KR101195852B1 - Optical filter for display device and display device having the same - Google Patents

Abstract

The present invention relates to an optical filter for a display device, and more particularly, an optical filter for a display device and a display device optical filter including the same, which can improve visibility by minimizing color deviation due to an increased viewing angle and reducing reflectance. It is about. In order to achieve the above object, the present invention comprises a first polarizing film, a first retardation film, a second thick film layer, a thin film layer and a first thick film layer sequentially, the thin film layer has a thickness of 780nm or less, the first The thick film layer and the second thick film layer is provided with an optical filter for a display device, characterized in that having a larger thickness than the thin film layer. Preferably, the first retardation film is a 1 / 4λ retardation film. Preferably, the refractive index of the thin film layer is larger than that of the first thick film layer and the second thick film layer. Preferably, the first thick film layer and the second thick film layer have a thickness of greater than 780 nm and 5 mm or less.

Preferably, the average value of the transmittance T according to the following formula for light having a wavelength λ of 380 nm or more and 500 nm or less is equal to the average value of the transmittance T according to the following formula for light having a wavelength greater than 500 nm and less than or equal to 780 nm. To be larger, the thickness l of the thin film layer, the refractive index n of the thin film layer, and the reflectance R at the interface with the thin film layer are adjusted.

T = (1-R) ² / (1 + R ² -2Rcosδ), δ = (2π / λ) 2n l cosθ, 0 ° <θ ≤ 80 °

The present invention also provides a display device comprising the optical filter for the display device.

Description

Optical filter for display device and display device having the same {OPTICAL FILTER FOR DISPLAY DEVICE AND DISPLAY DEVICE HAVING THE SAME}

The present invention relates to an optical filter for a display device, and more particularly, an optical filter for a display device and a display device optical filter including the same, which can improve visibility by minimizing color deviation due to an increased viewing angle and reducing reflectance. It is about.

As the modern society is highly informationized, image display-related components and devices have been remarkably advanced and widespread. Among them, display apparatuses for displaying images are widely used for television apparatuses, monitor apparatuses of personal computers, and the like, and are being enlarged and thinned.

In general, a liquid crystal display is a flat panel display that displays an image using liquid crystal, and is thinner and lighter than other display devices, and has a low driving voltage and low power consumption. It is widely used throughout the industry.

1 is a conceptual diagram conceptually showing the basic structure and driving principle of an LCD. Taking a conventional VA mode LCD as an example, the optical axes of the two polarizing films 110 and 120 are attached to be perpendicular to each other. The liquid crystal molecules 150 exhibiting birefringence are inserted and arranged between the two transparent substrates 130 coated with the transparent electrode 140. When the electric field is applied by the driving power supply unit 180, the liquid crystal molecules are arranged to move perpendicular to the electric field.

The light emitted from the backlight unit becomes linearly polarized light after passing through the first polarizing film 120. When the light is off, as shown in the left side of FIG. 1, the liquid crystal is vertically aligned with respect to the substrate. Is maintained as it is so as not to pass through the second polarizing film 110 perpendicular to the first polarizing film 120.

Meanwhile, in the on state as shown on the right side of FIG. 1, the liquid crystal is horizontally oriented between the optical axes of the two orthogonal polarizing films 110 and 120 in a direction parallel to the substrate by an electric field, and thus linearly polarized through the first polarizing film. The light passes through the second polarizing film by changing to a linearly polarized, circularly or elliptically polarized state in which the polarization state is rotated 90 degrees immediately before reaching the second polarizing film while passing through the liquid crystal molecules. By adjusting the intensity of the electric field, the alignment angle of the liquid crystal is gradually changed from the vertical alignment to the horizontal direction, and the intensity of light emitted from the liquid crystal can be adjusted.

2 is a conceptual diagram illustrating alignment states and light transmittances of liquid crystals according to viewing angles.

When the liquid crystal molecules are arranged in a predetermined direction in the pixel 220, the arrangement state is different depending on the viewing angle.

