JP5778489B2 - Method for producing hydrophilic porous membrane, hydrophilizing agent, hydrophilic porous membrane, and method for hydrophilizing porous membrane - Google Patents

Description

  The present invention relates to a method for producing a hydrophilic porous membrane, a hydrophilizing agent, a hydrophilic porous membrane, and a method for hydrophilizing a porous membrane.

  Membrane separation technology is recognized for its excellent economic efficiency and reliability, and is widely used in various fields such as various types of water and drinking water. Examples of the separation membrane used in this membrane separation technique include porous membranes such as microfiltration and ultrafiltration.

  A wide variety of organic polymer compounds such as polysulfone-based, cellulose-based, polyacrylonitrile-based, polyolefin-based, vinylidene fluoride-based fluorine-based, and polyamide-based materials are used as the material for the porous membrane. These porous membranes can be classified into a hydrophilic type having a high affinity with water and a hydrophobic type having a low affinity with water, depending on the type of the organic polymer compound. Hydrophobic porous membranes (hereinafter referred to as “hydrophobic membranes”) have less change in membrane structure before and after drying than hydrophilic porous membranes. Among them, the vinylidene fluoride-based hydrophobic film is very excellent in terms of chemical resistance, heat resistance, mechanical strength, and the like, and is widely used in many fields.

  However, when the hydrophobic membrane is dried after film formation, the water permeability performance is remarkably lowered as compared with that before drying. Such a hydrophobic membrane requires a treatment (hereinafter referred to as “hydrophilic treatment”) for allowing water to enter the pores of the membrane when used for filtration.

The following methods are generally known as methods for hydrophilizing a hydrophobic membrane that is at least partially dried.
(1) Method of physically injecting water into pores As such a method, for example, (1-1) a method of immersing in a solution such as alcohol having a small surface tension, and (1-2) in water There is a method of passing water (penetrating water) into the pores by applying a high pressure.
(2) Method of modifying membrane surface Examples of such a method include (2-1) a method of introducing a hydrophilic group into the membrane surface by contacting with an aqueous alkali solution, and (2-2) a hydrophilic monomer. Examples thereof include a method of graft polymerization on the membrane surface and (2-3) a method of introducing a hydrophilic functional group onto the membrane surface by plasma irradiation.
(3) Method for coating membrane surface with hydrophilic substance As such a method, for example, (3-1) a method for coating a membrane surface with a hydrophilic agent such as a fluorosurfactant or glycerin, and ( 3-2) A method of insolubilizing a film brought into contact with a water-soluble polymer aqueous solution with heat or radiation is exemplified.

  Further, as a hydrophilization treatment method other than the above, there has been proposed a method (for example, Patent Document 1) in which an extract of pentaploid tannin, which is a kind of polyphenol, or an extract of Japanese tea is attached to a polysulfone membrane to impart hydrophilicity. Yes. Here, pentaploid tannin is one type of hydrolyzed tannin.

JP-A-5-301036

  The membrane hydrophilicized by the method (1) above loses its hydrophilicity once dried. Therefore, after the hydrophilic treatment, the membrane must always be kept in contact with water. When a part of is dried, a hydrophilization treatment is required again. In addition, the method (1-2) has a problem in that the pore size of the membrane changes or the membrane strength decreases because the pressure required for water passage becomes extremely high when the pore size of the pores becomes small. There is also a problem that special high-pressure equipment that is not necessary for the original filtration is required as ancillary equipment.

  The methods (2) and (3) are disadvantageous from the viewpoint of productivity and economy because the process of hydrophilic treatment is complicated and expensive and special equipment is required. In addition, these methods have a problem that the film strength is deteriorated due to alkali, heat, or radiation, and the pore diameter changes, and there is another problem that the safety of equipment is ensured.

  Further, the method (3) has a problem that the coated substance is eluted. Moreover, in the method of (3-1), in the hydrophilizing agent, a solvent crack (a crack generated in a resin molded product by contact with a chemical) is caused in a membrane module which is a filtration case filled with a porous membrane. Some may trigger and damage the membrane module during use. Therefore, sufficient scrutiny is required for selection of the hydrophilizing agent to be adopted.

  And the method of using the extract of pentaploid tannin and Japanese tea described in Patent Document 1 is similar in effect to a porous membrane made of polyvinylidene fluoride, although the material of the porous membrane is limited to polysulfone. It has become clear from the examination so far.

  The present invention has been made in view of the above circumstances, a hydrophilic porous membrane excellent in water permeability, a method for producing a hydrophilic porous membrane that can be produced safely and easily without requiring special equipment, An object is to provide a hydrophilizing agent, a hydrophilic porous membrane, and a method for hydrophilizing the porous membrane.

  As a result of intensive studies by the present inventors in order to achieve the above object, hydrophilicity is imparted by impregnating a composition containing polyphenol derived from lychee skin into the pores of the polyvinylidene fluoride porous membrane. The present inventors have found a hydrophilic treatment method that can maintain the hydrophilicity even when the porous membrane is dried, and have completed the present invention.

