Classification and selection methods of plastic greenhouse films

Recently, vegetable farmers in various regions have entered the peak period of film purchase and replacement. How much do vegetable farmers know about film? What issues should vegetable farmers pay attention to when purchasing film?

Current main types of greenhouse films

At present, the structure of greenhouse film products should develop towards multi-layer composite, and the performance tends to develop towards functional integration such as high light transmittance, high heat preservation, high strength, long life and continuous dripping period, anti-fog period, and dustproof period. The development of greenhouse film has generally gone through four stages according to the different production raw materials: the first is polyethylene (PE) greenhouse film; the second is polyvinyl chloride (PVC) greenhouse film; the third is ethylene-vinyl acetate copolymer (EVA) greenhouse film; the fourth is PO film, and the fifth generation five-layer co-extruded film is in the research and development stage.

The main characteristics and differences of various types of greenhouse films

★PVC (polyvinyl chloride) greenhouse film. This type of film has good light transmittance, the new film has a full light transmittance of more than 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 has a large specific gravity. For a greenhouse of the same area, its usage is 1/3 more than that of polyethylene, resulting in increased costs; secondly, it becomes hard and brittle at low temperatures, and is easy to soften and relax at high temperatures; after the additives are precipitated, the film surface absorbs dust, and generally the light transmittance is very poor after one month of use. The residual film pollutes the soil and cannot be burned. Due to the generation of chlorine, it causes environmental pollution, and the current usage is gradually decreasing.

★PE greenhouse film. PE greenhouse film is light, soft, easy to shape, has good light transmittance, and is non-toxic. It is suitable for various greenhouse films and ground films. It is the main agricultural film variety in my country. According to the needs of farmers, different product types such as PE aging resistance (single protection), PE aging drip resistance (double protection), and PE aging drip defogging (three protections) can be produced, which have good aging resistance and drip defogging properties. Its disadvantages are: poor weather resistance, poor thermal insulation, and difficult to bond. Manager Song learned that the PE grouting film is currently used more in the market.

★ Grouting film is based on the original polyethylene greenhouse film, and is processed again. The inner surface of the agricultural film is treated by coating. In this way, the functional dripping and defogging agent of the treated greenhouse film is tightly attached to the inner wall of the greenhouse film, forming a layer of agent on the inner surface of the greenhouse film. Once the moisture in the greenhouse contacts the inner wall of the greenhouse film, a layer of water film will be formed, and then due to its own gravity, it will flow down along the slope of the greenhouse, thereby achieving the effect of defogging and dripping. The essential difference from the previous greenhouse film is that the functional agent exists independently outside the greenhouse film, so the time of 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 grouting film. First, the defogging and dripping agent is attached to the surface of the agricultural film, so its adhesion is not that strong. External force can easily cause damage to the coating, which can easily cause dripping in the damaged area. For example, when the shed is put up, the friction between the inner wall of the shed and the steel frame on the shed, and the high crops touching the agricultural film will cause the above situation. At the same time, crops that like high temperature and high humidity are not easy to use grouting film, such as cucumbers, bitter gourds, melons, etc. However, the disadvantages do not outweigh the advantages. Even if the above situation occurs, the overall effect of the agricultural film is still significantly better than that of traditional agricultural film. Because this product has obvious advantages in fog and drip removal, and the cost is relatively low, it is about 1.1-1.3 yuan per square meter. Compared with the price of EVA film, the input cost is low, so it is favored by many vegetable farmers. The current grouting film has different product quality due to different filling levels. Vegetable farmers should conduct multiple inspections on each product when purchasing and choose regular companies to purchase.

★EVA film EVA greenhouse film is a kind of greenhouse plastic film that is currently used in large quantities. This type of film has super light transmittance, with a transmittance of more than 92%; it has excellent drip and fog removal properties, with a drip period of more than 4-6 months; it has excellent thermal insulation, dust resistance and super aging resistance (more than 18 months). Three-layer EVA greenhouse film can be widely used in the production of high-end economical pollution-free vegetables, such as cucumbers, tomatoes, peppers, bitter gourds, etc. The disadvantage is that the price is relatively high. Depending on the thickness specifications, the current market price is: 0.08 mm is generally 2.05-2.1 yuan/square meter, and 0.09 mm is 2.15-2.2 yuan/square meter.

★In addition, PO film is also a new type of film developed in recent years. This type of film is a high-end functional polyolefin agricultural film made of polyolefin. Its light transmittance, continuous defogging, dripping, thermal insulation, etc. are in a leading position among greenhouse films. It has a high cost performance and is the most promising type of film for promotion. At the same time, due to the production technology of many domestic brands of PO films, the quality of PO films produced by many companies will be unstable. Vegetable farmers need to identify well-known brands when purchasing.