JP2020121263A - Composite semipermeable membrane - Google Patents

Abstract

To provide a composite semipermeable membrane having significantly high durability compared with previous ones.SOLUTION: In a composite semipermeable membrane, a support membrane including a base material and a porous support and a separation function layer disposed on the porous support are provided. The porous support includes a thermoplastic resin. The weight average molecular weight (Mw) of the thermoplastic resin is 140,000 or less, and peel strength measured by peeling the porous support from the base material in the conditions of 25°C, 10 mm/min and a peeling direction of 180° is 3.0 N/25 mm or more.SELECTED DRAWING: Figure 1

Description

The present invention relates to a composite semipermeable membrane useful for selective separation of a liquid mixture and a method for producing the same. The composite semipermeable membrane obtained by the present invention can be suitably used for desalination of seawater or brackish water, for example.

Regarding the separation of the mixture, there are various techniques for removing substances (eg salts) dissolved in a solvent (eg water), but in recent years, the use of the membrane separation method has expanded as a process for saving energy and resources. doing. Membranes used in the membrane separation method include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, composite semipermeable membranes, etc. These membranes are, for example, seawater, brackish water, water containing harmful substances, etc. It is used for obtaining drinking water, production of industrial ultrapure water, wastewater treatment, and recovery of valuables.

Most of the composite semipermeable membranes and nanofiltration membranes currently on the market are composite semipermeable membranes, and those that have an active layer obtained by crosslinking a gel layer and a polymer on the support membrane and the polycondensation of monomers on the support membrane. There are two types, one having an active layer. Among them, a composite semipermeable membrane obtained by coating a supporting membrane with a separation functional layer composed of a crosslinked polyamide obtained by a polycondensation reaction of a polyfunctional amine and a polyfunctional acid halide has a permeability and a selective separation property. Widely used as a high separation membrane.

When performing separation using a composite semipermeable membrane, the membrane is required to have mechanical strength. For example, when impurities contained in water are deposited on the surface of the composite semipermeable membrane, which causes clogging of the composite semipermeable membrane or decreases the production efficiency of pure water, the high pressure water flow is used to remove the composite semipermeable membrane. The method of flushing may be taken. At this time, if the strength of the composite semipermeable membrane is weak, peeling of the membrane occurs and damage occurs, so that a satisfactory salt removal rate cannot be obtained. The support film generally comprises a base material and a porous support, but peeling easily occurs near the interface between the base and the porous support.

Patent Document 1 discloses that high water permeability in the permeation direction and flow rate are improved, and the polyamide layer ensures stain resistance and chemical resistance.

Patent Document 2 discloses an example in which polyvinyl chloride or chlorinated vinyl chloride resin is used for the porous support of the composite semipermeable membrane.

Patent Document 3 discloses a composite semipermeable membrane in which a base material is impregnated with a resin.

Japanese Patent Laid-Open No. 2009-233666 Japanese Patent Laid-Open No. 2000-296317 WO14/192883

Despite the various proposals mentioned above, the strength and water permeability of the composite semipermeable membrane are not sufficiently compatible with each other. Particularly in terms of strength, stronger durability is required. An object of the present invention is to provide a composite semipermeable membrane having a significantly improved strength as compared with the conventional one.

The present invention for achieving the above object has the following configurations.

(1) A composite semipermeable membrane comprising a support membrane including a base material and a porous support, and a separation functional layer provided on the porous support,
The porous support contains a thermoplastic resin,
The weight average molecular weight (Mw) of the thermoplastic resin is 140,000 or less,
A composite semipermeable membrane having a peel strength of 3.0 N/25 mm or more, which is measured by peeling the porous support from the substrate at a temperature of 25° C. and a peeling direction of 180° at 10 mm/min.

(2) The composite semipermeable membrane according to (1), wherein the thermoplastic resin is a vinyl-based copolymer.

(3) The composite semipermeable membrane as described in (1) or (2), wherein the thermoplastic resin is a polymer of a vinyl cyanide-based monomer and an aromatic vinyl-based monomer.

(4) A step of applying a solution containing a thermoplastic resin and having a viscosity of 150 cP or less to a substrate,
Forming a porous support by solidifying the thermoplastic resin in the solution;
The method for producing a composite semipermeable membrane according to (1) to (3), wherein a separation functional layer is formed on the porous support.

According to the present invention, the composite semipermeable membrane has higher strength than ever before.

It is sectional drawing which shows the outline of the composite semipermeable membrane which concerns on embodiment of this invention.

1. Composite Semipermeable Membrane FIG. 1 shows an embodiment of the composite semipermeable membrane. The composite semipermeable membrane 1 shown in FIG. 1 comprises a support membrane 2 having a base material 3 and a porous support 4, and a separation functional layer 5 provided on the porous support 4.

(1-1) Support film The support film 2 includes the base material 3 and the porous support 4, and has substantially no separation performance for ions or the like and a separation functional layer 5 having substantially separation performance. It is a film for giving strength.

Part of the porous support 4 is impregnated in the base material 3, and the other part is present on the base material 3. Of the porous support 4, the portion existing on the base material 3 is called an exposed portion 40, and the impregnated portion is called an impregnated portion 41. That is, the exposed portion 40 exists between the base material and the separation functional layer 5.

Further, a layer formed of the base material 3 and the impregnated portion 41 (a layer obtained by removing the exposed portion 40 from the support film 2) is denoted by reference numeral 31 as a composite base material. In this document, the term "base material" does not include the porous support in the base material unless otherwise specified.

The peel strength measured by peeling the porous support 4 (more specifically, the exposed portion 40) from the substrate 3 at a temperature of 25° C. and a peeling direction of 180° at 10 mm/min is preferably It is 3.0 N/25 mm or more, more preferably 5.0 N/25 mm or more, and further preferably 7.0 N/25 mm or more.

The thickness of the support membrane 2 affects the strength of the composite semipermeable membrane and the packing density when it is used as a membrane element. In order to obtain sufficient mechanical strength and packing density, the thickness of the support film 2 is preferably in the range of 30 to 300 μm, more preferably 50 to 250 μm.

The thickness of each part can be measured by observing a cross section with a scanning electron microscope (SEM), an optical microscope, or the like. For example, when the thickness of the porous support layer is measured by SEM, a composite semipermeable membrane or a support membrane is cut by the freeze fracture method to prepare a section sample, and the section sample is observed by SEM at a cross section of 100 to 500 times. To do. From the obtained image, the thickness (measured at intervals of 10 μm) at arbitrary 10 points is measured using a scale or a caliper in the direction orthogonal to the thickness direction (plane direction of the film). The same operation is performed on five section samples, and the arithmetic mean of 50 pieces of data is calculated to obtain the thickness of the porous support. Before observing with SEM, the sample is thinly coated with platinum, platinum-palladium, or ruthenium tetroxide. As the SEM, a Hitachi High Technologies S-5500 scanning electron microscope or the like can be used, and observation is performed at an acceleration voltage of 3 to 6 kV.

The thickness of each part can also be measured by a dial thickness gauge or a digital thickness gauge. Since the thickness of the separation functional layer is much smaller than that of the base material or the porous support, the thickness of the composite semipermeable membrane may be regarded as the total thickness of the base material and the porous support (support membrane thickness). it can. Therefore, by measuring the thickness of the composite semipermeable membrane with a dial thickness gauge or a digital thickness gauge and subtracting the thickness of the base material from the thickness of the composite semipermeable membrane, the thickness of the porous support can be easily calculated. it can. When a dial thickness gauge or a digital thickness gauge is used, the thickness is measured at any 20 points and the arithmetic mean thereof is calculated.

(1-1-a) Base Material The base material is preferably porous. In particular, when the porosity of the base material is 25% or more and 80% or less, the amount of the porous support in the base material is preferably controlled, and both strength and water permeability can be achieved. When the porosity of the base material is 25% or more, the stock solution forming the porous support is sufficiently impregnated into the base material, so that part of the resin of the porous support in the support membrane is contained in the base material. Since it exists, an appropriate peel strength can be obtained. The porosity may further be 35% or more or 40% or more.

In addition, when the porosity of the base material is 80% or less, the amount of the porous support present in the base material does not become too large and can be suppressed to an appropriate amount. As a result, when the separation functional layer of polyamide or the like is formed by polymerization, the balance between the amount of monomer supplied to the polymerization field and the degree of progress of polymerization is appropriately maintained, and the obtained membrane achieves a good solute removal rate. To be done. In addition, as another effect, when the porosity is 80% or less, a high amount of fresh water can be obtained by appropriately leaving a gap between the fibers of the base material that is the flow path of the permeate. is there. The porosity of the substrate may be 75% or less, 70% or less, or 65% or less.

Here, the porosity refers to the ratio of voids per unit volume of the base material, and subtracts the dry weight of the base material from the weight when pure water is included in the base material having a predetermined apparent volume. It is possible to obtain a value obtained by dividing the value obtained by dividing the value by the apparent volume of the base material in percentage (%).

