JP2012071250A - Method of manufacturing regenerated cellulose multilayer structure flat membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a regenerated cellulose multilayer structure flat membrane improved in particle capturability by shortening an interlayer distance, while keeping horizontal-directional pore structure, in the regenerated cellulose multilayer structure flat membrane.SOLUTION: The regenerated cellulose multilayer structure flat membrane is obtained by saponifying a cellulose derivative. In manufacturing thereof, a membrane is designed to have an average pore size of 5-500 nm and a membrane thickness of 20-500 μm, and to be constituted of 100 layers or more of layered product, of which one layer has a thickness of 0.05-0.5 μm, and is compressed along a vertical direction before saponifying the cellulose derivative, and the interlayer distance is thereby brought into 10 times a capturing objective particle diameter or less and an interlayer porosity is 50% or less, to obtain the regenerated cellulose multilayer structure flat membrane enhanced in the particle capturability.

Description

The present invention relates to a porous polymer flat membrane used for separation, purification and removal. The present invention relates to a method for producing a membrane used for realizing high-level separation of a useful polymer dissolved in or dispersed in a liquid or gas, a physiologically active substance, and harmful particles, infectious microorganisms, and the like.

In biotechnology, fine particles contained in the raw material include aggregates and denatured bodies such as proteins in addition to infectious fine particles such as prions, viruses and bacteria. When these fine particles are mixed in the final product, it causes various infectious diseases and fever. Therefore, in the production process of products obtained by biotechnology (particularly biopharmaceuticals), the above-described removal or inactivation process of fine particles is necessary. In addition to biopharmaceuticals, countermeasures for fine particles are indispensable in the manufacturing process of foods and cosmetics that use biological materials.

Virus removal membranes and sterilization filters have already been commercialized as countermeasures against fine particles, and removal prion membrane technology may also appear in the market in the near future. As membrane separation methods, a membrane filtration technique using a transmembrane differential pressure as a driving force for mass transfer and a pore diffusion technique using a concentration gradient of a substance through a pore in the membrane as a driving force have been developed recently.

  The multilayer structure film is a film in which a layer having a thickness of 0.01 to 1 μm is observed when observed with an electron microscope from the cross-sectional direction of the film, and 100 or more of these layers are laminated. In the electron microscope observation from the surface of the film, it is a film in which a network or a gap between particles is formed as a hole and particles are fused.

A flat membrane is a planar membrane, and the average pore diameter is given by the square root of (viscosity, film thickness, filtration rate / intermembrane differential pressure, porosity). Here, the filtration rate is the filtration rate of pure water per square meter, measured in units of ml / min, the film thickness is in microns, the viscosity is in centipoise, the transmembrane pressure is in mmHg, and the porosity is a dimensionless unit. It is. The average pore diameter at this time is in nm units. The porosity is given by:
Porosity = (1- membrane density / material polymer density)
The density of the film is calculated by (film weight / film area × film thickness). The density of the material polymer is the density of the membrane when the porosity is 0%, and this is already given in the literature.

A method for producing a multilayer structure film by a basic microphase separation method is detailed in Patent Document 1. In this method, the average pore size on the surface of the membrane is small, and the average pore size on the back surface of the membrane is at least three times the surface (Patent Document 2).

The film surface in the multilayer structure film produced by the dry microphase separation method is a surface in contact with the gas layer and the good solvent evaporates, and the film back surface is a surface in contact with the solid (support).

Methods for compressing a cellulosic flat membrane and improving the properties of the membrane can be found in Patent Document 3, Patent Document 4 and Patent Document 5. Patent Document 3 relates to a reverse osmosis membrane, and does not compress the thin film itself, but provides a reverse osmosis membrane capable of stable operation even under high pressure by compressing and compacting a support. .

Patent Document 4 relates to a flat film in which a cellulosic polymer and a thermoplastic polymer are combined at the molecular level. A kneaded material composed of a cellulosic polymer and a thermoplastic polymer is formed by compression or extrusion to form a flat film.

