KR102481786B1 - Backlight unit and liquid crystal display device having the same - Google Patents

Abstract

A backlight unit and a liquid crystal display device having the same according to the present invention is a backlight unit having a thin structure to which a partial wedge-type light guide plate is applied, and a flat area is provided instead of a prism mountain in the upper prism sheet located in the light entrance part of the light guide plate It is characterized in that it blocks light traveling between the peaks and valleys of the prism sheet.
According to this, light leakage from the light entrance portion of the light guide plate is reduced, and at the same time, hot spot uniformity is improved.

Description

Backlight unit and liquid crystal display device having the same {BACKLIGHT UNIT AND LIQUID CRYSTAL DISPLAY DEVICE HAVING THE SAME}

The present invention relates to a backlight unit, and more particularly, to a backlight unit to which a wedge-shaped light guide plate is applied and a liquid crystal display device having the same.

In the recent information society, the importance of the display device as a visual information delivery medium is being emphasized, and in order to occupy an important position in the future, it must satisfy requirements such as low power consumption, thinning, light weight, and high definition.

Display devices include a cathode ray tube (CRT) that emits light itself, an electro luminescence (EL), a light emitting diode (LED), a vacuum fluorescent display (VFD), an electric field It can be divided into a light emitting type such as Field Emission Display (FED) and a Plasma Display Panel (PDP), and a non-emissive type such as Liquid Crystal Display (LCD) that does not itself emit light. .

A liquid crystal display is a device that expresses images by using the optical anisotropy of liquid crystal. It has excellent visibility compared to conventional cathode ray tubes, average power consumption is smaller than that of a cathode ray tube of the same screen size, and heat dissipation is also small, so it is in the spotlight as a display device. there is.

The liquid crystal display device includes a liquid crystal panel in which pixels are arranged in a matrix form, a driving unit for driving the pixels, and a backlight unit for supplying light to the liquid crystal panel.

1 is a perspective view showing the structure of a general backlight unit by way of example.

At this time, FIG. 1 shows a backlight unit to which a partial wedge-type light guide plate is applied for a thin structure.

Referring to FIG. 1, the backlight unit is described in detail. An LED array 31 for generating light is installed on one side of the light guide plate 42, and a reflector (not shown) is installed on the rear surface of the light guide plate 42. .

Therefore, the light emitted from the LED array 31 is incident on the side of the light guide plate 42 made of a transparent material, and the reflector disposed on the rear surface of the light guide plate 42 transmits the light transmitted to the rear surface of the light guide plate 42 through the light guide plate 42. The light is reflected toward the optical sheets 43 on the upper surface.

At this time, the optical sheet 43 is composed of a diffusion sheet 43a, a lower prism sheet 43b and an upper prism sheet 43c.

A recently developed smartphone model has a thin structure, and the light guide plate 42 in the backlight unit is divided into a light incident area and a light guide area having different thicknesses.

The step between the light incident area and the light guiding area is designed in the form of a slope, and a part of the light emitted from the LED array 31 is emitted to the sloped area.

The light emitted to the inclined region proceeds to the empty space between the crest and valley of the upper prism sheet 43c (refer to the dotted line arrow), and is recognized as light leakage during operation. This light leakage phenomenon occurs more severely as the level difference between the light incident area and the light guiding area of the light guide plate 42 increases.

That is, prism mountains 44 having the same shape are continuously disposed on the upper prism sheet 43c located at the top of the backlight unit. At this time, when the step difference of the inclined region of the light guide plate 42 is designed to be maximized to make the light guide plate 42 thinner, more light is emitted to the inclined region, and a part of the light emitted from the light guide plate 42 is emitted from the upper part of the light guide plate 42. It is directly incident on the prism sheet 43c. At this time, light is emitted through an empty space between peaks and valleys of the upper prism sheet 43c and is recognized as a light leak.

The present invention is to solve the above problems, in a thin structured backlight unit to which a partial wedge-shaped light guide plate is applied, a backlight unit that prevents light leakage by blocking light traveling between peaks and valleys of a prism sheet, and a liquid crystal display having the same The purpose is to provide a device.

Other objects and features of the present invention will be described in the following constitution of the invention and claims.

In order to achieve the above object, a backlight unit according to an embodiment of the present invention includes a light guide plate having a light incident area and a light guiding area having different thicknesses.

