JP4569970B2 - Air filter material - Google Patents

Description

  The present invention relates to an air filter material used for building air conditioning, automobile cabin filters, air purifiers, and the like.

  These air filter materials generally use a polypropylene fiber nonwoven fabric that is permanently charged, that is, subjected to electret processing, and is a melt blown nonwoven fabric (hereinafter referred to as “ultrafine PP”) having a thickness of 10 μm or less (hereinafter referred to as “ultrafine PP”). MB ”).

  The ultra-fine PP electret non-woven fabric made of conventional MB uses very thin fibers having a constituent fiber of 10 μm or less in order to increase the collection efficiency. For this reason, pressure loss is high, and since thin fibers are used, rigidity is insufficient, and there is a drawback that a hard support material is required to maintain the shape when forming a pleated shape. Further, as the support material, a resin-bonded nonwoven fabric, so-called chemical bond nonwoven fabric is generally used from the viewpoint of securing rigidity and pleatability. For this reason, since many chemical agents adhere to this support material, the effect of an electret cannot be expected. In addition, there is a problem in the working environment such as odor due to a volatile chemical agent in the heat treatment process during pleating.

  In Patent Document 1, a structure having a density gradient in the thickness direction using a heat-bonded fiber without using a chemical bond nonwoven fabric as a support material, and the thickness of the fiber is 1 denier (thickness 10.1 μm) or more. There is disclosed a filter medium in which a polyester nonwoven fabric is disposed on the upstream side and an ultrafine PP fiber nonwoven fabric electret nonwoven fabric (0.03 denier, thickness polypropylene = 2.1 μm) is thermally bonded to the downstream side and then electretized. This filter medium uses hard electret fibers such as polyester for the upstream side, so it has rigidity, but it has low collection efficiency for fine dust, and depending on the dust, the air outflow side and air inflow side The fiber thickness ratio is 2.1 / 10.1 = 0.21 and the difference in fiber thickness is too large (the ratio is small), so that dust is not collected on the inflow side and the downstream fiber layer Has the disadvantage of quickly clogging.

  Further, Patent Document 2 discloses that a heat-bonded fiber is used without using a chemical bond nonwoven fabric, a structure having a density gradient in the thickness direction, and an electret fiber, a self-bonding fiber, and a flame retardant fiber are used. A filter medium composed of fibers is disclosed. However, this filter medium has a drawback that the collection efficiency is low because only some of the fibers are electretized.

JP-A-62-83017 Japanese Patent Laid-Open No. 5-68823

  An object of the present invention is to provide an air filter material that has low pressure loss, does not require a chemical agent and a support material, is electretized as a whole, and has high collection efficiency.

In the present invention, an airlaid nonwoven fabric mainly composed of synthetic fibers (hereinafter also referred to as “non-hydrophilic thermoplastic synthetic fibers”) made of a thermoplastic polymer having a fiber length of 1 to 10 mm and having no hydrophilic group in the molecular structure is heated. The present invention relates to an air filter material composed of an electret airlaid nonwoven fabric (hereinafter also referred to as “electret airlaid nonwoven fabric”) that is melt bonded, integrated, and electret processed.
Here, the thermoplastic polymer having no hydrophilic group in the molecular structure includes at least one selected from the group consisting of polyethylene, polypropylene, polytetrafluoroethylene, polyvinyl chloride, polyvinylidene chloride, and modified products thereof. preferable.
Two or more kinds of non-hydrophilic thermoplastic synthetic fibers can be mixed and used.
Moreover, it is preferable that these non-hydrophilic thermoplastic fibers are composed mainly of heat-bonding short fibers having a composite structure composed of two or more components having different melting points.
In this case, preferably, the heat-bonding short fibers having a composite structure composed of two or more components having different melting points and having no hydrophilic group in the molecular structure are polypropylene and polyethylene, polypropylene and modified polyethylene, or polypropylene and modified polypropylene. It is a composite short fiber of side-by-side type or core-sheath type.
In addition, the air filter material of the present invention is a density obtained by laminating by the airlaid method with a density gradient so that the lowermost layer on the air outflow side is a thin fiber layer and gradually becomes a thick fiber layer toward the upper layer on the air inflow side. Those using a gradient type multilayer air-laid nonwoven fabric are preferred.
In this density gradient type multilayer air-laid nonwoven fabric, the thickness ratio of the fibers on the air outflow side and the air inflow side is preferably in the range of 0.25 to 0.7.

