JP2002298629A - Light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flat light emitting device with excellent uniformity enabled to emit the light with high brightness. SOLUTION: The light emitting device comprises a light guide plate (2) having an upper surface and a lower surface facing each other, and at least one LED element (1), and makes the light from the LED element enter into the light guide plate at its lower surface and get out from the upper surface of the light guide plate. Concavities (4) facing respective LED elements are formed on the upper surface of the light guide plate, and the concavities are formed so as to gradually broaden as it comes near to the upper surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has been made to provide a means for obtaining an efficient and uniform light emitting device for a wide variety of uses such as a liquid crystal backlight, a push button of a switch, a nameplate and various display panels. . Particularly, in the liquid crystal backlight, unnecessary non-light-emitting portions can be almost eliminated, which contributes to the miniaturization of portable devices and increases the light use efficiency, and uses a light guide plate that can be bright and consume low power. Light emitting device.

[0002]

2. Description of the Related Art Conventionally, in a liquid crystal backlight,
The so-called “side-type” or “edge-light” type, in which a light source is arranged around the light guide plate, was the mainstream (FIG. 5). On the other hand, there is a light emitting device in which a light source called a direct type is arranged in an effective light emitting portion.However, it is difficult to eliminate uneven brightness near the light source. Notwithstanding, it has been gradually replaced by the side type.

However, in the side type, since the light source is disposed at one end of the light guide plate, the vicinity of the light source is uneven, so that the effective light emitting unit cannot be provided, and an unnecessary space is required. This is a major obstacle for miniaturized devices such as mobile phones and mobile terminals. Further, when used for a backlight of a TFT color liquid crystal, etc., the required luminous intensity is high, so that the power consumption of the light source is large.
Local heat generation and temperature rise become large, and particularly when a semiconductor light emitting element light source is used, reliability and life are considerably affected.

[0004]

SUMMARY OF THE INVENTION The present invention has been made to solve such a drawback, and an object of the present invention is to provide a light emitting device capable of emitting white light which can be mainly used as a backlight by using an LED. To provide a light-emitting device capable of observing uniform white light emission, and to provide a light-emitting device capable of emitting light of any color other than white, and to utilize the characteristics of LEDs with excellent future potential. , And various operation switches.

[0005]

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 emits light from the LED element. A light emitting device that enters from the lower surface of the light guide plate and emits light from the upper surface of the light guide plate, wherein the light guide plate includes:
A recess (4) is provided on the upper surface facing the LED element, and the recess is formed so as to gradually expand as approaching the upper surface. As a result, the light emitted from the lower surface is totally reflected at the concave portion, 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 the upper surface corner of the depression is chamfered. By chamfering, uneven brightness is reduced. Further, the depression may penetrate from the upper surface to the lower surface of the light guide plate (

1 (c)). Since the light that hits the slope of the depression is totally reflected toward the periphery, the depression may be darker than the other parts when the light guide plate is viewed from the upper surface side. In order to solve this phenomenon, according to the present invention, a part of light incident from the lower surface is directly emitted from the penetrating part to an upper part of the concave part through the concave part.

Further, the recess is formed linearly so as to face at least two or more LED elements.
It is characterized by having been done. The present invention relates to the number of depressions and LE
It is not necessary to match the number of D elements, and it is sufficient if there is a depression on the upper surface of the light guide plate facing the LED element.
By forming the LED over one or more LED elements, the recess forming step can be simplified.

In addition, the light guide plate has a linear cut (9) penetrating from the upper surface to the lower surface and gradually expanding as approaching the upper surface. It is characterized in that LED elements having different wavelengths are arranged. Light traveling in a direction parallel to the upper surface of the light guide plate is totally reflected on the cut surface and confined in the cut, so that light of different wavelengths does not mix in the light guide plate.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention has been made in order to solve the above-mentioned various problems. The present invention rapidly spreads light emitted from an LED element in a lateral direction and emits light from a light guide plate toward an upper surface. An excellent light-emitting device that is uniform, bright, and efficient without obstructing incoming light can be provided. Further, by arranging the light source over the entire surface, a brighter design is possible (FIG. 1). For example, if 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 disposing it on the entire surface. Another advantage is that LEDs are not arranged on one side, so 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, semiconductors have high reliability, but are vulnerable to temperature rise. Therefore, lowering the operating temperature in this way leads to improvement in reliability. Further, the liquid crystal also has a temperature characteristic, and in-plane temperature unevenness may adversely affect display quality.

