JP2014151241A - Composite semipermeable membrane and production method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite semipermeable membrane having high water permeability without reducing separability and a production method of the same.SOLUTION: In a composite semipermeable membrane comprising: a base material; a porous support layer made on the base material; and a separation functional layer being made on the porous support layer and having a pleat structure including a convex part and a concave part and being continuously repeated, n, n, n, n, nand nin n-nsatisfy equation (1): (n+n+n)/(n+n+n)≥1.05 (1) when the number of the convex part per the length of 2.0 μm in the 12 direction of the separation functional layer is n, n, n-n, nand nin descending order.

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 brine or seawater desalination.

  Regarding the separation of mixtures, there are various techniques for removing substances (eg, salts) dissolved in a solvent (eg, water), but in recent years, the use of membrane separation methods has expanded as a process for saving energy and resources. doing. Membranes used in membrane separation methods include microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, and reverse osmosis membranes. These membranes can be used for beverages such as seawater, brine, and water containing harmful substances. It is used to obtain water, to manufacture industrial ultrapure water, to treat wastewater, to recover valuable materials.

  Most of the reverse osmosis membranes and nanofiltration membranes currently on the market are composite semipermeable membranes, which have an active layer in which a gel layer and a polymer are cross-linked on a support membrane, and monomers are polycondensed on the support membrane. There are two types, one with an active layer. In particular, a composite semipermeable membrane obtained by coating a support membrane with a separation functional layer made of a crosslinked polyamide obtained by polycondensation reaction of a polyfunctional amine and a polyfunctional acid halide has water permeability and solute removal properties. Widely used as a high separation membrane.

  A factor that affects the performance of the composite semipermeable membrane is a pleat structure formed on the surface of the separation functional layer. Regarding the relationship between the membrane performance and the pleat structure, it has been proposed to increase the substantial surface area by extending the height of the pleats and improve the water permeability (Patent Documents 1, 2, and 3).

Japanese Patent Laid-Open No. 9-19630 JP-A-9-85068 JP 2001-179061 A

However, since the separation performance such as the water permeability and salt removal rate of the composite semipermeable membrane is in a trade-off relationship, while higher water permeability is required, it is possible to improve the water permeability without reducing the separation performance. This is difficult, and there is room for improvement because the conventional technology may not sufficiently satisfy the requirement.
Then, an object of this invention is to provide the composite semipermeable membrane which can implement | achieve high water-permeable performance, and its manufacturing method, without reducing separability.

In order to achieve the above object, the present invention has the following configurations <1> to <4>.
<1> Separation functional layer having a pleat structure on the surface, including a base material, a porous support layer provided on the base material, and a pleated structure provided on the porous support layer and including continuously repeated convex portions and concave portions A composite semipermeable membrane comprising:
Draw a circle with a diameter of 3 cm around a randomly selected location on the separation functional layer,
Draw a line segment in 12 directions that passes through the center of the circle and divides the circle into 24 equal parts,
A section having a length of 2.0 μm in the horizontal direction is selected along one line segment among the 12 direction line segments, and
Observe the unevenness of the pleated structure of the section using an electron microscope, measure the 10-point average surface roughness of the section,
Obtain the number of protrusions having a height of 1/5 or more of the 10-point average surface roughness per section,
Further, similarly for the other 11 directions among the 12 directions, respectively, the number of convex portions per each section is obtained,
When the number of convex portions in the 12 directions is n ₁ , n ₂ , n ₃ ... N ₁₀ , n ₁₁ and n _{12 in the} descending order,
Composite _{semipermeable} membrane _{n 1, n 2, n 3} , n 10, n 11 and _{n 12} of said _n 1 _{~n 12} is characterized by satisfying the following equation (1).
(N ₁ + n ₂ + n ₃ ) / (n ₁₀ + n ₁₁ + n ₁₂ ) ≧ 1.05 (1)
<2> The composite semipermeable membrane according to <1>, wherein n ₁ , n ₂ , n ₃ , n ₁₀ , n _11, and n ₁₂ satisfy the following formula (2):
1.10 ≦ (n ₁ + n ₂ + n ₃ ) / (n ₁₀ + n ₁₁ + n ₁₂ ) ≦ 3.00 (2)
<3> The composite semipermeable membrane according to <1> or <2>, wherein the base material is a long-fiber nonwoven fabric containing polyester as a main component.
<4> Separation functional layer on the surface having a pleat structure including a base, a porous support layer provided on the base, and a convex part and a concave part provided on the porous support layer and continuously repeated A method for producing a composite semipermeable membrane according to any one of the above <1> to <3>, comprising a step of uniaxially stretching a membrane comprising:

  According to the present invention, a composite semipermeable membrane having high water permeability while maintaining the separation performance is realized. When the composite semipermeable membrane is used as a filtration membrane, energy saving can be achieved in desalination or ultrapure water production. It becomes.

FIG. 1 is a drawing schematically showing an example of measurement locations of the number of convex portions in 12 directions on a separation functional layer. FIG. 2 is a drawing schematically showing a method for measuring the 10-point average surface roughness of sections in the separation functional layer. FIG. 3 is a drawing schematically showing the structural change of the protrusions before and after stretching of the separation functional layer.

1. Composite semipermeable membrane The composite semipermeable membrane according to the present invention includes a support film including a base material and a porous support layer formed on the base material, and a convex portion and a concave portion formed on the porous support layer. And a separation functional layer having a pleated structure that is continuously repeated on the surface.
The separation functional layer has substantially separation performance, and the support membrane does not substantially have separation performance of ions or the like, and can give strength to the separation functional layer.

(1-1) Separation functional layer The inventors of the present invention focused on the structure of the convex portion on the surface of the separation functional layer and conducted intensive studies. As a result, it has been found that in the conventional composite semipermeable membrane, there is a contact portion with the adjacent convex portion as shown in the left of FIG. 3 in the convex portion after the separation functional layer is formed. In the contact portion, water and the separation functional layer do not come into contact with each other, so that it does not function effectively as a reverse osmosis membrane, and the entire surface of the separation functional layer is not used up effectively. Therefore, in the present invention, the composite semipermeable membrane is uniaxially stretched or the like to reduce the contact area of the projections (folds) of the separation functional layer in one direction, and to enlarge the effective membrane area (right in FIG. 3), It has been found that high water permeability can be achieved while maintaining the separation ability.