  The air filter material using the electret airlaid nonwoven fabric of the present invention has a low pressure loss because it is an airlaid method, and also has a higher pressure loss than a chemical bond because it is a thermal bond of non-hydrophilic thermoplastic synthetic fibers regardless of the chemical bond method. Since the thermoplastic synthetic fiber which is low and does not have a hydrophilic group in the molecular structure is electreted as a whole, an air filter material having a high collection efficiency and a long life (filterable time) can be supplied. Furthermore, since a filter material having a relatively high rigidity can be obtained in the present invention, a support material is not required, and it can be said that the filter material is environmentally friendly because no chemical agent is used.

It is a graph which shows transition of collection efficiency. It is a graph which shows transition of pressure loss. 2 is an electron micrograph (x750) of the filter material (lower layer part) of Example 1. FIG. 4 is an electron micrograph (x750) of a filter material (support material) of Comparative Example 1.

The air filter material of the present invention is formed by an airlaid nonwoven fabric manufacturing method. That is, a non-hydrophilic thermoplastic synthetic fiber having a fiber length of 1 to 10 mm is ejected from a single unit or a large number of ejection units located on a porous net conveyor while being sucked by an air suction unit disposed on the lower surface of the net conveyor. A fiber layer is formed on the conveyor.
At this time, preferably, the thick fiber layer is sequentially laminated from the upper layer side (fluid inflow side) to the lower layer side (fluid outflow side), and the laminated fiber layer is placed in a heat oven. Bring it in and combine the fibers with hot air to integrate them as a nonwoven fabric.
The air-laid nonwoven fabric used in the present invention can be obtained by finishing to a predetermined density and thickness according to the amount of fibers, ejection conditions, air suction conditions, hot air conditions, and the like. The temperature at the time of heat-bonding with a heat oven is appropriately selected depending on the type of non-hydrophilic thermoplastic synthetic fiber and heat-bonding short fiber used and the overall weight, but is usually 120 to 200 ° C., more preferably 130. ~ 180 ° C.

In the case of a conventional dry nonwoven fabric manufacturing method known in the past, that is, a short fiber carding method or a continuous fiber spunbond method, the fibers constituting the layer are arranged in a substantially planar shape and have a thickness. It is difficult to orient in the direction. Therefore, when it uses for the air filter material which this invention intends, it has the fault that a pressure loss is high. Although mechanical fiber entanglement methods such as needle punching and spunlace can be used to rearrange the fibers relatively in the thickness direction, fine dust is generated because the through-holes due to water streaks in the needle or spunlace remain. It will be lacking in the trapping action.
In contrast, the nonwoven fabric used in the air filter material of the present invention is based on the air-laid nonwoven fabric manufacturing method using short fibers, so the fibers are easy to arrange in the thickness direction, and fibers of different fiber diameters are mixed between layers. Matching also occurs, and the fiber diameter gradient between the fiber layers is relatively continuous.
Accordingly, the pressure loss is small, clogging is reduced, the life (filterable time) is increased, and the increase in pressure loss is small. In addition, according to the airlaid nonwoven fabric manufacturing method using such short fibers as raw fibers, it has a great feature that a filter with extremely good texture, that is, good uniformity can be obtained. Uniformity is extremely important in the use of the air filter material intended by the present invention, and is difficult to obtain with the above-described existing dry nonwoven fabric.
Furthermore, since no needle is used, the problem of performance degradation due to needle marks is also eliminated. Further, since no chemical binder is used, there is no adverse effect of pressure loss and collection efficiency reduction due to film formation, no volatile gas such as VOC generated from the filter material, and no risk of environmental pollution.

