RU2440181C2 - Porous membrane from vinylidene fluoride resin and method of its production - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to porous membrane intended for water treatment and to method of its production. Porous membrane made from vinylidene fluoride resin with limit of particles passage of at least 0.2 mcm comprises opposed first and second surfaces. Note here that first surface has micro pores of round or oval shape with mean relation between larger axis and smaller axis varying from 1:1 to 5:1, while second surface has slot-shaped micro pores with mean relation between larger axis and smaller axis making at least 5:1. Method of producing porous membrane comprises cooling of initial solution containing vinylidene fluoride resin, solvent, inorganic particles and agent provoking aggregation wherein inorganic particles and agent feature affinity while solvent and agent are immiscible or feature the maximum critical temperature of dissolution for inducing phase separation with subsequent hardening, and extraction of porous membrane before complete removal of solvent, inorganic particles and agent.

EFFECT: higher permeability, fractionation properties, physical and chemical strength.

11 cl, 6 dwg, 4 tbl, 6 ex

Description

FIELD OF TECHNOLOGY

The present invention relates to a porous membrane made of vinylidene fluoride resin having a high fractionating ability, permeability and suitable for use in the field of water treatment, such as, for example, water treatment, drinking water, water for industrial use, wastewater treatment, food industry, in charged membranes and fuel cells, as well as to a method of manufacturing such a porous membrane, which is the best from the point of view of controllability of production, estoimosti and pore formation parameters.

BACKGROUND OF THE INVENTION

In recent years, the technology of release agents using a porous membrane with selective permeability has been noticeably developing. Such separation technology is used in practice as a sequence of cleaning systems, including separation, cleaning and sterilization, for example, in the production of drinking water, highly pure water and medicines, as well as in the removal of microorganisms and the final processing of finished products. In these applications, the refining (high degree of purification) of water, as well as improving safety and increasing accuracy should be at a high level, and therefore the use of porous membranes is widespread. Given such situations, the mandatory characteristics of the porous membrane are complicated. Among these membrane characteristics, it is believed that the most important are permeability and fractionation ability. With regard to permeability and fractionation ability, they must be balanced relative to each other so that particles as small as possible can be removed at high flow rates of pure water permeate, to which pore continuity and membrane surface structure are of great importance. .

In order to sterilize permeate and prevent membrane biofouling, a disinfectant, such as, for example, sodium hypochlorite, is added to the membrane module zone during water treatment, and / or the membrane itself is washed with an acid, alkali, chlorine or surface-active agent, as a result of which, so that the porous membrane is chemically resistant. Since chlorine-resistant pathogens, such as, for example, cryptosloridia originating from excrement and urine from livestock, cannot be sufficiently removed in a water-filtering plant, and, as a result, since 1990, difficulties associated with the presence of impurities of pathogenic organisms in the treated water, upon receipt of tap water there are requirements for the porous membrane to have sufficient separation or fractionation characteristics, effective in order to prevent admixture of the unpurified water to the purified water, and, in addition, it should have a high physical strength sufficient to prevent rupture of the filaments.

As noted above, important characteristics that a porous membrane must have include separation or fractionation accuracy, permeability, mechanical strength, and chemical resistance. Accordingly, it has recently been proposed to improve the porous membrane by using polyvinylidene fluoride. The porous membrane, which uses vinylidene fluoride resin, not only has excellent strength, extensibility and chemical resistance, but also is resistant to oxidizing agents and can, therefore, be used in high-quality water treatment using ozone, which has recently acquired public interest.

As mentioned above, the mechanical strength of the porous membrane and its chemical strength, which is chemical resistance, are mainly related to the characteristics of the material used to make the porous membrane, and the permeability and fractionation ability of the porous membrane depend on the method of manufacturing such a porous membrane.

As a method of manufacturing a hollow fiber membrane, which allows to obtain a high flow rate of pure water permeate, we can call a method of drawing pores. This method is characterized by the fact that the material for the manufacture of the membrane is annealed and stretched under certain conditions, as a result of which a hollow fiber membrane can be obtained with many slit-shaped micropores formed in it, limited by microfibrils and nodes formed by multilayer plates (see, for example, patent document 1 below). However, a hollow fiber membrane made in accordance with the method described above entails the problem that since the fibers are oriented in the direction of the fibers as a result of the drawing, the circumferential strength is usually significantly reduced. In particular, since the strength tends to decrease with increasing pore size, it will be difficult to make a hollow fiber membrane with practical strength using the above method. In addition, although the flow rate of pure water is high, the pore size has a significant dispersion, and the pores formed in this case have a slit-like shape, the problem is that elongated substances are usually easily passed, which leads to a decrease in the accuracy of separation or filtration.

As a method of manufacturing a separation membrane with good permeability and fractionating ability, an example of the use of phase separation is widely known. A method of manufacturing a membrane using such phase separation can be broadly subdivided into non-solvent-induced phase separation and thermally induced phase separation.

In the case of non-solvent phase separation induced, a homogeneous polymer solution containing the polymer and the solvent mixed together results in phase separation due to a change in concentration caused by the entry of the non-solvent and evaporation of the solvent into the surrounding atmosphere. As a method for manufacturing a separation membrane using such a non-solvent phase separation, a method is known according to which, after dissolving the polysulfone resin in a solvent such as, for example, N, N-dimethylacetamide or the like, a non-solvent phase separation is initiated in a coagulation bath to form by this separation membrane (see, for example, patent document 2 below). However, the method of non-solvent phase separation usually encounters problems associated with the physical properties of the membrane, the ability to control the process and cost, since it is difficult to control the phase separation inside the non-solvent, the manufacturing cost is high due to the need to use a non-solvent, and there is a tendency to the formation of macro voids.

At the same time, thermally induced phase separation, as a rule, includes the following stages:

(1) a mixture of a polymer and a solvent having a high boiling point is melted at a high temperature;

(2) cooling is carried out at an appropriate rate to induce phase separation and thereby harden the polymer, and

(3) the used solvent is recovered.

The advantages of the thermal method of phase separation compared to phase separation induced by a non-solvent include the following:

(a) the formation of macro voids can be avoided, leading to a decrease in membrane strength; (b) in the case of non-solvent phase separation, the use of a non-solvent other than a solvent is required, and therefore it is difficult to provide control during the manufacturing process, which leads to a decrease in reproducibility. On the other hand, the thermal phase separation does not require the use of a non-solvent, process control and cost characteristics are excellent, and all this is accompanied by high reproducibility; (c) the regulation of pore sizes can be carried out quite easily, and the pore size distribution is very accurate, which leads to excellent pore formation parameters.

Thermo-induced phase separation includes solid-liquid thermal phase separation and liquid-liquid thermal phase separation, and which one will develop depends on the mutual miscibility of the polymer and the solvent. In cases where the mutual miscibility of the polymer and the solvent is very high, the thermal separation of the phases of the solid-liquid type will develop, however, if the mutual miscibility is reduced, the thermal separation of the phases of the liquid-liquid type will develop, and both of them will eventually become immiscible together. As a rule, since during thermally induced liquid-liquid phase separation, phase separation occurs as a result of spinodal decomposition, a feature of thermal liquid-liquid phase separation is that a continuous structure develops more easily compared to thermal solid-liquid phase separation , and as a result, a separation membrane can be obtained having excellent pore formation parameters, such as pore continuity and uniformity. In other words, for the manufacture of a separation membrane having good permeability and fractionating ability, it is desirable to choose the appropriate combination of polymer and solvent, which will lead to the development of thermal phase separation of the liquid-liquid type. Moreover, since the region in which the polymer and the solvent lead to the development of thermal phase separation of the liquid-liquid type is limited, in the case when it is necessary to produce a separation membrane according to a method such as the one mentioned above, the choice of the appropriate combination will play an important role polymer and solvent (see, for example, non-patent document 1 below).

A method of manufacturing a porous membrane of vinylidene fluoride resin, which uses thermally induced liquid-liquid phase separation, is well known in the art (see, for example, Patent Document 3 below). However, a porous membrane made in accordance with this method corresponds to or exceeds 30,000 l / m ² / h / 98 kPa, and the size of the fractionated particles is not less than 1 μm, a series of experiments conducted by the authors of the present invention showed that such a porous membrane a number of pores that are not connected to each other, that is, closed pores, and, in addition, pores of essentially the same size appearing on opposite surfaces of the membrane, and therefore such a porous membrane cannot have a high flow rate of pure water relative to size fractionated particles.

