Back light assembly, liquid crystal display apparatus and manufacturing method thereof

A iquid crystal display apparatus that comprises: a liquid crystal display panel that displays a picture; a plurality of light guide plates that are installed on a rear of the liquid crystal display panel and are spaced from each other; and a back light assembly with a lamp assembly that emits light toward each light guide plate. As described above, the present invention provides the back light assembly and the liquid crystal display apparatus improving the brightness, reducing the thickness, removing the bright lines and the waterfall on the liquid crystal display panel, and lowering the manufacturing cost.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Applications No. 2003-0034921, filed May 30, 2003, and No. 2002-0059207, filed Sep. 28, 2002, in the Korean Intellectual Property Office, the disclosure of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display apparatus, further particularly to a liquid crystal display apparatus having advantages that it provides high brightness, a reduced thickness, while removing bright lines and waterfall and lowering a manufacturing cost.

2. Description of the Related Art

A liquid crystal display is a display device using a liquid crystal cell for modification of light, or a device turning variation of optical property such as birefringence, circumpolarization, dichroism, and light scattering caused by rearrangement of liquid crystal particles into visual variation by applying voltage to the liquid crystal particles having a particular arrangement.

The liquid crystal display apparatus requires an additional light source or a back light assembly to emit light onto a liquid crystal display panel because the liquid crystal display apparatus is a light receptive display apparatus displaying by adjusting an amount of the light received from outside. Herein, the liquid crystal display apparatus is divided into an edge-type liquid crystal display apparatus and a direct-down type liquid crystal display apparatus according to a structure of the back light assembly.

First of all, the edge-type back light assembly of the liquid crystal display apparatus comprises a lamp installed on sides of a light guide plate guiding the light, and is usually used in a small-size liquid crystal display apparatus such as a monitor for a laptop computer or a desktop computer because it does not have as good brightness in a big-size LCD as the direct-down type back light assembly has, even though it has advantage that it has a good homogeneity of the light, long durability, and good adaptability to flattening of the liquid crystal display apparatus.

Meanwhile, the direct-down type back light assembly is mainly used for the liquid crystal display apparatus having a big screen requiring a high brightness because of higher utilization efficiency of the light compared to the edge-type back light assembly.

Hereinbelow, a conventional direct-down type liquid crystal display apparatus will be described. Also, a rear will refer to a direction toward a reflector, while a front will refer to a direction toward a liquid crystal display panel unless described otherwise.

As illustrated inFIG. 1, a conventional direct-down type liquid crystal display apparatus100comprises a liquid crystal display panel110displaying a picture, a back light assembly120provided on the rear of the liquid crystal display panel and emitting the light onto the liquid crystal display panel110, a PCB (printed circuit board)140transferring a visual signal to the liquid crystal display panel110, and a front chassis160covering front edges of the liquid crystal display panel110.

The liquid crystal display panel110comprises a first panel114formed with a switching component like a TFT (thin film transistor) and with a pixel electrode, a second panel112, and a liquid crystal (not shown) inserted between the first panel114and the second panel112. Herein, a visual signal applied by the PCB140is transferred to a thin film transistor on the first panel114via a drive IC (not shown). Accordingly, the liquid crystal applied with an electric signal displays a picture using the light emitted from the back light assembly120.

The back light assembly120comprises a lamp121emitting the light, a reflector122installed on the rear of the lamp121, an optical sheet layer123having a diffusion plate123aand a prism sheet123bprovided above the lamp121and being spaced from the reflector122, and a supporting frame124accommodating and supporting the reflector122and the optical sheet layer123.

The reflector122is installed on the rear of the optical sheet layer123and spaced from the optical sheet layer123. Further the plurality of lamps121are installed on the front side of the reflector122. The reflector122can minimize loss of the light by reflecting part of the light emitted from the lamp121to the rear toward the optical sheet layer123.

The supporting frame124comprises a front frame126covering the front edges of the optical sheet layer123, and a rear supporting frame125combined on the rear of the front frame126and accommodating and supporting the optical sheet layer123and the reflector122in an accommodating space formed between the front frame126and the rear frame125.