  The fiber used in the present invention has a fiber length of 1 to 10 mm. Use of fibers exceeding 10 mm is not preferable because uniformity as a non-woven fabric is difficult to obtain and productivity is lowered. On the other hand, if it is less than 1 mm, not only the strength of the nonwoven fabric is lowered, but also the falling fibers are easily generated, which is not preferable. Preferably it is 2-7 mm, More preferably, it is 3-5 mm.

The fiber that mainly constitutes the filter material of the present invention does not have hydrophilicity in the molecular structure, that is, is non-hydrophilic, and more preferably has excellent properties such as chemical resistance, heat resistance, durability, strength, and hardness. It consists of a thermoplastic polymer.
Examples of such non-hydrophilic thermoplastic synthetic polymers include polyolefins such as polyethylene and polypropylene, halogen-containing polymers such as polytetrafluoroethylene (PTFE), polyvinyl chloride, and polyvinylidene chloride, and modified products thereof. From the viewpoint of cost performance, polyolefins such as polyethylene and polypropylene are preferable. As a modified product, an unsaturated carboxylic acid such as maleic anhydride, acrylic acid or methacrylic acid, or an unsaturated carboxylic acid anhydride is used for the purpose of controlling the melting point, viscosity at the time of melting, adhesion to other fibers, etc. Alternatively, modified polyolefins obtained by graft polymerization of vinyl monomers, including saponified products thereof (Japanese Patent Laid-Open No. 2000-212866), ethylene-propylene-butene-1 copolymers, and the like can be given. Furthermore, for the purpose of controlling the electret effect or the like, a means such as adding a third component such as a hindered amine type or a triazine type (Japanese Patent Laid-Open No. 2003-260321) may be taken.
These non-hydrophilic thermoplastic synthetic polymers can be used alone or in combination of two or more.

Moreover, it is preferable that the non-hydrophilic thermoplastic fiber constituting the filter material of the present invention is mainly composed of a heat-bonding short fiber having a composite structure composed of two or more components having different melting points.
In this case, preferably, the above-mentioned heat-adhesive short fibers are composed of polypropylene and polyethylene, polypropylene and modified polyethylene, or polypropylene and modified polypropylene, and are side-by-side type or core-sheath type composite short fibers. In this case, the modified product may be an isomer.
The ratio of the heat-adhesive conjugate fiber in the total fibers is usually 30% by weight or more, preferably 50 to 100% by weight, and more preferably 70 to 100% by weight. When the amount is less than 30% by weight, falling fibers are likely to be generated, which is not suitable as an air filter material.

In addition to the non-hydrophilic thermoplastic synthetic fiber, the filter material of the present invention may contain other fibers as long as the electret effect is not hindered in order to have various functions as necessary. . For example, synthetic fibers such as polyester, polyamide, aromatic polyamide, polyvinyl alcohol, polyvinyl chloride, polyacrylonitrile, polyphenylene sulfite, inorganic fibers such as glass fiber, carbon fiber, ceramic fiber, metal fiber, polylactic acid, etc. Examples include biodegradable fibers. In this case, the blended cotton ratio is preferably 50% by weight or less, and more preferably 30% by weight or less. When it exceeds 50% by weight, electret processing is insufficient, mixed fibers are dropped, strength is lowered, and heat resistance is not preferred.
In addition, it is preferable to mix a fiber having a higher melting point than the non-hydrophilic thermoplastic synthetic fiber or a fiber having no melting point, because it has the advantage of increasing heat resistance and being less susceptible to thermal degradation.

  Furthermore, other hydrophilic low-melting-point binder fibers, for example, a heat-adhesive polyester-based composite fiber, may be blended within a range that does not impair the action / effect of the present invention. As this polyester type composite fiber, a core / sheath type or side-by-side type composite fiber is suitable. In this case, the polymer constituting the core component or the fiber inner layer is preferably a polymer having a melting point higher than that of the sheath and not denatured at the heat bonding temperature. Examples of such polymers include polyalkylene arylates mainly composed of aliphatic diol units and aromatic dicarboxylic acid units. Examples thereof include polyethylene terephthalate, polybutylene terephthalate, polypropylene terephthalate, and polyethylene naphthalate, which may be used alone or in combination of two or more, and may contain a copolymer component as necessary. Moreover, it may be denatured as long as it does not inhibit the action and effect of the present invention.