In addition, since the vinylidene fluoride resin is hydrophobic, water will not penetrate through the membrane made of polyvinylidene fluoride, unless otherwise specified, and therefore, hydrophilic treatment is necessary for the hydrophilic liquid, including water, to penetrate through the membrane.

The following literature is available in the form of patent documents, which are intended to be relevant to the present invention.

Patent Document 1: Patent Laid-Open Publication JP No. H05-49878 published March 2, 1993.

Patent Document 2: Patent Laid-Open Publication JP No. H11-104235, published April 20, 1999

Patent Document 3: Patent Laid-Open Publication JP No. 2005-194461 published July 21, 2005

Patent Document 4: Patent Laid-Open Publication JP No. 2003-138422 published May 14, 2003

Patent Document 5: Patent Laid-Open Publication JP No. 2005-200623, published July 28, 2005

Non-Patent Document 1: Chemical Engineenng, Kagaku Kogyosha, June 1998, p. 453-464.

SUMMARY OF THE INVENTION

Thus, the present invention has been developed taking into account the above problems and disadvantages characteristic of the prior art, and is intended to provide a porous membrane with good permeability, fractionation ability, physical strength and chemical resistance using an economical and easy method. for use in the field of water treatment, such as, for example, water treatment, production of drinking water, production of water for industrial consumption and sewage treatment water, as well as having good characteristics in terms of production controllability, cost and pore formation parameters.

In order to eliminate the above problems and disadvantages, the present invention provides a porous membrane made of vinylidene fluoride resin and having a particle limit of at least 0.2 μm, the membrane having first and second surfaces that are opposite to each other, while the first surface has micropores round or oval in such a size that the average ratio between the major axis and the minor axis lies in the range from 1: 1 to 5: 1; while the second surface has essentially slit-like micropores in which the average ratio between the major axis and the minor axis is at least 5: 1. Preferably, the porous membrane is made of a blended polymer containing vinylidene fluoride resin in an amount of from 90 to 99 wt.% And a hydrophilic resin in an amount of from 1 to 10 wt.%. In addition, it is preferable that the hydrophilic resin in question was a vinyl pyrrolidone resin, and the porous membrane is preferably made in the form of a hollow fiber membrane.

The authors of the present invention focused and carefully studied the mutual miscibility of the various components forming the initial solution used for the manufacture of the porous membrane, and as a result found that even if the combination of vinylidene fluoride resin and solvent allows the development of thermal phase separation in the form of a solid substance-liquid membrane will have characteristics comparable to or better than the characteristics of the porous membrane obtained if the combination is related to PU, allowing the thermal separation of the phases of the liquid-liquid type, provided that the solvent, inorganic particles and the agent that causes the aggregation are mixed properly.

The present invention is directed to the manufacture of a porous membrane from a vinylidene fluoride resin having the characteristics described above, in which an initial solution containing a vinylidene fluoride resin, a solvent, inorganic particles and an aggregation inducing agent, wherein the inorganic particles and the aggregation inducing agent, are used for the manufacture of the porous membrane affinity for each other, and the solvent and the agent causing the aggregation are mutually insoluble or have a higher critical temperature eniya and which includes a curing step after cooling induced phase separation, a step of stretching the porous membrane before completely removing the solvent, the inorganic particles and an agent causing aggregation.

According to the present invention, it is possible on an industrial scale using a continuous and inexpensive method to produce a porous membrane having good fractionating ability, permeability and physical strength. The use of the porous membrane according to the present invention allows filtering at a high feed rate of pure water and with high fractionation characteristics, thereby reducing the cost of producing fresh water.

BRIEF DESCRIPTION OF GRAPHIC MATERIALS

In any case, the present invention will be better understood on the basis of the following description of the preferred options for its implementation, given in combination with the accompanying graphic materials. However, embodiments and graphical materials are given solely for purposes of illustration and explanation and should not be construed as limiting the scope of the present invention in any way, the scope of the invention being defined by the appended claims. In the accompanying graphic materials, the same reference numbers are used to denote the same elements in each individual drawing, and:

Figure 1 is a photograph taken using a scanning electron microscope depicting the outer surface of a porous membrane of vinylidene fluoride resin made in accordance with the method of Example 3;

Figure 2 is a photograph taken using a scanning electron microscope depicting the inner surface of a porous membrane of vinylidene fluoride resin made in accordance with the method of Example 3;

Figure 3 is a photograph taken using a scanning electron microscope depicting the inner surface of a porous membrane of vinylidene fluoride resin made in accordance with the method of Example 3;

Figure 4 is a photograph obtained using a scanning electron microscope, depicting a cross section of a porous membrane of vinylidene fluoride resin made in accordance with the method of Example 3:

Figure 5 is a photograph taken using a scanning electron microscope, depicting the inner surface of a porous membrane of vinylidene fluoride resin made in accordance with the method of Comparative example 2; and

6 is an infrared spectrum of a hollow fiber membrane made in accordance with the method of Example 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The porous membrane of the vinylidene fluoride resin according to the present invention includes first and second surfaces that are opposite to each other, the first surface having micropores of a round or oval shape with an average ratio between the major axis and minor axis in the range from 1: 1 to 5: 1; and the second surface has micropores essentially slit-shaped with an average ratio between the major axis and minor axis of at least 5: 1. The porous membrane has a particle transmission limit of at least 0.2 μm.

The porous membrane of the present invention has a high fractionation ability, since the first surface, having micropores of a round or oval shape with an average ratio between the major axis and minor axis in the range from 1: 1 to 5: 1, acts as the active region responsible for the passage of particles through the membrane. In addition, the porous membrane of the present invention has a high flow rate of pure water, since a second surface having slit-like micropores formed by a microfibril-containing structure in which the average ratio between the major axis and minor axis is at least 5: 1 has a high speed transmission in the area of the hole. The porous membrane of the present invention having such features has high permeability relative to the size of the fractionated particles. Accordingly, it is possible to manufacture a membrane having high permeability and having a particle transmittance of at least 1 μm. In addition, since an increase in pore size causes a gaseous medium, such as, for example, air, to penetrate under a pressure of equal to or lower than 100 kLa even in wet conditions, it is possible to carry out a flushing by physical means, such as, for example gas flushing backflow.

Round or oval micropores with an average ratio between the major axis and minor axis ranging from 1: 1 to 5: 1, as mentioned above, mean micropores for which the average values measured using microphotographs of at least two local zones of the first surface with using an electron microscope (with an increase, for example, × 1000), as shown in the micrograph of the first surface in FIG. 1, lie in the range from 1: 1 to 5: 1, and the ratios between the major axes and the minor axes of all micropores visible in field of view micrographs, and repeat the above procedures until the number of measured micropores exceeds 30.

In addition, slit-like micropores with an average ratio between the major axis and minor axis of at least 5: 1, as mentioned above, mean micropores in which the average values measured from microphotographs of at least two local areas of the second surface using an electron microscope (with increasing , for example, × 500), as shown in micrographs of the second surface in FIG. 1 to 5 are at least 5: 1, and the ratio between the major axes and the minor axes of micropores formed by microfibrils oriented in the direction of the fibers and visible in the field of view of microphotographs is measured, and the above procedures are repeated until the number of micropores measured will not exceed 30.

The cross-sectional structure of the membrane is preferably a three-dimensional mesh structure with a pore size larger than the pore size of the first surface having round or oval pores, but may have a symmetrical structure, or an asymmetric structure, or a finger-like structure, or voids. In addition, the void ratio, which is the volume ratio of the space inside the porous membrane, lies in the range from 50 to 95%, and preferably in the range from 70 to 90%. If the void ratio is equal to or less than 50%, it is difficult to ensure a sufficient rate of clean water, however, if it exceeds 90%, the membrane strength will decrease and damage and cracking will occur during filtration through the membrane and, as a result, the membrane will not be sufficiently durable.

