JP2012106177A - Semipermeable membrane support - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semipermeable membrane support having sufficient resistance to alkali solution, with high strength, excellent in manufacturing stability and semipermeable membrane coatability, without strike-through to the surface where semipermeable membrane solution is not coated, and excellent in adhesion properties between a semipermeable membrane and the semipermeable membrane support.SOLUTION: In the semipermeable membrane support provided with the semipermeable membrane at least on one surface of a support, the support contains 30 mass% or more of sheath-core type conjugated fiber with a core component of polypropylene and a sheath component of high density polyethylene, a ratio (A/B) of a melting peak area (A) derived from high density polyethylene on the low melting point side of a DSC curve obtained by differential scanning calorimetry of the sheath-core type conjugated fiber and a melting peak area (B) derived from polypropylene on the high melting point side is 1.00 or more and 2.50 or less, the content of all polyolefin fiber including the sheath-core type conjugated fiber is 90 mass% or more, and air permeability is 1.0-30.0 cc/cm/sec.

Description

  The present invention relates to a semipermeable membrane support.

  Semipermeable membranes are widely used in the fields of desalination of seawater, water purifiers, food concentration, wastewater treatment, ultrapure water production for medical use and semiconductor cleaning, such as blood filtration. The semipermeable membrane is made of a synthetic resin such as a cellulose resin, a polysulfone resin, a polyacrylonitrile resin, a fluorine resin, a polyester resin, or a polyvinyl chloride resin. However, since the semipermeable membrane itself is inferior in mechanical strength, a semipermeable membrane is provided on one side (hereinafter referred to as “semipermeable membrane application surface”) of a semipermeable membrane support made of a fibrous base material such as a nonwoven fabric or a woven fabric. It is used in the form.

  The performance required for the semipermeable membrane support is excellent in smoothness of the semipermeable membrane application surface, there are few irregularities in the semipermeable membrane after film formation, and the semipermeable membrane solution does not penetrate the non-coated surface. Examples thereof include good adhesion between the semipermeable membrane and the semipermeable membrane support, and less curling and shrinkage of the sheet before and after application of the semipermeable membrane. For example, a polysulfone ultrafiltration membrane using a polyester nonwoven fabric is disclosed (for example, see Patent Document 1).

  On the other hand, there are uses such as using a semipermeable membrane for the treatment of an alkaline waste liquid, or using an alkaline cleaning solution when washing the semipermeable membrane, although the water to be treated is in the acidic to neutral range. However, a semipermeable membrane support using a polyester nonwoven fabric is easily hydrolyzed and damaged by an alkaline solution and cannot be used in such applications.

  For the purpose of imparting resistance to alkaline solutions, it has a semipermeable membrane support obtained by heat-treating a composite fiber using polypropylene as a core material and polyethylene as a sheath material, and a nonwoven fabric layer formed from a single polypropylene fiber on the surface. A semipermeable membrane support (for example, see Patent Documents 2 and 3) provided with a permeable membrane has been proposed. Such polyolefin fibers are excellent in alkali resistance and oxidation resistance, but it is relatively difficult to produce a nonwoven fabric with a high content of polyolefin fibers, resulting in uneven formation and poor production stability. . In addition, the polyolefin fiber is inferior in heat resistance, and there has been a problem that wrinkles and curls are generated in the manufacturing process in which the semipermeable membrane is provided on one surface of the semipermeable membrane support.

Japanese Patent Laid-Open No. 54-14376 JP 2001-17842 A JP-A-56-152705

  The object of the present invention is to have a sufficient resistance to an alkaline solution, strong, excellent in production stability and semi-permeable membrane application suitability, and without semi-permeable to the non-coated surface of the semi-permeable membrane solution. An object of the present invention is to provide a semipermeable membrane support having excellent adhesion between the permeable membrane and the semipermeable membrane support.

As a result of intensive studies to solve the above problems, the present inventors have
(1) In a semipermeable membrane support used by providing a semipermeable membrane on at least one surface, the semipermeable membrane support is 30 masses of core-sheath type composite fiber having polypropylene as a core component and high-density polyethylene as a sheath component. % Melting point area (A) derived from low melting point high density polyethylene and melting peak area derived from high melting point polypropylene in the DSC curve obtained by differential scanning calorimetry of the core-sheath composite fiber The ratio (A / B) of (B) is 1.00 or more and 2.50 or less, the content of all polyolefin fibers including the core-sheath composite fiber is 90% by mass or more, and the air permeability is A semipermeable membrane supporting material having a thickness of 1.0 to 30.0 cc / cm ² / sec.
(2) A semipermeable membrane support having a heat shrinkage rate of 8.0% or less after 130 ° C. heat treatment of the core-sheath composite fiber,
I found.

The semipermeable membrane support of the present invention contains 30% by mass or more of a core-sheath composite fiber having polypropylene as a core component and high-density polyethylene as a sheath component, and is obtained by differential scanning calorimetry of the core-sheath composite fiber. The ratio (A / B) of the melting peak area (A) derived from the high-density polyethylene on the low melting point side to the melting peak area (B) derived from the polypropylene on the high melting point side in the DSC curve is from 1.00 to 2.50. The content of all polyolefin fibers including the core-sheath type composite fiber is 90% by mass or more, and the air permeability is 1.0 to 30.0 cc / cm ² / sec. . With this configuration, it has sufficient resistance to an alkaline solution, has high strength, is excellent in production stability and semi-permeable membrane application suitability, does not show through to the non-coated surface of the semi-permeable membrane solution, and is semi-permeable. It has become possible to produce a semipermeable membrane support having excellent adhesion between the membrane and the semipermeable membrane support. Moreover, wrinkles and curling can be further suppressed by setting the heat shrinkage rate after the heat treatment at 130 ° C. of the core-sheath composite fiber to 8.0% or less, and the semipermeable membrane, the semipermeable membrane support, It is possible to improve the adhesion.

  The semipermeable membrane support in the present invention contains 30% by mass or more of a core-sheath type composite fiber having polypropylene as a core component and high-density polyethylene as a sheath component, and differential scanning calorimetry (DSC) of the core-sheath type composite fiber. The ratio (A / B) of the melting peak area (A) derived from high-density polyethylene on the low melting point side to the melting peak area (B) derived from polypropylene on the high melting point side is 1.00 or more in the DSC curve obtained by 2.50 or less. The present inventors paid attention to the problem of wrinkles and curling in the manufacturing process in which a semipermeable membrane is provided on one side of the semipermeable membrane support, and these phenomena are caused by the heat applied to the semipermeable membrane support in the manufacturing process. The semi-permeable membrane support was found to be caused by contraction in the width direction. As a result of intensive studies on the suppression of shrinkage in the width direction of the semipermeable membrane support, by using the core-sheath type composite fiber and controlling the ratio (A / B) of the melting peak area, the heat of the semipermeable membrane support They found that it was possible to suppress shrinkage in the width direction due to, and to suppress wrinkling and curling in the manufacturing process.