The thickness of the substrate is preferably in the range of 10 to 200 μm, more preferably 40 to 150 μm.
Examples of the base material include a cloth made of a polymer such as a polyester polymer, a polyamide polymer, a polyolefin polymer, or a mixture or copolymer thereof. As the base material, a polyester polymer is preferable because a support film having excellent mechanical strength, heat resistance, water resistance and the like can be obtained.

The polyester polymer is a polyester composed of an acid component and an alcohol component. As the acid component, aromatic carboxylic acids such as terephthalic acid, isophthalic acid and phthalic acid, aliphatic dicarboxylic acids such as adipic acid and sebacic acid, and alicyclic dicarboxylic acids such as cyclohexanecarboxylic acid can be used. Examples of the alcohol component include ethylene glycol, diethylene glycol and polyethylene glycol.

Examples of polyester-based polymers include polyethylene terephthalate resin, polybutylene terephthalate resin, polytrimethylene terephthalate resin, polyethylene naphthalate resin, polylactic acid resin and polybutylene succinate resin, and the copolymerization of these resins There is also a combination.

As the cloth used for the base material, it is preferable to use a nonwoven fabric in terms of strength, ability to form irregularities, and fluid permeability. As the nonwoven fabric, both long-fiber nonwoven fabric and short-fiber nonwoven fabric can be preferably used. In particular, long-fiber non-woven fabric has excellent permeability when a solution of a high-molecular polymer is cast on a substrate, the porous support is peeled off, and the composite semipermeable membrane is not formed due to fluffing of the substrate. It is possible to suppress the homogenization and the occurrence of defects such as pinholes. Further, since the long-fiber non-woven fabric composed of the thermoplastic continuous filament is less likely to fluff, the base material is a long-fiber non-woven fabric, so that it is possible to suppress non-uniformity during casting of the thermoplastic resin solution and a film defect. .. Further, in continuous film formation of a composite semipermeable membrane, a long fiber nonwoven fabric having excellent dimensional stability is preferable as a substrate because tension is applied to the substrate in the film forming direction.

In terms of moldability and strength, it is preferable that the fibers in the surface layer on the side opposite to the porous support side of the long-fiber non-woven fabric be oriented more longitudinally than the fibers of the surface layer on the porous support side. According to such a structure, not only a high effect of preventing film breakage is realized by maintaining strength, but also a laminate including a porous support and a base material when imparting unevenness to the separation functional layer is provided. Moldability as a body is also improved, and the uneven shape of the surface of the separation functional layer is stable, which is preferable. More specifically, the fiber orientation degree in the surface layer of the long-fiber nonwoven fabric on the side opposite to the porous support side is preferably 0° to 25°, and the fiber orientation degree in the porous support side surface layer is It is preferable that the difference in orientation degree is 10° to 90°.

In the production process of the separation membrane and the production process of the element, the work in progress of the separation membrane or the separation membrane may be heated. Such heating causes a phenomenon that the porous support or the separation functional layer contracts. In particular, it is remarkable in the width direction where tension is not applied in continuous film formation. Since shrinkage causes a problem in dimensional stability and the like, a substrate having a small thermal dimensional change rate is desired. When the difference between the fiber orientation degree in the surface layer on the side opposite to the porous support and the fiber orientation degree in the porous support side surface layer in the nonwoven fabric is 10° to 90°, a change in the width direction due to heat may be suppressed. it can.

Here, the fiber orientation degree is an index indicating the direction of the fibers of the non-woven fabric substrate, and the film-forming direction when performing continuous film formation is 0°, and the direction perpendicular to the film-forming direction, that is, the width of the non-woven fabric substrate. It means the average angle of the fibers constituting the nonwoven fabric substrate when the direction is 90°. Therefore, the closer the fiber orientation degree is to 0°, the more vertical orientation, and the closer the fiber orientation degree is to 90°, the more horizontal orientation.

The degree of fiber orientation was obtained by randomly taking 10 small sample pieces from the nonwoven fabric, and taking a photograph of the surface of the sample with a scanning electron microscope at a magnification of 100 to 1000 times, 10 pieces from each sample, for a total of 100 fibers, the nonwoven fabric. The longitudinal direction (longitudinal direction, film-forming direction) is 0°, and the width direction of the non-woven fabric (horizontal direction) is 90°, and the average value is rounded off to the first decimal place. The fiber orientation degree is obtained.

(1-1-b) Porous support The composition of the porous support is not particularly limited, but the porous support is preferably formed of a thermoplastic resin. Here, the thermoplastic resin refers to a resin which is made of a chain polymer and has a property of being deformed or flowed by an external force when heated.

Examples of the thermoplastic resin include homopolymers or copolymers of polysulfone, polyether sulfone, polyamide, polyester, cellulosic polymer, vinyl polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, polyphenylene oxide, etc., alone or blended. Can be used. Here, cellulose acetate, cellulose nitrate or the like can be used as the cellulosic polymer, and polyethylene, polypropylene, polyvinyl chloride, polyacrylonitrile, acrylonitrile-styrene copolymer or the like can be used as the vinyl polymer.

Cellulose acetate, polysulfone, polyphenylene sulfide sulfone, vinyl resin or polyphenylene sulfone are more preferable, and among these materials, chemical, mechanical and thermal stability is high, and molding is easy. Therefore, vinyl resins can be used. The porous support preferably contains these listed compounds as main components.

The porous support preferably contains at least one vinyl resin. Vinyl resins have high chemical, mechanical and thermal stability. Further, the vinyl-based resin also has an effect of facilitating control of the pore size of the porous support.

The vinyl resin may be a polymer of a vinyl cyanide monomer and an aromatic vinyl monomer.

The abundance ratio of the vinyl cyanide-based monomer can be determined by the following method. First, a support membrane or a composite semipermeable membrane cut into a predetermined area is thoroughly washed with warm water and air dried at room temperature. Next, by contacting with acetone, only the porous support is dissolved, and the obtained solution is filtered through a metal mesh (wire diameter 0.03 mm, mesh 300, manufactured by Kansai Wire Mesh Co., Ltd.) to obtain a base material and a function. Remove the layer. Then, cyclohexane is gradually added to the obtained filtrate, and the addition is stopped when it becomes cloudy. This cloudy solution was added to 8800 r.p.m. p. After centrifuging at m (10,000 G or more) for 40 minutes, the supernatant is separated to obtain an insoluble matter. The insoluble matter is dried under reduced pressure at 80° C. for 5 hours, and its weight is measured. Then, the insoluble matter is analyzed by the total reflection infrared absorption spectrum method, and the abundance ratio of the vinyl cyanide-based monomer can be determined from the intensity ratio of the following peaks appearing in the obtained spectrum.
Derived from aromatic vinyl-based monomer: peak at 1605 cm ^-1 attributable to vibration of benzene nucleus Derived from vinyl-cyanide-based monomer: peak at 2240 cm ^-1 attributed to -CN stretching Further in separated supernatant liquid 5 mL cyclohexane was added, and an insoluble matter was obtained from the white turbid liquid by the same method. The above operation is repeated, and 5 mL of cyclohexane is added until white turbidity disappears, and the abundance ratio and weight of the insoluble vinyl cyanide-based monomer in each addition amount of cyclohexane are measured. By the above method, the weight of the polymer having an abundance ratio of the vinyl cyanide-based monomer of 0.9 or more can be determined. Further, the content of the polymer in which the abundance ratio of the vinyl cyanide-based monomer is 0.9 or more can be determined from the total weight of the insoluble matter.

The infrared absorption spectrum can be measured by the ATR-FT-IR method. For example, the infrared absorption spectrum is measured using a single reflection type ATR measurement accessory device. As the FT-IR, an IR Tracker-100 manufactured by Shimadzu, and as a single reflection type ATR measurement accessory device, a MicromaATR Vision manufactured by Czitek can be used.

Examples of the vinyl cyanide-based monomer include acrylonitrile, methacrylonitrile, etaacrylonitrile, and the like, and acrylonitrile is preferably used. The vinyl cyanide-based monomer contained in the copolymer may be one kind or a mixture of two or more kinds.

Examples of aromatic vinyl-based monomers include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, t-butylstyrene, o-ethylstyrene, o-chlorostyrene, and o,p-dichlorostyrene. However, styrene and α-methylstyrene are particularly preferably used. The aromatic vinyl-based monomer contained in the copolymer may be one kind or a mixture of two or more kinds.

The proportion of the vinyl cyanide-based monomer in the vinyl-based monomer that constitutes the vinyl-based copolymer is preferably 5 to 60% by weight, more preferably 10 to 40% by weight.

The proportion of the aromatic vinyl-based monomer in the vinyl-based monomer constituting the vinyl-based copolymer is preferably 40 to 95% by weight, more preferably 60 to 90% by weight. If it is less than 40% by weight, the moldability of the porous support may be lowered, and if it exceeds 95% by weight, the pressure resistance of the porous support may be lowered.

The weight average molecular weight (Mw) of the tetrahydrofuran (THF)-soluble component in the porous support is preferably 140,000 or less, more preferably 120,000 or less, and further preferably 100,000 or less. When the Mw is 140,000 or less, it is possible to obtain favorable durability as a porous support.

