MXPA97010372A - Polymeric film in multicapas with additional coatings or layers - Google Patents

Abstract

A multilayer polymeric film having an optical stacking including a plurality of alternating polymer layers, with surface layers having mechanical, optical or chemical properties that differ from those of the layers in the optical stacking, is described.

Description

POLYMERIC FILM IN MULTICAPS WITH ADDITIONAL COATINGS OR LAYERS BACKGROUND OF THE INVENTION Layered optical stacks or stacks are well known to provide a wide variety of optical properties. Such multilayer stacks can act as reflective polarizers or mirrors, which reflect light of all polarizations. They can also function as selective wavelength reflectors such as "cold mirrors" that reflect visible light but transmit infrared or "hot mirrors" that transmit visible light and reflect the infrared. Examples of a wide variety of multi-layer stacks that can be constructed are included in the North American patent application 08 / 402,041 filed on March 10, 1995. A problem with multilayer stacking as known in the art is that the stacks themselves they may not have the desired physical, chemical or optical properties. Therefore some way to otherwise provide these desirable properties would be useful.

BRIEF DESCRIPTION OF THE INVENTION According to one embodiment of the invention, a multilayer film has one or both of its main surfaces adhered to at least one additional layer selected for its mechanical, chemical or optical properties, which differ from the properties of the materials of the layers of optical stacking.

REF: 26358 According to another embodiment of the invention, a multilayer film has an additional layer adhered to one or both of its surfaces that will protect the multilayer optical stack.

Brief description of the drawings. Figures 1A 1B and 2 show the preferred multilayer optical film; Figures 3 to 8 show the transmission spectra for the multilayer optical films of examples 1 to 6; Figure 9 shows a multilayer film of the invention having an additional layer adhered to one of its main surfaces; Figure 10 shows a multilayer film according to the invention, which has additional layers adhered to both of its main surfaces; and Figure 11 shows a multilayer film having an additional layer adhered to one of its main surfaces and two additional layers adhered to its other main surface.

