JP3666666B2 - Retardation selection method for liquid crystal display device and retardation selection device - Google Patents

Description

The present invention relates to a retardation selection method and a retardation selection device for a liquid crystal display device in a vertical alignment mode.

  Liquid crystal display devices that can easily reduce power consumption and dimensions as compared with CRTs are widely used, for example, as screens for word processors, computers, and televisions. Here, in recent years, VA (Verticically) is a combination of a negative liquid crystal material having negative dielectric anisotropy and a vertical alignment film as a method having a higher display contrast and faster response speed than the TN method. Aligned) type liquid crystal display devices are attracting attention.

The VA liquid crystal display device uses, for example, a birefringence mode instead of an optical rotation mode of liquid crystal molecules, as disclosed in Patent Document 1, and is vertically aligned in a state where no voltage is applied. The liquid crystal molecules exhibit little birefringence and display black, and when a voltage is applied, the liquid crystal molecules tilt and become substantially horizontal to the substrate, exhibiting high birefringence and displaying white.
Japanese Patent Laid-Open No. 11-258605 (publication date: September 24, 1999)

  However, since the liquid crystal display device configured as described above operates in the birefringence mode, it is difficult to increase the viewing angle, and a retardation film is often provided. However, in order to enlarge the viewing angle, it is necessary to set the retardation of the retardation film and the retardation of the liquid crystal layer to suitable values, but a method for deriving an appropriate combination of retardation is established. Therefore, a large amount of calculation and the number of measurements are required. As a result, there arises a problem that it is difficult to realize a liquid crystal display device set to a suitable value.

  Specifically, when measuring display quality in an experiment, it is necessary to create a liquid crystal display device, which is troublesome. On the other hand, even when calculating by simulation, it is necessary to calculate the equilibrium state by calculating the equilibrium state of the liquid crystal molecules, which increases the amount of calculation. Therefore, in order to derive a suitable combination, if retardation is set at random and the experiment / display quality evaluation in an arbitrary direction is repeated, a very large amount of labor is required.

  Further, in the liquid crystal display device, the transmittance varies depending on the applied voltage, but the voltage-transmittance curve is not only linear but also varies greatly depending on the viewing angle. Therefore, the viewing angle characteristic also changes depending on the setting of the applied voltage during white display. As a result, more labor is required for selecting a suitable retardation.

The present invention has been made in view of the above-mentioned problems, and its purpose is to derive a combination of retardations with the highest display quality without gradation inversion within a viewing angle and with relatively little effort. An object of the present invention is to provide a retardation selection method for a liquid crystal display device and a retardation selection device .

A method for selecting a retardation of a liquid crystal display device according to the present invention includes a liquid crystal layer including a liquid crystal having a negative dielectric anisotropy, and a polarizing element disposed on both sides of the liquid crystal layer. A retardation selection method for a liquid crystal display device having a retardation film disposed between both polarizing elements and performing black display in a state where liquid crystal molecules are aligned substantially perpendicular to the substrate, When deriving a combination of retardation of the liquid crystal layer and retardation of the retardation film, a condition setting step for setting a desired display quality and a viewing angle to secure the display quality, and among the viewing angles, the above Deriving the voltage-transmittance characteristics of the liquid crystal display device in a first direction that is tilted most from the normal direction of the substrate and the in-plane orientation of the substrate forms an angle of 45 degrees with the absorption axis of the polarizing element. ,maximum Including an applied voltage determination step for determining the display quality as a white voltage, and a determination step for determining whether or not the display quality satisfies the desired display quality based on the determined white voltage. . For example, characteristics of the liquid crystal display device such as voltage-transmittance characteristics may be calculated by simulation or may be derived by experiment.

In the above configuration, the first direction with the worst display quality is determined based on the desired viewing angle and the direction of the absorption axis of the polarizing element, and the maximum value of the voltage-transmittance curve in the first direction is determined. Determine as white voltage. Thereby, for example, compared with the case where a predetermined voltage is determined as a white voltage or a white voltage is determined based on the transmittance in another direction, the calculation amount or the measurement amount can be reduced within the viewing angle. The highest white voltage can be set within the range where gradation is not reversed. As a result, a combination of retardations with the highest display quality without gradation inversion within the viewing angle can be derived with relatively little effort.

In the above configuration, the display quality set in the condition setting step is a minimum contrast to be maintained within the viewing angle, and the determination step compares the contrast in the first direction with the minimum contrast. May be determined.

According to this configuration, it is possible to derive a combination in which the contrast in the first direction having the worst display quality within the viewing angle satisfies a desired condition. Accordingly, it is possible to derive a retardation combination capable of ensuring at least the minimum contrast over the entire viewing angle with relatively little effort.

Further, in each of the above configurations, the display quality set in the condition setting step may be a transmittance when a white voltage is applied in the front direction of the substrate. According to this configuration, it is possible to derive a retardation combination for realizing a liquid crystal display device with favorable luminance and contrast in the front direction.

Each of the above configurations further includes an intermediate gradation voltage determining step for determining an applied voltage of an intermediate gradation based on the white voltage and a voltage-transmittance characteristic in the front direction of the substrate, The display quality set in the setting step may be a degree of similarity between each gradation voltage-transmittance characteristic in the front direction and each gradation voltage-transmittance characteristic in the first direction.

In the above configuration, after determining the intermediate gradation voltage based on the white voltage determined in the applied voltage determination step, the degree of similarity between the first direction, the front direction, and the gradation voltage-transmittance characteristics is determined. . As a result, even if the image displayed on the liquid crystal display device is viewed from any direction within the viewing angle, a retardation combination in which the brightness ratio between the gradations is similar is relatively It can be derived with little effort.

