JPH039305A - Backlight device - Google Patents

Abstract

PURPOSE:To make a device thin and light and to maintain the uniformity of brightness in the device even when large area is acomplished by disposing a bar-like light source between two eliptical foci, reflecting radiated light on the inner surface of an elliptical lamp housing so that it may be condensed to be made incident on the end face of a transparent substrate and moreover irregularly reflecting the light on a light irregular reflection layer on the back surface of the transparent substrate so that it may be radiated to the outside. CONSTITUTION:The light source 2 is disposed on the side surface of the transparent substrate 1 and the bar-like light source functioning as the light source is housed in the lamp housing 5 whose cross section is elliptical and which is opened by notching the side of the transparent substrate 1 so as to be positioned between two elliptical foci. The virtual circumferential surface of the elliptical inner surface of the opening end of the lamp housing 5 is inscribed with the edge of the substrate 1 and the light irregula reflection layer 3 is installed on the back surface of the substrate 1. In such a case, when the radiated light from the light source 2 is reflected on the inner surface of the lamp housing 5, most of the radiated light is con densed to be made incident on the end face of the substrate 1, because the light source 2 is housed to be positioned between the two foci F1 and F2 in the lamp housing 5. Thus, the device is made thin and light and the excellent uniformity of brightness is obtained in the device even when the large area is accomplished.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a backlight device that is disposed on the back side of a liquid crystal display (LCD) and illuminates the liquid crystal display.

"Prior Art" In recent years, liquid crystal displays have excellent characteristics such as being thin, lightweight, and low power consumption, and there are great expectations for their use in various products as flat displays that can fully demonstrate these characteristics. It is being However, liquid crystal displays are based on C, which is currently widely used for industrial and consumer purposes.
It is inferior in image quality compared to RT (Cathode RayTube), and a backlight type liquid crystal display has been developed to improve this image quality.

This type of backlight device is desired to be thin and lightweight, and is also required to have uniform brightness over the entire screen area. Various proposals have already been made as techniques for improving the uniformity of brightness in backlight devices. For example, in the device described in JP-A-57-13478, a milky white light scattering body is provided above a linear light source, and the layer thickness of the milky white light scattering body is thickened at the center, and the layer thickness is increased toward the ends. This eliminates uneven illumination, and is also thin and compact.

Furthermore, the method described in JP-A No. 60-264039 uses a meandering cold cathode lamp;
The method described in Publication No. 0 utilizes a purple + line lamp and a phosphor coating layer provided around the purple line lamp.
2. In the device described in JP-A No. 62-10621, a light source is built into the light guide plate, and in the device described in JP-A-62-127717, concave-convex lenses are arranged on the upper and lower surfaces of a plurality of light sources, In the device described in Japanese Patent Laid-open No. 63-125975, T- and J-shaped lamps are used to eliminate uneven irradiation and achieve uniform brightness. Furthermore, in order to make the brightness uniform, a light scattering material is placed inside the transparent substrate, and the light scattering material is placed at a low concentration on the light source side, and as the distance from the light source increases,
JP-A-54. -105
The backlight device described in Japanese Patent Laid-open No. 562, and the backlight device described in Japanese Patent Application Laid-Open No. 63-309918, which depicts a light reflecting means on a coated transparent substrate with a density distribution that is inversely proportional to the distance from the illumination light source and the illuminance, are known. This is where you will be exposed.

In addition, when the light emitted from the light source is introduced into a transparent substrate, so-called light guide plate, a recess is provided on the rear surface of the light guide plate, and the light source is housed in the recess, which is described in JP-A-55-129383. The method described in JP-A-62-10621, in which a groove is provided on the peripheral edge of the light guide plate and a light source is built into the groove, and a recess is also provided in the peripheral edge of the light guide plate, and the light source is housed in the recess. A Hackley 1 device described in Japanese Patent Application Laid-Open No. 62-235905 has also been proposed.

"Problems to be Solved by the Invention" However, the above-mentioned conventional method has the following problems.

(1) When a light source is disposed on the lower surface of the light scattering body, there is a problem that the entire backlight 1 arrangement becomes thick and bulky.

