JP2005099534A - Liquid crystal display - Google Patents

Abstract

An inexpensive and lightweight liquid crystal display device capable of stably obtaining a good display quality in which background color is substantially eliminated.
A front alignment treatment direction 5a and a rear alignment treatment direction 7a applied to a front alignment film and a rear alignment film of a liquid crystal cell C are −35 ± 5 ° and 35 respectively with respect to a horizontal direction h of the display screen. ± 5 ° is formed, whereby the liquid crystal molecules are twisted and oriented over 250 ± 10 ° from the rear side to the front side, and Δn · d is set to 770 to 850 nm. On the front side of the liquid crystal cell C, the first retardation plate 8 and the second retardation plate 9 each having a retardation of 400 to 450 nm are respectively provided. The slow axes 8a and 9a are respectively 65 ± 5 °, 20 ° with respect to the horizontal direction h. The front polarizing plate 10 is laminated in such an arrangement that the absorption axis 10a forms 95 ± 5 ° with respect to the horizontal direction. Then, the rear polarizing plate 11 is laminated on the rear side of the liquid crystal cell C in an arrangement in which the absorption axis is 85 ± 5 ° with respect to the horizontal direction h.
[Selection] Figure 2

Description

  The present invention relates to a super twisted nematic (hereinafter abbreviated as STN) type liquid crystal display device in which liquid crystal molecules are twisted over a large angle range.

  Since the STN type liquid crystal display device has a large twist angle of the liquid crystal molecules forming the liquid crystal layer, the degree of birefringence acting on the light transmitted through the liquid crystal layer is relatively large. As a result, positive display (light background display) ), The background tends to be strongly colored.

  Conventionally, in order to eliminate the background coloring in the STN liquid crystal display device, a method of laminating another achromatic liquid crystal cell as an optical compensation plate has been adopted. However, in this method, since two liquid crystal cells are stacked, the liquid crystal display device becomes thicker and the entire weight increases, and the cost increases accordingly.

  Therefore, as disclosed in Patent Document 1, various methods using a phase difference plate as an achromatic optical compensation plate have been proposed and implemented.

  However, the birefringence action by the liquid crystal layer is expressed based on the product Δn · d of the refractive index anisotropy Δn of the liquid crystal and the layer thickness d, and the refractive index anisotropy Δn varies depending on the wavelength of transmitted light (hereinafter, Therefore, it is difficult to match the wavelength dependency of the refractive index anisotropy Δn with the wavelength dependency of the refractive index anisotropy Δn of the retardation plate. Therefore, it is extremely difficult to compensate for the birefringence effect received by the liquid crystal layer by simply adding a retardation plate to the wavelength light in the entire band of light transmitted through the liquid crystal layer.

Therefore, conventionally, retardation (magnitude of phase difference imparted to transmitted light) and number of retardation plates, their arrangement with respect to the liquid crystal cell, the slow axis or the fast axis of the optical axis of the polarizing plate and the orientation direction of the liquid crystal molecules. Attempts have been made to eliminate background coloring in STN type liquid crystal display devices by optimally setting various optical conditions such as angles. However, in any case, although the coloring is reduced to some extent, the background color remains and a good display quality cannot be obtained.
Japanese Patent Application Laid-Open No. 8-21225

  The present invention stabilizes a good display quality in which the background color is substantially eliminated by optimally setting various optical conditions such as the arrangement angle and retardation value of each optical axis of the retardation plate, polarizing plate and liquid crystal cell. It is an object to provide an inexpensive and lightweight STN liquid crystal display device that can be obtained in this manner.

