KR20050091908A - Direct lighting type back light - Google Patents

Abstract

The present invention aims to provide a direct type backlight which can suppress the deformation of the diffuser plate and improve the light emitting quality, and has a low component count. The direct type backlight of the present invention transmits and diffuses the light from the light source 10. And a diffuser plate integral frame portion 3 in which the diffuser plate 4 and the frame portion 5 provided around the diffuser plate 4 are integrally molded, and an opening 11 in which the diffuser plate 4 is disposed. And a lower frame 2 having a light source 10 disposed therein at the same time, and the diffusion plate 4 has a thickness change portion h whose thickness increases continuously from the center side toward the edge.

Description

Direct backlight type back light}

The present invention relates to a direct type backlight.

Backlights used in liquid crystal displays and the like are roughly classified into side light type backlights and direct type backlights. Among these, the direct type backlight has been widely used as a large flat light emitting device because it is suitable for large size and has a high brightness easily. In addition, a case where a direct type backlight is used as a flat light emitting device used for a large screen of 15 inches or more in a liquid crystal display device is increasing.

A conventional general direct type backlight is described with reference to the drawings. Here, the case where a display part, such as a liquid crystal panel, or an optical sheet is used is demonstrated as an example. 7 is a cross-sectional view in a plane perpendicular to the longitudinal direction of the linear light source 31. As shown in FIG. 7, the backlight includes a plurality of light sources (lamps) 31, a lower frame 32 as a casing having an opening, and a light source 31 therein, and a reflective layer provided on an inner surface of the lower frame. 33, a rim-shaped upper frame 34 provided with a display portion such as a liquid crystal panel 40, an optical sheet 35 and a diffusion plate 36 sandwiched and supported by the upper frame 34 and the lower frame 32; It is composed. As the light source 31, a fluorescent lamp in the form of a cold cathode tube is used. The upper frame 43 is provided with a resin guide rib 37 for supporting display portions such as a liquid crystal panel. As in the example shown in FIG. 7, in the conventional direct type backlight, the upper frame 34 and the diffusion plate 36 are each separate members, and only the diffusion plate 36 forms a single member. Moreover, the diffuser plate 36 is a flat plate-shaped member whose thickness is constant throughout (for example, refer patent document 1 and patent document 2 below).

<Patent Document 1> Japanese Unexamined Patent Publication No. 10-106342

<Patent Document 2> Japanese Unexamined Patent Publication No. 2002-182184

The conventional direct type backlight has a problem that deformation such as warpage is likely to occur in the diffusion plate. The deformation is caused by the influence of external stress, change over time, the influence of heat from the reflective sheet, in addition to the self weight of the diffusion plate. When deformation such as warpage occurs in the diffusion plate, the uniformity of diffusion of transmitted light is lowered, so that the light emitting quality as a backlight is lowered. For example, when using a display part or an optical sheet like a liquid crystal panel, a deformation | transformation also arises in these optical sheets or a liquid crystal panel according to the deformation | transformation of a diffuser plate, and a liquid crystal display unevenness arises. In addition, since the upper frame and the diffusion plate are separate, there is a problem in that the number of parts of the backlight is increased and the assembly cost is increased by increasing the parts management cost or the number of backlight assembly processes.

This invention is made | formed in view of the said situation, Comprising: It aims at setting it as the direct type backlight which can suppress the deformation | transformation of a diffuser plate, and can improve the light emitting quality, and there are few components.

The direct type backlight of the present invention includes a diffuser plate for transmitting and diffusing light from a light source, a diffuser plate integral frame portion in which a frame portion provided around the diffuser plate is integrally formed, and an opening in which the diffuser plate is disposed, and at the same time a light source therein. It is provided with the lower frame which is arrange | positioned, The said diffusion plate is characterized by having the thickness change part which continuously increases in thickness toward the edge from the center side.

In this case, since the diffusion plate and the frame portion are integrally formed, the diffusion plate is reinforced by the frame portion, thereby suppressing deformation of the diffusion plate and reducing the number of parts. In addition, the thickness change portion disperses the stress such as the magnetic weight acting on the diffuser plate, so that the diffuser plate is hardly bent.

In the direct backlight, the diffusion plate may be constituted of only the thickness change portion. In this case, since the entire diffuser plate is a thickness deformation portion, the thickness is continuously increased from the center portion of the diffuser plate toward the edge portion, thereby minimizing the warpage of the diffuser plate. In addition, since the center portion has higher luminance than the edge portion, it is possible to obtain a high light emitting quality, especially as an image backlight.

