JP2019157294A - Method for producing cellulose nanofiber molded body - Google Patents

Abstract

To provide a production method capable of obtaining a cellulose nanofiber molded body having a high elastic modulus.SOLUTION: A cellulose nanofiber molded body manufacturing method of this invention comprises a first pressurizing step for pressurizing a cellulose nanofiber hydrated body containing cellulose nanofibers and water without heating, and a second pressurizing step for pressurizing the cellulose nanofiber hydrated body in this order, in which the first pressurization step and the second pressurization step are continuously performed without depressurization between the first pressurization step and the second pressurization step. The pressurization in the first pressurization step and the second pressurization step is preferably performed on the cellulose nanofiber hydrated body in the mold using a hot press.SELECTED DRAWING: Figure 1

Description

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

  In recent years, nanotechnology that aims to refine materials to the nanometer level and obtain new physical properties that are different from conventional properties of materials has attracted attention. Cellulose nanofibers (hereinafter sometimes abbreviated as “CNF”) produced from pulp that is a cellulosic material by chemical treatment, pulverization treatment, etc. are excellent in strength, elasticity, thermal stability, and the like. The CNF compact is expected to be used in various applications as a biomass-derived high-strength material.

  CNF is usually obtained by refining water-dispersed pulp or the like. Therefore, when it is intended to obtain a CNF compact from a CNF slurry (CNF hydrous), it is necessary to dehydrate and mold the slurry. As a method for obtaining a CNF compact by dehydrating a CNF slurry as described above, a method of filling a CNF-containing slurry in a mold and applying a load to heat press has been proposed (Japanese Patent Laid-Open No. 2006-94683). reference).

Japanese Patent Laid-Open No. 2006-94683

  When a CNF molded body is obtained from a CNF hydrate, if the CNF hydrate is pressure dehydrated in a mold and then heated as it is or if it is heated simultaneously with pressure dehydration, extra energy is required to heat the mold It becomes. For this reason, it is considered that it is preferable to take out the CNF water-containing body subjected to pressure dehydration from the mold and perform pressure drying together with heating on the taken-out CNF water-containing body. However, the inventors have found that this method cannot obtain a CNF compact having a sufficiently high elastic modulus.

  This invention is made | formed based on the above situations, The objective is to provide the manufacturing method which can obtain a cellulose nanofiber molded object with a high elasticity modulus.

  The invention made in order to solve the above problems includes a first pressurizing step of pressurizing a cellulose nanofiber hydrate containing cellulose nanofiber and water without heating, and pressurizing the hydrated cellulose nanofiber while heating. Cellulose nano comprising the second pressurization step in this order and continuously performing the first pressurization step and the second pressurization step without depressurization between the first pressurization step and the second pressurization step. It is a manufacturing method of a fiber molded object.

  According to the said manufacturing method, a cellulose nanofiber molded object with a high elasticity modulus can be obtained. The reason for this is not clear, but by continuously performing without depressurization between the first pressurizing step of pressurizing without heating and the second pressurizing step of pressurizing while heating, It is presumed that a dense hydrogen bond network is formed, which increases the elastic modulus. Further, in the first pressurizing step, the moisture content is reduced only by pressurization without heating, and the cellulose is obtained by heating and pressurizing in the second pressurizing step while maintaining the pressurized state, that is, the cellulose is in a dense state. It can be presumed that obtaining a cellulose nanofiber molded body in which dense hydrogen bonds are formed is a factor for increasing the elastic modulus of the molded body.

  The pressurization in the first pressurization step and the second pressurization step is preferably performed using a hot press machine on the cellulose nanofiber hydrated body in the mold. By doing in this way, the molded object with a desired shape and a high elastic modulus can be obtained efficiently.

  The manufacturing method further includes a preliminary dehydration step of dehydrating the cellulose nanofiber hydrated body via the mesh-like member before the first pressurization step, and in the preliminary dehydration step, the addition in the first pressurization step is performed. It is preferable to pressurize the cellulose nanofiber hydrate with a pressure smaller than the pressure. By providing such a preliminary dehydration step, it is possible to efficiently perform preliminary dehydration while suppressing the outflow of cellulose nanofibers.

  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 nanosize (1 nm to 1000 nm).

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method which can obtain a cellulose nanofiber molded object with a high elasticity modulus can be provided.

FIG. 1 is a flow diagram of a method for producing a cellulose nanofiber shaped product according to an embodiment of the present invention. FIG. 2 is an explanatory view showing an apparatus and the like used for a preliminary dehydration step in the method for producing a cellulose nanofiber molded body of FIG.