  In order to solve the above problem, a liquid crystal display device according to one aspect of the present invention has a pair of transparent substrates facing each other with a predetermined gap therebetween, and a plurality of inner surfaces facing each transparent substrate are arranged in a direction orthogonal to each other. Stripe electrodes are laid in parallel, and alignment films are respectively deposited so as to cover the stripe electrodes, and each alignment film is subjected to an alignment treatment in a predetermined direction, and molecules between these pair of transparent substrates are arranged. A liquid crystal cell in which twisted nematic liquid crystal twisted and arranged at a predetermined angle from one alignment film surface to the other alignment film surface is sandwiched, and an outer surface of a front transparent substrate serving as an observation side of display of the liquid crystal cell A first retardation plate and a second retardation plate sequentially laminated on each other, a front polarizing plate laminated on the second retardation plate, and a rear polarizing plate laminated on the outer surface of the rear transparent substrate of the liquid crystal cell. And have In the liquid crystal display device, the angle formed with respect to the horizontal direction of the display screen in the alignment treatment direction applied to the front alignment film of the liquid crystal cell and the horizontal direction of the alignment treatment direction applied to the rear alignment film The twisted nematic liquid crystal sandwiched between these alignment films has an angle of 35 ° ± 5 °, and the twisted alignment angle of the twisted nematic liquid crystal is 250 ° ± 10 °. The product Δn · d with the gap d between the alignment films is 770 nm to 850 nm, the retardations of the first and second retardation plates are both 400 nm to 450 nm, and the retardation of the first retardation plate The angle formed by the axis and the slow axis of the second retardation plate is 45 ° ± 5 °, and the angle formed by the slow axis of the first retardation plate and the pre-alignment treatment direction of the front alignment film is 100 °. ± 5 °, the second phase difference The angle formed by the slow axis of the front polarizing plate and the absorption axis of the front polarizing plate is 75 ° ± 5 °, and the angle formed by the absorption axis of the rear polarizing plate and the post-alignment treatment direction of the rear alignment film is 50 ° ± 5. It is characterized by being °.

  In the liquid crystal display device of the other invention, in order to solve the above-described problem, a pair of transparent substrates are arranged to face each other with a predetermined gap, and the inner surfaces of the transparent substrates facing each other are orthogonal to each other. A plurality of stripe electrodes are laid in parallel, and an alignment film is deposited so as to cover the stripe electrodes, and each alignment film is subjected to an alignment treatment in a predetermined direction, and the pair of transparent substrates A liquid crystal cell in which a twisted nematic liquid crystal in which molecules are twisted and arranged at a predetermined angle from one alignment film surface to the other alignment film surface is sandwiched therebetween, and a transparent front side serving as an observation side of the display of the liquid crystal cell The first retardation plate and the second retardation plate sequentially laminated on the outer surface of the substrate, the front polarizing plate laminated on the second retardation plate, and the outer surface of the rear transparent substrate of the liquid crystal cell. Rear polarizing plate The liquid crystal display device has an angle formed with respect to the horizontal direction of the display screen in the alignment treatment direction applied to the front alignment film of the liquid crystal cell and the horizontal alignment treatment direction applied to the rear alignment film. The angle formed with respect to the direction is 35 ° ± 5 °, and the twisted nematic liquid crystal sandwiched between the two alignment films has a twist alignment angle of 250 ° ± 10 °, and the refractive index of the twisted nematic liquid crystal is anisotropic. The product Δn · d of the property Δn and the gap d between the two alignment films is 770 to 850 nm, each retardation of the first and second retardation plates is 400 to 450 nm, and the first retardation plate The angle formed by the slow axis of the second retardation plate and the slow axis of the second retardation plate is 45 ° ± 5 °, and the angle formed by the slow axis of the first retardation plate and the alignment treatment direction of the front alignment film is 100 ° ± 5 °, and the second phase difference The angle formed by the slow axis of the front polarizing plate and the absorption axis of the front polarizing plate is 165 ° ± 5 °, and the angle formed by the absorption axis of the rear polarizing plate and the alignment treatment direction of the rear alignment film is 140 ° ± 5 °. It is characterized by being.

