Melt spinning pack and synthetic fiber manufacturing method

A melt spinning pack, comprising:

• (a) a cylindrical pack case opened in the bottom surface and the top surface,
• (b) a spinneret having many spinning holes, positioned to close the opening in the bottom surface of the pack case,
• (c) a flow arranging plate having many flow arranging holes having upper holes and lower holes, positioned above the spinneret,
• (d) a pack cap having a polymer introducing hole at the center, positioned above the flow arranging plate and positioned to close the opening in the top surface of the pack case,
• (e) a first space in which the outlet of the polymer introducing hole in the bottom surface of the pack cap and the inlets of the flow arranging holes in the top surface of the flow arranging plate are opened,
• (f) a second space in which the outlets of the flow arranging holes in the bottom surface of the flow arranging plate and the inlets of the spinning holes in the top surface of the spinneret are opened, and in which the space thickness in the central axis direction of the pack case is substantially uniform in the entire range of the space, and
• (g) restricted portions reduced in cross sectional area compared to the inlets of the flow arranging holes in the respective sections between the inlets of the flow arranging holes and the outlets of the flow arranging holes in direct or indirect succession to the upper holes of said flow arranging holes, and satisfying the following formula:
• R≦50%,
• where:
• R=the contraction percentage represented by the formula (Sb/Sa)×100%;
• Sa=sectional area of said upper hole of said flow arranging hole;
• and
• Sb=sectional area of said lower hole of said flow arranging hole.