Anti-fogging greenhouse screen

Abstract

The present invention relates to a greenhouse screen comprising strips of film material (11) interconnected by a woven yarn system of warp threads (12, 14, 18) and weft threads (13a, 13b; 15; 19) through a knitting, warp-knitting, or weaving process to form a continuous product. At least 50% of the strips comprise a single- or multi-layer polyester film having a transparency of at least 92%, the polyester film having a first surface and a second surface, and a permanent anti-fog coating applied to at least one of the first or second surfaces of the polyester film. The anti-fog coating comprises at least one water-soluble polymer, an inorganic hydrophilic material, and a crosslinking agent, the water-soluble polymer being polyvinyl alcohol or a hydrophilic amorphous copolymer. The present disclosure also relates to a process for producing the coated polyester film and its use for producing an energy-saving greenhouse screen with excellent anti-fog properties.

Description

[Technical Field]

[0001] The present invention relates to a greenhouse screen comprising strips of a single- or multi-layer, highly transparent, biaxially oriented, UV-stable polyester film having a permanent anti-fog coating on at least one side. The greenhouse screen has exceptional transparency in addition to permanent anti-fog properties and high UV stability. The invention also relates to a method for producing the polyester film for the greenhouse screen and its use in greenhouses. [Background technology]

[0002] Greenhouse shade netting or screens in greenhouses must meet several requirements. They must provide high light transmittance in the photosynthetic wavelength range, as this is necessary for optimal plant growth. Where possible, light transmittance should not be affected by weather conditions that would cause condensation on the shade screen.

[0003] Because greenhouses are generally humid, under normal weather conditions (e.g., temperature differences between day and night), condensation water forms in the form of droplets on the surface of greenhouse shade screens, especially those facing the plants. In addition to weather conditions, the difference in surface tension between water and plastic also promotes the formation of condensation. In such situations, a film with anti-fog properties may prevent the formation of droplets, thereby enabling a clear view through the plastic film.

[0004] Generally, anti-fog additives can be incorporated into the polymer matrix during the film extrusion process or applied as a coating to the polymer matrix. Such anti-fog additives are typically divalent compounds with a non-polar aliphatic region to anchor them in the polymer matrix and a polar hydrophilic portion that can interact with water to reduce the surface tension of the water droplets, forming a continuous, transparent film of water (due to the hydrophilic surface) on the film.

[0005] In contrast to liquid films, water droplets have a high light scattering and increased reflectivity, which significantly reduces photosynthesis, especially during the morning hours when light is scarce. Furthermore, the anti-fog coating prevents the decay of plants and plant parts caused by non-sticky or dripping water droplets and reduces the damage caused by lens-like effects of water droplets that burn on the film surface when exposed to light. If water droplets still form in very strong condensation, the anti-fog component must not contain toxic substances or substances that are particularly harmful to the environment. Among undesirable substances, mention should be made of alkylphenol ethoxylates, which are frequently used in anti-fog systems (e.g., WO 1995 / 018210). Furthermore, greenhouse screens should be UV-stable, allowing them to be used in greenhouses for at least five years without significant yellowing or significant loss of transparency, which would indicate surface brittleness or cracking and / or a significant deterioration in mechanical properties.

[0006] To avoid reduced crop yields, the use of anti-fog additives in the film must not adversely affect the light transmittance and therefore the transparency of the greenhouse screen. Greenhouse screens made from polyester film with various transparent anti-fog coatings are well known. For example, surface-active coatings based on hydrophilic water-soluble polymers and / or surfactants are used to coat the surface of plastic films to achieve an anti-fog effect.

[0007] The fundamental problem with water-soluble polymers and / or surfactants is that the coatings are easily washed away, meaning that a permanent anti-fog effect cannot be achieved. Typical polyester films with anti-fog coatings are described in EP 1647568 and EP 1777251. These polyester films have excellent mechanical properties but exhibit poor transparency. Furthermore, they have poor long-term stability under weathering. Furthermore, the anti-fog effect of these polyester films only lasts a few months because the corresponding anti-fog additives are easily washed away and dissolve in water, meaning that the active ingredients are quickly depleted when used as greenhouse screens. EP 1152027, EP 1534776, and EP 2216362 describe polyolefin films based on low-density polyethylene (LDPE) or polyvinyl chloride (PVC) and ethylene vinyl acetate (EVA) with long-term anti-fog properties for food packaging and greenhouse applications, using anti-fog additives based on inorganic hydrophilic colloidal substances (e.g., colloidal silicon, aluminum), and nonionic, anionic, or cationic surfactants. These films exhibit durable anti-fog properties, but, in contrast to polyester-based greenhouse screens, suffer from significantly reduced mechanical properties. The use of polyolefin-based films can be completely ruled out for certain applications, since the desired long-term stability, and therefore a five-year service life, is not feasible due to the faster UV degradation of polyethylene (PE) compared to polyethylene terephthalate (PET), which adversely affects economic viability. Furthermore, the poor mechanical stability of polyolefins causes the screen to stretch and lose its large closed structure, reducing its insulating effectiveness.

[0008] EP 3456762 discloses polyester films with a permanent anti-fog coating based on a porous material, a polymer-based organic crosslinker, an organofunctional silane, and one or more surfactants, suitable for further processing as greenhouse screens. The anti-fog properties of these films are good in terms of durability, and the achievable transparency is within the desired range. Nevertheless, these films show that the quality of the anti-fog effect needs to be improved, especially at higher coating thicknesses. Furthermore, the use of organofunctional silanes is problematic and undesirable for regulatory reasons, so this solution must also be excluded.

[0009] State-of-the-art films used for greenhouse screens are at a disadvantage because they do not have long-lasting anti-fog properties or the anti-fog coating is applied to the film in an additional process step. Furthermore, state-of-the-art polyester films are at a disadvantage because they do not have a sufficiently durable anti-fog coating that combines high clarity with long-term stability. Summary of the Invention

[0010] The object of the present invention is to overcome or ameliorate at least some of the drawbacks of prior art screens or to provide a useful alternative. This object can be achieved by a greenhouse screen and a method for manufacturing a film for said greenhouse screen according to claim 1. Further embodiments are set out in the dependent claims, the description and the drawings.

[0011] As described herein, greenhouse screens are provided that include polyester films that exhibit durable anti-fog properties combined with high transparency of at least 92%, no significant yellowing, and UV stability for at least 5 years without exhibiting surface embrittlement or cracking or degradation of mechanical and optical properties important to the application. The greenhouse screen films can also be economically produced in thicknesses ranging from 10 to 40 μm on existing single-layer or multi-layer polyester film lines.

[0012] This object is achieved by providing a greenhouse screen comprising strips of film material interconnected by a weft and warp woven yarn system by a knitting, warp knitting, or weaving process to form a continuous product. At least 50% of the strips are comprised of a single-layer or multi-layer coated polyester film having a transparency of at least 92%. The polyester film has first and second surfaces, and at least one of the surfaces of the polyester film is coated with a permanent anti-fog coating. The anti-fog coating is a) at least one water-soluble polymer; b) an inorganic hydrophilic material, and c) a cross-linking agent; The water-soluble polymer is a polyvinyl alcohol copolymer, or a hydrophilic amorphous copolymer.

[0013] The inorganic hydrophilic material is preferably fumed silica, colloidal silica, or alumina, and the crosslinker is preferably based on an oxazoline-modified polymer, or other crosslinker.