  According to the liquid crystal display device of the present invention, the wavelength dependence of the refractive index anisotropy Δn in the STN liquid crystal layer that cannot be compensated for by simply disposing one retardation plate between the polarizing plate and the liquid crystal cell is reduced to two. Therefore, the wavelength dependence of the refractive index anisotropy Δn in the STN liquid crystal layer is substantially compensated, and the transmitted light In this case, the color light in the bright display based on the birefringence action of the liquid crystal layer is eliminated for the wavelength light of almost all the band, and it is possible to stably obtain a good display quality without the background color in the STN type liquid crystal display device.

  When the liquid crystal display device of the present invention is of a reflective type, two types of inclined surfaces having different angles are alternately provided along the horizontal direction of the display screen on the outer surface of the rear polarizing plate on the side opposite to the display observation side. It is preferable to arrange a light reflection plate having a light reflection surface formed by extending the light, and thereby the light reflected from the reflection screen is emitted from the display screen and the light reflected from the surface of the display screen. It is possible to improve the visibility of the reflective display by making the direction of reflection different.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a cross-sectional view showing a reflective black-and-white positive display type STN type liquid crystal display device as one embodiment of the present invention, and FIG. 2 is an explanatory view showing an arrangement relationship of optical axes of each member.

  In FIG. 1, a pair of transparent glass substrates 1 and 2 are joined by a sealing material 3 while maintaining a predetermined gap. Among the pair of glass substrates 1 and 2, a plurality of stripe electrodes as signal electrodes are provided on a surface facing the other rear glass substrate 2 of the front glass substrate 1 serving as a display observation side (hereinafter referred to as an inner surface). 4 are formed to extend in parallel at a predetermined pitch. The front alignment film 5 is uniformly applied over substantially the entire area of the inner surface of the front glass substrate 1 (within the range surrounded by the sealing material 3) so as to cover these signal electrodes 4. The front alignment film 5 is subjected to an alignment process in a predetermined direction by a rubbing method.

  On the inner surface of the other rear glass substrate 2, a plurality of stripe electrodes 6 as scanning electrodes are formed to extend in parallel at a predetermined pitch in a direction perpendicular to the signal electrodes 4. These scanning electrodes 6 are also covered with a rear alignment film 7 similar to the front alignment film 5. The rear alignment film 7 is subjected to an alignment process in a predetermined direction different from the alignment process applied to the opposed front alignment film 5.

  Nematic liquid crystal is sealed in the liquid crystal cell C configured as described above, that is, in a region surrounded by the sealing material 3 and the inner surfaces of the pair of front and rear glass substrates 1 and 2 facing each other. In this case, the liquid crystal molecules of the encapsulated nematic liquid crystal are twisted and arranged over an angle of 250 ° ± 10 ° from the rear glass substrate 2 toward the front glass substrate 1, and the twisted nematic liquid crystal layer Lc is formed.

  That is, as shown in FIG. 2, the angle formed by the alignment processing direction 7a applied to the rear alignment film 7 of the liquid crystal cell C indicated by the broken line with respect to the horizontal direction h of the display screen is 35 ° (counterclockwise direction). And the angle formed by the alignment treatment direction 5a applied to the front alignment film 5 with respect to the horizontal direction h of the display screen is −35 °, so that the liquid crystal molecules are aligned with the alignment films 5 and 7. In accordance with the alignment control by the applied alignment treatment, the twist alignment is performed in the clockwise direction from the rear alignment film 7 surface toward the front alignment film 5 surface over an angle of −250 ° ± 10 °.

  Further, the product Δn · d of the refractive index anisotropy Δn of the twisted nematic layer Lc and the layer thickness d in a state where the liquid crystal molecules are twisted and arranged over an angle of 250 ° ± 10 ° (initial alignment state) is 810 nm ± 40 nm. is there.

  Returning to FIG. 1, a first retardation plate 8, a second retardation plate 9, and a front polarizing plate 10 are sequentially laminated on the outer surface of the front glass substrate 1 of the liquid crystal cell C. The retardation values of the first retardation plate 8 and the second retardation plate 9 are both 425 nm ± 25 nm.

