KR102343050B1 - Optical film to reduce hotspots - Google Patents

Abstract

An optical film for reducing hot spots is disclosed. The optical film for reducing hot spots includes a first inverted prism sheet in which a plurality of first inverted prisms are disposed on a lower surface of the first base film, and a second plurality of inverted prisms opposite to a light source disposed in an edge of the light guide plate. 2 It may include a second inverted prism sheet disposed on the lower surface of the base film. Here, the heights of the plurality of second inverted prisms may decrease at a predetermined ratio from one end of the second plurality of inverted prisms to a predetermined distance from one end relatively close to the light source among both ends of the second plurality of inverted prisms.

Description

Optical film that reduces hot spots

The present invention relates to an optical film for reducing hotspots, and more particularly, to an optical film for reducing hotspots caused by a light source disposed on an edge of a light guide plate.

A flat panel display device is required to have excellent characteristics such as thinness, light weight, and low power consumption. As an example of a flat panel display, a liquid crystal display (LCD) has excellent resolution, color display, image quality, thinness, and light weight, and is therefore widely applied to mobile devices such as smartphones, TVs, and medium-sized display devices such as PCs. .

The liquid crystal display device is a transmissive display device and displays a desired image grayscale on the screen by controlling the amount of light passing through the liquid crystal layer by the refractive index anisotropy of liquid crystal molecules. Accordingly, in the liquid crystal display device, a backlight is provided for providing light passing through the liquid crystal layer to display an image.

In general, the backlight may be divided into a direct type type and an edge type type according to the arrangement method of the light source.

The direct type is a method in which a lamp or a light emitting diode (LED), which is a light source, is located on the rear surface of the liquid crystal panel and irradiates light from the bottom toward the panel. In the direct type, since the light emitted from the light source is directly supplied to the liquid crystal panel, high brightness can be realized, and it is easy to be applied to a large-area panel.

The edge type is installed on the side of the liquid crystal panel and supplies light to the liquid crystal panel through the light guide plate. For this reason, the edge-type method is difficult to apply to a large-area liquid crystal panel compared to the direct-type method. In addition, since light is supplied through the light guide plate, it is difficult to achieve high luminance. However, in the case of the edge type, since the backlight is located on the side, there is an advantage in that the thickness of the liquid crystal display can be reduced.

In the edge-type method, since the light source is disposed on the side of the liquid crystal panel, a technology for uniform brightness of the entire screen is essential.

As an example of such a technology, Korean Patent Laid-Open Publication No. 10-2017-0080313 (published date: July 10, 2017) provides a prism sheet with a flat area instead of a prism mountain on the upper prism sheet located in the light incident part of the light guide plate. Disclosed are a backlight unit for blocking light propagating between the mountains and valleys and a liquid crystal display having the same.

As another example, Patent Publication No. 10-1736922 (announcement date: May 18, 2017) has a hemispherical cross section each having an irregular height and width, and is disposed extending in the longitudinal direction from one surface of the base film. , Disclosed are a backlight unit constituting a separation space between two adjacent protrusions having a hemispherical cross section, and a method for manufacturing a diffusion sheet thereof.

In the case of the above-described edge type method, a hot spot appears that is brighter in the area of the liquid crystal panel relatively close to the light source installed on the side of the liquid crystal panel than in the area relatively far from the light source, which may negatively affect the user experience. .

The present invention has been devised to solve the above problems, and by disposing an optical film for uniform luminance of light on the light guide plate, it is possible to improve or reduce hot spots caused by light irradiated from an edge-type light source.

In the optical film for reducing hot spots according to various embodiments of the present invention, the first plurality of inverted prisms are disposed on the lower surface of the first base film and face the light source disposed on the edge of the first inverted prism sheet and the light guide plate. A second plurality of inverted prisms may include a second inverted prism sheet disposed on a lower surface of the second base film. Here, the heights of the plurality of second inverted prisms may decrease at a predetermined ratio from one end of the second plurality of inverted prisms to a predetermined distance from one end relatively close to the light source among both ends of the second plurality of inverted prisms.

According to various embodiments of the present disclosure, it is possible to improve or reduce hot spots caused by light irradiated from an edge-type light source.

