High transparency is conducive to the identification of goods; high longitudinal elongation is favorable for pre-stretching and saves material consumption; good puncture performance and transverse tear strength allow the stretched film to meet the sharpness of the goods at high stretch ratios Corners or edges do not break; high yield points make the packaged goods more secure. The film produced by the casting method has high transparency, which is not discussed here.


As the number of comonomers in the material increases, the branch chain length increases, the crystallinity decreases, and the "entanglement or kinking" effect of the resulting copolymer increases, so the elongation increases, and the puncture and tear strengths also increase. MPE is a high stereoregular polymer with a narrow molecular weight distribution, which can accurately control the physical properties of the polymer, so there is a further improvement in performance; and because of the narrow molecular weight distribution of MPE, the processing range is also narrow, and the processing conditions are difficult to control, usually Add 5% LDPE to reduce the melt viscosity and increase the flatness of the stretched film.


The price of stretched film is also high. In order to reduce the cost, stretched film is usually used with C4-LLDPE, but not all C4-LLDPE can be used with it, and there should be a choice. Machine stretch film use more C6, C8 materials, ease of processing, to meet packaging requirements. Due to the low stretch ratio, C4 materials are mostly used for manual packaging.


Material density also affects the properties of stretched films. With the increase of density, the degree of orientation increases, the flatness is good, the longitudinal elongation increases, and the yield strength increases, but the transverse tear strength, puncture strength, and light transmittance all decrease. Therefore, the performance of all aspects is often non-sticky. A layer of medium density linear polyethylene (LMDPE) was added to the layer. Add LMDPE may further reduce the friction coefficient of the non-adhesive layer, wrapped tray and the tray to avoid sticking. Effect of cooling roll temperature. Chill roll temperature, the yield strength increased, but the rest of performance degradation, it is generally the temperature of the cooling roll I is controlled to 20 ℃ ~ 30 ℃ appropriate.