JP2014089343A - Liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a contrast and steepness in a specific viewing angle direction.SOLUTION: A STN type liquid crystal display element includes a twisted phase difference plate that has a liquid crystal polymer layer. A liquid crystal molecule of a liquid crystal layer of a liquid crystal element is oriented at a twisted angle of almost 180°, and a polymer molecule of a liquid crystalline polymer layer is oriented at a twisted angle of almost 180°, and a mutual twisted direction is a reverse direction. A pretilt angle is 0.2° or more and 1.0° or less. A thickness of the liquid crystal layer is 6.0 μm or more, and a retardation of the liquid crystal layer and a retardation of the liquid crystalline polymer layer are almost equal. A R liquid crystal molecule orientation direction 13b and a F molecule orientation direction 43a are almost orthogonal to each other. An angle of an angle α1 formed with a liquid crystal orientation axis D and a F absorption axis 21 is 45° or more, an angle of an angle α2 formed with the liquid crystal orientation axis D and R absorption axis 31 is 45° or more and an angle of an angle β formed with the F absorption axis 21 and the R absorption axis 31 is 85° or more and less than 90°.

Description

  The present invention relates to a liquid crystal display element, and more particularly, to a super twisted nematic liquid crystal display element provided with a twisted phase difference plate having a liquid crystalline polymer layer.

  In a super twisted nematic (STN) type liquid crystal display element, if no countermeasures are taken, the STN type unique background coloring will occur remarkably, and the display quality will be degraded. In general, a phase difference plate is provided. In particular, when high durability is required, a liquid crystalline twisted phase difference plate (twisting position with a liquid crystalline polymer layer) that takes into account the temperature characteristics of the liquid crystal as a phase difference plate to eliminate changes in appearance due to ambient temperature. A phase difference plate is used.

  For example, Patent Document 1 discloses an STN type liquid crystal display element including a liquid crystal twisted phase difference plate. In the STN type liquid crystal display element according to Patent Document 1, the twist angle is set in a range of 180 ° to 270 °, the retardation Δnd1 of the liquid crystal layer is 0.7 to 0.9 μm, and the liquid crystal twisted position is calculated from this Δnd1. The value obtained by subtracting retardation Δnd2 of the retardation plate is set to 0.1 to 0.3 μm.

Republished patent International publication number WO00 / 11516

  By the way, if the STN type liquid crystal display element is dedicated for a specific application, a high contrast may be required in a specific viewing angle direction. As an example, when the STN type liquid crystal display element is for in-vehicle use, it is required to have a good appearance from a viewer such as a driver sitting in a seat, and thus a high contrast is required at a viewing angle from above. However, the STN type liquid crystal display element according to Patent Document 1 has a configuration in which front contrast is emphasized.

  Further, since the STN type liquid crystal display element has a large twist angle of liquid crystal molecules of about 180 ° to 240 °, the pretilt angle (the angle of inclination of the liquid crystal molecules at the substrate-liquid crystal interface) is about 3 ° to 4 °. Since it is generally set, there is room for improvement in terms of obtaining good steepness.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a liquid crystal display element having good contrast and steepness in a specific viewing angle direction.

In order to achieve the above object, the liquid crystal display element according to the present invention is
A first substrate and a second substrate facing each other, a liquid crystal layer positioned between the first substrate and the second substrate, and a liquid crystal layer side surface of each of the first substrate and the second substrate. A liquid crystal element having a transparent electrode patterned into a predetermined shape,
A first polarizing plate located on a side opposite to the liquid crystal layer side of the first substrate;
A second polarizing plate located opposite to the liquid crystal layer side of the second substrate and facing the first polarizing plate;
A twisted phase difference plate having a liquid crystalline polymer layer located between the liquid crystal element and the first polarizing plate or between the liquid crystal element and the second polarizing plate;
A super twisted nematic liquid crystal display element that displays a display element corresponding to the predetermined shape by applying a voltage from the transparent electrode to the liquid crystal layer,
The liquid crystal molecules of the liquid crystal layer are aligned with a twist angle of about 180 °,
The polymer molecules of the liquid crystalline polymer layer are aligned with a twist angle of about 180 °,
The twist direction of the liquid crystal molecules is opposite to the twist direction of the polymer molecules,
The pretilt angle of the liquid crystal layer is 0.2 ° to 1.0 °,
The liquid crystal layer has a thickness of 6.0 μm or more,
The retardation value of the liquid crystal layer and the retardation value of the liquid crystalline polymer layer are substantially equal,
The orientation direction of the liquid crystal molecules on the twisted phase difference plate side of the liquid crystal layer and the liquid crystal element side of the liquid crystalline polymer molecules as viewed from the normal direction of the opposing surfaces of the first substrate and the second substrate. Is substantially perpendicular to the orientation direction of the polymer molecules of
The axis along the alignment direction of the liquid crystal molecules on the twisted phase difference plate side of the liquid crystal layer is a liquid crystal alignment axis, the absorption axis of the first polarizing plate is a first absorption axis, and the absorption axis of the second polarizing plate is As the second absorption axis,
The angle formed by the liquid crystal alignment axis and the first absorption axis, which is an acute angle, is 45 ° or more,
The angle formed by the liquid crystal alignment axis and the second absorption axis, which is an acute angle, is 45 ° or more,
The angle formed by the first absorption axis and the second absorption axis, which is an acute angle, is 85 ° or more and less than 90 °.
It is characterized by that.

