JP7843032B2 - water filter - Google Patents

Description

This invention relates to a water purification filter.

Sodium hypochlorite is primarily used for disinfecting tap water. When sodium hypochlorite dissolves in water, the resulting hypochlorous acid and hypochlorite ions are called free residual chlorine. Free residual chlorine has a bactericidal or disinfectant effect. However, the reaction of ammonia and nitrogen oxides present in natural water with the added hypochlorous acid and hypochlorite ions generates combined residual chlorine, such as chloramine. Combined residual chlorine and free residual chlorine together are called residual chlorine. Depending on the condition of the raw water, the amount of free residual chlorine added, and even the amount of chloramine, odor can often become a problem.

Water purifiers are used to remove residual chlorine from drinking water, such as tap water. Such water purifiers have a structure that incorporates adsorption elements made of inorganic materials such as activated carbon or ceramics, and, if necessary, organic polymer membranes for filtration. In recent years, with the demand for higher performance in water purifiers and air purifiers, activated carbon has been widely used in these filters.

For example, a residual chlorine removal filter body is known that removes residual chlorine from water by mixing activated carbon adsorbent, fibrillated fiber binder, and calcium sulfite in water to form a mixed slurry, adsorbing the mixed slurry onto a hollow cylindrical core member while suctioning from the side surface, and then heating and drying the adsorbed material. The activated carbon adsorbent consists of either granular activated carbon or fibrous activated carbon, or both. The filter body is formulated with 100 parts by weight of the activated carbon adsorbent, and based on the weight of the activated carbon adsorbent, it contains 7 to 22 parts by weight of the fibrillated fiber binder and 10 to 100 parts by weight of the calcium sulfite (see, for example, Patent Document 1). This filter body is said to have good water permeability and to maintain a high level of performance in removing residual chlorine, including both free and bound residual chlorine.

Japanese Patent Publication No. 2020-179374

In the filter of the embodiment described in Patent Document 1, when drinking water with a combined residual chlorine concentration of 0.2 ppm (mg/L) was passed through at a water temperature of 20°C and a flow rate of 2.5 L/min, with an SV value of ^500hr⁻¹ , the amount of filtered water with combined residual chlorine was at most 1.1 ^m³ , indicating insufficient filtration capacity for combined residual chlorine.

Therefore, the main objective of this invention is to provide a water purification filter that solves the above problems and achieves a balance between the filtration capacity for combined residual chlorine and free residual chlorine.

The inventors considered using activated carbon with a high amount of acidic functional groups to solve the above problems. However, the inventors found that simply using activated carbon with a high amount of acidic functional groups did not result in excellent filtration capacity for free residual chlorine, although it did result in excellent filtration capacity for bound residual chlorine.

Here, the inventors investigated the reasons why it was difficult to achieve excellent filtration capacity for free residual chlorine. The following oxidation-reduction reaction is considered to be the filtration mechanism of free residual chlorine by activated carbon.
HClO (free residual chlorine) + C (activated carbon) → CO + HCl

In other words, C (activated carbon) acts as a reducing agent, decomposing free residual chlorine. Here, activated carbon with a high amount of acidic functional groups includes activated carbon in which acidic functional groups such as cyclic and chain carboxyl groups, lactone groups, phenol groups, hydroxyl groups, ketone groups, and sulfone groups are introduced to the carbon atoms. It is thought that the oxidation-reduction reaction described above proceeds less readily on the surface of activated carbon with introduced acidic functional groups because the portion that acts as a reducing agent is reduced compared to activated carbon without introduced acidic functional groups. That is, the greater the amount of acidic functional group in the activated carbon, and the higher the acidity of the acidic functional group, the more the oxidation-reduction reaction is inhibited.

Therefore, the inventors further investigated and found that the above problem can be solved by using, for example, activated carbon with a high amount of acidic functional groups and activated carbon with a low amount of acidic functional groups and a specific surface area within a certain range in combination, and adjusting the average particle size and blending ratio of these so that the amount of acidic functional groups in the water purification filter is 0.8 to 3.0 mmol/g and the specific surface area of the water purification filter is 1600 to 1900 ^m² /g to form an activated carbon layer. The present invention was completed based on this finding and through diligent research.

In other words, the present invention provides inventions in the following embodiments.
Item 1. A water purification filter comprising an activated carbon layer, wherein the specific surface area of the activated carbon layer is 1600 to 1900 ^m² /g, and the amount of acidic functional groups in the activated carbon layer, as measured by the following measurement method, is 0.8 to 3.0 mmol/g.
(Method for measuring the amount of acidic functional groups)
A portion of the activated carbon layer is scraped off with a utility knife, and the scraped material is finely ground and classified until the particle size distribution is 2 mm or less. 1.0 g of this material is taken and used as the sample for measurement. The sample is added to 50 mL of a 0.1 mol/L sodium hydroxide aqueous solution as the alkaline solution, shaken for 30 minutes, and then allowed to stand at 25°C for 24 hours. After that, the mixture is filtered using glass fiber filter paper (Whatman GF/C), and 10 mL of the resulting filtrate is titrated with a 0.1 mol/L hydrochloric acid solution to determine the amount of acidic functional groups (mol/g).
Item 2. The water filter comprises a cylindrical core and a cover layer included on the outer periphery of the activated carbon layer, wherein the activated carbon layer is included on the outer periphery of the core, and the ratio of the thickness of the activated carbon layer to the thickness of the water filter (thickness of the activated carbon layer / thickness of the water filter) is 0.7 to 0.9.
The water purification filter according to item 1, wherein the pressure loss A measured by the following measurement method of the water purification filter is 0.010 to 0.040 MPa.
(Method for measuring pressure loss A)
The ends of the water purification filter are sealed by bonding foamed polyethylene caps using hot melt or silicone sealant, then filled into a resin housing, and pure water is passed through from the outside to the inside at a space velocity (SV) of 2781/h. After maintaining this flow rate for 10 minutes, the pressure loss X1 (MPa) is measured using a Bourdon tube pressure gauge. Similarly, the pressure loss X2 (MPa) is measured in a blank sample with the water purification filter removed. The value obtained by subtracting the pressure loss X2 from the pressure loss X1 is defined as the water flow pressure loss A (MPa) through the water purification filter.
Item 3. The water filter according to item 1 or ² , wherein the combined residual chlorine filtered water volume measured by the following measurement method of the water filter is 20 to 100 m³, and the free residual chlorine filtered water volume measured by the following measurement method of the water filter is 40 to 140 ^m³ .
(Method for measuring the amount of combined residual chlorine filtered water)
The ends of the water purification filter are sealed by bonding foamed polyethylene caps using hot melt or silicone sealant, and then filled into a stainless steel housing. Based on the provisions of Article 4 of the Water Supply Act of Japan, ammonium chloride and sodium hypochlorite are added to tap water that conforms to the water quality standards stipulated in the "Ministerial Ordinance Concerning Water Quality Standards (Ministry of Health, Labour and Welfare Ordinance No. 101 of May 30, 2003)," and the mixture is stirred to prepare raw water with a combined residual chlorine concentration of 0.5 mg/L. The adjusted raw water is passed from the outside to the inside of the water purification filter at a flow rate of 2.0 L/min so that the space velocity (SV) is 370/h. The concentration of combined residual chlorine is quantitatively measured using the DPD reagent spectrophotometric method before and after passing through the water purification filter, and the point at which the water concentration of combined residual chlorine in the effluent (filtered liquid) relative to the influent (adjusted raw water) becomes 20% or more is defined as the breakthrough point, and the total filtered water volume ( ^m³ ) up to the breakthrough point is determined.
(Method for measuring the amount of free residual chlorine filtered water)
The ends of the water purification filter are sealed by bonding foamed polyethylene caps using hot melt or silicone sealant, and then filled into a stainless steel housing. Based on the provisions of Article 4 of the Water Supply Act of Japan, the raw water is prepared by adding sodium hypochlorite to tap water that conforms to the water quality standards stipulated in the "Ministerial Ordinance Concerning Water Quality Standards (Ministry of Health, Labour and Welfare Ordinance No. 101 of May 30, 2003)" so that the free residual chlorine concentration is 2.0 ± 0.2 mg/L. The raw water is passed from the outside to the inside of the water purification filter so that the space velocity (SV) is 741/h. The concentration of free residual chlorine is quantitatively measured using the DPD reagent spectrophotometric method before and after passing through the water purification filter, and the breakthrough point is defined as the point at which the water concentration of free residual chlorine in the effluent (filtered liquid) relative to the influent (raw water) becomes 20% or more initially, and the total filtered water volume ( ^m³ ) up to the breakthrough point is determined.

The water purification filter of this invention makes it possible to achieve both the filtration capacity for bound residual chlorine and free residual chlorine.

This is a schematic diagram illustrating an example of a manufacturing apparatus for the water purification filter of the present invention using a slurry suction method.

<Configuration of the water purification filter of the present invention>
The water purification filter of the present invention is a water purification filter including an activated carbon layer, wherein the specific surface area of the activated carbon layer is 1600 to 1900 ^m² /g, and the amount of acidic functional groups in the activated carbon layer, as measured by the following measurement method, is 0.8 to 3.0 mmol/g.