[0014] The polyester film comprises a base layer (B) and optionally a first cover layer (A), or a first cover layer (A) and a second cover layer (C). If present, the first cover layer (A) is applied to a first or second surface of the base layer (B), and if present, the second cover layer (C) is applied to a surface of the base layer (B) opposite the first cover layer (A).

[0015] A layer in the sense of the present invention is a polymer layer formed by coextrusion, i.e. the polyester film according to the invention is formed from one or more layers.

[0016] A coating in the sense of the present invention is the dried product of an aqueous dispersion applied to a polyester film and is not part of the extrusion process of the polyester film itself. The coating is applied to the surface of a single-layer or multilayer film.

[0017] The biaxially oriented polyester film (without coating) advantageously has a thickness of from 10 to 40 μm, preferably from 14 to 23 μm, most preferably from 14.5 to 20 μm.

[0018] The base layer (B) is advantageously at least 70% by weight of a thermoplastic polyester, which consists of at least 90 mol %, preferably at least 95 mol %, of units derived from ethylene glycol and terephthalic acid or of units derived from ethylene glycol and naphthalene-2,6-dicarboxylic acid.

[0019] It is advantageous for polyester films to contain particles to achieve a certain surface roughness and improve the film's windability. The particles are selected from the group consisting of calcium carbonate, amorphous silica, talc, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, lithium fluoride, calcium, barium, zinc, or manganese salts of the dicarboxylic acids used, titanium dioxide, kaolin, or particulate polymers such as cross-linked polystyrene or acrylate particles. Amorphous silica is preferably used as the particles. The particles are preferably used at a concentration of less than 0.5 wt. % based on the total weight of the film. Preferably, the particles are present in the cover layer (A) and / or (C), but if the film has a multilayer structure, the particles can be present in all layers.

[0020] The base layer (B) and, if present, the cover layers (A) and (C) advantageously contain UV stabilizers.

[0021] The UV stabilizer is selected from the group consisting of triazines, benzotriazoles, and benzoxazinones, with triazines being preferred. The base layer (B), and, if present, the cover layers (A) and (C), contain the UV stabilizer in an amount of 0.3 to 3 wt. %, preferably 0.75 to 2.8 wt. %, based on the total weight of each layer.

[0022] The anti-fog coating has a lower refractive index than the polyester film and a thickness of at least 60 nm and at most 150 nm, preferably at least 70 nm and at most 130 nm, particularly preferably at least 80 nm and at most 120 nm.

[0023] An advantage of the present invention is that the anti-fog coating according to the present invention does not contain adhesion-promoting organofunctional silanes, such as vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, or γ-glycidoxypropyltrimethoxysilane, which are suspected of being carcinogenic and should be avoided.

[0024] The anti-fog coating is applied to the first or second surface of the polyester film, and advantageously the surface of the polyester film opposite the anti-fog coating is a) anti-reflective coating, or b) Top layer modification It has anti-reflective modification.

[0025] The top layer modification is formed by coextrusion onto the base layer (B), and the top layer modification comprises a polyester having a lower refractive index than the polyester of the base layer (B). When applied to the surface opposite the antireflective modification, the antifog coating has a thickness of at least 30 nm, preferably at least 40 nm, particularly preferably at least 50 nm and up to 150 nm.

[0026] The coated polyester film of greenhouse screens is produced by extrusion and biaxial stretching, and a) applying the anti-fog coating composition wet in-line to the polyester film before the coated polyester film is heat cured and wound; or b) produced by heat curing and applying the anti-fog coating composition to the polyester film off-line by conventional coating techniques, followed by winding the polyester film onto a take-off roll, followed by drying and winding the polyester film. [Brief explanation of the drawings]

[0027] Examples of greenhouse screen arrangements are described below with reference to the accompanying drawings.

[0028] [Figure 1] FIG. 1 shows an enlarged portion of a warp knit screen according to one embodiment. [Figure 2] FIG. 2 shows a portion of a warp knit screen according to another embodiment. [Figure 3] FIG. 3 shows an enlarged portion of the woven screen. [Figure 4] FIG. 4 shows a portion of a woven screen according to a further embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0029] The present invention discloses a greenhouse screen including strips of film material 11 interconnected by a woven yarn system of warp yarns 12, 14, 18 and weft yarns 13a, 13b; 15; 19 by knitting, warp knitting, or weaving processes to form a continuous product as shown in Figures 1 through 4. The screen comprises multiple narrow strips of film material 11, 11' held together by the woven yarn framework 12, 13a, 13b; 14, 15; 18, 19. The strips of film material 11, 11' are preferably closely spaced end-to-end to form a substantially continuous surface. The screen has a longitudinal direction y and a transverse direction x, with the strips of film material 11 extending in the longitudinal direction. In some embodiments, the strips of film material 11' can also extend in the transverse direction. Typical widths of the strips are between about 2 mm and about 10 mm.

[0030] In Figure 1, strips of film material 11 are interconnected by a warp knitting procedure such as that described in EP 0109951. The yarn framework comprises warp yarns 12 which extend primarily in the longitudinal direction y, forming loops or stitches. The warp yarns 12 are connected to each other by weft yarns 13a and 13b which extend across the film strip.

[0031] FIG. 1 shows an example of a mesh pattern for a fabric produced through a warp knitting process, in which four guide bars are used: one for the strip of film material 11, two for the connecting weft yarns 13a and 13b that extend across the film strip, and one for the longitudinal warp yarns 12.

[0032] The spacing between the strips of film material 11 is greatly exaggerated in the drawings to clarify the mesh pattern. Typically, the strips of film material 11 are closely spaced end-to-end. The longitudinal warp yarns 12 are located on one side of the screen, i.e., the bottom side, and the transverse connecting weft yarns 13a and 13b are located on both sides of the fabric, i.e., the top and bottom sides. The term "transverse" in this context is not limited to a direction perpendicular to the longitudinal direction; it means that the connecting weft yarns 13a and 13b extend across the strips of film material 11 as shown. The connections between the longitudinal warp yarns 12 and the transverse weft yarns 13a and 13b are preferably made on the bottom side of the fabric. In this way, the strips of film material 11 can be closely spaced end-to-end without being limited by the longitudinal warp yarns 12.

[0033] The longitudinal warp yarns 12 in FIG. 1 extend continuously and uninterrupted along the opposing edges of adjacent film material strips 11 in a series of stitches, forming what are known as open pillar stitches.

[0034] The horizontal weft yarns 13a and 13b pass above and below the strip of film material 11 at the same position, i.e. opposite each other, to securely capture the strip of film material. Each stitch of the longitudinal warp yarns 12 has two horizontal weft yarns 13a and 13b engaging it.

[0035] Figure 2 shows another example of a fabric mesh pattern similar to that shown in Figure 1. The difference is that the horizontal weft yarns 13a and 13b pass alternately over one and two strips 11 of film material.

[0036] FIG. 3 shows a woven screen in which strips of film material 11 are interconnected by warp yarns 14 extending in a machine direction y and interwoven with weft yarns 15 extending primarily across the strips of film material 11 in a cross direction x.

[0037] FIG. 4 shows another embodiment of the woven screen described in U.S. Pat. No. 5,288,545, including strips of film material 11 (warp strips) extending in the longitudinal direction y and strips of film material 11' (weft strips) extending in the transverse direction x. The transverse weft strips 11' may always be on the same side of the longitudinal warp strips 11, as shown in FIG. 4, or may alternately be positioned above and below the longitudinal warp strips 11. The warp and weft strips 11' are held together by a thread framework including longitudinal threads 18 and transverse threads 19. The screen may also include open areas without the strips to reduce heat buildup below the screen.

