Patent Application
20180140983
The present invention relates to a structure of a pleated filter that is mainly used for filtration of a liquid. In particular, the present invention relates to a pleated filter used in a treatment system of ballast water stored in ships and used for filtration of a large amount of water, and a device using the same.
A wide variety of filters are used for the purpose of separating and removing a solid, which is a contaminant, from a gas or a liquid. Pleated filters whose filtration areas are increased by folding a filter so as to have a pleated shape are also used mainly in applications involving a gas, for example, in an air purification system. PTL 1 discloses an example of the use of a cylindrically shaped pleated filter as a filter device for removing sludge from a cutting fluid of a machine tool. Regarding this device, it is described that a filter device having a high cleaning effect of a filter can be provided by ejecting a liquid toward an outer surface of a cylindrical filter while rotating the filter.
In recent years, treatment of ballast water carried in ships has become an issue. Ballast water is seawater carried in a ship to provide safe voyage even when the ship is empty of cargo. Various methods for removing, killing, or inactivating microbes by purifying ballast water have been developed. Methods using filtration for the purpose of removing relatively large microbes have also been developed. For example, PTL 2 describes a ballast water treatment device using a filter membrane, the device being filed by the applicant of the present invention. PTL 3, which also relates to an invention filed by the applicant of the present invention, describes that splitting or the like of valleys of a pleated filter may cause a problem and discloses means for reinforcing the pleated filter.
PTL 1: Japanese Unexamined Patent Application Publication No. 2008-93783
PTL 2: Japanese Patent No. 4835785
PTL 3: Japanese Unexamined Patent Application Publication No. 2012-245428
In the case of seawater desalination, the use of brackish water/seawater for purposes such as ballast water, or the treatment of water such as sewage water, human sewage, or industrial wastewater, a preliminary filtration treatment for removing foreign matter, contaminants, and microbes in the water is necessary. The inventors of the present invention have been examining the application of a pleated filter to such filtration. In this case, it is necessary to filter a large amount of water in the shortest possible time. However, in general, the operation at a large scale/high flow rate causes a technical problem in that a decrease in the amount of treatment or the filtration function due to clogging at an early stage tends to occur.
The device disclosed in PTL 2 is a filtering device in which a cylindrical filter is installed in a tubular case and a liquid that is allowed to flow from the outside to the inside of the cylindrical filter is collected as a filtrate. A liquid to be filtered is ejected from a nozzle provided on a side face of the tubular case onto a part of a filtering surface of the filter. Filtered products deposited on a surface of the filter are washed to recover the permeation flux, and the filtered products that have been washed out are discharged from a filtration front chamber. With this structure, a stable filtration state is continuously maintained. An important factor for stably maintaining continuous filtration of such a system is the cleaning effect obtained by ejecting the unfiltered liquid onto the filtering surface of the filter. In order to efficiently and effectively clean the entire filter by changing a cleaning region of the filter with time, the cylindrical filter is rotated during filtration by driving a motor or the like, thus continuously and periodically changing the position to which the ejection of the unfiltered liquid from the ejection nozzle is applied to the filtering surface of the filter. In order to reliably perform this rotation cleaning and to stably maintain a high filtration flow rate, the ejection of the unfiltered liquid from the nozzle needs to be maintained at a certain high flow rate level or more. According to the studies conducted by the inventors, it was found that, as a result of being subjected to ejection of the unfiltered liquid at such a high flow rate, the cylindrical filter degrades with time and a failure occurs, and part of the unfiltered liquid may be mixed directly with the filtrate without passing through the filter.
As described in PTL 3, the applicant of the present invention has been focusing that a failure occurs in a valley. The applicant of the present invention assumes that the failure occurs due to the following mechanism. Specifically, force is applied to a valley in a direction in which a fold in the valley opens up, and a tensile stress is concentrated at a filter base. In view of this, the applicant of the present invent has examined means for reinforcing valleys. However, it is found that even if the valleys are reinforced, a failure may occur during a long-time operation.
Accordingly, an object of the present invention is to provide a pleated filter and a pleated filter cartridge whose degradation and failure due to use are prevented and which can be stably used for a long period of time, a ballast water treatment device functioning as a filtering device using the pleated filter or the pleated filter cartridge, and a ballast water treatment method using the same.
As a result of intensive studies on degradation of a filter, the inventors of the present invention confirmed a phenomenon in which a failure occurs in a folded portion corresponding to the mountain side of pleats of a filter that has been subjected to ejection of an unfiltered liquid at a high flow rate, and arrived at the following configurations.
Specifically, a pleated filter includes a filter base having folds that repeatedly form mountains and valleys and having a tubular shape whose axial direction is a ridge line direction of the folds, in which the pleated filter includes a reinforcing structure for folds in the mountains which are projecting portions projecting toward the outside of the tubular shape. A pleated filter cartridge includes a pleated filter that includes a filter base having folds that repeatedly form mountains and valleys and having a tubular shape whose axial direction is a ridge line direction of the folds; and fixing members disposed on an upper bottom portion and a lower bottom portion of the pleated filter, in which the pleated filter includes a reinforcing structure for folds in the mountains which are projecting portions projecting toward the outside of the tubular shape, and the reinforcing structure includes both a resin-reinforcing structure including, as a reinforcing body, a resin that covers a surface of the base in the folds or a resin that is allowed to permeate in the base in the folds, and a member-reinforcing structure in which reinforcing members provided separately from the filter base are disposed so as to extend along the folds.
The present invention discloses a ballast water treatment device including the pleated filter or the pleated filter cartridge used for filtration, a top surface of a cylinder and a bottom surface of the cylinder of the pleated filter each being sealed in a watertight manner, the pleated filter being rotatably held about a cylindrical axis; an untreated-water nozzle that ejects untreated water toward an outer circumferential surface of the pleated filter; a case that includes an outer tubular portion provided so as to surround the pleated filter and including a nozzle opening of the untreated-water nozzle therein; a filtered-water flow path that leads filtered water having passed through the pleated filter from the inside of the cylinder of the pleated filter to the outside of the case; and a discharge flow path that discharges discharge water that is not filtered by the pleated filter to the outside of the case.