As the polymer constituting the sheath or the fiber outer peripheral portion which is a heat-adhesive component, a polymer having a melting point lower than that of the polymer constituting the core component or the fiber inner layer portion is used. For example, a component used in the core or fiber inner layer part containing a diol such as diethylene glycol or a copolymer component such as dicarboxylic acid such as isophthalic acid, or a poly (alkylene oxaside) glycol such as tetramethylene glycol And polyester elastomers copolymerized as a soft segment, but is not limited thereto. Furthermore, these polymers may be modified as long as they do not inhibit the action / effect of the present invention. The melting point needs to be 110 ° C. or higher. When the temperature is lower than 110 ° C., problems such as heat-resistant dimensional stability and heat-resistant deformation occur as a cabin air filter material for automobiles, for example.
In this case, the blended cotton ratio is preferably 15% by weight or less, more preferably 10% by weight or less. If it exceeds 15% by weight, the heat-resistant dimensional stability and heat-resistant deformation are affected.

  Furthermore, the air-laid nonwoven fabric used in the present invention may contain fibers and substances having effects such as deodorizing, antibacterial, antifungal, water repellent, flame retardant, and coloring.

  Furthermore, the air-laid nonwoven fabric used in the present invention may be a multilayer of two or more layers, and the fibers constituting each layer may be the same or different.

  For example, the airlaid nonwoven fabric used in the present invention has a density gradient so that the lowermost layer on the air outflow side (final fluid outflow side) is a thin fiber layer, and gradually becomes a thick fiber layer toward the upper layer on the air inflow side. It is preferable to stack with a multilayer structure.

Unlike the surface filtration, the flow direction of the fluid of the air filter material having a fiber diameter gradient of the present invention is from the coarse layer side (thickness side), and the object to be filtered such as dust having a distribution in the particle size, It can be captured in a balanced manner on the surface of each fiber in each layer.
For example, in the case of a three-layer structure, the thick fiber layer on the upper layer side is 30 to 50 μm, preferably 35 to 45 μm, the weight per unit area is 5 to 45 g / m ² , preferably 10 to 35 g / m ² , and the thick fiber layer is a thick layer. 15 to 35 μm, preferably 18 to 25 μm, basis weight 5 to 45 g / m ² , preferably 10 to 35 g / m ² , thickness 8 to 15 μm, preferably 9 to 13 μm, basis weight 40 to 110 g as the lower fiber layer / m ² , preferably 40 to 80 g / m ² in combination, particles having a size of 1 μm or less can be efficiently filtered, and an air filter material having a long life can be obtained.

In the case of a two-layer structure, the upper fiber layer has a thickness of 15 to 45 μm, preferably 20 to 40 μm, the basis weight is 10 to 60 g / m ² , preferably 20 to 50 g / m ² , and the lower fiber layer has a thickness of 8 A combination structure of ˜15 μm, preferably 9 to 13 μm, basis weight 40 to 140 g / m ² , preferably 40 to 100 g / m ² is good.

  In addition, the ratio of the fiber thickness of each layer, that is, the fiber ratio of the fiber layer on the fluid outflow side / the fiber layer of the fiber layer on the fluid inflow side, If the ratio is 0.0.30 to 0.7, preferably 0.3 to 0.6, it has been found that fine dust of 1 μm or less can be efficiently collected and the life is long. If it exceeds 0.7, there is no difference between the layers and it approaches a single layer, which is contrary to the spirit of the present invention. On the other hand, when it is less than 0.30, many fine particles penetrate into the lower layer without being collected in the upper layer, and thus the life is shortened.

Incidentally, the basis weight of the airlaid nonwoven fabric used in the present invention is 50 to 200 g / ^{m 2,} preferably not 60 to 150 g / ^{m 2,} more preferably at 60 to 100 / ^{m 2.} If the basis weight is less than 50 g / m ² , the dust is less retained, the life is shortened, and the pleated shape is hindered. On the other hand, if it exceeds 200 g / m ² , not only will the pressure loss increase, but the thickness will increase, resulting in a practical problem that a large installation area cannot be obtained in a fixed installation area. In addition, the cost is increased, which is not preferable.

