Metal removal filter media and cartridge filters

Abstract

A metal removal filtering material according to the present invention comprises: a polyethylene porous substrate; and a graft chain that is fixed to the polyethylene porous substrate and has a functional group, the basis weight of the metal removal filtering material being 30 to 120 g / m2. The metal removal filtering material is characterized in that the graft chain has a graft ratio of 40 to 150%, and the functional group is selected from among: a quaternary ammonium group; a primary, secondary, or tertiary amino group; an iminodiacetate group; a phosphate group; and an iminodiethanol group.

Description

[Technical Field]

[0001] The present invention relates to a metal-removing filter medium and a cartridge filter. [Background technology]

[0002] In recent years, advances in semiconductor manufacturing technology have led to increasingly miniaturized semiconductors, placing increasingly stringent demands on the cleanliness of the chemicals used. For example, it is essential to reduce metal impurities in resist-related materials such as resists, anti-reflective coatings, and multilayer films, as well as in the polymers, monomers, and organic solvents that are the raw materials for these materials. In particular, metals such as Al, Ti, Cr, Fe, Ni, and Cu reduce semiconductor yields, so they must be removed from chemicals at a high level.

[0003] Currently, filters that have been given metal-trapping capabilities by graft polymerization are primarily used to remove metals from chemical solutions used in semiconductor manufacturing. For example, Patent Document 1 uses a cartridge filter made of a fibrous material in which ion-exchange groups or chelating functional groups have been introduced into polyethylene nonwoven fabric by radiation-induced graft polymerization. Furthermore, Patent Document 2 uses a cation-exchange membrane made of ultra-high molecular weight polyethylene with a pore size of approximately 2 μm to which sulfonic acid groups have been introduced by graft polymerization to remove metal impurities from photoresist solvents. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-251118 [Patent Document 2] Special Publication No. 2001-515113 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the configuration of Patent Document 1 has a problem in that the substrate is a nonwoven fabric, the gaps between the fibers are uneven, and the contact area with the liquid is small, making it difficult to obtain high metal removal performance. If the basis weight of the substrate is increased to increase the contact area, the flow rate per unit area decreases, making it difficult to achieve both a high flow rate and high removal performance.

[0006] In Patent Document 2, a polyethylene membrane with a larger contact area with the liquid than a nonwoven fabric is used as the base material, achieving high metal removal performance while maintaining a high flow rate. However, the membrane contains sulfonic acid groups, which are strongly acidic cation exchange groups, and the hydrogen ions released when capturing metals can denature the organic solvent.

[0007] A cartridge filter using a filter material that has high metal removal performance while maintaining a flow rate per unit area and does not denature organic solvents has not yet been obtained, and its development is strongly desired. Therefore, the present invention aims to provide a metal-removal filter medium that has high metal removal performance while maintaining a flow rate per unit area and does not denature organic solvents, a method for manufacturing the metal-removal filter medium, and a cartridge filter. [Means for solving the problem]

[0008] In order to achieve the above-mentioned purpose, the present inventors have carried out intensive research, and as a result, have found that in the metal-removing filter material that comprises polyethylene porous membrane and graft chain, by defining the graft rate of graft chain within a predetermined range, and introducing a predetermined functional functional group into side chain, and defining basis weight within a predetermined range, can obtain the metal-removing filter material that has high metal-removing performance while maintaining the flow rate per unit area, and does not denature organic solvent.

[0009] That is, the present invention provides a polyethylene porous substrate and a graft chain having a functional group fixed to the polyethylene porous substrate, the graft chain having a basis weight of 30 to 120 g / m 2The metal-removing filter medium is characterized in that the graft chains have a graft rate of 40 to 150%, and the functional groups are selected from a quaternary ammonium group, a primary, secondary or tertiary amino group, an iminodiacetic acid group, a phosphate group, and an iminodiethanol group.