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

The method for producing the CNF compact is as follows:
A first pressurizing step for pressurizing the CNF hydrous body containing CNF and water without heating, and a second pressurizing step for pressurizing the CNF hydrous body while heating are provided in this order.

  It is preferable that the manufacturing method of the said CNF molded object is further equipped with the preliminary | backup dehydration process which spin-dry | dehydrates a CNF hydrated body through the member which has water permeability, for example, a mesh-shaped member, before a 1st pressurization process. That is, as shown in FIG. 1, according to the manufacturing method, the CNF hydrated body is used, and the first pressurization step and the second pressurization step are performed. A CNF molded object can be obtained through a 2nd pressurization process. In the manufacturing method, the pressurizing process may be further divided into a plurality of stages, and may further include other processes other than these processes. Hereinafter, taking the means through the preliminary dehydration step, the first pressurization step and the second pressurization step as an example, the production method will be described in detail in the order of the above steps.

(Equipment, raw materials, etc. in preliminary dehydration process)
FIG. 2 is a schematic explanatory view showing an example of the preliminary dehydration step. First, the apparatus and raw materials used in the preliminary dehydration step will be described with reference to FIG.

  The form 11 of FIG. 2 is not limited in shape, but preferably has a rectangular parallelepiped inner surface shape in order to obtain versatility of the obtained molded body and uniform dehydration of the CNF-hydrated body. Moreover, the frame 11 preferably has a bottomless frame as appropriate. The material of the mold 11 is not particularly limited, and examples thereof include metals, resins, and wood. From the viewpoints of thermal conductivity, durability, and the like considering pressurization while heating, the metal is preferable.

  For example, the mold 11 is placed on a horizontal base (not shown) having a flat upper surface. The platform on which the mold 11 is placed is not particularly limited as long as it is strong enough to withstand pressurization, and a common metal, wooden, resin, or the like can be used. Further, at least the upper surface side of the table is made of a water-permeable material so that drainage can be efficiently performed, and may be, for example, a net shape, a mesh shape, or a porous shape.

  For example, paper 13 is laid as a water-permeable material on the bottom of the mold 11 (that is, the upper surface of a table (not shown) in the mold 11). By laminating the paper 13 in this way, the cushioning property is enhanced, the sudden pressure change is alleviated, and the pressure can be gradually increased, so that the outflow of CNF can be further suppressed. The paper 13 that is suitably employed is not particularly limited, such as Japanese paper, western paper, paperboard, and the like, and a paper having a known water permeability can be used. Further, the paper 13 may be a single sheet or a stack of two or more sheets.

  The lower limit of the thickness of the paper 13 is, for example, 0.05 mm, and preferably 0.1 mm. By setting the thickness of the paper 13 to be equal to or more than the above lower limit, more sufficient cushioning properties can be ensured, and the CNF outflow suppression function can be enhanced by alleviating the rapid pressure increase in the preliminary dehydration step. On the other hand, the upper limit of the thickness is 2 mm, for example. It should be noted that the thickness of the paper 13 refers to the thickness of the entire plurality of sheets in a stacked state when a plurality of sheets are stacked.

  In addition, since the paper 13 is laid, moisture in a filled CNF-containing body 15 to be described later moves to the paper 13 through the mesh sheet 14, so that the dehydration efficiency can be improved. In addition, when the thickness of the paper 13 is equal to or more than the above upper limit, the amount of moisture transferred to the paper 13 returns to the CNF water-containing body (molded body) after releasing the pressure, so that the efficiency of dehydration is reduced. . In addition, it is preferable that the paper 13 has a low density from the viewpoints of both cushioning properties and dehydrating properties. Further, from the viewpoint of dewaterability, the paper 13 preferably has a low size. From this point of view, filter paper can be suitably used as the paper 13.

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

  As a minimum of the mesh number of the mesh-like sheet | seat 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. Moreover, since the speed | rate which pressurizes in steps will become slow if the number of eyes is large even if it is more than the said minimum, 200 mesh or more is more efficient. On the other hand, the upper limit of the number of meshes is preferably 500 mesh, more preferably 400 mesh. By setting it to the upper limit or less, a sufficient opening can be secured and the efficiency of dehydration can be improved. However, 400 mesh or less is more preferable because dehydration becomes slow even if the upper limit is not reached, and stepwise pressurization control becomes difficult.

