阅读说明：本技术 复合结构体、其制造方法及包含所述复合结构体的滤材 (Composite structure, method for producing same, and filter containing same ) 是由 梅林阳 平本晋平 伊东秀実 于 2020-03-11 设计创作，主要内容包括：提供一种尘埃的捕集效率高、压力损失低、兼具长寿命的滤材、以及用于所述滤材的过滤器材料。一种复合结构体,包含纤维直径小于500nm的极细纤维以及珠粒,所述复合结构体中,在所述复合结构体的最表面包含500个/mm～(2)以上的直径5μm以上的珠粒。所述极细纤维与所述珠粒优选为相同的成分。(Provided are a filter medium having high dust collection efficiency, low pressure loss, and a long life, and a filter material used for the filter medium. A composite structure comprises very fine fibers having a fiber diameter of less than 500nmA fiber and a bead, wherein the outermost surface of the composite structure comprises 500 pieces/mm 2 The above beads having a diameter of 5 μm or more. The ultrafine fibers and the beads are preferably the same component.)

1. A composite structure comprising ultrafine fibers having a fiber diameter of less than 500nm and beads, wherein the outermost surface of the composite structure comprises 500 particles/mm²The above beads having a diameter of 5 μm or more.

2. The composite structure of claim 1 wherein the very fine fibers are the same composition as the beads.

3. The composite structure according to claim 1 or 2, wherein 50% or more of the ultrafine fibers having a fiber diameter of 200nm or less are contained in the entire fibers.

4. The composite structure according to any one of claims 1 to 3, further comprising 5% or more of fine fibers having a fiber diameter of 500nm or more with respect to the entire fibers.

5. A filter comprising the composite structure of any of claims 1 to 4.

6. A method of manufacturing a composite structure, the composite structure according to any one of claims 1 to 4 being manufactured, the method comprising:

a step for preparing a spinning solution in which at least one resin selected from the group consisting of polyvinylidene fluoride, polyamide, polyurethane, and polylactic acid is dissolved in a solvent; and

and a step of spinning the spinning solution by an electrospinning method to obtain a composite structure comprising ultrafine fibers having a fiber diameter of less than 500nm and beads.

Technical Field

The present invention relates to a composite structure, a method for producing the same, and a filter material containing the composite structure.

Background

Conventionally, nonwoven fabric sheets (sheets) have been used in many cases as a filter medium for an air filter (air filter) for removing fine dust (dust) such as pollen and dust. The filter medium for such a filter is required to have a performance of collecting dust with high efficiency (high collection efficiency) and a performance of reducing resistance when a fluid passes through the filter medium (low pressure loss).

As a method for achieving high collection efficiency and low pressure loss, a filter using ultrafine fibers has been proposed. For example, patent document 1 proposes a filter including an ultrafine fiber layer having an average fiber diameter of 170nm or less. However, since such a filter medium has a dense matrix (matrix) formed by ultrafine fibers, the pressure loss of the obtained filter tends to be large.

As a method for solving the problems of low pressure loss and long life of a filter medium using ultrafine fibers, a mixed fiber filter medium in which ultrafine fibers and fibers coarser than the ultrafine fibers are mixed has been proposed. For example, patent document 2 proposes a nonwoven fabric in which ultrafine fibers formed by electrospinning and meltblown fibers formed by a meltblowing (melt-blowing) method are mixed. However, the filter medium of patent document 2 is not necessarily preferable in terms of production efficiency because the production apparatuses are complicated because the production methods of fibers using different principles are combined.

Further, for example, patent document 3 proposes a nanofiber filter containing moniliform fibers in which nanofibers and beads are integrated. The filter medium of patent document 3 is for use in an air filter, and the average fiber diameter of the moniliform fibers is 0.001 to 0.13 μm. It is described that the bead diameter of the moniliform fiber is 2 to 10 times the average fiber diameter, and the bead diameter of the moniliform fiber shown in the examples is about several hundred nm. Patent document 3 discloses an air filter medium containing such moniliform fibers, which can ensure a desired distance between fibers while reducing the fiber diameter, and which achieves high performance of an air filter containing a filter medium using such moniliform fibers. However, the air filter medium of patent document 3 has room for further improvement in terms of reduction in pressure loss and increase in lifetime of the air filter.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open No. 2006-341233

Patent document 2: japanese patent laid-open No. 2009-057655

Patent document 3: japanese patent laid-open No. 2010-247035

Disclosure of Invention

Problems to be solved by the invention

The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a filter medium having high dust collection efficiency, low pressure loss, and a long life, and a filter material used for the filter medium.

Means for solving the problems

The present inventors have made extensive studies to solve the above problems, and found that a filter material of a composite structure including ultrafine fibers and beads is not sufficiently effective in improving the performance of an air filter when the beads are too small, focusing on the size of the beads. Further, it was confirmed that: the size of the beads and hence the content of the beads greatly affect the performance of the filter. As a result of further studies, it was found that a composite structure in which beads having a size in a specific range are contained in a matrix of ultrafine fibers at a density in a specific range can provide a filter medium having a high dust collection efficiency, a low pressure loss, and a long life, and it was confirmed that the composite structure can be produced at a reasonable process and cost by adjusting the material and conditions of electrospinning, thereby completing the present invention.

The present invention has the following structure.

[1]A composite structure comprising ultrafine fibers having a fiber diameter of less than 500nm and beads, wherein the outermost surface of the composite structure comprises 500 particles/mm²The above beads having a diameter of 5 μm or more.

[2] The composite structure according to [1], wherein the ultrafine fibers and the beads are the same component.

[3] The composite structure according to [1] or [2], wherein 50% or more of the ultrafine fibers having a fiber diameter of 200nm or less are contained in the entire fibers.

[4] The composite structure according to any one of [1] to [3], wherein 5% or more of fine fibers having a fiber diameter of 500nm or more are further contained with respect to the entire fibers.

[5] A filter comprising the composite structure according to any one of [1] to [4 ].