  According to the present invention, it is possible to provide a liquid crystal display element having good contrast and steepness in a specific viewing angle direction.

It is a figure for demonstrating schematic structure of the liquid crystal display element which concerns on one Embodiment of this invention. It is a figure which shows an example of a display element. (A) is a figure for demonstrating the relationship between the orientation direction of a liquid crystal layer, and the orientation direction of a liquid crystalline polymer layer. (B) is a figure for demonstrating the relationship between F absorption axis and R absorption axis. It is a figure for demonstrating the contrast characteristic etc. of the liquid crystal display element which concerns on one Embodiment of this invention, and the liquid crystal display element which concerns on a prior art example and a comparative example. It is a figure of the graph which shows the relationship between F absorption axis angle and contrast in a plurality of viewing angles. (A) is a figure which shows the table | surface of the data used as the origin of the graph shown in FIG. 5, Comprising: It is a figure of a table | surface which shows the contrast when changing F absorption axis angle and a viewing angle in the predetermined range. (B) is a table showing the contrast when the R absorption axis angle and the viewing angle are changed within a predetermined range. It is a figure for demonstrating a viewing angle and an azimuth.

  An embodiment of the present invention will be described with reference to the drawings.

  A liquid crystal display element 100 according to the present embodiment shown in FIG. 1 is configured as a super twisted nematic (STN) type, and includes a liquid crystal element 10, a first polarizing plate 20, a second polarizing plate 30, and a twisted phase difference. A plate 40.

  As shown in FIG. 1, the liquid crystal element 10 includes a first substrate 11 and a second substrate 12 which are a pair of transparent substrates facing each other, and a liquid crystal layer 13. The first substrate 11 and the second substrate 12 are made of, for example, glass, plastic, or the like, and are arranged so as to face each other with the liquid crystal layer 13 interposed therebetween, and their main surfaces (opposing surfaces) are parallel to each other. Has been. The first substrate 11 is located closer to the observer 1 who visually recognizes the display element than the liquid crystal layer 13.

  On the liquid crystal layer 13 side of the first substrate 11, a transparent electrode 11a and an alignment film 11b are provided. The alignment film 11b is located closer to the liquid crystal layer 13 than the transparent electrode 11a. A transparent electrode 12a and an alignment film 12b are provided on the liquid crystal layer 13 side of the second substrate 12. The alignment film 12b is located closer to the liquid crystal layer 13 than the transparent electrode 12a. If necessary, an insulating film may be provided between the transparent electrode 11a and the alignment film 11b and between the transparent electrode 12a and the alignment film 12b.

  The transparent electrodes 11a and 12a are made of, for example, an ITO (Indium Tin Oxide) film containing indium oxide as a main component, and each is patterned into a predetermined shape. The transparent electrode 11a is formed on the surface of the first substrate 11 on the liquid crystal layer 13 side, and the transparent electrode 12a is formed on the surface of the second substrate 12 on the liquid crystal layer 13 side by a known method (sputtering, vapor deposition, etching, etc.). ing. The transparent electrodes 11a and 12a may be formed of a material containing a π-conjugated conductive polymer such as polythiophene.

  The transparent electrode 11a is configured as a common electrode, and the transparent electrode 12a is configured as a segment electrode. A voltage is applied to both electrodes by a passive drive system. That is, the liquid crystal display element 100 is a segment display type and configured as a passive drive type liquid crystal display element. The transparent electrode 11a may be configured as a segment electrode, and the transparent electrode 12a may be configured as a common electrode.

  The liquid crystal display element 100 has the predetermined shape in a region where the transparent electrodes 11a and 12a overlap in the normal direction of the opposing surfaces of the first substrate 11 and the second substrate 12 (hereinafter also simply referred to as the substrate normal direction). The display element corresponding to is displayed. Here, the display element is an element for indicating information displayed on the liquid crystal display element 100, and refers to a symbol (including letters and numbers), a figure, or a combination thereof. In addition, the liquid crystal display element 100 displays the display element substantially white on the substantially black background region by transmitting light in the region where the ON voltage is applied to the transparent electrodes 11a and 12a (the display element is set to the display state). ) It is configured as a so-called negative display type (normally black mode).

