JP6627525B2 - Mixed non-woven fabric - Google Patents

Description

The present invention relates to a nonwoven fabric for a filter that exhibits high collection efficiency while having a low pressure loss.

  In recent years, there has been an increasing demand for space cleanliness. In a wide range of fields from the living environment to industry, such as countermeasures against health problems due to dust with a particle size of 2.5 μm or less and dust-free semiconductor and pharmaceutical manufacturing, An air filter that removes fine dust is used.

  The air filter captures dust-containing air and traps the dust in the filter medium, thereby purifying the passing air. This air filter is required to have the ability to collect dust with high efficiency.In addition, the lower the pressure loss when gas passes, the longer the life of the filter and the greater the processing air volume. Loss is also one of the important characteristics of an air filter.

  In particular, among air filters, bag filters having a bag-like form are widely used in purification of exhaust gas from factories, power plants, refuse incinerators, and the like. Filter media for purifying air include those for deep-layer filtration and those for surface filtration. For bag filters, surface filtration media are used. Surface filtration is a filtration mechanism that collects dust on the surface of a filter medium, deposits a dust cake layer, and further collects dust by the dust cake layer. When the dust cake layer reaches a certain thickness with the dust collection, the dust cake layer is removed from the surface of the filter medium, and the operation of forming a dust cake layer on the surface of the filter medium is repeated to collect dust.

  This bag filter not only collects dust in exhaust gas with high efficiency to prevent environmental pollution, but also consumes a lot of energy when the dust collector is in operation. Is also strongly desired.

  Generally, in order to increase dust collection efficiency, mechanical collection performance is improved by reducing the pore size of a filter medium used for a filter. The pore size refers to the size of the through hole formed by the fibers constituting the filter medium sheet. However, when the pore size of the filter medium sheet is reduced, a high pressure loss is caused by an increase in the airflow resistance, so that the collection efficiency and the pressure loss are opposite to each other.

  Furthermore, as a method of removing the dust cake layer from the filter medium surface of the bag filter, there are a method of applying mechanical vibration (mechanical vibration type), a method of changing an air flow in a reverse direction (back pressure / backwashing type), and a method of removing compressed air. There is a method (pulse jet method) of instantaneously spraying the filter medium surface, and in any of the methods, a physical impact is repeatedly applied to the filter medium. For this reason, bag filter media are also required to have shape stability against impact.

  Various efforts have been made to solve the problems of filter media, such as compatibility between high dust collection efficiency and low pressure loss, and impact resistance of the filter media structure. For example, Patent Literature 1 proposes a method in which a filter medium is formed as a nonwoven fabric in which a low-weight nanofiber layer and a non-nanofiber layer are laminated, thereby achieving both high dust collection and suppression of airflow resistance leading to low pressure loss. I have. By reducing the weight of the nanofiber layer, the minimization of the pore size is suppressed, and while collecting dust at a high level, the ventilation resistance is suppressed, but in applications where a longer life is required, There has been a problem that the pore size is still small and the ventilation resistance is at a high level.

  Patent Document 2 discloses a method of laminating a porous polytetrafluoroethylene (PTFE) membrane on a breathable support material to increase the collection of dust in a bag filter medium and improve the removability of a dust cake layer. Proposed. Due to the microporosity of the PTFE film, even fine dust can be collected with high efficiency, and the surface smoothness of the dust cake layer excels in releasability. In addition to the high pressure loss, There is a concern that the PTFE film may be peeled off from the support material due to the impact when the dust cake layer is removed, and there is a problem in the form stability.

JP 2009-233550 A (Claims) JP-A-2002-136812 (Claims)

  An object of the present invention is to solve the above-mentioned problems of the prior art, and in the nonwoven fabric of the present invention, both high collection efficiency and low pressure loss are used as a filter medium for an air filter, and the form stability of the nonwoven fabric against physical impact is improved. It is to provide a high nonwoven fabric.

The above object is achieved by the following means.

(1) The average pore size is 10.0 to 60.0 μm, the pore size distribution frequency of less than 15.0 μm is 5.0 to 35.0%, the basis weight is 120 g / m ² or more, and the thickness is 1.0 to 10 A mixed-fiber nonwoven fabric having a thickness of 0.0 mm.

(2) At least one layer composed of a mixture of ultrafine fibers having a single-fiber fineness of less than 1.0 × 10 ⁻² dtex and modified cross-sectional fibers having a single-fiber fineness of 1.0 × 10 ^{−1 to} 5.0 dtex. The mixed nonwoven fabric according to (1), comprising at least one layer.
(3) The mixed fiber nonwoven fabric according to any one of (1) and (2), wherein the cross-sectional shape of the cross-sectional fiber is 2.0 or more.
(4) The aspect ratio b / a is 3.0 or more when the short axis length is a and the long axis length is b with respect to the cross-sectional shape of the modified cross-section fiber, wherein (1) to (1). The mixed fiber nonwoven fabric according to any one of 3).

  (5) A fiber product in which the mixed-fiber nonwoven fabric according to any one of (1) to (4) forms at least a part.

  (6) A filter comprising the mixed nonwoven fabric according to any one of claims (1) to (4) at least partially.

  INDUSTRIAL APPLICABILITY The nonwoven fabric of the present invention has low dust loss while having high dust collection efficiency as an air filter medium, and can exhibit high form stability against physical impact.

FIG. 1 is a schematic view of the nonwoven fabric of the present invention. FIG. 2 is a schematic view of an example of a fiber having an irregular cross section.

Hereinafter, the present invention will be described in detail with preferred embodiments.
The nonwoven fabric of the present invention needs to have an average pore size of 10.0 to 60.0 μm and a frequency of pore size distribution of less than 15.0 μm of 5.0 to 35.0%.

  The pores here are through holes formed by the fibers constituting the nonwoven fabric.The smaller this size is, the easier it is for the dust in the gas passing through the nonwoven fabric to be physically captured, but the higher the ventilation resistance is. This leads to high pressure loss. When the average pore size of the nonwoven fabric is within the above range, the airflow resistance becomes sufficiently low, and the pressure loss becomes practical as an air filter medium. According to the study by the present inventors, by setting the average pore size to 10.0 μm or more, while maintaining the collection efficiency at a very high level, the rise in the ventilation resistance is suppressed, and the air filter medium is balanced. It will be excellent. On the other hand, when the average pore size is 60.0 μm or less, there is no problem in collecting fine dust.

  From the viewpoint of suppressing pressure loss while maintaining the dust collection efficiency at a high level as an air filter medium, the average pore size of the sheet is preferably 15.0 to 55.0 μm. It is more preferably 20.0 to 50.0 μm from the viewpoint of being excellent in the balance of low pressure loss and improving the energy saving of the dust collector.

Further, in the nonwoven fabric of the present invention, since a very high level of control is required as a manufacturing method in the prior art, it is important to design a pore size distribution frequency that has not been noticed. That is, in the nonwoven fabric of the present invention, the pore size distribution frequency of less than 15.0 μm needs to be 5.0 to 35.0%. Within such a range, pores contributing to dust collection in the nonwoven fabric will be sufficiently ensured, and a practical dust collection efficiency as an air filter medium will be exhibited.
When the pore size distribution frequency of less than 15.0 μm is 5.0% or more, pores contributing to dust collection are sufficient, and practical dust collection performance is exhibited. On the other hand, by setting the content to 35.0% or less, an increase in pressure loss is suppressed, and the pressure loss level becomes practical for a filter. Since the higher the distribution frequency within a range not exceeding 35.0%, the higher the dust collection, the distribution frequency is preferably 10.0 to 35.0%, and more preferably 15.0 to 35.0%. preferable.