More specifically, the light guide plate has depressions 4 and 5 having various shapes which gradually expand as approaching from the light source toward the upper surface, and light is transmitted to the upper and lower surfaces of the light guide plate. Scattering means are provided (not shown) to form a light emitting device configured to be uniform overall. The angle of the depression is optimized by the refractive index of the material of the light guide plate. It is not necessarily required to be symmetrical because it is used in combination with a means for diffusing light (usually a textured pattern, so that it is hereinafter simply referred to as a textured pattern), but a symmetrical shape is most preferred. Although various shapes of the depression are conceivable, a conical structure is preferable in consideration of the ease of mold production and design. Needless to say, a polygonal pyramid such as a triangular pyramid, a quadrangular pyramid, or a pentagonal pyramid may be used depending on the shape and arrangement of the light source (see the margin of FIG. 1B). To spread light in all directions, a conical shape is preferable, and to spread light in a specific direction, a shape such as a triangular pyramid is more preferable. It is necessary to use the function and effect of the shape depending on the purpose. Regardless of the shape, an acute angle is likely to cause linear luminance unevenness and requires a contrivance in a grain pattern. Similarly, the contact point between the depression and the upper surface of the light guide plate may cause unevenness with high brightness along the shape, and it is preferable that the chamfer is smooth.
Further, the depth of the dent is adjusted so that there is no difference in luminance between the flat part and the dent part (see the margin of FIG. 1C (including the penetration)). Thereby, uniform light emission luminance can be obtained from the upper surface of the light guide plate. As shown in FIG. 1, when the LED elements are dispersed on a circuit board, in-plane luminance unevenness hardly occurs,
Excellent heat dissipation. As shown in FIGS. 2 and 3, it can be used even if it is arranged continuously (including a straight line or a curved line). The light-emitting device thus manufactured can be used as an effective light-emitting portion in almost the entire area.

[0010] In the sidelight type, it is impossible to simultaneously emit a plurality of colors from different portions of the light guide. In the present invention, as shown in FIG.
A plurality of elements can be used, and the LED elements of different colors can be easily color-coded by making cuts in the light guide plate of the adjacent part. Here, there is no problem even if a cut is made in the light guide plate of the adjacent part where the LED element of the same color is adjacent, and it is also possible to emit a mixed color without intentionally making a cut in the light guide plate of the adjacent part where the LEDs of different colors are adjacent.

Hereinafter, preferred materials and the like for each element in the surface emitting device according to the present invention will be described. (Light guide plate) As the material used for the light guide plate in the present invention, it is preferable to use a material having excellent light transmittance and moldability, and examples thereof include an acrylic resin, a polycarbonate resin, an amorphous polyolefin resin, and a polystyrene resin. . These materials for the light guide plate have different refractive indices. However, by selecting the shape of the depression formed on the upper surface of the light guide plate, and further, the number and the like thereof, it is possible to cope with any refractive index material. (LED light source) In the LED light source of the present invention, 1 or 2
The above LED chips can be used. Also, LE
The light from the D chip may be directly incident on the light guide plate. For example, an LED chip capable of emitting ultraviolet to visible light, and a visible light having a longer wavelength by absorbing light from the LED chip. In combination with a fluorescent substance capable of emitting light,
Light having a different wavelength from the light output from the ED chip may be incident on the light guide plate.

That is, in the present invention, by using an LED chip in combination with a phosphor, it is possible to emit mixed colors of various colors depending on the combination of the light emitting element and the phosphor.

The following is most often used for liquid crystal backlights and the like.
For the white LED with high demand, nitride semiconductor
An LED chip having a body and capable of emitting blue light;
Yttrium aluminum gar activated with lium
An example using a net phosphor will be described. (LED chip) Nitride based that can be used here
Compound semiconductor (general formula In_iGa_jAl _kN, where 0
≦ i, 0 ≦ j, 0 ≦ k, i + j + k = 1)
Including nGaN and GaN doped with various impurities,
There are various things.

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 having a MIS junction, a PI junction, and a PN junction, a heterostructure, and a double heterostructure. The emission wavelength of the nitride semiconductor layer can be variously selected depending on the material and the degree of mixed crystal thereof. Also,
A single quantum well structure or a multiple quantum well structure in which the semiconductor active layer is formed of a thin film that produces a quantum effect can also be used.

