JP2003213538A - Method for stretching hollow fiber membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for stretching a hollow fiber membrane in a good accuracy, not giving damage and defect to the yarn, and preventing the hollow fiber membrane from flattening and compressing to become dense. <P>SOLUTION: This method for stretching the hollow fiber membrane continuously by making the yarn-conveying speed in the down stream side faster than that of the up stream side between ≥2 yarn conveying means is characterized by using a pair of opposing endless type belts as each of the yarn conveying means, sending yarn by nipping the hollow fiber membrane between the opposing belts and moving the both belts at a same speed in the same direction, sending out the hollow fiber membrane from between the belt in the same direction to the moving direction of the opposing belts making a contact with each other in the up stream side, and feeding the hollow fiber membrane into the belts in the same direction of the direction of moving the opposing belts making contact with each other in the down stream side. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a hollow fiber membrane suitable for the field of filtration such as turbidity, which has fine pores and high water permeability and is excellent in durability. Regarding

[0002]

2. Description of the Related Art Bacteria removal using a porous membrane such as a microfiltration membrane and an ultrafiltration membrane and filtration of turbid particles are carried out in the automobile industry (electrodeposition paint recovery and reuse system), the semiconductor industry (ultra pure water). Production), pharmaceutical food industry (sterilization, enzyme purification), etc., but it has been put to practical use in many fields, especially in recent years, in the tap water field for producing drinking water and industrial water by turbidizing river water, etc. Secondary application of sewage (secondarily treated water) is being actively applied to the field of sewage such as clarification and purification. In order for the membrane to be widely used in such fields, it is necessary to have a membrane that has higher permeability and strength and that does not cause contamination (clogging) with organic substances as much as possible. In response to such demands, the method for producing or modifying the hollow fiber membrane by stretching is a method that can be expected to have high permeability and high strength, but due to problems due to the hollow fiber membrane, another practical application is progressing. It wasn't.

As a conventional stretching method, a roll stretching method has been used in which stretching is performed between a plurality of stretching drive rolls having different peripheral speeds. The force for stretching the hollow fiber in the yarn length direction is retained in the hollow fiber by utilizing the friction between the stretching drive roll and the hollow fiber. Therefore, the hollow fiber is held around the stretching roll for about half a circumference. Therefore, the following problems have occurred. (1) The frictional force between the roll and the hollow fiber membrane was likely to be insufficient, resulting in slippage and uneven drawing. (2) Since the stretching force acts as a compression pressure on the hollow fiber membrane at the portion in contact with the roll, the hollow fiber membrane is easily crushed. The compression pressure was dispersed and decreased as the roll diameter increased, which was a factor of increasing the size of the apparatus. (3) In order to accurately set the draw ratio, the peripheral speed of the drawing roll needs to be accurate. Therefore, a hard drawing roll having a constant circumferential length has been used. If the roll is a hard stretch roll, the surface of the hollow fiber membrane in contact with the roll is flattened and compacted, or the circular cross section is easily flattened. Further, there is a drawback that the film is easily damaged when foreign matter adheres to the roll. A hollow fiber membrane that has been flattened is more likely to be flattened when used in external pressure filtration. Further, when the hollow portion is flat, the flow resistance of the permeated water is high and the permeability is low. Further, in the operation including backwashing operation at the internal pressure, the cross-sectional shape is repeatedly deformed from a flat shape to a perfect circle, and vertical cracking easily occurs.

(4) In the case of a soft stretching roll, the effective diameter of the roll changes due to the tensile force, so that the take-up speed changes, and in the case of stretching, the draw ratio and the drawing speed change. Further, when foreign matter adheres to the roll, the diameter of the roll changes due to the contact pressure of the hollow fiber membrane to the roll, and the peripheral speed is not constant, so the foreign matter is likely to rub the membrane and scratch it. (5) Since the drawing path is a path in which the drawing rolls are alternately bent, extra force was applied when the thick hollow fiber membrane was drawn, and the thread was broken or crushed. Due to such a problem of the roll stretching method, conventionally, the stretching of the hollow fiber membrane is difficult to be crushed and is limited to the stretching of the thin hollow fiber membrane under the present circumstances.

