Classification and selection methods for plastic greenhouse films

Recently, vegetable farmers in various regions have entered a peak period of purchasing and changing films. How much knowledge do vegetable farmers know about films? What issues should vegetable farmers pay attention to when choosing film?

The main types of greenhouse films currently available

At present, the structure of greenhouse film products is moving towards multi-layer composite development, with performance tending towards high transparency, high insulation, high strength, long service life, and continuous dripping period, anti fog period, dust-proof period and other functional and comprehensive directions. The development of greenhouse films has gone through four stages according to the different production materials: the first is polyethylene (PE) greenhouse films; The second is polyvinyl chloride (PVC) greenhouse film; The third is ethylene vinyl acetate copolymer (EVA) greenhouse film; The fourth is PO film, as well as the fifth generation five layer co extruded film currently under development.

The main characteristics and differences of various types of greenhouse films

★ PVC (polyvinyl chloride) greenhouse film. This type of film has good light transmittance, with a new film having a total light transmittance of over 85%, excellent moisture retention, low thermal conductivity, high tensile strength, and strong wind resistance. Good chemical stability, acid and alkali resistance. The disadvantage is that the film ratio is large, and the use of the same area of greenhouse is 1/3 more than that of polyethylene, resulting in an increase in cost; Secondly, it becomes hard and brittle at low temperatures, and is prone to softening and relaxation at high temperatures; After the auxiliary agent precipitates, the film surface is vacuumed. Generally, after one month of use, the transparency is poor, and the residual film pollutes the soil greatly and cannot be burned for treatment. Due to the generation of chlorine gas, environmental pollution is caused, and the current usage is gradually decreasing.

★ PE greenhouse film. PE greenhouse film is lightweight, soft, easy to shape, has good transparency, and is non-toxic. It is suitable for various greenhouse films and ground films and is currently the main agricultural film variety in China. Different product types can be produced according to the needs of farmers, including PE anti-aging (single prevention), PE anti-aging drip (dual prevention), and PE anti-aging drip defogging (three prevention), which have good anti-aging and drip defogging properties. Its disadvantages are poor weather resistance, poor insulation, and difficulty in bonding. According to Manager Song, PE grouting film is widely used in the current market,

★ Grouting film is a reprocessing process on the basis of the original polyethylene greenhouse film, and the inner surface of the agricultural film is treated by coating. In this way, the treated greenhouse film is tightly adhered to the inner wall of the greenhouse film with a functional droplet defogger, forming a layer of agent on the inner surface of the greenhouse film. When the moisture inside the greenhouse comes into contact with the inner wall of the greenhouse film, it forms a layer of water film, which flows down the slope of the greenhouse due to its own gravity, achieving the effect of defogging and dripping. The essential difference from previous greenhouse films is that functional agents exist independently outside the greenhouse film, so the time for defogging and dripping functions depends entirely on the control of the coating process, the quality of the coating agent, and the service life of the agricultural film, which can generally reach more than one year.

Of course, there are also individual defects in the grouting film. Firstly, the defogging droplet is attached to the surface of the agricultural film, so its adhesion is not as strong. External forces can easily cause damage to the coating, which can lead to dripping at the damaged area. For example, when going up the shed, the friction between the inner wall of the shed and the steel frame on the shed, as well as the collision of high crops with agricultural film, can all cause the above situation. Meanwhile, crops that prefer high temperature and humidity are less likely to use grouting film, such as cucumbers, bitter gourds, sweet melons, etc. However, the flaws do not hide the benefits. Even if the above situations occur, the overall effect of agricultural film is still more obvious than that of traditional agricultural film. Due to its significant advantages in defogging and dripping effects, as well as its relatively low cost, this product costs around 1.1-1.3 yuan per square meter. Compared to the price of EVA film, it has lower input costs and is therefore favored by many vegetable farmers. The current grouting film has varying product quality due to different filling levels. Vegetable farmers need to conduct multiple inspections of each product and choose reputable companies to purchase.

★ EVA film. EVA greenhouse film is a widely used type of greenhouse plastic film, which has super strong light transmittance with a transmittance rate of over 92%; Has excellent droplet defogging ability, with a droplet period of more than 4-6 months; Has excellent insulation, dust resistance, and strong aging resistance (over 18 months). The three-layer EVA greenhouse film can be widely used to produce high-end, economical and pollution-free vegetables, such as cucumbers, tomatoes, chili peppers, bitter gourds, etc. The disadvantage is that the price range is relatively high. Depending on the thickness specifications, the current market price is generally 2.05-2.1 yuan/square meter for 0.08mm, and 2.15-2.2 yuan/square meter for 0.09mm.

In addition, PO film is also a new type of film that has developed in recent years. This type of film is a high-end functional polyolefin agricultural film produced from polyolefin. Its transparency, continuous defogging, dripping, and insulation properties are in a leading position among greenhouse films, with high cost-effectiveness. It is the most promising type of film for promotion. At the same time, due to the influence of the production technology of many domestic brands of PO films, the quality of PO films produced by many companies may be unstable. Vegetable farmers also need to choose well-known brands when purchasing.