In addition, the retardation selection device of the liquid crystal display device of the present invention includes a liquid crystal layer including a liquid crystal layer having a negative dielectric anisotropy coated with a vertical alignment film on a substrate surface, and polarized light disposed on both sides of the liquid crystal layer. A retardation selection device for a liquid crystal display device having a device and a retardation film disposed between both polarizing devices, and performing black display in a state where liquid crystal molecules are aligned substantially perpendicular to the substrate. , When deriving a combination of the retardation of the liquid crystal layer and the retardation of the retardation film, condition setting means for setting a desired display quality and a viewing angle to ensure the display quality, The voltage-transmittance characteristics of the liquid crystal display device in the first direction that is tilted most from the normal direction of the substrate and the in-plane orientation of the substrate forms an angle of 45 degrees with the absorption axis of the polarizing element. Derived An applied voltage determining unit that determines a maximum point as a white voltage, and a determining unit that determines whether or not the display quality satisfies the desired display quality based on the determined white voltage. It is said. The applied voltage determination unit and the determination unit may calculate the characteristics of the liquid crystal display device by simulation, or may derive the characteristics of the liquid crystal display device based on an input of an experimental result.

Since the retardation selection device derives a combination of the retardation of the liquid crystal layer and the retardation film by the retardation selection method described above, for example, a predetermined voltage is determined as a white voltage or other directions Compared with the case where the white voltage is determined on the basis of the transmittance, the white voltage can be set highest with a smaller calculation amount or measurement amount within a range where the gradation is not inverted within the viewing angle. As a result, a combination of retardations with the highest display quality without gradation inversion within the viewing angle can be derived with relatively little effort.

In the above configuration, the first direction with the worst display quality is determined based on the desired viewing angle and the direction of the absorption axis of the polarizing element, and the maximum value of the voltage-transmittance curve in the first direction is determined. Determine as white voltage. Accordingly, a combination of retardations with the highest display quality without gradation inversion within the viewing angle can be derived with relatively little effort.

[First Embodiment]
An embodiment of the present invention will be described below with reference to FIGS. That is, the liquid crystal display device 1 according to the present embodiment includes a liquid crystal cell 3 including a liquid crystal layer 32 sandwiched between substrates 31a and 31b, and polarizing elements 5a disposed on both sides of the liquid crystal cell 3, as shown in FIG. 5b, and negative phase retardation films 7a and 7b arranged between the liquid crystal cell 3 and the polarizing element 5a and between the liquid crystal cell 3 and the polarizing element 5b, respectively.

  The directions of the absorption axes 51a and 51b of the polarizing elements 5a and 5b are set to be orthogonal to each other. Moreover, the direction (in-plane direction) of the slow axis of the retardation films 7a and 7b is set to be 45 degrees with respect to the absorption axes 51a and 51b of the polarizing elements 5a and 5b.

  On the other hand, the liquid crystal cell 3 is a vertical alignment (VA) type liquid crystal cell, and includes a TFT substrate (one of substrates 31a and 31b) in which thin film transistors (TFTs) and pixel electrodes 33 (described later) are arranged in a matrix. A vertical alignment film (not shown) is printed on a color filter (CF) substrate having the counter electrode (the other of the substrates 31a and 31b), the substrates 31a and 31b are bonded together, and a negative gap is formed between the substrates 31a and 31b. A liquid crystal layer 32 having a dielectric anisotropy of is encapsulated. Thereby, when no voltage is applied, the liquid crystal molecules of the liquid crystal layer 32 are aligned substantially vertically, and when a voltage is applied, the liquid crystal molecules can be tilted and aligned horizontally. Further, in the liquid crystal cell 3 according to the present embodiment, as shown in FIG. 2, a substantially square pyramid-shaped protrusion 34 is formed on each pixel electrode 33 provided on one substrate 31 a (31 b). The protrusion 34 has a 45 ° angle with respect to the absorption axes 51a and 51b of the polarizing elements 5a and 5b in the direction of each inclined surface, more specifically, the direction perpendicular to each inclined surface is projected in the plane of the substrates 31a and 32a. In the vicinity of the projection 34, the liquid crystal molecules are aligned so as to be perpendicular to the inclined surfaces. In addition, when a voltage is applied, the electric field at the portion of the protrusion 34 is inclined in a direction parallel to the inclined surface of the protrusion 34. As a result, when the liquid crystal molecules are tilted when a voltage is applied, the liquid crystal molecules are easily tilted in the direction of 45 degrees with respect to the absorption axes 51a and 51b in the in-plane direction. The protrusions 34 can be formed by applying a photosensitive resin on the TFT substrate and processing it by a photolithography process.

  In the liquid crystal display device 1 configured as described above, the liquid crystal molecules of the liquid crystal layer 32 are aligned substantially perpendicularly to the surface of the substrate 31a (31a) except for a small number of molecules near the protrusions 34 when no voltage is applied. Layer 32 has little birefringence. As a result, a good black display can be obtained. On the other hand, when an electrode is applied to the pixel electrode 33, the liquid crystal molecules of the pixel corresponding to the pixel electrode 33 are inclined so as to form an angle of 45 degrees with the absorption axes 51a and 51b in the in-plane direction, and the substrates 31a and 31b. Oriented substantially horizontally with respect to the surface. As a result, the liquid crystal layer 32 has a strong birefringence, and the pixel displays white.

  In addition, when a grayscale voltage is applied, the liquid crystal molecules of the pixel do not become horizontal with the substrates 31a and 31b, so that the user (observer) of the liquid crystal display device 1 can view the liquid crystal molecules from the long axis direction. When I see it, it looks black. However, in the present embodiment, since one pixel is divided into a plurality of (in this example, four) corresponding to each inclined surface, from the portion of the pixel where the liquid crystal molecules are aligned in the other direction. Is transmitted to the user in the above direction. As a result, the intermediate gradation can be identified from a wider viewing angle than when the orientation is not divided.

  Here, since the display quality from the oblique viewing angle varies greatly depending on the total retardation Rth of the retardation films 7a and 7b and the retardation Rlc of the liquid crystal cell 3, the display quality has good display quality. In order to realize the liquid crystal display device 1, it is necessary to select these values as appropriate values. However, as described above, in order to derive a suitable combination, if retardation is set at random and the experiment / display quality evaluation in an arbitrary direction is repeated, it takes a great deal of labor.

  In the present embodiment, the white voltage Vw is determined based on the voltage-transmittance curve Ta in the direction A determined from the structure of the liquid crystal display device 1 and the viewing angle α, and whether the display quality satisfies a desired condition. By determining whether or not, a numerical range was obtained in which high contrast was obtained, particularly at an oblique viewing angle, without much effort.