As a result of intensive studies, the present inventors have found that the weight average molecular weight (Mw) of the thermoplastic resin forming the porous support is set to the above range, whereby the durability is significantly improved. It is considered that this is because the viscosity of the resin solution at the time of applying the thermoplastic resin to the base material can be reduced as described later, and thereby the amount of resin impregnated into the base material increases. The impregnated amount will be described later.

The weight average molecular weight (Mw) of the tetrahydrofuran (THF)-soluble component in the porous support is preferably 40,000 or more, more preferably 70,000 or more, still more preferably 90,000 or more. .. When the weight average molecular weight is 40,000 or less, the solution viscosity at the time of forming the support film becomes extremely low, and it becomes difficult to apply the support film on the substrate, and the film forming property deteriorates.

The weight average molecular weight (Mw) of the THF soluble component in the porous support can be measured by the following method. First, a support membrane or a composite semipermeable membrane cut into a predetermined area is thoroughly washed with warm water and air dried at room temperature. Next, by contacting with THF, only the porous support is dissolved, and the obtained solution is filtered through a metal mesh (wire diameter 0.03 mm, mesh 300, manufactured by Kansai Wire Mesh Co., Ltd.) to obtain a base material and a function. Remove the layer. Subsequently, the obtained filtrate was treated with 8800 r.p.m. p. After centrifuging at m (10,000 G or more) for 40 minutes, the supernatant is collected. The resulting supernatant is measured by gel permeation chromatography (GPC) using THF as a solvent and polystyrene as a standard substance to determine the weight average molecular weight.

The thickness of the exposed portion 40 is preferably 10 μm or more and 100 μm or less. If it is less than 10 μm, the base material may be exposed to cause a defect, and if it exceeds 100 μm, the water permeability may be lowered due to the resistance due to the thickness of the porous support.

Further, the thickness of the exposed portion 40 is preferably 1% or more and 80% or less of the thickness of the base material 3, and more preferably 5% or more and 50% or less.

When the thickness of the impregnated portion 41 is 60% or more of the thickness of the base material, high peeling strength can be obtained, and further, when the peeling membrane element is formed, it is possible to reduce the drop into the flow path material. Further, when it is 99% or more of the thickness of the impregnated base material of the porous support, a skin layer is also formed on the back side, which causes a decrease in water permeability. Therefore, when the thickness of the base material is 99% or less, both strength and water permeability can be achieved.

The density of the exposed portion 40 of the porous support is preferably 0.3 g/cm ³ or more and 0.7 g/cm ³ or less, and the porosity of the exposed portion 40 is preferably 30% or more and 70% or less. .. When the density of the exposed portion 40 is 0.3 g/cm ³ or more or the porosity is 30% or more, suitable strength is obtained and a surface structure suitable for fold growth of the polyamide separation functional layer is obtained. be able to. Further, when the density of the exposed portion is 0.7 g/cm ³ or less or the porosity is 70% or less, good water permeability can be obtained.

Further, the sum (A+B) of the weight A of the base material per unit area and the weight B of the porous support (impregnated portion 41) inside the base material per unit area is 10 g/m ² or more. Is preferred and 30 g/m ² is more preferred. The sum (A+B) is preferably 100 g/m ² or less.

This sum (A+B) is the basis weight of the composite base material, and is obtained by dividing the weight of the composite base material 31 by the area of the composite base material. The composite base material 31 is obtained by peeling the exposed portion 40 from the base material 3. When the basis weight of the composite substrate is 10 g/m ² or more, high peel strength can be obtained. Further, when the basis weight of the composite base material is 100 g/m ² or less, the flow resistance can be suppressed low.

The ratio B/A of the weight B of the porous support in the composite substrate to the weight A of the substrate per unit area preferably satisfies 0.10≦B/A≦1 and 0.15≦ It is more preferable that B/A≦1 is satisfied. When the ratio B/A is 0.10 or more, a high peel strength can be obtained due to the anchor effect by impregnation of the porous support. Further, when the ratio B/A is 1 or less, the flow resistance can be suppressed low.

In order to adjust the relationship between the weight A of the base material 3 and the weight B of the impregnated portion 41 within the above range, the configurations of the thermoplastic resin and the base material may be appropriately adjusted as described above.

Regarding the total porosity of the substrate and the porous material, the total porosity is preferably 10% or more, and more preferably 60% or less, while satisfying the respective preferable numerical value ranges described above.

With the configuration described above, the thickness of the portion of the porous support 4 that is impregnated in the base material (the thickness of the portion indicated by reference numeral 41), and the composite of the porous support and the base material. The quantitative relationship between the base material 3 and the porous support 41 can be optimized. In this way, the peel strength between the base material 3 and the porous support 41 can be increased, and as a result, performance degradation can be suppressed even if the operating pressure fluctuates.

When the separation functional layer is formed by interfacial polymerization, the polyfunctional amine aqueous solution necessary for forming the separation functional layer is transferred to the polymerization field, that is, the surface of the porous support, through the inside of the porous support layer. In order to efficiently transfer the monomer, the porous support preferably has continuous pores, and the pore diameter thereof is preferably 0.1 μm or more and 1 μm or less. In addition, the surface of the porous support serves to supply and release the monomer to supply the monomer to the formed separation functional layer, and also to serve as a starting point of the fold growth of the separation functional layer. Therefore, the pore size on the surface of the porous support (portion in contact with the separation functional layer) is preferably smaller than the pore size inside the porous support.

Furthermore, the structure of the porous support is preferably continuous from the base material side to the separation functional layer side. The "structure is continuous" means that there is no portion having a high density, that is, a so-called skin layer. Specifically, the pores of the skin layer are in the range of 1 nm or more and 50 nm or less.

Further, substances such as particles may be added to the porous support as long as the function is not impaired. The particles may be rubbery particles.

The rubber particles are dispersed in the thermoplastic resin to improve pressure resistance and water permeability. The rubber-like particles include a rubber-like polymer, and examples of the rubber-like polymer include diene rubber, acrylic rubber, ethylene rubber, and the like. Specifically, polybutadiene, poly(butadiene-styrene), poly(butadiene) -Acrylonitrile), polyisoprene, poly(butadiene-methyl acrylate), poly(butadiene-ethyl acrylate), poly(butadiene-butyl acrylate), poly(butadiene-methyl methacrylate), ethylene-propylene rubber, ethylene- Examples thereof include propylene-diene rubber, poly(ethylene-isobutylene), poly(ethylene-methyl acrylate), poly(ethylene-ethyl acrylate) and the like.

The rubber-like particles may contain not only one kind of the rubber-like polymer exemplified above but also a plurality of kinds. Among them, polybutadiene and poly(butadiene-styrene) are preferable because the pressure resistance of the support layer is improved.

The weight average particle size of the rubber particles is preferably in the range of 100 nm to 2000 nm. Within this range, the rubber particles can be uniformly dispersed, and the support layer can easily contain the rubber particles.

The weight average particle diameter of the rubber particles can be calculated from the particle diameter distribution measured by a laser scattering diffraction method particle size distribution measuring device (LS 13 320 manufactured by Beckman Coulter, Inc.) by dispersing the rubber particles in an aqueous medium. Further, in the case of the weight average particle size of the rubber particles contained in the support layer, the insoluble component obtained when measuring the amount of the insoluble component contained in the support layer is dispersed in water, and the laser scattering diffraction method is used. It can be calculated by measuring the particle size distribution with a particle size distribution measuring device.

The content of rubber particles in the thermoplastic resin is preferably 50% by weight or less, more preferably 45% by weight or less, and further preferably 40% by weight or less. When the amount of the rubber particles exceeds 50% by weight, the support layer forming property is deteriorated and defects occur.

Further, the rubber particles are graft copolymer-containing rubber particles having a salami structure obtained by graft-copolymerizing a radical-polymerizable monomer with a rubber polymer, and block-copolymerizing a radical-polymerizable monomer with the rubber polymer. Block copolymer-containing rubber particles, a core-shell rubber having a layered structure composed of a rubber polymer and a styrene monomer or an unsaturated carboxylic acid alkyl ester monomer, and the salami structure and core. A rubbery polymer belonging to the middle of the shell structure and other resin components are preferably an onion structure or the like forming a multilayer structure, and more preferably rubber particles containing a graft copolymer.

Further, the graft copolymer-containing rubber particles include graft copolymer-containing rubber particles obtained by copolymerizing a vinyl cyanide monomer and an aromatic vinyl monomer in the presence of the rubber polymer. Is preferred. Further, one or more vinyl-based monomers selected from other vinyl-based monomers copolymerizable with these may be copolymerized.

Examples of the vinyl cyanide-based monomer include acrylonitrile, methacrylonitrile and etaacrylonitrile, and acrylonitrile is preferably used. These vinyl cyanide-based monomers do not necessarily have to be used in one kind, and may be used in a mixture of two or more kinds.

Examples of aromatic vinyl-based monomers include styrene, α-methylstyrene, p-methylstyrene, vinyltoluene, t-butylstyrene, o-ethylstyrene, o-chlorostyrene, and o,p-dichlorostyrene. However, styrene and α-methylstyrene are particularly preferably used. It is not always necessary to use one kind of these aromatic vinyl-based monomers, and it is also possible to use two or more kinds in combination.