  The composite semipermeable membrane according to the present invention has anisotropy in the number of convex portions per 2.0 μm on the surface of the separation functional layer (hereinafter sometimes simply referred to as “linear density”), for example, uniaxial stretching In this case, the linear density of the protrusions in the stretching direction is smaller than the linear density in the direction perpendicular to the stretching. The anisotropy of the linear density will be described in detail below.

The separation functional layer in the present invention has a convex portion having a specific structure. That is, in the convex portion, when the values of the linear densities n _{1 to} n _{12 in} 12 directions are obtained according to the following procedures (a) to (h), n _{1 to} n ₁₂ satisfy the formula (1). And
(N ₁ + n ₂ + n ₃ ) / (n ₁₀ + n ₁₁ + n ₁₂ ) ≧ 1.05 (1)
[How to obtain values of linear densities n _{1 to} n ₁₂ ]
(A) A circle having a diameter of 3 cm is drawn around a randomly selected place on the separation functional layer.
(B) Draw 12 line segments that pass through the center of the circle and divide the circle into 24 equal parts.
(C) A section having a length of 2.0 μm in the horizontal direction is selected along one line segment among the 12 line segments.
(D) The unevenness of the pleated structure in the section is observed with an electron microscope.
(E) The 10-point average surface roughness of the section is measured by the observation.
(F) A value of the number of convex portions having a height of 1/5 or more of the 10-point average surface roughness per section is obtained.
(G) Further, the above procedures (c) to (f) are similarly repeated in the other 11 directions among the 12 directions, and the values of the number of convex portions per each division are obtained.
(H) The numbers in the 12 directions are set to n ₁ , n ₂ , n ₃ ... N ₁₀ , n _11, and n _{12 in} descending order.
In this specification, (n ₁ + n ₂ + n ₃ ) / (n ₁₀ + n ₁₁ + n ₁₂ ) is referred to as anisotropy of linear density.

The method for obtaining the linear density is shown below.
As shown in FIG. 1, when a circle with a diameter of 3 cm drawn around a randomly selected place on the separation functional layer is divided into 24 equal parts, 12 line segments passing through the radius of the circle are equal to 15 degrees. Line up at intervals. One line segment is selected from the 12 direction line segments, and one arbitrary position is selected on the selected line segment.
The surface shape of the selected portion is observed in the range of 2.0 μm along the selected line segment direction, and the line density in the selected line segment direction on the surface of the separation functional layer is calculated using the method described later. be able to.

The linear density in the 12 directions of the separation functional layer in the present invention is calculated using a convex portion having a height of 1/5 or more of the 10-point average surface roughness. Here, the 10-point average surface roughness is a value obtained by the following calculation method.
A cross section perpendicular to the film surface is observed with an electron microscope. The depth of the cross section to be observed (the direction perpendicular to the film surface) is not particularly limited as long as the horizontal length of the film surface is 2.0 μm or more. From the cross-sectional image, a surface shape 1 of the separation functional layer having a pleated structure (curve) in which convex portions and concave portions are continuously repeated is observed on the surface (FIG. 2). About this curve, the roughness curve defined based on ISO4287: 1997 is calculated | required. Then, a cross-sectional image is extracted with a width of 2.0 μm as one section in the direction of the average line of the roughness curve (FIG. 2).
The average line is a straight line defined based on ISO 4287: 1997, and is drawn so that the total area of the region surrounded by the average line and the roughness curve is equal above and below the average line in the measurement length. Straight line that is parallel to the horizontal direction.

  In the extracted cross-sectional image of the section having a width of 2.0 μm, the height of the convex portion (H) and the depth of the concave portion (D) in the separation functional layer are measured using the average line as the reference line 2. The average value of the absolute values of the heights H1 to H5 of the five convex portions from the highest convex portion (H1) to the fifth height (H5) gradually decreasing, and the deepest concave portion (D1 ) To the fifth depth (D5), the average value of the absolute values of the depths D1 to D5 of the five recesses is calculated and the absolute value of the two average values obtained is calculated. The sum of is calculated. The sum value thus obtained is the 10-point average surface roughness.

The height of the convex portion and the depth of the concave portion of the separation functional layer can be analyzed using an electron microscope such as a transmission electron microscope (TEM) or a scanning electron microscope (SEM). For example, after embedding a composite semipermeable membrane sample with an epoxy resin, the composite semipermeable membrane sample is dyed with osmium tetroxide or ruthenium tetroxide, preferably osmium tetroxide. Thin sections are prepared and observed using a transmission electron microscope at an acceleration voltage of 50 to 200 kV. As the transmission electron microscope, an electron microscope such as Hitachi, H7100FA can be used.
The observation magnification is preferably 5,000 to 100,000 times, and preferably 20,000 to 100,000 times for obtaining the height of the convex portion and the depth of the concave portion of the separation functional layer. In order to obtain the height of the convex portion and the depth of the concave portion of the separation functional layer, it can be directly measured with a scale or the like in consideration of the observation magnification from the obtained electron micrograph.

  For the composite semipermeable membrane, by counting the number of convex portions that are 1/5 or more of the 10-point average surface roughness obtained above, the number of convex portions per unit length, that is, the line of the convex portion The density can be determined. Here, since each cross section has a width of 2.0 μm in the direction of the average line of the roughness curve, the convex portion that is 1/5 or more of the 10-point average surface roughness is t. In the case where there are pieces, the linear density becomes (t pieces / 2.0 μm).

