GLASS FIBER FORMING COMPOSITION, GLASS FIBERS OBTAINED FROM THE COMPOSITION AND SUBSTRATE FOR CIRCUIT BOARD INCLUDING THE GLASS FIBERS AS REINFORCING MATERIAL

摘要

A glass fiber forming composition exhibits a remarkably high dielectric constant .epsilon.r as well as superior chemical resistance, yet it is readily spun into glass fibers. The composition is characterized to show a devitrification temperature which is lower than a spinning temperature at which the glass composition exhibits a viscosity of 102.5 poise, so as to be readily spun into corresponding glass fibers. The composition consists essentially of 40 to 65 mol% of SiO2; 20 to 45 mol% of at least one component selected from the group consisting of MgO, CaO, SrO and BaO; 5 to 25 mol% of at least one component selected from the group consisting of TiO2 and ZrO2; and 0.5 to 15 mol% of NbO5/2 as calculated from an incorporated amount of Nb2O5. Alternately, the composition consist essentially of 40 to 65 mol% of SiO2; 20 to 45 mol% of at least one component selected from the group consisting of CaO, SrO and BaO; 5 to 25 mol% of at least one component selected from the group consisting of TiO2 and ZrO2; 0.5 to 15 mol% of NbO5/2 as calculated from an incorporated amount of Nb2O5; and 0.5 to 15 mol% of AlO3/2 as calculated from an incorporated amount of Al2O3. The composition is also characterized to incorporate at least 85 mol% of a total amount of the oxides and have a dielectric constant ¢.epsilon.r! of 9 or more at 1 MHz and 25.degree.C.