The nonwoven fabric of the present invention needs to have a basis weight of 120 g / m ² or more. When the basis weight is 120 g / m ² or more, it becomes possible to collect and hold dust sufficiently as an air filter medium. Considering the use as a bag filter medium, the basis weight is preferably in the range of 160 to 1000 g / m ² from the viewpoint of impact resistance in the washing step. If the basis weight is in the range, even if an impact is caused by a pulse or the like in the washing step, the nonwoven fabric serving as the base of the dust cake layer has a small fiber misalignment and can be repeatedly used. In consideration of the impact resistance to processing into the filter medium and the ease of processing, the basis weight is more preferably in the range of 200 to 800 g / m ² .

  Furthermore, the thickness of the nonwoven fabric of the present invention needs to be in the range of 1.0 to 10.0 mm. The greater the thickness, the higher the rigidity as a filter medium and the higher the morphological stability against physical impacts, but the worse the processability, the more likely it is that fiber misalignment in the nonwoven fabric occurs, and no fine pores are formed. Tend to form many coarse pores. Within such a range, both resistance to physical impact and formation of fine pores can be achieved, and sufficient performance as a filter medium can be exhibited. In addition, from the viewpoint of preventing fiber misalignment during processing, protecting fine pores, and increasing dust collection efficiency, the thickness of the nonwoven fabric is preferably 8.0 mm or less, and the morphological stability as a filter medium and dust are reduced. The thickness of the nonwoven fabric is more preferably 5.0 mm or less from the viewpoint of achieving a high level of collection efficiency.

  In the present invention, the average pore size and the pore size distribution frequency refer to the average size of the through holes formed by the fibers constituting the nonwoven fabric, and are values calculated by the bubble point method. As the bubble point method, for example, a porous material automatic pore measuring system Perm-Porometer (manufactured by PMI) can be used. In the Perm-Porometer measurement, the nonwoven fabric was immersed in a liquid having a known surface tension value, and supplied while increasing the gas pressure from above the nonwoven fabric. The pore size was determined from the relationship between this pressure and the liquid surface tension of the fiber sheet surface. Is measured. The pore size distribution frequency is calculated from the flow rate of the liquid at each pressure of the gas supplied from the upper part of the nonwoven fabric.

The nonwoven fabric of the present invention is constituted by blending ultrafine fibers having a single-fiber fineness of less than 1.0 × 10 ⁻² dtex and irregular-shaped fibers having a single-fiber fineness of 1.0 × 10 ^{−1 to} 5.0 dtex. It is preferable to include at least one layer. The ultrafine fibers having a single fiber fineness of less than 1.0 × 10 ⁻² dtex play a role of forming a fine pore structure in the nonwoven fabric, and the fine pores contribute to the physical collection of dust. When used as an air filter medium, from the viewpoint of exhibiting high collection performance, it is more preferable that the single-fiber fineness of the ultrafine fiber is 7.0 × 10 ⁻³ dtex or less. Within such a range, the frequency of distribution of fine pores that can capture small dust having a particle size of several μm or less in the nonwoven fabric increases, leading to high collection performance.

On the other hand, the modified cross-section fibers having a single yarn fineness of 1.0 × 10 ^{−1 to} 5.0 dtex have a three-dimensional void in the nonwoven fabric, and play a role of securing air permeability. By mixing fibers with large fineness to ultrafine fibers, a structure in which coarse pores and fine pores are dispersed in the nonwoven fabric is formed, and the nonwoven fabric has an excellent balance between high dust collection and low pressure loss Is obtained. From the viewpoint of mixing fibers of large fineness, the cross-sectional shape of the fineness fibers may be a round cross-section. It was found that the dispersion state of the ultrafine fibers in the nonwoven fabric was improved as compared with that of the nonwoven fabric, and a structure in which coarse pores and fine pores were dispersed more favorably was obtained. In addition, from the viewpoint of lowering the pressure loss while exhibiting high collection performance using fine pores as an air filter medium that forms coarse pores, the single-filament fineness of the modified cross-section fiber is 3.0 × 10 ^{−1 to} 3 0.0dtex is more preferable. By setting the single-fiber fineness to 3.0 × 10 ⁻¹ dtex or more, the rigidity of the modified cross-section fiber becomes sufficient, coarse pores are less likely to be misaligned, and stable filter performance is exhibited. By setting the average pore size of the nonwoven fabric to 0.0dtex or less, the average pore size of the nonwoven fabric does not become too large, which leads to prevention of a decrease in trapping performance.

Further, it is preferable to include at least one or more layers formed by blending the ultrafine fibers and the modified cross-section fibers. The nonwoven fabric of the present invention may be composed of only one mixed fiber layer, and it is also possible to laminate another nonwoven fabric on the mixed fiber layer. When the nonwoven fabric of the present invention is composed of only one mixed fiber layer, the basis weight must be 120 g / m ² or more from the viewpoint of retaining dust and securing rigidity as a filter medium. However, when another base nonwoven fabric is laminated on the mixed fiber layer, the base nonwoven fabric also contributes to dust retention and rigidity, so that the basis weight of the nonwoven fabric of the present invention is 120 g / m ² or more. The basis weight of the mixed fiber layer can be appropriately changed. In this case, the basis weight of the mixed fiber layer is preferably 40 to 150 g / m ² . By setting the basis weight of the mixed fiber layer to 40 g / m ² or more, a nonwoven fabric capable of capturing dust in a gas is obtained. On the other hand, by setting it to 150 g / m ² or less, the airflow resistance can be suppressed to a practical range. Further, from the viewpoint of achieving both a sufficient collection efficiency and a low pressure loss as a filter medium, the basis weight of the mixed fiber layer excluding the laminated base material is more preferably in the range of 50 to 120 g / m ² . By setting the basis weight to 50 g / m ² or more, it is possible to secure sufficient dust collection efficiency as a filter medium, and to control the pressure loss when used as a filter medium by 120 g / m ² or less. Is possible.

  Examples of the cross-sectional shape of the irregular cross-section fiber to be mixed include an ellipse, a flat shape, a Y shape, a triangle, and a polygon. However, from the viewpoint of controlling the pore size and the pore size distribution frequency, it is preferable that the cross-sectional shape of the modified cross-section fiber used in the present invention has a degree of irregularity of 2.0 or more. When the heterogeneity of the cross section is in the range, the dispersion state of the ultrafine fibers is clearly different from the dispersion state of the ultrafine fibers when mixed with the round cross section fiber, and a difference occurs in the pore size distribution.The dispersion state of the coarse pores and the fine pores is more It will be good. The upper limit of the degree of irregularity that can be achieved in the present invention is about 10.0. Here, the degree of irregularity is determined as follows. The cross-section of the short fiber is two-dimensionally photographed, and from the image, the diameter of the perfect circle circumscribing the short fiber cross-section is set as the circumscribed circle diameter, and the diameter of the inscribed perfect circle is set as the inscribed circle diameter. From the diameter of the circumscribed circle to the diameter of the inscribed circle, the second digit after the decimal point was rounded off, and the value obtained up to the first digit after the decimal point was defined as the irregularity. Here, the circumscribed circle is a portion 3 in FIG. 2, and the inscribed circle is a portion 5 in FIG. The degree of irregularity was measured for ten randomly extracted fibers, and a simple number average value of the measured values in each image was obtained, which was defined as the degree of irregularity.