  Here, in the present embodiment, the characteristics of the liquid crystal display device 1 are obtained by simulation, and the following steps are performed by, for example, the arithmetic device (retardation selection device) 101 shown in FIG. The arithmetic device 101 includes a simulation processing unit 102 that derives the transmittance at an arbitrary angle of the liquid crystal display device 1 to which a specified voltage is applied, by a simulation, and a parameter storage unit 103 that stores parameters necessary for the simulation. A condition setting unit (condition selection means) 104 for setting desired conditions such as viewing angle α and contrast, a retardation setting unit 105 for selecting retardations Rth and Rlc, and the simulation processing unit 102 to control the above An applied voltage determining unit (applied voltage determining means) 106 for deriving a white voltage and a black voltage in a range in which the liquid crystal display device 1 having the retardations Rth and Rlc does not invert the gradation within a desired viewing angle α, and the simulation processing unit Liquid crystal display device to which the voltage is applied by controlling 102 An evaluation unit (determination unit) 107 for evaluating the contrast of the apparatus 1 is provided. Each of the members 102 to 107 is a functional block realized by, for example, a calculation unit such as a CPU executing a program stored in a storage unit such as a ROM or RAM, and includes a calculation unit and a storage unit. The computer can operate as the arithmetic device 101 by acquiring and executing the program by reading the program from a recording medium on which the program is recorded or transmitting the program through a communication path.

  In the arithmetic unit 101 configured as described above, in step 1 shown in FIG. 4 (hereinafter abbreviated as S1), for example, liquid crystal in an arbitrary direction when an arbitrary voltage is applied based on a user's instruction or the like. Parameters for deriving the transmittance of the display device 1 are set in the parameter storage unit 103. The parameters include, for example, an elastic constant, a dielectric constant, a refractive index, a helical pitch, and the like as liquid crystal parameters. The parameters include, for example, parameters indicating the cell thickness, anchoring energy, pretilt angle, and cell structure as parameters of the liquid crystal cell 3. When the parameters are set in S1, the simulation processing unit 102 of the arithmetic unit 101 calculates the equilibrium state at each voltage based on the parameters in S2, and calculates the alignment state of the liquid crystal molecules at each voltage. To do.

On the other hand, in S3, the condition setting unit 104 inputs a desired viewing angle α (for example, 60 degrees) and a minimum necessary contrast (for example, 5) based on, for example, a user instruction. Furthermore, in S4, the retardation setting unit 105, for example, based on the refractive index ellipsoid forming the retardation films 7a and 7b and the film thickness, the initial value of the retardation Rth of the retardation films 7a and 7b (for example, 10 nm). Specifically, the retardation films 7a and 7b are negative films, where n1 = n2> n3 when the in-plane refractive index is n1 and n2 and the normal direction refractive index is n3. Therefore, the retardation Rth of the retardation films 7a and 7b is as shown in the following formula (1):
Rth = dth · {(n1 + n2) / 2−n3}
= Dth · (n1-n3) (1)
It becomes. In the above formula (1), dth is the total film thickness of the retardation films 7a and 7b. On the other hand, the retardation Rlc of the liquid crystal cell 3 is expressed by the following formula (2):
Rlc = dlc · Δn (2)
The initial value (for example, 10 nm) of the retardation Rlc is derived based on the birefringence Δn, the cell thickness dlc of the liquid crystal cell 3 set in S1 and the birefringence Δn. If the retardations Rlc and Rth are values that can be set, the retardations Rlc and Rth are set first, and the thicknesses dlc and dth are calculated backward based on the above formulas (1) and (2). Good.

  When the initial values of the retardations Rlc and Rth are set in S1 and S4, in S5, the applied voltage determination unit 106 sets the polarizing element 5a in the in-plane direction as the direction with the worst display quality (direction A). Selects the direction of 45 degrees with the absorption axes 51a and 51b of 5b and the maximum viewing angle determined in S3 (for example, the angle formed with the normal direction of the surfaces of the substrates 31a and 31b is 60 degrees) To do. Further, the applied voltage determination unit 106 controls the simulation processing unit 102 to derive a voltage-transmittance curve Ta in the direction A as shown by a broken line in FIG. 5, and the transmittance is maximal (Xw point). Is set as the white voltage Vw. Further, the voltage with the minimum transmittance is set as the black voltage Vb.

  Here, the direction A is an angle that forms an angle of 45 degrees with the absorption axes 51a and 51b in the plane, and is farthest from the normal direction in the viewing angle α set in S3. As a result, as shown in FIG. 5, the voltage-transmittance curve Tf in the front direction and the voltage-transmittance curve Tb in the direction B where the in-plane direction is parallel to the absorption axes 51a and 51b and the maximum viewing angle are displayed. Not only is the quality low and the variation range of the transmittance is narrow, but there is a maximum value of the transmittance, and the range in which the transmittance monotonously increases is also narrow. Therefore, if it is set to apply a voltage exceeding the maximum voltage, gradation inversion occurs in the direction A, and in the display image, a portion where brightness and darkness are reversed with respect to other directions appears. End up. In the figure, the transmittance is shown as a value that makes the air transmittance one time. The unit of voltage is [V].

  However, in S5, in the direction A, the highest voltage in the range where the transmittance increases monotonously is set as the white voltage (Vw). As a result, for example, the viewing angle α set in S3 can be reduced with a smaller amount of calculation than when the predetermined voltage is determined as the white voltage or the white voltage is determined based on the transmittance in the other direction. The white voltage can be set to the highest value within the range where the gradation is not inverted.

  When the white voltage Vw and the black voltage Vb are determined in S5, the evaluation unit 107 controls the simulation processing unit 102, and the display quality of the liquid crystal display device 1 when the voltage is applied in S6. In step S7, it is determined whether a favorable viewing angle characteristic is obtained.

  In the present embodiment, the display quality of the liquid crystal display device 1 is evaluated based on whether or not the minimum contrast value is a preset value (for example, 5) or more, and the evaluation unit 107 evaluates the minimum contrast value. In the direction A, the ratio between the transmittance Taw when the white voltage Vw is applied and the transmittance Tab when the black voltage Vb is applied is calculated, and the display quality is evaluated based on whether the value is equal to or higher than the set value. To do. Since both transmittances Taw and Tab are derived when deriving the voltage-transmittance curve Ta in S4, the minimum contrast value can be calculated with a small amount of calculation.

