IL106270A - Polymeric composition for plastic sheets for use in greenhouses - Google Patents

Description

1 9 3 4 6 "I'QLYMERIC CCMPOSITIONS FOR PLASTIC SilSETS FOR USE ■> IK GREENHOUSES" Τίίκ APPLICANTS: :««rpsa:i SSATF OF ISRAEL 5 ,~ΜΊΰ> tiWW MINISTRY OF DEtHNSE, OKai) mm tyx nurai> ijitnn ARMAMENT DEVELOPMENT AUTHORITY, .31021 na ,2250 .1.1» P.O.BOX 2250, HAIFA 31021.

THE INVENTOR: :iw>-rta3n SHULRMIT WA3SERMAN imtn Λη5»"5¾ 111, HATXSHBI ST. Ill »ΜΜΜ1 aim 8 4 I F A. .n o * n The present invention relates to plastic sheets or panels to be used in greenhouses. More particularly, the invent-on relates to plastic sheets or panels possessing a solar filter to be used in greenhouses for two or more seasons.

BACKGROUND OF THE INVENTION Greenhouse, as generally understood is an enclosed structure of glass or plastic sheets or panels, which provides protection from the extremes of hot and frost climates producing superior plant environment necessary for the production of fruit, vegetables and flowers. As known, best growing results are obtained when the light on a green house is even and shadowless.

Conventional plastic sheets or panels, such as polyethylene, copolymers of ethylene or other olefins, have been extensively used as cover materials for protecting crops in greenhouse and the like. In order to control the light transmission properties of such sheets, some prior publications mention the incorporation of some inorganic materials such as: silica or aluminium hydroxide (Israeli Patent No. 32015), metaphosphate (Israeli Patent Number 52412) or a double basic sulfate of and aluminium hydroxide (U.S. Patent No. 4,134,875). Although films of polyethylene containing silica possess indeed improved properties in respect to reduced transmi ttance in the area of spectrum included in the range of between 7 and 14 microns, they suffer from serious wear problems in the equipment used to produce such sheets, due to the abrasive properties of the additive. Also, silica has the effect of accelerating the degradation of the sheets. In a greenhouse covered with plastic sheets, at the end of the cold season, the plastic sheets have to be partially or fully removed or perforated or some means of ventilation being introduced, since otherwise during the summer very high temperatures in the order of about 50°C might be reached, fact which does affect the quality of the agricultural products. In addition, farmworkers will most prefer to leave the sheets covering the greenhouse for more than one season, thus saving the costs of new sheets of plastic as well as of the required work for installing thereof. In addition to the above, there are also the following main factors for leaving the sheets during the summer season: - The plastic sheets which are now on the market, possess a higher life-time use than those available in the past, being capable of withstanding more than one season .

- The saving in irrigation during the summer, due to the inhibition of evaporation.

- The decrease in the amount of plastic waste, which is an advantage from an environmental point of view.

- The required agricultural work in a greenhouse area, such as seeding, extermination of pests, etc. is much more easier to be carried out in the presence of such plastic sheets.

In order to be able to use such plastic sheets for more than one season, it was suggested to use a reagent which covers the plastic sheets and would serve as a light filter. This reagent w ll reflect part of the solar radiation so that the temperature in the greenhouse space will decrease and therefore, the plastic sheets may be left even during the summer. Known reagents used for this purpose are based generally on white powders such as zinc oxide. A water suspension of such a reagent is prepared and spread on the plastic sheet by spraying or brushing. The main disadvantages of such reagents are as follows: - The coverage of these suspensions is relatively low. Generally, about 20 kg of the powder is required for only 1 dunam of the greenhouse, a fact which again involves significant costs of transport and working.

- The adhering of the reagent to the plastic sheet, is quite low so that it can be easily removed by rain, fact which is most undesirable, particularly when the rain occurs even during the summer season.

According to the recent U.S. Patent Number 4,943,484, t is suggested to use a filter which comprises at least one coating formed by a layer of reflective material between two layers of dielectric mater ial . The reflective material is selected from aluminium, silver, gold and copper. The dielectric material is selected from zinc oxide, indium oxide, titanium oxide and tin oxide. The above filter composition is suggested especially for glass and of course seems to be quite expensive.

