KR102552031B1 - Reflective sheet for blu and direct type backlight unit using the same - Google Patents

Abstract

A reflective sheet for a backlight unit improved to prevent color discoloration from appearing on the front surface of the backlight unit and a direct type backlight unit employing the same are disclosed.
The disclosed direct type backlight unit includes a light emitting element mounted on a circuit board; and a reflective sheet disposed on the surface of the circuit board on which the light emitting element is mounted, and having an exposed through hole formed therein so that the portion where the light emitting element is mounted is opened, wherein the light emitted from the side surface of the light emitting element passes through the inner surface of the exposed through hole. The height of the light emitting element and the thickness of the reflective sheet are arranged to have the same size so as to be reflected in the light emitting element, and the planar shape formed by the inner surface facing the light emitting element of the exposed through hole is a polygonal shape.

Description

Reflective sheet for backlight unit and direct type backlight unit employing the same {REFLECTIVE SHEET FOR BLU AND DIRECT TYPE BACKLIGHT UNIT USING THE SAME}

The present invention relates to a reflective sheet for a backlight unit and a direct type backlight unit employing the same, and more particularly, to a reflective sheet for a backlight unit having a structure capable of reducing a discoloration phenomenon such as a yellow ring. and a direct type backlight unit employing the same.

A liquid crystal display (LCD) may include a liquid crystal panel and a backlight unit (BLU) for irradiating white light from a rear side of the liquid crystal panel to the liquid crystal panel. According to the position of the light source, the backlight unit is a direct type in which the light emitting diode package is disposed vertically behind the LCD, and the light emitting diode package is located on the side of the light guide plate. It is divided into a side type (edge type) in which the light emitted from the light source of the light emitting element is directed forward while passing through the light guide plate.

1 is a plan view illustrating a circuit board, a light emitting device, and a reflective sheet of a direct type backlight unit according to a conventional example. A conventional direct type backlight unit includes a plurality of light emitting elements 2 emitting white light, a circuit board 4 on which the plurality of light emitting elements 2 are mounted, and a reflective layer stacked on top of the circuit board 4. A reflective sheet 6 and a diffusing lens (not shown) are provided on the upper side of the reflective sheet 6 . The diffusion lens diffuses light projected from the light emitting element 2 and directed forward so as not to be concentrated. The reflective sheet 6 is a sheet that reflects the light projected from the light emitting device 2 but not forward or the light reflected from the diffusion lens and directed backward toward the front.

An exposure through hole 8 is punched through the reflective sheet 6 so that the light emitting element 2 is not covered. The conventional exposure through hole 8 has a circular shape centered on the position of the light emitting element 2 . On the other hand, the white light emitted from the light emitting element 2 in the lateral direction rather than forward is reflected from the inner circumferential edge of the exposed through hole 8 of the direct reflection sheet 6, or the light emitting element by the exposed through hole 8 ( 2) may be first reflected on the exposed front surface of the circuit board 4 and then reflected at the inner circumferential edge of the exposed through hole 8. As light reflected from the inner circumferential edge of the exposure through-hole 8 and its surroundings passes through the diffusion lens and is projected forward, a color discoloration phenomenon called color mura may occur. For example, a circular band of a yellowish color may be seen on the front surface of the backlight unit.

In other words, the light incident and reflected on the edge of the exposure through hole 8 and its surroundings is separated into colored light such as blue light and yellow light according to wavelength and proceeds. However, since the exposure through-hole 8 is circular, most of the light emitted from the light emitting element 2 and incident on the inner circumferential edge of the exposure through-hole 8 is incident at an angle of incidence within 10°, so that the exposure through-hole 8 ), the yellow light reflected from the edge of the inner circumferential surface and its surroundings is concentrated on a specific point, resulting in the above-described circular band of similar yellow color. The color imbalance of the backlight unit degrades the image quality of the LCD device.

Registered Patent Publication No. 10-2129974 (Public date: July 3, 2020)

An object of the present invention is to provide a reflective sheet for a backlight unit improved to prevent color discoloration from appearing on the front surface of the backlight unit and a direct type backlight unit employing the same.

