JP6427922B2 - Blended nonwoven fabric - Google Patents

Description

  The present invention is mainly suitable for use as a filter, and particularly relates to a mixed fiber nonwoven fabric having a bending resistance necessary for a pleated filter and having a high collection efficiency and a low pressure loss.

  In recent years, air pollution such as PM2.5 and the epidemic of infectious diseases have become a problem, and the need for living in a cleaner air environment has led to demand for filter media such as air purifiers, cabin filters for automobiles, and masks. It is growing. A technique commonly used for these applications is a technique for removing fine dust in the air with a filter medium composed of a nonwoven fabric or the like. These filter media are required to have a high collection efficiency.

  Here, as a method for achieving high collection efficiency, a filter medium using a nonwoven fabric made of fibers having a very thin fiber diameter is disclosed (see Patent Document 1). However, in the above-described filter medium, there is a problem that the pressure loss of the filter medium increases as the collection efficiency of the filtration increases, and that the energy required for air cleaning and filtration increases when the pressure loss increases in this way.

  Therefore, in order to solve the above-described problems, a filter medium using a fiber having a very small fiber diameter and a nonwoven fabric in which a fiber having a fiber diameter larger than that of the fiber having a very small fiber diameter is used is disclosed (Patent Document 2 and Patent). Reference 3).

  In addition, in order to solve the problem that the pleated shape of the filter medium cannot be maintained in the use process even if pleating is performed, the filter medium has a low bending resistance, so that a support layer having a high bending resistance is bonded to the filter medium. (Patent Document 4).

JP 2002-151560 A Special table 2010-511488 gazette Special table 2009-545682 Japanese Patent Laid-Open No. 06-198108

  As described above, the filter media disclosed in Patent Document 2 and Patent Document 3 are very thin fibers having a fiber diameter of about 0.1 to about 10 μm, and fibers having a fiber diameter larger than that of the very thin fibers (fiber diameters). : About 10 μm to about 70 μm), and the pressure loss is lower than that of a filter medium using a non-woven fabric composed only of very thin fibers. However, although the above filter medium has fibers having a large fiber diameter of about 10 μm to about 70 μm, the pleat shape is low in the process of using the filter medium in order to pleat the above filter medium in a single layer. There exists a subject that it cannot hold | maintain, ie, it becomes inferior to pleat workability. Here, in order to give a desired bending resistance to the filter medium in consideration of pleating, it is necessary to increase the basis weight. On the other hand, when the basis weight is increased without changing the thickness of the filter medium, the density of the filter medium increases and the pressure loss increases. On the other hand, even when the thickness of the blended nonwoven fabric is increased and the basis weight is increased, the increased thickness of the blended nonwoven fabric reduces the pleating processability, and the required amount of material increases and the environmental load increases. There is a problem. In addition, when a thick mixed nonwoven fabric is used for a pleated filter, if a mixed fiber nonwoven fabric with a large area is stored in a specific space volume, a sufficient gap between the pleated nonwoven fabric pleats cannot be secured. After all, there is a problem that the pleated filter has a large pressure loss.

  In addition to the above method, as a method for imparting a desired bending resistance to the filter medium in consideration of pleating, as disclosed in Patent Document 4, a means for attaching a support layer having a high bending resistance is also mentioned. However, there is a problem that the thickness of the entire filter medium obtained for bonding the support layer increases, and the pressure loss becomes high for the same reason as described above.

  Then, in view of said subject, this invention makes it a subject to provide the mixed-line nonwoven fabric provided with all of high collection efficiency, low pressure loss, and the outstanding pleat workability in a high level.

As a result of intensive studies, the present inventors have found that a mixed fiber nonwoven fabric capable of solving the above-described problems can be obtained by selecting an appropriate raw material type and an appropriate fiber diameter.
That is, the mixed fiber nonwoven fabric of the present invention has the following configuration.
(1) The thermoplastic resin A is mainly composed of at least a fiber having a fiber diameter of 0.01 to 20 μm and a fiber having a fiber diameter of 70 to 120 μm, and the component constituting the fiber having a fiber diameter of 0.01 to 20 μm. The main component of the component constituting the fiber having a fiber diameter of 70 to 120 μm is thermoplastic resin B, the fiber having a fiber diameter of 0.01 to 20 μm and / or the fiber having a fiber diameter of 70 to 120 μm. Is a charged fiber, the collection efficiency of particles having a particle diameter of 0.3 to 0.5 μm at a surface wind speed of 4.5 m / min is 85% or more, the thickness is 0.3 to 1.0 mm, and the bending resistance is Is a mixed fiber nonwoven fabric of 2.0 mN or more,
(2) The blended nonwoven fabric according to (1), wherein the thermoplastic resin A has a melt flow rate of 300 g / 10 min or more, and the thermoplastic resin B has a melt flow rate of 150 g / 10 min or less,
(3) The blended nonwoven fabric of (1) or (2), wherein the melting point of the thermoplastic resin A is 5 to 40 ° C. lower than the melting point of the thermoplastic resin B,
(4) The nonwoven fabric according to any one of (1) to (3), wherein the thermoplastic resin A is polyolefin.
(5) The mixed fiber nonwoven fabric according to (4), wherein the polyolefin is a polypropylene homopolymer,
(6) The mixed fiber nonwoven fabric according to any one of (1) to (5), wherein the thermoplastic resin B is a propylene-ethylene copolymer,
(7) A pleated filter comprising the mixed fiber nonwoven fabric of any one of (1) to (7),
(8) Any one of (1) to (7), which is a method for producing a mixed fiber nonwoven fabric by a melt blow method, and includes a step of simultaneously discharging the thermoplastic resin A and the thermoplastic resin B from different discharge holes. A method for producing a blended nonwoven fabric.

  ADVANTAGE OF THE INVENTION According to this invention, the mixed fiber nonwoven fabric which suppresses pressure loss low and has the outstanding pleatability which can be pleated by a single layer, showing high collection efficiency is obtained. Since the above mixed fiber nonwoven fabric exhibits high collection efficiency, it has a high fine particle removal performance when used as a filter. Furthermore, according to the mixed fiber nonwoven fabric of the present invention, since the pressure loss is kept low, the filtration device can be operated with smaller energy. In addition, since the mixed fiber nonwoven fabric has excellent bending resistance in a single layer, even if the mixed fiber nonwoven fabric is used in a single layer, it can take a pleated shape as a filter, and the pleated shape is in the process of use. Can also be retained. In addition, it does not require a support layer for imparting bending resistance to take a pleated shape, and does not require a step of laminating a support material, so that the productivity of the filter is extremely good. Can do.

The histogram which shows distribution of the fiber diameter of the fiber discharged only from the hole a of Example 1. FIG. The histogram which shows distribution of the fiber diameter of the fiber discharged only from the hole b of Example 1. FIG. The histogram which shows distribution of the fiber diameter of the fiber discharged only from the hole a of Example 2. FIG. The histogram which shows distribution of the fiber diameter of the fiber discharged only from the hole b of Example 2. FIG. The histogram which shows distribution of the fiber diameter of the fiber discharged only from the hole a of Example 3. FIG. 6 is a histogram showing a distribution of fiber diameters of fibers discharged from only the holes b of Example 3. The histogram which shows distribution of the fiber diameter of the fiber discharged only from the hole a of the comparative example 1. FIG. The histogram which shows distribution of the fiber diameter of the fiber discharged only from the hole b of the comparative example 1. FIG. The histogram which shows distribution of the fiber diameter of the fiber discharged only from the hole a of the comparative example 2. FIG. The histogram which shows distribution of the fiber diameter of the fiber discharged only from the hole b of the comparative example 2. FIG. The histogram which shows distribution of the fiber diameter of the fiber discharged only from the hole a of the comparative example 3. FIG. The histogram which shows distribution of the fiber diameter of the fiber discharged only from the hole b of the comparative example 3. FIG.

  Next, an embodiment of the mixed fiber nonwoven fabric of the present invention will be described.

