Air supply device

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

Air Supply Module

[0001] This disclosure relates to an air supply module. This application claims priority to Japanese Application No. 2021-80631, filed on May 11, 2021, and incorporates by reference all of the contents of the above-mentioned Japanese application.

[0002] In addition to being used for filtering in solid-liquid separators, air supply modules are also used in air supply modules that remove gases such as oxygen dissolved in liquids and air supply devices that supply gases to liquids. For example, air supply devices are known that produce gas-dissolved water by dissolving a gas in pure water for cleaning purposes in the field of electronic device manufacturing and for home appliances, and hydrogen water by dissolving hydrogen gas in pure water for beverages, and carbonated water by dissolving carbon dioxide gas in pure water.

[0003] As an air supply module for air supply or degassing, or an air supply module equipped with these, for example, an air supply module for air supply and degassing that is installed in parallel with a suction device that sucks gas from the air supply module and a gas supply device that supplies gas to the air supply module has been proposed (see Patent Document 1).

[0004] Patent Publication No. 2016-217649

[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 hollow fiber membranes, and includes a housing made primarily of a fluororesin and a plurality of hollow fiber membranes made primarily of polytetrafluoroethylene or modified polytetrafluoroethylene, wherein the porosity K [%], average thickness T1 [mm], and average outer diameter D2 [mm] of the hollow fiber membranes satisfy the relationship of the following formula (1): K / (T1×D2×100)≧2.0 (1)

[0006] Fig. 1 is a schematic cross-sectional view showing an air supply module according to an embodiment of the present disclosure. Fig. 2 is a schematic perspective view showing a hollow fiber membrane according to an embodiment of the present disclosure. Fig. 3 is a cross-sectional view of the hollow fiber membrane of Fig. 2 taken along line A-A.

[0007] [Problem to be Solved by the Present Disclosure] In recent years, air supply modules have been adopted for a variety of applications, such as semiconductors, food, medicine, and wastewater treatment, and there is a demand for them to be more compact and have improved air supply performance and chemical resistance.

[0008] The present disclosure has been made in light of the above circumstances, and aims to provide an air supply module that is compact and has excellent air supply performance and chemical resistance.

[0009] Effect of the Present Disclosure The air supply module according to one aspect of the present disclosure can be made compact, and has excellent air supply performance and chemical resistance.

[0010] [Description of Embodiments of the Present Disclosure] First, embodiments of the present 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 hollow fiber membranes, and includes a housing made primarily of a fluororesin and a plurality of hollow fiber membranes made primarily of polytetrafluoroethylene or modified polytetrafluoroethylene, wherein the porosity K [%], average thickness T1 [mm], and average outer diameter D2 [mm] of the hollow fiber membranes satisfy the relationship of the following formula (1): K / (T1×D2×100)≧2.0 (1)

[0012] The air supply module includes a plurality of hollow fiber membranes whose porosity K [%], average thickness T1 [mm], and average outer diameter D2 [mm] satisfy the relationship of formula (1) above, thereby achieving high air supply performance and water pressure resistance, and enabling miniaturization. Furthermore, the air supply module includes hollow fiber membranes whose main component is polytetrafluoroethylene or modified polytetrafluoroethylene, and a housing whose main component is a fluororesin, thereby providing excellent chemical resistance. Here, "main component" refers to the component with the largest content by mass, e.g., a component whose content is 50% by mass or more, preferably 70% by mass or more, and more preferably 95% by mass or more.

[0013] The "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 the mass in water of a sample are measured to the nearest 0.0001 g, and the volume of the sample is determined from the difference between these. The true specific gravity of polytetrafluoroethylene (PTFE) is 2.17 g / cm. ３The volume of the resin constituting the sample was calculated from the dry mass. The ratio of the void volume, obtained by subtracting the resin volume from the sample volume, to the sample volume is expressed as a percentage and is taken as the porosity. Specifically, the porosity can be measured by the following procedure as another method. First, the length (L) of the hollow fiber membrane for which porosity is to be measured is measured in 1 mm increments. Next, the weight (W) of the hollow fiber membrane is measured in 0.0001 g increments using an electronic balance. Then, based on the above measurements, the porosity [%] is calculated using the following formula: Porosity [%] = {1 - volume of resin only [cm 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 where "ρ" represents the true specific gravity of polytetrafluoroethylene, 2.17 [g / cm ３ ].

