Filled Polyester Film

Abstract

Provided herein is a biaxially oriented polyester film comprising first inorganic particles P1 and second inorganic particles P2. The film has a total thickness of 1.5 to 8.0 μm. The first inorganic particles P1 have an average particle size of 0.1 to 0.5 μm and are present in the film at a concentration of 100 to 3,000 ppm. The second inorganic particles P2 have an average particle size of 1.50 to 3.50 μm and are present in the film at a concentration of 100 to 2,000 ppm. The film exhibits a haze of 5.0% or less.

Description

[Technical Field]

[0001] The present invention relates to filled polyester films having low haze and low thickness, and to methods for their manufacture. The present invention also relates to the use of the films as functional layers, especially in laminated glass.

[0002] Laminated glass typically includes two or more glass sheets flanked by an interlayer containing one or more layers of adhesive resin, such as polyvinyl butyral (PVB) or ethylene vinyl acetate (EVA), with the resin layers traditionally having a thickness of 0.2 to 1 mm. The glass layers are typically inorganic glass, but can also be made from transparent, rigid organic polymer layers such as polycarbonate. The purpose of the adhesive resin layers and laminate structure is to impart additional or improved properties to the structure, such as improved strength or breakage resistance. Such laminate structures are particularly useful in automotive applications, particularly windshields, and in the construction industry.

[0003] It is also known to incorporate one or more functional layers containing thermoplastic polymers into laminated glass to impart additional desirable properties to the structure, such as light filtering (e.g., selective rejection of certain wavelengths) or reducing solar heat transfer. Various thermoplastic polymers, including polyethylene terephthalate (PET), have been proposed for this purpose. The functional layer may comprise a polymer substrate and one or more coating or lamination layers capable of imparting a desired functionality, such as electrical conductivity. Such conductive layers can provide conventional and known functionality, such as electrical heating. Therefore, the polymer substrate must exhibit not only the required optical properties (i.e., optical performance and / or optical activity), but also good dielectric strength and thermal dimensional stability. The functional layer is typically embedded between two or more layers of adhesive resin, such as PVB or EVA, because such adhesive layers typically adhere better to the outer glass layers than the thermoplastic polymer functional layer.

[0004] In the construction industry, functional laminated glass, sometimes referred to as "architectural glass," is a key technology that is driving demand for new functionalities in such materials. For example, the relatively high radio frequencies of 5G transmission signals (and future 6G and beyond) mean that they are attenuated by modern laminated glass. To enhance 5G signal propagation within buildings and avoid costly internal network installations, it is desirable to provide laminated glass with improved 5G signal transmission. Furthermore, higher-frequency 5G signals have a lower ability to travel long distances or penetrate solid objects (compared to 4G signals), necessitating the installation of more (generally smaller) base stations with line-of-sight to propagate signals, particularly within urban environments. Therefore, another desirable feature is the provision of optically transparent glass that can provide passive reflection of 5G signals, covering dead zones, without the need for a power source.

[0005] Therefore, there is a need for laminated glass that exhibits new functionality and the optical performance of conventional laminated glass. The challenge with using functional layers in laminated glass is to provide a thermoplastic polymer film substrate that has sufficiently high optical performance, including high transparency, low haze, and low optical defects, while maintaining ease of manufacture and good handling characteristics (especially rollability without adhesion or blocking). Optical defects can be particularly problematic in films with very smooth surfaces, which are more susceptible to defects due to rolling. There is a particular need for laminated glass that has new or improved electroactive properties that can be provided by an electroactive functional layer, and therefore the polymer substrate must also exhibit high dielectric strength.

[0006] To address one or more of the above-mentioned problems, it is an object of the present invention to provide a functional film and its polymer substrate suitable for use in laminated glazing. It is a particular object of the present invention to provide a functional film and its polymer substrate suitable for use in functional laminated glazing, the film and substrate exhibiting high transparency, low haze, low optical defects, and high dielectric strength, and in particular, the functional film is electroactive and preferably also has high thermal dimensional stability.

[0007] According to a first aspect of the present invention, there is provided a biaxially oriented polyester film comprising first inorganic particles P1 and second inorganic particles P2, wherein: (i) the film has a total thickness of 1.5 to 8.0 μm; (ii) the first inorganic particles P1 have an average particle size of 0.10 to 0.50 μm, (iii) the first inorganic particles P1 are present in the film at a concentration of 100 to 3000 ppm; (iv) the second inorganic particles P2 have an average particle size of 1.50 to 3.50 μm; (v) the second inorganic particles P2 are present in the film at a concentration of 100 to 2000 ppm; (vi) The film exhibits a haze of 5.0% or less.

[0008] The films of the present invention exhibit a surprisingly advantageous combination of low haze, high clarity, low optical defects, ease of manufacture, good handling properties, and high dielectric strength.

[0009] The polyester film described herein is a free-standing film or sheet, meaning a film or sheet that is capable of existing independently without a supporting base.

[0010] The polyester(s) constituting the film are preferably crystalline polyesters. The polyesters are suitably synthetic linear polyesters. Such polyesters can be obtained by condensing one or more dicarboxylic acids or their lower alkyl (up to 6 carbon atoms) diesters with one or more diols. The dicarboxylic acid component contains at least one aromatic dicarboxylic acid, preferably terephthalic acid, isophthalic acid, phthalic acid, 1,4-, 2,5-, 2,6- or 2,7-naphthalenedicarboxylic acid, preferably terephthalic acid (TA) or 2,6-naphthalenedicarboxylic acid, preferably terephthalic acid. Polyesters can also be used for 4,4'-diphenyldicarboxylic acid, hexahydroterephthalic acid, 1,10-decanedicarboxylic acid, or a compound of the general formula Cn H 2n The polyester may contain one or more residues from other dicarboxylic acids, such as aliphatic dicarboxylic acids including those of (COOH)2 (where n is 2 to 8) (e.g., succinic acid, glutaric acid, sebacic acid, adipic acid, azelaic acid, suberic acid, or pimelic acid, preferably sebacic acid, adipic acid, azelaic acid, more preferably azelaic acid). The diol is preferably selected from aliphatic and cycloaliphatic glycols, such as ethylene glycol (EG), 1,3-propanediol, 1,4-butanediol, and 1,4-cyclohexanedimethanol (CHDM), preferably ethylene glycol (EG). Preferably, the polyester contains only one dicarboxylic acid, preferably an aromatic dicarboxylic acid, preferably terephthalic acid. Preferably, the polyester contains only one glycol, preferably an aliphatic glycol, preferably ethylene glycol. Preferably, the polyester contains one aromatic dicarboxylic acid and one aliphatic glycol. Polyethylene terephthalate (PET) or polyethylene 2,6-naphthalate (PEN), especially PET, are preferred polyesters. The polyester may optionally contain relatively small amounts of one or more residues derived from other dicarboxylic acids and / or diols mentioned above, and if such small amounts are present, the total amount of other dicarboxylic acid(s) is preferably less than 10 mol %, preferably less than 5 mol %, preferably less than 1 mol %, of the total dicarboxylic acid fraction of the polyester in a given layer, and / or the total amount of other diol(s) is preferably less than 15 mol %, preferably less than 10 mol %, preferably less than 5 mol % of the total diol fraction of the polyester in a given layer.

