Classifications

• • 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
  • G02B1/002—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of materials engineered to provide properties not available in nature, e.g. metamaterials
  • G02B1/007—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of materials engineered to provide properties not available in nature, e.g. metamaterials made of negative effective refractive index materials
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C55/00—Shaping by stretching, e.g. drawing through a die; Apparatus therefor
  • B29C55/02—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets
  • B29C55/023—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets using multilayered plates or sheets
  • B29C55/026—Shaping by stretching, e.g. drawing through a die; Apparatus therefor of plates or sheets using multilayered plates or sheets of preformed plates or sheets coated with a solution, a dispersion or a melt of thermoplastic material
• • 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
  • G02B1/04—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of organic materials, e.g. plastics
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/28—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising
• • 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
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
  • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
  • G02F1/1333—Constructional arrangements; Manufacturing methods
  • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
  • G02F1/13363—Birefringent elements, e.g. for optical compensation
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
  • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
  • G02F1/1333—Constructional arrangements; Manufacturing methods
  • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
  • G02F1/13363—Birefringent elements, e.g. for optical compensation
  • G02F1/133637—Birefringent elements, e.g. for optical compensation characterised by the wavelength dispersion
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
  • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
  • G02F1/1333—Constructional arrangements; Manufacturing methods
  • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
  • G02F1/13363—Birefringent elements, e.g. for optical compensation
  • G02F1/133638—Waveplates, i.e. plates with a retardation value of lambda/n
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
  • Y10T428/24942—Structurally defined web or sheet [e.g., overall dimension, etc.] including components having same physical characteristic in differing degree
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
  • Y10T428/24942—Structurally defined web or sheet [e.g., overall dimension, etc.] including components having same physical characteristic in differing degree
  • Y10T428/2495—Thickness [relative or absolute]
  • Y10T428/24967—Absolute thicknesses specified
  • Y10T428/24975—No layer or component greater than 5 mils thick

Definitions

• This invention pertains to a wide-view optical film whose in-plane retardation exhibits the characteristic of reversed wavelength dispersion. More specifically, this invention relates to a wide-view optical film that is made by stretching a multilayer film comprising a polymer film and a retarder having positive out-of-plane birefringence.
• the optical film of the invention may be used in an optical device such as liquid crystal display (LCD), organic light emitting diode (OLED) display, 3D display, optical switch, or waveguide where a controlled light management is desirable.
• phase retardation of light varies according to wavelength, causing color shift.
• This wavelength dependence (or dispersion) characteristic of the compensation film may be taken into account when designing an optical device so that color shift is reduced.
• Wavelength dispersion curves are defined as "normal (or proper)” or “reversed” with respect to the compensation film having positive or negative retardance (or retardation).
• a compensation film with positive retardance positive A- or C- plate
• a compensation film with negative retardance may have a normal curve in which the value of phase retardation is increasingly negative toward shorter wavelengths or a reversed curve in which the value of phase retardation is decreasingly negative toward shorter wavelengths. Exemplary shapes of these curves are depicted in FIG. 1.
• the above wave plates are uniaxial birefringent plates.
• a wave plate can also be biaxial birefringent, where n x , n y , and n z are all not equal; it is customarily named as biaxial film.
• Re(450), Re(550), and R e (650) are in-plane retardations at the light wavelengths of 450 nm, 550 nm, and 650 nm respectively.
• An achromatic (or broadband) wave plate is highly desirable since it can direct the light in the same manner at each wavelength to yield the optimal viewing quality.
• a common wave plate however, exhibits a normal dispersion curve, which is not suitable for broadband wave plate application. Thus, there exists a need for a wave plate having reversed wavelength dispersion characteristics with respect to in-plane retardation.
• 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. For example, 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. For example, A-plate combining with C-plate is particularly useful in reducing light leakage of the crossed polarizers at oblique viewing angles.
• LCDs liquid crystal displays
• OLED organic light emitting diode
• the A-plate also exhibits a negative out-of-plane retardation R t , which is defined as arising from its orientation. This characteristic can be beneficial when a negative R th is desirable in an optical device.
• a negative R th is desirable in an optical device.
• VA vertically aligned
• the liquid crystal molecules in the LC cell are aligned in a homeotropic manner, which results in positive retardation.
• An A-plate thus, can provide an out-of-plane compensation in addition to in-plane compensation in VA-LCD.
• the Rt h exhibited in the A-plate is not desirable since it can give rise to phase shift in off-axis light and lead to light leakage.
• IPS in- plane switch
• US Patent No. 7,480,021 discloses an optical film having reversed birefringence dispersion comprising a first component having a normal dispersion and a second component having a reversed dispersion, wherein the two components have the same sign of birefringence.