For the remaining 11-direction line segments, similarly to the above, each line density can be calculated by performing observation with an electron microscope, measurement of 10-point average surface roughness, and the like.
When each linear density in 12 directions of the obtained separation functional layer is n ₁ , n ₂ , n ₃ ... N ₁₀ , n ₁₁ and n _{12 in} descending order, n ₁ , n ₂ , n ₃ , n ₁₀ , n ₁₁ and n ₁₂ preferably satisfy the following formula (1).
(N ₁ + n ₂ + n ₃ ) / (n ₁₀ + n ₁₁ + n ₁₂ ) ≧ 1.05 (1)

As shown in the formula (1), the anisotropy of the linear density ((n ₁ + n ₂ + n ₃ ) / (n ₁₀ + n ₁₁ + n ₁₂ )) is preferably 1.05 or more. Moreover, as shown by the following formula (2), the linear density anisotropy is more preferably 1.10 or more and 3.00 or less.
1.10 ≦ (n ₁ + n ₂ + n ₃ ) / (n ₁₀ + n ₁₁ + n ₁₂ ) ≦ 3.00 (2)

  When the anisotropy of the linear density is 1.05 or more, the composite semipermeable membrane including the separation functional layer exhibits the effect of improving water permeability while maintaining high separation ability. Moreover, the specific surface area of a functional layer required in order to ensure water permeability can be ensured because the anisotropy of linear density is 3.00 or less.

Each value of linear density _n 1 _{~n 12} is preferably present is 10 to 100 protrusions per horizontal 2.0 .mu.m, 15 to 80 pieces is preferable. When the linear density is 10 pieces / 2.0 μm or more, a composite semipermeable membrane having a minimum required water permeability can be obtained. Further, when the linear density is 100 pieces / 2.0 μm or less, the growth of the convex portions occurs sufficiently, and a composite semipermeable membrane having a desired water permeability can be easily obtained. Here, the number of convex portions includes the convex portions having a height of 1/5 or more of the 10-point average surface roughness.

The line segments in the upper 3 (n _{1 to} n ₃ ) direction with the higher line density may be adjacent or separated. In addition, the line segments in the upper 3 (n _{10 to} n ₁₂ ) direction with the smaller line density may be adjacent to each other or separated from each other.
From the viewpoint of the coexistence of the high permeability and high separation ability of the composite semipermeable membrane, it is preferable that the line segments in the upper three directions having a high linear density are adjacent to each other. For the same reason, it is preferable that the line segments in the upper three directions having a smaller line density are adjacent to each other.

  The height from the average line 2 of the convex portion of the separation functional layer in the present invention is preferably 70 nm or more, more preferably 90 nm or more. Moreover, the height from the average line 2 of the convex part of the separation functional layer is preferably 1000 nm or less, and more preferably 800 nm or less. When the height of the convex portion is 70 nm or more, a composite semipermeable membrane having sufficient water permeability can be easily obtained. Moreover, when the height of the convex portion is 1000 nm or less, stable membrane performance can be obtained without collapsing the convex portion shape even when the composite semipermeable membrane is operated at a high pressure.

  The separation functional layer is a layer responsible for separating solutes in the mixture 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, but the thickness of the separation functional layer is usually 0 in order to obtain sufficient separation performance and permeated water amount. The range of 0.01 to 1 μm is preferable, and the range of 0.1 to 0.5 μm is more preferable.

The separation functional layer may contain polyamide as a main component. The polyamide constituting the separation functional layer can be obtained by interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide. Here, it is preferable that at least one of the polyfunctional amine or the polyfunctional acid halide contains a trifunctional or higher functional compound.
In this specification, “X contains Y as a main component” means that Y occupies 50% by mass or more of X, and includes a configuration in which X substantially contains only Y. .

  The polyfunctional amine used to obtain the polyamide is an amine having at least one primary amino group in one molecule and further having at least one primary amino group and / or secondary amino group. Say.

For example, as a polyfunctional amine, phenylenediamine, xylylenediamine, 1,3,5-triaminobenzene in which two amino groups are bonded to a benzene ring in any of the ortho-position, meta-position, and para-position, Aromatic polyfunctional amines such as 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 3-aminobenzylamine and 4-aminobenzylamine; aliphatic amines such as ethylenediamine and propylenediamine; -An alicyclic polyfunctional amine such as diaminocyclohexane, 1,4-diaminocyclohexane, 4-aminopiperidine, 4-aminoethylpiperazine and the like can be mentioned.
Among them, considering the selective separation property, permeability, and heat resistance of the membrane, the polyfunctional amine is an aromatic polyfunctional having 2 to 4 primary amino groups and / or secondary amino groups in one molecule. An amine is preferred. As such a polyfunctional aromatic amine, m-phenylenediamine, p-phenylenediamine, and 1,3,5-triaminobenzene are preferably used. Among these, m-phenylenediamine (hereinafter sometimes referred to as m-PDA) is preferably used from the standpoint of availability and ease of handling.

  These polyfunctional amines may be used alone or in combination of two or more. When using 2 or more types simultaneously, the said amines may be combined and the said amine and the amine which has at least 2 secondary amino group 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-bispiperidylpropane.

The polyfunctional acid halide used for obtaining the polyamide refers to an acid halide having at least two carbonyl halide groups in one molecule.
For example, examples of the trifunctional acid halide include trimesic acid chloride, 1,3,5-cyclohexanetricarboxylic acid trichloride, 1,2,4-cyclobutanetricarboxylic acid trichloride, and the like.
Examples of the bifunctional acid halide include aromatic bifunctional acid halides such as biphenyl dicarboxylic acid dichloride, azobenzene dicarboxylic acid dichloride, terephthalic acid chloride, isophthalic acid chloride, and naphthalene dicarboxylic acid chloride; adipoyl chloride, sebacoyl chloride, and the like. Aliphatic bifunctional acid halides; cycloaliphatic difunctional acid halides such as cyclopentane dicarboxylic acid dichloride, cyclohexane dicarboxylic acid dichloride, and tetrahydrofuran dicarboxylic acid dichloride can be exemplified.
In consideration of the reactivity with the polyfunctional amine, the polyfunctional acid halide is preferably a polyfunctional acid chloride. In view of selective separation of the membrane and heat resistance, the polyfunctional acid chloride is more preferably a polyfunctional aromatic acid chloride having 2 to 4 carbonyl chloride groups in one molecule. Of these, trimesic acid chloride is preferable from the viewpoint of availability and ease of handling. These polyfunctional acid halides may be used alone or in combination of two or more.

