JP2008262906A - Back-light unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a back-light unit for a large-sized liquid crystal display in a low cost and with high luminance. <P>SOLUTION: The back-light unit 10 of the liquid crystal display has two pieces of light-guiding plates 100 of the same shape, with an optical-path controlling panels formed on its lower side and upper side where the liquid crystal is disposed. Light-source lamps 150 are arranged on each side of the light-guiding panels 100 with more lamps 150m corresponding to the lower light-guiding plate 100m than the lamps 150s corresponding to the upper light-guiding plate 100s. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a backlight unit of a liquid crystal display device, and more particularly to an edge light type backlight unit suitable for a large liquid crystal screen.

  Liquid crystal display devices are widely used as display devices for electronic devices such as personal computers and televisions. The liquid crystal display device uses the characteristic of liquid crystal molecules that the orientation changes when a voltage is applied, but the liquid crystal itself does not emit light, so a backlight unit that serves as a light source on the back of the liquid crystal display panel in which the liquid crystal is enclosed Arranged.

  The backlight unit of a liquid crystal display device has a lamp that serves as a light source on the side, an edge light system that guides light to the liquid crystal surface using a light guide plate, and a direct type that directly places the lamp on the back of the liquid crystal surface There are two methods.

  An edge light type backlight unit is thin and has low power consumption, but has a feature that it is difficult to increase luminance. In particular, as the size of the liquid crystal display panel increases, it becomes more difficult to ensure high brightness and uniformity. For this reason, it is mainly used in small and medium-sized liquid crystal display devices such as notebook personal computers and liquid crystal monitors. Patent Document 1 describes that the front luminance is increased by forming prism portions on the upper surface (liquid crystal surface side) and the lower surface of the light guide plate, and Patent Document 2 describes two wedge-shaped light guide plates. It is described that luminance is increased by crossing and overlapping.

On the other hand, the direct-type backlight unit has a feature that high luminance is easily obtained because the amount of emitted light can be used efficiently.
JP 2002-98960 A JP 2006-253104 A

  In recent years, with an increase in the size of a display device typified by a large-screen television, the size of a liquid crystal display device is also increasing. In a large-sized liquid crystal display device, a direct type backlight unit that can easily increase brightness by adding a light source lamp is widely used.

  On the other hand, since the direct type backlight unit uses a large number of light source lamps, the cost of the lamp driving circuit, the light source lamp, etc. is increased, and the power consumption is also increased. If the number of light source lamps is reduced in order to reduce costs, the luminance unevenness of the backlight, such as the shadow of the light source lamp being visible, occurs due to direct illumination, and the display quality of the liquid crystal display panel is impaired.

  In addition, for a direct type backlight with a short distance between the light source lamp and the liquid crystal display panel, the housing must be designed in consideration of the number of light source lamps, the arrangement, etc., as well as the heat dissipation and heat dissipation generated by the light source lamps. I must. Therefore, there is a restriction on thinning the liquid crystal display device.

  Therefore, from the viewpoint of cost reduction and thinning, it is desirable to apply an edge light type backlight unit that is indirect illumination to a large liquid crystal display device, but a problem that sufficient luminance cannot be obtained on a large screen. There is. Since the techniques described in Patent Document 1 and Patent Document 2 are not intended for a large screen, manufacturing efficiency and efficient use of a light source lamp are not sufficiently considered, and can be directly applied to a large liquid crystal display device. However, it is difficult to realize low cost and high brightness.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a backlight unit for a large-sized liquid crystal display device that is low in cost and high in luminance.

  In order to solve the above-described problem, the backlight unit of the present invention has at least two light guide plates having the same shape, each having an optical path control pattern formed on the upper surface and the lower surface, with the liquid crystal arrangement side facing upward, and the side surface of the light guide plate. The light path control pattern formed on the lower surface of the light guide plate is a prism pattern formed in a direction parallel to the side surface on which the light source lamp is disposed, and is formed on the upper surface of the light guide plate. The optical path control pattern is a prism pattern formed in a direction orthogonal to the side surface on which the light source lamp is disposed.

  By superimposing light guide plates of the same shape with optical path control patterns formed on both sides, the light incident on the lower light guide plate is higher in efficiency than the light incident on the upper light guide plate. Emits from the side. In addition, since the light guide plates to be stacked can have the same shape, cost reduction due to mass production can be expected.