When viewed from the front side in the right direction 210, the arrangement state of the liquid crystal molecules appears to be almost horizontally aligned 212, and the screen appears relatively bright. When viewed from the front of the screen 230, the arrangement state of the liquid crystal molecules 232 looks the same as the arrangement of liquid crystal molecules in the pixel 220. When viewed from the front in the left direction 250, the arrangement state of the liquid crystal molecules appears in the vertical alignment 252, and the screen appears relatively dark.

Therefore, the LCD generates light intensity and color change according to the change in the viewing angle, and the viewing angle is greatly limited compared to the self-luminous display. Therefore, much research has been conducted for improving the viewing angle.

3 is a conceptual diagram illustrating an example of the related art for improving the contrast ratio change and the color change according to a change in viewing angle.

Referring to FIG. 3, the pixel is divided into two partial pixels, that is, the first pixel portion 320 and the second pixel portion 340 so that the liquid crystal arrangement of each pixel portion is symmetrical to each other. According to the viewing direction, the arrangement of the liquid crystals in the first pixel unit 320 and the arrangement of the liquid crystals in the second pixel unit 340 are simultaneously seen, and the intensity of light visible to the viewer is determined by the light of each pixel unit. It is the sum of the strengths of.

That is, when viewed from the front side in the right direction 310, the liquid crystal of the first pixel portion 320 is shown as the horizontal alignment 312 and the liquid crystal of the second pixel portion 340 is shown as the vertical alignment 314. The screen may be made bright by the one pixel unit 320. Similarly, when viewed from the front in the left direction 350, the liquid crystal of the first pixel portion 320 is shown in the vertical alignment 352, and the liquid crystal of the second pixel portion 340 is shown in the horizontal alignment 354. By the two pixel unit 340, the screen can be seen brightly. When viewed from the front (330) is the same as the arrangement state of each pixel portion. As a result, the brightness of the screen when viewed by the viewer becomes the same or similar as the viewing angle changes, and becomes symmetric about the vertical direction with respect to the screen. Therefore, the change in contrast ratio and the degree of color change according to the change of viewing angle can be improved.

4 is a conceptual diagram illustrating another example of the related art for improving the change in contrast ratio and color change according to a change in viewing angle.

Referring to FIG. 4, an optical film 420 having a birefringence characteristic, the characteristic of which is the same as that of the liquid crystal molecules in the pixel 440 in the LCD panel, and which is symmetric with the arrangement state of the liquid crystal molecules, is added. Due to the arrangement state of the liquid crystal in the pixel 440 and the birefringence characteristic of the optical film 420 according to the viewing direction, the light intensity seen by the viewer is the sum of the light intensities.

That is, when viewed from the front to the right direction 410, the liquid crystal in the pixel 440 is shown in the horizontal alignment 414, the virtual liquid crystal by the optical film 420 is shown in the vertical alignment 412, the light intensity is Each sum. Similarly, when viewed from the front in the left direction 450, the liquid crystal in the pixel 440 is shown in the vertical alignment 454 and the virtual liquid crystal by the optical film 420 is shown in the horizontal alignment 452, the light intensity is Each sum. In the front view 430, the arrangement state of the liquid crystal molecules in the pixel 440 and the birefringent arrangement state of the optical film 420 appear to be the same (432 and 434).

As a result, the change in contrast ratio and color change due to the change of viewing angle is improved, but the luminance and color change according to the viewing angle remain a problem to be solved.

FIG. 5 is a graph illustrating a result of measuring a spectral change by emitting white light at a full gray scale level according to an increase in a viewing angle of an LCD according to the prior art to which the methods of FIGS. 3 and 4 are simultaneously applied.

As shown in FIG. 5, the intensity of the spectrum gradually decreases as the viewing angle increases. In order to accurately investigate the degree of reduction for each wavelength region, normalization is performed by dividing the maximum value of each spectrum as shown in FIG. 6.

As shown in FIG. 6, it can be seen that as the viewing angle increases, the intensity of the normalized spectrum decreases in the blue region of 400 to 500 nm while the other wavelength region is the same. This shows that the light in the blue region of 400 to 500 nm decreases in intensity of the spectrum as the viewing angle increases compared to other wavelength regions. Therefore, as the viewing angle increases, the white state becomes yellow, which is a complementary color of blue, and the image quality is degraded due to this color change.

