JP2013052324A - Composite filter medium and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composit filter medium for a filter in which collecting efficiency of dust in the air is high, pressure loss is low at that time, the coming off of micro glass fiber from the filter medium is a few, which is hardly broken when subjecting to filter processing and filter washing, which has compatively proper rigidity and strength by which mini pleat processing can be easily done, considers the reduction of nonflamable waste materials, can reduce a volume by incineration.SOLUTION: The composite filter medium comprising two layers of an upstream side filter medium layer and a downstream side filter medium layer contains the micro glass fiber having average fiber diameter of 0.1 to 1.0 mm and heat-fusible fiber having a melting point of 50 to 170°C measured by differential scanning calorimetry (DSC) in both layers of the upstream side filter medium layer and the downstream side filter medium layer and further contains polyvinyl alcohol base fiber having Young's modulus of 200 cN/dex or more in at least one layer. Thereby, the above problem can be solved.

Description

  The present invention relates to an air filter medium that collects dust in the air, and more particularly to a filter medium for medium performance and high performance air filters.

  As an air filter medium, an electret filter medium in which the collection efficiency of the melt blown nonwoven fabric is enhanced by electrostatic force is known. However, since the collection efficiency is significantly reduced due to the adhesion of moisture, a filter medium that physically captures particles is required from the viewpoint of reliability. As a filter medium that physically captures particles, a filter medium mainly composed of glass fibers is used.

  An air filter medium mainly composed of glass fibers is manufactured by a method in which chopped strand glass fibers and / or micro glass fibers are mixed and made by a wet papermaking method, and then a binder is added to increase the strength. However, there is a drawback that the filter medium is not elastic and that the folded portion is damaged when it is folded into a filter unit, and that the glass fiber is broken and dropped when an impact is applied. In addition, when the filter is washed and reused, the filter medium is damaged due to an impact at the time of washing, or the binder is eluted due to a detergent or the like, so that the strength of the filter medium is reduced. Further, when the used filter medium is discarded, the glass fiber does not burn even when incinerated, and the volume is hardly reduced.

  In order to solve these problems, a fibrillated organic fiber having a drainage value of 30 to 800 seconds comprising micro glass fibers having an average fiber diameter of 0.1 to 1.0 μm and a rigid linear synthetic polymer for improving the collection efficiency. Has been proposed (see, for example, Patent Document 1). By mixing micro glass fiber and fibrillated organic fiber in the filter medium and drawing out the entanglement effect of both fibers, the problem of fiber detachment from papermaking wire, which is a problem in the case of micro glass fiber alone, at the time of filter processing Resolves corruption issues. In addition, the filter medium can be reduced in volume by incineration. However, in recent years, in order to extend the filter life, a filter medium with lower pressure loss than before has been desired. However, a filter medium in which micro glass fibers and fibrillated organic fibers are mixed has a higher density. In some cases, the pressure loss is not sufficiently low.

  In order to extend the filter life, a method has been proposed in which filter media having different collection efficiencies are closely stacked and simultaneously folded to produce a filter. However, since the thickness of the filter medium is large, the area of the filter medium that can be folded into the filter unit is reduced, and as a result, it is difficult to extend the life (see, for example, Patent Document 2).

  In addition, as a high-performance air filter medium, a non-woven fabric in which glass fibers are mixed with polyester fibers and formed by integrally forming non-woven fabrics having different collection efficiencies, the multi-layer filter medium is made into a mini-pleated shape. Dust filters have been proposed. In this hybrid laminated filter medium, the polyester fiber becomes soft, so the breakage of the folded part is reduced, but the strength is not improved, so that the folded part breaks when processed into a mini-pleated shape. In addition, there remains a problem of damage due to filter cleaning (see, for example, Patent Document 3).

  In order to keep the pressure loss low and prevent the micro glass fiber from falling off, the heat melting fiber having a melting point of 50 to 170 ° C. and the micro glass fiber are contained, and a part of the heat fusible fiber is contained. A heat-fused filter medium (composite filter medium) has been proposed. In this filter medium, the fiber network is formed by the fusing effect of the heat-fusible fiber, so that high collection efficiency and low pressure loss are obtained, and delamination or the like hardly occurs at the time of folding, and the strength is high. A filter medium is obtained (see, for example, Patent Document 4). However, a filter medium mainly composed of micro glass fibers and heat-fusible fibers has a low rigidity, and thus there remains a problem that mini-pleating is difficult.

  In order to facilitate mini-pleating, a filter medium containing fibers having a high Young's modulus and a resin having a glass transition temperature of 30 ° C. or higher has been proposed. However, when the resin is contained, small pores in the filter medium are blocked, leading to deterioration of collection efficiency and pressure loss (for example, see Patent Document 5).

  Moreover, the strength of the filter medium is obtained by adding hot water-soluble polyvinyl alcohol fiber (polyvinyl alcohol fiber binder) to a filter medium containing ultrafine glass fibers having a fiber diameter of 4 μm or less and fusing the fibers together. Has been proposed (see, for example, Patent Documents 6 to 7). However, the polyvinyl alcohol-based fibrous binder has a problem that it clogs small pores in the filter medium and deteriorates the collection efficiency. In addition, the filter medium containing ultrafine glass fibers having a fiber diameter of 1.0 μm or less contains polyvinyl alcohol fibers (fibrous vinylon binder) that form a film in a wet state and heat-fusible fibers, and the strength of the filter medium A filter medium having an improved stencil has also been proposed (see, for example, Patent Document 8). However, the polyvinyl alcohol fiber that forms a film in a wet state also has a problem that it clogs small pores in the filter medium and deteriorates the collection efficiency.

  In this way, the collection efficiency of dust in the air is high, the pressure loss at that time is low, the micro glass fiber does not fall off from the filter medium, it is difficult to break during filter processing and filter cleaning, mini pleat processing There has not yet been obtained a filter medium that has both moderate rigidity and strength that are easy to dispose of and that is also suitable for reducing incombustible waste.

