Long glass fiber manufacturing method, and long glass fiber

A method for manufacturing glass long fiber, comprising:

• a glass melting step of melting a glass raw material containing glass fiber recovered from a glass fiber-reinforced resin molded product, and a glass fiber mineral material to obtain molten glass;
• and
• a spinning step of spinning the molten glass to obtain glass long fiber,
• wherein a content of the glass fiber recovered from the glass fiber-reinforced resin molded product in the glass raw material is in a range of 11 to 75% by mass, the glass long fiber is spun in such a manner as to contain, with respect to a total amount of the glass long fiber, SiO2 in a range of 48.00 to 62.00% by mass, Al2O3 in a range of 12.00 to 21.40% by mass, B2O3 in a range of 0.10 to 15.00% by mass, CaO in a range of 10.00 to 22.50% by mass, MgO in a range of 1.30 to 10.00% by mass, and P2O5, TiO2, and ZnO in a range of 0.01 to 10.00% by mass in total, and
• following expression (1) is satisfied:
• 5.2≤S+A−B−C≤46.9 (1)
• wherein S, A, B, and C are defined as follow:
• S=[a content (% by mass) of SiO2 with respect to a total amount of the glass fiber mineral material]−[a content (% by mass) of SiO2 with respect to a total amount of the glass fiber recovered from the glass fiber-reinforced resin molded product];
• A=[a content (% by mass) of Al2O3 with respect to the total amount of the glass fiber mineral material]−[a content (% by mass) of Al2O3 with respect to the total amount of the glass fiber recovered from the glass fiber-reinforced resin molded product];
• B=[a content (% by mass) of B2O3 with respect to the total amount of the glass fiber mineral material]−[a content (% by mass) of B2O3 with respect to the total amount of the glass fiber recovered from the glass fiber-reinforced resin molded product];
• and
• C=[a content (% by mass) of CaO with respect to the total amount of the glass fiber mineral material]−[a content (% by mass) of CaO with respect to the total amount of the glass fiber recovered from the glass fiber-reinforced resin molded product].