MXPA98006819A - A method to make a movie opt - Google Patents

Abstract

An optical film comprising a dispersed phase of polymer particles arranged in a continuous birefringent matrix is provided. The film is oriented, typically stretching in one or more directions. The size and shape of the particles of the dispersed phase, the volume fraction of the dispersed phase, the thickness of the film, and the amount of orientation are chosen to obtain a desired degree of diffuse reflection and total transmission of electromagnetic radiation from a desired wavelength in the film result

Description

A METHOD TO MAKE A PELÍCTJL? OPTICS.

Field of Invention . This invention relates to optical materials containing structures suitable for controlling optical characteristics, such as -reflectance and transmission. In a further aspect, it relates to the control of specific polarizations of reflected or transmitted light.

Background The optical films known in the art are constructed of scattered inclusions within a continuous matrix. The characteristics of these inclusions can be manipulated to provide a range of reflective and transmissive properties to the film. These characteristics include arriaño of the inclusion with respect to the wavelength inside the film, the form of the inclusion and the ordering, factor of filling volumetric of the inclusion and the degree of inequality of the index of refraction with the continuous matrix to the length of the three orthogonal axes of the film.

The polarizers of conventional absorption (dichroic) REF .: 28111 have, as their inclusion phase, light-absorbing iodine-like inorganic chains that are aligned within a polymer matrix. Such a film will tend to absorb polarized light with its electric field vector aligned parallel to the roller-type iodide chains, and to transmit the polarized light perpendicular to the rolls. Because iodide chains have two or more dimensions that are small compared to the wavelength of visible light, and because the number of chains per cubic wavelength of light is large, the optical properties of such a film are predominantly mirror-like. , with very small diffuse transmission through the film or diffuse reflection of the film surfaces. Like most other commercially suitable polarizers, these polarizing films rely on selective polarization absorption.

Films filled with inorganic inclusions with different characteristics can provide other optical and reflective transmission properties. For example, mica flakes coated with two or more dimensions that are large compared to visible wavelengths have been incorporated into polymeric films and paints to impart a metallic sheen. These flakes can be manipulated to keep in the plane of the film, thus imparting a strong directional dependence for reflective appearance. Such an effect can be used to produce security screens that are highly reflective for certain viewing angles, and transmissive to other viewing angles. The large leaflets that have a coloration (spectacularly selective reflection) that depend on the alignment with respect to. incident light, can be incorporated into a film to provide obvious manipulation. In this application, it is necessary that all the flakes in the film are aligned similarly one with respect to the other.

However, optical films made of polymers filled with inorganic inclusions suffer a variety of weaknesses. Typically, the adhesion between the inorganic particles and the polymer matrix is poor. Accordingly, the optical properties of the film decrease when force or force is applied across the matrix, both because the bond between the matrix and the inclusions is arranged, and because the rigid inorganic inclusions could fracture. In addition, the alignment of inorganic inclusions requires process steps and considerations that complicate the elaboration.

Other films, such as those exhibited in U.S. 4,688,900 (Doane et al.), Consist of a clear continuous polymer matrix that transmits light, with drops of liquid crystals that modulate the scattered light inside. The elongation of the material results in a distortion of the liquid crystal droplet from a spherical to an ellipsoidal shape, with the longitudinal axis of the ellipse parallel to the direction of stretching. U.S. 5, 301,041 (Konuma et al.) Makes a similar exposure, but achieves the distortion of the liquid crystal drop by means of the application of pressure. A. Aphonin, "Optical Properties of Stretched Polymer Dispersed Liquid Crystal Films: Angle-Dependent Polarized Light Scattering, Liquid Cristals, Vol. 19, No. 4,469-480 (1995), discusses the optical properties of stretched films consisting of liquid crystal droplets arranged within a polymer matrix It is reported that the elongation of the drops in an ellipsoidal shape, with their longitudinal axes parallel to the direction of elongation, imparts an oriented birefringence (difference of the refractive index between the dimensional axes) from the drop) to the drops, resulting in a relative inequality of the refractive index between the scattered and continuous phases along certain axes of the film, and a relative index equal along the other axes of the film. liquid crystal drops are not small since they are compared for visible wavelengths in the film, and thus the optical properties of such films have a compa Substantial diffuse intensity for its reflective and transmissive properties. Aphonin suggests the use of these materials as a polarizing diffuser for subsequent light nematic snaking LCDs. However, optical films employing liquid crystals such as the dispersed phase are substantially limited in the degree of refractive index inequality between the phase of the matrix and dispersed phase. In addition, the birefringeney of the liquid crystal component of such films is typically temperature sensitive.

U.S. 5,268,225 (Isayev) discloses a laminated composite made of thermotropic liquid crystal polymer blends. The mixture consists of two liquid crystal polymers that are immiscible with each other. The mixtures could be molded into a film consisting of a disperse inclusion phase and a continuous phase. When the film is stretched, the dispersed phase forms a series of fibers whose axes align in the direction of the stretch. While the film is described as having improved mechanical properties, no mention is made of the optical properties of the film. However, due to its liquid crystal nature, films of this type would suffer from the weaknesses of other liquid crystal materials discussed above.

Still other films have been made to exhibit desirable optical properties by the application of magnetic or electric fields. For example, U.S. 5,008,807 (Waters et al) discloses a liquid crystal device consisting of fiber layers impregnated with liquid crystal material and disposed between two electrodes. A voltage across the electrodes produces an electric field that changes the birefringent properties of the liquid crystal material, resulting in varying degrees of inequality between the refractive indices of the fibers and the. liquid crystal. However, the requirement of a magnetic or electric field is inconvenient and undesirable in many applications, particularly those where fields exist could cause interference.

Other optical films have been made by incorporating a dispersion of inclusions of a first polymer into a second polymer, and then stretching the resulting compound in one or two directions. U.S. 4,871,784 (Otonari et al.) Is an example of this technology. The polymers are selected such that there is low adhesion between the dispersed phase and the surrounding matrix polymer, so that an elliptical vacuum forms around each inclusion when the film is stretched.

Such voids have dimensions of the order of visible wavelengths. The. Index inequality of refraction between the vacuum and the polymer in these "micro-void" films is typically quite large (approximately 0.5), causing substantial diffuse reflection. However, other optical properties of microvacuum materials are difficult to control due to variations in the geometry of the interfaces, and it is not possible to produce a film axis for which the refractive indexes are relatively equal, since it would be useful for optical properties sensitive to polarization. In addition, voids in such material can easily collapse through exposure to heat and pressure.

Optical films have also been made where a dispersed phase is arranged deterministically in an ordered pattern within a continuous matrix. U.S. 5,217,794 (Schren) is an example of this technology. There, a lamellar polymer film is exposed which is made of polymeric inclusions which are large compared to the wavelength on two axes, arranged within a continuous matrix of another polymeric material. The refractive index of the dispersed phase differs significantly from that of the continuous phase along one or more of the axes of the sheet, and is relatively well matched along the other. Due to the arrangement of the dispersed phase, the films of this type exhibit strong iridescence (eg, color dependent on the interference of the base angle) for cases in which they are substantially reflective. As a result, such films have been of limited use for optical applications where optical diffusion is desirable.

Thus there is a need in the art for an optical material consisting of a continuous and a scattered phase, wherein the inequality of the refractive index between the two phases along the three dimensional axes of the material can be conveniently and permanently manipulated to achieve degrees desirable diffusion and reflection and transmission, speculate where the optical material is stable with respect to strength, stress, temperature differences, and magnetic and electric fields, and where the optical material has an insignificant level of iridescence. These and other needs are met by the present invention, as set forth below.

Brief description of the Drawings FIG. 1 is a schematic drawing illustrating an optical body made in accordance with the present invention, wherein the dispersed phase is arranged as a series of elongated masses having essentially a circular cross-section; FIG. 2 is a schematic drawing illustrating an optical body made in accordance with the present invention, wherein the dispersed phase is arranged in a series of elongated masses having an essentially elliptical cross section; FIGS. 3a-e are schematic drawings illustrating various forms of the dispersed phase in an optical body made in accordance with the present invention; FIG. 4a is a graph of the bidirectional scattered distribution as a function of the scattering angle for a film oriented in accordance with the present invention for polarized light perpendicular to the direction of orientation; FIG. 4b is a graph of the bidirectional scattered distribution as a function of the scattering angle for a oriented film according to the present invention for polarized light parallel to the direction of orientation; Y FIG. 5 is a schematic representation of a multilayer film made in accordance with the present invention.

Brief Description of the Invention In one aspect, the present invention relates to a diffusely reflective film or other optical body comprising a birefringent continuous polymer phase and a substantially non-birefringent dispersed phase disposed within the continuous phase. The refractive indices of the continuous and dispersed phases are substantially unequal (eg, they differ from each other by more than about 0.05) along the first of three mutually orthogonal axes, and are substantially equal (e.g., differ in less than about 0.05) along the second of three mutually orthogonal axes. In some embodiments, the refractive indices of the continuous and dispersed phases may be substantially the same or unequal along, or parallel to, the third of three mutually orthogonal axes to produce a mirror or a polarizer. The incident light polarized along, parallel to, an unequal axis is scattered, resulting in significant diffuse reflection. The incidence of polarized light along an even axis is dispersed to a much lesser degree and is transmitted significantly spectrally. These properties can be used to make optical films for a variety of uses, including low loss reflective polarizers (not significantly absorbing) for which light polarizations that are not significantly transmitted are diffusely reflected.

In a related aspect, the present invention relates to an optical film or other optical body comprising a continuous phase and a birefringent disperse phase, wherein the refractive indices of the continuous and dispersed phases are substantially equalized (e.g. wherein the difference of the index between the continuous and dispersed phases is less than about 0.05) along an axis perpendicular to a surface of the optical body.

In another aspect, the present invention relates to an optical body composite comprising a first continuous birefringent polymer phase in which the second dispersed phase could be birefringent, but in which the degree of equality and inequality in at least two orthogonal directions it is mainly due to the birefringence of the first phase.

In still another aspect, the present invention relates to a method for obtaining a diffuse reflector polarizer, comprising the steps of: providing a first resin, the degree of which birefringence can be altered by the application of a force field, as through a dimensional orientation or an applied electric field, such that the resulting resin material has, at least two orthogonal directions, a refractive index difference of more than about 0.05; providing a second resin, dispersed within the first resin; and applying said force field to the composite of both resins such that the rates of two resins are approximately equal to less than about 0.05 in one of the two directions, and the index difference between the first and second resins in the other two directions is greater than about 0.05. In a related embodiment, the second resin is dispersed in the first resin after the imposition of the force field and the subsequent alteration of the birefringence of the first resin.

In yet another aspect, the present invention relates to an optical body that acts as a reflective polarizer with a high extinction ratio. In this aspect, the difference of the index in the direction of equality is chosen as small as possible and the difference in the direction of inequality is maximized. The fraction of volume, thickness, and particle size and shape of the dispersed phase can be chosen to maximize the extinction ratio, although the relative importance of optical transmission and reflection for different polarizations could vary for different applications.

In another aspect, the present invention relates to an optical body comprising a continuous phase, a dispersed phase whose refractive index differs from said continuous phase by more than about 0.05 along a first axis and by less than about 0.05 a along a second axis orthogonal to said first axis, and a dichroic dye. The optical body is preferably oriented along at least one axis. The dichroic dye improves the extinction coefficient of the optical body by absorbing, in addition to dispersing, the polarized light parallel to the axis of orientation.

In various aspects of the present invention, the reflection and transmission properties of at least two orthogonal polarizations of incident light are determined by the selection or manipulation of various parameters, including the optical indices of the continuous and dispersed phases, the size and shape of the particles of the dispersed phase, the volume fraction of the dispersed phase, the thickness of the optical body through which some incident light fraction is to pass, and the wavelength or wavelength band of electromagnetic radiation of interest.

The magnitude of the equality or inequality index along a particular axis will directly affect the degree of dispersion of polarized light along that axis. In general, the dispersion power varies according to the square of the inequality index. Thus, the higher the index of inequality along a particular axis, the stronger the dispersion of polarized light along that axis. Conversely, when the inequality along a particular axis is small, light polarized along that axis is dispersed to a lesser degree and so is transmitted specularly through the volume of the body.

The size of the dispersed phase can also have a significant effect on the dispersion. If the particles of the dispersed phase are too small (eg, less than about 1/30 the wavelength of light in the medium of interest) and if there are many particles per wavelength: _bublic, the optical body is it behaves a bit like a medium with an effective refractive index between the indices of the two phases along any given axis. In such a case, very little light is scattered. If the particles are too large, the light is reflected spectacularly from the surface of the particle, with very little diffusion in other directions. When the particles are too large in at least two orthogonal directions, undesirable iridescence effects may also occur. The practical limits could also be reached when the particles become large that the thickness of the optical body becomes larger and the desirable mechanical properties are compromised.

The shape of the particles of the dispersed phase can also have an effect on the scattering of the light. The depolarization factors of the particles for the electric field in the directions of equality and inequality of the refractive index can reduce or increase the amount of dispersion in a given direction. The effect may add to or decrease the amount of dispersion of the inequality index, but in general it has a small influence on the dispersion in the preferred range of properties in the present invention.

The shape of the particles can also influence the degree of scattered light diffusion of the particles. This effect of the shape is generally small but increases according to the aspect ratio of the geometric cross-section of the particle in the plane perpendicular to the direction of incidence of the light increase and as the particles become relatively larger. In general, in the operation of this invention, the particles of the dispersed phase should measure less than several wavelengths of light in one or two mutually orthogonal dimensions if it is diffuse, rather than specular, reflection is preferred.

The dimensional alignment is also found to have an effect on the scattering behavior of the dispersed phase. In particular, it has been observed, in optical bodies made in accordance with the present invention, that the aligned dispersers will not scatter the light symmetrically in the directions of specular transmission or reflection since the dispersers would be randomly aligned. In particular, the inclusions that have been lengthened by orientation appear mainly light scattering rollers together (or close) to a central cone in the direction of orientation and having an edge along the direction transmitted specularly. For example, for light incident on such an elongated roller in a direction perpendicular to the direction of orientation, the scattered light appears as a band of light in the plane perpendicular to the direction of orientation with an intensity that decreases with the increase in angle away from The specular direction. By adjusting the geometry of the inclusions, some control in the distribution of the scattered light can be achieved in the transmissive hemisphere and in the reflector hemisphere.

The volume fraction of the dispersed phase also affects the light scattering in the optical bodies of the present invention. Within certain limits, the increase in the volume fraction of the dispersed phase tends to increase the amount of dispersion a light beam experiences after entering the body in the directions of equality and inequality of the polarized light. This factor is important to control the reflection and transmission properties for a given application. However, if the volume fraction of the dispersed phase becomes too large, the light scattering decreases. Without wishing to theorize, this seems to be due to the fact that the scattered phase particles are together, in terms of the wavelength of light, so that the particles tend to act together as a small number of large effective particles.

The thickness of the optical body is also an important control parameter that can be manipulated to affect the reflection and transmission properties in the present invention. As the thickness of the optical body increases, the diffuse reflection also increases, and the transmission, the specular and the diffusion, decreases.

While the present invention will sometimes be described "therein" with reference to the visible region of the spectrum, various embodiments of the present invention may be used to operate at different wavelengths (and hence frequencies) of electromagnetic radiation through Thus, as the wavelength increases, the linear size of the components of the optical body increases so that the dimensions, measured in units of wavelength, are approximately constant. The change in wavelength is that of, for most materials of interest, the refractive index and the change in absorption coefficient, however, the principles of equality and index inequality still apply to each wavelength of interest.

Detailed description of the invention Introduction As used here, the terms "specular reflection" and "Specular reflectance" refers to the reflectance of light rays in an emerging cone with a vertex angle of 16 degrees centered around the specular angle. The terms "diffuse reflection" or "diffuse reflectance" refer to the reflection of the rays that are outside the specular cone defined above. 'The terms "total reflectance" or "total reflection" refer to the combined reflectance of all the light of a surface. Thus, total reflection is the sum of specular and diffuse reflection.

Similarly, the terms "specular transmission" and "specular transmittance" are used herein in reference to the transmission of rays in an emerging cone with a vertex angle of 16 degrees centered around the specular direction. The terms "diffuse transmission" and "diffuse transmittance" are used herein in reference to the transmission of all rays that are outside the specular cone defined above. The terms "total transmission" or "total transmittance" refer to the combined transmission of all light through an optical body. Thus, the total transmission is the sum of the specular and diffuse transmission.

As used herein, the term "extinction ratio" is defined to indicate the ratio of total light transmitted in a polarization to the transmitted light in an orthogonal polarization.

FIGS. 1-2 illustrate a first embodiment of the present invention. According to the invention, a diffusely reflecting optical film 10 or another optical body is produced which consists of a birefringent matrix or continuous phase 12 and a discontinuous or dispersed phase 14. The birefringence of the continuous phase is typically at least about 0.05, preferably at least about 0.1, more preferably at least about 0.15, and more preferably at least about 0.2.

The refractive indices of the continuous and dispersed phases are substantially equal (eg, differ by less than about 0.05) along the first of three mutually orthogonal axes, and are substantially unequal (eg, it differs by more than about 0.05) along the second of three mutually orthogonal axes.

Preferably, the refractive indices of the continuous and dispersed phases differ by less than about 0.03 in the equality direction, more preferably, less than about 0.02, and more preferably, less than about 0.01. The refractive indices of the continuous and dispersed phases preferably differ in the direction of inequality by at least about 0.07, more preferably, by at least about 0.1, and preferably, by at least about 0.2.

Inequality in the refractive indices along a particular axis has the effect of incident light polarized along the axis that will substantially disperse, resulting in a significant amount of reflection. In contrast, incident light polarized along an axis in which refractive indices are equalized will be transmitted or reflected spectrally with a much lower degree of dispersion. This effect can be used to make a variety of optical devices, including polarizers and reflecting mirrors.

The present invention provides a practical and simple optical body and method for making a reflective polarizer, and also provides a means to obtain a continuous lag of optical properties according to the principles described herein. Also, very efficient low loss polarizers with high extinction ratios can be obtained. Other advantages are a wide range of practical materials for the dispersed phase and the continuous phase, and a high degree of control by providing high quality optical bodies of consistent and predictable operation.

Effect of the Equality / Inequality Index In the preferred embodiment, the materials of at least one of the continuous and dispersed phases are of a type that undergo a change in the refractive index in the orientation. Accordingly, as the film is oriented in one or more directions, the equalities or inequalities of the refractive index occur along one or more axes. By careful manipulation of orientation parameters and other processing conditions, positive or negative birefringence of the matrix can be used to induce reflection or diffuse transmission of one or both light polarizations along a given axis. The relative relation between transmission and diffuse reflection is dependent on the concentration of the inclusions of the dispersed phase, the thickness of the film, the square of the difference in the refractive index between the continuous and dispersed phases, the size and geometry of the inclusions of the dispersed phase, and the wavelength or band of the wavelength of the incident radiation.

The magnitude of the index of equality or inequality along a particular axis directly affects the degree of dispersion of polarized light along that axis. In general, the dispersion force varies with the square of the inequality index. Thus, the higher the index of inequality along a particular axis, the stronger will be the dispersion of polarized light along that axis. On the contrary, when the inequality along a particular axis is small, the polarized light along that axis is dispersed to a lesser degree and is therefore transmitted speculatively through the volume of the body.

FIGS. 4a-b demonstrate this effect in oriented films made in accordance with the present invention. There, a typical measurement of the Bidirectional Dispersion Distribution Function (BSDF) is shown for incident light normally at 632.8 nm. BSDF is described in J. Stover, "Optical Scattering Measurement and Analysis" (1990). The BSDF is shown as a function of the scattering angle for light polarizations perpendicular and parallel to the orientation axis. A scattering angle of zero corresponds to undispersed light (spectrally transmitted). For polarized light in the direction of the equality index (that is, perpendicular to the direction of orientation) as in FIG. 4a, there is a significant peak transmitted specularly with a regular component of diffusely transmitted light (scattering angle between 8 and 80 degrees), and a small component of diffusely reflected light (scattering angle greater than 100 degrees). For polarized light in the direction of index inequality (ie, parallel to the direction of orientation) as in FIG. 4b, there is specularly insignificant transmitted light and a highly reduced component of diffusely transmitted light, and a diffusely regular reflected component. It should be noted that the scattering plane shown in the graphs is the plane perpendicular to the direction of orientation where most of the scattering exists by these elongated inclusions. The contributions of light scattered outside this plane are greatly reduced.

If the refractive index of the inclusions (eg, the dispersed phase) equals that of the continuous base medium along some axis, then the polarized incident light with electric fields parallel to this axis will pass through regardless of the no dispersion of size, shape, and density of inclusions. If the indexes do not equal along an axis, then the inclusions will scatter the polarized light along this axis. For diffusers of a given cross-sectional area with dimensions greater than approximately? / 30 (where? Is the wavelength of light in the middle), the strength of the diffusion is determined primarily by the index inequality. The exact size, shape and arrangement of an inequality inclusion plays a role in determining how much light will be scattered in various directions from the inclusion. If the density and thickness of the diffusing layer is sufficient, according to the theory of multiple diffusion, the incident light will be reflected or absorbed, but will not transmit, regardless of the size and shape of the diffuser.

When the material is to be used as a polarizer, it is preferably processed, by stretching and allowing some dimensional relaxation in the cross stretch in the direction to the plane, so that the difference of the refractive index between the continuous and dispersed phases is large throughout of the first axis in a plane parallel to a surface of the material and small along the other two axes - orthogonal. This results in a large optical anisotropy of electromagnetic radiation of different polarizations.

Some of the polarizers in the scope of the present invention are elliptical polarizers. In general, elliptical polarizers will have a refractive index difference between the dispersed phase and the continuous phase in the directions of stretching and cross-stretching. The forward to backward dispersion ratio is dependent on the difference in the refractive index between the continuous and dispersed phases, the concentration of the dispersed phase, the size and shape of the dispersed phase, and the total thickness of the film. In general, elliptical diffusers have a small relative difference in the refractive index between the particles of the dispersed and continuous phases. Using a diffuser based on birefringent polymer, elliptical polarization of high sensitivity can be obtained (eg, diffuse reflectivity that depends on the polarization of the light). At one end, where the refractive index of the polymers is equalized on one axis, the elliptical polarizer will be a polarizer with diffuse reflection.

Methods for Obtaining the Equality / Inequality Index The materials selected for use in a polarizer according to the present invention, and the degree of orientation of these materials, are preferably chosen so that the phases in the final polarizer have at least one axis for which the refractive indices associated on substantially same. The equality of the refractive index associated with the axes, which typically, but not necessarily, is an axis transverse to the direction of orientation, results substantially without reflection of light in the plane of polarization.

The dispersed phase could also exhibit a decrease in the refractive index associated with the direction of orientation after stretching. If the birefringence of the base is positive, a birefringence induced by negative stress of the dispersed phase has the advantage of increasing the difference between the refractive indices of the adjacent phases associated with the axis of orientation while the reflection of light with its plane polarization perpendicular to the direction of orientation is still negligible. The differences between the refractive indices of the adjacent phases in the direction orthogonal to the direction of orientation should be less than about 0.05 after orientation, and preferably, less than about 0.02.

The dispersed phase could also exhibit a birefringence induced by positive stress. However, this can be altered by heat treatment to equalize the refractive index of the axis perpendicular to the orientation direction of the continuous phase. The temperature of the heat treatment should not be so high to relax the birefringence in the continuous phase.

Size of the Dispersed Phase The size of the dispersed phase could also have a significant effect on dispersion. If the particles of the dispersed phase are too small (eg, less than about 1/30 of the wavelength of light in the medium of interest) and if there are many particles per cubic wavelength, the optical body will be it behaves as a medium with a refractive index somewhat effective between the indices of the two phases along any given axis. In such a case, very little light is scattered. If the particles are too large, light is reflected specularly from the surface of the particle, with very little diffusion in other directions. When the particles are too large in at least two orthogonal directions, undesirable iridescence effects may occur. Practical limits could also be reached when the particles become large so that the thickness of the optical body becomes large and the desirable mechanical properties are compromised.

The dimensions of the particles of the dispersed phase after sorting may vary depending on the desired use of the optical material. Thus, for example, the dimensions of the particles could vary depending on the wavelength of the electromagnetic radiation that is of interest in a particular application, with different dimensions required to reflect to transmit visible, ultraviolet, infrared, and microwave radiation. In general, however, the length of the particles should be such that they are approximately larger than the wavelength of the electromagnetic radiation of interest in the medium, divided by 30.

Preferably, in applications where the optical body is to be used as a low loss reflecting polarizer, the particles will have a length that is greater than about 2 times the wavelength of the electromagnetic radiation in the wavelength range of interest , and preferably at 4 times the wavelength. The average diameter of the particles is preferably equal to or less than the wavelength of the electromagnetic radiation in the range of the wavelength of interest, and preferably less than 0.5 of the desired wavelength. While the dimensions of the dispersed phase are a secondary consideration in many applications, they become of great importance in thin film applications, where there is comparatively little diffuse reflection.

Geometry and Scattered Phase While index inequality is the predominant factor in which it falls to promote dispersion in the films of the present invention (eg, a mirror or diffuser polarizer made in accordance with the present invention has a substantial inequality in the indexes of refraction of the phases continuous and dispersed along at least one axis), the geometry of the particles of the dispersed phase may have a secondary effect on the dispersion. Thus, the depolarization factors of the particles for the electric field in the directions of equality or inequality of the refractive index can reduce or increase the amount of dispersion in a given direction. For example, when the scattered phase is elliptical in a cross section taken along a plane perpendicular to the axis of orientation, the shape of the elliptical cross section of the dispersed phase contributes to the asymmetric diffusion in the scattered back light and scattered light. lead. The effect may add or decrease the amount of dispersion of the equality of the index, but in general it has a small influence on the dispersion in the preferred range of the properties of the present invention.

The shape of the particles of the dispersed phase can also influence the degree of diffusion of scattered light from the particles. This shape effect is generally small but increases with the aspect ratio of the geometric cross section of the particle in the plane perpendicular to the direction of incidence of the light increase and as relatively larger particles are obtained.

In general, in the operation of this invention, the particles of the dispersed phase should measure less than several wavelengths of light in one or two mutually orthogonal dimensions if diffuse, rather than specular, reflection is preferred.

Preferably, for a low loss reflective polarizer, the preferred embodiment consists of a dispersed phase disposed in the continuous phase as a series of roller-like structures which, as a consequence of orientation, have a high aspect ratio which can increase the reflection of polarizations parallel to the direction of orientation increasing the dispersion force and polarization dispersion relative to the polarizations perpendicular to the direction of orientation. However, as indicated in FIGS. 3a-e, the dispersed phase could be provided with very different geometries. Thus, the dispersed phase could be disk-shaped or elongated disk-shaped, as in FIGS. 3a-c, in the form of a roller, as in FIG. 3d-e, or spherical. Other embodiments are contemplated wherein the dispersed phase has cross sections that are approximately elliptical (including circular), polygonal, irregular, or combination of one or more of these forms. The shape and size of the cross section of the particles of the dispersed phase could also vary from one particle to another, or from one region of the film to another (eg, from the surface to the center).

In some embodiments, the dispersed phase could have a core and shell construction, where the core and shell are made of the same or different material, or where the core is hollow. So, for example, the. Dispersed phase could consist of hollow fibers of equal or random length, and of uniform or non-uniform cross section. The anterior space of the fibers could be empty, or could be occupied by a suitable medium that could be a solid, liquid or gas, and could be organic or inorganic. The refractive index of the medium could be chosen in consideration of the refractive indices of the dispersed phase and the continuous phase to obtain a desired optical effect (e.g., reflection or polarization along a given axis).

The geometry of the dispersed phase could be obtained by proper orientation or processing of the optical material, through the use of particles having a particular geometry, or by a combination of the two. Thus, for example, a dispersed phase having substantially a roller-like structure can be produced by orienting a film consisting of approximately spherical particles of dispersed phase along a single axis .. Roller-like structures can occur in an elliptical cross-section orienting the film 'in a second direction perpendicular to the first. As a further example, a dispersed phase having substantially a roller-type structure in which the rollers are rectangular in cross section can be produced by orienting in a single direction a film having a dispersed phase consisting of a series of essentially rectangular flakes.

Stretching is a convenient way to achieve a desired geometry, since stretching can also be used to induce a difference in the refractive indices in the material. As indicated above, the orientation of the films according to the invention could be in more than one direction, and could be sequential or simultaneous.

In another example, the components of the continuous and dispersed phases could be extruded such that the dispersed phase is roller-like on an axis in the non-oriented film. Rollers with a high aspect ratio could be generated by orienting in the direction of the major axis of the rollers in the extruded film. The plate-like structures could be generated by orienting in a direction orthogonal to the major axis of the rollers in the extruded film.

The structure in FIG. 2 can be produced by asymmetric biaxial orientation of a mixture essentially of spherical particles in a continuous matrix. Alternatively, the structure could be obtained by incorporating a plurality of fibrous structures in the matrix material, aligning the structures along a single axis, and orienting the mixture in a direction transverse to 1 axis. Yet another method for obtaining this structure is by controlling the relative viscosities, shear, or surface tension of the components of a polymer mixture to increase a fibrous dispersed phase when the mixture is extruded into a film. In general, it is found that the best results are obtained when the cut is applied in the extrusion direction.

