JP6941263B2 - Cellulose nanofiber concentrated, dried product manufacturing method and cellulose nanofiber redispersion liquid manufacturing method - Google Patents

Description

In the present invention, a dispersion liquid having a predetermined concentration suitable for use of cellulose nanofibers (hereinafter, also referred to as "CNF") is concentrated and dried to obtain a CNF-concentrated and dried product having a predetermined concentration suitable for storage and transportation. The present invention relates to a technique for concentrating, drying and redispersing cellulose nanofibers, which obtains a CNF redispersion liquid by redispersing a CNF concentrated / dried product in water and returning the product to a predetermined concentration suitable for the above use.

Generally, CNF is produced in a state of being stably dispersed in water, and is usually used for various purposes as an industrial material or an additive material for foods and cosmetics as the produced CNF dispersion liquid having a predetermined concentration.
In order to keep the state of CNF stable, about several tens of times as much water as CNF is required, and the large amount of water leads to an increase in the cost of packaging, storage, transportation, etc. of CNF. Moisture reduction (concentration) and removal (drying) have been regarded as indispensable technologies for the spread of CNF.

On the other hand, in order to use the CNF concentrated and dried product obtained by concentrating and drying the CNF dispersion, the CNF dispersion must be redispersed in water to prepare a CNF redispersion having a predetermined concentration suitable for use again. If the prepared CNF redispersion liquid is significantly lower than the viscosity characteristics (thixotropy) of the CNF dispersion liquid before concentration and drying, the CNF redispersion liquid cannot be used for the above-mentioned various uses.
Therefore, a technique for increasing the viscosity characteristics of the CNF redispersion liquid to the same level as the initial viscosity characteristics of the CNF dispersion liquid is required, and the techniques for improving the viscosity characteristics are disclosed in Patent Documents 1 to 5 below. Has been done.

Specifically, Patent Document 1 discloses a technique in which CNF contains a predetermined weight% of a water-soluble polymer and then dehydrates and dries, and Patent Document 2 sets the pH of an aqueous suspension of CNF to 9 to 9 to 2. The technique of dehydrating and drying after adjusting to 11 is disclosed.
Further, Patent Document 3 discloses a technique of drying a CNF dispersion liquid to produce a dry solid substance of CNF, treating the CNF dispersion liquid with hot water, and dispersing the CNF dispersion liquid in a solvent to obtain a CNF redispersion liquid. A technique is disclosed in which a CNF dispersion is obtained by defibrating cellulose oxide fibers, reduced in a reaction solution containing a reducing agent, and then dried.

Further, Patent Document 5 discloses a technique in which a CNF dispersion liquid contains hydroxy acids and then is dried.
By executing the techniques disclosed in Patent Documents 1 to 5, it is said that the redispersibility is excellent and the viscosity characteristics equivalent to those of the original CNF dispersion can be obtained.

Japanese Unexamined Patent Publication No. 2017-8176 JP-A-2017-8175 JP-A-2017-2136 Japanese Unexamined Patent Publication No. 2017-2135 Japanese Unexamined Patent Publication No. 2017-2138

However, when the CNF dispersion is heated by hot air drying or the like to concentrate and dry, the surfaces of the CNF are strongly hydrogen-bonded to each other, and even if water is added again, the original CNF state cannot be restored. The excellent characteristics of the product cannot be exhibited. Specifically, when concentrated, dried CNF concentration, and dried products are redispersed to the initial concentration, the viscosity characteristics including thixotropy, which is the characteristic that the viscosity decreases when stirring or shearing force is applied, are CNF redispersion. It will drop with liquid.
Further, in hot air drying, while the surface layer portion of the object to be dried is excessively dried, the central portion of the object to be dried is insufficiently dried, so that it is unavoidable to dry for a long time at a low temperature. Further, in vacuum freeze-drying, since the sublimation rate from ice is slow, it takes time to dry, and both cooling means and heating means are required, which increases the equipment cost.

On the other hand, according to the techniques disclosed in Patent Documents 1 to 5, the decrease in viscosity characteristics is suppressed without increasing the drying time and equipment cost, and the viscosity is equivalent to that of the original CNF dispersion liquid. It is said that the characteristics can be obtained.
However, all of the above five techniques are techniques for improving redispersibility by adding chemicals to CNF or applying other treatments, and some of them cannot be used as food additives depending on the type of chemicals. Because of this, the usage is limited.
In addition, when the CNF redispersion liquid is produced, new steps such as injection of chemicals, mixing, and other treatments are required, so that the productivity of the CNF redispersion liquid also deteriorates, and the time required for drying described above is reduced. It cannot be shortened.

The present invention has been made based on these points, and an object of the present invention is to concentrate and dry a CNF dispersion to produce a CNF-concentrated and dried product, and then redisperse the CNF dispersion to produce a dried product. CNF concentrated, dried product or CNF redispersion liquid having the same viscosity characteristics as the original CNF dispersion liquid can be produced without containing chemicals in the CNF concentrated product or CNF dispersion liquid. The purpose is to provide a safe, secure, and highly productive method for producing cellulose nanofiber-enriched and dried products.