Patent Document 5 shows a method for compressing a flat membrane (porous body) having a pore structure. In this method, pressure is applied to a porous body having a thickness of 2 mm to obtain a separation material having a film thickness of 0.8 to 1.5 mm and having a stable capturing property for leukocytes.

JP 2009-274010 Multilayer structure film having different particle trapping performance on front and back surfaces and method for producing the same JP-A-58-089628 Regenerated cellulose porous membrane JP 2000-288368 composite reverse osmosis membrane JP 2004-283696 CELLULOSE COMPOSITE POROUS MEMBRANE Method for producing leukocyte separator

In the present invention, a cellulose derivative solution is cast on a support having excellent surface smoothness with a preset thickness using an applicator, microphase separation is caused by evaporation of a good solvent, and then alkaline When a flat film having an average pore diameter of 5 to 500 nm is prepared by a dry flat film forming method in which a saponification treatment is performed in a solution, the porosity calculated by observation with an electron microscope on the front and back surfaces is 50%. As a result, there is a problem that the porosity in the apparent density method becomes too large.

Specifically, the porosity in the apparent density method is 0.8 or more, and this is one of the reasons that the distance between layers, which is the distance between layers, is increased from the observation result of the electron microscope. It was thought that.

When the particle logarithmic removal rate of the film was measured, a tendency was found to be lower than the particle logarithmic removal rate estimated from the average pore size. The particle log removal rate is defined by the following equation.
Logarithmic particle removal rate (LRV) ≡-log ₁₀ (number of particles in the filtrate / number of particles in the solution before filtration)
The particle log removal rate is evaluated by filtering a solution in which iron hydroxide colloid particles having a particle diameter of 20 nm are dispersed at a concentration of 1200 ppm.

It was thought that the interlayer distance was increasing as one of the causes of the particle log removal rate. Since the interlayer distance is large, the particles move parallel to the layer within the layer, and by selectively flowing to the holes having a large hole diameter among the holes existing in the layer, the particles pass through, resulting in a particle logarithmic removal rate. It was thought that it might have declined.

As methods for compressing a cellulosic flat membrane, there are methods as shown in Patent Document 3 and Patent Document 4, but it is difficult to say that both methods focus on the interlayer distance as described above. The technique of Patent Document 3 is not a technique that essentially improves the properties of the membrane, but improves the stability by modifying the support that supports the membrane.

Further, in the method of Patent Document 4, a compressive force is applied when forming a raw material solution (kneaded material), which may affect not only the distance between layers but also the hole diameter in the planar direction.

Applying a compressive force to the membrane in a way that affects the pore size within the layer of the multi-layered membrane not only removes the particles of the membrane, but also the water permeability during filtration, the protein permeability, and the average Until the pore size is reached, the pore properties of the membrane are essentially changed. In order to stably obtain particle removal performance comparable to the average pore size, it is important to control or predict the pore size in the layer, and since the pore characteristics in the layer are not significantly changed, the vertical interlayer distance It is necessary to consider the compression method that only affects.

Patent Document 5 is a method for improving the particle trapping performance by applying pressure in a direction perpendicular to a flat membrane (porous material). The target porous material has a thickness of 0.5 to 1.5 mm. The particles to be captured are leukocytes, which is a technology that targets micron-order particles, and cannot be applied to a flat membrane having a nano-order pore structure that is the subject of this problem. The substance which comprises a porous material is a fiber etc., This porous material is classified into a depth filter, and a layered structure is not observed.

It was discovered that by compressing a regenerated cellulose multilayer structure flat membrane in the vertical direction before saponification and then performing saponification, only the vertical pore structure, that is, the interlayer distance, can be reduced, leading to the present invention. It was.

In addition, the interlayer distance and the film thickness remain almost unchanged after saponification after the compression treatment, and the same film thickness is maintained even during use of the film, for example, during filtration operation.

