METHOD FOR JOINING BRAIDS USED FOR BRAID-REINFORCED HOLLOW FIBER MEMBRANE AND METHOD FOR PRODUCING BRAID-REINFORCED POROUS HOLLOW FIBER MEMBRANE

Abstract

A method for joining braids that are used for a braid-reinforced hollow fiber membrane, produced by the method inserting a core material into the hollow parts of ends of two braids to be joined to connect the two braids, covering the joint part with a heat-shrinkable tube, and shrinking the heat-shrinkable tube by heating at 120 to 160 C., thereby joining the braid ends together, and that can exhibit sufficient joint strength when load is applied during spinning, or when a porous hollow fiber membrane is used as a treatment membrane for water purification treatment, sewage and waste water treatment, etc. A braid-reinforced porous hollow fiber membrane is produced by allowing braids whose ends are joined by the above method to pass through the inner nozzle of a double annular spinning nozzle, applying a membrane-forming dope discharged from the outer nozzle of the double annular spinning nozzle to the outer surfaces of the joined braids passing through the inner nozzle of the double annular spinning nozzle for impregnation, then coagulating the braids in a coagulating liquid, and winding the braids on a bobbin.

Claims

1. A method for joining braids used for a braid-reinforced hollow fiber membrane comprising inserting a core material into the hollow parts of ends of two braids to be joined to connect the two braids, covering the joint part with a heat-shrinkable tube, and shrinking the heat-shrinkable tube by heating at 120 to 160 C, thereby joining the braid ends together.

2. The method for joining braids used for a braid-reinforced hollow fiber membrane according to claim 1, wherein the core material has a hollow part.

3. The method for joining braids used for a braid-reinforced hollow fiber membrane according to claim 1, wherein the core material is a rubber.

4. The method for joining braids used for a braid-reinforced hollow fiber membrane according to claim 3, wherein the rubber is EPDM, chloroprene rubber, silicone-based rubber, or fluorine-based rubber.

5. The method for joining braids used for a braid-reinforced hollow fiber membrane according to claim 1, wherein the heat-shrinkable tube material is polyolefin resin-based materials, fluororesin-based materials, polyvinyl chloride-based materials, ethylene propylene rubber-based materials, or silicone resin-based materials.

6. A method for producing a braid-reinforced porous hollow fiber membrane, the method comprising allowing braids whose ends are joined by the method according to claim 1 to pass through the inner nozzle of a double annular spinning nozzle, applying a membrane-forming dope discharged from the outer nozzle of the double annular spinning nozzle to the outer surfaces of the joined braids passing through the inner nozzle of the double annular spinning nozzle for impregnation, then coagulating the braids in a coagulating liquid, and winding the braids on a bobbin.

7. The method for producing a braid-reinforced porous hollow fiber membrane according to claim 6, wherein in the spinning step, spinning is performed while stretching the joined braids under a tension of 2 to 30 N in the long axis direction of the joined braids from the spinning nozzle to the reel.

8. The method for joining braids used for a braid-reinforced hollow fiber membrane according to claim 2, wherein the core material is a rubber.

9. The method for joining braids used for a braid-reinforced hollow fiber membrane according to claim 8, wherein the rubber is EPDM, chloroprene rubber, silicone-based rubber, or fluorine-based rubber.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0026] FIG. 1: A drawing showing, of before joining two braids the braids, a core material, and a heat-shrinkable tube

[0027] FIG. 2: A perspective view showing a state in which the core material is inserted into the hollow parts of the two braids

EMBODIMENTS FOR CARRYING OUT THE INVENTION

[0028] Two braids are joined by inserting a core material into the end hollow part of each braid to be joined to connect the braids together, then placing a heat-shrinkable tube so as to cover the joint part, and heating the heat-shrinkable tube at 120 to 160 C., so that the braids are firmly fixed together by the shrunk tube.