In order to achieve the above object, the method for producing a dried product by concentrating cellulose nanofibers for redispersion according to claim 1 of the present invention uses a cellulose nanofiber dispersion having a predetermined concentration suitable for using the cellulose nanofibers as a raw material. , The cellulose nanofiber dispersion set or carried into the main body of the drying chamber that can be decompressed is irradiated with microwaves and dried at low temperature under reduced pressure. Concentration and drying steps are carried out to concentrate the cellulose nanofibers and dry products. The manufactured, concentrated and dried cellulose nanofibers are characterized in that they are redispersed in water and returned to a predetermined concentration suitable for the above use to obtain a cellulose nanofiber redispersion liquid. ..
The method according to claim 2 in accordance redispersion for cellulose nanofibers concentrated dried product, according to claim 1, wherein redispersion for cellulose nanofibers concentrated, in the manufacturing method of drying products, the cellulose nanofiber dispersion The concentration is characterized by being 1.7 to 2%.
The production method of claim 3 in accordance redispersion for cellulose nanofibers concentrated dried product, according to claim 1 or 2 redispersion The cellulose nanofiber concentration according a method of manufacturing a dry product, the cellulose nanofibers concentrated The concentration of the dried product is 2.5 to 10%.
Further, redistribution for cellulose nanofibers concentrated by claim 4, the manufacturing method of drying products, redispersion The cellulose nanofiber concentration according to any one of claims 1 to 3, in the manufacturing method of drying products, the The concentration and drying steps are characterized in that an inert gas is used as a carrier gas for the evaporated water to be introduced into the main body of the drying chamber.
Further, redistribution for cellulose nanofibers concentrated by claim 5, the manufacturing method of the dried product "is distributed for cellulose nanofibers concentrate according to claim 1, in the manufacturing method of drying products, the In the concentration and drying steps, the evaporation temperature of the water in the drying chamber is 20 ° C to 40 ° C, and the pressure is -80 to -90 kPa under a low-temperature reduced pressure atmosphere, the microwave frequency is 2450 MHz, and the microwave output is 180 to 180 to. It is characterized in that it is concentrated and dried for a predetermined time according to the amount of the cellulose nanofiber dispersion liquid to be concentrated and dried under the condition of 210 W.
Further, redistribution for cellulose nanofibers concentrated by claim 6, a manufacturing method of a dry product, re-dispersed for cellulose nanofibers concentrate according to any one of claims 1 to 5, in the manufacturing method of drying products, the The main body of the drying chamber includes a vacuum pump for reducing the atmosphere inside the main body of the drying chamber and a cold trap that takes out the water vapor in the main body of the drying chamber generated by microwave heating, cools it, and captures it. Connected and
The cellulose nanofiber dispersion liquid in the drying chamber body is concentrated and dried by being irradiated with microwaves in a reduced pressure atmosphere formed by the vacuum pump, and the generated water vapor is converted into an external air flow formed by the vacuum pump. It is characterized in that the concentration and drying steps are executed in a state where the liquid is discharged to the outside of the drying chamber body, cooled by a cold trap, and captured.

Then, the following effects can be obtained by the above means.
First, since the cellulose nanofiber dispersion liquid was concentrated, and the concentration and drying means using microwaves were adopted as the drying means, the surface layer of the object to be dried became excessively dried as in hot air drying, and the center of the object to be dried. The problem of insufficient drying of the part is solved, and the cellulose nanofiber dispersion liquid can be uniformly concentrated and dried.
Further, since the above-mentioned microwave irradiation is performed by low-temperature drying performed under reduced pressure, there is no damage such as concentration, dried cellulose nanofiber concentration, and deterioration due to oxidation of the dried product, and the cellulose nanofiber concentration and drying are performed. The viscosity characteristics of the product and the cellulose nanofiber redispersion liquid obtained by redispersing the product are also good, and high viscosity characteristics equivalent to those of the original cellulose nanofiber dispersion liquid can be obtained.

Further, when the concentration of the cellulose nanofiber dispersion liquid and the concentration of the cellulose nanofiber redispersion liquid are 1.7 to 2%, the effect of CNF is fully exhibited when used as an additive for foods and cosmetics. NS. The concentration of the cellulose nanofiber dispersion liquid and the concentration of the cellulose nanofiber redispersion liquid are not limited to 1.7 to 2%, but may be, for example, 1% to 3%.
Further, when the concentration of the cellulose nanofiber concentrate and the dried product is set to 2.5 to 10%, the water content can be reduced by about 20 to 80% as compared with the initial cellulose nanofiber dispersion liquid. It is possible to significantly reduce the cost of packaging, storing, and transporting cellulose nanofibers. Although the case where the concentration of cellulose nanofibers and the concentration of the dried product is set to 4 to 6% is shown, it is also possible to further increase the concentration of the dried product, and the concentration and drying are performed until the product is almost dry. It is also possible.

Further, when an inert gas is used as the carrier gas of the evaporated water introduced into the drying chamber body in the concentration and drying steps, deterioration due to oxidation of the cellulose nanofibers is suppressed.

In addition, when the concentration of cellulose nanofibers and the concentration of dried products are determined based on the weight change measured by the load cell set in the drying chamber body, the cellulose nanofiber dispersion liquid is concentrated and dried. Optimal concentration and drying of the cellulose nanofiber dispersion can be performed by adjusting the microwave output or the like based on the change in the weight of the cellulose nanofiber dispersion that changes from moment to moment without interruption.

Further, when the concentration of the cellulose nanofiber concentrate and the dried product is determined based on the weight change measured by the measuring instrument set outside the drying chamber body, the cellulose nanofiber dispersion liquid is concentrated and dried. Is interrupted each time weighing is performed, but accurate weighing that is not affected by microwaves can be realized with a simple configuration.

Further, in the concentration and drying steps, the microwave frequency is set to 2450 MHz and the microwave output is increased under a low pressure reduced atmosphere in which the evaporation temperature of water in the drying chamber body is 20 ° C to 40 ° C and the pressure is -80 to -90 kPa. When the cellulose nanofiber dispersion is concentrated and dried for a predetermined time according to the amount of the cellulose nanofiber dispersion to be concentrated and dried under the condition of 180 to 210 W, the cellulose nanofiber dispersion is deteriorated by local heating or oxidation. Can be suppressed. In addition, the cellulose nanofiber dispersion can be concentrated and dried in a short time with a small amount of energy consumption.

In addition, a vacuum pump for reducing the atmosphere inside the drying chamber body to a reduced pressure atmosphere, and a cold trap for taking out the water vapor in the drying chamber body generated by microwave heating to the outside, cooling it, and capturing it are provided in the drying chamber body. When these vacuum pumps and cold traps are used to concentrate and dry the cellulose nanofiber dispersion liquid, the atmosphere inside the drying chamber body becomes a reduced pressure atmosphere by the above vacuum pump at low temperature. It enables heating by microwaves.

Then, the water vapor generated by the heating by the microwave is discharged to the outside of the drying chamber main body on the outward airflow formed by the vacuum pump, cooled by the cold trap, and captured. Re-contact with the fiber dispersion can be prevented, and the inflow of water vapor into the vacuum pump, which causes a problem in the operation of the vacuum pump, can be prevented.