In the present invention, as the LED chip,
Having a semiconductor light emitting layer capable of emitting blue light,
Yttrium aluminum garnet activated by
Use an LED chip that can efficiently excite the phosphor
Is preferred. (Phosphor) Phosphors that can be used in the present invention include LEDs
Depending on the output light, visible light with a longer wavelength than LED light
Any fluorescent substance that can emit light,
All visible light from purple to red can be used.
Specifically, silicate-based phosphors, phosphate-based phosphors,
Luminic acid based phosphor, rare earth phosphor, acid rare earth phosphor
And a zinc sulfide-based phosphor. Specifically green
In the case of a color light-emitting phosphor, Y₂SiO₅: Ce, Tb, Mg
Al₁₁O₁₉: Ce, Tb, BaMg₂Al ₁₆O
₂₇: Mn, (Zn, Cd) S: Ag, ZnS: Au,
Cu, Al, ZnS: Cu, Al, SrAl₂O₄: E
u, (SrCaBa)₅(P
O₄)₃Cl: Eu, (BaCa)₅(PO₄)₃C
1: Eu, BaMg₂Al₁₆O₂₇: Eu, Sr
₅(PO₄)₃Cl: Eu, Sr₂P₂O₇: Eu, Z
nS: Ag, Al, ZnS: Ag, Al (pigmen
ted), ZnS: AgCl, ZnS: AgCl (pi
gmented), and Y for the red light-emitting phosphor.₂O₂S:
Eu, Y₂O₂S: Eu (pigmented), Y₂
O₃: Eu, 3.5MgO.0.5MgF₂・ Ge
O₂: Mn, Y (PV) O₄： Eu, 5MgO ・ 3Li
₂O ・ Sb₂O₅: Mn, Mg₂TiO₄: Mn, yellow
Mg for system-based phosphors₅Li₆Sb₆O₁₃: Mn, M
g₂TiO₄: Mn, (Y_ZGd_1-Z)₃Al₅O
₁₂: Ce and the like. Relatively high luminous efficiency
As the green light emitting phosphor, SrAl₂O₄: E
u, Sr for blue light emitting phosphor₅(PO₄)₃Cl: E
u, Y for the red light emitting phosphor₂O₂S: Eu, yellowish
In the photophosphor, (Y_ZGd_1-Z)₃Al₅O₁₂: Ce
Is mentioned.

An example which is an 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 a TFT color liquid crystal having an effective size of 1.5 inches and an aspect ratio of 3: 4 was manufactured.
Polycarbonate is used as a material of the light guide plate, and a mold for forming the light guide plate has four recesses formed on the upper surface of the light guide plate. Further, 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 molding of the light guide plate is performed by first setting the molding temperature to 280 ° C. and melting the polycarbonate while injecting an injection pressure of 1000 kgf / c.
Injection molding is performed at m2 and a mold temperature of 100 ° C. And 4
After cooling for 5 seconds, remove from the mold. Thus, a light guide plate was formed. As for the dimensions, a margin of 1 mm was provided around each. That is, the size was 25 mm in length and 33 mm in width.
Four LEDs were used to obtain the required luminance of 3000 nt, and the LEDs were equally divided and arranged at the center of the divided surface to make the entire surface an effective part. LED is a surface mount type (hereinafter abbreviated as SMD)
Was mounted on a printed circuit board having a thickness of 0.2 mm. In consideration of heat radiation, the printed board has a large pattern of the conductive portion on which the LED dice is mounted. Next, the light guide plate is 2m thick
At m, a continuous prism having the shape shown in FIG. 1 was formed at the position of the LED. The inclination angle of the upper surface of the depression with respect to the flat portion was 45 degrees. Since the present invention utilizes total reflection, the optimum angle is determined by the refractive index of the material. This was performed with a mold, and at the same time, a grain pattern was formed on the other surface so as to be uniform. The grain pattern was designed by computer-based optical simulation, but is not described here because it is complicated. Injection molding of acrylic resin was performed using this mold to obtain a completed 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 needs high reflectance processing. The whole was assembled, two prism sheets were crossed and overlaid, and a weak diffusion sheet was fixed at the top to make a product. As a control, a backlight in which the same number of LEDs were arranged on the side and the effective portion was the same size, and a direct-type backlight in which a simple plate was placed were made. The prism sheet has the same configuration, but the diffusion sheet has in-plane luminance unevenness of Min / Max = 0.7.
It was adjusted to be above. Comparison of the samples obtained in this way shows that the sample according to the invention has a current of 15%.
The surface temperature was 3400 nt at mA, and the junction temperature, which is a measure of the reliability of the LED, was 37 degrees and 12 degrees when the ambient temperature was 25 degrees. On the other hand, the side type used as a control
The junction temperature was 2800 nt, the junction temperature was 59 degrees, which was 22 degrees higher than that of the present invention, and only the vicinity of the light source part was significantly increased. On the other hand, the direct type of the conventional method has to use a diffusion sheet having a high degree of diffusion, in other words, a low transmittance, resulting in a luminance of 2,000 nt or less, and the practicality is lost. As described above, in the present invention, in each item of luminance, uniformity, and reliability, characteristics superior to those of the related art could be obtained.