A lower prism sheet is positioned above the light guide plate.

An upper prism sheet composed of a first region having prism mountains and a second region having a flat upper surface is positioned on the lower prism sheet.

In addition, the liquid crystal display device according to an embodiment of the present invention may further include a liquid crystal panel positioned above the backlight unit.

In this case, the second region may extend along a direction in which the light sources are arranged close to the light source, and the prism mountain may extend in a direction perpendicular to the extending direction of the second region.

An upper surface of the second region may be positioned on the same plane as a vertex of the prism mountain.

An upper surface of the second region may protrude beyond a vertex of the prism mountain.

As described above, in the backlight unit and the liquid crystal display device having the same according to an embodiment of the present invention, the upper prism sheet positioned at the light entrance part of the light guide plate has a flat region instead of a prism mountain, and the prism sheet extends between the peaks and valleys of the prism sheet. light can be blocked. Accordingly, light leakage from the light entrance portion of the light guide plate may be reduced and at the same time, hot spot uniformity may be improved.

1 is a perspective view showing the structure of a general backlight unit by way of example;
2 is an exploded perspective view showing the structure of a liquid crystal display device according to a first embodiment of the present invention as an example;
3 is a perspective view exemplarily showing the structure of a backlight unit in the liquid crystal display device according to the first embodiment of the present invention shown in FIG. 2;
4 is a view schematically showing a cross-sectional structure of a backlight unit in the liquid crystal display device according to the first embodiment of the present invention shown in FIG. 2;
5A and 5B are graphs showing luminance uniformity according to the position of the light entering part.
6 schematically shows a cross-sectional structure of a backlight unit according to a second embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings, a preferred embodiment of a backlight unit and a liquid crystal display device having the same according to the present invention will be described in detail so that those skilled in the art can easily implement the present invention.

Advantages and features of the present invention, and methods of achieving them, will become clear with reference to the detailed description of the following embodiments taken in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below and will be implemented in various forms different from each other, only these embodiments make the disclosure of the present invention complete, and common knowledge in the art to which the present invention pertains. It is provided to completely inform the person who has the scope of the invention, and the present invention is only defined by the scope of the claims. Like reference numbers designate like elements throughout the specification. The sizes and relative sizes of layers and regions in the drawings may be exaggerated for clarity of explanation.

When an element or layer is referred to as “on” or “on” another element or layer, it includes both cases where another element or layer is intervening as well as directly on another element or layer. do. On the other hand, when an element is referred to as “directly on” or “directly on”, it indicates that no other element or layer is intervening.

The spatially relative terms "below, beneath", "lower", "above", "upper", etc., refer to one element or component as shown in the drawing. It can be used to easily describe the correlation between and other elements or components. Spatially relative terms are to be understood as terms encompassing different orientations of elements in use or operation in addition to the orientations shown in the figures. For example, when flipping elements shown in the figures, elements described as “below” or “beneath” other elements may be placed “above” the other elements. Thus, the exemplary term “below” may include directions of both below and above.

Terminology used herein is for describing the embodiments, and therefore is not intended to limit the present invention. In this specification, singular forms also include plural forms unless specifically stated otherwise in a phrase. As used herein, "comprise" and/or "comprising" means that a stated component, step, operation, and/or element is the presence of one or more other components, steps, operations, and/or elements. or do not rule out additions.

2 is an exploded perspective view showing the structure of a liquid crystal display device according to a first embodiment of the present invention as an example.

FIG. 3 is a perspective view exemplarily showing the structure of a backlight unit in the liquid crystal display device according to the first embodiment of the present invention shown in FIG. 2 .

And, FIG. 4 is a view schematically showing a cross-sectional structure of a backlight unit in the liquid crystal display device according to the first embodiment of the present invention shown in FIG. 2 .

2 to 4, the liquid crystal display device according to the first embodiment of the present invention largely includes a liquid crystal panel 110 for outputting an image by injecting liquid crystal between a color filter substrate 105 and an array substrate 115. and a backlight unit 140 installed on the rear surface of the liquid crystal panel 110 to emit light across the entire surface of the liquid crystal panel 110 and a lower cover 150 accommodating the liquid crystal panel 110 and the backlight unit 140. It can be configured to include.