• US Patent No. 7,948,591 discloses a uniaxial retardation film satisfying the equations of
• 8,139,188 discloses a biaxial retardation film satisfying the equations of 220 nm ⁇ R xy (550) ⁇ 330nm, 1 lOnm ⁇ R xz (550) ⁇ 165nm, 0.75 ⁇ R xy (450)/ R xy (550) ⁇ 0.97, and 1.03 ⁇ R xy (650)/ R xy (550) ⁇ 1.25. In both patents, no materials that can satisfy the specified equations are disclosed.
• US Patent Application No. 2008/0068545 discloses a retardation film comprising a film, which is a film comprising a fumaric ester resin and satisfying n x ⁇ n y ⁇ n z , and a film satisfying n y >n x >n z or n y >n z >n x .
• the disclosed film may have a reversed dispersion characteristic.
• US Patent Application No. 2012/0003403 discloses a multilayer film comprising (a) a layer (A) comprising cellulose ester having a degree of substitution of hydroxyl groups (DSO H ) of 0 to 0.5 and (b) a layer (B) comprising cellulose ester having a DSO H of 0.5 to 1.3, wherein the film has a reversed optical dispersion.
• This invention provides an optical compensation film, which is made by uniaxially or biaxially stretching of a multilayer film comprising,
• n x and n y represent in-plane refractive indices and n z the thickness-direction refractive index of the films
• said optical compensation film has a positive in-plane retardation that satisfies the relations of 0.7 ⁇ R45o R55o ⁇ 1 and l ⁇ R65o R55o ⁇ 1.25, wherein R450, R550, and R650 are in-plane retardations at the light wavelengths of 450 nm, 550 nm, and 650nm respectively.
• the optical compensation film of the invention has an in-plane retardation (R e ) of about 80-300 nm at the wavelength ( ⁇ ) 550 nm.
• the optical compensation film of the invention has out-of-plane retardation (R th ) satisfying the equation of
• This invention further provides a method for making the optical compensation film of the present invention.
• FIG. 1 is a graph depicting the shapes of exemplary wavelength dispersion curves for: (a) a reversed curve for positive retardation, (b) a normal curve for positive retardation, (c) a normal curve for negative retardation and (d) a reversed curve for negative retardation;
• FIG. 2 is a graph depicting the wavelength dispersions of stretched cellulose ester film 1 with and without coating;
• FIG. 3 is a graph depicting the wavelength dispersions of stretched cellulose ester film 2 with and without coating.
• FIG. 4 is a graph depicting the wavelength dispersions of stretched cellulose ester film 3 with and without coating.
• an optical compensation film which is made by uniaxially or biaxially stretching of a multilayer film comprising, (c) a first polymer film having a refractive index profile satisfying the equations of
• a second polymer film having a refractive index profile satisfying the equations of (n x +n y )/2 ⁇ n z and
• the optical compensation film in accordance with the present invention has a positive in- plane retardation (R ⁇ ) and a reversed in-plane wavelength dispersion characteristic, in which the value of phase retardation is decreasingly positive toward shorter wavelengths.
• This dispersion characteristic is expressed by the ratios of the retardations as measured at the wavelengths of 450 nm, 550 nm, and 650 nm, which satisfy the relations of R450/R550 ⁇ 1 and R6 50 /R55o > l -
• the ratio of R450/R550 can be 0.71 to 0.99, 0.72 to 0.98, 0.74 to 0.97, 0.76 to 0.96, 0.78 to 0.95, 0.8 to 0.9, or 0.81 to 0.85.
• the ratio of f Rsso can be 1.01 to 1.24, 1.02 to 1.23, 1.03 to 1.22, 1.04 to 1.21, 1.05 to 1.2, or 1.1 to 1.19.
• Birefringence ( ⁇ ) 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.
• birefringence may be measured at a specific light wavelength.
• a birefringence or retardation relation is given without specifying a
• wavelength it is meant to be true throughout the wavelength range of about 400 nm to about 800 nm.
• the in-plane retardation (R e ) of the optical compensation film of this invention is about 80-300 nm at the wavelength ( ⁇ ) 550 nm.
• the optical compensation film in accordance with this invention is a quarter wave plate (QWP) having in- plane retardation (Rg) of about 120-160 nm at the wavelength ( ⁇ ) 550 nm and having a reversed in-plane dispersion characteristic.
• said quarter wave plate is a broadband
• QWP having Rg equal to about ⁇ /4 at each wavelength ranging from 400 nm to 800 nm.
• the optical film of the present invention is capable of providing a low out-of -plane retardation (R ⁇ ) value.