(1-2) Support Membrane The support membrane in the present invention comprises a base material and a porous support layer provided on the base material, has substantially no separation performance such as ions, and is separated. Strength can be imparted to the functional layer.
The thickness of the support membrane affects the strength of the composite semipermeable membrane and the packing density when the composite semipermeable membrane is used as a membrane element. In order to obtain sufficient mechanical strength and packing density, the thickness of the support membrane is preferably in the range of 30 to 300 μm, more preferably in the range of 50 to 250 μm.
In this document, unless otherwise specified, the thickness of each layer or film means an average value. Here, the average value is an arithmetic average value. That is, the thickness of each layer or film was measured at intervals of 20 μm in a direction orthogonal to the thickness direction of the layer or film (the surface direction of the layer or film, the horizontal direction) when a cross section of each layer or film was observed. It is obtained by calculating the average value of the thickness of the points.

[Porous support layer]
The porous support layer preferably contains the following materials as main components. As the material of the porous support layer, polysulfone, polyethersulfone, polyamide, polyester, cellulosic polymer, vinyl polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, polyphenylene oxide, or a homopolymer or a copolymer thereof alone or Can be blended and used.
Here, cellulose acetate, cellulose nitrate and the like are used as the cellulose polymer, and polyethylene, polypropylene, polyvinyl chloride, polyacrylonitrile and the like are used as the vinyl polymer.

Among them, a homopolymer such as polysulfone, polyamide, polyester, cellulose acetate, cellulose nitrate, polyvinyl chloride, polyacrylonitrile, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, or a copolymer thereof is preferable.
More preferred is cellulose acetate, polysulfone, polyphenylene sulfide sulfone, or polyphenylene sulfone.
Among these materials, polysulfone is particularly preferably used because of its high chemical, mechanical and thermal stability and easy molding.
Specifically, a polysulfone having a repeating unit represented by the following chemical formula as the main component of the porous support layer is preferable because the pore diameter can be easily controlled and the dimensional stability is high.

The polysulfone preferably has a mass average molecular weight (Mw) of 10000 to 200000, more preferably 15000 to 100,000 when measured by gel permeation chromatography (GPC) using N-methylpyrrolidone as a developing solvent and polystyrene as a standard substance. Is within the range of
When Mw is 10,000 or more, preferable mechanical strength and heat resistance can be obtained as the porous support layer. Moreover, when Mw is 200000 or less, the viscosity of the solution falls within an appropriate range, and good moldability can be realized.

  The porous support layer is formed by, for example, casting an N, N-dimethylformamide (hereinafter referred to as DMF) solution in which the polysulfone is dissolved to a certain thickness on a substrate, and wet coagulating it in water. Can be obtained. The porous support layer obtained by this method has many fine pores having a diameter of 1 to 30 nm on the surface.

When the porous support layer contains polysulfone, the content is preferably 50% by mass or more.
In addition to the polymer that is the main component of the porous support layer, an additive may be appropriately contained.
Moreover, it is preferable that the thickness of a porous support layer exists in the range of 10-200 micrometers, More preferably, it exists in the range of 20-100 micrometers.

  The porous support layer may have a multilayer structure. When the porous support layer has a multilayer structure, the main components and other components constituting the plurality of layers may be different for each layer.

[Base material]
As a base material which comprises the support film in this invention, a polyester-type polymer, a polyamide-type polymer, a polyolefin-type polymer, or these mixtures, a copolymer, etc. are mentioned as a main component, for example. Among these, a polyester polymer is preferable because a superior support film can be obtained due to mechanical strength, heat resistance, water resistance, and the like.

The polyester polymer is a polyester composed of an acid component and an alcohol component.
Examples of the acid component include 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.
Further, as the alcohol component, ethylene glycol, diethylene glycol, polyethylene glycol, or the like can be used.

  “Containing polyester as a main component” and “containing a polyester polymer as a main component” are synonymous. The ratio of the acid component and the alcohol component constituting the polyester polymer is not particularly limited as long as it is a range that is usually used.

Examples of the polyester polymer include polyethylene terephthalate resin, polybutylene terephthalate resin, polytrimethylene terephthalate resin, polyethylene naphthalate resin, polylactic acid resin, and polybutylene succinate resin. Examples include coalescence.
A homopolymer of polyethylene terephthalate or a copolymer thereof is preferable.

The base material in the present invention is a cloth-like material made of the polymer or the like. As the fabric used for the base material, it is preferable to use a fibrous polymer in terms of strength and fluid permeability.
As the fabric, either a long fiber nonwoven fabric or a short fiber nonwoven fabric can be preferably used.

In particular, when a long-fiber non-woven fabric is used as the base material, it has excellent permeability when cast a solution of a polymer that constitutes the porous support layer, and the porous support layer peels off. It can suppress that a film | membrane becomes non-uniform | heterogenous by etc. and defects, such as a pinhole, arise. Therefore, it is particularly preferable that the substrate is made of a long fiber nonwoven fabric. Among these, the long-fiber nonwoven fabric is more preferably composed of thermoplastic continuous filaments.
As mentioned above, it is preferable that the base material in this invention is a long fiber nonwoven fabric which contains polyester as a main component.

In the long-fiber nonwoven fabric and the short-fiber nonwoven fabric, in terms of moldability and strength, it is preferable that the fibers in the surface layer on the side opposite to the porous support layer are longitudinally oriented than the fibers in the surface layer on the porous support layer side. . That is, it means that the fiber orientation degree of the fiber in the surface layer opposite to the porous support layer is smaller than the fiber orientation degree of the fiber in the surface layer on the porous support layer side.
The above structure is preferable because the strength of the composite semipermeable membrane can be maintained and a high effect of preventing membrane breakage and the like can be realized.

