JP7099840B2 - 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 CNF molded product from a CNF slurry, it is necessary to dehydrate and dry the slurry. As a method for obtaining a CNF molded product from the CNF slurry as described above, a method of filling a mold with a CNF-containing slurry and applying a load to perform hot pressing has been proposed (see JP-A-2016-94683). ..

Japanese Unexamined Patent Publication No. 2016-94683

However, when an attempt is made to form a molded body using cellulose nanofibers as a raw material, the conventional molding method as described in Patent Document 1 is a so-called batch type manufacturing means, so that the productivity is low and the energy cost is high. .. Further, in the case of the above-mentioned conventional molding method, it is not possible to obtain a cellulose nanofiber molded body having sufficient mechanical properties, which realizes the high performance originally possessed by the cellulose nanofibers.

The present invention has been made based on the above circumstances, and an object thereof is a manufacturing method capable of obtaining a cellulose nanofiber molded body having sufficient mechanical properties with high productivity and low energy. To provide.

The invention made to solve the above problems is a laminate having a cellulose nanofiber layer containing cellulose nanofibers, pulp fibers and water, and a dehydrated substrate laminated on at least one surface of the cellulose nanofiber layer. A method for producing a cellulose nanofiber molded product, which comprises a laminating step of obtaining the above-mentioned laminate, a dehydration step of dehydrating the laminate by pressurizing it in the laminating direction, and a drying step of drying the laminate with substantially no pressure. be.

According to this production method, it is possible to obtain a cellulose nanofiber molded product having sufficient mechanical properties with high productivity and low energy, and particularly having high tensile strength and tensile elastic modulus. The reason for this is not clear, but by providing a dehydrated base material on at least one surface of the cellulose nanofiber layer containing cellulose nanofibers, pulp fibers and water, the outflow of the cellulose nanofibers is controlled and the cellulose nanofibers are combined with the cellulose nanofibers. The synergistic effect with the pulp fiber facilitates the formation of the cellulose nanofiber layer, and the cohesive force of the cellulose nanofiber itself forms a network-like tissue layer of the pulp fiber and the cellulose nanofiber, which improves dehydration in the next step. Improves quick-drying in the drying process, achieves high productivity and low energy, and in particular, by heating in the drying process and drying with virtually no pressure, cellulose nanofiber molding is performed by the behavior of the cellulose nanofiber itself. It is presumed that it is possible to uniformly increase the density of the body and obtain a cellulose nanofiber molded body having particularly high tensile strength. In addition, by heating and drying without pressurization, the strain generated during pressurization in the previous step is eliminated, and a dense hydrogen bond network between celluloses can be formed in a stable state. Guessed. In particular, when a sheet, which is a relatively thin molded body, is molded, the unevenness in the thickness and density of the cellulose nanofiber layer caused by the surface shape of the dehydrated base material becomes relatively large after dehydration. Therefore, when the molded product (sheet) is dried while being pressurized, unevenness in thickness and density remains even in the obtained molded product (sheet), and this unevenness tends to cause a portion having weak strength. On the other hand, it is presumed that the alleviation of unevenness in thickness and density by drying with substantially no pressure is also a factor in enhancing the mechanical properties of the obtained cellulose nanofiber molded product. ..

Further, when the raw material is produced only of cellulose nanofibers, a cellulose nanofiber molded body having excellent mechanical properties can be obtained, but there is a problem that enormous energy is required to remove the water content of the cellulose nanofibers. On the other hand, according to the findings of the inventors, by adding the pulp fiber together with the cellulose nanofiber, the dehydration efficiency can be increased and the energy for removing water can be reduced while maintaining the mechanical properties. On the other hand, in a cellulose nanofiber molded body made of a raw material containing cellulose nanofibers and pulp fiber, the mechanical properties of the cellulose nanofiber molded body may be deteriorated due to the influence of the voids of the pulp fiber itself. At the time of heat-drying, it may be necessary to perform heat-drying while applying a sufficient pressure to crush the voids of the pulp fiber, for example, a necessary pressure using a press machine or the like. However, as a result of diligent studies on this, a cellulose nanofiber molded product having a higher elastic modulus than that when dried while being sufficiently pressurized can be obtained by using a drying method that is substantially non-pressurized during drying. It was found that it can be obtained. By drying in a substantially non-pressurized state, the strain of the cellulose nanofibers and pulp fibers accumulated in the cellulose nanofiber layer due to external factors such as pressurization during dehydration is eliminated, and the state is stable. It is speculated that a dense hydrogen bond network between celluloses may have been formed.

