Liquid-crystal display device

Optical sheets can be fixed easily and positively in a liquid-crystal display device having a liquid-crystal display panel in which a liquid-crystal layer sandwiched between a pair of substrates and a lighting unit provided on a surface opposite to a display surface of the liquid-crystal display panel. For this purpose, a projection is provided on a sidewall of an accommodator, and the projection is inserted into a hole provided in optical sheets arranged within the accommodator, thereby fixing the optical sheets in the accommodator. The length along a certain straight line of a top plan form of a tip of the projection is longer than the length along the certain straight line of the hole formed in the optical sheets, thus preventing the optical sheets from falling out of the accommodator.

BACKGROUND OF THE INVENTION

The present invention relates in general to liquid-crystal display devices, and, more particularly, to a method of aligning optical sheets in a thicknesswise direction of the liquid-crystal display device.

TFT-type liquid-crystal display modules, using thin film transistors (TFTs) as active elements, are broadly used as display devices, such as in personal computers, monitors and television receivers. These liquid-crystal display modules are each constituted by a liquid-crystal display panel arranged with a drive circuit in the periphery thereof and a backlight for illuminating the liquid-crystal display panel.

The backlights are roughly divided into two basic types, including the under-lighting type backlight, in which a that the cold-cathode fluorescent lamp is arranged underneath a light conductor, and the side-lighting type backlight, in which the cold-cathode fluorescent lamp is arranged at one side face of the light conductor. In both types of backlights, optical sheets (diffusion sheets, prism sheets) are arranged over the top surface (the liquid-crystal display panel side) of the light conductor.

Conventionally, for the purpose of fixing such optical sheets is positioned, a hole is formed in the optical sheets so that a projection formed in a sidewall of an optical-sheet accommodating mold can be inserted in the hole, followed by adhering a tape over the projection from above in order to fix the projection in the hole.

However, with this method, the adhesive tape is readily peeled off the projection because the area of the projection in contact with the tape is small in diameter. In the worst case, it is possible for the optical sheets to move in a thicknesswise direction of the liquid-crystal display device and fall out of the mold. Besides, there is the possibility of inferior production efficiency due to the need to paste an adhesive tape on the assembly.

In order to solve the foregoing problem, Document 1 (Japanese Patent Laid-Open Hei 11-337942) discloses a technique in which an engagement claw is formed at the head of an engagement piece so that the optical sheets can be prevented from falling out of the engagement piece due to the providing of the engagement claw.

SUMMARY OF THE INVENTION

However, in the technique disclosed in Document 1, the diameter of the engagement claw is nearly the same as the diameter of the hole formed in the optical sheet. In the worst case, it is possible for the optical sheet to disengage from the engagement claw.

The present invention has been made in order to solve the problem discussed above. It is an object of the present invention to provide a technique that is capable of fixing optical sheets easily and positively.

The foregoing and other objects and novel features of the invention will be made apparent by the following description and the accompanying drawings.

An outline of representative aspects and features of the invention will be presented.

In order to achieve the foregoing object, the present invention provides a liquid-crystal display device comprising a liquid-crystal display panel having a liquid-crystal layer sandwiched between a pair of substrates, and a backlight unit provided on a surface opposite to a display surface of the liquid-crystal display panel. A projection is provided on a sidewall of an accommodator. A hole provided in the optical sheet arranged within the accommodator is disposed to allow the projection to be inserted therein to thereby fix the optical sheet in the accommodator. The projection has a tip having a top plan form having a length along a certain straight line which is longer than the length along the certain straight line of the hole formed in the optical sheet, thereby preventing the optical sheet from becoming disengaged from the accommodator.

Meanwhile, the present invention provides a liquid-crystal display device comprising a liquid-crystal display panel having a liquid-crystal layer sandwiched between a pair of substrates, and a backlight unit provided on a surface opposite to a display surface of the liquid-crystal display panel. A projection is provided on a sidewall of an accommodator. A hole provided in the optical sheet arranged within the accommodator is disposed to allow the projection to be inserted therein to thereby fix the optical sheet.

