JP7103871B2 - Non-woven filter - Google Patents

Description

The present invention relates to a non-woven fabric filter suitable for an air conditioner provided in a vehicle or a living environment, and in order to extend the life of a main filter having a particularly precise filtration function, the coarse dust suitable for the upstream side of the filtration of this filter. Regarding a pre-filter with excellent (dust) collection function.

Conventionally, as a non-woven fabric filter for long-term use, a pre-filter that collects dust having a relatively large particle size and a main filter that collects dust having a relatively small particle size on the downstream side of this pre-filter. The combination of is widely used. Of these, the pre-filter is used in various fields in order to allow the main filter to take only the function of collecting fine dust without allowing large dust to reach the main filter arranged on the downstream side of the filtration. ing. As an example, in Japanese Patent Application Laid-Open No. 2005-28253 (Patent Document 1), the present applicants comprehensively include atmospheric dust (hereinafter, coarse dust and atmospheric dust) from air introduced into, for example, a gas turbine or the like. We have proposed a filter medium for removing coarse dust, which is suitable for removal of (sometimes referred to as) and is arranged on the upstream side of filtration of a medium- and high-performance filter. In this technique, a non-woven fabric is prepared with a mass ratio of 80:20 to 30:70 of a thick fiber having a fiber diameter of 200 μm or more, a relatively thin fiber having a fiber diameter of 50 μm or more, and an adhesive, and the non-woven fabric is thick in the thickness direction of the non-woven fabric. The present invention provides a filter medium for removing coarse dust having a so-called density gradient by continuously changing the ratio of fibers to fine fibers.

On the other hand, in Japanese Patent Application Laid-Open No. 2004-290929 (Patent Document 2), which is also proposed by the present applicant, the fibers are composed only of fibers formed of a polyester-based resin, and the fibers are bonded to each other by heat-adhesive fibers. Moreover, it is a filter made of a non-woven fabric having a density gradient in the thickness direction, and the non-woven fabric has a flame retardancy evaluation value of Category 3 as an evaluation result of a flame retardant test method according to the JIS L1091 A-1 method. As a result of performing a filtration test on the filter made of the non-woven fabric by the mass method, a filter for coarse dust having an average particle collection efficiency of 50 to 99% has been proposed. As a preferred embodiment of this technique, the filter has a two-layer structure of a rough surface layer and a dense surface layer, and the rough surface layer and the dense surface layer each contain 50% by mass or more of heat-adhesive fibers and the rough surface layer. Is intended to realize a low pressure loss by further providing a bulky fiber structure on the upstream side of the filtration by further containing 1% by mass or more of hollow fibers.

As described above, in order to selectively filter and collect coarse dust, the coarse dust filter is a technique for forming a fiber structure with a density gradient from a low apparent density to a high apparent density from the upstream side to the downstream side of the filtration. Alternatively, it can be roughly divided into techniques for laminating and constructing fiber structures having at least two different apparent densities. Further, as a structure different from these, the present applicant, in International Application No. PCT / JP2018 / 16211 (hereinafter, Patent Document 3), uses microfibers corresponding to nanofibers substantially without using a binder. We are proposing a non-woven fabric filter technology that can be formed as a net-like portion inside a non-woven fabric base material having a relatively large fiber diameter. Hereinafter, the technique of Patent Document 3 will be described with reference to the figure shown by the substitute photograph.

FIG. 1 is a cross-sectional photograph of a non-woven fabric filter disclosed as [FIG. 1A] in Patent Document 3, and FIG. 2 is an enlarged photograph of a surface along the main surface of the filter shown as [FIG. 1B] in the same document. .. As can be understood from these drawing-substituting photographs, the technique according to Patent Document 3 has a predetermined depth in the thickness direction of the non-woven fabric base material composed of the constituent fibers having a relatively thick average fiber diameter, and is finer than the constituent fibers. It is configured to have fibers. In this literature technology, it is disclosed that a form having heat adhesiveness as a constituent fiber of a non-woven fabric base material and containing at least one composite fiber composed of, for example, a polyester resin and a modified polyester resin is preferable, and the group after heat bonding. If the material has high rigidity, the binder component is contained in the non-woven fabric base material side, and the fine fibers themselves are made of a thermoplastic resin, a relatively inexpensive non-woven fabric filter can be realized without impairing the fine fiber diameter. Further, in the publication according to Patent Document 3, the basis weight of the non-woven fabric base material is preferably 50 g / m ² or more and 450 g / m ² or less, and more preferably 100 g / m ² or more and 200 g / m ² or less. There is. If the basis weight is lower than the lower limit of this suitable numerical range, the texture of the non-woven fabric base material itself is poor, the existence form of the net-like portion formed on the non-woven fabric base material itself becomes non-uniform, and it may be difficult to improve the amount of dust retained. Further, it is disclosed that the basis weight of the microfibers constituting the network portion is preferably 0.1 g / m ² or more and 50 g / m ² or less, and 2.0 g / m ² or more and 15 g / m ² or less is the most preferable. ing.

