JP6271459B2 - Method for producing cellulose porous membrane - Google Patents

Description

The present invention relates to the production how the cellulose membrane.

Cellulose porous membranes are characterized by high mechanical strength among polysaccharide porous membranes, low non-specific adsorption of proteins, etc., and the ability to support various ligands by modifying hydroxyl groups. Have. For this reason, a cellulose porous membrane is used for various purposes as a carrier, a separation membrane, or a filtration membrane.
When cellulose porous membrane is used as a carrier, separation membrane, or filtration membrane, it is important to determine performance that the porous membrane has sufficient physical strength and that the pore diameter of the porous membrane is appropriately controlled. It is.
The function of the porous membrane greatly depends on the pore diameter of the porous membrane. For example, in gel chromatography, each component is separated by utilizing the difference in elution time depending on the molecular size of each component contained in the mixture. Therefore, the pore size of the porous membrane greatly affects the resolution. In the carrier for adsorption used in ion exchange chromatography, affinity chromatography, and the like, the amount of the target adsorbate that can be supported in a certain volume varies depending on the pore surface area of the porous carrier. Thus, in order to use the porous membrane as a carrier, it is required to control the pore diameter of the porous membrane within a desired range.

When the mechanical strength of the cellulose porous membrane is not sufficient, when the cellulose porous membrane is used as a separation membrane or a filtration membrane, if the flow rate of the fluid is increased, the porous membrane is compressed and deformed by the pressure of the fluid. The porous membrane may break. It is important to have sufficient mechanical strength when using the porous membrane for various carriers.
Furthermore, when the porous membrane is produced industrially, when the specific surface area is large and the breaking strength of the porous membrane having a large number of pores is not sufficient, for example, when the porous membrane formed into a sheet is wound up From the viewpoint of productivity, the porous membrane is required to have sufficient breaking strength.

As a method for producing a porous cellulose membrane, a porous body is prepared by dissolving cellulose in an aqueous lithium bromide solution, cooling the obtained cellulose solution in a container, allowing it to gel, and then immersing it in water. A technique is disclosed (for example, see Non-Patent Document 1).
Also proposed is a method for producing a cellulose porous membrane in which a solution containing cellulose and an ionic liquid is solidified by contacting with a cellulose-insoluble liquid to form a porous cellulose membrane having an arbitrary shape and thickness. (For example, refer to Patent Document 1).
There has been disclosed a method for producing cellulose porous particles in which an aqueous calcium thiocyanate solution is used as a solvent for cellulose and cellulose is directly dissolved and granulated (for example, see Patent Document 2).

JP 2012-57137 A Japanese Patent No. 3601229

Cellulose, 2014, vol. 21, p1175

However, in the method described in Non-Patent Document 1, it has been studied to form a porous body by coagulating a cellulose solution in a container as a test, and the obtained cellulose porous body has low mechanical strength. It is hard to say that it has mechanical strength for practical use. Non-Patent Document 1 does not discuss improving the uniformity of the pores of the porous membrane and the strength of the porous membrane.
In the production method described in Patent Document 1, it is necessary to use a large amount of an expensive ionic liquid for the production of the cellulose porous membrane, and there is a problem in production cost. Moreover, in the manufacturing method described in Patent Document 1, a porous film is formed by a mold, and productivity is poor. Furthermore, since the cellulose porous membrane obtained by the method described in Patent Document 1 has a large pore diameter and a small specific surface area, it cannot be expected to have high adsorption performance when used for a carrier such as chromatography. There is a problem that the physical strength is not in a region where the physical strength is practically satisfactory.
The calcium thiocyanate aqueous solution used in the production method described in Patent Document 2 is concerned with toxicity and corrosivity, and it takes time for post-treatment of the waste liquid. Moreover, in patent document 2, it is not examined about forming a cellulose porous membrane.
Therefore, a simple method for producing a porous cellulose membrane having uniform and controlled pores and good mechanical strength, and a porous cellulose membrane having uniform and controlled pores and good mechanical strength There is a current demand for membranes.

  An object of the present invention is to provide an efficient method for producing a porous cellulose membrane having a large specific surface area, controlled pores, and a practically required breaking strength, and a large specific surface area and controlled fineness. An object of the present invention is to provide a porous cellulose membrane having pores and having a breaking strength necessary for practical use.

As a result of intensive studies, the present inventors obtained a cellulose solution film on the surface of a plate-like support by controlling the composition and temperature of the cellulose solution, and the peripheral edge of the solution film was obtained in an unconstrained state. The present invention has been completed by finding that the above-mentioned problems can be solved by a step of coagulating the liquid film of the cellulose solution.
Means for solving the above problems include the following embodiments.

<1> A solution preparation step of dissolving cellulose in an aqueous lithium bromide solution to prepare a cellulose solution containing 2% by mass to 15% by mass of cellulose with respect to the total amount of the cellulose solution; A solution formed by applying a cellulose solution obtained by applying a cellulose solution to the support surface and adjusting the temperature of the cellulose solution to 90 ° C. or higher so that the periphery of the cellulose solution membrane is unconstrained. A film forming step, a gel film forming step of cooling the formed cellulose solution film at a cooling rate of 1 ° C./min to 300 ° C./min to obtain a gel film containing cellulose, and a coagulation solvent in the gel film containing cellulose And a coagulation step of coagulating cellulose to obtain a porous membrane, and a method for producing a porous cellulose membrane.

<2> The liquid film forming step applies a certain amount of the cellulose solution to the surface of the plate-like support in the press molding machine, and press-molds the applied cellulose solution at a pressure of 0.1 MPa to 35 MPa. The method for producing a porous cellulose membrane according to <1>, comprising forming a cellulose solution membrane.
<3> The porous cellulose membrane according to <1>, wherein the liquid film forming step includes forming the cellulose solution film by continuously or intermittently applying the cellulose solution to the plate-like support surface by a coating method. Manufacturing method.
<4> The cellulose according to <1>, wherein the liquid film forming step includes forming the cellulose solution film by continuously or intermittently applying the cellulose solution to the plate-like support surface by a melt extrusion apparatus. A method for producing a porous membrane.

The manufacturing method of the cellulose porous membrane as described in any one of <1>-<4> including the washing | cleaning process which wash | cleans the porous film obtained through the <5> coagulation | solidification process.
The manufacturing method of the cellulose porous membrane as described in any one of <1>-<5> including the bridge | crosslinking process which forms a crosslinked structure in a porous film obtained through the <6> solidification process using a crosslinking agent.
<7> The cellulose porous membrane according to any one of <1> to <6>, wherein the viscosity at 110 ° C. of the cellulose solution obtained by the solution preparation step is in the range of 0.5 Pa · s to 500 Pa · s. Manufacturing method.

<8> The method for producing a porous cellulose membrane according to any one of <1> to <7>, wherein the cellulose is cellulose having an average degree of polymerization of 50 to 2000.
<9> Any of <1> to <8>, wherein the coagulation step is a step of bringing a coagulation solvent into contact with the gel film containing cellulose in a temperature condition of 20 ° C. to 80 ° C. of the gel film containing cellulose. The manufacturing method of the cellulose porous film as described in any one.
<10> The method for producing a cellulose porous membrane according to any one of <1> to <9>, comprising a freeze-drying step of freeze-drying the cellulose porous membrane to obtain a freeze-dried cellulose porous membrane.

In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.
In this specification, the term “process” is not only an independent process, but is included in this term if the intended purpose of the process is achieved even when it cannot be clearly distinguished from other processes.
In this specification, when referring to the amount of each component in the composition, when there are a plurality of substances corresponding to each component in the composition, a plurality of substances present in the composition unless otherwise specified. Means the total amount.
The room temperature in this specification refers to 25 ° C.

  According to the present invention, a simple method for producing a porous cellulose membrane having a large specific surface area, controlled pores, and having a required breaking strength, and a controlled pore having a large specific surface area And the cellulose porous membrane which has the breaking strength required practically can be provided.

It is a schematic block diagram which shows an example of the cellulose porous membrane manufacturing apparatus which can be used for the manufacturing method of the cellulose porous membrane of this invention. 2 is a scanning electron micrograph of the cellulose porous membrane obtained in Example 3 taken at 200 times. 3 is a scanning electron micrograph of the porous cellulose membrane obtained in Example 3 taken at 30,000 times.

  Hereinafter, specific embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present invention. .

The method for producing a porous cellulose membrane of the present invention comprises: (I) a solution preparation step of preparing a cellulose solution containing 2% by mass to 15% by mass of cellulose based on the total amount of the cellulose solution by dissolving cellulose in an aqueous solution of lithium bromide. (Hereinafter, it may be referred to as a solution preparation step.) (II) The prepared cellulose solution is applied to the plate-like support surface, and the cellulose solution film made of the cellulose solution is applied to the support surface. A liquid film forming step (hereinafter referred to as a liquid film forming step) in which the peripheral edge of the cellulose solution film is unconstrained by adjusting the temperature to 90 ° C. or higher, and (III) the formed cellulose solution The film is cooled at a cooling rate of 1 ° C./min to 300 ° C./min to obtain a gel film containing cellulose (hereinafter sometimes referred to as a gel film forming process) and (IV) contacting the coagulated solvent gel film containing a cellulose solidified cellulose by coagulation to obtain a porous film containing a cellulose (hereinafter sometimes referred to as the coagulation step), including.
Hereafter, the manufacturing method of this invention is demonstrated in detail in order of a process.

(I) Solution preparation step (solution preparation step) in which cellulose is dissolved in an aqueous lithium bromide solution to prepare a cellulose solution containing 2% by mass to 15% by mass of cellulose with respect to the total amount of the cellulose solution.

[cellulose]
As the cellulose used in the present invention, any cellulose that can be dissolved in a lithium bromide aqueous solution described later can be used without particular limitation.
Examples of the cellulose that can be used in the present invention include substituted celluloses such as crystalline cellulose powder, regenerated cellulose, and cellulose acetate.
A cellulose may be used individually by 1 type and may use 2 or more types together.
Among these, in order for the produced cellulose porous membrane to achieve a practically preferable level of breaking strength, the cellulose used for the preparation of the cellulose solution is preferably crystalline cellulose or regenerated cellulose. More preferably.
The average degree of polymerization of cellulose is preferably 50 or more and 2000 or less. It is preferable for the average degree of polymerization of the cellulose to be 2000 or less because it is possible to suppress an increase in the viscosity of the solution during dissolution of the cellulose. It is preferable that the average degree of polymerization of the cellulose is 50 or more because physical properties suitable for forming a liquid film on the support can be obtained, and the breaking strength of the formed porous cellulose film is practically sufficient.
The average degree of polymerization of cellulose is more preferably in the range of 100 to 1700, and still more preferably in the range of 200 to 1300.