The greatest discovery leading to the present invention was that the change in water permeation rate with time when the membrane was compressed before saponification was almost constant. The water permeation rate is measured by a method in which the membrane is set in a filter, a water pressure of 2 atm is applied, and the RO water filtration rate is measured. In the case of an uncompressed membrane, the water transmission rate sometimes decreased with time. This was thought to be caused by the fact that the filtration pressure in the vertical direction was applied to the membrane in the filter in the water permeability test, and the film thickness became smaller. That is, it was considered that as the film thickness becomes smaller, the film becomes denser and the water permeation resistance increases, and as a result, the water permeation rate decreases. On the other hand, after conducting a water permeability test before saponification, that is, after applying a pressure of 2 atm to the membrane, a saponification treatment was performed. As a result, a membrane with no decrease in the water permeability rate was obtained. This film had a thickness of 2 to 10% smaller than the film not subjected to pressurization before the saponification treatment. That is, a film that was already densified and the distance between the layers was reduced to such an extent that the film thickness did not change even when filtration pressure was applied was obtained.

From this result, it was found that a film having a small interlayer distance can be obtained by compression before saponification, and the compression method was examined. However, the compression by the filtration pressure as described above has a compressibility of about 2 to 10% in the film thickness, and the improvement of the particle trapping property was not great. Here, the compression rate is the rate of change in film thickness before and after compression.
Compression rate = ((film thickness before compression−film thickness after compression) / film thickness before compression) × 100

On the other hand, in the method of mechanically compressing before saponification, the film thickness can be compressed by 10 to 40%, and the compression rate was maintained after saponification. Interlayer porosity is measured from an electron micrograph of the cross section of the membrane. That is, when the area occupied by the polymer material is S _p and the film cross-sectional area S is taken from the cross-sectional photograph, the interlayer porosity is given by (S−S _p ) / S. In the membrane before the compression treatment, the interlaminar porosity is in the vicinity of 0.75, and the particle trapping property increases rapidly when the porosity becomes 0.6 or less, and when the porosity becomes 0.4 or less, the water permeability decreases. Also happens. Therefore, from a practical viewpoint, an interlayer porosity of 0.5 or less and 0.25 or more is generally a highly effective compression treatment.

It was found that when the film was actually compressed to 10 to 40% in the film thickness using a flat plate hydraulic press, a film with improved film particle capturing performance was obtained. Moreover, the big change was not seen by this compression processing water transmission rate. In other words, although the membrane was compressed and densified in the vertical direction, the horizontal pore structure was maintained, and the water transmission rate was not greatly affected. However, there was variation in the improvement of particle trapping performance.

In the case of the membrane compressed after saponification, the particle trapping performance and the water permeation rate were not significantly changed, and were the same as the membrane not compressed. When compression is performed after saponification, the non-uniformity of the film is changed in a further increasing direction, and when the compression rate is 10% or more, the decrease in the water permeation rate is also increased.

On the other hand, when 10-20% was compressed using the roller press machine, the particle | grain capture | acquisition performance of the film | membrane improved and there was no big change in the water transmission rate. Further, there was no great variation in the particle trapping performance. The particle trapping performance is reproducible, and the compression process using a roller press machine is performed almost evenly in the film, whereas the flat plate press machine reflects uneven film thickness and compresses unevenly. Is done.

According to the present invention, in the process of preparing a regenerated cellulose multilayer structure flat membrane from a cellulose derivative, the pore structure characteristics and water permeability performance in the layer are not significantly impaired by compressing in a direction perpendicular to the membrane plane before saponification. In addition, a cellulose multilayer flat film having high dimensional accuracy and excellent particle trapping properties can be obtained.

In the production method disclosed in Patent Document 1 and Patent Document 2, when acetate is used as a cellulose derivative, when a cellulose acetate multilayer multilayer film is produced, the pressure in the direction perpendicular to the film is applied before saponification. Add Before saponification treatment, in the step of producing the flat film, the acetate solution is cast on a flat plate, washed with water, and then immersed in an alkaline solution to saponify, but before the saponification step is performed Say.

