Patent Application
20240255678
The present description generally relates to optically diffusive films that include particles dispersed in a binder and to methods of making optically diffusive films that include extruding an immiscible blend. The optically diffusive film may be more optically diffusive for a light polarized along a block-direction and less optically diffusive for light polarized along an orthogonal pass-direction.
In some aspects, the present description provides an optically diffusive film including a plurality of particles dispersed in a binder. The particles and the binder have respective indices n1b and n2b along a same in-plane block-direction of the optically diffusive film, and respective indices nip and n2p along an in-plane pass-direction orthogonal to the block-direction, such that for at least a first wavelength in a first wavelength range extending from about 400 nm to about 1000 nm: a magnitude of a difference between n1b and n2b is greater than about 0.05; and a magnitude of a difference between nip and n2p is less than about 0.05. In some embodiments, for a substantially normally incident light having the first wavelength, the optically diffusive film has: a diffuse optical transmittance TDb and a diffuse optical reflectance RDb when the incident light is polarized along the block-direction, where TDb/RDb≥4; and a total optical transmittance TTp and a diffuse optical transmittance TDp when the incident light is polarized along the pass-direction, where TTp/TDp≥1.1. In some such embodiments, or in other embodiments, for a substantially normally incident light having the first wavelength, the optically diffusive film has: a total optical transmittance TTb and a total optical reflectance RTb when the incident light is polarized along the block-direction, where TTb/RTb≥2; and a total optical transmittance TTp and a total optical reflectance RTp when the incident light is polarized along the pass-direction, where TTp/RTp≥6. In some such embodiments, or in other embodiments, for a substantially normally incident light having the first wavelength, the optically diffusive film has specular optical transmittances TSp and TSb when the incident light is polarized along the respective pass- and block-directions, where TSp/TSb≥2.
In some aspects, the present description provides an extruded optically diffusive film extruded along a pass-direction and including: a plurality of particles dispersed in a binder, where the particles are elongated along substantially a same in-plane block-direction orthogonal to the pass-direction and have an average aspect ratio of greater than about 5; and a plurality of substantially parallel extrusion die-lines making an angle of less than about 20 degrees with the pass-direction. In some embodiments, for a substantially normally incident light having a first wavelength in a first wavelength range extending from about 400 nm to about 1000 nm, the optically diffusive film has: a diffuse optical transmittance TDb and a diffuse optical reflectance RDb when the incident light is polarized along the block-direction, where TDb/RDb≥4; and a total optical transmittance TTp and a diffuse optical reflectance RDp when the incident light is polarized along the pass-direction, where TTp/RDp≥10. In some such embodiments, or in other embodiments, for a substantially normally incident light having the first wavelength, the optically diffusive film has specular optical transmittances TSp and TSb when the incident light is polarized along the respective pass- and block-directions, where TSp/TSb≥2.
In some aspects, the present description provides a method of making an optically diffusive film. The method includes extruding an immiscible blend of a minor phase material and a major phase material through a die and along a pass-direction at a first temperature greater than glass transition temperatures of the minor and major phase materials resulting in an extruded mixture at substantially the first temperature and comprising a plurality of substantially spherical domains; and stretching the extruded mixture along a block-direction, substantially orthogonal to the pass-direction, at a second temperature less than the first temperature resulting in a plurality of particles dispersed in a binder. The binder and each of at least a majority of the particles have respective indices n2b and n1b along the block-direction and respective indices n2p and nip along the pass-direction, such that for at least a first wavelength in a first wavelength range extending from about 400 nm to about 1000 nm: a magnitude of a difference between n1b and n2b is greater than about 0.05; and a magnitude of a difference between nip and n2p is less than about 0.05.
These and other aspects will be apparent from the following detailed description. In no event, however, should this brief summary be construed to limit the claimable subject matter.