[0029] Any braids can be used without limitation, as long as they are conventionally used cylindrical braids, regardless of the way of knitting, such as circular knitting or diagonal knitting. For example, cylindrical nets of monofilaments, multifilaments, and spun yarns are used. Specific examples thereof include those having a thickness of about 0.15 to 0.5 mm, a yarn fineness of about 200 to 600 dtex and a yarn density of 16 to 48, and made of organic fiber base materials, such as polyethylene terephthalate, polyphenylene sulfide, polyester, polypropylene, polyethylene, rayon, vinylon, polyamide, polyimide, and aramid; preferably used are those made of polyethylene terephthalate, polyphenylene sulfide, or polyester.

[0030] The core material is not particularly limited, as long as it has heat resistance so that it is not thermally deformed at the heating temperature (e.g., about 120 to 160 C.) of the heat-shrinkable tube; however, it is perferabe to use materials that have moderate rigidity and flexibility, in addition to heat resistance. Further, the core material preferably has a hollow part. Specifically, rubber materials, such as EPDM, chloroprene rubber, silicone-based rubber, and fluorine-based rubber are used, in terms of quality and price. Moreover, the size of the core material is such that the cross-sectional area in the long axis direction is about 85 to 97% of the cross-sectional area of the hollow part of the braid.

[0031] The heat-shrinkable tube is a cylindrical body that is shrunk by heating. Usable examples of the material thereof include commercial products, such as polyolefin resin-based materials, fluororesin-based materials, polyvinyl chloride-based materials, ethylene propylene rubber-based materials, and silicone resin-based materials. Specific examples thereof include Misumi products (polyolefin resin-based materials), SUMITUBE produced by Sumitomo Electric Industries (polyolefin resin-based materials, fluororesin-based materials, and polyvinyl chloride-based materials), HISHITUBE produced by Mitsubishi Resin Corporation (polyvinyl chloride-based materials), NISHITUBE produced by Telmax (ethylene propylene rubber and polyvinyl chloride-based materials), the ST series produced by Shin-Etsu Chemical Co., Ltd. (silicone resin-based materials), and the like, which can be used as they are.

[0032] FIGS. 1 and 2 are perspective views specifically showing a method for joining two braids. For example, a core material 2 having a length of about 10 to 30 mm is inserted into the end hollow parts of braids 1 and 1 to be joined to connect the braids 1 and 1 together. Then, a heat-shrinkable tube 3 is placed so as to cover the joint part. The heat-shrinkable tube 3 is heated at 120 to 160 C. using a heat-shrinkable tube heater or the like. The shrunk tube is pressed and brought into contact with the outer peripheral surfaces of the braids, so that the braids are firmly bonded together.

[0033] The braids whose ends are joined together are allowed to pass through, for example, the inner nozzle of a double annular spinning nozzle, and a membrane-forming dope discharged from the outer nozzle of the double annular spinning nozzle is applied to the outer surfaces of the braids passing through the inner nozzle of the double annular spinning nozzle for impregnation. Thereafter, the braids are coagulated in a coagulating liquid and then dried, thereby producing a braid-reinforced porous hollow fiber membrane.

[0034] Specifically, the braid-reinforced porous hollow fiber membrane is obtained by a method for producing a braid-reinforced porous hollow fiber membrane, the method comprising allowing braids whose ends are joined together (joined braids) to pass through the inner nozzle of a double annular spinning nozzle, applying a membrane-forming dope discharged from the outer nozzle of the double annular spinning nozzle to the outer surfaces of the joined braids passing through the inner nozzle of the double annular spinning nozzle for impregnation, then coagulating the braids in a coagulating liquid, and winding the braids on a bobbin; wherein in the spinning step, spinning is preferably performed while stretching the joined braids under a tension of 2 to 30 N in the long axis direction of the joined braids from the spinning nozzle to the reel. The obtained braid-reinforced porous hollow fiber membrane has a stable outside diameter shape and a uniform membrane thickness. In addition, no crack starting point is formed in the axial direction of the hollow fiber membrane, so that membrane cracking can be prevented.

