JP5290507B2 - Air filter medium and air filter including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a filter medium for an air filter with such advantages as low pressure loss, stably secured high uptake efficiency, high water resistant strength and high mass reduction rate after burning-disposal of a used filter medium, and to provide an air filter equipped with this filter medium. <P>SOLUTION: This filter medium for an air filter has a mixed fiber comprising a microorganic fiber content of not less than 2 mass% to less than 5 mass%, the content of 10 to 15 mass% of an extremely fine glass fiber with less than 0.5 &mu;m average fiber diameter, the content of 50 to 70 mass% of a small-diameter chopped organic fiber with 2.9 to 8.4 &mu;m average fiber diameter; and the content of not less than 10 mass% and not more than 38 mass% of either one of a large-diameter chopped organic fiber with 9.0 to 20 &mu;m average fiber diameter or a thermally fusible binder fiber with 9.0 to 20 &mu;m average fiber diameter, or the total content of both large-diameter chopped organic fiber and thermally fusible binder fiber. In addition, the mixed fiber is blended with not less than 0.5 pt.mass to less than 10 pts.mass fibrous binder or powdery binder in ratio for 100 pts.mass the former, and this mixture is formed into paper in a wet process fashion. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to air purification, dust collection and dust collection equipment in fields such as precision industry, electronics industry, pharmaceutical industry, medical care, nursing care and welfare, and building air conditioning, and air purification and dust collection in the field of home appliances, and vehicles. High performance air filter used for air purification and dust collection in transportation and transportation fields such as aircraft and air filter equipped with the same, high performance, practical strength, especially water resistance strength, incineration disposal when used The present invention relates to a filter medium for air filter and an air filter including the same.

  Conventionally, in order to collect fine particles in the air, an air filter collecting technique has been used. Air filters are roughly classified into coarse dust filters, medium performance filters, HEPA (High Efficiency Particulate Air) filters, and ULPA (Ultra Low Penetration Air) filters, depending on their collection performance.

  Among these, the HEPA filter has a DOP collection efficiency (hereinafter referred to as “DOP collection efficiency”) of 99.97% or more when it is ventilated at the rated air volume, that is, particles. The transmittance of a DOP having a diameter of 0.3 μm (hereinafter referred to as “DOP transmittance”) is regulated to 0.03% or less. For this reason, the high performance filter material for air filters used for the HEPA filter also has specifications corresponding to the filter design.

  Most high-performance air filter media are made of glass fiber and have the characteristics of low cost and high performance, but the risk of the air filter media being deformed or broken by external force due to the weakness of the glass fiber itself. There is. In addition, there is a problem that the strength of the filter medium for air filter is weak particularly when it gets wet with water. Furthermore, since the filter medium for air filter is nonflammable when used, there is a problem that it cannot be incinerated and only landfilled waste can be disposed.

  Therefore, in addition to high-performance glass fiber air filter media, organic filter-based air filter media that can be disposed of by incineration have been proposed in the past (see, for example, Patent Documents 1 to 6).

  For example, in Patent Document 1, for an air filter comprising an ultrafine glass fiber having a diameter of 4.0 μm or less, a fine denier polyvinyl alcohol fiber of 0.05 to 0.5 denier, and a polyvinyl alcohol fiber binder. Filter media have been proposed.

  In Patent Document 2, Patent Document 3 or Patent Document 4, an ultrafine glass fiber having an average fiber diameter of 0.3 to 4.0 μm and chop and strand vinylon fiber, chop and strand acrylic fiber or chop and strand rayon fiber are blended. A filter medium for air filters is proposed.

  Patent Document 5 proposes a filter paper for an air filter formed by blending 20% by mass of ultrafine glass fiber, 50% by mass of regenerated cellulose fiber, and 30% by mass of natural cellulose fiber.

  In the past, the present inventors have provided a high-performance filter material for an air filter obtained by blending a fibrous binder with 10 to 50% by mass of glass fibers having an average fiber diameter of 0.65 μm or less and 50 to 90% by mass of self-extinguishing organic fibers. (See Patent Document 6).

  Attempts have been made to reduce the mixing of glass fibers from the air filter media proposed in Patent Documents 1 to 6 (see, for example, Patent Documents 7 and 8). In Patent Document 7, microglass fibers having an average fiber diameter of 0.1 to 1.0 μm and fibrillated fine organic fibers having a drainage value of 30 to 800 seconds composed of a rigid linear synthetic polymer are blended.