The average degree of polymerization of cellulose can be measured by the method described in paragraph No. [0032] of JP-A-6-298999. More specifically, B.I. DALBE, A.D. “CELLULOSE CHEMISTRY AND TECHNOLOGY” Vol. 24, no. 3, P327-331 (1990). That is, in the measurement method described in this document, N-methylmorpholine-N-oxide hydrate, dimethyl sulfoxide, and propyl gallate were mixed at a weight ratio of 100/150/1, respectively. The solvent was used as a solvent for dissolving cellulose, cellulose was dissolved at a concentration of 0.2 g / 100 ml to 0.8 g / 100 ml, and the intrinsic viscosity of the obtained cellulose solution was measured at a temperature of 34 using an Ubbelohde dilution viscometer. The degree of polymerization of the cellulose was determined by the following viscosity formula (1).
Viscosity formula (1) [η] = 1.99 × (DP) v ^0.79
In the viscosity formula (1), [η] represents the intrinsic viscosity, and (DP) v represents the degree of polymerization of cellulose.

Commercially available cellulose may be used. When using a commercial product, the average degree of polymerization described in the catalog can be referred to.
Examples of commercially available cellulose that can be used in the present invention include Asola Kasei Chemicals Co., Ltd., Theolas (registered trademark) PH101 (trade name: average degree of polymerization 220), Other Theolas PH grades, KG grades, UF grades Various, manufactured by Nippon Paper Industries Co., Ltd., KC Flock W-400G (trade name: average polymerization degree 350), KC Flock W-300G (trade name: average polymerization degree 370), KC Flock W-200G (trade name: average polymerization) Degree 510), KC Flock W-100G (trade name: average polymerization degree 720), KC-Flock W-50G (trade name: average polymerization degree 820), sulfite pulp NDPT (trade name: average polymerization degree 1000) and the like. Can be mentioned.

[Lithium bromide aqueous solution]
The aqueous solution of lithium bromide is prepared by dissolving lithium bromide in water. The water used as the solvent is preferably ion-exchanged water or pure water with few impurities.
The content of lithium bromide contained in the lithium bromide aqueous solution is preferably 50% by mass to 70% by mass, more preferably 54% by mass to 69% by mass with respect to the total amount of the lithium bromide aqueous solution. More preferably, it is 55 mass%-68 mass%.
When the content of lithium bromide in the total amount of the lithium bromide aqueous solution is 50% by mass or more, the solubility of cellulose is improved, and when it is 70% by mass or less, the lithium bromide crystals are sufficiently dissolved and insoluble. Residue of substances, precipitation of lithium bromide crystals, and the like are suppressed.
The aqueous lithium bromide solution is prepared by dissolving lithium bromide in water while stirring as necessary. The lithium bromide aqueous solution may be prepared at room temperature, and may be carried out at about 0 ° C. to 80 ° C. if desired.

[Preparation of cellulose solution]
Cellulose is dissolved in the obtained aqueous lithium bromide solution to prepare a solution of cellulose in an aqueous lithium bromide solution (hereinafter sometimes referred to as a cellulose solution).
When dissolving cellulose in an aqueous lithium bromide solution, the aqueous lithium bromide solution is heated to 80 ° C. to 150 ° C., and the cellulose may be dissolved while stirring as necessary. As temperature in the case of making it melt | dissolve, it is more preferable that it is the range of 85 to 140 degreeC, and it is further more preferable that it is the range of 90 to 130 degreeC.
The lithium bromide aqueous solution used for preparing the cellulose solution is excellent in the solubility of cellulose. Therefore, the solution preparation step in the production method of the present invention has advantages such that a cellulose solution having an arbitrary concentration can be easily prepared, and coloring of cellulose due to heating in the cellulose solution preparation step is reduced.

The cellulose content with respect to the total amount of the cellulose solution prepared in the cellulose solution preparation step is in the range of 2% by mass to 15% by mass. The cellulose content can be appropriately adjusted in the range of 2% by mass to 15% by mass in consideration of various conditions in the liquid film forming step.
When the cellulose content in the cellulose solution is 2% by mass or more, the viscosity of the cellulose solution is appropriately maintained, and even under conditions where the peripheral portion of the liquid film is unconstrained, the fluidity is moderate while maintaining fluidity. The spread of the liquid film is maintained, and a desired liquid film can be formed on the surface of the plate-like support having no mold. Moreover, the viscosity of a cellulose solution is maintained appropriately and handling becomes favorable because content of the cellulose in a cellulose solution is 15 mass% or less.
The cellulose content relative to the total amount of the cellulose solution in the cellulose solution prepared in the solution preparation step is more preferably 3% by mass to 12% by mass, and further preferably 4% by mass to 10% by mass.

(II) The prepared cellulose solution is applied to the plate-like support surface, the cellulose solution film made of the cellulose solution is adjusted to the support surface, the temperature of the cellulose solution is adjusted to 90 ° C. or higher, and the cellulose solution film Liquid film formation process (liquid film formation process) formed under the condition that the peripheral edge is unconstrained
In the liquid film forming step, (I) the cellulose solution obtained in the cellulose solution preparation step is applied to the plate-like support surface, the temperature of the cellulose solution is adjusted to 90 ° C. or higher, and the cellulose solution film is formed on the support surface. (Hereinafter sometimes referred to as a liquid film).

The cellulose solution obtained in the solution preparation step is adjusted to a temperature of 90 ° C. or higher to form a cellulose solution film. The fluidity suitable for liquid film formation can be given to a cellulose solution because the temperature of the cellulose solution at the time of forming a liquid film is 90 degreeC or more. In addition, if the temperature of the cellulose solution subjected to the liquid film forming step is 90 ° C. or higher, the cellulose content in the cellulose solution, the thickness of the liquid film to be formed, and the method for forming the liquid film can be appropriately selected. . The upper limit of the temperature is not particularly limited, but is preferably 150 ° C. or less from the viewpoint of suppressing discoloration of cellulose due to heat.
Especially, from a viewpoint that a handleability and a favorable liquid film can be formed, 95 to 140 degreeC is preferable, 100 to 130 degreeC is more preferable, and 105 to 120 degreeC is further more preferable.
In addition to setting the temperature of the cellulose solution to 90 ° C. or higher, it is preferable to control the temperature of the member in contact with the cellulose solution to 90 ° C. or higher in the film forming apparatus or the like to be used. A liquid film forming apparatus used for forming the cellulose solution film will be described later.

In the production method of the present invention, a cellulose solution is applied to a smooth plate-like support surface without using a casting method in which a cellulose solution is poured into a conventionally known mold to form a liquid film. The cellulose solution film is formed under the condition that the periphery of the cellulose solution film formed by the above is unconstrained.
The condition that the peripheral part of the cellulose solution film is unconstrained is, for example, that when the cellulose solution applied to the support surface spreads on the support surface to form a liquid film, the peripheral part of the liquid film is the cellulose solution. The conditions which form the liquid film of a desired shape, without contacting the member which restrains liquid film peripheral parts, such as a frame which suppresses the spreading | diffusion of a liquid, are mentioned. According to the production method of the present invention, a cellulose solution film can be formed using a support that does not have a frame that rises perpendicularly from the surface.
In the liquid film forming step of the present invention, even if a support having no member such as a frame for controlling the spread of the solution is used, the solution does not flow down from the end of the support, and the uniform liquid A film is formed. For this reason, the formed liquid film can be subjected to a gel film forming process, which is the next process, without performing processing such as demolding required in the casting method.
In the liquid film forming step in the present invention, since a mold is not used for forming a cellulose solution film, the cellulose solution is injected into the mold and compared with a casting method in which demolding is performed after maintaining for a predetermined time. The productivity of film formation becomes better.

In order to form a good liquid film under the condition that the peripheral part of the liquid film formed by the cellulose solution is unconstrained, it is preferable to set the viscosity of the cellulose solution to be subjected to the liquid film forming step within an appropriate range.
As a preferable condition of the cellulose solution viscosity, the viscosity at 110 ° C. of the cellulose solution is preferably in the range of 0.5 Pa · s to 500 Pa · s, more preferably in the range of 2 Pa · s to 300 Pa · s, More preferably, it is in the range of 10 Pa · s to 200 Pa · s, and particularly preferably in the range of 30 Pa · s to 120 Pa · s.
When the viscosity of the cellulose solution at 110 ° C. is 500 Pa · s or less, for example, when a liquid film is formed by a melt extrusion apparatus, the extruded state is stabilized. Therefore, the film thickness of the formed liquid film becomes non-uniform, the liquid film partially thickens and whitens, and the occurrence of film failure such as the formation of spotted non-uniform parts is effectively suppressed. The Moreover, the fluidity | liquidity suitable for film formation is obtained because the viscosity in 110 degreeC of a cellulose solution is 0.5 Pa.s or more.

The value measured by the following method is used for the viscosity of the cellulose solution in the present invention.
A cellulose solution sample (40 mL) is placed in a 50 mL glass sample bottle, immersed in an oil bath, and the solution temperature is maintained at 110 ° C. A probe of a vibration viscometer (Viscomate VM-100A: trade name, manufactured by Seconic Corporation) is immersed in a cellulose solution at 110 ° C., and the viscosity is measured. Since the measurable viscosity differs depending on the type of probe used for measurement, the measurement is performed using an appropriate probe in consideration of the relationship between the viscosity and the usable probe.
L probe in the range of 0.04 Pa · s to 1 Pa · s, M probe in the range of 0.1 Pa · s to 10 Pa · s, H probe in the range of 5 Pa · s to 500 Pa · s. Is used. When measuring a cellulose solution having a viscosity where the measurement ranges of the probes overlap, for example, when measuring the viscosity of a cellulose solution having a viscosity of 5 Pa · s to 10 Pa · s, either the M probe or the H probe Measurements may be made using either of these probes, and the same result can be obtained using either probe.

