JPWO2009060836A1 - Cellulosic porous membrane - Google Patents

Abstract

Viscosity average molecular weight is 6 × 104 or more, average pore diameter (D) is 0.001 to 1000 μm, porosity (P) is 0.1 to 98%, tensile strength is 0.5 kPa or more, and heat shrinkage at 160 ° C. A film-like cellulosic porous membrane characterized by being 5% or less.

Description

  The present invention relates to a cellulose-based porous membrane that is useful in the field of separation and purification of substances as a separation membrane for aqueous liquid, organic liquid, blood, gas and the like.

  In the field of substance separation and purification, membrane separation technology is a very useful technique for separating nano-order substances such as ions and low-molecular substances, or micron-order substances such as turbidity and fine particles in liquids. is there. Fields that can benefit from membrane separation technology include (1) areas that require concentration, purification, and recovery at low temperatures (food and biochemical industries), (2) areas that require aseptic and dust-free (pharmaceutical and Therapeutic institutions, electronics industry), (3) Concentration and recovery of trace amounts of expensive substances (nuclear power, heavy metals), (4) Special small volume separation (pharmaceutical), (5) High energy consumption (distillation alternative), etc. Can be mentioned.

  In these fields, separation of substances from aqueous liquids is the main, so the membrane used is hydrophilic, has a pore size and membrane structure suitable for each application, has excellent mechanical properties, and is easy to handle. Porous membranes are desired.

  An example of the material rich in hydrophilicity is cellulose. Cellulose is the most abundant natural polymer on the earth and has been used in various forms for a long time. In recent years, it has been attracting attention as a polymer material that can be regenerated and has an enormous potential abundance in terms of energy problems and global environmental problems, and is an indispensable material in our lives.

  Cellulose is also excellent in organic solvent resistance and heat resistance, and has the characteristics of low toxicity to living bodies.

  Therefore, there is a great demand for a cellulose membrane having the above characteristics and having a pore size and a membrane structure suitable for each application.

  However, at present, there are not so many examples of cellulose membranes being used in certain applications. Because cellulose does not have a melting point, it cannot be melted by heat and cannot be molded from the molten state of the polymer, and even if dissolved in a certain solvent, cellulose does not form hydrogen bonds between molecules. This is because the solubility in a solvent is extremely low to form, and the solvent species used are very limited.

  Even if it is soluble, it is necessary to reduce the molecular weight (degree of polymerization) to such an extent that it can be dissolved by applying some pretreatment to the original cellulose raw material. As a result, the strength of the cellulose film formed from the cellulose solution is lowered depending on the molecular weight, so that there is a problem that the mechanical strength is insufficient depending on the application. The above problems are one of the causes that have hindered the use of cellulose.

  Although it is the above situations, cellophane (registered trademark) is mentioned as a practical example of a film-like cellulose membrane.

  Cellophane (registered trademark) is generally used as a packaging material in many cases. However, as a semipermeable membrane or a dialysis membrane, applications using the pores are also known. However, as can be seen from the fact that the pore size of cellophane (registered trademark) used in the semipermeable membrane is as small as several nm, generally, it is several tens nm or more from the viscose solution of cellulose which is the raw material of cellophane (registered trademark). It is extremely difficult to obtain a porous membrane having a pore size of 10 mm, and at present, at least industrially, a cellulose porous membrane having a pore size of several tens of nanometers or more is not produced from a viscose solution of cellulose.

In addition, as a characteristic of a viscose solution of cellulose, cellulose having a high degree of polymerization cannot be dissolved in a polymer concentration range (5 to 10 wt%) suitable for film formation. Therefore, the viscosity average molecular weight of the cellulose dissolved in the viscose solution is usually in the range of about 4.5 × 10 ^{4 to} 5.5 × 10 ⁴ . For this reason, the strength of the cellophane (registered trademark) film obtained from the viscose solution of cellulose in a dry state may be insufficient depending on the application, and there is a problem of causing breakage during handling.

  Further, in the wet state, the strength of the film is further reduced as compared with the dry state, so that the possibility of breakage during handling is further increased. As described above, the membrane obtained from the viscose solution of cellulose has a problem in that it has a pore size and a membrane structure suitable for a desired application for development in various applications, and also in terms of strength. It is not sufficient, and there are difficulties in handling.

  Other film-like cellulose porous membranes include various cellulose derivative porous membranes or regenerated cellulose porous membranes obtained by saponifying the cellulose derivative porous membrane (for example, Patent Document 1).

The average pore diameter (D) of the porous membrane obtained by such a method is in the range of 0.01 to 2 μm, the porosity (P) is relatively high, and good filtration characteristics are exhibited. However, since the cellulose derivative is used as a starting material, the viscosity average molecular weight of the regenerated cellulose film is 4 × 10 ⁴ or less, and is brittle in a dry state. Further, in the wet state, the strength of the film is further reduced as compared with the dry state, and may be damaged during handling. Further, when the membrane is used as a microfiltration membrane or the like, if the porosity of the membrane is increased in order to improve the filtration characteristics, the strength of the membrane is further reduced.

  Thus, the regenerated cellulose porous membrane obtained from the cellulose derivative is not sufficient in terms of strength and has a problem in handling.

In order to produce a cellulose porous film having a high strength, a solvent capable of dissolving cellulose with a high degree of polymerization is desirable. As a cellulose solution produced with such a solvent, there is a copper ammonia cellulose solution. In this solution, the tetraammine copper complex is coordinated to the hydroxyl group of cellulose, so that the hydrogen bond due to the hydroxyl group of cellulose is relaxed and the cellulose can be highly dissolved. Therefore, compared to other solvent systems, it is possible to dissolve cellulose with a high degree of polymerization, the viscosity average molecular weight of the porous cellulose membrane produced from the solution is usually 6 × 10 ⁴ or more, It is preferable from the viewpoint of strength.

  Practical examples of the porous membrane include a cellulose porous membrane for artificial kidneys (for example, Patent Document 2) and a cellulose porous membrane for virus removal (for example, Patent Document 3).

  Since these cellulose porous membranes are excellent in strength and have a pore size suitable for each application, they are very useful porous membranes.

  However, since all of these are hollow film-like, not in the form of a film, there are some limitations when considering use in applications other than the above, such as separation, purification, fractionation, and selective permeation. .

  As a film-like cellulose porous membrane from a copper ammonia cellulose solution, there is a film-like cellulose porous membrane for cell culture carriers (for example, Patent Document 4). The membrane has a structure composed of vacuoles in which pores larger than about 2 μm are relatively uniformly distributed. Therefore, it is very effective when used as a target for a relatively large object of several μm to several tens of μm like a cell. However, for separation in fields including relatively small substances (nano-order substances), such as separating particles and liquids from a solution in which particles of various sizes from tens of nanometers to several tens of micrometers are mixed, There is one aspect that is difficult to apply.

  Under such circumstances, a film-like cellulose porous membrane that is hydrophilic, excellent in mechanical properties, easy to handle, and has a pore size and a membrane structure suitable for a desired application is desired.

Special Report 2004-538143 Japanese Patent Laid-Open No. 3-8422 Japanese Patent Laid-Open No. 4-371221 JP-A-2-208330

  The problems to be solved by the present invention are hydrophilic, excellent in strength, heat resistance and organic solvent resistance, mainly excellent in filtration and separation efficiency for polar solvents such as water and blood, and suitable for various applications. Another object of the present invention is to provide a film-like cellulose-based porous membrane having a pore size and a membrane structure.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors set the viscosity-average molecular weight, the average pore diameter (D), and the porosity (P) in a specific range in the film-like cellulose-based porous membrane. It has been found that a cellulosic porous membrane having a pore size and membrane structure suitable for the above is excellent in mechanical properties, heat resistance, and organic solvent resistance, and may solve the above problems. And further examination was repeated and it came to complete this invention.

