We live in a world of plastics. They’re everywhere, from the phones in our hands to the cars we drive. But behind the scenes, a hidden hero is quietly revolutionizing the world of polymers: POE.
What is POE?
POE stands for Polyolefin Elastomer. This special type of plastic is a powerhouse of performance, boasting incredible properties like:
- High Elasticity: POE is incredibly flexible, able to stretch and bounce back to its original shape, making it ideal for applications where resilience is key.
- Low Density: POE is lightweight, making it perfect for applications where weight reduction is crucial, like automotive parts and packaging.
- Good UV Resistance: POE can withstand the harsh effects of sunlight, making it suitable for outdoor applications like solar panels and automotive components.
A Versatile Material:
POE’s impressive properties have made it a versatile material, finding its way into a wide range of applications, including:
- Automobiles: POE is used to create flexible and durable parts for cars, like bumpers, dashboards, and door panels. Its impact resistance and weather resistance make it a perfect choice for these demanding applications.
- Photovoltaics: POE is a key component in solar panels, providing a durable and weather-resistant encapsulation for the delicate solar cells. Its UV resistance ensures long-term performance in harsh outdoor conditions.
- Other Applications: POE is also used in a wide range of other applications, including:
- Packaging: POE’s flexibility and durability make it ideal for creating protective packaging for electronics, food, and other products.
- Foamed Materials: POE can be used to create lightweight and insulating foams for various applications, including insulation, cushioning, and packaging.
- Direct Modification: POE can be blended with other polymers, like polypropylene and polyethylene, to enhance their properties, making them more durable and flexible.
The Future of POE:
The global demand for POE is growing rapidly, driven by the increasing use of solar panels and the demand for lightweight and durable materials in the automotive industry. As the world transitions to a more sustainable future, POE’s excellent properties and versatility make it a key player in the development of innovative and environmentally friendly solutions.
A Material with a Bright Future
POE is a hidden hero of the plastics industry, quietly revolutionizing the way we manufacture and use materials. Its incredible properties, versatility, and growing demand make it a material with a bright future, shaping the world around us in innovative and sustainable ways.
- Overview of POE
Polyolefin elastomer (POE) is a type of high-end polyolefin. POE is a copolymer obtained by polymerizing ethylene as the main polymerization unit and α-olefins (mainly α-olefins with 4 to 8 carbon atoms, such as butene, hexene, and octene) as comonomers. Compared with ordinary polyolefins, it has a higher comonomer content and lower density in its molecular chain. Due to its special molecular structure, it has good rheological properties, mechanical properties, UV resistance, low-temperature toughness and other characteristics, and is known as Widely used in blending modification of polypropylene and polyethylene (auto parts, home appliance casings, waterproof membranes, pipes), and toughening modification of polyamide and polyester polymers (construction, machinery, electronics, automobiles, etc.) , foam modification (sole materials) and photovoltaic film and other fields.
- POE technical barriers
POE has high technical barriers in terms of metallocene catalysts, α-olefins (linear monoolefins with double bonds at the end of the molecular chain), and solution polymerization processes. At present, global POE production capacity is mainly concentrated in a few companies such as Dow Chemical, ExxonMobil, Japan’s Mitsui Chemicals, LG Chemical, SK/SABIC and Borealis. The only companies that produce POE for photovoltaics are Dow Chemical, Mitsui Chemicals and LG Chemical. enterprise.
►Metallocene catalyst: The current mainstream catalyst for synthesizing POE is metallocene catalyst, including main catalyst (metallocene compound, a complex formed by cyclopentadiene and transition metal elements) and cocatalyst (mainly methylaluminoxane ( MAO) or organic borides, of which MAO is the most widely used). The internal ligand structures and composition contents of catalysts used to produce polyethylene, polypropylene and POE are different. POE production mostly uses metallocene catalysts with limited geometric structures, metallocene catalysts with bridged double ligand structures, etc. Due to the difficulty in synthesizing metallocene compounds and cocatalyst methylaluminoxane (MAO), domestic metallocene catalysts have been gradually localized.
►Linear α-olefins: The processes for industrial production of linear α-olefins include ethylene oligomerization, paraffin cracking (the resulting mixed olefin composition is more complex), mixed C4 separation (only 1-butene can be produced), Fischer-Tropsch synthesis, High-carbon alcohol dehydration method, vegetable oil method (complex process, low yield), etc. Among them, the ethylene oligomerization method is currently the most important process for the production of linear α-olefins in the world because the products are all even-numbered carbon products and have high selectivity and purity. Due to the technological blockade of α-olefins by overseas companies and high technology transfer costs, domestic α-olefins currently mainly produce 1-butene, while 1-hexene and 1-octene mainly rely on imports, of which 1- Basically all octene is imported.
