Preface

The output of plastic film in my country accounts for about 20% of the total output of plastic products, and it is one of the categories with the fastest output growth among plastic products. As the demand for plastic film in my country’s packaging, agriculture and other fields continues to increase, it is expected that the demand for plastic film in my country will grow at a rate of more than 9% per year, and its market prospects are very broad.

From the application field of plastic film (thickness of 0.06mm~0.26mm) in my country, the packaging industry has the largest consumption, the most varieties and the widest application, accounting for about 2/3 of its consumption, followed by agriculture, accounting for about 30%, and then functional films, such as microporous films, shielding films, geomembranes, etc. In theory, almost all synthetic resins can form films, but the resins with economic significance, becoming commodities and the largest consumption are polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), ethylene/vinyl acetate (EVA), polyamide (PA) and other resins. If suitable plastic additives are added to the resin matrix, various functional films required can be prepared. The production methods of plastic film industry include extrusion and calendering. Extrusion is divided into extrusion blown film, extrusion cast film, extrusion stretching (also known as secondary molding), etc. At present, extrusion is the most widely used, especially for the processing of polyolefin films, while calendering is mainly used for the production of some polyvinyl chloride films.

Overview and development trend of plastic packaging film industry

I. Industry overview

Among plastic packaging materials, the market demand for film materials has the largest increase, accounting for about 46% of the total plastic packaging materials. Plastic packaging films mainly include: heat shrink packaging film, winding packaging film, food aseptic packaging film, fruit and vegetable cling film, liquid packaging film, etc. With the continuous improvement of the equipment level of my country’s plastic film industry, some have reached the advanced level of developed countries, and a number of new products have emerged. For example, as a composite packaging substrate, biaxially oriented film has not only overcome the situation of long-term imports, but also now exports about 300,000 tons each year, earning more than 3 billion US dollars in foreign exchange. The number of large-scale packaging film manufacturing enterprises in my country has developed rapidly, and has reached 2,240 so far. A number of industry leaders have emerged, such as Jiangyin Shen Da Group, Zhejiang Dadongnan Plastic Group, Foshan Dongfang Packaging Materials Company, Foshan DuPont Hongji Packaging Materials Company, Foshan Plastic Group Co., Ltd., Guangzhou Hongshun Plastic Industry Co., Ltd. and Nan Ya Plastic Industry (Guangzhou) Co., Ltd. They play a pivotal role in the industry.

1.1 Heat Shrinkable Packaging Film

At present, in my country, PVC heat shrinkable film is gradually decreasing, while PE, PP, PET, PVDC, PA and other heat shrinkable films are developing rapidly, and multi-layer co-extruded composite heat shrinkable films have emerged. Take the most commonly used three-layer co-extruded heat shrinkable film as an example. This film is a three-layer composite heat shrinkable film with linear low-density polyethylene as the middle layer and co-extruded polypropylene as the inner and outer layers. Because it has the advantages of both PE and PP, its performance is better than that of single-layer PE film and PP film. At present, there are nearly 20 enterprises in the industry that produce heat shrinkable films, and their production capacity has grown from 40,000 tons to nearly 80,000 tons. Among them, Baoshuo Group, Tianjin Shengda, Fuzhou Jiatong, and Jiangsu Nantong are backbone enterprises. Single-layer heat shrinkable packaging film can be widely used in fast food noodles, ceramic products, tea sets, mechanical parts, military machinery, hardware tools, construction and transportation materials bundling packaging. Multi-layer heat shrinkable film is mainly used for food packaging such as fresh meat, as well as daily necessities, medical and health products, cultural supplies and other packaging. It is predicted that the market demand for heat shrinkable packaging film in my country will increase by 20% in the next five years.

1.2 Wrapping packaging film

Wrapping packaging film is self-adhesive and does not require heat treatment during the packaging process, which saves energy and reduces packaging costs. At the same time, it can wrap the goods tightly as a whole, which is convenient for loading and unloading and saves transportation costs. Wrapping film generally uses linear low-density polyethylene LLDPE as raw material. Domestically, ethylene/butene copolymer with a melt index of 1-2 and a density of 0.98g/cm3 is used. It is produced on a single-layer or three-layer co-extrusion device by blow molding or cast film. The key to making the wrapping film self-adhesive is to add chemical additives, such as compatibilizers, adhesion promoters, etc., to two or more mutually compatible, partially compatible or incompatible resins, and then chemically compound or directly inject PIB and other viscous resins. In addition to its packaging function, wrapping film also has some special functions. For example, the grass wrapping film used for grass silage can maintain the moisture and nutrients of the grass, which is conducive to the absorption of nutrients by livestock, thereby promoting the development of animal husbandry. The research and development of grass wrapping film in China began in 1997 with the cooperation between the Light Industry Plastics Application Technology Research Institute of Beijing Institute of Light Industry (now Beijing Technology and Business University) and BP Company. The technology has been successfully put into use. Representative enterprises include Wuxi Rongsheng Protective Film Factory, Guangzhou Sanda Plastic Packaging Factory, etc.