[0038] The films used in the greenhouse screens described herein are well suited as highly transparent convection barriers. Here, the films are typically cut into narrow strips, typically 2 to 10 mm wide, from which fabrics or screens are made, along with polyester threads (which must also be UV-stabilized), for use as greenhouse covers. Greenhouse screens can include strips of the films described herein in combination with strips of other films, particularly films with light-scattering properties or films that promote further transparency. It is also possible to create screens with "open" areas without strips, allowing ventilation through the screen.

[0039] To provide the desired light transmission characteristics, at least 50%, preferably at least 60%, more preferably at least 70%, more preferably at least 80%, and more preferably at least 90% of the strips in the screen should be the coated single-layer or multi-layer film strips 11 described herein. According to one embodiment, all strips 11 in the screen are the single-layer or multi-layer polyester film described herein, and the strips 11 are closely arranged end-to-end to form a substantially continuous surface. Alternatively, the film itself can be installed in the greenhouse. Film

[0040] The strips of film material used to manufacture the greenhouse screens described above comprise a single- or multi-layer polyester film having a transparency of at least 92%, the polyester film having first and second surfaces, and a permanent anti-fog coating applied to at least one of the first and second surfaces of the polyester film. The polyester film described herein preferably comprises at least a base layer (B) containing at least 70% by weight of a thermoplastic polyester. Suitable polyesters include polyesters of ethylene glycol and terephthalic acid (=polyethylene terephthalate, PET), polyesters of ethylene glycol and naphthalene-2,6-dicarboxylic acid (=polyethylene-2,6-naphthalate, PEN), polyesters of 1,4-bis-hydroxymethyl-cyclohexane and terephthalic acid (=poly(1,4-cyclohexane-dimethylene terephthalate), PCDT), and polyesters of ethylene glycol, naphthalene-2,6-dicarboxylic acid, and biphenyl-4,4'-dicarboxylic acid (=polyethylene-2,6-naphthalate bibenzoate, PENBB). Preferred are polyesters consisting of at least 90 mol %, preferably at least 95 mol %, of units of ethylene glycol and terephthalic acid or of units of ethylene glycol and naphthalene-2,6'-dicarboxylic acid. In a particularly preferred version of the polyester film, the base layer (B) is made from a polyethylene terephthalate homopolymer.

[0041] The film material may include additional layers (intermediate or cover layers) as further described below. The cover layers are also preferably made from polyesters as described above, and may be the same or different in composition as the base layer described above.

[0042] Polyesters can be produced, for example, by the transesterification process. This process begins with a dicarboxylic acid ester and a diol, which are reacted with a conventional transesterification catalyst, such as zinc, calcium, lithium, magnesium, or manganese salts. The intermediate product is then polycondensed in the presence of a commonly used polycondensation catalyst, such as antimony trioxide or titanium salts. They can also be produced by the direct esterification process in the presence of a polycondensation catalyst. This process begins directly with a dicarboxylic acid and a diol.

[0043] Suitable aromatic dicarboxylic acids are benzenedicarboxylic acid, naphthalenedicarboxylic acid (for example naphthalene-1,4- or 1,6-dicarboxylic acid), biphenyl-x,x'-dicarboxylic acid (especially biphenyl-4,4'-dicarboxylic acid), diphenylacetylene-x,x'-dicarboxylic acid (especially diphenylacetylene-4,4'-dicarboxylic acid), or stilbene-x,x'-dicarboxylic acid. Among the cycloaliphatic dicarboxylic acids, cyclohexanedicarboxylic acid (especially cyclohexane-1,4-dicarboxylic acid) is advantageous. Among the aliphatic dicarboxylic acids, (C3 to C 19 ) Alkanedioic acids are particularly suitable, whereby the alkane moiety may be linear or branched. Among the heterocyclic dicarboxylic acids, 2,5-furandicarboxylic acid is preferred.

[0044] Aliphatic diols suitable for use in this process include, for example, diethylene glycol, triethylene glycol, aliphatic glycols of the general formula HO-(CH)-OH, where n is an integer from 3 to 6 (especially propane-1,3-diol, butane-1,4-diol, pentane-1,5-diol, and hexane-1,6-diol), or branched aliphatic glycols having up to 6 carbon atoms. Cycloaliphatic diols include cyclohexanediol (especially cyclohexane-1,4-diol). Other suitable aromatic diols include, for example, those of the formula HO-CH-X-CH-OH, where X is -CH-, -C(CH)-, -C(CF)-, -O-, -S-, or -SO-. Bisphenols of the formula HO-CH-CH-OH are also well suited.

[0045] The polyester film advantageously contains particles to achieve a consistent surface roughness and to improve winding of the film.

[0046] Usable particles include, for example, calcium carbonate, amorphous silica, talc, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, lithium fluoride, calcium, barium, zinc, or manganese salts of the dicarboxylic acids used, titanium dioxide, kaolin, or particulate polymers such as cross-linked polystyrene or acrylate particles. Amorphous silica is preferably used as the particles. The particles are preferably used at a concentration of less than 0.5 wt. % based on the total weight of the film. Other particles that affect the surface and rheological properties of the film are preferably not present in the film.

[0047] If the film has a multilayer structure, the particles can be present in all layers, preferably the cover layer.

[0048] The film must also have low transmittance in the wavelength range from below 370 nm to 300 nm. For each wavelength in this specified range, UV light transmittance is less than 40%, preferably less than 30%, and particularly preferably less than 15% (see Measurement Methods for measurement procedures). This not only protects the screen's film material from embrittlement and yellowing, but also protects the plants and equipment in the greenhouse from UV rays. Between 390 and 400 nm, transparency should exceed 20%, preferably more than 30%, and particularly preferably more than 40%, because this wavelength range is already clearly photosynthetically active and a filter that is too strong in this wavelength range can have a negative impact on plant growth.

[0049] The addition of an organic UV stabilizer results in a low UV light transmittance. This low transmittance also protects any flame stabilizers that may be present from rapid destruction and severe yellowing. The organic UV stabilizer is selected from the group of triazines, benzotriazoles, or benzoxazines. Triazines are particularly preferred because they exhibit good thermal stability and low outgassing from the film at processing temperatures of 275 to 310°C, which are typical for PET. Particularly suitable are 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-(hexyl)oxy-phenol (e.g., Tinuvin® 1577, BASF) or 2-(2'-hydroxyphenyl)-4,6-bis(4-phenylphenylphenyl)triazine (e.g., Tinuvin® 1577, BASF). TM 1600, BASF). Using these UV stabilizers, it is already possible to achieve favorable low transparency values ​​below 370 nm at lower stabilizer concentrations, while at the same time achieving higher transparency at wavelengths above 390 nm.

[0050] In the case of films, or in the case of multilayer films, all film layers contain at least one organic UV stabilizer. The UV stabilizer is preferably added to the cover layer or monofilm in an amount of 0.3 to 3 wt. % based on the weight of each layer. A UV stabilizer content of 0.75 to 2.8 wt. % is particularly preferred. Ideally, the cover layer should contain 1.2 to 2.5 wt. % UV stabilizer. In multilayer versions of films, both the base layer and the cover layer preferably contain UV stabilizers, and the weight % UV stabilizer content in the base layer is preferably lower than that in the cover layer. The content of the cover layer refers to triazine derivatives. If a UV stabilizer from the benzotriazole or benzoxazinone group is used in whole or in part instead of a triazine derivative, the substituted portion of the triazine component should be substituted in an amount 1.5 times that of the benzotriazole or benzoxazinone component.