[6] A manufacturing method of a composite structure, the composite structure according to any one of [1] to [4] being manufactured, the manufacturing method comprising:

a step for preparing a spinning solution in which at least one resin selected from the group consisting of polyvinylidene fluoride, polyamide, polyurethane, and polylactic acid is dissolved in a solvent; and

and a step of spinning the spinning solution by an electrospinning method to obtain a composite structure comprising ultrafine fibers having a fiber diameter of less than 500nm and beads.

ADVANTAGEOUS EFFECTS OF INVENTION

By using the composite structure of the present invention, a filter medium having a high dust collection efficiency, a low pressure loss, and a long life can be produced at a reasonable cost.

Drawings

Fig. 1 is a scanning electron microscope image of a composite structure (example 1) of the present invention.

Fig. 2 is a scanning electron microscope image of the composite structure (example 2) of the present invention.

Fig. 3 is a scanning electron microscope image of the composite structure (example 3) of the present invention.

Fig. 4 is a scanning electron microscope image of the composite structure (example 4) of the present invention.

Fig. 5 is a scanning electron microscope image of the composite structure (example 5) of the present invention.

FIG. 6 is a scanning electron microscope image of a fiber layer (comparative example 1) outside the scope of the present invention.

FIG. 7 is a SEM image of a fiber layer (comparative example 2) outside the scope of the present invention.

Detailed Description

The present invention will be described in detail below.

The composite structure of the present invention is characterized in that: comprises ultrafine fibers having a fiber diameter of less than 500nm and beads, and 500 particles/mm are contained in the outermost surface of the composite structure²The above beads having a diameter of 5 μm or more. It is considered that the composite structure of the present invention can provide a filter medium having a high dust collection efficiency, a low pressure loss, and a long life because the distance between ultrafine fibers can be appropriately maintained by the presence of a large amount of relatively large beads having a diameter of 5 μm or more in the matrix of ultrafine fibers. From this viewpoint, the number of beads having a diameter of 5 μm or more is more preferably 1000 beads/mm²More preferably 1500 pieces/mm²The above. The composite structure of the present invention is a film-like object having a substantially opaque and smooth surface when observed with naked eyes, and when observed by magnification using an electron microscope or the like, a structure in which a large number of beads are dispersed in a matrix of ultrafine fibers is observed. In the present specification, the term "ultrafine fiber" means a fiber having a fiber diameter of less than 500nm, and hereinafter, unless otherwise specified, "ultrafine fiber" means a fiber having a fiber diameter of less than 500 nm.

The ultrafine fibers contained in the composite structure of the present invention are not particularly limited as long as the effect of the present invention is obtained, and preferably 50% or more, more preferably 70% or more, and even more preferably 80% or more of the entire fibers are contained. When the proportion of the fibers having a fiber diameter of 200nm or less is 50% or more, the specific surface area of the ultrafine fibers becomes large, and when a composite structure is used as a filter medium, high filter performance such as low pressure loss, high collection efficiency, and the like can be obtained. The ratio of the fibers described herein is a ratio (%) of the number of fibers having a predetermined fiber diameter to the total number (number) of all the fibers.

The average fiber diameter of all the fibers contained in the composite structure of the present invention is not particularly limited as long as the effect of the present invention is obtained, and is preferably in the range of 10nm to 500nm, more preferably in the range of 20nm to 300nm, and still more preferably in the range of 30nm to 100 nm. When the average fiber diameter is 500nm or less, the specific surface area becomes large, and when a composite structure is used as a filter medium, high filter performance such as low pressure loss, high collection efficiency, and the like can be obtained. On the other hand, as the fiber diameter decreases, the strength per 1 fiber decreases, and there is a possibility that the fiber will break when processed into a filter or used, and if the average fiber diameter is 10nm or more, sufficient monofilament strength can be obtained. The coefficient of variation of the fiber diameter with respect to all the fibers contained in the composite structure is not particularly limited, and may be less than 0.5, or may be 0.5 or more. If the coefficient of variation in fiber diameter is less than 0.5, the proportion of fibers that effectively act on dust collection increases, and high collection efficiency can be obtained with a small amount of fibers. When the coefficient of variation of the fiber diameter is 0.5 or more, the interval between fibers is increased, and the life of the filter can be increased. The composite structure of the present invention may use fibers having a small coefficient of variation of fiber diameter (for example, less than 0.5, preferably less than 0.3), and preferably includes fibers having different fiber diameters, depending on the intended use, performance, and the like.

The composite structure of the present invention has 500 pieces/mm contained in the outermost surface thereof²The above beads having a diameter of 5 μm or more are not particularly limited, and the average diameter of the beads contained in the composite structure is preferably in the range of 3 μm to 30 μm, and more preferably in the range of 5 μm to 20 μm. When the average diameter is 3 μm or more, high filter performance such as low pressure loss and long life can be obtained when the composite structure is used as a filter medium, and therefore, it is preferable that the average diameter is 30 μm or less because the distance between the ultrafine fibers is not excessively increased, and the composite structure can maintain high strength and is less likely to break when processed into a filter. The diameter of the beads can be measured or calculated by measuring the diameter of the beads present on the outermost surface of the composite structure using a scanning electron microscope and image analysis software. More specifically, the method of measuring the diameter of the beads is described in the example section.

The beads contained in the composite structure of the present invention are spherical, spindle-shaped, or blocks having a form similar to these, and can be observed, for example, with an electron microscope. The beads themselves may be formed of one bead, or may be substantially spherical blocks having irregularities on the surface, which are formed by aggregating and integrating a large number of finer particles. In order to obtain beads having a relatively large size, a large number of fine particles are preferably aggregated and integrated into a shape. When the beads are spindle-shaped, the minor axis length of the spindle is defined as the diameter of the beads. The content of the beads is calculated from the number of beads per unit area present on the outermost surface of the composite structure. The composite structure of the present invention has a structure in which a large number of beads are dispersed in a three-dimensional matrix of fibers made of ultrafine fibers, and when calculating the content of the beads, the number of beads present on only the outermost surface is counted to calculate the content per area.