The apparent density of the airlaid nonwoven fabric used in the present invention is 0.04 to 0.3 g / cm ³ , preferably 0.09 to 0.2 g / cm ³ , more preferably 0.1 to 0.15 g / cm. ³ . If it exceeds 0.3 g / cm ³ , the pressure loss becomes high, and when used for a filter material such as an air purifier, practical problems such as noise being too high are not preferable. On the other hand, if it is less than 0.04 g / cm ^3, it is too bulky to make it difficult to maintain the pleat shape and maintain the shape of the filter material, and it tends to cause a decrease in efficiency due to dust blow-off.
The apparent density means a value obtained by dividing the basis weight of the air filter material by the thickness.

In order for the heat-adhesive short fibers that may constitute the air-laid nonwoven fabric used in the present invention to fully exert the adhesive effect, the heat-bonding temperature is the melting point of the adhesive component of the heat-adhesive short fibers or the melting temperature. Heat treatment at a temperature higher by 5 to 40 ° C. than the temperature capable of being worn is preferable. If it is less than 5 ° C, adhesion failure occurs, and if it exceeds 40 ° C, a uniform nonwoven fabric cannot be obtained due to fiber shrinkage or semi-melting. The temperature is usually 120 to 200 ° C., preferably 130 to 180 ° C., but can be appropriately selected according to the melting point of the adhesive component polymer.
Furthermore, the air-laid nonwoven fabric used in the present invention can also adjust the thickness and density of the resulting nonwoven fabric by calendering. In calendar processing, a method of adjusting a gap between a pair of heating rollers to process a nonwoven fabric having a desired thickness is preferable. In this case, the gap is 0.3 to 4 mm, more preferably 0.8 to 3 mm. The temperature is preferably set to be 50 to 110 ° C. lower than the melting point of the adhesive component of the heat-adhesive short fibers, or the temperature capable of being fused. When the temperature is lower than 50 ° C., the melting point approaches the melting point, so that the surface fibers begin to be deformed and a film is easily formed, resulting in an increase in pressure loss and a decrease in collection performance. On the other hand, when it exceeds 110 degreeC, it becomes difficult to show a calendar effect. When the nonwoven fabric is preheated in advance, it can be processed at a low temperature.
The surface of the calendar roller may be flat or may have an uneven shape.
As these conditions, conditions suitable for processing to a desired thickness and density can be appropriately selected within a range that does not impair the action and effect of the present invention.

In addition, the air laid nonwoven fabric used in the present invention can be used by stacking and integrating two or more air laid nonwoven fabrics in order to further improve the collection efficiency as the air filter material of the present invention. .
If there is dust that has leaked in the first sheet (fiber diameter gradient structure consisting of two or more layers), the effect of collecting in the second sheet (fiber diameter gradient structure consisting of two or more layers) can be expected. There is also an advantage that the filter material becomes hard and pleating becomes easier. In order to improve the efficiency of stacking and integrating two or more sheets, it is possible to form two or more layered structures at a time when the layers are sequentially formed in advance by the airlaid nonwoven fabric manufacturing method.

In addition, the air-laid nonwoven fabric used in the present invention is combined with other air-permeable sheets to improve performance such as dust collection property, improvement of processability such as filter material processability, and improvement of practical properties such as durability. Etc. For example, paper, wet nonwoven fabric, dry nonwoven fabric, spunbond, melt blow, plastic net, perforated film, woven or knitted fabric can be appropriately selected within the scope of the present invention. The breathable sheet to be combined may be integrated by a method such as an adhesive or a light needle punch process in a separate process, or put in any of the surface layer, the back surface layer, and the inner layer in the fiber lamination process, and then a heat oven It may be heated in and integrated at once.
It is also possible to apply a dotted resin block on the lower layer side or laminate an embossed material so that the adjacent filter materials do not contact each other.

  In addition, if necessary, the layer on the fluid inflow side of the filter or the entire layer may be subjected to water repellent treatment or flame retardant treatment. The water repellent finish can prevent an increase in pressure loss when the filter material gets wet with muddy water or rain.

