KR100719826B1 - Surface light source device of side light type and liquid crystal display - Google Patents

Abstract

The side light type surface light source device mounted to the liquid crystal display device for illuminating the liquid crystal display panel includes an additional sheet member having a rectangular shape disposed along the exit surface of the light guide plate. On each of the plurality of sides of the additional sheet member, a positioning portion for positioning the additional sheet member with respect to the approximately center portion of each side is provided. A frame member for stacking and mounting the light guide plate and the additional sheet member is provided, and the positioning portion is guided by a recess formed in the frame, including a flange portion protruding from the side of the additional sheet member. The frame has an edge portion that partially covers the exit face along the incident cross section. One of the sides of the additional sheet member positioned by the positioning unit may be the side corresponding to the incident end surface. The recess is formed so that the thickness remains to allow injection molding. If there is a separate additional sheet member between the exit surface, the thickness does not exceed the total thickness of the additional additional sheet member. It is possible to prevent misalignment and bending of additional sheet members such as a polarization separating sheet and a prism sheet while realizing a thin structure.

Sight light type surface light source device

Description

Side light type surface light source device and liquid crystal display device {SURFACE LIGHT SOURCE DEVICE OF SIDE LIGHT TYPE AND LIQUID CRYSTAL DISPLAY}

BRIEF DESCRIPTION OF THE DRAWINGS It is a top view which looked at the side light type surface light source device which concerns on embodiment of this invention from the emission surface side.

FIG. 2 is an exploded perspective view showing a liquid crystal display device equipped with the surface light source device shown in FIG. 1.

FIG. 3 is a cross-sectional view showing a vicinity of an incident surface of a light guide plate of the liquid crystal display shown in FIG. 2.

4 is a plan view showing a relationship between an additional sheet member such as a light diffusion sheet and a frame.

5 is a plan view illustrating an example in which positioning of the polarization separation sheet is performed using long sides.

6 is a plan view illustrating an example in which positioning of the polarization separation sheet is performed using two adjacent sides.

7 is a cross-sectional view showing the main portion of a conventional side light type surface light source device.

FIG. 8 is an exploded perspective view showing the side light type surface light source device shown in FIG. 7.

9 is a plan view for explaining the bending of the additional sheet member generated in the prior art.

10 is a plan view illustrating anisotropy of the linear expansion coefficient of the polarization separation sheet.

The present invention relates to a side light type surface light source device and a liquid crystal display device, and more particularly, to a side light type surface light source device having an additional sheet member such as a prism sheet and a polarization separating sheet on an emission surface of a light guide plate, and a surface light source thereof. It relates to a liquid crystal display device which is backlighted in the device.

The side light type surface light source device has been conventionally applied to, for example, a liquid crystal display device, and illuminates the liquid crystal panel from the back side. This arrangement is suitable for thinning the overall shape of the device.

The side light type surface light source device is usually provided with a rod type light source such as a cold cathode tube as a primary light source. The primary light source is disposed on the side of the light guide plate (plate type light guide). Illumination light emitted from the primary light source is introduced into the light guide plate through a cross section (incident cross section) of the light guide plate. The introduced illumination light propagates in the light guide plate, and in the process, emission is generated from one major surface (emission surface) of the light guide plate.

In many cases, sheet members such as a prism sheet and a polarization separating sheet are additionally disposed on the light emitting plate. In the present specification, the sheet member disposed on the emission surface of the light guide plate as a component of the side light type light source device will be referred to as an "additional sheet member".

When the additional sheet member is arranged, the output light from the light guide plate becomes the output illumination light via the additional sheet member (one or more sheets). This output illumination light is used for illumination of liquid crystal panels.

As the light guide plate, those of a type having a substantially uniform plate thickness and those of a type having a tendency to decrease the plate thickness by moving away from the primary light source are known. In general, the latter emits illumination light more efficiently than the former.

8 is an exploded perspective view showing a general configuration of a side light type surface light source device using the latter type light guide plate. FIG. 7 shows a main cross section of the device shown in FIG. 8. Referring to both drawings, the side light type surface light source device 1 includes a cold cathode lamp (fluorescent lamp) 2 and a light guide plate 3 having a reflector disposed behind.

Moreover, the reflection sheet 4 is arrange | positioned at the back surface 3C side of the light guide plate 3, and the additional sheet member 5, 6, 7 is arrange | positioned at the emission surface 3B side in order to fulfill various functions.

Various things are adopted for the additional sheet members 5, 6, 7. Typical additional sheet members include prism sheets, light diffusion sheets, polarization separation sheets, protective sheets, and the like. As can be seen from FIG. 8, the exit surface 3B of the light guide plate 3 is substantially rectangular, and therefore, the additional sheet members 5, 6 and 7 are also substantially rectangular. The light guide plate 3 is composed of a transparent resin such as an acrylic resin, a resin material having a scattering power therein (light scattering light guide), or the like.

