JP2015082014A - Liquid crystal display device - Google Patents

Abstract

In a liquid crystal display device in which a cover is bonded to a liquid crystal display panel, yellow unevenness around a screen is prevented.
[Solution]
A liquid crystal display panel in which a liquid crystal layer 60 is sandwiched between the TFT substrate 10 and the counter substrate 20, a lower polarizing plate 11 is attached to the lower side of the TFT substrate 10, and a polarizing plate 21 is attached to the upper side of the counter substrate 20. A cover 40 is affixed on the substrate 200 with an ultraviolet curable resin 50. By setting the volume shrinkage ratio at the time of curing of the ultraviolet curable resin 50 to 1% or less and the elastic modulus after curing of the ultraviolet curable resin 50 to 1 MPa or less, the stress due to the volume shrinkage of the ultraviolet curable resin 50 is reduced to the liquid crystal display panel. The counter substrate 20 is deformed to prevent yellow unevenness around the screen.
[Selection] Figure 1

Description

  The present invention relates to a liquid crystal display device, and more particularly to a display device having a cover on a liquid crystal display panel.

  In a liquid crystal display device, there are a TFT substrate in which pixel electrodes and thin film transistors (TFTs) are formed in a matrix, and a counter substrate in which color filters are formed at locations corresponding to the pixel electrodes of the TFT substrate, facing the TFT substrate. The liquid crystal is sandwiched between the TFT substrate and the counter substrate. An image is formed by controlling the light transmittance of the liquid crystal molecules for each pixel.

  In the liquid crystal display device, there is a strong demand for reducing the outer dimensions of the set while keeping the screen constant, and at the same time reducing the thickness of the liquid crystal display panel. In order to make the liquid crystal display panel thin, after manufacturing the liquid crystal display panel, the outside of the liquid crystal display panel is polished and thinned.

  A glass substrate of a counter substrate on which a pixel electrode, a TFT substrate, etc. forming a liquid crystal display panel, a color filter, etc. are formed is standardized to 0.5 mm or 0.7 mm, for example. Yes. It is difficult to obtain a glass other than these standardized glass substrates from the market. In addition, a very thin glass substrate causes problems due to mechanical strength, bending, and the like in the manufacturing process, and decreases the manufacturing yield. Therefore, after forming a liquid crystal display panel using a standardized glass substrate, the outer surface of the liquid crystal display panel is polished and thinned.

  When the liquid crystal display panel is made thin, mechanical strength becomes a problem. If mechanical pressure is applied to the display surface of the liquid crystal display panel, the liquid crystal display panel may be destroyed. In order to prevent this, a cover is attached to the screen side of the liquid crystal display panel when the liquid crystal display panel is incorporated into a set such as a mobile phone. After bonding the cover and the liquid crystal display panel, some defect may be found in the liquid crystal display panel. In such a case, it is necessary to regenerate and use the liquid crystal display panel.

  In “Patent Document 1”, in order to facilitate the reproduction of the cover and the liquid crystal display panel, a resin that adheres the cover and the liquid crystal display panel is formed with a first material formed in an annular shape so as to surround the display region. A configuration is described in which the second material formed in the display region is used inside the first portion, and the elastic modulus of the first material is larger than the elastic modulus of the second material.

JP 2011-158851 A

  In many cases, an ultraviolet curable resin is used to attach the cover to the liquid crystal display panel. In this case, as shown in FIG. 9, a defect occurred in which the periphery of the screen turned yellow. In FIG. 9, a display region 100 is formed inside a sealing material 15 that bonds the TFT substrate and the counter substrate. The yellow discoloration part 110 occurs in a ring around the display area 100.

  Such yellow discoloration tends to occur in a product in which a TFT substrate or a counter substrate is thinned by polishing. That is, in order to reduce the thickness of the liquid crystal display device, there is a demand to reduce the thickness of the TFT substrate or the counter substrate to about 0.2 mm or 0.15 mm. When the substrate becomes thin in this way, it is considered that the thickness of the liquid crystal layer changes due to the deformation of the substrate, causing color unevenness and the like.