The content of the pulp fibers in the total of the cellulose nanofibers and the pulp fibers in the cellulose nanofiber layer of the laminate in the laminating step is preferably 0.1% by mass or more and 70% by mass or less. Further, it is preferable that the content of the pulp fiber in the total of the cellulose nanofiber and the pulp fiber in the cellulose nanofiber layer of the laminate in the laminating step is less than 50% by mass. By setting the content ratio of pulp fibers as such, it is possible to obtain a cellulose nanofiber molded product having higher productivity, lower energy, and better mechanical properties.

In the laminating step, it is preferable that the laminated body further includes a water-absorbing base material to be laminated on the surface opposite to the cellulose nanofiber layer of the dehydrated base material. By arranging such a water-absorbing base material, moisture is transferred to the water-absorbing base material during the dehydration step, so that the dehydration efficiency is increased and the productivity can be increased.

It is preferable that the laminating step includes a step of applying a slurry containing cellulose nanofibers and pulp fibers to the surface of the dehydrated substrate. By performing such coating, the cellulose nanofiber layer can be efficiently formed, and dehydration of the cellulose nanofiber layer can be started at the same time as the coating, so that the productivity can be improved.

It is preferable that the manufacturing method further includes a step of peeling off the dehydrated substrate after the drying step. Thereby, a cellulose nanofiber molded body having only a cellulose nanofiber layer can be obtained. In addition, the dehydrated substrate that has been peeled off can be reused.

It is preferable that the manufacturing method further includes a step of winding up the cellulose nanofiber layer after the peeling step. By doing so, a long cellulose nanofiber molded product can be continuously produced.

Here, the "cellulose nanofiber" refers to a fine cellulose fiber obtained by defibrating a plant raw material such as pulp fiber and having a fiber width of nano size (1 nm or more and 1000 nm or less). The "pulp fiber" is a fiber obtained by defibrating a plant raw material and having a fiber width of more than 1 μm. Further, "substantially no pressurization" means a state in which the cellulose nanofiber layer is not substantially compressed, and is a degree in which a tubular dryer (drum) is brought into contact with a tubular dryer (drum) with felt or a cambus for drying. Is also included.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a production method capable of obtaining a cellulose nanofiber molded product having sufficient mechanical properties with high productivity and low energy.

FIG. 1A is an explanatory diagram showing a coating process in the method for producing a cellulose nanofiber molded product according to an embodiment of the present invention, and FIG. 1B is an explanatory diagram showing a laminating process. 1 (c) is an explanatory diagram showing a dehydration step, FIG. 1 (d) is an explanatory diagram showing a drying step, and FIG. 1 (e) is an explanatory diagram showing a peeling step.

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 manufacturing the CNF molded product is as follows.
(1) A laminating step of obtaining a laminate having a CNF layer containing CNF, pulp fibers and water, and a dehydrated base material laminated on at least one surface of the CNF layer.
(2) A dehydration step of dehydrating the laminate by pressurizing it in the stacking direction, and (3) a drying step of drying the laminate with substantially no pressure are provided in this order.

Further, the manufacturing method is performed after the above (3) drying step.
It is preferable to provide (4) a peeling step for peeling the dehydrated substrate and (5) a winding step for winding the CNF layer in this order. The manufacturing method may further include steps other than these steps. Hereinafter, the manufacturing method will be described in detail in the order of the above steps.

(1) Step of obtaining a laminated body The step of obtaining a laminated body is
(1-1) A coating process in which a slurry containing CNF and pulp fibers is applied to the surface of the dehydrated base material, and (1-2) The dehydrated base material coated with the above slurry is further coated with another base material. It is preferable to include a substrate laminating step of laminating.

