Optical film, polarizing plate and liquid crystal display device for improving contrast and viewing angle

Abstract

The present invention discloses an optical film, a polarizing plate and a liquid crystal display device for improving contrast and viewing angle, comprising an optical layer, wherein the optical layer comprises: a matrix; and a plurality of polymer dispersions, wherein the x-axis direction becomes the length direction among mutually perpendicular x-axis, y-axis and z-axis, and the plurality of polymer dispersions are randomly arranged in the matrix along the y-axis and z-axis directions, and the plurality of polymer dispersions contain a light absorber, and in the cut surface of the optical layer as the y-z plane, the width of the polymer dispersion is less than 300nm. The present invention can improve contrast, in particular, improve front contrast and side contrast at the same time, thereby improving visibility, and does not reduce brightness characteristics, and can improve viewing angle while improving contrast.

Description

Technical Field

[0001] The present invention relates to an optical film, and more particularly to an optical film, a polarizing plate and a liquid crystal display device for improving the contrast and viewing angle of a display device. Background Art

[0002] The liquid crystal display device operates in such a manner that light emitted from a backlight unit is emitted through a liquid crystal panel. Therefore, in a screen of the liquid crystal display device, the contrast ratio (CR) is excellent at the front side, but the contrast ratio at the side side is generally poorer than that at the front side.

[0003] In order to solve the above problems, attempts have been made to change the liquid crystal panel or liquid crystal structure to improve the side contrast. However, as the side contrast increases, the front contrast inevitably decreases. Therefore, it is necessary to minimize the reduction of the front contrast while increasing the side contrast.

[0004] In addition, as a method of improving the viewing angle, there is a method of diffusing light, and for this purpose, an optical film containing beads can be used. However, it is difficult for an optical film containing beads to ensure a sufficient viewing angle, or even if a sufficient viewing angle is ensured, the brightness can be reduced, and there is almost no contrast improvement effect. Furthermore, such an optical film is difficult to process to express the desired physical properties.

[0005] In order to solve the above-mentioned problems, various methods have been studied to process the difference in refractive index of resin and fine optical patterns on the optical film constituting the liquid crystal display device. However, as the area of ​​liquid crystal display devices gradually increases, it is difficult to form fine optical patterns on the large-area optical film. In particular, it is essentially impossible to uniformly form fine patterns between tens of nanometers and tens of micrometers on a large area, and it is very difficult to achieve large-area while ensuring a yield that can be mass-produced commercially. Summary of the invention

[0006] Technical issues

[0007] The present invention is proposed to solve the above-mentioned problems, and its object is to provide an optical film, a polarizing plate and a liquid crystal display device including the same: the contrast is improved, and in particular, the front contrast and the side contrast are improved at the same time, thereby improving visibility.

[0008] Furthermore, another object of the present invention is to provide an optical film, a polarizing plate including the same, and a liquid crystal display device that can improve the contrast ratio and the viewing angle without reducing the brightness characteristics.

[0009] Solutions to the problem

[0010] In order to solve the problems mentioned above, the present invention provides an optical film for improving contrast and viewing angle, which includes an optical layer, the optical layer includes: a matrix; and a plurality of polymer dispersions, among the mutually perpendicular x-axis, y-axis and z-axis, the x-axis direction becomes the length direction, the plurality of polymer dispersions are randomly arranged in the matrix along the y-axis and z-axis directions, the plurality of polymer dispersions contain black pigments, and in the cut surface of the optical layer serving as the yz plane, the width of the polymer dispersions is less than 300nm.

[0011] In one embodiment of the present invention, in the matrix and the polymer dispersion, the refractive index difference in any two of the three mutually orthogonal axes may be less than 0.05, and the refractive index difference in the remaining one axis may be greater than 0.1.

[0012] In addition, the polymer dispersion may be included in an amount of 35 wt % to 65 wt % relative to the total weight of the matrix and the polymer dispersion.

[0013] And, the light absorber may be included in an amount of 2 to 60 wt % relative to the total weight of the polymer dispersion.

[0014] Furthermore, in the cut surface as the yz plane, the number of polymer dispersions having a thickness of 250 nm or less as the polymer dispersion in the z-axis direction among all the polymer dispersions may be 95% or more.

[0015] Furthermore, in the cut surface as the yz plane, the number of polymer dispersions having a thickness of 120 nm or less as the polymer dispersion in the z-axis direction among all the polymer dispersions may be 60% or more.

[0016] Also, in the cut surface as the yz plane, the number of polymer dispersions having a thickness of less than 50 nm as the polymer dispersion in the z-axis direction among all the polymer dispersions may be 10% or less.

[0017] Furthermore, in the cut surface of the optical layer as the yz plane, the width of the polymer dispersion may be 200 nm or less.

[0018] Furthermore, the haze of the optical film may be 20% or less, and the thickness of the optical layer may be 100 μm or less.

[0019] Furthermore, the optical film may further include a surface layer, wherein the surface layer is integrally formed on at least one surface of the optical layer.

[0020] Furthermore, the present invention provides a polarizing plate, which is arranged on the upper part of the liquid crystal panel as the viewing side, and comprises: an absorbing polarizer; and the optical film of the present invention, which is arranged on the light emitting surface of the absorbing polarizer.

[0021] Furthermore, the present invention provides a liquid crystal display device, comprising: a liquid crystal unit; and the polarizing plate of the present invention, which is disposed at least on a light emitting surface of the liquid crystal unit.