JP-A-8-323121 JP 2001-263089 A International Publication No. WO03 / 043717 Pamphlet JP 2007-144415 A International Publication No. WO08 / 120572 Pamphlet Japanese Patent Laid-Open No. 62-110718 Japanese Patent Laid-Open No. 62-110719 JP 2008-246321 A

  The problem of the present invention is that the collection efficiency of dust in the air is high, the pressure loss at that time is low, the micro glass fiber is not dropped from the composite filter medium, and is difficult to break during filter processing and filter cleaning. An object of the present invention is to provide a composite filter medium for a filter which has moderate rigidity and strength that are easy to carry out mini-pleating processing, and is capable of reducing the volume by incineration in consideration of the reduction of incombustible waste.

  Specific means for solving this problem is as follows.

  (1) A composite filter medium composed of two layers of an upstream filter medium layer and a downstream filter medium layer, and a micro glass fiber having an average fiber diameter of 0.1 to 1.0 μm in both the upstream filter medium layer and the downstream filter medium layer And a heat-fusible fiber having a melting point of 50 to 170 ° C. measured by differential scanning calorimetry (DSC), and at least one layer contains a polyvinyl alcohol fiber having a Young's modulus of 200 cN / dtex or more. A composite filter medium characterized by that.

  (2) The composite filter medium according to (1), wherein the total content of polyvinyl alcohol fibers having a Young's modulus of 200 cN / dtex or more is 2 to 20% in terms of the composite filter medium mass ratio.

  (3) The composite filter medium according to (1) or (2), wherein the total content of the micro glass fibers contained in the upstream filter medium layer and the downstream filter medium layer is 10 to 40% in terms of the composite filter medium mass ratio.

  (4) The ratio of the content (A) of the micro glass fiber contained in the upstream filter medium layer to the content (B) of the micro glass fiber contained in the downstream filter medium layer is (B) / (A) The composite filter medium according to any one of (1) to (3), wherein is 1.0 to 10.0.

  (5) Any one of the above (1) to (4), wherein the average fiber diameter of the micro glass fibers contained in the downstream filter medium layer is smaller than the average fiber diameter of the micro glass fibers contained in the upstream filter medium layer. Composite filter media.

  (6) The total content of heat-fusible fibers having a melting point of 50 to 170 ° C. measured by differential scanning calorimetry (DSC) is 25 to 60% in terms of the mass ratio of the composite filter medium (1) to (5) The composite filter medium according to any one of the above.

  (7) A method for producing a composite filter medium according to any one of the above (1) to (6), wherein a wet paper web of an upstream filter medium layer and a downstream stream using a combination wet paper machine having a plurality of papermaking heads After forming the laminated web composed of the wet filter web of the side filter medium layer, the upstream filter medium layer is brought into close contact with a hot roll having a surface temperature higher than the melting point of the heat-fusible fiber by 10 ° C. or higher while pressing the laminated web. And a downstream filter medium layer are integrated and then dried, and then a method for producing a composite filter medium.

  According to the present invention, the collection efficiency of dust in the air is high, the pressure loss at that time is low, the micro glass fiber is not dropped from the composite filter medium, and is not easily damaged during filter processing or filter cleaning. It is possible to provide a composite filter medium for a filter that has moderate rigidity and strength that are easy to process, and that can reduce the volume by incineration in consideration of the reduction of incombustible waste.

  The composite filter medium of the present invention is a composite filter medium in which two layers of an upstream filter medium layer and a downstream filter medium layer are integrated, with an average fiber diameter of 0.1 to both layers of the upstream filter medium layer and the downstream filter medium layer. It contains 1.0 μm micro glass fiber and heat-fusible fiber having a melting point of 50 to 170 ° C. measured by differential scanning calorimetry (DSC), and at least one layer has a Young's modulus of 200 cN / dtex or more. It is the composite filter medium containing the polyvinyl alcohol type fiber of this.

  The polyvinyl alcohol fiber having a Young's modulus of 200 cN / dtex or more according to the present invention is a polyvinyl alcohol fiber having an increased Young's modulus by adjusting the shape of the fiber cross section, molecular orientation, crystallinity, etc. For example, although what is manufactured by a solvent wet cooling gel spinning method is known, this invention is not limited to this. Moreover, the polyvinyl alcohol fiber having such a high Young's modulus hardly dissolves in hot water or cold water, maintains the shape of the fiber even in the composite filter medium after paper making, and does not form a film in the paper making process. Therefore, the small pores in the filter medium are not blocked. Hereinafter, unless otherwise specified, “polyvinyl alcohol fiber” in the present invention refers to “polyvinyl alcohol fiber having a Young's modulus of 200 cN / dtex or more”.

  Stiffness can also be imparted by including fibers with high Young's modulus that are not polyvinyl alcohol fibers in the composite filter medium, but the affinity between fibers with high Young's modulus and micro glass fibers or heat-fusible fibers If it is low, it becomes a fragile composite filter medium with weak inter-fiber strength, and may be damaged during filter processing or filter cleaning, and mini-pleat processing may be difficult.

  Since the polyvinyl alcohol fiber has moderate hydrophilicity and hydrophobicity, it has a high affinity with both the microglass fiber and the heat-fusible fiber used in the present invention, and the wire from the wire during wet papermaking. Since the outflow of the micro glass fibers can be suppressed and the strength between the fibers is increased, a composite filter medium having a high strength can be obtained.

  Therefore, by containing polyvinyl alcohol fiber in the composite filter medium, it is possible to increase the strength between the fibers, it is possible to obtain a strong composite filter medium, difficult to break during filter processing and filter cleaning, Appropriate rigidity and strength that facilitates mini-pleating can be imparted.

  The total content of the polyvinyl alcohol fiber according to the present invention is preferably 2 to 20% in terms of the mass ratio of the composite filter medium, and particularly preferably 3 to 10%. If the content of the polyvinyl alcohol fiber is too small, sufficient rigidity may not be obtained. On the other hand, when the amount is too large, the content of the microglass fiber and the heat-fusible fiber is relatively low, and sufficient collection efficiency may not be obtained or sufficient strength may not be obtained.