  The mixed fiber nonwoven fabric of the present invention includes at least a fiber having a fiber diameter of 0.01 to 20 μm and a fiber having a fiber diameter of 70 to 120 μm, and a main component of components constituting the fiber having a fiber diameter of 0.01 to 20 μm. Is thermoplastic resin A, the main component of the component constituting the fiber having a fiber diameter of 70 to 120 μm is thermoplastic resin B, and the fiber diameter is 0.01 to 20 μm and / or the fiber diameter is The fibers having a diameter of 70 to 120 μm are charged fibers, the collection efficiency of particles having a particle diameter of 0.3 to 0.5 μm at a surface wind speed of 4.5 m / min is 85% or more, and the thickness is 0.3 to 1. 0 mm and the bending resistance is 2.0 mN or more. Although the details will be described later, the mixed fiber nonwoven fabric of the present invention has fine fibers of 0.01 to 20 μm and fibers having a fiber diameter of 0.01 to 20 μm and fibers having a fiber diameter of 70 to 120 μm in the mixed fiber nonwoven fabric. In this case, it is possible to obtain a high collection efficiency as described above, and further, due to having a very thick fiber of 70 to 120 μm and a melting point of the thermoplastic resin B, etc. Even though the efficiency is high and the thickness is small, excellent bending resistance can be obtained. Further, the above mixed nonwoven fabric can exhibit excellent pleatability even if it is a single layer without laminating a support layer due to its excellent bending resistance.

  Although it does not specifically limit as a form of the mixed fiber nonwoven fabric of this invention, A melt blown nonwoven fabric, a spun bond nonwoven fabric, a thermal bond nonwoven fabric, a needle punch nonwoven fabric, an airlaid nonwoven fabric, etc. are mentioned. Among these, a melt blown nonwoven fabric is preferable from the viewpoint that the fiber diameter can be reduced and that no oil is present on the surface of the fibers constituting the nonwoven fabric.

  The main component of the component constituting the fiber having a fiber diameter of 0.02 to 20 μm used in the mixed fiber nonwoven fabric of the present invention is thermoplastic resin A. Here, the main component means that the content of the thermoplastic resin A exceeds 50% by mass of the components constituting the fiber having a fiber diameter of 0.01 to 20 μm, preferably 70% by mass. More preferably, it is 90% by mass or more, more preferably 95% by mass or more, and particularly preferably 99% by mass or more.

  Moreover, as thermoplastic resin A used for the mixed fiber nonwoven fabric of this invention, polyolefin, such as polyethylene and a polypropylene, polyester, polyphenylene sulfide, polyamide etc. are mentioned, for example. It is possible to suppress the melting temperature when spinning a fiber having a fiber diameter of 0.01 to 20 μm using the thermoplastic resin A, and it is possible to suppress energy required for spinning and to improve productivity. In view of the above, the thermoplastic resin A is preferably a thermoplastic resin having a melting point of 230 ° C. or lower. Furthermore, from the viewpoint that fibers having a small fiber diameter such as fibers having a fiber diameter of 0.01 to 20 μm used for the mixed fiber nonwoven fabric of the present invention can be easily obtained, polyolefin or polyester is preferable, and polyolefin is more preferable. preferable. Further, when the fiber is subjected to a charging treatment, a polyolefin having a high volume resistivity and a low hygroscopic property is preferred, and a polyolefin having a high charge persistence when made into a fiber is more preferable, and a polypropylene is particularly preferable. In addition, a polypropylene homopolymer is particularly preferable from the viewpoints of excellent charge retention and easy availability.

  The thermoplastic resin A used for the mixed fiber nonwoven fabric of the present invention has a melt flow rate (hereinafter referred to as MFR) of a certain value or more so that a thin fiber having a fiber diameter of 0.01 to 20 μm can be easily spun. Is preferred. Specifically, it is preferable to use those having an MFR of 300 g / 10 min or more, and more preferably 500 g / 10 min or more. By using the thermoplastic resin A having an MFR of 300 g / 10 min or more, it becomes easy to further reduce the fiber diameter of the fiber, and fibers in the target fiber diameter range can be obtained. Moreover, as an upper limit of MFR, it is preferable that it is 2000 g / 10min or less. About the spinnability such that the melt viscosity at the time of spinning can be suppressed excessively by using the thermoplastic resin A having an MFR of 2000 g / 10 min or less, and polymer bulk defects called shots are likely to occur frequently. The occurrence of this problem can be suppressed. In addition, said MFR was measured based on JIS-K-7210, measurement conditions are based on Annex B, and about the resin which is not described, conditions higher than melting | fusing point are 20 degreeC or more according to Annex A. Selected and measured.

  The MFR of the thermoplastic resin A generally varies depending on the molecular weight of the polymer. If the molecular weight is large, the MFR is small, and if the molecular weight is small, the MFR is large. As a method for obtaining the desired MFR thermoplastic resin A, a polymer having a low molecular weight may be directly polymerized, or a polymer having a high molecular weight is polymerized in advance, and a reducing agent is reacted in a subsequent step. May reduce the molecular weight to obtain a desired range. Alternatively, a process may be used in which an unreacted reducing agent is added to a high molecular weight polymer chip and reacted during melt spinning to lower the molecular weight.

  Next, a thermoplastic resin B is the main component of the component constituting the fiber having a fiber diameter of 70 to 120 μm used for the mixed fiber nonwoven fabric of the present invention. Here, the main component means that the content of the thermoplastic resin B exceeds 50% by mass of the components constituting the fiber having a fiber diameter of 70 to 120 μm, preferably 70% by mass or more, More preferably, it is 90 mass% or more, More preferably, it is 95 mass% or more, Most preferably, it is 99 mass% or more.

  Moreover, as the thermoplastic resin B used for the mixed fiber nonwoven fabric of the present invention, for example, homopolymers such as polyethylene, polypropylene, polybutene, and methylpentene, and copolymers obtained by copolymerizing these polymers with different olefin components are used. Can do. In particular, it is preferable to use a copolymer obtained by copolymerizing two or more olefin components. As the copolymer, polymers having various melting points can be obtained by controlling the blending ratio and arrangement of the copolymer components. As a result, it becomes easier to achieve the low pressure loss and high collection efficiency which are the objects of the present invention.

  Also, from the viewpoint of easily obtaining a desirable melting point, among the copolymers, a polypropylene-based copolymer is preferable, and a propylene-ethylene copolymer obtained by copolymerizing a propylene component and an ethylene component is a more preferable embodiment. . The copolymer component may contain other olefin components or components other than olefins within a range not losing the effects of the present invention. Moreover, although a random copolymerization, a block copolymerization, etc. are mentioned as a copolymerization form, A random copolymer is a more preferable aspect. Moreover, the melting temperature at the time of spinning a fiber having a fiber diameter of 70 to 120 μm using the thermoplastic resin B can be suppressed, energy required for spinning can be suppressed, and productivity can be further improved. In view of the above, the thermoplastic resin B is preferably a thermoplastic resin having a melting point of 230 ° C. or lower.

  Moreover, it is preferable that the thermoplastic resin B used by this invention is not an elastomer. In the mixed fiber nonwoven fabric of the present invention, when an elastomer is used, the entire mixed fiber nonwoven fabric is highly stretchable. A highly elastic mixed fiber nonwoven fabric may be reduced in volume when stretched by process tension, and pressure loss may increase.