In the composite structure of the present invention, the ultrafine fibers and the beads may be present independently of each other, and the beads may be held by the beads entering into the voids of the matrix formed of the ultrafine fibers, or the beads may be formed by a part of the ultrafine fibers being swollen, that is, the fibers and the beads may be integrally connected (in the form of beads), or both of these forms may be present in a mixed form. Typically, the beads are present in a mixture in a matrix of ultrafine fibers, and in a mixture in a mode of moniliform connection.

The ultrafine fibers and the beads may be the same component or different components, and from the viewpoints of uniformity of the composite structure, stability during production, and the like, the same component is preferable, and specifically, the same component resin is preferable. Such a resin is not particularly limited, and examples thereof include: polyvinyl alcohol, polyethylene glycol, polyethylene oxide, polyvinyl pyrrolidone, polyethylene, polypropylene, polyethylene terephthalate, polylactic acid, polyamide, polyurethane, polystyrene, polysulfone, polyethersulfone, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyglycolic acid, polycaprolactone, polyvinyl acetate, polycarbonate, polyimide, polyetherimide, cellulose derivatives, chitin (chitin), chitosan, collagen, gelatin, and copolymers thereof. From the viewpoint of ease of bead formation, polyvinylidene fluoride, polyamide, polyurethane, and polylactic acid are preferable, and polyvinylidene fluoride is more preferable. The weight average molecular weight of the resin is not particularly limited, but is preferably within a range of 10,000 to 10,000,000, more preferably within a range of 50,000 to 1,000,000, and still more preferably within a range of 300,000 to 600,000. When the weight average molecular weight is 10,000 or more, the formability of ultrafine fibers and beads is excellent, and therefore, it is preferable that the weight average molecular weight is 10,000,000 or less, since the solubility and thermoplasticity are excellent, and the processing becomes easy.

The composite structure of the present invention may further contain fine fibers having an average fiber diameter larger than the average fiber diameter of the ultrafine fibers, in addition to the ultrafine fibers and the beads. When the fine fibers are contained, the fine fibers may be stacked on the composite structure containing the ultrafine fibers and the beads, or the fine fibers may be mixed. By containing the fine fibers, the strength of the composite structure is increased, and the composite structure can be processed into a filter without being easily broken. From such a viewpoint, the case where fine fibers are mixed in the composite structure is preferable because the strength of the composite structure is improved. The average fiber diameter of the fine fibers is not particularly limited, but is preferably in the range of 500nm to 5000nm, and more preferably in the range of 600nm to 2000 nm. When the average fiber diameter of the fine fibers is 500nm or more, not only the strength of the composite structural fabric is improved and the processability is improved, but also the distance between the fibers of the fine fibers is increased, and when the composite structural fabric is used as a filter medium of a filter, clogging due to collected dust is difficult, and the filter can have a long life. If the average fiber diameter of the fine fibers is 5000nm or less, even if the weight per unit area is relatively low, an effect according to the use can be obtained, and the thinning of the filter and the improvement of the productivity can be realized. The content of fine fibers having a fiber diameter of 500nm or more is preferably 5% or more, more preferably 10% or more, based on the entire fibers. The coefficient of variation of the fiber diameter of the fine fibers is not particularly limited, but is preferably 0.5 or less, and more preferably 0.3 or less. If the coefficient of variation of the fine fibers is 0.5 or less, the effect of improving the strength of the composite even with a low basis weight can be obtained, which is in accordance with the use, and therefore, the filter can be made thinner and smaller.

The resin of the fine fiber is not particularly limited, and a resin having the same composition as the fine fiber may be used, or a different type of component may be used. The combination of different types of resins is not particularly limited, and examples thereof include: non-elastomeric resin/elastomeric resin, high melting point resin/low melting point resin, high crystalline resin/low crystalline resin, hydrophilic resin/water repellent resin, and the like. For example, by combining microfine fibers containing a non-elastomeric resin with microfine fibers containing an elastomeric resin, the composite structure can be provided with stretchability, and the effect of suppressing breakage due to bending is exhibited when the composite structure is subjected to pleating (pleats) processing for use as an air filter. The elastomer resin is not particularly limited, and may be exemplified by: polyolefin-based elastomers, polyester-based elastomers, polyurethane-based elastomers, polyamide-based elastomers, fluorine-based elastomers, and the like. Further, by combining the ultrafine fibers containing a high-melting-point resin and the fine fibers containing a low-melting-point resin and performing heat treatment at a temperature lower than the melting point of the ultrafine fibers and equal to or higher than the melting point of the fine fibers, the ultrafine fibers and the fine fibers or the fine fibers are fused to each other, and thereby the processing strength can be improved while maintaining the collection efficiency of the obtained composite structure. Further, when the fine fibers are integrated with the base material or another layer, the fine fibers and the base material or another layer can be welded to each other, and therefore, the strength of the integrated laminate can be further improved. The combination of the high-melting-point resin and the low-melting-point resin is not particularly limited, and the difference in melting point is preferably 10 ℃ or more, and more preferably 20 ℃ or more. The combination of such resins is not particularly limited, and examples thereof include: copolymers of polyvinylidene fluoride/vinylidene fluoride with hexafluoropropylene, nylon 66/nylon 6, poly-L-lactic acid/poly-D, L-lactic acid, polypropylene/polyethylene, polyethylene terephthalate/polypropylene, and the like. In addition, by combining the ultrafine fibers containing a highly crystalline resin with the fine fibers containing a low crystalline resin, dimensional stability can be imparted to the composite structure, and when used as a filter medium for a filter, the filter performance can be maintained even under a wide range of temperature and humidity environments. The highly crystalline resin is not particularly limited, and examples thereof include: polyvinylidene fluoride, nylon 6, nylon 66, polyethylene, polypropylene, polyethylene terephthalate, polylactic acid, polyvinyl alcohol, polyethylene glycol, and the like. The low-crystalline resin is not particularly limited, and examples thereof include: copolymers of vinylidene fluoride and hexafluoropropylene, copolymers of ethylene and propylene, poly-D, L-lactic acid, polystyrene, polysulfone, polyethersulfone, polycarbonate, polymethylmethacrylate, polyurethane, polyvinyl acetate, and the like.