(Method for measuring the amount of acidic functional groups)
A portion of the activated carbon layer is scraped off with a utility knife, and the scraped material is finely ground and classified until the particle size distribution is 2 mm or less. 1.0 g of this material is taken and used as the sample for measurement. The sample is added to 50 mL of a 0.1 mol/L sodium hydroxide aqueous solution as the alkaline solution, shaken for 30 minutes, and then allowed to stand at 25°C for 24 hours. After that, the mixture is filtered using glass fiber filter paper (Whatman GF/C), and 10 mL of the resulting filtrate is titrated with a 0.1 mol/L hydrochloric acid solution to determine the amount of acidic functional groups (mol/g).

A preferred configuration of the water purification filter of the present invention includes a cylindrical core and a cover layer included on the outer periphery of the activated carbon layer, wherein the activated carbon layer is included on the outer periphery of the core. In this case, the activated carbon layer is preferably cylindrical.

The following describes in detail each component of the water purification filter of this invention.

1. Activated Carbon Layer The water purification filter of the present invention includes an activated carbon layer.

In the water purification filter of the present invention, the activated carbon layer has a specific surface area of 1600 to 1900 ^m² /g. This specific surface area means that there are many carbon atoms in the activated carbon layer. Furthermore, having the specific surface area within the above range and specifying the amount of acidic functional groups, as described later, means that the activated carbon layer contains specific amounts of carbon atoms with acidic functional groups introduced and carbon atoms without acidic functional groups introduced. As a result, the resulting water purification filter has excellent combined residual chlorine filtration capacity and free residual chlorine filtration capacity. Having the specific surface area within the above range and specifying the amount of acidic functional groups, as described later, can be achieved, for example, by using activated carbon with a high amount of acidic functional groups (e.g., 2 mmol/g or more) and activated carbon with a low amount of acidic functional groups (e.g., 0.2 mmol/g or less) in combination and adjusting their mixing ratio. From the viewpoint of achieving even better combined residual chlorine filtration capacity, the specific surface area is preferably 1700 to 1900 ^m² /g.

In this invention, the specific surface area of the activated carbon layer is calculated based on the nitrogen adsorption isotherm at 77.4 K. Specifically, first, using an automatic gas adsorption amount measuring device (product name "AUTOSORB-1-MP", manufactured by QUANTCHROME), the sample (activated carbon layer) is cooled to 77.4 K (the boiling point of nitrogen), and nitrogen gas is introduced. The amount of nitrogen gas adsorbed, V [cc/g], is measured by the volumetric method. At this time, the pressure P [hPa] of the introduced nitrogen gas is gradually increased, and the value obtained by dividing by the saturated vapor pressure P0 [hPa] of the nitrogen gas is defined as the relative pressure P/P0. A nitrogen adsorption isotherm is created by plotting the adsorption amount for each relative pressure. Using the analysis program attached to the above device, the specific surface area is determined according to the BET method based on the obtained nitrogen adsorption isotherm. The sample is sampled so that its mass is 0.1 g.

In the water purification filter of the present invention, the activated carbon layer has an acidic functional group content of 0.8 to 3.0 mmol/g, as measured by the following measurement method.
(Method for measuring the amount of acidic functional groups)
A portion of the activated carbon layer is scraped off with a utility knife, and the scraped material is finely ground and classified until the particle size distribution is 2 mm or less. 1.0 g of this material is taken and used as the sample for measurement. The sample is added to 50 mL of a 0.1 mol/L sodium hydroxide aqueous solution as the alkaline solution, shaken for 30 minutes, and then allowed to stand at 25°C for 24 hours. After that, the mixture is filtered using glass fiber filter paper (Whatman GF/C), and 10 mL of the resulting filtrate is titrated with a 0.1 mol/L hydrochloric acid solution to determine the amount of acidic functional groups (mol/g).

Furthermore, the particle size distribution of the pulverized and classified activated carbon layer is the volume-based particle size distribution of granular activated carbon, measured using a laser diffraction/scattering particle size distribution analyzer (product name LA-920, manufactured by Horiba, Ltd.).

As described above, specifying the specific surface area range and the amount of acidic functional groups (described later) means that the activated carbon layer contains specific amounts of carbon atoms with acidic functional groups introduced and carbon atoms without acidic functional groups introduced. This results in a water purification filter with excellent combined residual chlorine filtration capacity and free residual chlorine filtration capacity. This specific surface area range and the amount of acidic functional groups (described later) can be achieved, for example, by using activated carbon with a high amount of acidic functional groups (e.g., 2 mmol/g or more) and activated carbon with a low amount of acidic functional groups (e.g., 0.5 mmol/g or less) in combination and adjusting their mixing ratio. From the viewpoint of achieving superior combined residual chlorine filtration capacity, the amount of acidic functional groups is preferably 1.5 to 3.0 mmol/g.

The acidic functional groups present in the activated carbon layer of the present invention are not particularly limited, but examples include cyclic and linear carboxyl groups, lactone groups, phenol groups, hydroxyl groups, ketone groups, and sulfone groups.

The apparent density of the activated carbon layer can be, for example, 0.25 to 0.5 g/ ^cm³ , with 0.3 to 0.45 g/ ^cm³ being preferred. Furthermore, when the activated carbon layer is cylindrical, the thickness of the activated carbon layer can be, for example, 5 to 30 mm, with 10 to 25 mm being preferred.

<Examples of preferred raw materials for the activated carbon layer>
(1) Activated carbon with a high amount of acidic functional groups In the water purification filter of the present invention, the activated carbon layer preferably contains activated carbon with a high amount of acidic functional groups, specifically activated carbon with an acidic functional group content of 2 mmol/g or more as a raw material. This makes it easier to adjust the amount of acidic functional groups in the activated carbon layer to 0.8 to 3.0 mmol/g. The above amount of acidic functional groups is more preferably 2 to 4 mmol/g, and even more preferably 2.5 to 3.5 mmol/g.

In this invention, the amount of acidic functional groups in activated carbon is measured as follows.
(Measurement method)
Take 1.0 g of activated carbon and use it as the sample for measurement. Add the sample to 50 mL of 0.1 mol/L sodium hydroxide aqueous solution as the alkaline solution, shake for 30 minutes, and then let stand at 25°C for 24 hours. After that, filter using glass fiber filter paper (Whatman GF/C), and 10 mL of the resulting filtrate is titrated with 0.1 mol/L hydrochloric acid solution to determine the amount of acidic functional groups (mol/g).

Furthermore, the specific surface area of activated carbon with a high acidic functional group content is preferably 1800 to 2500 ^m² /g, and more preferably 2000 to 2300 ^m² /g. This allows for a greater number of carbon atoms with acidic functional groups to be present on the surface, making it easier to improve the combined residual chlorine filtration capacity of the water purification filter. The method for measuring the specific surface area of activated carbon is the same as that for measuring the specific surface area of a water purification filter.

Furthermore, activated carbon with a high acidic functional group content is preferably granular activated carbon, with an average particle size of 150 to 200 μm, and more preferably 160 to 200 μm. This average particle size makes it easier to achieve a pressure loss within the range described later for the resulting water purification filter. The average particle size of granular activated carbon refers to the particle size at which the cumulative volume value in the particle size distribution of the granular activated carbon accounts for 50%, as measured using a laser diffraction/scattering particle size distribution analyzer (product name LA-920, manufactured by Horiba, Ltd.).

In the activated carbon layer of the water purification filter of the present invention, the content of activated carbon with a high acidic functional group content can be 20 to 90% by mass, and from the viewpoint of further facilitating a balance between the filtration capacity of bound residual chlorine and free residual chlorine of the water purification filter, 45 to 90% by mass is preferred.

(2) Activated carbon with low acidic functional group content In the water purification filter of the present invention, the activated carbon layer preferably contains activated carbon with a low acidic functional group content, specifically activated carbon with an acidic functional group content of 0.5 mmol/g or less as a raw material. This makes it easier to adjust the acidic functional group content of the activated carbon layer to 0.8 to 3.0 mmol/g. The above acidic functional group content is more preferably 0.3 mmol/g or less, and even more preferably 0.2 mmol/g or less.

Furthermore, the specific surface area of activated carbon with a low acidic functional group content is preferably 1400 to 2000 ^m² /g, and more preferably 1500 to 1900 ^m² /g. This allows for a greater number of carbon atoms without acidic functional groups to be present on the surface, making it easier to improve the free residual chlorine filtration capacity of the water purification filter.

Furthermore, activated carbon with a low acidic functional group content is preferably granular activated carbon, with an average particle size of 120 μm to 300 μm being preferred, and more preferably 130 to 280 μm. By using such an average particle size, the resulting water purification filter can be more easily controlled within the pressure loss range described later. Moreover, from the viewpoint of further controlling the pressure loss range of the resulting water purification filter, it is more preferable to use a combination of activated carbon with an average particle size of 130 to 170 μm and activated carbon with an average particle size of 200 to 300 μm.