Detailed description. Multilayer optical film. The advantages, features and fabrication of multilayer optical films are described more fully in the commonly assigned and co-pending North American patent application 08 / 402,041, filed on March 10, 1995 entitled OPTICAL FILM which is incorporated in the present by reference. Multilayer optical film is useful, for example, as highly efficient mirrors and / or polarizers. A relatively brief description of the properties and characteristics of the multilayer optical film is presented below, followed by a description of the illustrative embodiments of the backlight systems using the multilayer optical film according to the present invention. Multilayer optical films as used in conjunction with the present invention exhibit a relatively low absorption of incident light, as well as high reflectivity for light rays centered on the shaft as well as normal light rays. These properties generally depend on whether the films are used for a pure reflection or a reflective polarization of the light. The unique properties and advantages of multilayer optical film provides an opportunity to design highly efficient backlight systems which exhibit low absorption losses when compared to known backlight systems. An exemplary multilayer optical film of the present invention as illustrated in Figures 1A and 1B includes a multilayer stack 10, having alternating layers of at least two materials 12 and 14. At least one of the materials has the property of effort-induced birefringence, in such a way that the refractive index (n) of the material is affected by the stretching process. Figure 1A shows a multilayer stack before the stretching process, in which both materials have the same refractive index. The light ray 13 undergoes relatively little change in refractive index and passes through the stack. In Figure 1B, the same stack has been stretched to thereby increase the refractive index of the material 12. The difference in refractive index at each boundary between the layers will cause part of the beam 15 to be reflected. By stretching the multilayer stack over a range of uniaxial to diaxial orientation, a film is created with a range of reflectivities for an incident light polarized in the plane oriented differently. Thus, multilayer stacking can be made useful as reflective polarizers or mirrors. Multilayer optical films, constructed according to the present invention, exhibit a Brewster angle (the angle at which the reflectance goes to zero for incident light at any of the interfaces of the layer) which is very large or is not existing for the polymer layer interfaces. In contrast, the known multilayer polymeric films exhibit relatively small Brewster angles at the interfaces of the layer, to result in undesirable light transmission and / or incidence. The multilayer optical films according to the present invention, however, allow the construction of mirrors and polarizers whose reflectivity for the p-polarized light decreases slowly with the angle of incidence, are independent of the angle of incidence or increase with the angle of incidence that is far from normal. As a result, multilayer stacks can be obtained that have high reflectivity for the s and p-polarized light over a broad bandwidth, and over a wide range of angles. Figure 2 shows two layers of a multilayer stack indicating the three-dimensional refractive indices for each layer. The refractive indices for each layer are n1x, nly and nlz for layer 102 and n2x, n2y and n2z for layer 104. The relationships between the refractive indices in each film layer to another and in relation to those of the others The layers in the stack of the film determine the reflectance behavior of the multilayer stack at any angle of incidence, from any azimuthal direction. The principles and design considerations described in US Patent Application 08 / 402,041 can be applied to create multi-layer stacks having the desired optical effects for a wide variety of circumstances and applications. The refractive indices of the layers in the multilayer stack can be manipulated and adjusted to produce the desired optical properties. Referring again to Figure 1B, multilayer stacking 10 may include tens, hundreds or thousands of layers and each layer may be fabricated from any number of different materials. The characteristics which determine the choice of materials for a particular stack depend on the desired optical performance of the stack. Stacking can contain as many materials as there are layers in the stack. For ease of manufacturing, preferred optical thin film stacks contain only a few different materials. The boundaries between chemically identical materials or materials with different physical properties can be abrupt or gradual. Except for some simple cases as analytical solutions, in analysis of the posterior type of stratified media with continually varying index it is usually treated as a much larger number of thinner uniform layers that have abrupt borders, but with only a small change in properties between the adjacent layers. Preferred multi-layer stacking consists of low / high refractive index pairs of film layers, wherein each pair of low / high index layers has a combined optical thickness of 1 of the central wavelength of the band that is designed to reflect. Stacks of such films are commonly referred to as quarter-wave stacks. For multilayer optical films concerned with the visible and far infrared wavelength, a quarter-wave stacking design results in each of the layers in the multilayer stack having an average thickness of no more than 0.5 mieras In those applications where reflective films (for example mirrors) are desired, the average transmission desired for the light of each polarization and plane of incidence generally depends on the proposed use of the reflective film. One way to produce a multilayer mirror film is to biaxially stretch a multilayer stack. For a high efficiency reflective film, the average transmission along each stretch direction at normal incidence over the visible spectrum (380-750 nm) is desirably less than 10% (reflectance greater than 90%), preferably less than 5% (reflectance greater than 95%), more preferably less than 2% (reflectance greater than 98%) and even more preferably less than 1% (reflectance greater than 99%). The average transmission at 60 ° from the normal of 380-750 nm is desirably less than 20% (reflectance greater than 80%), preferably less than 10% (reflectance greater than 90%), more preferably less than 5%. % (reflectance greater than 95%) and even more preferably less than 2% (reflectance greater than 98%) and even more preferably less than 1% (reflectance greater than 99%). In addition, asymmetric reflective films may be desirable for certain applications. In any case, the average transmission along a stretch direction may be desirably less than, for example 50%, while the average transmission along the other stretch direction may be desirable, less of for example 20%, on a bandwidth, for example, the visible spectrum (380-750 nm) or on the visible spectrum and the near infrared (380-850 nm). Multilayer optical films can also be designed to operate as reflective polarizers. One way to produce a multilayer reflector polarizer is to uniaxially stretch a multilayer stack. The resulting reflective polarizers have high reflectivity for light, with their plane of polarization parallel to an axis (in the direction of stretching) for a wide range of angles of incidence and simultaneously have low reflectivity and high transm ismissibility for the plane light of polarization parallel to the other axis (in the direction of no stretch) for a high range of incidence angles. By controlling the three refractive indices of each film, nx, ny and nz, the desired behavior of the polarizer can be obtained. For many applications, the ideal reflective polarizer has high reflectance along one axis (the so-called extinction axis) and zero reflectance along the other (the so-called transmission axis) at all incident angles. For the transmission axis of a polarizer, it is generally desirable to maximize the transmission of polarized light in the direction of the transmission axis over the bandwidth of interest and also over the range of angle of interest. The average transmission at normal incidence for a polarizer on the transmission axis through the visible spectrum (380-750 nm for a bandwidth of 300 nm) is desirably at least 50%, preferably at least 70% , more preferably at least 80% and even more preferably at least 90%. The average transmission at 60 ° from normal (measured along the transmission axis for polarized light p) for a 380-750 nm polarizer is desirably at least 50%, preferably at least 70%, more preferably at least 80% and even more preferably at least 90%. The average transmission for a multi-layer reflective polarizer at normal incidence for polarized light in the direction of the extinction axis through the visible spectrum (380-750 nm for a bandwidth of 300 nm) is desirably at least 50. %, preferably less than 30%, more preferably less than 15% and even more preferably less than 5%. The average transmission at 60 ° from normal (measured along the transmission axis for the p-polarized light) for a polarizer for polarized light in the direction of the extinction axis of 380-750 nm is desirably less than 50 %, preferably less than 30%, more preferably less than 15% and even more preferably less than 5%. For certain applications, the high reflectivity for p-polarized light with its polarization plane parallel to the transmission axis at off-center angles is preferred. The average reflectivity for polarized light along the axis of remission should be more than 20% at an angle of at least 20 ° from normal. In addition, although reflective polarizing films and symmetrical films are discussed separately herein, it should be understood that two or more such films could be provided to reflect substantially all of the light incident thereon (provided they are properly oriented). one with respect to the other to do this). This construction is normally desired when the layered optical film is used as a reflector in a backlight system according to the present invention. If any reflectivity occurs along the transmission axis, the efficiency of the polarizer at out-of-normal angles can be reduced. If the reflectivity along the axis of remission is different for several wavelengths, color can be introduced into the transmitted light. One way to measure color is to determine the root mean square (RMS) value of the transmitivity at an angle or selected angles over the wavelength range of interest. The color of RMS% CR S. can be determined according to the equation: where the range 11 to 12 is the range of wavelength or bandwidth of interest, C is the transmittance along the transmission axis and T is the average transmittance along the transmission axis in the range of wavelength of interest. For applications where a low color polarizer is desirable, the color of RMS% should be less than 10%, preferably less than 8%, more preferably less than 3.5%, and even more preferably less than 2% a an angle of at least 30 ° from normal, preferably at least 30% of normal, preferably at least 45% of normal and even more preferably at least 60% of normal. Preferably, a reflective polarizer combines the desired RMS% color along the transmission axis for the particular application with the desired amount of reflectivity along the extinction axis, through the bandwidth of interest. For polarizers having a bandwidth in the visible range (400-700 nm or a bandwidth of 300 nm), the average transmission along the axis of extinction at normal incidence is desirably less than 40%, more desirably less 25%, preferably less than 15%, more preferably less than 15% and even more preferably less than 3%.

