Heat-shrinkable film is also known as shrink film, and as the name suggests it is a film whose dimensions shrink significantly after the film is heated to a certain temperature. Shrinkable film is an important packaging film, the application of more functional film, mainly for shrink packaging, but also in some aspects of special applications (such as as bottle labels), shrink film than other packaging materials also has incomparable advantages.


1. Shrinkage mechanism of heat shrinkable film
Shrink film by heat shrinkage function, from the film has a high elasticity forced deformation, that is, in the process of manufacturing film, so that the plastic macromolecules in the high elasticity state (i.e., the temperature interval between the glass transition temperature and the melting temperature) by the tensile directional action, resulting in high elasticity forced deformation and in the cooling of the high elasticity forced deformation will be frozen down; in the temperature rises, the shrink film of the macromolecule chain of the activity of the capacity to continue to enhance, when the temperature reaches a high enough temperature, the film will be frozen down. Enhanced, when the temperature reaches a high enough time, the intermolecular movement is enough to make the high elasticity forced deformation disappears and de-orientation, and then produce macro size contraction.
According to the mechanism mentioned above, it is easy to see that the necessary condition for obtaining the shrinkable film is that the material used in the production of seafoam has a certain high elastic deformation temperature range, in which the stretching orientation is carried out and the molecules orientated to be obtained can be well frozen down through a specific cooling process, so as to confer the function of heat shrinkage. In order to obtain the actual value of the use of heat shrinkable film, to meet the needs of many practical applications, shrinkable film should have a large enough heat shrinkage in addition to shrinkable film should also have a wide enough temperature range of heat shrinkage, moderate heat shrinkage stress, as well as good physical and mechanical properties and other necessary performance indicators, in addition to the application of heat shrinkable film as a commodity packaging, the price of the right amount of money is also a very important factor. www.susumino.com南京住野精工机械有限公司专业研发生产薄膜生产设备
2. Plastics for heat-shrinkable films


In principle, all of the thermoplastic film may be made of shrink film, but at present has been a large-scale industrial application of shrink film, mainly limited to polyethylene, PVC and other general-purpose plastics, in addition to polyvinylidene chloride, nylon, EVOH and other "barrier class shrink film", in recent years, polyester, polystyrene and other heat shrink film In recent years, polyester, polystyrene and other heat shrinkable films have made great progress in research and development and application.



Shrinkable film ideal raw materials should have a wide range of high elastic deformation temperature range, which is not only conducive to the production of heat shrinkable film manufacturing - easier to get a high deformation of the film, and its shrink packaging performance is also better (to solve the forced deformation of the temperature range is broader, the temperature of the shrink wrapping machine to control the accuracy of the requirements of the lower packing is also more easily (the temperature range for unforced deformation is wider, requiring less precision in temperature control of the shrink packaging machine and easier to operate the packaging). This is the reason why lower density, lower melt flow rate polyethylene is generally used in the production of polyethylene heat shrink films, and why co-polyester resins are often used in the manufacture of polyester heat shrink films. www.susumino.com南京住野精工机械有限公司专业研发生产薄膜生产设备



3. Manufacturing methods for heat-shrinkable films

The current production process of heat-shrinkable film for packaging: first make a thicker blank film, and then heated to the appropriate temperature for stretching, that is, depending on the blank film, you can use the flat sheet stretching (flat sheet method), you can also use the adjusted second blowing account stretching (i.e., double-bubble stretching) method for production. Flat sheet stretching is currently BOPP, BOPET and other pull the common production method of the barrier with which to produce a variety of packaging heat-shrinkable film, from the control of the film's heat-shrinkage performance is ideal; the method of investment in equipment is larger, but the output is high, and thus the cost of the product but lower, while the thickness of the product uniformity is good, high mechanical strength, can be applied to the thickness of the thinner film, thus reducing the unit area of film The cost of the film per unit area, improve market competitiveness, so in recent years the development of faster. Double bubble stretching method compared with the flat sheet stretching method, energy consumption is larger, lower yield, and thus higher production costs, and thickness uniformity is not good, its main advantage is that the investment in equipment is less, is mainly used for polyvinyl chloride shrink film, co-extruded polyolefin heat shrinkable film production. For polyethylene heat shrinkable film can also be used for ordinary blown film equipment, equipment (mainly mouth mould) after the necessary improvements, the selection of specific grades of resin and specific process parameters, the application of similar to ordinary blown film method of direct manufacturing heat shrinkable film. www.susumino.com南京住野精工机械有限公司专业研发生产薄膜生产设备


4.Classification of heat shrinkable film

There are various classification methods for heat-shrinkable films, and the more commonly used ones are as follows