JP2010234285A - Filter medium for air filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filter medium for an air filter, for which safety and economical efficiency are compatibly achieved by substantially improving the catching performance of submicron particles, such as diesel exhaust particles, highly affecting the health of crew while achieving a dust collecting service life, that is a dust holding amount, longer than before, in the air filter for an automobile cabin. <P>SOLUTION: As for the filter medium for the air filter, in a laminated nonwoven fabric including at least two layers of an electret nonwoven fabric arranged so as to reduce a pore size stepwise, the average pore diameter of the upper layer electret nonwoven fabric is in the range of 50-150 μm, the average pore diameter of the lowest layer electret nonwoven fabric is in the range of 5-50 μm, respectively, and the average pore diameter of the upper layer side electret nonwoven fabric is 2-10 times of the average pore diameter of the lower layer side nonwoven fabric. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an air filter medium excellent in both fine dust collection performance and dust collection life.

  In an air filter application intended by the present invention, particularly an automobile cabin air filter, it is required to supply a large amount of air to a very small volume of filter space for processing, and therefore, it is necessary to keep the ventilation resistance of the filter medium low. The density of the filter medium could not be increased so much. For this reason, these air filters are excellent in the function of collecting a large amount of relatively large dust, but are not capable of collecting fine dust with high removal efficiency. However, the outside air actually taken into the car compartment contains various dusts, which vary greatly depending on the area and environment in which they are used. For example, in urban areas, the ratio of extremely fine particles due to automobile diesel exhaust gas and the like is high, while in the suburbs, the ratio of naturally derived particles such as pollen having a relatively large particle diameter is high. In recent years, research on the particle size of dust and health effects on the human body has progressed, and once microparticles of 2.5 μm or less and even ultrafine particles of 1 μm or less have been deposited deep in the lungs, they are not easily discharged outside the body. It is regarded as a problem that it can cause asthma and allergic diseases. For this reason, there is a need for an air filter that can prevent the intrusion of dusts with a wide particle size, from fine particles on the order of submicron to coarse particles, and can be used for a long time even if the particle size distribution changes. Those that satisfy all the characteristics have not been put into practical use.

  As filter media for air filters with improved fine dust removal performance, filter paper made from ultrafine fibers by a wet papermaking method, melt blown non-woven fabric, and microporous membrane laminated on a reinforced non-woven fabric have already been used. However, these filter materials for air filters are excellent in the efficiency of removing fine dust, but have a drawback that the pressure loss is high and clogging due to collected dust occurs early, resulting in a short life.

  As a method for extending the dust collection life, it has been proposed in the past to provide a density gradient in the thickness direction of the filter medium. The filter medium with a density gradient is formed so that the density of the filter medium changes from coarse to dense from upstream to downstream. Examples of these filter media are those in which density control is performed by increasing the number of thick fibers on the upstream side and increasing the number of thin fibers on the downstream side with respect to the fiber diameter forming the layer (Patent Document 1). Moreover, what sets the hole diameter of the nonwoven fabric of two layers of an upstream side and a downstream side to the predetermined range (patent document 2) etc. are mentioned. However, since these density gradient filter media depend only on the mechanical collection efficiency, there is a limit to the compatibility between the fine dust collection efficiency and the pressure loss characteristics.

  On the other hand, as a technology for solving this problem, a filter medium for electret-treated air filters capable of effectively removing fine particles in the air by the electrostatic force of electric charges semi-permanently fixed to the fiber has been proposed. Compared to conventional filter media for air filters that rely only on collection efficiency, high collection efficiency is achieved with low pressure loss. Electret-treated filter media for air filters include non-woven fabrics made of polypropylene, polyethylene, and other non-woven fabrics, and cast films made of polypropylene, polyethylene, and other resins, and then electret films by charging. Are known. In these filter media for electret filters, clogging due to collected dust can be delayed by increasing the fiber diameter of the electret fibers and increasing the hole diameter, but at high wind speed conditions, the ability to collect by electrostatic force is fully demonstrated. In other words, the collection efficiency of fine dust is extremely reduced. Moreover, if dust collection progresses and the electrostatic collection power of the electret fibers decreases with time, the collection efficiency becomes extremely low, making it impractical. By reducing the diameter of the electret fiber and reducing the hole diameter, it is possible to suppress the wind speed dependence of the collection efficiency and extreme performance degradation after attenuation of electrostatic force, but eventually the collected dust is clogged in the electret layer. Becomes faster and the service life is shortened.

  It has already been proposed that a plurality of electret non-woven fabrics are laminated to form a dense structure. Examples of these include a fibrous sheet having a low surface charge density and a surface having a fineness. An electret filter (Patent Document 3) in which a fibrous sheet having a high charge density is laminated, a filter (Patent Document 4) made of a laminated electret nonwoven fabric in which the average fiber diameter is gradually reduced from the upstream side to the downstream side, and the like. Can be mentioned. However, these laminated electret nonwoven fabrics are simply a combination of the electret nonwoven fabric and the conventionally proposed concept of a dense structure, and for each layer of the laminated electret nonwoven fabric to meet the requirements of a specific filter application. The specific pore size and its relative relationship were not devised, and the problem of the present invention could not be solved completely.

JP-A-2-45484 Japanese Patent Laid-Open No. 5-49825 Japanese Unexamined Patent Publication No. 62-19718 JP 2002-18217 A

  An object of the present invention is to provide a filter medium for an air filter that is excellent in fine dust collection performance while having low pressure loss, and can have a very long dust collection life even in an environment where the particle size distribution of dust is greatly different. .

  The present invention for solving the above-described problems is characterized by taking one of the following configurations.

(1) A laminated electret nonwoven fabric including at least two layers of electret nonwoven fabric, wherein the average pore diameter of the lowermost electret nonwoven fabric and the upper electret nonwoven fabric is within the following range, and the average pore diameter of the upper electret nonwoven fabric is A filter medium for an air filter comprising a laminated electret nonwoven fabric that is 2 to 10 times the average pore diameter of the lowermost electret nonwoven fabric.
Upper layer side electret non-woven fabric The average pore diameter is 50 to 150 μm
Lowermost electret non-woven fabric average pore size is 5-50μm
(2) Further, the aggregate nonwoven fabric is laminated on the uppermost layer side, and the average pore diameter of the aggregate nonwoven fabric is 0.6 to 1.5 times the average pore diameter of the upper-layer electret nonwoven fabric ( 1) The filter medium for air filters as described.

  (3) The filter medium for an air filter according to claim 1 or 2, wherein the 0.3 µm particle collection efficiency at a surface wind speed of 6.5 m / min is 40% or more.

  (4) The filter medium for an air filter according to any one of (1) to (3), comprising functional particles.

  (5) The functional particles are in contact with the upper-layer electret nonwoven fabric, and at least 50% or more of the functional particles are distributed in a particle size range of 100 to 300 μm. Air filter media.

  (6) The filter material for an air filter according to any one of (1) to (5), wherein the laminated electret nonwoven fabric has a tensile strength in the MD direction of at least 10 N / 5 cm.

  (7) The filter material for an air filter according to any one of (1) to (6), wherein the laminated electret nonwoven fabric has a Gurley bending resistance in the MD direction of 2000 μN or more.

  (8) The air filter according to any one of (1) to (7), wherein at least one layer of the laminated electret nonwoven fabric is mainly composed of thermoplastic resin short fibers having different fineness and does not contain a binder resin. Filter media.

  (9) The filter medium for an air filter according to any one of (1) to (8), wherein at least one layer of the laminated electret nonwoven fabric is a heat fusion wet nonwoven fabric.

  (10) At least one layer of the laminated electret nonwoven fabric contains a hindered amine-based additive in a range of 0.01 to 3% by mass and is electret-treated by a hydrocharge method (1) to (9) The filter material for air filters in any one of.

  (11) An automobile cabin filter using the air filter medium according to any one of (1) to (10).

  The filter medium for an air filter according to the present invention is a laminated nonwoven fabric including at least two layers of electret nonwoven fabric, and the average pore diameter of the lowermost electret nonwoven fabric is 5 to 50 μm, and the average pore diameter of the upper electret nonwoven fabric is 50 to 150 μm. And the average pore diameter of the electret non-woven fabric on the upper layer side is adjusted to be 2 to 10 times the average pore diameter on the lower layer side, so that the contradictory properties of fine dust collection efficiency and dust collection life are extremely high. Can be balanced at the level. Furthermore, the effect can be further enhanced by laminating an aggregate nonwoven fabric on the electret laminated nonwoven fabric and setting the average pore diameter within 0.6 to 1.5 times that of the upper electret nonwoven fabric. Further, the filter medium for air filter can be loaded with functional particles between the nonwoven fabric layers to combine functions such as deodorization in addition to the dust collection function of the present invention.

  The filter medium for an air filter of the present invention is particularly suitable for an automobile cabin filter used in various regions and environments, and is not easily clogged even when subjected to a dust load having a different particle size distribution pattern. For this reason, for air filters that have improved dust collection life, the collection performance of sub-micron particles such as diesel exhaust particles, which has a significant health impact on passengers, has been improved dramatically, and both safety and economic efficiency have been achieved. Filter media can be provided.

It is a photograph which shows the cross section of an example of the filter medium for air filters of this invention.

  The air filter medium of the present invention has a laminated electret nonwoven fabric including at least two layers of electret nonwoven fabrics having different average pore diameters (pore sizes), and the laminated electret nonwoven fabric has an air flow from an upper electret nonwoven fabric that is an air inflow side. It arrange | positions so that the pore size may become small toward the electret nonwoven fabric of the lower layer side which is an outflow side. That is, it is necessary that the upper layer side electret non-woven fabric is coarser and the lower layer side electret non-woven fabric is finer.

  About the specific pore size of a laminated electret nonwoven fabric, it is preferable that the average pore diameter of the electret nonwoven fabric of the lowest layer side is 5-50 micrometers first, More preferably, it is 10-40 micrometers. When the average pore diameter is 5 μm or less, the collection efficiency is extremely high, but the airflow resistance is too large, and a predetermined air volume cannot be obtained in applications such as a cabin filter that requires a large air volume treatment. On the other hand, when the average pore diameter is 50 μm or more, the airflow resistance is small, but the reduction in the efficiency of collecting fine dust after high wind speed conditions and the disappearance of electrostatic force is large, and sufficient performance cannot be obtained.

  Furthermore, the upper-layer electret non-woven fabric laminated on the lowermost electret non-woven fabric may be a single layer or two or more electret non-woven fabrics as needed and may be regarded as a single layer. It is necessary to have a larger pore size than the lowermost layer side, the average pore diameter is in the range of 50 to 150 μm, and preferably 2 to 10 times the average pore diameter of the lowermost layer side electret nonwoven fabric, more preferably Is 3 to 8 times. If the average pore diameter of the upper-layer electret nonwoven fabric is less than twice the average pore diameter of the lower-layer side, the difference in pore size between the two nonwoven fabrics is too small, resulting in faster clogging on the upper layer side and a sufficient life extension effect for the dust collection life. Not. On the other hand, when the pore size difference is 10 times or more, clogging on the upper layer side is less likely to occur, but the load of dust on the lower layer side becomes large, and eventually the dust collection life is shortened.

Thus, in addition to keeping the value of the average pore diameter of each electret nonwoven fabric layer within a specific range, a remarkable synergistic effect can be obtained by adjusting the relative relationship between the average pore diameters to a specific ratio.
In addition, the average pore diameter as used in the field of this invention is the value computed by the bubble point method (based on ASTMF-316-86). As the bubble point method, for example, a “porous material automatic pore measurement system Perm-Porometer” (manufactured by PMI) can be used. This measurement by Perm-Porometer is a method in which a nonwoven fabric is dipped in a liquid, supplied while increasing the gas pressure from the upper side of the nonwoven fabric, and the pore size is measured from the relationship between the pressure and the liquid surface tension on the nonwoven fabric surface.

