JP6061396B2 - Light guide plate and planar illumination device - Google Patents

Description

  The present invention relates to a light guide plate that arranges a light source on a light incident end face and emits planar illumination light from an emission portion, and a sidelight type planar illumination device including such a light guide plate.

  As a lighting means for a liquid crystal display panel, a side-light type planar lighting device (backlight) in which small and excellent environmentally friendly LEDs are arranged along the side end surface of a light guide plate is a small portable such as a mobile phone. Widely adopted mainly in the field of information equipment. In recent years, in order to cope with further thinning of a small portable information device, the incident light wedge portion whose thickness gradually decreases as the distance from the side end surface (hereinafter also referred to as a light incident surface) on which the LED is disposed is the light incident surface. A light guide plate formed between the light emitting part and the light emitting part is used. By using such a light guide plate, the emission part of the light guide plate can be made thin regardless of the thickness of the LED (see, for example, Patent Documents 1 and 2).

JP 2007-287550 A JP 2008-170739

  However, the demand for thinning the liquid crystal display device is not only severer, but there is a strong demand for further reduction in the thickness of the planar illumination device used as the backlight of the liquid crystal display device. For example, in order to reduce the thickness of the light emitting portion, given the thickness of the LED to be used and the length of the light incident wedge portion in the light guide direction, the inclination angle of the inclined surface constituting the light incident wedge portion is set to be thin. It needs to be bigger. However, when the inclination angle of the inclined surface is increased, leakage light from the vicinity of the light incident wedge portion and the light incident wedge portion of the light emission portion increases, and the luminance of light emitted from the light emission portion used as illumination light decreases. At the same time, there arises a problem that the luminance distribution of the illumination light deteriorates.

  The present invention has been made in view of the above problems, and provides a light guide plate and a planar illumination device that can reduce the thickness of an emission part without causing a decrease in luminance, a deterioration in luminance distribution, or the like. For the purpose.

  The following aspects of the present invention exemplify the configuration of the present invention, and will be described separately for easy understanding of various configurations of the present invention. Each section does not limit the technical scope of the present invention, and some of the components of each section are replaced, deleted, or further, while referring to the best mode for carrying out the invention. Those to which the above components are added can also be included in the technical scope of the present invention.

(1) A light incident surface that is an end surface on which light from a light source is incident and a surface that is connected to one of two end sides in the longitudinal direction of the light incident surface, and the light incident from the light incident surface is A light guide plate having an exit surface to be emitted, including a light incident wedge portion that includes an inclined surface and is provided such that the thickness decreases from the light incident surface side toward the light exit surface side; The writing light wedge portion includes a thick portion and a thin portion extending from the light incident surface side to the light exit surface side, and the difference between the thickness of the thick portion and the thickness of the thin portion is: It is configured to become smaller from the light incident surface side toward the light exit surface side, and the front portion of the light incident wedge portion in the region facing the light source of the light incident surface is composed of the thin portion. A light guide plate (Claim 1).

  According to the light guide plate described in this section, the light incident wedge portion includes a thick portion and a thin portion that extend from the light incident surface side to the light exit surface side, and the thickness and the thin portion of the thick portion. Since the difference from the thickness of the light incident surface decreases from the light incident surface side toward the light exit surface side, the inclined surface of the light incident wedge portion also has an inclination along the longitudinal direction of the light incident surface. Therefore, the incident light having an incident angle width in the thickness direction on the inclined surface is reflected so as to spread in the direction parallel to the emission surface, and as a result, the reflected light from the inclined surface is reflected. In addition, it becomes possible to reduce the incident angle when it is reflected by the surface opposite to the exit surface and is incident again on the inclined surface, and as a result, leakage light from the vicinity of the incident wedge portion of the inclined surface and the exit surface, It can be effectively reduced.

( 2 ) In the light guide plate according to item ( 1 ), an end of the thin-walled portion that extends to a front portion of a region of the light incident surface facing the light source is on the light incident surface side of the light source. A light guide plate comprising a portion having the same thickness as the thickness (Claim 2 ).

( 3 ) In the light guide plate according to ( 1 ) or ( 2 ), the light incident wedge portion includes one or both of a plurality of the thick portions and a plurality of the thin portions, The light guide plate, wherein the thin portions are alternately arranged (Claim 3 ).

( 4 ) In the light guide plate according to any one of (1) to ( 3 ), the inclined surface includes a first inclined surface portion, a second inclined surface portion, and a third inclined surface from the light incident surface side. And the second inclined surface portion has the same average inclination angle in a cross section perpendicular to the light incident surface and the light exit surface at an arbitrary position in the longitudinal direction of the light incident surface. A light guide plate characterized by being larger than an average inclination angle of the first inclined surface portion and the third inclined surface portion in a cross section (claim 4 ).

  Furthermore, as a result of intensive studies to solve the above-mentioned problems, the present inventor has found that the light-incident wedge portion of the light guide plate, which has been thinned and narrowed in recent years, has a region near the light incident surface and a light exit surface. It was found that the near area has a higher risk of leaking light than the central area.

