JP2008111911A - Liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display element that suppresses a difference in the transmittance between an OFF display region and a background region during high-duty driving. <P>SOLUTION: The liquid crystal display element 1 comprises: a liquid crystal cell 2 that has a liquid crystal layer comprising a liquid crystal having negative dielectric anisotropy and held between a pair of substrates the surfaces of which are subjected to vertical alignment treatment; and a pair of polarizing plates 3, 4 that interpose the liquid crystal cell 2 and are disposed in a crossed Nicole arrangement. A layer structure 5 showing a retardation value of larger than 0 nm and not more than 60 nm is formed between at least one of the polarizing plates 3, 4 and the liquid crystal cell 2. An OFF voltage is determined to control the OFF transmittance to be equal to the transmittance of the background during time-shared driving of the liquid crystal display element 1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a liquid crystal display element.

  In general, a transmissive liquid crystal display element includes an extremely thin liquid crystal layer of about several μm oriented in a predetermined direction, a pair of transparent thin substrates that sandwich the liquid crystal layer, and a polarizer that sandwiches the substrate. And a pair of polarizing plates constituting the analyzer. Here, an electrode patterned in a predetermined shape is formed on the substrate surface on the side where the liquid crystal layer is provided. When a voltage is applied to the liquid crystal layer through this electrode, the alignment of the liquid crystal changes, and the amount or wavelength of light transmitted through the liquid crystal display element changes. Thereby, a desired display can be performed.

  Thus, the liquid crystal display element has a relatively simple structure. In addition, since it is easy to reduce the thickness and weight by selecting components, and it is possible to drive at a low voltage, in recent years, it has been actively used as a display element for in-vehicle use as well as consumer use. ing.

  By the way, liquid crystal display elements are classified into several modes based on the initial alignment state of the liquid crystal layer, the operation state and the alignment state when a voltage is applied, and the like. For example, a VA (Vertical Alignment) mode is used for so-called in-vehicle liquid crystal display elements such as liquid crystal televisions and instrument panels of vehicles such as automobiles (see, for example, Patent Documents 1 and 2). The VA mode is a mode with excellent visibility since it has a high contrast ratio when viewed from the front and a wide viewing angle.

  In the VA mode, a liquid crystal layer having a negative dielectric anisotropy (Δε) whose initial alignment state is substantially perpendicular to the substrate (vertical alignment) is sandwiched between a pair of substrates. It is comprised by pinching with a pair of polarizing plate arrange | positioned so that Nicole may be comprised. When a voltage is applied to the liquid crystal layer through the electrode formed on the substrate surface, the alignment of the liquid crystal changes, and the liquid crystal layer is perpendicular to the electric field, that is, the alignment direction of the liquid crystal is parallel to the substrate. Thereby, the light transmission characteristics determined by the product (Δn · d) of the refractive index anisotropy (Δn) of the liquid crystal and the liquid crystal layer thickness (d) between the portion where the voltage is applied and the portion where the voltage is not applied, , There will be a difference in color. By utilizing this difference, a desired display can be performed.

  By the way, the initial alignment state of the liquid crystal is closely related to the alignment change of the liquid crystal. Here, the initial alignment state of the liquid crystal is formed substantially vertically as described above. That is, the liquid crystal often does not take a completely vertical alignment state. This is because when the vertical alignment is achieved, the direction in which the alignment of the liquid crystal changes when a voltage is applied is not determined, and it is difficult to perform a uniform alignment change in the display element.

  Therefore, in the vertical alignment type liquid crystal display element, in order to make the change in the alignment of the liquid crystal uniform, a slight horizontal alignment that matches the desired alignment change direction is added to the vertical alignment on the substrate surface. is doing. Specifically, first, a vertical alignment layer is provided on a pair of substrate surfaces sandwiching a liquid crystal layer. Thereby, the vertical alignment property of the liquid crystal layer on the substrate can be secured. Next, for example, a rubbing process with an appropriate strength is performed in a desired direction. Then, the horizontal orientation can be added to the vertical orientation substrate surface.

