WO2006137660A2

WO2006137660A2 - Back light unit

Info

Publication number: WO2006137660A2
Application number: PCT/KR2006/002339
Authority: WO
Inventors: Young Ho Yoo
Original assignee: Fawoo Technology Co., Ltd.
Priority date: 2005-06-22
Filing date: 2006-06-19
Publication date: 2006-12-28
Also published as: WO2006137660A3

Abstract

Disclosed herein is a black light unit. The back light unit includes a light guide plate (10), a light source unit (21, 23, 25) and a frame (30). The light guide plate (10) comprises a light plate having on one surface thereof a plurality of notches (11), an uneven dot pattern, a printed dot pattern, or a sanded surface, or a light diffusion plate. The light source unit includes a light source (21) for applying light to the light guide plate (10). In this case, the frame (30) comprises a heat emitting frame, and the PCB (23) equipped with the light source (21) is secured to the heat emitting frame (30). Further, the heat emitting frame (30) and the light guide plate (10) are coupled to form a plane without forming a step.

Description

Description BACK LIGHT UNIT

Technical Field

[1] The present invention relates to a back light unit, and more particularly to a back light unit having a heat emitting frame, which is constructed so that heat emission from a light source unit is efficiently conducted, thus preventing the luminous intensity of a light source from being reduced due to the heat emission, and preventing the lifespan of the light source unit from being shortened, and which is assembled with a light guide plate to form a plane without steps, thus being especially suitable for floor illumination, considerably increasing productivity, and enabling easy construction of a large-sized back light unit through continuous coupling. Background Art

[2] Generally, a back light unit used for an LCD (Liquid Crystal Display), advertisement, illumination, floor illumination, a decoration, etc. includes a light guide plate comprising an acrylic plate that transmits light. A light source, which emits light, is mounted to one side of the light guide plate. The light guide plate uses a light panel which has on one surface thereof a predetermined pattern of notches, an uneven dot pattern, a printed dot pattern, or a sanded surface, or a light diffusion plate, so as to guide the path or diffusion of light emitted from the light source.

[3] FIG. 1 is a rear view showing the construction of a conventional back light unit 100, and FIG. 2 is a detailed sectional view taken along line A-A of FIG. 1.

[4] Referring to FIGS. 1 and 2, the back light unit is constructed as follows. That is, a light source 120 that emits light is provided on one side of a light guide plate 110 which is made of a light transmitting material. A plurality of V-shaped notches 112 is formed on the back surface of the light guide plate 110 in horizontal and vertical directions so as to uniformly diffuse light emitted from the light source 120 toward the front of the light guide plate 110 to which a display film 140 is attached. A reflection sheet 150 made of a PET material may be adhered to the back surface of the light guide plate 110 having the V-shaped notches 112.

[5] FIG. 3 shows a back light unit adopting an LED (Light Emitting Diode) as a light source. A frame 170 for the light source is mounted to one side of the light guide plate 110. A PCB (Printed Circuit Board) 23 to which the LED 21 is secured is attached to the inner surface of the light source frame 170 using a heat conductive adhesive 41. Disclosure of Invention Technical Problem

[6] According to the prior art, a PCB for a light source is installed in a frame for the light source. However, in order to prevent the PCB from being spaced apart from the light source frame 170, the light source frame 170 must be pushed toward a light guide plate 110 when the PCB is attached to the light source frame 170 using a heat conductive adhesive 41. Thus, it is complicated to assemble the back light unit.

[7] Further, an end of the light guide plate 110 is inserted into the light source frame

170, and the light guide plate 110 and the light source frame 170 are coupled to each other using tape or the like. Thus, such a construction is vulnerable to moisture, so the light source may be damaged by moisture. Further, the assembly thereof is complicated, so that a lot of labor and time is required. In particular, when a large- sized light guide plate is built using a plurality of light guide plates, the work of coupling the light guide plates to each other is very complex.