  An example of information displayed by the liquid crystal display element 100 is shown in FIG. In the figure, the liquid crystal display element 100 is an example configured as a 7-segment display, and the liquid crystal display element 100 shows information on the total travel distance of a certain vehicle by indicating numerical values and units. In the figure, a combination of seven segments 2a (showing the numeral “8” when all of them are displayed), a segment 2b displaying the alphabet “k” in the display state, and “m” in the display state. The liquid crystal display element 100 displays information that the total travel distance of the current vehicle is “34888 km” in combination with the segment 2c that displays the alphabet. The segments 2a to 2c are examples of display elements. In the liquid crystal display element 100, a region where the transparent electrode 11a and the transparent electrode 12a do not overlap and a region where no ON voltage is applied become the substantially black background region 3. In FIG. 2, the routing electrode formed in the background region 3 is omitted.

  The alignment films 11b and 12b are in contact with the liquid crystal layer 13 and are for defining the alignment state of liquid crystal molecules included in the liquid crystal layer 13, and are made of, for example, polyimide and formed by a known method (for example, flexographic printing). Is done. The alignment film 11b is formed so as to cover the transparent electrode 11a from the liquid crystal layer 13 side, and the alignment film 12b is formed so as to cover the transparent electrode 12a from the liquid crystal layer 13 side.

  The alignment films 11b and 12b are rubbed. Thereby, the alignment direction of the liquid crystal molecules included in the liquid crystal layer 13 is defined. The alignment treatment performed on the alignment films 11b and 12b is not limited to the rubbing treatment, and may be other known treatments such as a photo-alignment treatment and a protrusion alignment treatment. By these treatments, the major axis direction of the liquid crystal molecules May be regulated. The rubbing direction applied to the alignment films 11b and 12b will be described later.

  Returning to FIG. 1, in the liquid crystal layer 13, a liquid crystal material is sealed in a sealed space formed by a sealing material (not shown) for joining the first substrate 11 and the second substrate 12 and both substrates. Formed by. The value of retardation Δnd1, which is the product of the refractive index anisotropy Δn1 of the liquid crystal layer 13 and the cell gap d1, is set substantially equal to the value of retardation Δnd2 of the twisted phase difference plate 40 described later. What value is set will be described together with the explanation of the twisted phase difference plate 40.

  The alignment direction of the liquid crystal molecules in the liquid crystal layer 13 is regulated by the alignment film 11b and the alignment film 12b as shown in FIG. Specifically, as shown in the figure, with reference to an axis along the left-right direction (same as the left-right direction in FIG. 3A) when the viewer 1 views the liquid crystal display element 100 from the substrate normal direction. In addition, when the angle is defined so that the angle increases counterclockwise from 0 ° (that is, the 3:00 direction is 0 ° as viewed from the observer 1), the liquid crystal at a position close to the first substrate 11 is used. The alignment direction 13a of molecules (hereinafter referred to as F liquid crystal molecule alignment direction 13a) is set to 0 °, and the alignment direction 13b of liquid crystal molecules at a position close to the second substrate 12 (hereinafter referred to as R liquid crystal molecule alignment direction 13b). Is also set in the 0 ° direction. If the viewer 1 side is the front side (upper side in FIG. 1) and the opposite side is the back side (lower side in FIG. 1) in the liquid crystal display element 100, the rubbing direction of the alignment film 11b on the front side is F liquid crystal. The rubbing direction of the alignment film 12b on the back side coincides with the R liquid crystal molecular alignment direction 13b (parallel rubbing). Thus, the liquid crystal molecules of the liquid crystal layer 13 have a major axis orientation of about 180 ° between the end of the liquid crystal layer 13 on the first substrate 11 side and the end of the second substrate 12 side. And is oriented so as to rotate (turn) little by little from one substrate side to the other substrate side (chiral structure). Thus, the liquid crystal layer 13 when no voltage is applied has chirality.

  In the present embodiment, the F liquid crystal molecule alignment direction 13a is twisted approximately 180 ° counterclockwise with respect to the R liquid crystal molecule alignment direction 13b. Note that “approximately 180 °” is a concept including exactly 180 ° and also includes a case where the angle is shifted from 180 ° due to an assembly error or the like. In the following description, “substantially” is used in the same meaning.

  Further, in the liquid crystal layer 13, the liquid crystal molecules at positions close to the first substrate 11 and the second substrate 12 are arranged with an inclination with respect to the substrate surface (pretilt is given). This tilt angle is called a pretilt angle θp. In this embodiment, the pretilt angle θp is 0.2 ° or more and 1.0 ° or less (0.2 °) in order to improve the steepness of the liquid crystal display element 100 in a favorable manner. ≦ θp ≦ 1.0 °), preferably 0.2 ° to 0.6 ° (0.2 ° ≦ θp ≦ 0.6 °). In the conventional STN type liquid crystal display element, as described above, the pretilt angle is set to about 3 ° to 4 °. Thus, the angle θp is set smaller than the conventional one.