  More specifically, the fiber orientation degree of the long-fiber nonwoven fabric, the short-fiber nonwoven fabric, and the surface layer opposite to the porous support layer is preferably 0 ° to 25 °. Moreover, it is preferable that the orientation degree difference between the fiber orientation degree in the surface layer opposite to the porous support layer and the fiber orientation degree in the surface layer on the porous support layer side is 10 ° to 90 °.

  In the present specification, the “degree of fiber orientation” is an index indicating the direction of the fiber when the substrate is a nonwoven fabric. Specifically, the fiber orientation degree is an average value of angles formed by the film forming direction in continuous film formation, that is, the longitudinal direction of the nonwoven fabric substrate and the longitudinal direction of the fibers constituting the nonwoven fabric substrate. . That is, if the longitudinal direction of the fiber is parallel to the film forming direction, the fiber orientation degree is 0 °. If the longitudinal direction of the fiber is perpendicular to the film forming direction, that is, parallel to the width direction of the nonwoven fabric substrate, the degree of orientation of the fiber is 90 °. Accordingly, the closer to 0 ° the fiber orientation, the longer the orientation, and the closer to 90 °, the lateral orientation.

The fiber orientation degree is measured as follows.
First, 10 small piece samples are randomly collected from the nonwoven fabric. Next, the surface of the sample is photographed with a scanning electron microscope at a magnification of 100 to 1000 times. In the photographed image, 10 fibers were selected for each sample, and the angle between the fibers and the longitudinal direction was measured when the longitudinal direction of the nonwoven fabric (also referred to as the longitudinal direction or film forming direction) was 0 °. To do.
That is, the angle is measured for a total of 100 fibers per nonwoven fabric sample. The average value of the angles for 100 fibers thus measured is calculated. A value obtained by rounding off the first decimal place of the average value of the obtained angles is defined as the fiber orientation degree.

  The thickness of the substrate is preferably in the range of 10 to 250 μm from the viewpoint of mechanical strength and packing density, and more preferably in the range of 20 to 200 μm.

2. Next, a method for producing a composite semipermeable membrane according to the present invention will be described. The manufacturing method includes a supporting film forming step, a separating functional layer forming step, and a step of imparting anisotropy to the linear density.

(2-1) Support film forming step The support film forming step includes a step of obtaining a base material using a polymer or the like, and a step of providing a porous support layer on the base material. Specifically, the support film may be formed using a method known among those skilled in the art, and is not particularly limited.
In the step of providing a porous support layer on the substrate, a step of applying a polymer solution constituting the porous support layer to the substrate, a step of impregnating the polymer solution into the substrate, and the polymer The base material impregnated with the solution is immersed in a coagulation bath of a solution (hereinafter, simply referred to as “non-solvent”) in which the solubility of the polymer is smaller than that of a good polymer solvent. A step of solidifying and forming a three-dimensional network structure of the polymer may be included. The polymer layer having the three-dimensional network structure is a porous support layer.

In addition, the step of forming the support film may further include a step of preparing a polymer solution by dissolving a polymer that is a component of the porous support layer in a good solvent for the polymer. As the good solvent, an appropriate one is appropriately selected and used depending on the type of polymer and the high molecular weight.
By controlling the step of impregnating the base material with the polymer solution, a support membrane having a predetermined structure can be obtained. In order to control the impregnation of the polymer solution into the base material, for example, a method of controlling the time until the polymer solution is immersed on the coagulation bath with a non-solvent after applying the polymer solution on the base material, or the polymer solution Examples include a method of adjusting the viscosity or the concentration of the polymer solution by controlling the temperature or concentration of these, and these methods can be used in combination.

  After applying the polymer solution which is a component of the porous support layer on the substrate, it is usually preferable that the time until it is immersed in the coagulation bath is in the range of 0.1 to 5 seconds. If the time until dipping in the coagulation bath is within this range, the polymer solution is sufficiently impregnated between the fibers of the base material and then solidified. In addition, the preferable range of time until it immerses in a coagulation bath can be suitably adjusted with the viscosity etc. of the polymer solution to be used.

The solid content concentration in the polymer solution is preferably 12% by mass to 35% by mass, and more preferably 13% by mass to 30% by mass. When the solid content concentration is 12% by mass or more, the communication holes in which the pores in the obtained porous support layer are connected to each other are formed relatively small, so that a porous support layer having a desired pore diameter is obtained. It is easy to be done. Further, when the solid content concentration is 35% by mass or less, the surface pore diameter of the porous support layer is adjusted so that the monomer supply rate at the time of forming the separation functional layer does not become too small. Therefore, a convex portion having an appropriate height is formed when the separation functional layer is formed.
The “solid content concentration” described above can be replaced with “polymer concentration”. That is, when the polymer compound forming the porous support layer is polysulfone, the above-mentioned “solid content concentration” can be replaced with “polysulfone concentration”.

The temperature of the polymer solution at the time of applying the polymer solution to the substrate is usually preferably in the range of 10 to 60 ° C. if the polymer is polysulfone, for example. Within this range, the polymer solution does not precipitate, and the organic solvent solution containing the polymer compound is sufficiently impregnated between the fibers of the base material and then solidified. As a result, the porous support layer is firmly bonded to the substrate by the anchor effect, and the support film in the present invention can be obtained. The temperature range of the polymer solution may be adjusted as appropriate depending on the viscosity of the polymer solution used.
The solvent constituting the polymer solution may be a single solvent or a mixed solvent of a plurality of solvents as long as it is a good polymer solvent. In consideration of the strength characteristics of the support membrane to be produced and the impregnation of the polymer solution into the substrate, the polymer solution can be appropriately prepared under various conditions.

  The good solvent means a solvent having high solubility with respect to the polymer forming the porous support layer. The good solvent used in the present invention varies depending on the type of polymer. For example, N-methyl-2-pyrrolidone (hereinafter referred to as NMP); tetrahydrofuran; dimethyl sulfoxide; amides such as tetramethylurea, dimethylacetamide, and dimethylformamide Lower alkyl ketones such as acetone and methyl ethyl ketone; esters and lactones such as trimethyl phosphate and γ-butyrolactone; and mixed solvents thereof.