[0014] The "average thickness" of the hollow fiber membrane can be calculated by dividing (average outer diameter - average inner diameter) by 2. When the cross section of the hollow fiber membrane is circular, the "average outer diameter" refers to the average value of the outer diameter at any two points. When the cross section of the hollow fiber membrane is elliptical, the diameters of the minor and major axes are measured at two points, and the average value is defined as the average outer diameter. When the cross section of the hollow fiber membrane is a regular circle or an irregular cross section other than an ellipse, edge information of the outer diameter of the cross section is extracted to approximate a circle, and the obtained inner perimeter is divided by pi to define the average outer diameter. The "average inner diameter" refers to the average value of the inner diameters at any two points. Specifically, the average outer diameter can be measured by the following procedure. First, the hollow fiber membrane is sliced ​​in a plane perpendicular to the longitudinal direction and observed under an electron microscope so that the entire cross section is visible. The outer diameter is measured at two positions that are approximately diagonally opposite each other on the cross section (positions that are approximately 90 degrees out of phase), and the average value is defined as the average outer diameter (D2).

[0015] The hollow fiber membrane preferably has a heat of fusion of 30 J / g to 45 J / g, and the heat of fusion of the hollow fiber membrane in this range allows for a hollow fiber membrane having a high crystallinity and a pore size and porosity in a more favorable range.

[0016] The heat of fusion of the hollow fiber membrane is measured using a differential scanning calorimeter, and is the endothermic amount 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 the heat of fusion from 296° C. to 343° C. in the third step when the membrane goes through a first step of heating from room temperature to 245° C. at a rate of 50° C. / min, followed by heating from 245° C. to 365° C. at a rate of 10° C. / min, a second step of cooling from 365° C. to 350° C. at a rate of −10° C. / min and holding the temperature, followed by cooling from 350° C. to 330° C. at a rate of −10° C. / min, and then 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, followed by heating from 245° C. to 365° C. at a rate of 10° C. / min. 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 membranes have 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 membranes are within the above ranges, a bundle of hollow fiber membranes can be formed that is thin and has a fine diameter but has high water pressure resistance and porosity, thereby enabling the air supply module to be made more compact and have improved air supply performance.

[0018] The "average inner diameter" refers to the average value of the inner diameters at any two points. The average inner diameter can be measured by the following procedure. First, the hollow fiber membrane is sliced ​​in a plane perpendicular to the longitudinal direction and observed under an electron microscope so that the entire cross section is visible. The inner diameter is measured at two positions that are approximately diagonally opposite each other on the cross section (positions that are approximately 90 degrees out of phase), and the average value is defined as the average inner diameter (D1). The "water pressure resistance" refers to the pressure at which water begins to leak from one side of the membrane when water pressure is applied to the other side, and is also called the water leakage pressure. Generally, the larger the pore size of the through-holes, the more likely water is to leak and the lower the water pressure resistance, while the smaller the pore size, the higher the water pressure resistance. Specifically, the water pressure resistance is measured in accordance with JIS-L1092 (2009). Specifically, the inner cavity of the hollow fiber membrane is filled with water, and the water pressure in the inner cavity is continuously increased at a rate of 100 kPa / min. The pressure at which water begins to leak out as droplets from the outer surface of the hollow fiber membrane is taken as the water resistance pressure.

[0019] When pure water having a dissolved oxygen concentration of 0.6 ppm or less is supplied to the inside of the hollow fiber membrane and air is passed through at a pressure of 10 kPa, the maximum flow rate per minute at which the pure water after the air supply treatment can maintain a dissolved oxygen concentration of 8 ppm or more is 0.035 mL / (cm) relative to the unit internal surface area of ​​the hollow fiber membrane. ２ In the aeration module, the maximum flow rate per minute at which the pure water after aeration treatment can maintain a dissolved oxygen concentration of 8 ppm or more is within the above range, so that a high flow rate can be achieved while supplying gas at a high concentration to the liquid with a smaller membrane area, resulting in a more excellent aeration effect. Here, the "internal surface area" means the surface area inside the hollow fiber membrane.

[0020] The main component of the housing is preferably a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, polytetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, or a combination thereof, which can improve chemical resistance and mechanical strength.

[0021] [Details of the embodiments of the present disclosure] Hereinafter, the air supply module according to each embodiment of the present disclosure will be described in detail with reference to the drawings.