The method for forming the liquid film is not particularly limited as long as the peripheral edge of the cellulose solution is unconstrained. From the viewpoint of productivity and application of a known manufacturing apparatus, it is preferable to apply a press molding method, a coating method, a melt extrusion method, or the like to the formation of the liquid film.
Among the liquid film forming methods, from the viewpoint of productivity, the melt extrusion method and the coating method are more preferable, and the melt extrusion method is more preferable.

(Press molding method)
As the press device used for the press molding method, any known press device capable of controlling the temperature of the press plate can be used. As a press apparatus that can be used in the present invention, a press apparatus including a press plate provided with a heating function, a water cooling function, and a vacuum chamber is preferable.
As a commercially available press apparatus that can be used in the present invention, a melt press apparatus, a Toyo Seiki Co., Ltd. product, a melt press equipped with three press plates having a heating function, a water cooling function, and a vacuum chamber. Apparatus: Minitest press-10 (trade name) and the like can be mentioned.
Using these devices, the temperature of the press plate is controlled to 90 ° C or higher, a cellulose solution heated to 90 ° C or higher is applied on the press plate, and the upper press is applied with a clearance according to the target film thickness. A liquid film having a film thickness corresponding to the clearance of the press plate can be obtained by press molding using a plate, preferably at a pressure of 0.1 MPa to 35 MPa. In the case of using an apparatus having three press plates, a liquid film is formed in two steps of the lowermost press plate and the intermediate press plate, and the intermediate press plate and the uppermost press plate in one step. be able to.

The press plate used in the press device is a temperature-controlled flat plate press plate and generally does not have a frame on the side of the press plate, so the peripheral portion of the liquid film formed by the cellulose solution is restrained. A liquid film can be formed under conditions that do not. Further, even if a press plate having a frame on the side is used, the peripheral portion of the liquid film is not in contact with the frame without the peripheral portion of the liquid film being in contact with the frame by controlling the amount of the cellulose solution applied on the press plate. A liquid film can be formed under restrictive conditions.
The temperature of the cellulose solution at the time of press molding is 90 ° C. or higher, and preferably 95 ° C. to 140 ° C., more preferably 100 ° C. to 130 ° C., from the viewpoint that a good surface shape can be obtained. More preferably, the temperature is from 120C to 120C.
The press pressure at the time of press molding is preferably from 0.1 MPa to 10 MPa, more preferably from 0.2 MPa to 7 MPa, and even more preferably from 0.5 MPa to 5 MPa from the viewpoint that a smooth surface can be obtained.
The press molding time is preferably 0.5 minutes to 60 minutes from the viewpoint that coloring of the formed film is suppressed and a smooth surface can be obtained. More preferably, it is more preferably 5 minutes to 10 minutes.
The clearance of the press plate is appropriately selected depending on the intended porous film, but is preferably 10 μm to 5000 μm, more preferably 20 μm to 3000 μm, and more preferably 50 μm to 1000 μm from the viewpoint of workability and uniformity of the formed film. Further preferred.
The amount of the cellulose solution applied on the press plate can be appropriately determined depending on the desired liquid film size.

By pressing the release film between the press plate and the cellulose liquid film applied on the press plate and between the surfaces of the applied cellulose solution (the surface on the side in contact with the upper press plate), the liquid film after pressing Can be easily peeled off.
Examples of the release film include a polyimide film and an aluminum sheet whose surface is treated with polytetrafluoroethylene.

(Coating method)
The coating method can be performed using a known coating apparatus.
The cellulose solution having a temperature of 90 ° C. or higher can be carried out by using a known coating apparatus such as a bar coater, a curtain coater, an air knife coater, a blade coater, or a roll coater, which is heated using a heating means. The cellulose solution applied on the support by the coating method becomes a cellulose solution film under the condition that the peripheral edge of the liquid film formed by coating is not constrained.
When forming a liquid film by a coating method, it is preferable to control the temperature of the support surface to which the cellulose solution is applied to 90 ° C. or higher from the viewpoint of forming a uniform liquid film.

When the liquid film is formed by the coating method, the amount of the cellulose solution applied, that is, the amount of the cellulose solution applied onto the support can be controlled in consideration of the thickness of the target porous film. The amount of the cellulose solution applied to the support can be controlled by the clearance of the bar coater, for example, when using a bar coater. Also in other coating apparatuses, the application amount can be controlled by a known method.
The amount of cellulose solution applied to the support in the coating method is appropriately determined according to the purpose. From the viewpoint of the uniformity of the liquid film to be formed, it is preferable to provide an amount such that the film thickness of the liquid film on the support of the cellulose solution is from 10 μm to 5000 μm, and more preferably from 20 μm to 3000 μm. Preferably, it is more preferable to apply an amount of 50 μm to 1000 μm.

When a liquid film is formed by a coating method, the liquid film may be formed intermittently by a batch method in which a fixed amount is applied to a plate-like support, and continuously applied on a belt-like long support. Thus, a liquid film may be formed. A liquid film can be continuously formed by applying a cellulose solution on a support using a belt-like long support, for example, a support such as an endless belt.
In the case of a belt-like support, the temperature of the support can be controlled by applying a known temperature control means such as bringing a heat roll into contact with the back surface.

(Melt extrusion method)
Formation of the cellulose solution film by the melt extrusion method can be performed using a known melt extrusion apparatus. The melt-extrusion apparatus can maintain the cellulose solution at a desired temperature of 90 ° C. or higher by controlling the temperature of the part having the screw inside the extrusion apparatus.

  Usually, the melt-extrusion apparatus is an apparatus that melts resin pellets and the like, kneads them with a screw, and forms the molten resin into a sheet or tube via a die. In the present invention, the material supplied to the melt-extrusion apparatus is a liquid cellulose solution or a cellulose solution cooled to a gel state, and strictly speaking, it does not correspond to melt-extrusion. However, in the melt extrusion method of the present invention, the liquid or gelled cellulose solution is heated to a properly controlled temperature in the melt extrusion apparatus to be in a fluid state, and cooled after being extruded through the die from the melt extrusion apparatus. In order to form a gel film, the melt-extrusion apparatus should behave in the same manner as film formation by melt extrusion using a thermoplastic resin, and the conditions suitable for temperature control of the cellulose solution and liquid film formation. Therefore, in this specification, liquid film formation using a melt extrusion apparatus is referred to as “melt extrusion method”.

The cellulose solution prepared in the solution preparation step and maintained at a predetermined temperature of 90 ° C. or higher is stirred with a screw in the melt extrusion apparatus and extruded into a sheet shape with a T-die, and the temperature is raised to 90 ° C. or higher. A liquid film is formed by applying on a controlled support. What is necessary is just to determine suitably the extrusion amount of a cellulose solution, ie, the provision amount to a support body, according to the thickness of the target porous membrane.
The amount of cellulose solution applied to the support in the melt extrusion method is appropriately determined according to the purpose. From the viewpoint of the uniformity of the liquid film to be formed, it is preferable to provide an amount such that the film thickness of the liquid film on the support of the cellulose solution is 10 μm to 5000 μm, and it is more preferable to provide an amount that is 20 μm to 3000 μm. Preferably, it is more preferable to apply an amount of 50 μm to 1000 μm.
The cellulose solution extruded from the T-die and applied onto the support becomes a cellulose solution film under the condition that the peripheral part, that is, the tip part and both immediate end parts of the liquid film are unconstrained.
In the liquid film forming step, as described above, various known methods are applied to form a liquid film of the prepared cellulose solution.

(III) Gel film forming step (gel film forming step) in which the formed cellulose solution film is cooled at a cooling rate of 1 ° C./min to 300 ° C./min to obtain a gel film containing cellulose.
In this step, the formed cellulose solution film is cooled to form a gel film containing cellulose.
In the liquid film forming step, the cellulose solution is maintained at a temperature of 90 ° C. or higher, and according to a preferred embodiment, at a temperature of 100 ° C. to 130 ° C. to form a cellulose solution film. By cooling the formed liquid film, the cellulose contained in the liquid film is gelled to form a gel film containing cellulose. Although the gelation temperature differs depending on the composition of the cellulose solution, gelation may occur at 80 ° C. to 90 ° C. depending on the composition.

Cooling is preferably performed until the temperature of the liquid film is in the range of 0 ° C. to 80 ° C. from the viewpoint that a gel film having excellent handleability can be obtained, and is cooled until the temperature is in the range of 1 ° C. to 70 ° C. More preferably, it is more preferably cooled to a range of 2 ° C to 60 ° C.
In consideration of productivity, the gel film is preferably formed in the liquid film in the range of 20 ° C to 60 ° C.

If the time required for cooling the cellulose solution film to the target temperature becomes long, there is a concern that the gelled cellulose film may be colored. If the cooling time is too short, a porous film having high mechanical strength cannot be obtained.
From the viewpoint described above, it is preferable to control the cooling rate of the liquid film according to the purpose. Specifically, the cooling rate is preferably 1 ° C / min to 300 ° C / min, more preferably 3 ° C / min to 200 ° C / min, and 10 ° C / min to 100 ° C / min. More preferably.
The crystallinity of cellulose in the resulting cellulose porous membrane can be controlled by adjusting the cooling rate. For example, the crystallinity can be lowered by increasing the cooling rate, and the crystallinity can be increased by reducing the cooling rate.
By suppressing the crystallinity to a low level, a cellulose porous membrane with little anisotropy can be obtained, and by increasing the crystallinity, a cellulose porous membrane having excellent mechanical strength can be obtained.

Cooling is performed subsequent to the liquid film forming step.
When a liquid film is formed by the press molding method, by controlling the temperature of the press plate in the press molding apparatus, the liquid film obtained is formed on the press plate after the liquid film is formed in the press molding apparatus. The gel film containing cellulose can be formed by cooling at a desired cooling rate using the temperature controller provided. Therefore, in the case of forming a liquid film by applying the press molding method, by using a press apparatus capable of controlling the temperature of the press plate, the liquid film and the gel film containing cellulose are formed in the press apparatus. Can be performed continuously.

  When forming a liquid film by the coating method or melt extrusion method, the temperature of the support itself is controlled, the liquid film is brought into contact with a cast roll, and the liquid film on the support is placed in the cooling device together with the support. It is possible to form a gel film containing cellulose by cooling by a method such as induction. As the cooling device used in the gel film forming step, a known cooling device can be appropriately used.