(1-1) Coating process and raw materials, etc. In the coating process, as shown in FIG. 1A, a slurry containing CNF and pulp fibers is applied to the surface (one surface) of the first dehydrated substrate 11a. This is the process of construction. By coating this slurry, a CNF layer 12 containing CNF, pulp fibers and water is formed on the surface of the first dehydrated base material 11a.

The first dehydrated base material 11a is a base material made of a material having dehydration and drainage properties. As the first dehydrated base material 11a, a mesh-shaped sheet can be used. Further, the first dehydrated base material 11a may be a porous body. The material of the first dehydrated base material 11a is not particularly limited, and may be a metal, a resin, or other fibrous material. That is, the first dehydrated base material 11a 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 first dehydrated base material 11a is not particularly limited, and may be any of plain weave, twill weave, twill weave, twill weave and the like.

When the first dehydrated substrate 11a is in the form of a mesh, 120 mesh is preferable and 200 mesh is more preferable as the lower limit of the number of meshes. By setting it to the above lower limit or more, it is possible to suppress the outflow of the applied CNF. 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.

When the first dehydrated substrate 11a has a mesh shape, the lower limit of the wire diameter 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 first dehydrated base material 11a to be equal to or greater than the above lower limit, it is possible to secure an appropriately small opening size and suppress the outflow of CNF in the dehydration step. On the other hand, by setting the wire diameter of the first dehydration base material 11a 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 the first dehydrated base material 11a before coating the slurry, it is preferable to use one that is substantially dry. As a result, the water content in the slurry is transferred to the first dehydration base material 11a at the same time as the coating, so that the dehydration efficiency is improved.

The slurry contains CNF, pulp fibers and water as a dispersion medium. As the dispersion medium, a liquid other than water may be used in combination.

(CNF)
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 fiber is preferable.

Examples of the pulp fiber used as a raw material for CNF include broad-leaved bleached kraft pulp (LKP) such as broad-leaved bleached kraft pulp (LBKP) and broad-leaved unbleached kraft pulp (LUKP), coniferous bleached kraft pulp (NBKP), and coniferous unbleached kraft pulp (NBKP). Chemical pulp such as coniferous kraft pulp (NKP) such as NUKP);
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 fiber 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 water-dispersed pulp 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 fiber 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 fiber used as a 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. 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 further enhances the elastic modulus, strength, etc. of the obtained molded product. Can be done. 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 used in the coating step is preferably more than 0.8% by mass, more preferably 1% by mass or more, further preferably 1.5% by mass or more, still more preferably 3% by mass or more. .. By setting the CNF content in this slurry to more than 0.8% by mass, efficient dehydration and drying in the subsequent process becomes possible. On the other hand, the upper limit of the CNF content is, for example, 20% by mass, 15% by mass, 10% by mass, or 5% by mass. By setting the CNF content in this slurry to the above upper limit or less, good coatability can be imparted.

The lower limit of the content of CNF in the solid content of the slurry may be, for example, 30% by mass, preferably 50% by mass, 70% by mass, or 80% by mass. .. By setting the CNF content in the solid content in the slurry to be at least the above lower limit, the CNF content ratio 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 CNF content may be 99.9% by mass, 90% by mass, or 80% by mass.

(Pulp fiber)
While the production cost of pulp fiber is lower than that of CNF, the mechanical properties of pulp fiber do not significantly deteriorate even when mixed with CNF. Therefore, by incorporating the pulp fiber together with CNF in the slurry (CNF layer 12), it is possible to suppress the production cost while maintaining sufficient mechanical characteristics. In addition, by using pulp fiber together, efficient dehydration becomes possible, so that productivity can be increased and energy can be reduced. The fiber width of the pulp fiber is usually preferably 5 μm or more, more preferably 10 μm or more.