  As the non-solvent for the polymer used in the coagulation bath, water is usually used, but any solvent that does not dissolve or hardly dissolve the polymer may be used. Depending on the type of polymer, for example, water, hexane, pentane, benzene, toluene, methanol, ethanol, trichloroethylene, ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butylene glycol, pentanediol, hexanediol, low molecular weight Examples thereof include aliphatic hydrocarbons such as polyethylene glycol, aromatic hydrocarbons, aliphatic alcohols, or mixed solvents thereof.

  Further, the temperature of the coagulation bath is preferably -20 ° C to 100 ° C. More preferably, it is 10-30 degreeC. When the temperature is 100 ° C. or lower, the magnitude of vibration of the coagulation bath surface due to thermal motion is suppressed, and the membrane surface of the porous support layer can be formed smoothly. Further, when the temperature is −20 ° C. or higher, the solidification rate can be kept relatively high, and good film forming properties are realized.

  Next, the support membrane obtained under the above conditions is washed with hot water in order to remove the membrane-forming solvent remaining in the membrane. The temperature of the hot water at this time is preferably 50 to 100 ° C, more preferably 60 to 95 ° C. If it is higher than this range, the degree of shrinkage of the support membrane will increase and the water permeability will decrease. On the other hand, if it is lower than the above range, the effect of removing the remaining solvent is small.

Further, the polymer solution may appropriately contain additives for adjusting the pore diameter, porosity, hydrophilicity, elastic modulus and the like of the support membrane. Additives for adjusting the pore size and porosity include water; alcohols; water-soluble polymers such as polyethylene glycol, polyvinyl pyrrolidone, polyvinyl alcohol and polyacrylic acid or salts thereof; lithium chloride, sodium chloride, calcium chloride Inorganic salts such as lithium nitrate; formaldehyde, formamide and the like are exemplified, but not limited thereto.
Examples of additives for adjusting hydrophilicity and elastic modulus include various surfactants.

(2-2) Formation of Separation Function Layer Next, as an example of the formation process of the separation function layer constituting the composite semipermeable membrane, description will be given by forming a layer containing polyamide as a main component (that is, a polyamide separation function layer). To do.
The step of forming the polyamide separation functional layer is carried out by performing interfacial polycondensation on the surface of the support film using the aqueous solution containing the polyfunctional amine and the organic solvent solution containing the polyfunctional acid halide, thereby forming a polyamide skeleton. Forming a step. The organic solvent solution and water are immiscible.

The concentration of the polyfunctional amine in the polyfunctional amine aqueous solution is preferably in the range of 0.1% by mass to 20% by mass, and more preferably in the range of 0.5% by mass to 15% by mass. . Within this range, sufficient water permeability and solute removal performance can be obtained.
The polyfunctional amine aqueous solution may contain a surfactant, an organic solvent, an alkaline compound, an antioxidant, or the like as long as it does not interfere with the reaction between the polyfunctional amine and the polyfunctional acid halide. The surfactant has the effect of improving the wettability of the support membrane surface and reducing the interfacial tension between the aqueous amine solution and the nonpolar solvent. Since the organic solvent may act as a catalyst for the interfacial polycondensation reaction, the interfacial polycondensation reaction may be efficiently performed by adding the organic solvent.

In order to perform the interfacial polycondensation on the support membrane, first, the polyfunctional amine aqueous solution is brought into contact with the support membrane. The contact is preferably performed uniformly and continuously on the support membrane surface.
Specifically, a method of coating a support membrane with a polyfunctional amine aqueous solution and a method of immersing the support membrane in a polyfunctional amine aqueous solution can be exemplified. The contact time between the support membrane and the polyfunctional amine aqueous solution is preferably in the range of 5 seconds to 10 minutes, and more preferably in the range of 10 seconds to 3 minutes.

After bringing the polyfunctional amine aqueous solution into contact with the support membrane, the solution is sufficiently drained so that no droplets remain on the membrane. The portion where the droplets remain may become a defect after the formation of the composite semipermeable membrane, and this defect reduces the salt and boron removal performance of the composite semipermeable membrane. As mentioned above, generation | occurrence | production of a fault can be suppressed by fully draining liquid.
As a method for draining, for example, as described in JP-A-2-78428, a method of allowing the excess aqueous solution to flow down naturally by holding the support film after contacting the polyfunctional amine aqueous solution in the vertical direction, For example, a method of forcibly draining air by blowing an air current such as nitrogen from an air nozzle can be used. In addition, after draining, the membrane surface can be dried to partially remove water from the aqueous solution.

  Next, a polyfunctional amine aqueous solution is brought into contact with the support membrane, which has been sufficiently drained, and then a water-immiscible organic solvent solution containing the polyfunctional acid halide is brought into contact therewith, and a crosslinked polyamide separation functional layer is obtained by interfacial polycondensation. To form.

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

The water-immiscible organic solvent is preferably one that dissolves the polyfunctional acid halide and does not destroy the support membrane, and may be any one that is inert to the polyfunctional amine compound and polyfunctional acid halide. . Preferable examples of the immiscible organic solvent include hydrocarbon compounds such as hexane, heptane, octane, nonane and decane.
The method of bringing the organic solvent solution containing the polyfunctional acid halide into contact with the support membrane can be performed in the same manner as the method of coating the support membrane with the polyfunctional amine aqueous solution.

In the interfacial polycondensation step of the present invention, the support membrane is sufficiently covered with a crosslinked polyamide thin film, and a water-immiscible organic solvent solution containing a polyfunctional acid halide in contact with the support membrane is left on the support membrane. It is important to keep it. For this reason, the time for performing the interfacial polycondensation is preferably from 0.1 second to 3 minutes, and more preferably from 0.1 second to 1 minute.
When the interfacial polycondensation time is 0.1 seconds or more and 3 minutes or less, the support membrane can be sufficiently covered with a crosslinked polyamide thin film, and an organic solvent solution containing a polyfunctional acid halide is supported on the support membrane. Can be held on.