• the low R ⁇ is desirable particularly for display application since it can increase the viewing angle and improve the contrast ratio of an image.
• this invention further provides a wide-view optical film having an out-of-plane retardation (Rt h ) that satisfies the equation of
• This wide -view feature when combined with the reversed dispersion characteristic of the present invention, will provide a broadband, wide-view wave plate for display application in LCD or OLED.
• a broadband, wide -view QWP is particular desirable since it can provide a broadband, wide-view circular polarizer when used in combination with a linear polarizer.
• Such a circular polarizer can be used in an OLED display device to reduce the ambient light and improve the viewing quality.
• this invention further provides a circular polarizer comprising a linear polarizer and a wide-view QWP of the present invention.
• an OLED display comprising a circular polarizer of the present invention.
• the first polymer film of (a) has an in-plane retardation (R e )
• the negative C-plate examples include, but not limited to, cellulose ester, polyimide, acrylic polymer, and polymer films having liquid crystalline moieties in the polymer chains or having liquid crystal molecules embedded in the polymer matrix.
• the negative C-plate has an out-of-plane birefringence ( ⁇ ) satisfying the equation of
• is advantageous in that it is capable of providing higher positive R e values when stretched.
• COP cyclic polyolefm
• the first polymer film of (a) will generate positive Rg when stretched.
• the first polymer film of (a) is capable of producing flat or reversed dispersion curve when stretched. Films based on cellulose ester are found to be particularly suitable. Additionally, the present inventors have discovered that stretching of polymer films having higher negative R th leads to higher Rg values.
• this invention further provides a first polymer film of (a) that is a cellulose ester film having an out-of-plane retardation (R th ) of -lOOnm to - 400 nm at the wavelength ( ⁇ ) 550 nm and a thickness of 20-100 ⁇ .
• the positive C-plate include, but not limited to, cellulose ester, polyester, polystyrene, polyacrylate, cellulose benzoate, cellulose acylate benzoate, cellulose arylate, cellulose acylate arylate, polymer films having liquid crystalline moieties in the polymer chains or having liquid crystal molecules embedded in the polymer matrix, poly( vinyl aromatics) as disclosed in US Patent Application Nos. 20080241565 and 20080241428, mesogen-jacked polymers as disclosed in US Patent Application No. 20080237552 , and f uoropolymers as disclosed in US Patent Application No. 201 10076487; the content of said US Patent Applications is incorporated herein by reference.
• the second polymer film of (b) has an out-of-plane birefringence (An th ) satisfying the equation of An th > 0.005, or >0.01 , or >0.15, or >0.2.
• Higher birefringence materials have an advantage in that they can provide sufficient positive out-of-plane retardations (R th ) with thin films to reduce or eliminate the negative R 3 ⁇ 4 typically exhibited in the first polymer film of (a).
• the stretched multilayer films thus obtained will have wide-view
• Particularly suitable for this purpose are homopolymers or copolymers of the monomers selected from the group comprising ⁇ , ⁇ , ⁇ -trifluorostyrene, ⁇ , ⁇ -difluorostyrene, ⁇ , ⁇ - difluorostyrene, a-fluorostyrene, and ⁇ -fluorostyrene.
• Poly(a, ⁇ , ⁇ -trifluorostyrene) is used in one example.
• the second polymer film of (b) is prepared by solution cast on a substrate.
• 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 triacetylcellulose (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 second polymer film of (b) may be soluble in, for example, toluene, methyl isobutyl ketone, cyclopentanone, methylene chloride, chloroform, 1,2- dichloroethane, methyl amyl ketone, methyl ethyl ketone, methyl isopropyl ketone, methyl isoamyl ketone, ethyl acetate, n-butyl acetate, propylene glycol methyl ether acetate, and mixtures thereof.
• the solution-cast polymer film may be removed from the substrate upon drying to yield a free-standing film.
• the free-standing film can be attached to the polymer film of (a) by lamination.
• the second polymer film on a substrate is laminated onto the first polymer film and the substrate subsequently removed.
• the multilayer film of the present invention may be obtained by lamination or co- extrusion of the first and the second polymer films, or it can be obtained by means of solution casting.
• the solution of the second polymer of (b) is cast onto the first polymer film of (a) to obtain a multilayer film.
• the thickness of the polymer film in (a) or (b) as a laminated film can be from about 3 to about 150 ⁇ or from about 20 to about 100 ⁇ ; whereas, the thickness as a coating film can be from about 2 to about 20 ⁇ or from about 3 to about 10 ⁇ .
