JP7153672B2 - liquid crystal display - Google Patents

Description

The present disclosure relates to liquid crystal display devices.

2. Description of the Related Art A liquid crystal display device using a display panel including a liquid crystal cell is used as a display such as a television or a monitor. However, a liquid crystal display device has a lower contrast ratio than an organic EL (Electro Luminescence) display device.

Therefore, conventionally, a liquid crystal display device has been proposed that can realize a contrast ratio equal to or higher than that of an organic EL display device by overlapping a plurality of display panels (for example, Patent Document 1).

This technology displays a color image on the display panel on the front side (viewer side) of the two display panels arranged in front and back, and displays a monochrome image on the display panel on the back side (backlight side). This is intended to improve the contrast ratio.

In this case, the two display panels are bonded together by a bonding member such as an optically clear adhesive sheet (OCA) or an optically clear adhesive resin (OCR).

WO2007/040127

However, when a liquid crystal display device in which two display panels are bonded together by a bonding member (bonding layer) is used for a long time, the display screen may become colored. In particular, the central portion of the display screen may appear brownish. When the display screen is colored in this way, the quality of the displayed image is degraded.

The present disclosure has been made in order to solve such problems, and provides a liquid crystal display device capable of suppressing degradation in display image quality even when a plurality of display panels are joined with a joining member such as OCA. intended to provide

In order to achieve the above object, one aspect of the liquid crystal display device according to the present disclosure is a first display panel including a first liquid crystal cell; 2 a display panel, a bonding member disposed between the first display panel and the second display panel for bonding the first display panel and the second display panel, and the bonding of the first liquid crystal cell. a first polarizing plate provided on a surface opposite to the member-side surface; a second polarizing plate provided on a surface of the second liquid crystal cell opposite to the bonding member-side surface; a third polarizing plate disposed between one of the first liquid crystal cell and the bonding member and between the second liquid crystal cell and the bonding member, wherein the third polarizing plate includes a polarizer; A first transparent film provided on the bonding member side of the polarizer, and a second transparent film provided on the opposite side of the polarizer to the bonding member side , wherein the polarizer contains iodine. The polyvinyl alcohol film containing the 3 The water content per unit area of the polarizing plate is 6 g/m ² or less, and the second transparent film does not contain a phosphoric acid-based plasticizer .

Advantageous Effects of Invention According to the present disclosure, it is possible to realize a liquid crystal display device capable of suppressing degradation in display image quality.

FIG. 1 is a diagram showing a schematic configuration of a liquid crystal display device according to an embodiment. FIG. 2 is a cross-sectional view of the liquid crystal display device according to the embodiment. FIG. 3 is a diagram showing changes over time in brownness of two polarizing plates bonded by OCA. FIG. 4 is a cross-sectional view of a liquid crystal display device according to a modification.

Embodiments of the present disclosure will be described below. It should be noted that each of the embodiments described below is a specific example of the present disclosure. Therefore, the numerical values, shapes, materials, constituent elements, and arrangement positions and connection forms of the constituent elements shown in the following embodiments are examples and are not intended to limit the present disclosure. Therefore, among the constituent elements in the following embodiments, constituent elements that are not described in independent claims representing the highest concept of the present disclosure will be described as optional constituent elements.

Each figure is a schematic diagram and is not necessarily strictly illustrated. Therefore, the scales and the like are not always the same in each drawing. Moreover, in each figure, the same code|symbol is attached|subjected to the substantially same structure, and the overlapping description is abbreviate|omitted or simplified. In this specification, the terms "substantially" or "approximately" mean including manufacturing errors and dimensional tolerances.

(Embodiment)
First, a liquid crystal display device 1 according to an embodiment will be described with reference to FIG. FIG. 1 is a diagram showing a schematic configuration of a liquid crystal display device 1 according to an embodiment.

The liquid crystal display device 1 is an example of an image display device in which a plurality of display panels are superimposed in the front-rear direction, and displays a still image or a moving image. In this embodiment, the liquid crystal display device 1 is composed of two display panels each including a liquid crystal cell.

As shown in FIG. 1 , the liquid crystal display device 1 includes a first display panel 100 and a second display panel 200 that overlaps the first display panel 100 . In the present embodiment, first display panel 100 is arranged in front (front side) of second display panel 200 . That is, the second display panel 200 is arranged behind (on the rear side of) the first display panel 100 .

The liquid crystal display device 1 further includes a backlight 300 facing the second display panel 200 . Specifically, the backlight 300 is arranged on the back side of the second display panel 200 . That is, the second display panel 200 is arranged between the first display panel 100 and the backlight 300, and the first display panel 100, the second display panel 200 and the backlight 300 are arranged in this order from the front to the rear. placed towards.

The first display panel 100 is a main panel arranged at a position closer to the observer (user) than the second display panel 200, and displays an image visually recognized by the observer. In this embodiment, the first display panel 100 displays a color image.

The first display panel 100 has a first image display area 101 (active area) in which a color image is displayed. The first image display area 101 is composed of a plurality of first pixels arranged in a matrix. The first pixel is composed of a red pixel, a green pixel and a blue pixel. In order to display a color image in the first image display area 101, the first display panel 100 is provided with a first source driver 102 and a first gate driver 103. FIG.

The second display panel 200 is a sub-panel arranged behind the first display panel 100 . In this embodiment, the second display panel 200 displays a monochrome image.

The second display panel 200 has a second image display area 201 (active area) in which a monochrome image is displayed. The second image display area 201 is composed of a plurality of second pixels arranged in a matrix. In order to display a monochrome image in the second image display area 201, the second display panel 200 is provided with a second source driver 202 and a second gate driver 203. FIG.

Note that the number of pixels in the first image display region 101 and the number of pixels in the second image display region 201 may be the same or different, but the number of pixels in the first image display region 101 is the highest. It is preferable that the number of pixels is larger than that of the two-image display area 201 . Moreover, in the present embodiment, the plurality of second pixels in the second image display region 201 are arranged corresponding to the plurality of first pixels in the first image display region 101 . Specifically, one second pixel corresponds to three first pixels, a pixel for red, a pixel for green, and a pixel for blue.

The first display panel 100 and the second display panel 200 configured in this manner are driven and controlled by a lateral electric field method such as an IPS (In Plane Switching) method or an FFS (Fringe Field Switching) method. The driving method of the first display panel 100 and the second display panel 200 is not limited to the horizontal electric field method, and may be a VA (Vertical Alignment) method, a TN (Twisted Nematic) method, or the like.