It is a figure which shows the 1st Embodiment of this invention, and is the front view which shows an example of the microwave vacuum dryer used in the cellulose nanofiber enrichment, the manufacturing method of the dried product of this invention. It is a figure which shows the 1st Embodiment of this invention, and is the left side view which shows an example of the microwave vacuum dryer used in the cellulose nanofiber enrichment, the manufacturing method of the dried product of this invention. The figure which shows the 1st Embodiment of this invention shows an example of the internal structure of the microwave vacuum dryer which shows the example of the microwave vacuum dryer used in the cellulose nanofiber enrichment, the manufacturing method of the dried product of this invention. It is a vertical sectional front view which shows. It is a figure which shows the 1st Embodiment of this invention, and is explanatory drawing which shows the image of concentration and drying of cellulose nanofiber by a microwave vacuum dryer. It is a figure which shows the 1st Embodiment of this invention, and is the rear view which shows the opening and closing door of a microwave vacuum dryer. It is a figure which shows the 1st Embodiment of this invention, and is the side sectional view which shows the microwave leakage prevention mechanism applied between the opening of the drying chamber main body of a microwave vacuum dryer and an opening / closing door. It is a figure which shows the 1st Embodiment of this invention, and is the wiring diagram which shows the connection state of the load cell installed in the drying chamber main body of the microwave vacuum dryer, and the control part. It is a figure which shows the 1st Embodiment of this invention, and is the block diagram which shows each process which constitutes the manufacturing method of the cellulose nanofiber enrichment | dry product of this invention. It is a figure which shows the result of the comparative test 1 performed in order to verify the effect of this invention, and is the graph which shows the relationship between the viscosity of the cellulose nanofiber concentrate, the dry product, and the shear rate. It is a figure which shows the result of the comparative test 1 performed in order to verify the effect of this invention, and is the graph which shows the relationship between the viscosity and the shear rate of the cellulose nanofiber redispersion liquid. It is a figure which shows the result of the comparative test 1 performed in order to verify the effect of this invention, and is the graph which shows the viscosity of the cellulose nanofiber redispersion liquid when the shear rate is 30 (1 / s). It is a figure which shows the result of the comparative test 2 performed in order to verify the effect of this invention, and is the graph which shows the relationship between the viscosity of the cellulose nanofiber concentrate, the dry product, and the shear rate. It is a figure which shows the result of the comparative test 2 performed in order to verify the effect of this invention, and is the graph which shows the relationship between the viscosity and the shear rate of the cellulose nanofiber redispersion liquid. It is a figure which shows the 2nd Embodiment of this invention, and is the longitudinal front view which shows the other example of the internal structure of the microwave vacuum dryer. It is a figure which shows the 3rd Embodiment of this invention, and is the longitudinal front view which shows the other example of the internal structure of the microwave vacuum dryer. It is a figure which shows the 4th Embodiment of this invention, and is the longitudinal front view which shows the other example of the internal structure of the microwave vacuum dryer.

Hereinafter, based on FIGS. 1 to 7, an example of the configuration of the microwave vacuum dryer used in the first embodiment of the method for concentrating cellulose nanofibers and producing a dried product of the present invention will be described first. Next, based on FIG. 8, concretely, each step in the method for producing the cellulose nanofiber concentration and the dried product and the method for producing the cellulose nanofiber redispersion liquid of the present invention, together with the operation mode of the microwave vacuum dryer. Explain to. Subsequently, the contents and results of the comparative test conducted to verify the effect of the present invention will be described with reference to FIGS. 9 to 13.
Next, based on FIGS. 14 to 16, the second and second configurations of the microwave vacuum dryer having a partial configuration different from that of the microwave vacuum dryer used in the first embodiment are described. Taking the fourth three embodiments as an example, the above-mentioned first method will be described with respect to each of these configurations and a method for concentrating cellulose nanofibers and producing a dried product when a microwave vacuum dryer having the configuration is used. The differences from the embodiments will be mainly described, and finally, other embodiments having a partial configuration different from those of these embodiments will be referred to.

(1) First Embodiment (see FIGS. 1 to 13)
A. An example of the configuration of a microwave vacuum dryer (see FIGS. 1 to 7)
In the method for producing a cellulose nanofiber concentrated and dried product of the present invention, a cellulose nanofiber dispersion liquid A1 having a predetermined concentration suitable for use of cellulose nanofibers is used as a raw material and set or carried into a decompressable drying chamber main body 5. The cellulose nanofiber dispersion liquid A1 is irradiated with microwaves and dried at a low temperature under reduced pressure. By carrying out the concentration and drying step P1, the cellulose nanofibers are concentrated and the dried product A2 is produced. .. The method for producing the cellulose nanofiber redispersion liquid is composed of two steps, a concentration / drying step P1 and a redispersion step P2. Then, in the concentration / drying step P1, a microwave vacuum dryer 1A having the following configuration is used as an example.
The microwave vacuum dryer 1A is attached to a drying chamber main body 5 having an opening 3 on the front surface and an openable / closable state to the opening 3 as an example of accommodating the cellulose nanofiber dispersion liquid A1 to be dried. The opening / closing door 7 is attached to the upper surface as an example of the drying chamber main body 5, and the opening / closing door 7 is brought into contact with the front surface of the drying chamber main body 5 outside the opening 3. As an example, a double choke integrated with a seal structure 13 having a seal member 11 provided on the back surface and a first choke 17 and a second choke 19 provided on an intermediate path 63 between the opening 3 and the seal structure 13. It is basically configured by including a microwave leakage prevention mechanism 21 having a structure and a vacuum pump 33 which is a main component of the pressure reducing device 32 for reducing the pressure in the drying chamber main body 5.

Further, in the illustrated microwave decompression dryer 1A, the drying chamber main body 5 and the opening / closing door 7 are used for drying the support pedestal 23 formed by assembling the angle material or the like into a rectangular frame shape. The chamber 25 is arranged closer to the front surface as an example, and a control box 31 having a display unit 27 and an operation button 29 is arranged on the right side as an example of the drying chamber 25.
Further, as an example of the drying chamber 25, the vacuum pump 33 described above is arranged at the lower part in the rear space, and a circulation type water supply / drainage device 34 for supplying / draining water for driving the vacuum pump 33 is arranged above the vacuum pump 33. Has been done. The decompression device 32 is configured by including the vacuum pump 33 and the circulation type water supply / drainage device 34. When the vacuum pump 33 is a water-sealed pump, the cold trap may not be provided.