  When a favorable viewing angle characteristic is obtained in the determination of S7, the arithmetic unit 101 ends the optimization because the combination of the retardations Rlc and Rth is appropriate. On the other hand, if a favorable viewing angle characteristic is not obtained (NO in S7), the evaluation unit 107 uses the retardation Rlc of the liquid crystal cell 3 that is currently set in S8 so far. Based on the display quality fluctuation history when Rth is changed, it is estimated whether the retardation Rth is further increased and the characteristics deteriorate, and it is determined whether the retardation Rlc needs to be changed. For example, when the current retardation Rth is determined to be maximal from the display quality fluctuation history, the evaluation unit 107 changes the value of the parameter storage unit 103 in S9, for example, by changing the value of the liquid crystal cell 3. By changing the cell thickness and the refractive index, the retardation Rlc of the liquid crystal cell 3 is changed in increments of a predetermined value, for example, by 10 nm. Thereafter, the processes after S2 are repeated. On the other hand, when it is estimated that the display quality is not lowered even if the retardation Rth is increased (NO in S8), the evaluation unit 107 repeats the above S4 and the retardation setting unit 105 For example, the display quality is reevaluated by increasing the retardation Rth of the retardation films 7a and 7b in increments of a predetermined value, such as by 10 nm.

  In the above configuration, the white and black voltages are determined based on the voltage-transmittance curve Ta in the specific direction A determined by the absorption axes 51a and 51b of the polarizing elements 5a and 5b and the desired viewing angle α. . As a result, for example, compared with a case where a predetermined voltage is determined as a white voltage, or a white voltage is determined based on transmittance in other directions, the gray level within the viewing angle α is reduced with a smaller amount of calculation. The highest white voltage can be set in a non-inverted range. Therefore, it is possible to manufacture the liquid crystal display device 1 that does not invert the gradation within the desired viewing angle α and has the highest transmittance (brightest) with less effort.

  In the flowchart of FIG. 4, the search is terminated when a favorable viewing angle characteristic is obtained. However, after the favorable viewing angle characteristic is obtained, the retardations Rlc and Rth are changed to obtain a favorable viewing angle characteristic. The obtained range is calculated as shown in FIGS. Even in this case, in each combination of the retardations Rlc and Rth, the viewing angle characteristic is determined in a state where the white voltage is set so as to be brightest in a range where the gradation is not within the viewing angle α. The amount of calculation can be reduced.

Here, each line in FIG. 6 indicates a retardation Rlc that can achieve the minimum contrast when the minimum contrast set as a condition in S3 is changed from 2.5 to 12.5 in increments of 2.5. , Rth is a contour line indicating the range of Rth. When contrast 5 is selected as a value that does not cause any problem in practical use, the range shown in FIG. 7 is obtained. Examining this figure in detail, in order to maintain the contrast 5 at least within the range up to a viewing angle of 60 degrees, and to maintain at least the contrast 5 within the range, the retardation Rlc of the liquid crystal cell 3 and the retardation film 7a. The total Rth of the 7b retardation is as follows:
Rth ≦ Rlc + 150 nm (3)
Rth ≧ 1.25 · Rlc−262.5 nm (4)
Rlc ≧ 75 nm (5)
Rth ≧ 30 nm (6)
It is understood that it is necessary to satisfy

  Therefore, when the liquid crystal display device 1 is manufactured, if the retardations Rlc and Rth of the liquid crystal cell 3 and the retardation films 7a and 7b are set so as to satisfy the above expressions (3) to (6), the liquid crystal display device 1 is inclined. Good contrast can be secured even at the viewing angle.

[Second Embodiment]
By the way, in the first embodiment, the display quality of the liquid crystal display device is determined depending on whether or not a desired contrast can be maintained within a desired viewing angle α range. In contrast, in the present embodiment, a case will be described in which the display quality is determined based on the transmittance at the time of white voltage in the front direction that affects the luminance and contrast in the front direction of the liquid crystal display device.

  That is, in this embodiment, as shown in FIG. 8, in S21 provided instead of S3 shown in FIG. 4, the condition setting unit 104 transmits the transmittance in the front direction (for example, as a condition of good viewing angle characteristics (for example, The air transmission rate is set to 1 (0.2 times, etc.). In S22 provided instead of S6, the evaluation unit 107 controls the simulation processing unit 102 to derive the transmittance Tfw in the front direction when the white voltage Vw determined in S5 is applied, It is evaluated whether or not the transmittance Tfw is greater than or equal to the value set in S21. For example, in the example shown in FIG. 9, it can be seen from the white voltage Vw determined in S5 that the transmittance Tfw in the front direction is about 0.4001, which satisfies the above condition. In addition, the said transmittance | permeability is a value which made the transmittance | permeability of air 1 time. Also in this case, the white voltage Vw is determined based on the voltage-transmittance curve Ta in the direction A, as in the first embodiment. Therefore, the parameters of the liquid crystal display device 1 can be set so that the gradation is not inverted within a desired viewing angle α and the transmittance is highest (brighter) with less effort.

Here, similarly to FIG. 6 and FIG. 7, when the retardation Rlc and Rth are changed after the favorable viewing angle characteristic is obtained, the range in which the favorable viewing angle characteristic is obtained is calculated. It becomes like this. In FIG. 10, each line indicates the transmittance when the transmittance Tfw at the time of white voltage in the front direction set as the condition in S21 is changed from 0.05 to 0.45 in increments of 0.05. Is a contour line showing the range of retardations Rlc and Rth that can achieve the above. When the transmittance Tfw = 0.2 at the time of white voltage in the front direction is selected as a value that does not cause any problem in practical use, the range shown in FIG. 11 is obtained. Examining this figure in detail, in order to make the gradation T inversion within the range of the viewing angle up to 60 degrees and to make the transmittance Tfw at the time of white voltage in the front direction 0.2 or more, the retardation of the liquid crystal cell 3 The total Rth of retardation of Rlc and retardation films 7a and 7b is as follows:
Rth ≦ 1.5 · Rlc + 80 nm (7)
Rlc ≧ 155 nm (8)
It is understood that it is necessary to satisfy

  Therefore, when the liquid crystal display device 1 is manufactured, if the retardations Rlc and Rth of the liquid crystal cell 3 and the retardation films 7a and 7b are set so as to satisfy the expressions (7) and (8), the front surface The gradation inversion of the oblique viewing angle can be suppressed without impairing the brightness and contrast.