The present invention further discloses a method for treating ballast water, the method including installing the ballast water treatment device in a hull; using, as untreated water, seawater taken from the outside of the hull; further applying a sterilization treatment to filtered water treated by the ballast water treatment device; and subsequently storing the resulting water in the hull as ballast water.
It is possible to provide a pleated filter and a pleated filter cartridge whose breakage due to use is prevented, thereby contributing to stable use for a long period of time, and a ballast water treatment device using the pleated filter or the pleated filter cartridge.
1, 11 base
2 resin
3 resin sheet
10, 101 pleated filter
12, 13 fixing member
20, 22 reinforcing sheet
51 tank
53 filtering device
54 sterilization means
52 pump
31, 32, 33, 34, 35, 36 pipe
102 untreated-water nozzle
103 case
106 untreated-water flow path
107 filtered water flow path
108 discharge flow path
121 nozzle opening
131 outer tubular portion
132 lid portion
133 bottom portion
140 central pipe
141 water intake hole
190 motor
Embodiments of the present invention will now be listed and described.
An embodiment disclosed in the present invention is a pleated filter that includes a filter base having folds that repeatedly form mountains and valleys and having a tubular shape whose axial direction is a ridge line direction of the folds, in which the pleated filter includes a reinforcing structure for folds in the mountains which are projecting portions projecting toward the outside of the tubular shape. In other words, the pleated filter has a ring shape as a whole while ridge lines of the folds alternately form a plurality of mountains and valleys in parallel. The pleated filter can be used for filtration from the outside to the inside or from the inside to the outside of the tubular shape.
Herein, the term “reinforcement” refers to a reduction in the occurrence of breakage generated in a fold of a filter base, that is, an increase in the strength against breakage. The term “reinforcement” is not used in the meaning of an increase in mechanical strength of the filter base itself or the meaning of an increase in mechanical strength of the whole pleated filter functioning as a structure. In this sense, the reinforcing structure is distinguished from a bone structure and a frame that are used in order to maintain the shape of the filter when the filter base is formed of a very thin film or the like. The term “breakage” refers to a split or a fine hole formed in a filter base, and refers to such damage that the original filtration function is impaired and substances that should be removed by filtration pass through the filter base. The term “reinforcing structure” refers to a structure for performing reinforcement in general and may also refer to “reinforcing means” or “reinforcing portion”. The term “reinforcing structure” is a generic term representing a structure that reduces or prevents breakage, and refers to a structure added to a filter in order to reduce the generation of such breakage, a process of a filter base, a combination thereof, and a reinforcing portion including a filter base.
In a pleated filter, stress or a stress change is applied to folds, which are folded portions of pleats, by a pressure of a fluid to be filtered or a change in the pressure. In particular, when the fluid to be filtered is a liquid such as water, the pressure applied to a filter is higher than that in the case of a gas such as air. Therefore, folds are deformed, and breakage easily occurs. Even in the case where a pleated filter is used in a state in which uniform pressure is applied to the whole pleated filter, the pressure is concentrated at folds. Furthermore, when the pressure varies, the folds are easily deformed, and the possibility of breakage may increase. According to experiments conducted by the inventors, it was confirmed that breakage easily occurs in folds, which form mountains and valleys. It was also found that the behaviors of the folds are different, and conditions under which breakage occurs are also different between a mountain and a valley.
Mountains and valleys will now be described under the assumption of the case where a liquid to be filtered is supplied from the outside of a tube, and a liquid filtered by the base of a filter is discharged from the inside of the tube. When the direction of the flow of the liquid to be filtered (unfiltered liquid) is reversed, the mountains become the valleys, and vice versa. Specifically, a fold whose surface on the side that receives a flow of a liquid to be filtered (surface that comes in contact with a liquid to be filtered) is on the mountain side is referred to as a mountain. In contrast, a fold whose surface on the side that receives a flow of a liquid to be filtered is on the valley side is referred to as a valley. If the filter does not have a tubular shape but has a flat-plate shape, regarding the reinforcement, the definition may be construed in accordance with the direction of the filtration.
When the liquid to be filtered comes into the inside of pleats, the width of the pleats expands. As a result of this movement, a flow of the liquid to be filtered is generated in the pleats, and the filter in the pleats is sufficiently cleaned. At this time, a force is applied, by the pressure of the liquid to be filtered, to a valley in a direction in which the fold opens up. Furthermore, since the bending angle of the folded portion is changed (that is, the pleat is opened up and closed) by a change in the pressure, the possibility of breakage of the valley is increased by the tensile stress and repetitive bending.
On the other hand, stress is applied to a mountain in a direction in which the fold is closed by the stress of the liquid to be filtered. Accordingly, unlike a valley, stress in a direction in which the fold opens up is unlikely to be applied to a mountain. Therefore, it is believed that breakage due to the same mechanism is unlikely to occur. In mountains, when the stress of the liquid to be filtered is concentrated at one mountain or a gap between mountains among a plurality of mountains that are continuously arranged, force is applied in a direction in which the mountains become separated. Upper and lower ends of the folds are fixed as a whole pleated filter. Therefore, when mountains are moved so as to be separated from each other, a tension is applied to ridge lines of the mountains, and a deformation easily occurs in which the ridge lines of the mountains are sharply bent near the center. Breakage tends to occur in such bent portions.
In order to prevent such breakage, by providing a reinforcing structure, the occurrence of filtration defects can be reduced, the strength of the pleated filter is increased to extend the lifetime, and a long-term operation of the filtering device can be further realized. Regarding the filtering device, the operating cost including components and work necessary for changing a filter can be reduced. Furthermore, the amount of filtration and the filtration rate of the filtering device can be improved.
