Glass composition for flat cross-section glass fibers, flat cross-section glass fibers and method for manufacturing flat cross-section glass fibers from glass material containing glass recycling material

A method for manufacturing flat cross-section glass fiber from a glass raw material comprising a glass recycling material, the method comprising:

• obtaining a flat cross-section glass filament having a flat cross-sectional shape comprising a major axis having a length in a predetermined range and a minor axis having a length in a predetermined range by using a glass raw material comprising a glass recycling material;
• and
• bundling a plurality of the flat cross-section glass filaments, wherein
• the glass raw material comprises the glass recycling material in a range of 1.0 to 50.0% by mass with respect to a total amount, and
• the flat cross-section glass filament comprises SiO2 in a range of 50.00 to 60.00% by mass, Al2O3 in a range of 9.00 to 18.00% by mass, B2O3 in a range of 3.00 to 9.00% by mass, CaO in a range of 15.00 to 30.00% by mass, MgO in a range of 0.10 to 5.00% by mass, Fe2O3 in a range of 0.01 to 1.00% by mass, TiO2 in a range of 0.01 to 1.00% by mass, and Na2O and K2O in a range of 0.10 to 2.00% by mass in total, with respect to a total amount of the flat cross-section glass filament, a ratio (K2O/Na2O) of a content of K2O to a content of Na2O is in a range of 0.05 or more and less than 0.50, a ratio (MgO/Fe2O3) of a content of MgO to a content of Fe2O3 is in a range of 4.10 or more and less than 10.00, and a content C of CaO, a content M of MgO, a content T of TiO2, and a total content NK of Na2O and K2O satisfy following formula (1):
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