The location of a surface having round or oval micropores with an average ratio between the major axis and the minor axis ranging from 1: 1 to 5: 1, and a surface having slit-like micropores with an average ratio between the major axis and the minor axis of at least 5: 1, is as, for example, one above the other, either inside or outside the other, may vary depending on the filtration system. However, since a surface having round or oval micropores is responsible for the separation function, and the cross-sectional structure determines physical strength, a surface having round or oval micropores is preferably located on the side facing the object to be divided. In particular, in order to weaken the reduction in permeability resulting from the deposition of contaminants, a surface having round or oval micropores responsible for the separation function is preferably located on the outer layer.

The porous membrane of the present invention can be made in the form of a hollow fiber membrane or a flat membrane. However, it is preferable to use a hollow fiber membrane, since the hollow fiber membrane can be effectively filled, whereby an increased effective membrane surface area per unit volume can be obtained.

The vinylidene fluoride resin used in the practice of the present invention is a resin containing a vinylidene fluoride homopolymer and / or vinylidene fluoride copolymer. Vinylidene fluoride resin may contain many types of vinylidene fluoride copolymers. Examples of vinylidene fluoride copolymers include copolymers of vinylidene and at least one chemical selected from the group consisting of vinyl fluoride, tetrafluoroethylene, hexafluoropropylene and chlorotrifluoroethylene. In addition, the weight average molecular weight of the vinylidene fluoride resin can be appropriately selected taking into account the strength and permeability of the desired membrane, however, if the weight average molecular weight increases, the membrane forming characteristics will decrease, and if the weight average molecular weight decreases, the strength will decrease. For this reason, the weight average molecular weight is preferably in the range of 50,000 to 1,000,000. With regard to the water treatment area where the porous membrane is chemically cleaned, the weight average molecular weight is preferably in the range of 100,000 to 700,000, and more preferably lies in the range of 150,000 to 600,000.

The hydrophilizing treatment that can be used in the practice of the present invention can be of any type well known to those skilled in the art (see, for example, Patent Document 4 above).

The hydrophilic resin used in the practice of the present invention is a resin having a strong affinity for water, and includes a polyvinylpyrrolidone resin, a polyvinyl alcohol, a saponified derivative of an ethylene polyvinyl acetate copolymer, polyethylene glycol, a polyether glycol mono ester, a polyethylene polyethylene glycol copolymer, polyethylene glycol acid, polystyrenesulfonate, cellulose derivatives and polysorbate. Of these, the use of polyvinylpyrrolidone resin is preferred.

The polyvinylpyrrolidone resin that can be used in the practice of the present invention is a homopolymer of polyvinylpyrrolidone or a copolymer of polyvinylpyrrolidone, as well as any other copolymerizable vinyl monomer. Of these, a homopolymer of polyvinylpyrrolidone is preferred.

The weight average molecular weight of these resins is not limited to any particular value. It can be appropriately selected taking into account the strength and permeability of the desired membrane, however, from the point of view of machinability with the formation of a porous membrane, it is preferable that it lies in the range from 5,000 to 2,000,000. In addition, a series of vinylpyrrolidone resins, such as, for example, polyvinylpyrrolidone may slowly dissolve when used in an aqueous system. In the event that the ingress of a water-soluble resin so dissolved onto the process fluid side can cause a problem, it is preferred that the water-soluble resin be converted to an insoluble form. Treatment to reduce the solubility of polyvinylpyrrolidone includes crosslinking polyvinylpyrrolidone using gamma radiation, crosslinking using ultraviolet radiation, or chemical crosslinking, which is heat treated in the presence of strong alkali or persulfate. Among them, chemical crosslinking with persulfate is preferred to reduce solubility.

In the practice of the present invention, a solvent that is capable of inducing thermal phase separation can be used. Although the type of thermal phase separation includes solid-liquid phase separation and liquid-liquid phase separation, any of them can be used in the practice of the present invention. As a solvent allowing solid-liquid phase separation with polyvinylidene fluoride, acetophenone, isophorone, cyclohexanone, dimethyl phthalate, diethyl phthalate, γ-butyrolactone and ε-caprolactone can be mentioned. As a solvent allowing solid-liquid phase separation with a polyvinylidene fluoride-propylene hexafluoride copolymer, acetophenone, dibutyl sebacinate and tricresyl phosphate can be mentioned. In addition, hexyl benzoate can be mentioned as a solvent allowing liquid-liquid phase separation with polyvinylidene fluoride, and propyl salicylate and pyridine can be mentioned as a solvent allowing liquid-liquid phase separation with a polyvinylidene fluoride-propylene hexafluoride copolymer. Among them, in the practice of the present invention, it is preferable to use a water-soluble solvent, such as, for example, γ-butyrolactone or ε-caprolactone. When using a water-soluble solvent, water can be used to extract the solvent from the porous membrane after the membrane is made, and the extracted solvent can be recovered by biological treatment. On the other hand, if a water-insoluble solvent is used, it is necessary to use an organic solvent, such as, for example, acetone, to extract it from the porous membrane after the manufacture of the membrane, and therefore, explosion-proof equipment may be required, depending on the properties of the solvent used. Based on the above reasons, on an industrial scale, the use of a water-soluble solvent is preferable in terms of safety, equipment and costs.

Inorganic particles that can be used in the practice of the present invention are used as micropores in a porous membrane, and they are preferably particles readily recoverable by chemical reagents and have a relatively narrow particle size distribution. Examples of inorganic particles include particles of silicon oxide, calcium silicate, aluminum silicate, magnesium silicate, calcium carbonate, magnesium carbonate, calcium phosphate, hydroxide or metal oxide, for example iron and zinc, and salts, for example sodium, potassium and calcium. In particular, inorganic particles coarsened when added to a composition in which the vinylidene fluoride resin and the solvent are usually phase separated with each other become more stable under conditions where the vinylidene fluoride resin and the solvent are mutually mixed with each other, which makes it possible to produce a membrane with a uniform porous structure and therefore they are conveniently used in the manufacture of a porous membrane having an even larger pore size. Due to this aggregative ability, it is convenient to use silicon oxide as inorganic particles. The particle size for inorganic particles (expressed as the size of the coagulating particles in the case of inorganic particles having aggregative properties) can be suitably selected taking into account the pore size of the desired porous membrane. In the case of an ultrafiltration membrane, inorganic particles having a particle size of not more than 0.01 μm are selected; in the case of microfiltration, in which the particle transmission limit is not more than 1 μm, inorganic particles having a particle size in the range from 0.01 to 1 μm are selected; and in the case of a macroporous membrane for which the particle transmission limit is more than 1 μm, an inorganic particle having a coagulating particle size of more than 1 μm is selected. In addition, inorganic particles having different sizes of coagulating particles can be mixed to control the particle size in the porous membrane, in particular to control the increase in the message of their pores. With regard to high permeability, which is one of the features exhibited by the porous membrane of the present invention, the greater the transmission limit of the particles of the porous membrane of the present invention, the higher the magnitude of the effect compared to that for the traditional model. In this regard, the transmission limit of the particles of the porous membrane of the present invention is not less than 0.2 μm, preferably lies in the range from 1 to 1.5 μm, and more preferably equal to 2.0 μm.

The aggregation inducing agent used in the practice of the present invention is a composition having such characteristics that (1) it has an affinity for inorganic particles, preferably sufficient to increase the aggregation of inorganic particles, and (2) it does not mix with a solvent or has a higher critical temperature of dissolution. In addition, the aggregation inducing agent is preferably a composition having characteristics (3) to (5), discussed below. (3) It does not mix with vinylidene fluoride resin, (4) it has a boiling point higher than the temperature at which vinylidene fluoride resin and solvent dissolve together, and (5) it has a hydrophilic group. Examples of an aggregating agent having characteristics (1) and (3) to (5) discussed above include polyhydric alcohols, such as, for example, ethylene glycol, propylene glycol, triethylene glycol, polyethylene glycol and glycerin, polyglycerol and fatty acid esters such as, for example, decaglyceryl monolaurate; polyoxymethylene glycerol fatty acid esters, such as, for example, polyoxyethylene glycerol monostearate, polyoxyethylene alkyl ethers, such as, for example, polyoxyethylene lauryl ether and polyoxyethylene acetyl ether; polyoxyethylene polyoxypropylene alkyl ethers, such as, for example, polyoxyethylene polyoxypropylene acetyl ether, polyoxyethylene alkylphenyl ethers, such as, for example, polyoxyethylene nonylphenyl ether; and polyoxyethylene sorbitan fatty acid esters, such as, for example, polyoxyethylene sorbitan monopalmiate. Of these, an aggregation inducing agent having the characteristics (2) described above is preferably selected.