  On the other hand, a rear polarizing plate 11 and a light reflection plate 12 are sequentially laminated on the outer surface of the rear glass substrate 2. As shown in FIG. 3, the light reflecting plate 12 of the present embodiment has a light reflecting surface 12a facing the rear polarizing plate 11, and two kinds of inclined surfaces 12a1 and 12a2 having different inclination angles are alternately displayed on the display screen. A cross-section extending along the horizontal direction h (see FIG. 2) is formed as a serrated uneven surface. By disposing the light reflecting plate 12 thus configured at the rearmost position of the liquid crystal display device, the liquid crystal display of the light incident from the same direction on the observation side surface of the liquid crystal display device, that is, the front polarizing plate 10 surface. The direction in which the light R1 incident on the inside of the device is transmitted through the liquid crystal cell C or the like and reflected by the reflecting surface 12a can be made different from the regular reflection direction of the light R2 reflected by the surface of the front polarizing plate 10. In addition, it is possible to prevent the occurrence of a problem of dazzling when the directions of light emitted from the display screen of the liquid crystal display device are aligned and to improve the visibility of the display screen.

Here, the arrangement configuration of the optical axis of each member in the liquid crystal display device of the present embodiment will be described with reference to FIG.
In the liquid crystal cell C, as described above, the front alignment processing direction 5a and the rear alignment processing direction 7a are set to −35 ° ± 5 ° and 35 ° ± 5 °, respectively, with respect to the display screen horizontal direction h. ing. Thereby, the liquid crystal molecules are twisted and arranged over an angle of −260 ° to −240 ° from the rear side to the front side.

  The first retardation plate 8 laminated on the front surface of the liquid crystal cell C is disposed at a position where the slow axis 8a forms 100 ° ± 5 ° with respect to the front alignment processing direction 5a. This position is a position that forms 65 ° ± 5 ° with respect to the display screen horizontal direction h. The second retardation plate 9 laminated on the first retardation plate 8 has a position where the slow axis 9 a forms −45 ° ± 5 ° with respect to the slow axis 8 a of the first retardation plate 8. That is, it is arranged at a position that forms 20 ° ± 5 ° with respect to the horizontal direction h.

  The front polarizing plate 10 stacked on the second retardation plate 8 has a position where the absorption axis 10a forms 75 ° ± 5 ° with respect to the slow axis 9a of the second retardation plate 9, that is, with respect to the horizontal direction h. Are arranged at a position of 95 ° ± 5 °.

  On the other hand, the rear polarizing plate 11 laminated on the rear surface of the liquid crystal cell C has a position where the absorption axis 11a forms 50 ° ± 5 ° with respect to the rear alignment processing direction 7a, that is, with respect to the horizontal direction h. Are arranged at a position of 85 ° ± 5 °.

In the reflective liquid crystal display device configured as described above, monochrome positive display can be obtained through the following operation.
First, background display in which the drive voltage is turned off will be described. In this case, external light such as natural light that has entered the front polarizing plate 10 from the observation side passes through the front polarizing plate and vibrates in a direction along the transmission axis (direction orthogonal to the absorption axis 10a). It becomes polarized light and enters the second phase difference plate 9. The linearly polarized light incident on the second retardation plate 9 is subjected to the birefringence action of the second retardation plate 9 that is an optical birefringence element. Here, since the optical birefringence element has a wavelength dependency in which the birefringence action based on the refractive index anisotropy Δn differs depending on each wavelength light, the polarization direction of the light passing through the optical birefringence element differs for each wavelength light. It becomes elliptically polarized light. The elliptically polarized light is sequentially transmitted through the first phase difference plate 8 which is an optical birefringent element and the liquid crystal cell C in the initial twisted alignment state in which the driving voltage is turned off. The retardation difference for each wavelength light is compensated. In this case, the light incident on the rear polarizing plate 11 through the second retardation plate 9, the first retardation plate 8, and the liquid crystal cell C is in a direction along the transmission axis of the rear polarizing plate 11 (absorption axis 11a). Linearly polarized light having a plane of polarization in the direction perpendicular to the surface. Therefore, white linearly polarized light along the transmission axis is emitted from the rear polarizing plate 11. The white linearly polarized light is reflected toward the rear polarizing plate 11 by the light reflecting plate 12 arranged in the following order. The reflected linearly polarized light is transmitted through each member in the reverse order of the outward path, is subjected to the same action, and is emitted from the front polarizing plate 10. As a result, a white display background with almost no coloring is obtained.