[8] Further, the conventional back light unit is problematic in that an end of the light guide plate 110 is inserted into the light source frame 130 to be secured to the light source frame, as shown in FIGS. 2 and 3, so that a step is inevitably formed at a junction between the exposed upper surface of the light guide plate 110 and the light source frame 130.

[9] When a plurality of back light units with smaller size are patched together to form a larger screen, steps are formed at coupling portions due to the light source frames 130. Hence, several small screens must be assembled with each other to make a large-sized screen. Due to such a construction, people may undesirably see grid lines.

[10] Further, when the back light unit is operated, most of the heat is generated at portions around leg pins of the LED. However, since heat is transmitted outside only through the PCB and the adhesive, rapid heat emission is impossible. Thus, the lifespan of the light source may be reduced, and the luminous intensity of the light source may be lowered.

[11] In the case of floor illumination, when many people step on and pass over the back light unit, people may trip over the step. Moreover, impurities or water may collect thereon. The step forms space between the back light unit and a floor, so that a filling material must be charged in the space, thus increasing the manufacturing cost.

[12] Thus, the conventional back light unit is problematic in that the appearance of the entire product is marred, and thus cannot be applied to floor illumination.

[13] Accordingly, the present invention has been made keeping in mind the above problem occurring in the prior art, and an object of the present invention is to provide a back light unit having a heat emitting frame, which is constructed so that heat emitted from a light source unit is efficiently conducted, thus preventing the luminous intensity of a light source from being lowered because of the heat emission, and preventing the life-span of the light source unit from being shortened, and which affords ease of assembly, thus considerably increasing productivity, and enabling easy building of a large-sized back light unit through continuous coupling.

[14] Another object of the present invention is to provide a back light unit, in which no step is formed at the junction between a heat emitting frame and a light guide plate, thus maintaining a planar shape, therefore allowing a large-sized back light unit to be assembled from a plurality of small back light units.

[15] A further object of the present invention is to provide a back light unit, which is easily sealed, thus preventing moisture from entering, therefore being efficiently applied to floor illumination. Technical Solution

[16] In order to accomplish the above objects, the present invention provides a back light unit including a light guide plate having on one surface thereof a plurality of notches, an uneven dot pattern, a printed dot pattern, or having a sanded surface, or a light diffusion plate; a light source unit including a light source for applying light to the light guide plate, and a PCB coupled to the light source; and a frame for mounting the light source unit to the light guide plate, wherein the frame comprises a heat emitting frame, the PCB equipped with the light source being secured to the heat emitting frame, and the heat emitting frame and the light guide plate are coupled to form a plane without forming a step at a junction between the heat emitting frame and the light guide plate.

[17] According to an aspect of this invention, a groove is formed at an end of the light guide plate to mount the heat emitting frame to the light guide plate.

[18] The heat emitting frame includes an embedded part and locking ends. The embedded part is fitted into the groove of the light guide plate, is open at an end thereof to receive the light source unit, and has internal space which receives the light source unit while permitting heat exchange between the heat source unit and the heat emitting frame.

[19] The locking ends form steps relative to the embedded part, and are integrally provided on the embedded part to be locked to the end of the light guide plate.

[20] According to another aspect of this invention, a protruding end is provided at an end of the light guide plate where the light source unit is mounted.

[21] The heat emitting frame defines space for receiving the light source unit while permitting heat exchange between the light source unit and the heat emitting frame, and a holding unit is provided at a predetermined position on the heat emitting frame to be coupled to the protruding end of the light guide plate.

[22] According to a further aspect of this invention, a predetermined thickness for light guidance and reflection remains at an end of the light guide plate, and a remaining thickness portion of the light guide plate is cut to form a light- source-unit mounting space. [23] The heat emitting frame has space for performing heat exchange, and is provided to correspond to the light-source-unit mounting space of the light guide plate.

