Air supply system

Abstract

An air-supply module according to one embodiment of the present disclosure can supply a gas to a liquid supplied inside hollow fiber membranes, and is provided with: a case containing a fluororesin as the main component; and a plurality of strands of the hollow fiber membranes containing, as the main component, a polytetrafluoroethylene or a modified polytetrafluoroethylene. Regarding the hollow fiber membranes, the porosity K[%], the average thickness T1 [mm], and the average outer diameter D2 [mm] satisfy the relationship of formula (1).　(1): K / (T1×D2×100)≥2.0

Description

[Technical Field]

[0001] This disclosure relates to an air supply module. This application claims priority under Japanese application No. 2021-80631 filed on 11 May 2021, and incorporates all the provisions of the said Japanese application. [Background technology]

[0002] In addition to their use in filtration systems for solid-liquid separation, air supply modules are also used in air supply devices that remove dissolved gases such as oxygen from liquids, and in supply gases to liquids. For example, air supply devices are known to produce gas-dissolved water (pure water with dissolved gas) for cleaning purposes in the field of electronic device manufacturing and for use in home appliances, as well as hydrogen water (pure water with dissolved hydrogen gas) and carbonated water (pure water with dissolved carbon dioxide gas) for drinking purposes.

[0003] As an air supply module for supplying or degassing air, or an air supply module equipped with the same, for example, an air supply and degassing air supply module has been proposed which is installed in parallel with a suction device for drawing gas from the air supply module and a gas supply device for supplying gas to the air supply module (see Patent Document 1). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2016-217649 [Overview of the Initiative]

[0005] An air supply module according to one aspect of the present disclosure is an air supply module capable of supplying gas to a liquid supplied inside a hollow fiber membrane, comprising a housing mainly composed of fluororesin and a plurality of the above-mentioned hollow fiber membranes mainly composed of polytetrafluoroethylene or modified polytetrafluoroethylene, wherein the porosity K[%], average thickness T1[mm], and average outer diameter D2[mm] of the above-mentioned hollow fiber membranes satisfy the relationship of the following formula (1). K / (T1×D2×100)≧2.0 ···(1) [Brief explanation of the drawing]

[0006] [Figure 1] Figure 1 is a schematic cross-sectional view showing an air supply module according to one embodiment of the present disclosure. [Figure 2] Figure 2 is a schematic perspective view showing a hollow fiber membrane according to one embodiment of the present disclosure. [Figure 3] Figure 3 is a cross-sectional view of the hollow fiber membrane shown in Figure 2, along line AA. [Modes for carrying out the invention]

[0007] [Issues this disclosure aims to address] In recent years, air supply modules have been adopted in a wide range of applications, including semiconductors, food, pharmaceuticals, and wastewater treatment, and there is a demand for miniaturization, as well as improved air supply performance and chemical resistance.

[0008] This disclosure is made in light of these circumstances and aims to provide an air supply module that is compact, has excellent air supply performance and chemical resistance.

[0009] [Effects of this disclosure] An air supply module according to one aspect of this disclosure is compact and offers excellent air supply performance and chemical resistance.

[0010] [Description of Embodiments in this Disclosure] First, the embodiments of this disclosure will be listed and described.

[0011] An air supply module according to one aspect of the present disclosure is an air supply module capable of supplying gas to a liquid supplied inside a hollow fiber membrane, comprising a housing mainly composed of fluororesin and a plurality of the above-mentioned hollow fiber membranes mainly composed of polytetrafluoroethylene or modified polytetrafluoroethylene, wherein the porosity K[%], average thickness T1[mm], and average outer diameter D2[mm] of the above-mentioned hollow fiber membranes satisfy the relationship of the following formula (1). K / (T1×D2×100)≧2.0 ···(1)

[0012] The air supply module, by comprising multiple hollow fiber membranes whose porosity K[%], average thickness T1[mm], and average outer diameter D2[mm] satisfy the relationship in formula (1) above, can achieve high air supply performance and water pressure resistance, as well as miniaturization. Furthermore, by comprising hollow fiber membranes mainly composed of polytetrafluoroethylene or modified polytetrafluoroethylene and a housing mainly composed of fluororesin, it has excellent chemical resistance. Here, "main component" refers to the component with the largest mass content, for example, a component with a content of 50% by mass or more, preferably 70% by mass or more, and more preferably 95% by mass or more.

[0013] The above-mentioned "porosity" refers to the ratio of the total volume of pores to the total volume of the hollow fiber membrane, and can be determined by measuring the density in accordance with ASTM-D-792. The dry mass and water mass of the sample are measured to the nearest 0.0001 g, and the volume of the sample is determined from the difference between these two values. In addition, the true specific gravity of polytetrafluoroethylene (PTFE) is 2.17 g / cm³. 3 The volume of the resin constituting the sample was calculated from its dry mass. The porosity was expressed as a percentage of the sample volume, representing the ratio of the void volume (the volume of the resin minus the volume of the sample) to the volume of the sample. Alternatively, the above porosity can be measured using the following procedure. First, the length (L) of the hollow fiber membrane to be measured is measured in 1 mm units. Next, the weight (W) of the hollow fiber membrane is measured in 0.0001 g units using an electronic balance. Then, based on the above measurements, the porosity [%] is calculated using the following formula. Porosity [%] = {1 - Volume of resin only [cm³] 3 ]÷Total volume of hollow fiber membrane [cm 3 ]}×100 ={1-(W[g]÷ρ[g / cm 3 ])÷(π(D2 2 [mm 2 ]-D1 2 [mm 2 ]) × L[mm] ÷ 1000)} × 100 Here, "ρ" represents the true specific gravity of polytetrafluoroethylene, which is 2.17 [g / cm 3 .