  The 1st polarizing plate 20 and the 2nd polarizing plate 30 radiate | emit the light which injects from the front side or back side as linearly polarized light along the transmission axis orthogonal to an absorption axis. Both polarizing plates are, for example, iodine-based polarizing plates (polarizing filters). The first polarizing plate 20 and the second polarizing plate 30 face each other, the first polarizing plate 20 is located on the side opposite to the liquid crystal layer 13 side of the first substrate 11, and the second polarizing plate 30 The two substrates 12 are located on the side opposite to the liquid crystal layer 13 side. In other words, the first polarizing plate 20 is located closer to the viewer 1 viewing the display element than the liquid crystal layer 13.

  When the liquid crystal display element 100 is viewed from the substrate normal direction, the absorption axis 21 of the first polarizing plate 20 (hereinafter referred to as F absorption axis 21) and the absorption axis 31 of the second polarizing plate 30 (hereinafter referred to as R absorption axis 31) The relationship is as shown in FIG. In addition, the reference | standard of the angle in FIG.3 (b) is the same as that of Fig.3 (a). That is, FIG. 3B is a diagram corresponding to FIG.

  Here, if the axis along the R liquid crystal molecule alignment direction 13b is the liquid crystal alignment axis D (note that the twist angle of the liquid crystal layer 13 is 180 °, it can also be said to be the axis along the F liquid crystal molecule alignment direction 13a). Specifically, the first polarizing plate 20 and the second polarizing plate 30 are set so as to satisfy the following conditions (1) to (3).

(1) The angle α1 (see FIG. 3B), which is an angle between the liquid crystal alignment axis D and the first absorption axis 21 and is an acute angle, is 45 ° or more. (2) The liquid crystal alignment axis D and the second angle. The angle α2 (see FIG. 3B) that is an acute angle with the absorption axis 31 is 45 ° or more. (3) The angle between the F absorption axis 21 and the R absorption axis 31 is an acute angle. The angle β (see FIG. 3B) is 85 ° or more and less than 90 °.

  For example, if the F absorption axis 21 is set along the 47 ° direction and the R absorption axis 31 is set along the 135 ° direction so as to satisfy these conditions, the angle β is 88 °. How the conditions (1) to (3) (hereinafter referred to as “liquid crystal alignment axis-absorption axis condition”) are determined will be described later.

  As shown in FIG. 1, the twisted phase difference plate (twisted phase difference film) 40 is located between the liquid crystal element 10 and the second polarizing plate 30, and includes both the first transparent portion 41 and the second transparent portion 42. And a liquid crystalline polymer layer 43 positioned between the two. The first transparent portion 41 is located closer to the liquid crystal element 10 than the second transparent portion 42. The twisted phase difference plate 40 is subjected to an alignment treatment so that the twist angle of the polymer molecules of the liquid crystalline polymer layer 43 is approximately 180 °. This alignment treatment is appropriately performed by a known method. Specifically, as shown in FIG. 3A, the alignment direction 43a of the polymer molecules at the position close to the first transparent portion 41 in the liquid crystalline polymer layer 43 (hereinafter referred to as F molecule alignment direction 43a) is In the 90 ° direction, the polymer molecule orientation direction 43b (hereinafter referred to as the R molecule orientation direction 43b) at a position close to the second transparent portion 42 is set to the 90 ° direction. That is, when viewed from the normal direction of the substrate, the R liquid crystal molecule alignment direction 13b and the F molecule alignment direction 43a are substantially orthogonal to each other.

  In the present embodiment, the F molecule orientation direction 43a is twisted by approximately 180 ° clockwise relative to the R molecule orientation direction 43b. That is, the twist direction of the polymer molecules is opposite to the twist direction of the liquid crystal molecules.

  The 1st transparent part 41 consists of a transparent film-like board | substrate, for example, and the liquid crystalline polymer layer 43 is formed with the liquid crystalline polymer apply | coated on one surface of this board | substrate. The twisted phase difference plate 40 is formed in this way as an example.

