JP2008198540A - Optical sheet, backlight device using optical sheet, and liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sheet of high quality to be made to hardly generate wrinkles or warpage of the sheet by absorbing reaction stress to be easily generated at a position fixing part of the sheet. <P>SOLUTION: In the optical sheet 3 with a positioning protruded part 3a formed at least on one side of a sheet material, and insertion-coupled with the protruded part into a positioning groove of a support frame 2 inside a backlight device, the sheet material is set close to the protruded part 3a, and a slit 3A is formed at a part separated with a predetermined distance from a side of the sheet material. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to an optical sheet, a backlight device using the optical sheet, and a liquid crystal display device, and more particularly to an improvement in the positioning and fixing means of the optical sheet.

A liquid crystal display panel that is frequently used as a display device for general electronic / electric equipment is provided with a backlight device for making it easy to see a display image of liquid crystal, which is a non-light emitting body, even in a dark place. The backlight device includes a light source, a light guide plate that guides light from the light source, and an optical sheet disposed on the light guide plate. For this optical sheet, for example, a plurality of sheet materials such as a lens sheet, a brightness enhancement sheet, and a light diffusion sheet are used, and these sheet materials are fixed in a state of being laminated on the light emitting surface of the light guide plate. Yes. However, these sheet materials are thermally deformed under the influence of heat from the light source, and the surface thereof is bent or wrinkled, and the display image may be difficult to see due to the bending or the like. Therefore, in order to prevent the occurrence of such bending or the like, a method for attaching the optical sheet has been devised (for example, Patent Documents 1 to 1 below).
3).

4 shows a backlight device of a conventional liquid crystal display device, FIG. 4 (a) is a plan view of the backlight device, and FIG. 4 (b) is an exploded perspective view of FIG. The backlight device 1A is of an edge light type, and has a rectangular light guide plate 17 and the light guide plate 17 as shown in FIG.
It comprises an optical sheet 13 made of a plurality of sheet materials (diffusion sheet 14, lens sheet 15 and brightness enhancement sheet 16) laminated thereon and a reflective sheet 18 disposed below the light guide plate 17, and these are EL, The structure is supported and fixed by a support frame 12 in which a light source (not shown) such as a cold cathode fluorescent tube or a light emitting diode is disposed. Light guide plate 17 and optical sheet 1
3 have substantially the same shape, and convex projections 17a, 14a, 15a, 16a, 18a are formed on the opposing short sides of these and the reflection sheet 18, respectively. Further, the support frame 12 has a convex projection 1 of the light guide plate 17, the optical sheet 13, and the reflection sheet 18 on the opposite short side of the frame.
A concave groove 12a into which 7a, 14a, 15a, 16a, 18a is fitted is formed.

In this way, the optical sheet 13, the light guide plate 17, and the reflection sheet 18 are accurately positioned and fixed to the support frame 12 simply by fitting the respective convex protrusions 17a, 14a, 15a, 16a, and 18a into the concave grooves 12a. It can be performed. Patent Document 2 below discloses a display device in which slits are provided along four sides of a rectangular optical sheet so as to absorb bending. Further, Patent Document 3 below describes a backlight device in which slit edges are provided on the edge of an optical sheet.
JP-A-11-306835 (paragraphs [0018] to [0020], FIG. 1) Japanese Patent Laid-Open No. 11-337942 (paragraphs [0010] to [0012], FIG. 1) Japanese Patent Laying-Open No. 2005-301147 (paragraphs [0028] to [0031], FIG. 1)

Usually, the backlight device 1A has a clearance (gap) between the convex protrusions 14a, 15a, 16a of the optical sheet 13 and the concave groove 12a of the support frame 12 in consideration of thermal expansion of each sheet material.
G is provided. FIG. 5 is an enlarged view of a portion X in FIG. 4A showing the state of the clearance between the convex protrusion and the concave groove.

