The shed film is one of the most critical materials used in the cultivation of flowers and vegetables. It plays a vital role in regulating temperature, light, and humidity within greenhouses. Currently, three main types of films are widely used in agriculture: polyethylene (PE), polyvinyl chloride (PVC), and polyvinyl acetate (PVA). These are all soft plastic films, each with unique properties that make them suitable for different agricultural needs.
In terms of mechanical strength, PVC is the strongest, followed by PVA and then PE. When it comes to light transmission, PVA performs best, followed by PE and then PVC. For insulation, PVC is the most effective, while PVA and PE offer moderate levels of heat retention. Each type of film has its own advantages and disadvantages, and farmers often choose based on specific environmental conditions and crop requirements.
Here are some common types of shed films available in the market:
1. **PVC Non-Dripping Film**: This film is treated with surfactants to prevent water droplets from forming on its surface, reducing humidity inside the greenhouse. Lower humidity helps reduce the risk of fungal diseases. It warms up quickly during sunny days, making it ideal for winter vegetable production and early flowering in greenhouses.
2. **New PVC Ordinary Film**: Known for good light transmission, night-time heat retention, and resistance to high temperatures and UV exposure, this film also offers good elasticity and aging resistance. It can last about a year but tends to lose transparency over time and may become difficult to clean. It’s best suited for areas where nighttime warmth is essential.
3. **Polyethylene Multi-functional Composite Film**: This film combines several functions, such as non-dripping, heat retention, and light transmission. Some versions even block UV light, helping to control diseases like sclerotinia and gray mold. It provides better insulation than standard anti-aging PE films.
4. **Polyethylene Longevity Non-Dripping Film**: By adding anti-aging agents and non-dripping surfactants, this film lasts more than two years without condensation. With a thickness of 0.1–0.12 mm, it weighs around 100–130 kg per acre and is suitable for use in various greenhouses, including double-layer coverage for winter cultivation.
5. **Polyethylene Light-Adjusting Film**: Made from low-density polyethylene with a light conversion agent, it offers long-lasting performance, good light transmission, and strong heat retention. It warms up quickly during the day and retains heat at night, making it ideal for winter greenhouse use and two-layer covering systems.
6. **Diffuse Reflection Film**: This film uses crystal nuclei to scatter sunlight, reducing the intensity of midday heat peaks and preventing overheating. As the sun sets, the light transmittance increases, allowing more natural light into the greenhouse. It provides excellent night-time insulation and helps maintain a higher overall temperature.
7. **Vinyl Acetate Film**: Known for superior weather resistance, tensile strength, adhesion, and light transmission compared to PE, this film can be mixed with additives to extend its non-dripping period. It is particularly suitable for cold regions and is often combined with PE in composite films.
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. Additionally, PVC has a specific gravity of 1.3 and sinks in water, whereas PE floats due to its lower density of 0.9.
Choosing the right shed film can significantly impact the success of your greenhouse farming. Understanding the properties and applications of each type will help you make an informed decision based on your specific needs.
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