Greenhouse roofing with temperature-dependent radiation transparency and method for cultivating crops

Description

[0001] The invention relates to a plant cultivation roof made of film or sheet material with temperature-dependent radiation transparency. Furthermore, the invention relates to a master blend for producing a temperature-dependent transparent film or plastic layer suitable for plant cultivation roofing. Finally, the invention relates to a method for cultivating crops under a plant cultivation roof according to the invention.

[0002] In plant cultivation, it is common practice to grow certain crops under plastic sheeting, in greenhouses, or under other roofing structures. Depending on the climate zone and the crop, this can, for example, serve to provide warmth by blocking sunlight or by using additional heating. In areas with significant temperature differences between day and night, covering or using a greenhouse roof can prevent excessive cooling overnight. Greenhouses and coverings can also help retain moisture on the crop or, depending on their design, allow for better drying by retaining heat. Especially with greenhouses and other roofing structures, additional shading of the crops against excessive sunlight is possible, for example, with blinds or sun sails. However, such mechanical shading involves considerable technical effort and therefore higher costs.

[0003] In southern countries, it is common practice to whitewash greenhouses and other roofs during particularly hot periods with high levels of sunlight. A lime solution is applied to the roofs, preventing sunlight from fully penetrating the glass or foil. Whitewashing primarily increases light reflection. However, it also incurs additional costs, namely for the material itself, its transport, and the labor involved in applying and washing it off if higher light transmission is required. Furthermore, the light reduction achieved through whitewashing is not self-adjusting, and plant growth conditions are not optimal.

[0004] Plastic films are becoming increasingly popular for greenhouses and other roofing applications, having seen improvements in elasticity, durability, and UV resistance over the years. Plastics can be significantly modified in many physical properties through additives and by altering the plastics themselves, which has, among other things, fostered the development of self-shading roofing films and those that influence plant growth.

[0005] Instead of liming, attempts have been made to pigment the films. However, pigments generally alter the spectral composition of the transmitted light, which can affect not only plant development itself, but also susceptibility to plant diseases and the orientation of pollinating insects. This is usually undesirable. Pigmented films also include thermochromic films, which provide a temperature-dependent color filter.

[0006] For photosynthesis and healthy growth, plants require the spectral range of 400 to 720 nanometers. This range is therefore referred to as "photosynthetically active radiation (PAR)." The covers used for cultivation should transmit these wavelengths as unaltered as possible. It is beneficial to increase the proportion of diffuse radiation within the PAR range. The transmittance for diffuse light components should generally remain high, as this best corresponds to natural light conditions. Especially in crops that cast a lot of shade, high light scattering results in better light supply and photosynthesis of the lower parts of the plant.

[0007] Generally, good thermal performance, i.e., good heat retention capacity, is expected of the covering materials. This is traditionally achieved using mineral additives in the covering films. For good thermal performance, a certain proportion of infrared radiation, especially near-infrared in the range between 780 and 3000 nm, should pass through the covering film or the covering plastic material. This infrared radiation is absorbed by the ground, partially stored, and then gradually released again at longer wavelengths. The covering material should be practically opaque to the longer-wavelength, far-infrared radiation with wavelengths of approximately 3 to 50 µm, so that the trapped heat can be retained under the covering.

[0008] To promote plant growth in colder climates, for example, DE 10 2004 051 354 A1 (Grafe) proposes a plastic material for greenhouse films and other roofing materials for agriculture and horticulture, modified with nanoparticles of semiconducting materials. Semi-crystalline thermoplastics, such as polyethylene, polypropylene, EVA, and PET, are used as matrix plastics. The doping achieves high absorption in the near-infrared range combined with high light transmittance in the PAR range. In hot climates, these roofing materials lead to overheating because the films and plastic materials are not self-shading and cannot regulate light penetration.

[0009] To further improve the growing conditions for greenhouse plants and plants protected by various types of covers and roofs, so-called thermotropic greenhouse films have been developed. Thermotropic behavior refers to the fact that the physical properties, and in particular the optical properties, of the material change with temperature. The desired outcome is higher light transmission at lower temperatures and lower light transmission or transparency at higher temperatures. This is often achieved through targeted measures that cause opacity at higher temperatures. The opacity of the plastic material generally increases abruptly above a certain temperature, which is usually due to demixing phenomena or changes in the microstructure, phase change or phase transition phenomena, or refractive index divergence (e.g., DE 44 33 090 A1).