►Solution polymerization: POE requires a continuous tubular method for solution polymerization, and it is necessary to strictly control the comonomer to stably exist in the solution in liquid form and participate in the polymerization. If the monomer becomes gaseous, the concentration and content of the comonomer in the solution will decrease, causing the overall viscosity of the solution to increase, which may ultimately prevent the polymerization reaction from occurring. Due to the restriction of technology transfer by the main technology vendors of polymerization process and the insufficient accumulation of domestic enterprises in solution polymerization process, it is also an important factor restricting the development of domestic POE.
- Main application fields of POE
At present, automobiles and photovoltaics are still the largest application fields of POE.
Due to POE’s excellent water vapor barrier and anti-PID properties, its penetration rate in N-type photovoltaic cell packaging films has increased. With the rapid growth of N-type photovoltaic installations such as TOPCon, the demand for POE from photovoltaic films will continue to increase.
From the perspective of downstream applications, POE is mainly used for direct modification, graft modification, foaming modification and use as a separate material. From the perspective of downstream terminal fields, automobiles are still the largest application field of POE. With the continued rapid growth of global photovoltaic installed capacity and the increase in the penetration rate of POE film, photovoltaics is the field with the fastest growing demand for POE.
►Direct modification: POE is mainly used for blending modification of polypropylene and polyethylene. The blended modified polyethylene and polypropylene have toughening and excellent impact resistance.
Polypropylene modified with POE has good fluidity and low linear expansion coefficient. It can better replace metal parts and be used in the production of automobile parts (car bumpers, door panels, interior decorations), etc., and home appliance casings (air conditioners, TVs, washing machines, etc.) shell). Polyethylene modified with POE can be used to produce waterproof membranes, pipes, etc.
► Graft modification: It is mainly used to toughen and modify polyamide and polyester polymers. By blending POE with polyamide and polyester polymers, the impact properties of the polymer can be significantly improved.
►Foaming modification: POE is mainly used to modify EVA to produce sports shoe midsoles, which can improve the elasticity of soles and provide better tear strength and tensile properties. POE can also be used alone to produce sports shoe midsoles instead of EVA.
►Single material use: Mainly used in the production of encapsulation films in photovoltaic modules. Since the photovoltaic cell packaging process is irreversible and has high requirements on the operating life of the modules, the quality of the packaging film is critical to the quality and life of the photovoltaic modules and cells. The adhesive film produced by POE has low water vapor transmission rate and high volume resistivity, and has good anti-PID performance.
As one of the materials of photovoltaic modules, photovoltaic adhesive film’s main function is to bond photovoltaic cells, photovoltaic glass and backsheets together. It can isolate external water vapor while ensuring the light transmission performance of the module, extend the life of photovoltaic modules and protect cells. , and package it into a photovoltaic module that can output direct current. According to the actual application requirements of photovoltaic modules, photovoltaic adhesive films should generally have excellent performance characteristics such as high transparency, high adhesion, good weather resistance, easy storage, good sound insulation, low melting point, and easy flow.
Photovoltaic packaging film is the core component of photovoltaic modules, and its cost accounts for 3% to 4% of the module cost.
The production of photovoltaic film usually uses resin (EVA, POE) as the main material. By adding cross-linking agents, thickeners, antioxidants, and light stabilizers, the finished product is obtained through melt extrusion and casting. Photovoltaic film is mainly divided into EVA film, POE film, EPE film, etc. Each type of adhesive film has its specific advantages and application scenarios. Among them, EVA film and POE film are the two main categories.
From the perspective of the industrial chain, the upstream of photovoltaic films mainly relies on the petrochemical industry, in which raw materials such as EVA resin and POE resin occupy an important position. EVA and POE resin are highly dependent on imports. The main global production capacity of midstream film and downstream components is mainly concentrated in my country.
EVA film
EVA (Ethylene-Vinyl Acetate Copolumer) film is a functional film made by adding ingredients such as cross-linking agents, coupling agents, and anti-UV agents to a resin based on ethylene/vinyl acetate copolymer (commonly known as thermoplastic resin). film. EVA film includes two types: transparent EVA film and white EVA film. Among them, transparent EVA film, with its mature technology, has become the mainstream packaging film in the current market.
The transparent EVA film has the characteristics of high light transmittance, resistance to UV yellowing, resistance to snail lines, and good adhesion. However, it has poor reflectivity and high water permeability, and is prone to potential induced attenuation (potential induced attenuation). degradation (PID) phenomenon, leading to a decrease in the power of the battery module; the white EVA film is an innovation based on the transparent EVA. It is pretreated by adding white seasoning and is used for packaging the underside of the photovoltaic module cells, which can reduce sunlight. Secondary reflection to the cell surface improves the power generation efficiency of solar modules. The disadvantage is that the price is higher.