Brief Description of the Drawings

[24] FIG. 1 is a rear view showing the construction of a general back light unit;

[25] FIG. 2 is a detailed sectional view taken along line A-A of FIG. 1 ;

[26] FIG. 3 is a vertical sectional view showing a conventional back light unit using an

LED; [27] FIGS. 4 to 8 show a back light unit, according to the first embodiment of the present invention, in which

[28] FIG. 4 is a cutaway perspective view of part of the back light unit;

[29] FIG. 5 is a front view of FIG. 4;

[30] FIG. 6 is a detailed sectional view taken along line B-B of FIG. 5;

[31] FIG. 7 is a view showing a heat emitting frame for the light source of FIG. 6;

[32] FIG. 8 is a view showing a light guide plate module, according to the first embodiment of the present invention; [33] FIGS. 9 and 10 are enlarged sectional views showing a back light unit, according to the second embodiment of the present invention; and [34] FIGS. 11 to 14 show a back light unit according to the third embodiment of the present invention, in which [35] FIG. 11 is an exploded perspective view showing the back light unit, according to the third embodiment of the present invention; and [36] FIGS. 12 to 14 are enlarged sectional views showing important parts of the back light unit.

Mode for the Invention [37] Hereinafter, a back light unit having a heat emitting frame, according to the preferred embodiment of the present invention, will be described in detail with reference to the accompanying drawings. [38] FIG. 4 is a partial cutaway perspective view showing the construction of a back light unit, according to the first embodiment of the present invention, FIG. 5 is a front view of FIG. 4, and FIG. 6 is a detailed sectional view taken along line B-B of FIG. 5. [39] A light guide plate 10 is made of a material through which light emitted from a light source 21 may be transmitted. That is, the light guide plate 10 comprises a transparent acrylic plate. A plurality of V-shaped notches 11 , a dot pattern, or a printed dot pattern is selectively formed on the back surface of the light guide plate 10, to which a display film is not attached. [40] A light source unit 20, transmitting light to the light guide plate 10, includes the light source 21, and a PCB 23 having a circuit which supplies proper power to the light source 21 or controls the power supply. [41] The light source unit 20 is secured to a heat emitting frame 30 so as to be in close contact with the heat emitting frame 30. Next, the heat emitting frame equipped with the light source unit is coupled to the light guide plate 10, thus forming a back light unit. [42] The key point of the invention is that no steps are formed at the junction between the frame 30 for the light source and the light guide plate 10, and the frame 30 and the light guide plate 10 are coupled to form a plane. [43] In this case, it is preferable that the light source 21 comprises a plurality of LEDs

23. [44] As shown in FIG. 7, an embedded part 31 of the heat emitting frame 30 includes

PCB holding parts 1 Ia, a light-source receiving part 3 Ib, and a power-cable receiving part 31c. The PCB holding parts 31a are in close contact with both sides of the PCB 23 of the light source unit to support the PCB 23. The light-source receiving part 31b is formed under the PCB holding parts 31a to be adjacent to the light source plate 10. The power-cable receiving part 31c is provided at a position adjacent to locking ends 35 so that a power cable 25 is installed in the power-cable receiving part 31c. Packing plugs

61 or airtight sealing grooves 63 are provided on both open ends of the heat emitting frame 30. [45] Further, the PCB holding parts 3 Ia of the embedded part 31 comprise 'U'-shaped grooves formed on opposite inner walls of the embedded part 31. Thus, the PCB holding parts 31a absorb and transmit heat generated from the PCB 23, in addition to stably holding the PCB 23. [46] The locking ends 35 of the heat emitting frame 30 protrude to correspond to the size of the light guide plate 10, so that the locking ends 35 and both sides of the light guide plate 10 form flat planes. [47] If the back light unit is assembled in this way, as shown in FIG. 6, no step is formed, but a flat plane is formed at the junction between the heat emitting frame 30 and the light guide plate 10. [48] Thus, even though a display film is attached to an advertisement display, wrinkles are not formed by the step, and the display film 40 is prevented from bending at the step. [49] More preferably, the heat emitting frame 30 is made of aluminum which permits smooth heat exchange and is light in weight. [50] Further, when the size of the light guide plate 10 is increased, it is preferable that the light source unit 20 be mounted to several sides of the light guide plate 10 to maintain the same brightness throughout the light guide plate 10. [51] FIG. 8 is a view showing a light guide plate module, according to the first embodiment of the present invention. Referring to the drawing, opposite ends of the light guide plate 10 are cut to light-source -unit mounting space 13, thus forming coupling grooves 15. A power connector 70 is provided in the coupling grooves 15 to be connected to neighboring light source units 20. A connection jack 71 for the power cable is provided on one side of the power connector, while a connection pin 73 is provided on the other side of the power connector, thus providing one light guide plate module which is to be used for a continuous coupling assembly.