A direct type backlight unit according to an embodiment of the present invention includes a light emitting element mounted on a circuit board; and a reflective sheet disposed on a surface of the circuit board on which the light emitting element is mounted, and having an exposure hole formed therein such that a portion where the light emitting element is mounted is opened. A height of the light emitting element and a thickness of the reflective sheet may be the same so as to be reflected on an inner surface of the exposed through hole, and a planar shape formed by an inner surface of the exposed through hole facing the light emitting element may be a polygonal shape. there is.

A planar shape formed by an inner surface of the exposure through-hole facing the light emitting device may be a symmetrical polygonal shape having no plane parallel to a side surface of the light emitting device.

A planar shape formed by the inner surface of the exposure through-hole facing the light emitting element may be one of a regular pentagon, a regular decagon, and a regular decagon.

A center of the light emitting element may be disposed at a geometric center of the through hole.

A yellow light suppression printing layer disposed at the edge of the exposure through hole on the surface of the reflective sheet facing the lens and printed with a blue-based color or gray-based color ink to suppress reflection of incident yellow light may be further provided. can

The yellow light suppression printed layer may be a full line pattern or a dot pattern printed around the light emitting device to surround the light emitting device.

It is disposed to surround the light emitting element at at least a part of the position where the exposure through-hole of the circuit board is disposed, and further includes a high reflection white printing layer printed with white ink so that incident light is reflected and emitted forward. can

The blue light reinforcing printed layer is disposed to surround the light emitting element in at least a part of the position where the exposure through hole is disposed on the circuit board, and is printed with blue-based or gray-based ink to dilute and reflect the incident yellow light. can be provided.

A blue light reinforcing printed layer that is disposed around the light emitting element in at least a part of the position where the exposure through hole is arranged on the circuit board, and is printed with blue-based or gray-based ink to dilute and reflect the incident yellow light. And, the blue light enhancement printing layer may be a dot pattern symmetrically surrounding the light emitting element.

The blue light enhancing printed layer may be disposed at a portion protruding from the light emitting element of the symmetrical polygon of the exposure through-hole or disposed at a concave portion of the symmetrical polygon of the exposed through-hole closest to the light emitting element.

The blue light enhancing printed layer may be a circular band pattern disposed around the light emitting device to surround the light emitting device.

A reflective sheet according to an embodiment of the present invention is disposed on a surface of a circuit board on which a light emitting device is mounted, and has exposed through-holes formed to open a portion where the light emitting device is mounted, wherein the reflective sheet comprises: It has a set thickness, an inner surface of the exposed through-hole is formed by the thickness, and a planar shape formed by the inner surface of the exposed through-hole may be a symmetrical polygonal shape.

A planar shape formed by the inner surface of the exposure through-hole may be a symmetrical polygonal shape having no side parallel to an edge of an imaginary quadrangle arranged at a geometric center of the exposure through-hole.

A yellow light suppression printing layer disposed at an edge of the exposure through-hole and printed with a blue-based color or gray-based color ink to suppress reflection of incident yellow light may be further included.

The yellow light suppression printed layer may have a full line pattern or a dot pattern printed along a circular trajectory centered on a mounting point of the LED package.

According to the present invention, a discoloration phenomenon that may occur in a direct type backlight unit may be reduced by changing the shape and structure of a reflective sheet attached to a circuit board.

In addition, most of the white light emitted from the side surface of the light emitting device and incident on the inner surface of the exposure through-hole of the reflective sheet is incident at an incident angle of 30° or more. Accordingly, light of a specific color (eg, yellow light) emitted while being reflected from the inner surface of the exposure through-hole and separated is scattered in various directions and is not concentrated on a specific point.

Accordingly, a color discoloration phenomenon, such as a circular band of a yellowish color being seen on the front surface of the direct type backlight unit equipped with the reflective sheet of the present invention, does not occur, and The picture quality of the LCD device is improved.