The backlight 300 emits light toward the first display panel 100 and the second display panel 200 . Light emitted from the backlight 300 enters the second display panel 200 , passes through the second display panel 200 , and enters the first display panel 100 .

In the present embodiment, the backlight 300 is a surface light source unit that emits planar and uniform diffused light (scattered light). The backlight 300 is, for example, an LED backlight using an LED (Light Emitting Diode) as a light source. As an example, the backlight 300 is a direct backlight in which a plurality of LEDs are two-dimensionally arranged in rows and columns.

Note that the backlight 300 is not limited to a direct type, and may be an edge type. Further, the light source of the backlight 300 is not limited to LEDs, and may be cold cathode tubes or the like. Further, the backlight 300 may have an optical member such as a diffusion plate for diffusing light from the light source (LED) or a prism sheet for controlling light distribution.

In the liquid crystal display device 1 according to the present embodiment, the second display panel 200 and the first display panel 100 are driven and controlled by the same input video signal (common video source). Specifically, the monochrome image displayed on the second display panel 200 has the same pattern as the color image displayed on the first display panel 100 . That is, the second display panel 200 displays a monochrome image in synchronization with the color image on the first display panel 100 .

Therefore, the liquid crystal display device 1 includes a first timing controller 410 that controls the first source driver 102 and the first gate driver 103 of the first display panel 100, and a second source driver 202 and the second gate driver of the second display panel 200. A second timing controller 420 that controls the driver 203 and an image processing unit 430 that outputs image data to the first timing controller 410 and the second timing controller 420 are provided.

The image processing unit 430 receives the input video signal Data transmitted from the outside, executes image processing, and then outputs the first image data DAT1 to the first timing controller 410 and outputs the second image data DAT1 to the second timing controller 420 . Image data DAT2 is output. The image processing unit 430 also outputs control signals such as synchronization signals (not shown in FIG. 1) to the first timing controller 410 and the second timing controller 420 . The first image data DAT1 is image data for color display, and the second image data DAT2 is image data for monochrome display. As a result, the liquid crystal display device 1 synchronously displays a color image and a monochrome image generated by the same input video signal.

As described above, in the liquid crystal display device 1 , two liquid crystal panels, the first display panel 100 and the second display panel 200 , are superimposed to display a color image on the first display panel 100 and display a monochrome image on the second display panel 200 . displaying an image. As a result, the monochrome image is superimposed on the color image, so that a color image with tight blacks can be displayed. Therefore, the contrast ratio can be improved. For example, when the contrast ratio of each display panel of the first display panel 100 and the second display panel 200 is 1000:1 or more, by overlapping the first display panel 100 and the second display panel 200, the contrast ratio is 1,000,000:1. A higher contrast ratio than the above can be realized.

Further, the liquid crystal display device 1 in the present embodiment is an image display device compatible with HDR (High Dynamic Range), and uses a backlight capable of performing local dimming control as the backlight 300 . As a result, a color image with a higher contrast ratio and higher image quality can be displayed.

Next, a specific structure of the liquid crystal display device 1 will be described with reference to FIG. FIG. 2 is a cross-sectional view showing the configuration of the liquid crystal display device 1 according to Embodiment 1. As shown in FIG. Note that the backlight 300 is schematically shown in FIG.

As shown in FIG. 2, the liquid crystal display device 1 includes a bonding member 500 that bonds the first display panel 100 and the second display panel 200 together. The joining member 500 is arranged between the first display panel 100 and the second display panel 200 . Although the specific structure is not shown, the first display panel 100 and the second display panel 200 joined by the joining member 500 form a single liquid crystal module together with the backlight 300 and a holding member (frame) made of metal or resin. or chassis).

The first display panel 100 and the second display panel 200 are liquid crystal display panels including liquid crystal cells (liquid crystal panels). Specifically, the first display panel 100 has a first liquid crystal cell 10 , a first polarizing plate 31 and a third polarizing plate 33 . Also, the second display panel 200 has a second liquid crystal cell 20 , a second polarizing plate 32 and a fourth polarizing plate 34 .

Since the second display panel 200 is arranged on the back side of the first display panel 100, the second liquid crystal cells 20 of the second display panel 200 are arranged on the back side of the first liquid crystal cells 10 of the first display panel 100. are placed.

The first liquid crystal cell 10 includes a first TFT (Thin Film Transistor) substrate 11 , a first opposing substrate 12 facing the first TFT substrate 11 , and a first TFT substrate 12 disposed between the first TFT substrate 11 and the first opposing substrate 12 . and a liquid crystal layer 13 . In the present embodiment, the first liquid crystal cell 10 is arranged such that the first opposing substrate 12 is located in front of the first TFT substrate 11 . That is, the first liquid crystal cell 10 is arranged so that the first TFT substrate 11 is located on the backlight 300 side.

The first TFT substrate 11 is a TFT array substrate in which a TFT layer (not shown) is formed on a transparent substrate such as a glass substrate. Although not shown, the TFT layer includes a plurality of TFTs provided corresponding to the respective first pixels of the first image display region 101 (see FIG. 1) and wiring for supplying voltage to each TFT. It is A pixel electrode for applying a voltage to the first liquid crystal layer 13 is formed on the flattened layer of the TFT layer. Furthermore, a common electrode is also formed on the first TFT substrate 11 so as to face the pixel electrode. That is, the first TFT substrate 11 includes pixel electrodes and common electrodes facing each other. In the first TFT substrate 11, a TFT, a pixel electrode and a counter electrode are formed for each pixel, and an alignment film is formed so as to cover the pixel electrode and the counter electrode.

The first opposing substrate 12 is a CF substrate in which a color filter layer is formed as a pixel forming layer on a transparent substrate such as a glass substrate. The pixel formation layer of the first counter substrate 12 has a black matrix formed with a plurality of openings corresponding to each of the plurality of first pixels, and a plurality of color filters formed in each opening of the black matrix. . The black matrix is formed, for example, in a grid pattern. Each of the plurality of color filters is a red color filter corresponding to the red pixel, a green color filter corresponding to the green pixel, or a blue color filter corresponding to the blue pixel, and corresponds to one first pixel. formed by Note that an overcoat layer is formed so as to cover the pixel formation layer. An alignment film is formed on the surface of the overcoat layer.