[0022] <Air Supply Module> An air supply module according to another aspect of the present disclosure is an air supply module capable of supplying gas to a liquid supplied into hollow fiber membranes. The air supply module includes a housing and a plurality of hollow fiber membranes. The hollow fiber membrane walls are capable of allowing gas to pass through while suppressing liquid leakage. The air supply module can be used in a variety of fields. For example, it can be used in a variety of applications, such as purifying and neutralizing cleaning water for semiconductors, electronic devices, and pharmaceutical applications, food and beverage production, industrial wastewater, river water, lake water, pool water, and public bath water, water treatment applications for drinking water and industrial water, and enriching a liquid with a specific gas such as oxygen, ozone, carbon dioxide, nitrogen, or hydrogen by allowing the gas to pass through the liquid.

[0023] The air supply module can be used in either an integrated type in which the air supply module is fixed within various devices, etc., or an exchangeable cartridge type in which the housing and the membrane component having multiple hollow fiber membranes are separate and the membrane component is inserted into the housing for use.

[0024] 1 shows an air supply module 3 for air supply as an example of an air supply module according to an embodiment of the present disclosure. The air supply module 3 includes a membrane element 2 having a plurality of the hollow fiber membranes 1 aligned in one direction, and a cylindrical housing 11 that houses the membrane element 2. The air supply module 3 is of a type that allows gas to pass through the hollow fiber membranes 1 and supplies the gas to a liquid supplied into the hollow fiber membranes 1.

[0025] The membrane element 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, a 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 is mainly composed of resin, rubber, or elastomer. Examples of the potting agent include, but are not limited to, epoxy resin, urethane resin, ultraviolet-curable resin, fluororesin, silicone resin, polyamide resin, polyolefin resin such as polyethylene or polypropylene, etc. Among these, fluororesin and silicone resin are preferred from the viewpoint of their excellent performance as adhesives for hollow fiber membranes mainly composed of polytetrafluoroethylene or modified polytetrafluoroethylene (modified PTFE) and for housings mainly composed of fluororesin.

[0027] The air supply module 3 can be configured to have a cylindrical housing 11, a first sleeve 12 attached to one end of the housing 11 and provided with an engagement structure for engaging the gas supply port 9 and the first sealing portion 4, a first cap 13 sealing the end of the housing 11 on the first sleeve 12 side and 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 for engaging the gas outlet 19 and the second sealing portion 5, and a second cap 15 sealing the end of the housing 11 on the second sleeve 14 side and 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 the multiple hollow fiber membranes 1 is discharged in the S2 direction. 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 are provided on the side of the housing 11. The positions and orientations of the gas supply port 9 and 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] The raw water supplied from the liquid supply port 7 toward the inside of the hollow fiber membrane 1 is supplied into the housing 11. Then, the liquid after the aeration treatment is discharged from the liquid discharge port 8 provided on the side surface near the other end of the housing 11.

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

[0031] In addition, the gas supplied from the gas supply port 9 is sucked from the wall surface of the hollow fiber membrane 1 toward the gas discharge port 19, and is discharged from the tip of the gas discharge port 19 while being supplied to the liquid supplied into the hollow fiber membrane 1.

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

[0033] The housing 11 is mainly made of a fluororesin. The housing 11 has excellent chemical resistance because it is made of a fluororesin as its main component. The fluororesin is preferably a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, polytetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, or a combination thereof. The housing 11 has these fluororesins as its main component, thereby improving chemical resistance and mechanical strength.

[0034] In the air supply module 3, when pure water having a dissolved oxygen concentration of 0.6 ppm or less is supplied to the inside of the hollow fiber membrane and air is passed through at a pressure of 10 kPa, the maximum flow rate per minute at which the pure water after the air supply treatment can maintain a dissolved oxygen concentration of 8 ppm or more is 0.035 mL / (cm) relative to the unit internal surface area of ​​the hollow fiber membrane 1. ２ In the gas supply module 3, since the maximum flow rate per minute at which the pure water after gas supply treatment can maintain a dissolved oxygen concentration of 8 ppm or more is in the above range, high-concentration gas can be efficiently supplied to the liquid, and the gas supply effect is more excellent.

[0035] 2 and 3 is composed mainly of polytetrafluoroethylene or modified polytetrafluoroethylene. Polytetrafluoroethylene and modified polytetrafluoroethylene are fluororesins with excellent chemical resistance and solvent resistance, which improves selectivity for the types of liquids and gases supplied to the air supply module 3. Furthermore, because 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 in which a small amount of hexafluoropropylene (HFP), alkyl vinyl ether (AVE), chlorotrifluoroethylene (CTFE), etc. is copolymerized, preferably in 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, 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, more preferably 0.4 mm. If the average outer diameter D2 is less than the lower limit, 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 become smaller, or the pressure resistance may decrease, resulting in 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, 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, more preferably 0.2 mm. If the average inner diameter D1 is less than the lower limit, pressure loss may increase. Conversely, if the average inner diameter D1 exceeds the upper limit, pressure resistance may decrease, and rupture due to internal pressure or buckling due to external pressure may occur.

