JP7102571B1 - Method for manufacturing semipermeable membrane support and semipermeable membrane support - Google Patents

Abstract

An object of the present invention is to provide a semipermeable membrane support which has few defects of the semipermeable membrane and has an improved salt rejection rate. A semipermeable membrane support made of a wet-laid nonwoven fabric containing a main synthetic fiber and a binder synthetic fiber has 30 or less detached fibers in a tape peeling test, and the semipermeable membrane is separated by a confocal laser microscope. A semipermeable membrane support, wherein the difference in level of the core portion obtained by measuring the surface roughness of the coating surface provided is 14 μm or less. [Selection figure] None

Description

The present invention relates to a semipermeable membrane support and a method for manufacturing a semipermeable membrane support.

Semipermeable membranes are widely used in fields such as seawater desalination, water purifiers, food concentration, wastewater treatment, medical use represented by hemofiltration, and ultrapure water production for semiconductor cleaning. The semipermeable membrane is composed of a synthetic resin such as a cellulosic resin, a polysulfone resin, a polyacrylonitrile resin, a fluorine resin, and a polyester resin. However, since the semipermeable membrane alone is inferior in mechanical strength, it is used as a separation membrane in the form of a composite in which a semipermeable membrane is provided on one side of a semipermeable membrane support made of a fiber base material such as a non-woven fabric or a woven fabric. Has been done. The surface of the semipermeable membrane support on which the semipermeable membrane is provided is referred to as a "coated surface", and the surface on the opposite side is referred to as a "non-coated surface".

As the semipermeable membrane support, a non-woven fabric containing synthetic fibers is mainly used. In particular, polyester-based wet non-woven fabrics are often used (see, for example, Patent Documents 1 and 2). Conventionally, antimony compounds typified by antimony trioxide have been widely used as polymerization catalysts for polyester fibers constituting these semipermeable membrane supports. Antimony trioxide is inexpensive and has excellent catalytic activity, but in recent years, environmental problems have been pointed out in various countries including Europe and the United States.

Further, as the performance required for the semipermeable membrane support, the adhesion between the semipermeable membrane and the semipermeable membrane support is good, and in order to provide the semipermeable membrane, the semipermeable membrane solution is a semipermeable membrane. When applied to the support, the semipermeable membrane solution does not strike through to the non-coated surface, and the semipermeable membrane has few defects.

In the step of wet-making a fiber slurry in which synthetic fibers are dispersed in water to form a non-woven fabric, for the purpose of improving the uniformity of the semi-transparent film support so that the semi-transparent solution does not strike through, the said at the time of paper making. The fiber content concentration of the fiber slurry is 0.01 to 0.1% by mass, and a water-soluble polymer having a molecular weight of 5 million or more is added to the fiber slurry as a polymer viscous agent from 3 to 3 based on the fiber content mass. A method of making paper with a content of 15% by mass has been proposed (see, for example, Patent Document 3). However, since the polymer viscous agent is excessively added, the uniformity is improved, but the viscosity of the fiber slurry on the papermaking net is increased, the dehydration property from the papermaking net is lowered, and the production rate cannot be increased. There was a possibility that the problem would occur. In addition, there is also a problem that the polymer viscous agent remains on the surface of the fiber forming the semipermeable membrane support after papermaking.

Also, from a multilayer structure non-woven fabric based on a double structure consisting of a surface layer with a large surface roughness using thick fibers (thick fiber layer) and a back layer with a dense structure using fine fibers (thin fiber layer). A semi-transparent membrane support has been proposed (see, for example, Patent Document 4). Specifically, a semipermeable membrane support having a thick fiber layer as a coated surface and a thin fiber layer as a non-coated surface, and a thin fiber layer sandwiched between thick fiber layers, and both the coated surface and the non-coated surface are thick fiber layers. A semipermeable membrane support is described. However, since thick fibers are used on the coated surface, the adhesiveness between the semipermeable membrane and the semipermeable membrane support is improved, but there is a problem that the smoothness is low and the semipermeable membrane tends to have defects. .. In addition, since thick fibers are used, the semipermeable membrane solution penetrates into the inside of the semipermeable membrane support, and a large amount of semipermeable membrane solution is required to obtain the desired semipermeable membrane thickness. There was a problem that it became.

Further, in order to solve the problem that a non-uniform semipermeable membrane is produced by bending the semipermeable membrane support in the width direction when the semipermeable membrane solution is applied, the paper flow direction and width are used. A semipermeable membrane support in which the tensile strength ratio in the direction is 2: 1 to 1: 1 and the fibers are in a disoriented state has been proposed (see, for example, Patent Document 1). Further, Patent Document 1 proposes a method of adjusting the air permeability and pore size of the semipermeable membrane support for the purpose of improving the adhesiveness between the semipermeable membrane and the semipermeable membrane support and preventing strike-through. .. However, the air permeability according to JIS L1096 is calculated based on the amount of air that passes from one side of the semipermeable membrane support through the inside of the semipermeable membrane support and permeates to the other side, and is calculated based on the amount of air that permeates the other side. It does not accurately reflect the strike-through of the semipermeable membrane solution applied to the surface to the non-applied surface. Therefore, when the semipermeable membrane solution is applied to the semipermeable membrane support having the air permeability in the range shown in Patent Document 1, the semipermeable membrane solution may strike through.

Further, in Patent Document 5, when the semipermeable membrane solution is applied to the defective portion locally existing on the wet non-woven sheet, which is the semipermeable membrane support, the permeability of the semipermeable membrane solution is partially changed. In order to solve the problem that the thickness of the semipermeable membrane in this portion may become extremely thin or the surface of the semipermeable membrane may become wrinkled due to the difficulty in penetrating, a synthesis constituting a wet non-woven fabric is performed. A method of optimizing the number of hot pressure processing of a wet non-woven film, the temperature, and the type of roll is used for the purpose of reducing the occurrence of low density defects, which is a place where the sheet density is low in a sparse fiber state. Proposed. Then, in Patent Document 5, there is no low density defect, it is uniform, the adhesion between the semipermeable membrane and the semipermeable membrane support is good, and the semipermeable membrane solution permeates the wet non-woven membrane too much and the semipermeable membrane becomes non-uniform. As a semipermeable membrane support that can prevent this from occurring, a semipermeable membrane support in which the sheet density and pressure loss are adjusted has been proposed. However, even a semipermeable membrane support having a sheet density and pressure loss in the range shown in Patent Document 5 may have a defect of the semipermeable membrane due to the convex portion of the semipermeable membrane support.