According to the U.S. Patent Number 4,426,465, a coating composition for selective solar absorption is claimed. The composition comprises an inorganic black pigment dispersed in a binder of a thermosetting acrylic resin and particles of a low molecular weight fluorocarbon resin in the presence of a solvent. The black pigment is selected from the group consisting of oxides of iron, manganese, copper, cobalt and nickel and mixtures thereof.

In the U.S. Patent Number 4,323,619 a flexible covering element having selective optical properties to provide refrigeration by a selective irradiation. The element comprises a film which is transparent to infrared radiations, consisting of two films coupled to each other. The films are made from a polymer selected from the group consisting of polyethylene and ethylene copolymers, one of them being white and the other being black. The wh te colour is obtained by a pigment selected from: calcium oxide, zinc sulfide, magnesium oxide, ti tani urn dioxide and magnesium oxide.

The above brief review, shows the importance attributed to provide a solution for alleviating the problem of using plastic sheets for covering greenhouses, capable to withstand to the environment for more than one season. It is an object of the present invention, to provide a novel composition for covering plastic sheets or panels for greenhouses, having the function of a solar filter to protect agricultural growths.lt is another object of the present invention to provide a novel composition for covering plastic sheets or panels for greenhouses, imparting to said sheets the property to withstand weather conditions for two or more seasons.

BRIEF DESCRIPTION OF THE INVENTION The invention relates to polymer compositions having the function of a solar filter, being spread on plastic sheets or panels, generally made from various materials such as: polyethylene or copolymers of ethylene and vinyl acetate etc., which are based on a paint, comprising a binder as the matrix which consists of an acrylic copolymer possessing between 15 and 150 carbon atoms and a molecular weight of between 1,000 and 22,000, having the property to provide a dispersion in water with a solid content between 16% to 64% by weight at a pH in the range between 6 to 9.5, with at least one filler which provides the film forming material to impart the optical property of the filter which consists of a metal oxide, said metal being selected from calcium, zinc, and titanium or any mixture thereof. A most preferred acrylic copolymer found to be useful according to the present invention, has to contain between 25 to 100 carbon atoms and a molecular weight in the range of between 5000 to 15,000. The novel polymer compositions possess a strong adherence to the plastic sheet, fact which improves signif cantly the withstanding of the plastic sheet to the environment conditions. Accordingly, the plastic sheets should not necessarily be removed after the cold season; also, the novel compositions, have the advantage of improving significantly the coverage property. An important advantage property of the compositions is the fact that at any desired period, the solar filter with the above polymeric composition may be easily removed by washing with an aqueous acidic or alkali solution.

DETAILED DESCRIPTION OF THE INVENTION The plastic sheet or panel containing the solar filter according to the present invention, possesses the basic requirements to withstand rains and other storms which might occur from bad weather. A particular advantage, is the fact that the layer of resin with the metal oxide covering the plastic sheet, may be easily removed when this is desired in order not to affect the growth of an agricultural product. This removal may be easily carried out by a slight heating, washing by a diluted alkaline or acidic solution, or by mechanical means such as abrading. When this removal will be carried out by an alkaline or acidic solution, there is a requirement that the resin should be soluble in this solution, or that it will lose the adhesion property to the plastic sheet due to the exposure to this chemical solution.

The basic requ rement of the metal oxide incorporated in the resin, is to impart to the plastic sheet the required properties for fulfilling the role of of a solar filter in a greenhouse. Preferred metal oxides are zinc oxide, titanium oxide or calcium oxide, the most preferred being titanium oxide. The amount of metal oxide may be varied over a broad range, generally being between 15% to 45% by weight and most preferably between 25% to 35%. The exact amount will depend on the particular requirements of the properties which have to be imparted to the plastic sheet or panels.

An important advantage of the polymer composition used according to the present invention, is that only a small amount of it is required in order to obtain a coverage of the plastic sheet possessing the above desired properties. Generally, the amounts of the above composition will be much below those known to be used in order to impart a solar filtration being in the range of between 2% to 10% by wt . and most preferable being between 4% to 7% by wt . In this manner, there is a significant reduction in the costs of the reagents, their transport and labour for covering the plastic sheets.

When necessary, the polymeric compositions may also contain additives, such as antioxidants, ultra-violet stabilizers, humectants, antistatic agents, their presence being advantageous in some specific cases as known in the art.