The weight per unit area of the composite structure of the present invention is not particularly limited, but is preferably 0.1g/m²～20g/m²More preferably 1g/m²～15g/m²More preferably 3g/m²～10g/m²The range of (1). If the weight per unit area is 0.1g/m²As described above, the filter medium as a filter has a long life, a high collection efficiency, and an improved strength for processing into a filter, and the weight per unit area is 20g/m²Hereinafter, the pressure loss can be reduced as a filter medium of the filter.

The average flow pore diameter of the composite structure of the present invention is not particularly limited, but is preferably in the range of 1.0 μm to 10.0. mu.m, and more preferably in the range of 1.5 μm to 5.0. mu.m. When the average flow pore diameter is 1.0 μm or more, clogging of dust is less likely to occur as a filter medium of the filter, and a long-life filter can be obtained. Further, it is preferable that the average flow rate pore diameter is 10.0 μm or less because a high collection efficiency can be obtained.

The composite structure of the present invention is not particularly limited, and may be laminated and integrated with other substrates such as nonwoven fabric, woven fabric, net (net), microporous film, and the like. By laminating and integrating the composite structure with the base material, a laminate in which the characteristics of the composite structure and the base material are combined can be obtained. When used as a filter medium of an air filter, the base material is preferably a nonwoven fabric from the viewpoint of processability or air permeability. The composite structure integrated with the base material can exhibit not only filter characteristics derived from the composite structure, such as high dust collection efficiency, high ventilation and liquid permeability characteristics, and long life characteristics that maintain high ventilation and liquid permeability characteristics even when dust is collected, but also excellent water and oil repellency characteristics, which are caused by the composite structure having a surface with very fine irregularities and a high void structure. Examples of the characteristics of the substrate combined with the composite structure include mechanical strength, abrasion resistance, drape workability, adhesion characteristics, filter characteristics, and the like, and the substrate having such characteristics can be appropriately selected depending on the application and form of the composite structure. The method of laminating and integrating the composite structure and the base material is not particularly limited, and the composite structure and the base material produced separately may be integrated by an adhesive or thermal welding, may be integrated by directly forming the composite structure on the base material, or may be integrated by directly forming the composite structure on the base material and then performing heat treatment.

When the composite structure of the present invention is further laminated with a substrate, the weight per unit area of the substrate is not particularly limited, and may be, for example, 5g/m²～200g/m²The range of (1). If the basis weight is 5g/m²As described above, the composite structure can be provided with a processing strength while suppressing shrinkage, crinkling, curling (curl) and the like, and when it is 200g/m²The air filter can be made thinner or improved in productivity as described below. If it is 60g/m²～120g/m²The range of (3) is more preferable because sufficient processing strength can be provided and the thickness can be reduced. The specific volume of the base material is not particularly limited, but is preferably 5cm from the viewpoint of improving the adhesion between the base material and the composite structure and reducing the friction between the base material and the composite structure³A value of less than or equal to g, and more preferably 3cm³The ratio of the carbon atoms to the carbon atoms is less than g.

The material constituting the base material is not particularly limited as long as it is appropriately selected according to need. When a polyolefin-based material such as polypropylene or polyethylene is used as the material, the material has a characteristic of excellent chemical resistance, and can be suitably used for applications such as liquid filters requiring chemical resistance. Further, when a polyester-based material such as polyethylene terephthalate, polybutylene terephthalate, polylactic acid, or a copolymer containing these as a main component is used as a material, the material is excellent in pleating properties, and therefore, the material can be suitably used for applications such as an air filter requiring pleating. The polyester-based material has high wettability with an adhesive component such as a hot melt, and can be suitably used in the case of processing a product by hot melt adhesion. The base material having a surface made of a polypropylene-based or polyester-based material can be suitably used because it can be bonded by ultrasonic waves.

When the composite structure and the substrate are integrated by heat treatment, the substrate is not particularly limited, and a nonwoven fabric including heat-fusible composite fibers including a low-melting-point component and a high-melting-point component is preferably used. The combination, composite form and cross-sectional shape of the raw material of the heat-fusible composite fiber are not particularly limited, and known ones can be used. Examples of combinations of raw materials include: copolymerized polyethylene terephthalate and polyethylene terephthalate, copolymerized polyethylene terephthalate and polypropylene, high-density polyethylene and polyethylene terephthalate, copolymerized polypropylene and polypropylene, copolymerized polypropylene and polyethylene terephthalate, and the like. Further, in view of availability of raw materials and the like, it is preferable to exemplify: copolymerized polyethylene terephthalate and polyethylene terephthalate, high density polyethylene and polypropylene, high density polyethylene and polyethylene terephthalate, and the like. Examples of the composite form of the fiber cross section of the heat-fusible composite fiber include a core-sheath type, an eccentric core-sheath type, and a side-by-side type. The cross-sectional shape of the fiber is not particularly limited, and may be any cross-sectional shape such as an oval, hollow, triangular, rectangular, octagonal, or other irregular cross-sectional shape, in addition to a general circular shape.

The laminate comprising the composite structure and the substrate may further comprise at least one layer selected from the group consisting of a nonwoven fabric, a woven fabric, a mesh, and a microporous membrane laminated on at least one surface or both surfaces of the laminate. By laminating at least one layer selected from the group consisting of a nonwoven fabric, a woven fabric, a mesh, and a microporous film on the composite structure surface of the laminate, the composite structure surface is not exposed to the surface, and thus the processability is further improved. Further, by laminating at least one layer selected from the group consisting of a nonwoven fabric, a woven fabric, a mesh and a microporous membrane as a pre-trapping layer on at least one surface of the laminate, the filter life can be further improved. The method for producing the laminate by laminating at least one layer selected from the group consisting of a nonwoven fabric, a woven fabric, a web and a microporous membrane on the laminate is not particularly limited, and examples thereof include: a method in which a laminate is produced by directly forming a composite structure on a substrate, and at least one layer selected from the group consisting of a nonwoven fabric, a woven fabric, a web, and a microporous membrane is further laminated on the laminate and integrated in a subsequent step; or a method in which at least one layer selected from the group consisting of a nonwoven fabric, a woven fabric, a web, and a microporous film is integrated with a substrate to form a sheet, and a composite structure is directly formed on the sheet thus formed to be integrated. The method of integration is not particularly limited, and the following methods can be employed: thermal compression bonding treatment using a heated smooth roll or an embossing roll, bonding treatment using a hot melt or a chemical adhesive, thermal bonding treatment using circulating hot air or radiant heat, and the like.

