KR20140046501A - Light guiding plate and backlight unit comprising the same - Google Patents

Abstract

The present invention relates to a light guide panel and a backlight unit comprising the same and, more specifically, to a light guide panel and a backlight unit comprising the same capable of being usefully used for a monitor having a narrow bezel by arranging unevenness of a surface roughness of 0.3-1.0 um and thus improving brightness and linearity of emitted light and the brightness of a brightness reduction unit.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a light guide plate and a backlight unit including the light guide plate.

The present invention relates to a light guide plate having improved brightness and linearity of emitted light, and a backlight unit including the same.

Recently, flat panel displays such as liquid crystal displays (LCDs) and plasma display panels (PDPs) are rapidly developing in place of cathode ray tubes (CRTs). Among the flat panel display devices, since the liquid crystal display device does not emit light by itself, a backlight unit is required to provide light for displaying an image on the rear surface so that the display contents can be visually recognized.

The direct type of the backlight unit is a method of directly dimming the rear surface of the liquid crystal display by placing a light source under the liquid crystal display panel. This can secure high luminance, and is generally used for large and medium sized liquid crystal display panels. Meanwhile, a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), or a light emitting diode (LED) may be used as a light source of the backlight unit.

The cold cathode fluorescent lamp includes a discharge tube filled with a discharge gas in an inner space and coated with a fluorescent material on an inner surface thereof, and a pair of electrodes formed on both sides of the discharge tube. The entire area of the cold cathode fluorescent lamp may be divided into a light emitting area between both electrodes and a non-light emitting area at both ends where the both electrodes are located, and these areas may be divided into a liquid crystal display device using the cold cathode fluorescent lamp as a backlight. The display area corresponds to the active area and the bezel area, respectively. In particular, it is very preferable in view of the uniformity of luminance that the luminance uniformity, that is, the effective emission region, is configured to correspond to the display region of the display device. Therefore, in the general liquid crystal display device, a minimum bezel area is secured so as to cover not only the non-light emitting area of the fluorescent lamp but also a part of the light emitting area adjacent thereto. However, recently, due to the slimming of the liquid crystal display device, there is a problem that it is difficult to sufficiently secure the bezel area, which causes a problem of deterioration in display quality due to uneven luminance in the display area adjacent to the bezel area.

Korean Patent Publication No. 2008-0002567 discloses a fluorescent lamp, a backlight unit having the same, and a liquid crystal display device.

Korean Patent Publication No. 2008-0002567

An object of the present invention is to provide a light guide plate in which the luminance of the luminance lowering portion near the bezel is improved.

An object of the present invention is to provide a light guide plate having high linearity and brightness of emitted light.

It is another object of the present invention to provide a backlight unit including the light guide plate.

1. A light guide plate having concavities and convexities having a surface roughness (Ra) of 0.3 to 1.0 um on a lower surface thereof.

2. The light guide plate of 1 above, further comprising an embossed or intaglio dot pattern on the concave-convex.

3. In the above 1, the light guide plate further having a line-shaped pattern on the upper surface.

4. The light guide plate of 3 above, wherein the line-shaped pattern is at least one selected from the group consisting of a round-prism pattern, a triangular-prism pattern, and a lenticular pattern.

5. The light guide plate of 3 above, wherein the line pattern is a lenticular pattern.

6. Backlight unit having a light guide plate of any one of the above 1 to 5.

7. The backlight unit of claim 6, further comprising a light source selected from the group consisting of a light emitting diode (LED), an organic light emitting diode (OLED), a hot cathode tube, and a cold cathode tube on the side of the light guide plate.

8. The backlight unit of claim 7, wherein the line pattern of the upper surface of the light guide plate is disposed such that a light source is positioned at an end thereof in a longitudinal direction thereof.

9. The image display device having a backlight unit of the above six.

The light guide plate of the present invention can be usefully used in a monitor having a narrow bezel by improving the luminance of the luminance lowering portion near the bezel.

