KR100807296B1 - backlight for liquid crystal display devices - Google Patents

Abstract

The present invention relates to a backlight of a liquid crystal display device.

Since the brightness of the liquid crystal display is affected by the distribution of light emitted from the backlight, it is important to increase the condensation of the backlight. Particularly, when the cholesteric liquid crystal color filter is used, color inversion occurs as the angle of the light incident from the backlight increases. In this case, a high-concentration backlight having a small distribution of the emitted angles is required.

In the backlight for a liquid crystal display according to the present invention, a prism film having a plurality of linear prisms may be disposed between a lamp and a light guide plate as a light source in an edge type backlight, thereby increasing the light condensation of the backlight and reducing manufacturing cost and volume.

Backlight, prism, luminance

Description

Backlight for liquid crystal display devices             

1 is a cross-sectional view of a backlight for a conventional liquid crystal display device.

FIG. 2 is a perspective view of a prism film disposed in the backlight of FIG. 1. FIG.

3 is a cross-sectional view of a backlight according to a first embodiment of the present invention;

4A and 4B show an example of a prism film according to the present invention.

FIG. 5 is a diagram illustrating a simulation result of angle-specific distribution of light emitted from the backlight of FIG. 3.

Fig. 6 is a diagram showing the distribution of the emitted light according to the side angle size of the linear prism.

7 is a cross-sectional view of a backlight according to a second embodiment of the present invention.

8 is a cross-sectional view of a backlight according to a third embodiment of the present invention.

9 is a sectional view of a backlight according to a fourth embodiment of the present invention;

FIG. 10 is a diagram illustrating a simulation result of angle-specific distribution of light emitted from the backlight of FIG. 9. FIG.

11A and 11B are cross-sectional views of backlights according to fifth and sixth embodiments of the present invention, respectively.

12A, 12B and 13 illustrate another example of a light collecting film according to the present invention.

The present invention relates to a light source for a liquid crystal display device, and more particularly, to a backlight of a liquid crystal display device.

Recently, with the rapid development of the information society, there is a need for a flat panel display having excellent characteristics such as thinning, light weight, and low power consumption, among which a liquid crystal display has a resolution, It is excellent in color display and image quality, and is actively applied to notebooks and desktop monitors.

In general, a liquid crystal display device is formed by arranging two substrates on which electric field generating electrodes are formed so that the surfaces on which the two electrodes are formed face each other, injecting a liquid crystal material between the two substrates, and then applying a voltage to the two electrodes. By moving the liquid crystal molecules by an electric field, the device expresses an image by the transmittance of light that varies accordingly.

However, the liquid crystal display does not emit light by itself and merely controls a light transmittance, and thus requires a separate light source.

Therefore, an image is displayed by arranging a backlight on the back of the liquid crystal panel and injecting light from the backlight into the liquid crystal panel to adjust the amount of light according to the arrangement of the liquid crystals.

Such a backlight is divided into a direct method of directly dimming the front surface of the substrate by placing a light source on the bottom of the liquid crystal display device and an edge method of reflecting and diffusing light rays by a light guide plate and a reflecting plate by placing the light source on one or both sides of the substrate. Currently, edge type backlights are mainly used to reduce volume.

Hereinafter, a backlight according to the related art will be described with reference to the accompanying drawings.

1 is a cross-sectional view of a conventional backlight structure, and relates to an edge type backlight.

As shown in FIG. 1, in the conventional edge type backlight, a lamp 11, which is a linear light source, and a lamp housing 12 surrounding the lamp 11 are disposed on one side of the light guide plate 13. 13) serves to convert the light from the lamp 11 into a surface light source. In general, the lower surface of the light guide plate 13 scatters the light to form a uniform surface light source. The created scattering pattern (not shown) is formed. Next, a reflecting plate 14 is disposed below the light guide plate 13 to prevent light leakage, and the first diffusion film 15 and the two prism films 16 are disposed on the light guide plate 13 to secure a desired viewing angle. , 17), and the second diffusion film 18 are sequentially arranged.

Here, a perspective view of the structure in which the two prism films 16 and 17 are arranged is shown in FIG. 2, and the prism films 16 and 17 have a plurality of triangular linear prisms 16a and 17a thereon. The linear prisms 16a and 17a are arranged to be perpendicular to each other.

