Carrier for fluid treatment

Abstract

This carrier for fluid treatment is an extruded foam body containing a polyolefin resin and a hydrophilizing agent. The carrier is cylindrical; contains 2 to 30 parts by mass of hydrophilizing agent with respect to 100 parts by mass of the polyolefin resin; and has a surface in a melt fracture state.

Description

Fluid treatment carrier

[0001] The present invention relates to a fluid treatment carrier used in fluid treatment.

[0002] Conventionally, foamed carriers made of foamed materials such as polyolefin resins have been widely used as microorganism immobilization carriers for water treatment such as BOD treatment, nitrification treatment, denitrification treatment, etc. However, because polyolefin resins are hydrophobic and foamed carriers contain many closed cells and semi-open cells, foamed carriers primarily composed of polyolefin resins have poor water wettability and do not have sufficient water treatment capabilities.

[0003] Therefore, in order to improve the water wettability of the foamed carrier, a hydrophilizing agent is added to the foamed carrier. For example, Patent Document 1 describes a thermoplastic resin foam whose main components are a hard thermoplastic resin and a grain husk, and which has a specific surface area of ​​5 to 50 m. ２ The document describes a microbial carrier for wastewater treatment characterized in that the minimum and maximum diameters of the carrier are 2 mm or more and 25 mm or less, respectively, at a dry weight of 100g / g, and the carrier has a hardness that prevents deformation by the force of fingers.

[0004] Furthermore, in order to improve the water permeability, water wettability, and water settling property of a foam, a hydrophilizing agent is incorporated into the foam, and the surface area of ​​the foam is increased by roughening the surface of the foam in a melt fracture state. For example, Patent Document 2 describes a fluid treatment carrier that contains 30 to 95 wt % of a polyolefin resin and 5 to 70 wt % of a cellulose powder hydrophilizing agent, and that is characterized in that the surface of the foam is in a melt fracture state.

[0005] JP 2004-358328 A JP 2009-66592 A

[0006] Patent Document 2 describes that the larger the surface area of ​​a foamed carrier, the greater the amount of microorganisms that adhere to the surface of the foamed carrier, resulting in improved water treatment capacity. Therefore, hollow foamed carriers have been considered. However, hollow foamed carriers are weaker and more susceptible to breakage than solid foamed carriers. Furthermore, as mentioned above, adding a hydrophilizing agent to the foamed carrier to improve settling properties makes the carrier brittle (resulting in reduced toughness), leading to problems such as breakage when the foamed carrier is stirred in the treated water. Patent Documents 1 and 2 do not address the problems of reduced strength and breakage associated with hollow foamed carriers. Furthermore, increasing the concentration of polyolefin resin in the foamed carrier to increase its strength reduces the hydrophilicity of the foamed carrier. Therefore, when the foamed carrier is introduced into the water to be treated, the foamed carrier floats to the water surface, delaying the attachment of microorganisms and lengthening the start-up period of the wastewater treatment facility. Furthermore, in order to improve the water treatment capacity of the foamed carrier, it is also necessary for the foamed carrier to flow sufficiently in water by stirring, aeration, etc. An object of the present invention is to provide a carrier for fluid treatment that has sufficient strength, excellent initial settling in water, excellent fluidity in water, and excellent microbial adhesion. Another object of the present invention is to provide a method for producing a carrier for fluid treatment that can produce a carrier for fluid treatment that has excellent molding stability, sufficient strength, excellent initial settling in water, excellent fluidity in water, and excellent microbial adhesion.

[0007] As a result of intensive research to solve the above problems, the present inventors have conceived the following invention and found that the above problems can be solved.