[0018]

Example 2 In the same manner as in Example 1, a 5-inch backlight for a TFT liquid crystal was prepared. Acrylic resin was used as the material of the light guide plate, a mold was used in which 42 depressions were formed on the upper surface of the light guide plate, the molding temperature was 250 ° C., the injection pressure was 1100 kgf / cm 2, the mold temperature was 80 ° C., and the cooling time was Molding was performed for about 30 seconds. The LEDs were arranged in a 6 × 7 array. The light guide plate was 104 mm x 79 mm, and the continuous prism had the same shape as in Example 1. The reason is that a circular shape is the easiest to process, and a triangle, a quadrangle, a pentagon, or the like can be freely selected unless labor for die processing is given. Even at that time, it is preferable to chamfer the corners in order to avoid unevenness. In other configurations, a backlight was created in the same manner. The characteristics of the obtained one are that the surface luminance is 3500 nt when the current is 15 mA,
The junction temperature, which is a measure of the reliability of the LED, was 39 degrees and 14 degrees when the ambient temperature was 25 degrees. On the other hand, in the side type as a control, the LEDs could not be arranged on one side, and were located on two opposing sides. Therefore, the size of the backlight is not
14mm of 7mm x 2 resulted in unnecessary space. Also, since more LEDs were concentrated on the light source, the junction temperature was 64 ° C., which was 25 ° C. higher than that of the present invention, and only the vicinity of the light source significantly increased. There was some concern about long-term life and failure rates.
The surface brightness was 2700 nt, 23% lower than that of the present invention, and the results were considerably inferior when compared side by side.

[0019]

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.
Further, since there is no need to provide an unnecessary space on the side, heat is radiated evenly from the entire surface, so that the temperature of the element can be prevented from rising. As a result, a long life and high reliability can be obtained. Although not shown in the embodiments, it goes without saying that the present invention can also be applied to a nameplate, various display devices, information boards, switches, and the like in addition to the backlight. In addition, by using LEDs of different emission colors, it is possible to easily color-code each section, and it is possible to expect a breakthrough effect 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, (c) is A in (b).
It is sectional drawing in the -A 'line.

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, (c) is B of (b)
It is sectional drawing in the -B 'line.

FIG. 3 is a light-emitting device according to an embodiment of the present invention.
(A) is a perspective view, (b) is a plan view, (c) is C in (b).
It is sectional drawing in the -C 'line.

FIG. 4 is a cross-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 of the related art.

FIG. 6 is a light-emitting device that is 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 ′ of (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 ... Cut

Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G09F 9/00 336 G09F 9/00 336G 13/04 13/04 Z // F21Y 101: 02 F21Y 101: 02 F term ( Reference) 2H038 AA52 AA55 BA06 2H091 FA23Z FA43Z FA45Z FB02 FD06 FD12 FD22 LA11 LA15 5C096 AA05 AA16 AA22 BA01 BA04 CA22 CC06 CC24 CD11 CD22 CD27 CD32 CD42 CD58 FA01 FA03 5G435 AA01 AA12 FF04 CC11

Claims (5)

[Claims] 1. A light guide plate (2) having an upper surface and a lower surface facing each other, and at least one LED element (1), wherein light from the LED element is incident from the lower surface of the light guide plate, and A light emitting device for emitting light from an upper surface of a light plate, wherein the light guide plate has a depression (4) on an upper surface facing the LED element, and the depression gradually widens as approaching the upper surface. A light-emitting device characterized by being formed. 2. The light-emitting device according to claim 1, wherein the light guide plate has a chamfer at an upper surface corner of the recess. 3. The light guide plate according to claim 1, wherein the recess penetrates from the upper surface to the lower surface of the light guide plate.
A light-emitting device according to claim 1. 4. The method according to claim 1, wherein the depression has at least two or more LEDs.
The light emitting device according to claim 1, wherein the light emitting device is formed in a linear shape so as to oppose each other over the elements. 5. The light guide plate penetrates from an upper surface to a lower surface,
A linear cutout (9) formed so as to gradually widen as approaching the upper surface, and LED elements having different wavelengths are arranged via the cutout. The light emitting device according to claim 1.