Strainer for producing pure water, ultrapure water production system using same, and ultrapure water production method

Abstract

Provided are a strainer for pure water capable of significantly suppressing elution of iron over a long period of time, an ultrapure water production system using the same, and an ultrapure water production method. A strainer 1 for producing pure water comprises: a cylindrical filter 11 having both ends opened and having a plurality of filtration holes on a side surface, and a cap member 12 liquid-tightly adhered to one end of the filter 11. The filter 11 includes a filter body made of a metal, and a fluororesin film provided on the entire surface of the filter body. The cap member 12 protrudes toward the outside of the filter body 11, and the whole liquid contact surface is made of a fluororesin.

Description

Strainer for producing pure water, ultrapure water production system using the same, and ultrapure water production method

[0001] The present invention relates to a strainer for producing pure water, an ultrapure water producing system using the same, and a method for producing ultrapure water.

[0002] Ultrapure water, from which impurities have been highly removed, is often used in semiconductor manufacturing processes, such as for cleaning semiconductor wafers. Ultrapure water is produced in an ultrapure water production system, which combines water treatment devices depending on the desired water quality. The ultrapure water production system includes a pretreatment device, a primary water purification device, and a secondary water purification device. Raw water, such as city water, well water, or industrial water, is treated in each device in sequence to produce ultrapure water. The produced ultrapure water is supplied to points of use (POUs) via supply lines for use.

[0003] Ultrapure water used in semiconductor manufacturing processes must have a metal (Fe, Cr, Ni, Mo, etc.) concentration of 1 ng / L or less, and sometimes 0.1 ng / L or less, in order to accommodate the advanced miniaturization of semiconductor products.

[0004] To improve the quality of ultrapure water, a non-regenerative mixed-bed ion exchange resin device (polisher) is installed near the end (most downstream) of the secondary water purification system to remove residual ionic components. Furthermore, to prevent deterioration of water quality due to leakage of trace amounts of resin from the polisher, especially resin damaged within the polisher, a strainer for capturing resin is sometimes installed downstream of the polisher. Strainers are generally made of stainless steel (SUS) for strength, corrosion resistance, and other reasons. However, when SUS strainers are used for long periods of time, metal components contained in the SUS, such as iron (Fe), nickel (Ni), and chromium (Cr), especially iron (Fe), can leach into the water. Since no device for removing eluted iron is installed downstream of the strainer, this can lead to a deterioration in the quality of the ultrapure water.

[0005] To solve the above problems, strainers have been proposed in which the water-contacting portions are made of a low-elution material, such as titanium, titanium alloys, nickel alloys, etc. (See, for example, Patent Document 1.) Also proposed is an ion exchange column in which the liquid-contacting surfaces of the container and container top lid are lined with synthetic resin (See, for example, Patent Document 2.)

[0006] International Publication No. 2023 / 053572 Japanese Patent Application Laid-Open No. 2011-67793

[0007] As described above, ultrapure water is required to have a metal (Fe, Cr, Ni, Mo, etc.) concentration of 0.1 ng / L or less to 1 ng / L or less in order to accommodate the advanced miniaturization of semiconductor products. In particular, it has been found that there is a problem in that it is difficult to avoid the inclusion of iron (Fe) when the pure water is heated or cooled in a secondary pure water system or when ultrapure water is produced over a long period of time.

[0008] Furthermore, titanium, titanium alloys, nickel alloys, etc. are generally expensive, which raises the problem of high production costs for strainers and the ultrapure water produced using them.

[0009] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a strainer for producing pure water that can significantly suppress iron elution over a long period of time, and an ultrapure water production system and method using the same.

[0010] As described above, further investigation was needed to prevent iron from being mixed into the pure water in the secondary pure water system. The inventors discovered that by forming the surface of the strainer installed downstream of the non-regenerative mixed-bed ion exchange resin system (polisher) out of a fluororesin, it is possible to prevent iron from eluting from the strainer and significantly reduce the iron concentration in the ultrapure water for a long period of time.

[0011] A pure water producing strainer, ultrapure water producing system, or ultrapure water producing method according to an embodiment of the present invention is as follows: [1] A pure water producing strainer comprising: a cylindrical filter body that is open at both ends and has a plurality of filter holes on a side surface; and a cap member that is liquid-tightly adhered to one end of the filter body, wherein the filter body comprises a filter body body made of metal and a fluororesin membrane provided on the entire surface of the filter body body, and the cap member is convex toward the outside of the filter body, and the entire liquid-contacting surface is made of fluororesin. [2] The pure water producing strainer according to [1] further comprises a cylindrical housing that has a water outlet at one end and a water inlet at the other end, the housing accommodates the filter body and the cap member so that the cap member faces the water inlet of the housing, and the opening of the filter body and the water outlet of the housing are in communication. [3] The strainer for producing pure water according to [2], wherein the housing and the filter body are cylindrical, and the cap member is a solid cone or a solid hemisphere. [4] The strainer for producing pure water according to [2] or [3], wherein the end of the filter body on the open side is connected to the outlet of the housing.