[0011] The polyester is the major component of the film, constituting at least 50% by weight of the total weight of the layers, preferably at least 65% by weight of the total weight of the film, preferably at least 80% by weight, more preferably at least 85% by weight, and typically at least 95% by weight of the total weight of the film.

[0012] The intrinsic viscosity of the polyester film is typically in the range of about 0.5 to about 0.8, preferably about 0.55 to 0.7, and more preferably about 0.55 to 0.65.

[0013] Formation of the polyester is conveniently carried out in well-known manner by condensation or transesterification, generally at temperatures up to about 295° C. In a preferred embodiment, solid state polymerization may be used to increase the intrinsic viscosity of the crystalline polyester to the desired value using conventional techniques well known in the art, for example, using a fluidized bed, such as a nitrogen fluidized bed or a vacuum fluidized bed, using a rotary vacuum dryer.

[0014] Film formation may be accomplished by conventional melt extrusion techniques well known in the art. Generally speaking, this process involves extruding a polymer layer at a temperature within a range appropriate for the melting temperature of the polymer, for example, from about 250°C to about 300°C (or typically not more than about 10°C above the crystalline melting point of the polymer), quenching the extrudate, and orienting the quenched extrudate.

[0015] Orientation may be accomplished by any process known in the art for producing oriented films, such as tubular or flat film processes. Biaxial orientation is achieved by stretching the film in two perpendicular directions within the plane of the film to achieve a satisfactory combination of mechanical and physical properties. Biaxial orientation may be achieved by simultaneous or sequential orientation. Simultaneous orientation is preferred.

[0016] Simultaneous biaxial orientation may be achieved, for example, in a tubular process by extruding a thermoplastic polyester tube, subsequently quenching, reheating, and then expanding it with internal gas pressure to induce transverse orientation and drawing it out at a rate to induce longitudinal orientation. Particularly suitable simultaneous biaxial orientation processes are disclosed in EP-2108673-A and US-2009 / 0117362-A1, the disclosures of which processes are incorporated herein by reference.

[0017] Another preferred approach is the flat-film process, in which the film-forming polyester is extruded through a slot die and rapidly quenched onto a chilled casting drum, quenching the polyester to an amorphous state. Orientation is then achieved by stretching the quenched extrudate in two mutually perpendicular directions at a temperature above the glass transition temperature(s) of the polyester. Sequential orientation can be achieved by stretching the flat, quenched extrudate first in one direction, usually the longitudinal (or machine) direction (MD), i.e., the forward direction through a film stretcher, and then in the transverse direction (TD). Forward stretching of the extrudate is conveniently achieved over a set of rotating rolls or between two pairs of nip rolls, and transverse stretching is then achieved in a stenter apparatus.

[0018] Stretching is generally carried out so that the dimensions of the oriented film are 2.0 to 5.0 times, preferably 4.0 times or less, preferably 3.7 times or less, preferably 2.0 to 4.0 times, more preferably 2.5 to 4.0 times, more preferably 3.0 to 4.0 times, more preferably 3.3 to 3.7 times the original dimensions in each direction of stretching. g Higher temperatures, preferably T g a temperature at least about 5°C higher, preferably at least about 15°C higher than, preferably about T g +5℃~approx.T g +30° C. Typically, stretching is carried out at temperatures ranging from about 5° C. to about 155° C., preferably from about 5° C. to about 110° C. If balanced film properties are desired, the film is suitably stretched equally in the machine and transverse directions.

[0019] It is preferred to use a simultaneous biaxial stretching process, which is particularly advantageous for producing the thin films of the present invention.

[0020] The stretched film is stretched to a temperature above the glass transition temperature(s) of the polyester but above its melting temperature (T MThe film may be, and preferably is, dimensionally stabilized by heat-setting under a dimensional support at a temperature of 0.1°C or less. During heat-setting, a small amount of dimensional relaxation may be performed in the transverse direction (TD) and / or machine direction (MD). The dimensional relaxation is preferably 5.0% or less, and preferably 1.0-3.0%. Dimensional relaxation can be achieved by conventional techniques in the art. In sequential orientation processes, dimensional relaxation in MD is relatively more complicated than in TD because of the need to reduce line tension or speed. For this reason, when MD relaxation is desired, a simultaneous orientation process is preferably used, and in this embodiment, simultaneous relaxation in MD and TD is typically performed. The actual heat-setting temperature and time will vary depending on the film's composition and its desired final heat shrinkage, but should not be selected so as to substantially degrade the film's toughness properties, such as tear resistance. Within these constraints, the heat-setting temperature is typically about 80°C below the film's melting temperature (i.e., T M -80℃~T M about 10°C lower than (i.e., T M −10° C.), more typically at about T M -70℃~approx.T M The heat-setting temperature is preferably −20° C., more preferably in the range of 150 to 245° C., more preferably 225° C. or less, and most preferably 200° C. or less. Preferably, the heat-setting temperature is in the range of 180 to 225° C., more preferably 180 to 200° C. After heat-setting, the film is typically rapidly quenched to induce the desired crystallinity in the polyester.

[0021] Advantageously, the films may be produced in air, and preferably the films are produced in air, i.e., the films are not produced (including the extrusion, casting, and stretching steps) under an atmosphere of an inert gas (such as nitrogen or a noble gas such as argon). Thus, the polyester compositions and films described herein are thermally stable and do not require special handling conditions, particularly an inert atmosphere, during production or storage.