[0008] [1] A carrier for fluid treatment that is an extruded foam containing a polyolefin resin and a hydrophilizing agent, the carrier being cylindrical, the content of the hydrophilizing agent being 2 to 30 parts by mass per 100 parts by mass of the polyolefin resin, and the carrier having a melt-fractured surface. [2] The carrier for fluid treatment according to [1] above, wherein the hydrophilizing agent is a cellulose-based powder. [3] The carrier for fluid treatment according to [1] or [2] above, wherein the ratio C / t is 0.5 to 22, where t (mm) is the thickness of the extruded foam and C (parts by mass) is the content of the hydrophilizing agent per 100 parts by mass of the polyolefin resin. [4] The carrier for fluid treatment according to any of [1] to [3] above, wherein the carrier for fluid treatment is cylindrical with an outer diameter of 6 mm or more and a length of 6 mm or more. [5] The carrier for fluid treatment according to any one of [1] to [4] above, wherein the polyolefin resin is polyethylene, a mixture of polyethylene and polypropylene, a mixture of polyethylene and ethylene-vinyl acetate copolymer, a mixture of polyethylene, polypropylene and ethylene-vinyl acetate copolymer, a mixture of polyethylene, polypropylene and polystyrene, or a mixture of polyethylene, polypropylene, polystyrene and ethylene-vinyl acetate copolymer. [6] The carrier for fluid treatment according to any one of [1] to [5] above, wherein, when the aspect ratio of an extruded foam is the ratio of the length in the extrusion direction to the length in the direction perpendicular to the extrusion direction (length in the extrusion direction / length in the direction perpendicular to the extrusion direction), the aspect ratio is 0.5 or more. [7] The carrier for fluid treatment according to any one of [1] to [6] above, which is used for denitrification treatment to reduce nitrogen in water. [8] A method for producing a carrier for fluid treatment, comprising extrusion foaming a composition containing a polyolefin resin, a hydrophilizing agent, and a foaming agent, wherein the carrier for fluid treatment is cylindrical and has a surface in a melt-fractured state, and the content of the hydrophilizing agent in the composition is 2 to 30 parts by mass per 100 parts by mass of the polyolefin resin. [9] The method for producing a carrier for fluid treatment according to [8] above, wherein the carrier for fluid treatment is the carrier for fluid treatment according to any one of [1] to [7] above.

[0009] According to the present invention, it is possible to provide a carrier for fluid treatment that has sufficient strength, excellent initial settling in water, excellent fluidity in water, and excellent microbial adhesion. Also, according to the present invention, it is possible to provide a method for producing a carrier for fluid treatment that has excellent molding stability, sufficient strength, excellent initial settling in water, excellent fluidity in water, and excellent microbial adhesion.

[0010] The following is a description based on one example of an embodiment of the present invention. However, the embodiment shown below is an example for embodying the technical idea of ​​the present invention, and the present invention is not limited to the following description. In this specification, preferred embodiments are shown, but a combination of two or more of the individual preferred embodiments is also a preferred embodiment. For matters shown as numerical ranges, when there are several numerical ranges, the lower limit and upper limit can be selectively combined to form a preferred embodiment. Furthermore, when a numerical range is described as "XX to YY," it means "XX or more and YY or less."

[0011] [Fluid treatment carrier (extruded foam)] The fluid treatment carrier according to this embodiment is a cylindrical extruded foam containing a polyolefin resin and a hydrophilizing agent, the hydrophilizing agent being present in an amount of 2 to 30 parts by mass relative to 100 parts by mass of the polyolefin resin, and having a melt-fractured surface. The fluid treatment carrier according to this embodiment has sufficient strength, excellent initial settling in water, excellent underwater fluidity, and excellent microbial adhesion.

[0012] Here, melt fracture refers to the phenomenon in which irregularities occur on the surface of a molded product during plastic molding (a state in which the surface is not smooth). For example, when extruding a plastic material, if the internal pressure of the extruder becomes extremely high, irregular irregularities occur on the surface of the molded product, resulting in melt fracture.

[0013] <Polyolefin Resin> Preferred polyolefin resins include polyethylene (hereinafter also referred to as "PE"), polypropylene (hereinafter also referred to as "PP"), ethylene-vinyl acetate copolymer (hereinafter also referred to as "EVA"), polystyrene (hereinafter also referred to as "PS"), and the like. These resins may be used alone or in appropriate combinations. Furthermore, other thermoplastic resin components may be added. Examples of other thermoplastic resin components include polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyvinylidene chloride (PVDC), polycarbonate (PC), polyurethane (PU), polyamide (PA), polyacetal (POM), polylactic acid (PLA), polymethyl methacrylate (PMMA), and ABS resin (ABS). The content of the olefin resin in the total amount of resin is preferably 60 to 100% by mass, more preferably 80 to 100% by mass, and even more preferably 90 to 100% by mass. Polyethylene is particularly preferred as the resin, but as long as it falls within the above MFI range, it may also be a mixture of PE and PP, a mixture of PE and EVA, a mixture of PE, PP and EVA, a mixture of PE, PP and PS, a mixture of PE, PP, EVA and PS, or a mixture of these with other thermoplastic resins. Specifically, the composition ratio (weight ratio) of the other thermoplastic resins including PE, PP, EVA, and PS, where the total resin is 100, is preferably [PE:PP:EVA:other thermoplastic resins including PS] = 100-60:40-0:20-0:15-0. These resins may also be recycled resins.

[0014] The content of the polyolefin resin in 100% by mass of the total amount of the fluid treatment carrier is preferably 60% by mass or more from the viewpoint of the toughness of the carrier. Furthermore, the content of the polyolefin resin in 100% by mass of the total amount of the fluid treatment carrier is preferably 99% by mass or less from the viewpoint of the toughness of the carrier. From this viewpoint, the content of the polyolefin resin in 100% by mass of the total amount of the fluid treatment carrier is preferably 60 to 99% by mass, more preferably 60 to 90% by mass, even more preferably 60 to 85% by mass, and may be 60 to 80% by mass or may be 65 to 85% by mass.

