JP7047593B2 - Wet non-woven fabric - Google Patents

Description

The present invention relates to a wet non-woven fabric for a filter whose dust collecting performance is maintained for a long time.

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

The air filter takes in air containing dust and captures the dust in the filter medium portion to purify the passing air. In addition to the ability to collect dust with high efficiency, this air filter has a low pressure loss because the lower the pressure loss when the gas passes through, the longer the life of the filter and the increase in the processing air volume. This is also one of the important performances of the air filter.

Generally, in order to improve the dust collection efficiency, the pore size of the filter medium sheet used for the filter is reduced to improve the mechanical collection performance. This pore size is 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, the ventilation resistance increases and a high pressure loss occurs, so that the collection efficiency and the pressure loss conflict with each other.

In order to achieve both high collection efficiency and low pressure loss, which are contradictory performances, electret filters that charge the filter media sheet and capture dust using the electrostatic force of the electric charge are widely used as air filters for air purifiers. It is used.

As a method of charging the filter medium sheet, electret processing by corona charge by corona discharge using electrodes or hydro charge by immersion and drying in water is applied to the fiber itself or the filter medium sheet before making the filter medium sheet. Therefore, a method of charging the constituent fibers is common. Since the electret filter attracts and captures dust in the air by static electricity, unlike physical collection, the pore size of the filter media sheet often does not significantly affect the collection efficiency. Therefore, it is possible to capture dust with high efficiency even if the pore size is increased, and it is possible to achieve both low pressure loss and low pressure loss. However, in the electret filter, as the captured dust accumulates on the filter media sheet, the electric charge charged on the constituent fibers is neutralized, and the electrostatic force decreases. Therefore, there is a problem that the dust collection efficiency is significantly lowered as compared with the initial state.

Various efforts have been made to solve the problems of these electret filters. For example, in Patent Document 1, a method of laminating a non-woven fabric sheet in which fibers having different fiber diameters are combined to capture a certain amount of dust before reaching the electric filter, thereby delaying the neutralization of electric charges due to dust accumulation. Has been proposed.

Further, Patent Document 2 proposes a method of increasing the mechanical collection efficiency by mixing electretized fibers having a small fiber diameter. Since the fiber diameter used is on the order of microns and the pore size of the filter media sheet is not extremely reduced, the increase in pressure loss is small and the collection efficiency can be improved to some extent.

JP-A-2007-307516 (Claims) Japanese Patent Application Laid-Open No. 10-46460 (Claims)

However, in Patent Document 1, it is necessary to bond the sheets when they are laminated, and there is a problem that the pressure loss increases at the bonded portion. Further, there is a problem that the filter medium becomes thick due to the laminating, which is not suitable for making the air filter compact.

Further, the fiber diameter on the order of micron in Patent Document 2 does not have a great effect on increasing the mechanical collection efficiency, and it is a problem that sufficient collection performance cannot be exhibited in a state where the electrostatic force is completely lost. Therefore, there was a problem in maintaining the high collection efficiency of the electret filter.

An object of the present invention is to solve the above-mentioned problems of the prior art, and in the wet nonwoven fabric of the present invention, as an electretized filter medium, the reduction in collection efficiency is small even after the electrostatic force is lost, and the collection efficiency is high. It is an object of the present invention to provide a wet non-woven fabric that achieves both collection efficiency and low pressure loss.

The above object is achieved by the following means. That is,
(1) A wet non-woven fiber composed of three or more types of short fibers, having eight or more slits on the surface and having a fiber diameter of 5.0 to 50.0 μm (short fibers A) and fibers. A wet non-woven fabric containing ultrafine fibers (short fibers B) having a diameter of 3.0 μm or less and irregular cross-sectional fibers (short fibers C) having a fiber diameter more than twice that of short fibers B and a degree of deformation of 1.2 or more.
(2) The wet nonwoven fabric according to (1), wherein the ultrafine fibers (staples B) have a degree of deformation of 1.1 or more.
(3) The wet non-woven fabric according to (1) or (2), wherein the ultrafine fibers (staples B) and the irregular cross-section fibers (staples C) are made of polyolefin.
(4) The wet non-woven fabric according to any one of (1) to (3), wherein the fiber having a slit (staple fiber A) is made of polyolefin.
(5) The wet non-woven fabric according to any one of (1) to (4), which is characterized by being electretized.
(6) A textile product in which at least a part of the wet nonwoven fabric according to any one of (1) to (5) constitutes.
(7) After wet-making a split-type composite fiber and a binder fiber capable of generating fibers having slits (short fibers A), ultrafine fibers (short fibers B) and irregularly shaped cross-sectional fibers (short fibers C), heat treatment and / The method for producing a wet nonwoven fabric according to (1) to (5), wherein the split-type composite fiber in the nonwoven fabric is divided by a physical impact.

In the wet non-woven fabric of the present invention, as an electretized filter medium, it exhibits high collection efficiency due to electrostatic force while having a low pressure loss, and the decrease in collection efficiency is small even after the electrostatic force is lost. It is possible to achieve both high collection efficiency and low pressure loss.

FIG. 1 is a schematic view of the fiber sheet of the present invention. FIG. 2 is a cross-sectional view (example) of a peeling split type composite fiber for producing the wet nonwoven fabric of the present invention. FIG. 3 is a schematic diagram for showing the degree of deformation in the fiber cross section of the present invention.

Hereinafter, the present invention will be described in detail together with desirable embodiments.
The wet non-woven fabric of the present invention needs to be composed of three or more kinds of fibers. Wet non-woven fabrics made of short fibers are characterized by excellent sheet uniformity and high rigidity as compared with sheets made of long fibers such as melt-blown non-woven fabrics. If there is a difference in density in the fiber sheet that is generally used as a filter filter medium, air will preferentially pass through the coarse-density portion, and dust that is the target of collection will also pass through, resulting in a desired filter. It may not function. Furthermore, in the case of an electret filter filter medium, if the charge distribution is biased in the fiber sheet, the dust collection force due to the electrostatic force of the entire sheet is lower than that of the one in which the charge is uniformly distributed. It ends up. Therefore, the filter filter medium is required to have a fiber sheet having as small a difference in coarseness and density as possible and having high uniformity. Further, the higher the rigidity of the filter filter medium, the larger the airflow resistance can be withstood and the higher the air volume can be processed. Therefore, a highly rigid fiber sheet is desired.

When the constituent fibers of the wet non-woven fabric are single, if the sheet weight is constant, the balance between the contradictory collection efficiency and the pressure loss is uniquely determined by the fiber diameter of the constituent fibers. Therefore, by using three or more types of constituent fibers, it is possible to control the balance between collection efficiency and pressure loss. By using ultrafine fibers as one of the constituent fibers, the wet non-woven fabric exhibits a high level of mechanical collection efficiency. However, as the fiber diameter of the constituent fibers becomes smaller, the mechanical collection efficiency increases, but the aeration resistance increases accordingly, resulting in a high pressure loss.

Therefore, as a result of diligent studies, the inventors have made a wet non-woven fabric in which ultrafine fibers responsible for collecting fine dust are mixed in a state of being bridged in through holes (pores) formed of other constituent fibers. We have found that the pressure loss is at a low level without extremely reducing the average pore size while exhibiting high mechanical collection efficiency. In particular, as a blended fiber of a wet non-woven fabric, it has a high fineness but has fine slits, so that it has a sheet strength that can withstand use as a filter filter medium, and the slits are very fine, so that it is mixed. It has been found that it contributes to dust collection and significantly improves the performance as well as the ultrafine fibers produced.