  The average fiber diameter of the fibers suitable for controlling the average pore diameter of the electret nonwoven fabric within the above range is preferably in the range of 0.5 to 8.0 μm, more preferably 2.0 for the lowermost electret nonwoven fabric. ˜7.0 μm. If the average fiber diameter is less than 0.5 μm, the collection efficiency of fine dust is excellent, but the pore size is too small and the pressure loss becomes excessive and cannot be used. When the average fiber diameter is larger than 8 μm, the pore size is too large, and the surface area of the fiber is also small, so that a sufficient electret performance cannot be obtained, and the collection efficiency of fine dust is insufficient, which is not preferable.

  In order to control the average pore diameter of the electret nonwoven fabric on the upper layer side within the above range, the fiber diameter is preferably larger than the nonwoven fabric on the lower layer side, specifically, a range of 3.5 to 30.0 μm is preferable. More preferably, it is 5.0-20.0 micrometers. When the average fiber diameter is less than 3.5 μm, clogging on the upper layer side is fast, and the dust collection life is short regardless of the state on the lower layer side. A pore size of 30 μm or more is not preferable because the pore size is too large and does not contribute to the extension of the dust collection life.

  As a manufacturing method of the nonwoven fabric for the electret nonwoven fabric, a melt blow method, a spunbond method, a thermal bond method, a needle punch method, a wet papermaking method, etc. can be preferably employed, but the electret nonwoven fabric on the lowermost layer side has a small pore size. Since it is necessary to enhance the function of collecting fine dust, a melt blown nonwoven fabric that can easily reduce the fiber diameter can be used particularly preferably. On the other hand, the electret non-woven fabric on the upper layer side can be preferably used as long as it is a non-woven fabric of the above production method including the melt-blown non-woven fabric, but in the sense of reinforcing the melt-blown non-woven fabric employed on the lower layer side, Bond nonwoven fabrics, wet papermaking nonwoven fabrics and the like can be used more preferably.

  Electret non-woven materials include high electrical resistance such as polypropylene, polyethylene, polystyrene, polyolefin resins such as polybutylene terephthalate and polytetrafluoroethylene, aromatic polyester resins such as polyethylene terephthalate, and synthetic polymer materials such as polycarbonate resin. A material having a rate is preferred. Among these, polypropylene and polybutylene terephthalate are more preferable, and polypropylene is most preferable because of its low melting point and easy production of a nonwoven fabric by a melt blow method.

  An additive may be added to the non-woven fabric to improve the electret performance. As such an additive, it is preferable to blend at least one hindered amine additive or triazine additive.

  Of the above two types of additives, the hindered amine-based additive may be 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 Ciba, Chimassorb) (Registered trademark) 944LD), dimethyl succinate-1- (2-hydroxyethyl) -4-hydroxy-2,2,6,6-tetramethylpiperidine polycondensate (manufactured by Ciba, Tinupin (registered trademark) 622LD) 2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-n-butylmalonate bis (1,2,2,6,6-pentamethyl-4-piperidyl) (manufactured by Ciba, Chinu Emissions (R) 144), and the like.

  Examples of the triazine-based additive include the aforementioned 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 Ciba, Chimassorb (registered trademark) 944LD), 2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5-((hexyl) oxy) -phenol (manufactured by Ciba, Tinupin (registered trademark) 1577FF), and the like. be able to. Among these, it is particularly preferable to use a hindered amine-based additive.

  The amount of the hindered amine-based additive or triazine-based additive added is not particularly limited, but is preferably in the range of 0.05 to 5% by mass, and more preferably in the range of 0.1 to 3% by mass. . When the additive amount of these additives is less than 0.05% by mass, it is difficult to obtain the desired high level electret performance. Moreover, when it mix | blends so much that it exceeds 5 mass%, it is unpreferable since it will worsen a spinning property and film forming property, and will become disadvantageous also in cost.

  As an electret processing method for converting the nonwoven fabric into an electret nonwoven fabric, an electro electret, a thermal electret, a radio electret, a mechano electret, a photo electret, a magnet electret, or the like can be used. In addition, it is more preferable to apply the electret by a hydrocharge method in which a polar solvent such as pure water or an organic solvent, which has been adopted in recent years, is applied to the nonwoven fabric or the like by applying the electret by vibration or the like. As the polar solvent used at this time, it is preferable to use pure water from the viewpoint of productivity such as drainage.

As for the timing of applying electret processing to the nonwoven fabric, good electret performance can be obtained by applying electret treatment to each layer in advance before the lamination process for lamination. It is also possible to apply electret processing to the laminated nonwoven fabric all at once. In this case, the process can be omitted, leading to cost reduction.
Electret processing of a laminated nonwoven fabric with a large basis weight tends to cause a difference in charge density in the thickness direction of the nonwoven fabric and tends to lower the charge density on the inner layer side. As long as it is allowed to penetrate, a difference in charge density between the inner and outer layers does not occur, so that a good electret performance can be obtained even if the basis weight is large. For this reason, it is particularly preferable to adopt the hydrocharge method even in the case of electretization after stacking.
In the present invention, at least one layer of the laminated electret nonwoven fabric preferably contains a hindered amine-based additive and is electretized by a hydrocharge method. When such an electret nonwoven fabric is used on the lowermost layer side, the fine dust collection efficiency is improved, and when used on the upper layer side, clogging of the electret nonwoven fabric of the lowermost layer is suppressed, and a longer life can be achieved. . Use in both layers is most preferred because it improves both collection efficiency and lifetime.

  When electret processing is performed by a hydrocharge method, it is necessary to pass through a drying step after impregnating a polar solvent. Drying is performed until the moisture contained in the nonwoven fabric reaches the official moisture content. The drying temperature is preferably 130 ° C. or lower, more preferably 120 ° C. or lower, and further preferably 100 ° C. or lower. The dried nonwoven fabric should be quickly discharged from the dryer so as not to deactivate the electret effect after drying. For example, it is preferably discharged within 30 minutes at a drying temperature of 100 ° C. or higher. Further, the lower limit of the drying temperature is preferably 80 ° C. or higher because if the temperature is too low, it takes too much time to dry and the productivity is deteriorated.