  Among the irregular cross sections, when the cross section is particularly flat, it is preferable that the oblateness ratio b / a is 3.0 or more when the short axis length of the cross section is a and the long axis length is b. When the oblateness is in the range, the second moment of area in the direction perpendicular to the major axis of the cross section is clearly reduced, becomes flexible, and the dispersion state of both fibers becomes more uniform when mixed with the ultrafine fibers. Will be done. For this reason, the distribution state of the coarse pores and the fine pores is excellent in the balance between high collection and low pressure loss. Further, the aspect ratio b / a is more preferably 5.0 or more from the viewpoint of increasing the resistance to mechanical vibration and impact due to compressed air in bag filter cleaning. If the flattening rate is in the range, the flat cross-section fibers are likely to be arranged in parallel with the side surface on the long-axis side of the cross section and in parallel with the surface direction of the nonwoven fabric. It is possible to use it suitably as a filter medium. The upper limit of the oblateness achievable in the present invention is about 10.0.

  Embodiments of the nonwoven fabric of the present invention are not particularly limited, and long fiber spunbonded nonwoven fabrics, melt blown nonwoven fabrics and the like, short fiber type airlaid nonwoven fabrics, needle punched nonwoven fabrics (felts), wet papermaking nonwoven fabrics, spunlace nonwoven fabrics, Nonwoven fabrics obtained by thermal or chemical bonding of these are exemplified. Above all, a needle-punched nonwoven fabric (hereinafter referred to as felt) which is bulky and has a strong entanglement force is preferable from the viewpoint of increasing the dust holding capacity or obtaining high form stability as an air filter medium.

  In addition, it is also possible to combine and laminate a plurality of types of nonwoven fabrics described above. In particular, for filter media applications, the higher the rigidity of the filter media, the greater the resistance to large airflow resistance and the ability to handle high airflows. Also, when used as a bag filter, the filter is resistant to the physical impact of removing the dust cake layer Is an important characteristic. From such a viewpoint, it is also preferable to adopt a laminated structure in order to obtain rigidity.

The polymer used for the fiber raw material constituting the nonwoven fabric is not particularly limited as long as it is used for the production of general synthetic fibers, and includes, for example, polyester, polyamide, polyolefin, and acryl. Polyester is preferred. Examples of the polyester to be used include polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate and a copolymer thereof.
The polymers other than polyester include, for example, nylon 6, nylon 66, nylon 46, nylon 11, nylon 12, polypropylene, polyethylene, polyphenylene sulfide, and copolymers thereof.

  In addition, from the viewpoint of reducing the environmental load at the time of disposal, a biodegradable polymer may be used.For example, polylactic acid, polyethylene succinate, polybutylene succinate, polybutylene succinate adipate, polybutylene succinate carbonate, Examples thereof include polybutylene adipate terephthalate and polyethylene terephthalate succinate or a copolymer thereof.

Although the method for producing the nonwoven fabric of the present invention is not particularly limited, an example of a production method by a needle punch method will be described below.
A sea-island conjugate fiber short fiber in which an easily elutable polymer that can be eluted with a chemical solution or the like is disposed in the sea component, and a thermoplastic polymer is disposed in the island component, and the fineness of the island component is less than 1.0 × 10 ⁻² dtex. Prepare short fibers of sea-island composite fibers in which similar sea components are arranged with irregular island components that are not round in shape.They are individually passed through a carding machine and opened as a pretreatment to be fed into a needle punch device. And The short fibers are preferably crimped with a crimper or the like from the viewpoint of increasing the entanglement force by the needle punch. Next, these raw cottons are charged into a mixer at an arbitrary weight ratio and mixed to obtain a mixed raw cotton. Then, the mixed raw cotton is put into the supply unit of the needle punching device, and further opened and aligned to form a sheet-like fibrous web, which is laminated into a sheet by the cross wrapper unit, and is fed to the needle punch unit. And transport. Upon reaching the needle punch portion, the mixed raw cotton arranged in a sheet shape is entangled with a needle that moves up and down to form a precursor of the ultrafine fiber / fiber-shaped fiber mixed felt. On the other hand, a felt to be used as a laminated base material is produced by a needle punching method using fibers of a micron order consisting of a thermoplastic polymer single component. By overlapping the precursor of the mixed felt on the thus obtained laminated base material felt and passing it through the needle punching device again, the felt integrated by entanglement between the felt layers is obtained.

  Next, it is preferable that the felt is immersed in a bath containing a chemical solution such as an alkali to dissolve and remove the sea component of the sea-island composite fiber, thereby exposing the island component and generating ultrafine fibers and irregular cross-section fibers. In addition, in the step of dissolving and removing the sea component, heat and stirring may be applied, and in this case, the ultrafine fibers and the irregular cross-section fibers are generated while being mixed, and both fibers are more uniformly mixed and the dispersion state is good. The felt is obtained, and at the same time, shrinkage due to heat is added, so that the fine pores for collecting dust and the coarse pores for breathability have a distribution state desirable for achieving both high collection and low pressure loss. In this way, a felt in which the ultrafine fiber / irregular-section fiber mixed felt and the base felt are laminated and integrated is obtained.

  In addition, a method of removing the sea component of the sea-island composite fiber in advance and forming a felt from a mixed raw cotton of ultrafine fibers and modified cross-section fibers is also considered. Due to the effects of static electricity, etc., a large amount of ultrafine fibers and irregular cross-section fibers adhere to the card machine and the needle punch section, increasing the material loss, equipment failure, and increasing the variation in the felt structure to be manufactured. It is preferable to select a production method that generates extra-fine fibers and irregular-shaped fibers after felting.

  When the felt has a laminated structure, from the viewpoint of suppressing peeling, the felt serving as a laminated base material may contain a low-melting fiber, a binder, or the like. After lamination, bonding by heat treatment or bonding using various adhesives can also be applied. It improves the integrity of the nonwoven fabric, prevents peeling between the ultrafine fiber / fiber-shaped cross-section fiber mixed felt and the laminated base material, and improves the form stability against physical impact. In addition, as a filter medium used in an air purifier or the like, a configuration in which the nonwoven fabric of the present invention has a density gradient in the thickness direction so that the upstream side is coarse and the downstream side is dense for the purpose of improving the amount of retained dust. May be provided, and a coarse / dense structure may be formed by laminating a coarse nonwoven fabric on the upstream side and a dense nonwoven fabric on the downstream side.

  The basis weight and thickness of the nonwoven fabric can be changed depending on the supply amount of raw cotton in the fiber web forming step and the laminating speed in the cross wrapper.

  Various functional agents may be added to the nonwoven fabric of the present invention for imparting functions. Examples of functional agents to be added include pigments, water repellents, water absorbents, flame retardants, stabilizers, antioxidants, ultraviolet absorbers, metal particles, inorganic compound particles, fragrances, deodorants, antibacterial agents, and gas adsorbents. And the like.

  The nonwoven fabric of the present invention, when used as a filter medium, achieves both high collection efficiency and low pressure loss, and has excellent morphological stability against physical impact, and is suitable for collecting exhaust gas and collecting valuable powder. It can be suitably used as a filter medium, a filter medium for an air purifier, an air conditioner, a building air conditioner, an industrial clean room, and a car room such as an automobile or a train, a surgical mask, a face mask, and a dust mask. .

Hereinafter, the nonwoven fabric of the present invention will be specifically described with reference to examples.
The following evaluation was performed about the Example and the comparative example.

