JP4557287B2 - Hollow fiber membrane defect inspection method and defect inspection apparatus - Google Patents

Description

  The present invention relates to a defect inspection method for a porous hollow fiber membrane.

Porous hollow fiber membranes are generally processed into bundle assemblies and used as filter units in many applications such as artificial organs, wastewater treatment, and gas separation. When used as a filter unit, if there are defects such as cracks, crevices, and small holes penetrating the outside and inside of the porous hollow fiber membrane, the undiluted solution is mixed directly into the permeate through the defects and is essentially removed. Since the amount of substances to be contained in the permeated liquid increases, it cannot be used for applications requiring strict selective permeability such as medical applications. Therefore, the filter unit must be inspected for defects after processing, and if a defect is found, it is repaired or discarded. In order to improve the processing yield of the filter unit, it is important to obtain a porous hollow fiber membrane constituting the filter unit that is free from defects and not to damage the porous hollow fiber membrane during processing. . On the other hand, if all the porous hollow fiber membranes are inspected in a non-destructive manner to detect defects and the portions are removed, a porous hollow fiber membrane having substantially no defects can be obtained. For this reason, development of the defect detection technique of the porous hollow fiber membrane which runs continuously is requested | required. Patent Document 1 is known as a method for inspecting a defect of a hollow fiber membrane.
JP 58-129230 A

  However, in the method of Patent Document 1, when a large hole such as a pinhole is present by passing the porous hollow fiber membrane through the pressurized liquid, the liquid is injected into the hollow portion through the portion, A defect is detected by detecting a liquid. This method is characterized in that a defective portion such as a pinhole is replaced with a liquid in a hollow portion, and the defective portion is detected by detecting the liquid. However, in the case of a highly hydrophilic porous hollow fiber membrane, there is a concern that even when there is no defect, the liquid penetrates into the hollow part when passing through the pressurized liquid, and that part is determined as a defect. The

  The present invention has been made in view of the problems of the prior art as described above, and the purpose thereof is continuously with respect to a porous hollow fiber membrane having any performance regardless of hydrophobicity or hydrophilicity. An object of the present invention is to provide a method capable of detecting a defect in a traveling hollow fiber membrane.

The present invention is a defect inspection method for sequentially performing the following steps on a continuously running porous hollow fiber membrane, wherein the porous hollow fiber membrane is immersed in a liquid in the following step (2). A method for inspecting a defect of a porous hollow fiber membrane, wherein the pressure in the hollow portion is 0.02 MPa to 0.1 MPa .
(1) Press-in step of press-fitting air into the hollow part from the outer surface of the porous hollow fiber membrane using a pressurizer (2) Immersion step of immersing the porous hollow fiber membrane in a liquid (3) Detection process for detecting bubbles generated from defects on the outer surface of a porous hollow fiber membrane in a liquid

  According to the present invention, defects of a hydrophobic or hydrophilic porous hollow fiber membrane that continuously runs can be detected.

  The porous hollow fiber membrane to be inspected according to the present invention is not particularly limited as long as it can be used as a filtration membrane without limitation on the material, fractionation characteristics, etc. in addition to the hydrophobic and hydrophilic characteristics. For example, a porous hollow fiber membrane made of a material such as polyethylene, polysulfone, polyvinylidene fluoride, or cellulose can be exemplified. Although the size is not limited, a porous hollow fiber membrane having an outer diameter of about 0.5 to 5 mm, an inner diameter of about 0.3 to 4.9 mm, and a fractionation characteristic of about 0.05 to 0.5 μm is exemplified. The

  In the pressurization process of the present invention, there is no particular limitation on the pressure and temperature of the air blown into the pressurizer. Various conditions of the pressurized air should be selected in consideration of characteristics such as the material of the porous hollow fiber membrane so as not to adversely affect the membrane structure of the porous hollow fiber membrane to be inspected. The air temperature is preferably as high as possible because the remaining moisture in the porous hollow fiber membrane is dried and air is blown into the hollow portion of the porous hollow fiber membrane. Then, the lower one is preferable. For this reason, the temperature of air becomes like this. Preferably it is room temperature-130 degreeC, More preferably, it is room temperature-100 degreeC. As for the air pressure, it is important not to pressurize the inside of the hollow part beyond the burst strength of the porous hollow fiber membrane from the viewpoint of not adversely affecting the membrane structure of the porous hollow fiber membrane, but the air pressure is low. Even if it is too much, pressurization into the hollow portion becomes difficult. For this reason, the air pressure outside the porous hollow fiber membrane is preferably about 0.2 MPa to 0.5 MPa, and more preferably about 0.2 MPa to 0.4 MPa. If the pressure in the hollow portion of the porous hollow fiber membrane in the dipping process is too high, bubbles are detected from the outer surface of the hollow fiber membrane where no defect exists. Moreover, if the pressure in the hollow part of the porous hollow fiber membrane is too low, a defective portion of the hollow fiber membrane cannot be detected. Therefore, the pressure in the hollow portion of the porous hollow fiber membrane during immersion in the liquid is preferably 0.02 MPa to 0.1 MPa, and more preferably 0.02 MPa to 0.08 MPa.