Dimensional Ordering of the Dispersed Phase The dimensional ordering was also found to have an effect on the diffusion behavior of the dispersed phase. In particular, it has been observed in optical bodies made in accordance with the present invention that the aligned diffusers will not symmetrically scatter light over the directions of transmission or specular reflection since the diffusers would be randomly aligned. In particular, the inclusions that have been lengthened in the orientation resemble light diffuser rolls mainly along (or near) the surface of a cone centered in the direction of orientation and along the specularly transmitted direction. This could result in an anisotropic distribution of scattered light over the directions of specular reflection and specular transmission. For example, for incident light in such an elongated roller in a direction perpendicular to the direction of orientation the scattered light appears as a band of light in the plane perpendicular to the direction of orientation with an intensity that decreases with increasing angle away from the specular directions. By adjusting the geometry of the inclusions, some control in the distribution of scattered light can be obtained in the transmissive hemisphere and in the reflective hemisphere.

Dimensions of the Scattered Phase In applications where the optical body will be used as a low loss reflecting polarizer, the structures of the dispersed phase preferably have a high aspect ratio, e.g. ex. , the structures are substantially larger in one dimension than in any other dimension. The aspect ratio is preferably at least 2, and more preferably at least 5. The largest dimension (e.g., the length) is preferably at least 2 times the wavelength of the electromagnetic radiation in the range of wavelength of interest, and more preferably at least 4 times the desired wavelength. On the other hand, the smaller dimensions (eg, cross section) of the structures of the dispersed phase are preferably less than or equal to the wavelength of interest and more preferably less than 0.5 times the wavelength of interest .

Fraction of Volume of the Dispersed Phase The volume fraction of the dispersed phase also affects the light scattering in the optical bodies of the present invention. Within certain limits, the increase in the volume fraction of the dispersed phase tends to increase the amount of scattering that a light beam experiences after entering the body through the directions of equality and inequality of the polarized light. This factor is important to control the reflection and transmission properties for a given application. However, without the volume fraction of the dispersed phase becoming too large, the light scattering may decrease. Without wishing to theorize, this seems to be due to the fact that the particles of the dispersed phase are closer together, in terms of the wavelength of light, so that the particles tend to act together as a small number of large effective particles.

The desired volume fraction of the dispersed phase will depend on many factors, including the specific selection of materials for the continuous and dispersed phase. However, the volume fraction of the dispersed phase will typically be at least about 1% by volume relative to the continuous phase, more preferably in the range of about 5 to about 15%, and more preferably in the range of about 15 to approximately 30%.

Thickness of the Optical Body The thickness of the optical body is also an important parameter that can be manipulated to affect the reflection and transmission properties in the present invention. As the thickness of the optical body increases, the diffuse reflection also increases, and the transmission increases, specular and diffuse. Thus, while the thickness of the optical body will typically be chosen to obtain a desired degree of mechanical strength in the finished product, it could also be used to directly control the reflection and transmission properties. ' The thickness can also be used to make final adjustments in the reflection and transmission properties of the optical body. Thus, for example, in film applications, the device used to extrude the film can be controlled by a downstream optical device which measures the transmission and reflection values in the extruded film, and which varies the thickness of the film (e.g. eg, adjusting the extrusion speeds or changing the speeds of the molding wheel) to maintain the reflection and transmission values within a predetermined range.

Materials for the Continuous / Dispersed Phases Very different materials such as the continuous and dispersed phases could be used in the optical bodies of the present invention, depending on the specific application to which the optical body is directed. Such materials include organic materials such as silica-based polymers, organic materials such as liquid crystals, and polymeric materials, including monomers, copolymers, polymers, inserts, and mixtures thereof. The exact choice of materials for a given application will be conducted by the desired equality and inequality obtainable in the refractive indices of the continuous and dispersed phases along a particular axis, as well as the desired physical properties in the resulting product. . However, the materials of the continuous phase will generally be characterized to be substantially transparent in the region of the desired spectrum.

An additional consideration and selection of materials is that the resulting product must contain at least two distinct phases. This could be done by molding the optical material of two or more materials that are immiscible with each other. Alternatively, if it is desired to make an optical material with a first and second material that are not immiscible with each other, and if the first material has a higher melting point than the second material, in some cases it might be possible to impregnate the particles. of appropriate dimensions of the first material within a fused matrix of the second material at a temperature below the melting point of the first material. The resulting mixture can then be molded into a film with or without subsequent orientation, to produce an optical device.

Polymeric materials suitable for use as the continuous or dispersed phase in the present invention could be amorphous, semi-crystalline, or crystalline polymeric materials, including materials made from carboxylic acid-based monomers such as isophthalic, azelaic, adipic, sebasic, dibenzoic, terephthalic, 2,7-naphthalene dicarboxylic, 2,6-naphthalene dicarboxylic, cyclohexanedicarboxylic, and bibenzoic (including 4, 4'-bibenzoic acid), or materials made from the corresponding esters of the aforementioned acids (e.g., dimethylterephthalate ). Of these, 2,6-polyethylene naphthalate (PEN) is especially preferred because of its strong induced birefringence, and because of its ability to remain permanently birefringent after stretching. The PEN has a refractive index for polarized incident light of 550 nm wavelength that increases after stretching when the plane of polarization is parallel to the axis of stretching from about 1.64 tan high to about 1.9, while the refractive index decreases to polarized light perpendicular to the stretch axis. The PEN exhibits a birefringence (in this case, the difference between the refractive index along the direction of stretching and the index perpendicular to the direction of stretching) from 0.25 to 0.40 in the visible spectrum. Birefringence can be increased by increasing molecular orientation. The PEN could be substantially heat stable from about 155 ° C to about 230 ° C, depending on the processing conditions used during the making of the film.

Polybutylene naphthalate is also an appropriate material as well as other crystalline naphthalene dicarboxylic polyesters. The crystalline naphthalene dicarboxylic polyesters exhibit a difference in the refractive indices associated with different axes in the plane of at least 0.05 and preferably above 0.20.

When PEN is used as a phase in the optical material of the present invention, the other phase is preferably polymethylmethacrylate (PMMA) or a syndiotactic vinyl aromatic polymer such as polystyrene (sPS) other preferred polymers for use with PEN are based on terephthalic acid , isophthalic, sebacic, azelaic or cyclohexanedicarboxylic related alkyl esters of these materials. The naphthalene dicarboxylic acid could also be used in smaller quantities to improve the adhesion between the phases. The diol component could be ethylene glycol a related diol. Preferably, the refractive index of the selected polymer is less than about 1.65, and more preferably, less than about 1.55, although a similar result could be obtained by using a polymer having a higher refractive index if the same index difference is obtained.

Syndiotactic vinyl aromatic polymers useful in the present invention include poly (styrene), poly (alkyl styrene), poly (styrene halide), poly (alkyl styrene), poly (vinyl benzoate ester), and these hydrogenated polymers and mixtures , or polymers that contain these structural units. Examples of poly (alkyl styrenes) include: poly (methyl styrene), poly (ethyl styrene), poly (propyl styrene), poly (butyl styrene), poly (phenyl styrene), poly (vinyl naphthalene), poly (vinyl styrene) , and poly (acenaphthalene) could be mentioned. For poly (styrene halides), examples include poly (chlorostyrene), poly (bromostyrene), and poly (fluorostyrene). Examples of poly (alkoxy styrene) include: poly (methoxy styrene), and poly (ethoxy styrene). Among these examples, particularly preferred polymers of the styrene group are: polystyrene, poly (p-methyl styrene), poly (m-methyl styrene), poly (p-butyl tertiary styrene), poly (p-chlorostyrene), poly ( m-chloro styrene), poly (p-fluoro styrene), and copolymers of styrene and p-methyl styrene could be mentioned.

In addition, as comonomers of copolymers of the syndiotactic vinyl aromatic group, in addition to the monomers of the styrene group polymer discussed above, there may be mentioned olefin monomers such as ethylene, propylene, butene, hexene, or octene; diene monomers such as butadiene, isoprene; polar vinyl monomers such as cyclic diene monomer, methyl methacrylate, maleic acid anhydride, or acrylonitrile.

The vinyl syndiotactic aromatic polymers of the present invention could be blocks of copolymers, random copolymers, or alternating copolymers.

The aromatic vinyl polymer having the high level syndiotactic structure referred to in this invention generally includes polystyrene having higher syndiotacticity of 75% or greater, as determined by carbon-13 nuclear magnetic resonance. Preferably the degree of syndiotacticity is greater than 85% of racemic diad, or greater than 30%, or more preferably, greater than 50%, pentad. racemic In addition, although there are no particular restrictions with respect to the molecular weight of this aromatic vinyl syndiotactic group polymer, preferably, the average molecular weight weight is greater than 10,000 and less than 1,000,000, and more preferably, greater than 50,000 and less than 800,000 . " For other resins, various types could be mentioned, for example, vinyl aromatic group polymers with atactic structures, vinyl aromatic group polymers with isotactic structures, and all polymers that are miscible. For example, polyphenylene ethers show good miscibility with the vinyl aromatic group polymers discussed above. In addition, the composition of these miscible resin components is preferably between 70 to 1% by weight, or more preferably 50 to 2% by weight. When the composition of the miscible resin component exceeds 70% by weight, the degradation of the thermal resistance could occur, and usually is not desired.

The polymer selected for a particular phase is not required to be a copolyester or copolycarbonate. Vinyl polymers and copolymers made of monomers such as naphthalenes, styrenes, ethylene, maleic anhydride, acrylates, and vinyl methacrylates could also be employed. Condensation polymers, other than polyesters and polycarbonates, could also be used. Suitable condensation polymers include polysulfones, polyamides, polyurethanes, polyamic acids, and polyimides.