[0012] [5] The strainer for producing pure water according to any one of [1] to [4], which has a connecting part connecting the filter body and the cap member. [6] The strainer for producing pure water according to [5], wherein the connecting part comprises a screw member penetrating the cap member and the end face of the filter body. [7] The strainer for producing pure water according to any one of [1] to [6], wherein the fluororesin membrane and the fluororesin contain polytetrafluoroethylene. [8] The strainer for producing pure water according to any one of [1] to [7], wherein the iron (Fe) concentration in the pure water passed through the strainer for producing pure water is 0.1 ng / L or less. [9] An ultrapure water producing system comprising a primary water purification system and a secondary water purification system in this order, wherein the secondary water purification system includes a non-regenerative mixed bed ion exchange resin device, and wherein the strainer for producing pure water according to any one of [1] to [8] is provided downstream of the non-regenerative mixed bed ion exchange resin device.

[10] The ultrapure water producing system according to [9], wherein the iron (Fe) concentration in the pure water passed through the strainer for producing pure water is 0.1 ng / L or less.

[0013] [Correction based on Rule 91 25.02.2025]

[11] An ultrapure water production method in which raw water is treated in a primary water purification system and a secondary water purification system in that order, wherein the secondary water purification system includes a non-regenerative mixed-bed ion exchange resin system and a pure water production strainer attached to the non-regenerative mixed-bed ion exchange resin system and positioned downstream of the non-regenerative mixed-bed ion exchange resin system, wherein the pure water production strainer has a cylindrical filter body with open ends and multiple filter holes on its side, and a cap member liquid-tightly attached to one end of the filter body, wherein the filter body has a metal filter body and a fluororesin membrane covering the entire surface of the filter body, and the cap member is convex toward the outside of the filter body and the entire liquid-contacting surface is made of fluororesin, producing ultrapure water with an iron (Fe) concentration of 0.1 ng / L or less. Note that the symbols "to" indicate a numerical range including the values ​​before and after it.

[0014] The strainer for producing pure water according to the embodiment can significantly suppress the elution of iron over a long period of time. Furthermore, the ultrapure water production system and ultrapure water production method using the strainer for producing pure water according to the embodiment can produce high-quality ultrapure water with an extremely low iron concentration over a long period of time.

[0015] Fig. 1 is a cross-sectional view schematically showing a strainer 1 for producing pure water according to an embodiment. Fig. 2 is a cross-sectional view schematically showing a first connection part 13 of another embodiment. Fig. 3 is a flow chart schematically showing a method for manufacturing a strainer for producing pure water according to an embodiment. Fig. 4 is a block diagram schematically showing an ultrapure water producing system according to an embodiment.

[0016] [Strainer for Pure Water Production] A strainer for pure water production according to an embodiment of the present invention will now be described with reference to the drawings. FIG. 1 is a cross-sectional view schematically illustrating a strainer for pure water production 1 according to the embodiment. The strainer for pure water production 1 according to the embodiment includes a cylindrical filter body 11 with both ends open, and a cap member 12. The side surface of the filter body 11 has a plurality of filter holes to form a filter surface 11a. In the strainer for pure water production 1, as the water to be treated flows from the filter surface 11a on the side surface of the filter body 11 into the filter body 11, impurities such as resin in the water to be treated are removed, and the treated water flows out from the opening at the downstream end of the filter body 11. Hereinafter, the opposite ends of the filter body 11 will be referred to as the upstream end and the downstream end, depending on the flow of water passing through the filter body 11.

[0017] The filter body 11 includes a metal filter body body and a fluororesin membrane disposed over the entire surface of the filter body body. The fluororesin membrane is disposed over the entire surface of the filter body body. Specifically, all liquid-contacting surfaces of the filter body 11, such as the filtration surface, the surfaces of the filter pores, and the inner wall surface of the filter body, are covered with the fluororesin membrane. Examples of metals constituting the filter body body include stainless steel (SUS) such as SUS304, SUS316, SUS316L, and SUS304L. SUS316 or SUS316L is more preferred in terms of strength and corrosion resistance. The filter body body includes, for example, a filter body element formed of a spirally wound wire and multiple rod-shaped support members disposed in the longitudinal direction of the spiral of the filter body element and spaced apart in the circumferential direction of the spiral. The cross-sectional shape of the wire is, for example, triangular, and the wire is arranged so that the apex of the triangle faces the interior of the filter body. The gaps between the spiral wire and the support members function as filter pores. The diameter of the filter holes may be any size that does not allow the ion exchange resin to pass through, for example, a diameter (inner diameter) of about 0.3 mm. The filter body 11 is cylindrical, for example, with an outer diameter of 15 mm to 220 mm or 15 mm to 165 mm.

[0018] The pure water producing strainer 1 of this embodiment can be easily lined or coated on the surface of the filter body 11 by forming a fluororesin membrane on the surface of the filter body 11, which is open at both ends, and then connecting the cap member 12, as described below. This allows for a simple and uniform formation of a fluororesin membrane even in a complex shape with numerous filter holes. If the lining or coating is insufficient and the fluororesin membrane has defects such as pinholes, even if the defects are minor, this can lead to a deterioration in the quality of ultrapure water. However, by forming a fluororesin membrane on the surface of the filter body 11, which is open at both ends, a fluororesin membrane without such defects can be formed by lining or coating, and the entire liquid-contacting surface of the filter body 11 can be covered with the fluororesin membrane.