  The Young's modulus of the polyvinyl alcohol fiber according to the present invention is not required to set an upper limit if sufficient rigidity can be secured, but if it is too strong, it becomes difficult to appropriately adjust the rigidity, so 200 to 400 cN / dtex. Is preferred, with 250 to 350 cN / dtex being particularly preferred.

  The fineness of the polyvinyl alcohol fiber according to the present invention is preferably 1 to 20 dtex, particularly preferably 1.5 to 10 dtex, and further preferably 2 to 7 dtex. If the fineness is too small, sufficient rigidity may not be obtained. If the fineness is too large, the formation may be poor, or the rigidity may be too strong, making mini-pleating difficult.

  The fiber length of the polyvinyl alcohol fiber according to the present invention is preferably 1 to 15 mm, particularly preferably 2 to 10 mm, and further preferably 3 to 7 mm. If the fiber length is too long, poor formation is likely to occur, thereby creating large pores and reducing the collection efficiency. On the other hand, when the fiber length is too short, the mechanical strength of the composite filter medium is lowered, and the composite filter medium may be easily damaged.

  A composite filter medium may be prepared by blending a plurality of polyvinyl alcohol fibers having different finenesses, different fiber lengths or different Young's moduli as necessary.

  The micro glass fiber according to the present invention is one of fibers that determine the collection efficiency. The average fiber diameter of the micro glass is 0.1 to 1.0 μm, and particularly preferably 0.3 to 0.8 μm. When the average fiber diameter is too large, the effect of improving the collection efficiency is reduced. On the other hand, if the average fiber diameter is too small, the flow of micro glass fibers from the wire increases during wet papermaking, and the yield may be very poor.

The “fiber diameter” as used in the present invention refers to the fiber diameter of a value converted into a true circular diameter having the same cross-sectional area when the cross section of the fiber is an ellipse or a polygon, and is referred to in the present invention. The “average fiber diameter” indicates a mass average fiber diameter calculated by ΣDi ² Ni / ΣDiNi when Ni fibers having a fiber diameter Di exist.

  The total content of micro glass fibers contained in the upstream filter medium layer and the downstream filter medium layer is preferably 10 to 40%, particularly preferably 15 to 30%, in terms of the mass ratio of the composite filter medium. If the total content of microglass is too high, the pressure loss may become too large. Moreover, when there is too little content of micro glass, sufficient collection efficiency may not be acquired.

  Also, from the viewpoint of environmental problems that are increasingly regarded as problems in the future, in order to reduce incombustible waste, the total content of micro glass fibers contained in the upstream filter medium layer and the downstream filter medium layer is Is preferably 50% or less, more preferably 40% or less. When it exceeds 50 mass%, since the glass fiber is nonflammable, the effect of volume reduction by incineration decreases.

  The ratio (B) / (A) of the content (A) of the micro glass fiber contained in the upstream filter medium layer and the content (B) of the micro glass fiber contained in the downstream filter medium layer was 1.0. -10.0 is preferable, Especially preferably, it is 1-5, More preferably, it is 1-3. When the content of micro glass fibers in the upstream filter medium layer is small, the content of micro glass fibers in the downstream filter medium layer is large, and (B) / (A) exceeds 10.0, the captured dust is upstream. Since it accumulates in the vicinity of the interface between the side filter medium layer and the downstream filter medium layer, and the pressure loss is likely to increase, the life of the composite filter medium may be shortened. On the other hand, when the content of the micro glass fiber in the upstream filter medium layer is large, the content of the micro glass fiber in the downstream filter medium layer is small, and (B) / (A) is less than 1.0, Most of the water is trapped by the upstream filter medium layer, and only a small amount of dust reaches the downstream filter medium layer, so that the pressure loss is likely to increase and the life of the composite filter medium may be shortened.

  Moreover, it is preferable that the average fiber diameter of the micro glass fiber contained in a downstream filter medium layer is smaller than the average fiber diameter of the micro glass fiber contained in an upstream filter medium layer. Particularly preferably, the ratio (D1) / (D2) of the average fiber diameter (D1) of the micro glass fibers contained in the downstream filter medium layer and the average fiber diameter (D2) of the micro glass fibers contained in the upstream filter medium layer. ) Is 0.5 to 0.9. By making the average fiber diameter of the micro glass fibers in the downstream filter medium layer smaller than the average fiber diameter of the micro glass fibers in the upstream filter medium layer, mainly the large particle size dust in the upstream filter medium layer By sequentially capturing mainly small particle size dust in the filter medium layer, the dust holding capacity can be increased and the pressure loss can be reduced. On the other hand, when the average fiber diameter of the micro glass fibers in the upstream filter medium layer is smaller than the average fiber diameter of the micro glass fibers in the downstream filter medium layer, most of the dust is captured by the upstream filter medium layer, and downstream Since only a small amount of dust reaches the side filter medium layer, pressure loss tends to increase, and the life of the composite filter medium may be shortened. Moreover, when ratio (D1) / (D2) of average fiber diameter exceeds 0.9, the average fiber diameter of the micro glass fiber in a downstream filter medium layer is set to the average fiber of the micro glass fiber in an upstream filter medium layer. The effect smaller than the diameter may not be recognized.

  In order to adjust the average fiber diameter, a plurality of micro glass fibers having different average fiber diameters may be mixed as necessary to produce a composite filter medium.

The material for the micro glass fiber according to the present invention is not particularly limited, and quartz glass having higher silica purity can be used in addition to a general borosilicate system. In the case of a general borosilicate system, when used in the semiconductor industry, the glass fiber surface is eroded by contact with a small amount of acid or alkali, and a small amount of metal (B ⁻ , Na ^+, etc.) is generated. It has been viewed as a problem. When micro glass fiber having an extremely low boron oxide content is used, there is no problem of deterioration due to acid or alkali in the semiconductor manufacturing process, and therefore, it can be applied to a clean room filter.

  The composite filter medium of the present invention contains heat-fusible fibers having a melting point of 50 to 170 ° C. measured by differential scanning calorimetry (DSC) in both the upstream filter medium layer and the downstream filter medium layer. Moreover, the melting point of the particularly preferable heat-fusible fiber is 60 to 140 ° C. When the melting point is less than 50 ° C., when the composite filter medium is exposed to a high temperature, the heat-fusible fiber may soften and the strength may be reduced. On the other hand, when the melting point exceeds 170 ° C., it is necessary to heat and dry at a high temperature in order to develop the heat fusion function, and much energy is required. The melting point can be measured according to JIS K7121.

