The shed film is one of the most critical materials used in the cultivation of flowers and vegetables. Currently, three main types of films are widely used in agricultural production: polyethylene (PE), polyvinyl chloride (PVC), and polyvinyl acetate (PVA). These are all soft plastic films. In terms of mechanical strength, PVC performs the best, followed by PVA and then PE. When it comes to light transmission, PVA is superior, followed by PE and then PVC. For insulation properties, PVC is the best, with PVA and PE coming next. Below are some of the common shed films available on the market, which are widely used and recommended for flower farmers.
1. **PVC Non-Dripping Film**
This type of film is made by adding surfactants to PVC, which prevents condensation from forming on the surface. This helps reduce humidity inside the greenhouse, lowering the risk of plant diseases. It warms up quickly during sunny days and is ideal for flowering plants, winter vegetables, and early maturing crops.
2. **New PVC Ordinary Film**
This film offers good light transmission, night-time heat retention, resistance to high temperatures and sunlight, good elasticity, low elongation, and strong aging resistance. It can last about a year. However, over time, it tends to develop vacuum bubbles, is difficult to clean, and its light transmittance decreases significantly. It also has poor moisture permeability and weak low-temperature resistance. It’s best suited for areas where nighttime heat preservation is crucial.
3. **Polyethylene Multi-functional Composite Film**
This film combines several functions, such as anti-drip, heat retention, and light transmission. Some versions can block UV rays, helping to control sclerotinia and gray mold in flowers and vegetables. It provides better insulation than standard anti-aging PE films.
4. **Polyethylene Longevity Anti-Drip Film**
By adding anti-aging agents and non-dripping surfactants, this film lasts over two years without condensation. Its thickness ranges from 0.1 to 0.12 mm, and it weighs around 100 to 130 kg per acre. It's suitable for use in various greenhouses and can be applied as a double-layer cover for winter continuous cultivation.
5. **Polyethylene Light-Adjusting Film**
Made from low-density polyethylene resin with a light conversion agent added, this film offers long life, good light transmission, and strong resistance to aging. It has a thickness of 0.08 to 0.12 mm and can be used for more than a year. It provides excellent light transmission and heat retention, making it ideal for winter greenhouse cultivation and two-layer covering systems.
6. **Diffuse Reflection Film**
This film uses crystalline nuclei to scatter sunlight, reducing the intensity of direct sunlight and preventing overheating in the greenhouse during midday. As the sun sets, the light transmission increases, allowing more natural light to enter and improve temperature conditions. It also offers good heat retention at night and helps accumulate warmth.
7. **Vinyl Acetate Film**
This film has better weather resistance, tensile strength, adhesion, and light transmission compared to PE. It can be mixed with various additives to extend its anti-fogging period and is ideal for cold regions. Some composite films combine PE and PVA for enhanced performance.
To distinguish between PVC and PE, you can perform a simple test: when burned, PVC emits a pungent smell of hydrogen chloride, while PE melts and drips like wax. PVC has a specific gravity of 1.3 and sinks in water, whereas PE has a specific gravity of 0.9 and floats.
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