Material selection and processing With the design considerations described in the aforementioned US Patent Application 08 / 402,041, those skilled in the art will readily appreciate that a wide variety of materials can be used to form multilayer reflecting films or polarizers according to the invention, when proceeding under the aforementioned conditions to produce the desired refractive index ratios. The desired refractive index ratios can be obtained in a variety of ways, including stretching during or after film formation (eg, in the case of organic polymers), extrusion (e.g. case of liquid crystalline materials) or coating. In addition, it is preferred that the two materials have similar rheological properties (e.g., melt viscosities) such that they can be coextruded. In general, appropriate combinations can be obtained by selecting, as the first material, a crystalline or semi-crystalline or liquid crystalline material, preferably a polymer. The second material, in turn, can be crystalline, semi-crystalline or amorphous. The second material may have an opposite birefringence or the same as that of the first material. Or the second material may not have birerefingency. It should be understood that in the polymer art, it is generally recognized that polymers are not normally fully crystalline and therefore, in the context of the present invention, crystalline or semi-crystalline polymers refer to those polymers that are non-amorphous and include any of those materials that are commonly referred to as crystalline, partially crystalline, semi-crystalline, etc. The second material may have a birefingency opposite to, or the same as, those of the first material. Or the second material may not have birerefingency. Specific examples of suitable materials include polyethylene naphthalate (PEN) and isomers thereof (eg, 2,6-, 1, 4-, 1,5-, 2,7- and 2,3-PEN), polyalkylene terephthalates , (for example, polyethylene terephthalate, polybutylene terephthalate and poly-1,4-cyclohexanedimethylene terephthalate), polyimides (e.g., polyacrylic imides), polyetherimides, atactic polystyrene, polycarbonates, poly methacrylates (e.g., polyisobutyl methacrylate) , polypropylmethacrylate, polethylmethacrylate and polymethylmethacrylate), polyacrylates (for example, polybutylacrylate and polymethyl acrylate), syndiotactic polystyrene (sPS), syndiotactic poii-alpha-methylstyrene, syndiotactic polydichlorostyrene, copolymers and blends of any of these polystyrenes, cellulose derivatives (e.g., ethyl cellulose, cellulose acetate, cellulose propionate, cellulose acetate butyrate and cellulose nitrate), polyalkylene polymers (e.g., polyethylene, polypropylene, polybutylene) , polyisobutylene and poly (4-methyl) pentene), fluorinated polymers (eg, perfluoroakoxy resins, polytetrafluoroethylene, fluorinated copolymers of ethylene-propylene, polyvinylidene fluoride and polychlorotrifluoroethylene), chlorinated polymers (eg, pilivinylidene chloride and polyvinyl chloride) , polysulfones, polyether sulfones, polyacrylonitrile, polyamides, silicone resins, epoxy resins, polyvinyl acetate, polyether-amides, ionomer resins, elastomers (for example, polybutadiene, polyisoprene and neoprene) and polyurethanes. Also suitable are copolymers, for example, PEN copolymers (for example, 2,6-, 1,4-, 1,5-, 2,7- and / or 2,3-naphthalene dicarboxylic acid copolymers or esters of the same, with (a) terephthalic acid or esters thereof; (b) isophthalic acid or esters thereof; (c) phthalic acid or esters thereof; (d) alkanoglycols; (e) cycloalkane glycols (e.g., cyclohexane, dimethanediol); (f) alean dicarboxylic acids; and / or (g) cycloalkane dicarboxylic acids (eg, cyclohexanedicarboxylic acid), copolymers of polyalkylene terephthalates (e.g., copolymers of terephthalic acid or esters thereof, with (a) naphthalene dicarboxylic acid or esters thereof; ) isophthalic acid or esters thereof, (c) phthalic acid or esters thereof, (d) alkane glycols, (e) cycloalkane glycols (eg, cyclohexane methanol diol), (f) alean dicarboxylic acids and / or (g) cycloalkane dicarboxylic acids (for example, cyclohexanedicarboxylic acid) and styrene copolymers (for example, styrene-butadiene copolymers and styrene-acrylonitrile copolymers), 4, 4'-dibenzoic acid and ethylene glycol In addition, each individual layer may include mixtures of two or more of the polymers or copolymers described above (for example, mixtures of sPS and atactic polystyrene) The described coPEN may also consist of a mixture of agglomerates, wherein at least one component is a naphthalene dicarboxylic acid-based polymer and other components are other polyesters or polycarbonates, such as PET, a PEN or a coPEN. Particularly preferred combinations of layers in the case of polarizers include PEN / coPEN, polyethylene terephthalate (PET) / coPEN, PEN / sPS, PET / sPS, PEN / Estar and PET / Estar where "coPEN" refers to a copolymer or mixture based on naphthalene dicarboxylic acid (as described above) and Estar is polycyclohexanedimethylene terephthalate, commercially available from Eastman Chemical Co. Particularly preferred combinations of layers, in the case of reflective films include PET / Ecdel, PEN / Ecdel, PEN / sPS, PEN / THV, PEN / co-PET and PET / sPS, where "co-PET" refers to a copolymer or mixture based on terephthalic acid (as described above), Ecdel is a polyester commercially available thermoplastic from Eastman Chemical Co. and THV is a commercially available fluoropolymer from Minnesota Mining and Manufacturing Co., St. Paul, Minnesota. The number of layers in the film is selected to obtain the desired optical properties by using the minimum number of layers for reasons of film thickness, flexibility and economy. In the case of polarizers and reflective films, the number of layers is preferably less than 10,000 more preferably less than 5,000 and even more preferably less than 2,000. As discussed above, the ability to obtain the desired relationships between the various refractive indices (and thus the optical properties of the multilayer film) is influenced by the processing conditions used to prepare the multilayer film. In the case of organic polymers which can be oriented by stretching, the films are generally prepared by coextruding the individual polymers to form a multilayer film and then film orientation by stretching at a selected temperature, optionally followed by setting thermal at a selected temperature. Alternatively, extrusion and orientation steps can be carried out simultaneously. In the case of polarizers, the film is stretched substantially in one direction (uniaxial orientation), whereas in the case of reflective films, the film is stretched substantially in two directions (biaxial orientation). The film can be allowed to relax dimensionally in the transverse stretch direction of the natural reduction in the transverse stretch (equal to the square root of the stretch ratio); it may simply be restricted to limit any substantial change in transverse stretch dimension or it may be actively stretched in the transverse stretch dimension. The film can be stretched in the direction of the machine, such as with an orientator of length or width when using a tensioner branch. The pre-stretching temperature, the stretching temperature, the drawing speed, the stretching ratio, the thermal setting temperature, the thermal setting time, the thermal setting relaxation and the stretching of the cross stretch are selected to produce a film in multilayer that has the desired ratio of the refractive index. These variables are interdependent; for example, a relatively low stretch speed could be used if it is coupled with, for example, a relatively low stretch temperature. It will be apparent to those of ordinary skill in the art how to select the appropriate combination of these variables to obtain the desired multilayer film. However, in general a stretch ratio in the range of 1: 2 to 1: 10 (more preferably 1: 3 to 1: 7) in the direction of stretching and from 1: 0.2 to 1: 10 (more preferably from 1: 0.2 to 1: 7) orthogonal to the direction of stretching is preferred. Suitable multilayer films can also be prepared by using techniques such as centrifugation coating (eg, as described in Boese et al., J. Polym, Sci .: Part B, 30: 1321 (1992)) for birefringent polyimides. and vacuum deposition (eg, as described by Zang et al., Appl. Phys. Letters, 59: 823 (1991)) for crystalline organic compounds; The latter technique is particularly useful for certain combinations of crystalline organic compounds and inorganic materials. Multilayer reflective mirror films and reflective multilayer reflective polarizers will now be described in the following examples.