Further, in Patent Document 6, a support for semitransparent film for film separation active sludge treatment, which has few defects generated in the film forming process of the semitransparent film and has good adhesion to a resin frame holding the semitransparent film, is obtained. Therefore, it is a non-woven film containing stretched polyester fibers and unstretched polyester fibers, has a density of 0.50 to 0.70 g / cm ³ , and has an internal bond strength of 490 mJ or more. A semitransparent support for separating active sludge treatment has been proposed. Then, in the examples, the surface strength of the semipermeable membrane support is evaluated. Specifically, a transparent adhesive tape is evenly attached to the surface of the semi-transparent film support so as not to allow air to enter, and after sufficiently pressing the transparent adhesive tape, the transparent adhesive tape is slowly peeled off to form an adhesive surface of the transparent adhesive tape. The state of the fibers remaining in the adhesive tape is visually evaluated to evaluate whether or not the fibers adhere to the adhesive tape, and is used as an index for fiber shedding when the semitransparent film is provided. The shortcomings have not been evaluated.

Further, in Patent Document 7, in order to obtain a semipermeable membrane support having excellent performance and workability, the texture is in the range of 10 to 200 g / m ² , and the maximum height of the surface roughness of the front or back surface is set. A semipermeable membrane support has been proposed, which is within 500 μm and has a difference in surface roughness between the front and back surfaces of 30 μm or more. However, although the semipermeable membrane is applied to the semipermeable membrane support obtained in the examples and the processability is evaluated, the defects of the semipermeable membrane caused by the semipermeable membrane support and the formation of the semipermeable membrane are evaluated. The post-membrane salt inhibition rate has not been evaluated.

JP-A-2002-95937 Japanese Unexamined Patent Publication No. 10-225630 Japanese Unexamined Patent Publication No. 2008-238147 Tokuho 4-21526 Gazette International Publication No. 2012/090874 Pamphlet Japanese Unexamined Patent Publication No. 2016-159197 JP-A-2018-153758

An object of the present invention is to provide a semipermeable membrane support having few drawbacks of the semipermeable membrane and an improved salt inhibition rate.

As a result of diligent studies to solve the above problems, the present inventors have been able to solve the problems by the following inventions.

(1) In a semipermeable membrane support made of a wet non-woven fabric containing a main synthetic fiber and a binder synthetic fiber, the number of detached fibers in the tape peeling test is 30 or less, and the semipermeable membrane is provided by a confocal laser microscope. A semipermeable membrane support characterized in that the level difference of the core portion obtained by measuring the surface roughness of the coated surface is 14 μm or less.
(2) The semipermeable membrane support according to (1), wherein the amount of antimony element eluted in the main synthetic fiber or the binder synthetic fiber is less than 5 μg / g.
(3) The semipermeable membrane support according to (1) or (2), wherein the amount of antimony element eluted from the semipermeable membrane support is less than 1.5 μg / g.
(4) In the method for producing a semipermeable membrane support according to any one of (1) to (3), the fiber obtained by dispersing the binder synthetic fiber and then the main synthetic fiber. A method for producing a semipermeable membrane support, which comprises producing a semipermeable membrane support from a dispersion liquid by a wet fabrication method.

According to the present invention, it is possible to obtain a semipermeable membrane support having few defects of the semipermeable membrane and an improved salt blocking rate.

The semipermeable membrane support of the present invention is made of a wet non-woven fabric containing a main synthetic fiber and a binder synthetic fiber, has 30 or less detached fibers in a tape peeling test, and is a semipermeable membrane by a confocal laser microscope. The level difference of the core portion obtained by measuring the surface roughness of the coated surface on which the is provided is 14 μm or less.

In the present invention, unless otherwise specified, the detached fibers are counted as single fibers. That is, the fiber bundles in which the side surfaces of two or more fibers are in close contact with each other and exist in parallel in a bundle form count each fiber.

The semipermeable membrane support of the present invention is a semipermeable membrane support in which the number of detached fibers in the tape peeling test is 30 or less. In particular, the number of detached fibers is 30 or less on the coated surface on which the semipermeable membrane is provided. Is a semipermeable membrane support. The detached fiber is a fiber that is loosely adhered between the main synthetic fiber and the binder synthetic fiber and is detached from the surface of the semipermeable membrane support by physical impact or rubbing.

In the method for producing a semipermeable membrane support of the present invention in which the semipermeable membrane support is produced by a wet fabrication method, a method for reducing detached fibers will be described. In order to reduce the number of detached fibers, it is important to disperse the main synthetic fiber and the binder synthetic fiber in water in a fiber disperser (palper) to loosen the fiber bundle into a single fiber. Examples of the method of unraveling into single fibers include addition of a dispersant, optimization of the shape of blades in the pulper, optimization of the clearance between the bottom surface of the pulper and the blades, installation of a weir plate on the wall surface of the pulper tank, and the like. Next, in the step of defibrating into single fibers, diluting the fiber dispersion with white water (diluted water), and sending the liquid to the papermaking net, the diluted fiber dispersion is dispersed by a stirrer to obtain single fibers. The degree of dilution can be increased. Further, by adding an aqueous solution of a water-soluble polymer having a molecular weight of 5 million or more as a polymer viscous agent after fiber dispersion with pulper and / or after dilution of the fiber dispersion liquid, the degree of monofiber formation is further increased.

Then, in the method for producing a semipermeable membrane support of the present invention, a semipermeable membrane support is dispersed by a wet fabrication method from a fiber dispersion obtained by two-step dispersion in which binder synthetic fibers are dispersed and then main synthetic fibers are dispersed. It is characterized by manufacturing. When the fibers are put into the pulper, the binder synthetic fibers are put in first and dispersed, and then the main synthetic fibers are put in and dispersed, so that even if the monofilament of the main synthetic fibers is insufficient, it is sufficient. It is possible to cover the main synthetic fiber with the binder synthetic fiber which is made into a single fiber, and it is possible to suppress the detached fiber from the semitransparent film support.