  It is important that the laminated nonwoven fabric constituting the filter medium for air filter of the present invention is not simply laminated, but is sufficiently close and integrated. As an integration method, thermal bonding is preferably employed. For example, after powder or fiber made of a heat-sealing resin is spread on the boundary surface of one nonwoven fabric, the other is laminated and heated and melt-bonded with hot air or an infrared heater. A method in which hot melt resin is sprayed on the boundary surface of one nonwoven fabric, and the other is immediately laminated and pressure bonded, and some of the constituent fibers of the electret nonwoven fabric are heated by a hot embossing roll or ultrasonic oscillation. A method of melting and bonding, and a method of melt lamination by spinning the constituent fibers of the electret nonwoven fabric directly on one nonwoven fabric can be employed.

  In order for the air filter medium of the present invention to obtain pleated stability as a pleated filter medium, an aggregate nonwoven fabric is further laminated on the upstream side of the laminated electret nonwoven fabric, that is, the uppermost layer, and a three-layer structure is obtained. In this case, the strength and rigidity of the filter medium can be greatly improved. FIG. 1 is an enlarged cross-sectional photograph of an example of an embodiment of the present invention in which an aggregate nonwoven fabric is laminated.

  An aggregate nonwoven fabric is a nonwoven fabric excellent in strength and rigidity in which constituent fibers are firmly joined by heat fusion or adhesion. The production method is not limited as long as it has a function of collecting relatively large dust on the uppermost stream side while maintaining the pleated form, but the Gurley bending resistance is at least 2000 μN and the average pore diameter is not limited. It shall refer to what satisfies 50 μm or more. As the structure of the aggregate nonwoven fabric excellent in dust collecting function, a short fiber nonwoven fabric in which a plurality of types of fibers having different fiber lengths and forms are mixed at a specific ratio is preferable, and a sheet formed by a dry method or a wet method Furthermore, those obtained by firmly bonding them by a chemical bond method or a thermal bond method are preferable because of their excellent strength and rigidity.

  Specifically, as an example of a preferable fiber configuration of the aggregate nonwoven fabric, (A) a short fiber having no crimp in a range of a fineness of 0.3 to 7.0 dtex and a fiber length of 1.0 to 10.0 mm, (B) Fine fibers having a fineness of 1.0 to 4.0 dtex and fiber lengths of 3.0 to 10.0 mm, excluding natural fibers having crimps, (C) Fineness of 7.0 to 20.0 dtex The aggregate nonwoven fabric is a mixture of a plurality of fibers having different fiber lengths and forms such as short fibers that do not have crimps in the fiber length range of 8.0 to 20.0 mm and (D) pulp. Is preferably adopted. Fibers with relatively fineness and short fiber length are the uniformity and thinness of the sheet. Fibers with crimps are bulky and thick, and fibers with long fiber length are the tensile strength and rigidity of the sheet. The pulp is well-balanced aggregate with elements necessary for high air volume air processing by appropriately combining the functions of various fibers, such as entanglement and integration of fibers with different characteristics. A non-woven fabric is obtained. Moreover, it is good to adjust suitably the structure ratio of said (A)-(D) according to the characteristic of the laminated electret nonwoven fabric to combine.

  Since the aggregate nonwoven fabric needs to collect a large amount of large dust on the most upstream side of the air filter medium, it needs to be adjusted to a relatively large pore size. Therefore, the pore size of the aggregate nonwoven fabric is preferably 50 to 250 μm, more preferably 70 to 150 μm as the range of the average pore diameter. Most importantly, the average pore diameter is relative to the average pore diameter of the electret nonwoven fabric. It is to determine the pore size of the material nonwoven fabric. In the conventional laminated nonwoven fabric of three or more layers, if the pore size is simply reduced stepwise from the upstream side to the downstream side, it has been common sense that better life performance can be obtained. It has been found that in a laminated nonwoven fabric of three or more layers including a laminated electret nonwoven fabric, it is not always optimal, and in some cases, better results can be obtained by reversing the pore size. That is, the aggregate nonwoven fabric disposed in the uppermost layer is preferably adjusted to a pore size equal to or smaller than the upper-layer electret nonwoven fabric of the laminated electret nonwoven fabric. Specifically, the average pore diameter of the aggregate nonwoven fabric is the upper-layer electret nonwoven fabric. The average pore diameter is preferably 0.6 to 1.5 times, and more preferably 0.8 to 1.2 times. When the average pore size is 0.6 times or less, the aggregate nonwoven fabric itself is clogged at an early stage, and when it is 1.5 times or more, the dust holding function is lowered, which can sufficiently contribute to the clogging suppression effect in the electret nonwoven layer. Disappear. That is, in addition to the pore size of the laminated electret nonwoven fabric, the dust collection life is further improved by controlling the relative relationship of the three-layer pore size including the aggregate nonwoven fabric.

  Next, as the material of each short fiber used for the aggregate nonwoven fabric, recycled fibers such as pulp, synthetic fibers, inorganic fibers such as glass fibers and metal fibers can be used. A synthetic fiber of thermoplastic resin that can be used is preferable.

  Examples of thermoplastic resins that form synthetic fibers include polyethylene terephthalate, polyamide, polyolefin, acrylic, vinylon, polystyrene, polyvinyl chloride, polyvinylidene chloride, polybutylene terephthalate, polyphenylene sulfide, polypropylene terephthalate, polytetrafluoroethylene, and polylactic acid. Can be selected according to the application. Moreover, you may use combining multiple types.

  Here, as main fibers of the aggregate nonwoven fabric, polyolefin fibers, particularly preferably polypropylene resins added with the hindered amine additives or triazine additives, are used to produce short fibers having different fiber diameters and fiber lengths. After forming an aggregate nonwoven fabric by combining the short fibers, the upper electret nonwoven fabric of the laminated electret nonwoven fabric and the aggregate nonwoven fabric can be shared, and only the laminated electret nonwoven fabric is used. Since the air filter medium of the invention can be realized, it is particularly preferable.

