JP2009183879A - Substrate sheet for separation membrane, manufacturing method thereof and separation membrane laminated sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate sheet for separation membrane which has both of such smoothness as to produce no pin-hole in a separation membrane and air permeability sufficient for providing excellent gas diffusion property, to provide a manufacturing method of the substrate sheet for separation membrane, and to provide a separation membrane laminated sheet using the substrate sheet for separation membrane. <P>SOLUTION: Extra-fine fibers having an average fiber diameter of ≤1 μm are fused and fixed on one surface of a support fiber sheet essentially composed of fused fibers by the fused fibers. The substrate sheet for separation membrane can be manufactured by laminating the extra-fine fibers having the average fiber diameter of ≤1 μm on the one surface of the support fiber sheet essentially composed of the fused fibers, thereafter, by pressing the extra-fine fibers at a fusing point or above of the fused fibers and by fusing and fixing the extra-fine fibers with the fused fibers. Further, in the separation membrane laminated sheet, the separation membrane is laminated on the extra-fine fiber side surface of the substrate sheet for separation membrane. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a base sheet for a separation membrane, a production method thereof, and a separation membrane laminated sheet. More specifically, the present invention relates to a base sheet that can support a gas separation membrane such as oxygen gas, nitrogen gas, or hydrogen gas, a manufacturing method thereof, and a separation membrane laminated sheet.

  Since the gas separation membrane is thin and brittle, it is generally performed to support the gas separation membrane with a base sheet. A microporous film is used as such a base sheet. However, since the microporous film has low air permeability and a problem in gas diffusibility, a base sheet made of a nonwoven fabric has been proposed.

  For example, “a separation membrane support comprising fibers mainly composed of irregular cross-section fibers having a fiber specific surface area larger than that of circular cross-section fibers and having a fineness of 1.0 to 6.0 denier” Has been proposed (Patent Document 1). This separation membrane support “forms a first web composed mainly of a modified cross-section fiber having a larger fiber specific surface area than a circular cross-section fiber, and is composed of a fiber composed mainly of a circular cross-section fiber. A second web is formed, and then the first and second webs are laminated and subjected to a calendering treatment, so that a surface layer and a circular cross section composed of fibers mainly composed of irregular cross-section fibers are formed from at least one surface. It is disclosed that a separation membrane support is obtained as a nonwoven fabric having layers composed of fibers mainly composed of fibers in this order. Although this separation membrane support uses irregular cross-section fibers, the fineness is 1.0 to 6.0 denier and the fibers are thick, so that the smoothness is inferior and pinholes are likely to occur in the separation membrane. Therefore, if the heating calendering conditions are increased to improve the smoothness, the air permeability of the separation membrane support is remarkably lowered, causing a problem in gas diffusibility.

  Further, as a hydrogen separation membrane structure, “a hydrogen separation membrane structure comprising a hydrogen separation membrane and a gas permeable support for supporting the hydrogen separation membrane, a hydrogen having a thickness in the range of 0.3 to 8 μm. A hydrogen separation membrane structure in which a separation membrane is bonded to a nonwoven fabric support formed by integrating fibrillated fibers with a binder has been proposed (Patent Document 2). Since this support is made of a nonwoven fabric in which fibrillated fibers are integrated with a binder, fibers protruding from the surface of the support are likely to exist, and the hydrogen separation membrane is damaged by the fibers and pinholes are likely to occur. there were. Therefore, if the amount of the binder is increased in order to suppress the protrusion of the fiber, the air permeability of the support is remarkably lowered, which causes a problem in gas diffusibility.

Japanese Patent Laid-Open No. 11-347383 (Claim 1, Claim 5, Claim 9, Claim 11) JP 2003-320214 A (Claim 1, paragraph number 0012)

  The present invention has been made to solve the above-described problems. That is, to provide a base sheet for a separation membrane that has both smoothness that does not cause pinholes in the separation membrane and sufficient air permeability that is excellent in gas diffusibility, a manufacturing method thereof, and a separation membrane laminated sheet With the goal.