[0022] The final thickness of the polyester film may be in the range of 1.5 to 8.0 μm, preferably 2.0 to 8.0 μm, preferably 2.5 to 8.0 μm, preferably 2.5 to 6.0 μm, preferably 2.5 to 5.0 μm, preferably 3.0 to 5.0 μm, preferably 3.0 to 4.0 μm.

[0023] The concentration and size of the inorganic particles in the film are important factors in providing the desired properties of the film. The concentration and size of the particles in the film, along with the film thickness, can be adjusted to achieve the desired combination of optical properties and handling characteristics of the film. The concentration and size of the first inorganic particles P1 are particularly important for achieving the desired optical properties, and the concentration and size of the second inorganic particles P2 are particularly important for achieving the desired handling characteristics.

[0024] The first inorganic particles P1 are present in the film at a concentration of 100 to 3000 ppm, preferably 100 to 1500 ppm, and preferably 500 to 1000 ppm by weight of the film, and the second inorganic particles P2 are present in the film at a concentration of 100 to 2000 ppm, preferably 200 to 600 ppm, and preferably 400 to 600 ppm by weight of the film.

[0025] The first inorganic particles P1 have an average particle size in the range of 0.10 to 0.50 μm, preferably 0.25 to 0.35 μm.

[0026] The second inorganic particles P2 have an average particle size in the range of 1.50 to 3.50 μm, preferably 1.8 to 3.1 μm, and preferably 1.8 to 2.3 μm.

[0027] The second inorganic particles P2 preferably have an average particle size smaller than the film thickness.

[0028] As used herein, the term "mean particle size" refers to the volume distribution median particle diameter (the equivalent spherical diameter corresponding to 50% of the volume of all particles as read on a cumulative distribution curve relating volume % to particle diameter; often referred to as the "Dv50" or "D50" value).

[0029] The inorganic particles are preferably selected from metalloid oxides (alumina, titania, zirconia, zinc oxide, talc and silica (especially precipitated or diatomaceous silica and silica gel)), silicones, calcined kaolin and alkaline metal salts (such as calcium and barium carbonates and sulfates). Preferably, the inorganic particles are selected from silica and silicones. Preferably, the silica is amorphous silica. Preferably, the silicone is methylsilsesquioxane. Preferably, the first inorganic particles P1 are selected from silica particles and amorphous silica particles. Preferably, the second inorganic particles P2 are selected from silicone particles, preferably spherical silicone particles. Preferably, the silicone is methylsilsesquioxane.

[0030] The polyester films described herein exhibit a haze of 5.0% or less, preferably 3.0% or less, and preferably 2.5% or less.

[0031] Preferably, the polyester film exhibits a total light transmittance (TLT) of at least 85.0%, preferably at least 88.0%, preferably at least 89.0% in the wavelength range of 300 to 800 nm.

[0032] The polyester films described herein preferably have a surface that is sufficiently smooth to allow for the subsequent deposition of a conductive layer or pattern to ensure its integrity and / or uniformity (i.e., the absence of breaks or pin pricks or other discontinuities therein), however, the film surface preferably also exhibits some surface roughness to facilitate manufacturing and handling while providing low haze.

[0033] Preferably, the films described herein exhibit a surface roughness (Ra) of 150 nm or less, preferably 120 nm or less, preferably 110 nm or less, preferably 100 nm or less, preferably in the range of 20 nm to 100 nm, preferably 20 nm to 50 nm.

[0034] The polyester film preferably exhibits a surface roughness (Rt) of 1800 nm or less, preferably 1500 nm or less, preferably 1250 nm or less, typically at least 250 nm, more typically at least 500 nm, preferably in the range of 500 nm to 1250 nm.

[0035] The polyester film preferably exhibits a surface roughness (Rz) of 400 nm or less, preferably 350 nm or less, preferably 300 nm or less, preferably 100 nm or less, more typically at least 150 nm, more typically at least 200 nm, preferably in the range of 100 to 400 nm.

[0036] The dielectric properties of the polyester film are important when the polyester film is used as a substrate for a conductive layer as described herein. Preferably, the film exhibits a thickness-normalized breakdown voltage of at least 350, preferably 350 to 500, typically in the range of 300 to 450 V / μm. Preferably, the breakdown voltage of the film is in the range of 1000 to 2000 V, preferably 1200 to 2000 V.

[0037] The polyester films described herein preferably have a defect density of no more than 20, preferably no more than 15, preferably no more than 10 defects per meter that are less than 500 μm in size. 2 and preferably for defects at least 2.0 mm in size, optical defects / m 2 Also show that is zero.

[0038] The polyester film preferably exhibits isotropic shrinkage, preferably with an MD / TD shrinkage ratio in the range of 1.1 to 1.7, preferably 1.2 to 1.5, with the film preferably shrinking no more than 4.0% in the machine direction (preferably in the range of 2.0 to 4.0%) and no more than 3.0% in the transverse direction (preferably in the range of 1.0 to 3.0%), as measured in air at 150°C for 30 minutes. Such isotropic shrinkage can be achieved by asymmetric stretch ratios and / or by asymmetric dimensional relaxation in the machine and transverse directions, but is preferably achieved by asymmetric dimensional relaxation when the film is stretched symmetrically. Isotropic shrinkage is particularly advantageous for the production of curved laminated glass, such as windshields, which can be curved in one direction and substantially linear in a second, orthogonal direction, or can be curved to different radii of curvature in the orthogonal directions. The manufacture of curved glass panels is generally known in the art and may be achieved, for example, by the method disclosed in US-2007 / 0029026-A.

[0039] In an alternative embodiment, the polyester film exhibits isostatic shrinkage, where the MD and TD shrinkage values ​​are substantially the same (i.e., the MD and TD shrinkage values ​​are within less than 5% of each other), preferably with a shrinkage in each direction of 4.0% or less, preferably 3.0% or less, preferably 1.0-4.0%, preferably 1.0-3.0%, wherein the shrinkage is measured in air at 150°C for 30 minutes.

