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WO2014068329A1 - Film de polyester stable aux uv - Google Patents

Film de polyester stable aux uv Download PDF

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Publication number
WO2014068329A1
WO2014068329A1 PCT/GB2013/052865 GB2013052865W WO2014068329A1 WO 2014068329 A1 WO2014068329 A1 WO 2014068329A1 GB 2013052865 W GB2013052865 W GB 2013052865W WO 2014068329 A1 WO2014068329 A1 WO 2014068329A1
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WO
WIPO (PCT)
Prior art keywords
film
absorber
triazine
layer
range
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/GB2013/052865
Other languages
English (en)
Inventor
Xavier Gabriel Philippe BORIES-AZEAU
William Alasdair Macdonald
Simon Shepherd
Nori Mandokoro
Jan Samuel Anthony LARIVIERE
Keith James KILMARTIN
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Mylar Specialty Films US LP
Original Assignee
DuPont Teijin Films US LP
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from GBGB1219780.2A external-priority patent/GB201219780D0/en
Priority claimed from GB201219779A external-priority patent/GB201219779D0/en
Application filed by DuPont Teijin Films US LP filed Critical DuPont Teijin Films US LP
Publication of WO2014068329A1 publication Critical patent/WO2014068329A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/36—Layered products comprising a layer of synthetic resin comprising polyesters
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/18—Layered products comprising a layer of synthetic resin characterised by the use of special additives
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
    • C08J5/18—Manufacture of films or sheets
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K5/00—Use of organic ingredients
    • C08K5/16—Nitrogen-containing compounds
    • C08K5/34—Heterocyclic compounds having nitrogen in the ring
    • C08K5/3467—Heterocyclic compounds having nitrogen in the ring having more than two nitrogen atoms in the ring
    • C08K5/3477—Six-membered rings
    • C08K5/3492—Triazines
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02S—GENERATION OF ELECTRIC POWER BY CONVERSION OF INFRARED RADIATION, VISIBLE LIGHT OR ULTRAVIOLET LIGHT, e.g. USING PHOTOVOLTAIC [PV] MODULES
    • H02S40/00—Components or accessories in combination with PV modules, not provided for in groups H02S10/00 - H02S30/00
    • H02S40/20—Optical components
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F19/00—Integrated devices, or assemblies of multiple devices, comprising at least one photovoltaic cell covered by group H10F10/00, e.g. photovoltaic modules
    • H10F19/80—Encapsulations or containers for integrated devices, or assemblies of multiple devices, having photovoltaic cells
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/50—Properties of the layers or laminate having particular mechanical properties
    • B32B2307/514—Oriented
    • B32B2307/518—Oriented bi-axially
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/50—Properties of the layers or laminate having particular mechanical properties
    • B32B2307/582—Tearability
    • B32B2307/5825—Tear resistant
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/70—Other properties
    • B32B2307/71—Resistive to light or to UV
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/70—Other properties
    • B32B2307/732—Dimensional properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2457/00—Electrical equipment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2457/00—Electrical equipment
    • B32B2457/12—Photovoltaic modules
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
    • C08J2367/02—Polyesters derived from dicarboxylic acids and dihydroxy compounds
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K77/00—Constructional details of devices covered by this subclass and not covered by groups H10K10/80, H10K30/80, H10K50/80 or H10K59/80
    • H10K77/10—Substrates, e.g. flexible substrates
    • H10K77/111—Flexible substrates
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy

Definitions

  • the present invention is concerned with a polyester film which exhibits long-term stability to UV light, in particular, UV light having a wavelength in the range from 360 to 400 nm, and which is of particular use in the manufacture of photovoltaic (PV) cells and other electronic devices, particularly flexible devices.
  • UV light in particular, UV light having a wavelength in the range from 360 to 400 nm
  • PV photovoltaic
  • polyester films offer advantages for their use in the manufacture of electronic or opto- electronic devices, such as electroluminescent (EL) display devices (particularly organic light emitting display (OLED) devices), electrophoretic displays (e-paper), photovoltaic (PV) cells and semiconductor devices (such as organic field effect transistors, thin film transistors and integrated circuits generally).
  • EL electroluminescent
  • OLED organic light emitting display
  • e-paper electrophoretic displays
  • PV photovoltaic
  • semiconductor devices such as organic field effect transistors, thin film transistors and integrated circuits generally.
  • a photovoltaic cell generally comprises a front-plane (or front-sheet); a front-side encapsulant material; the photoactive material on an electrode support substrate; a rear-side encapsulant; a rear back-plane (or back-sheet); and various components to collect and manage the electrical charge.
  • Polyester films have been proposed in the manufacture of various layers in PV cells, for instance the front-plane, the back-plane, the electrode support layer(s).
  • Photovoltaic modules often consisting of many photovoltaic cells, are usually categorized according to the active photovoltaic materials used.
  • Photovoltaic cells containing gallium-arsenide, amorphous silicon, cadmium-telluride, copper-indium-gallium-(di)selenide, dye-sensitized or conductive organic material are often referred to as thin-film photovoltaic cells (TFPV cells), which may or may not be flexible.
  • Thin-film silicon PV cells include protocrystalline, nanocrystalline (nc-Si or nc-Si:H) and black silicon PV cells.
  • Thin-film photovoltaic cells are made by depositing one or more thin layers of photovoltaic material on a substrate, the thickness range of a thin layer varying from 1 or 2 nanometers to tens of micrometer, using a variety of deposition methods and a variety of substrates.
  • a typical organic photovoltaic cell comprises a front-plane, electrodes, a photovoltaic-active layer comprised of a conductive organic polymer or organic small molecule and a back-plane.
  • a feature which the small molecules and polymers used to form the photovoltaic- active layer have in common is a conjugated system of ⁇ -electrons.
  • suitable materials include poly(phenylene vinylene), phthalocyanines, carbon fullerenes and the fullerene derivative [6,6]-phenyl-C 6 rbutyric acid methyl ester (PCBM).
  • the present invention is particularly directed to a film suitable for use as a transparent layer in a PV cell, particularly a thin-film PV cell, and particularly in an organic PV cell as described above.
  • a film should display one or more, and preferably all, the following combination of properties:
  • TLT total light transmission
  • the layer should also exhibit a low haze, although a certain amount of haze can be beneficial (US-5078803; Thin Solid Films 2007, 515, 8695) since it increases the path-length of light as it travels through the photo-active layer.
  • PV cells generally, poor dimensional stability of the polymeric layer, and particularly said transparent polymeric layer in organic PV cells, can result in the cracking of the overlying encapsulant barrier material, and particularly during the elevated temperatures (typically 130 to 160 °C; typically for up to 30 mins) and normally also low pressure experienced during manufacture of the device.
  • elevated temperatures typically 130 to 160 °C; typically for up to 30 mins
  • prior art films have been observed to exhibit wrinkling and movement during the manufacture of a PV device.
  • UV-stability (iv) Good UV-stability. Lack of UV-stability can manifest itself in a yellowing, hazing and cracking of the film on exposure to sunlight thereby decreasing the effective service lifetime of the PV cell, and it is desired to improve UV-stability without detriment to the cost and efficiency of film manufacture, and without detriment to the light transmittance of the film. This is particularly the case for organic PV cells where the photovoltaic-active layer is formed from components which degrade when subjected to UV radiation.
  • Polyester films such as PET (poly(ethylene terephthalate)) are not themselves stable to UV light and will, over time, degrade when exposed to UV light. This degradation of the polyester film impacts upon its optical properties, such as b*, haze and TLT, all of which are important considerations where the film is to be used in a PV cell.
  • optical properties such as b*, haze and TLT, all of which are important considerations where the film is to be used in a PV cell.
  • UV absorber it is common to incorporate a UV absorber into polyester films in order to improve their UV stability. UV absorbers have an extinction coefficient much higher than that of the polyester such that most of the incident UV light is absorbed by the UV absorber rather than by the polyester.
  • UV absorbers generally work by thermally dissipating the absorbed energy, thereby avoiding degradation of the polymer chain and improving the stability of the polyester to UV light.
  • UV absorbers which are used frequently in the field of polyester films are from the triazine family, including, for example, TinuvinTM 1577. This is a triazine UV absorber which is effective in stabilising polyester films to UV light having a wavelength of up to about 360nm.
  • Triazine UV absorbers are known to be stable to photodegradation over long periods of exposure (Rytz et al., Angewandte Makromolekulare Chemie 247, 213-224, 1997) and are therefore useful where the film will, in use, be exposed to UV radiation for prolonged periods of time, such as in a PV device.