[0010] EP 1 218 467 B1 (BASF) describes thermotropic films and film composites with at least one thermotropic polymer layer made from a fused polymer mixture of at least two polymer components with different refractive indices. The molecular mixture of the two components has a clouding temperature below which a single-phase, transparent mixture exists, and above which separation into the individual components occurs, resulting in cloudiness and reduced transparency of the layer due to increased refraction. The material may contain additional components such as crosslinkers, photoinitiators, and common additives like plasticizers, dyes, pigments, stabilizers, processing aids, and rheology additives. The thermotropic film can be subsequently crosslinked. Its properties are based on its microstructure. Changes in transparency are reversible.EP 1 218 467 B1 (BASF) lists numerous monomers for the two components that can be used for the thermotropic polymer film or polymer layer. The layer material is a mixture or a polymer blend.

[0011] DE 44 33 090 A1 (Fraunhofer Gesellschaft) describes very similar polymer materials, which are referred to there as "thermo-optical." The transparency of the composite material consisting of the polymer and an embedded monomer is reversibly altered by the temperature-dependent difference in refractive index. Alkanes with a strongly temperature-dependent refractive index are proposed as embedded monomers. These alkanes are crystalline below a certain temperature, rendering the polymer transparent, but above this temperature they become amorphous / molten, causing the polymer to become cloudy and less transparent overall. The preferred polymer is a polyester. The polymer is intended for use as a coating, for example, on glass or facade elements.

[0012] From DE 10 2007 061 513 A1 (Fraunhofer-Gesellschaft) it is further known to introduce the thermo-optically active substances, as described above, into so-called doping capsules and thus equip polymers to produce, for example, solar control films. The optical properties of the capsule wall must also be taken into account when designing the doping capsules.

[0013] DE 19841234 C1 describes a reversible thermotropic plastic molding compound, a process for its production and its use.

[0014] One disadvantage of systems that work via the refractive index is that the magnitude of the transparency reduction at a switching temperature is wavelength-dependent, because every light refraction is itself wavelength-dependent, resulting in a change in the spectrum of the incident light.

[0015] The general goal is to improve plant growth. The aim is to provide the plants with the best possible growing conditions.

[0016] The object of the invention is therefore to reduce or avoid the disadvantages in the prior art and to improve a self-shading or thermotropic film or plate so that it better meets the requirements of plant cultivation.

[0017] This problem is solved by a plant cultivation roof made of foil or sheet material according to claim 1, a method for cultivating crops according to claim 13 and a master blend according to claim 15. Plant cultivation roofing

[0018] The plant cultivation roofing system according to the invention consists of a film or panel material with temperature-dependent radiation transparency, as is generally known in the prior art and described above. The temperature-dependent radiation transparency is provided by at least one plastic layer in or on a panel or at least one film layer within a single- or multi-layered film. The temperature-dependent radiation transparency manifests itself as a reduced optical transparency above a switching temperature. The radiation or light incident on the cultivated plants is thereby regulated depending on the temperature. The switching temperature is understood to be the temperature at which the optical transparency (usually wavelength-dependent) decreases significantly and abruptly at higher temperatures.

[0019] The difference in optical transparency between below and above the switching temperature is also referred to as the switching range. Within the scope of this invention, the switching range is defined as the reduction in transmission or transparency of global radiation, determined from the difference in the integral of the transmission curves in the wavelength range between 300 and 3000 nm, relative to the higher transmission (initial curve) below the switching temperature. Relative to the original transmission of the film or roofing material below the switching temperature, the switching range can then be expressed as a percentage.

[0020] The distinctive feature of the invention is that the at least one layer with temperature-dependent radiative transparency exhibits a gradual or a two- or multi-stage reduction in transparency with increasing temperatures in a temperature range between 20 °C and 50 °C, wherein, in the case of a gradual reduction in transparency, a total switching range of 3 °C to 30 °C is achieved, or wherein, in the case of a two- or multi-stage reduction in transparency, the material has several switching temperatures in the desired temperature range from 20 °C to higher temperatures. This means that the layer or material according to the invention with temperature-dependent radiative transparency has, instead of a single switching temperature, a switching (temperature) interval between a lower temperature limit and an upper temperature limit.

