Single or multilayer polyester film with permanent anti-fog coating and transparency of at least 92%

Abstract

This invention relates to single-layer or multi-layer coated polyester films with a transparency of at least 92%, wherein the polyester film has a first surface and a second surface, wherein a permanent anti-fog coating is applied to at least one surface of the polyester film, and the anti-fog coating comprises at least one water-soluble polymer, an inorganic hydrophilic material, and a crosslinking agent, wherein the water-soluble polymer is polyvinyl alcohol or a hydrophilic polyvinyl alcohol copolymer. Furthermore, this invention also relates to a method for producing the coated polyester film and its use in the production of greenhouse energy-saving mats.

Description

Technical Field

[0001] This invention relates to single-layer or multi-layer highly transparent, biaxially oriented, UV-stable polyester films having a permanent anti-fog coating on at least one side. The films of this invention are suitable for producing greenhouse shading mats and possess specific transparency, permanent anti-fog properties, and high UV stability. This invention also relates to methods for producing said polyester films and their use in greenhouses. Background Technology

[0002] The film used for greenhouse shading mats must meet several requirements. High light transmittance must be ensured within the photosynthetic wavelength range, as this is essential for optimal plant growth. Light transmittance should also be maintained as much as possible even in weather conditions where condensation forms on the shading mat.

[0003] The term "anti-fog" is used to describe water droplets on the surface of a transparent polymer film. Due to the typically high humidity inside greenhouses, condensation forms as water droplets under certain weather conditions (such as diurnal temperature variations), especially on the plant-facing side of the greenhouse shading mat. Besides weather conditions, the different surface tensions of water and polymers promote condensation formation. Films with anti-fog properties prevent water droplet formation and allow for fog-free visibility through the polymer film.

[0004] Typically, antifogging additives are incorporated into the polymer matrix during extrusion or applied as a coating. These additives are usually divalent compounds with nonpolar aliphatic regions for anchoring to the polymer matrix and polar hydrophilic regions that interact with water and reduce the surface tension of water droplets, thus forming a continuous, transparent water film on the membrane surface (due to the hydrophilic surface). The application of antifogging additives should not impair light transmittance and therefore affect the light transmittance of the greenhouse film, thereby not reducing yield. Compared to liquid films, water droplets strongly scatter light and increase reflection, leading to a significant reduction in photosynthesis, especially in the early morning when light is insufficient. Additionally, the non-adhesion and non-falling of water droplets prevent fungal rot of plants and plant parts, and reduce sunburn on plants and plant parts caused by water droplets acting as focusing lenses for incident light on the film surface. However, in cases of severe condensation, droplets can still form, and the antifogging component must be free of any toxic or particularly environmentally harmful substances. Undesirable substances specifically include alkylphenol ethoxylates (e.g., WO1995018210) frequently used in antifogging systems.

[0005] In addition, it is desirable that the greenhouse film be UV-stable, so that the shading pad can be used in the greenhouse for at least 5 years without showing obvious yellowing, embrittlement or cracking on the surface, and without seriously impairing mechanical properties or significantly losing transparency.

[0006] Existing technology

[0007] Polyester films with various transparent anti-fog coatings are known. Therefore, for example, to achieve an anti-fog effect, an interfacial active coating based on a hydrophilic water-soluble polymer and / or surfactant is applied to the surface of the polymer film.

[0008] A fundamental problem associated with water-soluble polymers and / or surfactants is that coatings containing them are easily washed off, thus preventing permanent anti-fogging performance. Conventional polyester films with anti-fogging coatings are described in EP 1647568 B1 and EP 1777251 B1. These polyester films have good mechanical properties but relatively low transparency. Furthermore, their long-term stability under weathering is relatively low. Additionally, the anti-fogging effect of these polyester films has a short lifespan of only a few months because the corresponding anti-fogging additives are easily washed off and are water-soluble, thus the active materials are quickly consumed during use as greenhouse shading pads. EP 1152027 A1, EP 1534776 A1, and EP 2216362 A1 describe LDPE-based polyolefin films or PVC and EVA-based films that apply anti-fogging additives based on inorganic hydrophilic colloidal substances (colloidal silicon, aluminum, etc.) and nonionic, anionic, or cationic surfactants, providing durable anti-fogging performance for food packaging and greenhouse applications. While they offer permanent anti-fog properties, their mechanical properties are significantly reduced compared to polyester-based greenhouse shading mats. Polyethylene (PE) degrades more rapidly under UV radiation than polyethylene terephthalate (PET), making it impossible to achieve the desired long-term stability and corresponding 5-year lifespan, and its economic viability is also negatively impacted; therefore, these polyolefin-based films are excluded from the target application. Furthermore, the poor mechanical stability of polyolefins causes the shading mats to warp and lose most of their sealed structure, resulting in reduced insulation performance.

[0009] EP 3456762 A2 discloses a polyester film having a permanent antifog coating based on a porous material, a polymer-based organic crosslinking agent, an organofunctionalized silane, and one or more surfactants. The film is suitable for further processing into a sunshade mat. These films exhibit good antifog performance in terms of durability, and the achieved transparency is within the desired range. In any case, these films can improve the quality of the antifog effect, especially at relatively high coating thicknesses. Furthermore, the application of organofunctionalized silanes is problematic and undesirable due to regulatory reasons; therefore, such solutions must also be excluded.

[0010] Purpose of the invention

[0011] The drawback of existing membranes is that their anti-fogging performance is not durable or requires the application of an anti-fogging coating in an additional processing step. Furthermore, existing polyester films do not combine a sufficiently permanent anti-fogging coating with high transparency and long-term stability.

[0012] The object of this invention is to prepare a polyester film that has permanent anti-fogging properties and combines high transparency of at least 92% and UV stability for at least 5 years without significant yellowing, embrittlement, or surface cracking, and without compromising the mechanical and optical properties critical to the application. This film should also be economically producible on existing polyester film equipment, single-layer or multi-layer equipment, with a thickness of 10-40 μm.