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

  Thus, the CNF hydrate 15 is filled into the mold 11 in which the paper 13 and the mesh-like sheet 14 are sequentially laminated on the bottom. The CNF hydrate 15 is a slurry containing CNF and water as a dispersion medium, and may further contain other components.

  CNF can be usually obtained by fibrillating plant raw materials (fiber raw materials) by a known method. Although the raw material of this CNF will not be specifically limited if it is a plant raw material, A pulp is preferable.

Examples of pulp used as a raw material for CNF include hardwood kraft pulp (LKP) such as hardwood bleached kraft pulp (LBKP), hardwood unbleached kraft pulp (LUKP), softwood bleached kraft pulp (NBKP), and softwood unbleached kraft pulp (NUKP). ) Chemical pulp such as conifer kraft pulp (NKP);
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-thermomechanical pulp (CTMP) and bleached thermomechanical pulp (BTMP);
Waste paper pulp made from tea waste paper, craft envelope waste paper, magazine waste paper, newspaper waste paper, leaflet waste paper, office waste paper, corrugated waste paper, Kami white waste paper, Kent waste paper, imitation waste paper, lottery waste paper, waste paper waste paper, etc .;
Examples include deinked pulp (DIP) obtained by deinking waste paper pulp. These may be used singly or may be used in combination of plural kinds as long as the effects of the present invention are not impaired.

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

  The method for producing CNF is not particularly limited as long as the effects of the present invention are not impaired, and a known method can be used. For example, water-dispersed pulp may be subjected to defibration by mechanical treatment, or may be subjected to defibration after chemical treatment such as enzyme treatment, acid treatment, TEMPO catalytic oxidation, and phosphoric acid esterification. .

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

  The defibrating method by the mechanical treatment is preferably performed by a high-pressure homogenizer. By treating the pulp fibers with a high-pressure homogenizer, the pulp fibers collide with each other, and defibration occurs effectively. Thereby, the frequency | count of a process can be reduced and the productivity of a cellulose nanofiber can be improved more.

  The high-pressure homogenizer is a counter-collision type high-pressure homogenizer, and at this time, it is preferable that the slurry containing pulp fibers collide with each other on a straight line. By doing in this way, the energy given from a high pressure homogenizer can be converted into collision energy to the maximum, and more efficient pulp fiber defibration occurs. From the cellulose nanofibers thus obtained, a CNF molded article having a high elastic modulus, which is a problem of the present invention, can be obtained compared to other defibrating means, although the reason is not clear.

  In addition, you may attach | subject the pulp used as the raw material of CNF to pre-beating before defibration. Pre-beating (mechanical pretreatment) is not particularly limited, and a known method can be used. Specific examples of the method include a method using a refiner.

  Moreover, you may perform a chemical pre-process before the fiber opening to the pulp used as the raw material of CNF. Examples of the chemical pretreatment include hydrolysis treatment using an acid such as sulfuric acid, an enzyme, etc., and an oxidation treatment using an oxidizing agent such as ozone. Thus, CNF can be obtained efficiently by performing the defibrating treatment after the chemical pretreatment. In addition, as pretreatment, treatment using a TEMPO catalyst or the like, or phosphoric esterification may be performed.

  The water retention of CNF is, for example, 250% or more and 500% or less. Since CNF having a high water retention rate is inefficient in dehydration, there is a great advantage in using this preliminary dehydration step that can effectively perform dehydration. The water retention degree (%) of CNF is JAPAN TAPPI No. 26 is measured.

  CNF preferably has a single peak in a pseudo particle size distribution curve measured by laser diffraction in a water dispersion state. Thus, the CNF having one peak has been sufficiently refined, can exhibit good physical properties as CNF, and can further increase the elastic modulus, strength, etc. of the obtained molded body, etc. Can do. In addition, as a particle size (mode) of CNF used as the said single peak, 5 micrometers or more and 50 micrometers or less are preferable, for example. When CNF is the said size, various characteristics peculiar to CNF can be exhibited more favorably. The “pseudo particle size distribution curve” means a curve indicating 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 CNF hydrate 15 subjected to the preliminary dehydration step is preferably more than 0.8% by mass, more preferably 1% by mass or more, and further preferably 1.5% by mass or more. By setting the CNF content in the CNF hydrated body to be more than 0.8% by mass, the outflow of CNF in the preliminary dehydration step can be more sufficiently suppressed. In addition, the time for the preliminary dehydration process can be shortened. Further, when the CNF content is 0.8% by mass or less, the fluidity is high even without pressure, and CNF may flow out from the mesh sheet at the time of filling, but the content is more than 0.8% by mass. Thus, such inconvenience can be solved. 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 content of CNF in the CNF hydrate 15 to be equal to or lower than the above upper limit, good fluidity can be ensured, and the filling property to the mold 11 can be improved. Moreover, by making the content of CNF not more than the above upper limit, unevenness in thickness and density can be suppressed, and a molded product with high uniformity can be obtained.