[0021] The invention offers numerous advantages based on the switching interval. Crucially, this includes optimizing plant conditions, improving utilization of the PAR range, and regulating incoming heat radiation. Consider a film according to the invention with a switching interval between the lower temperature limit Ta and the upper temperature limit Tb. A conventional thermotropic film with a switching temperature at Ta would have optimally protected the crop from excessive sunlight and overheating above Ta, but would have deprived it of much valuable PAR radiation required for photosynthesis. A conventional film with a switching temperature Tb would have allowed more PAR radiation, which is important for the plant, to pass through, but would have provided less effective protection against overheating.By using multiple switching temperatures within a switching interval, or preferably by a gradual reduction in transparency from Ta to Tb, the plant is supplied with as much light as possible while still being protected. A relatively large portion of the incident PAR radiation is converted from direct PAR radiation into diffuse radiation, which has a very beneficial effect on plant development.

[0022] In contrast to the film or sheet material used in the invention, liming greenhouse films acts on the radiation-incident side and reflects a portion of this radiation directly. This provides good protection against high temperatures, but results in almost complete light loss for the plants. In contrast, modifying the plastic material of the thermotropic plastic layer within the film works partly through absorption and partly through scattering, thus significantly increasing the diffuse light component, which is crucial for plant cultivation, compared to simple liming. The switching interval optimally combines a maximum of transmitted PAR radiation with a relatively high conversion to diffuse radiation.

[0023] According to the invention, the lower temperature limit of the switching interval should be at least 20 °C, but can also be set higher, for example at approximately 25 °C, 28 °C, or 30 °C. Furthermore, the transparency reduction of the plant cultivation roof according to the invention takes place between 20 and 50 °C, preferably between 25 and 40 °C. The temperature interval or the switching interval can be less than 30 °C and, according to the invention, is within the range of 20 to 50 °C. For two-stage or multi-stage transparency reduction, the individual switching temperatures are also between 20 and 50 °C, more preferably between 25 and 40 °C.

[0024] In the case of graded switching behavior, the temperature interval between the lower switching limit (Ta) and the upper temperature switching limit (Tb) ranges from 3 °C to 30 °C, preferably from 5 °C to 30 °C, and more preferably from 10 °C to 30 °C. The total switching stroke is achieved within this temperature interval.

[0025] In the case of two- or multi-stage transparency reduction, the material has several switching temperatures within the desired temperature range from 20 °C to higher temperatures. Preferably, these are at least two switching temperatures at 28 °C ± 3 °C and at 32 °C ± 3 °C. More than two switching temperatures can also be provided, preferably between 25 °C and 45 °C, and these may include the two switching temperatures at 28 °C and 32 °C.

[0026] In the invention, the material providing the temperature-dependent radiation transparency is essentially a plastic or polymer material. Suitable optically transparent plastic materials for foil roofing or other plastic roofing applications are generally known in the art. These are typically semi-crystalline materials with good optical transparency, for example, polyolefins such as polyethylene, polypropylene, especially LDPEs, as well as polyethylene copolymers such as ethylene-butyl acrylate copolymer or ethylene-vinyl acetate copolymer (EVA), or mixtures or blends of such polymers. Polyesters, such as PET, are also suitable as base foil materials. These foil materials, as such, effectively block short-wave UV light to a high degree, due in part to the single and double bonds in the C-H group. In contrast, IR radiation is partially transmitted.

[0027] The plant-growing roofing according to the invention preferably allows the IR-A and IR-B components to pass through to such an extent that the transmitted component is reduced by at least 5%, and more preferably by at least 20%, compared to the incident radiation in the reduced-transparency state (the ON mode) of the film or panel material. This provides direct overheating protection. The transmitted IR-A and IR-B radiation is absorbed in the soil and gradually re-emitted at long wavelengths, resulting in good temperature regulation. This provides the plants with a balanced soil temperature and protection against nighttime cold.

