ES2259926B1 - POLYOLEFINE FILMS WITH AN IMPROVED ANTIGOTE BEHAVIOR FOR INTENSIVE CULTURE SYSTEMS UNDER PLASTIC COVER. - Google Patents

Abstract

This invention relates to thermal polymeric films with an improved anti-drip behavior comprising in their composition a polyolefin and an anti-drip additive characterized in that the anti-drip additive is a mixture of micronized anhydrous borax and, at least, a surfactant. These films, monolayer or multilayer, are used in intensive cultivation systems under plastic cover such as greenhouse film, small tunnel or padding in agriculture and greenhouse film in aquaculture.

Description

Polyolefin films with a behavior enhanced drip for intensive indoor cultivation systems plastic.

This invention relates to polymeric films. of polyolefins with thermal and anti-drip properties, which are they use in intensive cultivation systems under plastic cover as greenhouse film, small tunnel or padding in agriculture and Greenhouse film in aquaculture.

It is well known in the current state of the technique that of the different properties required to films used in intensive cultivation systems under plastic cover as, for example, those of greenhouse in agricultural applications, there are Several that are very important. These include the duration, global transmission of visible light, turbidity, thermicity and anti-drip. The last two are of special interest in this invention, since it is related to compositions for thermal and drip films.

The transmission of light through the films of plastic cover of intensive farming systems depends on various factors such as reflection, absorption, composition, thickness, dust accumulation, water condensation, etc. In In general, the intensity of the solar radiation that reaches the interior the cultivation site is always smaller than the one in the Exterior. The general requirement that these films must meet is allow maximum global transmission of visible light, which is the sum of the transmission of direct light and diffused light in the interval spectral between 0.4 and 0.7 micrometers. Diffuse light is which deviates more than 2.5º from the direction of the light beam incident. The percentage of diffused light transmission over the Global is called turbidity. The films are called "clear" when it is possible to see the objects clearly through them and "diffusers" or "shady" when they let the light through but the Objects are not seen clearly through. According to EN 13206, a film is diffuser when its turbidity is equal to or greater than 35%, for thicknesses greater than 150 micrometers. Some u are preferred others depending on the application and the geographical area to which They are directed.

As far as thermicity is concerned, they are also known the beneficial effects of films that are opaque to the long wave infrared radiation, especially in the interval between 7 and 13 micrometers in which the dry atmosphere is particularly transparent, with which crops have been obtained more abundant and early. The results are better the less infrared radiation let pass and at the same time the more Transparent are in visible light. These films, known internationally as "thermal" films, reduce the risk of frost damage when there is no heating in the greenhouse and reduce energy consumption when available. Both of them effects are attributable to the decrease in heat losses by radiation In the present invention films are preferred thermal over those that are not.

The most widely used polymer in the world manufacture of films for low intensive farming systems plastic cover, such as greenhouses, is polyethylene Due to other technical and economic advantages. However, it is very transparent to infrared radiation between 7 and 13 micrometers The most common way to make it thermal is to add additives, preferably mineral type, with absorptions in said interval. As representative examples of the state of the art, You can cite the following:

ES439227: Spanish patent on the use of silica, silicates and hydroxide of aluminum.

US4559381 and US4651467: American patents on the use of borates and borax anhydrous.

JP631175072 and JP1006041: Japanese patents on the use of hydrotalcite.

EP1095964: European patent on the use of a synergistic mixture of borates with silica, silicates, carbonates and sulfates.

As for the last mentioned property, it understood by films "drip" or "fog" those whose surface tension increases by incorporating some surfactant additive in its composition that causes the drops of water in contact with the film surface have an angle of minor contact The inner atmosphere of the closed systems of intensive cultivation under plastic such as greenhouses of vegetable or aquaculture culture, it is often saturated with water vapor that evaporates from soil, plants or farming ponds. If the film is drip, said water vapor condenses in the form of drops that tend to unite with each other as a continuous film and not as individual hemispherical drops, which is what happens in films without that kind of additivation. In addition, in the latter case there is a decrease in the transmission of visible light into the crop enclosure, with the consequent harvest reduction that this may entail, because part of the incident light is reflected in them.