In the technique of Patent Document 3, a known technique can be adopted as a specific method for producing a non-woven fabric base material, and a dry spinning method, a wet spinning method, and a direct spinning method (melt blow method, spunbond method, flash span method) can be adopted. ), Wet method, or dry method (for example, card method, air array method), after forming the fiber web, for example, a method of fusing the fiber web constituent fibers under pressure or no pressure, a method of bonding with a binder. , The method of entwining with a water stream or a needle is mentioned, and the fibers are adhered to each other. As the non-woven fabric base material obtained by these known techniques, it is preferable to prepare a non-woven fabric base material made of fibers having an average fiber diameter of 7 μm or more so that a net-like portion made of fine fibers can be easily formed inside. It is stated that a bulky structure obtained by using fibers having an average fiber diameter of 15 μm or more can be realized. In forming a network portion containing fine fibers on such a non-woven fabric base material, 30% or more and 100% or less, more preferably 50% or more and 100% or less with respect to the apparent thickness of the base material. It is preferable to provide the reticulated portion with the depth of. For the formation of such a reticulated part,
(A) Technology in which pulp-like fine fibers are placed inside the base material by a wet method and then fused and fixed. (B) Synthetic resin dissolved in a solvent such as water or an organic solvent is discharged and spun inside the base material by high-speed air. (C) A state in which fine fibers such as cellulose fibers having nano-order fiber diameters are dispersed in a solvent such as water and impregnated into at least a part of a pre-prepared non-woven base material. Technology (d) Dissolve the resin material that is the raw material of the fine fibers in a solvent, apply it to at least a part of the non-woven substrate, and freeze-dry (e) Apply the resin material of the fine fibers to the non-woven substrate. It is disclosed that a technique of applying a dissolved solution and causing an air flow in the thickness direction of the base material to generate a network portion containing fine fibers inside the non-woven base material can be used.

Japanese Unexamined Patent Publication No. 2005-28253 ([Claims], [0013] to [0048], [Fig. 1], etc.) Japanese Unexamined Patent Publication No. 2004-290929 ([Claims], [0011] to [0032], etc.) International application number PCT / JP2018 / 16211 ([Claims], [Modes for carrying out the invention] column, [Fig. 1A], [Fig. 1B], etc.)

Patent Document 3 described above exemplifies a filter that collects dust in the atmosphere by adhering fibers having a smaller fiber diameter to the inside of a base material having a relatively large fiber diameter. There is. In the technique of Patent Document 3, there is a disclosure that an adhesive component is arranged on the surface of the constituent fibers of the non-woven fabric base material, and the fine fibers are fixed to the non-woven fabric base material at a predetermined depth by exemplifying a plurality of adhesion techniques. The inventor of the present application has used these two types of filter structures having different fiber diameters to diligently study the fiber structures proposed in Patent Document 1 and Patent Document 2 described above. As described above, there are known filters as a main filter responsible for precise dust filtration and a pre-filter that collects only relatively coarse dust in order to prolong the life of the main filter. Therefore, the composite form of such fine fibers and the non-woven fabric base material that serves as a scaffold or base for fixing the network body is re-verified, and the dust collection efficiency and low pressure loss suitable as a pre-filter are efficiently obtained. A feasible fiber structure has been realized, and the present invention has been completed.