That is, the present invention is as follows.
[1] A method for producing a hydrophilic porous membrane, comprising a step of impregnating a composition containing polyphenol derived from lychee peel into the pores of the polyvinylidene fluoride porous membrane.
[2] The method according to [1], wherein the composition is a composition containing 30 to 90% by mass of a low molecular weight proanthocyanidin.
[ 3 ] In the impregnation step, the pores are impregnated with the composition contained in an aqueous solution, and the concentration of the composition in the aqueous solution is 0.2 to 2.0% by weight [1] or [2] production method.
[ 4 ] A hydrophilizing agent for a polyvinylidene fluoride porous membrane comprising a composition containing polyphenol derived from lychee peel as a main ingredient.
[5] The hydrophilizing agent according to [4], wherein the composition is a composition containing 30 to 90% by mass of low molecular weight proanthocyanidins.
[ 6 ] A hydrophilic porous membrane comprising a polyvinylidene fluoride porous membrane and a polyphenol derived from litchi skin provided in at least pores of the polyvinylidene fluoride porous membrane.
[7] The hydrophilic porous membrane according to [6], wherein the polyphenol derived from the lychee peel contains a low molecular weight proanthocyanidin.
[ 8 ] A method for hydrophilizing a porous membrane, comprising a step of impregnating a pore of the polyvinylidene fluoride porous membrane with a composition containing polyphenol derived from lychee peel.
[9] The hydrophilization method according to [8], wherein the composition is a composition containing 30 to 90% by mass of low molecular weight proanthocyanidins.

  According to the present invention, a hydrophilic porous membrane excellent in water permeability can be produced safely and easily without requiring special equipment, a hydrophilic porous membrane production method, a hydrophilizing agent, a hydrophilic porous membrane, And a method for hydrophilizing a porous membrane can be provided.

  Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) will be described in detail.

  The method for producing a hydrophilic porous membrane of the present embodiment includes a step of impregnating the composition containing polyphenol derived from lychee peel into the pores of the polyvinylidene fluoride porous membrane (hereinafter also referred to as “impregnation step”). I have it.

  In this production method, a polyvinylidene fluoride porous membrane is prepared prior to the impregnation step. Here, the “polyvinylidene fluoride porous film” means a porous film containing 50% by mass or more of polyvinylidene fluoride. As the polyvinylidene fluoride porous membrane, it is preferable that a porous membrane made of polyvinylidene fluoride has high water resistance and can be expected to have durability in filtration of a normal aqueous liquid. Examples of the polyvinylidene fluoride include a vinylidene fluoride homopolymer and a vinylidene fluoride copolymer in which the ratio of vinylidene fluoride as a monomer is 50 mol% or more. Examples of the vinylidene fluoride copolymer include a copolymer of vinylidene fluoride and one or more monomers selected from the group consisting of ethylene tetrafluoride, propylene hexafluoride, ethylene trifluoride chloride, and ethylene. . As the polyvinylidene fluoride, a vinylidene fluoride homopolymer is most preferable. Polyvinylidene fluoride is used alone or in combination of two or more.

  The polyvinylidene fluoride porous membrane may be prepared by a conventional method, or a commercially available product may be obtained. As a commercial item of a polyvinylidene fluoride porous membrane, a brand name "UNA-620A" (made by Asahi Kasei Chemicals) etc. is mentioned, for example.

  The polyvinylidene fluoride porous membrane is produced, for example, by a thermally induced phase separation method. More specifically, a polyvinylidene fluoride porous membrane having the form of a porous multilayer hollow fiber membrane may be produced by the following method described in International Publication No. 2007/043553. However, the production method of the polyvinylidene fluoride porous film is not limited to this, and the porous film may be produced by another thermally induced phase separation method, or may be produced by a stretched hole method or the like. In the following example, the polyvinylidene fluoride porous membrane has a form of a hollow fiber membrane, but is not limited thereto, and may be a form of a flat membrane or the like.

  First, polyvinylidene fluoride used as a raw material for the polyvinylidene fluoride porous film, and if necessary, an organic solvent and an inorganic powder are prepared, and they are melt-kneaded. Examples of polyvinylidene fluoride include those described above.

  As an organic solvent, it is preferable to use what becomes a latent solvent with respect to polyvinylidene fluoride. Here, the “latent solvent” refers to a solvent in which polyvinylidene fluoride is hardly dissolved at room temperature (25 ° C.) but can be dissolved at a temperature higher than room temperature. The organic solvent only needs to be liquid at the temperature in the melt-kneading with polyvinylidene fluoride described later, and does not necessarily need to be liquid at room temperature. Examples of the organic solvent include phthalates such as dimethyl phthalate, diethyl phthalate, dibutyl phthalate, dicyclohexyl phthalate, diheptyl phthalate, dioctyl phthalate, and di (2-ethylhexyl) phthalate; methyl benzoate; Benzoates such as ethyl benzoate; phosphates such as triphenyl phosphate, tributyl phosphate, tricresyl phosphate; ketones such as γ-butyrolactone, ethylene carbonate, propylene carbonate, cyclohexanone, acetophenone, isophorone; and Of these, a mixture of two or more of them may be mentioned. Of these, phthalates are preferred from the viewpoint of moldability.