Example 1 PEN THV 500, 499, mirror A coextruded film containing 499 layers is manufactured by extruding the melted ribbon in one operation and subsequent orientation of the film in a laboratory film stretching apparatus. A polyethylene naphthalate (PEN) with an intrinsic viscosity of 0.53 dl / g (60 wt.% Phenol / 40 wt.% Dichlorobenzene) is supplied by an extruder at a rate of 25.4 Kg. (56 Ib) per hour and THV 500 (a fluoropol available from Minnesota Mining and Manufacturing Company) is supplied by another extruder at a rate of 5.0 Kg / hour (11 pounds) per hour. The PEN was on the surface layers and 50% of the PEN was present in the two surface layers. The feed block method was used to generate 57 layers which were passed through 3 multipliers that produced an extruded product of 449 layers. The cast tape was 0.508 mm (20 mils) thick and 30.5 cm (12 inches) wide. Later the tape was biaxially oriented using a laboratory stretching device that uses a pantograph to hold a square section of film and simultaneously stretched in both directions at a uniform speed. A 7.46 cm square of tape was charged to the extruder at a temperature of about 100 ° C and heated to 140 ° C in 60 seconds. Stretching was then started at 10% / seconds (based on the original dimensions) until the sample was stretched approximately 3.5x3.5. Immediately after stretching the sample was cooled by blowing it with air at room temperature. Figure 3 shows the transmission of this film in multilayers. Curve (a) shows the response at normal incidence for polarized light in the direction of transmission, while curve (b) shows the response at 60 ° for p-polarized light in the direction of transmission.

Example 2 (PEN: PMMA, 601, mirror) A co-extruded film containing 601 layers was made on a sequential flat film manufacturing line via a co-extrusion process. Polyethylene naphthalate (PEN) with an intrinsic viscosity of 0.57 dl / g (60 wt.% Phenol / 40 wt.% Dichlorobenzene) was supplied by an extruder A at a rate of 51.7 Kg. (114 Ib) per hour, 29 Kg. (64 Ib) go to the feed block and the rest goes to the surface layers described below. PMMA (CP-82 of ICI of Americas) was supplied by extruder B at a speed of 27.5 Kg. (61 Ib) per hour, all of it is directed to the feed block. The PEN was on the surface layers of the feed block. The feed block method was used to generate 151 layers using the feed block such as that described in US Patent 3,801,429, after the feed block two symmetric surface layers were coextruded using extruder C, which dosed approximately 13.6 Kg. 30 Ib) per hour of the same type of PEN supplied by the extruder A. This extrusion product passed through two multipliers that produced an extrusion product of approximately 601 layers. U.S. Patent No. 3,565,985 describes similar coextrusion multipliers. The extruded product passes through another device that coextruded surface layers at a total speed of 22.7 Kg. (50 Ib) per hour of PEN from extruder A. The tape was oriented longitudinally at a stretch ratio of approximately 3.2, with the temperature of the tape at approximately 138 ° C (280 ° F). Subsequently the film was preheated to a temperature of about 154 ° C (310 ° F) in about 38 seconds and stretched in the transverse direction at a stretch ratio of about 4.5, at a rate of about 11% per second. Then the film was thermally set at 227 ° C (440 ° F) without allowing relaxation. The thickness of the finished film was approximately 0.0762 mm (3 mils). As seen in figure 4, curve (a), the bandwidth at normal incidence is approximately 350 nm, with an extinction, in band, average greater than 99%. The amount of optical absorption is difficult to measure due to its low value, but it is less than 1%. At an angle of incidence of 50% of normal the s-polarized light (curve (b)) and p-polarized light (curve (c)) showed similar extinctions and the bands moved to shorter wavelengths as Was expected. The red band edge for s-polarized light is not shifted to blue as much as for p-polarized light, due to the larger bandwidth expected for s-polarized light and due to the lower index seen by light p -polarized in the PEN layers.