Further, in the drying chamber main body 5, a microwave irradiation device 9 is arranged on the upper part of the top plate as shown in FIG. As an example, one microwave irradiation device 9 is provided in which the microwave frequency can be adjusted to 2450 MHz and the microwave output can be adjusted to 200 W.
Further, on the side of the microwave irradiation device 9, a stara fan 10 for stirring microwaves, a motor M for driving the stara fan 10, and infrared rays for measuring the temperature of the CNF dispersion liquid A1 during concentration and drying. A thermometer 79 and is arranged.

Further, a load cell 71, which is a strain gauge type load converter, is arranged above the bottom plate of the drying chamber main body 5 in a state of being shielded from the internal space of the external drying chamber main body 5 by a shield structure 73. A container body 82 made of synthetic resin is placed as an example in which the CNF dispersion liquid A1 can be accommodated.
Here, the CNF dispersion liquid A1 to be concentrated and dried in the present invention will be described. First, cellulose nanofiber (CNF) is a biomass material obtained from plant fibers such as wood, and is a fibrous substance having a fiber width of about several nm to several tens of nm. CNF is known to have a strength five times or more that of iron and a low expansion rate of about one-fiftieth that of glass, and is expected to be applied to various fields as a new material. ..

Methods for producing CNF include chemically defibrated TEMPO-oxidized CNF and mechanically defibrated fibrillated CNF. All of these CNFs are produced in a state of being stably dispersed in water at a low concentration of about 1.7 to 2%. Incidentally, in the present embodiment, a 2% concentration dispersion of "BiNFi-s" of mechanical defibration CNF sold by Sugino Machine Limited is used as the CNF dispersion A1.
Further, the opening / closing door 7 that closes the opening 3 on the front surface of the drying chamber main body 5 is composed of a single-opening rectangular door-shaped member that rotates around a hinge portion 43 arranged on the right side portion as an example. Has been done. A total of two hinge portions 43 are provided, one on the top and one on the bottom, and the opening / closing door 7 can rotate over a range of about 180 ° with respect to the drying chamber main body 5 with these hinge portions 43 as fulcrums. It is connected like.

An inspection window 39 is provided in the center of the front surface of the opening / closing door 7 so that the state of the CNF dispersion liquid A1 and the like during concentration and drying can be observed from the outside.
Further, a grip 41 that serves as a clue when opening / closing the opening / closing door 7 is provided at the central portion of the opening / closing door 7 in the height direction near the left and right free ends, and is provided on the upper and lower edges of the opening / closing door 7. As an example, two rotary lock handles 45 are provided, for a total of four.

In the lock handle 45, the locking claw 47 provided at the tip thereof is locked to the locking hook 49 provided at the center of the upper and lower edges of the opening 3 of the drying chamber main body 5. It is configured so that the closed state of the opening / closing door 7 can be locked.
Further, a microwave leakage prevention mechanism 21 is provided on the outer periphery of the back surface of the opening / closing door 7 as shown by a solid line in FIG. 5, and further, the outer periphery of the microwave leakage prevention mechanism 21 is shown in FIG. As an example of contacting the sealing surface 61 around the opening 3 of the drying chamber main body 5 when the opening / closing door 7 is closed, a sealing structure 13 including a sealing member 11 composed of a ring-shaped rubber packing is provided. Has been done.

The microwave leakage prevention mechanism 21 is provided on the intermediate path 63 between the opening 3 and the seal structure 13, and is located on the first choke 17 located on the opening 3 side and on the seal structure 13 side. The seal structure has a double choke integrated structure in which the second chokes 19 are continuously arranged at a predetermined pitch in the circumferential direction so as to face each other.
Specifically, as shown in FIG. 6, the base end portion 69 is vertically raised from one end edge of the shielding plate 65 arranged along the back surface of the opening / closing door 7, and the tip of the base end portion 69 is set to 90 °. The first choke 17 having an L-shaped cross section is provided by forming the tip portion 67 by bending inward.
Similarly, a second choke 19 having the same shape and size as the first choke 17 is provided on the other end edge of the shielding plate 65, and the first choke 17 and the second choke 19 are arranged at opposite positions. The microwave leakage prevention mechanism 21 is configured.

A gap G is formed between the tip portion 67 of the first choke 17 and the tip portion 67 of the second choke 19, and the first choke 17 and the second choke 19 are formed from the midpoint O of the gap G. The distance L1 from the middle point O to the connection point B between the tip end portion 67 and the base end portion 69 is the distance L2 from the vertical line drawn toward the shielding plate 65 to the contact point C between the facing surface of the shielding plate 65. It is set to be approximately equal and about 1/4 of the wavelength λ of the microwave used together.
Incidentally, by adopting such a dimensional setting, a detour having a length of about 1/4 of the wavelength λ is formed in the intermediate path 63, and from the reflected wave in the detour and the connection point B. The phase difference from the wave toward the midpoint O becomes about ½ of the wavelength λ and cancels each other out, so that the leakage of the microwave to the outside of the drying chamber 25 is prevented.

Further, the load cell 71 is a load converter that converts a load into an electric signal, including a strain-causing body, a strain gauge, and a bridge circuit. Then, in the present embodiment, as an example, three load cells 71 are used to measure the weight change of the CNF dispersion liquid A1, and as shown in FIG. 7, the data measured by each load cell 71 is used as an electric signal. It is output, the above three measurement data are summed in the summing box 115, and the summed data is transmitted to the control box 31.
The summed data transmitted to the control box 31 is displayed as a numerical value on the indicator 127 as an indicator provided on the front surface of the control box 31 and the monitor serving as the display unit 27, and is displayed as a numerical value on the control unit 117. It is transmitted to and used for concentration, drying time and control of microwave irradiation amount.

Further, the load cell 71 is arranged in a shielding space 75 partitioned by an upper surface shielding plate 93 and a lower surface blocking plate 97, and the outer peripheral portion of the shielding space 75 is an opening 3 of the drying chamber main body 5. The same double choke integrated structure or single choke structure microwave leakage prevention mechanism 22 as applied is provided.
Further, in the present embodiment, the shield structure 73 that covers the upper surface shielding plate 93, the lower surface shielding plate 97, and the microwave leakage prevention mechanism 22 is arranged, and the microwave leakage prevention mechanism 22 is used. In addition to the microwave shielding effect of a high frequency circuit, the shielding structure 73 is configured to exert a structural microwave shielding effect.