The naphthalene and halogen groups such as chlorine, bromine and iodine are useful to increase the refractive index of the selected polymer to the desired level (1.59 to 1.69) if it is necessary to substantially equalize the refractive index if the base is PEN. The acrylate and fluorine groups are particularly useful for ring the refractive index.

Minor amounts of comonomers could be substituted in the naphthalene dicarboxylic acid polyester as long as the difference of the large refractive index in the direction of orientation is not substantially compromised. A smaller index difference (and therefore decreased reflectivity) could be counterbalanced by means of advantages in any of the folng: improved adhesion between the continuous and dispersed phase, decreased extrusion temperature, and better equalization of the melt viscosities.

Spectrum Region While the present invention is frequently described herein with reference to the visible region of the spectrum, various embodiments of the present invention can be used to operate at different wavelengths (and hence frequencies) of electromagnetic radiation by appropriate scaling of the components of the spectrum. optical body. Thus, as the wavelength increases, the linear size of the components of the optical body could increase so that the dimensions of these components in units of wavelength remain approximately constant.

Of course, a greater effect of wavelength change is that, for most materials of interest, they change the refractive index and the absorption coefficient. However, the equality and inequality principles of the index still apply at every wavelength of interest, and could be used in the selection of materials for an optical device that will operate in a specific region of the spectrum. Thus, for example, the appropriate scale of dimensions will aloperation in the infrared, near ultraviolet, and ultraviolet regions of the spectrum. In these cases, the refractive indices refer to the values at these wavelengths of operation, and the thickness and size of the diffusive component body of the dispersed phase should also be scaled approximately at the wavelength. Even more of the electromagnetic spectrum can be used, including very high, ultra high wave frequencies, microwaves and millimeters. The effects of polarization and diffusion will be presented with the appropriate scale for the wavelength and the refractive indexes can be obtained from the square root of the dielectric function (including real and imaginary parts). The useful products in these larger wavelength bands can be diffuse reflector polarizers and partial polarizers.

In some embodiments of the present invention, the optical properties of the optical body will vary across the wavelength band of interest. In these embodiments, the materials could be used for the continuous and / or dispersed phases whose refractive indices, along one or more axes, vary from one region of wavelength to another. The selection of materials of the continuous and dispersed phase, in the optical properties (eg, diffuse and scattered reflection or specular transmission) resulting from a specific selection of materials, will depend on the wavelength band of interest.

Surface layers A layer of material that is substantially free of a dispersed phase could be arranged coextensively on one or both of the major surfaces of the film, p. ex. , the extruded mixture of the dispersed phase and the continuous phase. The composition of the layer also called the surface layer could be selected, for example, to protect the integrity of the dispersed phase within the extruded mixture, to add mechanical or physical properties to the final film or to add optical functionality to the final film. Suitable selection materials could include the material of the continuous phase or the material of the dispersed phase. Other materials with a melt viscosity similar to the extruded mix may also be useful. * A surface layer or layers could reduce the wide range of cutting intensities that the extruded mixture could experience in the extrusion process, particularly in the mold. A high cut environment could cause undesirable empty surface and could result in a textured surface. A wide range of cut values along the thickness of the film could also prevent the dispersed phase from forming the desired particle size in the mixture.

A surface layer or layers also adds physical strength to the resulting composite or reduces problems during processing, such as, for example, reducing the tendency of the film to slip during the orientation process. Surface materials that remain amorphous may tend to make films with higher strength, while materials in the top layer that are semicrystalline might tend to make films with a higher attention module. Other functional components such as antistatic additives, UV absorbers, colorants, antioxidants, and pigments, could be added to the surface film, without substantially providing interference with the desired optical properties of the resulting product.

The surface layers could be applied to one or both sides of the extruded mixture at the same point during the extrusion process, e.g. ex. , before the mixture and the surface layer come out of the extrusion mold. This could be done using conventional coextrusion technology, which could be included using a three layer coextrusion mold. Lamination of the surface layers for a previously formed film of an extruded mixture is also possible. The thickness of the surface layer could be in the range of about 2% to about 50% of the total thickness of the blend / surface layer.

A wide range of polymers is suitable for surface layers. Predominantly amorphous polymers include copolyesters based on one or more of terephthalic acid, 2,6-naphthalene dicarboxylic acid, isophthalic acid, phthalic acid, or their corresponding alkyl esters, and alkylene diols, such as ethylene glycol. Examples of semicrystalline polymers are 2,6-polyethylene naphthalate, polyethylene terephthalate, and nylon materials.

Anti-reflection layers These films and other optical devices made in accordance with the invention could also include one or more anti-reflective layers. Such layers, which may or may not be sensitive to polarization, serve to increase transmission and reduce reflective glare. An anti-reflective layer could be imparted to the films and optical devices of the present invention by means of an appropriate surface treatment, such as coating or chemical plating.

In some embodiments of the present invention, it is desired to maximize the transmission and / or minimize the specular reflection of certain light polarizations. In these embodiments, the optical body could comprise two or more layers in which at least one layer comprises an antireflection system in close contact with a layer provided by the continuous and dispersed phases. Such an antireflection system acts to reduce the specular reflection of the incident light and to increase the amount of incident light entering the portion of the body containing the continuous and dispersed layers. Such a function can be performed by a variety of means well known in the art.

Examples are quarter-wavelength antireflection layers, two or more antireflection layer stacks, graduated index layers, and graduated density layers. Such anti-reflective functions can also be used on the side of the transmitted light to increase the transmitted light if desired.

Microvacio In some embodiments, the materials of the continuous and dispersed phase could be chosen so that the interface is weak enough to result in vacuum when the film is oriented. The average dimensions of the voids could be controlled by careful manipulation of the processing parameters and stretching ratios, or by the selective use of compatibilizers. The voids could be filled before the finished product with a liquid, gas, or solid. The vacuum could be used in conjunction with the aspect ratios and the refractive indices of the dispersed and continuous phases to produce the desired optical properties in the resulting film.

More Than Two Phases The optical bodies made in accordance with the present invention could also consist of more than two phases. Thus, for example, an optical material made in accordance with the present invention may consist of two different dispersed phases in the continuous phase. The second dispersed phase could be randomly or non-randomly dispersed throughout the continuous phase, and can be randomly aligned or aligned along a common axis.

The optical bodies made in accordance with the present invention could also consist of more than one continuous phase. Thus, in some embodiments, the optical body could include, in addition to a first continuous phase and a dispersed phase, a second phase that is co-continuous in at least one dimension with the first continuous phase. In a particular embodiment the second continuous phase is a porous, sponge-like material that is coextensive with the first continuous phase (eg, the first continuous phase extends through a network of channels or spaces that extend through the second phase continues, just as water spreads through a network of channels in a wet sponge). In 'a related mode, the second continuous phase is in the form of a dendritic structure which is coextensive in at least one dimension with the first continuous phase.

Multilayer Combinations If desired, one or more sheets of a continuous / dispersed phase film made in accordance with the present invention could be used in combination with, or as a component in, a multilayer film (e.g., to increase reflectivity). Suitable multilayer films include those of the type described in WO 95/17303 (Ouderkirk et al.). In such a construction, individual sheets could be laminated or otherwise adhered together or spaced apart. If the optical thicknesses of the phases in the sheets are substantially the same (ie, if the two sheets have a substantially equal and large number of diffusers for incident light along a given axis), the composite will reflect, with an efficiency somewhat greater, substantially the same bandwidth and spectral range of reflectivity (eg, "band") as the individual sheets. If the optical thicknesses of the phases in the sheets are not substantially equal, the composite will reflect through a broader bandwidth than the individual phases. A compound that combines mirror sheets with polarizer sheets is useful for increasing the total reflectance while polarizing the transmitted light. Alternatively, a single sheet could be oriented asymmetrically and biaxially to produce a film having selective reflectivity and polarizing properties.

FIG. 5 illustrates an example of this embodiment of the present invention. There, the optical body consists of a multilayer film 20 in which the layers alternate between the layers of PEN 22 and co-PEN 24. Each PEN layer includes a dispersed phase of syndiotactic polystyrene (sPS) in a PEN matrix. This type of construction is desirable in that it promotes color out of a minor angle. Furthermore, since the coating or inclusion of diffusers averages the external light leakage, the control in the thickness of the layers is less critical, allowing the film to be more tolerable of variations in processing parameters.

Any of the materials previously observed could be used as any of the layers in this embodiment, or as the continuous or dispersed phase in a particular layer.

However, PEN and co-PEN are particularly desired as the major components of the adjacent layers, since these materials promote good sheet adhesion.

Also, a number of variations are possible in the arrangement of the layers. Thus, for example, layers can be made to follow a repeated sequence through part or all of the structure. An example of this is a construction that has the layer model ... ABCABC ..., where A, B, and C are different materials or different mixtures or mixtures of the same or different materials, and where one or more of A, B, or C contains at least one dispersed phase and at least one continuous phase. The surface layers are preferably identical or chemically similar materials.

Additives The optical materials of the present invention could also comprise other materials or additives as shown in the art. Such materials include pigments, dyes, binders, coatings, fillers, compatibilizers, antioxidants (including sterically opposed phenols), surfactants, antimicrobial agents, antistatic agents, flame retardants, foaming agents, lubricants, reinforcing agents, light stabilizers (including UV stabilizers or blockers), thermal stabilizers, impact modifiers, plasticizers, viscosity modifiers, and many other materials. In addition, the films and other optical devices made in accordance with the present invention could include one or more outer layers that serve to protect the device from abrasion, impact, or other damage, or that improve the processability or durability of the device.

Lubricants suitable for use in the present invention include calcium stearate, zinc stearate, copper stearate, cobalt stearate, molybdenum neodocanoate, and ruthenium (III) acetylacetonate.