Example 3 (PEN: PCTG, 449, polarizer) A coextruded film containing 481 layers was made by extruding the cast ribbon in one operation and later orienting the film in a laboratory film stretching apparatus. The power block method was used with a 61-layer power block and three multipliers (2x). Thick surface layers were added between the final multiplier and the nozzle or mold. Polyethylene naphthalate (PEN) with an intrinsic viscosity of 0.47 dl / g (60 wt.% Phenol / 40 wt.% Dichlorobenzene) was supplied to the feed block by an extruder at a speed of 11.3 Kg. (125.0 Ib. ) per hour. Glycol modified polyethylene dimethyl cyclohexane terephthalate (PCTG 5445 from Eastman) was supplied by another extruder at a rate of 11.3 Kg (25.0 Ib) per hour. Another PEN stream from the previous extruder was added as surface layers after the multipliers at a rate of 11.3 Kg (25.0 Ib) per hour. The cast tape was 0.017 cm (0.007 inches) thick and 30.48 cm (12 inches) wide. The tape was oriented in layers uniaxially using a laboratory stretching device that uses a pantograph to hold a section of film and stretched in one direction at a uniform speed, while allowing it to relax freely in the other direction. The loaded tape sample was approximately 5.40 cm wide (the direction unrestricted) and 7.45 cm long between the pantograph holders. The tape was loaded to the stretching apparatus at approximately 100 ° C and heated to 135 ° C for 45 seconds. Then the stretching was started at 20% / sec (based on the original dimensions) until the sample was stretched to approximately 6: 1 (based on measurements from fastener to fastener). Immediately after stretching, the sample was cooled by blowing with air at room temperature. In the center, it was found that the sample relaxed by a factor of 2.0. Figure 5 shows the transmission of this multilayer film, where curve (a) shows the transmission of polarized light in the non-stretch direction at normal incidence, curve (b) shows the transmission of p-polarized light , in the direction of non-stretching at an incidence of 60 ° and curve (c) shows the transmission of polarized light in the direction of stretching at normal incidence. The average transmission for curve (a) of 400-700 nm is 89.7%, the average transmission for curve (b) of 400-700 nm is 96.9% and the average transmission for curve (c) of 400- 700 nm is 4.0%. The color of RMS% for curve (a) is 1.05% and the color RMS% for curve (b) is 1.44%.

Example 4 (PEN: CoPEN, 601, polarizer) A coextruded film containing 601 layers is processed in a sequential flat film manufacturing line via a co-extrusion process. A polyethylene naphthalate (PEN) with an intrinsic viscosity of 0.54 dl / g (60% by weight of phenol plus 40% by weight of dichlorobenzene) is supplied by an extruder at a rate of 34 Kg. (75 Ib) per hour and the coPEN is supplied by another extruder at 29.5 kg (65 lb) per hour. The coPEN consisted of a copolymer of 70 mol% of methyl ester of 2,6-naphthalene dicarboxylate, 15% of dimethyl isophthalate and 15% of dimethyl terephthalate with ethylene glycol. The feed block method was used to generate 151 layers. The feed block was designed to produce a stack of films that have a thickness gradient from top to bottom, with a thickness ratio of 1.22 from thinner layers to thicker layers. The PEN surface layers were built on the outside of the optical stack with a total thickness of 8% of the co-extruded layers. The optical stacking was multiplied by 2 sequential multipliers. The multiplication ratio The nominal multipliers were 1.2 and 1.27 respectively. The film was subsequently preheated to a temperature of 154 ° C (310 ° F) in about 40 seconds and stretched in the transverse direction at a stretch ratio of about 5.0 at a rate of 6% per second. The finished film thickness was approximately 0.0508 mm (2 mils). Figure 6 shows the transmission for this film in multilayers. Curve (a) shows the transmission of polarized light in the direction of non-stretch at normal incidence, curve (b) shows the transmission of p-polarized light at incidence of 60 °, and curve (c) shows the transmission of polarized light in the direction of stretching at normal incidence. Note the very high transmission of p-polarized light in the direction of non-stretching at normal incidence and at 60 ° incidence (80-100%). Note also the very high reflectance of polarized light in the direction of stretching in the visible range (400-700 nm) shown by curve (c). The reflectance is almost 100% between 500 and 600 nm.

Example 5 (PEN: sPS, 481, polarizer) A multilayer film of 481 layers is made from a polyethylene naphthalate (PEN) with an intrinsic viscosity of 0.66 dl / g measured in 60 wt.% Phenol and 40% by weight of dichlorobenzene, purchased from Eastman Chemicals and a syndiotactic polystyrene homopolymer (sPS) (weight average molecular weight equal to 200,000 data, sample from Dow Corporation). The PEN was on the outer layers and was extruded at 11.8 Kg. (26 Ib) per hour and the sPS at 10.4 Kg. (26 Ib) per hour. The feed block used produced 61 layers, each of the 61 was approximately the same thickness. Then the three multipliers of the feed block (2x) were used. Surface layers of equal thicknesses that contained the same PEN feed to the feed block were added after the final multiplier at a total speed of 10 Kg. (22 Ib) per hour. The tape was removed through a 30.48 cm (12 inch) wide nozzle or mold to a thickness of approximately 0.276 mm (0.011 inches). The extrusion temperature was 290 ° C. This tape was stored at ambient conditions for 9 days and then it was oriented uniaxially in a tensor branch. The film was preheated to a temperature of about 160 ° C (320 ° F) in about 25 seconds and stretched in the transverse direction at a stretch ratio of about 6: 1 at a rate of about 28% per second. No relaxation was allowed in the stretched direction. The thickness of the finished film was approximately 0.046 mm (0.0018 inches). Figure 7 shows the optical performance of this PEN: sPS reflector polarizer containing 481 layers. Curve (a) shows the transmission of polarized light in the direction of non-stretching at normal incidence, curve (b) shows the transmission of p-polarized light at an incidence of 60 ° and curve (c) shows the transmission of polarized light in the direction of stretching at normal incidence. Note the very high transmission of the p-polarized light at a normal incidence and at an incidence of 60 °. The average transmission for curve (a) over 400-700 nm is 86.2%, the average transmission for curve (b) over 400-700 nm is 79.7%. Note also the very high reflectance of the polarized light in the direction stretched in the visible range (400-700 nm) shown by the curve (c). The film has a transmission of 1.6% for the curve (c) between 400 and 700 nm. The color RMS% for curve (a) is 3.2 while the color RMS% for curve (b) is 18.2%.

