MXPA98006941A - Optical film with phases co-contin - Google Patents

Abstract

An optical pulicel comprising a dispersed phase of polymeric particles disposed within a continuous birefringent matrix is provided. The filter is oriented, typically by 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 the total transmission of the electromagnetic radiation of a desired wavelength in the film result

Description

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

Background of the Invention Optical films are known in the art to be constructed of dispersed inclusions within a continuous matrix. The characteristics of these inclusions can be manipulated to provide a range of reflective and transmitting properties of the film. These characteristics include size of the inclusion material with respect to wavelength within the film, shape and alignment of the inclusion material, volumetric fill factor of the inclusion material and the degree of mismatch of the refractive index with the continuous matrix as length of the three orthogonal axes of the film. The conventional absorption polarizers REF. : 028144 (dichroic) have, as their inclusion material phase, strings similar to bars of inorganic iodine compounds that absorb light which are aligned within a polymer matrix. Such a film will tend to absorb polarized light within its electric field vector aligned in parallel to the bar-like iodine chains, and transmit polarized light perpendicular to the bars. Because iodine chains have two or more dimensions that are small compared to the wavelength of visible light, and because the number of chains per cubic foot of wavelength is greater, the optical properties of such The films are predominantly specular, with very little diffuse transmission through the film or diffuse reflection from the surface of the film. Like most other commercially available polarizers, these polarizing films rely on selective polarization absorption.

Films filled with inclusions of inorganic materials with different characteristics can provide other reflective and optical transmission properties. For example, mica flakes coated with two or more dimensions that are larger compared to visible wavelengths have been incorporated into polymeric films and paints to impart a metallic sheen. These flakes can be manipulated to fall in the plane of the film, whereby a strong directional dependence is imparted to the reflective appearance. Such an effect can be used to produce security meshes that are highly reflective for certain visual angles, and transmitters for other visual angles. Large flakes having a coloration (specularly selective reflection) that depends on the alignment with respect to incident light, can be incorporated into a film to provide evidence of reflection. In this application it is necessary that all the flakes in the film are aligned similarly with respect to each other.

However, optical films made of polymers filled with inclusions of inorganic materials suffer from a variety of weaknesses. Typically, the adhesion between the inorganic particles and the polymer matrix is poor. Consequently, the optical properties of the film decrease when stress or strain is applied through the matrix, this because the bond between the matrix and the inclusions is accommodated, and because the inclusions of rigid inorganic materials could fracture. In addition, the alignment of the materials of the inclusions of inorganic materials require 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 continuous polymer matrix that transmits clear light, with droplets of liquid crystals that modulate scattered light within. Stretching the material according to our sources results in a distortion of the liquid crystal drop from a spherical to an ellipsoidal shape, with the longitudinal axis of the ellipse parallel to the direction of the stretch. 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 Crystals, Vol. 19, No. 4, 469-480 (1995), discloses the optical properties of stretched films consisting of drops of liquid crystals arranged within a polymer matrix, reports that the elongation of the drops in an ellipsoidal shape, with their longitudinal axes parallel to the direction of the stretch, imparts a birefringence oriented (difference of refractive index between the axes) droplet dimensions) towards the drops, resulting in a mismatch of the refractive index between the continuous and scattered phases along certain film axes, and a relative index adjustment along the other axes of the film. Such drops of liquid crystals are not so small compared to the wavelengths visible in the film, and thus the optical properties of such films have a high omponent substantial diffuse with respect to its reflecting and transmitting properties. Aphonin suggests the use of these materials as a polarizing diffuser for LCDs with low twisted nematic lighting. However, optical films employing liquid crystals such as the dispersed phase are substantially limited in the degree of refractive index mismatch between the matrix phase and the dispersed phase. In addition, the birefringence of the liquid crystal component of such films is typically temperature sensitive.

U.S. 5,268,225 (Isayev) discloses a composite sheet made of liquid crystalline thermotropic polymer blends. The mixture consists of two liquid crystalline polymers that are immiscible between one and the other. The mixtures could be melted in a film consisting of a phase of dispersed inclusion material 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 crystalline nature, films of this type would suffer from the weaknesses of other liquid crystal materials discussed herein.

Still other films have been made to exhibit visible optical properties by means of the application of electric and magnetic fields. For example, U.S. 5,008,807 (Waters et al.) Discloses a liquid crystal device consisting of a fiber layer 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 mismatch between the refractive indices of the fibers and the liquid crystal. However, the requirement of an electric or magnetic field is inconvenient and in many undesirable applications, particularly those where there are fields that could cause interference.

Other optical films have been made by incorporating a dispersion of inclusion materials 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 polymer matrix, so that an elliptical vacuum forms around each inclusion material when the film is stretched. Such voids have dimensions of the order of the visible wavelengths. The mismatch of the refractive index between the vacuum and the polymer in these "vacuum-vortex" films is typically too large (approximately 0.5), causing substantial diffuse reflection. However, the optical properties of the micro-void materials are difficult to control due to the geometry variations of the interfaces, and it is not possible to produce a film axis for which the refractive indices are relatively adjusted, as would be useful for the 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 elaborated where a dispersed phase is arranged deterministically in an ordered pattern within a continuous matrix. U.S. 5,217,794 (Schrenk) is an example of this technology. A laminar polymer film is exposed, which is made of inclusions of polymeric materials that are larger compared to 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 material, and is relatively very tight along the other axis. Due to the arrangement of the dispersed phase, films of this type exhibit strong iridescence (eg, interference-dependent colouration based on interference) for example in which they are substantially reflective. As a result, such films have been limited for use in optical applications where optical diffusion is desired.

In this way a need remains in the art for an optical material consisting of a continuous and a dispersed phase, wherein the mismatch of the refractive index between the two phases along the three dimensional axes of the material can be handled conveniently and permanently to achieve the desirable degrees of reflection and diffuse and specular transmission, wherein the optical material is stable with respect to stress, temperature differences, and electric and magnetic fields, and wherein the optical material has an insignificant level of iridescence. These and other needs are established by the present invention, as set forth below.

Brief Description of the Drawings FIG. l is a schematic drawing illustrating an optical film made in accordance with the present invention, wherein the dispersed phase is arranged as a series of elongated masses having an essentially circular section; FIG. 2 is a schematic drawing illustrating an optical film made in accordance with the. present invention, wherein the dispersed phase is arranged as a series of elongated masses having an essentially elliptical section; FIG. 3a-e is a schematic drawing illustrating various forms of the dispersed phase in an optical film made in accordance with the present invention; FIG. 4a is a graph of the bidirectional diffusion distribution as a function of the diffuse angle for a oriented film according to the present invention for polarized light perpendicular to the direction of orientation; FIG. 4b is a graph of the bidirectional diffusion distribution as a function of the diffuse angle for a film oriented in accordance with the present invention for polarized light parallel to the orientation direction; FIG. 5 is a schematic representation of a multilayer film made in accordance with the present invention; FIGS. 6a and 6b are electronic micrographs of optical films made in accordance with the present invention; Description of the invention In one aspect, the present invention relates to a diffusely reflective film or other optical film 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 unadjusted (eg they differ from each other by more than about 0.05) along a first of the three mutually orthogonal axes, and are substantially adjusted (eg differ by less than about 0.05) over a second of the three mutually orthogonal axes. In some embodiments, the refractive index of the continuous and dispersed phases can be adjusted or mismatched substantially along, or parallel to, a third of the three mutually orthogonal axes to produce a mirror or a polarizer. Incident light polarized along, or parallel to, an unadjusted shaft is scattered, resulting in significant diffuse reflection. Incident light polarized along an adjusted axis is dispersed to a much lesser degree and is significantly spectrally transmitted. These properties can be used to make optical films for a variety of uses, including small loss reflector polarizers (significantly non-absorbent) for which light polarizations that are not significantly transmitted are reflected diffusely.

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

In another aspect, the present invention relates to a composite optical film comprising a first polymeric birefringent phase in which the second dispersed phase could be birefringent, but in which the degree of adjustment and mismatch in at least two orthogonal directions is primarily 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, whose degree of birefringence can be altered by the application of a force field, as by means of orientation dimensional or an applied electric field, such that the material of the resulting resin has, for 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 indexes of the two resins are approximately adjusted within less than about 0.05 in one or two directions, and the index difference between the first and second resin in the other two directions is greater than about 0.05. In a mentioned 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 still another aspect, the present invention relates to an optical film that acts as a reflective polarizer with a high extinction ratio. In this aspect, the index difference in the adjusted direction is chosen as small as possible and the difference in the mismatched direction is maximized. The volume fraction, the thickness, and the particle size of the dispersed phase and the shape can be chosen to maximize the extinction ratio, although the relative importance of optical transmission and reflection for the different polarizations could vary for different applications.

In another aspect, the present invention relates to an optical film 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 at along a second axis orthogonal to said first axis, and a dichroic dye. The optical film is preferably oriented along at least one axis. The dichroic dye improves the extinction coefficient of the optical film by absorbing, in addition to diffusion, the polarized light parallel to the orientation axis.

In another aspect of the present invention, there is provided an optical film having at least first and second phases that are co-continuous along at least one axis. The refractive index of the first phase differs from that of the second phase by more than about 0.05 along a first axis by less than about 0.05 along a second axis orthogonal to said first axis. In other embodiments, three or more co-continuous phases could be used to achieve the same or similar adjustments and misalignments along the mutually perpendicular axes.