1 is a plan view illustrating a circuit board, a light emitting device, and a reflective sheet of a direct type backlight unit according to a conventional example.
2 is a partially enlarged cross-sectional view of a direct type backlight unit according to an embodiment of the present invention.
FIG. 3 is a plan view illustrating a circuit board, a light emitting device, and a reflective sheet of the direct type backlight unit of FIG. 2 .
4 and 5 are plan views illustrating another embodiment of the reflective sheet of FIG. 3 .

Hereinafter, a reflective sheet according to an embodiment of the present invention and a direct type backlight unit including the same will be described in detail with reference to the accompanying drawings. Terminologies used in this specification are terms used to appropriately express preferred embodiments of the present invention, which may vary according to the intention of a user or operator or conventions in the field to which the present invention belongs. Therefore, definitions of these terms will have to be made based on the content throughout this specification.

FIG. 2 is a partially enlarged cross-sectional view of a direct type backlight unit according to an exemplary embodiment, and FIG. 3 is a plan view illustrating a circuit board, a light emitting device, and a reflective sheet of the direct type backlight unit of FIG. 2 . Referring to FIGS. 2 and 3 , the direct type backlight unit 10 according to an embodiment of the present invention is provided in an LCD device and projects white light from a rear side of a liquid crystal panel (not shown) forward toward the liquid crystal panel. It is a device that

The direct backlight unit 10 includes a plurality of light emitting elements 20 emitting white light, a circuit board 11 on which the plurality of light emitting elements 20 are mounted on the front surface, and a front side of the circuit board 11. and a diffusion lens 27 disposed on and a reflective sheet 30 disposed between the circuit board 11 and the diffusion lens 27. The plurality of light emitting devices 20, the circuit board 11, the diffusion lens 27, and the reflective sheet 30 are positioned behind the liquid crystal panel so as to overlap with the liquid crystal panel. Power is supplied to the plurality of light emitting devices 20 through the circuit board 11 . The white light emitted from the light emitting device 20 is diffused through the diffusion lens 27 and projected forward.

The reflective sheet 30 is a sheet that reflects the light emitted from the light emitting device 20 but not directed forward or the light reflected on the rear surface of the diffusion lens 27 and directed backward to be directed forward again. An exposed through hole 32 is formed in the reflective sheet 30 so that the light emitting device 20 mounted on the circuit board 11 is not covered. Corresponding to the plurality of light emitting elements 20 , the exposure through holes 32 are formed in the same number as the number of light emitting elements 20 .

Each light emitting element 20 includes a blue LED 21 emitting blue light and an encapsulation 22 containing a yellow phosphor to seal the blue LED 21 . The blue light emitted from the blue LED 21 and the yellow light generated and emitted when the yellow phosphor is stimulated by the blue light combine to emit white light out of the light emitting element 2 . Of the total amount of light emitted by the light emitting element 20, the amount of white light emitted to the front surface 23 of the light emitting element 20, that is, the front surface of the encapsulation 22, is 70 to 90%, and the light emitting element ( 20), the amount of white light emitted from the side surface 24 may be 10 to 30%.

The light emitting device 20 may be mounted on one surface of the circuit board 11 facing the diffusion lens 27 . The reflective sheet 30 is disposed on the surface of the circuit board 11 on which the light emitting device 20 is disposed, and an exposure through hole 32 may be formed to open a portion where the light emitting device 20 is mounted. The height of the light emitting device 20 and the thickness of the reflective sheet 30 may be arranged to have the same size. Accordingly, light emitted from the side surface 24 of the light emitting device 20 may be reflected from the inner surface of the exposure through hole 32 .

At this time, the exposure through hole 32 may be formed in a polygonal shape when viewed from a plane, as shown in FIG. 3 . For example, the exposed through hole 32 may have a polygonal shape with a symmetric planar shape. That is, the exposed aperture 32 may be one of a regular pentagon (see FIG. 5), a regular decagon, and a regular dodecagon (see FIG. 4).

In this case, the planar shape formed by the inner surface of the exposed through hole 32 facing the light emitting element 20 may be a symmetrical polygonal shape having no plane parallel to the side surface of the light emitting element. In this case, the exposed through hole 32 Unlike the case where the light input from the light emitting element 20 is circular, the inner surface facing the light emitting element 20 of ) can be minimized. In addition, the center of the light emitting device 20 may be disposed at a geometric center position of the exposure through hole 32 .