  The lower limit of the content of CNF in the solid content of the CNF hydrate 15 may be, for example, 30% by mass, preferably 50% by mass, 70% by mass, or 80% by mass. Also good. By setting the content of CNF in the solid content in the CNF water-containing body 15 to the above lower limit or more, the content ratio of CNF in the obtained molded body is increased, and the elastic modulus and the like of the obtained molded body 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.

  It is preferable that the CNF hydrate 15 includes a fibrous material other than CNF. As such a fibrous material, a fiber having a longer fiber length or a larger fiber diameter than CNF and capable of hydrogen bonding with CNF is preferable. By including such a fibrous material in the CNF hydrate 15, the fiber surface and CNF interact with each other, and the outflow of CNF can be suppressed. For this reason, the outflow of CNF is suppressed and efficient dehydration can be performed.

  Examples of such a fibrous material include pulps derived from herbs and woods, such as wood pulp, cotton fibers, silk fibers, hemp and wool, animal hair, rayon fibers, and cupra fibers. Pulp derived from the book, especially wood pulp, is preferred. Wood pulp is mainly composed of cellulose like CNF and has a high affinity for CNF. Therefore, the outflow of CNF can be more effectively suppressed by using pulp as the fibrous material. Moreover, wood pulp becomes a core material by adding wood pulp, and a molded article having excellent strength may be obtained. The fiber diameter of wood pulp is usually more than 1 μm, preferably 10 μm or more. Moreover, as a fibrous material other than CNF, glass fiber, carbon fiber, metal fiber, or the like can be used. By using these fibrous materials, it is possible to increase the strength of the obtained CNF molded body and to add other functions.

  As the wood pulp, LKP and NKP are preferable. In addition, it is also preferable to use the pulp which is the raw material of CNF as the said fiber. For example, it is possible to use CNF and LKP in combination with LKP as a raw material, or to use CNF and NKP in combination with NKP as a raw material by making the starting materials the same. It is preferable for obtaining a molded body having a desired shape while sometimes suppressing the outflow of CNF, leading to a reduction in total dehydration time. However, the raw material pulp of CNF and the pulp mixed with CNF may be different types.

  The pulp may be unbeaten pulp or may be beaten pulp. By using unbeaten pulp, dewatering efficiency can be increased. On the other hand, by using beaten pulp, CNF can be easily entangled and the outflow of CNF can be further suppressed, and the strength of the tensile modulus and the like of the molded product obtained by increasing the hydrogen bonding point can be increased. it can. Examples of the freeness of the unbeaten pulp include pulp exhibiting a freeness of 550 mL or more. Although the upper limit of the freeness of this unbeaten pulp is not specifically limited, For example, it can be set to 800 mL and can also be set to 750 mL.

  The lower limit of the content of the fiber in the solid content of the CNF hydrate 15 is preferably 0.1% by mass, more preferably 1% by mass, and even more preferably 3% by mass. By setting the fiber content to the above lower limit or more, the CNF outflow suppressing function can be enhanced, the dehydration efficiency can be increased, and the elastic modulus and the like of the obtained molded article can be improved. On the other hand, as an upper limit of this content, it is 70 mass%, for example, 50 mass% is preferable, and 30 mass% is more preferable. By setting the content of the fiber to the upper limit or less, the elastic modulus and the like of the obtained molded body can be increased.

  The CNF hydrate 15 may further contain other solids (components other than water) other than CNF and the fibrous material 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 CNF hydrate 15 is preferably 10% by mass, more preferably 3% by mass, and still more preferably 1% by mass. It is possible to increase the elastic modulus, strength, thermal stability, etc. of the molded product obtained when the content of other solids is not more than the above upper limit.

  The solid content concentration of the CNF hydrated body is 0.7 mass as the lower limit of the solid content concentration (content of components other than water) of the CNF hydrated body before pressurization, that is, before filling into the mold 11. % Is preferable, and 0.8% by mass is more preferable. Moreover, as an upper limit of this moisture content, 2.5 mass% is preferable and 2.2 mass% is more preferable. When the solid content concentration is lower than the lower limit, the viscosity of the CNF hydrated body becomes too small. Therefore, when the mold 11 is filled with the CNF hydrated body, the CNF hydrated body may flow out from the gap of the mold 11. It is not preferable. On the other hand, if the solid content concentration exceeds the above upper limit, the viscosity of the CNF hydrated body becomes too large. Therefore, when the CNF hydrated body is filled into the mold 11, the CNF hydrated body is not flattened by its own weight, This is not preferable because air is easily embraced.

