High-performance light control films with advanced structure for economical fabrication

Abstract

- 46 - BASF Coatings GmbH 240195 240195WO01 SUMMARY A light control film comprising a) a substrate, b) a microstructured light-transmissive layer on one surface of the substrate, the microstructured light-transmissive layer comprising a microlouver structure composed of periodically arranged louver elements with a louver pe- riod P along a first axis across the substrate surface and elongated along a second axis 5 across the substrate surface perpendicular to the first axis across the substrate surface, and c) a light-absorbing material filling the grooves of the microlouver structure, wherein the louver element has a geometric parameter GP as defined in formula (I) in a range of from 0.40 to 5.00 and wherein the light control film achieves a high transmission, a low cutoff angle, a narrow field of view and simultaneously provides a large angular range of 10 uniform light transmission within the narrow cutoff angle. (Fig. 3)

Description

[0001] BASF Coatings GmbH

[0002] GlasuritstraBe 1 , 48165 Munster

[0003] Germany

[0004] High-Performance Light Control Films with Advanced Structure for Economical Fabrication

[0005] FIELD OF THE INVENTION

[0006] The present invention relates to a light control film comprising a substrate, a microstructured light-transmissive layer on one surface of the substrate, the microstructured light- transmissive layer comprising a microlouver structure composed of periodically arranged louver elements with a louver period P along a first axis across the substrate surface and elongated along a second axis across the substrate surface perpendicular to the first axis across the substrate surface, and a light-absorbing material filling the grooves of the microlouver structure, wherein the microlouver structure is determined by certain geometric features and parameters in order to achieve a narrow cutoff angle and simultaneously pro- vide a large angular range of uniform light transmission within the narrow cutoff angle. The present invention also relates to the use of said light control film for narrowing the field of view and / or narrowing the cutoff angle of a display.

[0007] BACKGROUND OF THE INVENTION

[0008] Light control films, also called privacy films, monitor filters and the like, are used as an accessory to displays, screens, monitors or any other two-dimensional (flat) light source.

[0009] The main purpose of a light control film is to decrease the viewing angle, also called light emitting angle or field of view, of the two-dimensional (flat) light source, preventing it from being viewed from the side, see also Figure 1. BASF Coatings GmbH 240195

[0010] A light control film generally comprises a substrate, a microstructured light-transmissive layer on one surface of the substrate, the so called microlouver structure, and a light-absorbing material filling the grooves of the microlouver structure, see also Figure 2. The side of the surface of the substrate which is not covered by the microstructured light-transmissive layer is directed towards the light source, in most cases said side is in (direct) contact with the screen or display. Light emitted from the light source thus enters the light control film from the side of the surface of the substrate which is not covered by the microstructured light-transmissive layer, passes through the substrate and the light-transmissive parts of the coating and emerges on the other side of the surface as long as it is not hindered, reflected or absorbed in the regions formed by the light-absorbing grooves.

[0011] The microlouver structure of a light control film is generally composed of periodically arranged and parallel aligned louver elements, which are composed of any kind of light-transmissive material and which are elongated along one side / axis of the substrate surface. The geometric design of the microlouver structure in most cases can be simplified and characterised via a two-dimensional cross-sectional view, wherein the cross-section is equal to the plane perpendicular to the axis along which the louver elements are elongated across the substrate surface. Within said two-dimensional cross-sectional view the microlouver structure consists of trapezoidal transparent regions or in rare cases triangular transparent regions (cross section through the louver elements) which are separated from each other by trapezoidal grooves or triangular grooves, the grooves being filled with a light-absorbing material, e.g. with black ink. The microlouver structure can thus be considered as a linear structure with a (typically) trapezoidal or triangular cross-section.

[0012] A light ray entering the light control film from the side of the substrate which is directed towards the light source and not covered with the microstructured light-transmissive layer will only pass through the light control film if the light ray travels more or less vertically because otherwise, it would hit one of the light-absorbing grooves. Accordingly, the field of view is narrowed, since light from the light source is only transmitted in a certain angular range. The end point of said field of view, where essentially zero transmission is reached, is characterized by the so called cutoff angle.

[0013] State of the art light control films are mostly designed in a way that guarantees a narrow field of view and a low cutoff angle.

[0014] US 5,204,160 discloses a light control film wherein the microlouver elements comprise cylindrical lenses. With said geometrical structure of the microlouver elements a cutoff angle of around 35° can be reached. BASF Coatings GmbH 240195

[0015] KR 20240099095 A discloses a light control film wherein the microlouver elements have a trapezoidal shape, wherein said trapezoidal shape is divided in two different parts featuring different inclination angles. The light control film is described as being suitable to precisely control the light emitting angle (field of view).

[0016] However, state of the art light control films still suffer from performance issues and quite often do not meet the high requirements needed for most applications, in particular the requirements for displays in a means of transportation such as a car.

[0017] Beside the primary function of light control films which is the assurance of a narrow field of view, a low cutoff angle and sufficient maximum transmission, an important secondary requirement is to achieve a homogeneous brightness within the field of view and accordingly, a sharp cutoff. In other words: The light distribution curve which is the transmission or radiance plotted over the viewing angle should be close to a rectangle function with a controlled sidewall position and top height. Typical state of the art light control films do not meet this requirement. Their light distribution curves have the shape of a triangle instead of a rectangle. Thus, brightness uniformity within the field of view is relatively poor. Transmission decreases significantly and unfavourably even at small angles within the field of view. Furthermore, the light control film should be designed in a way that allows for a simple and economic production method.

[0018] Accordingly, there is a demand in industry for a light control film which is improved regarding the above-mentioned requirements.

[0019] Related prior art is also US 2010 / 271721 A1 and US 2017 / 108628 A1 .

[0020] SUMMARY OF THE INVENTION

[0021] It was a primary object of the present invention to provide such an improved light control film. The improved light control film should thus at least fulfil the following criteria:

[0022] - assurance of a narrow field of view, a low cutoff angle and sufficient maximum transmission, and

[0023] - brightness uniformity within the field of view as characterized by a light distribution curve in the form of a rectangle function. BASF 240195

[0024] Accordingly, the current incompatibility of the two aforementioned properties of privacy films should therefore be overcome with the light control film of the present invention.

[0025] Furthermore, the improved light control film should be designed in way that allows for a simple and economic production method.

[0026] Even further, the improved light control film should be applicable and compatible to a wide variety of different light sources such as displays in a means of transportation, preferably displays in a car, smartphone displays, laptop displays, TVs, computer screens, sensor displays, watches and the like.

[0027] The invention is defined in the claims as attached.

[0028] If not stated otherwise, preferred embodiments, aspects or features of the present invention can be combined with other embodiments, aspects or features, especially with other preferred embodiments, aspects or features, irrespectively of the categories to which the embodiments, aspects or features relate. The combination of preferred embodiments, aspects or features with other preferred embodiments, aspects or features in each case again results in preferred embodiments, aspects or features.

[0029] In accordance with the primary object of the invention as stated above, the present invention relates to a light control film comprising a) a substrate, b) a microstructured light-transmissive layer on one surface of the substrate, the microstructured light-transmissive layer comprising a microlouver structure composed of periodically arranged louver elements with a louver period P along a first axis across the substrate surface and elongated along a second axis across the substrate surface perpendicular to the first axis across the substrate surface, and c) a light-absorbing material filling the grooves of the microlouver structure, wherein

[0030] - the two-dimensional cross-sectional shape of the louver elements formed by an intersecting plane perpendicular to the second axis across the substrate surface is Coatings GmbH | 240195 composed of a two-dimensional cross-sectional bottom shape and a two-dimensional cross-sectional convex top shape,

[0031] - the two-dimensional cross-sectional bottom shape is nearest to the substrate and has the form of a trapezoid,

[0032] - the parallel sides of the two-dimensional cross-sectional trapezoid bottom shape are parallel to the substrate surface,

[0033] - both side wall inclination angles a1 and a2 formed between the parallel bottom side B nearest to the substrate surface and legs L1 and L2 of the two-dimensional cross- sectional trapezoid bottom shape are smaller than 90°,

[0034] - the two-dimensional cross-sectional convex top shape is composed of a linear bottom side T being equal to the parallel top side of the two-dimensional cross-sectional trapezoid bottom shape and a convex curve c connecting the end points of T, wherein both inner angles p1 and p2 formed between the linear bottom side T and the convex curve c are smaller than 90°,

[0035] - the louver element has a geometric parameter GP as defined in formula (I) in a range of from 0.40 to 5.00 with:

[0036] T = length of the linear bottom side of the two-dimensional cross-sectional convex top shape, n = refractive index (at A = 550 nm) of the microstructured light-transmissive layer, p being selected from inner angles p1 and p2 formed between the linear bottom side T and the convex curve c of the two-dimensional cross-sectional convex top shape,

[0037] H = height of the two-dimensional cross-sectional trapezoid bottom shape. BASF Coatings GmbH 240195

[0038] The inventors of the present invention have undertaken thorough investigations and modulations and have thus found, that a light control film which is characterized by the geometrical features as stated above and as defined in the claims is particularly suitable in terms of a narrow field of view, a low cutoff angle, sufficient maximum transmission, and a brightness uniformity within the field of view as characterized by a light distribution curve in the form of a rectangle function.

[0039] Herein und throughout the whole text the refractive index n refers to the refractive index at A = 550 nm.

[0040] Herein and throughout the whole text the term “substrate” designates any kind of light- transmissive material in the form of a film, i.e., a thin flexible strip of plastic or another material. The substrate comprises at least two different surfaces. One surface of the substrate is covered by the microstructured light-transmissive layer, also referred to as “first surface” herein.

[0041] Preferably the substrate has a second surface which is essentially parallel to the first surface of the substrate covered by the microstructured light-transmissive layer.

[0042] In a preferred embodiment of the present invention the light control film additionally comprises a light-transmissive and adhesive layer in direct contact with the second surface of the substrate. Said adhesive layer allows for a facile application of the light control film to a wide variety of different light sources such as screens, displays and the like.

[0043] In another preferred aspect of the present invention the substrate itself is designed in a way that allows for a facile application of the light control film to a wide variety of different light sources such as screens, displays and the like.