In the various aspects of the present invention, the reflection and transmission properties for at least two orthogonal polarizations of incident light are determined by the selection or manipulation of several 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 film by means of which some fraction of the incident light passes, and the wavelength or wavelength band of the electromagnetic radiation of interest.

The magnitude of the adjustment or mismatch of the index along a particular axis will directly affect the degree of dispersion of the polarized light along this axis. In general, the scattering energy varies as the square of the mismatch of the index. Thus, the greater the index mismatch along a particular axis, the stronger the scattering of polarized light along this axis. Conversely, when the mismatch along a particular axis is small, the polarized light along this axis is dispersed to a lesser degree and is therefore transmitted specularly through the volume of the film.

The size of the dispersed phase can 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 the light in the medium of interest) and if there are many particles per cubic foot of wavelength, the Optical film behaves as a medium with an effective refractive index somewhat 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 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, in which the thickness of the optical film becomes greater and the desirable mechanical properties are aligned.

The shape of the particles of the dispersed phase can also have an effect on the scattering of the light. The factors of depolarization of the particles by the electric field in the directions of adjustment and mismatch of the refractive index can reduce or improve the amount of dispersion in a given direction. The effect can either add or subtract from the dispersion amount of the index mismatch, but in general it has less influence on dispersion in the preferred range of properties in the present invention.

The shape of the particles can also influence the degree of diffusion of scattered light from the particles. This effect of the shape in general is small but increases as the dimensional proportion of the geometric cross section of the particle in the plane perpendicular to the direction of incidence of light increases and as the particles are relatively larger. In general, in the operation of this invention, the particles of the dispersed phase should be sized less than several wavelengths of light in one or two mutually orthogonal dimensions if it is diffuse, the reflection is preferred instead of specular.

It is also found that the dimensional alignment has an effect on the scattering behavior of the dispersed phase. In particular, it has been observed, in optical films made in accordance with the present invention, that the aligned dispersers will not scatter light symmetrically near the directions of the transmission or specular reflection as would be dispersed by the randomly aligned dispersers. In particular, inclusion materials that have been elongated by orientation to resemble bars that scatter light mainly along (or near) a cone centered on the direction of orientation and having an edge along the direction transmitted specularly . For example, for light incident on such an elongated bar 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 decreasing the geometry of the inclusion materials, some control over the distribution of scattered light in the transmitting hemisphere and in the reflecting hemisphere can be achieved.

The volume fraction of the dispersed phase also affects the scattering of light in the optical films 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 film of the directions of adjustment and misalignment 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 being bound by theory, this seems to be due to the fact that the particles of the dispersed phase are closer, in terms of the wavelength of light, so that the particles tend to act together as a smaller number of particles. effective large particles.

The thickness of the optical film 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 film increases, the diffuse reflection also increases, and the transmission, specular and diffuse, decreases.

While the present invention will often be described here with reference to the visible region of the spectrum, various embodiments of the present invention can be used to operate at different wavelengths (and thus frequencies) of electromagnetic radiation through the scale appropriate of the optical film components. Thus, as the wavelength increases, the linear size of the components of the optical film is increased so that the dimensions, measured in units of wavelength, remain approximately constant. Another important effect of changing the wavelength is that, for most materials of interest, the refractive index and the absorption coefficient change. However, the principles of index adjustment and misalignment still apply at each wavelength of interest.

Detailed description of the invention Introduction How it is 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 near the specular angle. The terms "diffuse reflection" or "diffuse reflectance" refer to the reflection of rays that are outside the specular cone defined above. The terms "total reflectance" or "total reflection" refer to the combined reflectance of all light from the surface. Thus, the total reflection is the sum of the specular and diffuse reflection.

Similarly, the terms "specular transmission" and "specular transmittance" as used herein in reference to the transmission of lightning in an emerging cone with a corner angle of 16 degrees centered near 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 the optical film. Thus, the total transmission is the sum of the specular and diffuse transmission.

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

FIGS. 1-2 illustrate a first embodiment of the present invention. According to the invention, a diffusively reflective optical film 10 or another optical film is produced consisting of a birefringent or continuous phase matrix 12 and a discontinuous or dispersed phase 14. The birefringence of the continuous phase is at least typically 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 adjusted (eg, differ by less than about 0.05) along a first of three mutually orthogonal axes, and are substantially mismatched (eg, differ by more than about 0.05) over a 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 adjustment 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 mismatch by at least about 0.07, more preferably, by at least about 0.1, and more preferably, by at least about 0.2.

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

The present invention provides a practical and simple optical film and a method for making a reflective polarizer, and also provides a means of obtaining a continuous range of optical properties according to the principles described herein. Also, small loss polarizers with high extinction ratios. Other advantages are a wide range of practical materials for the dispersed phase and the continuous phase, and a high degree of control in the proportion of optical films of consistent development and high predictable quality.

Effect of the Adjustment / Mismatch 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 due to orientation. Consequently, as the film is oriented in one or more directions, the adjustments or misalignments of the refractive index occur along one or more axes. By careful manipulation of orientation parameters and other processing conditions, the positive or negative birefringence of the matrix can be used to induce diffuse reflection or transmission in one or both light polarizations along a given axis. The relative relationship between transmission and diffuse reflection is dependent on the concentration of the inclusions materials 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 inclusion materials of the dispersed phase, and of the wavelength or wavelength band of the incident radiation.

The magnitude of the index adjustment or mismatch along a particular axis directly affects the degree of scattering of polarized light along this axis. In general, the scattering energy varies as the square of the mismatch of the index. Thus, the greater the mismatch of the index along a particular axis, the stronger the dispersion of the polarized light along that axis. On the other hand, when the mismatch along a particular axis is small, the polarized light along that axis is dispersed to a lesser degree and is therefore transmitted specularly through the volume of the film.

FIGS. 4a-b demonstrate this effect in oriented films made in accordance with the present invention. Here, a measurement of the typical Bidirectional Dispersion Distribution Function (FDDB) is shown for incident light normally at 632.8 nm. FDDB is described in J. Stsver, "Optical Scattering Measurement and Analysis" (1990). The FDDB is shown as a function of the scattered angle for light polarizations of the perpendicular and parallel to the orientation axes. A scattered angle of zero corresponds to undispersed light (spectrally transmitted). For polarized light in the direction of index adjustment (ie, perpendicular to the direction of orientation) as in FIG. 4a, there is a specularly significant transmitted peak with a considerable component of diffusely transmitted light (dispersion 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 misalignment of the index (that is, parallel to the direction of orientation) as in FIG. 4b, there is specularly insignificant transmitted light and a greatly reduced component of the diffusely transmitted light, and a diffusely considerable reflected component. It should be noted that the scattering plane shown by these graphs is the plane perpendicular to the direction of orientation where most of the scattered light exists for these elongate inclusion materials. The contributions of scattered light outside this plane are greatly reduced.

If the refractive index of the inclusion materials (eg, the dispersed phase) adjusts the continuous matrix medium along some axis, then the polarized incident light with electric fields parallel to this axis will pass through the light does not disperse whatever the size, shape, and density of the inclusions. If the indices do not fit along any axis, then the inclusions will scatter polarized light along this axis. For dispersions of a given cross-sectional area with dimensions greater than about? / 30 (where ~? Is the wavelength of the light in the middle), the intensity of the scattering is largely determined by the mismatch of the index. The exact size, shape and alignment of the mismatch inclusion material plays a role in determining how much light will be scattered in various directions from this inclusion material. If the density and thickness of the dispersion layer is sufficient, according to the theory of multiple dispersion, the incident light will be reflected or absorbed, but not transmitted, regardless of the details of the size and shape of dispersion.

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

Some of the polarizers within the scope of the present invention are elliptical polarizers. In general, the elliptical polarizers will have a difference in the refractive index between the dispersed phase and the continuous phase for both directions of stretching and transverse stretching. The ratio of forward dispersion with respect to backwards is dependent on the difference in the refractive index between the dispersed and continuous phases, the concentration of the dispersed phase, the size and shape of the dispersed phase and the overall thickness of the film. In general, elliptical diffusers have a relatively small difference in the refractive index between the particles of the dispersed and continuous phases. Using a birefringent polymer based diffuser, highly sensitive elliptical polarization (eg, diffuse reflectivity depending on the polarization of light) can be achieved. At one end, where the refractive index of polymers fitted on an axis, the elliptical polarizer will be a diffuse reflection polarizer.

Methods of Obtaining the Adjustment / Mismatch 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 finished polarizer have at least one axis by which the associated refractive indices are substantially same. The adjustment of the refractive indices associated with such axis, which typically, but not necessarily, is an axis transverse to the direction of orientation, which results in substantially no reflection of light in the plane of polarization.

The dispersed phase could also exhibit a decrease in the refractive index associated with the orientation direction after stretching. If the birefringence of the matrix is positive, an induced birefringence of negative tension of the dispersed phase has the advantage of increasing the difference between the refractive indices of the attached phases associated with the orientation axes 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 attached 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 an induced birefringence of positive voltage. However, this can be altered by means of heat treatment to adjust 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 as to relax the birefringence in the continuous phase.