An object of the present invention is to provide an optical filter for a display device that can improve the display image quality by reducing the color change by selectively increasing or decreasing the transmittance for each wavelength region as the viewing angle increases.

In addition, it is an object to provide an optical filter for a display device that can improve the visibility by reducing the reflectance.

Technical problems to be achieved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

In order to achieve the above object, the present invention comprises a first polarizing film, a first retardation film, a second thick film layer, a thin film layer and a first thick film layer sequentially, the thin film layer has a thickness of 780nm or less, the first The thick film layer and the second thick film layer is provided with an optical filter for a display device, characterized in that having a larger thickness than the thin film layer.

Preferably, the first retardation film is a 1 / 4λ retardation film.

Preferably, the refractive index of the thin film layer is larger than that of the first thick film layer and the second thick film layer.

Preferably, the first thick film layer and the second thick film layer have a thickness of greater than 780 nm and 5 mm or less.

Preferably, the average value of the transmittance T according to the following formula for light having a wavelength λ of 380 nm or more and 500 nm or less is equal to the average value of the transmittance T according to the following formula for light having a wavelength greater than 500 nm and less than or equal to 780 nm. To be larger, the thickness l of the thin film layer, the refractive index n of the thin film layer, and the reflectance R at the interface with the thin film layer are adjusted.

T = (1-R) ² / (1 + R ² -2Rcosδ), δ = (2π / λ) 2n l cosθ, 0 ° <θ ≤ 80 °

Preferably, the transmittance for light having a wavelength of 380 nm or more and 500 nm or less increases as the incident angle of the light increases from 0 degrees to 80 degrees.

Preferably, the transmittance for light with a wavelength greater than 500 nm and less than or equal to 780 nm decreases as the incident angle of the light increases from 0 degrees to 80 degrees.

Preferably, the ratio of the minimum transmittance to the maximum transmittance within a wavelength range of 380 nm or more and 780 nm or less is 0.5 or more and 0.9 or less.

The present invention also provides a display device comprising the optical filter for the display device.

According to the above configuration, color change can be reduced by selectively increasing or decreasing transmittance for each wavelength region as the viewing angle is increased, thereby improving display quality. In addition, there is an effect that can improve the visibility by reducing the reflectance.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

7 is a cross-sectional view for explaining the technical principle of color change reduction according to the viewing angle in the present invention.

As shown in the drawing, a thin film layer 820 is formed in the center, and first and second thick film layers 860 and 840 are formed on both surfaces of the thin film layer 820.

The thickness of the thin film layer 820 may be smaller than or equal to a wavelength range of visible light. Therefore, the thickness of the thin film layer 820 is 780 nm or less. This is because when the thickness of the thin film layer 820 is greater than 780 nm, constructive and destructive interference does not occur in the visible light region.

Meanwhile, the first thick film layer 860 and the second thick film layer 840 are larger in thickness than the thin film layer 820. Therefore, the thicknesses of the thick layers 860 and 840 may be greater than 780 nm and may reach 5 mm. The thicknesses of the first thick film layer 860 and the second thick film layer 840 may be the same or may be different.

The thin film layer 820 has a first refractive index, the first thick film layer 860 has a second refractive index, and the second thick film layer 840 has a third refractive index. The first refractive index may be lower or higher than the second refractive index and the third refractive index.

A low refractive index thin film layer may be formed between the high refractive index thick layers. For example, the refractive index of the first thick film layer 860 and the second thick film layer 840 may be 2 to 4, and the refractive index of the thin film layer may be 1 to 2.

On the contrary, a high refractive index thin film layer may be formed between the low refractive index thick layers. In this case, glass may be used as at least one of the thick film layers. Since the refractive index of the tempered glass is approximately 1.5, when the tempered glass is used as the transparent substrate, the second thick film layer formed in contact with the transparent substrate may be omitted in the configuration of the optical filter.

In addition to the transparent substrate, an adhesive layer or an air layer may also be used as the thick film layer. In addition, an antireflection film, an external light shielding film, an antifog film, and the like formed with a filled wedge pattern of carbon black may also be used as a thick film layer.

As such, in order to adjust the transmittance and reflectance of the light, the refractive indices of the first thick film layer, the second thick film layer, and the thin film layer may be variously modified.