In the activated carbon layer of the water purification filter of the present invention, the content of activated carbon with a low acidic functional group content can be 5 to 70% by mass, and from the viewpoint of further facilitating a balance between the filtration capacity of bound residual chlorine and free residual chlorine of the water purification filter, 5 to 50% by mass is preferred.

(3) Other Components The activated carbon layer contained in the water purification filter of the present invention may contain other components as raw materials other than the activated carbon with a high acidic functional group content and the activated carbon with a low acidic functional group content mentioned above. Examples of such other components include binder fibers. Binder fibers are formed by being integrated with the granular activated carbon mentioned above, thereby intertwining the granular activated carbon and shaping it into a cylindrical form. In the activated carbon layer contained in the water purification filter of the present invention, the granular activated carbon may be fused to the binder fibers. Known fibrillated binder fibers used in activated carbon layers can be used as binder fibers. Specific examples of such fibrillated binder fiber types include acrylic fibers, acrylic fibers, polyethylene fibers, cellulose fibers, and aramid fibers. Binder fibers may be used individually or in combination of two or more types.

In the activated carbon layer of the water purification filter of the present invention, the binder fiber content is, for example, about 2 to 7% by mass, preferably about 3 to 5% by mass.

2. Core The water purification filter of the present invention may include a cylindrical core. The core has pores through which the water to be purified can pass, and as a core member, it plays a role in increasing the strength of the water purification filter and also plays a role in reducing the shedding of carbon dust from the activated carbon layer.

The core material can be any known material, such as porous ceramics, porous metal filters, or nonwoven fabrics. Alternatively, a cylindrical member with pores may be molded from resin, metal, or other raw materials and used as the core. Among these, nonwoven fabrics are preferred, and those obtained by compression molding are more preferred. While there are no particular limitations on the fibrous material constituting the nonwoven fabric, polyester fibers are preferred.

The basis weight of the nonwoven fabric used to form the core is, for example, 30 to 100 g/ ^m² , with 50 to 90 g/ ^m² being preferred. The thickness of the core is, for example, 1 to 5 mm, with 2 to 4 mm being more preferred. The apparent density of the core is, for example, 0.2 to 0.6 g/ ^cm³ , with 0.25 to 0.35 g/ ^cm³ being preferred.

3. Cover Layer The water purification filter of the present invention may include a cover layer on the outer periphery of the activated carbon layer. The cover layer has pores through which the water to be purified can pass and plays a role in reducing the shedding of carbon dust from the activated carbon layer.

The cover layer is not particularly limited, but woven fabrics, knitted fabrics, nonwoven fabrics, and other types of fabrics are preferred, with nonwoven fabrics being particularly preferred. Among these, nonwoven fabrics made of long fibers or continuous fibers are preferred from the viewpoint of having relatively high tear strength and superior handling and processability.

The nonwoven fabric consisting of long fibers or continuous fibers is not particularly limited, but a spunbond nonwoven fabric is preferred. Examples of long fibers or continuous fibers constituting the spunbond nonwoven fabric include core-sheath type heat-fusible fibers in which a heat-fusible component is arranged in the sheath portion and a synthetic resin component having a melting point 20°C or more, more preferably 30°C or more, higher than the melting point of the sheath portion is arranged in the core portion. Examples of the core portion of the above core-sheath type heat-fusible fiber include a synthetic resin component having a melting point of 150 to 300°C, more preferably 200 to 300°C, and having a melting point 20°C or more higher than the melting point of the sheath portion, and more specifically, polyethylene terephthalate. Examples of the sheath portion of the above core-sheath type heat-fusible fiber include those having a melting point 80 to 170°C, more preferably 80 to 140°C, and more specifically, polyester resins such as olefin resins such as polypropylene and polyethylene, or copolymerized polyethylene terephthalate copolymerized with copolymerized components such as isophthalic acid. Among these, polyolefin resins are preferred, and polyethylene is more preferred, due to their superior flexibility, heat-sealability to activated carbon molded bodies, and ease of handling and processing.

The basis weight of the cover layer can be, for example, 20 to 100 g/ ^m² , with 40 to 60 g/ ^m² being preferred. The thickness of the cover layer can be, for example, 0.03 to 1.0 mm, with 0.05 to 0.6 mm being preferred. The apparent density of the cover layer can be, for example, 0.05 to 0.5 g/ ^cm³ , with 0.08 to 0.4 g/ ^cm³ being preferred.

4. Water Purification Filter The water purification filter of the present invention may include a cylindrical core, an activated carbon layer included on the outer circumference of the core, and a cover layer included on the outer circumference of the activated carbon layer. Preferably, the ratio of the thickness of the activated carbon layer to the thickness of the water purification filter (thickness of the activated carbon layer / thickness of the water purification filter) is 0.7 to 0.9.

The water purification filter of the present invention preferably has a pressure loss A of 0.010 to 0.040 MPa, as measured by the following measurement method.
(Method for measuring pressure loss)
(Method for measuring pressure loss A)
The ends of the water purification filter are sealed by bonding foamed polyethylene caps using hot melt or silicone sealant, then filled into a resin housing, and pure water is passed through from the outside to the inside at a space velocity (SV) of 2781/h. After maintaining this flow rate for 10 minutes, the pressure loss X1 (MPa) is measured using a Bourdon tube pressure gauge. Similarly, the pressure loss X2 (MPa) is measured in a blank sample with the water purification filter removed. The value obtained by subtracting the pressure loss X2 from the pressure loss X1 is defined as the water flow pressure loss A (MPa) through the water purification filter.

The above pressure loss A indicates that the average particle size of activated carbon with a high acidic functional group content (e.g., 2 mmol/g or more) and the average particle size of activated carbon with a low acidic functional group content (e.g., 0.2 mmol/g or less) are both within specific ranges. This makes it easier to achieve superior combined residual chlorine filtration capacity and free residual chlorine filtration capacity in the resulting water purification filter. Specifically, by setting the pressure loss within the range of A, the activated carbon layer achieves an appropriate density, maintaining flow paths within the activated carbon layer that better exhibit combined residual chlorine filtration capacity and free residual chlorine filtration capacity, resulting in superior combined residual chlorine filtration capacity and free residual chlorine filtration capacity. From the viewpoint of further improving combined residual chlorine filtration capacity, the above pressure loss A is preferably set to 0.015 to 0.028 MPa.

The water purification filter of the present invention preferably has a pressure loss B of 0.010 to 0.030 MPa, and more preferably 0.010 to 0.018 MPa, as measured by the following measurement method.
(Method for measuring pressure loss B)
The ends of the water purification filter are sealed by bonding foamed polyethylene caps using hot melt or silicone sealant, then filled into a resin housing, and pure water is passed through from the outside to the inside at a space velocity (SV) of 1854/h. After maintaining this flow rate for 10 minutes, the pressure loss Y1 (MPa) is measured using a Bourdon tube pressure gauge. Similarly, the pressure loss Y2 (MPa) is measured in a blank sample with the water purification filter removed. The value obtained by subtracting the pressure loss Y2 from the pressure loss Y1 is defined as the water flow pressure loss B (MPa) through the water purification filter.

The water purification filter of the present invention preferably has a combined residual chlorine filtration volume of 20 to 100 ^m³ , as measured by the following measurement method, and preferably has a free residual chlorine filtration volume of 40 to 140 ^m³ , as measured by the following measurement method.

(Method for measuring the amount of combined residual chlorine filtered water)
The ends of the water purification filter are sealed by bonding foamed polyethylene caps using hot melt or silicone sealant, and then filled into a stainless steel housing. Based on the provisions of Article 4 of the Water Supply Act of Japan, ammonium chloride and sodium hypochlorite are added to tap water that conforms to the water quality standards stipulated in the "Ministerial Ordinance Concerning Water Quality Standards (Ministry of Health, Labour and Welfare Ordinance No. 101 of May 30, 2003)," and the mixture is stirred to prepare raw water with a combined residual chlorine concentration of 0.5 mg/L. The adjusted raw water is passed from the outside to the inside of the water purification filter at a flow rate of 2.0 L/min so that the space velocity (SV) is 370/h. The concentration of combined residual chlorine is quantitatively measured using the DPD reagent spectrophotometric method before and after passing through the water purification filter, and the point at which the water concentration of combined residual chlorine in the effluent (filtered liquid) relative to the influent (adjusted raw water) becomes 20% or more is defined as the breakthrough point, and the total filtered water volume ( ^m³ ) up to the breakthrough point is determined.

(Method for measuring the amount of free residual chlorine filtered water)
The ends of the water purification filter are sealed by bonding foamed polyethylene caps using hot melt or silicone sealant, and then filled into a stainless steel housing. Separately, in accordance with Article 4 of the Water Supply Act of Japan, sodium hypochlorite is added to tap water that conforms to the water quality standards stipulated in the "Ministerial Ordinance Concerning Water Quality Standards (Ministry of Health, Labour and Welfare Ordinance No. 101 of May 30, 2003)" to prepare the raw water for adjustment, so that the free residual chlorine concentration is 2.0 ± 0.2 mg/L. The raw water for adjustment is passed from the outside to the inside of the water purification filter so that the space velocity (SV) is 741/h. The concentration of free residual chlorine is quantitatively measured using the DPD reagent spectrophotometric method before and after passing through the water purification filter, and the point at which the concentration of free residual chlorine in the water of the effluent (filtered liquid) relative to the influent (raw water for adjustment) becomes 20% or more is defined as the breakthrough point, and the total amount of filtered water ( ^m³ ) up to the breakthrough point is determined.