A. Single fiber fineness The long fiber before the short cut was cut into a 100 m length using a measuring machine, and the weight was measured using an electronic balance. The fineness was calculated by multiplying the measured weight by 100 and divided by the number of long fibers constituted. This was repeated 10 times, and the average value of the third decimal place was rounded off and the value obtained up to the second decimal place was taken as the single-fiber fineness. In addition, the single yarn fineness of the ultrafine fibers and the modified cross-section fibers was determined as follows. That is, 100 m of the sea-island composite fiber as a precursor was removed, immersed in a 0.2 wt% maleic acid aqueous solution, stirred at 130 ° C. for 30 minutes, and immersed in a 1 wt% sodium hydroxide aqueous solution. The sea component was removed by stirring at 40 ° C. for 40 minutes, and the dry weight was measured with an electronic balance. Then, the measured weight was multiplied by 100 to calculate the fineness, and divided by the total number of islands of the used islands-in-sea composite fiber bundle (the number of long fibers x the number of islands in one islands-in-sea composite fiber). This was repeated 10 times, and the average was obtained up to the second significant digit.

B. Fibers of irregular cross-section were extracted from the non-woven fabric of irregular degree, cut in a direction perpendicular to the fiber axis with a razor, and the cut surface was photographed with a scanning electron microscope SU-1510 manufactured by Hitachi High-Technologies Corporation. From this image, the diameter of the perfect circle circumscribing the cut surface was defined as the circumscribed circle diameter, and the diameter of the perfect circle circumscribed was defined as the inscribed circle diameter.
Deformity = (circumscribed circle diameter of fiber cross section) / (inscribed circle diameter of fiber cross section)
This was determined for 10 randomly extracted samples, and the average value was rounded off to the first decimal place and the value obtained to the first decimal place was taken as the irregularity.

C. Flatness The flat cross-section fiber was extracted from the nonwoven fabric, cut by a razor in the direction perpendicular to the fiber axis, and the cut surface was photographed with a scanning electron microscope SU-1510 manufactured by Hitachi High-Technologies Corporation. From this image, the major axis length and the minor axis length of the cut surface were measured for those having a flat cross section, and the flatness was calculated by the following equation.
Flatness = (long axis length of cross section) / (short axis length of cross section)
This was determined for 10 randomly selected samples, and the average was rounded off to the first decimal place and the value obtained to the first decimal place was taken as the oblateness.

D. Average pore size and pore size distribution frequency Evaluate the pore size distribution frequency and average pore size calculated by the bubble point method (based on ASTMF-316-86) using a porous material automatic pore measurement system Perm-Porometer (manufactured by PMI). did. The measurement sample diameter was set to 25 mm, and the pore diameter distribution was measured using Galwick (surface tension: 16 mN / m) as a measurement liquid with a known surface tension. The MEAN FLOW PORE DIAMETER obtained by automatic calculation by this measuring instrument was defined as the value of the average pore size. For the measurement, an arbitrary five points were sampled per sample, and the average value was rounded off to the second decimal place, and the value calculated to the first decimal place was used. The pore size distribution frequency was obtained by converting the value obtained by the automatic calculation into a percentage by converting the value to a percentage, rounding off the second digit after the decimal point, and using the value calculated to the first digit after the decimal point.

E. FIG. The weight of the nonwoven fabric cut into a square of 250 mm x 250 mm was weighed, and the value converted to the weight per unit area (1 m ² ) was rounded off to one decimal place to give an integer value, and the result was used as the weight of the nonwoven fabric.

F. Thickness of Nonwoven Fabric The thickness of the fiber sheet was measured using a dial thickness gauge (SM-114, measuring element shape: 10 mmφ, mesh size: 0.01 mm, measuring force: 2.5 N or less) by TECLOCK. The measurement was carried out at any five locations per sample, and the average value was rounded off to the first decimal place and the value determined to the first decimal place was taken as the thickness of the nonwoven fabric.

G. FIG. Collection efficiency The prepared nonwoven fabric was set in a holder having a measurement diameter of 15 cm, air was passed vertically at a surface wind speed of 3.0 m / min, and the number of atmospheric dust particles having a particle size of 2.0 μm or less upstream and downstream of the filter was measured. The measurement was performed with a counter (manufactured by RION, model: KC-01D), and the collection efficiency was calculated from the following equation.
Collection efficiency (%) = 1− (number of downstream particles / number of upstream particles) × 100
The measurement was carried out by sampling three samples from one sample arbitrarily, and the average was rounded off to the first digit after the decimal point to obtain an integer value, which was taken as the collection efficiency.

H. Pressure loss The produced nonwoven fabric was set in a holder having a measurement diameter of 15 cm, air was passed in the vertical direction at a surface wind speed of 3.0 m / min, and the pressure difference between the upstream and downstream of the filter was measured by a differential pressure gauge. The measurement was carried out by sampling three arbitrary points from one sample, and the average value was rounded off to one decimal place to obtain an integer value, which was taken as a pressure loss.

I. Evaluation of Dust Collection Performance Using an evaluation device based on VDI3926, using Pural NF for dust, under the conditions of inlet dust concentration of 5 g / m ³ , filtration speed of 2 m / min, and pressure drop control of 1000 Pa, dust collection was performed. Was performed 30 times in the initial stage (pulse compressed air tank pressure 500 kPa, pulse injection time 50 ms), and the outlet dust concentration was measured. Thereafter, as an aging process, the removal was repeated 5000 times at intervals of 5 seconds. Next, in order to stabilize the dust collection performance of the sample after the aging treatment, dust collection and removal are performed 10 times again, and as it is, the final 30 collection and removal processes are performed, and the outlet dust concentration is measured. did. Also, as an index of the pulse resistance, a value obtained by subtracting the final 30 exit dust concentration values from the initial 30 exit dust concentration values was used as the exit dust concentration difference. The exit dust concentration was a value obtained by rounding off the third digit after the decimal point to the second digit after the decimal point.

Example 1
Polyethylene terephthalate (PET) resin is an island component, and PET (copolymerized PET) obtained by copolymerizing 10% by mole of 5-sodium sulfoisophthalic acid is a sea component (island component / sea component = 70/30), and a spinning temperature of 295 ° C. After melt-spinning at a speed of 1500 m / min, a sea-island composite fiber (1) having a single yarn fineness of 5.5 dtex (island component fineness: 3.7 × 10 ⁻³ dtex) was produced by roll drawing. In addition, the base is changed, and a sea-island composite fiber (2) having a single yarn fineness of 5.5 dtex (island component fineness: 9.6 × 10 ⁻¹ ) in which four flat islands are arranged in the sea component of the fiber cross section. dtex, island component flatness ratio: 5.5). For these sea-island composite fibers, crimping was performed by a crimper (number of crimps: 12 peaks / 25 mm) and cut (fiber length: 51 mm). After the sea-island composite fibers were opened by passing through a card machine, the sea-island composite fibers (1) and (2) were mixed at a ratio of (1) / (2) = 50/50 and charged into a needle punch device. A fibrous web was formed while further expanding and aligning the charged sea-island composite fibers, and these were laminated at a cross-wrapper portion. Next, the laminated fiber web is conveyed to the needle punch portion by the conveyor of the apparatus, and the fibers in the laminated web are entangled by the needle (punch density: 40 needles / cm ² ) that moves up and down to form the surface layer (A). A felt (a unit weight: 100 g / m ² ) as a precursor was prepared.

On the other hand, using a PET fiber having a single yarn fineness of 2.2 dtex (number of crimps: 12 ridges / 25 mm, fiber length: 51 mm), a felt (basis weight: 160 g / m ² ) was produced in the same manner as described above. . A felt made of PET fiber is used as a base material (B), and a felt made of sea-island composite fiber is laid thereon, and the felt is entangled by passing through a needle punch device (punch density: 40 pieces / cm ² ). And a laminated felt was obtained.
Next, the laminated felt was immersed in a 0.2% by weight maleic acid aqueous solution and stirred at 130 ° C. for 30 minutes, and then immersed in a 1% by weight aqueous sodium hydroxide solution and stirred at 75 ° C. for 40 minutes. The laminated felt after the treatment was washed with pure water to remove the remaining sodium hydroxide and the decomposed product of the copolymerized PET, and then dried with a blow dryer (55 ° C.). By this chemical treatment, the sea component of the sea-island conjugate fiber is dissolved and removed, and the ultrafine fibers (single yarn fineness: 3.7 × 10 ⁻³ dtex) and the flat cross-section fibers (single yarn fineness: 9.6 × 10 ^-1 dtex, flatness: 5.5), and a felt in which the surface layer (A) was laminated on the base material (B) felt was obtained.