1.3 Food Aseptic Packaging Film

Food aseptic packaging film refers to a food packaging film that can withstand the ultra-high temperature required for instant sterilization of food (such as dairy products, beverages, and seasonings). This packaging film can make food have a longer shelf life without preservatives and refrigeration. This is a new technology and one of the development directions of plastic packaging. There are two types of food aseptic packaging. One is a large aseptic packaging bag with a capacity of 5 to 1000L. The composite film for bag making is mainly composed of PET aluminized film and PE film; the other is an aseptic cup packaging, which uses PP/PE/EVA/PVDC/PS multi-layer co-extruded composite film, in which PP is a protective layer film, EVA is an adhesive layer, and PVDC is an oxygen barrier layer.

1.4 Fruit and vegetable cling film

Fruit and vegetable cling film is used for fruit and vegetable packaging to inhibit the metabolism and nutrient loss of fruits and vegetables during the storage process, and maintain the flavor and quality of fruits and vegetables. my country is the world’s largest producer and consumer of fruits and vegetables, and about 30% of fruits and vegetables are lost during storage and transportation due to lack of freshness, so the preservation of fruits and vegetables in my country has great economic value. At present, polyethylene film and polypropylene film are widely used in fruit and vegetable fresh-keeping packaging. When selecting suitable fresh-keeping packaging films, their air permeability must be considered to maintain appropriate oxygen and carbon dioxide concentrations in the film. At the same time, a certain amount of porous materials (such as zeolite, Otani stone, etc.) can be added to absorb the ethylene gas released by fruits.

1.5 Metallocene-catalyzed polyolefin film

Polyolefin films prepared by metallocene single-center active catalysis have outstanding excellent properties. Currently, they mainly include MPE, MPP, MPS, etc. The heat sealing performance, tensile performance, and puncture resistance of this film are better than traditional films. It can effectively solve the problems of penetration rupture and heat sealing cracking in liquid packaging. It is mostly used in the heat sealing layer of composite films for liquid packaging such as milk, soy sauce, and shampoo.

1.6 Biaxially oriented film

Biaxially oriented film has always occupied an important position in film packaging, including biaxially oriented polypropylene (BOPP), biaxially oriented polyester (BOPET), biaxially oriented nylon (BOPA), etc., among which BOPP has the largest output. BOPP film is a new type of transparent packaging material developed in the 1960s. It has the advantages of light weight, non-toxicity, odorlessness, moisture resistance, high mechanical properties, good dimensional stability, and good printability. It can be widely used in the packaging of food, candy, cigarettes, tea, juice, milk, textiles, etc. The production methods of BOPP film include bubble tube method and tentering method, among which the tentering method is more commonly used. This method is to extrude the granular BOPP special material into a film through a flat die, and after sudden cooling on a cooling roller, it is preheated under different conditions, and the film is stretched longitudinally and transversely, so that the comprehensive performance of the film can be greatly improved. In my country, the huge demand for flexible packaging provides a good market opportunity for the development of the BOPP industry. However, since the late 1990s, the BOPP film industry has seen a wave of cross-industry competition to introduce BOPP production lines. It is expected that by the end of 2005, the national BOPP production capacity will exceed 2 million tons, while the annual market demand is only about 900,000 tons, that is, 1/2 of the production capacity will be vacant. The co-extruded heat-sealable biaxially oriented polypropylene film produced by Nanjing Zhongda, while maintaining the heat shrinkage of BOPP, adopts the hole positioning technology to solve the heat sealing and the adhesion of the middle strip film and the small strip film.

Among the biaxially oriented materials, the market share of BOPET and BOPA films follows BOPP. The domestic BOPET film industry has also seen overheated development and irrational investment, and it is expected that this oversupply situation will become more serious in the next few years.

1.7 CPP and CPE films

These two films are produced by the casting method, that is, by casting the PP or PE melt and quenching it to produce a non-stretched, non-directional PP or PE flat extruded film. CPP and CPE films have excellent performance balance, and subsequent processes such as printing and lamination are extremely convenient. They are widely used in the packaging field, especially CPP, which has a large market. At present, my country has introduced more than 60 CPP production lines with a total production capacity of more than 150,000 tons. The domestic market for CPP films is mainly composite packaging films, and the largest applications are aluminized films and cooking films. Among them, Shanghai Zijiang Color Printing Co., Ltd.’s laser anti-counterfeiting film, Zihua Co., Ltd.’s breathable cast film, and Ziteng Co., Ltd.’s anti-static CPP film are all included in the national torch project.