  When a liquid film is formed continuously or intermittently on a long support by a coating method or melt extrusion method, the support on which the liquid film is formed is guided into a cooling device such as a cooling zone. A method of passing through a cooling device, a method of cooling by bringing a cooling roll into contact with the side of the support that does not form a liquid film, and the like can be employed.

The cooling rate in the gel film forming step can be calculated by measuring the surface temperature of the gel film containing cellulose.
Using a midi LOGGER GL900 manufactured by GRAPFTEC, the thermocouple provided in the apparatus is directly brought into contact with the liquid film surface containing cellulose, and the liquid film surface temperature is measured. The cooling rate in the present invention is the temperature difference (° C.) in the cooling process from the temperature of the liquid film formed in the film forming process measured by the above-described method until the surface temperature of the gel film reaches 40 ° C. It is defined as the number divided by (minutes).
As in the press molding method, by controlling the temperature of the press plate, the temperature of the cellulose solution is set to 90 ° C. or higher to form a liquid film, and the liquid film formed between the press plates is cooled to contain cellulose. When forming a gel film, the temperature of the press plate that contacts the liquid film and the gel film containing cellulose is set as the surface temperature of the liquid film or the gel film containing cellulose, respectively, and the cooling rate in the present invention is calculated. can do.

  In addition, in the liquid film forming step, a mode in which the cellulose liquid film is continuously formed, the continuously formed liquid film is conveyed, and the gel film forming step and the coagulating step are subsequently performed will be described in detail below. To do.

(IV) A coagulation step (coagulation step) in which a coagulation solvent is brought into contact with a gel membrane containing cellulose to coagulate the cellulose to obtain a porous membrane containing cellulose.
In this step, a cellulose membrane is obtained by bringing the gel membrane containing cellulose obtained through the gel membrane formation step into contact with a coagulation solvent to coagulate the cellulose.
The porous film obtained by the coagulation step is a film having a porous structure formed by coagulation by contact with a coagulation solvent, and impurities remain in the obtained porous film. Hereinafter, the porous film in which impurities obtained by the solidification process remain in the film is appropriately referred to as “unpurified porous film”.
The gel film containing cellulose contains a lithium bromide aqueous solution or the like in the film. By bringing the coagulation solvent into contact with the gel film containing cellulose, the cellulose in the gel film is coagulated, the cellulose is regenerated, and a porous film containing cellulose is obtained. By regenerating cellulose and forming a porous film containing coagulated cellulose, lithium bromide contained in the gel film containing cellulose is separated.

As a coagulation solvent to be brought into contact with the gel film containing cellulose, a solvent capable of dissolving the lithium bromide salt is used.
The coagulation solvent is preferably a lower alcohol having 1 to 5 carbon atoms such as ethanol, methanol or isopropanol; a ketone such as acetone or methyl ethyl ketone; an ester such as ethyl acetate; an ether such as tetrahydrofuran;
A coagulation solvent may be used independently and may use 2 or more types together.

  The contact with the coagulation solvent is preferably performed after the gel film containing cellulose is cooled to a temperature of about 0 ° C. to 80 ° C. in the gel film forming step. A more preferable temperature of the gel film in contact with the coagulation solvent is the cooling temperature described in the gel film forming step.

There is no particular limitation on the method of bringing the coagulation solvent into contact with the gel film containing cellulose.
Since the gel film containing cellulose obtained in the gel film formation step is a self-supporting film, for example, a method of immersing the gel film peeled from the support in the coagulation solvent and bringing the gel film into contact with the coagulation solvent can be mentioned. .
Other methods for bringing the coagulation solvent into contact with the gel film include a method in which the support on which the gel film containing cellulose is formed is immersed in the coagulation solvent tank and brought into contact with the gel film, and the coagulation solvent is added to the gel film containing cellulose. The method of giving and making it contact with shower, spray, etc. is mentioned.

When the method of immersing a gel film containing cellulose in a coagulation solvent is taken, it is preferable to stir the coagulation solvent in the coagulation solvent tank from the viewpoint that cellulose is efficiently regenerated. As stirring speed of a coagulation solvent tank, it can be set as the range of 30 rpm-1000 rpm, for example. Agitation of the coagulation solvent tank can be performed by introducing an agitation device such as an agitation blade into the coagulation solvent tank or circulating the coagulation solvent in the coagulation solvent tank.
The above stirring speed is an example, and the stirring conditions are appropriately selected depending on the type of dispersion medium used, the cellulose raw material, the concentration and viscosity of the cellulose solution, the shape and size of the stirring blades in the stirrer, the type of the reaction vessel, and the like. .

In the coagulation step, a porous membrane coagulation film containing coagulated cellulose is formed by contact with a coagulation solvent, and the regenerated cellulose and lithium bromide are separated.
Hereinafter, the treatment for removing lithium bromide from the porous membrane coagulated membrane containing cellulose may be referred to as a desalting treatment.
It is preferable that impurities such as residual coagulation solvent and lithium bromide salt are removed from the porous membrane containing cellulose obtained in the coagulation step by washing with water to obtain the cellulose porous membrane of the present invention. Moreover, a cellulose porous film having a crosslinked structure can be obtained by bringing a crosslinking agent into contact with a porous film containing cellulose to form a crosslinked structure in cellulose.
First, the porous film obtained by removing the coagulation solvent by decantation, filtration, etc. from the regenerated cellulose-containing porous film obtained in the coagulation step is a dispersion medium, an organic solvent such as a coagulation solvent, a lithium bromide salt A porous film containing impurities such as a surfactant.

  When the cellulose solution is cooled to become a gel film containing cellulose and the gel film is solidified to become a porous film, the film thickness is not greatly changed in any step. Therefore, in the liquid film forming step, the film thickness of the resulting cellulose porous film can be controlled by controlling the film thickness of the cellulose solution film.

(IV) Additional optional steps In the method for producing a porous cellulose membrane of the present invention, in addition to the steps described above, additional optional steps as exemplified below may be included.
As optional steps, after the coagulation step, the unpurified porous membrane is washed to remove impurities, the crosslinking step is formed in the porous membrane to obtain a cellulose porous membrane with improved membrane strength, and the washing step And a freeze-drying step for sufficiently drying the wet cellulose porous membrane obtained through at least one of the crosslinking step and the like.

(IV-1) Cleaning Step In the present invention, it is preferable to include a cleaning step for cleaning the porous film obtained through the coagulation step.
The washing step is a step of obtaining a purified cellulose porous membrane by washing the unpurified porous membrane obtained through the coagulation step with a washing liquid containing water, an aqueous solvent, etc. to remove impurities.
In the unpurified porous film obtained through the coagulation step, various impurities such as bromide ions, lithium ions, and solvents derived from lithium bromide used for preparing the cellulose solution are contained.
In addition, after the porous film is subjected to a crosslinking step described later, the porous film contains various impurities such as a crosslinking agent, a surfactant, and a solvent.
For this reason, it is preferable to carry out a cleaning process to remove impurities.
When performing the crosslinking step described later, the washing step can be performed at least either before or after the crosslinking step.
From the viewpoint of improving the crosslinking reaction efficiency in the crosslinking step, it is preferable to carry out the washing step before the crosslinking step. Moreover, it is more preferable to perform a washing | cleaning process before and after a bridge | crosslinking process.
The cleaning liquid used in the cleaning process can contain at least one selected from the group consisting of water, methanol, ethanol and other organic solvents. As the main component of the cleaning liquid, water, ethanol, and a mixture of water and ethanol are preferable, and water is more preferable.
The cleaning liquid may further contain an additive such as a surfactant depending on the purpose.
Although there is no restriction | limiting in particular in the water used for a washing | cleaning liquid, From a viewpoint that there are few impurities, distilled water, ion-exchange water, a pure water etc. are preferable.
As a cleaning method in the cleaning step, a known method can be applied without limitation. As a cleaning method, for example, the porous membrane is cleaned by contacting with the cleaning liquid, and then the cleaned cellulose porous film and the cleaning liquid are separated, and the cleaning liquid is continuously applied to the porous film disposed in the liquid-permeable container. And a method of supplying to and cleaning.
When cleaning the porous membrane by bringing it into contact with the cleaning liquid, an operation of stirring the cleaning liquid may be performed. Further, the cleaning solution may be changed twice or more. In the case where the porous film is cleaned by contacting with the cleaning liquid, the amount of the cleaning liquid to be used is preferably an amount sufficiently contacting the porous film from the viewpoint of better cleaning properties.
The cellulose porous membrane from which impurities have been removed through the washing step can be used for various applications as it is.

(IV-2) Crosslinking step In order to further increase the strength of the cellulose porous membrane obtained by the production method of the present invention, in the production method of the present invention, the obtained cellulose porous membrane is converted into cellulose using a crosslinking agent. You may have further the bridge | crosslinking process which forms a crosslinked structure.
Cellulose porous membranes having a crosslinked structure are excellent in mechanical strength, particularly breaking strength, and are therefore suitable for use under high linear velocity, high pressure, etc. when used as separation membranes, filtration membranes, and the like.
Furthermore, by improving the tensile strength, even when winding the cellulose porous membrane continuously, the occurrence of a situation where the porous membrane breaks is suppressed, and the porous membrane is produced with higher productivity. Can do.
There is no restriction | limiting in particular in the crosslinking agent used by a bridge | crosslinking process, and bridge | crosslinking reaction conditions, In consideration of the conditions which provide intensity | strength required for the cellulose porous membrane obtained, it can carry out using a well-known technique.

  Examples of crosslinking agents that can be used in the crosslinking step include halohydrins such as epichlorohydrin, epibromohydrin, dichlorohydrin; trimethylolpropane polyglycidyl ethers such as trimethylolpropane triglycidyl ether, glycerol polyglycidyl ether, pentaerythritol poly Mention may be made of polyfunctional polyepoxides such as glycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, sorbitol polyglycidyl ether and the like. Especially, it is preferable to use epichlorohydrin as a crosslinking agent from a viewpoint that the intensity | strength of a cellulose porous membrane improves more.

