KR20170112520A - Light Guide Plate and Backlight Unit Assembly - Google Patents

Abstract

The present invention relates to a light guide plate having a plurality of engraved patterns formed on a lower surface thereof and a backlight unit including the same, and the present invention can provide a light guide plate suitable for a mobile backlight unit. In particular, it is possible to realize a high brightness while attaining slimness and light weight, overcome the limit of brightness drop caused by the material, and can improve the reproducibility and accuracy of pattern repeatedly by compression molding method It is possible to provide an improved light guide plate.

Description

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

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light guide plate used in a liquid crystal display and a backlight unit assembly including the same.

As the industrial society develops into a highly information age, the importance of electronic display devices as media for displaying and transmitting various information is increasing day by day. Particularly, in the case of a liquid crystal display device (LCD), a technology-intensive device in which liquid crystal and semiconductor technology are combined is advantageous in that it is thin, light and low in power consumption, and various manufacturing techniques have been developed and used in a wide area.

Since the liquid crystal display (LCD) device can not emit light, a separate light source is installed on the back of the device to realize color and screen. BACKGROUND ART [0002] In recent years, a backlight unit (BLU) has been widely used as a light emitting device. In recent years, a cold cathode fluorescent lamp (CCFL) The use of LED (Light Emitting Diode), which has the advantage of excellent color reproducibility, is increasing rapidly.

A typical backlight unit is classified into a side light type and a direct type according to the arrangement structure of a light source. Here, the sidelight type, that is, the edge type BLU in which the LEDs are distributed on the side is easier to manufacture than the direct type in which the LEDs are distributed on the entire surface of the backlight unit, and the power consumption and the product thickness can be reduced.

In the edge-type BLU, a light guide plate is provided to uniformly transmit light generated from the side to the front surface of the display. Light emitted from the light source is incident on the light guide plate from the side of the light guide plate to be emitted to the front side. In this method, since the light path passing through the light guide plate is relatively long, the light loss increases. Therefore, in order to prevent this phenomenon, materials of a polymethyl methacrylate (PMMA) type having low light loss and high transmittance are mainly used do. However, the polymethylmethacrylate-based raw materials are vulnerable to moisture in chemical structure, and thus there is a limit in that the stability of bending and dimensional stability is poor in a high temperature and high humidity environment.

On the other hand, in the case of a mobile display, in order to realize a thin thickness, it is the key to make the internal parts of the device as thin as possible without deteriorating the function, and the thickness of the light guide plate needs to be minimized. In this respect, PMMA is advantageous for preventing light loss, but it has a limitation that cracks are generated when it is removed from a mold at the time of injection at a thin thickness, and in some cases, a light guide plate is manufactured using polycarbonate (PC). However, due to the change of the material, a loss of light of about 3% (relative to PMMA) is generated in the light guide plate, which ultimately causes a significant difference in quality of the display.

In the conventional patent document disclosed for the purpose of improving the function of the light guide plate, Korean Patent Laid-Open Publication No. 10-2013-0030441, <Liquid Crystal Display Device>, a lenticular lens layer is formed on the upper surface of the light guide plate to improve the contrast ratio Korean Patent Laid-Open Publication No. 10-2015-0069324, < Liquid crystal display device > discloses a technique in which a dot pattern is formed on the upper surface of a light guide plate and an inverse prism- , And a technique capable of maintaining the polarization characteristic of a specific linearly polarized light incident into the light guide plate is disclosed.

Also, in Korean Patent Laid-Open Publication No. 10-2012-0088944, < a light guide plate and a manufacturing method thereof and a liquid crystal display device using the same, a cover layer made of a material having a low MMA content is cemented to a pattern layer made of a material having a high MMA content Discloses that the problem of yellowing due to laser or thermal processing can be solved while disclosing a light guide plate.

As described above, various efforts are constantly made to improve the function of the light guide plate in the field of liquid crystal display devices, and there is a continuing demand for a higher quality display in the future.