[0051] The film may contain other stabilizers such as phosphorus compounds such as phosphoric acid and its derivatives such as phosphate esters, or phosphorus compounds such as phosphoric acid and its derivatives such as phosphate esters, to provide the film with reduced flammability.

[0052] The total thickness of the polyester film according to the invention can vary within certain limits. It corresponds to 10 to 40 μm, preferably 14 to 23 μm, particularly preferably 14.5 to 20 μm, whereby the base layer (B) of the multilayer version preferably accounts for 60 to 90% of the total thickness. The proportion of the base layer (B) in the three-layer version is preferably at least 60%, particularly preferably at least 70%, and very particularly preferably at least 75% of the total film thickness.

[0053] In addition to self-regenerating materials, polyester raw materials that have undergone a recycling process can also be used. Because recycled polyester raw materials can be obtained from various sources with different raw material quality, it is important to only allow sources that can guarantee a certain degree of purity. In this regard, so-called PCR materials (Post-Consumer Reclaim Materials), which refer to raw materials obtained by recycling old products already used by customers, have been shown to be surprisingly successful for film production and are also suitable as the basis for the films disclosed herein. While the transparency of the film may then be slightly reduced, there may be a slight increase in turbidity due to the low likelihood of impurities. Surprisingly, as will be discussed below, the loss of transparency, which is important for greenhouse screen performance, was less than expected and is likely due to a leveling side effect of the permanent anti-fog coating.

[0054] The film may have a three-layer structure with a first cover layer (A) on one side of the base layer (B) and a second cover layer (C) on the opposite side of the base layer (B). In this case, the two cover layers (A) and (C) form the first and second cover layers (A) and (C). In some embodiments, the first and second cover layers (A) and (C) may be the same. The polyester film may have a two-layer structure with only the first cover layer (A) on the base layer (B).

[0055] Anti-fog coatings can be applied to the first cover layer (A) and / or the second cover layer (C). A three-layer structure can be used to ensure that the base layer (B) contains no particles other than those introduced by the self-regenerating material, resulting in a film with good transparency. In this way, the proportion of recycled reground can be increased, resulting in particularly economical film production. Self-regenerating material is a term used to describe film debris / waste (e.g., hem strips) generated during the film manufacturing process. These can be recycled directly during production or first collected and then added during the production of the base layer (B).

[0056] The proportion of recycled polyester material returned should be as high as possible without impairing the properties of the film described. In the films disclosed herein, the proportion of recycled polyester material in the base layer (B) can be 0 to 60% by weight, preferably 0 to 50% by weight, and particularly preferably 0 to 40% by weight, based on the total weight of the film.

[0057] Greenhouse screens comprising the films disclosed herein have a transparency of at least 92%, preferably 93%, particularly preferably 94%, and ideally at least 94.5%. The higher the transparency, the better the support for plant growth within the greenhouse.

[0058] The clarity of the present invention is achieved by a permanent anti-fog coating on at least one surface of the polyester film.

[0059] Anti-fog coating and anti-reflective modification In one version, an anti-fog coating is applied to one surface of the polyester film. This design achieves a minimum transparency value. The anti-fog coating, described below, must have a lower refractive index than the polyester film. The refractive index of the anti-fog coating at a wavelength of 589 nm in the machine direction of the film is less than 1.64, preferably less than 1.60, and ideally less than 1.58. Furthermore, the dry film thickness of the anti-fog coating must be at least 60 nm, preferably at least 70 nm, and especially at least 80 nm, and up to 150 nm, preferably at most 130 nm, and ideally at most 120 nm. This ensures an ideal transparency improvement in the required wavelength range. Below a thickness of 60 nm, the anti-fog coating no longer contributes significantly to transparency improvement. Above a dry coating thickness of 150 nm, additional applications do not further improve transparency. Furthermore, increased coating consumption reduces the economic viability of the film.

[0060] In another embodiment, the anti-fog coating has a dry film thickness of at least 30 nm, preferably at least 40 nm, and particularly preferably at least 50 nm, and at most <60 nm. This achieves the durable anti-fog effect of the present invention. However, in this embodiment, to achieve the transparency value of at least 92% required by the present invention, the polyester film must be anti-reflectively modified on the side of the film opposite the anti-fog coating. The anti-reflective modification can be formed by either an anti-reflective coating or a top layer modification, but both must have a lower refractive index than polyethylene terephthalate. If the anti-reflective modification is formed by an anti-reflective coating, this coating must have a lower refractive index than the polyester film. The refractive index of the anti-reflective coating at a wavelength of 589 nm in the machine direction of the film is less than 1.64, preferably less than 1.60, and ideally less than 1.58. The antireflective coating can be coated on either surface of the polyester film opposite the antifog coating, i.e., on the surface of the base layer (B) in the case of a single-layer or two-layer film, or on top of the top layer (A) or (C) in the case of a multilayer film.

[0061] Particularly suitable are polyacrylates, silicones and polyurethanes, and polyvinyl acetates.Suitable acrylates are described, for example, in EP-A-0144948, and suitable silicones are described, for example, in EP-A-0769540.Polyacrylate and polyurethane-based coatings are particularly preferred because coating components do not tend to bleed or peel off in greenhouses, whereas silicone-based coatings are much more likely to do so.

[0062] Preferably, the antireflective coating contains less than 10% by weight, more preferably less than 5% by weight, and most preferably less than 1% by weight, of repeating units containing aromatic structural elements. If the repeating units containing aromatic structural elements exceed 10% by weight, the weathering stability of the coating is significantly reduced. The antireflective coating contains at least 1% by weight (dry weight) of a UV stabilizer, preferably Tinuvin 479 or Tinuvin 5333-DW. HALS (hindered amine light stabilizers) are less preferred because they cause significant yellowing of the material during reclamation (recycling of film residues from manufacturing), resulting in a loss of transparency.

[0063] The thickness of the antireflective coating is at least 60 nm, preferably at least 70 nm, and particularly at least 80 nm, and up to 130 nm, preferably up to 115 nm, and ideally up to 110 nm. This provides an ideal transparency improvement in the required wavelength range. In a preferred design, the coating thickness exceeds 87 nm, and particularly preferably exceeds 95 nm. In this preferred design, the antireflective coating thickness is preferably less than 115 nm, and ideally less than 110 nm. Within this narrow thickness range, the increase in transparency is near-optimal, and at the same time, this thickness range increases the reflection of light in the UV and blue ranges compared to the rest of the visible spectrum. This saves on UV stabilizers, but above all, changes the blue / red ratio in favor of the red component. This improves plant growth and increases flowering and fruiting. Suitable antireflective coatings are described in Examples 1 to 3 of EP 3251841.