  In the past, in order to maintain the filter medium for air filters as high as the glass fiber filter medium in the past, the amount of inorganic and organic fine fibers was suppressed to 30% or less, and the remaining formulation was adjusted to a fiber diameter of 2.7 to 6 It is proposed to limit the organic fiber to 5 μm (see Patent Document 8).

Japanese Examined Patent Publication No. 6-13082 JP-A-63-44914 JP 63-44915 A JP 63-44916 A Japanese Examined Patent Publication No. 63-56806 Japanese Patent Laid-Open No. 10-180020 JP-A-8-323121 JP 2004-17041 A

  However, in the technique proposed in Patent Document 1, the mixing ratio of the ultrafine glass fiber is 60 to 97% by mass, and the glass is the main component.

  In the technique proposed in Patent Document 2, Patent Document 3 or Patent Document 4, the ultrafine glass fiber is regulated to 5.0 to 95% by mass. However, in order to obtain a filter medium for HEPA filter, the ultrafine glass fiber is 20% by mass. Or, more blending is required. For chop and strand vinylon fiber, chop and strand acrylic fiber or chop and strand rayon fiber, there is no restriction on the fiber diameter, and if the fiber diameter is thick, the collection efficiency decreases, and if the fiber diameter is thin, pressure loss There is a problem that leads to an increase. The balance between the collection efficiency and the pressure loss is indispensable for a useful air filter medium, and the technique proposed in Patent Document 2, Patent Document 3 or Patent Document 4 does not necessarily provide a useful air filter medium. It is not always possible.

  In the technique proposed in Patent Document 5, the blending ratio of ultrafine glass fibers is high as described above, and there is no restriction on the fiber diameter.

  In the technique proposed in Patent Document 6, the collection efficiency may be reduced.

  As described above, in the techniques proposed in Patent Documents 1 to 6, the blending ratio of the ultrafine glass fibers is 20% by mass or more, and as a result, the mass reduction rate after the incineration process is only about 80% at most.

  In the technique proposed in Patent Document 7, in order to ensure the collection efficiency of the air filter medium, the pressure loss of the air filter medium exceeds 490 Pa, and the air filter using this air filter medium is used. There was a problem that the pressure loss was too high.

  In the technique proposed in Patent Document 8, the pressure loss may be too high, and there is anxiety about the water resistance strength.

  Furthermore, in recent years, HEPA filters have been used in household appliances such as vacuum cleaners, air conditioners, and air purifiers to prevent polluted air, diesel exhaust gas, mite allergies, and contaminated air, such as SARS. And the use is expanding to the car. For this reason, a filter medium for an air filter that is tough and retains strength even when wet with water and can wash the dust after collection has been demanded.

  An object of the present invention is to provide a filter medium for an air filter that has a low pressure loss, stably secures a high collection efficiency, has high water resistance, and has a high mass reduction rate after used incineration, and an air filter including the same. And

As a result of intensive studies by the present inventors, the filter material for air filters using fine organic fibers has an excessive increase in pressure loss and a large variation in collection efficiency. It has been found that it is difficult to stably obtain the necessary pressure loss and collection efficiency. For this reason, the present inventors limit the blending ratio of fine organic fibers, minimize the blending ratio of glass fibers by blending a predetermined amount of small-diameter organic fibers, and, further, large-diameter chopped organic fibers and heat The inventors have found that the above problems can be solved by blending a predetermined amount of either one or both of the fused binder fibers, and have completed the present invention. Specifically, the filter medium for an air filter according to the present invention has a content of microfibrillated fine organic fibers having an average fiber diameter of 0.2 to 1.0 μm of 2% by mass or more and less than 5% by mass. The content of ultrafine glass fibers having a fiber diameter of less than 0.5 μm is 10 to 15% by mass, and the content of fine chopped organic fibers having an average fiber diameter of 2.9 to 8.4 μm is 50 to 70% by mass. When including at least one of a thick chopped organic fiber having an average fiber diameter of 9.0 to 20 μm and a heat-fusing binder fiber having an average fiber diameter of 9.0 to 20 μm, and including only one of them Is a mixed fiber having a total content of more than 10% by mass and 38% by mass or less when including both of them, or a hot water melt type fibrous binder or powder with respect to 100 parts by mass of the mixed fiber binder Of 0.5 to 10 parts by weight, and wet papermaking. When the surface wind speed is 5.3 cm / second, the pressure loss is 490 Pa or less, and when the surface wind speed is 3.0 cm / second, 0. The transmittance of DOP having a particle diameter of 3 μm is 0.03% or less.