  In order to solve the above-described problem, another aspect of the backlight unit of the present invention is a backlight unit of a liquid crystal display device, which has the same shape in which an optical path control pattern is formed on the upper surface and the lower surface with the liquid crystal arrangement side as an upward direction. At least two light guide plates are stacked, light source lamps are provided on the side surfaces of the respective light guide plates, and the number of light source lamps corresponding to the lower light guide plate is larger than the number of light source lamps corresponding to the upper light guide plate. It is characterized by having been arranged in.

  By overlapping the light guide plate with the optical path control pattern formed on both sides, the light incident on the lower light guide plate is emitted from the liquid crystal side of the upper light guide plate with higher efficiency than the light incident on the upper light guide plate. To do. For this reason, a light source lamp is used efficiently by increasing the number of light source lamps corresponding to a lower light guide plate.

  Therefore, the present invention can be applied to a large-sized backlight to make the light emission uniform and improve the overall luminance.

  Further, by stacking a plurality of light guide plates having the same shape, the thickness per sheet can be reduced, and the cost can be reduced. Moreover, since the same light guide plate can be used, cost reduction due to mass production can be expected.

  Here, the optical path control pattern formed on the lower surface of the light guide plate is a prism pattern formed in a direction parallel to the side surface on which the corresponding light source lamp is disposed, and the optical path control pattern formed on the upper surface of the light guide plate is The prism pattern can be formed in a direction perpendicular to the side surface on which the corresponding light source lamp is disposed.

  Further, it is desirable that the prism patterns formed on the lower surface of the light guide plate are formed so that the distance from the corresponding light source lamp becomes narrower, and the prism patterns formed on the upper surface of the light guide plate are formed at the same interval.

  In order to solve the above-described problem, another aspect of the backlight unit of the present invention is a backlight unit of a liquid crystal display device, which has the same shape in which an optical path control pattern is formed on the upper surface and the lower surface with the liquid crystal arrangement side as an upward direction. At least two light guide plates are stacked, a light source lamp is disposed on the side surface of the light guide plate, and an optical path control pattern formed on the lower surface of the light guide plate is formed in a direction parallel to the side surface on which the light source lamp is disposed. The prism pattern is formed so that the distance from the light source lamp becomes smaller, and the optical path control pattern formed on the upper surface of the light guide plate is formed in a direction perpendicular to the side surface on which the light source lamp is disposed. It is a pattern.

  According to the present invention, it is possible to realize a backlight unit for a large liquid crystal display device that is low in cost and high in luminance.

  Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a perspective view showing a light guide plate used in the backlight unit of the present embodiment. However, the scale and the like are different from the actual ones in order to show the feature of the shape in an easy-to-understand manner.

  As shown in the figure, the light guide plate 100 has a double-sided prism structure in which prism patterns are formed on the upper surface and the lower surface. In this figure, the upper surface is a light emitting surface on the liquid crystal surface side, and the lower surface is a reflecting surface. The left and right side surfaces are incident surfaces on which light from the light source lamp is incident.

  The prism pattern on the upper surface serving as the light exit surface functions as a condensing prism, and the prism pattern on the lower surface serving as the reflecting surface functions as a luminance uniformity control prism. For this reason, in this embodiment, the prism patterns are different between the upper surface and the lower surface.

  Specifically, the prism pattern on the upper surface serving as the light output surface is formed in parallel to the direction of light incident from the side surface, that is, in a direction orthogonal to the light source lamp. The prism shape can be, for example, a uniform pitch with an apex angle of 90 degrees and an interval of 50 μm.

  The prism pattern on the lower surface serving as the reflection surface is formed in a direction orthogonal to the direction of light incident from the side surface, that is, in a direction parallel to the light source lamp. Therefore, the prism pattern on the upper surface and the prism pattern on the lower surface are orthogonal to each other.

  The lower surface is formed such that the distance between the prism patterns increases as the distance from the light source increases, and the distance between the prism patterns decreases as the distance from the light source increases. Thus, when the light source lamps are arranged on both side surfaces, the distance between the prism patterns becomes narrower toward the center. This is to prevent a decrease in luminance due to light attenuation at a central portion far from the light source lamp. Further, when the light source lamp is disposed only on one side surface, the distance between the prism patterns becomes narrower as the distance from the light source lamp is increased. The method of narrowing the interval may be continuous or stepwise. In either case, it may be changed uniformly or non-uniformly. The internal angle of the prism pattern can be made slightly smaller than 90 degrees, for example.