In the following description, reference is made to the accompanying drawings that form a part hereof and in which various embodiments are shown by way of illustration. The drawings are not necessarily to scale. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present description. The following detailed description, therefore, is not to be taken in a limiting sense.
According to some embodiments of the present description, an optically diffusive film has a higher haze for light polarized along a first direction (which may also be referred to as a “block” direction) than for light polarized along an orthogonal second direction (which may also be referred to as a “pass” direction) and may have a larger scattering in a plane define by the second direction and a thickness direction than in a plane defined by the first and thickness directions. The optically diffusive film may be useful, for example, in display or sensor applications. For example, a display can be constructed where light passes through a liquid crystal display (LCD) panel with a narrow viewing angle (e.g., after passing through crossed prism films) and on the exit side of the LCD panel, the optically diffusive film can be disposed with the second direction oriented horizontally to broaden the viewing angle in the horizontal plane. As another example, the optically diffusive film can be used with a % wave retarder on an optical device (e.g., an optical sensor) so that when light polarized along the block direction is incident on the device with a broad angular distribution and any such light that is reflected from the device back toward the optically diffusive film through the retarder is incident on the optically diffusive film in the lower scattering pass state and/or so that when light polarized along the pass direction is incident on the device with a narrow angular distribution and any such light reflected from the device back toward the optically diffusive film through the retarder is incident on the optically diffusive film in the block state and is substantially transmitted through the optically diffusive film with a wider angular distribution.
According to some embodiments of the present description, an optically diffusive film includes a plurality of particles dispersed in a binder where the particles are substantially optically isotropic (e.g., a difference between largest and smallest refractive indices of the particles for at least one wavelength in a range of about 400 nm to about 1000 nm can be less than about 0.05, or less than about 0.04, or less than about 0.03, or less than about 0.02, or less than about 0.01) and where the binder is birefringent (e.g., a difference between largest and smallest refractive indices of the binder for at least one wavelength in a range of about 400 nm to about 1000 nm can be greater than about 0.05, or greater than about 0.06, or greater than about 0.07, or greater than about 0.08, or greater than about 0.09, or greater than about 0.1 and the difference may be up to about 0.35, or up to about 0.3, or up to about 0.25, for example). A difference in refractive indices of the binder and the particles can be substantially different (e.g., differ by greater than about 0.05, or greater than about 0.06, or greater than about 0.07, or greater than about 0.08, or greater than about 0.09, or greater than about 0.1 and the difference may be up to about 0.35, or up to about 0.3, or up to about 0.25, for example) along a first direction and substantially matched (e.g., differ by less than about 0.05, or less than about 0.04, or less than about 0.03, or less than about 0.02, or less than about 0.01) along an orthogonal second direction. The particles may be elongated along the first direction which can result larger scattering in the second direction (i.e., in a scattering plane comprising the second direction) than in the first direction.
The optical properties of the optically diffusive film can be adjusted by selecting the binder and particle materials to have differences in refractive indices in desired ranges along the block and pass axes, adjusting the number or volume of the particles, and adjusting the shape of the particles. Increasing the refractive index difference in the block direction generally increases scattering in the block polarization state. Increasing the number of particles also increases the scattering. The index difference and the number of particles can be selected to result in mostly forward scattering, for example. The optically diffusive film can be formed by extrusion followed by stretching (e.g., using a standard (linear) tenter or a nonlinear tenter such as a parabolic tenter) as described further elsewhere herein. The draw ratio used in the stretching can affect the refractive index of the binder (e.g., increasing in the draw direction for positively birefringent polymers) and the shape of the particles (e.g., resulting in particles elongated along the draw direction). The draw ratio can be at least about 1:1, or at least about 2:1, or at least about 3:1, or at least about 4:1, or at least about 4.5:1 and may be up to about 30:1, or up to about 20:1, or up to about 15:1, or up to about 10:1, or up to about 8:1, or up to about 7:1, for example. The draw ratio may be in a range from about 3:1 to about 10:1, or from about 4:1 to about 8:1, or from about 4.5:1 to about 7:1, for example. It has been found that elongating the particles along the draw direction, which may also be the block direction, can result in increased scattering in a scattering plane orthogonal to draw direction.