[0014] The "average thickness" of the above hollow fiber membrane can be obtained by dividing (average outer diameter - average inner diameter) by 2. The "average outer diameter" refers to the average value of outer diameters at any two points when the cross-section of the hollow fiber membrane is circular. When the cross-section of the hollow fiber membrane is elliptical, the diameters of the minor axis and the major axis are measured at two positions, and the averaged value is taken as the average outer diameter. In addition, when the cross-section of the hollow fiber membrane has a special-shaped cross-section other than a general circle or ellipse, the edge information of the outer shape of the cross-section is extracted and approximated to a circle, and the value obtained by dividing the obtained inner perimeter by the pi is taken as the average outer diameter. The "average inner diameter" refers to the average value of inner diameters at any two points. Specifically, the average outer diameter can be measured according to the following procedure. First, the hollow fiber membrane is sliced into round pieces on a plane perpendicular to the length direction, and the entire cross-section is observed with an electron microscope so as to be within the field of view. The outer diameter is measured at two positions at substantially diagonal positions of the cross-section (positions where the phases are shifted by approximately 90 degrees), and the averaged value is taken as the average outer diameter (D2).

[0015] It is preferable that the heat of fusion of the above hollow fiber membrane is 30 J / g or more and 45 J / g or less. When the heat of fusion of the hollow fiber membrane is within the above range, a hollow fiber membrane having high crystallinity, pore size and porosity in a better range can be obtained.

[0016] The heat of fusion of the hollow fiber membrane is measured using a differential scanning calorimeter, and is the endotherm between 296°C and 343°C in the third step of measurement by the differential scanning calorimeter. Specifically, the heat of fusion of the hollow fiber membrane is obtained after the following steps: a first step of heating from room temperature to 245°C at a rate of 50°C / min, then heating from 245°C to 365°C at a rate of 10°C / min; a second step of cooling and holding from 365°C to 350°C at a rate of -10°C / min, then cooling from 350°C to 330°C at a rate of -10°C / min, and further cooling from 330°C to 305°C at a rate of -1°C / min; and a third step of cooling from 305°C to 245°C at a rate of -50°C / min, then heating from 245°C to 365°C at a rate of 10°C / min, wherein the heat of fusion is the heat of fusion between 296°C and 343°C in said third step. The sample amount in the above measurement is 10 mg to 20 mg, and the sampling time is 0.5 seconds per measurement.

[0017] It is preferable that the hollow fiber membrane has an average outer diameter D2 of 0.70 mm or less, an average inner diameter D1 of 0.32 mm or less, a water pressure resistance of 0.3 MPa or more, and a porosity K of 30% or more. When the average outer diameter, average inner diameter, water pressure resistance and porosity K of the hollow fiber membrane are within the above ranges, a bundle of hollow fiber membranes having high water pressure resistance and porosity while being thin-walled and having a fine diameter can be formed, whereby the air supply module can be reduced in size and the air supply performance can be improved.

[0018] The "average inner diameter" mentioned above refers to the average value of the inner diameters at any two points. The average inner diameter can be measured using the following procedure. First, the hollow fiber membrane is sliced ​​crosswise with a plane perpendicular to its length, and the entire cross-section is observed with an electron microscope so that it is within the field of view. The inner diameter is measured at two locations approximately diagonally opposite each other on the cross-section (positions where the phase is shifted by approximately 90 degrees), and the average value is taken as the average inner diameter (D1). The "water pressure resistance" mentioned above refers to the pressure at which water begins to leak from the other side when water pressure is applied to one side of the membrane, and is also called leakage pressure. Generally, the larger the diameter of the through-hole, the more easily water leaks and the lower the water pressure resistance, while the smaller the diameter of the through-hole, the higher the water pressure resistance. Specifically, the water pressure resistance is measured in accordance with JIS-L1092 (2009). Specifically, the lumen of a hollow fiber membrane is filled with water, and the water pressure into the lumen is continuously increased at a rate of 100 kPa / min. The pressure at which water leaks out as droplets from the outer surface of the hollow fiber membrane is defined as the water pressure resistance.

[0019] When pure water with a dissolved oxygen concentration of 0.6 ppm or less is supplied to the inside of the hollow fiber membrane and air is permeated through it at a pressure of 10 kPa, the maximum flow rate per minute at which the pure water after air treatment can maintain a dissolved oxygen concentration of 8 ppm or higher is 0.035 mL / cm² relative to the unit internal surface area of ​​the hollow fiber membrane. 2 It is preferable that the flow rate is 8 ppm or more. The air supply module has a maximum flow rate per minute within the above range that allows the pure water after air supply treatment to maintain a dissolved oxygen concentration of 8 ppm or more. This allows for a higher flow rate while supplying gas at a higher concentration with a smaller membrane area relative to the liquid, resulting in a superior air supply effect. Here, "internal surface area" refers to the inner surface area of ​​the hollow fiber membrane.

[0020] The main component of the above-mentioned enclosure is preferably a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, polytetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, or a combination thereof. By using these fluororesins as the main component of the above-mentioned enclosure, the chemical resistance and mechanical strength can be improved.

[0021] [Details of the embodiments of this disclosure] The air supply modules according to each embodiment of this disclosure will be described in detail below with reference to the drawings.

[0022] <Air supply module> Another aspect of the present disclosure relates to an air supply module capable of supplying gas to a liquid supplied within a hollow fiber membrane. The module comprises a housing and a plurality of hollow fiber membranes. The hollow fiber membrane walls allow gas to permeate while suppressing liquid leakage. This air supply module can be applied to applications in any field. For example, it can be used in various applications such as purification and neutralization of cleaning water for semiconductors, electronic devices, and pharmaceuticals, in food and beverage manufacturing, industrial wastewater, river water, lake water, swimming pool water, and public bath water; water treatment applications for drinking water and industrial water; and enrichment of liquids by the permeation of specific gases such as oxygen, ozone, carbon dioxide, nitrogen, and hydrogen.

[0023] The air supply module can be used in both integrated types, where the air supply module is fixed within various devices, and replaceable cartridge types, where the housing and the membrane member having multiple hollow fiber membranes are separate components and the membrane member is inserted into the housing for use.