[0064] When the antireflective modification is formed by a top layer modification, the top layer modification is formed by coextrusion onto the base layer (B) and is located on the opposite side of the film from the antifog coating. Note that the top layer modification is never coextruded onto the cover layer (A) or (C). This top layer modification must be composed of a polyester with a lower refractive index than the polyester of the base layer (B). The refractive index at a wavelength of 589 nm in the machine direction of the top layer applied by coextrusion is less than 1.70, preferably less than 1.65, and particularly preferably less than 1.60. This refractive index is achieved by a polymer containing a comonomer content of at least 2 mol%, preferably at least 3 mol%, and ideally at least 6 mol%. These values ​​for the refractive index cannot be achieved with a comonomer content of less than 2 mol%. The comonomer content is less than 20 mol%, particularly preferably less than 18 mol%, and particularly preferably less than 16 mol%. Above 16 mole %, the UV stability is significantly reduced due to the amorphous nature of the layer, and above 20 mole %, the addition of additional UV stabilizer does not achieve the same level of UV stability as below 16 mole %.

[0065] The comonomer is any monomer except ethylene glycol and terephthalic acid (or dimethyl terephthalate). Preferably, no more than two comonomers are used simultaneously. Isophthalic acid is particularly preferred as a comonomer. Layers with a comonomer content of more than 8 mol % (based on the polyester or its dicarboxylic acid component in the layer) also preferably contain at least 1.5 wt %, and particularly preferably more than 2.1 wt %, of an organic UV stabilizer, based on the total weight of the layer, to compensate for the layer's poor UV stability due to the increased comonomer content.

[0066] In another particularly preferred design, both surfaces of the polyester film are provided with anti-fog coatings having thicknesses of at least 60 nm, preferably at least 70 nm, and particularly at least 80 nm, and up to 150 nm, preferably up to 130 nm, and ideally up to 120 nm. The refractive index of both anti-fog coatings is less than 1.64, preferably less than 1.60, and ideally less than 1.58 at a wavelength of 589 nm in the machine direction of the film. A preferred transparency value of at least 94.5% can be achieved by providing anti-fog coatings on both sides of the polyester film. By using a single coating composition, highly transparent films with very good, permanent anti-fog properties (cold fog and hot fog tests) can be produced in this manner in a particularly economical manner. This film is particularly suitable for use in greenhouses with persistently high humidity (condensation), since the double-sided anti-fog coatings effectively prevent the formation of water droplets on both film surfaces and the resulting light scattering.

[0067] To achieve the durable anti-fog effect of the present invention, a durable anti-fog coating must be applied to at least one side of the film. Durable anti-fog properties of a surface are achieved when the formation of fine water droplets (e.g., condensation in a greenhouse) is not observed on the surface of the polyester film and, at the same time, the coating has good wash-off resistance. The minimum requirement for good anti-fog properties is a high surface energy or a low contact angle α (see the Methods section). Anti-fog properties are sufficiently good if the surface tension of the anti-fog surface is at least 45 mN / m, preferably at least 55 mN / m, and particularly preferably at least 60 mN / m. Durable anti-fog effects can be achieved for at least one year in the cold fog test and at least three months in the hot fog test (desired ratings A and B, see the Methods section or the Examples table). Durable anti-fog properties and a transparency of at least 92% can be achieved by using the coating composition described below.

[0068] The anti-fog coating is formed by drying the anti-fog coating composition as described herein. In the case of a multilayer design with an anti-reflective modified co-extruded layer, the permanent anti-fog coating is applied to the side of the film opposite the anti-reflective modified co-extruded layer.

[0069] The anti-fog coating composition (also referred to herein as coating solution and coating dispersion) according to the present invention is an aqueous solution comprising a) polyvinyl alcohol (PVOH) or a hydrophilic PVOH copolymer, b) an inorganic hydrophilic material, and c) a crosslinker.

[0070] Conventional anti-fog coatings contain surfactants to achieve durable anti-fog properties. However, the use of surfactants is disadvantageous, especially in the case of in-line production. Surprisingly, it has been found that the use of polyvinyl alcohol or hydrophilic amorphous copolymers in anti-fog coatings can provide good durable anti-fog properties and can omit the use of surfactants in the anti-fog coatings.

[0071] Component a) is a polyvinyl alcohol copolymer, or a hydrophilic amorphous copolymer.

[0072] When polyvinyl alcohol copolymers are used, it is advantageous to have a medium to high degree of saponification, such as Gohsenol KP08R (71 to 73.5% saponification), of 60 to 95%, preferably 70 to 90%, to ensure water solubility without the raw material being washed away. Lower saponification copolymers are also possible if they contain functional groups that simplify water solubility in place of acetate groups. In this case, some of the acetate groups in the polyvinyl alcohol are replaced by polyethylene glycol. One example of such a polyvinyl alcohol copolymer is Gohsenol X-LW200, which is highly water-soluble despite having a degree of saponification of only 46 to 53%.

[0073] The polyvinyl alcohol copolymer according to the present invention is AlkenesIt is a diol-polyvinyl alcohol copolymer. Alkenes The diol-polyvinyl alcohol copolymer is preferably Propene diol-polyvinyl alcohol copolymer, Butene diol-polyvinyl alcohol copolymer, Pentene diol-polyvinyl alcohol copolymer, or a mixture thereof. Butene Diol-polyvinyl alcohol copolymers are particularly preferred.

[0074] This particularly preferred type of polyvinyl alcohol copolymer is commercially available under the trade name Nichigo G-Polymer and represents a butanediol-vinyl alcohol copolymer that is highly water soluble at saponification levels of 86 to 99%, exhibits low foaming tendency in aqueous media, and is easily wetted by water droplets as part of a coating on PET, such as G-Polymer OKS8089.

[0075] Polyethylene glycol or cellulose ethers are also commonly considered, but these types of substances are often difficult to coat onto film in so-called in-line processes or have a negative impact on the recyclability and recyclability of the film. Polyethylene glycol cannot be produced intact because its decomposition temperature is within the manufacturing temperature range of polyester film. If the film is coated with an anti-fog coating containing cellulose ether, the recyclability of the film is reduced because temperatures above 250°C, which occur during regeneration, decompose the cellulose ether, resulting in a noticeable yellow discoloration of the resulting regenerated material. Regenerated material produced in this way cannot be used to produce films where optical properties are important.

[0076] Component a) is used in a concentration of 2 to 10% by weight, and preferably 4 to 8% by weight, based on the total solids content of the coating solution. It is characterized by excellent film-forming properties, especially in inline processes.

[0077] Component b) can be inorganic and / or organic particles such as fumed silica, inorganic alkoxides containing silicon, aluminum, or titanium (as described in German Patent Application Publication No. 69833711), kaolin, cross-linked polystyrene, or acrylate particles. Preferably, porous SiO, such as amorphous silica, and pyrogenic metal oxides or aluminum silicates (zeolites) are used. These are used at concentrations of 1 to 6 wt. % (based on the coating dispersion), preferably 2 to 4 wt. % (based on the coating dispersion). Furthermore, SiO nanoparticles can be used, either alone or in combination, to further enhance the wettability of the film surface, absorbing enough water to form a uniform water film, thereby creating an anti-fogging effect. For example, hydrophilic fumed silica, such as Aerodisp W7622 (Evonik Resource Efficiency GmbH), containing 22 wt. % SiO particles with an average aggregate size of 0.10 μm, is particularly suitable.