[0010] The present invention also provides a method for producing the metal-removing filter medium, the method comprising the steps of: 2 This method for producing a metal-removing filter medium comprises the steps of polymerizing a vinyl group-containing reactive monomer by radiation graft polymerization onto a polyethylene porous substrate having a porosity of 70% or more to fix graft chains with a graft rate of 40 to 150%, and introducing a functional group selected from a quaternary ammonium group, a primary, secondary or tertiary amino group, an iminodiacetic acid group, a phosphate group, and an iminodiethanol group into the graft chains.

[0011] The present invention further provides a cartridge filter comprising a pleated filter medium, wherein the filter medium is the metal-removing filter medium described above. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a metal-removal filter medium that has high metal removal performance while maintaining a flow rate per unit area and does not denature organic solvents, a method for manufacturing a metal-removal filter medium, and a cartridge filter. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a partially cutaway perspective view of a cartridge filter according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The metal-removing filter medium and metal ion-removing filter of the present invention will be described in detail below. The metal-removing filter medium of the present invention comprises a polyethylene porous substrate to which graft chains are fixed, and has a basis weight of 30 to 120 g / m2 The graft chain has a grafting rate of 40 to 150%, and a functional group selected from a quaternary ammonium group, a primary, secondary or tertiary amino group, an iminodiacetic acid group, a phosphate group, and an iminodiethanol group is introduced.

[0015] In the present invention, examples of the polyethylene porous substrate include porous membranes and nonwoven fabrics made of high-density polyethylene, ultra-high-molecular-weight polyethylene, and mixtures of high-density polyethylene and ultra-high-molecular-weight polyethylene. The porous material has a basis weight of 15 to 50 g / m. 2 , and the porosity is specified to be 70% or more.

[0016] Among these, porous membranes with a large specific surface area and a relatively uniform pore size distribution are preferred. To enhance metal removal performance, it is necessary to maintain a high capacity of functional groups. Therefore, in the present invention, the basis weight and porosity of the polyethylene porous substrate are specified within a predetermined range. The basis weight is 15 g / m. 2 If the weight is less than 50g / m, the strength required for continuous roll processing cannot be ensured. 2 If it exceeds this value, the flow rate per unit area will decrease.

[0017] Furthermore, if the porosity of the polyethylene porous substrate is less than 70%, the contact area with the liquid will be small, and high metal removal performance will not be achieved. Other important characteristics of the polyethylene porous substrate include the bubble point, which is an index of pore size, and the air permeability or water permeability, which corresponds to the fluid permeation rate. The bubble point is preferably in the range of 10 to 30 kPa, and the water permeation rate should be 30 mL / min cm. 2 The above is preferable.

[0018] A polyethylene porous membrane as a polyethylene porous substrate can be produced, for example, by the following method. First, high-density polyethylene and / or ultra-high-molecular-weight polyethylene are uniformly mixed together with a solvent using a twin-screw extruder. Examples of solvents that can be used include decalin, paraffin, and phthalate esters. The temperature during this process is set to be equal to or higher than the melting point of polyethylene.

[0019] The resulting kneaded material is extruded through a T-die attached to the tip of the extruder, cooled, and processed into a film. The film is then immersed in a volatile organic solvent such as methylene chloride to extract and remove the solvent. The film is then stretched in the longitudinal and transverse directions, and heat-set as necessary to obtain a polyethylene porous membrane with a predetermined basis weight and porosity. The basis weight and porosity of the polyethylene porous membrane can be appropriately adjusted by the ratio of polyethylene to solvent and the stretching ratio in the longitudinal and transverse directions.

[0020] The metal-removing filter medium of the present invention can be produced by polymerizing a vinyl group-containing reactive monomer by radiation graft polymerization onto the above-mentioned polyethylene porous substrate to fix graft chains with a graft rate of 40 to 150%, and then introducing a functional group selected from a quaternary ammonium group, a primary, secondary or tertiary amino group, an iminodiacetic acid group, a phosphate group, and an iminodiethanol group into the graft chains.

[0021] The metal-removing filter medium of the present invention can be produced by batch processing of a sheet-shaped polyethylene porous substrate, or by continuous processing of a roll-shaped polyethylene porous substrate.