  According to the light guide plate described in this section, the inclined surface of the light incident wedge portion that is provided so that the thickness decreases from the light incident surface side toward the light exit surface side is 1 inclined surface portion, second inclined surface portion, and third inclined surface portion, and incident light at an arbitrary position in the longitudinal direction of the light incident surface of the second inclined surface portion (central region). The average inclination angle in the cross section orthogonal to the surface and the emission surface is the average inclination angle of the first inclined surface portion (region closer to the light incident surface) and the third inclined surface portion (region closer to the emission surface) in the same cross section. The leakage light from the area near the light incident surface and the area near the light exit surface of the light incident wedge portion, where the risk of leakage light is relatively high, is effectively reduced and emitted. It is possible to reduce the light emitted from the area near the light incident wedge portion of the surface.

( 5 ) In the light guide plate described in the item ( 4 ), the connection portion between the first inclined surface portion and the second inclined surface portion, and the connection between the second inclined surface portion and the third inclined surface portion. part is, the light guide plate, characterized in that it is configured as a curved surface (claim 5).

  According to the light guide plate described in this section, by appropriately setting the shape of the inclined surface based on the mode of change in the risk of leakage light generation along the distance from the light incident surface of the light incident wedge portion Thus, it becomes possible to reduce the leak light more effectively.

( 6 ) The light guide plate according to ( 4 ) or ( 5 ), wherein the inclined surface is configured as one continuous curved surface as a whole (claim 6 ).

  According to the light guide plate described in this section, since the inclined surface is configured as one continuous curved surface as a whole, the inclination angle of the inclined surface is along a direction orthogonal to the light incident surface in an arbitrary side cross section. In this way, the shape of the inclined surface has a higher degree of freedom based on the change in the risk of leakage light generation along the distance from the light incident surface of the light incident wedge portion. Therefore, it is possible to set appropriately, and it is possible to reduce the leakage light more effectively.

( 7 ) The light guide plate according to the item ( 6 ), wherein the continuous curved surface is a curved surface having a convex shape on the light incident surface side and a concave surface on the light exit surface side (Claim 7 ).

  According to the light guide plate described in this section, in the light incident wedge portion of the light guide plate that has been thinned and narrowed in frame, a typical change in the risk of leaking light along the distance from the light incident surface is typical. With respect to such a mode, the shape of the inclined surface can be set to the most appropriate shape, and leakage light can be reduced more effectively.

( 8 ) In the light guide plate described in the item ( 7 ), the continuous curved surface is formed in an S shape in a side view, and has an inflection point in the second inclined surface portion. Item 8 ).

According to the light guide plate described in this section, it is possible to easily and effectively form the inclined surface having the most appropriate shape.
( 9 ) In the light guide plate according to item ( 8 ), the inflection point is provided at a substantially center of the continuous curved surface in a direction perpendicular to the light incident surface, and the continuous curved surface is S-shaped in a side view. The shape of a convex part and the shape for a recessed part are substantially congruent, The light-guide plate characterized by the above-mentioned (Claim 9 ).

( 10 ) In the light guide plate according to ( 4 ) or ( 5 ), at least one of the first inclined surface portion, the second inclined surface portion, and the third inclined surface portion is formed from a plurality of planes. A light guide plate comprising the light guide plate (claim 10 ).

  According to the light guide plate described in this section, it is possible to easily form the shape of the inclined surface based on the aspect of the change in the risk of leakage light generation along the distance from the light incident surface of the light incident wedge portion. Thus, it is possible to reduce leakage light.

( 11 ) The light guide plate according to any one of items (1) to ( 10 ), wherein the inclined surface is provided on the exit surface side (claim 11 ).

( 12 ) In the light guide plate according to any one of (1) to ( 11 ), a flat portion having a constant thickness is provided between the light incident surface and the light incident wedge portion. A light guide plate characterized by the above (claim 12 ).

( 13 ) In the light guide plate according to any one of ( 3 ) to ( 12 ), when the light incident wedge portion includes a plurality of the thick portions, the shapes of the plurality of thick portions are the same as each other. includes a case where, and, the light incident when the wedge portion has a plurality of the thin portion, the light guide plate you comprising a case where the shape of the plurality of the thin portion are identical to each other (claim 13 ).

( 14 ) The light guide plate according to any one of (1) to ( 13 ), and a light source arranged so as to face the light incident surface and emitting light to the light incident surface. A planar lighting device characterized in that ( 14 ).

( 15 ) A light incident surface that is an end surface on which light from a light source is incident and a surface that is connected to one of two longitudinal edges of the light incident surface, and the light incident from the light incident surface is A light guide plate having an exit surface to be emitted, including a light incident wedge portion that includes an inclined surface and is provided such that the thickness decreases from the light incident surface side toward the light exit surface side; The writing light wedge portion includes a thick portion and a thin portion extending from the light incident surface side to the light exit surface side, and an average inclination angle of the thick portion of the inclined surface is the inclined surface the much larger than the average inclination angle of the thin portion of the inclined surface has a light incident surface side and the first inclined surface portion, a second inclined surface, a third inclined surface, said first Average inclination angle in a cross section orthogonal to the light incident surface and the light exit surface at an arbitrary position in the longitudinal direction of the light incident surface of the inclined surface portion of 2 , The same of the first inclined surface portion and the third light guide plate and greater than the average inclination angle of the inclined surface portion of the cross section (claim 15).

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the planar illuminating device which can make an output part thin, without producing the fall of a brightness | luminance, deterioration of a brightness distribution, etc.