However, even if the clearance G as shown in FIG. 5 is provided, if the ambient temperature and humidity of the optical sheet 13 increase due to changes in the use environment, for example, heat generation from the backlight light source, the more the respective sheet materials. Large thermal expansion or hygroscopic expansion occurs. Then, as indicated by arrow P ₁ in FIG. 5, the repulsion stress P ₂ is generated by the convex protrusions 13a of the sheet material collides with the bottom of the concave groove 12a of the support frame 12, which is the center of the sheet material It may propagate to the part and cause sheet wrinkles on the surface. Such sheet wrinkles are also caused by variations in dimensions when the optical sheet 13 is manufactured, or by shifting to one side of the opposing frame side of the support frame 12 when the optical sheet 13 is incorporated into the backlight device 1A. There are things to do. The optical sheets of Patent Documents 1 and 2 are provided with slits or cuts, but no countermeasures are taken into account for sheet wrinkles caused by repulsive stress generated between the fixing portions of the support frame. . Moreover, when a slit is provided along the sheet side as in the backlight device disclosed in Patent Document 3, the mechanical strength of the sheet material may be reduced, and fixing to the support frame may be difficult.

In recent years, in order to increase the luminance of the backlight device, it has been required to use a higher power light source to make the liquid crystal screen brighter. Since the temperature of heat generated from such a light source is high and the amount of heat is large, it is difficult to prevent wrinkles or deflection caused by heat generated from such a light source using conventional positioning and fixing means. It is becoming.

Therefore, the present invention has been made to solve the above problems, and the object of the present invention is to
An object of the present invention is to provide a high-quality optical sheet that can absorb repulsive stress that is likely to occur in the positioning and fixing portion of the sheet and is less likely to cause sheet wrinkling and bending.

Another object of the present invention is to provide a backlight device and a liquid crystal display device using the optical sheet.

In order to achieve the above object, in the optical sheet of the present invention, a positioning projection is formed on at least one side of the sheet material, and the projection is fitted into a positioning groove of a support frame in the backlight device. In the optical sheet, the sheet material is characterized in that a slit is formed along a side of the sheet material at a position that is close to the protruding portion and separated from the side of the sheet material by a predetermined distance.

According to the above aspect, by providing a slit that absorbs the repulsive stress at a location close to the positioning protrusion, the optical sheet generates heat from the light source in the ambient environment, for example, the backlight device,
Even if the protrusions collide with the support frame due to expansion due to the ambient temperature and humidity, and a repelling stress is generated by the collision, the repelling stress is not absorbed by the slit and propagated to the central portion of the optical sheet. As a result, it is possible to obtain a high-quality optical sheet that is not wrinkled or bent in an area corresponding to the display area of the optical sheet when incorporated in a display device.

Moreover, the said aspect of this invention WHEREIN: It is preferable when the said protrusion part is formed in the protrusion which protruded outward from the side of the said sheet | seat material, and the said slit is formed in the location facing the said protrusion.

According to the optical sheet of the above aspect, the slit is located at a position facing the protrusion, and is formed along this side by a predetermined distance away from the side of the sheet material, without reducing the mechanical strength, The above effects can be achieved.

In the above aspect of the present invention, the slit is preferably formed such that the length along the side is longer than the length of the protrusion, and the width is the same as the distance from the side. .

According to the said aspect, said effect can be achieved, without reducing mechanical strength by forming a slit in the location facing the processus | protrusion along the side apart from the side of the sheet | seat material predetermined distance.

Moreover, the said aspect of this invention WHEREIN: It is preferable when the said protrusion part and a slit are provided in the edge | side which the said sheet material opposes.

According to the said aspect, by providing a protrusion part and a slit in the edge | side which a sheet material opposes,
The repulsive stress generated in the sheet material can be effectively absorbed.

In the above aspect of the present invention, it is preferable that the optical sheet is a combination of one or more of a diffusion sheet, a lens sheet, and a brightness enhancement sheet.

According to the said aspect, a diffusion sheet, a lens sheet, and a brightness improvement sheet become difficult to generate | occur | produce a wrinkle and a bending, and can form a high quality optical sheet.

Moreover, in the above aspect of the present invention, it is preferable that the optical sheet includes a reflective sheet.

According to the said aspect, a reflection sheet becomes difficult to generate | occur | produce a wrinkle and a bending and can form a high quality reflection sheet.

Further, in the above aspect of the present invention, the support frame of the backlight device has an opening through which light from a light source passes, and the slit is not positioned inside the edge of the opening of the support frame. Preferably it is provided.

According to the above aspect, the light from the light source does not pass through the slit even when mounted on a display panel, for example, a liquid crystal display panel, the luminance of the backlight device is not lowered, and the display is adversely affected. Also disappear.