The binder 20 and the particles 10, 11 have refractive indices along each of the illustrated b-, p-, and z-directions. In some embodiments, an optically diffusive film 200, 201 includes a plurality of particles 10, 11 dispersed in a binder 20, where the particles and the binder have respective indices n1b and n2b along a same in-plane (pb-plane) block-direction (b-direction) of the optically diffusive film 200, 201, and respective indices nip and n2p along an in-plane pass-direction (p-direction) orthogonal to the block direction, such that for at least a first wavelength in a first wavelength range extending from about 400 nm to about 1000 nm: a magnitude of a difference between n1b and n2b is greater than about 0.05; and a magnitude of a difference between nip and n2p is less than about 0.05. In some such embodiments, or in other embodiments, for at least the first wavelength, a magnitude of a difference between n1b and n2b is greater than about 0.05, or greater than about 0.06, or greater than about 0.07, or greater than about 0.08, or greater than about 0.09, or greater than about 0.1. In some such embodiments, or in other embodiments, for at least the first wavelength, magnitude of a difference between nip and n2p is less than about 0.05, or less than about 0.04, or less than about 0.03, or less than about 0.02, or less than about 0.01.
The at least a first wavelength may include one or more wavelengths in a second wavelength range narrower than the first wavelength range. For example, the at least a first wavelength may include one or more wavelengths in a second wavelength range of about 400 nm to about 700 nm, or about 420 nm to about 680 nm, or about 450 nm to about 650 nm, for example. Alternatively, the first wavelength range may be a narrower range than about 400 nm to about 1000 nm (e.g., the first wavelength range may be any of the ranges described for the second wavelength range). A wavelength range (e.g., corresponding to the first or second wavelength ranges) extending from λ1 to λ2 is schematically illustrated in
In some embodiments, for a substantially normally incident light 30 having the first wavelength, the optically diffusive film 200, 201 has: a diffuse optical transmittance TDb and a diffuse optical reflectance RDb when the incident light is polarized along the block-direction, TDb/RDb≥4; and a total optical transmittance TTp and a diffuse optical transmittance TDp when the incident light is polarized along the pass-direction, TTp/TDp≥1.1. A low backscattering (e.g., as quantified by a TDb/RDb of at least 4) for light polarized along the block-direction may be desired while a limited diffuse transmittance relative to total transmittance (e.g., as quantified by a TTp/TDp of at least 1.1) for light polarized along the pass-direction may be desired in some applications.
Substantially normally incident light may be within 30 degrees, or 20 degrees, or 10 degrees of normal, or may be nominally normal, for example. For obliquely incident light, the light may be described as polarized along the block- or pass-directions when the polarization state projected onto the bp-plane is along the respective block- or pass-directions.
In some embodiments, for the substantially normally incident light 30 having the first wavelength, the optically diffusive film 200, 201 has a diffuse optical reflectance RDp when the incident light is polarized along the pass-direction. A low backscattering (e.g., as quantified by a TTp/RDp being at least 10 and/or as quantified by TTp/RTp, described elsewhere, being at least 6) for light polarized along the pass-direction may be desired in some applications. In some embodiments, TTp/RDp≥10, or TTp/RDp≥15, or TTp/RDp≥20, or TTp/RDp≥25, or TTp/RDp≥30, or TTp/RDp≥35. In some such embodiments, or in other embodiments, for the substantially normally incident light 30 having the first wavelength, the optically diffusive film 200, 201 has a total optical reflectance RTp when the incident light is polarized along the pass-direction, where TTp/RTp≥6, or TTp/RTp≥7, or TTp/RTp≥8, or TTp/RTp≥9. Typically, TTp/RDp and TTp/RTp generally increase when reducing the number or volume of particles included in the binder and/or when reducing the refractive index difference between the particles and the binder along the pass-direction. TTp/RDp can be up to about 100, or up to about 80, or up to about 70, for example. TTp/RTp can be up to about 25, or up to about 20, or up to about 18, for example.