[0015] <HydrophiliZing Agent> The hydrophiliZing agent is preferably a cellulose-based poWder. Examples of cellulose-based poWders include Wood ?uorose, cellulose poWder, grain husks, and hemp cellulose poWder. Examples include sawdust, Avicel, Arbocel, paper poWder, cellulose beads, microcrystalline cellulose, and micro?brillated cellulose, With wood ?uorose being particularly preferred. Any of these may be used alone, or tWo or more types may be mixed in an appropriate ratio. The ?uid treatment carrier according to this embodiment may or may not contain grain husks, but preferably does not contain grain husks.

[0016] The content of the hydrophilizing agent is 2 to 30 parts by mass relative to 100 parts by mass of the polyolefin-based resin. When the content is 2 parts by mass or more, the initial settling property is improved. When the content is 30 parts by mass or less, the strength is increased and breakage is prevented. From this viewpoint, the content of the hydrophilizing agent may be 2.8 to 30 parts by mass, or may be 5 to 30 parts by mass, relative to 100 parts by mass of the polyolefin-based resin. From the viewpoint of brittleness and stirring fluidity, the content may be 2 to 15 parts by mass.

[0017] <Foaming Agent> The carrier for fluid treatment is preferably an extruded foam formed by foaming with a foaming agent during extrusion molding. Examples of the foaming agent include sodium bicarbonate (baking soda) and azodicarbonamide (ADCA). The foaming agent is not limited to these, and examples include chemical foaming agents and physical foaming agents.

[0018] Examples of chemical foaming agents include azo compounds such as barium azodicarboxylate (Ba / AC), nitroso compounds such as N,N-dinitrosopentamethylenetetramine (DPT), hydrazine derivatives such as 4,4'-oxybis(benzenesulfonylhydrazide) (OBSH), semicarbazide compounds, azide compounds, triazole compounds, isocyanate compounds, bicarbonates such as sodium bicarbonate (baking soda), carbonates, nitrites, hydrides, mixtures of sodium bicarbonate and acids (e.g., sodium bicarbonate and citric acid), mixtures of hydrogen peroxide and enzymes, and mixtures of zinc powder and acids. Examples of physical blowing agents include aliphatic hydrocarbons (e.g., butane, pentane, hexane, etc.), chlorinated hydrocarbons (e.g., dichloroethane, dichloromethane, etc.), fluorochlorohydrocarbons (e.g., trichloromonofluoromethane, dichlorodifluoromethane, dichloromonofluoromethane, dichlorotetrafluoroethane, etc.), chlorofluorocarbon alternatives, air, carbon dioxide gas, nitrogen gas, water, etc. Among these blowing agents, sodium bicarbonate (baking soda) is particularly preferred because it has a low decomposition temperature and is inexpensive.

[0019] Furthermore, so-called self-supporting foaming agents (also referred to as self-supporting foaming agents, microspheres, or thermally expandable microcapsules) can be used as the foaming agent. Since this self-supporting foaming agent itself becomes hollow spherical particles with an outer wall upon foaming, even if the resin composition is extruded and foamed into a gas phase (e.g., air) instead of being extruded and foamed into water, the hollow portion of the foam remains intact, resulting in a carrier for fluid treatment with a desired expansion ratio. Examples of self-supporting foaming agents include those using, for example, vinylidene chloride-acrylonitrile copolymer or acrylonitrile-methacrylonitrile copolymer as the outer wall polymer, and using, for example, isobutane or isopentane as the volatile liquid contained therein. Specific examples include Expancel (Nippon Philite Co., Ltd.) and EPD-03 (Eiwa Chemical Industry Co., Ltd.). In the present invention, the presence of a hydrophilizing agent for the cellulose-based powder allows fluids such as water to penetrate the foam produced by the self-supporting foaming agent, resulting in a carrier with excellent water permeability.

