JP6220242B2 - filter - Google Patents

Description

  The present invention relates to a filter for filtering a slurry or a gel fluid containing a solid content.

  In general, in a fluid containing fine powder particles, a filter is used for purification filtration of a fluid having a low solid content and high fluidity.

  One indicator of filter performance is the filtration life, which represents the length of time the filter can be used and the cumulative flow rate. In an attempt to improve the filtration life, for example, at least two layers of a prefiltration layer and a microfiltration layer are provided in a filter made of a non-woven fiber assembly, and the prefiltration layer has a fiber diameter of the constituent fibers filtered. It is known that the microfiltration layer is configured to be thin in the direction, and the microfiltration layer is configured by a non-woven fiber assembly including fibers thinner than the minimum fiber diameter of the prefiltration layer (Patent Document 1).

  However, in order to configure the prefiltration layer so that the fiber diameter becomes narrower in the filtration direction, it was necessary to prepare in advance a nonwoven fiber assembly in which the average fiber diameter changed in the length direction. In order to produce such a nonwoven fiber assembly, special spinning conditions must be set, which is disadvantageous in terms of cost, and there is a limit to the minimum fiber diameter of the nonwoven fiber assembly that can be manufactured. Therefore, it was not always sufficient in terms of precision filterability.

  In addition, in order to obtain a high-accuracy filtration filter with good shape retention and excellent balance between filter filtration accuracy and filtration life, at least two layers of nonwoven fabric are laminated, and the filling rate of the nonwoven fabric on the upper layer side is 0.3 A non-woven fabric for a filter in which the filling rate of the non-woven fabric on the lower layer side is 0.01 to 0.25 is proposed (Patent Document 2). The present invention uses a filter by disposing a non-woven fabric layer having a low filling rate on the lower layer side of the filter, thereby maintaining a minute space on the contact surface between the non-woven fabric layer and the support material, and also acting as a cushioning material. It improves efficiency and form retention.

  However, the filtrate that is the object of the above-mentioned document is an aqueous solution in which 0.6 μm alumina particles are dispersed at a concentration of 50 ppm, that is, a liquid having an extremely small particle size and a low concentration is filtered.

On the other hand, in recent years, in order to shorten the drying time after filtration and to reduce the volume of condensed volatilized liquid, it is required to increase the concentration of solids.
When the solid content becomes high, the fluid loses fluidity, and the interaction between the powders that are solid content is strengthened. Therefore, in the case of conventional cartridge filters for water, even if the powder is smaller than the average pore diameter of the filter, a rush phenomenon occurs when the powder particles pass through the filter, and the powder is agglomerated (bridged). There are known problems that occur, the apparent particle size increases, and the filter becomes clogged.

  Patent Document 3 discloses that in the filtration of viscous fluid, the filtration accuracy changes due to the differential pressure or the problem that the filter life is shortened is solved, and even if a pulse pressure or a high differential pressure occurs, a soft gel solid We propose a filter that can capture The invention of Patent Document 3 includes a first main filtration layer having a porosity of 50 to 80% by pressure bonding in the main filtration layer of the filter, and a second main filtration having a porosity of 80% or more that has not been pressure-bonded. The second main filtration nonwoven fabric is configured such that the porosity is 1.2 times or more that of the first main filtration nonwoven fabric.

International Publication No. 98/13123 Pamphlet JP 2000-218113 A JP 2010-137121 A

Various improvements have been made to the filter as described above, and there is a need for a filter that can filter a higher-concentration filtrate and has a long filtration life.
That is, an object of the present invention is to provide a filter in which powder agglomeration (bridge) is unlikely to occur and the time until the differential pressure rises is long, that is, the filter has a long filtration life.