[0028] According to a particularly preferred embodiment, the plant cultivation roof can be made of a film material. Cover and greenhouse films are generally well-known in the prior art and are widely used. For greenhouses, the films are stretched in frames. However, other roofing forms, such as tent-like roofs, polytunnels, and the like, are also in use. The requirements for films used in greenhouse construction are described for Europe in DIN EN 13206 and KTBL Worksheet No. 0687. A wide variety of materials with additives are commercially available. Essential additive components include minerals for adjusting thermal conductivity (IR-C barrier) and UV stabilizers. The latter are intended to ensure the durability of the films.The film material for the plant cultivation roofing according to the invention is preferably a multilayer film, wherein at least one individual film or layer contained therein causes a temperature-dependent reduction in transparency. The multilayer film can, for example, consist of three layers, with thicknesses of 50 µm, 100 µm, and 50 µm respectively being typical. The three layers can be co-extruded. Advantageously, the film is produced entirely by blown film extrusion. Preferably, the middle layer of the three-layer film or an inner layer of a multilayer film is the layer with the temperature-dependent reduction in transparency. The matrix polymer is particularly preferably an LDPE, an ethylene-butyl acrylate copolymer, or, in particular, an EVA. The total layer thickness of the multilayer film or a corresponding single-layer film is preferably 150 µm to 300 µm.

[0029] In cases where the plant-growing roof is made of a sheet material, this is preferably a single- or multi-layered plastic sheet with at least one layer exhibiting temperature-dependent transparency reduction. Alternatively, a plastic or glass sheet can be coated with a layer of temperature-dependent radiative transparency. According to a further embodiment, the sheet can consist of a film or layer with temperature-dependent radiative transparency sandwiched between glass or plastic sheets. This sheet material is particularly advantageous for greenhouse construction. It can also be used for raised roofs, where, for example, a sheet is placed on posts at its four corners, thus protecting the plants from direct sunlight from above while allowing free circulation of ambient air from the sides.

[0030] Basically, the graded switching behavior in the foil or plate material or the alternative two- or multi-stage switching behavior can be implemented in different ways.

[0031] As described above, additives are known that can be added to a matrix polymer and cause a reduction in transparency at a switching temperature, generally by increasing opacity. To realize the invention, several such additives can be added to a matrix polymer, each of which individually achieves a specific switching temperature and together provides a multi-stage switching interval. However, it is also frequently possible to premix the required substances, i.e., the individual additives, and thus create a new additive from a mixture of substances that causes a gradual or stepwise reduction in transparency with increasing temperatures. A mixed additive is possible, for example, when using a homologous alkane series or other homologous or chemically similar substances where the switching temperature is controlled via the molecular weight or the degree of polymerization.

[0032] As described above in the prior art, thermotropic additives are also known that consist of polymer blends exhibiting demixing effects at a switching temperature, thereby increasing turbidity. These two-phase miscible and demixable polymer blends can, for example, be replaced by three-phase blends whose three phases have different refractive indices. In the case of copolymers, block copolymers are used whose domains generated by the blocks have different refractive indices. A person skilled in the art can readily select thermotropic or thermo-optical substances known to them and use them mixed in accordance with the invention. C10 to C30 n-alkanes and / or corresponding branched alkanes are particularly preferred, as they are mixed to exhibit stepwise or gradual switching behavior.

[0033] Furthermore, it is also possible to use the polymeric compounds mentioned in EP 1 218 467 B1 (BASF) in suitable combinations. Mixtures of different polymers with cyclic structural units and different polymers without cyclic structural units are preferred, as described in detail in EP 1 218 467 B1, to which specific reference is made herefor the selection of compounds.

[0034] According to one aspect of the invention, the transparency-regulating film or plastic layer is a layer containing one or more substances, a polymer blend, or a copolymer to effect a reduction in transparency by opacity above a threshold temperature. Polymer blends or copolymers can be used to create thermotropic or thermo-optical layers. Alternatively, the thermotropic or thermo-optical layers required for the invention can also be obtained by adding a thermotropic material to a matrix polymer. In other preferred embodiments, the transparency-regulating film or film layer contains an additive that causes a reduction in transparency above a switching temperature, more preferably an increasing opacity of the composite at higher temperatures.This is often achieved by using additives composed of monomeric substances, each of which exists in a crystalline or solid state below a temperature characteristic of the individual substance, which should be optically transparent. Above this temperature, or within a melting range, the substances change to an amorphous or molten state, resulting in opacity. Mixing several such monomers achieves a gradual or multi-stage reduction in transparency.