As a method of applying pressure in the vertical direction to the membrane, any method such as a flat plate hand press, a flat plate hydraulic press, a roller press, a rubber press, and a hydraulic press may be used. It is desirable to apply pressure more uniformly than the direction perpendicular to the film plane.

As a device for uniformly applying pressure, a film is sandwiched between plates or films with good smoothness and then compressed, or a medium to which pressure is applied, such as a hydraulic cylinder or roller press for a flat plate hydraulic press. If so, there is a method of attaching a plate or film having high smoothness to the roller and compressing it through the film. In this case, there is an effect that the applied pressure acts uniformly on the film plane while eliminating the uneven thickness of the film.

The plate or film having high smoothness may be any of resin, metal, glass, etc., and resinous properties are desirable. Since metal and glass have high compression elastic modulus, deformation of these materials due to load pressure is small. Therefore, the uneven thickness of the film tends to be uneven load stress as stress for compressive deformation.

The pressure applied is controlled by the compressibility of the membrane. That is, the pressure applied when compressing is controlled by the change in film thickness (compression rate) obtained after compression. The compression rate varies reflecting the local unevenness of the film, but it is desirable that this variation unevenness works in a direction to be eliminated by the compression process. Therefore, a device is also required for the pressurizing method. The pressing force and pressurizing time are also important, and it is desirable that the pressurizing speed be small.

When the compression rate is 5 to 50%, the particle log removal rate of the film is improved. Desirably, in the case of 10 to 20%, the particle log removal rate of the membrane is improved, and the water permeation rate is not greatly reduced. When the compression rate is too large, the water transmission rate is greatly reduced. When the compression ratio is 10 to 20%, the interlayer porosity is 60% or less. If the hole structure in each layer of the multilayer structure is a non-circular hole (Up hole), the compression ratio is 10 to 20%. Thus, the interlayer porosity is 50% or less.

Cellulose acetate having an average substitution degree of 2.50 cellulose acetate (average polymerization degree 210) by weight concentration (weight concentration in casting stock solution) 9.24%, acetone 54.17% by weight, methanol After dissolving in 6.21% by weight, calcium chloride dihydrate 1.92% by weight, RO water 0.95% by weight, cyclohexanol 27.50% by weight, filtration and defoaming were performed. The solution was cast on a ground glass with a thickness of 0.5 mm and left in an environment of 20 ° C. for 40 minutes to cause microphase separation to produce a porous multilayer flat film. Thereafter, the film was immersed in water to stop the progress of microphase separation, the film was peeled from the ground glass, and immersed in water to remove impurities remaining in the film.

The membrane was removed from the water, cut into a 47 mm diameter circle, sandwiched between 100 μm thick polyethylene films and compressed at 25 ° C. with a flat plate hand press. The compression force is 15 kN and the compression time is 30 seconds.

After compression, it was immersed in an aqueous 0.1 N sodium hydroxide solution at 20 ° C. for 4 hours to cause a saponification reaction to obtain a regenerated cellulose membrane. As a result, a regenerated cellulose membrane having a compression rate of 30%, a film thickness of 55 μm, an average pore diameter of about 30 nm, and a porosity of 80% was obtained.

The particle log removal rate of the film was evaluated using an aqueous solution of 20 nm iron hydroxide colloidal particles (concentration 1200 ppm). As a result, the particle log removal rate of the uncompressed film was 0, but the particle log removal rate of the compressed film was 1.05. The particle log removal rate of the compressed membrane gradually decreased from 1.05.

Further, the water permeation rate of the membrane was evaluated using RO water. The water permeation speed was measured by setting the membrane on a filter, applying a water pressure of 2 atm, and measuring the RO water filtration speed. As a result, the water transmission rate of the uncompressed membrane was 612 L / square meter · Hr, but the water permeability of the compressed membrane was 673 L / square meter · Hr.