Further, in the wet papermaking method, the fiber dispersion is supplied on the papermaking net, and in the process of squeezing excess water to obtain wet paper, a sheet-like wetness is placed on the papermaking net in which metal threads or plastic threads are woven. As the paper is formed, water is gradually squeezed under the papermaking net. The formation of wet paper on the papermaking net proceeds by depositing fibers on the surface of the papermaking net, and the formation of wet paper is completed when water is squeezed. At the start of wet paper formation, the fibers are deposited in the dispersed state of the fiber dispersion liquid supplied on the papermaking net, so that the surface in contact with the papermaking net (hereinafter, the "surface in contact with the papermaking net" is referred to as the "papermaking net surface". The loosened state of the fibers (sometimes referred to as) becomes uniform. On the other hand, the fiber dispersion still exists on the wet paper being formed on the paper net, and the wet paper formation is completed depending on the position of water extraction by suction, the strength of suction, the paper net speed, the flow velocity of the fiber dispersion, and the like. It is possible to adjust the loosened state of the fibers on the surface opposite to the papermaking net surface (hereinafter, the "surface opposite to the papermaking net surface" may be referred to as the "papermaking felt surface"). However, as compared with the papermaking net surface, the uniformity of the fibers in the loosened state is reduced on the papermaking felt surface. Further, in the middle to the latter half of the wet paper formation, when the thickness and length of the main synthetic fiber and the binder synthetic fiber are different, the same kind of fibers may gather together due to suction, and the uniformity may be further lowered. The gathering of the binder synthetic fibers may lead to a partial shortage of the binder synthetic fibers. Therefore, the surface strength of the papermaking mesh surface of the wet non-woven fabric is higher than the surface strength of the papermaking felt surface. Therefore, when the papermaking mesh surface is the coated surface, the defects of the semitransparent film due to the detached fibers are reduced, and the semitransparent film The salt blocking rate is improved during film formation.

The base paper obtained by drying the wet paper obtained by the wet papermaking method is preferably subjected to thermal pressure processing (thermal calendar) treatment with a thermal roll. In the thermal pressure processing device (thermal calendar device), the base paper is passed between the rolls that are nipped, and the base paper is thermally processed to melt and soften the binder synthetic fiber and fix the main synthetic fiber. do. If there is a place where the binder synthetic fiber does not exist in the base paper, the semi-transparent film is pierced by the detached fiber and film defects occur. Dispersibility of synthetic fibers and main synthetic fibers is important.

By taking the above measures, the detached fibers can be suppressed.

In the present invention, the number of detached fibers is 30 or less, more preferably 20 or less, and further preferably 10 or less. If the number of detached fibers exceeds 30, the fibers break through the surface of the semipermeable membrane during the formation of the semipermeable membrane, causing film defects and reducing the salt inhibition rate.

The semipermeable membrane support of the present invention is characterized in that the level difference Sk of the core portion obtained by measuring the surface roughness of the coated surface on which the semipermeable membrane is provided by a confocal laser microscope is 14 μm or less. The level difference Sk of the core portion is an index for comparing the surface roughness, and is the difference between the upper level and the lower level of the core portion in accordance with ISO25178.

When Sk is 14 μm or less, the defects of the semipermeable membrane during the formation of the semipermeable membrane are reduced, and the salt inhibition rate after the formation of the semipermeable membrane is unlikely to decrease. Sk is more preferably 13 μm or less, further preferably 12 μm or less, and particularly preferably 11.5 μm or less. When Sk exceeds 14 μm, the thickness of the semipermeable membrane provided on the semipermeable membrane support becomes non-uniform, defects occur in places where the semipermeable membrane is thin, and the membrane performance is deteriorated. The lower limit of Sk is preferably 8 μm. If Sk is smaller than 8 μm, the adhesiveness between the semipermeable membrane and the semipermeable membrane support may decrease.

Examples of the method for reducing the Sk of the semipermeable membrane support to 14 μm or less include the following.
(I) Improvement of fiber dispersibility by two-step dispersion (II) Optimization of compounding design (fiber selection and content of binder synthetic fiber)
(III) Optimization of papermaking conditions for base paper (IV) Adjustment of thermal pressure processing conditions

In the present invention, the amount of antimony (Sb) element eluted in the main synthetic fiber or the binder synthetic fiber is preferably less than 5 μg / g, and more preferably less than 1 μg / g. When the amount of antimony element eluted in the main synthetic fiber or the binder synthetic fiber is less than 5 μg / g, the detached fibers generated from the semipermeable membrane support can be suppressed, and the salt inhibition rate after the semipermeable membrane formation is improved. The effect is obtained.

Further, the amount of antimony element eluted from the semipermeable membrane support is preferably less than 1.5 μg / g, and more preferably the amount of antimony eluted from the semipermeable membrane support is less than 1.0 μg / g. When the amount of antimony element eluted from the semipermeable membrane support is less than 1.5 μg / g, it is possible to suppress the detached fibers generated from the semipermeable membrane support and improve the salt inhibition rate after the semipermeable membrane film is formed. The effect is obtained.

The "antimony element elution amount" in the present invention means that a main synthetic fiber, a binder synthetic fiber or a semitransparent film support is immersed in ultrapure water having a specific resistance of 18.2 MΩ · cm and a temperature of 25 ° C. for 24 hours to be ultrapure. The amount of antimony element eluted in water was calculated by using <Formula 1> from the value quantitatively analyzed by ICP-MS (Inductively Coupled Plasma-Mass Spectro-metri).