Geometry of the Dispersed Phase While the mismatch of the refractive index is the predominant factor that depends on the promoter dispersion in the films of the present invention (eg, a diffuse mirror or polarizer made in accordance with the present invention has a mismatch in the indexes of refraction of the continuous and scattered phases 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 adjustment or mismatch of the refractive index can reduce or improve 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 transverse elliptical cross-sectional shape of the scattered phase contributes to asymmetric diffusion in scattered light backwards and in light scatter forward. The effect may add or subtract from the dispersion amount of the index mismatch, 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 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 as the dimensional proportion of the cross-sectional geometry of the particle increases in the plane perpendicular to the direction of incidence of the light and as the particles become relatively larger. In general, in the operation of this invention, the particles of the dispersed phase should be sized less than several wavelengths of light in one or two mutually orthogonal directions if it is diffuse, reflection is preferred instead of specular.

Preferably, for a small loss reflecting polarizer, the preferred embodiment consists of a dispersed phase disposed within the continuous phase as a series of bar-like structures which, as a consequence of orientation, have a high dimensional proportion that can improve the reflection for polarizations parallel to the direction of orientation increasing the dispersion intensity for such polarization with respect to the polarizations perpendicular to the direction of orientation. Nevertheless, as indicated in FIGS. 3a-e, the dispersed phase could be provided with many different geometries. Thus, the dispersed phase could be disk-shaped or elongated disk-shaped, as in FIGS. 3a-c, in the form of a bar, 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 a 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 central construction and coating, wherein the center and the coating are made of the same or different materials, or where the center is hollow. Thus, for example, the dispersed phase could consist of hollow fibers of equal or random lengths, and of uniform or non-uniform cross section. The interior space of the fibers could be free, or could be occupied by an appropriate 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 achieve a desired optical effect (e.g., reflection or polarization along a given axis).

The geometry of the dispersed phase could be achieved through the proper orientation or processing of the optical material, through the use of particles having a particular geometry, or by means of a combination of the two. Thus, for example, a dispersed phase having a substantially bar-like structure can be produced by orienting a film consisting of approximately spherical dispersed phase particles along a single axis. Bar-like structures can be given in a form in an elliptical cross section by orienting the film in a second direction perpendicular to the first. As a further example, a dispersed phase having a substantially bar-like structure in which the bars are in rectangular 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 within 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 bar-like on an axis in the non-oriented film. Bars with a high dimensional proportion could be generated by orientation in the direction of the main axis of the bars in the extruded film. The plate-like structures could be generated by orientation in a direction orthogonal to the main axis of the bars in the extruded film.

The structure in FIG. 2 can be produced by asymmetric biaxial orientation of a mixture of essentially spherical particles within a continuous matrix. Alternatively, the structure could be obtained by incorporating a plurality of fibrous structures in a matrix material, aligning the structures along a single axis, and orienting the mixture in a direction transverse to this axis. Yet another method for obtaining this structure is by controlling the relative viscosities, the cut or surface tension of the components of a mixture of polymers to give rise to 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 direction of the extrusion.

Dimensional Alignment of the Dispersed Phase The dimensional alignment is also found to have an effect on the scattering behavior of the dispersed phase. In particular, it has been observed that in optical films made according to the present invention aligning dispersers will not disperse light symmetrically near the directions of the transmission or specular reflection as would be dispersed by randomly aligned dispersers. In particular, the inclusion materials that have been lengthened by orientation to resemble scattering bars > light mainly along (or near) the surface of a cone centered on the direction of orientation and along the direction transmitted specularly. This could result in an anisotropic distribution of scattered light near the reflection and specular transmission directions. For example, for light incident on such an elongated bar 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 decreasing the geometry of the inclusion materials, some control over the distribution of scattered light in the transmitting hemisphere and in the reflecting hemisphere can be achieved.

Dimensions of the Scattered Phase In applications where the optical film is to be used as a small loss reflecting polarizer, the structures of the dispersed phase preferably have a high dimensional proportion, e.g. ex. , the structures are substantially larger in one dimension than in any other dimension. The dimensional proportion is at least preferably 2, and more preferably at least 5. The largest dimension (eg, the length) is at least preferably 2 times the wavelength of the electromagnetic radiation over the wavelength range of interest, and more preferably at least 4 times the desired wavelength. Otherwise, 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 about 0.5 times the wavelength of interest.

Fraction Volume of the Dispersed Phase The volume fraction of the dispersed phase also affects the light scattering in the optical films of the present invention. Within certain limits, increasing the volume fraction of the dispersed phase tends to increase the amount of scattering that a light beam experiences after entering the film by the directions of adjustment and misalignment of the polarized light. This factor is important to control the reflection and transmission properties for a given application.

The desired volume fraction of the dispersed phase will depend on many factors, including the specific choice 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 within the range of about 5 to about 15%, and more preferably within the range of about 15 to about 30% Co-continuous phases When the volume fraction for binary mixtures of high polymers of equivalent viscosity about 50%, the distinction between the dispersed and continuous phases becomes difficult, as each phase becomes continuous in space. Depending on the materials of choice, they could also be regions where the first phase seems to be dispersed within the second, and vice versa.

For a description of a variety of co-continuous morphologies and for methods of evaluation, analysis and characterization, see Sperling and the references cited here (LH Sperling, "Microphase Structure", Enclyclopedia of Polymer Science and Engineering, 2nd Ed. Vol. 9 , 760-788, and LH Sperling, Chapter 1"Interpenetra ing Polymer Networks: An OverView", Interpenetrating Polymer Networks, edited by D. Klemper, LH Sperling, and LA Utracki, Advances in Chemistry Series # 239, 3-38, 1994 ).

Materials having co-continuous phases could be made according to the present invention by a number of different methods. Thus, for example, the polymeric first phase material could be mechanically mixed with the second polymeric phase material to obtain a co-continuous system. Examples of co-continuous morphologies obtained by means of mixing are described, for example, in D. Bourry and B.D. Favis, "Co-Continuity and Phase Investment in HDPE / PS Blends: The Role of Interfacial Modification", 1995 Annual Technical Conference of the Society of Plastics Ensineers ANTEC. Vol. 53, No. 2, 2001-2009 (polystyrene / polyethylene blends), and in A. Leclair and B.D. Favis "The Role of Interfacial contact in immiscible binary polymer blends and its influence on mechanical properties", Polymer, Vol. 37, No. 21, 4723-4728, 1996 (polycarbonate / polyethylene blends).

The co-continuous phases could also be formed in accordance with the present invention by first dissolving them out of extractions of supercritical fluids, such as those exposed for mixtures of polystyrene and poly (methyl methacrylate) in U.S. 4,281,084, and then allowing them to separate from the phase followed by exposure to heat and / or mechanical cutting, as described in N. Mekhilef, B.D. Favis and P.J. Carreau, "Morphological Stability of Polyethylene Blends", 1995 Annual Technical Conference of the Society of Plastics Engineers ANTEC, Vol. 53, No. -2, 1572-1579).

An additional method of producing co-continuous phases according to the present invention is through the creation of networks of interpenetrating polymers (RPIs). Some of the most important RPIs include simultaneous RPIs, sequential RPIs, gradient INPs, latex RPIs, thermoplastic RPIs, and semi-RPIs. These and other types of RPIs, their physical properties (e.g., phase diagrams), and methods for their preparation and characterization, are described, for example, in L.H. Sperling and V. Mishra, "Current Status of Interpetrating Polymer Networks", Polymer for Advanced Technologies. Vol. 7, No. 4, 197-208, April 1996, and in L.H. Sperling "Interpenetrating Polymer Networks: An Overview", Interpenetrating Polymer Networks, edited by D. Klemper, L.H. Sperling, and L.A. Utracki, Advances in Chemistry Series # 239, 3-38, 1994). Some of the main methods for the preparation of these systems are summarized below.

The simultaneous RPIs could be made by mixing together the respective monomers or prepolymers, plus the degraders and activators, of two or more polymer networks. The respective monomers or prepolymers are then reacted simultaneously, but in a non-interference manner. Thus, for example, one reaction could be performed to proceed as a chain-polymerization kinetics, and the other reaction could be performed to proceed by means of the polymerization kinetics step.

The sequential RPIs are made by first forming an initial polymer network. Then, the monomers, degraders, and activators of one or more additional networks swell in an initial polymer network, where they elongate in situ to produce additional polymer networks.

The gradient RPIs are synthesized in such a way that the overall composition or density of the RPl degrader varies macroscopically in the material from one location to another. Such systems could be made, for example, by forming a first polymer network predominantly on one surface of a film and a second polymer network predominantly on another surface of the film, with a gradient in the composition throughout the interior of the film .

Latex RPIs are made in the latex form (eg, with a central structure and coating). In some variations, two or more latexes could be mixed and formed into a film, which degrades the polymers.

The RPIs are hybrids between the polymer mixture and the RPIs that involve physical degradation instead of chemical degradation, as a result, these materials could be made to flow at elevated temperatures in a similar way to thermoplastic elastomers, but they are degraded and they behave like the RPIs at the temperatures of normal use.

Semi-RPIs are compositions of two or more polymers in which one or more of the polymers are degraded and one or more of the polymers are linear or branched.