As such, in order to secure a desired viewing angle, the two prism films 16 and 17 are disposed and used so that the linear prisms 16a and 17a are perpendicular to each other. As the number of the prism films 16 and 17 increases, the cost increases. The total reflection causes light feedback to occur, resulting in a lot of light loss.

On the other hand, the color filter of the upper substrate used to implement a color image in the liquid crystal display device is generally an absorption type color filter, and a lot of light loss occurs when light passes through the color filter, so that the brightness of the liquid crystal display device is increased. Degrades. Accordingly, recently, a liquid crystal display using a cholesteric liquid crystal color filter using the selective reflection characteristic of a cholesteric liquid crystal has been researched and developed. When the liquid crystal color filter is used, the luminance can be improved as compared with when the absorption type color filter is used.

The cholesteric liquid crystal has a selective reflection characteristic that mainly reflects only a specific wavelength according to a helical pitch rather than reflecting all incident light. However, since the thickness of the cholesteric liquid crystal color filter through which the light passes varies according to the incident angle of the incident light, the pitch size of the cholesteric liquid crystal experienced by the light is changed, and the wavelength of the reflected light is changed. Accordingly, color shift occurs according to the viewing angle of the liquid crystal display, and thus, a liquid crystal display using the cholesteric liquid crystal color filter requires a light converging backlight to allow light to be incident at a small angle distribution.

Japanese Laid-open Patent No. 6-160840 shows an example in which a prism film is further added in disposing a polarizing means between a lamp and a light guide plate in order to increase the light collecting efficiency. In this case, the prism film controls light incident to the polarizing means. It was used as an auxiliary means to Therefore, since the polarizing means and the prism film are formed together, there is a costly problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a light collecting backlight for a liquid crystal display device having a small emission angle distribution and which can reduce volume and cost.

According to an aspect of the present invention, a backlight for a liquid crystal display device includes: a linear light source emitting light and extending in a first direction; A lamp housing surrounding the light source and having an opening at one side; A light guide plate having one side connected to an opening of the lamp housing and receiving light from the light source from a side surface and guiding it in a second direction; A reflector disposed under the light guide plate and reflecting light in a third direction opposite to the second direction from the light guide plate in the second direction; A first prism film disposed between the light source and the light guide plate and having a plurality of linear prisms having a vertex angle of 60 degrees to 150 degrees; Between the first prism film and the light guide plate, a second prism film having a plurality of linear prisms having a vertex angle of 60 to 150 degrees.

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In this case, the linear prisms of the first prism film and the second prism film may be perpendicular to each other, or may be horizontal to each other.

Here, the linear prism of the first prism film may extend in the first direction or may extend in a direction perpendicular to the first direction.

In the backlight according to the present invention, the first and second prism films may be formed of a sheet having a linear prism and a base film under the sheet, wherein the refractive index of the sheet is preferably larger than that of the base film.

Meanwhile, the present invention may further include a diffusion film on the light guide plate, and may further include a prism film having a plurality of linear prisms between the light guide plate and the diffusion film.

In addition, the present invention may further include a light collecting film for collecting light on the light guide plate.

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In another backlight according to the present invention, a linear light source that emits light and extends in a first direction is surrounded by a lamp housing having an opening on one side, and the opening of the lamp housing receives light from the light source from the side and in a second direction. It is connected to one side of the guiding light guide plate. In the lower part of the light guide plate, a reflecting plate for reflecting light in the third direction opposite to the second direction from the light guide plate in the second direction is disposed, and a film having a plurality of pyramidal patterns is disposed between the light source and the light guide plate. .

As described above, in the present invention, by arranging at least one prism film or another type of light collecting film between the light source and the light guide plate, it is possible to reduce the volume and manufacturing cost of the backlight while providing a backlight having high light collection efficiency.

Hereinafter, a backlight for a liquid crystal display according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

3 is a cross-sectional view illustrating a structure of a backlight for a liquid crystal display according to a first embodiment of the present invention.

As shown, in the backlight according to the first embodiment of the present invention, a linear lamp 110 used as a light source, and a lamp housing 120 surrounding the lamp 110 and having an opening at one side thereof, the light guide plate 140 is provided. In one side of the), the opening of the lamp housing 120 is directed toward the light guide plate 140. Next, a prism film 130 in which the linear prism 131 extends in the longitudinal direction of the lamp 110 is positioned between the lamp 110 and one side of the light guide plate 140. Since the prism film 130 primarily condenses the light from the lamp 110 and emits the light to the light guide plate 140, the prism film 130 may increase the light condensing degree of the backlight. Next, a reflecting plate 150 is disposed below the light guide plate 140, and a diffusion film 160 is disposed above the light guide plate 140.