  In examining the layer structure of the laminate including the nonwoven fabric for filtration layer, in addition to the configuration of the nonwoven fabric for filtration layer such as fiber diameter and porosity, which has been conventionally considered, the thickness direction of the filter (filtered material) The idea was to control the composition of the (passing direction). And by densifying the fiber density in the thickness direction of the nonwoven fabric for filtration layer constituting the filter, that is, by providing an appropriate gap between the laminated nonwoven fabrics, the dispersion of the powder contained in the filtrate can be dispersed. It was found that the formation of bridges was suppressed. Furthermore, it was found that a suitable filtration layer can be created with a specific configuration, and that the pore size of other layers can be controlled to suppress the occurrence of bridging and to provide a filter with a long filtration life and excellent classification. The present invention has been completed.

That is, the present invention has the following configuration.
[1] A filter having a base material layer, a filtration layer, and a skin layer,
The base material layer is a layer in which a nonwoven fabric is wound in multiple layers and thermocompression bonded,
The filtration layer is a layer in which a laminate in which at least a through-air nonwoven fabric and a net are laminated is wound in multiple layers, and is not thermocompression bonded,
The skin layer is a layer containing a nonwoven fabric,
The average pore diameter of the nonwoven fabric which comprises the said base material layer and the said skin layer is a filter larger than the average pore diameter of the through-air nonwoven fabric which comprises the said filtration layer.
[2] The filter according to [1], wherein a melt blown nonwoven fabric is laminated in addition to the through-air nonwoven fabric and the net in the laminate constituting the filtration layer.
[3] The non-woven fabric constituting the base material layer is a melt blown non-woven fabric or a through-air non-woven fabric having an air permeability in the range of 200 to 300 cc / cm ² / sec when 10 sheets are stacked, described in [1] or [2]. Filter.
[4] The filter according to any one of [1] to [3], wherein the nonwoven fabric constituting the filtration layer is a through-air nonwoven fabric having an average fiber diameter in the range of 0.1 to 200 μm.
[5] The filter according to any one of [1] to [4], wherein the net has a scale in a range of 1 to 5 mm and has an average fiber diameter in a range of 50 to 300 μm.
[6] The filter according to any one of [1] to [5], wherein the through-air nonwoven fabric constituting the filtration layer has fibers fused and / or bonded at intersections of fibers in the nonwoven fabric. .
[7] A cylindrical filter having the filter according to any one of [1] to [6].

  ADVANTAGE OF THE INVENTION According to this invention, even if it is a fluid with a high density | concentration and viscosity, it is hard to generate | occur | produce agglomeration (bridge | bridging) of a powder, and provides a filter with a long time until a differential pressure rise occurs, ie, a long filtration life. be able to.

It is a graph which shows the test result which compared the filtration life of the Example of this invention and the filter of a comparative example. It is a graph which shows the test result which compared the initial collection performance of the filter of the Example of this invention, and a comparative example. It is a photograph which shows the cross section of the filter of the Example (lower stage) of this invention, and the comparative example 2 (upper stage).

  The filter of the present invention is a filter having a base material layer, a filtration layer, and a skin layer, wherein the base material layer is a layer formed by multiple windings of nonwoven fabric and thermocompression bonding, and the filtration layer Is a layer in which a laminate in which at least a through-air nonwoven fabric and a net are laminated is wound in multiple layers and is not thermocompression bonded, the skin layer is a layer containing a nonwoven fabric, and the base layer and the skin layer are The average pore diameter of the nonwoven fabric to be formed is larger than the average pore diameter of the through-air nonwoven fabric forming the filtration layer.

