CN101614910B - Liquid crystal display device - Google Patents

Abstract

A liquid crystal display device. A liquid crystal display device capable of preventing cracks between a light guide plate and a prism sheet positioned on its upper side and improving concentration efficiency of the present invention includes: a liquid crystal panel configured to present images; The liquid crystal panel provides light; a light guide plate at least on one side thereof is provided with the lamp; and a birefringent optical sheet is located between the liquid crystal panel and the light guide plate and has a first prism pattern having a first refractive index and It has a second prism pattern with a second refraction index, the first prism pattern faces the liquid crystal panel, the second prism pattern faces the light guide plate, and the second refraction index is higher than the first refraction index.

Description

Liquid crystal display device

technical field

The present invention relates to a liquid crystal display (LCD) device, and more particularly, the present invention relates to such an LCD device by using a first prism ridge having a low refractive index and a prism ridge formed between the first prism ridges and having a thickness higher than the prism ridge. The birefringent optical sheet of the second prism ridge has the refractive index of the first prism ridge, which can prevent cracks between the light guide plate and the prism sheet on the light guide plate and improve concentration efficiency.

Background technique

This application is related to the subject matter contained in priority Korean application No. 10-2008-0061097 filed on June 26, 2008 and priority Korean application No. 10-2008-0064242 filed on July 3, 2008, in The entire contents of these two priority Korean applications are hereby incorporated by reference.

In general, a liquid crystal display (LCD) device is a representative flat display device that displays images by controlling light transmittance according to image signals. However, the LCD device itself cannot emit light. Therefore, in order to visually display an image, an independent light source emitting light from the rear of the liquid crystal module is required.

In this way, in order to irradiate light from the rear of the liquid crystal module (LCM) onto the liquid crystal panel located in front of the liquid crystal module, the light source (i.e., lamp), the power supply circuit for driving the light source, and everything necessary to realize uniform planar light This part is called "backlight unit". These backlight units can be classified into two types, namely, a direct type backlight unit and an edge type backlight unit, according to a method of emitting light. Currently, various studies have been conducted on direct-type and edge-type backlight units employing surface light sources such as light emitting diodes (LEDs).

First, the edge type backlight unit is configured such that the light source is placed at the side of the LCD module, and the light from the light source becomes planar light through the light guide plate. The disadvantage of this edge-lit backlight unit is that, for example, it is difficult to avoid a decrease in overall brightness. Thus, in order to obtain a uniform brightness, a more efficient light guiding system is required, ie a system for guiding light from a light source all the way to a relatively long distance. In addition, enhanced optical techniques need to be utilized to minimize light loss in transmitting light from the light source all the way to relatively long distances.

1 is a perspective view of a backlight unit according to the related art, FIG. 2A is a graph showing the exit distribution of light transmitted through a prism light guide plate and the exit distribution of light transmitted through a diffusion sheet, and FIG. 2B is a graph showing the exit distribution of light transmitted through a prism light guide plate. Contour diagram of the light exit distribution of the light guide plate.

As shown in FIG. 1 , a backlight unit according to the related art includes a cold cathode fluorescent lamp 25 and a lampshade 26 on one side of the backlight unit, and a prism light guide plate 20, and a side surface of the prism light guide plate 20. The cold cathode fluorescent lamps 25 are adjacent to each other. In addition, the reflective plate 21 is positioned under the prism light guide plate 20 , and an inverted prism sheet 22 and a protection sheet 23 are sequentially laminated on the prism light guide plate 20 .

Now, the functions of the prism light guide plate 20 and the individual sheets will be described.

One side of the prism light guide plate 20 is disposed adjacent to the cold cathode fluorescent lamp 25 , thereby emitting light incident from the cold cathode fluorescent lamp 25 to its upper surface. In order for light incident from the side of the prism light guide plate 20 where the CCFLs 25 are disposed to be uniformly emitted to its upper surface, the prism light guide plate 20 is configured to become thinner away from the CCFLs 25 .

The reflection plate 21 is positioned under the prism light guide plate 20 to prevent light from leaking from the lower surface of the prism light guide plate 20 and at the same time reflect the light toward the upper surface of the prism light guide plate 20 .

Therefore, as shown in FIGS. 2A and 2B , the outgoing light transmitted through the prism light guide plate 20 is mainly distributed between the range of 40° and 80° (about 76°) with respect to the bottom surface, and the outgoing light with the highest brightness has about 80° exit angle.

However, in the LCD device of the related art, when an external impact such as a shock test is applied, friction occurs between the prism pattern formed on the lower surface of the prism light guide plate 20 and the reflective plate 21, more specifically, at the Collision occurs between the prism pattern and a lower cover (not shown) attached to the reflection plate 21 . Therefore, the prism pattern of the prism light guide plate 20 may be cracked or the pattern may be collapsed. Or, friction occurs between the prism light guide plate 20 formed of a rigid material and the prism pattern of the inverted prism sheet 22 formed of a flexible material, thereby causing cracking or collapse of the prism pattern of the inverted prism sheet 22 .

Therefore, the related art LCD device has a problem of so-called white spot phenomenon: a certain area is brighter or darker than its surroundings.