The refractive index of the thin film layer 820 is n, and the refractive indices of the first thick film layer 860 and the second thick film layer 840 are n _t . The refractive indexes of the first thick layer 860 and the second thick layer 840 may be the same, but are not limited thereto.

The first thick film layer 860 is formed on the panel side, and the second thick film layer 840 is formed on the viewer side. Incident and refraction angles of light incident on the first thick film layer 860 satisfy the following conditions according to Snell's law.

n _t sinθ _t = n _O sinθ _O

The thin film layer incident light 880 incident from the panel is partially transmitted while refracting and partially reflected by the difference in refractive index at the interface between the first thick film layer 860 and the thin film layer 820.

An angle formed by the normal to the interface and the incident light 880 is θ _t , and an angle formed by the transmitted light 881 inside the thin film layer that is refracted and transmitted into the thin film layer is θ.

The transmitted light 881 into the thin film layer is a thin film layer transmitted light 882 that is partially refracted at the interface between the thin film layer 820 and the second thick film layer 840 while passing through the second thick film layer. Becomes the internal reflected light 883 of the thin film layer.

In this case, an angle between the thin film layer transmitted light 882 and the normal to the interface between the thin film layer 820 and the second thick film layer 840 is determined by the difference in refractive index between the thin film layer 820 and the second thick film layer 840. . When the refractive indexes of the first thick film layer 860 and the second thick film layer 840 are the same, the angle formed by the thin film layer transmitted light 882 with the normal to the interface between the thin film layer 820 and the second thick film layer 840 is θ _t. to be.

The angle θ _t is the angle (θ _o) and the refractive index of the thick film layer n _t, the refractive index of air that enters the incident light (889) from the panel, the first thick film layer as shown in Equation 1 by the Snell's law (snell) n ₀ (= 1).

Then passes through the incident light (889) a thick film / thin film / thick film layer from the panel transmitting each of the finally emitted light are equal to the incident angle θ _O by Snell's law, and eventually each θ _O corresponds to the viewing angle of a viewer viewing .

The reflectance at each interface is as shown in Equations 2 and 3 below. Here, R _p is a reflectance when p-polarized light is reflected and R _s is a s polarized light is reflected.

R _p = [(n _t cosθ-ncosθ _t ) / (n _t cosθ + ncosθ _t )] ²

R _s = [(ncosθ-n _t cosθ _t ) / (ncosθ + n _t cosθ _t )] ²

It can be seen that the reflectances R _p and R _s are changed by the refractive indices (n, n _t ), the incident angle (θ _t ) and the refractive angle (θ) of the thin film layer and the thick film layer, respectively.

In Equation 4 below, the reflectance R is an average of R _p of Equation 2 and R _s of Equation 3 below.

The internal reflected light 883 of the thin film layer is transmitted while being partially refracted at the interface to become the thin film layer reflected light 887, and part of the reflected light becomes the internal reflected light 884 of the thin film layer, and this process is repeated.

To the transmittance T in the expression (4) is the sum of a transmittance T ₂ by a transmitted light transmissivity T ₁ and the thin film layer 885 by a thin film layer transmitting light (882). Although only two refractive lights are shown in FIG. 7, reflection and refraction continue to occur repeatedly at the interface, and the total transmittance by these refractive lights is the total transmittance T. FIG.

To the sum of a reflectivity R ₂ by a reflected light reflectivity R ₁ and the thin film layer (888) by the reflectance of the reflected light R is also the thin film layer (887) at the interface from the equation (4). Similarly, although only two reflected light are shown in FIG. 7, the total reflectance R by all the reflected light reflected from the interface is the total reflectance R.

In the process of multi-reflecting light by two interfaces by the first thick film layer 860, the thin film layer 820, and the second thick film layer 840, the transmittance may be changed depending on the wavelength due to interference. .

The thickness ( l ) of the thin film layer, the refractive index (n) of the thin film layer, and the first layer such that the average value of the transmittance (T) according to Equation 4 is maximum for light in a blue region having a wavelength λ of 380 to 500 nm. The reflectance R at the interface between the thick film layer and the thin film layer is adjusted.