In the filter medium for an air filter according to the present invention, the transmittance of DOP having a particle diameter of 0.3 μm when the surface wind speed is 5.3 cm / sec and the pressure loss is 490 Pa or less and the surface wind speed is 3.0 cm / sec. There Ri der 0.03% or less, and the balance being the pressure loss transmittance.

  In the filter material for air filters which concerns on this invention, it is preferable that the mass decreasing rate after a used incineration process is 85% or more. The filter medium for an air filter according to the present invention can be disposed of by incineration, eliminating the need for landfill disposal.

In the filter medium for an air filter according to the present invention, since the fine organic fiber has an average fiber diameter of 0.2 to 1.0 μm , the pressure loss can be further reduced and the collection efficiency can be further increased.

In the filter medium for an air filter according to the present invention, it is preferable that the tensile strength reduction rate with wet crease represented by Formula 1 is 60% or less. Water resistance can be increased.
(Equation 1) Wet crease tensile strength reduction rate (%) = {1− (wet crease tensile strength / normal tensile strength)} × 100

  An air filter according to the present invention includes any one of the air filter media described above.

  INDUSTRIAL APPLICABILITY The present invention can provide a filter medium for an air filter that has a low pressure loss, stably ensures high collection efficiency, has high water resistance, and has a high mass reduction rate after used incineration, and an air filter including the same.

  Hereinafter, the present invention will be described in detail, but the present invention is not construed as being limited to these descriptions.

In the filter medium for an air filter according to this embodiment, the content of fine organic fibers is 2% by mass or more and less than 5% by mass, and the content of ultrafine glass fibers having an average fiber diameter of less than 0.5 μm is 10 to 15% by mass. A thick chopped organic fiber having an average fiber diameter of 2.9 to 8.4 μm and a fine chopped organic fiber content of 50 to 70 mass% and an average fiber diameter of 9.0 to 20 μm; Including at least one of heat-fusing binder fibers having an average fiber diameter of 9.0 to 20 μm, when including only one of them, the total content exceeds 10% by mass when including the content or both A wet papermaking is carried out by blending a mixed fiber of 38% by mass or less with 0.5 parts by mass or more and less than 10 parts by mass of a hot water melt type fibrous binder or a powdery binder with respect to 100 parts by mass of the mixed fiber.

  Examples of the fine organic fibers in the present embodiment include microfibrillated fine organic fibers such as poly-P-phenylene terephthalamide fiber or poly-P-phenylene terephthalamide-3,4-diphenyl ether terephthalamide fiber (hereinafter referred to as the following). , "Microfibrillated product"). The microfibrillated product is, for example, a method in which highly crystalline and highly oriented fibers such as aramid fibers are cut to an appropriate length and then dispersed in water and fibrillated using a homogenizer or a beater, or the like. The synthetic polymer can be obtained by a method in which the synthetic polymer is explosively ejected from the high-pressure side to the low-pressure side above the boiling point of the solvent and fibrillated into a fibrous form. In addition, the microfibrillated product is a high-speed, high-speed, high-speed and high-speed passage of the synthetic polymer fiber or pulp-like fiber dispersed in water to impinge on the vessel wall and rapidly decelerate, It can also be obtained by applying a shearing force to a synthetic polymer fiber or pulp-like fiber to form a fiber.

  In the air filter medium according to this embodiment, the fine organic fibers preferably have an average fiber diameter of 0.2 to 1.0 μm, and more preferably 0.2 to 0.5 μm. The pressure loss can be reduced and the collection efficiency can be increased.

  The ultrafine glass fiber in this embodiment is a cotton-like glass fiber manufactured by a spinning method, a flame insertion method, or a rotary method, for example. In the filter medium for air filters which concerns on this embodiment, it is preferable that the mass decreasing rate after a used incineration process is 85% or more. The air filter medium according to the present embodiment can be disposed of by incineration, eliminating the need for landfill disposal. For this reason, it is desirable to reduce the blend of ultrafine glass fibers as much as possible.