The air-laid nonwoven fabric used in the present invention can produce a frame by an injection molding method using various resins according to a conventional method, or can fix and bond the frame with a urethane resin.
In order to improve the processability as an air filter material and / or to prevent deformation due to wind pressure as a filter material, heat such as phenol-based or melamine-based materials can be used as long as the action and effect of the present invention are not impaired. You may process with self-crosslinking type resin, such as curable resin and polyacrylic acid ester type | system | group.

The airlaid nonwoven fabric used in the present invention is used as the air filter material of the present invention by performing electret processing.
Here, the electret processing is a processing method disclosed in, for example, Japanese Patent Application Laid-Open No. 61-186568, and various known electret methods such as a thermal electret method, an electro electret method, a radio electret method, This is a processing method in which a sheet or the like is charged by applying a mechano-electret method or the like.
When electret processing, in order to remove the surface oil agent etc. adhering to the fibers constituting the airlaid nonwoven fabric used, it was washed with hot water at 50 to 100 ° C. for about 5 to 10 seconds. After that, it is preferable to perform a drying treatment for several tens of seconds to several tens of minutes at a temperature lower than the melting point of the polymer constituting the heat-adhesive short fibers, for example, 80 to 140 ° C. In addition, water jet treatment may be performed to remove the oil agent.
As a specific example of electret processing, in the case of a polyolefin airlaid nonwoven fabric, it is preferably 80 to 150 ° C., more preferably on the heating roller of about 90 ° C. to 110 ° C., −30 to −5 KV or +5 to Apply a DC voltage of +30 KV, more preferably about −30 to −5 KV, and then apply a DC voltage of about −30 to −5 KV or +5 to +30 KV, more preferably about −30 to −5 KV on the cooling roll. The method of doing is mentioned. Since most of the minute dust present in the living space is relatively positively charged, it is preferable that the applied voltage be negative.

Example 1
As a lower layer, a heat-adhesive binder composite fiber (ESC type, manufactured by Chisso Co., Ltd.) made of a polypropylene having a fineness of 1 dt (fine diameter of 11.8 μm) and a fiber length of 3 mm and having a fiber length of 3 mm is used with an A fiber injection nozzle. Spinned to ² and collected on the net.
Next, as an upper layer, a heat-bonding binder composite fiber (ESC type, manufactured by Chisso Corp.) made of a sheath part polyethylene core polypropylene having a fineness of 3.3 dt (fine diameter 21.6 μm) and a fiber length of 3 mm is used as a B fiber injection nozzle Was spun onto the lower layer and collected so as to have a basis weight of 30 g / m ² . This laminated airlaid web was transported on a net-like conveyor and subjected to hot air treatment at 140 ° C. to produce an airlaid nonwoven fabric 1 for a filter material having a thickness of 0.9 mm and a basis weight of 90.1 g / m ² .
Next, after the oil agent adhering to the fibers constituting the airlaid nonwoven fabric 1 for the filter material is washed with hot water at 90 ° C. and dried, electret processing is performed by applying a DC voltage of −14 KV, and the air of the present invention Filter material 1 was produced. In the lower layer formed from the A fiber injection nozzle, the entanglement points of the fibers were heat-melted and bonded, and more than 40 g / m ² , so that the shape could be sufficiently maintained during pleating. Moreover, the thickness ratio of the fiber of the air inflow side and the outflow side is 11.8 / 21.6 = 0.55, and it shows in Table 1 also including another filtration test result. Further, the transition of the collection efficiency is shown in FIG. 1, the transition of pressure loss is shown in FIG. 2, and an electron micrograph (750 times) of this filter material is shown in FIG.