That is, the present invention is as follows.
(1) Viscosity average molecular weight is 6 × 10 ⁴ or more, average pore diameter (D) is 0.001 to 1000 μm, porosity (P) is 0.1 to 98%, tensile strength is 0.5 kPa or more, at 160 ° C. A film-like cellulose porous membrane having a heat shrinkage rate of 5% or less.
(2) In the porous film, the average pore diameter (D) is 0.01 to 1000 μm, the porosity (P) is 5 to 98%, the tensile strength is 0.5 kPa or more, and the surface average pore diameter of one surface ( D ₁ ) is 0.01 to 500 μm, the surface average pore diameter (D ₂ ) of the other surface is 0.1 to 1000 μm, and D ₂ / D ₁ is 1.1 or more. The cellulosic porous membrane as described in (1) above, which has a plurality of boundary layers formed in the thickness direction.
(3) The porous membrane comprises at least two layers, a large pore diameter layer having a cross-sectional average pore diameter of 10 μm or more and a small pore diameter layer having a cross-sectional average pore diameter of 5 μm or less, and is formed in the film thickness direction in the large pore diameter layer. The cellulosic porous membrane as described in (2) above, further comprising a boundary layer.
(4) The cellulosic porous membrane according to (2) above, wherein the porous membrane has an inclined structure in which the pore diameter gradually decreases from one surface to the other surface.
(5) The cellulose-based porous membrane according to (2) above, wherein both D ₁ and D ₂ are 2 μm or less in the porous membrane.
(6) The cellulose-based porous membrane according to any one of (2) to (5), wherein the porous membrane has a thickness of 1 mm or more.
(7) In the porous film, the average pore diameter (D) is 0.001 to 0.1 μm, the porosity (P) is 0.1 to 40%, the tensile strength is 3 kPa or more, and the cross-sectional structure is uniform. The cellulose-based porous membrane according to (1) above, wherein
(8) In the porous film, the average pore diameter (D) is 0.001 to 1 μm, the porosity (P) is 0.1 to 50%, the tensile strength is 2 kPa or more, and the surface average pore diameter of one surface ( D ₁ ) is 0.001 to 0.01 μm, and the cellulose-based porous membrane according to (1) above.
(9) In the porous membrane, the average pore diameter (D) is 0.001 to 20 μm, the porosity (P) is 1 to 90%, the tensile strength is 0.5 kPa or more, and the air permeability is 5 to 500 seconds. / Μm · 100 ml, facing one surface, the porosity (P) is 50 to 95%, including 1 μm or more of pores and having a thickness of 10 μm or less, and pore diameters other than the coarse layer Is a shape that includes at least two layers of a substantially uniform layer, the pore diameter in the coarse layer has a tendency to sequentially decrease in the direction of the other surface, and D ₂ / D ₁ is 1.1 or more. The cellulose-based porous membrane according to (1) above.
(10) In the porous membrane, the average pore diameter (D) is 0.001 to 20 μm, the porosity (P) is 1 to 90%, the tensile strength is 0.5 kPa or more, and the air permeability is 2 to 250 seconds / μm. · 100 ml, 1.5 or more _tortuosity, cellulose porous membrane according to the above (1), wherein the D 2 / _{D 1} is 1.1 or more.
(11) In the porous membrane, the average pore diameter (D) is 0.01-20 μm, the porosity (P) is 30-90%, the tensile strength is 0.5 kPa or more, facing one surface, It has at least two layers of a dense layer having a porosity (P) of 5% or less and a thickness of 10 μm or less, and a coarse layer having a porosity (P) other than the dense layer of 40% or more. The cellulose porous membrane as described in said (1).
(12) The cellulose polymer is either cellulose or a cellulose derivative in which a part of hydroxyl groups of cellulose is substituted with a functional group other than hydroxyl groups, or any one of the above (1) to (10) including both Cellulosic porous membrane as described in 1.

  The present invention is described in detail below.

The cellulose porous membrane of the present invention has a viscosity average molecular weight of 6 × 10 ⁴ or more, an average pore diameter of 0.001 to 1000 μm, a porosity of 0.1 to 98%, a tensile strength of 0.5 kPa or more, and at 160 ° C. The heat shrinkage rate is 5% or less.

The viscosity average molecular weight of the polymer constituting the cellulose-based porous membrane of the present invention is 6 × 10 ⁴ or more from the viewpoint of strength. Cellulosic porous membranes are brittle in the dry state. However, as the viscosity average molecular weight increases, the strength of the porous film increases and the brittleness is improved. Therefore, handling of the porous film becomes easy, and damage to the porous film is reduced. The greater the viscosity average molecular weight, the lower the failure rate when compared at the same porosity, but the effect of the viscosity average molecular weight on film properties tends to saturate as the viscosity average molecular weight increases. Is recognized. Therefore, a viscosity average molecular weight of 6 × 10 ⁴ or more is sufficient from the viewpoint of practical handling ease. In addition, the viscosity average molecular weight is desirably 3 × 10 ⁵ or less because of the ease of producing the porous film.

  The polymer used for the cellulose-based porous membrane of the present invention is selected according to the actual separation object and the like, and even if the polymer is cellulose, some of the hydroxyl groups of cellulose are substituted with functional groups other than hydroxyl groups. It may be either a cellulose derivative or may contain both. As cellulose, regenerated cellulose and purified cellulose are preferably used. Moreover, as a cellulose derivative, the kind and substitution degree are not specifically limited, What is necessary is just to introduce | transduce an appropriate substituent according to a use. Examples of the derivatives include cellulose esterified derivatives, etherified derivatives, halogenated derivatives, oxidized derivatives, and grafted derivatives. Moreover, as a kind of derivatization, even if it is one type or a plurality of derivatives may be mixed, there is no problem.

  Furthermore, the esterified derivative of cellulose is not particularly limited as long as it is a compound formed by dehydration condensation of a hydroxyl group of cellulose and an organic acid such as carboxylic acid or an inorganic oxo acid such as sulfuric acid. For example, cellulose acetate , Cellulose nitrate, cellulose nitrite, cellulose phosphate, cellulose xanthate, cellulose sulfate, cellulose formate, cellulose propionate, cellulose acetate propionate, cellulose tangle, cellulose trifluoroacid, tosylcellulose and the like.

  The etherified derivative of cellulose is not particularly limited as long as it is a cellulose derivative having an ether structure, and examples thereof include carboxymethyl cellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, cyanoethyl cellulose, and diethylaminoethyl ethyl cellulose. .

However, in the production of the cellulose derivative porous membrane, when a cellulose derivative solution is prepared in advance and then produced in the production method described later, the viscosity average molecular weight is generally 4 × 10 ⁴ or less, from the viewpoint of strength, The solution of the above-described problem in the present invention is not achieved. Therefore, in order to solve this problem, a cellulose solution having a viscosity average molecular weight of 6 × 10 ⁴ or more at the stage of producing the porous membrane is cast into a film and immersed in a coagulation liquid. Then, a film structure is formed. Then, after removing the solvent, etc. by solvent removal treatment and water washing, after converting some of the hydroxyl groups of cellulose to the desired functional groups while maintaining the solid state of cellulose under conditions suitable for each derivative The manufacturing method which dries is employ | adopted.

  The average pore diameter of the cellulose porous membrane of the present invention is in the range of 0.001 to 1000 μm. Here, the average pore diameter in the present invention is described in a reference (Naoki Kimura, Kiyotaka Sakai, Toshikatsu Shirota, Tetsuo Ukai, edited by Membrane Separation Technology Manual: 147; published by ICP Publishing, Inc., August 10, 1990). It means the mean flow pore size obtained using the air flow method.

  This is a pressure at which the porous film is immersed in a liquid having a known surface tension in advance and all the pores of the porous film are covered with a liquid film, and pressure is applied to the porous film to break the liquid film. And the following relational expression regarding the surface tension of the liquid.

d = C · r / P
Here, d in the formula is a pore diameter, r is a surface tension of the liquid, P is a pressure at which the liquid film having the pore diameter is broken, and C is a constant.

  As can be seen from the above relational expression, when the pressure applied to the porous film immersed in the liquid is continuously changed from low pressure to high pressure, the initial pressure cannot destroy the liquid film with the largest pore, and the flow rate is Although it is 0, when the pressure is gradually increased, the liquid film with the largest pore is destroyed and a certain flow rate is generated (this point is called a bubble point). When the pressure is further increased, the liquid film with the smallest pores is destroyed, and the flow rate (Dry flow rate) when not immersed in the liquid is matched.

  Here, the average pore diameter of the present invention refers to a pore diameter at a pressure at which the flow rate (Wet flow rate) when the porous membrane is immersed in a liquid is 50% of the flow rate (Dry flow rate) when the porous membrane is not immersed.

  However, a membrane containing pores having a pore diameter of 0.05 μm or less could not be measured by a PMI measuring device using an air flow method. Such a case was determined using a measuring device made by Yuasa Ionics by the gas adsorption method described later.

The average pore diameter (D) varies depending on the use of the cellulosic porous membrane, and thus cannot be defined unconditionally. However, if the average pore diameter (D) is 0.001 to 1000 μm, various values can be used. Can be used for applications. In the case where the average pore diameter (D) is less than 0.001 μm, almost anything other than ions cannot be transmitted, so that the use is limited and it is difficult to use for separation of substances other than ions. On the other hand, when the thickness exceeds 1000 μm, the strength of the film is remarkably lowered, resulting in a fragile material. Therefore, the average pore diameter cannot be generally defined because the required size varies depending on the application, but a preferable range corresponding to various applications is set within the above range. This will be described later.
The porosity (P) of the cellulosic porous membrane of the present invention is 0.1 to 98%. Here, the porosity is a volume ratio of voids of the porous film obtained by a method described later. When the porosity exceeds 98%, there arises a problem that the strength of the film is remarkably lowered. A preferable numerical value of the upper limit value of the porosity is 95%. About the lower limit of a porosity, a preferable range is set according to various uses. This will be described later.

  The tensile strength of the cellulose porous membrane of the present invention is 0.5 kPa or more. The tensile strength is determined by a method described later. If it is less than 0.5 kPa, the strength is insufficient, which causes a problem in use in any application. Preferably it is 1.0 kPa or more. However, within the above range, a preferable range may be set according to various uses, which will be described later. Although higher tensile strength is preferable, there is a limit due to the characteristics of the material.

  The cellulose-based porous membrane of the present invention is excellent in heat resistance, and the heat shrinkage rate at 160 ° C. is 5% or less. In a porous film made of a general-purpose resin such as polyethylene and polypropylene, the heat shrinkage at 160 ° C. reaches several tens of percent. For this reason. Cellulose porous membranes are suitable for applications in which the membrane shape should be maintained in such a high temperature region. A preferable range of heat shrinkage at 160 ° C. is 3% or less. Further, the thermal shrinkage at 200 ° C. is preferably 10% or less. In addition, since heat shrink is so preferable that it may be 0%.

