JP2006322964A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of preventing the stripping of a film for improving brightness of a polarizing plate. <P>SOLUTION: A PVA film 13 is put between TAC films 11, 12 and is bonded. The film 14 for improving brightness of the polarizing plate is stuck to the under side of the TAC film 11 via an adhesive layer G1. The polarizing plate 3 is bonded to an array substrate 7 via an adhesive layer G2 disposed on the under side of the film 14 for improving brightness. The edge surface of the polarizing plate 3 is formed into a forwardly tapered shape of a taper angle of 30° to 60°. A stress applied to the edge part of the film 14 for improving brightness is dispersed by the forwardly tapered shape and the stripping of the film 14 for improving brightness can be prevented. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device including a pair of substrates and a polarizing plate bonded to at least one of these substrates.

  Conventionally, this type of liquid crystal display device has a liquid crystal cell in which a liquid crystal layer is injected between an array substrate and a counter substrate facing each other at a predetermined distance, and a polarizing plate is provided on at least one of the liquid crystal cells. Is affixed via an adhesive.

  Such a polarizing plate generally uses a TAC (Tri-Acetate Cellulose) as a film-like polarizer made of stretched and dyed PVA (Poly Vinyl Alcohol). The film is sandwiched between the formed films via an adhesive, and a pressure-sensitive adhesive is applied to the lowermost part of the film and is stuck to the liquid crystal cell.

By the way, in recent years, such liquid crystal display devices have been required to have high performance such as high brightness and wide viewing angle, and a brightness enhancement film inside the polarizing plate, that is, a high brightness film, or a viewing angle improvement. It is known to use an integrated polarizing plate with films for various uses such as films (see, for example, Patent Document 1).
JP 2005-31340 A

  When manufacturing the polarizing plate as described above, PVA and TAC are bonded with an adhesive, the bonded polarizing plate is cut into a predetermined size, and then a high-intensity film or the like is bonded later with an adhesive. Let

  As this pressure-sensitive adhesive, since it is necessary to be a material that does not optically influence, the same material as that for adhering the liquid crystal cell and the polarizing plate is often used.

  However, since such a pressure-sensitive adhesive is designed to optimize the adhesive strength with TAC and the adhesive strength with glass, the adhesive strength with a high-intensity film may be weaker than the adhesive strength with glass. There is.

  In such a case, in the manufacturing process of the liquid crystal display device, after the polarizing plate is attached to the liquid crystal cell, the protective film of the polarizing plate is peeled off from the intermediate layer which is an adhesive portion of the high brightness film. Therefore, there is a problem that the yield may be affected.

  As a solution to this problem, it is conceivable to develop a new pressure-sensitive adhesive, but it is not easy to control all the pressure-sensitive adhesive forces such as glass, TAC and intermediate layer films.

  For this reason, the further improvement is calculated | required so that peeling of a high-intensity film can be prevented.

  This invention is made | formed in view of such a point, and it aims at providing the liquid crystal display device which prevented peeling of the film of the polarizing plate.

  The present invention includes a pair of substrates, a liquid crystal layer provided between the substrates, a polarizer and one or more films, and a polarizing plate bonded to at least one of the pair of substrates. At least one of the films is bonded on both sides with an adhesive, and the polarizing plate is formed in a forward taper shape of 30 ° or more and 60 ° or less whose end surface becomes narrower as the distance from the substrate increases. is there.

  And the end surface of the polarizing plate provided with the film which both surfaces adhere with an adhesive is formed in the forward taper shape of 30 degrees or more and 60 degrees or less which becomes narrow as it leaves | separates from a board | substrate.

  According to this invention, the stress added to the edge part of a film can be disperse | distributed by a forward taper shape, and peeling of the film of a polarizing plate can be prevented.

  Hereinafter, a configuration of a liquid crystal display device according to an embodiment of the present invention will be described with reference to the drawings.

  In FIG. 1, reference numeral 1 denotes a liquid crystal cell as a liquid crystal display device. This liquid crystal cell 1 is a TN (Twisted Nematic) mode of 12-inch diagonal (normally white 90 ° twist). In addition, the liquid crystal cell 1 includes a liquid crystal panel 2 and rectangular flat plate-shaped polarizing plates 3 and 4 attached to the liquid crystal panel 2. A backlight (not shown) is provided.