Distribution pattern

China’s two major PP\PE film production centers are located in the adjacent coastal provinces/cities in eastern China – Jiangsu/Shanghai/Zhejiang – and Guangdong Province in the southeast, accounting for 33% and 32% of the country’s total production, respectively. Some of China’s largest film production converters, including Foshan Plastics Group Co., Ltd., Guangzhou Hongshun Plastic Industry Co., Ltd. and Nanya Plastic Industry (Guangzhou) Co., Ltd., are all located in Guangdong Province. Five provinces and cities, including Guangdong, Zhejiang, Shandong, Jiangsu, and Shanghai, account for more than half of the country’s total output.

Four major regions of PVC packaging in China

First, a high-end bag manufacturing base centered on Shiling Town, Huadu City, Guangdong, radiating the Pan-Pearl River Delta and dominated by foreign capital. 90% of its products are sold to the European and American markets, making it the “leader” of China’s PVC bag industry;

Second, a medium- and high-end PVC bag manufacturing base centered on Quanzhou, Fujian, dominated by Taiwanese and Hong Kong capital. Currently, there are more than 1,000 companies with an annual output value of more than 8 billion yuan, accounting for about 40% of the national total;

Third, the Pan-Yangtze River Delta region centered on Shanghai has built the Shanghai International Leather Goods and Luggage Trading Center. Foreign buyers place orders based on samples all year round, attracting a large number of private bag companies with strong financial strength in Guangdong, Fujian and Zhejiang to settle in;

Fourth, the Baigou area in Hebei has become the largest PVC bag professional market in the country with its successful experience in operating bags since the 1990s, driving the development of related companies in surrounding provinces and promoting the formation of a new industrial chain.

2. Development trend of packaging film

After the rapid development in the 1990s, China’s plastic flexible packaging has entered a period of stable development. The profit margin is gradually declining and the competition is increasingly fierce. At present, what aspects should the development of domestic plastic flexible packaging focus on? This is a common concern in the industry. The following are the development priorities of domestic plastic flexible packaging:

The 21st century is the century of environmental protection. Building a circular economy society and taking the path of sustainable development have become the focus of global attention and urgent tasks. In order to adapt to the requirements of the new era, in addition to meeting the market’s increasing requirements for packaging quality and quantity, the development of plastic packaging materials must be based on saving resources, easy recycling after use, easy disposal or easy environmental absorption or degradation as the starting point of technology development. New materials, new processes, new technologies and new products for plastic packaging are constantly emerging, and are developing in the direction of high performance, multi-function, active adoption of new raw materials, new technologies, broadening of application areas, and harmonious development of plastic packaging and environmental protection.

2.1 High barrier packaging materials that improve protection performance and extend shelf life.

Such as the development and application of high barrier co-extruded composite films; High-resistance plastic packaging materials have been rapidly developed and widely used because they can preserve quality, freshness, flavor and extend shelf life. In addition to the currently widely used polyvinylidene chloride (PVDC), ethylene, and vinyl alcohol copolymers (EVOH), in recent years, the development of environmentally friendly materials has promoted the development of polyvinyl alcohol (PVA), polyethylene terephthalate (PEN), copolyamide (MXD6), silicon or aluminum oxide steamed film (soft glass), and nano-inorganic materials, which will be more eye-catching.

The use of metallocene polyolefins (MHDPE, MLLDPE, MPP) can further improve many properties of soft packaging such as strength, toughness, transparency, barrier properties, heat resistance and processability. In 2006, the development trend of improving the technical level and environmental adaptability of soft plastic packaging films (bags) has become a hot spot in the industry. A number of new products with oil resistance, flavor retention, moisture resistance and mildew resistance have emerged in composite high-barrier, multifunctional packaging and aseptic packaging technologies. The demand for anti-counterfeiting and anti-static packaging has also developed rapidly. High-barrier and functional soft plastic composite packaging films (bags) have developed to a new technical level.

2.2 Development and application of aseptic packaging materials, antibacterial packaging films, and radiation-resistant packaging films;

the biggest advantage of aseptic packaging materials and technologies is that under aseptic conditions, no preservatives are added, no refrigeration is required, and the original nutrients and flavor of food can be retained to the maximum extent, which can greatly extend the shelf life and facilitate storage and transportation. The market has developed very rapidly and the uses have been continuously expanded. In addition to occupying a large share in dairy products and fruit drinks, it will be further expanded to the fields of pharmaceuticals, cosmetics and condiments.

In the process of development, the sanitation and safety of flexible packaging films (bags) are also facing serious challenges. Many food plastic packaging materials on the market are difficult to meet the national requirements for food safety, hygiene and environmental protection. In recent years, the sampling pass rate of packaging bags in various places has been low, only 50-60%. From the Lanzhou “toxic milk powder” incident broadcast by CCTV in July 2005 (the packaging film (bag) was unqualified due to excessive toluene and xylene solvent residues) to the toxicity of the plasticizer diisooctyl adipate (DIOA) added to PVC cling film in October, the reason for this situation is not only the problems of the enterprises themselves, but also inseparable from the lack of management and control of the industry by the state. The deep-seated problems and factors infiltrated by this incident deserve our deep consideration and attention.