[0078] The coating dispersion further contains component c) at a concentration of 2 to 10% by weight (based on the coating dispersion), preferably 4 to 8% by weight (based on the coating dispersion). The coating dispersion is preferably an oxazoline-modified polymer (an oxazoline-based crosslinker), available, for example, from Nippon Shokubai under the trade names EPOCROS WS-500 and, in particular, EPOCROS WS-700. The use of the crosslinker in the above amounts improves the abrasion resistance of the coating. Other crosslinkers, such as melamine, are compounds containing a large amount of nitrogen atoms, which tend to impart a yellow color to the film upon recycling. Therefore, melamine is not suitable for use in anti-fog coatings applied to film materials used in greenhouse screens.

[0079] To improve the anti-fog effect, surfactants can sometimes be added to the dispersion. However, this comes at the expense of the drawback of being unable to successfully apply a permanent anti-fog coating to the film in an inline process. Surfactants, in contrast to the other polymeric components of the coating dispersion, can evaporate during film production, rendering them unusable for their intended purpose. Offline processes can address this situation by preselecting milder drying conditions. However, the drawback of offline processes is the additional cost in the form of at least one additional processing step, so additional surfactants should be avoided whenever possible. Additional surfactants that can be added include polyalkylene glycol ethers, polysorbate 80 (polyoxyethylene (20) sorbitan monooleate), sulfosuccinates, alkyl sulfates, and alkylbenzene sulfates. Possible addition amounts are up to 7% by weight of the coating dispersion, preferably <0.2% by weight, and ideally 0% by weight.

[0080] Additionally, the coating solution can contain one or more antifoaming agents. The use of antifoaming agents has proven particularly beneficial for highly concentrated dispersions, as it can reduce foam formation at the applicator, ensuring a stable manufacturing process. However, it must be accepted that the addition of antifoaming agents, or even amphoteric or surfactant additives, can lead to uneven coating of the film surface. Therefore, the use of such additives must be carefully measured, and dosages kept fairly low.

[0081] Above the limits set by the present invention, the use of excess coating components reduces the economic efficiency of the film. Below the limits set by the present invention, the desired coating thickness is too thin, so the desired anti-fog properties are only exhibited to a limited extent (and not permanently). By observing the limits of the present invention, the reaction product of the coating dispersion, especially on biaxially oriented polyester film, provides good anti-fog effect, high wash-off resistance, and high hydrophilicity.

[0082] Manufacturing method The manufacturing process for polyester film is described, for example, in the chapter "Polyesters, Films" in "Handbook of Thermoplastic Polyesters, Ed. S. Fakirov, Wiley-VCH, 2002" or "Encyclopedia of Polymer Science and Engineering, Vol. 12, John Wiley & Sons, 1988." A preferred process for producing a film includes the following steps: The raw materials are melted in an extruder, layer by layer, and extruded through a single-layer or multi-layer slit die onto a cooled take-up roll. The film is then reheated and stretched ("oriented") in the longitudinal direction (MD or machine direction) and the transverse direction (TD or transverse direction), or in both the transverse and longitudinal directions. The film temperature during the stretching process is generally 10 to 60°C higher than the glass transition temperature (Tg) of the polyester used. The stretching ratio for longitudinal stretching is usually 2.5 to 5.0 times, particularly 3.0 to 4.5 times, and the stretching ratio for transverse stretching is 3.0 to 5.0 times, particularly 3.5 to 4.5 times. The longitudinal stretching and transverse stretching may be performed simultaneously (simultaneous stretching), or in any conceivable order. The film is then heat-set in an oven at a temperature of 180 to 240°C, particularly 210 to 230°C. The film is then cooled and rewound.

[0083] The biaxially oriented polyester films described herein are preferably coated in-line, i.e., the coating is applied during the film manufacturing process prior to longitudinal and / or transverse stretching. To achieve good wetting of the polyester film with the aqueous coating composition, the surface is preferably first corona treated. The anti-fog coating can be applied using any suitable conventional method, such as a slot caster or spray process. Particularly preferred is the application of the coating by the "reverse gravure roll coating" process, in which the coating is applied at a rate of 1.0 to 3.0 g / m. 2It can be applied very uniformly at a wet coating weight of 1000 nm. Application by the Mayer rod method is also preferred, as it allows for greater coating thicknesses to be achieved. The coating on the finished film preferably has a thickness of at least 60 nm, preferably at least 70 nm, and especially at least 80 nm. In this case, the inline process is economically more attractive because, by coating both sides, the anti-fog and anti-reflective coatings can be applied simultaneously, saving one process step (see offline process below).

[0084] In another process, the coatings are applied offline. In offline application processes, anti-reflective and / or anti-fog coatings are applied to the corresponding surfaces of polyester film in an additional process step after film production using an engraved roller (forward gravure). The maximum value is determined by the process conditions and the viscosity of the coating dispersion, and the upper limit of the processability of the coating dispersion is found. Anti-fog and anti-reflective coatings may be applied to the surface of multilayer films, i.e., films containing a base layer (B) and two cover layers (A) and (C), two-layer films, i.e., films containing a base layer (B) and one cover layer (A), or single-layer films, i.e., films containing only a base layer (B). While it is possible in principle to apply both anti-fog and anti-reflective coatings to the same surface of a polyester film, applying the anti-fog coating to the primer layer (anti-fog coating to anti-reflective coating) has proven undesirable due to increased material consumption and, on the other hand, the need for additional process steps, which reduces the economic viability of the film.

[0085] Some inline coating processes cannot achieve particularly desirable coating thicknesses due to the high viscosity of the coating dispersion. In these cases, choosing an offline coating process is advisable, as it can process dispersions with low solids content and are often used in wet applications, resulting in improved processability. Furthermore, offline coating can achieve higher coating thicknesses, which has proven advantageous for applications with high demands on the longevity of the anti-fog effect. For example, coating thicknesses of 80 nm or more are particularly easy to achieve with offline processes, which can achieve better and more durable anti-fog effects, but without further improvement in transparency.

[0086] Test method description The following measurement methods were used to evaluate the properties of raw materials and films within the scope of the present invention.

[0087] UV / Vis spectrum, transmittance at wavelength x The optical transmittance of the film at different wavelengths was measured with a UV / Vis two-beam spectrometer (Lambda 950S) from Perkin Elmer USA. A film sample of approximately 3 x 5 cm is inserted into the beam path perpendicular to the measurement beam via a flat sample holder. The measurement beam passes through an integrating sphere and reaches a detector, where the intensity is measured to determine the transparency at the desired wavelength. The background is air. The transmittance is read at the desired wavelength.

[0088] Haze, transparency This test is used to measure the haze and clarity of plastic films, where optical clarity or haze is essential for practical value. Measurements are performed using a BYK Gardner Hazegard Hazemeter XL-21 in accordance with ASTM D 1003-61.

[0089] Determination of refractive index as a function of wavelength Spectroscopic ellipsometry is used to determine the refractive index of the film substrate and applied coating as a function of wavelength.

[0090] The analysis was carried out according to the following references:

[0091] JAWoollam et al.

[0092] First, the uncoated base film or modified coextruded surface was analyzed. To reduce backside reflection, the backside of the foil was roughened with sandpaper of the finest possible grit (e.g., P1000). The films were then measured using a spectroscopic ellipsometer equipped with a rotational compensator, in this case an M-2000 from J.A. Woollam Co., Inc., Lincoln, Nebraska, USA. The machine direction of the sample was parallel to the light beam. The measurement wavelength ranged from 370 to 1000 nm, and the measurement angles were 65, 70, and 75°.

[0093] The ellipsometric data Ψ and Δ were then simulated with the model, where the Cauchy model n(λ)=A+B / λ 2 +C / λ 4 (wavelength λ in μm) is suitable.