[0013] Achievement of the goal

[0014] This objective is achieved by providing a single-layer or multi-layer coated polyester film with a transparency of at least 92%, the polyester film having a first surface and a second surface, wherein a permanent anti-fog coating is applied to at least one surface of the polyester film, the anti-fog coating comprising at least one water-soluble polymer, an inorganic hydrophilic material and a crosslinking agent, wherein the water-soluble polymer is polyvinyl alcohol (PVOH) or a hydrophilic polyvinyl alcohol copolymer. Detailed Implementation

[0015] The polyester film of the present invention comprises a base layer (B) having a first surface and a second surface. The polyester film of the present invention may additionally comprise a cover layer (A) applied to the first surface or the second surface of the polyester film. Furthermore, the polyester film of the present invention may additionally comprise another cover layer (C), wherein the cover layer (C) is applied to a surface of the polyester film opposite to the cover layer (A).

[0016] The polyester film of the present invention consists of polyester, additives and at least one coating.

[0017] The base layer (B) preferably comprises at least 70 wt% of a thermoplastic polyester. Polyesters derived from ethylene glycol and terephthalic acid (= polyethylene terephthalate, PET), ethylene glycol and naphthalene-2,6-dicarboxylic acid (= polyethylene 2,6-naphthalenedicarboxylic acid, PEN), 1,4-bis(hydroxymethyl)cyclohexane and terephthalic acid [= poly(1,4-cyclohexanedimethyl terephthalate), PCDT] or ethylene glycol, naphthalene-2,6-dicarboxylic acid and diphenyl-4,4′-dicarboxylic acid (= polyethylene 2,6-naphthalenedicarboxylic acid dibenzoate, PENBB) are suitable for this purpose. Polyesters comprising at least 90 mol%, preferably at least 95 mol%, of ethylene glycol and terephthalic acid units or ethylene glycol and naphthalene-2,6-dicarboxylic acid units are particularly preferred. In a particularly preferred embodiment, the layer consists of a homopolymer of polyethylene terephthalate.

[0018] Other suitable aliphatic diols include diethylene glycol and triethylene glycol, with the general formula HO-(CH2). nAliphatic diols with -OH groups, where n is an integer from 3 to 6 (especially 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol) or branched aliphatic diols having up to 6 carbon atoms. Cyclic aliphatic diols include cyclohexanediol (especially cyclohexane-1,4-diol). Other suitable aromatic diols, for example, correspond to the general formula HO-C6H4-X-C6H4-OH, where X is -CH2-, -C(CH3)2-, -C(CF3)2-, -O-, -S-, or -SO2-. Additionally, bisphenols with the general formula HO-C6H4-C6H4-OH are also suitable.

[0019] Other suitable aromatic dicarboxylic acids are preferably benzene dicarboxylic acid, naphthalene dicarboxylic acid (e.g., naphthalene-1,4- or -1,6-dicarboxylic acid), diphenyl-x,x′-dicarboxylic acid (especially diphenyl-4,4′-dicarboxylic acid), diphenylacetylene-x,x′-dicarboxylic acid (especially diphenylacetylene-4,4′-dicarboxylic acid), or stilbene-x,x′-dicarboxylic acid. Among cyclic aliphatic dicarboxylic acids, cyclohexane dicarboxylic acid (especially cyclohexane-1,4-dicarboxylic acid) may be mentioned. Among aliphatic dicarboxylic acids, (C3-C19)-alkane diacids are particularly suitable, and their alkane moiety can be straight-chain or branched. Among heterocyclic dicarboxylic acids, furan-2,5-dicarboxylic acid may be particularly mentioned.

[0020] For the purposes of this invention, the layer is a polymer layer formed by co-extrusion. This means that the polyester film of this invention is formed from one or more layers.

[0021] For the purposes of this invention, the coating is a dried product of an aqueous dispersion applied to a polyester film, rather than part of the extrusion process of the polyester film itself.

[0022] Any additional covering layers (A) and (C) present on the membrane are preferably also composed of the polyester described above, and their composition may be the same as or different from that of the base layer described above.

[0023] Polyester production can be carried out, for example, via a transesterification process. Here, dicarboxylic acid esters and diols are used as starting materials and reacted in the presence of conventional transesterification catalysts such as zinc, calcium, lithium, magnesium, and magnesium salts. The intermediates are then typically polycondensed in the presence of conventional polycondensation catalysts such as antimony trioxide or titanium salts. Polyester production can also be readily carried out via a direct esterification process in the presence of a polycondensation catalyst. This production method begins directly with dicarboxylic acid and diols.

[0024] To achieve a certain surface roughness and make the membrane easy to roll up, the membrane of the present invention contains particles.

[0025] Applicable particles include, for example, calcium carbonate, amorphous silica, talc, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, alumina, LiF, calcium, barium, zinc, or magnesium salts of the dicarboxylic acid used, titanium dioxide, kaolin, or particulate polymers such as cross-linked polystyrene or acrylate particles. Amorphous silica is preferred as the particles. Based on the total weight of the membrane, the particles are preferably used at a concentration of less than 0.5 wt%. Preferably, no other particles affecting the surface properties and rheological properties of the membrane are present in the membrane of the present invention.

[0026] If the membrane has a multilayer structure, particles can be present in all layers, preferably in the capping layer.

[0027] One advantage of this invention is that the anti-fog coating used in this invention does not contain adhesion-promoting organofunctional silanes. Examples of adhesion-promoting organofunctional silanes include vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, or γ-glycidoxypropyltrimethoxysilane. These silanes are suspected of being carcinogenic and should therefore be avoided.

[0028] The membrane must also have low transmittance in the wavelength range of <370 nm to 300 nm. At any wavelength within the indicated range, this transmittance is less than 40%, preferably less than 30%, and particularly preferably less than 15% (see Measurement Methods for details). This protects the membrane from embrittlement and yellowing, and also protects plants and equipment in the greenhouse from UV light. At 390–400 nm, transparency is greater than 20%, preferably greater than 30%, and particularly preferably greater than 40%, because this wavelength range is already significantly active for photosynthesis, and excessive filtration in this range would adversely affect plant growth. Low UV transparency is achieved by adding organic UV stabilizers. Low UV transparency protects any flame stabilizer, which in turn prevents rapid decomposition and excessive yellowing. Organic UV stabilizers are selected from triazine, benzotriazole, or benzoxazinone. Triazines are particularly preferred here, partly because they have good thermal stability and low membrane exhaust at the conventional processing temperatures of 275–310 °C for PET. 2-(4,6-Diphenyl-1,3,5-triazin-2-yl)-5-(hexyl)oxyphenol (e.g.) 1577 (BASF) or 2-(2′-hydroxyphenyl)-4,6-bis(4-phenylphenyl)triazine (such as Tinuvin) TM 1600 (BASF) is particularly suitable. If these are used, a preferred low transparency value below 370 nm can be obtained at relatively low stabilizer concentrations, while relatively high transparency can be obtained at wavelengths above 390 nm.