The light guide plate of the present invention improves the straightness of the emitted light.

The light guide plate of the present invention can be irradiated with a uniform amount of light can suppress the occurrence of hot spots.

1 is a view schematically showing an embodiment of the light guide plate of the present invention.
2 is a view schematically showing an embodiment of a backlight unit including a light guide plate of the present invention.
3 is a view showing a straightness evaluation method according to the present invention.
4 is a diagram illustrating a result of luminance measurement in an example.
5 is a diagram illustrating a luminance measurement result of Comparative Example 1. FIG.
6 is a diagram illustrating a luminance measurement result of Comparative Example 2. FIG.
7 is a diagram illustrating a luminance measurement result of Comparative Example 3. FIG.
8 shows the weakness of the luminance of Example (a) and Comparative Example 1 (b).
Fig. 9 is a photograph observing the dot pattern of the example by SEM.
10 is a photograph of the dot pattern of Comparative Example 1 observed with SEM.
11 is a photograph of the dot pattern of Comparative Example 2 observed with SEM.
12 is a photograph of a dot pattern of Comparative Example 3 observed with an SEM.

The present invention provides a light guide plate which can be usefully used in a monitor having a narrow bezel by providing irregularities having a surface roughness (Ra) of 0.3 to 1.0 μm on a lower surface thereof, thereby improving luminance and linearity of emitted light and improving luminance of a luminance lowering part. It relates to a backlight unit having the same.

Hereinafter, the present invention will be described in detail.

1 schematically shows an embodiment of the light guide plate of the present invention.

The light guide plate 100 of the present invention includes a concave-convex 102 having a surface roughness Ra of 0.3 to 1.0 um on a lower surface of the substrate 101.

Since the unevenness causes diffuse reflection and refraction at the interface thereof, the unevenness serves to improve the luminance of the luminance lowering portion around the polarizer.

When Ra is less than the above range, the luminance of the weak luminance portion may be lowered. In addition, when Ra exceeds the above range, it may be difficult to irradiate a uniform amount of light because the lower pattern formation degree is poor.

The method of forming the unevenness 102 is not particularly limited, and specific examples thereof include sandblast, shot blast, sandpaper polishing, brush polishing, chemical etching, laser processing, milling cutter processing, and the like. The surface can be formed in contact with the processed roll by the method of.

The substrate 101 may be made of an optically transparent resin. The optically transparent resin may be used alone or in mixture of two or more of (meth) acrylic resin, polycarbonate resin, styrene resin, olefin resin, polyester resin, and the like, but is not limited thereto.

As for the said olefin resin, it is more preferable that it is cyclic olefin resin, and it is more preferable that the said polyester resin is amorphous polyester resin.

It is preferable to use methacryl-type resin as said optically transparent resin. Examples of the methacrylic resin include methyl methacrylate, ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate, 2-hydroxyethyl methacrylate, Phenol methacrylate, chloro methacrylate, etc. are mentioned, Among these, the methyl methacrylate resin with high transmittance | permeability is more preferable.

More preferably, the methacrylic resin is copolymerized with a monofunctional unsaturated monomer, and the methacrylic resin is preferably copolymerized within about 40% by weight of the monofunctional unsaturated monomer, and more preferably within about 30% by weight. Even more preferably copolymerized within about 20% by weight.

Examples of the monofunctional unsaturated monomer copolymerized with the methacrylic resin include ethyl methacrylate, butyl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, 2-ethylhexyl methacrylate, and 2-hydroxy methacrylate. Acrylic acid including ethyl, phenyl methacrylate, chloro methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, cyclohexyl acrylate, phenyl acrylate, benzyl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate and the like Ester compound is preferable.

Examples of the monofunctional unsaturated monomer copolymerized with the methacrylic resin include unsaturated acid compounds including methacrylic acid and acrylic acid, styrene, acrylonitrile, maleic anhydride, phenyl maleimide, cyclohexyl maleimide, and the like. These may be used alone or in combination of two or more.