[0035] According to a particular embodiment, the additive can be encapsulated, as described, for example, in DE 10 2007 061 513 A1 (Fraunhofer). Different encapsulated additives with varying switching temperatures or switching ranges can be mixed to achieve the desired switching interval. As described above, the additive can preferably be contained within a transparent matrix polymer; unencapsulated additives can be polymerized into the matrix polymer in the form of minute droplets.

[0036] Suitable additives also include known phase-change materials (PCMs) that can change their refractive index and thus their optical transparency at the phase transition point. Therefore, organic phase-change materials with a crystalline and optically transparent solid state, such as fats and oils, are also suitable within the scope of the invention.

[0037] US 4,505,953 describes pellets made from PCMs. The phase transition temperatures are equivalent to the switching temperatures when used as thermotropic substances. Epoxy polymers, polyurethanes, acrylic polymers, cellulose acetate, and polyamides are among the materials listed as encapsulating the pelletized or encapsulated PCMs. Possible PCMs include polyethylene, Glauber's salt, sodium sulfate decahydrate, sodium thiosulfate pentahydrate, calcium chloride hexahydrate, magnesium nitrate hexahydrate, a eutectic mixture of magnesium nitrate hexahydrate and ammonium nitrate, potassium fluoride tetrahydrate, sodium acetate trihydrate, stearic acid, a eutectic mixture of naphthalene and benzoic acid, and paraffinic hydrocarbons.

[0038] In alternative embodiments, polymer blends or copolymers, as described by way of example in EP 1 218 467 B1, can also be mixed with a matrix polymer to produce a temperature-dependent transparent layer. As already described above, the matrix polymer is preferably a semi-crystalline polymer, in particular a polyolefin, polyolefin blend or polyolefin copolymer, preferably selected from the group consisting of PE, PP, LDPE, EVA and PET.

[0039] The plant cultivation roofing according to the invention is, as already mentioned, preferably part of a greenhouse or a raised roof structure, a sunshade system, or any field covering. Agricultural films for field covering are also considered plant cultivation roofing, even if they are used without a wire or frame structure. Masterblend

[0040] The invention further comprises a master blend for the production of a temperature-dependent transparent film or plastic layer suitable for a plant cultivation roof according to the invention. The films or plastic layers for the invention are preferably produced by extrusion or co-extrusion, or by extrusion coating onto a substrate, such as a panel.The master blend is characterized by a content of temperature-dependent transparency-regulating polymers and / or additives that, in the extruded film or layer, effect a stepwise or gradual reduction in transparency with increasing temperatures in the temperature range of 20 to 50 °C. In the case of a gradual reduction in transparency, a total switching range of 3 °C to 30 °C is achieved. Alternatively, in the case of two-stage or multi-stage reduction in transparency, the material exhibits multiple switching temperatures within the desired temperature range from 20 °C to higher temperatures. For this purpose, the transparency-regulating polymers and / or additives are mixed with a matrix polymer or base polymer. The master blend is further characterized by the content of a semi-crystalline, transparent matrix polymer and optionally other additives.Other additives include, in particular, mineral additives for adjusting thermal properties, UV protection additives, possibly plasticizers, and other common additives such as those used in agricultural films and known to those skilled in the art. The master blend is produced by manufacturing the desired plastic material for the film or layer and then granulating or pulverizing it. This powder or granules constitute the master blend, which is melted and extruded. For film production, blown extrusion is preferred, while sheet coating is preferably carried out as an extrusion coating through a slot die.

[0041] Other processing methods are possible and known to experts. Methods for cultivating crops

[0042] The problem underlying the invention is further solved by a method for cultivating crops in a greenhouse, under a roof or a foil cover, in which the incidence of light on the plants is regulated temperature-dependently by means of the plant-cultivation roof according to the invention. The advantages of this method have already been described above in connection with the plant-cultivation roof.