Meanwhile, the form of the hole formed in the optical sheet has the same top plan form so that of the tip of the projection. Furthermore, the hole is formed so that a certain rotation angle exists between the form of the hole and the top plan form of the tip of the projection in a state in which the optical sheet is accommodated in the accommodator. In the state in which the optical sheet is accommodated in the accommodator, the optical sheet at a peripheral part of the hole is engaged with the tip of the projection, thereby preventing the optical sheet from becoming disengaged from the accommodator.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the present invention will now be explained with reference to the drawings.

Note that those elements having the same function are identified in all of the views by the same reference numerals, and duplicated explanations thereof will be omitted.

FIG. 1is an exploded perspective view showing the structure of a TFT-type liquid-crystal display module according to an embodiment of the present invention.

The liquid-crystal display module of this embodiment is an active-matrix liquid-crystal display module having its drive element (semiconductor chip) mounted on one of a pair of substrates constituting a liquid-crystal display panel by means of a flip-chip attachment (FCA) type of mounting scheme. The main constituent elements are as follows.

The liquid-crystal display module (LCM) of this embodiment is constructed with a frame made of a metal plate (upper case)4, a liquid-crystal display panel5, and a backlight.

The liquid-crystal display panel5, shown as a panel provided with an assembled drive circuit board, has a pair of substrates superposed and jointed together so as to sandwich a liquid-crystal layer therebetween (e.g. formed of an optically transmissive, electrically insulative material, such as glass), a group of liquid-crystal-driving semiconductor integrated circuit elements (drive ICs) arranged at a peripheral edge of one of the pair of substrates, a flexible circuit board (not shown) for supplying signals or power to these drive ICs externally of the liquid-crystal display panel, and an interface circuit board (not shown).

The paired substrates are superposed so as to be spaced with a predetermined gap. Both substrates are bonded together by a seal member provided in a frame form close to a peripheral edge thereof. Liquid crystal is filled into the inside space defined by the seal member between the substrates through a liquid-crystal filling port provided in part of the seal member, and the filling port is then sealed. Furthermore, polarizer plates are bonded to the outer sides of both substrates.

A metal-plate frame (referred also to as a shield case, upper case or metal frame)4is arranged on the assembled liquid-crystal display panel5, such that its display window exposes the main surface of the liquid-crystal display panel5corresponding to the effective display region. Accordingly, the frame4has a frame-formed planar structure. Furthermore, a housing (not shown) is provided with a display window of the type employed in a personal computer, for example. In a personal computer, for example, the user is allowed to view the liquid-crystal panel5shown inFIG. 1from above and recognize an image displayed in the effective display region.

InFIG. 1, optical sheets (an upper diffusion sheet6, two prism sheets7and a lower diffusion sheet8) are arranged underneath the assembled liquid-crystal display panel5and are supported through use of a rubber cushion (not shown), for example. Incidentally, in accordance with the invention, the optical sheets include at least one optical sheet in the form of the upper diffusion sheet6, the two prism sheets7, the lower diffusion sheet8and the like.

As shown inFIG. 1, the optical sheets are laid one over another by arranging the upper diffusion sheet6and the lower diffusion sheet8above/beneath the two prism sheets7. The optical sheets are fixed at their one ends tab which extends into a recess formed, by a, in a sidewall at the peripheral edge of a mold14(referred to also as a lower case).

A light conductor9is accommodated in the mold14such that its upper surface is opposed to an underside of the lower diffusion sheet8. Furthermore, a reflection sheet (not shown) is arranged underneath the light conductor9. The mold14, in many cases, is formed by integral molding of a white synthetic resin or the like, on which a cold-cathode fluorescent lamp (not shown) and a lamp cable19are fixed by means of a rubber bush (not shown). The lamp cable19has respective ends provided with connectors12for connection to an inverter circuit (not shown), to supply power from the inverter circuit provided on the underside of the mold14to a cold-cathode fluorescent lamp.

In this manner, in the backlight of the liquid-crystal display module of this embodiment, the cold-cathode fluorescent lamp, the wedge-formed (trapezoid as seen in side form) conductor9, the diffusion sheets (6,8), the prism sheets7and the reflection sheet have sidewalls and are fitted in the mold14which is formed in the shape of a frame. The assembled liquid-crystal panel5is fixed by being sandwiched between the frame4and the backlight, thus forming complete liquid-crystal display module.

