JP4106876B2 - Light emitting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention has been made to provide means for obtaining an efficient and uniform light-emitting device for a wide range of applications such as liquid crystal backlights, switch push buttons, nameplates, and various display boards. In particular, in liquid crystal backlights, unnecessary light-emitting parts can be almost eliminated, contributing to downsizing of portable devices, light utilization efficiency is increased, bright and low power consumption is used. The present invention relates to a light emitting device.
[0002]
[Prior art]
Conventionally, the so-called “side type” or “edge light type” in which the light source is arranged around the light guide plate has been the mainstream in the backlight of the liquid crystal (FIG. 5). On the other hand, there is a light-emitting device that has a light source called a direct type in the effective light-emitting part, but it is difficult to eliminate luminance unevenness in the vicinity of the light source. There was a history of being gradually replaced by the side type.
[0003]
However, in the side type, since the light source part is arranged at one end of the light guide plate, the vicinity of the light source part is uneven, so that it is not an effective light emitting part, and an unnecessary space is required. This is a major obstacle for devices that are becoming smaller, such as mobile phones and mobile terminals.
In addition, when used in TFT color liquid crystal backlights, etc., the required light intensity is high, which increases the power consumption of the light source. However, since the light source is concentrated in a part, local heat generation and temperature rise increase. In particular, when a semiconductor light-emitting element light source is used, the reliability and lifetime are significantly affected.
[0004]
[Problems to be solved by the invention]
The present invention has been made to solve such drawbacks, and an object of the present invention is to realize a light emitting device capable of emitting white light that can be used mainly as a backlight, using LEDs, and uniform white light emission. To provide a light-emitting device that can observe light, and to provide a light-emitting device that can emit light of any color other than white, and to use it for various operation switches, etc., utilizing the characteristics of LEDs with excellent future potential It is in.
[0005]
[Means for Solving the Problems]
The light emitting device of the present invention has a light guide plate (2) having an upper surface and a lower surface facing each other, and at least one LED element (1), and light from the LED element is incident from the lower surface of the light guide plate, A light-emitting device that emits light from the upper surface of the light guide plate, wherein the light guide plate has a recess (4) on the upper surface facing the LED element, and the recess gradually spreads toward the upper surface. It is formed as follows. As a result, the light emitted from the lower surface is totally reflected at the depression, and the traveling direction is changed in a direction parallel to the upper surface of the light guide plate.
Further, the light guide plate is characterized in that an upper surface corner portion of the depression is chamfered. Uneven brightness is reduced by chamfering.
Further, the depression may penetrate from the upper surface to the lower surface of the light guide plate (see FIG. 1 (c)). Since the light striking the sloped portion of the recess is totally reflected toward the periphery, the recess may be darker than the other portions when the light guide plate is viewed from the upper surface side. In order to solve this phenomenon, the present invention allows a recess to penetrate and emits a portion of light incident from the lower surface directly from the penetration to the upper portion of the recess.
[0006]
Furthermore, the said hollow is linearly formed (5) so that it may oppose over at least 2 or more LED element, It is characterized by the above-mentioned. In the present invention, it is not necessary to match the number of depressions with the number of LED elements, and it is sufficient that there is a depression on the upper surface of the light guide plate facing the LED element, and one depression is formed across two or more LED elements. Thus, the depression forming process can be simplified.