For some applications, a higher haze is desired for light polarized along the block-direction than for light polarized along the pass-direction. In some embodiments, the optically diffusive film 200, 201 has an optical haze Hb for substantially normally incident light 30, 30b polarized along the block-direction and an optical haze Hp for substantially normally incident light 30, 30p polarized along the pass-direction, where Hb/Hp≥1.5, or Hb/Hp≥2, or Hb/Hp≥2.5, or Hb/Hp≥3, or Hb/Hp≥3.5. The optical haze of a film for a specified polarization state can be measured using a haze meter (e.g., a Haze-Gard haze meter available from BYK Corporation, Wesel, Germany) with an absorbing linear polarizer disposed on the film facing the light source of the haze meter with a pass axis of the polarizer aligned with the specified polarization state. The optical haze can be determined as described in the ASTM D1003-13 test standard except that the test specimen includes the absorbing linear polarizer disposed on the film. Typically, the optical haze Hb generally increases when increasing the difference in refractive indices of the particles and the binder along the block-direction and/or when increasing the number of the particles. The optical haze Hb can be high (e.g., greater than about 80% or greater than about 90%) when the refractive indices of the particles and the binder are substantially different (e.g., different by at least about 0.08 or at least about 0.1) along the block-direction, for example. The optical haze Hp can be low (e.g., less than about 2% or less than about 1%) when the refractive indices of the particles and the binder are closely matched (e.g., to within about 0.02, or about 0.01) along the pass-direction, for example. Hb/Hp may be up to about 100, or up to about 50, or up to about 25, or up to about 20, for example. In some embodiments, Hb is in a range of about 10% to about 100%, or about 15% to about 99%, or about 20% to about 98%, or about 20% to about 90%. In some such embodiments, or in other embodiments, Hp is in a range of about 0% to about 65%, or about 0.5% to about 60%, or about 1% to about 55%, or about 1.2% to about 50%, or about 5% to about 45%, or about 10% to about 40%. A higher haze for light 30b than for light 30p is schematically indicated in
In some embodiments, for a substantially normally incident light 30 having the first wavelength, the optically diffusive film 200, 201 has a total optical transmittance TTb when the incident light is polarized along the block-direction. TTb may be similar to TTp (e.g., both may be greater than about 60%, or greater than about 70%) while a specular optical transmittance TSp when the incident light is polarized along the pass-direction can be substantially greater than a specular optical transmittance TSb when the incident light is polarized along the block-direction (e.g., substantially larger diffuse transmittance and correspondingly substantially smaller specular transmittance may be desired for light polarized along the block-direction than for light polarized along the pass-direction).
In some embodiments, for the substantially normally incident light 30 having the first wavelength, the optically diffusive film 200, 201 has: a total optical transmittance TTb and a total optical reflectance RTb when the incident light is polarized along the block-direction, where TTb/RTb≥2; and a total optical transmittance TTp and a total optical reflectance RTp when the incident light is polarized along the pass-direction, where TTp/RTp≥6. Low backscattering (e.g., as quantified by a TTb/RTb of at least 2 and/or by a TTp/RTp of at least 6) may be desired in some applications.