[0029] In the case of the membrane or multilayer membrane, all membrane layers contain at least one organic UV stabilizer. In a preferred embodiment, the UV stabilizer is added to the cover layer or monolayer at an amount of 0.3-3 wt% based on the weight of each layer. Particularly preferred is a UV stabilizer content of 0.75-2.8 wt%. The cover layer preferably contains 1.2-2.5 wt% UV stabilizer. In multilayer membrane embodiments, it is preferred that both the cover layer and the base layer contain UV stabilizers, in which case the UV stabilizer content (wt%) in the base layer is preferably less than that in the cover layer. These contents in the cover layer are related to triazine derivatives. If a benzotriazole or benzoxazinone-based UV stabilizer is used to partially or completely replace the triazine derivative, the replacement portion of the triazine component must be replaced by 1.5 times the amount of the benzotriazole or benzoxazinone component.

[0030] Polyester films may contain other stabilizers, such as phosphorus compounds, such as phosphoric acid and its derivatives, such as phosphate esters, or phosphonic acid and its derivatives, such as phosphonate esters, thereby reducing the flammability of the film.

[0031] The total thickness of the polyester film of the present invention can vary within a specific range. The total thickness is 10-40 μm, preferably 14-23 μm, particularly preferably 14.5-20 μm, wherein the proportion of the multilayer intermediate layer B (=base layer) in the total thickness is preferably 60-90%. In a three-layer embodiment, the proportion of the base layer in the total film thickness is preferably at least 60%, particularly preferably at least 70%, and very particularly preferably at least 75%.

[0032] In one embodiment, the membrane has a three-layer structure, with a cover layer (A) on one side of layer (B) (=base layer) and a cover layer (C) on the other side of layer (B). In this case, two layers (A) and (C) form cover layers (A) and (C). An anti-fog coating can be applied to cover layers (A) and / or cover layer (C). The three-layer structure makes it possible to obtain a membrane with good transparency because layer (B) contains no particles other than those introduced by adding recycled materials derived from the same type of polyester membrane. In this way, the proportion of recycled materials can be increased, resulting in particularly economical membrane production. The term "recycled materials derived from the same type of polyester membrane" refers to membrane residues / waste (such as seam strips) generated during membrane production, which can be recycled directly during production or collected first and then added to the production of layer (B).

[0033] The proportion of recycled polyester material should be as high as possible without compromising the performance of the membrane of the present invention. In the membrane of the present invention, the proportion of recycled polyester material in the base layer (B) can be 0-60 wt%, preferably 0-50 wt%, and particularly preferably 0-40 wt%, based on the total weight of the membrane.

[0034] Besides recycled materials from the same type of polyester membrane, recycled polyester raw materials can also be used. Because recycled polyester raw materials can come from various sources and have different raw material qualities, it is important to allow only sources with the lowest possible sorting purity. In this case, it has been found that the application of PCR materials can surprisingly produce membranes suitable as the basis for the membrane of this invention. The membrane transparency then slightly decreases due to a small amount of possible impurities, while the turbidity slightly increases. Surprisingly, the decrease in transparency (as described below, it is a key parameter of the membrane of this invention) is less than expected, which may be due to the leveling side effect of the permanent anti-fog coating. PCR materials (post-consumer recycled materials) refer to raw materials recovered from used products that have already been used by customers.

[0035] The membrane of the present invention has a transparency of at least 92%, preferably 93%, particularly preferably 94%, and ideally at least 94.5%. Higher transparency is more beneficial to the growth of greenhouse plants.

[0036] The transparency of this invention is achieved by having a permanent anti-fog coating on at least one side.

[0037] Coating and Cover Modification

[0038] In one embodiment, an anti-fogging coating is provided on one side of the polyester film. Here, the refractive index of the anti-fogging coating, described below, must be lower than that of the polyester film. In the machine direction of the film, at a wavelength of 589 nm, the refractive index of the anti-fogging coating is less than 1.64, preferably less than 1.60, and ideally less than 1.58. Furthermore, the dry layer thickness of the anti-fogging coating must be at least 60 nm, preferably at least 70 nm, particularly at least 80 nm, and not more than 150 nm, preferably not more than 130 nm, and ideally not more than 120 nm. Thus, an ideal increase in transparency is achieved within the desired wavelength range. When the layer thickness is less than 60 nm, the anti-fogging coating is insufficient to increase transparency. According to the invention, if the dry layer thickness exceeds a maximum of 150 nm, the additional thickness does not result in any further increase in transparency. Additionally, the economics of the film are adversely affected due to the high coating consumption.

[0039] In another embodiment, the dry layer thickness of the anti-fog coating is at least 30 nm, preferably at least 40 nm, and particularly preferably at least 50 nm, and not greater than or equal to 60 nm. This achieves the permanent anti-fog effect of the present invention. To achieve a transparency value of at least 92% as described in the present invention, this embodiment requires anti-reflective modification of the polyester film surface on the reverse side of the anti-fog coating. This anti-reflective modification can be formed by an anti-reflective coating or a coating layer having a lower refractive index than polyethylene terephthalate.

[0040] If the antireflective modification is formed by an antireflective coating, such a coating has a lower refractive index than the polyester film. In this case, the refractive index of the antireflective coating 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. Polyacrylates, silicones, and polyurethanes, as well as polyvinyl acetates, are particularly suitable. Suitable acrylates are described, for example, in EP A 0 144 948, and suitable silicones are described, for example, in EP A 0 769 540. Coatings based on polyacrylates or polyurethanes are particularly preferred because they do not bleed from the coating components or partially peel off in a greenhouse environment, both of which are possible with silicone-based coatings.