  A plate-like lid body 16 is laminated on the CNF hydrate 15 filled in the mold 11. The length and width of the lid 16 are substantially the same as the inner dimensions of the mold 11 or slightly smaller. The CNF water-containing body 15 is substantially sealed in a space formed by the lid 16, the mold 11, and a table (not shown) on which the mold 11 is placed. That is, it becomes the outer surface shape of the molded body (plate body) from which the upper surface of the table and the inner surface shapes of the mold 11 and the lid body 16 are obtained.

  The material of the lid body 16 is not particularly limited, and examples thereof include metals, resins, and woods, but metals are preferable from the viewpoint of durability against high pressure. Note that 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 include a preparation step for preparing the state of FIG. 2 before performing the preliminary dehydration step. In this preparation step, the paper 13 and the mesh-like sheet 14 are sequentially laminated on the bottom of the mold 11 placed on the table so as to be in the state of FIG. 2, and the CNF water-containing body 15 is filled thereon. It is. Furthermore, the cover body 16 is arrange | positioned on the CNF hydrated body 15 after filling. As will be described later, when the dehydration starts at the stage when the CNF hydrate 15 is filled, the lid 16 may not be placed on the CNF hydrate 15 at this timing.

  Moreover, the said manufacturing method may have the preparation process of the CNF hydrated body (slurry) containing CNF as a preparatory process, and may have the mixing process of CNF and the said fiber.

(Preliminary dehydration process)
Hereinafter, the procedure of the pre-dehydration process preferable as a pre-process of the 1st pressurization process which pressurizes the CNF hydrated body which concerns on this invention without heating is explained in full detail. In this preliminary dehydration step, the CNF hydrated body 15 is pressurized without using a press machine or the like with dehydration due to its own weight or a relatively weak pressure. Furthermore, in this preliminary dehydration step, it is preferable to increase the pressure applied to the CNF water-containing body 15 stepwise or continuously. In this dehydration step, the water in the CNF hydrate 15 flows out from the bottom (lower side in FIG. 2) of the mold 11 via the mesh sheet 14 and the paper 13. In such a case, since the initial pressure is very weak, the CNF water-containing body 15 is maintained at a high viscosity, and the outflow of CNF can be suppressed. On the other hand, as the dehydration proceeds, the concentration of the CNF hydrate 15 increases and the fluidity decreases, so that it is difficult for CNF to flow out even if the pressure is increased to some extent. Thus, by gradually increasing the pressure, dehydration can be performed efficiently while suppressing the outflow of CNF.

  The preliminary dehydration step preferably has an initial step of applying pressure at 2.5 kPa or less. When a pressure exceeding 2.5 kPa is applied initially, CNF tends to flow out through the mesh sheet 14. In addition, if the mesh-like sheet | seat 14 with a fine mesh is used, even if it applies the pressure over 2.5 kPa initially, the outflow of CNF can be suppressed, However, In this case, the whole dehydration efficiency may fall. The pressurization in this initial step may be substantially 0 kPa or atmospheric pressure. Moreover, the pressurization by only the dead weight of the cover body 16 may be sufficient. For example, when water flows out through the mesh sheet 14 (when dehydration is started) when the CNF hydrate 15 is put (filled) into the formwork 11 through the paper 13 and the mesh sheet 14. In this state, the lid 16 can be placed on the CNF-containing body 15 when the outflow of water is settled for a while.

  It is preferable to increase the pressure 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 performed, for example, by placing a weight on the lid 16. Further, the applied pressure may be increased according to the degree of progress of dehydration (dehydrated amount), and the relationship between the composition of the CNF hydrate 15 and the applied pressure is stored in a database, and the applied pressure is controlled by time. May be.

  In the preliminary dehydration step, the pressure is increased in this way, and as a final step, pressurization is preferably performed at 4 kPa or more, more preferably 5 kPa or more, and further preferably 6 kPa or more. By passing through this final step, it is possible to obtain a CNF-containing body that has been sufficiently preliminary dehydrated. In addition, as an upper limit of the applied pressure of this last process, it can be set to 200 kPa, for example, 100 kPa may be sufficient, and 50 kPa may be sufficient.