[0005]

DISCLOSURE OF THE INVENTION It is an object of the present invention to provide a stretching method in which a hollow fiber membrane can be stretched with high precision and without causing yarn scratch defects, while preventing flattening and consolidation of the hollow fiber membrane. And

[0006]

The present inventors have found a method for stretching a hollow fiber membrane using a take-up machine comprising an endless track belt in order to solve the above problems, and have completed the present invention. That is, the present invention is: When the hollow fiber membrane is continuously stretched between two or more yarn feeding means by increasing the yarn feeding speed on the downstream side from the yarn feeding speed on the upstream side, a pair of endless tracks facing each other as the yarn feeding means. A type belt is used, and the yarn is fed by moving both belts at the same speed and in the same direction with a hollow fiber membrane sandwiched between the opposing belts. On the upstream side, the direction in which the opposing belts contact and move And stretching the hollow fiber membranes between the belts in the same direction, and on the downstream side, the hollow fiber membranes are fed between the belts in the same direction as the direction in which the opposing belts make contact and move. Method. 2. The stretching method according to 1, wherein the stretching treatment is performed in space. 3. The stretching method according to 1, wherein the stretching treatment is performed linearly without bending the hollow fiber membrane. 4. The drawing method according to 1, wherein the endless track belt is made of an elastic body having a substantially smooth surface.

The present invention will be described in detail below. The features of the present invention are the following (1) to (7). (1) Since a pair of opposing endless track type belts are used to sandwich the hollow fiber membranes between the opposing belts, a large frictional force can be obtained and slippage during stretching can be prevented. (2) The circumference of the belt is different from the yarn feeding speed because the speed is faster than that of the straight part due to the thickness of the belt, but the hollow fiber membrane during stretching is (the speed is high) of the belt. Since it does not contact the circumferential portion, there is no chance of rubbing between the belt and the hollow fiber membrane, and yarn scratches are less likely to occur. (3) Since the drawing process is performed in the space between the yarn feeding means, the drawing process can be performed accurately and without damage.

(4) Since the hollow fiber membrane is stretched linearly without bending, unnecessary deformation is not given to the hollow fiber membrane, and the thick fiber can be stretched. (5) Since the belt is a substantially smooth elastic body, the hollow fiber membrane is less likely to slip and crush during yarn feeding. (6) Since the belt is made of an elastic material and is soft and the yarn feeding speed does not change at the yarn feeding portion even if the thickness changes, highly accurate drawing can be performed. (7) Even if foreign matter adheres to the belt or the hollow fiber membrane, since the belt is an elastic body, the foreign matter has less force to push the hollow fiber membrane and is less likely to be pressed. Since the hollow fiber membrane and the belt move at the same speed, there is no difference in speed between the foreign matter and the hollow fiber membrane, so that scratches are less likely to occur.

In the present invention, the hollow fiber membrane means a membrane formed into a hollow fiber shape. With regard to the pore size of the membrane, it can be used as an ultrafiltration membrane or a microfiltration membrane starting from a reverse osmosis membrane having a small pore size. As a material for the hollow fiber membrane, hollow fiber membranes made of various polymer resins can be used. Among them, polymer resins such as polyolefin, polyvinylidene fluoride, halogenated polyolefin, polysulfone, polyether sulfone, and polyacrylonitrile are heat resistant, chemical resistant,
It is preferably used in terms of strength and the like.

The hollow fiber membrane of the present invention also includes a hollow fiber membrane precursor which has not yet become a hollow fiber membrane in the process. Therefore, the present invention also includes stretching the non-porous hollow fiber to form a hollow fiber membrane, and stretching and then performing a predetermined process to form a hollow fiber membrane. For example, when a hollow fiber is stretched to form pores to form a porous membrane, the hollow fiber before being stretched is not a membrane but a hollow fiber precursor. When a porous film is formed from a polymer and a solvent by the thermal phase separation method, the heated and mixed solution is extruded into a hollow shape and then cooled and fixed. Although a structure is formed, this is also a hollow fiber membrane precursor, and when the solvent is extracted from this precursor, it becomes a hollow fiber membrane having fine pores.