The plastic sheets with the polymeric compositions according to the present invention, are character zed by their improved mechanical strength, which is practically equivalent and even higher than that of the sheets made of polyethylene with known additives normally used for this application.

A greenhouse using the plastic sheets or panels according to the present invention will also have the advantage to cause an increase in the precocity of plants and crop growth, when compared with known polyethylene sheets, in addition to the main advantage that the sheets can be removed after more than one season.

One of the advantages of the method to obtain the compositions containing the resin to be used on the plastic sheet is the fact that they may be produced in conventional equipment used in the paints manufacture. A particular attention should be given to the milling operation of the metal oxide, which should possess a particle size below 3 mm, so that upon admixing with the resin, a homo- geneous mass would be obtained, in order to impart a high coverage of the composition on the plastic sheet.

While the invention will now be described in connection with certain preferred embodiments, which are presented for a better understanding, it should be understood that the invention is not limited only to the description of the Examples presented hereafter. A person ski 11 led in the art, after reading the present specification will be in a position to insert slight modifications, without being outside the invention, which is covered by the appended Claims.

EXAMPLE 1.

In a mixer, as used in paint manufacturing, the following reagents were introduced: - 60 grams of a colloidal acrylic copolymer having 45 carbon atoms and molecular weight of about 10,000, as a dispersion in water at a pH of 8.2 having a solid content of 25%; - 30 grams of titanium dioxide ground to a particle size below 35 micrometers; - 7 grams of methyl isobutyl-ketone; - 0.5 g of a cationic wetting agent (Antitera U, TM.) - 0.5 g of carboxy methyl cellulose.

The mixture was thoroughly agitated for about 15 minutes and after that it was ready for spraying on a polyethylene sheet, after diluting with water.

EXAMPLE 2.

In the same vessel as used in Example 1, the following reagents were introduced: - 50 g( , ~ f a colloidal acrylic copolymer having 60 carbon atoms and a molecular weight of about 12,500, as a dispersion in water at a pH of 9.0 having a solid content of 30%; - 40 grams of zinc oxide ground to a particle size below 30 micrometers; - 7 g of methyl isobutyl ketone; - 0.5 g of a cationic wetting agent (Antitera U.TM); - 0.6 g of organo-clay thickener (Laponite RD, trade mark) .

The mixture was thoroughly agitated for about 15 minutes and after that it was ready for spraying on a polyethylene sheet.

Claims (8)

- 11 - 106,270/3 C L A I M S :-

1. A polymeric composition having the function of a solar filter, when spread on conventional plastic sheets or panels, made from polyethylene, or copolymers such as ethylene and vinyl acetate or glass panels, which comprises a paint comprising: - a binder as the matrix, consisting of a copolymer in the form of an aqueous dispersion comprising between 16% to 64% by weight solids at a pH in the range of between 6 to 9.5, the said polymer having between 15 and 150 C atoms and a molecular weight in the range of 1,000 to 22,000; - at least one filler imparting the optical property of a filter, consisting of an oxide of a metal which is selected from titanium, zinc and calcium, or any mixture thereof , said polymeric composition being removed by washing with an alkaline or acidic solution.

2. The polymeric composition according to Claim 1, wherein said copolymer is an acrylic compound which contains between 25 to 100 carbon atoms and a molecular weight in the range of between 5,000 and 15,000.

3. The polymeric composition according to Claims 1 or 2, wherein the amount of said metal oxide is in the range of between 15% to 45% by weight of the composition. - 12 - 106.270/3

4. The polymeric composition according to Claim 3, wherein the amount of the metal oxide is in the range of between 25% to 35% by weight of the composition.

5. The polymeric composition according to Claims 3 or 4, wherein the metal oxide used has a particle size below 3 mm.

6. The polymeric composition according to Claims 1 to 5 , applied on plastic sheets in greenhouses having the advantage of an easy removal at any desired period.

7. The polymeric composition according to Claim 6, wherein said plastic sheets are removed by washing with a diluted alkaline or acidic solution, or by abrasion.

8. A polymeric composition having the function of a solar filter when spread on plastic sheets or panels, substantially as described in the specification and in any one of Claims 1 to 5. For the Applicant, Simon Lavie Patent Attorney