  As described above, the cellulose-based porous membrane of the present invention has more appropriate ranges for the average pore diameter (D), porosity (P), and tensile strength depending on various applications. In that case, the film structure is preferably a film structure suitable for various applications. These points will be described in detail below.

  (I) For example, in a case where substances having various sizes of several tens of nm to several hundreds of μm are mixed in a liquid and the substances are separated or removed, they are described in claim 2. A preferred example is the cellulose-based porous membrane according to the embodiment.

  The cellulose-based porous membrane according to the aspect described in claim 2 will be described.

The membrane has an average pore size (D) of 0.01 to 1000 μm, a porosity (P) of 5 to 98%, a tensile strength of 0.5 kPa or more, and a surface average pore size (D ₁ ) on _one surface. 0.01 to 500 μm, the surface average pore diameter (D ₂ ) of the other surface is in the range of 0.1 to 1000 μm, and D ₂ / D ₁ is 1.1 or more, and in at least a part of the porous membrane, It is a structure having a plurality of boundary layers formed in the film thickness direction.

  When the average pore diameter (D) is in the above range, a substance having a size of several tens of nm to several hundreds of μm can be effectively separated. In consideration of filtration rate, separation performance, membrane strength, etc., the average pore diameter (D) is more preferably 0.02 to 800 μm, further preferably 0.05 to 500 μm, particularly preferably 0.08 to 300 μm, most preferably. 0.1 to 100 μm.

When the porosity (P) is in the above range, it can be used without any major trouble in terms of filtration speed and strength. The porosity (P) is more preferably 10 to 95%, further preferably 20 to 95%, and most preferably 30 to 95%.
A preferred range of average surface pore diameter D ₁ and D ₂ are as described above.

When the surface average pore diameter (D ₁ ) of _one surface is smaller than 0.01 μm, clogging near the D ₁ surface becomes remarkable no matter how large the surface average pore diameter (D ₂ ) of the other surface is, A decrease in filtration performance is inevitable. Also, if D ₁ is larger than 500μm it may be difficult to capture, such as: the size of particles 1 [mu] m. D ₁ of the range is more preferably 0.02～400Myuemu, more preferably 0.03～300Myuemu, and most preferably in the range of 0.04～200Myuemu.

Further, when the surface average pore diameter (D ₂ ) of the other surface is smaller than 0.1 μm, from the relationship D ₂ > D ₁ , the diameter of D ₁ is also smaller than 0.1 μm. In this case, the filtration rate Becomes smaller. Further, _{D 2} is the case 1000μm larger, no strength reduction are avoided. Range of D ₂ is more preferably 0.2～800Myuemu, more preferably 0.3～700Myuemu, most preferably from 0.5 to 500.

  Generally, as described above, when substances of various sizes of several tens of nanometers to several hundreds of micrometers are mixed, a plurality of membranes having different pore diameters are used to separate each substance, It is necessary to perform the separation operation in several times. However, the cellulosic porous membrane according to the aspect described in claim 2 is extremely useful because there are cases where separation of each substance can be achieved by only one operation with the single membrane. .

  (II) For example, in the case where the size of the substance mixed in the liquid is about 1 μm even when the substance is large, and the substance is used for separating or removing the substance, the cellulose type according to the aspect described in claim 5 A porous film is a preferred example.

In the film, both D ₁ and D ₂ are preferably 2 μm or less. When both D ₁ and D ₂ are 2 μm or less, the particle capturing efficiency is further increased. Further, D ₂ / D ₁ is preferably 1.1 or more. The ratio (D ₂ / D ₁ ) between the surface average pore diameters of both surfaces should be appropriately selected depending on the size of the particles to be separated. Usually, since it is considered that there is some variation in the size of the particles to be separated, it is preferably 1.5 or more, more preferably 3 or more, still more preferably 5 or more, particularly preferably 10 or more, and extremely preferably. Is 15 or more, most preferably 20 or more.

  Next, the structural features of the cellulose-based porous membrane according to the aspects described in claims 2 and 5 will be described.

  It is a preferable example that at least a part of the film has a structure having a plurality of boundary layers formed in the film thickness direction. For example, as shown in FIG. 7, the boundary layer can be confirmed when a cross section of the film is observed, and is a wall-like layer existing between voids having a cross-sectional pore diameter of 1 μm or more. The boundary layer is formed so as to extend in the film thickness direction.

  For example, this layer plays a role like a pillar in a dwelling, and is a factor in developing the strength of the film.

  Usually, in order to be a film having excellent permeability, it is required that the pore diameter is large, the number of holes is large, and the porosity is high. However, generally, the higher the porosity, the lower the strength of the membrane, which may hinder use. On the other hand, in the film structure having the above boundary layer, even when the porosity of the entire film is high, the boundary layer itself is very solid, so that the film as a whole has very excellent mechanical characteristics. Therefore, a structure having a plurality of boundary layers in the film thickness direction is a preferable example.

  In order to contribute to the development of the strength of the film, the thickness of the boundary layer is preferably 0.5 μm or more, more preferably 1 μm or more, further preferably 3 μm or more, particularly preferably 5 μm or more, and most preferably 10 μm. That's it. Further, the length of the boundary layer extending in the film thickness direction is preferably 1 μm or more, more preferably 3 μm or more, still more preferably 5 μm or more, particularly preferably 10 μm or more, and most preferably 20 μm or more. .

  Furthermore, it is preferable that pores exist in this boundary layer in some places. Due to the presence of the pores, adjacent cavities are connected to each other, so that the entire membrane exhibits extremely excellent permeation performance.

  The presence or absence of this boundary layer can be observed and evaluated by magnifying the cross section of the porous film. If the thickness and length are as described above, the presence can be confirmed by magnifying and magnifying about 300 times.

  Further, the reason why such a boundary layer is formed will be described in detail later in the section of the manufacturing method.

  Furthermore, since the required pore size varies depending on the application, the pore size inside the membrane cannot be defined unconditionally. However, as described in claim 3, in the cross-sectional observation of the membrane, the cross-sectional average pore size is 10 μm. It is a preferable example that the membrane structure is composed of at least two layers of the above-described large pore diameter layer and the small pore diameter layer having a cross-sectional average pore diameter of 5 μm or less, and the boundary layer is included in the large pore diameter layer. Here, the cross-sectional average pore diameter is a pore diameter obtained by observing the film cross-section with a scanning electron microscope, as will be described in detail later.

  In a multilayer structure having a large pore diameter layer and a small pore diameter layer as described above, in the large pore diameter layer having a cross-sectional average pore diameter of 10 μm or more, the boundary layer becomes a factor of strength development and plays a role as a support. Because of the large pore diameter, permeation performance is exhibited, while in the small pore diameter layer having a cross-sectional average pore diameter of 5 μm or less, an excellent microfiltration function is exhibited. It is an example of a preferable structure having both strength and high transmission performance.

  In addition, as described in claim 4, it is also a preferable example that the hole diameter is an inclined structure that sequentially decreases from one surface to the other surface. With such an inclined structure, particles of various sizes existing in the processing liquid can be efficiently captured.

  Moreover, there is no restriction | limiting in particular in the film thickness of a cellulose-type porous film, However As described in Claim 6, 1 mm or more is a preferable example depending on a use. Cellulose-based porous membranes are originally porous membranes with excellent strength, but when the thickness is 1 mm or more, the strength of the membrane as a whole is further improved, and as a result, the applications of the membrane are further expanded. In addition, as a characteristic of such a relatively thick film, it has excellent liquid absorption performance and may have a liquid absorption capacity 20 times its own weight.

  Further, the uniformity of the film thickness may vary slightly within a range that does not cause a problem in use. Furthermore, it may be uneven depending on the application.

  The average pore diameter (D) according to claim 7 is 0.001 to 0.1 μm, the porosity (P) is 0.1 to 40%, the tensile strength is 3 kPa or more, and the cross-sectional structure of the film is uniform. A certain cellulosic porous membrane is also a preferred example. A uniform cross-sectional structure means a structure in which the hole diameter hardly changes from one surface to the other surface and is constant.

  The structure of the film is a film having a uniform cross-sectional structure and a very uniform pore size. Therefore, for example, in the field of substance separation by natural diffusion, it is very useful in applications that require a high degree of fractionation, such as allowing a certain size of material to permeate but not larger size. Useful for.

  In the cellulose-based porous membrane according to the aspect described in claim 7, the average pore diameter (D) is more preferably 0.003 to 0.08 μm, and further preferably 0.005 to 0.05 μm. The porosity (P) is more preferably 1 to 40%, further preferably 5 to 40%, particularly preferably 10 to 40%, and most preferably 20 to 40%.

  In general, when performing pressure or vacuum filtration, the porosity of the membrane affects the filtration rate, and the higher the porosity, the more convenient the filtration can be performed at a high speed, but this is the subject of the present invention. In such material separation by natural diffusion, the material separation is sufficiently achieved with the porosity in the above range. The tensile strength is more preferably 5 kPa or more. An example of the use of a film having such characteristics includes a molecular fraction film and the like, but is not limited thereto.

  In addition, when the membrane is used for the purpose of permeating proteins and separating and removing contaminants larger than the size of the protein in aqueous solutions of various proteins, a membrane having a pore size corresponding to the size of the protein may be used. It is possible to remove impurities. In addition, since the membrane has a feature of low protein adsorption, the protein is not adsorbed on the membrane and removed together with impurities, and can be recovered very efficiently in the filtrate. It is suitable for such applications.