In addition, the diffusion plate may be constituted of a thickness change portion where the thickness continuously increases from the center side toward the edge and the same thickness portion having a constant thickness. In the same thickness part, since the transmittance | permeability becomes constant and brightness is easy to be uniform, both uniformity of brightness and suppression of curvature can be achieved by combining suitably the same thickness part and thickness change part. In this case, it is preferable that the said thickness change part is provided in the edge part of the said diffusion plate, and the said same thickness part is provided in the center side of the said thickness change part. In this manner, the luminance of the central portion of the diffuser plate is made uniform by the same thickness portion, and the warpage of the diffuser plate by the thickness change portion can be suppressed. In addition, since the center portion has higher luminance than the edge portion, it is possible to obtain a high light emitting quality especially as an image backlight.

It is preferable that the thickness of a diffusion plate is 0.5 mm or more and 5 mm or less. This is because when the thickness is thinner than 0.5 mm, the rigidity is insufficient and the deformation is easy, and light diffusion is insufficient and the light emitting quality may be degraded. If the thickness is larger than 5 mm, the self weight may be too large to bend easily, or the amount of material used may increase, leading to an increase in manufacturing cost. Moreover, by making the thickness of a diffuser plate into the range of 0.5 mm-5 mm, it becomes suppressed that the difference of the thickness of a diffuser plate becomes too large and brightness becomes too nonuniform.

It is preferable that the surface of the said diffusion plate is continued smoothly. This is because when there is a portion that is not smoothly continuous, the light emission of the portion is uneven and the light emitting quality may be degraded.

1 is an exploded perspective view showing a schematic configuration of a direct backlight 1 for a liquid crystal display device according to a first embodiment of the present invention, and FIG. 3 is a cross-sectional view thereof (perpendicular to the longitudinal direction of the light source 10). Cross section in one section). The direct backlight 1 includes a box-shaped lower frame 2 having an opening 11 at an upper portion thereof, and several light sources 10 arranged in parallel to each other inside the lower frame 2. In addition, the direct backlight 1 includes a diffusion plate integrated frame portion 3 disposed in the opening 11 so as to block the opening 11 of the lower frame 2, and the diffusion plate integrated frame portion 3. Two optical sheets 12 and 13 disposed so as to overlap each other along the outer surface, and among these optical sheets 12 and 13, the optical sheet 12 and the diffuser plate integral frame portion on the diffuser plate integrated frame portion 3 side ( The double-sided tape 14 which adhere | attaches 3) is provided.

The lower frame 2 and the diffuser plate integral frame portion 3 are connected to each other by a connecting mechanism (not shown). As the connecting mechanism, for example, the projection part is provided on the side surface 16 of the diffusion plate integrated frame part 3, and the engaging part that can engage with the projection part is provided in the inner wall 2a of the lower frame 2, and this projection part is provided. And a combination of the coupling holes can be employed, and other mechanisms such as screws can also be employed.

As the material of the lower frame 2, a metal such as aluminum having excellent heat dissipation, mechanical strength, and shape stability can be suitably used. In addition, a reflector 15 is provided between the bottom of the lower frame 2 and the light source 10 in order to increase the luminous efficiency of the direct backlight 1 and to improve the brightness.

FIG. 2 is a plan view of the reflector integrated frame portion 3 seen from the outer surface side, and FIG. 4 is a cross-sectional view taken along the line A-A of FIG. As shown in FIG. 4, the diffuser integrated frame part 3 is configured to diffuse and diffuse light from the light source 10 to form a light emitting surface, and a frame part provided around the diffuser plate 4. It consists of (5). The frame portion 5 is thicker than the diffusion plate 4. Moreover, the outer surface 4a of the diffuser plate 4 is planar. Moreover, the outer surface 4a of the diffuser plate 4 becomes a rectangle, and becomes substantially the shape corresponding to the liquid crystal screen of a liquid crystal display device.

The frame part 5 is adjacent to the diffuser plate 4, and is provided around the first step portion 5a, which is further higher than the outer surface 4a of the diffuser plate 4, and the first step portion 5a. It is provided with the 2nd step part 5b provided in the circumference | surroundings, and being higher than the 1st step part 5a. As shown in the sectional view of FIG. 3, the inner optical sheet 12 of the two optical sheets 12 and 13 is restricted in the in-plane direction by the first step portion 5a, and the optical sheet 12 Movement of the optical sheet 13 disposed outside of the X-axis in the in-plane direction is regulated by the second step portion 5b.