In the liquid crystal panel 110, pixels are arranged in a matrix form to output an image, and a color filter substrate 105 facing each other and bonded to maintain a uniform cell gap, an array substrate 115, and a color filter substrate 105 and a liquid crystal layer formed in the cell gap between the array substrate 115 .

Although not shown in detail, a common electrode and a pixel electrode are formed in the liquid crystal panel 110 in which the color filter substrate 105 and the array substrate 115 are bonded to apply an electric field to the liquid crystal layer and apply a voltage to the common electrode. When the voltage of the data signal applied to the pixel electrode is controlled in , the liquid crystal in the liquid crystal layer rotates by dielectric anisotropy according to the electric field between the common electrode and the pixel electrode to transmit or block light for each pixel to display characters or images. can do.

In this case, a switching element such as a thin film transistor (TFT) may be individually provided in each pixel to control the voltage of the data signal applied to the pixel electrode for each pixel.

That is, the array substrate 115 has gate lines and data lines arranged vertically and horizontally to define pixel areas, and thin film transistors, which are switching elements, may be formed at intersections of the gate lines and data lines.

The thin film transistor may include a gate electrode connected to a gate line, a source electrode connected to a data line, and a drain electrode connected to a pixel electrode.

The color filter substrate 105 includes a color filter composed of a plurality of sub-color filters that implement red, green, and blue colors, a black matrix that distinguishes between the sub-color filters and blocks light passing through the liquid crystal layer, and color filters. It may consist of an overcoat layer formed on the filter and the black matrix.

Polarizers 101 and 111 may be attached to the outside of the color filter substrate 105 and the array substrate 115, respectively. In this case, the lower polarizer 111 polarizes light passing through the backlight unit 140, and the upper polarizer (101) polarizes the light passing through the liquid crystal panel (110).

For example, the lower cover 150 may include a bottom and a plurality of side parts. The bottom may have a square shape. The side parts may extend vertically from each corner of the bottom to have a predetermined height. Edges of side parts adjacent to each other may be connected to each other. The space surrounded by the side parts and the bottom forms a storage space in which the liquid crystal panel 110 and the backlight unit 140 are accommodated.

The guide panel 145 mounts the above-described liquid crystal panel 110 on an inner stepped portion, and supports and fixes the liquid crystal panel 110 by a light blocking tape 146 . Then, the backlight unit 140 is covered with an inner wall.

In this way, the liquid crystal panel 110 composed of the color filter substrate 105 and the array substrate 115 is seated on the upper part of the backlight unit 140 through the guide panel 145, and the lower cover 150 is coupled to the lower part. It constitutes a liquid crystal display device.

Describing the backlight unit 140 according to the first embodiment of the present invention in detail, the light source unit 130 including a light source 131 generating light is installed on one side of the light guide plate 142. A reflector 141 may be installed on the rear surface of the light guide plate 142 .

In addition, a plurality of optical sheets 143 may be disposed on the upper surface of the light guide plate 142 to improve the efficiency of light emitted from the light guide plate 142 and irradiate the liquid crystal panel 110 .

The light guide plate 142 receives light from the light source 131 and guides the light toward the liquid crystal panel 110 . At this time, the light provided from the light source 131 is provided to the incident surface (or light incident part) of the light guide plate 142 . This incident surface faces one of the side surfaces of the lower cover 150 . That is, since the light source 131 is positioned on one side surface of the lower cover 150, the incident surface of the light guide plate 142 faces the light exit surface of the light source 131.

The light guide plate 142 may be made of polymethyl methacrylate (PMMA) or polycarbonate (PC) plastic.

In particular, the light guide plate 142 according to the first embodiment of the present invention is characterized by applying a partial wedge shape divided into a light incident region 142c and a light guide region 142a having different thicknesses.

For a thin structure, the light guiding area 142a may have a thinner thickness than the light incident area 142c. In this case, each of the light incident area 142c and the light guiding area 142a may have a substantially uniform thickness.

A step between the light incident area 142c and the light guiding area 142a may be designed as a slope, and a part of the light emitted from the light source 131 may be emitted to the sloped area 142b.

The reflector 141 is positioned between the bottom of the lower cover 150 and the rear surface of the light guide plate 142 . The reflector 141 serves to reflect the light from the light source 131 and the light from the light guide plate 142 toward the liquid crystal panel 110 .