[52] The manufacture and operation of the back light unit 1 having the heat emitting frame, according to the present invention, which is constructed as described above, will be described below.

[53] The heat emitting frame 30 is made of aluminum and formed through extrusion or drawing. After the heat emitting frame 30 is cut to a proper size, according to the size of a light guide plate to be manufactured, the light source unit 20 is installed in the PCB holding parts 31a defined in the embedded part.

[54] Subsequently, the heat emitting frame 30 is inserted into the light-source-unit mounting space 13 of the light guide plate. The operation of assembly is completed when silicone is applied to the packing plugs 61 or the sealing grooves 63. Thereby, the installation of the light source unit 20 is simply completed.

[55] According to the present invention which is assembled and installed in this way, the

PCB 23 of the light source unit 20 is secured to the heat emitting frame 30, so that heat generated from the light source unit 20 is directly transferred to the heat emitting frame 30, thus being emitted to the outside.

[56] As such, since the light source unit 20 smoothly emits heat, the reduction in luminous intensity of the light source 21 and the reduction in lifespan of the light source unit are prevented due to heat emission. Further, the assembly of the back light unit is finished by applying silicone to the packing plugs 61 or the sealing grooves 63, thus preventing moisture from entering, therefore allowing a constant luminous intensity to be maintained semi-permanently.

[57] Further, LEDs are used as the light source 21, so that the back light unit may be installed under any circumstances without being affected by temperature. The LEDs are more resistant to impact and have a long lifespan in comparison with fluorescent lamps, adapted in the prior art.

[58] The power-cable receiving space is provided in the product, thus allowing more light sources to be installed, in addition to maintaining good appearance.

[59] Meanwhile, the light-guide-plate module IA is provided with male and female connectors 70 comprising the connection jack 71 and the connection pin 73. Thus, it is very convenient to continuously couple neighboring light-guide-plate modules. [60] The light-guide-plate module IA may be called a 'light tile'. Thus, a large-sized back light unit can be built through a patchwork assembly method, like tile construction. Such a back light unit is applicable to various fields, such as advertisement screens mounted on floors or walls of plazas or buildings, or the interior decoration of buildings.

[61] When the light-guide-plate module IA is mounted on the floor, a transparent protective cover 90 must be provided on the outer surface of the display film 40 to protect the display film, thus preventing the display film 40 from being damaged (see, FIG. 6).

[62] Since the display film 40 can be attached in a planar state without being wrinkled or bent, the degree of contact between the display film 40 and the protective cover 90 covering the upper portion of the display film 40 is increased.

[63] Meanwhile, according to the second embodiment of this invention, shown in FIGS.

9 and 10, a protruding end 13a is provided on the end of a light guide plate 10 on which a light source unit 20 is located, a pair of holding legs 33a is provided on a heat emitting frame 30 to engage with the protruding end 13a, and PCB holding parts 31a are provided between the holding legs 33a and come into close contact with both sides of a PCB 23 so as to support the PCB 23.

[64] Further, the protruding end 13a is positioned at the center in a thickness direction of the light guide plate 10, so that steps 13b are formed on the front and back surfaces of the light guide plate. A holding unit 33 of the heat emitting frame 30 is coupled to the protruding end 13a to form flat planes with the front and back surfaces of the light guide plate. To this end, the holding unit 33 preferably has a thickness corresponding to the steps 13b of the light guide unit 10.