The highest critical dissolution temperature, which was mentioned in characteristic (2), discussed above, means the maximum temperature at which phase separation occurs in the case of a combination in which the mutual miscibility of the solvent and the aggregation-causing agent varies with temperature. The term “mutually miscible (or mutual miscibility)”, used above and hereinafter, means that the solvent and the aggregation promoting agent can be mixed. The highest critical dissolution temperature, referred to in this context, is measured as follows, namely: a dispersion liquid containing a solvent and an aggregating agent, both of which are control-weighed to obtain a given mass concentration, are placed in a tube and then heated at high temperature in an adjustable bath filled with silicone oil until a solution is obtained. The heating temperature was set to a predetermined value, which was 10 ° C lower than the lowest of the corresponding boiling points of the solvent and the agent causing the aggregation. The solution was kept for five minutes at a heating temperature, after which the contents of the test tube were visually evaluated and, if phase separation was observed, the combination of such a solvent and such an aggregation-causing agent was considered immiscible with each other. In the case of a medium with a single homogeneous phase, the tube with the sample was cooled after being removed from the high-temperature controlled bath, and the temperature at which the homogeneous single-phase solution began to become opaque was determined as the highest critical dissolution temperature.

The solvent and aggregating agent used in the practice of the present invention are preferably not soluble at each other at a temperature at which thermally induced phase separation occurs, and in the context of the process, a combination thereof is selected that has a higher critical dissolution temperature above 30 ° C, and preferably, they do not dissolve each other at temperatures above 0 ° C and, more preferably, at no temperature in the specified range. In the general technology of membrane formation, due to the complexity of manufacturing a membrane with a uniform porous structure, there is a tendency to not choose the initial solution, which tends to exhibit a characteristic that matches the characteristic (2) discussed above. However, in the practice of the present invention, a solution exhibiting characteristic (2) discussed above can be selected using inorganic particles having the characteristic discussed above.

Using a combination of a solvent and an aggregation inducing agent having characteristic (2), as discussed previously, it is possible to easily and economically manufacture a porous membrane having high separation ability and high permeability. As a method of manufacturing porous membranes with high separation ability and high permeability, a method is shown according to which a combination of a solvent and vinylidene fluoride resin allows the development of thermal phase separation in the liquid-liquid type (see, for example, patent document 3 above), however the liquid-liquid phase separation region is usually so narrow that regulation is difficult to accomplish. In addition, it is extremely important to choose the appropriate combination that allows the development of phase separation of the liquid-liquid type, and this is not easy. On the other hand, the solvent used in the practice of the present invention, if it is capable of exhibiting the characteristic (2) discussed above, in combination with an aggregating agent, can be any type of solvent allowing the development of liquid-liquid phase separation or phase separation solid-liquid type in interaction with vinylidene fluoride resin. In a membrane made by the method according to the present invention, even if the solvent allows the development of solid-liquid phase separation, the porous membrane will have a separation capacity and permeability comparable to or greater than those of a porous membrane made by a standard method of manufacturing a membrane using phase separation according to type liquid-liquid. In accordance with this, the range of choice of options for the components that make up the initial solution for the manufacture of a porous membrane is expanded, contributing to the manufacture of a porous membrane that is superior in separation properties and permeability. In particular, the combination of a solvent and an aggregation promoting agent used in the practice of the present invention includes a combination of benzyl benzoate (non-aqueous solvent) and ethylene glycol (water soluble solvent), a combination of γ-butyrolactone (water soluble solvent) and glycerol (water soluble solvent), and a combination of ε -caprolactone (a water-soluble solvent) and glycerin (a water-soluble solvent). Of these, in the practice of the present invention, it is preferable to use a combination of a water-soluble solvent and a water-soluble aggregation inducing agent.

The composition of the initial solution for the manufacture of a porous membrane, comprising a vinylidene fluoride resin, a solvent, inorganic particles and an aggregation promoting agent, all of which are described above, can be selected appropriately if desired, provided that the porous membrane obtained in this way can be acceptable for in practice, strength and, in addition, will have the required pore size and that the continuity of the pores open from one surface of the porous membrane to its opposite surface will have such an extended be that satisfy required specifications. Although the composition of the initial solution for the manufacture of a porous membrane may vary depending on the chemical structure of each of the components mentioned above, it is preferable that the ratio vinylidene fluoride resin: solvent: inorganic particles: aggregation-causing agent equal to from 20 to 40: from 25 to 60 : from 10 to 30: from 20 to 50, provided that the sum of the ratios of the vinylidene fluoride resin, solvent, inorganic particles and aggregation agent is assumed to be 130 (the same assumption about refers to the following description). If the composition of the initial solution for the manufacture of the porous membrane deviates from this value, the stability during stretching of the initial solution for the manufacture of the porous membrane decreases, making it difficult to draw homogeneous hollow fibers, and if the amount of vinylidene fluoride resin used is greater than the amount indicated above, there is a tendency to the fact that the permeability and fractionation of hollow fibers obtained in the end will be poorly proportionate to each other, even if homogeneous e fibers may be twisted.

In the initial solution for the manufacture of a porous membrane having a composition comprising a vinylidene fluoride resin, a solvent, inorganic particles and an aggregation promoting agent, such as those described above, various additives may be added, if necessary, including an antioxidant, a UV absorbent, a sizing agent, a release agent and pigments or dyes, provided that they do not lead to the destruction of the object of the present invention.

A stock solution for the manufacture of a porous membrane having a composition comprising a vinylidene fluoride resin, a solvent, inorganic particles and an aggregation promoting agent, such as those described above, is mixed in a biaxial mixing device, a polymer mill, or a mixer. The mixing temperature is chosen so that it corresponds to a value at which the vinylidene fluoride resin and the solvent can dissolve, and any of the various components of the mixture described above will not decompose. After the initial solution for the manufacture of the porous membrane is kneaded, bubbles are sufficiently removed and weighed using a metering pump, such as, for example, a gear pump. After weighing, the initial solution for the manufacture of a porous membrane is extruded through a slotted extrusion head or a tip with a double annular head to obtain the desired shape. If it is necessary to form hollow fibers, a gaseous medium, such as, for example, air or nitrogen, or a liquid having a boiling point higher than the temperature at which the initial solution for the manufacture of the membrane is extruded, is simultaneously extruded from the central part of the double-ring head. The liquid that can be extruded from the center of the double-ring tip is preferably used in the form of a non-solvent (precipitant) or a weak solvent that does not dissolve or poorly dissolves vinylidene fluoride resin. An example is a polyhydric alcohol, such as, for example, tetraethylene glycol, propylene glycol or glycerol. With this choice, thermally induced phase separation occurs on the inner surface of the obtained hollow fibers and, therefore, the structure of the outer surface can be roughened, thereby effectively ensuring a large pore size. Pores thus coarsened are very important for the formation of slit-like micropores on the surface, whose average ratio between the major axis and the minor axis is at least 5: 1.