[0019] The presence of a fluororesin film on the entire surface of the filter body 11 can be confirmed, for example, by the following method. First, when the pure water production strainer 1 of this embodiment is installed downstream of a non-regenerative mixed-bed ion exchange resin apparatus in an ultrapure water production system and ultrapure water production is continued, for example, after 30 days of flushing, whether ultrapure water with an iron concentration of 1.0 ng / L or less can be obtained for 30 days or more can be confirmed. Second, as an accelerated test, for example, the pure water production strainer is immersed in ultrapure water for 7 days and the iron concentration in the ultrapure water after immersion is measured. Simultaneously, under the same conditions, a fluororesin piece or a stainless steel piece lined or coated with a fluororesin and having the same or an equivalent surface area (with an error of ±5%) as the pure water production strainer is immersed, and the iron concentration in the ultrapure water after immersion is measured. (Hereinafter, both are referred to as "comparison samples") It is also possible to compare the measured values ​​obtained from the strainer for pure water production with those from the comparative sample and to test whether the iron concentration in the ultrapure water in which the strainer for pure water production is immersed is significant compared to the iron concentration in the ultrapure water in which the comparative sample is immersed. In this case, for example, when the iron concentrations in the ultrapure water in which a plurality of comparative samples are immersed are tested at a significance level of 2.5%, the iron concentration in the ultrapure water in which the strainer for pure water production is immersed is compared to the iron concentration in the ultrapure water in which the comparative sample is immersed. ｓａｍｐ The average value calculated from the iron concentration in the ultrapure water in which the comparative sample was immersed was F. ａｖｅ , and the standard deviation is σ, F ｓａｍｐ ≦F ａｖｅIf the value is +1.96 × σ, it can be determined that a fluororesin film is formed over the entire surface of the filter body 11. Alternatively, the iron concentration in ultrapure water in which a single comparative sample has been immersed can be measured multiple times to make a similar determination. The test method is preferably based on, for example, the UC Standard: Leaching Test Method for Piping Materials for Ultrapure Water (UCS12 Semiconductor Industry Development and UCS12 Achievements, edited by the Semiconductor Fundamental Technology Research Group, pp. 1181-1188). This method is a non-flow system, and since eluates are eluted in a small amount of ultrapure water, it constitutes an accelerated test and allows for easy measurement. Third, as a further accelerated test, confirmation can be achieved by using the same method as in the second method, except that an aqueous solution of hydrogen peroxide, sulfuric acid, or a mixture thereof is used instead of ultrapure water. In this case, measurement can be performed within a immersion time of, for example, about one day.

[0020] In the pure water producing strainer 1, the cap member 12 is liquid-tightly adhered to the upstream end of the filter body 11. The cap member 12 has a convex shape extending outward from the upstream end of the filter body 11, and at least the liquid-contacting surface is made of fluororesin. The cap member 12 may be made of a metal cap member body such as SUS and a fluororesin film provided on the surface of the cap member body, or the entire cap member may be made of fluororesin. Because it is lightweight and easy to handle, it is preferable that the entire cap member 12 be made of fluororesin. The cap member may be hollow or solid, but a solid cap member is preferable for ease of manufacture, and it is particularly preferable that the entire cap member 12 be made of solid fluororesin.

[0021] The cap member 12 preferably has at least a bottom surface and a side surface rising from the bottom surface. The bottom surface, i.e., the side opposite the convex surface, of the cap member 12 is connected to the opening at the upstream end of the filter body 11 via a first connecting portion 13. Examples of the convex shape of the cap member 12 include those in which the convex cross section, i.e., the cross section perpendicular to the bottom surface and passing through the point farthest from the bottom surface, is polygonal, rectangular, triangular, semicircular, etc.

[0022] [Correction based on Rule 91, February 25, 2025] The convex shape of the cap member 12 is preferably such that the water flow on the surface of the cap member 12 does not produce unidirectional flow or vortexes. If unidirectional flow or vortexes occur on the surface of the convex cap member 12, the strainer will vibrate. Because ultrapure water production systems are operated continuously for at least one year, and in some cases for several years, long-term strainer vibration can accelerate the deterioration of the fluororesin membrane on the strainer's filtration surface, potentially causing resin fragments and iron leaching from the SUS surface that was previously covered by the resin. Convex cross-sections that do not produce unidirectional flow or vortexes are preferably triangular, semicircular, or semi-elliptical. When the convex cross-section is triangular, for example, one side of the triangle is located near the upstream end of the filter body 11. When the convex cross-section is semicircular, for example, the diameter of the semicircle is located near the upstream end of the filter body 11. When the convex cross section is semi-elliptical, for example, the major axis or minor axis of the semi-ellipse is located on the upstream end of the filter body 11. For example, when the opening of the filter body 11 is circular, the convex shape of the cap member 12 is preferably a hemisphere, semi-elliptical sphere, or cone, since this reduces the likelihood of one-sided flow on the surface of the cap member 12. In particular, a conical shape of the cap member 12 is more preferable because the side surface has a constant slope from the apex to the base, thereby achieving a rectifying effect on the treated water. Furthermore, water stagnation may occur on the surface of the cap member 12, and impurities eluted from each component may accumulate and accumulate in this stagnation. In this case, fluctuations in the treated water flow rate, such as sudden increases or decreases in volume or valve opening and closing, may result in a large amount of impurities being released into the pure water, potentially leading to deterioration of water quality.

[0023] The outer diameter of the cap member 12 is preferably the same as or approximately the same as the outer diameter of the opening of the filter body 11 but larger than the outer diameter of the opening of the filter body 11. This makes it possible to adjust the water flow around the first connecting portion 13 between the filter body 11 and the cap member 12, thereby suppressing the deterioration of the lining or coating as described above.

