JP4583072B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a transflective liquid crystal display device provided with a transflective film, and in particular, design of a liquid crystal panel (twist angle, optical path difference Δnd), optical path difference Δnd of a phase difference plate (actually a retardation film), and pasting The present invention relates to a liquid crystal display device in which the angle and the sticking angle of the polarizing plate are optimized.

  In recent years, transflective liquid crystal display devices that can be used both outdoors and indoors have been developed for portable information terminal applications.

  This transflective liquid crystal display device may be used as a reflection type device by external illumination such as sunlight or fluorescent lamp, or may be used as a transmission type device equipped with a backlight as internal illumination. In addition, a transflective plate is disposed on the back side of the liquid crystal panel, a polarizing plate and a backlight are sequentially disposed on the back side of the transflective plate, and the transflective plate and the polarizing plate are further disposed. There has been proposed a structure in which a phase difference plate for compensating coloring at the time of transmissive display is arranged.

  FIG. 4 is a schematic sectional view of a transflective liquid crystal display device using TFT (thin film transistor) switching elements in the prior art, and FIG. 5 shows the angle between the absorption axis of the polarizing plate and the stretching axis of the retardation plate in the device. FIG.

  In this transflective liquid crystal display device, reference numeral 2 denotes a liquid crystal panel. A counter electrode 25 as a transparent electrode is formed on one transparent substrate 12 of two transparent substrates arranged opposite to each other. The reflective electrode 26 and the transparent electrode 15 are formed side by side on the same surface. An alignment film is formed on the inner surface side of the substrate, and liquid crystal molecules are sandwiched between both transparent substrates.

  The retardation plates 4 and 5 and the polarizing plate 3 are laminated on the display surface side main surface (hereinafter, referred to as one main surface) of the transparent substrate 12, and the non-display surface side main surface (hereinafter, referred to as “the main surface”) The retardation plates 6 and 7 and the polarizing plate 8 are sequentially stacked on the other main surface), and the backlight 9 is disposed on the opposite side of the polarizing plate 8 from the retardation plate 7.

  When such a liquid crystal display device displays liquid crystal in the reflection mode, the reflective electrode 26 is used. That is, light incident from one main surface side passes through the liquid crystal layer, is reflected by the reflective electrode 26, passes through the liquid crystal layer again, and is emitted from the one main surface side which is the display surface.

  In addition, when the liquid crystal display is performed in the transmission mode, the transparent electrode 15 is used. That is, the light of the backlight 9 incident from the other main surface side passes through the transparent electrode 15 which is a portion where the reflective electrode 26 is not formed, passes through the liquid crystal layer, and is emitted from the one main surface side which is the display surface. Is emitted. That is, a region where the reflective electrode 26 is formed is a light reflective region, and a region where only the transparent electrode 15 is formed without the reflective electrode 26 is a light transmissive region.

  FIG. 5 shows each angle (reverse angle) of the stretching axis of each phase difference plate 4, 5, 6, 7 and the absorption axis of each polarizing plate 3, 8 with reference to the average rubbing direction of both rubbing directions in both alignment films. (Clockwise) is seen from the display surface. (A) shows the relationship of the 1st phase difference plate 4, the 2nd phase difference plate 5, and the 1st polarizing plate 3 which were formed on the transparent substrate 12 by the side of a display surface, and explanatory drawing seen from the display surface side as mentioned above. (B) shows the relationship between the third retardation plate 6, the fourth retardation plate 7, and the second polarizing plate 8 formed on the other main surface of the transparent substrate 13 on the non-display surface side, as described above. It is explanatory drawing seen from the display surface side.

