In the vast world of packaging materials, cross-linked shrink film is gradually emerging with its unique performance and wide application, becoming an important force in promoting the development of the packaging industry. This article will deeply explore the definition, principle, classification, characteristics, application field, production process, market status and future development trend of cross-linked shrink film, and present you with the charm of this innovative packaging material in all aspects.
Cross-linked shrink film is a specially treated heat shrink film. When heated, it can shrink quickly and tightly wrap the packaged object to form a strong and close-fitting packaging layer. This film is usually made of polymer materials such as polyolefins, and the molecular structure is changed through cross-linking technology, so that it has excellent shrinkage performance and physical and mechanical properties.
The cross-linking process of plastic processing mainly includes two methods: chemical cross-linking and physical radiation cross-linking. Chemical cross-linking is to add a cross-linking agent to the raw material to form a cross-linked structure between molecules through a chemical reaction. However, due to the influence of the cross-linking process on the melt index, it is easy to produce an over-polymerization reaction, forming a large number of infusible materials such as crystal points, which affects the film-making process. Therefore, its application in the production of cross-linked films is limited.
Physical radiation cross-linking generally uses high-voltage electron beam radiation, which is more commonly used. Ordinary polyethylene (PE) molecules are stable linear chain structures. Under the radiation of high-voltage electron beams, a large amount of energy is introduced to break the C-H bonds and form free radicals between molecules. These free radicals combine with each other to form stable chemical bonds, which transform the linear structure of PE into a network structure, thereby changing the performance of the product. This cross-linked structure gives the film higher strength, heat resistance and shrinkage performance.
Cross-linked shrink film has a "memory effect". During the production process, the film is stretched to a certain extent and shaped, at which time the molecular chains are in an extended state. When heated, the molecular chains gain energy, start to move and try to return to the initial unstretched state, causing the film to shrink. The cross-linked structure enhances the interaction between the molecular chains, making the shrinkage force more uniform and strong, and can closely fit the surface of the packaged object.
l POF cross-linked film : short for biaxially oriented polyolefin shrink film. It uses linear low-density polyethylene (LLDPE) as the middle layer and co-polypropylene (PP) as the inner and outer layers. It is plasticized and extruded by three extruders, and then processed by die head molding, film bubble blowing and other processes. Cross-linked POF film is an upgraded product of ordinary POF film. Its physical properties and heat sealing strength are further improved compared with ordinary POF film. It has a wider shrinking temperature window and better adaptability to packaging machines.
l PE cross-linked film : With polyethylene as the main raw material, the molecular structure is changed by radiation cross-linking and other methods. Multi-layer co-extruded PE cross-linked shrink film is a new type of high shrinkage biaxial stretch shrink film developed on the basis of POF shrink film in recent years, with unique performance advantages.
l Online cross-linked shrink film : In the plastic biaxial stretching process, a high-voltage electron beam irradiation device (EB) is introduced, and radiation cross-linking occurs during online continuous production, and the collected original film roll has become a cross-linked film. The online radiation process is generally carried out after the initial film tube is water-cooled. This process will replace and release hydrogen, so the hydrogen emission technology of the initial film tube is very important.
l Non-online cross-linked shrink film : First, a multi-layer PE shrink film roll is made using a double-bubble biaxial stretching process, and then the film roll is cross-linked by electron beam radiation by rewinding outside the production line.
l High shrinkage rate : The shrinkage rate of cross-linked shrink film is usually high, up to 50% - 80%, or even higher. For example, the shrinkage rate of POF cross-linked film is above 70% in both directions, which can tightly wrap products of various shapes and provide good packaging fit.
l High strength and toughness : The cross-linked molecular structure forms a network, which greatly improves the tensile strength and tear strength of the film, and can withstand greater tension and impact, effectively protecting the product during packaging and transportation and reducing the breakage rate.
l High transparency : It has good optical properties, high transparency, no patterns, no crystal points, good gloss, can clearly display the packaged objects, and improve the product's sales and aesthetics.
l Good heat sealing performance : high heat sealing strength, wide heat sealing temperature range, firm and long-lasting seal, which can effectively prevent leakage of packaging contents and ensure the integrity of the packaging.
