| 摘要 |
PROBLEM TO BE SOLVED: To obtain a preform for a bottle having a small acetaldehyde content by injection molding a polyester obtained by melt mixing a PET with a PEN in a specific range of a weight ratio in a mold obtained by pressure reducing in its cavity to a specific value or above of the degree of vacuum. SOLUTION: For a pressure reducing means in an injection mold, a through hole 8 is installed in a male mold 3. Its cavity 1 is connected to a male mold cooling water passage 6. In a female mold, its cavity 1 is connected to a female mold cooling water passage 7 by a slit of a divided part. When a cooling medium flows to the passage by a negative pressure type mold temperature regulator, the cavity is evacuated to a pressure reduced state through the medium. Here, a polyester obtained by melt mixing a PET with a PEN by a weight ratio of 90/10 to 25/75 is injection molded in a mold obtained by pressure reducing its cavity to 40 cmHg or above of the degree of vacuum to obtain the preform. |
