The invention relates to a surface light source device and a liquid crystal display device using the same. More particularly, the invention relates to a surface light source device capable of preventing a prism sheet from being broken due to external force, wherein a light utilizing efficiency can be enhanced by the use of the prism sheet.
In one example of surface light source devices, a light beam emitted from a light emitting plane of a light guiding plate is deflected in a direction perpendicular to the light emitting plane by the use of a prism sheet, thereby enhancing a light utilizing efficiency, as disclosed in Japanese Patent Application Laid-open No. 2003-215584 (Patent Literature 1).
In this way, a light beam p is emitted from the light emitting plane 409 of the light guiding plate 403 in a direction substantially parallel to the light emitting plane 409, and then, is incident into the prism 408 formed at the prism sheet 405 through the air in the liquid crystal display device 401, as shown in
However, if external force is exerted on the liquid crystal display device 401, the prism 408 is pressed against the light guiding plate 403, and therefore, the entire prism 408 or a part of the vertex of the prism 408 may be accidentally crushed. In such a case, the direction of the light beam p to be diffracted and reflected is changed at the crushed portion, and therefore, the light beam p incident into the crushed portion of the prism 408 cannot be emitted in the direction perpendicular to the light emitting plane 409, to be lost, as shown in
As means for solving the above-described problems, Japanese Patent Application Laid-open No. Hei 11-305011 (Patent Literature 2) discloses that abrasion resistance of a prism sheet is enhanced by forming a vertex of a prism into an arc having a radius of curvature of 10 μm to 25 μm. With this solving means, the vertex of the prism is hardly crushed, but the increased radius of curvature of the vertex, as described above, degrades optical characteristics of the prism sheet, thereby reducing a light beam to be emitted in a direction perpendicular to the prism sheet, so as to markedly decrease a frontal luminance in a liquid crystal display device.
Otherwise, Japanese Patent Application Laid-open No. 2001-343507 (Patent Literature 3) discloses a radius of curvature of a vertex of 5 μm or less in order to suppress a decrease in frontal luminance to the minimum. However, since the vertex of the prism becomes sharp by reducing the radius of curvature of the vertex, as described above, an effect of prevention of a crush of the prism is almost diminished. In particular, an effect is seldom produced in the case of a prism sheet having a small angle of a vertex of a prism. In view of this, such a shape of the prism merely devised as described above is not enough to prevent any crush of the prism while suppressing the decrease in frontal luminance.
Alternatively, Japanese Patent Application Laid-open No. 2002-231030 (Patent Literature 4) as other measures discloses a method for protecting a prism by the use of a shock absorbent. In this method, a fluid made of a gelled or liquefied translucent material is enclosed between a cover board for covering a prism forming surface of a light guiding plate having the prism formed thereon and the prism forming surface of the light guiding plate, and thus, the fluid is used as a shock absorbent. With this method, the prism forming surface of the light guiding plate and the fluid are brought into close contact with each other not via any air layer, and therefore, since a difference in refractive index therebetween is small, a light beam cannot be sufficiently deflected by the prism, thereby decreasing the frontal luminance with a leakage of the light beam. In addition, it is very difficult to uniformly fill and seal the fluid without any mixture of foreign matters such as bubbles with the fluid, thereby raising a problem of an increase in fabrication cost.
In the meantime, the prism sheet disclosed in Japanese Patent Application Laid-open No. 2003-215584 (Patent Literature 1) may be made of a soft elastic resin. With such a prism sheet, even if the prism collides with the light guiding plate, the vertex of the prism can be prevented from being broken, and further, the prism is restored to its original shape when the prism is separated from the light guiding plate. However, the prism sheet cannot achieve excellent transferability, unlike an ultraviolet curable resin in the prior art, and further, the radius of curvature of the vertex of the prism becomes increased in molding, thereby decreasing the frontal luminance in the liquid crystal display device.
[Patent Literature 1] Japanese Patent Application Laid-open No. 2003-215584
[Patent Literature 2] Japanese Patent Application Laid-open No. 1999-305011
[Patent Literature 3] Japanese Patent Application Laid-open No. 2001-343507
[Patent Literature 4] Japanese Patent Application Laid-open No. 2002-231030
The invention has been accomplished to solve the above-described problems experienced by the prior art. Therefore, an object of the invention is to provide a surface light source device, in which a vertex of a prism can be prevented from being broken by external force without decreasing a frontal luminance, and further, outward appearance cannot be degraded due to an optical close contact.
