EA041237B1 - ENERGY SAVING SCREEN FOR GREENHOUSE - Google Patents

Abstract

The invention discloses a greenhouse screen comprising strips (11) of film material that are interconnected by a system of threads consisting of transverse threads (12, 14, 18) and longitudinal threads (13a, 13b; 15; 19) by means of a knitting, warp knitting or weaving process to form a continuous product. The film material comprises a highly transparent, biaxially oriented, UV-resistant and fire-resistant polyester film, which is provided on at least one side with a coating that reduces the reflection of visible light. The greenhouse screen is particularly suitable for growing plants with high lighting requirements.

Description

Technical field

The present invention relates to a screen for a greenhouse of this type, which comprises a plurality of flexible film strips interconnected by a carcass of filaments through a knitting, warp knitting or weaving process to form a continuous product. In particular, the invention relates to an energy-saving greenhouse screen suitable for growing crops with high requirements for light transmission. The screen has special properties of transparency, high UV resistance and good fire resistance. The invention also relates to a method for the production of a polyester film and screen for greenhouses, as well as their use in greenhouses.

State of the art

The goal of protected growing in greenhouses is, among other things, to change the natural environment to increase yields, improve product quality, conserve resources and expand production areas and increase crop cycles. Depending on the location of the greenhouse and the crop grown in it, the crop must be protected for all or part of the year to prevent harmful effects that will reduce yields.

One known type of greenhouse screen comprises a plurality of flexible strips of film material arranged in parallel and which are connected together by a knitting, warp knitting or weaving process and a system of threads to form a continuous product in which the strips form the majority of the surface area of the product. Such a greenhouse screen is known, for example, from EP 0109951. Other examples of screens of this type are described in FR 2071064, EP 1342824 and WO 2008/091192. The flexible material strips can be made from selected film materials providing the desired light and/or heat transmission and reflection properties.

Greenhouse screens are often used for energy saving, shading and temperature control during greenhouse crop production. Such screens must meet a number of requirements. On the one hand, sufficient light must pass through the screens and reach the plants to ensure photosynthetic activity during daylight hours. On the other hand, during the night and early morning hours, the greenhouse screen must contain the heat rising from the ground due to convection inside the greenhouse, both by reflection and by re-radiation. Without a greenhouse screen, the energy consumption in the greenhouse increases and creating an ideal climate is difficult.

A greenhouse screen is of particular importance during the early hours of the morning because of the need to quickly reach the optimal temperature for plant growth while providing the maximum amount of light to ensure high photosynthetic activity without using excess energy for heating. However, in the morning the sun is at a slight angle to the horizon, and therefore the reflection of light on the screen surface is much higher than in the later hours when the sun rises higher above the horizon. To solve this problem, the films used in the screens are preferably provided with an anti-reflective/anti-reflection coating, which allows the sun's rays to enter the greenhouse at lower angles of incidence, and thereby improves photosynthetic activity also in the early morning hours.

The greenhouse screen must also have good UV resistance, with a guarantee of at least 5 years of use in the greenhouse without significant yellowing, embrittlement, cracking of the surface, or serious reduction in transparency or mechanical properties. In addition, greenhouse fires are a potential hazard and can result in significant economic damage in the event of an accident. Therefore, another important feature of the greenhouse screen is its high fire resistance to prevent fire from starting and spreading too quickly.

EP 3064549 describes a flame retardant biaxially oriented polyester film containing flame retardant particles based on aluminum dimethylphosphinate/diethylphosphinate. These particles are included in the extruded layers and have an average size of 2-3 microns. However, these particles tend to reduce transparency and increase film haze.

EP 1368405 describes several phosphorus-containing flame retardants such as DOPO (CAS 3594825-5) and its derivatives for use in biaxially oriented polyester films. These additives lead to the formation of a permeable film. DOPO derivatives that polymerize in the polyester backbone are preferred for the polyester extrusion process, but applying an anti-reflective coating to one or both sides of such stabilized films can significantly degrade the fire resistance of the entire structure.

In EP 1441001, a separate flame retardant layer is applied over a double-sided coated polyester film to improve the fire resistance of this laminate. Said flame retardant layer consists of a gas generating material such as magnesium hydroxide. Magnesium hydroxide is also used as a coating on polyester film as described in EP 1527110, but a layer of magnesium hydroxide (aluminum hydroxide) material is only effective at a certain thickness and is incompatible with in-line manufacturing processes that have a coating thickness limitation.

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In addition, magnesium hydroxide is incompatible with extrudable PET because it breaks the polymer chain and significantly reduces the viscosity of PET. Therefore, do not get a stable process.

EP3251841 describes a UV stabilized biaxially oriented polyester multilayer film with at least 93.5% transparency and an anti-reflective/anti-reflective coating on at least one side. Flame retardants are included in the polyester base film, but it is understood that below a certain particle concentration there is no need for flame retardant. However, experience has shown that when suitable anti-reflective coatings such as acrylic, polyurethane or silicone coatings are applied to at least one side of such a film, the fire resistance of the film is drastically reduced.

The films described in the prior art do not meet the optical requirements of at least 93.5% transparency and less than 8% haze and/or fire resistance requirements. Systems containing particles contribute to the tarnishing of the final laminate and reduce its transparency. In addition, known anti-reflective coatings impair the fire resistance of the entire structure, especially when they are applied to both sides of the film. Surprisingly, stabilization of the burn of only the base film and not of the coating, or the low total particle concentration in the base film, does not compensate for the negative combustion characteristics of the anti-reflection coating.

The essence of the invention

The aim of the present invention was to overcome the shortcomings of the prior art and to provide a greenhouse screen with an anti-reflective/anti-reflection coating that would allow sunlight to enter the greenhouse and improve photosynthetic activity also during the early morning hours or when sunlight falls at a low angle. The film must have a transparency of at least 93.5%, a haze of no more than 8% and meet the requirements for combustion characteristics (which means reduced flammability compared to coated unstabilized polyester films). In addition, it is important that the film does not break down and lose its flame retardant properties during its life in the greenhouse.

This goal is achieved with a greenhouse screen comprising strips of film material which are interconnected by a system of threads of transverse and longitudinal threads through a knitting, warp knitting or weaving process to form a continuous product. At least some of said strips comprise a film material in the form of a single or multilayer base film which is provided with at least a first anti-reflection/anti-reflection coating on the first surface of the base film. The film material has a transparency of at least 93.5% when measured according to ASTM-D1003-61, and the total number of particles is <0.5 wt.% based on the total weight of the film.

At least the first anti-reflective/anti-reflective coating has a dry thickness of 60 to 130 nm and contains at least one polymer based on acrylic acid and/or methacrylic acid, and contains at least one alkyl phosphonate and/or oligoalkyl phosphonate flame retardant, and contains phosphorus in an amount of 2 to 18 wt.% based on the total weight of the film.

The greenhouse screen described in this application has a haze of less than 8% and satisfactory burning characteristics for 3 or less samples out of 5 in a burning test conducted in accordance with EN ISO 9773:1998/A1:2003, both before and after atmospheric aging.

Brief description of the drawings

Examples of screens for greenhouses are described below with reference to the accompanying drawings.

In FIG. 1 is an enlarged view of a portion of a warp screen according to one embodiment.

In FIG. 2 shows part of a warp screen according to another embodiment.

In FIG. 3 is an enlarged view of part of the woven screen.

In FIG. 4 shows a portion of a woven screen according to a further embodiment.

Detailed description of the invention

The greenhouse screens described in this application comprise strips of film material that are interconnected by a system of threads of transverse and longitudinal threads through a knitting, warp knitting or weaving process to form a continuous product, as will be described below. The film strips constituting the screen material are composed of a single or multilayer polyester film (hereinafter also referred to as base film) provided with additives, and a coating (hereinafter also referred to as anti-reflection/anti-reflective coating) which is applied to at least one surface, preferably both surfaces of the base film.

The terms layers and coatings will be used later, but it is important to note that there is a distinction between layers and coating, whereby a layer is understood to mean an extruded or co-extruded layer of a polyester film consisting primarily of polyester (for example, a base layer, an intermediate layer or a cover layer), and the coating is applied to one or both surfaces of the base film (where the base film is optionally a single or multilayer polyester film) as a solution or dispersion, and then dried thereon; coatings can be applied in-line, i.e. during the actual film production process, or offline, i.e. after film production.

Main film

The total film thickness is at least 10 µm and not more than 40 µm. The total film thickness is preferably at least 11, 12, 13 or 14 µm and not more than 35, 30, 29, 28, 27, 26, 25, 24 or 23 µm and ideally at least 14.5 µm and not more than 20 µm. If the total thickness of the film is less than 10 µm, then the mechanical strength of the film is no longer sufficient to withstand the stresses that occur during use of the screen in a greenhouse without excessive tensile deformation. Above 40 µm, the film becomes too rigid, and when the screen is not in use and wound up, the resulting screen roll becomes excessively large and thus casts too much shadow.

The film comprises a base layer B. Single-layer films consist only of a base layer B, and in the case of a multilayer film embodiment, the base film consists of a base layer B and at least one additional layer, which, according to its position in the film, is called an intermediate layer (when there is at least one additional layer on each of the two surfaces) or outer layer (where this layer forms the outer layer of the film). In the case of a multilayer film embodiment, the thickness of the base layer B is at least the sum of the thicknesses of the other layers. Preferably the base layer B is at least 55% of the total film thickness and ideally at least 63% of the total film thickness.

The thickness of the other layers, preferably the outer layers, is at least 0.5 µm, preferably at least 0.6 µm, and ideally at least 0.7 µm. The thickness of the outer layers is less than 3 microns, preferably less than 2.5 microns and ideally less than 1.5 microns. At a thickness of less than 0.5 µm, the stability of the process is reduced, which may affect the uniformity of the thickness of the outer layer. Achieving very good machining stability starts at a thickness of 0.7 µm. Such additional layers are also referred to in this application as co-extruded layers.

If the outer layers become too thick, then the profitability is reduced, because in order to maintain good properties (in particular UV resistance), regenerates should be added only to the base layer B, and if the thickness of the base layer is too thin compared to the total film thickness, the percentage regenerates that must be added to this layer to complete the regeneration cycle is then redundant. In addition, because the composition of the base layer has an undesirable effect on properties such as UV resistance and transparency, since the outer layers often contain particles to improve slip (roll-up improvement). Such particles can lead to a loss of transparency due to backscattering, and if the proportion of such particles becomes excessive in the outer layers, it is much more difficult to achieve high transparency of the film.

UV stabilization of base film

Film intended for greenhouse use must have a low light transmittance in the wavelength range below 370 nm to 300 nm. Preferably the transmittance is less than 40%, preferably less than 30% and ideally less than 15% for each wavelength in the specified range. However, the transparency for light in the wavelength range of 390 to 400 nm should be greater than 20%, preferably greater than 30% and ideally greater than 40%, because this wavelength range is very efficient for photosynthesis, and excessive filtering in this wavelength range is negatively affect plant growth.

Low UV light transmission is achieved by adding an organic UV stabilizer. The low UV light transmission also protects the optional flame retardant from rapid degradation and severe yellowing. The organic UV stabilizer used in the film described herein is selected from the group consisting of triazines, benzotriazoles, or benzoxazinones. Particular preference in this application is given to triazines because, among other things, they have good thermal stability at processing temperatures from 275 to 310°C, typical for PET, and show little loss due to outgassing of the film. In particular, 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-(hexyl)oxyphenol (TINUVIN® 1577) is suitable for use. Most preferred in this application is given to 2-(240-hydroxyphenyl)-4,6-bis(4phenylphenyl)triazines, which are sold, for example, by BASF under the trade name TINUVIN 1600™. If these compounds are used, the preferred low transparency for light below 370 nm can be achieved even at relatively low stabilizer concentrations while achieving relatively high transparency at wavelengths above 390 nm.

Therefore, the base film, ie base layer B, or, in the case of a multilayer film, at least one outer layer, preferably both outer layers, contains at least one organic UV stabilizer. The amount of UV stabilizers added to the outer layer(s) or single layer film is 0.3 to 3%, preferably 0.75 to 2.8% by weight, based on

- 3 041237 weight of the corresponding layer. The outer layers ideally contain from 1.2 to 2.5 wt.% UV stabilizer. Preferably, in the multilayer film, the UV stabilizer is also present in the base layer, along with the outer layers. The content of UV stabilizer, in wt %, in said base layer is then preferably lower than in the outer layer(s). The above amounts in the outer layer(s) refer to triazine derivatives. If a UV stabilizer from the group of benzotriazoles or benzoxazinones is used to some extent or completely instead of a triazine derivative, then the proportion of the triazine component to be replaced must be replaced by 1.5 times the amount of the benzotriazole component or the benzoxazinone component. Thus, the film is protected from brittleness and yellowing, while the plants and equipment in the greenhouse are also protected from UV radiation.

Additives to improve screen rewindability

The base layer as well as the outer layer(s) may contain particles to improve rollability. These inorganic or organic particles are, for example, calcium carbonate, apatite, silica, alumina, silicas, alumina, cross-linked polystyrene, cross-linked polymethyl methacrylate (PMMA), zeolites and other silicates such as aluminum silicates, polydimethylsiloxane (PDMS) or compatible white pigments such as TiO ₂ or BaSO ₄ .

However, many whitening polymers, as well as some polyesters, such as, for example, polypropylene, cycloolefin copolymers (COS), polyethylene, non-crosslinked polystyrene, etc., are incompatible with the main film component and should preferably be present in amounts of less than 0.1 wt. % (based on the weight of the film) and ideally completely absent (i.e. 0 wt.%), because these particles greatly reduce transparency and can have a serious negative effect on the burning properties of the film. In addition, they tend to cause severe yellowing when exposed to UV radiation and therefore significant additional amounts of UV stabilizer will be required, which will significantly impair profitability.

Due to the negative effects of whitening particles, matting particles, such as silica particles, are preferably added to the outer layers to improve film windability. The advantage of using silica particles is that they have little transparency reduction effect. The proportion of these or other particles in any layer should not be more than 3 wt.%, preferably less than 1 wt.% and ideally less than 0.2 wt.% in each layer, calculated in each case on the total weight of the respective layer.