Meanwhile, the liquid display panel110is installed on the front of the supporting frame124to closely support rear edges of the liquid display panel110. Also, an inverter (not shown) inverting a direct current supplied from the outside into an alternating current to supply the alternating current to the lamp121is provided on the rear of the reflector122.

The PCB140is connected to the first panel114with a FPC (flexible printed circuit)150. The FPC150connected to the first panel114is folded twice at each corner on inside of the supporting frame124to install the PCB140connected to the other end of the FPC150on the rear of the rear frame125.

Meanwhile, the conventional direct-down type liquid crystal display apparatus100has following disadvantages.

Firstly, as illustrated inFIG. 2, the conventional direct-down type liquid crystal display apparatus100has the disadvantage that bright lines occur on an area “a” on the direct front of the lamp121becomes brighter than an area “b” on the front of a space positioned between the lamps121.

Secondly, to prevent the bright lines caused by difference of the brightness of each lamp121, a distance “Q” between the lamp121and the optical sheet layer123has to be increased, which makes the flattening of the liquid crystal display apparatus100hard. Also, in case that a distance “P” between the lamps121is decreased, it may prevent occurrence of the bright lines on the liquid crystal display panel110, however it has disadvantages that it increases a manufacturing cost and consumes more power.

Thirdly, in the conventional direct-down type liquid crystal display apparatus100, the lamp121on the rear of the optical sheet layer123radiates heat as well as it emits the light. The heat radiated from the lamp121deteriorates the liquid crystal display panel110and the optical sheet layer123and, as a result, it decreases the brightness of the liquid crystal display apparatus100due to the heat.FIG. 3illustrates variation of the brightness according to passage of time during an operation of the conventional direct-down type liquid crystal display apparatus100. Here, “A” inFIG. 3represents the variation of the brightness of the lamp121according to the passage of the time, and “B” inFIG. 3represents the variation of the brightness of liquid crystal display apparatus100measured when it is assembled completely. It can be inferred that decrease of the brightness by the deterioration of the LCD panel110or the optical sheet layer123is more intensified when the liquid crystal display apparatus100is assembled completely than decrease of the brightness of the lamp121itself when it is not assembled.

Fourthly, it has disadvantage that waterfall occurs on the liquid crystal display panel110by mutual interference on an area where a driving frequency of the lamp121and a driving frequency of the inverter are similar to each other when the inverter is installed on the rear of the reflector122which is close to the rear of the lamp121to operate the lamp121. A ITO (indium tin oxide) sheet123cis installed on the front of the diffusion plate123ato solve the problem, however, low transmittivity of the ITO sheet123cdecreases the brightness of the liquid crystal display apparatus100, increasing the manufacturing cost of the liquid crystal display apparatus100.

Fifthly, in the direct-down type liquid crystal display apparatus100, the front chassis160and the supporting frame124should be disassembled to open and replace a broken lamp among the plurality of lamps121.

SUMMARY OF THE INVENTION

Accordingly, it is an aspect of the present invention to provide to a liquid crystal display apparatus having advantages that it provides high brightness, a reduced thickness, while removing bright lines and waterfall and lowering a manufacturing cost.

The foregoing and other aspects of the present invention are achieved by providing a liquid crystal display apparatus that comprises: a liquid crystal display panel that displays a picture; a plurality of light guide plates that are installed on a rear of the liquid crystal display panel and are spaced from each other; and a back light assembly with a lamp assembly that emits light toward each light guide plate.

According to an aspect of the invention, the back light assembly further comprises: a spacing part installed between the light guide plates to install the light guide plates spaced from each other; and a mold frame covering the lamp assembly installed on the opposite ends of the light guide plates.

According to an aspect of the invention, the back light assembly further comprises a reflector provided on a rear of the lowest light guide plate installed below the other light guide plates and reflecting the light.

According to an aspect of the invention, the back light assembly further comprises an auxiliary reflector plate installed between the spacing part and each light guide plate.

According to an aspect of the invention, the spacing part comprises a blocking protrusion preventing the auxiliary reflector plate from moving toward the inside in a horizontal direction.

According to an aspect of the invention, the back light assembly further comprises an optical diffuser provided on a surface of each light guide plate facing each other light guide plate.