The first liquid crystal layer 13 is sealed between the first TFT substrate 11 and the first opposing substrate 12 . The first liquid crystal layer 13 is sealed, for example, by forming a frame-shaped sealing member along the outer peripheral edges of the first TFT substrate 11 and the first counter substrate 12 . The liquid crystal material of the first liquid crystal layer 13 can be appropriately selected according to the driving method.

The second liquid crystal cell 20 includes a second TFT substrate 21 , a second counter substrate 22 facing the second TFT substrate 21 , and a second liquid crystal layer 23 arranged between the second TFT substrate 21 and the second counter substrate 22 . Prepare. In the present embodiment, the second liquid crystal cell 20 is arranged such that the second opposing substrate 22 is located in front of the second TFT substrate 21 . That is, the second liquid crystal cell 20 is arranged so that the second TFT substrate 21 is located on the backlight 300 side. The second liquid crystal cell 20 may be arranged such that the second TFT substrate 21 is located in front of the second opposing substrate 22 .

The second TFT substrate 21 has the same structure as the first TFT substrate 11, and is a TFT array substrate in which a TFT layer (not shown) is formed on a transparent substrate such as a glass substrate. Although not shown, the TFT layer of the second TFT substrate 21 includes TFTs provided corresponding to the second pixels of the second image display region 201 (see FIG. 1) and wiring for supplying voltage to each TFT. and are formed. Further, on the second TFT substrate 21, a pixel electrode for applying a voltage to the second liquid crystal layer 23 and a common electrode facing the pixel electrode are formed. That is, the second TFT substrate 21 includes pixel electrodes and common electrodes facing each other. In the second TFT substrate 21, a TFT, a pixel electrode and a counter electrode are formed for each second pixel, and an alignment film is formed so as to cover the pixel electrode and the counter electrode.

The second counter substrate 22 is a substrate in which a pixel forming layer is formed on a transparent substrate such as a glass substrate. The pixel formation layer of the second counter substrate 22 has a black matrix in which a plurality of openings are formed corresponding to each of the plurality of second pixels. The black matrix is formed, for example, in a grid pattern. Note that an overcoat layer is formed so as to cover the pixel formation layer. An alignment film is formed on the surface of the overcoat layer. In the present embodiment, since the second display panel 200 displays a monochrome image, no color filter is formed in the pixel formation layer of the second counter substrate 22 . Therefore, the openings of the black matrix of the pixel forming layer of the second counter substrate 22 are filled with the overcoat layer.

The second liquid crystal layer 23 is sealed between the second TFT substrate 21 and the second opposing substrate 22 . The second liquid crystal layer 23 is sealed, for example, by forming a frame-shaped sealing member along the outer peripheral edges of the second TFT substrate 21 and the second counter substrate 22 . The liquid crystal material of the second liquid crystal layer 23 can be appropriately selected according to the driving method.

As described above, the liquid crystal display device 1 uses four polarizing plates, namely, the first polarizing plate 31, the second polarizing plate 32, the third polarizing plate 33, and the fourth polarizing plate . Specifically, the first polarizing plate 31 and the third polarizing plate 33 are arranged so as to sandwich the first liquid crystal cell 10 , and the fourth polarizing plate 34 and the second polarizing plate 32 are arranged so as to sandwich the second liquid crystal cell 20 . are arranged so as to sandwich the Also, the first polarizing plate 31, the third polarizing plate 33, the fourth polarizing plate 34, and the second polarizing plate 32 are arranged in this order from the viewer side toward the backlight 300. FIG.

In the present embodiment, the first polarizing plate 31 and the second polarizing plate 32 are arranged outside the first liquid crystal cell 10 and the second liquid crystal cell 20 .

Specifically, the first polarizing plate 31 is provided on the front surface (viewer side surface) of the first liquid crystal cell 10 . That is, the first polarizing plate 31 is provided on the surface of the first liquid crystal cell 10 opposite to the surface on the bonding member 500 side. In this embodiment, the first polarizing plate 31 is attached to the outer surface of the first opposing substrate 12 of the first liquid crystal cell 10 via an adhesive layer.

The second polarizing plate 32 is provided on the back surface of the second liquid crystal cell 20 (the surface on the backlight 300 side). That is, the second polarizing plate 32 is provided on the surface of the second liquid crystal cell 20 opposite to the surface on the bonding member 500 side. In this embodiment, the second polarizing plate 32 is attached to the outer surface of the second TFT substrate 21 of the second liquid crystal cell 20 via an adhesive layer.

On the other hand, the third polarizing plate 33 and the fourth polarizing plate 34 are arranged between the first liquid crystal cell 10 and the second liquid crystal cell 20 . That is, the third polarizing plate 33 and the fourth polarizing plate 34 are sandwiched between the first liquid crystal cell 10 and the second liquid crystal cell 20 .

The third polarizing plate 33 is arranged between the first liquid crystal cell 10 and the bonding member 500 or between the second liquid crystal cell 20 and the bonding member 500. The fourth polarizing plate 34 is disposed between the first liquid crystal cell 10 and the bonding member 500 1 between the liquid crystal cell 10 and the bonding member 500 and between the second liquid crystal cell 20 and the bonding member 500 .

In this embodiment, the third polarizing plate 33 is arranged between the first liquid crystal cell 10 and the bonding member 500, and the fourth polarizing plate 34 is arranged between the bonding member 500 and the second liquid crystal cell 20. there is

Specifically, the third polarizing plate 33 is provided on the back surface of the first liquid crystal cell 10 (the surface on the backlight 300 side). That is, the third polarizing plate 33 is provided on the surface of the first liquid crystal cell 10 on the bonding member 500 side. In this embodiment, the third polarizing plate 33 is attached to the outer surface of the first TFT substrate 11 of the first liquid crystal cell 10 via an adhesive layer.

Further, the fourth polarizing plate 34 is arranged on the front surface (viewer side surface) of the second liquid crystal cell 20 . That is, the fourth polarizing plate 34 is provided on the surface of the second liquid crystal cell 20 on the bonding member 500 side. In this embodiment, the fourth polarizing plate 34 is attached to the outer surface of the second counter substrate 22 of the second liquid crystal cell 20 via an adhesive layer.