[0043] In a further development of the invention, the method is carried out in such a way that the roofing or covering is temporarily additionally limed.

[0044] The following describes the usual liming process – without the roofing according to the invention: typically, three liming applications take place annually in southern European countries. These are applied at least between February and May, with varying concentrations, depending on the weather, the plant species under the roofing, and their growth phases. The campaign starting in winter, in January, generally does not require any lime initially. Liming continues between February and May until maximum shading is achieved during the transition period of spring / summer. The campaign starting in midsummer, around August, begins with a maximum amount of lime to protect the young plants. As summer fades and autumn approaches, the lime is removed.

[0045] The intensity of shading should be determined, among other things, by whether the plants are in vegetative or generative growth. The vegetative phase encompasses the growth of plant organs that serve to nourish the plant (roots, leaves, and shoots). Insufficient light leads to rapid plant growth with relatively few shoots and a poorly developed root system. Generative growth occurs when plant organs develop for sexual reproduction (formation of flowers, fruits, and seeds). Excessive light results in poorly developed flowers and the formation of spots on the fruits, which subsequently lead to soft spots and a significant decrease in fruit quality. The transition from vegetative to generative growth depends, among other things, on the duration of daylight.The presence of additional light in the morning and evening hours, as well as sufficient shading in the midday and afternoon hours, generally promotes growth.

[0046] The plant-growing roof according to the invention now enables the shading of the midday sun, which is particularly advantageous for plant development. Through the gradual or stepwise reduction of transparency, the highest possible proportion of PAR radiation is retained, and a large amount of diffuse light is generated. Depending on the intensity (length) of the switching stroke, additional radiation can be blocked from the crops by liming, if necessary, depending on the season and growing period. However, liming on the plant-growing roof according to the invention is shorter than is typical with a normal transparent greenhouse film. The switching stroke can also be designed in such a way that liming can be avoided altogether.

[0047] In southern European countries, liming of the plant cultivation roof according to the invention is preferably carried out only between approximately April and September, or also between March and October. This means that the foil or panel material in the plant cultivation roofs according to the invention optimally regulates the climatic conditions during the transitional periods of winter / spring and spring / summer, and that additional liming may only be necessary during the peak summer period.

[0048] In milder climates, for example in northern Germany, the plant cultivation roofing according to the invention is used without liming.

[0049] The invention promotes stronger growth in young plants and a robust root system by establishing optimal light and temperature conditions. This results in higher productivity and improved plant quality. WORK RESULTS - SAMPLE SLIDE

[0050] The sample film consists of the base polymer EVA with conventional additives and a thermotropic additive consisting of a finely dispersed n-alkane mixture of different alkanes, resulting in a graded change in transmission over a temperature range of 28 to 40 °C. This film was field-tested in Almeria, Spain, according to the criteria used for commercial films in greenhouse construction. The following laboratory results were also obtained: At constant temperature and with changing radiation intensity, the transmission behavior is stable, i.e., it is temperature-dependent and independent of the radiation intensity, both in ON and OFF modes. The change in transmission is graded in a temperature range of 28 to 40 °C, and the behavior of the film is reversibly repeatable.

[0051] The characterization of the optical properties yielded the following results: Table 1 transmission Thermotropic film Commercial film (INDASOL PLUS ®< ) OFF mode ON mode (50 °C) without lime with lime PAR 77 % 60 % 85 % 30 % Diffuse light component 70 % 100 % 45 % 80 % IR-A + IR-B 50 % 20 % 60 % 1 %

[0052] The thermality of the thermotropic film (transmittance for IR-C) is significantly lower (6%) than that of a commercial film with added minerals (10%), even without mineral additives. Furthermore, the higher proportion of diffuse light compared to the commercial film has a positive effect on plant growth. Comparative observations of plant growth

[0053] Since the beginning of March 2013, two test greenhouses, each with a floor area of ​​less than 4 m², have been operating in Almeria to compare plant growth under a thermotropic and a commercial lime-treated film. A total of three tomato plants, each with an initial height of approximately 30 cm and already developed blossoms, as well as four tomato plants with their first fruits and a height of approximately 1 m, were introduced into each greenhouse. Pollination is carried out by bumblebees.