In the liquid crystal display element 100 according to this embodiment, the value of retardation Δnd1 of the liquid crystal layer 13 and the value of retardation Δnd2 of the liquid crystalline polymer layer 43 are set to be approximately equal. Thus, the front contrast (contrast in the substrate normal direction) of the liquid crystal display element 100 is improved. Specifically, for example, the refractive index anisotropy (birefringence index) Δn of the liquid crystal layer 13 is set to 0.149, and the cell gap d1 is set to 6.25 μm. In this case, the value of the retardation Δnd1, which is the product of the refractive index anisotropy Δn1 of the liquid crystal layer 13 and the cell gap (thickness of the liquid crystal layer 13) d1, is about 0.931 μm (see FIG. 4). On the other hand, the value of retardation Δnd2, which is the product of the refractive index anisotropy Δnd2 of the liquid crystalline polymer layer 43 and the thickness of the liquid crystalline polymer layer 43, is set to about 0.93 μm (see FIG. 4). As a result, the value obtained by subtracting Δnd2 from Δnd1 is 0.001, and it can be seen that both are set to be approximately equal.
The twisted phase difference plate 40 is, for example, a temperature-compensated twisted phase difference plate that can suppress a change in color even with respect to a temperature change, and the value of Δnd2 becomes smaller at a high temperature. ing. In this case, for example, in the range of −40 ° C. to 90 ° C., the value of retardation Δnd1 of the liquid crystal layer 13 and the value of retardation Δnd2 of the liquid crystalline polymer layer 43 are substantially equal.

  In this embodiment, the pretilt angle θp is set to be smaller than that of the conventional STN and the cell gap d1 is set to a value of 6.0 μm or more, thereby making the liquid crystal display element 100 more steep. Is improved well. As an example, the cell gap d1 is set to 6.25 μm (see FIG. 4). Note that the cell gap d1 is maintained by a spacer (not shown) provided between the first substrate 11 and the second substrate 12.

On the back side of the second polarizing plate 30, for example, a reflective layer (not shown) is provided. The reflection layer is made of a mirror or a half mirror, and the liquid crystal display element 100 is configured as a so-called reflection type or semi-transmission type. The liquid crystal display element 100 may be configured as a transmissive type that does not include a reflective layer and performs transmissive display using light from a backlight.
As described above, the liquid crystal display element 100 of the present embodiment transmits light in a region where the liquid crystal molecules of the liquid crystal layer 13 are in an initial alignment state (a state having chirality) by applying no voltage or applying an OFF voltage. In other words, it is configured as a so-called negative display type (normally black mode) that transmits light in a region where liquid crystal molecules rise due to application of an ON voltage.

  The liquid crystal display element 100 having the above configuration is mounted on a vehicle, for example, so that the contrast is good at the viewing angle from above (that is, the display from above is easy to see). ), Various conditions are set. Here, the viewing angle is an inclination angle θ of the line of sight by the observer 1 with respect to the substrate normal N as shown in FIG. Also, the azimuth angle φ shown in the figure is a counterclockwise angle of the orthogonal projection of the line of sight onto the substrate with respect to the axis along the left-right direction as viewed from the observer 1. That is, the liquid crystal display element 100 is set so that the contrast is good when the viewing angle from above, that is, the azimuth angle φ is near 90 ° and the viewing angle θ is greater than 0 °.

  Here, the isocontrast characteristics and front contrast (θ = 0 °) of the liquid crystal display element 100 are shown in FIG. The contrast is a value obtained by dividing the transmittance at the time of applying the ON voltage by the transmittance at the time of applying the OFF voltage, and the larger the value, the easier the display is to be seen. Note that, in the conditions in the figure, voltages that give the maximum contrast at 1/48 Duty and 1/4 Bias are applied, respectively. Here, as an example, the ON voltage 2.18 V and the OFF voltage 1.96 V in the conventional example, the ON voltage 2.42 V and the OFF voltage 2.18 V in the comparative example, and the ON voltage 2.60 V and OFF in the liquid crystal display element 100. The voltage is set to 2.34V.

As described above, in the liquid crystal display element 100, the pretilt angle θp is 0.5 °, the cell gap d1 is 6.25 μm, the retardation Δnd1 of the liquid crystal layer 13 is 0.931, and the retardation Δnd2 of the twisted phase difference plate 40 is 0.93. (Δnd1−Δnd2 = 0.001. That is, Δnd1≈Δnd2).
In FIG. 4, as a comparison object, only the value of the pretilt angle θp is different from that of the liquid crystal display element 100, and a comparative example in which θp = 3 ° is set larger, and the retardation Δnd2 of the twisted phase difference plate 40 is a liquid crystal display. Although the same as the device 100 and the comparative example, other values are different from the pretilt angle θp = 3 ° and the retardation Δnd1 = 0.954 of the liquid crystal layer 13 (Δn1 = 0.163, d1 = 5.85). The iso-contrast characteristics and front contrast characteristics for “Example” are also shown.
In FIG. 4, in any of the liquid crystal display element 100, the comparative example, and the conventional example, the F absorption axis 21 is along the direction of φ = 45 °, and the R absorption axis 31 is along the direction of φ = 135 °. It is set as follows. The liquid crystal display element 100 according to the present embodiment is configured so as to satisfy the above-mentioned “liquid crystal alignment axis-absorption axis condition”, but here, in particular, the pretilt angle θp, the cell gap d1, Δnd1−Δnd2 In order to confirm the effect due to the difference, the F absorption axis 21 of the liquid crystal display element 100 is set to φ = 45 °. Further, in the circular chart showing the isocontrast characteristics shown in FIG. 4, the numerical values (0, 45, 90, etc.) shown along the outer periphery of the circle represent the azimuth angle φ and correspond to the broken line extending concentrically. The indicated numerical values (10, 20, 30, etc.) represent the viewing angle θ.