A surface light source device according to the invention including: a light source; a light guiding plate having uneven patterns formed for deflecting a light beam guided inward from the light source toward a light emitting plane, so as to emit the light beam from the light emitting plane in a direction substantially parallel to the light emitting plane; and a prism sheet having a plurality of prisms formed for deflecting the light beam emitted from the light emitting plane in a direction substantially perpendicular to the light emitting plane, the prisms being arranged in such a manner as to be oriented toward the light guiding plate; comprises: a transparent protecting sheet having a predetermined elasticity at the surface thereof, the surface having the predetermined elasticity facing the prisms.
In the surface light source device according to the invention, the transparent protecting sheet having the predetermined elasticity at the surface thereof is interposed between the light guiding plate and the prism sheet, so that the prism can be prevented from being broken due to the contact of the prism sheet with the light guiding plate without decreasing the frontal luminance of the surface light source device.
In an aspect of the surface light source device according to the invention, the protecting sheet includes one or a plurality of transparent rubber-like resins, each having a predetermined elasticity, formed on a transparent board.
In the aspect according to the invention, the transparent rubber-like resin is not directly on the light emitting plane of the light guiding plate or the prism forming surface of the prism sheet, but is independently formed as the protecting sheet, thus facilitating the fabrication of the protecting sheet having uniform optical characteristics. Moreover, it is possible to achieve easy handling by forming the transparent rubber-like resin on the transparent board.
In another aspect of the surface light source device according to the invention, the surface of the protecting sheet has the predetermined elasticity such that the surface is deformed only when external force is exerted on the prism sheet. In the aspect according to the invention, since the surface of the protecting sheet is not deformed in a normal state in which no external force is exerted on the prism sheet, no material for the surface of the protecting sheet is filled between the prisms formed at the prism sheet, thereby preventing any occurrence of the optical close contact, so as not to degrade the outward appearance. In contrast, if the external force is exerted on the prism sheet, the external force can be dispersed by deforming the surface of the protecting sheet, thus preventing any breakage of the prism sheet. Furthermore, when the external force is eliminated from the state in which the external force is exerted on the prism sheet, the prism sheet is restored to the state before the exertion of the external force, thereby preventing any occurrence of the optical close contact also in this case.
In a further aspect of the surface light source device according to the invention, the surface of the protecting sheet is brought into contact with a vertex of the prism, and further, has the elasticity enough to support the prism without deforming the surface. In the aspect according to the invention, the surface light source device can be reduced in thickness.
In a still further aspect of the surface light source device according to the invention, fine beads are dispersed in the protecting sheet.
In the aspect according to the invention, since the fine beads are dispersed in the protecting sheet, the prism sheet can be protected from the external force, and further, the protecting sheet can function as a diffusing plate for diffusing and transmitting an incident light beam, thus making it unnecessary to independently dispose any diffusing plate.
A liquid crystal display device according to the invention comprises: the surface light source device according to the invention; and a liquid crystal display panel. Thus, an image display screen can be free from a breakage such as a dent even if the external force is exerted on the liquid crystal display device without increasing the thickness of the liquid crystal display device.
Incidentally, the above-described constituent elements according to the invention may be arbitrarily combined with each other as possible.
Preferred embodiments according to the invention will be described below in reference to the attached drawings. Here, it is to be understood that the invention should not be restricted to the preferred embodiments, described below.
The liquid crystal panel 117 and the surface light source device 102 are arranged in such a manner that the liquid crystal panel 117 faces the light emission side of the surface light source device 102, and further, are housed inside a through hole 127 formed at the center of the holder 118. The liquid crystal panel 117 is slightly greater than the surface light source device 102. The liquid crystal panel 117 is held at a stepped surface 128 formed inside of the through hole 127 of the holder 118 by winding the periphery with a first double-sided tape 120, thereby defining a clearance between the surface light source device 102 and the liquid crystal panel 117. As a consequence, if no external force is exerted, the liquid crystal panel 117 cannot be brought into contact with the surface light source device 102.