1 is an exploded perspective view of a backlight unit according to an embodiment of the present invention.
2 is an exploded perspective view of an inverted prism sheet and a light guide plate according to an embodiment of the present invention.
3 shows a traveling direction of light according to an embodiment of the present invention.
4 shows a traveling direction of light according to another embodiment of the present invention.
5 is a side view of an inverted prism sheet and a light guide plate according to an embodiment of the present invention.
6 is a side view of an inverted prism sheet and a light guide plate according to another embodiment of the present invention.
7 is a side view of an inverted prism sheet and a light guide plate according to another embodiment of the present invention.
8 is a cross-sectional view of an inverted prism sheet according to an embodiment of the present invention.
9 is a cross-sectional view of an inverted prism sheet according to another embodiment of the present invention.
10 is a perspective view of an inverted prism sheet according to an embodiment of the present invention.
11 is an exploded perspective view of a light guide plate and a plurality of inverted prism sheets according to an embodiment of the present invention.
12 shows a performance test result of an optical film according to an embodiment of the present invention.

Hereinafter, the principle of operation of a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. In addition, when it is determined that a detailed description of a related well-known function or configuration may obscure the gist of the present disclosure in describing an embodiment of the present invention, the detailed description thereof will be omitted. And the terms used below are terms defined in consideration of functions in the present invention, which may vary depending on the intention or custom of the user or operator. Therefore, the definitions of the terms used should be interpreted based on the contents and corresponding functions throughout this specification.

1 is an exploded perspective view of a backlight unit according to an embodiment of the present invention.

In general, the liquid crystal display device requires a backlight unit 10 that provides uniform light to the entire screen, unlike the conventional CRT method. The backlight unit 10 may be provided at the rear of the liquid crystal panel to irradiate light to the liquid crystal panel.

For example, the backlight unit 10 may include a light source 11 , a reflective plate 12 , a light guide plate 13 , an optical film 14 , and a reflective polarizing sheet 15 .

The light source 11 emits light. The light source 11 may be composed of a light emitting body that emits light. For example, the light source 11 is an edge-type light source, and may emit light from the side of the light guide plate 13 to transmit light in the direction of the light guide plate 13 . By irradiating the light emitted from the light source 11 to the rear surface of the liquid crystal panel, an identifiable image may be realized.

For example, the light source 11 may be one of a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp, and a light emitting diode (LED, hereinafter referred to as LED). have.

The reflector 12 is disposed behind the light guide plate 13 to reflect the light emitted from the rear of the light guide plate 13 to the light guide plate 13 and thereby minimize light loss.

The light guide plate 13 converts the light incident from the reflection plate 12 into the form of a surface light source.

The optical film 14 is disposed on the light guide plate 13 , collects light transmitted from the light guide plate 13 and moves it upward. Here, the optical film 14 may have a laminated or laminated structure of the first inverted prism sheet 14-1 and the second inverted prism sheet 14-2.

For example, the first reverse prism sheet 14 - 1 may have a plurality of lenses for condensing light, so that light transmitted from the light guide plate 13 is totally internally reflected and refracted upward. Here, in the first inverted prism sheet 14-1, a plurality of first inverted prisms may be disposed on a lower surface of the first base film.

For example, in the second inverted prism sheet 14 - 2 , a plurality of second inverted prisms facing the light source 11 disposed at an edge of the light guide plate may be disposed on a lower surface of the second base film. In this case, the second inverted prism sheet 14 - 2 may reduce hot spots. For example, when the first inverted prism sheet 14 - 1 is disposed alone, a hot spot may be formed in a region adjacent to the light source 11 disposed on one side of the light guide plate 13 . In this case, by disposing the second inverted prism sheet 14-2 under the first inverted prism sheet 14-1, the luminance of the hotspot region and the non-hotspot region may be uniform. The structure of the second inverted prism sheet 14 - 2 will be described later in detail.

In the above-described example, the first inverted prism sheet 14-1 and the second inverted prism sheet 14-2 may have a structure in which a plurality of lenses are bonded to a base film. Here, the base film may be a material such as PET, PC, or PP. In addition, the plurality of lenses may be formed of an optical pattern layer in which an optical pattern in the form of a lens array including a plurality of inclined surfaces is formed on one surface of the translucent base film in order to improve the luminance of the emitted light.

The reflective polarizing sheet 15 transmits one polarized light with respect to the light collected by the optical film 14 and reflects the other polarized light downward to recycle the light. For example, the reflective polarizing sheet 15 may transmit P-polarized light and reflect S-polarized light.

For example, the reflective polarizing sheet 15 may be configured by stacking a plurality of layers having different refractive indices. In this case, the reflective polarizing sheet 15 may be configured by stacking tens, hundreds, or thousands of different high refractive index layers and low refractive index layers.

A plurality of components included in the above-described backlight unit 10 may be variously combined. For example, the backlight unit 10 includes a light source 11 , a reflective plate 12 , a light guide plate 13 , a first reverse prism sheet 14 - 1 , a second reverse prism sheet 14 - 2 , and a reflective polarizing sheet Some of (15) may be omitted, the arrangement order of the components may be combined differently, or additional components may be further included. For example, a diffusion sheet may be further included between the optical film 14 of the backlight unit 10 and the reflective polarizing sheet 15 .