  By the way, such deformation of the substrate hardly occurs in a liquid crystal display panel formed by injecting liquid crystal in a vacuum. FIG. 10 is a cross-sectional view of a portion including the sealing material 16 of the liquid crystal display panel subjected to vacuum injection. FIG. 10 is a cross-sectional view of the liquid crystal display panel at atmospheric pressure. The TFT substrate 10 and the counter substrate 20 are bonded by a sealing material 15, and the liquid crystal 60 sandwiched between the TFT substrate 10 and the counter substrate 20 is sealed by a sealing material 16. In the vacuum injection method, due to the liquid crystal sealing process, the TFT substrate 10 and the counter substrate 20 are slightly concaved outward. When the TFT substrate 10 and the counter substrate 20 have a slightly concave shape as described above, the substrate is hardly deformed by an external pressure or the like.

  On the other hand, as a filling method of the liquid crystal 60, there is a method called ODF (One Drop Fill). As shown in FIG. 11A, the liquid crystal 70 whose amount is accurately controlled is dropped into the counter substrate 20 on which the sealing material 15 is formed, and then the TFT substrate 10 and the counter substrate 20 are bonded together. It is. The dropping method has a higher liquid crystal filling speed than the vacuum injection method. On the other hand, as shown in FIG. 11B, the TFT substrate 10 or the counter substrate 20 is flat without being recessed outward. As described above, when the substrate is flat, it is likely to be deformed by an external force.

  An object of the present invention is to provide a liquid crystal display device in which the counter substrate is prevented from being deformed to prevent color unevenness in a liquid crystal display panel formed by a dropping method and having a thickness of the counter substrate within a predetermined range. It is to realize a manufacturing method.

  The present invention solves the above-mentioned problems, and specific means are as follows.

  (1) A liquid crystal is sandwiched between the TFT substrate and the counter substrate, a lower polarizing plate is attached to the lower side of the TFT substrate, and a cover is placed on the liquid crystal display panel having the polarizing plate attached to the upper side of the counter substrate. The liquid crystal display device is affixed, wherein the liquid crystal display panel and the cover are affixed with an ultraviolet curable resin, and a volume shrinkage ratio when the ultraviolet curable resin is cured is x (%), and the ultraviolet curable resin is A liquid crystal display device having a range of y <−0.75x + 1.5, where y (MPa) is an elastic modulus after curing.

  (2) A liquid crystal is sandwiched between the TFT substrate and the counter substrate, a lower polarizing plate is pasted on the lower side of the TFT substrate, and a cover is placed on the liquid crystal display panel on which the polarizing plate is pasted on the upper side of the counter substrate. The liquid crystal display device is affixed, wherein the liquid crystal display panel and the cover are affixed with an ultraviolet curable resin, and the volumetric shrinkage ratio when the ultraviolet curable resin is cured is 1% or less. A liquid crystal display device having an elastic modulus after curing of 1 MPa or less.

  (3) A liquid crystal is sandwiched between the TFT substrate and the counter substrate, a lower polarizing plate is pasted on the lower side of the TFT substrate, and a touch panel is placed on the liquid crystal display panel on which the polarizing plate is pasted on the upper side of the counter substrate. A liquid crystal display device that is affixed and a cover is affixed on a touch panel, wherein the liquid crystal display panel and the touch panel are affixed with an ultraviolet curable resin, and the volume shrinkage ratio when the ultraviolet curable resin is cured is x (%), And the elastic modulus after the ultraviolet curable resin is cured is y (MPa), the range is y <−0.75x + 1.5.

(4) A liquid crystal is sandwiched between the TFT substrate and the counter substrate, a lower polarizing plate is pasted on the lower side of the TFT substrate, and a touch panel is placed on the liquid crystal display panel on which the polarizing plate is pasted on the upper side of the counter substrate. A liquid crystal display device that is pasted and a cover is pasted on the touch panel,
The liquid crystal display panel and the touch panel are attached with an ultraviolet curable resin, the volumetric shrinkage ratio when the ultraviolet curable resin is cured is 1% or less, and the elastic modulus after the ultraviolet curable resin is cured is 1 MPa or less. A liquid crystal display device characterized by the above.

  According to the present invention, in the liquid crystal display device in which the TFT substrate and the counter substrate are small in thickness and the cover is attached to the liquid crystal display panel manufactured using the dropping method, the counter substrate of the liquid crystal display panel is deformed. Therefore, the thickness of the liquid crystal layer can be changed, and color unevenness can be prevented from occurring in that portion.