An embodiment of the reinforcing structure is a resin-reinforcing structure including, as a reinforcing body, a resin that covers a surface of the base in the folds or a resin that is allowed to permeate in the base in the folds. The possibility of breakage can be reduced by combining a resin material, which is less likely to be broken, with the filter base. This structure is particularly effective when a fibrous base such as a non-woven cloth is used as a filter base. In particular, a structure in which a resin is allowed to permeate in the filter base achieves a more significant effect.
A non-woven cloth such as a polyethylene terephthalate non-woven cloth is particularly preferably used as the filter base. In a microscopic view, a filter base formed of a non-woven cloth or the like has a structure in which fibers are multiply intertwined. A form of breakage of the filter base is a breakage of some fibers caused by a local force applied to the base as a result of repetitive deformation of a fold of the base. In such a folded portion in which breakage easily occurs, the connection between the fibers are reinforced and breakage can be reduced by covering the base surface with a resin or, in particular, by allowing a resin to permeate in the base.
The permeation of a resin is preferably performed by impregnating a base with a resin. This method is preferable in that a base can be strongly reinforced to an inner portion with a resin by relatively simple means. The integration of the base and the resin that forms a reinforcing body improves the strength, or the reduction in breakage effectively improves the lifetime. Various means, such as application of a resin and immersion in a resin, in which the resin is cured after being allowed to permeate in the base, can be employed as means for penetration. A polyurethane is particularly preferably used as the impregnating resin. The simplest impregnation method is a method including applying a resin along a fold, and curing the resin in a state in which the applied resin is allowed to penetrate in the filter base. The resin is preferably allowed to permeate from a base surface onto which the resin is applied to a surface on the opposite side because a high breakage-preventing effect is obtained. The resin is preferably applied with a roller or a brush so that at least end portions of a fold are included. The application is preferably performed so as to cover the entire fold. The term “entire fold” refers to, in a transverse section perpendicular to folds of pleats, a folded portion between two inflection points of the curvature, each of the inflection points being a position at which an original linear portion of the base lead to a bend.
The resin-reinforcing structure may be formed by applying a resin member to a surface of a base. This method is preferable in that the thickness of the resin that covers a surface can be particularly increased to achieve a strong reinforcement. The application may be performed using an adhesive or using adhesiveness of a resin itself. In an embodiment of this structure, when a resin sheet functioning as a reinforcing body is applied by heat fusion bonding, the base may be impregnated with a part of the fusion-bonded resin.
Another embodiment included in the present invention will be described. A pleated filter includes a filter base having folds that repeatedly form mountains and valleys and having a tubular shape whose axial direction is a ridge line direction of the folds, in which the pleated filter includes a reinforcing structure for the mountains which are projecting portions projecting toward the outside of the tubular shape, and the reinforcing structure is a member-reinforcing structure in which reinforcing members provided separately from the filter base are disposed on the back side of the folds in the mountains so as to extend along the folds.
Furthermore, the reinforcing structure in the pleated filter preferably includes both a resin-reinforcing structure including, as a reinforcing body, a resin that covers a surface of the base in the folds or a resin that is allowed to permeate in the base in the folds, and a member-reinforcing structure in which reinforcing members provided separately from the filter base are disposed so as to extend along the folds. Since each of the member-reinforcing structure and the resin-reinforcing structure is effective, reinforcement can be more effectively achieved by providing the two reinforcing structures.
The reinforcing member is a member that can be deformed with a deformation of a fold by, for example, being provided so as to reinforce a fold that forms a mountain and so as to extend along the fold near the recess side of the fold. For example, a rod-like member such as a columnar member or a prism member, or a sheet-like member can be used. In the case of a sheet-like member, the sheet-like member is arranged such that an end face thereof extends along a fold of the filter base (the end face may be constantly in contact with the fold, but need not be necessarily in contact with the fold). It is not preferable for the reinforcing member to reinforce a fold in such a manner that the fold does not deform. The reinforcing member preferably deforms so as to conform to the deformation of the fold. Preferably, the reinforcing member is a member that supports the base to prevent a local deformation, that is, bending, and that functions so as to help restoration from the deformation. A sheet-like member (hereinafter, may be referred to as “reinforcing sheet”) is suitable for reinforcing a fold because such a sheet-like member has an anisotropy in which the sheet-like member easily deforms in a direction in which the sheet bends, that is, in a direction perpendicular to a surface of the sheet, but does not deform in a direction of the surface of the sheet.
As each of the reinforcing sheets, a flat-sheet base having a large number of holes penetrating from a front surface to a back surface, that is, a porous sheet material is preferably used. In particular, the use of a mesh-like sheet material is simple and easy. The reinforcing sheet is a member having a strength enough to prevent a bending deformation of the filter. In addition, it is necessary to consider that the reinforcing sheet does not excessively disturb pleats of the filter from expanding by the pressure of untreated water. Furthermore, it is preferable to consider a smooth flow of a filtered liquid and a reduction in the weight of the whole filter.
The material of the reinforcing sheets is not particularly limited as long as the advantages described above are achieved. Typically, the reinforcing sheets are preferably formed of any resin selected from the group consisting of polypropylene, polyethylene (in particular, medium to low-density polyethylene in terms of restoring force), polyamide resins such as nylon, polyester resins such as polyethylene terephthalate, and polyvinyl chloride. In view of, for example, the ease of handling during production, a reduction in the weight, and the cost, a resin member having required strength is preferably used. Polypropylene is particularly preferable from the viewpoint of having an appropriate strength and an appropriate restoring force. Some metallic materials and nonmetallic materials such as glass-ceramics have a performance superior to that of resins in terms of strength. However, in the present embodiment, a restoring force for deformation is also required. Therefore, in the case of a metal, it is preferable to use a spring material or to perform a quenching treatment. However, comprehensively considering a processing for forming a mesh-like structure and corrosiveness for seawater, the resin materials mentioned above are more suitable.