  The invention according to claim 1 of the present invention is characterized in that “ultrafine fibers having an average fiber diameter of 1 μm or less are fused and fixed on one side of a supporting fiber sheet mainly composed of fused fibers by the fused fibers. "A base material sheet for a separation membrane."

  The invention according to claim 2 of the present invention is characterized in that "the fusion fiber is composed of a composite fusion fiber including a low melting point component and a high melting point component, and the low melting point component is exposed on the fiber surface. 1. The separation membrane substrate sheet according to 1.

  The invention according to claim 3 of the present invention is “the substrate sheet for a separation membrane according to claim 1 or 2, wherein the ultrafine fibers are obtained by an electrostatic spinning method”. It is.

The invention according to claim 4 of the present invention is "the substrate sheet for a separation membrane according to any one of claims 1 to 3, wherein the amount of ultrafine fibers is 500 mg or less per 1 m ^2. " It is.

  The invention according to claim 5 of the present invention is “after laminating ultrafine fibers having an average fiber diameter of 1 μm or less on one side of a supporting fiber sheet mainly composed of fused fibers, and then pressurizing at a melting point or higher of the fused fibers, A method for producing a base sheet for a separation membrane, wherein the ultrafine fibers are fused and fixed with the fused fibers. "

  The invention according to claim 6 of the present invention is “Manufacturing of substrate sheet for separation membrane according to claim 5, characterized in that ultrafine fibers obtained by an electrostatic spinning method are directly laminated on a supporting fiber sheet. Method. "

  The invention according to claim 7 of the present invention is characterized in that a separation membrane is laminated on the surface of the ultrafine fiber side of the base sheet for separation membrane according to any one of claims 1 to 4. Separation membrane laminated sheet. "

  The invention according to claim 1 of the present invention has smoothness in which pinholes are not generated in the separation membrane because the ultrafine fibers having an average fiber diameter of 1 μm or less are fused and fixed. Moreover, since the apparent density of the support fiber sheet is not extremely increased by the ultrafine fibers, and the voids of the support fiber sheet are not filled with the ultrafine fibers, excellent air permeability can be exhibited.

  In the invention according to claim 2 of the present invention, the composite fiber is used, the ultrafine fiber can be fused and fixed only with the low melting point component of the composite melt fiber, and when the ultrafine fiber is fused and fixed, Since the apparent density does not become extremely high, excellent air permeability is easily exhibited.

  In the invention according to claim 3 of the present invention, the ultrafine fiber obtained by the electrospinning method has a long fiber length, and the ultrafine fiber is difficult to be buried in the voids of the support fiber sheet, so that it is excellent in smoothness and air permeability. .

The invention according to claim 4 of the present invention is excellent in air permeability since the amount of ultrafine fibers is as small as 500 mg or less per 1 m ² and the ultrafine fibers do not impair the air permeability. Further, since the ultrafine fibers are surely fused and fixed by the fusion fibers and the ultrafine fibers themselves are not fluffed, pinholes in the separation membrane are hardly generated.

  The invention according to claim 5 of the present invention can produce the substrate sheet for separation membrane according to claim 1, which is smooth and excellent in air permeability.

  The invention concerning Claim 6 of this invention can manufacture the base material sheet for separation membrane concerning Claim 3 which is smoother and excellent in air permeability.

  In the invention according to claim 7 of the present invention, since the separation membrane is laminated on the ultrafine fiber side surface of the separation membrane substrate sheet according to claims 1 to 4, there is no pinhole, and air permeability is achieved. It is excellent.

  The base material sheet for separation membrane of the present invention (hereinafter simply referred to as “base material sheet”) is provided with a support fiber sheet so as to impart mechanical strength to the base material sheet and to allow fusion and fixing of ultrafine fibers. ing. The supporting fiber sheet is mainly composed of fused fibers so that the mechanical strength is excellent, and the fused fibers are fused. The main body in the present invention means that 50 mass% or more of the fibers constituting the supporting fiber sheet is a fused fiber. As the number of fusion fibers increases, the fine fibers can be surely fused and fixed, and the fuzz of the ultrafine fibers can be suppressed, so that the separation membrane can be prevented from being damaged. It preferably occupies 70 mass% or more, more preferably occupies 90 mass% or more, and most preferably occupies 100 mass%.

