Wide-view optical film having reversed wavelength dispersion

Abstract

An optical compensation film is disclosed herein, which is made by uniaxially or biaxially stretching of a multilayer film including a first polymer film having a refractive index profile satisfying the equations of (n.sub.x+n.sub.y)/2n.sub.z and |n.sub.xn.sub.y|<0.005 and a second polymer film having a refractive index profile satisfying the equations of (n.sub.x+n.sub.y)/2<n.sub.z and |n.sub.xn.sub.y|<0.005, wherein n.sub.x and n.sub.y represent in-plane refractive indices and n.sub.z the thickness-direction refractive index of the films, and wherein said optical compensation film has a positive in-plane retardation that satisfies the relations of 0.7<R.sub.450/R.sub.550<1 and 1<R.sub.650/R.sub.550<1.25, wherein R.sub.450, R.sub.550, and R.sub.650 are in-plane retardations at the light wavelengths of 450 nm, 550 nm, and 650 nm respectively.

Claims

1. An optical compensation film comprising: a first polymer film and a second polymer film that form a multilayer film, wherein (a) the first polymer film has a refractive index profile satisfying the equations of (n.sub.x+n.sub.y)/2n.sub.z and |n.sub.xn.sub.y|<0.005; wherein the first polymer film is either 1) a negative C-plate having a refractive index profile of n.sub.x=n.sub.y>n.sub.z and comprises a cellulose ester film having an out-of-plane retardation (R.sub.th) of 100 to 400 nm at the wavelength () 550 nm, and a thickness of 20-100 m or 2) an isotropic film selected from the group consisting of cyclic polyolefin (COP), polycarbonate, polyester, polysulfone, and acrylic polymer having a refractive index profile of n.sub.x=n.sub.y=n.sub.z; and (b) the second polymer film having a refractive index profile satisfying the equations of (n.sub.x+n.sub.y)/2<n.sub.z and |n.sub.xn.sub.y|<0.005; wherein the second polymer film is a positive C-plate having a refractive index profile of n.sub.x=n.sub.y<n.sub.z; and wherein the second polymer film has an out of plane birefringence (n.sub.th) satisfying the equation of n.sub.th>0.01 and is a homopolymer or a copolymer of monomers selected from the group comprising ,,-trifluorostyrene, ,-difluorostyrene, ,-difluorostyrene, -fluorostyrene, and -fluorostyrene, wherein n.sub.x and n.sub.y represent in-plane refractive indices and n.sub.z the thickness-direction refractive index of the films, and wherein said optical compensation film has a positive in-plane retardation and reversed in plane wavelength dispersion characteristics that satisfy the relations of 0.7<R.sub.450/R.sub.550<1 and 1<R.sub.650/R.sub.550<1.25, wherein R.sub.450, R.sub.550, and R.sub.650 are in-plane retardations at the light wavelengths of 450 nm, 550 nm, and 650 nm respectively, wherein the optical compensation film is formed by uniaxially or biaxially stretching the multilayer film formed from the combination of the first polymer film layer and the second polymer film layer, and wherein the resulting optical compensation film has an out of plane retardation (R.sub.th) that satisfies the equation of |R.sub.th|<100 nm throughout the wavelength range of about 400 nm to about 800 nm.

2. The optical compensation film of claim 1, wherein the second polymer film of (b) has an out-of-plane birefringence (n.sub.th) satisfying the equation of n.sub.th>0.15 or >0.2.

3. The optical compensation film of claim 1, wherein the second polymer film of (b) is poly(, , -trifluorostyrene).

4. The optical compensation film of claim 1, wherein the optical compensation film has an in-plane retardation (R.sub.e) of about 80-300 nm at the wavelength () 550 nm.

5. The optical compensation film of claim 1, wherein the optical compensation film has an in-plane retardation (R.sub.e) of about 120-160 nm at the wavelength () 550 nm.