A backlight device according to the present invention includes a light source, a light guide plate that derives light from the light source, an optical sheet that is placed and fixed on the light guide plate, and a support frame that houses these components. In the apparatus, a positioning groove is provided in the support frame, and the optical sheet is fixed to the support frame by using the optical sheet according to any one of the aspects of the invention described above. And

According to the backlight device of the above aspect, the optical sheet is formed with slits that absorb the repulsive stress, so that the optical sheet does not wrinkle or bend even when disposed in the backlight device. Therefore, a backlight device that does not adversely affect display can be provided.

The liquid crystal display device of the present invention includes the above-described backlight device and a liquid crystal display panel illuminated by the backlight device.

According to the liquid crystal display device of the said aspect, the liquid crystal display device which has the effect of the above-mentioned backlight apparatus can be provided.

Hereinafter, the best embodiment of the present invention will be described with reference to the drawings. However, the embodiment described below exemplifies an optical sheet for embodying the technical idea of the present invention, a backlight device using the optical sheet, and a liquid crystal display device. It is not intended to be specific, and other embodiments within the scope of the claims are equally applicable.

FIG. 1 shows a backlight device used in a liquid crystal display device according to an embodiment of the present invention.
FIG. 1A is a plan view thereof, FIG. 1B is an enlarged plan view of a portion X in FIG. 1A, and FIG. 2 is an exploded perspective view showing components stacked on the backlight device of FIG. FIG. In the following description, the term “optical sheet” refers to a generic term for a diffusion sheet, a lens sheet, and a brightness enhancement sheet, and the term “sheet material” refers to a material constituting the optical sheet. Shall be pointed to.

A backlight device 1 according to an embodiment of the present invention is an edge light type backlight device, and is laminated on a rectangular light guide plate 7 and the light guide plate 7 as shown in FIGS. An optical sheet 3 made of a plurality of sheet materials and a reflection sheet 8 disposed below the light guide plate 7 are provided, and these are supported and fixed by the support frame 2.

The optical sheet 3 includes a diffusion sheet 4, a lens sheet 5, and a brightness enhancement sheet 6. The light guide plate 7 has convex protrusions 7a formed on the opposing short sides. Diffusion sheet 4
The lens sheet 5 and the brightness enhancement sheet 6 have substantially the same shape as the light guide plate 7, and convex protrusions 4 a, 5 a, 6 a (hereinafter, these convex protrusions are provided as positioning protrusions on the opposing short sides, respectively. Collectively, it is referred to as a convex protrusion 3a of the optical sheet 3.) is formed by protrusions protruding outward from the respective sides. The reflective sheet 8 is also formed with a convex protrusion 8a as a similar positioning protrusion, and is formed by a protrusion protruding outward from the side, like the convex protrusion 3a of the optical sheet 3. . Further, the supporting frame 2 is a positioning groove into which the convex projection 3 a of the optical sheet 3, the convex projection 7 a of the light guide plate 7, and the convex projection 8 a of the reflection sheet 8 are fitted on the opposing short side of the frame. A concave groove 2a is formed. In addition, a light source (not shown) made of a fluorescent tube or a light emitting diode is disposed in the support frame 2, for example, inside one of the long sides where the concave groove 2 a is not provided.

Among these components, the light guide plate 7 is formed of a transparent plate having a certain thickness and excellent light transmittance. The light guide plate 7 is made of a material having a small light absorption rate and a refractive index of a predetermined value or more, for example, a refractive index n = 1.4 or more. Specifically, acrylic resin, polycarbonate resin, polystyrene resin, glass or the like is used for the light guide plate 7.

Convex protrusion 3a of the optical sheet 3, as shown in FIG. 1 (b), a pair of side edges 3 ₁ projecting by a predetermined length H outwardly from the side edges 3 ₀ of the optical sheet 3, a predetermined width dimension It had a top side 3 ₂ L ₁ has a protrusion. Further, the optical sheet 3 is in a location corresponding to the convex protrusion 3a,
Where recessed by a predetermined width dimension W ₁ from the end portion of the sides 3 ₀ of the optical sheet 3 toward the center of the sheet material, the slits 3A is the side 3 having the same width dimension W ₂ and the width dimension W _{1 0} It is formed along the extending direction. Each slit 3A has the same shape.