On the other hand, the absorption axis of the polarizing plate 3 on the main surface side is 15 ° in a direction not sandwiching the stretching axis of the retardation plate 4 with respect to the stretching axis of the retardation plate 5 and 75 ° with respect to the stretching axis of the retardation plate 4. The absorption axis of the polarizing plate 8 on the other main surface side is 15 ° in a direction not to sandwich the stretching axis of the retardation plate 7 with respect to the stretching axis of the retardation plate 6, and the retardation plate 7 is stretched. It is arranged with an inclination of 75 ° with respect to the axis. At the same time, the absorption axis of the polarizing plate 3 and the absorption axis of the polarizing plate 8 are orthogonal to each other, and the stretching axis of the retardation plate 4 and the stretching axis of the retardation plate 7 are also orthogonal to each other.
See JP2003-140154A

  However, even if the transflective liquid crystal display device having the above-described configuration is used, it still depends on the angle of the absorption axis of the polarizing plates 3 and 8, the optical path difference Δnd of the phase difference plates 4, 5, 6, and 7, and the angle of the stretching axis. There is a problem that contrast and color reproducibility change when used as a transmission mode and when used as a reflection mode.

  The present invention has been devised in view of the above-mentioned problems, and the object thereof is to achieve high brightness, high contrast ratio, and sufficient color compensation in both reflection mode and transmission mode applications. Therefore, an object of the present invention is to provide a liquid crystal display device in which the angle of the absorption axis of the polarizing plate, the optical path difference Δnd of the retardation plate, and the angle of the stretching axis are set.

The liquid crystal display device of the present invention includes one transparent member formed by sequentially laminating a transparent electrode and an alignment layer on a transparent substrate, a thin film transistor switching element on the transparent substrate, a transparent electrode connected to the thin film transistor switching element, and an alignment layer And the other transparent member formed by sequentially laminating
The film is bonded via a twisted nematic liquid crystal with a twist angle of 60 to 80 ° and a Δnd value of 230 to 250 nm, and a semi-transmissive film between the transparent substrate and the transparent electrode of any one of the transparent members. A liquid crystal panel comprising:
On the display surface side main surface of the liquid crystal panel, a second retardation plate having an optical path difference Δnd of 120 to 140 nm, a first retardation plate having an optical path difference Δnd of 260 to 280 nm, and a first polarizing plate are sequentially stacked. In addition, a third retardation plate having an optical path difference Δnd of 120 to 140 nm, a fourth retardation plate having an optical path difference Δnd of 260 to 280 nm, a second polarizing plate, and a backlight are sequentially provided on the non-display surface side main surface. In addition to the laminated arrangement, the second retardation is set such that the stretching axis of the first retardation plate is 130 to 140 ° when viewed from the display surface with reference to the average value of the rubbing directions of both surfaces in the twisted nematic liquid crystal. The stretching axis of the plate is 70 to 80 °, the absorption axis of the first polarizing plate is 145 to 155 °, the stretching axis of the third retardation plate is 115 to 125 °, and the stretching axis of the fourth retardation plate is 55 ~ 65 °, the absorption axis of the second polarizing plate is 130 ~ 140 ° respectively It was boss.

  As described above, according to the present invention, two transparent members obtained by sequentially laminating a transparent electrode and an alignment layer on a transparent substrate are bonded together via a twisted nematic liquid crystal that defines a twist angle and Δnd. A liquid crystal panel having a transflective film disposed between the substrate and the transparent electrode, a second retardation plate defining an optical path difference Δnd and a stretching axis on one main surface side, and an optical path difference Δnd and a stretching axis are defined. A first retardation plate and a first polarizing plate that defines an absorption axis are sequentially stacked and disposed, and a third retardation plate that defines an optical path difference Δnd and a stretching axis on the other main surface side, and an optical path difference Δnd and stretching A fourth retardation plate having an axis defined, a second polarizing plate having an absorption axis defined, and a backlight were sequentially stacked.

  When liquid crystal display is performed in the reflection mode, external light sequentially passes through the first polarizing plate, the first retardation plate, the second retardation plate, and the liquid crystal panel, and is transmitted through the transflective film of the liquid crystal panel. Thus, the reflected light passes through the liquid crystal panel, so that it does not pass through the second polarizing plate on the other main surface side, thereby increasing the luminance.