  The inorganic powder is not particularly limited, and examples thereof include silica, alumina, titanium oxide, zirconia oxide, and calcium carbonate powder. An inorganic powder is used individually by 1 type or in combination of 2 or more types. Among these, silica is preferable from the viewpoint of easily obtaining a desired particle size and particle size distribution and from the viewpoint of economy. Among the silicas, hydrophobic silicas that are less likely to aggregate and have good dispersibility are more preferred, and more preferred are hydrophobic silicas having a MW (methanol wettability) value of 30% by volume or more. The MW value here is a value of the minimum volume% of methanol necessary for the powder to be completely wetted. Specifically, when silica is put in pure water and methanol is gradually added below the liquid level with stirring, the volume percentage of methanol in the aqueous solution when 50% by mass of silica settles is obtained. Is determined as the MW value.

  The average primary particle size of the inorganic powder is not particularly limited, but is preferably 3 nm or more and 500 nm or less, and more preferably 5 nm or more and 100 nm or less.

  About the compounding quantity of inorganic powder, it is preferable in the mass ratio of the inorganic powder occupied in a melt-kneaded material being 5 to 40 mass%. If the mass ratio of the inorganic powder is 5% by mass or more, the following effects by kneading the inorganic powder tend to be more effective and surely expressed. If the mass ratio is 40% by mass or less, stable spinning can be achieved. It is in.

  The melt kneading of the polyvinylidene fluoride, the organic solvent, and the inorganic powder can be performed using a normal melt kneading means, for example, a twin screw extruder. For example, a hollow fiber molding nozzle having two or more annular discharge ports arranged concentrically is attached to the tip of an extruder, and melted and kneaded products are supplied and extruded from different extruders to the respective annular discharge ports. It can be so. A hollow fiber-like extrudate having a multilayer structure can be obtained by joining a plurality of melt-kneaded materials supplied from different extruders and superimposing them at the discharge port. At this time, by extruding melt-kneaded materials having different compositions from the annular discharge ports adjacent to each other, it is possible to obtain multilayer films having different pore diameters of the layers adjacent to each other. The compositions different from each other refer to the case where the constituent materials of the melt-kneaded material are different, or the case where the constituent materials are the same but the constituent ratio is different. Even for the same type of polyvinylidene fluoride, if the molecular weight and molecular weight distribution are clearly different, the constituent materials are considered different.

When producing a hollow fiber membrane having a multilayer structure as a polyvinylidene fluoride porous membrane, the addition of inorganic powder stabilizes the polyvinylidene fluoride porous membrane having excellent performance by the following three specific effects. Can get to.
(1) The extrusion stability (spinning stability) of the hollow fiber-shaped extrudate having a multilayer structure is remarkably improved. This is because the viscosity of the melt-kneaded material is greatly increased by adding inorganic powder. Multi-layer extrusion tends to be unstable compared to single-layer extrusion, but in this embodiment, at least one of the layers to be bonded has a high viscosity and becomes a “hard” layer, so that stability is imparted. Specifically, it becomes possible to easily obtain a multilayer hollow fiber-like extrudate in which the roundness is maintained and at the same time the disturbance of the layer interface is suppressed. Suppressing the disturbance of the layer interface, such as the waviness of the layer interface, is important for multilayer extrusion.
(2) A pore size distribution becomes sharp, and a membrane in which the blocking performance, water permeability performance and strength are balanced at a high level can be obtained. This is because the melt kneaded product has a high viscosity, or the aggregate of inorganic powder absorbs the organic solvent into the inside thereof, thereby suppressing the seepage of the organic solvent into the adjacent layer. It is considered that the inorganic powder absorbs oil even when the organic solvent is infiltrated from the water, that is, it plays a role of a buffer. This is because the movement of the organic solvent can be suppressed due to the high viscosity, or the change in the film structure due to the mixing of the organic solvent between layers can be mitigated.
(3) Although the reason is unknown, when the inorganic powder is added to at least one layer, the mechanical strength and chemical strength of the membrane both before and after extraction and removal of the organic solvent and inorganic powder ( The chemical resistance tends to be high.

  The above three effects are preferable because the effect is further enhanced when the inorganic powder is contained in the melt-kneaded material having the largest discharge amount among the plurality of melt-kneaded materials to be discharged. The case where inorganic powder is contained in all the melt-kneaded materials discharged is more preferable.