Therefore, an object of the present invention is to extend the life of a main filter having a highly accurate dust collecting performance, and as a prefilter installed and used on the upstream side of the filtration of the filter, a low pressure loss and a high dust are generated. It is an object of the present invention to provide a non-woven fabric filter which can realize both a holding capacity and a holding capacity.

In order to achieve the above-mentioned object, according to the structure of the non-woven fabric filter according to the present application, a minute fiber diameter of 0.1 μm or more and 10 μm or less is contained inside a non-woven fabric base material made of constituent fibers having an average fiber diameter of 15 μm or more. It has fibers, and the fine fibers are oriented at a depth of 10% or more and 100% or less with respect to the apparent thickness of the above-mentioned non-woven fabric base material, and the net-like portion in which the fibers constituting the above-mentioned fine fibers are adhered to each other. A non-woven fabric filter that forms and adheres to the constituent fibers of the non-woven fabric base material described above, wherein the non-woven fabric base material has a texture of 50 g / m ² or more and 1500 g / m ² or less, and the content ratio of the fine fibers is 0. It is characterized by being .08% by weight or more and less than 1.0% by weight. The "apparent thickness" referred to here is a dimension measured in a state where no external force is applied to the non-woven fabric filter, and the "depth" is a microfiber in the thickness direction with respect to this "apparent thickness". Refers to the ratio of the distance dimension reached by. Normally, the non-woven fabric filter is composed of two surfaces, but the surface that is the starting point of the "depth" referred to here corresponds to the surface in which the fibers have entered the inside of the non-woven fabric base material in the process of forming the mesh portion. .. On the surface serving as the starting point, microfibers adhered to the outermost surface of the constituent fibers of the non-woven fabric base material are observed, and the microfibers are substantially continuously adhered from this surface to a portion having a specified depth. Therefore, it is easy to distinguish.

Further, in carrying out the present invention, the above-mentioned non-woven fabric filter was subjected to a filtration performance test by a mass method using ASHRAE dust specified in ASHRAE 52.1-1992, and when a load of 150 g / m ² was applied at a wind speed of 2.5 m / sec. It is preferable that the particle collection rate is 60% or more and the dust holding capacity at the time when the pressure loss rises to 200 Pa is 360 g / m ² or more.

Further, as a preferred embodiment of the present invention, it is preferable that the surface of the above-mentioned non-woven fabric filter facing the surface that is the starting point of the depth is the surface for filtering dust.

By adopting the above-described configuration, the non-woven fabric filter of the present invention can achieve both extremely low pressure loss and dust retention capacity, and provides an excellent pre-filter capable of extending the life of the main filter. be able to.

The figure which shows by the electron micrograph which took the outline cross section of the non-woven fabric filter which concerns on a background technique. The figure which shows by the electron micrograph which magnified the surface corresponding to the filtration surface of the filter shown in FIG.

The non-woven fabric filter according to the present invention is based on the structure proposed in Patent Document 3, and has a non-woven fabric base material composed of constituent fibers having an average fiber diameter of 15 μm or more, and a fiber diameter of 0. It is composed of a reticulated portion made of fine fibers of 1 μm or more and 10 μm or less. The net-like portion produces fine fibers by various techniques disclosed in Patent Document 3, and is oriented and formed at a predetermined depth inside the non-woven fabric base material by a method such as spinning or papermaking. Hereinafter, the description will be given sequentially according to a preferred embodiment of the manufacturing process.