Hereinafter, the shape of the convex protrusion 3a and the slit 3A will be described in detail with reference to FIG.
The longitudinal length L ₃ of the slit 3A is slightly longer than the top side 3 _second length L ₁ of the convex projection 3a. The length L ₃ are each the same length L from both ends of the top edges of the convex projection 3a
_The length is preferably extended by _two . With such a length, as will be described later, the repulsive stress generated in the optical sheet 3 can be released to the slit portion in a well-balanced manner, thereby preventing the occurrence of wrinkling and bending in the display area. The slit 3A is provided outside an area corresponding to a display area of a liquid crystal display panel (not shown) disposed on the backlight device 1. That is, the optical sheet 3 is disposed on the back surface of the liquid crystal display panel, but the slit 3A is not a portion corresponding to the display area of the liquid crystal display panel in a state where the liquid crystal display panel is disposed, but the display area. It is located outside. By providing the slit 3A at this position, the display of the liquid crystal display panel is not adversely affected.

On the other hand, the support frame 2 has an opening through which light from the light source passes, and a concave groove 2a into which the convex protrusion 3a of the optical sheet is fitted is formed at the inner peripheral edge of the opening. The convex protrusion 3a and the concave groove 2a are designed such that a clearance (gap) G is formed between the convex grooves 3a when the convex protrusion 3a is fitted between the concave grooves 2a.

As described above, by providing the convex protrusions 3a and the slits 3A on the opposite sides of the optical sheet 3, the optical sheet 3 expands due to heat from the light source, ambient temperature, or humidity, and the convex protrusions 3a of the optical sheet. Even if it collides with the bottom of the concave groove 2a of the support frame 2 and a repulsive stress is generated due to the collision, the occurrence of wrinkles and bending can be prevented. That is, the optical sheet 3 disposed on the support frame 2 expands under the influence of, for example, heat from the light source, environmental temperature, or humidity. This expansion, as indicated by the arrow P ₁ in FIG. 1 (b), the convex projection 3a of the optical sheet 3 is pushed strongly concave groove 2a of the support frame 2, the convex end of the projection 3a concave groove 2a Collide with the bottom of the. The repulsive stress P ₂ is generated by this collision. However, since the slit 3A at a position corresponding to the convex protrusion 3a is formed, the longitudinal direction of the repulsive stress acts to narrow the gap distance of the slit 3A, wrinkles or bending the side edges 3 ₀ and the slit 3A only generated between the both ends of the (symbol W in FIG. 1 (b)), and it is eliminated propagate to the central portion of the repulsive force stress P ₂ becomes the display region of the optical sheet 3 beyond the slit 3A .

Accordingly, the tip of the convex projection 3a is even when the repulsion stress P ₂ collides with the bottom of the concave groove 2a, wrinkle and deflection that occurs eliminated at a location corresponding to the display area of the optical sheet 3. As described above, the length L ₃ of the slit 3A, the length L of extended length L ₂ from the convex protrusion 3a
₃ is preferable. Further, the slit 3A is, in the position corresponding to the convex projections 3a, arranged from the side edges 3 ₀ of the optical sheet 3 width dimension W ₁ inner toward the center, in a separate location from the outer shape of the optical sheet 3 It is done. The width length W ₂ of the slit 3A is preferably the width dimension W ₁ as wide as the length W ₂ of the sides 3 ₀ of the optical sheet 3. In this way, by providing the slit 3A at a position that is independent of the external shape of the optical sheet 3, it can be absorbed without efficiently rebound stress P ₂ to decrease the mechanical strength of the optical sheet 3.

Next, with reference to FIG. 2, the individual sheets constituting the optical sheet 3 will be described.
The diffusion sheet 4 diffuses light from a light source, and is made of a film-like sheet material made of polycarbonate resin or acrylic resin material. For example, random unevenness is formed on at least one surface of the front and back surfaces. Has been. The diffusion sheet 4 is provided with convex protrusions 4a on opposite short sides, and slits 4A are formed in the vicinity of these protrusions. Further, the lens sheet 5 is provided with convex protrusions 5a on opposite short sides, and slits 5A are formed in the vicinity of these protrusions. Further, the brightness enhancement sheet 6 is provided with convex protrusions 6a on the opposing short sides, and slits 6A are formed in the vicinity of these protrusions.