T = (1-R) ² / (1 + R ² -2Rcosδ)

Here, the phase difference δ of the thin film layer transmitted lights 882 and 885 is expressed by Equation 5 below.

δ = (2π / λ) 2n l cosθ (0 ° ≤ θ ≤ 80 °)

δ is determined by the refractive index n, the thickness l , the refractive angle θ, and the wavelength λ of the thin film layer 820. Depending on the phase difference, constructive interference may occur, and destructive interference may occur. The maximum transmittance is reached when the optical path length difference between each of the thin film layer transmitted lights 882 and 885 is an integer multiple of the wavelength.

The phase difference δ is determined when the refractive index n, the thickness l and the refractive angle θ of the thin film layer are determined for a specific wavelength range. Here, the refractive angle θ is a value that is automatically determined when the refractive indices n and n _t and the viewing angle θ _O of the thin film layer and the thick film layer are determined.

It can be seen from the equations (1) to (3) that the reflectance varies depending on the refractive indices (n, n _t ) and the viewing angle (θ _O ) of the thin film layer and the thick layer. Therefore, the reflectance can be determined by adjusting the refractive indices n and n _t of the thin film layer and the thick film layer with respect to the specific viewing angle θ _O.

As shown in Equation 4, the transmittance T is determined when the reflectance R and the phase difference δ are determined. Therefore, by selecting the refractive index (n, n _t ) and the thickness ( l ) of the thin film layer and the thick film layer it is possible to control the transmittance for light of a specific viewing angle and a specific wavelength.

For example, the thickness of the thin film layer may be selected to be 780 nm or less, and the refractive index of the thin film layer may be determined in the range of 1 to 2, and the refractive index of the thick layer may be in the range of 2 to 4, thereby increasing the transmittance of light in a specific wavelength region in a large viewing angle range. Will be. Alternatively, the same effect can be obtained when the refractive index of the thin film layer is 2 to 4, the refractive index of the thick film layer is 1 to 2, and the refractive index of the thin film layer is higher than that of the thick film layer.

As described above, as the viewing angle increases by using the multi-beam interference, a characteristic in which the intensity of light decreases relatively in the blue wavelength region (380 to 500 nm) may be compensated. That is, when the viewing angle is in the range of approximately 80 degrees, constructive interference occurs in the blue wavelength region to increase the transmittance, and offset interference occurs in the green and red wavelength regions to decrease the transmittance, thereby allowing light in all wavelength regions even when the viewing angle is large. The intensity reduction rate of is equal to or similar to compensate for the imbalance in the blue region. In addition, the transmittance of light having a wavelength of 380 nm or more and 500 nm or less decreases as the incident angle of the light increases from 0 degrees to 80 degrees, but the wavelength is reduced to less than the transmittance of light larger than 500 nm and less than 780 nm. You can also compensate. By using the thick film layer / thin film layer / thick film structure in this way it is possible to minimize the color change according to the change in viewing angle.

Hereinafter, a result of measuring transmittance by employing a thick film / thin film / thick film layer structure on the front of the LCD panel will be described.

As shown in FIG. 7, a thin film layer is formed between the first thick film layer 860 and the second thick film layer 840. The first thick film layer 860 and the second thick film layer 840 have a refractive index of 2.5 and a thickness of 1 mm. The thin film layer 820 has a refractive index of 1.5 and a thickness of 190 nm.

8 is a graph showing transmittance according to a change in viewing angle. As the viewing angle increases, the transmittance increases in some areas of the blue wavelength (380 nm to 460 nm), and the transmittance decreases in some areas of the green and red wavelengths (540 nm to 780 nm). Therefore, as described above, by reducing the sudden spectral reduction rate occurring in the blue wavelength region with increasing viewing angle, and increasing the spectral reduction rate in the green and red wavelength regions, the reduction ratio of the spectrum due to the viewing angle increase in the entire visible wavelength region is the same to It can be adjusted to be similar.

The ratio of the minimum transmittance to the maximum transmittance in the wavelength range of the entire visible light region of 380 to 780 nm is 0.5 to 0.9. That is, as shown in FIG. 8, when the maximum transmittance is 1 in the entire wavelength region, the minimum transmittance is approximately 0.8.