B. Contents of the method for producing cellulose nanofiber concentrated and dried products (see FIGS. 4 and 8)
Next, the contents of each step in the method of concentrating and drying CNF and the method of producing the CNF redispersion liquid, which are carried out by using the microwave vacuum dryer 1A according to the present embodiment, are described in the microwave vacuum dryer described above. This will be specifically described together with the operation mode of the above.
The method for concentrating and drying CNF according to the present invention includes a concentration and drying step P1, and the method for producing a CNF redispersion liquid according to the present invention is basically configured by including a redispersion step P2.
Then, in the concentration and drying step P1, the CNF dispersion liquid A1 is dried at a low temperature under reduced pressure by using microwaves.

i) Concentration / drying step Concentration / drying step P1 is a step of concentrating and drying a CNF dispersion liquid A1 having a predetermined concentration suitable for use of CNF and drying it to obtain a CNF concentration / dried product A2 having a predetermined concentration suitable for storage and transportation. Is.
As the CNF dispersion liquid A1, the CNF dispersion liquid A1 prepared to have a concentration of about 1.7 to 2% is used, and a predetermined amount of the CNF dispersion liquid A1 is put in the container main body 82 and inside the drying chamber main body 5. It is installed on the predetermined mounting plate 83 of. Next, the operator grasps the grip 41 of the opening / closing door 7 to close the opening / closing door 7, turns the lock handle 45, hooks the locking claw 47 on the locking hook 49, and locks the drying chamber 25 in a closed state. do.

Next, the operation button 29 on the front surface of the control box 31 is pressed to start the vacuum pump 33 to reduce the atmospheric pressure in the drying chamber main body 5 to a predetermined atmospheric pressure, for example, −80 to −90 kPa. Similarly, the operation button 29 is pressed to activate the microwave irradiation device 9 and the stara fan 10. As described above, the microwave irradiated from the microwave irradiation device 9 has a microwave frequency of 2450 MHz and a microwave output of 180 to 210 W as an example, and the microwave is stored in the container body 82 in a CNF dispersion. The liquid A1 is irradiated for a predetermined time according to the amount of the CNF dispersion liquid A1, and the CNF dispersion liquid A1 is concentrated and dried to a predetermined concentration. The evaporated water is sucked by the vacuum pump 33 and discharged to the outside.
The evaporation temperature of the water in the drying chamber main body 5 during concentration and drying is set to, for example, 20 ° C to 40 ° C. Further, at this time, the microwave irradiated in the drying chamber main body 5 is prevented from leaking to the outside of the drying chamber main body 5 by a microwave leakage prevention mechanism 21 provided around the opening 3 of the drying chamber main body 5 in a high frequency circuit. The microwave leakage prevention mechanism 22 and the shield structure 73 provided around the installation site of the load cell 71 prevent leakage to the load cell 71 side.

Further, the concentration of the CNF dispersion liquid A1 at the time of concentration and drying can be obtained from the weight change of the CNF dispersion liquid A1 measured by the load cell 71, and the concentration of the CNF dispersion liquid A1 is a predetermined concentration (for example, 4%, 6). %, 10%), stop microwave irradiation.
After stopping the microwave irradiation device 9, the stara fan 10, and the vacuum pump 33, turn the lock handle 45 to release the locked state between the locking claw 47 and the locking hook 49, grasp the grip 41, and open the opening / closing door 7. , The container body 82 containing the CNF concentrated and dried product A2 placed on the mounting plate 83 is taken out of the drying chamber body 5.

ii) Redispersion step In the redispersion step P2, the CNF concentration and dried product A2 obtained by the above concentration and drying steps P1 are redispersed in water W and returned to a predetermined concentration suitable for the above use to return the CNF redispersion liquid A3. Is the process of obtaining.
CNF-concentrated and dried product A2 having a concentration of, for example, 4%, 6% or 10% obtained by concentration and drying in the above concentration and drying step P1 is placed in a suitable container 85, and a predetermined amount of water W is further added. For example, the CNF redispersion liquid A3 is obtained by redispersing to the initial concentration of 2%.
The CNF redispersion liquid A3 thus obtained has a viscosity equal to or higher than that of the initial CNF dispersion liquid A1 as is clear from the results of the comparative test described below without containing a separate chemical or the like. Because of its characteristics, it is safe and secure, has excellent productivity and cost performance, and has excellent functional characteristics.

The improvement of the viscosity characteristics of the CNF redispersion liquid A3 is due to the fact that when the CNF dispersion liquid A1 was concentrated and dried in the concentration and drying step P1, it was dried at a low temperature by microwaves in a reduced pressure atmosphere. It is presumed that the water molecules of the existing bound water were directly moved to dehydrate as shown in FIG. As a result, it is considered that the dispersibility was improved because there were few heating spots and it was difficult to form hydrogen bonds between the celluloses.
In addition, the movement of water molecules may break the hydrogen bonds between the celluloses formed by aggregation, and it is considered that these act to improve the viscosity characteristics of the CNF redispersion liquid A3.

C. Contents and results of comparative test 1 (see FIGS. 9 to 11)
Next, the contents and results of the comparative test 1 conducted to verify the effect of the present invention will be described. In this comparative test, a dispersion of 2%, 5%, and 10% of the mechanical defibration CNF "BiNFi-s" sold by Sugino Machine Co., Ltd. (commercially available) was used, of which 2% was dispersed. The liquid was used as a standard product (CNF dispersion liquid A1), and the standard product was concentrated and dried to a concentration of 4% and 6% using the microwave vacuum dryer 1A, and concentrated to a concentration of 4% by a centrifugation method. The CNF concentrated and dried products obtained here were redispersed to prepare a CNF redispersion liquid having a concentration of 2%, and their viscosities and shear rates were compared.

First, as shown in FIG. 9, a commercially available CNF dispersion liquid A1 (standard product) having a concentration of 2% and the standard product having a concentration of 4% and 6 prepared by concentrating and drying the standard product with the microwave vacuum dryer 1A. The relationship between viscosity and shear rate was compared for four types of CNF-concentrated and dried product A2 of% and the standard product concentrated to a concentration of 4% by centrifugation.
In this case, it was confirmed that the higher the concentration, the higher the viscosity, and the difference becomes more remarkable as the shear rate decreases, and the viscosity gradually decreases as the shear rate increases. Further, when the microwave dried product having the same concentration of 4% and the centrifugally separated product were compared, it was confirmed that the microwave dried product had a higher viscosity.