[0024] Figure 1 shows an example of an air supply module according to one embodiment of the present disclosure, namely an air supply module 3. The air supply module 3 comprises a membrane member 2 having a plurality of hollow fiber membranes 1 aligned in one direction, and a cylindrical housing 11 that houses the membrane member 2. The air supply module 3 is of a type that supplies air to a liquid supplied into the hollow fiber membrane 1 by permeating gas through the hollow fiber membrane 1.

[0025] The membrane member 2 has a first sealing portion 4 that holds one end of the plurality of hollow fiber membranes 1, and a second sealing portion 5 that holds the other end of the plurality of hollow fiber membranes 1. In the first sealing portion 4 and the second sealing portion 5, potting agent is filled between the hollow fiber membranes 1 and between the bundle of hollow fiber membranes and the inner surface of the housing.

[0026] The potting agent described above mainly consists of a resin, rubber, or elastomer. While the potting agent is not particularly limited, examples include epoxy resins, urethane resins, UV-curing resins, fluororesins, silicone resins, polyamide resins, and polyolefin resins such as polyethylene and polypropylene. Among these, fluororesins and silicone resins are preferred from the viewpoint of having good performance as adhesives to hollow fiber membranes mainly composed of polytetrafluoroethylene or modified polytetrafluoroethylene (modified PTFE) and housings mainly composed of fluororesins.

[0027] The air supply module 3 can be configured to include a cylindrical housing 11, a first sleeve 12 attached to one end of the housing 11 and provided with an engagement structure that engages with a gas supply port 9 and a first sealing portion 4, a first cap 13 that seals the end of the housing 11 on the side of the first sleeve 12 and is provided with a liquid outlet 8, a second sleeve 14 attached to the other end of the housing 11 and provided with an engagement structure that engages with a gas outlet 19 and a second sealing portion 5, and a second cap 15 that seals the end of the housing 11 on the side of the second sleeve 14 and is provided with a liquid supply port 7.

[0028] The air supply module 3 has a liquid supply port 7 at one end face through which raw water is supplied in the S1 direction, and a liquid discharge port 8 at the other end face through which liquid that has permeated through multiple hollow fiber membranes 1 is discharged in the S2 direction. The side of the housing 11 is provided with a gas supply port 9 through which gas is supplied in the P1 direction and a gas discharge port 19 through which gas is discharged in the P2 direction. The position and orientation of the gas supply port 9 and the gas discharge port 19 are not particularly limited and can be configured according to the state in which the air supply module 3 is installed.

[0029] Raw water supplied from the liquid supply port 7 into the hollow fiber membrane 1 is then supplied into the housing 11. The treated liquid is then discharged from the liquid discharge port 8 located on the side near the other end of the housing 11.

[0030] The air supply module 3 has excellent chemical resistance because it comprises a housing mainly composed of fluororesin and multiple hollow fiber membranes mainly composed of polytetrafluoroethylene or modified polytetrafluoroethylene. Therefore, the type of raw water is not particularly limited, and various liquids such as pure water, drinking water, chemical solutions, and wastewater can be used depending on the purpose.

[0031] Furthermore, the gas supplied from the gas supply port 9 is drawn in from the wall surface of the hollow fiber membrane 1 toward the gas outlet 19, and is discharged from the tip of the gas outlet 19 while being supplied to the liquid being supplied inside the hollow fiber membrane 1.

[0032] Examples of the gas supplied include air, oxygen, carbon dioxide, hydrogen, ozone, nitrogen, hydrogen sulfide, and ammonia.

[0033] The housing 11 is mainly composed of fluororesin. The housing 11, being mainly composed of fluororesin, has excellent chemical resistance. Preferably, the fluororesin is a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, or a combination thereof. By making these fluororesins the main component of the housing 11, chemical resistance and mechanical strength can be improved.

[0034] In the air supply module 3, when pure water with a dissolved oxygen concentration of 0.6 ppm or less is supplied to the inside of the hollow fiber membrane and air is permeated at a pressure of 10 kPa, the maximum flow rate per minute at which the pure water after air supply treatment can maintain a dissolved oxygen concentration of 8 ppm or higher is 0.035 mL / cm² relative to the unit internal surface area of ​​the hollow fiber membrane 1. 2 It is preferable that the flow rate is 8 ppm or more. In the air supply module 3, the maximum flow rate per minute at which the pure water after air supply treatment can maintain a dissolved oxygen concentration of 8 ppm or more is within the above range, so that a high concentration of gas can be efficiently supplied to the liquid, resulting in a superior air supply effect.

[0035] [Hollow fiber membrane] The hollow fiber membrane 1 in Figures 2 and 3 is mainly composed of polytetrafluoroethylene or modified polytetrafluoroethylene. Since polytetrafluoroethylene and modified polytetrafluoroethylene are fluororesins with excellent chemical and solvent resistance, the selectivity of the types of liquids and gases supplied to the air supply module 3 is improved. Furthermore, since polytetrafluoroethylene and modified polytetrafluoroethylene are highly hydrophobic fluororesins, leakage of liquids from the hollow fiber membrane 1 is suppressed, and gas permeability can be improved.

[0036] Modified polytetrafluoroethylene refers to polytetrafluoroethylene copolymerized with small amounts of hexafluoropropylene (HFP), alkyl vinyl ether (AVE), chlorotrifluoroethylene (CTFE), etc., preferably at a molar ratio of 1 / 50 or less relative to tetrafluoroethylene.

[0037] The lower limit of the average outer diameter D2 of the hollow fiber membrane 1 is not particularly limited, but is preferably 0.1 mm and more preferably 0.2 mm. On the other hand, the upper limit of the average outer diameter D2 of the hollow fiber membrane 1 is preferably 0.70 mm and more preferably 0.4 mm. If the average outer diameter D2 is less than the lower limit, the pressure loss may increase. Conversely, if the average outer diameter D2 exceeds the upper limit, the membrane area that can be contained within the housing 11 may decrease, or the pressure resistance strength may decrease, potentially leading to rupture due to internal pressure or buckling due to external pressure.