Regarding the dimensions, considering, for example, the application to a ballast water treatment device described below, a size of a hole of about 0.5 to 8 mm (a pitch of 1 to 10 mm in the case of a mesh) is preferably used from the viewpoint of the balance between permeation of the filtered liquid and strength of the sheet. More preferably, the size of a hole is 3 to 5 mm (the pitch is 3 to 5 mm in the case of a mesh). The thickness of the sheet is selected in consideration of the pitch of pleats (spacing between adjacent valleys) and a desired strength. The thickness of the sheet used is preferably 0.3 to 2 mm and more preferably 0.5 to 1.5 mm.
The reinforcing sheets are not limited to sheet materials that are independent from each other. Alternatively, a reinforcing sheet having folds may be provided so as to extend along the inner surface of the tubular shape of the filter base.
Furthermore, the filter base may be subjected to an embossing process. The embossing process is a processing method that is generally used as a process for forming a large number of continuous irregularities on a filter base. The use of a filter base having such a surface suppresses bending of the resulting filter. This structure is preferred in that gaps formed by embossing function as a flow path that does not disturb inflow of untreated water to inner portions of folded pleats and discharge of treated water that has been filtered.
The pleated filter particularly preferably further includes, in addition to the reinforcing structure in the mountains, in folds that form the valleys, a resin-reinforcing structure including, as a reinforcing body, a resin that covers a surface of the base or a resin that is allowed to permeate in the base in the folds. The reason for this is as follows. When a liquid to be filtered flows in a valley, force is applied to the valley in a direction in which the fold opens up. Since a tensile stress is concentrated at the filter base, a failure such as splitting easily occurs. Furthermore, when the liquid to be filtered flows between pleats in mountains and the width of one pleat is thereby increased so as to expand to a width several times the original width, valleys of pleats adjacent to both sides of the expanded pleat are pressed from the original positions toward the left and the right. Consequently, deformation in which ridge lines are sharply bent may also occur in the valleys as in the phenomenon that occurs in mountains.
Still another embodiment of the present invention is a pleated filter cartridge including any one of the pleated filters described above, and fixing members disposed on an upper bottom portion and a lower bottom portion of the pleated filter. In order to use a tubular pleated filter for filtration, it is necessary that an upper bottom portion and a lower bottom portion be sealed so that liquid leakage does not occur between the inside and the outside of the tube. Such a sealing structure may be formed as a part of the filtering device. The sealing structure is preferably constituted, in advance, as a pleated filter cartridge that includes a pleated filter and fixing members integrated with the pleated filter. The handling during production and transportation of the pleated filter cartridge is easy. The pleated filter cartridge is also easily handled during installation in a device.
Reinforcing members whose upper and lower ends are fixed by fixing members are preferably provided on the back side of mountains viewed from the outside of the cylindrical shape of the pleated filter cartridge. A member-reinforcing structure in which an upper end and a lower end of each of the reinforcing members are fixed by fixing members is effective as means for reducing a failure of a fold in a mountain. A typical example of the reinforcing members are reinforcing sheets formed of a resin. The reinforcing members are not limited thereto. The reinforcing members may be replaced with other members or other reinforcing means. Alternatively, other reinforcing means may be used in combination. The resin-reinforcing structure described above is preferably used in combination as the other means for reinforcing mountains. It is expected that a synergistic reinforcing effect is obtained. The upper and lower ends of the reinforcing members are preferably fixed by the fixing members alone. That is, preferably, no other members that connect reinforcing members adjacent to each other are provided. Reinforcing members that are adjacent to each other can freely move and deform except for the upper and lower ends thereof. Accordingly, the reinforcing members easily conform to the deformation of pleats to increase the reinforcing effect.
The present invention discloses a ballast water treatment device in which the pleated filter or the pleated filter cartridge is used for filtration. Specifically, the ballast water treatment device includes the above-described tubular pleated filter that is used for filtration, a top surface of a cylinder and a bottom surface of the cylinder of the pleated filter each being sealed in a watertight manner, the pleated filter being rotatably held about a cylindrical axis; an untreated-water nozzle that ejects untreated water toward an outer circumferential surface of the pleated filter; a case that includes an outer tubular portion provided so as to surround the pleated filter and including a nozzle opening of the untreated-water nozzle therein; a filtered-water flow path that leads filtered water having passed through the pleated filter from the inside of the cylinder of the pleated filter to the outside of the case; and a discharge flow path that discharges discharge water that is not filtered by the pleated filter to the outside of the case.
In the device having the above structure, untreated water is ejected from the nozzle opening outside the cylinder of the cylindrical pleated filter toward an outer surface of the pleated filter, and thus the pressure of the untreated water concentrates at a part of pleats. Consequently, the pressure is applied in directions in which the pleats open up, and a failure of the filter is more likely to occur in each of a valley and a mountain. In view of this, by employing the reinforcing structure described above, it is possible to expect advantages such as the suppression of the occurrence of filtration defects, a long-term operation of the device due to extension of the lifetime of the pleated filter, and a reduction in the operation cost.
In this case, the top and the bottom of the pleated filter may be fixed and sealed with lid members. The pleated filter may be used in the form of a pleated filter cartridge in which the pleated filter and fixing members are integrated with each other. The fixing members may also function as lids.
A method in which the pleated filter or the pleated filter cartridge is used for filtration may be a method for treating ballast water, the method including installing the ballast water treatment device in a hull; using, as untreated water, seawater taken from the outside of the hull; further applying a sterilization treatment to filtered water treated by the ballast water treatment device; and subsequently storing the resulting water in the hull as ballast water.
