CN105935556B

CN105935556B - Semipermeable membrane support and preparation method thereof

Info

Publication number: CN105935556B
Application number: CN201610122818.XA
Authority: CN
Inventors: 吉田光男; 浅沼铁兵; 锻冶裕夫
Original assignee: Mitsubishi Paper Mills Ltd
Current assignee: Mitsubishi Paper Mills Ltd
Priority date: 2015-03-05
Filing date: 2016-03-04
Publication date: 2020-12-01
Anticipated expiration: 2036-03-04
Also published as: JP2017104840A; CN105935556A

Abstract

[ problem ] to provide a semipermeable membrane support which has excellent adhesion between a semipermeable membrane and a semipermeable membrane support and through which a semipermeable membrane solution does not penetrate. [ solution ] A semipermeable membrane support comprising a nonwoven fabric containing at least a main synthetic fiber and a binder synthetic fiber, characterized in that a fused whisker of the binder synthetic fiber is present on at least one surface of the semipermeable membrane support.

Description

Semipermeable membrane support and preparation method thereof

Technical Field

The invention relates to a semipermeable membrane support and a preparation method thereof.

Background

Semipermeable membranes are widely used in the fields of desalination of seawater, purification of water, concentration of food, wastewater treatment, and the like, the field of medical use represented by hemofiltration, the field of preparation of ultrapure water for semiconductor cleaning, and the like. The semipermeable membrane may be made of synthetic resin such as cellulose resin, polysulfone resin, polyacrylonitrile resin, fluorine resin, or polyester resin. However, since the semipermeable membrane is inferior in mechanical strength, a separation membrane in the form of a composite in which a semipermeable membrane is provided on one surface of a semipermeable membrane support composed of a fibrous base material such as a nonwoven fabric or a woven fabric is used. In the present specification, 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".

A nonwoven fabric containing synthetic fibers is mainly used as a semipermeable membrane support. Examples of the performance required for the semipermeable membrane support include: the semi-permeable membrane and the semi-permeable membrane support have good adhesion; when the semipermeable membrane support is coated with the semipermeable membrane solution for providing the semipermeable membrane, the semipermeable membrane solution does not penetrate to the non-coated surface or the like.

In order to improve the uniformity of the semipermeable membrane support so that the semipermeable membrane solution does not penetrate, the following methods are proposed: in a step of wet-papermaking a fiber slurry having synthetic fibers dispersed in water to form a nonwoven fabric, the fiber slurry is made into a nonwoven fabric by making the fiber slurry have a fiber component concentration of 0.01 to 0.1 mass% and by adding a water-soluble polymer having a molecular weight of 500 ten thousand or more as a polymer binder in the fiber slurry in an amount of 3 to 15 mass% based on the mass of the fiber component (see, for example, patent document 1). However, the excessive addition of the polymer binder improves the uniformity, but the viscosity of the fiber slurry on the paper web increases, which may cause problems such as a decrease in the dewatering property from the web and an inability to improve the production rate. In addition, there is a problem that a polymer adhesive remains on the surface of the fiber forming the semipermeable membrane support after the papermaking.

Further, a semipermeable membrane support has been proposed which is formed of a nonwoven fabric having a multilayer structure based on a double structure of a surface layer (coarse fiber layer) having a large surface roughness using coarse fibers and a back layer (fine fiber layer) having a dense structure using fine fibers (see, for example, patent document 2). Specifically, the following are described: the semipermeable membrane support comprises a semipermeable membrane support having a coarse fiber layer as a coating surface and a fine fiber layer as a non-coating surface, wherein the fine fiber layer is sandwiched between the coarse fiber layers, and both the coating surface and the non-coating surface are made into coarse fiber layers. However, since coarse fibers are used on the coated surface, the adhesiveness between the semipermeable membrane and the semipermeable membrane support is improved, but the smoothness is low. Further, since the coarse fibers are used, the semipermeable membrane solution penetrates into the semipermeable membrane support, and therefore, a large amount of the semipermeable membrane solution is required to obtain a desired thickness of the semipermeable membrane.

In order to solve the problem of producing a non-uniform semipermeable membrane by bending a semipermeable membrane support in the width direction when a semipermeable membrane solution is applied, a semipermeable membrane support in which the ratio of the tensile strength in the paper feeding direction to the tensile strength in the width direction is 2:1 to 1:1 and the orientation of the fibers is in a random state has been proposed (for example, see patent document 3). Patent document 3 proposes a method for adjusting the air permeability and pore diameter of a semipermeable membrane support for the purpose of improving the adhesion between the semipermeable membrane and the semipermeable membrane support and preventing penetration. However, the air permeability obtained according to JIS L1096 is calculated based on the amount of air that passes from one surface of the semipermeable membrane support to the other surface through the inside of the semipermeable membrane support, and does not accurately reflect the penetration of the semipermeable membrane solution applied to the surface of the coated surface to the non-coated surface. Therefore, when a semipermeable membrane solution is applied to a semipermeable membrane support having an air permeability within the range shown in patent document 3, the semipermeable membrane solution may penetrate.

In addition, patent document 4 proposes a method of optimizing the number of times, temperature, and type of rolls of hot press processing of a wet nonwoven fabric for the purpose of preventing low-density defects, which are portions where synthetic fibers constituting the wet nonwoven fabric are loose and the sheet density is reduced, from being generated, in order to solve the problem that when a semipermeable membrane solution is applied to a defective portion locally existing on a semipermeable membrane sheet as a semipermeable membrane support, the permeability of the semipermeable membrane solution changes partially, and the thickness of the semipermeable membrane at that portion becomes very thin, or the surface of the semipermeable membrane becomes wrinkled. Patent document 4 proposes a semipermeable membrane support in which the sheet density and the pressure loss are adjusted, as a semipermeable membrane support which is free from low-density defects, uniform, has good adhesion between the semipermeable membrane and the semipermeable membrane support, and can prevent the semipermeable membrane solution from excessively penetrating into the wet nonwoven fabric and the semipermeable membrane from becoming non-uniform. However, even a semipermeable membrane support having a sheet density and a pressure loss in the range shown in patent document 4 may sometimes cause penetration.

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2008-238147

Patent document 2: japanese examined patent publication (Kokoku) No. 4-21526

Patent document 3: japanese laid-open patent publication No. 2002-95937

Patent document 4: international publication No. 2012/090874 pamphlet.

Disclosure of Invention

Problems to be solved by the invention

The subject of the invention is: provided are a semipermeable membrane support which has excellent adhesion between a semipermeable membrane and a semipermeable membrane support and through which a semipermeable membrane solution does not penetrate, and a method for producing the same.

Means for solving the problems

The above problems can be solved by the following means.

(1) A semipermeable membrane support comprising a nonwoven fabric containing at least a main synthetic fiber and a binder synthetic fiber, characterized in that a molten whisker of the binder synthetic fiber is present on at least one surface of the semipermeable membrane support.

(2) The semipermeable membrane support according to item (1), wherein the melting whiskers observed in an electron micrograph of the surface of the semipermeable membrane support are 1.0mm per unit²More than 2.

(3) The semipermeable membrane support according to item (1) or (2), wherein the molten fibers of the binder synthetic fibers have a branched shape.

(4) The semipermeable membrane support according to any of (1) to (3), wherein the molten whiskers of the binder synthetic fiber have a tip diameter of the molten whiskers smaller than a diameter of the main synthetic fiber.

(5) The semipermeable membrane support according to any of (1) to (4), wherein the shape of the molten whiskers of the binder synthetic fibers is a shape in which the molten whiskers traverse at least one gap selected from a gap between the main synthetic fibers, a gap between the main synthetic fibers and the binder synthetic fibers, and a gap between the binder synthetic fibers.