(A) is a side view which shows the principal part of an example of the planar illuminating device for demonstrating a part of characteristic of this invention, (b) is the characteristic of the planar illuminating device shown to (a). It is a side view showing typically. (A), (b), (c) is a figure for demonstrating the concept of the light leakage risk in this invention, The light quantity of the 1st incident light with respect to an inclined surface, an incident angle, and a light leakage risk, It is a figure showing typically, respectively. In order to explain the concept of the risk of leakage light in the present invention, it is a diagram illustrating an angle formed by light incident on an inclined surface and an optical axis, and a distance on the inclined surface corresponding to a certain angular width. (A), (b), (c) is a figure for demonstrating the concept of the light leakage risk in this invention, The light quantity of the 2nd incident light with respect to an inclined surface, an incident angle, and a light leakage risk, It is a figure showing typically, respectively. It is a figure which shows distribution of the whole leak light risk degree corresponding to the shape of a light incident wedge part. (A) is a side view showing a conventional planar illumination device together with optical paths of a plurality of incident lights having different incident angles, and (b) is different in incident angle with respect to the planar illumination device shown in FIG. 1 (a). It is a side view shown with the optical path of several incident light. It is sectional drawing which shows the typical structure of pseudo white LED. It is a side view which shows the principal part of the other example of the planar illuminating device for demonstrating a part of characteristic of this invention. It is a side view which shows the principal part of the other example of the planar illuminating device for demonstrating a part of characteristic of this invention. (A) is the elevation which shows the principal part of the planar illuminating device in one Embodiment of this invention, (b) is AA sectional drawing of (a).

  Hereinafter, a light guide plate and a planar illumination device according to an embodiment of the present invention will be described with reference to the drawings. In the accompanying drawings, the shape, size, etc. of each component are exaggerated as appropriate for easy understanding of the present invention. Further, in the accompanying drawings, when two components are illustrated so as to be adjacent to each other through a space, the space is inserted or exaggerated for easy understanding of the present invention. It is shown that the configuration of the present invention does not depend on the presence or absence of spaces between adjacent components or, if present, their dimensions.

  As shown in FIG. 1A, the planar illumination device 10 includes an LED 11 as a light source and a light guide plate 20 for emitting light emitted from the LED 11 in a planar shape. The light guide plate 20 is formed in a rectangular shape in a top view using a transparent material (for example, polycarbonate resin), and has a light incident surface 21 that is an end surface on which the LED 11 is disposed on the outer surface thereof. Further, in the light guide plate 20, a surface connected to one end side 21 c of the two end sides 21 c and 21 d in the longitudinal direction of the light incident surface 21 (a direction orthogonal to the paper surface in FIG. 1A) is An emission surface 22 and an inclined surface 25 described later are included. Hereinafter, the surface including the emission surface 22 of the light guide plate 20 is also referred to as a front surface 23, and the surface facing the surface 23 is also referred to as a back surface 24.

Here, in the present invention, the direction from the light incident surface 21 toward the end surface (not shown) facing the light incident surface 21 (right direction in FIG. 1A) is “front” (the opposite direction). "Back"). “Front” defined in this way is also the direction in which the light incident on the light guide plate 20 from the light incident surface 21 is guided through the light guide plate 20 as a whole. The direction is also referred to as “light guide direction”.
In addition, the direction in which the back surface 24 faces the front surface 23 (upward direction in FIG. 1A) is defined as “upward” (the opposite direction is “downward”). Say. Further, the direction orthogonal to the front-rear direction and the vertical direction (direction orthogonal to the paper surface of FIG. 1A) (if necessary, define "right" and "left" toward the front) Also called. In other words, the left-right direction is the longitudinal direction of the light incident surface 21. Unless otherwise specified, “length”, “thickness (thickness)”, and “width” refer to dimensions in the front-rear direction, the up-down direction, and the left-right direction, respectively.

  The light guide plate 20 includes a light incident wedge portion 31 including an inclined surface 25 and an output portion 32 including an output surface 22 from the light incident surface 21 side toward the front. The back surface 24 of the light guide plate 20 is formed to be one flat surface through the light incident wedge portion 31 and the light emitting portion 32, while the inclined surface 25 of the light incident wedge portion 31 is on the light incident surface 21 side. In this way, the light incident wedge portion 31 is provided so that its thickness becomes thinner from the light incident surface 21 side toward the light emission surface 22 side. . The exit surface 22 is formed as a flat surface substantially orthogonal to the light incident surface 21 and connected to the front edge 26 of the inclined surface 25, and the back surface 24 faces the exit surface 22 substantially in parallel.

  Next, with reference to FIG. 1B together with FIG. 1A, the configuration of the inclined surface 25 of the light incident wedge portion 31 which is a main feature of the planar illumination device 10 will be described in detail. Here, FIG.1 (b) is the side view which showed typically the characteristic of the light entrance wedge part 31 of the light-guide plate 20 of the planar illuminating device 10 shown to Fig.1 (a) for description.

  In the surface illumination device 10, the cross-sectional shape of the cross section of the light incident wedge portion 31 perpendicular to the light incident surface 21 and the light exit surface 22 (cross section taken along a plane parallel to the paper surface in FIG. 1A) is At an arbitrary position in the longitudinal direction of the optical surface 21, it is the same as the side shape shown in FIG. Therefore, in the following description, the features common to such arbitrary cross sections will be described based on the side views shown in FIGS. 1 (a) and 1 (b).

