Wholly aromatic polyamide fibers, a sheet comprising same and method of producing the sheet

A wholly aromatic polyamide fiber sheet comprising,

• (A) 60 to 96% by weight of wholly aromatic polyamide staple fibers comprising wholly aromatic polyamide crystals having apparent crystal sizes determined from a wide angle X-ray diffraction intensity curve in accordance with Scherrer's equation and satisfying the requirements (1), (2), (3) and (4):
• (1) the crystal size (A) in a (110) plane is 7.5 nm (75 angstroms) or more,
• (2) the crystal size (B) in a (200) plane is 8.2 nm (82 angstroms) or more,
• (3) the product (A×B) of the crystal size (A) and the crystal size (B) is 61.50 to 630.00, and
• having a thermal linear expansion coefficient within the range of from −1.0×10−6/° C. to −7.5×10−6/° C., and
• (4) when the wholly aromatic polyamide stable fibers in an amount of 2 g are cut to a short length of 1 mm or less, immersed in 50 ml of a distilled water, and heat-treated in an autoclave at a temperature of 121° C. under a pressure of 2 kg/cm2G, to extract impurity ions from the fibers;
• the extracted impurity ion-containing water is subjected to an ICP analysis and to a chromatographic analysis to determine the amount of the extracted impurity sodium, potassium and chlorine ions per liter of the extracted impurity ion-containing water;
• and the extracted impurity ions satisfy the requirements (a), (b) and (c):
• (a) the amount of the extracted sodium ions is not more than 40 mg/liter,
• (b) the amount of the extracted potassium ions is not more than 3.0 mg/liter, and
• (c) the amount of the extracted chlorine ions is not more than 7.5 mg/liter, and
• (B) 4 to 40% by weight of at least one member selected from the group consisting of organic resin binders and heat-resistant organic polymer fibers.