  The light guide plate 100 can be formed of a transparent resin such as acrylic, polycarbonate resin, or cycloolefin resin as in the conventional case. The shape, direction, angle, pitch, and the like of the above-described prism pattern are examples, and are not limited to these.

  Next, the backlight unit of this embodiment will be described. In this embodiment, an edge light system is adopted. Then, two light guide plates 100 shown in FIG. At this time, the light guide plate disposed on the lower side is referred to as a main light guide plate, and the light guide plate disposed on the upper side, that is, the liquid crystal side is referred to as a sub light guide plate.

  FIG. 2 is a diagram illustrating a configuration of a backlight unit when two light guide plates 100 are used in an overlapping manner. As shown in the figure, in the backlight unit 10, a main light guide plate 100m and a sub light guide plate 100s are overlapped. As the main light guide plate 100m and the sub light guide plate 100s, light guide plates having the same shape and the same characteristics can be used. For this reason, it is suitable for mass production and can achieve cost reduction.

  As shown in the figure, a reflection sheet 130 is disposed on the lower surface of the main light guide plate 100m, and a diffusion sheet 140 is disposed on the upper surface of the sub light guide plate 100s. These can be the same as conventional ones.

  Light source lamps 150 corresponding to the respective light guide plates are arranged on both side surfaces of the main light guide plate 100m and the sub light guide plate 100s. In the example of this figure, three light source lamps 150m in total on one side corresponding to the main light guide plate 100m are arranged, and one light source lamp 150s in total on one side corresponding to the sub light guide plate 100s is arranged. Has been. That is, a total of eight light source lamps are used with four on one side. As the light source lamp, a general cold cathode tube can be used. Of course, other types of light source lamps may be used. For example, a light emitting element such as an LED may be used.

  The light from the light source lamp 150m is incident on the side surface of the main light guide plate 100m by the reflector 160m, and the light from the light source lamp 150s is incident on the side surface of the sub light guide plate 100s by the reflector 160s.

  The light incident on the side surface of the main light guide plate 100m is reflected by the prism pattern on the lower surface of the main light guide plate 100m, condensed on the upper surface of the main light guide plate 100m, and emitted. In the sub light guide plate 100s, in addition to the light incident from the side surface, the light emitted from the upper surface of the main light guide plate 100m and incident on the lower surface of the sub light guide plate 100s is condensed on the upper surface and emitted.

  The main light guide plate 100 m and the sub light guide plate 100 s are arranged in the same direction so that the prism pattern on the lower surface is parallel to the light source lamp 150. For this reason, the prism pattern on the upper surface of the main light guide plate 100m and the prism pattern on the lower surface of the sub light guide plate 100s face each other in an orthogonal state. Thereby, scattering and condensing of light are performed efficiently. That is, the light incident on the main light guide plate 100m is collimated and the directivity is increased, so that the light is efficiently emitted from the liquid crystal surface side of the sub light guide plate 100s.

  Specifically, when the double-sided prism-shaped light guide plate 100 is stacked, the light incident on the main light guide plate 100m is approximately 1.2 times more efficient than the light incident on the sub light guide plate 100s. The result of emitting from the liquid crystal side of 100 s was obtained.

  For this reason, if the number of light source lamps is the same (for example, 8), as shown in FIG. 3, the main light guide plate 100m and the sub light guide plate 100s are backed up equally (a total of four on each side). Compared to the light unit 10a, the backlight unit 10 in which many light source lamps are associated with the main light guide plate 100m as shown in FIG. 2 can obtain higher front luminance.

  That is, in this embodiment, the lower light guide plate of the two light guide plates stacked serves as the main light guide plate. For this reason, it is desirable to make more light source lamps correspond to the main light guide plate having a high light collecting effect. As a result, it is possible to realize an edge light type backlight unit with high efficiency and high brightness. Of course, in the backlight unit 10a shown in FIG. 3, the main light guide plate 100m and the sub light guide plate 100s shaped as shown in FIG. Can be obtained.

  Specifically, as shown in FIG. 4A, when the backlight 300a is configured using a double-sided prism light guide plate 100u having a thickness t and a total of six light source lamps 150u on one side, 4 (b), by applying the present invention, two double-sided prism light guide plates (100m, 100s) having a thickness of t / 2 are stacked, and the main light guide plate 100m has a total of four, two on each side. In the case where the backlight unit 10b is configured by using a total of six light source lamps (150 m, 150 s) on one side for a total of two on one side, the same thickness and the same number of light source lamps are used. The backlight unit 10b shown in FIG. 4B to which the present invention is applied has a brightness of about 15% higher.