[0024] The fluororesin used for the cap member 12 and the fluororesin film on the surface of the filter body 11 is not particularly limited, and examples thereof include tetrafluoroethylene and perfluoroether copolymer (PFA, perfluoroalkoxyalkane), polytetrafluoroethylene (PTFE), ethylene / tetrafluoroethylene copolymer (ETFE), etc. The fluororesin of the cap member 12 and the fluororesin film on the surface of the filter body 11 may be the same or different, but are preferably the same type.

[0025] When ETFE is used as the fluororesin, for the purpose of controlling crystallinity, it is preferable that the ETFE is obtained by copolymerizing ethylene and tetrafluoroethylene with other fluorine-containing monomers. The other fluorine-containing monomers are not particularly limited as long as they can be added to both ethylene and tetrafluoroethylene, but fluorine-containing vinyl monomers having 3 to 8 carbon atoms are easily used, for example, hexafluoroisobutylene, CH ２ = CFC ３ F ６ The amount of the other fluorine-containing monomer is preferably 5 mol % or less of the total monomers of the ETFE, in order not to impair the heat resistance, flame retardancy and chemical resistance.

[0026] When ETFE is obtained by copolymerizing other fluorine-containing monomers, the fluorine content in ETFE is preferably 50% by mass or more. A fluorine content of 50% by mass or more exhibits excellent heat resistance, flame retardancy, and chemical resistance. The fluorine content of ETFE is, for example, 70% by mass or less. The fluorine content can be adjusted by appropriately adjusting the ratio of ethylene, tetrafluoroethylene, and other monomers used as desired. The fluorine content is a value obtained by burning a fluororesin, absorbing the fluorine contained therein into alkaline water, etc., and measuring it by ion chromatography, etc.

[0027] Among the above-mentioned fluororesins, tetrafluoroethylene and perfluoroether copolymer (PFA, perfluoroalkoxyalkane) and polytetrafluoroethylene (PTFE) resin are materials that are widely and generally used in ultrapure water production systems due to their excellent heat resistance and chemical resistance, and can also be suitably used for the cap member 12 and the fluororesin membrane on the filter body 11.

[0028] The first connecting portion 13 is not particularly limited as long as it can connect the filter body 11 and the cap member 12 liquid-tightly. Examples of the first connecting portion 13 include a connecting portion formed by soldering, welding, or the like, which undergoes a change in the state of the material of the connecting portion when connected. Alternatively, the first connecting portion 13 may be a connecting portion formed by a mechanical structure without undergoing a change in the state of the material of the connecting portion when connected, for example, a connecting portion using threaded engagement or one or more screw members. It is preferable that the first connecting portion 13 be a connecting portion formed by a mechanical structure, in that no defects are generated in the fluororesin film on the surface of the filter body 11 when the filter body 11 and the cap member 12 are connected.

[0029] 1 , for example, a first connector 131 having ridges 131a on its outer surface can be connected to the bottom surface of the cap member 12, and a cylindrical second connector 132 having a spiral groove 132a on its inner wall that threadably engages with the ridges can be connected to the upstream end of the filter body 11, and the filter body 11 and the cap member 12 can be connected by threading the ridges of the first connector 131 into the groove of the second connector 132. In this case, the first connector 13 includes the first connector 131, the ridges 131a provided on the first connector 131, the second connector 132, and the groove 132a provided on the second connector 132. Furthermore, instead of the embodiment in which the first connector 131 has ridges and the second connector 132 has grooves, the first connector 131 may have grooves and the inner wall of the second connector 132 may have ridges. In order to improve the liquid-tightness between the filter body 11 and the cap member 12, a sealing member such as an O-ring made of resin or the like may be interposed between the end face of the second connector 132 of the filter body 11 and the vicinity of the outer periphery of the bottom surface of the cap member 12.

[0030] [Correction pursuant to Rule 91, February 25, 2025] Figure 2 is a cross-sectional view schematically illustrating another embodiment of the first connecting portion 13. As shown in Figure 2, a third connecting body 133 is provided on the end face of the upstream end of the filter body 11. The third connecting body 133 is, for example, arranged along the periphery of the upstream end of the filter body 11 and has a solid ring shape with thickness in the axial and circumferential directions. The filter body 11 and the cap member 12 can be connected by providing multiple threaded holes 134 near the outer periphery of the cap member 12 and inserting a screw member 142 or the like through the threaded holes 134 into the cap member 12 and the third connecting body 133. In this case, the first connecting portion 13 includes the cap member 12 and the screw member 142 that penetrates the cap member 12 and is inserted into the third connecting body 133. In order to improve the liquid-tightness between the filter body 11 and the cap member 12, a sealing member such as an O-ring made of resin or the like may be interposed between the end face of the upstream end of the third connector 133 and the bottom surface of the cap member 12. In this case, the first connector 13 further includes a sealing member.

[0031] 2 , when the filter body 11 and the cap member 12 are connected using the screw member 142, there is a possibility of water puddling on the surface (screw head) of the screw member 142 or in the vicinity thereof, or of iron elution from the screw member if the screw member 142 is made of metal. However, because the size of the screw member 142 is smaller than that of the filter body 11, the impact of these on the quality of the treated water is extremely small. If the surface of the screw member 142 or in the vicinity thereof has a depression, it is preferable to form a protective part by filling the depression with a fluororesin in order to improve the quality of the ultrapure water obtained as treated water. In this case, the material of the protective part may be a different fluororesin from or the same fluororesin as the cap member 12, but it is preferable that the protective part be the same fluororesin.