As indicated above, co-continuity can be achieved in multicomponent systems as well as in binary systems. For example, three or more materials could be used in combination to give the desired optical properties (e.g., transmission and reflectivity) and / or improved physical properties. All components could be immiscible, or two or more components could demonstrate miscibility. A number of ternary systems are described that exhibit co-continuity, for example, in L.H. Sperling, Chapter 1"Interpenetrating Polymer Networks: An Overview", Interpenetrating Polymer Networks, edited by D. Klemper, L.H. Sperling, and L.A. Utracki, Advances in Chemistry Series # 239, 3-38, 1994).

The characteristic sizes of the phase structures extend from the fraction of volume over which co-continuity could be observed, and stability of the morphology could be influenced by additives, such as compatibilizers, copolymers of mixtures or blocks, or reactive components, such as maleic anhydride or glycidyl methacrylate. Such effects are described, for example, for mixtures of polystyrene and poly (ethylene terephthalate) in H.Y. Tsai and K. Min, "Reactive Blends of Functionalized Polyestirene and Polyethylene Terephthalate", 1995 Annual Technical Conference of the Society of Plastics Engineers ANTECf Vol. 53, No. 2, 1858-1865. However, for particular systems, phase diagrams could be constructed by routine experimentation and used to produce co-continuous systems according to the present invention.

The microscopic structure of the co-continuous systems made in accordance with the present invention can vary significantly, depending on the method of preparation, the miscibility of the phases, the presence, of additives, and other factors that are known in the art. In this way, for example, one or more of the phases in the co-continuous system could be fibrillar, with the fibers either randomly oriented or oriented along a common axis. Other co-continuous systems could comprise an open-cell matrix in a first phase, with a second phase arranged in a continuous manner between the cells of the matrix. The phases in these systems could be co-continuous along a single axis, along two axes, or along three axes.

Optical films made in accordance with the present invention and having co-continuous phases (particularly RPls) will have, in several examples, properties that are advantageous over the properties of similar optical films that will be made with only one continuous phase, depending, Of course, the properties of the individual polymers and the method by which they are combined. Thus, for example, the co-continuous system of the present invention allows the chemical and physical combination of structurally dissimilar polymers, whereby a convenient route is provided by which the properties of the optical film could be modified to establish the specific needs. In addition, co-continuous systems will often be easier to process, and could impart such properties as strength, reduced flammability, greater impact strength and de-stress stress, improved flexibility, and superior chemical resistance. RPIs are particularly advantageous in certain applications, since they typically swell (but do not dissolve) in solvents, and exhibit slip and suppressed flow compared to analogous RPl systems (see, eg, D. Klempner and L. Berkowski , "Interpenetrating Polymer Networks", Encyclopedia of Polymer Science and Engineering, 2nd Ed., Vol. 9, 489-492.

One skilled in the art will appreciate that the principles of co-continuous systems as known in the art could be applied in the clarity of the teachings set forth herein to produce co-continuous morphologies having unique optical properties. Thus, for example, the refractive indices of known co-continuous morphologies could be manipulated as indicated herein to produce new optical films according to the present invention. Also, the principles shown here could be applied to known optical systems to produce co-continuous morphologies.

Thickness of the Optical Film The thickness of the optical film is also an important parameter that can be manipulated to affect the reflection and transmission properties of the present invention. As the thickness of the optical film increases, the diffuse reflection also increases, and the transmission, specular and diffuse, decreases. Thus, while the thickness of the optical film will typically be chosen to obtain a desired degree of mechanical strength in the finished product, it can 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 film. Thus, for example, in film applications, the device used to extrude the film can be controlled by a downward current optical device which measures the transmission and reflection values in the extruded film, and which varies the thickness of the film (eg, by adjusting the extrusion speeds or changing the speeds of the casting pulley) to maintain the reflection and transmission values within a predetermined range.

Materials for Continuous / Dispersed Phases Many different materials could be used as the continuous and dispersed phases in the optical films of the present invention, depending on the specific application to which the optical film is intended. Such materials include inorganic materials such as silica-based polymers, organic materials such as liquid crystals, and polymeric materials, which include monomers, copolymers, mixed polymers and mixtures thereof. The exact choice of materials for a given application will be manipulated by the desired adjustment or mismatch obtained in the refractive indices of the continuous and dispersed phases along a particular axis, in addition to the physical properties desired in the resulting product. However, the materials of the continuous phase will be characterized in general by being substantially transparent in the region of the desired spectrum.

An additional consideration in the choice of materials is that the resulting product must contain at least two distinct phases. This could be done by melting the optical material from two or more materials that are immiscible between one and the other. Alternatively, if it is desired to make an optical material with a first and second material which are not immiscible between one another, and if the first material has a higher melting point than the second material, in some cases it might be possible to introduce 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 melted into a film, with or without subsequent orientation, to produce an optical device.

The 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, sebacic, dibenzoic, terephthalic acid. , 7-naphthalene dicarboxylic, 2,6-naphthalene dicarboxylic, cyclohexanedicarboxylic and benzoic (including 4,4'-benzoic acid), or materials made from the corresponding esters of the above acids (e.g., dimethylterephthalate). Of these, 2,6-polyethylene naphthalate (PEN) is especially preferred because of its stress-induced birefringence, and because of its ability to retain birefringence permanently after stretching. The PEN has a refractive index for polarized incident light of wavelength of 550 nm which decreases after stretching when the plane of polarization is parallel to the axis of stretching from about 1.64 to as high as 1.9, while the refractive index decreases for 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 the stretch and the index perpendicular to the stretch direction) from 0.25 to 0.40 in the visible spectrum. Birefringence can be increased by decreasing the 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 in addition to other polyesters of crystalline naphthalene dicarboxylic acids. The crystalline naphthalene dicarboxylic polyesters exhibit a difference in refractive indices with different axes in the plane of at least 0.05 and preferably above 0.20.

When the 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, isophthalic, sebacic, azelaic or cyclohexanedicarboxylic acid or the related alkyl esters of these materials. The naphthalene dicarboxylic acid could also be used in minor amounts to improve the adhesion between the phases. The diol component could be ethylene glycol or a related diol. The diol component could be ethylene glycol or 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 reached.

Syndiotactic vinyl aromatic polymers useful in the present invention include poly (styrene), poly (alkyl styrene) ', poly (styrene halide), poly (alkyl styrene), poly (vinyl ester) benzoate, and hydrogenated polymers and mixtures, or copolymers containing 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). As examples of poly (styrene halides), they 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 styrene group polymers are: polystyrene, poly (p-methyl styrene), poly (m-methyl styrene), poly (p-tertiary butyl styrene), poly (p-chlorostyrene), poly (m-chloro styrene), poly (p-fluoro styrene), and copolymers of styrene and p-methyl styrene.

Further, as comonomers of syndiotactic vinyl aromatic group copolymers, in addition to monomers of the styrene group polymer explained above, there could 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 syndiotactic vinyl aromatic polymers of the present invention could be block copolymers, random copolymers or alternating copolymers.

The vinyl aromatic polymer having a high level syndiotactic structure referred to this invention, generally includes polystyrene having syndiotacticity greater than about 75% or more, as determined by carbon-13 nuclear magnetic resonance. Preferably, the degree of syndiotacticity is greater than 85% of racemic or greater than 30% or more preferably, greater than 50%, racemic.

In addition, although there are no particular restrictions with respect to the molecular weight of this syndiotactic vinyl aromatic group polymer, preferably, the average molecular weight is greater than 10,000 and less than 1,000,000, and more preferably, greater than 50,000 and less than 800,000.

As for the other resins, various types could be mentioned, including, for example, vinyl aromatic group polymer with atactic structures, vinyl aromatic group polymers with isotactic structures, and all polymers that are miscible. For example, the polyphenylene ethers show good miscibility with the polymers of vinyl aromatic groups discussed above. In addition, the composition of these immiscible resin components is preferably between 70 to 1% by weight, or more preferably, 50 to 2% by weight. When the composition of the immiscible resin component exceeds 70% by weight, the degradation of the heat resistance could occur, and is usually not desirable.

The polymer selected for a particular phase is not required to be a copolyester or copolycarbonate. Vinyl polymers and copolymers made from monomers such as vinyl naphthalenes, styrenes, ethylene, maleic anhydride, acrylates and methacrylates can also be used. Condensation polymers can also be used, apart from polyesters and polycarbonates. Suitable condensation polymers include polysulfones, polyamides, polyurethanes, polyamic acids, and polyimides. The naphthalene and halogen groups such as chlorine, bromine and iodine are used in increasing the refractive index of the selected polymer to the desired level (1.59 to 1.69) if the refractive index needs to be adjusted substantially if the matrix is the PEN. The acrylate and fluorine groups are particularly useful in reducing the refractive index.

Lower amounts of comonomers could be substituted in the naphthalene polyester of dicarboxylic acid until the large difference in the refractive index in the direction of orientation is not sufficiently modified. A smaller refractive index difference (and therefore decreased reflectivity) could be counterbalanced by advantages in any of the following: improved adhesion between the continuous and dispersed phase, reduced extrusion temperature, and better adjustment of the viscosities of the mass melted 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 thus frequencies) of electromagnetic radiation through the appropriate scale of the components of the optical film. Thus, as the wavelength increases, the linear size of the components of the optical film could be increased so that the dimensions of these components, measured in units of wavelength, remain approximately constant.