[0038] The lower limit of the average inner diameter D1 of the hollow fiber membrane 1 is not particularly limited, but is preferably 0.05 mm, and more preferably 0.1 mm. On the other hand, the upper limit of the average inner diameter D1 of the hollow fiber membrane is preferably 0.32 mm, and more preferably 0.2 mm. If the average inner diameter D1 is less than the lower limit, the pressure loss may increase. Conversely, if the average inner diameter D1 exceeds the upper limit, the pressure resistance strength will decrease, and there is a risk of rupture due to internal pressure or buckling due to external pressure.

[0039] The lower limit of the average thickness T1 of the hollow fiber membrane 1 is preferably 0.01 mm, and more preferably 0.02 mm. On the other hand, the upper limit of the average thickness T1 of the hollow fiber membrane 1 is preferably 0.20 mm, and more preferably 0.10 mm. If the average thickness T1 is less than the lower limit, the pressure resistance strength will be low, and there is a risk of rupture due to internal pressure or buckling due to external pressure. Conversely, if the average thickness T1 exceeds the upper limit, there is a risk of low gas permeability.

[0040] The lower limit of the porosity K of the hollow fiber membrane 1 is preferably 30%, and more preferably 40%. On the other hand, the upper limit of the porosity K of the hollow fiber membrane 1 is not particularly limited, but is preferably 80%, and more preferably 70%. If the porosity K of the hollow fiber membrane 1 is less than the lower limit, the gas permeability will decrease, and the air supply performance of the hollow fiber membrane 1 may decrease. If the porosity K of the hollow fiber membrane 1 exceeds the upper limit, the mechanical strength of the hollow fiber membrane 1 will decrease, and there is a risk of reduced durability or failure such as rupture due to internal pressure.

[0041] The porosity K[%], average thickness T1[mm], and average outer diameter D2[mm] of the above hollow fiber membrane 1 satisfy the relationship shown in equation (1) below. K / (T1×D2×100)≧2.0 ···(1) If the porosity K[%], average thickness T1[mm], and average outer diameter D2[mm] of the hollow fiber membrane 1 satisfy the relationship in formula (1) above, the air supply module can achieve high air supply performance and water pressure resistance, as well as miniaturization. If K / (T1×D2×100) is less than 2.0, the air supply module may experience reduced air supply performance or water pressure resistance, or miniaturization may become difficult.

[0042] The lower limit of the average pore diameter of the hollow fiber membrane 1 is preferably 3.0 nm, and more preferably 5.0 nm. On the other hand, the upper limit of the average pore diameter of the hollow fiber membrane 1 is preferably 50.0 nm, and more preferably 40.0 nm. If the average pore diameter is less than the lower limit, the air supply performance may be insufficient. Conversely, if the average pore diameter exceeds the upper limit, the water pressure resistance will decrease, and liquids such as water containing impurities such as surfactants may leak out.

[0043] The average pore size is measured using the bubble point method (ASTM F316-86, JIS K3832) with a pore size distribution analyzer, following the procedure below. First, the relationship between the differential pressure applied to the membrane and the air flow rate permeating through the membrane is measured using a pore size distribution analyzer, both when the membrane is dry and when it is wet with liquid. The resulting graphs are then designated as the dry curve and the wet curve, respectively. When the differential pressure at the intersection of the dry curve (with the flow rate halved) and the wet curve is P (Pa), the value of d (nm), expressed by the equation d = cγ / P, is the average pore size. Note that c is a constant of 2860, and γ is the surface tension of the liquid (dyn / cm = mN / m). Alternatively, the pore size of hollow fiber membranes can also be measured by the bubble point method using a porometer that performs liquid-liquid phase displacement. Furthermore, since PTFE, the main component of hollow fiber membranes, is a hydrophobic resin, the pore size of hollow fiber membranes can also be measured using the Washburn equation with a pure water porosimeter, which operates on the same principle as a mercury porosimeter.

[0044] In the air supply module 3, the water pressure resistance of the hollow fiber membrane 1 is preferably 0.3 MPa or higher, and more preferably 1.0 MPa or higher. The water pressure resistance of the hollow fiber membrane 1 being within this range allows liquid to be flowed through the air supply module 3 at high pressure. Because liquid can be flowed through the air supply module 3 at high pressure, bubbling does not occur in the liquid even when the pressure of the supply gas is increased, making it possible to produce a higher concentration dissolved gas liquid.

[0045] The upper limit of the heat of fusion of the hollow fiber membrane 1 is preferably 45 J / g, and more preferably 42 J / g. The lower limit of the heat of fusion of the hollow fiber membrane 1 is preferably 30 J / g, and more preferably 33 J / g. If the heat of fusion of the hollow fiber membrane 1 exceeds the upper limit, the pore size may increase. On the other hand, if the heat of fusion of the hollow fiber membrane 1 is less than the lower limit, the porosity may decrease. By keeping the heat of fusion of the hollow fiber membrane 1 within the above range, a hollow fiber membrane 1 with high crystallinity and a better range of pore size and porosity can be obtained. As described above, the heat of fusion of the hollow fiber membrane 1 is the heat of fusion from 296°C to 343°C in the third step when the process goes from the first step to the third step. When the hollow fiber membrane undergoes the above steps 1 through 3, the amount of heat of fusion from 296°C to 343°C in step 3 is between 30.0 J / g and 45.0 J / g, thus obtaining properties suitable for stretching. As a result, it has high deformability and can be stretched beyond the typical yield point that first appears on the load-elongation curve to the next inflection point that appears before fracture. Consequently, a porous hollow fiber membrane with minute pore sizes can be obtained. Therefore, the above hollow fiber membrane 1 has a porous structure that could not be obtained with conventional techniques, with an average outer diameter of 0.70 mm or less, an average inner diameter of 0.32 mm or less, and possesses high porosity K and high water pressure resistance.