Of the four polarizing plates arranged in this manner, the first polarizing plate 31 and the third polarizing plate 33 sandwiching the first liquid crystal cell 10 are arranged so that their polarizing axes are orthogonal to each other. That is, the first polarizing plate 31 and the third polarizing plate 33 are arranged so as to have a crossed Nicols positional relationship.

Similarly, the fourth polarizing plate 34 and the second polarizing plate 32 sandwiching the second liquid crystal cell 20 are arranged so that their polarization axes are orthogonal to each other. That is, the fourth polarizing plate 34 and the second polarizing plate 32 are arranged so as to have a crossed Nicols positional relationship.

Further, the third polarizing plate 33 and the fourth polarizing plate 34 located between the first liquid crystal cell 10 and the second liquid crystal cell 20 are arranged so that their polarizing axes are substantially parallel to each other. Therefore, the first polarizing plate 31 and the second polarizing plate 32 are arranged so that their polarizing axes are substantially parallel to each other. Specifically, the absorption axis of the third polarizing plate 33 and the absorption axis of the fourth polarizing plate 34 are substantially parallel, and the absorption axis of the first polarizing plate 31 and the absorption axis of the second polarizing plate 32 are substantially parallel. It has become.

Each of the four polarizing plates, the first polarizing plate 31, the second polarizing plate 32, the third polarizing plate 33, and the fourth polarizing plate 34, is a sheet-like polarizing film made of, for example, a resin material. and a transparent protective film laminated to the child. The polarizer and the transparent protective film are bonded together with an adhesive, for example. Moreover, in order to protect both surfaces of the polarizer, a transparent protective film may be provided on each of both surfaces of the polarizer. That is, the polarizer is preferably sandwiched between a pair of transparent protective films.

Each polarizer in the four polarizing plates is obtained by, for example, adsorbing a dichroic substance such as iodine on a resin film and orienting the molecules by stretching or the like. As the resin film of each polarizer, a polyvinyl alcohol (PVA) film can be used.

Polyvinyl alcohol (PVA) or a derivative thereof is used as the material of the PVA-based film applied to each polarizer. Polyvinyl formal, polyvinyl acetal and the like can be used as derivatives of polyvinyl alcohol. In addition, olefins such as ethylene and propylene, alkyl esters of unsaturated carboxylic acids such as acrylic acid, methacrylic acid and crotonic acid, acrylamide and the like can be used. You may use what was denatured by. As an example, polyvinyl alcohol having a degree of polymerization of about 1000 to 10000 and a degree of saponification of about 80 to 100 mol % is used.

Moreover, the PVA-based film constituting each polarizer may contain an additive such as a plasticizer. As the plasticizer, polyols, condensates thereof, and the like can be used. For example, glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, polyethylene glycol, and the like can be used. The amount of the plasticizer used is not particularly limited, but when the plasticizer is added to the PVA-based film, it is preferable that the PVA-based film contains 20% by weight or less of the plasticizer.

Each transparent protective film in the four polarizing plates is made of a transparent resin material and functions as a protective film that protects the polarizer and as a base film that supports the polarizer. Materials for the transparent protective film include cellulose-based resins such as triacetylcellulose (TAC), (meth)acrylic-based resins, polyester-based resins, polyethersulfone-based resins, polysulfone-based resins, polycarbonate-based resins, and polyamide-based resins. , polyimide resins, polyolefin resins, cyclic polyolefin resins (norbornene resins), polyarylate resins, polystyrene resins, polyvinyl alcohol resins, and mixtures thereof.

In the four polarizing plates of the first polarizing plate 31, the second polarizing plate 32, the third polarizing plate 33, and the fourth polarizing plate 34, the configuration of the third polarizing plate 33 and the fourth polarizing plate 34 is the same as that of the first polarizing plate 31 and the configuration of the second polarizing plate 32 .

Specifically, the third polarizing plate 33 includes a polarizer 33a, a first transparent film 33b which is a transparent protective film laminated on one surface of the polarizer 33a, and a transparent film 33b laminated on the other surface of the polarizer 33a. and a second transparent film 33c, which is a transparent protective film. That is, the polarizer 33a is sandwiched between the first transparent film 33b and the second transparent film 33c.

The polarizer 33a is a PVA-based film containing iodine. The thickness of the polarizer 33a is 26 μm or more and 30 μm or less.

The first transparent film 33b is provided on the bonding member 500 side of the polarizer 33a. Specifically, the first transparent film 33b is attached to the surface of the polarizer 33a on the bonding member 500 side with an adhesive or the like. The first transparent film 33b is a TAC-based film containing no phosphoric acid-based plasticizer. That is, the phosphoric acid-based plasticizer contained in the TAC-based film, which is the first transparent film 33b, is 0% by weight.

In this specification, "a TAC-based film containing no phosphoric acid-based plasticizer" means that the TAC-based film does not intentionally contain a phosphoric acid-based plasticizer. Therefore, when a trace amount of phosphoric acid-based plasticizer is unintentionally contained in the TAC-based film as an impurity, it is included in the concept of "a TAC-based film containing no phosphoric acid-based plasticizer."

The second transparent film 33c is provided on the opposite side of the polarizer 33a from the bonding member 500 side (first liquid crystal cell 10 side). Specifically, the second transparent film 33c is attached to the first liquid crystal cell 10 side surface of the polarizer 33a with an adhesive or the like. In the present embodiment, the second transparent film 33c is a (meth)acrylic resin-based film, but is not limited to this, and may be a TAC-based film like the first transparent film 33b. In this case, it is preferable that the second transparent film 33c also does not contain the phosphoric acid-based plasticizer.

The thickness of the first transparent film 33b and the second transparent film 33c is preferably thicker than that of the polarizer 33a, but is not limited to this. It may be thinner than the polarizer 33a.

The third polarizing plate 33 configured in this manner has a smaller amount of water than the first polarizing plate 31 and the second polarizing plate 32 . That is, the amount of water contained in the third polarizing plate 33 is less than the amount of water contained in the first polarizing plate 31 and less than the amount of water contained in the second polarizing plate 32 . Specifically, the water content per unit area of the third polarizing plate 33 is 6 g/m ² or less. As an example, the water content per unit area of the third polarizing plate 33 is about 5.3 g/m ² , and the water content per unit area of the first polarizing plate 31 and the second polarizing plate 32 is about 6.0 g/m 2 . 3 g/ ^m2 .

