How should the longitudinal and transverse stretching be controlled when producing biaxially oriented films by the flat film method?

How should the longitudinal and transverse stretching be controlled when producing biaxially oriented films by the flat film method?


When producing biaxially oriented films by the flat film method, the longitudinal stretching is carried out on a longitudinal stretching machine, which mainly consists of preheating rollers, stretching rollers and cooling rollers. The preheating rollers are composed of 4 to 5 rollers with different diameters, generally increasing in an arithmetic sequence along the stretching direction. The stretching rollers are composed of a pair of high-speed rollers and a pair of low-speed rollers, and the stretching is achieved by the speed difference between the high-speed and low-speed rollers. During longitudinal stretching, the rotational speeds of all preheating rollers are the same, and the temperature should be controlled above the glass transition temperature of the material but below the melting point. The stretching ratio during stretching can be achieved by controlling the speed difference between the high-speed and low-speed rollers, and the temperature of the stretching rollers is slightly higher than that of the preheating rollers. The diameter of the cooling roller is generally 300mm, and it is cooled by circulating water. The temperature of the cooling roller is slightly lower than that of the preheating rollers.

After the film is longitudinally stretched, it is then stretched transversely. Transverse stretching is carried out on a tenter frame, which has two sets of chains with clamps rotating horizontally in a guide rail at a certain angle. The guide rail section is placed in a heating oven, which is divided into a preheating zone, a stretching zone, a buffer zone and a heat setting zone. The preheating zone is to heat the film to the stretching temperature; the stretching zone is to gradually increase the width and gradually stretch the film transversely; the buffer zone is a region where the intermolecular forces of the stretched film are relatively relaxed, which can reduce stress and prevent temperature interference between the stretching zone and the heat setting zone; the heat setting zone is to reheat the stretched film to achieve the maximum crystallization rate. Generally, the exit width of the tenter frame is about three times the entrance width. The stretching temperature during transverse stretching is usually slightly higher than that during longitudinal stretching.
Top
Inquiry
Inquiry