(6) The semipermeable membrane support according to any of (1) to (5), wherein a face of the semipermeable membrane support on which the semipermeable membrane is applied, that is, a coated face, has molten whiskers of the binder synthetic fiber, and the coated face has molten whiskers in a state of lying down.

(7) The semipermeable membrane support according to any of (1) to (6), wherein the molten binder synthetic fiber is present on both surfaces of the semipermeable membrane support.

(8) A process for producing a semipermeable membrane support according to any one of (1) to (7), which comprises a step of preparing a sheet by wet-type papermaking from a slurry containing at least a host synthetic fiber and a binder synthetic fiber, and a step of hot-pressing the sheet obtained in the preceding step by a hot roll, wherein the hot-pressing is carried out while confirming the surface temperature of the semipermeable membrane support immediately after the hot-pressing.

(9) The process according to (8), wherein the surface temperature of the hot roll in the hot pressing is set so that the surface temperature of the semipermeable membrane support measured at a position less than 10cm from the nip immediately after the hot pressing is in the range of-65 ℃ to-20 ℃ relative to the melting point of the binder synthetic fiber.

Effects of the invention

The semipermeable membrane support of the present invention has molten whiskers of a binder synthetic fiber on at least one surface. The semipermeable membrane is less likely to be peeled off from the semipermeable membrane support due to an anchoring effect (anchor effect) between the adhesive synthetic fiber present on the coated surface of the semipermeable membrane support and the semipermeable membrane, and the adhesiveness between the semipermeable membrane and the semipermeable membrane support can be improved. In addition, the presence of the molten whiskers can achieve the effect of preventing penetration of the semipermeable membrane solution.

According to the method for producing a semipermeable membrane support of the present invention, the semipermeable membrane support of the present invention that can achieve the above-described effects can be efficiently produced.

Drawings

FIG. 1 is an electron micrograph of the semipermeable membrane support surface prior to melt-threading to produce binder synthetic fibers.

Fig. 2 is an electron micrograph of the surface of the semipermeable membrane support with molten whiskers of binder synthetic fibers.

Fig. 3 is an electron micrograph of the surface of a semipermeable membrane support showing an example of the shape of molten whiskers of the binder synthetic fibers.

Fig. 4 is an electron micrograph of the surface of a semipermeable membrane support showing an example of the shape of molten whiskers of the binder synthetic fibers.

Fig. 5 is an electron micrograph of the surface of a semipermeable membrane support showing an example of the shape of molten whiskers of the binder synthetic fibers.

Fig. 6 is an electron micrograph of the surface of a semipermeable membrane support showing an example of the shape of molten whiskers of the binder synthetic fibers.

FIG. 7 is an electron micrograph of a cross section of a semipermeable membrane support in which molten binder synthetic fibers are laid down.

FIG. 8 is an electron micrograph of a cross section of a semipermeable membrane support in which molten fibers of a binder synthetic fiber are present in an upright state.

Detailed Description

The semipermeable membrane support of the present invention is a semipermeable membrane support formed of a nonwoven fabric containing at least a main synthetic fiber and a binder synthetic fiber, and is characterized in that a molten whisker of the binder synthetic fiber is present on at least one surface of the semipermeable membrane support.

The semipermeable membrane support of the present invention can be prepared by the following method: after a sheet is produced by a wet papermaking method, the sheet is hot-pressed by a hot roll. When hot-pressing is performed using a heat roll, the binder synthetic fibers melted by contact with the heat roll become short whiskers when they are separated from the heat roll, thereby forming molten whiskers. FIG. 2 of patent document 3 (JP 2002-95937A) is a photomicrograph (200 times) of a semipermeable membrane support, but the binder synthetic fibers are not melt-deformed and short melting cannot be confirmed. The melting does not need to be a portion where the synthetic fibers of the binder are melted and deformed into a film shape. For example, in an electron micrograph (35 times) of the semipermeable membrane support shown in fig. 2 of patent document 4 (pamphlet of international publication No. 2012/090874), an extra (particularly) white portion is a binder synthetic fiber. The binder synthetic fibers are spread in a film form so as to fill the gaps between the main synthetic fibers, and are not whisker-like.

As a method for measuring the number of molten whiskers, a semipermeable membrane was photographedElectron micrographs of the surfaces on both sides of the support, and the measurement was carried out on a constant area (1.0 mm)²) The number of the melting whiskers. When the width of the semipermeable membrane support was 10 × Ncm, N sites were measured. Wherein N is a positive integer. For example, when the width of the semipermeable membrane support is 30cm, a total of 3 sites of a spot of 5cm, a spot of 15cm, and a spot of 25cm from one end in the width direction are measured. In the case of a width of 100cm, a total of 10 sites were measured at a point of 5cm, a point of 15cm, and a point of … … 95 cm. In this case, the number of molten whiskers smaller than the diameter of the binder synthetic fiber before melting was measured. In order to distinguish the melting whisker, the magnification at the time of taking an electron micrograph is preferably 100 times or more, and more preferably 200 times or more.

The number of the molten whiskers is 1.0mm per unit²Preferably 2 or more, more preferably 3 or more, and still more preferably 4 or more. The number of molten whiskers is preferably 1.0mm per unit²Less than 1000. When there are no molten whiskers or the number of molten whiskers is less than 2, the effect of covering the depressions between the main synthetic fibers is poor, and improvement in adhesion between the semipermeable membrane and the semipermeable membrane support cannot be observed in some cases. In addition, the semipermeable membrane solution may penetrate. Although the number of the molten whiskers was not limited to more than 1000, the effect was not improved as compared with the case of 1000 or less.

The melting fiber in the present invention is a part of the binder synthetic fiber which is greatly changed from the fiber shape before melting and becomes a whisker shape. The diameter of the molten whiskers is smaller than the diameter of the binder synthetic fibers before melting. In addition, the melting may be adhered without being separated from the binder synthetic fiber, or may be separated from the binder synthetic fiber and independent. The shape of the molten whisker may be a bifurcated shape branching into a fibril shape, a tapered shape, a shape in which both ends are connected to the main synthetic fiber or the binder synthetic fiber, a curved shape, or the like. Further, the length and thickness of the melting whisker are not constant.

In the present invention, the semipermeable membrane is less likely to be peeled off from the semipermeable membrane support due to the anchoring effect between the molten binder synthetic fiber present on the coated surface of the semipermeable membrane support and the semipermeable membrane, and the effect of improving the adhesion between the semipermeable membrane and the semipermeable membrane support can be achieved. When the semipermeable membrane solution is applied, most of the semipermeable membrane solution remains on the surface of the application surface of the semipermeable membrane support, but a part of the semipermeable membrane solution gradually enters the spaces between the fibers constituting the semipermeable membrane support, that is, the depressions. Then, it is presumed that, when the film is formed, the semipermeable membrane inserted into the recess cannot be easily detached due to the presence of the molten whisker, and the adhesiveness between the semipermeable membrane and the semipermeable membrane support is increased.

Further, since the melted whisker exists in the recess, which is the space between the fibers constituting the semipermeable membrane support, the melted whisker divides the space, and thus the effect of suppressing the penetration of the semipermeable membrane solution can be achieved. The molten whiskers present on the coated side also have the effect of inhibiting penetration of the semipermeable membrane solution, but the molten whiskers present on the non-coated side can inhibit penetration more effectively.

In the present invention, the molten fiber of the binder synthetic fiber may be present on at least one surface of the semipermeable membrane support, but the presence of the molten fiber on both surfaces further improves the effect of improving the adhesion between the semipermeable membrane and the semipermeable membrane support and the effect of preventing penetration of the semipermeable membrane solution.

In the case where the shape of the molten whisker is a bifurcated shape in which the molten whisker branches into fibril shapes, and the tip diameter of the molten whisker is smaller than the diameter of the main synthetic fibers, or the molten whisker traverses at least one type of void selected from the group consisting of voids between the main synthetic fibers, voids between the main synthetic fibers and the binder synthetic fibers, and voids between the binder synthetic fibers, the voids can be divided without suppressing the liquid permeability, and the adhesion between the semipermeable membrane and the semipermeable membrane support and the effect of suppressing the penetration can be further improved.