The wet non-woven fabric of the present invention needs to have eight or more slits on the surface and contain fibers (staple fibers A) having a fiber diameter of 5.0 to 50.0 μm. By having eight or more slits on the surface, the voids between the fibers can be increased, and the sheet has a bulky structure, which leads to a reduction in ventilation resistance when used as a filter filter medium. In addition, since the tip of the convex portion of the slit has the same size as the ultrafine fiber, it also contributes to the collection of fine dust. If there are eight or more slits, it is possible to sufficiently secure gaps between the fibers. From the viewpoint of promoting the securing of voids between fibers, it is preferable that the number of slits is 16 or more. Further, in order to improve the collection performance, it is more preferable to have 24 or more locations from the viewpoint of increasing the number of fine slits. The practical upper limit of the slit locations is about 100 locations in consideration of the processing accuracy of the spinneret for fiber production.

Further, since the fiber diameter of the staple fiber A is 5.0 to 50.0 μm, sufficient strength can be imparted when used as a filter filter medium. In wet papermaking of synthetic fibers, generally, the finer the fiber, the higher the water retention and the higher the uniformity of the papermaking. Therefore, it is possible to improve the collection efficiency in particular. On the other hand, as the fiber diameter becomes smaller, the porosity and strength of the sheet tend to decrease. Therefore, from the viewpoint of promoting the stabilization of the filter performance while ensuring the strength as the filter filter medium, the fiber diameter of the staple fiber A is preferably 7.0 to 40.0 μm, preferably 9.0 to 35. It is more preferably 0 μm.

The wet non-woven fabric of the present invention needs to contain ultrafine fibers (staples B) having a fiber diameter of 3.0 μm or less. When the fiber diameter of the ultrafine fiber is 3.0 μm or less, it exhibits a sufficiently high mechanical collection efficiency for fine dust as a filter filter medium. The smaller the fiber diameter of the ultrafine fibers, the higher the mechanical collection efficiency. Sufficient collection efficiency may not be obtained. Therefore, from the viewpoint of suppressing the aggregation of the ultrafine fibers, the fiber diameter of the ultrafine fibers is preferably 0.1 μm or more. Further, it is more preferably 0.2 to 2.0 μm from the viewpoint of exhibiting stable performance as a filter filter medium by further improving the dispersibility of the ultrafine fibers and increasing the uniformity of the fiber sheet. Further, 0.3 to 1.5 μm is more preferable from the viewpoint of achieving both low pressure loss and collection efficiency. As long as the fiber diameter of the ultrafine fibers is within the relevant range, it is practical for high collection efficiency during charging and static elimination while maintaining low pressure loss that can withstand high air volume processing when used as an electret filter filter medium. Demonstrates excellent mechanical collection efficiency.

The ultrafine fibers (staples B) constituting the wet papermaking nonwoven fabric of the present invention are preferably irregular cross-section fibers having a degree of deformation of 1.1 or more. Since the dispersed state of the ultrafine fibers, which are responsible for collecting fine dust, greatly contributes to the collection performance, the irregular cross-section fibers can suppress the adhesion with other mixed fiber, which is suitable. be. The degree of deformation is more preferably 1.5 or more from the viewpoint of preventing the constituent fibers of the wet non-woven fabric from adhering to each other and agglomerating with each other and improving the dust collecting performance. Considering the formation accuracy of the ultrafine fibers, the practical upper limit of the degree of deformation of the staple fibers B is 5.0.

The wet non-woven fabric of the present invention needs to contain deformed cross-sectional fibers (staples C) having a fiber diameter of 2 times or more that of the short fibers B and a degree of deformation of 1.2 or more. When the ultrafine fibers and the thicker base fibers are blended, the ultrafine fibers may adhere to each other or aggregate, or the ultrafine fibers may be entangled with the base fibers, resulting in poor formation of the obtained wet non-woven fabric. There is. Since the short fibers C have an intermediate size between the short fibers A constituting the wet nonwoven fabric and the short fibers B which are ultrafine fibers, they enter between the short fibers A and the short fibers B during stirring with white water to secure voids. , Suppresses adhesion and aggregation of short fibers B, which are ultrafine fibers. Therefore, the compounded fibers at the time of papermaking are uniformly dispersed, a wet non-woven fabric having a good texture can be obtained, and the filter performance is stabilized. From the viewpoint of promoting low-pressure loss while maintaining high collection performance by well dispersing the compounded fibers in the wet non-woven fabric, the degree of deformation is preferably 1.5 or more. The upper limit of the degree of deformation that can be implemented is about 10.0.

As the fiber diameter of the short fiber C is larger than that of the short fiber B, the effect of widening the space between the short fiber A and the short fiber B is enhanced, and the dispersed state of the compounded fiber tends to be improved. The fiber diameter of C is preferably 3 times or more, more preferably 5 times or more that of the short fiber B.

However, if the staple fiber C is equal to or larger than the fiber diameter of the staple fiber A, it behaves as a base fiber, and the effect of improving the dispersion of the compounded fiber cannot be obtained. Therefore, it is preferable to take an intermediate size between the short fibers A and the short fibers B, and the practical upper limit of the fiber diameter is 20.0 μm from the viewpoint of exerting a good dispersion effect of the compounded fibers.

Further, since the deformed cross-section fiber has a degree of deformation of 2.0 or more, it also has an effect of suppressing adhesion to the ultrafine fiber, which leads to improvement of the dispersibility of the compounded fiber. When the degree of deformation of the cross section is within the relevant range, the dispersed state of the ultrafine fibers is clearly different from that when mixed with the round cross-section fibers, and the pore size distribution is different. It will be better. The upper limit of the degree of deformation that can be achieved in the present invention is about 10.0. The degree of deformation referred to here is obtained as follows. The cross section of the short fiber is photographed two-dimensionally, and from the image, the diameter of the perfect circle circumscribing the short fiber cross section is defined as the circumscribed circle diameter, and the diameter of the inscribed perfect circle is defined as the inscribed circle diameter. From the circumscribed circle diameter ÷ inscribed circle diameter, the second digit after the decimal point was rounded off, and the one obtained up to the first digit after the decimal point was taken as the degree of irregularity. The circumscribed circle referred to here is the part 8 in FIG. 3, and the inscribed circle is the part 10 in FIG. This degree of deformation was measured for 10 randomly selected fibers, and a simple number average value of the measured values in each image was obtained and used as the degree of deformation.

The wet non-woven fabric of the present invention is particularly limited as long as it is used for producing general synthetic fibers as a polymer used for constituent short fibers, including binder fibers, microfibers, high-fineness fibers and the like, which will be described later. Examples thereof include polyester, polyamide, polyolefin, acrylic and the like.

From the viewpoint of using the wet non-woven fabric of the present invention as an electret filter filter medium, the ultrafine fibers (short fibers B) and the irregular cross-sectional fibers (short fibers C), which are mainly responsible for collecting dust in the sheet, are polypropylene, polyethylene, polystyrene, and the like. It is preferably made of a polyolefin such as polytetrafluoroethylene. By using these fibers as polyolefin, which has a high charging effect, it is possible to exhibit high collection efficiency for fine dust.

The constituent resin of the fiber having slits (staple fiber A), which is the constituent fiber of the wet nonwoven fabric of the present invention, is not particularly limited, but is preferably composed of polyolefin from the viewpoint of enhancing the charging effect of the sheet. ..

The average pore size of the wet non-woven fabric of the present invention is not particularly limited, but if it is 5.0 to 40.0 μm, it is about the same as that of a normal air filter filter medium, so that the pressure loss is within a practical range. It becomes a thing and is preferable. When the average pore size is 5.0 μm or more, the collection efficiency and the ventilation resistance are good, and the pressure loss does not become too high as an air filter filter medium, which is good. On the other hand, when the average pore size is 50.0 μm or less, the ventilation resistance is good, the pressure loss is small, the dust is less likely to pass through, and the collection efficiency is good. The average pore size of the wet non-woven fabric is more preferably 10.0 to 35.0 μm from the viewpoint of suppressing pressure loss so that it can be treated at a high air volume while maintaining the dust collection efficiency at a high level, and further after electretization. From the viewpoint of achieving both low pressure loss and high collection efficiency, 12.0 to 25.0 μm is more preferable.