In some embodiments, an optically diffusive film 200, 201 includes a plurality of particles 10, 11 dispersed in a binder 20. The particles 10, 11 and the binder 20 have respective indices n1b and n2b along a same in-plane (pb-plane) block-direction (b-direction) of the optically diffusive film 200, 201, and respective indices nip and n2p along an in-plane pass-direction (p-direction) orthogonal to the block-direction, such that for at least a first wavelength in a first wavelength range extending from about 400 nm to about 1000 nm (or in any wavelength range described elsewhere herein), a magnitude of a difference between n1b and n2b is greater than about 0.05 and a magnitude of a difference between nip and n2p is less than about 0.05. The magnitude of the difference between n1b and n2b can be in any range described elsewhere herein. The magnitude of the difference between nip and n2p can be in any range described elsewhere herein. In some embodiments, for a substantially normally incident light 30 having the first wavelength, the optically diffusive film 200, 201 has a total optical transmittance TTb and a total optical reflectance RTb when the incident light is polarized along the block-direction, and a total optical transmittance TTp and a total optical reflectance RTp when the incident light is polarized along the pass-direction. In some embodiments, TTb/RTb≥2 or TTb/RTb can be in any range described elsewhere herein. In some embodiments, or in other embodiments, TTp/RTp≥6 or TTp/RTp can be in any range described elsewhere herein. In some embodiments, for the substantially normally incident light having the first wavelength, 0.5≤TTp/TTb≤2 and the optically diffusive film 200, 201 has specular optical transmittances TSp and TSb when the incident light is polarized along the respective pass- and block-directions, where TSp/TSb≥2. TTp/TTb and TSp/TSb can be in any of the respective ranges described elsewhere herein.
In some embodiments, the optically diffusive film 200, 201 is formed by an extrusion process, as described further elsewhere herein. In some embodiments, the optically diffusive film 200, 201 includes a plurality of substantially parallel (e.g., within about 20, or within about 15 degrees, or within about 10 degrees, or within about 6 degrees, or within about 4 degrees of parallel) extrusion die-lines 40 making an angle θ of less than about 20, or less than about 15 degrees, or less than about 10 degrees, or less than about 6 degrees, or less than about 4 degrees with the pass-direction. The die-lines are marks or structures (e.g., ridges or channels) left in the film from the die used to extrude the film. The die-lines may be separated along the b-direction by greater distances than corresponding features of the die since the film may be stretched in a direction substantially orthogonal to the die-lines after extrusion. In some embodiments, at least some of the extrusion die-lines 40 form ridges 41. In some embodiments, the die-line ridges 41 have an average height h (see, e.g.,
In some embodiments, an extruded optically diffusive film 201 extruded along a pass-direction (p-direction) includes a plurality of particles 11 dispersed in a binder 20, where the particles 11 are elongated along substantially a same in-plane block-direction (b-direction) orthogonal to the pass-direction. For example, the particles 11 can be elongated along a direction within about 20 degrees, or within about 10 degrees, or within about 5 degrees of a same direction (b-direction). The particles can have an average aspect ratio of greater than about 5, or greater than about 10, or greater than about 15, or greater than about 20, or greater than about 40, or greater than about 45, or greater than about 50, for example. The average aspect ratio can be up to about 1000, or up to about 600, or up to about 400, or up to about 200, or up to about 100, or up to about 80, for example. Except where otherwise indicated, the aspect ratio of a particle is the length (Lb) of the particle along the elongation direction divided by a length of the particle (Lz) along the thickness direction (z-direction) of the film. The average aspect ratio is the average (e.g., unweighted mean) over the particles of the aspect ratio of the particle. In some embodiments, one or both of Lb/Lp and Lp/Lz, for example, can have an average in a range described herein for the average aspect ratio (average of Lb/Lz) of the particles. The optically diffusive film 201 can include a plurality of substantially parallel extrusion die-lines 40 making an angle θ of less than about 20 degrees with the pass-direction or the angle θ can be in any range described elsewhere herein. In some embodiments, for a substantially normally incident light 30 having a first wavelength in a first wavelength range extending from about 400 nm to about 1000 nm or in another range described elsewhere herein, the optically diffusive film 201 has: a diffuse optical transmittance TDb and a diffuse optical reflectance RDb when the incident light is polarized along the block-direction, where TDb/RDb≥4; and a total optical transmittance TTp and a diffuse optical reflectance RDp when the incident light is polarized along the pass-direction, where TTp/RDp≥10. TDb/RDb and TTp/RDp can be in any of the respective ranges described elsewhere herein. In some embodiments, the extruded optically diffusive film 201 has a length L of greater than about 40 inches along the pass-direction or the length L can be in another range described elsewhere herein.