Next, as shown in FIG. 10, a concentration 2 prepared by diluting a commercially available CNF dispersion A1 (standard product) having a concentration of 2% and two types of microwave-dried products having the above concentrations of 4% and 6%. The relationship between the viscosity and the shear rate was compared for four types of CNF redispersion solution A3 having a concentration of 2% and CNF redispersion solution having a concentration of 2% prepared by diluting the centrifugal product having a concentration of 4%.
In this case, the CNF concentrated product with a concentration of 4% of the microwave dried product and the CNF redispersion liquid A3 prepared from the dried product A2 have the highest viscosity, and the CNF concentrated product with a concentration of 6% of the microwave dried product and the dried product. The CNF redispersion liquid A3 prepared from A2 had the next highest viscosity.

The next highest viscosity is the commercially available product (standard product) with a concentration of 2% that is not concentrated and dried, and the lowest viscosity is the CNF concentration and drying with a concentration of 4% prepared by the centrifugation method. It was a CNF redispersion solution prepared from the product.
As is clear from the figure, all of these have a concentration of 2%, but there is a difference in viscosity by redispersing the once concentrated and dried ones. In particular, the CNF redispersion liquid A3 prepared by redispersing the CNF concentrated and dried product A2 concentrated and dried by microwaves to a concentration of 2% has a higher viscosity than the CNF dispersion liquid A1 (standard product) before concentration and drying. Shows high viscosity characteristics.

Next, as shown in FIG. 11, two types of CNF dispersions having a concentration of 5% and 10%, which are commercially available products, were prepared, and these two types of CNF dispersions were diluted to a concentration of 2% to prepare the above-mentioned ones. Commercially available CNF dispersion A1 (standard product) with a concentration of 2%, two types of CNF concentrates with a concentration of 4% and 6% described above, and two types of CNF redispersion A3 with a concentration of 2% prepared from the dried product A2. The magnitudes of the viscosities of the five types were compared under the conditions of a temperature of 25 ° C. and a shear rate of 30 (1 / s).
In this case, the two types of CNF redispersion liquid A3 prepared by redispersing the one concentrated and dried by microwaves have a higher viscosity than the standard CNF dispersion liquid A1 as described above. On the other hand, a commercially available product obtained by diluting two types of CNF dispersions having a concentration of 5% and 10% to a concentration of 2% has a considerably lower viscosity than the above standard product.

Based on the above results, two types of CNF-enriched and dried products A2, which are commercially available CNF dispersions A1 (standard products) with a concentration of 2% and concentrated and dried using microwaves, have a concentration of 4% and 6%. It was demonstrated that it exhibits high viscosity characteristics and also exhibits good characteristics in thixotropy, which is a characteristic that the viscosity decreases when stirring or shearing force is applied.
Thereby, by executing the method for producing a CNF-enriched and dried product of the present invention, it is possible to produce a CNF-enriched and dried product A2 having excellent viscosity characteristics, and the CNF is safe, secure and highly productive. A method for producing a concentrated and dried product can be constructed, and a CNF concentrated and dried product suitable for storage and transportation and having excellent dispersibility can be provided.
Further, the CNF redispersion liquid A3 obtained by concentrating and drying the standard product using microwaves and redistributing it to a concentration of 2% showed higher viscosity characteristics than the initial CNF dispersion liquid A1 (standard product). It was demonstrated that the thixotropy property, which is the property that the viscosity decreases when stirring or shearing force is applied, also shows good properties.
As a result, by executing the method for producing the CNF concentrated and dried product and the method for producing the CNF redispersion liquid of the present invention, the CNF redispersion having a viscosity characteristic equal to or higher than that of the commercially available CNF dispersion liquid A1 having a concentration of 2% is executed. CNF concentration that can generate liquid A3, is safe, secure, and has excellent productivity, and can construct a method for producing dried products and a method for producing CNF redispersion liquid, which is suitable for storage and transportation and has excellent viscosity characteristics. , The dried product A2 can be provided.

D. Contents and results of comparative test 2 (see FIGS. 12 and 13)
Next, the contents and results of the comparative test 2 conducted to verify the effect of the present invention will be described. In this comparative test, a 1.7% concentration dispersion (commercially available product) of the mechanical defibration CNF "BiNFi-s" sold by Sugino Machine Limited was used as the standard product (CNF dispersion A1), and the above microwave depressurization was performed. The standard product was concentrated for a predetermined time using a dryer 1A, and dried CNF concentration was prepared to prepare a dried product A2. Further, the CNF concentrated and dried product A2 obtained here was redispersed to prepare a CNF redispersion liquid A3 having a concentration of 1.7%, and their viscosities and shear rates were compared.

First, as shown in FIG. 12, a commercially available CNF dispersion liquid A1 (standard product) having a concentration of 1.7% and the standard product were subjected to 8 min, 12 min, 15 min, 16 min, 17 min by the microwave vacuum dryer 1A. The relationship between viscosity and shear rate was compared for 9 steps of 18 min, 19 min, 20 min, and 22 min, concentrated, dried CNF concentrated, and dried product A2.
The concentration of 8 min concentrated, dried CNF concentrated, and dried product A2 was 2.67%, and the concentration of 12 min concentrated, dried CNF concentrated, and dried product A2 was 3.85%, 15 min concentrated, and dried CNF concentrated. , Dried product A2 concentration is 4.63%, 16 min concentration, dried CNF concentration, dried product A2 concentration is 4.61%, 17 min concentration, dried CNF concentration, dried product A2 concentration is 5.34%, 18 min concentrated, dried CNF concentrated, dried product A2 concentration 6.22%, 19 min concentrated, dried CNF concentrated, dried product A2 concentration 7.05%, 20 min concentrated, dried CNF concentrated, dried product A2 The concentration was 7.85%, 22 min concentration, dried CNF concentration, and the concentration of dried product A2 was 9.63%.
In this case, although there are some errors, the longer the concentration and drying time, the higher the concentration and the higher the viscosity. Then, it was confirmed that the difference became more remarkable as the shear rate decreased, and that the viscosity gradually decreased as the shear rate increased.