[0032] The strainer 1 for producing pure water shown in FIG. 1 further includes a cylindrical housing 15 that houses the filter body 11. The housing 15 accommodates the entire filter body 11. The housing 15 has a water outlet 15a at the downstream end and a water inlet 15b at the upstream end. The housing 15 may have a continuous cylindrical shape with a constant inner diameter, or may have a shape in which multiple cylindrical sections with different inner diameters are connected in series. Furthermore, a portion of the cylindrical shape, particularly both ends or one end, may have a tapered shape with a diameter that decreases toward the end. It is preferable that a fluororesin film be provided on the inner surface of the housing 15 and, if necessary, on liquid-contacting surfaces other than the inner surface. The fluororesin film on the inner surface of the housing 15, etc., can be formed by lining or coating, similar to the filter body 11.

[0033] In the strainer 1 for producing pure water, the filter body 11 and the cap member 12 are arranged and housed in the housing 15 so that the cap member 12 faces the water inlet 15b of the housing 15. The opening at the downstream end of the filter body 11 communicates with the water outlet 15a of the housing 15, so that treated water that has passed through the filtering surface 11a of the filter body 11 is discharged from the water outlet 15a of the housing.

[0034] [Correction based on Rule 91, February 25, 2025] The filter body 11 and the housing 15 are connected via a second connecting portion 18. The second connecting portion 18 is not particularly limited as long as it can connect the filter body 11 and the housing 15 liquid-tightly. In the pure water production strainer 1 shown in FIG. 1 , a discharge pipe 20 is connected to the housing 15 via the second connecting portion 18. The discharge pipe 20 has a discharge pipe main body 24 and a flange portion 22 extending circumferentially from the upstream end of the discharge pipe main body 24. A threaded hole is provided in the flange portion 22. The housing 15 has a flange portion 151 extending circumferentially from the downstream end of the housing 15, and the flange portion 151 has a threaded hole. Furthermore, a fourth connecting portion 148 is connected to the downstream end of the filter body 11. The fourth connecting portion 148 is arranged around the downstream end of the filter body 11 and has a solid ring shape with thickness in both the axial and circumferential directions. A portion of the downstream end side of the outer periphery of the fourth connector 148 (opposite the side that contacts the downstream end of the filter body 11) has a larger outer diameter than the upstream end, and is provided with a notch into which the flange portion 151 fits.

[0035] [Correction based on Rule 91, February 25, 2025] In the pure water producing strainer 1, the second connecting portion 18 can be formed by arranging the notch of the fourth connecting body 148 between the flange portion 151 and the flange portion 22, passing a screw member 144a through the threaded holes in the flange portion 151 and the flange portion 22, and securing the passing screw member 144a with a screw fastener 144b. That is, the second connecting portion 18 includes the flange portion 151, the fourth connecting body 148, the flange portion 22, and the screw member 144a and screw fastener 144b that pass through the flange portion 151 and the flange portion 22. Note that, to improve the liquid-tightness of the second connecting portion 18, sealing members 146a, 146b, such as O-rings made of resin, may be interposed between the flange portion 151 and the notch of the fourth connecting body 148 and between the downstream end face of the fourth connecting body 148 and the flange portion 22. In this case, the second connection portion 18 further includes sealing members 146a and 146b.

[0036] Next, another method for connecting the filter body 11 and the housing 15 will be described. This method uses a structure similar to that of the filter body 11 and the cap member 12 shown in FIG. 1 . That is, a cylindrical sixth connector having a spiral groove on its inner wall is connected to the upstream end of the discharge pipe 20, and a cylindrical fifth connector having ridges on its outer surface that threadably engage with the groove is connected to the downstream end of the filter body 11, thereby achieving a connection by threading the groove and the ridge. In this case, the second connector 18 includes a fifth connector, ridges provided on the fifth connector, a sixth connector, and a groove provided on the inner wall of the sixth connector. Furthermore, instead of the fifth connector having ridges on its inner wall and the sixth connector having grooves, the fifth connector may have grooves on its inner wall and the sixth connector may have ridges. To improve the liquid-tightness between the filter body 11 and the housing 15, a sealing member such as an O-ring made of resin or the like may be interposed between the downstream end face of the fifth connector and the upstream end face of the sixth connector. In this case, the second connection portion 18 further includes a sealing member.

[0037] The strainer 1 for producing pure water according to this embodiment is preferably attached to a regenerative mixed-bed ion exchange resin device (polisher) in a secondary pure water system and placed after the device. In this case, the Fe concentration in the pure water that has passed through the strainer for producing pure water can be reduced to 0.1 ng / L or less.

[0038] [Correction based on Rule 91, 25.02.2025] [Method of Manufacturing a Strainer for Pure Water Production] A method of manufacturing a strainer for pure water production according to this embodiment will be described. Fig. 3 is a flow chart that schematically illustrates the method of manufacturing a strainer for pure water production according to this embodiment. The method of manufacturing the strainer for pure water production shown in Fig. 3 includes an assembly step S80 for assembling the filter body 11, a fluororesin film forming step S82 for forming a fluororesin film on the surface of the filter body, and a connection step S84 for connecting the cap member 12 and each connector (first connector and second connector, or third connector) to the filter body 11 with the fluororesin film formed on its surface.