  On the other hand, when the liquid crystal display is performed in the transmission mode, the backlight irradiation light sequentially passes through the second polarizing plate, the fourth retardation plate, the third retardation plate, and the semi-transmissive film, through the liquid crystal panel, The light passes through the second retardation plate, the first retardation plate, and the first polarizing plate in order, and is emitted from the display surface that is one main surface. As a result, the light passing through the second polarizing plate changes its deflection state by the fourth and third retardation plates, and as a result, the liquid crystal panel, the second retardation plate, and the first retardation plate used in the reflection mode. The first polarizing plate can be used as it is. Furthermore, by setting the twist angle of the liquid crystal layer, the optical path difference Δnd of the liquid crystal layer, the absorption axis of the polarizing plate, the optical path difference Δnd of the retardation film, and the stretching axis within a predetermined range, in either the reflection mode or the transmission mode However, stable and clear color display is possible, and color compensation is sufficient. As a result, a high-performance transflective liquid crystal display device with improved characteristics to the extent that both the reflection mode and the transmission mode can be satisfied is provided. it can.

  Hereinafter, the liquid crystal display device of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic sectional view of a liquid crystal display device of the present invention, and FIG. 2 is a sectional view showing the structure of a liquid crystal panel. In addition, the liquid crystal panel as used in the field of this invention means the panel of the state which excluded the phase difference plate and polarizing plate which are arrange | positioned on the outer main surface of the display surface and non-display surface of a board | substrate.

  That is, the liquid crystal display device of the present invention includes the liquid crystal panel 2, the phase difference plates 4 and 5, the polarizing plate 3 disposed on the outer main surface of the liquid crystal panel 2, and the other main surface of the liquid crystal panel 2. The phase difference plates 6 and 7 and the backlight 9 disposed further outside the polarizing plate 8 are included.

  In FIG. 1, a second retardation plate 5, a first retardation plate 4, and an iodine-based polarizing plate 3 are sequentially stacked and arranged on one main surface that is a display surface of the liquid crystal panel 2. . In addition, a third retardation plate 6, a fourth retardation plate 7, and an iodine-based polarizing plate 8 are sequentially stacked on the other main surface which is a non-display surface of the liquid crystal panel 2. Each of these retardation plates 4 to 7 and polarizing plates 3 and 8 are stuck in a laminated state using an adhesive material made of an acrylic material. Further, a backlight 9 is disposed on the polarizing plate 8.

  As the first phase difference plate 4, the second phase difference plate 5, the third phase difference plate 6, and the fourth phase difference plate 7, for example, a stretched synthetic resin film supplied under the trade name Arton manufactured by JSR is used. Further, a light scattering plate-like body 10 is interposed between the substrate 12 on one side and the second retardation plate 5 as necessary. In addition, the light-scattering plate-like body 10 includes, for example, a light scattering film such as SK80 manufactured by Sumitomo Chemical Co., Ltd., and an adhesive material containing beads or the like is used.

  FIG. 2 shows a specific structure of the liquid crystal panel 2. In FIG. 2, 12 is a segment-side transparent substrate made of, for example, a glass substrate, and 13 is a common-side transparent substrate made of a glass substrate. A transparent electrode 14 made of ITO for each pixel region and a TFT (thin film transistor) switching element (not shown) connected to the transparent electrode 14 are formed on the inner surface of the transparent substrate 12, and an overcoat made of acrylic resin is formed. A coating layer 16 and an alignment film 18 made of polyimide resin rubbed in a certain direction are deposited.

A semi-transmissive film 11 is formed on the inner surface side of the other transparent substrate 13, and a color filter 20 and a black matrix light-shielding film 21 are formed on the semi-transmissive film 11. In order to easily form the color filter 20 and the like, the color filter 20 may be provided on the semi-transmissive film via a SiO ₂ layer. The color filter 20 is provided for each pixel region, and a light shielding film 21 of a black matrix of chromium metal or photosensitive resist is formed between the color filters 20.