Accordingly, it is an object of the present invention to provide a light guide plate and a backlight unit including the light guide plate, which can overcome the limit of optical loss caused by the material through optimization of the lower pattern structure of the light guide plate and realize high brightness.

In order to achieve the above object, according to a first preferred embodiment of the present invention, there is provided a liquid crystal display comprising: a light-incident portion having a height h1 of an incident surface maintained constant; A connection part connected to the light-incident part and having a height lowered at a constant decreasing width; And a light guide part connected to the connection part and maintaining a height h2 at a ratio of 0.50 to 0.65 with respect to a height h1 of the incident surface, wherein a plurality of engraved patterns are formed on the bottom surface of the light guide part, Is a pentagonal light guide plate having an isosceles trapezoidal shape whose bottom face is a right-angled quadrangle and a side face facing the incident face is inclined and a side face perpendicular to the incident face is inclined.

The intaglio pattern according to the first embodiment has a ratio A1 / A2 of 2 to 6 of the lower side length A1 of the side face facing the incident face and the upper side length A2 of the side face facing the incident face of 2 to 6, (A1 / B) of the lower side length A1 of the side face facing the incident side and the lower side length (B) of the side face facing the direction perpendicular to the incident face can be 0.5 to 1.5.

The intaglio pattern according to the first embodiment may have a ratio A1 / C of the lower side length A1 of the side surface facing the incident surface to the depth C of the engraved pattern of 1.5 to 9.0, Side surface of the engraved pattern may be inclined such that the acute angle? ₂ with the lower surface of the light guide portion is 50 to 70 °.

The connecting portion according to the first embodiment includes an inclined surface whose height is reduced to a constant decreasing width. The inclined surface may have an acute angle? ₁ between 4 and 13 degrees with the lower surface of the light guide plate.

The light guide plate according to the first embodiment may have a ratio (h2 / C) of the height h2 of the light guiding portion to the depth C of the engraved pattern of 10 to 40.

The light guide plate according to the first embodiment may be formed of a resin having a refractive index of 1.49 to 1.59.

According to the present invention, a light guide plate suitable for a mobile backlight unit can be provided. In particular, it is possible to realize a high brightness while attaining slimness and light weight, overcome the limit of brightness drop caused by the material, and can improve the reproducibility and accuracy of pattern repeatedly by compression molding method It is possible to provide an improved light guide plate.

1 is a schematic diagram showing an outgoing light path for each of the incident light paths of the prism film.
2 is a side view of a light guide plate of the present invention.
FIG. 3 is a perspective view and a side view showing an engraved pattern under the light guide plate of the present invention.

According to the present invention, there is provided a liquid crystal display comprising: a light-incident portion having a height h1 of an incident surface maintained constant; A connection part connected to the light-incident part and having a height lowered at a constant decreasing width; And a light guide part connected to the connection part and maintaining a height h2 at a ratio of 0.50 to 0.65 with respect to a height h1 of the incident surface, wherein a plurality of engraved patterns are formed on the bottom surface of the light guide part, Wherein the light guide plate is a pentagonal prism having an isosceles trapezoid with a bottom surface being a right-angled quadrangle and a side surface facing the incident surface being inclined, and a side surface oriented in a direction perpendicular to the incident surface is a tilted triangle.

Hereinafter, the present invention will be described more specifically with reference to the drawings.

The light guide plate of the present invention has a height step so that the thickness of the mobile device itself can be reduced while absorbing all the light emitted from the light source into the light guide plate. However, the light incident portion (corresponding to the region D1 in Fig. 2) in which the height h1 of the incident surface that absorbs the light emitted from the light source is kept constant is set such that the height h1 is maximized It is preferable that the height of the light guide portion (corresponding to the region D3 in FIG. 2) be equal to or slightly larger than the height of the light source, and the height h2 of the ratio of 0.50 to 0.65 to the height h1 of the incident surface, , And it is preferable that the specific step is 50 to 150 mu m.