[0094] The parameters A, B, and C are varied to match the Ψ (amplitude ratio) and Δ (phase ratio) of the measured spectrum as closely as possible. To check the quality of the model, a mean squared error (MSE) value can be included, which should be as small as possible, and a comparison is made between the model and the measured data (Ψ(λ) and Δ(λ)).

[0095] JPEG0007823037000001.jpg15132a = number of wavelengths, m = number of fitting parameters, N = cos(2Ψ), C = sin(2λ)cos(Δ), S = sin(2Ψ)sin(Δ)

[0096] The Cauchy parameters A, B, and C obtained for the base film allow the calculation of the refractive index n as a function of wavelength, valid in the measurement range from 370 to 1000 nm.

[0097] Coated or modified coextruded layers can also be analyzed in a similar manner. To measure the refractive index of coated and / or coextruded layers, the backside of the film must also be roughened as described above. Here, the Cauchy model can also be used to describe the refractive index as a function of wavelength, but with each layer now on a known substrate. Since the film base parameters are now known, they must be kept constant during modeling and are taken into account in the respective evaluation software (CompleteEASE or WVase). The layer thickness affects the resulting spectrum and must be taken into account during modeling.

[0098] surface free energy The surface free energy was measured according to DIN 55660-1.2. Water, 1,5-pentanediol, and diiodomethane were used as test liquids. Measurements of the static contact angle between the coated film surface and the tangent to the surface contour of a horizontally lying droplet were carried out using a measuring device DSA-100 from Kruss GmbH, Hamburg, Germany. Measurements were performed at 23°C ± 1°C and 50% relative humidity on drained film samples that had been conditioned in a standard climate for at least 16 hours prior. Evaluation of the surface free energy σs (total) according to the Owens-Wendt-Rabel-Kaelble (OWRK) method was carried out using the software Advance Ver. 4 belonging to the device with the following parameters for the surface tension of three standard liquids, as shown in Table 1:

[0099] [Table 1]

[0100] Anti-fogging effect measurement Cold Fog Test: The anti-fog properties of polyester films are measured as follows: In a laboratory conditioned at 23°C and 50% relative humidity, a film sample is sealed onto a menu tray (approximately 17 cm long, 12 cm wide, and 3 cm high) made of amorphous polyethylene terephthalate (APET) containing approximately 50 ml of water. The tray is stored in a refrigerator at 4°C, placed at a 30° angle, and removed for evaluation after 12 hours, 24 hours, 1 week, 1 month, and 1 year. The occurrence of condensation is confirmed when 23°C warm air is cooled to refrigerator temperature. Films with effective anti-fog agents remain transparent even after condensation has formed, because the condensation forms a tightly adhered, transparent film. Without an effective anti-fog agent, a fine mist of droplets forms on the film surface, reducing the film's transparency and, in the worst case, obscuring the contents of the menu tray.

[0101] Another test method is the so-called hot vapor or hot fog test. For this, a Q-Lab QCT condensation tester is used. This simulates the effects of climatic humidity on the anti-fog effect by condensing hot water directly onto the film. Over the course of a few days or weeks, the effects caused by humidity are reproduced within months or years. For this purpose, the water is heated to 60°C in the QCT condensation unit, and the film is clamped in a corresponding holder. The coated film is tilted at an angle of approximately 30°. The evaluation is the same as above. In this test, vapor constantly condenses on the film and then runs off and / or drips again, allowing the film's long-term anti-fog and wash-off resistance to be tested. This can result in easily soluble substances being washed away and reducing the anti-fog effect. This test is also carried out in a laboratory at a temperature of 23°C and a relative humidity of 50%.

[0102] The anti-fogging effect (fog test) is evaluated visually. evaluation: A Transparent film with no visible moisture, i.e. completely transparent: Excellent anti-fogging effect B Random and irregularly distributed water droplets on the surface, discontinuous water film: acceptable anti-fogging effect C Complete layer of large transparent water droplets, poor visibility, lens formation, water droplet formation: low anti-fog effect D Opaque or transparent layer of large water droplets, no transparency, low light transmittance: very low anti-fog effect

[0103] Standard viscosity (SV value) The standard viscosity (SV) of the diluted solution was measured in an Ubbelohde viscometer at (25±0.05) °C according to DIN 53 728 Part 3. Dichloroacetic acid (DCE) was used as the solvent. The concentration of the dissolved polymer was 1 g of polymer / 100 ml of pure solvent. The polymer was dissolved at 60 °C for 1 h. If the sample was not completely dissolved after this, up to two dissolution tests were carried out at 80 °C for 40 min each, after which the solution was allowed to stand for 4100 min. -1 The mixture was centrifuged at a speed of 100 rpm for 1 hour.

[0104] Relative viscosity (η rel =η / η s ) the dimensionless SV value can be calculated as follows: SV=(η rel -1) × 1000

[0105] The proportion of particles in the film or polymer material was determined by ash measurement and corrected by appropriate additional weighing. Weight = (weight equivalent to 100% polymer) / [(100 particle content in wt%) / 100)] [Example]

[0106] The following base materials were used to prepare the films described below.

[0107] PET1 = polyethylene terephthalate from ethylene glycol and terephthalic acid, with an SV value of 820 and a DEG content of 0.9 wt% (diethylene glycol content as monomer).

[0108] PET2 = PCR raw material, e.g. MOPET®, available under the trade name Morssinkhof, is produced from PET flakes obtained from so-called "PET post-consumer products" (mainly PET bottles and trays). Due to the condensation process, the SV value is higher than conventional PET and often exceeds 950, with a DEG content of 1.5% by weight.

[0109] PET3 = polyethylene terephthalate composed of ethylene glycol and dimethyl terephthalate, with an SV value of 820 and a DEG content of 0.9 wt% (diethylene glycol content as a monomer), and a d of 2.5 μm. 50 Contains 1.5% by weight of silicon dioxide pigment Sylobloc 46 with a hydroxybenzoate content of 18 ppm. Produced by the PTA process. The catalyst is potassium titanyl oxalate with 18 ppm titanium. The transesterification catalyst is zinc acetate.

[0110] PET4 = polyethylene terephthalate with an SV value of 700 and containing 20 wt.% Tinuvin 1577. The UV stabilizer has the following composition: 2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-(hexyl)oxyphenol (Tinuvin® 1577 from BASF, Ludwigshafen, Germany). Tinuvin 1577 has a melting point of 149°C and is thermally stable at 330°C.

[0111] PET5 = polyethylene terephthalate with an SV value of 710 and containing 25 mole % isophthalic acid as a comonomer.

[0112] The above raw materials were melted layer by layer in one extruder and extruded through a three-layer slit die (ABA / C layer order) onto a cooled take-up roll. The amorphous pre-film thus obtained was then stretched first in the machine direction. The stretched film was corona treated with a corona discharger and then coated with the above solution by reverse engraving. The volume was 6.6 cm 3 / m2 An engraved roller of 100°C was used. The film was then dried at a temperature of 100°C, after which it was stretched in the transverse direction, heat-set and wound up. The conditions for the individual process steps were as follows: Longitudinal stretching: Temperature: 80 to 115°C Longitudinal stretching ratio: 3, 8 Transverse stretching: Temperature: 80 to 135°C Lateral stretching ratio: 3, 9 Annealing: 225°C for 2 seconds

[0113] Example 1 Surface layers (A) and (C): a mixture of the following: 10% by weight of PET4 7.2% by weight of PET3 82.8% by weight of PET1

[0114] Base layer (B): the following mixture 90% by weight of PET1 10% by weight of PET4

[0115] Coating applied only to the top layer C (single-sided coating): Coating 1: The anti-fogging coating liquid used had the following composition: 84.3% by weight deionized water 5.82 wt% G-polymer OKS 8089 (MCPP Europe GmbH) 6.05% by weight of Epocros WS700 (Nippon Shokubai Co., Ltd.) 3.83% by weight of Aerodisp W7622 (Evonik Resource Efficiency GmbH)

[0116] The different components were slowly added to deionized water under stirring and stirred for at least 30 minutes before use. The solids content was 15% by weight. The thickness of the dried coating was 80 nm.