According to an aspect of the invention, the back light assembly further comprises an optical diffuser provided on a surface of the light guide plate facing the liquid crystal display panel or on a surface of the light guide plate opposite to the surface facing the liquid crystal display panel.

According to an aspect of the invention, the optical diffuser is a convexo-concave pattern formed on the surface of the light guide plate.

According to an aspect of the invention, the optical diffuser is a convexo-concave pattern formed on the surface of the light guide plate.

According to an aspect of the invention, the lamp assembly comprises: a lamp; and a lamp reflector preventing the light of the lamp from radiating to a direction opposite to the light guide plate.

According to an aspect of the invention, the liquid crystal display apparatus further comprises a front frame installed between the liquid crystal display panel and the highest light guide plate positioned on the top of the other light guide plates.

According to an aspect of the invention, the liquid crystal display apparatus comprises: a PCB operating the liquid crystal display panel; and a FPC connecting the liquid crystal display panel and the PCB, and folded at an edge of the back light assembly to install the PCB on one side of the circumference of the back light assembly.

According to another aspect of the present invention, the above and other aspect may be also achieved by providing a manufacturing method of a liquid crystal display apparatus that comprises: providing a mold frame that is partitioned by a spacing part and is formed with a front accommodation space and a rear accommodation space; accommodating a second light guide plate into the rear accommodation space of the mold frame; installing a reflector on a rear of the second light guide plate; accommodating a first light guide plate into the front accommodation space of the mold frame; and inserting lamp assemblies into either of the opposite spaces which are formed between the mold frame and the first light guide plate and the second light guide plate.

According to an aspect of the invention, the manufacturing method of the liquid crystal display apparatus further comprises: placing an optical sheet layer on the front of the first light guide plate; and installing a front frame to closely contact the front edges of the first light guide plate and the optical sheet layer.

According to an aspect of the invention, the manufacturing method of the liquid crystal display apparatus further comprises covering the rear accommodation of the mold frame.

According to an aspect of the invention, the lamp assembly is inserted slidingly into the space formed between the mold frame and the circumference of the first light guide plate and the second light guide plate.

According to an aspect of the invention, the lamp assembly is inserted slidingly into the space formed between the mold frame and the circumference of the first light guide plate and the second light guide plate.

According to an aspect of the invention, the lamp assembly is inserted slidingly into the space formed between the mold frame and the circumference of the first light guide plate and the second light guide plate.

According to another aspect of the present invention, the above and other aspect may be also achieved by providing a back light assembly that is installed on a rear of a liquid crystal display panel of a liquid crystal display apparatus, comprising: a plurality of light guide plates that are installed on the rear of the liquid crystal display panel and are spaced from each other; and a lamp assembly that emits light toward each light guide plate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As illustrated inFIG. 4, a liquid crystal display apparatus1according to a first embodiment of the present invention comprises a liquid crystal display panel10displaying a picture, a back light assembly20provided on a rear of the liquid crystal display panel10and emitting light onto the liquid crystal display panel10, a PCB (printed circuit board)40to apply a visual signal to the liquid crystal display panel10, and a front chassis60covering front circumference of the liquid crystal display panel10.

The liquid crystal display panel10comprises a first panel14formed with a switching component like a TFT (thin film transistor) and with a pixel electrode, a second panel12, and a liquid crystal (not shown) inserted between the first panel14and the second panel12. Herein, the visual signal applied by the PCB40is transferred to a thin film transistor on the first panel14via a drive IC (not shown). Accordingly, the liquid crystal applied with an electric signal displays a picture with the light emitted from the back light assembly20.

The back light assembly20comprises a first light guide plate21and a second light guide plate22installed on the rear of the liquid crystal display panel10being spaced from each other, and a first lamp assembly23and a second lamp assembly24installed at least on one side of the opposite ends of the light guide plates21and22and emitting the light toward the respective light guide plates21and22.

The first light guide plate21and the second light guide plate22is spaced from each other in parallel by a spacing part25. The lamp assemblies23and24are supported by a mold frame28, as it is covered and accommodated by the mold frame28on the opposite ends of the light guide plates21and22. Herein, the spacing part25functions to prevent electrical interference between both lamp assemblies23and24by separating the first lamp assembly23and the second lamp assembly24. Also, an inner space of the mold frame28is partitioned into a front accommodation space and a rear accommodation space by the spacing part25. The embodiment of the present invention adopts the mold frame28integrated with the spacing part25.

