Abstract: The present invention provides an electret fiber sheet having superior recovery of airflow volume by heat treatment and having high air permeability. The electret fiber sheet of the present invention is a nonwoven fabric formed from long fibers that are formed from a thermoplastic resin and have an average single fiber diameter of 0.1 to 8.0 ?m, wherein a bulk density of the nonwoven fabric is 0.05 to 0.30 g/cm3 and the long fibers contain a crystal nucleating agent at 0.005 to 1.0% by mass.

Abstract: The present invention provides an electret fiber sheet having superior recovery of airflow volume by heat treatment and having high air permeability. The electret fiber sheet of the present invention is a nonwoven fabric formed from long fibers that are formed from a thermoplastic resin and have an average single fiber diameter of 0.1 to 8.0 ?m, wherein a bulk density of the nonwoven fabric is 0.05 to 0.30 g/cm3 and the long fibers contain a crystal nucleating agent at 0.005 to 1.0% by mass.

Abstract: A fiber sheet is densely charged with electric charge and provides an electret fiber sheet that has excellent dust collecting performance. The electret fiber sheet is an electret fiber sheet in which averages of a* values and b* values satisfy all requirements of the following (a) to (c): (a) 10?average of (a* values)?40; (b) ?25?average of (b* values)?0; and (c) ?5?average of [(a* values)+(b* values)]?40; wherein a* and b* are values measured by a spectrophotometer when a red positive charge toner and a blue negative charge toner are attached.

Abstract: Problem: The present invention allows a fiber sheet to be densely charged with electric charge and provides an electret fiber sheet that has excellent dust-collecting characteristics. Solution: The electret fiber sheet according to the present invention is an electret fiber sheet in which the relationship between a* and b* measured by a spectrophotometer when a red positive charge toner and a blue negative charge toner are attached to the sheet satisfies the expression: [12?{?(b*)?(a*)}Ave?50].

Abstract: A fiber sheet is densely charged with electric charge and provides an electret fiber sheet that has excellent dust collecting performance. The electret fiber sheet is an electret fiber sheet in which averages of a* values and b* values satisfy all requirements of the following (a) to (c): (a) 10?average of (a* values)?40; (b) ?25?average of (b* values)?0; and (c) ?5?average of [(a* values)+(b* values)]?40; wherein a* and b* are values measured by a spectrophotometer when a red positive charge toner and a blue negative charge toner are attached.

Abstract: Problem: The present invention allows a fiber sheet to be densely charged with electric charge and provides an electret fiber sheet that has excellent dust-collecting characteristics. Solution: The electret fiber sheet according to the present invention is an electret fiber sheet in which the relationship between a* and b* measured by a spectrophotometer when a red positive charge toner and a blue negative charge toner are attached to the sheet satisfies the expression: [12?{?(b*)?(a*)}Ave?50].

Abstract: Provided are a mixed-fiber nonwoven fabric suitable for air filters and a filter medium using the mixed-fiber nonwoven fabric. The nonwoven fabric includes at least two types of fibers having different melting points, which fibers are low melting point fibers made of a polyolefin resin component A, and high melting point fibers made of a high melting point resin component B having a higher melting point than that of the polyolefin resin component A. The number average fiber diameter of the high melting point fibers is larger than that of the low melting point fibers. At least one high melting point fiber having a fiber diameter of 20 ?m to 100 ?m is present per 1.00 mm of the length of the cross section of the nonwoven fabric. The number average fiber diameter of all fibers constituting the nonwoven fabric falls within the range of 0.3 ?m to 10 ?m.

Abstract: A nonwoven fabric includes mixed fibers having different fiber diameters. A group of fibers having a fiber diameter of 5.0 ?m or less (fiber group A) is present at a volume fraction of 20 to 80 vol %, a group of fibers having a fiber diameter of 50.0 ?m or more (fiber group B) is present at a volume fraction of 1 to 40 vol %, and a group of fibers having a fiber diameter of more than 5.0 ?m and less than 50.0 ?m (fiber group C) is present at a volume fraction of 0 to 79 vol %. The ratio of the median fiber diameter (B?) of fiber group B to the median fiber diameter (A?) of fiber group A (B?/A?) is 35 or more.

Abstract: A nonwoven fabric includes mixed fibers having different fiber diameters. A group of fibers having a fiber diameter of 5.0 ?m or less (fiber group A) is present at a volume fraction of 20 to 80 vol %, a group of fibers having a fiber diameter of 50.0 ?m or more (fiber group B) is present at a volume fraction of 1 to 40 vol %, and a group of fibers having a fiber diameter of more than 5.0 ?m and less than 50.0 ?m (fiber group C) is present at a volume fraction of 0 to 79 vol %. The ratio of the median fiber diameter (B?) of fiber group B to the median fiber diameter (A?) of fiber group A (B?/A?) is 35 or more.

Abstract: Provided are a mixed-fiber nonwoven fabric suitable for air filters and a filter medium using the mixed-fiber nonwoven fabric. The nonwoven fabric includes at least two types of fibers having different melting points, which fibers are low melting point fibers made of a polyolefin resin component A, and high melting point fibers made of a high melting point resin component B having a higher melting point than that of the polyolefin resin component A. The number average fiber diameter of the high melting point fibers is larger than that of the low melting point fibers. At least one high melting point fiber having a fiber diameter of 20 ?m to 100 ?m is present per 1.00 mm of the length of the cross section of the nonwoven fabric. The number average fiber diameter of all fibers constituting the nonwoven fabric falls within the range of 0.3 ?m to 10 ?m.