<Equation 1>
Antimony element elution amount (μg / g) = Antimony element content of eluent (μg / L) × Volume of ultrapure water used in elution test (L) / Main synthetic fiber, binder synthetic fiber or semi-transparent film support Mass (g)

In the present invention, the main synthetic fiber is a fiber that forms the skeleton of the semipermeable membrane support, and is difficult to soften or melt in the step of raising the temperature to near the softening point or melting temperature (melting point) of the binder synthetic fiber, and the fiber. A fiber that maintains its shape. Examples of the main synthetic fiber include polyolefin-based, polyamide-based, polyacrylic-based, vinylon-based, vinylidene-based, polyvinyl chloride-based, polyester-based, benzoate-based, polyclaral-based, and phenol-based fibers, which are heat-resistant. Higher polyester fibers are more preferred. In addition, semi-synthetic fibers such as acetate, triacetate and promix, and regenerated fibers such as rayon, cupra and lyocell fibers may be contained within a range that does not impair the performance.

The fiber diameter of the main synthetic fiber is not particularly limited, but is preferably 30 μm or less. If the fiber diameter of the main synthetic fiber exceeds 30 μm, there may be a problem that a large amount of semipermeable membrane solution is required to obtain a desired semipermeable membrane thickness, or strike-through of the semipermeable membrane solution. May occur. In addition, the main synthetic fibers on the surface of the wet non-woven fabric tend to stand up and penetrate the semipermeable membrane, which may reduce the performance of the semipermeable membrane. It is more preferably 2 to 20 μm, still more preferably 4 to 20 μm, and particularly preferably 6 to 20 μm. If it is less than 2 μm, the semipermeable membrane solution may not easily penetrate into the semipermeable membrane support, and the adhesiveness between the semipermeable membrane and the semipermeable membrane support may be deteriorated.

The fiber length of the main synthetic fiber is not particularly limited, but is preferably 1 to 12 mm, more preferably 3 to 10 mm, and further preferably 4 to 6 mm. The cross-sectional shape of the main synthetic fiber is preferably circular, and the cross-sectional aspect ratio (fiber cross-sectional major axis / fiber cross-sectional minor axis) of the fiber before dispersion in water in the papermaking process is preferably 1.0 to less than 1.2. .. When the fiber cross-sectional aspect ratio is 1.2 or more, the fiber dispersibility may decrease, or the uniformity of the semipermeable membrane support and the smoothness of the coated surface may be adversely affected due to the occurrence of fiber entanglement and entanglement. be. However, fibers having irregular cross sections such as T-type, Y-type, and triangular can also be contained within a range that does not impair other characteristics such as fiber dispersibility in order to prevent strike-through and surface smoothness.

The aspect ratio (fiber length / fiber diameter) of the main synthetic fiber is preferably 200 to 1000, more preferably 220 to 900, and further preferably 280 to 800. When the aspect ratio is less than 200, the dispersibility of the fibers is good, but when the fibers fall off from the papermaking net during papermaking, or when the fibers are stuck in the papermaking net, the peelability from the papermaking net deteriorates. In some cases. On the other hand, if it exceeds 1000, although it contributes to the formation of a three-dimensional network of fibers, the uniformity of the semipermeable membrane support and the smoothness of the coated surface may be adversely affected by the occurrence of entanglement and entanglement of the fibers. , It may lead to the generation of detached fibers, or Sk may exceed 14 μm.

The content of the main synthetic fiber is preferably 40 to 90% by mass, more preferably 50 to 80% by mass, and even more preferably 60 to 75% by mass with respect to the nonwoven fabric related to the semipermeable membrane support of the present invention. If the content of the main synthetic fiber is less than 40% by mass, the liquid permeability may decrease. Further, if it exceeds 90% by mass, there is a risk of frequent occurrence of detached fibers or tearing due to insufficient strength.

The semipermeable membrane support of the present invention contains a binder synthetic fiber. By incorporating the step of raising the temperature to near the softening point or the melting temperature (melting point) of the binder synthetic fiber into the manufacturing process of the semipermeable membrane support, the binder synthetic fiber improves the mechanical strength of the semipermeable membrane support. For example, the semipermeable membrane support can be manufactured by a wet fabrication method, and the binder synthetic fiber can be softened or melted in a subsequent drying step.

Examples of the binder synthetic fiber include core-sheath fibers (core-shell type), parallel fibers (side-by-side type), composite fibers such as radial split fibers, and undrawn fibers. Since the composite fiber is difficult to form a film, the mechanical strength can be improved while maintaining the space of the semipermeable membrane support. More specifically, a combination of polypropylene (core) and polyethylene (sheath), a combination of polypropylene (core) and ethylene vinyl alcohol (sheath), a combination of high melting point polyester (core) and low melting point polyester (sheath), polyester, etc. Undrawn fibers can be mentioned. In addition, single fibers (zen'yu type) composed only of low melting point resins such as polyethylene and polypropylene, and hot water-soluble binders such as polyvinyl alcohols tend to form a film in the drying process of the semitransparent film support. However, it can be used as long as the characteristics are not impaired. In the present invention, a combination of a high melting point polyester (core) and a low melting point polyester (sheath), and undrawn polyester fibers can be preferably used.

The fiber diameter of the binder synthetic fiber is not particularly limited, but is preferably 2 to 20 μm, more preferably 5 to 15 μm, and even more preferably 7 to 13 μm. Further, it is preferable that the fiber diameter is different from that of the main synthetic fiber. Since the fiber diameter is different from that of the main synthetic fiber, it also plays a role of forming a uniform three-dimensional network together with the main synthetic fiber.

The fiber length of the binder synthetic fiber is not particularly limited, but is preferably 1 to 12 mm, more preferably 3 to 10 mm, and further preferably 4 to 6 mm. The cross-sectional shape of the binder synthetic fiber is preferably circular, but fibers having irregular cross-sections such as T-type, Y-type, and triangular are also used for preventing strike-through, smoothness of coated surfaces, and adhesion between non-coated surfaces. Can be contained within a range that does not impair the characteristics of.

