Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/30—Polarising elements
  • G02B5/3083—Birefringent or phase retarding elements
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
  • G02B1/08—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of polarising materials

Definitions

• This invention pertains to a multilayer optical film whose out-of-plane retardation has been reduced to provide a wide viewing characteristic. More specifically, this invention relates to a wide-view optical film comprising a positive in-plane birefringent film and a fluoropolymer film.
• the optical film of the invention can be used in an optical device such as liquid crystal display, OLED display, 3D glasses, optical switch, or waveguide where a controlled light management is desirable.
• An A-plate is a wave plate commonly used as a retarder in an optical device. It is a birefringent material capable of manipulating the polarization state or phase of the light beam traveling through the medium.
• An A-plate having in-plane retardation (R e ) equal to a quarter of a light wavelength ( ⁇ ), R e ⁇ /4, is called quarter wave plate (QWP).
• QWP quarter wave plate
• an A-plate having R e equal to half of the wavelength, R e ⁇ /2, is called half wave plate (HWP).
• a QWP is capable of converting an incident linearly polarized light to circularly polarized light. Thus, it is commonly used in combination with a linear polarizer to provide a circular polarizer in an optical device.
• An HWP is capable of rotating the plane of polarization by ⁇ , where ⁇ is the angle of the plane polarized light with respect to the slow (or fast) axis of the wave plate.
• A-plates are commonly used in liquid crystal displays (LCDs) as compensation films to improve the viewing angles. They can also be used in an OLED (organic light emitting diode) display device.
• OLED organic light emitting diode
• a QWP is being used with a linear polarizer to provide a circular polarizer in an OLED device to reduce the ambient light reflected by OLED for improved viewing quality.
• These applications typically utilize the in-plane retardation provided by the A- plate for in-plane phase-shift compensation.
• A-plate combining with C-pIate is particularly useful in reducing light leakage of the crossed polarizers at oblique viewing angles.
• R th a negative out-of-plane retardation
• R th a negative out-of-plane retardation
• the liquid crystal molecules in the LC cell are aligned in a homeotropic manner, which results in positi ve out-of-plane retardation.
• An A-plate thus, can provide an out- of-plane compensation in addition to in-plane compensation in VA-LCD.
• US Patent No. 7,211,316 discloses an optical multilayer comprising a polymeric substrate and an amorphous polymer having Tg above 160°C and positive birefringence so as to provide a total out-of-plane phase retardation of said multilayer of between -30nm and 30 nm.
• This invention provides a multilayer optical film comprising,
• R 1 , R 2 , and R 3 are each independently hydrogen atoms, alkyl groups, substituted alkyl groups, or halogens, wherein at least one of R 1 , R 2 , and R 3 is a fluorine atom, wherein R is each independently a substituent on the styrenic ring, n is an integer from 0 to 5 representing the number of the substituents on the styrenic ring, and wherein n x and n y represent in-plane refractive indices and 3 ⁇ 4 the thickness-direction refractive index of the wave plates; wherein said multilayer optical film has a positive in-plane retardation (R e ) and an out-of-plane retardation (R th ) that satisfies the equation of
• the multilayer optical film in accordance with the present invention has an out-of-plane retardation (R th ) that satisfies the equation of
• the multilayer optical film of the invention is a quarter wave plate
• the multilayer optical film of this invention can be used in a liquid crystal display device including an in-plane switching liquid crystal display device, in an OLED display device, in a circular polarizer, or in 3D glasses.
• Said display devices may be used for television, computer, cell phone, camera, and the like.
• FIG. 1 is a schematic view illustrating a stacking pattern in which a quarter wave plate is sandwiched between a linear polarizer and a reflector;
• FIG. 2 is a schematic view illustrating a stacking pattern in which a half wave plate is sandwiched between two parallel linear polarizers;
• FIG. 3 is a contour plot showing the light l eakage of the optical device provided in Comparative Example 1 ;
• FIG. 4 is a contour plot showing the light leakage of the optical device provided in Example 1 ;
• FIG. 5 is a contour plot showing the light leakage of the optical device provided in Comparative Example 2;
• FIG. 6 is a contour plot showing the light leakage of the optical device provided in Example 2;
• FIG. 7 is a graph showing the retardations of a cellulose ester wave plate coated with fluoropolymer as described in Example 3.