As described above, by using activated carbon with a high acidic functional group content and activated carbon with a low acidic functional group content and a specific surface area within a certain range, and by adjusting the mixing ratio so that the acidic functional group content of the activated carbon layer is 0.8 to 3.0 mmol/g and the specific surface area of the activated carbon layer is 1600 to 1900 ^m² /g, and by adjusting their average particle size to fall within the range of pressure loss A and/or pressure loss B described above, it becomes possible to further achieve a balance between the amount of combined residual chlorine and free residual chlorine filtered out. From the viewpoint of further ensuring a balance between the filtration capacity of combined residual chlorine and free residual chlorine, it is preferable that the amount of combined residual chlorine filtered out and the amount of free residual chlorine filtered out are 50 to 100 ^m³ .

The height of the water purification filter of this invention (the length from one bottom surface to the other bottom surface) can be appropriately set according to the type of water purifier used, etc., but examples include 10 to 300 mm.

The thickness of the water purification filter of the present invention can be appropriately set according to the type of water purifier used, etc., but from the viewpoint of water purification performance and water permeability, for example, a thickness of 2.5 to 50 mm is recommended. In this invention, the thickness of the cylindrical water purification filter is the value obtained by subtracting the inner diameter from the outer diameter. The inner diameter is the diameter of the space that connects the center of one bottom surface to the center of the other bottom surface in a cross-section perpendicular to the height direction of the water purification filter. The outer diameter is the diameter of the water purification filter, including the space, in a cross-section perpendicular to the height direction of the water purification filter.

When the water purification filter of the present invention is cylindrical, its inner and outer diameters can be appropriately set to satisfy the thickness described above. Specifically, an inner diameter of 5 mm or more and an outer diameter of 15 to 150 mm are examples.

<Method of manufacturing a water purification filter>
The method for manufacturing the water purification filter of the present invention is not particularly limited, and examples include the following methods.

First, a core and preferred raw materials for the activated carbon layer described above are prepared, and an intermediate in which the core and activated carbon layer are integrated is manufactured by slurry suction. Specifically, a slurry is obtained by mixing granular activated carbon with a high acidic functional group content, granular activated carbon with a low acidic functional group content, and binder fibers with water. Next, for example, a double-tubular container having an inner tube and an outer tube with numerous small holes is used, the core is set on the outer circumference of the inner tube, the slurry is poured between the core and the outer tube, and a cylindrical molded body is obtained by suctioning the slurry from the center. The intermediate is obtained by drying this molded body. The molded body may be subjected to heat treatment and compression treatment as needed. The ratio of powdered activated carbon to binder fibers in the slurry can be set to the ratio described above in the water purification filter. In addition, in the slurry suction method, the shape of the water purification filter corresponds to the shape of the container into which the slurry is poured, so the shape of the water purification filter can be made into various shapes by changing the shape of the container. Next, a cover layer is wrapped around the outer circumference of the obtained intermediate, thereby manufacturing the water purification filter of the present invention.

Another specific example of a method for producing an intermediate in which the core and activated carbon layer are integrated by the slurry suction method described above will be explained. Figure 1 is a schematic diagram illustrating an example of a production apparatus for the intermediate in which the core and activated carbon layer are integrated by the slurry suction method. The production apparatus in Figure 1 comprises a mold 6 having a cylindrical core 62 with numerous suction holes 61 on its surface, and flanges that are detachable from the core and positioned at both ends of the core 62; a suction tube 7 that is connected to the cylindrical interior of the core 62 in a way that allows for air and liquid flow; and a container 9 containing a slurry 8 obtained by mixing the above-mentioned granular activated carbon with a high acidic functional group content, the above-mentioned granular activated carbon with a low acidic functional group content, and the above-mentioned binder fibers with water.

First, a uniform aqueous slurry is prepared containing granular activated carbon with a high acidic functional group content, granular activated carbon with a low acidic functional group content, and the binder fibers in a predetermined proportion. While the solid content concentration in the aqueous slurry is not particularly limited, it is preferably around 0.1 to 4% by mass from the viewpoint of ease of handling and ease of molding. During slurry preparation, mechanical dispersion, stirring, and beating can be performed using a beater or similar device.

The obtained slurry 8 is placed in the container 9. Next, one flange of the mold 6 is removed, the aforementioned cylindrical core is inserted into the core body 62, the flange is reattached, and the mixture is immersed in the slurry 8. Then, using a pump, the pressure inside the core body 62 is reduced through the suction tube 7, causing the granular activated carbon with a high acidic functional group content, the granular activated carbon with a low acidic functional group content, and the binder fibers to deposit on the surface of the core body 62.

Then, the mold 6 is withdrawn from the slurry 8, the intermediate in which the core and activated carbon layer are integrated is extracted, and it is dried. The drying temperature can be, for example, around 80 to 150°C. Although not shown in the figures, it is preferable to include a step of compressing the layer containing granular activated carbon with a high acidic functional group content, granular activated carbon with a low acidic functional group content, and the binder fibers, which has been deposited on the mold 6, either while the slurry is being aspirated or after the mold 6 has been withdrawn from the slurry 8. The method of compression is not particularly limited, but for example, a rotating roller may be pressed against the layer so that the activated carbon layer reaches a predetermined apparent density, and the activated carbon layer containing granular activated carbon with a high acidic functional group content, granular activated carbon with a low acidic functional group content, and the binder fibers, which has been deposited on the mold 6, is compressed while the mold 6 is rotated around its cylindrical long axis. After drying, a cover layer is wrapped around the outer circumference of the obtained intermediate to manufacture the water purification filter of the present invention.

<Uses of water purification filters>
Applications of the water purification filter of the present invention include water purifiers that filter raw water, such as tap water, to make it drinking water, and water purifiers that filter raw water to obtain dialysis water for hemodialysis.

The present invention will be described in detail below with reference to examples and comparative examples. However, the present invention is not limited to these examples.

<Example 1>
(1) Preparation of raw materials for the activated carbon layer The following raw materials were prepared.
- Activated carbon with a high acidic functional group content: A carbide made from phenolic resin and potassium hydroxide were mixed in a mass ratio (potassium hydroxide/carbide) of 3. This mixture was placed in a furnace and heated to 800°C at a heating rate of 10°C/min under a nitrogen flow (1 L/min), then held for 2 hours for alkaline activation treatment. Next, it was boiled in a 5.25 wt% hydrochloric acid (HCl) aqueous solution and then filtered. The filtered sample was washed with 60°C hot water and vacuum filtered, and the washing and dewatering were repeated until the pH of the filtrate was 6.5 or higher, and then dried at 115°C. After drying, it was heated to 300°C in an air atmosphere (heating rate of 10°C/min) and held for 24 hours for oxidation treatment. After the oxidation treatment, it was pulverized in a ball mill and adjusted to an average particle size of 180 μm. When the acidic functional group content and specific surface area of this activated carbon were measured, the acidic functional group content was 2.73 mmol/g and the specific surface area was 2180 ^m² /g.
- Activated carbon A with a low amount of acidic functional groups: Carbonized material made from coconut shells was placed in a furnace and heated to 900°C (10°C/min). While maintaining this temperature, steam was circulated into the furnace along with nitrogen (1 L/min) (steam concentration 70 vol%) to activate the carbon with steam. Next, it was pulverized in a ball mill and adjusted to an average particle size of 250 μm. The amount of acidic functional groups and specific surface area of this activated carbon were measured and found to be: amount of acidic functional groups: 0.13 mmol/g, specific surface area: 1700 ^m² /g.
- Activated carbon B with a low amount of acidic functional groups: The aforementioned activated carbon A with a low amount of acidic functional groups was pulverized in a ball mill to prepare it so that the average particle size was 150 μm, thereby obtaining activated carbon B with a low amount of acidic functional groups. When the amount of acidic functional groups and specific surface area of this activated carbon were measured, the amount of acidic functional groups was 0.13 mmol/g and the specific surface area was 1700 ^m² /g.
• Binder fiber: Fibrillated acrylic fiber, product name Vipal (registered trademark), manufactured by Nippon Exlan Industries Co., Ltd.