  In addition, by incorporating a heat-fusible fiber and incorporating a step of raising the temperature above the melting temperature of the heat-fusible fiber, the mechanical strength against bending when the composite filter medium is filtered is improved. Can do. In addition, since the heat-fusible fiber forms a network, it not only exhibits strength against bending, but can also form a uniform network with other fibers constituting the composite filter medium, and has strength while capturing. It becomes a composite filter medium with high collection efficiency.

  Examples of the heat-fusible fiber according to the present invention include single fibers, and composite fibers such as core-sheath fibers (core-shell type), parallel fibers (side-by-side type), and radial split fibers. Since the composite fiber hardly forms a film, the mechanical strength can be improved while maintaining the space of the composite filter medium. Examples of heat-fusible fibers include polypropylene fiber, a combination of polypropylene (core) and polyethylene (sheath), a combination of polypropylene (core) and ethylene vinyl alcohol (sheath), polypropylene (core) and vinyl acetate alcohol (sheath). , A combination of polypropylene (core) and polyethylene (sheath), a combination of high-melting polyester (core) and low-melting polyester (sheath), and the like. In addition, a single fiber (total melt type) composed only of a low melting point resin such as polyethylene and a hot water soluble binder such as a hot water soluble polyvinyl alcohol fiber can easily form a film in the drying step of the composite filter medium. , Can be used as long as the properties are not impaired.

  As for the content of the heat-fusible fiber, the total content in the upstream filter medium layer and the downstream filter medium layer is preferably 25 to 60%, more preferably 30 to 55% in terms of mass ratio of the filter medium. . If there are too few heat-fusible fibers, the peel strength and folding strength of the composite filter medium will be insufficient, delamination will occur during folding, and the folds will swell, increasing structural pressure loss, Cracks may occur. If the amount is too large, the composite filter medium may become dense, pressure loss may increase, and filter life may be shortened.

  Although the fiber diameter of a heat-fusible fiber is not specifically limited, It is preferable that it is 3-25 micrometers, More preferably, it is 5-20 micrometers. When the fiber diameter is less than 3 μm, the pressure loss of the composite filter medium increases, and the life of the filter tends to be shortened. Also, when the fiber diameter exceeds 25 μm, the pressure loss of the composite filter medium is reduced, but the voids of the network increase, so that other fibers (for example, micro glass fibers) constituting the composite filter medium from the papermaking wire at the time of papermaking There are cases where the number of omissions increases and the collection efficiency decreases. In addition, the specific surface area to be fused is reduced, and it may be difficult to improve the strength of the composite filter medium such as folding strength and peel strength.

  In order to increase the bending resistance, the fiber length of the heat-fusible fiber is preferably 2 to 15 mm, more preferably 3 to 10 mm. When the fiber length is less than 2 mm, since the number of fibers intersecting with the single fiber of the heat-fusible fiber is small, the fiber intersection that is fused by the impact in the folding process such as pleating at the time of manufacturing the filter unit is It may come off or the fibers may fall off. On the other hand, when it exceeds 15 mm, the fiber dispersibility before papermaking is poor, resulting in a poor composite filter medium, which may deteriorate the yield of microglass fibers.

  In the composite filter medium of the present invention, the upstream filter medium layer and / or the downstream filter medium layer may contain non-heat-bondable fibers that do not have heat-bondability, if necessary. In particular, fibers that are thinner than heat-fusible fibers and polyvinyl alcohol fibers and thicker than micro glass fibers are entangled so as to converge on thick fibers, so that the number of junctions can be increased and the fixing force between fibers can be increased. This is preferable. In the fiber dispersion process of a paper machine, when all the fibers are dispersed in water with a pulper stirrer, each fiber is randomly arranged and then dehydrated at the paper machine wire section to form a web. By disposing the fusible fibers with other fibers, the fibers are entangled with each other while forming voids, thereby forming a good three-dimensional network. Therefore, it becomes uniform formation, air permeability can be ensured by maintaining appropriate space while maintaining the collection performance, and appropriate pressure loss can be obtained.

  In addition, as for content in the case of containing a non-heat-bondable fiber, 20-60 mass% is preferable by composite filter medium mass ratio. When there are few non-heat-fusible fibers, the contained effect may not be recognized. On the other hand, if there are too many non-heat-fusible fibers, the content of microglass fibers and heat-fusible fibers will be relatively low, and sufficient collection efficiency will not be obtained, and sufficient strength will be obtained. There may not be.

  In the present invention, an organic fiber having a fiber diameter of 1 to 20 μm can be suitably used as the non-heat-bondable fiber. Specific examples of natural fibers include hemp pulp, cotton linter, and lint with few coatings; recycled fibers include lyocell fiber, rayon, and cupra; semi-synthetic fibers include acetate, triacetate, and promix; synthetic fibers , Polyolefin-based, polyamide-based, polyacrylic-based, vinylon-based, vinylidene, polyvinyl chloride, polyester-based, nylon-based, polyolefin-based, benzoate, polyclar, and phenol-based fibers. In addition to the above-mentioned fibers, wood fibers such as conifer pulp and hardwood pulp, woods such as bamboo pulp, bamboo pulp, kenaf pulp, and herbs can be used as plant fibers. These fibers may be fibrillated as long as they do not impair liquid permeability and air permeability. Furthermore, pulp fibers obtained from waste paper, waste paper, etc. can also be used. Further, fibers having an irregular cross section such as a T-shape, Y-shape, or triangle can be included for ensuring air permeability and liquid permeability. Further, the non-heat-fusible fiber contained in the composite filter medium of the present invention also has an aspect of adding a new function to the composite filter medium. For example, by using a flame retardant fiber, a composite filter medium having flame retardancy can be obtained without post-processing such as application of a flame retardant.