[0117] Unless otherwise noted, the coatings are applied in an in-line process. The properties of the resulting films are shown in Table 2.

[0118] Example 2 Compared with Example 1, the second upper layer (A) was also coated with Coating 1 in the same manner as in Example 1. Coating of upper layer (C): same as in Example 1

[0119] The individual components were added slowly to deionized water with stirring and stirred for at least 30 minutes before use.

[0120] The solids content was 15 wt %. The dry coating thickness was 80 nm.

[0121] Example 3 In comparison with Example 1, the base layer (B) was produced using PCR raw materials, i.e., 90% PET2 + 10% PET4, and the resulting film showed minimal traces of contaminants originating from the PCR raw materials.

[0122] Examples 4 and 5 The remaining examples are based on the same manufacturing procedure as Inventive Example 1. The base film and coating formulations are listed in Table 2 below.

[0123] Comparative Example 1 Coating 2: In the coating of EP 1 777 251, the dry product of the coating composition consists of a hydrophilic coating containing water, sulfopolyester, a surfactant, and optionally an adhesion-promoting polymer. The film has a hydrophilic surface, which prevents the film from fogging due to water droplets in a short time. The following coating solution composition was used: 1.0 wt. % sulfopolyester (a copolyester of 90 mole % isophthalic acid and 10 mole % sodium sulfoisophthalic acid and ethylene glycol) 1.0 wt. % acrylate copolymer consisting of 60 wt. % methyl methacrylate, 35 wt. % ethyl acrylate, and 5 wt. % N-methylolacrylamide 1.5% by weight of diethylhexyl sulfosuccinic acid sodium salt (Lutensit A-BO BASF AG).

[0124] [Table 2]

[0125] [Table 3]

Claims

1. 1. A greenhouse screen comprising strips (11) of film material interconnected by a knitting, warp knitting or weaving process with a textile system of warp threads (12, 14, 18) and weft threads (13a, 13b; 15; 19) to form a continuous product, at least 50% of said strips (11) comprising a single or multi-layer polyester film having a transparency of at least 92%, said polyester film comprising polyethylene terephthalate and having a first surface and a second surface, and a permanent anti-fog coating applied to at least one of said first surface or said second surface of said polyester film, said anti-fog coating comprising: a) at least one water-soluble polymer; b) an inorganic hydrophilic material, and c) a cross-linking agent; the anti-fog coating is formed from a coating dispersion, the coating dispersion comprising a water-soluble polymer at a concentration of 2 to 10% by weight, an inorganic hydrophilic material at a concentration of 1 to 6% by weight, and a cross-linking agent at a concentration of 2 to 10% by weight; A greenhouse screen, wherein the water-soluble polymer is an alkenediol-polyvinyl alcohol copolymer.

2. 2. The greenhouse screen of claim 1, wherein the polyester film comprises a base layer (B) and a first cover layer (A), or a first cover layer (A) and a second cover layer (C), the first cover layer (A) being applied to a first surface or a second surface of the base layer (B), and the second cover layer (C), if present, being applied to the surface of the base layer (B) opposite the first cover layer (A).

3. 3. A greenhouse screen according to claim 1 or 2, wherein the polyester film has a thickness of at least 10 μm and at most 40 μm.

4. 4. The greenhouse screen according to claim 2 or 3, wherein the base layer (B) is at least 70% by weight of a thermoplastic polyester, based on the total weight of the base layer (B), and the thermoplastic polyester consists of at least 90 mol % of units derived from ethylene glycol and terephthalic acid, or units derived from ethylene glycol and naphthalene-2,6-dicarboxylic acid.

5. 5. The greenhouse screen according to claim 1, wherein the polyester film comprises particles selected from the group consisting of calcium carbonate, amorphous silica, talc, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, aluminum oxide, lithium fluoride, calcium, barium, zinc, or manganese salts of the dicarboxylic acids used, titanium dioxide, kaolin, or particulate polymers from the group consisting of cross-linked polystyrene and acrylate particles.

6. 6. The greenhouse screen according to claim 2, wherein the base layer (B) and, if present, the first cover layer (A) and the second cover layer (C), comprise a UV stabilizer.

7. 7. The greenhouse screen of claim 6, wherein the UV stabilizer is selected from the group consisting of triazines, benzotriazoles, and benzoxazinones, the base layer (B) comprises the UV stabilizer in an amount of 0.3 to 3 wt %, based on the weight of the base layer (B), the first cover layer (A) comprises the UV stabilizer in an amount of 0.3 to 3 wt %, based on the weight of the first cover layer (A), and the second cover layer (C), if present, comprises the UV stabilizer in an amount of 0.3 to 3 wt %, based on the weight of the second cover layer (C).

8. 8. The greenhouse screen of claim 1, wherein the anti-fog coating has a lower refractive index than the polyester film.

9. 9. The greenhouse screen of any one of claims 1 to 8, wherein the alkenediol-polyvinyl alcohol copolymer is selected from the group consisting of propenediol-polyvinyl alcohol copolymer, butenediol-polyvinyl alcohol copolymer, pentenediol-polyvinyl alcohol copolymer, or mixtures thereof.

10. The inorganic hydrophilic material may be fumed silica, inorganic alkoxides containing silicon, aluminum, or titanium, kaolin, cross-linked polystyrene, acrylate particles, porous SiO ２ , amorphous silica, pyrogenic metal oxides, aluminum silicate, SiO ２ 10. The greenhouse screen of claim 1, wherein the surface is selected from the group consisting of nanoparticles and hydrophilic fumed silica.

11. 11. The greenhouse screen of any one of claims 1 to 10, wherein the cross-linking agent is an oxazoline-based cross-linking agent.

12. 12. A greenhouse screen according to any one of claims 1 to 11, wherein the anti-fog coating has a thickness of at least 60 nm and at most 150 nm.

13. the anti-fog coating is applied to the first surface or the second surface of the polyester film, and the surface of the polyester film opposite the anti-fog coating is a) an anti-reflective coating, or b) Top layer modification 13. A greenhouse screen according to any one of claims 1 to 12, having an anti-reflective modification.

14. 14. The greenhouse screen of claim 13, wherein the top layer modification comprises a polyester formed by co-extrusion onto the base layer (B) and having a lower refractive index than the polyester of the base layer (B).

15. 15. A greenhouse screen according to claim 13 or 14, wherein the anti-fog coating has a thickness of at least 30 nm and at most 150 nm when arranged on the side opposite the anti-reflection modification.

16. 16. A greenhouse screen according to any one of claims 1 to 15, wherein at least 60% of the strips in the screen are strips (11) of the coated single or multi-layer polyester film.

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