[0040] As described hereinabove, polyester films can be used as a substrate for conductive layers suitable for providing electrical heating functionality to laminated glass, as is well known in the art, particularly in the automotive industry, where the conductive layer typically takes the form of a pattern of conductive wires. Polyester films with the above-described thermal dimensional stability characteristics are particularly useful in such applications.

[0041] The components of the polyester film can be incorporated into the polyester composition in a conventional manner. For example, the additive(s) can be incorporated by mixing with the monomer reactants from which the film-forming polyester composition is derived, or the additive(s) can be mixed with the polyester composition by tumbling or dry mixing, or by compounding in an extruder, followed by cooling and typically grinding into granules or chips. Masterbatching techniques can also be used.

[0042] The polyester film described herein preferably has a conductive layer disposed on its surface. Preferably, the conductive layer is disposed on the first surface of the film. For the primary end uses described herein, the conductive layer is a transparent conductive layer, which is well known in the art. Suitable transparent conductive layers can be made of any conductive material, particularly metals (e.g., gold and silver), metal alloys and metal oxides (especially doped or mixed metal oxides), and metal nitrides (e.g., titanium nitride). Suitable materials include doped or mixed zinc oxides (e.g., fluorine-doped zinc oxide (FTO), or zinc oxide doped with tin, indium, boron, gallium, or aluminum (e.g., AZO)), doped or mixed tin oxides (e.g., fluorine-doped tin oxide, or indium tin oxide (ITO)), and cadmium oxides (e.g., cadmium stannate). ITO is particularly preferred. The conductive layer is comprised of a conductive material, which may include conductive particles in a binder. The conductive material may be a conductive ink.

[0043] The conductive layer can include a pattern or mesh of conductive material. Such patterns and meshes can be nanoscale and provide various functions. For example, improved 5G transmission in architectural glass can be achieved with a transparent, conductive nanoscale metal mesh. Improved 5G reflectivity can be achieved with a nanoscale patterned transparent conductive layer.

[0044] The conductive material can be deposited by any suitable technique, such as printing, sputtering, or vacuum deposition, particularly sputtering. Any suitable printing technique can be used to apply the conductive ink to the polyester film substrate, including offset, gravure, silkscreen, flexography, thermal transfer printing (TTP), or laser transfer printing (LTP). Other suitable techniques include chemical vapor deposition (CVD), plasma-enhanced CVD, inductively coupled plasma CVD, capacitively coupled CVD, atomic layer deposition (ALD), or reactive thermal evaporation or electron beam evaporation.

[0045] Preferred methods of applying a conductive layer (particularly a silver, zinc boride, or ITO layer, especially an ITO layer), as is well known in the art, are carried out at temperatures below 150°C, preferably below 120°C, preferably not more than 100°C, more preferably not more than 70°C, preferably without the additional step of heating the substrate prior to deposition of the conductive material (i.e., the method is carried out at room temperature (20°C)), more typically at a temperature of at least 40°C. Such methods reduce the demands on the polyester film regarding its dimensional stability requirements, thus allowing the film to be produced at lower heat-setting temperatures (preferably not more than 200°C), which advantageously results in a reduction in the haze component of the film associated with increased crystallization, thereby allowing for the production of thinner films with improved optical clarity.

[0046] A particularly preferred method of preparing conductive layers (especially ITO) comprises sputtering a conductive material, especially at temperatures below 150°C, preferably below 120°C, preferably below 100°C.

[0047] The thickness of the conductive layer is preferably in the range of about 1 nm to about 1000 nm, preferably at least 3 nm, preferably at least about 5 nm, preferably at least about 10 nm, preferably at least about 25 nm, and preferably about 300 nm or less, preferably about 150 nm or less, preferably about 100 nm or less, preferably about 50 nm or less, and preferably about 3 nm to about 300 nm, preferably about 10 nm to about 150 nm, preferably about 25 to 50 nm.

[0048] As used herein, the term "transparent" in the context of a conductive layer means transparent to visible light (preferably measured in the range of 300 to 800 nm herein), whereby an assembly of the polyester film described herein and the conductive film also meets the aforementioned thresholds of total light transmittance and haze specified for the polyester film itself.

[0049] The polyester films described herein above may optionally be provided with one or more optically active layers, particularly layers that at least partially filter or reflect selected wavelengths of radiant solar energy in one or more of the visible, UV, or other wavelength regions, including tinted or colored layers to provide colored and / or UV absorbing or reflective layers. Such layers are well known in the art and comprise materials that absorb or reflect wavelengths in desired regions of the electromagnetic spectrum.

[0050] Advantageously, the polyester films described herein are useful as functional layers in laminated glass, particularly electroactive layers.

[0051] According to a second aspect of the present invention, there is provided a method of making a film as described herein, the method comprising: (i) extruding a layer of molten polyester; (ii) biaxially stretching the layer of molten polyester in two mutually perpendicular directions, preferably by simultaneous biaxial stretching; (iii) heat-curing the film under tension, preferably at a temperature of 225°C or less, preferably 200°C or less, preferably in the range of 180 to 225°C, more preferably 180 to 200°C; (iv) dimensionally relaxing the film by 1.0 to 3.0% in the machine dimension of the film at a temperature in the range of 180 to 200°C, and / or by 1.0 to 3.0% in the transverse dimension of the film at a temperature in the range of 180 to 200°C, and preferably the dimensional relaxation is performed in both directions; (i) optionally disposing a conductive layer on the surface of the film, preferably by sputtering.

[0052] According to a third aspect of the present invention, there is provided a multi-layer assembly comprising a polyester film, preferably having a conductive layer disposed on a surface thereof, as described above in relation to the first aspect of the present invention, and one or more glass layers, preferably the polyester film being sandwiched between two glass layers.

[0053] In a third embodiment, the polyester film may be placed directly on the surface of the glass layer, however, it is preferred that the assembly further comprises an adhesive resin layer between the polyester film and the glass layer.

[0054] In a preferred embodiment of the third aspect (hereinafter referred to as Embodiment 3A), the multilayer assembly includes the polyester film (preferably having a conductive layer disposed on its surface) and further includes first and second glass layers and first and second adhesive resin layers, with the layer order being first glass layer / first adhesive resin layer / polyester film / second adhesive resin layer / second glass layer. In this embodiment, the multilayer assembly is preferably curved at least in part, such that the assembly can be curved in a first direction and substantially linear in a second, orthogonal direction, or can be curved with different degrees of curvature in the orthogonal directions. Such curved laminated glass panels are particularly suitable for windshields or rear windows in automotive applications. As described above, such assemblies containing a conductive layer are particularly suitable as laminated glass panels with electrical heating functions, particularly in the automotive industry. Polyester films with the above-mentioned thermal dimensional stability characteristics, particularly the isotropic shrinkage characteristics, are particularly useful in such applications.