  • triazine UV absorbers have limitations as they only absorb UV light having a wavelength of up to about 360 nm, whereas the UV spectrum extends up to 400 nm.
  • UV absorbers which absorb UV light of higher wavelengths in this range have also been developed. Examples of such UV absorbers include benzotriazoles, benzoxazinones and benzophenones.
  • benzotriazole UV absorber is TinuvinTM 360 (also known as MixximTM).
  • MixximTM An example of a benzotriazole UV absorber
  • the disadvantage of benzotriazole UV absorbers is that they are more prone to photodegradation than their triazine counterparts and hence do not provide stability for such prolonged periods of time as the triazine UV absorbers do. Accordingly, it is an object of this invention to provide a polyester film which exhibits long-term and preferably high, UV-stability, in particular to UV light having a wavelength in the range from 360 to 400 nm, without loss of optical properties (e.g. haze, b*, TLT).
  • optical properties e.g. haze, b*, TLT
  • the present invention provides the use of a triazine UV absorber for improving the long-term stability to UV light (particularly UV light having a wavelength in the range from 360 to 400 nm) of a first UV absorber having an absorbance of greater than 0.01 at a concentration of 10ppm in CHCI 3 at a wavelength in the range from 360 to 400nm.
  • the present invention provides a method for improving the long-term stability to UV light (particularly UV light having a wavelength in the range from 360 to 400 nm) of a first UV absorber having an absorbance of greater than 0.01 at a concentration of 10ppm in CHCI 3 at a wavelength in the range from 360 to 400nm, said method comprising adding a triazine UV absorber thereto, preferably wherein the first UV absorber is present in a polymeric matrix, preferably a polymeric film, preferably a polyester film.
  • the present invention provides a method for improving the long-term stability to UV light having a wavelength in the range from 360 to 400nm of a polyester film comprising a first UV absorber having an absorbance of greater than 0.01 at a concentration of 10ppm in CHCI 3 at a wavelength in the range from 360 to 400nm, said method comprising incorporating a triazine UV absorber into the film.
  • a triazine UV absorber which is effective at stabilising a polyester film to UV light of wavelengths of up to 360 nm for periods of prolonged exposure can be used to improve the long-term stability of a first UV absorber which absorbs UV light having wavelengths of up to 400 nm.
  • the triazine UV absorber has a stabilising effect in a region in which it is not, itself, capable of imparting UV stability.
  • long-term refers to UV-stability following prolonged exposure to UV light.
  • the term is used to refer to polyester films which are stable to UV light following exposure to UV light for about 2000 hours or more, preferably about 2500 hours or more, preferably about 3000 hours or more, preferably about 4000 hours or more, preferably about 5000 hours or more, preferably about 6000 hours or more, preferably about 7000 hours or more, preferably about 8000 hours or more, and preferably about 12000 hours or more, in the accelerated ageing (weatherability) test disclosed herein.
  • UV-stability may be assessed by measuring the optical properties of the polyester film (in particular the b*, haze and TLT values) and/or the mechanical properties (in particular the elongation to break), which remain superior relative to films not comprising said first UV absorber and said triazine over this period of time.
  • a triazine UV absorber into a polyester film which comprises a first UV absorber having an absorbance of greater than 0.01 at a concentration of 10ppm in CHCI 3 at a wavelength in the range from 360 to 400nm, a film is produced which will demonstrate excellent UV stability and optical properties even following prolonged exposure to UV light.
  • the present invention provides a polyester film comprising:
  • a first UV absorber having an absorbance of greater than 0.01 at a concentration of 10ppm in CHCI 3 at a wavelength in the range from 360 to 400nm in an amount in the range from 0.1 to 10% based on the total weight of the film; and (ii) a triazine UV absorber in an amount in the range from 0.1 to 30% based on the total weight of the film.
  • the polyester film is a self-supporting film or sheet by which is meant a film or sheet capable of independent existence in the absence of a supporting base.
  • the film is uniaxially or biaxially oriented, preferably biaxially oriented.
  • the polyester(s) which constitute the film is/are typically synthetic linear polyester(s). Suitable polyesters are obtainable by condensing one or more dicarboxylic acid(s) or their lower alkyl (up to 6 carbon atoms) diesters with one or more diols.
  • the dicarboxylic acid component typically contains at least one aromatic dicarboxylic acid, which is preferably terephthalic acid, isophathalic acid, phthalic acid, 1 ,4-, 2,5-, 2,6- or 2,7-naphthalenedicarboxylic acid, and is preferably terephthalic acid or 2,6-naphthalenedicarboxylic acid, and preferably terephthalic acid.
  • the polyester may also contain one or more residues derived from other dicarboxylic acids such as 4,4'-diphenyldicarboxylic acid, hexahydro-terephthalic acid, 1 ,10-decanedicarboxylic acid, and in particular aliphatic dicarboxylic acids including those of the general formula C n H2n(COOH) 2 wherein n is 2 to 8, such as succinic acid, glutaric acid sebacic acid, adipic acid, azelaic acid, suberic acid or pimelic acid, preferably sebacic acid, adipic acid and azelaic acid, and more preferably azelaic acid.
  • dicarboxylic acids such as 4,4'-diphenyldicarboxylic acid, hexahydro-terephthalic acid, 1 ,10-decanedicarboxylic acid, and in particular aliphatic dicarboxylic acids including those of the general formula C n H2n(COOH
  • the diol(s) is/are preferably selected from aliphatic and cycloaliphatic glycols, e.g. ethylene glycol, 1 ,3-propanediol, 1 ,4-butanediol, neopentyl glycol and 1 ,4-cyclohexanedimethanol, preferably from aliphatic glycols.
  • the polyester contains only one glycol, preferably ethylene glycol.
  • the synthetic linear polyester contains one aromatic dicarboxylic acid and one glycol.
  • PET polyethylene terephthalate
  • PEN polyethylene 2,6-naphthalate
  • the film-forming polyester resin is the major component of the substrate, and makes up at least 50% by weight of the total weight of the substrate layer, and in one embodiment at least 65%, typically at least 80%, more typically at least 90%, more typically at least 95%, and in one embodiment at least 99% by weight of the total weight of the substrate layer.
  • the intrinsic viscosity of the polyester film is at least 0.55, preferably at least 0.60, preferably at least 0.65 and preferably at least 0.70.
  • the film of the present invention preferably has a thermal shrinkage after being held at a temperature of 150°C for 30 minutes in the machine direction in the range from about 0.1 to 5, preferably 0.3 to 1.5.
  • the film of the present invention preferably has a thermal shrinkage after being held at a temperature of 150°C for 30 minutes in the transverse direction in the range from 0 to about 5, preferably 0.1 to 1.2.
  • the thermal shrinkage of the film after being held at a temperature of 150°C for 30 minutes is in the range from about 0.01 to 1 , preferably from 0.05 to 0.5 and more preferably no more than 0.10 in the machine direction, and preferably no more than 0.10 and more preferably no more than 0.05 in the transverse direction.
  • Formation of the polyester is conveniently effected in a known manner by condensation or ester interchange, generally at temperatures up to about 295°C.
  • solid state polymerisation may be used to increase the intrinsic viscosity to a desired value, using conventional techniques well-known in the art, for instance using a fluidised bed such as a nitrogen fluidised bed or a vacuum fluidised bed using a rotary vacuum drier.
  • the first UV absorber used in the present invention absorbs UV light in the range from 360 to 400 nm such that it has an absorbance of greater than 0.01 at a concentration of 10ppm in CHCI 3 at a wavelength in the range from 360 to 400nm.
  • the first UV absorber used in the present invention has an absorbance of greater than 0.05, preferably greater than 0.1 , preferably greater than 0.2, preferably greater than 0.3, and preferably greater than 0.4 at a concentration of 10ppm in CHCI 3 at a wavelength in the range from 360 to 400nm, preferably in the range from 380 to 400nm.
  • UV absorbers which have an absorbance of greater than 0.01 at a concentration of 10ppm in CHCI 3 at a wavelength in the range from 360 to 400nm are known.
  • the first UV absorber having an absorbance of greater than 0.01 at a concentration of 10ppm in CHCI 3 at a wavelength in the range from 360 to 400nm is selected from the group consisting of benzotriazole, benzophenone and benzoxazinone UV absorbers.
  • the first UV absorber having an absorbance of greater than 0.01 at a concentration of 10ppm in CHCI 3 at a wavelength in the range from 360 to 400 nm is a benzotriazole UV absorber.
  • Benzotriazole UV absorbers are known and are described in, for example, US-4684679, US- 4812498 and US-4681905, the contents of which are herein incorporated by reference.