  Further, as shown in FIG. 5 (a), a backlight unit 300b using a double-sided prism light guide plate 100u having a thickness t and four light source lamps 150u in total, two on each side and four on each side. As shown in FIG. 5B, by applying the present invention, two double-sided prism light guide plates (100 m, 100 s) having a thickness of t / 2 are stacked, and one side 3 is placed on the main light guide plate 100 m. The same thickness and the same light source in the case where the backlight unit 10c is configured using a total of six light source lamps (150m, 150s), a total of six light sources lamps (150m, 150s). Regardless of the number of lamps, the backlight unit 10c shown in FIG. 5B to which the present invention was applied obtained about 20% higher luminance.

  In addition, when the light source lamp 150m is increased, the size (width) of the backlight unit 10 is increased accordingly. Therefore, the number of the light source lamps 150m corresponding to the main light guide plate 100m and the number of the light source lamps 150s corresponding to the sub light guide plate 100s are flexibly determined due to the size limitation of the liquid crystal display device, allowable power consumption, and the like. Can be determined.

  As described above, in this embodiment, two double-sided prism light guide plates are stacked, and the light condensing effect by the prism pattern on the light exit surface of each light guide plate and the light flux are collimated by the prism pattern on the reflection surface. The directivity and the light transmission of the light guide plate are improved.

  By the way, in the backlight unit of the edge light system, the thickness of the light guide plate needs to be secured about 1.5 times the width of the light source lamp. Therefore, in order to reduce the thickness of the backlight unit for a large-sized liquid crystal device using multiple light source lamps. There was a limit. In the present invention, since one light guide plate may correspond to one layer of the light source lamp, the thickness per light guide plate can be reduced.

  Specifically, for example, a thickness of about 3 mm can be realized even for a large liquid crystal display device. With this thickness of the light guide plate, low-cost injection molding is possible. Conventionally, for example, if it is necessary to ensure a thickness of 6 mm corresponding to a two-layer light source lamp, the light guide plate has to be manufactured by costly extrusion molding. For this reason, in this invention, manufacturing cost can be reduced significantly.

  Furthermore, in the present invention, light guide plates having the same shape and characteristics can be used as the main light guide plate and the sub light guide plate. That is, it is not necessary to manufacture the light guide plate separately for the main light guide plate and the sub light guide plate. For this reason, cost reduction by mass production can also be expected.

  Further, since the prism pattern is formed on the light guide plate, there is an advantage that an expensive prism sheet is unnecessary and the viewing angle is not impaired.

  Thus, since a thin and high-brightness backlight unit can be realized at low cost, the backlight unit of the present invention can be effectively applied particularly to a large-screen liquid crystal display device.

  The present invention is not limited to the above embodiment, and various modifications can be made. For example, instead of the reflective sheet 130 shown in FIG. 2, a light impermeability treatment may be performed on the lower surface of the main light guide plate 100m.

  In the above example, the two light guide plates, the main light guide plate 100m and the sub light guide plate 100s, are used. However, the number of light guide plates is not limited to two, and a plurality of light guide plates may be used. Alternatively, a plurality of light guide plates having the same shape may be stacked, and light guide plates having different characteristics may be stacked.

  In the example shown above, the reflector 160m and the reflector 160s are partitioned and configured as independent housings, but may be configured integrally without providing a partition.

  FIG. 6 is a diagram illustrating an example in which a backlight unit is configured without partitioning the reflector 160. The backlight unit 10d shown in FIG. 6A and the backlight unit 10e shown in FIG. 6B use a main light guide plate 100m and a sub light guide plate 100s, and further have a high light collection effect. In addition, when more light source lamps are made to correspond, the reflector 160 is configured without partitioning. The backlight unit 10f shown in FIG. 6 (c), the backlight unit 10f shown in FIG. 6 (d), and the backlight unit 10g shown in FIG. 6 (e) include a main light guide plate 100m and a sub light guide plate 100s. This is an example in which the reflector 160 is not partitioned when the light source lamps are made to correspond equally to each other. In this way, by configuring the reflector 160 without providing a partition, it is possible to eliminate the vertical relationship of the light source lamp and improve the luminous flux utilization efficiency.