Semipermeable membrane supports comprising fibrillated lyocell (lyocell) fibers, acrylic fibers, aramid fibers, and the like as fibrillated fibers are known. However, since these fibrillated fibers do not have self-adhesiveness, they may fall off without coming into contact with the binder synthetic fibers, and may cause defects in the semipermeable membrane. On the other hand, in the present invention, the molten fibers are branched into fibril-like branched shapes, and the molten fibers themselves are synthetic fibers as a binder, and therefore have self-adhesive properties and are not likely to fall off.

Fig. 1 is an electron micrograph of the semipermeable membrane support surface before melt-whisker of the binder synthetic fiber is generated, in which only the main synthetic fiber and the binder synthetic fiber not generating melt-whisker are present. The magnification of the electron micrograph is 100 times, and the linear scale bar indicates 100. mu.m.

Fig. 2 is an electron micrograph of the surface of the semipermeable membrane support with molten whiskers of binder synthetic fibers. The magnification of the electron micrograph is 100 times, and a linear scale bar (scale bar) indicates 100. mu.m. The melt must be present so as to cover the voids, i.e., depressions, between the randomly arranged main synthetic fibers. The melting must be caused by the binder synthetic fiber, and firmly bonded to the main synthetic fiber without falling off.

Fig. 3 is an electron micrograph of the surface of a semipermeable membrane support showing an example of the shape of molten whiskers of the binder synthetic fibers. The magnification of the electron micrograph is 200 times, and the linear scale bar indicates 100. mu.m. The shape of the molten whisker existing in the portion surrounded by ○ was a bifurcated shape branching into fibrils.

Fig. 4 is an electron micrograph of the surface of a semipermeable membrane support showing an example of the shape of molten whiskers of the binder synthetic fibers. The magnification of the electron micrograph is 200 times, and the linear scale bar indicates 100. mu.m. The shape of the molten whisker existing in the portion surrounded with ○ is a shape in which the tip diameter of the molten whisker is smaller than the diameter of the main synthetic fiber. In the case where the molten whisker is attached without being detached from the binder synthetic fiber, the tip diameter of the molten whisker is the diameter of the tip of the molten whisker generated from the branch point of the binder synthetic fiber as a starting point. In addition, in the case of detachment from the binder synthetic fiber, the tip diameter of the molten whisker is the diameter of both ends of the molten whisker. The diameter of the tip of the molten whisker is the width of the tip of the molten whisker calculated based on the length of the linear scale of the electron micrograph.

Fig. 5 is an electron micrograph of the surface of a semipermeable membrane support showing an example of the shape of molten whiskers of the binder synthetic fibers. The magnification of the electron micrograph is 200 times, and the linear scale bar indicates 100. mu.m. The melt existing in the portion surrounded by ○ must traverse at least one kind of voids selected from the group consisting of voids between the main synthetic fibers, voids between the main synthetic fibers and the binder synthetic fibers, and voids between the binder synthetic fibers. In addition, the tip diameter of the molten whiskers is finer than the diameter of the bulk synthetic fibers.

Fig. 6 is an electron micrograph of the surface of a semipermeable membrane support showing an example of the shape of molten whiskers of the binder synthetic fibers. The magnification of the electron micrograph is 100 times, and the linear scale bar indicates 100. mu.m. The melt existing in the portion surrounded by ○ must traverse at least one kind of voids selected from the group consisting of voids between the main synthetic fibers, voids between the main synthetic fibers and the binder synthetic fibers, and voids between the binder synthetic fibers. However, since the tip diameter of the melting whisker is larger than the diameter of the main synthetic fiber, the effect of dividing the gap is inferior when compared with the melting whisker existing in the portion surrounded by o in fig. 5.

When the molten whisker is present on the coated surface, the molten whisker is preferably laid down. By arranging the melting whiskers in a state of lying down, the melting whiskers can be randomly arranged in the gaps between the fibers constituting the semipermeable membrane support, large gaps between the fibers can be effectively divided, and the adhesiveness between the semipermeable membrane and the semipermeable membrane support and the effect of suppressing penetration of the semipermeable membrane solution can be further improved. When the melting thread is erected in a vertical direction or an oblique direction with respect to the surface of the semipermeable membrane support, the melting thread is stuck into the semipermeable membrane in the vicinity of the semipermeable membrane support. The semi-permeable membrane performance may be improved in a state where the melt must lie down as compared with a state where the melt must stand up in a vertical direction or an oblique direction.

FIG. 7 is an electron micrograph of a cross-section of a semipermeable membrane support having molten whiskers of binder synthetic fibers. The magnification of the electron micrograph is 200 times, and the linear scale bar indicates 100. mu.m. However, the melting whisker is in a lying state, and the melting whisker in a standing state cannot be confirmed.

FIG. 8 is an electron micrograph of a cross-section of a semipermeable membrane support having molten whiskers of binder synthetic fibers. The magnification of the electron micrograph is 200 times, and the linear scale bar indicates 100. mu.m. It was confirmed that the melting element existing in the 2 portions surrounded by ○ existed in a standing state.

Examples of the method for laying down the molten metal include: a method of performing hot press processing using a heated hot roll and a heated hot roll, hot press processing using a heated roll and an unheated roll, press processing using an unheated roll and an unheated roll, or the like after generation of molten whiskers; a method in which the surface on which the molten whisker is generated is wrapped around a hot roll to be in contact with the hot roll, and the like. These methods may be carried out alone or in combination.

In the present invention, the main synthetic fiber is a fiber forming the skeleton of the semipermeable membrane support. Examples of the main synthetic fibers include fibers of polyolefins, polyamides, polyacrylics, vinylons, vinylidene chloride fibers (vinylidene fibers), polyvinyl chloride, polyesters, benzoates, polyvinyl chloride alcohols (polychlal), phenols, and the like, and fibers of polyesters having high heat resistance are more preferable. In addition, acetate, triacetate, promix (promix), rayon of regenerated fiber, cuprammonium fiber, lyocell (lyocell) fiber, and the like of semi-synthetic fiber may be included in the range in which the performance is not inhibited.

The diameter of the main synthetic fiber is not particularly limited, but is preferably 30 μm or less. More preferably 2 to 20 μm, still more preferably 4 to 20 μm, and particularly preferably 6 to 20 μm. If the thickness is less than 2 μm, the semipermeable membrane solution may be less likely to permeate into the semipermeable membrane support, and the adhesiveness between the semipermeable membrane and the semipermeable membrane support may be poor. If the diameter of the main synthetic fiber exceeds 30 μm, a problem may occur in that a large amount of semipermeable membrane solution is necessary to obtain a desired thickness of the semipermeable membrane, or penetration of the semipermeable membrane solution may occur. In addition, the main synthetic fibers on the surface of the nonwoven fabric tend to rise, and may penetrate through the semipermeable membrane, thereby degrading the performance of the semipermeable membrane.

The fiber length of the main synthetic fiber is not particularly limited, and is preferably 1 to 12mm, more preferably 3 to 10mm, 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 into water in the papermaking step is preferably 1.0 to less than 1.2. When the cross-sectional aspect ratio of the fibers is 1.2 or more, the dispersibility of the fibers may be reduced, or entanglement of the fibers may adversely affect the uniformity of the semipermeable membrane support and the smoothness of the coated surface. However, for the purpose of preventing penetration and surface smoothness, fibers having an irregular cross section such as T-shaped, Y-shaped, or triangular cross section may be included within a range in which other properties such as fiber dispersibility are not inhibited.