[0039] The lower limit of the average thickness T1 of the hollow fiber membrane 1 is preferably 0.01 mm, 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, more preferably 0.10 mm. If the average thickness T1 is less than the lower limit, the pressure resistance 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%, 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%, more preferably 70%. If the porosity K of the hollow fiber membrane 1 is less than the lower limit, the gas permeability may be reduced, and the air supply performance of the hollow fiber membrane 1 may be reduced. If the porosity K of the hollow fiber membrane 1 exceeds the upper limit, the mechanical strength of the hollow fiber membrane 1 may be reduced, and durability may be reduced or destruction such as rupture due to internal pressure may occur.

[0041] The porosity K [%], average thickness T1 [mm], and average outer diameter D2 [mm] of the hollow fiber membrane 1 satisfy the relationship of the following formula (1): K / (T1×D2×100)≧2.0 (1) When the porosity K [%], average thickness T1 [mm], and average outer diameter D2 [mm] of the hollow fiber membrane 1 satisfy the relationship of the above formula (1), the air supply module can achieve high air supply performance and water pressure resistance, and can be made smaller. If K / (T1×D2×100) is less than 2.0, the air supply module may exhibit reduced air supply performance or water pressure resistance, or it may be difficult to make it smaller.

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

[0043] The average pore size is measured by the bubble point method (ASTM F316-86, JIS K3832) using a pore size distribution measuring instrument or the like, according to the following procedure. First, the relationship between the differential pressure applied to the membrane and the air flow rate permeating the membrane is measured using a pore size distribution measuring instrument or the like, for both the case where the membrane is dry and the case where the membrane is wet with a 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 curve obtained by dividing the flow rate of the dry curve by half and the wet curve is P (Pa), the value of d (nm) expressed by the formula 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 a hollow fiber membrane can also be measured by the bubble point method using a porometer that performs liquid-liquid phase substitution. Furthermore, since PTFE, which is the main component of the hollow fiber membrane, is a hydrophobic resin, the pore size of the hollow fiber membrane can also be measured using the Washburn equation with a pure water intrusion type porosimeter, which operates on the same principle as a mercury intrusion type porosimeter.

[0044] In the air supply module 3, the water pressure resistance of the hollow fiber membrane 1 is preferably 0.3 MPa or more, and more preferably 1.0 MPa or more. When the water pressure resistance of the hollow fiber membrane 1 is in the above range, it is possible to flow a liquid at high pressure through the air supply module 3. Since it is possible to flow a liquid at high pressure through the air supply module 3, bubbling does not occur in the liquid even when the pressure of the air supply gas is increased, and it is possible to produce a liquid with a higher concentration of dissolved gas.

[0045] The upper limit of the heat of fusion of the hollow fiber membrane 1 is preferably 45 J / g, more preferably 42 J / g. The lower limit of the heat of fusion of the hollow fiber membrane 1 is preferably 30 J / g, more preferably 33 J / g. If the heat of fusion of the hollow fiber membrane 1 exceeds the upper limit, the pore size may become large. 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 ensuring that the heat of fusion of the hollow fiber membrane 1 is within the above range, a hollow fiber membrane 1 having 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 first to third steps are performed. When the hollow fiber membrane undergoes the first to third steps, the heat of fusion from 296°C to 343°C in the third step is 30.0 J / g or more and 45.0 J / g or less, thereby obtaining properties suitable for stretching. Therefore, the hollow fiber membrane has high deformability and can be stretched beyond the typical yield point that first appears on the stress-strain curve to the next inflection point that appears before breakage. As a result, a porous hollow fiber membrane with a small pore size can be obtained. Therefore, the hollow fiber membrane 1 is porous, has an average outer diameter of 0.70 mm or less, an average inner diameter of 0.32 mm or less, has a high porosity K, and exhibits high water pressure resistance, properties not obtainable by conventional technology.

[0046] The heat of fusion of conventionally commonly used molding polytetrafluoroethylene in the third step after the first to third steps is less than 30 J / g. Therefore, the heat of fusion of hollow fiber membranes made from this resin is also considered to be less than 30 J / g. It is believed that such resins are used after considering the formability of molding, paste extrusion molding, etc., and the strength of the molded product. For example, in paste extrusion, polytetrafluoroethylene with a heat of fusion of 20 J / g or less or approximately 25 J / g is used depending on the molding dimensions, etc., to ensure uniformity in qualities such as molding dimensions and mechanical strength. The hollow fiber membrane 1 differs from conventional hollow fiber membranes in that the heat of fusion range from 296°C to 343°C in the third step is 30.0 J / g or more and 45.0 J / g or less. This difference results in higher deformability and significantly better shock absorption and deformation adhesion than conventional hollow fiber membranes. Furthermore, the stretching process allows for the production of porous hollow fiber membranes with small pore sizes and high porosity.