  The semi-transmissive film 11 has both light-transmitting properties and light-reflecting properties, and prevents a phase difference from occurring when the two polarizing plates 3 and 8 are used. Further, the semi-transmissive film 11 may be specular or scattering. In order to provide the semi-transmissive film 11, an uneven shape is provided with a resin or the like, and the semi-transmissive film 11 is formed thereon. It is obtained by forming. When the light-scattering translucent film 11 is formed in this way, the light-scattering plate-like body 10 need not be provided.

The semi-transmissive film 11 may be formed of a metal layer or a dielectric layer. For example, when a metal layer is used, it is composed of Al, Cr, SUS, Ag, and the film thickness may be 50 to 300 mm in order to satisfy both light transmittance and light reflectivity. If importance is attached to 50 to 150 mm, and if light reflectivity is important to 150 to 300 mm. For each pixel region, a light transmission hole is formed in the metal layer, the region where the light transmission hole is formed is used as a light transmission region, and the region where the metal layer remains is used as a light reflection region. May be. When a dielectric layer is used, for example, a film in which a TiO ₂ film of a high refractive index material and a SiO ₂ film of a low refractive index material are alternately laminated may be used. It is good to form with. The semi-transmissive film 11 having such a configuration is provided on the transparent substrate 13. In addition, the formation with a metal layer is low in that a single material is used, and furthermore, a high-quality film can be easily and stably formed by a sputtering method.

  The color filter 20 is formed by a pigment dispersion method, that is, a photosensitive resist previously prepared with a pigment is applied on a substrate and is formed by photolithography. Each of the R, G, and B displays in the figure is a color filter 20 colored red, green, and blue, and one color filter 20 is formed for each pixel region.

The overcoat layer 17 is made of an acrylic resin, and is formed to reduce unevenness on the surface of the color filter 20 as a result of forming the color filter 20. A transparent electrode 15 made of ITO is formed on the surface of the overcoat layer 17. Further, an alignment film 19 made of polyimide resin rubbed in a certain direction is formed on the transparent electrode 15. An insulating layer made of SiO ₂ or the like may be interposed between the transparent electrode 15 and the alignment film 19.

  A liquid crystal layer 22 made of nematic liquid crystal twisted at an angle of, for example, 60 to 80 ° is disposed between the two transparent substrates 12 and 13 formed in this way. The liquid crystal layer 22 is sealed with a sealant 23 formed on the outer periphery of the inner surfaces of the transparent substrates 12 and 13, and at the same time, the two transparent substrates 12 and 13 are firmly bonded together.

  The thickness of the liquid crystal layer 22 between the transparent substrates 12 and 13 has a uniform predetermined value due to the spacers 24 mixed therein. Although the overcoat layer 17 is provided in the liquid crystal panel 2 in the figure, it can be omitted when the surface shape of the color filter 20 has a smoothness sufficient to form the transparent electrode 15.

  Thus, the liquid crystal display device having such a configuration displays liquid crystal in the reflection mode and the transmission mode. The reflection mode uses external light such as sunlight and fluorescent lamps, and light incident from one main surface side which is a display surface is the first polarizing plate 3, the first retardation plate 4, and the second light. The phase difference plate 5, the light scattering plate 10 and the liquid crystal panel 2 are sequentially passed, and further reflected by the semi-transmissive film 11. The reflected light passes through the liquid crystal panel 2, and the light scattering plate 10. And the second retardation plate 5, the first retardation plate 4, and the first polarizing plate 3 to be emitted from the display surface side. In this case, since it does not pass through the transparent substrate 13, the third phase difference plate 6, the fourth phase difference plate 7, and the second polarizing plate 8, the luminance is increased.

In particular, when the semi-transmissive film 11 is formed on the transparent substrate 13 as described above, it does not pass through the transparent substrate 13 even if it is used as a reflection type, and thus the display appears to be double due to the transparent substrate 13. There is no phenomenon.