Examples of other copolymerizable vinyl-based copolymers include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, n-hexyl methacrylate and methacrylic acid. Cyclohexyl, chloromethyl methacrylate, 2-chloroethyl methacrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl methacrylate, 2,3,4,5,6-pentahydroxy methacrylate, 2,3,4,methacrylic acid Examples include unsaturated carboxylic acid alkyl esters such as 5-tetrahydroxypentyl, unsaturated amides such as acrylamide, and maleimide compounds such as N-maleimide, N-cyclohexylmaleimide, and N-phenylmaleimide. Among them, unsaturated carboxylic acid alkyl ester is preferably used, and methyl methacrylate is more preferably used. These do not necessarily have to be used alone, and two or more kinds can be mixed and used.

The graft ratio in the rubber particles containing the graft copolymer is preferably in the range of 10 to 80% by weight. If the graft ratio is less than 10% by weight, the pressure resistance of the support layer may decrease, and if it exceeds 80% by weight, the moldability of the support layer may be deteriorated and defects may easily occur. The graft ratio can be determined by the following method.

First, 100 ml of acetone is added to a predetermined amount (m; about 1 g) of the rubber particles containing a graft copolymer that have been vacuum dried at 80° C. for 4 hours, and the mixture is refluxed for 3 hours in a water bath at 70° C. This solution was then added to 8800 r. p. After centrifuging at m (10000 G or more) for 40 minutes, the supernatant is removed, and the precipitate is vacuum dried at 40° C. for 8 hours. Finally, the weight (n) of the precipitate after drying is measured. The graft ratio is calculated by the following formula. Here, L is the rubber content (% by weight) of the rubber particles containing the graft copolymer.
Grafting ratio [%]={[(n)-((m)×L/100)]/[(m)×L/100]}×100
The proportion of the vinyl cyanide-based monomer in the vinyl-based monomer that constitutes the rubber particles containing the graft copolymer is preferably 5 to 60% by weight, more preferably 10 to 40% by weight. ..

The proportion of the aromatic vinyl-based monomer in the vinyl-based monomer that constitutes the rubber particles containing the graft copolymer is preferably 40 to 95% by weight, more preferably 60 to 90% by weight. ..

The proportion of the other vinyl-based monomer in the vinyl-based monomer constituting the rubber particles containing the graft copolymer is preferably 0 to 30% by weight.

(1-2) Separation Functional Layer The separation functional layer is a layer having a solute separating function in the composite semipermeable membrane. The composition such as the composition and thickness of the separation functional layer is set according to the purpose of use of the composite semipermeable membrane.

(Polyamide separation functional layer)
The separation functional layer may contain, for example, polyamide as a main component. The polyamide that constitutes the separation functional layer can be formed by interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide. Here, it is preferable that at least one of the polyfunctional amine and the polyfunctional acid halide contains a trifunctional or higher functional compound.

Here, the polyfunctional amine has two or more of at least one of a primary amino group and a secondary amino group in one molecule, and at least one of the amino groups is a primary amino group. Say an amine. For example, phenylenediamine, xylylenediamine, 1,3,5-triaminobenzene, 1,2,4 in which two amino groups are bonded to a benzene ring in any of the ortho, meta, and para positions. -Aromatic polyfunctional amines such as triaminobenzene, 3,5-diaminobenzoic acid, 3-aminobenzylamine and 4-aminobenzylamine, aliphatic amines such as ethylenediamine and propylenediamine, 1,2-diaminocyclohexane, 1 And alicyclic polyfunctional amines such as 4-diaminocyclohexane, 4-aminopiperidine, and 4-aminoethylpiperazine. Above all, considering the selective separation property, permeability and heat resistance of the membrane, it should be an aromatic polyfunctional amine having 2 to 4 at least one of a primary amino group and a secondary amino group in one molecule. Is preferred. As such a polyfunctional aromatic amine, m-phenylenediamine, p-phenylenediamine, and 1,3,5-triaminobenzene are preferably used. Among them, it is more preferable to use m-phenylenediamine (hereinafter, m-PDA) from the viewpoint of easy availability and easy handling. These polyfunctional amines may be used alone or in combination of two or more. When using 2 or more types together, the said amine may be combined and the said amine and the amine which has at least 2 secondary amino groups in 1 molecule may be combined. Examples of the amine having at least two secondary amino groups in one molecule include piperazine and 1,3-bispiperidyl propane.

The polyfunctional acid halide means an acid halide having at least two carbonyl halide groups in one molecule. For example, as the trifunctional acid halide, trimesic acid chloride, 1,3,5-cyclohexanetricarboxylic acid trichloride, 1,2,4-cyclobutanetricarboxylic acid trichloride and the like can be mentioned. As the bifunctional acid halide, Aromatic bifunctional acid halides such as biphenyldicarboxylic acid dichloride, azobenzenedicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride and naphthalene dicarboxylic acid chloride, aliphatic bifunctional acid halides such as adipoyl chloride and sebacyl chloride, Examples thereof include alicyclic bifunctional acid halides such as cyclopentane dicarboxylic acid dichloride, cyclohexane dicarboxylic acid dichloride, and tetrahydrofuran dicarboxylic acid dichloride. Considering the reactivity with a polyfunctional amine, the polyfunctional acid halide is preferably a polyfunctional acid chloride. Further, in consideration of the selective separation property and heat resistance of the membrane, the polyfunctional acid chloride is more preferably a polyfunctional aromatic acid chloride having 2 to 4 carbonyl chloride groups in one molecule. Among them, trimesic acid chloride is more preferably used from the viewpoint of easy availability and easy handling. These polyfunctional acid halides may be used alone or in combination of two or more.

The thickness of the separation functional layer is usually in the range of 0.01 to 1 μm, preferably in the range of 0.1 to 0.5 μm in order to obtain sufficient separation performance and the amount of permeated water.

2. Method for Manufacturing Composite Semipermeable Membrane Next, a method for manufacturing the composite semipermeable membrane will be described. The manufacturing method includes a supporting film forming step and a separation functional layer forming step. The composite semipermeable membrane of the present invention is not limited to the manufacturing method and the method of forming each layer described in this document.

(2-1) Support Film Forming Step The support film forming step described below is, for example, as follows.
A step of dissolving a thermoplastic resin, which is a component of the porous support, in a good solvent for the thermoplastic resin to prepare a thermoplastic resin solution,
A step of applying a solution of a thermoplastic resin, which is a component of the porous support, to the base material; and a solubility of the thermoplastic resin in comparison with the good solvent of the thermoplastic resin of the base material coated with the solution. Is immersed in a small coagulation bath to coagulate the thermoplastic resin to form a three-dimensional network structure.

The type of thermoplastic resin that constitutes the porous support is as described above.

When the porous support is formed using a vinyl resin, the concentration of the vinyl resin (that is, the solid content concentration) of the thermoplastic resin solution is preferably 10% by weight or more, more preferably 13% by weight or more. %, and more preferably 15% by weight or more. The concentration of the vinyl resin in the thermoplastic resin solution is preferably 25% by weight or less, more preferably 20% by weight or less.

When the vinyl resin concentration is 10% by weight or more, the amine aqueous solution can be supplied from the pores formed by phase separation when forming the polyamide separation functional layer. Further, when the vinyl-based resin concentration is 25% by weight or less, a structure having water permeability can be obtained. Within this range, it is preferable from the viewpoint of performance and durability of the composite semipermeable membrane.

The temperature of the thermoplastic resin solution at the time of coating is preferably about 0 to 60°C, and when a vinyl resin is used, it is usually preferably within the range of 10 to 60°C. Within this range, the thermoplastic resin solution does not precipitate, and the organic solvent solution containing the thermoplastic resin is sufficiently impregnated between the fibers of the base material and then solidified. As a result, the porous support can be firmly bonded to the substrate by the impregnation.

The polymer contained in the thermoplastic resin solution can be appropriately adjusted in consideration of various characteristics such as strength characteristics, permeation characteristics, and surface characteristics of the supporting film to be manufactured.

The solvent contained in the thermoplastic resin solution may be the same solvent as long as it is a good polymer solvent, or a mixed solvent obtained by mixing different solvents. It can be adjusted appropriately in consideration of the strength characteristics of the supporting film to be produced and the impregnation of the substrate with the thermoplastic resin solution.

A good solvent is one that dissolves a polymeric material. Examples of the good solvent include N-methyl-2-pyrrolidone (NMP), tetrahydrofuran, dimethylsulfoxide, amides such as tetramethylurea/dimethylacetamide/dimethylformamide, lower alkyl ketones such as acetone/methylethylketone, trimethyl phosphate, γ- Examples thereof include esters such as butyrolactone, lactones and mixed solvents thereof.

Examples of the non-solvent of the polymer include water, hexane, pentane, benzene, toluene, methanol, ethanol, trichloroethylene, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butylene glycol, pentanediol, hexanediol, and low Examples thereof include aliphatic hydrocarbons such as polyethylene glycol having a molecular weight, aromatic hydrocarbons, aliphatic alcohols, and mixed solvents thereof.