Although the thickness of the composite filter medium of this invention is not specifically limited, It is preferable that it is 100-800 micrometers, More preferably, it is 200-500 micrometers. If it is less than 100 μm, the composite filter medium may not be sufficiently firm, and good pleating may not be possible. On the other hand, if the thickness exceeds 800 μm, pleating is possible, but the gap between the folded composite filter media in the filter unit is reduced, the structural pressure loss is increased, and as a result, the filter may have a short life. Although the basic weight of the composite filter medium of the present invention is not particularly limited, it is preferably ²⁰ to 150 g / m ² , more preferably 50 to 120 g / m ² in consideration of strength when processing into a filter and a necessary filter medium area. is there.

Since dust is first captured by the upstream filter medium layer, the upstream filter medium layer needs to have a certain thickness and / or basis weight. On the other hand, the downstream filter medium layer supplements only the dust that has passed through the upstream filter medium layer, and may be thinner and / or lighter than the upstream filter medium layer, but in order to obtain sufficient collection efficiency Some degree of thickness and / or basis weight is required. Moreover, when both the upstream filter medium layer and the downstream filter medium layer are too thick / heavy, the composite filter medium may be cracked during pleating, and the pressure loss may become too large. Therefore, the basis weight of the upstream filter medium layer is preferably 10 to 120 g / m ² , more preferably 20 to 100 g / m ² . Moreover, 5-80 g / m < ² > is preferable and, as for the basic weight of a downstream filter medium layer, More preferably, it is 10-50 g / m < ² >. Further, the thickness of the upstream filter medium layer is preferably 100 to 600 μm, more preferably 100 to 400 μm. Moreover, 20-300 micrometers is preferable and, as for the thickness of a downstream filter medium layer, More preferably, it is 30-200 g / m < ² >.

  The composite filter medium of the present invention preferably has a bending strength of 1.0 or more according to JIS P8115 MIT testing machine. When the composite filter medium of the present invention is folded (pleated), the blade of the folding machine is pressed against the composite filter medium to make a crease, or after passing between concavo-convex rolls, Folded. When the folding strength is less than 1.0, the composite filter medium may be cracked or broken by wind pressure after the filter is completed. In addition, when the filter is washed and reused, the composite filter medium may be damaged by the impact during washing.

  The composite filter medium of the present invention is a paper machine for producing general paper or wet nonwoven fabric, for example, a long net paper machine, a circular net paper machine, an inclined wire type paper machine, etc. The above is preferably manufactured by a combination paper machine installed on-line. At that time, the laminating method is a method of laminating wet paper webs made by each paper machine, forming one wet paper web, and then forming a raw material slurry in which fibers are dispersed on the wet paper web. A method of forming a composite filter medium by pouring may be used. Moreover, the method of flowing the raw material slurry which disperse | distributed the fiber on the dry web and forming a composite filter medium may be used.

  The wet paper web produced by these paper machines is dried by heating, and a composite filter medium is formed by the heat-fusible fibers contained in the wet paper web. As a means for drying by heating, methods such as a cylinder dryer, an air dryer, a suction drum type dryer, and an infrared type dryer can be used, but a heat-sealable fiber can be fused efficiently to obtain higher strength. As a method, a heating method using a cylinder dryer is preferable. As a heating method using a cylinder dryer, only one side may be brought into contact with a hot roll while being pressed with a touch roll, or a composite filter medium is passed between cylinder dryers held in a felt, and the front and back are sequentially heated. You may make it contact.

  A particularly preferable method for producing a composite filter medium is to use a combination wet paper machine having a plurality of paper making heads to form a laminated web composed of a wet paper web of an upstream filter medium layer and a wet paper web of a downstream filter medium layer, A composite filter medium to be dried after the upstream filter medium layer and the downstream filter medium layer are integrated by bringing the laminated web into close contact with a hot roll having a surface temperature of 10 ° C. or more higher than the melting point of the heat-fusible fiber. It is a manufacturing method. According to this manufacturing method, due to the fusing effect of the heat-fusible fiber, a fiber network is formed in each layer, and both layers can be fused, and delamination or the like hardly occurs during folding. A composite filter medium having high strength can be obtained.

The composite filter medium of the present invention preferably has a water repellency as defined in JIS B9927 of 1 kPa or more, more preferably 5 kPa or more. The water repellency of the HEPA filter medium defined in MIL-STD-282 is 508 mmH ₂ O (4.98 kPa) or more, but not all HEPA filter media comply. However, when the water repellency is measured by a method defined in JIS B9927 with reference to the MIL standard as a necessary and sufficient value, a value of 5 kPa or more can be said to be a filter medium having sufficient water repellency.

  In the composite filter medium of the present invention, in order to make the water repellency 1 kPa or more, it is preferable that at least the upstream filter medium layer contains a water repellency compound. The content of the water repellent compound is preferably 0.01 to 10% by mass, more preferably 0.1 to 5% by mass with respect to the fibers constituting the upstream filter medium layer. When the content of the water repellent compound is less than 0.01% by mass, the water repellency of 1 kPa or more may not be obtained. When the content exceeds 10% by mass, the water repellent effect is excessive and not economically preferable. In addition, there is a possibility that the collection efficiency is lowered by excessively blocking the micropores of the composite filter medium. In the composite filter medium of the present invention, when the environment (temperature, humidity, etc.) in which the composite filter medium is used is not so severe, or when it is unlikely that the air to be ventilated will be highly humid, only the upstream filter medium layer is water repellent. A compound may be included, but a water-repellent compound may also be included in the downstream filter medium layer.

  In the composite filter medium of the present invention, as the water-repellent compound, for example, silicon-based and fluorine-based compounds are used, and when imparted by an internal addition method, rosin-based, reinforced rosin-based, alkyl ketene dimer-based, alkenyl succinic anhydride-based A paper sizing agent such as can be suitably used.

  In the composite filter medium of the present invention, as a method for imparting water repellency, an internal addition method in which a water-repellent compound is added to a raw material slurry before paper making, and a wet paper state after paper making or impregnation or coating after drying are performed. Examples include an external addition method in which a water-repellent compound is applied and dried. The composite filter medium of the present invention can be used by either method. In the external addition method, the impregnation or coating method is not particularly limited, and examples thereof include a size press method, a tab size press method, a spray method, an internal addition method, and a gravure coating method.