Furthermore, the first transparent film 33b and the second transparent film 33c in the third polarizing plate 33 preferably have high moisture permeability (moisture permeability). As a result, the moisture in the polarizer 33a is easily diffused outside the third polarizing plate 33 through the first transparent film 33b and the second transparent film 33c. 33 tends to suppress a decrease in transmittance.

Further, the fourth polarizing plate 34, like the third polarizing plate 33, includes a polarizer and transparent protective films that protect both sides of the polarizer. Specifically, the fourth polarizing plate 34 includes a polarizer 34a, a first transparent film 34b which is a transparent protective film laminated on one surface of the polarizer 34a, and a transparent film 34b laminated on the other surface of the polarizer 34a. and a second transparent film 34c, which is a transparent protective film. That is, the polarizer 34a is sandwiched between the first transparent film 33b and the second transparent film 33c.

In this embodiment, the fourth polarizing plate 34 is the same as the third polarizing plate 33 . Specifically, the fourth polarizing plate 34 and the third polarizing plate 33 are the same product. Therefore, the material, thickness, etc. of the polarizer 34a are the same as the material, thickness, etc. of the polarizer 33a. The material, thickness, etc. of the first transparent film 34b are the same as the material, thickness, etc., of the first transparent film 33b, and the material, thickness, etc., of the second transparent film 34c are also the same as those of the second transparent film 33c. is the same as The amount of water contained in the fourth polarizing plate 34 is also the same as that of the third polarizing plate 33, which is approximately 5.3 g/m ² .

The fourth polarizing plate 34 is arranged such that the first transparent film 33b of the first transparent film 34b and the second transparent film 34c is located on the bonding member 500 side. Therefore, in the fourth polarizing plate 34, the first transparent film 34b, which is a TAC-based film containing no phosphoric acid-based plasticizer, is bonded to the surface of the polarizer 34a on the bonding member 500 side, and the (meth)acrylic A second transparent film 34c, which is a resin-based film, is attached to the surface of the polarizer 34a opposite to the bonding member 500 side (the surface on the second liquid crystal cell 20 side).

Note that the first polarizing plate 31 and the second polarizing plate 32 have transparent protective films laminated on both sides of the polarizer in the same manner as the third polarizing plate 33, but they are different products from the third polarizing plate 33. is. Specifically, the first polarizing plate 31 and the second polarizing plate 32 are the same as the third polarizing plate 33 and the fourth polarizing plate 34 in that the polarizer is a PVA-based film containing iodine. It differs from the third polarizing plate 33 and the fourth polarizing plate 34 in that the two transparent protective films sandwiching the child are both TAC films.

A first display panel 100 in which a first polarizing plate 31 and a third polarizing plate 33 are bonded to the first liquid crystal cell 10, and a second display panel 100 in which a fourth polarizing plate 34 and a second polarizing plate 32 are bonded to the second liquid crystal cell 20. 2 is joined to the display panel 200 via a joining member 500 . Specifically, the first display panel 100 and the second display panel 200 are bonded together by a bonding member 500 .

In the present embodiment, the bonding member 500 is arranged between the third polarizing plate 33 of the first display panel 100 and the fourth polarizing plate 34 of the second display panel 200, and the third polarizing plate 33 and the fourth polarizing plate 34 are arranged. 4 The polarizing plate 34 is joined.

The joining member 500 is an adhesive agent such as a film-like optically transparent adhesive sheet (OCA), and is made of, for example, an acrylic resin material. Note that the joining member 500 may be composed of a plurality of laminated adhesive resin sheets.

Also, the thickness of the bonding member 500 is preferably equal to or greater than the thickness of the polarizer 33 a of the third polarizing plate 33 . In this embodiment, the thickness of the bonding member 500 is greater than the thickness of the entire third polarizing plate 33 .

Next, the effects of the liquid crystal display device 1 according to the present embodiment will be described, including the circumstances leading to the present disclosure.

A display panel used in a liquid crystal display device has a liquid crystal cell and a pair of polarizing plates sandwiching the liquid crystal cell. Conventionally, an image display device with a high contrast ratio has been studied by stacking a plurality of such display panels and bonding them together with a bonding member such as an OCA.

However, when a liquid crystal display device in which a plurality of display panels are bonded together with a bonding member is used for a long time, the display screen may become colored. In particular, the central portion of the display screen may appear brownish. When the display screen is colored in this way, the quality of the displayed image is degraded.

When the inventors of the present invention investigated the cause of such coloring of the display screen, they found that the polarizing plate bonded to the liquid crystal cell was discolored. In particular, in a liquid crystal display device in which two display panels are superimposed, three or four polarizing plates are used, and among these polarizing plates, the polarizing plate disposed between two liquid crystal cells changes color. I found out. In particular, it was found that the in-plane central portion of the polarizing plate was discolored to brown.

As a result of intensive studies on the cause of such discoloration of the polarizing plate, the present inventors found that the polarizing plate is discolored due to the material of the polarizing plate and moisture contained in the polarizing plate. This point will be described below.

A polarizing plate has a polarizer and a transparent protective film laminated on the polarizer. As a material for the polarizer, for example, a PVA-based film containing iodine is used.

The PVA in the PVA-based film dehydrates and polyenes when heated. That is, a polyene structure (-(C=C) _n -) is formed in PVA, and PVA is denatured. Thus, when PVA becomes polyene, the polarizing plate changes color and absorbs visible light.

As a material for the transparent protective film of the polarizing plate, for example, a TAC-based film is used. In this case, a phosphoric acid-based plasticizer may be added to the TAC-based film in order to impart a function such as flexibility.

Here, when a TAC film containing a phosphoric acid plasticizer is exposed to a high temperature and high humidity environment for a long time, the acid impurity contained in the phosphoric acid plasticizer hydrolyzes the TAC film, resulting in an acid. is generated. Specifically, acetic acid is produced when the TAC-based film is hydrolyzed.

At this time, if moisture is contained in the polarizing plate, the hydrolysis of the TAC film due to the acid impurities of the phosphoric plasticizer will be promoted, and a large amount of acetic acid will be present in the polarizing plate. .

Here, the polyene formation of PVA is mainly due to a dehydration reaction, but is accelerated by the presence of acid. That is, the acid acts as a catalyst to promote the dehydration reaction of PVA.

Therefore, as described above, when the TAC-based film is hydrolyzed by acid impurities in the phosphoric acid-based plasticizer to produce acid (acetic acid), this acid acts as a catalyst to promote the dehydration reaction of PVA, thereby Polyenization of will proceed.

