| 摘要 |
PURPOSE:To enable to obtain a dense multi-axially oriented sheet of polytetra fluoroethylene (PTFE) with excellent optical characteristics by a method wherein a performed part of PTFE heated up to a temperature near its melting point is ori ented under pressure in a lubricated die. CONSTITUTION:The inner surface 2 of a compression die 1 is coated with lubricant and heated up to a temperature nearly equal to that of PTFE base 3. A PTFE sheet is once heated up to a temperature exceeding TM in order to melt crystals and cooled down to a temperature lower than TM. The resultant PTFE films are laminated to one another to be used as PTFE base 3. The PTFE base 2 placed in the die 1 is plug-flowed by compression so as to be biaxially oriented in order to be cooled or stabilized by holding it at a temperature suitable for crystallization. Finally, the multi- axially oriented PTFE 4 is taken out of the die 1 and separated from one another in order to obtain sheets. The rsultant sheet is made of polytetrafluoroethylene, multi- axially oriented with a minimum area ratio of 2:1, has the total light ray transmittance of 50% or more and has the absorptivity of 0.7mm<-1> or less. According to the above- mentioned forming the sheet can be favoravly used as electronic material and as solar energy utilization appliance material. |