The EVA film will produce cross-linking and curing reactions under certain temperatures and pressures, bonding the battery, glass and backplane into a whole. It not only provides strong mechanical protection, but also effectively protects the battery from erosion by the external environment. This ensures that the solar cells can be used normally under long-term outdoor exposure to the sun and rain. During the component lamination process, after EVA is melted, one end of the coupling agent is combined with EVA and the other end is combined with glass, increasing the interaction between the two.
The performance of EVA mainly depends on the content of vinyl acetate (expressed in VA%) and the melting index (Melting Idex, MI). The greater the VA content, the stronger the polarity of the molecule. The adhesion, light transmittance, and The softer it is, the better. Melt index MI refers to the weight value of a thermoplastic melt that passes through a standard capillary tube within 10 minutes under a certain temperature and pressure. The melt index is used to describe the melt fluidity during the component packaging process. The larger the MI, the better the fluidity and flatness of EVA. However, due to the smaller molecular weight, the tensile strength and elongation at break of EVA itself also increase with the It is easy to tear off after bonding, and the peeling strength is reduced. Since the reactivity rate of VA monomer during copolymerization is much smaller than the activity of vinyl monomer, the MI of EVA resin with high VA content will not be too high. For example, the minimum MI of EVA with VA content of 33% is about 25. , the current EVA resin suitable for photovoltaic packaging in the industry generally has a VA content of 28% to 33% and an MI of 10 to 100.
In order to ensure the reliability of components, the cross-linking rate (also called cross-linking degree) of EVA is generally controlled at 75% to 90%. If the cross-linking rate is too low, it means that the EVA has not fully reacted, and cross-linking reactions may continue to occur during subsequent outdoor use, accompanied by risks such as bubbles and delamination; if the cross-linking rate is too high, cross-linking reactions may occur during subsequent use. Cracks will appear, leading to battery cracks and other situations.
In addition to VA, MI and cross-linking degree, EVA’s shrinkage, light transmittance, volume resistivity, etc. are also key factors to measure whether it can meet the requirements of component production and use. In addition, yellowing resistance, water absorption, breakdown Voltage, etc. also need to be confirmed. After the components are made, various reliability tests such as DH1000 and TC200 must be carried out in accordance with the relevant retest guidelines of the IEC 61215 standard.
POE film
POE (Polyolefin elastomer) film is a metallocene polyethylene elastomer polymerized by ethylene and 1-hexene or 1-octene under the action of a metallocene catalytic system. The earliest POE used in photovoltaics was non-cross-linked. However, due to the high temperature when the modules are operated outdoors (especially in high-temperature and high-irradiation areas), the POE will soften. For early double-glass modules with heavy weight and no frame, heat will be generated. Shearing phenomenon occurs and slip occurs, thus affecting the appearance and reliability of the component. In response to this problem, POE manufacturers have optimized and modified it into cross-linked POE, which effectively solves the above problems.
Compared with EVA, which releases acetic acid gas during long-term use, POE has a more stable molecular structure with almost no gas release, and POE has higher volume resistivity, better thermal stability, and UV aging resistance. The biggest advantage of POE is that its water vapor permeability is only about 1/8 of EVA and silica gel. It can effectively block water vapor, better protect solar cells, and suppress the power attenuation of components. Its high body resistivity and low water permeability It is one of the important features to improve the anti-PID performance of components. Of course, POE also has shortcomings. Its glass bonding ability is not as good as EVA, which can easily cause interface failure. Moreover, the lamination time is long and the process window is narrow. The lamination process can easily cause bubbles, resulting in poor appearance. Moreover, a large number of its raw materials are imported, so the price is relatively high. expensive. POE film is mainly used for the packaging of single-crystal emitter and rear passivated cells (PERC) double-sided and N-type battery components. At present, domestic and foreign companies are stepping up the research and development and application of POE. If the cost can be reduced, I believe there will be good development prospects.
EPE film
EPE film, that is, “EVA-POE-EVA” three-layer composite structural film, is a composite modified EVA material and POE material, manufactured through a co-extrusion process, and is a co-extruded POE film. In terms of materials, POE resin accounts for 60% and EVA resin accounts for about 40%.
EPE co-extruded film combines the advantages of EVA film and POE film, providing more combination options. This allows module manufacturers to avoid choosing only high-cost pure POE packaging films or pure EVA packaging films with high water permeability, low volume resistivity, and high warranty pressure, thereby achieving a more comprehensive and economical packaging effect. .
EPE film not only retains the convenience of lamination process and high adhesion of EVA material, but also integrates the high barrier properties and weather resistance of POE material, and is suitable for bonding HJT battery (heterojunction battery) components.