• a multilayer optical film comprising,
• R 1 , R 2 , and R 3 are each independently hydrogen atoms, alkyl groups, substituted alkyl groups, or halogens, wherein at least one of R 1 , R 2 , and R 3 is a fluorine atom, wherein R is, each independently, a substituent on the styrenic ring, n is an integer from 0 to 5 representing the number of the substituents on the styrenic ring, and wherein n x and n y represent in-plane refractive indices and n z the thickness-direction refractive index of the wave plates; wherein said multilayer optical film has a positive in-plane retardation (R e ) and an out-of-plane retardation (Rth) that satisfies the equation of
• R 1 , R 2 , and R 3 are fluorine atoms; in another aspect, R 1 , R 2 , and R 3 are all fluorine atoms.
• Examples of the substituent R on the styrenic ring include alkyl, substituted alkyl, halogen, hydroxyl, carboxyl, nitro, alkoxy, amino, sulfonate, phosphate, acyl, acyloxy, phenyl, alkoxycarbonyl, cyano, and the like.
• Birefringence ( ⁇ n) of a wave plate may be measured by determining the birefringence of a wave plate over a wavelength range of about 400 nm to about 800 nm at different increments. Alternatively, birefringence may be measured at a specific light wavelength. When the values of the birefringence or retardation are compared as described in this invention, they are meant to be compared at the same wavelength throughout out the wavelength range of about 400 nm to about 800 nm.
• the multilayer optical film in accordance with the present invention has an out-of-plane retardation (R th ) that satisfies the equation of
• R th out-of-plane retardation
• polycarbonate cyclic olefin polymer (COP), polyester, cellulose ester, polyacrylate, polyolefin, polysulfone, and polyurethane.
• COP cyclic olefin polymer
• polyester cellulose ester
• polyacrylate polyolefin
• polysulfone polysulfone
• the QWP may be a broadband QWP having R e equal to about ⁇ /4 at each wavelength ranging from about 400 nm to about 800 nm.
• An example of the QWP is a wave plate having in-plane retardation (R e ) of about 120-160 nm at the wavelength ( ⁇ ) 560 nm.
• the fluoropolymer film of (b) can be prepared by solution cast using polymer solution or melt extrusion using polymer melt.
• the fluoropolymer film is a coating film having been cast on a substrate from a solution comprising a fluoropolymer and a solvent.
• the solution-cast polymer film is capable of forming an out-of-plane anisotropic alignment (positive C-plate) upon solvent evaporation without being subject to heat treatment, photo irradiation, or stretching, and has a positive out-of-plane birefringence greater than about 0.005, greater than about 0.01, or greater than about 0.015 throughout the wavelength range of 400 nm ⁇ ⁇ ⁇ 800 nm.
• the solution-cast fluoropolymer film is removed from the substrate upon drying to yield a free-standing film.
• the free-standing film prepared either by solution cast or melt extrusion, can be attached to the wave plate of (a) by lamination.
• the fluoropolymer film on the substrate is laminated onto the wave plate of (a) and the substrate subsequently removed.
• the thickness of the fluoropolymer film in (b) as a laminated film can be from about 3 to about 150 ⁇ m, or, in another embodiment, from about 10 to about 100 ⁇ m.
• the fluoropolymer film is cast directly onto the wave plate of (a) from the polymer solution to yield a coating film.
• the solution-cast fluoropolymer film may be further stretched uniaxially or biaxially by a method known in the art to yield an in-plane retardation satisfying the equation of
• a unique feature of the present invention is its ability to provide a multilayer optical film with a low out-of-plane retardation (R th ) value.
• the low R th is desirable particularly for display application since it can increase the viewing angle and improve the contrast ratio of an image.
• This is made possible by the high, positive R th characteristic of the fluoropolymer film of (b), which enables the reduction or elimination of the negative Ro, typically exhibited in the wave plate of (a) with a thin coating film.