(2) When a plurality of lamps are provided in order to make the brightness uniform, there is a problem that the larger the area, the more lamps are required, leading to higher costs.

(3) When using a serpentine lamp, there is a problem that it lacks productivity if applied to a large area later.

(4) When a light scattering body is placed in a transparent substrate, there is a problem that it is not possible to produce uniform brightness with good reproducibility.

(5) When a light reflecting means is depicted on a coated transparent substrate, there is a problem in that the cost is higher than when an uncoated transparent substrate is used.

(6) Machining the back side and edges of the light guide plate 11. If the light source is housed in a light guide plate, there is a problem in that the processing cost of the light guide plate increases.

Therefore, the present invention has been made to overcome the above problems.In addition to being low in processing cost, the present invention is thin and lightweight, and even with a large area, it is possible to maintain uniformity of brightness and utilize light. It is an object of the present invention to provide a backlight device with good efficiency.

"Means for Solving the Problem" The present invention has been made to achieve the above object, and in claim (1), at least one of the four circumferences of the transparent substrate is
A light source is disposed at a location, and a rod-shaped light source at 1° with the light source is located between two focal points of the ellipse in a lamp housing having an elliptical cross section and an opening with a cutout on the transparent substrate side. The present invention is characterized by a backlight device that is housed in a lamp housing, has a virtual peripheral surface of an elliptical inner surface of an open end of a lamp housing inscribed in an edge of a transparent substrate, and has a light-scattering reflective layer attached to the back surface of the transparent substrate. . In claim (2), the light scattering reflection layer is formed on the back surface of a transparent substrate in a pattern that increases in density according to the distance from the light source, and a light diffusing layer is attached to the surface of the transparent substrate. ) is characterized by the backlight device described in (a).

"Function" In the above configuration, the present invention has the property that the light emitted from one elliptical focus is focused on the other elliptical focus in claim (1), but in reality, the light emitted from one elliptical focus is focused on the other elliptical focus. Since there is no rod-shaped light source, but a rod-shaped light source with a certain thickness is used, the rod-shaped light source is placed between two elliptical focal points, and the emitted light from the rod-shaped light source is directed to the inner surface of the elliptical lamp housing. The light is reflected to be focused on the end face of the transparent substrate, and is then diffusely reflected by the light-diffusing reflection layer on the back surface of the transparent substrate, so that the light is radiated to the outside from the surface of the transparent substrate. In claim (2), as the light that enters the interior from the end face of the transparent substrate is repeatedly reflected due to the difference in optical density at the interface between the transparent substrate and the air, a pattern is depicted with higher density as the distance from the light source increases. The light is diffusely reflected by the light reflecting layer, and after this diffused reflection, the light is diffused by the light diffusing layer and radiated to the outside, thereby making it possible to obtain uniform brightness without uneven brightness over the entire surface.

"Example" Below, an example of a backlight device according to the present invention will be described based on the drawings. In FIGS. 1 and 2, 1 is a transparent substrate. The transparent substrate 1 is a thin plate with good light transmittance, and is made of an inorganic or synthetic resin material such as a glass plate, an acrylic resin plate, a polycarbonate resin plate, etc. A light source 2 is disposed on one side edge of the four peripheral parts of the transparent substrate 1. On the back surface of the transparent substrate 1, a light-diffusing reflection layer 3 that diffusely reflects the light emitted from the light source 2 is drawn in a pattern whose density increases in proportion to the distance from the light source 2. The light-scattering reflection layer 3 uses a volatile-curable or ultraviolet-curable white ink containing titanium oxide as reflective particles, or a colored ink of a color according to the wishes of the user. As a method for forming the light-scattering reflective layer 3 on the back surface of the transparent substrate 1, a known technique such as screen printing or a stamp method is used. When forming the light scattering reflection layer 3 on the back surface of the transparent substrate 1, as shown in FIG. 3, the number of dots per unit area is the same, and the diameter of the dots increases as the distance from the light source increases. However, the occupation rate of the light diffused reflection N3 per unit area of the transparent substrate 1 is changed. The diameter of the point on the light scattering reflection layer 3 is
The thickness is set to 1 to 3000μ, preferably 10 to 1000μ. On the other hand, a light diffusion layer 4 is attached to the surface of the transparent substrate 1. For the light diffusion layer 4, so-called frosted glass or a plastic film with a roughened surface is used, and a polyester film having a light diffusion layer with a roughened surface is preferable from the viewpoint of cost and durability. The light source 2 is generally a wide-diameter fluorescent lamp, or a cold cathode tube with a narrow tube diameter, which is used to reduce the overall thickness of the backlight device and to improve the thickness of the liquid crystal display (LCD).
) It is advantageous in terms of use because it can suppress the influence of temperature on the panel.