  In the present invention, the inclination angle θp of the inclined surface 25 at an arbitrary position (for example, position P) on the inclined surface 25 of the light incident wedge portion 31 passes through the position P to the light incident surface 21 and the light exit surface 22. A half straight line K extending in parallel with the exit surface 22 from the position P to the light incident surface 21 side in an orthogonal cross section (a cross section taken along a cut surface parallel to the paper surface in FIG. 1A). And an angle formed by a half line L extending in contact with the inclined surface 25 from the position P toward the light incident surface 21 (in other words, corresponding to an ascending gradient in the side section passing through the position P at the position P of the inclined surface 25). Angle).

  In the light guide plate 20, the inclined surface 25 is configured as one continuous curved surface as a whole, and therefore, the inclination angle of the inclined surface 25 continuously varies spatially along the front-rear direction within an arbitrary side cross section. To do.

  However, the inclined surface 25 of the light guide plate 20 is formed so that the inclination angle satisfies the following conditions. That is, the inclined surface 25 includes, in order from the light incident surface 21 side, a first inclined surface portion 25a (a range indicated by “I” in FIG. 1A) and a second inclined surface portion 25b (FIG. 1A). (The range indicated by “II”) and the third inclined surface portion 25c (the range indicated by “III” in FIG. 1A), and the average inclination angle θ2 of the second inclined surface portion 25b is It is configured to be larger than the average inclination angle θ1 of the first inclined surface portion 25a and larger than the average inclination angle θ3 of the third inclined surface portion 25c. Here, the average inclination angle in the specific range of the inclined surface 25 is an angle obtained by averaging the inclination angles at the respective positions in the range over the entire range.

  Further, in the illustrated example, the average inclination angles θ1 and θ3 of the first and third inclined surface portions 25a and 25c are formed to be smaller than the average inclination angle θ over the entire length of the light incident wedge portion 31 of the inclined surface 25. Has been. In FIG. 1B, the average inclination angles θ1, θ2, θ3 of the first, second, and third inclined surface portions 25a, 25b, and 25c, and the light incident wedge portion 31 of the inclined surface 25 are shown. An example of the average inclination angle θ over the entire length is shown together with virtual planes 35 a, 35 b, 35 c, 36 with the respective average inclination angles θ 1, θ 2, θ 3, θ as inclination angles. In FIG.1 (b), the virtual plane 36 is corresponded in the inclined surface shape of the general light entrance wedge part in the conventional planar illuminating device.

  Further, in the light guide plate 20, the inclined surface 25 having the first, second, and third inclined surface portions 25a, 25b, and 25c is realized as one continuous curved surface as a whole. The light entrance surface 21 side is formed into a convex curved surface while the light exit surface 22 side is formed into a concave curved surface, while approaching the back surface 24 side as going forward from the light entrance surface 21 side. In the illustrated example, in the side surface shape (arbitrary side cross-sectional shape) shown in FIG. 1A, the S-shaped curve indicating the inclined surface 25 has an inflection point A in the second inclined surface portion 25b. The first inclined surface portion 25a and the first inclined surface portion 25a side from the inflection point A of the second inclined surface portion 25b are convex, and the second inclined surface A from the inflection point A of the second inclined surface portion 25b. The inclined surface portion 25c side and the third inclined surface portion 25c form a concave shape.

Next, with reference to FIGS. 2-6, the effect of the planar illuminating device 10 is demonstrated.
First, in the conventional planar illumination device in which the inclined surface of the light incident wedge portion is configured by an inclined surface having a single inclination angle θ like the virtual plane 36 shown in FIG. The position dependency of the leaked light characteristics on the inclined surface will be described.
In the following description, for the sake of convenience, the inclined surface of the conventional planar illumination device is referred to with reference numeral 36, and the other components are referred to with the same reference numerals as those of the planar illumination apparatus 10. To do.

Of the light incident on the inclined surface 36, the relative amount of light that leaks from the incident wedge portion 31 and the vicinity of the incident wedge portion 31 of the exit surface 22 due to the inclined surface 36 (hereinafter referred to as " The “leakage light risk level” or simply “risk level” refers to the amount of light incident on the inclined surface 36 (light quantity) and the angle with respect to the optical axis when entering the inclined surface 36 (in the present invention, this angle is referred to as “incident” It is thought that it depends on the following equation:
“Light intensity” × “incident angle” = “Leakage light risk”
Here, in the present invention, the “optical axis” refers to a central axis that extends from the center of the light emitting surface 11 a of the LED 11 at right angles to the light emitting surface 11 a (and hence the light incident surface 21).

  The reason for the risk of leaking light depends on the incident angle is that the transmittance of light transmitted from the inside of the light guide plate 20 to the outside on the inclined surface 36 depends on the incident angle. These light amounts and incident angles depend on the distance in the optical axis direction from the light emitting surface 11a of the LED 11 (substantially coincident with the light incident surface 21 of the light guide plate 20).

  Further, in the light guide plate 20 that has been thinned and narrowed in recent years, the light incident on the inclined surface 36 is mainly incident on the inclined surface 36 first after entering the light guide plate 20 from the light incident surface 21. Light (hereinafter referred to as “first-time incident light”) and light that the first-time incident light is reflected by the inclined surface 36 and then incident on the inclined surface 36 (hereinafter referred to as “second-time incident light”). ) However, the first-time incident light includes light that is incident on the light guide plate 20 from the light incident surface 21 and is first reflected on the inclined surface 36 after being reflected by the back surface 24. There is also light that is reflected by the back surface 24 more than once and then enters the inclined surface 36 again. However, the amount of light is less than that of the first-time incident light and the second-time incident light, and the proportion of the leaked light is small.