First, by using constituent fibers with an average fiber diameter of 15 μm or more as the non-woven fabric base material, it is possible to keep the voids between the fibers stable, and to keep the distance between the fibers stable even when the fine fibers are adhered. It is possible to realize a filter with high shape maintenance characteristics, which is bulky and has low pressure loss even when wind pressure is sometimes applied. As a specific technique for producing a non-woven fabric base material, known methods such as a dry spinning method, a wet spinning method, and a direct spinning method (melt blow method, spun bond method, needle punch, etc.) can be used. As the material of the constituent fibers of such a non-woven substrate, a polyolefin resin (polyethylene, polypropylene, polymethylpentene, a polyolefin having a structure in which a part of hydrocarbon is replaced with a cyano group or a halogen such as fluorine or chlorine), a styrene resin, etc. Polyether resin (polyether ether ketone, polyacetal, phenol, melamine, urea, epoxy, modified polyphenylene ether, aromatic polyether ketone, etc.), polyester resin (polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.) Polybutylene naphthalate, polycarbonate, polyarylate, total aromatic polyester, unsaturated polyester, etc.), modified polyester resin, polyimide resin, polyamideimide resin, polyamide resin (for example, aromatic polyamide, aromatic polyetheramide, nylon, etc.) , Resin having a nitrile group (for example, polyacrylonitrile, etc.), urethane resin, epoxy resin, polysulfone resin (polysulfone, polyethersulfone, etc.), fluororesin (polytetrafluoroethylene, polyvinylidene fluoride, etc.), cellulose resin, polybenzo Known organic polymers such as imidazole resin, acrylic resin (for example, polyacrylonitrile in which acrylic acid ester or methacrylate ester is copolymerized, modaacrylic in which acrylonitrile is copolymerized with vinyl chloride or vinylidene chloride, etc.), glass fiber, metal fiber, etc. And other known inorganic fibers can be used. Further, the organic polymer thereof may be either a linear polymer or a branched polymer, and the polymer may be a block copolymer, a random copolymer, or the like, and has a three-dimensional structure and crystallinity thereof. Regardless of the presence or absence of the above-mentioned polymer, the polymer having the above-mentioned shape-maintaining characteristics can be arbitrarily and preferably selected.

The constituent fibers of these non-woven fabric base materials may be one kind of component or a mixture of a plurality of components as long as there is little change in shape and thickness in the process of adhering the mesh portion described later. In particular, it is preferable to use a composite fiber in which a plurality of components are divided into different sections and combined. As the form of the composite fiber, any of core sheath type, sea island type, side-by-side type, orange type and the like may be used. Of these composite fibers, if the core-sheath type is capable of forming a substantially entire surface where the fibers can be adhered to each other, the shape-maintaining characteristics due to the adhesive strength during the process of forming the net-like portion and when the non-woven fabric filter is used. And durability can be imparted, which is the most preferable. Furthermore, it is clear that the combination of such a heat-bondable composite fiber and a general-purpose regular fiber composed of a single component also contributes to the shape-maintaining property. Further, as previously known, when resistance to various chemicals is required as a non-woven fabric filter, a composite fiber made of polyester resin and modified polyester resin is adopted because it has high rigidity after heat bonding and is relatively inexpensive. It is better to do it.

As disclosed in Patent Document 3, the texture of such a non-woven fabric base material is dominant in maintaining the shape of the non-woven fabric filter. Therefore, in order to suppress an increase in pressure loss and increase the amount of dust retained, 50 g. It is preferably / m ² or more and 400 g / m ² or less, more preferably 100 g / m ² or more and 200 g / m ² or less. If the texture is lower than the lower limit of this suitable numerical range, deformation may occur even in the process of adhering the fine fibers, and the shape of the obtained net-like body may become non-uniform, leading to an increase in pressure loss and a decrease in the amount of dust retained. If the grain size is set higher than the above range, the pressure loss may increase early and the life of the non-woven fabric filter may be significantly shortened.