  On the other hand, in the liquid crystal cell C, light transmitted through an on-pixel portion in which each liquid crystal molecule is oriented in a direction substantially perpendicular to the glass substrates 1 and 2 when a driving voltage is applied has an apparent refractive index anisotropy Δn ′. Since almost no birefringence is applied to the on-pixel portion that is substantially zero, the polarization direction of the elliptically polarized light for each wavelength light enters the rear polarizing plate 11 while being dispersed, and most of the wavelength light is absorbed here. Or reflected. As a result, good black display can be obtained in the on-pixel. In this way, according to the present reflective liquid crystal display device, a high-quality positive-type black and white display with high contrast and almost no color on the background can be obtained.

Next, an embodiment of the liquid crystal display device of another invention will be described with reference to FIG.
The liquid crystal display device of the present invention is the liquid crystal display device of the above-described invention in which the front polarizing plate and the rear polarizing plate are arranged so that the respective absorption axes are different from each other by 90 °, and the other configurations are the same. is there.

  That is, as shown in FIG. 4, the front polarizing plate 10 ′ is placed at a position where its absorption axis 10′a forms 165 ° ± 5 ° with respect to the slow axis 9a of the second retardation plate. Are arranged at positions where the absorption axis 11′a forms 140 ° ± 5 ° with respect to the rear alignment treatment 7a of the liquid crystal cell C.

  The above-described liquid crystal display device of the present embodiment also provides a high-quality positive-type black-and-white reflective display with high contrast and almost no color on the background, similar to the liquid crystal display device of the embodiment shown in FIGS. It is done.

  In addition, this invention is not limited to embodiment mentioned above. For example, each of the above embodiments is a reflective liquid crystal display device in which a light reflecting plate is disposed on the rear side. However, the present invention is not limited to this, and a backlight device is disposed in place of the light reflecting plate as a transmissive liquid crystal display device. Also good. In this case, the configuration other than the backlight device is the same. Also with this transmissive liquid crystal display device, a high-quality positive-type black-and-white transmissive display with high contrast and almost no coloration in the background can be obtained, similar to the reflective liquid crystal display device described above.

  In addition, the light reflecting plate is not limited to the one shown in FIG. 3, but a metal is deposited on an embossed base material to form a light reflecting surface, or a metal is deposited on a flat base material. A light reflection layer may be further laminated with a scattering layer using scattering particles. In the latter case, since the substrate is made flat, the unevenness of the reflecting surface is eliminated, and a good reflective display that is smooth and free from glare can be obtained.

  Further, the light reflection plate may be a semi-transmission reflection plate, and a backlight device may be disposed on the rear side thereof to form a semi-transmission reflection type liquid crystal display device. In addition, it is possible to provide a color liquid crystal display device by disposing a color filter layer in the liquid crystal cell.

It is a typical sectional view showing a liquid crystal display device as an embodiment of one invention. It is explanatory drawing which shows the arrangement configuration of the optical axis of each member which comprises the said liquid crystal display device. It is explanatory drawing which shows the structure and effect | action of the light reflection board in the said liquid crystal display device. It is explanatory drawing which shows the optical axis arrangement | positioning in the liquid crystal display device as embodiment of the other invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Front glass substrate 2 Rear glass substrate 4 Signal electrode 5 Front alignment film 6 Scan electrode 7 Rear alignment film 8 1st phase difference plate 9 2nd phase difference plate 10 Front polarization plate 11 Rear polarization plate 12 Light reflection plate C Liquid crystal Cell Lc Twisted Nematic Liquid Crystal Layer

Claims (3)