The composite structure of the present invention may be subjected to electret processing, antistatic processing, water repellent processing, hydrophilic processing, antibacterial processing, ultraviolet absorption processing, near infrared absorption processing, antifouling processing, and the like according to the purpose, within a range in which the effects of the present invention are not significantly impaired.

The composite structure of the present invention is not particularly limited, and can be suitably used as a filter medium for a filter. When the composite structure of the present invention is used as a filter medium, the use thereof is not particularly limited, and the composite structure may be an air filter used in air conditioning, a clean room, or the like, or a liquid filter used for filtration of drainage, paint, abrasive particles, or the like. The shape of the filter is not particularly limited, and may be a flat membrane filter, a pleated filter after pleating, or a depth filter (depth filter) rolled into a cylindrical shape. Since the composite structure of the present invention contains ultrafine fibers and a large amount of beads, a filter medium having a high dust collection efficiency, a low pressure loss, and a long life as a filter can be provided.

When the composite structure and the laminate of the present invention are used as a filter medium of an air filter, the pressure loss when air is passed at a flow rate of 5.3 cm/sec is preferably in the range of 10Pa to 300Pa, more preferably in the range of 20Pa to 200Pa, and still more preferably in the range of 30Pa to 150 Pa. When the pressure loss is 10Pa or more, sufficient collection efficiency can be obtained, and when it is 300Pa or less, effects such as reduction in power consumption when used as a filter medium of an air filter, reduction in load on a fan, and the like are exhibited. Further, air containing particles having a particle diameter of about 0.3 μm was made to flow at a flow rate of 5.3The collection efficiency of the particles at the passage of cm/sec is preferably 90% or more, more preferably 99% or more. Further, the PF value (log (1-collection efficiency/100)/pressure loss × 1000) is preferably 20 or more, and more preferably 25 or more. The PF value is a value used as an index indicating the magnitude of the trapping performance of the air filter medium, and the higher the performance, the larger the PF value. The lifetime of the air filter is not particularly limited, and can be evaluated by, for example, the weight of particles adhering to the air filter when the air containing particles having a particle diameter of about 0.3 μm is continuously ventilated at a flow rate of 5.3 cm/sec and the pressure loss is increased by 250 Pa. The larger the adhering weight, the longer the life of the air filter medium. The trapping particles may be solid particles such as sodium chloride, or liquid particles of poly- α -olefin (poly- α -olefin) or dioctyl phthalate. The weight of the poly-alpha-olefin to be adhered is not particularly limited, but is preferably 50mg/100cm²The concentration is preferably 100mg/100cm²The above. The collection efficiency, pressure loss, PF value, and weight attached can be adjusted by appropriately changing the average fiber diameter of the ultrafine fibers, the average diameter or content of the beads, the average fiber diameter or proportion of the fine fibers when the fine fibers are contained, the basis weight of the composite structure, and the like.

Although not particularly limited, the composite structure of the present invention is preferably produced by an electrospinning method. By using the electrospinning method, very fine ultrafine fibers and beads can be produced at a time, and a composite structure exhibiting excellent filter characteristics can be obtained by a reasonable process without requiring a special apparatus or special conditions. The electrospinning method is a method in which a spinning solution is discharged and an electric field is applied to fibrillate the discharged spinning solution, and ultrafine fibers of a submicron order are collected in a nonwoven fabric form on a collector (collector). The method of electrospinning is not particularly limited, and may be a generally known method, for example, a needle method using 1 or more needles, an air blow (air blow) method in which a gas flow is sprayed to the tip of a needle to improve productivity per 1 needle, a multi-hole spinneret method in which a plurality of solution discharge holes are provided in 1 spinneret (spinneret), a free surface (free surface) method using a cylindrical or spiral rotating electrode half-immersed in a solution tank, an electro bubble (electro bubble) method in which electrospinning is performed using bubbles generated on the surface of a polymer solution by supplying air as a starting point, and the like, and may be appropriately selected in consideration of the quality, productivity, or workability of the desired ultrafine fibers or first beads. As the electrospinning method of the composite structure in the present invention, in order to form beads well, a needle method, an air blowing method, and a multi-hole spinneret method are particularly preferable, which can control the ejection amount per 1 spinning nozzle (jet).

The spinning solution is not particularly limited as long as it has spinnability, and a solution in which a resin is dispersed in a solvent, a solution in which a resin is dissolved in a solvent, a solution in which a resin is melted by heat or laser irradiation, or the like can be used. In order to obtain a very fine and uniform fiber, it is preferable to use a solution obtained by dissolving a resin in a solvent as a spinning solution.

Examples of the solvent for dispersing or dissolving the resin include: water, methanol, ethanol, propanol, acetone, N-dimethylformamide, N-dimethylacetamide, dimethylsulfoxide, N-methyl-2-pyrrolidone, toluene, xylene, pyridine, formic acid, acetic acid, tetrahydrofuran, dichloromethane, chloroform, 1,1,2, 2-tetrachloroethane, 1,1,1,3,3, 3-hexafluoroisopropanol, trifluoroacetic acid, a mixture of these, and the like. The mixing ratio in the mixing is not particularly limited, and may be appropriately set in consideration of the required spinnability or dispersibility and the physical properties of the obtained fiber.

The spinning solution may further contain a surfactant for the purpose of improving the stability of electrospinning or fiber formation. Examples of the surfactant include: anionic surfactants such as sodium lauryl sulfate, cationic surfactants such as tetrabutylammonium bromide, and nonionic surfactants such as polyoxyethylene sorbitan monolaurate. The concentration of the surfactant is preferably in the range of 5 wt% or less with respect to the spinning solution. The content of 5% by weight or less is preferable because the effect corresponding to the use can be improved. In order to obtain the composite structure of the present invention, it is also preferable to prepare a spinning solution containing no surfactant and perform electrospinning.