The surface light source device 102 includes a light guiding plate 111, a prism sheet 115, a protecting sheet 112, a light source 122 and a reflecting plate 119. The light guiding plate 111 is molded with a transparent resin having a high index of refraction such a polycarbonate resin or a methacrylic resin. Moreover, diffusion patterns 124 formed into a triangular pyramid are recessed at the reverse of the light guiding plate 111 in molding the light guiding plate 111.
The light source 122 is constituted by sealing one or several LEDs in a transparent mold resin, and then, covering a surface other than a front surface of the mold resin with a white resin, although not particularly shown. A light beam emitted from the LED is reflected directly or on an interface between the mold resin and the white resin, to be then emitted from the front surface of the light source 122. The light source 122 faces, at the front surface thereof, a light incident plane 125 formed at a side surface of the light guiding plate 111.
The reflecting plate 119 is subjected to mirror-finishing by plating its surface with Ag, and it is disposed in such a manner as to face the entire reverse of the light guiding plate 111. Moreover, the reflecting plate 119 is adhesively secured at the periphery thereof to the holder 118 via a second double-sided tape 121.
The prism sheet 115 includes a prism 116 having an incident plane 134 and a reflecting plane 135 at a surface facing the light guiding plate 111. The prism 116 is molded by dropping an ultraviolet ray curable resin at an upper surface of a plastic sheet 126, pressing the ultraviolet ray curable resin by a stamper, spreading the ultraviolet ray curable resin between the stamper and the plastic sheet 126, and then, curing the ultraviolet ray curable resin with the irradiation of ultraviolet rays (i.e., photo polymerization). A surface opposite to the surface, at which the prism 116 is formed, faces the liquid crystal panel 117. The prism 116 has a uniformly cross-sectional shape in the preferred embodiment, as shown, and is formed in the entire width of the plastic sheet 126 along a direction parallel to the light incident plane 125.
The protecting sheet 112 is interposed between the light guiding plate 111 and the prism sheet 115, and is formed by laminating a transparent rubber-like resin 113 on a transparent board 114. The transparent board 114 faces a light emitting plane 123 of the light guiding plate 111: in contrast, the transparent rubber-like resin 113 faces the prism sheet 115 at the surface, at which the prism 116 is formed. As shown in
The optical close contact herein signifies a status which induces a phenomenon in which patterns different in luminance (i.e., optical close contact patterns) such as a region A and a region B (i.e., a region having a satin pattern) accidentally occur when a light beam transmitting the prism sheet 115 is observed, as shown in
Next, explanation will be made on each of parameters shown in
The minimum thickness of the transparent rubber-like resin 113 need be about a half of a height of the prism 116. This is because when the prism 116 is pushed down to a half level of the transparent rubber-like resin 113, the transparent rubber-like resin 113 raised by the embedded prism 116 is relieved to the air layer between the prisms 116, and then, fills the entire air layer between the prisms 116. For example, in the case where the height of the prism 116 is 30 μm, the transparent rubber-like resin need be 15 μm in thickness to the minimum.
It is desirable from the viewpoint of thinness that the thickness of the protecting sheet 112 should be set to about 65 μm to 250 μm. If the protecting sheet 112 is thinner than 65 μm, the protecting sheet 112 is weak in stiffness, and therefore, the protecting sheet 112 is bent by its own weight in assembling, thereby deteriorating handling performance, or the protecting sheet 112 is warped due to a difference in coefficient of thermal expansion between the transparent rubber-like resin 113 and the transparent board 114 in the case where the device is left at high temperature for a long period of time inside of an automobile in summer or the like, whereby the optical close contact is liable to occur between the protecting sheet 112 and the light guiding plate 111 or between the protecting sheet 112 and the prism sheet 115. With a thickness to some extent, the external force P acts, so that the protecting sheet 112 can be restored even when the protecting sheet 112 is locally warped. However, if the protecting sheet 112 is thinner than 65 μm, there may possibly occur the optical close contact between the protecting sheet 112 and the light guiding plate 111 or between the protecting sheet 112 and the prism sheet 115.