Of course, a greater effect of changing the wavelength is that, for most materials of interest, the refractive index and the absorption coefficient change. However, the principles of index adjustment and misalignment still apply at each wavelength of interest, and could be used in the selection of materials for an optical device that will operate over a specific region of the spectrum. Thus, for example, the appropriate scale of dimensions will allow the operation in the infrared, almost ultraviolet and ultraviolet spectrum regions. In these cases, the refractive index refers to the values at these operating wavelengths, and the thickness of the film and the size of the dispersed components of the dispersed phase should also be approximately dispersed with the wavelength. However, the electromagnetic spectrum can be used, including very high, ultra high, microwave, and millimeter wave frequencies. The polarization and diffusion effects will be present with the appropriate scale for the wavelength and the refractive indices can be obtained from the square root of the dielectric function (including the real and imaginary parts). Useful products in these large wavelength bands can be diffuse reflector polarizers and partial polarizers.

In some embodiments of the present invention, the optical properties of the optical film vary across the wavelength band of interest. In these embodiments, the materials could be used for continuous and / or dispersed phases whose refractive indices, along one or more axes, vary from one region of wavelength to another. The choice of the materials of the continuous and dispersed phase, and the optical properties (eg, diffuse and scattered reflection or specular transmission) resulting from a choice of specific 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 disposed coextensively on one or both surfaces of the principal surfaces of the film, e.g. ex. , the extruded mixture of the dispersed phase and the continuous phase. The composition of the layer, also called a surface layer, could be chosen 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 . Appropriate materials of choice 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 mixture could also be useful.

A surface layer or layers could reduce the wide range of cutting intensities that the extruded mixture could experience within the extrusion process, particularly in the mold. A high cut environment could cause undesirable surface vacuum and could result in a textured surface. A wide range of cut values across the entire thickness of the film could also prevent the dispersed phase from forming the desired particle size in the mixture.

A surface layer or layers could also add physical strength to the resulting composite or reduce problems during processing, such as, for example, reducing the tendency for the film to split during the orientation process. The materials of the surface layer that remain amorphous could tend to make the films with a higher hardness, while the materials of the surface layer that are semicrystalline could tend to make the films with a higher modulus of tension. Other functional components such as antistatic additives, UV absorbers, antioxidant dyes and pigments, could be added to the surface layer, providing substantially no interference with the desired optical properties of the resulting product.

The surface layers could be applied to one or two sides of the extruded mixture at some point during the extrusion process, e.g. ex. , before the extruded mixture and the surface layer (s) leave the extrusion mold. This could be done using conventional coextrusion technology, which could include using a three layer co-extrusion mold.

It is also possible to laminate the surface layer (s) to a pre-formed film of an extruded mixture. The thickness of the total surface layer could be in the range of about 2% to about 50% of the total mixed / surface layer thickness.

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

Anti-reflection layers The films and other optical devices made in accordance with the invention could also include one or more anti-reflective layers or coatings. Such layers, which may or may not be sensitive to polarization, serve to increase the transmission or to reduce the reflecting dazzling light. An anti-reflective layer could be imparted to the optical films and devices of the present invention by means of appropriate surface treatment, such as coating or etching by electronic deposition.

In some embodiments of the present invention, it is desired to maximize the transmission and / or minimize the specular reflection for certain polarizations of light. In these embodiments, the optical film could comprise two or more layers in which at least one layer comprises an anti-reflective system in close contact with a layer providing the continuous and dispersed phases. Such an anti-reflective system acts to reduce the specular reflection of the incident light and to increase the amount of incident light entering the portion of the film containing the continuous and dispersed layers. Such a function can be performed by a variety of means well known in the art. Examples are one-wave wave antireflection layers, two or more superimposed anti-reflective layers, graduated index layers and graduated density layers. Such antireflection functions can also be used on the lateral transmitted light of the film to increase the transmitted light if desired.

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

More Than Two Phases The optical films 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 can consist of two different dispersed phases within the continuous phase. The second dispersed phase could be scattered randomly or non-randomly throughout the continuous phase, and can be randomly aligned along a common axis.

The optical films made in accordance with the present invention could also consist of more than one continuous phaseThus, in some embodiments, the optical film 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 extending to through the second continuous phase, as much as water is spread through a network of channels of a wet sponge). In a related embodiment, the second continuous phase is in the form of a dendritic structure that 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 (eg to increase reflectivity). Suitable multilayer films include those of the type described in WO 95/17303 (Ouderkirk et al.). In such a construction, the individual sheets could be laminated or otherwise adhered together or spaced apart from one another. If the optical thicknesses of the phases within the sheets are substantially equal (that is, if two sheets have a large number of substantially equal diffusers for incident light along a given axis), the composite will reflect, in somewhat higher efficiency , substantially the same bandwidth and the spectral range of reflectivity (eg, "band") as the individual sheets. If the optical thicknesses of the phases within the sheets are not substantially equal, the composite will reflect through a wider bandwidth than the individual phases. A composite that combines mirror sheets with polarizing sheets is useful for increasing total reflectance while still transmitting polarized light. Alternatively, a single sheet could be oriented asymmetrically or biaxially to produce a film having selective polarizing and reflecting properties.

FIG. 5 illustrates an example of this embodiment of the present invention. Here, the optical film consists of a multilayer film 20 in which the layers alternate between the PEN 22 layers and the co-PEN 24 layers.

PEN includes a dispersed phase of syndiotactic polystyrene (sPS) within a PEN matrix. This type of construction is desirable in that it promotes the lower fading angle. In addition, since the layer or material of inclusion of the averages of diffusions outside the light filter, the control over the thickness of the layer is less critical, allowing the film to be more tolerable of variations in the 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 within a particular layer. However, PEN and co-PEN are particularly desirable as the main 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. In this way, for example, the layers could be made to follow a repetition sequence through part or all of the structure. An example of this is a construction that has the pattern of the layer ... ABCABC ..., where A, B and C are different materials or different mixtures of the same or different materials, and where one or more of A , B and C contains at least one dispersed phase and at least one continuous phase. The surface layers are preferably the same or chemically different materials.

Additives The optical materials of the present invention could also comprise other materials or additives as are known in the art. Such materials include pigments, colorants, binders, coatings, fillers, compatibilizers, antioxidants (including sterically hindered phenols), surfactants, antimicrobial agents, antistatic agents, foaming agents, reinforcing agents, light stabilizers, (including UV stabilizers or blockers) thermal stabilizers, modifiers of impact, plasticizers, viscosity modifiers and other of these materials. In addition, the films and other optical devices of 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 process or durability of the device.

Suitable lubricants for use in the present invention include calcium stearate, zinc 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) (((3,5-bis (1,1-dimethylethyl) ) -4-hydroxyphenyl) methyl) -dioctadecyl ester of phosphonic acid), Irganox ™ 1098 (N, N * -1, 6-hexanediylbis (3,5-bis (1,1-dimethyl) -4-hydroxy-benzenepropanamide) , Naugaard ™ 445 (aryl amine), Irganox ™ L 57 (alkylated diphenylamine), Irganox ™ L 115 (bisphenol containing sulfur), Irganox ™ LO 6 (alkylated phenyl-delta-naphthylamine), Ethanox 398 (fluorophosphonate), and 2 , 2'-ethylenebis (4,6'-di-t-burylphenyl) fluorophosphonite.

A group of antioxidants which are especially preferred are sterically hindered phenols, including butylated hydroxytoluene (BHT), Vitamin E (di-alpha-tocopherol), Irganox ™ 1425WL (calcium bis- (O-ethyl (3, 5'-di -t-butyl-4-hydroxybenzyl)) phosphonate), Irganox ™ 1010 (tetrakis (methylene (3, 5-di-t-butyl-4-idroxyhydrocinnamate)) methane), Irganox ™ 1076 (octadecyl 3,5-di) -tert-butyl-4-hydroxyhydrocinnamate), Ethanox ™ 702 (hindered bisphenolic), Ethanox 330 (hindered high molecular weight phenolic) and Ethanox ™ (hindered amine).

Dichroic dyes are a particularly useful additive for many of the applications for which the optical films and devices of the present invention are concerned, due to their ability to absorb light of a particular polarization when they are molecularly aligned within the material. When used in a film or other material that predominantly disperses only one polarization of light, the dichroic dye causes the material to absorb one polarization of light more than another. Suitable dichroic dyes for use in the present invention include Congo Red (sodium diphenyl-bis-a-naphthylamine sulfonate), methylene blue, stilbene dye (Chromatic index (IC) = 620), and chloride of 1.1. '-diethyl-2, 2'-cyanine (IC = 374 (orange) or IC = 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 lower dichroism in cellulose. There is a slight dichroism with the Congo Red in the PEN.

Other suitable colorants include the following materials: The properties of these dyes, and methods of making them, are discussed in Kirk Othmer Encyclopedia of Chemical Technology, Vol. 8, p. 652-661 (4th Ed. 1993), and references cited here.

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

The dichroic dyes in combination with. Certain polymer systems exhibit the ability to polarize light to 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 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 ratio of dichroism than, for example, the same dye in another film forming polymer systems. A higher dichroism ratio indicates a greater ability to polarize light.