As the pulp fiber, LKP and NKP are preferable. It is also preferable to use pulp fiber which is a raw material of CNF. For example, using a combination of CNF and LKP made from LKP or using a combination of CNF and NKP made from NKP increases the affinity between the two by using the same starting material, and dehydration occurs. It is preferable to suppress the outflow of CNF at the time of pressurization, which leads to shortening of the total dehydration time, and to obtain a molded body having a desired shape. By using the pulp fiber which is the raw material of CNF in this way, the affinity between CNF and the pulp fiber is further enhanced, and the outflow of CNF can be further suppressed. However, the raw material pulp of CNF and the pulp fiber mixed with CNF may be different types.

The pulp fiber 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 freeness of unbeaten pulp can be, for example, 550 mL or more. The upper limit of the freeness of this unbeaten pulp is not particularly limited, but it can be, for example, 800 mL or 750 mL.

The lower limit of the content of pulp fiber in the total of CNF and pulp fiber in the slurry, that is, the content of pulp fiber in the total of CNF and pulp fiber in the CNF layer 12 of the laminate in the laminating step is 0. .1% by mass is preferable, 1% by mass is more preferable, 3% by mass, 5% by mass, 10% by mass, or 20% by mass may be used. By setting the content of the pulp fiber to the above lower limit or more, the production cost can be suppressed, the productivity can be sufficiently increased, and the energy can be further reduced. On the other hand, as the upper limit of the content of the pulp fiber, 70% by mass is preferable, 50% by mass is more preferable, and 30% by mass is further preferable. Further, the content of the pulp fiber is preferably less than 50% by mass. By setting the content of the pulp fiber to the above upper limit or less, the voids in the obtained molded product are reduced, and the mechanical properties of the molded product can be further improved.

The slurry, that is, the CNF layer 12, may also contain fibers other than CNF and pulp fibers. As such a fiber, a fiber other than a pulp fiber, which has a longer fiber length or a larger fiber diameter than the CNF and can hydrogen bond with the CNF, is preferable. By containing such fibers in the slurry, the surface of the fibers and CNF interact with each other, and the outflow of CNF can be suppressed. Therefore, the outflow of CNF is suppressed, and efficient dehydration can be performed.

Examples of such fibers include cotton fibers, silk fibers, hemp, wool, animal hair, rayon fibers, cupra fibers and the like. In addition, glass fiber, carbon fiber, metal fiber and the like can also be used. By using these fibers, it is possible to increase the strength of the obtained cellulose nanofiber molded product and to add other functions.

The slurry may further contain CNF, pulp fibers and other 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 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, elastic modulus, thermal stability and the like of the obtained molded product can be enhanced.

The lower limit of the solid content concentration (content of components other than the dispersion medium) of the slurry is preferably 0.7% by mass, more preferably 1% by mass, further preferably 2% by mass, still more preferably 3% by mass. .. The upper limit of the water content is preferably 10% by mass, more preferably 7% by mass, and even more preferably 5% by mass. By setting the solid content concentration in the above range, coatability, drying efficiency and the like can be improved in a well-balanced manner.

The coating of the slurry can be carried out by a known method. The coating can be performed by, for example, blade coating, curtain coating, spray coating or the like. As the lower limit of the coating amount of the slurry, the solid content is preferably 5 g / m ² , more preferably 10 g / m ² , further preferably 20 g / m ² , and even more preferably 40 g / m ² . By setting the coating amount to the above lower limit or more, a molded product having more sufficient mechanical properties can be obtained. On the other hand, the upper limit of the coating amount is preferably 1,000 g / m ² , more preferably 500 g / m ² , further preferably 400 g / m ² , and even more preferably 200 g / m ² . By setting the coating amount to the above upper limit or less, a thin film molded body having sufficient mechanical properties, that is, a sheet can be obtained, and the handleability and the like are improved. Further, when the coating amount is not more than the above upper limit, the effect of the present invention that the strength is increased by drying with substantially no pressure is more fully exhibited.

(1-2) Substrate Laminating Step The laminating step is a step of laminating another base material on the dehydrated base material coated with the above slurry. Specifically, as shown in FIG. 1 (b), the first dehydrating group is obtained with respect to the laminated body having the two-layer structure of the first dehydrating base material 11a and the CNF layer 12 obtained in the coating step. The first water-absorbing base material 13a is laminated on the outer surface of the material 11a (lower surface in FIG. 1 (b)), and the second dehydrated base material 11b is laminated on the outer surface of the CNF layer 12 (upper surface in FIG. 1 (b)). Further, the second water-absorbing base material 13b is laminated on the outer surface (upper surface in FIG. 1B) of the second dehydrated base material 11b. These laminations can be performed by sequentially laminating each base material or the like.