Further, the thermoplastic resin solution may contain additives for controlling the pore size, porosity, hydrophilicity, elastic modulus and the like of the porous support. Additives for controlling the pore size and porosity include water, alcohols, polyethylene glycol, polyvinyl pyrrolidone, polyvinyl alcohol, water-soluble polymers such as polyacrylic acid or salts thereof, and further lithium chloride, sodium chloride, chloride. Examples thereof include inorganic salts such as calcium and lithium nitrate, formaldehyde, formamide, etc., but are not limited thereto. As the additive for adjusting the hydrophilicity and elastic modulus, various surfactants can be mentioned.

The viscosity of the thermoplastic resin solution is preferably 200 cP or less, more preferably 150 cP or less, still more preferably 130 cP or less, at the stage of coating on the substrate. The lower the viscosity of the thermoplastic resin solution, the faster the thermoplastic resin solution penetrates between the fibers of the substrate. On the other hand, when the viscosity is 40 cP or more, the solution stays on the base material, so that the exposed portion can be formed on the base material with an appropriate thickness, and the exposure of the base material can be suppressed. it can.

The application of the thermoplastic resin solution onto the substrate can be carried out by various coating methods, but pre-metering coating methods such as die coating, slide coating and curtain coating, which can supply an accurate amount of the coating solution, are preferably applied. It As the die coating, the slit die method is particularly preferably used.

By coating the base material with the thermoplastic resin solution as described above, the base material is impregnated with the thermoplastic resin solution. As a method for controlling the impregnation of the base material with the thermoplastic resin solution, for example, after applying the thermoplastic resin solution on the base material, the time until it is immersed in the coagulation bath is controlled, or the molecular weight of the thermoplastic resin is adjusted. The viscosity of the thermoplastic resin solution can be adjusted by changing it, or the viscosity can be adjusted by controlling the temperature or the concentration of the thermoplastic resin solution, and these methods can be combined.

After the thermoplastic resin solution is applied on the substrate, the time until it is immersed in the coagulation bath is usually preferably in the range of 0.1 to 5 seconds. If the time until immersion in the coagulation bath is within this range, the thermoplastic resin solution is sufficiently impregnated between the fibers of the base material and then solidified.

Specifically, when the porosity of the base material is 35% or more and 50% or less, the solution contains a vinyl resin as a thermoplastic resin, and the viscosity of the solution is 100 cP or less, a coagulation bath is applied after coating. The time until immersion may be 0.1 second or more and 1 second or less.

The coagulation bath may be one that does not dissolve the polymer, preferably contains a so-called non-solvent, and water is usually used. The temperature of the coagulation bath is preferably -20°C to 100°C, more preferably 10 to 30°C. When it is at most the above upper limit, vibration of the coagulation bath surface due to thermal motion is not intensified, and the smoothness of the film surface after formation is good. Further, if it is at least the above lower limit, a sufficient solidification rate is obtained, and the film forming property is good.

Next, the obtained supporting film is washed with pure water in order to remove the solvent remaining in the film. The temperature of pure water at this time is preferably 25 to 80°C.

Rubber particles may be added to the thermoplastic resin solution. The graft copolymer-containing rubbery particles can be produced by any polymerization method such as emulsion polymerization, suspension polymerization, bulk polymerization and solution polymerization. You may combine 2 or more types of these. Further, the charging method of each monomer is not particularly limited, initial batch charging, or in order to know the composition distribution of the copolymer, a part or all of the charged monomers are continuously or dividedly charged and polymerized. May be. The emulsion polymerization method or the bulk polymerization method is preferable, and the emulsion polymerization method is more preferable from the viewpoint that deterioration of the rubber component due to excessive heat history can be suppressed.

When the graft copolymer-containing rubbery particles are produced by an emulsion polymerization method, it is common to emulsion-polymerize the monomer mixture in the presence of the rubbery latex. The emulsifier used in the emulsion polymerization method is not particularly limited, and various surfactants can be used. As the surfactant, anionic surfactants such as carboxylate type, sulfate ester type and sulfonate type are preferably used. You may use 2 or more types of these.

Specific examples of the anionic surfactant include caprylate, caprate, laurate, mistyphosphate, palmitate, stearate, oleate, linoleate, linolenate and rosinate. , Behenate, castor oil sulfate, lauryl alcohol sulfate, other higher alcohol sulfate, dodecylbenzenesulfonate, alkylnaphthalenesulfonate, alkyldiphenyletherdisulfonate, naphthalenesulfonate condensate , Dialkyl sulfosuccinate, polyoxyethylene lauryl sulfate, polyoxyethylene alkyl ether sulfate, polyoxyethylene alkyl phenyl ether sulfate, and the like. Examples of the salt here include ammonium salts, potassium salts, sodium salts, alkali metal salts such as lithium salts, and the like. Among them, potassium salt or sodium salt of palmitic acid, stearic acid or oleic acid is preferably used.

The initiator used for the polymerization is not particularly limited, and peroxides, azo compounds, persulfates and the like are used.

Specific examples of the peroxide include benzoyl peroxide, cumene hydroperoxide, dicumyl peroxide, diisopropylbenzene hydroperoxide, t-butyl hydroperoxide, t-butylperoxyacetate, t-butylperoxybenzoate, t-butyl isopropyl carbonate, di-t-butyl peroxide, t-butyl peroctate, 1,1-bis(t-butylperoxy)3,3,5-trimethylcyclohexane, 1,1-bis(t -Butylperoxy)cyclohexane, t-butylperoxy-2-ethylhexanoate and the like.

Specific examples of the azo compound include azobisisobutyronitrile, azobis(2,4-dimethylvaleronitrile, 2-phenylazo-2,4-dimethyl-4-methoxyvaleronitrile, and 2-cyano-2-propylazo. Formamide, 1,1'-azobiscyclohexane-1-carbonitrile, azobis(4-methoxy-2,4-dimethylvaleronitrile), dimethyl 2,2'-azobisisobutyrate, 1-t-butylazo-2 -Cyanobutane, 2-t-butylazo-2-cyano-4-methoxy-4-methylpentane and the like can be mentioned.

Specific examples of the persulfate include potassium persulfate, sodium persulfate, ammonium persulfate and the like.

You may use 2 or more types of these initiators. In the emulsion polymerization method, potassium persulfate, cumene hydroperoxide and the like are preferably used. Also, the initiator can be used in a redox system.

A chain transfer agent may be used for the purpose of adjusting the degree of polymerization and the graft ratio of the rubber particles containing the graft copolymer. Specific examples of the chain transfer agent include mercaptans such as n-octyl mercaptan, t-dodecyl mercaptan, n-dodecyl mercaptan, n-tetradecyl mercaptan and n-octadecyl mercaptan, and terpenes such as terpinolene. You may use 2 or more types of these. Among these, n-octyl mercaptan and t-dodecyl mercaptan are preferably used.

By adding a coagulating agent to the graft copolymer latex produced by the emulsion polymerization method, the latex component can be coagulated and the rubber-containing graft copolymer can be recovered. An acid or a water-soluble salt is used as the coagulant. Specific examples of the coagulant include acids such as sulfuric acid, hydrochloric acid, phosphoric acid and acetic acid, calcium chloride, magnesium chloride, barium chloride, aluminum chloride, magnesium sulfate, aluminum sulfate, ammonium aluminum sulfate, potassium aluminum sulfate, sodium aluminum sulfate and the like. And water-soluble salts thereof. You may use 2 or more types of these. When coagulated with an acid, a method of recovering the rubber particles containing the graft copolymer after neutralizing the acid with an alkali can also be used. From the viewpoint of handleability, it is preferable that the graft copolymer-containing rubbery particle slurry obtained by coagulating the latex component is subjected to dehydration/washing/re-dehydration/drying steps to be in powder form.

(2-2) Step of forming separation functional layer Next, as an example of the step of forming the separation functional layer forming the composite semipermeable membrane, formation of the separation functional layer containing polyamide as a main component will be described. In the step of forming the polyamide separation functional layer, an aqueous solution containing the above-mentioned polyfunctional amine and an organic solvent solution immiscible with water containing the polyfunctional acid halide are used to carry out the interfacial polycondensation on the surface of the supporting membrane. By doing so, a polyamide skeleton can be formed.

The concentration of the polyfunctional amine in the polyfunctional amine aqueous solution is preferably 0.1% by weight or more and 20% by weight or less, more preferably 0.5% by weight or more and 15% by weight or less. Within this range, sufficient water permeability and salt and boron removal performance can be obtained. The polyfunctional amine aqueous solution may contain a surfactant, an organic solvent, an alkaline compound, an antioxidant and the like as long as they do not interfere with the reaction between the polyfunctional amine and the polyfunctional acid halide. The surfactant has the effects of improving the wettability of the surface of the supporting film and reducing the interfacial tension between the amine aqueous solution and the nonpolar solvent. The organic solvent may act as a catalyst for the interfacial polycondensation reaction, and if added, the interfacial polycondensation reaction may be performed efficiently.