The average pore size in the present invention is the average size of the through holes formed by the short fibers constituting the wet nonwoven fabric, and is a value calculated by the bubble point method. As the bubble point method, for example, a porous material automatic pore measurement system Perm-Polymeter (manufactured by PMI) can be used. In the measurement by this Perm-Polymeter, the wet non-woven fabric is dipped in a liquid having a known surface tension value and supplied while increasing the gas pressure from the upper side of the sheet, and the relationship between this pressure and the liquid surface tension on the surface of the wet non-woven fabric Measure the pore size.

The pore size distribution of the wet nonwoven fabric of the present invention is not particularly limited, but it is preferable that the distribution frequency of the pore size of 15.0 μm or more is 10.0% or more.

The present invention aims to improve the collection performance of the air filter filter medium, but in order to improve the physical collection performance of dust, simply reducing the pore size of the fiber sheet causes an increase in pressure loss and the filter. This leads to problems such as shortened life and increased power consumption of the air purifier, making it unsuitable for air filter filter media that require low pressure loss. The inventors focused on the pore size distribution of the wet non-woven fabric, and as a result of diligent studies, the wet non-woven fabric has sufficient air permeability and is applicable as an air filter filter medium because the distribution frequency is within the range of the pore size of 15.0 μm or more. At that time, it was found that the pressure loss can be suppressed to a level sufficiently low for practical use.

From the viewpoint of promoting low pressure loss as a filter medium, it is preferable that many large pores are present in the wet nonwoven fabric, and the distribution frequency of pore size 15.0 μm or more is more preferably 15.0% or more, 20.0%. The above is more preferable. However, since the physical dust collection performance deteriorates only with a coarse pore, the pore size is 15.0 μm or more from the viewpoint of reducing the pressure loss as a filter medium and not practically impairing the dust collection performance during static elimination. The practical upper limit of the distribution frequency of is 98.0%.
The pore size frequency distribution in the wet nonwoven fabric of the present invention is a value measured by a Perm-Polymeter by the bubble point method in the same manner as the above-mentioned average pore size.

The blending ratio of each staple fiber constituting the wet nonwoven fabric of the present invention in terms of fiber weight is not particularly limited, but is not limited.
The short fibers A having slits affect the strength and thickness of the wet nonwoven fabric, and are preferably 50% by weight or more from the viewpoint of designing a bulky structure. From the viewpoint of preventing a decrease in the collection efficiency of fine dust, the practical upper limit is 85% by weight. Further, since the short fibers B, which are ultrafine fibers, are mainly responsible for collecting dust, the blending ratio of the short fibers B is preferably 5% by weight or more from the viewpoint of exhibiting the collection performance as a filter filter medium. From the viewpoint of collecting more fine dust, it is more preferably 10% by weight or more. On the other hand, from the viewpoint of preventing an increase in pressure loss due to an increase in the amount of ultrafine fibers, the practical upper limit of the blending ratio is about 30% by weight. Further, the short fiber C, which is a modified cross-sectional fiber, has an effect of improving the uniformity of the wet nonwoven fabric, and the blending ratio of the short fiber C is 5% by weight or more from the viewpoint of stabilizing the performance as a filter filter medium. Is preferable. It is more preferably 10% by weight or more from the viewpoint of further improving the uniformity of the sheet and maintaining a good balance between collection performance and pressure loss. On the other hand, from the viewpoint of preventing an increase in pressure loss due to the high density of the wet nonwoven fabric, the practical upper limit of the blending ratio of the staple fibers C is about 30% by weight.

In the wet non-woven fabric of the present invention, binder fibers may be mixed, if necessary, for the purpose of improving the sheet strength and suppressing the falling off of the constituent fibers. Since the above-mentioned compounded fibers alone have few adhesive points and the sheet strength may be insufficient, it is possible to improve the sheet strength by mixing the heat-adhesive binder fibers. However, since the number of adhesive points of the binder fibers increases, the sheet density may increase after fusion and the pressure loss may increase significantly. Therefore, the mixing ratio of the binder fibers is preferably 30% by weight or less, and the air permeability is preferable. 20% by weight or less is more preferable from the viewpoint of ensuring. From the viewpoint of ensuring the adhesiveness between the blended fibers in the sheet, the substantially lower limit of the blending ratio of the binder fibers is 5% by weight.

The thermal properties of the binder fiber are not particularly limited, but a core-sheath composite fiber in which a polymer having a melting point of 150 ° C. or lower is arranged in a sheath is preferable. After forming the wet non-woven fabric, heat treatment such as a calendar melts the sheath part on the surface of the binder fiber, and after cooling, heat adhesion can increase the rigidity of the fiber sheet, so that it is durable as a filter filter medium. It is possible to purify more air under improved and high air volume. Further, from the viewpoint of heat-bonding by heat treatment at a lower temperature in order to suppress heat shrinkage of the fiber sheet, the melting point of the polymer used for the sheath component of the binder fiber is more preferably 130 ° C. or lower. By suppressing the shrinkage of the wet nonwoven fabric during the heat treatment, the reduction width of the average pore size due to the shrinkage of the wet nonwoven fabric is suppressed, which leads to a reduction in pressure loss when used as a filter filter medium. The melting point of the core component of the binder fiber is higher than the melting point of the sheath component, and the melting point difference is 20 ° C. or higher, so that the sheath component on the surface of the binder fiber is sufficiently melted and the orientation of the core component is lowered. Since the width is suppressed, it is possible to obtain sufficient thermal adhesion and high rigidity.

Microfibers may be appropriately mixed in the wet non-woven fabric of the present invention. The microfiber refers to a fiber having a fiber diameter in the range of 1.0 to 5.0 μm. By blending the microfiber, the water retention is improved in the papermaking process, and the papermaking property at the time of making white water is improved. In addition, as an effect on the sheet, the pore size is reduced and the finely dispersed ultrafine fibers may fall off from the sheet when the pores are coarse, but when used as a filter medium, it collects fine dust. It suppresses the falling off of the ultrafine fibers that carry it, and is fixed in the pores. Therefore, the dust collecting ability by the ultrafine fibers in the fiber sheet is exhibited, and the high collecting efficiency as a filter filter medium is exhibited. On the other hand, when the blending amount of the microfiber is increased, the pressure loss of the wet nonwoven fabric tends to increase. Therefore, from the viewpoint of suppressing the increase in the pressure loss of the wet nonwoven fabric, the blending ratio of the microfiber is 30% by weight or less. Is preferable. 20% by weight or less is more preferable from the viewpoint of lower pressure loss so that it can withstand use at a high air volume. When trying to obtain the papermaking property improving effect, the lower limit of the microfiber blending ratio is 5% by weight or less.

The wet non-woven fabric of the present invention may be appropriately blended with thick fiber as an aggregate. In particular, when applied as an air filter filter medium, it is preferable to blend thick fiber from the viewpoint of increasing the sheet strength or making the wet non-woven fabric a bulky structure to reduce low pressure loss. In particular, from the viewpoint of providing bulkiness and cushioning property, a thick fiber having crimped by a crimper or the like may be blended. However, if too thick fibers are blended, the papermaking property will deteriorate, so from the viewpoint of avoiding an extreme increase in pore size and poor formation, stabilizing the filter performance, improving the sheet strength and reducing the low pressure loss, the fineness The fiber diameter of the fiber is preferably 15.0 to 100.0 μm.
Further, in the case of performing electret processing, an additive may be added from the viewpoint of further charging the constituent fibers of the wet nonwoven fabric, and at least one hindered amine-based additive or triazine-based additive is blended as the additive. Is preferable.