In some embodiments, the binder 20 comprises a first thermoplastic polymer and the particles 10, 11 comprise a different second thermoplastic polymer. In some embodiments, the first and second thermoplastic polymers are immiscible at a temperature greater than melting temperatures of the first and second thermoplastic polymers (i.e., at a temperature that is greater than each of a melting temperature of the first thermoplastic polymer and a melting temperature of the second thermoplastic polymer). In some such embodiments, or in other embodiments, the first thermoplastic polymer is birefringent and the second thermoplastic polymer is substantially optically isotropic.
Suitable materials for the binder 20 include, for example, polyethylene naphthalate (PEN), coPEN (copolyethylene naphthalate terephthalate copolymer), polyethylene terephthalate (PET), polyhexylethylene naphthalate copolymer (PHEN), glycol-modified PET (PETG or PETg), glycol-modified PEN (PENG), syndiotactic polystyrene (sPS), or blends thereof. Suitable sPS can be obtained from Idemitsu Kosan Co., Ltd. (Tokyo, Japan), for example. Atactic polystyrene (aPS) can optionally be blended with sPS (e.g., at about 5 to about 30 weight percent aPS) to adjust the refractive indices of the resulting layer and/or to reduce the haze of the layer (e.g., by reducing a crystallinity of the layer). Suitable PET can be obtained from Nan Ya Plastics Corporation, America (Lake City, SC), for example. PETG can be described as PET with some of the glycol units of the polymer replaced with different monomer units, typically those derived from cyclohexanedimethanol. PETG can be made by replacing a portion of the ethylene glycol (e.g., about 15 to about 60 mole percent or about 30 to about 40 mole percent) used in the transesterification reaction producing the polyester with cyclohexanedimethanol, for example. Suitable PETG copolyesters include GN071 available from Eastman Chemical Company (Kingsport, TN). PEN and coPEN can be made as described in U.S. Pat. No. 10,001,587 (Liu), for example. Glycol-modified polyethylene naphthalate (PENG) can be described as PEN with some of the glycol units of the polymer replaced with different monomer units and can be made by replacing a portion of the ethylene glycol (e.g., about 15 to about 60 mole percent or about 30 to about 40 mole percent) used in the transesterification reaction producing the polyester with cyclohexanedimethanol, for example. PHEN can be made as described for PEN in U.S. Pat. No. 10,001,587 (Liu), for example, except that a portion of the ethylene glycol (e.g., about 15 to about 60 mole percent, or about 30 to about 50 mole percent, or about 40 mole percent) used in the transesterification reaction is replaced with hexanediol. In some embodiments, the binder 20 comprises one or more of a polyester and a copolyester. For example, the binder may include a blend of a polyester and a copolyester. In some embodiments, the binder 20 comprises one or more of polyethylene terephthalate, glycol-modified polyethylene terephthalate, polyethylene naphthalate, and glycol-modified polyethylene naphthalate.