  Differential scanning calorimetric analysis of the core-sheath composite fiber using polypropylene as the core component and high-density polyethylene as the sheath component is performed according to JIS K 7121, and the area of the melting peak is determined according to JIS K 7122. In the differential scanning calorimetry, the melting peak derived from each of the core component and the sheath component may be single or may be a series of a plurality of overlapping peaks. In the case of a series of a plurality of overlapping peaks, the peak area is obtained as one melting peak, and the larger peak height is defined as the melting point of the core component and the sheath component.

  In the present invention, the melting peak derived from high-density polyethylene on the low melting point side in the DSC curve obtained by differential scanning calorimetry is an endothermic peak having the largest peak height in the range of 125 ° C. or higher and 140 ° C. or lower. The melting peak derived from polypropylene on the high melting point side is an endothermic peak having a peak with the largest peak height in the range of 155 ° C. or higher and 180 ° C. or lower.

  In the present invention, the melting peak area (A) derived from the high melting point polyethylene on the low melting point side and the melting peak derived from the polypropylene on the high melting point side obtained from the DSC curve obtained by differential scanning calorimetry of the core-sheath type conjugate fiber. The area (B) ratio (A / B) is in the range of 1.00 to 2.50, more preferably 1.20 to 2.00, and particularly preferably 1.30 to 1.80. It is. When A / B is less than 1.00, the adhesive strength between the fibers due to the high-density polyethylene which is the heat-sealing component is not sufficient, and the strength of the semipermeable membrane support is lowered. On the other hand, when A / B exceeds 2.50, the shrinkage ratio of the fibers increases, and cracks, wrinkles and the like are likely to occur during the production of the nonwoven fabric, and the uniformity of the formation and the production stability are lowered. In addition, wrinkles and curls are generated in the manufacturing process in which the semipermeable membrane is provided on one surface of the semipermeable membrane support, and the adhesion between the semipermeable membrane support and the semipermeable membrane is also reduced.

  In the present invention, the molecular weight and density of polypropylene as the core component of the core-sheath composite fiber and the high-density polyethylene as the sheath component, the composition ratio between the core component and the sheath component, and the draw ratio of the core-sheath composite fiber are appropriately changed. Thus, the thermal behavior in the differential scanning calorimetry can be controlled.

  The core-sheath type composite fiber having polypropylene as a core component and high-density polyethylene as a sheath component used in the present invention is melt-spun using a melt-spinning machine and using a core-sheath type composite spinning die. The spinning temperature is a temperature at which the high density polyethylene as the sheath component does not change, and the polymer is extruded at a spinning temperature of 200 ° C. or higher and 300 ° C. or lower to produce a spinning filament having a predetermined fineness. The spinning filament is subjected to a stretching treatment as necessary. The stretching treatment is performed at a temperature at which the high-density polyethylene as the sheath component is not fused. For example, when the stretching temperature is 50 ° C. or more and 100 ° C. or less and the treatment is performed at a draw ratio of 2 times or more, the fiber strength is preferably improved. . The obtained filament is provided with a fiber treatment agent as necessary, and after controlling hydrophilicity and dispersibility, it is cut into a predetermined length and used as a core-sheath type composite fiber for manufacturing a nonwoven fabric. .

  Polypropylene is used as the core component constituting the core-sheath composite fiber, but polyolefin such as high-density polyethylene and polymethylpentene can be mixed as necessary in order to adjust fiber properties. The mixing ratio of the polyolefin is preferably 10% by mass or less of the core component. Moreover, the resin additive used for normal polyolefin can be added as needed. Examples of the resin additive include various antioxidants, neutralizers, light stabilizers, ultraviolet absorbers, nucleating agents, lubricants, antistatic agents, and the like. It is used in the range of 0.01% by mass or more and 1.0% by mass or less.

  Next, as the sheath component constituting the core-sheath type composite fiber, high-density polyethylene is used, but in order to adjust the fiber physical properties, polyolefin such as polypropylene or ethylene-propylene copolymer is mixed as necessary. be able to. The mixing ratio of the polyolefin is preferably 10% by mass or less of the sheath component. Moreover, the resin additive used for normal polyolefin can be added as needed. Examples of the resin additive include various antioxidants, neutralizers, light stabilizers, ultraviolet absorbers, nucleating agents, lubricants, antistatic agents, and the like. It is used in the range of 0.01% by mass or more and 1.0% by mass or less.

In the present invention, the heat shrinkage ratio after heat treatment at 130 ° C. for 30 minutes of the core-sheath composite fiber having polypropylene as the core component and high-density polyethylene as the sheath component is preferably 8.0% or less, more preferably 6 0.0% or less, particularly preferably 5.0% or less. When the thermal shrinkage rate exceeds 8.0%, the shrinkage in the width direction due to heat of the semipermeable membrane support increases, and in the manufacturing process of providing a semipermeable membrane on one side of the semipermeable membrane support, And the adhesion between the semipermeable membrane support and the semipermeable membrane tends to be lowered. Here, the heat shrinkage rate is calculated by the following method. That is, the core-sheath composite fiber conditioned at a temperature of 23 ° C. and 50% RH for 24 hours is put in a glass capillary tube, photographed with a digital microscope, and the fiber length (L ₁ ) before heating is measured. Next, after heating at 130 ° C. for 30 minutes and allowing to cool at 23 ° C. and 50% RH for 1 hour, the fiber length (L ₂ ) after heating is measured in the same manner as before heating. The ratio of the difference in fiber length before and after heating (L ₁ -L ₂ ) to the fiber length before heating (L ₁ ), expressed as a percentage, is defined as the thermal shrinkage rate (%).

  The semipermeable membrane support of the present invention contains 30% by mass or more of core-sheath type composite fiber having polypropylene as a core component and high-density polyethylene as a sheath component. Preferably it is 50 mass% or more, More preferably, it is 70 mass% or more, Most preferably, it is 90 mass% or more. If it is less than 30% by mass, cracks, wrinkles and the like are likely to occur during the production of the nonwoven fabric, and the uniformity of the formation and the production stability are reduced. In addition, wrinkles and curls are generated in the manufacturing process in which the semipermeable membrane is provided on one surface of the semipermeable membrane support, and the adhesion between the semipermeable membrane support and the semipermeable membrane is also reduced.