In order to carry out the interfacial polycondensation on the support film, first, the above-mentioned polyfunctional amine aqueous solution is brought into contact with the support film. The contact is preferably carried out uniformly and continuously on the surface of the supporting film. Specifically, for example, a method of coating a polyfunctional amine aqueous solution on a support film and a method of immersing the support film in a polyfunctional amine aqueous solution can be mentioned. The contact time between the support film and the polyfunctional amine aqueous solution is preferably in the range of 5 seconds or more and 10 minutes or less, more preferably 10 seconds or more and 3 minutes or less.

After the polyfunctional amine aqueous solution is brought into contact with the support membrane, it is sufficiently drained so that no droplets remain on the membrane. By sufficiently draining, it is possible to prevent the removal performance of the composite semipermeable membrane from being deteriorated due to a defect of the remaining portion of the droplet after the formation of the composite semipermeable membrane. As a method of draining, for example, as described in Japanese Patent Application Laid-Open No. 2-78428, a method of vertically gripping a supporting film after contact with an aqueous solution of a polyfunctional amine to allow an excessive aqueous solution to flow down naturally, A method of blowing a stream of nitrogen or the like from an air nozzle to forcibly drain the liquid can be used. Further, after draining, the film surface can be dried to partially remove the water content of the aqueous solution.

Then, a water-immiscible organic solvent solution containing a polyfunctional acid halide is brought into contact with the support film after contact with the polyfunctional amine aqueous solution to form a crosslinked polyamide separation functional layer by interfacial polycondensation.

The concentration of the polyfunctional acid halide in the water-immiscible organic solvent solution is preferably in the range of 0.01% by weight or more and 10% by weight or less, and 0.02% by weight or more and 2.0% by weight or less. More preferably, it is within the range. When the polyfunctional acid halide concentration is 0.01% by weight or more, a sufficient reaction rate can be obtained, and when it is 10% by weight or less, the occurrence of side reactions can be suppressed. Furthermore, when an acylation catalyst such as DMF is contained in this organic solvent solution, interfacial polycondensation is promoted, which is more preferable.

The water-immiscible organic solvent is preferably one that dissolves the polyfunctional acid halide and does not destroy the support film, and may be one that is inert to the polyfunctional amine compound and the polyfunctional acid halide. .. Preferred examples include hydrocarbon compounds such as hexane, heptane, octane, nonane and decane.

The method of contacting the support membrane with the organic solvent solution containing the polyfunctional acid halide may be the same as the method of coating the support membrane with the polyfunctional amine aqueous solution.

In the interfacial polycondensation step, the support film should be sufficiently covered with a crosslinked polyamide thin film, and the contacted water-immiscible organic solvent solution containing the polyfunctional acid halide should remain on the support film. Is essential. Therefore, the time for carrying out the interfacial polycondensation is preferably 0.1 seconds or more and 3 minutes or less, and more preferably 0.1 seconds or more and 1 minute or less. When the time for carrying out the interfacial polycondensation is 0.1 seconds or more and 3 minutes or less, the support film can be sufficiently covered with the crosslinked polyamide thin film, and the organic solvent solution containing the polyfunctional acid halide is used as the support film. Can be held on.

After forming the polyamide separation functional layer on the support membrane by interfacial polycondensation, the excess solvent is drained off. As a method of draining, for example, a method of holding the film in the vertical direction and allowing the excess organic solvent to flow down naturally is removed.

Further, in the present invention, the formed polyamide separation functional layer may be brought into contact with an amine reactive reagent. By this step, the amount of amino groups in the polyamide is reduced, so that the chemical resistance of the composite semipermeable membrane can be further improved. Examples of the amine reactive reagent include acid halides, acid anhydrides, esters, nitrosyl compounds, nitrous acid and its salts, hypochlorite and the like. In particular, it is preferable to contact with a nitrosyl compound which reacts with a primary amino group in the polyamide separation functional layer to form a diazonium salt or a derivative thereof, nitrous acid and a salt thereof.

The method for contacting the polyamide separation functional layer with a compound which reacts with a primary amino group to form a diazonium salt or a derivative thereof is not particularly limited as long as the separation functional layer surface and the above compound are in contact, and various known methods are used. Can be used.

In the present invention, the compound that reacts with a primary amino group to form a diazonium salt or a derivative thereof is preferably used as an aqueous solution. Since an aqueous solution of a nitrosyl compound or nitrous acid easily generates a gas and decomposes, it is preferable to sequentially generate nitrous acid by, for example, reacting a nitrite with an acidic solution. Generally, nitrite reacts with hydrogen ions to produce nitrous acid, but it is efficiently produced at 20° C. when the pH of the aqueous solution is 7 or less, preferably 5 or less, more preferably 4 or less. Among them, an aqueous solution of sodium nitrite reacted with hydrochloric acid or sulfuric acid in an aqueous solution is particularly preferable because of its easy handling.

The concentration of nitrous acid or nitrite in a compound solution which reacts with a primary amino group to form a diazonium salt or a derivative thereof is preferably 0.01 to 1% by weight at 20°C. If the concentration is lower than 0.01% by weight, a sufficient effect cannot be obtained, and if the concentration of nitrous acid or nitrite is higher than 1% by weight, it becomes difficult to handle the solution.

The temperature of the nitrous acid aqueous solution is preferably 15°C to 45°C. If the temperature is lower than 15°C, the reaction takes a long time, and if the temperature exceeds 45°C, the decomposition of nitrous acid is rapid and the handling is difficult. The contact time between the nitrous acid aqueous solution and the primary amino group may be any time as long as the diazonium salt is formed. High concentration allows treatment in a short time, but low concentration requires long-term contact. When the diazonium salt is formed at a low concentration for a long time to form the diazonium salt, the generated diazonium salt reacts with water before reacting with the reactive compound. Therefore, it is preferable to perform the treatment at a high concentration for a short time. For example, it is preferable to perform the treatment for 30 seconds to 10 minutes with a 2,000 mg/liter nitrous acid aqueous solution.

The composite semipermeable membrane thus obtained can be used as it is, but it is preferable to hydrophilize the surface of the membrane with an alcohol-containing aqueous solution or an alkaline aqueous solution before use.

3. Use of Composite Semipermeable Membrane The composite semipermeable membrane described above is used for raw water flow path materials such as plastic nets, permeate flow path materials such as tricots, and if necessary, a film for increasing pressure resistance. It is wound around a cylindrical water collecting pipe having holes, and is suitably used as a spiral type composite semipermeable membrane element. Further, the elements can be connected in series or in parallel and housed in a pressure vessel to form a composite semipermeable membrane module.

The above-mentioned composite semipermeable membrane, its element, and module can be combined with a pump for supplying raw water to them, a device for pretreating the raw water, and the like to form a fluid separation device. By using this separation device, raw water can be separated into permeated water such as drinking water and concentrated water that has not permeated through the membrane to obtain water suitable for the purpose.

The higher the operating pressure of the fluid separation device, the higher the salt removal rate, but the energy required for operation also increases, and considering the durability of the composite semipermeable membrane, the treated water is applied to the composite semipermeable membrane. The operating pressure for permeation is preferably 0.2 MPa or more and 5.0 MPa or less. When the feed water temperature is higher, the salt removal rate is lower, but as the feed water temperature is lower, the membrane permeation flux is also reduced. Therefore, the feed water temperature is preferably 5° C. or higher and 45° C. or lower. In addition, when the feed water pH is high, in the case of feed water with a high salt concentration such as seawater, scales such as magnesium may be generated, and there is a concern that the membrane may deteriorate due to high pH operation. Driving is preferred.

Examples of raw water treated by the composite semipermeable membrane include liquid mixtures containing 500 mg/L to 100 g/L TDS (Total Dissolved Solids) such as seawater, brackish water, and wastewater. Generally, TDS refers to the total amount of dissolved solids and is represented by "mass/volume", but it may be represented by "weight ratio" by regarding 1 L as 1 kg. By definition, a solution filtered through a 0.45 micron filter can be evaporated at a temperature of 39.5-40.5° C. and calculated from the weight of the residue, but more simply converted from practical salt.

<Note>
In this document, the thickness of each layer and film means an average value unless otherwise specified. Here, the average value represents an arithmetic mean value. That is, the thickness of each layer and the film is obtained by calculating the average value of the thicknesses at 20 points measured at 20 μm intervals in the direction (plane direction of the film) orthogonal to the thickness direction by cross-sectional observation.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

<1. Base material porosity>
As described above, first, the apparent volume (cm ³ ) of the dried substrate is measured. Next, pure water is added to the base material and the weight is measured. The value obtained by subtracting the dry weight of the base material from the base material containing water, that is, the weight of water that has entered the voids in the base material (g: water volume cm ³ ) is calculated, and the apparent volume of the base material is calculated. The porosity was obtained as the divided percentage (%).

<2. Weight of Support Membrane, Composite Substrate, Substrate, Porous Support in Substrate>
Each support membrane was cut to obtain 5 sections. Each section was dried at 130° C. for 3 hours, and the weight after drying was measured.

An aluminum tape having high adhesiveness (AT-75 manufactured by Nitto Denko Corporation) was attached to the surface of the porous support of each section after the measurement. By using a Tensilon tester (RTG-1210), the aluminum tape was pulled at a gripping moving speed of 10 mm/min at a peeling direction of 180° at 25°C to remove the porous support existing on the substrate from the substrate. Peeled off. Thus, a composite substrate (portion indicated by "31" in FIG. 1) composed of the substrate and the resin inside the substrate was obtained. This was dried at 130° C. for 3 hours, and the weight of the dried composite substrate was measured.