It is preferable that the first water-absorbing base material 13a, the second dehydrated base material 11b, and the second water-absorbing base material 13b are substantially dried before stacking. As a result, at the same time as laminating each base material, the water content mainly in the CNF layer 12 is effectively transferred to each base material, so that efficient dehydration can be performed.

By this base material laminating step, as shown in FIG. 1 (b), the first water-absorbing base material 13a, the first dehydrated base material 11a, the CNF layer 12, the second dehydrated base material 11b and the second water-absorbing group. A laminated body 14 having a five-layer structure in which the materials 13b are laminated in this order is obtained. In other words, the laminate 14 is the CNF layer 12, the first dehydrated base material 11a laminated on one surface of the CNF layer 12 (lower surface in FIG. 1B), and the other of the CNF layer 12. The second dehydrated base material 11b laminated on the surface (upper surface in FIG. 1 (b)) and the surface of the first dehydrated base material 11a opposite to the CNF layer 12 (lower surface in FIG. 1 (b)). The first water-absorbing base material 13a to be laminated and the second water-absorbing base material 13b laminated on the surface (upper surface in FIG. 1B) opposite to the CNF layer 12 of the second dehydrated base material 11b. Has.

As the second dehydrated base material 11b, the same one as the above-mentioned first dehydrated base material 11a can be used. By arranging the first dehydration base material 11a and the second dehydration base material 11b (hereinafter, collectively referred to as simply "dehydration base material") on both surfaces of the CNF layer 12, a dehydration step and a drying step are performed. In, the water in the CNF layer 12 can flow out and volatilize from each dehydrated base material, and effective dehydration and drying can be performed.

As the first water-absorbing base material 13a and the second water-absorbing base material 13b (hereinafter, collectively referred to as simply "water-absorbing base material"), a sheet having water absorption can be used. By arranging the water-absorbing base material on the outside of each dehydrated base material, the moisture in the CNF layer 12 and the dehydrated base material can be effectively transferred to the water-absorbing base material, and the CNF layer 12 can be efficiently dehydrated and dried. It can be performed.

Examples of the water-absorbent base material include cloth and paper, but paper is preferable. The paper is not particularly limited to Japanese paper, Western paper, paperboard and the like. Considering water absorption, filter paper can be preferably used. The paper as the water-absorbing base material may be one sheet or two or more sheets may be laminated. On the other hand, when a cloth is used, a cloth containing synthetic resin fiber having a hydrophilic group, cotton fiber, silk fiber, linen, wool, animal hair, rayon fiber, cupra fiber and the like is preferable in consideration of water absorption. Examples of the hydrophilic group include a hydroxy group, a carboxy group, an amino group and the like.

The lower limit of the thickness of the water-absorbent base material is, for example, 0.05 mm, preferably 0.1 mm. By setting the thickness of the water-absorbing base material to the above lower limit or more, more sufficient water absorption can be ensured and the dehydration efficiency can be improved. On the other hand, the upper limit of this thickness is, for example, 2 mm.

The coating process and the base material laminating process do not have to be performed in this exact order. For example, the first dehydrated base material 11a may be laminated on the upper surface of the first water absorbing base material 13a, and the CNF slurry may be applied on the upper surface of the first dehydrated base material 11a to laminate the CNF layer 12. Then, the second dehydrated base material 11b and the second water-absorbing base material 13b, which have been laminated in advance, may be laminated together on the upper surface of the CNF layer 12. Regardless of the order, it suffices to obtain the laminated body 14 having a five-layer structure in the step of obtaining the laminated body.

