KR20060073371A - Backlight unit and liquid crystal display module having the same - Google Patents

Abstract

The present invention relates to a backlight unit capable of improving light utilization efficiency and a liquid crystal display module having the same.

A liquid crystal display module according to the present invention includes a liquid crystal panel; A polarizer attached to at least one of a front surface and a rear surface of the liquid crystal panel; A brightness enhancing film for selectively transmitting light of a polarization component parallel to the polarizing plate and reflecting the remaining light; And a polarization conversion film for converting the light reflected from the brightness enhancement film to have an optical axis parallel to the transmission axis of the brightness enhancement film.

Description

Backlight unit and liquid crystal display module having the same             

1 is a cross-sectional view showing a conventional liquid crystal display module.

2 is a perspective view illustrating a liquid crystal display module according to the present invention.

3 is a cross-sectional view illustrating the liquid crystal display module illustrated in FIG. 2.

4 is a diagram illustrating a polarization change state of light of the liquid crystal display module illustrated in FIGS. 2 and 3.

FIG. 5 is a diagram illustrating a transmission axis of the polarization conversion film and the lower polarizer shown in FIGS. 2 and 3.

6A and 6B are views for explaining light efficiency with or without a polarization conversion film.

<Description of Symbols for Main Parts of Drawings>

2,4,112,120: polarizer 6,102: light guide plate

8,118 light source 10 liquid crystal display panel

12: color filter array substrate 14: thin film transistor array substrate

104: lamp housing 106: reflecting plate

108: polarization conversion film 110: brightness enhancement film

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight unit, and more particularly, to a backlight unit capable of increasing light utilization efficiency and a liquid crystal display module having the same.

Liquid crystal display devices can meet the trend of light and short and short of electronic products and mass production is improving, and are rapidly replacing cathode ray tubes in many applications.

In particular, an active matrix type liquid crystal display device that drives a liquid crystal cell using a thin film transistor (hereinafter referred to as "TFT") has the advantages of excellent image quality and low power consumption, and secures the latest mass production technology. As a result of research and development, it is rapidly developing into larger size and higher resolution.

The active matrix type liquid crystal display device includes a color filter substrate 12 and a TFT array substrate 14 bonded together with a liquid crystal layer interposed therebetween as shown in FIG. 1.

In the color filter substrate 12, a black matrix, a color filter, and a common electrode (not shown) are formed on the rear surface of the upper substrate. The upper polarizing plate 2 is attached on the front surface of the upper substrate. The color filter includes color filters of red (R), green (G), and blue (B) colors to allow color display by transmitting visible light in a specific wavelength band.

In the TFT array substrate 14, data lines and gate lines cross each other in front of the lower substrate, and TFTs are formed at the intersections thereof. A pixel electrode is formed on the front surface of the lower substrate in the cell region between the data line and the gate line. The TFT drives the pixel electrode by switching the data transfer path between the data line and the pixel electrode in response to the scanning signal from the gate line. The lower polarizing plate 4 is attached to the rear surface of the TFT array substrate 14.

The liquid crystal layer is generated in the light source 8 by an electric field applied to it and adjusts the amount of light transmitted through the light guide plate 6 and the TFT array substrate 14.

The polarizing plates 2 and 4 attached to the color filter substrate 12 and the TFT substrate 14 transmit light polarized in either direction, and their polarization directions are perpendicular to each other when the liquid crystal is in the 90 ° TN mode. Done.

The lower polarizer 4 selectively emits only light having a polarization component parallel to the lower polarizer 4 among light emitted through the light source 8 and the light guide plate 6 and absorbs the remaining light. In this case, since the light emitted from the light source 8 and reaching the liquid crystal panel 10 is about 50% at maximum, there is a problem that light utilization efficiency is lowered.

Accordingly, it is an object of the present invention to provide a backlight unit and a liquid crystal display module having the same capable of increasing light utilization efficiency.

In order to achieve the above object, the liquid crystal display module according to the present invention comprises a liquid crystal panel; A polarizer attached to at least one of a front surface and a rear surface of the liquid crystal panel; A brightness enhancing film for selectively transmitting light of a polarization component parallel to the polarizing plate and reflecting the remaining light; And a polarization conversion film for converting the light reflected from the brightness enhancement film to have an optical axis parallel to the transmission axis of the brightness enhancement film.

The polarizing plate is characterized in that attached to the back of the liquid crystal panel.

The polarization converting film is characterized by polarizing the light reflected by the brightness enhancement film 90 degrees.