[0022] Effects of the Invention

[0023] The optical film of the present invention can improve the contrast without reducing the brightness or minimizing the reduction in brightness, and in particular, can simultaneously improve the front contrast and the side contrast, thereby improving visibility. And at the same time, the viewing angle can be improved together with the brightness characteristics. At the same time, the optical film of one embodiment of the present invention can prevent the polymer dispersion provided to express this effect from being recognized, and can also prevent the side effects such as the visible bright line phenomenon or light leakage, so it can be widely used as a component of a liquid crystal display device such as a light source component. In addition, it can be applied to glass windows and various polarized lighting industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 FIG. 5 is a scanning electron microscope (SEM) photograph of an optical layer in an optical film according to an embodiment of the present invention.

[0025] Figure 2 and Figure 3 1 is a cross-sectional view and an enlarged cross-sectional view of an optical film according to an embodiment of the present invention.

[0026] Figure 4 The diagram is a schematic diagram illustrating the arrangement of the polymer dispersion in the length direction of the optical layer in the optical film according to one embodiment of the present invention.

[0027] Figure 5a to Figure 5c The figure is a schematic diagram illustrating an aspect ratio, a width, and a thickness of a polymer dispersion disposed in an optical layer in an optical film according to an embodiment of the present invention.

[0028] Figure 6 FIG. 4 is a cross-sectional view of a polarizing plate according to an embodiment of the present invention.

[0029] Figure 7 FIG. 4 is a cross-sectional view of a liquid crystal display device according to an embodiment of the present invention.

[0030] Figures 8 to 10 The following is a schematic diagram of a manufacturing apparatus for manufacturing a comparative example of the present invention and a schematic cross-sectional diagram of the manufactured optical film. DETAILED DESCRIPTION

[0031] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that it can be easily implemented by those skilled in the art. The present invention can be implemented in various different embodiments and is not limited to the embodiments described herein. In the accompanying drawings, parts not related to the description are omitted in order to clearly illustrate the present invention. In the entire specification, the same or similar structural elements are given the same figure numbers. Furthermore, the present invention is not limited to the size or shape of a structure shown in the accompanying drawings. As an example, it should be clear that in Figure 2 and Figure 3 The number and size of the plurality of polymer dispersions shown are merely examples for explaining the present invention, and are not intended to indicate the thickness of the polymer dispersions that fully conform to the present invention. Figure 3 The dotted line shown on one side of the diagram merely illustrates the length direction of the polymer dispersion and does not mean the length of the polymer dispersion inside the matrix which is not shown.

[0032] Reference Figures 2 to 3 An optical film 1000 according to an embodiment of the present invention includes an optical layer 100 , wherein the optical layer 100 includes: a matrix 110 ; and a plurality of polymer dispersions 120 located in the matrix.

[0033] The above-mentioned multiple polymer dispersions 120 may be in a shape such as a rod or fiber that is long in one direction. Therefore, in the multiple polymer dispersions 120, the aspect ratio, which is the ratio between the length of the main axis of the dispersion 120 in the longitudinal direction and the length of the horizontal axis of the cross section perpendicular to the main axis, may be greater than 10. As another example, it may be greater than 100, greater than 1000, greater than 10000, or greater than 100000. When the shape of the above-mentioned cross section is a circle, the above-mentioned horizontal axis length refers to the diameter of the circle. When the cross section is not a circle, the above-mentioned horizontal axis length refers to the length of the longest line segment of the two line segments connecting the surroundings. And, as Figure 5a As shown, in the cross section of the polymer dispersion 120 based on the cut surface of the yz plane of the optical layer 100, the cross-sectional aspect ratio, which is the ratio of the short axis length b to the long axis length a (a / b), may also be greater than 1. When the axis that divides the long axis perpendicularly is referred to as the short axis, the short axis length b refers to the length of the short axis.

[0034] In addition, the plurality of polymer dispersions 120 are arranged in the matrix 110 such that the x-axis direction among the three mutually perpendicular x-axis, y-axis, and z-axis is the longitudinal direction. Figure 2 It is briefly shown in the figure, wherein the arrangement in such a manner that the x-axis direction becomes the length direction does not mean that the length directions of all polymer dispersions 120 are arranged in a manner parallel to the x-axis, but means that the direction of the main axis of the length direction of the polymer dispersion 120 is closer to the x-axis direction than the y-axis and the z-axis.

[0035] In this regard, refer to Figure 4 Specifically, in the xz plane of the optical layer 100, the first polymer dispersion 123 is arranged in a manner that the length direction is parallel to the x-axis direction, and the second polymer dispersion 121 and the third polymer dispersion 122 can be arranged in a manner that the length direction is inclined at a predetermined angle toward the z-axis direction. Figure 4 It is shown, but it should be clear that the polymer dispersion can also be arranged at a predetermined angle tilted toward the y-axis direction. However, as an example, the predetermined angle here can be less than (±) 45°, less than (±) 35°, less than (±) 25°, less than (±) 15°, less than (±) 10°, less than (±) 5°, less than (±) 3°, and less than (±) 1°.

[0036] The polymer dispersions 120 are randomly arranged based on the y-axis and z-axis directions. That is, in the y-axis and z-axis cross sections of the optical layer 100 , the positions of the polymer dispersions 120 are randomly arranged regardless of the cross-sectional size and shape of the polymer dispersions.