  As described above, the operation direction of the liquid crystal layer can be determined by adding the horizontal alignment slightly while ensuring the vertical alignment. At this time, the initial alignment state of the liquid crystal layer is slightly inclined from the thickness direction of the liquid crystal layer sandwiched between the substrates, that is, vertically aligned with a pretilt angle. As a result, when a voltage is applied to the liquid crystal layer, the liquid crystal tilts from the initial substantially vertical state to the direction of forming the pretilt angle, which is the rubbing direction, strengthens the tilt, and as a result, performs an orientation change operation that tilts to the horizontal state. To do.

  In the VA mode, the liquid crystal only operates so as to be parallel to the substrate from the vertical alignment as described above. That is, in general, no optical rotation is required in the liquid crystal layer, and other liquid crystal modes, such as twisted nematic (TN) mode and super twisted nematic (STN) mode, are obtained from cholesteric liquid crystal, chiral agent and nematic liquid crystal. The twisted nematic liquid crystal is not used. In the case of the VA mode, normally, a configuration is adopted in which nematic liquid crystal having negative dielectric anisotropy is sandwiched between substrates subjected to the alignment treatment as described above. When no voltage is applied, the liquid crystal layer is oriented substantially perpendicularly to the pair of substrates that sandwich the liquid crystal layer, so that a good black display can be obtained in the viewing angle direction parallel to the normal direction of the liquid crystal cell. High contrast ratio image display can be realized.

  However, there is a problem in the change in the transmittance of the liquid crystal display element caused by the change in the alignment of the liquid crystal, particularly the change in the alignment of the liquid crystal caused by the application of voltage. Specifically, the change in transmittance of the liquid crystal display element with respect to voltage application becomes slow. In particular, the liquid crystal display element begins to change its orientation when a voltage is applied, and the transmittance of the liquid crystal display element starts to change rapidly. The so-called rise characteristic is gentle, and the rise of the voltage-transmittance characteristic of the liquid crystal display element is steep. Not enough.

  When such a VA mode is applied to a simple matrix type liquid crystal display element by a time-division driving method, the problem becomes clearer.

  In recent years, liquid crystal display elements have been required to increase the amount of display information and display with higher definition. However, in order to meet such a demand, high-density display is necessary, and a matrix-driven liquid crystal display element needs to be driven with a higher duty.

  In a simple matrix type liquid crystal display element using a time-division driving method, when high duty driving is to be performed, an ON voltage for performing ON display and an OFF voltage for performing non-selection voltage, that is, OFF voltage for performing OFF display. The difference is smaller. In other words, the difference between the ON voltage and the OFF voltage cannot be sufficiently secured as the duty is high. Therefore, if the VA mode is applied to a matrix-driven liquid crystal display element, the steepness of the rise in the voltage-transmittance characteristic is not sufficient, and the difference between the ON voltage and the OFF voltage is insufficient. The ON transmittance cannot be obtained, or the sufficiently low OFF transmittance cannot be realized. As a result, the contrast ratio in the liquid crystal display element is reduced. In particular, the contrast ratio is drastically reduced during high duty driving.

  As described above, in the VA mode, there is a problem that the contrast ratio of the display image is lowered and the display performance is lowered when the duty is driven above a certain level.

  Therefore, Patent Document 1 discloses a method of providing a uniaxial retardation film having a predetermined retardation value outside the liquid crystal cell as a method for improving the shortage of steepness in the voltage-transmittance characteristics in the VA mode. ing.

JP-A-10-197858

  The method described in Patent Document 1 is effective in improving the rising characteristics in the voltage-transmittance characteristics in the VA mode. FIG. 3 is a schematic voltage transmittance curve for explaining the effect of the method described in Patent Document 1. 3A schematically shows voltage-transmittance characteristics in the conventional VA mode, and FIG. 3B schematically shows voltage-transmittance characteristics in the VA mode according to the method described in Patent Document 1.