The obtained felt has an average pore size of 34.8 μm, a pore size distribution frequency of less than 15.0 μm of 15.5%, and a basis weight of 230 g / m ² (surface layer (A): 70 g / m ² , base material (B) : 160 g / m ² ) and a thickness of 1.6 mm. The felt was evaluated for the efficiency of collecting air dust having a particle diameter of 2.0 μm or less. As a result, the felt exhibited an excellent collection efficiency of 80%, and exhibited an excellent low pressure loss of 15 Pa. Further, as a result of evaluating the dust collecting performance, the outlet dust concentration in the initial 30 times was 0.13 mg / m ^3, and exhibited excellent dust collecting performance. Next, after the pulse aging, the final 30 times of the exit dust concentration was 0.06 mg / m ³ , and the difference between the initial 30 times and the final 30 times of the exit dust concentration was 0.07 mg / m ³ , indicating excellent pulse resistance. showed that.

Examples 2 to 7
By changing the supply amounts of the mixed sea-island composite fiber and the PET fiber used for the base material to the needle punching device, the basis weight of the surface layer (A) and the base material (B) was 90 g / m ² , respectively. Base material (B): 140 g / m ² (Example 2), surface layer (A): 120 g / m ² , Base material (B): 110 g / m ² (Example 3), surface layer (A): 150 g / m ² , substrate (B): 80 g / m ² (Example 4), surface layer (A): 40 g / m ² , substrate (B): 190 g / m ² (Example 5), surface layer (A): 45 g / m ² , Substrate (B): 185 g / m ² (Example 6), Surface layer (A): 55 g / m ² , Substrate (B): 175 g / m ² (Example 7) Except for the above, the procedure was performed according to Example 1.

The felt obtained in Example 2 had an average pore size of 20.3 μm, a pore size distribution frequency of less than 15.0 μm of 15.9%, a basis weight of 230 g / m ² , and a thickness of 1.6 mm.
As a result of evaluating the air dust collection efficiency, an excellent collection efficiency of 84% was exhibited, and an excellent low pressure loss property of 29 Pa was exhibited. Further, the outlet dust concentration in the dust collection performance evaluation is excellent at 0.11 mg / m ³ at the initial 30 times, and 0.05 mg / m ³ at the final 30 times, and the outlet dust concentration difference is excellent at 0.06 mg / m ^3. Showed pulse tolerance.

The felt obtained in Example 3 had an average pore size of 15.1 μm, a frequency of pore size distribution of less than 15.0 μm of 16.3%, a basis weight of 230 g / m ² , and a thickness of 1.6 mm.
As a result of evaluating the air dust collection efficiency, an excellent collection efficiency of 85% was exhibited, and a good low pressure loss property of 46 Pa was exhibited. Further, the outlet dust concentration in the dust collection performance evaluation is excellent at 0.11 mg / m ³ at the initial 30 times, and 0.05 mg / m ³ at the final 30 times, and the outlet dust concentration difference is excellent at 0.06 mg / m ^3. Showed pulse tolerance.

The felt obtained in Example 4 had an average pore size of 12.8 μm, a pore size distribution frequency of less than 15.0 μm of 18.0%, a basis weight of 230 g / m ² , and a thickness of 1.6 mm.
As a result of evaluating the air dust collection efficiency, an excellent collection efficiency of 88% was exhibited, and a sufficiently low pressure loss of 63 Pa was exhibited. Outlet dust concentration in the further dust collecting performance evaluation, and excellent 0.0 mg / ^{m 3} in the early 30 times, the last 30 runs was 0.06 mg / ^{m 3,} good outlet dust concentration difference between 0.02 mg / ^{m 3} Showed pulse tolerance.

The felt obtained in Example 5 had an average pore size of 59.7 μm, a frequency of pore size distribution of less than 15.0 μm of 15.2%, a basis weight of 230 g / m ² , and a thickness of 1.6 mm.
As a result of evaluating the air dust collection efficiency, a sufficient collection efficiency of 70% was exhibited, and an excellent low pressure loss property of 9 Pa was exhibited. Further, the outlet dust concentration in the dust collection performance evaluation was sufficient at the initial 30 times of 0.24 mg / m ^3, and the final 30 times was 0.31 mg / m ³ , and the difference of the outlet dust concentration was −0.07 mg / m ^3. And sufficient pulse tolerance.

The felt obtained in Example 6 had an average pore size of 54.8 μm, a pore size distribution frequency of less than 15.0 μm of 15.6%, a basis weight of 230 g / m ² , and a thickness of 1.6 mm.
As a result of evaluating the air dust collection efficiency, a good collection efficiency of 76% was exhibited, and an excellent low pressure loss property of 11 Pa was exhibited. Outlet dust concentration in the further dust collecting performance evaluation is good in the initial 30 times with 0.19 mg / ^{m 3,} the last 30 runs was 0.23 mg / ^{m 3,} the outlet dust concentration difference -0.04 mg / ^{m 3} And good pulse resistance.

The felt obtained in Example 7 had an average pore size of 50.0 μm, a pore size distribution frequency of less than 15.0 μm of 15.5%, a basis weight of 230 g / m ² , and a thickness of 1.6 mm.
As a result of evaluating the air dust collection efficiency, an excellent collection efficiency of 80% was exhibited, and an excellent low pressure loss property of 11 Pa was exhibited. Outlet dust concentration in the further dust collecting performance evaluation, and excellent 0.14 mg / ^{m 3} in the early 30 times, the last 30 runs was 0.06 mg / ^{m 3,} good outlet dust concentration difference between 0.08 mg / ^{m 3} Showed pulse tolerance.

Comparative Example 1
By changing the supply amounts of the mixed sea-island composite fiber and the PET fiber used for the base material to the needle punch device, the basis weight of the surface layer (A) and the base material (B) was changed to the surface layer (A): 30 g / m ² , Material (B): was changed to 200 g / ^{m 2} was performed in accordance with example 1.
The obtained felt had an average pore size of 62.4 μm, a pore size distribution frequency of less than 15.0 μm of 15.2%, a basis weight of 230 g / m ² , and a thickness of 1.6 mm.
As a result of evaluating the air dust collection efficiency, an excellent low pressure loss property of 11 Pa was exhibited, but the collection efficiency was insufficient at 66%. Further, the outlet dust concentration in the dust collection performance evaluation is insufficient in the initial 30 times with 0.30 mg / ^{m 3,} the last 30 runs was 0.47 mg / ^{m 3,} the outlet dust concentration difference -0.17Mg / It was poor in m ³ and pulse resistance.

Examples 8 to 10
The mixing ratio of the sea-island composite fibers (1) and (2) was respectively (1) / (2) = 70/30 (Example 8), (1) / (2) = 40/60 (Example 9), Example 1 was carried out except that (1) / (2) was changed to 20/80 (Example 10).
The felt obtained in Example 8 had an average pore size of 34.7 μm, a frequency of pore size distribution of less than 15.0 μm of 35.0%, a basis weight of 230 g / m ² , and a thickness of 1.6 mm.
As a result of evaluating the air dust collection efficiency, an excellent collection efficiency of 90% was exhibited, and an excellent low pressure loss property of 26 Pa was exhibited. Outlet dust concentration in the further dust collecting performance evaluation, and excellent 0.05 mg / ^{m 3} in the early 30 times, the last 30 runs was 0.03 mg / ^{m 3,} good outlet dust concentration difference between 0.02 mg / ^{m 3} Showed pulse tolerance.