The polarization converting film is characterized in that the lambda / 4 film.

The liquid crystal display module may include a lamp for generating the light and a light guide plate for guiding the light generated by the lamp toward a display panel; And a reflecting plate for reflecting light incident through the rear surface of the light guide plate toward the light guide plate.

The reflecting plate is characterized by re-reflecting the light reflected by the brightness enhancement film to enter the polarization converting film.

In order to achieve the above object, the backlight unit according to the present invention comprises an optical axis parallel to the lamp for generating light, a light guide plate for guiding the light generated by the lamp toward the display panel, and a polarizing plate positioned on one side of the display panel. A first optical film for transmitting the light having the branch light and reflecting the remaining light; The second optical film is provided by converting the polarization of the light reflected from the first optical film to be located between the light guide plate and the first optical film to have an optical axis parallel to the polarizing plate.

The first optical film is characterized in that the brightness enhancement film.

The second optical film is a λ / 4 film.

The display panel may be a liquid crystal display panel that implements an image using liquid crystal.

Other objects and features of the present invention in addition to the above object will be apparent from the description of the embodiments with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 2 to 6B.

2 is a plan view illustrating a liquid crystal display module according to the present invention, and FIG. 3 is a cross-sectional view illustrating the liquid crystal display device illustrated in FIG. 2.

2 and 3, the liquid crystal display module according to the present invention includes a backlight unit and a liquid crystal display panel 120 that implements an image by light generated by the backlight unit.

The backlight unit includes a lamp 118 for generating light, a lamp housing 104 in which the lamp 118 is mounted, a light guide plate 102 for converting light incident from the lamp 118 into a surface light source, and a light guide plate ( The reflective plate 106 is attached to the rear surface of the light guide plate 102 to reflect the light emitted to the rear surface of the light guide plate 102 to the liquid crystal display panel 120, and the light efficiency attached to the light guide plate 102 to be incident toward the display panel. The polarization conversion film 108 and the brightness improving film 110 for heightening are provided.

A cold cathode fluorescent lamp is mainly used as the lamp 118, and the light generated by the lamp 118 is incident on the light guide plate 102 through an incident surface existing on the side of the light guide plate 102.

The lamp housing 104 is installed to have a reflecting surface on the inner surface in a form surrounding the lamp 118 to reflect light from the lamp 118 toward the incident surface of the light guide plate 102.

The light guide plate 102 converts light incident from the lamp 118 into a surface light source. The light guide plate 102 has a top surface that is horizontal to the inclined bottom surface and is manufactured to be perpendicular to the incident surface and the top surface of the light guide plate 102. The lower surface of the light guide plate 102 is provided to face the reflecting plate 106. The light guide plate 102 allows the light incident from the lamp 118 to reach a distance far from the lamp 118. The light guide plate 12 is generally formed of polymethylmethacrylate (PMMA) having high strength and not easily being deformed or broken and having good transmittance.

The reflecting plate 106 serves to reduce light loss by reflecting light incident to itself through the rear surface of the light guide plate 102 toward the light guide plate 102. When the light from the lamp 118 is incident on the light guide plate 102, the light is reflected at a predetermined inclination angle from the lower surface, which is an inclined surface, to uniformly move toward the exit surface. At this time, the light propagated toward the lower surface and the side surface of the light guide plate 102 is reflected by the reflecting plate 106 to proceed toward the exit surface.

The polarization conversion film 108 polarizes the light that is not passed through the brightness enhancement film 110 and is reflected by 90 degrees, so that the polarization conversion film 108 is parallel to the transmission axis of the brightness enhancement film 110 and the lower polarizer 120. Detailed description of the polarization conversion film 108 will be described later in detail with reference to FIG. 4.

The Double Brightness Enhancement Film (DBEF) 110 transmits light parallel to its own transmission axis and reflects light perpendicular to the transmission axis. The transmission axis of the brightness enhancement film 110 is the same as the direction of the transmission axis of the lower polarizing plate 120 to increase the transmission efficiency.

Light passing through the lower polarizer 120 having the same optical axis as the brightness enhancement film 110 is incident on the liquid crystal display panel 114. The liquid crystal display panel 14 includes a color filter substrate 114a and a TFT array substrate 114 bonded together with a liquid crystal layer interposed therebetween.