Examples of the hindered amine compound include poly [(6- (1,1,3,3-tetramethylbutyl) imino-1,3,5-triazine-2,4-diyl) ((2,2,6,6-). Tetramethyl-4-piperidyl) imino) Hexamethylene ((2,2,6,6-tetramethyl-4-piperidyl) imino)] (BASF, Kimasorb® 944LD), dimethyl-1- (succinate) 2-Hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate (BASF, tinubin® 622LD), 2- (3,5-di-t-butyl-4) -Hydroxybenzyl) -2-n-Butylmalonate bis (1,2,2,6,6-pentamethyl-4-piperidyl) (BASF, Tinubin® 144), dibutylamine 1,3,5 -Triazine N, N'-bis (2,2,6,6-tetramethyl-4-piperidyl-1,6-hexamethylenediamine N- (2,2,6,6-tetramethyl-4-piperidyl) ) Butylamine polycondensate (BASF, Kimasorb® 2020 FDL) and the like, but are not limited thereto.

Examples of the triazine-based additive include the above-mentioned poly [(6- (1,1,3,3-tetramethylbutyl) imino-1,3,5-triazine-2,4-diyl) ((2,2). , 6,6-Tetramethyl-4-piperidyl) imino) Hexamethylene ((2,2,6,6-tetramethyl-4-piperidyl) imino)] (BASF, Kimasorb® 944LD), 2- (4,6-diphenyl-1,3,5-triazine-2-yl) -5-((hexyl) oxy) -phenol (manufactured by BASF, tinubin (registered trademark) 1577FF) and the like can be mentioned, but are limited thereto. Not done. Among these, hindered amine compounds are particularly preferable.
The content of the hindered amine compound or the triazine compound is not particularly limited, but is not limited.
It is preferably in the range of 0.5 to 5.0% by weight, more preferably in the range of 0.7 to 3.0% by weight, based on the weight of each staple fiber constituting the wet nonwoven fabric of the present invention. .. When the content is 0.5% by weight or more, a high level of electret performance can be obtained, which is preferable. On the other hand, when the content is 5.0% by weight or less, there is no deterioration in the silk-reeling property and the influence on the cost is small, which is preferable.

The wet non-woven fabric of the present invention is preferably electretized. By electret processing, the fiber sheet is charged, dust can be collected by electrostatic force, and high collection efficiency exceeding the mechanical collection efficiency of the sheet can be exhibited. The method of electret processing on the sheet is not particularly limited, but is limited to a triboelectric charging method using mechanical friction, a corona charging method using corona discharge using electrodes, and vacuuming after immersing the fiber sheet in pure water. A hydrocharging method or the like in which charging is performed by applying ultrasonic treatment is preferably used.

In the production of the wet nonwoven fabric of the present invention, the method of blending the fibers is not particularly limited, but it is preferable to use the split type composite fiber for the wet papermaking. By configuring the cross-sectional structure of the split type composite fiber as shown in FIG. 3, for example, it is possible to generate the short fibers A, the short fibers B and the short fibers C constituting the nonwoven fabric of the present invention by the split treatment. be. For the division treatment of the split type composite fiber, it is possible to utilize a physical impact by stirring with white water, a heat treatment during sheet drying, and a physical impact by a water jet or the like. Of these, a method of splitting the split type composite fiber by applying heat treatment or physical impact after wet papermaking is preferable. In the wet papermaking method, when ultrafine fibers having a fiber diameter of nano-order are used, water retention is high, so that it is difficult for water to escape when forming the sheet, and if there is a rough portion on the sheet, this portion. There is a problem that coarse holes (pinholes), which are a drawback when used as a filter medium, are generated because water is concentrated and drained from the fiber. When the split type composite fiber is wet-made, the papermaking property is as good as that of the general-purpose synthetic fiber, and by subjecting the composite fiber to the split treatment after forming the sheet, nanometer-order ultrafine fibers are generated in the sheet. However, it is possible to produce the desired wet non-woven fabric.

Further, if this split type composite fiber is used, the sea removal step by alkali, which is necessary when the sea island type composite fiber is used to generate ultrafine fibers, is unnecessary, and the step can be simplified. In particular, when a wet non-woven fabric containing ultrafine fibers is used as an electret filter medium, surface cleanliness is important during the charging process. In wet papermaking using sea-island type composite fibers, the residue of the polymer decomposed in the sea-removing process cannot be sufficiently removed, which may adversely affect the charging process. desirable.

The method for producing the wet nonwoven fabric of the present invention is not particularly limited, but an example of the production method will be described below. In the cross section shown in FIG. 2, polyester is arranged in the region A (5) having a slit, and the hindered amine or triazine-based compound that promotes charging is placed in the regions B (6) and C (7), which are the portions to be separated and divided later. Short fibers such as split-type composite fibers with the added polyolefin polymer and heat-sealing core-sheath composite fibers (binder fibers) whose sheath component is a low-melting-off polymer are put into water and stirred uniformly with a disintegrator. Disperse to make white water. In this charging step, the dispersibility can be adjusted by adjusting the amount of fiber charged, the amount of white water, the stirring time, etc., and it is preferable that the short fibers are uniformly dispersed in white water as much as possible. Further, a dispersant may be added to improve the dispersibility in water, but the amount of the dispersant added should be minimized so as not to affect the processability when the wet non-woven fabric is post-processed. It is preferable to keep it. Further, as the short fibers constituting the white water, microfibers having a fiber diameter of 1.0 to 5.0 μm may be further mixed. In the papermaking process described later, in general, white water prepared with fibers having low water retention is quickly drained when it is formed into a sheet, and a portion where the fibers are aggregated is formed, resulting in a sheet with many unevenness. Since the water retention is improved by mixing the microfibers, the fibers in the white water can be kept in a well-dispersed state at the time of forming into a sheet, and a highly uniform wet non-woven fabric can be obtained.

The white water prepared above is diluted to a certain concentration and adjusted, and dehydrated on an inclined wire, a circular net, or the like to form a sheet. Examples of the device used for paper making include a circular net paper machine, a long net paper machine, an inclined short net paper machine, and a paper machine combining these. In the papermaking process, a uniform sheet can be produced by adjusting the papermaking speed, the amount of fibers, and the amount of white water. Further, from the viewpoint of sheet formability, the fiber length of the constituent fibers is preferably 30.0 mm or less. Within this range, a wet non-woven fabric having practical uniformity as a filter filter medium can be formed. If the fiber length exceeds 30.0 mm, the fibers are strongly entangled with each other during the preparation of white water and form fiber lumps, which tends to make it difficult to obtain a uniform sheet.

The sheet formed by wet papermaking is then passed through a drying step to remove moisture. As the drying method, a method using hot air ventilation (air through) or a method of contacting with a thermal calendar roll is preferable from the viewpoint that the sheet can be dried and the binder fibers can be thermally bonded at the same time.
When used as a filter medium for an electret filter, it is preferable to electret-process the wet non-woven fabric by the above-mentioned method. If a charged substance is present in the fiber sheet, the charging of the ultrafine fibers by the electret processing is hindered, and sufficient electrostatic force for collecting dust cannot be obtained.

The basis weight and thickness of the wet nonwoven fabric can be changed depending on the amount of white water supplied in the wet papermaking process and the papermaking speed. The basis weight of the wet nonwoven fabric of the present invention is not particularly limited, but is preferably 10 to 150 g / m ² . By setting the basis weight to 10 g / m ² or more, a uniform fiber sheet with a small difference in roughness can be obtained. On the other hand, when the weight is 150 g / m ² or less, the thickness of the fiber sheet can be suppressed, and post-processing such as pleating as a filter medium becomes possible. Further, from the viewpoint of achieving both sufficient collection efficiency and low pressure loss as a filter medium, the basis weight of the sheet is more preferably in the range of 15 to 100 g / m ² . By setting the basis weight to 15 g / m ² or more, sufficient dust collection efficiency can be ensured as a filter filter medium, while by setting the basis weight to 100 g / m ² or less, pressure loss when used as a filter filter medium can be suppressed. Is possible.