Copolymerization of the methacrylic resin with a monofunctional unsaturated monomer can be easily carried out by those skilled in the art.

The resin may further include at least one of an ultraviolet absorber, a bluing agent, an antioxidant, and a release agent.

The light guide plate 100 of the present invention may further include an embossed or intaglio dot pattern on the concave-convex as needed. 1 illustrates a light guide plate 100 having an embossed dot pattern 104.

The method of forming the dot pattern is not particularly limited, and specific examples thereof include silk printing, inkjet printing, injection, v-cutting, laser processing, and the like.

The dot pattern scatters or refracts the light, thereby inducing the light emitted from the light source to the upper surface of the light guide plate (light emitting part), and also allowing the emitted light to be widely diffused to enable uniform light irradiation. It is possible to suppress the occurrence of hot spots in which a specific area of the skin is noticeably brighter.

The light guide plate 100 of the present invention may further include a line pattern 103 on the upper surface of the substrate 101 as necessary.

The upper linear pattern 103 may use the same or different material as that of the substrate 101. For example, the pattern 103 may include an optically transparent resin. The optical transparent resin may be a (meth) acrylic resin, polycarbonate resin, styrene resin, olefin resin, polyester resin and the like, but is not necessarily limited thereto.

The upper line pattern 103 may have various pattern cross sections, and there is no particular limitation on the shape thereof. For example, it may be a round-prism pattern, a triangular-prism pattern, or a lenticular pattern, and preferably a lenticular pattern in terms of brightness and straightness of the emitted light. In this invention, when using a lenticular pattern, it is more preferable that a cross section is semi-ellipse.

In the present invention, the round-prism pattern means a pattern in which the cross-sectional shape of the pattern is a triangle having an arc shape at the top vertex, and the triangle-prism pattern means a pattern in which the cross-sectional shape of the pattern is a triangle, and a lenticular pattern It means the pattern whose shape of the cross section of a pattern is semi-circle or semi-ellipse.

The light guide plate of the present invention may further include a functional layer on any one of the lower surface and the upper surface, or impart functionality to the light guide plate, like a conventional light guide plate. As the base resin of the functional layer, a resin exemplified as the base resin of the light guide plate, which is a base material layer, may be used. The same resin as the base resin of the light guide plate may be used, but another one may be used. The functional layer may further contain at least one of an ultraviolet absorber, a heat stabilizer, an antioxidant, an antistatic agent, a fluorescent whitening agent, a releasing agent and a dispersing agent. The functional resin may be contained in the base resin, It is possible.

The manufacturing method of the light guide plate is not particularly limited, and various methods such as extrusion molding, vacuum molding, hot press molding, film lamination, solvent bonding, surface coating, ultraviolet curing, and thermal curing may be used. However, extrusion molding or ultraviolet curing is preferable from the standpoint of manufacturing easiness, and extrusion molding is preferable considering production cost and productivity.

The light guide plate of the present invention may constitute a backlight unit together with the light source 105 and the like. The light emitted from the light source is incident on the side surface of the light guide plate. The light source may be located on the side of the side or may be located elsewhere. An edge type backlight unit in which a light source is positioned opposite to a side surface of the light guide plate is preferable, but the light source may be located in another place if a separate reflecting means can appropriately introduce light into the side surface of the light guide plate. The light source may be, for example, a light emitting diode (LED), an organic light emitting diode (OLED), a hot cathode tube, a cold cathode tube,

In the backlight unit according to the present invention, as shown in FIG. 2, when the light source 105 is positioned on the side of the light guide plate 100, the direction of the line pattern 103 on the light guide plate 100 is aligned. The light source 105 may be disposed at one or both ends in the longitudinal direction, or may be disposed such that the light source 105 is positioned at a position perpendicular to the direction. Preferably, the direction of the line pattern 103 is arranged such that the light source is positioned at its end in the longitudinal direction, which is advantageous in terms of reducing the hot spot and in terms of uniformity of the emitted light.