A pair of transparent substrates are arranged facing each other with a predetermined gap, and a plurality of stripe electrodes are laid in parallel in directions orthogonal to each other on each opposed inner surface of each transparent substrate, and the alignment film covers the stripe electrodes. Each alignment film is subjected to an alignment treatment in a predetermined direction, and molecules between the pair of transparent substrates are directed from one alignment film surface toward the other alignment film surface. A liquid crystal cell in which twisted nematic liquid crystal twisted over the angle of
A first retardation plate and a second retardation plate sequentially laminated on the outer surface of the front transparent substrate serving as an observation side of the display of the liquid crystal cell;
A front polarizing plate laminated on the second retardation plate;
A polarizing plate laminated on the outer surface of the rear transparent substrate of the liquid crystal cell;
A liquid crystal display device comprising:
The angle formed with respect to the horizontal direction of the display screen in the alignment treatment direction applied to the front alignment film of the liquid crystal cell and the angle formed with respect to the horizontal direction of the alignment treatment direction applied to the rear alignment film are each 35 °. At ± 5 °, the twisted alignment angle of the twisted nematic liquid crystal sandwiched between these alignment films is 250 ° ± 10 °, and the refractive index anisotropy Δn of the twisted nematic liquid crystal and the gap d between the alignment films Product Δn · d is 770 nm to 850 nm,
The retardations of the first and second retardation plates are both 400 nm to 450 nm, and the angle formed by the slow axis of the first retardation plate and the slow axis of the second retardation plate is 45 ° ± 5. ° and
An angle formed by the slow axis of the first retardation plate and the alignment treatment direction of the front alignment film is 100 ° ± 5 °,
The angle formed by the slow axis of the second retardation plate and the absorption axis of the front polarizing plate is 75 ° ± 5 °, and the angle formed by the absorption axis of the rear polarizing plate and the alignment treatment direction of the rear alignment film Is a liquid crystal display device characterized by being 50 ° ± 5 °. A pair of transparent substrates are arranged facing each other with a predetermined gap, and a plurality of stripe electrodes are laid in parallel in directions orthogonal to each other on each opposed inner surface of each transparent substrate, and the alignment film covers the stripe electrodes. Each alignment film is subjected to an alignment treatment in a predetermined direction, and molecules between the pair of transparent substrates are directed from one alignment film surface toward the other alignment film surface. A liquid crystal cell in which twisted nematic liquid crystal twisted over the angle of
A first retardation plate and a second retardation plate that are sequentially laminated on the outer surface of the front transparent substrate serving as an observation side of the display of the liquid crystal cell;
A front polarizing plate laminated on the second retardation plate;
A polarizing plate laminated on the outer surface of the rear transparent substrate of the liquid crystal cell;
A liquid crystal display device comprising:
The angle formed with respect to the horizontal direction of the display screen in the alignment treatment direction applied to the front alignment film of the liquid crystal cell and the angle formed with respect to the horizontal direction of the alignment treatment direction applied to the rear alignment film are each 35 °. At ± 5 °, the twisted alignment angle of the twisted nematic liquid crystal sandwiched between these alignment films is 250 ° ± 10 °, and the refractive index anisotropy Δn of the twisted nematic liquid crystal and the gap d between the alignment films Product Δn · d is 770 to 850 nm,
Each retardation of the first and second retardation plates is 400 to 450 nm, and an angle formed by the slow axis of the first retardation plate and the slow axis of the second retardation plate is 45 ° ± 5. ° and
An angle formed by the slow axis of the first retardation plate and the alignment treatment direction of the front alignment film is 100 ° ± 5 °,
The angle formed by the slow axis of the second retardation plate and the absorption axis of the front polarizing plate is 165 ° ± 5 °,
An angle formed by an absorption axis of the rear polarizing plate and an alignment treatment direction of the rear alignment film is 140 ° ± 5 °.   The light reflecting plate having a light reflecting surface formed by alternately extending two kinds of inclined surfaces having different angles along the horizontal direction is disposed on an outer surface of the rear polarizing plate. The liquid crystal display device according to claim 1.

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