[0054] The thermotropic film does not negatively affect the orientation and activity of beneficial pollinating insects. The same behavior is expected for insects used in the increasingly common practice of ecological pest control.

[0055] After planting the plants, which are traditionally planted in topsoil mixed with humus and sand, a more stable and less stressed behavior of the younger plants under the thermotropic film was observed in the first few days. This observation suggests faster root development and thus improved nutrient and water uptake.

[0056] The principles of the invention are explained again below with reference to illustrations: They show: Figure 1 schematic representation of a greenhouse structure in cross section, Figure 2 schematic representation of a framed roof structure, Figure 3 comparison of the optical properties between roofing material according to the invention (top), reference film and limed reference film (bottom), Figure 4 PAR radiation transmission versus air temperature, switching range 28 to 38 °C.

[0057] Figure 1Figure 1 shows a greenhouse, labeled 100, in which the plant-building roofing material 10, in the form of foil, is used for the roof and walls of greenhouse 100. Inside the greenhouse are plants 20, which are cultivated in greenhouse 100. As indicated by the arrows, global radiation, including UV radiation, PAR radiation, and IR radiation, strikes the roofing material 10, primarily from above, depending on the position of the sun. A portion of the incident radiation is always reflected, a portion is absorbed by the foil, i.e., the material of the roofing material 10, and a portion is transmitted. The transmitted radiation is distinguished as direct radiation and radiation converted into diffuse light by refraction. The UV radiation is partially blocked by the foil material. The infrared radiation is partially transmitted. It is absorbed by the ground and slowly released back into the environment.

[0058] In Figure 2 A supported roof structure 200 is shown, in which the plant cultivation roof 10 is a panel or a film within a frame. The roof structure 10 is held by the supports 30. In this construction, air and pollinating insects have free access to the crop from the plants 20. The construction according to Figure 2 It is suitable, for example, for southern countries where the sun is very high in the sky. However, it can also protect certain crops in more northerly regions from rain and at the same time from excessive sun exposure, for example during the midday heat.

[0059] The optical properties of the new film are in Figure 3As shown, in the unshaded state (OFF mode), over 70% of the PAR spectrum, which is important for the plant, is transmitted and, in addition, largely converted into the desired diffuse light. Compared to the reference film shown below, not only is a larger proportion of the PAR spectrum important for photosynthesis transmitted, but the stronger conversion to diffuse light is also advantageous. Compared to the reference film, less near-infrared (IR-A + IR-B) is transmitted, but still enough to ensure a balanced temperature under the plant cultivation roof, especially during cold night periods. After the switching interval has completely passed, in the ON mode shown in the upper right, more PAR radiation is reflected, and the transmitted radiation is almost completely converted into diffuse light.This provides excellent protection for the plants against the effects of direct radiation without impairing photosynthesis due to insufficient light. In ON mode, the new film transmits significantly less near-infrared radiation than in OFF mode, which is desirable due to the higher temperature levels during ON mode. In comparison, the film shown in the lower right corner... Figure 3In the illustrated limed reference film, only 30% of the PAR spectrum reaches the plant culture, as 70% of the incident light is reflected. The degree of liming in this example was 75 g / m². Despite the high reflectance, the proportion of diffuse light is lower than with the thermotropic film according to the invention. 6%, i.e., approximately 20% of the transmitted light, remains as direct radiation. Liming takes effect on the light-incident side. This explains the high reflectance and the low transmission of near-infrared light. It is evident that liming can be carried out as an additional measure on the film according to the invention during particularly hot periods, thus enabling radiation to be blocked overall, including thermal radiation.

[0060] Figure 4Figure 1 shows an experiment on a film according to the invention on a chamber. The PAR radiation transmission versus air temperature is shown. The lower switching temperature of the switching interval Ta to Tb is between 26 and 28 °C. The switching interval ends at Tb ≃ 42 °C. As can be seen, the switching range is distributed over the switching interval, and the transmission decreases with increasing temperature. In this way, the PAR radiation, which is important for the plant, can be optimally utilized. The transmission decreases by only about 15%. Nevertheless, good protection at high temperatures is ensured.

