How to solve the bonding problem of polyethylene stretch wra
Polyethylene resins used for stretch packaging films are mainly LDPE and LLDPE. Stretch packaging films need to have some adhesive to carry out packaging. PVC and high tensile vinyl acetate films have self bonding properties. In the flat film method, the film can be caking through sudden cooling of the cooling roller. However, the LDPE and LLDPE stretch packaging films obtained by blow molding method are lack of self adhesion.
Two methods can be used to solve the problem of film adhesion.
1. adding tackifier
The commonly used tackifier is glycerol monooleate, polybutene, random PP, EVA, etc. The thickening effect of polybutene is more prominent. When the addition amount is 3%, the adhesion of the film can be maintained when stretching 200 to 300%. However, because of the high viscosity of polybutene, it is difficult to measure hopper and must be made into masterbatch.
With the development of no pallet packaging, the requirements for the adhesion of the tensile film have changed, that is, the demand for the non adhesive tensile packaging film on the outside is required to avoid the sticky phenomenon caused by the direct contact of the bags without pallets and the tear cracking of the film caused by the sticky package.
EVA generally uses the method of blending to enhance viscosity. Because of the good adhesion of EVA, EVA and LLDPE were co extruded and EVA was used as the inner layer. LLDPE is also a stretch wrap composite film on the outer surface, which also meets the requirement of single side bonding.
2. hot-melt bonding
In order to solve the bonding problem and adapt to the requirement of no pallet packaging, the hot melt bonding is also developed, that is, the usual heat sealing. EVA and LLDPE blend or co extrusion can produce heat sealed stretch wrap film. However, if EVA and lLDPE are blended to produce the tensile packaging film, the effective thermal sealing must be added to 8~12%EVA, and the bond problem caused by EVA is not suitable for no tray packaging, so it is suitable for CO extrusion. Another way to solve this problem is to search for new materials to replace EVA and LLDPE blends, because they have good thermal sealing properties without cohesiveness.
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