First, comparing the conventional example and the comparative example, the comparative example in which the value of the cell gap d1 is larger than the conventional example is the upper viewing angle direction (the direction in which φ is in the vicinity of 90 ° and the viewing angle θ is greater than 0 °). It can be seen that the high contrast region C_hi having a contrast of 20.7 or more spreads well. Next, when comparing the comparative example and the liquid crystal display element 100, the liquid crystal display element 100 in which the pretilt angle θp is set smaller than the comparative example shows that the high contrast region C_hi spreads more favorably in the upper viewing angle direction. Recognize. On the other hand, if attention is focused on the low contrast region C_low having a contrast of 2.30 or less, the comparative example has a smaller area occupied by the low contrast region C_low than the conventional example, and the liquid crystal display element 100 has a lower contrast region than the comparative example. It can be seen that the range occupied by C_low is small. That is, in the liquid crystal display element 100, since the pretilt angle θp is set small (for example, 0.5 °), the steepness is improved, the contrast is improved, and the cell gap d1 is set large (example). 625 μm), it can be seen that the contrast is improved.
In addition, in the liquid crystal display element 100, the value of the retardation Δnd1 of the liquid crystal layer 13 is set to be substantially equal to the value of the retardation Δnd2 of the twisted phase difference plate 40. It can be seen that “99” is higher than “38” in the conventional example and “77” in the comparative example, and is excellent in display quality.

  That is, referring to FIG. 4, the liquid crystal display element 100 in which the pretilt angle θp is smaller than that of the conventional example, the cell gap d1 is increased, and Δnd1 and Δnd2 are set to be substantially equal, while maintaining a high front contrast. It can be seen that the contrast in the upper viewing angle direction is earned.

  In the description using FIG. 4, the F absorption axis 21 is φ = 45 ° and the R absorption axis 31 is φ = 135 °. However, from here, the F absorption axis 21 and the R absorption axis 31 are described. FIG. 5 and FIG. 6 show how much the contrast in a specific viewing angle direction can be maintained, that is, how the above-mentioned “liquid crystal alignment axis-absorption axis condition” is determined, no matter how much the axial direction is shifted. This will be described with reference to (a) and (b).

  FIG. 5 is a graph showing the relationship between the F absorption axis 21 angle and contrast when the viewing angle θ is changed by 10 ° in the range of 0 ° to 40 °. This graph is created based on the data shown in FIG.

  Note that the contrast shown in FIG. 6A is derived by simulation using simulation software “LCD MASTER ver. 8.1” manufactured by Shintec Corporation. The same applies to the equicontrast characteristics and the front contrast in FIG. 4 and the contrast shown in FIG. 6B. In this simulation, the cell gap d1 of the liquid crystal layer 13 was set to 6.25 μm. Further, the F liquid crystal molecular alignment direction 13a, the R liquid crystal molecular alignment direction 13b, the F molecular alignment direction 43a, and the R molecular alignment direction 43b satisfy the above-described relationship shown in FIG.

FIG. 6A shows an example in which the angle direction of the F absorption shaft 21 is changed in the range of 40 ° to 55 ° while the R absorption shaft 31 is kept in the 135 ° direction. The azimuth angle φ is 90 °.
In the same figure, attention is paid to a portion where the contrast becomes maximum at each viewing angle θ (a portion surrounded by a thick frame line). When the viewing angle θ is θ = 0 °, 99 (at this time, the F absorption axis 21 is in the 45 ° direction), 101 at θ = 10 ° (in this case, F absorption axis 21 is in the direction of 46 °), 95 at θ = 20 ° (at this time, F absorption axis 21 is 47 ° and 48 °), and 77 at θ = 30 ° (at this time F The absorption axis 21 is 49 ° and 50 °), and when θ = 40 ° is 50 (the F absorption axis 21 is 52 ° at this time). Referring to this result and the graph of FIG. 5, it can be seen that the viewing angle θ at which the contrast is maximized increases as the angle of the F absorption axis 21 is increased from 45 °. That is, it can be seen that if the angle is increased in this way, the display quality can be improved when the observer 1 looks into the liquid crystal display element 100 from above. However, when the F absorption axis 21 is 52 °, the contrast is as low as 50, and the viewing angle θ at this time is 40 °. It cannot be adopted as a product. Based on such considerations, the present inventors have found that the angle direction of the F absorption axis 21 is optimally in the range of 45 ° to 50 ° in a state where the R absorption axis 31 is maintained in the 135 ° direction. It was.

