JP4736810B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device in which display quality does not deteriorate even when used for a long time under high temperature conditions.

  The structure of a liquid crystal display device that has been generally used will be described with reference to FIGS. FIG. 1 is an exploded perspective view of a conventional liquid crystal display device, and FIG. 2 is a schematic longitudinal sectional view for explaining an arrangement relationship among a liquid crystal display panel, an optical sheet, and a backlight unit. The liquid crystal display device 10 includes a liquid crystal display panel 11, a frame body 12, a backlight unit 13, a back case 14, a front frame 15, and an insulating sheet 16.

  The liquid crystal display panel 11 has a known configuration in which a pair of glass substrates are bonded together with a sealing material, and a liquid crystal layer is formed therein, and a driver IC (not shown) for performing display control is mounted on one side surface thereof. A plurality of wiring boards 17 (TCP: Tape Carrier Package) are provided, and the wiring boards 17 are connected to a control board 18 on which a controller or the like is mounted.

  The backlight unit 13 includes a plurality of optical sheets (four in FIG. 1) 18, a light guide plate 19, backlight light sources 20 a and 20 b, and a reflection sheet 21, and opposite edges of the light guide plate 19. Back light sources 20a and 20b are attached to the so-called sidelights, attached to the bottom of the light guide plate 19 and a reflection sheet 21 is attached so as to cover the backlight light sources 20a and 20b. Assembly is performed by placing a plurality of optical sheets 18 made of sheets or the like. On the other hand, polarizing plates 22 and 23 (see FIG. 2) are respectively attached to the front and back surfaces of the liquid crystal display panel 11 by glue materials 22a and 23a, respectively, and are substantially integrated with the liquid crystal display panel.

  In FIG. 2, the liquid crystal display panel 11 to which the polarizing plates 22 and 23 are attached, a plurality of optical sheets 18, such as a diffusion sheet and a prism sheet, the light guide plate 19, and the reflection sheet 21 are in contact with each other for the sake of clarity. Although not shown, these components are pressed to come into contact with each other when assembled in the frame 12 and the back case 14 shown in FIG.

  By the way, in Patent Document 1 below, when a liquid crystal display device operating normally at room temperature is operated, the operating temperature rises to 45 to 50 ° C. or higher, but the operating environment temperature reaches a high temperature of 60 ° C. Since the liquid crystal material undergoes a large temperature expansion, stress is concentrated on the central part of the liquid crystal display panel, resulting in a large cell gap at the central part of the liquid crystal display panel, uneven color, non-uniform response speed, etc. It is shown that the display quality of the image is reduced.

And in the invention disclosed in the following Patent Document 1, it is composed of at least a dyeing film as a polarizing plate and a plurality of first and second polymer films arranged so as to sandwich the dyeing film, and each polymer Using a film with a coefficient of thermal expansion set differently, especially by increasing the coefficient of thermal expansion of the polymer film on the side in contact with the liquid crystal display panel, the warping stress is generated in the polarizing plate as the temperature rises, The stress based on the temperature expansion of the liquid crystal material in the central portion of the liquid crystal display panel is dispersed to suppress deterioration in display quality such as color unevenness and in-plane non-uniform response speed.
Japanese Patent Laying-Open No. 2003-222849 (Claims, paragraphs [0009] to [0013], FIG. 8)

  The range of use of the liquid crystal display device has expanded to various fields, and the opportunity to use it in a temperature atmosphere higher than room temperature has increased. Generally, in order to test the durability in a high-temperature and high-humidity atmosphere, an accelerated deterioration test of 60 ° C. and 90% RH × 24 hours is usually adopted. In addition, even in the case of a conventional liquid crystal display device in which no problems are found in the accelerated deterioration test of 60 ° C. and 90% RH × 24 hours, the high temperature non-humidifying condition of 80 ° C. × 24 hours is required. In the accelerated deterioration test, the liquid crystal display panel was warped, and some of the display quality deteriorated. Such warpage of the liquid crystal display panel is based on a cause different from the problem based on the stress generated in the central portion of the liquid crystal display panel based on the thermal expansion of the liquid crystal molecules as disclosed in Patent Document 1. It is clear.

  The inventor of the present application, as a result of repeating various experiments to elucidate the cause of the warpage of the liquid crystal display device that occurs when the accelerated deterioration test is performed under such a high temperature non-humidifying condition of 80 ° C. × 24 hours, The back side of the liquid crystal display panel is hermetically sealed by a backlight unit and a back case, so that the solvent component of the paste is less evaporated even under high temperature and dry conditions, and there is little change in the physical properties of the paste for attaching the polarizing plate. Since the surface side of the display panel is open to the atmosphere, the solvent component of the paste gradually evaporates under high temperature and dry conditions, so the viscosity of the paste gradually increases. As a result, the liquid crystal display panel It has been found that the contraction force by the polarizing plate is activated on the surface side, and as a result, the liquid crystal display panel is warped.