[Third Embodiment]
By the way, when the liquid crystal display device 1 performs gradation display, it is preferable that the luminance ratio of each gradation is kept the same regardless of the viewing angle of the viewer. In the present embodiment, in order to ensure good display quality during gradation display within a desired viewing angle range, as another evaluation criterion, the transmittance Tan in the direction A and the transmission in the front direction at each gradation n. A case will be described in which the display quality is determined based on whether the ratio with the rate Tfn is within a predetermined range.

  That is, in this embodiment, as shown in FIG. 12, in S31 provided in place of S3 shown in FIG. 4, the condition setting unit 104 transmits the transmission in the direction A at each gradation n as a condition of favorable viewing angle characteristics. A ratio that the rate Tan and the transmittance Tfn in the front direction should satisfy is set. Although the ratio itself may be set, in this embodiment, the range of the transmittance Tan in the direction A is set. Specifically, for example, in the case of 8 gradations, that is, when black is the 0th gradation and white is the 7th gradation, the transmittance Tfw at the time of white voltage in the front direction is normalized as 100%. The transmittance Tf6 of the sixth gradation in the front direction is 6/7, that is, about 85.7%. In this case, as a condition of favorable viewing angle characteristics, the transmittance Ta6 of the sixth gradation in the direction A is set to a range of, for example, 80% to 95%, where the transmittance Taw at the white voltage in the direction A is 100%. Is done.

  Further, in the present embodiment, after setting the white voltage Vw and the black voltage Vb in S5 described above, the applied voltage determination unit 106 controls the simulation processing unit 102 in S32 to perform the front direction in the white voltage Vw. The front-side transmittance Tfn at each gradation is calculated based on the transmittance Tfw of the black voltage Vb and the front-side transmittance Tfb at the black voltage Vb. Further, an applied voltage for each transmittance Tfn is determined for each gradation from the voltage-transmittance curve Tf in the front direction. As described above, taking the case of 8 gradations as an example, the transmittance Tf6 of the sixth gradation in the front direction is about 85.7% of the transmittance Tfw at the time of white voltage, and therefore the front surface shown in FIG. On the voltage-transmittance curve Tf in the direction, the voltage V6 corresponding to the point X6 of the transmittance Tf6 is set as the applied voltage V6 of the sixth gradation.

  Further, when the applied voltage of each gradation is determined, in S33 provided instead of S6, the evaluation unit 107 controls the simulation processing unit 102 to change the direction A in each applied voltage determined in S32. The transmittance Tan is derived, and it is determined whether or not the transmittance Tan is within the range set in S31. Even in this case, the white voltage Vw is determined based on the voltage-transmittance curve Ta in the direction A, as in the first embodiment. Accordingly, the gradation is not inverted within a desired viewing angle α with less effort, and the gradation similar to the gradation in the front direction is obtained even in the direction with the worst display quality within the viewing angle α. The parameters of the liquid crystal display device 1 can be set.

Here, similarly to FIG. 6 and FIG. 7, when the retardation Rlc and Rth are changed even after the favorable viewing angle characteristic is obtained, the range in which the favorable viewing angle characteristic is obtained is calculated. It becomes like this. In FIG. 14, each line is a contour line indicating the range of the retardations Rlc and Rth in which the transmittance Ta6 in the direction A when the sixth applied voltage V6 is applied is a predetermined value, and the white voltage in the direction A When the transmittance Taw at the time of application is 100%, the contour lines are in increments of 0.75% from 57.5% to 95%. If a range of 95% to 80% is selected in the case of the sixth gradation as a value that causes no problem in practical use among the above, the range shown in FIG. 15 is obtained. Examining this figure in detail, in order to make the gradation characteristic in the direction A substantially similar to the characteristic in the front direction without reversing the gradation in the range up to a viewing angle of 60 degrees, the retarder of the liquid crystal cell 3 is used. The total Rth of the retardation Rlc and retardation of the retardation films 7a and 7b is as follows:
Rth ≦ 250 nm (9)
Rlc ≧ 30 nm (10)
It is understood that it is necessary to satisfy

  Accordingly, if the retardations Rlc and Rth of the liquid crystal cell 3 and the retardation films 7a and 7b are set so as to satisfy the above formulas (9) and (10), within the range of the desired viewing angle α, It is possible to realize the liquid crystal display device 1 that does not invert the gradation and exhibits characteristics similar to the gradation characteristics in the front direction.

[Fourth Embodiment]
In the present embodiment, a case will be described in which display quality is determined based on all the determination criteria in the first to third embodiments. That is, as shown in FIG. 16, in this embodiment, in S41 instead of S3 in FIG. 4, the contrast in the direction A, the brightness in the front direction, the transmittance in the direction A and the transmittance in the front direction in each gradation. Is set as a condition for good display quality.

  Further, after the applied voltage of each gradation is determined in S42 similar to S32 in FIG. 12, in S43 instead of S6, the contrast in the direction A, the brightness in the front direction, and the transmission in the direction A in each gradation. The relationship between the rate and the transmittance in the front direction is derived, and the display quality of the liquid crystal display device 1 is determined. Even in this case, the white voltage Vw is determined based on the voltage-transmittance curve Ta in the direction A, as in the first embodiment. Therefore, the parameters of the liquid crystal display device 1 can be set with less effort so that the gradation is not inverted within the desired viewing angle α and the effects of the first to third liquid crystal display devices are combined.

  Here, as in FIG. 7, when the retardation Rlc and Rth are changed even after the favorable viewing angle characteristic is obtained, and the range in which the favorable viewing angle characteristic is obtained is calculated, as shown in FIG. The range shown in FIG. 11, the range shown in FIG. 11, and the range shown in FIG. 15 overlap each other. Therefore, if the retardations Rlc and Rth of the liquid crystal cell 3 and the retardation films 7a and 7b are set so as to satisfy all the above formulas (3) to (10), the transmittance in the front direction is not impaired. The liquid crystal display device 1 can be realized in which the gradation is not inverted within the range of the desired viewing angle α, the minimum contrast is a predetermined value or more, and the gradation characteristics in the front direction and the arbitrary direction are similar.