  Next, it is preferable to use the thermoplastic resin B having an MFR smaller than the MFR of the thermoplastic resin A as the melt flow rate (MFR) of the thermoplastic resin B used for the mixed fiber nonwoven fabric of the present invention. In particular, when spinning from the same die as the thermoplastic resin A which is the main component of the component constituting the fiber having a fiber diameter of 0.01 to 20 μm, the MFR thermoplastic resin B is smaller than the MFR of the thermoplastic resin A. Is preferably used. Specifically, the MFR of the thermoplastic resin B is preferably 150 g / 10 min or less. In particular, when spinning from the same die as the thermoplastic resin A which is the main component of the component constituting the fiber having a fiber diameter of 0.01 to 20 μm, the thermoplasticity of the MFR smaller than the MFR of the thermoplastic resin A It is preferable to use the resin B, specifically, it is more preferable that the amount is 100 g / 10 min or less. By setting the MFR of the thermoplastic resin B to 150 g / 10 min or less, in a mixed fiber nonwoven fabric having at least a fiber having a fiber diameter of 0.01 to 20 μm and a fiber having a fiber diameter of 70 to 120 μm, the fiber diameter is 0.01 to A state in which 20 μm fibers and fibers having a fiber diameter of 70 to 120 μm are more sufficiently mixed can be achieved. On the other hand, the lower limit of the MFR of the thermoplastic resin B is not particularly limited, but it is possible to suppress the base back pressure from becoming excessively high during spinning, and to further suppress the leakage of the plastic resin B, the deformation of the base, and the like. In view of the above, the lower limit of the MFR of the thermoplastic resin B is preferably 3 g / 10 min or more, more preferably 5 g / 10 min or more, and further preferably 10 g / 10 min or more. In addition, said MFR was measured based on JIS-K-7210, measurement conditions are based on Annex B, and about the resin which is not described, conditions higher than melting | fusing point are 20 degreeC or more according to Annex A. Selected and measured.

  Further, when comparing the MFR of the thermoplastic resin A and the thermoplastic resin B, the MFR of the thermoplastic resin A is preferably 5 times or more the MFR of the thermoplastic resin B. By making it 5 times or more, the difference between the MFR of the thermoplastic resin A and the MFR of the thermoplastic resin B is sufficiently large, and when producing the mixed nonwoven fabric of the present invention using the melt blow spinning apparatus described later, When the thermoplastic resin A and the thermoplastic resin B are simultaneously spun from the two spinning nozzles of the melt blow spinning apparatus, two types of fibers having different fiber diameters can be obtained simultaneously. The upper limit of the magnification is not particularly limited, but is preferably 100 times or less from the viewpoint of production stability. From the above viewpoint, the magnification is more preferably 10 to 25 times.

  Next, when the melting points of the thermoplastic resin A and the thermoplastic resin B are compared, the melting point of the thermoplastic resin B is preferably 5 to 40 ° C. lower than the melting point of the thermoplastic resin A. By mixing fibers mainly composed of a thermoplastic resin having a melting point difference as described above, the collection efficiency of the resulting mixed fiber nonwoven fabric is further improved, and the bending resistance thereof is also improved. . The mechanism is not clear, but is presumed as follows. When the mixed fiber nonwoven fabric of the present invention is produced by, for example, the melt blow method, the thermoplastic resin A having a high melting point and containing a thermoplastic resin A that is rapidly solidified has a small single fiber fineness (fiber diameter of 0.01 to 20 μm). Thermoplastic resin fibers having a low melting point, a slow solidification and containing a thermoplastic resin B in a semi-molten state and having a large single fiber fineness (fiber diameter of 70 to 120 μm) are formed into a sheet while being entangled. Therefore, the generation of fly is suppressed, and as a result, a mixed fiber nonwoven fabric having a high collection efficiency and containing a large number of thin fibers having a single fiber fineness can be obtained. Fly refers to a fiber mass floating in the air that occurs when trying to obtain a non-woven fabric containing ultrafine fibers using the melt-blowing method, and the occurrence of fly causes deterioration in quality and efficiency. In addition, a fiber having a fiber diameter of 0. 0 is obtained by entanglement of a fiber having a thin single fiber fineness containing a thermoplastic resin A which is quickly solidified and a fiber having a single fiber fineness containing a slow solidified and semi-molten thermoplastic resin B. It is presumed that the contact point between the fibers of 01 to 20 μm and the thermoplastic resin fibers having a fiber diameter of 70 to 120 μm increases, and the bending resistance of the mixed fiber nonwoven fabric is improved.

  Moreover, it is preferable that it is 100 degreeC or more from a viewpoint that both melting | fusing point of the thermoplastic resin A and the thermoplastic resin B can make the heat resistance of the whole mixed fiber nonwoven fabric excellent. It is more preferable that the temperature is 130 ° C. or higher. On the other hand, the upper limit is not particularly limited, but is preferably 230 ° C. or lower and 200 ° C. or lower from the viewpoint of suppressing the energy required to melt the thermoplastic resins A and B. Is more preferable, and it is more preferable that it is 180 degrees C or less.

  Weight ratio of fibers having a fiber diameter of 0.01 to 20 μm and fibers having a fiber diameter of 70 to 120 μm in the mixed fiber nonwoven fabric of the present invention (fibers having a fiber diameter of 0.01 to 20 μm: fibers having a fiber diameter of 70 to 120 μm) Is preferably 10:90 to 40:60, more preferably 15:85 to 40:60, and still more preferably 20:80 to 30:70. By setting the weight of the fiber having a fiber diameter of 0.01 to 20 μm used in the present invention to 10:90 or more, the fiber surface area in the melt blown mixed nonwoven fabric can be increased, and the mixing efficiency is high. A fine nonwoven fabric can be obtained. On the other hand, by increasing the weight of fibers having a fiber diameter of 70 μm to 120 μm used in the present invention to 40:60 or more, a mixed nonwoven fabric having excellent rigidity can be obtained. From the above viewpoint, the weight ratio of the fiber having a fiber diameter of 0.01 to 20 μm and the fiber having a fiber diameter of 70 to 120 μm is more preferably 20:80 to 30:70.

  The total content ratio of the fibers having a fiber diameter of 0.01 to 20 μm and the fibers having a fiber diameter of 70 to 120 μm in the mixed fiber nonwoven fabric of the present invention is preferably 90% or more with respect to the entire mixed fiber nonwoven fabric. Weight ratio of fibers having a total content ratio of 90% or more and fibers having a fiber diameter of 0.01 to 20 μm to fibers having a fiber diameter of 70 to 120 μm (fibers having a fiber diameter of 0.01 to 20 μm: fiber diameter) Is within a specific range, it is possible to obtain a mixed fiber nonwoven fabric having high collection efficiency and bending resistance. From the above viewpoint, the total content rate is more preferably 95% or more.

  In addition, the mixed fiber nonwoven fabric of the present invention may contain a flame retardant fiber or a flame retardant as long as the effects of the present invention are not impaired.

  In order to enhance or improve the chargeability, weather resistance, thermal stability, mechanical properties, coloration, surface properties, or other properties of one or both of thermoplastic resin A and thermoplastic resin B An additive may be added to. In particular, when a mixed fiber nonwoven fabric is charged, it is a preferred embodiment that an electret additive is included for the purpose of enhancing the chargeability.

  In particular, the electret additive preferably contains at least one selected from the group consisting of hindered amine compounds and triazine compounds.

  As the hindered amine compound, 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)] (manufactured by BASF Japan Ltd., “Kimasorb” (registered trademark) 944LD), succinic acid Dimethyl-1- (2-hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate (manufactured by BASF Japan Ltd., “Tinuvin” (registered trademark) 622LD), and 2- ( 3,5-di-t-butyl-4-hydroxybenzyl) -2-n-butylmalonate bis (1,2,2,6,6-pentamethyl-4-piperidyl) (BASF Japan) , And "Tinuvin" ® 144), and the like.

  Examples of the triazine compound include the 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)] (manufactured by BASF Japan Ltd., “Kimasorb” (registered trademark) 944LD ), And 2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5-((hexyl) oxy) -phenol (manufactured by BASF Japan Ltd., and “Tinuvin” (registered trademark)) 1577FF).

  Among these electret additives, hindered amine compounds are particularly preferably used.

  The content of the hindered amine compound and / or triazine compound is preferably in the range of 0.1 to 5.0% by weight, more preferably 0.5 to 3% by weight based on the total weight of the mixed fiber nonwoven fabric. It is a range, More preferably, it is the range of 0.8 to 2.0 weight%. Moreover, when attaching these hindered amine type compounds and triazine type compounds to a nonwoven fabric or the fiber surface, it is preferable to make it adhere in 0.1 to 5.0 weight% with respect to the nonwoven fabric total weight.

  In addition to the above compounds, the mixed fiber nonwoven fabric of the present invention may be added with conventional additives generally used for nonwoven fabrics of electret processed products such as heat stabilizers, weathering agents and polymerization inhibitors. Good.