Conversely, when the angle direction of the R absorption shaft 31 is changed in a state where the F absorption shaft 21 is kept in the 45 ° direction, the relative positional relationship between the F absorption shaft 21 and the R absorption shaft 31 is the same. Therefore, it can be assumed that the result is similar to the result of FIG. For confirmation, the inventors of the present application changed the angle direction of the R absorption axis 31 in the range of 125 ° to 135 ° and performed a simulation in a state where the F absorption axis 21 was kept in the 45 ° direction. The simulation result at this time is shown in FIG.
Referring to FIG. 6B, it can be seen that the same contrast characteristics as in FIG. Also, since this is only for confirmation, the simulation when θ = 10 ° and θ = 40 ° is omitted here. Specifically, in FIG. 6B, when attention is paid to a portion where the contrast is maximum (location surrounded by a thick frame line) at each viewing angle θ, the viewing angle θ is 99 when θ = 0 ° (R at this time). The absorption axis 31 is in the direction of 135 °, 95 at θ = 20 ° (in this case, the R absorption axis 31 is 133 ° and 132 °), and 77 at θ = 30 ° (in this case, the R absorption axis 31 is 131 ° and 130 °). It has become. According to this result, it can be seen that as the angle of the R absorption axis 31 is decreased from 135 °, the viewing angle θ at which the contrast becomes maximum increases. That is, it can be seen that if the angle is reduced in this way, the display quality can be improved when the observer 1 looks into the liquid crystal display element 100 from above. Based on such considerations, the present inventors have found that the angle direction of the R absorption axis 31 is optimally in the range of 135 ° to 130 ° when the F absorption axis 21 is kept in the 45 ° direction. It was.

  6 (a) and 6 (b), the relative angular relationship between the F absorption axis 21 and the R absorption axis 31 is “the angle formed by the F absorption axis 21 and the R absorption axis 31”. If the angle β (see FIG. 3B), which is an acute angle, is 85 ° or more and less than 90 °, it can be seen that good contrast can be obtained when the viewing angle θ is in the range of 0 ° to 30 °. (Especially, 10 ° ≦ θ ≦ 20 ° is the best viewing direction since the contrast becomes the maximum value in the range of θ from 10 ° to 20 °). 3B, in addition to this, “the angle α1 that is the angle between the liquid crystal alignment axis D and the F absorption axis 21 and is an acute angle is 45 ° or more, and the liquid crystal alignment axis It can be seen that the condition that the angle α2 formed by D and the R absorption axis 31 and an acute angle α2 is 45 ° or more must also be satisfied. In this way, the above-mentioned “liquid crystal alignment axis-absorption axis condition” was derived.

  In the above description, an example has been described in which the contrast in the upper viewing angle direction (φ = 90 °) is improved satisfactorily, but the relative positional relationship among the F absorption axis 21, the R absorption axis 31, and the liquid crystal alignment axis D. Needless to say, if the image is rotated by a predetermined angle while maintaining the relationship shown in FIGS. 3A and 3B, the contrast and steepness in the desired viewing angle direction can be improved. For example, if 90 ° is rotated counterclockwise while maintaining the relationship shown in FIGS. 3A and 3B, the contrast in the left viewing angle direction (φ = 180 °) can be increased.

  The liquid crystal display element 100 described above includes a first substrate 11 and a second substrate 12 facing each other, a liquid crystal layer 13 positioned between the first substrate 11 and the second substrate 12, a first substrate 11 and a second substrate. A liquid crystal element 10 having transparent electrodes 11a and 12a that are provided on the surface of each substrate 12 on the liquid crystal layer 13 side and patterned in a predetermined shape, and on the opposite side of the first substrate 11 from the liquid crystal layer 13 side. The first polarizing plate 20 positioned, the second polarizing plate 30 facing the first polarizing plate 20 located on the side opposite to the liquid crystal layer 13 side of the second substrate 12, the liquid crystal element 10 and the second polarizing plate 30. And a twisted phase difference plate 40 having a liquid crystalline polymer layer 43, and a display element corresponding to the predetermined shape by applying a voltage to the liquid crystal layer 13 from the transparent electrodes 11a and 12a. Super twisted nematic liquid crystal display The liquid crystal molecules of the liquid crystal layer 13 are aligned at a twist angle of approximately 180 °, and the polymer molecules of the liquid crystalline polymer layer 43 are aligned at a twist angle of approximately 180 °. The twist direction of the liquid crystal layer 13 is opposite to the twist direction of the polymer molecules, the pretilt angle θp of the liquid crystal layer 13 is 0.2 ° or more and 1.0 ° or less, and the thickness of the liquid crystal layer 13 (cell gap d1). Is 6.0 μm or more, and the value of retardation Δnd1 of the liquid crystal layer 13 and the value of retardation Δnd2 of the liquid crystalline polymer layer 43 are substantially equal, and the twisted position of the liquid crystal layer 13 when viewed from the normal direction N of the substrate. The alignment direction of the liquid crystal molecules (R liquid crystal molecule alignment direction 13b) on the phase difference plate 40 side and the alignment direction of polymer molecules on the liquid crystal element 10 side (F molecular alignment direction 43a) among the liquid crystalline polymer molecules are substantially orthogonal to each other, and the liquid crystal Arrangement The angle α1 formed between the axis D and the F absorption axis 21 and an acute angle is 45 ° or more, and the angle α2 formed between the liquid crystal alignment axis D and the R absorption axis 31 is an acute angle α2. Is an angle formed by the F absorption axis 21 and the R absorption axis 31 and an acute angle β is not less than 85 ° and less than 90 °. According to this, as described above, the contrast and steepness in a specific viewing angle direction are good. In order to further increase the steepness, the pretilt angle θp is preferably 0.2 ° or more and 0.6 ° or less.