[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 limitation on the upper limit of the isopropanol bubble point of the hollow fiber membrane 1. If the isopropanol bubble point of the hollow fiber membrane 1 is lower than the lower limit, the liquid retention force 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 indicates the minimum pressure required to push the liquid out of the pores, and is an index corresponding to the average pore size.

[0048] The lower limit of the filling rate of the hollow fiber membranes 1 in the air supply module 3 is preferably 30%, more preferably 40%. On the other hand, the upper limit of the filling rate of the hollow fiber membranes 1 is preferably 70%, more preferably 60%. If the filling rate of the hollow fiber membranes 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 membranes 1 exceeds the upper limit, the hollow fiber membranes 1 may be crushed when packed into the housing 11, or difficulty may arise when packing the hollow fiber membranes 1 into the housing. The air supply module 3 has excellent air supply performance because the filling rate of the hollow fiber membranes 1, which have high porosity and bubble point, is 30% or more and 70% or less. Here, the "filling rate of hollow fiber membranes" refers to the packing density of hollow fiber membranes 1 packed in the housing 11, and is the ratio (%) of the sum of the cross-sectional areas occupied by each hollow fiber membrane 1, calculated from the outer diameter of each hollow fiber membrane 1 packed, to the cross-sectional area of ​​the lumen of the housing 11 perpendicular to the longitudinal direction of the hollow fiber membranes 1 packed in the housing 11.

[0049] In addition to polytetrafluoroethylene and modified polytetrafluoroethylene, the hollow fiber membrane 1 may contain other fluororesins and additives within a range that does not impair the desired effects of the present disclosure. Examples of the additives include inorganic fillers, metal powders, metal oxide powders, and metal sulfide powders for improving abrasion resistance, preventing low-temperature flow, and facilitating pore formation.

[0050] [Method for producing hollow fiber membrane] Next, an example of a method for producing the hollow fiber membrane will be described. The method for producing the hollow fiber membrane preferably includes, for example, a molding step of forming particles of polytetrafluoroethylene or modified polytetrafluoroethylene into a tubular shape, a sintering step of heating the tubular molded product to a temperature equal to or higher than 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 forming the hollow fiber membrane by stretching after molding, it is possible to form a porous hollow fiber membrane while reducing the diameter of the pores of the hollow fiber membrane.

[0051] The hollow fiber membrane can be obtained, for example, by melting polytetrafluoroethylene or modified polytetrafluoroethylene, the heat of fusion of which is 30.0 J / g or more and 45.0 J / g or less from 296°C to 343°C in the third step, to eliminate the interparticle gaps, and then slowly cooling it. That is, the process includes a step of heating the polytetrafluoroethylene or modified polytetrafluoroethylene to or above its melting point to melt it, and a step of cooling the molten resin, and / or a step of maintaining the molten resin 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 a method of irradiating polytetrafluoroethylene having 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 a method utilizing a decomposition reaction due to 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 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. A polytetrafluoroethylene or modified polytetrafluoroethylene dispersion, which is an emulsion in which these fine particles of polytetrafluoroethylene or modified polytetrafluoroethylene (polytetrafluoroethylene or modified polytetrafluoroethylene powder) are dispersed 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 is a powder consisting of fine particles of polytetrafluoroethylene or modified polytetrafluoroethylene, produced by emulsion polymerization, and polytetrafluoroethylene or modified polytetrafluoroethylene molding powder, which is produced by suspension polymerization.

[0054] When polytetrafluoroethylene or modified polytetrafluoroethylene powder is molded into a tube shape to obtain a tube-shaped molded product of predetermined shape and dimensions, known methods for molding a film from powder can be mentioned, such as the method of compounding an extrusion aid with raw material powder, mixing, and then paste extrusion molding into a tube shape, or the method of molding using polytetrafluoroethylene or modified polytetrafluoroethylene dispersion etc., and then removing dispersion medium by drying (casting method).Polytetrafluoroethylene or modified polytetrafluoroethylene usually has high melt viscosity, so that it is difficult to melt extrude, and also difficult to prepare its solution, so the above-mentioned method is generally adopted.