6. The optical compensation film of claim 1, wherein the optical compensation film has an in-plane retardation (R.sub.e) equal to about /4 at each wavelength ranging from 400 nm to 800 nm.

7. The optical compensation film of claim 1, wherein the optical compensation film has an out-of-plane retardation (R.sub.th) satisfying the equation of |R.sub.th|<80 nm throughout the wavelength ranging from 400 to 800 nm.

8. The optical compensation film of claim 5, wherein the optical compensation film has an out-of-plane retardation (R.sub.th) satisfying the equation of |R.sub.th|<80 nm throughout the wavelength ranging from 400 to 800 nm.

9. The optical compensation film of claim 1, wherein the optical compensation film has a positive in-plane retardation satisfying the relations of 0.76<R.sub.450/R.sub.550<0.96 and 1.03<R.sub.650/R.sub.550<1.22.

10. The optical compensation film of claim 1, wherein the first polymer film of (a) and the second polymer film of (b) are laminated.

11. The optical compensation film of claim 1, wherein the second polymer film of (b) is coated on the first polymer film of (a).

12. The optical compensation film of claim 11, wherein the second polymer film of (b) has a thickness of 2 to 20 m.

13. The optical compensation film of claim 1, wherein the first polymer film of (a) is a cellulose ester film having an out-of-plane retardation (R.sub.th) of 100 to 400 nm at the wavelength () 550 nm and a thickness of 20-100 m, and the second polymer film of (b) is poly(, , -trifluorostyrene) having a thickness of 2 to 20 m.

14. A circular polarizer comprising the optical compensation film of claim 1.

15. A liquid crystal display comprising the optical compensation film of claim 1.

16. An OLED display comprising the optical compensation film of claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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;

(2) FIG. 2 is a graph depicting the wavelength dispersions of stretched cellulose ester film 1 with and without coating;

(3) FIG. 3 is a graph depicting the wavelength dispersions of stretched cellulose ester film 2 with and without coating; and,

(4) FIG. 4 is a graph depicting the wavelength dispersions of stretched cellulose ester film 3 with and without coating.

DETAILED DESCRIPTION

(5) In one embodiment, there is provided 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 (n.sub.x+n.sub.y)/2n.sub.z and |n.sub.xn.sub.y|<0.005 and, (d) a second polymer film having a refractive index profile satisfying the equations of (n.sub.x+n.sub.y)/2<n.sub.z and |n.sub.xn.sub.y|<0.005;
wherein n.sub.x and n.sub.y represent in-plane refractive indices and n.sub.z the thickness-direction refractive index of the films, and wherein said optical compensation film has a positive in-plane retardation that satisfies the relations of 0.7<R.sub.450/R.sub.550<1 and 1<R.sub.650/R.sub.550<1.25, wherein R.sub.450, R.sub.550, and R.sub.650 are in-plane retardations at the light wavelengths of 450 nm, 550 nm, and 650 nm respectively.

(6) The optical compensation film in accordance with the present invention has a positive in-plane retardation (R.sub.e) 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 R.sub.450/R.sub.550<1 and R.sub.650/R.sub.550>1. The ratio of R.sub.450/R.sub.550 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 R.sub.650/R.sub.550 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.

(7) Retardation (R) of a wave plate is defined as R=nd, wherein n is the birefringence and d is the thickness of the wave plate. Birefringence is classified into in-plane birefringence n.sub.in=n.sub.xn.sub.y and out-of-plane birefringence n.sub.th=n.sub.z(n.sub.x+n.sub.y)/2. Thus, in-plane retardation is represented by R.sub.e=(n.sub.xn.sub.y)d and out-of-plane retardation by R.sub.th=[n.sub.z(n.sub.x+n.sub.y)/2]d.

(8) 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. Throughout this description, when 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.

