIG. 1, the paper 13 and the mesh-like sheet 14 may be laminated in order on a table, and the formwork 11 may be placed on the stack.

Further, the shape of the formwork is not limited to the rectangular parallelepiped, and may be any shape. The formwork may have a bottom plate. If the formwork has a bottom plate, the formwork may be provided with a drain for dehydration. In this case, it is preferable to arrange the mesh-like member so as to cover the drainage port. Further, in this case, it is preferable to arrange the paper between the formwork and the mesh-like member. By doing so, the cushioning property is enhanced, the sudden pressure change is alleviated, and the dehydration efficiency by paper can be enhanced.

Further, in the above embodiment, the dehydration step is performed without particularly heating or the like, but dehydration (pressurization) can also be performed while heating. By performing the dehydration step without heating as in the above embodiment, dehydration can be efficiently performed at low cost until the water content reaches a certain level. After dehydration does not proceed only by pressurization, dehydration can be performed efficiently in terms of time, energy, and cost by performing dehydration while heating as a post-process.

Further, in the production method, it is not necessary to increase the pressing force on the slurry stepwise or continuously in the dehydration step. Even if dehydration is performed at a constant pressure in this way, since the fibers are added to the slurry containing CNF, efficient dehydration can be performed while suppressing the outflow of CNF.

Further, unlike FIG. 1, a second mesh-like sheet is laminated on the upper surface of the slurry 15, a second paper is laminated on the upper surface of the second mesh-like sheet, and a lid is attached to the upper surface of the second paper. The body 16 may be placed. By laminating paper on the upper surface side of the slurry 15 in this way (the state of sandwiching the slurry 15 with a pair of papers), the cushioning property is further enhanced and the CNF flows out due to pressurization. Can be further suppressed. Further, the paper may be laminated only on the upper surface side of the slurry 15. The second mesh-like sheet laminated on the upper side plays a role of preventing the slurry 15 and the second paper from coming into direct contact with each other. That is, since the CNF molded body and the paper have a high affinity, when the slurry and the paper are pressed in direct contact with each other and dehydrated, the paper sticks to the obtained CNF molded body and the paper is peeled off. Becomes difficult. Therefore, by laminating a mesh-like sheet between the slurry and the paper, the paper or the like can be easily peeled off from the obtained CNF molded product. Further, since the water content in the slurry is transferred to the paper through the mesh-like member, the dehydration efficiency can be improved.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

<Evaluation method>
The following various physical properties were measured according to the following evaluation method.

(Pseudo particle size distribution curve)
In accordance with ISO-13320 (2009), a curve showing a volume-based particle size distribution was measured using a particle size distribution measuring device (HORIBA, Ltd. particle size distribution measuring device "LA-960S").

(Water retention (%))
The water retention rate (%) of the cellulose nanofibers is determined by JAPAN TAPPI No. Measured according to 26: 2000.

[Manufacturing Example 1]
The raw material pulp (LBKP) was refined as a preliminary beat and then defibrated (miniaturized) with a high-pressure homogenizer to obtain a CNF slurry (aqueous dispersion: concentration 2.2% by mass). In both the refiner treatment and the high-pressure homogenizer treatment, the circulation treatment was performed a plurality of times. The CNF contained in the obtained slurry had one peak in the pseudo particle size distribution of the particle size distribution measurement using laser diffraction (mode 45 μm), and the water retention degree was 343%.

[Comparative Example 1]
Paper 13 was laid on the bottom of the rectangular metal mold 11 shown in FIG. 1, and then a mesh-like sheet 14 was laid. Both the paper 13 and the mesh-shaped sheet 14 were used in the same size as the bottom surface of the mold 11. As the paper 13, a filter paper having a thickness of 0.28 mm was used. As the mesh-shaped sheet, a sheet made of SUS316 having a mesh number of 300 meshes and a wire diameter of 40 μm was used.

Next, the CNF slurry obtained in Production Example 1 is filled in the mold 11 as it is, and a mesh sheet, paper and a metal plate-shaped lid 16 (bottom area 0.067 m ² , mass 8) are placed thereon. .0 kg) was placed in this order. The mesh-like sheet and paper stacked on the slurry are the same as the previously laid mesh-like sheet and paper. Due to the weight of the lid 16, the slurry 15 was pressurized at 1.2 kPa and water began to flow out from the bottom (dehydration was started). It was visually confirmed that this water was transparent and that CNF did not flow out. Pressurization by the weight of the lid 16 was set as the initial step.