By using the device or using the method, a failure of a filter is reduced as compared with existing techniques, and the filter can be stably used for a long period of time without causing filtration defects. Consequently, the labor cost of maintenance and the cost of materials to be exchanged can be reduced, and the production of ballast water can be further facilitated.
Structures of a pleated filter, a pleated filter cartridge, and a ballast water treatment device according to the present invention will now be described with reference to the drawings. The scope of the present invention is not limited to these embodiments but is defined by the claims described below. It is intended that the scope of the present invention includes equivalents of the claims and all modifications within the scope of the claims.
A description will be made under the assumption that, in
A porous resin sheet is used as the base of the filter. Examples of the base that can be used include porous structures such as a stretched porous body, a porous body by phase separation, and a non-woven cloth that are formed of a material such as polyester, nylon, polyethylene, polypropylene, polyurethane, polytetrafluoroethylene (PTFE), or polyvinylidene fluoride (PVdF). For the purpose of performing a treatment at a high flow rate, a non-woven cloth formed of a polyester such as polyethylene terephthalate is particularly suitably used.
In
Furthermore, in the state illustrated in
In an embodiment of a breakage-preventing structure of a folded portion of a filter base which is a porous resin sheet, a potion near the folded portion may be reinforced with a resin. Examples of means for applying, as a reinforcing structure, a resin to a filter base include application of a resin to a base surface, impregnation of a base surface with a resin, and application of a resin sheet. Any other method may be used as long as the method is means for integrating a resin with a base surface or means for impregnating a base with a resin. The simplest method is a method including applying a resin along a ridge line of a folded base. The application can be performed with known means such as a brush, a roller, or a spray. After the resin is applied to the base surface, the resin is cured. The filter base is preferably impregnated with a resin because the base can be reinforced more strongly. Also in the case where a resin is applied onto a base surface, curing is preferably performed in a state in which the base is impregnated with at least a part of the resin, and the resin is more preferably allowed to permeate on the back surface side of the application and cured.
A region to which a resin-reinforcing structure is applied will be described with reference to
In the transverse section of a fold, preferably, the resin-reinforcing structure is provided over the entire portion R, and ends (boundaries) of a resin-reinforced portion are located in the portions L, which are the linear portions of the base. Stress tends to be concentrated at a boundary between the reinforced portion and a non-reinforced portion. Accordingly, such a boundary is preferably located in a linear portion, which is unlikely to deform, because breakage does not easily occur.
The resin-reinforcing structure is provided at least in a central portion in a longitudinal direction of a folded portion (a direction in which the ridge line extends). The term “central portion” refers to a portion near the center of a length of a pleat in the vertical direction when the upper and lower ends of the pleat are fixed, and preferably a portion having a length of at least ¼ of the length of the folded portion. The folded portion is preferably reinforced over its entirety in the longitudinal direction thereof. This is because a boundary between a reinforced portion and a non-reinforced portion has a discontinuous hardness, and thus stress tends to become concentrated at the boundary, which may easily cause breakage during long-term use.
Examples of the impregnating resin that can be used include thermosetting resins such as silicones, epoxy resins, and polyurethanes; thermoplastic resins such as polyvinyl chloride (PVC), polyesters, nylons, polyethylene, polypropylene, ETFE, and PVdF; solutions prepared by diluting PVdF or a silicone with a solvent; and elastomers containing another synthetic rubber or natural rubber. Resins that easily permeate into the material of the filter are desirable. In particular, when pleats are formed and subsequently reinforced by application, polyvinyl chloride and polyurethanes are preferable, and polyurethanes are particularly preferably used because, for example, the application is easily performed.
During impregnation, the impregnating resin needs to have a fluidity for entering a porous body. On the other hand, after impregnation, it is necessary that the resin be integrated with a filter so as not to be easily separated from the filter. In the case of a thermosetting resin, the resin can be cured by heating after impregnation. In the case of a two-component curable resin, immediately after mixing, a filter is impregnated with the mixed resin, and the mixed resin can then be cured. In the case of a resin that is diluted with a solvent to decrease the viscosity, after impregnation, curing is preferably performed after a while in order to give the solvent time to dry.
Still more preferably, the impregnating resin is a resin having a low hardness. The impregnating resin is cured in a state in which the resin is allowed to permeate so as to fill an inner part of a porous body or gaps between fibers of the filter base. In the case of a soft resin, with a deformation of a filter base, the resin can also be flexibly deformed with a certain degree of elasticity, and thus breakage of the base can be suppressed. In particular, when the filter base is formed of fibers such as a non-woven cloth, the impregnating resin covers the fibers and binds the fibers to each other to reduce the movement of the fibers. Consequently, it is believed that breakage of the fibers due to repetitive deformation can be prevented. The hardness of the resin is preferably, in terms of durometer hardness, a Shore hardness of 20 A to 60 A (in accordance with rubber-elastomer (JIS K6253), standard measurement time: 3 seconds for vulcanized rubber, and 15 seconds for elastomer) or a Shore hardness of 5 D to 30 D (plastic (JIS K7215), a maximum value of an indicator is read within one second). The resin is required to have characteristics that the resin does not excessively hinder deformation of the shape of the filter (expansion of pleats) and reduces a failure of the filter base. If the hardness is less than 20 A (or 5 D), the strength of the resin is insufficient, and the resin may be broken with the deformation of the filter. Therefore, for example, unraveling of fibers of a non-woven cloth cannot be prevented. If the hardness exceeds 60 A (or 30 D), flexible deformability becomes poor, which is not preferable from the viewpoint of excessively hindering deformation of the pleated filter.
In particular, soft polyurethanes are preferably used from a comprehensive viewpoint of, for example, the adhesive strength with a non-woven cloth, the ease of application, the effect of suppressing breakage, and the cost. Regarding knowledge of the difference between a soft polyurethane and a hard polyurethane, for example, a soft polyurethane including two components of SA-7073A and SA-7502B manufactured by Sanyu Rec Co., Ltd. is soft and has a good breakage-preventing effect compared with a hard polyurethane including two components of SA-7073A and SA-7068B manufactured by Sanyu Rec Co., Ltd.