  The liquid crystal panel 2 includes an array substrate 7 as a rectangular substrate in plan view, a counter substrate 8 that is a color filter substrate as a rectangular substrate in plan view provided opposite to the array substrate 7, and these substrates 7. , 8 and a liquid crystal layer 9 as a light modulation layer.

  The array substrate 7 includes a glass substrate (not shown) that is a substantially rectangular flat plate that is an insulating substrate having translucency, and has a function of electrically driving the liquid crystal layer 9 for each pixel individually.

  A rectangular display region is provided on one main surface of the glass substrate of the array substrate 7, that is, the surface on the counter substrate 8 side. This display area is a display screen area as an effective display area for displaying an image. Further, in the display area, a plurality of pixels each having a thin film transistor (TFT) and a transparent pixel electrode (ITO) (not shown) are formed in a matrix.

  On the other hand, the counter substrate 8 includes a rectangular flat plate-shaped glass substrate (not shown) corresponding to the display area of the glass substrate of the array substrate 7. Further, on one surface of the glass substrate, that is, the surface on the side of the array substrate 7, a colored layer made of, for example, red (R), green (G), and blue (B) is opposed to a transparent electrode (not shown). The electrodes are sequentially stacked.

  The counter substrate 8 is disposed and bonded with a certain gap between the glass substrates while the surface of the glass substrate is opposed to the surface of the glass substrate of the array substrate 7.

  The liquid crystal layer 9 is formed by injecting a liquid crystal composition (not shown). The liquid crystal layer 9 is aligned and sandwiched between the glass substrate of the array substrate 7 and the glass substrate of the counter substrate 8.

  The polarizing plate 3 is an array substrate side polarizing plate bonded to the back surface of the glass substrate of the array substrate 7 of the liquid crystal panel 2, that is, the main surface opposite to the counter substrate 8, as shown in FIGS. . The polarizing plate 3 has a PVA (polyvinyl alcohol: PVA) film 13 as a polarizer sandwiched between TAC (Tri-Acetate Cellulose) films 11 and 12 as a pair of protective film layers, A brightness enhancement film 14 as a film is bonded to the array substrate 7 of the TAC film 11 on the array substrate 7 side, that is, the lower side via an adhesive layer G1 provided in a layer form with an adhesive (not shown). Therefore, the adhesive layer G1 and the brightness enhancement film 14 are intermediate layers of the polarizing plate 3.

  The polarizing plate 3 is attached to the glass substrate of the array substrate 7 through an adhesive layer G2 provided in a layer form with an adhesive (not shown) on the lower side of the brightness enhancement film 14, and the surface, that is, the upper surface thereof. The side surface is covered with a protective film 15 made of PET (Poly Ethylene Terephtalate). Therefore, the brightness enhancement film 14 is bonded on both sides by the adhesive layers G1 and G2.

  Further, the polarizing plate 3 is formed to have a total thickness of 300 μm or more, for example, about 320 μm, and each end surface has a forward taper shape with an inclination angle, that is, a taper angle θ = 45 °, that is, an upper side away from the array substrate 7. In other words, the brightness enhancement film 14, the adhesive layer G1, the TAC film 11, the PVA film 13, and the TAC film 12 are inclined so as to become narrower in this order.

  Here, if the taper angle θ is too small, as shown in FIG. 3, the area not functioning as the polarizing plate 3, that is, the width of the ineffective area A becomes excessive, and if too large, the intermediate layer is peeled off when the protective film 15 is peeled off. The stress F1 applied to the end becomes excessive. For this reason, the taper angle θ is set to 30 ° or more in order to set the ineffective area A to about 0.6 mm, for example, and the taper angle θ is set to 60 ° or less in order to suppress the stress F1.

  The PVA film 13 is stretched and dyed, and is provided between the TAC films 11 and 12. Further, the PVA film 13 has an absorption axis direction L set to 45 °, for example, with the screen facing up. Therefore, the PVA film 13 has a transmission axis direction along a direction orthogonal to the absorption axis direction L on the PVA film 13, and an optical axis along the absorption axis direction L and the direction orthogonal to the transmission axis direction. have.