2.3 Nanocomposite packaging materials will be industrialized rapidly with the rapid development of nanotechnology.

Due to the obvious enhancement and improvement of wear resistance, hardness, strength, barrier property and plasticity, in addition to food packaging, they can also be used for special packaging such as anti-static, anti-electromagnetic, invisible, dangerous goods packaging, etc., and heat-resistant packaging materials suitable for electromagnetic cookers and microwave ovens. It will promote a huge change in traditional plastic packaging materials.

2.4 Environmentally friendly (environmentally friendly) plastic packaging materials (or green plastic packaging materials) have become a hot topic of global concern with the implementation of the environmental management standard IS 14000 series.

Among them, plastic packaging materials that are easy to recycle and reuse, such as PET and PEN, and biodegradable plastics in environmentally degradable plastics (EDP), have become the hottest of the hot spots. Others such as zero-pollution foam plastics, thin-walled bottles and bag-shaped packaging containers have also attracted much attention. The packaging materials suitable for the storage of agricultural products such as grain can be controlled atmosphere packaging;

But no matter which kind of plastic packaging is used, the hygienic safety of VC cling film has caused problems, and more plastic packaging companies have been encouraged to take the road of green packaging. In addition to developing water-soluble inks and water-soluble alcohol-soluble alcohol adhesives that meet hygienic safety requirements, they should also develop new products of co-extrusion technology. The development of the co-extrusion film application market has become a hot spot in the development of the industry in the past two years and has made progress.

Last year, the country paid more attention to food safety and the safety and quality of packaging that comes into direct contact with food. Green packaging that meets environmental protection requirements and is pollution-free will receive more and more attention from the society. Vigorously develop green packaging, do a good job in packaging waste treatment and resource recycling and reuse, and achieve sustainable development requirements. Therefore, relevant government departments and relevant associations, such as the Composite Film Committee of the China Plastics Processing Industry Association, are working closely together to implement the spirit of the document No. 86 of the General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China on food safety supervision (2006), and implement the market access system for plastic packaging containers, tools and other products for food. On December 27, 2006, the first batch of 29 companies that obtained market access qualifications were issued production licenses. A total of 97 products applied for access, covering all 39 product varieties for this access. In the future, food production companies and consumers should choose products with the QS mark when purchasing plastic packaging, containers, tools and other products for food.

Foreign countries have produced solvent-free and water-based environmentally friendly adhesives required for composite films, and they are still under development in China. The biggest gap in my country, as Vice President Li of the China Plastics Processing Industry Association said when he met with foreign experts, is that my country’s current output of plastic products ranks first in the world, but the quality lags far behind that of developed countries, mainly due to the backwardness of talents. Strengthening the cultivation and training of talents, taking the path of technological innovation and independent intellectual property rights, and fully implementing the scientific development concept to build an innovative plastic packaging enterprise are our future development options.

Summary and development trend of agricultural film industry

I. Industry summary

Since 1979, agricultural film covering cultivation technology has been vigorously promoted in my country. In 1980, the area covered by agricultural film was only 25,000 mu, and in 2005, the area covered by agricultural film reached 170 million mu. my country has more than 400 million mu of land that can be covered with film, so the demand for agricultural film in my country will continue to increase, reaching 2.7 million tons in 2010.

Since the production of agricultural plastic film, China has achieved two world firsts, namely the first in output and the first in coverage area, which is roughly equivalent to 1.6 times the total of other countries in the world. Agricultural plastic film is mainly greenhouse film and ground film, and also includes sunshade nets, insect-proof nets, forage film and agricultural non-woven fabrics. Plastic film is widely used as covering material for solar greenhouses, plastic greenhouses and various small plastic arch sheds. The annual consumption of greenhouse film has reached 700,000 tons, covering an area of ​​50 million mu; the annual consumption of ground film is about 450,000 tons, covering an area of ​​more than 220 million mu. With the rapid development of agricultural science and technology, the demand for agricultural film will continue to grow. According to incomplete statistics, there are nearly 1,000 agricultural film production enterprises in the industry, with a production capacity of more than 2 million tons, including about 60 enterprises with an annual production capacity of more than 10,000 tons and about 30 large backbone enterprises. The more well-known agricultural film manufacturing enterprises are mainly concentrated in Henan, Hebei and Shandong, including Henan Shuanghui Plastic Factory, Shandong Rixin Chemical Co., Ltd., Hebei Baoshuo Group, Zhongyuan Plastic Products Factory, Tianjin Ersu, Anhui Guofeng Plastic Industry, Beijing Huadun, Sinochem Import and Export Corporation and Shandong Zibo Tianhe.