There are three parameters that characterize the behavior of an anti-drip film: blooming or excessive surface migration, the duration of the effect and its quality. For the latter, a series of qualitative scales has been defined, one of which is that described in Table 4 of Example 4 of this invention. The duration of the effect is usually limited, since the condensed water is extracting the drip additive. It depends on factors such as the thermal jump between inside and outside, film temperature, ambient humidity, ventilation, etc. The evolution of the quality of the anti-drip effect over time can be measured directly in the field, in the real conditions of application, or in the laboratory, through accelerated tests. Blooming or excessive surface migration is an unwanted effect that is unacceptable for the market for cover films of intensive farming systems. The drip additives have to be partially incompatible with the polymer matrix in order for their migration to the surface of the film to take place and thereby modify their surface tension. If the incompatibility is excessive, a whitish layer is formed on said surface by the accumulation of the additive, which makes the light transmission and physical appearance worse.

According to the state of the art, there are three methods to provide films with drip properties:

one)

Incorporation of drip additives within the polymer matrix as pure additives or as concentrated. These additives migrate to the surface of the film. In Monolayer films migration occurs in both directions, that is, to the face directed towards the interior of the crop enclosure where the drip effect is required, but also to the one located outward where it is not necessary, and even harmful, since which increases the accumulation of dust, which reduces the transmission of light.

2)

Application of drip additives by coating the surface of the film. In general, the Used surfactant molecules usually form weak bonds with the polymers such as polyethylene, so the drip effect lasts very little since they are easily removed by water from condensation and rain, in addition to the temperature influence.

3)

Chemical modification of the base resin polyolefin or film surface by introduction of a hydrophilic group. However, this technique is high cost today and it is difficult to apply in cover films for intensive farming systems.

The following patents can be cited as representation of the current state of the art:

ES2127696: Spanish patent where films are claimed for cover of greenhouse with anti-drip properties that are achieved through absorption, prior to incorporation into the polymer matrix, of a non-ionic surfactant in a micronized mineral filler and microporous amorphous silica type, diatomaceous earth, kaolin, natural silicates, zeolite, alumina, sepiolite or hydrotalcite

EP0500073: European patent where the face coating is claimed inside the film with an inorganic hydrophilic colloidal substance and a hydrophilic organic compound.

WO2004022639: PCT application where a drip polyolefin film is claimed wherein said effect is achieved by a drip additive formed by two components, a linear ethoxylated alcohol and a fluorinated surfactant, incorporated in the composition or applied to the surface of the film as a coating.

WO02072530: PCT application where the chemical modification of the film surface by incorporating drip additives that migrate to the surface and anchor to it by a reaction light induced.

However, there is still great interest in have alternative films with drip behavior enhanced for intensive cultivation systems under plastic cover, especially of thermal films, since with the current state of the technique not all requirements are satisfactorily met necessary.

Surprisingly, it has been found that mixtures of anhydrous micronized borax with at least one surfactant It is especially suitable in the preparation of compositions for thermal films containing polyolefins with anti-drip properties improved.

One aspect of the present invention relates to a film with thermal and anti-drip properties that includes in its composition a polyolefin and a drip additive, characterized because the drip additive is a mixture of anhydrous borax and, at less, a compound selected from the group consisting of surfactants nonionic, cationic and anionic.

Most of the additives that are added to polyolefins, such as polyethylene, to get its IR effectiveness is greater than 75%, so that the corresponding film can be denominate thermal according to EN 13206, increase its turbidity above 35%. It is what happens, for example, in patents EP1095964 and ES2127696 cited above. The only two charges thermal inorganic that do not modify this last parameter are the hydrotalcite and anhydrous borax. The first is a bad agent thermal, which means you have to add a percentage a lot greater than the second to achieve the same thermicity value. That is a disadvantage from the point of view of others film properties such as mechanics. According to him current state of the art, the combination of anhydrous borax with drip additives. However, it has been found that when it is mixed with drip additives belonging to the group of nonionic, cationic or anionic surfactants in the Composition for manufacturing a plastic cover film for intensive farming systems, surprisingly, the behavior drip that is obtained with anhydrous borax is clearly superior as much as one would expect if it were not present as at which is obtained with the rest of the thermal additives used usually in this type of films and described in the state of the technique.

