A flame retardant resin composition includes a thermoplastic resin, flame retardant reinforced fibers, and a flame retardant. The flame retardant reinforced fibers include cellulosic fibers, a phosphorus compound that is grafted to the surface of the cellulosic fibers, and a polyamine compound that is bound to the phosphorus compound. The flame retardant is a phosphorus-based flame retardant. A method for producing the flame retardant resin composition includes the following: grafting a vinyl phosphate compound to cellulosic fibers by bringing the vinyl phosphate compound into contact with the cellulosic fibers after the cellulosic fibers have been irradiated with an electron beam, optionally followed by electron beam irradiation; binding a polyamine compound to the vinyl phosphate compound, which is grafted to the cellulosic fibers, to form flame retardant reinforced fibers; grinding the flame retardant reinforced fibers; and melt-kneading and pelletizing a thermoplastic resin, the flame retardant reinforced fibers, and a component containing a phosphorus-based flame retardant. This can provide a non-halogen flame retardant resin composition with sufficient flame resistance.

A mold-preventing air filter filtration medium loaded with a water-retaining macromolecule polymer, a mold-preventing agent, and a binder resin, is formed by immersing a filter material or a reinforcing nonwoven fabric (a backing material) in a mold-preventing composition in which the water-retaining macromolecule polymer, the mold-preventing agent and the binder resin are dissolved, and drying the filter material or the reinforcing nonwoven fabric. The reinforcing nonwoven fabric (a backing material) may be bonded to a filter material to form a mold-preventing air filter filtration medium. A mold-preventing air filter includes the mold-preventing air filter filtration medium that is pleated and accommodated in a frame.

A flame retardant resin composition includes a thermoplastic resin, flame retardant reinforced fibers, and a flame retardant. The flame retardant reinforced fibers include cellulosic fibers, a phosphorus compound that is grafted to the surface of the cellulosic fibers, and a polyamine compound that is bound to the phosphorus compound. The flame retardant is a phosphorus-based flame retardant. A method for producing the flame retardant resin composition includes the following: grafting a vinyl phosphate compound to cellulosic fibers by bringing the vinyl phosphate compound into contact with the cellulosic fibers after the cellulosic fibers have been irradiated with an electron beam, optionally followed by electron beam irradiation; binding a polyamine compound to the vinyl phosphate compound, which is grafted to the cellulosic fibers, to form flame retardant reinforced fibers; grinding the flame retardant reinforced fibers; and melt-kneading and pelletizing a thermoplastic resin, the flame retardant reinforced fibers, and a component containing a phosphorus-based flame retardant. This can provide a non-halogen flame retardant resin composition with sufficient flame resistance.