[0044] In yet another preferred embodiment of the present invention the light control film comprises a second substrate layer, wherein said second substrate layer is preferably in direct contact with the top shape of the microlouver structure.

[0045] The light-transmissive layer is generally obtained / produced from a coating composition which is applied to the substrate surface and substantially cured thereafter.

[0046] Herein and throughout the whole text the term “light-transmissive” designates that the respective material allows for the transmittance of light, in particular transmittance of light BASF 240195 within the visible light spectrum (400 nm to 700 nm) and the ultraviolet light spectrum, more particular transmittance of light with wavelength of > 300 nm, preferably > 350 nm. Vice versa, the term “light-absorbing” designates that the respective material absorbs light and thus does not allow for the transmittance of light, in particular does not allow for the transmittance of light within the visible light spectrum (400 nm to 700 nm). Materials can be classified as either light-transmissive or light-absorbing according to known methods and tabulated values of the absorption coefficient.

[0047] Accordingly, the microstructured light-transmissive layer and the (light-transmissive) substrate preferably comprises or consist of a light-transmissive material with an absorption coefficient of less than 0.15 mm'1, more preferably of less than 0.10 mm'1.

[0048] The light-absorbing material filling the grooves of the microlouver structure preferably comprises or consist of a light-absorbing material with an absorption coefficient of more than 50 mm'1, more preferably of more than 100 mm1.

[0049] Accordingly, the (light-transmissive) substrate comprises or consists of any type of material that it is substantially light-transmissive and is substantially optically clear, and that preferably also has enough mechanical strength, flexibility, as well as chemical and thermal stability to allow handling during fabrication. In addition, the material should be chosen so that it has sufficient thermal, chemical, and weathering stability so that performance of the final product is not compromised over its typical lifetime.

[0050] The (light-transmissive) substrate preferably comprises or consists of one or more of the following materials: polyamides, polyimides, polyether sulfones, polymethyl pentene, polyvinyl chloride (PVC), polyacetals such as polyvinyl acetal, polyvinyl alcohol, polyacrylnitril (PAN), polyacrylnitril ethylene / propylene-diene styrene copolymers (A-EPDM), polyethers, polyether imides, polyether ketones, polyesters such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polyethylene naphthalate (PEN), poly(meth)acry- lates such as polymethyl methacrylate (PMMA), polymethyl acrylate, polyethyl (methacrylate, and polybutyl (meth)acrylate, polycarbonates (PC), polystyrene (PS), polyethylene (PE), polypropylene (PP), polybutadiene, cyclic olefin polymers (COP) and cyclic olefin copolymers (COC) such as ethylene-norbornene copolymer and ethylene-tetracyclodode- cene copolymers (commercially available, i. a., under the trade-marks TOPAS from Polyplastics and APEL from Mitsui Chemicals), polyurethanes such as thermoplastic polyurethanes (TPU), polyphenylene sulfides, acetylated cellulose derivates such as diacetyl celluse, triacetyl cellulose (TAC), and cellulose acetate butyrate. BASF 240195

[0051] More preferably, the light-transmissive substrate comprises or consists of one or more of the following materials: PVC, polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyacrylates such as polymethyl methacrylate (PMMA) and polymethyl acrylate, PC, PS, PE, PP, COP and COC, TPU, and TAC.

[0052] Even more preferably, the light-transmissive substrate comprises or consists of one or more of the following thermoplastic materials: PVC, PET, PEN, PMMA, PC, COP, COC, TAC.

[0053] Most preferably, the light-transmissive substrate comprises or consists of one or more of the following thermoplastic materials: PET, PMMA, PC, TAC.

[0054] In a particular preferred embodiment of the present invention the light-transmissive substrate comprises or consists of biaxially oriented polyethylene terephthalate (BoPET).

[0055] Preferably, the substrate is on at least one side pre-treated to ensure good adhesion to the light-transmissive layer composition. Suitable methods are generally known and include corona activation, plasma activation, chemical activation, and chemical pre-treatment to afford a thin layer of adhesion promoter (so-called primer layer).

[0056] To provide sufficient mechanical stability and flexibility, the thickness of the substrate should be chosen appropriately. The preferred thickness of the substrate generally is in the range from about 25 to about 750 pm, preferably in the range from about 50 to about 500 pm. In case of PET substrates, a thickness of about 125 to about 250 pm is even more preferred. In case of PC substrates, a thickness of about 250 to about 500 pm is even more preferred.

[0057] The microstructured light-transmissive layer preferably comprises or consists of a substantially cured coating composition.

[0058] Preferred coating compositions used for production of the light-transmissive layer can be at least partially, more preferably substantially be cured by heat, chemical activation, and / or radiation such as electron beams and UV light. More preferably, the coating composition can be substantially cured by radiation, even more preferably by UV radiation, yet even more preferably by UV light with wavelengths of about 330 to 400 nm, most preferably around 365 nm that can be emitted from UV-LED systems. BASF 240195

[0059] Coating compositions suitable for curing by UV light around 365 nm are well-known. Suitable components for such coating compositions are well-known and commercially available. Specific components can be chosen by the skilled person with respect to specific requirements such as processability of the coating composition as well as properties for the substantially cured coating composition such as mechanical strength, heat stability, weathering resistance, and transparency.

[0060] Preferred UV-curable coating compositions used for production of the light-transmissive layer comprise at least one (meth)acryl-fu notional oligomer / polymer, at least one (meth)acryl-functional monomer, and at least one photoinitiator. Throughout this text, the term “(meth)acryl” is an abbreviation for “methacryl and / or acryl”.

[0061] (Meth)acryl-functional oligomers / polymers are commonly well-known, commercially available, and preferably have more than one, more preferably 2 to 6 (meth)acryl functionalities. Preferred (meth)acryl-functional oligomers / polymers include polyester (meth)acrylates, polyether (meth)acrylates, epoxy (meth)acrylates, melamine (meth)acrylates, polyacryl (meth)acrylates, and polyurethane (meth)acrylates. Even more preferred (meth)acryl-func- tional oligomers / polymers include polyester (meth)acrylates, epoxy (meth)acrylates, polyacryl (meth)acrylates, and polyurethane (meth)acrylates.

[0062] (Meth)acryl-fu notional monomers are commonly well-known, commercially available, and have one or more, preferably 1 to 6 (meth)acryl functionalities. Preferred (meth)acryl-func- tional monomers include linear and cyclic alkyl (meth)acrylates such as butyl acrylate, hexyl acrylate, cyclohexyl methacrylate, lauryl methacrylate, 4-t-butylcyclohexyl acrylate; linear and cyclic alkyl di(meth)acrylates such as 1 ,4-butanediol diacrylate, 1 ,6-hexanediol diacrylate (HDDA), and tricyclodecane dimethanol diacrylate; alkylether-based (meth)acrylates with 2 to 6 (meth)acryl functionalities such as ethyleneglycol diacrylate, dipropyleneglycol diacrylate, tripropyleneglycol diacrylate, cyclic trimethylolpropane formalacry late, trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylates (monomers with different number of ethoxy units available, including about 3, about 6, about 9, and about 12, as well as mixtures thereof), pentaerythritol triacrylate, pentaerythritol tetraacrylate, and dipentaerythritol hexaacrylate; as well as mixtures thereof.

[0063] Photoinitiators are commonly well-known and commercially available. Common types of photoinitiators include phosphine oxides, benzophenones, a-hydroxyalkyl aryl ketones, thioxanthones, anthraquinones, acetophenones, benzoines and benzoin ethers, ketals, imid- azols, phenyl glyoxylic acids, and mixtures thereof. Preferably, photoinitiators marketed as suitable for the wavelength of the UV curing system chosen should be used. Preferably, a BASF 240195

[0064] UV curing system using UV LEDs emitting at around 365 nm is used, and photoinitiators marked for use at around 365 nm are used accordingly. Examples of such photoinitiators include ethyl 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-oxy-phenyl-acetate, ethyl 2-[2-hydroxy- ethoxy] oxy-phenyl-acetate, methyl benzoyl formate, 2,4,6-trimethylbenzoyl diphenyl phos- phinoxide, ethyl 2,4,6-trimethylbenzoyl phenyl phosphinate and bis-(2,4,6-trimethylben- zoyl) phenyl phosphinoxide. Commercial photoinitiators include pure substances and mixtures. Examples of such products are Omnirad 73, Omnirad 184, Omnirad 500, Omnirad 754, Omnirad 819, Omnirad 907, Omnirad 1173, Genocure® DETX, Genocure® EMK, Genocure® ITX, Genocure® LBC, Genocure® LTD, Genocure® LTM, Omnirad MBF and Genocure® MBF, Genocure® PMP, Genocure® TPO, and Omnirad TPO-L and Genocure® TPO-L.

[0065] A preferred coating composition used for production of the light-transmissive layer may further comprise additives such as light stabilisers, levelling agents, rheology additives such as thickening agents and thixotropy agents, and surface-active additives such as wetting agents, dispersion agents, tensides, slip agents, and anti-block agents. All such additives are commonly known and commercially available, and terms are defined, e. g., in Rbmpp Lexikon, „Lacke und Druckfarben", Thieme Verlag, 1998. Examples of commercially available additives include Efka® SL 3259, Byk® 377, Tego® Rad 2500, Tego® Rad 2800, Byk® 394, Byk-SILCLEAN 3710, Silixan® L250, Novec FC 4430, and Novec FC 4432.

[0066] Furthermore, limited amounts of dyes (amount limited so that the required degree of light- transmissiveness is not compromised) may also be comprised in the coating compositions used for production of the light-transmissive layer. It is well-known that in certain cases, adding fluorescent and / or phosphorescent dyes may increase effective, visual brightness in the visible range of the spectrum.

[0067] The light-absorbing material filling the grooves of the microlouver structure preferably comprises or consists of a substantially cured coating composition.