[0022] Radiation-induced graft polymerization is a technique in which a polymer substrate is irradiated with radiation such as electron beams or gamma rays to generate radicals, which are then brought into contact with a monomer containing a vinyl group, and polymer chains with the desired functionality are chemically grafted onto the substrate using the radicals as the starting point. The number and length of graft chains can be freely controlled, and graft chains can be introduced into polymer materials of various shapes.

[0023] In the present invention, a polyethylene porous substrate is irradiated with radiation and then immersed in a reactive monomer solution to allow the reaction. This fixes graft chains to the polyethylene porous substrate, producing a graft substrate. The reactive monomer can be selected from vinyl-containing glycidyl methacrylate, styrene, chloromethylstyrene, acrylonitrile, and the like. However, the graft ratio is limited to 40 to 150%. A graft ratio of less than 40% does not provide high metal removal performance. On the other hand, a graft ratio of more than 150% causes cracks to form at the folds when the metal-removing filter medium is pleated, making it impossible to ensure the integrity of the filter.

[0024] The graft ratio of the graft chains can be calculated using the masses before and after graft polymerization, that is, the graft ratio is calculated by the following formula:

number

[0025] The grafting rate can be controlled by the conditions during graft polymerization, particularly the irradiation dose and the monomer concentration. For example, a high irradiation dose and a high monomer concentration result in a high grafting rate. On the other hand, a low irradiation dose and a low monomer concentration result in a low grafting rate.

[0026] Next, the graft substrate is immersed in a functional group introduction solution to introduce a functional group having metal removal ability into the graft side chain. The functional group introduction solution is selected depending on the target functional group, such as a salt containing a functional group having metal removal ability. For example, in the case of an iminodiacetic acid group, an aqueous solution of sodium iminodiacetate is used, in the case of a phosphate group, an aqueous solution of phosphoric acid is used, and in the case of an iminodiethanol group, an aqueous solution of diethanolamine is used. Note that, in the case of a conventional sulfonic acid group, a sodium sulfite aqueous solution is used.

[0027] Finally, if necessary, acid washing and water washing are carried out to obtain the metal-removing filter material of the present invention.The functional group is required not to denature the organic solvent.The functional group in the present invention is selected from the group consisting of a quaternary ammonium group, a primary, secondary or tertiary amino group, an iminodiacetic acid group, a phosphate group and an iminodiethanol group on the graft chain.These functional groups do not release hydrogen ions during metal capture, so they do not denature the organic solvent. Iminodiacetic acid groups, phosphate groups, and iminodiethanol groups, which have a chelating function, are preferred because they exhibit superior metal removal performance. The chelating function refers to the ability to bind to specific metal ions to form complexes and thereby capture the metal ions.

[0028] In this way, a polyethylene porous substrate and a graft chain having a functional group fixed to the polyethylene porous substrate are obtained, and the basis weight is 30 to 120 g / m 2 The metal-removing filter medium of the present invention has a basis weight of 30 g / m 2 On the other hand, metal removal filter media with a weight of less than 120 g / m have a low amount of functional groups and do not achieve high metal removal performance. 2 Metal removal filter media exceeding this limit have a water permeability rate of 30 mL / min cm 2 This results in a decrease in processing efficiency.

[0029] The basis weight of the metal-removing filter medium can be controlled by the grafting rate, etc. For example, a low grafting rate tends to result in a low basis weight, and a high grafting rate tends to result in a high basis weight.

[0030] The metal-removing filter medium of the present invention has graft chains with a grafting rate of 40 to 150%, and functional groups selected from a quaternary ammonium group, a primary, secondary or tertiary amino group, an iminodiacetic acid group, a phosphate group, and an iminodiethanol group are introduced into the graft chains. The filter medium also has a basis weight of 30 to 120 g / m. 2 Since the range is within this range, it has high metal removal performance while maintaining the flow rate per unit area, and does not denature the organic solvent.