[0039] First, in an assembly step S80, the filter body 11 is assembled and manufactured. In the assembly step S80, a commercially available bag-shaped strainer having a sealed upstream end and an open downstream end may be used as a raw material, and the upstream end of the strainer may be opened to obtain the filter body 11 of the embodiment.

[0040] Subsequently, in the fluororesin film forming step S82, the above-described fluororesin film is formed on the surface of the filter body. The fluororesin film may be formed by a coating method such as dip coating, spray coating, electrostatic painting, brush painting, or roll coating, or by a lining method such as electrostatic powder painting or sheet lining. Spray coating is preferred because it allows the fluororesin film to be formed uniformly on the inner surfaces of the filter pores of the filter surface 11a. The thickness of the fluororesin film formed on the surface of the filter body 11 in this manner is usually about 200 μm to 300 μm.

[0041] The cap member 12 and each connector are then connected to the filter body 11 as described above. If necessary, the filter body 11 with the cap member 12 connected thereto is housed in the housing 15. When using a hollow or solid cap member 12 made of fluororesin, the cap member 12 can be obtained by forming the fluororesin into a block and then cutting the fluororesin block using a machine tool or the like. More specifically, the cap member 12 can be manufactured into the desired shape by cutting a cylindrical fluororesin rod from a block of fluororesin, or by forming the fluororesin into a cylindrical fluororesin rod and then cutting it. The solid cap member 12 prevents pure water from stagnating inside the cap. Therefore, a solid cap member 12 is preferable because it does not cause deterioration of water quality. The cap member may be made of stainless steel, polypropylene, or polyethylene. In these cases, it is preferable to coat or line the surface with a fluorine-based material.

[0042] Although the above describes an embodiment in which the fluororesin membrane is formed on the filter body 11 and then the connectors are connected, the fluororesin membrane may also be formed after the connectors are connected to the filter body 11. In the method for manufacturing a strainer for pure water production according to this embodiment, forming a fluororesin membrane on the surface of the filter body 11, which is open at both ends, allows for easy lining or coating. Therefore, it is possible to easily and uniformly form a fluororesin membrane even on a complex shape with numerous filter holes. If the lining or coating is insufficient and the fluororesin membrane has defects such as pinholes, even minor defects can lead to deterioration of the quality of ultrapure water. However, by forming a fluororesin membrane on the surface of the filter body 11, which is open at both ends, a fluororesin membrane without such defects can be formed by lining or coating, resulting in a strainer for pure water production suitable for producing ultrapure water.

[0043] [Ultrapure Water Production System and Ultrapure Water Production Method] Next, an ultrapure water production system and ultrapure water production method according to the present embodiment will be described. The ultrapure water production system according to the present embodiment includes a primary water purification system that performs primary water purification treatment to convert raw water or pretreated water into primary pure water, and a secondary water purification system that includes the above-mentioned pure water production strainer and performs secondary water purification treatment to convert the primary pure water into secondary pure water.

[0044] 4 is a block diagram showing an outline of an ultrapure water production system 100 according to this embodiment. The ultrapure water production system 100 includes a pretreatment device 112, a primary pure water system 114, a pure water tank 116, and a secondary pure water system 117. The secondary pure water system 117 includes a water pump 118, a heat exchanger 120, an ultraviolet irradiation device 122, a membrane degassing device 124, a non-regenerative mixed-bed ion exchange resin system (polisher) 126, and an ultrafiltration (UF) device 128. The strainer 1 for producing pure water according to the embodiment described above is provided downstream of the non-regenerative mixed-bed ion exchange resin system 126.

[0045] (Pretreatment Device) Raw water is supplied to the pretreatment device 112. The pretreatment device 112 is equipped with a coagulation sedimentation device, a sand filter, a membrane filter, etc., and clarifies the raw water to produce pretreated water from which suspended solids and a portion of organic matter have been removed. Examples of raw water include industrial water, tap water, groundwater, and river water.

[0046] (Primary pure water system) The primary pure water system 114 further purifies the pretreated water to remove impurities from the pretreated water and produce primary pure water. Specifically, the primary pure water system 114 includes various devices such as a demineralizer that removes impurity ions, a reverse osmosis membrane device that removes inorganic ions, organic matter, fine particles, etc., a vacuum degasser or membrane degasser that removes dissolved gases such as dissolved oxygen, and a regenerative mixed-bed demineralizer that removes remaining ions, etc.

[0047] (Pure Water Tank) The primary pure water obtained in the primary pure water unit 114 is sent to the pure water tank 116. The pure water tank 116 temporarily stores the primary pure water obtained in the primary pure water unit 114. The material and shape of the pure water tank 116 are not particularly limited as long as it is free from rust, causes little leaching of components from the container, and can stably store the primary pure water. Preferred materials for the pure water tank 116 include fiber-reinforced plastics (FRP), polyethylene, SUS304, and Teflon (registered trademark)-lined versions of these materials. The top of the pure water tank 116 is preferably purged with pure nitrogen to prevent absorption of impurity gases such as carbon dioxide and dissolved oxygen. As described below, the pure water tank 116 can also store a mixture of the primary pure water and ultrapure water when circulating unused ultrapure water produced.

[0048] (Water Pump) The water pump 118 delivers primary pure water from the pure water tank 116 to the heat exchanger 120. The configuration of the water pump is not particularly limited. For example, even if the portion that comes into contact with the primary pure water is made of a material that elutes small amounts of metal components, such as stainless steel, the eluted metal components are adsorbed by the ion exchange resin in the non-regenerative mixed-bed ion exchange resin device (polisher) 126. Therefore, the material of the portion of the water pump 118 that comes into contact with the primary pure water has almost no effect on the quality of the ultrapure water produced. Therefore, a water pump commonly used in the production of pure water can be used as the water pump 118.