(2) Manufacturing of water purification filters (2-1) Preparation of nonwoven cores Polyester fiber A (Tetron polyester staple (Safmet), manufactured by Toray Industries, Inc.) and polyester fiber B (Tetron polyester staple (SD), manufactured by Toray Industries, Inc.) were carded to form a thin web, and the web was subjected to needle punching, heat treatment at a temperature of 163°C, and cooled to obtain a nonwoven fabric. This nonwoven fabric had a basis weight of 80 g/ ^m² , a thickness of 0.32 mm, and an apparent density of 0.25 g/ ^cm³ . A cylindrical iron pipe with an outer diameter of 30.0 mm was prepared as a core, and the nonwoven fabric was wound around the core so that the outer diameter of the core was 37 mm. The pipe was placed in a furnace and heat treatment was performed at an ambient temperature of 150°C for 2 hours, followed by natural cooling. After that, the core was removed, and the pipe was cut to lengths of 124 mm and 248 mm using a cutting machine to obtain nonwoven cores. The obtained nonwoven fabric core had an inner diameter of 30.0 mm, an outer diameter of 37.0 mm, a thickness of 3.5 mm, and an apparent density of 0.30 g/ ^cm³ .

(2-2) Manufacturing of water purification filters A slurry was obtained by mixing activated carbon with a high acidic functional group content, activated carbon A with a low acidic functional group content, activated carbon B with a low acidic functional group content, and binder fibers with water to obtain the composition shown in Table 1. A 124 mm core prepared was set in the core body of a mold, the slurry was sucked out from the center and pulled out, and dried in a drying oven at 120°C for 15 hours to obtain an intermediate in which the core and activated carbon layer were integrated, with an outer diameter of 64.32 mm, an inner diameter of 30 mm, and a length of 124 mm. A nonwoven fabric (Elves S0503, manufactured by Unitika Ltd., a spunbond nonwoven fabric made of continuous fibers which are core-sheath type composite fibers with a polyester resin core and a polyolefin resin sheath, and the accumulated continuous fibers are partially pressed together by heat embossing to form a unified nonwoven fabric, the basis weight of the nonwoven fabric is 50 g/ ^m² , the thickness is 0.34 mm, and the apparent density is 0.15 g/ ^cm³ ) was wrapped around this intermediate as a cover layer to cover the outer layer, and the beginning and end of the wrapping were heat-bonded with an iron heated to 150°C to obtain a water purification filter 1A. Similarly, using the prepared 248 mm long core, an intermediate was obtained in which the core and activated carbon layer were integrated, with an outer diameter of 64.32 mm, an inner diameter of 30 mm, and a length of 248 mm. A nonwoven fabric (Elves S0503, manufactured by Unitika Ltd.) was wrapped around it as a cover layer to cover the outer layer, and the beginning and end of the wrapping were heat-sealed with an iron heated to 150°C to obtain a water purification filter 1B. The volume of water purification filter 1A was 324 ^cm³ , and the volume of water purification filter 1B was 648 ^cm³ . Furthermore, the outer diameter of water purification filters 1A and 1B was 65 mm, the inner diameter was 30 mm, and the thickness was 17.5 mm. The nonwoven fabric core in water purification filters 1A and 1B had an inner diameter of 30.0 mm, an outer diameter of 37.0 mm, a thickness of 3.5 mm, and an apparent density of 0.30 g/cm³ ^. The mass of the activated carbon layer in water purification filter 1A was 100 g, and the mass of the activated carbon layer in water purification filter 1B was 199 g. The outer diameter of the activated carbon layer in water purification filters 1A and 1B was 64.32 mm, the thickness was 13.66 mm, and the apparent density was 0.37 g/ ^cm³ . The ratio of the thickness of the activated carbon layer to the thickness of water purification filters 1A and 1B (thickness of activated carbon layer / thickness of water purification filter) was 0.78.

<Example 2>
(1) Preparation of raw materials for the activated carbon layer The same raw materials as in Example 1 were prepared.

(2) Manufacturing of water purification filters (2-1) Preparation of nonwoven core The same nonwoven core as in Example 1 was prepared.

(2-2) Manufacturing of water purification filters A slurry was obtained by mixing activated carbon with a high acidic functional group content, activated carbon A with a low acidic functional group content, activated carbon B with a low acidic functional group content, and binder fibers with water to obtain the composition shown in Table 1. A 124 mm core prepared was set in the core body of a mold, the slurry was sucked out from the center and pulled out, and dried in a drying oven at 120°C for 15 hours to obtain an intermediate in which the core and activated carbon layer were integrated, with an outer diameter of 64.32 mm, an inner diameter of 30 mm, and a length of 124 mm. A nonwoven fabric (Elves S0503, manufactured by Unitika Ltd., a spunbond nonwoven fabric made of continuous fibers which are core-sheath type composite fibers with a polyester resin core and a polyolefin resin sheath, and the accumulated continuous fibers are partially pressed together by heat embossing to form a unified nonwoven fabric, the basis weight of the nonwoven fabric is 50 g/ ^m² , the thickness is 0.34 mm, and the apparent density is 0.15 g/ ^cm³ ) was wrapped around this intermediate as a cover layer to cover the outer layer, and the beginning and end of the wrapping were heat-bonded with an iron heated to 150°C to obtain a water purification filter 2A. Similarly, using the prepared 248 mm long core, an intermediate was obtained in which the core and activated carbon layer were integrated, with an outer diameter of 64.32 mm, an inner diameter of 30 mm, and a length of 248 mm. A nonwoven fabric (Elves S0503, manufactured by Unitika Ltd.) was wrapped around it as a cover layer to cover the outer layer, and the beginning and end of the wrapping were heat-sealed with an iron heated to 150°C to obtain a water purification filter 2B. The volume of water purification filter 2A was 324 ^cm³ , and the volume of water purification filter 2B was 648 ^cm³ . Furthermore, the outer diameter of water purification filters 2A and 2B was 65 mm, the inner diameter was 30 mm, and the thickness was 17.5 mm. The nonwoven fabric core in water purification filters 2A and 2B had an inner diameter of 30.0 mm, an outer diameter of 37.0 mm, a thickness of 3.5 mm, and an apparent density of 0.30 g/cm³ ^. The mass of the activated carbon layer in water purification filter 2A was 100 g, and the mass of the activated carbon layer in water purification filter 2B was 200 g. The outer diameter of the activated carbon layer in water purification filters 2A and 2B was 64.32 mm, the thickness was 13.66 mm, and the apparent density was 0.37 g/ ^cm³ . The ratio of the thickness of the activated carbon layer to the thickness of water purification filters 2A and 2B (thickness of activated carbon layer / thickness of water purification filter) was 0.78.

<Example 3>
(1) Preparation of raw materials for the activated carbon layer The same raw materials as in Example 1 were prepared.

(2) Manufacturing of water purification filters (2-1) Preparation of nonwoven core The same nonwoven core as in Example 1 was prepared.

(2-2) Manufacturing of water purification filters A slurry was obtained by mixing activated carbon with a high acidic functional group content, activated carbon A with a low acidic functional group content, activated carbon B with a low acidic functional group content, and binder fibers with water to obtain the composition shown in Table 1. A 124 mm core prepared was set in the core body of a mold, the slurry was sucked out from the center and pulled out, and dried in a drying oven at 120°C for 15 hours to obtain an intermediate in which the core and activated carbon layer were integrated, with an outer diameter of 64.32 mm, an inner diameter of 30 mm, and a length of 124 mm. A nonwoven fabric (Elves S0503, manufactured by Unitika Ltd., a spunbond nonwoven fabric made of continuous fibers which are core-sheath type composite fibers with a polyester resin core and a polyolefin resin sheath, and the accumulated continuous fibers are partially pressed together by heat embossing to form a unified nonwoven fabric, the basis weight of the nonwoven fabric is 50 g/ ^m² , the thickness is 0.34 mm, and the apparent density is 0.15 g/ ^cm³ ) was wrapped around this intermediate as a cover layer to cover the outer layer, and the beginning and end of the wrapping were heat-bonded with an iron heated to 150°C to obtain a water purification filter 3A. Similarly, using the prepared 248 mm long core, an intermediate was obtained in which the core and activated carbon layer were integrated, with an outer diameter of 64.32 mm, an inner diameter of 30 mm, and a length of 248 mm. A nonwoven fabric (Elves S0503, manufactured by Unitika Ltd.) was wrapped around it as a cover layer to cover the outer layer, and the beginning and end of the wrapping were heat-sealed with an iron heated to 150°C to obtain a water purification filter 3B. The volume of water purification filter 3A was 324 ^cm³ , and the volume of water purification filter 3B was 648 ^cm³ . Furthermore, the outer diameter of water purification filters 3A and 3B was 65 mm, the inner diameter was 30 mm, and the thickness was 17.5 mm. The nonwoven fabric core in water purification filters 3A and 3B had an inner diameter of 30.0 mm, an outer diameter of 37.0 mm, a thickness of 3.5 mm, and an apparent density of 0.30 g/cm³ ^. The mass of the activated carbon layer in water purification filter 3A was 100 g, and the mass of the activated carbon layer in water purification filter 3B was 201 g. The outer diameter of the activated carbon layer in water purification filters 3A and 3B was 64.32 mm, the thickness was 13.66 mm, and the apparent density was 0.37 g/ ^cm³ . The ratio of the thickness of the activated carbon layer to the thickness of water purification filters 3A and 3B (thickness of activated carbon layer / thickness of water purification filter) was 0.78.

<Example 4>
(1) Preparation of raw materials for the activated carbon layer The same raw materials as in Example 1 were prepared.