Next, as shown in FIG. 13, a commercially available CNF dispersion liquid A1 (standard product) having a concentration of 1.7%, the above 9-step concentration, concentration in a drying time, 9 types of CNF concentration dried, and a dried product A2 The relationship between the viscosity and the shear rate was compared with 9 kinds of CNF redispersion liquids A3 having a concentration of 1.7% prepared by diluting.
In this case, the commercially available CNF dispersion A1 (standard product) with a concentration of 1.7% has the highest viscosity, followed by the 12-minute concentrated and dried CNF-concentrated and dried product with a concentration of 3.85%. The CNF redispersion liquid A3 prepared from A2, the one having the lowest viscosity was the CNF concentration concentrated for 22 minutes and dried to a concentration of 9.63%, and the CNF redispersion liquid A3 prepared from the dried product A2.

As is clear from the figure, all of these have a concentration of 1.7%, but there is a difference in viscosity by redispersing the once concentrated and dried ones. Although no clear relationship is found between the difference in viscosity and the difference in concentration and drying time (CNF concentration, concentration of dried product A2), the relationship between viscosity and shear rate is almost the same as that of the standard product. It has been reproduced, and it is considered that all of them belong to the range that does not hinder the use.

From the above results, using a commercially available CNF dispersion liquid A1 (standard product) with a concentration of 1.7%, the above 9-step concentration by microwave, concentration in the drying time, and drying of 9 types of CNF concentration were performed. It has been demonstrated that the dried product A2 has a high viscosity property and also exhibits a good property of thixotropy, which is a property that the viscosity decreases when agitation or shearing force is applied.
As a result, by executing the method for producing the CNF concentrated and dried product and the method for producing the CNF redispersion liquid of the present invention, the CNF dispersion is dispersed even when the commercially available CNF dispersion liquid A1 having a concentration of 1.7% is used. CNF redispersion liquid A3 that can produce CNF redispersion liquid A3 that has the same viscosity characteristics as liquid A1 and does not interfere with use, and is safe, secure, and highly productive. A method can be constructed, and a CNF-concentrated, dried product A2 suitable for storage and transportation and having excellent viscosity characteristics can be provided.

(2) Second embodiment (see FIG. 14)
The method for producing a CNF concentrated product and a dried product and the method for producing a CNF redispersion liquid according to the second embodiment of the present invention are the method for producing a CNF concentrated product and a dried product and the CNF redispersion liquid according to the first embodiment described above. It has the same concentration / drying step P1 as the production method of There is.
Therefore, only a part of the contents of the concentration / drying step P1 is different from the first embodiment, and the other configurations are the same as those of the first embodiment. The differences from the first embodiment will be mainly described.

In the present embodiment, as shown in FIG. 14, a microwave vacuum dryer 1B in which the gas introduction unit 35 for introducing the inactivating gas into the drying chamber main body 5 is arranged in the drying chamber main body 5 is used.
Then, in the present embodiment, when the vacuum pump 33 is started in the concentration / drying step P1, the operation button 29 of the control box 31 is pressed to introduce nitrogen gas as an inert gas into the gas introduction unit 35, and the drying chamber main body 5 Is filled with nitrogen gas.

Then, the method for producing the CNF-enriched and dried product according to the present embodiment and the method for producing the CNF redispersion liquid, which are configured in this manner, also determine the method for producing the CNF-enriched and dried product according to the first embodiment described above. And the same action and effect as the method for producing the CNF redispersion liquid are exhibited.
Further, in the present embodiment, by using an inert gas as the carrier gas for the evaporated water, deterioration due to oxidation of the cellulose nanofibers can be suppressed.

(3) Third Embodiment (see FIG. 15)
The method for producing the CNF concentration and the dried product and the method for producing the CNF redispersion liquid according to the third embodiment of the present invention are the method for producing the CNF concentration and the dry product and the CNF redispersion liquid according to the first embodiment described above. It has the same concentration and drying steps P1 as the production method of At that time, it is determined based on the weight change measured by the measuring instrument 87 set outside the drying chamber main body 5.
That is, the load cell 71 provided in the first embodiment and the shield structure 73 covering the load cell 71 are not provided in the present embodiment, and the measuring instrument 87 described above is replaced with the load cell 71. Is provided outside the drying chamber main body 5.

Therefore, only a part of the contents of the concentration / drying step P1 is different from the first embodiment, and the other configurations are the same as those of the first embodiment. The difference from the first embodiment will be mainly described.
Along with this, in the present embodiment, as shown in FIG. 15, the load cell 71 for measuring the weight change of the CNF dispersion liquid A1 and the shield structure 73 for covering the load cell 71 are not provided in the drying chamber main body 5. A configuration in which a microwave vacuum dryer 1C is used, and the CNF dispersion liquid A1 during concentration and drying, the CNF concentration after drying, and the weight change of the dried product A2 are measured outside the microwave vacuum dryer 1C. Has been adopted.

Specifically, the operation of the microwave vacuum dryer 1C is temporarily stopped each time the weights of the CNF dispersion liquid A1 and the CNF concentrated and the dried product A2 are measured, the opening / closing door 7 is opened, and the container body 82 is opened. Is taken out of the drying chamber main body 5, and the weights of the CNF dispersion liquid A1 and the CNF concentrated and dried product A2 are measured to determine their concentrations.
Then, the method for producing the CNF-enriched and dried product according to the present embodiment and the method for producing the CNF redispersion liquid, which are configured in this manner, also determine the method for producing the CNF-enriched and dried product according to the first embodiment described above. And the same action and effect as the method for producing the CNF redispersion liquid are exhibited.
In the case of this embodiment, the operation of the microwave vacuum dryer 1C must be temporarily stopped each time the CNF dispersion liquid A1 and CNF are concentrated and the weight of the dried product A2 is measured, so that the productivity is high. Is inferior to the first embodiment, but the microwave vacuum dryer 1C having a simple structure without the load cell 71 or the shield structure 73 may be used, so that the equipment cost can be reduced.

(4) Fourth Embodiment (see FIG. 16)
The method for concentrating CNF, producing a dried product, and the method for producing a CNF redispersion liquid according to the fourth embodiment of the present invention are the method for concentrating CNF, the method for producing a dried product, and the CNF redispersion according to the first embodiment described above. It has the same concentration and drying step P1 as the method for producing the dispersion liquid, and a cold trap 89 is arranged in the middle of the path connecting the drying chamber main body 5 and the vacuum pump 33, and the cold trap 89 provides the drying chamber main body. The water vapor generated in 5 and discharged to the outside is cooled and captured.