The extrusion of cast material extruded through a slit die or tip is accompanied by phase separation of the vinylidene fluoride resin and solvent as a result of temperature changes caused, for example, by cooling, followed by curing of the vinylidene fluoride resin. When a mixture of vinylidene fluoride resin with a solvent miscible with such a vinylidene fluoride resin hardens when treated with a weak solvent of vinylidene fluoride resin, the portion corresponding to the interface between the above mixture and the non-solvent will form a dense layer, and the resulting porous membrane will have an uneven structure, not allowing to obtain high-precision separation. The cooling method includes cooling in air, immersion in liquid and immersion in liquid after a single passage through the air, any of these methods may be used, however, it is preferable that the ambient temperature be controlled using hot air and / or controlled the temperature of the liquid used for cooling so that the cooling rate can be controlled, since the cooling rate affects the strength and elongation of the porous membrane, and akzhe to regulate the pore size. As the liquid used for cooling, water and an organic liquid may be mentioned. The fluid may be a coolant containing many components in which at least one or more of the components are dissolved. From an environmental and production point of view, it is preferable to use water. It should be noted that in cases where a water-soluble solvent and water are used in the cooling bath, a mixed liquid can be used with success in which at least one or several salts are dissolved / dissolved or which contains many salts. When using a concentrated solution of sodium chloride at the coagulation stage, the exchange rate between water (insolvent) and a water-soluble solvent can be reduced, which allows one to obtain a porous membrane in which the formation of a dense layer on the surface of the membrane, resulting from a sharp fixation of the structure, is suppressed. The higher the salt concentration, the lower the exchange rate between water and a water-soluble solvent, which leads to the formation of a porous membrane, in which the formation of a dense layer on the membrane surface, resulting from a sharp fixing of the structure, is suppressed. The term "salt" in this context refers to a monovalent or multivalent compound, such as, for example, a halide, hydrosulfate, nitrate, chlorate, lactate or acetate, and can also be used in relation to an aqueous salt or a salt hydrate. Examples include salts such as sodium sulfate and potassium sulfate.

The following describes the inclusion of the step of drawing a porous membrane from a cast material formed in such a manner as described above before the complete extraction of the solvent, inorganic particles and the aggregation inducing agent. It is expected that in the case where the porous membrane is stretched before extraction is complete, the resulting porous membrane may have high permeability. The stretching is preferably carried out at a temperature in the range from 0 to 160 ° C. It is undesirable for the temperature to exceed 160 ° C, since the stretched sections become significant, and, in addition, the elongation at break and water permeability decrease, and in cases where the temperature is below 0 ° C, it is difficult to stretch constantly and evenly, and the most structurally fragile parts break down. A predetermined porous membrane can be obtained by performing extrusion with an extrusion coefficient of 1.1 to 4, preferably 1.1 to 3.5, and more preferably 1.1 to 3, at a temperature preferably in the range of 30 to 120 ° 0 and more preferably in the range of 30 to 100 ° C. The term “stretch coefficient” used above means a value determined from the length of the porous membrane when the latter is maximally stretched during the stretching step. In addition, although it is desirable to draw in the liquid, since it is easy to control the temperature, it can also be performed in a gaseous medium, such as, for example, steam. In the case of a liquid, it is preferable to use water, since this may be convenient, a low molecular weight polyethylene glycol or the like can also be used with success if the drawing is carried out at a temperature above 95 ° C. In addition, extrusion in a mixed liquid containing several liquid media, such as a mixed liquid containing water and polyethylene glycol, can be used. According to the present invention, it is preferable to stretch a porous membrane containing a solvent and an aggregation promoting agent. A porous membrane containing a solvent and an aggregating agent is less susceptible to degradation during stretching compared to a porous membrane containing neither a solvent nor an aggregating agent. In addition, it is preferable to stretch the porous membrane containing inorganic particles. In a porous membrane containing inorganic particles, the integrity of the membrane zone can be increased, since closed pores are present in the inorganic particles in the slits of the membrane zone, and they then turn into continuous pores. In addition, the ruined pores present on one side of the porous membrane can be replaced by slit-like micropores, as a result of which the permeability of the porous membrane can be significantly increased. In the practice of the present invention, it is preferable to stretch a porous membrane containing a solvent, inorganic particles and an aggregation promoting agent. In addition, the extraction of a porous membrane that is elongated is preferable, since, as a result of stretching, the fraction of voids in the surface and inside the porous membrane increases, the extraction solvent easily penetrates into the porous membrane.

Thus, from a cast material obtained as described above, a porous membrane is obtained by extracting a solvent, inorganic particles and an aggregation inducing agent. The extraction of these components can be carried out continuously during the technological operation together with extrusion and curing, or it can be performed after once wrapping the cast material around the core or skein, or after the cast material is placed inside the housing of a given configuration and then a modular structure is formed. The solvent used to extract each of the components used must be a non-solvent with respect to the vinylidene fluoride resin at the extraction temperature. Although the extraction solvent may vary depending on the chemical structure or other characteristics of the components to be extracted, if the solvent is, for example, a non-aqueous solvent, acetone or methanol may be used, and if the solvent is water, a water-soluble solvent may be used. . In addition, if the inorganic particles are silicon oxide, it is advisable to carry out the extraction using an alkaline solution. Moreover, for cases where the aggregation causing agent is slightly soluble in water, hexane, acetone or methanol may be proposed, and in the case of a water-soluble aggregation causing agent, water may be called. The porous membrane, after performing the specified manipulations with it, is dried wrapped around the frame or wound in a skein.

In addition, the porous membrane of the present invention can be suitably heat treated. Heat treatment is designed to increase the fraction of the α-type crystal structure in a porous membrane made of vinylidene fluoride resin. As a result of the study of the chemical resistance of a porous membrane made of vinylidene fluoride resin by the inventors of the present invention, it was found that not only the crystallinity index, but also the crystalline structure contributes to chemical resistance. Further intensive studies showed that chemical stability increases when the fraction of the α type of crystal structure is higher than the fraction of the crystal structure of β type. The increase in chemical resistance in cases where the fraction of the crystal structure of type α exceeds the fraction of the crystal structure of type β, apparently, stems from the following reasons. Compared to the β type of crystalline structure, the α type of crystalline structure contains hydrogen atoms and fluorine atoms, which are delocalized, and, accordingly, this is apparently why there is insufficient depolarization of electric charges. In other words, since the fraction of the crystal structure of the α type, which is non-polar, is higher than the fraction of the crystal structure of the β type, in which the hydrogen atoms and fluorine atoms are delocalized and intermolecular polarization takes place, it turns out that the porous membrane made of polyvinylidene fluoride in accordance with the present invention has high chemical resistance. In view of this, the porous membrane of the present invention is preferably heat treated in a free state, that is, in a state in which the porous membrane is not fixed. For example, it is possible to conduct heat treatment on a porous membrane at the same time as extracting the solvent and the aggregating agent, when the porous membrane after the drawing process is temporarily wound on a skeleton or wound in a skein and is then kept in a free state. If the heat treatment is carried out while the porous membrane is held in a fixed state, thermal shrinkage occurs, accompanied by deformations that entail changes in the crystal structure in the microenvironment. In particular, the crystal structure of the α type is transformed into the crystal structure of the β type, the proportion of the crystal structure of the β type in the porous membrane increases and, as a result, it may turn out that the desired effect will not be achieved.

The determination of the type ratio of the crystal structure in a porous membrane made of polyvinylidene fluoride in accordance with the present invention is carried out as follows. It is expressed by the value of R ₁ calculated in accordance with equation (1) using the absorbance value (A ₇₆₃ ) at a wavelength of 763 cm ^-1 , and the absorbance value (A ₈₄₀ ) at a wavelength of 840 cm ^-1 , both obtained at Based on IR measurements.

where A ₇₆₃ represents the absorption capacity assigned to the α type of crystal structure, and A ₈₄₀ represents the absorption capacity referred to to the β type of crystal structure (see, for example, patent document 5 above). The value of R ₁ is an indicator of the quantitative ratio of α type and β type inside the crystalline region of polyvinylidene fluoride. In the IR spectrum of the porous membrane shown in FIG. 6, a line is drawn between the corresponding minimum values in the IR spectrum in the region of 763 cm ^-1 and 780 cm ^-1 , and then the height of the characteristic absorption peak related to the α type of crystal structure in an area of 763 cm ^-1 . Along with this, a line was drawn between the corresponding minimum values in the IR spectrum in the region of 810 cm ^-1 and 925 cm ^-1 , and then the characteristic absorption peak related to the β type of crystal structure in the region of 840 cm ^{-1 is} read, resulting in the value of R ₁ . The value of R ₁ according to the present invention is preferably equal to or greater than 1.5.