In the color filter substrate 114a, a black matrix, a color filter, and a common electrode (not shown) are formed on the rear surface of the upper substrate. The upper polarizer 120 is attached on the front surface of the upper substrate. The color filter includes color filters of red (R), green (G), and blue (B) colors to allow color display by transmitting visible light in a specific wavelength band.

In the TFT array substrate 114b, data lines and gate lines cross each other on the front surface of the lower substrate, and TFTs are formed at the intersections thereof. A pixel electrode is formed on the front surface of the lower substrate in the cell region between the data line and the gate line. The TFT drives the pixel electrode by switching the data transfer path between the data line and the pixel electrode in response to the scanning signal from the gate line. The lower polarizing plate 112 is attached to the rear surface of the TFT array substrate 114b.

The liquid crystal layer is generated by the light source 118 by an electric field applied to the liquid crystal layer to adjust the amount of light transmitted through the light guide plate 102 and the TFT array substrate 114b.

The polarizers 120 and 112 attached to the color filter substrate 114a and the TFT substrate 114b transmit light polarized in either direction, and their polarization directions are perpendicular to each other when the liquid crystal is in the 90 ° TN mode. .

4 is a view for explaining the operation of the polarization conversion film shown in Figures 2 and 3 in detail.

The polarization conversion film 108 illustrated in FIG. 4 serves to convert the reflected light without passing through the brightness enhancement film 110 in parallel with the optical axis of the brightness enhancement film 110. The light reflected by the brightness enhancing film 110 passes through the polarization converting film 108 once and then is reflected back by the reflecting plate 106 to pass through the polarization converting film 108 twice. The light reflected from the brightness enhancing film 110 passes through the polarization converting film 108 twice, so that the polarization state is converted by 90 degrees in order to have an optical axis parallel to the optical axis of the brightness enhancing film 110. To this end, the polarization conversion film 108 is formed of a λ / 4 phase film having an angle of 45 degrees with the optical axis of the brightness enhancement film 110. That is, the optical axis of the polarization conversion film 108 has a phase difference of 45 degrees with the optical axis of the brightness enhancement film 110.

As described above, the polarization converting film 108 is a λ / 4 phase film.

The first light parallel to the optical axis of the brightness enhancement film 110 among the lights X and Y passing through the light source 104, the light guide plate 102, and the polarization conversion film 108, for example, the first linearly polarized light X ) Is sequentially transmitted through the brightness enhancing film 110 and the lower polarizing plate 112 to be incident on the liquid crystal display panel 114. On the other hand, the second light, for example, the second linearly polarized light Y, which is not parallel to the optical axis of the brightness enhancement film 110 is reflected. The reflected second linearly polarized light Y is converted into circularly polarized light while passing through the polarization conversion film 108. The converted circularly polarized light passes through the light guide plate 102 and is then reflected back by the reflecting plate 106 and reincident to the polarization conversion film 108. The circularly polarized light incident on the polarization conversion film 108 is converted into a first linearly polarized light X in which the optical axis is converted by 90 degrees and the optical axis is parallel with the brightness enhancement film 110. The converted first linearly polarized light X passes through the brightness enhancement film 110 and passes through the lower polarizing plate 112 parallel to the brightness enhancement film 110 and is incident on the liquid crystal display panel 114.

6A and 6B are views for explaining light efficiency with or without a polarization conversion film.

As shown in FIG. 6A, when there is no polarization converting film, the first linearly polarized light X parallel to the transmission axis of the lower polarizing plate 112 first transmits the luminance enhancing film 110 and the lower polarizing plate 112 to display a liquid crystal display. Is incident on the panel 114. On the other hand, the second linearly polarized light Y perpendicular to the transmission axis of the lower polarizer 112 does not pass through the brightness enhancement film 110 and is primarily reflected. The reflected second linearly polarized light Y is scattered by the light guide plate 102 and reflected by the reflective plate 106 to maintain some polarization as it is, and partially converts the polarized light to the first linearly polarized light X, thereby forming a conversion line polarization. . The first linearly polarized light X having the transmission axis parallel to the luminance enhancement film 110 is first transmitted, and the second linear polarization Y whose transmission axis is perpendicular to the luminance enhancement film 110 is secondarily reflected. The second reflected second linearly polarized light Y is repeated as described above.                     

Here, when the light efficiency of the first linearly polarized light X incident on the brightness enhancing film 110 and incident on the lower polarizing plate is 100%, some of the converted linearly polarized light is reflected back by the brightness enhancing film 110, so the light efficiency is improved. This is 50%. Accordingly, the light efficiency of the backlight unit without the polarization conversion film does not exceed 150%. In addition, the light reflected from the brightness enhancing film 110 undergoes scattering and reflection by the light guide plate 102 and the reflecting plate 106 a plurality of times. .