The aspect ratio (fiber length/diameter) of the main synthetic fiber is preferably 200 to 1000, more preferably 220 to 900, and still more preferably 280 to 800. When the aspect ratio is less than 200, the dispersibility of the fibers is good, but in the case of papermaking, the fibers may fall off from the wire (wire) or the fibers may penetrate into the wire and the releasability from the wire may be poor. On the other hand, when the amount exceeds 1000, the fibers contribute to the formation of a three-dimensional network, but entanglement or entanglement of the fibers may adversely affect the uniformity of the semipermeable membrane support and the smoothness of the coated surface.

The nonwoven fabric constituting the semipermeable membrane support of the present invention preferably contains 40 to 90 mass%, more preferably 50 to 80 mass%, and still more preferably 60 to 70 mass% of the main synthetic fiber. When the content of the main synthetic fibers is less than 40 mass%, the liquid permeability may decrease. When the content exceeds 90% by mass, the steel sheet may be broken due to insufficient strength.

The semipermeable membrane support of the present invention contains a binder synthetic fiber. The binder synthetic fiber improves the mechanical strength of the semipermeable membrane support by incorporating a step of softening or melting the binder synthetic fiber in the step of producing the semipermeable membrane support. For example, the semipermeable membrane support can be produced by a wet papermaking method, and the binder synthetic fiber is softened or melted in the subsequent drying step.

Examples of the binder synthetic fiber include core-sheath fibers (core-sheath type), side-by-side fibers (side-by-side type), composite fibers such as radially divided fibers, and undrawn fibers. Since the composite fiber is less likely to form a coating 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 polyester (core) and low-melting polyester (sheath), and undrawn fibers such as polyester can be mentioned. Further, although a single fiber (all-melt type) composed of only a low-melting resin such as polyethylene or polypropylene or a hot-water-soluble binder such as polyvinyl alcohol is likely to form a coating film in the drying step of the semipermeable membrane support, it can be used within a range in which the properties are not inhibited. In the present invention, a combination of a high-melting polyester (core) and a low-melting polyester (sheath), or undrawn polyester fibers can be preferably used.

The diameter of the binder synthetic fiber is not particularly limited, but is preferably 2 to 20 μm, more preferably 5 to 15 μm, and further preferably 7 to 12 μm. In addition, the diameter is preferably different from the main synthetic fiber, and particularly preferably smaller than the main synthetic fiber. The binder synthetic fiber has a diameter different from that of the main synthetic fiber, and thus not only serves to improve the mechanical strength of the semipermeable membrane support but also serves to form a uniform three-dimensional network together with the main synthetic fiber. In addition, the smoothness of the surface of the semipermeable membrane support can be improved even in the step of raising the temperature to the softening temperature or the melting temperature of the binder synthetic fiber or higher, and it is more effective if pressurization is accompanied in this step. In the present invention, the number of molten whiskers smaller than the diameter of the binder synthetic fiber before melting was measured. In a preferred embodiment, when the diameter of the binder synthetic fiber is smaller than the diameter of the main synthetic fiber, the molten fibers having a diameter smaller than the diameter of the binder synthetic fiber before melting are also smaller than the diameter of the main synthetic fiber, and it can be determined that the molten fibers have a diameter smaller than the diameter of the main synthetic fiber.

The fiber length of the binder synthetic fiber is not particularly limited, and is preferably 1 to 12mm, more preferably 3 to 10mm, and further preferably 4 to 6 mm. The cross-sectional shape of the binder synthetic fiber is preferably circular, but fibers having an irregular cross-section such as T-shaped, Y-shaped, triangular, etc. may be included in the range where other characteristics are not suppressed in order to prevent penetration and smoothness of the coated surface.

The aspect ratio (fiber length/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 possibility that the fibers may fall off from the paper web or the fibers may penetrate into the paper web and become poor in the releasability from the web during the papermaking. On the other hand, when the amount exceeds 1000, the binder synthetic fibers contribute to the formation of a three-dimensional network, but may be entangled with each other or may adversely affect the uniformity of the nonwoven fabric or the smoothness of the coated surface due to entanglement.

The content of the binder synthetic fiber in the nonwoven fabric constituting the semipermeable membrane support of the present invention is preferably 10 to 60 mass%, more preferably 20 to 50 mass%, and still more preferably 25 to 40 mass%. Within the above range, the molten whiskers can be increased by increasing the content of the binder synthetic fibers. When the content of the binder synthetic fiber is less than 10% by mass, the fiber may be broken due to insufficient strength, and the fiber may not be melted. When the content exceeds 60% by mass, the liquid permeability may be lowered.

In order to make the shape of the molten whisker branched, the tip diameter of the molten whisker smaller than the diameter of the main synthetic fiber, or the molten whisker traversing at least one type of gap selected from the group consisting of a gap between the main synthetic fibers, a gap between the main synthetic fiber and the binder synthetic fiber, and a gap between the binder synthetic fibers, it is necessary to arrange the main synthetic fiber and the binder synthetic fiber constituting the nonwoven fabric in a random direction, and it is necessary to have the binder synthetic fiber present in a portion in contact with the hot roll. In order to arrange randomly, the ratio of the diameter of the main synthetic fiber to the diameter of the binder synthetic fiber (diameter of the main synthetic fiber/diameter of the binder synthetic fiber) is preferably 0.2 to 4.0/1.0, more preferably 0.3 to 3.0/1.0, and still more preferably 0.4 to 2.5/1.0. When the diameter of the main synthetic fibers/the diameter of the binder synthetic fibers is less than 0.2/1.0, the number of the binder synthetic fibers is insufficient because the diameter of the binder synthetic fibers is large, and the binder synthetic fibers may not be randomly arranged with respect to the main synthetic fibers. On the other hand, when the diameter of the main synthetic fibers/the diameter of the binder synthetic fibers exceeds 4.0/1.0, the binder synthetic fibers are buried between the main synthetic fibers, and the binder synthetic fibers existing in a portion in contact with the heat roller may be insufficient.

The method for producing the semipermeable membrane support of the present invention will be described. The semipermeable membrane support of the present invention is produced by a wet papermaking method, and then the sheet is hot-pressed by a hot roll.

In the wet papermaking method, a slurry having a final fiber concentration adjusted to 0.01 to 0.50 mass% is first uniformly dispersed in water at least in the main synthetic fiber and the binder synthetic fiber, and then subjected to a step of screening (removal of foreign matter, lumps, and the like) and the like, and is collected with a paper machine, thereby obtaining a wet paper. In order to make the fiber uniformly dispersible, chemicals such as a dispersant, an antifoaming agent, a hydrophilic agent, an antistatic agent, a polymer binder, a release agent, an antibacterial agent, and a bactericide may be added in the process.

As the paper making method, for example, a paper making method such as a fourdrinier wire, a cylinder wire, or an inclined wire can be used. A paper machine having at least one paper making method selected from these paper making methods, or a combined paper machine having 2 or more frames of paper making methods selected from these paper making methods, which are the same or different, in-line may be used. In addition, in the case of preparing a nonwoven fabric of a multilayer structure of 2 or more layers, it is possible to use: a method of laminating wet papers obtained by each paper machine, a method of forming a sheet and then casting a slurry having fibers dispersed therein on the sheet, and the like.

The wet paper prepared by the paper machine is dried by a yankee dryer (yankee dryer), an air dryer, a drum dryer, an absorption drum dryer, an infrared ray dryer, or the like, to obtain a sheet. When the wet paper is dried, the wet paper is closely adhered to a hot roll such as a yankee dryer to be hot-pressed and dried, whereby the smoothness of the closely adhered surface is improved. Hot press drying refers to drying a wet paper web by pressing it against a hot roll with a touch roll or the like. The surface temperature of the hot roller is preferably 100 to 180 ℃, more preferably 100 to 160 ℃, and further preferably 110 to 160 ℃. The pressure is preferably 50 to 1000N/cm, more preferably 100 to 800N/cm.