The type α of the crystal structure of the polyvinylidene fluoride resin is characterized by the fact that hydrogen atoms (or fluorine atoms) connected to a carbon atom adjacent to one side of the carbon of the main chain contained in the polymer molecule are in a trans position relative to fluorine atoms (or hydrogen atoms) connected to the carbon of the main chain, while the hydrogen atoms (or fluorine atoms) connected to the carbon atom adjacent to the carbon of the main chain are in the Ghosh position (60 °) relative to the fluorine atoms (or atoms Hydrogen s) connected to the carbon main chain, wherein two or more of these steric structures are continuations of each other; the molecular chain is of the TG ⁺ TG type, and the dipole moment of the CF ₂ bond and the С-Н ₂ bond has the corresponding components in the vertical and parallel directions relative to the molecular chain. When conducting an IR analysis of a polyvinylidene fluoride resin having an α type crystal structure, characteristic peaks (characteristic absorption) are in the region of 1212 cm ⁻¹ , 1183 cm ⁻¹ and 763 cm ^−1, respectively, and in powder X-ray diffraction characteristic peaks appear at 2θ = 17.7 °, 18.3 ° and 19.9 ° respectively.

The type β of the crystalline structure of the polyvinylidene fluoride resin is characterized in that the hydrogen atoms and fluorine atoms connected to the carbon atoms adjacent to one of the carbon atoms of the main chain contained in the polymer molecule have the corresponding steric trans orientation (TT type structure), namely atoms hydrogen and fluorine atoms connected to adjacent carbon atoms are in the 180 ° position when viewed in the direction of the carbon-carbon bond. The carbon-carbon bond, in which the fragment forming the structure of the TT type, forms the main chain of the TT type, has a flat zigzag structure, and the dipole moment of the C-F ₂ bond and C-H ₂ bond has a component in the vertical direction relative to the molecular chain. When conducting IR analyzes of a β-type crystal structure, characteristic peaks (characteristic absorption) appear in the region of 1274 cm ^-1 , 1163 cm ^-1 , and 840 cm ^-1, respectively, and in powder X-ray diffraction, characteristic peaks appear at 2θ = 21 °, respectively.

As a method of heat treatment, it can be carried out after the formation of the membrane and before the extracted components are removed by washing, or after they are removed. In addition, it can be carried out in such a state of the membrane, when the filament threads form nodes and undergo drying stages, or heat treatment can be carried out after the membrane is composed of modules. It should be noted that if heat treatment is carried out after modularization, in order to avoid membrane stretching, allowance for possible shrinkage, which may occur as a result of heat treatment, should be taken into account.

As heat treatment methods, one can list the method of drying with hot air, the wet method by immersion in a liquid, the method in which the porous membrane is in contact with metal rollers that heat and modulate, the method that is carried out in a gaseous medium, such as, for example, steam, and the method in which electromagnetic waves are emitted, all of these methods can be carried out even when the porous membrane is in a wet or dry state. Among them, the method of immersion in water is convenient in terms of ease of temperature control. Preferably, a non-solvent of the polyvinylidene fluoride resin, such as, for example, low molecular weight polyethylene glycol, can be used. In addition, it is possible to conduct heat treatment in a mixed liquid containing many components, such as, for example, a mixed liquid containing water and polyethylene glycol or a solution of a surface-active agent.

Depending on the choice of liquid for immersion in a wet system, the extraction and removal of the extracted components in a membrane-forming initial solution and heat treatment can be carried out simultaneously.

Considering that it is possible to obtain heat treatment results without compromising the required characteristics of the porous membrane other than chemical strength, the heat treatment is preferably carried out at a temperature in the range of 70 ° C. to 160 ° C.

The heat treatment time is not limited to a specific value, however, an interval of 1 to 5 hours is preferable in terms of productivity. Choosing a higher heat treatment temperature reduces the heat treatment time.

After heat treatment, it is preferable to leave the membrane at room temperature for slow cooling.

A porous membrane made of vinylidene fluoride resin, as described above, is used as a membrane module located inside a casing equipped with an inlet for the initial solution and an opening for supplying permeate. The membrane module, in which the membrane is a hollow fiber membrane, includes a large number of hollow fibers bonded together and then placed inside a cylindrical container, with the opposite ends or the same ends being fixed in this way with polyurethane or epoxy resin so that it can be removed permeate, or fixed in a flat plate form so that it was possible to remove permeate. If the membrane is a flat membrane, the flat membrane is helically wound onto the liquid collector, it is folded like a mail envelope, and then placed in a cylindrical container so that permeate can be removed, or the flat membrane is placed on opposite surfaces of the liquid collector and is firmly fixed its edge so that permeate can be removed.

Also, the membrane module is equipped with at least one of the devices for generating increased pressure from the side of the crude liquid and a device for suctioning from the side of the permeate, and is further used as a dividing device for separating water or the like. As a device for creating high pressure, a pump can be used or pressure obtained due to the difference in water levels can be used. In addition, a pump or a siphon can be used as a suction device.

Such a separation device can be used for water treatment, for water treatment, wastewater treatment and production of industrial water, since we are talking about the field of water treatment, as well as the liquid to be treated, use river water, lake water, groundwater, sea water , drains and / or wastewater.

In addition, a porous membrane made of vinylidene fluoride resin, as described above, can be used for a battery separator to separate the positive and negative electrodes from each other inside the battery, in which case it can be expected that the characteristics of the resulting battery will be improved by due to high ion permeability, and the service life of such a battery can be increased due to the high tensile strength.

In addition, it can be expected that a porous membrane made of vinylidene fluoride resin obtained in accordance with the method described above, when used as a charged membrane with a charged group (ion-exchange group) introduced, will enhance ion recognition and / or increase the life of the charged membrane due to high tensile strength.

However, if a porous membrane made of vinylidene fluoride resin is impregnated with an ion exchange resin and then used as an ion exchange membrane in a fuel cell, and in particular if methanol is used as fuel, the expansion resulting from the presence of methanol in the ion exchange membrane can be weakened, and as a result, improvements in fuel cell performance can be expected. In addition, due to the high tensile strength, an increase in the life of the fuel cell can be expected.

The present invention will now be illustrated by way of illustrative examples, which should not be interpreted as limiting the scope of the present invention.

Example 1

Polyvinylidene fluoride (hereinafter sometimes abbreviated as “PVDF”. Available as “SOLEF6010” manufactured and available from Solvay Solexis Kabushiki Kaisha) as vinylidene fluoride resin, γ-butyrolactone as solvent, silica (“Fine Seal X-45”, manufactured and available from Kabushiki Kaisha Tokuyama) as inorganic particles and glycerin (purified glycerin manufactured and available from Kao Kabushiki Kaisha) was mixed in a mass ratio of 36: 47: 18: 19 to obtain a membrane-forming stock solution. The composition of this membrane-forming stock solution is shown in Table 1. The highest critical dissolution temperature of γ-butyrolactone and glycerol contained in the composition ratio was 40.6 ° C.

The membrane-forming stock solution obtained as described above was crushed using rods, heated and stirred (at a temperature of 150 ° C) inside a biaxial mixer-extruder and then extruded from it through a granulator. The resulting granulate was extruded using an extruder (150 ° C.) equipped with a double ring tip having an outer diameter of 1.6 mm and an inner diameter of 0.8 mm. At the same time, tetraethylene glycol was injected into the cavity of the resulting extruded material.

The extruded and cast material extruded from dies into the air was introduced into a water bath (at a temperature of 60 ° C) containing an aqueous solution of 20 wt.% Sodium sulfate, after being transferred through the air to a distance of 3 cm and then passed at a distance of about 100 cm through a water bath for cooling and curing. Then, while the solvent, the aggregating agent, and most of the inorganic particles still remained in the hollow fiber product, it was drawn in hot water at a temperature of 90 ° C in the direction of the fibers so as to obtain a length of approximately 1.5 times the original length, and then the resulting hollow fiber product was heat treated for 180 minutes in running water at a temperature of 95 ° C, at the same time the solvent (γ-butyrolactone), the aggregation-causing agent (glycerin) and the injected liquid (tetraethylenegly ol) were removed by extraction.