  • the benzotriazole UV absorber provides the polyester film with stability to UV radiation up to wavelengths in the range from 360 to 400 nm.
  • the benzotriazole UV absorber used in the present invention absorbs UV light in the range from 360 to 400 nm such that it has an absorbance of greater than 0.01 at a concentration of 10ppm in CHCI 3 at a wavelength in the range from 360 to 400nm.
  • the benzotriazole UV absorber used in the present invention has an absorbance of greater than 0.05, in one embodiment greater than 0.1 , in one embodiment greater than 0.2, in one embodiment greater than 0.3, in one embodiment greater than 0.4 at a concentration of 10ppm in CHCI 3 at a wavelength in the range from 360 to 400nm, preferably 380 to 400nm.
  • the benzotriazole UV absorber is a hydroxyphenyl-benzotriazole, preferably a 2- (hydroxyphenyl)-benzotriazole.
  • the benzotriazole UV absorber is a compound of formula (I):
  • R 1 is H or halogen (preferably H)
  • R 2 is H, CMS alkyl optionally substituted with one or more alkyl, alkenyl, halogen, aryl or heteroaryl, C 2 -is alkenyl optionally substituted with one or more alkyl, alkenyl, halogen, aryl or heteroaryl or C 3 .
  • i 8 cycloalkyl optionally substituted with one or more alkyl, alkenyl, halogen, aryl or heteroaryl
  • R 3 is CMS alkyl optionally substituted with one or more alkyl, alkenyl, halogen, aryl or heteroaryl, CMS alkyl-C(0)0-Ci-i 8 alkyl, wherein the alkyl groups may be optionally substituted with one or more alkyl, alkenyl, halogen, aryl or heteroaryl.
  • the compound of formula (I) is a dimer wherein the link between the two units is provided by R 2 .
  • R 3 is CMe 2 CH 2 CMe 3 .
  • a particularly preferred benzotriazole UV absorber is phenol-2,2'-methylene-bis(6-(2H benzotriazol-2-yl)-4-(1 , 1 ,3,3-tetramethylbutyl), which is available commercially as TinuvinTM 360 (also known as MixximTM BB100) from BASF.
  • TinuvinTM 360 is a dimer of formula (I) wherein R 1 is H, R 2 is CH 2 and R 3 is CMe 2 CH 2 CMe 3 .
  • the benzotriazole UV absorber used may be 2-(2H-benzotriazol-2-yl)-4,6-bis(1- methyl-1-phenylethyl)phenol which is available commercially as TinuvinTM 234 from BASF.
  • TinuvinTM 234 is a benzotriazole of formula (I) wherein R 1 is H, R 2 is CMe 2 Ph and R 3 is CMe 2 Ph.
  • the benzotriazole UV absorber used may be 2-(5-chloro-2H-benzotriazole-2-yl)-6- (1 , 1-dimethylethyl)-4-methyl phenol (also referred to in the literature as 2-(3'-tert-butyl-2'-hydroxy- 5'-methylphenyl)-5-chlorobenzotriazole) which is available commercially as TinuvinTM 326 from BASF.
  • TinuvinTM 326 is a benzotriazole of formula (I) wherein R 1 is CI, R 2 is 'Bu and R 3 is Me.
  • the first UV absorber having an absorbance of greater than 0.01 at a concentration of 10ppm in CHCI 3 at a wavelength in the range from 360 to 400 nm is a benzophenone UV absorber.
  • Benzophenone UV absorbers are known.
  • the benzophenone UV absorber provides the polyester film with stability to UV radiation up to wavelengths in the range from 360 to 400 nm.
  • the benzophenone UV absorber used in the present invention absorbs UV light in the range from 360 to 400 nm such that it has an absorbance of greater than 0.01 at a concentration of 10ppm in CHCI 3 at a wavelength in the range from 360 to 400nm.
  • the benzophenone UV absorber used in the present invention has an absorbance of greater than 0.05, in one embodiment greater than 0.1 , in one embodiment greater than 0.2, in one embodiment greater than 0.3, in one embodiment greater than 0.4 at a concentration of 10ppm in CHCI 3 at a wavelength in the range from 360 to 400nm, preferably 380 to 400nm.
  • the benzophenone UV absorber is a compound of formula (II):
  • R x is H, CMS alkyl optionally substituted with one or more alkyl, alkenyl, halogen, aryl or heteroaryl, C 2 -is alkenyl optionally substituted with one or more alkyl, alkenyl, halogen, aryl or heteroaryl or C 3 .i 8 cycloalkyl optionally substituted with one or more alkyl, alkenyl, halogen, aryl or heteroaryl.
  • the benzophenone UV absorber may be (2-hydroxy-4-methoxyphenyl)-(2- hydroxyphenyl)methanone, which is available commercially as CyasorbTM UV24 from Cytec. CyasorbTM UV24 is a compound of formula (I) wherein R x is Me.
  • the benzophenone UV absorber may be 2-hydroxy-4-n- octoxybenzophenone, which is available commercially as TinuvinTM 531 from BASF. TinuvinTM 531 is a compound of formula (II) wherein R x is C 8 H 17 .
  • the benzophenone UV absorber is of the type described in US 4,456,746, the contents of which is herein incorporated by reference.
  • the benzophenone UV absorber may be present in the form of a linear polyester which contains in its molecule esterification residues of a 1-hydroxy-3,6-bis(hydroxyalkoxy)xanth-9-one, wherein the amount of said residues is in the range from 0.01 to 30% by weight based on the total polymer.
  • Said polyester may be the polyester of the polyester film.
  • the first UV absorber having an absorbance of greater than 0.01 at a concentration of 10ppm in CHCI 3 at a wavelength in the range from 360 to 400 nm is a benzoxazinone UV absorber.
  • Benzoxazinone UV absorbers are known and are described in, for example, US 4,446,262, US 5,251 ,064 and US 5,264,539, the contents of which are herein incorporated by reference.
  • the benzoxazinone UV absorber provides the polyester film with stability to UV radiation up to wavelengths in the range from 360 to 400 nm.
  • the benzoxazinone UV absorber used in the present invention absorbs UV light in the range from 360 to 400 nm such that it has an absorbance of greater than 0.01 at a concentration of 10ppm in CHCI 3 at a wavelength in the range from 360 to 400nm.
  • the benzoxazinone UV absorber used in the present invention has an absorbance of greater than 0.05, in one embodiment greater than 0.1 , in one embodiment greater than 0.2, in one embodiment greater than 0.3, in one embodiment greater than 0.4 at a concentration of 10ppm in CHCI 3 at a wavelength in the range from 360 to 400nm, preferably 380 to 400nm.
  • R y is a hydrocarbon substituent which may contain a heteroatom
  • R z is H, halogen or a hydrocarbon substituent which may contain a heteroatom
  • n is 1 , 2 or 3.
  • R y is a divalent or trivalent group, respectively.
  • R y is a monovalent, divalent or trivalent aromatic group which may comprise one or more aromatic rings.
  • the benzoxazinone UV absorber is 2,2'-benzene-1 ,4-diylbis(4H-3, 1-benzoxazin-4-one), which is available commercially as CyasorbTM 3638 from Qingdao Fusilin Chemical Science & Technology Co., LTD.
  • CyasorbTM3638 is a compound of formula (III), wherein n is 2, R y is phenylene and R z is H and has the structure below:
  • the first UV absorber comprises a mixture of one or more selected from the group consisting of benzotriazole UV absorbers, benzophenone UV absorbers and benzoxazinone UV absorbers.
  • the first UV absorber is included in the polyester film in an amount in the range from 0.1 % to 10%, more preferably 0.2% to 5%, more preferably 0.5% to 4%, and particularly 1 % to 3% by weight, relative to the total weight of the polyester film. Where the content of the first UV absorber in the film is less than 0.1 %, it will not impart adequate UV stability to the film.
  • the long-term UV stability of the first UV absorber is improved by the inclusion of a triazine UV absorber.
  • the triazine UV absorber is a hydroxyphenyltnazine UV absorber, and particularly a hydroxyphenyltnazine compound of formula
  • R is hydrogen, C Ci 8 alkyl, C 2 -C 6 alkyl substituted by halogen or by C1-C12 alkoxy, or is benzyl and R 4 and R 5 are independently selected from hydrogen, alkyl, alkoxy or phenyl.
  • R is preferably C1-C12 alkyl or benzyl, more preferably C 3 -C 6 alkyl, and particularly hexyl.
  • R 4 and R 5 are preferably hydrogen.