[0055] Preferably, the adhesive resin layer is selected from PVB or EVA, preferably PVB.

[0056] In a further preferred embodiment of the third aspect (hereinafter referred to as embodiment 3B), the multilayer assembly includes a conductive layer comprised of a pattern or mesh of conductive material, particularly one that functionally interacts with radio frequency wavelengths in a range suitable for 5G (or later generation) mobile communication technologies. Thus, the conductive layer is preferably suitable for functionally interacting with radio frequency wavelengths selected from the ranges of 600 MHz to 70 GHz, preferably 600 to 900 MHz (the so-called "low band"), 1.7 to 4.7 GHz (particularly 3.3 to 4.2 GHz) (the so-called "mid band"), and 24 to 54 GHz (particularly 24 to 47 GHz, typically 24 to 30 GHz) (the so-called "high band"), particularly one or more of the mid-band and high-band ranges. This embodiment of the invention is particularly useful for the propagation of mobile communication (particularly 5G) transmission signals in the high-band range, particularly in metropolitan or urban areas. This embodiment of the present invention is also applicable to subsequent generations of mobile communication signals, such as 6G (95 GHz to 3 THz). Such patterns and meshes are nanoscale (i.e., less than 1000 nm, typically 100 nm or less). Such multilayer assemblies are particularly useful as architectural glazing in building structures, especially in metropolitan or urban areas. As described herein above, improved 5G transmission in architectural glazing can be achieved by transparent, conductive nanoscale metal meshes. Improved 5G reflectivity can be achieved by nanoscale patterned transparent conductive layers.

[0057] Particularly useful in the third aspect is the inclusion of one or more optically active layers, as previously mentioned, particularly layers that at least partially filter or reflect selected wavelengths of radiant solar energy in one or more of the visible, UV, or other wavelength ranges, including tinted or colored layers for providing colored and / or UV-absorbing or reflective layers. The optically active layer(s) are preferably disposed between the polyester film and the glass layer, and, if an adhesive resin layer is present, the optically active layer(s) are disposed between the polyester film and the adhesive resin layer. Thus, in embodiment 3A, the optically active layer(s) are preferably disposed between the first adhesive resin layer and the second adhesive resin layer, along with the polyester film.

[0058] The glass in the glass layer is typically an inorganic glass, but can also be made from a transparent, rigid organic polymer layer such as polycarbonate. Preferably, the glass is an inorganic glass (i.e., a silicate or silicon-based glass).

[0059] The multilayer assembly of the third aspect of the present invention is preferably a glass panel, preferably a window, preferably a window (preferably a windscreen or rear window) of an automobile, or an architectural window of a building.

[0060] In a fourth aspect of the present invention, there is provided an electrically heatable laminated glass panel, the laminated glass panel comprising the multilayer assembly of the third aspect, the polyester film having a conductive layer disposed thereon, the multilayer assembly further comprising first and second glass layers and first and second adhesive resin layers, the layer order being first glass layer / first adhesive resin layer / polyester film / second adhesive resin layer / second glass layer. In a preferred embodiment of the fourth aspect, the glass panel is curved, and the polyester film preferably exhibits isotropic shrinkage such that the MD / TD shrinkage ratio is in the range of 1.1 to 1.7, wherein the polyester film exhibits shrinkage of 4.0% or less in the machine direction of the film and shrinkage of 3.0% or less in the transverse direction of the film, the shrinkage being as defined herein above.

[0061] In a fifth aspect of the present invention, there is provided a use of the multilayer assembly of the third aspect, the multilayer assembly comprising the polyester film having a conductive layer disposed thereon, and the multilayer assembly further comprising first and second glass layers and first and second adhesive resin layers as an electrically heatable laminated glass, particularly for automotive applications. In a preferred embodiment of the fifth aspect, the multilayer assembly is curved, and the polyester film preferably exhibits isotropic shrinkage such that the MD / TD shrinkage ratio is in the range of 1.1 to 1.7, where the shrinkage in the machine direction of the film is 4.0% or less and the shrinkage in the transverse direction of the film is 3.0% or less, the shrinkage being as defined herein above.

[0062] In a sixth aspect of the present invention, there is provided a laminated glass panel comprising the multilayer assembly of the third aspect (particularly embodiment 3B), wherein the polyester film has disposed thereon the conductive layer and optionally the one or more optically active layers, the conductive layer comprising a pattern or conductive mesh of conductive material suitable for functionally interacting with radio frequency wavelengths of mobile communication technologies, preferably selected from one or more of the ranges of 600 to 900 MHz, 1.7 to 4.7 GHz and 24 to 54 GHz.

[0063] In a seventh aspect of the present invention, there is provided the use of the multilayer assembly of the third aspect (particularly embodiment 3B) as a laminated glazing panel in the construction of a building, wherein the polyester film has disposed thereon the conductive layer and optionally the one or more optically active layers, the conductive layer comprising a pattern or conductive mesh of conductive material suitable for functionally interacting with radio frequency wavelengths of mobile communication technologies, preferably selected from one or more of the ranges 600-900 MHz, 1.7-4.7 GHz and 24-54 GHz.

[0064] It will be understood that the preferred selection and description of polyester films as set forth above with respect to the first embodiment of the present invention apply equally to each of the second and subsequent embodiments.