  The semipermeable membrane support of the present invention contains 30% by mass or more of a core-sheath type composite fiber having polypropylene as a core component and high-density polyethylene as a sheath component, and all polyolefins including the core-sheath type composite fiber. The content rate of a system fiber is 90 mass% or more. Preferably it is 95 mass% or more, Most preferably, it is 98 mass% or more. When the content of the polyolefin fiber is less than 90% by mass, resistance to an alkaline solution is lowered.

  In the present invention, a polyolefin-based fiber is a single resin or copolymer resin obtained by polymerizing one or more monomers having one or more double bonds in the molecule and carbon and hydrogen as constituent elements. A single resin or copolymer resin obtained by polymerizing monomers containing constituent elements other than carbon and hydrogen, such as vinylon fiber and ethylene-vinyl alcohol copolymer fiber. Does not include melt-spun fibers. Examples of polyolefin fibers that can be used in combination with the core-sheath type composite fibers include fibers composed of a single component such as polyethylene fibers and polypropylene fibers, mixed polyolefin fibers composed of a mixture of two or more different polyolefins, 2 Examples thereof include a core-sheath type, a side-by-side type, an eccentric type, and a splittable composite fiber, which are appropriately combined with a copolymer polyolefin fiber composed of copolymers of different types of olefins, polyethylene, polypropylene, copolymer polyolefin, and the like. .

  In the semipermeable membrane support of the present invention, fibers other than polyolefin fibers may be contained in an amount of 10% by mass or less. Examples of fibers other than polyolefin-based fibers include, for example, polyacrylic, vinylon-based, vinylidene-based, polyvinyl chloride-based, polyester-based, polyamide-based nylon, benzoate-based, polyclar-based, phenol-based synthetic fibers, acetate, Examples include triacetate, promix, semi-synthetic fibers such as regenerated fiber rayon, cupra, and lyocell fiber, and composite fibers of these fibers and polyolefin fibers.

  The fiber diameter and fiber length of the fiber used in the semipermeable membrane support of the present invention are not particularly limited, but the fiber diameter is preferably 1 μm or more and 30 μm or less, more preferably 3 μm or more and 25 μm or less from the nonwoven fabric strength and manufacturability. Particularly preferably, it is 5 μm or more and 20 μm or less. The fiber length is preferably 1 mm or more and 20 mm or less, more preferably 1 mm or more and 12 mm or less, and particularly preferably 3 mm or more and 10 mm or less. The cross-sectional shape of the fiber is preferably a circular shape, but fibers having irregular cross-sections such as T-type, Y-type, and triangle are also within a range that does not hinder other properties such as fiber dispersibility for preventing back-through and surface smoothness. Can be contained. Further, the splittable composite fiber can be used after being subdivided by hydroentanglement or refiner.

The air permeability of the semipermeable membrane support of the present invention is 1.0 to 30.0 cc / cm ² / sec. Preferably it is 2.0-25.0 cc / cm < ² > / sec, More preferably, it is 3.0-20.0 cc / cm < ² > / sec, Most preferably, it is 4.0-16.0 cc / cm < ² > / sec. If it is less than 1.0 cc / cm ² / sec, the adhesion between the semipermeable membrane and the semipermeable membrane support is poor. If it is greater than 30.0 cc / cm ² / sec, a strike-through occurs when the semipermeable membrane solution is applied, and the smoothness of the semipermeable membrane application surface is also poor.

  The method for producing the semipermeable membrane support of the present invention will be described. As the method for producing the semipermeable membrane support of the present invention, any general method for producing a nonwoven fabric can be used, and it is produced by forming a fiber web and bonding, fusing, and intertwining the fibers in the fiber web. can do. Examples of the method for producing the fiber web include a wet papermaking method, a dry method such as a card method and an airlaid method. However, dry methods such as the card method and the airlaid method can use fibers having a long fiber length, but it is difficult to form a uniform fiber web, and the formation is generally inferior to the wet papermaking method. There is.

  On the other hand, the wet papermaking method has an advantage that the production rate is higher than that of the dry method, and fibers having different fiber diameters or a plurality of types of fibers can be uniformly mixed at an arbitrary ratio in the same apparatus. In other words, there are a wide selection of fiber forms such as staple and pulp, and the usable fiber diameter can be used from ultrafine fibers to thick fibers. It is done. For these reasons, the semipermeable membrane support of the present invention is preferably a wet nonwoven fabric obtained by a wet papermaking method.

  In the wet papermaking method, a slurry in which fibers are uniformly dispersed in water and then passed through a process such as screen (removal of foreign matters, lumps, etc.) and the final fiber concentration is adjusted to 0.001 to 0.50 mass%. Paper is made by a paper machine to obtain wet paper. In order to make the dispersibility of the fibers uniform, chemicals such as dispersants, antifoaming agents, hydrophilic agents, antistatic agents, polymer thickeners, mold release agents, antibacterial agents, bactericides, etc. may be added during the process. is there.

  As the paper machine, for example, a long net paper machine, a circular net paper machine, or an inclined wire type paper machine can be used. These paper machines can be used alone, or a combination paper machine in which two or more same or different types of paper machines are installed online may be used. When two or more layers are made, the composition of each layer may be the same or different. In the case of two or more layers, a paper making method in which wet papers made by each paper machine are laminated, or after forming one sheet, a slurry in which fibers are dispersed is flown on the sheet. Any of the extending methods may be used.

  Sheets are obtained by drying wet paper produced by a paper machine with a Yankee dryer, air dryer, cylinder dryer, suction drum dryer, infrared dryer, or the like. When the wet paper is dried, it is brought into close contact with a hot roll such as a Yankee dryer and dried by heat and pressure to improve the smoothness of the contacted surface. Hot-pressure drying means that the wet paper is pressed against the heat roll with a touch roll or the like and dried. The surface temperature of the hot roll is preferably 90 to 150 ° C, more preferably 100 to 140 ° C, and still more preferably 110 to 140 ° C. The pressure is preferably 50 to 1000 N / cm, more preferably 100 to 800 N / cm, and particularly preferably 150 to 700 N / cm.

