Air filter medium and air filter product

Abstract

Provided are an air filter medium and an air filter product that can have a long life. The air filter medium includes a filter medium layer that includes first fibers having an average fiber diameter of not less than 5 μm and not greater than 50 μm and second fibers disposed in gaps between the first fibers and having an average fiber diameter of not less than 30 nm and not greater than 1 μm.

1 . An air filter medium comprising:
 a filter medium layer that includes
 first fibers having an average fiber diameter not less than 5 μm and not greater than 50 μm, and 
 second fibers disposed in gaps between the first fibers and having an average fiber diameter not less than 30 nm and not greater than 1 μm. 
   
     
     
         2 . The air filter medium according to  claim 1 ,
 wherein the first fibers are fibers obtained by applying tension to a tow band to spread the tow band, the tow band being obtained by crimping a tow formed by combining a plurality of filaments.   
     
     
         3 . The air filter medium according to  claim 1 ,
 wherein the first fibers include one or two or more selected from the group consisting of cellulose acetate, rayon, polypropylene, polyethylene terephthalate, and polyethylene.   
     
     
         4 . The air filter medium according to  claim 1 ,
 wherein the second fibers are composed of a fibrillated polymer subjected to drawing.   
     
     
         5 . The air filter medium according to  claim 4 ,
 wherein the fibrillated polymer includes a fluororesin.   
     
     
         6 . The air filter medium according to  claim 1 ,
 wherein the filter medium layer includes a particulate resin having the same composition as the second fibers, and   a ratio W1/W2 of a weight W1 of the first fibers to a total weight W2 of the second fibers and the particulate resin is not less than 3.0 and not greater than 18.0.   
     
     
         7 . The air filter medium according to  claim 1 ,
 wherein the filter medium layer includes a particulate resin having the same composition as the second fibers, and   a ratio V1/V2 of a volume V1 of the first fibers to a total volume V2 of the second fibers and the particulate resin is not less than 1.9 and not greater than 124.0.   
     
     
         8 . The air filter medium according to  claim 1 ,
 wherein the filter medium layer has a thickness not less than 3 mm.   
     
     
         9 . The air filter medium according to  claim 1 ,
 wherein the filter medium layer through which air is passed at a flow velocity of 5.3 cm/s has a pressure loss not greater than 35 Pa.   
     
     
         10 . The air filter medium according to  claim 1 ,
 wherein a collection efficiency of the filter medium layer for NaCl particles having a particle size of 0.4 μm is not less than 35%.   
     
     
         11 . The air filter medium according to  claim 1 ,
 wherein the filter medium layer has a PF value of 16 or more, the PF value being defined by the following formula: PF value={−log((100−collection efficiency (%))/100)}/(pressure loss (Pa)/1000).   
     
     
         12 . The air filter medium according to  claim 1 ,
 wherein when air containing NaCl particles having a particle size of 0.4 μm is continuously passed through the filter medium layer at a flow velocity of 5.3 cm/s, a dust-holding capacity for the NaCl particles at which a pressure loss increases by 50 Pa is not less than 18 g/m 2 .   
     
     
         13 . An air filter product obtained by processing the air filter medium according to  claim 1  into a bag shape. 
     
     
         14 . The air filter medium according to  claim 2 ,
 wherein the first fibers include one or two or more selected from the group consisting of cellulose acetate, rayon, polypropylene, polyethylene terephthalate, and polyethylene.   
     
     
         15 . The air filter medium according to  claim 2 ,
 wherein the second fibers are composed of a fibrillated polymer subjected to drawing.   
     
     
         16 . The air filter medium according to  claim 3 ,
 wherein the second fibers are composed of a fibrillated polymer subjected to drawing.   
     
     
         17 . The air filter medium according to  claim 2 ,
 wherein the filter medium layer includes a particulate resin having the same composition as the second fibers, and   a ratio W1/W2 of a weight W1 of the first fibers to a total weight W2 of the second fibers and the particulate resin is not less than 3.0 and not greater than 18.0.   
     
     
         18 . The air filter medium according to  claim 3 ,
 wherein the filter medium layer includes a particulate resin having the same composition as the second fibers, and   a ratio W1/W2 of a weight W1 of the first fibers to a total weight W2 of the second fibers and the particulate resin is not less than 3.0 and not greater than 18.0.   
     
     
         19 . The air filter medium according to  claim 4 ,
 wherein the filter medium layer includes a particulate resin having the same composition as the second fibers, and   a ratio W1/W2 of a weight W1 of the first fibers to a total weight W2 of the second fibers and the particulate resin is not less than 3.0 and not greater than 18.0.   
     
     
         20 . The air filter medium according to  claim 5 ,
 wherein the filter medium layer includes a particulate resin having the same composition as the second fibers, and   a ratio W1/W2 of a weight W1 of the first fibers to a total weight W2 of the second fibers and the particulate resin is not less than 3.0 and not greater than 18.0.