In the case of a multilayer film embodiment, these particles are preferably added to only one or both of the outer layers, and only a small part of them gets into the main layer due to the addition of regenerates. Thus, the reduction in transparency due to particles required to improve rollability is minimal. In one preferred embodiment with good rollability, at least one outer layer contains at least 0.07 wt.% matting particles.

Added particles such as whitening particles or opacifying agents can degrade the flame retardant properties of the biaxially oriented film as a whole. Depending on the compatibility of the particle with the polymer matrix, cavities may form around the particles during film stretching. The less compatible the particles are with the polymer matrix, the more cavities can form. Air can migrate into such cavities and, in the event of a fire, add oxygen to the fire, making the fire worse. For this reason, it is advantageous to minimize the use of added particles in films where combustion characteristics matter. The exception is flame retardant particles like those described in the prior art. This is the reason why the proportion of particles such as whitening particles (ZnO, TiO ₂ , BaSO ₄ ) or matting agents (PMMA, SiO ₂ , polydimethylsiloxane (PDMSQ)) is preferably limited to a maximum of 0.5 wt.% (calculated on total weight of the film).

Anti-glare/anti-reflective coatings

Film transparency is achieved when the starting materials, additives and/or particles described in this application are used in the indicated proportions. However, the increase in transparency is achieved mainly by anti-reflective/anti-reflective coatings present on one or both of the outer sides of the film.

The film material of the present invention is coated on at least one surface with a material that has a lower refractive index than the base polyester film (ie, single base layer B or multilayer polyester film). The refractive index of the coating is less than 1.64, preferably less than 1.60 and ideally not less than 1.58 for a wavelength of 589 nm in the longitudinal direction of the film.

The coating of the present invention contains at least two components, in particular at least one acrylic component and a component that serves to stabilize the flame. These components are described below.

Suitable acrylic components are described, for example, in EP-A-0144948. Acrylate-based coatings are preferred because they do not tend to bleed components of the coating or delaminate portions of the coating when used in a greenhouse. Polyacrylates are particularly suitable. For

- 4 041237 silicones, polyurethanes or polyvinyl acetates can also be used as an anti-reflection/anti-reflective coating to achieve good optical properties. However, it was shown that the burning characteristics of acrylates were the best and therefore acrylates were chosen as the coating material to further improve the fire resistance of the film.

The acrylic component of the present invention consists essentially of at least 50% by weight of one or more polymerized acrylic and/or methacrylic monomers.

The acrylic component preferably consists of an ester of acrylic or methacrylic acid, in particular an alkyl ester whose alkyl group contains up to ten carbon atoms, for example methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, hexyl, 2-ethylhexyl, heptyl and n-octyl groups. The most preferred adhesion promoters are copolymers of an alkyl acrylate, for example ethyl acrylate or butyl acrylate with an alkyl methacrylate, for example methyl methacrylate, in particular in equal mole fractions and in a total amount of 70 to 95 wt.%. The acrylate comonomer in such acrylic/methacrylic combinations is preferably present in an amount of 15 to 65 mole percent (mole %) and the methacrylate comonomer is preferably present in an amount typically 5 to 20 mole % more than the amount of the acrylate comonomer. The methacrylate is preferably introduced in an amount of 35 to 85 mole % in an acrylic/methacrylic combination.

In an additional embodiment, the acrylic component may contain additional comonomers in an amount of from 0 to 15 wt.%, which are suitable for the formation of intermolecular crosslinking under the influence of elevated temperature.

Suitable crosslinkable comonomers are, for example, N-methylolacrylamide, N-methylolmethacrylamide and the corresponding ethers; epoxy materials such as, for example, glycidyl acrylate, glycidyl methacrylate and allyl glycidyl ether; monomers containing carboxyl groups such as, for example, crotonic acid, itaconic acid or acrylic acid; anhydrides, for example maleic anhydride or itaconic anhydride; hydroxyl-containing monomers such as, for example, allyl alcohol and hydroxyethyl or hydroxypropylacrylate or methacrylate; amides such as, for example, acrylamide, methacrylamide or maleic acid amide; and isocyanates, such as, for example, vinyl isocyanate or allyl isocyanate.

Of the above comonomers, preference is given to N-methylolacrylamide and N-methylolmethacrylamide, especially because the copolymer chains containing one of these monomers are capable of condensing with each other under the action of elevated temperatures and thus forming the desired intermolecular cross-links. For copolymers containing other functional monomers, it is necessary to prepare blends of at least two copolymers with different functional comonomers to achieve the desired crosslinking, for example by blending an acrylic/crotonic acid copolymer with an acrylic copolymer containing isocyanate, epoxy or N-methylol functional groups. groups capable of reacting with acid functional groups.

Other specific combinations of such mixed acrylic copolymers include copolymers with monomers containing epoxy groups as functional groups, in combination with copolymers containing monomers containing as functional groups an amino group, anhydride acid group, carboxyl, hydroxyl or N-methylol groups; copolymers containing monomers containing N-methylol or N-methylol ether groups as functional groups, in combination with copolymers containing monomers containing carboxyl, hydroxyl or amino groups as functional groups; copolymers with monomers containing isocyanate groups as functional groups, in combination with copolymers containing monomers containing carboxyl or hydroxyl groups as functional groups, etc. Preferably, the functional monomers contained in the mixed copolymer systems are present in approximately equimolar amounts.

Acrylic copolymers can also be interpolymerized with no more than 49 wt.

% of one or more halogen-free, non-acrylic, monoethylenically unsaturated monomers. Suitable comonomers are, for example, dialkyl maleates such as, for example, dioctyl maleate, diisooctyl maleate and dibutyl maleate, versatic acid vinyl ester, vinyl acetate, styrene, acrylonitrile and the like.

Preferred crosslinkable mixed copolymer compositions for the purposes of the present invention are mixtures in a ratio of about 50:50 (wt.%) of an ethyl acrylate/methyl methacrylate/crotonic acid copolymer with an ethyl acrylate/methyl methacrylate/glycidyl acrylate copolymer; mixtures of an ethyl acrylate/methyl methacrylate/methacrylamide copolymer with an ethyl acrylate/methyl methacrylate/M-methylol acrylamide copolymer; or compositions based on ethyl acrylate/methyl methacrylate/M-methylolacrylamide copolymers, for example copolymers containing from 50 to 99 wt.% acrylic and/or methacrylic monomers, from 0 to 49 wt.% monoethylenically unsaturated monomer and from 1 to 15 wt.% N- methylolacrylamide. Particular preference is given to the use of copolymers which contain from 70 to 95% by weight of acrylic and/or methacrylic monomers, from 0 to 25% by weight of monoethylenically unsaturated monomer and from 5 to 10% by weight of N-methylolacrylamide.

In addition, in addition to the acrylate component, a structurally different crosslinking agent such as a condensate of melamine or urea with formaldehyde can be used. However, their content in the coating should be no more than 3 wt.% (calculated on the dried coating composition), in particular because crosslinkers of different structure, having a high nitrogen content (for example, melamine), during regeneration can cause yellowing of the PET film .

In a preferred embodiment, the dried acrylate coating contains less than 10 wt.%, more preferably less than 5 wt.% and ideally less than 1 wt.% of repeating units containing an aromatic building block. When the content of repeating units containing an aromatic structural element, above 10 wt.%, there is a noticeable deterioration in the resistance of the coating to weathering.