FIG. 2is an enlarged view of part A inFIG. 1. As shown inFIG. 2, in this embodiment, a projection (or pin)1is formed on the sidewall141of the mold14.

FIG. 3shows an example of the configuration of the optical sheet (upper diffusion sheet6, two prism sheets7and lower diffusion sheet8) shown inFIG. 1. As shown inFIG. 3, the optical sheet is formed with a hole2into which the projection1is to be inserted. The hole2formed in the optical sheets is positioned over the projection1formed in the sidewall141of the mold14to allow the projection1to come into engagement therewith, thereby fixing the optical sheets.

Meanwhile, inFIG. 3, the reference152refers to a tab to be inserted in a recess142formed in the sidewall141of the mold14.

FIGS. 4A to 4Cillustrate a method of fixing the optical sheets of this embodiment. For this purpose, the hole2formed through the optical sheets is positioned over the projection1formed on the sidewall141of the mold14to allow the projection1to engage therewith, thereby arranging the upper diffusion sheet6, the two prism sheets7and the lower diffusion sheet8onto the light conductor plate, as shown inFIG. 4B.

Then, the projection1is crushed at its top end (or its head) by a technique such as heating, for example, as shown inFIG. 4C. Thus, the top end of the projection1is enlarged in diameter so as to be greater than the diameter of the hole2formed in the optical sheets.

FIG. 4Ashows a state in which the upper diffusion sheet6, the two prism sheets7and the lower diffusion sheet8are arranged on the light conductor plate within the mold.

As shown inFIG. 4A, in this embodiment, the tabs152formed on the optical sheet are inserted in the recesses142formed in the sidewall141of the mold14, thus aligning the optical sheet. Furthermore, the crushed tip of the projection1formed on the sidewall141of the mold14prevents the optical sheets from moving in a direction thicknesswise of the liquid-crystal display device and falling out of the mold14.

FIGS. 16A and 16Billustrate a conventional method of fixing the optical sheets. In the conventional optical sheet fixing method, the hole2formed through the optical sheets is positioned over the projection1formed on the sidewall141of the mold14so that the projection1engages with the hole2, as shown inFIG. 16A, thereby arranging the upper diffusion sheet6, the two prism sheet7and the lower diffusion sheet8on the light conductor plate.

Then, as shown inFIG. 16B, an adhesive tape30is pasted over the hole2onto the tip of the projection1. This is intended to prevent the optical sheets from moving in a direction of the thickness of the liquid-crystal display device and falling out of the mold14. However, with use of this method, the adhesive tape30is readily peeled off the projection because the projection1is small in diameter and, therefore, has only a small surface in contact with the tape. It can be considered that, in the worst case, the optical sheet can move in a direction thicknesswise of the liquid-crystal display device and disengage from the mold14.

On the contrary, in the present embodiment, the tip of the projection1formed on the sidewall141of the mold14, which has been crushed to a size larger than the hole, can positively prevent the optical sheets from moving in a direction thicknesswise of the liquid-crystal display device and fall out of the mold14. This makes it possible to fix the optical sheets easily and positively.

FIGS. 5A to 5Cillustrate a method of fixing the optical sheets according to an embodiment 2 of the invention.

Although in the foregoing embodiment the projection1is formed integrally with the mold14, this embodiment provides a projection1which is formed separately therefrom, as shown inFIG. 5A. In this case, the projection1, which is made separately, is inserted in the sidewall141of the mold14, as shown inFIG. 5B.

Then, as shown inFIG. 5C, a hole2formed through the optical sheets is positioned over the projection1formed on the sidewall141of the mold14so that the projection1engaged with the hole2, thereby arranging the upper diffusion sheet6, the two prism sheets7and the lower diffusion sheet8on the light conductor plate.

In this case, because the diameter of the hole2formed through the optical sheets is smaller than the diameter at the tip of the projection1, the hole2formed through the optical sheets is placed onto the light conductor plate while screwing it onto the projection1.

After this, in accordance with the present embodiment, the tabs152formed on the optical sheets are inserted in the recesses142formed in the sidewall141of the mold14, thus aligning the optical sheets. Moreover, the enlarged tip of the projection1prevents the optical sheets from moving in a direction thicknesswise of the liquid-crystal display device and falling out of the mold14. Accordingly, the present embodiment also makes it possible to fix the optical sheets easily and positively.