The reflection sheet 8 efficiently guides the reflected light from the light source to the light guide plate 7, and is formed of a white plastic sheet material or a plastic sheet material on which silver, aluminum, or the like is vapor-deposited. The reflective sheet 8 is provided with convex protrusions 8a on opposite short sides, and slits 8A are formed in the vicinity of these protrusions. Each slit 8 </ b> A has the same shape as the slit 3 </ b> A of the optical sheet 3.

In the optical sheet 3 described above, slits are provided in all the sheets, that is, the diffusion sheet 4, the lens sheet 5, the brightness enhancement sheet 6, and the reflection sheet 8. Of these sheets,
You may make it provide only in either sheet | seat.

FIG. 3 shows a modification in which slits are provided only in any one of the sheets constituting the optical sheet.
That is, the optical sheet 3 ′ according to this modification is only the diffusion sheet 4 and the lens sheet 5 among the diffusion sheet 4, the lens sheet 5, the brightness enhancement sheet 16, and the reflection sheet 18 constituting the optical sheet 3 ′. The slits 4A and 5A are formed, and the brightness enhancement sheet 16 and the reflection sheet 18 are made of the same sheet material as shown in the prior art. This is because the diffusion sheet 4 and the lens sheet 5 are formed of members having a higher coefficient of thermal expansion than other sheet materials. Also in the optical sheet 3 ′ configured as described above, the backlight device 1 is formed by being mounted in the support frame 2.

The backlight device is used by being attached to a liquid crystal display panel (not shown). Further, even when this backlight device is incorporated in a liquid crystal display device together with a liquid crystal display panel illuminated by the backlight device, the sheet material does not wrinkle or bend, and a high-quality image is displayed on the liquid crystal display device. Can be displayed.

The preferred embodiment of the present invention has been described above, but the present invention is not limited to this and can be variously modified. For example, as the optical sheet, not only a diffusion sheet, a lens sheet, and a brightness enhancement sheet, but also other sheets may be added, and the shape thereof may be any shape according to the liquid crystal display panel, such as a square or a rectangle. It may be.

It is a figure which shows the backlight apparatus used for the liquid crystal display device of this invention. It is a disassembled perspective view of the optical sheet which comprises the backlight apparatus of FIG. It is an exploded view which shows the modification of an optical sheet. It is a figure which shows the backlight apparatus of the liquid crystal display device of a prior art. It is an enlarged view of the X part of Fig.4 (a).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Backlight apparatus, 2 ... Support frame, 2a ... Concave groove, 3 ... Optical sheet, 4 ... Diffusion sheet, 5 ... Lens sheet, 6 ... Brightness improvement sheet, 7 ... Light guide plate, 3a-8a ... Convex protrusion, 3A ~
6A, 8A ... slit, G ... clearance, P 2 _... repulsive stress

Claims (9)

In the optical sheet in which the positioning protrusion is formed on at least one side of the sheet material and the protrusion is fitted in the positioning groove of the support frame in the backlight device, the sheet material is close to the protrusion. An optical sheet, wherein a slit is formed along a side of the sheet material at a predetermined distance from the side. 2. The optical sheet according to claim 1, wherein the protruding portion is formed by a protrusion protruding outward from a side of the sheet material, and the slit is formed at a location facing the protrusion. 3. The optical device according to claim 2, wherein the slit is formed such that a length along the side is longer than a length of the protrusion, and a width of the slit is the same as a distance from the side. Sheet. The optical sheet according to claim 1, wherein the protrusion and the slit are provided on opposite sides of the sheet material. The optical sheet according to claim 1, wherein the optical sheet is one of a diffusion sheet, a lens sheet, and a brightness enhancement sheet or a combination of a plurality of sheets. The optical sheet according to claim 5, wherein the optical sheet includes a reflective sheet. The support frame of the backlight device has an opening for allowing light from a light source to pass therethrough, and the slit is provided so as not to be located inside the edge of the opening of the support frame. The optical sheet according to claim 1. In a backlight device including a light source, a light guide plate for deriving light from the light source, an optical sheet placed and fixed on the light guide plate, and a support frame for housing these components, the backlight unit is positioned on the support frame. A backlight device, wherein a groove is provided, and the optical sheet is fixed to the support frame using the optical sheet according to claim 1. A liquid crystal display device comprising the backlight device according to claim 8 and a liquid crystal display panel illuminated by the backlight device.

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