[0007]
In addition, the light guide plate has a linear notch (9) formed so as to penetrate from the upper surface to the lower surface and gradually spread as approaching the upper surface, and the wavelengths different from each other through the notch. The LED element is arranged. The light traveling in the direction parallel to the top surface of the light guide plate is totally reflected on the cut surface, and is confined in the cut, so that light of different wavelengths does not mix in the light guide plate.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The present invention has been made to solve the above-described various problems, and quickly spreads the light emitted from the LED element in the lateral direction without interfering with the light emitted from the light guide plate toward the upper surface. An excellent light-emitting device that is uniform, bright, and efficient can be provided. In addition, a brighter design is possible by arranging the light source over the entire surface (FIG. 1). For example, when the light source is arranged on one side, the number of LED elements that can be dimensionally mounted is limited, but an arbitrary number can be used by arranging the light source on the entire surface. Another advantage is that the LEDs are not arranged together on one side, so that local heat generation is suppressed, the overall reliability is improved, and the influence on the temperature characteristics of the liquid crystal is reduced. In general, although semiconductors have high reliability, they are vulnerable to temperature rise, and thus lowering the operating temperature in this way leads to improvement in reliability. Liquid crystals also have temperature characteristics, and uneven temperature in the surface may adversely affect display quality.
[0009]
Specifically, the light guide plate has depressions 4 and 5 having various shapes that gradually spread as approaching the upper surface from the light source unit, and means for scattering light on the upper and lower surfaces of the light guide plate. (Not shown) to form a light-emitting device configured to be uniform as a whole. The angle of the depression is optimized by the refractive index of the light guide plate material. Since it is used in combination with a means for diffusing light (usually called a wrinkle pattern since it is often a wrinkle pattern), it is not necessarily required to be symmetric, but the most preferable is a symmetric shape. Various shapes of the recess are conceivable, but a conical structure is preferable in view of ease of mold production and design. Of course, it may be a polygonal pyramid shape such as a triangular pyramid shape, a quadrangular pyramid shape, a pentagonal pyramid shape or the like depending on the shape and arrangement of the light source (see the margin of FIG. 1B). A conical shape is preferable if light is spread in all directions, and a triangular pyramid shape or the like is preferable for spreading light in a specific direction. Depending on the purpose, it is necessary to use different effects from the shape. In any form, sharp corners are less likely to cause linear luminance unevenness, and the wrinkle pattern needs to be devised, so chamfering is preferable. Similarly, the contact between the recess and the upper surface of the light guide plate may cause uneven brightness with high shape, and is preferably chamfered smoothly.
Further, the depth of the dent is adjusted so that there is no difference in luminance between the flat portion and the dent portion (see the margin in FIG. 1C (including the penetration)). Thereby, uniform light emission luminance is obtained from the upper surface of the light guide plate.
As shown in FIG. 1, when LED elements are dispersed on a circuit board, in-plane luminance unevenness hardly occurs and the heat dissipation is excellent.
As shown in FIGS. 2 and 3, they can be used even if they are arranged continuously (including straight lines or curves). In the light emitting device thus manufactured, almost the entire region can be used as an effective light emitting unit.
[0010]
In the side light type, it is impossible to simultaneously emit light from a plurality of colors from different portions of the light guide. In the present invention, as shown in FIG. 6, a plurality of LED elements of different colors are used, and the different color LED elements can be easily color-coded by making a cut in the light guide plate in the adjacent part. Here, there is no problem even if the LED elements of the same color are cut into adjacent light guide plates, and different color LEDs can emit mixed colors without being cut into adjacent light guide plates.
[0011]
Hereinafter, preferred materials and the like regarding each element in the surface light emitting device according to the present invention will be described.
(Light guide plate)
In the present invention, the material used for the light guide plate is preferably a material excellent in light transmittance and moldability, and examples thereof include acrylic resin, polycarbonate resin, amorphous polyolefin resin, and polystyrene resin. These light guide plate materials have different refractive indexes, but any refractive index material can be used by selecting the shape of the recess formed on the upper surface of the light guide plate, and the number of the recesses.
(LED light source)
In the LED light source of the present invention, one or two or more LED chips can be used. Further, the light from the LED chip may be directly incident on the light guide plate. For example, the LED chip capable of emitting ultraviolet to visible light, and the light from the LED chip are absorbed to have a longer wavelength than that. In combination with a fluorescent material capable of emitting visible light, light having a wavelength different from that of the light output from the LED chip may be incident on the light guide plate.
