Process Mechanism And Technology Study On Transverse Drawing Of Strap-on Biaxially Stretching Polyolefin Film

Biaxially oriented film has excellent comprehensive performance and numerous applications. The most primary industrial process is the tenter method which uses clamps gripping films’ edges. This method has not only tedious process, but also complex equipment structure, So it often appear some problems, such as clip off, rupture of films etc.. Strap-on biaxially stretching film has abandoned the complex clamp-chain system, and presented a continuous uniform drawing force in the film’s edges. Due to the big expanding angle, it can still have a short thermal-tensile history even at high conveying speed. The device has the advantages of simple structure, low control requirements, so it contains a huge application prospect and important scientific research value.Based on the idea of strap-on biaxially stretching film, a new device have been first successfully developed to stretch plastic film by double chevron wheels and strapping, and then the paper realized the biaxially stretched progress of films. This paper has also completed the mathematical model’s establishment and the mechanism’s theoretical analysis of the strap-on transverse drawing process. Finally, three experiments of stretching polyolefin film have been carried out to explore this technology’s performance and characters.The movement characteristics analysis of membrane’s two edges show that: a) The edges appear as the trigonometric function curve shape; b) The dynamic self-synergistic effect between the transverse drawing speed and the longitudinal conveying speed, results to reduce the internal stress of longitudinal shrinkage which caused by the transverse drawing; c) The expanding angle begin to increase from zero, and then decrease to zero, so it’s able to realize transverse drawing at a large dilation angle. By analyzing the distribution of the longitudinal component of the conveying speed, this paper discusses the formation and development of geometric bowing, analyzes the influence on products of wheel radius and flare angle.Experiment of cold and heating stretching LDPE film confirmed that the concentrated stress does not exist in the boundaries; some problems(removal tied, rupture of film, high sensitivity to temperature) have been improved. Tests of biaxially stretching HDPE films show that the drawing velocity and ratio along transverse or longitudinal direction would have influence on the bowing’s deflection, and the factors affecting the average thickness is only the area expanding ratio. From the micro morphology of strap-on biaxially stretching PP, it could be found that the tensile action make the craze generated and presented a symmetrical distribution along the lateral side; the number and extension lengths of crazes decreased with the increase of conveying speedThrough the theoretical analysis and experiment in this paper shows that the method, strap-on biaxially stretching film, has many obvious advantages compared to the traditional method and technology. The theoretical analysis and experimental research results lay a theoretical foundation for the development and progress of this film processing method, and also provide a strong support for the improvement and extension of the technology.