9 shows the change in normalized spectrum with increasing viewing angle. It can be seen that the rate of decrease of the spectrum as the viewing angle increases in the entire wavelength region as well as the blue region is almost the same. This shows that the color change almost disappeared with increasing viewing angle.

FIG. 10 is a graph of change (Δu′v ′) of color coordinates (CIE 1976 L u′v ′) with increasing viewing angle. In the graph, the horizontal axis represents a horizontal angle, that is, a viewing angle. It can be seen from FIG. 10 that the amount of color change in the case of adopting the thick film layer / thin film layer / thick film layer structure is greatly reduced compared with the case in which no thick film layer is employed.

FIG. 11 illustrates a case in which the high refractive index thin film layer is formed to an optimal thickness as a result of changing the color deviation according to the refractive index of the thin film layer (the refractive index of the thick film layer is 1.5) when the structure of FIG. 7 is adopted. The optimum thickness is shown in Table 1 below.

Thin film refractive index 2.065 2.375 2.665 2.965 3.265 Optimum thickness (nm) 246 215 192 173 158

It can be seen that the greater the refractive index of the thin film layer, the greater the effect of improving color shift.

12 is a view showing a change in reflectance according to the refractive index of the thin film layer, when employing the structure of FIG.

As the refractive index of the thin film layer increases, the color shift improvement effect increases. However, as shown in the drawing, the reflectance caused by the difference in refractive index between the thin film layer and the thick film layer increases, which may cause a problem of poor visibility.

13 is a schematic cross-sectional view of an optical filter according to a first exemplary embodiment of the present invention.

The optical filter of the present invention is disposed in front of the display panel.

The present invention aims to improve visibility by reducing the reflectance while maximizing the effect of color change. To this end, the optical filter of FIG. 13 sequentially includes a first polarizing film, a first phase difference film, a second thick film layer, a thin film layer, and a first thick film layer.

In addition, the optical filter of the present invention may include a transparent substrate, an antireflection film, an external light shielding film formed with a filled wedge pattern of carbon black, an anti-fog film, and the like.

Although FIG. 13 illustrates an embodiment in which the constituent layers are formed in close contact with each other, other layers may be interposed between the constituent layers.

In FIG. 13, the optical filter may be directly adhered to the display panel through an adhesive layer PSA, but is not necessarily limited thereto. For example, the optical filter may be disposed spaced apart from the display panel.

Typically, the first polarizing film, the first retardation film, the second thick film layer, the thin film layer, and the first thick film layer are provided from the front. That is, the first polarizing film is the viewer and the first thick film layer is the display panel.

It is preferable that the first polarizing film, the first retardation film, the second thick film layer, and the first thick film layer except for the thin film layer have the same refractive index so that reflection does not occur at the interface.

The thin film layer is a high refractive index transparent thin film layer causing multiple interferences of 780 nm or less, and the thick film layer is preferably formed of a transparent thin film layer having a larger thickness than the thin film layer and having a smaller refractive index than the thin film layer.

The thin film layer may be a metal oxide having a high refractive index characteristic such as Nb ₂ O ₅ , TiO ₂ , or a high refractive polymer resin, or a metal oxide or metal oxide to which a metal is added, and a polymer mixture.

As described above, a transparent substrate, an adhesive layer, an air layer, an antireflection film, an external light shielding film, an antifog film, etc., in which a filled wedge pattern of carbon black is formed, may be used as the first and / or second thick layer. have. As illustrated in FIG. 13, an adhesive layer may be used as the second thick film layer, and a transparent resin film may be used as the first thick film layer.

The polarizing film typically has a laminated configuration of a TAC film PVA polarizer film TAC film, but various other configuration modifications are possible.

The polarizer film performs a function of polarizing light. The polarizer film may be formed by adsorbing a dichroic dye to polyvinyl alcohol (PVA) which is a polymer material.

The TAC film is formed on both sides of the polarizer to support the polarizer, and is made of TriAcetyl Cellulose (TAC).

The principle of reducing the reflectance in the present invention is as follows.