Moreover, once PVA is polyene-formed, water is generated by the dehydration reaction of PVA, the amount of water in the polarizing plate increases, the TAC film is more likely to be hydrolyzed, and acetic acid is more likely to be generated. As a result, polyenization of PVA proceeds at an accelerated pace.

Therefore, when the polarizing plate in the liquid crystal display device is heated by, for example, a backlight, the PVA of the PVA-based film constituting the polarizer of the polarizing plate undergoes a dehydration reaction. The acetic acid produced by the hydrolysis of the TAC-based film that constitutes the transparent protective film of the polarizing plate with moisture serves as a catalyst to accelerate the dehydration reaction. As a result, polyene conversion of PVA proceeds and the polarizing plate discolors.

In particular, the main surface of the polarizing plate positioned between the two liquid crystal cells is in a sealed state in close contact with the bonding member. For this reason, in the peripheral portion of the polarizing plate, some moisture is considered to escape from the edges, but it is difficult to escape in the central portion of the plane of the polarizing plate. As a result, more water is present in the in-plane central portion of the polarizing plate than in the peripheral portion of the polarizing plate, which promotes hydrolysis of the TAC-based film and tends to generate more acetic acid. In addition, since the in-plane central portion of the polarizing plate tends to be heated to a higher temperature than the peripheral portion of the polarizing plate, polyene conversion of PVA easily progresses.

Therefore, in the in-plane central portion of the polarizing plate, the reaction promotion by the acetic acid (catalyst) generated by the hydrolysis of the TAC film and the reaction promotion by the high temperature of the polarizing plate are combined to further promote the dehydration reaction of PVA. , the polyene conversion of PVA proceeds at an accelerated rate. Conversely, since the temperature of the reaction system is less likely to rise in the peripheral portion of the polarizing plate, the dehydration reaction of PVA is less likely to proceed. As a result, the in-plane central portion of the polarizing plate disposed between the two liquid crystal cells is discolored to brown.

As described above, the present inventors found that when a liquid crystal display device is configured by bonding display panels in which a polarizing plate is bonded to a liquid crystal cell with a bonding member, the polarizer is a PVA-based film and the transparent protective film is It has been found that when a polarizing plate that is a TAC film containing a phosphoric acid plasticizer is used, the polarizing plate is discolored.

The present disclosure has been made based on such findings, and the present inventors have investigated the polarizing plate placed between two liquid crystal cells, and the materials of the polarizer and the transparent protective film in the polarizing plate and the polarized light. It was found that discoloration of the polarizing plate can be suppressed by specifying the amount of water contained in the plate.

Specifically, in the liquid crystal display device 1 according to the present embodiment, the third polarizing plate 33 disposed between the first liquid crystal cell 10 and the bonding member 500 has a PVA film containing iodine as the polarizer 33a. , a TAC-based film containing no phosphoric acid-based plasticizer is used as the first transparent film 33b, and the water content per unit area of the third polarizing plate 33 is set to 6 g/m ² or less. .

In this way, the water content per unit area of the third polarizing plate 33 is reduced to a small amount of 6 g/m ² or less, and the TAC film of the first transparent film 33b does not contain a phosphoric acid plasticizer. Hydrolysis of the system film can be suppressed. As a result, it is possible to suppress the production of acetic acid, which is a catalyst for the dehydration reaction of PVA, due to the hydrolysis of the TAC-based film, so that the occurrence of the dehydration reaction of PVA can be suppressed. As a result, polyene conversion of PVA can be suppressed, so that discoloration of the third polarizing plate 33 can be suppressed.

Moreover, the third polarizing plate 33 configured in this manner has better weather resistance than the first polarizing plate 31 and the second polarizing plate 32, in which the two transparent protective films on both sides of the polarizer are both made of TAC-based films. It has excellent durability and heat resistance. Therefore, by using the third polarizing plate 33 as the polarizing plate between the first liquid crystal cell 10 and the second liquid crystal cell 20, a highly reliable liquid crystal display device with excellent weather resistance and heat resistance is realized. be able to.

Further, in the liquid crystal display device 1 according to the present embodiment, the first display panel 100 and the second display panel 200 are joined by the joining member 500, and the third polarizing plate 33 of the first display panel 100 is It is in close contact with the member 500 .

As the bonding member 500, for example, OCA such as acrylic resin is used. When OCA is exposed to a high-temperature environment, OCA vaporizes and generates acid. For example, when the OCA is made of acrylic resin, the OCA vaporizes to generate acrylic acid.

In this case, when the acid generated by the vaporization of the bonding member 500 moves to the polarizer 33a of the third polarizing plate 33, not only the acid generated by the hydrolysis of the TAC-based film but also the acid generated by the vaporization of the bonding member 500 may act as a catalyst to accelerate the dehydration reaction of PVA constituting the polarizer 33a.

However, in the liquid crystal display device 1 according to the present embodiment, the water content per unit area of the third polarizing plate 33 is reduced to 6 g/m ² or less, and the Since the TAC-based film constituting the first transparent film 33b does not contain a phosphoric acid-based plasticizer, generation of acetic acid due to hydrolysis of the TAC-based film can be suppressed, and polyene formation of PVA can be suppressed.

As described above, according to the liquid crystal display device 1 of the present embodiment, discoloration of the third polarizing plate 33 arranged between the first liquid crystal cell 10 and the bonding member 500 can be suppressed. As a result, it is possible to suppress the occurrence of coloring on the display screen, and it is possible to suppress the deterioration of the quality of the display image.

Here, the present inventors conducted an experiment on the relationship between the material and water content of the polarizing plate and the discoloration of the polarizing plate, which will be described below.

In this experiment, two substrates each having a polarizing plate attached to a 200 μm square glass plate were prepared, and the two substrates were arranged so that the polarizing plates faced each other and were attached by OCA, which was used as a sample. Each of the polarizing plates used in this experiment has a polarizer made of PVA and transparent films laminated on both sides of the polarizer. Also, in this experiment, four types of samples A to D were prepared. Samples A to D all had the same glass plate, and were mainly changed in the material of the transparent film of the polarizing plate, the amount of water contained in the polarizing plate, and OCA.