[0068] Preferred coating compositions used for production of the light-absorbing material can be at least partially, more preferably substantially be cured by heat, chemical activation, and / or radiation such as electron beams and UV light. More preferably, the coating composition can be substantially cured by radiation, even more preferably by UV radiation, yet even more preferably by UV light with wavelengths of about 330 to 400 nm, most preferably around 365 nm that can be emitted from UV-LED systems. BASF 240195

[0069] Preferred UV-curable coating compositions for production of the light-absorbing material comprise at least one (meth)acryl-functional oligomer / polymer, at least one (methacryl- functional monomer, at least one photoinitiator, and at least one light-absorbing substance (dye or pigment) in amounts that suffice in order to achieve the desired light-absorbing properties.

[0070] Preferred light-absorbing pigments are black pigments of natural or synthetic origin, in particular carbonaceous pigments like carbon black, ivory black, vine black, lamp black, iron pigments like mars black or iron black, manganese pigments like manganese dioxide or titanium pigments like titanium black.

[0071] Preferred light-absorbing dyes are black dyes of natural or synthetic origin such as nigrosin (Cl 50415, Solvent black 5).

[0072] Preferred UV-curable coating compositions for production of the light-absorbing material comprise at least one (meth)acryl-functional oligomer / polymer, at least one (methacryl- functional monomer, and at least one photoinitiator, preferably comprise at least one (meth)acryl-functional oligomer / polymer, at least one (meth)acryl-functional monomer, and at least one photoinitiator as described and disclosed with respect to the UV-curable coating compositions used for production of the light-transmissive layer.

[0073] A preferred coating composition used for production of the light-absorbing material may further comprise additives such as light stabilisers, levelling agents, rheology additives such as thickening agents and thixotropy agents, and surface-active additives such as wetting agents, dispersion agents, tensides, slip agents, and anti-block agents. All such additives are commonly known and commercially available, and terms are defined, e. g., in Rbmpp Lexikon, „Lacke und Druckfarben", Thieme Verlag, 1998. Examples of commercially available additives include Efka® SL 3259, Byk® 377, Tego® Rad 2500, Tego® Rad 2800, Byk® 394, Byk-SILCLEAN 3710, Silixan® L250, Novec FC 4430, and Novec FC 4432.

[0074] A light control film according to the present invention can be produced with common methods known in the art. The simple geometric design of the microstructured light-transmissive layer allows for an economical fabrication. The production process usually involves two main steps, a first step, wherein a composite of the microstructured light-transmissive layer on one surface of the substrate is fabricated, and a second step, wherein the light-absorbing material is applied in order to fill the grooves of the microlouver structure. BASF 240195

[0075] A light control film according to the present invention can be prepared by common methods known in the art, e.g. by methods as described in US 5204160 A, JP 2012093416 A, KR 20240099095 A or WO 2019118685 A1. The first step, wherein a composite of the microstructured light-transmissive layer on one surface of the substrate is produced can inter alia be conducted via roll-to-roll processes, in particular via roll-to-roll nanoimprint lithography processes, e.g. as by a process as described in EP 0428628 A1 , US 2003108710 A1 or JP 2002148417 A. The second step, wherein the light-absorbing material is applied in order to fill the grooves of the microlouver structure can be conducted by any suitable process such as spraying, dipping or rolling, e.g. by a process as described in KR 20240099095 A.

[0076] Preferred is a light control film according to the present invention, wherein the grooves of the microlouver structure are filled with the light-absorbing material up to the upper end of the trapezoidal bottom shapes and wherein the surfaces of the convex top shapes on top of the trapezoidal bottom shapes are essentially uncovered from light-absorbing material.

[0077] The main aspect of the present invention lies within the geometric features of the microstructured light-transmissive layer.

[0078] Herein and throughout the whole text the terms “microstructured”, “layer” and “coating” have the general and accepted technical meanings. The microstructured light-transmissive layer on one surface of the substrate, thus designates a covering that is applied to at least one surface of the substrate. Said layer (or covering) features microstructures, i.e. very small scale structures that cannot be resolved by the human eye without assistance, as described in detail below.

[0079] Geometric features of the light control film according to the present invention can be investigated via common and established methods known in the art. The geometric structure of the light control film according to the present invention can in particular be analysed by microscopic measurements of the microlouver structure or cross sections of the microlouver structure, in particular analysed by optical microscopy, scanning electron microscopy, transmission electron microscopy and / or fluorescence microscopy.

[0080] The microstructured light-transmissive layer according to the present invention comprises a microlouver structure, i.e., comprises a first superordinate geometric structure formed by individual elongated elements arranged parallel to each other. A certain analogy to window blinds can be drawn here, albeit shifted by a few orders of magnitude. BASF 240195

[0081] Furthermore, the microlouver structure is composed of periodically arranged louver elements as subordinate geometric structures. These louver elements are arranged in parallel within the microlouver structure with a louver period P, which is the average distance of the center of a louver element to the center of its adjacent (next-neighbour) louver element, along a first axis across the substrate surface and are at the same time elongated along a second axis across the substrate surface perpendicular to the first axis across the substrate surface.

[0082] The louver elements itself are geometrically described via the two-dimensional cross-sectional shape of the louver elements formed by an intersecting plane perpendicular to the second axis across the substrate surface, i.e. perpendicular to the axis along which the louver elements are elongated. The size dimensions of the individual components (length of sides) within the two-dimensional cross-sectional shape of the louver elements are in the range of about 1 pm to about 1000 pm, i.e., in microscale dimensions.

[0083] According to the present invention each louver element is composed of i) a two-dimensional cross-sectional bottom shape (nearest to the substrate) and ii) a two-dimensional cross- sectional convex top shape (furthest from the substrate). Accordingly, the louver element is divided into two different geometric shapes that are connected to each other, see also Figure 3.

[0084] The two-dimensional cross-sectional bottom shape is nearest to the substrate and has the form of a trapezoid. Every trapezoid per definition is a quadrilateral that has one pair of parallel sides. Trapezoids can be geometrically parameterized by the lengths of the two parallel sides, the lengths of the other two sides (called legs), the height, i.e., the distance between the two parallel sides, and the inclination angles, i.e., the angles formed between the parallel sides and the legs.

[0085] According to the present invention the two-dimensional cross-sectional trapezoid bottom shape of the louver element must at least fulfil the following geometrical conditions: i) the parallel sides of the two-dimensional cross-sectional trapezoid bottom shape are parallel to the substrate surface, and ii) both side wall inclination angles a1 and a2 formed between the parallel bottom side B nearest to the substrate surface and legs L1 and L2 of the two-dimensional cross-sectional trapezoid bottom shape are smaller than 90°. BASF Coatings GmbH 240195

[0086] According to the present invention the two-dimensional cross-sectional convex top shape of the louver element is described as follows and must at least fulfil the following geometrical conditions: i) the linear bottom side T of the two-dimensional cross-sectional convex top shape being equal to the parallel top side of the two-dimensional cross-sectional trapezoid bottom shape, and ii) the two-dimensional cross-sectional convex top shape features a convex curve c connecting the end points of T, and iii) both inner angles p1 and p2 formed between the linear bottom side T and the convex curve c are smaller than 90°.

[0087] Herein and throughout the whole text the term “convex curve c” has a broad meaning and includes a continuous line without corners, preferably in the form of an arc of a conic section, as well as a continuous line with corners, preferably in the form of a convex polygon.

[0088] The term “linear bottom side T of the two-dimensional cross-sectional convex top shape being equal to the parallel top side of the two-dimensional cross-sectional trapezoid bottom shape” nevertheless allows for small deviations between the lengths of both sides which might appear under production conditions.

[0089] The inventors of the present invention have carried out numerous investigations, simulations and considerations in order to optimise the shape of the louver elements so that the light control film features a narrow field of view, a low cutoff angle, sufficient maximum transmission, and a brightness uniformity within the field of view as characterized by a light distribution curve in the form of a rectangle function. They have thus discovered that certain geometries of the louver elements are particularly suitable in order to fulfil those beneficial effects. In that regard, it has been found that selected geometric features must be placed in relation to each other. As a result of this optimization effort it has been found, that a light control film according to the present invention features louver elements characterized as follows:

[0090] The louver element has a geometric parameter GP as defined in formula (I) in a range of from 0.40 to 5.00 | BASF Coatings GmbH | 240195 formula (I) with:

[0091] T = length of the linear bottom side of the two-dimensional cross-sectional convex top shape, n = refractive index (at A = 550 nm) of the microstructured light-transmissive layer, p being selected from inner angles p1 and p2 formed between the linear bottom side T and the convex curve c of the two-dimensional cross-sectional convex top shape,

[0092] H = height of the two-dimensional cross-sectional trapezoid bottom shape.

[0093] For determining the geometric parameter GP it has been considered that a light ray traverses the louver element. Said light ray has further being considered to traverse the louver element with an angle 0 with respect to the central axis of the louver element - the central axis of the louver element being defined as being perpendicular to the substrate surface and crossing the center of the parallel bottom side B - and exiting the louver element at one of the points A or A’ of the linear bottom side T of the two-dimensional cross- sectional convex top shape, with the additional condition that the light ray exits the louver element parallel to the central axis of the louver element. For a schematic representation we refer to Figure 4 of the present application.

[0094] These assumptions lead to the following figure of merit F for the louver element: with:

[0095] T = length of the linear bottom side T of the two-dimensional cross-sectional convex top shape, n = refractive index (at A = 550 nm) of the louver element, | BASF Coatings GmbH | 240195

[0096] 0 = angle of light ray traversing the louver element with respect to the central axis of the louver element.

[0097] Using Snell’s law of refraction it can then be shown that:

[0098] 0 = P — asin[^sin(p)] with:

[0099] 0 = angle of light ray traversing the louver element with respect to the central axis of the louver element, p being selected from inner angles p1 and p2 formed between the linear bottom side T and the convex curve c of the two-dimensional cross-sectional convex top shape, n = refractive index (at A = 550 nm) of the louver element.

[0100] Considering paraxial rays, i.e., assuming that tan(0) ~ 0 and sin(p) ~ p, the figure of merit F can be written as:

[0101] In the case of c being a circular section with a radius R and considering p = (T / 2) / R we obtain: which equals the simplified lens maker equation for a plano-convex spherical lens and further motivates the use of the figure of merit F.