The average pore diameter (D) according to claim 8 is 0.001 to 1 μm, the porosity (P) is 0.1 to 50%, the tensile strength is 2 kPa or more, and the surface average pore diameter (D It is also a preferable example that ₁ ) is 0.001-0.01 micrometer.

  The structure as described above is particularly suitable for separating very small size particles. For example, among the substances that are dissolved and dispersed in the liquid, only the extremely small substances such as ions are allowed to pass through, and the use of the low molecular weight having a molecular weight of about several hundreds and the substances with larger sizes is prevented as much as possible. It is very preferable to use the membrane for the above. Therefore, when used in such applications, the average pore diameter (D) is more preferably 0.001 to 0.5 μm, still more preferably 0.001 to 0, although it depends on the size of the substance to be prevented from permeation. 0.3 μm, particularly preferably 0.001 to 0.2 μm, and most preferably 0.001 to 0.1 μm.

The porosity (P) is more preferably 0.1 to 30%, further preferably 0.1 to 20%, particularly preferably 0.1 to 10%, and most preferably 0.1 to 5%. . The tensile strength is more preferably 3 kPa or more, and particularly preferably 5 kPa or more. The surface average pore diameter (D ₁ ) is more preferably 0.001 to 0.008, further preferably 0.001 to 0.005, particularly preferably 0.001 to 0.003, and most preferably 0.001. 0.002 μm.

  The average pore diameter (D) according to claim 9 is 0.001 to 20 μm, the porosity (P) is 1 to 90%, the tensile strength is 0.5 kPa or more, and the air permeability is 5 to 500 seconds / It has a porosity (P) of 50 to 95%, includes a pore of 1 μm or more, has a thickness of 10 μm or less, and has a pore diameter other than the coarse layer. It is a structure that includes at least two layers with a substantially uniform layer, the pore diameter in the coarse layer has a tendency to sequentially decrease in the other surface direction, and D2 / D1 is 1.1 or more. is there.

  The film having the structure as described above, for example, keeps a large amount of liquid in the porous film, while allowing a very small substance such as ions or a substance having a molecular weight or less to pass through as smoothly and without resistance as possible. This is suitable for the purpose of capturing particles without passing through them. This is because the presence of the coarse layer facilitates the movement of the liquid from the outside to the inside of the film and can hold a large amount of liquid inside the film. Furthermore, it becomes possible to prevent permeation of particles, dust and the like by the layer having a substantially uniform pore size.

  In the membrane, the average pore diameter (D) is more preferably 0.005 to 10 μm, further preferably 0.01 to 5 μm, particularly preferably 0.01 to 3 μm, and most preferably 0.01 to 1 μm. . The porosity (P) is more preferably 5 to 80%, further preferably 10 to 70%, particularly preferably 30 to 70%, and most preferably 40 to 70%.

The air permeability is more preferably 5 to 300 seconds / μm · 100 ml, further preferably 5 to 100 seconds / μm · 100 ml, and most preferably 5 to 80 seconds / μm · 100 ml. The tensile strength is more preferably 1.0 kPa or more. D ₂ / D ₁ should be appropriately selected depending on the size of the particles to be separated, but is preferably 1.5 or more, more preferably 3 or more, still more preferably 5 or more, and particularly preferably It is 10 or more, very preferably 15 or more, and most preferably 20 or more.

  An example of the use of the film having such characteristics includes separators for various batteries, but is not limited thereto.

The average pore diameter (D) according to claim 10 is 0.001 to 20 μm, the porosity (P) is 1 to 90%, the tensile strength is 0.5 kPa or more, and the air permeability is 2 to 250 seconds / μm · 100 ml. A structure in which the curvature is 1.5 or more and D ₂ / D ₁ is 1.1 or more is also a preferable example.

  Each physical property value has a more preferable range. The average pore diameter (D) is more preferably 0.01 to 10 μm, further preferably 0.02 to 5 μm, and particularly preferably 0.03 to 4 μm. If it is the above structures, this film | membrane can be used suitably for the use which capture | acquires and removes microparticles | fine-particles of about several nm-1 micrometer, for example. In such applications, when the pore size is smaller than the size of the fine particles in the relationship between the fine particles to be captured and the size of the pores, the particles can be efficiently captured at the initial stage of filtration. Layers are generated and treatment such as backwashing is required.

  On the other hand, by setting the pore diameter to be slightly larger than the fine particle size, fine particles can be captured not only on the surface of the film but also inside the film, and the film performance can be maintained for a long time. In capturing the fine particles, the curvature of the film is also important, more preferably 2 or more, and further preferably 5 or more. Even when the fine particles are smaller than the average pore diameter (D) of the membrane, the larger the curvature of the membrane, the higher the possibility that the fine particles will be captured, which is preferable. A large curvature of the film means that the path of fine particles passing through the inside of the film is long. The longer the path, the higher the probability that the microparticles will encounter pores that are less than or equal to the particle size, resulting in an increased likelihood of the microparticles being captured.

The porosity (P) is more preferably 5 to 80%, further preferably 10 to 70%, particularly preferably 30 to 70%, and most preferably 40 to 70% from the viewpoints of permeability and strength. . The air permeability is more preferably 5 to 200 seconds / μm · 100 ml, further preferably 5 to 100 seconds / μm · 100 ml, and most preferably 5 to 80 seconds / μm · 100 ml. The tensile strength is more preferably 1.0 kPa or more. D ₂ / D ₁ should be appropriately selected depending on the size of the particles to be separated, but is preferably 1.5 or more, more preferably 3 or more, even more preferably 5 or more, and particularly preferably Is 10 or more, very preferably 15 or more, most preferably 20 or more.

  Examples of the use of the membrane having such characteristics include various separation membranes, but are not limited thereto.

  The average pore diameter (D) according to claim 11 is 0.01 to 20 μm, the porosity (P) is 30 to 90%, the tensile strength is 0.5 kPa or more, facing one surface, the pores A structure having at least two layers of a dense layer having a rate (P) of 5% or less and a thickness of 10 μm or less and a coarse layer having a porosity (P) of 40% or more in addition to the dense layer is also preferable. It is an example. The cellulose-based porous membrane having such a structure is suitable for use in capturing and removing fine particles of about several nm to several tens of nm, for example.

  Moreover, about each physical-property value, there exists a more preferable range, respectively, From a viewpoint of filtration performance, permeation performance, and intensity | strength, an average pore diameter (D) becomes like this. More preferably, 0.01-10 micrometers, More preferably, 0.01- 5 μm. Further, the porosity (P) is preferably in the range of 40 to 80% from the same viewpoint. Further, the film has a dense layer facing one side, more preferably, the porosity (P) of the dense layer is 3% or less, the thickness is 3 μm or less, most preferably, 1% or less, 1 μm or less. An example of the use of such a membrane includes, but is not limited to, a low molecular fraction membrane.

  Next, the manufacturing method of the cellulose type porous membrane of this invention is demonstrated.

First, the cellulose raw material is not particularly limited, and examples thereof include cotton linter, pulp, waste paper, bacterially produced cellulose, and regenerated cellulose. The degree of polymerization of the raw material is not particularly limited as long as the viscosity average molecular weight of the porous film can be 6 × 10 ⁴ or more at the stage of producing the porous film from the viewpoint of strength.

Regarding the solvent, in the present invention, there is no particular limitation on other points as long as the viscosity average molecular weight of the porous film is 6 × 10 ⁴ or more at the stage of producing the porous film. Specific types of solvents include, for example, solvents having solubility in cellulose, such as copper ammonia, caustic soda, sulfuric acid, liquid ammonia / ammonium thiocyanate, N-methylmorpholine N-oxide, and DMAc / LiCl. . Among these solvents, a copper ammonia solution is preferable from the viewpoint of dissolution stability as a cellulose solution.

  The concentration of cellulose in a dope prepared by dissolving cellulose using the above solvent is preferably in the range of 2 to 20 wt%, more preferably 3 to 15 wt%, and most preferably 4 to 12 wt%. When the cellulose concentration is in the above range, the cellulose is uniformly dissolved in the solvent, and it is easy to control the casting thickness in the film casting process described later, and the strength is also excellent. A cellulosic porous membrane is obtained. Next, this cellulose solution is cast into a film using a film die or a doctor blade. At this time, the casting method is not limited to the above method, and the shape of the die to be used is not particularly limited, and a known one can be applied.

  The subsequent steps will be described by taking a copper ammonia cellulose solution, which is a preferred cellulose solution in the present invention, as an example.

  After casting the cellulose solution, the film-like cellulose solution is introduced into a coagulation medium to form a film structure (hereinafter referred to as a coagulation step). Subsequently, a solvent or the like dissolving cellulose is extracted or removed, or its dissolving ability is lowered to form a solidified cellulose porous membrane (hereinafter referred to as a regeneration step).

  The regeneration solution used in this regeneration step may be any acid that can elute copper forming a complex with cellulose. For example, inorganic acids such as sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, odorous acid, and hydrofluoric acid. Organic acids such as acetic acid, succinic acid and tartaric acid can be used. Sulfuric acid is preferred. The concentration may be a minimum concentration at which regeneration is completed, and is preferably 15 wt% or less in consideration of economy. The regenerating method is performed by immersing in a tank filled with an acid or spraying using a device such as a shower.

  The above solidification step and regeneration step are very important steps that greatly influence the structure of the finally obtained film. Accordingly, the solidification method and the regeneration method used to achieve the film structure described in each claim will be described below in order.