The aspect ratio (fiber length / fiber diameter) of the binder synthetic fiber is preferably 200 to 1000, more preferably 300 to 800, and further preferably 400 to 700. When the aspect ratio is less than 200, the dispersibility of the fibers is good, but there is a risk that the fibers may fall off from the papermaking net during papermaking, or the fibers may stick into the papermaking net, resulting in poor peelability from the papermaking net. There is a fear. On the other hand, if it exceeds 1000, the binder synthetic fiber contributes to the formation of the three-dimensional network, but the fibers may be entangled or entangled, which may adversely affect the uniformity of the non-woven fabric and the smoothness of the coated surface. , It may lead to the generation of detached fibers, or Sk may exceed 14 μm.

The content of the binder synthetic fiber is preferably 10 to 60% by mass, more preferably 20 to 50% by mass, and even more preferably 25 to 40% by mass with respect to the nonwoven fabric related to the semipermeable membrane support of the present invention. In the above range, by increasing the content of the binder synthetic fiber, the fluffing of the desorbed fiber and the main synthetic fiber can be suppressed. If the content of the binder synthetic fiber is less than 10% by mass, it may be torn due to insufficient strength, and the number of fibers for covering the main synthetic fiber may be insufficient to generate detached fibers. On the other hand, if it exceeds 60% by mass, the liquid permeability may be lowered and the adhesiveness between the semipermeable membrane and the semipermeable membrane support may be deteriorated.

The method for producing the semipermeable membrane support of the present invention will be described. In the semipermeable membrane support of the present invention, after a base paper is produced by a wet papermaking method, the base paper is thermally pressure-processed by a heat roll.

In the wet papermaking method, first, the binder synthetic fiber or the like is uniformly dispersed in water by a disperser such as a pulper, and then the main synthetic fiber is charged and dispersed, so that the binder synthetic fiber is uniformly mixed with the main synthetic fiber. do. After that, through steps such as screen (removal of foreign matter, lumps, etc.), a slurry diluted with white water (diluted water) and prepared to have a final fiber concentration of 0.01 to 0.50% by mass is made with a paper machine. Raised to obtain wet paper. Stirring the diluted slurry with a stirrer is preferable because it promotes monofilament of the fiber bundle. In order to make the dispersibility of fibers uniform, chemicals such as dispersants, defoamers, hydrophilic agents, antistatic agents, polymer viscous agents, mold release agents, antibacterial agents, and bactericidal agents may be added in the process. be.

As the papermaking method, for example, a papermaking method such as a long net, a circular net, or an inclined wire type can be used. Use a paper machine with one paper machine selected from these paper machines, or a combination paper machine with two or more paper machines of the same type or different types selected from these paper machines online. can do. Further, in the case of producing a non-woven fabric having a multi-layer structure of two or more layers, a "slurry method" in which wet papers made by each paper machine are laminated, or after forming one layer, on the layer. A "casting method" or the like can be used in which a slurry in which fibers are dispersed is cast to form another layer.

The wet paper produced by the paper machine is dried with a Yankee dryer, an air dryer, a cylinder dryer, a suction drum type dryer, an infrared type dryer, or the like to obtain a base paper. When the wet paper is dried, it is brought into close contact with a heat roll such as a Yankee dryer and heat-pressure dried, so that the smoothness of the adhered surface is improved. Hot pressure drying means drying by pressing wet paper against the hot roll with a touch roll or the like. The surface temperature of the heat roll is preferably 100 to 180 ° C, more preferably 100 to 160 ° C, and even more preferably 110 to 160 ° C. The pressure is preferably 50 to 1000 N / cm, more preferably 100 to 800 N / cm.

Since Sk of the semipermeable membrane support is affected by the surface smoothness of the wet paper and the heat pressure drying on the heat roll, it is necessary to adjust the pressing pressure of the wet paper on the heat roll during the heat pressure drying. Even if the surface of the wet paper is rough or uneven, the Sk of the semipermeable membrane support can be adjusted by adjusting the surface temperature of the heat roll and the pressing pressure of the wet paper against the heat roll. Can be done. In order to reduce the Sk of the semipermeable membrane support to 14 μm or less, the pressing pressure of the wet paper against the heat roll is set high during hot pressure drying, and 300 to 800 N / cm is more preferable.

In order to reduce the Sk of the semipermeable membrane support to 14 μm or less, when the wet paper is hot-pressure dried, the surface with improved smoothness is brought into close contact with a heat roll such as a Yankee dryer to make the surface of the semipermeable membrane support improved. It is also effective to use the coated surface of.

Next, thermal pressure processing using a thermal roll will be described, but the present invention is not limited to the following description. In the thermal pressure processing device (thermal calendar device), the base paper is thermally processed by passing the base paper between the nipped rolls. Examples of the combination of rolls include two metal rolls, a metal roll and a resin roll, a metal roll and a cotton roll, and the like. At least one of the two rolls is heated and used as a heat roll. Mainly, metal rolls are used as thermal rolls. The thermal pressure processing by the thermal roll can be performed twice or more, and in that case, two or more sets of the above roll combinations arranged in series may be used, or one set of roll combinations may be used. It may be processed twice. If necessary, the front and back of the base paper may be reversed. The desired semipermeable membrane support can be obtained by controlling the surface temperature of the thermal rolls, the nip pressure between the rolls, and the processing speed of the base paper.

In addition, even if fluffing of the main synthetic fibers occurs on the base paper, the binder synthetic fibers are optimally melted and softened during thermal pressure processing with a hot roll to hold the fluffing, so that detached fibers are generated and the film is applied. It is possible to prevent it from becoming a drawback later. For that purpose, it is important to raise the thermal roll temperature to near the melting point of the binder synthetic fiber and to raise the nip pressure. Further, by controlling the processing speed, the hold of fluffing by the binder synthetic fiber can be adjusted to some extent. Further, by increasing the content of the binder synthetic fiber, the degree of holding by the fluffy binder synthetic fiber can be increased.

In order to reduce the Sk of the semipermeable membrane support to 14 μm or less, it is necessary to optimize the conditions of thermal pressure processing. Semipermeable membrane defects can be prevented by adjusting the conditions of thermal pressure processing and increasing the smoothness of the coated surface. For that purpose, it is important to raise the heat roll temperature to near the melting point of the binder synthetic fiber, control the processing speed to give a sufficient amount of heat to the semipermeable membrane support, and increase the nip pressure.