The greenhouse film covering cultivation technology has been applied as early as the late 1950s. This technology can not only promote crop growth and increase crop yields, but also realize the cultivation of fruits and vegetables in cold seasons. According to the function, greenhouse films are divided into: long-life film, drip-free film, thermal insulation film, light-converting film, diffuse scattering film, reflective film, etc. At present, the main greenhouse film material in my country is polyethylene (PE), and some polyvinyl chloride (PVC), ethylene/vinyl acetate (EVA), and metallocene polyethylene (mPE). Foreign countries also use polyethylene terephthalate (PET), polycarbonate (PC), and polytetrafluoroethylene (PTFE) to prepare greenhouse films. Although they have excellent performance, they are used in small quantities due to their high prices.

Plastic mulch can play the role of heat preservation and root protection, anti-freeze, moisture conservation, light regulation, water saving, weeding, and control of soil salinity, thereby promoting early maturity of crops and improving crop yield and quality. According to their functions, mulch films are divided into: ordinary colorless transparent film (also known as drip film), drip-free film (also known as drip film), light-efficient film (including colored film and light-converting film), weeding film, insulation film, degradable film, aging-resistant film, water-permeable film (including small-pore film and microporous film), etc. At present, the main mulch film material in my country is polyethylene (PE), and some polyvinyl chloride (PVC) are also used. Although ethylene/vinyl acetate (EVA) film has better thermal insulation and transparency than PE film, better compatibility with drip-free agents, good stretchability and easy film formation, and is resistant to aging and impact, it is expensive and used in small quantities. If its cost is reduced, it is expected that the amount will gradually increase.

1.1 Long-life aging-resistant film

Most of the aging-resistant greenhouse films produced in my country are thinner greenhouse films (thickness is 0.06mm~0.10mm), and their service life generally reaches 1.5~2 years. Compared with the thicker greenhouse films (thickness is 0.18mm~0.20mm) produced abroad, there is still a big gap in service life. For example, Japan’s PVC long-life film can be used for 2~3 years, and PET film can be used for 10 years. By optimizing general resin materials and stabilizers, the service life of greenhouse films can be extended. Specifically, in terms of optimizing basic resin materials, agricultural film manufacturers often use melt flow rate (MFR) as the basis, and select resins with higher molecular weight, narrower molecular weight distribution, and fewer branches to produce aging-resistant PE greenhouse films. In addition, the residual amount of transition metal ions, crystal form and crystallinity of the base resin are also important indicators for optimizing functional greenhouse films. For example, Beijing Yanshan Petrochemical Company, Qilu Petrochemical Company, Tianjin United Chemical Company, etc. have developed special resins for the production of functional PE greenhouse films; in terms of adding composite non-toxic light stabilizers and developing efficient anti-aging systems, my country has used the GW540/2002 anti-aging system for more than ten years. Due to its serious irritation and sensitization, it needs to be gradually replaced by a non-toxic anti-aging system. Foreign non-toxic polymeric hindered amine light stabilizers have entered the Chinese market one after another, including Swiss Ciba Specialty Chemicals, American Cytec, Swiss Clariant, Italian 3VSigma, etc., but the price of polymeric hindered amine light stabilizers launched abroad is relatively high, and most Chinese manufacturers can hardly afford it. The new BW6911 light stabilizer and 6911/B215 anti-aging system launched by Beijing Institute of Chemical Industry not only have excellent performance, but also are cheap. The polyolefin greenhouse film produced by this system has achieved satisfactory results in the Northeast, North China and Southwest regions, and has better overcome the “backboard effect” and extended the service life of the greenhouse film, which is worthy of further promotion and application.

The requirements for aging resistance of ground film are not as high as those of greenhouse film. Among plastic ground films, PVC is the earliest used ground film resin, which has the characteristics of high strength, UV resistance, aging resistance, transparency and good thermal insulation. However, due to its high density, thick film, complex formulation process and high cost, it has been gradually replaced by PE film. At present, except for the three provinces in Northeast China and some areas in Shandong, PE film is almost used in other regions. Among PE ground films, HDPE, LDPE and LLDPE are all used. Among them, HDPE has high strength but is not resistant to aging; LDPE has low strength but good light transmittance; LLDPE has good strength and aging resistance, so LLDPE is the most suitable material for ground film. Considering the cost, most of the aging-resistant PE ground film materials in my country are blended with 70% LLDPE and LDPE.

1.2 Anti-fog dripping film

Dripping film has a high temperature inside the film, which is suitable for spring and autumn, and has a good effect on thermophilic crops. The disadvantage is that fog droplets are easily formed inside the film, which affects light transmission. The surface of the drip-free film (also known as dripping film) contains hydrophilic substances, and the water droplets inside the film flow down along the film. The humidity is low, the light transmittance is good, and the temperature difference between the inside and outside of the film is large. The performance is generally better than that of the dripping film. In order to improve the dripping performance of the film, it is generally possible to modify the surface polarity of the film or add a dripping agent. When used, dripping agents and anti-fogging agents are often added or coated on the surface of the film at the same time, even if it has both anti-fogging and dripping functions, thereby further improving the light transmittance of the film. The dripping agent is a compound of various non-ionic surfactants, and the defogging agent is a special type of surfactant, such as a fluorine-containing surfactant and/or a silicon-containing surfactant. Studies have found that the “cooperation effect” of the dripping agent and the defogging agent is crucial. Beijing Institute of Chemical Industry and Lin’an Plastic Chemical Additive Factory have both developed dripping defogging systems with good dripping defogging effects. The coating type drip defogging agent was originally intended to play a complementary role so that the performance and life of the film can be synchronized as much as possible. At present, the development of the coating type drip defogging system has become one of the important ways to produce functional greenhouse films.