Here, the lamp 110 may use a fluorescent lamp such as a cold cathode tube or a hot cathode tube having high brightness while having low power consumption, and may be disposed only on one side of the light guide plate 140 as shown, or the light guide plate 140. It may be arranged on both sides of. The lamp housing 120 reflects the light emitted from the lamp 110 to allow light to be emitted only through the opening, thereby preventing light from leaking in portions other than the opening. The light guide plate 140 has a function of converting the light emitted from the lamp 110 into a surface light source to guide the light guide plate 140 in the first direction of the upper part of the light guide plate 140 in FIG. 3, wherein the lower surface of the light guide plate 140 is obliquely formed. The further away from the housing 120 may have a thinner thickness, or may have a uniform thickness. Although not shown, a plurality of patterns are formed on the lower surface of the light guide plate 140 to refract the light in the first direction. On the other hand, the reflector 150 below the light guide plate 140 serves to reflect the light emitted in the second direction opposite to the first direction in the first direction so that the light does not leak.

In the backlight according to the present invention, the diffusion plate 160 on the light guide plate 140 may be omitted.

Here, the case where the linear prism 131 is disposed in parallel with the extending direction of the lamp 110 has been described. However, the linear prism 131 may be disposed to be perpendicular to the extending direction of the lamp 110.

An example of the prism film structure of the backlight device according to the present invention is shown in FIGS. 4A and 4B.

As shown in FIGS. 4A and 4B, the prism film may consist only of the sheet 132 having the linear prism 131, or the base film 133 may be disposed under the sheet 132 having the linear prism 131. It may form further.

When formed from a PMMA material having a refractive index of 1.49, the prism film consists only of a sheet 132 having a linear prism 131 as shown in FIG. 4A.

On the other hand, a prism film such as 3M BEF (brightness enhancement film) is made of a sheet 132 having a linear prism 131 on the base film 133, as shown in Figure 4b, which is polyethylene terephthalate (PET: polyethylene terephthalate) The polymer-type transparent resin is formed on the base film 133 made of a transparent resin such as), and the linear prism 131 is formed. In order to minimize total reflection, the refractive index of the sheet 132 is higher than that of the base film 133. It must be large.

The results of the simulation (simula-tion) on the angle distribution of the light emitted from the backlight are shown in FIG. 5. Here, the dotted line is a guide line, and since the angle-specific distribution of the emitted light has a form of a cosine function, it illustrates a distribution curve of the cosine function. At this time, the size of the vertex angle was 90 degrees.

The distribution curve of the outgoing light is obtained when the linear prism (131 in FIG. 3) of the prism film (130 in FIG. 3) is horizontal (a dashed line) and the perpendicular (straight line) in the direction of the lamp (110 in FIG. 3), respectively. As shown, it can be seen that the angular distribution of the emitted light is generally within ± 30 degrees, and is maximum when the angle of the emitted light is 0 degrees.

Next, FIG. 6 shows simulation results of the change in the flow rate of the emitted light when the vertex angle of the linear prism (131 in FIG. 3) is changed, and the horizontal axis represents the size of the side angle, and the vertical axis represents the emission. The flux of light is shown. Here, the flow rate of the outgoing light is illustrated for the case where the total flux and the intensity of the outgoing light are the peaks, that is, the outgoing angle of the outgoing light is 0 degrees.

As shown, when the vertex angle of the linear prism (131 in FIG. 3) is 90 degrees, that is, the side angle is 45 degrees, the amount of light lost by total reflection of the light is larger than the other angles, but the intensity of the emitted light is maximum. The flow rate is higher than other angles. In addition, as the vertex angle is greater than 90 degrees, the amount of emitted light is counted, but the light collection efficiency is not good, whereas when the vertex angle is smaller than 90 degree, the light collection efficiency is good, but light loss occurs, so that the linear prism (131 in FIG. 3) The vertex angle is preferably formed in the range of 60 to 150 degrees.