l Strong cold resistance : Even in low temperature environments, such as -50℃, it can still maintain softness and achieve normal product shrinkage, which is suitable for packaging needs under various climatic conditions.
l Environmental protection characteristics : Partially cross-linked shrink film is made of environmentally friendly materials, is odorless, and can be recycled, meeting the requirements of today's society for green packaging.
l Food industry : widely used in food packaging, such as bread, cakes, candies, vegetables, fruits, meat, beverages, etc. Its high shrinkage rate and good sealing can effectively preserve freshness, moisture and dust, and extend the shelf life of food; high transparency can show the color and quality of food, attracting consumers to buy. The cross-linked film processed by hot punching can also be used for packaging vegetables, eggs, etc., to ensure the gas exchange between food and the outside world, which helps to preserve freshness.
l Electronics industry : used for packaging of electronic products, such as mobile phones, computers, tablet computers, electronic accessories, etc. High strength and toughness can protect electronic products from collisions and scratches during transportation and storage; good insulation performance can also ensure the safety of electronic products; at the same time, high transparency can show the appearance of the product and enhance the product image.
l Pharmaceutical industry : Suitable for drug packaging, such as medicine boxes, medicine bottles, medical devices, etc. Its characteristics of sterility, environmental protection, and good sealing performance can ensure the quality and safety of drugs and prevent drugs from moisture, deterioration, and contamination.
l Daily chemical industry : used for packaging of daily chemical products such as cosmetics, shampoo, shower gel, etc. High transparency and beautiful packaging effect can enhance the grade and attractiveness of the product; good shrinkage performance can fit closely to containers of various shapes, making the packaging more exquisite.
l Other industries : It is also widely used in books, stationery, daily necessities, wood products, handicrafts and other fields to protect products and beautify packaging. For some special products, such as banknotes and lottery tickets, cross-linked shrink film can also meet special packaging needs due to its excellent shrinkage rate and strong sealing performance.
l Online cross-linking : In the double-bubble biaxial stretching process, the material is plasticized by the extruder and then forms a primary film tube through the die head. After water cooling, the primary film tube enters the high-voltage electron beam irradiation device (EB) for radiation cross-linking. During the irradiation process, the energy and dose of the electron beam are controlled to cause cross-linking reactions in the PE molecules. The cross-linked film is further stretched, cooled, and pulled, and finally rolled up to obtain a multi-layer co-extruded PE cross-linked shrink film with online cross-linking. In this process, attention should be paid to the hydrogen emission of the primary film tube to ensure production safety.
l Non-online cross-linking : First, the double-bubble biaxial stretching process is used to plasticize raw materials such as polyethylene through an extruder, and then formed into a primary film tube through a die head, and then biaxially stretched to align the molecular chains and improve the performance of the film. The stretched film is cooled, pulled, and made into a multi-layer PE shrink film roll. After that, the original roll is passed through a rewinding device outside the production line and cross-linked by radiation using an electron beam. During the cross-linking process, the radiation dose and time are precisely controlled to achieve the ideal cross-linking effect. Finally, the cross-linked film roll is post-processed by slitting, packaging, and other post-processing to obtain a non-online cross-linked multi-layer co-extruded PE cross-linked shrink film.
POF cross-linked film usually adopts a three-layer co-extrusion process. Linear low-density polyethylene (LLDPE) is used as the raw material for the middle layer, and co-polypropylene (PP) is used as the raw material for the inner and outer layers, which are added to three extruders respectively. After the raw materials are heated and melted in the extruder, they are co-extruded through a specially designed die head to form a composite film bubble. After the film bubble undergoes processes such as blowing, cooling, and pulling, it is initially formed into a POF ordinary film. To achieve cross-linking, radiation cross-linking or chemical cross-linking methods can be used. During radiation cross-linking, high-energy rays (such as electron beams and gamma rays) are used to irradiate the formed POF film to induce a cross-linking reaction between the molecular chains; chemical cross-linking is to add a cross-linking agent to the raw materials to cross-link the molecular chains under certain temperature and time conditions. The cross-linked POF film is then subjected to subsequent stretching, shaping, slitting and other process treatments to finally obtain a POF cross-linked film product.