(2) Manufacturing of water purification filters (2-1) Preparation of nonwoven core The same nonwoven core as in Example 1 was prepared.

(2-2) Manufacturing of water purification filters A slurry was obtained by mixing activated carbon with a high acidic functional group content, activated carbon A with a low acidic functional group content, activated carbon B with a low acidic functional group content, and binder fibers with water to obtain the composition shown in Table 1. A 124 mm core prepared was set in the core body of a mold, the slurry was sucked out from the center and pulled out, and dried in a drying oven at 120°C for 15 hours to obtain an intermediate in which the core and activated carbon layer were integrated, with an outer diameter of 64.32 mm, an inner diameter of 30 mm, and a length of 124 mm. A nonwoven fabric (Elves S0503, manufactured by Unitika Ltd., a spunbond nonwoven fabric made of continuous fibers which are core-sheath type composite fibers with a polyester resin core and a polyolefin resin sheath, and the accumulated continuous fibers are partially pressed together by heat embossing to form a unified nonwoven fabric, the basis weight of the nonwoven fabric is 50 g/ ^m² , the thickness is 0.34 mm, and the apparent density is 0.15 g/ ^cm³ ) was wrapped around this intermediate as a cover layer to cover the outer layer, and the beginning and end of the wrapping were heat-bonded with an iron heated to 150°C to obtain a water purification filter 4A. Similarly, using the prepared 248 mm long core, an intermediate was obtained in which the core and activated carbon layer were integrated, with an outer diameter of 64.32 mm, an inner diameter of 30 mm, and a length of 248 mm. A nonwoven fabric (Elves S0503, manufactured by Unitika Ltd.) was wrapped around it as a cover layer to cover the outer layer, and the beginning and end of the wrapping were heat-sealed with an iron heated to 150°C to obtain a water purification filter 4B. The volume of water purification filter 4A was 324 ^cm³ , and the volume of water purification filter 4B was 648 ^cm³ . Furthermore, the outer diameter of water purification filters 4A and 4B was 65 mm, the inner diameter was 30 mm, and the thickness was 17.5 mm. The nonwoven fabric core in water purification filters 4A and 4B had an inner diameter of 30.0 mm, an outer diameter of 37.0 mm, a thickness of 3.5 mm, and an apparent density of 0.30 g/cm³ ^. The mass of the activated carbon layer in water purification filter 4A was 98 g, and the mass of the activated carbon layer in water purification filter 4B was 197 g. The outer diameter of the activated carbon layer in water purification filters 4A and 4B was 64.32 mm, the thickness was 13.66 mm, and the apparent density was 0.37 g/ ^cm³ . The ratio of the thickness of the activated carbon layer to the thickness of water purification filters 4A and 4B (thickness of activated carbon layer / thickness of water purification filter) was 0.78.

<Example 5>
(1) Preparation of raw materials for the activated carbon layer The same raw materials as in Example 1 were prepared.

(2) Manufacturing of water purification filters (2-1) Preparation of nonwoven core The same nonwoven core as in Example 1 was prepared.

(2-2) Manufacturing of water purification filters A slurry was obtained by mixing activated carbon with a high acidic functional group content, activated carbon A with a low acidic functional group content, activated carbon B with a low acidic functional group content, and binder fibers with water to obtain the composition shown in Table 1. A 124 mm core prepared was set in the core body of a mold, the slurry was sucked out from the center and pulled out, and dried in a drying oven at 120°C for 15 hours to obtain an intermediate in which the core and activated carbon layer were integrated, with an outer diameter of 64.32 mm, an inner diameter of 30 mm, and a length of 124 mm. A nonwoven fabric (Elves S0503, manufactured by Unitika Ltd., a spunbond nonwoven fabric made of continuous fibers which are core-sheath type composite fibers with a polyester resin core and a polyolefin resin sheath, and the accumulated continuous fibers are partially pressed together by heat embossing to form a unified nonwoven fabric, the basis weight of the nonwoven fabric is 50 g/ ^m² , the thickness is 0.34 mm, and the apparent density is 0.15 g/ ^cm³ ) was wrapped around this intermediate as a cover layer to cover the outer layer, and the beginning and end of the wrapping were heat-bonded with an iron heated to 150°C to obtain a water purification filter 5A. Similarly, using the prepared 248 mm long core, an intermediate was obtained in which the core and activated carbon layer were integrated, with an outer diameter of 64.32 mm, an inner diameter of 30 mm, and a length of 248 mm. A nonwoven fabric (Elves S0503, manufactured by Unitika Ltd.) was wrapped around it as a cover layer to cover the outer layer, and the beginning and end of the wrapping were heat-sealed with an iron heated to 150°C to obtain a water purification filter 5B. The volume of water purification filter 5A was 324 ^cm³ , and the volume of water purification filter 5B was 648 ^cm³ . Furthermore, the outer diameter of water purification filters 5A and 5B was 65 mm, the inner diameter was 30 mm, and the thickness was 17.5 mm. The nonwoven fabric core in water purification filters 5A and 5B had an inner diameter of 30.0 mm, an outer diameter of 37.0 mm, a thickness of 3.5 mm, and an apparent density of 0.30 g/cm³ ^. The mass of the activated carbon layer in water purification filter 5A was 100 g, and the mass of the activated carbon layer in water purification filter 5B was 200 g. The outer diameter of the activated carbon layer in water purification filters 5A and 5B was 64.32 mm, the thickness was 13.66 mm, and the apparent density was 0.37 g/ ^cm³ . The ratio of the thickness of the activated carbon layer to the thickness of water purification filters 5A and 5B (thickness of activated carbon layer / thickness of water purification filter) was 0.78.

<Example 6>
(1) Preparation of raw materials for the activated carbon layer The following raw materials were prepared.
- Activated carbon with a high acidic functional group content: A carbide made from phenolic resin and potassium hydroxide were mixed in a mass ratio (potassium hydroxide/carbide) of 3. This mixture was placed in a furnace and heated to 800°C at a heating rate of 10°C/min under a nitrogen flow (1 L/min), then held for 2 hours for alkaline activation treatment. Next, it was boiled in a 5.25 wt% hydrochloric acid (HCl) aqueous solution and then filtered. The filtered sample was washed with 60°C hot water and vacuum filtered, and the washing and dewatering were repeated until the pH of the filtrate was 6.5 or higher, and then dried at 115°C. After drying, it was heated to 300°C in an air atmosphere (heating rate of 10°C/min) and held for 24 hours for oxidation treatment. After the oxidation treatment, it was pulverized in a ball mill and adjusted to an average particle size of 180 μm. When the acidic functional group content and specific surface area of this activated carbon were measured, the acidic functional group content was 2.73 mmol/g and the specific surface area was 2180 ^m² /g.
- Activated carbon B with a low amount of acidic functional groups: The aforementioned activated carbon A with a low amount of acidic functional groups was pulverized in a ball mill to prepare it so that the average particle size was 150 μm, thereby obtaining activated carbon B with a low amount of acidic functional groups. When the amount of acidic functional groups and specific surface area of this activated carbon were measured, the amount of acidic functional groups was 0.13 mmol/g and the specific surface area was 1700 ^m² /g.
• Binder fiber: Fibrillated acrylic fiber, product name Vipal (registered trademark), manufactured by Nippon Exlan Industries Co., Ltd.

(2) Manufacturing of water purification filters (2-1) Preparation of nonwoven core The same nonwoven core as in Example 1 was prepared.

(2-2) Manufacturing of water purification filters A slurry was obtained by mixing activated carbon with a high acidic functional group content, activated carbon B with a low acidic functional group content, and binder fibers with water to obtain the composition shown in Table 1. A 124 mm core prepared was set in the core body of a mold, the slurry was sucked out from the center and pulled out, and dried in a drying oven at 120°C for 15 hours to obtain an intermediate in which the core and activated carbon layer were integrated, with an outer diameter of 64.32 mm, an inner diameter of 30 mm, and a length of 124 mm. A nonwoven fabric (Elves S0503, manufactured by Unitika Ltd., a spunbond nonwoven fabric made of continuous fibers which are core-sheath type composite fibers with a polyester resin core and a polyolefin resin sheath, and the accumulated continuous fibers are partially pressed together by heat embossing to form a unified nonwoven fabric, the basis weight of the nonwoven fabric is 50 g/ ^m² , the thickness is 0.34 mm, and the apparent density is 0.15 g/ ^cm³ ) was wrapped around this intermediate as a cover layer to cover the outer layer, and the beginning and end of the wrapping were heat-bonded with an iron heated to 150°C to obtain a water purification filter 6A. Similarly, using the prepared 248 mm long core, an intermediate was obtained in which the core and activated carbon layer were integrated, with an outer diameter of 64.32 mm, an inner diameter of 30 mm, and a length of 248 mm. A nonwoven fabric (Elves S0503, manufactured by Unitika Ltd.) was wrapped around it as a cover layer to cover the outer layer, and the beginning and end of the wrapping were heat-sealed with an iron heated to 150°C to obtain a water purification filter 6B. The volume of water purification filter 6A was 324 ^cm³ , and the volume of water purification filter 6B was 648 ^cm³ . Furthermore, the outer diameter of water purification filters 6A and 6B was 65 mm, the inner diameter was 30 mm, and the thickness was 17.5 mm. The nonwoven fabric core in water purification filters 6A and 6B had an inner diameter of 30.0 mm, an outer diameter of 37.0 mm, a thickness of 3.5 mm, and an apparent density of 0.30 g/cm³ ^. The mass of the activated carbon layer in water purification filter 6A was 100 g, and the mass of the activated carbon layer in water purification filter 6B was 199 g. The outer diameter of the activated carbon layer in water purification filters 6A and 6B was 64.32 mm, the thickness was 13.66 mm, and the apparent density was 0.37 g/ ^cm³ . The ratio of the thickness of the activated carbon layer to the thickness of water purification filters 6A and 6B (thickness of activated carbon layer / thickness of water purification filter) was 0.78.