Moreover, although the overall shape of the frame part 5 becomes substantially rectangular, the guide protrusion 5c which protrudes along the outer periphery of the 2nd step part 5b is provided in the four corners of the outer surface. Each of the four guide protrusions 5c has a portion along the long side and the short side of the outer periphery of the second stepped portion 5b which are rectangular. When the liquid crystal display 20 is mounted on the direct type backlight 1 to form a liquid crystal display device, the liquid crystal display 20 shown in FIG. 3 as an imaginary line is inserted inside the guide protrusion 5c. Then, the movement to the inner surface direction of the liquid crystal screen 20 is regulated by the guide protrusion 5c, and the liquid crystal screen 20 is fixed to the diffuser integrated frame part 3. Moreover, although it is different from this 1st Embodiment, you may make it the structure which the optical sheet 12,13 is sandwiched in this guide protrusion 5c, and the movement in the in-plane direction of an optical sheet is controlled by the guide protrusion 5c. .

In this way, the diffusion plate integrated frame portion 3 regulates the movement in the in-plane direction of the members (optical sheets 12 and 13, the liquid crystal screen 20, etc.) provided outside the diffusion plate integrated frame portion 3. Since the guide protrusions 5c and the stepped portions 5a and 5b are provided as the restricting means, the members (the optical sheets 12 and 13, the liquid crystal screen 20 and the like) are easily mounted. In addition, since these restricting means (guide protrusions 5c and stepped portions 5a and 5b) are integrally formed as the diffusion plate integral frame portion 3, when a liquid crystal screen fixing rib or the like is mounted as a separate member, In comparison, the number of parts is reduced and the assembly process is reduced.

As shown in FIG. 3, of the two optical sheets 12 and 13, the optical sheet 12 on the diffusion plate 4 side has the first stepped portion in a state where a predetermined clearance is provided in consideration of expansion and contraction due to heat. It is accommodated in the step of 5a). And the optical sheet 13 arrange | positioned outside the optical sheet 12 is larger than the optical sheet 12, and the 2nd step part 5b and the optical sheet 13 are fixed by the double-sided tape 14. . In this case, since the optical sheet 13 functions as a cover and covers the optical sheet 12, and the optical sheet 12 is accommodated in the first stepped portion 5a, the plurality of optical sheets are spread over the diffusion plate 4. ) Can be easily attached to the outside. Moreover, it is difficult to fix several optical sheets with the conventional diffuser plate (separate member). This is because if the diffuser plate is flat and fixed at the end with glue or adhesive, the deformation (bending) of the diffuser plate causes warpage of the optical sheet, and it is not necessary to place the fixing portion at which the end is fixed with glue such as glue outside the light emitting area. This is because there is a danger that the diffusion plate becomes larger and the backlight itself becomes larger.

The whole diffusion plate integrated frame portion 3 is integrally molded with the same resin. In this case, since the diffusion plate integrated frame portion 3 is made of resin, it is easy to mold, and since the diffusion plate 4 and the frame portion 5 are made of the same resin, the diffusion plate 4 and the frame portion 5 are formed. Differences in the material properties therebetween are reduced so that distortion caused by the difference in shrinkage of both is suppressed, and deformation of the diffusion plate 4 caused by the distortion is more effectively suppressed. In addition, when the diffusion plate integrated frame portion 3 is made of resin, heat shielding characteristics are superior to the case where the frame portion 5 is made of metal, so that heat of the backlight is hardly transferred to the liquid crystal surface 20.

The material of the diffuser plate integral frame portion 3 is not particularly limited, but in the case where the diffuser plate 4 and the frame portion 5 are made of the same material, the diffused light diffusion function as the diffuser plate 4 is excellent. Materials having excellent heat shielding properties for panels and the like are preferable, and polycarbonate resins, acrylic resins, polypropylene resins and the like of white systems (milky whites) are particularly preferable. Moreover, when injection molding is employ | adopted as a method of integrated molding, since the productivity of a diffuser plate integrated upper frame becomes high, it is more preferable.