  Further, the composition of the melt-kneaded product containing the inorganic powder is obtained by dividing the mass ratio D of the organic solvent by the mass ratio S of the inorganic powder, and further the maximum mass M at which the inorganic powder per unit mass absorbs the organic solvent. If the value obtained by dividing the composition is in the range of 0.2 or more and 2 or less, the effect of suppressing the movement of the organic solvent between the melt-kneaded materials can be further enhanced, and therefore, it is more preferable. The organic solvent here is the same as the composition contained in the melt-kneaded product, that is, the same mixing ratio as long as it is a single organic solvent or a mixed organic solvent. If the said value is 0.2 or more, the movement of the organic solvent from the adjacent layer near the layer interface is suppressed, a dense layer is not formed, and a high pure water permeability is maintained. When the above value is 2 or less, the organic solvent not absorbed in the inorganic powder is sufficiently small, and the organic solvent does not easily move near the interface. This leads to mitigation of changes in the membrane structure, and as a result, the blocking performance is maintained. The above value is more preferably from 0.3 to 1.5, and still more preferably from 0.4 to 1.0. This effect is also preferable because the effect is further enhanced when the inorganic powder is contained in the melt-kneaded material having the largest discharge amount among the plurality of melt-kneaded materials to be discharged. The case where inorganic powder is contained in all the melt-kneaded materials discharged is still more preferable. Here, the maximum mass M at which the inorganic powder absorbs the organic solvent per unit mass is referred to as dropping the organic solvent while kneading the inorganic powder, and the torque during kneading is initially 70% of the maximum torque. This can be determined by dividing the added mass of the organic solvent by the added mass of the inorganic powder.

  In addition, since at least one kind of organic solvent kneaded in two adjacent melt-kneaded materials is common, the influence of the structural change when the organic solvent moves between the melt-kneaded materials is reduced, preferable. Furthermore, it is more preferable that the types of organic solvents used in adjacent melt-kneaded materials are the same and the mixing ratio is different. When all the organic solvents are common, it is more preferable because recovery of the extracted organic solvent becomes easy.

  The difference in resin temperature when the melt-kneaded materials adjacent to each other are merged is preferably 20 ° C. or less. If it is 20 ° C. or lower, densification and void formation hardly occur at the interface of the melt-kneaded product. As a result, a film having high water permeability and strength can be obtained. The difference in resin temperature at the time of merging is more preferably 10 ° C. or less, and further preferably 0 ° C.

  The number of layers forming the multilayer, the pore size of each layer, and the ratio of the thickness of each layer can be appropriately set depending on the purpose. For example, if the purpose is a two-layer membrane, (i) a combination of a small pore diameter and a thin outer layer and a larger pore diameter and a thicker inner layer than the outer layer, or (ii) a large pore diameter and a thicker outer layer and a smaller pore diameter than the outer layer In addition, the combination with the thin inner layer is effective in order to have dense pores and high water permeability. Further, for example, in the case of a three-layer film, (iii) a combination of a small pore diameter and thin outer layer and inner layer and an intermediate layer having a larger pore diameter and thicker than the outer layer and inner layer, or (iv) a large pore diameter and thick outer layer and The combination of the inner layer and the outer layer and the intermediate layer having a smaller pore diameter and thinner than the inner layer is effective in order to have dense pores and high water permeability.

  The hollow fiber melt-kneaded product extruded from the discharge port with a multilayer structure is cooled and solidified by passing through a refrigerant such as air or water, and is wound up into skeins or the like as necessary. Thermally induced phase separation is induced during cooling. In the hollow fiber-like product after cooling and solidification, the polymer-rich partial phase and the organic solvent-rich partial phase are finely divided and exist. When the inorganic powder is finely divided silica, the finely divided silica is unevenly distributed in the organic solvent concentrated partial phase. By extracting and removing the organic solvent and the inorganic powder from the cooled and solidified hollow fiber-like material, the organic solvent concentrated phase portion becomes pores. Thereby, a porous multilayer hollow fiber membrane can be obtained.

  Extraction and removal of the organic solvent and extraction and removal of the inorganic powder can be performed simultaneously as long as they can be extracted and removed with the same solvent. Usually extracted and removed separately.

  For extraction and removal of the organic solvent, a liquid suitable for extraction that is mixed with the organic solvent without dissolving or modifying the used polyvinylidene fluoride is used. Specifically, the organic solvent can be extracted and removed by bringing the cooled and solidified hollow fiber-like material into contact with the liquid by a technique such as immersion. The liquid is preferably volatile so that it can be easily removed from the hollow fiber membrane after extraction. Examples of the liquid include alcohols and methylene chloride. If the organic solvent is water-soluble, water can also be used as the extraction liquid.

  The inorganic powder is usually extracted and removed using an aqueous liquid. For example, when the inorganic powder is silica, the cooled solidified hollow fiber is first contacted with an alkaline solution to convert the silica to silicate, and then contacted with water to extract and remove the silicate. Can be done.

  Either the extraction removal of the organic solvent or the extraction removal of the inorganic powder can be performed first. When the organic solvent is immiscible with water, it is preferable to first extract and remove the organic solvent, and then extract and remove the inorganic powder. Usually, the organic solvent and the inorganic powder are mixed and coexisting in the organic solvent-concentrated partial phase, so that the extraction and removal of the inorganic powder can proceed smoothly, which is advantageous.

  Thus, a porous multilayer hollow fiber membrane can be obtained by extracting and removing the organic solvent and inorganic powder from the cooled and solidified multilayer hollow fiber.

