In the field of plastic film manufacturing, three-layer blown film machines are key equipment for producing high performance film with their unique layered structure design. This kind of design can combine the materials with different characteristics into layers and achieve comprehensive properties that are difficult for a single material to achieve. It meets the different requirements of food packaging, agricultural film, industrial packaging and so on. It is of great significance to study the layered structure design of three-layer blown film machines and the mechanism of optimizing film performance.
Principle of Layered Structure Design of Three-layer Membrane Blower
The core of a three-layer membrane blower lies in its layered structure, which is generally composed of surface, middle and bottom layers. Each layer can be selected from different materials according to specific needs. Three independent extruders are used for melting and plasticizing different materials. The molten material is then coalesced into a three-layer composite tubular melt through a co-extrusion die. After blowing molding, cooling, stretching, winding and so on a series of processes, the final formation of a three-layer composite film with specific properties. In this process, the three-layer blown film machine enables precise control over each layer's thickness and material distribution.
The principle of this layered structure design is based on the complementary properties of different materials. For example, surface materials may focus on printing, scratch resistance and barrier properties; middle materials may focus on providing mechanical strength, barrier performance or thermal stability; and bottom materials may focus on heat-sealability, anti-blocking properties and compatibility with packaged products. By reasonably matching each layer of material, we can make full use of the advantages of each layer and achieve an optimized combination of the properties of the films.
Optimizing the Physical Properties of Thin Films Through Layered Structure Design
Mechanical Properties
The layered structure design of a three-layer blown film machine can really help make the film stronger. The middle layer often uses strong and stiff materials like high-density polyethylene (HDPE) or nylon (PA). These give the film most of its strength. The top and bottom layers can use soft and stretchy materials like LDPE or linear LDPE. These help make the film better at resisting punctures and tears.
For example, high-density HDPE (HDPE) is used in the production of high-strength packing films. Its high strength and modulus make the film able to withstand large external forces without breaking. LDPE or LLDPE is used for surface and bottom layers. Its excellent flexibility and elongation can effectively disperse stress and prevent the crack from spreading when the film is pierced or torn. Through this layered structure design, the tensile strength, penetration and tear resistance of the film are greatly improved, and the requirements of heavy packing and transportation are met.
Optical Properties
The optical properties of thin films, like transparency and glossiness, are very important in areas like food packaging and display packaging. The layered structure design of a three-layer film blower can make the film's optical properties better. It does this by picking the right materials and by making the process parameters better.
The choice of surface layer material has an important influence on the transparency of films. High transparency materials such as metallocene linear low-density polyethylene (mLLDPE) are used to make the film have good light transmittance and clearly display the products inside the packaging. At the same time, the crystallization and orientation of the film can be reduced, fog haze can be reduced and the transparency of the film can be improved by optimizing the blowing sweep ratio and cooling process. For example, in the production of high transparency food packaging films, mLLDPE is used in the surface layer with an explosion ratio of between 2.5 and 3.0 and a rapid cooling process is used. This can make the film over 90 transparent and meet the transparency requirements of food packaging.
Barrier Characteristics
Barrier properties are an important index of film quality, which directly influences the shelf life and quality of packaging products. The layered structure design of the three-layer fan can make the barrier performance of the film better. It is achieved by adding high barrier materials such as ethylene-vinyl alcohol copolymer (EVOH), polyvinylidene chloride (PVDC) or nylon (PA) to the middle of the film.
EVOH is a material that has very good oxygen barrier properties. Its oxygen permeability is thousands of times lower than that of ordinary polyethylene. By adding EVOH in the middle, it can stop oxygen, water vapor, and aroma substances from getting through. It can also make the shelf life of packaging products longer. For example, in the production of food packaging films, EVOH is used in the middle layer. Through reasonable layer ratio design and process control, the oxygen permeability of the films can be reduced to less than 0.5 cm³/(m²·24h·0.1 MPa) and the water vapor permeability to less than 2 g/(m²·24h), which meets the requirements of food preservation.