As shown in FIG. 13, when unpolarized external light is incident, the polarized light is changed into linearly polarized light by the first polarizing film, and circularly polarized light by the 1 / 4λ first phase difference film. When circularly polarized light reaches and reflects at both interfaces of the thin film layer, which is a problem by increasing the reflectance, the circularly polarized light is changed into circularly polarized light having an opposite direction of rotation. The reflected circularly polarized light passes through the 1 / 4λ first retardation film again and becomes linearly polarized light perpendicular to the transmission axis of the first polarizing film, so that the reflected light at the interface with the thin film layer is not emitted. Therefore, the reflection due to the thin film layer is prevented, thereby increasing the contrast ratio and improving the visibility.

As the first phase difference film, a 1 / 4λ retardation film is preferably used, but is not necessarily limited thereto. A retardation film larger than zero and causing a retardation smaller than 1/2 lambda may be used, but in this case, part of the reflected light reflected at the interface with the thin film layer is emitted toward the viewer.

Table 2 below shows the reflectance measurement results according to the viewing angle when the optical filter of the first embodiment of the present invention is employed.

rescue reflectivity Thin film / glass 21.4% Anti-reflection layer / adhesive layer / thin film / glass 11.0% Polarizing Film / Adhesive Layer / Thin Film / Glass 10.3% Polarizing Film / Retardation Film / Adhesive Layer / Thin Film / Glass (First Embodiment) 1.5%

From Table 2, it can be seen that when the optical filter according to the embodiment of the present invention is adopted, the reflectance can be significantly lowered.

14 is a graph showing a color shift measurement result according to a viewing angle when the optical filter of the first embodiment of the present invention is employed.

As shown, it can be seen that even if the optical filter according to the embodiment of the present invention is employed, excellent color shift reduction performance can be achieved.

15 is a schematic cross-sectional view of an optical filter according to a second exemplary embodiment of the present invention.

The optical filter of FIG. 13 has a disadvantage in that loss of screen light emitted from the display panel occurs.

This disadvantage can be solved by placing the second phase difference film behind the first thick film layer as shown in FIG.

It is preferable that a 2nd phase difference film is a 1/4 (lambda) retardation film.

In addition, the first polarizing film is preferably configured to be perpendicular to the transmission axis of the polarizing film (not shown) attached to the front of the display panel, but is not necessarily limited thereto. However, when these transmission axes are not perpendicular, loss of screen light occurs.

16 is a schematic cross-sectional view of an optical filter according to a third exemplary embodiment of the present invention.

In the optical filter of FIG. 15, instead of or in conjunction with a polarizing film (not shown) attached to the front surface of the display panel, the optical filter of the present invention may include a second polarizing film. (Likewise, the optical filter of FIG. 13 may also include a second polarizing film.)

In this case, the first polarizing film is configured such that the transmission axis is perpendicular to the polarizing film attached to the front of the display panel, and the second polarizing film is configured so that the transmission axis is coincident with the polarizing film attached to the front of the display panel. desirable.

Until now, for convenience of description, the LCD filter and the LCD device have been described as an example. However, the present invention is not limited thereto. It can be applied to a large display device such as an FED device, ii) a small mobile display device such as PDA (Personal Digital Assistants), a small game machine display window, a mobile phone display window, and iii) a flexible display device. .

1 is a conceptual diagram conceptually showing the basic structure and driving principle of an LCD.

2 is a conceptual diagram illustrating alignment states and light transmittances of liquid crystals according to viewing angles.

3 is a conceptual diagram illustrating an example of the related art for improving the contrast ratio change and the color change according to a change in viewing angle.

4 is a conceptual diagram illustrating another example of the related art for improving the change in contrast ratio and color change according to a change in viewing angle.

5 is a graph showing a result of measuring a change in emission spectrum with increasing viewing angle of the LCD according to the prior art.

FIG. 6 is a graph normalizing the result of FIG. 5.

7 is a cross-sectional view for explaining a technical principle of color change reduction according to a viewing angle in the present invention.

FIG. 8 is a graph showing the transmittance according to the change in viewing angle, employing the thick film layer / thin film layer / thick film layer structure of FIG. 7.

9 is a graph showing normalized LCD spectrum results to which the results of FIG. 8 are applied.