  In order to obtain a structure having a boundary layer in the film thickness direction according to claim 2, it may be introduced into a coagulating liquid placed in a low temperature state in which the solvent component in the solution solidifies. As a result, the solvent component changes to a solid state, and as a result, a large number of small particles formed by the solidification of the solvent component are present in the solution. At this time, the cellulose component is present together with the solvent component that has not solidified while maintaining the solution state without solidifying, but is driven away from the space where the solidified solvent component exists, and into the minute space between the solidified solvent components. Exists. As a result, the cellulose component exists in the boundary layer shape extending in the film thickness direction and exists between the solidified solvent components, and in addition, it exists in a state of being concentrated at a higher concentration than the initial charged concentration. To do.

  When the solvent is removed in the next regeneration step, the cellulose component is regenerated and precipitated. At this time, by using a regeneration method that maintains the structure formation in the solidification step, that is, by using a low-temperature regeneration solution, cellulose precipitates from a high concentration state, and thus precipitates as a very tough boundary layer. . This is the reason why this boundary layer becomes a factor of strength development. At this time, the temperature of the regenerating liquid is not particularly limited as long as the temperature can be regenerated while maintaining the structure in the solidification step. For example, if the temperature is −5 ° C. or lower, the regeneration is performed while maintaining the structure. Is possible.

  In order to obtain a structure composed of at least two layers of a large pore layer and a small pore layer according to claim 3, after the introduction into a low-temperature coagulating liquid that solidifies the solvent component, the next regeneration is performed as described above. In the process, it is achieved by regenerating with a regenerating solution having a temperature of about 5 ° C. or higher. This is because, for example, when a film-like cellulose solution having a structure formed by solidification of the solvent component in the coagulation step is immersed in the regenerating solution at the above temperature, the regenerating solution is heated on the surface of the membrane. As the solution penetrates into the solution, the solidified component of the solvent formed at the time of coagulation of the cellulose solution is melted, and the solidified component of the solvent and the cellulose component are mixed again. Since regeneration takes place from this state, as a result, there is no boundary layer extending in the film thickness direction, and a small pore diameter layer having a cross-sectional average pore diameter of 5 μm or less is formed.

  Moreover, this regenerated solution is cooled by the cellulose solution as it penetrates into the membrane. For this reason, it becomes a temperature at which a solidified component of the solvent is not melted at a certain part inside the film, and as a result, the structure formed in the solidification process is maintained and regenerated from that part to the back side. It has a boundary layer extending in the thickness direction and precipitates in the state of a large pore diameter layer having a cross-sectional average pore diameter of 10 μm or more, thereby forming a structure composed of at least two layers.

In order to obtain an inclined structure in which the hole diameter is gradually reduced from one surface to the other surface according to claim 4, the method is the same as that of the structure of claim 2, but for the coagulating liquid, This is achieved by using a low temperature one.
In order to obtain a structure in which both D1 and D2 according to claim 5 are 2 μm or less, the cellulose concentration and ammonia concentration in the dope are set high, the casting thickness is reduced, and the temperature of the coagulation liquid is lowered. To achieve this.

  The structures of claims 7 to 11 are structures that do not have a boundary layer extending in the film thickness direction, and for these, the formation of the structure is achieved using a coagulating liquid of 1 ° C. or higher.

  For example, the structure as in claim 7 is an alkaline aqueous solution, the structure as in claim 8 is an aqueous solution containing a high concentration organic solvent such as acetone, and the structure as in claim 9 is The structure as claimed in claim 10 is an aqueous solution containing an organic solvent such as acetone, and the structure as claimed in claim 11 is aimed at using an acidic aqueous solution such as dilute sulfuric acid. Although it is possible to form the structure which does, it is not necessarily limited to the above.

  In addition, the regeneration is achieved by, for example, precipitating cellulose by extracting the solvent component or reducing its dissolution ability by immersing it in a regeneration solution at about room temperature.

  The porous cellulose membrane deposited through the coagulation and regeneration steps is washed with water or other cleaning agents.

  Thereafter, when the cellulose membrane is derivatized, at the stage where the washing with this water or other cleaning agent is completed, while maintaining the solid state of the cellulose, in each reaction condition, a part of the hydroxyl group of the cellulose, Derivatives are obtained by conversion to the desired functional groups. At this time, in order to advance various reactions while maintaining the solid state of cellulose, it is preferable to use an appropriate organic solvent system and a mixed system of an organic solvent and water as the reaction solvent instead of an aqueous system.

  Next, the cellulose porous membrane after washing may be replaced with moisture retained by the porous membrane with an appropriate organic solvent, if necessary. By carrying out like this, when drying is carried out while heating in the drying step described later, the degree of contraction of the film by drying can be reduced.

  In the cellulose derivative porous membrane after the derivatization reaction, water or an organic solvent retained by the membrane may be replaced with another organic solvent for the same purpose as described above.

  Finally, the cellulosic porous membrane that has undergone the above steps is dried. The conditions are not particularly limited, and for example, conditions depending on the purpose and application of the film, such as natural drying at room temperature, heat drying (40 to 200 ° C.), and freeze drying, are arbitrarily selected. good.

  The film-like cellulose porous membrane of the present invention is excellent in strength, heat resistance and organic solvent resistance, various separation membranes such as aqueous liquid, polar organic solvent, blood and oil, molecular fractionation membranes, various separators, microorganism capture membranes It is possible to provide a cellulose-based porous film that can be suitably used for, for example.

It is a figure which illustrates the example of a non-circular hole typically. 2 is a SEM photograph (magnification: 20,000 times) of one surface of the film obtained in Example 1. 2 is a SEM photograph (magnification: 1,000 times) of the other surface of the film obtained in Example 1. FIG. 2 is a SEM photograph (magnification: 300 times) of a cross section of the film obtained in Example 1. 4 is a SEM photograph (magnification: 10,000 times) of one surface of the film obtained in Example 2. 4 is a SEM photograph (magnification: 500 times) of the other surface of the film obtained in Example 2. 4 is a SEM photograph (magnification: 300 times) of a cross section of the film obtained in Example 2. 2 is a SEM photograph (magnification: 30000 times) of one surface of the film obtained in Example 10. 2 is a SEM photograph (magnification 30000 times) of the other surface of the film obtained in Example 10. 4 is a SEM photograph (magnification: 2500 times) of a cross section of the film obtained in Example 10. It is a SEM photograph (magnification: 20000 times) of one surface of the film obtained in Example 14. It is a SEM photograph (magnification 20000 times) of the other surface of the film | membrane obtained in Example 14. It is a SEM photograph (magnification: 2000 times) of the cross section of the film obtained in Example 14. 2 is a SEM photograph (magnification: 30000 times) of one surface of the film obtained in Example 16. 2 is a SEM photograph (magnification: 30000 times) of the other surface of the film obtained in Example 16. 4 is a SEM photograph (magnification: 2500 times) of a cross section of the film obtained in Example 16. It is a SEM photograph (magnification: 2500 times) of the cross section of the film obtained in Example 20. 4 is a SEM photograph (magnification: 1000 times) of a cross section of the film obtained in Example 24.

Explanation of symbols

1 hole 2 circumscribed circle 3 inscribed circle

EXAMPLES The present invention will be further described below with reference to examples and the like, but the present invention is not limited to these examples and the like. The measurement method is as follows.
(1) Viscosity average molecular weight A cellulose-based porous membrane is dissolved in cadoxen, a dilute cellulose-based solution is prepared, its specific viscosity is measured with an Ubbelohde viscometer, and the following viscosity formula (η) Calculated according to 1). The same operation was carried out on five samples, and the arithmetic average value was taken as the viscosity average molecular weight. (Reference: Eur. Polym. J., 1, 1 (1996))
[Η] = 3.85 × 10 ⁻² × M _W ^0.76 formula (1)
(2) Average pore diameter (D)
A cellulosic porous membrane sample was immersed in a liquid having a surface tension of 20.1 dynes / cm (manufactured by PMI: Silwick) and degassed at -80 kPa so that no bubbles remained in the sample. . After completion of the pretreatment, the sample was measured using a palm porometer (manufactured by PMI: CFP-1200AEX) (sample measurement diameter: 20 mm).