• the first polymer film of (a) is a cellulose ester film having an out-of-plane retardation (R th ) of -100 to -400 nm at the wavelength
• the second polymer film of (b) is poly(a, ⁇ , ⁇ - trifluorostyrene) having a thickness of 2 to 20 ⁇ .
• Stretching of the multilayer film can be carried out by any method known in the art.
• the temperature suitable for stretching may be around the Tg of the first polymer film of (a), may be about 5-50°C higher than said Tg, or may be about 5-50°C lower than said Tg.
• the coated film may be stretched while it still contains some solvent and is not completely dried (wet stretching).
• a lower temperature may be employed for stretching.
• a higher temperature for example, around the Tg of the polymer or about 5-30 °C higher may be used for stretching.
• the extension ratio (elongation) of the film after stretching may be about 2-200 % (defined as the percentage of the length that is longer than the unstretched film). In one embodiment, the extension ratio is about 2-100%.
• This invention further provides a method for making a wide-view optical compensation film, which has a positive in-plane retardation that satisfies the relations of 0.7 ⁇ R 4 5o/Rs5o ⁇ 1 and l ⁇ R 6 5o/R55o ⁇ 1.25, comprising the steps of:
• the optical compensation 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 3D 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.
• Example 1 Stretched Multilayer Film 1 Having Reversed Dispersion Curve Based on Cellulose Ester
• PTFS poly(a,P,P-trifluorostyrene)
• the polymer solution was cast on half area of the cellulose ester film (thickness, 80 ⁇ ) using a knife applicator while leaving the other half uncoated. Immediately after casting, the coated film was placed in a force-air oven at 85 °C for 10 minutes to yield a dried coating. The thickness of the PTFS coating was determined to be 13.75 ⁇ by using Metricon Prism Coupler 2010 (Metricon Corp.). [045] A non-constrained uniaxial stretching method was used for film stretching. The half- coated film prepared above was mounted on a stretching machine (Kara IV laboratory film stretcher available from Bruckner) equipped with a heating chamber in a manner that the coated/uncoated borderline is aligned along the stretching direction.
• Kara IV laboratory film stretcher available from Bruckner
• the film was pre-heated for 25 seconds to reach the stretching temperature- 173°C and subsequently stretched in the machine direction (MD) at a speed of 7.0 mm/sec to a stretch ratio of 1.45.
• MD machine direction
• TD transverse direction
• the retardations (R th and R e ) of the coated and uncoated parts of the cellulose ester film (CE-1) were measured by M-2000V Ellipsometer (J. A. Woollam Co.). The results are listed in Table 1, which shows the representative retardations at the wavelength 589 nm, R e (589) and R ft (589), and the values of R e (450)/R e (550) and R e (650)/R e (550).
• the coated film is characterized in that it has lower in- plane retardation (R s ), reduced absolute value of out-of-plane retardation, and much steeper reversed wavelength dispersion as depicted in FIG. 1.
• the film thus obtained has a R s value of 130 nm, which is in the range of a quarter wave plate.
• Example 2 Stretched Multilayer Film 2 Having Reversed Dispersion Curve Based on Cellulose Ester
• a second cellulose film was prepared and coated with the PTFS solution (dried coating thickness: 11.91 ⁇ ) as described in Example 1.
• the resulting film (CE-2) was stretched according to Example 1 at 173°C to a stretch ratio of 1.40.
• the results are listed in Table 2 and plotted in FIG. 2. When compared to the uncoated part of the film, the coated film is
• Example 3 Stretched Multilayer Film 3 Having Reversed Dispersion Curve Based on Cellulose Ester
• a third cellulose film was prepared and coated with the PTFS solution (dried coating thickness: 17.79 ⁇ ) as described in Example 1.
• the resulting film (CE-3) was stretched according to Example 1 at 173°C to a stretch ratio of 1.45.
• the results are listed in Table 3 and plotted in FIG. 3.
• the coated film is characterized in that it has lower in-plane retardation (R ⁇ ), reduced absolute value of out-of-plane retardation, and much steeper reversed wavelength dispersion as depicted in FIG. 3.
• Example 4 Stretched Multilayer Films Having Reversed Dispersion Curve Based on COP
• COP cyclic olefin polymer
• Four COP films were prepared (4 inch x 4 inch) and coated with the PTFS solution as described in Example 1. The resulting films (COP-1 to -4) were stretched according to Example 1 at 150° C to a stretch ratio ranging from 1.40 to 1.5. The results are listed in Table 4.
• the dispersion curves of the coated films thus obtained all have reversed wavelength dispersion characteristics as indicated by the values of R e (450)/R s (550) and R s (650)/R s (550), although they are much flatter as compared to those of cellulose ester based films.

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