In addition, in the present invention, the connecting portion (corresponding to the region D2 in FIG. 2) connecting to the light-incident portion and lowering the height to a constant decreasing width includes an inclined surface in which the height is reduced to a constant decreasing width, It is preferable that the inclined surface has an acute angle? ₁ with the lower surface of the light guide plate of 4 to 13 degrees. When the inclination (θ ₁ ) is less than 4 °, the effect due to the occurrence of the step is hardly observed, and when the inclination (θ ₁ ) of the light-entering portion and the light-guiding portion is more than 13 °, the brightness may be drastically reduced.

The light guide plate of the present invention has a recessed pattern formed on the lower surface thereof, so that the light can be uniformly moved toward the upper surface of the light guide plate more effectively. However, it is preferable that the engraved pattern is not formed on the bottom surface of the light-incoming portion located close to the light source in terms of improving the luminance uniformity, and it is advantageous that the number of formed patterns increases as the light source is further away from the light source. Also, although not limited thereto, it may be preferable that the pattern starts to be formed at a position spaced apart from the connection portion, and this can be appropriately adjusted according to the final specification required in the display.

In the present invention, the engraved pattern serves to change the optical path so that the light from the light source passes the inside of the light guide plate and rises toward the upper face of the light guide plate while engaging the oblique sides of the engraved pattern. Generally, (Angular luminance profile) of light emitted to the upper surface of the light guide plate is determined, and this serves as an element for determining the direction of light incident on the prism film (BEF) positioned on the upper surface of the light guide plate as shown in FIG. In theory, the ideal incidence angle of the prism film should be Path D in FIG. 1, and the brightness of the display can be improved if the angular distribution of the light rays coming from the light guide plate coincides with each other.

Accordingly, the ideal angle (? _{In, on - axis, ideal} ) calculated by the following formula (1) is 25.8 to 36.8 占 and the light is incident on the upper surface of the light guide plate at an angle within the range of 25.8 to 36.8 占The probability of exporting can be significantly increased.

(1)

In the above equation (1), N _{resin and BEF} are resin refractive indexes, which indicate the degree of bending when light enters the resin layer from the air as air 1, and when the material is a relatively dense material, the refraction angle increases, .

In order to achieve this, the engraved pattern of the present invention is an isosceles trapezoid in which the bottom surface drawn on the lower surface of the light guide plate is a right-angled quadrangle and the side facing the incident surface is inclined, and the inclined triangle And is a prism. Such an engraved pattern having a pentahedron shape has a narrow width in a direction perpendicular to the incident surface and a wide inclined surface in a direction toward the incident surface in comparison with a pattern of a conventional triangular pyramid, pyramid or prism So that the efficiency of raising the light at an ideal angle can be further improved, and ultimately a high luminance can be realized.

In the present invention, the intaglio pattern has a ratio (A1 / A2) of a lower side length A1 of the side face facing the incident face to an upper side length A2 of the side face facing the incident face of 2 to 6, It is preferable that the ratio A1 / B of the side length A1 of the lower side to the side length B of the side face perpendicular to the incident side is 0.5 to 1.5, Which is preferable in terms of interference prevention. In particular, when A1 / B is less than 0.5, it is impossible to achieve a sufficient slope at a narrow inclination angle to reach the target luminance, and when A1 / B 1.5 is exceeded, it may be disadvantageous to form a pattern. Therefore, A1 / B may be more preferably 0.5 to 0.7.