As a method for producing a resin-reinforcing structure other than application of a resin, a method using a resin sheet will be described. A resin to be attached to or to be allowed to permeate in a filter base is prepared in the form of a sheet. The size of the sheet is determined in accordance the size of a portion to be reinforced with a resin. First, the sheet-like resin is placed on one surface of the filter base. The resin is a thermoplastic resin having a melting point lower than that of the filter base. For example, as a porous resin sheet, a polyester non-woven cloth containing, as a main component, polyethylene terephthalate having a melting point of about 260° C. can be suitably used. As an impregnating thermoplastic resin, polymethylpentene, 66-nylon, or polycarbonate having a melting point of about 230° C., polyethylene that usually has a melting point of about 120° C., or polypropylene that usually has a melting point of about 160° C. can be suitably used. A part or the whole of the resin sheet is melted by heating the resin sheet and the filter base with a heating-pressurizing device such as a heat sealer. In this step, an inner part of a porous body constituting the filter base is impregnated with a part or the whole of the resin. The filter base is bent after the heating or in parallel with the heating. In this bending, by bending the filter base while bringing a metal jig with a desired radius into contact with the filter base, the curvature of folded portions can be made uniform.
The method described above is a method for producing a pleated filter, the method including periodically bending a planar base to form mountains and valleys continuously and repeatedly. The method for producing a pleated filter includes a step of placing a resin sheet on at least one surface of a base that forms the folded portion, an impregnation step of impregnating the base with at least a part of the resin sheet by heating the resin sheet and a part of the base, the part having the resin sheet thereon, and a cooling step of performing cooling and fixing in a state in which the folded portion is bent.
The description has been made of a case where a base is impregnated with a resin for reinforcement. Alternatively, a resin-reinforcing structure other than a structure obtained by impregnation can be formed by a method including bonding a resin sheet with an adhesive or a method including bonding a resin sheet by heat fusion bonding. Even in the case of impregnation, a predetermined portion of a base may be impregnated with a resin by another method without using a resin sheet, and the portion may then be bent. Alternatively, a method may also be used in which a base is bent and then impregnated with a resin. Furthermore, the use of the jig for determining the curvature is not essential in bending, and the base may be bent by an ordinary folding operation. Even when a filter base is folded without using a particular jig, the folds are bent in a curved manner with a certain radius or more in accordance with the material and the thickness of the filter base. The method for applying a resin may be a known application method. Examples of the application includes not only application with a roller and application with a brush or a writing brush but also a method including pouring a resin directly onto a surface of a base.
Embodiments of a member-reinforcing structure in which reinforcing members provided separately from a filter base are disposed along folds will be described with reference to the drawings.
In this structure, when force is applied to folds of the filter base 11 in a direction in which the folds bend, the reinforcing sheets 20 support the filter base 11 so that the folds are unlikely to bend. The reinforcing sheets 20 are members having a strength enough to prevent deformation by bending. Furthermore, preferably, the reinforcing sheets 20 do not excessively hinder the expansion of corresponding pleats due to the pressure of a liquid to be filtered. Specifically, while the reinforcing sheets 20 prevent the filter base from bending as illustrated in the portions D in
In the structure in which reinforcing sheets are arranged so as to extend along a filter base, preferably, the filter base is further subjected to an embossing process.
When a pleated filter includes a member-reinforcing structure, reinforcing members used in the reinforcing structure are fixed to the fixing members. The reinforcing members are preferably fixed using an adhesive as in the fixation of the pleated filter. When a filter base and reinforcing members can be bonded and fixed at the same time using the same adhesive, an assembling step can be simplified.
As a preferred application example of a filtering device using the pleated filter described above, a structure of a ballast water treatment device will be described with reference to drawings.
In this embodiment, the untreated water ejected from the untreated-water nozzle 102 is applied to the outer circumferential surface of pleats of the pleated filter 101, and an effect of cleaning the pleated filter 101 is obtained by the pressure of the untreated water. The untreated water that is not filtered and suspended substances settled in the case are sequentially discharged from the discharge flow path 108 on the bottom portion 133 of the case. This point that filtration is performed while continuously and constantly discharging suspended substances and residual untreated water in this manner is also a feature of this device. This feature is advantageous for reliably achieving a large amount of treatment of 50 to 100 ton/hour and, in a larger system, 4,000 ton/hour, which are required for ballast water. In such a large-sized filtering device that treats a large amount of water, the size of the pleated filter is large, and thus it is particularly important to prevent the breakage of the pleated filter. Although valves and other components are not illustrated in the discharge flow path 108 in the figure, devices necessary for maintenance and flow rate control may be provided. The filtered water filtered by the pleated filter 101 is guided to a filtered water flow path 107 through a water intake hole 141 provided in the central pipe 140 in the inside of the filter, and is discharged to the outside of the case 103.