Example 2
As a lower layer, a heat-adhesive binder composite fiber (ESC type, manufactured by Chisso Co., Ltd.) made of a polypropylene having a fineness of 1 dt (fine diameter of 11.8 μm) and a fiber length of 5 mm and a fiber length of 50 mm / m with an A fiber injection nozzle. Spinned to ² and collected on the net.
As an upper layer, a polyethylene-polypropylene heat-bonding binder composite fiber (ES type, made of side-by-side type) having a fineness of 11 dt (fine diameter of 39.2 μm) and a fiber length of 3 mm, and a basis weight of 10 g / m with a B fiber injection nozzle ^It was spun on the lower layer so as to be ² and collected. The laminated air laid eb was conveyed onto a net-like conveyor and treated with hot air at 140 ° C. to produce an air laid nonwoven fabric 2 for filter material having a thickness of 0.5 mm and a basis weight of 61.3 g / m ² .
Next, after the oil agent adhering to the fibers constituting the airlaid nonwoven fabric 2 for the filter material is washed with hot water at 90 ° C. and dried, it is electret processed by applying a DC voltage of −14 KV. Air filter material 2 was produced. In the lower layer formed from the A fiber injection nozzle, the entanglement points of the fibers were heat-melted and bonded, and more than 40 g / m ² , so that the shape could be sufficiently maintained during pleating. The fiber ratio between the air inflow side and the outflow side is 11.8 / 39.2 = 0.30, and other filtration test results are shown in Table 1. Moreover, the transition of the collection efficiency is shown in FIG. 1, and the transition of the pressure loss is shown in FIG.

Comparative Example 1
70 g / m of fabric weight using a polyester fiber having a fineness of 3.3 dt (fine diameter of 17.5 μm) in an MB made of electret ultrafine PP (fine diameter of 5 μm) with a basis weight of 20 g / m ² marketed as 90% colorimetric method. Comparative Example 1 was obtained by laminating ² chemical bond nonwoven fabrics. The fiber ratio of the air inflow side and the outflow side of Comparative Example 1 is 5 / 17.5 = 0.29, and other filtration test results are shown in Table 1. Moreover, the transition of the collection efficiency is shown in FIG. 1, and the transition of the pressure loss is shown in FIG. Furthermore, the electron micrograph (750 times) of a laminate is shown in FIG.

<Filtration test>
Filtration test 1 shows the pressure loss when atmospheric dust (0.3-5 μm) is filtered at 5 cm / sec and the collection efficiency by a particle counter.
Filtration test 2 uses a TSI tester at a filtration rate of 10.7 cm / sec, and increases the collection efficiency and pressure loss until NaCl (dust average particle size 75 nm) dust is supplied up to 40% increase in initial pressure loss. Are shown in FIGS. In filtration test 2, the dusts of Examples 1 and 2 were fed from the 3.3 dt and 11 dt sides, and Comparative Example 1 was fed from the polyester nonwoven fabric side.

The PF values in Table 1 are
It is expressed as PF = −LN (1−collection efficiency) / pressure loss, and it can be said that the larger the absolute value of the PF value is, the better the air conditioning filter is.
From Table 1, since the absolute values of PF of Examples 1 and 2 of the present invention are 0.34 and 0.21, which are larger than 0.14 of Comparative Example 1, it can be said to be an excellent filter material.

The following can be said from FIG. 1 (transition of collection efficiency due to dust load) and FIG. 2 (transition of pressure loss increase due to dust load) showing the results of filtration test 2.
That is, since the electret filter absorbs and collects dust by static electricity on the surface of the fiber, if the dust adheres, the electrostatic adsorption action of the fiber decreases, and as shown in FIG. If the filter is clogged with dust, the collection efficiency increases due to the sieving effect. However, when this sieving effect is produced, the pressure loss increases rapidly and the filter cannot be used.