As shown in FIG. 3 , the planar shape of the exposure through hole 32 may be a regular hexagonal star shape. The regular hexagonal star shape includes six outward vertices 34 protruding outward from the inside of the regular hexagonal star shape, and six inwardly facing vertices 35 that are dug inward from the outside of the regular hexagonal star shape. The six outward facing vertices 34 and the six inward facing vertices 35 may be alternately arranged.

The point at which the light emitting element 20 is mounted on the circuit board 11 inside the exposure through hole 32 is at any one of the outward facing vertices 34 of the regular hexagonal star and the arbitrary outward facing vertex 34. It may be located outside the imaginary triangle TR1 bounded by two adjacent inward facing vertices 35 .

Specifically, the point where the light emitting device 20 is mounted on the circuit board 11 may be the center of the regular hexagonal star. The central point of the regular hexagonal star can be found in the following way. An average coordinate value of the largest coordinate value and the smallest coordinate value in the X-axis direction among all the points constituting the boundary line of the regular hexagonal star is obtained. In addition, among all the points constituting the boundary line of the regular hexagonal star, an average coordinate value of the largest coordinate value and the smallest coordinate value in the Y-axis direction is obtained. The average coordinate value in the X-axis direction and the average coordinate value in the Y-axis direction may be the X coordinate value and the Y coordinate value of the center point, respectively.

In the case of the conventional direct type backlight unit shown in FIG. 1 , yellow light emitted from the side of the light emitting element 2 and reflected from the inner circumferential surface of the exposure through-hole 8 has the greatest contribution to color imbalance. In the case of the direct type backlight unit 10 according to the embodiment of the present invention shown in FIGS. 2 and 3 , the light is emitted from the side surface 24 of the light emitting element 20 and covers the exposed through hole 32 of the reflective sheet 30. Most of the white light incident on the inner surface is incident at an incident angle (AI) of 30° or more. In other words, in FIG. 3 , the dashed-dotted line 'NL' represents a normal line at an arbitrary point on the inner surface of the exposure through-hole 32, and the dashed-dotted line 'IL' diverges from the side surface 24 of the light emitting device 20, It represents white light incident at one point, and the dotted-dashed line 'OL' represents that the white light incident at the one point is reflected and then separated into yellow light and blue light and then emitted. In this case, when the exposure through-hole has a circular shape, a region in which the incident angle is 0 degrees with respect to the normal may occur.

Since the inner surface of the exposed through hole 32 of the regular hexagonal shape is limited by the side connecting the outward vertex 34 and the inward vertex 35, the normal line (NL) at an arbitrary point on the inner surface of the exposed through hole 32 ) and the white light IL emitted from the side surface 24 of the light emitting device 20 and incident to the point is 30 degrees or more in most cases. Therefore, the yellow light and the blue light, which are reflected from the inner surface of the exposure through-hole 32 and separated in color, are scattered in various directions and projected forward of the diffusion lens 27, and are projected to a specific point on the front of the direct backlight unit 10. not focused Accordingly, a color discoloration phenomenon, such as a circular band of a yellowish color being seen on the entire surface of the direct type backlight unit 10 having the reflective sheet according to the present invention, does not occur.

The yellow light suppressing printed layers 36 and 38 are disposed at the edges of the exposure through holes 32 on the side facing the diffusion lens 27 of the reflective sheet 30, and have a blue-based color that suppresses the reflection of incident yellow light. Alternatively, gray-based color ink may be printed. At this time, the yellow light suppressing printed layers 36 and 38 reduce the amount of yellow light reflected from the reflected light, thereby reducing the discoloration when it is secondarily reflected to the outside. The yellow light suppression printed layers 36 and 38 may include a first yellow light suppression printed layer 36 and/or a second yellow light suppression printed layer 38 .

As another embodiment, as shown in FIG. 3 , blue-based or gray-based ink may be printed along the inner surface of the exposure through-hole 32 . In this case, reflection of yellow light emitted from the side of the light emitting device 20 can be suppressed, thereby reducing the resulting discoloration.