Also, in the present invention, the intaglio pattern has a ratio (A1 / C) of a length A1 of the lower side of the side face toward the incident surface to a depth C of the engraved pattern of 1.5 to 9.0, It can be more advantageous to go. If the ratio is less than 1.5, it is very difficult to process and it can be broken structurally. If the ratio is over 9.0, the amount of light to be diverted may be lowered and the brightness may be deteriorated. Particularly, the depth of the engraved pattern may affect the brightness increase. Therefore, it is preferable that the ratio (h2 / C) of the height h2 of the light guiding portion to the depth C of the engraved pattern satisfies 10 to 40.

Further aspects of the intaglio pattern faces the incident surface in the present invention is advantageous in workability is inclined such that a 50 to 70 ° an acute angle (θ ₂₎ forms with the lower portion light guide, in a 50 ° the inclination (θ ₂₎ If it is not enough, the light is disadvantageously spread to the side, and it is disadvantageous to go up. When the angle is more than 70 degrees, the light is not easily processed and the amount of light emitted toward the top surface is decreased. Particularly, since the side inclination angle of the engraved pattern toward the incident surface plays a crucial role in changing the direction by colliding with the light, it is most important that the angle is satisfied.

Also, in the present invention, the light guide plate may be formed of a resin having a refractive index of 1.49 to 1.59 for optical properties, and a suitable resin may be a thermoplastic resin such as PMMA, MS, PC, and the like.

In addition, the present invention provides a backlight unit assembly including a light guide plate having the above-described features. Here, the backlight unit is disposed at a lower portion of the liquid crystal panel and serves to provide light to a liquid crystal panel that implements an image using light. Basically, the backlight unit is provided with a light source, a light guide plate, It may be that the sheet is included.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples. These examples are for the purpose of illustrating the present invention more specifically, and the present invention is not limited thereto.

Example  One

400 kg / hr of PC (Teijin, PC-1151 light guide plate grade) was fed into an extruder having a uniaxial screw diameter of 120 mm and extruded at 280 ° C., and a height difference of 100 μm was generated between the light- A pattern mold was fabricated on the lower surface by the embossing process and the nickel electrophotographic copying method to form a pattern mold having a side length A1 on the side facing the incident surface of 30 mu m and an upper side length A2 of 15 mu m on the side facing the incident surface, A light guide plate was produced by forming a pentagonal engraved pattern having a side length B of the lower side of 60 mu m and a pattern depth C of 60 mu m.

Example  2 to Example  12

The light guide plates of Examples 2 to 12 were prepared in the same manner as in Example 1 except that the engraved patterns were changed to the sizes shown in Table 1 below.

Comparative Example  1 to Comparative Example  4

The light guide plates of Comparative Examples 2 to 4 were prepared in the same manner as in Example 1, except that the engraved patterns were changed to the sizes shown in Table 1 below.

A1 (占 퐉) A2 (占 퐉) B (占 퐉) C (탆) Example 1 30 15 60 5 Example 2 30 15 60 10 Example 3 30 15 60 15 Example 4 30 15 60 20 Example 5 60 15 60 5 Example 6 60 15 60 10 Example 7 60 15 60 15 Example 8 60 15 60 20 Example 9 90 15 60 5 Example 10 90 15 60 10 Example 11 90 15 60 15 Example 12 90 15 60 20 Comparative Example 1 15 15 60 5 Comparative Example 2 15 15 60 10 Comparative Example 3 15 15 60 15 Comparative Example 4 15 15 60 20

The total luminous flux and luminance were measured for the light guide plate manufactured in Examples and Comparative Examples in the following manner, and the results are shown in Table 2. (Reference in Table 2 indicates an incandescent light guide plate of a conventional PMMA material).

(1) Total luminous flux: The ratio of the luminous flux emitted to the upper surface of the light guide plate was calculated to derive the total luminous flux of the light guide plate. At this time, the luminous flux was measured with a total luminous flux measuring integration system (Neolight PL5000), and it can be judged that the luminance is improved when the luminous flux is 1 or more.