Next, hot press working using a hot roll will be described, but the method for producing the semipermeable membrane support of the present invention is not limited to the following description. In a hot press (calender) apparatus, a sheet is hot-pressed by passing the sheet between rollers that are engaged with each other. The combination of the rolls includes 2 metal rolls, a metal roll and a resin roll, a metal roll and a cotton roll, and the like. Of the 2 rolls, at least one roll was heated to be used as a heat roll. A metal roll is mainly used as the heat roll. The hot press working with the heat roller can be carried out 2 times or more, and in this case, 2 or more sets of the above-mentioned roller combination arranged in series or 2 times of the combined working with 1 set of rollers can be used. The surface and back of the sheet may be reversed as desired. By controlling the surface temperature of the hot roll, the nip pressure between the rolls, and the processing speed of the sheet, a desired semipermeable membrane support can be obtained.

In order to generate the molten whisker, it is important to laminate the sheet on a heat roll in the hot-pressing process using the heat roll. For this reason, it is important to increase the temperature of the hot roll to the vicinity of the melting point of the binder synthetic fibers to increase the nip pressure. Further, by controlling the processing speed, the length of the molten whisker can be adjusted to some extent. In addition, by increasing the content of the binder synthetic fiber, the molten whiskers can be increased.

As an index to be generated by melting, it is necessary to confirm heat actually transferred to the semipermeable membrane support, not to control the surface temperature of the heat roll. For this reason, it is important to confirm the surface temperature of the semipermeable membrane support immediately after hot-roll hot-pressing. In order to generate the molten whiskers, the surface temperature of the semipermeable membrane support measured at a position of less than 10cm immediately after the nip (nip) after the semipermeable membrane support is hot-pressed by a hot roll is preferably in the range of-65 ℃ to-20 ℃ relative to the melting point of the binder synthetic fibers. More preferably from-60 ℃ to-25 ℃, still more preferably from-55 ℃ to-25 ℃. The surface temperature of the semipermeable membrane support at the time of occlusion can be estimated by measuring the surface temperature of the semipermeable membrane support at a position of less than 10cm immediately after the nip. It is known empirically that the surface temperature of the semipermeable membrane support measured at a position less than 10cm immediately after the nip is 1 to 5 ℃ lower than the surface temperature at the time of nip. The hot press working conditions are preferably set so as to attain the above temperature range.

For example, when the melting point of the binder synthetic fiber is 260 ℃, the surface temperature of the semipermeable membrane support is preferably 195 to 240 ℃, more preferably 200 to 235 ℃. The surface temperature of the heat roller needs to be set in correspondence with the surface temperature of the semipermeable membrane support. For example, in the case where the surface temperature of the semipermeable membrane support measured at a position 9cm immediately after the nip after the semipermeable membrane support is hot-pressed by a hot roll is 220 ℃, the hot roll surface temperature is set to 221 ℃ to 225 ℃.

The nip pressure of the roller in the hot pressing is preferably 250 to 1700N/cm, more preferably 450 to 1400N/cm. In order to generate the melting whisker, it is important to attach the sheet to a heat roll in the hot-pressing process using the heat roll, and for this reason, it is important to increase the nip pressure. When the nip pressure is less than 250N/cm, there is a case where fusion whisker does not occur due to poor adhesion between the heat roll and the sheet. On the other hand, in the case of more than 1700N/cm, the effect of the increase in melting temperature is not changed and the excessive load on the roll is increased as compared with the case of 1700N/cm, thereby possibly shortening the roll life.

The processing speed in the hot pressing is preferably 4 to 100m/min, and more preferably 10 to 80 m/min. By adjusting the processing speed in the hot press processing, the length of the molten whiskers can be adjusted to some extent. In the case where the melting whisker is attached without being detached from the binder synthetic fiber, the length of the melting whisker is a length from a branch point of the binder synthetic fiber to a tip of the melting whisker. In addition, when the molten whisker is separated from the binder synthetic fiber, the length of the molten whisker is from the tip of the molten whisker to the opposite tip. By slowing down the processing speed, the molten whiskers can be increased. For example, the length of the molten whisker is 50 to 400 μm at a processing speed of 10m/min, and 10 to 150 μm at a processing speed of 40 m/min.

In order to attach the sheet hot-pressed by the heat roller to the heat roller, it is important that: when a chemical such as a release agent is not applied to the heat roll or when a chemical is applied, the amount of the chemical applied is suppressed to a minimum. When a large amount of the release agent is applied, the sheet may not adhere to the heat roll and the melting whisker may not occur even if the temperature and the nip pressure of the heat roll are increased.

The weight per unit area of the semipermeable membrane support is not particularly limited, but is preferably 20 to 150g/m²More preferably 50 to 100g/m². At less than 20g/m²In some cases, sufficient tensile strength may not be obtained. In addition, in excess of 150g/m²In the case of (2), the liquid permeation resistance may be high, or the thickness may be increased so that a predetermined amount of the semipermeable membrane cannot be accommodated in the cell or the module.

The density of the semipermeable membrane support is preferably 0.5-1.0 g/cm³More preferably 0.6 to 0.9g/cm³. The density of the semi-permeable membrane support is less than 0.5g/cm³In the case of (2), since the thickness is increased, the area of the semipermeable membrane incorporated in the cell is reduced, and as a result, the lifetime of the semipermeable membrane may be shortened. On the other hand, in excess of 1.0g/cm³In this case, the liquid permeability may be low, 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 still more preferably 70 to 120 μm. If the thickness of the semipermeable membrane support exceeds 150 μm, the area of the semipermeable membrane incorporated in the cell becomes small, and as a result, the life of the semipermeable membrane may become short. On the other hand, when the thickness is less than 50 μm, a sufficient tensile strength may not be obtained.

Examples

The present invention is illustrated in more detail by examples. Unless otherwise specified, the parts and ratios described in the examples are based on mass.

(example 1-1)

A main synthetic fiber (drawn polyester fiber, diameter 12.5 μm, fiber length 5mm) and a binder synthetic fiber (undrawn polyester fiber, diameter 10.5 μm, fiber length) were blended at a blending ratio of 70:30The resulting mixture was dispersed in water at a temperature of 5mm and a melting point of 260 ℃ to form a wet paper web by a cylinder machine, and then dried by hot pressing with a yankee dryer (yankee dryer) having a surface temperature of 130 ℃ to obtain a basis weight of 80g/m²The sheet of (1).

The resulting sheet was hot-pressed under the conditions of a heated metal roll surface temperature of 215 ℃, a pressure of 1000N/cm and a processing speed of 30m/min using a calender apparatus comprising a combination of a heated metal roll and a resin roll in stage 1, and the semi-permeable membrane support was obtained by continuously performing hot-pressing under the conditions of a heated metal roll surface temperature of 220 ℃, a pressure of 1000N/cm and a processing speed of 30m/min using a calender apparatus comprising a combination of a resin roll and a heated metal roll in stage 2 so that the surface of the sheet that was in contact with the heated metal roll was in contact with the resin roll. The surface that first contacted the heated metal roll was referred to as the coated surface.

(examples 1 to 2)

A semipermeable membrane support was obtained in the same manner as in example 1-1, except that the temperatures of the heated metal roll in stage 1 and the heated metal roll in stage 2 were changed to 220 ℃ and 220 ℃. The surface that first contacted the heated metal roll was referred to as the coated surface.

(examples 1 to 3)

A semipermeable membrane support was obtained in the same manner as in example 1-1, except that the temperatures of the heated metal roll in stage 1 and the heated metal roll in stage 2 were changed to 230 ℃ and 240 ℃. The surface that first contacted the heated metal roll was referred to as the coated surface.