The illumination light supplied from the fluorescent lamp 2 is introduced into the light guide plate 3 through the incident surface 3A and propagates toward the end while repeatedly reflecting between the exit surface 3B and the back surface 3C. In the meantime, the light-scattering operation is performed inside the light guide plate 3 (when the light scattering light guide member is adopted), the back surface, or the like. In the case where the reflective sheet 4 made of the diffuse reflection member is adopted, the diffuse reflection action is also received.

Through this process, the illumination light is slowly emitted from the exit surface 3B. The reflective sheet 4 returns the light leaked from the back surface 3C into the light guide plate 3 to prevent light energy loss.

As is well known, light exit from exit surface 3B occurs mainly in the inclined front. This property is called directed emergence. The prism sheet, which is a typical additional sheet member, is frequently used because it corrects this output orientation and directs the output light in the front direction, for example. On the other hand, the light diffusion sheet has a function of smoothing the illumination light by varying the traveling direction of the light. In addition, the polarization separation sheet has a function of reflecting a polarization component orthogonal thereto while transmitting a specific polarization component. The protective sheet is used to protect other sheets and the like from damage, dust adhesion, and the like.

The frame 8 shown at the top in FIG. 8 is used to collectively support all members included in the surface light source device 1. The frame 8 is provided with a rim 8A having a shape and a size surrounding the edge of the exit surface 3B.

As shown in Fig. 7, the frame 8 supports the reflection sheet 4, the light guide plate 3, and the additional sheet members 5, 6, 7 in the c-shaped portion. The fluorescent lamp 2 and the reflector behind it are supported so as to be surrounded by the c-shaped portion. In assembling the liquid crystal display device, the surface light source device 1 made of all members including the frame 8 is attached to the rear surface of the liquid crystal display panel (not shown).

However, there is a demand for whether the thickness of the device can be made thinner with respect to such a surface light source device 1 or a liquid crystal display device equipped with the same. From this point of view, when the conventional apparatus shown in Figs. 7 and 8 is viewed, it is understood that the edge portion 8A of the frame 8 has a considerable thickness D, which is one factor that prevents the thinning of the apparatus. have.

Therefore, if the edge portion 8A is omitted, the hatched portion is removed, and the thickness almost equivalent to D can be reduced. Also in this case, a slight gap is required between the liquid crystal panel and the additional sheet member 7 in order to avoid direct contact between the liquid crystal panel and the exit surface 3B of the outermost additional sheet member 7. It may be much smaller than the thickness (D).

However, if the liquid crystal display panel is disposed close to the emission surface 3C by omitting the edge portion 8A in this way, the positioning of the additional sheet member disposed on the emission surface will not be accurately performed. There is a fear that the alignment relationship between 8) and the exit surface 3C cannot be maintained.

FIG. 9 is a diagram schematically showing this, in which a state in which the additional sheet member is erroneously arranged with respect to the frame 8 at the time of assembling the apparatus is shown. In such a case, a part of the sheet member may be pinched between the frame 8 and the rear surface of the liquid crystal display panel. If the liquid crystal display device is assembled by overlooking this, the additional sheet member may be bent (curved wave). This bending becomes a factor that breaks the uniformity of the output illumination light of the surface light source device. In addition, the liquid crystal display panel can be observed in the form of unnatural contrast.

In particular, when such bending occurs at a short pitch, it is observed that the contrast is repeated on the LCD panel side, and the display quality is significantly reduced. In addition, even when the pitch of the bend is large, a part of the additional sheet member may excessively approach the rear surface of the liquid crystal display panel, and in some cases, there is a possibility of generating an interference fringe on the near side which is in contact. The interference fringe also naturally degrades the quality of the output illumination light and the display quality of the liquid crystal display using the same.

If the quality defect caused by this cause is found in the inspection process, it is necessary to remove the surface light source device from the liquid crystal display panel, arrange the curvature of the additional sheet member, and then reassemble the liquid crystal display device carefully. In addition, the replacement of the additional sheet member may be necessary. In addition, if quality defects are missed in the inspection process, defective products are shipped.

Flexural problems are also caused by temperature changes. Especially when the polarization separation sheet is disposed as an additional sheet member, remarkable bending occurs well. It has a structure in which most of the polarization separation sheet is rolled and laminated with a sheet member (for example, a sheet member made of liquid crystal polymer material) having optical anisotropy, and the value of the coefficient of linear expansion varies greatly depending on the direction, and the maximum value of the coefficient of linear expansion is very large. Because.

FIG. 10 is a plan view illustrating this, in which the linear expansion coefficients in the transmission axis direction and the reflection axis direction orthogonal to the polarization separation sheet which have been used are shown. In this example, the coefficient of linear expansion varies by a factor of 5 or more depending on the direction (1.5 × 10 ⁻⁵ cm / cm / ° C. and 8.1 × 10 ⁻⁵ cm / cm / ° C.). Such a member easily causes bending deformation due to temperature change.