  After the polyamide separation functional layer is formed on the support membrane by interfacial polycondensation, excess solvent is drained. As a liquid draining method, for example, a method of removing the excess organic solvent by flowing down naturally by holding the film in the vertical direction can be used. In this case, the time for gripping in the vertical direction is preferably 1 minute or more and 5 minutes or less, and more preferably 1 minute or more and 3 minutes or less. If it is too short, the separation functional layer will not be completely formed, and if it is too long, the organic solvent will be overdried and a defective part will occur in the polyamide separation functional layer, resulting in poor membrane performance.

  Subsequently, the composite semipermeable membrane obtained as described above is provided with anisotropy in the linear density of the unevenness (folded structure) on the surface of the polyamide separation functional layer. Specifically, a method of stretching the obtained film in at least one direction is preferably used, and a method of uniaxial stretching is particularly preferably used. Examples of the stretching method include a method of longitudinally stretching in the longitudinal direction and a method of performing lateral stretching in the width direction. However, it is preferable to perform stretching in a direction perpendicular to the fiber orientation direction of the nonwoven fabric substrate because shrinkage after stretching can be suppressed.

Moreover, even if it extends | stretches in multiple directions (multiaxial stretching), anisotropy can be given to the said linear density by changing tensile strength by each direction.
The stretching temperature is preferably in the range of room temperature to 120 ° C, more preferably in the range of room temperature to 90 ° C. When the stretching temperature exceeds 120 ° C., the hydration structure change of the separation functional layer and the structure change of the polysulfone porous layer occur, and the water permeability of the membrane decreases. Stretching may be performed in the air or in a solvent such as water. Moreover, you may perform the moisture retention process with respect to a composite semipermeable membrane before heating. In order to obtain the linear density anisotropy, the draw ratio is preferably 1.05 times or more, more preferably 1.15 times or more and 4.00 times or less.

3. Use of the composite semipermeable membrane The composite semipermeable membrane manufactured in this way is, for example, a raw water channel material such as a plastic net, a permeate channel material such as a tricot, and, if necessary, to increase pressure resistance. A spiral composite semipermeable membrane element can be formed by being wound around a cylindrical water collecting tube having a large number of holes, together with the film. Further, this element can be connected in series or in parallel and housed in a pressure vessel to constitute a composite semipermeable membrane module.
In addition, the composite semipermeable membrane, the composite semipermeable membrane element, and the composite semipermeable membrane module described above are combined with a pump that supplies raw water to them, a device that pretreats the raw water, and the like to constitute a fluid separation device. Can do. 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, and water suitable for the purpose can be obtained.

The higher the operating pressure of the fluid separator, the better the solute removal, but the energy required for operation also increases, and considering the durability of the composite semipermeable membrane, water to be treated is added to the composite semipermeable membrane. The operating pressure at the time of permeation is preferably 1.0 MPa or more and 10 MPa or less. The operating pressure is a so-called transmembrane pressure.
As the feed water temperature increases, the solute removability decreases, but as it decreases, the membrane permeation flux also decreases. In addition, when the feed water pH becomes high, scales such as magnesium (precipitation of poorly soluble substances) may occur in the case of feed water with a high salt concentration such as seawater, and there is a concern about membrane deterioration due to high pH operation. Therefore, operation in a neutral region is preferable.

Examples of raw water to be treated by the composite semipermeable membrane include liquid mixtures containing TDS (Total Dissolved Solids) of 500 mg / L to 100 g / L such as seawater, brine, and drainage. Generally, TDS refers to the total amount of dissolved solids and is expressed as “mass ÷ volume”, or expressed as “weight ratio” by regarding 1 liter as 1 kg.
According to the definition, the TDS can be calculated from the weight of the residue by evaporating the solution filtered through a 0.45 μm filter at a temperature of 39.5 to 40.5 ° C. To do.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples. Various changes and modifications can be made without departing from the technical scope of the present invention.

<Creation of composite semipermeable membrane>
In the following examples, polysulfone UDEL p-3500 manufactured by Solvay Advanced Polymers Co., Ltd. was used as the polysulfone.
Example 1
Polysulfone and DMF solution were mixed and stirred at 90 ° C. for 2 hours to prepare a DMF solution (polymer solution) in which 16% by mass of polysulfone was dissolved. The prepared polymer solution was cooled to room temperature, supplied to an extruder, and filtered with high precision. Thereafter, the filtered polymer solution was cast at a thickness of 160 μm on a long-fiber nonwoven fabric made of polyethylene terephthalate fibers (thread diameter: 1 dtex, thickness: about 90 μm, air permeability: 1.3 cc / cm ² / sec). Immediately, it was immersed in pure water at 25 ° C. and washed for 5 minutes to obtain a support membrane.
The obtained support membrane was immersed in a 4.0% by mass aqueous solution of m-PDA for 2 minutes, and then slowly pulled up so that the membrane surface was vertical. After removing excess m-PDA aqueous solution by blowing nitrogen from an air nozzle, an n-decane solution containing 0.12% by mass of trimesic acid chloride was applied so that the film surface was completely wetted. After leaving still for 1 minute, in order to remove excess n-decane solution from the membrane, the membrane surface was held vertically for 1 minute and drained. Thereafter, the membrane was washed with water at 45 ° C. for 2 minutes to obtain a membrane provided with a separation functional layer on the support membrane.
The obtained film was stretched by 1.30 times over 2 minutes in a direction perpendicular to the fiber orientation direction of the long-fiber nonwoven fabric in a water at 45 ° C. using a uniaxial stretching device (stretching ratio: 1.30 times). And the composite semipermeable membrane A in Example 1 was obtained by leaving still as it is for 2 minutes.