[0102] It has further been found out in simulations and optimization efforts that there is a correlation between said figure of merit F and the height of the two-dimensional cross-sectional trapezoid bottom shape H. Accordingly, the geometric parameter GP was developed and defined as being F / H. Best results in terms of a narrow field of view, a low cutoff angle, BASF Coatings GmbH 240195 sufficient maximum transmission, and a brightness uniformity were obtained with louver elements, wherein the figure of merit F is close to the height of the two-dimensional cross- sectional trapezoid bottom shape H. It follows that the light control film according to the present invention is characterized by a geometric structure of the louver elements, wherein the louver element has a geometric parameter GP as defined in formula (I) in a range of from 0.40 to 5.00.

[0103] Preferred is a light control film according to the present invention, wherein the geometric parameter GP is in a range of from 0.40 to 5.00 for both inner angles p1 and p2 formed between the linear bottom side T and the convex curve c of the two-dimensional cross- sectional convex top shape.

[0104] Also preferred is a light control film according to the present invention, wherein the geometric parameter GP, preferably the geometric parameter GP for both inner angles p1 and p2 formed between the linear bottom side T and the convex curve c of the two-dimensional cross-sectional convex top shape, is in a range of from 0.50 to 4.00, preferably in a range of from 0.60 to 3.00, more preferably in a range of from 0.70 to 2.00.

[0105] Said preferred embodiments of the louver element pertaining to the geometric parameter GP allow for even better results in terms of a narrow field of view, a low cutoff angle, sufficient maximum transmission, and a brightness uniformity.

[0106] Besides the definition and refinement of the geometric parameter GP the design of the overall microlouver structure and specific geometric features of the louver elements has been studied and further optimized. In particular the size dimensions of the louver period P, the length of the parallel bottom side B of the two-dimensional cross-sectional trapezoid bottom shape and the height of the two-dimensional cross-sectional trapezoid bottom shape H have been studied with respect to the performance of the light control film in terms of a beneficial narrow field of view, a low cutoff angle, sufficient maximum transmission, and a brightness uniformity.

[0107] It has thus been found that a light control film according to the present invention is preferred, wherein the louver period P is in a range of from 10 pm to 150 pm, preferably in a range of from 15 pm to 100 pm, more preferably in a range of from 20 pm to 80 pm.

[0108] Also preferred is a light control film according to the present invention, wherein the length of the parallel bottom side B of the two-dimensional cross-sectional trapezoid bottom shape BASF 240195 is in a range of from 10 pm to 110 pm, preferably in a range of from 10 pm to 90 pm, more preferably in a range of from 15 pm to 70 pm.

[0109] Likewise preferred is light control film according to the present invention, wherein the height of the two-dimensional cross-sectional trapezoid bottom shape H, defined as the distance between both parallel sides B and T, is in a range of from 20 pm to 140 pm, preferably in a range of from 30 pm to 130 pm, more preferably in a range of from 40 pm to 120 pm.

[0110] In a particular preferred embodiment the light control film according to the present invention fulfils at least two, preferably all, of the above stated preferred embodiments pertaining to the louver period P, the length of the parallel bottom side B of the two-dimensional cross- sectional trapezoid bottom shape and the height of the two-dimensional cross-sectional trapezoid bottom shape H.

[0111] Further optimization efforts were directed to the side wall inclination angles a1 and a2 of the two-dimensional cross-sectional trapezoid bottom shape and the inner angles p1 and p2 formed between the linear bottom side T and the convex curve c of the two-dimensional cross-sectional convex top shape.

[0112] It has thus been found that a light control film according to the present invention is preferred, wherein at least one, preferably both, of the side wall inclination angles a1 and a2 of the two-dimensional cross-sectional trapezoid bottom shape are in a range of from 80.0° to 89.5°, preferably in a range of from 81 .0° to 88.0°, more preferably in a range of from 82.0° to 86.0°.

[0113] Also preferred is light control film according to the present invention, wherein at least one, preferably both, of the inner angles p1 and p2 formed between the linear bottom side T and the convex curve c of the two-dimensional cross-sectional convex top shape are in a range of from 6.0° to 85.0°, preferably in a range of from 8.0° to 80.0°, more preferably in a range of from 10.0° to 75.0°, even more preferably in a range of from 12.0° to 70.0°.

[0114] In a particular preferred embodiment the light control film according to the present invention fulfils all of the above stated preferred embodiments pertaining to the side wall inclination angles a1 and a2 of the two-dimensional cross-sectional trapezoid bottom shape and the inner angles p1 and p2 formed between the linear bottom side T and the convex curve c of the two-dimensional cross-sectional convex top shape. BASF 240195

[0115] It is preferred that the side wall inclination angles a1 and a2 of the two-dimensional cross- sectional trapezoid bottom shape are greater than the inner angles p1 and p2 formed between the linear bottom side T and the convex curve c of the two-dimensional cross-sectional convex top shape.

[0116] Said preferred and particular preferred embodiments of the louver element pertaining to the side wall inclination angles a1 and a2 of the two-dimensional cross-sectional trapezoid bottom shape and / or the inner angles p1 and p2 formed between the linear bottom side T and the convex curve c of the two-dimensional cross-sectional convex top shape allow for even better results in terms of a narrow field of view, a low cutoff angle, sufficient maximum transmission, and a brightness uniformity.

[0117] Also preferred is a light control film according to the present invention, wherein the crosssection of the two-dimensional trapezoid bottom shape has the form of an isosceles trapezoid. In this preferred embodiment the side wall inclination angles a1 and a2 of the two- dimensional cross-sectional trapezoid bottom shape are equal, i.e., a1 = a2. According to this preferred embodiment the two-dimensional trapezoid bottom shape is axially symmetrical (features a vertical axis of symmetry) which allows for an even better performance of the light control film in terms of a narrow field of view, a low cutoff angle, sufficient maximum transmission, and a brightness uniformity and which further allows for a particularly simple and economic production method.

[0118] More preferred is a light control film according to the present invention, wherein the entire two-dimensional cross-sectional shape of the louver elements has a vertical axis of symmetry. According to this more preferred embodiment the angles of the louver element are defined as follows: a1 = a2 and p1 = p2. Again this high degree of symmetry allows for an even better performance of the light control film in terms of a narrow field of view, a low cutoff angle, sufficient maximum transmission, and a brightness uniformity and further allows for a particularly simple and economic production method.

[0119] Preferred is a light control film according to the present invention, wherein the light control film has a narrow cutoff angle along the direction of the first axis across the substrate surface of at most 45°, preferably of at most 30°, more preferably of at most 25°.

[0120] The cutoff angle is determined from light distribution curves obtained after the light from a light source has passed through the light control film. Light distribution curves depict the transmission or radiance plotted over the viewing angle along the direction of the first axis BASF 240195 across the substrate surface, i.e. vertical to the louver direction (grooves). Often a logarithmic scale is used for the light distribution curves, which simplifies the visual determination of the cutoff angle and other performance parameters. For calculating the cutoff angle, intensity is converted to radiance (radiance = radiant intensity divided by the product of the surface area from which the light is emitted and the solid angle over which the intensity is measured). The cutoff angle is defined as the average of the magnitude of the two cutoff angles obtained from light distribution curves, wherein cutoff is reached at 0.01 of the maximum radiance or reached at 1 % of the radiance normalised to the maximum value. An exemplary light distribution curve obtained after the light of a light source has passed through the light control film is depicted in Figure 6.

[0121] A light control film according to the present invention is thus able to reach favourably low cutoff angles and thus decreases the viewing angle (field of view) of the light source, preventing it from being viewed from the side. The light control film according to the present invention also allows for a certain flexibility as the cutoff angle can be customised to the requirements of different application areas by simple modifications of the microlouver structure.

[0122] Also preferred is a light control film according to the present invention, wherein the light control film has an angular range of uniform light transmission of at least 45%, preferably at least 50%, more preferably at least 60% of the cutoff angle along the direction of the first axis across the substrate surface. In general the angular range of uniform light transmission is determined from light distribution curves and designates the angular range of the light distribution curves wherein the radiance allows for a good visibility of the light source, i.e. wherein the radiance is between 0.8 and 1 .0 of the normalized radiance.

[0123] In other words: The light distribution curve which is the transmission or radiance plotted over the viewing angle is close to a rectangle function with a controlled sidewall position and top height. Accordingly, a light control film according to the present invention is able to achieve a favourable homogeneous brightness (transmission) within the field of view and an also favourable sharp cutoff. The light control film according to the present invention guarantees a high brightness / transmission within the field of view. Images sent from a light source, e.g. from an infotainment screen in a car, thus appear clear, bright and sharp when the viewer is positioned within the field of view. The sharp cutoff (narrow field of view) at the same time guarantees that viewers positioned outside the field of view are not able to see light emitted from the light source and accordingly are not disturbed. E.g., the driver of a car cannot be distracted by an infotainment screen positioned in front of the passenger BASF Coatings GmbH 240195 seat while the passenger can clearly see the image of said screen when a light control film according to the present invention is applied.

[0124] Also preferred is a light control film according to the present invention, wherein the light control film has a light transmission of at least 15%, preferably at least 20%, more preferably at least 25%.

[0125] The light transmission of the light control film is the ratio of luminous flux from the light source with and without light control film.

[0126] A light control film according to the present invention is thus able to achieve a beneficially high transmission of light (brightness) which is another important performance aspect, since a high transmission of light ensures a good visibility of the light source within the field of view.

[0127] The present invention pertains to a light control film, wherein each louver element is composed of i) a two-dimensional cross-sectional bottom shape (nearest to the substrate) and ii) a two-dimensional cross-sectional convex top shape (furthest from the substrate). Accordingly, the louver element is divided into two different geometric shapes that are connected to each other.

[0128] It has been found that there are at least two preferred embodiments with respect to the geometry of the convex top shape.

[0129] The first preferred embodiment of the convex top shape pertains to a light control film according to the present invention, wherein the convex curve c of the two-dimensional cross- sectional convex top shape has the form of an arc of a conic section.

[0130] According to this first preferred embodiment, the convex curve c is a continuous (round) line without corners. The convex top shape of the louver element can thus be described in simplified terms as a cylindrical lens.