Next, fine fibers are mainly adhered to the inside of the non-woven fabric base material designed and obtained as described above to form a network. For the formation of the network, any of the adhesion techniques (see "a" to "e" described above) as proposed in Patent Document 3 can be adopted. Of these, in the case of the above-mentioned technique "b", that is, a technique in which synthetic resin dissolved in various solvents is discharged and spun by high-speed air and fixed inside the base material, it is about 100 mm or less from one surface of the non-woven fabric base material. It is preferable that the constituent resin of the fine fibers is sprayed and suction is performed from the other surface of the non-woven fabric base material by a mouthpiece used for melt spinning or flash spinning arranged at the distance of. It is necessary that the constituent resin of the fine fibers discharged from the mouthpiece is carried out in a state where the fluidity remains without solidifying until it reaches the constituent fibers of the non-woven fabric base material, and the formation depth of the fine fibers is increased. The distance between the surface of the non-woven fabric base material and the base is more preferably 50 mm or less in order to obtain a deep depth. By making the fiber diameter of these microfibers smaller than that of the constituent fibers of the non-woven fabric base material, it is possible to efficiently adhere to the inside of the non-woven fabric base material, and the fiber diameter is designed to be 0.1 μm or more and 10 μm or less. Is preferable. As the constituent resin of the fine fibers, a solvent-soluble polyvinylidene fluoride (PVDF) resin, vinylidene polyvinylidene-hexafluoropropylene copolymer resin, polyacrylonitrile (PAN) resin, polyacrylonitrile-methacrylate copolymer resin, and poly Methacrylate resin, polymethyl methacrylate resin, polyvinyl chloride resin, polyvinylidene chloride-acrylate copolymer resin, polycarbonate resin, polystyrene resin, polyethylene resin, polyether sulfone resin, polyolefin resin, polyester resin, polypropylene resin, nylon 12 , Nylon-based resins such as Nylon-4,6, aramid resin, polyimide resin, polybenzimidazole resin, cellulose resin, cellulose acetate resin, cellulose acetate butyrate resin, polyvinylpyrrolidone-vinyl acetate resin, poly (bis- (2- (2-) (2-methoxy-ethoxyethoxy)) phosphazene) (poly (bis- (2- (2-methoxy-ethoxyethoxy)) phosphazene); MEEP) resin, polypropylene oxide resin, polyethyleneimide (PEI) resin, ethylene polysuccinate (2-methoxy-ethoxyethoxy)) poly (ethylene succinate) resin, polyaniline resin, polyethylene sulfide resin, polyoxymethylene-oligo-oxyethylene (poly (oxymethylene-oligo-oxythyrene)) resin, SBS copolymer resin, polyhydroxybutyric acid resin, polyvinyl acetate resin, Polyethylene glycol resin, polyvinyl alcohol resin (partially saponified polyvinyl alcohol, fully saponified polyvinyl alcohol), polyvinylpyrrolidone resin, polyethylene terephthalate resin, polyethylene oxide resin, collagen resin, polylactic acid resin, polyglycolic acid resin, poly D, L-lactic acid- Glycolic acid copolymer resin, polyarylate resin, polypropylene fumarate resin, biodegradable polymer such as polycaprolactone, water-soluble resin such as polypeptide and protein, or coal tar pitch and petroleum pitch. And the like, pitch-based resins and the like can be exemplified. Among these, a resin selected from a polyacrylonitrile resin, a polyether sulfone resin, a polyolefin resin, a polyester resin, or a polyvinyl alcohol resin is preferable, and can be arbitrarily and preferably selected according to the usage environment of the non-woven filter.

The texture of the fine fibers is a value obtained by expressing the weight ratio of the fine fibers to the weight of the non-woven fabric filter as a percentage in order to suppress an increase in pressure loss of the base non-woven fabric base material and to improve the dust retention amount. (Content ratio of fine fibers) needs to be 0.08% by weight or more and less than 1.0% by weight. If a large amount of fine fibers is adhered beyond this range, the production efficiency of the non-woven fabric filter is lowered and the pressure loss becomes excessively large. In addition, if the amount of adhesion is too small, it becomes difficult to obtain the initial dust collection rate.

The fine fibers are preferably oriented at a depth of 10% or more and 100% or less with respect to the apparent thickness of the non-woven fabric base material. To measure this "depth", 10 electron micrographs of the cross section of the non-woven fabric filter are taken, and any 10 points that are uniform in the plane direction of the non-woven fabric filter are selected from each photograph, and the length of the mesh portion extending in the thickness direction is selected. Measure up to 3 significant digits on the photo. The 10-point average was calculated 10 times, and the average value was defined as "depth" (two significant figures). Here, "alignment with a depth of 10% or more and 100% or less with respect to the apparent thickness" means that the value of the thickness is 10% or more and 100% or less with respect to the apparent thickness of the base material. It refers to the state in which the "reticulated part" has reached the depth. That is, as illustrated in FIG. 1 described above, the net-like fine fibers are widely distributed inside the base non-woven fabric base material, or there are many net-like bodies formed by adhesion of the fine fibers to each other. When using a non-woven fabric filter, deep filtration is possible by efficiently using the thickness direction for collecting dust, and clogging is less likely to occur. Therefore, it is possible to suppress the increase in pressure loss and realize a high dust retention amount. By selecting the technique of the adhesion process for orienting such fine fibers in the thickness direction and appropriately selecting the condition setting, the net-like portion can be formed at a deeper position and the dust holding capacity can be increased. can.