[0012]
That is, in the present invention, by using the LED chip in combination with the phosphor, it is possible to emit mixed colors having various color tones depending on the combination of the light emitting element and the fluorescent material.
[0013]
In the following, for white light-emitting LEDs that are most often used for liquid crystal backlights and the like, LED chips that have nitride semiconductors and can emit blue light, and yttrium, aluminum, and garnet activated with cerium An example using a phosphor will be described.
(LED chip)
A nitride compound semiconductor (general formula In _i Ga _j Al _k N, where 0 ≦ i, 0 ≦ j, 0 ≦ k, i + j + k = 1) that can be used here is doped with InGaN or various impurities. There are various types including GaN.
[0014]
This LED chip is formed by growing a semiconductor such as InGaN or GaN as a light emitting layer on a substrate by MOCVD or the like. Examples of the semiconductor structure include a homostructure, a heterostructure, or a double heterostructure having a MIS junction, a PI junction, a PN junction, and the like. The nitride semiconductor layer can have various emission wavelengths depending on the material and the degree of mixed crystal. Moreover, it can also be set as the single quantum well structure and multiquantum well structure which formed the semiconductor active layer with the thin film which produces a quantum effect.
[0015]
In the present invention, it is preferable to use an LED chip that has a semiconductor light emitting layer capable of emitting blue light and can efficiently excite cerium-activated yttrium / aluminum / garnet phosphors, which will be described later.
(Phosphor)
The fluorescent material usable in the present invention may be any fluorescent material capable of emitting visible light having a wavelength longer than that of the LED light by the light output from the LED, and the emission color is all from purple to red. The visible light can be applied. Specific examples include silicate phosphors, phosphate phosphors, aluminate phosphors, rare earth phosphors, rare earth acid phosphors, and zinc sulfide phosphors. Specifically, in a green light emitting phosphor, Y ₂ SiO ₅ : Ce, Tb, MgAl ₁₁ O ₁₉ : Ce, Tb, BaMg ₂ Al ₁₆ O ₂₇ : Mn, (Zn, Cd) S: Ag, ZnS: Au , Cu, Al, ZnS: Cu, Al, SrAl ₂ O ₄ : Eu, (SrCaBa) ₅ (PO ₄ ) ₃ Cl: Eu, (BaCa) ₅ (PO ₄ ) ₃ Cl: Eu BaMg ₂ Al ₁₆ O ₂₇ : Eu, Sr ₅ (PO ₄ ) ₃ Cl: Eu, Sr ₂ P ₂ O ₇ : Eu, ZnS: Ag, Al, ZnS: Ag, Al (pigmented), ZnS: AgCl, ZnS: AgCl (pigmented), the red-emitting phosphor _{Y 2 O 2 S: Eu,} Y 2 O 2 S: Eu (pigmented), Y 2 O 3: Eu, 3.5MgO · _{.5MgF 2 · GeO 2: Mn,} Y (PV) O 4: Eu, 5MgO · 3Li 2 O · Sb 2 O 5: Mn, Mg 2 TiO 4: Mn, is yellow-emitting phosphor _Mg 5 _{Li 6} Sb 6 _{O 13: Mn, Mg 2 TiO} 4: Mn, (Y Z Gd 1-Z) 3 Al 5 O 12: Ce and the like. As for those having relatively high luminous efficiency, SrAl ₂ O ₄ : Eu is used for green light emitting phosphors, Sr ₅ (PO ₄ ) ₃ Cl: Eu is used for blue light emitting phosphors, and Y ₂ O ₂ is used for red light emitting phosphors. For S: Eu, a yellow light-emitting phosphor, (Y _Z Gd _1-Z ) ₃ Al ₅ O ₁₂ : Ce is exemplified.
[0016]
An example which is one embodiment of the present invention will be described below. However, the present invention is not limited to this.