The light source 2 is housed in a lamp housing 5 having an elliptical cross section. The elliptical lamp housing 5 has a property that the light generated from one elliptical focal point is focused on the other elliptical focal point. Therefore, a linear light source is arranged at one elliptical focal point, and the end of the transparent substrate is When the part is placed at the focus of the other ellipse,
If we ignore the reflection loss on the elliptical circumferential surface and the incident loss on the end face of the transparent substrate, all the light from the line light source will be 1 on the elliptical circumferential surface.
The light can enter the transparent substrate by multiple reflections, making it the method with the highest light utilization efficiency. However, in reality, there is no ideal linear light source, but a rod-shaped light source with a certain thickness, such as a commonly used fluorescent lamp or cold cathode tube, as described above. Therefore, from the viewpoint of effective use of light, it is an important issue as to which position of the elliptical lamp housing 5 to arrange the lamp housing 5 as described above. Therefore, as a result of various trial experiments and considerations, we found that the method with the highest light utilization efficiency is between two focal points F, A rod-shaped light source 2 is housed. Further, one end surface of the transparent substrate 1 is provided so as to fit tightly into the opening 5a of the lamp housing 5 and to be inscribed in an imaginary surface obtained by extending the elliptical inner circumferential surface of the lamp housing 5. The transparent substrate 1 has a thickness of about 5 mm, and faces slightly inward from the inner circumferential surface of the ellipse by an amount corresponding to this thickness. Allows sufficient light to enter.

As described above, the lamp housing 5 is made of metal or plastic and has at least an elliptical cross section on the inside, and has the functions of reflecting the light generated from the light source 2 on its inner surface and guiding it to the end surface of the transparent substrate 1, and the function of guiding the light generated from the light source 2 to the end surface of the transparent substrate 1. It has the function of preventing light leakage and the function of dissipating heat generated from the light source.

For this reason, the lamp housing 5 is preferably made of an aluminum case whose inner surface is subjected to aluminum vapor deposition treatment with high reflection efficiency, or a metal such as aluminum coated with white paint with high reflection efficiency. As for the size of the elliptical shape of the lamp housing 5, the larger the ellipse, the larger the relative difference from the thickness of the rod-shaped light source 2.
Although it is ideal because it can be handled as a cotton-like light source 2, it should be set appropriately based on the constraints on the thickness and external dimensions of the backlight device, the thickness of the light source, and the thickness of the transparent substrate 1. Further, a reflective tape 6 is provided on the transparent substrate 1 other than the end surface where the light from the light source 2 enters.
can be attached to prevent light from leaking from the periphery of the transparent substrate 10.

In the backlight device having the above configuration, first, the emitted light from the light source 2 is reflected on the inner surface of the lamp housing 5 and focused on the end face of the transparent substrate 1, as shown by the arrow in FIG. Light enters inside. As described above, the light source 2 is housed between the two focal points F, , F in the lamp housing 5, so that the emitted light from the light source 2 enters the lamp housing 5.
When reflected on the inner surface of the transparent substrate 1, most of the emitted light is focused on the end surface of the transparent substrate 1 and enters the end surface. The emitted light that has entered the transparent substrate 1 travels while repeating irregularities depending on the incident angle t7 due to the difference in optical density at the interface between the transparent substrate 1 and the air. As this progresses, when the light reaches the diffuse reflection layer 3, it is diffusely reflected by the titanium oxide contained therein, and as a result, the diffusely reflected light hits the interface between the surface of the transparent substrate 1 and the air, and 9 that is below the angle and radiates to the outside from the surface of the transparent substrate 10
In other words, the light scattering reflection layer 3 is formed on the transparent substrate 1 as shown in FIG.
Since the occupancy rate per unit area increases as the distance from the light source 2 increases, unevenness of light from the light source 2 due to the distance plane 1 is prevented, and light intensity is reduced from the vicinity of the light source 2, which has a large amount of light. It is possible to obtain a uniform amount of diffusely reflected light over the top surface up to a distance.