The first light guide plate21is accommodated in the front accommodation space of the mold frame28as a rear of the first light guide plate21is closely supported by the spacing part25. Also, the second light guide plate22is accommodated in the rear accommodation space of the mold frame28as a front of the second light guide plate22is closely supported by the spacing part25. In other words, the first light guide plate21and the second light guide plate22are spaced from each other with a predetermined distance by the spacing part25as they are accommodated in the front and rear accommodation spaces, respectively.

The rear of the light guide plate21is provided with an optical diffuser21a. The optical diffuser21afunctions to improve brightness of the liquid crystal display apparatus1by spreading the light emitted from the second light guide plate22and the first lamp assembly23evenly throughout all area of the liquid crystal display panel10as the optical diffuser21adiffuses the light emitted from the second light guide plate22and the first lamp assembly23toward the liquid crystal panel10. Herein, the optical diffuser21amay be provided as a convexo-concave pattern on the rear of the first light guide plate21, or diffusing effect may be achieved by printing the rear of the first light guide plate21with light-diffusing ink or by inserting material having a light-diffusing property into the first light guide plate21.

Additionally, the optical diffuser22amay be provided on the front of the second light guide plate22. The optical diffuser22aprovided on the second light guide plate22is preferably made of the same material and the same shape used for the optical diffuser21aon the first light guide plate21.

The first lamp assembly23and the second lamp assembly24is installed in spaces formed between the circumference of the first and the second light guide plates21and22and inside walls of the front and the rear accommodation spaces of the mold frame28, respectively.

The first lamp assembly23and the second lamp assembly24comprises lamps23aand24aemitting the light, and lamp reflectors23band24breflecting the light emitted from the lamps23aand24ain the direction opposite to the first and the second light guide plates21and22toward the first light guide plate21and the second light guide plate22. Such configuration of the first lamp assembly23and the second lamp assembly24as described above minimizes loss of the light caused by the light emitted in direction opposite to the first light guide plate21and the second light guide plate22. Also, by providing the lamps23aand24aaround the circumference of the first and the second light guide plates21and22, the waterfall occurring on the liquid crystal display panel10by the mutual interference can be removed by spacing an inverter (not shown) installed on the rear of the back light assembly20from the lamps23aand24a.

A reflector plate26is provided on the rear of the second light guide plate22. The reflector plate26is made of material having a regular reflection property such as a silver fusion film or a white film. Accordingly, the reflector plate26minimizes the loss of the light emitted from the lamp24aof the second lamp assembly24by reflecting the light transmitted through the rear of the second light guide plate22toward the second light guide plate22.

Here, a rear frame30is provided on the rear of the reflector plate26to protect the rear of the rear accommodation space of the mold frame28as combined with the mold frame28. Herein, a screw hole30ais provided on the rear frame30, and a screw combining part28ais provided on the mold frame28on a position corresponding to the screw hole30aso that the rear frame30combined to the mold frame28by combining a screw90passing through the screw hole30awith the screw combining part28a. The embodiment of the present invention illustrates the rear frame30combined to the mold frame28with the screw90, however, various combining means such as a hook coupling or an adhesive member may be employed as well.

The PCB40is connected to the first panel14of the liquid crystal display panel10with a FPC (flexible printed circuit)50. The FPC50connected to the first panel14is folded at an edge of the back light assembly20to install the PCB40connected to the other end of the FPC50on one side of the circumference of the back light assembly20.

Meanwhile, an optical sheet layer31may be provided on the front of the first light guide plate21to improve the quality of the liquid crystal display panel10. The optical sheet layer31preferably comprises a diffusion panel31adirecting the light entering from the first light guide plate21toward the liquid crystal display panel10in a perpendicular direction, and a prism sheet31bimproving the brightness of the liquid crystal display apparatus1.

The diffusion panel31acan improve front brightness of the liquid crystal display apparatus1by directing the light entering in a normal line direction toward the perpendicular direction according to the refraction of the light, because the light from the first light guide plate21has more amount of the light in the normal line direction than amount of the light in the perpendicular direction.