Coating stabilization against flammability

As discussed above, the application of known anti-reflective coatings to the outer surfaces of a polyester film appears to degrade the fire resistance of the entire film structure. One would expect that an obvious solution to this problem in this case would be to add flame retardant particles also to the base film to reduce the flammability of the entire laminate. However, it has proven that flammability stabilization of a single or multilayer film coated with known anti-reflection/anti-reflection coatings will not eliminate the negative combustion properties of these coatings.

In addition, although the non-weathered sample having only the base film but no anti-reflection/anti-reflection coating(s) was stabilized against flammability initially passed the flammability test, the same sample unexpectedly failed the same test after atmospheric aging . The detrimental effect of anti-reflective/anti-reflective coating(s) on flammability appears to be enhanced after exposure to (UV) light and water.

In addition, as discussed above, when particulate flame retardant additives are added to polyester films, there is a tendency to haze and reduce light transmittance and, therefore, this is not a suitable solution to the problem of flammability.

Surprisingly, the addition of the flame retardant described in this application to only the anti-reflective/anti-reflection coating (s) stabilized the entire laminate, so that additional film stabilization is not required. The coating components described in this application are suitable for applying an anti-reflective/anti-reflection coating and can be applied to at least one surface, but preferably they are applied to both surfaces of the base film. In addition, the coating(s) that includes at least one of the flame retardants described below is relatively thin compared to the base film, but the flammability of the entire laminate deteriorates compared to the uncoated base film. The improved flame retardancy is maintained with both the non-weathered film and the weathered film.

It should be noted that, in principle, it is also possible to add a flame retardant to the base film, whereby the anti-reflective/anti-reflective coating(s) is also stabilized by the flame retardant. However, this approach does not improve the fire resistance of the laminate enough to outweigh the economics.

Film samples made in accordance with this specification, where at least one, preferably both, surfaces of the base film were coated with an anti-reflective/anti-reflection coating containing at least one flame retardant, described below, passed the test for flammability both before and after atmospheric aging. Such a sample burns in less than 3 out of 5 samples to the mark of 125 mm after the first ignition (see test methods below). The base film itself may or may not contain a flame retardant.

The anti-reflective/anti-reflective coating contains one or more flame retardants that improve the fire test performance of the entire polyester base film.

The flame retardant of the present invention preferably has the following structures (I) and/or (II):

In the structures above, R ¹ , R ² , R ³ and R ⁴ independently of each other may represent the following radical groups: H; linear alkyl -(CH ₂ ) _p -CH ₃ (n = 0-7); isopropyl; iso- or tert-butyl; linear alkyl alcohols -(CH ₂ ) _p -CH ₂ -OH (n = 0-3), isopropyl alcohol or linear alkyl acids/esters of alkyl acids with the structure -(CH ₂ ) _n -COOR ⁵ (R ⁵ = H; -(CH ₂ ) _n CH ₃ (n = 0-3)), where at least one radical group (R ¹ -R ⁴ ) is not H.

Z represents the remainder of the following groups: H; linear alkyl -(CH ₂ ) _P -CH ₃ (n = 0-10); isopropyl; iso- or tert-butyl; linear alkyl alcohols -(CH ₂ ) _n -CH ₂ -OH(n = 0-5); isopropyl alcohols or linear alkyl acids/alkyl esters of the structure -(CH2) _n -COOR ⁵ (R ⁵ =H; -(CH2)p-CH3 (n = 0-3)).

Particularly preferred fire retardants include compounds based on organophosphorus compounds. However, phenyl-substituted phosphate compounds such as triphenyl phosphate, bisphenol A bis(diphenyl phosphate) (CAS 5945-33-5) or hexaphenoxycyclotriphosphazene oligomeric compounds (CAS 28212-48-8) can cause problems during production because PET can be released during the extrusion process. phenol and therefore they are incompatible with PET.

Therefore, compounds of oligo- and/or alkyl esters of phosphonic acid or phosphoric acid are preferred. These compounds can be dissolved in the polymer matrix of the anti-reflective/anti-reflective coating and, unlike embedded particles, do not reflect or refract light. The refractive index of the resulting coating after the addition of such flame retardants is in the preferred range. In addition, they are compatible with the manufacturing method. The refractive index w of the alkyl phosphonate is below 1.500, preferably below 1.480 and particularly preferably below 1.470. If the refractive index of the alkyl phosphonate used is too high, the anti-reflection effect of the entire coating is reduced and the transparency of the film becomes too low.

Preferred compounds are alkyl phosphonates and/or oligoalkyl phosphonates (preferably with a molecular weight < 1000 g/mol). However, the polyalkyl phosphonate is not effective as a fire retardant because it does not sufficiently migrate into the polymer matrix of the anti-reflective/anti-reflective coating under the conditions of the manufacturing process. Therefore, it does not sufficiently bind to the polymer matrix and can be rubbed off the film surface.

A preferred alkyl phosphonate is Rucocoat FR2200 from Rudolf Chemie.

The proportion of phosphorus in the anti-reflective/anti-reflection coating is 2 to 18 wt.%, preferably 3 to 17 wt.% and most preferably 4 to 16 wt.%, based on the total weight of each coating. If the proportion of the flame retardant relative to the anti-reflection/anti-reflection component is below the above limits, the fire resistance of the entire laminate becomes too low. If the proportion of the flame retardant is too high, the flame retardant does not dissolve in the polymer matrix of the anti-reflection/anti-reflection coating well enough and may sweat out during manufacture and/or during use. It can also cause the coating to be worn off the surface.

It should be noted that compounds such as ammonium phosphate, aluminum hydroxide or magnesium hydroxide can also improve the flame retardant performance of the layered structure, but they tend to adversely affect the optical properties of the film and are therefore preferably not used.

Depending on the particle size of the compounds added, haze may increase and clarity may decrease. Aluminum hydroxide and magnesium hydroxide, which are described in EP 1441001, act by forming water and therefore require a certain concentration to be effective. Films which contain a large amount of these particles also tend to be very cloudy and have low light transmission. In addition, direct extrusion with polyester is difficult because such compounds promote hydrolytic degradation of the polymer. If the film is made from reclaimed materials, particles that are only present in the coatings will end up being extruded with polyester. The described hydrolytic degradation reduces the viscosity of the polyester, which will be difficult to handle during the manufacturing process. The preferred manufacturing method also uses reclaims and coats one or both surfaces of the film in-line with the coating of the present invention in order to be able to produce films economically.

Additional coating components

In addition, up to 10% by weight of additives can be added to the coating. These include surfactants (ionic, non-ionic and amphoteric), protective colloids, UV stabilizers, defoamers and biocides. Particularly suitable surfactants are SDS (sodium dodecyl sulfate), polyethylene glycol-based surfactants with a C ₈ -C ₂₀ acyl tail (branched or unbranched) and a polar head with -(CH2-O) _n R (where n = 8-100 and R = -OH, -CH ₃ or -CH2-CH3), such as: Lutensol AT50 or Tergitol.

In a particularly preferred embodiment, the coating contains at least 1% by weight of a UV stabilizer on a dry basis, with particular preference being given to Tinuvin 479 or Tinuvin 5333-DW (BASF, Ludwigshafen, Germany). Less preferred are HALS (Hindered Amine Light Stabilizers) because during regeneration (recycling of film residues from production) they lead to a noticeable yellowing of the material and therefore to a decrease in transparency.