  As described above, the filtration layer of the filter of the present invention is a layer in which a laminate in which at least a through-air nonwoven fabric and a net are laminated is wound and is not thermocompression bonded. The through-air nonwoven fabric is bulky and has a characteristic that fiber orientation is distributed also in the thickness direction of the nonwoven fabric (flow direction of the fluid to be filtered). For this reason, the pressure loss of the fluid is reduced, and even a fluid having a high concentration and viscosity can be filtered without being retained. Further, by laminating the through-air nonwoven fabric and the net, an appropriate gap is formed between the through-air nonwoven fabric that substantially assumes the filtration function. Therefore, the fluidity of the fluid and the powder in the fluid is improved in the filtration layer, and the formation of bridges is suppressed, so that a filter having a long filtration life can be obtained. Moreover, since the gap between the nonwoven fabrics prevents the pores from being reduced in diameter and blocked by the nonwoven fabric overlay, the collection efficiency and filtration efficiency are also excellent. Furthermore, by not performing thermocompression bonding, the gap between the nonwoven fabrics is maintained, the nonwoven fabric can move slightly in the filtration layer, and the fluidity of the fluid and the powder in the fluid is further improved. Therefore, the filtration performance is stably exhibited because the shape of the filtration layer is maintained.

<Nonwoven fabric for filtration layer>
As described above, the filtration layer is formed using a laminate in which at least a through-air nonwoven fabric and a net are laminated. In the present invention, the through-air nonwoven fabric refers to a nonwoven fabric obtained by a hot air bonding process. The hot air bonding process is a method for improving the bonding effect and obtaining a uniform nonwoven fabric in the thickness direction by providing a conveyor belt or a rotary drum in an oven, passing the web, and sucking it to one side. Also called the air-through method.
In general, the hot air bonding process has advantages such as 1) production of a nonwoven fabric having bulkiness, 2) relatively simple and uniform temperature control, and 3) shrinkage control.
Utilizing this advantage, crimped short fibers are passed through a card machine to form a web, the obtained web is subjected to hot air treatment, and the entanglement points of the short fibers are thermally fused to obtain a through-air nonwoven fabric. By using a non-woven fabric in which the entanglement points are heat-sealed, the average pore diameter in the non-woven fabric is kept constant, and the inherent filtering performance can be stably exhibited, so that the stable performance as a filter can be maintained.

As the short fibers constituting the through-air nonwoven fabric, it is preferable that the short fibers are fused and / or bonded at the intersection of the short fibers in order to maintain stable performance. From this, a heat-fusible conjugate fiber can be preferably used as the short fiber. The kind of heat-fusible conjugate fiber is not particularly limited, and a known conjugate fiber can be used. As the heat-fusible conjugate fiber, a conjugate fiber composed of two or more components having a difference in melting point can be used, and specifically, a conjugate fiber composed of a high melting point component and a low melting point component can be exemplified. Examples of the high melting point component of the composite fiber include thermoplastic resins such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate, polytrimethylene terephthalate, nylon 6, nylon 6,6, and poly-L-lactic acid. As the low melting point component of the composite fiber, polyethylene (PE) such as low density polyethylene, linear low density polyethylene, and high density polyethylene, polyethylene terephthalate copolymer, poly-DL-lactic acid, propylene copolymer, polypropylene, etc. These thermoplastic resins can be exemplified. The difference in melting point between the high-melting component and the low-melting component of the heat-fusible composite fiber is not particularly limited, but is preferably 15 ° C. or higher, and 30 ° C. or higher in order to widen the processing temperature range of heat-sealing It is more preferable that The composite form is not particularly limited, and composite forms such as a concentric sheath core type, an eccentric sheath core type, a parallel type, a sea island type, and a radial type can be employed. In particular, an eccentric sheath-core type composite fiber is suitable for providing bulkiness.
Also, the cross-sectional shape of the heat-fusible conjugate fiber is not particularly limited. For example, the cross-sectional shape may be any shape such as a circle, an ellipse, a triangle, a square, a U-shaped, a boomerang type, an eight-leaf type, or a hollow shape. Also good. Examples of the composite fiber include PE / PP composite fiber and PE / PET composite fiber. Further, special fibers such as fluorine fibers and glass fibers may be blended depending on the characteristics and purpose of the filtrate.