[0020] The amount of foaming agent per 100 parts by mass of polyolefin resin is preferably 0.1 parts by mass or more from the viewpoint of surface roughening. Furthermore, the amount of foaming agent per 100 parts by mass of polyolefin resin is preferably 10 parts by mass or less from the viewpoint of molding stability. From this viewpoint, the amount of foaming agent per 100 parts by mass of polyolefin resin is preferably 0.1 to 10 parts by mass, more preferably 0.2 to 10 parts by mass, even more preferably 0.2 to 5 parts by mass, and even more preferably 0.5 to 3 parts by mass. <Inorganic Powder> The fluid treatment carrier according to this embodiment may or may not contain an inorganic powder in addition to the polyolefin resin and hydrophilizing agent. However, it is preferable to include an inorganic powder from the viewpoint of functioning as a nucleus material during foaming and adjusting the specific gravity. Examples of inorganic powders include barium sulfate, calcium carbonate, zeolite, talc, titanium oxide, potassium titanate, and aluminum hydroxide. From the viewpoint of functioning as a nucleus material during foaming and adjusting the specific gravity, it is particularly preferable to use barium sulfate. These inorganic powders may be contained alone or in combination of two or more kinds. The purpose of containing inorganic powder is to act as a nucleus material during foaming and to adjust the specific gravity, but it also serves the purpose of reducing the amounts of polyolefin resin and hydrophilizing agent used, thereby reducing production costs.

[0021] From this viewpoint, the content of the inorganic powder relative to 100 parts by mass of the polyolefin resin is preferably 1 to 50 parts by mass, and more preferably 10 to 50 parts by mass.

[0022] <Other Components> The fluid treatment carrier may contain, or may not contain, components other than the above-mentioned components, as long as the effects of the present invention are not impaired. The content of other components in 100% by mass of the total amount of the fluid treatment carrier is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 1% by mass or less, and may even be 0% by mass.

[0023] <Contents of Essential Components, etc.> The total content of the olefin resin and hydrophilizing agent in 100% by mass of the total amount of the fluid treatment carrier is preferably 40 to 100% by mass, more preferably 50 to 95% by mass, even more preferably 60 to 95% by mass, and still more preferably 65 to 95% by mass. When the fluid treatment carrier contains an inorganic powder, the total content of the olefin resin, hydrophilizing agent, blowing agent, and inorganic powder in 100% by mass of the total amount of the fluid treatment carrier is preferably 40 to 100% by mass, more preferably 60 to 100% by mass, even more preferably 80 to 100% by mass, and still more preferably 90 to 100% by mass.

[0024] (Ratio C / t) When the thickness of the extruded foam is t (mm) and the content of the hydrophilizing agent relative to 100 parts by mass of the polyolefin resin is C (parts by mass), the ratio C / t is preferably 0.5 to 22. When the ratio C / t is 0.5 or more, the amount of hydrophilizing agent exposed on the surface of the fluid treatment carrier is increased, which facilitates water permeation into the interior of the fluid treatment carrier through the hydrophilizing agent, improving initial settling properties. Furthermore, when the ratio C / t is 22 or less, a decrease in the strength of the fluid treatment carrier and breakage can be prevented. From these viewpoints, the ratio C / t is more preferably 0.5 to 20, even more preferably 0.5 to 15, and may be 5 to 15 or even 0.5 to 8.

[0025] In the present embodiment, the thickness t (mm) of the extruded foam can be measured using a vernier caliper. Specifically, the thickness is measured at two to five locations, preferably three locations, using the vernier caliper, and the average of these measurements is taken as the thickness (average value). Specifically, it can be calculated using the method described in the examples.

[0026] (Dimensions) The fluid treatment carrier is preferably cylindrical with an outer diameter of 6 mm or more and a height of 6 mm or more. This prevents the fluid treatment carrier from being discharged outside the system during water treatment. Furthermore, the fluid treatment carrier is preferably cylindrical with an outer diameter of 30 mm or less and a length of 30 mm or less. This reduces the voids in the carrier, improving various performances, and the small dimensions improve fluidity. From this perspective, the outer diameter of the fluid treatment carrier is preferably 6 to 30 mm, more preferably 8 to 25 mm, even more preferably 10 to 20 mm, and even more preferably 12 to 18 mm. From this perspective, the length of the fluid treatment carrier is preferably 6 to 30 mm, more preferably 8 to 25 mm, and even more preferably 10 to 20 mm. The thickness of the fluid treatment carrier is preferably 0.5 to 5 mm, more preferably 1 to 4 mm, even more preferably 1.5 to 3 mm, and still more preferably 1.5 to 2.5 mm, from the viewpoint of providing a fluid treatment carrier that has sufficient strength, excellent initial settling in water, excellent fluidity in water, and excellent microbial adhesion properties.

[0027] (Strength (applied load at 2 mm displacement)) From the viewpoint of preventing breakage of the extruded foam, the applied load in the orthogonal direction at 2 mm displacement of the extruded foam is preferably 0.5 kg or more, more preferably 1.0 kg or more, even more preferably 1.5 kg or more, still more preferably 2.0 kg or more, and still more preferably 3.0 kg or more.