Alternatively, formation of finely projecting patterns at the reverse of the transparent board 114 or the light emitting plane 123 of the light guiding plate 111 can prevent any optical close contact from occurring as a result of the optical interference caused by the air layer between the light emitting plane 123 of the light guiding plate 111 and the protecting sheet 112. When the projecting patterns are formed at the light guiding plate 111, recessed patterns are formed at a die by subjecting the die on a side of the light emitting plane 123 of the light guiding plate 111 to blasting, so that the projecting patterns are formed on the light emitting plane 123 by inversing the recessed patterns formed on the die when the light guiding plate 111 is formed. Otherwise, the projecting patterns can be formed on the transparent board 114 by coating a side of the transparent board 114 facing the light emitting plane 123 of the light guiding plate 111 with a transparent resin including fine powder (i.e., beads) in mixture (i.e., bead coating). In this case, it was confirmed that no optical close contact occurred if the size of a bead was greater than 2 μm. Moreover, the finely projecting patterns are formed at the reverse of the transparent board 114 or the light emitting plane 123 of the light guiding plate 111, or the reverse of the transparent board 114 or the light emitting plane 123 of the light guiding plate 111 is subjected to the bead coating, thereby equipping the prism sheet 115 or the light guiding plate 111 with a light diffusing effect, so as to reduce variations in luminance.
As shown in
That is to say, if the prism 116 is broken by the external force P, the broken portion of the prism 116 is changed in orientation in the same manner as in the prior art shown in
In the liquid crystal display device 101 in the first preferred embodiment, requirements capable of satisfying the above-described load resistance characteristics were found, through an experiment, to be such that the universal hardness was greater than 0.2 N/mm2 and smaller than 2.3 N/mm2 and the elastic restoration power was 70% or more.
Prior to explaining an experiment for determining the ranges of the universal hardness (HU) and elastic restoration power, simple explanation will be made on the universal hardness and the elastic restoration power. First of all, the universal hardness is obtained by a test with a configuration shown in
The above-described test reveals a graph illustrating the relationship between the pushing load F and the pushing quantity h in
Subsequently, the universal hardness and the elastic restoration power were measured by the test explained in reference to
Next, a predetermined load F′ was exerted on a plane opposite to the light emitting plane 123 of the light guiding plate 111, and then, the surface light source device 102 was lighted. As a result, it was visually determined as to whether or not the appearance was marred. In addition, it was visually confirmed as to whether or not the protecting sheet 112 (i.e., each of Samples 1 to 6) was damaged. Incidentally, the prism sheet 115 was made of a material having a density of 9.5×10−4 g/mm3 and a universal hardness of about 9.2 N/mm2.
With the configuration of the liquid crystal display device 101 in the first preferred embodiment, the optical close contact occurred if the universal hardness was 0.2 N/mm2 or less (Sample 6); the vertex of the prism 116 was broken and the transparent rubber-like resin 113 remained dented if the universal hardness was 2.3 N/mm2 or more (Samples 4 and 5). In addition, the vertex of the prism 116 was broken and the transparent rubber-like resin 113 remained dented if the elastic restoration power was 70% or less (Samples 4 and 5).
It is found from the above description that the universal hardness need be more than 0.2 N/mm2 and less than 2.3 N/mm2 and the elastic restoration power need be 70% or more in order to secure the load resistance in the configuration of the liquid crystal display device 101 in the first preferred embodiment.
As a consequence, the protecting sheet 112 including the transparent rubber-like resin 113 formed on the transparent board 114 is interposed between the light guiding plate 111 and the prism sheet 115 in such a manner that the transparent rubber-like resin 113 is disposed on the side of the prism sheet 115, and further, the transparent rubber-like resin 113 is featured in that the transparent rubber-like resin 113 cannot be deformed only by the self weight of the prism sheet 115, that is, the transparent rubber-like resin 113 is deformed only with the application of the external force stronger than usual, thus preventing any occurrence of the optical close contact in the normal state, and preventing any breakage of the prism sheet 115 or any damage on the protecting sheet 112 even if the external force acts within the imaginary range while suppressing the decrease in frontal luminance to the minimum. In other words, the protecting sheet 112 including the transparent rubber-like resin 113 having the proper universal hardness and elastic restoration power, which were measured by the method explained in reference to
Furthermore, the protecting sheet 112 is not formed directly on the light guiding plate 111 but formed as an independent sheet, thus facilitating the fabrication of the protecting sheet 112 having the uniform optical characteristics. Moreover, the protecting sheet 112 is not deformed by the self weight of the prism sheet 115, thus making it unnecessary to dispose a special fixing mechanism for fixing the prism sheet 115. Additionally, the air layer can be held between the prisms 116 formed on the prism sheet 115 only by placing the prism sheet 115 on the protecting sheet 112, thus efficiently emitting the light beam in the vertical direction with the inexpensive configuration even if the surface light source device 102 is not made thicker than required.