  By the way, in the first to fourth embodiments, the total retardation Rth of the retardation films 7a and 7b is changed from the initial value, and when the display quality deteriorates, the retardation Rlc of the liquid crystal cell 3 is changed. Thus, although the change of the retardation Rth is repeated, the method of selecting the evaluation point (combination of the retardations Rlc and Rth) is not limited to this. For example, as shown in FIG. 18, the optimum value may be searched for while changing both of the retardations Rlc and Rth based on the evaluation result.

  Specifically, on the two-dimensional map with the retardation Rlc and the retardation Rth as axes, initially, three points (Rlc, Rth) are arbitrarily selected, and the display quality of the liquid crystal display device 1 at each point is evaluated. . For example, in the example of the first embodiment, the processing in S5 and S6 shown in FIG. 4 is performed for each point to evaluate the contrast in the direction A.

  Here, when the points C1, C2, and C3 are ranked in ascending order of evaluation among the points, the midpoint of the points C2 and C3 is calculated as a point C4. Further, on the basis of the point C1 and the point C4, a 1: 2 outer dividing point, a middle point, a 2: 1 outer dividing point, and a 3: 2 outer dividing point are calculated as D1 to D4, respectively. Moreover, the display quality of the liquid crystal display device 1 is evaluated about each point D1-D4.

  Further, among the points D1 to D4, the point E having the highest evaluation is replaced with the point C1, the evaluations of the point E, the point C2 and the point C3 are compared, and as the new points C1, C2 and C3 in the descending order of evaluation, The calculation of the points D1 to D4 and the evaluation of the display quality are repeated. Note that the evaluation is not limited to the contrast in the direction A, but is comprehensively determined based on a comprehensive evaluation value calculated by a predetermined evaluation function from the contrast in the direction A, the luminance in the front direction, and the gradation characteristics. May be.

  Even in the above method, since the white voltage Vw is determined based on the voltage-transmittance curve Ta in the direction A, the retardations Rlc and Rth that satisfy a desired condition can be calculated with a smaller amount of calculation. Furthermore, in this method, unlike FIGS. 4, 8, 12, and 16, the range satisfying the desired condition cannot be calculated, but both retardations Rlc and Rth are adjusted according to the evaluation results. Therefore, the retardations Rlc and Rth for manufacturing the liquid crystal display device 1 having the optimum display quality can be calculated with a smaller amount of calculation than the above figures.

[Fifth Embodiment]
By the way, in the first to fourth embodiments, the case where various characteristics of the liquid crystal display device 1 such as a voltage-transmittance curve are derived, for example, is described as an example. On the other hand, in this embodiment, the case where various characteristics are derived | led-out by experiment is demonstrated.

  That is, in the arithmetic device 101a shown in FIG. 19, in place of the simulation processing unit 102 and the parameter storage unit 103 shown in FIG. 3, for example, measured values from which measurement results are input from a user of the arithmetic device 101a or a measuring device. An input unit 108 is provided, and the applied voltage determination unit 106 and the evaluation unit 107 receive values similar to the values from the simulation processing unit 102 from the measurement value input unit 108. Thereby, each retardation Rlc and Rth can be determined by the method similar to 1st thru | or 4th embodiment, and the same result can be derived | led-out. Also in this configuration, since the white voltage Vw is determined based on the voltage-transmittance curve Ta in the direction A, the retardations Rlc and Rth that satisfy the desired condition can be calculated with a smaller number of measurements.

By the way, in 1st thru | or 5th embodiment, although the case where a negative film was used as an example was demonstrated as retardation film 7a * 7b, it is not restricted to this, Even when a positive film is used, the same method Thus, the optimum combination of retardations Rlc and Rth can be derived. The positive film is a film in which n1> n2 = n3 when the in-plane refractive indexes n1 and n2 and the refractive index n3 in the normal direction are set, and the retardation Rth of the retardation film Rth of both retardation films Assuming the total thickness,
Rth = dth · {(n1 + n2) / 2−n3} (11)
Is calculated as

  Also in this liquid crystal display device, when the optimum ranges of the retardations Rlc and Rth were obtained by the same method as in the first to fifth embodiments, it was confirmed that they were the same as the respective ranges.

  Further, the retardation films 7a and 7b may be retardation films expressed by a biaxial refractive index ellipsoid. The retardation Rth of the film is also calculated by the above formula (11). Also in this liquid crystal display device, the optimum retardation Rlc and Rth ranges can be derived by the same method as in the first to fifth embodiments, and it was confirmed that they were the same as the respective ranges.

  Furthermore, in each said embodiment, although the case where the phase difference films 7a and 7b were distribute | arranged to the both sides of the liquid crystal cell 3 was demonstrated as an example, you may distribute | arrange only to one side. Further, a plurality of types of retardation films may be stacked to realize the retardation film 7a (7b). In any case, the optimum range of the retardations Rlc and Rth can be derived by the same method, and the total retardation Rth of the retardation film disposed between the polarizing elements 5a and 5b and the liquid crystal cell 3 It was confirmed that the optimum range of the retardation Rlc is the same as that shown in the first to fifth embodiments.

  In each of the embodiments described above, the case where the liquid crystal cell 3 is set to the four-divided vertical alignment mode by the protrusions 34 shown in FIG. 2 has been described as an example, but the present invention is not limited to this. For example, as shown in FIG. 20, the pixel electrode 33 is provided with a projection 35 having an L-shape in the plane and a mountain shape in the normal direction, and the projection 36 having the same shape also on the counter electrode of the CF substrate. May be provided. The distance between the protrusions 35 and 36 in the in-plane direction of the substrates 31 a and 31 b is arranged so that the normal line of the inclined surface of the protrusion 35 coincides with the normal line of the inclined surface of the protrusion 36. Each of the protrusions 35 and 36 can be formed by applying a photosensitive resin on the pixel electrode 33 and the counter electrode and processing it in a photolithography process, like the protrusion 34.