  Unlike FIG. 2, a second mesh sheet is laminated on the upper surface of the CNF water-containing body 15, a second paper is laminated on the upper surface of the second mesh sheet, and the upper surface of the second paper. You may put the cover body 16 in. Thus, by stacking paper on the upper surface side with respect to the CNF hydrated body 15 (with the CNF hydrated body 15 sandwiched between a pair of papers), the cushioning property is further increased and the pressure is increased. The accompanying outflow of CNF can be further suppressed. Further, paper may be laminated only on the upper surface side with respect to the CNF hydrate 15. In addition, the 2nd mesh sheet | seat laminated | stacked on the upper side bears the role etc. which prevent the CNF hydrated body 15 and 2nd paper from contacting directly. That is, since CNF and paper have high affinity, when the CNF hydrated body and paper are pressed and dehydrated in direct contact, the paper sticks to the CNF, making it difficult to remove the paper. Therefore, by laminating a mesh sheet between the CNF-containing body and paper, the paper or the like can be easily peeled off from the finally obtained CNF molded body. Moreover, since the water | moisture content in a CNF hydrous body transfers to paper through a mesh-like sheet | seat, dehydration efficiency can also be improved.

(First pressurization process)
In the first pressurizing step, the CNF hydrate containing the preliminary dehydration step is pressurized without heating. The term “without heating” as used herein is in contrast to the second pressurizing step involving subsequent heating. For example, the processing temperature may be lower than 100 ° C., or the so-called normal temperature is exceeded. The processing temperature may be within a non-temperature range. This 1st pressurization process can be performed using the hot press machine which has a pair of heating plate, for example. When the force acts in the direction in which the distance between the pair of heating plates is narrowed, the CNF water-containing body is pressurized. In addition, since this 1st pressurization process does not involve what is called a heating, it is used without heating a heating plate. The hot press machine can control the heating temperature and the pressurizing pressure. The temperature control and pressure control by the hot press machine may be automatic control or manual control. Moreover, this heat press machine is not particularly limited, such as a hydraulic heat press machine, a pneumatic heat press machine, and a vise heat press machine.

  The CNF hydrated body that has undergone the preliminary dehydration step is subjected to the first pressurizing step while being filled in the mold. That is, the CNF hydrated body in the mold is pressurized by a hot press. Specifically, for example, when pressure is applied by weight in the final step of the preliminary dewatering step, the weight can be lowered and set in a hot press as shown in FIG. That is, for example, the CNF-containing body 15 is pressed in the vertical direction by a hot press while being filled with the mold 11 shown in FIG.

  Here, you may arrange | position the heat insulation board between the CNF hydrated body with which the formwork was filled, and the heating board of a hot press machine. In addition, you may arrange | position a heat insulation board so that a formwork and a CNF hydrated body may be covered. By doing in this way, in the 2nd pressurization process with a heating, the heating efficiency of the CNF hydrated body in a mold can be improved.

  In the first pressurizing step, the applied pressure may be gradually increased, or a constant pressure may be maintained from the beginning. When the pressure is gradually increased, the lower limit of the initial pressure in the first pressurizing step is preferably 0.1 MPa, and more preferably 0.2 MPa. The lower limit of the applied pressure at the final stage in the first pressurizing step or a constant pressure is preferably 1 MPa and more preferably 5 MPa. On the other hand, the upper limit of the applied pressure is preferably 200 MPa, more preferably 100 MPa, and even more preferably 30 MPa.

  As a minimum of processing time in the 1st pressurization process, 5 minutes are preferred and 15 minutes are more preferred. On the other hand, the upper limit of the treatment time is preferably 60 minutes, and more preferably 50 minutes.

  In the first pressurizing step, moisture flows out of the CNF hydrated body by pressurization. It is possible to proceed to the second pressurizing step as it is in a state where it is determined that the water has substantially come out at a predetermined pressure and time in the first pressurizing step without heating.

(Second pressure process)
In the 2nd pressurization process, it pressurizes, heating the CNF hydrated body which passed through the 1st pressurization process. It is important to continuously perform the first pressurization step and the second pressurization step without releasing the pressure between the first pressurization step and the second pressurization step. That is, from the first pressurizing step in which the CNF molded body in the mold is pressed without being heated by the hot press machine, the pair of heating plates of the hot press machine is heated while maintaining this pressurized state. Thus, it is possible to shift to the second pressurizing step. As a result, the CNF hydrated body is heated together with the mold, and the water in the CNF hydrated body is volatilized, whereby drying proceeds and a CNF molded body having a high elastic modulus and high strength can be obtained.