[0041] The antireflective coating preferably contains less than 10 wt%, particularly preferably less than 5 wt%, and very particularly preferably less than 1 wt% of repeating units containing aromatic structural elements. When the proportion of repeating units containing aromatic structural elements exceeds 10 wt%, the weather resistance stability of the coating is significantly impaired. The antireflective coating particularly preferably contains at least 1 wt% (based on dry weight) of a UV stabilizer, particularly preferably Tinuvin 479 or Tinuvin 5333-DW. HALS (hindered amine light stabilizers) are less preferred because they cause significant yellowing of the material, thereby reducing transparency during recycling (recycling of film residues during production).

[0042] The antireflective coating has a thickness of at least 60 nm, preferably at least 70 nm and particularly at least 80 nm, and no greater than 130 nm, preferably no greater than 115 nm and ideally no greater than 110 nm. In this way, an ideal increase in transparency is achieved within the desired wavelength range. In a preferred embodiment, the antireflective coating thickness is greater than 87 nm and particularly preferably greater than 95 nm. In this preferred embodiment, the coating thickness is preferably less than 115 nm and ideally less than 110 nm. Within this narrow thickness range, the increase in transparency is close to optimal, while reflection in the UV and blue light regions increases compared to the rest of the visible light in this range. This primarily saves on UV stabilizers, but first and foremost, it causes a shift in the blue / red ratio towards a ratio favorable to red. This thus improves plant growth and increases flower and fruit set rates.

[0043] If the antireflective modification is formed through capping layer modification, the capping layer modification is formed by co-extrusion on the base layer B and located on the film side opposite to the antifog coating. In this case, the layer must be composed of a polyester with a refractive index lower than that of the polyester of the base layer B. The refractive index of the capping layer applied by co-extrusion at a wavelength of 589 nm in the machine direction 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 at least 2 mol%, preferably at least 3 mol%, and ideally at least 6 mol% of comonomers. The refractive index value of the present invention cannot be achieved at less than 2 mol%. The proportion of comonomers is less than 20 mol%, particularly preferably less than 18 mol%, and particularly preferably less than 16 mol%. When it exceeds 16 mol%, the UV stability deteriorates significantly due to the amorphous nature of the layer, and when it exceeds 20 mol%, it is impossible to achieve the same UV stability as when it is less than 16 mol%, even with further addition of UV stabilizers. The comonomers are all monomers 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 greater 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 greater than 2.1 wt%, of an organic UV stabilizer (based on the total weight of the layer) to compensate for the poorer UV stability of the layer when the comonomer content increases.

[0044] In another particularly preferred embodiment, both surfaces of the polyester film have an anti-fogging coating with a thickness of at least 60 nm, preferably at least 70 nm, especially at least 80 nm, and no more than 150 nm, preferably no more than 130 nm, and ideally no more than 120 nm. In this case, the refractive index of the anti-fogging coating at a wavelength of 589 nm in the film machine direction is less than 1.64, preferably less than 1.60, and ideally less than 1.58. A preferred transparency value of at least 94.5% can be achieved by the double-sided anti-fogging coating. Highly transparent films with very good permanent anti-fogging properties (cold fog test and hot fog test) can be prepared in this way particularly economically due to the use of a single coating composition. This film is particularly suitable for greenhouses with consistently high atmospheric humidity (condensation) because the formation of water droplets on both sides of the film surface can be avoided, and the associated light scattering can be effectively prevented by the double-sided anti-fogging coating.

[0045] To achieve the permanent anti-fogging effect of this invention, the polyester film must have a permanent anti-fogging coating on at least one side. Permanent anti-fogging performance is achieved when no fine water droplets (such as condensation in a greenhouse) are observed on the polyester film surface, and the coating exhibits good wash-off resistance. A minimum prerequisite for good anti-fogging performance is high surface energy or a low contact angle α (see Method section). Sufficiently good anti-fogging performance is achieved when the surface tension of the anti-fogging surface is at least 45 mN / m, preferably at least 55 mN / m, and particularly preferably at least 60 mN / m. In cold fog tests, a permanent anti-fogging effect of at least one year can be achieved, and in hot fog tests, a permanent anti-fogging effect of at least three months can be achieved (desired ratings A and B; see Method section or Example table). The permanent anti-fogging performance and at least 92% transparency of this invention are achieved by applying the coating composition described below. The anti-fogging coating is formed by drying the coating composition. In a multilayer embodiment with an anti-reflective modified co-extruded layer, the permanent anti-fogging coating is applied to the polyester film surface opposite to the anti-reflective modified co-extruded layer.

[0046] The anti-fog coating composition of the present invention comprises an aqueous solution containing the following: a) polyvinyl alcohol or hydrophilic PVOH copolymer, b) inorganic hydrophilic material, and c) crosslinking agent.

[0047] To achieve permanent antifogging performance, conventional antifogging coatings contain surfactants. However, the application of surfactants is disadvantageous, especially when produced using online methods. It has been surprisingly found that the use of polyvinyl alcohol or hydrophilic PVOH copolymers in antifogging coatings can result in excellent permanent antifogging performance, potentially eliminating the need for surfactants in such coatings.

[0048] Component a) is polyvinyl alcohol or a hydrophilic PVOH copolymer. It is advantageous to use polyvinyl alcohol with a medium to high degree of hydrolysis (e.g., Gohsenol KP08R (71-73.5% degree of hydrolysis)) having 60-95%, preferably 70-90%, to ensure solubility in water without causing the raw material to be washed away too quickly. Copolymers with a lower degree of hydrolysis may also be used when groups that reduce water solubility replace acetic acid groups. In this case, some of the acetic acid groups in the polyvinyl alcohol are replaced by polyethylene glycol. An example of such polyvinyl alcohol is GohsenX-LW200, which, despite having only a degree of hydrolysis of 46-53%, exhibits excellent water solubility.

[0049] The polyvinyl alcohol copolymer of the present invention is an alkyl glycol-polyvinyl alcohol copolymer. The alkyl glycol-polyvinyl alcohol copolymer is preferably selected from propylene glycol-polyvinyl alcohol copolymer, butanediol-polyvinyl alcohol copolymer, pentanediol-polyvinyl alcohol copolymer, and mixtures thereof. The polyvinyl alcohol copolymer is particularly preferably a butanediol-polyvinyl alcohol copolymer.