In the cross-linking step, the porous film obtained through the coagulation step is brought into contact with an alkaline aqueous solution containing a cross-linking agent or an organic solvent containing a cross-linking agent, and fully in a temperature range of 0 to 90 ° C. for 1 to 24 hours. It can be carried out by a reaction method.
Although there is no restriction | limiting in particular in content of the crosslinking agent in alkaline aqueous solution or an organic solvent, It is preferable that it is the range of 0.1 volume part-10 volume parts of crosslinking agents with respect to 1 volume part of cellulose porous membranes. In order to increase the efficiency of the crosslinking reaction, it is desirable to contain a reducing agent such as sodium borohydride in the alkaline aqueous solution or organic solvent containing the crosslinking agent.
By carrying out a crosslinking step on the porous membrane, the cellulose contained in the porous membrane forms a crosslinked structure, and as a result, the cellulose porous membrane obtained through the crosslinking step is a crosslinking step obtained through the coagulation step. Compared with a porous membrane not subjected to the above, the strength is further improved.

Prior to the above-described crosslinking step, it is preferable to perform a water washing step of washing the porous film obtained in the coagulation step with a washing liquid containing water.
The unpurified porous film contains various impurities such as bromide ions and lithium ions derived from lithium bromide used for forming the porous film, and a solvent.
According to the study by the present inventors, when bromide ions, lithium ions, etc. remain in the porous film during the crosslinking step, aggregation of cellulose molecules and formation of a crosslinked structure between celluloses by a crosslinking agent are inhibited. I found out there was a concern. On the other hand, it is considered that the remaining amount of lithium ions and bromide ions makes the aggregation of cellulose molecules strong and a strong cross-linked structure is formed, and the obtained porous cellulose membrane can express better mechanical strength. It is done.
Therefore, from the viewpoint of obtaining a cellulose porous membrane having higher mechanical strength, it is preferable to obtain an unpurified porous membrane and then carry out a water washing step to remove impurities in the porous membrane and then carry out a crosslinking step.
The cleaning liquid used in the water washing step may be water, or may be a cleaning liquid containing water and one or more components selected from a hydrophilic solvent, a surfactant and the like. Among these, water is preferable as the cleaning liquid.
Although there is no restriction | limiting in particular in the water used for a washing | cleaning liquid, From a viewpoint that there are few impurities, distilled water, ion-exchange water, a pure water etc. are preferable.

In the washing step prior to the crosslinking step, the lithium ion and bromide ion contained in the porous membrane are washed with water until each of lithium ions and bromide ions is 2000 mmol or less per 1 kg of the dry mass of the porous membrane, thereby improving the formation efficiency of the crosslinked structure. To preferred. Lithium ions and bromide ions are more preferably 1000 mmol or less, more preferably 800 mmol or less, and particularly preferably 200 mmol or less, per 1 kg of the dry mass of the porous membrane.
A dried cellulose porous membrane which is a measurement target of the content of lithium ions and bromide ions contained in the porous membrane before the crosslinking step can be obtained as follows.
A dry cellulose porous membrane suitable as a measurement target for the content of lithium ions and bromide ions is obtained by subjecting a porous membrane obtained through a coagulation step, preferably a wet cellulose porous membrane that has been washed with water, to solvent replacement with acetone. It can be produced by drying. As a drying condition, for example, a condition of drying at 40 ° C. for 5 hours under vacuum is preferably exemplified.

The measurement of residual lithium ions in the porous film can be performed using an ICP emission spectroscopic analyzer (Optima 7300 DV, manufactured by Perkin Elmer) under the standard conditions of the apparatus. In the measurement, the dried porous membrane is made into a solution with an acid (70% by mass aqueous solution of nitric acid), the lithium ions contained in the solution are quantified, and the lithium ion content per 1 kg of the dry mass of the porous membrane is calculated.
The measurement of residual bromide ions in the porous membrane can be performed using a combustion halogen analyzer (AQF-100, manufactured by Mitsubishi Chemical Analytech Co., Ltd.) under the standard conditions of the apparatus. The dried porous film is burned, and the generated bromine is absorbed by the absorbing solution (hydrogen peroxide solution). The determination of bromide ions is performed using an ion chromatograph (ICS-1500, manufactured by Dionex), and the bromide ion content per kg dry mass of the porous membrane is calculated.

As described above, in the washing step prior to the crosslinking step, washing is preferably performed until the measured lithium ion and bromide ion contents are each 2000 mmol or less. The cleaning method is not particularly limited, and any known cleaning method can be arbitrarily applied as long as the target lithium ion and bromide ion content reduction can be achieved.
As the cleaning step, for example, the cleaning process with a cleaning liquid containing a sufficient amount of water may be performed once, or the cleaning process may be performed twice or more by changing the cleaning liquid.
The number and conditions of the washing treatment in the washing step can be appropriately determined in consideration of the required strength of the porous cellulose membrane and the target impurity content reduction amount.

  After the cross-linking step, it is preferable to further perform the above-described washing step to remove impurities such as a cross-linking agent and a solvent remaining in the cellulose porous membrane having a cross-linked structure.

(IV-3) Freeze-drying step In order to obtain a dried cellulose porous membrane by removing liquid components such as cleaning liquid, moisture, and solvent remaining in the membrane from the obtained cellulose porous membrane, A freeze-drying step of freeze-drying the cellulose porous membrane may be further included.
In the freeze-drying step, first, ethanol or the like is brought into contact with the wet cellulose porous membrane, and after replacing the water or the like contained in the cellulose porous membrane with ethanol or the like, ethanol is further substituted with t-butanol. The solvent replacement step and the step of freezing the porous cellulose membrane after the solvent replacement step at −18 ° C. or lower and lyophilization by a conventional method can be included.
By performing a freeze-drying step as desired, a dried cellulose porous membrane free from liquid components such as water and organic solvents can be obtained.
When measuring the specific surface area, pore diameter, etc. of the cellulose porous membrane, it is preferable to use a dried cellulose porous membrane, more preferably a freeze-dried cellulose porous membrane.

[Continuous production of porous membrane]
Among the steps described above, in the liquid film forming step, a liquid film is continuously formed on the support, and the formed liquid film is cooled while being conveyed to form a gel film containing cellulose. A porous film can be continuously manufactured by contacting.
Hereinafter, an example of the continuous manufacturing method of the porous film using a melt extrusion apparatus is demonstrated.
FIG. 1 is a schematic configuration diagram illustrating an example of a porous membrane manufacturing apparatus 10 used in a continuous manufacturing method of a porous membrane. The porous membrane production apparatus 10 includes a melt extrusion apparatus 18 including a raw material tank 12 filled with a cellulose solution, a heater 14, and a screw 16, and a cooling apparatus 20 that cools the obtained cellulose solution film to form a gel film. The gel film is brought into contact with a coagulation solvent to form a porous film, the coagulation solvent tank 22 having a gel film conveyance drive roll 22A, and the porous film conveyance drive roll 24A for washing the formed porous film with water. The water washing tank 24 provided, the take-up machine 26 which conveys the cellulose porous membrane washed with water, and guide | induces it to the winder 28, and the winder 28 which winds up the formed cellulose porous film are provided.

The cellulose solution prepared in the cellulose solution preparation step is supplied to the raw material tank 12 of the melt extrusion device 18. The cellulose solution may be cooled and gelled for the purpose of improving handleability and then supplied to the raw material tank 12. The cellulose solution in the raw material tank 12 is supplied into a melt extrusion device 18 including a heater 14 and a screw 16. The melt-extrusion apparatus 18 is maintained at a predetermined temperature of 90 ° C. or higher by a heater, and the cellulose solution is maintained at a temperature of 90 ° C. or more in the melt-extrusion apparatus 18, mixed by the screw 16, and provided with a T die. The cellulose solution film (F) having a desired film thickness is supplied onto the support through the T die provided to the discharge port 18A and provided in the discharge port 18A.
The cellulose solution film (F) on the support is conveyed into the cooling device 20 through a sizing die 20 </ b> A connected to the cooling device 20.
The cooling device 20 includes a cooling member (not shown), and the cellulose solution film (F) transported in the cooling device 20 is cooled at a predetermined cooling rate in the cooling device 20 and is transferred to an outlet of the cooling device 20. In the meantime, it becomes a gel film (G1). The cooling rate can be controlled by controlling the temperature in the cooling device 20 and the conveyance speed.

The formed gel film (G1) is a self-supporting film. Here, the self-supporting film refers to a film that maintains its shape as a film without stretching or breaking when the formed gel film is gripped and lifted.
The formed gel film (G1) is introduced into the coagulation solvent tank 22 containing the coagulation solvent by a driving roller 22A provided in the coagulation solvent tank 22, and the gel film (G1) and the coagulation solvent come into contact with each other. Is formed in the coagulation solvent tank 22. The coagulation solvent tank 22 is provided with a stirring device (not shown) for stirring the coagulation solvent for sufficiently bringing the gel film into contact with the coagulation solvent. The gel film (G1) that efficiently contacts the coagulation solvent in the coagulation solvent tank 22 becomes an unpurified porous film (G2) in which cellulose contained in the gel film is regenerated.
The formed unpurified porous membrane (G2) is unloaded from the coagulation solvent tank 22, transported to the water washing tank 24 by the drive roll 24A, washed in the water washing tank 24, and remaining in the porous film. Impurities such as a coagulation solvent and a lithium bromide salt are removed, and a purified cellulose porous membrane (C) is formed.
The cellulose porous membrane (C) is conveyed to the winder 28 via the take-up machine 26 for preventing damage and efficiently winding, and is taken up by the winder 28.
By using the porous membrane manufacturing apparatus 10 as shown in FIG. 1, a cellulose porous membrane can be continuously manufactured.

In the porous membrane production apparatus 10 of FIG. 1, the cellulose porous membrane (C) that has been washed in the washing tank 24 is wound as it is on the winder 28, but the production method of the present invention is not limited to this embodiment. .
For example, if necessary, a drying device may be provided between the washing tank 24 and the take-up machine 26, and the cellulose porous membrane (C) may be dried and wound by the winder 28.
Furthermore, in order to carry out the optional cross-linking step, the porous membrane obtained through the coagulation step downstream of the coagulation solvent tank 22 and before the water washing tank 24 or downstream of the water washing tank 24 You may provide the crosslinking agent containing tank provided with the temperature control apparatus which contacts with a crosslinking agent and bridge | crosslinks.
The porous film obtained through the coagulation step is brought into contact with the crosslinking agent solution in the crosslinking agent-containing tank to form a crosslinked structure in the cellulose contained in the porous film, thereby making it stronger than an uncrosslinked porous film. A high cellulose porous membrane can also be formed continuously.
The crosslinking step may be carried out continuously using a crosslinking agent-containing tank as described above, but the obtained porous film is taken out and cut into a predetermined length, and the cut porous film is cut into a crosslinking agent. You may carry out by the batch process made to contact with.