The prism sheet31bis provided on the front of the diffusion panel31a. The prism sheet31bimproves the frontal brightness of the liquid crystal display apparatus1and reduces power consumption by decreasing a view angle of the light emitted from the diffusion panel31a, because the light emitted from the diffusion panel31ais diffused light having a broad view angle.

A front frame29protects the front edges of the first light guide plate21and the front edges of the optical sheet layer31.FIG. 4illustrates the front frame29covering up the outer wall of the mold frame28having the front accommodation space. However, the front frame29may be provided just to contact the front of the first light guide plate21, the optical sheet layer31, and the mold frame28. Herein, the front frame29covers the front as combined with the mold frame28using various types of combining structures such as a screw, a hook, and an adhesive member. Also, a supporting groove29amay be provided on a front of the front frame29to accommodate and support the liquid crystal display panel10.

FIG. 5is a cross-sectional view of a liquid crystal display apparatus1′ according to a second embodiment of the present invention. As illustrated, the liquid crystal display apparatus1′ according to the second embodiment of the present invention comprises auxiliary reflector plates27installed between the spacing part25and the rear of the first light guide plate21, between the spacing part25and the front of the second light guide plate22, and between the front of the first light guide plate21and the rear of the front frame29. Accordingly, it reduces the loss of the light by reflecting the light emitted from the lamps23aand24awith a predetermined incidence angle toward the first light guide plate21and the second light guide plate22.

Herein, a spacing part25′ provided with the auxiliary reflector plate27is preferably formed with a blocking protrusion25ato prevent the auxiliary reflector panel27from moving toward the inside in a horizontal direction. Also, the rear side of the front frame29is preferably formed with a blocking protrusion29bto prevent the auxiliary reflector panel27from moving.

FIG. 6is a cross-sectional view of a liquid crystal display apparatus1″ according to a third embodiment of the present invention. The liquid crystal display apparatus1″ according to the third embodiment of the present invention is provided with an optical diffusion part22a′ for a second light guide plate22′ on the rear of the second light guide plate22′.

Hereinbelow, an assembly process of the liquid crystal display apparatus1′ according to the second embodiment of the present invention, for example, will be described in reference toFIGS. 7 through 10.

Firstly, as illustrated inFIG. 7, the mold frame28is provided on a predetermined working table in a way that the rear accommodation space of the mold frame28integrated with the spacing part25′ faces upward. The second light guide plate22is place on the spacing part25′ to accommodate the second light guide plate22in the rear accommodation space of the mold frame28, and then the reflector panel26is installed on the second light guide plate22.

Upon completing the process described above, as illustrated inFIG. 8, the rear frame30covers the rear accommodation space of the mold frame28as the second light guide plate22and the reflector panel26is accommodated in the rear accommodation space. Herein, the rear frame30may be combined to the mold frame28by the screw90as described above.

Upon completing combination of the rear frame30, as illustrated inFIG. 9andFIG. 10, the mold frame28is placed upside down so that the front accommodation space faces upward. The first light guide plate21is place on the spacing part25′ of the mold frame28to accommodate the first light guide plate21in the front accommodation space of the mold frame28, and then the optical sheet layer31is installed on the first light guide plate21. The front frame29is closely installed on the side of the circumference of the first light guide plate21and the optical sheet layer31.

Upon completing installation of the front frame29, the lamp assemblies23and24are inserted into the spaces formed between the mold frame28and the sides of the circumference of the first and the second light guide plates21and22, completing assembly of the back light assembly20. Herein, the lamp assemblies23and24are inserted slidingly into the space formed between the mold frame28and the sides of the circumference of the first and the second light guide plates21and22. In this way, the lamps23aand24acan be replaced without disassembling the back light assembly20by providing the lamp assemblies23and24to be insertable slidingly into the space between the mold frame28and the sides of the circumference of the first and the second light guide plates21and22.

Meanwhile, the auxiliary reflector panel27can be installed by sliding into the space between the mold frame28and the first and the second light guide plate21and22in the same manner described above for the lamp assemblies23and24after or before the insertion of the lamp assemblies23and24. Also, it may be installed onto the spacing part25′ of the mold frame28when installing the first and the second light guide plates21and22.