  As shown in FIG. 3A, the conventional VA mode generally exhibits the lowest transmittance when no voltage is applied, and shows a characteristic in which the transmittance gradually increases with the application of voltage. On the other hand, as shown in FIG. 3B, in the VA mode according to the method described in Patent Document 1, the transmittance is not so low when no voltage is applied, and as a result, the minimum transmittance is not exhibited. This is a so-called “floating” state in the display. Then, a phenomenon in which the transmittance is lowered by gradually increasing the applied voltage starts to appear, and a negative peak of the transmittance with respect to the applied voltage appears in a direction in which the transmittance is lowered.

  That is, as in Patent Document 1, in order to improve the lack of steepness of rising in the voltage-transmittance characteristics of the VA mode, when a uniaxial retardation film having a predetermined retardation value is provided outside the liquid crystal cell, A region having a very low transmittance can be formed by applying a voltage. However, on the other hand, as described above, the transmittance increases when no voltage is applied due to the influence of the retardation film. As a result, the transmittance and voltage are not applied to the non-selection region to which the non-selection voltage is applied during time-division driving, that is, the OFF display region (low transmittance region) formed by applying a predetermined voltage. There is a difference between the transmittance of the background display area and the uniformity of display may be significantly impaired.

  The present invention has been made in view of these problems. That is, an object of the present invention is to suppress a decrease in contrast ratio of a display image at the time of high duty driving as seen in a conventional VA mode liquid crystal display element and to ensure display uniformity. Is in the provision of. More specifically, when driving the VA mode, the steepness of the rise in the voltage-transmittance characteristics is improved by optimizing the drive voltage, and both the realization of a high contrast ratio and the improvement of display uniformity are achieved. It is an object of the present invention to provide a vertical alignment type liquid crystal display element that can be used.

  Other objects and advantages of the present invention will become apparent from the following description.

The present invention includes a liquid crystal cell including a liquid crystal layer composed of a liquid crystal having negative dielectric anisotropy sandwiched between a pair of substrates whose surfaces are each subjected to vertical alignment treatment;
Sandwiching the liquid crystal cell, and having a pair of polarizing plates arranged such that the crossing angle between the absorption axis of one polarizing plate and the absorption axis of the other polarizing plate is 90 ° ± 5 °,
In a liquid crystal display element that performs display by changing the transmittance between the pair of polarizing plates by applying a voltage to the liquid crystal layer,
Between at least one of the pair of polarizing plates and the liquid crystal cell, there is at least one retardation film,
The retardation film has an optical axis arranged so as to have an intersection angle of 90 ° ± 5 ° with respect to a direction in which molecules constituting the liquid crystal start to fall when a voltage is applied to the liquid crystal layer. When a predetermined voltage is applied to the liquid crystal layer, the transmittance between the pair of polarizing plates is lower than when no voltage is applied, and takes a minimum value.
The display is performed by applying only a voltage higher than the predetermined voltage to the liquid crystal layer.

  In the liquid crystal display element of the present invention, the lower limit of the transmittance between the pair of polarizing plates when performing the display is preferably 0.8 to 1.2 times the transmittance when no voltage is applied. .

  In the liquid crystal display element of the present invention, it is particularly preferable that the lower limit value of the transmittance between the pair of polarizing plates when performing the display is substantially equal to the transmittance value when no voltage is applied.

  The liquid crystal display element of the present invention can be a passive matrix liquid crystal display element.

  The liquid crystal display element of the present invention can be a passive matrix liquid crystal display element using a time-division driving method. In this case, the transmittance when a non-selection voltage is applied is preferably 0.8 to 1.2 times the transmittance of the liquid crystal display element when no voltage is applied, and in particular, the liquid crystal when no voltage is applied. It is preferably substantially equal to the transmittance of the display element.