The molecular alignment of a dichroic collorant within an optical film made in accordance with the present invention is preferably performed by stretching the optical film after the dye has been incorporated therein. However, other methods could also be used to achieve molecular alignment. Thus, in one method, the dichroic dye crystallizes, by sublimation or by crystallization of the solution, in a series of slots that are cut, engraved, or otherwise formed on the surface of a film or other optical film, either before or after the optical film 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 film. The slots could be created according to a particular pattern or pattern, and with a predetermined amount of spacing between the slots, to achieve the desired optical properties.

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

In yet another embodiment, the dichroic dye is disposed along the interfacial layer of a multilayer construction, such as 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 to at least partially fill the voids in a microvacuum film made in accordance with the present invention.

General Applications of the Present Invention The optical films of the present invention are particularly useful as diffuse polarizers. However, the optical films could also be made according to the invention which operates as reflective polarizers or diffuse mirrors. In these applications, the construction of the optical material is similar to that of the applications in the diffusers described above. However, these reflectors will generally have a much greater difference in the refractive index along at least one axis. This index difference is typically at least about 0.1, more preferably about 0.15, and more preferably about 0.2.

The reflective polarizers have a difference in refractive index along one axis, and substantially the indexes of adjustment along the other. The reflective films, otherwise, differ in the refractive index along at least two axes in the orthogonal plane of the film. However, the reflective properties of these modalities do not need to be reached solely because of dependence on index mismatches. Thus, for example, the thicknesses 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 transmitting diffuser to a diffuse reflector.

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

Perspective of Examples The following Examples illustrate the production of various optical materials according to the present invention, in addition to the spectral properties of these materials. Unless otherwise indicated, the composition in percent refers to the composition in percent 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, IL. These reagents were polymerized at various intrinsic viscosities (VI) using conventional polymerization techniques of the polyester resin. 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 additive or process changes as discussed below.

The elongation or orientation of the samples was provided using conventional orientation equipment used for the production of polyester film or an intermittent laboratory orienter. The intermittent laboratory orienter was designed to use a small piece of molten material (7.5 cm by 7.5 cm) cut from the molten material network and extruded by a square arrangement of 24 bras (6 on each side). The orientation temperature of the sample was controlled by a hot air blower and the film sample was oriented by a mechanical system that increased the distance between the fasteners in one or both directions at a controlled rate. The samples stretched in both directions could be oriented sequentially or simultaneously. For samples that were oriented in the compressed form (C), all the fasteners hold the net and the fasteners move only one dimension. While, in the uncompressed form (U), the fasteners holding the film, in a fixed dimension perpendicular to the direction of the stretch does not engage and the film is allowed to relax in such a dimension.

Polarized diffuse transmission and reflection were measured using a Perkin Elmer Lambda 19 ultraviolet / visible / near-infrared spectrophotometer equipped with a 150 mm Perkin Elmer Labsphere S900-1000 integrating a 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 stretching of the film. All detections were continuous and were carried out with a detection speed of 480 nanometers per minute and a slot width of 2 nanometers. The reflection was carried out in the form of "reflection V". Transmission and reflectance values are averages of all wavelengths of 400 to 700 nanometers.

The transmission of electronic icrographs were taken from the finished film, cross section in a plane perpendicular to the machine direction to determine the nature of the dispersed phase. The outer layers of the three-layer constructions were removed from the oriented film, leaving only the layer of mixture for fixation. The samples were fixed in a 3M Scotchcast ™ Electrical Resin which was cured at room temperature. The fixed samples were microvoluminated using a diamond knife, on a Reichert Ultracut ™ microvolume at room temperature, in thin sections of approximately 90 nm thickness, using a cutting speed of 0.2 millimeters per second. The thin sections were floated on distilled, deionized water and collected for electron microscopic evaluation on a 200 mesh copper reinforced with a carbon / formvor substrate. The photomicrographs were taken using a JEOL 200CX Electronic Transmission Microscope.

Microscopic electronic detection evaluations were performed on melt networks prior to film orientation to determine the nature of the dispersed phase. The pieces of the network fractured to expose a plane perpendicular to the direction of the machine while they were submerged in liquid nitrogen. The samples were then fitted and mounted on aluminum fragments before coating by electronic deposition with golden palladium. The photomicrographs were taken using a Hitachi S530 Electronic Detection Microscope.

EXAMPLE 1 In Example 1, an optical film according to the invention was made by extruding a mixture of 75% polyethylene naphthalate (PEN) as the continuous or larger phase and 25% polymethyl methacrylate (PMMA) as the dispersed or smaller phase in a film. cast or sheet approximately 380 micrometers thick using conventional extrusion and casting techniques. The PEN had an intrinsic viscosity (VI) of 0.52 (measured in 60% phenol, 40% dichlorobenzene).

The PMMA was obtained from ICI Americas Inc., Wilmington, DE, under the product designation CP82. The extruder used was a 3.15 cm (1.24") Brabender with a 60 μm Tegra tube filter, the mold was a 30.4 cm (12") Ultraflex ™ 40 EDI.

Approximately 24 hours later the film was extruded, the molten film was oriented in the direction wide or transverse (DT) on 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). 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 a parallel reflectivity of 75% (e.g., reflectivity was measured with the direction of stretch of the film parallel to the vector e of polarized light), and cross-reflectivity of 52% (e.g., reflectivity was measured with vector e of 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 polystyrene glycidyl methacrylate compatibilizer is used. , and 0.25% each of Irganox ™ 1010 and Ultranox ™ 626. The synthesis of polystyrene glycidyl methacrylate is described in Polymer Processes, "Chemical Technology of Plastics, Resins, Rubbers, Adhesives and Fibers", Vol. 10, Chap. 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 weight of approximately 200,000, subsequently designed as sPS-200-0. The parallel reflectivity in the sample of the stretched film 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 sample 4, a three-layer optical film was made in accordance with 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% para-methyl styrene), and each surface layer consisted of 100% PEN having an intrinsic viscosity of 0.56 measured in 60% methanol, 40% dichlorobenzene.

The resulting three-layer cast layer had a core layer thickness of approximately 415 micrometers, and each surface layer was approximately 110 micrometers thick for a total thickness of 635 micrometers. The intermittent laboratory extruder was used to stretch the three layer cast film resulting in about 6 to 1 in the machine direction (DM) at a temperature of about 129 ° C. Because the edges of the sample of the film parallel to the direction of the stretch were not held by the laboratory extruder, the sample was not compressed in the transverse direction (DT) and the sample was lowered in the DT direction approximately 50% as a result of the stretching procedure.

The optical development 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 is developed as an energy conservation system, with low absorption.

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 were varied as shown in the Table. l. The IV of the PEN resin in the central layer and that of the surface layers was the same for a given sample. The total thickness of the cast sheet was approximately 625 micrometers with approximately two thirds of this total in the core layer and the balance in the surface layers that were approximately equal in thickness. Several mixtures of PEN and sPS were produced in the central layer, as indicated in Table 1. The films were stretched at a stretch ratio of approximately 6: 1 in the machine direction (MD) or in the transverse direction (DT) at various temperatures as indicated in Table 1. Some of the samples were compressed (C) in the direction perpendicular to the direction of the stretch to prevent the sample from being lowered during stretching. The samples marked "U" in Table 1 were not compressed and allowed to decrease in the uncompressed direction. Certain optical properties of the stretched samples, including percent transmission, reflection and absorption, were measured along the axes parallel and transverse or perpendicular to the direction of the stretch. The results are summarized in TABLE 1.

The heat setting, as indicated in Examples 24-27, was performed by manually compressing the two ends of the stretched sample which were perpendicular to the direction of the stretch by fastening them to a properly dimensioned rigid frame and casting the sample fastened in an oven. at the indicated temperature for 1 minute. The two sides of the sample parallel to the direction of the stretch were not compressed (U) or not clamped and allowed to lower. The heat setting of Example 29 was similar, except that all four ends of the stretched sample were compressed (C) or clamped. In Example 28, the heat was not fixed.

TABLE 1 00 All the above samples were observed to contain forms that vary from the dispersed phase depending on the location of the dispersed phase within the body of the film sample. The inclusion materials of the dispersed phase located closer to the surfaces of the samples were observed to be of an elongated form rather than closer to the spherical one. Inclusion materials that did not focus more closely 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 tendency for cracking during the stretching operation.

Without wishing to be bound by theory, the elongation of the inclusion materials (dispersed phase) in the central layer of the molten film is thought to be the result of cutting as it is transported through the mold. This characteristic of elongation could be altered by varying the physical dimensions of the mold, the extrusion temperatures, the 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 from the ratio of some elongation to the dispersed phase during extrusion. For those applications that are subsequently stretched in the machine direction, starting with the elongated dispersed phase during extrusion could allow a greater dimensional proportion to be reached in the resulting dispersed phase.

Another notable feature is the fact that a perceptible improvement is observed when the same sample stretches without compressing. Thus, in Example 13, the% transmission was 79.5% and 20.3% in the parallel and perpendicular directions, respectively. In contrast, the transmission in Example 20 was only 75.8% and 28.7% in the parallel and perpendicular directions, respectively. There is an increase in thickness relative to the compressed stretch when the samples are stretched uncompressed, but because the transmission and the extinction improve, the adjustment of the index is probably being improved.