Hereinafter, the above-described second inverted prism sheet 14 - 2 will be described in detail, but a detailed description of the configuration overlapping with the above will be omitted for convenience of description.

2 is an exploded perspective view of an inverted prism sheet and a light guide plate according to an embodiment of the present invention.

Referring to FIG. 2 , the inverted prism sheet 210 may include a base film 211 and a plurality of inverted prisms 212 .

A plurality of inverted prisms 212 may be attached or adhered to the lower surface of the base film 211 .

The plurality of inverted prisms 212 may reduce hot spots.

Specifically, in FIG. 2 , since the light source 230 is disposed on the edge 221 of the light guide plate 220 , the intensity of light emitted from the light source 230 is at the periphery 222 of the edge 221 of the light guide plate 220 . It is strong and the farther from the edge 221 of the light guide plate 220, the weaker. Accordingly, a hot spot may be observed in an area of the liquid crystal screen close to the light source 230 . Such hotspots may be associated with degradation of the display device. In order to reduce the hot spots, it is necessary to diffuse (or disperse) the light in the periphery 222 of the edge 221 of the light guide plate 220 .

The plurality of inverted prisms 212 according to an embodiment of the present invention may be disposed on the upper side of the light guide plate 220 to diffuse light in the periphery 222 of the edge 221 of the light guide plate 220 . In this case, the plurality of inverted prisms 212 may be disposed to face the light source 230 disposed on the edge 221 of the light guide plate 220 .

The plurality of inverted prisms 212 may diffuse light.

For example, FIG. 3 illustrates a case in which light is emitted from the light source 230 into air without a medium. In FIG. 3 , the light emitted from the light source 230 travels in a straight line.

4 illustrates a case in which light emitted from the light source 230 passes through a plurality of inverted prisms 213 . In FIG. 4 , the light emitted from the light source 230 is refracted and diffused by the light incident surfaces of the plurality of inverted prisms 213 . Here, the apex angle 2131 of the plurality of inverted prisms 213 may be an acute angle.

Meanwhile, the intensity of light emitted from the light source 230 disposed on the edge 221 of the light guide plate 220 becomes weaker as it is further away from the light source 230 . Accordingly, in the above-described example, the heights of the plurality of inverted prisms 212 may be formed to decrease at a predetermined ratio as they move away from the light source 230 . Here, the heights of the plurality of inverted prisms 212 may be defined as the shortest distance from the lower surface of the base film 211 to a point on the corners of the plurality of inverted prisms 212 .

For example, the height of the plurality of inverted prisms 212 is set from one end 2121 of the plurality of inverted prisms 212 at one end 2121 relatively close to the light source 230 among both ends of the plurality of inverted prisms 212 , from one end 2121 of the plurality of inverted prisms 212 . It can be reduced at a predefined rate up to the specified distance. Here, the predefined distance may be equal to the width of the base film 211 or smaller than the width of the base film 211 . In addition, the predefined ratio may be defined as a decrease rate of the height of the plurality of inverted prisms 212 or the slope of the corners of the plurality of inverse prisms 212 . For example, the predefined ratio may be a value obtained by dividing the height of the plurality of inverted prisms 212 at the one end 2121 of the plurality of inverted prisms 212 by the width of the base film 211 .

Through this, a portion closer to the light source 230 among the plurality of inverted prisms 212 may increase light diffusion performance to reduce hot spots caused by the light source 230 .

5 is a side view of an inverted prism sheet and a light guide plate according to an embodiment of the present invention.

Referring to FIG. 5 , the height of the plurality of inverted prisms 510 is from one end 511 relatively close to the light source 520 among both ends of the plurality of inverted prisms 510 to the other end 512 relatively far from the light source 520 . can be reduced at a predefined rate.

6 is a side view of an inverted prism sheet and a light guide plate according to another embodiment of the present invention.

Referring to FIG. 6 , the heights of the plurality of inverted prisms 610 include one end 611 relatively close to the light source 620 among both ends of the plurality of inverted prisms 610 , and one end 611 of the plurality of inverted prisms 610 . ) to a predefined distance 612 may decrease at a predefined rate.

7 is a side view of an inverted prism sheet and a light guide plate according to another embodiment of the present invention.

Referring to FIG. 7 , the height of the plurality of inverted prisms 710 is at one end 711 relatively close to the light source 720 among both ends of the plurality of inverted prisms 710 , and at one end 711 of the plurality of inverted prisms 710 . ) to a predefined distance 712 may decrease at a predefined rate. In addition, the height of the plurality of inverted prisms 710 may be constant when the predetermined distance 712 exceeds 713 .