(2) Luminance ratio : manufactured in the above example and comparative example in a backlight unit (model name: I-Pad Air 2, manufactured by Apple Inc., light guide plate + diffusion 1 + prism 2 + diffusion 2) for a liquid crystal display panel of 9.7 inches And the luminance was measured at each of 17 points using a luminance meter (model name: BM-7, Japan TOPCON), and the average value was obtained.

A1 / B A1 / A2 A1 / C Light guide plate Total luminous flux
(lumen) Luminance ratio Reference 1,000 1,000 Example 1 0.50 2.00 6.00 1.057 1.048 Example 2 0.50 2.00 3.00 1.063 1.071 Example 3 0.50 2.00 2.00 1.092 1.104 Example 4 0.50 2.00 1.50 1.032 1.036 Example 5 1.00 4.00 12.00 1.004 0.995 Example 6 1.00 4.00 6.00 1.075 1.080 Example 7 1.00 4.00 4.00 1.089 1.101 Example 8 1.00 4.00 3.00 1.067 1.070 Example 9 1.50 6.00 18.00 1.003 0.994 Example 10 1.50 6.00 9.00 1.048 1.046 Example 11 1.50 6.00 6.00 1.070 1.085 Example 12 1.50 6.00 4.50 1.048 1.048 Comparative Example 1 0.25 1.00 3.00 0.895 0.894 Comparative Example 2 0.25 1.00 1.50 0.962 0.970 Comparative Example 3 0.25 1.00 1.00 0.916 0.924 Comparative Example 4 0.25 1.00 0.75 0.842 0.851

As can be seen from the result table of Table 2, in the case of Examples 1 to 12, the total luminous flux was increased as compared with the control group of Comparative Examples 1 to 4, as a matter of course, and the brightness was improved overall. Also, among the examples, when the depth C of the pattern was 15 탆 (Examples 3, 7 and 11) under the same conditions, the brightness was high. In the overall evaluation, when the light guide plate of Example 3 was applied, And brightness were the best.

Claims (8)

A light-incident portion in which the height h1 of the incident surface is kept constant;
A connection part connected to the light-incident part and having a height lowered at a constant decreasing width; And
And a light guide portion connected to the connection portion and maintained at a height h2 at a ratio of 0.50 to 0.65 with respect to the height h1 of the incident surface,
A plurality of engraved patterns are formed on the bottom surface of the light guide portion,
Wherein the engraved pattern is a pentagon, the bottom surface of which is a right-angled quadrangle, an isosceles trapezoid with its side facing the incident surface tilted, and a triangular shape with its side face oriented in a direction perpendicular to the incident surface.
The optical device according to claim 1, wherein the engraved pattern has a ratio A1 / A2 of 2 to 6 of a lower side length A1 of the side face facing the incident face and an upper side length A2 of the side face facing the incident face of 2 to 6, (A1 / B) of the lower side length (A1) of the side surface facing the incident side to the lower side length (B) of the side surface facing the vertical direction is 0.5 to 1.5.
3. The light guide plate according to claim 2, wherein the intaglio pattern has a ratio A1 / C of a length A1 of the lower side of the side surface facing the incident surface to a depth C of the engraved pattern of 1.5 to 9.0.
The light guide plate according to claim 1, wherein a side face of the engraved pattern facing the incident surface is inclined so that an acute angle (? ₂ ) with the lower surface of the light guide portion is 50 to 70 degrees.
The light guide plate according to claim 1, wherein the connecting portion includes an inclined surface whose height is reduced to a predetermined reduction width, and the inclined surface has an acute angle &amp;thetas; ₁ with the lower surface of the light guide plate of 4 to 13 DEG.
2. The light guide plate according to claim 1, wherein the light guide plate has a ratio (h2 / C) of a height (h2) of the light guiding portion to a depth (C)
The light guide plate according to claim 1, wherein the light guide plate is formed of a resin having a refractive index of 1.49 to 1.59.
A backlight unit assembly comprising a light guide plate according to any one of claims 1 to 7.

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