  The porous hollow fiber membrane in which air is pressed into the hollow part in the pressurizing device is guided into the liquid in the dipping process through a free guide or the like. When a defective part exists in the porous hollow fiber membrane, the defective part is detected in a form in which bubbles are generated in the liquid immediately after being immersed in the liquid. Although there is no restriction | limiting in particular about the liquid used as an immersion medium, In selecting a liquid, the surface tension characteristic of a liquid is especially important, Methanol, ethanol, formamide, water, etc. which are used as a wet tension test reagent are preferable.

  It is preferable that the liquid tank is placed as close as possible to the pressurizing device as an immersion device. In particular, depending on the structure of the porous hollow fiber membrane, the pressure retention in the hollow portion is poor, so even if the inside of the hollow portion is pressurized with a pressurizing device, the porous hollow fiber membrane flows downstream. In some cases, the pressure in the hollow portion is attenuated, and a defect may not be detected, and it is preferable that the distance between the dipping start point and the outlet portion of the pressurizer is as short as possible. A preferable distance is within 200 mm, more preferably within 100 mm.

The defect location in the present invention refers to a location having a large pore size deviating from the average fraction pore size of the fractionation layer. In the dipping process, when a defective portion exists in the porous hollow fiber membrane in which air is pressed into the hollow portion, bubbles are generated from the defective portion immediately after being immersed in the liquid. The means for detecting bubbles is not limited as long as it is a means capable of detecting the generation of bubbles in the liquid, such as a bubble detector using ultrasonic waves or a bubble detector using image processing. The porous hollow fiber membrane that has passed through the free guide or the like in the liquid of the dipping device is drawn out of the liquid by a drawing drive roll or the like.
Next, the configuration of the present invention will be described in detail with reference to FIG.

  First, the porous hollow fiber membrane 1 is passed through a pressurizing device 2 that pressurizes air from the outer surface. The pressurizing device is installed vertically so that the porous hollow fiber membrane can maintain linearity in the device by gravity. And the free guides 3 and 4 are installed before and behind a pressurization apparatus, and a porous hollow fiber membrane is allowed to pass through the center part of a pressurization apparatus as much as possible. A pressure gauge 5 is attached to the pressurizing device, and the pressure state inside the pressurizing device is detected. Air is blown into the pressurizing device from the air inlet 6 through the tubes connected by tube fitting. The pressurizing device is required to have a structure that can efficiently put the inside of the hollow portion of the porous hollow fiber membrane into a pressurized state by pressurized air. Is the clearance 7 between the inlet / outlet part of the pressure device and the porous hollow fiber membrane. It is desirable to make this clearance small in order to suppress air leakage as much as possible. However, if the clearance is made too small, the porous hollow fiber membrane is pressurized by minute vibrations caused by air velocity spots blown into the pressure device. It is expected that the surface slides at the entrance / exit of the device and its surface is damaged. Considering such points, the clearance is preferably about 0.1 mm to 2 mm, and more preferably about 0.1 mm to 1 mm.

  About the structure of the entrance / exit part of a pressurization apparatus, it is preferable to set it as the labyrinth structure which can ensure high sealing performance about the pressure inside an apparatus. There are no particular restrictions on the type of labyrinth structure, and various types such as a straight-through type and a staggered type that are often used as a basic structure can be used.

  Further, when the inside of the pressurizing apparatus is put into a pressurized state, it is preferable that the pressure is applied uniformly to the outer surface of the porous hollow fiber membrane that passes through the pressurizing apparatus. A cylindrical perforated plate is inserted into the inside of the pressurizing device, circulates around the porous hollow fiber membrane through which blown air passes, and air is uniformly distributed from the outer peripheral portion toward the center of the porous hollow fiber membrane. It is preferable to have a structure that flows in.

  Next, the porous hollow fiber membrane in which air is pressed into the hollow portion in the pressurizing device is introduced into the liquid stored in the liquid tank 8 through the free guide 4. It passes through the in-liquid free guide 10 in the liquid tank, and is drawn out by a drawing drive roll 11 installed downstream of the liquid tank. At this time, when a defect point exists in the porous hollow fiber membrane immersed in the liquid tank, bubbles 9 are generated from the defect point.