  When electret treatment is performed on the aggregate nonwoven fabric, that is, when the aggregate electret nonwoven fabric is used, the binding of the polypropylene fibers constituting the aggregate electret nonwoven fabric is performed with a binder resin such as an acrylic or urethane emulsion resin so as not to impair the electret performance. It is desirable to carry out thermal bonding of the constituent fibers themselves instead of treating them. For example, a core-sheath or bimetallic heat-bonded composite fiber may be used. For example, the core is polypropylene (melting point 160 ° C.) and the sheath is modified polypropylene. A fiber having a melting point of 130 ° C. can be preferably used.

  In addition, as a manufacturing method of the aggregate electret nonwoven fabric, either a dry method or a wet method is possible, but a method of manufacturing a web by a wet papermaking method and subsequently welding by an air-through heat treatment exhibits an electret performance on the fiber surface. Most of the impurities that hinder the residual are left behind, and the subsequent electret treatment makes it possible to express high electret performance, so that it can be most preferably employed.

  The total thickness of the filter medium for the air filter of the present invention needs to be thin in order to suppress an increase in pressure loss of the pleated filter medium, and the thickness of the entire nonwoven fabric layer is in the range of 0.3 to 2.5 mm. Yes, preferably 0.4 to 1.5 mm. If the thickness is less than 0.3 mm, it is difficult to obtain the shape retention of the filter medium against the passage of high air volume air, which is not preferable. If the thickness exceeds 2.5 mm, the filter medium is stored when used as an air filter. This is not preferable because the properties are lowered.

The basis weight of each nonwoven layer of the air filter for medium of the present invention, preferably in the range of 5 to 100 g / ^{m 2,} more preferably in the range of 10 to 80 g / ^{m 2.} If the basis weight of each non-woven fabric is less than 5 g / m ² , the density gradient at the time of lamination cannot be sufficiently obtained, and the life extension effect of the dust collection life cannot be obtained. Conversely, when the basis weight of each nonwoven fabric exceeds 100 g / m ² , the thickness of the entire filter medium increases, the filter medium storage capacity decreases, and the influence of the nonwoven fabric layer in the laminated nonwoven fabric increases too much, and the density The effect of the gradient cannot be obtained sufficiently.

The basis weight of the entire laminated nonwoven fabric, in the case of not including the ability particles to be described later, preferably in the range of 50 to 200 g / ^{m 2,} more preferably in the range of 60 to 150 g / ^{m 2.} If the basis weight of the nonwoven fabric is less than 50 g / m ² , the amount of fibers is insufficient and sufficient dust collection performance cannot be obtained, and the filter medium has insufficient rigidity, so that the shape retention of the pleated filter medium cannot be obtained. If it exceeds 200 g / m ² , the filter medium is too thick and the rigidity is too high, which impairs pleatability, which is not preferable. The preferred Gurley bending resistance of the air filter medium suitable for pleating is 2000 to 20000 μN, and more preferably 3000 to 15000 μN. The fiber structure and basis weight of the aggregate nonwoven fabric, or laminating and bonding of functional particles described later It is necessary to adjust and control the conditions. In the present invention, an aggregate nonwoven fabric may be laminated in order to make the Gurley stiffness of the filter medium for air filters 2000 μN or more. However, when the aggregate nonwoven fabric is not used, the Gurley stiffness of the laminated electret nonwoven fabric is 2000 μN or more. More preferably, it may be 3000 μN or more.

The air filter medium of the present invention may contain functional particles in the laminated nonwoven fabric. As the types of functional particles, deodorizers, fragrances, antibacterial / antifungal agents, and the like can be used. In particular, activated carbon, ion exchange resins, porous inorganic particles, catalyst-supported particles, and the like can be preferably combined as deodorant particles.
The number average particle size suitable as deodorant particles is preferably 50 to 1000 μm, more preferably 100 to 600 μm, and most preferably 100 to 400 μm. By making it less than 1000 μm, it becomes difficult to break through the nonwoven fabric layer when combining the deodorant particles with the nonwoven fabric, and by making it 50 μm or more, scattering is suppressed and handling as the deodorant particles becomes easy, and the deodorant particles are placed between the fibers. Or deodorized fiber structure by being sandwiched between non-woven fabric sheets. Furthermore, by making the deodorant particles 600 μm or less, post-processing such as bending of the deodorant fiber structure becomes easy, and by making it 100 μm or more, the deodorant does not fall out from the voids of the deodorant fiber structure. Can be. Furthermore, when the deodorant particles adjusted to 100 to 400 μm are brought close to the upstream electret non-woven fabric, the functional particles partly enter between the fibers, so that the integrity thereof is increased and the strength as a laminated non-woven fabric is high. Moreover, since the thickness can be kept small, the pleat processability and the shape retention after processing are increased, and the filter performance is improved, which is preferable. Furthermore, by adjusting the particle size so that at least 50% or more of the deodorant particles are distributed in the range of 100 to 300 μm, the effect of the integration becomes more remarkable.

  The deodorant particles can be added between the fibers of the filter medium for the air filter or sandwiched between the laminated nonwoven fabrics to add deodorizing performance while maintaining the fine dust collection efficiency and dust collection life of the present invention. it can. As a specific manufacturing method, for example, the mixture obtained by mixing and dispersing the deodorant particles and the heat-adhesive fiber is sucked and laminated on the aggregate nonwoven fabric on the collection net, and then fused and integrated in a heating furnace, The so-called airlaid method, in which the electret nonwoven fabric is bonded at the heating furnace outlet, may be adopted, and as another method, for example, the above-mentioned deodorant particles and powdered thermal adhesive resin particles are quantitatively uniformly dispersed on the aggregate nonwoven fabric. The electret nonwoven fabric may be laminated and then integrated by thermocompression bonding.

A preferable loading amount of the deodorant particles is preferably 30 to 400 g / m ² , more preferably 50 to 300 g / m ² . If it is less than 30 g / m ² , the deodorizing performance is not practical, and if it is 400 g / m ² or more, the thickness and rigidity of the laminated nonwoven fabric become excessive, making it difficult to handle as a filter medium for an air filter.