The procedure passes dry air through the sample containing Silwick and measures the gas flow at that time while increasing the pressure of the dry air stepwise. The pressure P ₅₀ (PSI) when the flow rate was 50% of the flow rate (Dry flow rate) when the sample was dried was determined, and the average pore diameter was determined from Equation (2).

d ₅₀ (μm) = C · r / P ₅₀ (2)
_{Here, d 50} is the average pore diameter ([mu] m). r was the surface tension of the liquid 20.1 (dynes / cm), and C was a constant 0.451 (μm · cm · PSI / dynes). The same operation was performed on five samples, and the arithmetic average value was defined as the average pore diameter.
(3) Average pore diameter (D) (when measurement was not possible in (2) above)
The pore size distribution was measured by the BJH method using a specific surface area / pore distribution measuring device (manufactured by Yuasa Ionics Co., Ltd .: NOVA4200e) by a nitrogen adsorption / desorption method, and the average pore size (D) was determined from this. . Each sample was measured for 5 samples, and the arithmetic average value was defined as the average pore diameter (D) (μm).
(4) average surface pore diameter (D ₁ and D ₂₎
Both surfaces of the cellulosic porous membrane were observed with a scanning electron microscope (SEM: manufactured by JEOL Ltd .: JSM-6380), and SEM photographs were obtained. The holes on both surfaces were relatively nearly circular. From these photographs, particle analysis by an image processing device (for example, manufactured by Asahi Kasei Co., Ltd .: IP1000-PC) is performed on at least 100 holes on each of both surfaces, and the equivalent circular hole diameter (equal to the hole area). The radius of the perfect circle was obtained. The same operation was performed on five samples, and the arithmetic average value was defined as the surface average pore diameter.
(5) Cross-sectional average pore diameter Cellulosic porous membranes were immersed in liquid nitrogen, frozen and cleaved to adjust the cross-sectional sections of the membranes, and then observed by SEM. From the cross-sectional photograph, when the shape was relatively close to a circle, particle analysis using an image processing apparatus was performed to obtain the equivalent circle diameter. Moreover, when the hole was non-circular, the shortest diameter was made into the diameter of the hole. Here, the noncircular hole in FIG. 1 represents the radius of the circumscribed circle 2 circumscribing the hole 1 at two points, r ₂ , and the radius of the inscribed circle 3 of the hole 1 having the same center as the circumscribed circle is r. _{When it is 3} , it is defined as a hole having r ₃ / r ₂ of less than 0.5. About 100 or more of these holes were measured, and the average value was obtained. The same operation was performed on five samples, and the arithmetic average value was defined as the cross-sectional average pore diameter.
(6) Film thickness (d)
The cellulosic porous membrane was allowed to stand in a constant temperature and humidity atmosphere at a temperature of 23 ± 2 ° C. and a relative temperature of 65 ± 3% for 24 hours, and then a 100 mm square measurement sample was cut out and a digimatic indicator (manufactured by Mitutoyo Corporation: 543-). 450B), the thickness of 9 points was measured, and the average value was obtained. The same operation was performed on five samples, and the arithmetic average value was defined as the thickness d (μm).
(7) Porosity (P)
The sample after the film thickness measurement is dried in a vacuum so that the moisture content is 0.5% or less. With the weight after drying as W (g), the porosity (%) was calculated from the following formula.

Porosity (%) = {1-W / (1.5 × d × 10 ⁻² )} × 100
(8) Tensile strength Measured according to JIS-L-1013. A strip-shaped measurement sample having a width of 10 mm and a length of 100 mm was cut out from a cellulosic porous membrane that was allowed to stand for 24 hours in a constant temperature and humidity atmosphere having a temperature of 23 ± 2 ° C. and a relative humidity of 65 ± 3%. For the measurement, a small material tester (EZ Test-50N manufactured by Shimadzu Corporation) was used. For two directions orthogonal to each other, measurement was performed on five samples, and the arithmetic average value was taken as the tensile strength.

Tensile strength (kPa) = breaking strength (N) × 10 ⁻³ / cross-sectional area of microporous membrane (m ² )
The cross-sectional area of the sample was 10 × d × 10 ⁻⁹ (m ² ).
(9) Thermal contraction rate at 160 ° C. The cellulosic porous membrane was allowed to stand in a constant temperature and humidity atmosphere at a temperature of 23 ± 2 ° C. and a relative humidity of 65 ± 3% for 24 hours. A 100 mm square measurement sample was cut out from the microporous membrane, and the sample was placed in a hot air circulation oven at 160 ° C. for 1 hour to conduct a heat shrink test. After completion of the test, the sample was cooled and placed in the constant temperature and humidity atmosphere for 2 hours, and then the sample size S (mm ² ) was measured again, and the heat shrinkage rate was calculated from the following formula.

Thermal contraction rate = (10000−S) / 100 (%)
(10) Presence / absence of boundary layer formed in the film thickness direction The cross section of the cellulosic porous film was observed at a magnification of 300 times using a scanning electron microscope, and the degree of the boundary layer within the range was evaluated.

○ Many exist. (Number: 6 or more)
△ A little exists. (Number: 3-5)
× Almost no (Number: 2 or more)
(11) Air permeability The cellulosic porous membrane sample was allowed to stand in a constant temperature and humidity atmosphere at a temperature of 23 ± 2 ° C. and a relative humidity of 65 ± 3% for 24 hours, and then a Gurley type densometer (G manufactured by Toyo Seiki Seisakusho Co., Ltd.) -B2), and measured based on JIS P8117. The same operation was performed for each of the five samples, and the arithmetic value was averaged for the value obtained by dividing the measured value by the film thickness of each sample, and the value was defined as the air permeability (seconds / μm · 100 ml).
(12) Curvature The curvature τ of the cellulosic porous membrane was calculated from the air permeability. The air permeability is defined as the time required for a certain volume of gas to permeate a sample having a certain area under a certain condition, and therefore depends on the gas movement speed, the shape of the through hole, and the like. The following formula described in the reference (edited by Masayuki Yoshio and Tomoya Ozawa: Lithium ion secondary battery: 115 pages; published by Nikkan Kogyo Shimbun, published on January 27, 2000) is used to calculate the curvature. It was.

t = 5.18 × 10 ⁻³ (τ ² d / εD)
Here, t is the air permeability (second), d is the film thickness (μm), ε is the porosity (volume ratio) D, and the average pore diameter (μm).

The curvature was calculated for each of the five samples, and the arithmetic average value was defined as the curvature τ (−).
(13) Confirmation of carboxymethylation reaction After carboxymethylation of the cellulose-based porous membrane, the membrane sample was subjected to absorbance measurement using a universal ATR of a Fourier transform infrared spectroscopic analyzer (manufactured by JASCO Corporation: Spectrum 100). The degree of substitution confirmed the absorbance intensity at 1730 cm ⁻¹ derived from the protonic carboxyl group.
Example 1
A copper ammonia cellulose solution (cellulose: 8 wt%, ammonia concentration: 6 wt%, copper concentration: 2.9 wt%, and most others: water) prepared according to a known method was cast on a metal plate to a thickness of 500 μm using a doctor blade. . Next, the film-like solution was immersed in a coagulation bath (liquid nitrogen: −196 ° C.) for 1 hour together with a metal plate to coagulate. Next, after immersing in a sulfuric acid bath (40 wt% / − 30 ° C.) for 30 minutes to remove the solvent, the membrane was washed with water and freeze-dried to obtain a white porous devitrified cellulose porous membrane.

SEM photographs of both surfaces and a cross section of the obtained film are shown in FIGS. In cross-sectional observation, a plurality of boundary layers formed in the film thickness direction could be confirmed. Further, this membrane was a membrane having a feature that the size of the pores gradually decreased from one surface to the other surface. Table 1 shows the measurement results of the physical properties of the obtained film.
(Example 2)
A white devitrified cellulose was obtained in the same manner as in Example 1 except that the composition of the copper ammonia cellulose solution was “cellulose: 4 wt%, ammonia: 6 wt%, copper: 1.4 wt%, and the rest were mostly water”. A porous membrane was obtained. The obtained film has a plurality of boundary layers formed in the film thickness direction in the same manner as in Example 1, and the size of the holes is sequentially reduced from one surface toward the other surface. It was a film with characteristics. Table 1 shows the measurement results of physical properties of the obtained film.
(Example 3)
The composition of the copper ammonia cellulose solution is “cellulose: 6 wt%, ammonia: 6 wt%, copper: 2.2 wt%, and others are almost water”, and this copper ammonia cellulose solution is cast on a glass plate at a thickness of 600 μm, As in Example 1, except that the coagulation bath was immersed in oil cooled to −40 ° C. (manufactured by Matsumoto Yushi Co., Ltd .: TT-200) for 1 hour and the temperature of the sulfuric acid bath was changed to 18 ° C. Coagulation, washing, and drying were performed to obtain a white cellulose devitrified porous membrane.