[0035] A membrane-forming dope for forming a porous hollow fiber membrane is attached to the outer peripheral surfaces of the joined braids. The membrane-forming dope is attached to the outer peripheral surfaces of the joined braids by a method comprising applying the membrane-forming dope discharged from the outer nozzle of a double annular spinning nozzle to the outer surfaces of the joined braids passing through the inner nozzle of the double annular spinning nozzle.

[0036] Usable examples of the film-forming resin include polyvinylidene fluoride, polysulfone, polyphenylsulfone, polyetherimide, polyethersulfone, polyamide, preferably polyvinylidene fluoride or polysulfone, and the like, in terms of heat resistance, strength and separation.

[0037] The membrane-forming dope is, for example, a solution in which polyvinylidene fluoride is dissolved in a solvent capable of dissolving polyvinylidene fluoride resin so that the concentration thereof is about 16 to 27 wt. %, preferably about 18 to 25 wt. %. If the polyvinylidene fluoride concentration is lower than this range, the membrane pore diameter increases too much. In contrast, if the concentration is higher than this range, it is difficult to dissolve the polyvinylidene fluoride. Examples of the soluble solvent for polyvinylidene fluoride resin include various alcohols or non-protonic polar solvents such as dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, dimethyl sulfoxide and N-methyl-2-pyrrolidone, and triethyl phosphate etc.

[0038] The joined braids to which the membrane-forming dope for forming a porous hollow fiber membrane is attached are coagulated using a coagulating liquid by a dry-wet spinning method or a wet spinning method, followed by washing and drying, thereby forming a braid-reinforced porous hollow fiber membrane.

[0039] In the spinning step of the present invention, spinning is preferably performed while stretching the joined braids under a tension of 2 to 30 N, preferably 4 to 15 N, in the long axis direction of the joined braids from the spinning nozzle to the reel (e.g., a bobbin). The tension is adjusted by, for example, making the winding speed faster than the feeding speed so as to make a difference between the feeding speed and the winding speed. If the tension is less than this range, the obtained braid-reinforced porous hollow fiber membrane has neither a stable outside diameter shape nor a uniform membrane thickness. As a result, a crack starting point is formed in the axial direction of the hollow fiber membrane, so that membrane cracking may occur. By applying such a tension, spinning can be performed at a speed 1 to 50 m/min.

[0040] In Patent Document 11, when a braid (cylindrical braid) is allowed to pass through the inner nozzle of a double annular spinning nozzle, a tension of about 4 to 50 N is generally applied to the braid; however, in the present invention, tension is applied to the joined braids not only when they pass through the inner nozzle of the double annular spinning nozzle, but also when they are sent from the spinning nozzle to the bobbin. If tension is applied to the joined braids only when they pass through the inner nozzle of the double annular spinning nozzle, the outside diameter shape is not stable, and membrane cracking may occur, which is not preferable.

EXAMPLES

[0041] The following describes the present invention with reference to Example.

Example

[0042] A tubular EPDM core material having an outer diameter of 1.5 mm and a length of 10 mm was inserted into one end parts of two polyethylene terephthalate braids having an outer diameter of 2.1 mm, an inner diameter of 1.7 mm, and a yarn density of 24 so that the two braids were connected. A heat-shrinkable tube (HSTT09-YK1, produced by Misumi) was placed on the outside of the braids so as to cover the connected part. This part was heated at 150 C. for 30 seconds to contact bonding the heat-shrinkable tube, thereby joining the two braids.

[0043] The joint part of the braids was placed in a tensile tester (EZ Test Compact Tabletop Tester, produced by Shimadzu Corporation). When the joint part was stretched at a speed of 20 mm/min at room temperature, the maximum load was 22 N.

REFERENCE SIGN LIST

[0044] 1, 1 Braid [0045] 2 Core material [0046] 3 Heat-shrinkable tube