Although the filter of Example 1 has an initial efficiency of 75.2% as shown in Table 1, which is higher than 46.8% of Comparative Example 1, the initial pressure loss shown in Table 1 is 16.9 Pa, which is a comparative example. 1 is lower than 20.6 Pa.
From FIG. 1, the decrease in the collection efficiency with respect to the dust load indicates that in the case of Example 1, the collection efficiency is high with a relatively gentle decrease.
In addition, as seen in FIG. 2, in Comparative Example 1, the pressure loss increases rapidly with the amount of dust (that is, the sieve effect is early and the life is short), whereas in Examples 1 and 2, the pressure loss is high. The rise is slow and the life is longer than that of Comparative Example 1.
One reason for this is that the rapid increase in pressure loss in Comparative Example 1 is because the ratio of the fiber thickness between the dust side and the outflow side is 0.30 or less, so that fine dust is not collected by the fiber layer on the inflow side. The fiber layer, which is the fine structure on the side, is packed quickly, the pressure loss increases rapidly, and the final dust amount is 5.4 mg, which is 1/3 to 1/4 of the life of Examples 1 and 2. ing.
On the other hand, in Example 1, since the ratio of the fiber thickness between the inflow side and the outflow side is 0.55 and the balance of the fiber thickness is good, the increase in pressure loss is small and the final dust amount is 22.3 mg, which is a long life filter material. I can say that.
Further, the product of the present invention (Example 1) is integrated as a sheet by bonding the intersections of the fibers with heat-adhesive synthetic fibers as shown in FIG. 3, and there is no need for a chemical binder resin. Compared to existing chemical bond nonwoven fabrics, it can be said that the chemical agent is not volatilized during the pleating process, and it is a filter material that is friendly to the working environment. Furthermore, since there is no web-like portion formed at the fiber intersection of the support material (chemical bond nonwoven fabric) of Comparative Example 1 shown in FIG. 4, it can be said that it is an ideal air filter material with a moderate increase in pressure loss.

<Pressure loss (1), efficiency (1)>
Pressure loss (1) and collection efficiency (1) when atmospheric dust (0.3-5 μm) is filtered at a speed of 5 cm / sec on a particle counter
<Initial pressure loss, initial efficiency>
Initial pressure loss and initial efficiency when Nacl (0.075 μm, 16.5 mg / m ³ ) is filtered at 10.7 cm / sec with a TSI tester <Final efficiency, dust amount>
Final efficiency and amount of dust until the pressure loss is increased by 40% of the initial pressure loss by loading Nacl with TSI tester

The present invention relates to an air filter material used for building air conditioning, automobile cabin filters, air purifiers, and the like.
The air filter material of the present invention has no environmental pollution, no needle marks, high dust collection efficiency, long life, thin and high uniformity, building air conditioning filter materials, automobile cabin filter materials, air purification It is useful for applications such as machine filter materials.

Claims (6)

An air made of electret airlaid nonwoven fabric, which is obtained by hot-melt bonding, integrating and electret-processing an airlaid nonwoven fabric having a fiber length of 1 to 10 mm and a synthetic fiber composed of a thermoplastic polymer having no hydrophilic group in the molecular structure. It is a filter material, the lowermost layer on the air outflow side is a thin fiber layer, and it is laminated with a density gradient so that it gradually becomes a thick fiber layer toward the upper layer on the air inflow side, and the air outflow side and the air inflow side An air filter material having a fiber thickness ratio of 0.30 to 0.7.   2. The thermoplastic polymer having no hydrophilic group in the molecular structure is at least one selected from the group consisting of polyethylene, polypropylene, polytetrafluoroethylene, polyvinyl chloride, polyvinylidene chloride, and modified products thereof. Air filter material.   The air filter material according to claim 1 or 2, wherein the synthetic fiber comprising a thermoplastic polymer having no hydrophilic group in the molecular structure is composed mainly of a heat-adhesive short fiber having a composite structure comprising two or more components having different melting points. .   A heat-bonding short fiber having a composite structure composed of two or more components having different melting points and no hydrophilic group in the molecular structure is composed of polypropylene and polyethylene, polypropylene and modified polyethylene, or polypropylene and modified polypropylene, side-by-side type, or The air filter material according to claim 3, which is a core-sheath type composite short fiber. When the air filter material according to claim 1 has a two-layer structure, an air filter material using fibers having a thickness of 15 to 45 μm as an upper fiber layer and fibers having a thickness of 8 to 15 μm as a lower fiber layer. When the air filter material according to claims 1 to 4 has a three-layer structure, the upper fiber layer is 30 to 50 μm thick, the middle fiber layer is 15 to 35 μm thick, and the lower fiber layer is thick. An air filter material using 8 to 15 μm fiber.

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