In the range not significantly impairing the effects of the present invention, components other than the above-described components such as hydrophilizing agents, water-repelling agents, weather-resistant agents, and stabilizers may be contained as components of the spinning solution. In particular, when the material of the composite structure contains a water-repellent oil-repellent component, the energy of adhesion of water droplets on the surface thereof is extremely low, and the adhered dust can be easily cleaned with water or the like. The water-and oil-repellent agent is not particularly limited as long as it exerts an effect of reducing the adhesion energy, and examples thereof include a silicon-based silane compound, a fluorine-based silane compound, fluorooctylsilsesquioxane, a fluorine-modified polyurethane, and a silicon-modified polyurethane resin. The concentration of the water-and oil-repellent agent is preferably in the range of 0.1 to 20% by weight, more preferably 1 to 15% by weight, relative to the resin. The water-repellent and oil-repellent agent concentration is preferably not more than 0.1% by weight because the water-repellent and oil-repellent properties are improved, and preferably not more than 20% by weight because the effects according to the use can be improved.

The method for preparing the spinning solution is not particularly limited, and stirring, ultrasonic treatment, or the like can be exemplified. The order of mixing is not particularly limited, and the mixing may be carried out simultaneously or sequentially. The stirring time for preparing the spinning solution by stirring is not particularly limited as long as the resin is uniformly dissolved or dispersed in the solvent, and may be, for example, about 1 to 24 hours.

In order to obtain a composite structure containing ultrafine fibers and beads by electrospinning, the viscosity of the spinning solution is preferably set to a range of 10cP to 10,000cP, more preferably 50cP to 8,000 cP. When the viscosity is 10cP or more, spinnability and formability for forming ultrafine fibers or beads can be obtained, and when the viscosity is 10,000cP or less, a spinning solution can be easily prepared and discharged. The viscosity of the spinning solution can be adjusted by appropriately changing the molecular weight or concentration of the resin, the kind of the solvent, or the mixing ratio.

The temperature of the spinning solution is not particularly limited, and may be normal temperature, or may be higher or lower than normal temperature by heating or cooling. Examples of a method of discharging the spinning solution include a method of discharging the spinning solution filled in a syringe (syring) from a nozzle using a pump. The inner diameter of the nozzle is not particularly limited, but is preferably in the range of 0.1mm to 1.5 mm. The discharge rate is not particularly limited, but is preferably 0.1mL/hr to 10 mL/hr.

The method of applying an electric field to the spinning solution is not particularly limited as long as the electric field can be formed between the nozzle and the collector, and for example, a high voltage may be applied to the nozzle to ground the collector. The voltage to be applied is not particularly limited as long as the fiber can be formed, and is preferably in the range of 5kV to 100 kV. The distance between the nozzle and the collector is not particularly limited as long as the ultrafine fibers and the first beads can be formed, and is preferably in the range of 5cm to 50 cm. The collector is not particularly limited as long as it can collect the spun composite structure, and the raw material, shape, and the like thereof are not particularly limited. As a material of the collector, a conductive material such as metal can be suitably used. The shape of the collector is not particularly limited, and examples thereof include a flat plate shape, a roll shape, a shaft (draft) shape, a conveyor (conveyor) shape, and the like. The fiber aggregate can be collected in a sheet form if the collector has a flat plate shape or a roll shape, or in a tubular form if the collector has a shaft shape. In the case of a belt conveyor, a fiber aggregate collected in a sheet form can be continuously produced.

Examples

The following examples are for illustrative purposes only. The scope of the present invention is not limited to the present embodiment.

The measurement methods and definitions of the physical property values shown in the examples are shown below.

< fiber diameter of very fine fiber >

The composite structure was observed at a magnification of 10,000 to 30,000 times using a scanning electron microscope (SU-8000) manufactured by hitachi gmbh, the diameter (fiber diameter) of 500 or more fibers was measured using image analysis software, and the average value was defined as the average fiber diameter. The variation coefficient is calculated by dividing the standard deviation by the average value. The proportion (%) of fibers having a fiber diameter of 200nm or less is calculated by dividing the number of fibers having a fiber diameter of 200nm or less by the total number of fibers and multiplying by 100, and the proportion (%) of fibers having a fiber diameter of 500nm or more is calculated by dividing the number of fibers having a fiber diameter of 500nm or more by the total number of fibers and multiplying by 100.

< diameter of beads >

The surface of the composite structure was observed at 200-2,000 times at an acceleration voltage of 3kV using a scanning electron microscope (SU-8000) manufactured by hitachi gmbh, and the diameters of 50 or more beads present on the outermost surface were measured using image analysis software, and the average value thereof was defined as the average diameter. The content of beads having a diameter of 5 μm or more was calculated by dividing the number of beads having a diameter of 5 μm or more by the image area. The diameter of the spindle-shaped beads is defined as the minor axis length.

< mean flow pore size >

The mean flow pore diameter (Japanese Industrial Standards (JIS) K3822) was measured using a Capillary flow pore meter (Capillary flow pore meter) (CFP-1200-A) manufactured by POROUS Material (POROUS MATERIAL) Co.

< Filter Performance >

Using an automatic filter efficiency measuring apparatus (Model 8130) manufactured by TSI, poly-alpha-olefin (particle diameter: 0.3 μm (number center diameter) and particle concentration: 150mg/m were measured³) The pressure loss and the trapping efficiency were measured at a flow rate of 5.3 cm/sec when the composite structure was passed through a laminate obtained by laminating the composite structure on a substrate.

In addition, the poly-alpha-olefin (particle diameter: 0.3 μm (number center diameter) and particle concentration: 150mg/m were measured using an automatic filter efficiency measuring apparatus (Model 8130) manufactured by TSI Inc³) The filter life was determined by the weight of particles adhering to the filter when the air was continuously blown at a measurement flow rate of 5.3 cm/sec and the pressure loss increased by 250 Pa. The larger the weight of the particles adhered before the pressure loss increased by 250Pa, the longer the filter life.