  The heat-fusible conjugate fiber used in the present invention may contain a functional agent as long as the effects of the present invention are not hindered. As the functional agent, an antibacterial agent, a deodorant, an antistatic agent, a smoothing agent, Examples include hydrophilic agents, water repellents, antioxidants, weathering agents and the like. In addition, the surface of the heat-fusible conjugate fiber may be treated with a fiber finishing agent, thereby imparting functions such as hydrophilicity, water repellency, antistatic, surface smoothness, and abrasion resistance. Can do.

  The fibers constituting the filtration layer nonwoven fabric preferably have a fiber diameter in the range of 0.1 to 200 μm, more preferably a fiber diameter in the range of 1 to 180 μm, and a fiber diameter in the range of 15 to 160 μm. Most preferably it is. By setting it as the fiber diameter of the range of 0.1-200 micrometers, the nonwoven fabric for filter layers obtained is excellent in bulkiness and cushioning properties. If fibers having a small fiber diameter are used, the collection efficiency is improved, but the filtration life (life) tends to be shortened. Therefore, by setting the fiber diameter in the range of 15 to 160 μm, the balance between the filtration life and the collection efficiency is particularly good.

  The average pore diameter of the nonwoven fabric for the filtration layer needs to be adjusted with the average pore diameter of the nonwoven fabric for the base layer and the net, but it can be appropriately selected according to the properties of the filtrate and the purpose of filtration. Designed to match the particle size intended for collection. For example, when the particle diameter for collection is 50 μm, the average pore diameter is preferably in the range of 40 to 60 μm, more preferably 45 to 50 μm. In general, the bridge formation limit depends on the particle size of the powder, but it is considered that the design is such that the relationship between the pore size (De) and the particle size (Dp) is De> 5Dp. The average pore diameter can be set based on the index. The pore size is selected according to the above formula, the physical properties such as the large particle size to be removed using a filter, the small particle size to be passed, the desired collection efficiency, and the like.

The basis weight of the nonwoven fabric for the filtration layer is specified to some extent in relation to the material of the fiber, the fiber diameter and the average pore diameter, but, for example, 5 to 40 g / m ² can be used, and more preferably 10 ˜30 g / m ² . A basis weight of 5 to 40 g / m ² is preferable because the selection range for adjusting the thickness and average pore diameter of the filtration layer is widened.

<Net>
The net inserted into the filtration layer does not affect the collection efficiency of the filter, but is used to create a gap between the through-air nonwoven fabrics, maintain the shape of the filtration layer, and maintain and improve the pressure resistance. Therefore, the net is preferably a monofilament having a fiber diameter in the range of 50 to 300 μm, and more preferably a monofilament having a fiber diameter in the range of 60 to 280 μm. Furthermore, the mesh of the net is preferably in the range of 1 to 5 mm, and more preferably in the range of 1 to 4 mm. By using a net in this range, the filter efficiency is not affected, and the strength of the filter is ensured, so that a filter with a longer filtration life can be obtained.

  The monofilament is preferably made of a thermoplastic resin, and single component fibers, composite fibers, and mixed fibers can be used. The thermoplastic resin that can be used for the monofilament is not particularly limited as long as it is a melt-spinnable thermoplastic resin. For example, the thermoplastic resin exemplified in the heat-fusible conjugate fiber can be used, and a single thermoplastic resin can be used. Even a mixture of two or more thermoplastic resins may be used. When the monofilament is a composite fiber, for example, a combination of thermoplastic resins as exemplified in the heat-fusible composite fiber can be used. For example, PE, PP, PET, nylon 6, nylon 6,6, nylon 6,12 and the like can be mentioned, and PP or nylon is particularly preferable.

<Configuration of filtration layer>
The filter layer of the filter is formed by multiply winding a laminate in which at least the filter layer through-air nonwoven fabric and the net are stacked. The stacking order of the through-air nonwoven fabric and the net is not particularly limited, but it is preferable to wind the through-air nonwoven fabric and the net one by one, that is, the through-air nonwoven fabric and the net alternately. The filtration layer formed in this way has a structure in which a coarse mesh is sandwiched between through-air nonwoven fabrics, and the through-air nonwoven fabric layers are laminated without being in close contact with each other.