[0031] Fig. 1 shows a partially cutaway perspective view of a cartridge filter of the present invention. The cartridge filter 1 of the present invention comprises a cylindrical core 2, a filter medium 4 covering the outer periphery of the core 2, a cylindrical protector 6 covering the outer periphery of the core 2, and end caps 7 sealing both ends of the cylinder. The core 2 and the protector 6 have multiple liquid passage holes on their circumferential surfaces. The core 2, the protector 6, and the end caps 7 are all made of high-density polyethylene.

[0032] The filter medium 4 is sandwiched between support nets 3 and 5 made of high-density polyethylene, laminated, and pleated. This is formed into a cylindrical shape, and both ends of the cylinder are vertically sealed and welded together before use. As filter material 4, the metal-removing filter material of the present invention is used.The metal-removing filter material can be pleated by using one single layer, or the same metal-removing filter material can be pleated by two or more layers.In addition, the metal-removing filter material with different functional groups can be combined to form a multilayer, and this can be pleated for use.

[0033] The pleated filter medium is housed between the core 2 and the protector 6, and both ends are sealed by heat welding with end caps to produce the cartridge filter 1 of the present invention. This cartridge filter 1 may be acid washed or washed with water as needed.

[0034] The cartridge filter of the present invention can remove a high level of metals while maintaining a high flow rate, and can also remove trace metals from organic solvents without denaturing the organic solvent. [Example]

[0035] The present invention will be specifically described below with reference to examples. The materials, amounts used, ratios, processing procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0036] <Preparation of metal removal filter media> Various porous polyethylene membranes were used to prepare metal-removing filter media in Examples 1 to 5. The physical properties of the porous polyethylene membranes used are summarized in Table 1 below.

[0037] [Table 1]

[0038] The bubble point (BP) was measured using isopropanol (IPA) in accordance with JIS K3832-1990. The water flow rate (WFR) is 9.6 cm3, based on JIS K3831-1990, with a test pressure of 69.3 kPa. 2 The area was calculated by measuring the time it took for 500 mL of water at 25°C to pass through.

[0039] Example 1 The polyethylene porous membrane was irradiated with an electron beam at a dose of 60 kGy under a nitrogen atmosphere, then immersed in a 25% glycidyl methacrylate solution and reacted at 60°C for 40 minutes to carry out graft polymerization, yielding a graft substrate with a graft ratio of 121%. The graft substrate was immersed in an 8% aqueous solution of sodium iminodiacetate and treated at 80°C for 10 hours to introduce iminodiacetic acid groups. The graft substrate with the introduced functional groups was then immersed in 1 mol / L hydrochloric acid, rinsed with ultrapure water, and dried to obtain a functional group introduction amount of 217 mmol / m. 2 The metal removal filter medium had a weight per unit area of ​​120 g / m. 2 It was.

[0040] Example 2 The polyethylene porous membrane was irradiated with an electron beam at a dose of 60 kGy under a nitrogen atmosphere, then immersed in a 15% glycidyl methacrylate solution and reacted at 60°C for 40 minutes to carry out graft polymerization, yielding a graft substrate with a graft ratio of 81%. The graft substrate was immersed in an 8% aqueous solution of sodium iminodiacetate and treated at 80°C for 5 hours to introduce iminodiacetate groups. The graft substrate with the introduced functional groups was then immersed in 1 mol / L hydrochloric acid, rinsed with ultrapure water, and dried to obtain a functional group introduction amount of 41 mmol / m.2 The metal removal filter medium had a weight per unit area of ​​37 g / m. 2 It was.

[0041] Example 3 The polyethylene porous membrane was irradiated with an electron beam at a dose of 60 kGy under a nitrogen atmosphere, then immersed in a 20% glycidyl methacrylate solution and reacted at 60°C for 40 minutes to carry out graft polymerization, yielding a graft substrate with a graft ratio of 84%. This was immersed in an 85% aqueous solution of phosphoric acid and treated at 95°C for 24 hours to introduce phosphate groups. The graft substrate with the introduced functional groups was then immersed in 1 mol / L hydrochloric acid, rinsed with ultrapure water, and dried to obtain a functional group introduction amount of 141 mmol / m 2 The metal removal filter medium had a weight of 68 g / m 2 It was.