  According to the present invention, in the vertical alignment type liquid crystal display element, it is possible to improve the steepness of the rise in the voltage-transmittance characteristics. As a result, a high contrast ratio can be achieved even during high-duty driving, and display uniformity can be ensured.

Embodiment 1 FIG.
FIG. 1 is a schematic exploded perspective view for explaining characteristic portions of the liquid crystal display element in the present embodiment. FIG. 1 is also a schematic configuration diagram for explaining the structure and optical specifications of the liquid crystal display element.

  As shown in FIG. 1A, the liquid crystal display element 1 according to the present embodiment sandwiches the liquid crystal cell 2 and the liquid crystal cell 2, and has an absorption axis of one polarizing plate and an absorption axis of the other polarizing plate. Provided between the pair of polarizing plates 3 and 4 disposed so that the crossing angle is 90 ° ± 5 °, and between the polarizing plate 3 and the liquid crystal cell 2, a predetermined retardation value = Δn · d 2 (Δn Is a layer structure 5 having a refractive index anisotropy and d2 is a layer thickness. The layer structure 5 has a retardation value larger than 0 nm and 60 nm or less, and realizes a so-called minute phase difference.

  Detailed specifications of the arrangement of the polarizing plate 3 and the polarizing plate 4 are shown in FIGS. In these drawings, the arrow indicates the direction of the absorption axis of the polarizing plate. Further, the numbers added indicate the installation angles of the absorption axes of the polarizing plates 3 and 4. In this case, the horizontal direction in the figure corresponds to the front left and right direction of the liquid crystal display element, and the counterclockwise direction is the positive direction with reference to this direction.

The liquid crystal cell 2 is configured by sandwiching a liquid crystal layer (not shown) made of liquid crystal having negative dielectric anisotropy between a pair of substrates (not shown). The surfaces of these substrates are each subjected to an alignment treatment such that the liquid crystals are vertically aligned with a predetermined pretilt angle. And the predetermined retardation value = Δn ·
d1 (Δn is the refractive index anisotropy of the liquid crystal and d1 is the thickness of the liquid crystal layer).

  FIG. 1D shows the formation direction of the pretilt angle of the liquid crystal layer in the liquid crystal cell 2. The solid line arrow indicates the direction of formation of the pretilt angle of the vertical alignment of the liquid crystal layer on the F-side substrate surface on the viewer side. A dotted arrow indicates the direction of formation of the pretilt angle of the vertical alignment of the liquid crystal layer on the surface of the R-side substrate on the anti-viewer side. As shown in FIG. 1D, the pretilt angle forming directions in the vertical alignment of both the F and R substrate surfaces are substantially the same and are in a so-called parallel alignment state.

  Such an alignment state of the liquid crystal can be achieved by subjecting both the F and R substrates subjected to the vertical alignment treatment by providing a vertical alignment layer to a pararubbing treatment having an appropriate strength. The layer structure 5 is configured using a retardation film. In FIG.1 (c), the arrow shows the azimuth | direction of the optical axis of the layer structure 5 comprised using the phase difference film. Further, the numerals added indicate the installation angle of the optical axis of the layer structure 5. The counterclockwise direction is defined as the positive direction with reference to the horizontal direction in the figure, that is, the front left / right direction of the liquid crystal display element.

  Further, the structure of the layer structure 5, particularly the method for forming the layer structure 5, can be composed of a single retardation film, or can be composed by laminating two or more retardation films. Is possible. When laminating a plurality of films, it is only necessary to realize a desired optical axis direction and a desired retardation value as the entire layer structure.

  The liquid crystal display element in the present embodiment having the above configuration already has the voltage-transmittance characteristics shown in FIG. That is, the transmittance is not so low when no voltage is applied, and as a result, the lowest transmittance is not exhibited when no voltage is applied. Then, a phenomenon in which the transmittance is lowered by gradually increasing the applied voltage appears, and a negative peak of the transmittance with respect to the applied voltage (minimum value of the transmittance) appears in the direction in which the transmittance is lowered.