After that, at the timing when the outflow of water weakened, a weight was placed on the lid 16 to increase the pressing force. Finally, the slurry 15 was pressurized at 50 MPa to complete the final step. The total dehydration time from the initial step to the final step was 180 minutes. As a result, a CNF molded product dehydrated to a water content of 54.2% by mass was obtained. It was visually confirmed that CNF did not flow out from the initial process to the final process.

[Example 1]
Example 1 was carried out in the same manner as in Comparative Example 1 except that a slurry having a solid content concentration of 2.3% by mass in which CNF and pulp were mixed at a mass ratio of 95: 5 was used as the slurry. As the pulp, unbeaten pulp (LBKP) having a concentration of 21.6% by mass and a freeness of 580 mL was used. The total dehydration time from the initial step to the final step was 90 minutes. It was visually confirmed that CNF did not flow out from the initial process to the final process.

[Example 2]
Example 2 was carried out in the same manner as in Comparative Example 1 except that a slurry having a solid content concentration of 2.7% by mass in which CNF and pulp were mixed at a mass ratio of 80:20 was used as the slurry. As the pulp, unbeaten pulp (LBKP) having a concentration of 21.6% by mass and a freeness of 580 mL was used. The total dehydration time from the initial step to the final step was 60 minutes. It was visually confirmed that CNF did not flow out from the initial process to the final process.

[Example 3]
Example 3 was carried out in the same manner as in Comparative Example 1 except that a slurry having a solid content concentration of 2.0% by mass in which CNF and pulp were mixed at a mass ratio of 80:20 was used as the slurry. As the pulp, beaten pulp (LBKP) having a concentration of 1.5% by mass and a freeness of 460 mL was used. The total dehydration time from the initial step to the final step was 75 minutes. It was visually confirmed that CNF did not flow out from the initial process to the final process.

[Comparative Example 2]
Comparative Example 2 was performed in the same manner as in Comparative Example 1 except that the weight was placed on the lid 16 and the initial step was performed at a pressing force of 2.6 kPa. Cloudy water spilled. It was confirmed that CNF was leaked.

[Comparative Example 3]
Comparative Example 3 was carried out in the same manner as in Comparative Example 1 except that the weight was placed on the lid 16 and the pressing force in the initial step was maintained as it was and the pressing force was not increased. Sufficient dehydration could not be performed.

A list of the above examples and comparative examples is shown in Table 1.

As shown in Table 1, it can be seen that by using a slurry in which pulp is added to CNF as in Examples 1 to 3, efficient dehydration can be performed without causing CNF to flow out. On the other hand, in Comparative Example 1, which has the same conditions as in Examples 1 to 3 except that pulp is not added, dehydration can be performed at a certain rate without causing CNF to flow out, but Example 1 The dehydration rate is slower than that of ~ 3. Further, in Comparative Example 2 in which no pulp was added and the pressure was high from the initial step, CNF outflow occurred, and in Comparative Example 3 in which pulp was not added and the pressure in the initial step remained, the dehydration was sufficient. Could not be done.

The method for producing a CNF molded product of the present invention can be suitably used for producing a CNF molded product having high strength. This CNF molded body is excellent in strength, elasticity, thermal stability, etc., and can be used as a material or the like as an alternative to a metal molded body, a resin molded body, wood, or the like.

11 Formwork 13 Paper 14 Mesh sheet 15 Slurry 16 Closure

Claims (3)

A step of dehydrating a slurry containing cellulose nanofibers via a mesh-like member is provided.
The slurry contains fibers having a longer fiber length or a larger fiber diameter than the cellulose nanofibers and capable of hydrogen bonding with the cellulose nanofibers.
The cellulose nanofibers have a single peak in the pseudo particle size distribution curve measured by a laser diffraction method in a water-dispersed state, and the particle size of the cellulose nanofibers having the single peak is 5 μm or more and 50 μm or less.
The fibers are hardwood kraft pulp and / or softwood kraft pulp.
The content of the cellulose nanofibers in the solid content of the slurry is 70% by mass or more, and the content is 70% by mass or more.
A method for producing a cellulose nanofiber molded product in which the content of the fibers in the solid content of the slurry is 3% by mass or more and 30% by mass or less. The method for producing a cellulose nanofiber molded product according to claim 1, wherein the pulp is unbeaten pulp. The method for producing a cellulose nanofiber molded product according to claim 1 or 2, wherein the pressing force on the slurry is gradually or continuously increased in the dehydration step.

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