The outer diameter of the hollow fiber membrane is not particularly limited, but the stretching method of the present invention is particularly suitable for stretching a thick fiber membrane from the viewpoint of film collapse and stretching accuracy, and an outer diameter of 0.5 mm or more and 10 mm.
The following is more preferably suitable for stretching a hollow fiber membrane having an outer diameter of 0.7 mm or more and 7 mm or less, and even more preferably an outer diameter of 1 mm or more and 5 mm or less. As the material of the endless track belt, a fiber reinforced belt or the like is used because it has mechanical strength inside. The part that contacts the outer hollow fiber membrane is selected from materials that can withstand the environment of temperature, moisture, solvent, etc., and have a large friction with the hollow fiber, and the surface is substantially smooth from scratches and uneven drawing. It is preferably an elastic body. Above all, a belt made of a silicone rubber type sponge as an elastic body is excellent in heat resistance and chemical resistance and is preferably used. In addition, to increase the contact area between the hollow fiber membrane and the belt, a groove that corresponds to the thickness of the hollow fiber membrane gripped on the surface of a smooth belt and that partially contains the hollow fiber membrane for thread feeding is parallel to the stretching direction. May be there.

The compressive elastic modulus in the thickness direction of the elastic body is preferably 1/100 or more and 1 or less, more preferably 1/50, of the compressive elastic modulus in the radial direction of the hollow fiber to be gripped.
It is not less than 1/2 and more preferably not less than 1/20 and not more than 1/5. Although the thickness of the belt is not particularly limited, the thickness of the elastic body portion is preferably in the range of 1 to 100, more preferably in the range of 3 to 50, with respect to the diameter of the hollow fiber to be grasped in view of the thread crushing and the thread sliding. preferable.

The endless track type belt comprises a pair of two belts which face each other as a yarn feeding means. The method of adjusting the gap between the belts facing each other is to keep the length of the gap constant, and between the two belts. There is a method of making the pressing pressure of the belt constant, and a method of making the length of the belt gap constant makes it difficult for the belt to vibrate and stretch easily. When the hollow fiber membrane is continuously stretched, the hollow fiber membrane is linearly drawn between the two or more yarn feeding means, which means that the hollow fiber membrane can be stretched without being bent and extra deformation is caused. There is an advantage of not giving. Furthermore, in the circumferential portion of the belt, the circumferential speed increases by the ratio of the thickness to the roll diameter of the belt, which causes excessive rubbing between the hollow fiber membrane and the belt, which may cause yarn scratches. , And has an advantage that it does not come into contact with the circumferential portion and is less likely to be damaged by yarn.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below based on Examples.

[0015]

Example 1 Hydrophobic silica (Aerosil R-9) having an Mw value (volume% of methanol that completely wets powder) of 50%, an average primary particle size of 0.016 μm and a specific surface area of 110 m ² / g.
72 (trade name)) 23% by weight, dioctyl phthalate 3
0.8% by weight and 6.2% by weight of dibutyl phthalate were mixed in a Henschel mixer, and the weight average molecular weight was 2420.
00 polyvinylidene fluoride (Kureha KF Polymer # 1
000 (trade name) 40% by weight was added and mixed again with a Henschel mixer.

The mixture was mixed with a 30 mmφ twin-screw extruder and pelletized. This pellet was melt extruded at a spinning speed of 20 m / min into a water tank at 40 ° C. through the air in a hollow fiber manufacturing apparatus equipped with a 30 mmφ twin-screw extruder with a hollow fiber-shaped spinneret to form a hollow fiber membrane. A precursor was obtained. Using a pair of opposing endless track type belts, sandwiching between the opposing belts, two yarn feeding means for moving both belts in the same direction at the same speed are arranged at the same height with a space distance of 1.2 m. First, the hollow fiber membrane precursor is first taken up by a yarn feeding means on the upstream side at a speed of 20 m / min, and moves at 30 m / min via a heating space (0.8 m length) controlled to a temperature of 100 ° C. The yarn was taken up by the yarn feeding means on the downstream side and drawn 1.5 times, and then wound up with a cassette. The hollow fiber membrane was arranged in a straight line from the yarn inlet of the upstream yarn feeding means to the yarn outlet of the downstream yarn feeding means, and was stretched linearly without bending.