[ example 1]

Preparation of a composition comprising polyvinylidene fluoride manufactured by Arkema (ARKEMA)Spinning solution 1 of 16 parts by weight of ethylene (Kynar 761; melting point 165 ℃ C.) and 84 parts by weight of N, N-dimethylformamide. As the collecting part, a drum-shaped rotary collector having a diameter of 200mm was used, and a nonwoven fabric made of polyethylene terephthalate (basis weight: 80 g/m) was attached to the surface of the collector²) As a substrate. Then, 1 needle with an inner diameter of 0.22mm was installed in the rotation direction and the horizontal direction of the rotary collector. The spinning solution 1 was supplied to the tip of the needle at 2.0mL/hr, and electrostatic spinning was performed by applying a voltage of 35kV to the needle. The distance between the needle tip and the grounded collector was set to 20 cm. The spinning was carried out for 90 minutes by setting the rotational speed of the drum-like rotating collector to 50rpm and traversing the needle in the perpendicular direction to the rotational direction at a width of 200mm and a speed of 100 mm/sec, thereby laminating a weight of 3.4g/m per unit area on the base material²The composite structure of (1). The laminate was subjected to a filter performance test. The fibers in the composite structure had an average fiber diameter of 90nm, a coefficient of variation of the fiber diameter of 0.47, a proportion of ultrafine fibers having a fiber diameter of 200nm or less of 98.3%, and a proportion of fine fibers having a fiber diameter of 500nm or more of 0%. Further, the number of beads having an average diameter of 5.6 μm and a diameter of 5 μm or more in the composite structure was 2709 beads/mm². The average flow pore diameter of the obtained laminate was 2.1 μm, the pressure loss with respect to the filter performance was 69.7Pa, the trapping efficiency was 99.67%, the PF value was 35.5, and the dust holding amount was 57mg/100cm². Fig. 1 shows a scanning electron microscope image of the obtained composite structure.

[ example 2]

A spinning solution 2 containing 16 parts by weight of polyvinylidene fluoride (Kynar (Kynar) 761; melting point 165 ℃ C., manufactured by Arkema (ARKEMA) Inc., 67.2 parts by weight of N, N-dimethylformamide, and 16.8 parts by weight of acetone was prepared. A weight per unit area of 3.4g/m was laminated on a base material in the same manner as in example 1, except that the spinning solution 2 was used²The composite structure of (1). The laminate was subjected to a filter performance test. The fibers in the composite structure are fine fibers having an average fiber diameter of 200nm, a coefficient of variation of the fiber diameter of 0.41, a proportion of ultrafine fibers having a fiber diameter of 200nm or less of 51.1%, and a proportion of ultrafine fibers having a fiber diameter of 500nm or moreThe proportion of (B) is 0%. Further, the number of beads having an average diameter of 6.1 μm and a diameter of 5 μm or more in the composite structure was 1696 beads/mm². The average flow pore diameter of the obtained laminate was 2.4 μm, the pressure loss with respect to the filter performance was 74.7Pa, the trapping efficiency was 95.22%, the PF value was 17.7, and the dust holding amount was 121mg/100cm². Fig. 2 shows a scanning electron microscope image of the obtained composite structure.

[ example 3]

A spinning solution 3 for forming fine fibers was prepared, which contained 25 parts by weight of polyvinylidene fluoride (Kynar 2500-20; melting point 125 ℃ C., manufactured by Arkema (ARKEMA)), 37.5 parts by weight of N, N-dimethylformamide, and 37.5 parts by weight of tetrahydrofuran. As the collecting part, a drum-shaped rotary collector having a diameter of 200mm was used, and a nonwoven fabric made of polyethylene terephthalate (basis weight: 80 g/m) was attached to the surface of the collector²) As a substrate. Then, 2 needles with an inner diameter of 0.22mm were installed in the rotation direction and the horizontal direction of the rotary collector. The spinning solution 1 and the spinning solution 3 were supplied to the tip of the needle at a rate of 2.0mL/hr, and electrostatic spinning was performed by applying a voltage of 35kV to the needle. The distance between the needle tip and the grounded collector was set to 20 cm. The spinning was carried out for 90 minutes by setting the rotational speed of the drum-like rotating collector to 50rpm and traversing the needle in the perpendicular direction to the rotational direction at a width of 200mm and a speed of 100 mm/sec, thereby laminating a weight of 8.8g/m per unit area on the base material²The composite structure of (1). The laminate was subjected to a filter performance test. The fibers in the composite structure had an average fiber diameter of 250nm, a coefficient of variation of the fiber diameter of 1.14, a proportion of ultrafine fibers having a fiber diameter of 200nm or less of 72.6%, and a proportion of fine fibers having a fiber diameter of 500nm or more of 16.7%. Further, the number of beads having an average diameter of 5.6 μm and a diameter of 5 μm or more in the composite structure was 2709 beads/mm². The average flow pore diameter of the obtained laminate was 1.8 μm, the pressure loss with respect to the filter performance was 145.8Pa, the trapping efficiency was 99.96%, the PF value was 23.0, and the dust holding amount was 91mg/100cm². Even if the surface of the laminated body on the composite structure body side is rubbed, the fluffing does not occur, and the abrasion resistance is goodThe fuel consumption and the processability are very excellent. Fig. 3 shows a scanning electron microscope image of the obtained composite structure.