(Example 2)
A composite semipermeable membrane B in Example 2 was obtained in the same manner as Example 1 except that the draw ratio was 1.15 times.
Example 3
A composite semipermeable membrane C in Example 3 was obtained in the same manner as in Example 1 except that the temperature of water for stretching was 25 ° C.
Example 4
A composite semipermeable membrane D in Example 4 was obtained in the same manner as in Example 1 except that the temperature of water for stretching was 25 ° C. and the stretching ratio was 1.15 times.

(Comparative Example 1)
A composite semipermeable membrane E in Comparative Example 1 was obtained in the same manner as in Example 1 except that the membrane was attached to a uniaxial stretching apparatus in water at 45 ° C., but not stretched and left to stand for 4 minutes.
(Comparative Example 2)
A composite semipermeable membrane F in Comparative Example 2 was obtained in the same manner as in Example 1 except that the membrane was attached to a uniaxial stretching apparatus in water at 25 ° C., but not stretched and left to stand for 4 minutes.

<Measurement of linear deviation of convex portions, average height of convex portions and standard deviation of thickness of separation functional layer>
Each of the 12 cross sections obtained from the samples of the composite semipermeable membranes A to F by the above-described method was embedded with an epoxy resin, and stained with osmium tetroxide for easy cross-sectional observation. This was cut with an ultramicrotome to prepare an ultrathin section.
A cross-sectional photograph of the obtained ultrathin slice was taken using a transmission electron microscope. The acceleration voltage at the time of observation was 100 kV, and the observation magnification was 20,000 times. With respect to the obtained cross-sectional photograph, the number of convex portions was measured while measuring the height of the convex portions of the separation functional layer with a scale at a distance of 2.0 μm in width in the film surface direction of the support membrane. The point average surface roughness was calculated. Based on this 10-point average surface roughness, the number of protrusions having a height of 1/5 or more of the 10-point average surface roughness was counted, and the linear density of the protrusions of the separation functional layer was determined.

For each of the composite semipermeable membranes A to F, the values of n _{1 to} n ₁₂ were obtained, and the anisotropy of the linear density (n ₁ + n ₂ + n ₃ ) / (n ₁₀ + n ₁₁ + n ₁₂ ) was calculated.
The water temperature, stretching ratio, linear density, and linear density anisotropy when the composite semipermeable membrane is stretched are shown in Table 1 described later.

<Salt removal rate>
Seawater (feed water) having a NaCl concentration of 3.5% by mass, a temperature of 25 ° C., and a pH of 6.5 is supplied to the composite semipermeable membrane at an operating pressure of 5.5 MPa and treated for 24 hours. After the operation, permeated water was obtained at an operating pressure of 5.5 MPa. The ionic conductivity of the feed water and the obtained permeated water was measured, the salt concentration was calculated using the ionic conductivity, and the salt removal rate (TDS removal rate) was determined according to the following formula (3).
Salt removal rate (%) = 100 × {1− (salt concentration in permeated water / salt concentration in supply water)} (3)

  The ion conductivity was measured with an electric conductivity meter manufactured by Toa Radio Industry Co., Ltd. A calibration curve was prepared by measuring ionic conductivity of a NaCl aqueous solution having a known concentration, and using this, the salt concentration was calculated from the value of ionic conductivity measured above.

<Membrane permeation flux>
The permeated water amount obtained by the above water treatment operation for 24 hours is expressed as a membrane permeation flux (m ³ / m ² / day) with a water permeation amount (cubic meter) per day per square meter of the apparent surface area of the membrane surface. did.
The results of salt removal rate and membrane permeation flux are also shown in Table 1.

  As shown in Table 1, according to Examples 1 to 4 of the present invention, it is understood that a composite semipermeable membrane excellent in water permeability can be obtained without reducing the separation ability (TDS removal rate).

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

DESCRIPTION OF SYMBOLS 1 Separation functional layer 2 Reference line H1, H2, H3, H4, H5 Height of convex part in pleat structure of separation functional layer D1, D2, D3, D4, D5 Depth of concave part in pleat structure of separation functional layer

Claims (4)

A substrate;
A porous support layer provided on the substrate;
A separation semi-permeable membrane provided on the porous support layer and having a pleated structure including convex and concave portions that are continuously repeated on the surface;
Draw a circle with a diameter of 3 cm around a randomly selected location on the separation functional layer,
Draw a line segment in 12 directions that passes through the center of the circle and divides the circle into 24 equal parts,
A section having a length of 2.0 μm in the horizontal direction is selected along one line segment among the 12 direction line segments, and
Observe the unevenness of the pleated structure of the section using an electron microscope, measure the 10-point average surface roughness of the section,
Obtain the number of protrusions having a height of 1/5 or more of the 10-point average surface roughness per section,
Further, similarly for the other 11 directions among the 12 directions, respectively, the number of convex portions per each section is obtained,
When the number of convex portions in the 12 directions is n ₁ , n ₂ , n ₃ ... N ₁₀ , n ₁₁ and n _{12 in the} descending order,
Composite _{semipermeable} membrane _{n 1, n 2, n 3} , n 10, n 11 and _{n 12} of said _n 1 _{~n 12} is characterized by satisfying the following equation (1).
(N ₁ + n ₂ + n ₃ ) / (n ₁₀ + n ₁₁ + n ₁₂ ) ≧ 1.05 (1) _2. The composite semipermeable membrane according to claim ₁ , wherein the n ₁ , n ₂ , n ₃ , n ₁₀ , n _11, and n ₁₂ satisfy the following formula (2).
1.10 ≦ (n ₁ + n ₂ + n ₃ ) / (n ₁₀ + n ₁₁ + n ₁₂ ) ≦ 3.00 (2)   The composite semipermeable membrane according to claim 1 or 2, wherein the base material is a long fiber nonwoven fabric containing polyester as a main component. A substrate;
A porous support layer provided on the substrate;
A separation functional layer provided on the porous support layer and having a pleat structure including convex and concave portions that are continuously repeated on the surface;
The manufacturing method of the composite semipermeable membrane of any one of Claims 1-3 including the process of extending | stretching a film | membrane provided with uniaxially.

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