  In the above-described structure, in one part of the L-shaped corner portion of the protrusion 35, the liquid crystal molecules in the regions 37 and 38 in the vicinity of the portion are aligned along both chevron slopes, and in the in-plane direction of the substrates 31a and 31b. Referring to the absorption axes 51a and 51b of the polarizing elements 5a and 5b shown in FIG. 1, the orientation is in the direction of 45 degrees and the direction of 225 degrees. On the other hand, in the other portion of the L-shaped corner portion of the protrusion 35, the liquid crystal molecules in the regions 39 and 40 in the vicinity of the portion are aligned along both chevron slopes, and the absorption axes 51a and 51b are in the in-plane direction. Is the orientation in the direction of 135 degrees and 315 degrees. Thereby, similarly to the case of FIG. 2, in each pixel, the liquid crystal molecules can be divided in four directions.

  Further, the number of alignment divisions is not limited to four, and the present invention can be applied to a vertical alignment mode in which a plurality of alignment divisions are performed. Further, as shown in FIG. 21, the pixel electrode 33 may be provided with a hemispherical protrusion 34a and applied in the case of the vertical alignment mode in which the axis is symmetrically aligned. The protrusion 34a is formed by applying a photosensitive resin on the TFT substrate (31a or 31b) in which the pixel electrodes (33) are arranged in a matrix and processing it by a photolithography process, so that one protrusion is formed for each pixel. 34a can be formed. In any case, the optimal ranges of the retardations Rlc and Rth can be calculated by the same method, and it was confirmed that the similar ranges are optimal.

  For example, when forming a large-sized liquid crystal television such as 40 inches, the size of each pixel is as large as about 1 mm square, and only by providing one projection (34, 34a) on the pixel electrode, the orientation is achieved. There is a possibility that the regulation force becomes weak and the orientation becomes unstable. Therefore, when the alignment regulating force is insufficient, it is desirable to provide a plurality of protrusions on each pixel electrode 33.

  As described above, the liquid crystal display device according to the present embodiment includes a liquid crystal layer that includes a liquid crystal having a negative dielectric anisotropy and a polarizing element that is disposed on both sides of the liquid crystal layer. And a retardation film disposed between both polarizing elements, and the thickness of the retardation film in a liquid crystal display device performing black display in a state where liquid crystal molecules are aligned substantially perpendicular to the substrate The total retardation Rth in the direction and the retardation Rlc of the liquid crystal layer satisfy Rth ≦ Rlc + 150 nm, Rth ≧ 1.25 · Rlc−262.5 nm, Rlc ≧ 75 nm, and Rth ≧ 30 nm. It is characterized by that.

  In the above configuration, an upper limit and a lower limit are set for the retardation combination of the liquid crystal layer and the retardation film, and if this range is set, in the entire viewing angle range from the normal direction of the substrate to the direction inclined by 60 degrees, Contrast 5 or higher can be maintained without tone reversal. As a result, a liquid crystal display device with good display quality at an oblique viewing angle can be reliably realized.

  In the liquid crystal display device having the above configuration, the total retardation Rth in the thickness direction of the retardation film and the retardation Rlc of the liquid crystal layer are Rth ≦ 1.5 · Rlc + 80 nm and Rlc ≧ It is preferable to satisfy 155 nm.

  According to the said structure, the transmittance | permeability of the front direction of a liquid crystal display device can be kept 0.2 times or more of the transmittance | permeability of air. As a result, a liquid crystal display device having a good display quality at an oblique viewing angle can be reliably realized without impairing the luminance and contrast in the front direction.

  In addition, the liquid crystal display device of the present embodiment includes a liquid crystal layer including a liquid crystal having a negative dielectric anisotropy coated with a vertical alignment film on the substrate surface, polarizing elements disposed on both sides of the liquid crystal layer, and both And a retardation film disposed between the polarizing elements, wherein the liquid crystal molecules perform black display in a state in which liquid crystal molecules are aligned substantially perpendicular to the substrate. The total Rth of the retardation and the retardation Rlc of the liquid crystal layer satisfy Rth ≦ 1.5 · Rlc + 80 nm and Rlc ≧ 155 nm.

  Even in the above configuration, the upper limit and the lower limit are set for the retardation combination of the liquid crystal layer and the retardation film, and if this range is set, in the entire viewing angle range from the normal direction of the substrate to the direction inclined by 60 degrees, Further, the transmissivity in the front direction can be maintained at 0.2 times or more the transmissivity of air without reversing the tone. As a result, a liquid crystal display device having a good display quality at an oblique viewing angle can be reliably realized without impairing the luminance and contrast in the front direction.

  Furthermore, in the liquid crystal display device having each configuration described above, it is desirable that the total retardation Rth in the thickness direction of the retardation film satisfies Rth ≦ 250 nm and Rlc ≧ 30 nm.

  According to this configuration, the voltage-transmittance characteristic that is generally similar to the voltage-transmittance characteristic in the front direction can be maintained in the entire viewing angle range from the normal direction of the substrate to the direction inclined by 60 degrees. As a result, in the image displayed on the liquid crystal display device, the brightness ratio between the gradations becomes almost the same value when viewed from any direction of the viewing angle range, and the gradation characteristics of the oblique viewing angle are good. A liquid crystal display device can be realized.

  In the liquid crystal display device having each configuration described above, the liquid crystal layer may be provided with a plurality of regions having different response directions of liquid crystal molecules for each pixel. Further, in the liquid crystal layer, the response direction of the liquid crystal molecules may be set to be approximately axisymmetric for each pixel. In addition, a plurality of axes having the axially symmetric orientation may be provided for each pixel. According to these configurations, the mutual regions are optically compensated by the division of the pixels, so that it is possible to realize a liquid crystal display device with better display quality at an oblique viewing angle.

The liquid crystal display device according to the present embodiment includes a liquid crystal layer including a liquid crystal layer having a negative dielectric anisotropy coated with a vertical alignment film on a substrate surface, polarizing elements disposed on both sides of the liquid crystal layer, and both polarizing elements A liquid crystal display device that performs black display in a state in which liquid crystal molecules are aligned substantially perpendicular to the substrate, and in order to solve the above problems, In the first direction in which the in-plane orientation of the substrate is at an angle of 45 degrees with the absorption axis of the polarizing element, the maximum of the viewing angle to the normal direction of the substrate and the in-plane orientation of the substrate makes an angle of 45 degrees with the polarizing element A voltage indicating a point is set as a white voltage.