[0037] Furthermore, according to an embodiment of the present invention, a birefringent interface may be formed between the matrix 110 and the polymer dispersion 120 contained in the matrix, thereby facilitating the effect of improving contrast. To this end, the matrix 110 and the polymer dispersion 120 need to form a birefringent interface, so that when the matrix 110 is optically isotropic, the polymer dispersion 120 may have birefringence, and conversely, when the matrix 110 is optically birefringent, the polymer dispersion 120 may have optical isotropy. Specifically, when the refractive index of the polymer dispersion 120 in the x-axis direction is nX1, the refractive index in the y-axis direction is nY1, and the refractive index in the z-axis direction is nZ1, and the refractive indexes of the matrix 110 are nX2, nY2, and nZ2, in-plane birefringence between nX1 and nY1 may occur. More preferably, at least one of the X-axis, Y-axis, and Z-axis refractive indices of the matrix 110 and the polymer dispersion 120 may be different. More preferably, when the length direction of the polymer dispersion is the X-axis, the refractive index difference in the Y-axis and Z-axis directions may be 0.05 or less, and the refractive index difference in the X-axis direction may be 0.1 or more. If the refractive index difference in all axes is 0.05 or less, it is difficult to achieve the effects of improving contrast and improving viewing angle. In addition, when the refractive index difference in at least one of the other two axes is 0.1 or more in addition to the X-axis, a linear moiré problem may occur, and in the portion where such a problem occurs, the transmittance may be reduced, thereby having the risk of causing a reduction in brightness.

[0038] Preferably, the matrix 110 may have optical isotropy, and the polymer dispersion 120 may have birefringence, thereby having advantages of reducing distortion of light transmitted through the optical layer 100 and minimizing or preventing color change.

[0039] The above-mentioned matrix 110 can use materials commonly used for optical films without limitation. Preferably, polyethylene naphthalate (PEN), co-polyethylene naphthalate (co-PE N), polyethylene terephthalate (PET), polycarbonate (PC), polycarbonate alloy, polystyrene (PS), heat-resistant polystyrene, polymethyl methacrylate (PMMA), polybutylene terephthalate (PBT), polypropylene (PP), polyethylene (PE), acrylonitrile-butadiene-styrene (ABS), polyurethane (PU), polyimide (PI), polyvinyl chloride (PVC), styrene acrylonitrile (SAN), ethylene vinyl acetate (EVA), polyamide (PA), polyacetal (POM), phenol, epoxy (EP), urea (UF), melanin (MF), unsaturated polyester (UP), silicon (SI) and cycloolefin polymer can be used. As an example, it can be a polycarbonate alloy.

[0040] Furthermore, the above-mentioned polymer dispersion 120 may also use materials commonly used for optical films without limitation. Preferably, polyethylene naphthalate, copolymerized polyethylene naphthalate, polyethylene terephthalate, polycarbonate, polycarbonate alloy, polystyrene, heat-resistant polystyrene, polymethyl methacrylate, polybutylene terephthalate, polypropylene, polyethylene, acrylonitrile-butadiene-styrene, polyurethane, polyimide, polyvinyl chloride, styrene acrylonitrile, ethylene vinyl acetate, polyamide, polyacetal, phenol, epoxy, urea, melanin, unsaturated polyester, silicon and cycloolefin polymers may be used alone or in combination. As an example, polyethylene naphthalate may be used.

[0041] Furthermore, based on the total weight of the matrix 110 and the polymer dispersion 120, the polymer dispersion 120 contained in the optical layer 100 may be contained in an amount of 35 to 65 weight %, and more preferably, the polymer dispersion 120 contained in the optical layer 100 may be contained in an amount of 40 to 65 weight %. If the polymer dispersion is contained in an amount of less than 35 weight %, the density of the polymer dispersion in the optical layer 100 is reduced, and it is difficult to control the size of the polymer dispersion within the scope of the present invention. Furthermore, if the polymer dispersion is contained in an amount of more than 65 weight %, inversion between the matrix and the polymer dispersion may occur. When the matrix is ​​an optically isotropic material, the polymer dispersion having birefringence may become the matrix according to the inversion, thereby increasing the distortion of the light output due to the birefringence of the transmitted light. Furthermore, when the light transmitted through the optical layer 100 is light passing through a color conversion layer such as a color filter, color inversion and color change problems may occur at a large viewing angle.

[0042] And, if Figure 5b As shown, with the cut surface of the optical layer 100 as the yz plane as a reference, the widths W1, W2, W3, and W4 of the polymer dispersion 120 can be less than 300 nm, preferably less than 200 nm, thereby minimizing the light loss of the transmitted light that transmits the optical layer 100 along the z-axis direction to prevent the brightness from being reduced and prevent the polymer dispersion from being recognized by the naked eye. The width of the polymer dispersion 120 refers to the width W1, W2, W3, and W4 projected in two dimensions when the polymer dispersion 120 is observed in the z-axis direction. It should be clear that it is different from the long axis length of the polymer dispersion in the cut surface of the optical layer 100 as the yz plane.

[0043] Furthermore, according to an embodiment of the present invention, in order to achieve a further improved contrast and viewing angle improvement effect, the number of polymer dispersions with a thickness of 250 nm or less in the z-axis direction of all polymer dispersions can be 95% or more, with the cut surface of the optical layer 100 as the yz plane as the reference. The light transmitted through the lower part of the optical film 1000 undergoes light modulation such as reflection and transmission at the interface between the matrix 110 and the plurality of polymer dispersions 120, and constructive interference and destructive interference occur between the lights with different optical paths of reflection and transmission, thereby, a part of the light is emitted through the upper part of the optical film, and another part of the light disappears by destructive interference, and the remaining light can be emitted toward the lower surface or side of the optical film. Therefore, it is difficult for 100% of the light incident from the bottom of the optical film 1000 to be emitted upward, thereby reducing the contrast, viewing angle, and brightness, but the number of polymer dispersions with a thickness of 250 nm or less satisfies 95% or more, which is conducive to preventing such a reduction in contrast, viewing angle, and brightness. If the amount of polymer dispersions having a thickness of less than 250 nm is less than 95%, in other words, if the amount of polymer dispersions having a thickness of more than 250 nm is more than 5%, the brightness, contrast and viewing angle improvement effects may be minimal, and on the contrary, there is a risk of reducing the brightness, contrast and / or viewing angle.