  Moreover, the filtration layer laminated body is not thermocompression bonded, and the bulkiness of the through-air nonwoven fabric is maintained. However, “not thermocompression-bonded” means that the entire filtration layer is not integrally hardened by thermocompression bonding. The part may be thermocompression bonded. Further, the filtration layer and the base material layer, or the filtration layer and the skin layer may be fused or bonded.

  In addition to the through-air non-woven fabric and the net, further non-woven fabric or net may be laminated as necessary. For example, in addition to a through-air nonwoven fabric and a net, a melt blown nonwoven fabric having a coarser mesh than the through-air nonwoven fabric can be inserted to wind a three-layer laminate, thereby improving the shape retention and collection efficiency of the filtration layer. . When using a melt blown nonwoven fabric, the same melt blown nonwoven fabric as used for the base material layer and the skin layer can be preferably used.

  It is known that the collection efficiency is controlled by the thickness of the filtration layer through which the fluid passes from the logarithmic transmission law, and the thickness of the filtration layer (the number of turns of the laminate) is appropriately selected according to the desired collection efficiency. be able to. As the thickness of the filtration layer (the number of windings of the laminate) is larger, the collection efficiency is improved, and a powder having a small particle diameter can be collected.

<Nonwoven fabric for base material layer>
The base layer nonwoven fabric used in the present invention may be either a melt blown nonwoven fabric or a through-air nonwoven fabric as long as it has an air permeability in the range of 200 to 300 cc / cm ² / sec when 10 sheets are stacked. Nonwoven fabrics having an air permeability in this range are preferable in terms of low pressure loss.

When using a meltblown nonwoven fabric, the kind of ultrafine fiber which comprises a meltblown nonwoven fabric, and its manufacturing method are not specifically limited, A well-known ultrafine fiber and manufacturing method can be used. For example, a melt-blown nonwoven fabric was obtained by melt-extruding a thermoplastic resin, spinning from a melt-blow spinneret, blow-spinning as a flow of ultra-fine fibers with a high-temperature and high-speed gas, and collecting the ultra-fine fibers as a web with a collection device. It can be manufactured by heat-treating the web and thermally fusing the ultrafine fibers together. As the high-temperature and high-speed gas used in melt blow spinning, an inert gas such as air or nitrogen gas is usually used. The temperature of the gas is generally 200 to 500 ° C., and the pressure is generally in the range of 0.1 to 6.5 kgf / cm ² .

  When the melt blown nonwoven fabric is used for the nonwoven fabric for the base material layer, the average fiber diameter is preferably 1 to 100 μm, more preferably 6 to 60 μm, and most preferably 8 to 30 μm. If the average fiber diameter of the melt blown nonwoven fabric is 1 μm or more, the productivity is good, the mechanical strength of the ultrafine fibers constituting the meltblown nonwoven fabric is high, and the single fiber breakage of the ultrafine fibers and the breakage of the ultrafine fiber layer are less likely to occur. Moreover, if the average fiber diameter of the ultrafine fibers constituting the meltblown nonwoven fabric is 100 μm or less, the original characteristics of the ultrafine fibers derived from the small fiber diameter (fineness) are sufficiently exhibited.

