Polyethylene film application overview
As we all know, polyethylene has a wide range of applications, can be used for the production of plastic film by blowing or casting, can be used for injection molding or blow molding to produce hard plastic products, can be used for wire and cable and so on. In this article, we focus on the main film applications of polyethylene.
The composite film is generally composed of a composite substrate (OPA, OPP, OPET)-adhesive-PE (heat seal). The composite substrate provides stiffness, strength, optical properties, printability, barrier properties, and the like, depending on the particular requirements. The PE heat seal structure mainly provides heat sealing performance, plus additional toughness and stiffness. Composite membranes are used in a wide range of applications, such as most frozen or non-frozen food packaging, non-food packaging such as laundry detergents and cosmetics. The composite process mainly uses dry method, wet method, extrusion compounding, solventless compounding, etc., which is described in the previous article: Overview and introduction of the composite membrane process. Since polyethylene mainly provides heat sealing properties, it is necessary to consider the use of a polyethylene resin having a good heat sealing property such as metallocene polyethylene or octacarbon linear low density polyethylene. It is necessary to pay attention to controlling the friction coefficient of the heat seal layer, and it is possible that the friction coefficient will increase after the compounding.
2. Heat shrinkable film
As the name suggests, the heat shrinkable film refers to a film that shrinks automatically when heated, and is mainly used for beverage packaging, such as mineral water, carbonated drinks, and the like. The main performance requirements of the film are: lateral shrinkage and shrinkage speed, tensile strength, puncture resistance, and drop resistance. In the formulation, it is necessary to contain LDPE with higher degree of branching. In the process of film blowing, a large lateral orientation is obtained by freezing at a high blow ratio of 2.8-3.5, and most of the orientation is frozen due to the long relaxation time of LDPE. And with memory, and in the case of heating, the oriented molecules want to return to the previous state and thus contract. Sometimes it is necessary to add HDPE to improve stiffness and tightness. The addition of LLDPE or metallocene is for strength and heat sealing.
3. Stretch film
Stretch film is mainly used to wrap and reinforce some bulk items to prevent loosening during transportation. There are also hand-held film and machine film. The available casting can also be used in the blown film process. The main performance requirements of the film are: tensile properties, puncture resistance, clamping force, tear strength, and tack. The stretch ratio of the hand-drawn film is small, generally less than 100%, and the film needs to have a good tensile hardness, so that a higher clamping force can be obtained, and a material with a long branch chain such as LDPE can be introduced to increase the tensile curve. At the same time, it can reduce necking and tiger skin. The machine pull film requires a higher stretch ratio, especially in high speed packaging, to ensure that the film does not break during rapid stretching. Generally, the casting uses a linear low density polyethylene or a metallocene material with a higher melting index. Viscosity is generally achieved by the addition of PIB (polyisobutylene) or by the addition of an elastomer having a lower crystallinity to the adhesive layer. Since the stretch ratio of the drawn film is higher, less (light) film is required to achieve the same winding effect, which is more economical. In terms of trends, the machine pull film will gradually replace the hand film.
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