[0131] This first preferred embodiment of the present invention includes convex top shapes in the form of spherical lenses as well as aspheric lenses. BASF Coatings GmbH 240195

[0132] Preferably the convex curve c of the two-dimensional cross-sectional convex top shape has the form of a circular arc, an elliptical arc, a prolate elliptical arc, a parabolical arc or a hyperbolical arc, even more preferably the convex curve c is a circular arc.

[0133] The convex curve c in the form of an arc of a conic section can be further parametrized by the conic constant K. Accordingly, the convex curve c can be classified as being oblate elliptical (K > 0), spherical or circular (K = 0), prolate elliptical (0 > K > -1), parabolic (K = -1), and hyperbolic (K < -1).

[0134] For a convex curve c in the form of a circular arc (K = 0) with a radius of curvatur R, both, of the inner angles p1 and p2 formed between the linear bottom side T and the convex curve c of the two-dimensional cross-sectional convex top shape are equal (p1 = p2) and the inner angle p can be calculated as follows: p = asin (T / 2 R).

[0135] For a convex curve c in the form of an elliptical arc, a prolate elliptical arc, a parabolical arc or a hyperbolical arc (K 0) the following equation can be used to calculate the inner angle p numerically: wherein: z is the height of arc segment, r is the distance to the apex of arc segment,

[0136] RO is the radius at r = 0, and

[0137] K is the conic constant of the arc.

[0138] More preferred is a light control film according to the present invention, wherein the convex curve c of the two-dimensional cross-sectional convex top shape is a circular arc with a radius R, and wherein the ratio of the radius R to the height of the two-dimensional cross- sectional trapezoid bottom shape H is in a range of from 0.3:1 to 2:1 , preferably in a range of from 0.35:1 to 0.8:1 , more preferably of from 0.4:1 to 0.8:1. BASF 240195

[0139] All of the above mentioned (preferred) embodiments pertaining to a convex top shape, wherein the convex curve c of the two-dimensional cross-sectional convex top shape has the form of an arc of a conic section are particularly suitable in order to create a light control film which exhibits excellent properties in terms of a narrow field of view, a low cutoff angle, sufficient maximum transmission, brightness uniformity within the field of view as characterized by a light distribution curve in the form of a rectangle function and furthermore allow for a simple and economic production method.

[0140] The second preferred embodiment of the convex top shape pertains to a light control film according to the present invention, wherein the two-dimensional cross-sectional convextop shape has the form of a convex polygon.

[0141] According to this second preferred embodiment, the convex curve c is a continuous line with corners. The convex top shape of the louver element can thus be described in simplified terms as a prismatic lens.

[0142] Preferably the convex polygon is a tetragon, a pentagon, a hexagon, a heptagon, or an octagon. More preferably the convex polygon is a tetragon, a pentagon, ora hexagon. Even more preferably the convex polygon is a trapezoid.

[0143] It is particularly preferred that the convex polygon is an isosceles trapezoid.

[0144] Said isosceles trapezoid preferably features inner angles formed between T and c are in a range of from 10° to 30°, preferably in a range of from 12° to 30°, more preferably in a range of from 14° to 30°.

[0145] Said isosceles trapezoid preferably also features a height defined as the distance between both parallel sides of the isosceles trapezoid is in a range of from 0.5 to 2.5 pm.

[0146] All of the above mentioned (preferred) embodiments pertaining to a convex top shape, wherein the two-dimensional cross-sectional convex top shape has the form of a convex polygon are particularly suitable in order to create a light control film which exhibits excellent properties in terms of a narrow field of view, a low cutoff angle, sufficient maximum transmission, brightness uniformity within the field of view as characterized by a light distribution curve in the form of a rectangle function and furthermore allow for a simple and economic production method. BASF 240195

[0147] The present invention also pertains to the use of a light control film according to the present invention for narrowing the field of view and / or narrowing the cutoff angle of a display.

[0148] The light control film according to the present invention is preferably used as a part of a display in a means of transportation, preferably a display in a car, smartphone display, laptop display, TV, computer screen, sensor display, or watch.

[0149] The light control film according to the present invention is very versatile and can be used in many different application areas. The light control film according to the present invention is applicable and compatible to a wide variety of different light sources and materials.

[0150] The light control film according to the present invention may either be directly implemented into the respective product at the beginning of the life cycle or may be added to the respective product at a later stage.

[0151] EXAMPLES

[0152] The following examples according to the present invention are meant to further explain and illustrate the present invention without limiting its scope.

[0153] As is customary in the technical field of light control film development, the impact of the louver geometry on the light distribution curve has been tested and evaluated in optical simulations. In the following several louver geometries according to the present invention have been tested and evaluated in terms of cutoff angle, transmission, angular range of uniform light transmission and shape of the light distribution curve. Furthermore, louver geometries not according to the present invention have also been tested and evaluated under the same conditions, thus allowing for a fair comparison. Among the tested and evaluated louver geometries not according to the present invention are the structures according to prior art documents US 5,204,160 and KR 20240099095 A.

[0154] 1. Optical Simulations

[0155] For the optical simulations a common raytracing software (Lighttools from Synopsys) has been used. The general simulation layout consists of a planar surface light source emitting light with a defined light distribution and a light control film consisting of a substrate, a coating and black ink. In the optical simulations the (far-field) light distribution after the light control film and the light transmission through the light control film have been examined. BASF Coatings GmbH 240195

[0156] Results of the optical simulations were obtained in the form of light distribution curves which allow for the determination of cutoff angle, transmission, angular range of uniform light transmission and shape of the light distribution curve.

[0157] The unchanging parameters (identical for all examples) of the optical simulations were as follows:

[0158] - light source with a defined light distribution: the light distribution used can be described as the result of a Lambertian-like light source with an additional brightness enhancement film; the light distribution of the light source used in the simulations is depicted in Figure 5.

[0159] - distance of light source to light control film was set to be 1 mm;

[0160] - substrate: amorphous material with a refractive index n = 1 .654 (at A = 550 nm) and an absorption coefficient a_c = 0 mm-1(light-transmissive), thickness: 250 pm;

[0161] - microstructured coating material: amorphous material with an absorption coefficient a_c = 0 mm'1(light-transmissive); geometry and refractive index n (at A = 550 nm) have been varied in the different examples;

[0162] - material filling the grooves of the microlouver structure: amorphous material with an absorption coefficient a_c = 1000 mm-1(light-absorbing); the grooves of the microlouver structure have been simulated to be filled until the upper edge of the bottom shape of the louver elements.

[0163] All investigated louver elements feature a louver element with a trapezoidal bottom shape.

[0164] Parameters that have been varied in the optical simulations (not identical in the examples) mainly pertain to the geometric features of the microlouver structure and the louver elements and were the following:

[0165] - presence of a convex top shape (not present in example 1 -flat which is an example not according to the present invention);

[0166] - louver period P; BASF 240195

[0167] - length of the parallel bottom side B of the two-dimensional cross-sectional trapezoid bottom shape;

[0168] - length of the linear bottom side T of the two-dimensional cross-sectional convextop shape (which corresponds to the parallel top side of the two-dimensional cross-sectional trapezoid bottom shape);

[0169] - height of the two-dimensional cross-sectional trapezoid bottom shape H;

[0170] - side wall inclination angles a1 and a2 formed between the parallel bottom side B nearest to the substrate surface and legs L1 and L2 of the two-dimensional cross-sectional trapezoid bottom shape (a1 = a2 in all examples, accordingly a was used as general term for a1 and a2);

[0171] - inner angles p1 and p2 formed between the linear bottom side T and the convex curve c in the two-dimensional cross-sectional convex top shape (p1 = p2 in all examples, accordingly p was used as general term for p1 and p2), in the case of examples 7a and 7b p has been obtained upon analytical or numerical calculations;

[0172] - form of the convex curve c of the two-dimensional cross-sectional convex top shape;

[0173] - refractive index n (at A = 550 nm) of the microstructured light-transmissive layer;

[0174] - refractive index n (at A = 550 nm) of the material filling the grooves of the microlouver structure; the refractive index of the material filling the grooves of the microlouver structure was set to a similar value as the refractive index of the microstructured light-transmissive layer and was 1 .52 in all examples except in examples 1 b and 1 c.

[0175] For each of the examples the geometric parameter GP has been determined by using formula (I).

[0176] Accordingly, the results of the optical simulations allow for a direct comparison of the impact of the louver geometries and the geometric parameter GP on the performance of the light control films in terms of cutoff angle, transmission, angular range of uniform light transmission and shape of the light distribution curve.

[0177] 2. Exemplary light control films with different microlouver structures | BASF Coatings GmbH | 240195

[0178] A detailed summary of all varied parameters in the investigated examples can be found in table 1 below. Examples 1 a, 1 b, 1 c, 2, 3, 4, 5b, 6, 7a and 7b are light control films according to the present invention. Examples 1 -flat, 5a, 8a and 8b are light control films not according to the present invention. Table 1 . Geometric features of investigated louver structures

[0179] = not according to the present invention

[0180] 1= analytical or numerical calculation

[0181] 2= refractive index of louver material at A = 550 nm

[0182] Inventive examples 1a, 1b and 1c: BASF 240195

[0183] In the light control films according to examples 1 a, 1 b and 1 c some of the dimensions of the microlouver structure were chosen for practical reasons, oriented on a practical example (LCD screen). For a given LCD pixel pitch, the louver period P should be in the range of ~ 0.5 x of the pitch, above which Moire can be a problem. A typical LCD pitch has size of ~ 110 pm. Due to the scalability reasons, a higher value of the louver period P increases the height H of the two-dimensional cross-sectional trapezoid bottom shape. Above a certain height H fabrication becomes difficult (for example > 70 pm). Accordingly, the louver period P has been set to be 32 pm and the height H of the two-dimensional cross-sectional trapezoid bottom shape has been set to 55 pm. Secondly (and also for practical reasons), the length of the parallel bottom side B of the two-dimensional cross-sectional trapezoid bottom shape was set to 24 pm. The closer B to P, the higher the transmission of the light control film. However, an upper limit of the length of B is given by the lower limit of the interlouver base width (P - B), which is about 6 pm, below this fabrication becomes difficult. In examples 1 a, 1 b and 1 c the inter-louver base width was set to 8 pm (P - B = 32 pm - 24 pm). The refractive index of the material filling the grooves of the microlouver structure was set to a similar value as the refractive index of the microstructured light-transmissive layer and was n = 1 .52 in 1 a, n = 1 .4 in 1 b and n = 1 .7 in 1 c (in each case A = 550 nm).