[0050] These particularly preferred copolymers are marketed under the trade name Nichigo G Polymer, and are butanediol-vinyl alcohol copolymers that are readily soluble in water at a degree of hydrolysis of 86-99%, do not readily foam in aqueous media, and are easily wetted by water droplets when present as part of a PET coating, such as G-Polymer OKS8089.

[0051] Polyethylene glycol (PEG) or cellulose ethers might also come to mind, but these substances are generally difficult to apply as coatings to membranes in in-line processes, or they negatively impact the membrane's regenerability / recyclability. PEG decomposes within the production temperature range of polyester membranes, making non-destructive production impossible. If the membrane has a coating containing cellulose ethers, this leads to poor regenerability because temperatures exceeding 250°C during regeneration cause the cellulose ethers to decompose, resulting in a clearly visible yellow color in the recycled material. Recycled material produced in this way cannot be used to produce membranes where optical performance is critical.

[0052] Based on the total solids content of the coating solution, the application concentration of component a) is 2-10 wt%, preferably 4-8 wt%. It exhibits excellent film-forming properties, especially in online processes.

[0053] As component b), inorganic and / or organic particles such as pyrolytic silica, inorganic alkoxides containing silicon, aluminum, or titanium (as described in DE 698 33 711), kaolin, cross-linked polystyrene, or acrylate particles can be used. Porous SiO2, such as amorphous silica, and pyrolytic metal oxides or aluminosilicates (zeolites) are preferred. Their application concentration is 1-6 wt%, preferably 2-4 wt%, based on the coating dispersion. Additionally, SiO2 nanoparticles can be used, either additionally or alone, to further increase the wettability of the film surface and absorb sufficient water to form a uniform water film, thereby producing an anti-fogging effect. Hydrophilic pyrolytic silica is particularly suitable.

[0054] Additionally, the coating dispersion may contain component c) at a concentration of 2-10 wt%, preferably 4-8 wt%, based on the coating dispersion. This component is preferably an oxazoline-modified polymer (oxazoline-based crosslinking agent), which is available, for example, from Nippon Shokubai under the trade names EPOCROS WS-500 and, in particular, EPOCROS WS-700. Using the crosslinking agent in the mentioned amounts improves the abrasion resistance of the coating.

[0055] To improve the anti-fogging effect, other surfactants may optionally be added to the dispersion. However, this comes at the cost of not being able to apply a permanent anti-fogging coating to the membrane as easily as in an online process. This is presumably because the surfactant evaporates during membrane production and is therefore no longer used for its intended purpose compared to the other polymer components of the coating dispersion. This situation can be addressed in an offline process by pre-selecting milder drying conditions. However, the disadvantage of the offline method is that at least one further processing step incurs additional costs, so the use of other surfactants should be avoided if possible. Possible surfactants for further addition include, for example, polyalkylene glycol ethers, Polysorbat 80 (polyoxyethylene (20)-sorbitan monooleate), sulfosuccinates, alkyl sulfates, and alkylbenzene sulfates. The possible addition amount in the coating dispersion is up to 7 wt%, but preferably <0.2 wt% and ideally 0 wt%.

[0056] In addition, the coating solution may contain one or more defoamers. The application of defoamers has been found advantageous, particularly in the case of high-concentration dispersions, as it reduces foam formation at the application unit, thereby ensuring a stable production process. However, it must be accepted that the addition of defoamers or further amphoteric substances or surfactants may lead to uneven coating on the film surface. Therefore, the use of such additives must be carefully considered, and the amount added should be kept low.

[0057] Beyond the scope of this invention, the use of excessive coating components is detrimental to the economics of the membrane. Below the scope of this invention, the required coating thickness is too small, thus the desired antifogging performance is obtained only to a limited extent (rather than permanently). If the scope of this invention is followed, the reaction products of the coating dispersion exhibit excellent antifogging effect, strong wash-off resistance, and strong hydrophilicity, particularly on biaxially oriented polyester membranes.

[0058] Production methods

[0059] For example, methods for producing polyester films are described in the "Polyesters, Films" chapter of "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 the film includes the following steps: Each layer of raw material is melted in an extruder and extruded through a single or multiple slit die onto cooled output rolls. This film is then reheated and stretched ("orientation") in the longitudinal (MD or machine direction) and transverse (TD) directions, or in both the transverse and longitudinal directions. The film temperature during the orientation process is typically 10-60°C higher than the glass transition temperature (Tg) of the polyester used, and the longitudinal stretching ratio is typically 2.5-5.0, particularly 3.0-4.5, and the transverse stretching ratio is 3.0-5.0, particularly 3.5-4.5. Longitudinal stretching can also be performed simultaneously with transverse stretching (simultaneous stretching) or in any conceivable order. The film is heat-set in an oven at 180-240°C, especially 210-230°C. It is then cooled and rolled up.

[0060] The biaxially oriented polyester film of the present invention is preferably coated online, i.e., the coating is applied during film production before longitudinal and / or transverse orientation. To obtain good wetting properties of the polyester film with the aqueous coating composition, it is preferable to first perform a corona treatment on the surface. Suitable conventional methods such as slot casting or spraying can be used to apply the coating. Particularly preferred is the application of the coating via a "reverse gravure roll coating" process, wherein the coating concentration can be 1.0-3.0 g / m³. 2 The coating weight (wet) is applied with extreme uniformity. The Meyer bar method is also preferred, as it allows for greater coating thickness. The coating thickness on the finished film is preferably at least 60 nm, more preferably at least 70 nm, and particularly at least 80 nm. The online method is more economically attractive because the anti-fogging and anti-reflective coatings can be applied simultaneously in a double-sided coating operation, thus saving a process step (see the offline method below).