[65] When a power cable of the power source unit 20 is integrally embedded in the PCB

23, the PCB is fitted into the PCB holding parts 31a of the heat emitting frame 30 to be directly mounted on the bottom of the heat emitting frame (see, FIG. 9).

[66] However, when a power cable 25 is separately arranged, as shown in FIG. 10, PCB holding parts 31a are oppositely disposed on the inner wall of the heat emitting frame 30, thus defining space for receiving the power cable.

[67] FIGS. 11 to 14 show the third embodiment of the present invention.

[68] In order to prevent a joint portion from being formed because of the installation of a heat emitting frame, a predetermined thickness tl is provided on the front of a light guide plate 10, and a light- source-unit mounting space 13a is defined on the back of the light guide plate.

[69] The light guide frame 30 secured to the light guide plate 10 defines a space 31 in which a light source unit 20 is provided.

[70] In this case, the predetermined thickness tl is 30% or more of the total thickness of the light guide plate. [71] Preferably, the light-source-unit mounting space 13a of the light guide plate 10 has on a front end thereof a locking step 14 to guide and support the heat emitting frame

30. [72] The heat emitting frame 30 has the LED receiving space 31 therein, with PCB holding parts 31a being formed on the inner wall of the heat emitting frame 30. [73] Further, a protruding end 35a is provided on the front of the light guide plate 10 to correspond to the locking step 14. [74] One surface of the heat emitting frame 30 forms a flat plane with a back surface 17 of the light guide plate. The protruding end 35a forms flat planes with the back surface

17 and an upper end 18 of the light guide plate. Further, one or more grooves 36 may be formed on the heat emitting frame 30 to increase the heat emission surface. [75] Further, the heat emitting frame 30 is secured to the light guide plate 10 using engagement of the locking step 14 with the protruding end 35a or sealing adhesion. [76] Thus, the heat emitting frame 30 preferably has one or more sealing grooves 63 on the surface of the frame that contacts the light guide plate 10. [77] When the power cable of the light source unit 20 is integrally embedded in the PCB

23, the PCB is directly mounted on the bottom of the heat emitting frame 30 (FIG. 13). [78] The heat emitting frame 30 of the present invention may be directly adhered to the light guide plate 10 without the locking step 14 (FIG. 14). [79] According to the present invention, the part which has a predetermined thickness tl and realizes light guidance and reflection is provided on the light guide plate 10 in front of the light-source-unit mounting space, so that a light guide plate having no optical dead zone is achieved, and the strength of the light guide plate is maximally increased. [80] Therefore, when a plurality of back light units is coupled to each other in a patchwork assembly method without using an additional frame, boundary lines are not formed at joint portions, thus enabling the display of a large image at low cost. [81] As such, the present invention is capable of easily forming the large-sized back light unit through a continuous coupling method using the connector 70, thus being applicable to various fields, such as advertisement screens or the interior design of buildings. [82] According to the third embodiment of the present invention, the connector 70 may be installed in the light- source-unit mounting space 13a, so that the coupling grooves

15 of the first and second embodiments are not required, thus being convenient to produce and assemble. [83] Hereinbefore, the preferred embodiments of the present invention have been described with reference to the accompanying drawings. [84] It is to be understood that the words used herein are those for description rather than for limitation and that changes within the appended claims may be made without departing from the true scope and spirit of the invention.

[85] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Industrial Applicability

[86] As described above, a back light unit according to the present invention has several advantages, which will be described below.

[87] First, a light guide plate and a heat emitting frame may be continuously assembled to form a plane without a step, thus allowing a large-sized back light unit to be manufactured using small and cheap back light units.

[88] Second, the back light unit of this invention is especially suitable for floor illumination.