  The fusion fiber constituting the support fiber sheet is not particularly limited, but preferably comprises a composite fusion fiber including a low melting point component and a high melting point component, and the low melting point component exposed on the fiber surface. Even if it is heated and pressurized to fuse and fix the ultrafine fibers, such a composite fused fiber stays in the melting of only the low melting point component, without significantly increasing the apparent density of the supporting fiber sheet, This is because the air permeability is not impaired. Examples of such composite fused fibers include a core-sheath type (whether the core is biased), a sea-island type, a side-by-side type, a multi-layer bonded type, etc. Among these, the low melting point component can occupy the entire fiber surface (excluding the ends), and is preferably a core-sheath type or sea-island type that is excellent in fusion fixing strength.

  In addition, the melting point difference between the low melting point component and the high melting point component is not particularly limited, but it is 10 ° C. or higher so that the high melting point component is not easily melted by heat at the time of fusing with the low melting point component. Preferably, it is 15 ° C. or higher, more preferably 20 ° C. or higher. The combination of the low melting point component and the high melting point component is not particularly limited. For example, low density polyethylene-polypropylene, high density polyethylene-polypropylene, propylene copolymer-polypropylene, copolymer polyester-polyester, 6 nylon-66. Conventionally known combinations such as nylon, copolymer nylon-6 nylon, and 6 nylon-polyester can be listed.

  Further, the volume ratio of the low melting point component and the high melting point component is not particularly limited, but 30:70 to be excellent in the balance between the fusion fixing force by the low melting point component and the fiber shape maintaining performance by the high melting point component. 70:30 is preferable, and 40:60 to 60:40 is more preferable. Further, the degree of exposure of the low melting point component on the fiber surface is not particularly limited, but it accounts for 50% or more of the fiber surface (excluding the end) so that the fusion fixing force of the ultrafine fiber is excellent. It is preferable that it occupies 70% or more, more preferably 90% or more, and most preferably 100%.

  The average fiber diameter of the fusion fiber of the present invention is not particularly limited. However, the smaller the average fiber diameter of the fusion fiber, the higher the smoothness of the support fiber sheet. Since smoothness can be improved, the thickness is preferably 50 μm or less, and more preferably 20 μm or less. On the other hand, it is preferably thicker than 1 μm and more preferably 5 μm or more so that mechanical strength can be imparted to the base sheet. Further, the fiber length is not particularly limited, but is preferably 1 mm or more, more preferably 5 mm or more so that a large number of fiber end portions cannot be projected.

  In addition, the support fiber sheet of this invention can also contain a well-known fiber in addition to the above fusion fibers. Further, the supporting fiber sheet may be in any form, and is not particularly limited. For example, the supporting fiber sheet can be a nonwoven fabric or a woven fabric. Among these, the nonwoven fabric is suitable because it can take a dense structure and can be a smoother substrate sheet. As this suitable nonwoven fabric, there can be mentioned, for example, a fused nonwoven fabric fused with a fused fiber, an entangled nonwoven fabric entangled with a water stream or a needle, a spunbond nonwoven fabric, and a melt blown nonwoven fabric. Among these, a fused nonwoven fabric fused with a fused fiber having excellent mechanical strength is preferable.

  The base sheet of the present invention is obtained by fusing and fixing ultrafine fibers with fusing fibers on one side of the support fiber sheet as described above. Therefore, the smoothness which does not generate a pinhole in the separation membrane is given. In addition, since the support fiber sheet is crushed by the ultrafine fibers and the apparent density becomes extremely high, or the voids of the support fiber sheet are not filled with the ultrafine fibers, it is a base sheet that can exhibit excellent air permeability. is there.