(9) In one embodiment, the in-plane retardation (R.sub.e) of the optical compensation film of this invention is about 80-300 nm at the wavelength () 550 nm. In a further aspect, the optical compensation film in accordance with this invention is a quarter wave plate (QWP) having in-plane retardation (R.sub.e) of about 120-160 nm at the wavelength () 550 nm and having a reversed in-plane dispersion characteristic. In another aspect, said quarter wave plate is a broadband QWP, having R.sub.e equal to about /4 at each wavelength ranging from 400 nm to 800 nm.

(10) Besides having a reversed in-plane dispersion characteristic, the optical film of the present invention is capable of providing a low out-of-plane retardation (R.sub.th) value. The low R.sub.th is desirable particularly for display application since it can increase the viewing angle and improve the contrast ratio of an image. Thus, this invention further provides a wide-view optical film having an out-of-plane retardation (R.sub.th) that satisfies the equation of |R.sub.th|<100 nm, or <80 nm, or <50 nm, or <30 nm, or <10 nm, or <5 nm throughout the wavelength range of about 400 nm to about 800 nm.

(11) 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.

(12) Thus, this invention further provides a circular polarizer comprising a linear polarizer and a wide-view QWP of the present invention. In another embodiment, there is provided an OLED display comprising a circular polarizer of the present invention.

(13) In one embodiment, the first polymer film of (a) has an in-plane retardation (R.sub.e) satisfying |R.sub.e|<100 nm, or <50 nm, or <30 nm, or <10 nm.

(14) In one aspect, the polymer film of (a) is a negative C-plate having a refractive index profile of n.sub.x=n.sub.y>n.sub.z. In another aspect, the polymer film of (a) is an optically isotropic film having n.sub.x=n.sub.y=n.sub.z.

(15) Examples of the negative C-plate 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. In one embodiment, the negative C-plate has an out-of-plane birefringence (n.sub.th) satisfying the equation of |n.sub.th|>0.002, or >0.005, or >0.01 or >0.015, or >0.02. A negative C-plate having higher |n.sub.th| is advantageous in that it is capable of providing higher positive R.sub.e values when stretched.

(16) Examples of the isotropic film include cyclic polyolefin (COP), polycarbonate, polyester, cellulose ester, polysulfone, and acrylic polymer. It is noted that said isotropic films may still exhibit negligible differences in the values of n.sub.x, n.sub.y, and n.sub.z, which could result in a relation of (n.sub.x+n.sub.y)/2<n.sub.z by a small value such as 0.001 or less. For the purpose of simplicity of the description, this would be considered as (n.sub.x+n.sub.y)/2=n.sub.z and is within the scope of the present invention.

(17) The first polymer film of (a) will generate positive R.sub.e 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.sub.th leads to higher R.sub.e values. Thus, this invention further provides a first polymer film of (a) that is a cellulose ester film having an out-of-plane retardation (R.sub.th) of 100 nm to 400 nm at the wavelength () 550 nm and a thickness of 20-100 m.

(18) In one aspect, the second polymer film of (b) is a positive C-plate having a refractive index profile of n.sub.x=n.sub.y<n.sub.z. Examples of 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 fluoropolymers as disclosed in US Patent Application No. 20110076487; the content of said US Patent Applications is incorporated herein by reference.

(19) In one embodiment, the second polymer film of (b) has an out-of-plane birefringence (n.sub.th) satisfying the equation of n.sub.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.sub.th) with thin films to reduce or eliminate the negative R.sub.th typically exhibited in the first polymer film of (a). The stretched multilayer films thus obtained will have wide-view characteristics. Particularly suitable for this purpose are homopolymers or copolymers of the monomers selected from the group comprising ,,-tritluorostyrene, ,-difluorostyrene, ,-difluorostyrene, -fluorostyrene, and -fluorostyrene. Poly(,,-trifluorostyrene) is used in one example.

(20) Stretching of the polymer film of (b) will result in a negative R.sub.e value and a normal dispersion curve, which when combined with the polymer film of (a) (for example, co-stretching) will provide the optical properties desirable in this invention positive R.sub.e and reversed dispersion curve.