[0044] The thickness of the polymer dispersion means the length of the longest line segment among the line segments around the cross section of the polymer dispersion parallel to the z-axis direction when observing the cross section of the polymer dispersion in the cut surface of the optical layer 100 in the yz plane, and the z-axis direction corresponds to the thickness direction of the optical layer 100. Figure 5c Specifically, the thickness of the fourth polymer dispersion 124 is d1, the thickness of the fifth polymer dispersion 125 is d2, the thickness of the sixth polymer dispersion 126 is d3, and the thickness of the seventh polymer dispersion 127 is d4.

[0045] Furthermore, preferably, the amount of polymer dispersions with a thickness of 120 nm or less may be 60% or more, more preferably 65% ​​or more, even more preferably 70% or more, and further preferably 80% or more, which is conducive to achieving further improved contrast and viewing angle improvement effects and improved brightness characteristics. If the amount of polymer dispersions with a thickness of 120 nm or less is less than 60%, there is a risk of significantly reduced brightness, excessive destructive interference of light in a specific wavelength band, and problems such as reddening of the optical film surface showing a specific color. Furthermore, in the visible light wavelength range, the reflective properties are reduced, which may have the risk of reduced contrast or viewing angle.

[0046] Furthermore, more preferably, when the number of polymer dispersions with a thickness of less than 120 nm is more than 60%, the number of polymer dispersions with a thickness of less than 50 nm is preferably less than 10%. If the number of polymer dispersions with a thickness of less than 50 nm is greater than 10%, the number of polymer dispersions with a thickness of more than 50 nm is relatively reduced, thereby having the risk of reducing the contrast and viewing angle improvement effect. Furthermore, there is a risk of increasing haze characteristics and reducing brightness. Furthermore, an increase in the number of polymer dispersions with a thickness of less than 50 nm not only has the risk of reducing the number of polymer dispersions with a thickness of more than 50 nm, but also has the risk of increasing the distance between these polymer dispersions and further reducing the contrast and viewing angle improvement effect.

[0047] Furthermore, the amount of polymer dispersions having a thickness of greater than 50 nm and less than 120 nm may be greater than 50%, more preferably greater than 60%, and even more preferably greater than 70%, greater than 80%, or greater than 90%, thereby further improving the contrast and viewing angle, while minimizing or preventing color changes in transmitted light through the color filter, thereby further improving color reproducibility.

[0048] And, more preferably, the larger the proportion of the polymer dispersion with a thickness of 50 nm to 90 nm, the better the contrast and viewing angle and the color reproducibility. For example, 45% or more, 55% or more, 60% or more, or 70% or more is preferred.

[0049] Furthermore, the plurality of polymer dispersions 120 disposed in the optical layer are colored by light absorbers, respectively, thereby further improving the contrast improvement effect intended by the present invention. The light absorber may be a pigment such as iodine, Herapathit, or a dichroic substance or carbon black. Based on the total weight of the polymer dispersion, the light absorber may be contained in an amount of 2 wt % to 60 wt %. When the light absorber is contained in an amount of less than 2 wt %, the contrast improvement effect is negligible. When the light absorber is contained in an amount of more than 60 wt %, the amount of transmitted light decreases rapidly relative to the contrast improvement effect, thereby causing a risk of reduced brightness.

[0050] In addition to the light absorber, the polymer dispersion 120 may further include a known pigment having a light absorbing function. The pigment may be an organic pigment, for example, a porphyrin pigment, which can exhibit an effect of absorbing light only in a specific wavelength band.

[0051] In addition, if Figure 2 and Figure 3As shown, the optical film 1000 of one embodiment of the present invention may further include surface layers 211 and 212 disposed on both sides of the optical layer 100. The surface layers 211 and 212 complement the mechanical strength of the optical layer 100 and have the function of protecting the optical layer 100 from external factors. In this case, a separate adhesive layer may be provided between the optical layer 100 and the surface layers 211 and 212, but preferably, the surface layers 211 and 212 may be co-extruded with the optical layer 100 without a separate adhesive layer to form a whole. As a result, not only can the degradation of optical properties caused by the adhesive layer be prevented, but also it is conducive to realizing a further thinned optical film.

[0052] Furthermore, unlike the conventional case where the optical layer is stretched and then bonded to the unstretched surface layer, the surface layers 211 and 212 included in one embodiment of the present invention are co-extruded with the optical layer 100 and then stretched, so that the surface layers 211 and 212 can be stretched along at least one axial direction. As a result, the surface hardness is increased compared to the unstretched surface layer, and the scratch resistance and heat resistance can be improved.

[0053] In order to perform the supporting function of the optical film, the above-mentioned surface layers 211 and 212 can be commonly used surface layer materials. Preferably, polyethylene naphthalate, copolymerized polyethylene naphthalate, polyethylene terephthalate, polycarbonate, polycarbonate alloy, polystyrene, heat-resistant polystyrene, polymethyl methacrylate, polybutylene terephthalate, polypropylene, polyethylene, acrylonitrile-butadiene-styrene, polyurethane, polyimide, polyvinyl chloride, styrene acrylonitrile, ethylene vinyl acetate, polyamide, polyacetal, phenol, epoxy, urea, melanin, unsaturated polyester, silicon and cycloolefin polymer can be used alone or in combination. More preferably, the same material as the composition of the matrix 110 as described above can be used.