  Examples of the method for producing a mixed fiber nonwoven fabric of the present invention include a spunbond method, a melt blow method, an airlaid method, an electrospinning method, and a method of blowing short fibers into a melt blown nonwoven fabric. The method is preferably used. By using the melt blow method, a group of fibers having greatly different fiber diameters can be simultaneously spun and manufactured without requiring a complicated process. While spinning a fiber having a fiber diameter of 0.01 to 20 μm by an electrospinning method, a method of spinning a fiber having a fiber diameter of 70 to 120 μm by a melt blow method, or a fiber having a fiber diameter of 0.01 to 20 μm by a melt blow method While spinning, a method of mixing by blowing short fibers separately manufactured as fibers having a fiber diameter of 70 to 120 μm is conceivable, but a fiber having a fiber diameter of 0.01 to 20 μm and a fiber diameter of 70 can be considered. It is possible to simplify the process if both of the fibers having a diameter of ˜120 μm are produced by the melt-blowing method, and the obtained mixed fiber nonwoven fabric is a mixture of fine fibers and fibers having a large fiber diameter. From the viewpoint of Also, in the melt blow method, it is not necessary to coat the surface of each fiber with an oil agent or the like so that the short fibers manufactured separately do not get entangled with each other. It will be better.

  Spinning conditions in the melt-blowing method include polymer single-hole discharge rate, nozzle temperature, pressurized air pressure and pressurized air temperature. By optimizing these spinning conditions, the spinning conditions are made of fibers with a desired fiber diameter. A mixed fiber nonwoven fabric having a desired basis weight can be obtained.

  Specifically, (1) a material having a large MFR, that is, a material having a low melt viscosity is used as the thermoplastic resin A, and a material having a low MFR, that is, a material having a high melt viscosity, is used as the thermoplastic resin B. 2) The polymer single hole discharge amount from the discharge hole of the fiber having a fiber diameter of 0.01 to 20 μm is reduced, and the polymer single hole discharge amount from the discharge hole of the fiber having a fiber diameter of 70 to 120 μm is set large. (3) When the production process of each fiber is a melt blow method, adjusting the melting temperature of each thermoplastic resin or the wind speed of the hot air in the production process, and (4) the fiber diameter is 0.01 to 20 μm A desired fiber diameter (fiber diameter distribution) and a desired fiber diameter can be appropriately combined by increasing the number of fiber discharge holes as compared with the number of fiber discharge holes having a fiber diameter of 70 to 120 μm. Fiber diameter can be obtained combined filament nonwoven fabric fibers and fiber diameter of 0.01~20μm have such weight ratio of the fibers of 70 to 120.

  As equipment for producing the mixed fiber nonwoven fabric of the present invention, for example, the one described in US Pat. No. 3,981,650 can be used when the melt blow method is employed. Specifically, it is possible to use a spinneret having a structure in which spinning holes from which different types of resin flow out are arranged in a single spinneret. The mixed non-woven fabric obtained using the above manufacturing equipment is obtained by more uniformly mixing two kinds of fibers.

  In addition, for example, a method of spinning a fiber having a fiber diameter of 0.01 to 20 μm and a fiber having a fiber diameter of 70 to 120 μm with different spinnerets and mixing them as described in JP-A-8-13309. It can also be used. Alternatively, a non-woven fabric made of fibers having a fiber diameter of 0.01 to 20 μm and a non-woven fabric made of fibers having a fiber diameter of 70 to 120 μm may be laminated, and then entangled with a needle punch or the like. Use a spinneret with a structure in which spin holes from which different types of resin flow out are arranged in a single spinneret because a mixed fiber nonwoven fabric in which two types of fibers are more uniformly mixed in a single process is obtained. Is a preferred embodiment.

  The mixed fiber nonwoven fabric of the present invention achieves high collection performance and low pressure loss by sufficiently mixing fibers having at least two different fiber diameters. Although this mechanism is not clear, it is estimated as follows.

  Of the two types of fibers, the fibers having a small fiber diameter of 0.01 to 20 μm bear the function of improving the collection efficiency in the mixed fiber nonwoven fabric of the present invention. Further, the fiber having a large fiber diameter of 70 to 120 μm imparts a high bending resistance to the mixed fiber nonwoven fabric of the present invention, reduces the pressure loss of the filter using the mixed fiber nonwoven fabric, and a single layer of the mixed fiber nonwoven fabric. The function which makes the pleat workability excellent when pleating is done with is added.

  That is, since the fiber having a small fiber diameter of 0.01 to 20 μm has a large specific surface area, the particles can be efficiently collected on the fiber surface. In the fiber network having a fiber diameter of 0.01 to 20 μm, fibers having a large fiber diameter of 70 to 120 μm are dispersed and mixed, thereby improving the bending resistance of the mixed nonwoven fabric and increasing the fiber diameter. Large voids are generated between the fibers of 0.01 to 20 μm, and the presence of the interfiber spaces improves air permeability of the nonwoven fabric, thereby reducing pressure loss. In order to exhibit this effect more efficiently, it is more preferable that two types of fibers having different fiber diameters are more uniformly dispersed and mixed in the thickness direction of the nonwoven fabric.

  It is important that the mixed fiber nonwoven fabric of the present invention contains fibers having a fiber diameter of 0.01 to 20 μm. When the mixed fiber nonwoven fabric contains fibers having a fiber diameter of 0.01 to 20 μm, the collection efficiency of the mixed fiber nonwoven fabric can be improved. The average fiber diameter of fibers having a fiber diameter of 0.01 to 20 μm is preferably 0.3 μm to 7.0 μm, and more preferably 0.5 μm to 4.0 μm. By setting the average fiber diameter of the fibers having a fiber diameter of 0.01 to 20 μm to 7.0 μm or less, it becomes possible to increase the specific surface area of the fiber, and the collection capacity of the mixed fiber nonwoven fabric is further improved. be able to. On the other hand, the pressure loss can be further reduced by setting the average fiber diameter of fibers having a fiber diameter of 0.01 to 20 μm to 0.3 μm or more.

  It is important that the mixed nonwoven fabric of the present invention contains fibers having a fiber diameter of 70 to 120 μm. When the mixed fiber nonwoven fabric includes fibers having a fiber diameter of 70 to 120 μm, the bending resistance of the mixed fiber nonwoven fabric can be improved. Moreover, the average fiber diameter of fibers having a fiber diameter of 70 to 120 μm is preferably 80 μm to 120 μm, and more preferably 85 μm to 110 μm. By setting the average fiber diameter of fibers having a fiber diameter of 70 to 120 μm to 80 μm or more, the bending resistance of the mixed nonwoven fabric can be improved. On the other hand, when the average fiber diameter of fibers having a fiber diameter of 70 to 120 μm is 120 μm or less, the amount of material used can be reduced, and the environmental load can be reduced.

  Moreover, it is preferable that the average fiber diameter of a fiber with a fiber diameter of 70-120 micrometers is 10 times or more larger than the average fiber diameter of a fiber with a fiber diameter of 0.01-20 micrometers. This is because the fiber diameter distribution of the fibers having a fiber diameter of 0.01 to 20 μm and the fibers having a fiber diameter of 70 to 120 μm are clearly different, so that the two types of fiber groups clearly share their functions. This is because it is possible to achieve both an improvement in the collection efficiency of the fine nonwoven fabric and a reduction in pressure loss by imparting excellent bending resistance to the mixed nonwoven fabric. Moreover, it is more preferable that said ratio is 20 times or more larger. On the other hand, the upper limit of the ratio is preferably 150 times or less, and more preferably 100 times or less. However, the mixed nonwoven fabric of the present invention may contain fibers other than fibers having a fiber diameter of 0.01 to 20 μm and fibers having a fiber diameter of 70 to 120 μm within a range not impairing the effects of the present invention.