Further, in carrying out the present invention, it is preferable that the surface for filtering dust is the surface opposite to the surface on which the fine fibers are adhered to the non-woven fabric base material (the surface serving as the starting point of the depth described above). This is because, in the non-woven fabric filter of the present invention prepared according to various requirements, the fine fibers are absolutely less distributed on the surface opposite to the surface in which the fine fibers are introduced into the non-woven fabric base material. Produces a density gradient structure. Therefore, by setting the region with relatively few fine fibers on the upstream side of the filtration, efficient dust collection becomes possible and the dust retention capacity is improved.

The preferred embodiment of the present invention has been described above by exemplifying specific conditions such as specific materials, arrangement relationships, and numerical conditions, but the present invention is not limited to these specific conditions. It should be understood that any suitable design modification or modification may be made within the scope of the object of the invention.

Hereinafter, examples of the present invention will be given to describe the production of a non-woven fabric filter and the evaluation results of the produced filter. The present invention is not limited to the examples shown below.

[Preparation of non-woven fabric base material]
First, as a non-woven fabric base material, a short-fiber non-woven fabric produced by a card machine will be described as an example. In this example, one kind of non-woven fabric base material was prepared in order to facilitate understanding of the dust removal evaluation described later. First, 80% by mass of a core-sheath composite fiber (fineness 17.0 decitex, fiber length 51 mm) made of a commercially available polyester resin and a modified polyester resin, and a core-sheath composite made of a commercially available polyester resin and a modified polyester resin. 20% by mass of fibers (6.6 decitex, fiber length 51 mm) and cotton were mixed. This was applied to a card machine to form a web, entangled by a needle punching method, and then bonded between fibers with a hot air dryer at 150 ° C. to obtain a non-woven fabric substrate having a basis weight of 150 g / m ² . When this cross section was observed with an electron microscope and only 50 constituent fiber portions excluding the fusion point between the fibers were measured and observed, the average fiber diameter was about 37 μm.

[Formation of reticulated part by discharge spinning of fine fibers]
For the formation of the reticulated portion inside the non-woven fabric base material described above, the manufacturing apparatus described in Japanese Patent Application Laid-Open No. 2012-15409 disclosed in Patent Document 3 as a background technique was used. The spinning liquid to be discharged was prepared by dissolving a commercially available polyvinyl alcohol resin at a weight concentration of 12% using water as a solvent. The separation distance between the conveyor arranged in the device and the base is variously changed, suction is performed from the back side of the conveyor to adhere the fine fibers to the non-woven fabric base material, and the depth of the mesh portion and the inclusion of the fine fibers described later are described. Nonwoven fabric filters for evaluation with different ratios were prepared.

[Dust load test]
The composition of the evaluation sample will be described later, but the filtration performance of a total of 18 types of non-woven fabric filters including the reference example composed of only the non-woven fabric base material was carried out according to the test method of ASHRAE 52.1-1992. First, considering the use as a pre-filter, the wind speed is 2.5 m / sec, and commercially available ASHRAE dust (composition: 72% Arizona street dust, 23% carbon black, 5% cotton linter) is used until the pressure loss reaches 200 Pa. It was supplied at a concentration of 70 mg / m ³ . During this period, the dust collection rate up to the time when the dust is supplied at 150 g / m ² is used as the particle collection rate under a load of 150 g / m ² , and the dust supply amount up to the pressure loss of 200 Pa, which is the end point, is used as the dust holding capacity. Recorded as. In this test, since the surface of the non-woven fabric base material to which the fine fibers were discharged and adhered was relatively high in density, it was mounted on the test apparatus so that the surface was downstream. However, with respect to Comparative Example 6, the surface opposite to this was used for evaluation and analysis as a filtration surface. Table 1 shows the network structure and the evaluation results of each evaluation sample.