The EPE film has excellent anti-PID performance, especially for the back side of monocrystalline PERC cells and the front side of N-type monocrystalline cells. In addition, it also has comprehensive properties such as high water resistance, resistance to ultraviolet radiation, and resistance to moisture and heat aging. From a cost-effective perspective, it is superior to traditional pure POE packaging films. Moreover, the use of EPE packaging film can reduce the use of POE materials, thereby alleviating the problem of raw material supply constraints.
In terms of application, EVA film is mainly used for P-type single-sided cells, while POE/EPE film is more suitable for P-type double-sided cells and N-type cells. EPE film is suitable for the packaging of PERC double-sided double glass, N-type double-sided double glass and other photovoltaic modules with high weather resistance requirements.
In particular, the multi-layer co-extruded POE film combines the high water resistance and high PID resistance of POE with the double glass and high yield lamination process characteristics of EVA material, effectively overcoming the shortage of POE resin raw material supply. Considered as an upgraded alternative to EVA materials.
At present, the demand for photovoltaics is increasing rapidly, and the global demand for plastic films is gradually increasing with the growth of installed capacity.
The current trend of double glass and N-type is becoming more and more clear. POE (POE+EPE) film packaging performance is better, and the film industry will upgrade to a product structure of high-quality film.
Competitive landscape of photovoltaic film market
In recent years, with the rapid development of the photovoltaic industry, the size of the photovoltaic film market has also been expanding. According to data from the China Photovoltaic Industry Association and industry reports, the global photovoltaic film market demand in 2022 will be approximately 2.85 billion square meters, with a market size of approximately 35 billion yuan, and will continue to grow rapidly. In 2023, China’s photovoltaic film demand will reach approximately 2.6 billion square meters, a year-on-year increase of 14.54%.
In terms of production capacity, as of the end of 2023, the total production capacity of photovoltaic film will reach 9.1 billion square meters, a year-on-year increase of 51.5%. Among them, five major film manufacturers, Foster, Swick, Haiyou New Materials, Parkson Technology, and Xiangbang Technology, have a combined production capacity of more than 6 billion square meters, accounting for about 67% of the industry.
China’s photovoltaic film industry started in 2005. In the early days, it relied heavily on imports, and the market was dominated by foreign companies. After 2011, with the vigorous development of the photovoltaic industry and policy support, domestic companies such as Foster and Haiyou New Materials emerged. Through technology introduction and independent innovation, they broke the foreign technology monopoly and realized the localized production of adhesive films. .
According to incomplete statistics, there are more than 40 photovoltaic film manufacturers in China. Most of them rely on the “chain master” enterprises of local photovoltaic industry clusters, that is, large photovoltaic module manufacturers or petrochemical bases with raw material supply advantages. Overseas expansion also follows this logic.
Photovoltaic film layout companies present a competitive pattern with one superpower and many strong players. As of the end of 2023, in the field of photovoltaic film, industry leader Foster is far ahead, with its market share remaining between 45% and 50% for a long time, and its production and sales data far exceed the total sales of the next five companies. Haiyou New Materials ranked second and Saiwu Technology ranked third. Under this competitive landscape, my country’s photovoltaic film manufacturers will continue to accelerate R&D and innovation, reduce production costs through technological upgrading and large-scale production, and improve the quality and performance of photovoltaic film products to better meet market share.
Photovoltaic film development trends
As one of the main materials for photovoltaic modules, photovoltaic packaging film has strong consumer demand and huge market potential. Overall, the future development trends of photovoltaic films can be summarized into three points:
First, the iteration of film production technology is accelerating, and product substitution is accelerating. At present, EVA film is the mainstream material in the photovoltaic packaging film market. With its excellent performance, POE film and multi-layer co-extruded film (EPE), consumer demand continues to expand, and the replacement of EVA film is accelerated. In the future, there will be EVA, POE, EPE and other types of adhesive films coexist with each other.
Second, the localization of POE film technology will be a hot topic in the next few years. At present, the production and supply of EVA film have been completely localized, and some of them have replaced imported products and are in the stage of improving quality and expanding production. However, due to the late start of domestic technology research and development, POE film relies heavily on imported products for market consumption. , driven by market demand, POE technology research and development and industrialization have become a major focus of the new materials industry.
Third, investment in domestic POE technology research and development and industrialization projects is active. Thanks to the efforts of the new energy and new material industries, POE pilot technology research has made rapid progress. Breakthroughs have gradually been made in polymerizing monomer high-carbon α-olefin technology, metallocene catalyst technology and high-temperature solution polymerization technology. The construction of POE industrial equipment is very intensive, 2025 will usher in a period of concentrated release of domestic POE production capacity, which will strongly support the accelerated localization of POE film technology and promote the high-quality development of my country’s photovoltaic industry and new energy industry.