In this manner, a prism film (130 of FIG. 3) may be disposed between the lamp 110 (FIG. 3) and the light guide plate (140 of FIG. 3) to obtain a focused backlight. In order to increase the display quality of the backlight, the light guide plate (FIG. 140) may be further formed on the prism film.

7 illustrates a structure of a backlight for a liquid crystal display according to a second exemplary embodiment of the present invention. In the second embodiment of the present invention, since it is almost the same as the structure in the first embodiment, the description of the same parts will be simplified.                     

As shown, in the backlight according to the second embodiment of the present invention, the lamp 210 and the lamp housing 220 are disposed on one side of the light guide plate 240 as in the first embodiment. The first prism film 230 is disposed between the light guide plate 240 and the light guide plate 240, and the reflector plate 250 is disposed below the light guide plate 240, and the second prism film 260 is diffused on the light guide plate 240. The films 270 are sequentially arranged. Here, the second prism film 260 and the diffusion film 270 on the light guide plate 240 may be arranged in a reversed order. That is, the diffusion film 270 may be disposed on the light guide plate 240, and the second prism film 260 may be disposed thereon.

Therefore, in the second exemplary embodiment of the present invention, the second prism film 260 may be further disposed to improve display quality by preventing the light emitted by the film of the backlight from having a shape such as unevenness.

Meanwhile, the diffusion film 270 and the second prism film 260 on the light guide plate 240 may be removed, and the light collecting film may be disposed to have the same effect.

The backlight structure for the liquid crystal display according to the third exemplary embodiment of the present invention is illustrated in FIG. 8, except that the light guide plate 340 is the same as the second exemplary embodiment except for the upper part of the light guide plate 340. Since the description of the same parts will be omitted. As shown, in the backlight according to the third embodiment of the present invention, the light collecting film 360 having a plurality of array patterns having the same shape as a microlens (not shown) is formed on the light guide plate 340 to thereby emit light. The same effect can be obtained as in the second embodiment. Here, reference numerals 310, 320, 330, 350 denote a lamp, a lamp housing, a prism film, and a reflecting plate, respectively.

Next, FIG. 9 illustrates a structure of a backlight for a liquid crystal display according to a fourth embodiment of the present invention.

As illustrated, in the fourth embodiment of the present invention, a lamp 410 which is a linear light source and a lamp housing 420 surrounding the lamp 410 and having an opening at one side thereof are disposed at one side of the light guide plate 450. The first prism film 430 and the second prism film 440 are disposed between the lamp 410 and the light guide plate 450. The reflective plate 460 is disposed below the light guide plate 450, and the diffusion film 470 is disposed above the light guide plate 450.

In this case, the first prism film 430 and the second prism film 440 are arranged such that the extending directions of the linear prisms 431 and 441 are perpendicular to each other, and the diffusion film 470 is omitted as in the first embodiment. You may.

As such, when two prism films 430 and 440 are disposed between the lamps 410 and the light guide plate 450 so that the linear prisms 431 and 441 are orthogonal to each other, the result of simulating the distribution of the emitted light by the exit angle is described. 10 is shown. Here, the dotted line represents the guide line, and the straight line represents the case where the emitted light is perpendicular to the direction of the lamp 410 of FIG. 9, and the dashed-dotted line represents the case where the emitted light is horizontal to the direction of the lamp 410 of FIG. 9. The vertex angle is 90 degrees.

As shown in FIG. 10, when two prism films (430, 440 in FIG. 9) orthogonal to the linear prisms (431, 441 in FIG. 9) are used, the exiting light is emitted at an angle within ± 20 degrees. , It can be seen that the light collecting degree is higher than when only one prism film (130 of FIG. 3) of FIG.

Meanwhile, in the fourth embodiment, the two prism films 430 and 440 of FIG. 9 are arranged such that the linear prisms 431 and 441 are perpendicular to each other, but the linear prism is focused to further collect light distribution in a specific direction. (431, 441 of FIG. 9) can also be arrange | positioned so that it may have the same direction.

11A and 11B illustrate the structure of the backlight according to the fifth and sixth embodiments.