The hollow fiber product thus obtained was immersed for 120 minutes in an aqueous solution containing 5 wt.% Sodium hydroxide and heated to a temperature of 40 ° C to extract and remove inorganic particles (silicon oxide), followed by a flushing process or a washing process to obtain hollow fiber membrane. The test results for a hollow fiber membrane made in this way are presented in Table 2. The value of R ₁ measured on the basis of the IR spectrum of the hollow fiber membrane thus obtained was 2.5.

In order to evaluate the stability of the manufactured hollow fiber membrane with respect to the oxidizing reagent, it was immersed in an aqueous solution of sodium hypochlorite (5000 ppm in an effective concentration of chlorine) for 7 days at a temperature of 60 ° C and then its physical characteristics were measured (tensile strength tensile), the measurement results are presented in Table 3.

Methods and devices for various measurements (analyzes)

(1) Particle transmittance

The retention coefficient of at least two types of particles having different particle sizes is determined to obtain a measured value, which in turn is used in the following approximation (1), as will be described later, to determine the value of S, at which R becomes equal to 90, the value S describes the size of the fractionated particles

where "a" and "m" respectively are constants defined for a hollow fiber membrane and can be calculated based on the measured value of the retention coefficients of two or more kinds. However, it should be noted that the size of the fractionated particles in the case where the particle retention coefficient of 0.1 μm particles is equal to or greater than 90% is expressed as <0.1 μm.

(2) Pure water penetration rate

Using an open end through-type hollow fiber membrane module having an effective length of 3 cm and pure water as raw water, filtering (filtering with external pressure) from the outside to the inside of the hollow fiber membrane was performed under conditions at which the filtration pressure was 50 kPa, and temperature 25 ° C to measure the amount of water filtered per unit time, and the penetration rate was calculated based on the value converted to the amount of water through the unit surface area of the membranes us per unit time in a unit of pressure.

Example 2

A hollow fiber membrane was obtained by a method similar to that described above Example 1, except that ε-caprolactone was used as a solvent. The highest critical temperature for the dissolution of ε-caprolactone and glycerol contained in the composition ratio described above was 47.3 ° C. The results of the study of the hollow fiber membrane made in this way are presented in Table 2.

Comparative Example 1

Except that polyvinylidene fluoride (hereinafter sometimes abbreviated as "PVDF") ("SOLEF6010" manufactured and available from Solvay Solexis Kabushiki Kaisha), γ-butyrolactone, silica as inorganic particles and polyoxyethylene nonylphenyl ether ("NP-5", manufactured and available from Nikko Chemicals Kabushiki Kaisha) was mixed in a mass ratio of 36: 47: 18: 19 to obtain a membrane-forming stock solution, a hollow fiber membrane was obtained by a method similar to that described in Example 1. For γ-butyrolactone and polyoxyethylene nonylphenyl ether contained in and the composition ratio, the highest critical temperature of dissolution was not observed, and they were mixed with each other at any temperature. The results of the study of the fabricated hollow fiber membrane are presented in Table 2.

Example 3

Polyvinylidene fluoride (hereinafter sometimes abbreviated as "PVDF") ("SOLEF6010" manufactured and available from Solvay Solexis Kabushiki Kaisha), γ-butyrolactone as a solvent, silica ("Fine Seal X-80" manufactured and available from Kabushiki Kaisha Tokuyama ) as inorganic particles, glycerin (purified glycerin manufactured and available from Kao Kabushiki Kaisha) and polyvinylpyrrolidone ("K-90" manufactured and available from BASF Corporation) as a hydrophilic resin were mixed in a weight ratio of 35: 43: 19: 20 : 3 to obtain a membrane-forming stock solution. The composition of this membrane-forming stock solution is presented in Table 1. The highest critical dissolution temperature of γ-butyrolactone and glycerol contained in the composition ratio was 41.6 ° C.

The membrane-forming stock solution obtained as described above was crushed using rods, heated and stirred (at a temperature of 150 ° C) inside a biaxial mixer-extruder and then extruded from it through a granulator. The resulting granulate was extruded using an extruder (150 ° C.) equipped with a double ring tip having an outer diameter of 1.6 mm and an inner diameter of 0.8 mm. At the same time, tetraethylene glycol was injected into the cavity of the resulting extruded material.

The extruded and cast material extruded from dies into the air was introduced into a water bath (at a temperature of 30 ° C) containing an aqueous solution of 10 wt.% Sodium sulfate, after being transferred through the air to a distance of 3 cm and then passed at a distance of about 100 cm through a water bath for cooling and curing. Then, while the solvent, the aggregating agent, and most of the inorganic particles still remained in the hollow fiber product, it was drawn in hot water at a temperature of 90 ° C in the direction of the fibers so as to obtain a length of approximately 1.8 times the original length, and then the resulting hollow fiber product was heat treated for 180 minutes in running water at a temperature of 95 ° C, at the same time a solvent (γ-butyrolactone), an aggregation inducing agent (glycerin), and an injected liquid (tetraethyl nglikol) were removed by extraction.

The hollow fiber product thus obtained was immersed for 120 minutes in an aqueous solution containing 5 wt.% Sodium hydroxide and heated at 40 ° C to extract and remove inorganic particles (silicon oxide), followed by a flushing process or a washing process to obtain hollow fiber membrane.

After that, the resulting hollow article, thus obtained, was immersed in an aqueous solution (30 ° C) containing 5 wt.% Peroxodisulfate for 30 minutes, the resulting hollow article was removed from the aqueous solution, after which the excess solution remaining on hollow product, and then placed in a chemical reactor. Steam was supplied to the chemical reactor at a temperature of about 120 ° C and heat treatment was carried out for 30 minutes, while at the same time maintaining a temperature inside the reactor equal to or higher than 90 ° C. The hollow product, heat-treated in this way, was washed for 30 minutes in hot water at a temperature of 90 ° C, obtaining a hollow fiber membrane. The test results for the obtained hollow fiber membrane are presented in Table 2. After that, the manufactured hollow fiber membrane was dried for 12 hours in a stream of air and in a drying unit at a temperature of 40 ° C. The permeability retention before and after drying of the hollow fiber membrane is shown in Table 3. In addition, in FIG. From 1 to 4, scanning electron micrographs are presented, taken during the study of the membrane structure.

Reference Example 2

Polyvinylidene fluoride (hereinafter sometimes abbreviated as "PVDF") ("SOLEF6010" manufactured and available from Solvay Solexis Kabushiki Kaisha), hexyl benzoate (a class I reagent manufactured and available from Wako Junyaku Kabushiki Kaisha) as a solvent, silica (Fine X-45 ", manufactured and available from Kabushiki Kaisha Tokuyama) as inorganic particles and hexaglyceryl monolaurate (" Hexaglyn 1-L ", manufactured and available from Nikko Chemicals Kabushiki Kaisha) as an aggregating agent, were mixed in a weight ratio of 20:80 : 10: 10 to obtain a membrane-forming stock solution. The composition of this membrane-forming stock solution is presented in Table 1. For the hexyl benzoate and hexaglyceryl monolaurate contained in the composition ratio, the highest critical dissolution temperature was not observed, and they mixed with each other at any temperature.

The membrane-forming stock solution obtained as described above was crushed using rods, heated and stirred (at a temperature of 240 ° C) inside a biaxial mixer-extruder and then extruded from it through a granulator. The resulting granulate was extruded using an extruder (230 ° C.) equipped with a double ring tip having an outer diameter of 1.6 mm and an inner diameter of 0.8 mm. At the same time, tetraethylene glycol was injected into the cavity of the resulting extruded material.

The extruded and cast material extruded from the spinnerets into the air was introduced into a water bath (at a temperature of 30 ° C) after being transferred through air to a distance of 3 cm and then passed through a water bath at a distance of about 100 cm for cooling and curing. Next, the resulting hollow fibers were immersed for two times twice in a bath from methanol heated to a temperature of 50 ° C to extract and remove the solvent (hexyl benzoate), aggregation-causing agent (hexaglyceryl monolaurate), and injected liquid (tetraethylene glycol).