1 is a cross-sectional view of a liquid crystal display device of Example 1. FIG. It is sectional drawing with which the cover and the liquid crystal display panel are laminated | stacked through ultraviolet curing resin. It is sectional drawing which shows the state which irradiates an ultraviolet-ray to ultraviolet-ray cured resin and has hardened ultraviolet-ray cured resin. It is sectional drawing which shows the state which causes volume shrinkage when ultraviolet curing resin hardens | cures. It is sectional drawing which shows the state which the opposing board | substrate of the liquid crystal display panel deform | transformed as a result of the ultraviolet curable resin volume shrinking. It is a graph which shows the relationship between the fluctuation | variation of the layer thickness of a liquid crystal layer, and a yellow nonuniformity level in a liquid crystal display panel. It is a graph which shows the influence which the cure shrinkage rate and elastic modulus in ultraviolet curable resin exert on yellow unevenness. 6 is a cross-sectional view of a liquid crystal display device of Example 2. FIG. It is a top view of the screen which shows the range which yellow unevenness produces. It is sectional drawing of the liquid crystal display panel with which the liquid crystal was filled with the vacuum injection method. It is sectional drawing of the liquid crystal display panel after filling the liquid crystal with ODF and the liquid crystal with ODF.

  Hereinafter, the present invention will be described in detail by way of examples.

  FIG. 1 is a cross-sectional view of a liquid crystal display device according to the present invention. In FIG. 1, the TFT substrate 10 and the counter substrate 20 are bonded by a sealing material 15, and a liquid crystal layer 60 is sealed inside. The liquid crystal is filled with ODF. A lower polarizing plate 11 is bonded to the lower side of the TFT substrate 10, and an upper polarizing plate 21 is bonded to the upper side of the counter substrate 20. The TFT substrate 10, the counter substrate 20, the lower polarizing plate 11, and the upper polarizing plate 21 constitute a liquid crystal display panel 200.

  In the liquid crystal display panel 200, the TFT substrate 10 is formed larger than the counter substrate 20, and a flexible portion for sending power and signals from the outside to the liquid crystal display panel 200 in a portion where the TFT substrate 10 is larger than the counter substrate 20. An IC driver 90 for driving the wiring board 80 and the liquid crystal display panel 200 is disposed. A backlight 300 is disposed on the back surface of the lower polarizing plate 11. The backlight 300 includes a light source such as an LED (not shown), an optical sheet group such as a light guide plate or a diffusion plate, a diffusion sheet, and a prism sheet.

  A cover 40 is bonded to the upper polarizing plate 21 of the liquid crystal display panel 200 by an ultraviolet curable resin 50. The cover 40 is made of glass, plastic, or the like, but the cover 40 mechanically protects the liquid crystal display panel 200, so the thickness is relatively thick, about 0.5 to 1.2 mm. On the other hand, in the liquid crystal display panel 200, the thickness of the TFT substrate 10 or the counter substrate 20 is 0.15 mm to 0.2 mm. Moreover, the thickness of the upper polarizing plate 21 and the lower polarizing plate 11 is about 0.13 mm. In the liquid crystal display device having such a configuration, a touch panel function may be incorporated in the cover 40 or the counter substrate 20 of the liquid crystal display panel 200 in some cases.

  FIG. 2 is a cross-sectional view in which an ultraviolet curable resin 50 is disposed in order to bond the cover 40 and the liquid crystal display panel 200. 2 may be applied to the cover 40 side or may be applied to the liquid crystal display panel 200 side. In FIG. 2, the ultraviolet curable resin 50 is in a liquid state.

  FIG. 3 is a diagram in which the cover 40 and the liquid crystal display panel 200 in the state of FIG. Since scanning lines, signal lines, light shielding films, and the like are formed on the liquid crystal display panel 200 side, it is more efficient to irradiate ultraviolet rays from the cover 40 side.