  The brightness enhancement film 14 is formed in a predetermined thickness using, for example, DBEF (trade name, manufactured by Sumitomo 3M Limited). The brightness enhancement film 14 has an optical axis in a direction different from the optical axis direction of the PVA film 13.

  The adhesive layers G1 and G2 are made of materials that do not optically affect the light from the backlight passing through the liquid crystal cell 1, and are formed on the entire surface of the brightness enhancement film 14 and the entire back surface, respectively. It is configured. The pressure-sensitive adhesive layers G1 and G2 are formed of a pressure-sensitive adhesive designed so as to optimize the adhesive force between the TAC film 11 and the glass. For this reason, the adhesive strength of the brightness enhancement film 14, that is, the adhesive strength between the adhesive layers G 1 and G 2 and the brightness enhancement film 14, is the adhesive strength of the array substrate 7 and the brightness enhancement film 14, ie the adhesive layer G 2 and the glass substrate of the array substrate 7. It is smaller than the adhesive strength.

  The protective film 15 protects one main surface of the TAC film 12, that is, the surface side of the polarizing plate 3, and in the manufacturing process of the liquid crystal cell 1, the polarizing plate 3 is used with a jig T such as tweezers as shown in FIG. Is peeled in the direction of arrow D from the end face side to the center side.

  The polarizing plate 4 is a color filter side polarizing plate as a counter substrate side polarizing plate bonded to the back surface of the glass substrate of the counter substrate 8 of the liquid crystal panel 2, that is, the main surface opposite to the array substrate 7.

  Next, the function and effect of the liquid crystal display device according to the embodiment will be described.

  In manufacturing the polarizing plate 3, first, the stretched and dyed PVA film 13 is sandwiched between the TAC films 11 and 12 and bonded. At this time, a protective film 15 is pasted on the TAC film 12 in advance.

  Next, these adhered films 11, 12, 13 are cut into a predetermined size.

  Further, the brightness enhancement film 14 is bonded to the TAC film 11 with the adhesive layer G1.

  Thereafter, the bonded films 11, 12, 13, and 14 and the adhesive layer G1 are die-cut by setting a die-cutting angle (not shown) so that the end surface has a forward tapered shape with a predetermined taper angle θ. The board 3 is completed.

  The polarizing plate 3 manufactured in this way is adhered to the glass substrate of the array substrate 7 of the liquid crystal panel 2 formed in advance by the adhesive layer G2, and the liquid crystal cell 1 is obtained.

  As described above, in the above embodiment, the taper angle θ is 30 ° or more and 60 ° or less on the end surface of the polarizing plate 3 that is provided with the PVA film 13 and the brightness enhancement film 14 and is bonded to the glass substrate of the array substrate 7. The forward tapered shape was adopted.

  Here, in the conventional liquid crystal cell shown in FIG. 6, the stress F2 when the protective film 15 is peeled off, or the jig T is caught by the thickness of the polarizing plate 3, thereby causing the adhesive layer G1 and the brightness enhancement film to be caught. In some cases, peeling may occur at the adhesive portion with 14, that is, at the intermediate layer of the polarizing plate 3.

  In particular, since the adhesive layer G1 is designed to optimize the adhesive force between the TAC film 11 and the glass, the adhesive force with respect to the brightness enhancement film 14 becomes weaker than the adhesive force with respect to the glass substrate of the array substrate 7, Peeling at the intermediate layer was easy to occur.

  Therefore, as described above, the end face of the polarizing plate 3 has a forward taper shape with a taper angle θ of 30 ° or more and 60 ° or less, thereby suppressing the stress F1 on the end surface side of the polarizing plate 3 from the center side. Peeling of the brightness enhancement film 14 can be prevented.