The felt obtained in Example 9 had an average pore size of 34.5 μm, a pore size distribution frequency of less than 15.0 μm of 10.4%, a basis weight of 230 g / m ² , and a thickness of 1.6 mm.
As a result of evaluating the air dust collection efficiency, a good collection efficiency of 75% was exhibited, and an excellent low pressure loss property of 13 Pa was exhibited. Outlet dust concentration in the further dust collecting performance evaluation is good in the initial 30 times with 0.18 mg / ^{m 3,} the last 30 runs was 0.21 mg / ^{m 3,} the outlet dust concentration difference -0.03 mg / ^{m 3} And good pulse resistance.

The felt obtained in Example 10 had an average pore size of 34.8 μm, a pore size distribution frequency of less than 15.0 μm of 5.2%, a basis weight of 230 g / m ² , and a thickness of 1.6 mm.
As a result of evaluating the air dust collection efficiency, a sufficient collection efficiency of 72% was exhibited, and an excellent low pressure loss property of 9 Pa was exhibited. Further, the outlet dust concentration in the dust collection performance evaluation was as excellent as 0.24 mg / m ³ in the initial 30 times, 0.30 mg / m ³ in the final 30 times, and the outlet dust concentration difference was −0.06 mg / m ³ . Sufficient pulse tolerance was shown.

Comparative Example 2
Example 1 was repeated except that the mixing ratio of the sea-island composite fibers (1) and (2) was changed to (1) / (2) = 80/20.
The obtained felt had an average pore size of 32.3 μm, a pore size distribution frequency of less than 15.0 μm of 47.0%, a basis weight of 230 g / m ² , and a thickness of 1.6 mm.
As a result of evaluating the air dust collection efficiency, the collection efficiency was as excellent as 91%, and the outlet dust concentration in the dust collection performance evaluation was as excellent as 0.04 mg / m ³ in the initial 30 times and in the final 30 times. 0.03 mg / m ³ , and the difference in dust concentration at the outlet was 0.01 mg / m ³ , showing excellent pulse resistance. However, the pressure loss was as high as 72 Pa, and the low pressure loss was insufficient.

Comparative Examples 3 to 5
The fiber composition of the felt which is the precursor of the surface layer (A) is 60 sea-island composite fibers (1), and the PET fiber (round cross section) having a single yarn fineness of 2.2 dtex is mixed at a ratio of 40, respectively. The basis weight was 85 g / m ² (Comparative Example 3), 41 PET fibers (round section) having a single yarn fineness of 1.1 dtex were mixed at a ratio of 59, and the sea-island composite fiber (2) was mixed at a ratio of 59, and the precursor felt was 146 g / m2. m ² (Comparative Example 4), except that only the sea-island composite fiber (1) was used, and the basis weight of the precursor felt was changed to 160 g / m ² (Comparative Example 5).

The felt obtained in Comparative Example 3 had an average pore size of 47.0 μm, a pore size distribution frequency of less than 15.0 μm of 3.1%, a basis weight of 230 g / m ² , and a thickness of 1.6 mm.
As a result of evaluating the air dust collection efficiency, the low pressure loss property was excellent at 8 Pa, but the collection efficiency was insufficient at 62%. Further, the outlet dust concentration in the dust collection performance evaluation is insufficient in the initial 30 times with 0.32 mg / ^{m 3,} the last 30 runs was 0.45 mg / ^{m 3,} the outlet dust concentration difference -0.13Mg / It was poor in m ³ and pulse resistance.

The felt obtained in Comparative Example 4 had an average pore size of 52.3 μm, a pore size distribution frequency of less than 15.0 μm of 4.6%, a basis weight of 230 g / m ² , and a thickness of 2.0 mm.
As a result of evaluation of the air dust collection efficiency, an excellent low pressure loss property of 7 Pa was exhibited, but the collection efficiency was insufficient at 32%. The outlet dust concentration in the dust collection performance evaluation was insufficient at 0.92 mg / m ³ at the initial 30 times, and 1.77 mg / m ³ at the final 30 times, and the difference of the outlet dust concentration was −0.85 mg / m ^3. It was poor in m ³ and pulse resistance.

The felt obtained in Comparative Example 5 had an average pore size of 7.8 μm, a pore size distribution frequency of less than 15.0 μm of 99.8%, a basis weight of 272 g / m ² , and a thickness of 1.7 mm.
As a result of evaluating the air dust collection efficiency, the collection efficiency was excellent at 94%, but the pressure loss was extremely high at 617 Pa, and the low pressure loss was insufficient. Further, the outlet dust concentration in the dust collection performance evaluation was superior in the initial 30 times with 0.01 mg / ^{m 3,} the last 30 runs was 2.88 mg / ^{m 3,} the outlet dust concentration difference -2.87mg / M ³ , which was inferior to pulse resistance. In addition, when the felt surface after the dust collection performance evaluation was observed with a scanning electron microscope (SU-1510 manufactured by Hitachi High-Technologies Corporation), it was confirmed that the felt was broken, and the felt surface was damaged by a pulse impact. It is assumed that the outlet dust concentration has increased 30 times.

Examples 11 to 14
Each weight per unit area of the base material ^{(B), 30g / m 2} ( Example 11), 80g / ^{m 2} (Example 12), 680g / ^{m 2} (Example 13), to 930 g / ^{m 2} (Example 14) Except having changed, it carried out according to Example 1.
The felt obtained in Example 11 had an average pore size of 34.8 μm, a pore size distribution frequency of less than 15.0 μm of 15.5%, a basis weight of 120 g / m ² , and a thickness of 1.0 mm.
As a result of evaluating the air dust collection efficiency, an excellent collection efficiency of 80% was exhibited, and an excellent low pressure loss property of 14 Pa was exhibited. Outlet dust concentration in the further dust collecting performance evaluation is sufficient in the initial 30 times with 0.21 mg / ^{m 3,} the last 30 runs was 0.27 mg / ^{m 3,} the outlet dust concentration difference -0.06 mg / ^{m 3} And sufficient pulse tolerance.

The felt obtained in Example 12 had an average pore size of 34.6 μm, a frequency of pore size distribution of less than 15.0 μm of 15.1%, a basis weight of 160 g / m ² , and a thickness of 1.2 mm.
As a result of evaluating the air dust collection efficiency, an excellent collection efficiency of 83% was exhibited, and an excellent low pressure loss property of 15 Pa was exhibited. Outlet dust concentration in the further dust collecting performance evaluation is good in the initial 30 times with 0.17 mg / ^{m 3,} the last 30 runs was 0.20 mg / ^{m 3,} the outlet dust concentration difference -0.03 mg / ^{m 3} And good pulse resistance.

The felt obtained in Example 13 had an average pore size of 34.8 μm, a frequency of pore size distribution of less than 15.0 μm of 15.3%, a basis weight of 750 g / m ² , and a thickness of 3.9 mm.
As a result of evaluating the air dust collection efficiency, an excellent collection efficiency of 80% was exhibited, and an excellent low pressure loss property of 18 Pa was exhibited. Furthermore, the outlet dust concentration in the dust collection performance evaluation was excellent at 0.15 mg / m ³ at the initial 30 times, 0.06 mg / m ³ at the final 30 times, and the outlet dust concentration difference was excellent at 0.09 mg / m ^3. Showed pulse tolerance.