At this time, the light source 131 is a means for emitting light, for example, CCFL (Cold Cathode Fluorescence Lamp), HCFL (Hot Cathode Fluorescence Lamp), EEFL (External Electrode Fluorescence Lamp) or LED can be selected and used. However, it is not limited thereto. Hereinafter, for convenience of description, a case in which an LED is used as the light source 131 is taken as an example.

As the light source 131, a red, green, and blue LED emitting red, green, and blue monochromatic light, or an LED emitting white light may be used.

In the case of an LED array emitting monochromatic light, red, green, and blue monochromatic LEDs are alternately arranged at regular intervals, the monochromatic light emitted therefrom is mixed with white light, and then supplied to the liquid crystal panel 110 to emit white light. In the case of an LED array, a plurality of LEDs are arranged at regular intervals to supply white light to the liquid crystal panel 110 .

At this time, the white light LED may be composed of a blue LED emitting blue light and a phosphor emitting yellow light by absorbing blue monochromatic light, and the blue monochromatic light output from the blue LED and the yellow monochromatic light emitted from the phosphor are mixed to produce white light It can be supplied to the liquid crystal panel 110 as.

The LED array may be formed of a light emitting package equipped with at least one LED.

The LED array as the light source 131 may be installed on the printed circuit board 132 so that the light exiting surface faces the incident surface of the light guide plate 142 .

At this time, the printed circuit board 132 according to the first embodiment of the present invention may be composed of a flexible printed circuit board (FPCB) having a copper foil layer therein.

The printed circuit board 132 may be installed above the light incident area 142c of the light source 131 and the light guide plate 142 . For example, the printed circuit board 132 may be installed above the light incident area 142c of the light source 131 and the light guide plate 142 through a heat dissipation tape (not shown). However, the present invention is not limited thereto, and as shown in FIG. 4 , the printed circuit board 132 covers not only the light source 131 and the upper part of the light incident area 142c of the light guide plate 142 but also a portion of the inclined area 142b. It can be installed up to the top. In this case, the printed circuit board 132 may be partially bent according to the inclination of the inclination region 142b.

A plurality of power lines (not shown) and electrical components (not shown) that transmit power to the light source 131 may be formed on the printed circuit board 132 .

Light emitted from the light source 131 is incident on the side of the light guide plate 142 made of a transparent material. In addition, the reflector 141 disposed on the rear surface of the light guide plate 142 reflects light transmitted through the rear surface of the light guide plate 142 toward the optical sheets 143 on the upper surface of the light guide plate 142 to reduce loss of light and improve uniformity. will make

In this case, the optical sheets 143 include a diffuser sheet 143a and upper and lower prism sheets 143b and 143c, and a protective sheet may be added.

The prism sheets 143b and 143c condense the light from the light guide plate 142, and the diffusion sheet 143a diffuses the light from the prism sheets 143b and 143c. In addition, the protective sheet serves to protect the prism sheets 143b and 143c and the diffusion sheet 143a. Light passing through the protective sheet is provided to the liquid crystal panel 110 side.

In this case, the diffusion sheet 143a protrudes more than the upper prism sheets 143b and 143c and may be positioned above the light guide area 142a of the light guide plate 142 . This is to minimize the case where backlight light without passing through the diffusion sheet 143a directly enters the prism sheets 143b and 143c.

Accordingly, the prism sheets 143b and 143c may be positioned at a predetermined distance from the boundary between the inclined area 142b and the light guiding area 142a of the light guide plate 142 .

The prism sheets 143b and 143c include a lower prism sheet 143b located above the diffusion sheet 143a to contact the diffusion sheet 143a and a lower prism sheet 143b located above the lower prism sheet 143b to contact the lower prism sheet 143b. It may be made of an upper prism sheet (143c).

The upper prism sheet 143c and the lower prism sheet 143b may have prism mountains arranged in a direction crossing each other. At this time, in FIG. 3, the lower prism peaks 143b' are arranged so that the lower prism sheet 143b has an angle of about 0 degrees with respect to the arrangement direction of the light source 131, and the upper prism sheet 143c is aligned with the light source 131. An example is shown in which the upper prism peaks 143c' are arranged to have an angle of about 90 degrees with respect to the arrangement direction of the prism peaks 143c'. However, the present invention is not limited thereto.