  Specifically, as shown in FIG. 5, when measured by a peel test at 90 °, the stress applied to the end of the intermediate layer is 5.3 in the conventional product in which the taper angle θ is 90 °, that is, the end surface is not tapered. (N / 25mm), the force to peel off the end of the intermediate layer against the adhesive force at the end of the intermediate layer, that is, the peeling force exceeds 3.5 (N / 25mm), and the intermediate layer peels off. On the other hand, when the taper angle θ is 60 °, the stress applied to the end of the intermediate layer is 2.9 (N / 25 mm), and when the taper angle θ is 45 °, the stress applied to the end of the intermediate layer. When the taper angle θ is 30 °, the stress applied to the end of the intermediate layer is 0.6 (N / 25 mm), and both may exceed the peeling force. Without being peeled off by the intermediate layer of the polarizing plate 3.

  That is, by sequentially reducing the taper angle θ from 60 °, the stress applied to the end of the intermediate layer can be sequentially reduced. Therefore, by setting the upper limit value of the taper angle θ to 60 °, the intermediate layer of the polarizing plate 3 Can be reliably prevented.

  Further, when the taper angle θ is sequentially reduced to 60 °, 45 °, and 30 °, the ineffective area A increases to 0.18 mm, 0.32 mm, and 0.55 mm, so the lower limit value of the taper angle θ is set to 30 °. By doing so, the ineffective area A can be suppressed to 0.6 mm or less, and the ineffective area A can be prevented from becoming unnecessarily wide.

  In particular, by setting 45 ° to the design value of the taper angle θ, the die cutting angle of the polarizing plate 3 can be set to the design value to give a tolerance of ± 10 °. Even when the tolerance is taken into account, since the taper angle θ is not less than 35 ° and not more than 55 °, peeling of the intermediate layer of the polarizing plate 3 can be reliably prevented.

  Further, even if the brightness enhancement film 14 is adhered to the brightness enhancement film 14 using a conventional adhesive having a weak adhesive force, the interlayer of the polarizing plate 3 can be prevented from being peeled off. The manufacturing cost of the polarizing plate 3 can be suppressed as compared with the case of newly using a pressure-sensitive adhesive or the like that has improved the peeling force of the brightness enhancement film.

  In the above embodiment, the polarizing plate 3 may be attached to the counter substrate 8 side.

  Further, even when another film such as a viewing angle enhancement film is used in place of the brightness enhancement film 14, the same effect can be obtained.

  Further, the liquid crystal cell 1 using the TN type liquid crystal layer 9 has been described. For example, the liquid crystal panel 1 can be applied to an OCB (Optically Compensated Birefringence) type, a VA (Vertical Aligned) type, or a homogeneous type liquid crystal panel 1. The display form is not limited to the transmissive type, but can be applied to various liquid crystal cells such as a transflective type and a reflective type.

It is explanatory sectional drawing which shows the liquid crystal display device of one embodiment of this invention. It is explanatory drawing which shows the polarizing plate of a liquid crystal display device same as the above. It is explanatory sectional drawing which shows a polarizing plate same as the above. It is explanatory drawing which shows the peeling process of the protective film of a polarizing plate same as the above. It is a table | surface which shows the example of a relationship between the taper angle of a liquid crystal display device same as the above, stress, and an ineffective area. It is explanatory drawing which shows the peeling process of the protective film of the liquid crystal display device of a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal cell as a liquid crystal display device 3 Polarizing plate 7 Array substrate as a substrate 8 Counter substrate as a substrate 9 Liquid crystal layer
13 Polyvinyl alcohol film as a polarizer
14 Brightness enhancement film as a film

Claims (5)

A pair of substrates;
A liquid crystal layer provided between the substrates;
Comprising a polarizer and one or more films, and comprising a polarizing plate adhered to at least one of the pair of substrates,
At least one of the films is bonded on both sides with an adhesive,
The liquid crystal display device, wherein the polarizing plate is formed in a forward taper shape having an end surface that becomes narrower as the distance from the substrate increases from 30 ° to 60 °. The liquid crystal display device according to claim 1, wherein an adhesive force between the film and the adhesive is smaller than an adhesive force between the substrate and the polarizing plate. The liquid crystal display device according to claim 1, wherein the film has an optical axis in a direction different from that of the polarizer. The liquid crystal display device according to claim 1, wherein the film is a brightness enhancement film. The liquid crystal display device according to claim 1, wherein the film is a viewing angle improving film.

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