| 摘要 |
<p>PURPOSE:A polyester obtained from 4,4-dipheyldicarboxylic acid and ethylene glycol is made into a film, which is oriented in two directions at right angle with each other, thus producing said biaxially oriented polyester film with high elasticity and dimensional stability. CONSTITUTION:A polyester that is prepared from the acid component consisting of 25-60 mol% of 4,4'-diphenyldicarboxylic acid and 75-40 mol% of terephtalic acid and the glycol component mainly consisting of ethylene glycol and has a relative viscosity of higher than 1.7, which is measured using 1,2g/dl solution in o- chloro-phenol at 35 deg.C, is made into films. The undrawn film is biaxially drawn in the directions at right angle with each other so that product of the draw ratios in both directions becomes 12 or more. When the draw square ratio is lower than 12, the elasticity of the resulting film does not attain the high level and further, uniform drawing difficult, resulting undesirably in large uneveness in film thickness.</p> |