[0054] In the above optical film 1000, the thickness of the matrix 110 may be 100 μm or less, more preferably 80 μm or less, more preferably 60 μm or less, further preferably 50 μm or less, further more preferably 15 μm to 50 μm. If the thickness of the matrix 110 is greater than 100 μm, the contrast and viewing angle improvement effects are minimal when the polymer dispersion having the ideal size distribution as described above is dispersed.

[0055] Meanwhile, the thickness of the surface layer may be 5 μm to 20 μm, but is not limited thereto.

[0056] Furthermore, the haze of the optical film 1000 may be 20% or less. If the haze is greater than 20%, the brightness may be reduced, making it difficult to achieve the purpose of the present invention.

[0057] The following is a method for manufacturing the optical film 1000. The optical film 1000 according to an embodiment of the present invention can be manufactured by the following steps: a step of supplying a matrix component, a light absorber, and a polymer dispersion component to an extrusion unit; a step of inducing diffusion in a flow control unit in a manner such that the polymer dispersion component contained in the matrix is ​​randomly arranged; a step of cooling and smoothing; a step of stretching the cooled and smoothed film; and a step of thermally fixing the stretched film.

[0058] First, as step (1), a step of supplying a matrix component, a light absorber, and a polymer dispersion component to an extrusion section may be performed. These components are first mixed and then supplied to a single extrusion section, or each component may be supplied to multiple independent extrusion sections individually, in which case the extrusion section may be composed of more than two. However, preferably, before these components are supplied to the extrusion section, they are sufficiently stirred and mixed and then supplied to a single extrusion section. In this case, the extrusion section may be an extruder, which may also include a heating means to convert the supplied polymer component in a solid phase into a liquid phase.

[0059] In addition, in order to arrange the polymer dispersion component inside the matrix component, it is preferred that there is a fluidity difference between the matrix component and the polymer dispersion component. For this purpose, the two components are designed in a manner that there is a viscosity difference, preferably, the fluidity of the matrix component is better than that of the polymer dispersion component. The matrix component and the polymer dispersion component can be randomly arranged in the matrix component by the viscosity difference while passing through the mixing zone and the screen filtering zone.

[0060] The thickness of the polymer dispersion 120 can be adjusted for the first time by adjusting the process of step (1). Specifically, the thickness or dispersibility of the polymer dispersion can be adjusted by whether the components are sufficiently stirred before being added to the extrusion part to mix the two components or by the discharge amount during extrusion.

[0061] Next, as step (2) of the present invention, diffusion can be induced in the flow control part in such a way that the polymer dispersion components located inside the matrix are randomly arranged. The flow control part can utilize a known flow control part, and as an example, a hanger mold can be utilized. The thickness or dispersibility of the polymer dispersion can be adjusted for the second time by inducing diffusion by means of the flow control part in step (2).

[0062] Then, as step (3) of the present invention, a cooling and smoothing step may be performed. As a step of cooling and smoothing the transferred film in the flow control unit, the film is cooled and solidified under conditions used in a conventional optical film manufacturing process, and then the smoothing step may be performed by a casting roll process or the like.

[0063] Next, as step (4) of the present invention, a step of stretching the cooled and smoothed film may be performed. The stretching may be performed by a stretching process generally performed in an optical film, thereby inducing a refractive index difference between the matrix component and the polymer dispersion component, thereby inducing a light modulation phenomenon at the interface. The stretching may be performed by uniaxial stretching or biaxial stretching, and more preferably, uniaxial stretching may be performed. In the case of uniaxial stretching, as an example, the stretching direction may be the x-axis direction. Furthermore, the stretching ratio may be 3 to 12 times.

[0064] Then, as step (5) of the present invention, a step of heat-fixing the stretched film may be performed. The heat-fixing may be performed by a conventional method, preferably, by using an infrared (IR) heater at a temperature of 180° C. to 200° C. for 0.1 to 3 minutes.

[0065] Reference Figure 6 It is explained that the optical film 1000 of one embodiment of the present invention manufactured by the above manufacturing method can be used to realize the polarizing plate 4000, and is particularly suitable for use as the upper polarizing plate of the lower polarizing plate and the upper polarizing plate. The lower polarizing plate is arranged on the light incident surface of the liquid crystal panel in a manner facing the backlight unit located below the liquid crystal panel, and the upper polarizing plate is arranged on the light emitting surface of the liquid crystal panel. When the optical film 1000 of one embodiment of the present invention is arranged on the light emitting surface of the polarizer of the upper polarizing plate, it has the advantages of significantly improving the contrast through internal light, increasing the viewing angle, and achieving excellent brightness characteristics.

[0066] The polarizing plate 4000 includes an absorbing polarizer 2000 and an optical film 1000 disposed on an upper portion of the absorbing polarizer 2000 for improving contrast and viewing angle.

[0067] The above-mentioned absorption polarizer 2000 is a polarizer that transmits the first polarization (or the second polarization) and absorbs the second polarization (or the first polarization) in the first polarization and the second polarization with mutually orthogonal vibration planes, and is provided with a known polarization layer 2100 having such an optical function. As an example, the above-mentioned polarization layer 2100 can be a substrate film of polyvinyl alcohol or the like dyed with an iodine component or a dichroic pigment. In addition, the above-mentioned iodine component as one of the pigments dyed on the above-mentioned substrate can be iodine and / or an iodine-based compound such as potassium iodide. In addition, the above-mentioned dichroic pigment can use the following known dichroic pigments without restriction, that is, it has a large absorbance in a wide range of wavelengths in the long axis direction of the molecule, and the absorbance in the short axis direction is extremely small, and it has good affinity for the film as a substrate, and can also be dyed in the crystalline region. When the substrate is stretched, it is easy to be oriented together, the color is clear, and the visual contrast is high. Therefore, the present invention does not particularly limit it and omits specific description.

