There are four main types of greenhouse films commonly used in my country: the first is polyvinyl chloride (pvc) greenhouse film; the second is polyethylene (pe) greenhouse film; the third is ethylene-vinyl acetate copolymer greenhouse film; The four types are light-adjustable agricultural films.
These types of shed films have similarities and differences in nature, so the effects of use are also different.
(1) Polyvinyl chloride (pvc) shed film has good thermal insulation, light transmission, weather resistance, softness, and easy modeling. It is suitable as an outer covering material for greenhouses, greenhouses and small and medium-sized arch sheds. The disadvantage is that the specific gravity of the film is large (1.3 g/cm3), the coverage area of a certain weight of shed film is reduced by 1/3 compared with polyethylene film (PE), and the cost increases; it becomes hard and brittle at low temperature, and it is easy to soften and relax at high temperature; After the additives are precipitated, the film surface is vacuumed, which affects the light transmission, and the residual film cannot be burnt due to the generation of chlorine gas. At present, the main products of PVC shed film are:
①Ordinary pvc shed film does not add anti-aging additives in the film making process, and the service life is only 4-6 months. It can produce one season of crops, waste energy, increase labor and investment, and is currently being phased out.
②The pvc anti-aging film is formed into a film by adding anti-aging additives to the raw material. The effective use period is 8-10 months, and it has good light transmission, heat preservation and weather resistance. It is the main material for covering in greenhouses and small and medium-sized arched sheds. It is mostly used for cultivation in early spring and late autumn.
③ pvc non-drip anti-aging film (pvc double anti-shed film) has anti-aging and dripping properties at the same time, good light transmission and heat preservation, non-drip performance can last 4-6 months, and safe service life is 12-18 months It is widely used and is the preferred covering material for high-efficiency and energy-saving solar greenhouses, and it is more effective as a greenhouse covering material.
④In addition to the weather-resistant and drip-resistant pvc dustproof film, the surface of the film is treated to reduce the amount of plasticization and precipitation, and the dust absorption is lighter, which improves the light transmittance, which is more beneficial for winter and spring cultivation in solar greenhouses and greenhouses.
(2) Polyethylene (pe) shed film is light in texture (specific gravity 0.92 g/cm3), soft, easy to shape, good in light transmission, non-toxic, suitable for all kinds of shed film and mulch film, and is the main agricultural film in my country Variety. The disadvantage is that it has poor weather resistance and thermal insulation, and is not easy to bond. If the greenhouse film is produced, additives such as anti-aging agent, non-drip agent and heat preservation agent must be added to meet the production requirements. The main products are:
①Ordinary PE shed film is a "white film" produced by blow molding directly with raw materials without adding additives such as anti-aging. At present, greenhouses and small and medium-sized sheds are widely used. Generally, the shed is closed in spring and autumn, and the service period is only 4-6 months. , can only grow one season of crops, waste energy, increase labor, and gradually be eliminated in production.
②PE anti-aging film (longevity gate film) is a film formed by adding anti-aging additives to pe resin. The thickness of this shed film is 0.08-0.12 mm, the service period can reach 12 to 18 months, and it can be used for 2-3 seasons of crop cultivation, which not only prolongs the service period, reduces the cost, saves energy, but also greatly increases the output and output value. At present, the agricultural film varieties that are mainly promoted in facility cultivation.
③PE non-drip anti-aging film (double anti-agricultural film) also has dripping, weather resistance, light transmission and thermal insulation, the anti-fog effect can be maintained for 2-4 months, and the aging resistance life can reach 12-18 It is currently the most comprehensive and widely used agricultural film variety, which can not only be used in greenhouses and large and medium-sized sheds, but also suitable for early spring cultivation in energy-saving solar greenhouses.
④PE insulation film is a covering material that can prevent infrared radiation from radiating into the atmosphere, and can increase the temperature of the greenhouse by 1-2 °C, and the application effect is better in cold areas.
⑤PE multifunctional composite film has many functions such as non-drip, heat preservation, weather resistance and longevity, and some have the function of blocking ultraviolet rays, which reduces the transmission of ultraviolet rays in the shed. Some can inhibit the formation of sclerotinia ascomyci and Botrytis cinerea spores. Use period of up to 12-18 months.
(3) Ethylene-vinyl acetate copolymer (eva) shed film Eva resin is a new agricultural film material used in agriculture in recent years. The agricultural film made with it has better light transmittance, heat preservation and weather resistance than pvc Or pe agricultural film. Compared with other shed films, eva agricultural film covering can increase production by about 10%, can be used continuously for more than 2 years, does not deform before aging, can be easily recycled after use, and is not easy to cause soil or environmental pollution.
(4) Light-adjustable agricultural film The light-adjustable film made of rare earth and other functional additives added to pe resin can selectively transmit light and is a new type of covering material that can make full use of solar energy. Compared with shed film, the effect of heating and heat preservation in the shed is good, and the biochemical effect of crops is strong. It has the functions of early maturity, high yield, and improvement of nutrients for different crops. Rare earth can also absorb ultraviolet rays and prolong the service life of agricultural film. Among them, the special purple film for leafy vegetables (leek film) is to add purple masterbatch and weather-resistant, heat-insulating, drip-free masterbatch into the film, which is blown into a film. The film is slightly blue-violet, reducing strong light, increasing temperature, early growth period, high quality and high yield. It is suitable for the cultivation of chives and various green leafy vegetables.