[0049] (Heat Exchanger) The heat exchanger 120 adjusts the temperature of the primary pure water by heat exchange (heating or cooling). The heat exchanger 120 may be, for example, a plate-type heat exchanger, but the specific structure is not particularly limited. A heat exchanger generally adjusts the water temperature to room temperature, for example, about 20°C. However, it may also be adjusted to, for example, 60 to 80°C, in which case the produced ultrapure water is called hot ultrapure water. When producing hot ultrapure water, a further heat exchanger may be installed in addition to the heat exchanger 120. In this case, the heat exchanger is installed, for example, between the pure water producing strainer 1 and the ultrafiltration (UF) device 128.

[0050] (Ultraviolet Irradiation Device) The primary pure water whose temperature has been adjusted in the heat exchanger 120 is sent to the ultraviolet irradiation device 122. The ultraviolet irradiation device 122 irradiates the primary pure water with ultraviolet light to decompose organic matter in the primary pure water and kill (sterilize) live bacteria. The ultraviolet irradiation device 122 is equipped with an ultraviolet lamp capable of irradiating, for example, with wavelengths around 185 nm or 254 nm, thereby ensuring the decomposition and sterilization of organic matter in the primary pure water. The ultraviolet lamp used in the ultraviolet irradiation device 122 is not particularly limited, but a low-pressure mercury lamp is preferred for ease of handling. Examples of the ultraviolet irradiation device 122 include a flow-through type in which the ultraviolet lamp is arranged inside a housing along the flow path of the water to be treated, and an immersion type in which the ultraviolet lamp is immersed in a tank storing the water to be treated. However, a flow-through type is preferred from the standpoint of treatment efficiency.

[0051] (Membrane Degassing Device) The membrane degassing device 124 removes gases, particularly dissolved oxygen, from the primary pure water using a gas separation membrane that does not allow water to pass through but allows gas to pass through.

[0052] (Non-regenerative mixed-bed ion exchange resin device) The primary pure water from which the dissolved oxygen concentration has been removed by the membrane degassing device 124 is sent to the non-regenerative mixed-bed ion exchange resin device 126. The non-regenerative mixed-bed ion exchange resin device 126 adsorbs and removes organic acids produced by decomposition of organic matter in the ultraviolet irradiation device 122 and impurity ions such as metal ions remaining in the water.

[0053] (Strainer for producing pure water) In the ultrapure water producing system 100, the strainer for producing pure water 1 described above is provided downstream of the non-regenerative mixed bed ion exchange resin apparatus 126. This prevents iron from leaching out from the metal constituting the strainer, improving the quality of the treated water.

[0054] (Ultrafiltration Unit) The primary pure water from which impurity ions have been removed by the non-regenerative mixed-bed ion exchange resin unit 126 is sent to an ultrafiltration (UF) unit 128. The ultrafiltration (UF) unit 128 removes fine particles to produce ultrapure water. The ultrafiltration (UF) unit 128 is disposed at the end of the secondary pure water unit 117. Note that the secondary pure water unit 117 may be provided with other treatment devices as needed, such as a catalytic resin-packed tower, for example, to remove hydrogen peroxide generated secondarily in the ultraviolet irradiation unit, thereby obtaining ultrapure water of the desired purity.

[0055] Furthermore, in order to increase the water supply pressure to the ultrafiltration unit 128, for example, a booster pump may be provided between the non-regenerative mixed-bed ion exchange resin unit 126 and the ultrafiltration (UF) unit 128. However, contact with the booster pump may cause metal components to elute, increasing the metal concentration. Therefore, when producing ultrapure water with a lower metal concentration, it is preferable to either not provide a booster pump or to use a booster pump whose contact portion with the water to be treated is made of a material that does not or does not easily elute metal components. Alternatively, it is preferable to install the booster pump upstream of the non-regenerative mixed-bed ion exchange resin unit 126.

[0056] The secondary pure water (ultrapure water) obtained by the secondary pure water apparatus 117 after passing through the above-mentioned devices (steps) is delivered to a use point 160, such as a process point in a semiconductor manufacturing process, via a water delivery pipe 162. Unused ultrapure water from the delivered ultrapure water is circulated to the pure water tank 116 via a circulation pipe 164 and stored in the pure water tank 116 together with the primary pure water.

[0057] The above-described pure water producing strainer 1 and ultrapure water producing system 100 can produce ultrapure water with an iron content of 1 ng / L or less, or even 0.1 ng / L or less, making them particularly suitable for use in producing ultrapure water to be supplied to process points in semiconductor manufacturing processes. Furthermore, ultrapure water containing components such as nickel and chromium at 0.1 ng / L or less can be produced. These nickel and chromium components are primarily derived from stainless steel.

[0058] Examples of this embodiment will be described below, but this embodiment is not limited to the following examples.

[0059] Example 1 In an ultrapure water production system similar to that shown in Figure 4, ultrapure water was produced using a strainer manufactured by the method of the above-mentioned embodiment, which was equipped with a solid conical cap member at the upstream end of the filter body. The water flow conditions were as follows: Strainer: Linear velocity 1.2 m / h; Strainer: PTFE-coated with both ends open (slot (filter hole) width on filter surface 0.3 mm, prototype manufactured by Nomura Micro Science Co., Ltd.).