8 is a cross-sectional view of an inverted prism sheet according to an embodiment of the present invention.

Referring to FIG. 8 , a bottom surface of each of the plurality of inverted prisms 810 may be disposed in close contact with each other.

9 is a cross-sectional view of an inverted prism sheet according to another embodiment of the present invention.

Referring to FIG. 9 , the bottom surfaces of each of the plurality of inverted prisms 910 may be disposed to be spaced apart from each other. In this case, a flat portion 920 having the distance between the plurality of inverted prisms 910 as a width may be disposed between the plurality of inverted prisms 910 .

9 , as an example, the width of the flat portion 920 may be constant. As another example, the width of the flat portion 920 may increase as the flat portion 920 moves away from the light source. In this case, the height of the plurality of inverted prisms 910 may decrease as the distance from the light source increases.

10 is a perspective view of an inverted prism sheet according to an embodiment of the present invention.

Referring to FIG. 10 , a pattern layer 1011 for light diffusion may be formed on the upper surface of the base film 1010 .

In addition, a plurality of dot-type ink patterns 1012 and 1013 for light diffusion may be formed in a region 1014 within a predetermined distance from the light source on the upper surface of the base film 1010 . Here, the plurality of ink patterns 1012 and 1013 diffuse the light emitted from the light source to reduce hot spots caused by the edge type light source.

In the above-described example, the number of the plurality of ink patterns 1012 and 1013 may be decreased by a predefined ratio as the distance from the light source 1013 in the region 1012 close to the light source increases. Alternatively, the plurality of ink patterns 1012 and 1013 may be reduced at a predetermined ratio as at least one of the area of the plurality of ink patterns 1012 and 1013 per unit area and the number of ink patterns moves away from the light source. Here, the predefined ratio may be defined as, for example, 1/2.

In addition, the sizes (or widths) of the plurality of ink patterns 1012 and 1013 may be decreased at a predefined ratio as they move away from the light source ( 1013 ) in the region 1012 close to the light source. Here, the predefined ratio may be defined as, for example, 1/2.

Meanwhile, the backlight unit according to an embodiment of the present invention may include the above-described optical film according to various embodiments of the present invention.

For example, referring to FIG. 11 , the backlight unit according to an embodiment of the present invention may include an optical film 1100 including a first reverse prism sheet 1110 and a second reverse prism sheet 1120 . . Here, the first inverted prism sheet 1110 may be disposed to perform light collection, and the second inverted prism sheet 1120 may be disposed to perform hotspot reduction.

The first inverted prism sheet 1110 may include a first base film 1112 and a plurality of first inverted prisms 1111 disposed on one side of the first base film 1112 .

The second inverted prism sheet 1120 may include a second base film 1122 and a plurality of second inverted prisms 1121 disposed on one side of the second base film 1122 . For example, a plurality of patterns 1123 for light diffusion may be formed on the other side of the second base film 1122 .

In the above-described example, the arrangement order of the first inverted prism sheet 1110 and the second inverted prism sheet 1120 may be random. For example, the first inverted prism sheet 1110 may be disposed above or below the second inverted prism sheet 1120 .

In the above-described example, the first plurality of inverted prisms 1111 included in the first inverted prism sheet 1110 and the second plurality of inverted prisms 1121 included in the second inverted prism sheet 1120 are the first plurality of inverted prisms 1111 . The longitudinal direction of the inverted prism 1111 and the longitudinal direction of the plurality of second inverse prisms 1121 may be arranged to cross each other to form a predefined angle. For example, the longitudinal direction of the plurality of first inverted prisms 1111 and the longitudinal direction of the plurality of second inverted prisms 1121 may be disposed to cross each other orthogonally.

A liquid crystal display (LCD) device according to an embodiment of the present invention may include an LCD panel and the aforementioned backlight unit positioned below the LCD panel.

12 shows a performance test result of an optical film according to an embodiment of the present invention.

In FIG. 12 , Experiment 1 is a photograph of a result of irradiating light onto a structure in which one inverted prism sheet 1110 is disposed on an upper portion of the light guide plate. Experiment 2 is a photograph of a result of irradiating light to a structure in which the reverse prism sheet 600 and the reverse prism sheet 1110 of FIG. 6 described above for reducing hot spots are sequentially stacked on the light guide plate. In Experiment 3, in the same structure as Experiment 2, a plurality of ink patterns having a width of 40 μm were disposed at intervals of 60 μm in an area relatively close to the light source among the upper surface of the reverse prism sheet 600, and the reverse prism sheet 600 ), the result of forming the pattern layer on the remaining area of the upper surface was photographed.