Example 6 (PEN: coPEN, 603, polarizer) A reflective polarizer comprising 603 layers is made in a sequential flat film manufacturing line via a co-extrusion process. A polyethylene naphthalate (PEN) with an intrinsic viscosity of 0.47 dl / g (in 60% by weight of phenol plus 40% by weight of dichlorobenzene) is supplied by an extrusion apparatus at a speed of 38 Kg. (83 Ib) per hour and the coPEN is supplied by another extrusion apparatus at 34 Kg. (75 Ib) per hour. The coPEN consisted of a copolymer of 70 mol%, of 2,6-naphthalene dicarboxylate methyl ester, 15 mol% of dimethyl terephthalate and 15 mol% of dimethyl isophthalate with ethylene glycol. The feed block method was used to generate 151 layers. The feed block was designed to produce a film stack that has a thickness gradient from top to bottom, with a ratio of 1.22 from the thinnest layers to the thickest layers. This optical stacking was multiplied by 2 sequential multipliers. The nominal multiplication ratio of the multipliers was 1.2 and 1.4, respectively. Between the final multiplier and the nozzle or mold, composite surface layers were added from the same coPEN described above, supplied by a third extruder to a total speed of 48 Kg (106 Ib) per hour. The film was subsequently preheated to 150 ° C (300 ° F) in about 30 seconds and stretched in the transverse direction at a stretch ratio of about 6 at an initial velocity of about 20% per second. The thickness of the finished film was approximately 0.089 mm (0.0035 in.). Figure 8 shows the optical performance of the polarizer of Example 6. The curve a shows the transmission of polarized light in the direction of non-stretch at normal incidence, curve b shows the transmission of p-polarized light in the direction of non-stretching at an angle of incidence of 50 ° and curve c shows the transmission of polarized light in the direction of stretching at normal incidence. Note the very high transmission of polarized light in the non-stretch direction. The average transmission for the curve at about 400-700 nm is 87%. Note also the very high reflectance of polarized light in the direction stretched in the visible range (400-700 nm) shown by curve b. The film has an average transmission of 2.5% for curve b between 400-700 nm. In addition, the color RMS% of this polarizer is very low. The color RMS% for curve b is 5%. While multilayer optical stacks, as described above, can provide significant and desirable optical properties, other properties, which can be mechanical, optical or chemical, are difficult to provide in the optical stack itself without degrading optical stacking performance . Such properties can be provided by including one or more layers with the optical stack, which provide these properties, while not contributing to the primary optical function of the optical stack itself. Since these layers are normally provided on the main surfaces of the optical stack, they are commonly known as "surface layers".

A surface layer can be co-extruded on one or both of the major surfaces of the multilayer stack during fabrication to protect the multilayer stack from high shear stress along the feed block and nozzle walls and often a foreign layer with the properties The desired chemical or physical properties can be obtained by mixing an additive, such as an ultraviolet light stabilizer, to the polymer melt that makes up the surface layer and coextruding the surface layer with the altered properties on either side of the optical stack. in multilayers during manufacturing. Alternatively, additional layers can be coextruded on the outside of the surface layers during the manufacture of the multilayer film; they can be coated on the multilayer film in a separate coating operation; or the multilayer film can be laminated as a separate film, sheet or rigid or semi-rigid reinforcement substrate such as polyester (PET), acrylic (PMMA), polycarbonate, metal or glass. The adhesives useful for the lamination of the multilayer polymer film to another surface include optically clear and diffuse adhesives and pressure sensitive adhesives and non-pressure sensitive adhesives. Pressure sensitive adhesives are normally adherent at room temperature and can be adhered to a surface by applying almost light finger pressure while non-pressure sensitive adhesives include adhesive systems activated by solvent, heat or radiation. Examples of adhesives useful in the present invention include those based on polyacrylate, polyvinyl ether, diene-containing rubber such as natural rubber, polyisoprene and polyisobutylene; polychloroprene; butyl rubber; butadiene-acrylonitrile polymer; thermoplastic elastomer; block copolymers such as styrene-isoprene and styrene-isoprene-styrene block copolymers, ethylene-ipropylene-diene polymers and styrene-butadiene polymer; poly-a-oletrin; amorphous polyolefin; silicone; ethylene-containing copolymer, such as ethylene vinyl acetate, ethyl acrylate and ethyl methacrylate; polyurethane; polyamide; epoxy; copolymers of polyvinylpyrrolidone and vinylpyrrolidone; polyesters; and mixtures of the above. Additionally, the adhesives may contain adhesives such as adhesives, plasticizers, fillers, antioxidants, stabilizers, pigments, diffusing particles, curing agents, biocides and solvents. Preferred adhesives useful in the present invention include VITEL 3300 a thermal fusion adhesive available from Shell Chemical Co., (Akron, OH) or an acrylic pressure sensitive adhesive, such as Minnesota IOA / AA 90/10 acrylic adhesive Mining and Manufacturing Company, St. Paul, Minnesota. When a laminating adhesive is used to adhere the multilayer film to another surface, the adhesive composition and the thickness are preferably selected so as not to interfere with the optical properties of multilayer stacking. For example, when additional layers are laminated to a multilayer polymer polarizer or mirror, where a high degree of transmission is desired, the lamination adhesive must be optically clear in the wavelength region in which the polarizer or mirror is designed to be transparent. Figures 10 and 11 illustrate multilayer stacks having respectively one and two additional layers respectively. Figures 10 and 11 will be used below to describe a variety of additional layers that can be applied.