  Thus, since an ultrafine fiber has the effect | action which provides smoothness to a base material sheet, the one where an average fiber diameter is smaller is preferable. More specifically, it needs to be 1 μm or less, preferably 0.6 μm or less, more preferably 0.4 μm or less, and still more preferably 0.2 μm or less. The lower limit of the average fiber diameter of the ultrafine fibers is not particularly limited, but is suitably 0.01 μm or more. The average fiber diameter in the present invention is the diameter (fiber diameter) of the cross section of 50 fibers measured from a scanning electron micrograph taken at a magnification such that the fiber thickness in the scanning electron micrograph is 1 mm to 5 mm. Means the arithmetic mean of

  The fiber length of the ultrafine fiber is not particularly limited, but the longer the fiber length, the harder the ultrafine fiber is buried in the voids of the support fiber sheet, and the smooth surface can be obtained. Is preferable, and it is more preferable that it is 50 micrometers or more. Ideally a continuous fiber. This fiber length means the arithmetic average value of the length of 50 fibers measured from the scanning electron micrograph of 500-5000 times. If the end of the fiber cannot be confirmed in this measurement range and the fiber length cannot be measured, it is regarded as a continuous fiber.

  The ultrafine fibers of the present invention may be obtained by any method as long as the average fiber diameter is 1 μm or less. For example, those obtained by electrospinning method, those obtained by removing sea components from sea-island type composite fibers, those obtained by melt blow method, bacterial cellulose fibers, or 2,2,6,6-tetramethylpiperidine- Examples thereof include plant-derived cellulose fibers using 1-oxyl as an oxidation catalyst. Among these, the ultrafine fibers obtained by the electrospinning method are preferable because the fiber length is long and the ultrafine fibers are not easily embedded in the gaps of the supporting fiber sheet, and thus it is easy to produce a base sheet having excellent smoothness.

  This ultrafine fiber may be composed of any resin and is not particularly limited. For example, polyethylene glycol, partially saponified polyvinyl alcohol, fully saponified polyvinyl alcohol, polyvinyl pyrrolidone, polylactic acid, polyglycolic acid, poly It can be composed of one or more types such as acrylonitrile, polymethacrylic acid, polymethyl methacrylate, polycarbonate, polystyrene, polyamide, polyimide, polyethersulfone, and polysulfone. In addition, since the ultrafine fiber is fused and fixed by the fusion fiber, the component (particularly, the low melting point component) of the fusion fiber is fused so as not to be affected by heat when the fusion fiber is fused and fixed. It is preferable that the resin is composed of a resin having a higher melting point, softening point, or decomposition temperature.

The ultrafine fibers preferably have a mass of 500 mg or less per 1 m ² . Since the amount of ultrafine fibers is small and the ultrafine fibers do not impair the breathability, they have excellent breathability, and there is little overlap between the ultrafine fibers, and the ultrafine fibers can be securely fused and fixed by the fused fibers. This is because there is no fluffing and it is difficult to generate pinholes in the separation membrane. More preferably, it is 200 mg or less, More preferably, it is 100 mg or less. On the other hand, as described above, the ultrafine fiber has an effect of imparting smoothness to the substrate sheet, and is preferably 5 mg or more, and more preferably 10 mg or more.

  Such ultrafine fibers are fused and fixed on one side of the support fiber sheet, but if necessary, the ultrafine fibers may be fused and fixed on both sides. In addition, when the ultrafine fiber is fused and fixed with the fusion fiber, the ultrafine fiber at the fusion-fixed portion is in a state of being partially buried even if it is completely buried in the fusion fiber. However, it may be in a state where it is not buried and is fused at the contact point.

  Such a base sheet of the present invention is obtained by, for example, laminating ultrafine fibers having an average fiber diameter of 1 μm or less on one side of a supporting fiber sheet mainly composed of fused fibers, and then pressurizing at a temperature equal to or higher than the melting point of the fused fibers. , And can be produced by fusing and fixing the ultrafine fibers with the fusing fibers.

  More specifically, first, a support fiber sheet mainly composed of the above-described fused fiber is prepared. As described above, it is preferable to prepare a fused nonwoven fabric in which fused fibers are fused. In addition, the low-melting-point component includes a low-melting-point component and a high-melting-point component so that the apparent density of the support fiber sheet does not become extremely high when the ultrafine fibers are fused and fixed, and excellent air permeability is easily exhibited. It is preferable to use a composite fused fiber in which is exposed on the fiber surface. In addition, as a support fiber sheet, the thing which heat-pressed with the heat | fever calendar roller etc., improved smoothness, or suppressed fluff can be used.