[Cellulose porous membrane]
Cellulose porous membrane obtained by the method for producing a cellulose porous membrane of the present invention described above, may be referred to as cellulose porous membrane of the present invention.
The cellulose porous membrane of the present invention has pores formed by removing lithium bromide and the like from a porous membrane containing cellulose regenerated through a coagulation step, and becomes a porous membrane with good mechanical strength. .
Since the porous cellulose membrane obtained by the production method of the present invention has pores inside and has good mechanical strength, it can be suitably used for various applications.

  Below, the preferable physical property of the cellulose porous membrane of this invention is mentioned.

[Average pore diameter]
The pore diameter of the porous cellulose membrane of the present invention is preferably 10 nm or more and 2000 nm or less in terms of average pore diameter. The pore diameter of the cellulose porous membrane is more preferably 20 nm or more and 1000 nm or less, and further preferably 50 nm or more and 800 nm or less.
When the pore diameter of the obtained cellulose porous membrane is within the above range, for example, when used as a chromatography carrier, a filtration membrane, a separation membrane, etc., the substance applied as a sample is sufficiently diffused, Since the membrane has a high specific surface area as shown below, excellent adsorption performance is exhibited.
The method for measuring the average pore diameter will be described in detail in Examples.

[Specific surface area]
The specific surface area of the cellulose porous membrane is preferably 140 m ² / g or more, more preferably 150 m ² / g or more, further preferably 160 m ² / g or more, and 180 m ² / g or more. It is particularly preferred.
The upper limit of the specific surface area is not particularly limited, but if the specific surface area is too large, the material diffusion in the porous film may be inhibited, and from the viewpoint of suppressing the substance diffusion inhibition in the porous film, 1000 m ² / g or less is preferable.
For example, when the specific surface area is 140 m ² / g or more, for example, when used as a chromatography carrier, the adsorption performance is further improved.
According to the production method of the present invention, it is a great feature that a cellulose porous film having an arbitrary film thickness and specific surface area can be prepared by adjusting the various conditions described above.
The method for measuring the specific surface area will be described in detail in Examples.

[Tensile breaking strength]
Considering the use of the cellulose porous membrane of the present invention for filtration membranes, separation membranes, various carriers, etc., the cellulose porous membrane preferably has a good mechanical strength that satisfies practical requirements.
“Mechanical strength” in the present invention means that the tensile strength at break of the cellulose porous membrane is practically sufficient.
The tensile strength at break in the present invention is the lyophilized film obtained through the lyophilization process described above, cut into 2 cm × 7 cm strips, sandwiched 1 cm at both ends by the chuck part, manufactured by A & D, Tensile breaker: Tensillon RTG-1310 (trade name) is used, and the point of maximum stress until breakage when a tensile test is performed at 1 cm / min at room temperature is defined as tensile break strength.
Cellulose porous membrane obtained by the method of the present invention has a tensile strength measured in the measurement conditions described above is preferably at 450 N / mm ² or more, more preferably 550 N / mm ² or more, 650 N / More preferably, it is mm ² or more.

[Ion content]
The lithium ion content and bromide ion content in the cellulose porous membrane are preferably 0.0001 mmol or more and 100 mmol or less, respectively, per 1 kg of the dry porous membrane.
In the cellulose porous membrane of the present invention, the amount of remaining lithium ions and bromide ions are respectively different from those obtained from the viewpoint of suitability for applications such as mechanical strength of the obtained cellulose porous membrane and few impurities such as antibody purification. It is preferably 100 mmol or less per kg of membrane, more preferably 20 mmol or less. When at least one of lithium ions and bromide ions remains in the cellulose porous membrane, for example, when the cellulose porous membrane is used as an adsorption carrier, various chromatographic carriers, etc., This is because lithium ions and bromide ions remaining in the porous film may be mixed to cause deterioration of the quality of the purified product. In the case where ions as impurities are contained in the obtained purified product, it is necessary to increase the number of washings of the purified product in order to reduce the ion content, resulting in an increase in production cost. As described above, the lithium ion content and bromide ion content are preferably in the range of 100 mmol or less per 1 kg of the dried cellulose porous membrane.
Considering the productivity of the cellulose porous membrane and the detection limit when measured using a general measuring device, the lithium ion content and bromide ion content were 0.01 mmol or more and 100 mmol or less, respectively, per 1 kg of dry particles. It may be 0.1 mmol or more and 100 mmol or less, or 1 mmol or more and 100 mmol or less.

The dry cellulose porous membrane used for the measurement of the lithium ion or bromide ion content is prepared by solvent-substituting the cellulose porous membrane in a wet state with acetone and vacuum drying at 40 ° C. for 5 hours under reduced pressure. be able to.

  The residual lithium ion content is measured using an ICP emission spectroscopic analyzer (Optima 7300 DV, manufactured by Perkin Elmer) under the standard conditions of the apparatus. The measurement is performed by obtaining a solution obtained by dissolving a dry cellulose porous membrane with an acid (70% by mass aqueous solution of nitric acid), and quantifying lithium ions in the obtained solution.

  The residual bromide ion content is measured using a combustion halogen analyzer (AQF-100, manufactured by Mitsubishi Chemical Analytech) under the standard conditions of the apparatus. The dried cellulose porous membrane was burned, and the generated bromine was absorbed into the absorption liquid (hydrogen peroxide solution), and the amount of bromide ions in the absorption liquid was measured. An ion chromatograph (ICS-1500, manufactured by Dionex) is used for quantification of bromide ions.

  The novel cellulose porous membrane of the present invention is a carrier for various chromatography such as ion exchange chromatography, affinity chromatography, size exclusion chromatography, and distribution chromatography, separation membrane, filtration membrane, adsorbent, test drug and bioreactor. It can be used as a carrier, a scaffold for cell culture, and the like.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist thereof.

[Example 1]
(Cellulose solution preparation process)
2.5 g of crystalline cellulose powder [KC Flock W-50G (trade name), average degree of polymerization 820, manufactured by Nippon Paper Industries Co., Ltd.]] was added to 47.5 g of a 60% by mass lithium bromide aqueous solution at 110 ° C. A cellulose solution was prepared by heating and dissolving.

(Liquid film formation process)
The obtained cellulose solution was allowed to cool until the temperature reached 40 ° C., and gelled. 10 g of the gelatinized cellulose solution was weighed, sandwiched between two stainless steel plates with a clearance of 500 μm in thickness, and pressed with a press device to form a cellulose solution film.
A melt press apparatus (Mini Test Press-10 manufactured by Toyo Seiki Co., Ltd.) was used for press film formation. The gel-like cellulose solution sandwiched between the stainless steel plates was compressed by a press apparatus at 110 ° C. and a pressure of 2 MPa to form a cellulose solution film. The temperature was adjusted by a temperature adjusting device provided on the press plate.

(Gel film formation process)
While the formed cellulose solution film was sandwiched between press plates, a temperature adjusting device provided on the press plate was controlled to cool to near room temperature at 1 ° C./min to form a cellulose-containing gel film. . The obtained gel film was a self-supporting film.

(Coagulation process)
The gel film containing cellulose obtained from between the press plates is taken out, and the gel film obtained is immersed in a container containing 500 mL (500 cm ³ ) of methanol as a coagulation solvent, and shaker (Neo Shaker, manufactured by ASONE Corporation). NS-S: trade name) was used for 1 day at room temperature under the condition of shaking rotation speed: 30 rpm to coagulate the cellulose contained in the gel membrane, thereby obtaining a porous membrane containing cellulose.
The obtained porous membrane was washed with methanol and then washed with a large amount of ion-exchanged water to remove the remaining salt, solvent and the like, and a wet cellulose porous membrane having a thickness of 500 μm was obtained.

[Evaluation of Cellulose Porous Membrane]
The cellulose porous membrane obtained in Example 1 was sequentially subjected to a substitution treatment with a 50% by volume ethanol aqueous solution, a 70% by volume ethanol aqueous solution, a 95% by volume ethanol aqueous solution, and 100% by volume ethanol. Furthermore, after substituting ethanol contained in the cellulose porous membrane with t-butanol, it was frozen (−18 ° C. or lower) and then freeze-dried to obtain a freeze-dried cellulose porous membrane for measuring the ion content and pore diameter. It was. Also in the following examples and comparative examples, a freeze-dried cellulose porous film was used as the evaluation porous film.
The evaluation results of the cellulose porous membrane obtained in the following Examples and Comparative Examples are shown in Tables 1 to 4 below.

(Measurement of ion content)
The lithium ion in the cellulose porous membrane is measured using an ICP emission spectroscopic analyzer (Optima 7300 DV, manufactured by Perkin Elmer) under the standard conditions of the apparatus. First, the freeze-dried cellulose porous membrane was dissolved with an acid (70% by mass aqueous solution of nitric acid), the lithium ions contained in the solution were quantified, and the lithium ion content per kg dry mass of the porous membrane was calculated.
The measurement of bromide ions in the cellulose porous membrane is performed using a combustion halogen analyzer (AQF-100, manufactured by Mitsubishi Chemical Analytech Co., Ltd.) under the standard conditions of the apparatus. The freeze-dried cellulose porous membrane was burned, and the generated bromine was absorbed into the absorbing solution (hydrogen peroxide solution). The determination of bromide ions was performed using an ion chromatograph (ICS-1500, manufactured by Dionex), and the bromide ion content per kg dry mass of the porous membrane was calculated.
When the contents of lithium ions and bromide ions remaining in the freeze-dried cellulose porous membrane were measured, the lithium ions were 14.5 mmol per kg of the dry membrane, and the bromide ions were 16.3 mmol per kg of the dry membrane.