The hollow fiber product obtained in this way, after drawing in hot water at a temperature of 80 ° C in the direction of the fibers so as to obtain a length of approximately two times the original length, was thermally fixed in hot water at a temperature of 100 ° C and then immersed in an aqueous solution containing 5 wt.% sodium sulfate, and heated at a temperature of 40 ° C for 120 minutes to extract and remove inorganic particles (silicon oxide), receiving after the washing stage hollow fiber membrane. The test results are presented in Table 2. After that, the fabricated hollow fiber membrane was dried for 12 hours in a stream of air and in a drying unit at a temperature of 40 ° C. Preservation of permeability before and after drying the hollow fiber membrane is shown in Table 3. In addition, figure 5 presents scanning electron micrographs taken in the study of the structure of the membrane.

Example 4

Polyvinylidene fluoride ("SOLEF6010" manufactured and available from Solvay Solexis Kabushiki Kaisha), ε-caprolactone as a solvent, hydrophobic silica ("R-972" produced and available from Nippon Aerozil Kabushiki Kaisha) as inorganic particles and glycerin the aggregating agent was mixed in a mass ratio of 36: 54: 18: 12 to obtain a mixed solution. The highest critical dissolution temperature of ε-caprolactone and glycerol contained in the composition ratio was 35.8 ° C.

The mixed solution obtained as described above was crushed using rods, heated and stirred (at a temperature of 165 ° C) inside a biaxial mixer-extruder and then extruded from it through a granulator. The resulting granulate was extruded using an extruder (150 ° C.) equipped with a double ring tip having an outer diameter of 1.6 mm and an inner diameter of 0.8 mm. At the same time, tetraethylene glycol was injected into the cavity of the resulting extruded material.

The extruded and cast material extruded from dies into the air was introduced into a water bath (at a temperature of 40 ° C) containing an aqueous solution of 20 wt.% Sodium sulfate, after being transferred through the air to a distance of 3 cm and then passed at a distance of about 100 cm through a water bath for cooling and curing. Then, while the solvent, the aggregation causing agent, and most of the inorganic particles still remained in the hollow fiber product, it was drawn in hot water at a temperature of 90 ° C in the direction of the fibers so as to obtain a length of approximately 2 initial lengths, after which As a result, the hollow fiber product was heat treated for 180 minutes in running water at a temperature of 95 ° C, at the same time a solvent (γ-butyrolactone), an aggregation-causing agent (glycerin), and an injected liquid (tetraethylene glycol ) Were removed by extraction.

The hollow fiber product thus obtained was immersed for 120 minutes in an aqueous solution containing 5 wt.% Sodium hydroxide and heated at 40 ° C to extract and remove inorganic particles (silica) followed by a flushing process or a washing process with obtaining a hollow fiber membrane. The test results for a hollow fiber membrane made in this way are presented in Table 2.

Example 5

Except that heat treatment for 120 minutes and extraction and removal of solvent, aggregation agent, and injected liquid were carried out in running water heated to a temperature of 95 ° C, a hollow fiber membrane was obtained by a method similar to that described in Example 1. The value of R ₁ made hollow fiber membrane, determined on the basis of the IR spectrum, turned out to be 2.1.

In order to evaluate the resistance of the fabricated hollow fiber membrane to oxidizing agents, it was immersed in an aqueous solution of sodium hypochlorite (5000 ppm in an effective concentration of chlorine) for 7 days at a temperature of 60 ° C and then its physical characteristic was measured (tensile strength ), the measurement results are presented in Table 3.

Example 6

Except that heat treatment for 180 minutes and extraction and removal of solvent, aggregation agent, and injected liquid were carried out in running water heated to a temperature of 85 ° C, a hollow fiber membrane was obtained by a method similar to that described in Example 1. The value of R ₁ made hollow fiber membrane, determined on the basis of the infrared spectrum, was equal to 1.9.

In order to evaluate the resistance of the fabricated hollow fiber membrane to oxidizing agents, it was immersed in an aqueous solution of sodium hypochlorite (5000 ppm in an effective concentration of chlorine) for 7 days at a temperature of 60 ° C and then its physical characteristic was measured (tensile strength ), the measurement results are presented in Table 3.

Reference Example 3

Except that heat treatment for 180 minutes and extraction and removal of solvent, aggregation agent, and injected liquid were carried out in running water heated to a temperature of 45 ° C, a hollow fiber membrane was obtained by a method similar to that described in Example 1. The value of R ₁ made hollow fiber membrane, determined on the basis of the infrared spectrum, was equal to 1.9.

In order to evaluate the resistance of the fabricated hollow fiber membrane to oxidizing agents, it was immersed in an aqueous solution of sodium hypochlorite (5000 ppm in an effective concentration of chlorine) for 7 days at a temperature of 60 ° C and then its physical characteristic was measured (tensile strength ), the measurement results are presented in Table 3.

In Table 1 above, “γ-” means γ-butyrolactone, and “ε-” means ε-caprolactone.

table 2 Pure water permeate consumption l / (h · m ² · 98 kPa) Particle Transmission Limit (μm) The major axis of the pore: the minor axis of the pore Outside surface Inner surface Note one 130,000 3.3 3.5: 1 5.8: 1 Note 2 124000 2,8 3.4: 1 5.5: 1 Note 3 90,000 1.8 4.0: 1 6.1: 1 Note four 6500 0.4 2.9: 1 6.3: 1 Compares. example 1 5000 0.4 3.4: 1 4.4: 1 Compares. example 2 60,000 2.0 2.7: 1 3.6: 1

Table 3 R ₁ Preservation of tensile strength (%) Note one 2.5 98 Note 5 2.1 98 Note 6 1.9 96 Compares. example 3 0.9 72

Table 4 Saving the flow of permeate pure water (%) Note 3 one hundred Compares. example 2 13

Claims (11)

1. A porous membrane made of vinylidene fluoride resin with a particle transmission limit of at least 0.2 μm, including a first surface and a second surface that are opposite to each other, while the first surface has micropores of a round or oval shape with an average ratio between the major axis and minor axis in the range from 1: 1 to 5: 1, and the second surface has micropores, essentially slit-shaped with an average ratio between the major axis and the minor axis of at least 5: 1. 2. The porous membrane according to claim 1, additionally containing a vinylidene fluoride resin, a hydrophilic resin in the form of a mixed polymer containing vinylidene fluoride resin in an amount of from 90 to 99 wt.% And a hydrophilic resin in an amount of from 1 to 10 wt.%. 3. The porous membrane according to claim 2, where the hydrophilic resin is a vinyl pyrrolidone resin. 4. The porous membrane according to claim 1, which is a hollow fiber membrane. 5. The porous membrane according to claim 4, where the first surface having micropores of round or oval shape with an average ratio between the major axis and minor axis in the range from 1: 1 to 5: 1, is the outer surface of the hollow fiber membrane, and the second surface having micropores essentially slit-shaped with an average ratio between the major axis and minor axis of at least 5: 1, is the inner surface of the hollow fiber membrane. 6. A method of obtaining a porous membrane made of vinylidene fluoride resin, including:
cooling the stock solution for the manufacture of a porous membrane containing a vinylidene fluoride resin, a solvent, inorganic particles and an aggregation agent, in which the inorganic particles and the aggregation agent have an affinity, and the solvent and the aggregation agent are not miscible with each other or have a higher critical temperature of dissolution to induce phase separation followed by curing; and
stretching the porous membrane before the complete removal of the solvent, inorganic particles, and aggregation agent. 7. The method according to claim 6, characterized in that the solvent is a water-soluble solvent. 8. The method according to claim 6, characterized in that the porous membrane is made of a mixed polymer containing vinylidene fluoride resin in an amount of from 90 to 99 wt.% And a hydrophilic resin in an amount of from 1 to 10 wt.%. 9. The method of claim 8, wherein the hydrophilic resin is a vinyl pyrrolidone resin. 10. The method according to claim 6, characterized in that the porous membrane is a hollow fiber membrane. 11. The method according to claim 10, characterized in that the first surface having micropores of round or oval shape with an average ratio between the major axis and minor axis in the range from 1: 1 to 5: 1, is the outer surface of the hollow fiber membrane, and the second surface having micropores essentially slit-shaped with an average ratio between the major axis and minor axis of at least 5: 1, is the inner surface of the hollow fiber membrane.

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