A metal wire, which is one of a tungsten wire and a tungsten alloy wire, includes alkali metal on the surface thereof. The amount of alkali metal is at most 2.0 μg per 1 g of the metal wire.

A metal wire, which is one of a tungsten wire and a tungsten alloy wire, includes alkali metal on the surface thereof. The amount of alkali metal is at most 2.0 g per 1 g of the metal wire.

A rolling apparatus for evaluating durability of a flexible material includes a base unit, a rolling unit rotatably coupled to the base unit and around which the flexible material is wound, and a sliding unit which grips an end of the flexible material wound around the rolling unit and is spaced apart from the rolling unit to be slidably coupled to the base unit. The sliding unit is set to at least one of a preset speed and torque in the direction in which the flexible material is pulled, and at least one of the speed and torque of the rolling unit for an unrolling operation of the rolling unit and a rolling operation of the rolling unit is controlled such that the flexible material can maintain a flat state.

A rolling apparatus for evaluating durability of a flexible material includes a base unit, a rolling unit rotatably coupled to the base unit and around which the flexible material is wound, and a sliding unit which grips an end of the flexible material wound around the rolling unit and is spaced apart from the rolling unit to be slidably coupled to the base unit. The sliding unit is set to at least one of a preset speed and torque in the direction in which the flexible material is pulled, and at least one of the speed and torque of the rolling unit for an unrolling operation of the rolling unit and a rolling operation of the rolling unit is controlled such that the flexible material can maintain a flat state.