First, the evaluation sample used as a reference example consists of only the non-woven fabric base material commonly used for the other evaluation samples without being coated with fine fibers. The initial pressure drop in this reference example is 21 Pa, and it can be understood that the pressure drop is higher than this in each of the examples and the comparative examples in which the fine fibers are adhered and formed in various forms. Further, the particle collection rate under a load of 150 g / m ² (hereinafter, simply referred to as the particle collection rate) of the reference example is 60%, and this particle collection rate depends on the adhered form of the fine fibers (reticular body). Is changing. First, in both Examples 1 and 2, the fine fiber content is 0.08%, and only the depth of the reticulated portion is different. Comparing these two examples with the reference example, the initial pressure drop and the particle collection rate were slightly higher in the examples, and the amount of dust retained until rupture was improved by about 10%. On the other hand, in Comparative Example 1 prepared by reducing the fine fiber content ratio to 0.03%, the initial pressure drop was the same as that of the reference example, and no improvement effect was observed in the particle collection rate and the dust retention amount. rice field. From this, it was determined that the reticulated portion formed inside the non-woven fabric base material is adhered with a fine fiber content ratio of 0.08% or more to improve the dust retention amount.

Further, in Examples 3 to 6, the fine fiber content ratio was increased to about 1.5 to 2 times from the above-mentioned Examples. In these four samples, the particle collection rate was improved by more than 10% of the reference example. Further, when the depth of the fine fibers is increased, the fine fibers are dispersed in the thickness direction of the non-woven fabric base material, and the apparent density is reduced. Therefore, the fine fiber content ratio is the same and only the depth of the mesh portion is different. From the comparison between the examples, it was observed that the initial pressure drop tended to decrease slightly by increasing the depth of the reticulated portion. This tendency was also confirmed in Examples 7 to 11 in which the fine fiber content ratio was 0.27% to 0.53%, and in Example 9 in which the deepest reticulated portion was formed in each Example, Example. The initial pressure loss was about 20% lower than that of the above. In order to further verify this point, a non-woven fabric filter equivalent to that of Example 8 is shown as Comparative Example 6. In Comparative Example 6, since the surface used as the starting point of the depth was the filtration upstream surface, as compared with Example 8, dust is likely to accumulate in the mesh portion existing on the filtration upstream surface of the non-woven fabric base material, and dust is retained. The capacity has decreased.

Further, as Comparative Example 2, a sample having a depth of 5%, that is, a sample in which fine fibers were substantially laminated only on the surface serving as the starting point of the depth was evaluated. As a result, although the fine fiber content ratio was the same as that of Examples 8 and 9, the initial pressure loss was 3 times that of the reference example, and the dust retention amount was only 1/8 of that of the reference example. From this, it was confirmed that the non-woven fabric base material can be efficiently used by setting the depth of the fine fibers to a predetermined value by utilizing the configuration of the present invention. In addition, as Comparative Examples 3 to 5, as a result of preparing a sample having a fine fiber content ratio of 1.00% or more, improvement in the dust retention amount from the non-woven fabric base material cannot be expected, and the initial pressure loss increases. It was only. From this result, it was confirmed that the preferable range for adhering the fine fibers on the non-woven fabric base material was less than 1%.

Claims (3)

Inside the non-woven fabric base material made of constituent fibers having an average fiber diameter of 15 μm or more, microfibers having a fiber diameter of 0.1 μm or more and 10 μm or less are provided, and the fine fibers are relative to the apparent thickness of the non-woven fabric base material. A non-woven fabric filter that is oriented with a depth of 10% or more and 100% or less, forms a net-like portion in which the fibers constituting the fine fibers are adhered to each other, and is adhered to the constituent fibers of the nonwoven fabric base material.
A non-woven fabric filter characterized in that the basis weight of the non-woven fabric base material is 50 g / m ² or more and 1500 g / m ² or less, and the content ratio of the fine fibers is 0.08% by weight or more and less than 1.0% by weight. In the filtration performance test by the mass method using ASHRAE dust specified in ASHRAE 52.1-1992, the particle collection rate under a load of 150 g / m ² at a wind speed of 2.5 m / sec is 60% or more, and the pressure loss is high. The non-woven fabric filter according to claim 1, wherein the dust holding capacity at the time of increasing to 200 Pa is 360 g / m ² or more. The non-woven fabric filter according to claim 1 or 2, wherein the surface facing the surface that is the starting point of the depth of the non-woven fabric filter is a filtration surface.

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