<Comparative Example 1>
(1) Preparation of raw materials for the activated carbon layer The following raw materials were prepared.
• Activated carbon A with a low amount of acidic functional groups: Activated carbon A with a low amount of acidic functional groups was prepared in the same manner as in Example 1. (Amount of acidic functional groups: 0.13 mmol/g, specific surface area: 1700 ^m² /g, average particle size: 250 μm)
• Activated carbon B with a low amount of acidic functional groups: Activated carbon B with a low amount of acidic functional groups was prepared in the same manner as in Example 1. (Amount of acidic functional groups: 0.13 mmol/g, specific surface area: 1700 ^m² /g, average particle size: 150 μm)
• Activated carbon fiber: Product name A-15, manufactured by Adore Co., Ltd. (Amount of acidic functional groups: 0.37 mmol, specific surface area: 1700 ^m² /g, average fiber diameter: 16 μm)
• Binder fiber: Fibrillated acrylic fiber, product name Vipal (registered trademark), manufactured by Nippon Exlan Industries Co., Ltd.

(2) Manufacturing of water purification filters (2-1) Preparation of nonwoven core The same nonwoven core as in Example 1 was prepared.
(2-2) Manufacturing of water purification filters A slurry was obtained by mixing water with activated carbon A, activated carbon B, activated carbon fibers, and binder fibers, which have a low acidic functional group content, so that they have the composition shown in Table 1. A 124 mm core prepared was set into the core of a mold, the slurry was sucked out from the center and pulled out, and dried in a drying oven at 120°C for 15 hours to obtain an intermediate in which the core and activated carbon layer were integrated, with an outer diameter of 64.32 mm, an inner diameter of 30 mm, and a length of 124 mm. A nonwoven fabric (Elves S0503, manufactured by Unitika Ltd., a spunbond nonwoven fabric made of continuous fibers which are core-sheath type composite fibers with a polyester resin core and a polyolefin resin sheath, and the accumulated continuous fibers are partially pressed together by heat embossing to form a unified nonwoven fabric, the basis weight of the nonwoven fabric is 50 g/ ^m² , the thickness is 0.34 mm, and the apparent density is 0.15 g/ ^cm³ ) was wrapped around this intermediate as a cover layer to cover the outer layer, and the beginning and end of the wrapping were heat-bonded with an iron heated to 150°C to obtain a water purification filter 7A. Similarly, using the prepared 248 mm long core, an intermediate was obtained in which a core with an outer diameter of 64.32 mm, an inner diameter of 30 mm, and a length of 248 mm was integrated with an activated carbon layer. A nonwoven fabric (Elves S0503, manufactured by Unitika Ltd.) was wrapped around it as a cover layer to cover the outer layer, and the beginning and end of the wrapping were heat-sealed with an iron heated to 150°C to obtain a water purification filter 7B. The volume of water purification filter 7A was 324 ^cm³ , and the volume of water purification filter 7B was 648 ^cm³ . Furthermore, the outer diameter of water purification filters 7A and 7B was 65 mm, the inner diameter was 30 mm, and the thickness was 17.5 mm. The nonwoven fabric core in water purification filters 7A and 7B had an inner diameter of 30.0 mm, an outer diameter of 37.0 mm, a thickness of 3.5 mm, and an apparent density of 0.30 g/cm³ ^. The mass of the activated carbon layer in water purification filter 7A was 98 g, and the mass of the activated carbon layer in water purification filter 7B was 196 g. The outer diameter of the activated carbon layer in water purification filters 7A and 7B was 64.32 mm, the thickness was 13.66 mm, and the apparent density was 0.37 g/cm³. The ratio of the thickness of the activated carbon layer to the thickness of water purification filters ^7A and 7B (thickness of activated carbon layer / thickness of water purification filter) was 0.78.

<Measurement methods for various physical properties, etc.>
(1) Amount of acidic functional groups in activated carbon and activated carbon layer: Measured as described above.

(2) Pressure loss A and pressure loss B of the water purification filter
Using water purification filters 1B, 2B, 3B, 4B, 5B, 6B, and 7B, pressure loss A and pressure loss B were measured as described above.

(3) Specific surface area of activated carbon and activated carbon layer: Measured as described above.

(4) Average particle size of activated carbon: Measured as described above.

(5) Amount of water filtered with combined residual chlorine Measured using water filters 1A, 2A, 3A, 4A, 5A, 6A and 7A as described above.

(6) Amount of water filtered with free residual chlorine Measured as described above using water filters 1A, 2A, 3A, 4A, 5A, 6A and 7A.

(7) Evaluation of the degree of carbon dust generation in the water purification filters Both ends of water purification filters 1B, 2B, 3B, 4B, 5B, 6B and 7B were sealed by bonding foamed polyethylene caps using hot melt or silicone sealant, and then filled into resin housings. Pure water was passed from the outside to the inside at a space velocity (SV) of 463/h, and after 5 minutes, 0.5 L of water that had passed through the water purification filters was collected and filtered using a white membrane filter (pore size 0.45 μm). The amount of carbon dust remaining on the membrane filter was evaluated according to the following criteria. △ or higher was considered acceptable.
○: No coal dust was visible to the naked eye.
△: A small amount of coal dust can be seen with the naked eye.
×: Coal dust is clearly visible to the naked eye.

The results are shown in Table 1.

As is clear from Table 1, the water purification filters of Examples 1 to 6 are water purification filters that include an activated carbon layer, and the specific surface area of the activated carbon layer is 1600 to 1900 ^m² /g, and the amount of acidic functional groups in the activated carbon layer, as measured by the following measurement method, is 0.8 to 3.0 mmol/g, thus making it possible to achieve both the filtration capacity for bound residual chlorine and free residual chlorine.

On the other hand, the water purification filter in Comparative Example 1 had an acidic functional group content of less than 0.8 mmol/g in the activated carbon layer, resulting in inferior combined residual chlorine filtration capacity.

Claims (4)