The films comprise in their composition 85% a 99% of a polyolefin and 1% to 15% of the mixture formed by the anhydrous borax and surfactants, preferably between 1% to a 10% and more preferably between 1.5% to 7%. Weight ratio between the two components of the mixture must be between 1:10 and 50: 1, respectively, preferably between 1: 6 and 10: 1 and more preferably between a 1: 4 and a 7: 1. In the compositions of the films can also be added other processing additives or functional that may be considered necessary for manufacturing of films or to provide them with certain properties. Between they include antioxidant or stabilizer additives thermal; light stabilizing additives, such as sterically hindered amines (HALS), UV absorbers or deactivators of excited states; antacid additives; the antistatic additives; lubricant additives; the additives anti-lock the pigments; etc.

The base polymers used in the films of the The present invention are polyolefins, preferably polyethylene, a copolymer of ethylene and an alpha-olefin, a ethylene copolymer and a vinyl ester, an ethylene copolymer and an alkyl acrylate, a copolymer of ethylene and methacrylate of alkyl or mixtures thereof in any proportion; and more preferably, low density polyethylene (LDPE), polyethylene Linear Low Density (LLDPE), copolymers of ethylene and acetate vinyl (EVA) and copolymers of ethylene and butyl acrylate (EBA)

The preferred anhydrous borax is tetraborate. sodium, product resulting from dehydration and fusion of borax, which has the structural formula Na 2 B 4 O 7 and a size particle medium between 0.5 and 10 micrometers, preferably between 1 and 5 micrometers. Particle size it is important since if these are thick it is more difficult to disperse the additive homogeneously in the polymer and the surface of the film may be grainy instead of smooth.

The surfactants belong to the groups of nonionic, cationic or anionic surfactants, preferably non-phonic surfactants and more preferably to esters of fatty acids and sorbitan, esters of fatty acids and glycerol, fatty acid esters and polyglycerol, esters of fatty acids and trimethylopropane, esters of fatty acids and pentaerythritol, fatty acid esters and alkylene glycol, fatty acid esters and polyoxyalkylene sorbitan, esters of fatty acids and polyoxyalkylene glycerol, esters of fatty acids and polyoxyalkylene polyglycerol, acid esters fatty and bis (alkylene glycol) alkylamines, acid esters fatty and polyoxyalkylene alkylamines, alkylamines polyoxyalkylenic, polyoxyalkylene alkyl ethers or mixtures of The same in any proportion. Fatty acids of esters and the alkyl groups of the ethers and the amines can be pure or mixtures of hydrocarbon chains of different length. The best Preferred are cigars or mixtures containing total or mostly chains of 16 or 18 carbon atoms. The Polyalcohols may be totally or partially esterified. He most preferred "rent" group in all cases cited is the "ethylene." Within all the mentioned types are preferred those whose physical state is solid and, more preferably, solid powdered.

The processing temperature of the concentrates, The compounds and films depend on the polymer. Usual value of these processes is between 160ºC and 240ºC. He preferred transformation process to prepare the concentrates is the mixing, dispersion and homogenization of the additives in the polymer matrix by internal mixers or mixers continuous; preferred to prepare the compounds is the extrusion; and the preferred to make the films is extrusion of tubular or blown film. Films can have a thickness between 10 and 250 micrometers, depending on the application and geographic location to which they are directed. For example, if the film is for greenhouse cover, the value preferred is between 150 and 250 micrometers, more preferably, between 170 and 220 micrometers; if the film is for Small tunnel, the preferred value is between 35 and 100 micrometers, more preferably between 50 and 80 micrometers; if the film is for padded, the preferred value is between 10 and 35 micrometers, plus preferably between 15 and 30 micrometers.

