The main factors affecting the self-adhesiveness of stretched films

(1) Additives in basic resins used in the production of stretched films include LLDPE, mLLDPE, LDPE, EVA, and other basic resins. If additives such as smoothing agents, lubricants, and surfactants are included, it will cause the film to

There is a significant decrease in adhesion.

(2) The lower the resin density of the stretched film, the better the softness and adhesion of the film. Some types of resins such as mLLDPE and ULDPE have densities below 0.923g/cm2. When mixing these ultra-low density polyethylene resins during production, even without the addition of tackifiers, they still have good self-adhesiveness.

(3) When the extrusion casting film method is used to produce stretched films under the molding process conditions, due to the rapid cooling of the melt after leaving the mold mouth, only a small amount of tackifier is added to the film, which can achieve good self sealing properties.

When using extrusion blown film method to produce stretched film, the cooling rate of the film bubble is slow, and even with the same formula, the self-adhesiveness of the film is not as good as that of extrusion cast stretched film. Therefore, a large amount of tackifier needs to be added, but the temperature of the cooling air in the air ring can also affect the self-adhesiveness of the stretched film. From Figure 5-10, it can be seen that the lower the temperature of the cooling air, the better the cooling of the membrane bubble, and the corresponding increase in the shear viscosity of the membrane. Moreover, the viscosity of the stretched film increases with increasing storage time.

When using extrusion blown film method to produce stretched film, the lateral blowing ratio of the film also affects the viscosity of the stretched film. For films of the same thickness, the larger the blowing ratio, the better the self-adhesiveness.

(4) Adding an appropriate amount of tackifier during the production of stretched films can improve the self-adhesiveness of the film. Moreover, the self viscosity of the membrane increases with the increase of the amount of tackifier added.

Thickeners include ethylene vinyl acetate copolymer (EVA), ultra-low density polyethylene (ULDPE), random polypropylene (APP), polyisobutylene (PIB), and glycerol monooleate. PIB is the most commonly used and effective tackifier.