[0184] The light control films of all inventive examples 1 a, 1 b and 1 c feature louver elements with a two-dimensional cross-sectional bottom shape and a two-dimensional cross-sectional convex top shape, wherein the two-dimensional cross-sectional convex top shape has the form of a circular arc. The radius R of the circular arc has been varied as well as the refractive index n of louver material at A = 550 nm. The geometric parameter GP, calculated according to formula (I), is 0.95 in example 1 a, 0.91 in example 1 b and 0.89 in example 1 c.

[0185] Non-inventive example 1-flat:

[0186] The light control film of non-inventive example 1-flat corresponds to example 1 a but does not feature a convex top shape on the louver element. Accordingly, for the light control film of non-inventive example 1 -flat the geometric parameter GP cannot be determined.

[0187] Inventive examples 2, 3 and 4:

[0188] Based on inventive example 1 a some geometric parameters of the microlouver structure I louver elements have been varied in inventive examples 2, 3 and 4 in order to show that the main principle according to the present invention is feasible over a wide range of different louver sizes. In example 4 the dimensions of P, B, T, H and R were scaled by a factor | BASF Coatings GmbH | 240195 of 2 in comparison to inventive example 1 a. The geometric parameter GP, calculated according to formula (I), is 0.96 in example 2, 1 .00 in example 3 and 0.95 in example 4.

[0189] Non-inventive example 5a:

[0190] Geometric parameters of the light control film according to non-inventive example 5a were obtained from the teaching according to Figure 3 of US 5,204,160. Said non-inventive prior art light control film has a geometric parameter GP, calculated according to formula (I), of 0.36.

[0191] Inventive example 5b:

[0192] Based on the geometric parameters of the light control film according to non-inventive example 5a the light control film in inventive example 5b was modified by changing the radius R of the circular arc in the two-dimensional cross-sectional convex top shape from R = 42 pm (in non-inventive example 5a) to R = 90 pm (in inventive example 5b). Accordingly, the inner angle p formed between the linear bottom side T and the convex curve c in the two- dimensional cross-sectional convex top shape was also changed from p = 23.2° (in non- inventive example 5a) to p = 57.4° (in inventive example 5b). All other geometric parameters and the refractive index of the louver material remained unchanged. Said inventive light control film has a geometric parameter GP, calculated according to formula (I), of 1 .10.

[0193] Inventive example 6:

[0194] The light control film according to inventive example 6 features a two-dimensional cross- sectional convex top shape in the form of an isosceles trapezoid with inner angles of 14.0° and a height of 1 pm. All other geometric parameters and the refractive index are the same as in inventive example 1 a. Said inventive light control film has a geometric parameter GP, calculated according to formula (I), of 1 .02.

[0195] Inventive examples 7a and 7b:

[0196] The light control films according to inventive examples 7a and 7b are based on the geometric parameters of the microlouver structure I louver element base shape of inventive example 1 a. The convex curve c of the two-dimensional cross-sectional convex top shape BASF 240195 has the form of an arc of a conic section with an apex R = 20 pm and a conic constant of K = 0 in example 7a and K = -6 in example 7b respectively. The inner angle p formed between the linear bottom side T and the convex curve c in the two-dimensional cross- sectional convex top shape has been obtained from analytical or numerical calculations and was 21 .1 ° in inventive example 7a and 15.7° in inventive example 7b respectively. The geometric parameter GP, calculated according to formula (I), is 0.67 in example 7a and 0.91 in example 7b.

[0197] Non-inventive examples 8a and 8b:

[0198] The light control films according to non-inventive examples 8a and 8b are based on the geometric parameters according to Example 1 of KR 20240099095 A. Example 1 of KR 20240099095 A gives a range from about 1 .511 to 1 .541 for the refractive index n. This is why the refractive index n has been set to 1 .511 in non-inventive example 8a (lower boundary) and to 1 .541 in non-inventive example 8b (upper boundary). The geometric parameter GP, calculated according to formula (I), is 5.8 in example 8a and 5.5 in example 8b.

[0199] 3. Performance data of investigated louver structures

[0200] The results of the optical simulations for light control films according to the invention, i.e., examples 1 a, 1 b, 1 c, 2, 3, 4, 5b, 6, 7a and 7b, and light control films not according to the present invention, i.e., examples 1 -flat, 5a, 8a and 8b were obtained in the form of light distribution curves, see also Figure 7 to Figure 20. From these light distribution curves performance data can be obtained.

[0201] Light distribution curves depict the radiance plotted over the viewing angle along the direction of the first axis across the substrate surface, i.e. vertical to the louver direction (grooves). The shape of the light distribution curve either follows a triangular or a rectangular function. A logarithmic scale is used for the light distribution curves, which simplifies the visual determination of the cutoff angle. The cutoff angle is defined as the average of the magnitude of the two cutoff angles obtained from the light distribution curves, wherein cutoff is reached at 0.01 of the radiance maximum. The angular range of uniform light transmission is the angular range of the light distribution curves wherein the radiance is between 0.8 and 1.0 of the normalized radiance. Transmission (through the light control film) can be directly obtained from the simulation data. | BASF Coatings GmbH | 240195

[0202] The results of the investigated light control films in terms of cutoff angle, transmission, angular range of uniform light transmission and the shape of the light distribution curves are summarized in table 2 below.

[0203] Table 2. Performance data of investigated light control films * = not according to the present invention

[0204] As can be seen from the results of the optical simulations all of the light control films according to the invention show beneficially low cutoff angles in a range from 22.2° (example 4) to 36° (example 5b) and furthermore show a beneficially high transmission of at least 27.6% (example 1 a) and up to 35.3% (example 5b). The shape of the light distribution curve for all the light control films according to the invention is rectangular with a controlled sidewall position and top height. The light control films according to the invention also feature an angular range of uniform light transmission (as defined above) of at least 42 % (example 5b) and up to 72 % (example 4) of the cutoff angle along the direction of the first axis across the substrate surface (i.e., the angular range defined between the two cutoff angles). Ac- cordingly, the light control films according to the invention achieve a homogeneous brightness within the field of view and a sharp cutoff.

[0205] Light control films according to the present invention are thus suitable to assure a narrow field of view, a low cutoff angle and sufficient maximum transmission, and at the same time provide for a brightness uniformity within the field of view. | BASF Coatings GmbH | 240195

[0206] This becomes particularly evident when looking at the transformation of the non-inventive light control film according to example 5a into a light control film featuring a microlouver structure with geometric properties according to the present invention (light control film according to example 5b). All performance data of the light control film could be substantially improved as the cutoff was advantageously lowered from 50° in non-inventive example 5a to 36° in inventive example 5b, transmission was advantageously increased from 28.1 % in non-inventive example 5a to 35.3 % in inventive example 5b, and the angular range of uniform light transmission was advantageously increased from 28 % in non-inventive example 5a to 42 % in inventive example 5b.

[0207] Light control films not according to the invention also achieve acceptable transmission of around 27 % to 36 %. Yet, all other performance values are significantly worse. First of all, the cutoff angles are considerably higher (up to 50° in example 5a) than the cutoff angles in light control films according to the invention. The main object of a light control film, which is to decrease the viewing angle of the light source and prevent it from being viewed from the side is thus not fulfilled. Furthermore, the light distribution curves of all light control films not according to the invention are in the form of a triangle, which corresponds to a non- uniform brightness within the field of view, since transmission decreases significantly and unfavourably even at small angles within the field of view which is disadvantageous in many applications. This also becomes apparent from the very low angular range of uniform light transmission of only28 % in non-inventive example 5a, 32 % in example 8b, 34 % in example 8a and 40 % in example 1 -flat. Light control films not according to the invention (and based on prior art) are thus only able to achieve sufficient maximum transmission, but are not able to assure a low cutoff angle and a narrow field of view, and are in particular not able to provide for a brightness uniformity within the field of view and a sharp cutoff.

[0208] BRIEF DESCRIPTION OF THE DRAWINGS

[0209] Further advantages, features and details of the invention result from the following description of the preferred embodiments as well as from the drawings. In the following, a summary of the figures is given.

[0210] Fig. 1 is a schematic representation of the main principle of a light control film. BASF Coatings GmbH 240195

[0211] Fig. 2 is a schematic representation of the main components and basic parameters of a light control film.

[0212] Fig. 3 is a schematic representation showing the two main embodiments of a louver element according to the present invention.

[0213] Fig. 4 is a schematic representation of a louver element according to the present invention including geometric details for determining the geometric parameter GP.

[0214] Fig. 5 is a diagram showing the light distribution of a typical light source without the use of a light control film.

[0215] Fig. 6 shows a typical light distribution curve obtained after the light of a light source has passed through a light control film.

[0216] Fig. 7 shows the light distribution curve obtained from a light control film according to the present invention (inventive example 1a).

[0217] Fig. 8 shows the light distribution curve obtained from a light control film according to the present invention (inventive example 1 b).

[0218] Fig. 9 shows the light distribution curve obtained from a light control film according to the present invention (inventive example 1c).

[0219] Fig. 10 shows the light distribution curve obtained from a light control film not according to the present invention (non-inventive example 1 -flat).

[0220] Fig. 11 shows the light distribution curve obtained from a light control film according to the present invention (inventive example 2).

[0221] Fig. 12 shows the light distribution curve obtained from a light control film according to the present invention (inventive example 3).

[0222] Fig. 13 shows the light distribution curve obtained from a light control film according to the present invention (inventive example 4). BASF 240195

[0223] Fig. 14 shows the light distribution curve obtained from a light control film as disclosed in the prior art and not according to the present invention (non-inventive example 5a).

[0224] Fig. 15 shows the light distribution curve obtained from a light control film according to the present invention (inventive example 5b).

[0225] Fig. 16 shows the light distribution curve obtained from a light control film according to the present invention (inventive example 6).

[0226] Fig. 17 shows the light distribution curve obtained from a light control film according to the present invention (inventive example 7a).