In the case of the prism sheet that has been typically used for comparison, the coefficient of linear expansion is 2.0 × 10 ⁻⁵ cm / cm / ° C.

Summary and purpose of the invention

SUMMARY OF THE INVENTION The present invention has been made under the above-described background, and is a liquid crystal display in which a side light type surface light source device and a surface light source device thereof that can prevent bending or misalignment of an additional sheet member disposed on an exit surface of a light guide plate are applied to illumination of a liquid crystal display panel. It is an object to provide a device. Moreover, through this, this invention aims at the improvement of the illumination quality of a side light type surface light source device, and the display quality of a liquid crystal display device.

The present invention provides a side light type surface light source device having a light guide plate having an emission surface and a rear surface, a primary light source for supplying illumination light from an incident end surface of the light guide plate, and an additional sheet member having a rectangular shape disposed along the emission surface, and A side light type surface light source device such as the above is applied to a liquid crystal display device for mounting a liquid crystal display panel.

According to a basic feature of the invention, at least two sides of the additional sheet member are provided with a positioning portion for positioning the additional sheet member with respect to the approximately center portion of each side.

  This basic feature makes it possible to stably position the additional sheet member. That is, unlike the case of positioning by one side of the rectangle as in the related art (see Fig. 7), the state of attaching the additional sheet member at an angle (see Fig. 9) is prevented.

The positioning portion is provided on, for example, two opposite sides of the additional sheet member. In this case, it is easier to avoid the attachment of the additional sheet member at an angle (see FIG. 9), and the positioning accuracy can be improved.

In addition, positioning of the additional sheet member with respect to the approximately center portion of each side of the positioning portion improves resistance to temperature changes. That is, since the expansion or contraction due to the temperature change can be divided from the center to both sides, the phenomenon that the cross section of the additional sheet member hits various members is less likely to occur. As a result, bending caused by collision with various members of the cross section of the additional sheet member is prevented.

According to a typical embodiment of the present invention, there is further provided a frame member for laminating and mounting the light guide plate and the additional sheet member. And the positioning part is guided by the recessed part provided in the frame, including the flange part which protrudes from the side of the additional sheet member. By adopting this form, the additional sheet member can be positioned with a simple and convenient configuration.

Further, in one preferred embodiment, the frame has a border portion that partially covers the exit surface along at least the incident cross section of the light guide plate, and one of the sides positioned by the positioning portion of the additional sheet member corresponds to the incident cross section. It becomes a mutation. The edge portion is formed in the recess formed in the frame such that a very thin thickness remains on the exit surface side. However, "thin thickness" is designed in the range which allows manufacture by injection molding.

Adopting such a structure prevents light leakage on the light source side even when the recess is formed in the frame.

In addition, when a plurality of additional sheet members are disposed, a separate additional sheet member is disposed between the outermost additional sheet member and the exit surface. In this case, it is preferable that the remaining thickness of the edge portion is set not to exceed the thickness of the additional sheet member. In the case where two or more "additional sheet members" are present, it is preferable that they are set not to exceed the thickness of these totals.

Even in the case where the linear expansion coefficient of one of the plurality of additional sheet members laminated in this setting is large, bending due to thermal expansion of the additional sheet member can be prevented. In addition, light leakage can be prevented.

As the additional sheet member, for example, a prism sheet, a polarization separating sheet, a light diffusion sheet, a protective sheet, and the like may be used. However, the position of the additional sheet member is particularly significant when the positioning according to the present invention is performed. This is because, as described above, the polarization separation sheet has a property of generating bending in particular.                         

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

Embodiment

2 and 3, there is shown a liquid crystal display device 10 equipped with a side light type surface light source device 12 for backlighting of the liquid crystal display panel 12. As shown in FIG. The display screen size in this example is 15 inches (diagonal).

The surface light source device 12 includes a frame 13 on which all members are mounted. First, the reflector 24 (refer FIG. 3, not shown in FIG. 2), the fluorescent lamp 14, and the cover 15 are arrange | positioned. The light guide plate 17 is arranged such that its incident end face 17A follows the fluorescent lamp 14. The light guide plate 17 has a wedge-shaped cross section, and the incident end surface 17A is a cross section on the thickness side. The reflective sheet 16 is disposed along the back surface 17B of the light guide plate 17.

On the exit surface 17C of the light guide plate 17, a light diffusion sheet 18, a prism sheet 19, 20, a polarization separating sheet 21 and a protective sheet 22 are disposed as additional sheet members.

The light guide plate is an injection molded body made of transparent resin such as acrylic resin (PMMA resin), for example. Back surface 17B is partially roughened. Thereby, the illumination light propagating inside the light guide plate is scattered, and the emission from the emission surface 17C is promoted. The installation density per unit area of the rough surface is adjusted so that the emission intensity from the exit surface 17C is made uniform.