A protecting sheet in a second preferred embodiment is different in configuration from the protecting sheet 112 for use in the liquid crystal display device 101 in the first preferred embodiment.
Consequently, since rolls can be allotted to the first transparent rubber-like resin 212 and the second transparent rubber-like resin 213, respectively, required performance (i.e., a load resistance) can be implemented within a range wider than that of the characteristics of the protecting sheet 112 in the first preferred embodiment by effectively combining transparent rubber-like resins having different characteristics with each other. In addition, since there are more kinds of usable materials, cost reduction is achieved with a more inexpensive material or a high-value-added product can be fabricated by using a material having a new function. Incidentally, although three or more transparent rubber-like resins may be laminated, the total number of layers should be preferably smaller from the viewpoint of mass production, and therefore, two layers or so should be desirably laminated. It is to be understood that the degree of freedom of combination of resins for use in each of layers should become greater as the number of layers becomes greater.
A protecting sheet in a third preferred embodiment is different in configuration from the protecting sheet 112 for use in the liquid crystal display device 101 in the first preferred embodiment.
Here, a frontal luminance becomes lower than that in the protecting sheet without any beads or the like mixed in the transparent rubber-like resin 215. Therefore, it is necessary to mix the beads 216 at a density enough to secure the required frontal luminance. Additionally, there may be provided a function of readily correcting the variations in luminance by partly varying the density of the beads 216 in the transparent rubber-like resin 215.
In the third preferred embodiment, the protecting sheet 214 may be equipped with a diffusing plate by dispersing the beads 216 in not the transparent rubber-like resin 215 but the transparent board 114, or dispersing the beads 216 in both of the transparent rubber-like resin 215 and the transparent board 114.
Although the description has been given of the liquid crystal display device of a single-sided light emitting type according to the invention, the protecting sheet may be incorporated in a liquid crystal display device of a double-sided light emitting type and a double-sided light emitter for use in such a liquid crystal display device.
The protecting sheet 112 for use in the fourth preferred embodiment integrally includes a transparent rubber-like resin 113 laminated at an upper surface of a transparent board 114 and another transparent rubber-like resin 302 laminated also at a lower surface of the transparent board 114. Although the transparent rubber-like resin 302 laminated at the lower surface may be made of the same material as that of the transparent rubber-like resin 113 laminated at the upper surface, they may be made of different materials as long as it is a transparent rubber-like resin.
The transparent rubber-like resin 302 formed at the lower surface is air-tightly brought into close contact with a light emitting plane 123 of a light guiding plate 111. The protecting sheet 112 and the light guiding plate 111 are integrated with each other by bringing the transparent rubber-like resin 302 into close contact with the light emitting plane 123. In order to bring the transparent rubber-like resin 302 into close contact with the light emitting plane 123, the transparent rubber-like resin 302 may be brought into close contact with the light emitting plane 123 by utilizing the viscoelasticity of the transparent rubber-like resin 302, or the transparent rubber-like resin 302 may be brought into close contact with the light emitting plane 123 by the use of an adhesive agent or matching oil. Here, since a light beam transmits through the protecting sheet 112, a material of each of the layers constituting the protecting sheet 112 should preferably have little light absorption and a low light diffusion.
Although the air layer has been formed between the light emitting plane 123 and the reverse of the transparent board 114 by forming the projecting pattern on either the light emitting plane 123 or the transparent board 114 or mixing the beads in the first preferred embodiment, the light emitting plane 123 and the transparent rubber-like resin 302 are brought into close contact with each other in the fourth preferred embodiment, thereby forming no air layer between the light guiding plate 111 and the protecting sheet 112.