On the front surface of the reflective sheet 30 facing the diffusion lens 27, ink for suppressing reflection of yellow light incident on the front surface of the reflective sheet 30 is printed and laminated on the first and second layers. Second yellow light suppression printed layers 36 and 38 may be provided. As described above, the amount of white light emitted from the front surface 23 of the light emitting device 20 is greater than the amount of white light emitted from the side surface 24 . Some of the white light emitted from the front surface 23 does not pass through the diffusion lens 27 and is reflected from the rear surface of the diffusion lens 27, separated into yellow light and blue light, and emitted backward to the front surface of the reflection sheet 30. are hired Among the color-separated yellow light and blue light, color imbalance caused by blue light rarely occurs, and color imbalance may be mainly caused by yellow light.

By printing ink of a color that dilutes the color imbalance caused by yellow light, such as a blue-based color and/or a gray-based color, on the front side of the reflective sheet 30 where the yellow light reflected from the diffusion lens 27 is incident. The amount of yellow light that is reflected by the reflective sheet 30 and emitted forward again may be reduced. This suppresses the color imbalance in which the circular bands of the yellow-like color described above are seen.

The first yellow light suppressing printed layer 36 may be formed by printing blue-based color ink such as blue, sky blue, and indigo. The first yellow light suppression printed layer 36 is a dot pattern printed along a circular trajectory centered on the mounting point of the light emitting element 20, that is, the central point of the exposed through hole 32 in the shape of a regular hexagonal star. can have The second yellow light suppressing printed layer 38 may be formed by printing gray-based color ink such as, for example, light gray or dark gray. The second yellow light suppressing printed layer 38 may have a full line pattern printed along a circular trajectory centered on the mounting point of the light emitting device 20 .

Meanwhile, the shapes, patterns, colors, and line thicknesses of the first and second yellow light suppressing printed layers 36 and 38 shown in FIG. 3 are merely exemplary. In other words, the shape of the yellow light suppressing printed layer is not limited to a circular shape, and may be other shapes such as, for example, a convex polygon or a regular polygon. The pattern of the yellow light suppression printed layer is not limited to a solid line pattern and a dot pattern, and may be other patterns such as a wavy pattern, a sawtooth pattern, and a hatching pattern. The color of the yellow light suppressing printed layer is not limited to blue-based colors and gray-based colors, and may be other colors other than yellow or white that promotes reflection. On the other hand, the printing method of the yellow light suppressing printed layers 36 and 38 is not limited, and can be printed by various methods such as silk screen printing, printer printing, pad printing, offset printing, and the like. .

Most areas of the front surface of the circuit board 11 are not exposed due to the reflective sheet 30 stacked so as to overlap the circuit board 11, but the exposure through holes 32 cover the circuit board 11. Some areas of the front are exposed without being covered. The circuit board 11 includes a first blue light enhancement printing layer 13 and a second blue light enhancement printing layer in which blue-based color ink is printed and stacked around the light emitting device 20 in the area of the front surface of the circuit board 11 that is not covered. Layer 15 may be included.

Further, in the circuit board 11, white ink with high reflectivity is printed and laminated on a portion of the front surface of the circuit board 11 where the first and second blue light enhancing printed layers 13 and 15 are not stacked. A highly reflective white printed layer 17 may be provided.

The highly reflective white printed layer 17 is disposed to surround the light emitting element 20 at least in part where the exposure through hole 32 of the circuit board 11 is disposed, so that the incident light is reflected and emitted forward. White ink can be printed. Like the reflective sheet 30, the highly reflective white printed layer 17 is reflected from the rear surface of the diffusion lens 27 and color-separated so that yellow light and yellow light emitted backward are reflected again and emitted forward. That is, light loss of light emitted from the light emitting device 20 can be reduced and light efficiency can be increased.

The blue light enhancing printed layers 13 and 15 are disposed around or surrounding the light emitting element 20 in at least a part of the position where the exposed through hole 32 of the circuit board 11 is disposed, Blue-based or gray-based ink may be printed to dilute and reflect incident yellow light. The blue light enhancement printed layers 13 and 15 may include the first blue light enhancement printed layer 13 and/or the second blue light enhancement printed layer 15 .