The reflective sheet 16 is composed of a sheet member which diffusely reflects or specularly reflects the illumination light, and reflects the illumination light leaking from the back surface 17B of the light guide plate 17 to return to the light guide plate 17. This prevents illumination light loss.

The light diffusion sheet 18 is an additional sheet member made of PET having weak light diffusion, and weakly scatters the illumination light emitted from the exit surface 17C. As a result, the rough surface formed on the back surface 17B, the minimum radiance due to the light that comes through the reflection of the edge of the light guide plate, and the like are not visible.

The prism sheets 19 and 20 are additional sheet members made of polycarbonate, for example, and a prism surface (light control surface) is formed on the side of the liquid crystal display panel 11. These prism faces are provided with a large number of projection strings as partially enlarged by symbols A and B. As shown in FIG. Each protrusion has a pair of slopes 19A, 19B or 20A, 20B and has a triangular shape in cross section. The extension direction of each projection line of the prism sheet 19 is substantially parallel to the incident end surface 17A, and the extension direction of each projection line of the prism sheet 20 is substantially perpendicular to the incident end surface 17A.

As is well known, illumination output light whose directivity is corrected can be obtained in any of the in-plane parallel to the in-plane perpendicular to the incident end surface 17A by the orientation of the prism sheet 20. In most cases, the directivity correction is made so that a large amount of illumination light is output toward the periphery in the front direction.

The action of the polarization separating sheet 21 is also well known. That is, the polarized light component in any specific direction of the transmitted light of the prism sheet 20 is transmitted and the polarized light component perpendicular to the specific direction is reflected. Here, the "polarization component in a specific direction" is set so as to correspond to the component of the polarization plane which can contribute to image formation in the liquid crystal display panel 11. That is, the polarization component contributing to image formation by the liquid crystal display panel 11 is transmitted, and the remaining components are reflected.

Most of the components reflected by the polarization splitting sheet 21 are incident on the polarization splitting sheet 21 again through various optical paths to be given a chance of transmission. This is because the polarizing component is allowed to pass through various optical paths. Therefore, a substantial part of the reincident light passes through the polarization separating sheet 21 and contributes to image formation in the liquid crystal display panel 11.

As described above, the re-reflected light that does not use the chance is again given the chance of transmission through the polarization separation sheet again through various optical paths. Through this recycling process, the polarization separation sheet 21 increases the proportion of the illumination light that contributes to image formation.

The protective sheet 22 is an additional sheet member made of almost transparent polycarbonate, and protects another additional sheet member. For example, when transporting the surface light source device 12 to the assembly site of the liquid crystal display device, the polarization separating sheet 21 is protected from damage.

Next, the positioning and the holding | maintenance of the additional sheet members 18-22 arrange | positioned at the exit surface 17C side of these light guide plates 17 are demonstrated in detail.

First, the frame 13 is an injection molded product of a white resin, and integrally includes a wall portion surrounding side surfaces of the light guide plate 17, the reflective sheet 16, and the like, and an elongated plate 13C connecting the wall portions. . The frame 13 prevents dropping to the back side (bottom side) of the light guide plate 17 and the like by the plate 13C and at the same time prevents deformation. In addition, the whole of the weight is reduced by removing the thick portion leaving the plate 13 at the bottom of the frame 13.

The light guide plate 17 and the frame (the distance along the direction parallel to the incidence end surface 17) between both wall portions of the frame 13 extending to sandwich the side surface (wedge shape) of the light guide plate 17 therebetween. 13) in consideration of the deviation (manufacturing error) of the width (lengthwise dimension of the incident cross section 17) of the back and the like, it is set to have a slight clearance. That is, the space is not actively left between the side surface (wedge shape) of the light guide plate 17.

On the other hand, as shown in FIG. 3, the space of the light guide plate 17 is set so that a space having a predetermined width is left on the incident end surface 17A side of the light guide plate 17 in the depth direction (in this example, the longitudinal direction of the light guide plate).

Moreover, the front-end | tip part of the frame 13 on the exit surface 17C side is provided with the edge part 13D, extending so that a part of exit surface 17C may be covered. The reflector 24 and the fluorescent lamp 14 are provided in the space formed between the frame 13 and the incident end surface 17A. The cover 15 is attached after installation of the reflector 24 and the fluorescent lamp 14.

The cover 15 is composed of a plate-like member having elasticity. Thus, as shown in FIG. 3, after placing the light guide plate 17 on the frame 13, the light guide plate 17 is disposed between the cover 15 and the edge portion 13D by using the elasticity of the cover 15. The incidence end surface 17A side of the can be inserted. This prevents the light guide plate 17 from falling off to the exit surface side.