The temperature of the heat roll is preferably in the range of −50 ° C. to −10 ° C. with respect to the melting point of the binder synthetic fiber. More preferably, it is in the range of −40 ° C. to −15 ° C., and even more preferably, it is in the range of −30 ° C. to −15 ° C. When the temperature of the thermal roll in the thermal pressure processing is lower than -50 ° C with respect to the melting point of the binder synthetic fiber, the temperature of the binder synthetic fiber does not rise sufficiently and adhesion failure with the main synthetic fiber occurs and detachment fiber occurs. , The base paper is hard to be crushed, and the Sk of the coated surface of the semitransparent film support may exceed 14 μm. On the other hand, when the temperature exceeds -10 ° C, the binder synthetic fiber is inactivated, the adhesion between the binder synthetic fiber and the main synthetic fiber becomes insufficient, and detachment fiber is generated, or the coated surface of the semipermeable membrane support. Sk may exceed 14 μm.

The nip pressure of the roll in the hot pressure processing is preferably 19 to 180 kN / m, more preferably 45 to 140 kN / m. When the nip pressure is less than 19 kN / m, the adhesion between the thermal roll and the base paper becomes low and the fibers may fluff, and detached fibers may occur or the Sk of the semipermeable membrane support may exceed 14 μm. On the other hand, when it exceeds 180 kN / m, the density of the semipermeable membrane support becomes high, the penetration of the film-forming solution decreases, the adhesiveness between the semipermeable membrane and the semipermeable membrane support decreases, or the excess on the roll. The increased load may shorten the roll life.

The processing speed in the hot pressure processing is preferably 4 to 100 m / min, and more preferably 10 to 80 m / min. When the speed is less than 4 m / min, the productivity is inferior, the density of the semipermeable membrane support is increased, the air permeability is lowered, the semipermeable membrane solution is difficult to permeate, and the adhesiveness between the membrane and the support is lowered. In some cases. On the other hand, if it exceeds 100 m / min, heat transfer to the base paper becomes insufficient and fluffing of the main synthetic fiber occurs, resulting in detachment fiber or Sk on the coated surface of the semipermeable membrane support. May exceed 14 μm.

The basis weight of the semipermeable membrane support is not particularly limited, but is preferably 20 to 150 g / m ² , and more preferably 50 to 100 g / m ² . If it is less than 20 g / m ² , sufficient tensile strength may not be obtained. Further, if it exceeds 150 g / m ² , the liquid passage resistance may increase or the thickness may increase and a specified amount of semipermeable membrane may not be stored in the unit or module.

The density of the semipermeable membrane support is preferably 0.5 to 1.0 g / cm ³ , and more preferably 0.6 to 0.9 g / cm ³ . If the density of the semipermeable membrane support is less than 0.5 g / cm ³ , the thickness becomes thicker, so that the area of the semipermeable membrane that can be incorporated into the unit becomes smaller, and as a result, the life of the semipermeable membrane becomes shorter. It may end up. On the other hand, if it exceeds 1.0 g / cm ³ , the liquid permeability may be lowered and the life of the semipermeable membrane may be shortened.

The thickness of the semipermeable membrane support is preferably 50 to 150 μm, more preferably 60 to 130 μm, and even more preferably 70 to 120 μm. If the thickness of the semipermeable membrane support exceeds 150 μm, the area of the semipermeable membrane that can be incorporated into the unit becomes small, and as a result, the life of the semipermeable membrane may be shortened. On the other hand, if it is less than 50 μm, sufficient tensile strength may not be obtained or the liquid permeability may be lowered, so that the life of the semipermeable membrane may be shortened.

The present invention will be described in more detail by way of examples. Hereinafter, unless otherwise specified, the parts and ratios described in the examples are based on mass.

≪Main synthetic fiber≫
PET fiber 1: A stretched polyester fiber made of polyethylene terephthalate, having a fiber diameter of 7.5 μm, a fiber length of 5 mm, and an Sb element elution amount of 0.01 μg / g or less.

PET fiber 2: A stretched polyester fiber made of polyethylene terephthalate, having a fiber diameter of 7.5 μm, a fiber length of 5 mm, and an Sb element elution amount of 0.12 μg / g.

PET fiber 3: A stretched polyester fiber made of polyethylene terephthalate, having a fiber diameter of 7.5 μm, a fiber length of 6 mm, and an Sb element elution amount of 10.3 μg / g.

PET fiber 4: A stretched polyester fiber made of polyethylene terephthalate, having a fiber diameter of 12.5 μm, a fiber length of 5 mm, and an Sb element elution amount of 11.9 μg / g.

≪Binder synthetic fiber≫
PET fiber 5: An undrawn polyester fiber made of polyethylene terephthalate, having a fiber diameter of 11.8 μm, a fiber length of 5 mm, and an Sb element elution amount of 2.3 μg / g.

PET fiber 6: An undrawn polyester fiber made of polyethylene terephthalate, having a fiber diameter of 10.5 μm, a fiber length of 5 mm, and an Sb element elution amount of 0.04 μg / g.

PET fiber 7: An undrawn polyester fiber made of polyethylene terephthalate, having a fiber diameter of 11.8 μm, a fiber length of 5 mm, and an Sb element elution amount of 0.01 μg / g or less.

PET fiber 8: An undrawn polyester fiber made of polyethylene terephthalate, having a fiber diameter of 13.6 μm, a fiber length of 5 mm, and an Sb element elution amount of 0.01 μg / g or less.

PET fiber 9: An undrawn polyester fiber made of polyethylene terephthalate, having a fiber diameter of 13.6 μm, a fiber length of 10 mm, and an Sb element elution amount of 0.01 μg / g or less.

(Manufacturing of base papers 1 to 3 and 5 to 16: with two-step dispersion)
After water is poured into a 2 m ³ dispersion tank, the binder synthetic fiber is first charged into the dispersion tank and dispersed for 3 minutes with the fiber composition shown in Table 1, and then the main synthetic fiber is charged into the dispersion tank and mixed and dispersed for 7 minutes ( Dispersion concentration is 2.0%), and after laminating the wet paper formed on the inclined wire and the wet paper formed on the circular net using an inclined wire / circular net composite paper machine, the surface temperature is 130 ° C. It was hot-pressure dried with a Yankee dryer to obtain base papers 1 to 3 and 5 to 16 having a target basis weight of 70 g / m ² . The fiber composition of the inclined wire and the circular net is the same.