In addition, the lower surface of the light guide plate 100 may further include a reflective sheet 106. Reflective sheet 106 is for reflecting the light exiting the lower portion of the light guide plate 100 to re-incident into the light guide plate 100, a general reflective sheet used in the art can be used without limitation.

Meanwhile, the upper surface of the light guide plate 100 may further include a diffusion sheet, a micro lens sheet, a prism sheet, a brightness enhancement (DBEF) sheet, a protective sheet, and the like, as necessary.

The light guide plate 100 of the present invention may be included as one component of an image display device. The image display device is not particularly limited as long as it is an apparatus requiring a separate surface light source for displaying an image, and may be, for example, a liquid crystal display. In addition, the light guide plate 100 as described above may also be used as one component for supplying a surface light source to a general lighting device.

Hereinafter, preferred examples are provided to aid the understanding of the present invention, but these examples are merely illustrative of the present invention and are not intended to limit the scope of the appended claims. It is apparent to those skilled in the art that various changes and modifications can be made to the present invention, and such modifications and changes belong to the appended claims.

Example  And Comparative Example  1-3

A light guide plate having a width of 716 mm was manufactured from poly (methyl methacrylate) (PMMA) (refractive index: 1.49), and a semi-elliptic lenticular pattern was formed on the upper surface of the light guide plate, and an extrusion process was performed on the lower surface of the light guide plate. As shown in Table 1, irregularities were formed, and a dot pattern was formed thereon by silk printing.

Example Comparative Example 1 Comparative Example 2 Comparative Example 3 Uneven formation O X O O Surface roughness (Ra) 0.65 0 1.25 2.5

Test Example

1. Straightness and N-region luminance evaluation

Straightness is shown in FIG. 3, when the LED light sources of the Nth block (each block contains seven LED light sources) are turned on and the light sources of the other blocks are all off. The luminance of the light emitted from the straight line connecting the light source of the N-th block is evaluated as the ratio of the brightness of the light emitted from the straight line connecting the light source of the N + 3th block. The smaller the ratio, the better the straightness of the light.

The measurement results are shown in Table 2.

division Example Comparative Example 1 Brightness (nit) Normalization (%) Brightness (nit) Normalization (%) Measuring position LED Light receiver Center Light distribution part Light receiver Center Light distribution part Light receiver Center Light distribution part Light receiver Center Light distribution part N + 4 OFF 41 82 56 1.28% 3.39% 5.69% 31 75 62 1.10% 3.30% 6.03% N + 3 OFF 54 129 102 1.69% 5.33% 10.37% 48 136 109 1.70% 5.99% 10.60% N + 2 OFF 108 327 230 3.38% 13.52% 23.37% 96 355 232 3.39% 15.64% 22.57% N + 1 OFF 458 1099 551 14.32% 45.45% 56.00% 389 1206 594 13.75% 53.13% 57.78% N ON 3199 2418 984 100.00% 100.00% 100.00% 2829 2270 1028 100.00% 100.00% 100.00% N-1 OFF 469 1385 619 14.66% 57.28% 62.91% 499 1256 684 17.64% 55.33% 66.54% N-2 OFF 182 388 258 5.69% 16.05% 26.22% 118 389 289 4.17% 17.14% 28.11% N-3 OFF 67 173 136 2.09% 7.15% 13.82% 63 169 146 2.23% 7.44% 14.20% Straightness Contrast ((N + 3) / N) 1.69% 5.33% 10.37% Contrast ((N + 3) / N) 1.70% 5.99% 10.60%

Referring to Table 2, it can be seen that the linearity of the light emitting portion, the central portion and the light distribution portion is slightly superior to Comparative Example 1 of 1.70%, 5.99%, 10.60% to 1.69%, 5.33% and 10.37%, respectively.

2. Evaluation of luminance uniformity

The luminance of the light emitted from the light guide plate was measured using a luminance meter (model name: BM-7, TOPCON Japan).