  In the filter medium for an air filter according to this embodiment, the pressure loss is 490 Pa or less at a surface wind speed of 5.3 cm / second, and the DOP having a particle diameter of 0.3 μm at a surface wind speed of 3.0 cm / second is transmitted. The rate is preferably 0.03% or less. The filter medium for an air filter according to this embodiment can balance the pressure loss and the transmittance, and can be used as a filter medium for a HEPA filter. Here, if the ultrafine glass fiber has an average fiber diameter of 0.5 μm or more, in order to obtain the above-described collection efficiency, it must be blended in an amount exceeding 15% by mass, and quality design cannot be performed. On the other hand, if the ultrafine glass fiber is less than the average fiber diameter of 0.5 μm, the fiber network of the filter medium for the air filter becomes fine and the above collection efficiency can be achieved. Here, if the average fiber diameter of the ultrafine glass fiber is less than 0.5 μm, it is preferable that the average fiber diameter of the ultrafine glass fiber is reduced because the blending of the ultrafine glass fiber can be reduced. The thinnest average fiber diameter at present is, for example, 0.2 μm. Moreover, in the use of a semiconductor process, a low boron glass fiber or a silica glass fiber can also be used for the purpose of preventing boron contamination of a silicon wafer.

  Since both the fine organic fiber and the ultrafine glass fiber have a small average fiber diameter, they are necessary components for ensuring the collection performance of the air filter medium. However, in addition to the fact that the ultrafine glass fiber has an upper limit on the blending ratio as described above, the present inventors also note that the fine organic fiber should also limit its blending ratio in order to obtain stable collection performance. As a result of these studies, it has become clear.

  That is, the cause of the increase in pressure loss of air filter media and the decrease and variation in collection efficiency is that the fine organic fibers in the paper layer structure are clogging the fiber network. I understood. By clogging the fine organic fibers, the function of the ultrafine glass fibers is reduced at the same time as the pressure loss is increased, and the collection efficiency is lowered. This is a phenomenon that occurs when water-dispersed raw material slurry is dewatered on a papermaking wire (net) of a papermaking machine for wet papermaking, and also due to differences in papermaking conditions (dehydration speed, turbulent flow of slurry) Depending on the presence of fine organic fibers. Because the fine organic fibers are fine and flexible, they tend to get entangled with ultra-fine glass fibers, fine chopped organic fibers, or large chopped organic fibers, and this seems to be the cause of blocking the fiber network composed of these fibers. . In this respect, since the ultrafine glass fiber is rigid, a certain gap can be secured.

  As a result of the study by the present inventors, it has been found that the above phenomenon can be suppressed by limiting the blending ratio of fine organic fibers. Therefore, an appropriate blending ratio of the fine organic fibers is 2% by mass or more and less than 5% by mass, and preferably 3 to 4% by mass. When the fine organic fiber is 5% by mass or more, an extreme increase in pressure loss due to the above phenomenon, and a decrease and variation in collection efficiency occur. On the other hand, if the fine organic fiber is less than 2% by mass, it becomes impossible to obtain sufficient collection efficiency as a filter medium for an air filter. Moreover, the suitable mixture rate of an ultrafine glass fiber is 10-15 mass%. When the ultrafine glass fiber is less than 10% by mass, it is impossible to obtain sufficient collection efficiency as a filter medium for an air filter even with the ultrafine glass fiber having the thinnest fiber diameter at present. On the other hand, if the ultrafine glass fiber exceeds 15% by mass, a high mass reduction rate after used incineration disposal, for example, 85% or more cannot be secured.

  Furthermore, the blending of the small-diameter chopped organic fiber, which is the main component of the air filter medium, is an indispensable condition for ensuring the collection performance of the air filter medium. The fine chopped organic fiber makes the mesh of the fiber network fine, which promotes uniform dispersion of the fine organic fiber and the ultrafine glass fiber, and is more effective for improving the collection performance. The fiber diameter is 2.9 to 8.4 μm, preferably 2.9 to 5.0 μm, corresponding to 0.1 to 0.5 dtex. Examples of the small-diameter chopped organic fiber include various fibers such as rayon fiber, polyethylene fiber, polypropylene fiber, polyester fiber, vinylon fiber, and acrylic fiber. The thin chopped organic fiber has a cut length of, for example, 1 to 20 mm, preferably 3 to 10 mm.

  However, it has been found that excessive blending of small-diameter chopped organic fibers, on the contrary, becomes a second cause of increased pressure loss and worsening collection efficiency and dispersion. That is, the chopped organic fiber having a small fiber diameter makes the network of the fiber network composed of fibers finer, so that the fine organic fiber is more easily clogged, and the fiber has poor dispersibility in wet papermaking. For this reason, unevenness of density is easily generated in the formed filter medium for air filter, which causes a decrease in the collection efficiency and a variation.