(2) Dehydration Step As shown in FIG. 1 (c), the dehydration step is a step of dehydrating the laminated body 14 by pressurizing it in the stacking direction (vertical direction in FIG. 1 (c)). By this pressurization, the water content in the CNF layer 12 is transferred to the dehydrated base material and the water-absorbing base material, and the water content in the CNF layer 12 and other base materials is squeezed out of the laminate 14, thereby dehydrating. Will be done.

This pressurization can be performed by a known method. For example, it can be performed by a press machine such as a hydraulic press machine, a pneumatic press machine, a universal press machine, a screw press machine, and a roll press machine. If, for example, a roll press machine is used, it is possible to continuously dehydrate the long laminated body 14.

The lower limit of the pressing force in this dehydration step is preferably 0.1 MPa, more preferably 0.2 MPa, still more preferably 0.5 MPa, still more preferably 1 MPa, still more preferably 2 MPa. On the other hand, the upper limit of this pressing force is preferably 200 MPa, more preferably 100 MPa, further preferably 50 MPa, still more preferably 20 MPa, still more preferably 10 MPa, still more preferably 5 MPa. In the dehydration step, the pressing force may be gradually increased or the constant pressure may be maintained from the beginning. For example, by using a press machine such as a hydraulic press machine, the pressing force can be gradually increased. Although this dehydration step is usually performed without heating, it may be performed while heating.

As the lower limit of the treatment time in this dehydration step, 1 minute is preferable, and 3 minutes is more preferable. On the other hand, the upper limit of this processing time is preferably 30 minutes, more preferably 10 minutes.

(3) Drying Step As shown in FIG. 1D, the drying step is a step of drying the laminate 14 that has undergone the dehydration step in a substantially non-pressurized state. As a result, the laminated body 14, and thus the CNF layer 12, is dried.

This drying method is not particularly limited and may be natural drying or warm air drying, but drying is performed by bringing the laminated body 14 into contact with a heated tubular dryer (drum) using felt, cambus or the like. , It is preferable to use a paper-making dryer. By adopting such a drying method, continuous drying can be performed on the long laminated body 14.

The lower limit of the heating temperature in the drying step is preferably 100 ° C, more preferably 110 ° C. On the other hand, as the upper limit of this heating temperature, 190 ° C. is preferable, and 180 ° C. is more preferable. In addition, this heating temperature can be set to the surface temperature of the dryer when drying is performed by contacting with a cylindrical dryer. Further, when drying is performed by contacting with a rotating tubular dryer, the transport speed of the laminated body 14 can be, for example, 0.01 m / min or more and 100 m / min or less.

During this drying step, the pressure applied to the laminate 14 is substantially zero. Specifically, the upper limit of the pressure applied to the laminated body 14 during this drying step is preferably 100 kPa. The lower limit of this pressure may be 0 kPa.

By performing the drying step in the state of the laminated body 14 in which the dehydrated base material and the water-absorbing base material are laminated in this way, there is an advantage that the dried dehydrated base material and the water-absorbing base material can be used immediately again. Further, when the heated dryer is brought into direct contact with the CNF layer 12, the heat of the dryer is transferred to the CNF layer 12 at once, the moisture evaporates at once, and there is no escape route for steam, so that the steam penetrates the inside of the CNF layer 12. And it is released to the outside. Therefore, holes may easily occur in the obtained CNF molded product. On the other hand, the presence of a dehydrating base material or a water-absorbing base material between the dryer and the CNF layer 12 gradually transfers heat to the CNF layer 12 and secures an escape route for steam, so that holes are generated. It is possible to obtain a CNF molded product that is suppressed and has high strength.

(4) Peeling step In the peeling step, the dehydrated base material (first dehydrated base material 11a and the second dehydrated base material 11b) and the water-absorbing base material (first water-absorbing base material) are removed from the laminated body 14 that has undergone the drying step. The 13a and the second water-absorbing base material 13b) are peeled off. As a result, the dried CNF layer 12 remains, which becomes the target CNF molded product 15.