[0017]
[Example 1]
As an example, a backlight for TFT color liquid crystal having an effective size of 1.5 inches and an aspect ratio of 3: 4 was made. Polycarbonate is used as the material of the light guide plate, and the mold for forming the light guide plate has four depressions on the upper surface of the light guide plate. In addition, the mold is manufactured such that the lower surface of the light guide plate is subjected to unevenness (texture) processing for improving the uniformity of light emitted from the upper surface. The light guide plate is molded by first injection molding at an injection pressure of 1000 kgf / cm 2 and a mold temperature of 100 ° C. while melting the polycarbonate by setting the molding temperature to 280 ° C. And after cooling for 45 seconds, it takes out from a metal mold | die. In this way, a light guide plate was formed. As for the dimensions, a margin of 1 mm was provided around the periphery. That is, the size was 25 mm in length and 33 mm in width. In order to obtain the required brightness of 3000 nt, four LEDs were used, and the entire surface was used as an effective part, so that the LEDs were equally divided and placed at the center of the divided surface. The LED was mounted on a printed circuit board having a thickness of 0.2 mm using a surface mount type (hereinafter abbreviated as SMD). In consideration of heat dissipation, the printed circuit board has a large pattern of conductive portions on which the LED dice are mounted. Next, the light guide plate had a thickness of 2 mm, and a continuous prism having the shape shown in FIG. 1 was formed at the position of the LED. The inclination angle with respect to the flat portion of the upper surface of the depression was 45 degrees. Since the present invention uses total reflection, the optimum angle is determined by the refractive index of the material. This was done with a mold, and at the same time, a wrinkle pattern was made on the other surface to make it uniform. The wrinkle pattern was designed by optical simulation using a computer, but it is not touched here because it is complicated. Using this mold, injection molding of acrylic resin was carried out to obtain a finished light guide plate. A frame is provided around the light guide plate to prevent light leakage and to attach a liquid crystal. This frame also requires high reflectivity processing. The whole was assembled, and two prism sheets were crossed and overlapped, and a weak diffusion sheet was fixed at the top to make a product.
As a control, a backlight having the same number of LEDs arranged on the side and having an effective portion of the same size and a direct type backlight with a simple plate were made. The prism sheet has the same configuration, but the diffusion sheet was adjusted so that the in-plane luminance unevenness was Min / Max = 0.7 or more.
As a result of comparing the samples obtained in this way, the sample according to the present invention has a surface brightness of 3400 nt at a current of 15 mA, and the junction temperature that is a measure of LED reliability is 37 degrees and 12 degrees when the ambient temperature is 25 degrees. The temperature increased. On the other hand, the control side type had a surface brightness of 2800 nt and a junction temperature of 59 ° C., which was 22 ° C. higher than that of the present invention. The other direct type of the other conventional type is forced to use a diffusion sheet having a high diffusivity, in other words, a low transmittance, resulting in a luminance of 2000 nt or less, and the practicality is lost. As described above, in the present invention, it was possible to obtain characteristics superior to conventional products in each of the items of luminance, uniformity, and reliability.