[0061] In another method, the coating is applied offline. Here, in an additional process step after film production, the anti-reflective coating and / or anti-fog coating of the present invention is applied to a suitable surface of the polyester film offline using a gravure roller (forward gravure). The maximum limit is determined by the process conditions and the viscosity of the coating dispersion, while the upper limit is determined by the processability of the coating dispersion. Although it is theoretically possible to apply the anti-fog coating and anti-reflective coating to the same side surface of the base layer B, it has been found that applying the anti-fog coating over a previously applied coating (the anti-fog coating on top of the anti-reflective coating) is disadvantageous because, firstly, material consumption increases, and secondly, further process steps are required, both of which negatively impact the economics of the film. In some online coating processes, a particularly preferred coating thickness cannot be obtained due to the high viscosity of the coating dispersion. In such cases, an offline coating process can be chosen because it allows for the handling of dispersions with lower solids content and higher wet application rates, thus achieving simpler processability. In addition, a greater coating thickness can be obtained in the offline coating process, which has been found to be advantageous in applications where the lifespan of the anti-fog effect is critical. Therefore, a coating thickness of ≥80nm can be achieved particularly easily through an offline process, which makes it possible to achieve better permanent anti-fog performance without further increasing transparency.

[0062] use

[0063] The membrane of this invention is ideally suited as a highly transparent convection barrier, particularly for the production of energy-saving mats in greenhouses. Here, the membrane is typically cut into narrow strips and then used with polyester yarn (which must also be UV-stable) to produce fabrics / layouts suspended in the greenhouse. The membrane strips of this invention can be combined with other membrane strips (especially those with light-scattering effects or further enhanced transparency).

[0064] Alternatively, the membrane itself (full area, non-woven fabric) can also be installed in the greenhouse.

[0065] method

[0066] To characterize the raw materials and the membrane, the following measurement methods were employed for the purposes of this invention:

[0067] UV / Visible light spectrum and transmission at x wavelength

[0068] Transmittance of the film was measured using a UV / visible dual-beam spectrometer (Lambda 950S) from Perkin Elmer, USA. For this purpose, a film sample of approximately (3 × 5) cm in size was placed in the beam path perpendicular to the measurement beam using a planar sample holder. The measurement beam passed through an Ulbricht sphere to the detector, where the intensity was measured to determine the transparency at the desired wavelength.

[0069] Air is used as the background. Transmittance is read at the desired wavelength.

[0070] Turbidity, transparency

[0071] This test is used to determine the turbidity and transparency of polymer films, for which optical clarity or turbidity is critical to the application. Measurements were performed according to ASTM D 1003 61 on a BYK Gardner Hazegard Hazemeter XL 211.

[0072] Measuring the change of refractive index with wavelength

[0073] To determine the refractive index of the film matrix and the coating applied thereon as a function of wavelength, an elliptic polarimeter was used.

[0074] The analysis was conducted using methods based on the following references:

[0075] JAWoollam et al.: Overview of variable-angle spectroscopicellipsometry (VASE): I.Basic theory and typical applications. In: OpticalMetrology, Proc.SPIE, Vol.CR 72 (Ghanim AA-J., Ed.); SPIE-The International Society of Optical Engineering, Bellingham, WA, USA (1999), p.3-28.

[0076] For this purpose, the base film with uncoated or unmodified co-extruded sides was first analyzed. To suppress back-side reflections, the back side of the film was roughened using sandpaper with a very fine abrasive grit (e.g., P1000). The film was then measured using an elliptic polarimeter, specifically an M-2000 from JA Woollam Co., Inc., Lincoln, NE, USA, equipped with a rotation compensator. The sample was machine-oriented parallel to the beam. The measurement wavelength range was 370–1000 nm, and the measurement angles were 65°, 70°, and 75°.

[0077] The model is then applied to replicate the elliptic polarization data ψ and Δ. In this case, the Cauchy model... (Wavelength λ is in μm) is suitable for this purpose. Parameters A, B, and C are varied to make the data as consistent as possible with the measured spectra ψ (amplitude ratio) and Δ (phase ratio). To test the quality of the model, an MSE value, which should be as small as possible, can be included, and the model can be compared with the measured data (ψ(λ) and Δ(λ)).

[0078]

[0079] a = number of wavelengths, m = number of fitting parameters, N = cos(2ψ), C = sin(2ψ)cos(Δ), S = sin(2ψ)sin(Δ)

[0080] The Cauchy parameters A, B, and C obtained from the base film make it possible to calculate the refractive index n as a function of wavelength, effective in the measurement range of 370-1000 nm.

[0081] Coatings or modified co-extruded layers can be analyzed similarly. As mentioned above, the back of the film must also be roughened for analysis of coatings and / or co-extruded layers. The Cauchy model can also be applied here, thus describing the refractive index as a function of wavelength. However, the layers are now situated on a previously known matrix, and since the parameters of the base film are now known, they need to be considered in the respective evaluation software (Complete EASE or WVase) if these parameters are to be kept constant during the simulation. The layer thickness affects the resulting spectrum and must also be considered during the simulation.

[0082] Surface energy

[0083] Surface energy (surface free energy) was measured according to DIN 55660-1,2. Water, 1,5-pentanediol, and diiodomethane were used as test liquids. The static contact angle between the coated film surface and the tangent of the horizontal droplet surface profile was determined using a DSA 100 measuring instrument from Krüss GmbH, Hamburg, Germany. Measurements were performed on film samples that had been discharged and conditioned in standard atmosphere for at least 16 hours prior to the measurement at 23 ± 1 °C and 50% relative humidity. The surface energy σ was evaluated using the Owens-Wendt-Rabel-Kaelble (OWRK) method, with the surface tension parameters of the three standard liquids as specified in Software Advance version 4 of the instrument. s (total):

[0084] Table 1 Surface tension parameters of three standard liquids

[0085]

[0086] Determine the anti-fog effect

[0087] Cold Fog Test: The antifogging performance of the polyester film was determined as follows: In a laboratory environment maintained at 23°C and 50% relative humidity, a film sample was sealed onto a plate (approximately 17cm long, 12cm wide, and 3cm high) composed of amorphous polyethylene terephthalate (APET) and containing approximately 50ml of water. The plate was stored in a refrigerator at 4°C, upright at a 30° angle, and evaluated after 12 hours, 24 hours, 1 week, 1 month, and 1 year. The condensation formed when air at 23°C was cooled to the refrigerator temperature was tested. Films with an effective antifogging agent remained transparent even after condensation, as the condensate formed a continuous, transparent film. Without an effective antifogging agent, fine fog-like droplets formed on the film surface, resulting in reduced film transparency. In the worst-case scenario, the contents of the plate were no longer visible.