[0227] Fig. 18 shows the light distribution curve obtained from a light control film according to the present invention (inventive example 7b).

[0228] Fig. 19 shows the light distribution curve obtained from a light control film as disclosed in the prior art and not according to the present invention (non-inventive example 8a).

[0229] Fig. 20 shows the light distribution curve obtained from a light control film as disclosed in the prior art and not according to the present invention (non-inventive example 8b).

[0230] DETAILED DESCRIPTION OF THE DRAWINGS

[0231] Fig. 1 is a schematic representation of the main principle of a light control film 100. Light is emitted from a two-dimensional (flat) light source 200, e.g. a LCD screen, in an angular range of from -90° to 90° (non-directed) and passes through the light control film 100 after which the field of view is narrowed in at least one direction which prevents the light source from being viewed from the side.

[0232] Fig. 2 is a schematic representation of the main components and basic parameters of a light control film 100, which generally comprises a substrate 101 , a microstructured light- transmissive layer on one surface of the substrate 102, the so called microlouver structure, and a light-absorbing material filling the grooves of the microlouver structure 103. The microstructured light-transmissive layer on one surface of the substrate 102 is composed of periodically arranged and parallel aligned louver elements. The louver elements have a two-dimensional cross-sectional shape in the form of a trapezoid. The microlouver structure BASF 240195 can be characterized with the following geometric parameters: louver period P, height of the louver element H, base length of the louver element B and side wall inclination angles a.

[0233] Fig. 3 is a schematic representation showing the two main embodiments of a louver element 300 according to the present invention. Fig. 3 shows the two-dimensional cross-sectional shape of the louver element 300. It can be seen that the louver element 300 is composed of a two-dimensional cross-sectional bottom shape 400 in the form of a trapezoid and a two-dimensional cross-sectional convex top shape 501 or 502. The two-dimensional cross-sectional convex top shape 501 or 502 is composed of a linear bottom side T being equal to the parallel top side of the two-dimensional cross-sectional trapezoid bottom shape and a convex curve c connecting the end points of T with an inner angles p formed between the linear bottom side T and the convex curve c. In the embodiment according to Fig. 3 A) the convex curve c of the two-dimensional cross-sectional convex top shape 501 has the form of an arc of a conic section (here: a circular arc with a radius R). In the embodiment according to Fig. 3 B) the two-dimensional cross-sectional convex top shape 502 has the form of a convex polygon (here: an isosceles trapezoid).

[0234] Fig. 4 is a schematic representation of a louver element 300 according to the present invention including geometric details for determining the geometric parameter GP. Said louver element 300 is composed of a two-dimensional cross-sectional bottom shape 400 in the form of a trapezoid and a two-dimensional cross-sectional convex top shape 501 which has the form of a circular arc. For determining the geometric parameter GP it has been considered that a light ray traverses the louver element 300. Said light ray has further being considered to traverse the louver element with an angle 0 with respect to the central axis of the louver element - the central axis of the louver element being defined as being perpendicular to the substrate surface and crossing the center of the parallel bottom side B - and exiting the louver element at one of the points A or A’ of the linear bottom side T of the two-dimensional cross-sectional convex top shape 501 , with the additional condition that the light ray exits the louver element parallel to the central axis of the louver element.

[0235] Fig. 5 is a diagram showing the light distribution of a typical light source without the use of a light control film. The light distribution curve depicts the radiance (a.u.) plotted over the viewing angle in vertical direction to the light source. A logarithmic scale is used. It can be seen that the light distribution curve of a typical light source has a Gaussian-like distribution, i.e. no sharp cutoff angles and a wide field of view.

[0236] Fig. 6 shows a typical light distribution curve obtained after the light of a light source has passed through a typical light control film. The light distribution curve depicts the radiance BASF 240195

[0237] (a.u.) plotted over the viewing angle along the direction of the first axis across the substrate surface, i.e. vertical to the louver direction (grooves). A logarithmic scale is used. It can be seen the light distribution curve now has a more triangular / rectangular function and the field of view is narrowed.

[0238] Fig. 7 shows the light distribution curve obtained from a light control film according to the present invention (inventive example 1 a). The light distribution curve depicts the radiance (a.u.) plotted over the viewing angle along the direction of the first axis across the substrate surface, i.e. vertical to the louver direction (grooves). As can be seen from the light distribution curve obtained from the light control film according to inventive example 1 a follows a rectangular function, shows a beneficially low cutoff angle of 22.5° and a beneficially high angular range of uniform light transmission of 71 %. Accordingly, the light control film according to inventive example 1 a achieves a narrow field of view, a low cutoff angle and a homogeneous brightness within the field of view and accordingly, a sharp cutoff.

[0239] Fig. 8 shows the light distribution curve obtained from a light control film according to the present invention (inventive example 1 b). The light distribution curve depicts the radiance (a.u.) plotted over the viewing angle along the direction of the first axis across the substrate surface, i.e. vertical to the louver direction (grooves). As can be seen from the light distribution curve obtained from the light control film according to inventive example 1 b follows a rectangular function, shows a beneficially low cutoff angle of 23.0° and a beneficially high angular range of uniform light transmission of 57 %. Accordingly, the light control film according to inventive example 1 b achieves a narrow field of view, a low cutoff angle and a homogeneous brightness within the field of view and accordingly, a sharp cutoff.

[0240] Fig. 9 shows the light distribution curve obtained from a light control film according to the present invention (inventive example 1 c). The light distribution curve depicts the radiance (a.u.) plotted over the viewing angle along the direction of the first axis across the substrate surface, i.e. vertical to the louver direction (grooves). As can be seen from the light distribution curve obtained from the light control film according to inventive example 1 c follows a rectangular function, shows a beneficially low cutoff angle of 25.0° and a beneficially high angular range of uniform light transmission of 60 %. Accordingly, the light control film according to inventive example 1 c achieves a narrow field of view, a low cutoff angle and a homogeneous brightness within the field of view and accordingly, a sharp cutoff.

[0241] Fig. 10 shows the light distribution curve obtained from a light control film not according to the present invention (non-inventive example 1 -flat). The light distribution curve depicts the radiance (a.u.) plotted over the viewing angle along the direction of the first axis across the BASF 240195 substrate surface, i.e. vertical to the louver direction (grooves). As can be seen from the light distribution curve obtained from the light control film according to non-inventive example 1 -flat follows a triangular function, shows a rather high cutoff angle of 30.0° and a disadvantageous^ low angular range of uniform light transmission of only 40 %. Accordingly, the light control film according to non-inventive example 1 -flat is not able to assure a low cutoff angle and a narrow field of view, and is also not able to provide for a brightness uniformity within the field of view.

[0242] Fig. 11 shows the light distribution curve obtained from a light control film according to the present invention (inventive example 2). The light distribution curve depicts the radiance (a.u.) plotted over the viewing angle along the direction of the first axis across the substrate surface, i.e. vertical to the louver direction (grooves). As can be seen from the light distribution curve obtained from the light control film according to inventive example 2 follows a rectangular function, shows a beneficially low cutoff angle of 24.2° and a beneficially high angular range of uniform light transmission of 62 %. Accordingly, the light control film according to inventive example 2 achieves a narrow field of view, a low cutoff angle and a homogeneous brightness within the field of view and accordingly, a sharp cutoff.

[0243] Fig. 12 shows the light distribution curve obtained from a light control film according to the present invention (inventive example 3). The light distribution curve depicts the radiance (a.u.) plotted over the viewing angle along the direction of the first axis across the substrate surface, i.e. vertical to the louver direction (grooves). As can be seen from the light distribution curve obtained from the light control film according to inventive example 3 follows a rectangular function, shows a beneficially low cutoff angle of 26.5° and a beneficially high angular range of uniform light transmission of 57 %. Accordingly, the light control film according to inventive example 3 achieves a narrow field of view, a low cutoff angle and a homogeneous brightness within the field of view and accordingly, a sharp cutoff.

[0244] Fig. 13 shows the light distribution curve obtained from a light control film according to the present invention (inventive example 4). The light distribution curve depicts the radiance (a.u.) plotted over the viewing angle along the direction of the first axis across the substrate surface, i.e. vertical to the louver direction (grooves). As can be seen from the light distribution curve obtained from the light control film according to inventive example 4 follows a rectangular function, shows a beneficially low cutoff angle of 22.2° and a beneficially high angular range of uniform light transmission of 72 %. Accordingly, the light control film according to inventive example 4 achieves a narrow field of view, a low cutoff angle and a homogeneous brightness within the field of view and accordingly, a sharp cutoff. BASF 240195

[0245] Fig. 14 shows the light distribution curve obtained from a light control film as disclosed in the prior art, according to Figure 3 of US 5,204,160, and not according to the present invention (non-inventive example 5a). The light distribution curve depicts the radiance (a.u.) plotted over the viewing angle along the direction of the first axis across the substrate surface, i.e. vertical to the louver direction (grooves). As can be seen from the light distribution curve obtained from the light control film according to non-inventive example 5a follows a triangular function, shows a disadvantageously high cutoff angle of 50° and a disadvanta- geously low angular range of uniform light transmission of only 28 %. Accordingly, the light control film according to non-inventive example 5a is not able to assure a low cutoff angle and a narrow field of view, and is also not able to provide for a brightness uniformity within the field of view.

[0246] Fig. 15 shows the light distribution curve obtained from a light control film according to the present invention (inventive example 5b). The light distribution curve depicts the radiance (a.u.) plotted over the viewing angle along the direction of the first axis across the substrate surface, i.e. vertical to the louver direction (grooves). As can be seen from the light distribution curve obtained from the light control film according to inventive example 5b follows a rectangular function, shows a cutoff angle of 36° and a beneficially high angular range of uniform light transmission of 42 %. Accordingly, the light control film according to inventive example 5b achieves a narrow field of view, a low cutoff angle and a homogeneous brightness within the field of view and accordingly, a sharp cutoff.