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

[0056] (Cooling process) After the sintering process, it is preferable to carry out a process of cooling the polytetrafluoroethylene or modified polytetrafluoroethylene by slow cooling. In the cooling process, a method of heating above the melting point of polytetrafluoroethylene or modified polytetrafluoroethylene and then slowly cooling to below the crystalline melting point, or a method of heating at a temperature slightly lower than the melting point of polytetrafluoroethylene or modified polytetrafluoroethylene for a certain period of time (hereinafter sometimes referred to as "constant temperature treatment"). This cooling produces crystals in the polytetrafluoroethylene or modified polytetrafluoroethylene, and before the next stretching process, the crystallinity of the polytetrafluoroethylene or modified polytetrafluoroethylene resin can be saturated, so that the reproducibility of pore size in the production of porous membranes can be improved. Note that in the crystallization process, the lower the cooling rate or the longer the constant temperature treatment time, the higher the 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 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 produced, which in turn is affected by the cooling rate. Therefore, to obtain a heat of fusion within the above range, cooling is carried out by slow cooling or / and by cooling that includes holding at a temperature of 310°C or higher but lower than 325°C for 10 minutes or longer. Slow cooling is preferably carried out 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 temperature at 310°C or higher but lower than 325°C for 10 minutes or more. While slow cooling requires advanced temperature control, heat treatment methods using constant temperature holding do not require advanced temperature control and allow for more stable and uniform heat treatment. Furthermore, slow cooling from temperatures above the melting point cannot be performed in the form of a long product roll because the polytetrafluoroethylene or modified polytetrafluoroethylene will fuse together. Therefore, the sintering and cooling steps must be performed over a long period of time while the product is drawn out at a very slow linear speed. On the other hand, the heat treatment method using constant temperature holding allows for cooling below the melting point, forming a long product roll, and promoting crystallization in the rolled state, enabling mass production by batch processing in large quantities. The step of holding the temperature at 310°C or higher but lower than 325°C for 10 minutes or more can be performed during the cooling process after the sintering process, or by heating and holding the product in the above temperature range after cooling.

[0059] The polytetrafluoroethylene or modified polytetrafluoroethylene powder or granules used as the raw material may be polytetrafluoroethylene powder or granules whose heat of fusion has been adjusted to fall within the above range and used as is, or a mixture of two or more polytetrafluoroethylene powders or granules, at least one of which has a heat of fusion within the above range, may be used.

[0060] (Stretching Step) In the stretching step, the nonporous tubular molded article obtained in this manner is stretched to make it porous. A porous hollow fiber membrane can be obtained by stretching the nonporous tubular molded article. In the stretching step, stretching may be performed only in the axial direction, or in both the axial and circumferential directions (diametric expansion directions). The stretching ratio in the axial direction can be, for example, 3 to 10 times, and the stretching ratio in the circumferential direction can be, for example, 2 to 4 times. The size and shape of the pores of the hollow fiber membrane can be adjusted by adjusting the stretching conditions, such as the stretching temperature and stretching ratio.

[0061] The stretching is preferably carried out from the first general yield point (hereinafter also referred to as the "first yield point") that appears on the stress-elongation curve to the next inflection point (hereinafter also referred to as the "second yield point") that appears before the breakage.

[0062] According to the above-described method for producing a hollow fiber membrane, a hollow fiber membrane having excellent air supply performance and chemical resistance can be produced.

[0063] [Other Embodiments] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present disclosure is not limited to the configurations of the above-described embodiments, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0064] For example, in the above embodiment, the air supply module is configured to perfuse a liquid through the hollow fiber membrane and supply a gas to the liquid, but the air supply module may be configured to supply a gas into the hollow fiber membrane and supply the gas to the liquid perfusing outside the hollow fiber membrane. The air supply module has similar air supply performance whether it is configured to supply a liquid into the hollow fiber membrane or to supply a gas into the hollow fiber membrane.

[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, the methods for measuring physical properties in the following examples and comparative examples will be described.

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

[0068] This sample was heated and cooled under the following conditions: heated from room temperature to 245°C at a rate of 50°C / min, then heated from 245°C to 365°C at a rate of 10°C / min (first step); next, 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 further cooled from 330°C to 305°C at a rate of -1°C / min (second step); next, 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 time of 0.5 seconds, and the endothermic and exothermic amounts were determined using a heat flux differential scanning calorimeter DSC-60A manufactured by Shimadzu Corporation. The endothermic amount in the first step was determined by integrating the interval from 303°C to 353°C, the exothermic amount in the second step was determined by integrating the interval from 318°C to 309°C, and the endothermic amount in the third step was determined by integrating the interval from 296°C to 343°C. The endothermic amount in this third step was taken as the heat of fusion.