• the thickness of the fluoropolymer film in (b) as a coating can be from about 2 to about 20 ⁇ m, or, in another embodiment, from about 3 to about 10 ⁇ .
• ⁇ RJ2 or a half wave plate (HWP) having R e ⁇ /2 and
• this invention provides a multilayer optical film having an in-plane retardation (R e ) of about 120-160 nm at the wavelength ( ⁇ ) 560 nm.
• the multilayer optical film has an in-plane retardation (R e ) of about 120-160 nm at the wavelength ( ⁇ ) 560 nm and an out-of-plane retardation (R t ) that satisfies the equation of jR th
• the QWP may be a broadband QWP having R ⁇ . equal to about ⁇ /4 at each wavelength ranging from about 400 nm to about 800 nm.
• this invention provides a multilayer optical film, which has an in-plane retardation (R e ) equal to about ⁇ 4 at each wavelength ranging from 400 nm to 800 nm and an out-of-plane retardation (R t3 ⁇ 4 ) that satisfies the equation of
• the QWP may be combined with a linear polarizer to yield a circular polarizer.
• this invention further provides a circular polarizer comprising a linear polarizer and a QWP of the present invention.
• an OLED display comprising a circular polarizer of the present invention.
• the casting of a polymer solution onto a substrate may be carried out by a method known in the art such as, for example, spin coating, spray coating, roll coating, curtain coating, or dip coating.
• Substrates are known in the art, which include triacetylcel!ulose (TAC), cyclic olefin polymer (COP), polyester, polyvinyl alcohol, cellulose ester, cellulose acetate propionate (CAP), polycarbonate, polyacrylate, polyolefm, polyurethane, polystyrene, glass, and other materials commonly used in an LCD device.
• the fluoropolymer of the present invention may be soluble in. for example, toluene, methyl isobutyl ketone, cyclopentanone, methylene chloride, chloroform, 1 ,2-dichloroethane, methyl amy! ketone, methyl ethyl ketone, methyl isopropyl ketone, methyl isoamyl ketone, ethyl acetate, n-butyl acetate, propylene glycol methyl ether acetate, and a mixture thereof.
• toluene methyl isobutyl ketone, cyclopentanone, methylene chloride, chloroform, 1 ,2-dichloroethane, methyl amy! ketone, methyl ethyl ketone, methyl isopropyl ketone, methyl isoamyl ketone, ethyl acetate, n-butyl acetate,
• the fluoropolymer film of the present invention may be a homopolymer or a copolymer.
• the homopolymer may be prepared b polymerization of a fluorine-containing monomer having the structures below:
• R 1 , R 2 , and R 3 are each independently hydrogen atoms, alkyl groups, substituted alkyl groups, or halogens and wherein at least one of R 1 , R 2 , and R 3 is a fluorine atom, wherein R is, each independently, a substituent on the styrenic ring, n is an integer from 0 to 5 representing the number of the substituents on the styrenic ring.
• fluorine-containing monomers include, but not limited to, ⁇ , ⁇ , ⁇ - trifluorostyrene, , ⁇ -difluorostyrene, ⁇ , ⁇ -difluorostyrene, a-fluorostyrene, and ⁇ -fluorostyrene.
• the homopolymer is
• the copolymer may be prepared by copolymerization of one or more of the fluorine- containing monomers with one or more of ethylenically unsaturated monomers.
• ethylenically unsaturated monomers include, but not limited to, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, ethylhexyl acrylate, 2-ethyIhexyl methacrylate, 2-ethylhexyl acrylate, isoprene, octyl acrylate, octyl methacrylate, iso-octy acrylate, trimethyolpropyl triacrylate, styrene, a-methyl st
• the fluoropolymer is a copolymer of ⁇ , ⁇ , ⁇ -trifluorostyrene with one or more of ethylenically unsaturated monomers selected from the group consisting of styrene, methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, acrylic acid, methacrylic acid, a-methyl styrene, 4-methyl styrene, vinyl biphenyl, acrylonitrile, and isoprene.
• Polymerization may be carried out by a method known in the art such as bulk, solution, emulsion, or suspension polymerization.