As shown in FIG. 6B, the first linearly polarized light X parallel to the transmission axis of the lower polarizer 112 when the polarization conversion film 108 is present transmits the luminance enhancement film 110 and the lower polarizer 112 to the primary transmission. Incident on the liquid crystal display panel 114. On the other hand, the second linearly polarized light Y perpendicular to the transmission axis of the lower polarizer 112 does not pass through the brightness enhancement film 110 and is primarily reflected. The reflected second linearly polarized light Y is polarized in circularly polarized light while passing through the polarization converting film 108. After the circularly polarized light passes through the light guide plate 102 and the reflecting plate 106, the converted polarized light polarized by the first linearly polarized light X is formed while passing back through the polarization converting film. The converted polarized light passes through the brightness enhancing film 110 and the lower polarizer 112 and is incident on the liquid crystal display panel 114.

Here, when the light efficiency of the first linearly polarized light X transmitted through the brightness enhancement film 110 is 100%, the light efficiency of the converted polarization polarized by the polarization conversion film 108 after being reflected by the brightness enhancement film 110 is 100%. That is, since the polarization conversion occurs by the polarization converting film 108, the second linearly polarized light Y reflected by the brightness enhancement film 110 does not leave light perpendicular to the transmission axis of the brightness enhancement film 110. Accordingly, the light efficiency of the backlight unit having the polarization conversion film 108 is 200%, and an image may be realized by using 100% of the light emitted from the backlight unit. Then, the light reflected by the brightness enhancing film 110 is reflected only once by the reflecting plate 106 and then incident on the liquid crystal display panel 114. Accordingly, as illustrated in FIG. 6A, light is absorbed due to scattering of the light guide plate 102 and reflection of the reflecting plate 106, rather than repeatedly reflected by the reflecting plate 106 and incident on the liquid crystal display panel 114. And leakage is minimized.

As described above, in the backlight unit and the liquid crystal display module using the same according to the present invention, a polarization conversion film is positioned between the light guide plate and the brightness enhancement film. The polarization of the light reflected by the brightness enhancing film is converted by this polarization converting film so that light perpendicular to the transmission axis of the brightness improving film is not left. Thereby, the light efficiency of the backlight unit which has a polarization conversion film improves. Further, the backlight unit and the liquid crystal display panel having the same according to the present invention are all incident on the liquid crystal display panel after the light reflected by the brightness enhancement film is reflected only once by the reflecting plate. Accordingly, the number of times of passing through the light guide plate and the reflecting plate is reduced by one, thereby minimizing light absorption and leakage due to scattering of the light guide plate and reflection of the reflecting plate.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (10)

A liquid crystal panel; A polarizer attached to at least one of a front surface and a rear surface of the liquid crystal panel; A brightness enhancing film for selectively transmitting light of a polarization component parallel to the polarizing plate and reflecting the remaining light; And a polarization conversion film for converting the light reflected from the brightness enhancement film to have an optical axis parallel to the transmission axis of the brightness enhancement film. The method of claim 1, And the polarization converting film polarizes the light reflected by the brightness enhancing film by 90 degrees. The method of claim 2, The polarization converting film is a λ / 4 film, characterized in that the liquid crystal display module. The method of claim 1, A lamp for generating the light, A light guide plate for guiding light generated by the lamp toward a display panel; And a reflecting plate for reflecting light incident through the rear surface of the light guide plate toward the light guide plate. The method of claim 4, wherein And the reflecting plate reflects light reflected by the brightness enhancing film to be incident on the polarization converting film. The method of claim 1, And the polarizing plate is attached to the rear surface of the liquid crystal panel. A lamp for generating light, A light guide plate for guiding light generated by the lamp toward a display panel; A first optical film for transmitting light having an optical axis parallel to a polarizing plate positioned on one surface of the display panel and reflecting the remaining light; And a second optical film provided between the light guide plate and the first optical film to convert polarized light reflected from the first optical film to have an optical axis parallel to the polarizing plate. The method of claim 7, wherein The first optical film is a backlight unit, characterized in that the brightness enhancement film. The method of claim 7, wherein The second optical film polarizes the light reflected by the brightness enhancement film by 90 degrees. The method of claim 7, wherein And the second optical film is a λ / 4 film.

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