  In the case of performing display using a liquid crystal display element exhibiting such characteristics, the negative peak (minimum value) of the transmittance described above is realized if an attempt is made to increase the contrast ratio so that better display can be realized. By applying a voltage, display with the minimum transmittance is realized, and a voltage with a higher value is usually applied to realize a display state with maximum transmittance. As a result, the contrast ratio of display is maximized.

  However, when such a predetermined voltage is applied to achieve the lowest transmittance state (OFF display), there is a difference in transmittance between the non-voltage applied region in the display region, that is, the background display region and the OFF display region. Resulting in. In the liquid crystal display having the voltage-transmittance characteristics shown in FIG. 3B, the transmittance of the background display region to which no voltage is applied is usually higher than the transmittance of the OFF display region. As a result, in the image display, when the transmittance is low, that is, when black display is performed, the transmittance is higher in the background display area than in the OFF display area, and the so-called “floating” black display state is in the background display area. Although the contrast ratio of the display itself is improved, the display uniformity of the entire display element is deteriorated.

  Therefore, the liquid crystal display element in the present embodiment optimizes the set value of the applied voltage during driving, and achieves both a good display contrast ratio and display uniformity.

  That is, in the liquid crystal display element in the present embodiment having the voltage-transmittance characteristics shown in FIG. 3B, when a predetermined voltage (OFF voltage) is applied to realize low transmittance OFF display, The voltage value that realizes the minimum value of the negative peak of the transmittance with respect to the applied voltage is not intentionally applied, but a voltage with a slightly deviated value is applied as the OFF voltage. Realize display and use for display.

  At this time, it is desirable to shift the voltage value in a direction that is larger than the voltage that realizes the negative transmittance peak (minimum value).

  As a guide for shifting, the transmittance of the background display area to which no voltage is applied is considered. That is, the transmittance of OFF display realized by application of the OFF voltage is made to be close to the transmittance of the background display area where no voltage is applied. In that case, it is desirable to set the applied voltage (OFF voltage) so that the transmittance of 0.8 to 1.2 times the transmittance of the background display area is realized by OFF display. By doing so, in the image display, when the voltage is applied and the transmittance is the lowest, that is, black display is performed, the transmittance is higher in the background display area where no voltage is applied than in the OFF display area. The occurrence of such a black display state becomes inconspicuous, and both improvement in display contrast ratio and display uniformity can be achieved.

  It is more desirable to set the applied voltage (OFF voltage) so that the transmittance of 0.8 to 1 times the transmittance of the background display area is realized by OFF display. In this way, in the image display, when the transmittance is low, that is, when black display is performed, the transmittance is higher in the background display area than in the OFF display area, and the so-called “floating” black display state is in the background. In addition to being inconspicuous in the display area, the display contrast ratio is further improved, and compatibility with display uniformity can be achieved.

  Further, it is more desirable to set the applied voltage (OFF voltage) so that the transmittance substantially equal to the transmittance of the background display area is realized by OFF display. In this way, in the image display, when the transmittance is low, that is, when black display is performed, the transmittance in the background display area does not become higher than the OFF display area, and the so-called “floating” black display state Will not occur. Therefore, the contrast ratio of the display is improved and the compatibility with the excellent display uniformity can be achieved.

  Next, the characteristics of the liquid crystal display element in this embodiment were evaluated and compared with the characteristics of the corresponding conventional VA mode liquid crystal display element.

  First, an example of a manufacturing method for the liquid crystal display element 1 to be evaluated will be described.

  The structure of the liquid crystal display element 1 is as already described with reference to FIG.

  In FIG. 1B, the arrow shown on the polarizing plate 3 on the viewer side indicates the direction of the absorption axis of the polarizing plate 3. Further, in FIG. 1E, the arrow shown on the polarizing plate 4 on the anti-viewer side indicates the direction of the absorption axis of the polarizing plate 4.