At this time, the lower prism sheet 143b according to the first embodiment of the present invention has a lower prism peak 143b' formed over the entire surface, that is, the entire surface of the rear surface. On the other hand, the upper prism sheet 143c consists of a first region 144a in which upper prism peaks 143c' are formed and a second region 144b in which upper prism peaks 143c' are not formed and the upper surface is substantially flat. to be characterized

The second region 144b may be located close to the light source 131 and may have a constant width along the arrangement direction of the light source 131 . That is, the second region 144b may extend along the arrangement direction of the light source 131 in proximity to the light source 131, and the upper prism peak 143c' is perpendicular to the extending direction of the second region 144b. direction can be extended.

Also, the upper surface of the second region 144b may be positioned on the same plane as the vertex of the upper prism mountain 143c'. However, the present invention is not limited thereto, and the bottom surface of the second region 144b may be located on the same plane as the vertex of the upper prism mountain 143c'. That is, the upper surface of the second region 144b may protrude beyond the vertex of the upper prism mountain 143c'.

The second region 144b is at least larger than the wavelength of light (~550 nm) and may have a width up to the light blocking region A covered by the light blocking tape 146 . If the second region 144b has a width smaller than the wavelength of light, light leakage may occur through the second region 144b as in the past, and if the width exceeds the light-shielding region A, the upper prism sheet 143c ) will not be able to function properly.

For reference, B shown in FIG. 4 represents a bezel width excluding an active area where an actual image is displayed.

For example, the backlight unit 140 having the above-described structure may be attached and fixed to the liquid crystal panel 110 by a light blocking tape 146 and stored in the bottom of the lower cover 150 positioned at the bottom. In particular, the light blocking tape 146 not only serves to attach and fix the liquid crystal panel 110 and the backlight unit 140, but also leaks light emitted from the backlight unit 140 to the outside through the side of the liquid crystal panel 110. It can also play a role in blocking out.

The light blocking tape 146 may be attached to the upper surface of the printed circuit board 132 and may extend to the second region 144b of the upper prism sheet 143c and be attached to the upper surface.

At this time, the liquid crystal panel 110 composed of the color filter substrate 105 and the array substrate 115 is seated on the light blocking tape 146 through the guide panel 145 . And, the lower cover 150 is coupled to the lower portion to form a liquid crystal display device.

As described above, the liquid crystal display device according to the present invention is provided with a flat second region 144b instead of the upper prism peak 143c' on the upper prism sheet 143c located in the light entrance part of the light guide plate 142 as described above. This is characterized in that light traveling between the peaks and valleys of the upper prism sheet 143c is blocked.

That is, when the partial wedge-shaped light guide plate 142 having a thin structure is applied as in the prior art, a step is generated in the inclined region 142b of the light guide plate 142, and a part of the light emitted to the inclined region 142b is reflected in the upper prism. It progresses to the empty space between the peaks and valleys of the sheet 143c and can be visually recognized as light leakage.

In order to prevent this, the present invention is characterized in that the upper prism sheet 143c close to the light source 131 of the backlight unit is provided with a flat second region 144b without distinction between peaks and valleys. That is, a portion of the upper prism sheet 143c close to the light source 131 forms a second area 144b having a flat shape without a prism shape, so that the light incident through the inclined area 142b of the light guide plate 142 is transmitted to the rear side. It is characterized in that light leakage is prevented by guiding to the first area 144a.

According to this, light leakage at the light entrance part of the light guide plate 142 is reduced, and at the same time, hot spot uniformity is improved.

5A and 5B are graphs showing luminance uniformity according to the position of the light incident part.

At this time, FIG. 5A shows the luminance uniformity according to the position of the light entrance in the case of a comparative example in which prism mountains are formed on the entire surface of the upper prism sheet, and FIG. The luminance uniformity according to the position of the miner is shown through simulation.

The diffusion sheet, lower prism sheet, and upper prism sheet used in this simulation have thicknesses of about 0.04 mm, 0.065 mm, and 0.070 mm, and the light guide plate has thicknesses of about 0.40 mm and 0.28 mm in the light incident area and light guiding area. For example, a case with

In addition, in the graphs shown in FIGS. 5A and 5B, the horizontal axis represents 70 points in the light incident part, and the vertical axis represents luminance.

Luminance on the vertical axis is expressed in an arbitrary unit, where 1 means maximum luminance.

The greater the luminance difference between adjacent points is, the greater the luminance non-uniformity determined as light leakage or hot spot is.