As shown in FIG. 4, the diffuser plate 4 in the diffuser plate integral frame portion 3 in which the diffuser plate 4 and the frame portion 5 are integrally formed is not uniform in thickness, and the diffusion plate 4 is It consists of the thickness change part h which thickness increases continuously from a center side toward an edge part, and the same thickness part t which is constant in thickness. The thickness change part h is provided in the edge part of the diffuser plate 4, and the same thickness part t is located in the center side (center side in the diffuser plate 4) of the thickness change part h. As a result, the cross section of the diffuser plate 4 becomes substantially arcuate (refer FIG. 4). The same thickness portion t is flat in its entirety and is a vertical line drawn down from the center point c of the same thickness portion t to the outer surface 4a of the diffuser plate 4 from the center of gravity of the same thickness portion t. And the intersection of the outer surface 4a) with the vertical line c and the outer surface 4a lowered from the center point c of the diffuser plate 4 (from the center of gravity of the diffuser plate 4 to the outer surface 4a of the diffuser plate 4). Intersection with)). Therefore, the self weight of the diffuser plate 4 is easily distributed evenly to the edge portion of the diffuser plate 4.

The thickness distribution of the diffuser plate 4 is the thinnest at the same thickness portion t and the thickest at the edge of the thickness change portion h (that is, at the edge of the diffuser plate 4). The minimum thickness t1 of the diffusion plate 4 is 0.5 mm or more, and the maximum thickness t2 of the diffusion plate 4 is 5 mm or less. Further, the thickness (maximum thickness) t5 of the frame portion 5 is thicker than the maximum thickness t2 of the diffusion plate 4.

As described above, since the outer surface 4a of the diffuser plate 4 is flat, the thickness change of the diffuser plate 4 is imparted by making the inner surface 4b of the diffuser plate 4 entirely non-planar. Since there are no steps on the surfaces (outer surface 4a and inner surface 4b) of the diffusion plate 4, no abnormal light emission due to the step (the step is seen as a band-shaped pattern on the light emitting surface) does not occur. The surfaces (outer surface 4a and inner surface 4b) of the diffusion plate 4 are not only free from steps but are smoothly continuous as a whole. That is, the boundary between the same thickness part t and the thickness change part h is smoothly continued, and the surface (inner surface and outer surface of the thickness change part h) of the thickness change part h is also smoothly continued. 4 is a cross-sectional view taken along the line A-A of FIG. 2, but the direction perpendicular to this, that is, the cross-sectional view taken along the line B-B (not shown) of FIG. 2, has the same shape as that of FIG. That is, the thickness change of the thickness change part h changes both the long side direction and the short side direction of the rectangular diffusion plate 4. The diffuser plate 4 has a concave lens-shaped thickness distribution.

Moreover, as shown in FIG. 4, the diffuser plate 4 has a cross section (cross section perpendicular to the outer surface 4a of the diffuser plate 4) at arbitrary positions in the short side direction and the long side direction of the diffuser plate 4. The cross-sectional shape is linearly symmetrical with respect to the straight line tx perpendicular to the outer surface 4a and passing through the center point of the cross-sectional line of the outer surface 4a. Moreover, the cross-sectional shape by any plane passing through the center point c of the diffuser plate 4 and perpendicular to the outer surface 4a of the diffuser plate 4 is a straight line passing through the center point and perpendicular to the cross-sectional line of the outer surface 4a. It is linearly symmetric about (tz). Therefore, since the thickness distribution of the diffuser plate 4 is in a symmetrical state, the self weight of the diffuser plate 4 is more evenly distributed, so that deformation of the diffuser plate 4 due to the self weight is very effectively suppressed, and the diffuser plate 4 The luminance distribution is also in a symmetrical state, and the light emitting quality is increased.

The direct type backlight 1 configured as described above has the following effects.

Since the diffusion plate 4 and the frame portion 5 are integrally formed and the diffusion plate 4 is reinforced by the frame portion 5, the deformation of the diffusion plate 4 is suppressed. Moreover, since the thickness (maximum thickness) t5 of the frame part 5 is thicker than the maximum thickness t2 of the diffuser plate 4, the reinforcing effect of the diffuser plate 4 by the frame part 5 is further improved. do. In addition, the number of parts of the direct type backlight 1 is reduced compared to the case where the frame portion 5 and the diffusion plate 4 are separate members.

In addition, the thickness change part h disperses stresses such as the magnetic weight acting on the diffuser plate 4, and the diffuser plate 4 is less likely to bend.