Claims

1. Plant-growing roof made of film or sheet material with a temperature-dependent transparency to radiation, which is provided by at least one plastic layer in or on a sheet or at least one film layer and manifests itself by a reduced optical transparency above a switching temperature, wherein the layer with the temperature-dependent transparency to radiation exhibits a gradual or a two- or multi-stage transparency reduction at increasing temperatures in a temperature range between 20°C and 50°C, wherein in the case of a gradual transparency reduction an overall switching stroke is realised within a temperature interval of 3°C to 30°C temperature difference, or wherein in the case of a two- or multi-stage transparency reduction the material has several switching temperatures in the desired temperature range from 20°C to higher temperatures.

2. Plant-growing roof according to claim 1, characterised in that there is a graduated switching behaviour with a switching step within a temperature interval of 5 to 30°C temperature difference, preferably 10 to 30°C temperature difference.

3. Plant-growing roof according to claim 1, characterised in that, in the case of two-stage or multi-stage transparency reduction, at least two switching temperatures are present at approximately 28°C ± 3°C and at approximately 32°C ± 3°C.

4. Plant-growing roof according to one of the claims 1 to 3, characterised in that the transparency reduction in the spectral range between 400 nm and 720 nm is at most 50%, preferably at most 20%, more preferably at most 5%.

5. Plant-growing roof according to one of claims 1 to 4, characterised in that the IR-A and IR-B component of the transmitted radiation is reduced by at least 5%, preferably at least 20%, in comparison with the incident radiation in the transparency-reduced state (ON mode).

6. Plant-growing roof according to one of claims 1 to 5, characterised in that the film material is a multi-layer film and that at least one individual film or layer contained therein effects a temperature-dependent transparency reduction.

7. Plant-growing roof according to one of claims 1 to 5, characterised in that the plate material is a plastic plate which is single-layer or multi-layer and has at least one layer with temperature-dependent transparency reduction behaviour, that the plate is a glass or plastic plate coated with a layer having temperature-dependent radiation transparency, or that the plate is formed from a film or layer having temperature-dependent radiation transparency and enclosed between glass plates.

8. Plant-growing roof according to one of claims 1 to 7, characterised in that the transparency-regulating film layer or plastic layer is a layer which contains one or more substances, a polymer blend or a copolymer, in order to bring about a reduction in transparency by clouding from a threshold temperature.

9. Plant-growing roof according to one of claims 1 to 8, characterised in that the transparency-regulating film or film layer contains an additive comprising one or more substances which, above a switching temperature, causes a gradual or a two- or multi-stage reduction in transparency.

10. Plant-growing roof according to claim 9, characterised in that the additive is encapsulated.

11. Plant-growing roof according to one of claims 9 to 10, characterised in that the additive is present in a transparent matrix polymer or that a polymer blend or a copolymer is mixed with a matrix polymer, the matrix polymer preferably being a partially crystalline polymer and more preferably a polyolefin, wherein the matrix polymer is preferably selected from the group PE, PP, LDPE, EVA, PET.

12. Plant-growing roof according to one of claims 1 to 11, characterised in that it is part of a greenhouse, a raised roof, a sun protection system or a field covering.

13. A method for cultivating crops under the plant-growing roof according to one of claims 1 to 12, characterised in that the incidence of light on the plants is regulated in a temperature-dependent manner with the aid of the plant-growing roofing.

14. A method according to claim 13, characterised in that the plant-growing roof is additionally whitewashed from time to time.

15. A master blend for the production by extrusion of a temperature-dependent transparent film or plastic layer suitable for a plant-growing roof according to one of claims 1 to 12, characterized by a content of temperature-dependent transparency-regulating polymers and / or additives which, in the extruded film or layer, cause a stepwise or gradual transparency reduction at increasing temperatures in the temperature range from 20 to 50°C, wherein in the case of a gradual transparency reduction, a total switching stroke within a temperature range of 3 °C to 30°C temperature difference is realised, or wherein in the case of a two- or multi-stage transparency reduction the material has several switching temperatures in the desired temperature range from 20°C to higher temperatures.

16. Masterblend according to claim 15, characterised by a content of a partially crystalline, transparent matrix polymer and optionally further additives.