Specifically, in samples A and B, the thickness of the polarizer was 28 μm, the water content per unit area of the polarizing plate was 6.3 g/m ² , and the phosphoric acid-based plasticizer was triphenyl phosphate (TPP ), and as the OCA, a 600 μm-thick acrylic OCA was used for sample A, and a 1000 μm-thick acrylic OCA was used for sample B. Samples A and B correspond to the first polarizing plate 31 .

On the other hand, in samples C and D, the thickness of the polarizer was 28 μm, the water content per unit area of the polarizer was 5.3 g/m ² , and the phosphoric acid-based plasticizer provided on the OCA side of the polarizer was and a transparent film made of a (meth)acrylic resin film provided on the glass plate side of the polarizer. An acrylic material having a thickness of 1000 μm was used for sample D. Note that samples C and D correspond to the third polarizing plate 33 .

In this experiment, the samples A to D were allowed to stand for 2500 hours in an environment of 80° C. and 3% humidity, and the durability was confirmed by confirming the color change of each sample. Specifically, a sample with a large change in color was evaluated as having no durability, and a sample with a small change in color was evaluated as having durability. The results are shown in Table 1 below.

As shown in Table 1, it can be seen that samples C and D show less color change after a long period of time than samples A and B, and are excellent in durability.

Furthermore, the inventors of the present invention have found from this experimental result that the more thick the bonding member 500 that bonds the first display panel 100 and the second display panel 200 is, the more the third polarizing plate 33 can be prevented from browning. I wondered if this was the case, and conducted an experiment on this matter as well. The results of this experiment will be described below.

The same samples A and B as above were used in this experiment. The samples A and B were then left in an environment of 80° C. and 3% humidity, and the chromaticity of each of the samples A and B was measured over time using a surface colorimeter. At this time, the chromaticity difference between the peripheral part and the central part of each sample (the chromaticity of the peripheral part - the chromaticity of the central part) is defined as the V' value, and using this V' value, the "brown color" of sample A and sample B degree” was evaluated.

The results of this experiment are shown in FIG. FIG. 3 is a diagram showing changes over time in brownness of two polarizing plates bonded by OCA. In FIG. 3, the vertical axis indicates the ratio of the V' values, and the lower the numerical value on the vertical axis, the higher the degree of browning in the central portion of the sample. In other words, the lower the numerical value on the vertical axis, the more browned. In FIG. 3, the horizontal axis indicates time (h).

In FIG. 3, the dashed line indicates the time-dependent change in chromaticity of sample A (OCA 600 μm thick), and the solid line indicates the time-dependent change in chromaticity of sample B (OCA 1000 μm thick).

As shown in FIG. 3, it can be seen that sample B is less likely to be browned than sample A. In particular, in sample A, the degree of browning tends to increase after about 1000 hours, and browning tends to be conspicuous. It can be seen that it does not turn brown. Thus, it can be seen that the thicker the OCA, the less likely it is to be browned, and conversely, the thinner the OCA, the more likely it is to be browned.

From this experimental result, it was found that the thicker the bonding member 500 that bonds the first display panel 100 and the second display panel 200 is, the more the brown discoloration of the third polarizing plate 33 can be suppressed.

One of the reasons why the browning of the third polarizing plate 33 can be suppressed by increasing the thickness of the bonding member 500 is that the moisture contained in the third polarizing plate 33 is removed by increasing the thickness of the bonding member 500. This is probably because the amount of water that can be absorbed by the joint member 500 (water absorption capacity) has increased. In other words, it is considered that the amount of water contained in the third polarizing plate 33 can be reduced by increasing the thickness of the bonding member 500 . By reducing the amount of water contained in the third polarizing plate 33 in this way, it is possible to effectively suppress the generation of acid due to hydrolysis of the TAC-based film forming the first transparent film 33b. As a result, it is possible to suppress polyene conversion of PVA constituting the polarizer 33a, and it is possible to suppress discoloration of the third polarizing plate 33 to brown.

Therefore, in the liquid crystal display device 1 according to the present embodiment, the thickness of the bonding member 500 is made equal to or greater than the thickness of the polarizer 33 a of the third polarizing plate 33 in order to increase the thickness of the bonding member 500 .

Thus, when the first display panel 100 and the second display panel 200 are bonded by the bonding member 500 and the third polarizing plate 33 is arranged between the first liquid crystal cell 10 and the bonding member 500, Also, discoloration of the third polarizing plate 33 can be effectively suppressed. Therefore, it is possible to further suppress deterioration in the quality of the display image.

It should be noted that the thickness of the bonding member 500 is preferably greater than the thickness of the entire third polarizing plate 33 . Further, in the present embodiment, the thickness of the bonding member 500 is thicker than the thickness of the fourth polarizing plate 34, and further thicker than the thicknesses of the first polarizing plate 31 and the second polarizing plate 32. .

Moreover, in the liquid crystal display device 1 according to the present embodiment, the second transparent film 33c of the third polarizing plate 33 is a (meth)acrylic resin film.

With this configuration, the oblique viewing angle can be improved. Thereby, the quality of the display image can be improved.

Further, in the liquid crystal display device 1 of the present embodiment, the fourth polarizing plate 34 is arranged between the second liquid crystal cell 20 and the bonding member 500 . And the fourth polarizing plate 34 is the same as the third polarizing plate 33 .

As a result, in the fourth polarizing plate 34 as well, it is possible to suppress the production of acetic acid, which is a catalyst for the dehydration reaction of PVA, due to hydrolysis of the TAC-based film. As a result, in the fourth polarizing plate 34 as well, the dehydration reaction of PVA can be suppressed, and polyenization of PVA can be suppressed. As a result, discoloration of the fourth polarizing plate 34 can also be suppressed. Therefore, it is possible to further suppress deterioration in the quality of the display image.

(Modification)
Although the liquid crystal display device according to the present disclosure has been described above based on the embodiments, the present disclosure is not limited to the above embodiments.

For example, the first diffusion layer 41 may be arranged between the third polarizing plate 33 and the bonding member 500 as in the liquid crystal display device 2 according to the modification shown in FIG. The first diffusion layer 41 is a diffusion film (diffusion plate) having a light diffusion function. The first diffusion layer 41 may have a structure in which a light diffusing material is dispersed (internal haze structure), or may have an uneven surface structure (external haze structure) formed by anti-glare treatment or the like. It may have both an internal haze structure and an external haze structure.