[0088] Another testing method is the hot steam or hot fog test. The QCT condensation tester from Q-Lab is used for this purpose. The anti-fogging effect of climatic humidity is simulated by directly condensing hot water onto the membrane. Results resulting from months or years of humidity can be replicated in this way over days or weeks. For this purpose, water is heated to 60°C in the QCT condenser, and the membrane is clamped on a suitable support. The clamping angle is approximately 30°. The evaluation is the same as described above. The long-term anti-fogging effect or washout resistance of the membrane can be tested in this test because steam continuously condenses on the membrane and flows down and / or drips. As easily soluble substances are washed away, the anti-fogging effect decreases. This test is also conducted in a laboratory maintained at 23°C and 50% relative humidity.

[0089] The evaluation of the anti-fog effect (anti-fog test) is conducted visually.

[0090] Rating:

[0091] A transparent film, completely clear with no visible water, is excellent.

[0092] On surface B, water droplets are randomly and irregularly distributed, forming a discontinuous water film, which is acceptable.

[0093] C. A large, intact, transparent layer of water falls away, resulting in poor transparency. This forms a lens, creating water droplets.

[0094] D. A large, opaque or transparent layer of water has fallen, making it impossible to see through; the light transparency is very poor.

[0095] SV value (standard viscosity)

[0096] The standard viscosity in dilute solution SV was measured in an Ubbelohde viscometer at (25 ± 0.05) °C using the method based on DIN 53 728 Part 3. Dichloroacetic acid (DCA) was used as the solvent. The concentration of the polymer was 1 g polymer / 100 ml pure solvent. The polymer was dissolved at 60 °C for 1 hour. If the sample was not completely dissolved after this time, a further dissolution test was performed at 80 °C for 40 minutes in each case, followed by a further dissolution test at 4100 min. -1 The rotation speed was used to centrifuge the solution for 1 hour.

[0097] The dimensionless SV value is derived from the relative viscosity (η). rel =η / η s Determine using the following formula:

[0098] SV=(η rel -1)×1000

[0099] The particle ratio in the membrane or polymer raw material is determined by ash content measurement, and corrected by weighing the corresponding additional amount; that is:

[0100] The amount weighed = (amount corresponding to 100% polymer) / [(content of 100 particles in wt%) / 100]

[0101] Example:

[0102] The following initial materials were used to produce the membrane described below:

[0103] PET1 = polyethylene terephthalate raw material obtained from ethylene glycol and terephthalic acid, with SV of 820 and DEG content of 0.9wt% (diethylene glycol content as monomer).

[0104] PET2 = PCR raw material, obtained from "PET post-consumer goods" (mainly bottles and plates made of PET) and, for example, from PET scraps obtained by Morssinkhof under the trademark MOPET®. Due to the condensation process, its SV is increased compared to conventional PET and is typically higher than 950, with a DEG content of approximately 1.5 wt%.

[0105] PET3 is a polyethylene terephthalate raw material obtained from ethylene glycol and dimethyl terephthalate, with an SV of 820, a DEG content of 0.9 wt% (diethylene glycol content as monomer), and 1.5 wt% of Sylobloc 46 silica pigment with a d50 of 2.5 μm. It is produced via the PTA process. The catalyst is potassium titanium oxalate containing 18 ppm titanium. The transesterification catalyst is zinc acetate.

[0106] PET4 = SV 700 polyethylene terephthalate raw material 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.

[0107] PET5=SV is a polyethylene terephthalate raw material containing 25 mol% isophthalic acid as a comonomer.

[0108] The raw materials are melted in an extruder for each layer and extruded through a three-slot die (ABA sequence) onto a cooled output roll. The amorphous preform obtained by this method is then first longitudinally oriented. The longitudinally oriented film is corona-treated in a corona discharge apparatus and then coated with the above solution using a reverse gravure coating process. The application volume is 6.6 cm³. 3 / m 2 The gravure printing rollers are then used. The film is then dried at 100°C, followed by transverse orientation, fixing, and winding. The conditions for each process step are as follows:

[0109] Vertical orientation:

[0110] Temperature: 80-115℃

[0111] Longitudinal stretch ratio: 3.8

[0112] Lateral orientation:

[0113] Temperature: 80-135℃

[0114] Lateral stretch ratio: 3.9

[0115] Fixed: 2s at 225℃

[0116] Example 1:

[0117] The covering layers (A) and (C) are a mixture of the following substances:

[0118] 10wt% PET4

[0119] 7.2 wt% PET3

[0120] 82.8 wt% PET1

[0121] The base layer (B) is a mixture of the following substances:

[0122] 90wt% PET1

[0123] 10wt% PET4

[0124] Coating on cover layer C (applied on one side):

[0125] Coating 1:

[0126] Apply a coating solution with the following composition:

[0127] 84.3 wt% deionized water

[0128] ·5.82wt% G-Polymer OKS 8089 (MCPP Europe GmbH)

[0129] ·6.05wt% Epocros WS700 (Nippon Shokubai Co.,Ltd.)

[0130] ·3.83wt% Aerodisp W7622 (Evonik Resource Efficiency GmbH)

[0131] Add each component slowly to deionized water while stirring, and stir for at least 30 minutes before use. Solid content is 15 wt%. Dry coating thickness is 80 nm.

[0132] Unless otherwise specified, the coating is applied online. The properties of the resulting film are shown in Table 2.

[0133] Example 2:

[0134] Unlike Example 1, a second cover layer (A) was also applied.

[0135] The coating on the cover layer (C) is the same as in Example 1.

[0136] Add each component slowly to the deionized water while stirring, and stir for at least 30 minutes before use.

[0137] The solid content is 15 wt%. The thickness of the dry coating is 80 nm.

[0138] Example 3:

[0139] Unlike Example 1, the substrate was produced using PCR raw materials. Tiny amounts of very small dust particles derived from the PCR raw materials were visible in the resulting membrane.