Referring to Experiment 1, the hotspot appeared up to a region corresponding to 5 mm from one end of the inverted prism sheet 1110 that is relatively close to the light source.

Referring to Experiment 2, the hot spots appeared up to a region corresponding to 2 mm from one end of the inverted prism sheet 1110 that is relatively close to the light source.

Referring to Experiment 3, the hot spots appeared up to an area corresponding to 1 mm from one end of the inverted prism sheet 1110 that is relatively close to the light source.

It can be seen that in Experiments 1 to 3 described above, the hot spots in Experiment 2 were reduced than in Experiment 1, and the hotspots in Experiment 3 were reduced compared to Experiments 1 and 2. That is, it can be seen that hot spots can be reduced by disposing the above-described reverse prism sheet 600 of FIG. 6 for reducing hot spots on the light guide plate. In addition, arranging a plurality of ink patterns in a region relatively close to the light source among the regions of the upper surface of the inverted prism sheet 600 of FIG. In this case, it can be seen that the hotspan reduction performance is further improved.

In the above description, a plurality of prisms 510 , 610 , 710 according to various embodiments of the present invention, a patterned layer 1011 according to an embodiment of the present invention, and a plurality of prisms according to an embodiment of the present invention The ink patterns 1012 and 1013 have been described in detail. According to the arrangement of the plurality of prisms (510, 610, 710), the pattern layer (1011), and the plurality of ink patterns (1012, 1013), hot spots caused by light irradiated from the edge-type light source can be improved or reduced. have.

While the embodiments of the present invention have been shown and described, various changes in form and details may be made by those skilled in the art without departing from the spirit and scope of the embodiments as defined by the appended claims and their equivalents. you will understand that you can

Backlight unit: 10
Light source: 11, 230, 520, 620, 720
Reflector: 12
Light guide plate: 13, 220
Inverted Prism Sheet: 14, 210, 600
First inverted prism sheet: 14-1, 1110
Second inverted prism sheet: 14-2, 1120
Reflective polarizing sheet: 15
Multiple inverted prisms: 212, 213, 510, 610, 710, 810, 910, 1111, 1121
Plains: 920
Ink pattern: 1012, 1013

Claims (14)

In the optical film for reducing hot spots,
a first inverted prism sheet having a plurality of first inverted prisms disposed on a lower surface of the first base film; and
a second inverted prism sheet in which a plurality of second inverted prisms facing the light source disposed at an edge of the light guide plate are disposed on a lower surface of the second base film;
Each prism height of the second plurality of inverted prisms,
From one end of both ends of the second plurality of inverted prisms that are relatively close to the light source, the optical film decreases at a predefined rate up to a predefined distance as the distance from the light source increases.
According to claim 1,
The height of the second plurality of inverted prisms,
The shortest distance from the lower surface of the second base film to a point on the corners of the second plurality of inverted prisms, the optical film.
According to claim 1,
The height of the second plurality of inverted prisms,
An optical film that decreases at a predetermined ratio from one end relatively close to the light source to the other end relatively far from the light source among both ends of the second plurality of inverted prisms.
4. The method of claim 3,
The height of the second plurality of inverted prisms is constant in a portion exceeding the predetermined distance from the one end relatively close to the light source.
According to claim 1,
Between the second plurality of inverted prisms, a flat portion having a distance between the second plurality of inverted prisms as a width is disposed, an optical film.
6. The method of claim 5,
The width of the flat portion is constant, an optical film.
6. The method of claim 5,
The width of the flat portion is wider as the flat portion is farther from the light source, the optical film.
According to claim 1,
On the upper surface of the second base film, a pattern layer for light diffusion is formed, an optical film.
9. The method of claim 8,
A diffusion pattern for light diffusion is formed in a region within a predetermined distance from the light source among the upper surface of the second base film.
10. The method of claim 9,
The diffusion pattern is a plurality of ink patterns of a dot (dot) type, optical film.
11. The method of claim 10,
The plurality of ink patterns,
The optical film, wherein at least one of the area of the plurality of ink patterns and the number of ink patterns per unit area decreases at a predefined rate as the distance from the light source increases.
According to claim 1,
A longitudinal direction of the plurality of first inverted prisms and a longitudinal direction of the plurality of second inverted prisms are orthogonal to each other, an optical film.
A backlight unit comprising the optical film of any one of claims 1 to 12.
LCD (liquid crystal display) panels; and
The LCD device comprising a; the backlight unit according to claim 13 located under the LCD panel.

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