As a consequence, the projecting pattern or the beads, which are provided for preventing any close contact in the first preferred embodiment, become unnecessary in the liquid crystal display device 301 in the fourth preferred embodiment, thereby enhancing the frontal luminance of the liquid crystal display device 301 since the light beam emitted from the light guiding plate 111 cannot be diffused due to the projecting pattern or the beads. However, the protecting sheet 112 can be displaced in a direction of the force in parallel to the light guiding plate 111 if the force is slantwise exerted on the prism sheet 115 in the configuration of the first preferred embodiment in which the protecting sheet 112 is not brought into close contact with the light guiding plate 111, thereby producing a more excellent effect of impact absorption.
Incidentally, the lower surface of the transparent board 114 may be brought into close contact with the light emitting plane 123 with the adhesive agent or the matching oil also in the case of the use of the protecting sheet 112 including the transparent board 114 and the light emitting plane 123, like in the first preferred embodiment.
Although the transparent rubber-like resins 113 and 302 are laminated on both sides of the transparent board 114 in the fourth preferred embodiment, the protecting sheet 112 may include only the transparent rubber-like resin 113 in the case of small importance of the handling performance of the protecting sheet 112. In this case, the prism sheet 115 is protected at the upper surface of the transparent rubber-like resin 113 whose lower surface is brought into close contact with the light emitting plane 123 of the light guiding plate 111.
The above-described fine patterns 312 are formed at the surface of the protecting sheet 112, so that the transparent rubber-like resin 113 is hardly brought into close contact with the vertex of the prism 116, thus more preventing any occurrence of an optical close contact. In addition, it is possible to enhance the effect of the prevention of the crush of the vertex of the prism 116.
Additionally, a light beam p transmitting through the protecting sheet 112 can be deflected in an arbitrary direction by the effect of the fine patterns 312 by forming the fine pattern 312 into a conical shape such as a triangle cone or a circular cone, as shown in
A vertical distance between the stepped surface 128 and the step 322 is substantially equal to the thickness of the prism sheet 115. The prism sheet 115 is pressed at the periphery thereof by a first double-sided tape 120 stuck to the stepped surface 128.
Since the prism sheet 115 is placed on the protecting sheet 112 in the liquid crystal display device 101 in the first preferred embodiment, the hardness of a transparent rubber-like resin 113 need be set to a level enough to prevent any optical close contact by the self weight of the prism sheet 115. However, the protecting sheet 112 or the prism sheet 115 is flexed due to the deformation or the like of the holder 118 depending on the configuration or usage of the liquid crystal display device, thereby raising a possibility of occurrence of the optical close contact all the time with the application of a load larger than the self weight of the prism sheet 115 on the protecting sheet 112.
Thus, the clearance 323 is defined between the prism sheet 115 and the protecting sheet 112 as measures against the above-described possibility in the sixth preferred embodiment. Specifically, even if the protecting sheet 112 is warped under severe conditions in which a heat cycle occurs (for example, from −50° C. to +100° C.) or the holder 118 is flexed due to its low rigidity to constantly warp the protecting sheet 112 or the prism sheet 115 with the application of external force in the liquid crystal display device 321 in the sixth preferred embodiment, the prism 116 of the prism sheet 115 and the protecting sheet 112 can be prevented from being brought into quasi-stationary contact with each other. Moreover, the transparent rubber-like resin 113 can prevent any breakage of the vertex of the prism 116 in the case where the vertex of the prism 116 is brought into contact with the protecting sheet 112 with the application of the external force in addition to the occurrence of the warp.
Otherwise, in order to prevent the protecting sheet 112 from floating, the periphery of the lower surface of the protecting sheet 112 may be stuck to the periphery of the upper surface of the light guiding plate 111 via a third double-sided tape 335 out of an effective region of the light guiding plate 111 in a liquid crystal display device 334 in another modification, as shown in
Number | Date | Country | Kind |
---|---|---|---|
2004-355785 | Dec 2004 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/JP2005/019892 | 10/28/2005 | WO | 00 | 3/4/2008 |