Next, ultrafine fibers are laminated on one side of the supporting fiber sheet. In addition, air permeability is not hindered, air permeability is excellent, and there is little overlap between the ultrafine fibers, and the ultrafine fibers can be securely fused and fixed by the fused fibers, the ultrafine fibers themselves are not fluffy, and the separation membrane It is preferable that the ultrafine fiber has a mass of 500 mg or less per 1 m ² so that pinholes are hardly generated.

  The lamination method is not particularly limited. For example, a method in which ultrafine fibers obtained by an electrospinning method are directly laminated on a support fiber sheet, and a slurry in which the ultrafine fibers are dispersed is sprinkled on the support fiber sheet. The method, the method of laminating | stacking the ultrafine fiber obtained by the melt blow method directly on a support fiber sheet, etc. can be mentioned. Among these, the ultrafine fibers obtained by the electrospinning method are preferable because the fiber length is long and the ultrafine fibers are not easily buried in the voids of the support fiber sheet, and thus it is easy to produce a base sheet having excellent smoothness.

  This electrostatic spinning method is a conventionally known method, in which a polymer solution is fiberized by applying an electric field to the polymer solution supplied from the polymer solution supply material to the spinning space. The polymer solution can be supplied from the polymer solution supply material to the spinning space with, for example, one or more nozzles, and the nozzles are reciprocated so that the ultrafine fibers are uniformly dispersed. Is preferred. In particular, when the nozzle is circulated and moved in an oval shape, the moving speed of the nozzle can be made constant, so that the ultrafine fibers can be uniformly dispersed (for example, the method disclosed in JP-A-2006-112023). In addition, since a polymer solution is a raw material for ultrafine fibers, the ultrafine fiber constituent material as described above is dissolved in a solvent. In addition, the electric field is applied to the polymer solution supply material side (for example, the polymer solution supply material itself, the polymer supply path to the polymer solution supply material) and the collector side facing the polymer solution supply material (for example, the collector itself, the collector). Can be made to act by providing a potential difference with the counter electrode located on the back surface side of the electrode.

  In order to laminate the ultrafine fibers obtained by such an electrospinning method directly on the support fiber sheet, for example, by placing the support fiber sheet on the collector facing the polymer solution supply material as described above. Can be implemented. Thus, “directly” means that the ultrafine fibers are not collected and laminated on the support fiber sheet, but are accumulated and laminated on the support fiber sheet.

Next, pressurization is performed at a temperature equal to or higher than the melting point of the fused fiber, and the ultrafine fiber is fused and fixed with the fused fiber, whereby the base sheet of the present invention can be manufactured. The pressure is preferably higher than the temperature 5 ° C. higher than the melting point, more preferably higher than the temperature higher than 10 ° C., more preferably higher than the temperature higher than 15 ° C. The melting point of the fused fiber refers to the melting peak temperature (T _pm ) of the heat flux DSC curve defined in JIS K ^7121-1987 (Plastic Transition Temperature Measurement Method) 9.1 (2). When the fusion fiber contains a low melting point component and a high melting point component, the melting point of the low melting point component is set.

The pressurization is not particularly limited as long as it is a pressurization capable of fusing and fixing ultrafine fibers. With this applied pressure, the fusion-fixed state of the ultrafine fibers by the fusion fibers changes. That is, the state changes from a state in which the ultrafine fiber is completely buried in the fusion fiber to a state in which the ultrafine fiber is not buried but is fused at the contact point. As described above, when the amount of ultrafine fibers is as small as 500 mg or less per 1 m ² , the ultrafine fibers can be surely fused and fixed even if the applied pressure is small, and the decrease in air permeability due to pressurization is also kept low. be able to. In addition, this pressurization can be performed simultaneously with heating, and can also be performed after heating. In either case, the pressurization can be performed by, for example, a flat plate press device or a roll press device. When only heating is performed, for example, an oven, a hot air transmission heat treatment machine, an infrared heater, and a microwave can be used.