In addition, for the multilayer hollow fiber after cooling and solidification, (i) before extraction removal of the organic solvent and inorganic powder, (ii) after extraction removal of the organic solvent and before extraction removal of the inorganic powder, (iii) inorganic powder (Iv) After extraction and removal of the organic solvent and (iv) after extraction and removal of the organic solvent and inorganic powder, the multilayer hollow fiber is stretched in the longitudinal direction at a stretching ratio of 3 times or less. Can be done in a range. In general, when the multilayer hollow fiber membrane is stretched in the longitudinal direction, the water permeability is improved, but the pressure resistance (rupture strength and compressive strength) is lowered, so that the membrane does not often have a practical strength after stretching. However, the porous multilayer hollow fiber membrane obtained by the above production method has high mechanical strength. Therefore, stretching at a draw ratio of 1.1 to 3 times can be performed. By stretching, the water permeability of the porous multilayer hollow fiber membrane is improved. The draw ratio here refers to a value obtained by dividing the hollow fiber length after drawing by the hollow fiber length before drawing. For example, when a hollow fiber having a hollow fiber length of 10 cm is stretched to extend the hollow fiber length to 20 cm, the draw ratio is 2 times according to the following formula.
20cm ÷ 10cm = 2

  Further, if necessary, the stretched film may be heat treated to increase the compressive strength. The heat treatment temperature is usually preferably below the melting point of polyvinylidene fluoride.

  When the porous multilayer hollow fiber membrane obtained as described above is used as a polyvinylidene fluoride porous membrane, the blocking performance, water permeability performance, and strength are balanced at a high level.

  In the obtained polyvinylidene fluoride porous membrane, examples of the component that may be contained in addition to the polyvinylidene fluoride include the above-mentioned organic solvents and inorganic powders. However, as is clear from the above, the organic solvent and the inorganic powder are used in the step of preparing the polyvinylidene fluoride porous membrane, and from the viewpoint of preventing elution during filtration in advance, the final polyvinylidene fluoride porous It is preferable that it does not remain in the film.

  Although the porosity of the obtained polyvinylidene fluoride porous film is not particularly limited, it is preferably 30 to 90%, more preferably 40 to 80%. When the porosity is equal to or higher than the lower limit, an effect of improving water permeability is obtained, and when the porosity is equal to or lower than the upper limit, an effect of improving chemical resistance and mechanical strength is obtained. For example, as described in International Publication No. 2001/53213, the porosity in the present specification is obtained by overlaying a transparent sheet on a copy of an electron microscopic image of a porous film, and using a black pen or the like to form a hole portion. By painting black and then copying the transparent sheet onto a white paper, the hole portion is clearly distinguished from black and the non-hole portion is clearly distinguished from white, and thereafter, it can be obtained using commercially available image analysis software.

  The average pore size of the polyvinylidene fluoride porous membrane is not particularly limited, but is preferably 0.01 to 5.0 μm, and more preferably 0.01 to 1.0 μm. The average pore diameter in this specification is measured as follows. First, using a scanning electron microscope, the surface of the porous film is photographed at a magnification that allows the shape of a large number of holes to be clearly confirmed as much as possible. Next, on the photograph, five lines are drawn at almost equal intervals so as to be orthogonal to the vertical and horizontal directions, and the length of these lines across the hole in the photograph is measured. And the arithmetic average value of those measured values is calculated | required, and let this be an average hole diameter. In order to increase the accuracy of the hole diameter measurement, it is preferable that the number of hole diameters traversed by the 10 lines in the vertical and horizontal directions is 20 or more. If the pore diameter is about 0.1 μm to 1 μm, it is appropriate to use an electron microscope image with a magnification of about 5000 times.

  Next, prior to the impregnation step, the polyvinylidene fluoride porous membrane is immersed in a water-soluble organic solvent so that at least the pores are wetted with the water-soluble organic solvent, and then the organic solvent is replaced with water. The pores may be kept wet. Thereby, in an impregnation process, the polyphenol derived from a lychee skin can be easily impregnated in a pore. Examples of the water-soluble organic solvent include alcohols such as ethanol and isopropyl alcohol. Among these, ethanol is preferable from the viewpoints of safety and versatility.

  Next, in the impregnation step, a composition containing polyphenol derived from lychee peel is impregnated in the pores of the polyvinylidene fluoride porous membrane. The composition containing polyphenol derived from lychee peel functions as a hydrophilizing agent. As a composition containing polyphenol derived from lychee peel (hereinafter, also simply referred to as “lychee polyphenol composition”), an extract extracted from lychee peel may be used as it is. This extract contains the above-mentioned polyphenol.

  Moreover, it is preferable that the lychee polyphenol composition contains tannin (low molecular proanthocyanidins) obtained by lowering the molecular weight of proanthocyanidins derived from lychee peel from the viewpoint of more reliably achieving the effects of the present invention. Such a composition has a significantly increased content of low molecular weight proanthocyanidins compared to the raw material lychee peel. From the viewpoint of more effectively and reliably achieving the effects of the present invention, the content of the low molecular weight proanthocyanidins in this composition is preferably 30 to 90% by mass relative to the total amount of the composition. Such a composition containing low molecular weight proanthocyanidins is obtained by heating an extract extracted from lychee peel to 40 to 100 ° C. in a state diluted 2 to 20 times in a solvent (alcohol or the like), for example. , Ultrasonic treatment, or microwave treatment.