[0042] Example 4 The polyethylene porous membrane was irradiated with an electron beam at a dose of 60 kGy under a nitrogen atmosphere, then immersed in a 20% glycidyl methacrylate solution and reacted at 60°C for 40 minutes to carry out graft polymerization, yielding a graft substrate with a graft ratio of 84%. This was immersed in a 40% aqueous solution of diethanolamine and treated at 80°C for 24 hours to introduce iminodiethanol groups. The grafted substrate with the functional groups introduced was then immersed in 1 mol / L hydrochloric acid, rinsed with ultrapure water, and dried to obtain a functional group introduction amount of 221 mmol / m 2 The metal removal filter medium had a weight of 77 g / m 2 It was.

[0043] Example 5 The polyethylene porous membrane was irradiated with an electron beam at a dose of 60 kGy under a nitrogen atmosphere, then immersed in a 20% glycidyl methacrylate solution and reacted at 60°C for 60 minutes to carry out graft polymerization, yielding a graft substrate with a graft ratio of 73%. The graft substrate was immersed in a 6.6% aqueous solution of sodium iminodiacetate and treated at 80°C for 5 hours to introduce iminodiacetic acid groups. The graft substrate with the introduced functional groups was then immersed in 1 mol / L hydrochloric acid, rinsed with ultrapure water, and dried to obtain a functional group introduction amount of 22 mmol / m. 2 Metal removal filter media The weight of this metal-removing filter media was 66 g / m 2 It was.

[0044] The metal-removing filter media of Examples 1 to 5 were examined for metal-removing performance, discoloration of organic solvents, and crack occurrence. To examine the metal removal performance, each metal removal filter medium was placed in a 47 mm diameter (effective filtration area 13.5 cm 2 ) and placed in a PFA holder. PGMEA containing Cr, Fe, and Ti at concentrations of approximately 20 ppb each was used as the metal-containing organic solvent. This metal-containing organic solvent was filtered at a flow rate of 5 mL / min using each metal-removal filter medium, and the metal removal rate was calculated from the amount of metal before and after filtration. A removal rate of 85% or higher for all metals was considered acceptable.

[0045] Discoloration of the organic solvent was confirmed by immersing each metal-removing filter medium in an organic solvent (cyclohexanone, PGMEA) and visually checking the discoloration of the organic solvent and filter medium after one week. In addition, each metal-removing filter medium was folded in half to create a light crease, and then a 2.5 kg weight was dropped onto the crease from a height of 10 cm, and the condition of the crease was visually observed to check for damage such as cracks.

[0046] The evaluation results of the metal-removing filter media of Examples 1 to 5 are summarized in Table 2 below, along with their respective configurations.

[0047] [Table 2]

[0048] The metal-removing filter media of Examples 1 to 5 have a basis weight of 37 to 120 g / m 2The graft rate of the graft chains is 73 to 121%. Moreover, since iminodiacetic acid groups, phosphoric acid groups, or iminodiethanol groups are introduced into the graft chains, the metal removal rate is 85% or more, and there is no discoloration due to organic solvents, and no cracks occur.

[0049] Various porous membranes or nonwoven fabrics were used to prepare metal-removing filter media in Comparative Examples 1 to 6. The physical properties of the porous membranes or nonwoven fabrics used are summarized in Table 3 below. In Comparative Examples 1, 2, 5, and 6, a polyethylene porous membrane was used, and in Comparative Examples 3 and 4, a polyethylene nonwoven fabric was used.