  As a minimum of processing temperature (heating temperature) in the 2nd pressurization process, 100 ° C is preferred and 110 ° C is more preferred. On the other hand, the upper limit of the treatment temperature is preferably 190 ° C and more preferably 180 ° C. Moreover, as a minimum of the processing time in a 2nd pressurization process, after reaching predetermined processing temperature, 1 minute is preferable, 5 minutes are more preferable, and 10 minutes are more preferable. On the other hand, the upper limit of this treatment time is preferably 60 minutes, more preferably 50 minutes, and even more preferably 30 minutes. By performing a 2nd pressurization process with the said processing temperature and processing time, the elasticity modulus and intensity | strength of the CNF molded object obtained can be raised more. In addition, this processing temperature (heating temperature) can be made into the temperature of a heating plate.

  The pressurizing force in the second pressurizing step may be the same as the pressurizing force in the first pressurizing step. Moreover, the pressurizing force in the second pressurizing step can be larger than the pressurizing force in the first pressurizing step. The applied pressure in the second pressurizing step is preferably constant at a predetermined temperature. As a minimum of pressurization pressure in the 2nd pressurization process, 0.1 MPa is preferred, 0.2 MPa is more preferred, 1 MPa is still more preferred, and 5 MPa is still more preferred. On the other hand, the upper limit of the applied pressure is preferably 200 MPa, more preferably 100 MPa, and even more preferably 30 MPa.

  The second pressurization step involving such heating and pressurization is performed, and the second pressurization step is completed when the water in the CNF-containing body is sufficiently volatilized and further drying does not proceed. can do. Thereby, a CNF molded object is obtained. In addition, you may provide additional processes, such as a cooling process and a humidity control process, after a 2nd pressurization process. In addition, the first pressurizing step and the second pressurizing step can be performed step by step by dividing the processing temperature, the applied pressure and the like into a plurality of steps.

(Advantages etc.)
According to the said manufacturing method, a CNF molded object with a high elastic modulus and tensile strength can be obtained by performing continuously between the 1st pressurization process and the 2nd pressurization process, without releasing pressure. For example, the elastic modulus at 23 ° C. of the CNF molded product obtained by the production method is 15 GPa or more, and may be 17 GPa or more. In addition, the upper limit of the elasticity modulus in 23 degreeC of the CNF molded object obtained by the said manufacturing method is 30 GPa, for example, and may be 25 GPa or 20 GPa.

  The shape of the CNF molded object obtained by the said manufacturing method is not specifically limited. The shape of the CNF molded body may be a plate shape, a rod shape, a sheet shape, or the like. The shape of a CNF molded object can be made into arbitrary shapes with the formwork to be used.

  Moreover, according to the said manufacturing method, since it pressurizes and heats with respect to the CNF hydrated body in a mold, the molded object as a mold can be obtained. Further, since the entire mold is heated, heating from the entire periphery is possible, and a molded body with high homogeneity can be obtained. Furthermore, according to the manufacturing method, preliminary dehydration can be efficiently performed while suppressing the outflow of CNF by performing the preliminary dehydration step of dehydrating the CNF-containing body through the mesh member.

(Other embodiments)
The present invention is not limited to the above-described embodiment, and can be implemented in a mode in which various changes and improvements are made in addition to the above-described mode. For example, the preliminary dehydration step may not be provided, and a preliminary dehydration step different from the above embodiment may be performed.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples.

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

(Pseudo particle size distribution curve)
Based on ISO-13320 (2009), the curve which shows a volume reference | standard particle size distribution was measured using the particle size distribution measuring apparatus (The particle size distribution measuring apparatus "LA-960S" of Horiba Seisakusho).

(Water retention (%))
The water retention (%) of the cellulose nanofiber is determined by JAPAN TAPPI No. 26: 2000.

(Tensile modulus (MPa))
The tensile elastic modulus of the CNF compact was measured according to JIS K7127: 1999. The test piece was a tensile No. 2 type dumbbell defined by JIS-K6251. The test speed was 10 mm / min. Moreover, it measured in the environment of temperature 23 degreeC or 90 degreeC, and humidity 50%.

(Tensile strength (MPa))
The tensile strength of the CNF compact was measured according to JIS K7127: 1999. The test piece was a tensile No. 2 type dumbbell defined by JIS-K6251. The test speed was 10 mm / min. Moreover, it measured in the environment of temperature 90 degreeC and humidity 50%.