An area in which a surface layer having different mechanical properties is desirable, is related in particular to unilaxially oriented multilayer optical stacks, such as reflective polarizers. Such stacks often tend to show low tear strength in the direction of the main stretch. This can lead to reduced performances during the manufacturing process or subsequent breakage of the film during handling or handling. In order to resist thisTear-resistant layers can be adhered to the outer main surfaces of the optical stack. These hard layers may be of any suitable material and may still be the same as one of the materials used in optical stacking. Factors to be considered in the selection of a material for a tear-resistant layer include percent elongation at break, Young's modulus, tear strength, adhesion to inner layers, percent transmittance and absorbance. in an electromagnetic bandwidth of interest, clarity or optical turbidity, refractive indexes as a function of frequency, texture and roughness, thermal stability in the molten state, molecular weight distribution, melt rheology and coextrusion capacity, miscibility and speed of interdifusion between the materials between the hard and optical layers, viscoelastic response, relaxation and crystallization behavior under stretching conditions, thermal stability at use temperatures, weather resistance, ability to adhere to the coatings and permeability to several gases and solvents. Of course, as stated previously, it is important that the chosen material does not have optical properties that are detrimental to those of the optical stack. They can be applied during the manufacturing process or subsequently coated or laminated to the optical stack. The adhesion of these layers to the optical stacking during the manufacturing process such as by means of a co-extrusion process, provides the advantage that the optical stacking is protected during the manufacturing process. In using Figure 10 to illustrate this aspect of the invention, an optical multilayer stack having tear resistant layers 400 is shown. The film 400 includes an optical stack 410. Optical stacking 410 includes alternating layers 412 and 414 of two polymers having different optical properties. Attached to the main surfaces of the optical stack 410 are tear resistant layers 416 and 418. It should be noted that, although layers 416 and 418 in Figure 10 are shown to be thicker than layers 412 and 414, Figure 10 is not to scale for a preferred modality in general. In general it is desirable that each of the layers 416 and 418 have a thickness greater than 5% of the thickness of the optical stack. It is preferred that each of the layers 416 and 418 have a thickness in the range of 5 to 60% of the thickness of the optical stack, to provide tear strength without unnecessarily increasing the amount of material used. Thus, if the optical stack has 600 layers in such a preferred embodiment, the thickness of each of the tear-resistant layers 416 and 418 would be equal to the thickness of 30 to 360 of the layers of the stack. In a more preferred embodiment, each of the tear-resistant layers 416 and 418 would have a thickness in the range of 30% to 50% of that of the optical stack. In a particularly desirable embodiment, the tear-resistant outer layers can be one of the same materials used in the alternating layers 412 and 414. In particular, it has been found that in a reflective polarizer comprising alternating layers PEN and coPEN the outer layers Tear-resistant coPEN can be coextruded during the manufacturing process.

Example 7 A multilayer composite of alternating PEN and coPEN layers to form a reflective polarizer was co-extruded with thick coPEN surface layers to form a tear-resistant reflective polarizer. A coextruded film containing 603 layers was made in a sequential flat film extrusion apparatus. A polyethylene naphthalate (PEN) with an intrinsic viscosity of 0.47 dl / g (in 60% by weight of phenol plus 40% by weight of dichlorobenzene) was supplied by an extruder at a rate of 39 Kg (86 Ib) per hour and the coPEN was supplied by another extruder at 35.4 Kg (68 Ib) per hour. The coPEN was a copolymer of 70 mol% of methyl ester of 2,6-naphthalene dicarboxyiate and 30% of dimethyl terephthalate with ethylene glycol. The feed block extruded 151 layers. The feed block was designed to produce a stack of films that have a thickness gradient from top to bottom, with a thickness ratio of 1.22 from the thinnest layers to the thickest layers. This optical stacking was multiplied by two multiplier sequences. The nominal multiplication ratio of the multipliers was 1.2 and 1.27 respectively. Between the final multipliers and the nozzle, composite layers of coPEN were added, as described above, these layers were loaded and supplied by a third extruder at a total speed of 84.8 Kg (187 Ib) per hour. The film with additional outer layers of coPEN was preheated to 160 ° C (320 ° F) in about 40 seconds and stretched in the transverse direction at a stretch ratio of about 6 at an initial velocity of about 20% per second. The finished film had a thickness of approximately 100 microns, which includes an internal multilayer optical stack of approximately 50 microns and two outer layers (one on each side of the film) of approximately 25 microns in thickness each. The resistance to tearing was improved on the case that did not contain surface coatings, which allowed the creation of coiled rolls of hard reflector polarization. Specifically the tear strength was measured on the films manufactured according to this example and on the film made similar to similar conditions but without surface layers of coPEN using a tear test along the main stretch direction according to ASTM D -1938. The average film thicknesses were 100 microns and 48 microns respectively. The values of the average tear strength were 60.2 and 2.9 grams force with standard deviations of 4.44 and 0.57 grams force respectively. The analysis of the surface layers of coPEN showed low orientation with refractive indexes of 1.63, 1.6 and 1.61 at 633 nm. Good interlayer adhesion was demonstrated by the difficulty of cleanly separating the construction. For further comparison, an optical stacking of 48 microns having external layers of 3.8 microns PEN was tested and found to have an average tear strength of 2.8 grams with a standard deviation of 1.07. The appearance and / or performance of a film can be altered by the inclusion of a surface layer having a dye or pigment that it has in one or more selected regions of the spectrum. This can include portions of the entire spectrum also visible in the ultraviolet and infrared. Of course, if the entire visible spectrum is absorbed, the layer will be opaque. These can be selected in order to change the apparent color of the light transmitted or reflected by the film. They can also be used to complement the properties of the film, in particular where the film transmits some frequencies while reflecting others. The use of the UV absorbent material in a cover layer is particularly desirable because it can be used to protect the inner layers which may be unstable when exposed to UV radiation. A) Yes, Figure 9 illustrates such a film with layer 316 representing a layer containing a material that absorbs the electromagnetic spectrum. Similar to the electromagnetic absorbent materials described above, a fluorescent material could be incorporated in layer 316 of Figure 9 or one or both of layers 416 and 418 of Figure 9. Fluorescent materials absorb electromagnetic energy in the ultraviolet region of the spectrum and re-emit in the invisible. Desirable fluorescent materials include hindered amine light stabilizers (HALS) and are described in more detail in U.S. Patent Application 08 / 345,608, filed on November 28, 1994, the description of which is disclosed herein by reference. Pressure sensitive adhesives form another desirable class of materials that can be applied to a multilayer stack such as layer 316 of FIG. 9 or one of layers 416 or 418 of FIG. 10. In general, adhesives sensitive to Pressure can be applied when the optical stacking is proposed for subsequent lamination to another material, such as a glass or metal substrate. Another material that could be incorporated into a surface layer such as layer 316 or one of layers 416 or 418 would be a slip or slip agent. A slipping agent will make the film easier to handle during the manufacturing process. Normally, a slip or slip agent would be used with a mirror film instead of a film proposed to transmit a portion of the light that hits it. The side that includes the slip agent would normally be the side proposed to be laminated to a support substrate in order to prevent the slip agent from increasing the diffusion associated with reflection. Another type of additional layer that could be used is a protective layer. Such a layer could be resistant to abrasion or resistant to weathering and / or chemical action. Such coatings would be particularly useful in situations where the multilayer film will be exposed to a severe or corrosive environment. Examples of hard or abrasion resistant coatings include hard acrylic coatings such as Acryloid A-11, Paraloid K-120N available from Rhom & amp;; Haas, urethane acrylates such as described in the North American patent No. 4,249,011 and those available from Sartomer Corp.; and hard urethane coatings such as those obtained by reacting an aliphatic polyisocyanate such as Desmodur N-3300, available from Miles Inc., with a polyester such as Tone Polyol 0305, available from Union Carbide. Such layers could also provide protection against the transmission of gases such as oxygen or carbon dioxide or water vapor through the film. Again, this could be a single layer as shown in Figure 9 or layers on both sides as shown in Figure 10. Other layers that could be added include layers containing holographic images, holographic diffusers or other diffusing layers. Such layers could be in a hard polymer or an adhesive. Figure 11 shows an alternative multilayer film 500 having alternating layers 512 and 514 with protective layers 516, 518 and 520. Thus, multiple additional layers could be provided adjacent to a single main surface of the multilayer optical stack. An example of a use for a group structure shown in Figure 11 would be one in which the protective layers 516 and 518 consisted of tear-resistant structures, as described above and the layer 520 an abrasion-resistant layer. The above have been examples of several coatings that could be applied to the exterior of a multilayer stack to alter their properties. In general, any additional layer could be added, which would have mechanical, chemical or optical properties different from those of the layers of the stack itself. 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 refers. Having described the invention as above, property is claimed as contained in the following