  Further, when the liquid crystal display device is used as a transmission mode, the light emitted from the backlight 9 passes through the second polarizing plate 8, the fourth retardation plate 7, the third retardation plate 6, and the semi-transmissive film 11. The light passes through the liquid crystal panel 2 and sequentially passes through the light scattering plate 10, the second retardation plate 5, the first retardation plate 4, and the first polarizing plate 3, and is emitted from the display surface side. . As a result, the light passing through the second polarizing plate 8 changes its polarization state by the fourth retardation plate 7 and the third retardation plate 6, and as a result, the liquid crystal panel 2 is changed in the reflection mode and the second retardation is changed. It can permeate | transmit the board 5 and the 1st phase difference plate 4 as it is. Further, the twist angle of the liquid crystal layer 22, the optical path difference Δnd of the liquid crystal layer 22, the absorption axis of the polarizing plates 3, 8, the optical path difference Δnd of the phase difference plates 4, 5, 6, 7 and the stretching axis are defined in the present invention. By setting this range, sufficient color compensation was obtained in both the reflection mode and the transmission mode, and a high saturation display could be realized.

  For example, these preferable conditions will be described with reference to FIGS. FIG. 3 shows the phase difference between the liquid crystal layer 22 with a twist angle of 60 to 80 °, an optical path difference Δnd of 230 to 250 nm, and an average rubbing direction of both rubbing directions in both alignment films 18 and 19 as a reference. A case where the angles (counterclockwise) of the stretching axes of the plates 4, 5, 6, and 7 and the absorption axes of the polarizing plates 3 and 8 are viewed from the display surface is shown. (A) shows the relationship of the 1st phase difference plate 4, the 2nd phase difference plate 5, and the 1st polarizing plate 3 which were formed on the transparent substrate 12 by the side of a display surface, and explanatory drawing seen from the display surface side as mentioned above. (B) shows the relationship between the third retardation plate 6, the fourth retardation plate 7 and the second polarizing plate 8 formed on the other main surface of the transparent substrate 13 on the non-display surface side, as described above. It is explanatory drawing seen from the display surface side.

  As shown in FIG. 3A, the absorption axis of the first polarizing plate 3 is 145 to 155 ° counterclockwise from the direction (reference direction) obtained by averaging the two rubbing directions defined by the alignment films 18 and 19. , Preferably 147 to 153 °.

  Further, the optical path difference Δnd of the first retardation plate 4 is 260 to 280 nm, preferably 265 to 275 nm, and the stretching axis is similarly set to 125 to 135 °, preferably 127 to 133 °. The optical path difference Δnd of the second retardation plate 5 is 120 to 140 nm, preferably 125 to 135 nm, and the stretching axis is similarly set to 70 to 80 °, preferably 72 to 78 °.

  As shown in FIG. 3B, the optical path difference Δnd of the third retardation plate 6 is 120 to 140 nm, preferably 125 to 135 nm, and the stretching axis is also 115 to 125 °, preferably 117 to 123 °. It is set. Further, the optical path difference Δnd of the fourth retardation plate 7 is 260 to 280 nm, preferably 265 to 275 nm, and the stretching axis is similarly set to 55 to 65 °, preferably 57 to 63 °.

  Similarly, the absorption axis of the second polarizing plate 8 is set to 130 to 140 °, preferably 132 to 138 °.

  By setting in this way, when used as a reflection mode, high luminance was achieved, and further high contrast (sufficient color compensation) was obtained. Even when the liquid crystal display device used as the reflection mode is used in the transmission mode, sufficient color compensation can be obtained, and high saturation display can be realized in either the reflection mode or the transmission mode.

When the luminance was measured when the liquid crystal display element device was used in a transmission type and a reflection type, the results shown in Table 1 were obtained.

Minolta CS-100 is used for measurement of chromaticity and luminance, a backlight having a certain chromaticity and luminance is used for the transmission type, and the same light source is used for the liquid crystal panel for the reflection type. On the other hand, each chromaticity and luminance were measured by irradiating at a constant angle.