In addition, since the edge portion 13D and the emission surface 17C are in close contact with each other, a gap is formed therein, whereby the phenomenon that the illumination light leaks toward the liquid crystal display panel 11 (so-called light leakage) is prevented.

Referring to Fig. 2, the frame 13 usually has a flange 13A integrally at each corner of both wall portions on the short side. These flanges 13A are used when the liquid crystal display panel 11 and the surface light source device 12 are integrated by a metal frame (not shown) to be combined with the frame 13.

The frame 13 also has a projection 13E which abuts on the side of the liquid crystal display panel 11 inside the wall portion. When the liquid crystal display panel 11 and the surface light source device 12 are integrated, the liquid crystal display panel 11 is guided by the projection 13E so that the position shift with respect to the direction along the inside of the display surface of the liquid crystal display device 11 is eliminated. Is prevented.

In addition, when the frame 13 is integrated with the liquid crystal display panel 11, the cross section of the wall portion abuts on the rear surface of the liquid crystal display panel 11 and is minutely disposed between the rear surface of the liquid crystal display panel 11 and the protective sheet 22. One gap is installed. As a result, the liquid crystal display panel 11 can be positioned at a small distance from the light guide plate 17.

It should be noted here that this small distance is small compared to the above-described thickness D (see FIG. 7). In this respect, it can be seen that the present embodiment is advantageous for thinning the overall shape.

FIG. 4 is a plan view of the frame 13 viewed from the exit surface 17C side of the light guide plate 17, with the additional sheet members 18, 19, 20, 22 and the frame 13 except for the polarization separating sheet 21; The relationship between In addition, in FIG. 4, illustration of recessed part 30A, 30B (refer FIG. 1) formed separately on the frame 13 is abbreviate | omitted as mentioned later.

As shown in Fig. 4, the light diffusing sheet 18, the prism sheets 19, 20 and the protective sheet 22 are emitted except for the portion on the incident end surface 17A side covered by the edge portion 13D. It has a shape which can cover and hide the surface 17C.

And the wall part of the frame 13 can be guided when arrange | positioning these additional sheet members 18, 19, 20, 22 in the inner surface.

In addition, the frame 13 is such that even if these sheet members 18, 19, 20, 22 are thermally expanded in accordance with the temperature change, the edges thereof do not strike the inner surface of the wall portion. That is, predetermined clearance is set with respect to the external dimension of each additional sheet member 18, 19, 20, 22, and the inner surface dimension of a wall part is set. In addition, in order to reliably prevent a collision due to temperature change, these additional sheet members 18, 19, 20, and 22 can be positioned with high precision by a flange as described below.

Each of the additional sheet members 18, 19, 20, 22 is provided with a pair of flanges 28 on the wedge tip side. The frame 13 is provided with the recessed part 13F as shown in the cross section of the wall part of the wedge tip side so that these flanges 28 can be guided. Here, the flange 28 has a cross section on the wedge tip side of the light guide plate symmetrically with respect to the center line LO dividing each short side of these additional sheet members 18, 19, 20, 22 into a rectangular shape. Installed to come out. On the other hand, the recessed portion 13F of the frame 13 for guiding the flange 28 is provided with a predetermined dimensional accuracy. This recess 13F guides the additional sheet members 18, 19, 20, 22 to enable their correct orientation. That is, the obliquely arranged arrangement (see Fig. 9) is avoided.

The additional sheet members 18, 19, 20, and 22 fix the flange 28 to the frame 13 using double-sided tape (indicated by hatched in Fig. 4). Thereby, an accident (falling out of the frame 13, position shift, etc.), such as the case where the surface light source device 12 is transported in the assembly process with a liquid crystal display panel, is prevented.

The means for fixing the additional sheet members 18, 19, 20, and 22 to the frame 13 is not limited to double-sided tape, and suitable fixing means such as pins or screws may be used.

Next, the positioning and fixing of the polarization separation sheet 21 will be described. FIG. 1 is a plan view of the frame 13 viewed from the emission surface 17C side of the light guide plate 17, and illustrates the relationship between the polarization separating sheet 21 and the frame 13. In addition, illustration of the recessed part 13F (refer FIG. 4) mentioned above on the frame 13 is abbreviate | omitted in FIG.

As shown in FIG. 1, the polarization splitting sheet 21 has a shape that can cover and hide the exit surface 17C except for a portion on the incident end surface 17A side covered by the frame edge portion 13D. .

And the wall part of the frame 13 can be guided when arrange | positioning these polarization separation sheets 21 in the inner surface.

The frame 13 is such that the edge does not hit the inner surface of the wall even when the polarization separation sheet 21 is thermally expanded in accordance with the temperature change. That is, in order to reliably prevent the collision by the temperature change, the polarization separation sheet 21 can also be positioned with high accuracy by the flange as described below.