(21) In one embodiment, 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, polyolefin, polyurethane, polystyrene, glass, and other materials commonly used in an LCD device.

(22) Depending on the composition, 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.

(23) 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. Alternatively, the second polymer film on a substrate is laminated onto the first polymer film and the substrate subsequently removed.

(24) 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. In one embodiment, 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 m or from about 20 to about 100 m; whereas, the thickness as a coating film can be from about 2 to about 20 m or from about 3 to about 10 m.

(25) In a further embodiment of the present invention, the first polymer film of (a) is a cellulose ester film having an out-of-plane retardation (R.sub.th) of 100 to 400 nm at the wavelength () 550 nm and a thickness of 20-100 m, and the second polymer film of (b) is poly(,,-trifluorostyrene) having a thickness of 2 to 20 m.

(26) 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.

(27) Alternatively, the coated film may be stretched while it still contains some solvent and is not completely dried (wet stretching). In this case, a lower temperature may be employed for stretching. It is also possible to stretch the coated film with a support underneath (e.g. on a steel belt); in this case, a higher temperature, for example, around the Tg of the polymer or about 5-30 C. higher may be used for stretching.

(28) 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%.

(29) 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.sub.450/R.sub.550<1 and 1<R.sub.650/R.sub.550<1.25, comprising the steps of: I. dissolving a polymer whose solution cast film has a refractive index profile satisfying the equations of (n.sub.x+n.sub.y)/2<n.sub.z and |n.sub.xn.sub.y<0.005 in one or more organic solvents. II. solution casting the polymer solution of (i) on a polymer film having a refractive index profile satisfying the equations of (n.sub.x+n.sub.y)/2n.sub.z and |n.sub.xn.sub.y|<0.005, III. allowing the resulting coating to dry until it is suitable for stretching, and IV. biaxially or uniaxially stretching the coated polymer film at a suitable temperature to a stretching ratio that is capable of providing said optical properties;
wherein R.sub.450, R.sub.550, and R.sub.650 are in-plane retardations at the light wavelengths of 450 nm, 550 nm, and 650 nm respectively, and wherein n.sub.x and n.sub.y represent in-plane refractive indices and n.sub.z the thickness-direction refractive index of the films.

(30) 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.

EXAMPLES

Example 1: Stretched Multilayer Film 1 Having Reversed Dispersion Curve Based on Cellulose Ester

(31) A solution of poly(,,-trifluorostyrene) (PTFS) was prepared by mixing PTFS powder (10 g; intrinsic viscosity=1.0 dL/g) and plasticizer (Abitol E available from Eastman Chemical Co.) (0.75 g) in the solvent, methyl isopropyl ketone (60.93 g). Separately, a sample (4 inch4 inch) of a cellulose ester film (thickness, 80 m) having R.sub.th(0.589)=222 nm and R.sub.e(589) 3.1 nm (essentially a negative C-plate) 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 half area of the cellulose ester film (thickness, 80 m) 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 PITS coating was determined to be 13.75 m by using Metricon Prism Coupler 2010 (Metricon Corp.).

(32) A non-constrained uniaxial stretching method was used for film stretching. The half-coated film prepared above was mounted on a stretching machine (Karo IV laboratory film stretcher available from Brckner) equipped with a heating chamber in a manner that the coated/uncoated borderline is aligned along the stretching direction. 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. The transverse direction (TD) was left un-constrained.

(33) After stretching, the retardations (R.sub.th and R.sub.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.sub.e(589) and R.sub.th(589), and the values of R.sub.e(450)/R.sub.e(550) and R.sub.e(650)/R.sub.e(550). When compared to the uncoated part of the film, the coated film is characterized in that it has lower in-plane retardation (R.sub.e), 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.sub.e value of 130 nm, which is in the range of a quarter wave plate.