In the same thickness part t, the light transmittance is constant and the brightness can be made uniform. Therefore, by combining the same thickness part t and the thickness change part h properly, both luminance uniformity and suppression of warpage are achieved. At the same time, the desired luminance distribution can be obtained. Moreover, since the thickness change part h is provided in the edge part of the diffuser plate 4, and the same thickness part t is provided in the center of the thickness change part h, the luminance of the center part of the diffuser plate 4 becomes uniform, The warpage of the diffusion plate 4 can be suppressed. In particular, regarding the bending caused by the weight of the diffuser plate 4, the same thickness portion t, which is thinner than the thickness change portion h, is disposed at the center portion of the diffuser plate 4, whereby the center portion of the diffuser plate 4 is thus provided. Since the weight is reduced, the warpage caused by the weight of the diffusion plate 4 is improved very effectively together with the self-weight stress dispersion effect caused by the thickness change portion h.

Moreover, since the same thickness part t thinner than the thickness change part h is provided in the center of the thickness change part h, the luminance distribution in the diffuser plate 4 is relatively brighter in the center part than the edge part of the diffuser plate 4. Lose. If the center part is brighter than the edge part, the light emitting surface tends to look beautiful, so that the light emitting quality is increased. In particular, when an image is projected from a liquid crystal screen or the like, brightening the center portion rather than the edge portion of the screen makes the image look beautiful, so that a light emitting quality suitable for a backlight for an image display device used for a liquid crystal screen, a liquid crystal TV or the like can be obtained.

The thickness of the diffuser plate 4 is 0.5 mm or more and 5 mm or less. When the thickness of the diffuser plate 4 is thinner than 0.5 mm, the rigidity of the diffuser plate 4 may be insufficiently deformed, or the light emission quality may be degraded due to insufficient diffusion of light. Moreover, when the thickness of a diffuser plate is thicker than 5 mm, the self-weight of the diffuser plate 4 may become large too much, it may bend easily, or the usage-amount of material may increase and manufacturing cost may increase. In the first embodiment, the problem is minimized by setting the thickness of the diffusion plate 4 to be within a range of 0.5 mm to 5 mm. Moreover, by making the thickness of the diffuser plate 4 into the range of 0.5 mm-5 mm, it becomes suppressed that the difference of the thickness of the diffuser plate 4 in the thickness change part h becomes large too much, and unevenness | luminance becomes excessively uneven.

Moreover, since the surface of the diffuser plate 4 is smoothly continued, high light emission quality can be obtained. If there is a part that is not smoothly continuous, the light emission of the part may be particularly uneven and the light emission quality may be degraded. Since there is no angle at the cross-sectional line of the diffusion plate 4 due to the smooth continuous (bent part Light emission quality increases). Thus, in the present invention, it is preferable that the surface of the diffusion plate 4 is smoothly continuous. More preferably, the cross section of the diffusion plate 4 is formed by an arbitrary plane perpendicular to the outer surface 4a of the diffusion plate 4. In consideration of the contour of, it is desirable that the contour line is smoothly continuous to draw a tangent line at all points on the contour line.

Conventionally, in order to prevent the warpage of the diffusion plate due to its own weight or the like, a support pin for supporting the diffusion plate on the inner surface side has been provided in the vicinity of the central portion of the diffusion plate 4. Since the warpage is minimized, the number of support pins or the like can be reduced or the support pins can be eliminated.

In the prior art, the upper frame 34 (see FIG. 7) is often made of metal such as stainless steel or aluminum in consideration of cost, etc. In this case, metal having a relatively good thermal conductivity due to heat radiation from a light source, especially an electrode, is used. The temperature of the frame rises. When the liquid crystal panel is in contact with the metal frame, the temperature of the liquid crystal panel at that portion becomes partially high, and thus the temperature distribution of the liquid crystal panel becomes nonuniform, causing deterioration such as color bleeding on the liquid crystal screen. In this case, therefore, it was necessary to provide a guide rib for fixing the liquid crystal panel while fixing the heat shielding resin (foaming resin spacer) between the metallic frame and the liquid crystal panel. When the diffusion plate integrated frame portion 3 including the frame portion 5 is made of resin as in the present embodiment, the thermal conductivity is smaller than that of the metal. Accordingly, the liquid crystal panel may be a liquid crystal display device in which the liquid crystal panel is directly attached to the diffusion plate integrated frame portion 3, thereby eliminating the need for the heat shielding resin, and suppressing the deterioration of the liquid crystal display due to the temperature difference in the liquid crystal panel. can do. Thus, when the diffuser integrated frame part 3 is formed of resin, it is further suitable as a direct type backlight for liquid crystal display.