  As a result of performing the above measurement under various conditions, the contrast of the liquid crystal display device is transmitted when the angle of the absorption axis of the polarizing plate and the optical path difference Δnd of the retardation plate and the angle of the stretching axis are matched. A high value of 34 was obtained in the mode (transmission type) and 43 in the reflection mode (reflection type).

In Table 1, in the case of the transmissive type, the brightness and chromaticity of white, black, red, green, blue, and backlight light source color are shown from the top, and the contrast, transmittance, and ratio to NTSC are shown. Good brightness can be obtained in color.

  In the case of the reflective type, the brightness and chromaticity of white, black, red, green, and blue are shown from the top, and the contrast, the reflectance, and the ratio to NTSC are shown. Even in the case of this reflection type, good luminance can be obtained in any color.

  However, a liquid crystal material having a dielectric anisotropy (Δε) of 8.2 is used for the liquid crystal layer 22 of the liquid crystal display device of this embodiment. Since the contrast value depends on Δε, the contrast value when the liquid crystal materials having different Δε are used is not limited to that in Table 1.

  It should be noted that the present invention is not limited to the above embodiment, and various changes and improvements can be made without departing from the scope of the present invention.

1 is a schematic cross-sectional view of a liquid crystal display device of the present invention. It is sectional drawing of the liquid crystal panel used for the liquid crystal display device of this invention. (A), (b) is explanatory drawing which shows the angle which looked at the extending | stretching axis | shaft of the phase difference plate of this invention, and the absorption axis of a polarizing plate from the display surface. It is the cross-sectional schematic of the liquid crystal display device of a prior art. (A) (b) is explanatory drawing which shows the angle which looked at the extending | stretching axis | shaft of the phase difference plate and the absorption axis of a polarizing plate in the conventional liquid crystal display device from the display surface.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 2 Liquid crystal panel 3 1st polarizing plate 4 1st phase difference plate 5 2nd phase difference plate 6 3rd phase difference plate 7 4th phase difference plate 8 2nd polarizing plate 9 Backlight 10 Light-scattering plate shape Body 11 Semi-transmissive film 12, 13 Transparent substrate 14, 15 Transparent electrode 16, 17 Overcoat layer 18, 19 Alignment film 20 Color filter 21 Light shielding film 22 Liquid crystal layer

Claims (1)

One transparent member formed by sequentially laminating a transparent electrode and an alignment layer on a transparent substrate, and the other layer formed by sequentially laminating a thin film transistor switching element, a transparent electrode connected to the thin film transistor switching element, and an alignment layer on the transparent substrate. A transparent member of
The film is bonded via a twisted nematic liquid crystal with a twist angle of 60 to 80 ° and a Δnd value of 230 to 250 nm, and a semi-transmissive film between the transparent substrate and the transparent electrode of any one of the transparent members. A liquid crystal panel comprising:
On the display surface side main surface of the liquid crystal panel, a second retardation plate having an optical path difference Δnd of 120 to 140 nm, a first retardation plate having an optical path difference Δnd of 260 to 280 nm, and a first polarizing plate are sequentially stacked. In addition, a third retardation plate having an optical path difference Δnd of 120 to 140 nm, a fourth retardation plate having an optical path difference Δnd of 260 to 280 nm, a second polarizing plate, and a backlight are sequentially provided on the non-display surface side main surface. In addition to the laminated arrangement, the second retardation is set such that the stretching axis of the first retardation plate is 130 to 140 ° when viewed from the display surface with reference to the average value in the rubbing direction of both surfaces of the twisted nematic liquid crystal. The stretching axis of the plate is 70 to 80 °, the absorption axis of the first polarizing plate is 145 to 155 °, the stretching axis of the third retardation plate is 115 to 125 °, and the stretching axis of the fourth retardation plate is 55 ~ 65 °, the absorption axis of the second polarizing plate is 130 ~ 140 ° respectively The liquid crystal display device, characterized in that was boss.

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