  Regarding the arrangement in which the deodorant particles and the laminated electret nonwoven fabric are combined, the deodorant particles may be arranged in the middle of the laminated electret nonwoven fabric, but preferably the upstream electret nonwoven fabric and deodorizer of the laminated electret nonwoven fabric. It is preferable that the particles are bonded so that they are brought into contact with each other, and the lowermost electret nonwoven is not directly brought into contact with the deodorant particles so that the particles are not damaged. In other words, when melt blow with a small fiber diameter is adopted for the lowermost electret nonwoven fabric, the upstream electret nonwoven fabric can be selected from among spunbond, thermal bond, needle punch, wet papermaking, etc. that have excellent strength. It is possible to avoid the lowering of the collection performance due to tearing and perforation of the melt blow electret nonwoven fabric of the lower layer. As a measure of the strength of the laminated electret non-woven fabric at that time, when the tensile strength in the MD direction is at least 10 N / 5 cm or more, preferably 20 N / 5 cm or more, the processability of the bonding process and the pleating process is remarkably high. This is preferable.

The filter medium for an air filter of the present invention thus obtained is a laminated nonwoven fabric containing at least two layers of electret nonwoven fabric, so that dust with a wide particle size can be removed while efficiently removing submicron particles caused by automobile diesel exhaust gas. As a result, a sufficient dust collection life can be achieved. As the collection efficiency at a wind speed of 6.5 m / min of 0.3 μm atmospheric dust particles targeted by the present invention, preferably 40% or more, more preferably 60% or more, particularly preferably 80% or more, Further, in a dust holding test using two types of representative test dusts having different particle size distributions, JIS 15 type dusts, and ISO-FINE A2 dust, the dust is reduced to a wind speed of 6.5 m / min and a final pressure loss (up to 150 Pa from the initial pressure loss). The amount of dust retained when adding is preferably 30 g / m ² or more, more preferably 40 g / m ² or more.

[Measuring method]
(1) Average pore diameter [μm]
The average pore diameter was calculated by the bubble point method (based on ASTMF-316-86) using “Perm-Poromometer” (manufactured by PMI). The measurement sample diameter was 25 mm, and as the measurement liquid, Galwick was used for the nonwoven fabric having a pore diameter of 180 μm or less, and pore diameter distribution measurement was performed using pure water for the nonwoven fabric having a pore diameter exceeding 180 μm.

  The mean pore size was defined as a mean flow pore diameter (MEAN FLOW PORE DIAMETER) obtained by automatic calculation by a measuring instrument under the above conditions. The measurement was performed by sampling 5 points arbitrarily from one sample, and the average value was used.

(2) Average fiber diameter [μm]
The fiber was magnified and photographed with an SEM photograph, the width of 100 fibers was measured, and the median value was shown.

(3) Weight per unit [g / m ² ]
It measured based on JIS-L1085.

(4) Thickness [mm]
The thickness was measured using a dial thickness gauge (manufactured by TECLOCK Co., Ltd., SM-114 probe shape: 10 mmφ, scale: 0.01 mm, measuring force: 2.5 N or less). The measurement was performed by sampling 5 points arbitrarily from one sample, and the average value was used.

(5) Collection efficiency [%]
A flat filter medium is set in a holder having an effective frontage area of 0.1 m ² , air is passed in a vertical direction at a surface wind speed of 6.5 m / min, and the air has a particle size of 0.3 to 0.5 μm upstream and downstream of the filter. The number of dust was measured with a particle counter (manufactured by RION, model: KC-01D) and calculated from the following formula.
Collection efficiency (%) = 1− (number of downstream particles / number of upstream particles) × 100.
The measurement was performed by sampling 5 points arbitrarily from one sample, and the average value was used.

(6) Pressure loss [Pa]
A flat filter medium is set in a holder having an effective frontage area of 0.1 m ² , air is passed in the vertical direction at a surface wind speed of 6.5 m / min, and the pressure difference between the upstream and downstream of the filter is changed by a digital manometer MA2-04P manufactured by MODUS. Measured with a pressure gauge. The measurement was performed by sampling 5 points arbitrarily from one sample, and the average value was used.

(7) Dust collection amount [g / m ² ]
When setting the planar filter medium in the effective frontage area 0.1 m ² holder, it is passed through the air in a vertical direction at a face velocity 6.5m / min, and the JIS15 or dust from the upstream side provided in a concentration 70 mg / ^{m 3} The pressure difference between the upstream and downstream of the filter was measured with a differential pressure gauge, and the amount of dust retained was measured from the change in filter mass when the pressure rose from the initial pressure loss to the final 150 Pa. Moreover, the dust holding amount was measured by the same method for ISO-FINE A2 dust. The measurement was performed by sampling 5 points arbitrarily from one sample, and the average value was used.

(8) Tensile strength [N / 5cm]
A test piece of 5 cm (TD direction) × 20 cm (MD direction) was collected, and the tensile strength in the MD direction was measured according to JIS L-1096.

(9) Gurley type bending resistance [μN]
Based on the JIS L-1096 A method (Gurley method), the bending resistance in the MD direction was measured.

[Production example]
About the aggregate nonwoven fabric and the electret nonwoven fabric used by the Example and the comparative example, it manufactured with the following method.

(Aggregate nonwoven fabric)
Table 1 shows a list of manufacturing methods, fiber compositions, resin compositions, and evaluation results of the aggregate nonwoven fabrics A to D. All of the aggregate nonwoven fabrics in Table 1 were produced by the wet papermaking chemical bond method. That is, a slurry obtained by dispersing and mixing the short fibers and papermaking additives described in the table fiber composition in water, papermaking on an inclined wire, impregnating with a binder resin blended with a flame retardant, heat drying By doing so, these aggregate nonwoven fabrics were obtained. By changing the composition of the fiber, the average pore diameter was changed stepwise in the range of 78 to 234 μm.