[0050] [Table 3]

[0051] (Comparative Example 1) The polyethylene porous membrane was irradiated with an electron beam at a dose of 60 kGy under a nitrogen atmosphere, then immersed in a 20% glycidyl methacrylate solution and reacted at 60°C for 60 minutes to carry out graft polymerization, yielding a graft substrate with a graft ratio of 38%. The graft substrate was immersed in a 6.6% aqueous solution of sodium iminodiacetate and treated at 80°C for 5 hours to introduce iminodiacetic acid groups. The graft substrate with the introduced functional groups was then immersed in 1 mol / L hydrochloric acid, rinsed with ultrapure water, and dried to obtain a functional group introduction amount of 13 mmol / m. 2 The metal removal filter medium had a weight of 52 g / m 2 It was.

[0052] (Comparative Example 2) The polyethylene porous membrane was irradiated with an electron beam at a dose of 60 kGy under a nitrogen atmosphere, then immersed in a 25% glycidyl methacrylate solution and reacted at 60°C for 40 minutes to carry out graft polymerization, yielding a graft substrate with a graft ratio of 84%. This was immersed in a 10% aqueous solution of sodium sulfite and treated at 95°C for 24 hours to introduce sulfonic acid groups. The graft substrate with the introduced functional groups was then immersed in 1 mol / L hydrochloric acid, rinsed with ultrapure water, and dried to obtain a functional group introduction amount of 234 mmol / m 2The metal removal filter medium had a weight of 78 g / m 2 It was.

[0053] (Comparative Example 3) A polyethylene nonwoven fabric was irradiated with an electron beam at a dose of 60 kGy under a nitrogen atmosphere, then immersed in a 100% glycidyl methacrylate solution and reacted at 60°C for 40 minutes to carry out graft polymerization, yielding a graft substrate with a graft ratio of 119%. This was immersed in a 10% aqueous solution of sodium sulfite and treated at 95°C for 24 hours to introduce sulfonic acid groups. The graft substrate with the introduced functional groups was then immersed in 1 mol / L hydrochloric acid, rinsed with ultrapure water, and dried to obtain a functional group introduction amount of 970 mmol / m 2 The metal removal filter medium had a weight of 250 g / m 2 It was.

[0054] Comparative Example 4 A polyethylene nonwoven fabric was irradiated with an electron beam at a dose of 60 kGy under a nitrogen atmosphere, then immersed in a 100% glycidyl methacrylate solution and reacted at 60°C for 40 minutes to carry out graft polymerization, yielding a graft substrate with a graft ratio of 119%. The graft substrate was immersed in a 20% aqueous solution of sodium iminodiacetate and treated at 60°C for 24 hours to introduce iminodiacetate groups. The graft substrate with the introduced functional groups was then immersed in 1 mol / L hydrochloric acid, rinsed with ultrapure water, and dried to obtain a functional group introduction amount of 506 mmol / m. 2 The metal removal filter medium had a weight per unit area of ​​240 g / m. 2 It was.

[0055] (Comparative Example 5) The polyethylene porous membrane was irradiated with an electron beam at a dose of 150 kGy under a nitrogen atmosphere, then immersed in a 100% glycidyl methacrylate solution and reacted at 60°C for 60 minutes to carry out graft polymerization, yielding a graft substrate with a graft ratio of 547%. This was used as a metal removal filter medium. The weight per unit area was 241 g / m 2 It was.

[0056] (Comparative Example 6) The polyethylene porous membrane was irradiated with an electron beam at a dose of 60 kGy under a nitrogen atmosphere.Then, it was immersed in a 25% glycidyl methacrylate solution and reacted at 60 ° C for 40 minutes to attempt graft polymerization.However, the roll broke during continuous processing, and no metal-removing filter material was obtained.

[0057] The metal-removing filter media of the comparative examples were examined for metal-removing performance, discoloration of organic solvents, and cracking in the same manner as described above. The evaluation results are summarized in Table 4 below, along with the respective configurations.

[0058] [Table 4]

[0059] The metal-removing filter medium of Comparative Example 1 had an Fe removal rate of less than 85%, which is presumably because the graft rate was less than 40% (38%). The metal-removing filter medium of Comparative Example 2 exhibited discoloration of the organic solvent. The metal-removing filter medium of Comparative Example 3 not only exhibited discoloration of the organic solvent, but also exhibited a metal removal rate of less than 85%. The discoloration of the organic solvent was due to the influence of sulfonic acid groups. In the case of Comparative Example 3, the basis weight was 120 g / m 2 Over (250g / m 2 ), and because nonwoven fabric is used, a high metal removal rate cannot be achieved.