The felt obtained in Example 14 had an average pore size of 34.7 μm, a pore size distribution frequency of less than 15.0 μm of 15.7%, a basis weight of 1000 g / m ² , and a thickness of 4.6 mm. As a result of evaluating the air dust collection efficiency, an excellent collection efficiency of 82% was exhibited, and an excellent low pressure loss property of 21 Pa was exhibited. Outlet dust concentration in the further dust collecting performance evaluation is good in the initial 30 times with 0.19 mg / ^{m 3,} the last 30 runs was 0.21 mg / ^{m 3,} the outlet dust concentration difference -0.02 mg / ^{m 3} And good pulse resistance.

Comparative Example 6
Example 1 was repeated except that the base material (B) was not laminated and the basis weight of the surface layer (A) was changed to 90 g / m ² .
The obtained felt had an average pore size of 20.5 μm, a pore size distribution frequency of less than 15.0 μm of 15.7%, a basis weight of 90 g / m ² , and a thickness of 0.5 mm.
As a result of evaluating the air dust collection efficiency, the collection efficiency was excellent at 83%, and the pressure loss was 28 Pa, showing excellent low pressure loss. Further, the outlet dust concentration in the dust collection performance evaluation, despite excellent as 0.11 mg / ^{m 3} in the early 30 times, the last 30 runs was 1.58 mg / ^{m 3,} the outlet dust concentration difference -1.47mg / M ³ , which was inferior to pulse resistance. The felt after the dust collection performance evaluation was torn, and it is assumed that the final 30 times of the exit dust concentration increased due to the damage due to the impact of the pulse.

Examples 15 to 17
Change the fibers constituting the base material (B) to the PET fibers of single fiber fineness of 3.3 dtex, respectively weight per unit area of the base material ^{(B), 300g / m 2} ( Example 15), 530g / ^{m 2} (Example 16) and 630 g / m ² (Example 17), except that the procedure was changed to 630 g / m ² (Example 17).

The felt obtained in Example 15 had an average pore size of 35.4 μm, a pore size distribution frequency of less than 15.0 μm of 15.2%, a basis weight of 370 g / m ² , and a thickness of 4.8 mm. As a result of evaluating the air dust collection efficiency, an excellent collection efficiency of 80% was exhibited, and an excellent low pressure loss property of 13 Pa was exhibited. Outlet dust concentration in the further dust collecting performance evaluation, and excellent 0.13 mg / ^{m 3} in the early 30 times, the last 30 runs was 0.09 mg / ^{m 3,} good outlet dust concentration difference between 0.04 mg / ^{m 3} Showed pulse tolerance.

The felt obtained in Example 16 had an average pore size of 35.9 μm, a pore size distribution frequency of less than 15.0 μm of 13.4%, a basis weight of 600 g / m ² , and a thickness of 7.9 mm. As a result of evaluating the air dust collection efficiency, a good collection efficiency of 75% was exhibited, and an excellent low pressure loss property of 13 Pa was exhibited. Outlet dust concentration in the further dust collecting performance evaluation is good in the initial 30 times with 0.18 mg / ^{m 3,} the last 30 runs was 0.18 mg / ^{m 3,} the outlet dust concentration difference between registers 0.00 mg / ^{m 3} It showed excellent pulse tolerance.

The felt obtained in Example 17 had an average pore size of 36.5 μm, a pore size distribution frequency of less than 15.0 μm of 9.6%, a basis weight of 700 g / m ² , and a thickness of 10.0 mm. As a result of evaluating the air dust collection efficiency, a sufficient collection efficiency of 71% was exhibited, and an excellent low pressure loss property of 12 Pa was exhibited. Further, the exit dust concentration in the dust collection performance evaluation was sufficient at the initial 30 times of 0.23 mg / m ³ , the final 30 times was 0.11 mg / m ³ , and the difference of the exit dust concentration was 0.12 mg / m ³ . It showed excellent pulse tolerance.

Comparative Example 7
Example 1 was repeated except that the fibers constituting the base material (B) were changed to PET fibers having a single yarn fineness of 3.3 dtex, and the basis weight of the base material (B) was changed to 730 g / m ² .
The obtained felt had an average pore size of 43.0 μm, a pore size distribution frequency of less than 15.0 μm of 4.8%, a basis weight of 800 g / m ² , and a thickness of 11.2 mm. As a result of evaluation of the air dust collection efficiency, an excellent low pressure loss property of 8 Pa was exhibited, but the collection efficiency was insufficient at 38%. The outlet dust concentration in the dust collection performance evaluation was insufficient at 0.89 mg / m ³ at the initial 30 times, but was small at 0.91 mg / m ³ at the final 30 times, and the outlet dust concentration difference was small. The pulse resistance was −0.02 mg / m ^3, which was good.

Examples 18 to 20
The fineness of the ultrafine fibers contained in the surface layer (A) was changed to 1.2 × 10 ⁻² dtex (Example 18) and 9.6 × 10 ⁻³ , respectively, by changing the island component fineness of the sea-island composite fiber (1). The procedure was performed in the same manner as in Example 1 except that dtex (Example 19) and 7.0 × 10 ⁻³ dtex (Example 20) were changed.

The felt obtained in Example 18 had an average pore size of 55.4 μm, a pore size distribution frequency of less than 15.0 μm of 9.3%, a basis weight of 230 g / m ² , and a thickness of 1.7 mm.
As a result of evaluating the air dust collection efficiency, a sufficient collection efficiency of 71% was exhibited, and an excellent low pressure loss property of 9 Pa was exhibited. Further, the outlet dust concentration in the dust collection performance evaluation was sufficient at the initial 30 times of 0.25 mg / m ^3, and the final 30 times was 0.33 mg / m ³ , and the difference of the outlet dust concentration was −0.08 mg / m ^3. And sufficient pulse tolerance.

The felt obtained in Example 19 had an average pore size of 50.2 μm, a frequency of pore size distribution of less than 15.0 μm of 14.3%, a basis weight of 230 g / m ² , and a thickness of 1.6 mm.
As a result of evaluating the air dust collection efficiency, a good collection efficiency of 75% was exhibited, and an excellent low pressure loss property of 12 Pa was exhibited. Outlet dust concentration in the further dust collecting performance evaluation is good in the initial 30 times with 0.20 mg / ^{m 3,} the last 30 runs was 0.25 mg / ^{m 3,} the outlet dust concentration difference -0.05 mg / ^{m 3} And good pulse resistance.

The felt obtained in Example 20 had an average pore size of 36.9 μm, a pore size distribution frequency of less than 15.0 μm of 15.1%, a basis weight of 230 g / m ² , and a thickness of 1.6 mm.
As a result of evaluating the air dust collection efficiency, an excellent collection efficiency of 80% was exhibited, and an excellent low pressure loss property of 16 Pa was exhibited. Outlet dust concentration in the further dust collecting performance evaluation, and excellent 0.10 mg / ^{m 3} in the early 30 times, the last 30 runs was 0.08 mg / ^{m 3,} good outlet dust concentration difference between 0.02 mg / ^{m 3} Showed pulse tolerance.

Examples 21 and 22
By changing the island component fineness of the sea-island composite fiber (2), the fineness of the flat cross-section fiber contained in the surface layer (A) is 1.0 × 10 ⁻¹ dtex (Example 21), 3.0 × 10 ^{−, respectively. The} procedure was performed in the same manner as in Example 1 except that ¹ dtex (Example 22) was used.