[0068] As an example, the thickness of the polarizing layer 2100 may be 10 μm to 200 μm, but is not limited thereto and may be changed according to the purpose.

[0069] Furthermore, in order to support and protect the polarizing layer 2100, the above-mentioned absorbing polarizer 2000 may be provided with protective films 2210 and 2220 on one side or both sides. The above-mentioned protective films 2210 and 2220 may be used without limitation as protective films used in conventional absorbing polarizing films, and may preferably use polymers with excellent transparency, mechanical strength, thermal stability or moisture resistance. As an example, the above-mentioned protective films 2210 and 2220 may use acetate resins such as triacetyl cellulose (TAC), polyester resins, polyethersulfone resins, polycarbonate resins, polyamide resins, polyimide resins, polyolefin resins, acrylic resins, polynorbornene resins, etc. As an example, the above-mentioned protective film may use triacetyl cellulose film in consideration of optical properties. Alternatively, from the aspects of heat resistance and moisture resistance, it may be a polyester film, and as a specific example, it may be a polyethylene terephthalate film. The in-plane phase difference of the polyethylene terephthalate film may be greater than 8000 nm, or may be 10000 nm to 15000 nm. In addition, the thickness of the protective films 2210 and 2220 may be 50 μm to 150 μm, but is not limited thereto.

[0070] Furthermore, a separate adhesive layer (not shown) may be provided at the interface between the above-mentioned absorption polarizer 2000 and the optical film 1000 to bond them together. The above-mentioned adhesive layer is used for the attachment between the optical films, and can be realized by using a known adhesive component that does not reduce the optical properties. As an example, an adhesive component containing a vinyl alcohol polymer, or a water-soluble crosslinking agent of a vinyl alcohol polymer such as boric acid, boron, glutaraldehyde, melamine, diacetic acid, etc., in combination with an adhesive component can be used alone. Furthermore, the above-mentioned adhesive can be combined with other additives or catalysts such as acids.

[0071] In addition, the polarizing plate 4000 may further include a functional layer 3000 on the optical film 1000. The functional layer 3000 may be a primer layer, a hard coating layer, an anti-fingerprint layer, an anti-reflection layer, an anti-glare layer, a low-reflection layer, an ultra-low-reflection layer, etc. In addition, in order to exert a composite function, the functional layer 3000 may be implemented by stacking a plurality of layers. The thickness of the functional layer 3000 may be appropriately changed in consideration of the type and number of stacked functional layers, and therefore, the present invention has no particular limitation thereto.

[0072] And, if Figure 7As shown, the polarizing plate 4000 of one embodiment of the present invention can be arranged above the liquid crystal panel 5000, that is, the visible side of the liquid crystal display device 8000, facing the backlight unit 7000 arranged below the liquid crystal panel 5000. Specifically, the polarizing plate 4000 can be arranged above the absorptive polarizer to improve the contrast of the internal light emitted from the backlight unit 7000 and passing through the absorptive polarizer 2000 as the lower polarizer, the liquid crystal panel 5000, and the absorptive polarizer in the upper polarizer. In particular, it can prevent the reduction of the front contrast or minimize the reduction of the front contrast while improving the side contrast. At the same time, the viewing angle of the liquid crystal display device 8000 can be improved.

[0073] Specifically, the liquid crystal display device 8000 can be implemented by sequentially arranging a backlight unit 7000, an absorbing polarizer 2000 as a lower polarizer, a liquid crystal panel 5000, a color conversion layer 5300, and a polarizing plate 4000 as an upper polarizer.

[0074] The backlight unit 7000 may be one used in a common liquid crystal display (LCD), and as an example, may be composed of known structures such as a light source, a reflective film, a light guide plate, a light diffusion film, a light focusing film, and a reflective polarizing film.

[0075] Furthermore, the liquid crystal panel 5000 includes: a liquid crystal layer 5100; and support plates 5210 and 5220, which support the upper and lower parts of the liquid crystal layer 5100, and may also include known structures such as electrode lines. Furthermore, the liquid crystal panel 5000 may adopt a vertical alignment (VA) mode, an IPS mode, a patterned vertical alignment (PVA) mode, or a super-patterned vertical alignment (S-PVA) mode, but is not limited thereto.

[0076] In addition, in the present invention, the use of the optical film is explained with liquid crystal display devices as the center, but it is not limited to this. It can be widely used in flat panel display technologies such as projection display, plasma display, electric field emission display, organic light emitting diode (OLED) display, etc. It is not limited to this, and can also be widely used in glass windows, work lighting that requires polarized light, etc.

[0077] The present invention is more specifically described by the following examples, but the following examples do not limit the scope of the present invention, which should be construed as helping to understand the present invention.