Antioxidants useful in the present invention include 4,4'-thiobis- (6-t-butyl-m-cresol), 2,2'-methylenebis- (4-methyl-6-t-butyl-butylphenol), octadecyl- 3, 5-di-t-butyl-4-hydroxyhydrocinnamate, bis- (2,4-di-t-butylphenyl) pentaerythritol diphosphite, Irganox * ^ 1093 (1979) (ester phosphonic acid ((3-5)) bis (1,1-dimethylethyl) -4-hydroxyphenyl) methyl) -dioctadecyl), Irganox ^ 1098 (N, N '-1,6-hexanediylbis (3,5-bis (1,1-dimethyl) -4-hydroxy) -benzenepropanamide), Naugaard "445 (amino aryl), Irganox® L 57 (alkylated diphenylamine), Irganox" L 115 (bisphenol containing sulfur), Irganox "LO 6 (alkylated phenyl-delta-naphthylamine), Ethanox 398 (fluorophosphonate) , and 2,2'-ethylidenebisbis (4,6-di-t-butylphenyl) fluorophosnite.

A group of antioxidants which are especially preferred are sterically opposed phenols, including butylated hydroxytoluene (BHT), Vitamin E (di-alpha-tocopherol), Irganox1 ^ 1425WL (calcium phosphonate bis- (O-ethyl (3, 5-di-t-butyl-4-hydroxybenzyl))), Irganox® 1010 (tetracis (methylene (3, 5, it-but-il-4-hydroxydrocinnamate)) methane), Jrganox ^ 1076 (octadecyl 3,5-di-tert-butyl-4-hydroxydrocinnamate), Ethanox ^ 702 (phenolic bis opposite ), Ethanox 330 (opposite phenolic of high molecular weight), and Ethanoxm 703 (opposite phenolic amine).

Dichroic dyes are a particularly useful additive in some applications to which the optical materials of the present invention could be targeted, due to their ability to absorb light from a particular polarization when they are molecularly aligned in the material. When a polarization of light is predominantly used in a film or other dispersed material, the dichroic dyes cause the material to absorb one polarization of light more than another. Suitable dichroic dyes for use in the present invention include Congo Red (diphenyl-his-a-naphthylamine sodium sulfonate), methylene blue, stilbene dye (Color Index (CI) = 620), and chloride of 1.1. '-diethyl-2, 2'-cyanine (CI = 374 (orange) or CI = 518 (blue)). The properties of these dyes, and methods of making them, are described in E.H. Land, Colloid Chemistry (1946). These dyes have remarkable dichroism in polyvinyl alcohol and a smaller dichroism in cellulose. A slight dichroism is observed with Congo Red in PEN.

Other suitable colorants include the following materials: where R is (2: or; (4) The properties of these dyes, and methods for making them, are discussed in the Kirk Othmer 'Encyclopedia of Chemical Technology, Vol. 8, pp. 652-661 (4th Ed. 1993), and references cited therein.

When a dichroic dye is used in the optical bodies of the present invention, it could be incorporated in the continuous phase or dispersed phase. However, it is preferred that the dichroic dye be incorporated into the dispersed phase.

Dichroic dyes in combination with certain polymer systems exhibit the ability to polarize light in various degrees. Polyvinyl alcohol and certain dichroic dyes could be used to make films with the ability to polarize light. Other polymers, such as polyethylene terephthalate or polyamides, such as nylon-6, do not exhibit such a strong ability to polarize light when combined with a dichroic dye. The combination of polyvinyl alcohol and dichroic dye is said to have a higher dichroism ratio than, for example, the same dye in another film that forms the polymer systems. A higher dichroism ratio indicates a higher capacity to polarize light.

The molecular arrangement of a dichroic dye in an optical body made in accordance with the present invention is preferably performed by stretching the optical body after the dye has been incorporated therein. However, other methods could also be used to obtain molecular ordering. Thus, in one method, the dichroic dye is crystallized, by sublimation or crystallization from the solution, in a series of elongated slits that are cut, chemically coated or otherwise formed on the surface of a film or other optical body, before or after the optical body has been oriented. The treated surface could then be coated with one or more surface layers, could be incorporated into a polymer matrix or used in a multilayer structure, or could be used as a component of another optical body. The slits could be created according to a predetermined pattern or diagram, and with a predetermined amount of spacing between the slits, to achieve the desirable optical properties.

In a related embodiment, the dichroic dye could be disposed within one or more hollow fibers or other conduits, before or after the hollow fibers are disposed in the optical body. The hollow fibers or ducts could be constructed of a material that is the same or different from the material surrounding the optical body.

In yet another embodiment, the dichroic dye is disposed along the interface of the layer of a multilayer construction, by sublimation on the surface of a layer before it is incorporated into the multilayer construction. In still other embodiments, the dichroic dye is used at least to partially fill voids in a microvacuum film made in accordance with the present invention.

Applications of the Present Invention The optical bodies of the present invention are particularly useful as diffuse polarizers. However, the optical bodies could also be made according to the invention which operate as reflective polarizers or diffuser mirrors. In these applications, the construction of the optical material is similar to that of the diffuser applications described above. However, these reflectors will generally have a much greater difference in the refractive index along an axis.

This difference of the index is typically at least about 0.1, more preferably about 0.15, and more preferably about 0.2.

Reflective polarizers have a difference in refractive index along one axis, and substantially equal indexes along another. The reflecting films, on the other hand, differ in the refractive index along at least two orthogonal plane axes in the film. However, the reflecting properties of these modalities need not be achieved solely by confidence in refractive index differences. Thus, for example, the thickness of the films could be adjusted to achieve a desired degree of reflection. In some cases, adjusting the thickness of the film could cause the film to go from a diffuser to a diffuse reflector.

The reflective polarizer of the present invention has many different applications, and is particularly useful in liquid crystal display panels. In addition, the polarizer can be constructed with a different one from PEN or similar materials that are good ultraviolet filters and which absorb ultraviolet light efficiently to the end of the visible spectrum. The reflective polarizer can also be used as a thin-sheet infrared polarizer.

General view of Examples The following Examples illustrate the production of various optical materials according to the present invention, as well as the spectrum properties of these materials. Unless stated otherwise, the percentage composition refers to the percentage composition by weight. The polyethylene naphthalate resin used was produced for these samples using ethylene glycol and dimethyl-2,6-naphthalenedicarboxylate, available from Amoco Corp., Chicago, Illinois. These reagents are polymerized at various intrinsic viscosities (IV) using conventional polyester resin polymerization techniques. The syndiotactic polystyrene (sPS) could be produced according to the method set forth in U.S. Pat. 4,680,353 (Ishihara et al). Examples include - various polymer pairs, various continuous and dispersed phase fractions and other additives or process changes as discussed below.

Stretching or orientation of the samples was performed using either conventional orientation equipment used to make polyester film or a laboratory batch oriented. The used laboratory batch orienter was designed to use a small piece of deposited material (7.5cm by 7.5cm) cut from the extruded deposited sheet and held by a square array of 24 staples (6 on each side). The orientation temperature The sample was controlled with a hot air blower and the film sample was oriented by means of a mechanical system that increased the distance between the staples in one or both directions at a controlled speed. The samples stretched in both directions could be oriented sequentially or simultaneously. For the samples that were oriented in the directed mode (C), all the staples hold the sheet and the staples move only in one dimension. On the other hand, in the non-directed mode (U), the staples holding the film in a fixed dimension perpendicular to the direction of stretching are not used and the film is allowed to relax or reduce in that dimension.

Polarized diffuse transmission and reflection was measured using a Perkin Elmer Lambda 19 ultraviolet / visible / near infrared spectrophotometer equipped with a 150 millimeter Perkin Elmer Labsphere S900-1000 integrating dial accessory and a Glan-Thompson cube polarizer. The values of transmission and parallel and cross reflection were measured with the vector e of the polarized light parallel or perpendicular, respectively, to the direction of narrowing of the film. All searches were continuous and were conducted with a search speed of 480 nanometers per minute and an aperture width of 2 nanometers. The reflection was carried out in the "V-reflection" mode. The values of transmission and reflectance are averages of wavelengths of 400 to 700 nanometers.

EXAMPLE 1 In Example 1, an optical film was measured according to the invention by extruding a mixture of 75% polyethylene naphthalate (PEN) as the continuous or main phase and 25% polymethylmethacrylate (PMMA) as the dispersed phase or smaller in a molded film or sheet approximately 380 microns thick using conventional extrusion and molding techniques. The PEN has an intrinsic viscosity (IV) of 0.52 (measured in 60% phenol, 40% dichlorobenzene). The PMMA was obtained from ICI Americas, Inc., Wilmington, Delaware, under the product designation CP82. The extruder used was a 3.15 cm (1.24") Brabender with a 60 μm Tegra filter tube, the mold was a 30.4 cm (12") Ultraflex ™ 40 EDI.

Approximately 24 hours later the film was extruded, the molded film oriented widthwise or transverse direction (TD) in a polyester film stretch device. Stretching was performed at approximately 9.1 meters per minute (30 ft / min) with an exit width of approximately 140 cm (55 inches) and a stretch temperature of approximately 160 ° C (320 ° F). The total reflectivity of the stretched sample was measured with an integration sphere attached to a Lambda 19 spectrophotometer with the polarized beam sample with a Glan-Thompson cube polarizer. The sample had 75% parallel reflectivity (e.g., reflectivity was measured with the direction of stretch of the film parallel to the vector e of polarized light), and 52% cross-reflectivity (eg, the reflectivity was measured with the vector e of the polarized light perpendicular to the direction of stretching).