That is, the polarization separation sheet 21 is provided with flanges 29A and 29B on the wedge tip side and the incident surface incidence end surface 17A side, respectively. On the other hand, the frame 13 has recesses 30A and 30B so as to guide the flanges 29A and 29B as enlarged and depicted by the symbols C and D. FIG.

The flanges 29A and 29B have a center line LO such that the edges of the cross section side and the incidence cross section 17A side of the wedge tip side protrude in a rectangular shape on the center line LO dividing the short sides of the polarization separation sheet 21 in two. It is formed in a symmetrical shape with respect to.

On the other hand, the frame 13 enables the accurate orientation of the sheet 21 while the recesses 30A and 30B are provided with a predetermined dimensional accuracy and guide the polarization separating sheet 21. That is, the obliquely inclined arrangement (see Fig. 9) is avoided.

At present, considering the case where the polarization separation sheet 21 is thermally expanded due to temperature change, the edge of the sheet 21 hits the inner wall portion of the recesses 30A and 30B at the portions of the flanges 29A and 29B. As a result, the flanges 29A and 29B are stressed. However, stressed is a narrow width (WI) range. Therefore, the stress which the whole polarization separation sheet 21 receives does not become large. The width WI is, for example, about 15 mm. Generally it is preferable that it is 20 mm or less, especially 10 mm or less.

The protruding lengths W2 of the flanges 29A and 29B only need to have a length that can be reliably positioned by the recesses 30A and 30B, but generally it is 2 mm or more.

The concave portions 30A and 30B are formed of an additional sheet member (herein, the light diffusion sheet 18 and the prism) in which the remaining thickness T after the formation thereof is disposed on the inner side (the light guide plate 17 side) than the polarization separation sheet 21. It is determined so as not to be larger than the total lamination thickness of the sheets 19 and 20). However, when the thickness T is excessively thin, it is difficult to form the shape by injection molding. Therefore, the minimum of thickness T becomes "the minimum thickness which can produce the shape by injection molding."

Note that the edge portion 13D is partially thinned at the recesses 30A and 30B. Moreover, even if the recessed part 30B is formed in the groove shape continuous from the light guide plate 17 side of the edge part 13D to the opposite side, and thickness T is 0, it is especially troubled to guide the flange 29B. none. However, it is not preferable to do so because light leaks from the recesses 30B. This is the reason why the thickness T is left while being thin in the present embodiment.

In addition, the thickness of the light-diffusion sheet 18 and prism sheets 19 and 20 of this embodiment is 0.13 mm, 0.16 mm, and 0.16 mm, respectively. In addition, the thickness T is set to about 0.4 mm.

The polarization separating sheet 21 fixes a portion of the flange 29A to the frame 13 using a double-sided tape (indicated by hatched in FIG. 1). Thereby, an accident (falling out of the frame 13, position shift, etc.), such as the case where the surface light source device 12 is transported in the assembly process with a liquid crystal display panel, is prevented. The means for fixing is not limited to double-sided tape, and suitable fixing means such as pins or screws may be used. Note that the flange 29B on the incident end surface 17A side is not fixed here.

The polarization separating sheet 21 also expands in the longitudinal direction by heat. However, since the flange 29B on the incident end surface 17A side is not fixed, this expansion can be absorbed at the displacement with respect to the wedge tip direction. Therefore, it is not stressed by thermal expansion in the longitudinal direction and does not cause deformation or position shift.

The procedure at the time of assembly of the side light type surface light source device 12 which has the above structure is briefly written (refer FIG. 2, FIG. 3 especially).

After the reflective sheet 16 and the light guide plate 17 are disposed on the frame 13, the reflector 24, the fluorescent lamp 14, and the cover 15 are arranged in the frame 13 and assembled. The surface light source device 12 is fixed at this time between the edge portion 13D formed in the frame 13 and the cover 15 with the incident end surface 17A side of the light guide plate 17 interposed.

As a result, the state in which the exit surface 17C is in close contact with the thin-walled edge portion 13D formed along the incident end surface 17A is supported. Therefore, the leakage of the illumination light in the gap between the edge portion 13D and the exit surface 17C is prevented.

Then, in the surface light source device 12, the light diffusion sheet 18 and the prism sheets 19 and 20 are arranged on the frame 13 and the light guide plate 17 in order on the emission surface 17C side. At this time, the pair of flanges 28 with respect to the additional sheet members 18, 19, and 20 are guided by the recesses 13F of the frame 13 and positioned with respect to the exit surface 17C of the light guide plate 17. .

Since the additional sheet members 18, 19, and 20 are positioned using a pair of flanges 28, the clearance of the frame 13 (the clearance of the dimension) even if it is arranged at a slight inclination within the range of the positioning accuracy. By a part of the additional sheet member between the frame 13 and the rear surface of the liquid crystal display panel 11 is avoided.