[0070] (Porosity) The dry mass and the mass in water of the sample were measured, and the volume of the sample was calculated from the difference between these. The true specific gravity of PTFE was 2.17 g / cm ３ The volume of the resin constituting the sample was calculated from the dry mass as follows: The ratio of the void volume obtained by subtracting the volume of the resin from the volume of the sample to the volume of the sample was expressed as a percentage and was taken as the porosity.

[0071] (Isopropanol (IPA) Bubble Point) A hollow fiber membrane was immersed in an isopropyl alcohol container, and the pores in the tube wall were filled with isopropyl alcohol. After that, air pressure was gradually applied from the inside of one end face of the hollow fiber membrane while it was immersed. The pressure at which air bubbles first appeared at the opposite end face was taken as the bubble point. The maximum pressure measured at this time was 500 kPa.

[0072] (Average Pore Diameter) Measured using a pure water injection type porosimeter according to the Washburn equation.

[0073] (0.3 MPa Water Pressure Resistance Test) The inner cavity of the hollow fiber membrane was filled with water, and the water pressure on the inner cavity was continuously increased to 0.3 MPa at a rate of 100 kPa / min, and leakage was 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 PTFE fine powder shown below was used as the raw material powder. The PTFE fine powder used here is a powder obtained by drying a product (emulsion polymerization product) consisting of PTFE particles (primary particles) with particle sizes of 0.15 μm to 0.35 μm produced by emulsion polymerization of tetrafluoroethylene, and granulating the resulting product to a size of several hundred μm to several thousand μm.

[0075] The raw material resins used in Test No. 1 and Test No. 2 are as follows: Test No. 1 (F208 manufactured by Daikin Industries, Ltd.: modified PTFE) Test No. 2 (CD-123E manufactured by AGC Corporation irradiated with 1.0 kGy of gamma rays: homo-PTFE) The heat of fusion of each raw material in the third step is shown in Table 1.

[0076] [Molding Process] The obtained PTFE powder was molded into a tube under the following conditions. Examples of methods for molding into a tube include the paste extrusion method and ram extrusion method described in "Fluororesin Handbook" (by Satokawa Takaomi, published by Nikkan Kogyo Shimbun). Test No. 1 and Test No. 2 used the paste extrusion method. 23 parts by mass of a liquid lubricant ("Solvent Naphtha" manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was mixed with the PTFE powder, compressed into a cylindrical shape using a pre-molding machine, and then extruded into a coil using an extruder. The cylinder and die temperatures were 50°C. Test No. 1 used 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. In No. 2, an extruder having 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 was used.

[0077] [Drying Step] In the drying step, the liquid lubricant was dried in a hot air circulating thermostatic bath at 200°C.

[0078] [Sintering Step] The tubular molded article was heated in a continuous stretch sintering machine at a furnace temperature of 420° C., which is equal to or higher than the melting point of PTFE or modified PTFE, and sintered at a stretch ratio of 0.9 to obtain a semi-transparent non-porous tube.

[0079] [Slow Cooling Step] The semi-transparent non-porous tube was placed in a coiled state in a hot air circulating thermostatic chamber, heated at 350°C for 5 minutes or more, and then slowly cooled continuously to 300°C or lower at a cooling rate of -1°C / min or less.

[0080] [Stretching Step] In the stretching step, the obtained nonporous tubular molded article was stretched under the following conditions to obtain a porous tubular molded article. Stretching was performed using a tensile tester (Shimadzu Corporation's Autograph AG500 with a thermostatic bath) with a chuck width of 10 mm, a stretching speed of 500 mm / min, and 170°C. The average outer diameter and average inner diameter were measured at any two points and averaged, and the average thickness was calculated using the formula (average outer diameter - average inner diameter) / 2 at any two points. The axial stretch ratio of the hollow fiber membrane for each test number is shown in Table 1, and the average outer diameter D2, average inner diameter D1, and average thickness T1 are shown in Table 2.