At present, the cross-linked shrink film market is showing a steady growth trend. With the continuous improvement of consumers' requirements for product packaging and the emphasis of various industries on product protection and display effects, cross-linked shrink film has been increasingly widely used in the packaging field due to its excellent performance, and the market demand continues to increase.
Globally, the cross-linked shrink film market in developed countries and regions such as Europe and the United States is relatively mature, and the demand is growing steadily. Consumers in these regions have high requirements for the environmental protection, safety and aesthetics of packaging, which has promoted the development of high-performance cross-linked shrink films. At the same time, emerging economies such as China and India, with the rapid economic development and the rise of the manufacturing industry, have also shown a strong growth momentum in demand for cross-linked shrink films. In particular, driven by the food, electronics, daily chemicals and other industries, the scale of the cross-linked shrink film market continues to expand.
In terms of market competition, many packaging material companies have set foot in the field of cross-linked shrink film, and the market competition is fierce. Some large companies have taken a leading position in the market with advanced production technology, high-quality product quality and a complete sales network. At the same time, some small and medium-sized enterprises have also focused on specific fields or products through differentiated competition and strived to get a share of the market. In addition, with the increasingly stringent environmental protection requirements, cross-linked shrink film products with environmental protection characteristics are more favored by the market. Enterprises are also continuously increasing their R&D investment to develop more environmentally friendly and high-performance cross-linked shrink film products to meet market demand and policy requirements.
l High-performance development : As the requirements for packaging performance in various industries continue to increase, cross-linked shrink films will develop towards higher strength, higher shrinkage, wider shrinkage temperature range, better chemical resistance and weather resistance. Enterprises will increase R&D investment, improve raw material formulas, optimize production processes and cross-linking technology, and continuously improve the performance of cross-linked shrink films to meet the needs of high-end product packaging.
l Environmentally friendly and sustainable development : The enhancement of environmental awareness and the promotion of relevant policies will drive the cross-linked shrink film to develop in an environmentally friendly and sustainable direction. In the future, degradable and recyclable cross-linked shrink film products will become the mainstream of the market. Enterprises will be committed to developing new environmentally friendly materials and production processes to reduce the impact on the environment while meeting consumers' demand for green packaging. For example, cross-linked shrink film can be prepared using bio-based materials, or recyclable cross-linking technology can be developed to enable cross-linked shrink film to be effectively recycled and reused after use.
l Functional diversification : In order to meet the special packaging needs of different industries and products, cross-linked shrink films will show a trend of functional diversification. For example, cross-linked shrink films with special functions such as antibacterial, antistatic, anti-counterfeiting, and preservation are developed. Antibacterial cross-linked shrink films can be used for food and pharmaceutical packaging to effectively inhibit bacterial growth and extend the shelf life of products; antistatic cross-linked shrink films can be used for electronic product packaging to prevent static electricity from damaging electronic components; anti-counterfeiting cross-linked shrink films can provide anti-counterfeiting functions for products through special printing or material technology to protect brand rights.
l Intelligent development : With the development of the Internet of Things and intelligent packaging technology, cross-linked shrink film is expected to be combined with intelligent technology to achieve intelligent development. For example, adding sensors or smart labels to cross-linked shrink film can monitor the temperature, humidity, shelf life and other information of the product in the package in real time, and transmit this information to consumers or related companies through wireless communication technology, so as to realize intelligent management and traceability of products.
l Development of customized services : The personalization and diversification of consumer demand will drive cross-linked shrink film companies to develop in the direction of customized services. Companies will provide one-stop customized services from product design, raw material selection, production process to packaging solutions based on the different needs of customers, meet customers' unique requirements for packaging, and improve customer satisfaction and market competitiveness.
As an innovative packaging material, cross-linked shrink film plays an important role in the packaging field with its unique properties and wide application. With the continuous advancement of technology and changes in market demand, cross-linked shrink film will usher in a broader development space and continue to inject new vitality into the innovation and development of the packaging industry.
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