An example of a device that performs a treatment at a rate of 100 ton/hour includes a pleated filter having an outer diameter of 700 mm, a length in the axial direction of 320 mm, a height as an effective area of 200 mm, a pleats depth of 70 mm, and a number of pleats of 420. Another example of a device that performs a treatment at a rate of 250 ton/hour includes a pleated filter having an outer diameter of 810 mm, a length in the axial direction of 399 mm, a height as an effective area of 377 mm, a pleats depth of 70 mm, and a number of pleats of 517. The nozzle opening 121 of the untreated-water nozzle 102 preferably has a rectangular opening. A large amount of water is ejected from the untreated-water nozzle onto the pleated filter surface, thereby applying a force in a direction in which mountains of the pleated filter are pushed and become separated. The mountains become separated, and a liquid flows in and out from gaps between pleats. Consequently, a flow is generated on a surface of the filter base, and an effect of cleaning the filter is obtained. When the mountains are separated in this manner and folds in the mountains are bent, breakage of the folds easily occurs. The concentration of the stress at a valley also easily forms a hole such as splitting in the fold of the valley. By using the pleated filter whose folds are reinforced as described above, such a breakage can be effectively reduced, and the device can be stably operated for a long period of time. In particular, in order to prevent mountains from bending, the member-reinforcing structure with a reinforcing sheet is effective. By combining the member-reinforcing structure with the resin-reinforcing structure, a stronger breakage-preventing structure can be obtained. Each of the valleys also preferably includes the resin-reinforcing structure. In order to suppress breakage and to effectively obtain a cleaning effect, the hardness of the resin is preferably a Shore hardness of 20 A to 60 A or 5 D to 30 D. When the filter base is formed of a non-woven cloth, a polyurethane resin is particularly preferably used.
In order to confirm the effect obtained by a resin-reinforcing structure, impregnation with a resin and the comparison of strength of portions subjected to bending were performed. Materials used are as follows.
Porous filter: Polyethylene terephthalate non-woven cloth (trade name: AXTAR™ G2260-1S BK0, manufactured by Toray Industries, Inc.)
Impregnating resin: Polypropylene non-woven cloth (trade name: STRATECH RW2100, manufactured by Idemitsu Unitech Co., Ltd.)
Heat sealer: Desktop sealer NL-301J, manufactured by ISHIZAKI ELECTRIC MFG. CO., LTD.
An impregnating resin was placed on a folded portion of a porous filter serving as a base, and heat-sealed while a seal timer of a heat sealer was set to 4 (heating time: about one second). Cooling was performed in a state in which the impregnating resin was completely heat-melted and the porous filter was impregnated with the resin. Immediately after heating was further performed under the same heating conditions, a stainless rod having a diameter of 3 mm was inserted in the folded portion, and the folded portion was bent along the shape of the stainless rod. The resulting porous filter having a fold with a curvature radius of 1.5 mm was used as a filter of Example. The same type of porous filter was bent at an angle of 180 degrees without further treatment. The resulting porous filter was used as a filter of Comparative Example.
The folded portion of each of the porous filters was opened up, and the porous filter was punched into a dumbbell shape such that the folded portion was located at a position near the center of the dumbbell and in a direction perpendicular to a tensile direction. In addition, a filter base having no folded portion was punched so as to have the same shape. Thus, a sample for comparison was prepared. The breaking strength was measured using these dumbbells as samples at a chuck distance of 3 cm and a tensile speed of 100 mm/min. According to the results, in Comparative Example, all the samples were broken in the folded portions, and the breaking strength was 33 MPa. The measurement results of the base having no folded portion was 40 MPa. These results suggest that the strength was decreased by bending. In contrast, in Example, breaking did not occur in the folded portions impregnated with the resin, and all the samples were broken in other flat portions. The breaking strength thereof was 41 MPa. Specifically, it was confirmed that the folded portions had a strength higher than 41 MPa.
An experiment for confirming a breakage-preventing effect obtained by applying a polyurethane resin was conducted. A filter base was folded at an angle of 180 degrees, and a polyurethane resin was applied onto a mountain of the filter base with a roller. The resulting filter base was used as a sample of Example. The applied resin impregnated to the back side of the base and cured. A filter base which was similarly folded but to which no resin was applied was prepared as a sample of Comparative Example. The filter and the resin used are as follows. Note that the manufacturers, the model names, and the like are not limited thereto. The same types of alternative products may be used within a range where the advantages of the present embodiment are achieved.
Porous filter: Polyethylene terephthalate non-woven cloth (trade name: AXTAR™ G2260-1S BK0, manufactured by Toray Industries, Inc.)
Applied impregnating resin: Soft polyurethane resin (trade name: A main agent SA-7073A and a hardening agent SA-7502B manufactured by Sanyu Rec Co., Ltd. were mixed at a ratio of 23:100.)
The breaking strength was measured by the same method as that used in Experimental Example 1. Regarding the impregnation of the resin, no significant difference in strength was observed between Example and Comparative Example. Next, the fold was bent (opened up and closed) 50,000 times, and the breaking strength was then measured by the same procedure. The rate of decrease in strength between the sample that was not subjected to bending and the sample after bending was compared. In Example, in which the porous filter was impregnated with the polyurethane resin, the strength was decreased by about 10% due to bending. On the other hand, in Comparative Example, in which the porous filter was not impregnated with the resin, the strength was decreased by about 40%. According to the observation of the samples, in the sample impregnated with the resin, the sample was impregnated with the resin so as to connect fibers of the base to one another. Accordingly, it was confirmed that unraveling and breakage of the fibers could be prevented.
In order to confirm the effect obtained by applying a resin, the effectiveness of a breakage-preventing structure was examined using a ballast water treatment device including cylindrical pleated filters. A resin-reinforcing structure obtained by applying a resin onto all mountains of a pleated filter was used as the breakage-preventing structure. The filter base and the resin used were the same as those in Experimental Example 2. The application was performed only on the mountains with a roller. For comparison, a pleated filter onto which no resin was applied was used. In addition, the effect was also confirmed in the sample which was used in Experimental Example 1 and in which mountains and valleys were impregnated with polypropylene.
The ballast water treatment device used has the structure illustrated in
With an increase in the operation time, failure was generated in projecting portions of pleats, and failure points gradually increase. A lifetime estimation was performed by the Weibull plot on the basis of the time at which such failure was generated and the number of failures.