  2 (a), 2 (b), and 2 (c) show the amount of light incident on the inclined surface 36, the incident angle, and the distribution of the risk for the first-time incident light in the direction of the optical axis from the LED 11, respectively. It is a figure shown with respect to distance. 2A, 2 </ b> B, and 2 </ b> C are schematic diagrams for easily explaining the characteristics of the risk level.

  First, the amount of light is examined. The orientation distribution of the light emitted radially from the LED 11 as a whole and incident on the light guide plate 20 is a distribution in which the light amount decreases in the optical axis direction as the maximum light amount and the angle formed with the optical axis increases. However, the width of the inclined surface 36 (corresponding to the width D in the optical axis direction) corresponding to the unit angle starting from the center of the light emitting surface 11a of the LED 11 is such that the light beam is directed in the optical axis direction as shown in FIG. It becomes longer and shorter as the angle with the optical axis becomes larger (D1 <D2 <D3). Therefore, the amount of light per unit distance (unit area) incident on the inclined surface 36 increases as the distance from the LED 11 increases in the region close to the light incident surface 21 as shown in FIG. However, after reaching the peak (maximum region), it reverses and decreases as the distance from the LED 11 increases.

  Next, the incident angle will be examined. As shown in FIG. 2B, the incident angle of the light incident on the inclined surface 36 has a width (range) corresponding to the distance from the LED 11, but the upper limit of this range is a large distance from the LED 11. Thus, the transmittance on the inclined surface 36 decreases as the distance from the LED 11 increases.

  Therefore, as shown in FIG. 2 (c), the leakage light risk (a value obtained by multiplying the light amount and the upper limit value of the incident angle) becomes maximum when the distance from the LED 11 is near zero, and is further forward than that point. Then, as the distance from the LED increases, the distance decreases.

  Next, the second incident light will be examined with reference to FIG. 4A, 4 </ b> B, and 4 </ b> C are diagrams showing the amount of light incident on the inclined surface 36, the incident angle, and the distribution of the risk with respect to the distance from the LED 11 for the second incident light. It is. 4A, 4 </ b> B, and 4 </ b> C are schematic diagrams for easily explaining the characteristics of the risk level.

  First, the amount of light is examined. As shown in FIG. 4A, the distribution of the amount of light of the second incident light is a distribution having a peak (maximum region) ahead of the first incident light. Next, with reference to FIG. 4B, the incident angle of the second incident light will be examined. The upper limit of the incident angle changes during the first reflection on the inclined surface 36 (the incident angle increases by about twice the inclination angle θ of the inclined surface 36), so that the distribution of the first incident light is forwarded. And a distribution in which the angle change is superimposed. Further, the lower limit value of the incident angle is a positive value corresponding to the distance from the LED 11, and this lower limit value tends to become smaller as the distance from the LED becomes larger, like the upper limit value.

  Accordingly, the leakage light risk level of the second incident light is basically a distribution obtained by moving the leakage light risk level distribution of the first incident light forward as shown in FIG. 4C. However, depending on the amount of change in angle at the time of reflection on the first inclined surface 36, the risk of leakage light of the second incident light may be greater than the risk of leakage light of the first incident light.

  The risk obtained by adding the risk of leakage of the first incident light and the risk of leakage of the second incident light obtained as described above is the overall risk of leakage of light on the inclined surface 36 (see FIG. 5). )become. As shown in FIG. 5, there is a portion (a portion showing a maximum value) where the risk of leakage light is large at a position where the distance from the LED 11 is small (position near the light incident surface 21), and the distance from the LED 11 is larger than that position. The leaked light risk gradually decreases. When the distance from the LED 11 is further increased, the leakage light risk is reversed and gradually increases, and again shows a maximum value. As a whole, a concave shape having a curved center part is formed.

One of the features of the present invention is that, as described above, the overall risk of light leakage is two regions including the maximum (the maximum region on the light incident surface 21 side and the maximum region on the output surface 22 side), and the minimum. In the range corresponding to the maximum regions on the incident surface 21 side and the emission surface 22 side, respectively, of the inclined surface 25 of the light incident wedge portion 31, respectively. An average of the first inclined surface portion 25a and the third inclined surface portion 25c is provided by providing the first inclined surface portion 25a and the third inclined surface portion 25c, and providing the second inclined surface portion 25b in a range corresponding to the central minimum region. The inclination angles θ1 and θ3 are to be relatively smaller than the average inclination angle θ2 of the second inclined surface portion 25b. Thereby, the leakage light generated on the inclined surface 25 can be effectively reduced.
In the planar illumination device 10, it becomes possible to improve the luminance of the illumination light emitted from the emission surface 22.

  Furthermore, in the planar lighting device 10, the shape of the inclined surface 25 is a S-shaped continuous curved surface in a side view in which the region near the light incident surface 21 is convex and the region near the output surface 22 is concave, An optimum inclined surface shape can be realized in order to reduce the leakage light from the inclined surface 25 in accordance with the overall distribution of the risk of leakage light.