EXAMPLE 2 In Example 2, an optical film was made and evaluated in a manner similar to Example 1 except that a mixture of 75% PEN, 25% syndiotactic polystyrene (sPS), 0.2% of a glycidyl methacrylate polystyrene compatibilizer was used. , and 0.25% of each of Irganox1 ^ 1010 and Ultranox ^ 626. The synthesis of glycidyl polystyrene methacrylate is described in Polymer Processes, "Chemical Technology of Plastics, Resins, Rubbers, Adhesives and Fibers", Vol. 10, Cap. . 3, pp. 69-109 (1956) (Ed. By Calvin E. Schildknecht).

The PEN had an intrinsic viscosity of 0.52 measured in 60% phenol, 40% dichlorobenzene. The sPS was obtained from Dow Chemical Co. and had an average molecular weight weight of approximately 200,000, it was subsequently designated as sPS-200-0. The parallel reflectivity in the stretched film sample was determined to be 73.3%, and the cross reflectivity was determined to be 35%.

EXAMPLE 3 In Example 3, an optical film was made and evaluated in a manner similar to Example 2 except that the level of compatibilizer was increased to 0.6%. The resulting parallel reflectivity was determined to be 81% and the cross reflectivity was determined to be 35.6%, EXAMPLE 4 In Example 4, a three layer optical film was made according to the present invention using conventional three layer coextrusion techniques. The film had a central layer and a surface layer on each side of the central layer. The core layer consisted of a mixture of 75% PEN and 25% sPS 200-4 (the designation sPS-200-4 refers to a syndiotactic polystyrene copolymer containing 4 mol% of paramethyl styrene), and each surface layer it consisted of 100% PEN having an intrinsic viscosity of 0.56 measured in 60% phenol, 40% dichlorobenzene.

The resulting three-layer molded film had a core layer of thickness of approximately 415 microns, and each surface layer was approximately 110 microns in thickness for a total thickness of approximately 635 microns. A laboratory batch stretcher was used to stretch the three layer molded film resulting in about 6 to 1 in the machine direction (MD) at a temperature of about 129 ° C. Because the ends of the film sample parallel to the direction of stretching were not stapled by the laboratory extruder, the sample was not forced in the transverse direction (TD) and the sample was reduced in the TD approximately 50% as a result of the stretching procedure.

Optical performance was evaluated in a manner similar to Example 1. The parallel reflectivity was determined to be 80.1%, and the cross reflectivity was determined to be 15%. These results show that the film functions as a low absorption energy conservation system.

EXAMPLES 5-29 In Examples 5-29, a series of optical films were produced and evaluated in a manner similar to Example 4, except that the sPS fraction in the central layer and the IV of the PEN resin used was varied as shown in the Table. 1. The IV of the PEN resin in the central layer and that of the surface layers were the same for a given sample. The total thickness of the molded sheet was approximately 625 microns with approximately two thirds of this total in the core layer and the balance in the surface layers which were approximately equal in thickness. Several mixtures of PEN and SPS were produced in the core layer, as indicated in Table 1. The films were stretched at a stretch ratio of about 6: 1 either in the machine direction (MD) or in the direction cross (TD) at various temperatures as indicated in Table 1.

Some of these samples were forced in the direction perpendicular to the direction of stretch to avoid that the sample will be lowered during the stretch. Samples labeled "U" in Table 1 were not forced and slimming allowed in the unforced dimension. Certain optical properties of the stretched samples, including transmission, reflection, and absorption percent, were measured along both axes parallel and crossed or perpendicular to the direction of stretching. The results are summarized in TABLE 1.

The thermal fixation, as indicated for Examples 24-27, was performed manually by forcing the two ends of the stretched sample that were perpendicular to the direction of stretching 'subjecting them to a stiff frame of appropriate size and placing the sample fastened in a stove at the indicated temperature for 1 minute. The two sides of the sample parallel to the stretch direction were not forced (U) or not clamped and allowed to lower. The thermal fixation of Example 29 was similar except that the four ends of the stretch sample were forced or clamped. Example 28 was not thermally fixed.

TABLE 1 -4 -If YES 4 -o cp All of the above samples were observed to contain various forms of the dispersed phase depending on the location of the dispersed phase within the body of the film sample. The inclusions of the dispersed phase located closer to the surfaces of the samples were observed to be of an elongated shape rather than more closely spherical. The. inclusions that are more closely centered between the surfaces of the samples could be more closely spherical. This is true even for samples with surface layers, but the magnitude of the effect is reduced with the surface layers. The. addition of the surface layers improves the processing of the films by reducing the separation tendency during the stretching operation.

Without wishing to theorize, the elongation of the inclusions (dispersed phase) in the central layer of the molded film is thought to be the result of cutting into the mixture as it is transported through the mold. This characteristic of elongation could be altered by varying the physical dimensions of the mold, extrusion temperatures, flow velocity of the extrudate, as well as chemical aspects of the materials of the continuous and dispersed phase that would alter their relative melt viscosities. Certain applications or uses could benefit by providing some elongation to phase _. dispersed during extrusion. For these applications that subsequently stretch in the direction of the machine, starting with a dispersed phase during extrusion could allow a higher aspect ratio to be achieved in the resulting dispersed phase.

Another notable feature is the fact that a noticeable improvement in performance is observed when the same sample is stretched without forcing. So, in the Example 9, the% transmission was 79.5% and 20.3% in the parallel and perpendicular directions, respectively. In contrast, the transmission in Example 16 was only 75.8% and 28.7% in the parallel and perpendicular directions, respectively. There is an increase in relative thickness for forced narrowing when the samples are stretched without forcing, but since they improve transmission and extinction, the equalization index is probably improved.

An alternative way to provide control of the refractive index is to modify the chemistry of the materials. For example, a copolymer of 30% p of interpolymerized units derived from terephthalic acid and 70% p units derived from 2,6-naphthalic acid has a refractive index of 0.02 units less than a 100% PEN polymer. Other monomers or ratios may have slightly different results. This type of change could be used to more closely match the refractive indices on an axis while only causing a slight reduction in the axis at which a large difference is desired. In other words, the benefits are obtained by more closely matching the values of the index on one axis rather than compensating for the reduction on an orthogonal axis on which a large difference is desired. Then, a chemical change may be desired to alter the temperature range at which the stretching occurs. An sPS copolymer and varying ratios of para-methyl styrene monomer will alter the optimum stretch-temperature range. A combination of these techniques may be necessary to more effectively optimize the total system for processing and equalizations and differences in the resulting refractive index. A) Yes, an improved control of the final performance could be obtained by optimizing the process and the chemistry in terms of the stretching conditions and also adjusting the chemistry of the materials to maximize the difference in the refractive index on at least one axis and minimizing the difference in the minus an orthogonal axis.

These samples exhibit better optical performance if they are oriented in the MD direction rather than the TD (compare Examples 14-15). Without wishing to theorize, it is believed that inclusions of different geometry develop with an orientation 'MD' that with a TD orientation and that these inclusions have higher aspect ratios, producing less important non-ideal end effects. The non-ideal final effects refer to the complex geometry / refractive index ratio at the tip of each end of the elongated particles. The interior or non-end of the particles is thought to have a uniform geometry and refractive index that is thought to be desirable. Thus, the higher percentage of the elongated particle that is uniform, the better optical operation.

The extinction ratio of these materials is the ratio of the transmission for the polarizations perpendicular to the direction of stretching to the parallel to the direction of stretching. For the examples cited in Table 1, the extinction ratio is in the range of between about 2 and about 5, although extinction ratios of up to 7 have been observed in optical bodies made in accordance with the present invention. It is expected that even higher extinction ratios can be obtained by adjusting the thickness of the film, the fraction of the inclusion volume, particle size, and the degree of equality and inequality index.

EXAMPLES 30-100 In Examples 30-100, samples of the invention are made using various materials as listed in Table 2. PEN 42, PEN 47, PEN 53, PEN 56, and PEN 60 refer to polyethylene naphthalate having a viscosity intrinsic (IV) of 0.42, 0.47, 0.53.0.56, and 0.60, respectively, measured at 60% phenol, 40% dichlorobenzene. The particular sPS-200-4 used was obtained from Dow Chemical Co. Ecdel ^ 9967 and Eastar * ^ are copolyesters which are commercially available from Eastman Chemical Co., Rochester, New York. Surlyn * ® 1706 is an ionomer resin available from E.I. du Pont de Nemours & Co., Wilmington, Delaware. Materials listed as Additive 1 or 2 include glycidyl polystyrene methacrylate. The designations GMAPS2, GMAPS5, and GMAPS8 refer to glycidyl methacrylate having 2.5, and 8% by weight, respectively, of glycidyl methacrylate in the total copolymer. ETPB refers to the crosslinking agent ethyltriphenyl phosphonium bromide. PMMA V044 refers to a polymethyl methacrylate commercially available from Atohaas North America, Inc.

Optical film samples were produced in a manner similar to Example 4 except the differences are seen in Table 2 and discussed below. The continuous phase and its relation of the total phase is reported as the major phase. The dispersive phase and its relation of the total is reported as a minor phase. The value reported for the thickness of the mixture represents the approximate thickness of the core layer in microns. The thickness of the surface layers varied when the thickness of the core layer varied, but remained at a constant ratio, e.g. ex. , the surface layers were approximately equal and the total of the two surface layers was approximately one third of the total thickness. The size of the dispersed phase was determined for some samples either by scanning electron microscopy (SEM) or transmission electron microscopy (TEM). Examples that were subsequently stretched using the laboratory batch oriented are shown by an "X" in the marked Batch Stretch column.

TABLE 2 03 ÍA CD O.

CD cica 00 O OR DJ The presence of several compatibilizers was found to reduce the size of the included or dispersed phase.

EXAMPLE 101 In Example 101, an optical film was made in a manner similar to Example 4 except that the resulting center thickness was about 420 microns thick, and each surface layer was about 105 microns thick. The PEN had an IV of 0.56. The optical film was oriented as in Example 1, except the stretching temperature was 165 ° C and there was a delay of 15 days between molding and stretching. The transmission was 87.1% and 39.7% for parallel and perpendicular polarized light, respectively.