Upon completing assembly of the back light assembly20according to the process described above, the liquid crystal display panel10is inserted into the supporting groove29aof the front frame29, and then it is placed on the front of the back light assembly20. Lastly, the front chassis60covers the front edges of the liquid crystal display panel10.

In the embodiments described above, the liquid crystal display apparatuses1,1′, and1″ comprise two light guide plates21and22, however, they may comprise more than three light guide plates being spaced from each other.

Additionally, the first and the second lamp assemblies23and24are installed on the opposite ends of the first and the second light guide plates21and22, respectively, however, the lamp assemblies may be provided on either of the opposite ends of the respective light guide plate with the rear of the light guide plate formed to be sloped.

In the embodiments described above, the liquid crystal display apparatuses1,1′, and1″ comprise the optical sheet layer31, however, the optical sheet layer31does not necessarily include both the diffusion panel31aand the prism sheet31b, in case that the first and the second light guide plates21and22and the optical diffuser21aand22aon the respective light guide plates21and22improves the quality of the brightness.

Hereinbelow, advantages of the liquid crystal display apparatuses1,1′, and1″ according to embodiments of the present invention compared to the convention direct-down type liquid crystal display apparatuses100will be described.

Firstly, the liquid crystal display apparatuses1,1′, and1″ according to the embodiments of the present invention improve the brightness as a whole compared to the convention direct-down type liquid crystal display apparatuses100. If the light enters into the second light guide plate22as to proceed toward the optical diffuser22a, the light is diffused by the optical diffuser21aformed on a rear surface of the first light guide plate21, and then enters the first light guide plate21. Accordingly, as illustrated inFIG. 11, it improves the brightness as a whole compared to the conventional direct-down type liquid crystal display apparatus100.

Additionally, the liquid crystal display apparatuses1,1′, and1″ according to embodiments of the present invention is less affected by heat from the lamp23aas the lamp23ais installed on the opposite sides on the light guide plate.FIG. 12illustrates temperature distribution of the liquid crystal display apparatuses1,1′, and1″ according to embodiments of the present invention and the conventional direct-down type liquid crystal display apparatus100, andFIG. 13illustrates variation of the brightness according passage of time in the liquid crystal display apparatuses1,1′, and1″ according to embodiments of the present invention. As illustrated in those drawings, the liquid crystal display apparatuses1,1′, and1″ according to embodiments of the present invention reduces effect of the heat from the lamp23aand prevents the heat from decreasing the brightness of the liquid crystal display apparatuses1,1′, and1″.

Also, the liquid crystal display apparatuses1,1′, and1″ according to embodiments of the present invention is thinner than the conventional direct-down type liquid crystal display apparatus100. In the conventional direct-down type liquid crystal display apparatus100, the lamps121and the liquid crystal display panel110is required to be spaced from each other to prevent the bright lines caused by the variation of the brightness between the lamps121as the lamps121are installed on the rear of the liquid crystal display panel110. However, in the liquid crystal display apparatuses1,1′, and1″ according to embodiments of the present invention, any additional space is not required other than the space that the first light guide plate21and the second light guide plate22take, which reduces the thickness. Additionally, the liquid crystal display apparatuses1,1′, and1″ according to embodiments of the present invention provides the same view angle as the view angle provided by the conventional direct-down type liquid crystal display apparatus100as well as it reduces the thickness.

Also, the liquid crystal display apparatuses1,1′, and1″ according to embodiments of the present invention reduces manufacturing cost visibly compared to the conventional direct-down type liquid crystal display apparatus100as well as it improves the quality of the product. The conventional direct-down type liquid crystal display apparatus100used the ITO sheet having high price to remove the waterfall, however, it appears that the liquid crystal display apparatuses1,1′, and1″ according to embodiments of the present invention does not require additional diffusion sheet other than the optical diffuser21aprovided on the first and the second light guide plate21and22. Accordingly, it reduces the manufacturing cost visibly.

As described above, the present invention provides the back light assembly and the liquid crystal display apparatus improving the brightness, reducing the thickness, removing the bright lines and the waterfall on the liquid crystal display panel, and lowering the manufacturing cost.