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Heat shrink film, also known as shrink film, as the name suggests, is a film that shrinks significantly in size when heated to a certain temperature. Heat shrink film is one of the more important and functional packaging films, mainly used for shrink packaging, but also in some aspects of special applications (such as the use of labels for bottles), heat shrink film has incomparable advantages over other packaging materials.
1. Shrinkage mechanism of heat shrink film
The function of shrink film shrinkage by heat originates from the high elastic forced deformation in the film, that is, in the process of manufacturing film, the macromolecules of plastic are subject to stretching and orientation in the high elastic state (i.e., the temperature range between glass transition temperature and melting temperature), resulting in high elastic forced deformation and freezing down the high elastic forced deformation when cooling; when the temperature rises, the activity of macromolecular chains of heat shrink film is constantly When the temperature is high enough, the intermolecular motion is sufficient to make the high-elasticity forced deformation disappear and unorientation occurs, resulting in macroscopic dimensional shrinkage.
According to the described mechanism, it is easy to see that the necessary condition for obtaining shrink films is the production of materials used in Haibin, with a certain temperature range of high elasticity deformation, where the stretching and orientation can be performed and where the molecular orientation obtained can be well frozen by a specific cooling process, thus giving the heat shrinkage function. In order to obtain heat-shrinkable films with practical use value to meet the needs of many practical applications, shrinkable films should have a sufficiently large heat shrinkage rate in addition to the necessary performance indicators such as a sufficiently wide heat shrinkage temperature range, moderate heat shrinkage stress and good physical and mechanical properties, in addition to being a heat shrinkable film for commodity packaging applications, the moderate price 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 shrink film
In principle, all thermoplastic films can be made into shrink film, but the current large-scale industrial application of shrink film, mainly limited to polyethylene, PVC and other general-purpose plastics, in addition to polyvinyl chloride, nylon, EVOH and other "barrier-type heat shrink film", in recent years, polyester, polystyrene and other heat shrink film R & D and application of polystyrene film has made great progress.
Heat shrinkable films should have a wider temperature range of high elastic deformation of raw materials, which is not only conducive to the manufacture of heat shrinkable films - easier to get a film with high forced deformation, and its shrink packaging performance is also better (to solve the forced deformation of a wider temperature range, the shrink packaging machine temperature control precision requirements are lower, packaging is also easier to (easier to operate). This is the reason why polyethylene with lower density and melt flow rate is generally used in the production of polyethylene heat shrink films; co-polyester resins are usually used in the manufacture of polyester heat shrink films, also for this reason. 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. Heat shrink film manufacturing methods
The current production process of heat shrinkable film for packaging: a thicker blank film is made first, and then heated to the appropriate temperature for stretching, i.e., depending on the blank film, it can be produced by flat sheet stretching (flat sheet method), or by the second blowing account stretching (i.e., double-bubble stretching) method. Flat sheet stretching is the current BOPP, BOPET and other common production method of pulling the middle barrier with it to produce a variety of packaging with heat-shrinkable film, from the control of the film's heat shrinkage performance is more desirable; the method of equipment investment is larger, but the output is high, and thus the cost of the product instead of lower, while the product thickness uniformity is good, mechanical strength is higher, can be applied to thin film thickness, thereby reducing the unit area of film The cost of the film per unit area is reduced and the competitiveness of the market is improved, so the development is faster in recent years. Compared with the flat sheet stretching method, the double-bubble stretching method has higher energy consumption and lower output, resulting in higher production costs and poor thickness uniformity, with the main advantage of less investment in equipment, and is currently mainly used for the production of polyvinyl chloride shrink films and co-extruded polyolefin heat shrink films. For polyethylene heat-shrinkable film can also be used for ordinary blown film equipment, the necessary improvements to the equipment (mainly the mouth die), the selection of specific grades of resin and specific process parameters, the application of a method similar to the ordinary blown film directly manufacturing heat-shrinkable film. www.susumino.com
4. Classification of heat-shrinkable films
There are various classifications of heat shrinkable films, and the more common ones are described below.
(1) Classification according to the different types of plastics
Such as common polyethylene heat shrinkable film, PVC heat shrinkable film, polyolefin heat shrinkable film, as well as polystyrene heat shrinkable film, polyester heat shrinkable film, etc.
(2) Classification according to the different film structures
Such as single-layer heat-shrinkable film, multi-layer heat-shrinkable film (also often specifying the layer structure, such as five-layer co-extruded heat-shrinkable film containing EVOH).
(3) Classification according to the different shrinkage situations
Such as bi-directional shrinkage film (the shrinkage rate of the longitudinal direction when the film shrinks is comparable to that of the transverse direction) and one-way shrinkage film (the shrinkage rate of the transverse direction when the film shrinks is significantly greater than that of the longitudinal direction, or the shrinkage rate of the longitudinal direction is significantly greater than that of the transverse direction); shrinkage film with high shrinkage (shrinkage rate above 50%) and shrinkage film with low shrinkage (shrinkage rate around 20%), etc.