[0046] Conventional polytetrafluoroethylenes commonly used for molding have a heat of fusion of less than 30 J / g in the third step when going through the first to third steps described above. Therefore, the heat of fusion of the hollow fiber membrane made of this resin is also considered to be less than 30 J / g. It is believed that such resins are used as a result of considering the moldability in mold molding, paste extrusion molding, etc., and the strength of the molded product. For example, in paste extrusion, in order to make the quality such as molded dimensions and mechanical strength uniform, polytetrafluoroethylenes with a heat of fusion of 20 J / g or less or about 25 J / g are used depending on the molded dimensions, etc. The hollow fiber membrane 1 described above differs from conventional hollow fiber membranes in that the heat of fusion in the third step from 296°C to 343°C is between 30.0 J / g and 45.0 J / g. Due to this difference, it has higher deformability and significantly better shock absorption and deformation adhesion than conventional hollow fiber membranes. Furthermore, a porous hollow fiber membrane with a minute pore size and high porosity can be obtained by the stretching process.

[0047] The lower limit of the isopropanol bubble point of the hollow fiber membrane 1 is preferably 500 kPa, and more preferably 1000 kPa. On the other hand, there is no particular upper limit to the isopropanol bubble point of the hollow fiber membrane 1. If the isopropanol bubble point of the hollow fiber membrane 1 is less than the lower limit, the liquid retention capacity of the hollow fiber membrane 1 may be insufficient. The "isopropanol bubble point" is a value measured using isopropanol in accordance with ASTM-F316-86, and represents the minimum pressure required to push liquid out of the pores, and is an index corresponding to the average pore diameter.

[0048] The lower limit of the filling rate of the hollow fiber membrane 1 in the air supply module 3 is preferably 30%, and more preferably 40%. On the other hand, the upper limit of the filling rate of the hollow fiber membrane 1 is preferably 70%, and more preferably 60%. If the filling rate of the hollow fiber membrane 1 is less than the lower limit, the air supply performance of the air supply module 3 may be reduced. Conversely, if the filling rate of the hollow fiber membrane 1 exceeds the upper limit, the hollow fiber membrane 1 may collapse when it is filled into the housing 11, or difficulties may arise when filling it into the housing. The air supply module 3 has excellent air supply performance because the filling rate of the hollow fiber membrane 1, which has high porosity and bubble points, is between 30% and 70%. Here, "filling density of hollow fiber membranes" refers to the packing density of the hollow fiber membranes 1 packed into the housing 11, and is the ratio (%) of the total cross-sectional area occupied by each hollow fiber membrane 1, determined by the outer diameter of each hollow fiber membrane 1, to the inner lumen cross-sectional area of ​​the housing 11 perpendicular to the length direction of the hollow fiber membranes 1 packed into the housing 11.

[0049] The hollow fiber membrane 1 described above may contain other fluororesins and additives in addition to polytetrafluoroethylene and modified polytetrafluoroethylene, to the extent that they do not impair the desired effects of this disclosure. Examples of such additives include inorganic fillers for improving wear resistance, preventing low-temperature flow, and facilitating pore formation, as well as metal powders, metal oxide powders, metal sulfide powders, and the like.

[0050] [Method for manufacturing hollow fiber membranes] Next, an example of a method for manufacturing the hollow fiber membrane described above will be explained. Preferably, the method for manufacturing the hollow fiber membrane includes a molding step of forming particles of polytetrafluoroethylene or modified polytetrafluoroethylene into a tube shape, a sintering step of heating the tubular molded product to a temperature above the melting point of polytetrafluoroethylene or modified polytetrafluoroethylene, a step of cooling the molten resin, and a stretching step of stretching the non-porous tubular molded product to make it porous. In this way, by stretching the hollow fiber membrane after molding, it is possible to form a porous hollow fiber membrane while reducing the diameter of the pores in the hollow fiber membrane.

[0051] The hollow fiber membrane described above is obtained, for example, by melting polytetrafluoroethylene or modified polytetrafluoroethylene, which has a heat of fusion value of 30.0 J / g or more and 45.0 J / g or less from 296°C to 343°C in the third step above, to eliminate the interparticle gaps, and then slowly cooling it. That is, the process includes a step of heating the polytetrafluoroethylene or modified polytetrafluoroethylene above its melting point to melt it, and a step of cooling the molten resin, and / or a step of holding it at 313°C or more and less than 321°C for 10 minutes or more.

[0052] Polytetrafluoroethylene or modified polytetrafluoroethylene having a heat of fusion of 30.0 J / g or more and 45.0 J / g or less can be obtained, for example, by irradiating polytetrafluoroethylene with a heat of fusion of less than 30.0 J / g with ionizing radiation such as gamma rays, X-rays, ultraviolet rays, or electron beams, or by utilizing decomposition reactions by heating.

[0053] (molding process) In the molding process, polytetrafluoroethylene or modified polytetrafluoroethylene powder, produced by emulsion polymerization or the like, is molded into a tube shape to obtain a tubular molded product. The raw material polytetrafluoroethylene or modified polytetrafluoroethylene particles are a powder consisting of fine particles of polytetrafluoroethylene or modified polytetrafluoroethylene. Polytetrafluoroethylene or modified polytetrafluoroethylene dispersion, which is an emulsion obtained by dispersing these fine particles of polytetrafluoroethylene or modified polytetrafluoroethylene (polytetrafluoroethylene or modified polytetrafluoroethylene powder) in a liquid (dispersion medium), can also be used as the raw material polytetrafluoroethylene or modified polytetrafluoroethylene powder. Examples of polytetrafluoroethylene or modified polytetrafluoroethylene powder include polytetrafluoroethylene or modified polytetrafluoroethylene fine powder, which consists of fine particles of polytetrafluoroethylene or modified polytetrafluoroethylene and is produced by emulsion polymerization, and polytetrafluoroethylene or modified polytetrafluoroethylene molding powder, which is produced by suspension polymerization.