[0081] <Hollow Fiber Membrane Test No. 3 (Comparative Example)> A liquid lubricant (solvent naphtha manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was mixed with the PTFE powder shown below as raw material powder and compacted. The mixture was then paste-extruded into a tube to produce a tubular molded body. 19 parts by mass of liquid lubricant was added. The extrusion molded product was heated to 200°C, and the liquid lubricant was dried and removed to obtain an unsintered tube. The extrusion molded product was then stretched in the longitudinal direction at 280°C using a continuous stretching and sintering machine to make it porous, followed by sintering at 380°C to produce a porous tubular molded product. The die temperature and axial stretch ratio used in the extrusion molding and stretching process in Test No. 3 are shown in Table 1, and the average outer diameter D2, average inner diameter D1, and average thickness T1 are shown in Table 2. CD123E (homo PTFE) manufactured by AGC was used as the raw material resin for Test No. 3. The heat of fusion of the raw material resin No. 3 in the third step is shown in Table 1.

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

[0083]

[0084]

[0085] <Air Intake Module Test No. 11 to Test No. 14 (Hollow Fiber Membrane Test No. 1 to Test No. 3)> Air intake modules (Air Intake Module Test No. 11 to Test No. 14) equipped with hollow fiber membranes of Test No. 1 to Test No. 3 were fabricated. In these air intake modules, the hollow fiber membrane filling rate was set to 40%, and two different sizes of body inner diameter and effective length were fabricated. Four types of air intake modules were fabricated, differing in the number of hollow fiber membranes enclosed. In addition, these air intake modules used housings whose main component was fluororesin. The housing volume, number of hollow fiber membranes enclosed, and filling rate of the air intake module are shown in Table 3. The housing volume was calculated by calculating the product of the cross-sectional area inside the body and the effective length.

[0086] [Evaluation of Air Intake Performance of Air Intake Module] At a room temperature of 25°C, pure water with a dissolved oxygen concentration of 0.6 ppm was passed through the hollow fiber lumen of the air intake module, while air at a gauge pressure of 10 kPa was swept into contact with the outer surface of the hollow fiber membrane, to evaluate the air intake performance of the air intake module. 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 intake treatment could maintain a dissolved oxygen concentration of 8 ppm or more was defined as the maximum flow rate per minute at which 8 ppm or more could be achieved. Table 3 shows the maximum flow rate per minute at which a dissolved oxygen concentration of 8 ppm or more could be maintained and the maximum flow rate per minute at which a dissolved oxygen concentration of 8 ppm or more could be maintained per unit internal surface area of ​​the air intake module.

[0087]

[0088] As shown in Table 3, the air intake modules of Tests No. 11 to No. 13, which were primarily composed of polytetrafluoroethylene or modified polytetrafluoroethylene and whose hollow fiber membrane porosity K [%], average thickness T1 [mm], and average outer diameter D2 [mm] satisfied K / (T1 x D2 x 100) ≥ 2.0, were shown to be capable of achieving high treatment capacity. In particular, the air intake module of Test No. 13, which included the hollow fiber membrane of No. 2, which had a high K / (T1 x D2 x 100) value, exhibited extremely high treatment capacity per internal surface area. On the other hand, the air intake module of Test No. 14, which included a hollow fiber membrane that did not satisfy K / (T1 x D2 x 100) ≥ 2.0, exhibited inferior treatment capacity per internal surface area. Furthermore, the maximum flow rate of pure water with a dissolved oxygen concentration of 8 ppm or higher for the air intake module of Test No. 14 was significantly lower than that of the air intake module of Test 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, and is therefore suitable for use in air supply devices in semiconductor manufacturing processes, wastewater treatment, beverage and food manufacturing processes, chemical manufacturing processes, etc.

[0090] REFERENCE SIGNS LIST 1 hollow fiber membrane 2 membrane member 3 air supply module 4 first sealing part 5 second sealing part 7 liquid supply port 8 liquid discharge port 9 gas supply port 19 gas discharge port 11 housing 12 first sleeve 13 first cap 14 second sleeve 15 second cap

Claims

1. An air supply device using an air supply module capable of supplying gas to a liquid supplied inside a hollow fiber membrane, The air supply module, A housing made mainly of fluororesin; A plurality of the hollow fiber membranes, each of which is mainly composed of polytetrafluoroethylene or modified polytetrafluoroethylene; Equipped with The porosity K [%], average thickness T1 [mm], and average outer diameter D2 [mm] of the hollow fiber membrane satisfy the relationship of the following formula (1), K / (T1×D2×100)≧2.0 (1) The heat of fusion of the hollow fiber membrane is 30 J / g or more and 45 J / g or less, 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 pure water having a dissolved oxygen concentration of 0.6 ppm or less is supplied to the inside of the hollow fiber membrane and air is passed through 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 more is 0.035 mL / (cm2·min) or more per unit internal surface area of ​​the hollow fiber membrane.

2. An air supply device as described in claim 1, wherein the main component of the housing is tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, or a combination thereof.

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