The main purpose for the green-houses covering is to create an internal environment regardless the external environmental. The better the control the better the crop yield and quality. The controlled microclimate in term of light, temperature, humidity and physical protection of the crop (winds, rain snow etc) maintaining controlled environmental at different climatic condition. Controlling the internal environment gives the possibility to extend the growing season, fresh fruit all around the year and enhanced crop quality and crop yield.
Cover film properties:
- High mechanical properties:
The film mechanical properties depend on the used polymers and production technique. In Politiv we used only sophisticated materials supplied by the leading producers of polymers and additives and with fully computerized extruders. Our films meets the Israeli Standard 821, ISO and ASTM (click here to view the standards certifications
- UV Stability (film durability):
Film without UV stabilizers will fail after few months (4-6 depend on the film thickness). In order to achieve the required durability UV stabilizers should be added. The UV stabilizers type and percentage depends on the film life time, area (total radiation), film thickness, greenhouse structure and agrochemicals usage. When Sulfur and chlorine is used, a special UV stabilizers package should be used.
- Maximum light transmission at the visible range (TLT):
Energy from the sun is transmitted through the greenhouse covering to the plant where it drives the photosynthetic process. The total light transmision of the greenhouse covering in the photo-synthetic active radiation (400-700 nanometer) is extremely important. The intensity of these wavelengths (PAR range) directly influences growth and development green plants.
- Thermal additives (IR):
During day, the greenhouse air heats up. At night when the outside temperature cools down, with regular cover there is loss of heat from the greenhouse by radiation towards outside and the greenhouse temperature is reduced by re-emitting radiation in the Infra red range. To prevent this radiation loss, special additives are incorporated within the film. These additives block the IR radiation and help to maintain the temperature in the greenhouse preventing freeze and low temperature damage.
- Light diffusion:
Direct sunlight (undefused light) can cause “shadow” effect and “sun burns”. Light diffusers additives will scatter the direct light. Thus, prevent the shadow effect and the sun burns. The light deffusion increase the photo-syntetic efficiency by providing more homogeneous light from all directions and gives advantage to growth with self-shading, such as cucumbers, tomatos, squash, roses and others. The film is suitable for area with high radiation.
Hot air contains more moisture than cold air. At night, the temperature inside the greenhouse decrease, as a result, the water vapor in the air condenses in form of small discrete droplets. The effect of fog formation:
*- light transmission reduction with consequent reduction in growth.
*- dripping on the plants causing diseases
In order to prevent the above, special additives are added. These additives modify the film surface so the water droplets are speared into a continuous invisible water layer.
- Anti- virus:
The human being eyes are sensitive to 400-700 nm, while the insects are sensitive to the UV range (less than 400 nm), so, by blocking the UV range, the insects inside the greenhouses are less active. As a result, less agro-chemical are used. With red roses, UV blocking prevents the roses blackening.
Mist forms in a greenhouse when the temperature drops and the relative humidity reach saturation and the greenhouse cover has Anti-fog/Anti Drip Function. Mist has negative impact on the plants, the leaves are subjected to a thin moist layer, top and bottom, also, mist blocks out the sun’s rays for hours in the “morning after”.
The multi-layer construction and special polymers usage result in a smooth film that prevents dust accumulation on the outside. This is an important feature to insure maximum light transmission and very easy film cleaning .
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