  The ultraviolet curable resin 50 has a property of shrinking in volume when cured by being irradiated with ultraviolet rays. This is called curing shrinkage in this specification. FIG. 4 is a schematic cross-sectional view showing a state in which the ultraviolet curable resin 50 between the liquid crystal display panel 200 and the cover 40 contracts when being cured under the influence of ultraviolet rays. When the ultraviolet curable resin 50 contracts, stress is generated on the cover 40 side and the liquid crystal display panel 200 side to which the resin is bonded. This stress is greatest at the end of the ultraviolet curable resin 50.

  As shown in FIG. 4, the stress caused by the ultraviolet curable resin 50 can be decomposed in a direction parallel to the main surface of the counter substrate 20 such as the liquid crystal display panel 200 and a normal direction. Of these, the counter substrate 20 etc. is strong against stress in the direction parallel to the main surface of the counter substrate 20 etc., and hardly deforms. However, in the normal direction relative to the main surface of the counter substrate 20 or the like, the strength is weak and deformation occurs.

  FIG. 5 is a cross-sectional view showing deformation of the cover 40 and the liquid crystal display panel 200 caused by the shrinkage of the ultraviolet curable resin 50. As shown in FIG. 5, the cover 40 is hardly deformed, and the peripheral portion of the upper polarizing plate 21 and the counter substrate 20 on the liquid crystal display panel 200 side is deformed. That is, the cover 40 is as thick as 0.5 mm to 1.2 mm, whereas the upper polarizing plate 21 on the liquid crystal display panel 200 side is as thin as 0.13 mm, and the counter substrate 20 is as thin as 0.15 mm to 0.2 mm. Since the bending strength of the substrate or the like is proportional to the cube of the plate thickness, the upper polarizing plate 21 and the counter substrate 20 of the liquid crystal display panel 200 are deformed.

  In the deformation as shown in FIG. 5, the deformation of the counter substrate 20 is particularly important for the characteristics of the liquid crystal display panel 200. When the counter substrate 20 is deformed, the layer thickness of the liquid crystal layer 60, that is, the gap between the TFT substrate 10 and the counter substrate 20 changes. Although the stress due to the shrinkage of the ultraviolet curable resin 50 is large in the vicinity where the ultraviolet curable resin 50 is formed, the portion where the counter substrate 20 is bonded to the sealing material 15 is suppressed by the sealing material 15 as shown in FIG. As a result, there is almost no gap variation. Therefore, the counter substrate 20 is deformed inside the sealing material 15, and the variation in the gap between the TFT substrate 10 and the counter substrate 20 becomes large.

  When the gap between the TFT substrate 10 and the counter substrate 20, that is, the layer thickness of the liquid crystal layer 60 increases, the light on the long wavelength side among the light passing through the liquid crystal increases. Then, when white display is performed, the transmitted light in this portion is shifted to the yellow side, and yellow unevenness around the screen as shown in FIG. 8 occurs. In FIG. 5, the liquid crystal layer thickness at the center side of the display area is g1, and the liquid crystal layer thickness in the vicinity of the sealing material 15 is g2. The difference in layer thickness of the liquid crystal layer 60 indicated by g2-g1 or the gap difference (gap difference) between the TFT substrate 10 and the counter substrate 20 causes yellow unevenness.

  FIG. 6 is a graph showing the relationship between the gap difference and the uneven yellow level. In FIG. 6, the horizontal axis represents the uneven yellow level around the screen, and the vertical axis represents the gap difference between the TFT substrate and the counter substrate. The horizontal axis in FIG. 6 is a numerical value obtained by standardizing the yellow unevenness level. In this value, 0 is a level where no yellow unevenness is observed. Although 1 is yellow unevenness, it is slight and is a level that is not a problem in practical use, and 2 is an upper limit yellow unevenness that is allowed as a practical use level. A value of 3 or more is a level where yellow unevenness is large and is not acceptable in practice. In this embodiment, a yellow unevenness level exceeding 2 is counted as defective.

  The vertical axis in FIG. 6 is the gap difference between the TFT substrate and the counter substrate, and the unit is μm. As the gap difference increases, the yellow unevenness level increases. According to FIG. 6, when the gap difference becomes 0.6 μm, the limit of the allowable range is approached. Therefore, if the allowable range of the gap is set to 0.5 μm or less, the yellow unevenness level can be stably suppressed within the allowable range.