[0247] Fig. 16 shows the light distribution curve obtained from a light control film according to the present invention (inventive example 6). The light distribution curve depicts the radiance (a.u.) plotted over the viewing angle along the direction of the first axis across the substrate surface, i.e. vertical to the louver direction (grooves). As can be seen from the light distribution curve obtained from the light control film according to inventive example 6 follows a rectangular function, shows a beneficially low cutoff angle of 23.5° and a beneficially high angular range of uniform light transmission of 60 %. Accordingly, the light control film according to inventive example 6 achieves a narrow field of view, a low cutoff angle and a homogeneous brightness within the field of view and accordingly, a sharp cutoff.

[0248] Fig. 17 shows the light distribution curve obtained from a light control film according to the present invention (inventive example 7a). The light distribution curve depicts the radiance (a.u.) plotted over the viewing angle along the direction of the first axis across the substrate surface, i.e. vertical to the louver direction (grooves). As can be seen from the light distribution curve obtained from the light control film according to inventive example 7a follows a rectangular function, shows a beneficially low cutoff angle of 26.0° and a beneficially high BASF 240195 angular range of uniform light transmission of 54 %. Accordingly, the light control film according to inventive example 7a achieves a narrow field of view, a low cutoff angle and a homogeneous brightness within the field of view and accordingly, a sharp cutoff.

[0249] Fig. 18 shows the light distribution curve obtained from a light control film according to the present invention (inventive example 7b). The light distribution curve depicts the radiance (a.u.) plotted over the viewing angle along the direction of the first axis across the substrate surface, i.e. vertical to the louver direction (grooves). As can be seen from the light distribution curve obtained from the light control film according to inventive example 7b follows a rectangular function, shows a beneficially low cutoff angle of 22.5° and a beneficially high angular range of uniform light transmission of 67 %. Accordingly, the light control film according to inventive example 7b achieves a narrow field of view, a low cutoff angle and a homogeneous brightness within the field of view and accordingly, a sharp cutoff.

[0250] Fig. 19 shows the light distribution curve obtained from a light control film as disclosed in the prior art, according to Example 1 of KR 20240099095 A, and not according to the present invention (non-inventive example 8a). The light distribution curve depicts the radiance (a.u.) plotted over the viewing angle along the direction of the first axis across the substrate surface, i.e. vertical to the louver direction (grooves). As can be seen from the light distribution curve obtained from the light control film according to non-inventive example 8a follows a triangular function, shows a comparatively high cutoff angle of 26.8° and a disad- vantageously low angular range of uniform light transmission of only 34 %. Accordingly, the light control film according to non-inventive example 8a is not able to assure a low cutoff angle and a narrow field of view, and is also not able to provide for a brightness uniformity within the field of view.

[0251] Fig. 20 shows the light distribution curve obtained from a light control film as disclosed in the prior art, according to Example 1 of KR 20240099095 A, and not according to the present invention (non-inventive example 8b). The light distribution curve depicts the radiance (a.u.) plotted over the viewing angle along the direction of the first axis across the substrate surface, i.e. vertical to the louver direction (grooves). As can be seen from the light distribution curve obtained from the light control film according to non-inventive example 8b follows a triangular function, shows a comparatively high cutoff angle of 27.9° and a disad- vantageously low angular range of uniform light transmission of only 32 %. Accordingly, the light control film according to non-inventive example 8b is not able to assure a low cutoff angle and a narrow field of view, and is also not able to provide for a brightness uniformity within the field of view. | BASF Coatings GmbH | 240195

[0252] List of reference signs:

[0253] 100 light control film

[0254] 101 substrate

[0255] 102 microstructured light-transmissive layer with microlouver structure 103 light-absorbing material filling the grooves of the microlouver structure

[0256] 200 two-dimensional (flat) light source

[0257] 300 louver element

[0258] 400 two-dimensional cross-sectional bottom shape in the form of a trapezoid

[0259] 501 two-dimensional cross-sectional convex top shape, wherein the convex curve c has the form of an arc of a conic section (circular arc)

[0260] 502 two-dimensional cross-sectional convex top shape in the form of a convex polygon (isosceles trapezoid)

Claims

BASF240195CLAIMS1 . Light control film comprising a) a substrate, b) a microstructured light-transmissive layer on one surface of the substrate, the microstructured light-transmissive layer comprising a microlouver structure composed of periodically arranged louver elements with a louver period P along a first axis across the substrate surface and elongated along a second axis across the substrate surface perpendicular to the first axis across the substrate surface, and c) a light-absorbing material filling the grooves of the microlouver structure, wherein- the two-dimensional cross-sectional shape of the louver elements formed by an intersecting plane perpendicular to the second axis across the substrate surface is composed of a two-dimensional cross-sectional bottom shape and a two-dimensional cross-sectional convex top shape,- the two-dimensional cross-sectional bottom shape is nearest to the substrate and has the form of a trapezoid,- the parallel sides of the two-dimensional cross-sectional trapezoid bottom shape are parallel to the substrate surface,- both side wall inclination angles a1 and a2 formed between the parallel bottom side B nearest to the substrate surface and legs L1 and L2 of the two-dimensional cross- sectional trapezoid bottom shape are smaller than 90°,- the two-dimensional cross-sectional convex top shape is composed of a linear bottom side T being equal to the parallel top side of the two-dimensional cross-sectional trapezoid bottom shape and a convex curve c connecting the end points of T, wherein both inner angles p1 and p2 formed between the linear bottom side T and the convex curve c are smaller than 90°,| BASF Coatings GmbH| 240195- the louver element has a geometric parameter GP as defined in formula (I) in a range of from 0.40 to 5.00formula (I) with:T = length of the linear bottom side of the two-dimensional cross-sectional convex top shape, n = refractive index (at A = 550 nm) of the microstructured light-transmissive layer, p being selected from inner angles p1 and p2 formed between the linear bottom side T and the convex curve c of the two-dimensional cross-sectional convex top shape,H = height of the two-dimensional cross-sectional trapezoid bottom shape.

2. Light control film according to claim 1 , wherein the geometric parameter GP is in a range of from 0.40 to 5.00 for both inner angles p1 and p2 formed between the linear bottom side T and the convex curve c of the two-dimensional cross-sectional convex top shape.

3. Light control film according to any of the preceding claims, wherein the geometric parameter GP, preferably the geometric parameter GP for both inner angles p1 and p2 formed between the linear bottom side T and the convex curve c of the two-dimensional cross-sectional convex top shape, is in a range of from 0.50 to 4.00, preferably in a range of from 0.60 to 3.00, more preferably in a range of from 0.70 to 2.00.

4. Light control film according to any of the preceding claims, wherein- the louver period P is in a range of from 10 pm to 150 pm, preferably in a range of from 15 pm to 100 pm, more preferably in a range of from 20 pm to 80 pm,BASF240195and / or- the length of the parallel bottom side B of the two-dimensional cross-sectional trapezoid bottom shape is in a range of from 10 pm to 110 pm, preferably in a range of from 10 pm to 90 pm, more preferably in a range of from 15 pm to 70 pm, and / or- the height of the two-dimensional cross-sectional trapezoid bottom shape H, defined as the distance between both parallel sides B and T, is in a range of from 20 pm to 140 pm, preferably in a range of from 30 pm to 130 pm, more preferably in a range of from 40 pm to 120 pm.

5. Light control film according to any of the preceding claims, wherein at least one, preferably both, of the side wall inclination angles a1 and a2 of the two-dimensional cross- sectional trapezoid bottom shape are in a range of from 80.0° to 89.5°, preferably in a range of from 81.0° to 88.0°, more preferably in a range of from 82.0° to 86.0°.

6. Light control film according to any of the preceding claims, wherein at least one, preferably both, of the inner angles p1 and p2 formed between the linear bottom side T and the convex curve c of the two-dimensional cross-sectional convex top shape are in a range of from 6.0° to 85.0°, preferably in a range of from 8.0° to 80.0°, more preferably in a range of from 10.0° to 75.0°, particularly preferably in a range of from 12.0° to 70.0°.

7. Light control film according to any of the preceding claims, wherein the cross-section of the two-dimensional trapezoid bottom shape has the form of an isosceles trapezoid, preferably the entire two-dimensional cross-sectional shape of the louver elements has a vertical axis of symmetry.

8. Light control film according to any of the preceding claims, wherein the light control film has a narrow cutoff angle along the direction of the first axis across the substrate surface of at most 45°, preferably of at most 30°, more preferably of at most 25°.

9. Light control film according to any of the preceding claims, wherein the light control film has an angular range of uniform light transmission of at least 45%, preferably at least 50%, more preferably at least 60% of the cutoff angle along the direction of the first axis across the substrate surface.BASF24019510. Light control film according to any of the preceding claims, wherein the convex curve c of the two-dimensional cross-sectional convextop shape has the form of an arc of a conic section, preferably has the form of a circular arc, an elliptical arc, a prolate elliptical arc, a parabolical arc or a hyperbolical arc, even more preferably the convex curve c is a circular arc.

11. Light control film according to claim 10, wherein the convex curve c of the two-dimensional cross-sectional convex top shape is a circular arc with a radius R, and wherein the ratio of the radius R to the height of the two-dimensional cross-sectional trapezoid bottom shape H is in a range of from 0.3:1 to 2:1 , preferably in a range of from 0.35:1 to 0.8:1 , more preferably of from 0.4:1 to 0.8:1.

12. Light control film according to any of claims 1 to 9, wherein the two-dimensional cross-sectional convex top shape has the form of a convex polygon.

13. Light control film according to claim 12, wherein the convex polygon is a tetragon, a pentagon, a hexagon, a heptagon, or an octagon, preferably a tetragon, a pentagon, or a hexagon, more preferably a trapezoid.

14. Light control film according to claim 12 or 13, wherein the convex polygon is an isosceles trapezoid, wherein preferably- the inner angles of the isosceles trapezoid formed between T and c are in a range of from 10° to 30°, preferably in a range of from 12° to 30°, more preferably in a range of from 14° to 30°, and / or- the height of the isosceles trapezoid defined as the distance between both parallel sides of the isosceles trapezoid is in a range of from 0.5 to 2.5 pm.

15. Use of a light control film according to any of the preceding claims for narrowing the field of view and / or narrowing the cutoff angle of a display,Coatings GmbH| 240195wherein preferably the light control film is used as a part of a- display in a means of transportation, preferably a display in a car,- smartphone display,- laptop display, - TV,- computer screen,- sensor display, or- watch.

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