  The present invention has been made to solve the above-described problems, and its purpose is to cause warpage of the liquid crystal display panel even in an accelerated deterioration test under a high temperature non-humidifying condition of 80 ° C. × 24 hours. Even if it is used for a long time at a temperature higher than room temperature, the contraction force by the polarizing plate provided on the surface side of the liquid crystal display panel does not work, the liquid crystal display panel is less warped, and the display quality is good The object is to provide a liquid crystal display device.

  In order to solve the above-mentioned object, the invention of the liquid crystal display device according to claim 1 of the present application includes: a liquid crystal display panel; a polarizing plate affixed to a front surface and a back surface of the liquid crystal display panel, respectively; and the liquid crystal display In a liquid crystal display device comprising a backlight source disposed on the back side of the panel, the softness of the first paste material for applying a polarizing plate on the surface of the liquid crystal display panel is determined by the softness of the second adhesive material for applying a polarizing plate on the back surface. It is characterized by greater than softness.

  The invention according to claim 2 is the liquid crystal display device according to claim 1, wherein the first paste material and the second paste material have substantially the same thickness and the viscosity of the first paste material. Is made smaller than the viscosity of the second glue material, the softness of the first glue material is made larger than the softness of the second glue material.

  According to a third aspect of the present invention, in the liquid crystal display device according to the first aspect, the same material is used as the first adhesive material and the second adhesive material, and the thickness of the first adhesive material is set to the first adhesive material. The softness of the first glue material is made larger than the softness of the second glue material by making it thicker than the thickness of the two glue materials.

  According to a fourth aspect of the present invention, in the liquid crystal display device according to any one of the first to third aspects, the backlight light source includes a light guide plate and a sidelight.

  The invention according to claim 5 is the liquid crystal display device according to any one of claims 1 to 4, wherein the liquid crystal display panel is a transmissive or transflective liquid crystal display panel.

  By providing the above-described configuration, the present invention has the following excellent effects. That is, according to the first aspect of the present invention, the softness of the first paste material for sticking the polarizing plate on the front surface of the liquid crystal display panel is made larger than the softness of the second paste material for sticking the polarizing plate on the back surface. Even in an accelerated deterioration test of 24 hours, the warp of the liquid crystal display panel is small, and the softness of the first paste material of the polarizing plate provided on the surface side of the liquid crystal display panel even when used for a long time under conditions higher than room temperature Since it takes a very long time for the change to become smaller than the softness of the paste material provided on the back surface side, the contraction force due to the polarizing plate does not substantially act on the front surface side of the liquid crystal display panel. As a result, the invention according to claim 1 can provide a liquid crystal display device in which the display quality is less deteriorated due to the warping of the liquid crystal display panel even when used for a long time under conditions higher than room temperature. In the present invention, the “softness” of the adhesive layer represents the amount of deformation when a predetermined force is applied to the adhesive. Accordingly, if the thickness of the paste material is the same, the softness increases as the viscosity of the paste material decreases, and if the viscosity of the paste material is the same, the softness increases as the thickness of the paste material increases.

  According to the invention of claim 2, if the thickness of the first paste material for sticking the polarizing plate on the front surface of the liquid crystal display panel and the second paste material for sticking the polarizing plate on the back surface are the same, generally the viscosity Since the amount of the solvent in the smaller paste material is large, the softness is increased, so that a liquid crystal display device having the effect of the invention according to claim 1 can be obtained.

  Moreover, according to the invention which concerns on Claim 3, if the same material is used as the 1st paste material for polarizing plate sticking on the surface of a liquid crystal display panel and the 2nd paste material for polarizing plate sticking on a back surface, it will be thickness. Since the softer the thicker the film, the liquid crystal display device having the effect of the first aspect of the invention can be obtained.

  According to the invention of claim 4, if the backlight light source includes a light guide plate and a side light, the back surface of the liquid crystal display panel is in close contact with the light guide plate via the light guide plate, the optical sheet, or the like. Therefore, since there is no free space, the solvent in the second paste material for sticking the polarizing plate hardly evaporates, and thus the effect of the invention according to claim 1 is remarkably exhibited.

  Furthermore, according to the fifth aspect of the present invention, a liquid crystal display device having a backlight light source can achieve the desired effect. Therefore, when the liquid crystal display panel is a transmissive or transflective liquid crystal display panel. A liquid crystal display device having the effect of the period can be obtained.

  BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. The experimental examples described below are differences in physical properties of the adhesive material of a polarizing plate for embodying the technical idea of the present invention. The present invention is intended to confirm the degree of warpage of the liquid crystal display panel according to the present invention, and is not intended to specify the present invention in this experimental example, and the present invention departs from the technical idea shown in the claims. The present invention can be equally applied to various modifications without any change. FIG. 3 is a longitudinal sectional view showing a method for measuring the warpage of the glass plate, and FIG. 4 shows a state in which the polarizing plate-attached glass sample is placed on a placing table simulating the backlight unit of the liquid crystal display device. It is sectional drawing shown.