In some embodiments, the particles in the plurality of particles 10, 11 comprise a styrene-based polymer or copolymer (a polymer or copolymer containing styrene groups). In some embodiments, the particles in the plurality of particles 10, 11 comprise one or more of styrene butadiene, styrene acrylonitrile, styrene methyl methacrylate, and impact modified styrene acrylic. Impact modified styrene acrylic can incorporate monomer groups for improved impact resistance and/or toughness, as is known in the art. Suitable impact modified styrene acrylic include those available from Ineos Americas (League City, TX) under the ZYLAR tradename, for example. Other suitable styrene-based copolymers include those available from Ineos Americas (League City, TX) under the STYROLUX, STYROLUTION, and NAS tradenames, for example. Other classes of materials useful as the particles in the plurality of particles include polycarbonate polymers including bisphenol A; nylon polymers, such as Poly(hexamethylene adipamide) (Nylon 6,6) and Poly(caprolactam) (Nylon 6); and methacrylate polymers, such as Poly(2-phenylethyl methacrylate), for example. Choosing a polymer useful as the particles in the plurality of particles may be generally guided by choosing the polymer to substantially match the refractive index of the birefringent binder in the non-stretch in-plane direction, and by choosing the polymer being immiscible with the binder polymer system, remaining non-birefringent during the stretching process, and not degrading during the melt processing stage.
In some embodiments, the first temperature T1 is greater than melt temperatures of the minor and major phase materials 310 and 320. In some embodiments, the first temperature T1 is greater than about 200 degrees centigrade, or greater than about 220 degrees centigrade, or greater than about 240 degrees centigrade, or greater than about 260 degrees centigrade, or greater than about 270 degrees centigrade, for example. In some embodiments, the first temperature is less than about 400 degrees centigrade, for example. In some embodiments, the second temperature is about 5 to about 50, or about 5 to about 40, or about 5 to about 30, or about 5 to about 20, or about 8 to about 30 degrees centigrade greater the glass transition temperatures of the minor and major phase materials. In some such embodiments, or in other embodiments, prior to the stretching of the extruded mixture 264 along the block-direction at the second temperature T2, a temperature of the extruded mixture 264 is reduced to a third temperature T3 less than the second temperature T2. For example, the extruded mixture can be cast against a casting wheel (sometimes referred to in the art as a chill roll or a casting drum) to rapidly cool the mixture resulting in a cast film. In some embodiments, the third temperature T3 is about a room temperature (e.g., a temperature in a range of about 18 to about 30 degrees centigrade).
In some embodiments, the discrete domains in the extruded mixture and/or the substantially spherical domains in the extruded mixture at least mostly comprise the minor phase material. For example, the minor phase material can make up at least about 80 percent, or at least about 90 percent, or at least about 95 percent by weight of the domains. In some embodiments, the discrete domains in the extruded mixture and/or the substantially spherical domains in the extruded mixture are dispersed in a material at least mostly comprises the major phase material. For example, the major phase material can make up at least about 70 percent, or at least about 80 percent, or at least about 90 percent, or at least about 95 percent by weight of the material in which the domains are dispersed.
Optically diffusive films of Examples 1-5 were made via coextrusion and batch orienting using materials shown in Table 2. The temperature of the extruder was about 277 degrees Celsius.
75%/7.5
Material #1 and material #3 (when included) were the polyester phase materials and Materials #2 was the co-polystyrene phase material. The weight percent and the pounds per hour (pph) of these materials in the extruder input are indicated in Table 2. The polyester phase and the co-polystyrene phase were immiscible and exhibited two distinct phases after extrusion and after stretching.
After extrusion and before stretching, the extruded mixtures were cooled by casting the extruded mixtures against a casting wheel. For Examples 1 to 4, a two layer co-extrusion was performed where the layer already described (the blend layer) was on the air-side during the casting process and the wheel-side layer was composed of the same composition as the polyester phase in the blend layer and was fed at the same rate as the total blend layer. For Example 5, a 3 layer coextrusion was utilized where the center layer was the blend layer and the other two layers had the same composition as the polyester phase of the blend layer and each of the two streams was fed at a rate of half of the total blend layer rate. An 8″ extrusion die was used for all examples. The die gap was 60 mils for Examples 1-4 and 100 mils for Example 5.