The first and second blue light enhancing printed layers 13 and 15 reflect white light emitted from the side surface 24 of the light emitting device 20 incident to the first and second blue light enhancing printed layers 13 and 15 . so that it emits blue light. In other words, the white light emitted from the side surface 24 of the light emitting element 20 and incident on the area of the circuit board 11 not covered by the reflective sheet 30 is reflected and separated into yellow light and blue light. When the white light incident to the first and second blue light-enhancing printed layers 13 and 15 is reflected and color-separated and emitted, the amount of yellow light is reduced and the amount of blue light is increased.

The increased blue light may pass through the diffusion lens 27 again and be combined with the yellow light transmitted through the diffusion lens 27 to become white light. As a result, as described above, the phenomenon of concentration of yellow light at a specific point is mitigated, color imbalance is suppressed, and light efficiency of the direct type backlight unit can be improved by increasing the amount of white light projected forward. At this time, the planar shape of the first blue light enhancing printed layer 13 may be a circular pattern surrounding the light emitting device 20 with the mounting point of the light emitting device 20 as a center. In this case, it is possible to alleviate the influence of yellow light by reinforcing the blue light of the light output from the light emitting device 20 .

As another embodiment, as shown in FIG. 6 , the planar shape of the first blue light enhancing printed layer 73 may be a circular band pattern centered on the mounting point of the light emitting device 20 . In this case, the highly reflective white printed layer 17 is formed inside the first blue light enhancing printed layer 73 to improve both the blue light enhancing effect and the reflection effect.

The second blue light enhancement printed layer 15 may be located farther from the mounting point of the light emitting device 20 than the first blue light enhancement printed layer 13 . The planar shapes and positions of the first and second blue light enhancing printed layers 13 and 15 shown in FIG. 3 are illustrative, and various modifications are possible. In this case, the second blue light enhancing printed layer 15 may be a dot pattern symmetrically surrounding the light emitting device 20 as a center.

As another embodiment, the second blue light enhancement printed layer 15 is disposed in the concave portion closest to the light emitting element from the symmetrical polygonal light emitting element 20 of the exposed through hole 32, as shown in FIG. 32), it is possible to increase the blue light reinforcement effect. As another embodiment, the second blue light enhancement printed layer 15 is disposed at a corner farthest from the light emitting element 20 of the symmetrical polygon of the exposure through hole 32, and is a balance point between the blue light compensating effect and the white light reflection effect. will be able to find

Although not shown in FIG. 3 , the circuit board 11 further includes, for example, a yellow light suppression printing layer in which gray-based color ink is printed and laminated on the front area of the circuit board 11 that is not covered by the reflective sheet 30 . can also be provided. The white light emitted from the side surface 24 of the light emitting device 20 and incident on the yellow light suppressing printed layer of the circuit board 11 is reflected and color-separated, and when emitted, the amount of yellow light is reduced. The printing method of the blue light enhancement printed layers 13 and 15 and the high reflection white printed layer 17 is not limited, and various methods such as silk screen printing, printer printing, pad printing, offset printing, etc. can be formed by printing.

4 and 5 are plan views illustrating another embodiment of the reflective sheet of FIG. 3 . Referring to FIG. 4 , an exposure through hole 52 having a planar shape of a twelve-pointed star is formed in a reflective sheet 50 according to another embodiment of the present invention. The 12-pointed star shape includes 12 outward vertices 54 protruding outward from the inside of the 12-pointed star shape, and 12 inward-facing vertices 55 that are hollowed inward from the outside of the 12-pointed star shape. . The 12 outward vertices 54 and the 12 inward vertices 55 may be alternately arranged.