  • An especially preferred UV absorber is 2-(4,6-diphenyl-1 ,3,5-triazin-2-yl)-5-(hexyl)oxy-phenol, which is commercially available as TinuvinTM 1577 from BASF.
  • TinuvinTM 1577 is a compound of formula (IV) above, wherein R is C 6 H 13 and R 4 and R 5 are both H.
  • a further preferred example of a triazine UV absorber is a 2-(2'-hydroxyphenyl)-4,6-diphenyl triazine which is commercially available as Tinuvin 1600TM from BASF.
  • Tinuvin 1600TM is a triazine of formula (IV) above, wherein R is CH2CH(C2H5)C 4 l-l9, R 4 group is phenyl and R 5 is hydrogen.
  • the amount of triazine UV absorber in the polyester film is in the range from 0.1 % to 30%, preferably 0.1 % to 20%, preferably 0.2% to 10%, preferably 0.5% to 5% and preferably 0.5% to 3% by weight, relative to the total weight of the polyester film.
  • the amount of triazine UV absorber in the polyester film is in the range from 1.0% to 4.0% % by weight, relative to the total weight of the polyester film.
  • the triazine UV absorber has a stabilising effect on the first UV absorber such that the combined benefits of prolonged stability to UV radiation of a long wavelength (360 to 400 nm) and stable excellent optical properties are observed.
  • the total content of UV absorber (i.e. said first UV absorber and said triazine UV absorber) in the film is less than about 10%, preferably less than about 7%, in particular less than about 5% by weight, relative to the total weight of the polyester film. This ensures that the film exhibits good optical properties.
  • alkyl is used herein to refer to an unsubstituted, monovalent straight chain or branched, saturated, acyclic hydrocarbyl group.
  • alkyl is Ci-i 0 alkyl, in another embodiment Ci -6 alkyl, in another embodiment Ci -4 alkyl, such as methyl, ethyl, n-propyl, / ' -propyl or / ' -, n-, secondary or f-butyl groups.
  • alkenyl is used herein to refer to monovalent straight or branched, unsaturated, acyclic hydrocarbyl groups having at least one carbon-carbon double bond and, in one embodiment, no carbon-carbon triple bonds.
  • alkenyl is C 2 -ioalkenyl, in another embodiment, C 2 - 6 alkenyl, in another embodiment C 2 . 4 alkenyl.
  • cycloalkyl is used herein to refer to monovalent, saturated, cyclic hydrocarbyl groups.
  • cycloalkyl is C 3 .i 0 cycloalkyl, in another embodiment, C 3 . 6 cycloalkyl, such as cyclopentyl and cyclohexyl.
  • alkoxy is used herein to refer to a monovalent group of formula R'-O-, wherein R' is an alkyl group.
  • aryl is used herein to refer to monovalent, aromatic, cyclic hydrocarbyl groups, such as phenyl or naphthyl (e.g. 1-naphthyl or 2-naphthyl). In general, the aryl group may be a monocyclic or polycyclic fused ring aromatic group. Preferred aryl groups are C 6 -Ci 4 aryl.
  • heteroaryl is used herein to refer to monovalent, heteroaromatic, cyclic hydrocarbyl groups additionally containing one or more heteroatoms independently selected from O, S, N and NR N , wherein R N is preferably H, alkyl (e.g. Ci -6 alkyl) or cycloalkyl (e.g. C 3 . 6 cycloalkyl).
  • the first UV absorber is phenol-2,2'-methylene-bis(6-(2H benzotriazol- 2-yl)-4-(1 , 1 ,3,3-tetramethylbutyl) and the triazine UV absorber is 2-(4,6-diphenyl-1 ,3,5-triazin-2-yl)- 5-(hexyl)oxy-phenol.
  • the first UV absorber is phenol-2,2'-methylene-bis(6-(2H benzotriazol-2-yl)-4-(1 , 1 ,3,3-tetramethylbutyl) and the triazine UV absorber is a 2-(2'- hydroxyphenyl)-4,6-diphenyl triazine of formula (IV) above, wherein R is CH 2 CH(C2H5)C 4 H9, R 4 group is phenyl and R 5 is hydrogen. This combination has been shown to provide particularly effective long term protection.
  • the polyester film is a monolayer film and the triazine UV absorber and said first UV absorber are both incorporated into the monolayer film.
  • the polyester film may include two or more layers (i.e. it may be a multilayer film).
  • the triazine UV absorber and the first UV absorber may either be incorporated into the same layer (or layers) of the multilayer film or into different layers of the multilayer film.
  • the UV absorbers are incorporated into different layers of the multilayer film, preferably the triazine UV absorber is incorporated into a layer which, in use, will be closer to the surface of the film which will be exposed to UV radiation than the layer into which the first UV absorber is incorporated, and such multilayer embodiments are preferred embodiments of the invention.
  • the film is a multilayer film having an AB structure, wherein said first UV absorber is incorporated into the A layer and the triazine UV absorber is incorporated into the B layer, wherein, in use, the B layer is positioned closer to the source of UV radiation than the A layer.
  • the film is a multilayer film having an BAB structure, wherein said first UV absorber is incorporated into the A layer and the triazine UV absorber is incorporated into one or both, in one embodiment both, B layers of the film.
  • the amounts of UV-absorber are preferably:
  • the triazine UV absorber is incorporated in an amount such that it is present in the range from 0.1 % to 30%, preferably 0.1 % to 20%, preferably 0.2% to 10%, preferably 0.5% to 5% and preferably 0.5% to 3% by weight relative to the total weight of the polyester film, and preferably the triazine UV absorber is present in an amount in the range from 2% to 20%, preferably from 3% to 15%, preferably from 4 to 12%, and preferably from 5% to 10% by weight relative to the total weight of that B layer; and (ii) In the A layer or in a layer other than said layer which will in use be closer to the surface of the film which will be exposed to UV light, the first UV absorber is incorporated in an amount such that it is present in an amount in the range from 0.1 % to 10%, more preferably 0.2% to 5%, more preferably 0.5% to 4%, and particularly 1
  • the triazine UV-absorber is preferably selected from a compound of formula (IV) above wherein either R is C 6 H 13 and R 4 and R 5 are both H, or R is CH 2 CH(C2H5)C4H 9 and R 4 is phenyl and R 5 is hydrogen, and preferably the triazine UV-absorber is a compound of formula (IV) above wherein R is CH 2 CH(C2H5)C4H 9 and R 4 is phenyl and R 5 is hydrogen, and preferably said first UV absorber is a benzotriazole and is preferably phenol-2,2'- methylene-bis(6-(2H benzotriazol-2-yl)-4-(1 , 1 ,3,3
  • the thickness of the A layer is preferably greater than 50%, preferably at least 60%, more preferably at least 70% and preferably from about 75% to about 95% of the total thickness of the film.
  • the thickness of the or each B layer is preferably no more than 40%, more preferably no more than 30% and more preferably no more than 25%, and preferably at least 5% more preferably at least 10%, and preferably from about 5% to about 25%, of the total thickness of the film.
  • the thickness of the or each B layer is preferably from about 3 to about 30 ⁇ , preferably from about 4 to about 25 ⁇ , and preferably from about 5 to about 20 ⁇ .
  • the total thickness of the polymer film is preferably in the range from 12 to 350 ⁇ , in one preferred embodiment 12 to 250 ⁇ , and in a further embodiment 50 to 125 ⁇ .
  • the invention as disclosed herein provides a preferred thicker film embodiment in which the total film thickness is in the range of from 75 to 350 ⁇ , more preferably 150 to 320 ⁇ .
  • the invention as disclosed herein provides a preferred thinner film embodiment in which the total film thickness is in the range of from 12 to 75 ⁇ , more preferably 23 to 50 ⁇ .
  • the polyester film of the present invention is typically optically clear or transparent, which is used herein to mean preferably having a % of scattered visible light (haze) of no more than 30%, preferably no more than 15%, preferably no more than 10%, preferably no more than 6%, more preferably no more than 3.5% and particularly no more than 1.5%, and/or a total luminous transmission (TLT) for light in the visible region (400 nm to 700 nm) of preferably at least 85%, preferably at least 90%, more preferably at least about 92%, more preferably at least about 95%.
  • a % of scattered visible light (haze) of no more than 30%, preferably no more than 15%, preferably no more than 10%, preferably no more than 6%, more preferably no more than 3.5% and particularly no more than 1.5%
  • TLT total luminous transmission
  • the polyester film of the present invention has a b* value of about 6 or less, preferably about 5 or less, preferably about 4 or less, preferably about 3 or less.