The thickness of the wet nonwoven fabric of the present invention is not particularly limited, but is preferably 0.10 to 2.50 mm. By setting the thickness to 0.10 mm or more, it is possible to obtain the strength for post-processing such as pleating and dipping the filter medium with a functional agent or the like. Further, by setting the thickness to 2.50 mm or less, pleating can be performed, and the portion where the filter media come into contact with each other can be reduced depending on the thickness of the filter media when the filter is used, and the filtration area can be secured, so that an increase in pressure loss can be suppressed. For the purpose of improving the amount of dust retained, the filter medium of the present invention itself may have a structure having a density gradient in the thickness direction so that the upstream side is coarsely dense and the downstream side is dense. A coarse non-woven fabric may be formed by laminating a coarse non-woven fabric on the upstream side of the wet non-woven fabric and a dense non-woven fabric on the downstream side.

In particular, filter media are often required to have additional functions in addition to dust collection, and there is a strong demand for functions such as water repellency, oil repellency, antibacterial, antiviral, and deodorant. From this point of view, various functional agents may be added to the wet nonwoven fabric of the present invention in order to impart functions. Examples of the functional agent 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. Etc., but are not limited to these. Further, the method of adding various additives is not particularly limited, and it is also possible to use fibers in which various additives are kneaded, or to spray a wet non-woven fabric or impregnate a solution of a functional agent to add the additives. be.

The wet non-woven fabric of the present invention achieves both high collection efficiency and low pressure loss when used as an electretized filter medium, and is used for air purifiers, air conditioners, building air conditioners, industrial clean rooms, and passenger compartments of automobiles and trains. It can be suitably used as a filter medium for use, a surgical mask, a face mask and a dustproof mask.

Hereinafter, the wet nonwoven fabric of the present invention will be specifically described with reference to examples.
The following evaluations were made for Examples and Comparative Examples.

A. Fiber diameter In an image of the cross section of a fiber taken with an electron microscope SU-1510 manufactured by Hitachi High-Technologies Corporation, the circumscribed circle diameter of the fiber cross section is measured for any 100 fibers, and the second digit after the decimal point of the average is rounded off. The value obtained up to the first digit after the decimal point was taken as the fiber diameter.

B. Degree of Deformity In an image of the cross section of a fiber taken with an electron microscope SU-1510 manufactured by Hitachi High-Technologies Corporation, the circumscribed circle diameter and inscribed circle diameter of the fiber cross section were measured for 20 arbitrary constituent fibers, and the ratio was determined. The calculated value was rounded off to the first decimal place of the average, and the value obtained up to the first decimal place was taken as the degree of deformation of the constituent fibers.

C. Average pore size and pore size distribution frequency The average pore size was calculated by the bubble point method (based on ASTMF-316-86) using the porous material automatic pore measurement system Perm-Porometer (manufactured by PMI). The measurement sample diameter was 25 mm, and the pore size distribution was measured using Galwick (surface tension: 16 mN / m) as a measuring solution having a known surface tension. The MEAN FLOW PORE DIAMETER automatically calculated by this measuring instrument was used as the average pore size value. In addition, for the measurement, an arbitrary 5 points were sampled per sample, and the value obtained by rounding off the 2nd decimal place of the average to the 1st decimal place was used. For the pore size distribution frequency, the value obtained by automatic calculation was converted into a percentage and displayed as a percentage, and the value obtained by rounding off the second decimal place to the first decimal place was used.

D. Weight of fiber sheet cut into 250 mm x 250 mm square is weighed, and the value converted to weight per unit area (1 m ² ) is rounded off to the first decimal place to obtain an integer value. bottom.

E. Thickness The thickness of the wet nonwoven fabric was measured using a dial thickness gauge (TECLOCK SM-114 transducer shape 10 mmφ, mesh size 0.01 mm, measuring force 2.5 N or less). The measurement was performed at any 5 points per sample, and the value obtained by rounding off the 3rd digit after the decimal point to the 2nd digit after the decimal point was taken as the thickness of the wet nonwoven fabric.

F. Collection efficiency The prepared wet non-woven fabric is set in a holder with an effective frontage area of 0.1 m ² and air is passed through in the vertical direction at a surface wind speed of 6.5 min, and the particle size upstream and downstream of the filter is 0.3 to 0.5 μm. The number of air dust was measured with a particle counter (manufactured by RION, model: KC-01D), and the collection efficiency was calculated from the following formula.
Collection efficiency (%) = 1- (number of downstream particles / number of upstream particles) x 100
The measurement was carried out by arbitrarily sampling three places from one sample, and the first digit after the decimal point of the average was rounded off to obtain an integer value, which was used as the collection efficiency. The collection efficiency was measured at the time of charging by electret processing (corona charging method) and after immersing the charged fiber sheet in isopropyl alcohol for 2 minutes and then drying and removing static electricity.

G. Pressure loss The prepared fiber sheet was set in a holder with an effective frontage area of 0.1 m ² , air was passed in the vertical direction at a surface wind speed of 6.5 m / min, and the pressure difference between the upstream and downstream of the filter was measured with a differential pressure gauge. The measurement was carried out by sampling any three points from one sample, and the first digit after the decimal point of the average was rounded off to obtain an integer value, which was defined as the pressure loss.

H. Toner particle adhesion test (confirmation test for electret formation)
A mixture of positively charged red toner particles and negatively charged blue toner particles was sprinkled on the electret-processed fiber sheet. After shaking off the excess toner particles that had accumulated regardless of the electrostatic force, the fiber sheet was observed with a digital microscope (VHX-2000, manufactured by KEYENCE CORPORATION).
It is judged that the red and blue toner particles are separated and adhered to each other, and it is judged that the red and blue toner particles are adhered while being mixed and appear purple, and the toner particles are dropped and adhered. Those that did not exist were judged not to be electrified.

Example 1
Polybutylene terephthalate (PBT) resin Trecon 1200S (manufactured by Toray Industries, Inc.) is the core of polypropylene (PP) resin S135 (manufactured by Prime Polymer) plus 2 wt% of Kimasorb (registered trademark) 944LD (manufactured by BASF). As a component, (peeling split type composite fiber having a cross section having a shape as shown in the figure (island component diameter: 0.7 μm, composite ratio (weight ratio): split component / core component = 30/70) was produced by melt spinning. This peel-off split type composite fiber is 80% by weight, and as a binder fiber, a heat-sealing core-sheath composite fiber (core component: PET, sheath component: terephthalic acid 60 mol%, isophthalic acid 40 mol%, Short fibers (5 mm length) of polyester (polybutylene terebra 1) having a melting point of 110 ° C., which is copolymerized at a ratio of 85 mol% of ethylene glycol and 15 mol% of diethylene glycol, are uniformly mixed and dispersed with water by a disintegrator so as to be 20% by weight. Then, white water was prepared. Then, paper was made using a circular net paper making machine (manufactured by Kawanoe Zoki Co., Ltd.), contacted with a thermal calendar roll at 110 ° C., and dried and heat-treated to obtain a wet non-woven fabric. In the wet non-woven fabric, the separation-split type composite fiber is being divided, and short fiber A (fiber diameter: 16.0 μm) having 29 slits on the outer periphery of the fiber cross section is 56% by weight, and the fiber diameter is 0.5 μm. Contains 12% by weight of short fiber B with a degree of deformation of 1.5, 12% by weight of short fiber C with a fiber diameter of 5.0 μm, and 20% by weight of heat-adhesive core-sheath composite fiber. The wet non-woven fabric was obtained. The fiber diameter of the fiber C was 10 times that of the short fiber B. The fibers constituting the non-woven fabric were heat-bonded by a heat-sealing binder fiber. Met.