In addition, the light diffusion sheets 18 and the prism sheets 19 and 20 which are usually used have relatively small linear expansion coefficients of about 2.0 x 10 ^-5 cm / cm / 占 폚. Therefore, even if positioning is performed using a pair of flanges 28 formed on one side, the possibility of bending due to thermal expansion between the flanges 28 is very low. Moreover, even if it is arrange | positioned inclined somewhat in the range of the positioning accuracy, it can prevent that an edge hits the wall part of the frame 13 by expansion. Therefore, bending of these additional sheet members 18, 19, and 20 is prevented.

It is as described above that the light diffusing sheets 18 and the prism sheets 19 and 20 are fixed to the frame 13 with double-sided tapes at the portions of the flanges 28, thereby preventing the dropping and the position shift during conveyance.

Subsequently, the polarization separation sheet 21 having a large linear expansion coefficient and anisotropic linear expansion coefficient is disposed. In the polarization separating sheet 21, flanges 29A, 29B formed so as to face the short sides are guided and positioned by recesses 30A, 30B formed in the frame 13 (see Fig. 1).

As a result, the polarization separation sheet 21 is positioned and supported with high accuracy compared to other additional sheet members 18 to 20 having a small coefficient of linear expansion. Therefore, when attaching the liquid crystal display panel 11, a situation where a part of the polarization separating sheet 21 is sandwiched between the frame 13 and the rear surface of the liquid crystal display panel 11 is avoided.

In addition, even in the case of thermal expansion in response to a temperature change, this expansion is divided into two sides at the central portion where the flanges 29A and 29B are formed. And since it is positioned with high precision with respect to the direction orthogonal to this (the longitudinal direction of the light guide plate 17), the displacement of the outer edge by expansion is accommodated in the range of clearance formed in the frame 13. As shown in FIG.

In other words, the cross-section does not hit the wall of the frame 13 due to the expansion of the polarization separation sheet 21, so that bending is prevented.

In addition, as described above, when positioning the polarization separation sheet 21 by the recessed portion 30B leaving a thin thickness T on the incident end surface 17A side, the exit surface 17C by the edge portion 13D. It can be used to prevent light leakage.

By setting the thickness T to be smaller than the total thickness of the light diffusion sheet 18 and the prism sheets 19 and 20, the polarization separation sheet 21 is prevented from being floated at the portion of the flange 29B. Therefore, a gap is prevented from occurring between the polarization separation sheet 21 and the prism sheet 20. In addition, an obstacle such as that the protective sheet 22 disposed on the polarization separation sheet 21 comes into close contact with the rear surface of the liquid crystal display panel 11 is prevented.

In addition, when a gap is generated between the polarization separation sheet 21 and the prism sheet 20, the function of the polarization separation sheet 21 may not be sufficiently exhibited. That is, the function of selectively transmitting / reflecting the illumination light in accordance with the direction of the polarization plane is lowered, so that the utilization efficiency of the light cannot be sufficiently improved.

In addition, when the protective sheet 22 comes in close contact with the rear surface of the liquid crystal display panel 11, an interference fringe is generated to deteriorate illumination quality or display quality.

The protective sheet 22 is disposed following the arrangement of the polarization separating sheet 21. Arrangement and positioning of the protective sheet 22 are the same as those of the light diffusion sheet 18 and the bending is also prevented. The protective sheet 22 protects other additional sheet members including the polarization separating sheet 21.

The assembled surface light source device 12 is transported to the assembly process of the liquid crystal display device 10, where the liquid crystal display panel 11 is disposed on the protective sheet 22 side. At this time, the surface light source device 12 is surrounded only by the incident end surface 17A side and is not bordered at all by the protective sheet 22 or the like arranged on the exit surface 17C.

Therefore, the rear surface of the liquid crystal display panel 11 can be arranged closer to the protective sheet 22 than in the prior art. This makes it possible to reduce the thickness of the entire liquid crystal display device 10.

In the above-described embodiment, it should be noted that the part used for positioning of the polarization separating sheet 21 is the opposite short side, which is advantageous in increasing the positioning accuracy. The high positioning accuracy eliminates the phenomenon that the polarization separating sheet 21 is sandwiched between the frame 13 and the liquid crystal display panel 11, thereby preventing the occurrence of bending.

The embodiment described above is not intended to limit the present invention. For example, the following modifications are possible.

(1) In the above-described embodiment, a case has been described in which flanges are formed on both opposite sides of four sides of the rectangular polarization separation sheet 21 to be positioned. However, this does not limit the present invention.

In other words, positioning the polarization separation sheet with respect to approximately two centers of these sides at two or more other sides as a reference enables high-precision positioning. And thermal expansion by temperature change can be divided into both sides at the positioning part.