[Production Example 1]
The raw pulp (LBKP) was subjected to a refiner treatment as a preliminary beating, followed by a defibration (miniaturization) treatment with a high-pressure homogenizer to obtain an aqueous dispersion of CNF. The refiner treatment and the high-pressure homogenizer treatment were both circulated a plurality of times. CNF contained in the obtained aqueous dispersion of CNF had one peak in the pseudo particle size distribution measured by laser diffraction (mode value 45 μm), and the water retention was 343%. Pulp (LBKP) was added to an aqueous dispersion of CNF so that the dry mass ratio of CNF and pulp (LBKP) was 80:20, and the mixture was stirred until the pulp was uniformly dispersed. This obtained the CNF hydrated body (solid content concentration 2.2 mass%).

[Example 1]
(Preparation process)
Paper 13 was laid on the bottom of a rectangular metal mold 11 shown in FIG. 2, and then a mesh sheet 14 was laid. Both the paper 13 and the mesh sheet 14 were used with the same size as the bottom surface of the mold 11. As the paper 13, a 0.28 mm thick filter paper was used. The mesh sheet used was made of SUS316 having a mesh size of 300 mesh and a wire diameter of 40 μm. Subsequently, the CNF hydrated body obtained in Production Example 1 is filled into the mold 11, and a mesh-like sheet, paper, and a metal plate-like lid 16 (bottom area 0.067 m ² , mass 8) are formed thereon. .0 kg) was placed in this order. The mesh sheet and paper stacked on the CNF-containing body are the same as the mesh sheet and paper laid on top.

(Preliminary dehydration process)
Due to the weight of the lid body 16 placed, the CNF water-containing body 15 was pressurized at 1.2 kPa, and water began to flow out from the bottom (dehydration was started). In addition, this water was transparent and it confirmed visually that CNF did not flow out. Pressurization by the dead weight of the lid body 16 was set as an initial step.

  Thereafter, at the timing when the outflow of water was weakened, a pressure was applied on the lid body 16 to increase the pressure. Finally, the CNF water-containing body 15 was pressurized at 10 kPa to obtain the final step. The total dehydration time from the initial process to the final process was 60 minutes. Thereby, the CNF hydrated body dehydrated to a moisture 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.

(First and second pressurizing steps)
The CNF hydrate containing the preliminary dehydration step was set in a general-purpose hot press machine in a state where it was placed in a mold. As a 1st pressurization process, it pressurized for 30 minutes with the pressure of 10 MPa, without heating. Next, as a second pressurizing step, pressurization was performed for 15 minutes at a temperature of 140 ° C. and a pressure of 10 MPa. Between the 1st pressurization process and the 2nd pressurization process, it carried out continuously, without releasing pressure. Thereby, the CNF molded object of Example 1 was obtained.

[Comparative Example 1]
A CNF molded body of Comparative Example 1 was obtained in the same manner as in Example 1 except that the pressure was released between the first pressure step and the second pressure step.

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

  As shown in Table 1, it can be seen that according to the production method of the example, a CNF compact having a high tensile elastic modulus can be obtained. Moreover, it turns out that the CNF molded object obtained by the manufacturing method of the Example also has high tensile strength at 90 degreeC.

  The manufacturing method of the CNF molded object of this invention can be used suitably for manufacture of a CNF molded object. This CNF molded body has a high elastic modulus, and can be used as a material that replaces a metal molded body, a resin molded body, wood, or the like.

11 Formwork 13 Paper 14 Mesh-like sheet 15 CNF hydrated body 16 Lid

Claims (3)

A first pressurizing step for pressurizing the cellulose nanofiber hydrate containing cellulose nanofiber and water without heating, and a second pressurizing step for pressurizing the hydrated cellulose nanofiber while heating the cellulose nanofiber hydrate.
The manufacturing method of the cellulose nanofiber molded object which performs a 1st pressurization process and a 2nd pressurization process continuously, without depressurizing between a 1st pressurization process and a 2nd pressurization process.   The cellulose nanofiber molded body according to claim 1, wherein the pressurization in the first pressurization step and the second pressurization step is performed on the cellulose nanofiber hydrated body in a mold using a hot press. Method. Before the first pressurizing step,
A preliminary dehydration step of dehydrating the cellulose nanofiber hydrated body through the mesh-like member;
The method for producing a cellulose nanofiber molded body according to claim 1 or 2, wherein, in the preliminary dehydration step, the cellulose nanofiber hydrated body is pressurized with a pressing force smaller than that in the first pressurizing step.

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