First, a method for measuring warpage of a liquid crystal display panel when a polarizing plate common to various experimental examples is attached to the liquid crystal display panel and left under various conditions will be described.
A 15-inch glass substrate 30 having a thickness of 0.7 mm was prepared, and predetermined polarizing plates 31 and 32 were attached to both surfaces, and left in a constant temperature / humidity bath at a predetermined temperature and humidity for 24 hours. Thereafter, the glass plate with the polarizing plates 31 and 32 attached thereto is taken out and left at room temperature for 30 minutes to cool the glass plate 30 to room temperature, and then the polarizing plate is attached onto the surface plate 33 as shown in FIG. The glass plate 30 thus mounted was placed, the heights of the corners h1 to h4 at the four corners were measured, and the average value of h1 to h4 was determined as the warp amount H.

[Experimental example]
An acrylic adhesive is used for the adhesive layer applied to the polarizing plate. The acrylic pressure-sensitive adhesive material contains an acrylic polymer and a polyfunctional compound, and the pressure-sensitive adhesive layer is formed by a crosslinked product of these compositions. The acrylic polymer has a monomer unit of alkyl (meth) acrylate as a main skeleton, and copolymerizes a monomer having a functional group that reacts with a polyfunctional compound. Alkyl (meth) acrylates include butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, and the like, and monomers having functional groups include monomers containing carboxyl groups, hydroxyl groups, epoxy groups, and the like. . Examples of the polyfunctional compound include organic crosslinking agents such as isocyanate crosslinking agents and epoxy crosslinking agents, and multifunctional metal chelates. Then, two types of paste material layers A and B having different viscosities were prepared by changing the concentration of the acrylic polymer. The paste material layer B has a lower viscosity than the paste material layer A. The paste material layers A and B were applied to the polarizing plate with substantially the same thickness, and a polarizing plate provided with the adhesive material layer A and a polarizing plate provided with the adhesive material layer B were prepared.

  Next, a polarizing plate 32 provided with the adhesive material layer A as the adhesive material layer 35 is pasted on the back surface side of the glass plate 30, and as Experimental Example 1, a polarizing plate provided with the adhesive material layer B as the adhesive material layer 34 on the front surface side. Using the sample to which 31 was applied, as a second experimental example, a sample having the polarizing plate 31 provided with the adhesive material layer A as the adhesive material layer 34 on the surface side was used, and the warpage was measured.

  First, for each sample of Experimental Example 1 and Experimental Example 2, a stainless steel mounting table 36 having the shape shown in the cross-sectional view of FIG. 4 capable of covering the back side surface is prepared, and the back side of each sample is placed on this mounting side. The sample was placed on the table 5 and left in a predetermined atmosphere for a predetermined time to be used for measuring the amount of warpage.

Then, the mounting table 36 on which the samples of Experimental Example 1 and Experimental Example 2 are mounted is left in a constant temperature / humidity tank maintained at 60 ° C., 90% RH, and 80 ° C. in a non-humidified condition for 24 hours. Then, the warpage amount H was determined according to the method described above.
The measurement results are summarized in Table 1.

  From the results shown in Table 1, the following can be understood. That is, in Experimental Example 2 using the same adhesive material A on both sides as the adhesive material for attaching the polarizing plate, the warpage amount H after leaving for 24 hours at 60 ° C. and 90% RH was as small as 3.5 mm, but 80 ° C. The warpage amount H when left for 24 hours at a constant temperature of 8.8 mm, which is more than twice the warpage amount after standing for 24 hours at 60 ° C. and 90% RH, is very large.

  On the other hand, the same paste material A as in Experimental Example 2 was used as the paste material for sticking the polarizing plate on the back side, and the paste material B having a lower viscosity than the paste material A was used as the paste material for sticking the polarizing plate on the front surface side. In Experimental Example 1, the amount of warpage H after leaving for 24 hours at 60 ° C. and 90% RH was 3.0 mm, which was slightly smaller than in the case of Experimental Example 2, but left for 24 hours at a constant temperature of 80 ° C. The warpage amount H in this case is 4.5 mm, which is about 1.5 times the warpage amount after standing for 24 hours at 60 ° C. and 90% RH, which is much smaller than in the case of Experimental Example 2. .

  In addition, as a reference example, a sample using the same adhesive material A as the polarizing plate pasting material similar to the sample used in Experimental Example 2 is used, and the four corners and the central part of the glass plate are point-supported in an open state. The warpage amount H when left at a constant temperature of 60 ° C., 90% RH and 80 ° C. for 24 hours was substantially 0 mm.