The obtained wet non-woven fabric had a basis weight of 45 g / m ² and a thickness of 0.28 mm. The average pore size calculated by the bubble point method was 13.2 μm, and the distribution frequency with a pore size of 15.0 μm or more was 20.3%. The ultrafine fibers were dispersed in the wet non-woven fabric and distributed in a mesh pattern, and the dispersed state was excellent. As a result of measuring the atmospheric dust collection efficiency and pressure loss with a particle size of 0.3 to 0.5 μm in a state where this wet non-woven fabric is charged by the corona charging method, the collection efficiency is excellent at 96% and the pressure loss is 50 Pa. It was excellent in low pressure loss. Further, the collection efficiency in the state where the wet non-woven fabric was immersed in isopropyl alcohol and statically removed was 45%, and the collection efficiency after static elimination was excellent. As a result of the toner particle adhesion test after charging, it was determined that both the red and blue particles were separated and adhered to the wet nonwoven fabric and were electretized.

Examples 2-4
In the fiber cross section of the peel-off split type composite fiber, the number of split points is different, and the number of slits of the short fibers A generated in the wet nonwoven fabric is 17 (Example 2) and 9 (Example 3). , Except for the change to 68 locations (Example 4), the procedure was carried out according to Example 1.

The wet nonwoven fabric of Example 2 had a thickness of 0.24 mm, an average pore size of 12.7 μm, and a distribution frequency of a pore size of 15.0 μm or more was 17.6%. The collection efficiency during charging was 93%, and the collection efficiency after static elimination was 52%, which were excellent. The pressure loss was 53 Pa, which was good for low pressure loss.

The wet nonwoven fabric of Example 3 had a thickness of 0.22 mm, an average pore size of 11.8 μm, and a distribution frequency of 15.0 μm or more with a pore size of 12.4%. The collection efficiency at the time of charging was 95%, and the collection efficiency after static elimination was 56%, which were excellent in the collection efficiency. The pressure loss was 71 Pa, which was a sufficient low pressure loss.

The wet nonwoven fabric of Example 4 had a thickness of 0.30 mm, an average pore size of 17.5 μm, and a distribution frequency of a pore size of 15.0 μm or more was 25.2%. The collection efficiency during charging was 81%, the collection efficiency after static elimination was 47%, and the pressure loss was 39 Pa, which were excellent in collection efficiency and low pressure loss.
As a result of the toner particle adhesion test after charging, it was determined that all of the wet nonwoven fabrics of Examples 2 to 4 were electretized.

Comparative Example 1
Example 1 except that the number of slits of the short fiber A generated in the wet nonwoven fabric was changed to 7 by using the fiber cross section of the peeling split type composite fiber having 7 split points. It was carried out according to.

The obtained wet nonwoven fabric had a thickness of 0.18 mm, an average pore size of 10.3 μm, and a distribution frequency of a pore size of 15.0 μm or more was 9.7%. The collection efficiency during charging was 96%, and the collection efficiency after static elimination was 58%, which was excellent, but the pressure loss was as high as 93 Pa, and the low pressure loss was insufficient.

Examples 5-10
The fiber diameters of the short fibers A generated in the wet non-woven fabric are 5.0 μm (Example 5) and 7.0 μm (Example 6) using fibers having various core portions of the peel-off split type composite fibers. , 9.0 μm (Example 7), 35.0 μm (Example 8), 40.0 μm (Example 9), and 50.0 μm (Example 10), except that the procedure was carried out according to Example 1.

The wet nonwoven fabric of Example 5 had a thickness of 0.13 mm, an average pore size of 9.6 μm, and a distribution frequency of a pore size of 15.0 μm or more was 10.2%. The collection efficiency at the time of charging was 92%, and the collection efficiency after static elimination was 53%, which were excellent in the collection efficiency. The pressure loss was 88 Pa, which was a sufficient low pressure loss.

The wet nonwoven fabric of Example 6 had a thickness of 0.14 mm, an average pore size of 11.2 μm, and a distribution frequency of a pore size of 15.0 μm or more was 15.1%. The collection efficiency at the time of charging was 92%, and the collection efficiency after static elimination was 51%, which were excellent in the collection efficiency. The pressure loss was 69 Pa, which was good for low pressure loss.

The wet nonwoven fabric of Example 7 had a thickness of 0.17 mm, an average pore size of 12.8 μm, and a distribution frequency of a pore size of 15.0 μm or more was 17.7%. The collection efficiency during charging was 93%, the collection efficiency after static elimination was 51%, and the pressure loss was 50 Pa, which were excellent in collection efficiency and low pressure loss.

The wet nonwoven fabric of Example 8 had a thickness of 0.73 mm, an average pore size of 23.9 μm, and a distribution frequency of a pore size of 15.0 μm or more was 66.7%. The collection efficiency during charging was 80%, the collection efficiency after static elimination was 41%, and the pressure loss was 25 Pa, which were excellent in collection efficiency and low pressure loss.

The wet nonwoven fabric of Example 9 had a thickness of 0.92 mm, an average pore size of 28.6 μm, and a distribution frequency of a pore size of 15.0 μm or more was 77.2%. The collection efficiency at the time of charging was 61%, and the collection efficiency after static elimination was 30%, and the collection efficiency was good. The pressure loss was 20 Pa, which was excellent in low pressure loss.

The wet nonwoven fabric of Example 10 had a thickness of 1.06 mm, an average pore size of 32.3 μm, and a distribution frequency of a pore size of 15.0 μm or more was 93.5%. The collection efficiency during charging was 50%, and the collection efficiency after static elimination was 22%, showing sufficient collection efficiency. The pressure loss was 18 Pa, which was excellent in low pressure loss.

As a result of the toner particle adhesion test after charging, it was determined that all of the wet nonwoven fabrics of Examples 5 to 10 were electretized.

Comparative Examples 2 and 3
The fiber diameters of the staple fibers A generated in the wet non-woven fabric are 4.0 μm (Comparative Example 2) and 60.0 μm (Comparative Example 3) by using different fiber diameters of the core portion of the peeling split type composite fiber. It was carried out according to Example 1 except that it was changed to.

The wet nonwoven fabric of Comparative Example 2 had a thickness of 0.12 mm, an average pore size of 8.4 μm, and a distribution frequency of a pore size of 15.0 μm or more was 3.8%. The collection efficiency during charging was 94% and the collection efficiency after static elimination was 56%, which were excellent, but the pressure loss was as high as 104 Pa, and the low pressure loss was insufficient.

The wet nonwoven fabric of Comparative Example 3 had a thickness of 1.18 mm, an average pore size of 41.3 μm, and a distribution frequency of a pore size of 15.0 μm or more was 98.7%. Although the pressure loss was 12 Pa, which was excellent in low pressure loss, the collection efficiency during charging was 38%, and the collection efficiency after static elimination was 9%, which was insufficient.

Examples 11-16
The fiber diameters of the short fibers B generated in the wet non-woven fabric are 0.1 μm (Example 11) and 0.2 μm (Example 12) using fibers having variously different fiber diameters at the split portions of the peelable split type composite fiber. , 0.3 μm (Example 13), 1.5 μm (Example 14), 2.0 μm (Example 15), 3.0 μm (Example 16), except that the procedure was carried out according to Example 1.

The wet nonwoven fabric of Example 11 had a thickness of 0.25 mm, an average pore size of 8.8 μm, and a distribution frequency of a pore size of 15.0 μm or more was 10.1%. The collection efficiency at the time of charging was 98%, and the collection efficiency after static elimination was 63%, which were excellent in the collection efficiency. The pressure loss was 82 Pa, which was a sufficient low pressure loss.

The wet nonwoven fabric of Example 12 had a thickness of 0.25 mm, an average pore size of 11.3 μm, and a distribution frequency of a pore size of 15.0 μm or more was 12.2%. The collection efficiency at the time of charging was 97%, and the collection efficiency after static elimination was 58%, which were excellent in the collection efficiency. The pressure loss was 68 Pa, which was good for low pressure loss.

The wet nonwoven fabric of Example 13 had a thickness of 0.26 mm and an average pore size of 12.5 μm, and the distribution frequency of the pore size of 15.0 μm or more was 17.9%. The collection efficiency during charging was 94%, the collection efficiency after static elimination was 52%, and the pressure loss was 50 Pa, which were excellent in collection efficiency and low pressure loss.