  The lychee polyphenol composition may be produced by a conventionally known method, or a commercially available product may be obtained. Examples of conventionally known methods include the methods described in JP 2007-215492 A and International Publication No. 2006/090830. Moreover, as a commercial item, the brand name "Oligonol" made from Amino Up Chemical Co., Ltd. is mentioned, for example.

  A composition containing polyphenols derived from lychee peel is registered as NDI (New Dietary Ingredient) in the US FDA (Food and Drug Administration), and its safety as a food is recognized as extremely safe It is a serious substance.

  Here, tannin refers to plant seeds, fruit shells, leaves, roots, wood, bark, etc. (for example, beech bark such as oak, oak, etc., leaves such as goby, urushi, tea leaves, buds, gallics, quintuplets. Etc.) is a general term for substances that can be extracted with warm water and used as leather for animal hides, and is a natural polyphenolic compound. Tannin is a safe substance that is used as a food additive, as a clarifier such as wine and beer, and as a refining agent for animal fat, and its safety as a food is recognized.

  Tannins are divided into two groups, condensed tannins and hydrolyzed tannins. Condensed tannin is a polymer of a compound having a flavanol skeleton, and has a carbon-carbon bond and is not hydrolyzed. On the other hand, hydrolyzable tannin is an ester of an aromatic carboxylic acid, has an ester bond, and is hydrolyzed by an acid, an alkali, or an enzyme. The low molecular weight proanthocyanidins according to this embodiment belong to the condensed tannin among the above.

  In the impregnation step, a hydrophilic agent other than the lychee polyphenol composition may be impregnated, or before or after the impregnation step, the hydrophilic agent other than the lychee polyphenol composition is added to the pores of the polyvinylidene fluoride porous membrane. It may be impregnated inside. Examples of such a hydrophilizing agent include ethanol and isopropyl alcohol.

  The lychee polyphenol composition and other hydrophilizing agents are preferably used in the form of an aqueous solution from the viewpoint of uniform permeability into the membrane. From the viewpoint of improving the solubility, the aqueous solution concentration of the hydrophilizing agent is preferably 0.2 to 2.0% by mass, and more preferably 0.5 to 1.0% by mass. When it is 0.2% by mass or more, it becomes easier to obtain a sufficient hydrophilic effect, and when it is 2.0% by mass or less, when proteins and heavy metal ions coexist, the polyphenol is combined with them or self Oxidation can be prevented from becoming a complex multimer, and the formation of precipitates can be further suppressed. The aqueous solution concentration of the hydrophilizing agent is preferably determined as appropriate according to the pore diameter and membrane structure of the polyvinylidene fluoride porous membrane.

  As is clear from the above, the lychee polyphenol composition can be used in combination with other hydrophilizing agents.

  In the impregnation step, the sterilizing agent may be impregnated in the pores of the polyvinylidene fluoride porous membrane together with at least one of the lychee polyphenol composition and the other hydrophilizing agent. Before and after, a sterilizing agent may be impregnated in the pores of the polyvinylidene fluoride porous membrane. Thereby, propagation of microorganisms and fungi can be suppressed. Examples of the sterilizing agent include sodium hypochlorite and formaldehyde. In addition, a sterilizing agent can be used individually by 1 type or in combination of 2 or more types.

  As a method of impregnating the polyvinylidene fluoride porous membrane with the lychee polyphenol composition, other hydrophilizing agent or sterilizing agent, for example, when the polyvinylidene fluoride porous membrane is in a wet state, those liquids or those are included. Examples include a method of immersing the porous film in an aqueous solution, and a method of spraying or flowing the aqueous solution onto the porous film. In addition, when the polyvinylidene fluoride porous membrane is in a dry state, these liquids or an aqueous solution containing them may be impregnated into the pores so as to be pressed into the pores of the porous membrane under pressure conditions. Is possible.

  Conditions such as the time required for impregnating the polyvinylidene fluoride porous membrane with the lychee polyphenol composition and the usage amount of the lychee polyphenol composition are such that the water permeability of the finally obtained hydrophilic porous membrane becomes a desired level. As long as it is a necessary condition, there is no particular limitation.

  The porous membrane that has undergone the above-described impregnation step may be used as it is as a hydrophilic porous membrane, or may be used as a hydrophilic porous membrane after being appropriately dried as necessary.

  The hydrophilic porous membrane thus obtained includes a polyvinylidene fluoride porous membrane and a polyphenol derived from litchi pericarp provided in at least the pores of the polyvinylidene fluoride porous membrane. This hydrophilic porous membrane may contain a hydrophilizing agent other than the lychee polyphenol composition or a sterilizing agent at least in the pores. Moreover, components other than the polyphenol derived from lychee skin contained in the lychee polyphenol composition may remain in the pores. Furthermore, each of the above components may be provided in a region other than the pores of the polyvinylidene fluoride porous membrane. Moreover, the well-known component contained in the conventional hydrophilic porous membrane may be contained.