[0065] Characteristic measurements The following analyses are used to characterize the films described herein: (i) The optical clarity of the film is assessed by measuring the total luminance transmission (TLT) and haze (% of transmitted visible light scattered) through the total thickness of the film using a BYK Gardner HazeGard Dual in accordance with standard test method ASTM D1003. TLT values ​​and ranges are reported herein over the wavelength range of 300 to 800 nm, unless otherwise specified. (ii) Intrinsic viscosity (in dL / g) of polyesters and polyester films is measured in accordance with ASTM D5225-98 (2003) using a Viscotek™ Y-501C relative viscometer (see, e.g., Hitchcock, Hammons & Yau, American Laboratory (August 1994), "The dual-capillary method for modern-day viscometry") at 25°C using a 0.5 wt% solution of polyester in o-chlorophenol, and the intrinsic viscosity is calculated using the Billmeyer single-point method: η=0.25η red +0.75(ln η rel ) / c During the ceremony, η=intrinsic viscosity (dL / g), η rel = relative viscosity, c = concentration (g / dL), and η red = reduced viscosity (dL / g), which is (η rel -1) / c (η sp It is also expressed as / c, where η sp is the specific viscosity). (iii) Heat shrinkage at a specific, predetermined temperature was evaluated on film samples measuring 254 mm x 254 mm, cut at specific orientations relative to the machine and transverse directions of the film, and marked for visual measurement. After the sample was heated to a predetermined temperature (by placing it in an oven heated to that temperature) and held for a predetermined time interval, it was cooled to room temperature and the dimensions were again measured manually. Heat shrinkage was calculated and expressed as a percentage of the original length. (iv) Measure the film thickness using a Hildebrand Thickness Gauge Series HTG-B according to standard test method ISO 4593:1993. The average of nine measurements is taken. (v) Average particle size is measured by laser light diffraction (preferably Fraunhofer diffraction). Particle sizes referred to herein are measured using a Mastersizer (e.g., 3000) commercially available from Malvern. The median particle size is determined by plotting a cumulative distribution curve representing the percentage of particle volume below a selected particle size and measuring the 50th percentile. (vi) Surface roughness is measured by the mechanical contact method in accordance with ISO 21920-3:2021 using a Form Talysurf® i60 guidance system (Taylor-Hobson Precision) with a 450 mm motorized column, a 60 mm horizontal traverse unit, and a 1 mm vertical range, running Ultra 6.1.12.1 software. The following surface roughness parameters are calculated: Ra is defined as the arithmetic mean peak height of the measured surface, where the peak height is the absolute value of the surface profile deviation from the centerline mean value. Rt is defined as the total height of the roughness profile, which is the difference between the height of the highest peak and the depth of the deepest valley on the measured surface. Rz is defined as the average roughness depth of five Rzi values ​​from five sampling lengths of the surface, and each Rzi (maximum height of the roughness profile) is the sum of the height of the highest peak and the depth of the deepest valley relative to the mean line within the sampling length. Therefore, as is conventional in the art, surface roughness parameters are calculated relative to the average value of the center line of the surface. The center line average value is also called the "mean line" and is the average level of the sample surface. It will be understood that the surface of a polymer film may not be perfectly flat, but may have gentle undulations across the surface. The mean line is a straight line that passes centrally through the waviness and surface height deviations, dividing the profile so that there is equal area above and below the mean line. (vii) Thickness-normalized breakdown voltage (unit: V / μm) is defined herein as the breakdown voltage (V) per micron of film thickness. The breakdown voltage (V) is measured by placing a polyester film (25 cm) between a pair of aluminum foil electrodes. 2 The film breakdown voltage is measured by placing a sample on a film and increasing the voltage (usually 0-3000 V) until film breakdown is observed. The film breakdown voltage is defined as the voltage at which a current of 10 microamperes is detected through the film thickness. The breakdown voltage is reported as the average of 10 measurements. (viii) Optical defect count is a measure of the optical quality of a film and is the number of defects per meter visible on the surface or in the bulk material. 2The number of defects per film is measured using a Dr. Schenk Web Inspection System WFF-1320, consisting of six cameras (camera type: DC-13, 4k, 24V power supply, air-cooled) and six CL40 beamline illumination units (LED type: Luxeon Star LXHL-LD3C: wavelength 627nm; optical output 690mW; beam divergence 130°) installed above the film to be inspected in the film rewinder. The distance between each camera was 400mm, providing a visual inspection range of 420.5mm (on the film surface). The overlap between adjacent cameras was 20.5mm, resulting in a total inspection range of 2420.5mm. The inclination of the illumination and camera to the film surface was 90°. Each illumination unit illuminates the scanning range of one camera unit. The web material was inspected in transmission. The focal length of each camera objective was 105mm. The pixel size was 10 x 10 μm, the number of pixels was 4096, giving a line length of 40.96 mm, and an optical resolution of 103 μm / pixel. The pixel clock was 50 MHz, and the scan rate was 11.95 kHz. In this work, measurements were taken along the film length during the film rewinding operation at a web speed of 10 m / min. Defects are preferably classified by size, typically 110-220 μm, 220-500 μm, and >500 μm, and ≥ 2.0 mm, where the term "size" refers to the longest dimension of the defect and the number of defects is calculated by the number of defects per 1 m. 2 Optical defects are reported as the number of each category size detected per film. Optical defects are defined as irregularities in the film that result in variations in the amount of light transmitted through the film compared to adjacent areas of the film. This manifests as variations in the brightness of the transmitted light signal, commonly referred to as dark or bright events relative to the baseline (defined as the average brightness across the film web). Optical defects in polyester film are typically classified as streaks, gels, catalyst residues, and additive agglomerates.

[0066] The invention is further illustrated by reference to the following examples and accompanying figures, which are not intended to limit the scope of the invention described above. [Example]

[0067] Examples G1 to G10 PET compositions were prepared using conventional techniques to contain various amounts and identities of inorganic particles. The first two series of films were prepared by extruding these compositions in a laboratory-scale film stretching apparatus to obtain amorphous cast extrudates with thicknesses of either 75 μm or 110 μm (i.e., the first "thin" series and the second "thick" series). The cast extrudates were simultaneously stretched in both MD and TD at a temperature of 100°C with a stretch ratio of about 3.5 in each direction. The films were then heat-set under dimensional restraint at an average temperature of about 190°C. The following particles were used: Particle P1: Density 1.32g / cm 3 The amorphous silica particles were used in all Examples G1 to G10. Particles P2: selected from one type of particles of Examples G1 to G3, a different type of particles of Examples G4 to G6, and a mixture of these particles of Examples G7 to G10, with a density of 1.43 g / cm 3 Spherical methylsilsesquioxane particles.