Referring to FIGS. 5A and 5B , it can be seen from the simulation results that the luminance difference between adjacent points in the embodiment is smaller than that in the comparative example.

Therefore, it can be seen that in the case of the embodiment, compared to the comparative example, light leakage caused by peaks and valleys of the prism sheet is prevented, and hot spot uniformity of the light entrance part is improved.

The luminance uniformity of the comparative example was measured at about 54.9%, whereas the luminance uniformity of the example was measured at about 61.5%, indicating an improvement of about 10.7%.

Meanwhile, the present invention is applicable even when the partial wedge-shaped light guide plate has an inclined light incident area instead of a light incident area having a uniform thickness, and this will be described in detail through a second embodiment of the present invention.

6 is a diagram schematically showing a cross-sectional structure of a backlight unit according to a second embodiment of the present invention.

At this time, the second embodiment of the present invention shown in FIG. 6 has substantially the same structure as the backlight structure of the first embodiment of the present invention described above except for the structure of the light guide plate.

Referring to FIG. 6, the liquid crystal display device according to the second embodiment of the present invention includes a liquid crystal panel 210 for outputting an image by injecting liquid crystal between a color filter substrate 205 and an array substrate 215, and a liquid crystal It may include a backlight unit installed on the rear surface of the panel 210 to emit light across the entire surface of the liquid crystal panel 210 and a lower cover (not shown) accommodating the liquid crystal panel 210 and the backlight unit.

As described above, the liquid crystal panel 210 outputs an image in which pixels are arranged in a matrix form, and the color filter substrate 205, the array substrate 215, and the color filter are bonded to each other so as to maintain a uniform cell gap. It may be made of a liquid crystal layer formed in a cell gap between the substrate 205 and the array substrate 215 .

Polarizers 201 and 211 may be attached to the outside of the color filter substrate 205 and the array substrate 215, respectively. At this time, the lower polarizer 211 polarizes light passing through the backlight unit, and the upper polarizer 201 polarizes the light passing through the liquid crystal panel 210.

For example, the lower cover may include a bottom and a plurality of side parts. The bottom may have a square shape. The side parts may extend vertically from each corner of the bottom to have a predetermined height. Edges of side parts adjacent to each other may be connected to each other. The space surrounded by the side parts and the bottom constitutes a storage space in which the liquid crystal panel 210 and the backlight unit are accommodated.

The guide panel 245 mounts the aforementioned liquid crystal panel 210 on an inner stepped portion, supports and fixes the liquid crystal panel 210 by a light blocking tape 246, and wraps the backlight unit with an inner wall.

In this way, the liquid crystal panel 210 composed of the color filter substrate 205 and the array substrate 215 is seated through the guide panel 245 on the upper part of the backlight unit, and the lower cover is coupled to the lower part to form the liquid crystal display device. do.

Describing the backlight unit according to the second embodiment of the present invention in detail, a light source unit 230 including a light source 231 generating light may be installed on one side of the light guide plate 242, and the light guide plate 242 A reflector 241 may be installed on the rear surface of the.

In addition, a plurality of optical sheets 243 may be disposed on an upper surface of the light guide plate 242 to improve the efficiency of light emitted from the light guide plate 242 and irradiate the liquid crystal panel 210 .

The light guide plate 242 receives light from the light source 231 and guides the light toward the liquid crystal panel 210 . At this time, the light provided from the light source 231 is provided to the incident surface (or light incident part) of the light guide plate 242 . This incident surface faces one of the side surfaces of the lower cover 250 . That is, since the light source 231 is positioned on one side surface of the lower cover 250, the incident surface of the light guide plate 242 faces the light exit surface of the light source 231.

The light guide plate 242 may be made of PMMA or PC plastic.

In particular, the light guide plate 242 according to the second embodiment of the present invention is characterized by applying a partial wedge shape divided into a light incident region 242c and a light guide region 242a having different thicknesses.

For a thin structure, the light guiding area 242a may have a smaller thickness than the light incident area 242c. In this case, the light guiding area 242a has a substantially uniform thickness, but the light incident area 242c is light guiding in the light incident part. It may have an inclined shape in which the thickness decreases toward the region 242a.

Therefore, unlike the above-described first embodiment of the present invention, the light incident area 242c may be expressed as an inclined area, and a part of the light emitted from the light source 231 may be emitted to this inclined area.