  Further, although a triangular prism pattern is used as a pattern for controlling the optical path, other shapes such as a lens shape and an uneven shape may be used. For example, a light guide plate 100a as shown in FIG. 7 can be used. The light guide plate 100a functions as a condensing prism, and the prism pattern on the upper surface serving as the light output surface has a shape in which a prism ridge line is formed in the middle of the cutout as shown in FIG. This figure shows the prism pattern shape on the upper surface of the light guide plate 100a as viewed from the light incident side.

  In general, the prism pattern for controlling the optical path is applied to the light guide plate by a mold forming process such as injection molding or thermal transfer. However, as the size of the liquid crystal display panel increases, the prism pattern portion is separated from the mold. The mold gets worse. This may adversely affect productivity and quality. In the light guide plate 100a shown in FIG. 7, the optical prism characteristics of the light guide plate 100 using a triangular prism pattern having a height H as shown in FIG. 8B are not impaired. Since the prism pattern can be set to a height h (<H) as shown in FIG. 5, the adhesion with the mold when the prism pattern is molded is reduced, and the releasability is improved.

It is a perspective view which shows the light-guide plate used for a backlight unit. It is a figure which shows the structure of the backlight unit at the time of using two light-guide plates in piles. It is a figure at the time of making a light source lamp respond | correspond equally to a main light-guide plate and a sub light-guide plate. It is a figure which shows the example of arrangement pattern of a light source lamp. It is a figure which shows the example of arrangement pattern of a light source lamp. It is a figure which shows the example which comprised the backlight unit, without partitioning a reflector. It is a perspective view which shows another example of the light-guide plate used for a backlight unit. It is a figure which shows the optical path control pattern of the upper surface of a light-guide plate.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Backlight unit, 100 ... Light guide plate, 130 ... Reflection sheet, 140 ... Diffusing sheet, 150 ... Light source lamp, 160 ... Reflector

Claims (6)

A backlight unit of a liquid crystal display device,
With the LCD side up
At least two light guide plates having the same shape with optical path control patterns formed on the upper and lower surfaces are stacked,
A light source lamp is disposed on a side surface of the light guide plate;
The optical path control pattern formed on the lower surface of the light guide plate is a prism pattern formed in a direction parallel to the side surface on which the light source lamp is disposed,
The backlight unit, wherein the optical path control pattern formed on the upper surface of the light guide plate is a prism pattern formed in a direction orthogonal to a side surface on which the light source lamp is disposed. A backlight unit of a liquid crystal display device,
With the LCD side up
At least two light guide plates having the same shape with optical path control patterns formed on the upper and lower surfaces are stacked,
A light source lamp is arranged on the side surface of each light guide plate so that the number of light source lamps corresponding to the lower light guide plate is larger than the number of light source lamps corresponding to the upper light guide plate. Light unit. The backlight unit according to claim 2,
The optical path control pattern formed on the lower surface of the light guide plate is a prism pattern formed in a direction parallel to the side surface on which the corresponding light source lamp is disposed,
The backlight unit according to claim 1, wherein the optical path control pattern formed on the upper surface of the light guide plate is a prism pattern formed in a direction orthogonal to the side surface on which the corresponding light source lamp is disposed. The backlight unit according to claim 1 or 3,
The prism pattern formed on the lower surface of the light guide plate is formed such that the interval is narrowed away from the corresponding light source lamp,
The backlight unit, wherein the prism patterns formed on the upper surface of the light guide plate are formed at the same interval. A backlight unit of a liquid crystal display device,
With the LCD side up
At least two light guide plates having the same shape with optical path control patterns formed on the upper and lower surfaces are stacked,
A light source lamp is disposed on a side surface of the light guide plate;
The optical path control pattern formed on the lower surface of the light guide plate is a prism pattern formed in a direction parallel to the side surface on which the light source lamp is disposed, and is formed with a smaller interval as the distance from the light source lamp increases.
The backlight unit, wherein the optical path control pattern formed on the upper surface of the light guide plate is a prism pattern formed in a direction orthogonal to a side surface on which the light source lamp is disposed. The backlight unit according to any one of claims 2 to 5,
The backlight unit according to claim 1, wherein the prism pattern formed on the upper surface has a shape in which a prism ridge is formed in the middle of the notch.