(Electret aggregate nonwoven fabric)
Aggregate nonwoven fabrics E and F in Table 2 were produced by a wet papermaking thermal bond method. First, heat-bonded sheets made by a circular paper machine using a core-sheathed heat-adhesive composite short fiber made of polypropylene resin containing electret additives as a main fiber and passed through a suction drum type air-through dryer When the sheath component of the conductive composite short fiber was melted, it was pressed to a predetermined thickness to obtain a heat-sealed nonwoven fabric. Since the circular net paper machine used here is capable of multi-layering, it is possible to obtain a laminated heat-sealed non-woven fabric in one step by changing the composition of the fibers and carrying out double-layering. F was produced by double layering. In addition, the obtained heat-bonding nonwoven fabric was electret-treated by a hydrocharge method. Normally, if the impurities such as oil used for the surface treatment of short fibers remain on the fiber surface or post-processing with a binder resin or the like, electret performance does not appear, but the aggregate nonwoven fabric produced here is The surface treatment agent for short fibers has been washed away in the wet papermaking process, and it has been made into a sheet by thermal bonding of the constituent fibers themselves without using a binder resin, and for reasons such as blending of electret additives, An aggregate nonwoven fabric having extremely high electret performance was obtained.

(Electret nonwoven fabric and nonwoven fabric)
Table 3 shows the production conditions and evaluation results of the electret nonwoven fabric. Melt blows A to D are based on the melt blow method, and the fiber diameter was changed stepwise from 3.9 to 6.5 μm and the average pore diameter from 15 to 104 μm by changing the spinning conditions. Melt blow A-1, A-2, and melt blow D-1, D-2 are the same melt blown nonwoven fabrics with or without electret treatment, and melt blow A-1, B, C, D-1 are hydrocharge methods. The electret process by was performed, and melt blow A-2 and D-2 did not perform the electret process.

  Spunbonds A-1 to A-3 and B are based on the spunbond method, and A-1 to A-3 are different in the presence or absence of the electret treatment and the method of the same spunbond nonwoven fabric, and spunbond A-1 And B were hydrocharged, spunbond A-2 was not subjected to corona discharge, and spunbond A-3 was not subjected to electret treatment. In addition, about the said melt blown nonwoven fabric used for the electret nonwoven fabric, and the spun bond nonwoven fabric, 1 mass% is added to the polypropylene resin as the base resin, using Kimasorb 944 (registered trademark) LD (manufactured by Ciba) as an electret additive. did.

  The aggregate nonwoven fabric and the electret nonwoven fabric were combined, and a small amount of heat bonding powder was sprayed on the interface and melt bonded to produce filter media samples of Examples and Comparative Examples, and each performance was evaluated. Tables 4 and 5 show the results. Also, as a functional particle between the aggregate nonwoven fabric and electret nonwoven fabric, a granular coconut shell activated carbon adjusted to a particle size of 0.18 to 0.36 mm and a thermal bonding powder are mixed so as to have a mass ratio of 3: 1. A sample that was sandwiched and fused was prepared, and it was confirmed whether the same dust collection performance improvement effect as that in which the activated carbon was not sandwiched was exhibited. In addition, the obtained filter material for air filter was subjected to pleating processing, and it was confirmed that there was no problem with its workability.

[Examples 1 to 10]
The aggregate nonwoven fabric and the electret nonwoven fabric were combined, and a small amount of heat bonding powder was sprayed on the interface and melt bonded, thereby producing filter media samples of Examples 1 to 10 and evaluating each performance. In addition, the obtained filter material for the air filter is folded so that two folding blades alternately fold the filter material at a predetermined pitch, and a pleat process is performed by a so-called reciprocating method in which a valley is formed. In addition to the quality of the pleated shape when the pleat processing was performed at a peak height of 25 mm, it was visually confirmed whether there was any damage to the nonwoven fabric or leakage of functional particles at the tip of the mountain valley where the folding blade was abraded. Tables 4 and 5 show the results.
In Example 8, as a functional particle between the aggregate nonwoven fabric and the upper electret nonwoven fabric, a granular coconut shell activated carbon having a particle size adjusted to 180 μm to 360 μm mm and a thermal bonding powder so as to have a mass ratio of 3: 1. The sample was mixed and sandwiched and fused. In addition, the said coconut husk activated carbon exists in the particle size range whose 86.5% is 100-300 micrometers by mass fraction.

  The composition of the filter media and the evaluation results are summarized in Tables 4 and 5.

In each of Examples 1 to 10, the average pore diameter of the laminated electret nonwoven fabric and the average pore diameter on the upper layer side were adjusted to be within the range of 2 to 10 times the average pore diameter on the lowermost layer side. Despite the extremely high dust particle collection efficiency of 69 to 94%, the dust holding amount of JIS 15 type dust and ISO-FINE A2 dust was never less than 30 g / m ² .

  Examples 2, 6, and 7 differed only in the aggregate nonwoven fabric, and the laminated electret nonwoven fabric had the same melt-blow laminate pattern, but Example 2 had the best balance with the aggregate nonwoven fabric and was most excellent.

  In Examples 4 and 5, a spunbond nonwoven fabric was laminated instead of a meltblown nonwoven fabric on the upper layer side of the laminated electret nonwoven fabric, and the same effects as the meltblown nonwoven fabric were obtained and both were excellent. In particular, the difference between Examples 4 and 5 is only the upper-layer electret nonwoven fabric, but in Example 4, since any electret nonwoven fabric adopts the hydrocharge method, the lifetime performance was much better than Example 5. . That is, it can be seen that this life-prolonging effect of the dust collection life was not obtained merely by the pore diameter balance of each nonwoven fabric layer, but was also obtained by a synergistic effect taking into account the balance of electret performance.

  In Example 8, granular activated carbon is sandwiched between the nonwoven nonwoven fabric and the electret nonwoven fabric as functional particles together with the thermal adhesive powder and heat-sealed, but the same effect as in Example 4 in which the activated carbon is not sandwiched is obtained. It was.