The wet nonwoven fabric of Example 14 had a thickness of 0.28 mm, an average pore size of 24.3 μm, and a distribution frequency of a pore size of 15.0 μm or more was 64.5%. The collection efficiency during charging was 81%, the collection efficiency after static elimination was 40%, and the pressure loss was 26 Pa, which were excellent in collection efficiency and low pressure loss.

The wet nonwoven fabric of Example 15 had a thickness of 0.28 mm, an average pore size of 27.5 μm, and a distribution frequency of a pore size of 15.0 μm or more was 78.4%. The collection efficiency at the time of charging was 61%, and the collection efficiency after static elimination was 32%, and the collection efficiency was good. The pressure loss was 19 Pa, which was excellent in low pressure loss.

The wet nonwoven fabric of Example 16 had a thickness of 0.28 mm, an average pore size of 34.4 μm, and a distribution frequency of a pore size of 15.0 μm or more was 93.8%. The collection efficiency during charging was 53%, and the collection efficiency after static elimination was 21%, showing sufficient collection efficiency. The pressure loss was 15 Pa, which was excellent in low pressure loss.

As a result of the toner particle adhesion test after charging, it was determined that all of the wet nonwoven fabrics of Examples 11 to 16 were electretized.

Comparative Example 4
It was carried out according to Example 1 except that the fiber diameter of the split portion of the peeling split type composite fiber was 4.0 μm and the fiber diameter of the staple fiber B generated in the wet nonwoven fabric was changed to 4.0 μm. bottom.
The obtained wet nonwoven fabric had a thickness of 0.28 mm, an average pore size of 39.6 μm, and a distribution frequency of a pore size of 15.0 μm or more was 98.0%. Although the pressure loss was 13 Pa, which was excellent in low pressure loss, the collection efficiency during charging was 44%, and the collection efficiency after static elimination was 16%, which was insufficient.

Examples 17 and 18
The degree of deformation of the staple fibers B generated in the wet non-woven fabric was set to 1.1 (Example 17) and 5.0 (Example 18) by using different shapes of the divided portions in the peeling-divided composite fiber. Except for the changes, it was carried out according to Example 1.

The wet nonwoven fabric of Example 17 had a thickness of 0.27 mm, an average pore size of 19.1 μm, and a distribution frequency of a pore size of 15.0 μm or more was 22.7%. The collection efficiency during charging was 94%, the collection efficiency after static elimination was 42%, and the pressure loss was 46 Pa, which were excellent in collection efficiency and low pressure loss.

The wet nonwoven fabric of Example 18 had a thickness of 0.28 mm, an average pore size of 12.2 μm, and a distribution frequency of a pore size of 15.0 μm or more was 20.6%. The collection efficiency during charging was 96%, the collection efficiency after static elimination was 56%, and the pressure loss was 44 Pa, which were excellent in collection efficiency and low pressure loss.

As a result of the toner particle adhesion test after charging, it was determined that the wet nonwoven fabrics of Examples 17 and 18 were electretized.

Examples 19 and 20
The fiber diameters of the short fibers C generated in the wet non-woven fabric are 1.0 μm (Example 19) and 1.5 μm (Example 20) by using different fiber diameters of the split portions of the peeling split type composite fiber. It was carried out according to Example 1 except that it was changed to.

In the wet non-woven fabric of Example 19, the fiber diameter of the short fiber C is twice as large as that of the short fiber B, the thickness is 0.22 mm, the average pore size is 10.8 μm, and the pore size is 15.0 μm or more. The distribution frequency was 11.0%. The collection efficiency at the time of charging was 93%, and the collection efficiency after static elimination was 56%, which were excellent in the collection efficiency. The pressure loss was 82 Pa, which was a sufficient low pressure loss.

In the wet non-woven fabric of Example 20, the fiber diameter of the short fiber C is three times as large as that of the short fiber B, the thickness is 0.23 mm, the average pore size is 12.5 μm, and the pore size is 15.0 μm or more. The distribution frequency was 14.3%. The collection efficiency at the time of charging was 91%, and the collection efficiency after static elimination was 52%, which were excellent in the collection efficiency. The pressure loss was 67 Pa, which was good for low pressure loss.
As a result of the toner particle adhesion test after charging, it was determined that the wet nonwoven fabrics of Examples 19 and 20 were electretized.

Comparative Example 5
Except for the fact that the fiber diameter of the short fiber C generated in the wet non-woven fabric was changed to 0.8 μm by using a split portion of the peel-off split type composite fiber having a fiber diameter of 0.8 μm at one location. , It was carried out according to Example 1.

The obtained wet non-woven fabric has a fiber diameter of 1.5 times that of the short fiber B, a thickness of 0.18 mm, an average pore size of 16.3 μm, and a pore size of 15.0 μm or more. The distribution frequency was 7.8%. The collection efficiency during charging was 88% and the collection efficiency after static elimination was 48%, which were excellent, but the pressure loss was as high as 98 Pa, and the low pressure loss was insufficient.

Examples 21 and 22
The degree of deformation of the staple fibers C generated in the wet nonwoven fabric was 1.2 (Example 21) and 8.0 (flat) by using one of the split portions of the peelable split type composite fiber having various different shapes. It was carried out according to Example 1 except that the shape was changed to Example 22).

The wet nonwoven fabric of Example 21 had a thickness of 0.27 mm, an average pore size of 15.9 μm, and a distribution frequency of a pore size of 15.0 μm or more was 10.2%. The collection efficiency at the time of charging was 90%, and the collection efficiency after static elimination was 46%, which were excellent in the collection efficiency. The pressure loss was 81 Pa, which was sufficient for low pressure loss.

The wet nonwoven fabric of Example 22 had a thickness of 0.28 mm, an average pore size of 13.0 μm, and a distribution frequency of a pore size of 15.0 μm or more was 23.1%. The collection efficiency during charging was 96%, the collection efficiency after static elimination was 50%, and the pressure loss was 36 Pa, which were excellent in collection efficiency and low pressure loss.
As a result of the toner particle adhesion test after charging, it was determined that all of the wet nonwoven fabrics of Examples 21 to 22 were electretized.

Comparative Example 6
It was carried out except that the deformability of one of the split portions of the peelable split type composite fiber was 1.0 and the deformity of the staple fiber C generated in the wet nonwoven fabric was changed to 1.0. It was carried out according to Example 1.

The obtained wet nonwoven fabric had a thickness of 0.27 mm, an average pore size of 15.2 μm, and a distribution frequency of a pore size of 15.0 μm or more was 7.3%. The collection efficiency during charging was 90% and the collection efficiency after static elimination was 46%, which were excellent, but the pressure loss was as high as 93 Pa, and the low pressure loss was insufficient.

Example 23
A peeling split type composite fiber having a composite ratio (weight ratio) of split component / core component = 15/85 was used, and the split type composite fiber was changed to 95% by weight and the binder fiber was changed to 5% by weight at the time of papermaking. Other than that, it was carried out according to Example 1.

The obtained wet nonwoven fabric had a thickness of 0.35 mm, an average pore size of 31.4 μm, and a distribution frequency of a pore size of 15.0 μm or more was 94.1%. The collection efficiency during charging was 52%, and the collection efficiency after static elimination was 21%, showing sufficient collection efficiency. The pressure loss was 15 Pa, which was excellent in low pressure loss.

Example 24
The composite ratio (weight ratio) is set to split component / core component = 20/80, and the weight of the portion corresponding to the short fiber B after peeling and splitting is 2.2 times the weight of the portion corresponding to the staple fiber C after peeling and splitting. It was carried out according to Example 1 except that the stripping split type composite fiber was used.

The obtained wet nonwoven fabric had a thickness of 0.29 mm, an average pore size of 13.6 μm, and a distribution frequency of a pore size of 15.0 μm or more was 20.4%. The collection efficiency during charging was 90%, the collection efficiency after static elimination was 46%, and the pressure loss was 40 Pa, which were excellent in collection efficiency and low pressure loss.

