Alkali resistant glass compositions and alkali resistant glass fibers prepared therefrom

Claim 1

An alkali resistant glass fiber comprising a glass fiber having a diameter of 5 to 50 microns and a glass composition consisting essentially of SiO.sub.2 55 to 69 mol% ZrO.sub.2 11.5 to 14 mol% R.sub.2 O 12 to 23 mol% B.sub.2 O.sub.3 1 to 6 mol% P.sub.2 O.sub.5 1 to 5 mol% R'O 0 to 0.3 mol% TiO.sub.2 0 to 1 mol% M.sub.x O.sub.y 0 to 1 mol% wherein R is an alkali metal, R' is an alkaline earth metal, M x O y represents metal oxide impurities, wherein M is at least one metal selected from the group consisting of V, Cr, Mn, Fe, Co, Al, Cu, Zn, As, Y, Mo, Cd, Sn, Sb, Hf and Ce, x and y are positive integers with the proviso that the valence of M multiplied by x equals 2y, and when M x O y is MnO or ZnO, the total content of M x O y and R'O does not exceed 0.5 mol%, and the content of fluorides, calculated as F 2 , does not exceed 0.5 mol%, said glass composition being such that the liquidus temperature (T L ) is more than 50°C. below the spinning temperature (T F ) at which the glass viscosity is 1,000 poises, said spinning temperature (T F ) being not higher than 1,320°C.