  As a result of the study by the present inventors, it was found that the above phenomenon can be suppressed by limiting the blending ratio of fine organic fibers and blending the remainder with thick organic fibers. Therefore, the compounding ratio of the small-diameter chopped organic fiber is 50 to 70% by mass, and preferably 60 to 65% by mass. When the blending ratio of the small diameter chopped organic fiber is more than 70% by mass, the above phenomenon becomes remarkable. On the other hand, if it is less than 50% by mass of the small-diameter chopped organic fibers, improvement in the collection efficiency of the air filter medium cannot be expected.

  The blending of large-diameter chopped organic fibers in this embodiment is effective for alleviating clogging of fine organic fibers. This is thought to be because the unevenness of the surface of the filter medium for the air filter increases due to the blending of the large-diameter chopped organic fibers, and the gap is secured even if fine organic fibers are present because it becomes three-dimensional. However, if the blending of large-diameter chopped organic fibers is too large, the fiber network configuration as the filter medium for the air filter is disturbed and the voids become too large, leading to a decrease in collection efficiency.

  The large diameter chopped organic fiber in the present embodiment is not particularly limited as long as the average fiber diameter is 9.0 to 20 μm, preferably 10 to 17 μm. Examples of the large-diameter chopped organic fiber include rayon fiber, polyethylene fiber, polypropylene fiber, polyester fiber, vinylon fiber, and pulp fiber. When the average fiber diameter of the large-diameter chopped organic fiber is less than 9.0 μm, the above-described performance deterioration and variation phenomenon occur. On the other hand, if the average fiber diameter of the large-diameter chopped organic fibers exceeds 20 μm, the diameter is too large, the fiber network configuration as the filter medium for the air filter is disturbed, the voids become too large, and the collection efficiency is lowered. The cut diameter of the large-diameter chopped organic fiber is, for example, 1 to 20 mm, preferably 3 to 10 mm.

In the filter material for an air filter according to this embodiment, the mixed fiber contains fine organic fibers, ultrafine glass fibers, and fine chopped organic fibers together with large chopped organic fibers exceeding 10 mass% and 38 mass% or less. Containing 10% by weight of binder fiber or 38% by weight or less, or when containing large diameter chopped organic fiber and heat-bonded binder fiber, the total of them is more than 10% by weight and 38% by weight or less. There is either case. Furthermore, when including at least any one of a large diameter chopped organic fiber and a heat-fusing binder fiber and including only one of them, the total content is 15-30 mass% when including both of them. Preferably there is. Here, the use of the heat-fusing binder fiber is extremely effective for improving the water-resistant strength level. Examples of the heat-sealable binder fiber include a core-sheath binder fiber having a high melting point component on the core side and a low melting point component on the sheath side, and a parallel binder fiber in which the high melting point component and the low melting point component are arranged. Examples of the combination of the high melting point component and the low melting point component include a combination of polypropylene and polyethylene or a combination of high boiling point polyester and low boiling point polyester. The average fiber diameter of the heat-fusible binder fiber is 9.0 to 20 μm, preferably 10 to 17 μm, like the large-diameter chopped organic fiber.

In the filter medium for an air filter according to the present embodiment, it is preferable that the tensile strength reduction rate with wet crease expressed by the equation 1 is 60% or less. The air filter medium according to the present embodiment has sufficient actual use strength even when the filter medium is wet or washed with water during actual use.
(Equation 1) Wet crease tensile strength reduction rate (%) = {1− (wet crease tensile strength / normal tensile strength)} × 100

  The effect of improving the strength when using the heat-fusing binder fiber is that, as in this embodiment, each fiber has a dense and uniform fiber network configuration by an optimum blend, so that the heat-fusing binder is used. It is thought that it was obtained because the adhesion area with the fiber was increased.

  The hot water-melting type fibrous binder or powdered binder such as PVA fiber binder or PVA powder binder may be blended if it is less than 10 parts by mass with respect to 100 parts by mass of the mixed fiber, but if exceeding this, , Causing a decrease in collection performance. In order to obtain sufficient strength, it is necessary to add 0.5 parts by mass or more of a fibrous binder or a powdery binder, and 2 to 7 parts by mass is preferable. These binders are effective for the expression of the normal strength of the filter medium, and also contribute to the promotion of the water resistance strength if properly formulated.