  In the semipermeable membrane supporting material of the present invention, it is preferable that after forming into a sheet, it is further subjected to a hot pressing step with a hot roll. The sheet manufactured by the wet papermaking method is passed through the hot pressing process while niping between the rolls of the sheet hot pressing apparatus. Examples of the combination of rolls include two metal rolls, a metal roll and a resin roll, and a metal roll and a cotton roll. Two rolls heat one or both. At that time, by controlling the surface temperature of the hot roll, the nip pressure between the rolls, and the processing speed of the sheet, the air permeability, thickness and the like are controlled to obtain a desired semipermeable membrane support. The surface temperature of the hot roll is preferably 50 to 140 ° C, more preferably 70 to 135 ° C, and particularly preferably 90 to 130 ° C. The roll nip pressure is preferably 190 to 1800 N / cm, more preferably 290 to 1600 N / cm, and particularly preferably 390 to 1500 N / cm. The processing speed is preferably 4 to 100 m / min, more preferably 10 to 80 m / min, and particularly preferably 15 to 70 m / min. It is also possible to perform the hot pressing with a hot roll two or more times. In that case, two or more sets of rolls arranged in series may be used, or one set of rolls may be used. You may process twice. If necessary, the front and back of the sheet may be reversed.

The basis weight of the semipermeable membrane support is not particularly limited, but is preferably ²⁰ to 150 g / m ² , more preferably 30 to 120 g / m ² , and particularly preferably 40 to 100 g / m ² . If it is less than 20 g / m ² , sufficient tensile strength may not be obtained. Moreover, when it exceeds 150 g / m < ² >, liquid flow resistance may become high, or thickness may increase and a predetermined amount of semipermeable membranes may not be accommodated in a unit or a module.

The density of the semi-permeable membrane support is preferably 0.25~0.9g / cm ^3, more preferably 0.3 to 0.7 g / cm ^3, particularly preferably 0.4 to 0. 65 g / cm ³ . When the density of the semipermeable membrane support is less than 0.25 g / cm ³ , the thickness is increased, so that the area of the semipermeable membrane that can be incorporated into the unit is reduced, and as a result, the life of the semipermeable membrane is shortened. May end up. On the other hand, when it exceeds 0.9 g / cm ³ , the liquid permeability may be lowered, and the life of the semipermeable membrane may be shortened.

  The thickness of the semipermeable membrane support is preferably 50 to 200 μm, more preferably 60 to 150 μm, and still more preferably 70 to 130 μm. When the thickness of the semipermeable membrane support exceeds 200 μm, the area of the semipermeable membrane that can be incorporated into the unit is reduced, and as a result, the life of the semipermeable membrane may be shortened. On the other hand, when the thickness is less than 50 μm, sufficient tensile strength may not be obtained or liquid permeability may be reduced, and the life of the semipermeable membrane may be shortened.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example.

[Evaluation of peak area ratio (A / B)]
A core-sheath type composite fiber having polypropylene as a core component and high-density polyethylene as a sheath component was washed with ethanol, dried at 80 ° C. for 30 minutes, and then subjected to conditioning at a temperature of 23 ° C. and 50% RH for 24 hours. The sample is sealed in an Al sample container, subjected to differential scanning calorimetry specified in JIS K 7121, a DSC curve is obtained, and the melting peak area on the low melting point side derived from high-density polyethylene is obtained by the method specified in JIS K 7122. The melting peak area (B) on the high melting point side derived from (A) and polypropylene was calculated, and the peak area ratio (A / B) was obtained from the following formula (1).

Peak area ratio (A / B) = melting peak area (A) / melting peak area (B) (1)

[Evaluation of heat shrinkage]
A sample obtained by conditioning a core-sheath type composite fiber containing polypropylene as a core component and high-density polyethylene as a sheath component at a temperature of 23 ° C. and 50% RH for 24 hours is placed in a glass capillary tube, and the length of the fiber before heating. (L ₁ ) was photographed with a digital microscope (product name: VHX-900, manufactured by Keyence Corporation) and measured in a distance measurement mode. Next, after heating at 130 ° C. for 30 minutes and allowing to cool at 23 ° C. and 50% RH for 1 hour, the length (L ₂ ) of the heated fiber was measured in the same manner as before heating. The thermal contraction rate was calculated | required by following Formula (2).

Thermal contraction rate (%) = (L ₁ −L ₂ ) / L ₁ × 100 (2)

Example 1
In the DSC curve of differential scanning calorimetry, the ratio (A / B) of the melting peak area (A) on the low melting point side to the melting peak area (B) on the high melting point side is 1.04, and the thermal contraction rate is 5. 4%, 100 parts by mass of a core-sheath type composite fiber (fineness 0.8 dtex, fiber length 5 mm) whose core component is polypropylene and whose sheath component is high-density polyethylene is disaggregated and dispersed in water of a pulper. By stirring gently, a uniform papermaking slurry was prepared. This slurry for paper making is made by a wet paper making method using a circular paper machine and dried by a hot air hood attached to a Yankee dryer set at 135 ° C, and the sheath part of the core-sheath type composite fiber is melted by heat. By bonding, a nonwoven fabric having a width of 500 mm and a basis weight of 50 g / m ² was obtained.

The obtained nonwoven fabric was processed under the conditions of each heated metal roll temperature of 115 ° C., pressure of 785 N / cm, and processing speed of 20 m / min using a calender device comprising two heated metal rolls, and the semipermeable membrane of Example 1 A support was obtained. When the air permeability of the semipermeable membrane support thus obtained was measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079, it was 9.2 cc / cm ² / sec. It was.

(Example 2)
In the DSC curve of differential scanning calorimetry, the ratio (A / B) of the melting peak area (A) on the low melting point side to the melting peak area (B) on the high melting point side is 1.25, and the thermal contraction rate is 5. Example 2 was carried out in the same manner as in Example 1 except that a core-sheath composite fiber (fineness 0.8 dtex, fiber length 5 mm) having a core component of polypropylene and a sheath component of high-density polyethylene was used. 2 semipermeable membrane supports were obtained. The air permeability of the semipermeable membrane support thus obtained was measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079, and was 8.8 cc / cm ² / sec. It was.

(Example 3)
In the DSC curve of differential scanning calorimetry, the ratio (A / B) of the melting peak area (A) on the low melting point side to the melting peak area (B) on the high melting point side is 1.52, and the thermal contraction rate is 5. Except that a core-sheath type composite fiber (fineness 0.8 dtex, fiber length 5 mm) in which the core component is polypropylene and the sheath component is high-density polyethylene is used in the same manner as in Example 1, 3 semipermeable membrane support was obtained. The air permeability of the semipermeable membrane support thus obtained was measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079, and found to be 8.6 cc / cm ² / sec. .