Claims (14)

1. Claims 1. A multilayer film including an optical stack comprising layers of a semicrystalline polymer having an average thickness of no more than 0.5 microns and layers of a second polymer having an average thickness of no more than 0.5 microns, characterized in that the optical stack has been stretched in at least one direction to at least twice that dimension in the undrawn direction, the optical stack has first and second major surfaces, the film further comprises a first additional layer adhered to the first main surface , the additional layer is of a material selected in terms of its mechanical properties, the mechanical properties differ from the mechanical properties of the layers of the optical stack.
2. 2. The multilayer film according to claim 1, characterized in that it comprises a second additional layer adhered.
3. 3. An optical film in multilayers having layers of first and second polymers, characterized in that the first and second polymers differ in composition, each of the layers has a thickness of no more than 0.5 microns, the optical stack has first and second major surfaces, the first main surface has a first tear-resistant layer adhered thereto.
4. 4. The multilayer optical film according to claim 3, characterized in that the second main surface has a second tear-resistant layer adhered thereto.
5. 5. The multilayer optical film according to claim 4, characterized in that each of the tear-resistant layers has a thickness greater than 5 percent of the thickness of the optical stack.
6. 6. The multilayer optical film according to claim 5, characterized in that each of the tear-resistant layers has a thickness in the range of 5 percent to 60 percent of the thickness of the optical stack.
7. 7. The multilayer optical film according to claim 6, characterized in that each of the tear-resistant layers has a thickness in the range of 30 percent to 50 percent of the thickness of the optical stack.
8. 8. The multilayer optical film according to claim 5, characterized in that the tear-resistant layers have a composition that is substantially the same as the composition of the second polymers.
9. 9. The multilayer optical film according to claim 8, characterized in that the first polymer is polyethylene naphthalate and the second polymer is a copolyester comprising units of naphthalate and terephthalate.
10. 10. The multilayer optical film according to claim 3, characterized in that the first polymer has a positive tension (or stress) coefficient.
11. 11. A multilayer optical film, which includes an optical stacking comprising layers of a semicrystalline polymer having an average thickness of no more than 0.5 microns and layers of a second polymer having an average thickness of no more than 0.5 microns, characterized in that the optical stacking has been stretched in at least one direction to at least twice that dimension in the undrawn direction, the optical stacking has first and second major surfaces, the film further comprises a first additional layer adhered to the first main surface, the additional layer is of a material selected in terms of its chemical properties, the chemical properties differ from the chemical properties of the layers of the optical stack.
12. 12. The multilayer optical film according to claim 11, characterized in that it also comprises a second adhered additional layer.
13. 13. A multilayer film characterized in that it includes an optical stack comprising layers of a semicrystalline polymer having an average thickness of no more than 0.5 microns and layers of a second polymer having an average thickness of no more than 0.5 microns, wherein the optical stack has been stretched in at least one direction to at least twice that dimension in the undrawn direction, the optical stack has first and second major surfaces, the film further comprises a first additional layer adhered to the first main surface, the additional layer is of a material selected in terms of its optical properties, the optical properties differ from the optical properties of the layers of the optical stack.
14. 14. The multilayer optical film according to claim 13, characterized in that it further comprises a second adhered additional layer.