(examples 1 to 4)

A semipermeable membrane support was obtained in the same manner as in example 1-1, except that the temperatures of the heated metal roll in stage 1 and the heated metal roll in stage 2 were changed to 230 ℃ and 240 ℃. The surface that first contacted the resin roll was referred to as the coated surface.

(examples 1 to 5)

A semipermeable membrane support was obtained in the same manner as in example 1-1, except that the temperatures of the heated metal roll in stage 1 and the heated metal roll in stage 2 were changed to 225 ℃ and 213 ℃. The surface that first contacted the heated metal roll was referred to as the coated surface.

(examples 1 to 6)

A semipermeable membrane support was obtained in the same manner as in example 1-3 except that the blending ratio of the main synthetic fiber (drawn polyester-based fiber, diameter: 12.5 μm, fiber length: 5mm) and the binder synthetic fiber (undrawn polyester-based fiber, diameter: 10.5 μm, fiber length: 5mm, melting point: 260 ℃) was changed to 75: 25. The surface that first contacted the heated metal roll was referred to as the coated surface.

(examples 1 to 7)

A semipermeable membrane support was obtained in the same manner as in example 1-3 except that the blending ratio of the main synthetic fiber (drawn polyester-based fiber, diameter: 12.5 μm, fiber length: 5mm) and the binder synthetic fiber (undrawn polyester-based fiber, diameter: 10.5 μm, fiber length: 5mm, melting point: 260 ℃) was changed to 60: 40. The surface that first contacted the heated metal roll was referred to as the coated surface.

Comparative example 1-1

A semipermeable membrane support was obtained in the same manner as in example 1-1, except that the temperatures of the heated metal roll in stage 1 and the heated metal roll in stage 2 were changed to 205 ℃ and 205 ℃. The surface that first contacted the heated metal roll was referred to as the coated surface.

The content (%) of the binder synthetic fibers, the melting point (. degree. C.) of the binder synthetic fibers, the combination of rolls in the hot press (stage 1) and the hot press (stage 2), the kind of hot roll, the surface temperature (. degree. C.) of the semipermeable membrane support, the nip pressure (N/cm), and the processing speed (m/min) are shown in Table 1.

In the examples and comparative examples, the surface temperature of the semipermeable membrane support was measured at a position immediately 9cm after the nip after hot-pressing the semipermeable membrane support by a hot roll, and was measured by a laser-attached radiation thermometer AD-5611A manufactured by a & D Company, Limited (エー, アンド, デイ). In the examples and comparative examples, the melting point was the maximum point measured at 25 to 300 ℃ under a temperature rise condition of 10 ℃ per minute using a differential scanning thermal analyzer DSC7 manufactured by PERKIN ELMER.

[ Table 1]

The semipermeable membrane supports obtained in examples and comparative examples were evaluated for observation of molten whiskers, penetration of the semipermeable membrane, adhesiveness of the semipermeable membrane, and observation of the surface of the semipermeable membrane, and the results are shown in table 2.

(Observation of molten whiskers of the Binder synthetic fiber)

An electron micrograph of the coated and non-coated surfaces of the semipermeable membrane support was taken at a magnification of 200 times, and the thickness of each 1.0mm was measured²The number of the melting whiskers. In addition, the shape and state (standing/lying) of the molten whiskers observed were also observed. The "fibrils", "fibrils" and "crosses" in table 2 have the following meanings:

"fibril": the molten whiskers are branched into fibril-like branched shapes

"thin": the tip diameter of the molten whisker is smaller than the diameter of the synthetic fiber of the main body

"traverse": the molten fibers have a shape that traverses at least one gap selected from the group consisting of gaps between the main synthetic fibers, gaps between the main synthetic fibers and the binder synthetic fibers, and gaps between the binder synthetic fibers.

(semipermeable membrane penetration)

The penetration evaluation of the semipermeable membrane was carried out by fixing a semipermeable membrane support on a backing paper using a constant speed coater (trade name: Automatic Film Applicator, manufactured by Antaha Seisaku Co., Ltd.), applying a DMF solution (concentration: 19%) of polysulfone resin mixed with black oily ink to the coated surface of the semipermeable membrane support, and visually observing the amount of polysulfone resin which penetrates the semipermeable membrane support and is transferred to the backing paper after the application.

1: completely without penetration. Very good level.

2: small dots, very little penetration. Good level.

3: small dots, through. Levels that are usable in practical use.

4: large dots, largely penetrated. Levels that are not practical to use.

(adhesiveness to semipermeable Membrane)

A DMF solution (concentration: 19%) of polysulfone resin was applied to the coated surface of a semipermeable membrane support using a constant speed coater (trade name: TQC full-automatic thin film coater, Cotec Ltd. (コーテック Co.) having a constant gap, and the resultant was washed with water and dried to prepare a semipermeable membrane made of polysulfone resin on the surface of the semipermeable membrane support. The adhesiveness between the semipermeable membrane and the semipermeable membrane support was determined by the following method.

The semipermeable membrane support on which the semipermeable membrane was prepared was cut into a width of 24mm (in the direction intersecting the application direction) × a length of 50mm (in the application direction) as a sample. Only a portion having a length of 10mm was bonded to the non-coated surface of the cut semipermeable membrane support with cellophane tape (product name: L-Pack (エルパック) (registered trademark) LP24, manufactured by Nichiban co., ltd. (ニチバン)) cut to a width of 24mm and a length of 30mm, and the remaining portion having a width of 24mm and a length of 20mm was left as a bonded portion. Subsequently, an adhesive portion to which a sticky note (product name: Stick on Notes (スティックオンノート) SN-23, manufactured by Lion Office Products Corp. (ライオン food Co., Ltd.) was attached was pasted to a portion of the coated surface having a width of 24mm × a length of 10 mm. The adhesiveness of the semipermeable membrane was determined by holding the adhesive portion (24 mm. times.20 mm) of the cellophane tape and the non-adhesive portion to which the memo could be attached, and pulling them by hand in the direction in which the semipermeable membrane and the semipermeable membrane support were peeled off, and by the state when a force was applied. 5 samples were prepared and 5 trials were performed.

In the case of sticking cellophane tapes to the coated surface and the non-coated surface and pulling both cellophane tapes, peeling occurred between the semipermeable membrane and the semipermeable membrane support in many cases, and it was difficult to evaluate the adhesiveness of the semipermeable membrane. By using a sticky note having lower adhesiveness than the cellophane tape, it is possible to confirm where the sheet is peeled off, and thereby to determine the adhesiveness between the semipermeable membrane and the semipermeable membrane support.

Judgment criteria

1: in all 5 tests, peeling occurred between the semipermeable membrane and the sticky note. Very good level.

2: in 3-4 tests, peeling occurred between the semipermeable membrane and the sticky note. Good level.

3: in 1-2 tests, peeling occurred between the semipermeable membrane and the sticky note. The lower level in practical use.

4: in all 5 tests, separation occurred between the semipermeable membrane and the semipermeable membrane support. Unusable levels.

(observation of surface of semipermeable membrane)

For the semipermeable membrane prepared in the above evaluation (adhesiveness of the semipermeable membrane), the surface of the semipermeable membrane was observed randomly with a microscope at 5 sites, and the presence or absence of fibers and melting streaks was confirmed on the surface of the semipermeable membrane and in the vicinity of the surface of the semipermeable membrane.

[ Table 2]

The semipermeable membrane supports of examples 1-1 to 1-7 were used to a level that can be practically used for semipermeable membrane penetration, semipermeable membrane adhesion, and observation of the surface of a semipermeable membrane. In particular, the semipermeable membrane supports of examples 1 to 3, 1 to 4 and 1 to 7, in which the coating surface had many melting points, exhibited very good adhesion to the semipermeable membrane. In addition, the semipermeable membrane supports of examples 1-3, 1-4, 1-6 and 1-7, in which the amount of the melting of the non-coated side was large, did not cause penetration at all. The semipermeable membrane supports of examples 1 to 6 having a binder synthetic fiber content of 25 mass% had fewer molten whiskers on the coated surface and had a satisfactory level of adhesiveness of the semipermeable membrane, but had sites that were easily peeled off in part, as compared with the semipermeable membrane supports of examples 1 to 3 and 1 to 7.