  In FIG. 1 (d), the solid line arrow shown in the liquid crystal cell 2 is the direction of the liquid crystal alignment treatment on the viewer side F substrate (not shown) that sandwiches the liquid crystal layer. The rubbing direction with respect to the vertical alignment film provided on the substrate is shown. Similarly, the dotted arrow shown in the liquid crystal cell 2 is the direction of the liquid crystal alignment treatment in the R substrate (not shown) on the side opposite to the viewer who sandwiches the liquid crystal layer, and specifically, on this substrate. The direction of rubbing with respect to the provided vertical alignment film is shown.

  When a voltage is applied, the liquid crystal changes its alignment from a vertical alignment state in a direction parallel to the arrow.

  In the manufacturing process of the liquid crystal display element 1, first, an electrode layer patterned so as to display a desired image is provided on a pair of glass substrates. The electrode layer can be, for example, an ITO (Indium Tin Oxide) electrode.

Next, an insulating film is provided on the glass substrate so as to cover the electrode layer. The insulating film can be, for example, a film made of SiO ₂ —TiO ₂ formed by a sol-gel method.

  Next, an alignment film is formed in the liquid crystal layer so that the liquid crystal is vertically aligned as an initial alignment state. For example, an alignment film having a thickness of about 600 mm can be formed by forming an alignment film material (trade name: JALS-2021) manufactured by JSR Corporation by flexographic printing and baking the substrate at 180 ° C. it can. Next, a rubbing process is performed on the surface of the alignment film to form a pretilt angle, and the operation direction of the liquid crystal when the electric field is applied is determined. At this time, the pretilt angle is 0.5 degrees when expressed as 0 degrees with respect to the thickness direction of the liquid crystal layer, that is, the normal line direction of the liquid crystal display element, but may be greater than 0 degrees and 5 degrees or less. It is desirable to keep the transmittance low when no voltage is applied.

  Next, the liquid crystal layer is sandwiched between the substrates after the alignment film formation step. The liquid crystal layer is made of a mixture of nematic liquid crystals.

  At this time, for example, the distance (d) between the substrates can be kept constant by using a resin spacer. As the liquid crystal layer, for example, a liquid crystal layer having a refractive index anisotropy (Δn) of 0.08918 can be used. In this case, when d = 3.03 μm, the retardation value (Δn · d1) of the liquid crystal cell 2 is 270 nm.

  Next, the layer structure 5 is disposed. Specifically, as described above, by using a retardation film having a retardation value = 575 nm and a retardation film having a retardation value = 550 nm, the optical axes are laminated so as to be orthogonal to each other. Layer structure 5 having an optical axis in the same direction as the optical axis of the retardation film having a retardation value of 575 nm and having a minute retardation value of 25 nm. Next, while maintaining the orientation of the optical axis provided in the horizontal direction, a layer is formed on the liquid crystal cell 2 so as to form an angle of 90 degrees with the direction in which the liquid crystal of the liquid crystal cell 2 is aligned as shown in FIG. Overlay structure 5.

  In addition, when constructing the layer structure 5 having a minute retardation value of 25 nm, the retardation values of the two retardation films to be laminated are not limited to 575 nm and 550 nm as described above. In the present embodiment, the retardation value difference between the two retardation films may be 25 nm. For example, a combination of 580 nm and 555 nm, a combination of 550 nm and 525 nm, and the like are possible.

  Moreover, it is also possible to comprise the layer structure 5 with one retardation film which has a retardation value of 25 nm.

  Next, the polarizing plates 3 and 4 are installed. Specifically, the liquid crystal cell 2 and the layer structure 5 are sandwiched and pasted so that the polarizing plates 3 and 4 are in a crossed Nicol arrangement. At this time, as shown in FIG. 1, the absorption axis of the uppermost F-polarizing plate is set in the direction indicated by the arrow in FIG. 1B, that is, in the direction of 45 degrees counterclockwise from the horizontal direction.