[0028] (Aspect Ratio) Extruded foams are obtained by cutting a foam extruded through a die outlet hole in a direction perpendicular to the extrusion direction. Therefore, while the outer and inner peripheral surfaces of the extruded foam can be melt fractured by adjusting the die temperature, extrusion speed, etc., it is difficult to melt fracture the cut surfaces (cut surfaces). Therefore, by increasing the ratio of the length in the extrusion direction to the length in the direction perpendicular to the extrusion direction (aspect ratio = length in the extrusion direction / length in the direction perpendicular to the extrusion direction) of the extruded foam, the proportion of the outer and inner peripheral surfaces that can be melt fractured relative to the total surface area of ​​the extruded foam can be increased, thereby increasing the specific surface area of ​​the extruded foam, thereby allowing a large amount of microorganisms to adhere and improving water treatment performance. From this perspective, the ratio of the length in the extrusion direction to the length in the direction perpendicular to the extrusion direction (aspect ratio) of the extruded foam is preferably 0.5 or more. Furthermore, from the perspective of making the extruded foam less likely to break, the aspect ratio is preferably 5.0 or less. From these viewpoints, the aspect ratio is preferably 0.5 to 5.0, more preferably 0.6 to 3.0, even more preferably 0.8 to 2.0, and even more preferably 0.9 to 1.5. Here, "the length of the extruded foam in the direction perpendicular to the extrusion direction" means the maximum Feret diameter of the extruded foam in the direction perpendicular to the extrusion direction. The maximum Feret diameter means the maximum distance between parallel tangents to opposing contour lines of the object.

[0029] (Ratio (B / A)) When the extruded foam is assumed to have a smooth surface, the ratio (B / A) of the specific surface area B of the extruded foam to the specific surface area A of the hypothetical extruded foam is 2.5 or more. This increases the proportion of the melt fracture area in the total surface area of ​​the extruded foam, thereby increasing the amount of attached microorganisms and improving water treatment capacity. In this embodiment, having a melt fractured surface means that the ratio (B / A) is 2.5 or more. Here, the specific surface area A of the hypothetical extruded foam can be calculated as follows, where 2R is the outer diameter, 2r is the inner diameter, and h is the height. Specific surface area A=2πRh+2πrh+2π(R ２-r ２ Furthermore, the ratio (B / A) is preferably 20 or less. In other words, in the extruded foam, the cut surfaces (both longitudinal end surfaces) are non-melt fractured, while the outer and inner peripheral surfaces are melt fractured. In this case, as the aspect ratio (length in the extrusion direction / length perpendicular to the extrusion direction) of the extruded foam increases, the proportion of the total surface area (outer and inner peripheral surfaces) accounted for by the outer and inner peripheral surfaces increases, and thus the ratio (B / A) increases. However, as the ratio (B / A) increases, and thus the aspect ratio (length in the extrusion direction / length perpendicular to the extrusion direction) increases, the extruded foam becomes more fragile. Therefore, from the viewpoint of making the extruded foam less fragile, the ratio (B / A) is preferably 20 or less. From these viewpoints, the ratio (B / A) is preferably 2.5 to 20, more preferably 3 to 20, even more preferably 3.5 to 15, even more preferably 4 to 10, and even more preferably 4.5 to 10.

[0030] (Ratio (particle size of hydrophilizing agent / thickness)) The ratio (particle size of hydrophilizing agent / thickness) obtained by dividing the particle size (μm) of the hydrophilizing agent by the thickness (mm) of the extruded foam is preferably 10 to 100. Within this range, a carrier for fluid treatment can be obtained that has sufficient strength, excellent initial settling in water, excellent fluidity in water, and excellent microbial adhesion. From this perspective, the ratio (particle size of hydrophilizing agent / thickness) is more preferably 20 to 80, even more preferably 30 to 70, and even more preferably 40 to 60.

[0031] (Apparent Specific Gravity of Extruded Foam) The apparent specific gravity of the extruded foam is preferably 0.1 to 0.4. Within this range, a carrier for fluid treatment can be obtained that has sufficient strength, excellent initial settling in water, excellent fluidity in water, and excellent microbial adhesion. From this viewpoint, the apparent specific gravity of the extruded foam is more preferably 0.1 to 0.3, even more preferably 0.15 to 0.3, and even more preferably 0.2 to 0.3.

[0032] <Uses> The fluid treatment carrier is preferably used for water treatment such as BOD treatment, nitrification treatment, and denitrification treatment, and more preferably for denitrification treatment to reduce nitrogen in water.