  Further, as shown in FIG. 6, in the conventional planar illumination device (see FIG. 6A) provided with the inclined surface 36 whose inclination angle is constant over the entire area of the light incident wedge portion 31, the light from the LED 11 As a result, the light L1 incident on the region (I) near the light incident surface 21 of the inclined surface 36 at a relatively large incident angle is emitted as a second incident light. In addition to a high risk of entering the region (III) near the exit surface 22 and generating leakage light there, the reflected light component is repeatedly reflected between the inclined surface 36 and the back surface 24 depending on conditions. Thus, the light is easily emitted from the vicinity of the light incident wedge portion 31 of the emission surface 22. In the conventional planar illumination device, this kind of leakage light also has a problem that the uniformity of the luminance distribution of the illumination light emitted from the emission surface 22 deteriorates.

On the other hand, in the planar lighting device 10, the average inclination angles θ1 and θ3 of the first inclined surface portion 25a and the third inclined surface portion 25c are relatively reduced, as shown in FIG. 6B. Even light incident on the inclined surface 25 under the same conditions as in the above L1 (similarly, denoted by L1) is guided into the emitting portion 32 without being emitted from the vicinity of the light incident wedge portion 31 of the emitting surface 22. It becomes possible.
In the planar illumination device 10, it is possible to improve the uniformity of the luminance distribution of the illumination light emitted from the emission surface 22 as described above.

  In addition, this feature of the planar illumination device 10 also has the following effects when the LED 11 is a so-called pseudo white LED. In general, as shown in FIG. 7, the pseudo white LED has a configuration in which a blue light emitting chip 41 is sealed with a transparent resin 42 in which a yellow phosphor is dispersed, and blue light emitted from the blue light emitting chip 41, An emission spectrum that looks white is realized by mixing with yellow light emitted by the yellow phosphor that absorbs the blue light. At that time, the light L1 emitted from the LED 11 in a direction having a large angle with the optical axis passes through the transparent resin 42 as compared with the light L2 and L3 emitted in a direction having a small angle with the optical axis. Since the distance is long, it tends to be yellowish white light. As a result, as described above with reference to FIG. 6A, the leakage light derived from the light L <b> 1 is easily emitted from the vicinity of the light incident wedge portion 31 of the emission surface 22. It also causes the problem of being partially yellowish.

  Therefore, in the planar illumination device 10, the reduction of leakage light from the vicinity of the light incident wedge portion 31 of the emission surface 22 has the effect of reducing or eliminating such problems and improving the chromaticity distribution of the illumination light. It also plays.

  According to the investigation and examination of the present inventor, in the planar illumination device 10, compared to the conventional planar illumination device in which the light incident wedge portion 31 is provided with the inclined surface 36 having a constant inclination angle, It has been clarified that the leakage light generated due to this can be reduced by about 25%. In addition, it was confirmed that the luminance of the illumination light emitted from the emission surface 22 was improved by 4.5% by actual machine prototype verification.

  Furthermore, in the planar illumination device 10, the average inclination angle θ3 of the third inclined surface portion 25c, which is a portion connected to the emission surface 22 of the inclined surface 25, is smaller than the constant inclination angle θ of the conventional inclined surface 36. Therefore, it is possible to suppress luminance unevenness (abrupt change in luminance) that occurs when the inclined surface 25 and the emission surface 22 are discontinuously connected with a constant crossing angle. And this inhibitory effect is that the inclined surface 25 of the planar illumination device 10 is formed in a concave shape in the third inclined surface portion 25c, and the inclination angle of the portion connected to the emission surface 22 is further smaller than the average inclination angle θ3. Depending on the situation.

  In the planar illumination device 10, the average inclination angle θ <b> 1 of the first inclined surface portion 25 a, which is the portion of the inclined surface 25 near the light incident surface 21, is smaller than the constant inclination angle θ of the conventional inclined surface 36. Therefore, when the flexible printed wiring board (FPC) (not shown) on which the LED 11 is mounted is directly fixed on the inclined surface 25 of the light guide plate 20, the light emitting surface 11 a of the LED 11 is incident on the light guide plate 20. Problems on mounting the LED 11 such as tilting with respect to the surface 21 can be reduced.

  In addition, since the second inclined surface portion 25b having the largest average inclination angle among the three inclined surface portions is arranged at the central portion in the light guide direction, even if leakage light is generated from the second inclined surface portion 25b. Normally, the light leakage can be reliably absorbed by the light shielding member disposed on the upper surface of the inclined surface 25.

  In the example shown in FIG. 1 (a), the inclined surface 25 has an inflection point A at substantially the center along the length direction (front-rear direction) of the light incident wedge portion 31, and the shape of the convex portion. However, in the present invention, it is needless to say that the shape of the inclined surface 25 is not limited to the case of having such symmetry. In the planar lighting device 10, the ratio of the lengths of the first inclined surface portion 25a, the second inclined surface portion 25b, and the third inclined surface portion 25c to the entire length of the light incident wedge portion 31, and the first inclined surface portion 25a. The average inclination angles θ1, θ2, and θ3 of the second inclined surface portion 25b and the third inclined surface portion 25c are appropriately set according to the actual distribution of the leakage light risk degree.

  Here, as in the planar illumination device 50 illustrated in FIG. 8, the planar illumination device includes a flat portion 33 (“IV” in FIG. 8) between the light incident surface 21 of the light guide plate 51 and the light incident wedge portion 31. Range) may be provided. The flat portion 33 extends from the light incident surface 21, is connected to the first inclined surface portion 25 a, has an upper surface 52 parallel to the emission surface 22, and has a certain thickness.