The point at which the light emitting element 20 is mounted on the circuit board 11 (see FIG. 2) inside the exposure through hole 52 is an arbitrary one of the outward facing vertices 54 of the twelve-pointed star and the arbitrary outward facing point. It lies outside the imaginary triangle TR2 bounded by the two inward facing vertices 55 adjacent to vertex 54 . Specifically, the point at which the light emitting element 20 is mounted on the circuit board 11 may be the center of the twelve-pointed star. Since the method of finding the center point of the regular decagonal star is the same as the method of finding the center point of the regular hexagonal star described with reference to FIG. 3, duplicate descriptions will be omitted.

The planar shape of the exposed aperture formed in the reflective sheet of the present invention is not limited to the regular hexagonal star shown in FIG. 3 and the twelve-pointed star shown in FIG. 4 . In general, the planar shape of the exposure through-hole is an N-pointed star, and a point where the light emitting device 20 is mounted in the inner region of the exposed through-hole is adjacent to any one of the outward-facing vertices of the N-pointed star and the arbitrary outward-facing vertex. It lies outside an imaginary triangle bounded by one or two inward facing vertices. Here, N may be a natural number greater than 2, such as 3, 4, 5, or 6.

The front surface of the reflective sheet 50 has a dot pattern printed along a circular trajectory centered on the mounting point of the light emitting device 20, and a yellow light suppression printing layer in which blue-based color ink is printed and laminated ( 56) is formed. Since the function, shape, and formation method of the yellow light suppressing printed layer 56 have already been described in the description of the reflective sheet 30 shown in FIGS. 2 and 3 , overlapping descriptions will be omitted. Although only one yellow light suppression printed layer 56 is shown in FIG. 4 , a plurality of yellow light suppression printed layers having different colors may be provided as in the examples shown in FIGS. 2 and 3 .

Referring to FIG. 5 , an exposure through hole 62 having a planar shape of a regular pentagon is formed in a reflective sheet 60 according to another embodiment of the present invention. The regular pentagonal shape has five vertices 64 protruding from the inside of the regular pentagonal shape toward the outside. A point at which the light emitting element 20 is mounted on the circuit board 11 (see FIG. 2) inside the exposure through hole 62 is the central point of the regular pentagon. Since the method of finding the center point of the regular pentagon is similar to the method of finding the center point of the regular hexagonal star described with reference to FIG. 3, duplicate descriptions will be omitted.

The planar shape of the exposed aperture formed in the reflective sheet of the present invention is not limited to the regular pentagon shown in FIG. 5 . In general, the planar shape of the exposure through-hole is a convex M-angle, and a point at which the light emitting device 20 is mounted in the inner region of the exposure through-hole is the central point of the convex M-angle. Here, M may be a natural number of 3 to 6, that is, a natural number of 3, 4, 5, and 6.

As in the embodiment shown in FIG. 4, the front surface of the reflective sheet 60 has a dot pattern printed along a circular trajectory centered on the mounting point of the light emitting device 20, and blue-based color ink. A yellow light suppressing printed layer 66 may be formed. Since the function, shape, and formation method of the yellow light suppressing printed layer 66 have already been described in the description of the reflective sheet 30 shown in FIGS. 2 and 3 , repeated descriptions will be omitted. Although only one yellow light suppression printed layer 66 is shown in FIG. 5 , a plurality of yellow light suppression printed layers having different colors may be provided as in the examples shown in FIGS. 2 and 3 .

In the reflective sheets 30, 50, and 60 described above, radiation is emitted from the side surface 24 of the light emitting element 20 to the inner surface of the exposed through-holes 32, 52, and 62 of the reflective sheets 30, 50, and 60. Most of the incident white light is incident at an incident angle of 30° or more. Accordingly, light of a specific color (eg, yellow light) emitted while being reflected from the inner surface of the exposure through-holes 32, 52, and 62 and separated is scattered in various directions and is not concentrated on a specific point. Accordingly, a color discoloration phenomenon, such as a circular band of a yellowish color being seen on the front surface of the direct type backlight unit 10 having the reflective sheets 30, 50, and 60, does not occur. , the image quality of the LCD device having the direct type backlight unit 10 is improved.

Although the present invention has been described with reference to the embodiments shown in the drawings, this is only exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. Therefore, the true scope of protection of the present invention should be defined only by the appended claims.