Example 4
In the DSC curve of differential scanning calorimetry, the ratio (A / B) of the melting peak area (A) on the low melting point side to the melting peak area (B) on the high melting point side is 1.96, and the thermal contraction rate is 7. Example 5 is the same as Example 1 except that a core-sheath composite fiber (fineness 0.8 dtex, fiber length 5 mm) in which the core component is polypropylene and the sheath component is high-density polyethylene is 5%. 4 semipermeable membrane support was obtained. The air permeability of the semipermeable membrane support thus obtained was 8.7 cc / cm ² / sec when measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) in accordance with JIS L 1079. .

(Example 5)
In the DSC curve of differential scanning calorimetry, the ratio (A / B) of the melting peak area (A) on the low melting point side to the melting peak area (B) on the high melting point side is 2.45, and the thermal contraction rate is 7. Example 1 was carried out in the same manner as in Example 1 except that a core-sheath composite fiber (fineness 0.8 dtex, fiber length 5 mm) having a core component of polypropylene and a sheath component of high-density polyethylene was used. 5 semipermeable membrane support was obtained. The air permeability of the semipermeable membrane support thus obtained was 8.5 cc / cm ² / sec when measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079. .

(Example 6)
In the DSC curve of differential scanning calorimetry, the ratio (A / B) of the melting peak area (A) on the low melting point side to the melting peak area (B) on the high melting point side is 2.40, and the thermal contraction rate is 8. Example 2 was carried out in the same manner as in Example 1 except that a core-sheath composite fiber (fineness 0.8 dtex, fiber length 5 mm) having a core component of polypropylene and a sheath component of high-density polyethylene was used. 6 semipermeable membrane support was obtained. The air permeability of the semipermeable membrane support thus obtained was measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079, and found to be 8.6 cc / cm ² / sec. .

(Example 7)
In the DSC curve of differential scanning calorimetry, the ratio (A / B) of the melting peak area (A) on the low melting point side to the melting peak area (B) on the high melting point side is 1.65, and the thermal contraction rate is 5. 90% by mass of a core-sheath type composite fiber (fineness 0.8 dtex, fiber length 5 mm) having a core component of polypropylene and a sheath component of high-density polyethylene, a single fiber (fineness 0.8 dtex, Fiber length 5 mm) and 10 parts by mass were mixed, disaggregated and dispersed in water of a pulper, and gently stirred with an agitator to prepare a uniform papermaking slurry. This slurry for paper making is made by a wet paper making method using a circular paper machine and dried by a hot air hood attached to a Yankee dryer set at 135 ° C, and the sheath part of the core-sheath type composite fiber is melted by heat. By bonding, a nonwoven fabric having a width of 500 mm and a basis weight of 50 g / m ² was obtained. The obtained nonwoven fabric was subjected to thermal calendering in the same manner as in Example 1 to obtain a semipermeable membrane support of Example 7. The air permeability of the semipermeable membrane support thus obtained was measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079, and found to be 9.3 cc / cm ² / sec. .

(Example 8)
In the DSC curve of differential scanning calorimetry, the ratio (A / B) of the melting peak area (A) on the low melting point side to the melting peak area (B) on the high melting point side is 1.65, and the thermal contraction rate is 5. 70% by mass of a core-sheath type composite fiber (fineness 0.8 dtex, fiber length 5 mm) having a core component of polypropylene and a sheath component of high-density polyethylene, a single fiber (fineness 0.8 dtex, Fiber length 5 mm) and 30 parts by mass were mixed, disaggregated and dispersed in water of a pulper, and gently stirred with an agitator to prepare a uniform papermaking slurry. This slurry for paper making is made by a wet paper making method using a circular paper machine and dried by a hot air hood attached to a Yankee dryer set at 135 ° C, and the sheath part of the core-sheath type composite fiber is melted by heat. By bonding, a nonwoven fabric having a width of 500 mm and a basis weight of 50 g / m ² was obtained. The obtained nonwoven fabric was subjected to thermal calendering in the same manner as in Example 1 to obtain a semipermeable membrane support of Example 8. The air permeability of the semipermeable membrane support thus obtained was 10.7 cc / cm ² / sec as measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079. .

Example 9
In the DSC curve of differential scanning calorimetry, the ratio (A / B) of the melting peak area (A) on the low melting point side to the melting peak area (B) on the high melting point side is 1.65, and the thermal contraction rate is 5. 70% by mass of a core-sheath type composite fiber (fineness 0.8 dtex, fiber length 5 mm) having a core component of polypropylene and a sheath component of high-density polyethylene, a single fiber (fineness 0.8 dtex, (Fiber length 5 mm) 22 parts by mass and polyester single fiber (fineness 1.7 dtex, fiber length 5 mm) 8 parts by mass are mixed, disaggregated and dispersed in water in a pulper, and gently stirred with an agitator to make uniform A papermaking slurry was prepared. This slurry for paper making is made by a wet paper making method using a circular paper machine, dried by a hot air hood attached to a Yankee dryer set at 135 ° C, and the sheath portion of the core-sheath composite fiber is melted by heat. By bonding, a nonwoven fabric having a width of 500 mm and a basis weight of 50 g / m ² was obtained. The obtained nonwoven fabric was subjected to thermal calendering in the same manner as in Example 1 to obtain a semipermeable membrane support of Example 9. The air permeability of the semipermeable membrane support thus obtained was 11.5 cc / cm ² / sec as measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079. .

(Example 10)
In the DSC curve of differential scanning calorimetry, the ratio (A / B) of the melting peak area (A) on the low melting point side to the melting peak area (B) on the high melting point side is 1.65, and the thermal contraction rate is 5. 50% by mass of a core-sheath type composite fiber (fineness 0.8 dtex, fiber length 5 mm) having a core component of polypropylene and a sheath component of high-density polyethylene, and a single fiber (fineness 0.8 dtex, (Fiber length 5 mm) 48 parts by mass and vinylon binder fiber (fineness 1.1 dtex, fiber length 3 mm) 2 parts are mixed, disaggregated and dispersed in water in a pulper, and stirred gently with an agitator to make uniform paper. A slurry was prepared. This slurry for paper making is made by a wet paper making method using a circular paper machine and dried by a hot air hood attached to a Yankee dryer set at 135 ° C, and the sheath part of the core-sheath type composite fiber is melted by heat. By bonding, a nonwoven fabric having a width of 500 mm and a basis weight of 50 g / m ² was obtained. The obtained nonwoven fabric was subjected to thermal calendering in the same manner as in Example 1 to obtain a semipermeable membrane support of Example 10. The air permeability of the semipermeable membrane support thus obtained was measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079, and found to be 13.8 cc / cm ² / sec. .