[0060] The metal-removing filter medium of Comparative Example 4 has a basis weight of 120 g / m 2 The metal removal rate exceeds 76.9% because a nonwoven fabric is used. In the metal-removing filter medium of Comparative Example 5, the basis weight is 120 g / m 2 The graft ratio exceeds 150%, which causes cracks and makes pleating impossible.

[0061] It was confirmed that if any one of the conditions of basis weight, grafting rate, or introduced functional group is not met, it is impossible to obtain a metal-removal filter medium that has high metal removal performance while maintaining flow rate per unit area and does not denature organic solvents.

[0062] <Making a cartridge filter> Using the metal-removing filter medium of Example 1 as the filter medium, a cartridge filter as shown in Figure 1 was produced. First, the metal-removing filter medium was sandwiched between polyethylene meshes as supports 3 and 5, and then laminated and pleated. This was placed circumferentially between the core 2 and the protector 6, and both ends were heat-sealed with end caps 7. Thus, a filter having dimensions of φ70 mm x 250 mm and an effective filtration area of ​​0.79 m was produced. 2 The cartridge filter was then immersed in 5% hydrochloric acid for 24 hours, and then washed with ultrapure water until no residual hydrochloric acid remained.

[0063] A metal-containing organic solvent (solvent: PGMEA) prepared so that Ti, Cr, and Fe were each approximately 20 ppb was filtered through this cartridge filter at a flow rate of 3 L / min, and the metal removal rate was calculated from the amount of metal before and after filtration. As a result, the removal rate for each metal was 93-98%, confirming good metal removal performance.

[0064] According to the present invention, the basis weight is 15 to 50 g / m 2 By using a polyethylene porous substrate with a porosity of 70% or more and a grafting ratio of 40 to 150%, it is possible to increase the contact area between the liquid being treated and the metal-removing filter material, resulting in a filter with high metal removal performance while maintaining a high flow rate. Moreover, by introducing chelating groups or anion-exchange groups, it is possible to remove trace metals from organic solvents without denaturing the organic solvent. [Explanation of symbols]

[0065] 1... Cartridge filter 2... Core 3,5... Support 4...Filter material 6...Protector 7...End cap

Claims

1. A porous polyethylene substrate and a graft chain fixed to the porous polyethylene substrate, having a functional group, and derived from glycidyl methacrylate (excluding those having a graft chain derived from p-haloalkylstyrene), the porous polyethylene substrate having a basis weight of 30 to 120 g / m ２ A metal-removing filter medium comprising: the graft chain has a graft rate of 40 to 150%, The functional group is selected from a quaternary ammonium group, a primary, secondary or tertiary amino group, an iminodiacetic acid group, a phosphate group, and an iminodiethanol group. A metal-removing filter medium characterized by:

2. 2. The metal-removing filter medium according to claim 1, wherein the porous polyethylene substrate is a porous polyethylene membrane.

3. The method for producing the metal-removing filter medium according to claim 1, Weight 15 to 50 g / m ２ a step of polymerizing a vinyl group-containing reactive monomer by radiation-induced graft polymerization onto a polyethylene porous substrate having a porosity of 70% or more to fix graft chains having a graft rate of 40 to 150%; a step of introducing a functional group selected from a quaternary ammonium group, a primary, secondary or tertiary amino group, an iminodiacetic acid group, a phosphate group, and an iminodiethanol group into the graft chain. A method for manufacturing a metal-removing filter medium, comprising:

4. 4. The method for producing a metal-removing filter medium according to claim 3, wherein the polyethylene porous substrate is a polyethylene porous membrane.

5. 3. A cartridge filter comprising a pleated filter medium, wherein the filter medium is the metal-removing filter medium according to claim 1 or 2.

Images