  Further, the planar illumination device is similar to the planar illumination device 60 shown in FIG. 9 in that the first inclined surface portion 65a, the second inclined surface portion 65b, and the third inclined surface portion 65c of the inclined surface 65 of the light guide plate 61 are used. May be configured as inclined surfaces having constant inclination angles θ1, θ2, and θ3, respectively. In other words, the planar illumination device 60 has a configuration in which the virtual planes 35a, 35b, and 35c shown in FIG. 1B are realized as actual inclined surfaces. The planar lighting device 60 is advantageous in that the inclined surface 65 can be formed relatively easily.

  Further, the planar illumination device 60 includes any one of a connecting portion 66 between the first inclined surface portion 65a and the second inclined surface portion 65b and a connecting portion 67 between the second inclined surface portion 65b and the third inclined surface portion 65c. Either one or both may be configured as a curved surface. Further, in the planar illumination device 60, one or more of the first, second, and third inclined surface portions 65a, 65b, and 65c are configured from a plurality of inclined surfaces having different inclination angles. In that case, at least one of the connecting portions between the inclined surfaces may be configured as a curved surface.

  Here, in the above description, for convenience of explanation, the cross-sectional shape of the cross section (side cross section) orthogonal to the light incident surface 21 and the light exit surface 22 of the light incident wedge portion 31 of the light guide plate is used for any planar illumination device. It is assumed that the shape of the side surface is the same as that of the side surface at an arbitrary position in the longitudinal direction of the light incident surface 21. However, in the light guide plate according to the present invention, the shape of the inclined surface of the light incident wedge portion has an inclination along the longitudinal direction of the light incident surface 21.

  FIG. 10 is a diagram illustrating an example of the planar lighting device 70 including the light guide plate 71 and the light guide plate 71 according to the embodiment of the present invention. FIG. 10A illustrates the planar lighting device 70 from the light incident surface 21 side. The front view (elevation view) and (b) which were seen are AA sectional drawings of (a). In the planar illumination device 70, the light incident surface 21 of the light guide plate 71 is configured such that its thickness spatially varies along the longitudinal direction of the light incident surface 21. Specifically, the thickness of the light incident surface 21 is set such that the thickness at the position where each LED 11 is disposed is approximately the same as the thickness of the LED 11, and the thickness on both sides of the position where each LED 11 is disposed is greater than the thickness at the position where the LED 11 is disposed. The inclined surface 75 is configured to be thicker, and is inclined downward from the light incident surface 21 toward the front over the entire width along the longitudinal direction of the light incident surface 21, and is emitted at the front end of the inclined surface 75. It is configured to be connected to the surface 22.

  Thus, the inclined surface 75 has not only the inclination along the front-rear direction (light guide direction) but also the inclination along the left-right direction (longitudinal direction of the light incident surface 21). With this configuration, the longitudinal angle of the light incident surface 21 is such that the average inclination angle over the entire length of the light incident wedge portion 31 of the inclined surface 75 is also the smallest at the placement position of each LED and the largest at both sides of the placement position of each LED 11. It will vary spatially along the direction. However, in the planar illumination device 70, the average inclination angle in the side cross section of the second inclined surface portion 75b in the side cross section at an arbitrary position along the longitudinal direction of the light incident surface 21 is the first inclined surface portion. It is the same as that of the planar illumination device 10 that it is larger than the average inclination angle in the same side cross section of 75a and the 3rd inclined surface part 75c. Furthermore, the planar illumination device 70 is also an average of the first inclined surface portion 75a and the third inclined surface portion 75c in an arbitrary side cross section in a side cross section at an arbitrary position along the longitudinal direction of the light incident surface 21. The inclination angle is formed so as to be smaller than the average inclination angle over the entire length of the light incident wedge portion 31 in the same side cross section.

  With the configuration described above, the planar illumination device 70 has the same effect as the planar illumination device 10, and the inclined surface 75 has an inclination along the longitudinal direction of the light incident surface 21. Therefore, the incident light having an incident angle width in the thickness direction on the inclined surface 75 is reflected so as to spread in the direction parallel to the emission surface 22, and as a result, the reflected light from the inclined surface 75 is reflected. However, since the incident angle when the light is reflected by the back surface 24 and is incident again on the inclined surface 75 (typically, the third inclined surface portion 75c) can be reduced, the incident wedges of the inclined surface 75 and the exit surface 22 can be reduced. Light leaked from the vicinity of the portion 31 can be further effectively reduced.

  In the planar illumination device 70, the length of the light incident wedge portion 31 is constant along the longitudinal direction of the light incident surface 21, but in the light guide plate and the planar illumination device according to the present invention, Inclining along the longitudinal direction of the light incident surface 21 on the inclined surface of the light incident wedge portion 31 by spatially varying the length of the light incident wedge portion 31 along the longitudinal direction of the light incident surface 21 It may be. In this case, compared with the planar illumination device 70 shown in FIG. 10, the spatial variation along the longitudinal direction of the light incident surface 21 of the average inclination angle over the entire length of the light incident wedge portion 31 of the inclined surface is caused. It can be kept relatively small.

  Here, in the example and the embodiment for explanation described above, the inclined surfaces 25, 65, 75 of the light incident wedge portion 31 are all formed on the surface 23 side of the light guide plates 20, 51, 61, 71. However, in the light guide plate and the planar lighting device according to the present invention, the inclined surface 75 may be formed on the back surface 24 side of the light guide plate 71. Or the light-guide plate and planar illumination device which concern on this invention have the inclined surface of the light incident wedge part 31 in both the surface 23 side and the back surface 24 side of the light-guide plate 71, and among two inclined surfaces Any one or both of these may be configured as the inclined surface 75 according to the present invention. In that case, when only one of the two inclined surfaces is configured as the inclined surface 75 according to the present invention, the other inclined surface is an inclined surface having a constant inclination angle similar to the conventional one. There may be.