  Hereinafter, examples using a hydrophilic porous hollow fiber membrane will be shown. However, since the method of the present invention applies pressure in the hollow portion by air pressurization, any porous hollow fiber regardless of hydrophilicity or hydrophobicity is used. It can be easily analogized that it can be applied to a membrane.

[Example 1]
Using the apparatus shown in FIG. 1, a defect inspection was performed on a porous hollow fiber membrane made of polyvinylidene fluoride having an inner diameter of 1000 μm and an outer diameter of 2100 μm, and a hydrophilic polymer coated on the surface thereof. The characteristics of this membrane were a fractional pore diameter of 0.4 μm and a water passage performance of 100 m ³ / m ² / hr / MPa. The entrance / exit part of the pressurizing device had a diameter of 3 mm and a direct labyrinth structure. The distance between the outlet of the pressure device and the immersion start point of the liquid tank was 100 mm.

  Since it is difficult to measure the pressure inside the hollow part of the porous hollow fiber membrane at the time of defect inspection, stop running the porous hollow fiber membrane in advance of the defect inspection and check the pressure outside the porous hollow fiber membrane. The pressure in the hollow portion of the porous hollow fiber membrane was measured in the state of 0.35 MPa which was the same as the pressure at the time of inspection. That is, a porous hollow fiber membrane having a length of 30 m was introduced into a pressurizing device, and a pressure gauge was attached to the tip of the porous hollow fiber membrane protruding downstream from the outlet of the pressurizing device. In this state, the distance from the outlet of the pressurizing device to the tip of the porous hollow fiber membrane was changed to 40 mm, 50 mm, 60 mm, 70 mm, 80 mm, and 100 mm, and the pressure was measured to be 150 kPa, 100 kPa, and 70 kPa, respectively. , 50 kPa, 30 kPa, and 20 kPa.

  After the above preliminary operation, defect inspection was performed. First, the porous hollow fiber membrane is unwound from the bobbin, and the tip of the membrane is wound on the take-up bobbin through a free guide 3, a pressurizing device, a water tank installed as a dipping device, and a drawing drive roll according to the route of FIG. The tapping attachment and the pulling drive roll were operated, and the vehicle was continuously run at a speed of 4 m / min. In this state, when air having a temperature of 30 ° C. and a pressure of 0.35 MPa was supplied from the air inlet into the pressure device, the pressure outside the porous hollow fiber membrane in the pressure device was 0.35 MPa. .

  Thus, when the defect inspection of the porous hollow fiber membrane was carried out for 1 hour, bubbles were generated several times from the outer surface of the porous hollow fiber membrane immersed in the water tank. Mark with black magic near the bubble, cut out a 700mm long sample around the marked part, and inspect by bubble point method using ethanol as filling liquid into the hollow part did. As a result, the bubble points for the four inspection locations detected as defective locations were 50 kPa, 30 kPa, 40 kPa, and 50 kPa. On the other hand, when the bubble point was measured at a location where no marking was applied, that is, at any 10 locations that were not considered defective in this inspection method, the lowest value was 80 kPa. From the above results, according to the present example, it was confirmed that a defective portion corresponding to a bubble point of about 50 kPa or less can be detected.

It is a schematic diagram which shows an example of the defect inspection apparatus for performing the defect inspection of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Porous hollow fiber membrane 2 Pressurization apparatus 3 Free guide 4 Free guide 5 Pressure gauge 6 Air inlet 7 Clearance 8 Liquid tank 9 Bubble generated from the defect point 10 Underwater free guide 11 Drawer drive roll 12 Immersion start point of liquid tank

Claims (3)

A defect inspection method for sequentially performing the following steps on a continuously running porous hollow fiber membrane, wherein the pressure in the hollow portion of the porous hollow fiber membrane during immersion in the liquid in step (2) is A method for inspecting a defect of a porous hollow fiber membrane, characterized by being 0.02 MPa to 0.1 MPa .
(1) Press-in step of press-fitting air into the hollow part from the outer surface of the porous hollow fiber membrane using a pressurizer (2) Immersion step of immersing the porous hollow fiber membrane in a liquid (3) Detection process for detecting bubbles generated from defects on the outer surface of a porous hollow fiber membrane in a liquid   The method according to claim 1, wherein the pressure outside the porous hollow fiber membrane in the press-fitting step is 0.2 MPa or more. A hollow fiber membrane defect inspection device comprising a pressurizing device for pressurizing the inside of a hollow hollow fiber membrane by pressurizing air from the outer surface, an immersion device having a liquid tank, and a bubble detector. And
Defect inspection apparatus in which a traveling path of the porous hollow fiber membrane is formed so that the porous hollow fiber membrane to be inspected can continuously travel in the pressurization apparatus and the liquid tank in this order. .

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