1. Shrinkage mechanism of heat shrink film
The function of shrink film shrinkage by heat originates from the high elastic forced deformation in the film, that is, in the process of manufacturing film, the macromolecules of plastic are subject to stretching and orientation in the high elastic state (i.e., the temperature range between glass transition temperature and melting temperature), resulting in high elastic forced deformation and freezing down the high elastic forced deformation when cooling; when the temperature rises, the activity of macromolecular chains of heat shrink film is constantly When the temperature is high enough, the intermolecular motion is sufficient to make the high-elasticity forced deformation disappear and unorientation occurs, resulting in macroscopic dimensional shrinkage.
According to the described mechanism, it is easy to see that the necessary condition for obtaining shrink films is the production of materials used in Haibin, with a certain temperature range of high elasticity deformation, where the stretching and orientation can be performed and where the molecular orientation obtained can be well frozen by a specific cooling process, thus giving the heat shrinkage function. In order to obtain heat-shrinkable films with practical use value to meet the needs of many practical applications, shrinkable films should have a sufficiently large heat shrinkage rate in addition to the necessary performance indicators such as a sufficiently wide heat shrinkage temperature range, moderate heat shrinkage stress and good physical and mechanical properties, in addition to being a heat shrinkable film for commodity packaging applications, the moderate price 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 shrink film
In principle, all thermoplastic films can be made into shrink film, but the current large-scale industrial application of shrink film, mainly limited to polyethylene, PVC and other general-purpose plastics, in addition to polyvinyl chloride, nylon, EVOH and other "barrier-type heat shrink film", in recent years, polyester, polystyrene and other heat shrink film R & D and application of polystyrene film has made great progress.
Heat shrinkable films should have a wider temperature range of high elastic deformation of raw materials, which is not only conducive to the manufacture of heat shrinkable films - easier to get a film with high forced deformation, and its shrink packaging performance is also better (to solve the forced deformation of a wider temperature range, the shrink packaging machine temperature control precision requirements are lower, packaging is also easier to (easier to operate). This is the reason why polyethylene with lower density and melt flow rate is generally used in the production of polyethylene heat shrink films; co-polyester resins are usually used in the manufacture of polyester heat shrink films, also for this reason. 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. Heat shrink film manufacturing methods
The current production process of heat shrinkable film for packaging: a thicker blank film is made first, and then heated to the appropriate temperature for stretching, i.e., depending on the blank film, it can be produced by flat sheet stretching (flat sheet method), or by the second blowing account stretching (i.e., double-bubble stretching) method. Flat sheet stretching is the current BOPP, BOPET and other common production method of pulling the middle barrier with it to produce a variety of packaging with heat-shrinkable film, from the control of the film's heat shrinkage performance is more desirable; the method of equipment investment is larger, but the output is high, and thus the cost of the product instead of lower, while the product thickness uniformity is good, mechanical strength is higher, can be applied to thin film thickness, thereby reducing the unit area of film The cost of the film per unit area is reduced and the competitiveness of the market is improved, so the development is faster in recent years. Compared with the flat sheet stretching method, the double-bubble stretching method has higher energy consumption and lower output, resulting in higher production costs and poor thickness uniformity, with the main advantage of less investment in equipment, and is currently mainly used for the production of polyvinyl chloride shrink films and co-extruded polyolefin heat shrink films. For polyethylene heat-shrinkable film can also be used for ordinary blown film equipment, the necessary improvements to the equipment (mainly the mouth die), the selection of specific grades of resin and specific process parameters, the application of a method similar to the ordinary blown film directly manufacturing heat-shrinkable film. www.susumino.com
4. Classification of heat-shrinkable films
There are various classifications of heat shrinkable films, and the more common ones are described below.
(1) Classification according to the different types of plastics
Such as common polyethylene heat shrinkable film, PVC heat shrinkable film, polyolefin heat shrinkable film, as well as polystyrene heat shrinkable film, polyester heat shrinkable film, etc.
(2) Classification according to the different film structures
Such as single-layer heat-shrinkable film, multi-layer heat-shrinkable film (also often specifying the layer structure, such as five-layer co-extruded heat-shrinkable film containing EVOH).
(3) Classification according to the different shrinkage situations
Such as bi-directional shrinkage film (the shrinkage rate of the longitudinal direction when the film shrinks is comparable to that of the transverse direction) and one-way shrinkage film (the shrinkage rate of the transverse direction when the film shrinks is significantly greater than that of the longitudinal direction, or the shrinkage rate of the longitudinal direction is significantly greater than that of the transverse direction); shrinkage film with high shrinkage (shrinkage rate above 50%) and shrinkage film with low shrinkage (shrinkage rate around 20%), etc.