Although not shown in detail in the drawings, a typical prism sheet (not shown) may be disposed on the upper surface of the prism light guide plate 20 so that prism mountains protrude toward the liquid crystal panel. Even in this case, as shown in FIG. 2c, in order to refract incident light on the prism sheet in the vertical direction, first light L1 incident on the prism surface at an angle of about 24° to 32° is required according to Snell's law.

However, for the prism light guide plate 20, most of the light has an angle of 40°, and the fourth light L4 not incident within 24° to 32° is refracted on the prism sheet to become the fifth light L5. Then, the fifth light L5 emerges from the prism sheet and travels laterally, thereby becoming the sixth light L6, which is called "side lobe phenomenon", as shown in part A of FIG. 2c. This phenomenon leads to a drastic drop in luminous efficiency. Therefore, in order to change the range of the main emitted light from the prism light guide plate 20, a diffusion sheet (not shown) is further provided between the prism light guide plate 20 and the prism sheet.

When using a diffuser for the above purpose, the main exit distribution of light passing through the prismatic light guide plate 20 is then changed from the range of 40° to 80° as shown in Fig. 2a to the range of 10° to 45°. Therefore, the first light L1 having an angle of 24° to 32° exiting through the prism light guide plate 20 and the diffusion sheet becomes the second light L2 having an angle of 15° to 20° to a vertical line of the prism sheet within the prism sheet. The second light L2 emitted from the prism sheet comes into contact with air to be vertically refracted, thereby becoming third light L3. Therefore, the vertical luminance of the prism sheet with respect to the upper surface of the prism light guide plate 20 increases.

However, the exit light diverging in the range of 24° to 32° exiting through the prismatic light guide plate 22 still suffers from the side lobe phenomenon as shown in part A of FIG. 2c. That is to say, without utilizing the main outgoing light of the prism light guide plate 20 , the low concentration efficiency is still difficult to solve.

Contents of the invention

Accordingly, an object of the present invention is to prevent cracks from occurring between a light guide plate and a prism sheet positioned on the light guide plate and to improve concentration efficiency.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied herein and described in its broadest sense, there is provided a liquid crystal display device comprising: a liquid crystal panel configured to present an image; a lamp positioned at Under the liquid crystal panel, for providing light to the liquid crystal panel; a light guide plate, having the lamp at least on one side thereof; and a birefringent optical sheet, located between the liquid crystal panel and the light guide plate, and having a first refraction A first prism pattern with a second refractive index and a second prism pattern with a second refractive index, the first prism pattern faces the liquid crystal panel, the second prism pattern faces the light guide plate, the second refractive index is higher than the first refractive index.

The light guide plate has a prism pattern formed on an upper surface thereof in a direction facing the liquid crystal panel, wherein the prism pattern of the light guide plate is at least one of a prism ridge, a lens form, and a pyramid form. Alternatively, the prism pattern of the light guide plate is at least one of concave and convex.

The above and other objects, features, aspects and advantages of the present invention will become more apparent by describing the present invention in detail below with reference to the accompanying drawings.

Description of drawings

The accompanying drawings, which are included to assist in a better understanding of the invention and constitute a part of this application, illustrate embodiments of the invention and together with the description explain the principle of the invention.

In these drawings:

FIG. 1 is a perspective view of a backlight unit according to the related art;

2A is a graph showing an exit distribution of light transmitted through a prism light guide plate and an exit distribution of light transmitted through a diffusion sheet;

2B is a contour diagram showing the exit distribution of light transmitted through a prismatic light guide plate;

2C is an enlarged cross-sectional view of one prism ridge of the prism sheet in the case of employing a prism sheet having a prism ridge facing a liquid crystal panel;

3A is a cross-sectional view of a liquid crystal display device showing a liquid crystal display device with a flat-plate light guide plate according to the present invention;

Figure 3B is a diagram illustrating how light is concentrated by the birefringent optical sheet of Figure 3A;

Figure 3C is a diagram illustrating in detail how light is concentrated by the birefringent optical sheet of Figure 3B;

4 is a cross-sectional view of a liquid crystal display device showing a liquid crystal display device with a wedge-shaped light guide plate according to the present invention;

5A is a graph showing the exit distribution of light transmitted through a prism light guide plate;

5B is a contour diagram showing the exit distribution of light transmitted through a prism light guide plate;

5C is a contour diagram showing the exit distribution of light transmitted through a birefringent optical sheet; and

6 to 10B are diagrams showing different modifications of the birefringent optical sheet according to the present invention.

Detailed ways

Now, the structure of the present invention will be described in detail with reference to the accompanying drawings.

3A is a cross-sectional view of a liquid crystal display device showing a liquid crystal display device having a flat-plate type light guide plate according to the present invention. A liquid crystal display (LCD) device according to the present invention may include a liquid crystal panel 131 configured to present an image according to an external signal, backlight units 121-126, and a birefringent optical sheet 123, and the backlight units 121-126 are disposed on the liquid crystal panel. 131 to emit light, the birefringent optical sheet 123 is located between the liquid crystal panel 131 and the backlight unit and is provided with a first prism ridge 123b and a second prism ridge 123c, the first prism ridge 123b is formed on the flat prism light guide plate 122 To have a pattern facing the liquid crystal panel, the second prism ridges 123c are each formed between the first prism ridges 123b, that is, formed along the valleys of the first prism ridges 123b, and its refractive index is higher than that of the first prism ridges 123b. the refractive index.