The endless belt of the yarn feeding means on the upstream side and the downstream side is 11 mm outside the fiber reinforced belt having a thickness of 4 mm.
A sponge-like elastic body made of silicone rubber having a substantially smooth surface is integrally bonded. The yarn feeding means has an endless track type belt stretched between two metal rolls (one of which is a drive roll) having a diameter of 80 mm, which are separated by a distance of about 400 mm in the front and back. The belt width is 80 mm and the belt length is a fiber reinforced belt. The circumference was about 1050 mm as measured at the portion. The hollow fiber membrane precursor was sandwiched between the two belts, which were linearly moved in the same direction at the same speed and in the same direction, and stretched. The belt intervals were both 1.0 mm. The diameter of the hollow fiber membrane precursor is 1.25 mm before stretching and 1.2 after stretching.
It was 4 mm. The compression modulus in the radial direction of the hollow fiber precursor was 7 MPa before stretching and 5 MPa after stretching. The compression elastic modulus in the thickness direction of the silicone rubber belt is 0.9M
It was Pa.

The compressive elastic modulus of the hollow fiber membrane was measured by using a compression measuring machine (manufactured by Shimadzu Corporation: AGS-H / EZTest) with a compression jig having a width of 5 mm to compress the compression displacement and the load for a length of 5 mm. Measured at a speed of 1 mm / min, the load at 100% displacement was calculated from the load at 0.1% displacement and 5% displacement with respect to the initial hollow fiber diameter, and the initial hollow fiber diameter and hollow fiber membrane length were 5 mm. The projected cross-sectional area obtained was standardized and calculated. For the elastic modulus of the belt, a compression jig with a diameter of 5 mm is used.
The same was done.

Then, the wound film was immersed in methylene chloride at 30 ° C. for 1 hour three times to extract dioctyl phthalate and dibutyl phthalate, and then dried at 60 ° C. Then, soak in 50% ethanol aqueous solution for 30 minutes,
Further, the hollow fiber membrane was transferred to water and immersed for 30 minutes to wet the hollow fiber membrane with water. After further dipping in a 5% caustic soda aqueous solution at 40 ° C. for 1 hour twice to extract the hydrophobic silica, it was washed with hot water at 60 ° C. for 12 hours and dried at 60 ° C.

The hollow fiber membrane thus obtained had an outer diameter of 1.22 mm, an inner diameter of 0.65 mm and a circular cross-sectional shape, and neither crushing nor scratches on the membrane surface were observed. There was no slippage during drawing, and drawing was performed in the space between the two yarn feeding means, and uniform drawing was possible.

[0021]

EFFECTS OF THE INVENTION By using the treatment method of the present invention, it is possible to continuously obtain a hollow fiber having a circular cross section without unevenness in drawing in the drawing of the hollow fiber membrane and without any yarn scratches.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a stretching method of the present invention.

[Explanation of symbols]

1: Endless track type yarn feeding means (upstream side) 2: Endless track type yarn feeding means (downstream side) 3: Hollow fiber membrane 4: Endless track belt 5: Freeroll 6: Drive roll

Continued front page    F-term (reference) 4D006 GA03 GA06 GA07 HA01 MA01                       MB11 MB15 MB16 MC22X                       MC25X MC29X MC39X MC62X                       MC63X NA21 NA25 NA34                       NA64 PB04 PC02 PC41                 4L036 MA04 MA19 PA03 RA13 UA08

Claims (4)

[Claims] 1. When the hollow fiber membrane is continuously stretched between two or more yarn feeding means by setting the downstream yarn feeding speed to be higher than the upstream yarn feeding speed, the hollow fiber membranes are used as respective yarn feeding means. Using a pair of endless track type belts, the hollow fiber membrane is sandwiched between the opposing belts and both belts are moved in the same direction at the same speed to perform yarn feeding. Sending out the hollow fiber membrane from between the belts in the same direction as the contacting and moving direction,
On the downstream side, the hollow fiber membrane is fed between the belts in the same direction as the belts facing each other move in the same direction. 2. The stretching method according to claim 1, wherein the stretching treatment is performed in space. 3. The stretching method according to claim 1, wherein the stretching treatment is performed linearly without bending the hollow fiber membrane. 4. The stretching method according to claim 1, wherein the endless track belt is made of an elastic body having a substantially smooth surface.