  Moreover, the melt blown nonwoven fabric which consists of a single component fiber, the melt blow nonwoven fabric which consists of composite fibers, the melt blow nonwoven fabric which consists of mixed fiber, etc. can be utilized for a melt blow nonwoven fabric. The resin that can be used for the melt blown nonwoven fabric is not particularly limited as long as it is a melt-spinnable thermoplastic resin. For example, the thermoplastic resin exemplified in the heat-fusible conjugate fiber can be used, and a single heat can be used. A plastic resin may be used, or a mixture of two or more thermoplastic resins may be used. Furthermore, the thermoplastic resin may contain various functional agents as long as the effects of the present invention are not hindered. Specifically, the antibacterial agent, deodorant, hydrophilizing agent, water repellent, surface activity. An agent etc. can be illustrated. In addition, the melt blown nonwoven fabric may be subjected to secondary processing for imparting functions within a range that does not impede its effects, and it is specific to the surface of the ultrafine fibers constituting the hydrophilic or hydrophobic coating treatment and the melt blown nonwoven fabric. Examples thereof include chemical treatment for introducing a functional group and sterilization treatment.

  As resin used for the nonwoven fabric for base material layers, PE, PP, PET, nylon 6, nylon 6,6, nylon 6,12 etc. are mentioned, for example. Moreover, when using a through air nonwoven fabric for the nonwoven fabric for base materials, the general through air nonwoven fabric illustrated by the nonwoven fabric for filtration layers can be utilized.

The average pore diameter of the nonwoven fabric for the base material layer can be appropriately selected according to the properties of the filtrate and the purpose of filtration, but a material larger than the average pore diameter of the through-air nonwoven fabric for the filtration layer is used. Usually, it is preferable to be in the range of 90 μm to 130 μm, and it is particularly preferable to be in the range of 100 μm to 120 μm. The basis weight of the nonwoven fabric for the base material layer is defined to some extent in relation to the material of the fiber, the fiber diameter and the average pore diameter. For example, a basis weight of 5 to 50 g / m ² can be used. It is more preferable to use the m ² basis weight. A basis weight in this range is preferable from the viewpoint of adjusting the outer diameter of the filter and adjusting the strength design of the base material layer.

  The base material layer is a layer mainly for ensuring the strength of the filter, and is preferably a layer in which melt blown nonwoven fabrics are laminated and integrated by thermocompression bonding. The thickness and the number of turns of the base material layer are appropriately set according to the melt blown nonwoven fabric to be used, but are not particularly limited as long as the strength of the filter is ensured and a certain filtration performance is obtained.

<Skin layer>
The skin layer is the layer located on the outermost side of the filter (upstream side of the filtrate), and in particular blocks and prevents large particle aggregates and contaminants from entering the filtration layer, protecting the filtration layer, This layer is mainly intended to maintain the filter form.
The skin layer is a layer containing a nonwoven fabric, and is preferably a layer made of a nonwoven fabric. Although the nonwoven fabric used for a skin layer is not specifically limited, It is preferable that an average pore diameter is a nonwoven fabric larger (coarse) than the average pore diameter of the nonwoven fabric for filtration layers.
Although the material of the nonwoven fabric is not particularly limited, for example, the same melt blown nonwoven fabric as that used for the base material layer is preferably used.

  The number of turns and thickness of the skin layer are not particularly limited, but if the number of turns or thickness increases, there may be a problem that a bridge forms in the skin layer before the filtrate reaches the filtration layer. A layer is preferred. For example, the melt blown nonwoven fabric is preferably wound 1 to 5 times, preferably 1 to 2 times, and thermocompression-bonded.

<Filter manufacturing method>
The filter of this invention can be manufactured by winding, laminating | stacking in order of the nonwoven fabric for base materials, the nonwoven fabric for filtration layers, and a net | network. Specifically, for example, a melt blown nonwoven fabric, which is a nonwoven fabric for a base material layer, is first wound around a cylindrical iron rod while being thermocompression bonded to form a base material layer that becomes a core. Subsequently, a through-air nonwoven fabric and a net, which are nonwoven fabrics for the filtration layer, are sequentially inserted, and rolled up without heating to form a filtration layer. Finally, the meltblown nonwoven fabric is wound 1-2 times and thermocompression bonded to form a skin layer.