Next, the dried composite substrate was immersed in a DMF solution for 3 hours or more to dissolve and remove the porous support inside the substrate. In this way, only the base material was taken out from the composite base material. Then, this base material was washed with pure water and then dried at 130° C. for 3 hours. The weight of the substrate thus obtained was measured.

The weight of the porous support inside the substrate was determined by subtracting the weight of the substrate from the weight of the composite substrate.

The above operation was performed on the five sections, and the obtained value was divided by the area of the sample to calculate the basis weight of each constituent element per unit area of the supporting film. In this way, five values were obtained for the weight of each constituent element in each supporting film, and thus the arithmetic mean was calculated. The obtained arithmetic mean value is shown in the table as weight (basis weight) per area of the supporting film (that is, per area of the substrate) for each element.

<3. Ratio B/A of substrate weight A and porous support weight B inside the substrate B/A>
<2. B/A was calculated from the weight A of the base material and the weight B of the porous support inside the base material, which were obtained by the same operation as in <>.

<4. Thickness of support membrane, substrate, impregnated portion of substrate on porous support, and thickness of porous support on substrate>
Each support membrane was cut to obtain 5 sections. Ten small sample pieces were taken from each section, and the cross section of the sample was photographed with a scanning electron microscope at 100 to 1000 times. The thickness of the support film was measured in each image obtained by photographing. The arithmetic mean was calculated from the 50 values obtained for one support film, and this is shown in the table as the thickness of the support film.

In addition, another 5 slices were obtained from each supporting membrane, and the above-mentioned <2. By the same operation as described above, a section of five composite base materials (portion indicated by “31” in FIG. 1) was obtained from one support film.

Ten small piece samples were taken from each section. A cross section of the sample was photographed with a scanning electron microscope at 100 to 1000 times. In each image obtained by photographing, the thickness of the base material and the thickness of the resin impregnated from the surface layer (front surface) to the back surface of the base material were measured. In this way, 50 values were obtained for each of the thickness of the substrate and the impregnation thickness in one support film. The arithmetic mean value was calculated from these values, and the first decimal place was rounded off. The values thus obtained are shown in the table as the thickness of the base material of each supporting film and the thickness of the impregnated portion of the porous support into the inside of the base material.

The thickness of the porous support on the base material was calculated from the thickness of the above-mentioned support film and the thickness of the base material.

<5. Desalination rate (TDS removal rate)>
The feed water (NaCl concentration 500 ppm) adjusted to a temperature of 25° C. and pH 7 was fed to the composite semipermeable membrane at an operating pressure of 0.5 MPa to perform a filtration treatment for 3 hours. The obtained permeated water was used for measuring the TDS removal rate.

Practical salinity was obtained by measuring the electric conductivity of feed water and permeated water with an electric conductivity meter manufactured by Toa Denpa Kogyo Co., Ltd. From the TDS concentration obtained by converting this practical salt content, the desalination rate, that is, the TDS removal rate was calculated by the following formula.

TDS removal rate (%)=100×{1-(TDS concentration in permeated water/TDS concentration in feed water)}
<6. Transmembrane flux>
The amount of permeated water obtained by the filtration treatment for 3 hours was converted into the amount of permeated water (cubic meter) per 1 square meter of the membrane area per day and expressed as a membrane permeation flux (m ³ /m ² /day).

<7. Durability>
The peel strength was measured as durability by a Tensilon tester (RTG-1210). Specifically, a new membrane sample that had not undergone pressure application or water passage was cut and dried at 130° C. for 3 hours to obtain 10 pieces. For each section, an aluminum tape having high adhesiveness (AT-75 manufactured by Nitto Denko Corporation) was attached to the surface of the porous support, and the aluminum tape was peeled in a peeling direction of 180 at a gripping moving speed of 10 mm/min at 25°C. The maximum value of the peeling force was obtained by performing peeling at °. The peel strength was obtained by calculating the average of the 10 values obtained for each sample. When the peel strength measured in this way is 4.0 N/25 mm or more, it is considered to have very high durability.

<8. Measurement of Abundance Ratio and Content of Vinyl Cyanide Monomer>
A support membrane (area: 0.1 m ² ) washed with pure water at 70° C. for 1 hour or more is air-dried at 25° C. and immersed in 200 ml of acetone at 25° C. for 20 hours to dissolve the support layer portion to obtain a solution It was Next, the obtained solution was filtered through a metal mesh (wire diameter 0.03 mm, mesh 300, manufactured by Kansai Wire Mesh Co., Ltd.) to remove the base material. Then, cyclohexane was gradually added to the obtained filtrate, and the addition was stopped when it became cloudy. This cloudy solution was centrifuged at 8800 rpm with a centrifuge (KUBOTA 6900). p. m (12,300G), after centrifugation at 5° C. for 40 minutes, the supernatant was separated to obtain an insoluble matter. The insoluble matter was dried under reduced pressure at 80° C. for 5 hours, and the weight was measured. Then, the insoluble matter was analyzed by the total reflection infrared absorption spectrum method, and the abundance ratio of the vinyl cyanide-based monomer was determined from the intensity ratio of the following peaks appearing in the obtained spectrum.
Derived from aromatic vinyl-based monomer: peak at 1605 cm ^-1 attributable to vibration of benzene nucleus Derived from vinyl-cyanide-based monomer: peak at 2240 cm ^-1 attributed to -CN stretching Further in separated supernatant liquid 5 mL cyclohexane was added, and an insoluble matter was obtained from the white turbid liquid by the same method. The above operation was repeated, and 5 mL of cyclohexane was added until white turbidity disappeared, and the abundance ratio and weight of the insoluble vinyl cyanide-based monomer in each addition amount of cyclohexane were measured. By the above method, the weight of the polymer having a vinyl cyanide-based monomer abundance of 0.9 or more is determined, and the polymer having a vinyl cyanide-based monomer abundance of 0.9 or more is calculated from the total weight of the insoluble matter. Was determined.

FT-IR: Shimadzu IR Tracker-100
Accessories: Czitek MicroATR Vision
Crystal: made of germanium Measurement conditions: resolution 4 cm ^-1 , scan number 64 times <9. Measurement of Weight-Average Molecular Weight Mw of THF-soluble component in porous support>
The support membrane or composite semipermeable membrane (area 0.1 m ² ) washed with pure water at 70° C. for 1 hour or more is air-dried and immersed in THF (200 ml) at 25° C. for 4 hours to remove the porous support portion. It melt|dissolved and the thermoplastic resin solution was obtained (250 ml container was used at the time of immersion). Next, the obtained solution was filtered through a metal mesh (wire diameter 0.03 mm, mesh 300, manufactured by Kansai Wire Mesh Co., Ltd.) to remove the base material and the functional layer. Subsequently, the obtained filtrate was centrifuged at 8800 rpm with a centrifugal separator (KUBOTA 6900). p. m (12,300G), centrifuged at 5° C. for 40 minutes, and the supernatant was collected. The weight of the obtained supernatant was measured using GPC under the following conditions to calculate the weight average molecular weight (Mw). In addition, polystyrene was used for the calibration curve.

Solvent: Tetrahydrofuran Device: Waters 2695 Separation Module Column: Tosoh TSKgel Super IIZM-M, Super IIZM-N, Super HZ-L (3 in total)
Column temperature: 40°C
Solvent flow rate: 0.35 ml/min Detector: Waters 2414 differential refractive index detector Materials used in each Example and Comparative Example are shown below.

(Production Example 1) Suspension polymerization medium (methyl methacrylate/acrylamide copolymer)
20 parts by weight of methyl methacrylate, 80 parts by weight of acrylamide, 0.3 parts by weight of potassium persulfate, and 1800 parts by weight of ion-exchanged water were charged into the reactor, and the gas phase in the reactor was replaced with nitrogen gas. The temperature was maintained at 70° C. with good stirring, and the polymerization was terminated when the polymerization rate reached 99% to obtain an aqueous solution of a copolymer of methyl methacrylate and acrylamide. To this aqueous solution, 35 parts by weight of sodium hydroxide and 15000 parts by weight of ion-exchanged water were added to obtain 0.6% by weight of an aqueous solution of a copolymer of methyl methacrylate and acrylamide. After stirring at 70° C. for 2 hours for saponification, the mixture was cooled to room temperature to obtain an aqueous solution of a suspension polymerization medium.

(Production Example 2) Vinyl copolymer (A-1)
A 20 L autoclave made of stainless steel was charged with 6 parts by weight of the methyl methacrylate/acrylamide copolymer aqueous solution produced in Production Example 2 and 150 parts by weight of pure water and stirred at 400 rpm, and the system was replaced with nitrogen gas. Next, a mixed solution of 72 parts by weight of styrene and 28 parts by weight of acrylonitrile, a total of 100 parts by weight, 0.40 parts by weight of t-dodecyl mercaptan, and 0.4 parts by weight of 2,2′-azobisisobutyronitrile was stirred. Was added to the system and the temperature was raised to 60° C. to initiate polymerization. After the polymerization was started, the reaction temperature was raised to 65°C over 30 minutes and then raised to 100°C over 3 hours. Then, the system was cooled to room temperature, and the vinyl copolymer A was obtained by separating, washing and drying the polymer. The weight average molecular weight Mw of this vinyl copolymer A was 100,000.