An alternative way to provide control of the refractive index is by modifying the chemistry of the materials. For example, a 30% weight copolymer of interpolymerized units derived from terephthalic acid and 70% weight of units derived from 2,6-naphthalic acid has a refractive index 0.02 units less than 100% PEN polymer. Other monomers or ratios may have slightly different results. This type of change could be used to more closely adjust the refractive index on an axis while only causing a slight reduction in the axis that you want a big difference. In other words, the benefits achieved by greater adjustment of the values of the index in one axis than compensation for the reduction in an orthogonal axis in which a large difference is desired. Subsequently, a chemical change may be desirable to alter the temperature range at which the stretching occurs. A sPS copolymer and variation ratios of the 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 adjustments and differences in the resulting refractive index. A) Yes, an improved control of the final development could be achieved 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 at least one orthogonal axis.

These samples showed better optical development if they are oriented in the MD direction instead of the DT (compare Examples 18 and 19). Without wishing to be bound by theory, it is believed that inclusion materials of different geometry are developed with a DM orientation than with a DT orientation and that these inclusion materials have larger dimensional proportions, making non-ideal lateral effects less important. Non-ideal side effects refer to the ratio of the geometry / refractive index complex at the point of each end of the elongated particles. The interior and non-end of the particles are thought to have a uniform geometry and it is thought that the refractive index is desirable. Thus, the greater the percentage of the elongated particle that is uniform, the better the optical development.

The extinction ratio of these materials is the ratio of the transmission for polarizations perpendicular to the direction of the stretch to the parallel direction of the stretch. 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 without any attempt to optimize the extinction ratio. It is expected that even at higher extinction ratios (eg, greater than 100) can be achieved by adjusting the thickness of the film, volume fraction of the inclusion material, particle size, and the degree of adjustment and mismatch of the index, or through the use of iodine or other dyes.

EXAMPLES 30-100 In Examples 30-100, the samples of the invention were 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 an intrinsic viscosity (VI) of 0.42, 0.47, 0.53, 0.56 and 0.60, respectively, measured in 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., Rochester, NY. Surlyn ™ 1706 is an ionomeric resin available from E.I. du Pont de Nemours & Co., Wilmington, DE. 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 degradation agent of ethyltriphenylphosphonium bromide. PMMA V044 refers to a polymethyl methacrylate commercially available from Atohaas North America, Inc.

Samples of the optical film were produced in a manner similar to Example 4 except for the differences observed in Table 2 and discussed below. The continuous phase and its relation of the total is reported as the major phase. The dispersed phase and its relation of the total is reported as the minor phase. The value reported for the thickness of the mixture represents the approximate thickness of the central layer in micrometers. The thickness of the surface layers varies when the thickness of the surface layer varies, but it was maintained at a constant ratio, p. 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 by electronic detection microscopy (SEM) or electron transmission microscopy (TEMP). Examples in which they were subsequently stretched using an intermittent laboratory orienter are shown by an "X" in the column marked intermittent elongation.

TABLE 2 00 00 00 -OR vO 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 similar to Example 4 except that the thickness of the resulting core layer was about 420 microns. and each surface layer was approximately 105 microns. The PEN had a VI of 0.56. The molten film was oriented as in Example 1, except that the temperature of the stretch was 165 ° C and here it was 15 days of delay between melting and stretching. The transmission was 87.1% and 39.7% for the polarized light, parallel and perpendicular, respectively.

EXAMPLES 102-121 In Examples 102-121, the optical film was made as in Example 101, except that the orientation conditions were varied and / or the sPS-200-0 was replaced with sPS copolymers containing either 4 or 8 mol% of para-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. The Transmission values were averaged over all wavelengths between 450-700 nm.

TABLE 3 These Examples indicate that the particles of the included phase elongate more in the machine direction in the high PEN IV than in the low PEN IV. This is consistent with the observation that, in the low PEN IV, stretching occurs to a greater degree near the surface of the film than at points inside the film, with the result that the fibrillar structures are formed near the film. 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 in achieving the desired effect. Examples 109 to 114 suggest that quiescent crystallization need not be just the reason for the lack of transmission of a preferred polarization of light.

EXAMPLES 122-124 In Example 122, a multilayer optical film was made according to the invention by means of a layer feed block 209. The feed block was fed with two materials: (1) PEN at 38.6 kg per hour (intrinsic viscosity of 0.48); and (2) a mixture of coPEN at 95% and 5% by weight of sPS homopolymer (molecular weight of 200,000). The 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 mixture of coPEN / sPS 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 extruded material, and the composition of the layer of the resulting overlapping layers alternated between the two materials. The thicknesses of the layers were designed to result in a quarter wavelength of the superposed layer with a linear gradient of thickness, and having a ratio of 1: 3 from the thinnest layer to the thickest layer. Next, a thicker surface layer of coPEN (made according to the method described above to make the mixture of coPEN / sPS, except that the molar ratios were naphthalene dicarboxylate / dimethyl terephthalate / dimethyl isophthalate 70/15/15) devoid of sPS was added to each side of the compound of layer 209. The total surface layer was added at a rate of 29.5 kg per hour, with about a quarter of this amount on each side surface of the overlap.

The multilayer composite coated with the resulting surface layer was extruded by means of a multiplier to achieve a multilayer composite of 421 layers. The resultant multilayer composite was coated with another surface layer of coPEN 70/15/15 on each surface at a total rate of 29.5 kg per hour with about one quarter of this amount on each side. Because this second surface layer could not be separately detectable from the existing surface layer (as the material is the same), for the purpose of this discussion, the resulting additional thickness surface layer will be counted as a single layer.

The composite of the resulting layer 421 was extruded again by means of a 1:40 ratio of asymmetric multiplier to achieve a layer film 841 which was then melted into a sheet by extruding it by means of a mold and turning it off in a sheet of approximately 30 mils of thickness. The resulting cast sheet after oriented in the wide direction using a film-making stretching 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 measurement of the optical gain of the film. The optical gain of a film is the ratio of light transmitted through a low-illumination LCD crystal to the film inserted between the two in transmitted light without the film in the plane. The meaning of optical gain in the context of optical films is described in WO 95/17692 in relation to Figure 2 of this reference. In general, a higher gain value is desired. The transmission values include the values obtained when the light source was polarized parallel to the direction of the stretch (T () and polarized light perpendicular to the direction of the stretch (Tt) The deviated chromatic angle was measured (ACD) using an Oriel spectrophotometer as the square root of the deviation medium of the p-polarized transmission to incident light of 50 degrees wavelength between 400 and 700 nm.

TABLE 4 The value of the deviated chromatic angle (ACD) 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 the ACD with only a modest reduction in gain. This exchange could have advantages in some applications.

The values of T (for the examples of the invention could be lower than expected because the scattered light by the dispersed sPS phase could not be received by the detector.

EXAMPLE 125 A three-layer film was made according to the Example 4. The central layer consisted of 70% coPEN (whose intrinsic viscosity was 0.55 measured in 60% phenol, 40% dichlorobenzene), 30% sPS 200-7, plus an additional 2% Dylark 332-80 ( available from NOVA Chemical). Each layer consisted of 100% coPET having an intrinsic viscosity of 0.65 measured in methylene chloride.

CoPEN was a copolymer based on 62% mol naphthalene dicarboxylate and 38% mol dimethyl terephthalate. The coPET was a copolymer based on 80% mol dimethyl carboxylate and 20 mol% dimethyl isophthalate.

The cast film was oriented in a manner consistent with Example 1. Stretching was performed at 5.8 meters per minute (19 feet per minute) with an output width of 147 cm (58 inches). The stretching temperature was 124 ° C. The heat fixation temperature was 163 ° C. The perpendicular transmission was 85.3% and the parallel transmission was 21.7%.

EXAMPLES 126-130 The following Examples illustrate the production of a co-continuous morphology in an optical system of the present invention.

In Examples 126 to 130, a series of optical films were produced and evaluated in a manner similar to Example 125, except that the fraction of sPS in the core layer and the stretching temperature were varied as shown in Table 5.

TABLE 5 The values of the parallel and perpendicular transmission for Examples 125 to 130 show good optical development. The high value for the perpendicular transmission for Example 130 suggests an effective adjustment of the transmission in the refractive indices in the phases for the polarized light aligned in the direction perpendicular to the direction of the stretch.

Electron detection micrographs were taken from fractured surfaces of the molten network for Examples 126 and 127. As in Example 125, there was clear evidence of spherical and elliptical particles otherwise dispersed in a continuous matrix. The transmission electron micrographs were taken for Examples 129 and 130; these are shown respectively in Figs. 6a and 6b, respectively. Fig. 6a illustrates the morphology of the co-continuous phases. The inspection of the micrograph shows the inclusion materials of the coPEN and the sPS phases, in addition to the regions where each appears to be a continuous phase. On the contrary, Fig. 6b shows the coPEN dispersed in a sPS matrix.

The foregoing description of the present invention is merely illustrative, and is not intended to be limiting. Therefore, the scope of the present invention should be explained only with 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 (63)

1. An optical film, characterized in that it comprises: a first phase; Y a second phase that is co-continuous with the first phase in at least one direction; wherein the first and second phases are polymeric and have refractive indices between the first and second phase of at least about 0.05 along a first axis and less than about 0.05 along a second axis.

