| 摘要 |
<p>A multifilament type plastic optical fiber having a substantially uniform cross-section and an islands-in-sea structure, in which 10 to 10,000 islands are arranged in the sea, the respective islands have a substantially uniform cross-section having a diameter of 10 to 200 mu and the sea occupancy ratio in the cross-s ection of the optical fiber is 5 to 40%, said optical fiber being prepared by constructing a true conjugate spinning spinneret by (a) an orifice plate (21) having 10 to 10,000 core-forming holes (21a) (b) an orifice plate (22) having 10 to 10,000 sheath-forming holes (22a) and (c) an orifice plate (23) having 10 to 10,000 sea-forming holes (23a) having an opening expanded downward, the lower ends of every two adjacent sea-forming holes having contacted with each other on the lower end face of said orifice plate, so that a fiber comprising the sea and islands having a core-sheath structure is formed by true conjugate spinning without using a filament-gathering orifice plate, supplying a core-forming polymer, a sheath-forming polymer and a sea-forming polymer to respective spinning holes, melt-spinning the polymers under such conditions that the spinning draft D defined by the following formula [I]: D = (hole diameter of core-forming orifice plate)<2>/(core diameter of multifilament optical fiber)<2> ... [I] is 20 to 5,000, fusion-bonding the spun filaments on the lower end face of the spinneret, and taking up the formed fiber.</p> |