In the conventional backlight shown in Fig. 7, since the diffusion plate 36 and the upper frame 34 are separate, a constant gap is provided between the two in consideration of the dimensional tolerance, the difference in shrinkage rate, the deformation, and the like. As a result, the size of the backlight was not only increased, but foreign matters (house dust, cigarette ash, etc.) were easily invaded from the gaps. In addition, the diffusion plate 36 is deformed due to a poor setting of the clearance, the diffusion plate 36 and the upper frame 34 are rubbed with each other, and scratches occur, or debris is attached to the inside of the backlight to deteriorate the emission quality. There was a case.

On the other hand, in the diffuser integrated frame part 3 of the first embodiment, since there is no gap between the diffuser plate 4 and the frame part 5, foreign matter (house dust, cigarette ash, etc.) is difficult to enter the backlight. The deterioration of the light emitting quality due to the adhesion of foreign matter to the inside of the diffuser plate 4 (especially the inner surface 4b) is suppressed, and the direct backlight 1 is miniaturized and the diffuser plate 4 due to the setting failure of the clearance. ) There is no variation.

In addition, as in the prior art (see FIG. 7), the upper frame 34, the diffusion plate 36, and the optical sheet 35 are each independently separated, and the optical sheet 35 is not fixed to the diffusion plate 36. In this case, since these members cannot be handled integrally, it is cumbersome and foreign matter enters between the diffusion plate 36 and the optical sheet 35 or between the optical sheets 35 (when there are a plurality of optical sheets 35). There is concern. In particular, when the lamp 31 of the light source is replaced, the upper frame 34, the diffusion plate 36, and the optical sheet 35 are separately taken out, which is cumbersome, and the possibility of foreign matter invading becomes very high. In this case, therefore, troublesome lamp replacement is performed in a clean room. Since the optical sheet 12 and 13 are fixed to the diffuser integrated frame part 3 as in this embodiment, these diffuser integrated frame parts 3 and the optical sheets 12 and 13 can be handled integrally. The lamp replacement operation of the light source 10 becomes easy, and foreign matter does not enter between the optical sheets 12 and 13 or between the optical sheets 12 and 13 and the diffusion plate 4 at the time of lamp replacement.

In addition, the luminance distribution of the light emitting surface can be arbitrarily adjusted by appropriately studying the thickness distribution of the thickness varying portion h or by appropriately studying the arrangement of the thickness varying portion h and the same thickness portion t.

In addition, since the diffuser plate 4 and the frame portion 5 are integral, there is no rattling between them, and the noise generated when the direct type backlight 1 is shaken to a minimum is suppressed to be very quiet. It is.

5A to 5D are cross-sectional views of a modification of the diffusion plate integrated frame portion 3.

In FIG. 5A, the entirety of the diffusion plate 4 is the thickness change portion h. That is, this diffuser plate 4 consists only of the thickness change part h whose thickness continuously increases toward the edge from the center side. The thinnest portion of the diffuser plate 4 is a vertical line drawn from the center point c of the diffuser plate 4 (ie, from the center of gravity of the diffuser plate 4 to the outer surface 4a of the diffuser plate 4 and its vertical line). The intersection of the outer surface 4a).

In this case, since the entire diffusion plate is a thickness change portion, the thickness is continuously increased from the center portion of the diffusion plate toward the edge portion, thereby minimizing the warpage of the diffusion plate. In addition, since the center portion has higher luminance than the edge portion, it is possible to obtain a high light emitting quality especially as an image backlight. Moreover, since the thinnest part of the diffuser plate 4 is located at the center point c of the diffuser plate 4, the magnetic weight acting on the diffuser plate 4 tends to be evenly distributed, thereby reducing the warpage caused by the self weight. .

In addition, in the modification of FIG. 5A, the outer surface 4a of the diffuser plate 4 is planar, and the inner surface 4b of the diffuser plate 4 is a spherical curved surface. And in the cross section (FIG. 5 in the cross section parallel to the long side and short side of the diffuser board 4) of FIG. 5 (a), the cross section of the inner surface 4b becomes constant curvature with respect to the whole range. Thus, when the cross-sectional shape of the inner surface of the thickness change part h is made into the shape with a constant curvature, the deformation stress acting on the diffuser plate 4 will spread easily, and the deformation suppression effect of the diffuser plate 4 will become high.

In the modified example of FIG. 5B, the center portion of the diffuser plate 4 becomes the same thickness part t, and the edge portion of the diffuser plate 4 becomes the thickness change part h, and the thickness change part h is It is flat. Thus, the surface of the thickness change part h may not only be curved but also planar. Also, when two different straight lines intersect with each other in the cross section by a plane perpendicular to the outer surface 4a of the diffuser plate 4, as shown in the cross-sectional line of Fig. 5 (b), the angle? 20 degrees or less are preferable, 10 degrees or less are more preferable, 5 degrees or less are especially preferable. The larger the angle [theta], the more the intersections of these two straight lines are likely to cause abnormal light emission. For example, a band-shaped pattern may be seen on the light emitting screen. The smaller the angle [theta], the closer the cross-section line is to a smooth state. This is because the pattern does not appear well.