(Example 11)
In the DSC curve of differential scanning calorimetry, the ratio (A / B) of the melting peak area (A) on the low melting point side to the melting peak area (B) on the high melting point side is 1.65, and the thermal contraction rate is 5. 50% by mass of a core-sheath type composite fiber (fineness 0.8 dtex, fiber length 5 mm) having a core component of polypropylene and a sheath component of high-density polyethylene, and a single fiber (fineness 0.8 dtex, Fiber length 5 mm) 45 parts by weight and vinylon binder fiber (fineness 1.1 dtex, fiber length 3 mm) 5 parts by weight are mixed, disaggregated and dispersed in water in a pulper, and stirred gently with an agitator to make uniform paper. A slurry was prepared. This slurry for paper making is made by a wet paper making method using a circular paper machine and dried by a hot air hood attached to a Yankee dryer set at 135 ° C, and the sheath part of the core-sheath type composite fiber is melted by heat. By bonding, a nonwoven fabric having a width of 500 mm and a basis weight of 50 g / m ² was obtained. The obtained nonwoven fabric was subjected to thermal calendering in the same manner as in Example 1 to obtain a semipermeable membrane support of Example 11. The air permeability of the semipermeable membrane support thus obtained was 13.9 cc / cm ² / sec as measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079. .

(Example 12)
In the DSC curve of differential scanning calorimetry, the ratio (A / B) of the melting peak area (A) on the low melting point side to the melting peak area (B) on the high melting point side is 1.65, and the thermal contraction rate is 5. 50% by mass of a core-sheath type composite fiber (fineness 0.8 dtex, fiber length 5 mm) having a core component of polypropylene and a sheath component of high-density polyethylene, and a single fiber (fineness 0.8 dtex, Fiber length 5 mm) 40 parts by mass and vinylon binder fiber (fineness 1.1 dtex, fiber length 3 mm) 10 parts by weight are mixed, disaggregated and dispersed in water in a pulper, and stirred gently with an agitator to make uniform paper. A slurry was prepared. This slurry for paper making is made by a wet paper making method using a circular paper machine and dried by a hot air hood attached to a Yankee dryer set at 135 ° C, and the sheath part of the core-sheath type composite fiber is melted by heat. By bonding, a nonwoven fabric having a width of 500 mm and a basis weight of 50 g / m ² was obtained. The obtained nonwoven fabric was subjected to thermal calendering in the same manner as in Example 1 to obtain a semipermeable membrane support of Example 12. The air permeability of the semipermeable membrane support thus obtained was 14.2 cc / cm ² / sec when measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079. .

(Example 13)
In the DSC curve of differential scanning calorimetry, the ratio (A / B) of the melting peak area (A) on the low melting point side to the melting peak area (B) on the high melting point side is 1.65, and the thermal contraction rate is 5. 8%, 32 parts by mass of core-sheath type composite fiber (fineness 0.8 dtex, fiber length 5 mm) whose core component is polypropylene and sheath component is high-density polyethylene, single fiber (fineness 0.8 dtex, Fiber length 5 mm) 60 parts by mass and vinylon binder fiber (fineness 1.1 dtex, fiber length 3 mm) 8 parts by mass are mixed, disaggregated and dispersed in water in a pulper, and stirred gently with an agitator to make uniform paper. A slurry was prepared. This slurry for paper making is made by a wet paper making method using a circular paper machine and dried by a hot air hood attached to a Yankee dryer set at 135 ° C, and the sheath part of the core-sheath type composite fiber is melted by heat. By bonding, a nonwoven fabric having a width of 500 mm and a basis weight of 50 g / m ² was obtained. The obtained nonwoven fabric was subjected to thermal calendering in the same manner as in Example 1 to obtain a semipermeable membrane support of Example 13. The air permeability of the semipermeable membrane support thus obtained was 17.6 cc / cm ² / sec when measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079. .

(Example 14)
In the DSC curve of differential scanning calorimetry, the ratio (A / B) of the melting peak area (A) on the low melting point side to the melting peak area (B) on the high melting point side is 1.65, and the thermal contraction rate is 5. 30% by mass of a core-sheath type composite fiber (fineness 0.8 dtex, fiber length 5 mm) whose core component is polypropylene and whose sheath component is high-density polyethylene, single fiber (fineness 0.8 dtex, Fiber length 5 mm) 60 parts by weight and vinylon binder fiber (fineness 1.1 dtex, fiber length 3 mm) 10 parts by weight are mixed, disaggregated and dispersed in water in a pulper, and stirred gently with an agitator to make uniform paper. A slurry was prepared. This slurry for paper making is made by a wet paper making method using a circular paper machine and dried by a hot air hood attached to a Yankee dryer set at 135 ° C, and the sheath part of the core-sheath type composite fiber is melted by heat. By bonding, a nonwoven fabric having a width of 500 mm and a basis weight of 50 g / m ² was obtained. The obtained nonwoven fabric was subjected to thermal calendering in the same manner as in Example 1 to obtain a semipermeable membrane support of Example 14. The air permeability of the semipermeable membrane support thus obtained was measured by an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079, and found to be 18.2 cc / cm ² / sec. .

(Example 15)
In Example 3, the semi-permeable membrane support of Example 15 was obtained by changing the calendar processing conditions to a pressure of 1200 N / cm and a processing speed of 10 m / min. The air permeability of the semipermeable membrane support thus obtained was 1.2 cc / cm ² / sec when measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079. .

(Example 16)
In Example 3, the calendering condition was changed to a processing speed of 10 m / min, and the semipermeable membrane supporting material of Example 16 was obtained. When the air permeability of the semipermeable membrane support thus obtained was measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079, it was 3.7 cc / cm ² / sec. .

(Example 17)
In Example 3, the calendering conditions were changed to each heated metal roll temperature of 110 ° C. and a processing speed of 30 m / min to obtain a semipermeable membrane support of Example 17. When the air permeability of the semipermeable membrane support thus obtained was measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079, it was 19.5 cc / cm ² / sec. .

(Example 18)
In Example 3, the calendering conditions were changed to each heated metal roll temperature of 100 ° C. and a processing speed of 30 m / min, to obtain a semipermeable membrane support of Example 18. The air permeability of the semipermeable membrane support thus obtained was 29.6 cc / cm ² / sec as measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079. .

(Comparative Example 1)
In the DSC curve of differential scanning calorimetry, the ratio (A / B) of the melting peak area (A) on the low melting point side to the melting peak area (B) on the high melting point side is 0.94, and the thermal contraction rate is 5. Comparative Example as in Example 1 except that a core-sheath type composite fiber (fineness 0.8 dtex, fiber length 5 mm) in which the core component is polypropylene and the sheath component is high-density polyethylene is 5%. 1 semipermeable membrane support was obtained. When the air permeability of the semipermeable membrane support thus obtained was measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079, it was 9.4 cc / cm ² / sec. .