The light diffusely reflected by the light-diffusing reflection layer 3 passes through the light-diffusing layer 4 on the surface of the transparent substrate l, but since the light-diffusing layer 4 is made up of minute irregularities, the light is diffused and emitted to the outside. This eliminates the change in the amount of light between the light scattering reflection layer 3 and the area other than the pattern of the light scattering reflection N3, that is, the so-called "shadow effect 7", and makes it possible to obtain uniform brightness. Heat generated from the light source 2 is dissipated to the outside through the housing 5.

In addition, in the present invention, in addition to the above-mentioned embodiments, as the light scattering reflection layer, the number of points per unit area may be changed depending on the distance from the light source, or the diameter of the points and the unit area may be changed depending on the distance from the light source. It is also possible to change both the number of winning points, and it is also possible to use not only points but also lines to change the thickness of the cotton and the corners between the cotton. Furthermore, the light scattering reflection layer 3
is attached to the back surface of the transparent substrate 1 on which a metal such as aluminum is vapor-deposited to prevent light from leaking from below the transparent substrate 1 and to further increase the light utilization efficiency. It can also be done.

Regarding the light source 2, in the above embodiment, it is arranged only on one end side of the transparent substrate 1, but it may be arranged in a format in which two light sources are used, in which it is arranged in both opposing ends, or it is arranged in all four peripheries. The brightness can be improved by increasing the number of light sources. In this case as well, it goes without saying that the light-scattering reflection layer can be formed in a pattern with a density that corresponds to the distance from each light source, and a backlight device with improved light utilization and excellent brightness uniformity can be achieved.

"Effect of the Invention J As described above, according to the puncture light device according to the present invention, since the light source is disposed not in the thickness direction of the transparent substrate but on the peripheral edge side, the overall thickness of the backlight device and 7. but,
The thickness of the transparent substrate including the diameter of the light source, the multilayer thickness of the light diffusion layer and the light scattering reflection layer, the slight clearance when attaching this to the housing, and the total thickness of other necessary components such as the housing are all that is required. It has excellent brightness uniformity, and is therefore thin and lightweight, which was difficult with conventional technology.
Furthermore, the present invention can provide a backlight device that can maintain excellent brightness uniformity even when the area is increased, and has high light utilization efficiency. The backlight device is a liquid crystal display (LCD).
By installing the screen behind the LCD, it is possible to realize a thin and easy-to-read screen with no uneven brightness, making it possible to create
It can greatly contribute to improving the function of D), and can also be used as various other backlight devices.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of the backlight I/device according to the present invention, and FIG. 2 is an explanatory diagram of main parts showing a state of convergence of light by the lamp housing of the backlight device shown in FIG. 1.
FIG. 3 is an explanatory diagram showing a depiction of a light-scattering reflective layer attached to the back surface of a transparent substrate. 1... Transparent substrate 2... Light source 3... Light scattering reflection layer 4... Light diffusion layer 5... Lamp housing

Claims (2)

[Claims] (1) A light source is disposed at at least one of the four circumferences of the transparent substrate, and the rod-shaped light source as the light source is placed in a lamp housing having an elliptical cross section and an opening on the transparent substrate side. The elliptical inner surface of the open end of the lamp housing is housed between the two focal points, and the virtual peripheral surface of the elliptical inner surface of the open end of the lamp housing is inscribed in the edge of the transparent substrate, and a light-scattering reflective layer is attached to the back surface of the transparent substrate. A backlight device featuring: (2) Claim (2) characterized in that the light scattering reflection layer is formed on the back surface of a transparent substrate in a pattern that becomes denser depending on the distance from the light source, and a light diffusion layer is attached to the surface of the transparent substrate.
1) The backlight device described.