[0033] [Method for Manufacturing a Fluid Treatment Carrier] Next, a method for manufacturing a fluid treatment carrier according to this embodiment will be described. The raw material components, such as a polyolefin resin, a hydrophilizing agent, and an inorganic powder, and the foaming agent used in this manufacturing method are the same as those described for the fluid treatment carrier described above. The method for manufacturing a fluid treatment carrier according to this embodiment is a method for manufacturing a fluid treatment carrier by extrusion foaming a composition containing a polyolefin resin, a hydrophilizing agent, and a foaming agent. The fluid treatment carrier is cylindrical and has a melt-fractured surface, and the content of the hydrophilizing agent in the composition is 2 to 30 parts by mass per 100 parts by mass of the polyolefin resin. This method for manufacturing a fluid treatment carrier according to this embodiment can provide a method for manufacturing a fluid treatment carrier that has excellent molding stability, sufficient strength, excellent initial settling in water, and excellent underwater fluidity. The fluid treatment carrier is preferably the fluid treatment carrier described above.

[0034] Next, the method for producing a carrier for fluid treatment according to this embodiment will be described in more detail. Examples of methods for producing a carrier for fluid treatment include the following production methods A and B. Production method A: A primary mixture obtained by kneading and pulverizing raw material components excluding the blowing agent using a melt mixer is charged into a single-screw or twin-screw extruder and kneaded with the blowing agent, followed by extrusion foaming into water and cutting with a pelletizer to obtain a foam. Production method B: A primary mixture obtained by kneading and pelletizing raw material components excluding the blowing agent using a twin-screw extruder is charged into a single-screw or twin-screw extruder and kneaded with the blowing agent, followed by extrusion foaming into a gas phase and cutting with a pelletizer such as a hot-cut pelletizer to obtain a foam.

[0035] Here, underwater cutting refers to the process of rotating the cutter blade of the underwater pelletizer in contact with the front surface of the die to cut the extruded resin composition underwater (JIS B8650:2006). In Production Method A and Production Method B, when obtaining a primary mixture, the raw material components, polyolefin resins, are kneaded at a temperature equal to or higher than the melting point. The foaming agent used may be a chemical foaming agent, a physical foaming agent, a self-supporting foaming agent, or a combination thereof. Among these, sodium bicarbonate (baking soda), which has a low decomposition temperature and is inexpensive, is preferably used.

[0036] In the above-described production methods A and B, when a self-supporting foaming agent is used as all or part of the foaming agent, the resin composition can be extruded into a gas phase without being extruded into water, and then cut to obtain a foam. This method of cutting the extruded resin composition in a gas phase, such as in air, by rotating a cutter blade in contact with the front surface of a die is called hot cutting (JIS B8650:2006).

[0037] Here, an example of a twin-screw extruder is an extruder in which two identical screws are arranged in parallel so that their threads and grooves intermesh with each other. The screws may rotate in the same direction or in opposite directions, but in either case, a strong shear force acts on the molten material at the intermeshing portion of the screw grooves, which has the advantage of increasing the kneading effect and also increasing the extrusion pressure compared to a single-screw extruder. In addition to twin-screw extruders, multi-screw extruders with three or more screws can also be used if cost is acceptable.

[0038] The raw material components excluding the blowing agent are a polyolefin resin and a hydrophilizing agent (hereinafter referred to as raw material [1]), or a polyolefin resin, a hydrophilizing agent, and an inorganic powder (hereinafter referred to as raw material [2]). The polyolefin resin, hydrophilizing agent, and inorganic powder described above can be used as raw material [1] and raw material [2]. The blowing agent can also be one described above.

[0039] The blending ratio of each raw material component is the ratio of each component in the above-mentioned carrier for fluid treatment. That is, the blending ratio of each raw material component is the composition ratio of the above-mentioned carrier for fluid treatment.

[0040] Another example of a method for producing a carrier for fluid treatment is Production Method C described below. Production Method C: The raw materials and the foaming agent are fed into a twin-screw extruder at a temperature equal to or higher than the melting point of the polyolefin resin, kneaded, extruded directly into a gas phase to cause foaming, cooled in water, and then cut with a rotary blade to obtain a foam (strand cut method). In this case, a multi-screw extruder having three or more screws can be used in addition to a twin-screw extruder.

[0041] In the above-described Production Methods A, B, and C, extruded foams are obtained by extrusion foaming through the nozzles of the extruders. In this case, the temperature of the single-screw extruder or twin-screw extruder is preferably controlled to a temperature at least 10°C higher than the decomposition temperature of the foaming component contained in the foaming agent and not higher than 120°C higher than the melting temperature of the polyolefin resin. The nozzle temperature is controlled within this range to induce melt fracture on the surface of the foam produced, thereby obtaining a foam of the present invention in which the hydrophilizing agent is exposed or protrudes from the surface of the foam. Specifically, when polyethylene (melting temperature: 120°C) is used as the polyolefin resin and sodium bicarbonate (decomposition temperature: 150°C) is used as the foaming agent, the extruder temperature is preferably controlled to a temperature at least 160°C and not higher than 240°C.

[0042] The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to these.