  The temperature which forms a base material layer in the said method should just be the temperature by which the nonwoven fabric for base material layers fuse | melts and crimps | bonds in a winding part (cylindrical iron bar). The speed of the production line is not particularly limited, but when forming the filtration layer, the tension applied to the nonwoven fabric is preferably 10 N or less, and it is preferable to wind up without applying tension.

The filter manufactured as described above is suitably used as a cylindrical filter by cutting into an appropriate size and attaching end caps to both ends.
Moreover, said manufacturing method is only an outline | summary and well-known processes, such as heat processing, cooling, chemical | medical agent processing, a shaping | molding, and washing | cleaning, can be implemented as needed other than said process.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not restrict | limited by them.
The measurement methods and definitions of the physical property values shown in the examples are as follows.
1) Measuring method of average pore diameter The average pore diameter was measured by a palm porometer CFP-1200-A manufactured by PMI based on the bubble point method (ASTM F316-86).
2) Measuring method of basis weight The weight of the nonwoven fabric cut into 250 mm × 250 mm was measured to determine the weight per unit area (g / m ² ), which was used as the basis weight.
3) Measuring method of air permeability It measured using the fragile type testing machine as described in JIS L1096.

[Example]
(material)
As the nonwoven fabric for the base material layer, a polypropylene melt blown nonwoven fabric having a basis weight of 42 g / m ² and an air permeability of 10 sheets over 280 cc / cm ² / sec was used.
As a nonwoven fabric for filtration layer, a through-air nonwoven fabric made of polypropylene / polyethylene eccentric sheath-core composite fiber (average fiber diameter 31 μm), having a basis weight of 30 g / m ² and an average pore diameter of 46 μm (4 layers) is used. It was.
As the net, a net made of polypropylene monofilament (average fiber diameter 250 μm) and having a mesh of 2.0 mm was used.

(Filter manufacturing method)
The core (iron bar) was heated to 215 ° C. in advance, and the melt blown nonwoven fabric used for the base material layer was adhered to the core and wound. At this time, the output of the winding heater (the heater immediately adjacent to the winding portion) was set to about 7.8 kW and heated.
The melt blown non-woven fabric used for the base material layer has a total length of 8.6 m, and about 5.6 m of the base material layer is heated at a heater output of 7.8 kW and wound up while being heat-sealed to create a base material layer. .
After winding the melt blown nonwoven fabric by 5.6 m, the insertion of the through-air nonwoven fabric and the net constituting the filtration layer was subsequently started. The insertion length was 2 m, and the film was wound up together with the melt blown nonwoven fabric. At this time, the first 1 m was heat-fused by heating at a heater output of 7.8 kW, and the remaining 1 m was heated at a heater output of 0 kW, and was wound without being heated and heat-sealed to form a filtration layer. Subsequently, the heater output was heated at 7.8 kW, and 1 m was wound up while the melt blown nonwoven fabric was heat-sealed as a skin layer to produce a cylindrical filter.

  A sectional photograph of the filter of the example is shown in FIG.

[Comparative Example 1]
A cylindrical filter was produced in the same manner as in Example except that the filtration layer through-air nonwoven fabric was wound while being thermocompression bonded.

[Comparative Example 2] (conventional product equivalent)
A melt blown nonwoven fabric and a net as a base material are wound around a molded product core (outer diameter 36 mm, thickness 3 mm, length 254 mm, porous cylinder) formed by injection molding, etc. A melt blown nonwoven fabric with a small basis weight was also inserted. Thereafter, only the melt blown nonwoven fabric of the base material was wound up. Thermocompression bonding was not performed.
A cross-sectional photograph of the filter of Comparative Example 2 is shown in FIG.

[performance test]
1. Filtration Life For the cylindrical filters of Examples and Comparative Examples 1 and 2, the change in differential pressure before and after the filter with respect to the cumulative amount of powder added was measured according to the following powder and method.
Seven kinds of test powders described in JIS Z 8901 test powder were used.
The test fluid added with the test powder at a rate of 0.3 g / min in water with a circulating water volume of 30 L / min was passed through the filter, and the change in pressure difference before and after the filter with respect to the cumulative powder addition amount was traced (references: Filter Guidebook for Users Japan Liquid Clarification Technology Association)
The results are shown in FIG.