  The content of polyphenol derived from lychee skin in the hydrophilic porous membrane is not particularly limited.

  The polyphenol derived from lychee peel is considered to be adsorbed on the membrane in the pores of the polyvinylidene fluoride porous membrane. The reason is not clear, but the hydrophilic porous membrane is excellent in water permeability because the polarities of polyvinylidene fluoride having a strong C—F bond and the low molecular weight polyphenol retain an electrically strong bond. it is conceivable that. However, the factor by which a hydrophilic porous membrane is excellent in water permeability is not limited to this.

  The porosity of the hydrophilic porous membrane is not particularly limited, but is preferably 30 to 90%, and more preferably 40 to 80%. When the porosity is equal to or higher than the lower limit, an effect of improving water permeability is obtained, and when the porosity is equal to or lower than the upper limit, an effect of improving chemical resistance and mechanical strength is obtained.

  The average pore size of the hydrophilic porous membrane is not particularly limited, but is preferably 0.01 to 5.0 μm, and more preferably 0.01 to 1.0 μm.

  As apparent from the above, the method for producing a hydrophilic porous membrane of the present embodiment can also be said to be a hydrophilic treatment method for the porous membrane.

  The hydrophilic porous membrane of this embodiment is suitably used as a filtration membrane represented by a microfiltration membrane (MF), an ultrafiltration membrane (UF), a reverse osmosis membrane (RO), and a dialysis membrane.

  According to the present embodiment, as is apparent from the above, the hydrophilic porous membrane can be manufactured safely and easily without requiring special equipment. Further, the hydrophilic porous membrane obtained by the production method of the present embodiment can easily recover its hydrophilicity even when the membrane is dried. Moreover, the lychee polyphenol composition used as the hydrophilizing agent is a plant-derived safe material, and is extremely useful in practice because it is easy to clean the porous membrane and treat waste water.

  As mentioned above, although the form for implementing this invention was demonstrated, this invention is not limited to the said this embodiment. The present invention can be variously modified without departing from the gist thereof.

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

(Pure water permeability)
“Pure water permeability” is the pure water permeation amount of the porous membrane per unit time and unit membrane area, and was measured by the following procedure.
First, one end of a porous membrane (hollow fiber membrane) as a sample having a length of about 10 cm was sealed, and an injection needle was inserted into the hollow portion at the other end. From the injection needle, pure water at a pressure of 0.1 MPa and 25 ° C. was injected into the hollow portion, and the amount of pure water permeated from the inside to the outside of the hollow fiber membrane was measured. Asked. The effective membrane length refers to the net membrane length excluding the portion where the injection needle is inserted from the length of the hollow fiber membrane.
Pure water permeability [L / (m ² · hr)] = permeated water amount [L] / (π × membrane inner diameter [m] × membrane effective length [m] × measurement time [hr])

Example 1
A hollow fiber membrane was produced according to Example 2 of International Publication No. 2007/043553. That is, vinylidene fluoride homopolymer [manufactured by Kureha Co., Ltd., trade name: KF # 1000], di (2-ethylhexyl) phthalate (manufactured by CG Esther Co., Ltd.) and dibutyl phthalate (manufactured by CG Esther Co., Ltd.) as organic solvents The mixture shown in FIG. 2 is made of silica fine powder (manufactured by Nippon Aerosil Co., Ltd., trade name: AEROSIL-R972, having a primary particle size of about 16 nm), and is hollow as shown in FIG. 2 of WO2007 / 043553. A two-layer hollow fiber membrane was melt-extruded by two extruders using a yarn forming nozzle. As the melt-kneaded product (a) for the outer layer, the composition is vinylidene fluoride homopolymer: di (2-ethylhexyl) phthalate: dibutyl phthalate: fine powder silica = 34: 33.8: 6.8: 25.4 (mass ratio) )) As a melt-kneaded product (b) for the inner layer, and the composition is vinylidene fluoride homopolymer: di (2-ethylhexyl) phthalate: dibutyl phthalate: finely divided silica = 36: 35.3: 5.0 : 23.7 (mass ratio) of melt-kneaded material and air as a hollow portion forming fluid, respectively, for forming hollow fibers having an outer diameter of 2.00 mm and an inner diameter of 0.92 mm at a resin temperature of 250 ° C. The nozzle was extruded from the nozzle at a discharge linear velocity of 14.2 m / min and an amount ratio such that the outer layer: inner layer thickness ratio = 10: 90. The outer diameter of the nozzle here refers to the outermost diameter of the discharge port in FIG. 2 of International Publication No. 2007/043553. The inner diameter of the nozzle refers to the maximum diameter of the lower end of the partition wall between the inner layer melt-kneaded product discharge port and the hollow portion forming fluid discharge port.