The stretching process for all these films was performed on a batch orientor (Karo IV from Brueckner Group, Portsmouth, NH). A pre-heat and stretch temperature of 95° C. was utilized. The stretching was a constrained stretch with a draw ratio of about 6:1 in the transverse direction (TD) orthogonal to the machine direction (MD). PET stretched at these conditions has refractive indices of about 1.66 in the stretch direction (TD), 1.56 in the in-plane direction perpendicular to the stretch direction (the MD direction), and 1.53 in the thickness direction measured at 631 nm with a refractometer (Metricon Corporation, Pennington, NJ). The thicknesses of the films after stretching are given in Table 2.
The tendency of the films to scatter polarized light was characterized using a Haze Gard (BYK Corporation, Wesel, Germany). The haze of light polarized in the block direction (TD) was determined by positioning a high contrast ratio absorbing polarizer (with its pass-state transmission axis aligned with the stretch direction of the example film) on the incoming light side of the example film with transparent tape (3M 375 from 3M, Saint Paul, MN) applied to the air-side of the film to reduce scattering from the surface roughness of the example films. The samples were oriented so that the wheel-side of the film was toward the incoming light. For the pass-state haze the absorbing polarizer is aligned with the non-stretch direction (MD) of the example film. Results from the polarized haze measurements are provided in Table 3.
The angular distribution of the scattered light was measured with a Conoscope (ELDIM Corporation, Hérouville-Saint-Clair, France) with a cone angle of 80 degrees. A collimated white (LED) light source was utilized with an absorbing polarizer placed between the light source and the example film. Measurements were taken with the transmission axis of the polarized in the block direction and the Full Width Half Max (FWHM) of the scattering patterns along the MD and TD directions were determined and are reported in Table 3.
The reflective characteristics of the example films were determined by measuring the films reflectivity in an integrating sphere. The total reflectance, which is also referred to as the Reflectance with the Specular Included (RSIN), was measured by collecting all light reflecting from the example films impinging from all angles while the diffuse reflectance, which is also known as the Reflectance with the Specular Excluded (RSEX), was measured by allowing light to escape the integrating sphere that would produce a specular reflection. A LAMBDA 1050 spectrophotometer (PerkinElmer, Inc., Waltham, MA) was used in the measurements. The resulting reflectances averaged over a wavelength range of 450 nm to 650 nm are shown in Table 4.
The scattering of example films in a plane defined by the machine direction and the thickness direction (pz-plane) for the block-state polarization (normalized by the maximum counts achieved) is shown in
Average aspect ratios of the particles before stretching the cast films were determined using an optical microscope to examine cross-sections in the bz-plane and the pz-plane. The ratios Lp/Lz and Lb/Lz were determined for particles in the cross-section and an average of the ratios were determined. Results are provided in Table 5.
The corresponding aspect ratios for the stretched films were calculated assuming that the draw ratio of about 6 resulted in stretching by a factor of 6 in the TD direction and thinning by a factor of 6 in the thickness direction, as would be expected for a standard tenter as used in the Examples. Results are provided in Table 6.
The aspect ratios that would have resulted if the cast films were stretched using a parabolic tenter with a draw ratio of 6 was calculated by assuming stretching by a factor of 6 in the TD direction and contraction and thinning by a factor of the square root of 6 in the respective MD and thickness directions. Results are provided in Table 7.
Terms such as “about” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “about” as applied to quantities expressing feature sizes, amounts, and physical properties is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “about” will be understood to mean within 10 percent of the specified value. A quantity given as about a specified value can be precisely the specified value. For example, if it is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, a quantity having a value of about 1, means that the quantity has a value between 0.9 and 1.1, and that the value could be 1.
All references, patents, and patent applications referenced in the foregoing are hereby incorporated herein by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control.
Descriptions for elements in figures should be understood to apply equally to corresponding elements in other figures, unless indicated otherwise. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations, or variations, or combinations of the specific embodiments discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2022/054163 | 5/5/2022 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63193842 | May 2021 | US |