[0060] Comparative Example 1 Ultrapure water was produced under the same conditions as in Example 1, except that the following strainer was used instead of the strainer used in Example 1. Strainer: Made of SUS, open on only one side (slot width on filter surface: 0.3 mm, prototype manufactured by Nomura Micro Science Co., Ltd.)

[0061] Comparative Example 2 Ultrapure water was produced under the same conditions as in Comparative Example 1, except that the strainer used in Comparative Example 1 was replaced with a strainer whose surface was coated with PTFE.

[0062] The water quality at the outlet (i.e., strainer inlet) of the non-regenerative mixed-bed ion exchange resin device (polisher) and at the strainer outlet after 30 days in the above cases is shown in Table 1. The iron concentration was measured by evaporating and concentrating samples taken from each location and then using inductively coupled plasma mass spectrometry (ICP-MS).

[0063]

[0064] From the above results, it was confirmed that sufficient performance could not be obtained with the existing strainer of Comparative Example 2, which is open on one side and coated with a fluororesin. The strainer of Comparative Example 2 is a strainer open on one side that has been coated with a fluororesin, but this process is not easy, and although the coating appears uniform to the naked eye, it is thought that very small areas are not coated or that the coating is insufficient. On the other hand, when the method of the embodiment was used, the fluororesin coating was uniform and formed without defects, so it is thought that iron elution was sufficiently suppressed.

[0065] [Correction based on Rule 91 25.02.2025] 1... Strainer for producing pure water, 11... Filter body, 11a... Filter surface, 12... Cap member, 13... First connecting portion, 131... First connecting body, 131a... Groove portion, 132... Second connecting body, 132a... Crook portion, 133... Third connecting body, 134... Screw hole, 146a, 146b... Sealing member, 142... Screw member, 15... Housing, 15a... Water outlet, 15b... Water inlet, 18... Second connecting portion, 20... Discharge pipe, 24... Discharge pipe main body, 22, 151... Flange portion, 144a... Screw member, 144b... Screw fastening member, 148... Fourth connecting body, 100... ultrapure water production system, 112... pretreatment device, 114... primary pure water device, 116... pure water tank, 117... secondary pure water device, 118... water pump, 120... heat exchanger, 122... ultraviolet irradiation device, 124... membrane degassing device, 126... non-regenerative mixed bed ion exchange resin device (polisher), 128... ultrafiltration (UF) device, 160... point of use (use point), 162... water supply piping, 164... circulation piping, S80... assembly process, S82... fluororesin film forming process, S84... connection process

Claims

1. A strainer for producing pure water, comprising: a cylindrical filter body that is open at both ends and has a plurality of filtering holes on the side; and a cap member that is liquid-tightly adhered to one end of the filter body, wherein the filter body comprises a filter body body made of metal and a fluororesin membrane provided on the entire surface of the filter body body, and the cap member is convex toward the outside of the filter body, and the entire liquid-contacting surface is made of fluororesin.

2. A strainer for producing pure water as described in claim 1, further comprising a cylindrical housing having a water outlet at one end and a water inlet at the other end, the housing containing the filter body and the cap member so that the cap member faces the water inlet of the housing, and the opening of the filter body and the water outlet of the housing are in communication.

3. A strainer for producing pure water according to claim 2, wherein the housing and the filter body are cylindrical, and the cap member is shaped like a solid cone or a solid hemisphere.

4. A strainer for producing pure water according to claim 2 or 3, wherein the open end of the filter body is connected to the discharge port of the housing.

5. A strainer for producing pure water according to claim 1 or 2, which has a connecting portion for connecting the filter body and the cap member.

6. A strainer for producing pure water as described in claim 5, wherein the connecting portion comprises a screw member that penetrates the cap member and the end face of the filter body.

7. A strainer for producing pure water according to claim 1 or 2, wherein the fluororesin membrane and the fluororesin contain polytetrafluoroethylene.

8. A strainer for producing pure water according to claim 1 or 2, wherein the iron (Fe) concentration in the pure water passed through the strainer for producing pure water is 0.1 ng / L or less.

9. An ultrapure water production system comprising a primary pure water system and a secondary pure water system in this order, the secondary pure water system including a non-regenerative mixed bed ion exchange resin system, and a strainer for producing pure water according to claim 1 or 2 provided downstream of the non-regenerative mixed bed ion exchange resin system.

10. The ultrapure water producing system according to claim 9, wherein the iron (Fe) concentration in the pure water passed through the strainer for producing pure water is 0.1 ng / L or less.

11. A method for producing ultrapure water in which raw water is treated in a primary water purification system and a secondary water purification system in that order, wherein the secondary water purification system includes a non-regenerative mixed-bed ion exchange resin system and a pure water production strainer attached to the non-regenerative mixed-bed ion exchange resin system and arranged downstream thereof, wherein the pure water production strainer has a cylindrical filter body that is open at both ends and has a plurality of filter holes on the side, and a cap member that is liquid-tightly adhered to one end of the filter body, wherein the filter body comprises a metal filter body body and a fluororesin membrane provided on the entire surface of the filter body body, and the cap member is convex toward the outside of the filter body and the entire liquid-contacting surface is made of fluororesin, and a method for producing ultrapure water with an iron (Fe) concentration of 0.1 ng / L or less.

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