First, a reflection plate 121 formed of iron or electro galvanized steel (EGI) is combined on the lower cover 110 . The reflective plate 121 may be implemented with a white polyester film or a film coated with metal (eg, Ag, Al, etc.). The reflection plate 121 has a visible light reflectance of about 90-97%, and this reflectance increases when a thicker coating film is used.

In addition, lamp units 125 and 126 are located at both sides of the lower cover 110 to which the reflection plate 121 is combined. Here, the lamp units 125 and 126 may include a lamp 125 emitting light by receiving an external voltage and a lamp cover 126 protecting the lamp 125 from external impact. Here, the lamp 125 may be one of a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), and a hot cathode fluorescent lamp (HCFL).

The prism light guide plate 122 on one side of the lamp units 125 and 126 is laminated on the reflection plate 121 on the lower cover 110 . Here, the prism light guide plate 122 is configured to have a uniform thickness. Although substantially not shown in detail in FIG. 3A, the prism ridges 122a are formed on the prism light guide plate 122 in such a manner that the extending direction of the prism ridges 122a is perpendicular to the extending direction of the lamps 125 arranged in the main axis direction. , to focus the light.

Here, it is preferable to configure the prism ridges 122 a of the prism light guide plate 122 such that the prism ridges constituting the ridges along the traveling direction of light are formed on the prism light guide plate 122 . Alternatively, they may be arranged uniformly in a lens shape or a pyramid shape or randomly arranged. These prism patterns can be implemented in a concave-convex form, and can also be arranged in a direction parallel to the lamps 125 located in the main axis direction. However, the present invention may not be limited to these configurations.

As mentioned above, the prismatic light guide plate 122 is formed of a polymeric material such as polymethylmethacrylate (PMMA) or cycloolefin polymer (COP). In order to make the light emitted from the lamp 125 located on the side surface of the prism light guide plate 122 incident on the liquid crystal panel 131, the light from the lamp 125 is guided via the prism light guide plate 122 so that it falls on the reflection plate located under the prism light guide plate 122. 121 is reflected. Here, this light is emitted in one direction such that the main emission peak intensity is approximately 76° with respect to the upper side surface of the prism light guide plate 122 .

In addition, the prismatic light guide plate 122 provides the lowest absorption of light in the visible region among other polymeric materials, and thus provides very high transparency and high gloss. Furthermore, it does not break or deform due to high mechanical strength. In addition, the prism light guide plate 122 is light in weight and has strong chemical stability. In addition, the prismatic light guide plate 122 provides this high visible light transmittance of 90-91% and low internal loss. The prismatic light guide plate 122 also has strong mechanical characteristics, such as tensile strength, flexural strength, elongational strength, and the like.

Although not shown in detail in the drawings, a plurality of etching patterns for blocking light leakage may be disposed on the lower surface of the prism light guide plate 122 .

The LCD device according to the preferred embodiment of the present invention is exemplarily described as being provided with the prism light guide plate 122 having the prism ridges 122a formed on the upper surface thereof; however, the present invention may not be limited thereto. Variations can be implemented without departing from the inventive concept, such as providing a typical type of light guide plate without prismatic ridges or the like.

Referring to FIG. 3, the prism light guide plate 122 includes a birefringent optical sheet 123 thereon. The birefringent optical sheet 123 includes a first prism ridge 123b and a second prism ridge 123c, the extension direction of the first prism ridge 123b is perpendicular to the extension direction of the prism ridge 122a disposed on the prism light guide plate 122 to form an upward pattern, Each of the second prism ridges 123c is formed between two first prism ridges 123b to form a downward pattern.

This birefringent optical sheet 123 allows light exiting through the prism light guide plate 122 at 76° with respect to the upper surface of the prism light guide plate 122 to exit in a direction perpendicular to the bottom surface of the prism light guide plate 122 , thereby reaching the liquid crystal panel 131 .

For example, as shown in FIG. 3A, a birefringent optical sheet 123 according to the present invention includes a first prism ridge 123b and a second prism ridge 123c, and the first prism ridge 123b is formed to be compatible with the prism ridge 122a of the prism light guide plate 122 constituting the base. The direction of extension is orthogonal, the first prism ridges 123b have a low refractive index, and by filling the valley between the two first prism ridges 123b with high refractive index acrylic resin (acryl resin) (that is, ultraviolet rays curing resin) to form the respective second prism ridges 123c. It is preferable that an upper base film 123d is formed on the second prism ridge 123c. Therefore, the upper and lower surfaces of the birefringent optical sheet 123 may be configured as a plane.

The two base films 123a and 123d and the first and second prism ridges 123b and 123c may be substantially formed of polyethylene (PET) suitable for pattern formation and acrylic resin as an ultraviolet curable resin, respectively.

The two base films 123a and 123d can be made of such as polyethylene terephthalate, polyethylene naphthalate, acrylic resin, polycarbonate, polystyrene, polyolefin, cellulose acetate, waterproof chlorine Formation of synthetic resins such as ethylene. It is preferable that the two base films 123a and 123d are transparent films because they should transmit the outgoing light of the prism light guide plate 122 .