[0054] When forming polytetrafluoroethylene or modified polytetrafluoroethylene powder into a tube shape to obtain a tubular molded product of a predetermined shape and size, known methods for forming a film from powder include, for example, a method of mixing an extrusion aid with the raw material powder and then paste-extruding it into a tube, or a method of forming it using polytetrafluoroethylene or modified polytetrafluoroethylene dispersion and then drying and removing the dispersion medium (casting method). Since polytetrafluoroethylene or modified polytetrafluoroethylene usually has a high melt viscosity, making melt extrusion difficult and the preparation of its solution also difficult, the above methods are generally employed.

[0055] (Sintering process) In the sintering process, the tubular molded product is heated to a temperature above the melting point of polytetrafluoroethylene or modified polytetrafluoroethylene to obtain a non-porous tubular molded product. Hollow fiber membranes produced by compressing polytetrafluoroethylene particles or modified polytetrafluoroethylene particles manufactured by emulsion polymerization, etc., have pores and voids due to gaps between particles and the elimination of extrusion aids. However, by completely melting the polytetrafluoroethylene or modified polytetrafluoroethylene powder, these pores and voids disappear or substantially continuous voids are minimized. As a result, a non-porous tubular molded product is produced. A non-porous film-like molded product means a film with almost no pores penetrating the film, and specifically, a film with a Gurley second of 5000 seconds or more is preferred. In order to completely melt the polytetrafluoroethylene or modified polytetrafluoroethylene powder and produce a non-porous film-like molded product with a large Gurley second, it is preferable to heat it at a temperature higher than the melting point of the raw material, and in order to suppress the decomposition and modification of the resin, the heating temperature is preferably 450°C or lower.

[0056] (cooling process) After the sintering process described above, it is preferable to perform a step of cooling the polytetrafluoroethylene or modified polytetrafluoroethylene by slow cooling. In the cooling process, methods such as raising the temperature above the melting point of the polytetrafluoroethylene or modified polytetrafluoroethylene and then slowly cooling it to below the crystal melting point, or heating it at a temperature slightly below the melting point of the polytetrafluoroethylene or modified polytetrafluoroethylene for a certain period of time (hereinafter sometimes referred to as "constant temperature treatment") are used. This cooling generates crystals in the polytetrafluoroethylene or modified polytetrafluoroethylene, and the degree of crystallinity of the polytetrafluoroethylene or modified polytetrafluoroethylene resin can be saturated before the next stretching process, thereby improving the reproducibility of pore size in the production of porous films. In the crystallization process, the lower the cooling rate or the longer the constant temperature treatment time, the higher the degree of crystallinity and the higher the heat of fusion tend to be. On the other hand, the higher the cooling rate or the shorter the constant temperature treatment time, the lower the degree of crystallinity and the lower the heat of fusion tend to be.

[0057] The heat of fusion of the hollow fiber membrane depends on the amount of crystals formed, and the amount of crystals formed is affected by the cooling rate. Therefore, in order to obtain the heat of fusion within the above range, cooling is performed by slow cooling, and / or holding at 310°C or higher but less than 325°C for 10 minutes or more. Slow cooling is preferably performed at a cooling rate of -3.0°C / min or less, and more preferably at a rate of -2.0°C / min or less.

[0058] Even if the cooling rate is outside the above range, crystallization can be promoted by holding the product at 310°C or above but below 325°C for 10 minutes or more. In other words, while slow cooling requires sophisticated temperature control, the heat treatment method by holding at a constant temperature does not require sophisticated temperature control and allows for more stable and homogeneous heat treatment. Furthermore, slow cooling from temperatures above the melting point cannot be performed in the form of long product rolls because polytetrafluoroethylene or modified polytetrafluoroethylene fuses together, requiring the sintering and cooling processes to be carried out over a long period of time while the product is drawn out at a very slow linear speed. On the other hand, with the heat treatment method by holding at a constant temperature described above, it is possible to form long product rolls after cooling to below the melting point and promote crystallization in the rolled state, enabling mass production by batch processing in large quantities. Note that the process of holding at 310°C or above but below 325°C for 10 minutes or more may be performed during the cooling process after the sintering process, or it may be performed after cooling and then heated and held within the above temperature range.

[0059] As the raw material, the polytetrafluoroethylene or modified polytetrafluoroethylene powder or granules may be used as is, with the heat of fusion of the polytetrafluoroethylene powder or granules adjusted to the above range, or a mixture of two or more types of polytetrafluoroethylene powder or granules, at least one of which has a heat of fusion within the above range, may be used.

[0060] (Stretching process) In the stretching process, the non-porous tubular molded product obtained in this way is stretched to make it porous. A porous hollow fiber membrane can be obtained by stretching the above non-porous tubular molded product. In the stretching process, stretching may be performed only in the axial direction, or in the axial direction and the circumferential direction (radial expansion direction). The stretching ratio in the axial direction can be, for example, 3 times or more and 10 times or less, and the stretching ratio in the circumferential direction can be, for example, 2 times or more and 4 times or less. The size and shape of the pores in the above hollow fiber membrane can be adjusted by adjusting the stretching conditions such as the stretching temperature and stretching ratio.

[0061] The above stretching is preferably performed between the first general yield point (hereinafter also referred to as the "first yield point") that appears on the load-elongation curve and the next inflection point (hereinafter also referred to as the "second yield point") that appears before fracture.

[0062] According to the above method for manufacturing hollow fiber membranes, it is possible to produce hollow fiber membranes with excellent air supply performance and chemical resistance.

[0063] [Other embodiments] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is not limited to the configurations of the embodiments described above, but is indicated by the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included.

[0064] For example, in the above embodiment, the air supply module was configured to supply gas to a liquid that perfuses the hollow fiber membrane, but it may also be configured to supply gas to a liquid that perfuses the outside of the hollow fiber membrane. The air supply module has the same air supply performance whether it is configured to supply liquid to the hollow fiber membrane or to supply gas to the hollow fiber membrane. [Examples]

[0065] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0066] [Measurement of physical properties] First, we will explain the methods used to measure physical properties in the following examples and comparative examples.

[0067] (Measurement of heat of fusion) Take 10 to 20 mg of the sample and seal it in an aluminum cell with PTFE as needed. It is important to keep the PTFE as free as possible so that it can shrink and deform as much as possible, so do not crush the cell or crush it completely.

[0068] This sample will be heated and cooled under the following conditions. The mixture is heated from room temperature to 245°C at a rate of 50°C / min, and then heated from 245°C to 365°C at a rate of 10°C / min (first step). Next, the temperature is cooled from 365°C to 350°C at a rate of -10°C / min and held there, then cooled from 350°C to 330°C at a rate of -10°C / min, and then further cooled from 330°C to 305°C at a rate of -1°C / min (second step). Next, the temperature is cooled from 305°C to 245°C at a rate of -50°C / min, and then heated from 245°C to 365°C at a rate of 10°C / min (third step).

[0069] Sampling was performed at a rate of 0.5 seconds per step, and the amount of heat absorbed and exothermic generated was determined using a Shimadzu Corporation DSC-60A differential scanning calorimeter. The amount of heat absorbed in the first step was calculated by integrating the interval from 303°C to 353°C, the amount of exothermic generated in the second step was calculated by integrating the interval from 318°C to 309°C, and the amount of heat absorbed in the third step was calculated by integrating the interval from 296°C to 343°C. This amount of heat absorbed in the third step is defined as the heat of fusion.

[0070] (Porosity) The dry mass and water mass of the sample were measured, and the volume of the sample was determined from the difference between these two values. The true specific gravity of PTFE was also determined to be 2.17 g / cm³. 3The volume of the resin constituting the sample was calculated from its dry mass. The porosity was defined as the ratio of the void volume (the sample volume minus the resin volume) to the sample volume, expressed as a percentage.

[0071] (Isopropanol (IPA) bubble point) A hollow fiber membrane was immersed and impregnated in an isopropyl alcohol container, filling the pores in the tube wall with isopropyl alcohol. Then, while the membrane was immersed, air pressure was gradually applied from the inside of one end face. The pressure at which the first bubble emerged from the opposite end face was defined as the bubble point. The maximum measured pressure at this time was 500 kPa.

[0072] (Average pore size) The measurement was performed using a pure water pressure-type porosimeter and the Washburn equation.

[0073] (0.3 MPa water pressure resistance test) The lumen of a hollow fiber membrane was filled with water, and the water pressure into the lumen was continuously increased at a rate of 100 kPa / min up to 0.3 MPa. Leakage was then observed as water droplets from the outer surface of the hollow fiber membrane.

[0074] <Hollow fiber membrane: Test No. 1 and No. 2 (Examples)> [Preparation of raw material powder] The raw material used was the PTFE fine powder shown below. The PTFE fine powder used here is a powder obtained by drying an emulsion polymer product consisting of PTFE particles (primary particles) with a particle size of 0.15 μm to 0.35 μm, which are produced by emulsion polymerization of tetrafluoroethylene, and then granulating it to several hundred to several thousand μm.

[0075] The raw resins used in Test No. 1 and Test No. 2 are as follows: Test No. 1 (Daikin Industries, Ltd. F208: Modified PTFE) Test No. 2 (Irradiation of AGC CD-123E with 1.0 kGy of gamma rays: Homo PTFE) Table 1 shows the heat of fusion for each raw material in the third step.

[0076] [Molding process] The obtained PTFE powder was molded into tubes under the following conditions. For molding into tubes, for example, the paste extrusion method or ram extrusion method described in "Fluororesin Handbook" (by Takaomi Satokawa, Nikkan Kogyo Shimbun) could be used. For Test No. 1 and Test No. 2, the paste extrusion method described above was used. PTFE powder was mixed with 23 parts by mass of liquid lubricant ("solvent naphtha," manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), compressed into a cylindrical shape using a pre-molding machine, and then molded by extruding it into a coil shape using an extruder. The cylinder and die temperatures were set to 50°C. For Test No. 1, an extruder with a cylinder diameter of 40 mm, a mandrel diameter of 10 mm, a die diameter of 1.0 mm, a core pin diameter of 0.5 mm, and a reduction ratio (reduction cross-sectional area ratio) of 2000 was used. Test No. 2 used an extruder with a cylinder diameter of 30 mm, a mandrel diameter of 10 mm, a die diameter of 0.8 mm, a core pin diameter of 0.4 mm, and a reduction ratio of 1667.

[0077] [Drying process] In the drying process, the liquid lubricant was dried in a constant temperature bath with hot air circulation at 200°C.

[0078] [Sintering process] The above tubular molded product was heated in a continuous stretch sintering machine at a furnace temperature of 420°C, which is above the melting point of PTFE or modified PTFE, and sintered at a stretch ratio of 0.9 times to obtain a translucent, non-porous tube.

[0079] [Slow cooling process] The translucent, non-porous tube described above was coiled and placed in a hot air circulating constant temperature bath, heated at 350°C for more than 5 minutes, and then slowly cooled to below 300°C at a cooling rate of -1°C / minute or less.

[0080] [Stretching process] In the stretching process, the obtained non-porous tubular molded product was stretched under the following conditions to obtain a porous tubular molded product. Stretching was performed using a tensile testing machine (Shimadzu Autograph AG500 with a constant temperature chamber) with a chuck width of 10 mm, a stretching speed of 500 mm / min, and a temperature of 170°C. The average outer diameter and average inner diameter were measured at two arbitrary points and their average values ​​were calculated. The average thickness was calculated using the formula (average outer diameter - average inner diameter) / 2 at two arbitrary points. Table 1 shows the axial stretching ratio of the hollow fiber membrane for each test number, and Table 2 shows the average outer diameter D2, average inner diameter D1, and average thickness T1.