[0078] Example 1

[0079] A dispersion component of 97.0 wt% of polyethylene naphthalate with a refractive index of 1.65 and 3 wt% of carbon black as a light absorber and a polycarbonate alloy with a refractive index of 1.58 as a matrix component are dispersed for the first time and fed into a first extrusion section, wherein the polycarbonate alloy comprises 38 wt% of polycyclohexylene dimethylene terephthalate (PCTG) obtained by polymerizing terephthalate with ethyl glycol and cyclohexanedimethanol at a molar ratio of 1:2, 60 wt% of polycarbonate and 2.0 wt% of a heat stabilizer comprising phosphate. As a surface layer component, a raw material comprising the same components as the matrix component is fed into a second extrusion section, and the second extrusion section is prepared by using a flow path machine so that the surface layer is provided on the upper and lower surface layers of the matrix with the same thickness.

[0080] The extrusion temperature of the matrix component and the dispersion component is set to 245°C, and the Cap.Rheo meter is used to confirm that the polymer flow is corrected in such a way that the IV difference between the two components becomes 0.013, and the dispersion is induced in such a way that it is randomly dispersed inside the matrix component through the flow path of the FilterationMixer, and then the surface component is attached to both sides of the matrix component. After that, the polymer is induced to diffuse in the hanger mold with the corrected flow rate and pressure gradient. Specifically, the width of the mold inlet is 200 mm and the thickness is 10 mm, the width of the mold outlet is 1260 mm and the thickness is 0.75 mm, and the flow rate is 1.0 m / min. After that, a smoothing process is performed in the cooling and casting rollers, and the film is stretched 6 times in the longitudinal direction (MD). Next, heat fixing is performed for 2 minutes at a temperature of 180°C in a heater chamber to produce a film having the following characteristics: Figure 2 The cross-sectional structure of the dispersion is randomly dispersed in the optical layer inside the matrix, such as the optical film shown in Table 1 below. In the optical film, the matrix thickness is 60 μm, and a surface layer with a thickness of 30.25 μm is provided on both sides of the main surface of the matrix, that is, the total thickness of the optical film is 125 μm. In the manufactured optical film, the refractive index of the dispersion component is (n x : 1.88, n y : 1.58, n z : 1.58), the refractive index of the matrix component is 1.58.

[0081] Examples 2 to 3

[0082] The production was carried out in the same manner as in Example 1, and an optical film having a changed thickness of the polymer dispersion as shown in Table 1 below was produced by adjusting the extrusion temperature and viscosity of the product.

[0083] Examples 4 to 6

[0084] The optical film was manufactured in the same manner as in Example 2, and the thickness of the manufactured optical layer was changed to manufacture an optical film as shown in the following Table 1.

[0085] Examples 7 to 8

[0086] The optical film was manufactured in the same manner as in Example 3, and the carbon black content was adjusted to produce an optical film as shown in Table 1 below.

[0087] Comparative Example 1

[0088] Specifically, polyethylene naphthalate with a refractive index of 1.65 as a polymer dispersion component (hereinafter referred to as the first component), a polycarbonate alloy with a refractive index of 1.58 as a matrix component (hereinafter referred to as the second component), and a component identical to the matrix component as a surface layer component were added to the Figure 8 The first extrusion part 220, the second extrusion part 221 and the third extrusion part 222, the polycarbonate alloy comprises 38 wt% of polycyclohexylene dimethylene terephthalate obtained by polymerization of terephthalate with ethyl glycol and cyclohexanedimethanol in a molar ratio of 1:2, 60 wt% of polycarbonate and 2 wt% of a heat stabilizer comprising a phosphate. The extrusion temperature of the first component and the second component is set to 295°C, confirmed by a Cap.Rheometer, and the polymer flow is calibrated by IV adjustment, and the extrusion process is performed on the surface layer at a temperature of 280°C. The first component is transferred to the first pressurizing unit 230 (Kawasaki gear pump), and the second component is also transferred to the second pressurizing unit 231 (Kawasaki gear pump). The discharge amount of the first pressurizing unit is 8.9 kg / h, and the discharge amount of the second pressurizing unit is 8.9 kg / h, respectively. The discharged first component and the second component are transferred to the island-type extrusion nozzle 223. At this time, as an island-type extrusion nozzle 223, use such as Fig. 9The island-type extrusion nozzle is used to manufacture the island-type composite material. Specifically, the island-type extrusion nozzle is composed of a total of five nozzle distribution plates (S1, S2, S3, S4, S5). The first component is fed through the first component supply path 50 of the first nozzle distribution plate S1, and the second component is fed through the second component supply path 51, and then sequentially passes through the second nozzle distribution plate S2 to the fourth nozzle distribution plate S4 to be branched and transferred. In the fifth nozzle distribution plate S5, the second component penetrates between the first components to form an island-type composite material in which the first component is dispersed inside the second component, and then is discharged through the discharge port 70 of the sixth nozzle distribution plate S6. At this time, the number of island component layers of the fourth nozzle distribution plate T4 is 400, the diameter of the nozzle hole of the island component supply path is 0.17 mm, and the number of island component supply paths is 25,000. The diameter of the discharge port 70 of the sixth nozzle distribution plate S6 is 15 mm×15 mm. In the feed block 224 of the three-layer structure, the surface layer component flows in from the third extrusion section through the flow path and forms a surface layer on the upper and lower surfaces of the island-type composite flow (matrix polymer). Diffusion of the substrate layer polymer having the surface layer is induced in the hanger mold 225 that corrects the flow rate and pressure gradient in such a way that the aspect ratio of the island-type composite flow becomes 1 / 30295. Specifically, the width of the mold inlet is 200 mm and the thickness is 20 mm, the width of the mold outlet is 960 mm and the thickness is 2.4 mm, and the flow rate is 1 m / min. Thereafter, a smoothing process is performed in the cooling and casting rollers, and the film is stretched 6 times in the longitudinal direction. As a result, the length of the major axis of the first component in the cross section in the longitudinal direction does not change, but the length of the minor axis decreases. Thereafter, heat fixing is performed for 2 minutes at a temperature of 180°C by an infrared heater, thereby producing a film such as Fig.10 An optical film comprising an optical layer in which a plate-shaped polymer dispersion is dispersed. The refractive index of the polymer dispersion component in the manufactured optical film is (n x : 1.88, n y : 1.58, n z : 1.58), the refractive index of the matrix component is 1.58, the aspect ratio of the polymer is about 1 / 180000, the number of layers is 400, the thickness is 84nm, and the major axis length is 15.5mm. In this case, the thickness of the manufactured optical layer is 100μm, including the surface layer on both sides, so that the total thickness of the optical film is 125μm.