Finally, another aspect of this invention refers to the use of a film with thermal properties and anti-drip, as described here, in intensive farming systems under plastic cover. Illustrative examples, although not limiting, can be greenhouse cover in agriculture or in aquaculture and small tunnel or padding in agriculture. The films They can be monolayer or multilayer. In the first case, the film has The same composition in all its thickness. In the last one, the film is composed of several layers that can have the same or different composition. Monolayer films are preferred for Small tunnel and padding applications. The multilayer films are preferred for the application of greenhouse cover. He preferred multilayer film manufacturing process is called coextrusion of tubular film. The preferred combination is the called tricapa, which is the one with a layer directed towards the outside of the crop enclosure, a central layer and another layer inward oriented. The most preferred combination is that wherein the compositions of the present invention are used in the central and inner layers. Outside it is preferred to use a composition without drip additive to prevent the accumulation of powder.

The examples shown below they serve to illustrate, not to limit, the present invention.

Example one

To evaluate the influence of additives thermal over the global visible light transmission (TGLV) and the turbidity of drip films, various compositions were prepared anti-drip in which polyethylene based polymers of low density (LDPE, ALCUDIA PE-033, Repsol YPF, Madrid, Spain), characterized by a density of 0.922 g / cm3 and a flow rate of 0.3 g / 10 min at 190 ° C, 2.16 kg, or a ethylene vinyl acetate copolymer (EVA, ALCUDIA PA-570, Repsol YPF, Madrid, Spain), characterized for a vinyl acetate content of 14%, a density of 0.932 g / cm3 and a flow rate of 0.3 g / 10 min at 190 ° C, 2.16 kg, to which 2% of a drip additive was added (fatty acid esters and glycerol; the additive was not formed by a single chemical species, but by a mixture of different fatty acids and glycerol was mono-, di- and triesterified) and 3% of the inorganic thermal additives indicated in the Table 1. The mixtures were made in a twin screw extruder. at 180-200 ° C. The compounds obtained were processed in a tubular film extrusion and blowing machine, where they obtained the corresponding monolayer films with a thickness of 200 micrometers

The total visible light transmission (TGLV) and the turbidity was measured with a turbidimeter according to the EN standard 2155-5 and EN 2155-9, respectively. According to EN 13206, a film is diffuser when its turbidity is equal to or greater than 35%, for thicknesses greater than 150 micrometers Therefore, drip films made from Compositions with silica or zinc borate are considered diffusers or turbines, while those that incorporate hydrotalcite or Anhydrous borax are clear. Between the first two, the films that they carry zinc borate are more diffusers than those that incorporate silica. Between the last two, the films obtained with borax anhydrous are slightly more transparent than those that have hydrotalcite

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TABLE 1

Thermal additive LDPE EVE (14% AV) TGLV (%) Turbidity (%) TGLV (%) Turbidity (%) Silica 88.4 49.6 91.2 47.0 Borate of zinc 90.8 66.0 92.4 64.2 Hydrotalcite 90.9 20.3 92.5 17.4 Borax anhydrous 91.2 19.8 92.9 16.5

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Example 2

To evaluate the influence of additives thermal on IR efficiency or thermality of drip films, several drip compositions were prepared in which the same low density polyethylene (LDPE) described in Example 1, to which 2% of the same drip additive described in the Example 1 and 0%, 1%, 3% or 5% of inorganic thermal additives indicated in Table 2. The mixtures were performed in a twin screw extruder at 200 ° C. The compounds obtained are processed in a tubular film extrusion machine, where they obtained the corresponding monolayer films with a thickness of 200 micrometers