(Manufacturing of base paper 4: No two-step dispersion)
After pouring water into a 2 m ³ dispersion tank, the binder synthetic fiber and the main synthetic fiber are simultaneously put into the dispersion tank with the fiber composition shown in Table 1, mixed and dispersed for 7 minutes (dispersion concentration 2.0%), and the inclined wire. / Using a circular net composite paper machine, the wet paper formed on the inclined wire and the wet paper formed on the circular net are laminated, and then hot-pressure dried with a Yankee dryer with a surface temperature of 130 ° C to achieve the target basis weight. A base paper 4 of 70 g / m ² was obtained. The fiber composition of the inclined wire and the circular net is the same.

(Thermal calendar processing)
For the obtained base paper, use a thermal calendar device with a combination of a metal roll (heat roll) and an elastic roll, or a thermal calendar device with a combination of a metal roll (heat roll) and a metal roll (heat roll). The semitransparent film supports of Examples 1 to 16 and Comparative Examples 1 to 7 were obtained under the thermal calendar conditions described in 1. In the first stage where the thermal pressure processing is performed first, the surface (processed surface) where the base paper is in contact with the metal roll (thermal roll) is set as the coating surface, and the treated surface in the second stage where the thermal pressure processing is performed second time is , The opposite side of the first stage. In Table 2, the circular net surface is a surface formed by a circular net, and the inclined surface is a surface formed by an inclined wire.

The semipermeable membrane supports obtained in Examples 1 to 16 and Comparative Examples 1 to 7 were measured and evaluated as follows, and the results are shown in Table 3.

[Basis weight]
Basis weight was measured according to JIS P8124: 2011.

[Thickness and density of semipermeable membrane support]
Measured according to JIS P8118: 2014.

[Tape peeling test: number of detached fibers]
The semipermeable membrane support is cut into a width of 45 mm and a length of 60 mm to prepare a sample. A cellophane adhesive tape (manufactured by Nichiban Co., Ltd., trade name: Elpack (registered trademark) LP24) cut into a width of 24 mm and a length of 100 mm is taped to the center of the sample in the length direction on the coated surface of the cut semipermeable membrane support. Stick it on a rubber mat so that both ends stick out. A metal roll (diameter 4 cm, length 30 cm, weight 3 kg) having a smooth surface is rotated three times on the sample to which the tape is attached, and the tape is uniformly attached to the sample. Hold the part of the tape that sticks out of the sample, slowly peel off the tape from the sample, and observe the fibers that stick to the tape. Five samples were prepared and tested five times. The number of detached fibers present in the central portion (20 mm × 50 mm) of the tape peeled from the sample was measured, and the average number of five tests was calculated.

[Measurement of core level difference Sk]
The semipermeable membrane support is cut into a width of 45 mm and a length of 60 mm to prepare a sample. Using a confocal laser scanning microscope (trade name: VK-X1050, manufactured by KEYENCE CORPORATION), the observation magnification is set to 20 times, the imaging size is set to 3 mm in length × 2 mm in width, and imaging is performed. The entire area is specified as the measurement area, and Sk is measured.

[Measurement of antimony element elution amount]
Collect 30 mL of the eluate obtained by immersing 1.6 g of a main synthetic fiber, a binder synthetic fiber or a semitransparent film support in 0.20 L of ultrapure water having a specific resistance of 18.2 MΩ · cm and a temperature of 25 ° C. for 24 hours. Then, after adding 1 μL of nitrate (Kishida Chemical Co., Ltd., for precision analysis, concentration 60%), inductively coupled plasma mass spectrometer (ICP-MS) (device name: iCAP-Qc, manufactured by Thermo Fisher Scientific). ), The antimony element content contained in the eluent was measured and then quantified by the calibration linear method. Further, the amount of antimony element eluted was calculated by <Equation 1>. The lower limit of antimony quantification of the ICP-MS was 0.1 ppb, and the antimony content of the ultrapure water used for the measurement was equal to or less than the lower limit of quantification.

[Measurement of salt inhibition rate]
Using a constant-speed coating device (trade name: TQC fully automatic film applicator, manufactured by Cortec) with a constant clearance, 125 μm of DMF solution (concentration: 18%) of polysulfone resin was applied to the coated surface of the semipermeable membrane support. It was applied to a thickness and phase-separated in a coagulation bath to prepare a porous polysulfone membrane. An aqueous solution A containing 2% by mass of m-phenylenediamine and 0.15% by mass of sodium lauryl sulfate was brought into contact with the porous polysulfone film, and then the excess aqueous solution A was removed to form a coating layer of the aqueous solution A. .. Next, a solution B containing 0.3% by mass of trimesic acid chloride was brought into contact with the surface of the coating layer of the aqueous solution A, and the excess solution B was discharged. Then, it was dried at 120 ° C. to form a separation functional layer, and a separation membrane in which a composite semipermeable membrane composed of a porous polysulfone membrane and a separation functional layer was provided on a coating surface of a semipermeable membrane support was obtained.

The separation membrane was cut into 14 cm × 19 cm and set in a flat membrane test device (trade name: SEPA CFII, SUEZ). A 3.0 mass% sodium chloride aqueous solution at 25 ° C. was passed through the membrane at a differential pressure of 5.0 MPa between the supply side and the permeation side. The conductivity of the permeated water obtained by this operation was measured, and the salt inhibition rate (%) was calculated. The salt blocking rate was calculated from <Equation 2> by preparing a calibration curve from the sodium chloride concentration and the aqueous conductivity.