The thicknesses of the two base films 123a and 123d are each one of 100 μm, 125 μm, 188 μm, and 250 μm. An ultraviolet curing resin for pattern formation is deposited on the lower base film 123a, and then the first prism ridges 123b are molded thereon and hardened using ultraviolet rays. Next, ultraviolet curing resin is filled in the valleys between the first prism ridges 123b to form the second prism ridges 123c, which are then hardened. The upper base film 123d is superimposed on the second prism ridge 123c.

As described above, in the present invention, the lower and upper base films 123a and 123d are formed of a material having a thermal expansion rate consistent with the average value of thermal expansion rates of the first and second prism ridges 123b and 123c. The average thermal expansion rate may be calculated by considering the volumes of the first and second prism ridges 123b and 123c, the interval between the ridges, and the like. In order to prevent deformation due to different thermal expansion rates, it is preferable that a first boundary between the lower base film 123a and the first prism ridges 123b is the same as a second boundary between the upper base film 123d and the second prism ridges 123c.

As one method for preventing deformation of the lower and upper base films 123a and 123d, they can be obtained by averaging the thermal expansion rates of the first and second prism ridges 123b and 123c by the same average thermal expansion rate. material formed. The lower and upper base films 123a and 123d may serve to support the first and second prism ridges 123b and 123c, thereby preventing them from being wrinkled and bent. In the case where the lower and upper base films 123a and 123d are thicker than the first and second prism ridges 123b and 123c, bending due to thermal expansion of the first and second prism ridges 123b and 123c can be prevented.

As described above, the birefringent optical sheet 123 is called because it is provided with the first prism ridges 123b having a low refractive index and the second prism ridges 123c having a higher refractive index than the first prism ridges 123b. If the reference used to indicate the difference between the low refractive index and the high refractive index is 1.51, the high refractive index may be greater than 1.51 and the low refractive index may be less than 1.51. The optical characteristics may then depend on what reference is assigned to the difference between them.

The first prism ridge 123b is configured to have a first refractive index, and the second prism ridge 123c is configured to have a second refractive index by adding different additives to the acrylic resin. Here, the first refractive index may be in a range of 1.3 to 1.9, and the second refractive index may be in a range of 1.4 to 2.0. Preferably, the first refractive index is in the range of 1.3 to 1.49, and the second refractive index is in the range of 1.5 to 1.7.

Here, the difference between the first and second refractive indices is 0.1 or more, and preferably, in the range of 0.1 to 0.2.

Briefly explaining the characteristics of light refracted at the interface between the first and second prism ridges 123b and 123c, a part of this light may be reflected and the remaining part of the light may be refracted at the interface. Here, when using Snell's law, the condition of n1·sinθ1=n2·sinθ2 should be satisfied. Here, n1 represents a low refractive index, and n2 represents a high refractive index. Thus, to satisfy this condition, θ2 should be smaller than θ1. Therefore, in this way, light can be emitted perpendicularly to the liquid crystal panel 131 .

This optical characteristic corresponds to the specific characteristics of a particular material with a low or high refractive index, which means that this refractive index can vary depending on the type of material used and the type of materials mixed together. Therefore, the present invention typically shows an acrylic type UV curable resin. As shown in the related art, for example, the inner angle based on each prism ridge is 54° or 58°. However, in the present invention, such optical characteristics may be changed depending on how to design the inner angle of the first prism ridge 123b and the material having a low or high refractive index.

Also, similar to the prism light guide plate 122, the birefringent optical sheet 123 of the present invention may preferably be implemented such that prism ridges are arranged in a direction perpendicular to the traveling direction of light to form ridges. Alternatively, it may be formed in a constant arrangement in one of lens form, pyramid form, polygon form, etc., or formed randomly. Such a prism pattern may be configured in a concave or convex form, and also arranged in a direction horizontal to the lamps 125 located in the main axis direction. Therefore, the configuration may not be limited to the above manner.

A sub-optical sheet 124 for supplementing optical characteristics of light transmitted through the birefringent optical sheet 123 is laminated on the birefringent optical sheet 123 . Here, the sub optical sheet 124 may be, for example, a diffusion sheet having a diffusion pattern for compensating for non-uniformity of light or a protection sheet for protecting the birefringent optical sheet 123 from external impact and scratches.

In addition, a main supporter (not shown) molded in the form of a rectangular frame using synthetic resin or SUS steel is attached to the upper side of the sub optical sheet 124 .

The liquid crystal panel 131 is laminated on the main support. The liquid crystal panel 131 includes a thin film transistor (TFT) array substrate, a color filter substrate having red (R), green (G) and blue color filters, and a liquid crystal layer sandwiched between the two substrates, which are connected to each other. Face and bond to maintain a uniform cell gap. In addition, the upper polarizer 131a and the lower polarizer 131b are located on the upper side and the lower side of the liquid crystal panel 131, respectively.

The upper cover 140 covers four edge regions of the liquid crystal panel 131 and is also assembled/connected to the main support or the lower cover 110 .

FIG. 3B is a diagram illustrating how light is concentrated by the birefringent optical sheet of FIG. 3A.