[0068] The average particle size and concentration in these films are reported in Table 1 below. The density of PET is 1.35 g / cm 3 It was. [Table 1]

[0069] The film properties were measured according to the test methods disclosed herein. The final thickness of the "thin film" was about 6 μm (i.e., within the scope of the present invention), and the final thickness of the "thick film" was about 9 μm (i.e., outside the scope of the present invention). The TLT of the films was at least 89.0%.

[0070] Haze was observed to be primarily correlated with the concentration of the larger second inorganic particles P2. Examples G1, G4, G5, and G6, especially the "thin film" sample of Example G1, provided advantageously low haze values, and therefore these formulations were the subject of further investigation.

[0071] The surface roughness of the film is R a was in the range of 40–110 nm. At the same particle concentration, each film in the “thin” series was observed to exhibit higher surface roughness than the corresponding formulation in the “thick” series.

[0072] Examples M1 to M3 A second series of particle-containing PET compositions corresponding to formulation G1 were made using conventional techniques at different film thicknesses, i.e., polyester compositions comprising: (i) 780 ppm of amorphous silica particles P1 having an average particle size of 0.3 μm, and (ii) 540 ppm of spherical methylsilsesquioxane particles P2 having an average particle size of 2.05 μm.

[0073] Films were prepared on a production-scale film line by extruding these compositions at 275°C through a film-forming die onto a water-cooled rotary quenching drum maintained at 25°C, resulting in an amorphous cast extrudate, which was heated to 100°C and then simultaneously stretched in both the MD and TD at a draw ratio of 3.45 in each direction. The films were then heat-set under dimensional restraint at a temperature of approximately 190°C and then subjected to simultaneous dimensional relaxation of 2% in each of the machine and transverse directions at a temperature of 190°C. The optically transparent films were then characterized using the test methods referenced herein. Table 2 below reports the identity and some of the properties of these films (n / m = not determined) and demonstrates that the films of the present invention have an advantageous combination of low caliper, low haze, and low surface roughness with acceptable electrical resistivity properties. Despite their very smooth surfaces, the films were easily manufactured and processed, and no adverse handling or winding characteristics were observed.

[0074] The inventors have determined that dimensional relaxation of the film reduces the heat-set temperature, thereby advantageously resulting in reduced haze in the final film without significantly affecting the shrink performance at 150°C.

[0075] A conductive and transparent ITO layer was deposited on the film surface by sputtering at temperatures below 100 °C to provide a transparent and conductive functional composite film, which enabled the production of functional laminated glass. [Table 2]

Claims

1. A biaxially oriented polyester film comprising first inorganic particles P1 and second inorganic particles P2, (i) the film has a total thickness of 1.5 to 8.0 μm; (ii) the first inorganic particles P1 have an average particle size of 0.1 to 0.5 μm; (iii) the first inorganic particles P1 are present in the film at a concentration of 100 to 3000 ppm; (iv) the second inorganic particles P2 have an average particle size of 1.50 to 3.50 μm; (v) the second inorganic particles P2 are present in the film at a concentration of 100 to 2000 ppm; (vi) The biaxially oriented polyester film, wherein the film exhibits a haze of 5.0% or less.

2. 2. The polyester film according to claim 1, wherein the total thickness is in the range of 2.0 to 8.0 μm, preferably 2.5 to 8.0 μm, preferably 2.5 to 6.0 μm, preferably 2.5 to 5.0 μm, preferably 3.0 to 5.0 μm, preferably 3.0 to 4.0 μm.

3. 10. The polyester film according to any one of the preceding claims, wherein the first inorganic particles P1 are present in the film at a concentration of 100 to 1500 ppm, preferably 500 to 1000 ppm by weight of the film.

4. 10. The polyester film according to any one of the preceding claims, wherein the second inorganic particles P2 are present in the film at a concentration of 200 to 600 ppm, preferably 400 to 600 ppm by weight of the film.

5. 10. The polyester film according to any one of the preceding claims, wherein the first inorganic particles P1 have an average particle size in the range of 0.25 to 0.35 μm and / or the second inorganic particles P2 have an average particle size in the range of 1.8 to 3.1 μm, preferably 1.8 to 2.3 μm.

6. 10. The polyester film according to claim 1, wherein the first inorganic particles P1 are selected from amorphous silica particles.

7. 10. The polyester film according to claim 1, wherein the second inorganic particles P2 are selected from silicone particles, preferably spherical silicone particles, wherein the silicone is methylsilsesquioxane.

8. 10. The polyester film according to any one of the preceding claims, wherein the polyester is polyethylene terephthalate.

9. 10. The polyester film according to claim 1, wherein the second inorganic particles P2 have an average particle size smaller than the film thickness.

10. 10. A polyester film according to any of the preceding claims, exhibiting a surface roughness (Ra) of at most 150 nm, preferably at most 120 nm, preferably at most 110 nm, preferably at most 100 nm, preferably in the range of 20 nm to 100 nm, preferably 20 nm to 50 nm.

11. 10. The polyester film according to any of the preceding claims, exhibiting a surface roughness (Rt) of at most 1800 nm, preferably at most 1500 nm, preferably at most 1250 nm, and preferably in the range of 500 nm to 1250 nm, and / or a surface roughness (Rz) of at most 400 nm, preferably at most 350 nm, preferably at most 300 nm, preferably at least 100 nm, more typically at least 150 nm, more typically at least 200 nm, and preferably in the range of 100 to 400 nm.

12. 10. A polyester film according to any of the preceding claims, exhibiting isotropic shrinkage, preferably with a ratio of MD / TD shrinkage in the range of 1.1 to 1.7, preferably 1.2 to 1.5, wherein preferably said shrinkage in the machine direction of the film is not more than 4.0% (preferably in the range of 2.0 to 4.0%) and said shrinkage in the transverse direction of the film is not more than 3.0% (preferably in the range of 1.0 to 3.0%), said shrinkage being measured in air at 150°C for 30 minutes.

13. 12. The polyester film according to claim 1, which exhibits isostatic shrinkage, wherein the shrinkage in each of the MD and TD directions is at most 4.0%, preferably at most 3.0%, preferably 1.0-4.0%, preferably 1.0-3.0%, measured in air at 150°C for 30 minutes.

14. 10. The polyester film according to any of the preceding claims, wherein the film exhibits a thickness-normalized breakdown voltage of 350 to 500 V / μm and / or a breakdown voltage of 1000 to 2000 V, preferably 1200 to 2000 V.