[0018]
[Example 2]
In the same manner as in Example 1, a TFT liquid crystal backlight having a size of 5 inches was prepared. Acrylic resin is used as the material of the light guide plate, a mold having 42 depressions formed on the upper surface of the light guide plate, a molding temperature of 250 ° C., an injection pressure of 1100 kgf / cm 2, a mold temperature of 80 ° C., and a cooling time are set. Molded for about 30 seconds. The LEDs were arranged in a 6 × 7 array. The light guide plate was 104 mm × 79 mm, and the continuous prism had the same shape as in Example 1. The reason is that a circle is the easiest to machine, and a triangle, a quadrangle, a pentagon, etc. can be freely selected unless much effort is required for mold processing. Even at that time, it is preferable to chamfer the corners in order to avoid unevenness. Backlights were created in the same manner for other configurations. The characteristics of the obtained product were a surface brightness of 3500 nt when the current was 15 mA, and the junction temperature, which is a measure of LED reliability, was a temperature increase of 39 degrees and 14 degrees when the ambient temperature was 25 degrees. On the other hand, the side type used as a control could not place an LED on one side, and was positioned on two opposite sides. Therefore, as for the size of the backlight, the non-light emitting part has a space of 7mm x 2 14mm which is unnecessary. Further, since many LEDs were concentrated in the light source part, the junction temperature was 64 degrees, which is 25 degrees higher than the present invention, and only the vicinity of the light source part was significantly increased. There was some concern about long-term life and failure rates. The brightness was 2700 nt, which was 23% lower than that of the present invention, which was considerably inferior when compared side by side.
[0019]
【The invention's effect】
As described above in detail, according to the present invention, a uniform, high-efficiency, and high-luminance light-emitting device can be obtained by dispersing or continuously arranging LEDs on the lower surface of the light guide plate. In addition, since it is not necessary to provide an unnecessary space on the side, heat radiation is performed uniformly from the entire surface, so that the temperature of the element can be prevented from increasing, and as a result, a long life and high reliability can be obtained. Although not shown in the embodiments, it is natural that the present invention can be applied to a nameplate, various displays, a guide plate, a switch and the like in addition to the backlight.
In addition, by using LEDs of different emission colors, it is possible to easily perform color coding for each section, and an epoch-making effect can be expected in product design.
[Brief description of the drawings]
FIG. 1 is a light emitting device according to an embodiment of the present invention. (A) is a perspective view, (b) is a plan view, and (c) is a cross-sectional view taken along line AA ′ of (b).
FIG. 2 is a light emitting device according to an embodiment of the present invention. (A) is a perspective view, (b) is a plan view, and (c) is a cross-sectional view taken along line BB ′ of (b).
FIG. 3 shows a light emitting device according to an embodiment of the present invention. (A) is a perspective view, (b) is a plan view, and (c) is a sectional view taken along line CC ′ of (b).
FIG. 4 is a sectional view of a completed light emitting device according to the present invention.
FIG. 5 is a cross-sectional view of a completed light emitting device according to the prior art.
FIG. 6 is a light emitting device color-coded for each section according to the present invention. (A) is a perspective view, (b) is a plan view, and (c) is a cross-sectional view taken along line DD ′ in (b).
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... LED element 2 ... Light guide plate 3 ... Circuit board 4 ... Depression 5 ... Linear depression 6 ... Prism sheet 7 ... Diffusion sheet 8 ... Frame 9 ... Notch

Claims (5)

A light guide plate (2) having an upper surface and a lower surface facing each other, and at least one LED element (1), light from the LED element is incident from the lower surface of the light guide plate, and light is emitted from the upper surface of the light guide plate. A light emitting device that emits light,
The light guide plate has a recess (4) in which a penetrating portion is formed from the upper surface to the lower surface facing the LED element, and the recess has an inclined portion formed so as to gradually spread toward the upper surface. And
The light from the LED element is reflected in the parallel direction with respect to the upper surface of the light guide plate by the inclined portion of the recess, and a part of the light from the LED element is directly emitted from the through portion of the recess. A light emitting device characterized by the above.   The light-emitting device according to claim 1, wherein the light guide plate has a chamfered upper corner portion of the recess.   The light emitting device according to claim 1, wherein the LED elements are distributed and mounted on a circuit board.   4. The light emitting device according to claim 1, wherein the recess is linearly formed (5) so as to face over at least two or more LED elements. 5.   The light guide plate has linear incisions (9) formed so as to penetrate from the upper surface to the lower surface and gradually spread toward the upper surface, and LED elements having different wavelengths from each other through the notches. The light-emitting device according to claim 1, wherein the light-emitting device is arranged.

Images