  The mixed fiber nonwoven fabric of the present invention preferably contains 7 or more fibers having a fiber diameter of 70 to 120 μm in the cross section of the mixed fiber nonwoven fabric between 1 mm in the direction perpendicular to the thickness direction of the mixed fiber nonwoven fabric. . The number of fibers having a fiber diameter of 70 to 120 μm is more preferably 10 or more, and even more preferably 15 or more. By setting the number of fibers having a fiber diameter of 70 to 120 μm to 7 or more, fibers having a fiber diameter of 70 to 120 μm are present in a high density and sufficiently dispersed in the mixed fiber nonwoven fabric. The bending resistance can be made more excellent. On the other hand, the upper limit is not particularly limited, but is preferably 500 or less, and more preferably 200 or less. By setting it to 500 or less, the basis weight of the entire mixed nonwoven fabric can be reduced, and the productivity can be improved.

  A method for measuring and evaluating the number of fibers contained in the cross section of the mixed fiber nonwoven fabric will be described in Examples.

  In the mixed nonwoven fabric of the present invention, it is preferable that the fiber having a fiber diameter of 70 to 120 μm retains the form of the fiber. Here, “holding the form of the fiber” means that the fiber is not melted by heat treatment after the cloth is formed. For example, Japanese Patent Application Laid-Open No. 7-82649 discloses a method in which a low melting point fiber is melted by heat treatment at a temperature higher than the melting point and used as a binder fiber to improve the strength of the nonwoven fabric. However, when the low melting point fiber is melted in this way, the fiber surface area is reduced, and not only the collection efficiency is lowered, but also a problem that the interfiber gap is reduced and the pressure loss is increased. In the mixed fiber nonwoven fabric of the present invention, a fiber having a fiber diameter of 70 to 120 μm, which is lower than the melting point of a fiber having a fiber diameter of 0.01 to 20 μm, is present in a state in which the fiber shape is maintained. The effect of pressure loss and high collection can be demonstrated.

  In the mixed fiber nonwoven fabric of the present invention, the ratio X / Y is 10 to 100 times greater than the number X of fibers having a fiber diameter of 0.01 to 20 μm and the number Y of fibers having a fiber diameter of 70 to 120 μm. preferable.

  As can be seen from the above X / Y values, the mixed fiber nonwoven fabric of the present invention has an overwhelmingly larger number of fibers having a small fiber diameter of 0.01 to 20 μm than fibers having a large fiber diameter of 70 to 120 μm. Therefore, the mixed fiber nonwoven fabric of the present invention can increase the specific surface area of the mixed fiber nonwoven fabric while including thick fibers having a fiber diameter of 70 to 120 μm. Due to this effect, when the mixed nonwoven fabric of the present invention is used as a filter, high collection efficiency can be achieved. Further, the number of fibers having a fiber diameter of 0.01 to 20 μm is larger than the number of fibers having a fiber diameter of 70 to 120 μm, a thin fiber having a fiber diameter of 0.01 to 20 μm, and a fiber diameter of 70 to 120 μm. A state in which thermoplastic resin fibers having a fiber diameter of 0.01 to 20 μm occupy most of the surface area of the mixed nonwoven fabric due to a characteristic fiber configuration in which fibers having fiber diameters significantly different from thick fibers are mixed. And can. For this reason, when the mixed fiber nonwoven fabric is charged, even if the fiber having a fiber diameter of 70 to 120 μm contains a component having low charge retention, the nonwoven fabric as a whole has high chargeability and charge retention. Can have.

  There are various methods for determining the fiber diameter, average fiber diameter, and total content ratio of fibers having a fiber diameter of 0.01 to 20 μm and fibers having a fiber diameter of 70 to 120 μm contained in the mixed fiber nonwoven fabric of the present invention. Can be used. For example, the method of measuring a fiber diameter using various microscopes, such as an optical microscope and a scanning electron microscope, can be mentioned. In addition, the fiber diameter of the remaining fiber is lost by using the difference in melting point between the fiber having a fiber diameter of 0.01 to 20 μm and the fiber having a fiber diameter of 70 to 120 μm and the difference in resistance to chemicals, and removing only one of the fibers. May be measured. In addition, fiber components can be analyzed using techniques that can analyze the material distribution in various microregions, such as micro-Raman spectroscopy, micro-infrared spectroscopy, electron beam microanalyzer, or time-of-flight secondary ion mass spectrometry. A method of measuring while determining may be used. For example, in the mixed fiber nonwoven fabric of the present invention, when there is a difference in melting point between a resin having a fiber diameter of 70 to 120 μm and a fiber having a fiber diameter of 0.01 to 20 μm, the difference in fiber diameter distribution can be confirmed. The mixed fiber nonwoven fabric can be heat treated at a temperature between the melting points of the two components, and the average fiber diameter of the entire nonwoven fabric when one of the fibers is melted can be compared with the average fiber diameter before the heat treatment. .

The basis weight of the mixed nonwoven fabric of the present invention is preferably 60 g / m ² or more, more preferably 80 g / m ² or more from the viewpoint of improving the bending resistance of the mixed nonwoven fabric, and more preferably 80 g / m ^2. When it is used as a filter medium for a filter to which the above is applied, a higher rigidity is required, so that it is more preferably 100 g / m ² or more. In addition, the basis weight of the mixed nonwoven fabric is preferably 1000 g / m ² or less, more preferably 500 g / m ² or less, from the viewpoint of improving the productivity of the mixed nonwoven fabric. When it is used as a filter medium, it is a more preferable aspect that it is 130 g / m ² or less.

  The longitudinal elongation of the mixed fiber nonwoven fabric of the present invention is less than 30% from the viewpoint of suppressing elongation by process tension and lowering the pressure loss when used as a filter. Preferably, it is less than 20%.

  The mixed non-woven fabric of the present invention is charged (electret treatment), and fibers having a fiber diameter of 0.01 to 20 μm and / or fibers having a fiber diameter of 70 to 120 μm are charged fibers. Thus, if a mixed fiber nonwoven fabric is made into an electret nonwoven fabric sheet, a further low pressure loss and high collection efficiency can be obtained due to the electrostatic adsorption effect. As a method for electretization, a method of electretization by applying water to the nonwoven fabric and then drying it is preferably used to obtain a nonwoven fabric having high performance. As a method for imparting water to a mixed fiber nonwoven fabric, a method of spraying a water jet or water droplet at a pressure sufficient to allow water to penetrate into the nonwoven fabric, or a mixed fiber nonwoven fabric after or while applying water A method of allowing water to permeate into the nonwoven fabric by sucking from one side of the fiber, or immersing the mixed nonwoven fabric in a mixed solution of water and a water-soluble organic solvent such as isopropyl alcohol, ethyl alcohol and acetone so that the water penetrates into the nonwoven fabric. There are methods.

  The mixed fiber nonwoven fabric of the present invention exhibits high collection efficiency suitable for the purpose of use as a filter medium. The value of the collection efficiency after the charging treatment is characterized in that the collection efficiency of particles having a particle diameter of 0.3 to 0.5 μm at a wind speed of 4.5 m / min is 85% or more. More preferably, it is 90% or more, and still more preferably 95% or more. In particular, a mixed fiber nonwoven fabric having a collection efficiency of 95% or more can be suitably used as a filter medium for a high dust collection air filter. Such high collection efficiency, as described above, appropriately adjusts the degree of dispersion and mixing of two or more kinds of fibers having different fiber diameters and the average fiber diameter of the smaller fiber used. This can be achieved.

The mixed fiber nonwoven fabric of the present invention has a feature that high collection efficiency can be achieved with low pressure loss. The mixed fiber non-woven fabric of the present invention, QF value defined by the following equation is preferably at 0.10 Pa ^-1 or more, more preferably 0.15 Pa ^-1 or higher, 0.18Pa ^-1 or Is a more preferred embodiment. The larger the QF value, the same collection efficiency can be achieved with lower pressure loss.
QF value (Pa ⁻¹ ) = − In (1— [collection efficiency (%)] / 100) / pressure loss (Pa).

  Furthermore, the mixed fiber nonwoven fabric of the present invention may be given a function in a later step. For example, the function imparting includes a method of spraying particles that exhibit antibacterial properties, antiallergenic properties, fungicidal properties, flame retardancy, and the like by spraying or the like.