  • the b* value provides a measure of the yellowness of a colour.
  • the polyester films of the present invention maintain these excellent optical properties even following prolonged exposure to UV radiation, including UV radiation having a wavelength in the range from 360 to 400 nm.
  • UV radiation including UV radiation having a wavelength in the range from 360 to 400 nm.
  • weathering is used to describe exposure of the film to conditions wherein it will be exposed to UV radiation.
  • the effect of including both the triazine UV absorber and said first UV absorber together in the film is such that the polyester film comprising a first UV absorber into which the triazine UV absorber has been incorporated has a b* value of less than about 6, preferably less than about 5, preferably less than about 4, preferably less than about 3 after weathering for about 2000 hours or more, preferably for about 2500 hours or more, preferably for about 3000 hours or more, preferably for about 3500 hours or more, preferably for about 4000 hours or more, preferably for about 4500 hours or more, in the accelerated ageing (weatherability) test disclosed herein.
  • the polyester film comprising only the first UV absorber would have a change in b* value after exposure to weathering for about 2000 hours or more of higher than this and hence, would no longer be useful in a PV cell.
  • the inclusion of the combination of the triazine UV absorber and the first UV absorber ensures that the polyester film maintains good light transmission following prolonged exposure to UV radiation. This is particularly important where the film is to be used in a PV cell, wherein the operational lifetime of the cell will be dependent on the film remaining transparent to visible (400 to 700 nm) light.
  • the polyester film comprising said first UV absorber into which the triazine UV absorber has been incorporated has a total luminous transmission (TLT) for light in the visible range of greater than about 85%, preferably greater than about 88%, preferably greater than about 90%, preferably greater than about 92%, preferably greater than about 95% after weathering for about 2000 hours or more, preferably about 2500 hours or more, preferably about 3000 hours or more, preferably for about 3000 hours or more, preferably for about 3500 hours or more, preferably for about 4000 hours or more, preferably for about 4500 hours or more, in the accelerated ageing (weatherability) test disclosed herein.
  • TLT total luminous transmission
  • the polyester film comprising said first UV absorber and into which the triazine UV absorber has been incorporated has a haze value of no more than 30%, preferably no more than about 15%, preferably no more than about 10%, preferably no more than about 6%, preferably no more than about 3.5%, preferably no more than about 1.5% after weathering for about 2000 hours or more, preferably about 2500 hours or more, preferably about 3000 hours or more, preferably for about 3500 hours or more, preferably for about 4000 hours or more, preferably for about 4500 hours or more, in the accelerated ageing (weatherability) test disclosed herein.
  • the method of the present invention makes it possible to provide a polyester film which exhibits both long-term UV-stability and long-term excellent optical properties, even when exposed to UV radiation having a wavelength in the range from 360 to 400 nm for prolonged periods of time.
  • the polyester film of the present invention may further comprise any of the additives conventionally employed in the manufacture of polyester films.
  • agents such as: cross-linking agents; dyes; pigments; voiding agents; lubricants; anti-oxidants; radical scavengers; thermal stabilisers; end- capping agents; flame retardants and inhibitors; anti-blocking agents; surface active agents; slip aids; gloss improvers; prodegradents; viscosity modifiers; and dispersion stabilisers may be incorporated as appropriate.
  • the components of the polyester film may be mixed together in a conventional manner.
  • the components may be mixed with the polymer by tumble or dry blending or by compounding in an extruder, followed by cooling and, usually, comminution into granules or chips. Masterbatching technology may also be employed. Formation of the polyester may be effected by conventional extrusion techniques well-known in the art. In general terms the process comprises the steps of extruding a layer of molten polymer, quenching the extrudate and orienting the quenched extrudate in at least one direction.
  • the substrate may be uniaxially-oriented, but is preferably biaxially-oriented.
  • Orientation may be effected by any process known in the art for producing an oriented film, for example a tubular or flat film process.
  • Biaxial orientation is effected by drawing in two mutually perpendicular directions in the plane of the film to achieve a satisfactory combination of mechanical and physical properties.
  • simultaneous biaxial orientation may be effected by extruding a thermoplastics polyester tube which is subsequently quenched, reheated and then expanded by internal gas pressure to induce transverse orientation, and withdrawn at a rate which will induce longitudinal orientation.
  • the film-forming polyester is extruded through a slot die and rapidly quenched upon a chilled casting drum to ensure that the polyester is quenched to the amorphous state.
  • Orientation is then effected by stretching the quenched extrudate in at least one direction at a temperature above the glass transition temperature of the polyester.
  • Sequential orientation may be effected by stretching a flat, quenched extrudate firstly in one direction, usually the longitudinal direction, i.e. the forward direction through the film stretching machine, and then in the transverse direction.
  • Forward stretching of the extrudate is conveniently effected over a set of rotating rolls or between two pairs of nip rolls, transverse stretching then being effected in a stenter apparatus. Stretching is generally effected so that the dimension of the oriented film is from 2 to 5, more preferably 2.5 to 4.5 times its original dimension in the or each direction of stretching.
  • stretching is effected at temperatures higher than the T g of the polyester, preferably about 15 °C higher than the T g .
  • Greater draw ratios may be used if orientation in only one direction is required. It is not necessary to stretch equally in the machine and transverse directions although this is preferred if balanced properties are desired.
  • the stretched film is dimensionally stabilised by heat-setting under dimensional support at a temperature above the glass transition temperature of the polyester but below the melting temperature thereof, to induce the desired crystallisation of the polyester.
  • a small amount of dimensional relaxation may be performed in the transverse direction, TD by a procedure known as "toe-in".
  • Toe-in can involve dimensional shrinkage of the order 2 to 4% but an analogous dimensional relaxation in the process or machine direction, MD is difficult to achieve since low line tensions are required and film control and winding becomes problematic.
  • the actual heat-set temperature and time will vary depending on the composition of the film and its desired final thermal shrinkage but should not be selected so as to substantially degrade the toughness properties of the film such as tear resistance. Within these constraints, a heat-set temperature of about 180 ° to 245 °C is generally desirable. After heat-setting the film is typically quenched rapidly in order induce the desired crystallinity of the polyester.
  • the film may be and preferably is further heat-stabilized using a relaxation stage, either in-line or off-line.
  • a relaxation stage either in-line or off-line.
  • the film is heated at a temperature lower than that of the heat-setting stage, and with a much reduced MD and TD tension.
  • the tension experienced by the film is typically less than 5 kg/m, preferably less than 3.5 kg/m, more preferably in the range of from 1 to about 2.5 kg/m, and typically in the range of 1.5 to 2 kg/m of film width.
  • the reduction in film speed (and therefore the strain relaxation) is typically in the range 0 to 2.5%, preferably 0.5 to 2.0%. There is no increase in the transverse dimension of the film during the heat-stabilisation step.
  • the temperature to be used for the heat- stabilisation step can vary depending on the desired combination of properties from the final film, with a higher temperature giving better, i.e. lower, residual shrinkage properties.
  • a temperature of 135 to 250°C is generally desirable, preferably 150 to 230°C, more preferably 170 to 200°C.
  • the duration of heating will depend on the temperature used but is typically in the range of 10 to 40 seconds, with a duration of 20 to 30 seconds being preferred.
  • This heat-stabilisation process can be carried out by a variety of methods, including flat and vertical configurations and either "off-line” as a separate process step or "in-line” as a continuation of the film manufacturing process. Film thus processed will exhibit a smaller thermal shrinkage than that produced in the absence of such post heat-setting relaxation.
  • the polyester film discussed hereinabove may be advantageously used in the manufacture of electronic or opto-electronic devices, such as electroluminescent (EL) display devices (particularly organic light emitting display (OLED) devices), electrophoretic displays (e-paper), photovoltaic (PV) cells and semiconductor devices (such as organic field effect transistors, thin film transistors and integrated circuits generally), particularly flexible such devices.
  • EL electroluminescent
  • OLED organic light emitting display
  • e-paper electrophoretic displays
  • PV photovoltaic
  • semiconductor devices such as organic field effect transistors, thin film transistors and integrated circuits generally, particularly flexible such devices.
  • the polyester film discussed hereinabove is of particular advantage in the manufacture of a PV cell further comprising a photovoltaic-active layer, particularly a thin-film PV cell including those wherein the photovoltaic material is selected from amorphous silicon (a-Si) and other thin-film silicon (TF-Si) including proto-crystalline, nano-crystalline (nc-Si or nc-Si:H) and black silicon; cadmium-telluride (CdTe); copper-indium-gallium-(di)selenide (CIGS); dye-sensitized photo-voltaic cells; organic photovoltaic cells which utilise conductive organic compounds.