[89] Third, a light source unit is mounted to be in direct contact with a heat emitting frame, so that heat is efficiently emitted, thus preventing the luminous intensity of a light source from being lowered, in addition to preventing the life-span of the light source from being shortened, due to the heat emission.

[90] Fourth, it is easy to seal a light-source-unit mounting part, and the sealing capability thereof is superior, thus reducing costs spent on moisture prevention.

[91] Fifth, an LED is used as a light source, so that the back light unit of this invention may be installed under any circumstances without being affected by temperature.

[92] Sixth, since a light guide plate is not spaced apart from a heat emitting frame, there is no light leakage, thus improving light efficiency and achieving a slim product.

[93] Seventh, a power-cable receiving space is provided in a product, thus allowing more light sources to be installed, in addition to maintaining good appearance.

[94] Eighth, it is easy to assemble and handle, thus remarkably increasing productivity.

[95] Ninth, the coupling of a light source unit with a light guide plate is strong, thus protecting a light source against impacts.

[96] Therefore, it is easy to construct.

[97] Tenth, the assembly of continuously coupling neighboring back light units is very easily executed.

[98] Eleventh, it is easy to build a large-sized back light unit.

Claims

[ 1 ] A back light unit comprising : a light guide plate having on one surface thereof a plurality of notches, uneven dots, printed dots or sanded surface, or a light diffusion plate; a light source unit comprising a light source for applying light to the light guide plate and a PCB coupled to the light source; and a frame for mounting the light source unit on the light guide plate, wherein the frame comprises a heat emitting frame, and the PCB equipped with the light source is secured on the heat emitting frame, and the heat emitting frame and the light guide plate are coupled to form a plane without a step at a junction therebetween.

[2] The back light unit according to claim 1 , wherein a groove is formed at an end of the light guide plate to mount the heat emitting frame on the light guide plate, the heat emitting frame fitted into the groove of the light guide plate is provided with an embedded part, which is open at an end to receive the light source unit and has an internal space to receive the light source unit, and locking ends are integrally provided on both sides of the embedded part to form a plane with both sides of the light guide plate.

[3] The back light unit according to claim 1, wherein a protruding end is provided at an end of the light guide plate, and a holding unit is provided on both sides of the heat emitting frame secured on the light guide plate, so that an internal space is provided in the heat emitting frame to receive the light source unit therein.

[4] The back light unit according to claim 3, wherein the protruding end is protruded at a center of the light guide plate to form steps with the same width on both side ends of the light guide plate, and the holding unit of the heat emitting frame, coupled to the protruding end, has such a thickness that the heat emitting frame and the light guide plate can form a plane.

[5] The back light unit according to claim 1, wherein a predetermined thickness remains at an end of the light guide plate, and a remaining thickness portion of the light guide plate is cut to form a light- source-unit mounting space, and the heat emitting frame installed in the light-source-unit mounting space has a space for receiving the light source unit.

[6] The back light unit according to claim 5, wherein a locking step is provided at an end of the light guide plate to guide and support the heat emitting frame.

[7] The back light unit according to claim 2, wherein the embedded part of the heat emitting frame comprises: a PCB holding part provided in a center of the internal space of the heat emitting frame to closely contact with both sides of the PCB to support the PCB; a light source receiving part provided in the PCB holding part to receive the light source therein; and a power-cable receiving part provided above the light source receiving part to be adjacent to the locking ends, and wherein both open ends of the embedded part of the heat emitting frame are closed with packing plugs or airtight sealings.

[8] The back light unit according to claim 7, wherein the PCB holding part of the embedded part is provided as a 'U'-shaped groove having opposite inner walls.

[9] The back light unit according to claim 2, wherein coupling grooves are formed on opposite ends of adjacent light guide plates to be exposed to outside, a first coupling groove being provided with a connection jack of the power cable connected to the light source unit, and a second coupling groove provided on a neighboring light guide plate being provided with a connection pin to be connected to the connection jack, thus forming a light guide module plate, which enables continuous coupling assembly of light guide plates.