[0089] Comparative Example 2

[0090] By carrying out the same operation as in Example 1, an optical film containing no carbon black in the polymer dispersion was produced.

[0091] Experimental Example 1

[0092] The following physical properties were measured for the optical films produced in Examples and Comparative Examples, and the results are shown in Table 1 below.

[0093] 1. Haze

[0094] The haze was measured using a haze and transmittance measuring instrument (product of Nippon Den shoku Kogyo Co.) analyzing device.

[0095] 2. Thickness of polymer dispersion

[0096] When the optical film of the embodiment and comparative example is elongated in the x-axis direction and in the z-axis direction, the film is vertically cut so that the yz plane becomes the cut surface, and a scanning electron microscope photograph is taken of the cut surface. In the taken scanning electron microscope photograph, the thickness of the polymer dispersion in the 5 μm×5 μm area is measured.

[0097] Experimental Example 2

[0098] The optical films manufactured in the examples and comparative examples were subjected to low refractive coating on the upper surface. A polarizing plate was manufactured in which the prepared optical film was bonded to the upper surface of an absorbing polarizer and triacetyl cellulose was provided on the lower surface of the absorbing polarizer. The manufactured polarizing plate was replaced with the polarizing plate on the upper part of the liquid crystal panel of a commercially available liquid crystal display, and the brightness and contrast in the front and side directions were measured, and the results are shown in Table 1 below.

[0099] In this case, the brightness is marked as follows: the brightness measured after replacing the polarizing plate using the embodiment and the comparative example is expressed as a relative percentage, with the brightness measured in the corresponding liquid crystal display without replacing the upper polarizing plate with the polarizing plate provided with an optical film using the embodiment and the comparative example as a benchmark of 100%.

[0100] Table 1

[0101]

[0102]

[0103] As can be confirmed from Table 1, the front and side contrast improvement effects of the examples are greatly improved compared to the optical films of Comparative Examples 1 and 2. However, among the examples, the contrast improvement effect of Example 7, which contains too little light absorber, is negligible, and the brightness is significantly reduced in Example 8, which contains too much light absorber.

Claims

1. An optical film for improving contrast and viewing angle, characterized in that: Comprising an optical layer, the optical layer comprising: matrix; and a plurality of polymer dispersions, wherein among the mutually perpendicular x-axis, y-axis and z-axis of the matrix, the x-axis direction becomes the length direction of the plurality of polymer dispersions, and the plurality of polymer dispersions are randomly arranged in the matrix along the y-axis and z-axis directions; The plurality of polymer dispersions contain a light absorber, the thickness of the optical layer is 100 μm or less, and the width of the polymer dispersion is 300 nm or less in a cut surface of the optical layer with the optical layer being a yz plane; In the cut surface of the optical layer serving as the yz plane, the number of polymer dispersions whose thickness in the z-axis direction is less than 250 nm among all polymer dispersions is more than 95%; in the cut surface of the optical layer serving as the yz plane, the number of polymer dispersions whose thickness in the z-axis direction is less than 120 nm among all polymer dispersions is more than 60%.

2. The optical film for improving contrast and viewing angle according to claim 1, characterized in that: In the matrix and the polymer dispersion, the difference in refractive index in the y-axis and z-axis directions is 0.05 or less, and the difference in refractive index in the x-axis direction is 0.1 or more.

3. The optical film for improving contrast and viewing angle according to claim 1, characterized in that: The polymer dispersion comprises 35 wt % to 65 wt % of the polymer dispersion relative to the total weight of the matrix and the polymer dispersion.

4. The optical film for improving contrast and viewing angle according to claim 1, characterized in that: The light absorber is contained in an amount of 2 to 60 wt % relative to the total weight of the polymer dispersion.

5. The optical film for improving contrast and viewing angle according to claim 1, characterized in that: In the cut surface of the optical layer as the yz plane, the number of polymer dispersions having a thickness of less than 50 nm as the polymer dispersion in the z-axis direction among all the polymer dispersions is 10% or less.

6. The optical film for improving contrast and viewing angle according to claim 1, characterized in that: The width of the polymer dispersion in the cut surface of the optical layer as the yz plane is 200 nm or less.

7. The optical film for improving contrast and viewing angle according to claim 1, characterized in that: The optical film has a haze of 20% or less.

8. The optical film for improving contrast and viewing angle according to claim 1, characterized in that: The optical film further includes a surface layer, and the surface layer is integrally formed on at least one surface of the optical layer.

9. A polarizing plate, arranged on the upper part of a liquid crystal panel as a viewing side, characterized in that: The polarizing plate includes: An absorbing polarizer; and an optical film according to any one of claims 1 to 8, arranged on the light emitting surface of the absorbing polarizer.

10. A liquid crystal display device, characterized in that: include: Liquid crystal cell; And the polarizing plate according to claim 9 is arranged at least on the light emitting surface of the liquid crystal cell.

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