FIG. 10 is a graph illustrating changes in color coordinates with increasing viewing angles when the structures of the thick film layer, the thin film layer, and the thick film layer of FIG. 7 are adopted.

FIG. 11 is a view illustrating a change in color deviation according to the refractive index of the thin film layer in the structure of FIG. 7.

FIG. 12 is a view illustrating a change in reflectance according to the refractive index of the thin film layer in the structure of FIG. 7.

13 is a schematic cross-sectional view of an optical filter according to a first exemplary embodiment of the present invention.

14 is a diagram illustrating color deviation according to a viewing angle when the optical filter according to the first embodiment of the present invention is employed.

15 is a schematic cross-sectional view of an optical filter according to a second exemplary embodiment of the present invention.

16 is a schematic cross-sectional view of an optical filter according to a third exemplary embodiment of the present invention.

Claims (18)

A first polarizing film, a first retardation film, a second thick film layer, a thin film layer, and a first thick film layer are sequentially provided, The thin film layer is 780nm or less in thickness, The first thick film layer and the second thick film layer has a larger thickness than the thin film layer, The refractive index of the thin film layer is different from the refractive index of the first thick film layer and the refractive index of the second thick film layer. The method of claim 1, The first retardation film is an optical filter for a display device, characterized in that the 1 / 4λ retardation film. The method of claim 1, And a first polarizing film, a first phase difference film, a second thick film layer, a thin film layer, and a first thick film layer from a front side. The method of claim 1, And a second retardation film subsequent to the first thick film layer. 5. The method of claim 4, The second retardation film is an optical filter for a display device, characterized in that the 1 / 4λ retardation film. The method of claim 5, The first polarizing film is an optical filter for a display device, characterized in that the transmission axis is perpendicular to the polarizing film attached to the front of the display panel. 5. The method of claim 4, And a second polarizing film, following the second retardation film. The method of claim 7, wherein The first polarizing film and the second polarizing film are optical filters for display devices, characterized in that the transmission axis is perpendicular to each other. The method of claim 1, The refractive index of the thin film layer is greater than the refractive index of the first thick film layer and the second thick film layer, an optical filter for a display device. The method of claim 1, The first thick film layer and the second thick film layer is an optical filter for a display device, characterized in that the thickness is greater than 780nm and 5mm or less. The method of claim 1, For light having a wavelength λ of 380 nm or more and 500 nm or less, the average value of the transmittance T according to the following formula is larger than the average value of the transmittance T according to the following formula for light having a wavelength greater than 500 nm and 780 nm or less, And a thickness ( l ) of the thin film layer, a refractive index (n) of the thin film layer, and a reflectance (R) at an interface with the thin film layer. T = (1-R) ² / (1 + R ² -2Rcosδ), δ = (2π / λ) 2n l cosθ, 0 ° <θ ≤ 80 ° The method of claim 1, An optical filter for display device, characterized in that the transmittance for light having a wavelength of 380 nm or more and 500 nm or less increases or decreases as the incident angle of the light increases from 0 degrees to 80 degrees. The method of claim 1, An optical filter for a display device, the transmittance of light having a wavelength greater than 500 nm and less than or equal to 780 nm decreases as the incident angle of the light increases from 0 degrees to 80 degrees. 14. The method of claim 13, Display apparatus characterized in that the transmittance for light having a wavelength of 380 nm or more and 500 nm or less decreases as the incident angle of the light increases from 0 degrees to 80 degrees, but decreases to a width smaller than the transmittance for light having a wavelength greater than 500 nm and less than 780 nm. Dragon optical filter. The method of claim 1, An optical filter for display device, characterized in that the ratio of the minimum transmittance to the maximum transmittance within a wavelength range of 380 nm or more and 780 nm or less is 0.5 or more and 0.9 or less. The method of claim 1, At least one of the first thick film layer and the second thick film layer is any one of a transparent substrate, an anti-reflection film, an external light shielding film, an anti-fog film, an adhesive layer and an air layer. 17. The method of claim 16, The second thick film layer is an optical filter for a display device, characterized in that the adhesive layer.  A display device comprising the optical filter for display device according to any one of claims 1 to 17.

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