An experiment for confirming the effects of the presence or absence of application of a polyurethane resin and reinforcement of mountains was performed. A pleated filter used was a single pleated filter having an outer diameter of 350 mm, a length in the axial direction of 200 mm, a pleats depth of 70 mm, and a number of pleats of 210. Other structures and conditions are the same as those in Experimental Example 3. A soft polyurethane resin and a hard polyurethane resin were applied onto mountains or valleys as shown in Sample 1 to Sample 7 in Table 1. The application was performed with a roller over the entire height of the pleated filter between fixing members. The polyurethane resins (PU) used were as described below. Herein, in the effect of preventing breakage, the term “soft” used for a polyurethane refers to a Shore hardness of 20 A to 60 A (in accordance with rubber-elastomer (JIS K6253) standard measurement time: 3 seconds for vulcanized rubber, and 15 seconds for elastomer) in terms of hardness. As the reinforcement of the mountains of all pleats, a member-reinforcing structure with reinforcing sheets was formed. The reinforcing sheets used were described below. The reinforcing sheets are arranged on the back side of the mountains and along the mountains, as illustrated in
Reinforcing sheet: Polypropylene mesh sheet (trade name: TRICAL NET SN-598, manufactured by Takiron Co., Ltd.), mesh pitch: 4.8 mm×4.8 mm, thickness: 1.5 mm (warp 1.5 mm, weft 1.2 mm)
Soft polyurethane resin: A main agent SA-7073A and a hardening agent SA-7502B manufactured by Sanyu Rec Co., Ltd. were mixed at a ratio of 23:100. Hardness: 23 A (at 23° C.)
Hard polyurethane resin: A main agent SA-7073A and a hardening agent SA-7068B manufactured by Sanyu Rec Co., Ltd. were mixed at a ratio of 1:2. Hardness: 90 A (at 23° C.)
Two hundred ten folds of the pleated filter cartridge were divided into groups each including 30 folds. The groups have the structures of Sample 4-1 to Sample 4-7. The effect due to the difference in structure can be confirmed by performing a filtration operation at one time using this cartridge. The filtration operation was performed for 50 hours under accelerated test conditions in which the flow rate was higher than that in usual conditions. After the filtration operation, the number of failures of mountains was examined. In Sample 4-7, which had no resin-reinforcing structure in mountains and valleys, the failure was observed in 25 folds out of 30 folds. In contrast, in Sample 4-1 to Sample 4-6, whose mountains were reinforced with a resin, the effect of a resin impregnation could be confirmed. In addition, the numbers of failures in Sample 4-1 to Sample 4-3, in which the soft PU having a low hardness was used as the resin, were smaller than those in Sample 4-4 to Sample 4-6, in which the hard PU was used. These results show that a high breakage-preventing effect is obtained in Sample 4-1 to Sample 4-3. Furthermore, the comparison of Samples 4-1 and 4-2 with Sample 4-3 and the comparison of Samples 4-4 and 4-5 with Sample 4-6 show that a failure-preventing effect in mountains is also increased by combining the application of a resin to valleys.
Another experiment for confirming a breakage-preventing effect obtained by applying a polyurethane resin was performed. A pleated filter used was a single pleated filter having an outer diameter of 810 mm, a length in the axial direction of 380 mm, a pleats depth of 70 mm, and a number of pleats of 517. Other structures and conditions are the same as those in Experimental Example 3. The same soft polyurethane resin as that used in Experimental Example 4 was applied onto all mountains. The application was performed over the entire height of the pleated filter between fixing members. As the reinforcement of the mountains of all pleats, a member-reinforcing structure with reinforcing sheets was formed. The reinforcing sheets used were the same as those in Experimental Example 4 except that the length was changed to about 380 mm so as to adjust to the length of the pleated filter.
Three types of reinforcement of valleys were performed as described below, and Sample 5-1 to Sample 5-3 were prepared. The failure lifetime of the samples was compared. In Sample 5-1 to Sample 5-3, only the resin-reinforcing structures of the valleys were different. The application of the soft polyurethane (PU) and the reinforcing structure with reinforcing sheets in mountains are common. In Sample 5-1, only ⅓ of the center of each of the valleys in the height direction was reinforced by being impregnated with the soft PU. In Sample 5-2, the valleys were impregnated with the soft PU over the entire height thereof. In Sample 5-3, the valleys were not impregnated with a resin. The resin used was the same as the resin applied onto the mountains.
Table 2 shows the results. The comparison of Samples 5-1 and 5-2 with Sample 5-3 shows that the breakage lifetime (hours) can be significantly improved by further providing a resin-reinforcing structure in valleys. The breakage can be prevented more effectively by employing the reinforcement in the valleys in addition to the reinforcing structures of the mountains. Since breakage of a valley tends to occur near the center of the valley, a significant effect is obtained by reinforcing a portion near the center (⅓ of the center in the experiment) by impregnation (Sample 5-1). However, in this case, a non-application portion becomes relatively weak, and breakage occurs. Accordingly, by applying the soft polyurethane over the entire height of valleys as in Sample 5-2, breakage of a valley can be particularly effectively prevented.
In order to confirm the effect obtained by reinforcing sheets, filtration was performed with the same device as that used in Experimental Example 5. The filter base and the reinforcing-sheet material that were used were the same as those in Experimental Example 5. The reinforcing sheet was cut into strips. The strips were attached, as independent reinforcing sheets, to the back side of mountains of the filter by the method illustrated in
According to the pleated filter of the present invention, a decrease in the performance due to clogging does not occur, and the pleated filter has good durability. Accordingly, the pleated filter of the present invention can be suitable for use in preliminary filtration treatment for removing foreign matter, contaminants, and microbes in water in the cases of seawater desalination, the use of brackish water/seawater for purposes such as ballast water, or the treatment of water such as sewage water, human sewage, industrial waste water, or the like. Furthermore, the pleated filter is suitable for the treatment of water having a high suspended substance/high SS (suspended solid) content and a concentration treatment, and thus can also be used in the field of collection of valuable recyclable materials, for example, in the field of food.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-124109 | Jun 2014 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2015/067287 | 6/16/2015 | WO | 00 |