Therefore, only the point where the cold trap 89 is arranged is different from the first embodiment, and the other configurations are the same as those of the first embodiment. The difference from the embodiment of the above will be mainly described.
That is, in the present embodiment, a microwave vacuum dryer 1D in which a cold trap 89 is arranged in the middle of the path connecting the drying chamber main body 5 and the vacuum pump 33 is used, and the CNF dispersion liquid A1 is concentrated and dried at the time of drying. The water vapor generated in the chamber body 5 is discharged to the outside of the drying chamber body 5 on the air flow to the outside formed by the vacuum pump 33.

Further, the water vapor is cooled and captured by the cold trap 89, so that the inflow of water vapor into the vacuum pump 33, which adversely affects the operation of the vacuum pump 33, is prevented.
Then, the method for producing the CNF-enriched and dried product according to the present embodiment and the method for producing the CNF redispersion liquid, which are configured in this manner, also determine the method for producing the CNF-enriched and dried product according to the first embodiment described above. And the same action and effect as the method for producing the CNF redispersion liquid are exhibited.
Further, in the present embodiment, the water vapor discharged from the drying chamber main body 5 by the cold trap 89 is cooled and captured and does not flow into the vacuum pump 33, so that the microwave vacuum dryer 1D can be continuously and stably operated. Becomes possible.

The method for producing a cellulose nanofiber concentrated and dried product and the method for producing a cellulose nanofiber redispersion liquid of the present invention are not limited to those of the above-described embodiment, and can be changed within the gist of the present invention. be. For example, the opening / closing means for closing the opening 3 of the drying chamber main body 5 so as to be openable / closable is not limited to the single-door opening / closing type opening / closing door 7 adopted in each of the above-described embodiments, but is a double-door Kannon door type opening / closing door. It may be a sliding door or a sliding door.
Further, the opening 3 provided in the drying chamber main body 5 may be provided at only one place, or at a plurality of places such as two places on the carry-in side and the carry-out side. Incidentally, if the openings 3 are provided at two locations, the carry-in side and the carry-out side, it is possible to fully automate the concentration and drying process P1 of the cellulose nanofibers by combining with a transport means such as a conveyor.

The method for producing cellulose nanofiber enrichment and dried products and the method for producing cellulose nanofiber redispersion liquid of the present invention include working fields in which cellulose nanofiber concentration, production of dry products and production of cellulose nanofiber redispersion liquid are performed. In particular, it can be used when it is desired to produce a CNF redispersion liquid having a viscosity characteristic equal to or higher than that of the original CNF dispersion liquid without containing chemicals or the like in the CNF dispersion liquid.

1 Microwave decompression dryer 3 Opening 5 Drying chamber body 7 Opening / closing door (opening / closing means)
9 Microwave irradiation device 10 Stara fan 11 Seal member 13 Seal structure 17 1st choke 19 2nd choke 21 Microwave leakage prevention mechanism 22 Microwave leakage prevention mechanism 23 Support stand 25 Drying chamber 27 Display 29 Operation button 31 Control box 32 Decompression Device 33 Vacuum pump 34 Circulation type water supply / drainage device 35 Gas introduction part 39 Inspection window 41 Grip 43 Hing part 45 Lock handle 47 Locking claw 49 Locking hook 61 Sealing surface 63 Intermediate path 65 Shielding plate 67 Tip part 69 Base end part 71 Load cell 73 Shield structure 75 Shield space 79 Infrared thermometer 82 Container body 83 Mounting plate 85 Container 87 Weighing instrument 89 Cold trap 93 Top shield plate 97 Bottom shield 115 Addition box 117 Control unit 127 Indicator (indicator)
A1 Cellulose Nanofiber (CNF) Dispersion A2 Cellulose Nanofiber (CNF) Concentrated, Dry Product A3 Cellulose Nanofiber (CNF) Redispersion G Gap O Midpoint B Connection Point C Contact L Distance P1 Concentration, Drying Step P2 Redispersion Process M Motor W Water

Claims (6)

Using a cellulose nanofiber dispersion having a predetermined concentration suitable for the use of cellulose nanofibers as a raw material, the cellulose nanofiber dispersion set or carried into the drying chamber body that can be depressurized is irradiated with microwaves to reduce the pressure. Concentration and drying steps are carried out under low temperature drying to produce cellulose nanofiber concentrate and dried products, and the cellulose nanofiber concentrate and dried products are redispersed in water to return to a predetermined concentration suitable for use and cellulose. A method for producing a dried product by concentrating cellulose nanofibers for redispersion, which is used to obtain a nanofiber redispersion liquid. The method for producing a dried product by concentrating cellulose nanofibers for redispersion according to claim 1, wherein the concentration of the cellulose nanofiber dispersion liquid is 1.7 to 2%. The method for producing a cellulose nanofiber concentrate for redispersion according to claim 1 or 2, wherein the concentration of the cellulose nanofiber concentrate and the dried product is 2.5 to 10%. The cellulose nano for redispersion according to any one of claims 1 to 3, wherein an inert gas is used as a carrier gas for evaporated water to be introduced into the drying chamber body in the concentration and drying steps. Fiber concentration, manufacturing method of dried products. In the above concentration and drying steps, the microwave frequency is 2450 MHz and the microwave output is 180 under a low-temperature reduced pressure atmosphere in which the evaporation temperature of water in the drying chamber body is 20 ° C to 40 ° C and the pressure is -80 to -90 kPa. The redispersion according to any one of claims 1 to 4 , wherein the cellulose nanofiber dispersion liquid is concentrated and dried under the condition of ~ 210 W for a predetermined time according to the amount of the cellulose nanofiber dispersion liquid . use the cellulose nanofiber concentration, method of manufacturing a dry product. The drying chamber main body includes a vacuum pump for reducing the atmosphere inside the drying chamber main body, a cold trap that takes out water vapor in the drying chamber main body generated by microwave heating to the outside, cools it, and captures it. Is connected and
The cellulose nanofiber dispersion liquid in the drying chamber body is concentrated and dried by being irradiated with microwaves in a reduced pressure atmosphere formed by the vacuum pump, and the generated water vapor is converted into an external air flow formed by the vacuum pump. ride is discharged out of the drying chamber body, the concentration in a state of being caught by cooling the cold trap, according to any one of claims 1 to 5, characterized by being configured so that the dry process is performed A method for producing a dried product by concentrating cellulose nanofibers for redispersion.

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