As shown in FIG. 3B, assume that the birefringent optical sheet 123 of the present invention includes a first prism ridge 123b having a refractive index n3 of 1.5 and a second prism ridge 123c having a refractive index n4 of 1.51, and the inner angle of the first prism ridge 123b are 54° and 58°.

Here, light emitted based on the prism ridges 122a stacked on the prism light guide plate 122 is emitted through the air layer having a refractive index n1 of 1 to be incident on the lower base film 123a of the birefringent optical sheet 123, thereby forming a certain incidence. Angle θ1. The light also has an exit angle θ2 with an optical path changed according to the incident angle θ1 at the lower base film 123a. Here, since the refractive index n2 of the lower base film 123a is higher than the refractive index n1 of air, in order to satisfy Snell's law, the outgoing angle θ2 should be smaller than the incident angle θ1.

If the first prism ridge 123b formed on the lower base film 123a is formed of the same material as the lower base film 123a, the refractive indices n2 and n3 are the same as each other, which means: the incident angle and the outgoing angle of light passing through the base film 123a equal to each other.

In addition, light is refracted at the interface between the first prism ridge 123b having a low refractive index n3 and the second prism ridge 123c having a high refractive index n4 higher than that of the first prism ridge 123b. For example, if the refractive index n3 of the first prism ridge 123b is 1.5 and the refractive index n4 of the second prism ridge 123c is 1.51, the exit angle θ4 with respect to the interface should satisfy Snell's law. Therefore, if the incident angle θ3 is 27°, the outgoing angle θ4 is smaller than the incident angle θ3.

Thus, the refracted light is incident on the interface between the second prism ridge 123c and the first prism ridge 123b at a certain incident angle θ5. This incident light is then reflected at a reflection angle θ6 equal to the incident angle θ5 of the light incident on the interface, thereby being concentrated in a direction perpendicular to the liquid crystal panel 131 .

Here, if the second prism ridge 123c is formed of the same material as the upper base film 123d laminated on the second prism ridge 123c, the upper base film 123d has the same refractive index n5 as the second prism ridge 123c. Therefore, the angle of incidence can be the same as the angle of exit. Thus, the light having a certain refraction angle θ6 is reflected on the interface between the first prism ridge 123b and the second prism ridge 123c to be concentrated in a direction perpendicular to the liquid crystal panel 131 .

In the LCD device having the above-mentioned principle of concentrating light according to a preferred embodiment of the present invention, the principle will now be described in more detail with reference to FIG. 3C.

As shown in FIG. 3C, the birefringent optical sheet 123 is configured such that the first refractive index of the first prism ridge 123b is lower than the second refractive index of the second prism ridge 123c. Accordingly, the outgoing light of the prism light guide plate 122 is refracted more than three times, thereby being supplied to the liquid crystal display 131 . Each of the first prism ridges 123b includes a first inclination angle a, a second inclination angle b, an apex angle c determined by the first inclination angle a and the second inclination angle b, a first inclination surface 141 extending from the first inclination angle a, and The second slope 142 extending from the second slope b. The first and second inclination angles a and b are formed in a range of 60° to 89°, and are also formed symmetrically or asymmetrically. Assuming that the first prism ridge 123b has a first refractive index of 1.48, the second prism ridge 123c has a second refractive index of 1.61, the first inclination a is 69°, and the second inclination b is 67°, the optical path will be described in detail below .

The first light L1 having the first incident angle θi1 from the prism light guide plate 122 is refracted into the second light L2 having the first refraction angle θr1 smaller than the first incident angle θi1. The second light L2 incident at the second incident angle θi2 is refracted to have a second refraction angle θr2 smaller than the second incident angle θi2 at the second interface 142, that is, the interface between the first and second prism ridges 123b and 123c. The third light L3. The third light L3 incident at the third incident angle θi3 is refracted into the fourth light L4 having the third reflection angle θr3 at the first inclined surface 141, that is, the interface between the second and first prism ridges 123c and 123b. Thus, the fourth light L4 travels to the lower side of the liquid crystal display 131 in the vertical direction.

The first incident angle θi1 emitted from the prism light guide plate 122 is based on a peak angle of 72° to an extension line extending perpendicularly to the lower side of the first prism ridge 123b. According to Snell's law, the first refraction angle θr1 is 40° based on the vertical extension line. The second incident angle θi2 is 27° based on the normal of the second inclined surface 142 . The second refraction angle θr2 is 24° based on the normal of the second inclined surface 142 . The third incident angle θi3 is 68° based on the normal of the first inclined surface 141 . The third refraction angle θr3 is 68° based on the normal of the first inclined surface 141 . The fourth light L4 is vertically refracted by total reflection.

The first and second oblique angles a and b of the first prism ridge 123b can adjust the irradiation angle of the fourth light L4 irradiated to the liquid crystal panel 131 according to the inclination angle of the first light L1. Snell's law is n2/n1=sinθ2/sinθ1, where n1 represents the first refractive index of the first prism ridge 123b, and n2 represents the second refractive index of the second prism ridge 123c. According to Snell's law, it can be seen that when light enters a medium with a high refractive index from a medium with a low refractive index, scattering of the light can be reduced, thereby concentrating the light. In order to overcome the limitation of refraction according to the related art, the LCD device of the present invention can use the principle of total reflection to concentrate the outgoing light passing through the prism light guide plate 122, as shown in FIG. 3C. In order to obtain vertical light through total reflection, most of the light emitted through the prism light guide plate 122 is utilized, thereby obtaining high concentration efficiency.