[0140] Examples 4-5:

[0141] The compositions of the films and coatings in these two embodiments are shown in Table 2. The properties of the resulting films are also shown in Table 2.

[0142] Comparative Example 1

[0143] Coating 2:

[0144] Coatings according to EP 1 777 251 A1 consist of a hydrophilic coating, wherein the dried product of the coating composition comprises water, a sulfonated polyester, a surfactant, and optionally an adhesion-promoting polymer. These films have a hydrophilic surface that prevents the film from being fogged by water droplets in the short term. Coating solutions with the following compositions are applied:

[0145] • 1.0 wt% sulfonated polyester (copolyester of 90 mol% isophthalic acid and 10 mol% sodium sulfonated isophthalate with ethylene glycol);

[0146] • 1.0 wt% of an acrylic copolymer composed of 60 wt% methyl methacrylate, 35 wt% ethyl acrylate and 5 wt% N-hydroxymethylacrylamide;

[0147] • 1.5 wt% sodium diethylhexyl sulfosuccinate (Lutensit A-BO BASF AG).

[0148] The properties of the membranes obtained in this way are shown in Table 2.

[0149]

Claims

1. A single-layer or multi-layer polyester film with a permanent anti-fog coating having a transparency of at least 92%, the polyester film having a first surface and a second surface, wherein a permanent anti-fog coating is applied to at least one surface of the polyester film, the anti-fog coating composition for the permanent anti-fog coating being an aqueous solution comprising: 2-10 wt% polyvinyl alcohol or a hydrophilic polyvinyl alcohol copolymer, 1-6 wt% an inorganic hydrophilic material, and 2-10 wt% an oxazoline crosslinking agent.

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

3. The polyester film of claim 1 or 2, wherein the thickness of the polyester film is at least 10 µm and not more than 40 µm.

4. The polyester film of claim 3, wherein the thickness of the polyester film is at least 14µm and not more than 23µm.

5. The polyester film of claim 4, wherein the thickness of the polyester film is at least 14.5 µm and not more than 20 µm.

6. The polyester film of claim 2, wherein the base layer (B) comprises at least 70 wt% thermoplastic polyester, wherein the thermoplastic polyester comprises 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.

7. The polyester film of claim 6, wherein the thermoplastic polyester comprises at least 95 mol% of units derived from ethylene glycol and terephthalic acid or units derived from ethylene glycol and naphthalene-2,6-dicarboxylic acid.

8. The polyester film of claim 1 or 2, wherein the polyester film comprises particles selected from: calcium carbonate, amorphous silica, talc, magnesium carbonate, barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, magnesium phosphate, alumina, LiF, calcium, barium, zinc or magnesium salts of dicarboxylic acids, titanium dioxide, kaolin or polymer particles.

9. The polyester film of claim 8, wherein the polymer particles are cross-linked polystyrene or acrylate particles.

10. The polyester film of claim 2, wherein the base layer (B) and, if present, the cover layers (A) and (C) both contain a UV stabilizer.

11. The polyester film of claim 10, wherein the UV stabilizer is selected from triazine, benzotriazole, benzoxazinone, and wherein the base layer (B) and, if present, the cover layers (A) and (C) each contain 0.3-3 wt% of the UV stabilizer on a per-layer weight basis.

12. The polyester film of claim 11, wherein the UV stabilizer is triazine, and wherein the base layer (B) and, if present, the cover layers (A) and (C) each contain 0.75-2.8 wt% of the UV stabilizer on a weight basis.

13. The polyester film of claim 1 or 2, wherein the refractive index of the antifog coating is lower than that of the polyester film.

14. The polyester film of claim 1 or 2, wherein the dry layer thickness of the antifog coating is at least 60 nm and not more than 150 nm.

15. The polyester film of claim 13, wherein the dry layer thickness of the antifog coating is at least 80 nm and not more than 120 nm.

16. The polyester film of claim 1 or 2, wherein the antifog coating is applied to a first or second surface of the polyester film, and the polyester film surface opposite to the antifog coating has been antireflectively modified, which is (1) an antireflective coating or (2) formed by a cover layer modification.

17. The polyester film of claim 16, wherein the cover layer modification is formed by co-extrusion on the base layer (B), wherein the cover layer modification comprises a polyester with a refractive index lower than that of the base layer (B).

18. The polyester film of claim 16, wherein the dry layer thickness of the antifog coating is at least 30 nm and not more than 150 nm.

19. The polyester film of claim 18, wherein the dry layer thickness of the antifog coating is at least 40 nm and not more than 150 nm.

20. The polyester film of claim 19, wherein the dry layer thickness of the antifog coating is at least 50 nm and not more than 150 nm.

21. The polyester film of claim 1 or 2, wherein the aqueous solution of the antifog coating composition comprises 4-8 wt% polyvinyl alcohol or a hydrophilic polyvinyl alcohol copolymer, wherein the polyvinyl alcohol has a degree of hydrolysis of 60-95%, and the hydrophilic polyvinyl alcohol copolymer is an alkanediol-polyvinyl alcohol copolymer.

22. The polyester film of claim 1 or 2, wherein the aqueous solution of the antifog coating composition comprises an inorganic hydrophilic material at a concentration of 2-4 wt%, and the inorganic hydrophilic material is silicon dioxide or an inorganic alkoxide containing silicon, aluminum or titanium.

23. The polyester film of claim 1 or 2, wherein the aqueous solution of the antifog coating composition comprises 4-8 wt% of an oxazoline-based crosslinking agent, and the oxazoline-based crosslinking agent is an oxazoline-modified polymer.

24. A method for producing a coated polyester film according to any one of claims 1-23, wherein the polyester film is prepared by extrusion and is biaxially oriented, an antifog coating composition is applied inline to the polyester film, and the coated polyester film is heat-fixed and rolled up.

25. A method for producing a coated polyester film according to any one of claims 1-23, wherein the polyester film is prepared by extrusion, biaxial orientation, heat fixation and roll-up, and then an antifog coating composition is applied offline to the polyester film by conventional coating techniques, and the polyester film is subsequently dried and rolled up.

26. Use of the coated polyester film according to any one of claims 1-23 for the production of greenhouse energy-saving mats.

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