SEM photographs of both surfaces and a cross section of the obtained film are shown in FIGS. In cross-sectional observation, a plurality of boundary layers formed in the film thickness direction could be confirmed. Moreover, it was a multilayer structure film including a large pore diameter layer having a cross-sectional average pore diameter of 10 μm or more and a small pore diameter layer having a pore diameter of 5 μm or less (cross-sectional average pore diameter: 2.1 μm). Table 1 shows the measurement results of each physical property of the obtained film.
Example 4
A white devitrified cellulose was obtained in the same manner as in Example 3 except that the composition of the copper ammonia cellulose solution was “cellulose: 10 wt%, ammonia: 6 wt%, copper: 3.6 wt%, and the rest were mostly water”. A porous membrane was obtained. As in Example 3, the obtained film had a plurality of boundary layers formed in the film thickness direction, and was a multilayer structure film including a large pore diameter layer and a small pore diameter layer. Table 1 shows the measurement results of each physical property of the obtained film.
(Example 5)
Using a copper ammonia cellulose solution having the same composition as in Example 4, cast on a glass plate at a thickness of 500 μm, and operating in the same manner as in Example 3 except that the temperature of the sulfuric acid bath was −30 ° C., whitening A devitrified cellulose porous membrane was obtained. Table 1 shows the measurement results of each physical property of the obtained film.
(Example 6)
A cellulose porous membrane that was white and devitrified in the same manner as in Example 5 except that the composition of the copper ammonia cellulose solution was “cellulose: 3 wt%, ammonia: 6 wt%, copper: 1 wt%, and others were almost water”. Got. As in Example 3, the obtained film had a plurality of boundary layers formed in the film thickness direction, and was a multilayer structure film including a large pore diameter layer and a small pore diameter layer. Table 1 shows the measurement results of each physical property of the obtained film.
(Example 7)
In Example 5, the membrane after washing with water was not lyophilized, but immersed in isopropyl alcohol (IPA: 100 wt% / 25 ° C./2 hours) to replace the moisture retained by the membrane with IPA, and then heated. Except for drying (150 ° C./10 minutes), the same operation as in Example 5 was performed to obtain a white porous devitrified cellulose porous membrane. Table 1 shows the measurement results of each physical property of the obtained film.
(Example 8)
The composition of the copper ammonia cellulose solution is “cellulose: 12 wt%, ammonia: 7.2 wt%, copper: 4.3 wt%, and most others are water”, the substrate is a metal plate, the casting thickness is 100 μm, and the coagulation bath temperature is − The cellulose porous membrane which was white and devitrified in the same manner as in Example 5 except that the membrane after washing with water at 60 ° C. was dried by heating (105 ° C./30 minutes) instead of freeze drying. Got. Table 1 shows the measurement results of each physical property of the obtained film.
Example 9
A copper ammonia cellulose solution having the same composition as in Example 1 was white devitrified in the same manner as in Example 5 except that it was cast at a thickness of about 3.0 mm using a polyvinyl chloride spacer. A thick cellulose porous membrane having a thickness of about 2.5 mm was obtained. The membrane was excellent in water absorption performance and absorbed water as soon as it was immersed in water. In addition, Table 1 shows the measurement results of the physical properties of the obtained film.
(Example 10)
A copper ammonia cellulose solution having the same composition as in Example 1 was cast on a glass plate at a thickness of 250 μm by a doctor blade. Next, the film-like solution was immersed in a coagulation bath (aqueous sodium hydroxide / 11 wt% / 25 ° C./10 minutes) together with a glass plate. Next, the substrate was immersed in a sulfuric acid bath (3 wt% / 25 ° C./10 minutes) to remove the solvent, and then washed with water (30 ° C./10 minutes). Thereafter, the film was heat-dried at 105 ° C. for 30 minutes to obtain a transparent and tough film. When both surfaces and a cross section of the obtained film were observed with a scanning electron microscope (SEM), it was confirmed that the cross section had a uniform structure. The results of SEM observation are shown in FIGS. In addition, Table 2 shows the measurement results of the physical properties of this film.
(Example 11)
In this example, one useful application of the film obtained in Example 10 is shown.

The blocking rate of the membrane was measured using several types of marker molecules having different molecular weights. When the results were plotted against the molecular weight, the molecular weight cut-off (molecular weight with a blocking rate of 90%) of this film was 5000 (estimated molecular diameter: 2.6 nm).
(Example 12)
The composition of the copper ammonia cellulose solution is “cellulose: 4 wt%, ammonia: 6 wt%, copper: 1.4 wt%, and most others are water”, and the water-washed membrane is replaced with IPA and dried by heating (150 The same procedure as in Example 10 was performed except that the temperature was changed to 10 ° C./10 min. To obtain a slightly whitened cellulose porous membrane. Table 2 shows the measurement results of the physical properties of the obtained film.
(Example 13)
In this example, one useful application of the film obtained in Example 12 is shown.

Using the membrane, 1 L of albumin / phosphate buffer aqueous solution (albumin: 1 wt%, phosphate buffer aqueous solution: pH 7.4) containing impurities of several tens to several hundreds of nanometers was filtered. Thereafter, albumin adhering to the membrane was extracted with a surfactant, colored with a BCA solution that reacts with protein, measured with a spectrophotometer (wavelength 562 nm), and the amount of albumin adhering to the membrane was quantified. As a result, the amount of albumin adsorbed was as extremely low as 255 μg per gram of cellulose. Similarly, when a commercially available polyether sulfone membrane (manufactured by Pall Co., Ltd .: nominal pore size 0.1 μm) characterized by low protein adsorption is evaluated, it is 100 times or more the evaluation result of the above-mentioned cellulose porous membrane. It was 27700 μg per 1 g of polyethersulfone.
(Example 14)
A transparent and tough film was obtained in the same manner as in Example 7 except that the composition of the coagulation bath was “acetone / water = 90 wt% / 10 wt%)”. When both surfaces and a cross section of this film were observed with a scanning electron microscope (SEM), it was confirmed that the pore diameter of one surface was very small and the structure had a dense layer including the surface. The results of SEM observation are shown in FIGS. Table 2 shows the measurement results of the physical properties of this film.
(Example 15)
In this example, one useful application example of the film obtained in Example 14 is shown.

In order to suppress the swelling of the film during water immersion, the film obtained in Example 14 was further heated at 150 ° C. for 30 minutes. Subsequently, the permeability of the membrane to small molecules was evaluated. Using a membrane permeation experiment apparatus (KH-5P) manufactured by Beadrex Co., Ltd., the membrane was sandwiched between glass cells. One glass cell had 0.4 mol / L of sucrose (estimated molecular diameter: 1.1 nm). An aqueous solution (50 ml) was added, and pure water (50 ml) was added to the other glass cell, and sucrose permeability at 25 ° C. was evaluated. Similarly, a commercially available cellophane (registered trademark) (# 300) was also evaluated as a comparison. After 5 hours, Cellophane (registered trademark) had a sucrose permeation rate of 0.04 mol / L, whereas the cellulose membrane had a very low molecular permeation blocking performance of 0.008 mol / L. there were.
(Example 16)
The composition of the copper ammonia cellulose solution was “cellulose: 6 wt%, ammonia: 6 wt%, copper: 2.2 wt%, and most others were water”, and the same as Example 12 except that 30 ° C. warm water was used for the coagulation bath. As a result, a translucent film was obtained. When both surfaces and a cross section of this film were observed with an SEM, it was confirmed that the film had a structure composed of a coarse layer facing one surface and a layer having a substantially uniform pore diameter. The results of SEM observation are shown in FIGS. Table 2 shows the measurement results of the physical properties of this film.
(Example 17)
Except that methanol was used in place of IPA as a solvent for replacing water, the same operation as in Example 16 was performed, and the degree of devitrification was further reduced compared to Example 16, and the film had a color tone almost transparent. Got. Table 2 shows the measurement results of the physical properties of the obtained film.
(Example 18)
A translucent film was obtained in the same manner as in Example 16 except that the temperature of the water in the coagulation bath was 10 ° C. Table 2 shows the measurement results of the physical properties of the obtained film. Compared with the film of Example 16, it was slightly white and had a high porosity.
(Example 19)
A translucent film was obtained in the same manner as in Example 18 except that ammonia was added to the coagulation bath so that the concentration became 1500 ppm. Table 2 shows the measurement results of the physical properties of the obtained film. Compared with the film of Example 18, it was whiter and the porosity was higher.
(Example 20)
Similar to Example 16, except that the same copper ammonia cellulose solution as in Example 10 was used, and an acetone / water / ammonia mixed solution (50 wt% / 48 wt% / 2% wt%, respectively) was used as the coagulation liquid. Operation was performed to obtain a white devitrified film. When the cross section of this film was observed with an SEM, it was confirmed that the entire structure was sparse. The result of SEM observation is shown in FIG. In addition, Table 2 shows the measurement results of physical properties of the obtained film.
(Example 21)
A white devitrified film was obtained in the same manner as in Example 20 except that the casting thickness was 600 μm and the immersion time in the coagulation liquid was 60 minutes. Table 2 shows the measurement results of the physical properties of the obtained film.
(Example 22)
Using the membrane obtained in Example 21, the same operation as in Example 13 was performed to evaluate the protein adsorptivity. As a result, it was 6500 μg per 1 g of cellulose, which was ¼ or less of a commercially available polyethersulfone membrane (manufactured by Pall Corp .: nominal pore diameter: 0.1 μm).
(Example 23)
The same procedure as in Example 20 was followed, except that the composition of the copper ammonia cellulose solution was “cellulose: 8 wt%, ammonia: 4.8 wt%, copper: 2.9 wt%, acetone 4 wt%, and the rest were mostly water”. A white devitrified film was obtained. Table 2 shows the measurement results of the physical properties of the obtained film. The obtained film had a larger hole diameter on the back surface as compared with the film obtained in Example 20.
(Example 24)
A white devitrified film was obtained in the same manner as in Example 9 except that a dilute sulfuric acid aqueous solution (3 wt% / 25 ° C./10 minutes) was used as the coagulation bath. When the cross section of this film was observed by SEM, a dense layer existing on one side and a rough layer other than the dense layer were confirmed. The result of SEM observation is shown in FIG. In addition, Table 2 shows the measurement results of the physical properties of the obtained film.
(Example 25)
A derivatization reaction of the cellulosic porous membrane was performed. This time, carboxymethylation was performed as an example of derivatization.
A part (0.6 g) of the membrane obtained in Example 20 was placed in an eggplant-shaped flask, and pure water and IPA were added thereto, the ratio of IPA to water was 85:15, and the solvent weight was 90 g. Adjusted as follows. After putting the rotor into this, a glass reflux tube was attached, and the whole eggplant-shaped flask was immersed in a 50 ° C. water bath and heated for 30 minutes while refluxing and cooling tap water at about 10 ° C. The heating was performed while gently stirring using a magnetic stirrer. Further, an 11% caustic soda solution was added to the flask so that the molar ratio of cellulose to caustic soda was 1: 1. Stirring was further continued for 30 minutes to prepare alkali cellulose. After adjusting the alkali cellulose, sodium chloroacetate was added so that the molar ratio of cellulose and sodium chloroacetate was 1: 3 while continuing stirring.

