| 摘要 |
PURPOSE:To obtain a sheet with smooth surface and no defect by a method wherein a molding mouthpiece is employed, which is mainly made of iron having a degree of surface corrosion below a specified value under the condition that it is immersed in a solution of polyester compound in triethylene glycol. CONSTITUTION:A molding mouthpiece is made of stock mainly consisting of iron, wherein the elution concentration of iron ion, that is, the corrosion degree is at most 30 ppm, when the surface of the mouthpiece is immersed in triethylene glycol solution of a polyester compound. If a stock, the degree of corrosion of which exceeds 30 ppm, is employed, rust develops in accompany with the elution of iron ion from the surface of the molding mouthpiece or metallic antimony, which is produced by reduction of antimony compound in the polymerization catalyst for polyester, separates out in unevenly distributed state at the portion, at which iron ion easily elutes. As a result, projections are generated on the surface of the mouthpiece, resulting in causing to produce score-like defects on the surface of a delivered polymer film. The stock mainly consisting of iron is selected from stocks, which are chrome-plated, copper- plated, spattered with titanium nitride, silicon carbide or the like, and from the combination of above-mentioned stocks. |