As a result of observing the shape of the molten whiskers, the shape of the molten whiskers in the semipermeable membrane support of examples 1-1 to 1-7 was mostly: the molten fibers are branched into fibril-like branched shapes, the tip of the molten fibers has a diameter smaller than the main synthetic diameter, and the molten fibers traverse at least one of the gaps selected from the group consisting of the gaps between the main synthetic fibers, the gaps between the main synthetic fibers and the binder synthetic fibers, and the gaps between the binder synthetic fibers.

The observation under a microscope of the surface of the semipermeable membrane revealed that the semipermeable membrane support of examples 1 to 4, which had a large amount of melting whiskers on the coated surface and was in an upright state, did not penetrate through the semipermeable membrane, but melting whiskers were observed in the vicinity of the surface of the semipermeable membrane. However, this is a level that is not problematic in practical use.

In the semipermeable membrane supports of examples 1 to 5, the melting requirements were low on the non-coated side and high on the coated side, and therefore, the penetration of the semipermeable membrane solution was suppressed by the melting requirements on the coated side, and a small spot-like penetration occurred, but the level that can be used in practical use.

The semipermeable membrane supports of comparative example 1-1 were small spot-like penetrations because no molten whiskers were generated on both the coated side and the non-coated side, as compared with the semipermeable membrane supports of examples 1-1 to 1-7, but the semipermeable membrane supports were usable in actual use. However, the semi-permeable membrane has poor adhesion and is at a level that is not practical. In addition, when the surface of the semipermeable membrane is observed with a microscope, it is observed that the synthetic fiber penetrates the semipermeable membrane at a level that is not practically usable.

(example 2-1)

Mixing and dispersing a main synthetic fiber (drawn polyester fiber, diameter of 17.5 μm and fiber length of 5mm) and a binder synthetic fiber (undrawn polyester fiber, diameter of 10.5 μm, fiber length of 5mm and melting point of 260 ℃) in water at a blending ratio of 70:30, forming a wet paper with a cylinder machine, and drying by hot pressing with a Yankee dryer having a surface temperature of 130 ℃ to obtain a wet paper having a basis weight of 80g/m²The sheet of (1).

The resulting sheet was hot-pressed under the conditions of a heated metal roll surface temperature of 225 ℃, a pressure of 1000N/cm and a processing speed of 30m/min using a calender apparatus comprising a combination of a heated metal roll and a resin roll in stage 1, and the semi-permeable membrane support was obtained by continuously hot-pressing under the conditions of a heated metal roll surface temperature of 225 ℃, a pressure of 1000N/cm and a processing speed of 30m/min using a calender apparatus comprising a combination of a resin roll and a heated metal roll in stage 2 so that the surface of the sheet that was in contact with the heated metal roll was in contact with the resin roll. The surface that first contacted the heated metal roll was referred to as the coated surface.

(example 2-2)

A semipermeable membrane support was obtained in the same manner as in example 2-1, except that the temperatures of the heated metal roll in stage 1 and the heated metal roll in stage 2 were changed to 230 ℃ and 230 ℃. The surface that first contacted the heated metal roll was referred to as the coated surface.

(examples 2 to 3)

A semipermeable membrane support was obtained in the same manner as in example 2-1, except that the temperatures of the heated metal roll in stage 1 and the heated metal roll in stage 2 were changed to 235 ℃ and 240 ℃, respectively. The surface that first contacted the heated metal roll was referred to as the coated surface.

(examples 2 to 4)

A semipermeable membrane support was obtained in the same manner as in example 2-1, except that the temperatures of the heated metal roll in stage 1 and the heated metal roll in stage 2 were changed to 235 ℃ and 240 ℃, respectively. The surface that first contacted the resin roll was referred to as the coated surface.

(examples 2 to 5)

A semipermeable membrane support was obtained in the same manner as in example 2-1, except that the temperatures of the heated metal roll in stage 1 and the heated metal roll in stage 2 were changed to 230 ℃ and 220 ℃. The surface that first contacted the heated metal roll was referred to as the coated surface.

Comparative example 2-1

A semipermeable membrane support was obtained in the same manner as in example 2-1, except that the temperatures of the heated metal roll in stage 1 and the heated metal roll in stage 2 were changed to 210 ℃ and 210 ℃. The surface that first contacted the heated metal roll was referred to as the coated surface.

The content (%) of the binder synthetic fibers, the melting point (. degree. C.) of the binder synthetic fibers, the combination of rolls in the hot press (stage 1) and the hot press (stage 2), the kind of hot roll, the surface temperature (. degree. C.) of the semipermeable membrane support, the nip pressure (N/cm), and the processing speed (m/min) are shown in Table 3.

[ Table 3]

The results of observation of the molten whisker and observation of the semipermeable membrane penetration, adhesion of the semipermeable membrane, and surface of the semipermeable membrane support obtained in examples and comparative examples are shown in table 4.

[ Table 4]

The semipermeable membrane supports of examples 2-1 to 2-5 were used to a level that can be practically used for the observation of the semipermeable membrane penetration, the adhesion of the semipermeable membrane, and the surface of the semipermeable membrane. In particular, the semipermeable membrane supports of examples 2-2 to 2-5, which had many melting requirements on the coated surface, exhibited very good adhesion to the semipermeable membrane. Further, the evaluation of the penetration of the semipermeable membrane was good in the semipermeable membrane support of examples 2-1 to 2-4 in which the amount of the melting of the non-coated surface was large.

As a result of microscopic observation of the surface of the semipermeable membrane, it was found that the semipermeable membrane support of examples 2 to 4, in which the amount of the molten whiskers was large on the coated surface and which was in an upright state, did not penetrate the semipermeable membrane, but molten whiskers were observed in the vicinity of the surface of the semipermeable membrane. However, this is a level that is not problematic in practical use.

In the semipermeable membrane supports of examples 2 to 5, the melting of the non-coated surface was small, and the melting of the coated surface was large, so that the penetration of the semipermeable membrane solution was suppressed by the melting of the coated surface, and a small spot-like penetration occurred, but the level that can be used in practical use was high.

As a result of observing the shape of the molten whiskers, the shape of the molten whiskers in the semipermeable membrane support of examples 2-1 to 2-5 was mostly: the molten fibers are branched into fibril-like branched shapes, the tip of the molten fibers has a diameter smaller than the main synthetic diameter, and the molten fibers traverse at least one of the gaps selected from the group consisting of the gaps between the main synthetic fibers, the gaps between the main synthetic fibers and the binder synthetic fibers, and the gaps between the binder synthetic fibers.

The semipermeable membrane supports of comparative example 2-1 were small spot-like penetrations because no molten whiskers were generated on both the coated side and the non-coated side, as compared with the semipermeable membrane supports of examples 2-1 to 2-5, but the semipermeable membrane supports were usable in actual use. However, the semi-permeable membrane has poor adhesion and is at a level that is not practical. In addition, when the surface of the semipermeable membrane is observed by a microscope, the synthetic fiber is observed as a main body penetrating the semipermeable membrane, and the level is not usable in practical use.

(example 3-1)

A main synthetic fiber 1 (drawn polyester fiber, diameter 12.5 μm, fiber length 5mm), a main synthetic fiber 2 (drawn polyester fiber, diameter 7.5 μm, fiber length 5mm), a binder synthetic fiber (undrawn polyester fiber, diameter 10.5 μm, fiber length 5mm, melting point 260 ℃) were mixed and dispersed in water at a blending ratio of 35:35:30, wet paper was formed with a cylinder machine, and then hot-pressed and dried with a Yankee dryer having a surface temperature of 130 ℃ to obtain a basis weight of 80g/m²The sheet of (1).