2. The optical film of claim 1, characterized in that the second phase is co-continuous with the first phase along at least two mutually orthogonal axes.

3. The optical film of claim 1, characterized in that the second one is co-continuous with the first phase along three mutually orthogonal axes.

4. The optical film of claim 1, characterized in that the optical body is a film, and wherein the second axis is perpendicular to the phase of the plane of the film.

5. The optical film of claim 1, characterized in that the first and second phase are co-continuous in two mutually orthogonal directions.

6. The optical film of claim 1, characterized in that one of the first and second phase has a birefringence of at least about 0.05, and the other of the first and second phase has a birefringence of less than about 0.05.

7. The optical film of claim 1, characterized in that the first phase has a birefringence of at least about 0.1, and the second phase has a birefringence of less than about 0.05.

8. The optical film of claim 1, characterized in that the first phase has a birefringence of at least about 0.2, and the second phase has a birefringence of less than about 0.05.

9. The optical film of the. claim 1, characterized in that the first phase has a birefringence of at least about 0.05, and the second phase has a birefringence of less than about 0.02.

10. The optical film of claim 1, characterized in that the first phase has a birefringence of at least about 0.05, and the second phase has a birefringence of less than about 0.01.

11. The optical film of claim 1, characterized in that the first phase has a refractive index that differs from the second phase by more than about 0.1 along the first axis.

12. The optical film of claim 1, characterized in that the first phase has a refractive index that differs from the second phase by more than about 0.15 along the first axis.

13. The optical film of claim 1, characterized in that the first phase has a refractive index that differs from the second phase by more than about 0.2 along the first axis.

14. The optical film of claim 1, characterized in that the first phase has a refractive index that differs from the second phase by more than about 0.03 along the second axis.

15. The optical film of claim 1, characterized in that the first phase has a refractive index that differs from the second phase by more than about 0.01 along the second axis.

16. The optical film of claim 1, characterized in that the first phase and second phase taken together have a diffuse reflectivity along at least one axis approximately 50% in at least one polarization of electronic radiation.

17. The optical film of claim 1, characterized in that the optical film has a total reflectivity greater than about 50% for a first polarization of electromagnetic radiation and a total transmission greater than about 50% for a second polarization of electromagnetic radiation orthogonal to the first polarization .

18. The optical film of claim 17, characterized in that the optical film has a total reflectivity greater than about 60% for a first polarization of electromagnetic radiation.

19. The optical film of claim 17, characterized in that the optical film has a total reflectivity greater than about 70% for a first polarization of electromagnetic radiation.

20. The optical film of claim 17, characterized in that it has a total transmission greater than about 60% for a second polarization of electromagnetic radiation.

21. The optical film of claim 17, characterized in that it has a total transmission greater than about 70% for a second polarization of electromagnetic radiation.

22. The optical film of claim 1, characterized in that a first polarization of light is reflected substantially diffusely, and wherein at least about 40% of the second polarization of polarized light orthogonal to the first polarization of light is transmitted through the optical film. with a deflection angle of less than about 8o.

23. The optical film of claim 22, characterized in that at least about 60% of the second polarization of light is transmitted through the optical body with a deflection angle of less than about 8 ° C.

24. The optical film of claim 22, characterized in that at least about 70% of the second polarization of light is transmitted through the optical body with a deflection angle of less than about 8 ° C.

25. The optical film of claim 1, characterized in that at least one of the first and second phase comprises a thermoplastic resin.

26. The optical film of claim 25, characterized in that the thermoplastic resin is an aromatic vinyl syndiotactic polymer derived from an aromatic vinyl monomer.

27. The optical film of claim 25, characterized in that the thermoplastic resin comprises interpolymerized units of syndiotactic polystyrene.

28. The optical film of claim 25, characterized in that the thermoplastic resin comprises polyethylene naphthalate.

29. The optical film of claim 25, characterized in that one of the first and second phase comprises syndiotactic polystyrene, and the other of the first and second phase comprises polyethylene naphthalate.

30. The optical film of claim 25, characterized in that both of the first and second phases comprise a thermoplastic polymer.

31. The optical film of claim 1, characterized in that the optical body is stretched at a stretch ratio of at least about 2.

32. The optical film of claim 1, characterized in that the optical body is stretched at a stretch ratio of at least about 4.

33. The optical film of claim 1, characterized in that the optical body is stretched at a stretch ratio of at least about 6.

34. The optical film of claim 1, characterized in that the first and second phases are immiscible.

35. The optical film of claim 1, characterized in that the first phase is an open cell material, and wherein the cells of the first phase are substantially aligned along at least one common axis.

36. The optical film of claim 35, characterized in that the second phase is dispersed within the cells of the first phase.

37. The optical film of claim 35, characterized in that the cells have a dimensional proportion of at least about 2.

38. The optical film of claim 35, characterized in that the cells have a dimensional proportion of at least about 5.

39. The optical film of claim 35, characterized in that the cells are essentially elliptical in cross section.

40. The optical film of claim 1, characterized in that the optical body is stretched in at least two directions.

41. The optical film of claim 1, characterized in that the optical body has a plurality of layers.

42. The optical film of claim 1, characterized in that the extinction ratio of the optical body is greater than about 3.

43. The optical film of claim 1, characterized in that the extinction ratio of the optical body is greater than about 5.

44. The optical film of claim 1, characterized in that the extinction ratio of the optical body is greater than about 10.

45. The optical film of claim 1, characterized in that the optical body is a film, and wherein the difference of the refractive index between the first and second phase is less than about 0.05 along an axis perpendicular to the surface of the film .

46. The optical film of claim 1, characterized in that the diffuse reflectivity of the first and second phases taken together along at least one axis for at least one polarization of visible, ultraviolet or infrared electromagnetic radiation is at least about 30%.

47. The optical film of claim 1, characterized in that the optical body has a specular reflection axis, and wherein the electromagnetic radiation is distributed anisotropically near the axis of specular reflection.

48. The optical film of claim 1, characterized in that the optical body is stretched in at least one direction and has a specular reflection axis, wherein the diffusely reflected portion of at least one polarization of electromagnetic radiation is distributed mainly along or near of the surface of a cone whose axis is centered in the direction of the stretch and whose surface contains the specularly reflected direction.

49. The optical film of claim 1, characterized in that the first and second phase are aligned along a common axis, wherein the optical body is stretched in at least one direction, and wherein the diffusely reflected portion of at least one polarization of electromagnetic radiation is distributed mainly along or near the surface of a cone whose axis is centered on the axis of alignment of the first and second phase and whose surface contains the reflected direction specularly.

50. The optical film of claim 1, characterized in that the optical body has a specular transmission axis, and wherein the electromagnetic radiation is distributed anisotropically near the specular transmission axis.

51. The optical film of claim 1, characterized in that the optical body is stretched in one direction and transmits a first polarization of light spectrally in at least one direction, wherein at least 40% of polarized light orthogonal to a first polarization of light is transmitted diffusely through the optical body, and where the rays of diffusely transmitted light are distributed mainly along or near the surface of a cone whose surface contains the direction of the spectral transmission and whose axis is centered on the direction of the stretch .

52. The optical film of claim 1, characterized in that the second phase comprises elongate inclusion materials whose elongation axes are aligned in a common direction, wherein the optical body is stretched in at least one direction, and wherein at least one polarization of light is transmitted diffusely, and wherein the diffusely transmitted portion of at least one polarization of electromagnetic radiation is distributed mainly along or near the surface of a cone whose axis is centered on the axis of elongation and whose surface contains the transmitted direction diffusely

53. The optical film of claim 1, characterized in that the optical body is a film, and wherein the difference of the refractive index between the first and second phase is at least about 0.02 along an axis perpendicular to the surface of the film .

54. The optical film of claim 1, characterized in that it further comprises a dichroic dye.

55. An optical film, characterized in that it comprises: an interpenetrating network of a first polymer and a second polymer; wherein the difference in refractive index between the first and second polymer is at least about 0.05 along a first axis and less than about 0.05 along a second axis.

56. The optical film of claim 55, characterized by the absolute value of the difference in the refractive index of the first and second phase is? Nx along a first axis and? N2 at the direction of a second orthogonal axis. , and where the absolute value of the difference between n-, and n2 is at least about 0.05.

57. An optical film, characterized in that it comprises: a first open-cell polymer phase a second phase disposed within the cells of the first phase; where the absolute value of the difference in the refractive index of the first and second phase is An ± a along a first y axis? n2 along a second axis orthogonal to the first axis, and wherein the absolute value of the difference between? nj, and? n2 is at least about 0.05.

58. The optical film of claim 57, characterized in that the diffuse reflectivity of the first and second phases taken together along at least one axis for at least one polarization of electromagnetic radiation is at least about 30%.

59. The optical film of claim 57, characterized by the absolute value of the difference between nj. and n2 is at least about 0.1.

60. The optical film of claim 57, characterized in that the first phase has a longer birefringence than the second phase.

61. The optical film of claim 57, characterized in that the birefringence. of the first phase is at least approximately 0.02 greater than the birefringence of the second phase.

62. The optical film of claim 57, characterized in that the birefringence of the first phase is at least about 0.05 greater than the birefringence of the second phase.

63. The optical film of claim 57, characterized in that the first phase contains a network of interconnected pores, and wherein the second phase is arranged in the network.