FIG. 4 is a diagram of an LCD device according to the present invention, showing the LCD device having a wedge-shaped prism light guide plate.

As shown in FIG. 4, the LCD device according to the present invention may include a liquid crystal panel 231 for realizing an image according to an external signal, backlight units 221, 222, 223, and 225 arranged under the liquid crystal panel 231 to emit light, and Between the panel 231 and the backlight unit and provided with the birefringent optical sheet 223 of the first prism ridge 223b and the second prism ridge 223c, the first prism ridge 223b is formed on the wedge-shaped prism light guide plate 222 to have a pattern facing the liquid crystal panel, The second prism ridges 223c are each formed between the first prism ridges 223b, ie, along valleys of the first prism ridges 223b and have a higher refractive index than the first prism ridges 223b.

Here, unlike the LCD device having the flat prism light guide plate 122 shown in FIG. 3, the LCD device having the wedge-shaped prism light guide plate 222 shown in FIG. One side of the lower side is to accommodate the lamp unit, namely the lamp 225 . Here, the lampshade may be formed by extending the reflection plate 221 . In addition, the wedge prism light guide plate 222 is characteristically configured to have different thicknesses on its one side surface facing the lamps 225 arranged in the main axis direction and on its other side surface.

Here, similar to the flat type prism light guide plate 122, the wedge type prism light guide plate 222 has a prism ridge 222a laminated thereon. The prism ridge 222a is configured to be perpendicular to the extension direction of the lamp 225 arranged in the main axis direction, that is, in the light propagation direction.

Accordingly, the light emitted from the lamp 225 located at one side of the wedge prism light guide plate 222 is guided into the wedge prism light guide plate 222 to be reflected on the reflection plate 221 . Then, this reflected light exits in a direction inclined at approximately 76° with respect to the wedge prism light guide plate 222 via the prism ridge 222 a laminated on the wedge prism light guide plate 222 . Here, with reference to the upper side surface of the wedge-shaped prism light guide plate 222 , the light emitted through the prism light guide plate 222 obliquely at 76° exits in the same direction as in the related art.

The birefringent optical sheet 223 located on the upper side of the wedge-shaped prism light guide plate 222 is the same as the previous embodiment. In other words, the birefringent optical sheet 223 includes a first prism ridge 223b, a second prism ridge 223c and a base film 223d. Formed on the base film 223a constituting the base in the direction of the extension direction and has a low refractive index, the second prism ridge 223c is formed by filling UV curable resin or the like in each valley of the first prism ridge 223b, and the base film 223d is stacked on the second prism ridge 223b. on the second prism ridge 223c. Therefore, the birefringent optical sheet 223 is configured to have planar upper and lower surfaces.

The light exiting through the wedge prism light guide plate 222 at approximately 76° with respect to the upper side surface of the wedge prism light guide plate 222 passes through the birefringent optical sheet 223 laminated on the wedge prism light guide plate 222, that is, passes continuously through the lower base film 223a. , the first prism ridge 223b, the second prism ridge 223c, and the upper base film 223d are transmitted, thereby being refracted. Therefore, this refracted light exits in a direction perpendicular to the bottom surface.

In this way, the light emitted in the direction perpendicular to the bottom surface via the birefringent optical sheet 223 is uniformly diffused via a sub-optical sheet such as a diffusion sheet (not shown) laminated on the birefringent optical sheet 223, thereby being applied to the liquid crystal. panel 231 .

With this structure, even if an external impact is applied to the LCD device and thus the plane of the prism ridge 222a of the wedge-shaped light guide plate 222 formed of a rigid material and the birefringent optical sheet 223 formed of a flexible material laminated on the prism ridge 222a The friction of the lower surface can also prevent the prism ridges 222a of the wedge-shaped light guide plate 222 from being cracked or collapsed.

In addition to the above structure, the features of the reflective plate 221 and the wedge-shaped light guide plate 222 and the detailed description about the liquid crystal panel 231 can be understood through the previous description.

Fig. 5 A is a graph showing the exit distribution of light passing through the prism light guide plate, Fig. 5B is a contour diagram showing the exit distribution of light passing through the prism light guide plate, Fig. 5C is a graph showing the emission distribution of light passing through the prism light guide plate, and Fig. Contour diagram of the light emission distribution of the slice.

As shown in FIGS. 5A and 5B , it can be seen that, in LCD devices having flat prism light guide plates and wedge prism light guide plates respectively, most of the light passing through the prism light guide plate with upward facing prism ridges relative to The upper surface of the light guide plate is inclined at approximately 76° to have a main emission peak intensity. From this, it can be noticed that, as shown in the related art, most of the light exits in the same direction compared to the prism light guide plate having the prism ridges facing downward.

Then, as shown in FIG. 5C, after passing through the prism light guide plates 122 and 222, the light exiting with an oblique angle of approximately 76° proceeds through the birefringent optical sheets 123 and 223 laminated on the prism light guide plates 122 and 222, so as to be separated from the bottom surface. The vertical direction is provided to the liquid crystal panels 131 and 231 .