In the liquid crystal display device according to the present invention, in the liquid crystal display device, the first direction is preferably a direction inclined by 60 degrees from a normal direction of the substrate.

In the above configuration, the first direction with the worst display quality is determined based on the desired viewing angle and the direction of the absorption axis of the polarizing element, and the maximum value of the voltage-transmittance curve in the first direction is determined. Determine as white voltage. Thereby, for example, compared with the case where a predetermined voltage is determined as a white voltage or a white voltage is determined based on the transmittance in another direction, the calculation amount or the measurement amount can be reduced within the viewing angle. The highest white voltage can be set within the range where gradation is not reversed. As a result, a combination of retardations with the highest display quality without gradation inversion within the viewing angle can be derived with relatively little effort.

  The present invention can be applied to a vertical alignment mode liquid crystal display device.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1, showing an embodiment of the present invention, is a configuration diagram showing a main configuration of a liquid crystal display device. In the said liquid crystal display device, it is a perspective view which shows the structure of a pixel electrode. In the liquid crystal display device having the above-described configuration, it is a block diagram illustrating a main configuration of an arithmetic device for deriving an optimum combination of retardation of a liquid crystal layer and retardation of a retardation film. It is a flowchart which shows the derivation method of the said retardation combination. It is a graph explaining the value referred by the said method, and showing the voltage-transmittance curve of a liquid crystal display device. It is a graph which shows the range of the retardation combination derived | led-out by the said method. It is a graph which shows a suitable range among the ranges of the retardation combination derived | led-out by the said method. The other embodiment of this invention is shown and it is a flowchart which shows the derivation | leading-out method of the said retardation combination. It is a graph explaining the value referred by the said method, and showing the voltage-transmittance curve of a liquid crystal display device. It is a graph which shows the range of the retardation combination derived | led-out by the said method. It is a graph which shows a suitable range among the ranges of the retardation combination derived | led-out by the said method. It is a flowchart which shows other embodiment of this invention, and shows the derivation | leading-out method of the said retardation combination. It is a graph explaining the value referred by the said method, and showing the voltage-transmittance curve of a liquid crystal display device. It is a graph which shows the range of the retardation combination derived | led-out by the said method. It is a graph which shows a suitable range among the ranges of the retardation combination derived | led-out by the said method. It is another embodiment of this invention, and is a flowchart which shows the derivation method of the said retardation combination. It is a graph which shows the range of the retardation combination derived | led-out by the said method. It is explanatory drawing which shows the modification of each said embodiment, and demonstrates the selection method of the retardation combination used as evaluation object. Another embodiment of the present invention is shown, and is a block diagram showing another configuration example of the arithmetic device. It is a top view which shows the modification of each said embodiment, and shows the structure of a pixel electrode. It is a perspective view which shows the other modification of each said embodiment, and shows the structure of a pixel electrode.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Liquid crystal display device 5a * 5b Polarizing element 7a * 7b Phase difference film 31a * 31b Substrate 32 Liquid crystal layer 51a * 51b Absorption axis 101 * 101a Arithmetic apparatus (retardation selection apparatus)
104 Condition setting section (condition setting means)
106 Applied voltage determining unit (applied voltage determining means)
107 Evaluation part (determination means)

Claims (5)

A liquid crystal layer including a liquid crystal having a negative dielectric anisotropy coated with a vertical alignment film on the substrate surface, a polarizing element disposed on both sides of the liquid crystal layer, and a retardation film disposed between both polarizing elements, A retardation selection method for a liquid crystal display device that performs black display in a state in which liquid crystal molecules are aligned substantially perpendicular to the substrate,
When deriving a combination of the retardation of the liquid crystal layer and retardation of the retardation film, a condition setting step for setting a desired display quality and a viewing angle to secure the display quality,
Among the viewing angles, the voltage of the liquid crystal display device in the first direction that is the most inclined from the normal direction of the substrate and the in-plane orientation of the substrate forms an angle of 45 degrees with the absorption axis of the polarizing element. An applied voltage determination step of deriving transmittance characteristics and determining a maximum point as a white voltage;
And a determination step of determining whether or not the display quality satisfies the desired display quality based on the determined white voltage. The display quality set in the condition setting step is the minimum contrast to be maintained within the viewing angle, and the determination step is to determine by comparing the contrast in the first direction with the minimum contrast. The method for selecting a retardation of a liquid crystal display device according to claim 1. 3. The retardation selection method for a liquid crystal display device according to claim 1, wherein the display quality set in the condition setting step is a transmittance when a white voltage is applied in a front direction of the substrate. Furthermore, based on the white voltage and the voltage-transmittance characteristics in the front direction of the substrate, an intermediate gradation voltage determining step for determining an applied voltage of the intermediate gradation is included.
The display quality set in the condition setting step is a degree of similarity between each gradation voltage-transmittance characteristic in the front direction and each gradation voltage-transmittance characteristic in the first direction. Item 4. A method for selecting a retardation of a liquid crystal display device according to item 1, 2 or 3. A liquid crystal layer including a liquid crystal having a negative dielectric anisotropy coated with a vertical alignment film on the substrate surface, a polarizing element disposed on both sides of the liquid crystal layer, and a retardation film disposed between both polarizing elements, A retardation selection device for a liquid crystal display device that performs black display in a state in which liquid crystal molecules are aligned substantially perpendicular to the substrate,
When deriving a combination of the retardation of the liquid crystal layer and the retardation film, condition setting means for setting a desired display quality and a viewing angle to ensure the display quality,
Among the viewing angles, the voltage of the liquid crystal display device in the first direction that is the most inclined from the normal direction of the substrate and the in-plane orientation of the substrate forms an angle of 45 degrees with the absorption axis of the polarizing element. An applied voltage determining means for deriving a transmittance characteristic and determining a maximum point as a white voltage;
A retardation selection device for a liquid crystal display device, comprising: a determination unit that determines whether or not the display quality satisfies the desired display quality based on the determined white voltage.

Images