  The filter medium for an air filter according to this embodiment can be obtained using the following manufacturing method. That is, the glass fiber constituting the filter medium for air filter is dispersed in water using a dispersing machine such as a pulper, and this slurry is wet-made by a paper machine to obtain wet paper.

  In the raw fiber dispersion step, the effect can be improved even if the pH neutral water is used as it is, but in order to improve the raw material dispersibility, for example, it is adjusted in the range of pH 2 to 4 with sulfuric acid acidity, or A surfactant such as a dispersant is used at a neutral pH.

  Further, in order to impart water repellency or flame retardancy, a water repellant or a flame retardant is added to the raw material system within the scope of the object of the present invention, or a water repellant or a flame retardant is added to the wet paper or the dried sheet. It is also possible to add a flame retardant.

  As a wet paper drying method, for example, a hot air dryer or a roll dryer is used, and the drying temperature is 120 ° C. or higher, preferably 140 ° C. or higher. Here, when the wet paper contains the heat-fusing binder fiber, the drying temperature is 110 ° C. or higher, preferably 130 ° C. or higher.

  Next, although this invention is demonstrated in detail, this invention is limited to these description and is not interpreted.

Example 1
2% by mass of micro-fibrillated poly-P-phenylene terephthalamide fiber (Daicel Chemical Industries, Tiara KY-400S) as fine organic fiber, product with an average fiber diameter of 0.20 μm (produced by John Mannville) , Code # 90) 10% by mass, 0.1 decitex as the chopped organic fiber (average fiber diameter 3.5 μm; estimated value) 65% by mass of acrylic fiber 3 mm cut product (Mitsubishi Rayon Co., Ltd., Bonnell MVP), thick As a chopped organic fiber, 2.2 decitex (average fiber diameter 14.3 μm; estimated value) polyester fiber 5 mm cut product (Kuraray Co., Ltd., EP203) mixed fiber containing 23% by mass, and 100 parts by mass of mixed fiber As a fibrous binder, PVA fiber binder (manufactured by Kuraray Co., Ltd., VP 101) 5 parts by mass were blended, which in water of sulfuric acid pH 3.5, were macerated with 2L mixer. Next, papermaking was performed using a hand-making apparatus to obtain a wet paper having a size of 28 cm × 28 cm. This wet paper was dried with a hot air dryer at 120 ° C. to obtain a sheet-like air filter medium having a basis weight of 80 g / m ² .

(Example 2)
A filter medium for an air filter having a basis weight of 80 g / m ² was obtained in the same manner as in Example 1, except that the ultrafine glass fiber was 15% by mass and the large-diameter chopped organic fiber was 18% by mass.

(Example 3)
A filter medium for an air filter having a basis weight of 80 g / m ² was obtained in the same manner as in Example 2, except that the fine organic fiber was 3% by mass and the large-diameter chopped organic fiber was 17% by mass.

Example 4
In Example 2, a filter medium for an air filter having a basis weight of 80 g / m ² was obtained in the same manner except that the ultrafine glass fiber was 4 mass% and the large-diameter chopped organic fiber was 16 mass%.

(Example 5)
In Example 4, as an ultrafine glass fiber, instead of an ultrafine glass fiber having an average fiber diameter of 0.20 μm, an ultrafine glass fiber having an average fiber diameter of 0.32 μm (manufactured by John Mannville, code # 100) was 15% by mass. In the same manner, a filter medium for an air filter having a basis weight of 80 g / m ² was obtained.

(Example 6)
In Example 5, instead of all large-diameter chopped organic fibers, a core-sheath binder fiber (N720, manufactured by Kuraray Co., Ltd.) having 2.2 decitex (average fiber diameter: 16 μm; estimated value) fiber length as a heat-fusing binder fiber. ) A filter medium for an air filter having a basis weight of 80 g / m ² was obtained in the same manner except that the content was 16% by mass.

(Example 7)
In Example 6, the blended raw material of Example 6 was disaggregated in a sulfuric acid acidic pH 3.5 water using a 10 m ³ pulper disperser. Next, the paper is continuously made with a paper machine, and the wet paper obtained by the paper making is dried with a roll dryer at 120 ° C., and a filter medium for air filter having a basis weight of 80 g / m ² , a width of 610 mm and a length of 300 m is wound. An article was made.