• the reaction may be free radical, cationic, anionic, zwitterionic, Ziegler- atta, or atom transfer radical type of polymerization.
• Emulsion polymerization is one method of polymerization when a particularly high molecular weight is desirable. A high molecular weight polymer may lead to better film quality and higher positive birefringence.
• the fluoropolymer solution further comprises one or more of the plasticizers selected from the group consisting of triphenylphosphate, tri(ethylene glycol) bis(2- ethylhexanoate), tri(ethylene glycol) bis(n-octanoate); Optifilm Enhancer 400, Abitol E, and Admex 523 available from Eastman Chemical Company; Uniplex 552, Uniplex 809, and Uniplex 280 available from Unitex Chemical Corp.
• the plasticizers selected from the group consisting of triphenylphosphate, tri(ethylene glycol) bis(2- ethylhexanoate), tri(ethylene glycol) bis(n-octanoate);
• Optifilm Enhancer 400, Abitol E, and Admex 523 available from Eastman Chemical Company; Uniplex 552, Uniplex 809, and Uniplex 280 available from Unitex Chemical Corp.
• the multilayer optical film of the present invention may be used in a liquid crystal display device including an in-plane switching liquid crystal display device, in an OLED display device, in a circular polarizer, or in 3D glasses.
• Said display devices may be used for television, computer, cell phone, camera, and the like.
• the optical simulation program employed is written in computer language MATLAB based on the 4x4 matrix method, which deals with multilayer optical structure for viewing angle and contrast ratio calculations.
• the program is utilized to determine light leakage in an optical device having a QWP sandwiched between a linear polarizer and a reflector. As illustrated in FIG. 1 , the optical axis of the QWP is aligned at 45° angle with respect to the transmission axis of the polarizer.
• the linearly polarized light passed through a QWP, it becomes a circularly polarized light. The one handedness circularly polarized light is then reflected by the reflector and rotated to the other handedness direction.
• the HWP is placed between two parallel linear polarizers, in which the two transmission axes are at 0° angle.
• the optical axis of the HWP is aligned at a 45° angle with respect to the transmission axes of the polarizers.
• the HWP will rotate the incident linearly polarized light by 90° and cause the light to be blocked by the second polarizer.
• this configuration will have the same optical effect as the reflective mode in FIG. 1.
• Comparative Example 1 Computer Simulation of Light Leakage of an Optical Device Having Quarter Wave Plate Sandwiched Between Linear Polarizer and Reflector without Compensation
• Comparative Example 2 Simulation of Light Leakage of an Optical Device Having Biaxial Wave Plate Sandwiched between Linear Polarizer and Reflector without Compensation [050
• the slow axis of the biaxial wave plate was aligned at 45° angle with respect to the transmission axes of the polarizers.
• the light leakage was determined, and the result is shown by the contour plot in FIG. 5.
• the minimum leakage was 2.55 x 10 "3 % and the maximum 21.4%.
• Example 2 Simulation of Light Leakage of an Optical Device Having Biaxial Film Sandwiched between Linear Polarizer and Reflector with Compensation
• PTFS poly(a,p,p-trifluorostyrene)
• 550 nm was prepared and treated with corona discharge using Laboratory Corona Treater (Model BD-20C; Electro-Technic Products, INC.) for about two minutes.
• the polymer solution was cast on the cellulose ester film (thickness, 70 ⁇ ) using a knife applicator. Immediately after casting, the coated film was placed in a force-air oven at 85°C for 5 minutes to yield a dried coating. Two samples coated with PTFS were prepared; the thickness of the coatings was determined to be
• the thickness and the out-of-plane optical retardation (R th ) of the samples were measured.
• the thickness was measured by Metricon 2010 prism coupler, while the retardation by J. A. Woollam M-2000V.
• the cellulose ester films coated with PTFS had much reduced retardation values as compared to the cellulose ester film without PTFS coating.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Polarising Elements (AREA)
• Electroluminescent Light Sources (AREA)
• Laminated Bodies (AREA)

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• 2012
  • 2012-11-02 US US13/667,219 patent/US9234987B2/en active Active
• 2013
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