(Comparative Example 2)
In the DSC curve of differential scanning calorimetry, the ratio (A / B) of the melting peak area (A) on the low melting point side to the melting peak area (B) on the high melting point side is 2.55, and the thermal contraction rate is 8. Comparative Example as in Example 1 except that a core-sheath type composite fiber (fineness 0.8 dtex, fiber length 5 mm) in which the core component is polypropylene and the sheath component is high-density polyethylene is 5%. 2 semipermeable membrane supports were obtained. The air permeability of the semipermeable membrane support thus obtained was 8.5 cc / cm ² / sec when measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079. .

(Comparative Example 3)
Except for 17 parts by mass of a single fiber made of polypropylene (fineness 0.8 dtex, fiber length 5 mm) and 13 parts by mass of a single fiber made of polyester (fineness 1.7 dtex, fiber length 5 mm), the same as in Example 9. Thus, a semipermeable membrane support of Comparative Example 3 was obtained. The air permeability of the semipermeable membrane support thus obtained was 13.0 cc / cm ² / sec as measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079. .

(Comparative Example 4)
The ratio (A / B) of the melting peak area (A) on the low melting point side to the melting peak area (B) on the high melting point side is 1.65, the heat shrinkage rate is 5.8%, and the core component is polypropylene. And 27 mass parts of core-sheath type composite fiber (fineness 0.8 dtex, fiber length 5 mm) whose sheath component is high density polyethylene, 60 mass parts of single fiber (fineness 0.8 dtex, fiber length 5 mm) made of polypropylene, vinylon A semipermeable membrane support of Comparative Example 4 was obtained in the same manner as in Example 13, except that the binder fiber (fineness 1.1 dtex, fiber length 3 mm) was 13 parts by mass. When the air permeability of the semipermeable membrane support thus obtained was measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079, it was 19.2 cc / cm ² / sec. .

(Comparative Example 5)
The ratio (A / B) of the melting peak area (A) on the low melting point side to the melting peak area (B) on the high melting point side is 1.65, the heat shrinkage rate is 5.8%, and the core component is polypropylene. And 27 mass parts of core-sheath type composite fiber (fineness 0.8 dtex, fiber length 5 mm) whose sheath component is high-density polyethylene, 65 mass parts of single fiber (fineness 0.8 dtex, fiber length 5 mm) made of polypropylene, vinylon A semipermeable membrane support of Comparative Example 5 was obtained in the same manner as in Example 13 except that the binder fiber (fineness 1.1 dtex, fiber length 3 mm) was 8 parts by mass. The air permeability of the semipermeable membrane support thus obtained was 18.8 cc / cm ² / sec as measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079. .

(Comparative Example 6)
In Example 3, the calendering condition was changed to a pressure of 1200 N / cm and a processing speed of 6 m / min to obtain a semipermeable membrane support of Comparative Example 6. The air permeability of the semipermeable membrane support thus obtained was 0.7 cc / cm ² / sec when measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079. .

(Comparative Example 7)
In Example 3, the calendering condition was changed to each heated metal roll temperature of 100 ° C. and the processing speed of 35 m / min to obtain a semipermeable membrane support of Comparative Example 7. The air permeability of the semipermeable membrane support thus obtained was 30.8 cc / cm ² / sec when measured with an air permeability meter (KES-F8-AP1: manufactured by Kato Tech Co., Ltd.) according to JIS L 1079. .

<Evaluation>
The semipermeable membrane supports obtained in Examples and Comparative Examples were evaluated as follows, and the results are shown in Table 1.

[Nonwoven fabric production stability]
The semipermeable membrane supporting materials of Examples and Comparative Examples were produced by 5000 m, and the production stability was evaluated according to the following criteria.
(Double-circle): There is no malfunctions, such as a sheet piece, crack formation, a grain, uneven shading, and a curl. Very good level.
○: Minor inconveniences such as shading unevenness and curly wrinkles occur. Good level.
Δ: Minor inconveniences such as shading unevenness and curly wrinkles frequently occur. Practically usable level.
X: Major defects such as sheet breakage and cracking frequently occur. Unusable level for practical use.

[Thickness]
The thickness was measured according to JIS P 8118.

[Tensile strength]
Ten samples having a winding direction of 250 mm and a width direction of 50 mm were cut out from the semipermeable membrane supports obtained in Examples and Comparative Examples, and a tabletop material testing machine (apparatus name: STA) according to JIS P8113. -1150, manufactured by Orientec Co., Ltd.), the tensile strength was measured, and the average value of 10 sheets was taken as the tensile strength.

[Alkali resistance]
The semipermeable membrane supports obtained in Examples and Comparative Examples were immersed in a 10% by mass sodium hydroxide solution at a temperature of 60 ° C. for 1 week. After washing with water and drying, the tensile strength was measured, and the residual ratio of the tensile strength relative to the initial value was used as an indicator of alkali resistance. If the residual ratio is 90% or more, it is at a level where there is no practical problem.

[Semipermeable membrane applicability]
A semipermeable membrane was applied to the semipermeable membrane supports obtained in Examples and Comparative Examples. A dimethylformamide solution of polysulfone resin (concentration: 16% by mass) was applied to one surface of the semipermeable membrane support with a coating width of 450 mm and a coating thickness of 200 μm. At this time, a drum was disposed on the back side of the semipermeable membrane support to which the polysulfone solution was not applied so that the semipermeable membrane support was conveyed. The semipermeable membrane support to which the polysulfone solution was applied was immersed in pure water at 20 ° C. to solidify the polysulfone, thereby obtaining a composite membrane of a microporous polysulfone membrane and a semipermeable membrane support. The composite membrane was washed with a hot bath at 80 ° C. to remove the solvent remaining in the membrane, and then dried with hot air at 80 ° C. The occurrence of wrinkles and undulations of the composite film thus obtained was evaluated.
A: No wrinkles or undulations. Very good level.
○: There is no wrinkle at all, but a slightly weak wave is seen. Good level.
Δ: No wrinkles are observed, but slightly larger undulations are observed. Practically usable level.
X: Not only wavy but also wrinkles are observed. Unusable level for practical use.

[curl]
The composite membrane of the polysulfone membrane obtained in [Semipermeable membrane applicability] and the semipermeable membrane support was cut into a size of 10 cm square and left for 24 hours in an environment of 23 ° C. and 50% RH. After 24 hours, the sheet was placed on a flat desk, and the maximum value of the four floating heights was taken as the curl value. If the curl value is 2 mm or less, the curl value is satisfactory if it is 4 mm or less. If it is 5 mm or more, the handling becomes complicated and impossible.