(Comparative Example 1)
In Example 5, the filter medium for air filters having a basis weight of 80 g / m ² is used except that the ultrafine glass fiber is 10% by mass, the fine organic fiber is 5% by mass, and the large-diameter chopped organic fiber is 20% by mass. Got.

(Comparative Example 2)
In Example 4, a filter medium for an air filter having a basis weight of 80 g / m ² was obtained in the same manner except that the fine organic fiber was 5 mass% and the large-diameter chopped organic fiber was 15 mass%.

(Comparative Example 3)
In Example 1, an air filter medium having a basis weight of 80 g / m ² was obtained in the same manner except that the fine organic fiber was 6 mass%, the ultrafine glass fiber was not blended, and the large-diameter chopped organic fiber was 29 mass%. Obtained.

(Comparative Example 4)
In Example 5, a filter medium for an air filter having a basis weight of 80 g / m ² was obtained in the same manner except that the fine chopped organic fiber was 75% by mass and the large chopped organic fiber was 6% by mass.

(Comparative Example 5)
In Example 5, a filter medium for an air filter having a basis weight of 80 g / m ² was obtained in the same manner except that the fine chopped organic fiber was 45% by mass and the large chopped organic fiber was 36% by mass.

(Comparative Example 6)
In Example 4, as an ultrafine glass fiber, instead of an ultrafine glass fiber having an average fiber diameter of 0.20 μm, an ultrafine glass fiber having an average fiber diameter of 0.50 μm (manufactured by John Mannville, code # 104) was 15% by mass. In the same manner, a filter medium for an air filter having a basis weight of 80 g / m ² was obtained.

(Comparative Example 7)
In Example 2, a filter medium for an air filter having a basis weight of 80 g / m ² was obtained in the same manner except that the fine organic fiber was not blended and the large-diameter chopped organic fiber was changed to 20% by mass.

(Comparative Example 8)
A filter medium for an air filter having a basis weight of 80 g / m ² was obtained in the same manner as in Example 2, except that the fine organic fiber was 1% by mass and the large-diameter chopped organic fiber was 19% by mass.

  In each of Examples 1 to 6 and Comparative Examples 1 to 8, three air filter media were produced. In the items of pressure loss, normal tensile strength, wet crease tensile strength, and mass reduction rate, measurement was performed by sampling a test piece from one filter medium for air filter. In the item of DOP transmittance, measurement was performed by sampling test pieces from all three air filter media in order to see variation in data.

  In the air filter filter product of Example 7, in the items of pressure loss, normal tensile strength, wet crease tensile strength, and mass reduction rate, the test piece was sampled from the winding end of the filter material for air filter. Measured. Moreover, in the item of DOP transmittance | permeability, it measured by sampling a test piece at three places every 1 m from the winding end of the filter medium for air filters.

(Pressure loss)
Using a self-manufactured device, pressure loss was measured with a micro differential pressure gauge when a test piece having an effective area of 100 cm ² was ventilated at a surface wind speed of 5.3 cm / sec.

(DOP transmittance)
RION Co., Ltd. calculated DOP transmittance from the number ratio of upstream and downstream when air containing polydisperse DOP particles generated by a Ruskin nozzle was passed through a test piece with an effective area of 100 cm ^{2 at} a surface wind speed of 3.0 cm / sec. It measured using the laser particle counter made from a company. The particle diameter of the polydisperse DOP particles was 0.3 μm. Further, the DOP transmittance was determined by a geometric average of the DOP transmittance of the particle size classification 0.2-0.3 μm and the DOP transmittance of 0.3-0.4 μm. The relationship between DOP collection efficiency and DOP transmittance is shown in Equation 2.

(Equation 2) DOP collection efficiency (%) = 100-DOP transmittance (%)

(Normal tensile strength)
A test piece having a width of 25.4 mm and an effective length of 100 mm was measured according to a paper and paperboard-tensile property test method (JIS P8113 1998). With respect to the wound product of the filter material for air filter of Example 7, the longitudinal direction of the sheet (flow direction of the paper machine) and the lateral direction (transverse direction of the paper machine) were measured.

(Wet crease tensile strength)
Applying a 1 mm thick plate to the center of a test piece of the same size as that for measuring the normal tensile strength, bending the test piece 180 ° along the plate, and then returning the test piece to its flat state before bending. The test piece was creased repeatedly. This was immersed in water at room temperature for 15 minutes, and then the tensile strength with wet creases was measured according to a paper and paperboard-tensile property test method (JIS P8113 1998). For the wound product, only the longitudinal direction was measured.