Incidentally, in this embodiment, the projection1also may be formed integral with the mold14, as shown inFIG. 6.

As an alternative, the tip of the projection1may have a semispherical form, as shown inFIGS. 7A and 7B, without being limited to the spherical form shown inFIGS. 5A to 5C. Note thatFIG. 7Ais a diagrammatic top plan view (hereinafter, referred to as the top plan form) of the projection1as viewed from above, whileFIG. 7Bis a diagrammatic sectional view showing the sectional shape of the projection1.

On the other hand, the top plan form at the tip of the projection1also may be in a semispherical form, as shown inFIG. 8, without being limited to the circular form shown inFIGS. 5A to 5C. Note thatFIG. 8is a top plan view showing the top side form of the projection1.

In addition, the sectional form of the projection1in the other portion than the tip (portion B shown inFIG. 7B) is not limited to the circular form shown inFIG. 7A, but may be have an elliptical form or a polygonal form, such as rectangular. Meanwhile, by forming slits21, as shown inFIGS. 9 and 10at around the periphery of the hole2formed through the optical sheets, the hole2formed through the optical sheets can easily pass over the enlarged projection1formed on the sidewall141of the mold14.

In the foregoing embodiment 2, there is a fear that the optical sheet may be deformed due to the necessity to place the hole2, which is formed through the optical sheets, onto the light conductor plate by screwing it onto the projection1. The present embodiment is designed to avoid such a disadvantage.

FIGS. 11A to 11Care diagrams which illustrate a method of fixing the optical sheets in accordance with embodiment 3 of the invention.

In this embodiment, the hole2that is formed through the optical sheets is made to have the same non-circular shape as the shape of the tip of the projection1formed in the sidewall141of the mold14(elliptical inFIG. 11).

The hole2is formed in the optical sheets such that a certain rotational angle is established between the long axis of the hole2and the long axis of the tip of the projection1in a state in which the optical sheets are arranged on the light conductor plate within the mold.

For this reason, in this embodiment, the projection1is inserted into the hole2of the optical sheets by rotating the optical sheets about the projection1through a certain rotation angle, as shown inFIG. 11A, until the shape of the hole2matches the shape of the projection1. In this case, because the hole2formed in the optical sheets is aligned with the tip of the projection1, the projection1can be easily inserted into the hole2formed in the optical sheets without applying a force.

Thereafter, the optical sheets are rotated again on the light conductor plate such that the tab152of the optical sheets is received in the recess142of the sidewall141of the mold14, as shown inFIG. 11B. In this state, the hole2of the optical sheets at its peripheral part is engaged by the tip of the projection1.

Due to this, in this embodiment, the tab152formed in the optical sheets is inserted in the recess142formed in the sidewall141of the mold14, thereby aligning the optical sheets. Furthermore, the tip of the projection1prevents the optical sheets from moving in a direction thicknesswise of the liquid-crystal display device and falling out of the mold14. Therefore, this embodiment also makes it possible to fix the optical sheets easily and positively.

Incidentally, in this embodiment, the shape at the tip of the projection1is not limited to elliptical form, as shown inFIGS. 11A to 11C, but may be in the form of a cross, as shown inFIG. 12, a combined circle and rectangular part, as shown inFIG. 13, or a rectangular form, as shown inFIGS. 14A and 14B. Note thatFIG. 14Ais a top plan view showing the top of the projection1, whileFIG. 14Bis a sectional view showing the side of the projection1.

FIG. 15shows the shape and orientation there is shown a form of the hole2formed in the optical sheets that are arranged on the light conductor plate in the case where the top plan form at the tip of the projection1is a square as shown inFIG. 14A.

Incidentally, although the foregoing embodiment has been explained mainly in conjunction with examples where the invention is applied to TFT-type liquid-crystal display module, the invention is not limited to that. In this regard, it should be understood that the invention is applicable also to an STN-type liquid-crystal display module.

Although the invention made by the present inventor has been explained on the basis of the foregoing embodiments, the invention is not limited to the foregoing embodiments, but can be modified in various ways within a scope not departing from the gist thereof.

According to the liquid-crystal display device of the present invention, optical sheets can be fixed easily and positively in the liquid-crystal display device.