(Measurement of average pore diameter, maximum pore diameter, and specific surface area)
Using the obtained freeze-dried cellulose porous membrane, pore distribution analysis was performed by a mercury intrusion method using a micromeritic pore distribution measuring device Autopore 9520 (trade name) manufactured by Shimadzu Corporation.
Using a freeze-dried cellulose porous membrane as a sample, about 0.05 g was weighed into a 5 cm ³ cell and measured at an initial pressure of about 5 kPa. The calculated median diameter was adopted as the average pore diameter.
In the obtained pore distribution, the value of the largest pore diameter detected was taken as the maximum pore diameter. The surface area per unit mass was calculated from the obtained pore distribution, and the obtained numerical value was taken as the specific surface area.

(Measurement of tensile strength)
The freeze-dried cellulose porous membrane was cut into a 2 cm × 7 cm strip, and 1 cm at both ends were sandwiched between chuck portions, and a tensile test was performed. In the tensile test, Tensilon RTG-1310 manufactured by A & D Co., Ltd. was used, and the point of maximum stress until tensile and ruptured at a speed of 1 cm / min at room temperature was defined as tensile strength. The average value measured 10 times in each example was determined and evaluated according to the following criteria.
Ranks A to C are practically sufficient breaking strengths as a cellulose porous membrane, and rank D is a breaking strength that cannot be practically used.
A: 650 N / mm ² or more B: 550 N / mm ² or more 650 N / mm ² lower than C: 450 N / mm ² or more 550 N / mm ² smaller than D: 450 N / mm less than ²

[Example 2]
A porous cellulose membrane was obtained in the same manner as in Example 1 except that the cooling rate of the liquid film in the gel film forming step was changed from 1 ° C./min to 3 ° C./min.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Example 3]
A porous cellulose membrane was obtained in the same manner as in Example 1 except that the cooling rate of the liquid film in the gel film forming step was changed from 1 ° C./min to 10 ° C./min.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

Further, the lyophilized cellulose porous film obtained in Example 3 was subjected to vapor deposition treatment with osmium for photographing. Then, the scanning electron microscope (SEM) image (magnification: 200 times and 30,000 times) was image | photographed with respect to the cellulose porous film which performed the vapor deposition process by osmium. FIG. 2 is an SEM image of the lyophilized cellulose porous membrane obtained in Example 3 taken with a scanning electron microscope at a magnification of 200. FIG. 3 is an image of the lyophilized cellulose porous membrane obtained in Example 3. It is the SEM image of the magnification of 30,000 times.
From the SEM image of FIG. 2, it can be seen that the cellulose porous membrane obtained in Example 3 has a smooth surface. From the SEM image of FIG. 3, it can be seen that the cellulose porous membrane obtained in Example 3 is fine and has uniform voids.

[Example 4]
A porous cellulose membrane was obtained in the same manner as in Example 1 except that the cooling rate of the liquid film in the gel film forming step was changed from 1 ° C./min to 20 ° C./min.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Example 5]
A porous cellulose membrane was obtained in the same manner as in Example 1 except that the cooling rate of the liquid film in the gel film forming step was changed from 1 ° C./min to 60 ° C./min.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Example 6]
A porous cellulose membrane was obtained in the same manner as in Example 1 except that the cooling rate of the liquid film in the gel film forming step was changed from 1 ° C./min to 100 ° C./min.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Example 7]
A porous cellulose membrane was obtained in the same manner as in Example 1, except that the cooling rate of the liquid film in the gel film forming step was changed from 1 ° C./min to 300 ° C./min.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Example 8]
A porous cellulose membrane was obtained in the same manner as in Example 3 except that methanol, which is a coagulation solvent in the coagulation step, was changed to acetone.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Example 9]
A porous cellulose membrane was obtained in the same manner as in Example 3 except that methanol, which is a coagulation solvent in the coagulation step, was changed to water.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Example 10]
In the cellulose solution preparation step, 3.5 g of crystalline cellulose powder was added to 46.5 g of a 60% by mass lithium bromide aqueous solution and dissolved by heating at 110 ° C. to prepare a cellulose solution having a concentration of 7% by mass. A porous cellulose membrane was obtained in the same manner as in Example 3 except that the obtained cellulose solution was used.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Example 11]
A cellulose porous membrane was formed in the same manner as in Example 3, and the obtained porous membrane was washed with methanol and then washed with a large amount of ion-exchanged water. Then, the following bridge | crosslinking processes were implemented with respect to the porous film after washing | cleaning.
(Crosslinking process)
After adding 10 mL of 0.5 mol aqueous sodium hydroxide solution to 10 g of wet cellulose porous membrane and heating at 45 ° C. for 10 minutes, 20 mg of sodium borohydride (manufactured by Wako Pure Chemical Industries, Ltd.) Epichlorohydrin (10 mL) was added as a crosslinking agent and reacted at 45 ° C. for 3 hours to form a crosslinked structure in the cellulose porous membrane. Then, the cellulose porous membrane in which the crosslinked structure was formed was obtained by washing with a large amount of water.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Example 12]
(Cellulose solution preparation process)
2.5 g of crystalline cellulose powder [KC-Flock W-50G (trade name), average polymerization degree 820, manufactured by Nippon Paper Industries Co., Ltd.] was added to 47.5 g of a 60% by mass aqueous lithium bromide solution at 110 ° C. A cellulose solution was obtained by heating and dissolving.

(Measurement of cellulose solution viscosity)
40 mL of the cellulose solution obtained in the cellulose solution preparation step was placed in a 50 mL glass sample bottle, immersed in an oil bath, and the solution temperature was maintained at 110 ° C. A probe of a vibration viscometer (Viscomate VM-100A: trade name, manufactured by Seconic Co., Ltd.) was immersed in a cellulose solution at 110 ° C., and the viscosity was measured. Since the measurable viscosity differs depending on the type of probe used for the measurement, the measurement was performed using an appropriate probe in consideration of the relationship between the viscosity and the usable probe.
L probe in the range of 0.04 Pa · s to 1 Pa · s, M probe in the range of 0.1 Pa · s to 10 Pa · s, H probe in the range of 5 Pa · s to 500 Pa · s. Was used.
The viscosity of the cellulose solution prepared in Example 12 at 110 ° C. was 46 Pa · s.

(Liquid film formation process)
A bar coater (clearance 500 μm) used in a thermostat and a stainless plate used for the support were heated to 110 ° C. in advance.
The cellulose solution obtained in the solution preparation step was heated to 110 ° C. and quickly applied onto a flat stainless steel plate as a support using a bar coater to form a cellulose solution film on the stainless steel plate. The cellulose solution spreads moderately on the support, and a liquid film having a uniform thickness was formed.
Thereafter, the entire stainless steel plate was immediately returned to a thermostat of 110 ° C.

(Gel film formation process)
The cellulose solution film was cooled to room temperature at a cooling rate of 1 ° C./min by lowering the temperature setting of a thermostatic chamber containing the support on which the liquid film was formed, and a gel film was formed at room temperature.
The cooling rate was measured as follows. First, the temperature of the liquid film surface is measured by contacting the thermocouple provided in the apparatus directly with the liquid film surface containing cellulose using the GRIDFGL Corp. midi LOGGER GL900, and then cooled to room temperature. The temperature of the gel film was the same as the measurement of the liquid film surface temperature. When the difference between the liquid film surface temperature and the gel film surface temperature was divided by the time taken to cool the liquid film to room temperature, the cooling rate was 1 ° C./min.

(Coagulation process)
The obtained gel film was peeled from the support, immersed in 500 mL of methanol as a coagulation solvent, and shaken for 1 day at room temperature using a shaker.
The obtained porous membrane containing cellulose was washed with methanol and then washed with a large amount of ion-exchanged water to remove remaining salts, solvents, etc., and a wet cellulose porous membrane was obtained.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Example 13]
A porous cellulose membrane was obtained in the same manner as in Example 12 except that the cooling rate of the liquid film in the gel film forming step was changed from 1 ° C./min to 3 ° C./min.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Example 14]
A porous cellulose membrane was obtained in the same manner as in Example 12 except that the cooling rate of the liquid film in the gel film forming step was changed from 1 ° C./min to 10 ° C./min.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Example 15]
A porous cellulose membrane was obtained in the same manner as in Example 12 except that the cooling rate of the liquid film in the gel film forming step was changed from 1 ° C./min to 100 ° C./min.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Example 16]
A porous cellulose membrane was obtained in the same manner as in Example 12 except that the cooling rate of the liquid film in the gel film forming step was changed from 1 ° C./min to 300 ° C./min.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Example 17]
A porous cellulose membrane was obtained in the same manner as in Example 14 except that methanol, which is a coagulation solvent in the coagulation step, was changed to acetone.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Example 18]
In the cellulose solution preparation step, 3.5 g of crystalline cellulose powder was added to 46.5 g of a 60% by mass lithium bromide aqueous solution and dissolved by heating at 110 ° C. to prepare a cellulose solution having a cellulose concentration of 7% by mass. A porous cellulose membrane was obtained in the same manner as in Example 14 except that the obtained cellulose solution was used.
When the viscosity at 110 ° C. of the cellulose solution was measured in the same manner as in Example 12, it was 114 Pa · s. The cellulose solution spreads moderately on the support, and a liquid film having a uniform thickness was formed.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Example 19]
A cellulose porous membrane was formed in the same manner as in Example 14, and the obtained porous membrane was washed with methanol and then washed with a large amount of ion-exchanged water. Then, the following bridge | crosslinking processes were implemented with respect to the porous film after washing | cleaning.
(Crosslinking process)
After adding 10 mL of 0.5 mol aqueous sodium hydroxide solution to 10 g of wet cellulose porous membrane and heating at 45 ° C. for 10 minutes, 20 mg of sodium borohydride (manufactured by Wako Pure Chemical Industries, Ltd.) Epichlorohydrin (10 mL) was added as a crosslinking agent and reacted at 45 ° C. for 3 hours to form a crosslinked structure in the cellulose porous membrane. Then, the cellulose porous membrane in which the crosslinked structure was formed was obtained by washing with a large amount of water.

[Example 20]
In this example, a cellulose porous membrane was produced using the cellulose porous membrane production apparatus 10 shown in FIG.
(Cellulose solution preparation process)
250 g of crystalline cellulose powder [KC-Flock W-50G (trade name), average polymerization degree 820, manufactured by Nippon Paper Industries Co., Ltd.] was added to 4750 g of a 60 mass% lithium bromide aqueous solution, and heated and dissolved at 110 ° C. A cellulose solution was obtained.