The peeled dehydrated substrate can be used repeatedly. The peeled water-absorbent base material may be used repeatedly, but if the water-absorbent base material is paper or the like, a new one may be used once or multiple times. Further, at the time of peeling, the first dehydrated base material 11a and the first water-absorbing base material 13a, and the second dehydrated base material 11b and the second water-absorbing base material 13b may be peeled together. By doing so, the laminated body of the dried dehydrated base material and the water-absorbing base material can be used as it is in the step of obtaining the laminated body, and the production efficiency is improved.

(5) Winding Step When the CNF molded body 15 to be manufactured has a long strip shape, it is preferable to provide this winding step. In the winding step, the CNF layer 12 (CNF molded body 15) that has undergone the peeling step is wound by a reel or the like. As a result, the long CNF molded body 15 can be continuously manufactured, and the CNF molded body 15 wound in a roll shape can be obtained.

The lower limit of the length of the long CNF molded product is, for example, 10 m, and may be 50 m, 100 m, or 200 m. The upper limit of this length is not particularly limited and may be, for example, 10,000 m, 1,000 m or 200 m per roll.

(Advantages, etc.)
According to the production method, a CNF molded product having high tensile strength and the like can be obtained by dehydrating by pressurization and then drying with substantially no pressurization. Further, the CNF molded product obtained by the manufacturing method has a high elastic modulus. Further, the CNF molded product maintains high strength and elastic modulus even in a high temperature environment. That is, the CNF molded product maintains good physical properties even in a high temperature environment. Further, according to the manufacturing method, the molded product can be manufactured with low energy by increasing the productivity by drying with substantially no pressure.

The lower limit of the tensile strength of the CNF molded product obtained by the production method at 23 ° C. is preferably 20 MPa, more preferably 22 MPa. On the other hand, the upper limit is, for example, 30 MPa and may be 26 MPa.

Further, as the lower limit of the elastic modulus of the CNF molded product obtained by the production method at 23 ° C., 3.8 GPa is preferable, and 4.0 GPa is more preferable. On the other hand, the upper limit is, for example, 10.0 GPa and may be 5.0 GPa.

The lower limit of the average thickness of the CNF molded product obtained by the production method is, for example, 5 μm, preferably 10 μm, further preferably 20 μm, and even more preferably 40 μm. When the average thickness of the CNF molded product is at least the above lower limit, more excellent strength can be exhibited. On the other hand, as the upper limit of this average thickness, 1,000 μm is preferable, 500 μm is more preferable, 400 μm is further preferable, and 200 μm may be further preferable. When the average thickness of the CNF molded product is not more than the above upper limit, workability, handleability and the like can be improved.

(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, in the above embodiment, the dehydration base material and the water absorption base material are laminated on both sides of the CNF layer, but these may be laminated only on one surface side of the CNF layer. However, by laminating the dehydration base material and the water absorption base material on both sides, more efficient dehydration and drying can be performed.

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.

(Tension modulus (GPa))
The tensile modulus of elasticity of the CNF molded product was measured according to JIS K7127: 1999. The test piece had a tension type 2 dumbbell shape defined by JIS-K6251. The test speed was 10 mm / min. Further, the measurement was carried out in an environment where the temperature was 23 ° C. or 90 ° C. and the humidity was 50%.

(Tensile strength (MPa))
The tensile strength of the CNF molded product was measured according to JIS K7127: 1999. The test piece had a tension type 2 dumbbell shape defined by JIS-K6251. The test speed was 10 mm / min. Further, the measurement was carried out in an environment where the temperature was 23 ° C. or 90 ° C. and the humidity was 50%.

[Manufacturing Example 1]
The raw material pulp (LBKP) was refined as a preliminary beating, and then defibrated (miniaturized) with a high-pressure homogenizer to obtain an aqueous dispersion of CNF. 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 aqueous dispersion of CNF 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%. Pulp fiber (LBKP) was added to the aqueous dispersion of CNF so that the dry mass ratio of CNF and pulp fiber (LBKP) was 80:20, and the mixture was stirred until the pulp fiber was uniformly dispersed. Then, after concentrating using a centrifuge (Hitachi Centrifuge "himac CR22N"), water was added and stirred to prepare the solid content concentration to 5% by mass. As a result, a slurry to be used in the coating process was obtained.