As shown in FIG. 11A, the backlight according to the fifth embodiment of the present invention has the linear prisms 531 and 541 of the first and second prism films 530 and 540 parallel to the extension direction of the lamp 510. The light distribution in a direction parallel to the lamp 510 may be further concentrated, and the backlight according to the sixth embodiment of the present invention may have the first and second prism films 630 as illustrated in FIG. 11B. , The linear prisms 631 and 641 of 640 may be disposed to be perpendicular to the extending direction of the lamp 610 to further collect light distribution in a direction perpendicular to the lamp 610.

In the first to sixth embodiments of the present invention, although a prism film having a plurality of linear prisms having a triangular cross section is used, a light condensing film having a plurality of round patterns, such as a micro lens, is used. It may be.

12A and 12B show a part of the light collecting film having a plurality of micro lenses formed therein, and the light collecting film 730 is made of only a sheet 732 including a plurality of micro lenses 731 like the previous prism film. Alternatively, the base film 733 may be further formed under the sheet 732 including the microlens 731. In this case, the material may be formed using a material such as the above prism film, and when the base film 733 is included, the refractive index of the sheet 732 is larger than the refractive index of the base film 733 to minimize the total reflection. desirable.

Thus, even when using a light condensing film having a plurality of micro lenses, it can be applied to the structure of the first to sixth embodiments.

On the other hand, another example of the film for condensing is shown in FIG.

As shown, the light collecting film 830 is composed of a sheet 832 having a pyramid shape 831, and the light collecting film 830 is formed of a lamp (410 of FIG. 9) and a light guide plate (440 of FIG. 9). In the case of disposing between the two prism films (430 and 440 of FIG. 9), the linear prism of FIG. 9 (431 and 441 of FIG. 9) is arranged vertically using only one film. The light in both the vertical and horizontal directions with respect to the lamp 410 of FIG. 9 may be collected.

The present invention is not limited to the above embodiments, and various changes and modifications can be made without departing from the spirit of the present invention.

In the backlight for a liquid crystal display according to the present invention, a prism film having a plurality of linear prisms may be disposed between a lamp and a light guide plate as a light source in an edge type backlight, thereby increasing the light condensation of the backlight and reducing manufacturing cost and volume. .

In addition, two linear prisms may be arranged between the lamp and the light guide plate to further increase the concentration of light. The linear prisms may be arranged to have the same direction, thereby increasing the degree of condensing of light in a specific direction. A light condensing film having a pyramid shape may be arranged to have a direction, and the light condensing degree of light in all directions may be increased.

Claims (13)

A linear light source emitting light and extending in a first direction; A lamp housing surrounding the light source and having an opening at one side; A light guide plate having one side connected to an opening of the lamp housing and receiving light from the light source from a side surface and guiding it in a second direction; A reflector disposed under the light guide plate and reflecting light in a third direction opposite to the second direction from the light guide plate in the second direction; A first prism film disposed between the light source and the light guide plate and having a plurality of linear prisms having a vertex angle of 60 degrees to 150 degrees; A second prism film having a plurality of linear prisms having a vertex angle of 60 degrees to 150 degrees between the first prism film and the light guide plate; Backlight for a liquid crystal display device comprising a. delete The method of claim 1, And a linear prism of the first prism film and the second prism film are perpendicular to each other. The method of claim 1, And a linear prism of the first prism film and the second prism film are horizontal to each other. The method according to any one of claims 1, 3 and 4, The linear prism of the first prism film extends in the first direction. The method according to any one of claims 1, 3 and 4, The linear prism of the first prism film extends in a direction perpendicular to the first direction. The method of claim 1, And the first and second prism films comprise a sheet having the linear prism and a base film under the sheet. The method of claim 7, wherein The refractive index of the sheet is greater than the refractive index of the base film, the backlight for a liquid crystal display device. The method of claim 1, The backlight for a liquid crystal display device further comprising a diffusion film on the light guide plate. The method of claim 9, And a prism film having a plurality of linear prisms between the light guide plate and the diffusion film. The method of claim 1, The backlight for a liquid crystal display device further comprising a light collecting film for collecting light on the light guide plate. delete Linear light source that emits light and extends in the first direction A lamp housing surrounding the light source and having an opening at one side; A light guide plate having one side connected to an opening of the lamp housing and receiving light from the light source from a side surface and guiding it in a second direction; A reflector disposed under the light guide plate and reflecting light in a third direction opposite to the second direction from the light guide plate in the second direction; A film having a plurality of pyramidal patterns between the light source and the light guide plate. Backlight for a liquid crystal display device comprising a.

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