5 (c) shows that the entirety of the diffuser plate 4 is a thickness change part h, and the thickness change part h is located at the edge of the diffuser plate 4 and is inclined in opposite directions. A planar thickness varying portion h2 consisting of two planes and a curved surface interposed between the planar thickness varying portions h2 and smoothly connecting two planes constituting the planar thickness varying portion h2. ) In the present invention, the surface of the diffusion plate 4 may have a configuration in which curved surfaces and flat surfaces are continuous. Moreover, curved surfaces with different curvatures may be continuous. Even in this case, the surface of the diffuser plate 4 needs to be continuously connected, i.e., there should be no step difference. And it is preferable that all the surfaces of the diffuser plate 4 continue smoothly. In addition, the corner portion k in the cross-sectional view of FIG. 5C is in a state where the angle θ is relatively large, but is outside the range of the diffusion plate 4, and thus does not affect the light emitting quality.

In the modified example of FIG. 5D, the outer surface 4a of the diffuser plate 4 is planar, and the thickness change portion h provided at the edge of the diffuser plate 4 at the inner surface 4b of the diffuser plate 4. ) And the same thickness portion t provided inside thereof are all flat except for the rounded portion described later, but the curved portion having a predetermined radius of curvature R1 at the corner portion generated by the intersection of these two planes. Is given. That is, the curved surface is provided to the said edge part. By this curved surface, the same thickness part t and the thickness change part h which are planar mutually are continued smoothly. Therefore, it is the direct type | mold backlight 1 with a high luminous quality without a strip | belt-shaped pattern generate | occur | producing in a light emitting surface.

6 is a cross-sectional view of the direct backlight 6 according to the second embodiment of the present invention. In this direct type backlight 6, the diffuser plate 4 has a thickness change portion h whose thickness increases continuously from the center side toward the edge and at the same time corresponds to the position of the light source 10. The local thickness part 7 in which the thickness of 4) increases locally is provided. In the direct type backlight 6, since the linear light sources 10 are arranged in parallel to each other, the local thickness portions 7 are also provided at predetermined intervals in parallel with each other corresponding to the positions of these light sources 10. In addition, the outer surface 4a of the diffusion plate 4 is a smoothly continuous curved surface. As a result, the cross-sectional shape of the inner surface 4b of the diffuser plate 4 is in the shape of a continuous waveform. In this embodiment of FIG. 6, as a result of providing the local thickness portion 7, there is an inverse change portion g in which the thickness of the diffuser plate 4 is continuously reduced from its center toward the edge. It is supposed to. As described above, in the present invention, the thickness change portion h may be present in at least part of the diffusion plate 4, and the reverse change portion g may be present in a part of the diffusion plate 4. In the embodiment of FIG. 6, the apex position and the valley position of the corrugated portion constituting the local thickness portion 7 are convex arcs toward the outer surface 4a of the diffuser plate 4 in the cross section of FIG. 6 (in FIG. 6). It is located along the dashed line), and the effect which provided the thickness change part h by the inverse change part g is not impeded as much as possible.

As a material characteristic of the diffusion plate integrated frame part 3, the following is preferable. First, the water absorption is preferably at most 0.5%, preferably at most 0.3%. If the absorption rate is greater than 0.5%, it may cause deformation such as warping when the environment such as humidity is different inside and outside the backlight. The coefficient of linear expansion is preferably 1.5 × 10 ⁻⁴ / ° C. or less, more preferably 0.7 × 10 ⁻⁴ / ° C. or less. If the coefficient of linear expansion is large, there is a problem that the dimensional difference with other components such as the lower frame 2 becomes large. The light transmittance is preferably 20% or more, more preferably 40% or more. If it is too small, the brightness of light emission cannot be secured and the light emission efficiency is lowered. In addition, the luminous efficiency is preferably 80% or less, more preferably 65% or less. When too large, it may be difficult to ensure uniformity of light emission. 100 degreeC or more is preferable and 120 degreeC or more of load deflection temperature is more preferable. If the warpage temperature is too low, warpage or deformation is easily caused by the heat generated by the lamp or inverter.