[Example 1]
(Coating process)
A mesh-like sheet made of SUS316 having a mesh number of 300 mesh and a wire diameter of 40 μm was prepared as the first dehydrating base material. The slurry obtained in Production Example 1 was applied to the surface of the first dehydrated substrate to form a CNF layer. The coating amount was 100 g / m ² (in terms of solid content).

(Base material laminating process)
Next, dried paper as the first water-absorbing base material was laminated on the back surface of the first dehydrated base material. As this paper, a filter paper having a thickness of 0.28 mm was used. Next, the second dehydrated base material was laminated on the surface of the CNF layer, and the second water-absorbing base material was laminated on the surface of the second dehydrated base material. As the second dehydrated substrate, the same one as that of the first dehydrated substrate was used. As the second water-absorbing base material, the same one as the first water-absorbing base material was used. As a result, a laminated body having a five-layer structure similar to that in FIG. 1 (b) was obtained.

(Dehydration process)
The obtained laminate was set in a general-purpose press machine. Then, this laminated body was dehydrated by pressurizing it in the laminating direction at a pressure of 2.6 MPa for 5 minutes.

(Drying process)
Next, the laminate was dried by a dryer (Kumaya Riki Kogyo Co., Ltd.'s high-temperature rotary dryer "2575-II"). The surface temperature of the drum of the dryer was 120 ° C., and the transport speed was 0.7 m / min.

(Peeling process)
By peeling each dehydrated base material and water-absorbing base material from the laminate that had undergone the drying step, the dried CNF molded product of Example 1 was obtained. The average thickness of the obtained CNF molded product was about 100 μm.

[Comparative Example 1]
A CNF molded product of Comparative Example 1 was obtained in the same manner as in Example 1 except that the drying step was performed by pressurizing at a temperature of 120 ° C. and a pressure of 2.6 MPa for 5 minutes using a hot press. ..

Table 1 shows the tensile elastic modulus (23 ° C. and 90 ° C.) and the tensile strength (23 ° C. and 90 ° C.) of the obtained CNF molded product.

As shown in Table 1, it can be seen that according to the manufacturing method of the example, a CNF molded product having high tensile strength and tensile elastic modulus can be obtained. Further, it can be seen that the CNF molded product obtained by the production method of the example has a small decrease in tensile strength and tensile elastic modulus even at 90 ° C.

The method for producing a CNF molded body of the present invention can be suitably used as a method for producing a CNF molded body that can replace a resin molded body, a metal molded body, paper, or the like.

11a First dehydration base material 11b Second dehydration base material 12 CNF layer 13a First water absorption base material 13b Second water absorption base material 14 Laminated body 15 CNF molded body

Claims (4)

Laminating step of obtaining a laminate having a cellulose nanofiber layer containing cellulose nanofibers, pulp fibers and water, and a dehydrated base material laminated on at least one surface of the cellulose nanofiber layer.
A dehydration step of dehydrating the laminate by pressurizing it in the stacking direction and a drying step of drying the laminate with substantially no pressure are provided in this order.
The cellulose nanofibers have a single peak in the pseudo particle size distribution curve measured by the laser diffraction method in an aqueous dispersion state, and the cellulose nanofibers having the single peak have a particle size of 5 μm or more and 50 μm or less. A method for manufacturing a nanofiber molded body. The first aspect of claim 1, wherein the content of the pulp fiber in the total of the cellulose nanofiber and the pulp fiber in the cellulose nanofiber layer of the laminate in the laminating step is 0.1% by mass or more and 70% by mass or less. Method for manufacturing cellulose nanofiber molded product. Claim 1 or claim that the content of the pulp fiber in the total of the cellulose nanofiber and the pulp fiber in the cellulose nanofiber layer of the laminate in the laminating step is 0.1% by mass or more and less than 50% by mass. Item 2. The method for producing a cellulose nanofiber molded body according to Item 2. The invention according to any one of claims 1 to 3, wherein in the laminating step, the laminated body further includes a water-absorbing base material laminated on a surface opposite to the cellulose nanofiber layer of the dehydrated base material. A method for manufacturing a cellulose nanofiber molded body.

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