As described above, in the light guide plate 242 according to the second embodiment of the present invention, the light incident area 242c also serves as an inclined area, so that the length of the light guide plate 242 can be reduced compared to the first embodiment described above. It is advantageous in terms of area and has the effect of giving design freedom in relation to the arrangement of other parts.

The reflector 241 is positioned between the bottom of the lower cover and the rear surface of the light guide plate 242 . The reflector 241 serves to reflect the light from the light source 231 and the light from the light guide plate 242 toward the liquid crystal panel 210 .

In this case, the light source 231 is a means for emitting light, and for example, CCFL, HCFL, EEFL, or LED may be selected and used, but is not limited thereto. Hereinafter, for convenience of description, a case in which an LED is used as the light source 231 is taken as an example.

The LED array may be formed of a light emitting package equipped with at least one LED.

The LED array as the light source 231 may be installed on the printed circuit board 232 so that the light exiting surface faces the incident surface of the light guide plate 242 .

At this time, the printed circuit board 232 according to the second embodiment of the present invention may be composed of an FPCB having a copper foil layer therein.

The printed circuit board 232 may be installed above the light source 231 and the light incident area 242c of the light guide plate 242 . For example, the printed circuit board 232 may be installed on top of the light source 231 and the light guide plate 242 and on a portion of the light incident area 242c through a heat dissipation tape (not shown). Accordingly, the printed circuit board 232 may be partially bent according to the inclination of the light incident area 242c.

A plurality of power lines (not shown) and electrical components (not shown) that transmit power to the light source 231 may be formed on the printed circuit board 232 .

Light emitted from the light source 231 is incident on the side of the transparent light guide plate 242 . In addition, the reflector 241 disposed on the rear surface of the light guide plate 242 reflects the light transmitted through the rear surface of the light guide plate 242 toward the optical sheets 243 on the upper surface of the light guide plate 242 to reduce light loss and improve uniformity. will make

The optical sheets 243 include a diffusion sheet 243a and upper and lower prism sheets 243b and 243c, and a protective sheet may be added.

The prism sheets 243b and 243c condense the light from the light guide plate 242, and the diffusion sheet 243a diffuses the light from the prism sheets 243b and 243c. In addition, the protective sheet serves to protect the prism sheets 243b and 243c and the diffusion sheet 243a. Light passing through the protective sheet is provided to the liquid crystal panel 210 side.

As described above, the diffusion sheet 243a protrudes more than the upper prism sheets 243b and 243c and may be positioned above the light guide area 243a of the light guide plate 242 . This is to minimize the case where backlight light without passing through the diffusion sheet 243a directly enters the prism sheets 243b and 243c.

Accordingly, the prism sheets 243b and 243c may be positioned at a predetermined distance from the boundary between the light incident area 242c and the light guiding area 243a of the light guide plate 242 .

The prism sheets 243b and 243c include a lower prism sheet 243b located above the diffusion sheet 243a to contact the diffusion sheet 243a and a lower prism sheet 243b located above the lower prism sheet 243b to contact the lower prism sheet 243b. It may be made of an upper prism sheet 243c.

Although not shown in detail, prism mountains may be arranged in a direction in which the upper prism sheet 243c and the lower prism sheet 243b intersect each other. At this time, for example, the lower prism peaks are arranged such that the lower prism sheet 243b has an angle of about 0 degrees with respect to the arrangement direction of the light sources 231, and the upper prism sheet 243c has an angle of about 0 degrees with respect to the arrangement direction of the light sources 231. The upper prism peaks may be arranged to have an angle of 90 degrees. However, the present invention is not limited thereto.

At this time, substantially the same as the above-described first embodiment of the present invention, the lower prism sheet 243b according to the second embodiment of the present invention has lower prism mountains formed over the front surface, that is, the entire surface of the rear surface. On the other hand, the upper prism sheet 243c is characterized in that it consists of a first region in which upper prism mountains are formed and a second region in which upper prism mountains are not formed and the upper surface is substantially flat.

The second region may be located close to the light source 231 and may have a constant width along the arrangement direction of the light source 231 . That is, the second region 244b may extend along the arrangement direction of the light source 231 in proximity to the light source 231, and the upper prism peak may extend in a direction perpendicular to the extending direction of the second region 244b. there is.