  In the application method of water repellent compounds, the external addition method requires steps from impregnation or coating to drying and the accompanying production equipment, and in some cases, can reduce the performance of the filter media obtained by papermaking. There is sex. Therefore, the internal addition method is preferable. In addition, when the use environment of the filter is not so severe, or when the possibility that the air to be ventilated will be high is low, water repellency may be given only to the upstream filter medium layer. The internal addition method is suitable for the composite filter medium of the invention. In addition, in the external addition method, in order to impart water repellency only to the upstream filter medium layer, a water repellent compound may be supplied from the upstream filter medium layer side in the coating process, and a spray method or a gravure coating method is used. It is preferable.

  In the composite filter medium of the present invention, additives such as a cross-linking agent, a dispersant, a yield improver, a paper strength agent, a flame retardant, a dye, and a resin are appropriately blended as needed, as long as the characteristics of the composite filter medium are not impaired. be able to. As a method for applying these additives, an internal addition method and an external addition method can be appropriately selected and used in the same manner as in the case of applying the water repellent compound. For example, by adding a flame retardant, a composite filter medium having flame retardancy is obtained. The flame retardant used in the present invention is preferably a halogen-free flame retardant from the viewpoint of safety and environment, and examples thereof include inorganic phosphorus, organic phosphorus, and metal hydroxides.

  Moreover, in order to provide mechanical strength and water resistance, a thermoplastic resin and a thermosetting resin can be contained. Examples of such resins include latexes such as acrylic, vinyl acetate, epoxy, synthetic rubber, urethane, polyester, and vinylidene chloride, polyvinyl alcohol, starch, and phenol resin. These can be used alone or in combination of two or more. The amount of the thermoplastic resin to be contained in the composite filter medium is suitably 0.01 to 10% by mass with respect to the composite filter medium. If it exceeds 10% by mass, the pressure loss of the composite filter medium increases. Moreover, if it is less than 0.01 mass%, compared with the composite filter medium which does not contain a thermoplastic resin, mechanical strength and water resistance may not improve.

  Further, in order to further extend the filter life, in order to obtain a composite filter medium having a three-layer structure or more, if necessary, the nonwoven fabric manufactured by a dry method such as spunbond, chemical bond, melt blow, and the paper machine manufactured according to the present invention. The composite filter medium having a two-layer structure may be laminated with a paper machine, or may be laminated with a separate processing machine. In that case, it is preferable to laminate the nonwoven fabric manufactured by the dry method on the upstream filter medium layer surface of the composite filter medium of the present invention.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to the examples. First, a method for measuring the melting point of the heat-fusible fiber and a method for evaluating the filter medium will be described.

Measuring method of melting point of heat-fusible fiber <Melting point of heat-fusible fiber (unit: ° C.)>
The melting point of the heat-fusible fiber was measured using a differential scanning calorimeter DSC7 manufactured by PERKIN ELMER. The measurement was performed under a temperature rising condition of 10 ° C./min up to 25 to 300 ° C.

Evaluation method of filter medium <pressure loss (unit: Pa)>
In accordance with JIS B9927, aeration was conducted at a wind speed of 5.3 cm / sec, the difference in static pressure between the upstream side and the downstream side of the filter medium was measured, and the pressure loss ΔP was calculated from Equation 1 below.

(Formula 1)
ΔP = SP1-SP2
ΔP: Pressure loss (Pa)
SP1: Upstream static pressure (Pa)
SP2: Downstream static pressure (Pa)

  A lower pressure loss is better, and 350 Pa or less is a practically usable level. Moreover, 250 Pa or less is an excellent filter medium, and 150 Pa or less is a particularly excellent filter medium.

<Particle collection efficiency (unit:%)>
The surface wind speed was measured at 5.3 cm / sec in accordance with JIS B9908. Particles to be measured are measured using a particle counter (trade name “KC-11”, manufactured by Rion Co., Ltd.) for the collection efficiency of particles having a particle diameter of 0.3 to 0.5 μm using atmospheric dust. From the following formula 2, the collection efficiency η was calculated.

(Formula 2)
η = (1−C2 / C1) × 100
η: Collection efficiency (%)
C1: Number of particles on the upstream side of the filter medium (per unit time, per unit flow rate)
C2: Number of particles downstream of the filter medium (per unit time, per unit flow rate)

  The higher the collection efficiency, the better, and 60% or more can be used as a filter medium. Moreover, in a high performance filter, the thing of 90% or more, 97% or more, 99% or more, and 99.9% or more is used according to a use.

<Folding resistance>
Ten test pieces each having a width of 15 mm and a length of 110 mm were collected from the filter medium. For each test piece, the number of foldings was measured with a load of 500 g using a MIT tester by the method specified in JIS P8115. Folding strength was calculated from the obtained folding resistance value from the following Equation 3, and the average value of 10 test pieces was compared for each filter medium.

(Formula 3)
FE = log ₁₀ N
FE: Folding strength N: Folding resistance

  The higher the bending strength, the better, and 1.0 or more is practically necessary, and 3.5 or more is an excellent filter medium.

<Mini-pleated processing>
The ease with which the filter medium was processed into mini-pleats with an interval of 5 cm, or whether there was a problem such as breakage or peeling during processing, was evaluated according to the following criteria.
○: Can be processed without problems. Good workability.
Δ: Workability is inferior due to rigidity, but processing is possible. There are no problems such as filter media breakage.
X: There is a problem such as breakage, and it cannot be processed into mini-pleats.

<Water repellency (unit: kPa)>
Three test pieces of about 100 × 100 mm square were collected from the filter medium, measured for water repellency using a water repellency measuring device according to JIS B9927, and compared with the minimum values.

  If the water repellency is 1 kPa or more, it is a practically usable level, and particularly 5 kPa or more is an excellent filter medium.