  • a-Si amorphous silicon
  • TF-Si thin-film silicon
  • CdTe cadmium-telluride
  • CGS copper-indium-gallium-(di)selenide
  • dye-sensitized photo-voltaic cells organic photovoltaic cells which utilise conductive organic compounds
  • polyester film discussed hereinabove is used in the manufacture of an organic PV cell as described herein.
  • the film may be used in another application where UV stability is important, including outdoor applications such as in signage and building materials, including cladding, windows and greenhouses, etc.
  • a PV cell particularly a thin-film PV cell as described immediately hereinabove, and particularly an organic PV cell comprising a front-plane, electrode layers, a photovoltaic-active layer and a back-plane, wherein a film according to the present invention is disposed between the photovoltaic-active layer and a surface of the PV cell which will be exposed to UV radiation.
  • the front-plane and/or the backplane comprises a film of the present invention
  • the back-plane comprises a film of the present invention.
  • the film of the present invention is disposed between the photovoltaic-active layer and the front-plane and/or back-plane of the PV cell.
  • the photovoltaic-active layer may be encapsulated with an optically clear material having barrier properties to provide high resistance to gas and solvent permeation, as described herein.
  • the photovoltaic-active layer is an organic photovoltaic-active layer and the PV cell is an organic PV cell.
  • the photovoltaic-active layer is a dye-sensitized photovoltaic active layer and the PV cell of the present invention is a dye-sensitized solar cell (DSSC).
  • DSSC dye-sensitized solar cell
  • the polyester film of the present invention shows long-term stability to UV light having a wavelength in the range from 300 to 400 nm, in particular 360 to 400 nm, when used in the construction of a PV cell, it is effective at providing long term UV protection to the the other layers which comprise the PV cell.
  • the PV cell is an organic PV cell, wherein the photovoltaic-active layer is vulnerable to UV radiation.
  • the present invention further provides a method of providing long term protection to a photovoltaic- active layer of a photovoltaic cell which comprises a front-plane, electrode layers, the photovoltaic- active layer and a back-plane, from UV radiation having a wavelength in the range from 300 to 400 nm, in particular 360 to 400 nm, comprising disposing a film according to the present invention between the photovoltaic-active layer and a surface of the cell which is exposed to UV radiation.
  • the method comprises forming the front-plane and/or back plane of the PV cell from a film according to the present invention.
  • the method comprises disposing a film of the present invention between the photovoltaic-active layer and the front-plane and/or back-plane of the PV cell.
  • the shielding effect provided by the film of the present invention is long term which means that the effective lifetime of the PV cell is increased.
  • the film of the present invention provides a shielding effect such that it provides protection against UV-induced degradation of the photovoltaic-active layer of an organic PV cell for about 2000 hours or more, in one embodiment, 2500 hours or more, in one embodiment 3000 hours or more, in one embodiment, 4000 hours or more, in one embodiment, 5000 hours or more, in one embodiment, 6000 hours or more, ine one embodiment, 7000 hours or more, in one embodiment, 8000 hours or more.
  • the polyester film may have disposed thereon a barrier layer, which is particularly important where the film is used as a partial or complete replacement for glass as the substrate layer in an organic OLED light source, for instance in order to provide flexibility.
  • Organic light-emitting layers are very sensitive to air and moisture.
  • the barrier layer in particular provides barrier properties to water vapour and/or oxygen transmission, particularly such that the water vapour transmission rate is less than 10 "3 g/ m2 /day and/or the oxygen transmission rate is less than 10 "3 /mL/m 2 /day.
  • the water vapour transmission rate is less than 10 "4 g/ m2 /day, preferably less than 10 "5 g/m 2 /day, preferably less than 10 "6 g/ m2 /day.
  • the oxygen transmission rate is less than 10 " 4 g/m 2 /day, preferably less than 10 "5 g/m 2 /day.
  • a barrier layer may be applied to the film of the present invention, such as by sputtering, atomic layer deposition (ALD) and other techniques with which the skilled person will be familiar.
  • a barrier layer may be applied in a sputtering process at elevated temperatures, and may be organic or inorganic.
  • a barrier layer can itself comprise one or more discrete layers, and may comprise one or more organic layer(s) and one or more inorganic layer(s).
  • multi-layer arrangements, particularly of inorganic and organic layer combinations are less preferred since they may increase wave-guiding and reduce extraction efficiency. Materials which are suitable for use to form a barrier layer are disclosed, for instance, in US-6,198,217.
  • Typical organic barrier layers include photocurable monomers or oligomers, or thermoplastic resins.
  • Photocurable monomers or oligomers should have low volatility and high melting points.
  • Examples of such monomers include trimethylol acrylates such as trimethylolpropane triacrylate, ditrimethylolpropane tetraacrylate and the like; long-chain acrylates such as 1 ,6-hexanediol diacrylate, 1 ,6-hexanediol dimethacrylate and the like; and cyclohexyl acrylates such as dicyclopentenyloxyethyl acrylate, dicyclopentenyloxy acrylate, cyclohexyl methacrylate and the like.
  • oligomers examples include acrylate oligomers, epoxy acrylate oligomers, urethane acrylate oligomers, ether acrylate oligomers, and the like.
  • Photoinitiators such as benzoin ethers, benzophenones, acetophenones, ketals and the like, may be used to cure the resin.
  • suitable thermoplastic resins include polyethylene, polymethyl methacrylate, polyethylene terephthalate and the like. These organic materials are typically applied by vacuum deposition.
  • Typical inorganic barrier layers are made of a material which exhibits low moisture permeability and is stable against moisture.
  • oxides, nitrides and sulphides of Groups IVB, VB, VIB, MIA, MB, IVA, VA and VIA of the Periodic Table and combinations thereof include oxides such as Si0 2 , SiO, GeO, Al 2 0 3 , ZnO, Zr0 2 , Hf0 2 and the like, nitrides such as AIN, TiN, Si 3 N 4 and the like, and metals such as Al, Ag, Au, Pt, Ni and the like. Mixed oxide-nitrides such as may also be used.
  • the inorganic material is usually applied using a vapour phase technique such as vacuum deposition, sputtering and the like under standard conditions. Where the polyester film is used as a transparent substrate in the OLED, the barrier layer must also exhibit optical transparency.
  • the oxides noted above, as well as the nitrides of Si and Al are of particular utility here.
  • the thickness of the barrier layer is preferably in the range of 2nm to 100 nm, more preferably 2 to 50 nm. Thinner layers are more tolerant to flexing without causing the film to crack, which is an important property of flexible substrates in OLED light sources since cracking compromises barrier properties. Thinner barrier films are also more transparent.
  • an encapsulating barrier material may be an ionomer-based material, i.e. a polymer made up primarily of non-polar repeat units with a minor proportion (typically no more than about 15 wt%) of salt-containing units.
  • Preferred ionomers are selected from thermoplastic carboxylate ionomers wherein the non-polar comonomers are typically selected from ethylene and styrene (preferably ethylene), and containing a minor proportion of salt- containing units such as metal salts (for instance, alkali metal or zinc salts) of methacrylic acid and/or acrylic acid.
  • Preferred ionomers for the encapsulant are the copolymers of ethylene and methacrylic acid and/or acrylic acid partially or completely neutralised with alkali metals or zinc, for instance Surlyn ® (DuPont; for instance grade 1702).
  • Other suitable encapsulant materials include ethylene vinyl acetate (EVA) copolymer resins, commercially available for instance as Elvax ® resins (DuPont, for instance grades PV1410 to PV1650Z), typically wherein the vinyl acetate component is in the range of from about 28 to about 33 wt%.
  • EVA ethylene vinyl acetate
  • encapsulant materials are selected from polyvinylbutyral resins, also commercially available from DuPont (for instance the PV5200 series), and from silicone resins (for instance, Dow Coming's PV-6100 series of optically clear silicone encapsulants).
  • polyvinylbutyral resins also commercially available from DuPont (for instance the PV5200 series)
  • silicone resins for instance, Dow Coming's PV-6100 series of optically clear silicone encapsulants.
  • Clarity was evaluated by measuring total luminance transmission (TLT) and haze (% of scattered transmitted visible light) through the total thickness of the film using an M57D spherical hazemeter (Diffusion Systems) according to the standard test method ASTM D1003.