In this way, light transmitted through the birefringent optical sheets 123 and 223 is diffused by a diffusion sheet or the like laminated on the birefringent optical sheets 123 and 223 , thereby being uniformly supplied to the liquid crystal panels 131 and 231 .

6A and 6B are diagrams showing various modifications of the birefringent optical sheet according to the present invention. These variants have the advantage of reduced costs compared to the previous embodiments of the invention.

As shown in FIG. 6A, the first prism ridges 323b having a low refractive index are formed on the base film 323a facing the prism ridges of the prism light guide plate formed of PET or PC, and have a higher refractive index than the first prism ridges 323b. The second prism ridges 323c are each formed between two first prism ridges 323b. Here, the upper surface of the second prism ridge 323c exposed to the outside is formed as a plane.

On the other hand, as shown in FIG. 6B, first, second prism ridges 423b having a high refractive index are formed on the base film 423a, and first prism ridges 423c having a lower refractive index than the second prism ridges 423b are each formed on the base film 423b. between the two second prism ridges 423b. Here, the first prism ridge 423b having a low refractive index exposed to the outside is configured as a planar surface. This planar surface may face the prismatic ridges of the prismatic light guide plate.

Like this, even if the plane surface of the first prism ridge 423c faces the prism ridge of the prism light guide plate, since the prism ridge of the prism light guide plate is formed of a rigid material compared with the first prism ridge 423c formed of a flexible material, even when the Even when an external impact is applied, the pattern of the prism ridges will not be cracked or collapsed due to friction between the two components, that is, between the prism light guide plate and the birefringent optical sheet.

FIGS. 7A and 7B show a structure capable of cost reduction in view of the overall structure of the LCD device, compared with the structure shown in FIGS. 6A and 6B .

In other words, in the structure of FIG. 7A, similar to the structure of FIG. 6A, the first prism ridge 523b having a low refractive index is formed on the base film 523a facing the prism ridge of the prism light guide plate formed of PET or PC, and has a high The second prism ridges 523c having a refractive index different from the first prism ridges 523b are each formed between two first prism ridges 523b. Another base film is laminated on the second prism ridge 523c. The base film is configured as a diffusion base film 523d having diffusion patterns or diffusion particles inside or outside of the diffusion base film 523d. Here, the diffusion pattern or the diffusion particles may be formed of at least one material among PMMA, silicon dioxide and PC.

In this structure, the related art diffusion sheet laminated on the birefringent optical sheet 523 can be eliminated.

In addition, in the structure of FIG. 7B, the first prism ridges 623b having a low refractive index are formed on the first diffusion base film 623a facing the prism ridges of the prism light guide plate. Second prism ridges 623c having a higher refractive index than the first prism ridges 623b are each formed between the two first prism ridges 623b, and then, a second diffusion base film 623d is laminated on the second prism ridges 623c.

Here, diffusion patterns or diffusion particles are also contained inside or outside the first and second diffusion base films 623a and 623d. The diffusion patterns or diffusion particles may be formed of at least one material among PMMA, silicon dioxide and PC.

As shown in FIG. 8, the present invention can be applied such that one of the lower base film 723a and the upper base film 723d of the birefringent optical sheet 723 has a diffusion pattern on its surface or has diffusion particles inside or outside it, And the other base film has a prism pattern including microlenses on its surface.

Here, the microlenses are formed of ultraviolet curable resin.

As shown in FIG. 9 , the present invention can be applied such that at least one of the lower base film 823 a and the upper base film 823 d of the birefringent optical sheet 823 is deposited with an adhesive containing beads 862 . In this variation, adhesive 860 is used to secure beads 862 to lower and upper base films 823a and 823d. The beads 862 serve to protect the outgoing light of the birefringent optical sheet 823 from being affected by particles, and to achieve smooth-looking outgoing light.

10A and 10B show another modification of the present invention, in which the thickness of the lower base films 923a and 1023a is asymmetric to the thickness of the upper base films 923d and 1023d, thereby reducing the thickness of the birefringent optical sheets 923 and 1023.

As shown in FIG. 9A, the upper base film 923d of the birefringent optical sheet 923 is set to be thinner than the lower base film 923a. This structure is intended to prevent both ends of the birefringent optical sheet 923 from being rolled down caused when the thermal expansion coefficient of the upper base film 923d is greater than that of the lower base film 923a in the case where the lower and upper base films 923a and 923d have the same thickness. up the hat-shaped bend.

As shown in FIG. 10B, the upper base film 1023d of the birefringent optical sheet 1023 is set thicker than the lower base film 1023a. This structure is intended to prevent both ends of the birefringent optical sheet 1023 from being rolled up caused when the thermal expansion coefficient of the upper base film 1023d is smaller than that of the lower base film 1023a in the case where the lower and upper base films 1023a and 1023d have the same thickness. The bend in the shape of the cup.

In the LCD device according to the preferred embodiment of the present invention which can be realized in various modifications as described above, when external vibration or shock is applied, it is possible to prevent the The cracking or collapse of the prism pattern caused by the friction between the parts. Therefore, the occurrence of the white spot phenomenon caused by such cracking and collapse can be minimized. Thus, light with uniform brightness is applied to the liquid crystal panel, thereby improving image quality.