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Coating thickness

The dry thickness of the anti-reflective/anti-reflection coating(s) is in each case at least 60 nm, preferably at least 70 nm and in particular at least 78 nm, and is at most 130 nm, preferably at most 115 nm and ideally no more than 110 nm. In this way an ideal increase in transparency is achieved in the desired wavelength range. Preferably, the thickness of the coating is more than 87 nm, and in particular more than 95 nm. In this preferred embodiment, the coating thickness is preferably less than 115 nm, and ideally less than 110 nm.

Within such a narrow thickness range, not only does transparency increase to near-optimal levels, but ultraviolet and blue light reflectance also increases compared to the rest of the visible spectrum. On the one hand, this saves UV stabilizer, but, in particular, also leads to a shift in the blue/red ratio towards red. This improves plant growth, increases flowering and fruiting, and reduces the frequency of plant growth stunting due to insufficient lighting.

The surface of the film opposite the first anti-reflection/anti-reflection coating described above is also preferably provided with an anti-reflection modification. In a preferred embodiment, this is the same anti-reflection coating that is applied to the second surface of the film opposite the first surface of the film. This second coating corresponds to the description of the coating applied to the first surface, and in one preferred embodiment is the same as the first coating in terms of coating material and thickness.

The coating(s) are preferably applied to the film in-line prior to transverse stretching by known methods (eg reverse gravure roller or Meyer bar), preferably from an aqueous dispersion.

To obtain an anti-reflection coating, all components can be presented either in dry form or without impurities (i.e., in an undissolved or non-dispersed state), and then they are dispersed (or dissolved) in an aqueous medium, or each separately is pre-dispersed or dissolved in aqueous medium and then loaded, mixed and, if necessary, diluted with water. It has been shown that if each component is dispersed separately or used in solution, it is preferable if the resulting mixture (anti-reflection coating) is homogenized with a stirrer for at least 10 minutes before using it. It has been shown that if the components are used in a pure state (ie, in an undissolved or undispersed state), it is particularly advantageous if high shear forces are applied during dispersion using appropriate homogenization techniques.

Depending on the type of application/application method, i.e. in-line (eg reverse printing, Meyer bar, etc.) or off-line (eg direct printing), the non-aqueous fraction of the dispersion is preferably in the range of 5 to 35 wt.% and more preferably in the range from 10 to 30 wt.%.

Transparency values >95.3%, which are particularly preferred according to the present invention, can be achieved with an anti-reflection coating applied to both surfaces of the film.

Mode of production

Polyester polymers for individual layers are produced by polycondensation of either dicarboxylic acids and a diol, or esters of dicarboxylic acids, preferably dimethyl ethers, and a diol. Suitable polyesters preferably have a standard viscosity (SV) value in the range of 500 to 1300, where the individual values are less important, but the average SV value of the starting materials used should be greater than 700 and preferably greater than 750.

Particles as well as UV stabilizers can be added before polyester production is complete. To do this, the particles are dispersed in a diol, optionally crushed, decanted and/or filtered and added to the reactor either in the (trans)esterification step or in the polycondensation step. In a preferred technique, a concentrated polyester masterbatch containing particulates or additives can be produced using a twin screw extruder and diluted with particulate-free polyester during film extrusion. It has been found that it is better to avoid masterbatches containing less than 30 wt.% polyester. In particular, master batches containing particles of SiO ₂ should contain no more than 20 wt.% SiO ₂ (because of the risk of gelation). Another possibility is to add particles and additives directly during film extrusion in a twin screw extruder.

It has been found that polyesters are best pre-dried when using single screw extruders. When using a twin screw extruder with a degassing zone, the drying step can be omitted.

The polyester or polyester blend of the layer or individual layers in the case of multilayer films is first compressed and fluidized in extruders. The melt(s) are then formed into flat films of melt in a mono- or co-extrusion die by being forced through a slot die and drawn on a chilled roll and then on one or more spreading rolls where the material is cooled and solidified.

The film of the present invention is biaxially oriented, i. stretched along two axes. Most often, the biaxial orientation of the film is carried out sequentially. The orientation in this application is preferably performed first in the longitudinal direction (ie in the machine direction = MD) and then in the transverse direction (TD), ie perpendicular to the machine direction. Orientation in the longitudinal direction can be carried out using two rollers rotating at different speeds, corresponding to the desired degree of drawing. In the transverse orientation process, an appropriate tenter frame is usually used.

The temperature at which stretching is performed can vary within a relatively wide range and depends on the desired properties of the film. Stretching in the longitudinal direction is usually carried out in the temperature range from 80 to 130°C (heating temperature from 80 to 130°C), and stretching in the transverse direction is usually carried out in the temperature range from 90°C (start of stretching) to 140°C (end hoods). The stretch ratio in the longitudinal direction is in the range of 2.5:1 to 4.5:1, preferably 2.8:1 to 3.4:1. At draw ratios above 4.5, a significant reduction in machinability (tearing) occurs. The stretch ratio in the transverse direction is usually in the range of 2.5:1 to 5.0:1, preferably 3.2:1 to 4:1. With a transverse draw ratio above 4.8, a significant reduction in workability (tearing) occurs and is therefore preferably avoided. It has been found that in order to achieve the desired film properties, the draw temperature (in MD and TD) is advantageously below 125°C and preferably below 118°C.

Before stretching in the transverse direction, one or both surfaces of the film can be coated in-line using methods known per se. The in-line coating can preferably be used for coating to increase transparency (anti-reflection). During subsequent thermosetting, the film is held at 150 to 250°C for a period of 0.1 to 10 s in tension and to achieve the preferred shrinkage and elongation values, weakened in the transverse direction by at least 1%, preferably by by at least 3% and particularly preferably by at least 4%. Such weakening is preferably carried out in the temperature range from 150 to 190°C.

In order to reduce transparency deflection, the temperature in the first curing zone should preferably be below 220°C and particularly preferably below 190°C. In addition, for the same reason, at least 1%, preferably at least 2% of the total cross stretching ratio should preferably be assigned to the first curing zone, where normally no further stretching occurs. Then the film is wound in the usual way.

In a particularly economical process for the production of polyester film, up to 70% by weight of recycled/recycled material is used, based on the total weight of the film. Recycled material can be added to polymer extrusion without adversely affecting the physical properties of the film.

In one embodiment, the film is coated using offline technology in an additional process step that occurs after film production. In this case, the front gravure roller can be used to apply an anti-reflection/anti-reflection coating to the surface of the film. Upper limits (ie, maximum wet application) are set based on the process conditions and the viscosity of the coating dispersion, and their upper limits are determined based on the workability of the coating dispersion.

Application

The films described in this application have high transparency, UV and flame resistance, and are coated on at least one side to reduce visible light reflection. These characteristics make them excellently suited as convection barriers with high transparency, in particular for the production of energy-saving sheet materials for greenhouses. The film material described in this application is cut into narrow strips for this purpose, from which, in combination with polyester threads (which must also be UV resistant), a woven fabric / braided screen, described below, is obtained, which is then hung in a greenhouse. The film strips described in this application can be combined with other film strips (particularly films with a light-diffusing effect). Alternatively, the film as such (without textiles) can be installed in the greenhouse.