  The liquid crystal cell is a vertical alignment type. The direction of the pretilt angle of the liquid crystal is determined by the rubbing direction indicated by the arrow in FIG. In FIG. 1D, the solid arrow indicates the rubbing direction of the F-side substrate, and the dotted arrow indicates the rubbing direction of the R-side substrate. The direction in which the liquid crystal tilts when a voltage is applied is the direction of the pretilt angle of the liquid crystal, and in this case, the direction indicated by each arrow, that is, the direction horizontal to the substrate.

  Although not shown in detail, the liquid crystal display element 2 in the present embodiment has a simple matrix type liquid crystal display element structure. That is, each pixel portion constituting the image display is not provided with a switching element such as a TFT, and a target image is displayed by driving in a time division driving method using an electrode layer.

  Then, the set value of the driving voltage was optimized using the liquid crystal display element 2 in the present embodiment. That is, when realizing a low transmittance OFF display by applying a predetermined voltage (OFF voltage), the voltage value that realizes the minimum value of the transmittance with respect to the applied voltage is not intentionally applied, and the larger side A voltage slightly deviated from the above is applied as an OFF voltage, and an OFF display with a low transmittance is realized which is slightly higher than the minimum value but used for display.

  At this time, this OFF voltage is shifted in the direction of increasing from the voltage value indicating the minimum transmittance, and the realized transmittance is set to be the same value as the transmittance of the background region where no voltage is applied in the display region. did.

  Next, the characteristics of the liquid crystal display element in this embodiment were evaluated and compared with the characteristics shown by the corresponding prior art.

  FIG. 2 is a diagram for explaining the effect of the liquid crystal display element 2 in the present embodiment in comparison with the conventional technique in which the OFF voltage value is set to match the voltage value that realizes the minimum value of the transmittance.

  Table 1 is a table summarizing the effects of the liquid crystal display element 2 in the present embodiment, focusing on the OFF transmittance, as compared with the prior art.

Table 1.

  In FIG. 2, when the liquid crystal display element 2 according to the present embodiment is driven in a time-sharing manner under the conditions of 1/32 Duty and 1/6 bias, the transmittance change curve with respect to ON voltage application and the transmittance change with respect to OFF voltage application. The curve relationship is shown. Table 1 shows the set OFF voltage under the above driving conditions and the realized OFF transmittance in comparison with the background transmittance with no voltage applied.

  As shown in FIG. 2, the liquid crystal display element 2 according to the present embodiment exhibits excellent voltage-transmittance characteristics having a steep rising characteristic even when driven under the conditions of 1/32 Duty and 1/6 bias. . In the prior art, when time-division driving is performed under the conditions of 1/32 Duty and 1/6 bias, as shown in Table 1, the OFF voltage under this driving condition is set to the minimum transmittance value of the OFF voltage-transmittance curve. Is set to a voltage value (11.29 V) that realizes. As a result, the OFF transmittance shows a very low value of 0.004%.

  On the other hand, in this embodiment, when time-division driving is performed under the conditions of 1/32 Duty and 1/6 bias, as shown in Table 1, the OFF voltage under this driving condition is the minimum of the OFF voltage-transmittance curve. It sets so that it may become larger than the voltage value (11.29V) which implement | achieves a transmittance | permeability value, and is set to 12.67V. As a result, the OFF transmittance was 0.85%, a low transmittance, and the same value as the transmittance of the background region, which is a non-voltage applied region in the display region.

  From the above, in the conventional technique in which the OFF voltage in the time-division driving method is set to a voltage value that realizes the minimum transmittance value of the OFF voltage-transmittance curve, OFF display in which the OFF voltage is applied from the transmittance of the background region It can be seen that the transmittance of the region is lowered. As a result, when a low transmittance display, for example, a black display is performed, the background area has a higher transmittance than the OFF display area, so that the background becomes a so-called “floating” feeling, and the display uniformity is significantly impaired. It was.