  The reason why the above results are obtained is understood to be as follows. That is, in a normal liquid crystal display device, the back surface of the liquid crystal display panel is sealed by a backlight unit and a back case, so that the solvent component of the paste material is hardly evaporated even under high temperature and dry conditions, and for polarizing plate pasting. Although there is little change in the physical properties of the paste material, the surface of the liquid crystal display panel is open to the atmosphere, so the solvent component of the paste material gradually evaporates under high temperature and dry conditions, so the viscosity of the paste material gradually As a result, it is estimated that the contraction force due to the polarizing plate acts on the surface side of the liquid crystal display panel, and as a result, the liquid crystal display panel is warped.

  In Experimental Example 1 and Experimental Example 2, paste materials with substantially the same thickness and different viscosities were used as the paste materials for attaching the polarizing plates, but those having the same viscosity and different thicknesses were used as the paste materials. Even if the thickness of the adhesive layer on the front surface side is increased (for example, 60 to 70 μm) and the thickness of the adhesive layer on the rear surface side is decreased (for example, 40 μm), the solvent component is increased by the thickness of the adhesive layer on the front side. Since it takes a long time until the viscosity of the paste layer is reduced due to the evaporation of, a similar result is obtained.

  In Experimental Examples 1 and 2, the experiment was performed by attaching polarizing plates on both sides of one glass plate so that the warp clearly appears. However, a general liquid crystal display panel has a configuration in which liquid crystal is sealed in the center of two glass plates, and a polarizing plate is attached to the front and back surfaces of the liquid crystal display panel. Although the amount of deformation is smaller than the above results, it is clear that the same tendency as that shown in Experimental Examples 1 and 2 is shown.

  In the liquid crystal display device 10 having the same configuration as the conventional example shown in FIGS. 1 and 2, the paste material 22 a used as the polarizing plate 22 to be attached to the surface side of the liquid crystal display panel 11 is the paste material B used in Experimental Example 1 above. A liquid crystal display device having the same configuration as that of the liquid crystal display device 10 of the conventional example except that the paste material 23a includes the paste material A used in Experimental Examples 1 and 2 as the polarizing plate 23 attached to the back surface side. 10 was created.

  When this liquid crystal display device was placed in a constant temperature and humidity chamber at 60 ° C., 90% RH and 80 ° C. in a non-humidified state and left for 24 hours, the display image quality was investigated. Was not recognized. Therefore, it is clear that the liquid crystal display device having the configuration of the present invention is less likely to cause deterioration in display image quality due to warpage of the liquid crystal display panel even when used for a long time at a temperature higher than room temperature.

It is a disassembled perspective view of the liquid crystal display device of a prior art example. It is a schematic longitudinal cross-sectional view for demonstrating the arrangement | positioning relationship between a liquid crystal display panel, an optical sheet, and a backlight unit. It is a longitudinal cross-sectional view which shows the measuring method of the curvature of a glass plate. It is sectional drawing which shows the state which mounted the polarizing plate sticking glass sample on the mounting base imitating the backlight unit of a liquid crystal display device. It is sectional drawing which shows the state which mounted the polarizing plate sticking glass sample on the mounting base imitating the backlight unit of a liquid crystal display device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Liquid crystal display device 11 Liquid crystal display panel 12 Frame 13 Backlight unit 14 Back case 15 Front frame 16 Insulation sheet 17 Wiring board 18 Optical sheet 19 Light guide plate 20a, 20b Backlight light source 21 Reflection sheet 22,23,31,32 Polarization Plates 22a, 23a Glue material 30 Glass plate 33 Surface plate 34, 35 Glue material layer 36 Mounting table

Claims (5)

  In the liquid crystal display device comprising: a liquid crystal display panel; a polarizing plate affixed to each of the front and back surfaces of the liquid crystal display panel with a paste material; and a backlight source disposed on the back side of the liquid crystal display panel. A liquid crystal display device, characterized in that the softness of the first paste material for sticking a polarizing plate on the front surface of the display panel is greater than the softness of the second paste material for sticking a polarizing plate on the back surface.   The first glue material and the second glue material have substantially the same thickness, and the viscosity of the first glue material is made smaller than the viscosity of the second glue material, thereby softening the first glue material. The liquid crystal display device according to claim 1, wherein the degree is greater than the softness of the second adhesive material.   By using the same material as the first glue material and the second glue material, and making the thickness of the first glue material thicker than the thickness of the second glue material, the softness of the first glue material is The liquid crystal display device according to claim 1, wherein the liquid crystal display device is larger than the softness of the second adhesive material.   The liquid crystal display device according to claim 1, wherein the backlight light source includes a light guide plate and a sidelight.   The liquid crystal display device according to claim 1, wherein the liquid crystal display panel is a transmissive or transflective liquid crystal display panel.

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