In FIG. 1-4 show greenhouse screens 10 which according to the invention comprise a plurality of narrow film strips 11 held together by a thread frame 12, 13a, 13b; 14, 15; 18, 19. The strips are preferably closely joined so that they form a substantially continuous surface. In all embodiments, the spacing between the strips has been widened for clarity so that the thread system is visible in the drawings. The screen has a longitudinal direction y and a transverse direction x, while the strips 11 extend in the longitudinal direction y. In some embodiments, the strips 11' may also extend in the transverse direction x. Typical strip widths range from 2 mm to 10 mm.

In FIG. 1 strips of film are joined together using the warp knitting method as described in

- 9 041237

EP 0109951. The thread frame contains warp threads 12 forming loops or stitches and extending mainly in the longitudinal direction y. Warp threads 12 are connected to each other by weft threads

13a and 13b passing through the film strips.

In FIG. 1 shows an example of a mesh pattern for a warp knit fabric using four guide combs: one for the strips 11, two for the connecting threads 13a and 13b running transversely to the film strips, and one for the longitudinal warp threads 12.

The space between the film strips 11 has been greatly expanded to make the mesh pattern clear. Typically, the strips 11 of the film are closely joined. Longitudinal warp threads 12 are located on one side of the screen, purl, while transverse connecting threads 13a and 13b are located on both sides of the fabric, front and back. The term transverse in this respect is not limited to a direction perpendicular to the longitudinal direction, but means that the connecting threads 13a and 13b pass through the film strips 11 as shown in the drawings. The connection between the longitudinal weft threads and the transverse threads is carried out on the wrong side of the fabric. In this way, the film strips can be butted end-to-end without being limited by the longitudinal weft threads.

Longitudinal weft threads 12 in FIG. 1 run continuously and in a continuous manner along opposite edges of adjacent film strips in a series of knitted stitches, in the form of a so-called open loop chain.

The transverse threads 13a and 13b extend above and below the film strips in the same place, i.e. opposite each other, in order to securely grip the film strips. Each knitted loop in the longitudinal warp threads 12 has two such transverse threads 13a and 13b interlocked with it.

In FIG. 2 shows another example of a mesh pattern for a web similar to the web shown in FIG. 1. The difference is that the transverse threads 13a and 13b pass through one and the second film strip 11 alternately.

In FIG. 3 shows a woven screen in which film strips 11 are interconnected by warp threads 14 running in the longitudinal y direction and intertwined with weft threads 15 running across the film strips, mainly in the transverse x direction.

In FIG. 4 shows another embodiment of the woven screen described in US Pat. No. 5,288,545, comprising film strips 11 (warp strips) extending in the longitudinal y direction and film strips 11' (weft strips) extending in the transverse x direction. Weft strips 11' extending in the transverse direction can, as shown in FIG. 4 always be on the same side of the warp strips 11 running in the longitudinal direction, or may alternate on the front and back sides of the warp strips 11. The warp and weft strips 11 and 11' are held together by a thread carcass comprising longitudinal and transverse threads 18 and 19. The screen may include open areas free of bands to reduce heat buildup under the screen.

Description of test methods

The following test methods were used to characterize the raw materials and films.

Spectra in the UV/visible region of the spectrum or transmission at wavelength x

The transmission of the films at certain wavelengths was measured on a two-beam spectrophotometer LAMBDA® 12 or 35UV/Vis manufactured by Perkin Elmer, USA. A large film sample of approximately (3.times.5) cm was placed on a flat sample holder perpendicular to the measuring beam with respect to the beam path. The measuring beam passes through a 50 mm integrating sphere in the direction of the detector, where the transparency intensity of the film is determined at the desired wavelength. The background medium was air.

Transparency and haze

Film transparency and haze were measured according to ASTM-D1003-61 using a HazegardHazemeter XL-21 1 manufactured by BYK-Gardner (Wesel, Germany).

UV stability

UV stability was determined as described in DE69731750 on p. 8 (DE application for WO9806575), the atmospheric aging time was 2000 hours, not 1000 hours, and the tensile strength (UTS) value was indicated in % of the original value.

SV (standard viscosity)

The standard viscosity (SV) in the dilute solution was measured by a method based on DIN 53726 part 3 in an Ubbelohde viscometer at (25 ± 0.05)°C. Dichloroacetic acid (DCA) was used as a solvent. The dissolved polymer concentration was 1 g polymer/100 ml pure solvent. It took 1 hour at 60°C to dissolve the polymer. After this time, if the samples did not dissolve completely, up to two dissolution attempts were made, in each case for 40 min at 80°C, and then the solutions were centrifuged for 1 h at a rotation speed of 4100 rpm. The dimensionless SV value is determined as shown below in terms of relative viscosity:

- 10 041237 (η _Γ εΐ=η/ηδ):

SV=(nrei- 1) x YuOO

The proportion of particles in the film or polymer was determined by the ashing method and corrected by a corresponding increase in the initial mass, i.e. (Initial mass corresponding to 100% polymer)

Initial mass = ----------------------------------------------- -------[(100 - particle content, in May %) x 0.01]

Determination of the refractive index depending on the wavelength

The refractive index of the film substrate and the applied coating was determined as a function of wavelength using spectroscopic ellipsometry: J.A. Woollam et al, Overview of variable-angle spectroscopic effipsometry (VASE): I. Basic theory and typical applications, Proc. SPIE Vol. CR72, p. 3-28, Optical Metrology, Ghanim A. Al-Jumaily; Ed.

First, the uncoated film base or the modified co-extruded side is analyzed. Reverse side reflection is suppressed with the smallest possible particle diameter sandpaper (eg P1000) to roughen the reverse side of the film. The film is then measured with a spectroscopic ellipsometer, in this case an M-2000 manufactured by J.A. Woollam Co., Inc., equipped with a rotating compensator. The machine direction (MD) of the sample is parallel to the light beam. The wavelength used for measurement is in the range from 370 to 1000 nm; measuring angles 65, 70 and 75°.

The model is then used to model the ellipsometric data ψ and Δ.

Cauchy model = A + +

X X (wavelength λ in µm) is suitable for this purpose in this case. The parameters A, B and C are varied so that the data provide the best possible fit with ψ and Δ in the measured spectrum. The validity of the model can be checked using the mean square error (MSE) value, which compares the model with the measured data (ψ(λ) and Δ(λ)), and should be the smallest possible.

mse= 1 ooo where n = number of wavelengths, m = number of satisfying parameters,

N = cos(2ψ), С = sin(2λ)cos(Δ), S = sin(2ψ)sin(Δ) [1]

The Cauchy parameters A, B, and C obtained for the base film make it possible to calculate the refractive index n as a function of the wavelength with confidence in the measurement range from 370 to 1000 nm.

Similarly, the coating or modified co-extruded layer can be analyzed. The film base parameters are now known and must remain constant during simulation. Measuring the coverage of the co-extruded layer also requires roughening the back of the film as described above. The Cauchy model can also be used in this application to describe the refractive index as a function of wavelength. However, the corresponding layer is now present on a known basis and this is taken into account in the appropriate evaluation software (CompleteEASE or WVase). The layer thickness affects the resulting spectrum and must be taken into account in the simulation process.