Also, the upper surface of the second region 244b may be positioned on the same plane as the vertex of the upper prism mountain. However, as described above, the present invention is not limited thereto, and the bottom surface of the second region 244b may be located on the same plane as the vertex of the upper prism mountain. That is, the upper surface of the second region 244b may protrude beyond the vertex of the upper prism mountain.

The second region is at least larger than the wavelength of light (~550 nm) and may have a width up to the light blocking region covered by the light blocking tape 246 .

For example, the backlight unit having the above-described structure may be attached and fixed to the liquid crystal panel 210 by the light blocking tape 246, and is accommodated in the bottom of the lower cover positioned below. In particular, the light blocking tape 246 not only serves to attach and fix the liquid crystal panel 210 and the backlight unit, but also serves to block light emitted from the backlight unit from leaking out through the side of the liquid crystal panel 210. can be done

The light blocking tape 246 may be attached to the upper surface of the printed circuit board 232 and may extend to the second region of the upper prism sheet 243c and be attached to the upper surface.

At this time, the liquid crystal panel 210 composed of the color filter substrate 205 and the array substrate 215 is seated on the light blocking tape 246 through the guide panel 245 . In addition, a lower cover 250 is coupled to the lower portion to form a liquid crystal display device.

As described above, the liquid crystal display device according to the present invention configured as described above has a flat second region instead of an upper prism mountain in the upper prism sheet 243c located in the light entrance part of the light guide plate 242 to form an upper prism sheet 243c. It is characterized in that it blocks light traveling between the peaks and valleys of the

According to this, light leakage from the light entrance part of the light guide plate 242 is reduced and at the same time, hot spot uniformity is improved.

Although many details are specifically described in the above description, this should be interpreted as an example of a preferred embodiment rather than limiting the scope of the invention. Therefore, the invention should not be defined according to the described examples, but should be defined according to the scope of the claims and the scope of the claims.

110,210: liquid crystal panel 131,231: light source
132,232: printed circuit board 141,241: reflector
142,242: light guide plate 142a, 242a: light guide area
142b: inclined area 142c, 242c: light incident area
143,243: optical sheet 143a, 243a: diffusion sheet
143b, 243b: lower prism sheet 143c, 243c: upper prism sheet
144a: first area 144b: second area

Claims (14)

a light guide plate having a light incident area and a light guiding area having different thicknesses;
a light source disposed toward the light incident area of the light guide plate;
a lower prism sheet positioned above the light guide plate; and
An upper prism sheet disposed on the lower prism sheet and comprising a first region having prism mountains and a second region having a flat upper surface,
The light incident area has an inclined shape in which the thickness decreases as it goes from the light incident surface to the light guide area, and the light guide area has a uniform thickness,
The upper surface of the second region protrudes beyond the apex of the prism mountain of the first region,
The backlight unit of claim 1 , wherein the first region and the second region are formed on an upper surface of the upper prism sheet. The backlight unit of claim 1 , wherein the second area extends along a direction in which the light sources are arranged close to the light source, and the prism mountain extends in a direction perpendicular to the extending direction of the second area. delete delete The backlight unit of claim 1 , further comprising a diffusion sheet disposed between the light guide plate and the lower prism sheet. The backlight unit of claim 5 , wherein the diffusion sheet protrudes more than the lower prism sheet and the upper prism sheet and is positioned above the light guide area of the light guide plate. delete delete The backlight unit of claim 1 , further comprising a printed circuit board that transmits power to the light source and is installed over the light source and the light incident area of the light guide plate. The backlight unit of claim 9 , further comprising a light blocking tape covering the printed circuit board and extending to a second region of the upper prism sheet and attached to the upper surface of the printed circuit board. The backlight unit of claim 10 , wherein the second area has a width greater than at least a wavelength of light and extends to a light blocking area covered by the light blocking tape. delete The backlight unit of any one of claims 1, 2, 5, 6, 10, and 11;
a liquid crystal panel on the backlight unit; and
A liquid crystal display device comprising a lower cover accommodating the liquid crystal panel and the backlight unit. According to claim 1,
The prism mountain of the lower prism sheet is formed downward and extends in a first direction,
The prism mountain of the upper prism sheet is formed toward the upper direction and extends in a second direction perpendicular to the first direction,
The second area is formed on the upper surface of the upper prism sheet to a width set along the second direction and extends along the first direction.

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