Vegtech 2000 - The leading company in the Greenhouse Industry in Southern Africa - greenhouse films
Vegtech supplies various plastic films for use in agriculture. There are a number of additives that can be added to the basic film to give effects required by the specific crop. Any combinations of these additives are available.
All the films except for the simple UVA diffused film are five layer films.
Films are available in widths up to 16m (only 14m in 200 micron) and thicknesses of 150, 180 and 200 micron.
These are the properties available in the films.
- Clear or Diffused films
In the South African scenario where we have intense UV radiation most of the year clear films are dangerous and will lead to fruit burn and other damages related to harsh radiation. We therefore recommend Diffused Films which soften the radiation and also make sure that the bottom of tall trellised crops receives light. In greenhouse with double inflated cladding we use the ultra clear films as the outer film. In crops where high radiation is not a problem then clear films can be used.
This property was (and still is, by some) erroneously called Anti Fog. In reality we are talking about preventing the formation of large drops of water on the inner surface of the plastic greenhouse cover and the side curtains. By its very function, the air inside a greenhouse will always have high moisture content. Water is always condensing on the inner plastic surfaces of the structure. If the moisture forms large drops, the grower will suffer in two ways, from a loss of essential light reflected back to the atmosphere by the large drops and the risk of fungal and bacterial disease development on the plants where the drops came to rest once leaving the surface.
At first glance we assume that the main benefit from the use of thermal films is the effect on the air temperature of the greenhouse, which is the criterion most frequently measured in order to determine whether the film is doing its job. The truth lies elsewhere, without underestimating the importance of nocturnal greenhouse air temperature. Of prime importance is the maintenance of optimal temperatures of the plants we are growing in the greenhouse. If the air is warm at night it will impart some of its energy to the plants which it envelopes. But air, by its very nature, carries relatively little energy because its mass is so small. So there are limits to how much the air in the greenhouse can warm up plants rapidly losing energy (heat) through radiation and convection. In other words, plants in a greenhouse covered with a thermal film which is absorbing heat radiation and is relatively warm will (theoretically, at least) be warmer than they would if they were exposed to the sky above with no plastic cover or with a non-thermal cover.
This additive blocks UV radiation coming into the Greenhouse up to 380nm. Certain Insects need UV light to navigate and by removing it from the greenhouse it becomes impossible for them to move around the greenhouse and do damage. What is important is that the blocking is done to 380nm exactly. If you block further than that you enter the PAR range and this will create problems with the growing of the crops if you block less than that the insects will acclimatize to the reduced UV and return to normal activity.
Within a week following greenhouse cover installation there could be a reduction of 40% in transmitted visible radiation solely because of the accumulation of dust on the upper surface of the plastic. It is true that there are areas where dust is more abundant than in other areas, but all in all, dust is ubiquitous. Dust is attached to the plastic cover through electrostatic forces. The dust particles are charged, as is the film cover. We produce films with an Anti-Dust additive in the top, outside, layer. The additive does not prevent dust from settling on the greenhouse cover, but it makes it more difficult for the dust to remain on the plastic and makes it easier for the wind, the rain and cleaning the dust from the plastic.
- Anti-Mist (Fog):
Growers have learned from their own experience that a film which performs well against the phenomenon of "drip" will inevitably give rise to the appearance of mist in the greenhouse when relative humidity, resulting from temperature reduction, usually at night, reaches saturation. If the excess moisture has no cold, free surface on which to condense, mist will form. This hovering fog will cover the plants not only on the upper surfaces. A layer of moisture enveloping all the plant parts will result. Today it is possible to enjoy both worlds, using a film enhanced by the cutting edge technology of anti drip additives without incurring the risk of mist formation, due to the availability of anti-mist additives which prevent mist from forming. However, one should take note of the fact that, although the anti mist property is beyond the experimental stage, we are still learning how to make a film with an anti mist property which will perform in the field longer that two years.
Almost any combination of these properties is possible, but below are some of the most common films.
|FILM ||PROPERTIES |
| || |
|LIGHT transmission ||LIGHT DIFFUSION ||% thermisity ||AD EFFect |
|UVA Clear || |
|UVA Diffused || |
|UVA AV Diffused (205) || |
|Dripblock Diffused || |
|AD IR AV Diffused || |
|IR 504 || |
| || |