Refractive index n _D of liquid material

An Abbe refractometer is used to determine the refractive index of a liquid.

The apparatus must have a temperature of 23 °C. The liquid is applied with a pipette to a well-cleaned prism. The entire surface of the prism is covered with liquid. Then a second prism is applied and pressed firmly. The top thumb screw is adjusted while looking through the eyepiece of the refractometer until a clear border of the transition from bright to dark appears. The sharp transition line is then blended with a second thumb screw until it is in the crosshairs of the eyepiece shadow. Now you can read the refractive index on the indicator scale.

Burn test

The combustion test is carried out in accordance with the test method described in Plastics - Determination of burning behavior of thin flexible vertical specimens in contact with a small-flame ignition source - Amendment 1 Specimens (EN ISO 9773:1998/Amd 1:2003). The samples are kept for one day at a temperature of (23 ± 2)°C and a relative humidity of (50 ± 5)%. With regard to the present invention, of particular concern is whether the sample burns up to the 125 mm mark or not. The test result also contains information on whether the sample reached this mark after the first or second ignition or did not reach at all. For each film, the test is carried out on five samples.

Examples

In the examples and comparative examples given in this application, the following starting materials are used:

PET1 = polyethylene terephthalate made from ethylene glycol and terephthalic acid with an SV value of 820 and a DEG content (diethylene glycol monomer content) of 0.9 wt. %.

PET2 = polyethylene terephthalate with an SV value of 730 containing (6-oxodibenzo[c,e]-[1,2]oxaphosphorin-6-ylmethyl)succinic acid bis(2-hydroxyethyl) ester (e.g., the compound is a flame stabilizer, which is usually added when extruded as a masterbatch (see EP 1368405) as a comonomer, resulting in a phosphorus content of the polymer of 18,000 ppm.

PET3 = polyethylene terephthalate made from ethylene glycol and dimethyl terephthalate with an SV value of 820 and a DEG content (diethylene glycol monomer content) of 0.9 wt% containing 1.5 wt% Sylobloc 46 with a d50 of 2.5 µm. Manufactured using the purified terephthalic acid (PTA) process. The catalyst is potassium titanyl oxalate with 18 ppm titanium. The transesterification catalyst is zinc acetate.

PET4 = polyethylene terephthalate with an SV value of 700 containing 20 wt. % TINUVIN® 1577. The composition of the UV stabilizer is as follows: 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-(hexyl)oxyphenol (TINUVTN® 1577 from BASF, Ludwigshafen, Germany) . TINUVIN® 1577 has a melting point of 149°C and is thermally stable at 330°C.

Example 1

Cover layers (A) and (C) of polyester film:

Blend of 10% PET4, 7.2% PET3 and 82.8% PET1

Base layer (B) of polyester film:

Blend of 90% PET1 and 10% PET4

Coating (applied to the co-extruded cover layers (A) and (C) of the polyester film):

As a flame retardant, 13 wt.% alkyl phosphonate (RUCO-COAT FR2200, Rudolf Chemie) is dissolved in water. The pH is adjusted by adding ammonia solution to 7.5-8.0. With stirring, an aqueous dispersion of acrylate is added at a concentration of 10 wt.% (EP-A-0144948, example 1 with SDS surfactant and Tergitol 15-S-40).

The raw materials listed were melted in each case in a layer extruder at 292°C and extruded through a three-layer slotted die onto a draw roll at a temperature of 50°C. The obtained amorphous pre-film was then first stretched in the longitudinal direction. The elongated film was corona treated and then reverse gravure coated using the described coating composition on the first surface of the film. The second surface of the film can be processed using the second reverse gravure roller. After that, the film was dried at 100°C and stretched in the transverse direction. After that, thermosetting and winding of the film are carried out. The final film thickness is 19 µm (each A and C coating layer is 1 µm thick). The conditions of the individual stages are given in table. 1.

Table 1. PET manufacturing process parameters for Example 1

Longitudinal hood (MD) Preheat temperature 75-115 °C Extract temperature 115 °C Degree of drawing 3.8 Cross hood (TO) Preheat temperature 100 °C Extract temperature 112 °C Degree of drawing 3.9 heat curing Temperature 237 - 150 °C Duration 3 With Maintenance tempering at 200-150 °C 5 % Temperature 1 area 170 °C

The thickness of the coating deposited on one or two surfaces of the film is 80 nm each. The properties of the films are described in Table. 3.

Examples 2-4 and Comparative Examples 1-10:

The production process for other examples and comparative examples is the same as described for example 1. The compositions of the base film, coextruded layers and coatings are shown in table. 2.

Comparative example 4.

The coating dispersion for Comparative Example 4 consisted of 7.5% by weight of Neorez R600 polyurethane from DSM and 7.5% by weight of Epocros WS-700 oxazoline crosslinker from Sumitomo.

Comparative example 5.

The coating dispersion for comparative example 5 consists of the silicone coating described in example 1 of EP-A-0769540.

Comparative examples 6 and 7.

The coating dispersions for Comparative Examples 6 and 7 consisted of the acrylate described in EPA-0144948 and ammonium phosphate (Exolit AP420 from Clariant, 45 wt%, aqueous dispersion).

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Claims (17)