  • Intrinsic viscosity in units of dl_/g is measured by solution viscometry in accordance with ASTM D5225-98(2003) on a ViscotekTM Y-501 C Relative Viscometer (see, for instance, Hitchcock, Hammons & Yau in American Laboratory (March 1994) "The dual-capillary method for modern-day viscometry") by using a 0.5% by weight solution of polyester in o- chlorophenol at 25°C and using the Billmeyer single-point method to calculate intrinsic viscosity:
  • Hred reduced viscosity (in dl_/g), which is equivalent to (n r ei-1)/c (also expressed as n, sp /c where ⁇ 3 ⁇ is the specific viscosity).
  • the longer dimension of the sample corresponds to the film direction for which shrinkage is being tested, i.e. for the assessment of shrinkage in the machine direction
  • the 200 mm dimension of the test sample is oriented along the machine direction of the film.
  • Weatherability is measured in an atmosphere of 100% relative humidity (RH) at 121 °C, in an atmosphere of 85% RH at 85°C, and in a weatherometer (Atlas Ci65 Weather-o-meter) running to ISO-4892-2.
  • weatherability is tested in a QUV Accelerated Weatherometer (Q-Lab) running to ISO-4892-3.
  • UV transmission is measured using a UV-visual spectrometer (e.g. Perkin Elmer Lambda 20 or Shimadzu UV-2700) in transmission mode.
  • a UV-visual spectrometer e.g. Perkin Elmer Lambda 20 or Shimadzu UV-2700
  • the UV absorbance of the first UV absorber in isolation is measured in a corresponding manner.
  • Adhesion strength of the film to an encapsulant barrier layer (8 mil (approx. 203 ⁇ ) EVA layer, post curing, with a three-ply PE/PET/PE back sheet for stability) is assessed using the peel method of ASTM D903. Adhesion strength may be expressed either as the linear peak load or linear average load,
  • Oxygen transmission rate is measured using ASTM D3985.
  • Elongation to break is measured according to test method ASTM D882. Using a straight edge and a calibrated sample cutter (10mm+ ⁇ -0.5mm) five strips (100mm in length) of the film are cut along the machine direction. Each sample is tested using an Instron model 31 1 1 materials test machine, using pneumatic action grips with rubber jaw faces. Temperature (23°C) and relative humidity (50%) are controlled. The crosshead speed (rate of separation) is 25 mm.min "1 . The strain rate is 50%/min. It is calculated by dividing the rate of separation by the initial distance between grips (sample length) - the jaw speed is 25mm/minute and the inter-jaw length is 50mm. The equipment records the elongation at break of each sample. The elongation to break (C B (%)) is defined as:
  • ETB is the original length of the sample between grips.
  • the measurement of ETB provides a measure of the mechanical properties, particularly the tensile strength (brittleness), of the polyester film, and this was measured before and during the accelerated ageing of the film as described above (in the Atlas weatherometer, unless otherwise indicated).
  • An ETB value of over 100 % is typically exhibited by a polyester film which has not been aged. In general, a film remains useful in its end-use up to the time at which its ETB is reduced to less than 10 %.
  • Figure 1 shows the UV transmission of the films of Examples 2 to 8;
  • Figure 2 illustrates the UV absorbance of the films of Examples 2 to 8 after weathering for 4400 hours
  • Figure 3 shows the UV transmission of the films of Examples 2 to 8 after weathering for 4400 hours
  • Figure 4 shows the UV transmission of the films of Examples 2 to 8 after weathering for 6400 hours
  • Figure 5 shows how b* values of the films of Examples 1 to 8 vary as the films are weathered;
  • Figure 6 shows how haze values of the films of Examples 1 to 8 vary as the films are weathered;
  • Figure 7 shows the UV transmission of the films of Examples 9 to 12;
  • Figure 8 shows the UV transmission of the films of Examples 9 to 12 after weathering for 4400 hours
  • Figure 9 shows the UV transmission of the films of Examples 9 to 12 after weathering for 6400 hours
  • Figure 10 shows how b* values of the films of Examples 9 to 12 vary as the films are weathered
  • Figure 11 shows how haze values of the films of Examples 9 to 12 vary as the films are weathered
  • Figure 12 shows a comparison of haze values of the films of Examples 5 to 8 and Examples 9 to 12 as the films are weathered
  • Figure 13 shows the UV transmission of the films of Examples 13 and 14;
  • Figure 14 shows the UV transmission of the films of Examples 13 and 14 before weathering and after 3600 hours of weathering
  • Figure 15 shows how haze values of the films of Examples 13 and 14 vary as the films are weathered.
  • Figure 16 shows how b* values of the films of Examples 13 and 14 vary as the films are weathered.
  • the examples are not intended to limit the invention as described above. Modification of detail may be made without departing from the scope of the invention.
  • a benzotriazole UV absorber is used as the first UV absorber having an absorbance of greater than 0.01 at a concentration of 10 ppm in CHCI 3 at a wavelength in the range from 360 to 400 nm.
  • a polymer composition comprising polyethylene terephthalate was melt extruded, cast onto a cooled rotating drum and stretched in the direction of extrusion to approximately 3 times its original dimensions at a temperature of about 80°C.
  • the film was then passed into a stenter oven at a temperature of 110°C where the film was stretched in the sideways direction to approximately 3 times its original dimensions.
  • the biaxially stretched film was heat set at a temperature of about 220°C.
  • the heat-set biaxially stretched film had a thickness of 50 ⁇ .
  • Example 1 The procedure of Example 1 was repeated except that triazine (TinuvinTM1577, available commercially from BASF) and benzotriazole (TinuvinTM360, available commercially from BASF) UV absorbers were added to the film composition in the amounts detailed in Table 1 below.
  • Figure 2 illustrates the effect of weathering on the UV absorption of the films of the examples described above.
  • Figure 2 shows the UV absorbance of the films of examples 2 to 8 following 4400 hours of weathering.
  • the film includes only a benzotriazole UV absorber
  • a film containing a triazine UV absorber retains its stability to UV light having a wavelength of less than 360 nm, despite prolonged exposure to weathering conditions.
  • incorporation of a triazine UV absorber has the effect of increasing the stability of the polyester film which also includes a benzotriazole stabiliser, to UV light having a wavelength in the range from 360 to 400 nm.
  • Figures 3 and 4 illustrate the effect of weathering on the UV transmission of the films of the examples described above.
  • Figure 3 shows the UV transmission of the films of examples 2 to 8 following 4400 hours of weathering
  • Figure 4 shows the UV transmission of the films of examples 3 to 8 following 6400 hours of weathering.
  • the film includes only a benzotriazole UV absorber
  • a film containing a triazine UV absorber retains its stability to UV light having a wavelength of less than 360 nm, despite prolonged exposure to weathering conditions.
  • incorporation of a triazine UV absorber has the effect of increasing the stability of the polyester film which also includes a benzotriazole stabiliser, to UV light having a wavelength in the range from 360 to 400 nm.
  • Figure 6 demonstrates the long-term stabilising effects of the triazine UV absorber on a polyester film comprising a benzotriazole UV stabiliser in relation to the haze of the film after weathering.
  • the haze value starts to increase significantly, for instance to levels which would mean that the films would no longer be useful in a PV application.
  • the films which comprise the combination of a triazine UV absorber and a benzotriazole UV absorber retain good haze even after weathering for longer than 5200 hours. This is illustrated further by reference to Table 3 below which shows the change in % change in haze value (Ahaze) following weathering for 5200 hours for Examples 1 to 8.
  • a second series of multilayer polyester films having a BAB structure were prepared.
  • Table 4 below shows the UV-absorbers used in these three layer films.
  • Example 9 a film comprising three layers was extruded and cast using a standard melt coextrusion system.
  • the coextrusion system was assembled using two independently operated extruders which fed separate streams of polymer melt to a standard coextrusion block or junction at which these streams were joined.
  • One stream of melt was split prior to the coextrusion junction and fed to two ports of the junction, which provided a common melt channel comprising three distinct streams.
  • a triazine UV absorber (TinuvinTM1600 commercially available from BASF) was added in an amount of 10% by weight to the two streams which form the outer B layers of the multilayer structure.
  • the melt was thereafter transported to a simple, flat film extrusion die which allowed the melt curtain to be cast and quenched in temperature onto a rotating, chilled metal drum.
  • the extrusion temperature was about 275°C.
  • the film was reheated to a temperature of about 80°C and stretched in the forward or machine direction to a stretch ratio of x3.3.
  • the film was then stretched in the sideways or transverse direction to a stretch ratio x3.5 at a temperature of about 110°C in a stenter apparatus.
  • the stretched film was then heat-set at an elevated temperature to induce further crystallisation of the polyester layer.
  • the final heat-set stage was performed at an oven temperature of about 220°C.