15. The film has no more than 20, preferably no more than 15, preferably no more than 10 defects per meter that are less than 500 μm in size. 2 and preferably for defects at least 2.0 mm in size, optical defects / m 2 10. The polyester film according to claim 9, further comprising:

16. 10. A polyester film according to any one of the preceding claims, wherein the film has a first surface and a second surface, and wherein on the first surface is disposed a conductive layer preferably selected from metals, metal alloys and metal oxides (especially doped or mixed metal oxides), and metal nitrides, such as doped or mixed zinc oxides (especially fluorine-doped zinc oxide, or zinc oxide doped with tin, indium, boron, gallium, or aluminium), doped or mixed tin oxides (especially fluorine-doped tin oxide, or indium tin oxide), and cadmium oxides (especially cadmium stannate), preferably the conductive layer is a layer of indium tin oxide, and preferably the conductive layer has a thickness in the range from 1 nm to 1000 nm, preferably from 3 nm to 300 nm, preferably from 10 nm to 150 nm, preferably from 25 to 50 nm.

17. 10. A polyester film according to any one of the preceding claims, exhibiting a haze of not more than 3.0%, preferably not more than 2.5%.

18. 10. A polyester film according to any of the preceding claims, exhibiting a total light transmittance (TLT) in the wavelength range of 300 to 800 nm of at least 85.0%, preferably at least 88.0%, preferably at least 89.0%.

19. 10. The polyester film of claim 1, further comprising one or more optically active layers disposed thereon that at least partially filter or reflect selected wavelengths of radiant solar energy in one or more of the visible, UV, or other wavelength regions.

20. A multilayer assembly comprising a polyester film according to any of the preceding claims and one or more glass layers, preferably said polyester film being sandwiched between two glass layers.

21. 21. The multilayer assembly of claim 20, comprising the polyester film, first and second glass layers, and first and second adhesive resin layers, the order of the layers being first glass layer / first adhesive resin layer / polyester film / second adhesive resin layer / second glass layer.

22. 22. The multi-layer assembly according to claim 21, wherein the adhesive resin layer is selected from polyvinyl butyral (PVB) or ethylene vinyl acetate (EVA), preferably PVB.

23. 23. The multilayer assembly of any one of claims 20 to 22, wherein the polyester film has disposed thereon a conductive layer and / or one or more optically active layers that at least partially filter or reflect selected wavelengths of radiant solar energy in one or more of the visible, UV, or other wavelength regions.

24. The multi-layer assembly of any one of claims 20 to 23, which is curved.

25. 25. The multi-layer assembly of claim 24, wherein the polyester film exhibits isotropic shrinkage, preferably with a ratio of MD / TD shrinkage in the range of 1.1 to 1.7, preferably 1.2 to 1.5, and preferably said shrinkage in the machine direction of the film is not more than 4.0% (preferably in the range of 2.0 to 4.0%) and said shrinkage in the transverse direction of the film is not more than 3.0% (preferably in the range of 1.0 to 3.0%), said shrinkage being measured in air at 150°C for 30 minutes.

26. The multilayer assembly according to any one of claims 20 to 25, which is a glass panel.

27. 26. An electrically heatable laminated glazing panel comprising the multilayer assembly according to any one of claims 23 to 25, wherein the polyester film has disposed thereon the electrically conductive layer and, optionally, the one or more optically active layers.

28. 26. Use of the multilayer assembly according to any one of claims 23 to 25 as an electrically heatable laminated glass in automotive applications, wherein the polyester film has disposed thereon the electrically conductive layer and, optionally, the one or more optically active layers.

29. 26. The multilayer assembly according to any one of claims 20 to 25, comprising a conductive layer constituted by the polyester film and a pattern or conductive mesh of a conductive material suitable for functionally interacting with radio frequency wavelengths of mobile communication technologies, preferably selected from one or more of the ranges of 600-900 MHz, 1.7-4.7 GHz and 24-54 GHz.

30. 26. A laminated glass panel comprising the multilayer assembly of any one of claims 20 to 25, wherein the polyester film has disposed thereon the electrically conductive layer and, optionally, the one or more optically active layers, the electrically conductive layer comprising a pattern or mesh of electrically conductive material suitable for functionally interacting with radio frequency wavelengths of mobile communication technologies, preferably selected from one or more of the following ranges: 600-900 MHz, 1.7-4.7 GHz and 24-54 GHz.

31. 26. Use of a multilayer assembly as defined in any one of claims 20 to 25 as a laminated glazing panel in a building construction, wherein said polyester film has disposed thereon said conductive layer and optionally said one or more optically active layers, said conductive layer being constituted by a pattern or conductive mesh of conductive material suitable for functionally interacting with radio frequency wavelengths of mobile communication technologies, preferably selected from one or more of the ranges 600-900 MHz, 1.7-4.7 GHz and 24-54 GHz.

32. A method for producing a biaxially oriented polyester film as defined in any one of claims 1 to 19, comprising the steps of: (i) extruding a layer of molten polyester; (ii) biaxially stretching the layer of molten polyester in two mutually perpendicular directions, preferably by simultaneous biaxial stretching; (iii) heat-setting the film under tension at a temperature of 225°C or less; (iv) dimensionally relaxing the film by 1.0 to 3.0% in the film's mechanical dimension at a temperature in the range of 180 to 200°C, and / or by 1.0 to 3.0% in the film's transverse dimension at a temperature in the range of 180 to 200°C; (v) optionally disposing a conductive layer on the first surface of the film, preferably by sputtering; The method comprising:

33. 33. The method of claim 32, wherein the biaxial stretch ratio in each direction is 4.0 or less, preferably 3.7 or less, preferably in the range of 2.5 to 4.0, preferably in the range of 3.0 to 4.0, preferably in the range of 3.3 to 3.

7.

34. 34. The method of claim 32 or 33, wherein the film is symmetrically stretched, and optionally the dimensional relaxation is asymmetric.

35. A method according to any of claims 32 to 34, wherein the heat curing is carried out at a temperature of up to 200°C, preferably from 180 to 200°C.

36. A method according to any of claims 32 to 35, wherein the conductive layer is disposed on the first surface of the film at a temperature below 150°C, preferably below 120°C, preferably 100°C or less.

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