Table 2. Formulations for Examples and Comparative Examples Etc. 1 Etc. 2 Etc. 3 Etc. 4 Wed Etc. 1 Wed Etc. 2 Wed Etc. 3 Wed Pr. 4 Wed Etc. Wed Etc. 6 Wed Etc. 7 Wed Etc. 8 Wed Etc. 9 Wed Etc. 10 Film composition Soextrud. layer A 1 µm 1 µm 1 µm 1 µm 1 µm 1 µm 1 µm 1 µm 1 µm 1 µm 1 µm 1 µm 1 µm 1 µm PET4 (%) 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 PETZ (%) 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7.2 PET1 (%) 82.8 82.8 82.8 82.8 82.8 82.8 82.8 82.8 82.8 82.8 82.8 74.8 74.8 74.8 PET2(%) 8.0 8.0 8.0 Base layer 17 micron 17 micron 17 micron 17 micron 17 µm 17 µm 17 µm 17 µm 17 µm 17 µm 17 µm 17 µm 17 micron 17 micron PET4(%) 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 PET2(%) 8.0 8.0 PET1 (%) 90.0 90.0 90.0 90.0 90.0 90.0 90.0 90.0 90 90.0 90.0 82.0 82.0 90.0 Soextrud. layer C 1 µm 1 micron 1 µm 1 µm 1 µm 1 µm 1 µm 1 µm 1 µm 1 µm 1 µm 1 µm 1 µm 1 µm PET4(%) 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 10.0 PETZ (%) 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7.2 7.2 PET1 (%) 82.8 82.8 82.8 82.8 82.8 82.8 82.8 82.8 82.8 82.8 82.8 74.8 74.8 74.8 PET2(%) 8.0 8.0 8.0 Coating composition Surface coating A or A&C A&C A&C A&C A No coverage A A&C A&C A A&C A&C No coverage A&C A&C Acrylate 10 5 15 10 15 15 13 10 15 15 Alkylphosphonate 13 25 5 15 ammonium phosphate 2 5 Polyurethane 7.5 Oxazoline Crosslinking Agent 7.5 Silicone as per EPA-0769540 14 Share R May. % in anti-reflective coating 10.7% 15.8% 4.8% 11.4% Dry coating thickness (nm) (for each side if both sides of the film are coated) 80 80 105 80 0 80 80 80 105 80 80 0 60 60 Table 3 Characteristics for Examples and Comparative Examples Etc. 1 Etc. 2 Etc. 3 Etc. 4 Wed Etc. 1 Wed Etc. 2 Wed Etc. 3 Wed Etc. 4 Wed Etc. 5 Wed Etc. 6 Wed Etc. 7 Wed Etc. 8 Wed Etc. 9 Wed Etc. 10 Refractive index n _D of coating at 589 nm in MD 1.503 1.483 1.522 1.523 -/- 1.508 1.508 1.475 1.410 1.510 1.509 -/- 1.508 1.508 Transparency [%] 96.5 95.6 96.4 93.5 90.4 93.3 96.2 95.3 94.4 95.6 94.1 90.8 94.8 94.7 Haze [%] 3.94 4.01 3.53 2.00 3.87 4.66 5.72 7.09 2.4 8.54 27.1 2.3 3.5 3.5 Flame test before weathering The number of samples burning to the mark after the 1st and 2nd ignitions 5 4 5 5 3 5 5 4 5 5 4 5 5 5 The number of samples burning to the mark after the 1st ignition 0 0 2 2 0 3 4 4 5 2 2 0 2 3 Combustion test after atmospheric aging The number of samples burning to the mark after the 1st and 2nd ignitions 5 5 5 5 4 5 5 5 5 5 5 The number of samples burning to the mark after the 1st ignition 1 0 2 3 1 2 5 5 5 4 4 CLAIM 1. A screen for a greenhouse containing strips (11) of film material, which are interconnected by a system of threads of transverse threads (12, 14, 18) and longitudinal threads (13a, 13b; 15; 19) through a knitting, warp knitting or weaving process with the formation of a continuous product, and at least a part of said strips (11) contains a film material in the form of a single or multilayer polyester base film provided with at least one anti-reflective/anti-reflective coating on the first surface of the base film, said film material has a transparency of at least at least 93.5%, and the total number of particles is less than 0.5 wt.% based on the total weight of the film material, characterized in that said at least the first anti-reflective/anti-reflective coating has a dry thickness of 60 to 130 nm, and contains at least one polymer based on acrylic acid and/or methacrylic acid, and contains at least one alkyl phosphonate and/or oligoalk ylphosphonate flame retardant, and contains phosphorus in an amount of from 2 to 18 wt.% based on the total weight of the coating. 2. The greenhouse screen of claim 1, wherein said base film is provided with a second anti-reflective/anti-reflective coating on the second surface of the film. - 13 041237 3. Greenhouse screen according to claim 2, wherein the refractive index of the anti-reflective/anti-reflective coating(s) is lower than the refractive index of the base film and is less than 1.64, preferably less than 1.60, and most preferably less than 1.58 in length 589 nm wavelength when measured in the machine direction (MD) of the film. 4. Greenhouse screen according to claim 1, wherein said acrylic component consists of at least 50% by weight of one or more polymerized acrylic and/or methacrylic monomers. 5. Greenhouse screen according to claim 4, wherein said acrylic component consists of an ester of acrylic or methacrylic acid, preferably an alkyl ester whose alkyl group contains up to ten carbon atoms, more preferably of an alkyl acrylate together with an alkyl methacrylate. 6. Greenhouse screen according to any one of claims 4, 5, wherein said acrylic component contains additional comonomers in an amount of from 0 to 15 wt.%, capable of forming intermolecular crosslinking under the influence of elevated temperature. 7. Greenhouse screen according to any one of the preceding claims, wherein the dried anti-reflective/anti-reflective coating(s) contains less than 10% by weight of repeating units containing an aromatic building block. 8. Greenhouse screen according to any one of the preceding claims, wherein the anti-reflective/anti-reflective coating(s) comprises a flame retardant with the following structure (I) and/or (II): in which R ¹ , R ² , R ³ and R ⁴ are independent of each other and may represent H; linear alkyl with the structure -(CH2)n-CH3 (n = 0-7); isopropyl; iso- or tert-butyl; linear alkyl alcohols with the structure -(CH2)n-CH2-OH (n = 0-3), isopropyl alcohol or linear alkyl acids/alkyl esters with the structure -(CH2)n-COOR ⁵ (R ⁵ = H; - (CH2) _p -CH ₃ (n = 0-3)), where at least one radical group R1-R ⁴ is not H, and Z may be selected from the group H; linear alkyl with the structure -(CH ₂ ) _p -CH ₃ (n = 0-10); isopropyl; iso- or tert-butyl; linear alkyl alcohols with the structure -(CH ₂ ) _p -CH ₂ -OH (n = 0-5); isopropyl alcohols or linear alkyl acids/alkyl esters with the structure -(CH2)n-COOR ⁵ (R ⁵ = H; -(CH2)p-CH3 (n = 0-3)). 9. A greenhouse screen according to claim 8, wherein the flame retardant is an oligo- and/or alkyl ester of phosphoric acid or phosphonic acid. 10. Screen for greenhouse according to any one of claims 8, 9, in which the proportion of phosphorus in the anti-reflective/anti-reflective coating (coatings) is from 3 to 17 wt.%, preferably from 4 to 16 wt.%, based on the total weight of the anti-reflective/ anti-reflective coating. 11. Greenhouse screen according to any one of the preceding claims, wherein the thickness of the anti-reflective/anti-reflection coating(s) in each case is at least 70 nm, preferably at least 78 nm, and is at most 115 nm and ideally at most 110 nm. 12. Greenhouse screen according to any one of the preceding claims, wherein the total film thickness is at least 10 µm and not more than 40 µm, preferably the total film thickness is at least 11, 12, 13 or 14 µm and not more than 35, 30 , 29, 28, 27, 26, 25, 24 or 23 µm. 13. Greenhouse screen according to any one of the preceding claims, wherein the base film comprises a base layer B and one or more additional layers, said additional layers having a thickness of at least 0.5 µm, preferably at least 0.6 µm and most preferably at least 0.7 µm, said thickness being less than 3 µm, preferably less than 2.5 µm and most preferably less than 1.5 µm. 14. Greenhouse screen according to any one of the preceding claims, wherein said base film comprises a UV stabilizer selected from the group consisting of triazines, benzotriazoles, or benzoxazinones in at least one base film layer at a concentration of 0.3 to 3 wt. .% based on the weight of the respective layer. 15. Greenhouse screen according to any one of the preceding claims, wherein the base film contains matting particles selected from the group consisting of cross-linked polymethyl methacrylate (PMMA), SiO ₂ and polydimethylsiloxane (PDMSQ) at a concentration of less than 3% by weight, based on total the mass of each layer, to improve the windability of the film. 16. A greenhouse screen as claimed in claim 15, wherein at least one outer layer of the base film contains at least 0.07% by weight of matting particles. 17. The use of a greenhouse screen according to claims 1 to 16 in a greenhouse to improve photosynthetic activity also in the early morning hours or when the sunlight has a small angle of incidence. -