  • the final film thickness was 50 ⁇ , wherein the outer B layers were each 5 ⁇ thick.
  • Example 10 the procedure of Example 9 was repeated except that a benzotriazole (TinuvinTM360, available commercially from Ciba-Geigy) UV absorber was added to the A layer of the multilayer film in the amounts detailed in Table 4 below.
  • a benzotriazole TinuvinTM360, available commercially from Ciba-Geigy
  • UV absorber was added to the A layer of the multilayer film in the amounts detailed in Table 4 below.
  • Figures 8 and 9 illustrate the effect of weathering on the UV transmission of the films of the examples described above.
  • Figure 8 shows the UV transmission of the films of examples 9 to 12 following 4400 hours of weathering
  • Figure 9 shows the UV transmission of the same films after 6400 hours of weathering.
  • the long-term stabilising effects of the triazine UV absorber on the benzotriazole UV absorber can be seen as compared to Examples 2 to 4.
  • the films which comprise the combination of a triazine UV absorber and a benzotriazole UV absorber retain a low b* value. This is further illustrated by the Ab* values recorded in Table 5 below. Table 5
  • Figure 1 1 demonstrates the long-term stabilising effects of the triazine UV absorber on a polyester film comprising a benzotriazole UV stabiliser in relation to the haze of the film after weathering.
  • the haze value starts to increase, for instance to levels which would mean that the films would no longer be useful in a PV application.
  • the films which comprise the combination of a triazine UV absorber and a benzotriazole UV absorber retain good haze even after weathering for longer than 6400 hours. This is further illustrated by the Ahaze values recorded in Table 6 below.
  • Figure 12 shows that, while both Tinuvin 1577 and Tinuvin 1600 are both effective in maintaining excellent optical properties even after prolonged exposure (up to 4000 hours) to UV light having a wavelength in the range from 360 to 400 nm, TinuvinTM1600 in particular provides a stabilising effect when weathered for a time period in excess of 6000 hours.
  • Example 1 The procedure of Example 1 was repeated except that triazine (TinuvinTM1577 or TinuvinTM1600, available commercially from BASF) and benzotriazole (TinuvinTM360, available commercially from BASF) UV absorbers were added to the film composition in the amounts detailed in Table 7 below.
  • triazine TinuvinTM1577 or TinuvinTM1600, available commercially from BASF
  • benzotriazole TinuvinTM360, available commercially from BASF
  • the data demonstrate that the incorporation of a triazine UV-absorber into an outer layer and a benzotriazole UV-absorber into a core layer provides a surprising improvement in the UV-stability of the film, as demonstrated by a comparison between monolayer Example 14 on the one hand and the multilayer Examples 10 to 12 on the other hand.
  • the multilayer films of Examples 10 to 12 exhibit much lower Ab* and Ahaze values than the monolayer Example 14.
  • UV stability of the film samples was also assessed by measuring the elongation to break of the film samples over the course of the weathering test. Examples 10, 13 and 14 were analysed in this way, and the results are shown in Table 10 below.
  • Table 10 also confirm the technical effect shown by the data in Tables 8 and 9, which is that the combination of TinuvinTM 1600 and TinuvinTM 360 provides UV stability which is superior to that exhibited by the combination of TinuvinTM 1577 and TinuvinTM 360.
  • a further series of multilayer polyester films having an AB structure were prepared, using a method similar to that described for Examples 9 to 12, and varying the amount of TinuvinTM1600 and TinuvinTM360 in the layers.
  • the final film thickness was 50 ⁇ , wherein the skin layer (B) was 20 ⁇ thick and the base layer (A) was 30 ⁇ thick.
  • the amounts of additive in each layer are detailed in Table 1 1 below.
  • the b* values of the film samples were recorded before and after weathering using the test set out in (iv) above. The results are also presented in Table 1 1 below.
  • Examples 15 to 18 confirm the results noted above, namely that increasing the amount of a triazine UV-absorber in a polyester film comprising a benzotriazoles UV-absorber improves the long-term stability of the film to UV light and better maintains its optical properties on exposure to UV light. Examples 15 to 18 also confirm the results noted above which demonstrate that the incorporation of triazine UV-absorber into an outer layer and the benzotriazole into a core layer, provides a surprising improvement in the UV-stability of the film relative to a film in which the triazine and benzotriazole are incorporated into a single layer.

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  • Chemical & Material Sciences (AREA)
  • Health & Medical Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Organic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Laminated Bodies (AREA)
  • Compositions Of Macromolecular Compounds (AREA)

Abstract

La présente invention concerne un procédé pour améliorer la stabilité durable à la lumière UV d'un film de polyester comprenant un premier absorbeur d'UV possédant une absorbance supérieure à 0,01 à une concentration de 10 ppm dans du CHCl3 à une longueur d'onde comprise dans la plage allant de 360 à 400 nm, et un procédé pour améliorer ladite stabilité durable aux UV dudit premier absorbeur d'UV présent dans un film de polyester, ledit procédé consistant à intégrer un absorbeur d'UV à base de triazine dans le film ; et des films multicouches comprenant ledit premier absorbeur d'UV et ladite triazine.
PCT/GB2013/052865 2012-11-02 2013-11-01 Film de polyester stable aux uv Ceased WO2014068329A1 (fr)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GBGB1219780.2A GB201219780D0 (en) 2012-11-02 2012-11-02 Polyester film
GB201219779A GB201219779D0 (en) 2012-11-02 2012-11-02 Polyester film
GB1219780.2 2012-11-02
GB1219779.4 2012-11-02

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WO2014068329A1 true WO2014068329A1 (fr) 2014-05-08

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Cited By (1)

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EP3659798A1 (fr) * 2018-11-29 2020-06-03 Röhm GmbH Feuilles acryliques présentant des propriétés améliorées de protection contre les uv

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US20100292367A1 (en) * 2009-05-12 2010-11-18 E.I. Du Pont De Nemours And Company Polyester compositions for long-term outdoor exposure
WO2011117694A1 (fr) * 2010-02-05 2011-09-29 Dupont Teijin Films U.S. Limited Partnership Film de polyester ayant une stabilité aux uv et une transmittance optique élevée
US20110306257A1 (en) * 2010-06-14 2011-12-15 E. I. Du Pont De Nemours And Company Long-term outdoor exposure resistant polyester composite structures and processes for their preparation
US20120227801A1 (en) * 2009-09-08 2012-09-13 Dupont Teijin Films U.S. Limited Partnership Hydrolysis resistant polyester films
US20120248497A1 (en) * 2011-04-01 2012-10-04 Sabic Innovative Plastics Ip B.V. Optoelectronic devices and coatings therefore, and methods for making and using the same

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Publication number Priority date Publication date Assignee Title
US20100292367A1 (en) * 2009-05-12 2010-11-18 E.I. Du Pont De Nemours And Company Polyester compositions for long-term outdoor exposure
US20120227801A1 (en) * 2009-09-08 2012-09-13 Dupont Teijin Films U.S. Limited Partnership Hydrolysis resistant polyester films
WO2011117694A1 (fr) * 2010-02-05 2011-09-29 Dupont Teijin Films U.S. Limited Partnership Film de polyester ayant une stabilité aux uv et une transmittance optique élevée
US20110306257A1 (en) * 2010-06-14 2011-12-15 E. I. Du Pont De Nemours And Company Long-term outdoor exposure resistant polyester composite structures and processes for their preparation
US20120248497A1 (en) * 2011-04-01 2012-10-04 Sabic Innovative Plastics Ip B.V. Optoelectronic devices and coatings therefore, and methods for making and using the same

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3659798A1 (fr) * 2018-11-29 2020-06-03 Röhm GmbH Feuilles acryliques présentant des propriétés améliorées de protection contre les uv
WO2020108992A1 (fr) * 2018-11-29 2020-06-04 Röhm Gmbh Feuilles acryliques présentant des propriétés de protection contre les uv améliorées
CN113165359A (zh) * 2018-11-29 2021-07-23 罗姆化学有限责任公司 具有改进的uv防护性能的丙烯酸系膜片
JP2022509284A (ja) * 2018-11-29 2022-01-20 レーム・ゲーエムベーハー 改善されたｕｖ保護特性を有するアクリル箔
JP7411657B2 (ja) 2018-11-29 2024-01-11 レーム・ゲーエムベーハー 改善されたｕｖ保護特性を有するアクリル箔
AU2019387174B2 (en) * 2018-11-29 2025-11-13 Polyvantis Gmbh Acrylic foils with improved UV-protection properties

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