<Equation 2>
Salt inhibition rate (%) = (1- (sodium chloride concentration of permeate) / (sodium chloride concentration of feed solution)) x 100

[Semipermeable membrane defect evaluation]
The separation membrane was cut into 14 cm × 19 cm and set in a flat membrane test device (trade name: SEPA CFII, SUEZ). An aqueous solution containing a 200 ppm dye (Direct Blue 1, molecular weight: 993) was passed at 25 ° C. at a differential pressure of 1.5 MPa between the membrane supply side and the permeation side. Then, the dye accumulated on the surface of the composite semipermeable membrane was washed away with pure water, the separation membrane was dried, and the number of dyed portions (membrane defect portions) was measured.

0 to 1 points are very good levels, 2 to 3 places are good levels, 4 to 6 places are usable levels, and 7 or more places are inferior in film performance and unusable.

[Semipermeable membrane strike through]
Using a constant-speed coating device with a certain clearance (trade name: Automatic Film Applicator, manufactured by Yasuda Seiki Seisakusho Co., Ltd.), set the semipermeable membrane support on the mount, and black on the coated surface of the semipermeable membrane support. Apply a DMF solution (concentration: 18%) of polysulfone resin mixed with the oil-based ink of the above, and after application, visually observe the amount of polysulfone resin reflected on the mount through the semipermeable membrane support, and observe the amount of polysulfone resin reflected in the semipermeable membrane. A strike-through evaluation was performed.

1: There is no strike-through. Very good level.
2: It is a small dot, and it is very slightly strike-through. Good level.
3: It is a small dot and strikes through. Practically usable level.
4: Large dots, many strike through. Practically unusable level.

The semipermeable membrane supports of Examples 1 to 16 are made of a wet non-woven fabric containing a main synthetic fiber and a binder synthetic fiber, have 30 or less detached fibers in the tape peeling test, and are semi-permeable by a confocal laser microscope. Since the level difference of the core portion obtained by measuring the surface roughness of the coated surface on which the permeable membrane is provided is 14 μm or less, the salt blocking rate is high, there are few defects of the semipermeable membrane, and the semipermeable membrane strikes through. It turned out to be difficult.

From the comparison between Examples 1 to 3 and Comparative Examples 1 and 2 and the comparison between Example 7 and Comparative Examples 4 and 5, the temperature of the heat roll of the first stage or the heat roll of the second stage was low. And 2 and the semipermeable membrane supports of Comparative Examples 4 and 5 had more than 30 detached fibers and a low salt inhibition rate.

The semipermeable membrane support of Example 5 having a binder synthetic fiber content of 25% has a salt inhibition rate as compared with the semipermeable membrane support of Example 1 having a binder synthetic fiber content of 30%. Although it was low and had many drawbacks of the semipermeable membrane, it was at a usable level. On the other hand, it can be seen that in Comparative Example 6 in which the PET fiber 1 of Example 5 was changed to the PET fiber 3 having a large amount of Sb element elution, the number of detached fibers was large and the salt inhibition rate was low.

Comparative Example 7 in which PET fiber 3 having a large amount of Sb element elution and PET fiber 4 having a large amount of Sb element elution and a large fiber diameter were blended, and the combination of rolls in the first stage was changed to a metal roll-metal roll. It can be seen that the salt blocking rate is low because there are many detached fibers and the core level difference Sk exceeds 14 μm.

In the semipermeable membrane supports of Examples 1 to 15 and Comparative Examples 1, 2, 4 and 5 in which the Sb element elution amount of the semipermeable membrane support is 1.5 μg / g or less, the first stage or the second stage In Comparative Examples 1, 2, 4 and 5 in which the temperature of the heat roll is low, it can be seen that the salt inhibition rate is low because the number of detached fibers exceeds 30 and the core level difference Sk is high.

The semipermeable membrane support of Example 4 in which the coating surface is an inclined wire surface is a semipermeable membrane support, although the coating surface is a usable level, as opposed to the semipermeable membrane support of Example 1 in which the coating surface is a circular mesh surface. It can be seen that the defects increase and the salt inhibition rate decreases.

In contrast to the semipermeable membrane support of Example 6 in which two-step dispersion was performed during the production of the base paper, the semipermeable membrane support of Comparative Example 3 in which the two-step dispersion was not performed had a core level difference Sk of more than 14 μm, which was half. It was a level that could not be used in the evaluation of defects in the permeable membrane.

The number of detached fibers in the tape peeling test is 30 or less, the core level difference Sk is 14 μm or less, the amount of antimony element eluted from the main synthetic fiber and the binder synthetic fiber is less than 5 μg / g, and the semipermeable membrane support. The number of detached fibers is 30 or less and the core level difference Sk is 14 μm or less with respect to the semipermeable membranes of Examples 1 and 7 in which the amount of antimony element eluted is less than 1.5 μg / g. The semipermeable membrane support of Example 16 in which the amount of antimony element eluted from the fiber exceeds 5 μg / g and the amount of antimony element eluted from the semipermeable membrane support exceeds 1.5 μg / g is semipermeable, although it is at a usable level. It can be seen that the defects of the permeable membrane increase and the salt inhibition rate decreases.

The semipermeable membrane support of the present invention can be used in fields such as seawater desalination, water purifiers, food concentration, wastewater treatment, medical use represented by hemofiltration, and ultrapure water production for semiconductor cleaning. can.

Claims (4)

In a semipermeable membrane support made of a wet non-woven fabric containing a main synthetic fiber and a binder synthetic fiber, the number of detached fibers in the tape peeling test is 30 or less, and the coated surface on which the semipermeable membrane is provided by a confocal laser microscope. A semipermeable membrane support characterized in that the level difference of the core portion obtained by measuring the surface roughness of the above is 14 μm or less. The semipermeable membrane support according to claim 1, wherein the amount of antimony element eluted from the main synthetic fiber or the binder synthetic fiber is less than 5 μg / g. The semipermeable membrane support according to claim 1 or 2, wherein the amount of antimony element eluted from the semipermeable membrane support is less than 1.5 μg / g. In the method for producing a semipermeable membrane support for producing the semipermeable membrane support according to any one of claims 1 to 3, wet fabrication is performed from a fiber dispersion obtained by dispersing the binder synthetic fiber and then dispersing the main synthetic fiber. A method for producing a semipermeable membrane support, which comprises producing a semipermeable membrane support by a method.