  It is important that the mixed nonwoven fabric of the present invention has a bending resistance of 2 mN or more. A mixed fiber nonwoven fabric having a bending resistance of 2 mN or more can be pleated by a single layer. The pleated filter has a large filter medium area with respect to a constant air volume, and accordingly, the wind speed penetrating the filter medium is slowed. Therefore, a filter having high collection efficiency and low pressure loss can be obtained. Examples of equipment that performs pleating include a reciprocating pleating machine and a rotary pleating machine. In the pleated shape, when the apex portion is crushed or the filter medium is significantly curved between the apex portion of the mountain and the apex portion of the valley, the pressure loss becomes high. Therefore, in order to give a sharp pleated shape, a bending resistance of 2 mN or more is required. Furthermore, since the mixed fiber nonwoven fabric has a bending resistance of 2 mN or more, the pleated shape can be sufficiently retained even during the use process. In addition, the bending resistance of the mixed nonwoven fabric is the thickness of the mixed nonwoven fabric, the average fiber diameter of fibers having a fiber diameter of 70 to 120 μm, the fibers having a fiber diameter of 0.01 to 20 μm and the fibers having a fiber diameter of 70 to 120 μm. The weight ratio (fiber having a fiber diameter of 0.01 to 20 μm: fiber having a fiber diameter of 70 to 120 μm), the melting point of the thermoplastic resin B, and the like can be adjusted as appropriate.

  Further, the mixed fiber nonwoven fabric of the present invention is characterized by having a thickness of 0.3 to 1.0 mm. Conventionally, in order that the collection efficiency of particles having a particle diameter of 0.3 to 0.5 μm at a wind speed of 4.5 m / min is 85% or more and has a bending resistance of 2 mN or more, a collection efficiency of 85% or more is required. It is necessary to bond a non-woven fabric having a strength and a non-woven fabric having a strength of 2 mN or more, and it is difficult to reduce the thickness to 1.0 mm or less because of a laminated structure. However, in the present invention, as described above, the degree of dispersion and mixing of two or more kinds of fibers having different fiber diameters in the mixed fiber nonwoven fabric, the fiber diameter of the smaller fiber diameter used, and the larger fiber diameter used. By appropriately adjusting the fiber diameter of the fibers and the melting point of the thermoplastic resin B, the collection efficiency of particles having a particle diameter of 0.3 to 0.5 μm at a wind speed of 4.5 m / min is 85% or more, and the thickness is A mixed fiber nonwoven fabric having a bending resistance of 0.3 to 1.0 mm and 2 mN or more can be obtained.

  According to the present invention, a mixed fiber nonwoven fabric having a low pressure loss and a high collection efficiency can be obtained, and this mixed fiber nonwoven fabric can be suitably used as a filter medium for a pleated filter.

  This filter medium is suitable for high-performance applications of air filters in general, especially air-conditioning filters, air purifier filters, and automobile cabin filters, but the application range is not limited thereto.

  Next, an Example is given and it demonstrates more concretely about the mixed fiber nonwoven fabric of this invention. The characteristic values used in the examples are measured by the following measuring method.

(1) Weight of blended nonwoven fabric Samples with a size of 15 cm square were collected from different locations of the blended nonwoven fabric based on 6.4.2 A method (mass per unit area in the standard state) of JIS-L-1096. Each weight (g) was measured and converted to a weight per 1 m ² (g / m ² ). The said measurement was implemented by n = 3 and the average value was made into the fabric weight (g / m < ² >) of a nonwoven fabric.

(2) Fiber diameter and average fiber diameter Twenty measurement samples of length × width = 3 mm × 3 mm were collected from any location of the nonwoven fabric made of fibers obtained from the discharge holes a of Example 1 described later, and scanned. A total of 12 photographs of the surface of the nonwoven fabric were taken one by one using an electron microscope (magnification: 1000 times). The fiber diameter was measured for all fibers in the photograph where the fiber diameter could be clearly confirmed. Each fiber diameter was measured with a measurement accuracy of an effective number of 0.1 μm. Moreover, the value of the fiber diameter of each fiber was totaled, and the value divided by the measured number of fibers was defined as the average fiber diameter. The average fiber diameter was calculated as two significant figures for 1.0 μm or more and one significant figure for less than 1.0 μm. Next, ten measurement samples of length × width = 3 mm × 3 mm were collected from an arbitrary location of the nonwoven fabric made of fibers obtained from the ejection holes b of Example 1 described later, and a scanning electron microscope (magnification: 100). 10 times), a total of 10 surface photographs of the nonwoven fabric were taken. The fiber diameter was measured for all fibers in the photograph where the fiber diameter could be clearly confirmed. Each fiber diameter was measured with a measurement accuracy of an effective number of 0.1 μm. Moreover, the value of the fiber diameter of each fiber was totaled, and the value divided by the measured number of fibers was defined as the average fiber diameter. The average fiber diameter was calculated as two significant figures for 1.0 μm or more and one significant figure for less than 1.0 μm.

(3) Number of fibers contained in the cross-section of the blended nonwoven fabric Twelve blended nonwoven fabric pieces of length x width = 20 mm x 5 mm are collected from any location of the blended nonwoven fabric, and the pieces are impregnated with an epoxy resin and solidified. It was. This mixed non-woven fabric was cut with a single-blade razor to obtain fragments of length × width = 1 mm × 5 mm. About the cut surface of this fragment | piece, it image | photographed with the scanning electron microscope, and obtained the mixed fiber nonwoven fabric cross-section photograph of 12 sheets in total. The magnification was set to 200 to 1000 times, and all the fiber cross-sectional shapes in the photograph that could be clearly confirmed were counted.

(4) QF value The QF value, which is an index of filtration performance, is calculated by the following equation using the collection efficiency and pressure loss. The lower the pressure loss and the higher the collection efficiency, the higher the QF value, indicating better filtration performance.
QF value (Pa ⁻¹ ) = − In (1— [collection efficiency (%)] / 100) / pressure loss (Pa).

(5) Bending softness Bending softness was measured with a Gurley / flexibility testing machine manufactured by Toyo Seiki Seisakusho Co., Ltd. based on the 6.7.4 Gurley method of JIS L 1913 (2010). The bending resistance with a Gurley tester was determined by the following method. Five test pieces were collected with the length direction of the nonwoven fabric as the length direction of the test piece. Using the following formula, the average value of 10 times for each of the front and back surfaces and a total of 5 points of the test piece was obtained, and rounded to the nearest significant figure to calculate the bending resistance (mN) of the sample. In addition, about the front and back of a nonwoven fabric, the single side | surface was arbitrarily set as the surface and the opposite surface was set as the back surface.
S = R × (D ₁ W ₁ + D ₂ W ₂ + D ₃ W ₃ ) × (L−12.7) ² /b×3.375×10 ⁻⁵
Here, S: Bending softness (Gurley stiffness) (mN)
R: Reading of scale plate D ₁ , D ₂ , D ₃ : Rejection from pendulum fulcrum to weight mounting position [25.4 mm (1 in.), 50.8 mm (2 in.) And 101.6 (4 in)]
W ₁ , W ₂ , W ₃ : mass (g) of weights attached to the holes of D ₁ , D ₂ and D ₃
L: Length of test piece (mm)
b: Width of test piece (mm).

(6) Pressure loss Five samples for measurement having a diameter of 25 cm were taken from any five locations of the mixed fiber nonwoven fabric, and the above samples were set in a holder having an effective frontage size of cm ² and air at a wind speed of 4.5 m / min. , And the differential pressure upstream and downstream of the sample was measured with a digital manometer (MA2-04P manufactured by MODUS). The average value of the above five samples was taken as the pressure loss.

(7) Collection efficiency At the time of the measurement of (6) above, a polystyrene 0.309 U10% solution (manufacturer: Nacalai Tesque) was diluted 200 times with distilled water and used as measurement particles. The wind speed is 4.5 m / min and the particle concentration of the above polystyrene particles is stabilized in the range of 10,000 to 40,000 particles / 2.83 × 10 −4 m ³ , and the particle diameters upstream and downstream of the measurement sample are 0.00. The number of polystyrene particles of 3 to 0.5 μm was measured with a particle counter (KC-01D manufactured by RION). The collection efficiency was calculated using the obtained measured value and the following formula. Moreover, the average value of five measurement samples was made into collection efficiency.
Collection efficiency (η) = (1− (number of downstream particles / number of upstream particles)) × 100
Note that the higher the collection efficiency of the mixed fiber nonwoven fabric, the lower the number of downstream dusts, and thus the higher the collection efficiency value.