  The extruded hollow fiber-shaped extrudate was cooled and solidified by being introduced into a 40 ° C. water bath after running in the air of 45 cm, and wound up skein at a speed of 30 m / min. The obtained two-layer hollow fiber was immersed in methylene chloride to extract and remove di (2-ethylhexyl) phthalate and dibutyl phthalate, and then dried. Next, after being immersed in a 50% by weight ethanol aqueous solution for 30 minutes, then immersed in water for 30 minutes, then immersed in a 20% by weight sodium hydroxide aqueous solution at 70 ° C. for 1 hour, and further washed with water to repeat fine powder. Silica was extracted and removed.

  The obtained hollow fiber membrane, which is a polyvinylidene fluoride porous membrane, had a porosity of 70%, an average pore diameter of 0.2 μm, an inner diameter of 0.7 mm, and an outer diameter of 1.2 mm. The hollow fiber membrane was immersed in 100% ethanol to make the pores wet, and then replaced with water to obtain a “standard membrane”.

  Next, a 1.0% by mass aqueous solution (oligonol aqueous solution) of oligonol (trademark, manufactured by Amino Up Chemical Co., Ltd.), which is a composition containing polyphenol derived from lychee peel, is prepared, and 20 g thereof is placed in a test tube. Encapsulated. Next, four 120 mm long standard membranes were immersed in the aqueous solution in the test tube for 24 hours, and then the membrane was removed from the test tube and air-dried for 3 days to return to a dry state. The hydrophilic porous membrane obtained through such a series of operations was defined as a “treated membrane”.

Next, the pure water permeability after the standard membrane and the treated membrane were immersed in pure water for 24 hours was 7900 and 7500 [L / (m ² · hr)], respectively.

(Example 2)
A treated membrane was obtained in the same manner as in Example 1 except that the concentration of the oligonol aqueous solution was changed from 1.0 mass% to 0.5 wt%. Next, 20 g of an oligonol aqueous solution was sealed in the test tube, and four 120 mm long standard membranes were immersed in the aqueous solution in the test tube for 24 hours. Then, the membrane was removed from the test tube and air-dried for 3 days to return to a dry state. A treated membrane which is a hydrophilic porous membrane was obtained.

After this treated membrane was immersed in pure water for 24 hours, the pure water permeability was measured and found to be 6800 [L / (m ² · hr)].

(Comparative Example 1)
The above oligonol aqueous solution was changed to a 1.0 mass% aqueous solution (pentol tannin aqueous solution) of pentaploid tannin (manufactured by Wako Pure Chemical Industries, Ltd.) used in Example 1 described in JP-A-5-301036. A treated film was obtained in the same manner as in Example 1 except that. Next, 20 g of the above aqueous solution is sealed in a test tube, and four 120 mm long standard membranes are immersed in the aqueous solution in the test tube for 24 hours, and then the membrane is removed from the test tube and air-dried for 3 days to form a porous membrane. Got.

  When this treated membrane was immersed in pure water for 24 hours and then the pure water permeability was measured, no permeation was observed.

  From the results of Examples 1 and 2, the hydrophilic porous membrane obtained by immersing the polyvinylidene fluoride porous membrane in the aqueous solution of the composition containing polyphenol derived from lychee skin as a hydrophilizing agent is water again even after drying. It was shown that the water permeation performance was recovered by simply immersing the film in water.

  Even if the hydrophilic porous membrane obtained by the production method of the present invention is dried, it is possible to prevent a decrease in water permeability when immersed in water again. Therefore, the hydrophilic porous membrane according to the present invention has industrial applicability as a filtration membrane represented by a microfiltration membrane (MF), an ultrafiltration membrane (UF), a reverse osmosis membrane (RO), and a dialysis membrane. is there.

Claims (9)

  A method for producing a hydrophilic porous membrane, comprising a step of impregnating a pore of the polyvinylidene fluoride porous membrane with a composition containing polyphenol derived from lychee peel. The said composition is a manufacturing method of Claim 1 which is a composition containing 30-90 mass% of low molecular weight proanthocyanidins. In the step of the impregnation, the composition contained in the aqueous solution is impregnated into the pores, the concentration of the composition in the aqueous solution is 0.2 to 2.0 wt%, according to claim 1 or 2 Manufacturing method.   A hydrophilizing agent for a polyvinylidene fluoride porous membrane comprising a composition containing polyphenol derived from lychee pericarp as a main ingredient. The hydrophilizing agent according to claim 4, wherein the composition is a composition containing 30 to 90% by mass of low molecular weight proanthocyanidins.   A hydrophilic porous membrane comprising a polyvinylidene fluoride porous membrane and a polyphenol derived from lychee skin provided in at least pores of the polyvinylidene fluoride porous membrane. The hydrophilic porous membrane according to claim 6, wherein the polyphenol derived from the lychee peel contains a low molecular weight proanthocyanidin.   A method for hydrophilizing a porous membrane, comprising a step of impregnating a pore of the polyvinylidene fluoride porous membrane with a composition containing polyphenol derived from lychee peel. The hydrophilization method according to claim 8, wherein the composition is a composition containing 30 to 90% by mass of a low molecular weight proanthocyanidin.