An LCD device according to a preferred embodiment of the present invention may have a birefringent optical sheet having second prism ridges filling in valley regions of first prism ridges alternately having peaks and valleys, the second prism ridges It has a higher refractive index than the first prism ridge, so that the outgoing light through the prism light guide plate can be concentrated vertically, thereby improving the brightness.

The above-mentioned embodiments and advantages are merely exemplary and should not be construed as limiting the present disclosure. The present teachings can be readily applied to other types of devices. This description is illustrative, and does not limit the scope of the claims. Many alternatives, modifications and changes will be apparent to those skilled in the art. The features, structures, methods, and other features of the exemplary embodiments described herein can be combined in various ways to obtain additional and/or alternative exemplary embodiments.

Since these features can be embodied in various forms without departing from their characteristics, it should also be understood that the above embodiments are not limited to any details of the above description unless otherwise indicated, and should be interpreted broadly as described in the appended All changes and modifications which come within the scope defined in the claims, and which come within the metes and bounds of the claims, or equivalents of such metes and bounds, are therefore intended to be embraced in the appended claims.

Claims (20)

1. A liquid crystal display device, the liquid crystal display device comprising: a liquid crystal panel configured to present an image; a lamp positioned under the liquid crystal panel to provide light to the liquid crystal panel; a light guide plate, at least at one end of the light guide plate, the lamp is disposed, and the light from the lamp becomes planar light through the light guide plate; and A birefringent optical sheet, which is located between the liquid crystal panel and the light guide plate, and has a first prism pattern with a first refractive index and a second prism pattern with a second refractive index, the first prism pattern faces In the liquid crystal panel, the second prism pattern faces the light guide plate, the second refractive index is higher than the first refractive index, Wherein, each ridge of the first prism pattern includes first and second inclination angles and an apex angle determined by the first and second inclination angles, and the first and second inclination angles are symmetrical or asymmetrical to each other, Wherein, the first light having a first incident angle incident on the first prism pattern through the light guide plate is refracted into second light having a first refraction angle smaller than the first incident angle, so that The second light incident on the interface between the first and second prism patterns at a second incident angle is refracted at the second prism pattern to have a second refraction angle smaller than the second incident angle. The third light incident on the interface between the second and first prism patterns at a third incident angle is refracted into fourth light having a reflection angle equal to the third incident angle. 2. The liquid crystal display device of claim 1, wherein the light guide plate has a prism pattern formed on an upper surface thereof in a direction facing the liquid crystal panel. 3. The liquid crystal display device of claim 2, wherein the prism pattern of the light guide plate is at least one of a prism ridge, a lens form, and a pyramid form. 4. The liquid crystal display device of claim 1, wherein the prism pattern of the light guide plate is formed as at least one of concave and convex. 5. The liquid crystal display device of claim 1, wherein the first prism pattern of the birefringent optical sheet is at least one of a prism ridge, a lens form, a pyramid form, and a polygon form. 6. The liquid crystal display device of claim 1, wherein the birefringent optical sheet further comprises a base film on at least one side surface of the first prism pattern or the second prism pattern. 7. The liquid crystal display device according to claim 6, wherein the base film is formed of at least one of polyethylene or polycarbonate. 8. The liquid crystal display device of claim 6, wherein the at least one base film is a diffusion base film. 9. The liquid crystal display device of claim 8, wherein the diffusion base film includes a diffusion pattern on a surface thereof or diffusion particles inside or outside it. 10. The liquid crystal display device of claim 8, wherein the diffusion base film has a prism pattern including microlenses on a surface thereof. 11. The liquid crystal display device according to any one of claims 8 to 10, wherein the diffusion base film on one side of the birefringent optical sheet has a diffusion pattern or diffusion particles on the outside or inside thereof, And/or the diffusion base film on the other side of the birefringent optical sheet has a prism pattern including microlenses on its surface. 12. The liquid crystal display device according to claim 10, wherein the microlenses are formed of ultraviolet curable resin. 13. The liquid crystal display device of claim 9, wherein the diffusion pattern or the diffusion particles are formed of at least one material selected from polymethyl methacrylate, silicon dioxide and polycarbonate. 14. The liquid crystal display device of claim 6, wherein an adhesive including beads is deposited on a surface of the at least one base film. 15. The liquid crystal display device of claim 14, wherein the beads and the adhesive are formed of a transparent material. 16. The liquid crystal display device of claim 6, wherein the base film and the first and second prism patterns are formed of a transparent film. 17. The liquid crystal display device according to claim 1, wherein a difference between the first refractive index of the first prism pattern and the second refractive index of the second prism pattern is 0.1 or more big. 18. The liquid crystal display device according to claim 17, wherein a difference between the first refractive index of the first prism pattern and the second refractive index of the second prism pattern is 0.1 to 0.2 In the range. 19. The liquid crystal display device according to claim 1, wherein the first refractive index of the first prism pattern is in the range of 1.3 to 1.9, and the second refractive index of the second prism pattern is In the range of 1.4 to 2.0. 20. The liquid crystal display device according to claim 19, wherein the first refractive index of the first prism pattern is in the range of 1.3 to 1.49, and the second refractive index of the second prism pattern is In the range of 1.5 to 1.7.

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