<Dust retention amount A (unit: g / m ² )>
A filter was prepared using a filter medium so as to have a filter medium area (30 m ² ). Using a dust retention meter, load dust until the filter pressure loss reaches 300 Pa under the conditions of dust: JIS 15 types, air volume: 56 m ³ / min, dust concentration: 70 mg / m ³ The dust holding capacity per area was calculated.

(Formula 4)
W1 = (W1a−W1b) / 15
W1: Dust holding capacity per unit area (g / m ² )
W1a: Mass of the filter unit at the end of the dust holding capacity test (g)
W1b: Mass of filter unit at start of dust holding capacity test (g)

The larger the number, the better the dust holding amount A, 20 g / m ² or more is a practically usable level, and particularly 40 g / m ² or more is an excellent filter medium.

<Dust retention amount B (unit: g / m ² )>
A filter was prepared using a filter medium so as to have a filter medium area (30 m ² ). With a dust retention meter, load dust until the filter pressure loss reaches 1000 Pa under the conditions of dust: JIS 15 types, air volume: 70 m ³ / min, dust concentration: 70 mg / m ³ The dust holding capacity per area was calculated.

(Formula 5)
W2 = (W2a−W2b) / 30
W2: Dust holding capacity per unit area (g / m ² )
W2a: Mass of the filter unit at the end of the dust holding capacity test (g)
W2b: Mass of filter unit at start of dust holding capacity test (g)

The larger the number, the better the dust holding amount B, and 40 g / m ² or more is a practically usable level, and particularly 70 g / m ² or more is an excellent filter medium.

<Ashes after incineration (Unit:%)>
The ash content after incineration was calculated by calculating the ash content using Equation 6 by heating and burning the filter medium in an electric furnace at 900 ° C. for 2 hours.

(Formula 6)
X = (m1 / m2) × 100
X: Ash content (%)
m1: Mass of filter medium after combustion (g)
m2: Mass of filter medium before combustion (g)

  The smaller the number of ash after incineration, the higher the incineration volume reduction effect of incombustible waste.

<Fiber>
The fibers used in Examples and Comparative Examples are shown in Table 1.

Examples 1-12 and Comparative Examples 1-8
After adding water to a dispersion tank of 2 m ³ , blended in the ratios shown in Tables 2 to 4 and dispersed for 5 minutes at a dispersion concentration of 0.2% by mass, the upstream with different types and / or contents of polyvinyl alcohol fibers A fiber dispersion for the side filter medium layer and a fiber dispersion for the downstream filter medium layer were prepared. In order to have water repellency, at the time of preparation of the upstream filter medium layer fiber dispersion, an alkyl ketene dimer sizing agent (trade name: AD1602, manufactured by Seiko PMC Co., Ltd.) is added at 1% by mass to the upstream filter medium layer. A fiber dispersion was prepared.

Using a combination paper machine in which a long net paper machine and a circular net paper machine are installed online, the upstream filter media layer is formed on the long net paper machine so that the dry mass is 40 g / m ² , and the downstream side After forming the web so that the filter medium layer has a dry mass of 40 g / m ² with a circular paper machine and making both webs before drying, the touch roll is set to 400 N / min with a cylinder dryer having a surface temperature of 130 ° C. pressure while drying and integrated under a pressure of cm ^2, and obtain a composite filter media 12 and Comparative filter medium 1-2.

  Table 5 shows the evaluation results of the composite filter media 1-12 and the comparative filter media 1-8.

  From the comparison of Example 4, Examples 9 to 12, and Comparative Examples 1 and 2, by including a polyvinyl alcohol fiber having a Young's modulus of 200 cN / dtex or more, the bending strength is reduced without impairing other properties. A high composite filter medium can be obtained. In addition, from the comparison of Examples 1 to 8, Example 1 has a low folding strength compared to Examples 2 to 8, and the mini-pleating process is slightly difficult, and Example 8 has a high folding resistance. However, since the mini-pleating process was slightly difficult, by making the content of polyvinyl alcohol fiber 2% to 20% by mass ratio of the composite filter medium, a composite filter medium particularly excellent in folding resistance and mini-pleating process can be obtained. Can be obtained.

  Further, from the comparison between Example 4 and Comparative Example 3, the polyvinyl alcohol that forms a film in a wet state without containing any of the polyvinyl alcohol fiber having a Young's modulus of 200 cN / dtex or more and the heat-fusible fiber. When a system fiber (fibrous vinylon binder) is used, the pressure loss is high and the collection efficiency is low. Moreover, folding resistance is also low.

  Further, from comparison between Example 4 and Comparative Examples 4 to 5, when a polyvinyl alcohol-based fibrous binder is used without including a heat-fusible fiber, a Young's modulus of 200 cN / dtex or more is included. Even if it was made to have, the folding resistance was low and it was difficult to carry out the mini-pleating process. In particular, when the content of the polyvinyl alcohol-based fibrous binder was increased, the filter medium was damaged during the mini-pleating process. Moreover, the pressure loss is high and the collection efficiency is low.

  Further, from the comparison between Example 4 and Comparative Examples 6 to 7, if a polyvinyl alcohol-based fibrous binder is used, sufficient folding resistance cannot be obtained even if heat-fusible fibers are contained. Moreover, the pressure loss is high and the collection efficiency is low.

  On the other hand, from the comparison between Example 4 and Comparative Example 8, even when a fiber having a Young's modulus of 200 cN / dtex or more, which is not a polyvinyl alcohol fiber, is used, the bending resistance is low.

Examples 13 to 27 and Comparative Examples 9 to 10
The upstream filter medium which mix | blends by the ratio shown to Tables 6-8, and differs in the ratio of the average fiber diameter and / or content of micro glass system fiber, and the content of the micro glass contained in an upstream filter medium layer and a downstream filter medium layer Composite filter media 13 to 27 and comparative filter media 9 to 10 are obtained in the same manner as in Examples 1 to 12 and Comparative Examples 1 to 8 except that the fiber dispersion for layers and the fiber dispersion for downstream filter media layers are used. It was.

  Table 9 shows the evaluation results of the composite filter media 13 to 27 and the comparative filter media 9 to 10.