(Mass reduction rate)
It heated at 550 degreeC for 2 hours with the electric furnace, and divided | segmented the mass difference before and behind the heating in a test piece with the mass before a heating, and calculated | required as a percentage.

(Evaluation of measurement results)
Table 1 shows the measurement results and wet crease tensile strength reduction rate of each test piece of Examples 1 to 7, and Table 2 shows the measurement results and wet crease tensile strength reduction rate of each test piece of Comparative Examples 1 to 8. Shown in In Tables 1 and 2, production conditions are also shown.

  According to the comparison between Examples 1 and 2 and Comparative Examples 7 and 8, when the fine organic fiber is less than 2% by mass, even if the finest ultrafine glass fiber is blended by the maximum amount of 15% by mass, the fine organic fiber is fine organic. Since the absolute amount of fibers is insufficient, the pressure loss is too low, and the DOP permeability exceeds 0.03% which does not reach the performance of the filter medium for HEPA filter. Moreover, it turned out that the compounding rate of an ultrafine glass fiber needs 10 mass% or more.

  According to the comparison between Examples 2, 3, 4, and 5 and Comparative Examples 1, 2, and 3, when 5 mass% or more of fine organic fibers are blended, the pressure loss of the filter material for the air filter is excessively increased and the transmittance is also deteriorated. In other words, it was found that even when a thicker ultrafine glass fiber was blended and the pressure loss was reduced to 490 Pa or less, the DOP transmittance exceeded 0.03% and the variation in transmittance increased.

  According to the comparison between Example 5 and Comparative Examples 4 and 5, when the compounding ratio of the fine chopped organic fibers is more than 70% by mass or less than 50% by mass, the transmittance deteriorates and the transmittance varies. It turns out that will become big.

  According to the comparison between Examples 4 and 5 and Comparative Example 6, when ultra-thin glass fibers having an average fiber diameter of 0.5 μm or more were blended, the pressure loss was too low and the collection efficiency was HEPA filter media. It turned out that it will exceed 0.03% which does not reach the performance of.

  According to Examples 6 and 7, by blending the heat-fusing binder fiber, the tensile strength, particularly the wet creased tensile strength can be improved, and the wet creased tensile strength reduction rate can be reduced to 60% or less. I understood. If the rate of decrease in wet creased tensile strength is 60% or less, even when the filter medium for air filter is wet or when the filter medium for air filter is washed with water, it has sufficient use strength.

  As mentioned above, it turned out that the filter material for air filters which concerns on this invention satisfy | fills the performance as a filter medium for HEPA filters. Furthermore, it turned out that the filter medium for air filters which concerns on this invention has high water-proof strength, and the mass reduction | decrease rate after used incineration disposal is high.

Claims (4)

The content of microfibrillated fine organic fibers having an average fiber diameter of 0.2 to 1.0 μm is 2% by mass or more and less than 5% by mass, and the content of ultrafine glass fibers having an average fiber diameter of less than 0.5 μm is 10-15 mass%, the average fiber diameter is 2.9-8.4 μm, the content of fine chopped organic fibers is 50-70 mass%, and the average fiber diameter is 9.0-20 μm thick. Including at least one of the diameter chopped organic fiber and the heat-fusing binder fiber having an average fiber diameter of 9.0 to 20 μm , when only one of them is included, the content is included or when both are included, the total content is A mixed fiber of more than 10% by mass and 38% by mass or less is blended with 0.5 parts by mass or more and less than 10 parts by mass of a hot water melt type fibrous binder or powdery binder with respect to 100 parts by mass of the mixed fiber. Wet paper extraction The transmittance of DOP having a particle diameter of 0.3 μm is 0.03% when the surface wind speed is 5.3 cm / sec and the pressure loss is 490 Pa or less and the surface wind speed is 3.0 cm / sec. An air filter medium characterized by the following.   The filter material for an air filter according to claim 1, wherein the mass reduction rate after the used incineration treatment is 85% or more. The filter medium for an air filter according to claim 1 or 2, wherein the rate of decrease in tensile strength with wet crease represented by the formula 1 is 60% or less.
(Equation 1) Wet crease tensile strength reduction rate (%) = {1− (wet crease tensile strength / normal tensile strength)} × 100   An air filter comprising the air filter medium according to claim 1, 2 or 3.