FIG. 7 is a graph showing the relationship between the characteristics of the ultraviolet curable resin that causes such a gap variation between the TFT substrate and the counter substrate and the uneven yellow level. Among the characteristics of the ultraviolet curable resin cured by ultraviolet irradiation, the characteristics that affect the gap fluctuation are the curing shrinkage rate and the elastic modulus. The curing shrinkage rate refers to the volume shrinkage rate at which the volume shrinks when the ultraviolet curable resin is cured. The same applies hereinafter. In FIG. 7, the horizontal axis represents the curing shrinkage rate of the ultraviolet curable resin, and the unit is%. The vertical axis represents the elastic modulus after curing of the ultraviolet curable resin, and the unit is MPa (10 ⁶ Pa).

  In FIG. 7, even if the shrinkage rate is large, the gap fluctuation can be suppressed small if the elastic modulus is small. On the other hand, even if the shrinkage rate is the same, if the elastic modulus is large, the gap variation becomes large, and there is a risk of generating yellow unevenness. The right side of the dotted line shown in FIG. 7 is a region where yellow unevenness is a problem, and the left side is a region where yellow unevenness does not occur or yellow unevenness is at an acceptable level.

  The dotted line in FIG. 7 can be expressed as y = −0.75X + 1.5, where% is the unit of cure shrinkage on the horizontal axis x and MPa is the unit of elastic modulus on the vertical axis y. That is, by setting y <−0.75X + 1.5, yellow unevenness does not occur or even if yellow unevenness occurs, it can be within an allowable range.

  In the development of an actual ultraviolet curable resin or the like, a required resin may be selected by setting a curing shrinkage rate and evaluating an elastic modulus after curing. In such a case, by setting the curing shrinkage rate to 1% or less and the cured elastic modulus to 1 MPa or less, it is possible to obtain a display in which yellow unevenness is hardly noticeable. Further, by setting the curing shrinkage rate to 0.8% or less and the cured elastic modulus to 1 MPa or less, it is possible to obtain a display in which the yellow unevenness is further unnoticeable.

  A liquid crystal display device generally has a problem of viewing angle characteristics. The viewing angle characteristic is a phenomenon in which contrast changes or chromaticity changes depending on the angle at which the screen is viewed. An IPS (In Plane Switching) type liquid crystal display device is a method in which an image is formed by changing the transmittance of a liquid crystal layer by rotating liquid crystal molecules in a direction parallel to the substrate, and has excellent viewing angle characteristics. doing.

  Since the IPS liquid crystal display device has a small gap between the counter substrate and the TFT substrate, that is, the liquid crystal layer has a small thickness, it reacts sensitively to a gap variation between the counter substrate and the TFT substrate. Therefore, the present invention is particularly effective for an IPS liquid crystal display device.

  FIG. 8 is a sectional view showing a second embodiment of the present invention. 8 differs from FIG. 1 of the first embodiment in that a touch panel 30 is independently formed between the cover 40 and the liquid crystal display panel 200. FIG. The cover 40 and the touch panel 30 are bonded by an ultraviolet curable resin 50, and the liquid crystal display panel 200 and the touch panel 30 are also bonded by an ultraviolet curable resin.

  In the process of forming the configuration as shown in FIG. 8, first, the cover 40 and the touch panel 30 are bonded. Also in this case, if the shrinkage rate of the ultraviolet curable resin 50 is large, the touch panel 30 is deformed. However, in the case of the touch panel 30, unlike the liquid crystal display panel 200, there is no change in the layer thickness of the liquid crystal layer 60, so that there is no problem of yellow shift of the screen.

  Next, the assembly in which the cover 40 and the touch panel 30 are bonded together and the liquid crystal display panel 200 are bonded with the ultraviolet curable resin 50. At this time, the same deformation as described in the first embodiment occurs in the upper polarizing plate 21 and the counter substrate 20 of the liquid crystal display panel 200. And the deformation | transformation which arose in the counter substrate 20 brings about the fluctuation | variation of the gap between the TFT substrate 10 and the counter substrate 20, ie, the fluctuation | variation of the layer thickness of the liquid crystal layer 60, As a result, the yellow nonuniformity in the periphery of a screen will arise. .