The felt obtained in Example 21 had an average pore size of 18.7 μm, a pore size distribution frequency of less than 15.0 μm of 30.1%, a basis weight of 230 g / m ² , and a thickness of 1.6 mm.
As a result of evaluation of the air dust collection efficiency, an excellent collection efficiency of 96% was exhibited, and a good low pressure loss property of 48 Pa was exhibited. Further, the outlet dust concentration in the dust collection performance evaluation was as excellent as 0.06 mg / m ³ in the initial 30 times, 0.13 mg / m ³ in the final 30 times, and the outlet dust concentration difference was −0.07 mg / m ³ . It showed good pulse tolerance.

The felt obtained in Example 22 had an average pore size of 20.3 μm, a pore size distribution frequency of less than 15.0 μm of 27.2%, a basis weight of 230 g / m ² , and a thickness of 1.6 mm.
As a result of evaluating the air dust collection efficiency, an excellent collection efficiency of 92% was exhibited, and an excellent low pressure loss property of 26 Pa was exhibited. Outlet dust concentration in the further dust collecting performance evaluation, and excellent 0.07 mg / ^{m 3} in the early 30 times, the last 30 runs was 0.04 mg / ^{m 3,} good outlet dust concentration difference between 0.03 mg / ^{m 3} Showed pulse tolerance.

Examples 23 and 24
4. In place of the sea-island composite fiber (2), two flat islands are arranged in the sea component of the fiber cross section. The single component fineness is 15.0 dtex and the island component fineness is 3.0 dtex (Example 23). It carried out according to Example 1 except having used the sea-island composite fiber of 0dtex (Example 24).

The felt obtained in Example 23 had an average pore size of 46.7 μm, a pore size distribution frequency of less than 15.0 μm of 15.4%, a basis weight of 230 g / m ² , and a thickness of 1.9 mm.
As a result of evaluating the air dust collection efficiency, an excellent collection efficiency of 83% was exhibited, and an excellent low pressure loss property of 11 Pa was exhibited. Further, the outlet dust concentration in the dust collection performance evaluation is excellent at 0.11 mg / m ³ at the initial 30 times, and 0.05 mg / m ³ at the final 30 times, and the outlet dust concentration difference is excellent at 0.06 mg / m ^3. Showed pulse tolerance.

The felt obtained in Example 24 had an average pore size of 52.1 μm, a pore size distribution frequency of less than 15.0 μm of 10.3%, a basis weight of 230 g / m ² , and a thickness of 2.3 mm.
As a result of evaluating the air dust collection efficiency, a good collection efficiency of 76% was exhibited, and an excellent low pressure loss property of 10 Pa was exhibited. Further, the outlet dust concentration in the dust collection performance evaluation was as good as 0.18 mg / m ³ at the initial 30 times, 0.22 mg / m ³ at the final 30 times, and the difference of the outlet dust concentration was −0.04 mg / m ^3. And good pulse resistance.

Examples 25 and 26
Example 1 was repeated except that the flat cross-section fibers included in the surface layer (A) were changed to equilateral cross-section fibers (Example 25) and Y-shaped cross-section fibers (Example 26).

The felt obtained in Example 25 had an average pore size of 53.4 μm, a pore size distribution frequency of less than 15.0 μm of 11.3%, a basis weight of 230 g / m ² , and a thickness of 1.6 mm.
As a result of evaluating the air dust collection efficiency, a good collection efficiency of 75% was exhibited, and an excellent low pressure loss property of 12 Pa was exhibited. Outlet dust concentration in the further dust collecting performance evaluation is good in the initial 30 times with 0.19 mg / ^{m 3,} the last 30 runs was 0.23 mg / ^{m 3,} the outlet dust concentration difference -0.04 mg / ^{m 3} And good pulse resistance.

The felt obtained in Example 26 had an average pore size of 52.1 μm, a pore size distribution frequency of less than 15.0 μm of 12.7%, a basis weight of 230 g / m ² , and a thickness of 1.6 mm.
As a result of evaluating the air dust collection efficiency, a good collection efficiency of 76% was exhibited, and an excellent low pressure loss property of 11 Pa was exhibited. Outlet dust concentration in the further dust collecting performance evaluation is good in the initial 30 times with 0.18 mg / ^{m 3,} the last 30 runs was 0.21 mg / ^{m 3,} the outlet dust concentration difference -0.03 mg / ^{m 3} And good pulse resistance.

Examples 27 and 28
It carried out according to Example 1 except having changed the oblateness of the flat cross section fiber contained in the surface layer (A) into 3.0 (Example 27) and 8.0 (Example 28).

The felt obtained in Example 27 had an average pore size of 50.8 μm, a pore size distribution frequency of less than 15.0 μm of 13.2%, a basis weight of 230 g / m ² , and a thickness of 1.6 mm.
As a result of evaluating the air dust collection efficiency, a good collection efficiency of 79% was exhibited, and an excellent low pressure loss property of 13 Pa was exhibited. Further, the outlet dust concentration in the dust collection performance evaluation was as good as 0.16 mg / m ³ in the initial 30 times, and 0.18 mg / m ³ in the final 30 times, and the difference in the outlet dust concentration was −0.02 mg / m ^3. And good pulse resistance.

The felt obtained in Example 28 had an average pore size of 31.7 μm, a pore size distribution frequency of less than 15.0 μm of 26.3%, a basis weight of 230 g / m ² , and a thickness of 1.6 mm.
As a result of evaluating the air dust collection efficiency, an excellent collection efficiency of 98% was exhibited, and an excellent low pressure loss property of 23 Pa was exhibited. Outlet dust concentration in the further dust collecting performance evaluation, and excellent 0.04 mg / ^{m 3} in the early 30 times, the last 30 runs was 0.02 mg / ^{m 3,} good outlet dust concentration difference between 0.02 mg / ^{m 3} Showed pulse tolerance.

  With the mixed fiber nonwoven fabric of the present invention, a filter medium that achieves both high collection efficiency and low pressure loss is obtained, and is used for houses, hospitals, offices, etc., for air cleaners, air conditioners, building air conditioners, industrial clean rooms, and the like. It is useful as a filter medium, a surgical mask, a face mask, and a dust mask for a vehicle room such as an automobile or a train.

REFERENCE SIGNS LIST 1 surface layer made of ultrafine fiber and modified cross-section fiber 2 substrate 3 supporting the surface layer of 1 3 circumscribed circle in cross section of modified cross section fiber 4 cross section of modified cross section fiber 5 inscribed circle in cross section of modified cross section fiber

Claims (6)

The average pore size is 10.0 to 60.0 μm, the pore size distribution frequency of less than 15.0 μm is 5.0 to 35.0%, the basis weight is 120 g / m ² or more, and the thickness is 1.0 to 10.0 mm. A mixed-fiber nonwoven fabric characterized by the following. Includes at least one or more layers composed of a mixture of ultrafine fibers having a single-fiber fineness of less than 1.0 × 10 ⁻² dtex and irregular-shaped cross-sectional fibers having a single-fiber fineness of 1.0 × 10 ^{−1 to} 5.0 dtex. The mixed-fiber nonwoven fabric according to claim 1, characterized in that: The mixed fiber nonwoven fabric according to any one of claims 1 and 2, wherein the irregular cross-section fiber has a cross-sectional irregularity of 2.0 or more. The flattening ratio b / a is 3.0 or more when the minor axis length is a and the major axis length is b, with respect to the cross-sectional shape of the modified cross-section fiber, wherein it is 3.0 or more. Nonwoven. A fiber product comprising the mixed nonwoven fabric according to any one of claims 1 to 4 at least partially. A filter comprising the mixed nonwoven fabric according to any one of claims 1 to 4 at least partially.