EXAMPLES 102-121 In Examples 102-121, the optical films were made as in Example 101, except that the orientation conditions were varied and / or the sPS-200-0 was replaced with other sPS copolymers containing either 4 or 8% in mol of for methyl styrene or with an atactic form of styrene, Styron 663 (available from Dow Chemical Company, Midland, Michigan) as listed in Table 3. Transmission properties assessments are also reported. Transmission values are averages of all wavelengths between 450-700 nm.

TABLE 3 These examples indicate that the particles of the included phase are more elongated in the direction of the machine in PEN of IV high that in PEN of IV low. This consistent with the observation that, in P N N of low IV, the elongation to a greater degree is presented near the surface of the film than at points inside the film, with the result that the fibrillar structures are formed near the surface and the spherical structures are formed towards the center.

Some of these Examples suggest that the orientation temperatures and the degree of orientation are important variables to achieve the desired effect. Examples 109 to 114 suggest that quiescent crystallization need not be the only reason for the lack of transmission of a preferred polarization of light.

EXAMPLES 122-124 In Example 122, a multilayer optical film according to the invention was made by means of a feed block of the layer 209. The feed block was fed with two materials: (1) the PEN at 38.6 kg per hour (viscosity intrinsic of 0.48); and (2) a mixture of 95% CoPEN and 5% by weight of sPS homopolymer (molecular weight of 200,000). CoPEN was a copolymer based on 70 mol% of naphthalene dicarboxylate and 30 mol% of dimethyl isophthalate polymerized with ethylene glycol at an intrinsic viscosity of 0.59. The CoPEN / sPS mixture was fed into the feed block at a speed of 34.1 kg per hour.

The material of the CoPEN mixture was on the outside of the extrudate, and the composition of the stack layer resulted in alternating layers between the two materials. The thickness of the layers was designed to result in a wavelength stack of one quarter with a linear gradient of thickness, and having a 1.3 ratio of the thinnest layer to the thickest. Then, a thicker surface layer of CoPEN (made according to the method described above to make the CoPEN / sPS mixture, except that the molar ratios were 70/15/15 naphthalene dicarboxylate / dimethyl terephthalate / dimethyl isophthalate) devoid sPS was added to each side of the composite layer of 209. The total surface layer was added at a rate of 29.5 kg per hour, with approximately one-half of this amount on each side of the pile surface.

The coated multilayer of the resulting surface layer was extruded by means of a multiplier to obtain a multilayer composed of 421 layers. The resulting composite multilayer was then coated with another surface layer of CoPEN 70/15/15 on each surface at a total rate of 29.5 kg per hour with approximately one-third of this amount on each side. Since this second surface layer could not be detected separately from the existing surface layer (since the material is the same), for the purposes of this discussion, the resulting extra thick surface layer will be counted only as one layer.

The resulting composite layer of 421 was extruded again by means of an asymmetric multiplier of 1.40 ratio to obtain a 841 layer film which was then molded into a sheet by extruding through a mold and cushioning in a sheet of approximately 30 mils. thickness. The resulting molded sheet was then oriented in width direction using a conventional film making the damping device. The sheet was stretched at a temperature of about 300 ° F (149 ° C) at a stretch ratio of about 6: 1 and at a drawing speed of about 20% per second. The resulting stretched film was approximately 5 mils thick.

In Example 123, a multilayer optical film was made as in Example 122, except that the amount of sPS in the CoPEN / sPS mixture was 20% instead of 5%.

In Example 124, a multilayer optical film was made as in Example 122, except that sPS was not added to the film.

The results reported in Table 4 include a measure of the optical gain of the film. The optical gain in addition to a film is the ratio of light transmitted through an LCD panel of a backup light 5 with the film inserted between the two in the light transmitted without the film in place. The meaning of optical gain in the context of optical films is described in WO 95/17692 in relation to Figure 2 of that reference. In general, a higher gain value is desirable. The values of the transmission include values obtained when the light source was polarized parallel to the direction of stretching (Tt) and polarized light perpendicular to the direction of stretching (Tx). Color outside the angle (OAC) was measured using an Oriel spectrophotometer as the deviation of the mean square of the p-polarized transmission root to 50 degrees of incident light of wavelength between 400 and 700 nm.

TABLE 4 The out-of-angle color value (OAC) demonstrates the advantage of using a multilayer construction within the context of the present invention. In particular, such a construction can be used to substantially reduce OAC with only a modest reduction in gain. This solution could have advantages in some applications. The Tx values for the examples of the invention could be lower than expected because the light scattered by the dispersed phase of sPS could not be received by the detector.

The foregoing description of the present invention is illustrative only, and is not intended to be limiting. Therefore, the scope of the present invention should be constructed only by reference to the appended claims.

It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates.

Having described the invention as above, the content of the following is claimed as property.

Claims (29)

1. A method for producing an optical body, characterized in that it comprises the steps of: providing a composition comprising a continuous phase and a dispersed phase, wherein the refractive index of at least one of the continuous and dispersed phases is adjusted by orientation; Y orienting the composition until the birefringence of the continuous phase is at least about 0.05, the diffuse reflectivity of the composition is greater than about 30% and the refractive indices of the first and second phases differ by more than about 0.05 throughout of a first of three mutually orthogonal axes but differing less than about 0.05 over a second of three mutually orthogonal axes.

2. The method of claim 1, characterized in that the composition is oriented until the birefringence of the continuous phase is at least about 0.1.

3. The method of claim 1, characterized in that the composition is oriented until the birefringence of the continuous phase is at least about 0.15.

4. The method of claim 1, characterized in that the composition is oriented until the refractive indices of the first and second phases differ by more than about 0.1 along the first of three mutually orthogonal axes.

5. The method of claim 1, characterized in that the composition is oriented until the refractive indices of the first and second phases differ by more than about 0.15 along the first of three mutually orthogonal axes.

6. The method of claim 1, characterized in that the composition is oriented until the refractive indices of the first and second phases differ by less than about 0.03 along the second of three mutually orthogonal axes.

7. The method of claim 1, characterized in that the composition is oriented until the refractive indices of the first and second phases differ by less than about 0.01 along the second of three mutually orthogonal axes.

8. The method of claim 1, characterized in that the composition is oriented until the diffuse reflectivity of the composition is greater than about 50%.

9. The method of claim 1, characterized in that the second of the three mutually orthogonal axes is perpendicular to the plane of the film.

10. The method of claim 1, characterized in that the composition is oriented uniaxially.

11. The method of claim 1, characterized in that the composition is biaxially oriented.

12. The method of claim 1, characterized in that the composition is stretched at a stretch ratio of at least about 2.

13. The method of claim 1, characterized in that the composition is stretched at a stretch ratio of at least about 4.

14. The method of claim 1, characterized in that the composition is stretched at a stretch ratio of at least about 6.

15. The method of claim 1, characterized in that the 'continuous phase and the dispersed phase are thermoplastic polymers.

16. The method of claim 1, characterized in that at least one of the continuous and dispersed phases comprises a polymer selected from the group consisting of polyethylene naphthalate, polymethacrylate, syndiotactic polystyrene, and the alkyl derivatives of these polymers.

17. The method of claim 1, characterized in that the dispersed phase is dispersed randomly through the continuous phase, and wherein the composition is oriented in at least one direction.

18. A method for producing an optical film, characterized in that it comprises the steps of: providing a first resin whose refractive index is adjusted by orienting along the first of three mutually orthogonal axes; provide a second resin; incorporating the second resin as a dispersed phase within a matrix of the first resin; Y orienting the first resin along the first axis until (i) the absolute value of the difference in the refractive index of said first and second resins is? nx along the first axis y? n2. along the second axis orthogonal to said first axis, (ii) the absolute value of the difference between? nx and? n2 is at least about 0.05, and (iii) the diffuse reflectivity of said first and second phases are taken together along at least one axis so that at least one polarization of electromagnetic radiation is at least about 30%.

19. The method of claim 18, characterized in that the absolute value of the difference between? Nx and? N2 is at least about 0.1.

20. The method of claim 18, characterized in that said first resin has a higher birefringence than said second resin.

21. The method of claim 18, characterized in that the birefringence of said first resin is at least 0.02 larger than the birefringence of said second resin.

22. The method of claim 18, characterized in that the birefringence of said first resin is at least 0.05 larger than the birefringence of said second resin.

23. A method to produce an optical body that diffusely reflects wavelength electromagnetic radiation? that has a first-polarization and that specularly transmits wavelength electromagnetic radiation? having a second polarization, characterized in that it comprises the steps of: providing a composition comprising a continuous phase of the stress-induced birefringent material and a dispersed phase disposed in the continuous phase, wherein the dispersed phase comprises a plurality of particles that are larger than about 2? in a first dimension and are larger than approximately? / 30 but smaller than approximately? in a second and third dimension; Y Orient the composition until the refractive indices of the continuous and scattered phases differ by more than about 0.05 of wavelength electromagnetic radiation? polarized along the first of three mutually orthogonal axes but differs by less than about 0.05 electromagnetic radiation? polarized along the second of three mutually orthogonal axes, and the diffuse reflectivity of the composition along at least one axis of at least one polarization of electromagnetic radiation of wavelength? It is at least about 30%.

24. The method of claim 23, characterized in that the composition is oriented until the diffuse reflectivity of the composition towards the first polarization of electromagnetic radiation of wavelength? is greater than about 50%.

25. The method of claim 23, characterized in that the plurality of particles is greater than about 4? in the first dimension.

26. The method of claim 23, characterized in that the plurality of particles is less than about 0.5? in at least one of the second and third dimensions.

27. The method of claim 23, characterized in that the plurality of particles is less than about 0.5? in the second and third dimensions.

28. The method of claim 23, characterized in that? it is in the visible region of the spectrum.

29. The method of claim 23, characterized in that the continuous phase and the dispersed phase are various thermoplastic polymers.