Example 25
The composite ratio (weight ratio) is set to split component / core component = 35/65, and the weight of the portion corresponding to the staple fiber B after peeling and splitting is 4.6 times the weight of the portion corresponding to the staple fiber C after peeling and splitting. It was carried out according to Example 1 except that the stripping split type composite fiber was used.
The obtained wet nonwoven fabric had a thickness of 0.20 mm, an average pore size of 12.0 μm, and a distribution frequency of a pore size of 15.0 μm or more was 10.4%. The collection efficiency at the time of charging was 98%, and the collection efficiency after static elimination was 60%, which were excellent in the collection efficiency. The pressure loss was 71 Pa, which was a sufficient low pressure loss.

Example 26
The composite ratio (weight ratio) is set to split component / core component = 20/80, and the weight of the portion corresponding to the short fiber C after peeling and splitting is 2.2 times the weight of the portion corresponding to the short fiber B after peeling and splitting. (Except for the use of the stripped split type composite fiber, the procedure was carried out according to Example 1.

The obtained wet nonwoven fabric had a thickness of 0.29 mm, an average pore size of 11.6 μm, and a distribution frequency of a pore size of 15.0 μm or more was 17.2%. The collection efficiency during charging was 75%, the collection efficiency after static elimination was 35%, and the pressure loss was 52 Pa, and the collection efficiency and low pressure loss were good.

Example 27
The composite ratio (weight ratio) is set to split component / core component = 35/65, and the weight of the portion corresponding to the staple fiber C after the peel split is 4.6 times the weight of the portion corresponding to the staple fiber B after the peel split. It was carried out according to Example 1 except that the stripping split type composite fiber was used.
The obtained wet nonwoven fabric had a thickness of 0.23 mm, an average pore size of 10.4 μm, and a distribution frequency of a pore size of 15.0 μm or more was 13.3%. The collection efficiency at the time of charging was 77%, and the collection efficiency after static elimination was 38%, and the collection efficiency was good. The pressure loss was 72 Pa, which was a sufficient low pressure loss.
As a result of the toner particle adhesion test after charging, it was determined that all of the wet nonwoven fabrics of Examples 23 to 27 were electretized.

Examples 28 and 29
The fiber composition at the time of papermaking was changed to 95% by weight of the peeling split type composite fiber and 5% by weight of the binder fiber (Example 28), or 72% by weight of the peeling split type composite fiber and 28% by weight of the binder fiber (Example 29). Other than that, it was carried out according to Example 1.

The wet non-woven fabric of Example 28 had a thickness of 0.32 mm, an average pore size of 12.6 μm, and a distribution frequency of a pore size of 15.0 μm or more was 17.9%. The collection efficiency during charging was 82%, the collection efficiency after static elimination was 42%, and the pressure loss was 38 Pa, which were excellent in collection efficiency and low pressure loss.

The wet nonwoven fabric of Example 29 had a thickness of 0.21 mm, an average pore size of 10.6 μm, and a distribution frequency of a pore size of 15.0 μm or more was 11.3%. The collection efficiency at the time of charging was 93%, and the collection efficiency after static elimination was 52%, which were excellent in the collection efficiency. The pressure loss was 65 Pa, which was good for low pressure loss.

Examples 30 and 31
The procedure was carried out according to Example 1 except that the basis weight of the wet nonwoven fabric was changed to 20 g / m ² (Example 30) and 100 g / m ² (Example 31) by adjusting the amount of white water supplied at the time of papermaking.

The wet nonwoven fabric of Example 30 had a thickness of 0.17 mm, an average pore size of 30.7 μm, and a distribution frequency of a pore size of 15.0 μm or more was 93.3%. The collection efficiency during charging was 58%, and the collection efficiency after static elimination was 26%, showing sufficient collection efficiency. The pressure loss was 18 Pa, which was excellent in low pressure loss.

The wet nonwoven fabric of Example 31 had a thickness of 0.46 mm, an average pore size of 8.2 μm, and a distribution frequency of a pore size of 15.0 μm or more was 10.3%. The collection efficiency at the time of charging was 99%, and the collection efficiency after static elimination was 65%, which were excellent in the collection efficiency. The pressure loss was 87 Pa, which was a sufficient low pressure loss.

Example 32
It was carried out according to Example 1 except that the split component in the peel-split type composite fiber was changed to PBT and the core component was changed to PP.

The obtained wet nonwoven fabric had a thickness of 0.28 mm, an average pore size of 13.1 μm, and a distribution frequency of a pore size of 15.0 μm or more was 20.5%. The collection efficiency during charging was 96%, the collection efficiency after static elimination was 50%, and the pressure loss was 45 Pa, which were excellent in collection efficiency and low pressure loss.

Example 33
A peeling split type composite fiber having a core component of polyethylene (PE) resin ULT-ZEX20100J (manufactured by Prime Polymer Co., Ltd.) was prepared, and the process was carried out according to Example 1 except that papermaking was performed.
The obtained wet nonwoven fabric had a thickness of 0.28 mm, an average pore size of 13.2 μm, and a distribution frequency of a pore size of 15.0 μm or more was 21.3%. The collection efficiency during charging was 99%, the collection efficiency after static elimination was 51%, and the pressure loss was 43 Pa, which were excellent in collection efficiency and low pressure loss.
As a result of the toner particle adhesion test after charging, it was determined that all of the wet nonwoven fabrics of Examples 28 to 33 were electretized.

The wet non-woven fabric of the present invention provides an electretized filter medium that achieves both high collection efficiency and low pressure loss over the long term, and is used for air purifiers, air conditioners, building air conditioners, etc. used in houses, hospitals, offices, etc. It is useful as a filter filter medium for industrial clean rooms and for passenger compartments of automobiles and trains, surgical masks, face masks and dustproof masks.

1 Staple A (fiber with slit)
2 Staple B (ultrafine fiber)
3 Staple C (deformed cross-section fiber)
4 Heat-sealed binder fiber 5 Core portion in cross section of peeling split type composite fiber (corresponding to short fiber A after peeling split)
6 Split portion in the cross section of the peel-off split type composite fiber (corresponding to the short fiber B after peel-splitting)
7 Divided portion in the cross section of the peeling split type composite fiber (corresponding to the short fiber C after peeling split)
8 Circumscribed circle in cross section of deformed cross section fiber 9 Cross section of deformed cross section fiber 10 Inscribed circle in cross section of deformed cross section fiber

Claims (7)

A wet non-woven fiber composed of three or more kinds of fibers, having eight or more slits on the surface, a fiber having a fiber diameter of 5.0 to 50.0 μm (short fiber A), and a fiber having a fiber diameter of 3. A wet non-woven fabric containing ultrafine fibers (short fibers B) of 0 μm or less and irregular cross-sectional fibers (short fibers C) having a fiber diameter twice or more that of short fibers B and a degree of deformation of 1.2 or more. The wet non-woven fabric according to claim 1, wherein the ultrafine fibers (staples B) have a degree of deformation of 1.1 or more. The wet non-woven fabric according to claim 1 or 2, wherein the ultrafine fibers (staples B) and the irregular cross-section fibers (staples C) are made of polyolefin. The wet non-woven fabric according to any one of claims 1 to 3, wherein the fiber having a slit (staple fiber A) is made of polyolefin. The wet non-woven fabric according to any one of claims 1 to 4, which is characterized by being electretized. A textile product in which at least a part of the wet non-woven fabric according to any one of claims 1 to 5 constitutes. After wet-making a split-type composite fiber and a binder fiber capable of generating fibers having slits (short fibers A), ultrafine fibers (short fibers B) and irregularly shaped cross-sectional fibers (short fibers C), heat treatment and / or physical impact The method for producing a wet non-woven fabric according to any one of claims 1 to 5, wherein the split-type composite fiber in the non-woven fabric is divided according to the method.

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