(34) TABLE-US-00001 TABLE 1 Retardations of the Stretched Cellulose Film 1 Stretch Ratio R.sub.th(589), R.sub.e(450)/ R.sub.e(650)/ (TD MD) R.sub.e(589), nm nm R.sub.e(550) R.sub.e(550) CE-1 1 1.45 247 142 0.987 1.005 without Coating CE-1 1 1.45 130 78 0.909 1.047 with Coating

Example 2: Stretched Multilayer Film 2 Having Reversed Dispersion Curve Based on Cellulose Ester

(35) A second cellulose film was prepared and coated with the PIES solution (dried coating thickness: 11.91 m) 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 characterized in that it has lower in-plane retardation (R.sub.e), reduced absolute value of out-of-plane retardation, and much steeper reversed wavelength dispersion as depicted in FIG. 2.

(36) TABLE-US-00002 TABLE 2 Retardations of the Stretched Cellulose Film 2 Stretch Ratio R.sub.th(589), R.sub.e(450)/ R.sub.e(650)/ (TD MD) R.sub.e(589), nm nm R.sub.e(550) R.sub.e(550) CE-2 1 1.40 232 144 0.988 1.005 without Coating CE-2 1 1.40 100 67 0.896 1.052 with Coating

Example 3: Stretched Multilayer Film 3 Having Reversed Dispersion Curve Based on Cellulose Ester

(37) A third cellulose film was prepared and coated with the PTFS solution (dried coating thickness: 17.79 m) 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. When compared to the uncoated part of the film, the coated film is characterized in that it has lower in-plane retardation (R.sub.e), reduced absolute value of out-of-plane retardation, and much steeper reversed wavelength dispersion as depicted in FIG. 3.

(38) TABLE-US-00003 TABLE 3 Retardations of the Stretched Cellulose Film 3 Stretch Ratio R.sub.th(589), R.sub.e(450)/ R.sub.e(650)/ (TD MD) R.sub.e(589), nm nm R.sub.e(550) R.sub.e(550) CE-2 1 1.45 253 151 0.987 1.004 without Coating CE-2 1 1.45 50 31 0.777 1.108 with Coating

Example 4: Stretched Multilayer Films Having Reversed Dispersion Curve Based on COP

(39) A cyclic olefin polymer (COP) film was used as the base film for this study. The film has a thickness of 98 m and retardations of R.sub.e(589)=3.41 nm and R.sub.th(589)=10.65 nm, indicating essentially an optically isotropic film. Four COP films were prepared (4 inch4 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.sub.e(450)/R.sub.e(550) and R.sub.e(650)/R.sub.e(550), although they are much flatter as compared to those of cellulose ester based films.

(40) TABLE-US-00004 TABLE 4 Retardations of the Stretched COP Films Coating Thickness Stretch after Ratio Stretching, R.sub.e (589), R.sub.th (589), R.sub.e (450)/ R.sub.e (650)/ (TD MD) m nm nm R.sub.e (550) R.sub.e (550) COP-1 without coating 1 1.5 N/A 174 119 1.009 0.995 COP-1 with coating 1 1.5 4.30 98 18 0.970 1.015 COP-2 without coating 1 1.45 N/A 204 132 1.009 0.995 COP-2 with coating 1 1.45 4.28 117 37 0.975 1.014 COP-3 without coating 1 1.40 N/A 190 118 1.009 0.995 COP-3 with coating 1 1.40 7.58 85 9 0.955 1.022 COP-4 without coating 1 1.43 N/A 172 117 1.009 0.995 COP-4 with coating 1 1.43 7.69 76 11 0.935 1.035

(41) The embodiments have been described, hereinabove. It will be apparent to those skilled in the art that the above methods and apparatuses may incorporate changes and modifications without departing from the general scope of this invention. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof. Although the description above contains much specificity, this should not be construed as limiting the scope of the invention, but as merely providing illustrations of some of the embodiments of this invention. Various other embodiments and ramifications are possible within its scope.

(42) Furthermore, notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.