  It goes without saying that the light guide plate and the planar illumination device according to the present invention include a light guide plate and a planar illumination device having a configuration in which the features described in connection with the individual examples described above are arbitrarily combined. Yes. For example, the light guide plate 71 of the planar illumination device 70 may include the flat portion 33 described in relation to the planar illumination device 50.

10, 50, 60, 70: planar illumination device, 11: LED, 20, 51, 61, 71: light guide plate, 21: light incident surface, 21c: surface of light incident surface (surface including emission surface) side End side, 21d: End side of light incident surface on back surface (surface including reflection surface), 22: Output surface, 23: Front surface, 24: Back surface, 25, 65, 75: Inclined surface, 25a, 65a, 75a: First inclined surface portion, θ1: Average inclination angle of first inclined surface portion, θ2: Average inclination angle of second inclined surface portion, θ3: Average inclination angle of third inclined surface portion

Claims (15)

A light incident surface that is an end surface on which light from a light source is incident;
A light guide plate having an exit surface that is included in a surface connected to one of two longitudinal sides of the light incident surface and emits light incident from the light incident surface;
An incident wedge portion provided so as to be thinner as it goes from the light incident surface side to the light exit surface side including an inclined surface, and the light incident wedge portion is formed from the light incident surface side. It includes a thick part and a thin part extending to the exit surface side, and the difference between the thickness of the thick part and the thickness of the thin part is directed from the light incident surface side to the exit surface side. is configured to be smaller in accordance with,
A light guide plate , wherein a front portion of a region of the light incident wedge portion facing the light source on the light incident surface includes the thin portion . The end on the light incident surface side of the thin wall portion extending to the front portion of the region of the light incident surface facing the light source includes a portion having the same thickness as the light source. The light guide plate according to claim 1 . The light entering the wedge portion, claim 1, characterized in that has one or both of the plurality of the thick portions and a plurality of the thin portion, the thin portion and the thick portion are arranged alternately or the light guide plate according to. The inclined surface includes a first inclined surface portion, a second inclined surface portion, and a third inclined surface portion from the light incident surface side, and a longitudinal direction of the light incident surface of the second inclined surface portion. An average inclination angle in a cross section orthogonal to the light incident surface and the emission surface at an arbitrary position is larger than an average inclination angle of the first inclined surface portion and the third inclined surface portion in the same cross section. the light guide plate according to any one of claims 1 to 3, characterized in that. The connecting portion between the first inclined surface portion and the second inclined surface portion, and the connecting portion between the second inclined surface portion and the third inclined surface portion are configured as curved surfaces. The light guide plate according to claim 4 . The light guide plate according to claim 4 or 5 , wherein the inclined surface is configured as one continuous curved surface as a whole. The light guide plate according to claim 6 , wherein the continuous curved surface is a curved surface having a convex shape on the light incident surface side and a concave shape on the light emitting surface side. The light guide plate according to claim 7 , wherein the continuous curved surface is formed in an S shape in a side view and has an inflection point in the second inclined surface portion. The inflection point is provided at substantially the center of the continuous curved surface in a direction orthogonal to the light incident surface, and the shape of the convex portion of the continuous curved surface, which is S-shaped in a side view, is substantially congruent. The light guide plate according to claim 8 , wherein the light guide plate is provided. Said first inclined surface, the second inclined surface portion, and said third inclined at least one of the surface portions, guide according to claim 4 or 5, characterized in that it is composed of a plurality of planes Light board. The inclined surface, the light guide plate according to any one of claims 1 to 10, characterized in that provided on the emission surface side. Between the light incident surface and the light incident wedge light guide plate according to any one of claims 1 to 11, characterized in that the flat portion of the thickness is constant is provided. When the light incident wedge portion has a plurality of thick portions, including the case where the plurality of thick portions are the same in shape, and when the light incident wedge portion has a plurality of thin portions, The light guide plate according to any one of claims 3 to 12 , including a case where the plurality of thin-walled portions have the same shape. A planar illumination comprising: the light guide plate according to any one of claims 1 to 13 ; and a light source disposed so as to face the light incident surface and emitting light to the light incident surface. apparatus. A light incident surface that is an end surface on which light from a light source is incident;
A light guide plate having an exit surface that is included in a surface connected to one of two longitudinal sides of the light incident surface and emits light incident from the light incident surface;
An incident wedge portion provided so as to be thinner as it goes from the light incident surface side to the light exit surface side including an inclined surface, and the light incident wedge portion is formed from the light incident surface side. and a said thick portion extends to the exit plane side and the thin portion, and the average tilt angle in the thick portion of the inclined surface is much larger than the average inclination angle of the thin portion of the inclined surface ,
The inclined surface includes a first inclined surface portion, a second inclined surface portion, and a third inclined surface portion from the light incident surface side, and a longitudinal direction of the light incident surface of the second inclined surface portion. An average inclination angle in a cross section orthogonal to the light incident surface and the emission surface at an arbitrary position is larger than an average inclination angle of the first inclined surface portion and the third inclined surface portion in the same cross section. A light guide plate characterized by that.

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