1.3 Light-efficient film

For greenhouse films, in order to obtain sunlight to promote crop growth, light-converting agents are often added to the film, while light-converting agents are rarely used in ground films, and colored films are more often used. In the development and application of light-converting agents, only by converting green light can the light conversion effect be truly exerted. At present, the light-converting agents used in the production of light-converting greenhouse films mainly include rare earth light-converting agents or light-converting agents composed of organic fluorescent pigments. The “single-base dual-energy rare earth light-converting agent” developed by the Luminescent Materials Research Laboratory of Hunan Normal University has the function of converting ultraviolet light into blue light and red light and converting green light into red light, and has a good application effect. The light-converting greenhouse films produced by some companies are also called high-light energy films, light-ecological films, and high-light quality films. The high-light-energy greenhouse film developed by Beijing Huadun Plastics Company has the characteristics of wide excitation and emission spectra. The emission spectra in the blue light region (420nm~460nm) and the red light region (620nm~660nm) have high relative luminous intensity. Since blue-violet light is conducive to crop growth and red light can promote fruit formation, it can make crops mature early, increase early yields, and have a good effect of increasing production and income.

There are many varieties of colored films in ground films to suit different crops. For example, purple film can transmit red and blue light and absorb green light, which can increase spinach yield and extend the market period; red film can transmit red and blue light to promote cucumber growth; silver-gray film and aluminum foil reflective film have strong light reflection effect, which can repel aphids, maintain ground temperature, supplement light on the back of crops with insufficient light, promote fruit coloring, and increase fruit yield and sugar content. Colored ground film materials are generally PE, and there are also a small amount of PVC, and the pigment is added in the form of masterbatch. Most of the colored ground films are single-layer films, except for aluminum foil reflective film and black and white double-sided ground film, which are composite films. Both light-converting greenhouse film and colored ground film are developing towards high efficiency and specialization.

1.4 Multifunctional composite film

With the improvement of production technology, agricultural film is developing towards a multifunctional film that can simultaneously meet the requirements of long life, heat preservation, fog removal, and good light transmittance. The advanced three-layer co-extrusion composite blown film process technology has been successfully applied in the production of many enterprises. Some enterprises use internal cooling devices to improve the stability of wide-width blown film bubbles and the transparency of greenhouse films, and improve the dripping of greenhouse films; some enterprises have adopted domestic three-layer composite wide-width blown film units, which can produce functional greenhouse films with a width of 12m to 20m; some enterprises have improved the insertion and stacking mechanism of blown film bubbles and the traction and winding technology, effectively solving the creep problem of the folding part of the greenhouse film and improving the flatness of the greenhouse film; some enterprises have improved the masterbatch manufacturing process, the resin and masterbatch mixing process and the extrusion process technology, so that the functional additives are dispersed more evenly and stably in the greenhouse film, thereby improving the quality of the functional greenhouse film. For example, the EVA multifunctional three-layer composite greenhouse film (thickness of 0.10mm) with the addition of dripping and fogging system and inorganic thermal insulation agent has a good effect of covering the winter in the suburbs of Shenyang City, Liaozhong County and Anshan area in Liaoning Province.

1.5 Degradable agricultural film

In order to solve the white pollution problem of agricultural film, in addition to strengthening the recycling of aging-resistant agricultural film, it is more important to strengthen the development and application of degradable ground film, which is also a development trend of agricultural film. Traditional degradable mulch is mainly prepared by blending, that is, adding biodegradable substances to polyethylene resin, or adding other ingredients such as photodegradants, so that it can be partially broken during use, and then large pieces of film are turned into small pieces that are not noticed and enter the soil. However, this only turns visible pollution into invisible pollution, and does not fundamentally solve the problem of soil pollution. At present, the hot spot of degradable mulch development is to replace polyolefins with photodegradants with degradable polymer materials of other structures, or to blend new degradable materials with polyolefins and degradants, combine biodegradation and photodegradation, improve degradation efficiency and controllability, and fundamentally solve the problem of incomplete degradation.

2. Development trend of agricultural film

It will become the main development trend in the future for agricultural film enterprises in my country to exert their comprehensive advantages through asset restructuring, strong alliance and listing, and to impact the high-end market of agricultural film. It will mainly improve the overall quality of enterprises, solve problems such as market planning, technological innovation, teamwork, etc., focus on the implementation of new ideas, new thinking and new methods, and narrow the gap with foreign-funded enterprises.