  In addition, this invention is not limited by said embodiment and drawing. Of course, changes (including deletion of components) can be added to these.

  In the above description, the example in which the twisted phase difference plate 40 is disposed between the liquid crystal element 10 and the second polarizing plate 30 has been described, but the twisted phase difference plate 40 may be disposed between the liquid crystal element 10 and the first polarizing plate 20. Good. The same effect can be obtained also by this.

  Further, the liquid crystal display element 100 is not limited to the segment display type, and may be a passive matrix type. In this case, a pixel (dot) is an example of a display element. Further, the liquid crystal display element 100 is not limited to a vehicle-mounted one, and can be applied to all devices that require high contrast in a specific viewing angle direction.

  In the above description, in order to facilitate understanding of the present invention, the description of known technical matters that are not important is omitted as appropriate.

100 liquid crystal display element 10 liquid crystal element 11 first substrate 11a transparent electrode 11b alignment film 12 second substrate 12a transparent electrode 12b alignment film 13 liquid crystal layer 13a F liquid crystal molecule alignment direction 13b R liquid crystal molecule alignment direction 20 first polarizing plate 21 F absorption Axis 30 second polarizing plate 31 R absorption axis 40 twisted phase difference plate 43 liquid crystal polymer layer 43a F molecule alignment direction 43b R molecule alignment direction D liquid crystal alignment axis

Claims (2)

A first substrate and a second substrate facing each other, a liquid crystal layer positioned between the first substrate and the second substrate, and a liquid crystal layer side surface of each of the first substrate and the second substrate. A liquid crystal element having a transparent electrode patterned into a predetermined shape,
A first polarizing plate located on a side opposite to the liquid crystal layer side of the first substrate;
A second polarizing plate located opposite to the liquid crystal layer side of the second substrate and facing the first polarizing plate;
A twisted phase difference plate having a liquid crystalline polymer layer located between the liquid crystal element and the first polarizing plate or between the liquid crystal element and the second polarizing plate;
A super twisted nematic liquid crystal display element that displays a display element corresponding to the predetermined shape by applying a voltage from the transparent electrode to the liquid crystal layer,
The liquid crystal molecules of the liquid crystal layer are aligned with a twist angle of about 180 °,
The polymer molecules of the liquid crystalline polymer layer are aligned with a twist angle of about 180 °,
The twist direction of the liquid crystal molecules is opposite to the twist direction of the polymer molecules,
The pretilt angle of the liquid crystal layer is 0.2 ° to 1.0 °,
The liquid crystal layer has a thickness of 6.0 μm or more,
The retardation value of the liquid crystal layer and the retardation value of the liquid crystalline polymer layer are substantially equal,
The orientation direction of the liquid crystal molecules on the twisted phase difference plate side of the liquid crystal layer and the liquid crystal element side of the liquid crystalline polymer molecules as viewed from the normal direction of the opposing surfaces of the first substrate and the second substrate. Is substantially perpendicular to the orientation direction of the polymer molecules of
The axis along the alignment direction of the liquid crystal molecules on the twisted phase difference plate side of the liquid crystal layer is a liquid crystal alignment axis, the absorption axis of the first polarizing plate is a first absorption axis, and the absorption axis of the second polarizing plate is As the second absorption axis,
The angle formed by the liquid crystal alignment axis and the first absorption axis, which is an acute angle, is 45 ° or more,
The angle formed by the liquid crystal alignment axis and the second absorption axis, which is an acute angle, is 45 ° or more,
The angle formed by the first absorption axis and the second absorption axis, which is an acute angle, is 85 ° or more and less than 90 °.
The liquid crystal display element characterized by the above-mentioned. The pretilt angle of the liquid crystal layer is 0.2 ° or more and 0.6 ° or less.
The liquid crystal display element according to claim 1.