For example, as shown in FIG. 5, you may form and position a flange in the opposing long side. Alternatively, as shown in FIG. 6, a flange may be formed on two adjacent sides to perform positioning. It is also possible to form and position a flange on all three adjacent sides or four sides.

(2) In the above-described embodiment, only the polarization separation sheet is positioned on two sides. However, this does not limit the present invention. That is, the prism sheet or the like may be positioned in two sides as necessary.

In this case, if the positioning is performed at the same short side side as the above-described polarization separation sheet 21, it is preferable to take measures to prevent light leakage separately.

(3) In the above-mentioned embodiment, the case where a light-diffusion sheet, a prism sheet, a polarization separating sheet, and a protective sheet are arrange | positioned at the exit surface of the light guide plate was described. However, this does not limit the present invention. That is, the number of sheets and the number of arrangement of these additional sheet members may be determined as necessary.

(4) In the above-described embodiment, the present invention is applied to a configuration in which the light guide plate and the additional sheet member are arranged in a frame on the liquid crystal display panel side. However, this does not limit the invention. That is, the present invention can also be applied to a configuration in which these members are arranged in the frame in the opposite order.

(5) The cross-sectional shape of the light guide plate may not be a wedge shape. For example, a light guide plate having a uniform thickness may be adopted.

(6) The incident end surface of the light guide plate may be set to two or more end faces, and a plurality of primary light sources may be provided accordingly.

(7) The primary light source may be provided with a light source element other than a rod-shaped light source such as a fluorescent lamp. For example, a plurality of point light sources such as light emitting diodes may be arranged to form a primary light source.

(8) In the above embodiment, the present invention is applied to a backlight liquid crystal display device. However, the present invention is not limited to this, but can also be applied to the case where a side light type surface light source device is adopted for illumination of a so-called reflective liquid crystal display panel.

In addition, the present invention can be widely applied to a side light type surface light source device used as lighting means such as various lighting devices and display devices other than the liquid crystal display device.

Provided are a side light type surface light source device capable of preventing bending and misalignment of an additional sheet member disposed on an emission surface of a light guide plate, and a liquid crystal display device having the surface light source device applied to the illumination of a liquid crystal display panel.

Claims (14)

A side light type surface light source device including a light guide plate having an emission surface and a rear surface, a primary light source for supplying illumination light from an incident end surface of the light guide plate, and an additional sheet member having a rectangular shape disposed along the emission surface. On each of two or more sides of the additional sheet member, a positioning portion for positioning the additional sheet member with respect to the center of each side is provided. And a frame member for laminating and mounting the light guide plate and the additional sheet member. And the positioning portion includes a flange portion protruding from the side of the additional sheet member, and is guided by a recess formed in the frame. The method of claim 1, A side light type surface light source device in which the positioning portions are provided on two opposite sides of the additional sheet member. delete The method of claim 1, The frame has a border portion at least partially covering the exit surface along the incident end surface of the light guide plate, One of the sides positioned by the positioning portion of the additional sheet member is a side corresponding to the incident cross section, And the edge portion is formed in the concave portion formed in the frame so that at least the thickness of the injection surface is allowed to remain on the exit surface side. The method of claim 4, wherein Between the additional sheet member and the exit surface, a separate additional sheet member is disposed, The thickness of the side light type surface light source device is set so as not to exceed the thickness of the separate additional sheet member. The method according to claim 1 or 2, The side sheet-type surface light source device of the additional sheet member is a polarization separation sheet. A liquid crystal display device comprising a liquid crystal display panel and a side light type surface light source device for illuminating the liquid crystal display panel. The side light type light source device includes a light guide plate having an emission surface and a rear surface, a primary light source for supplying illumination light from an incident end surface of the light guide plate, and an additional sheet member having a rectangular shape disposed along the emission surface, On each of two or more sides of the additional sheet member, a positioning portion for positioning the additional sheet member with respect to the central portion of each side is provided. Further provided with a frame member for laminating and mounting the light guide plate and the additional sheet member, And the positioning portion includes a flange portion protruding from the side of the additional sheet member, and is guided by a recess formed in the frame. The method of claim 7, wherein And the positioning portion is provided on two opposite sides of the additional sheet member. delete The method of claim 7, wherein The frame has a border portion at least partially covering the exit surface along the incident end surface of the light guide plate, One of the sides positioned by the positioning portion of the additional sheet member is a side corresponding to the incident cross section, And the edge portion is formed such that the thickness of the concave portion formed in the frame is such that at least an injection molding is allowed on the exit surface side. The method of claim 10, Between the additional sheet member and the exit surface, a separate additional sheet member is disposed, And the edge portion is set not to exceed the thickness of the additional sheet member. The method according to claim 7 or 8, And the additional sheet member is a polarization separating sheet. The method of claim 1, The side sheet-type surface light source device of the additional sheet member is a polarization separation sheet. The method of claim 7, wherein And the additional sheet member is a polarization separating sheet.

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