A water purification filter containing an activated carbon layer,
The specific surface area of the activated carbon layer, as measured by the following measurement method, is 1600 to 1900 ^m² /g.
A water purification filter wherein the amount of acidic functional groups in the activated carbon layer, as measured by the following measurement method, is 0.8 to 3.0 mmol/g,
The aforementioned activated carbon layer is
Activated carbon having an acidic functional group content of 2 mmol/g or more as measured by the following measurement method, and a specific surface area of 1800 to 2500 ^m² /g as measured by the following measurement method ,
Activated carbon having an acidic functional group content of 0.5 mmol/g or less as measured by the following measurement method, and a specific surface area of 1400 to 2000 ^m² /g as measured by the following measurement method ,
A water filter containing fibrillated binder fibers.
(Method for measuring the amount of acidic functional groups in the activated carbon layer )
A portion of the activated carbon layer is scraped off with a utility knife, and the scraped material is finely ground and classified until the particle size distribution is 2 mm or less. 1.0 g of this material is taken and used as the sample for measurement. The sample is added to 50 mL of a 0.1 mol/L sodium hydroxide aqueous solution as the alkaline solution, shaken for 30 minutes, and then allowed to stand at 25°C for 24 hours. After that, the solution is filtered using glass fiber filter paper, and 10 mL of the resulting filtrate is titrated with a 0.1 mol/L hydrochloric acid solution to determine the amount of acidic functional groups (mol/g).
(Method for measuring the amount of acidic functional groups in activated carbon)
Take 1.0 g of activated carbon and use it as the sample for measurement. Add the sample to 50 mL of 0.1 mol/L sodium hydroxide aqueous solution as the alkaline solution, shake for 30 minutes, and then let stand at 25°C for 24 hours. After that, filter using glass fiber filter paper, and 10 mL of the resulting filtrate is titrated with 0.1 mol/L hydrochloric acid solution to determine the amount of acidic functional groups (mol/g).
(Method for measuring the specific surface area of the activated carbon layer)
0.1 g of activated carbon is sampled, and using an automated gas adsorption measurement device, the activated carbon is cooled to 77.4 K (the boiling point of nitrogen), and nitrogen gas is introduced. The amount of nitrogen gas adsorbed, V [cc/g], is measured by volumetric method. At this time, the pressure P [hPa] of the introduced nitrogen gas is gradually increased, and the value obtained by dividing it by the saturated vapor pressure P0 [hPa] of the nitrogen gas is defined as the relative pressure P/P0. A nitrogen adsorption isotherm is created by plotting the amount of adsorption for each relative pressure. Based on the obtained nitrogen adsorption isotherm, the specific surface area is determined according to the BET method.
(Method for measuring the specific surface area of activated carbon)
0.1 g of activated carbon is taken, and using an automated gas adsorption measurement device, the activated carbon is cooled to 77.4 K (the boiling point of nitrogen), nitrogen gas is introduced, and the amount of nitrogen gas adsorbed, V [cc/g], is measured by the volumetric method. At this time, the pressure P [hPa] of the introduced nitrogen gas is gradually increased, and the value obtained by dividing by the saturated vapor pressure P0 [hPa] of the nitrogen gas is defined as the relative pressure P/P0. A nitrogen adsorption isotherm is created by plotting the amount of adsorption for each relative pressure. Based on the obtained nitrogen adsorption isotherm, the specific surface area is determined according to the BET method. A cylindrical core,
The activated carbon layer includes a cover layer laminated on the outer periphery of the activated carbon layer,
The activated carbon layer is stacked on the outer periphery of the core.
The ratio of the thickness of the activated carbon layer to the thickness of the water purification filter (thickness of the activated carbon layer / thickness of the water purification filter) is 0.7 to 0.9.
The water purification filter according to claim 1, wherein the pressure loss A measured by the following measurement method of the water purification filter is 0.010 to 0.040 MPa.
(Method for measuring pressure loss A)
The ends of the water purification filter are sealed by bonding foamed polyethylene caps using hot melt or silicone sealant, then filled into a resin housing, and pure water is passed through from the outside to the inside at a space velocity (SV) of 2781/h. After maintaining this flow rate for 10 minutes, the pressure loss X1 (MPa) is measured using a Bourdon tube pressure gauge. Similarly, the pressure loss X2 (MPa) is measured in a blank sample with the water purification filter removed. The value obtained by subtracting the pressure loss X2 from the pressure loss X1 is defined as the water flow pressure loss A (MPa) through the water purification filter. The combined residual chlorine filtration volume of the aforementioned water purification filter, as measured by the following measurement method, is 20 to 100 ^m³ .
The water purification filter according to claim 1 or 2, wherein the amount of free residual chlorine filtered water measured by the following measurement method of the water purification filter is 40 to 140 ^m³ .
(Method for measuring the amount of combined residual chlorine filtered water)
The ends of the water purification filter are sealed by bonding foamed polyethylene caps using hot melt or silicone sealant, and then filled into a stainless steel housing. Based on the provisions of Article 4 of the Water Supply Act of Japan, ammonium chloride and sodium hypochlorite are added to tap water that conforms to the water quality standards stipulated in the "Ministerial Ordinance Concerning Water Quality Standards (Ministry of Health, Labour and Welfare Ordinance No. 101 of May 30, 2003)," and the mixture is stirred to prepare raw water with a combined residual chlorine concentration of 0.5 mg/L. The adjusted raw water is passed from the outside to the inside of the water purification filter at a flow rate of 2.0 L/min so that the space velocity (SV) is 370/h. The concentration of combined residual chlorine is quantitatively measured using the DPD reagent spectrophotometric method before and after passing through the water purification filter, and the point at which the water concentration of combined residual chlorine in the effluent (filtered liquid) relative to the influent (adjusted raw water) becomes 20% or more is defined as the breakthrough point, and the total filtered water volume ( ^m³ ) up to the breakthrough point is determined.
(Method for measuring the amount of free residual chlorine filtered water)
The ends of the water purification filter are sealed by bonding foamed polyethylene caps using hot melt or silicone sealant, and then filled into a stainless steel housing. Based on the provisions of Article 4 of the Water Supply Act of Japan, the raw water is prepared by adding sodium hypochlorite to tap water that conforms to the water quality standards stipulated in the "Ministerial Ordinance Concerning Water Quality Standards (Ministry of Health, Labour and Welfare Ordinance No. 101 of May 30, 2003)" so that the free residual chlorine concentration is 2.0 ± 0.2 mg/L. The raw water is passed from the outside to the inside of the water purification filter so that the space velocity (SV) is 741/h. The concentration of free residual chlorine is quantitatively measured using the DPD reagent spectrophotometric method before and after passing through the water purification filter, and the breakthrough point is defined as the point at which the water concentration of free residual chlorine in the effluent (filtered liquid) relative to the influent (raw water) becomes 20% or more initially, and the total filtered water volume ( ^m³ ) up to the breakthrough point is determined. A cylindrical core,
An activated carbon layer is stacked on the outer circumference of the cylindrical core,
A water purification filter comprising a cover layer laminated on the outer periphery of the activated carbon layer,
The ratio of the thickness of the activated carbon layer to the thickness of the water purification filter (thickness of the activated carbon layer / thickness of the water purification filter) is 0.7 to 0.9.
The pressure loss A of the aforementioned water purification filter, as measured by the following measurement method, is 0.010 to 0.040 MPa.
The specific surface area of the activated carbon layer measured by the following measurement method is 1600 to 1900 m². ² /g,
A method for manufacturing a water purification filter, wherein the amount of acidic functional groups in the activated carbon layer, as measured by the following measurement method, is 0.8 to 3.0 mmol/g,
As raw materials constituting the activated carbon layer,
The amount of acidic functional groups in the activated carbon measured by the following method is 2 mmol/g or more, and the specific surface area of the activated carbon measured by the following method is 1800 to 2500 m². ² Activated carbon that is /g,
The amount of acidic functional groups in the activated carbon measured by the following method is 0.5 mmol/g or less, and the specific surface area of the activated carbon measured by the following method is 1400 to 2000 m². ² Activated carbon that is /g,
A method for manufacturing a water purification filter, comprising the steps of preparing fibrillated binder fibers.
(Method for measuring the amount of acidic functional groups in the activated carbon layer)
A portion of the activated carbon layer is scraped off with a utility knife, and the scraped material is finely ground and classified until the particle size distribution is 2 mm or less. 1.0 g of this material is taken and used as the sample for measurement. The sample is added to 50 mL of a 0.1 mol/L sodium hydroxide aqueous solution as the alkaline solution, shaken for 30 minutes, and then allowed to stand at 25°C for 24 hours. After that, the solution is filtered using glass fiber filter paper, and 10 mL of the resulting filtrate is titrated with a 0.1 mol/L hydrochloric acid solution to determine the amount of acidic functional groups (mol/g).
(Method for measuring the amount of acidic functional groups in activated carbon)
Take 1.0 g of activated carbon and use it as the sample for measurement. Add the sample to 50 mL of 0.1 mol/L sodium hydroxide aqueous solution as the alkaline solution, shake for 30 minutes, and then let stand at 25°C for 24 hours. After that, filter using glass fiber filter paper, and 10 mL of the resulting filtrate is titrated with 0.1 mol/L hydrochloric acid solution to determine the amount of acidic functional groups (mol/g).
(Method for measuring the specific surface area of the activated carbon layer)
0.1 g of activated carbon is sampled, and using an automated gas adsorption measurement device, the activated carbon is cooled to 77.4 K (the boiling point of nitrogen), and nitrogen gas is introduced. The amount of nitrogen gas adsorbed, V [cc/g], is measured by volumetric method. At this time, the pressure P [hPa] of the introduced nitrogen gas is gradually increased, and the value obtained by dividing it by the saturated vapor pressure P0 [hPa] of the nitrogen gas is defined as the relative pressure P/P0. A nitrogen adsorption isotherm is created by plotting the amount of adsorption for each relative pressure. Based on the obtained nitrogen adsorption isotherm, the specific surface area is determined according to the BET method.
(Method for measuring the specific surface area of activated carbon)
0.1 g of activated carbon is taken, and using an automated gas adsorption measurement device, the activated carbon is cooled to 77.4 K (the boiling point of nitrogen), nitrogen gas is introduced, and the amount of nitrogen gas adsorbed, V [cc/g], is measured by the volumetric method. At this time, the pressure P [hPa] of the introduced nitrogen gas is gradually increased, and the value obtained by dividing by the saturated vapor pressure P0 [hPa] of the nitrogen gas is defined as the relative pressure P/P0. A nitrogen adsorption isotherm is created by plotting the amount of adsorption for each relative pressure. Based on the obtained nitrogen adsorption isotherm, the specific surface area is determined according to the BET method.
(Method for measuring pressure loss A)
The ends of the water purification filter are sealed by bonding foamed polyethylene caps using hot melt or silicone sealant, then filled into a resin housing, and pure water is passed through from the outside to the inside at a space velocity (SV) of 2781/h. After maintaining this flow rate for 10 minutes, the pressure loss X1 (MPa) is measured using a Bourdon tube pressure gauge. Similarly, the pressure loss X2 (MPa) is measured in a blank sample with the water purification filter removed. The value obtained by subtracting the pressure loss X2 from the pressure loss X1 is defined as the water flow pressure loss A (MPa) through the water purification filter.