Thereafter, stirring and refluxing were continued for 3 hours to carboxymethylate the cellulose. After 3 hours, heating was stopped and the membrane was removed from the eggplant type flask. This membrane was washed with 1N hydrochloric acid, and then thoroughly washed with 80 wt% methanol water and 100 wt% methanol, and then left at room temperature for 24 hours between commercial filter papers to dry the membrane. About the obtained carboxymethylated cellulose membrane, it confirmed that carboxylation was advancing using the Fourier-transform infrared spectroscopy analyzer.
(Example 26)
The membrane obtained in Example 25 was evaluated for protein adsorptivity in the same manner as in Example 22. As a result, it was 520 μg per 1 g of carboxymethylated cellulose, which was 1/10 or less compared to Example 22. It was.
(Comparative Example 1)
A cellulose acetate porous membrane (USP38883626) obtained by a known method was saponified at 25 ° C. using an aqueous sodium hydroxide solution having a pH of 13 to obtain a regenerated cellulose porous membrane. When this film was observed by SEM, a boundary layer extending in the film thickness direction could not be confirmed. Table 2 shows the measurement results of the physical properties of this film. Due to the low degree of polymerization of the starting dope, the resulting film had a viscosity average molecular weight of about 21,000. The measurement results of other physical properties are shown in Table 3. The obtained film has low strength and may be damaged when carelessly handled. When it was bent, it easily broke.
(Comparative Example 2)
The copper ammonia cellulose solution having the same composition as in Example 5 was stirred with a kneader for 48 hours to reduce the degree of polymerization of cellulose. Then, ammonia etc. were added and the solution of the same composition as Example 1 was obtained. Using this dope, the same operation as in Example 9 was performed to obtain a translucent film. Table 3 shows the measurement results of the physical properties of this film.

Compared with the film of Example 9, the difference was not clear by SEM observation, but the molecular weight was low in physical properties, and the film could be damaged if handled carelessly.
(Comparative Example 3)
Using a copper ammonia cellulose solution having the same composition as in Example 1 stored at room temperature for about 1 year, the same operation as in Example 9 was performed to obtain a translucent film. Table 3 shows the measurement results of the physical properties of this film.
The obtained film had a lower molecular weight than the film of Example 9, and the film could be damaged when handled carelessly. This was presumably because the molecular weight of the cellulose was reduced during storage due to the cleavage of the molecular chain of cellulose due to the influence of oxygen dissolved in the dope.
(Comparative Example 4)
Using the copper ammonia cellulose solution having a low polymerization degree prepared in Comparative Example 2, the composition was set to “cellulose: 0.5 wt%, ammonia: 6.1 wt%, copper: 0.36 wt%, and others were mostly water”. The solution was poured into a glass petri dish that had been cooled in a refrigerator having a temperature of 2 ° C. in advance so as to have a thickness of 1 mm, and this was immersed in an oil bath of −15 ° C. together with the petri dish. Operation was performed to obtain a white devitrified film. Table 3 shows the measurement results of the physical properties of this film. Although this membrane has a large pore diameter, the strength of the membrane is weak, and the membrane was easily damaged by careless handling. Further, when the same operation was repeated several times, the membrane was frequently damaged in the drying process.
(Comparative Example 5)
Table 3 shows the physical properties of commercially available ordinary cellophane (registered trademark) (# 300). When the viscosity average molecular weight is small and careless handling is performed particularly in a wet state, the film may be damaged.
(Comparative Example 6)
The same operation as in Comparative Example 34, except that the degree of polymerization of the copper ammonia solution was as high as Example 1 (degree of polymerization: 650 to 700) and the solution having the same composition as Comparative Example 4 was prepared. Thus, a white devitrified film was obtained. Similar to Comparative Example 4, the strength of the film was weak, and damage during the drying process and damage when careless handling occurred frequently.
(Comparative Example 7)
A commercially available cellulose nonwoven fabric (Asahi Kasei Fibers: UR601) was used to filter an aqueous liquid containing particles having a size of several nanometers to several hundred micrometers. However, particles having a size of several nanometers to several hundred micrometers could hardly be separated. The nonwoven fabric had pores having a size that can be clearly confirmed visually, and the size was about 1000 μm in the minor axis direction and longer than 1000 μm in the major axis direction.
(Comparative Example 8)
An aqueous liquid containing fine particles of several nm to several tens of nm was filtered using a commercially available reverse osmosis membrane. However, the liquid hardly passed through and was unsuitable for filtration of a liquid in which particles of such a size were mixed.
(Comparative Example 9)
For the purpose of using a commercially available polypropylene porous membrane (Celgard: No2500) under aseptic conditions, it was sterilized by dry heat (160 ° C / 1 hour), and the membrane contracted about 40% in area ratio and could not be used. It was.
(Comparative Example 10)
When a commercially available nitrocellulose porous membrane (manufactured by Pall Co., Ltd .: nominal pore size 0.2 μm) was subjected to the same operation as in Comparative Example 7, the membrane contracted by about 60% in area ratio and could not be used.
(Comparative Example 11)
The same operation as in Comparative Example 7 was performed on a commercially available cellulose mixed ester porous membrane (manufactured by Advantech Co., Ltd .: nominal pore size: 0.3 μm). As a result, the membrane contracted by about 50% in area ratio and could not be used.

The cellulose-based porous membrane of the present invention is a porous membrane that is excellent in strength, heat resistance and organic solvent resistance, and is hydrophilic. Utilizing this characteristic, it can be suitably used as a separation membrane for aqueous liquids, polar organic solvents, blood and the like.

Claims (12)

Viscosity average molecular weight is 6 × 10 ⁴ or more, average pore diameter (D) is 0.001 to 1000 μm, porosity (P) is 0.1 to 98%, tensile strength is 0.5 kPa or more, and heat shrinkage at 160 ° C. Is a film-like cellulose porous membrane, characterized by being 5% or less. In the porous film, the average pore diameter (D) is 0.01 to 1000 μm, the porosity (P) is 5 to 98%, the tensile strength is 0.5 kPa or more, and the surface average pore diameter (D ₁ ) on _one surface. Is 0.01 to 500 μm, the surface average pore diameter (D ₂ ) of the other surface is 0.1 to 1000 μm, and D2 / D1 is 1.1 or more. At least a part of the porous film is formed in the film thickness direction. The cellulosic porous membrane according to claim 1, further comprising a plurality of boundary layers.   In the porous film, a boundary layer formed of at least two layers, a large pore diameter layer having a cross-sectional average pore diameter of 10 μm or more and a small pore diameter layer having a cross-sectional average pore diameter of 5 μm or less, and formed in the large pore diameter layer in the film thickness direction. The cellulosic porous membrane according to claim 2, comprising:   The cellulosic porous membrane according to claim 2, wherein the porous membrane has an inclined structure in which the pore diameter gradually decreases from one surface to the other surface. 3. The cellulose-based porous membrane according to claim ₂ , wherein both D ₁ and D ₂ are 2 μm or less in the porous membrane.   The cellulosic porous membrane according to any one of claims 2 to 5, wherein the porous membrane has a thickness of 1 mm or more.   In the porous film, the average pore diameter (D) is 0.001 to 0.1 μm, the porosity (P) is 0.1 to 40%, the tensile strength is 2 kPa or more, and the cross-sectional structure is uniform. The cellulosic porous membrane according to claim 1, wherein In the porous film, the average pore diameter (D) is 0.001 to 1 μm, the porosity (P) is 0.1 to 50%, the tensile strength is 2 kPa or more, and the surface average pore diameter (D ₁ ) on _one surface. The cellulosic porous membrane according to claim 1, wherein is from 0.001 to 0.01 μm. In the porous membrane, the average pore diameter (D) is 0.001 to 20 μm, the porosity (P) is 1 to 90%, the tensile strength is 0.5 kPa or more, and the air permeability is 5 to 500 seconds / μm · 100 ml, facing one surface, the porosity (P) is 50 to 95%, including 1 μm or more of pores, and having a thickness of 10 μm or less, and the pore diameters other than the coarse layer are almost uniform A layer having a tendency that the pore diameter in the coarse layer gradually decreases in the direction of the other surface, and D ₂ / D ₁ is 1.1 or more. Item 2. The cellulose-based porous membrane according to Item 1. In the porous membrane, the average pore diameter (D) is 0.001 to 20 μm, the porosity (P) is 1 to 90%, the tensile strength is 0.5 kPa or more, the air permeability is 2 to 250 seconds / μm · 100 ml, The cellulosic porous membrane according to claim 1, wherein the curvature is 1.5 or more and D ₂ / D ₁ is 1.1 or more.   In the porous film, the average pore diameter (D) is 0.01 to 20 μm, the porosity (P) is 30 to 90%, the tensile strength is 0.5 kPa or more, facing one surface, the porosity 2. The method according to claim 1, wherein (P) has at least two layers: a dense layer having a thickness of 5% or less and a thickness of 10 μm or less; and a coarse layer having a porosity (P) other than the dense layer of 40% or more. Cellulosic porous membrane as described in 1.   The cellulosic polymer according to any one of claims 1 to 11, wherein the cellulosic polymer is either cellulose or a cellulose derivative in which a part of the hydroxyl group of cellulose is substituted with a functional group other than a hydroxyl group, or both. Porous membrane.