In the case where the diffusion plate 4 and the frame portion 5 are formed of the same resin as in the above embodiment, the frame portion 5 is made of a material having light transmittance, so that the specifications such as thickness, shape or material composition may be used. Therefore, a case where the frame portion 5 also has light transmission may occur. In this case, the uniformity of light emission may be impaired by the transmitted light from the frame portion 5, which may deteriorate the light emission quality. In this case, by appropriately providing the light shielding means in the frame portion 5, light leakage from the frame portion 5 can be prevented and the light emission of the diffusion plate 4 can be made uniform, thereby improving the light emission quality. As an example of this shading means, a metal thin film treatment such as coating or vapor deposition of a shading paint, or shading tape (black tape or the like) can be employed. In addition, the lower frame 2 is made of a material having high light shielding properties (such as a metal or a resin having high light shielding properties), and the lower frame 2 is provided with a light shielding portion capable of shielding the transmitted light of the frame portion 5. The shape of the frame 2 may be studied to prevent unnecessary transmission of light from the frame portion 5.

In addition, extra transmission light from the frame part 5 can be suppressed by making the frame part 5 the material with high light shielding property, and making the light transmittance of the frame part 5 higher than the light transmittance of the diffuser plate 4. Specifically, for example, the diffusion plate 4 can be made of white resin and the frame portion 5 can be made of black resin. In this case, the material composition of both materials is preferable because the physical properties of the diffusion plate 4 and the frame part 5 are similar to each other except for coloring colorant. In this manner, when the colors of the diffusion plate 4 and the frame portion 5 are separated from each other, a method of two-color molding or multi-color molding can be employed. This two-color molding or multi-color molding also corresponds to the integral molding referred to herein.

Moreover, although the direct type backlight 1 for liquid crystal display devices using the liquid crystal panel and the optical sheet was illustrated in the said embodiment, the direct type backlight 1 of this invention may be a light box, a shower curtain, etc.

In addition, the thickness change part h of this invention may change thickness only in one direction (for example, the longitudinal direction of the light source 10), and may be changed in two directions (for example, the longitudinal direction of the light source 10 in addition to the longitudinal direction of the light source 10). The thickness may be changed in the direction perpendicular to and parallel to the outer surface 4a of the diffuser plate 4).

Since the diffusion plate and the frame portion are integrally molded, deformation of the diffusion plate is suppressed and the number of parts is reduced. Moreover, since the thickness change part was provided, the stress, such as self weight which acts on a diffuser plate, is disperse | distributed and a diffuser plate does not bend easily.

1 is an exploded perspective view of a direct type backlight that is a first embodiment of the present invention.

FIG. 2 is a plan view of the diffuser plate integral frame part of the direct backlight of FIG. 1. FIG.

3 is a cross-sectional view of the direct type backlight of FIG. 1.

4 is a cross-sectional view taken along the line A-A of FIG.

5A to 5D are cross-sectional views of a modification of the diffuser plate integral frame portion.

6 is a cross-sectional view of a direct type backlight that is a second embodiment of the present invention.

7 is a cross-sectional view of a conventional direct backlight.

<Description of the symbols for the main parts of the drawings>

1 direct backlight

2 lower frame

3 diffuser integrated frame part

4 diffuser plate

4a Outside surface (surface) of diffuser plate

4b inner surface (surface) of diffuser plate

5 frame parts

6 direct backlight

h thickness change

t equal thickness

10 light source

11 opening

Claims (7)

A diffuser plate for transmitting and diffusing light from the light source, a diffuser plate integral frame portion integrally formed with a frame portion provided around the diffuser plate, and a lower frame having a light source disposed therein while having an opening in which the diffuser plate is disposed; , And said diffuser plate has a thickness change portion whose thickness increases continuously from the center side toward the edge side. The direct type backlight of claim 1, wherein the diffusion plate is formed of only the thickness change part. The direct type backlight of claim 1, wherein the diffusion plate is formed of a thickness change part whose thickness increases continuously from the center side toward the edge, and the same thickness part having a constant thickness. The direct type backlight of claim 3, wherein the thickness change part is provided at an edge of the diffusion plate, and the same thickness part is provided at the center of the thickness change part. The direct type backlight of any one of claims 1 to 4, wherein the thickness of the diffusion plate is 0.5 mm or more and 5 mm or less. The direct type backlight according to any one of claims 1 to 4, wherein the surface of the diffusion plate is smoothly continuous. 6. The direct type backlight of claim 5, wherein the surface of the diffusion plate is smoothly continuous.