[0043] The compounds used in the examples and comparative examples are as follows: Polyolefin resin (60% by mass of Akita Ecoplush Co., Ltd.'s product name "AE-EZ", 40% by mass of Taisei Resin Co., Ltd.'s product name "G-30") Hydrophilizing agent (wood flour, manufactured by Obayashi Kogyo Co., Ltd., 100 mesh pass product) Foaming agent (baking soda, manufactured by Tosoh Corporation, product name "sodium bicarbonate") Inorganic powder (barium sulfate, manufactured by Sakai Chemical Industry Co., Ltd., product name "elutriated barium sulfate")

[0044] The physical properties of the extruded foams in the examples and comparative examples were measured by the following methods. (1) Apparent Specific Gravity: 1000 mL of the extruded foam was weighed into a 1000 mL measuring cylinder with an apparent volume, and the weight (g) was divided by the apparent volume (1000 mL) to determine the apparent specific gravity of the extruded foam (unit: g / mL). (2) Dimensions of the Extruded Foam: Each dimension of the extruded foam (outer diameter, inner diameter, thickness, length (height)) was measured with a vernier caliper. Specifically, the outer diameter was measured at three locations using a vernier caliper, and the average of these measurements was taken as the outer diameter (average value). Other dimensions were also measured at three locations using a vernier caliper, and the average of these measurements was taken as the dimension (average value). (3) Specific Surface Area B of the Extruded Foam: The specific surface area B of the extruded foam was measured using an X-ray analyzer "inspeXio SMX-225CT FPD HR Plus" manufactured by Shimadzu Corporation. (4) Specific Surface Area A of Hypothetical Extruded Foam The specific surface area A of the hypothetical extruded foam was calculated as follows, where the outer diameter is 2R, the inner diameter is 2r, and the height is h. Specific surface area A=2πRh+2πrh+2π(R ２ -r ２ )

[0045] [Examples 1 to 4 and Comparative Examples 1 to 4] The raw materials shown in Table 1 were blended in the proportions shown in Table 1 and kneaded under the melt stirring conditions (extrusion conditions) shown in Table 1 to obtain kneaded mixtures. The kneaded mixtures were fed into an extrusion molding machine, extrusion foamed under the extrusion foaming conditions shown in Table 1, and cut with a pelletizer to obtain extruded foams. The physical properties of the obtained extruded foams were measured by the methods described above. The results are shown in Table 1.

[0046] [Evaluation] (1) Strength of extruded foam (load applied at 2 mm displacement) The extruded foam was pressurized with a pressure plate using a Shimadzu Autograph AG-20kNI (Shimadzu Corporation). The pressure was applied at a rate of 5.0 mm / min. The load applied in the orthogonal direction at 2 mm displacement of the extruded foam was measured and used as an index for evaluating the strength of the extruded foam.

[0047] (2) Molding Stability of Extruded Foam When the kneaded material described below was extrusion foamed, the extruded foam was observed at the time of being extruded from the die and rated as follows: A: The shape of the extruded foam was stable. B: The shape of the extruded foam was distorted, but production was possible. C: Cracks and chips occurred in the extruded foam, causing problems in production.

[0048] (3) Initial Settling Property of Extruded Foam (Settling Property in Water) After tap water (20°C) was poured into a 1000 mL metal container and brought to a boil, 10 extruded foams were placed in the container and covered with a metal mesh to prevent them from floating up. After boiling the extruded foams for 5 minutes, the extruded foams alone were transferred to a 500 mL plastic container containing 450 mL of tap water (20°C). The container was left to stand until the next day, and the number of extruded foams that had sunk to the bottom of the plastic container was counted and evaluated as follows: A: 7 to 10 pieces B: 3 to 6 pieces C: 0 to 2 pieces

[0049] (4) Melt fracture state The ratio (B / A) of the specific surface area B of the extruded foam to the specific surface area A of the hypothetical extruded foam was calculated and evaluated as follows: A: Melt fracture state (ratio (B / A) is 2.5 or more). B: Not melt fracture state (ratio (B / A) is less than 2.5).

[0050] (5) Fluidity of Extruded Foam in Water (Agitated Fluidity) 2.0 L of tap water (20°C) and 200 mL of extruded foam in bulk density were placed in a plastic test tank with a volume of 2.1 L. The stirring blades of the stirrer were positioned 70 mm from the bottom of the test tank, and stirring was started at 50 rpm. After 1 minute, the extruded foam in the test tank was checked for flow and evaluated as follows: A: Flowed throughout the entire test tank. B: Flowed from the middle to lower part of the test tank. C: Stagnated at the bottom of the test tank and did not move.