(Liquid film formation process)
The obtained cellulose solution was allowed to cool to room temperature to obtain a gel-like cellulose solution. Using the obtained gel-like cellulose solution as a raw material,
The gel-like cellulose solution was supplied to the raw material tank 12 of the melt extrusion apparatus 18 in the cellulose porous membrane manufacturing apparatus 10 shown in FIG. The melt extrusion device 18 includes a heater 14 and the temperature inside the device is maintained at 110 ° C. The gel-like cellulose solution supplied from the raw material tank 12 is mixed by the screw 16 in the melt-extrusion apparatus 18 having a diameter of 50 mmφ, and the temperature is maintained at 110 ° C., and the sheet is formed by the T-die 18A having a width of 40 mm. The cellulose solution film (F) was formed by continuously extruding the film.
The extrusion amount of the cellulose solution was adjusted to an amount by which the cellulose solution film (F) having a thickness of 500 μm was formed.

(Gel film formation process)
The extruded cellulose solution film (F) is introduced into the cooling device 20 through the sizing die 20A, and the cooling rate is 15 ° C. by controlling the temperature in the cooling device and the conveying speed in the cooling device 20. The solution was cooled until the surface temperature of the film reached 50 ° C. to form a gel film (G1) containing cellulose.

(Coagulation process)
The formed gel film (G1) containing cellulose was conveyed by the drive roll 22A and introduced into the coagulation solvent tank 22 having a capacity of 50 L filled with methanol as the coagulation solvent. In the coagulation solvent tank, the gel film (G1) and methanol were brought into contact with each other to coagulate the cellulose in the gel film, thereby forming a porous film (G2) containing cellulose.

(Formation of porous cellulose membrane)
The porous membrane (G2) containing cellulose was transported by the driving roll 24A, introduced into a 200 L capacity washing tank 24 filled with ion-exchanged water, and washed with excess ion-exchanged water. The cellulose porous membrane (C) after washing was conveyed to a winder 28 via a take-up machine 26, and wound on a roll with the winder 28 to obtain a long cellulose porous film (C).
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Example 21]
On the downstream side of the water rinsing tank 24 of the cellulose porous film forming apparatus 10 used in Example 20, the porous film formed in the same manner as in Example 20 until the coagulation step was recovered.
A porous membrane containing long cellulose was cut to a length of 100 mm and subjected to the following crosslinking step.
(Crosslinking process)
After heating for 10 minutes at 45 ° C. in a reaction tank filled with 10 mL of a 0.5 molar aqueous sodium hydroxide solution per 10 g of wet cellulose porous membrane, sodium borohydride (Wako Pure) In a cross-linking agent-containing tank filled with a cross-linking agent-containing solution prepared by adding 20 mg of Yaku Kogyo Co., Ltd. and 10 mL of epichlorohydrin as a cross-linking agent, the reaction is carried out at 45 ° C. for 3 hours to cross-link the cellulose porous membrane A structure was formed.
Then, the cellulose porous membrane in which the crosslinked structure was formed was obtained by washing with a large amount of water.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Comparative Example 1]
To 80 g of 1-ethyl-3-methylimidazolium acetate (Sigma Aldrich), crystalline cellulose powder [KC-Flock W-50G (trade name), average degree of polymerization 820, manufactured by Nippon Paper Industries Co., Ltd.] 2.9 g Was added to prepare a cellulose solution having a cellulose content of 3.5% by mass.
2.5 g of the obtained cellulose solution was poured into a rectangular parallelepiped container 5 cm long, 10 cm wide and 8 cm high containing 500 mL of a mixed solvent having an ethyl acetate / ethanol volume ratio of 80/20. The cellulose solution spread on the bottom of the container, and a cellulose porous membrane was formed. The cellulose porous membrane was recovered by maintaining at 30 ° C. for 2 hours.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Comparative Example 2]
To 80 g of 1-ethyl-3-methylimidazolium acetate (Sigma Aldrich), crystalline cellulose powder [KC-Flock W-50G (trade name), average degree of polymerization 820, manufactured by Nippon Paper Industries Co., Ltd.] 2.9 g Was added to prepare a cellulose solution having a cellulose content of 3.5% by mass.
10 g of the obtained cellulose solution was applied on the press plate of the melt press apparatus used in Example 1, and at room temperature, the press plate temperature was 110 ° C., and the press pressure was 2 MPa and the compression was performed with a clearance of 1 mm thickness. Then, a cellulose solution film was formed. The obtained liquid film was cooled to 40 ° C. at 10 ° C./min while being sandwiched between press plates, but no gel film was obtained.

[Comparative Example 3]
To 80 g of 1-ethyl-3-methylimidazolium acetate (Sigma-Aldrich), crystalline cellulose powder [KC-Flock W-50G (trade name), average degree of polymerization 820, manufactured by Nippon Paper Industries Co., Ltd.] 2.9 g Was added to prepare a cellulose solution having a cellulose content of 3.5% by mass.
A liquid film was formed from the obtained cellulose solution using the bar coater used in Example 12. The bar coater (clearance 500 μm) and the stainless steel plate to be used were heated to 110 ° C. with a thermostat in advance. The cellulose solution was heated to 110 ° C., quickly applied onto a stainless steel plate using a bar coater, and the whole stainless steel plate was returned to a thermostat of 110 ° C. Thereafter, the cellulose solution film was cooled to 40 ° C. at a cooling rate of 10 ° C./min by lowering the temperature setting of the thermostat, but no gel film was obtained.

[Comparative Example 4]
A cellulose solution was prepared in the same manner as in Example 3 except that the cellulose solution was prepared using an equal amount of calcium thiocyanate instead of lithium bromide used in the preparation of the cellulose solution in Example 3, and the obtained cellulose solution was used. A membrane was obtained.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Comparative Example 5]
A cellulose solution was prepared in the same manner as in Example 14 except that a cellulose solution was prepared using an equal amount of calcium thiocyanate instead of lithium bromide used in the preparation of the cellulose solution in Example 14, and the obtained cellulose solution was used. A membrane was obtained.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Comparative Example 6]
In the cellulose solution preparation process, the cellulose solution was prepared by changing the blending amount of the crystalline cellulose powder from 2.5 g to 0.5 g, and the same procedure as in Example 9 was used except that the obtained 1% by mass cellulose solution was used. Thus, a cellulose porous membrane was obtained.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

[Comparative Example 7]
In the cellulose solution preparation step, the cellulose solution was prepared by changing the blending amount of the crystalline cellulose powder from 2.5 g to 0.5 g, and the obtained 1% by weight cellulose solution was used, and replaced with methanol as the coagulation solvent. A porous cellulose membrane was obtained in the same manner as in Example 14 except that water was used.
The obtained cellulose porous membrane was evaluated in the same manner as in Example 1.

From the results of Tables 1 to 4, the cellulose porous membrane obtained by the production method of the present invention has fine pores, a large specific surface area, and a tensile strength at a practically sufficient level. It can be seen that it can be suitably used for various applications such as a carrier, a filtration membrane, and a separation membrane.
On the other hand, it can be seen that any of the cellulose porous membranes obtained by the method of the comparative example has a larger pore diameter and a smaller specific surface area than the examples, and the tensile strength of the porous membrane has not reached the practical level. From the results of Comparative Examples 1 to 3, it can be seen that when an ionic liquid is used as the cellulose solvent, the porous film cannot be formed under the condition that the peripheral edge of the cellulose solution film is unconstrained. From the results of Comparative Examples 6 and 7, when the concentration of the cellulose solution is too low, the pore diameter of the obtained porous membrane is larger than that of the Examples, and a practically sufficient tensile strength cannot be obtained. I understand.

Claims (10)

A solution preparation step of dissolving cellulose in an aqueous lithium bromide solution to prepare a cellulose solution containing 2% by mass to 15% by mass of cellulose with respect to the total amount of the cellulose solution;
The prepared cellulose solution is applied to the plate-like support surface, the cellulose solution film made of the cellulose solution is adjusted to the support surface, the temperature of the cellulose solution is adjusted to 90 ° C. or more, and the periphery of the cellulose solution film is A liquid film forming step for forming under unconstrained conditions;
A gel film forming step of cooling the formed cellulose solution film at a cooling rate of 1 ° C./min to 300 ° C./min to obtain a gel film containing cellulose;
A coagulation step of contacting a coagulation solvent with a gel film containing cellulose to coagulate the cellulose to obtain a porous film;
The manufacturing method of the cellulose porous membrane containing this.   In the liquid film forming step, a certain amount of cellulose solution is applied to the surface of the plate-like support in a press molding machine, and the applied cellulose solution is press-molded at a pressure of 0.1 MPa to 35 MPa to obtain a cellulose solution. The method for producing a porous cellulose membrane according to claim 1, comprising forming a membrane.   2. The production of a cellulose porous membrane according to claim 1, wherein the liquid film forming step includes forming a cellulose solution film by continuously or intermittently applying a cellulose solution to a plate-like support surface by a coating method. Method.   2. The cellulose porous membrane according to claim 1, wherein the liquid film forming step includes forming a cellulose solution film by continuously or intermittently applying a cellulose solution to a plate-like support surface by a melt extrusion apparatus. Production method.   The manufacturing method of the cellulose porous membrane of any one of Claims 1-4 including the washing | cleaning process which wash | cleans the porous film obtained through the said coagulation | solidification process.   The manufacturing method of the cellulose porous membrane of any one of Claims 1-5 including the bridge | crosslinking process which forms a crosslinked structure in a porous film obtained through the said coagulation | solidification process using a crosslinking agent.   The method for producing a porous cellulose membrane according to any one of claims 1 to 6, wherein the cellulose solution obtained by the solution preparation step has a viscosity at 110 ° C in a range of 0.5 Pa · s to 500 Pa · s. .   The method for producing a porous cellulose film according to any one of claims 1 to 7, wherein the cellulose is cellulose having an average degree of polymerization of 50 to 2000.   The said coagulation | solidification process is a process of making a coagulation | solidification solvent contact the gel film | membrane containing a cellulose in the temperature conditions whose temperature of the gel film | membrane containing a cellulose is 20 to 80 degreeC. The manufacturing method of the cellulose porous membrane as described in a term.   The method for producing a cellulose porous membrane according to any one of claims 1 to 9, further comprising a lyophilization step of freeze-drying the cellulose porous membrane to obtain a freeze-dried cellulose porous membrane.