(8) Pleating processability Pleating was performed with a reciprocal folding pleating machine at a pleated folding height of 30 mm, a slit width of 150 mm, and a folding speed of 30 mountains / minute. If the peak height is stable and the peaks and valleys are bent at acute angles, the pleatability is good. Yes, pleating can be done, but the peak height is not stable, or more than 50 peaks cannot be continuously pleated. The case where the crease was not obtained and the ridge of the mountain valley was not formed and the predetermined height was not achieved was evaluated as x when the pleating process was not possible.

(9) Thickness of blended nonwoven fabric Based on 8.4 A method (JIS method) of JIS-L-1096, the thickness is measured at three arbitrary locations of the blended nonwoven fabric, and the average value of the measured values is calculated. The thickness of the mixed fiber nonwoven fabric.

(10) Weight ratio (fiber having a fiber diameter of 0.01 to 20 μm: fiber having a fiber diameter of 70 to 120 μm)
Non-woven fabric made of fibers having a fiber diameter of 0.01 to 20 μm (hereinafter referred to as non-woven fabric I) and non-woven fabric made of fibers having a fiber diameter of 70 to 120 μm under the same conditions as the production conditions for the melt blown nonwoven fabric of Example 1 described later ( Hereinafter, the nonwoven fabric II) was obtained, and the basis weight was measured for each by the above-described basis weight measuring method (1). The ratio of the basis weight of the nonwoven fabric I and the nonwoven fabric II (the basis weight of the nonwoven fabric I: the basis weight of the nonwoven fabric II) was set to the weight ratio (fiber having a fiber diameter of 0.01 to 20 μm: fiber having a fiber diameter of 70 to 120 μm).

[ Comparative Example 5 ]
As a thermoplastic resin A, a polypropylene (PP) resin having an MFR of 860 g / 10 min at a temperature of 230 ° C. and a load of 21.18 N and a melting point of 163 ° C., “KIMASORB” (registered trademark) 944 (manufactured by BASF Japan Ltd.) Is used as a thermoplastic resin B, a propylene-ethylene copolymer having an MFR of 60 g / 10 min at a temperature of 230 ° C. under a load of 21.18 N and a melting point of 155 ° C. is used. Melt blow nozzle for mixed fiber spinning (a hole diameter: 0.25 mm, b hole diameter) provided with an extruder, a gear pump, and two types of discharge holes a (hereinafter referred to as holes a) and discharge holes b (hereinafter referred to as holes b) : 0.6 mm, a hole depth: 2.5 mm, b hole depth: 3.5 mm, a hole number: 285 holes, b hole number: 60 holes, base width 450 mm, aa hole pitch: 1 m, ab hole pitch: 2 mm, hole arrangement: five a holes are inserted between b holes and arranged in a line), a device comprising a compressed air generator, an air heater, a collecting conveyor, and a winder The melt blown non-woven fabric was produced.

Into each extruder, the pellets of the thermoplastic resin A constituting the fibers having the above fiber diameter of 0.01 to 20 μm and the pellets of the thermoplastic resin B constituting the fibers having the above fiber diameter of 70 to 120 μm are respectively charged. Then, the thermoplastic resin A is heated and melted at a temperature of 260 ° C. and the thermoplastic resin B is heated and melted at a temperature of 210 ° C., and the gear pump is made of the thermoplastic resin A: fiber constituting the fiber having the fiber diameter of 0.01 to 20 μm. The weight ratio of the thermoplastic resin B constituting the fiber having a diameter of 70 to 120 μm was set to 1: 3, and the thermoplastic resin constituting the 0.01 to 20 μm fiber and the fiber of 70 to 120 μm were The thermoplastic resin to be constituted was guided and discharged to the a-hole and the b-hole of the melt blow nozzle for mixed fiber spinning. The discharged polymer was thinned with high-temperature pressurized air having a wind speed of 4 m / sec, and formed into a sheet by spraying it onto the collecting conveyor from the nozzle discharge hole. The collection conveyor speed was adjusted to obtain a mixed nonwoven fabric having a basis weight of 96 g / m ² .

Next, under the conditions of Comparative Example 5 , a sample of the nonwoven fabric made of each fiber discharged from only the hole a and only the hole b was collected, and observed with a scanning electron microscope, and the average fiber diameter was measured. Here, FIG. 1 shows a histogram showing the fiber diameter distribution of the fibers discharged from only the holes a of Comparative Example 5 , and FIG. 2 shows the fiber diameter distribution of the fibers discharged from only the holes b of Comparative Example 5 . A histogram is shown. The fiber diameter of the ejection fiber group from the hole a is 0.01 to 20 μm, and the majority of the fiber diameter of the ejection fiber group from the hole b is 70 to 120 μm, confirming that the fiber diameter distribution is clearly different. . From each basis weight, an apparent weight ratio of fibers having a fiber diameter of 0.01 to 20 μm and fibers having a fiber diameter of 70 to 120 μm was calculated. The results are shown in Table 1.

The cross section of the nonwoven fabric obtained in Comparative Example 5 is observed with a scanning electron microscope, and it is confirmed that a fiber group having a fiber diameter of 0.01 to 20 μm and a fiber group having a fiber diameter of 70 μm to 120 μm are mixed. did. The number of fibers per unit cross-sectional length was measured for fibers having a fiber diameter of 70 μm to 120 μm.

Next, the mixed fiber nonwoven fabric obtained in Comparative Example 5 was impregnated with a mixed aqueous solution having a component weight ratio of pure water and isopropyl alcohol of 70:30, and then naturally dried to obtain an electret melt blown mixed fiber nonwoven fabric. Obtained. The characteristic values of this electret meltblown mixed nonwoven fabric were measured and are shown in Table 1.

[ Comparative Example 6 ]
As the thermoplastic resin B, MFR is using 60 g / 10min, melting point 163 ° C. of polypropylene (PP) resin at 21.18N load at a temperature 230 ° C., comparing the temperature of heating the melt in the extruder of the thermoplastic resin A Example A nonwoven fabric was produced in the same manner as in Comparative Example 5 except that the temperature was increased by 20 ° C. compared to the temperature of 5 and the wind speed of the pressurized air was 3.0 m / sec. With respect to the mixed fiber nonwoven fabric obtained in Comparative Example 6 , various characteristic values were measured in the same manner as in Comparative Example 5, and are shown in Table 1.

Here, FIG. 3 shows a histogram showing the fiber diameter distribution of the fibers discharged from only the holes a of Comparative Example 6 , and FIG. 4 shows the fiber diameter distribution of the fibers discharged from only the holes b of Comparative Example 6 . A histogram is shown. The fiber diameter of the ejection fiber group from the hole a is 0.01 to 20 μm, and the majority of the fiber diameter of the ejection fiber group from the hole b is 70 to 120 μm, confirming that the fiber diameter distribution is clearly different. .

[Example 3]
The temperature at which the thermoplastic resin A is heated and melted by the extruder is higher by 8 ° C. than the temperature of Comparative Example 5 , and the temperature at which the thermoplastic resin B is heated and melted by the extruder is 5 ° C. lower than the temperature of Comparative Example 5. And the nonwoven fabric was manufactured by the method similar to the comparative example 5 except having set the wind speed of the pressurized air to 3.8 m / sec. With respect to the mixed fiber nonwoven fabric obtained in Example 3, various characteristic values were measured in the same manner as in Comparative Example 5, and are shown in Table 1.

  Here, FIG. 5 shows a histogram showing the fiber diameter distribution of the fibers discharged from only the holes a of Example 3, and FIG. 6 shows the fiber diameter distribution of the fibers discharged from only the holes b of Example 3. A histogram is shown. The fiber diameter of the ejection fiber group from the hole a is 0.01 to 20 μm, and the majority of the fiber diameter of the ejection fiber group from the hole b is 70 to 120 μm, confirming that the fiber diameter distribution is clearly different. .