[0051] (6) Water Treatment Performance of Extruded Foam (Microbial Adhesion) 2 L of tap water, Hi-Polka CR (Shikoku Kasei) as seed sludge, and 0.2 L of extruded foam were placed in a 2 L plastic tank (test tank) for test water, and a nitrogen source (sodium nitrate; nitrate nitrogen (NO ３While adding 100 mg / L (i.e., 200 mg per 2 L of tap water) of sodium nitrate, the mixture was stirred with a propeller stirrer at 25°C for 3 days to allow the microorganisms to become accustomed to the extruded foam. A test raw water containing mainly sodium nitrate was passed through the tank as simulated wastewater, and the treated water was appropriately sampled from the tank to measure the residual NO. ３ The NO concentration (N1) in the test raw water was measured. ３ The -N concentration (NO) of the test raw water was also measured. ３ -NO relative to N concentration (NO) ３ The ratio of the decrease in the N concentration (N0-N1) is NO ３ -N removal rate [%] was calculated. ３ -N removal rate [%] = (NO - N) / NO x 100 ３ - The nitrogen concentration and raw water flow rate were adjusted to place the test tank under a high nitrogen volume load condition (1.0 kg / m ３ The treatment effect was confirmed by changing the pressure to 1.0 kg / m ３ In d), the amount of sludge adhered per extruded foam was measured and rated as follows: A: 20 mg / piece or more B: 15 mg / piece or more and less than 20 mg / piece C: Less than 15 mg / piece

[0052]

[0053] The fluid treatment carriers (extruded foams) of Examples 1 to 4 have sufficient strength (load capacity at 2 mm displacement), high molding stability, excellent initial settling in water, excellent underwater fluidity, and excellent water treatment performance (microbial adhesion). Furthermore, Example 4 contains a more appropriate amount of specific gravity adjuster than Example 1, resulting in improved water settling properties and strength. On the other hand, the fluid treatment carrier (extruded foam) of Comparative Example 1 does not contain a hydrophilizing agent, resulting in poor initial settling in water and poor water treatment performance (microbial adhesion). The fluid treatment carrier (extruded foam) of Comparative Example 2 contains too much hydrophilizing agent, resulting in insufficient strength (short breaking distance), poor molding stability, and poor stirring fluidity in water due to its high specific gravity. The fluid treatment carrier (extruded foam) of Comparative Example 3 does not have a melt-fractured surface, resulting in poor microbial adhesion to the carrier surface. The carrier for fluid treatment (extruded foam) of Comparative Example 4 was made of a resin with a diameter of 15 mm and no hollow core, and therefore extrusion was difficult to carry out and molding was not possible.

Claims

1. A carrier for fluid treatment that is an extruded foam containing a polyolefin resin and a hydrophilizing agent, the carrier being cylindrical, the content of the hydrophilizing agent being 2 to 30 parts by mass per 100 parts by mass of the polyolefin resin, and the carrier having a surface in a melt fracture state.

2. The carrier for fluid treatment according to claim 1, wherein the hydrophilizing agent is a cellulose-based powder.

3. The carrier for fluid treatment according to claim 1 or 2, wherein the ratio C / t is 0.5 to 22, where t (mm) is the thickness of the extruded foam, and C (parts by mass) is the content of the hydrophilizing agent relative to 100 parts by mass of the polyolefin resin.

4. A fluid treatment carrier according to claim 1 or 2, wherein the fluid treatment carrier is cylindrical with an outer diameter of 6 mm or more and a length of 6 mm or more.

5. The carrier for fluid treatment according to claim 1 or 2, wherein the polyolefin resin is polyethylene, a mixture of polyethylene and polypropylene, a mixture of polyethylene and ethylene-vinyl acetate copolymer, a mixture of polyethylene, polypropylene and ethylene-vinyl acetate copolymer, a mixture of polyethylene, polypropylene and polystyrene, or a mixture of polyethylene, polypropylene, polystyrene and ethylene-vinyl acetate copolymer.

6. A carrier for fluid treatment according to claim 1 or 2, wherein the aspect ratio of the extruded foam is the ratio of the length in the extrusion direction to the length in the direction perpendicular to the extrusion direction (length in the extrusion direction / length in the direction perpendicular to the extrusion direction), and the aspect ratio is 0.5 or more.

7. The carrier for fluid treatment according to claim 1 or 2, which is used for denitrification treatment to reduce nitrogen in water.

8. A method for producing a carrier for fluid treatment, which comprises extrusion foaming a composition containing a polyolefin resin, a hydrophilizing agent, and a foaming agent, wherein the carrier for fluid treatment is cylindrical and has a surface in a melt fracture state, and the content of the hydrophilizing agent in the composition is 2 to 30 parts by mass per 100 parts by mass of the polyolefin resin.

9. A method for producing a carrier for fluid treatment according to claim 8, wherein the carrier for fluid treatment is the carrier for fluid treatment according to claim 1 or 2.

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