The effectiveness against IR radiation or thermicity was measured according to EN 13206, that is, to through the IR radiation transmission spectrum of each film in a range of wave numbers between 1430 cm -1 and 770 cm -1 (wavelengths between 7 and 13 micrometers). According said standard, a film of more than 150 micrometers thick is considered thermal if its value is equal to or greater than 75%. How I know You can see in Table 2, none of the four additives has sufficient thermality at 1%, silica, zinc borate and Anhydrous borax is provided at 3% (but not hydrotalcite) and, although at 5% all four are thermal, the order of IR efficiency is anhydrous borax> zinc borate> silica> hydrotalcite. He Anhydrous borax and zinc borate are the only ones that exceed the 90%

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TABLE 2

Thermal additive IR efficiency (%) according to the percentage of additive thermal 0% one% 3% 5% Silica 43.9 64.7 80.3 87.1 Borate of zinc 43.9 67.4 86.1 92.9 Hydrotalcite 43.9 58.9 74.1 82.4 Borax anhydrous 43.9 64.5 85.2 93.6

Example 3

To assess the influence on the blooming of thermal additives in drip films, several compositions were prepared in which the same ethylene vinyl acetate copolymer (EVA) described in Example 1 was used, to which a 3 was added. % of the drip additives indicated in Table 3 and 0%, 1% or 3% of the silica, zinc borate, hydrotalcite and anhydrous borax thermal additives. The mixtures were made in a twin screw extruder at 180 ° C. The compounds obtained were processed in a tubular film extrusion machine, where the corresponding monolayer films with a thickness of 200 microns were obtained. As can be seen in Table 3, the only compositions that did not give blooming were those containing anhydrous borax.

TABLE 3

Additive drip (%) Additive thermal (%) Blooming - - 0 - - 0 Do not Esters of fatty acids and sorbitan (mixture) 3 - - 0 Yes Esters of fatty acids and glycerol (mixture) 3 - - 0 Yes Esters of fatty acids and sorbitan (mixture) 3 Silica one Yes Esters of fatty acids and sorbitan (mixture) 3 Borate of zinc one Yes Esters of fatty acids and sorbitan (mixture) 3 Hydrotalcite one Yes Esters of fatty acids and sorbitan (mixture) 3 Borax anhydrous one Do not Esters of fatty acids and glycerol (mixture) 3 Silica one Yes Esters of fatty acids and glycerol (mixture) 3 Borate of zinc one Yes Esters of fatty acids and glycerol (mixture) 3 Hydrotalcite one Yes Esters of fatty acids and glycerol (mixture) 3 Borax anhydrous one Do not Esters of fatty acids and sorbitan (mixture) 3 Silica 3 Yes Esters of fatty acids and sorbitan (mixture) 3 Borate of zinc 3 Yes Esters of fatty acids and sorbitan (mixture) 3 Hydrotalcite 3 Yes Esters of fatty acids and sorbitan (mixture) 3 Borax anhydrous 3 Do not Esters of fatty acids and glycerol (mixture) 3 Silica 3 Yes Esters of fatty acids and glycerol (mixture) 3 Borate of zinc 3 Yes Esters of fatty acids and glycerol (mixture) 3 Hydrotalcite 3 Yes Esters of fatty acids and glycerol (mixture) 3 Borax anhydrous 3 Do not

Example 4

To evaluate the quality and duration of the effect anti-drip, several compositions were prepared in which the same copolymer of ethylene and vinyl acetate (EVA) described in the Example 1, to which 2% of the described drip additive was added in Example 1 and 5% of the thermal additives indicated in Table 5. The mixtures were performed in a double extruder. spindle at 180 ° C. The compounds obtained were processed in a tubular film extrusion machine, where the corresponding monolayer films with a thickness of 200 micrometers, whose drip behavior was evaluated as indicated by continuation.