By arranging the first diffusion layer 41 in this way, it is possible to suppress the occurrence of moire caused by the pattern shape of the black matrix of the second liquid crystal cell 20 or the like. The first diffusion layer 41 is bonded to the third polarizing plate 33 with an adhesive or the like, for example. Note that the first diffusion layer 41 may be an optical film integrated with the third polarizing plate 33 .

Furthermore, in the liquid crystal display device 2 shown in FIG. 4, the second diffusion layer 42 is also arranged between the fourth polarizing plate 34 and the bonding member 500 . As the second diffusion layer 42, one having the same structure as the first diffusion layer 41 can be used.

By arranging the second diffusion layer 42 in this way, it is possible to further suppress the occurrence of moire. The second diffusion layer 42 is attached to the fourth polarizing plate 34 with an adhesive or the like, for example. The second diffusion layer 42 may also be an optical film integrated with the fourth polarizing plate 34 .

In addition, in the above-described embodiment and modifications, the first polarizing plate 31, the second polarizing plate 32, the third polarizing plate 33, and the fourth polarizing plate 34 have other functions such as retardation plates (retardation films). A film may be laminated. These functional films may be optical films integrated with each of the first polarizing plate 31, the second polarizing plate 32, the third polarizing plate 33, and the fourth polarizing plate 34, or may be separate bodies. .

Further, in the above-described embodiment and modification, the first polarizing plate 31, the second polarizing plate 32, the third polarizing plate 33, and the fourth polarizing plate 34 are a polarizer and a pair of transparent protective films sandwiching the polarizer. Although a layered structure is used, the present invention is not limited to this. The first polarizing plate 31, the second polarizing plate 32, the third polarizing plate 33 and the fourth polarizing plate 34 have other resin base layers or adhesive layers in addition to the polarizer and the pair of transparent protective films. good too. In this case, the resin substrate layer or adhesive layer may be provided on the outer surface of the transparent protective film, or may be inserted between the polarizer and the transparent protective film. That is, the first polarizing plate 31, the second polarizing plate 32, the third polarizing plate 33, and the fourth polarizing plate 34 are not formed by continuously laminating the three resin films of the polarizer and the pair of transparent protective films. may

Further, in the above embodiments and modifications, the second polarizing plate 32 may also be the same as the third polarizing plate 33 . Of the four polarizing plates, the second polarizing plate 32 is located closest to the backlight 300, so it is exposed to the highest temperature among the four polarizing plates. Therefore, by using the same material as the third polarizing plate 33, which is excellent in weather resistance and heat resistance, as the second polarizing plate 32, it is possible to suppress deterioration of the second polarizing plate 32 due to heat. Thereby, a more reliable liquid crystal display device can be realized.

In addition, in the above embodiment and modified example, two polarizing plates, the third polarizing plate 33 and the fourth polarizing plate 34, are inserted between the first liquid crystal cell 10 and the second liquid crystal cell 20. However, only one of the third polarizing plate 33 and the fourth polarizing plate 34 may be arranged between the first liquid crystal cell 10 and the second liquid crystal cell 20 . In addition, when the third polarizing plate 33 is not arranged and only the first polarizing plate 31, the second polarizing plate 32, and the fourth polarizing plate 34 are configured, the fourth polarizing plate 34 serves as the third polarizing plate. Become.

In addition, although two display panels are used in the above-described embodiment and modifications, the present invention is not limited to this. For example, three or more display panels may be used.

In addition, forms obtained by applying various modifications that a person skilled in the art can think of to the above embodiments and modifications, and arbitrarily combining the components and functions in the embodiments and modifications within the scope of the present disclosure The present disclosure also includes a mode realized by

Reference Signs List 1, 2 liquid crystal display device 10 first liquid crystal cell 11 first TFT substrate 12 first opposing substrate 13 first liquid crystal layer 20 second liquid crystal cell 21 second TFT substrate 22 second opposing substrate 23 second liquid crystal layer 31 first polarizing plate 32 Second polarizing plate 33 Third polarizing plate 33a, 34a Polarizer 33b, 34b First transparent film 33c, 34c Second transparent film 34 Fourth polarizing plate 41 First diffusion layer 42 Second diffusion layer 100 First display panel 101 Second 1 image display area 102 first source driver 103 first gate driver 200 second display panel 201 second image display area 202 second source driver 203 second gate driver 300 backlight 410 first timing controller 420 second timing controller 430 image Processing unit 500 joining member

Claims (8)

a first display panel including a first liquid crystal cell;
a second display panel disposed over the first display panel and including a second liquid crystal cell;
a joining member disposed between the first display panel and the second display panel and joining the first display panel and the second display panel;
a first polarizing plate provided on the surface of the first liquid crystal cell opposite to the surface on the bonding member side;
a second polarizing plate provided on the surface of the second liquid crystal cell opposite to the surface on the bonding member side;
a third polarizing plate disposed between the first liquid crystal cell and the bonding member and between the second liquid crystal cell and the bonding member;
The third polarizing plate includes a polarizer, a first transparent film provided on the bonding member side of the polarizer, and a second transparent film provided on the opposite side of the polarizer to the bonding member side. has
The polarizer is a polyvinyl alcohol film containing iodine,
The thickness of the polarizer is 26 μm or more and 30 μm or less,
The first transparent film is a triacetyl cellulose film containing no phosphoric acid plasticizer,
The water content per unit area of the third polarizing plate is 6 g/m ² or less,
The second transparent film does not contain a phosphoric acid-based plasticizer,
Liquid crystal display. The thickness of the bonding member is equal to or greater than the thickness of the third polarizing plate.
The liquid crystal display device according to claim 1. The second transparent film is a (meth)acrylic resin film,
3. The liquid crystal display device according to claim 1. The second transparent film is a triacetyl cellulose film containing no phosphoric acid plasticizer,
3. The liquid crystal display device according to claim 1. A diffusion layer is arranged between the third polarizing plate and the bonding member,
The liquid crystal display device according to any one of claims 1 to 4 . a fourth polarizing plate disposed between the first liquid crystal cell and the bonding member and between the second liquid crystal cell and the bonding member;
The fourth polarizing plate is the same as the third polarizing plate,
The liquid crystal display device according to any one of claims 1 to 5 . The second polarizing plate is the same as the third polarizing plate,
The liquid crystal display device according to any one of claims 1 to 6 . further comprising a backlight arranged to face the second display panel;
wherein the second display panel is arranged between the first display panel and the backlight;
The liquid crystal display device according to any one of claims 1 to 7 .

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