  In Examples 9 and 10, by producing an aggregate nonwoven fabric capable of electret processing, the functions of the aggregate nonwoven fabric and the electret nonwoven fabric on the upper layer side can be shared, and the process can be greatly reduced. This is also a preferred embodiment in terms of cost reduction. In particular, the bilayer electret aggregate nonwoven fabric used in Example 10 itself has both a dense structure and electret performance, so that particularly high performance was obtained.

  For the air filter media of the examples, pleatability was also confirmed using a reciprocating machine, but all could be processed satisfactorily and there was no problem at all.

[Comparative Examples 1-7]
The aggregate nonwoven fabric and the electret nonwoven fabric were combined, and a small amount of heat bonding powder was sprayed on the interface and melt bonded, thereby preparing filter media samples of Comparative Examples 1 to 7, and evaluating each performance. Table 6 shows the results. In addition, the obtained filter material for air filter was subjected to pleating processing, and it was confirmed that there was no problem with its workability.

  Moreover, in the comparative example 7, as a functional particle between the layers of the aggregate nonwoven fabric and the upper electret nonwoven fabric, 3: 1 mass of granular coconut husk activated carbon adjusted to a particle size of 0.18 to 0.36 mm and thermal bonding powder is used. Samples were mixed and sandwiched and fused so as to obtain a ratio. In addition, the said coconut husk activated carbon exists in the particle size range whose 86.5% is 100-300 micrometers by mass fraction.

  The composition of the filter media and the evaluation results are summarized in Table 6.

  For Comparative Examples 1 and 2, the laminated electret nonwoven fabric was not used, and the high-performance meltblown nonwoven fabric having a small average pore diameter was directly bonded to the aggregate nonwoven fabric, so the electret nonwoven fabric was clogged quickly, and the amount of dust retained was higher than in the examples. Remarkably reduced.

  Comparative Example 3 used a laminated electret non-woven fabric, but in addition to using a melt-blown non-woven fabric with a small average pore size in both layers, the ratio of the average pore size of the two layers was 1.4 and less than 2, so A rough and dense structure could not be obtained, and the amount of dust retained was reduced.

  Although the comparative example 4 has the same laminated structure as Example 4, 5, since the electret process was not performed to the spunbond nonwoven fabric which is an upper layer side electret nonwoven fabric, the dust retention amount fell extremely.

  Although the comparative example 5 has the same laminated structure as Example 1, since the electret process was not performed to the melt blown nonwoven fabric which is an electret nonwoven fabric in both the upper layer side and the lowermost layer side, here also the amount of dust retention is extremely reduced. The dust collection efficiency was also very low.

Comparative Examples 6 and 7 employ a spunbond nonwoven fabric that has been electret-treated by the hydrocharge method on the upper layer side of the laminated electret nonwoven fabric, but the basis weight is too small at 12 g / m ² , and the fiber diameter is a meltblown nonwoven fabric. Since it was relatively thick, a sufficient stacking effect was not obtained, and the amount of dust retained was small. In Comparative Example 7, since the strength of the spunbond layer is insufficient, the electret nonwoven fabric side of the pleated bent portion is broken due to activated carbon and perforated, and the activated carbon particles are scattered during the process. Therefore, processing was stopped.

  From the results of the above comparative examples and examples, the air filter medium of the present invention has a very large dust holding amount, which is usually a contradictory characteristic, despite the extremely high collection efficiency of fine dust, and has a long service life. It was confirmed that the air filter medium can be realized.

  The filter medium for air filter according to the present invention is excellent in fine dust collection performance and dust collection life with low pressure loss, and is used in air filters, hospitals, offices, etc. Air filter air filter, air conditioner filter, OA equipment intake / exhaust filter, building air conditioner filter, industrial clean room filter, etc. Suitable for filter applications.

1: Aggregate nonwoven fabric 2: Electret nonwoven fabric (spunbond)
3: Electret nonwoven fabric (melt blow)

Claims (11)

A laminated electret nonwoven fabric comprising at least two layers of electret nonwoven fabric, wherein the average pore diameter of the lowermost electret nonwoven fabric and the upper electret nonwoven fabric is within the following range, and the average pore diameter of the upper electret nonwoven fabric is the lowermost electret A filter medium for an air filter comprising a laminated electret nonwoven fabric that is 2 to 10 times the average pore diameter of the nonwoven fabric.
Upper layer side electret non-woven fabric The average pore diameter is 50 to 150 μm
Lowermost electret non-woven fabric average pore size is 5-50μm   The aggregate nonwoven fabric is further laminated on the uppermost layer side, and the average pore diameter of the aggregate nonwoven fabric is 0.6 to 1.5 times the average pore diameter of the upper-layer electret nonwoven fabric. Air filter media.   The filter medium for an air filter according to claim 1 or 2, wherein a 0.3 µm particle collection efficiency at a surface wind speed of 6.5 m / min is 40% or more.   The filter medium for an air filter according to claim 1, comprising functional particles.   The air filter according to claim 4, wherein the functional particles are in contact with the upper-layer electret nonwoven fabric, and at least 50% or more of the functional particles are distributed in a particle size range of 100 to 300 µm. Filter media.   The filter medium for an air filter according to any one of claims 1 to 5, wherein the laminated electret nonwoven fabric has a tensile strength in the MD direction of at least 10 N / 5 cm or more.   The filter material for an air filter according to any one of claims 1 to 6, wherein the laminated electret nonwoven fabric has a Gurley bending resistance in the MD direction of 2000 µN or more.   The filter medium for an air filter according to any one of claims 1 to 7, wherein at least one layer of the laminated electret nonwoven fabric mainly comprises short thermoplastic resin fibers having different finenesses and does not contain a binder resin.   The filter medium for an air filter according to any one of claims 1 to 8, wherein at least one layer of the laminated electret nonwoven fabric is a heat fusion wet nonwoven fabric.   10. At least one layer of the laminated electret nonwoven fabric contains a hindered amine-based additive in a range of 0.01 to 3% by mass and is electret-treated by a hydrocharge method. Air filter media.   A filter for an automobile cabin, wherein the filter medium for an air filter according to any one of claims 1 to 10 is used.