The competition in the agricultural film market is becoming increasingly fierce, and the market demand is constantly changing, but the market development potential is huge, and the overall application level of agricultural film needs to be further improved. The structure of greenhouse film products is developing towards multi-layer, and the performance is developing towards high light transmittance, high heat preservation, high strength, long life, continuous dripping period, anti-fog period, light conversion period, dust prevention period, anti-bacteria period and other functional and comprehensive performance aspects; ground film products are developing towards moisture conservation, warming, weeding, insect prevention and other functional development, and the variety is developing towards asparagus, cotton, tobacco, garlic, leek and other specialization.

In short, the agricultural film industry will continue to develop towards enterprise scale and product functionalization. At the same time, improving the recycling and degradation technology of agricultural films and reducing environmental pollution will not only promote the sustainable development of agriculture, but also ensure the future development of the agricultural film industry. At the same time, it is in line with the national industrial policy. The development of pollution-free agricultural films will be very important. Among agricultural plastics, the functionality of greenhouse films should be improved to achieve longevity and aging resistance, anti-fog and anti-drip, high transparency and high heat preservation, and realize light energy conversion to improve the photosynthesis of crops; for ground films, the problem of white pollution remaining in the soil should be solved, and various functional ground films such as aphid removal and weed removal should be developed.

Developed countries have developed light ecological greenhouse films, which can retain ultraviolet light that is beneficial to crop growth, filter out or convert ultraviolet light or green-yellow light that is harmful to crops into blue-violet light and red-orange light required for crop photosynthesis. The ultraviolet light conversion range is wide, the conversion spectrum is consistent with photosynthesis, and the conversion life can be as long as 180-300 days, which can significantly improve the quality of crops and reduce pests and diseases. However, my country’s light ecological greenhouse film development is still blank. Although the light conversion greenhouse film has been successfully developed, it is mainly used for warming, with a narrow light conversion range and poor effect. The light conversion life is only 20-30 days, and the ultraviolet light that can be converted is only 1%-3%. The red-orange light peak does not match photosynthesis well, and the yield-increasing effect is limited. It basically has no effect on improving crop quality and reducing pests and diseases.

Developed countries currently mainly use special greenhouse films, which can be used according to the different light requirements of different crops, so the crops cultivated have high yields and good quality; my country currently still uses one film for multiple purposes, so the phenomenon of “persimmons are not red, eggplants are not purple” is quite common. In the process of developing factory agriculture, developed countries have developed modern greenhouses. The covering material is no longer the traditional plastic film, but a thick film or thicker sheet with high strength, good light transmittance, strong thermal insulation performance, and can be used for 15-30 years at a time. It can also easily integrate multiple functions, such as selective light conversion, drip prevention, and anti-fog; while my country is basically still using traditional plastic films in general, with short service life and poor functionality.

my country’s agricultural industry layout will develop towards regionalization and specialization, and the industrial center will continue to develop towards advantageous production areas. The facility structure will tend to be large-scale, and the environmental control will tend to be intelligent. The diversification of cultivated horticulture will become a new growth point for the horticultural industry. Furthermore, at present, high-end agricultural films account for only 2% of the total agricultural film production in China, mid-range agricultural films account for 20%, and low-end products account for 78%. Low-end agricultural film products are in oversupply, which is far from the level of developed countries where high-end products account for 20%, mid-range agricultural films account for 50%, and low-end products account for only 30%. Data show that there is a lot of room for the development of my country’s agricultural film industry: first, more than half of the planting area suitable for agricultural film coverage in China is still blank; second, the proportion of functional films accounts for only 30%, while it reaches 80% abroad; third, the output of high-end and medium-end agricultural films cannot meet market needs.

However, since agricultural films are agricultural products, agricultural film designated enterprises have long made concessions to farmers and made great sacrifices for many years. They have been in a state of small profits and even losses, resulting in a serious lack of development momentum. After joining the WTO, all domestic enterprises are facing fierce competition in both domestic and foreign markets. Product replacement, equipment renewal, and technological progress all require policy and financial support. If the relevant national departments can get financial and policy support, the agricultural film industry will develop faster.

In order to adapt to the requirements of the situation, enterprises in the industry should pay attention to the following when developing: First, the more promising the situation is, the more we should avoid blindly launching projects, overcome the drawbacks of low-level repeated construction in the past, change the situation of large number of agricultural film enterprises, small scale and low level, and concentrate on making existing backbone enterprises bigger and stronger; second, conscientiously implement the scientific development concept, save resources, reduce energy consumption, pay attention to recycling, protect the environment, and take the path of green, sustainable and healthy development; third, strengthen internal management, continuously improve the core competitiveness of enterprises, and implement brand strategy.