The measurement results are shown in Table 3, FIG. 4 (Example), FIG. 5 (Comparative Example 1), FIG. 6 (Comparative Example 2), and FIG. 7 (Comparative Example 3).

division Brightness (nit) Average brightness (nit) Uniformity (%) Example 5589 5052 4490 5106 78.6 5716 5530 4556 5610 5156 4462 Comparative Example 1 4551 5210 4303 4804 76.4 4947 5629 4573 4450 5085 4489 Comparative Example 2 8207 4497 2313 5174 26.9 8499 4878 2549 8593 4623 2403 Comparative Example 3 11750 1413 165 4584 1.3 12650 1682 224 11490 1641 240

Referring to Table 3 and FIGS. 4 to 7, in the case of the embodiment, it was confirmed that the light is uniformly emitted by the light incident part, the light distribution part, and the bezel part.

In Comparative Example 1, the luminance of the central portion is high, but the luminance decreases toward the light incident portion and the light distribution portion. In addition, Comparative Examples 2 and 3 can be seen that only the luminance of the light incident portion is high and the luminance is sharply lowered toward the center portion and the light distribution portion, so that the uniformity of light is significantly reduced.

3. Luminance assessment of weak spots

The luminance of the luminance weak part shown in Figure 8 was evaluated in the same manner as above, and the results are shown in Table 4 below.

division Example Comparative Example 1 Luminance increase rate Zone 1 4385 3403 30% Zone 21 4024 3361 18%

Referring to Table 4, compared with Comparative Example 1, the light quantity of the weak part of the brightness is increased by 30% in one zone, 18% in 21 zones, it can be seen that the uniform emission of the light is made.

4. Comparison of lower pattern formation degree

Formation degree of the silk printing pattern formed on the lower part of the light guide plate was observed by SEM, and the results were evaluated in Table 5 and 9 (Example), FIG. 10 (Comparative Example 1), FIG. 11 (Comparative Example 2), and FIG. 12. It is shown in (Comparative Example 3).

○: Good print pattern appearance

(Triangle | delta): Some form defects in the appearance of a printing pattern

Х: Print pattern appearance front shape bad

division Bottom pattern
Degree of formation Example ○ Comparative Example 1 ○ Comparative Example 2 △ Comparative Example 3 Х

Referring to Table 5 and FIGS. 9 to 12, the Example of Ra 0.65 was confirmed that the silk printing pattern was formed well to the extent that there is no difference in appearance from Comparative Example 1.

However, in the case of Comparative Examples 2 to 3 in which Ra exceeded 1.0, it was confirmed that the degree of pattern formation was poor, and in Comparative Example 3, the shape of the front surface of the printed pattern was poor, and thus the shape could not be maintained.

100: light guide plate 101: base material
102: unevenness 103: line pattern
104: dot pattern 105: light source
106: reflective sheet

Claims (9)

The light guide plate which has the unevenness | corrugation of surface roughness Ra 0.3-1.0um in a lower surface.
The light guide plate according to claim 1, further comprising an embossed or intaglio dot pattern on the unevenness.
The light guide plate according to claim 1, further comprising a line pattern on the upper surface.
The light guide plate of claim 3, wherein the line pattern is at least one selected from the group consisting of a round-prism pattern, a triangular-prism pattern, and a lenticular pattern.
The light guide plate of claim 3, wherein the line pattern is a lenticular pattern.
The backlight unit provided with the light guide plate of any one of Claims 1-5.
The backlight unit of claim 6, further comprising a light source selected from a group consisting of a light emitting diode (LED), an organic light emitting diode (OLED), a hot cathode tube, and a cold cathode tube on a side of the light guide plate.
The backlight unit of claim 7, wherein the line pattern of the upper surface of the light guide plate is disposed such that a light source is positioned at an end thereof in a longitudinal direction thereof.
An image display device comprising the backlight unit of claim 6.

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