The accelerated test that is commonly used in the laboratory to determine the quality and duration of the effect anti-drip is based on the use of a closed structure, similar to that of a greenhouse, where the conditions of temperature and condensation by means of a full thermostatic bath of water and in which several films can be tested simultaneously manufactured from different compositions. There is no regulations on the conditions under which said test. Some of the most normal are that the bath water is at 50ºC so that the interior of the chamber is saturated with water vapor and with a temperature gradient from water to the films above the outside temperature, which is usually the standard environment (25ºC). By increasing the temperature and quantity of condensed water inside the extraction of the anti-drip additive, so the duration of this effect is shortened. From time to time the appearance of the samples is observed and classifies its drip quality according to the scale that appears in the Table 4. A film without drip additives always has a quality B. The ideal drip film would be the one that kept permanently a quality E. A film is considered anti-drip while 50% of its surface has a better quality than C.

TABLE 4

Classification Description B Film completely covered with small drops round and "fog". BC Film completely covered with fat drops and Small round and "fog." C Film completely covered with fat drops well adhered and areas with "fog". CD Transparent film with enough fat drops irregular isolated and well attached. D Transparent film with very few fat drops irregular isolated. FROM Film transparent. A sheet of condensed water is seen. AND Film completely transparent. I dont know see water

The correlation between the duration of the effect anti-drip in the accelerated test and what you would have in a system of actual intensive cultivation depends, among other factors, on the geographic location. In general, it's about getting that said Effect is maintained throughout the life of the film. For example, if an average acceleration factor is supposed to exist camera / field 4, the drip effect of a film for cover greenhouse that lasted two years outdoors would have to stay with a quality higher than C for 6 months. As it looks in Table 5, after 180 days of accelerated testing the only one of the films of this example that remained anti-drip, and also it maintained a good quality, it was the one that contained anhydrous borax as thermal additive

TABLE 5

Thermal additive Quality initial After 180 days of accelerated test Silica FROM BC Zinc borate FROM C Hydrotalcite FROM BC Borax anhydrous AND D

Claims (10)

1. A polymeric film with thermal properties and drip that comprises in its composition

to)

a polyolefin

b)

a drip additive

characterized in that the drip additive is a mixture of anhydrous borax and, at least, a compound selected from the group consisting of non-ionic, cationic and anionic surfactants. 2. A film according to claim 1, which comprises in its composition between approximately 85% and, approximately 99% by weight of a polyolefin and between, approximately 1% and approximately 15% by weight of the Anhydrous borax mixture and the surfactant group. 3. A film according to the claims 1 and 2, in which the weight ratio of the anhydrous borax and the group of The surfactants are between approximately 1:10 and approximately 50: 1. 4. A film according to the claims 1 to 3, wherein said polyolefin is polyethylene, a copolymer of ethylene and an alpha-olefin, an ethylene copolymer and a vinyl ester, an ethylene copolymer and an acrylate of alkyl, a copolymer of ethylene and alkyl methacrylate or mixtures thereof in any proportion. 5. A film according to the claims 1 to 4, in which the anhydrous borax has an average size of particle between approximately 0.5 micrometers and, approximately 10 micrometers. 6. A film according to the claims 1 to 5, in which the surfactants are preferably esters of fatty acids and sorbitan, esters of fatty acids and glycerol, esters of fatty acids and polyglycerol, esters of fatty acids and trimethylolpropane, fatty acid esters and pentaerythritol, fatty acid and alkylene glycol esters, fatty acid esters and polyoxyalkylene sorbitan, fatty acid esters and polyoxyalkylene glycerol, fatty acid esters and polyoxyalkylene polyglycerol, fatty acid esters and bis (alkylene glycol) alkylamines, acid esters fatty and polyoxyalkylene alkylamines, alkylamines polyoxyalkylenic, polyoxyalkylene alkyl ethers or mixtures of The same in any proportion. 7. A film according to the claims 1 to 6 which also includes additives in its composition selected from the group consisting of antioxidants, stabilizers against the light, antacids, antistatic, lubricants, anti-lock and pigments 8. A film according to the claims 1 to 7, in which the thickness is between 10 and 250 micrometers 9. A film according to the claims 1 to 8, in which said film is a monolayer film or a film multilayer, in the latter case preferably done by coextrusion of tubular film. 10. The use of a film in accordance with the claims 1 to 9 in low intensive farming systems plastic cover.