[Semipermeable membrane permeation]
A cross-sectional SEM photograph of the composite membrane of the polysulfone membrane and the semipermeable membrane support obtained in [Semipermeable membrane coating suitability] was taken to evaluate the degree of penetration of the polysulfone resin into the semipermeable membrane support.
(Double-circle): The polysulfone resin has soaked only to the vicinity of the center of the semipermeable membrane support. Very good level.
○: The polysulfone resin does not ooze out on the non-coated surface of the semipermeable membrane support. Good level.
Δ: The polysulfone resin oozes partly on the non-coated surface of the semipermeable membrane support. Practically usable level.
X: The polysulfone resin oozes out on the non-application surface of the semipermeable membrane support. Unusable level for practical use.

[Semipermeable membrane adhesion]
About the composite membrane of the polysulfone membrane obtained in [Semipermeable membrane coating suitability] and the semipermeable membrane support, after one day of production, slowly peel off the semipermeable membrane and the semipermeable membrane support so that they are peeled off at the interface. Judgment was made based on the degree of resistance when peeling.
(Double-circle): The adhesiveness of a semipermeable membrane and a semipermeable membrane support body is very high, and cannot peel. Very good level.
○: There is a place where it is easy to partially peel off. Good level.
Δ: The semipermeable membrane and the semipermeable membrane support are adhered, but are easy to peel off as a whole. Practically lower limit level.
X: Peeling occurs in the water washing or drying step after the semipermeable membrane application. Unusable level.

The semipermeable membrane supports shown in Examples 1 to 18 are derived from the melting peak area (A) derived from the high melting point polyethylene on the low melting point side and the polypropylene on the high melting point side in the DSC curve obtained by differential scanning calorimetry. The melting peak area (B) ratio (A / B) is 1.00 or more and 2.50 or less, and contains 30% by mass or more of core-sheath type composite fiber having polypropylene as a core component and high-density polyethylene as a sheath component And the content rate of all the polyolefin-type fibers including this core-sheath-type composite fiber is 90 mass% or more, and an air permeability is 1.0-30.0 cc / cm < ² > / sec. These semipermeable membrane supports have sufficient resistance to alkaline solutions, high strength, excellent production stability, semipermeable membrane application suitability, and no see-through to the non-coated surface of the semipermeable membrane solution, Excellent adhesion between semipermeable membrane and semipermeable membrane support. When Examples 1 to 5 are compared, Examples 2 to 4 in which the ratio (A / B) of the melting peak area is in the range of 1.20 or more and 2.00 or less have high tensile strength and suitability for application of a semipermeable membrane. Excellent curling when semi-permeable membrane is applied. Among them, Examples 2 and 3 are particularly excellent in that the core-sheath composite fiber has a heat shrinkage of 6.0% or less, and the sheet curl is small. From the comparison between Examples 5 and 6, Example 5 in which the heat-shrinkage rate of the core-sheath-type composite fiber is 8.0% or less is greater than that in Example 6 in which the heat-shrinkage rate is greater than 8.0%. It is excellent in stability, semipermeable membrane application suitability, and semipermeable membrane adhesion.

In Examples 3, 7, 10, 13, and 14, the ratio (A / B) of the melting peak area (A) derived from the high melting point polyethylene on the low melting point side and the melting peak area (B) derived from the polypropylene on the high melting point side. ) Is not less than 1.00 and not more than 2.50, and the content of the core-sheath composite fiber having polypropylene as the core component and high-density polyethylene as the sheath component is changed, but the content exceeds 30% by mass. As it increases, the non-woven fabric production stability, suitability for semipermeable membrane application, and semipermeable membrane adhesion are improved, and curling after semipermeable membrane application is also reduced. From the comparison of Examples 8 to 14, the alkali resistance is preferably improved as the content of all polyolefin fibers including the core-sheath composite fiber exceeds 90% by mass. From the comparison of Examples 3 and 15 to 18, Examples 3, 16, and 17 in which the permeability of the semipermeable membrane support is 3.0 to 20.0 cc / cm ² / sec are the curls after the semipermeable membrane application. Is small, the penetration of the semipermeable membrane is small, and the semipermeable membrane adhesion is good, which is particularly preferable.

On the other hand, the comparative example 1 whose melting peak area ratio (A / B) is smaller than 1.00 has a reduced tensile strength. Comparative Example 2 in which the ratio (A / B) of the melting peak area is greater than 2.50 is inferior in the production stability of the nonwoven fabric, and wrinkles are generated even when the semipermeable membrane is applied. Comparative Examples 3 and 4 in which the content of all polyolefin fibers including the core-sheath composite fiber is less than 90% by mass are inferior in alkali resistance. Moreover, Comparative Examples 4 and 5 in which the content of the core-sheath type composite fiber is less than 30% by mass are inferior in semipermeable membrane coating suitability. Comparative Example 6 in which the air permeability of the semipermeable membrane support is less than 1.0 cc / cm ² / sec is inferior in the adhesion of the semipermeable membrane. In Comparative Example 7 in which the air permeability of the semipermeable membrane support exceeded 30.0 cc / cm ² / sec, the penetration at the time of semipermeable membrane application was large, and it was a practically unusable level.

  The semipermeable membrane support of the present invention is used for desalination of seawater, water purifiers, food concentration, wastewater treatment, medical use represented by blood filtration, production of ultrapure water for semiconductor cleaning, membrane separation activated sludge treatment, etc. In the field, it can be suitably used as a support for microfiltration membranes, ultrafiltration membranes, and MBR membranes.

Claims (2)

In a semipermeable membrane support used by providing a semipermeable membrane on at least one surface, the semipermeable membrane support contains 30% by mass or more of core-sheath type composite fiber having polypropylene as a core component and high-density polyethylene as a sheath component In the DSC curve obtained by differential scanning calorimetry of the core-sheath composite fiber, the melting peak area derived from the high melting point polyethylene on the low melting side (A) and the melting peak area derived from the high melting point polypropylene (B) Ratio (A / B) is 1.00 or more and 2.50 or less, the content of all polyolefin fibers including the core-sheath composite fiber is 90% by mass or more, and the air permeability is 1.0. A semipermeable membrane support characterized in that it is ˜30.0 cc / cm ² / sec.   The semipermeable membrane supporting material according to claim 1, wherein the heat-shrinkage rate of the core-sheath composite fiber after heat treatment at 130 ° C is 8.0% or less.