(Production Example 3) Vinyl copolymer (A-2)
A vinyl-based copolymer B was obtained in the same manner as in Production Example 2 except that t-dodecyl mercaptan was changed to 0.30 parts by weight. The weight average molecular weight Mw of this vinyl copolymer B was 140,000.

(Production Example 4) Vinyl copolymer (A-3)
A vinyl-based copolymer C was obtained in the same manner as in Production Example 2 except that t-dodecyl mercaptan was changed to 0.20 part by weight. The weight average molecular weight Mw of this vinyl-based copolymer C was 180,000.

(Production Example 5) Graft copolymer-containing rubber particles (B)
150 parts by weight of pure water, 0.5 parts by weight of glucose, 0.5 parts by weight of sodium pyrophosphate, 0.005 parts by weight of ferrous sulfate and 60 parts by weight of polybutadiene latex (weight average particle diameter 350 nm), in a reactor purged with nitrogen. Part (solid matter conversion) was charged, and the temperature in the reactor was raised to 65° C. while stirring. The polymerization was initiated when the internal temperature reached 65° C., and 28 parts by weight of styrene, 12 parts by weight of acrylonitrile, and 0.2 parts by weight of t-dodecyl mercaptan were continuously added over 4 hours. At the same time, an aqueous solution containing 0.2 part by weight of cumene hydroperoxide and potassium oleate was continuously added over 7 hours to complete the reaction. Then, it is added to a 0.3 wt% dilute sulfuric acid aqueous solution at a temperature of 90° C. to agglomerate, neutralized with an aqueous sodium hydroxide solution, and washed, filtered, dehydrated, and dried, to contain a powdery graft copolymer. Rubber particles A were obtained. The graft ratio of the rubber particles A containing the graft copolymer was 41%. Further, in the acetone-soluble component of the rubber particles A containing the graft copolymer, the ratio of the acrylonitrile-derived component and the styrene-derived component was styrene:acrylonitrile=72:28 in the total 100% by weight of both components.

<Example 1>
The graft copolymer-containing rubbery particles B obtained in Production Example 5 and the vinyl copolymer A-1 obtained in Production Example 2 were added to DMF at a ratio shown in Table 1 so as to be 16% by weight. The resin solution was prepared by heating and holding at 90° C. for 3 hours while stirring.

The prepared resin solution was cooled to 25° C. and filtered using a metal mesh (wire diameter 0.03 mm, mesh 400, manufactured by Kansai Wire Mesh Co., Ltd.). Then, the support film was obtained by casting on a long-fiber non-woven fabric made of polyethylene terephthalate fiber, immediately immersing it in pure water (for 1 second or less) and washing for 5 minutes.

The obtained support film was immersed in a 2.0 wt% aqueous solution of m-phenylenediamine (m-PDA) adjusted with pure water for 10 seconds, and then slowly pulled up so that the film surface became vertical. After removing excess aqueous solution from the surface of the supporting film by blowing nitrogen from an air nozzle, the supporting film is placed so that the film surface becomes horizontal, and a 25°C n-decane solution containing 0.07% by weight of trimesic acid chloride is formed into a film. It was applied so that the surface was completely wet.

After standing for 30 seconds, the membrane surface was held vertically for 1 minute to remove excess solution from the membrane, drained, and dried at 25° C. using a blower. Then, the composite semipermeable membrane was obtained by washing with pure water at 70° C. for 5 minutes. The membrane performance of the obtained composite semipermeable membrane is shown in Table 1.

<Example 2>
A composite semipermeable membrane was obtained in the same manner as in Example 1 except that the vinyl copolymer was changed to the proportion shown in Table 1. The membrane performance of the obtained composite semipermeable membrane is shown in Table 1.

<Example 3>
A composite semipermeable membrane was obtained in the same manner as in Example 1, except that the rubber particles containing the graft copolymer were removed and the vinyl copolymer was changed to the proportion shown in Table 1. The membrane performance of the obtained composite semipermeable membrane is shown in Table 1.

<Examples 4 to 5>
A composite semipermeable membrane was obtained in the same manner as in Example 1, except that the long fiber non-woven fabric made of polyethylene terephthalate fiber was changed to the long fiber non-woven fabric having the thickness and porosity shown in Table 1. The membrane performance of the obtained composite semipermeable membrane is shown in Table 1.

<Example 6>
A composite semipermeable membrane was obtained in the same manner as in Example 1, except that the long fiber nonwoven fabric made of polyethylene terephthalate fiber was changed to the short fiber nonwoven fabric having the thickness and porosity shown in Table 1. The membrane performance of the obtained composite semipermeable membrane is shown in Table 1.

<Example 7>
In Example 1, except that the thermoplastic resin was changed to ABS resin (TOYOLAC (registered trademark) 100), and the long-fiber non-woven fabric made of polyethylene terephthalate fiber was changed to the long-fiber non-woven fabric having the thickness and porosity shown in Table 1. A composite semipermeable membrane was obtained in the same manner as in Example 1. The membrane performance of the obtained composite semipermeable membrane is shown in Table 1.

<Comparative Example 1>
A composite semipermeable membrane was obtained in the same manner as in Example 1 except that the vinyl copolymer was changed to the composition shown in Table 1. The membrane performance of the obtained composite semipermeable membrane is shown in Table 2.

<Comparative example 2>
A composite semipermeable membrane was obtained in the same manner as in Example 7, except that the concentration of the thermoplastic resin was changed to 20 wt %. The membrane performance of the obtained composite semipermeable membrane is shown in Table 2.

<Comparative example 3>
A composite semipermeable membrane was obtained in the same manner as in Example 1 except that polysulfone (UDEL (registered trademark) P-3500 manufactured by Solvay Advanced Polymers) was used as the thermoplastic resin. The membrane performance of the obtained composite semipermeable membrane is shown in Table 2.

<Comparative example 4>
A composite semipermeable membrane was obtained in the same manner as in Comparative Example 3 except that the long fiber nonwoven fabric made of polyethylene terephthalate fiber in Comparative Example 3 was changed to a short fiber nonwoven fabric having the thickness and porosity shown in Table 2. The membrane performance of the obtained composite semipermeable membrane is shown in Table 2.

<Comparative Example 5>
A composite semipermeable membrane was obtained in the same manner as in Comparative Example 3 except that the concentration of the thermoplastic resin was changed to the concentration shown in Table 2 in Comparative Example 4. The membrane performance of the obtained composite semipermeable membrane is shown in Table 2.

From Examples 1 to 7, a composite semipermeable membrane having unprecedented durability (peel strength) was obtained by setting the composition of the specific thermoplastic resin.

Particularly in Example 1, by lowering the weight average molecular weight of the thermoplastic resin to 100,000, the viscosity of the resin solution was lowered, and the impregnation of the nonwoven fabric with the resin was improved, so that the durability (peeling strength) was improved. ..

Further, in Comparative Example 2, since the concentration of the thermoplastic resin was high, the viscosity of the resin solution was increased, and the impregnation of the nonwoven fabric with the resin was reduced, so that the durability (peel strength) was only at a normal level.

Further, in Comparative Examples 3 and 4, polysulfone was used as the thermoplastic resin, but the viscosity of the resin solution was high, the non-woven fabric was not impregnated with the resin, and the durability (peel strength) was only at a normal level.

Further, in Comparative Example 5, although the resin concentration of polysulfone was lowered, the obtained support film was brittle and the durability (peel strength) was low because the resin solid content was small.

The composite semipermeable membrane of the present invention can be suitably used particularly for desalination of brine and seawater.

1: Composite semipermeable membrane 2: Supporting membrane 3: Base material 4: Porous support 40: Porous support existing outside the base material 41: Porous support existing inside the base material 31: Composite base material 5 : Separation function layer

Claims (4)

A composite semipermeable membrane comprising a support membrane including a base material and a porous support, and a separation functional layer provided on the porous support,
The porous support contains a thermoplastic resin,
The weight average molecular weight (Mw) of the thermoplastic resin is 140,000 or less,
A composite semipermeable membrane having a peel strength of 3.0 N/25 mm or more, which is measured by peeling the porous support from the substrate at a peeling direction of 180° at a temperature of 25° C. for 10 mm/min. The composite semipermeable membrane according to claim 1, wherein the thermoplastic resin is a vinyl-based copolymer. The composite semipermeable membrane according to claim 1, wherein the thermoplastic resin is a polymer of a vinyl cyanide-based monomer and an aromatic vinyl-based monomer. Applying a solution containing a thermoplastic resin and having a viscosity of 150 cP or less to a substrate,
Forming a porous support by solidifying the thermoplastic resin in the solution;
The method for producing a composite semipermeable membrane according to claim 1, wherein a separation functional layer is formed on the porous support.

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