Optimizing the Chemical Properties of Thin Films Through Layered Structure Design
Chemical Corrosion Resistance
In some applications, films need to be chemically corrosion resistant to protect packaged products from chemical corrosion. The layered structure design of a three-layer membrane blower can be achieved by selecting a chemical corrosion resistant material.
For example, in the area of chemical product packaging, polytetrafluoroethylene (PTFE) or polypropylene (PP) can be used as surface layers. These materials have very good chemical corrosion resistance. They can resist acid, alkali, salt, and other chemical substances. Materials with good mechanical properties, like high density polyethylene (HDPE) or polyacrylonitrile (PAN), can be used in the middle layer. This gives support and protection for the film. With this layered structure design, the film can keep stable properties in harsh chemical environments. It also helps keep packaged products safe.
Thermal Stability
Thermal stability means the film can stay stable under high temperature conditions. Some uses need high temperature treatment or high temperature use. These include heat shrink packaging and retort packaging. For these applications, films require good thermal stability. The layered structure design of a three-layer film blower can improve the thermal stability of the film by selecting heat resistant materials in the lower and middle layers.
For example, in the making of retort packaging films, polyamide (PA) or polyethylene terephthalate (PET) can be used in the middle layer. These materials have high melting points and good thermal stability. They also stay stable under high temperature sterilization conditions. Materials with good heat sealability, like LDPE or ethylene-vinyl acetate copolymer (EVA), can be used on the top and bottom layers. This helps make sure the film can seal well at high temperatures. With the layered structure design, the film can handle retort temperatures above 120°C. This meets the needs of food retort packaging.
Optimization of Film Processing Performance Through Layered Structure Design
Heat-Sealability
Heat sealability is an important processing property of the film. It directly affects the sealing and reliability of packaging. The layered structure design of the three-layer blower can make the film's heat sealability better. It does this by adding heat sealable materials like EVA or LDPE to the bottom layer of the film.
EVA is a kind of material with excellent heat-sealability, wide thermalsealing temperature range and high thermalsealing strength. After adding EVA to the bottom, it can achieve good heat-sealing effect at lower temperature, has high heat sealing strength and reduces the risk of air leakage. For example, in the production of food packaging bags, EVA is used at the bottom. By adjusting EVA content and thermalsealing process parameters, the thermalsealing temperature of the film can be reduced to less than 100°C, and the thermalsealing strength can reach over 5 N/15 mm, satisfying the requirements of food packaging.
Printability
Printability is an important application property of film in packaging field, which directly influences the aesthetic and information transmission effect of packaging. The layered structure of the three-layer blower can improve the printability of the film by adding printable materials such as copolypropylene (CPP) or high-density polyethylene (HDPE) to the surface.
CPP is an excellent printability material, high surface tension, strong ink adhesion, can achieve high quality printing effect. After adding CPP to the surface layer, the film can meet the requirements of gravure printing, flexo printing, screen printing and other printing processes. For example, in the production of high-end food packaging films, CPP is used on the surface. Adopt the surface treatment process to improve the surface tension of the film. Each inch of printing can be more than 150 lines of clarity, bright colors and meet the printing requirements of high-end packaging.
Conclusion
The layered structure design of three-layer blown film machines provides a wide space for optimizing the properties of the membrane. The mechanical properties, optical properties, barrier properties, chemical properties and processing properties of the films can be significantly improved by selecting each layer of material and optimizing the layer ratio design and technological parameters, so as to meet the different requirements of different fields. With the continuous development of materials science and manufacturing technology, the layered structure design of three-layer film blowers will be continuously innovative and perfect, bringing more development opportunities and challenges to the film manufacturing industry. In the future, we should further strengthen the layered structural design of three-layer film blowers, explore new material combinations and process methods, promote the continuous improvement of film performance, and provide higher quality film products for the development of all industries.