  On the other hand, in the liquid crystal display element 2 according to the present embodiment, the OFF voltage in the time-division driving method is larger than the voltage value that realizes the minimum transmittance value of the OFF voltage-transmittance curve, and the voltage in the display area is not marked. The background area which is the additional area and the transmittance of the OFF display area are set to be equal. As a result, when a low transmittance display, for example, a black display is performed, the background area has the same transmittance as the OFF display area, and thus a highly uniform display in which the background and the OFF display area are integrated is realized. . And in the liquid crystal display element 2 in this Embodiment, the high-quality display of the outstanding appearance was attained.

  The present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention.

  As described above, in the liquid crystal display element according to the present invention, since the liquid crystal display element is configured using a retardation film having a minute retardation value, an effect of improving the viewing angle characteristic that widens the viewing angle and voltage-transmittance can be expected. The steepness of the rise in the characteristics can be easily improved, high-contrast ratio image display is realized, and the transmittance in the OFF display area to which the OFF voltage is applied in the time-division drive and the background display in which no voltage is applied Since the transmittances of the regions are substantially equal, display uniformity can be improved.

(A) is a typical exploded perspective view of the liquid crystal display element of this Embodiment, (b)-(e) is a figure explaining the structure and optical specification of this liquid crystal display element. It is a figure explaining the effect of the liquid crystal display element in this Embodiment compared with a prior art. (A) is a figure which shows typically the voltage-transmittance characteristic in the conventional VA mode, (b) is a figure which shows typically the voltage-transmittance characteristic of the VA mode by the method of patent document 1. It is.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal display element 2 Liquid crystal cell 3, 4 Polarizing plate 5 Layer structure

Claims (6)

A liquid crystal cell comprising a liquid crystal layer composed of a liquid crystal having negative dielectric anisotropy sandwiched between a pair of substrates whose surfaces are each subjected to vertical alignment treatment;
Sandwiching the liquid crystal cell, and having a pair of polarizing plates arranged such that the crossing angle between the absorption axis of one polarizing plate and the absorption axis of the other polarizing plate is 90 ° ± 5 °,
In a liquid crystal display element that performs display by changing the transmittance between the pair of polarizing plates by applying a voltage to the liquid crystal layer,
Between at least one of the pair of polarizing plates and the liquid crystal cell, there is at least one retardation film,
The retardation film has an optical axis arranged so as to have an intersection angle of 90 ° ± 5 ° with respect to a direction in which molecules constituting the liquid crystal start to fall when a voltage is applied to the liquid crystal layer. When a predetermined voltage is applied to the liquid crystal layer, the transmittance between the pair of polarizing plates is lower than when no voltage is applied, and takes a minimum value.
The liquid crystal display element, wherein the display is performed by applying only a voltage higher than the predetermined voltage to the liquid crystal layer.   The lower limit value of the transmittance between the pair of polarizing plates when performing the display is 0.8 to 1.2 times the transmittance when no voltage is applied. Liquid crystal display element.   The liquid crystal display element according to claim 2, wherein a lower limit value of the transmittance between the pair of polarizing plates when performing the display is substantially equal to a transmittance value when no voltage is applied.   The liquid crystal display element according to claim 1, wherein the liquid crystal display element is a passive matrix type liquid crystal display element. The liquid crystal display element is a passive matrix type liquid crystal display element by a time-division driving method,
The liquid crystal display element according to claim 4, wherein the transmittance when a non-selection voltage is applied is 0.8 to 1.2 times the transmittance of the liquid crystal display element when no voltage is applied.   The liquid crystal display element according to claim 5, wherein the transmittance when the non-selection voltage is applied is substantially equal to the transmittance of the liquid crystal display element when no voltage is applied.

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