The resulting sheet was hot-pressed under the conditions of a heated metal roll surface temperature of 230 ℃, a pressure of 1000N/cm and a processing speed of 30m/min using a calender apparatus comprising a combination of a heated metal roll and a resin roll in stage 1, and the semi-permeable membrane support was obtained by continuously performing hot-pressing under the conditions of a heated metal roll surface temperature of 230 ℃, a pressure of 1000N/cm and a processing speed of 30m/min using a calender apparatus comprising a combination of a resin roll and a heated metal roll in stage 2 so that the surface of the sheet that was in contact with the heated metal roll was in contact with the resin roll. The surface that first contacted the heated metal roll was referred to as the coated surface.

(example 3-2)

A semipermeable membrane support was obtained in the same manner as in example 3-1, except that the processing speeds in the 1 st and 2 nd stages were changed to 10 m/min. The surface that first contacted the heated metal roll was referred to as the coated surface.

(examples 3 to 3)

A semipermeable membrane support was obtained in the same manner as in example 3-1, except that the processing speeds in the 1 st and 2 nd stages were changed to 40 m/min. The surface that first contacted the heated metal roll was referred to as the coated surface.

(examples 3 to 4)

A semipermeable membrane support was obtained in the same manner as in example 3-1, except that the pressures in the 1 st and 2 nd stages were changed to 800N/cm. The surface that first contacted the resin roll was referred to as the coated surface.

(examples 3 to 5)

A semipermeable membrane support was obtained in the same manner as in example 3-1, except that the pressures in the 1 st and 2 nd stages were changed to 1200N/cm. The surface that first contacted the heated metal roll was referred to as the coated surface.

(examples 3 to 6)

A semipermeable membrane support was obtained in the same manner as in example 3-1 except that in stage 1, hot press working was performed using a calender stack comprising a combination of a heated metal roll and a heated metal roll under conditions of a surface temperature of the two heated metal rolls of 230 ℃, a pressure of 1000N/cm and a working speed of 30m/min, and that in stage 2, hot press working was performed continuously using a calender stack comprising a combination of a resin roll and a heated metal roll under conditions of a surface temperature of the heated metal roll of 150 ℃, a pressure of 1000N/cm and a working speed of 30 m/min. Note that the surface that contacted the resin roll in stage 2 was referred to as the coated surface.

Comparative example 3-1

A semipermeable membrane support was obtained in the same manner as in example 3-1 except that in stage 1, hot press working was performed using a calender stack comprising a combination of a heated metal roll and a heated metal roll under conditions of a surface temperature of the two heated metal rolls of 210 ℃, a pressure of 1000N/cm and a working speed of 30m/min, and that in stage 2, hot press working was performed continuously using a calender stack comprising a combination of a resin roll and a heated metal roll under conditions of a surface temperature of the heated metal roll of 150 ℃, a pressure of 1000N/cm and a working speed of 30 m/min. Note that the surface that contacted the resin roll in stage 2 was referred to as the coated surface.

The content (%) of the binder synthetic fibers, the melting point (. degree. C.) of the binder synthetic fibers, the combination of rolls in the hot press (stage 1) and the hot press (stage 2), the kind of hot roll, the surface temperature (. degree. C.) of the semipermeable membrane support, the nip pressure (N/cm), and the processing speed (m/min) are shown in Table 5.

[ Table 5]

The results of observation of the molten whisker and observation of the semipermeable membrane penetration, adhesion of the semipermeable membrane, and surface of the semipermeable membrane support obtained in examples and comparative examples are shown in table 6.

[ Table 6]

The semipermeable membrane supports of examples 3-1 to 3-6 achieved very good levels of semipermeable membrane penetration, semipermeable membrane adhesion, and observation of the surface of the semipermeable membrane. The length of the molten whisker observed in the semipermeable membrane support of example 3-2 having a hot press working speed of 10m/min was as long as 150 μm, and a state in which 1 molten whisker simultaneously crossed several spaces between fibers constituting the semipermeable membrane support was observed. In the semipermeable membrane supports of examples 3 to 6 in which a calender press apparatus comprising a combination of a heated metal roll and a heated metal roll was used in the hot press process of stage 1 and the surface temperature of the semipermeable membrane support was 227 ℃, the melting occurred on both sides in stage 1 required to be caused to lie down by the hot press process of stage 2, and therefore the melting required to lie down on both surfaces, i.e., the coated surface and the non-coated surface, was very good in the observation of the surface of the semipermeable membrane, and was also very good in the evaluation of the adhesiveness of the semipermeable membrane and the penetration of the semipermeable membrane.

The semipermeable membrane support of comparative example 3-1 was excellent in the penetration of the semipermeable membrane because it contained the host synthetic fibers having diameters of 7.5 μm and 12.5 μm, but was poor in the adhesiveness of the semipermeable membrane because no molten whiskers were generated on both the coated side and the non-coated side, and was at a level that was not practically usable. In addition, when the surface of the semipermeable membrane is observed by a microscope, the synthetic fiber is observed as a main body penetrating the semipermeable membrane, and the level is not usable in practical use.

Industrial applicability

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

Claims

1. A semipermeable membrane support comprising a nonwoven fabric comprising at least a main synthetic fiber and a binder synthetic fiber, characterized in that the binder synthetic fiber comprises a core-sheath fiber comprising a combination of a high-melting polyester as a core and a low-melting polyester as a sheath or an undrawn fiber of a polyester, and that a melt whisker of the binder synthetic fiber is present on at least one surface of the semipermeable membrane support.

2. The semipermeable membrane support according to claim 1, wherein the melting whisker observed in the electron micrograph of the surface of the semipermeable membrane support is 1.0mm per unit²More than 2.

3. The semipermeable membrane support according to claim 1 or 2, wherein the shape of the fused whiskers of the binder synthetic fiber is a branched shape.

4. The semipermeable membrane support according to claim 1 or 2, wherein the shape of the molten whiskers of the binder synthetic fiber is such that the tip diameter of the molten whiskers is smaller than the diameter of the main synthetic fiber.

5. The semipermeable membrane support according to claim 1 or 2 wherein the shape of the fused whiskers of the binder synthetic fibers is such that the fused whiskers traverse at least one void selected from the group consisting of: the voids between the main body synthetic fibers, the voids between the main body synthetic fibers and the binder synthetic fibers, and the voids between the binder synthetic fibers.

6. The semipermeable membrane support according to claim 1 or 2, wherein the molten whiskers of the binder synthetic fiber are present on a coated surface of the semipermeable membrane support, and the molten whiskers of the coated surface are in a lying-down state, and wherein the coated surface is a surface of the semipermeable membrane support coated with the semipermeable membrane.

7. The semipermeable membrane support according to claim 1 or 2, wherein the molten whiskers of the binder synthetic fiber are present on both surfaces of the semipermeable membrane support.

8. A process for producing a semipermeable membrane support according to any of claims 1 to 7, which comprises a step of preparing a sheet by wet-type papermaking from a slurry containing at least a host synthetic fiber and a binder synthetic fiber, and a step of hot-pressing the sheet obtained in the preceding step by a hot roll,

the slurry contains, as a binder synthetic fiber, a core-sheath fiber of a combination of a high-melting polyester as a core and a low-melting polyester as a sheath or an undrawn fiber of a polyester, and the hot-pressing is performed while confirming the surface temperature of the semipermeable membrane support immediately after the hot-pressing.

9. The method for producing a semipermeable membrane support according to claim 8, wherein the surface temperature of the hot roll in the hot-pressing is set so that the surface temperature of the semipermeable membrane support measured at a position less than 10cm from the nip immediately after the hot-pressing is in the range of-65 ℃ to-20 ℃ relative to the melting point of the binder synthetic fiber.