  In this embodiment, the only difference is that an assembly of the cover 40 and the touch panel 30 is used instead of the cover 40 in the first embodiment. It occurs on the display panel 200 side. That is, the deformation of the counter substrate 20 of the liquid crystal display panel 200 is in the same range as described in the first embodiment with respect to the curing shrinkage rate and the cured elastic modulus of the ultraviolet curable resin 50 as described in the first embodiment. By setting, it is possible to prevent the occurrence of yellow unevenness, or to suppress it to an allowable level even if yellow unevenness occurs.

  In the above description, in FIG. 8, the cover 40 and the touch panel 30 are bonded by the ultraviolet curable resin 50. However, the present invention is not limited to this, and a thermosetting resin or an adhesive sheet is used instead of the ultraviolet curable resin. I can do it. Note that the present embodiment is also particularly effective for the IPS liquid crystal display device as in the first embodiment.

  DESCRIPTION OF SYMBOLS 10 ... TFT substrate, 11 ... Lower polarizing plate, 15 ... Sealing material, 16 ... Sealing material, 20 ... Opposite substrate, 21 ... Upper polarizing plate, 30 ... Touch panel, 40 ... Cover, 50 ... UV curable resin, 60 ... Liquid crystal 70: Dropped liquid crystal, 80 ... Flexible wiring board, 90 ... IC driver, 100 ... Display area, 110 ... Yellow discoloration part, 200 ... Liquid crystal display panel, 300 ... Backlight

Claims (6)

A liquid crystal is sandwiched between the TFT substrate and the counter substrate, a lower polarizing plate is pasted on the lower side of the TFT substrate, and a cover is pasted on the liquid crystal display panel on which the polarizing plate is pasted on the upper side of the counter substrate. A liquid crystal display device,
The liquid crystal display panel and the cover are affixed with an ultraviolet curable resin, the volumetric shrinkage rate when the ultraviolet curable resin is cured is x (%), and the elastic modulus after the ultraviolet curable resin is cured is y (MPa). In this case, the liquid crystal display device is in a range of y <−0.75x + 1.5. A liquid crystal is sandwiched between the TFT substrate and the counter substrate, a lower polarizing plate is pasted on the lower side of the TFT substrate, and a cover is pasted on the liquid crystal display panel on which the polarizing plate is pasted on the upper side of the counter substrate. A liquid crystal display device,
The liquid crystal display panel and the cover are attached with an ultraviolet curable resin, the volumetric shrinkage ratio when the ultraviolet curable resin is cured is 1% or less, and the elastic modulus after the ultraviolet curable resin is cured is 1 MPa or less. A liquid crystal display device characterized by the above.   3. The liquid crystal display device according to claim 2, wherein the ultraviolet curable resin has a volume shrinkage ratio of 0.8% or less when cured, and an elastic modulus after the ultraviolet curable resin is cured is 1 MPa or less. . A liquid crystal is sandwiched between the TFT substrate and the counter substrate, a lower polarizing plate is pasted on the lower side of the TFT substrate, and a touch panel is pasted on the liquid crystal display panel on which the polarizing plate is pasted on the upper side of the counter substrate. A liquid crystal display device in which a cover is attached on the touch panel,
The liquid crystal display panel and the touch panel are attached with an ultraviolet curable resin, and the volumetric shrinkage ratio when the ultraviolet curable resin is cured is x (%), and the elastic modulus after the ultraviolet curable resin is cured is y (MPa). In this case, the liquid crystal display device is in a range of y <−0.75x + 1.5. A liquid crystal is sandwiched between the TFT substrate and the counter substrate, a lower polarizing plate is pasted on the lower side of the TFT substrate, and a touch panel is pasted on the liquid crystal display panel on which the polarizing plate is pasted on the upper side of the counter substrate. A liquid crystal display device having a cover attached on the touch panel,
The liquid crystal display panel and the touch panel are attached with an ultraviolet curable resin, the volumetric shrinkage ratio when the ultraviolet curable resin is cured is 1% or less, and the elastic modulus after the ultraviolet curable resin is cured is 1 MPa or less. A liquid crystal display device characterized by the above.   6. The liquid crystal display device according to claim 5, wherein the ultraviolet curable resin has a volume shrinkage ratio of 0.8% or less when cured, and an elastic modulus after the ultraviolet curable resin is cured is 1 MPa or less. .

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