10: direct backlight unit 11: circuit board
13, 15: blue light enhancement printed layer 17: high reflection white printed layer
20: light emitting element 27: diffusion lens
30: reflective sheet 32: exposure through-hole

Claims (16)

A light emitting device mounted on a circuit board; and
A reflective sheet disposed on the surface of the circuit board on which the light emitting element is mounted, and having exposed through-holes formed so that a portion where the light emitting element is mounted is opened;
A height of the light emitting device and a thickness of the reflective sheet are arranged to have the same size so that light emitted from a side surface of the light emitting device can be reflected on an inner surface of the exposure through-hole;
The direct type backlight unit of claim 1 , wherein a planar shape formed by an inner surface of the exposure through-hole facing the light emitting element has a polygonal shape. According to claim 1,
A direct type backlight unit having a symmetrical polygonal shape in a planar shape formed by an inner surface of the exposure through-hole facing the light emitting element. According to claim 1,
A direct backlight in which a planar shape formed by the inner surface of the exposure through-hole facing the light emitting element has a symmetrical polygonal shape without a plane parallel to the side surface of the light emitting element (a plane on which light input from the light emitting element is perpendicularly incident). unit. According to claim 1,
The direct backlight unit of claim 1 , wherein a planar shape formed by an inner surface of the exposure through-hole facing the light emitting element has any one of a regular pentagon, a regular decagon, and a regular decagon. According to claim 1,
A direct type backlight unit in which a center of the light emitting element is disposed at a geometric center position of the exposure through hole. According to claim 1,
Disposed at the edge of the exposed through hole on the surface of the reflective sheet facing the light emitting element,
A direct type backlight unit further comprising a yellow light suppression printing layer printed with blue-based color or gray-based color ink to suppress reflection of incident yellow light. According to claim 6,
The yellow light suppression printed layer has a full line pattern or a dot pattern printed around the light emitting element to surround the light emitting element. According to claim 1,
Arranged so as to surround the light emitting element in at least a part of a position where the exposed through hole of the circuit board is disposed,
A direct type backlight unit further comprising a high reflection white printing layer printed with white ink so that incident light is reflected and emitted forward. According to claim 1,
Arranged so as to surround the light emitting element in at least a part of a position where the exposed through hole of the circuit board is disposed,
A direct backlight unit having a blue light reinforcing printed layer printed with blue or gray ink to dilute and reflect incident yellow light. According to claim 1,
Arranged around the light emitting element at least a part of the position where the exposed through hole of the circuit board is disposed,
A blue light reinforcing printing layer on which blue-based or gray-based ink is printed so that incident yellow light can be diluted and reflected,
The direct type backlight unit of claim 1 , wherein the blue light enhancing printed layer is a dot pattern symmetrically surrounding the light emitting element. According to claim 10,
The blue light enhancing printed layer is disposed at a portion protruding from the light emitting element of the symmetrical polygon of the exposure through-hole or disposed at a concave portion closest to the light emitting element of the symmetrical polygon of the exposure through-hole. According to claim 10,
The blue light enhancement printed layer,
A direct type backlight unit having a circular band pattern disposed around the light emitting element to surround the light emitting element. A reflective sheet disposed on a surface of a circuit board on which a light emitting element is mounted, and having exposed through-holes formed to open a portion where the light emitting element is mounted,
The reflective sheet has a set thickness, and an inner surface of the exposed through-hole is formed by the thickness;
A reflective sheet having a symmetrical polygonal shape in a planar shape formed by inner surfaces of the exposed through-holes. According to claim 13,
The reflective sheet of claim 1 , wherein a planar shape formed by the inner surface of the exposure through-hole has a symmetric polygonal shape having no side parallel to an edge of an imaginary quadrangle disposed at a geometric center of the exposure through-hole. According to claim 13,
The reflective sheet further comprises a yellow light suppression printed layer disposed at an edge of the exposure hole and printed with a blue-based color or gray-based color ink to suppress reflection of incident yellow light. According to claim 15,
The yellow light suppression printed layer has a full line pattern or a dot pattern printed along a circular trajectory centered on a mounting point of the light emitting device.

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