Cellulose acetate having an average substitution degree of 2.50 cellulose acetate (average polymerization degree 210) by weight concentration (weight concentration in casting stock solution) 9.70%, acetone 61.12% by weight, methanol After dissolution at 15.28% by weight, calcium chloride dihydrate 6.26% by weight, RO water 0% by weight, cyclohexanol 7.64% by weight, filtration and defoaming were performed. The solution was cast on a ground glass at a thickness of 0.5 mm and left in an environment of 20 ° C. for 20 minutes to generate microphase separation to produce a porous multilayer structure flat membrane. Thereafter, the film was immersed in water to stop the progress of microphase separation, the film was peeled from the ground glass, and immersed in water to remove impurities remaining in the film.

The membrane was taken out of water, sandwiched between 100 μm-thick polypropylene plates and compressed at 25 ° C. with a roller press. The clearance between rollers of the roller press was set to 100 μm.

After compression, it was immersed in an aqueous 0.1 N sodium hydroxide solution at 20 ° C. for 4 hours to cause a saponification reaction to obtain a regenerated cellulose membrane. As a result, a regenerated cellulose membrane having a compression rate of 13%, a film thickness of 33 μm, an average pore diameter of about 30 nm, and a porosity of 75% was obtained.

The particle log removal rate of the film was evaluated using an aqueous solution of 20 nm iron hydroxide colloidal particles (concentration 1200 ppm). As a result, the particle log removal rate of the uncompressed film was 0, but the particle log removal rate of the compressed film was 2. Although the particle log removal rate of the compressed film tended to decrease slightly, it remained at a substantially constant value (1.5).

Further, the water permeation rate of the membrane was evaluated using RO water. The water permeation speed was measured by setting the membrane on a filter, applying a water pressure of 2 atm, and measuring the RO water filtration speed. As a result, the water transmission rate of the uncompressed membrane was 414 L / square meter · Hr, but the water transmission rate of the compressed membrane was 390 L / square meter · Hr. The reason why the water permeation rate slightly decreased even though the film thickness was small is considered to be because the flow resistance of water in the film slightly increased. This increase is thought to be due to a significant increase in flow resistance along the layer.

The present invention can be used in industries that require separation and purification under mild conditions (eg, pharmaceutical industry, food industry), particularly separation and purification of substances having physiological activity such as proteins. In particular, the present invention contributes to these industries as a technology that satisfies safety requirements for products in various industries using biotechnology (for example, biopharmaceuticals and food industries). For medical use and environmental use, it is also used to remove harmful substances such as viruses, bacteria, and heavy metals, and harmful fine particles. It can be incorporated into an industrial process as a method of purifying and separating specific fine particles including colloidal particles in the industry handling colloidal systems. In addition, safety and energy-saving separation for the recycling field and the environmental industry, which were thought to be impossible to apply the conventional membrane separation technology due to the high particle trapping performance and removal ability of the membrane and the features that prevent clogging. Used as technology.

Compression method 1: A static load is applied from the direction of the mechanical flat plate press arrow. Compression method 2: Roller press The film is compressed and deformed to a certain thickness by a roller rotating in the direction of the arrow.

1, flat plate hydraulic press machine upper cylinder 2, polyethylene film 3, regenerated cellulose flat membrane 4, flat plate hydraulic press machine lower base 5, roller press machine roller

Claims (2)

A regenerated cellulose multilayer flat membrane obtained by saponifying a cellulose derivative, having an average pore diameter of 5 nm to 500 nm, a film thickness of 20 μm to 500 μm, and a laminate of 100 layers or more and a thickness of one layer of 0.05 μm to 0.5 μm A regenerated cellulose multilayer flat membrane in which the interlaminar porosity is 50% or less and 25% or more and the particle trapping property is improved by designing the membrane and compressing the cellulose derivative in the vertical direction before saponification The manufacturing method. The method according to claim 1, wherein a roller press is used as the compression method and the compression rate is 5 to 50%.