  As shown in FIG. 1, in the filter of the example, the cumulative amount of powder added until the differential pressure rises is significantly larger than those of Comparative Examples 1 and 2. Since the powder is added at a constant flow rate, this indicates that the time until the differential pressure rises is longer, that is, the filter of the example has a longer filtration life than the filters of Comparative Examples 1 and 2. ing. It is considered that the filter of the example uses a bulky through-air non-woven fabric and maintains an appropriate gap between the non-woven fabric without performing thermocompression bonding, thereby suppressing the formation of bridges and being excellent in filter life.

2. Collection efficiency For the cylindrical filters of Examples and Comparative Example 2, the collection efficiency was measured as the initial collection performance according to the following test powder and method.
Seven kinds of test powders described in JIS Z 8901 test powder were used.
A test fluid obtained by adding JIS 7 seed powder in water at a speed of 0.3 g / min was passed through a filter at a flow rate of 30 L / min, and the number of particles before and after the filter was measured (reference filter filter guidebook for users Nippon Liquid Clarification) Japan Chemical Industry Association).
The number of particles was measured using a particle sensor (manufactured by KS-63 Lion) and a particle counter (manufactured by Lion KL-11).
The collection efficiency was determined by the following definition formula.

Collection efficiency (%) = (1−number of particles having a particle diameter of x μm after passing through the filter / number of particles having a diameter of μm before passing through the filter) × 100
The results are shown in FIG.

  As shown in FIG. 2, the filter of the example collected 90% or more of particles having a size of 50 μm or more and passed almost half of the particles having a size of 30 μm. On the other hand, the filter of Comparative Example 2 collected 90% or more of particles of 50 μm or more, but collected 70% of particles of 30 μm. This result shows that, compared with the filter of Comparative Example 2, the filter of the example can collect the large particles to be removed, but can reliably pass the small particles to be passed, that is, the classification property. It shows that it is excellent.

  Since the filter of the present invention suppresses the occurrence of powder aggregation (bridge), the filter life is long and the classification is excellent. The filter of the present invention removes aggregates and contaminants from suspensions, slurries, and gel fluids containing fine particles (powder) having a low concentration to a high concentration (10 ppm to 70%), and has a particle size of a certain value or less. It is suitably used as a filtration filter used for obtaining fine particles.

Claims (6)

A filter having a base material layer, a filtration layer, and a skin layer,
The base material layer is a layer in which a nonwoven fabric is wound in multiple layers and thermocompression bonded,
The filtration layer is a layer in which a laminate in which at least a through-air nonwoven fabric and a net are laminated is wound in multiple layers, and is not thermocompression bonded,
The skin layer is a layer containing a nonwoven fabric,
The average pore diameter of the nonwoven fabric which comprises the said base material layer and the said skin layer is a filter larger than the average pore diameter of the through-air nonwoven fabric which comprises the said filtration layer.   The filter according to claim 1, wherein in the laminate constituting the filtration layer, a melt blown nonwoven fabric is laminated in addition to the through-air nonwoven fabric and the net. The filter according to claim 1 or 2 , wherein the nonwoven fabric constituting the filtration layer is a through-air nonwoven fabric having an average fiber diameter in the range of 0.1 to 200 µm. The filter according to any one of claims 1 to 3 , wherein the net has a scale in the range of 1 to 5 mm and has an average fiber diameter in the range of 50 to 300 µm. The filter according to any one of claims 1 to 4 , wherein the through-air nonwoven fabric constituting the filtration layer has the fibers fused and / or bonded at the intersection of the fibers in the nonwoven fabric. Having a filter according to any one of claims 1 to 5 cylindrical filter.