  Since the separation membrane laminated sheet of the present invention is obtained by laminating a separation membrane on the surface of the substrate sheet as described above, there is no pinhole and excellent air permeability. In addition, as a separation membrane, a conventionally well-known thing can be used, For example, an oxygen enriched membrane, a nitrogen enriched membrane, a hydrogen separation membrane, a dehumidification membrane, an organic gas permeable membrane etc. can be mentioned. If the substrate sheet of the present invention is used, even if the separation membrane is an ultra-thin film having a thickness of 1 μm or less, there can be no pinholes and excellent air permeability. In addition, a separation membrane lamination sheet can be manufactured by laminating | stacking a separation membrane on the ultrafine fiber side surface of a base material sheet by the well-known water surface expansion | deployment method and the solvent casting method, for example.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples. The air permeability is a value measured according to JIS L 1096: 1999 8.27.1 A method (Fragile method).

Example 1
A core-sheath-type composite fused fiber (average fiber diameter: 10.6 μm, fiber length: 5 mm, sheath) whose sheath component is made of high-density polyethylene (melting point: 127 ° C.) and whose core component is polypropylene (melting point: 165 ° C.) After forming the fiber web by a wet method using the volume ratio of the component and the core component = 40: 60, and the sheath component occupying 100% of the fiber surface (excluding both ends), supply to an oven set at a temperature of 138 ° C. Wet non-woven fabric fused with the sheath component of the core-sheath type composite fusion fiber (= support fiber sheet, basis weight: 15 g / m ² , thickness: 80 μm, air permeability: 544 cm ³ / (cm ² · sec) ) Was prepared.

  On the other hand, homopolyacrylonitrile having a weight average molecular weight of 400,000 was dissolved in dimethylformamide to prepare a solution having a concentration of 10.5% by weight as a polymer solution for electrospinning.

  As an electrostatic spinning device, a grounded stainless steel drum having a diameter of 20 cm and a length of 40 cm was used as a collector and counter electrode, and a metal nozzle having an inner diameter of 0.4 mm was used as a polymer solution supply material. The metal nozzle was installed so that the distance between the tip and the drum surface was 10 cm.

Next, the wet-bonded nonwoven fabric is wrapped around the drum surface, and the end in the longitudinal direction of the drum is fixed with tape, and then the polymer solution is supplied from a metal nozzle in an amount of 1 g / hour in an environment of a temperature of 20 ° C. and a relative humidity of 25%. While applying extrusion, a DC high voltage of +12 kV was applied to the metal nozzle, and at the same time, the drum was rotated at a constant speed (15 rpm). On the wet-bonded nonwoven fabric, ultrafine continuous fibers (average fiber diameter: 400 nm, melting point: 320 C.) was directly laminated to form a wet-fused nonwoven fabric-ultrafine continuous fiber laminated sheet. Incidentally, the amount of lamination of ultrafine continuous fibers was 50 mg / ^{m 2.} Moreover, when extruding the polymer solution from the metal nozzle, the metal nozzle was reciprocated in the length direction of the drum (reciprocal width: 20 cm) at a constant speed (1 cm / second).

Next, after this wet-bonded nonwoven fabric-extra-fine continuous fiber laminated sheet was heated at a temperature of 135 ° C., it was pressed with a flat press machine at a pressure of 50 g / cm ² for 15 seconds to obtain a wet-bonded nonwoven fabric (= support fiber sheet). A base sheet of the present invention (breathability: 167 cm ³ / (cm ² · sec)) in which ultrafine continuous fibers were fused and fixed on one side was produced. As shown in FIG. 1, this base sheet is completely buried, partially buried, or melted at a contact point only in the contact region with the core-sheath type composite fused fiber that constitutes the wet fused nonwoven fabric. It was in a fixed state.

  And using this base material sheet, the separation membrane lamination sheet was produced with the following procedure.

  First, polytrimethylsilylpropyne was dissolved in hexane to obtain a water surface developing solution. This solution was dropped on the pure water surface using an injection needle to form a thin film. And the said base material sheet is immersed in pure water, it pulls up diagonally upward from pure water slowly, and the said thin film (thickness: about 0.2 micrometer) is carried out on the ultrafine continuous fiber lamination surface of a base material sheet. It laminated | stacked and air-dried and the separation membrane laminated sheet of this invention was manufactured. The separation membrane of this separation membrane laminated sheet was observed with an electron microscope, but no pinholes were observed in the separation membrane, and it had a smooth surface.