[ example 4]

A spinning solution 4 for forming fine fibers was prepared, which contained 30 parts by weight of polyvinylidene fluoride (Kynar) 2500-20; melting point 125 ℃ C., manufactured by Arkema (ARKEMA), 17.5 parts by weight of N, N-dimethylformamide, and 52.5 parts by weight of tetrahydrofuran. Then, a weight per unit area of 9.9g/m was laminated on the base material in the same manner as in example 3, except that the spinning solution 4 was used instead of the spinning solution 3²The composite structure of (1). The laminate was subjected to a filter performance test. The fibers in the composite structure had an average fiber diameter of 300nm, a coefficient of variation of the fiber diameter of 1.89, a proportion of ultrafine fibers having a diameter of 200nm or less of 85.7%, and a proportion of fine fibers having a diameter of 500nm or more of 10.1%. Further, the number of beads having an average diameter of 5.6 μm and a diameter of 5 μm or more in the composite structure was 2709 beads/mm². The average flow pore diameter of the obtained laminate was 2.2 μm, the pressure loss with respect to the filter performance was 114.3Pa, the trapping efficiency was 99.89%, the PF value was 25.8, and the dust holding amount was 113mg/100cm². Even if the surface of the friction laminate on the composite structure side is not fluffed, the abrasion resistance and the processability are excellent. Fig. 4 shows a scanning electron microscope image of the obtained composite structure.

[ example 5]

A spinning solution 5 was prepared which contained 20 parts by weight of polyvinylidene fluoride (Solifef) 6010; melting point 171 ℃ C., manufactured by Solvay Specialty Polymers, Inc., and 80 parts by weight of N, N-dimethylformamide. A weight per unit area of 4.3g/m was laminated on a base material in the same manner as in example 1, except that the spinning solution 5 was used²The composite structure of (1). The laminate was subjected to a filter performance test. The fibers in the composite structure had an average fiber diameter of 60nm, a coefficient of variation of the fiber diameter of 0.45, a proportion of ultrafine fibers having a fiber diameter of 200nm or less of 97.3%, and a proportion of fine fibers having a fiber diameter of 500nm or more of 0%. The beads in the composite structure had an average diameter of 8.5 μm or more and an average diameter of 5 μm or lessThe number of the beads on the surface is 1773/mm². The average flow pore diameter of the obtained laminate was 3.6 μm, the pressure loss was 44.0Pa, the trapping efficiency was 99.85%, the PF value was 64.2, and the dust holding amount was 150mg/100cm with respect to the filter performance². Fig. 5 shows a scanning electron microscope image of the obtained composite structure.

Comparative example 1

A spinning solution 6 containing 16 parts by weight of polyvinylidene fluoride (Kynar (Kynar) 761; melting point 165 ℃ C., manufactured by Arkema (ARKEMA) Inc., 84 parts by weight of N, N-dimethylformamide, and 0.05 part by weight of sodium lauryl sulfate was prepared. Then, a weight per unit area of 1.5g/m was laminated on the base material in the same manner as in example 1, except that the spinning solution 6 was used, and the distance between the needle tip and the grounded collector was set to 15cm, and the spinning time was set to 39 minutes²The fibrous layer of (2). The laminate was subjected to a filter performance test. The fibers in the fiber layer had an average fiber diameter of 90nm, a coefficient of variation of the fiber diameter of 0.49, a proportion of fibers having a diameter of 200nm or less of 86.2%, and a proportion of fibers having a diameter of 500nm or more of 0.7%. Further, the number of beads having an average diameter of 2.5 μm and a diameter of 5 μm or more in the fiber layer was 397 beads/mm². The average flow pore diameter of the obtained laminate was 0.9 μm, the pressure loss was 126.3Pa, the trapping efficiency was 99.55%, the PF value was 18.6, and the dust holding amount was 16mg/100cm with respect to the filter performance²The PF value is low and the service life is short. A scanning electron microscope image of the obtained fiber layer is shown in fig. 6.

Comparative example 2

A spinning solution 7 comprising 15 parts by weight of polyamide 6(1011 FB; melting point 220 ℃ C.) produced by Yujuxing, 42.5 parts by weight of formic acid and 42.5 parts by weight of acetic acid was prepared. Then, a spinning solution 7 was used, and a weight per unit area of 0.2g/m was laminated on the base material in the same manner as in example 1 except that the solution supply amount was set to 0.5mL/hr, the distance between the needle tip and the grounded collector was set to 7.5cm, and the spinning time was set to 24 minutes²The fibrous layer of (2). The laminate was subjected to a filter performance test. With respect to the fibers in the fiber layer, the average fiber diameter was 70nm, and the fibers wereThe coefficient of variation of the diameter was 0.25, the proportion of fibers having a diameter of 200nm or less was 100%, the proportion of fibers having a diameter of 500nm or more was 0%, and no beads were present. The average flow pore diameter of the obtained laminate was 0.6 μm, the pressure loss with respect to the filter performance was 125.0Pa, the trapping efficiency was 99.81%, the PF value was 21.8, and the dust holding amount was 5mg/100cm²The PF value is slightly high, but the life is very short. Fig. 7 shows a scanning electron microscope image of the obtained fiber layer.

The average fiber diameter of the fibers, the proportion of fibers of 200nm or less, the proportion of fibers of 500nm or more, the average diameter of the beads, the number of beads of 5 μm or more, the weight per unit area, the pressure loss, the collection efficiency, the PF value, and the filter life of the composite structures of examples 1 to 5, and the fiber layers of comparative examples 1 and 2 are shown in table 1.

[ Table 1]

As is clear from Table 1, 500 pieces/mm or less²Comparative examples 1 and 2, which contained 500 beads having a diameter of 5 μm or more, each mm²The beads having a diameter of 5 μm or more in examples 1 to 5 had a large PF value, a large dust holding amount, and a long filter life. In examples 3 and 4, which include microfine fibers having a fiber diameter of 200nm or less and fine fibers having a fiber diameter of 500nm or more, fuzz did not occur even when the composite structure surface was rubbed, and workability in processing into a filter such as crimping was excellent.

Industrial applicability

The composite structure and the filter medium using the same of the present invention have high dust collection efficiency, low pressure loss, long life, excellent balance of these effects, and excellent processing strength for processing into a filter, and therefore can be suitably used as a filter medium for an air filter or a filter medium for a liquid filter. In particular, it is possible to provide a filter medium suitable for an Air filter for household appliances such as a vacuum cleaner and an Air cleaner, an Air filter for Air conditioning for buildings, a High performance filter for industrial use, a High Efficiency Particulate Air (HEPA) filter for clean rooms, and an Ultra Low Permeability Air (ULPA) filter.