[0081] <Hollow fiber membrane test No. 3 (comparative example)> A tubular molded body was produced by mixing a liquid lubricant (solvent naphtha manufactured by Fujifilm Wako Pure Chemical Industries) with the PTFE powder shown below, compressing the mixture, and then paste extrusion molding into a tubular shape. In this process, 19 parts by mass of liquid lubricant were added. The extruded product was heated to 200°C to dry and remove the liquid lubricant, obtaining an unsintered tube. Subsequently, a porous tubular molded body was produced by stretching the tube longitudinally at 280°C using a continuous stretch sintering machine, followed by sintering at 380°C. Table 1 shows the die temperature used in the extrusion molding process and the axial stretch ratio during the stretching process in Test No. 3, while Table 2 shows the average outer diameter D2, average inner diameter D1, and average thickness T1. CD123E (homo PTFE) manufactured by AGC was used as the raw material resin for Test No. 3. Table 1 also shows the heat of fusion for the raw material resin in the third step of Test No. 3.

[0082] Table 1 shows the extrusion conditions for the hollow fiber membranes in Tests No. 1 to No. 3. Table 2 shows the measurement results for porosity K, isopropanol bubble point and average pore diameter, the results of the 0.3 MPa water pressure resistance test, and the calculation results for K / (T1×D2×100).

[0083] [Table 1]

[0084] [Table 2]

[0085] <Air supply module test No. 11 to test No. 14 (Hollow fiber membrane test No. 1 to test No. 3)> Air supply modules equipped with hollow fiber membranes (Air supply modules Test No. 11 to Test No. 14) were fabricated. In these air supply modules, the filling rate of the hollow fiber membranes was set to 40%, and the inner diameter of the shell and the effective length were made in two different sizes, large and small. Four types of air supply modules with different numbers of enclosed hollow fiber membranes were fabricated. These air supply modules also used a housing mainly composed of fluororesin. The housing volume, the number of enclosed hollow fiber membranes, and the filling rate of the air supply modules are shown in Table 3. The housing volume was calculated by multiplying the internal cross-sectional area of ​​the shell by the effective length.

[0086] [Evaluation of the air supply performance of the air supply module] At a room temperature of 25°C, the air supply performance of the air supply module was evaluated by passing pure water with a dissolved oxygen concentration of 0.6 ppm through the lumen of the hollow fibers of the air supply module while sweeping air at a gauge pressure of 10 kPa into contact with the outer surface of the hollow fiber membrane. During this process, the pure water flow rate was gradually increased from 0.5 ml / min, and the maximum flow rate per minute at which the pure water after air supply treatment could maintain a dissolved oxygen concentration of 8 ppm or higher was defined as the maximum flow rate per minute at which 8 ppm could be achieved. Table 3 shows the maximum flow rate per minute at which a dissolved oxygen concentration of 8 ppm or higher can be maintained, and the maximum flow rate per minute at which a dissolved oxygen concentration of 8 ppm or higher can be maintained per unit internal surface area of ​​the air supply module.

[0087] [Table 3]

[0088] As shown in Table 3, the air supply modules of Tests No. 11 to No. 13, which mainly consist of polytetrafluoroethylene or modified polytetrafluoroethylene and satisfy the conditions of K / (T1×D2×100) ≥ 2.0 for the porosity K[%], average thickness T1[mm], and average outer diameter D2[mm] of the hollow fiber membrane, demonstrated that modules with high processing capacity could be realized. In particular, the air supply module No. 13, which had a hollow fiber membrane with a high K / (T1×D2×100) value (No. 2), showed very high processing capacity per unit of internal surface area. On the other hand, the air supply module of Test No. 14, which had a hollow fiber membrane that did not satisfy K / (T1×D2×100) ≥ 2.0, showed inferior processing capacity per unit of internal surface area. Furthermore, the maximum flow rate of pure water with a dissolved oxygen concentration of 8 ppm or higher in Test No. 14 was also significantly lower compared to the air supply module No. 12, which had the same internal volume.

[0089] As described above, the air supply module has been shown to have excellent air supply performance and chemical resistance. Therefore, the air supply module is suitable for use in air supply equipment in semiconductor manufacturing processes, wastewater treatment, beverage and food manufacturing processes, and pharmaceutical manufacturing processes. [Explanation of Symbols]

[0090] 1. Hollow fiber membrane 2 Membrane members 3. Air supply module 4. First sealing section 5. Second sealing section 7 Liquid supply port 8 Liquid outlet 9. Gas supply port 19 Gas outlet 11 cabinets 12 First Sleeve 13 First Cap 14. Second sleeve 15 2nd Cap

Claims

[Claim 1] An air supply device using an air supply module capable of supplying gas to a liquid supplied inside a hollow fiber membrane, The above air supply module, A housing primarily composed of fluororesin, Multiple hollow fiber membranes, mainly composed of polytetrafluoroethylene or modified polytetrafluoroethylene, Equipped with, The porosity K [%], average thickness T1 [mm], and average outer diameter D2 [mm] of the above hollow fiber membrane satisfy the relationship in the following formula (1): K / (T1×D2×100)≧2.0 (1) The heat of fusion of the above hollow fiber membrane is 30 J / g or more and 45 J / g or less. The above hollow fiber membrane has an average outer diameter D2 of 0.70 mm or less, an average inner diameter D1 of 0.32 mm or less, a water pressure resistance of 0.3 MPa or more, and a porosity K of 30% or more. The filling rate of the hollow fiber membrane in the above air supply module is 40% or more and 60% or less. When pure water with a dissolved oxygen concentration of 0.6 ppm or less is supplied to the inside of the hollow fiber membrane and air is permeated through it at a pressure of 10 kPa, the maximum flow rate per minute at which the pure water after air treatment can maintain a dissolved oxygen concentration of 8 ppm or higher is 0.035 mL / cm² relative to the unit internal surface area of ​​the hollow fiber membrane. ２ - An air supply device that is 20 minutes or longer.

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