(Example 2)
A base sheet was prepared in the same manner as in Example 1 except that the amount of superfine continuous fibers was about 20 mg / m ² . When the air permeability of this base material sheet was measured, it was 412 cm ³ / (cm ² · sec), and the air permeability was high. In this base sheet, the ultrafine continuous fiber is completely buried, partially buried, or fused and fixed at the contact point only in the contact region with the core-sheath type composite fused fiber constituting the wet fused nonwoven fabric. It was in the state.

  Subsequently, when a separation membrane laminated sheet was produced in the same manner as in Example 1, no pinholes were observed in the separation membrane, and it had a smooth surface.

(Example 3)
A substrate sheet was prepared in the same manner as in Example 1 except that the amount of superfine continuous fibers was about 100 mg / m ² . When the air permeability of this base material sheet was measured, it was 75 cm ³ / (cm ² · sec), and the air permeability was relatively high. In this base material sheet, the ultrafine continuous fibers are completely buried, partially buried, or fused and fixed at the contact points only in the contact area with the core-sheath type composite fused fiber constituting the wet fused nonwoven fabric. It was in the state.

  Subsequently, when a separation membrane laminated sheet was produced in the same manner as in Example 1, no pinholes were observed in the separation membrane, and it had a smooth surface.

Example 4
A base sheet was prepared in the same manner as in Example 1 except that the amount of superfine continuous fibers was about 400 mg / m ² . When the air permeability of this substrate sheet was measured, it was 18 cm ³ / (cm ² · sec), and the air permeability was relatively high. In this base sheet, the ultrafine continuous fiber is completely buried, partially buried, or fused and fixed at the contact point only in the contact region with the core-sheath type composite fused fiber constituting the wet fused nonwoven fabric. It was in the state.

  Subsequently, when a separation membrane laminated sheet was produced in the same manner as in Example 1, no pinholes were observed in the separation membrane, and it had a smooth surface.

(Comparative Example 1)
A thin film on a pure water surface is laminated on one side of the wet-fused nonwoven fabric in the same manner as in Example 1 except that the wet-fused nonwoven fabric in Example 1 (not laminated with ultrafine continuous fibers) was used. Air-dried to produce a comparative separation membrane laminated sheet. When the separation membrane of this separation membrane laminated sheet was observed with an electron microscope, it was not only a separation membrane having a concavo-convex structure along the gap between the fibers, but the separation membrane was broken in some places.

Electron micrograph (1000 times) of the ultrafine continuous fiber laminate surface side of the base material sheet in Example 1

Claims (7)

A base sheet for a separation membrane, wherein ultrafine fibers having an average fiber diameter of 1 µm or less are fused and fixed to one side of a supporting fiber sheet mainly composed of fused fibers by the fused fibers. The base sheet for a separation membrane according to claim 1, wherein the fusion fiber comprises a composite fusion fiber including a low melting point component and a high melting point component, and the low melting point component is exposed on the fiber surface. The substrate sheet for a separation membrane according to claim 1 or 2, wherein the ultrafine fibers are obtained by an electrostatic spinning method. The substrate sheet for a separation membrane according to any one of claims 1 to 3, wherein the amount of ultrafine fibers is 500 mg or less per 1 m ² . After laminating ultrafine fibers having an average fiber diameter of 1 μm or less on one side of a support fiber sheet mainly composed of fused fibers, pressurization is performed at a temperature equal to or higher than the melting point of the fused fibers, and the ultrafine fibers are fused and fixed by the fused fibers. A process for producing a base sheet for a separation membrane. 6. The method for producing a base sheet for a separation membrane according to claim 5, wherein ultrafine fibers obtained by an electrostatic spinning method are directly laminated on a supporting fiber sheet. A separation membrane laminated sheet, characterized in that a separation membrane is laminated on the surface of the ultrafine fiber side of the separation membrane substrate sheet according to any one of claims 1 to 4.

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