With the development of my country’s national economy and the improvement of people’s living standards, fog prevention has put forward higher requirements for the quality of agricultural products such as vegetables. Therefore, it has become an urgent task for my country’s agricultural film industry to develop a new generation of functional greenhouse films that are suitable for the current market needs, can increase production, significantly improve crop quality and reduce crop diseases and insect pests, which can not only increase production, but also significantly improve crop quality and reduce crop diseases and insect pests.

Functional film

2.1 Barrier composite film

This is a functional film that is widely used in the field of food packaging and medical packaging in my country. Barrier composite film refers to a composite film with high barrier properties to oxygen, moisture, aromatics and volatile substances. It is generally composed of three parts: gas barrier layer (barrier resin), water barrier layer (polyolefin resin) and adhesive layer (adhesive resin). Multi-layer co-extrusion is the main method for producing barrier composite film. According to the shape and structure of the die, multi-layer co-extrusion can be divided into multi-layer co-extrusion tube film composite process and multi-layer co-extrusion cast composite process. Barrier composite film can be divided into symmetrical type and asymmetrical type according to its structural characteristics. At present, the main type on the market is asymmetrical. According to the number of composite layers, there are 3, 5, 7, 9, and 11 layers of composite film. Commonly used barrier resins include PA, EVOH, PET, PVDC, PAN, etc.; polyolefin resins include PE, PP, EVA, mPE, etc.; adhesive resin is a resin that has a stable bonding effect on barrier resin and polyolefin resin, such as maleic anhydride grafted PP, etc.

In recent years, high-barrier silicon oxide film has also attracted much attention in the market. It is a layer of silicon oxide coated on PET and nylon film, which has the advantages of high barrier, oil resistance, chemical resistance, transparency, flex resistance, environmental adaptability, microwave adaptability, etc. Its development trend is: not only to improve its printability and barrier, but also to make it have functions such as blocking ultraviolet rays and anti-charge.

2.2 Antibacterial film

Antibacterial film is made by adding silver ions, fluorite, hinokitiol and other antibacterial substances into the film to make a sterilization type fresh-keeping film. This product has been successfully used in the packaging of tofu, fish, meat and pickles abroad, but it is still basically in the experimental stage in China. For example, Haier Chemical Company added nano inorganic antibacterial materials to the film to produce an antibacterial film with better comprehensive performance.

2.3 Electromagnetic shielding film

Electromagnetic shielding film can block the electromagnetic waves of microwave ovens, avoid electromagnetic wave leakage, facilitate the safe use of microwave ovens, and can be widely used in food packaging and decoration. The film is an aluminum-plated composite film. Its process is to coat a layer of aluminum film with a thickness of 400-500μm on the surface of polyester film by vacuum evaporation.

2.4 Microporous film

Specialized microporous film is a highlight of the current fruit and vegetable preservation film. That is, according to the preservation requirements of the packaged fruits and vegetables, different numbers of small holes are opened on the plastic film to improve the gas permeability. Data show that when the oxygen permeability of the film is 800-200ml/m2?24h?MPa, the freshness of fruits and vegetables is best. In addition, microporous film is also used in ground film for air permeability and water seepage, which can reduce the number of crop irrigations and has a water-saving effect.

2.5 Water-soluble film

As a novel green packaging material, water-soluble plastic film is widely used in Europe, America, Japan and other countries for the packaging of various products, such as pesticides, fertilizers, pigments, dyes, detergents, water treatment agents, mineral additives, detergents, concrete additives, chemical reagents for photography and chemical reagents for gardening care. Its characteristics are: complete degradation, non-toxic and safe, high heat sealing strength, anti-counterfeiting function, good printing performance, anti-static and dustproof, etc. Its main raw material is polyvinyl alcohol (PVA) with low alcoholysis degree, and various additives are added, such as surfactants, plasticizers, anti-sticking agents, etc. At present, the water-soluble film market is emerging in China. The Institute of Plastic Application Technology of Light Industry of Beijing Technology and Business University has realized PVA dry melt granulation and film blowing processing by screening out plasticizing modifiers that can reduce the plasticizing temperature of PVA, and applied for 5 patents. Now some patents have been transferred and put into production; Zhuzhou Institute of Technology and Guangdong Zhaoqing Fangxing Packaging Materials Company jointly developed water-soluble films and production equipment, and their products are entering the market. Compared with foreign water-soluble film products, the price of domestic water-soluble film products is highly competitive. The price of water-soluble PVA film in the United States is 130,000 to 170,000 yuan/ton, and that in Japan is 200,000 to 250,000 yuan/ton, while the price of domestic products is only 60,000 yuan/ton.

In addition, functional films include transparent wear-resistant films, rainbow films, special medical packaging films, selective permeable films, geomembranes, etc., which have been widely used in various aspects of production and life.

Summary

my country’s plastic film industry is in a stage of vigorous development. According to statistics, the demand for plastic films in my country will increase at a rate of more than 9% per year. Moreover, with the continuous emergence of various new materials, new equipment and new processes, my country’s plastic films will be driven towards the direction of diversified, specialized and multifunctional composite films.

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