[Comparative Example 1]
As the thermoplastic resin B, a polypropylene (PP) resin having an MFR of 30 g / 10 min and a melting point of 163 ° C. under a temperature of 230 ° C. and a 21.18 N load condition is used, and is heated and melted by an extruder of the thermoplastic resin A and the thermoplastic resin B. Except that the temperature to be used is 20 ° C. higher than that of Comparative Example 5 , the weight ratio of the thermoplastic resin A to the thermoplastic resin B is 43:57, and the wind speed of the pressurized air is 6.0 m / min. A mixed fiber nonwoven fabric was produced by the same method as in Comparative Example 5 .

The mixed fiber nonwoven fabric obtained in Comparative Example 1 was electret-treated in the same manner as in Comparative Example 5, and the characteristic values were measured and shown in Table 1. In addition, the bending resistance of the mixed fiber nonwoven fabric obtained in Comparative Example 1 was very low and could not be measured.

  Here, FIG. 7 shows a histogram showing the fiber diameter distribution of the fibers discharged from only the holes a of Comparative Example 1, and FIG. 8 shows the fiber diameter distribution of the fibers discharged from only the holes b of Comparative Example 1. A histogram is shown. The fiber diameter of the ejected fiber group from the hole a was 0.01 to 20 μm, but the fiber diameter of the ejected fiber group from the hole b was only a thin fiber that was significantly smaller than 70 μm.

[Comparative Example 2]
A blended nonwoven fabric was produced by the same method as in Comparative Example 1 except that the weight ratio of the thermoplastic resin A and the thermoplastic resin B was 54:46 and the wind speed of the pressurized air was 5.0 m / min.

The mixed fiber nonwoven fabric obtained in Comparative Example 2 was electret-treated in the same manner as in Comparative Example 5, and the characteristic values were measured and are shown in Table 1. In addition, the bending resistance of the mixed fiber nonwoven fabric obtained in Comparative Example 2 was very low and could not be measured.

  Here, FIG. 9 shows a histogram showing the fiber diameter distribution of the fibers discharged from only the holes a of Comparative Example 2, and FIG. 10 shows the fiber diameter distribution of the fibers discharged from only the holes b of Comparative Example 2. A histogram is shown. The fiber diameter of the ejected fiber group from the hole a was 0.01 to 20 μm, but the fiber diameter of the ejected fiber group from the hole b was only a thin fiber that was significantly smaller than 70 μm.

[Comparative Example 3]
A mixed fiber nonwoven fabric was produced by the same method as in Comparative Example 1 except that the weight ratio of the thermoplastic resin A and the thermoplastic resin B was 15:85.

The mixed fiber nonwoven fabric obtained in Comparative Example 3 was electret-treated in the same manner as in Comparative Example 5, and the characteristic values were measured and are shown in Table 1.

  Here, FIG. 11 shows a histogram showing the fiber diameter distribution of the fibers discharged from only the holes a of Comparative Example 3, and FIG. 12 shows the fiber diameter distribution of the fibers discharged from only the holes b of Comparative Example 3. A histogram is shown. The fiber diameter of the ejected fiber group from the hole a was 0.01 to 20 μm, but the fiber diameter of the ejected fiber group from the hole b was only a thin fiber that was significantly smaller than 70 μm.

[Comparative Example 4]
A wet papermaking nonwoven fabric having a bending resistance of 3.7 mN and a thickness of 1.480 mm was laminated as a support layer on the mixed fiber nonwoven fabric of Comparative Example 1 using polypropylene heat fusion powder (5 g / m ² ). The characteristic values were measured and are shown in Table 1.

As is apparent from Table 1, in Comparative Example 5 , it was obtained by adjusting two types of raw materials, the discharge amount, the wind speed of pressurized air, the extruder temperature, etc., using a mixed fiber melt blow spinning facility. The mixed fiber nonwoven fabric is composed of fibers with a fiber diameter of 0.01 to 20 μm and fibers with a fiber diameter of 70 to 120 μm, and the bending resistance of the mixed fiber nonwoven fabric is 2.1 mN, which is necessary for pleating. Said mixed fiber nonwoven fabric had. Moreover, since this mixed fiber nonwoven fabric has a melting point of the thermoplastic resin constituting the fibers of 70 to 120 μm lower than the melting point of the thermoplastic resin constituting the fibers of 0.01 to 20 μm, the fly of 0.01 to 20 μm is used. Further, by performing the charging treatment, a high collection efficiency exceeding 95% was exhibited with a low pressure loss.

Further, in Comparative Example 6 , the basis weight was increased, the fiber diameter was increased, and the rigidity was improved by changing the discharge amount and the wind speed of the pressurized air. The mixed non-woven fabric having such rigidity can be suitably used as a filter medium for pleating.

  On the other hand, since the nonwoven fabrics shown in Comparative Examples 1 to 3 do not contain a necessary amount of thermoplastic resin fibers having a fiber diameter of 70 to 120 μm, the JIS L 1913 (2010 edition) 6.7.4 Gurley method is used. It was so soft that it could not be measured by the test method based on it. Therefore, the pleated processing cannot be performed with the mixed fiber nonwoven fabric alone.

  As described above, in the mixed fiber nonwoven fabric in which two kinds of fibers having different fiber diameter distributions are mixed, the fiber diameters of the fine fibers and the thick fibers and the components of the respective fibers are specified, thereby reducing the pressure loss. In addition to being low, it was possible to obtain a mixed fiber nonwoven fabric that was excellent in collection efficiency and could have a pleated shape as a filter shape, and the manufacturing cost of the filter medium and the filter could be reduced.

Claims (8)

Including at least a fiber having a fiber diameter of 0.01 to 20 μm and a fiber having a fiber diameter of 70 to 120 μm,
The main component of the component constituting the fiber having a fiber diameter of 0.01 to 20 μm is the thermoplastic resin A,
The main component of the component constituting the fiber having a fiber diameter of 70 to 120 μm is the thermoplastic resin B,
The fiber having a fiber diameter of 0.01 to 20 μm and / or the fiber having a fiber diameter of 70 to 120 μm is a charged fiber,
The collection efficiency of particles having a particle diameter of 0.3 to 0.5 μm at a surface wind speed of 4.5 m / min is 85% or more, the thickness is 0.3 to 1.0 mm, and the bending resistance is 2.0 mN or more. Yes,
The weight ratio of the fiber having a fiber diameter of 0.01 to 20 μm and the fiber having a fiber diameter of 70 to 120 μm (fiber having a fiber diameter of 0.01 to 20 μm: fiber having a fiber diameter of 70 to 120 μm) is 10:90. ~ 40: 60,
The total content rate of the fiber having a fiber diameter of 0.01 to 20 μm and the fiber having a fiber diameter of 70 to 120 μm is 95% or more,
The number average fiber diameter of the fibers having a fiber diameter of 0.01 to 20 μm is 0.5 to 4.0 μm,
A mixed fiber nonwoven fabric having a basis weight of 100 to 500 g / m ² . The mixed fiber nonwoven fabric according to claim 1, wherein the thermoplastic resin A has a melt flow rate of 300 g / 10 min or more and the thermoplastic resin B has a melt flow rate of 150 g / 10 min or less. The mixed fiber nonwoven fabric according to claim 1 or 2, wherein the melting point of the thermoplastic resin A is 5 to 40 ° C lower than the melting point of the thermoplastic resin B. The mixed nonwoven fabric according to any one of claims 1 to 3, wherein the thermoplastic resin A is a polyolefin. The mixed fiber nonwoven fabric according to claim 4, wherein the polyolefin is a polypropylene homopolymer. The mixed fiber nonwoven fabric according to any one of claims 1 to 5, wherein the thermoplastic resin B is a propylene-ethylene copolymer. A pleated filter comprising the nonwoven fabric according to claim 1. It is a manufacturing method of the mixed fiber nonwoven fabric by the melt blow method, Comprising: It has the process of discharging simultaneously the said thermoplastic resin A and the said thermoplastic resin B from a respectively different discharge hole, The mixed fiber nonwoven fabric in any one of Claims 1-7 Manufacturing method.