  From the comparison of Example 4, Examples 13 to 17 and Comparative Examples 9 to 10, by using micro glass fibers having an average fiber diameter of 0.1 to 1.0 μm, the collection efficiency is high and the dust holding amount is large. A composite filter medium can be obtained. In particular, when a micro glass fiber having a thickness of 0.3 to 0.8 μm is used, the pressure loss can be kept low. From the comparison of Example 18 with Examples 13 to 17 and Examples 19 to 27, in order to increase the collection efficiency, the content of the microglass fiber is 10% or more in terms of the mass ratio of the composite filter medium. From the comparison between Example 27 and Examples 13 to 26, if the content of the micro glass fiber is large, the bending strength is lowered. Therefore, the content of the micro glass fiber is 10 to 40% in terms of the mass ratio of the composite filter medium. Especially excellent.

  Further, from comparison between Example 21 and Example 22 and comparison between Example 23 and Example 24, the content (A) of the microglass contained in the upstream filter medium layer and contained in the downstream filter medium layer When the ratio (B) / (A) of the content (B) of the micro glass is 1.0 to 10.0, both the collection efficiency and the dust holding amount are excellent. This was captured when the content of micro glass fibers in the upstream filter medium layer was small, the content of micro glass fibers in the downstream filter medium layer was large, and (B) / (A) exceeded 10.0. This is presumably because dust tends to accumulate near the interface between the upstream filter medium layer and the downstream filter medium layer, and pressure loss tends to increase. In addition, when the content of the micro glass fiber in the upstream filter medium layer is large, the content of the micro glass fiber in the downstream filter medium layer is small, and (B) / (A) is less than 1.0, It is presumed that most of this is trapped by the upstream filter medium layer and the pressure loss is likely to increase.

  Further, from comparison between Example 4 and Examples 13 to 17, when the average fiber diameter of the microglass fibers in the downstream filter medium layer is smaller than the average fiber diameter of the microglass fibers in the upstream filter medium layer, There is much holding capacity. This is because, by sequentially capturing mainly large particle size dust in the upstream filter medium layer and mainly small particle size dust in the downstream filter medium layer, the dust holding capacity can be increased and the pressure loss can be reduced. This is presumed.

Examples 28-32 and Comparative Example 11
Example 1-12 except having mix | blended by the ratio shown in Table 10, and using the fiber dispersion liquid for upstream filter media layers and the fiber dispersion liquid for downstream filter media layers from which the kind and content of heat-fusible fiber differ. Composite filter media 28-32 and comparative filter media 11 were obtained in the same manner as in Comparative Examples 1-8.

  Table 11 shows the evaluation results of the composite filter media 28 to 32 and the comparative filter media 11. In the comparative filter medium 11, the filter medium was easily damaged during filter processing, and a filter could not be obtained.

  From the comparison between Examples 4 and 28 to 32 and Comparative Example 11, by including heat-fusible fibers in both the upstream filter medium layer and the downstream filter medium layer, the other characteristics were not impaired, and the folding resistance was improved. A composite filter medium having high strength can be obtained. Moreover, by comparing the content of the heat-fusible fiber with the composite filter medium mass ratio of 25% or more from the comparison between Examples 4 and 28 to 31 and Example 32, a composite filter medium having high folding resistance is obtained. And a composite filter medium excellent in mini-pleating can be obtained. However, as shown in Example 30, a composite filter medium can be produced even when the content of heat-fusible fibers exceeds 60% by mass ratio of the composite filter medium, but the content of microglass fibers is relatively Since the amount of heat-fusible fiber is 25 to 60% in the mass ratio of the composite filter medium, the composite filter medium particularly excellent in both the collection efficiency and folding resistance can be obtained. Can be obtained.

  The composite filter medium of the present invention is used for air filters for semiconductor, liquid crystal, bio, pharmaceutical, food industry clean rooms and clean benches, air filters for air conditioning, air filters for air cleaners, gas turbines and steam turbines on the intake side It can be suitably used for an industrial air filter suitable for collecting particles in air or gas. It can also be used as a liquid filtration filter.

Claims (7)

  A composite filter medium comprising two layers of an upstream filter medium layer and a downstream filter medium layer, wherein both the upstream filter medium layer and the downstream filter medium layer have micro glass fibers having an average fiber diameter of 0.1 to 1.0 μm, and a differential It contains a heat-fusible fiber having a melting point of 50 to 170 ° C. measured by scanning calorimetry (DSC), and at least one layer contains a polyvinyl alcohol fiber having a Young's modulus of 200 cN / dtex or more. A composite filter medium.   The composite filter medium according to claim 1, wherein the total content of polyvinyl alcohol fibers having a Young's modulus of 200 cN / dtex or more is 2 to 20% in terms of the composite filter medium mass ratio.   The composite filter medium according to claim 1 or 2, wherein the total content of the microglass fibers contained in the upstream filter medium layer and the downstream filter medium layer is 10 to 40% in terms of the composite filter medium mass ratio.   The ratio of the content (A) of the micro glass fiber contained in the upstream filter medium layer to the content (B) of the micro glass fiber contained in the downstream filter medium layer is 1.0 (B) / (A). The composite filter medium according to claim 1, which is ˜10.0.   The composite filter medium according to any one of claims 1 to 4, wherein an average fiber diameter of the micro glass fibers contained in the downstream filter medium layer is smaller than an average fiber diameter of the micro glass fibers contained in the upstream filter medium layer.   6. The total content of heat-fusible fibers having a melting point of 50 to 170 ° C. measured by differential scanning calorimetry (DSC) is 25 to 60% in terms of the composite filter medium mass ratio. 6. Composite filter media.   A method for producing a composite filter medium according to any one of claims 1 to 6, wherein a wet paper web of an upstream filter medium layer and a wet paper of a downstream filter medium layer are produced using a combination wet paper machine having a plurality of paper making heads. After forming the laminated web composed of the web, the upstream filter medium layer and the downstream filter medium layer are adhered to a hot roll having a surface temperature higher by 10 ° C. or higher than the melting point of the heat-fusible fiber while pressing the laminated web. A method for producing a composite filter medium, wherein the composite filter medium is dried after being integrated.