The family of shrink films has broadened over the years with many multi-layer constructions being sold today. Upon inflation, the tube is oriented in both directions simultaneously. After the primary tube has been cooled, it is then reheated and inflated into a second bubble using air much like a balloon is blown. It is common to use water to help cool the primary tube at this point. In this process, a primary tube is produced by either blowing or casting the tube onto an external or internal mandrel, respectively. The second commercial process is the bubble process, sometimes referred to as the tubular process. Tenterframe technology is used to produce a variety of “heat-set” products, with biaxially oriented polypropylene (BOPP) being the most common (heat-setting is a process whereby a film is reheated in a constrained state such that the shrink properties are destroyed). Orientation on a commercial scale can be achieved using either of two processes: a tenterframe or a bubble process. However, when enough heat energy is applied, the rubber band will shrink back to its original relaxed state. ![]() The band will remain in this state as long as it is kept at sufficiently cold temperatures. One can visualize this phenomenon by stretching a rubber band and dipping it into liquid nitrogen so as to freeze in the stretched state. By applying proper cooling, the molecules will be frozen in this state until sufficient heat energy is applied to allow the chains to shrink back. However, when a draw force is imposed, the amorphous regions of the chains are straightened and aligned to the direction of orientation. The molecules are coiled and twisted and have no particular alignment. Prior to orientation, the molecules of a sheet or tube are randomly intertwined like a bowl of spaghetti. Cooling the film sets the film's characteristics until it is reheated: this causes it to shrink back toward its initial dimensions. Manufacture A machine designed to continuously wrap up to 35 packets per minuteĪ shrink film can be made to shrink in one direction (unidirectional or mono-directional) or in both directions (bidirectional).įilms are stretched when they are warm to orient the molecules from their initial random pattern. The disadvantage for PE is that it does not have a great shrink rate, and has lower clarity than other wraps. PE gauges can go all the way up to 1200, allowing for a great range of gauges. These wraps can also have graphic images printed on them, and LDPE provides the greatest quality. For shrink wrapping LDPE would be the best choice, as it has a higher strength, and more durability for heavier items. These include Low-Density Polyethylene (LDPE), Linear Low-Density Polyethylene (LLDPE), and High-Density Polyethylene (HDPE). There are 3 different forms PE can take place in. PE, a polyolefin, is used in several forms of flexible protective packaging. POF is great for bundling multiple items together, and has the ability to shrink completely and quickly. ![]() It has great clarity, and a glossy self-appearance, as appearance is critical. POF shrink wrap is made from 100% recyclable materials, and is FDA approved. POF is available in 35, 45, 60, 75, and 100, 1 mil gauges. POF is puncture resistant, and has a strong seal strength, which allows it to be used for irregularly shaped items. Polyolefin or POF shrink wrap is a premium shrink wrap, as it's extremely durable and versatile. PVC has some negative qualities including, it is not good for bundling, leaves carbon deposits, and has a low shrink force. PVC has been banned in many countries, due to the harmful products created by its decomposition. However, it should be used in a well-ventilated area, as it can give off a strong, harmful odor. PVC is durable, and can be used for many different purposes. PVC is the most used shrink wrap, due to its light weight, and inexpensive capabilities. For example, five layers might be configuration as EP/ EVA/ copolyester/EVA/EP, where EP is ethylene-propylene and EVA is ethylene-vinyl acetate copolymer. Other shrink films include PVC, Polyethylene, Polypropylene, and several other compositions.Ĭoextrusions and laminations are available for specific mechanical and barrier properties for shrink wrapping food. The two primary films can be either crosslinked, or non crosslinked. It is available in a variety of thicknesses, clarities, strengths and shrink ratios. ![]() The most commonly used shrink wrap is polyolefin. Heat can be applied with a handheld heat gun (electric or gas), or the product and film can pass through a heat tunnel on a conveyor. When heat is applied, it shrinks tightly over whatever it is covering. Shrink wrap, also shrink film, is a material made up of polymer plastic film. ![]() Grocery vegetables wrapped with a plastic shrink film. For other uses, see Shrink wrap (disambiguation).
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |