JP2006085204A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device which has an excellent viewing field angle characteristic and permits high quality display. <P>SOLUTION: A pixel includes four-divided domains D constituted by arranging first, second, third and fourth domains (D1-D4), in which the alignment directions of liquid crystal molecules 30a located near the center in the thickness direction of liquid crystal layers are different from each other, in the order along a certain direction. A first substrate 10 comprises two first regions A1 having a regulation force that aligns liquid crystal molecules 30a in a first direction R1 and a second region A2 which has a regulation force of aligning the liquid crystal molecules 30a in a second direction opposite to the first direction and is disposed between the two first regions A1. A second substrate 20 comprises a third region A3 having a regulation force that aligns the liquid crystal molecules 30a in a third direction R3 intersecting the first direction R1 and a fourth region A4 having a regulation force that aligns the liquid crystal molecules 30a in a fourth direction R4 opposite to the third direction R3. The boundary between respective domains (D1-D4) is extended in the direction orthogonal to alignment directions of the respective domains (D1-D4). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device having a wide viewing angle characteristic.

  As a liquid crystal display device, a TN mode or an STN mode in which display is performed by eliminating a twisted alignment of liquid crystal molecules by applying a voltage to the liquid crystal layer, or a change caused by a change in the alignment state of the liquid crystal layer by applying a voltage. An ECB mode for performing display using a change in refractive index is widely used. However, these liquid crystal display devices have a drawback of poor viewing angle characteristics.

  On the other hand, as liquid crystal display devices become widespread, required characteristics are becoming increasingly strict. For example, the development of a liquid crystal display device having a wide viewing angle characteristic that is suitably used as a liquid crystal display device for portable information terminals, personal computers, word processors, amusement equipment, educational equipment, and television devices used by large numbers of people. It is strongly desired.

  As a method for improving the viewing angle characteristics of a liquid crystal display device, a so-called pixel division method (also called a multi-domain method) is known.

  For example, Kato et al. In Non-Patent Document 1 propose a TN alignment four-division method using a nematic (Np) liquid crystal material having positive dielectric anisotropy and a horizontal alignment film. It is described that the disclination line generated between domains, which is a problem in the TN-oriented pixel division method, does not occur when the four-division method of the above-mentioned document is used. However, a normally white mode (NW mode) TN liquid crystal display device generally tends to cause light leakage in a black display state, and it is difficult to realize a display with a high contrast ratio. This is because the liquid crystal molecules in the vicinity of the alignment film (sometimes referred to as “anchoring layer”) maintain the horizontal alignment state even when a voltage is applied. Therefore, as with other TN liquid crystal display devices, it is difficult for the 4-split TN liquid crystal display device disclosed in the above document to realize the high-quality display currently required.

On the other hand, in Patent Document 1, in the vertical alignment type liquid crystal display device, the liquid crystal molecules fall in the boundary region between the two domains whose directions in which the liquid crystal molecules fall are 180 ° different from each other. It is described that the viewing angle characteristic and the response characteristic of the liquid crystal display device are improved by forming a micro domain orthogonal to any of the directions in which the liquid crystal tilts. Further, since this liquid crystal display device is a vertical alignment type, there is no deterioration in the quality of black display generated in the above-described TN type liquid crystal display device.
JP-A-10-301113 IDW'97, p.163-p.166, "Four-Domain TN-LCD Display Using New Division Pattern and Special Arrangement"

  However, according to the study of the present inventor, the vertical alignment type liquid crystal display device disclosed in the above publication generates a disclination line between domains by turning on / off the voltage. As a result, there is a problem that when the display surface is observed from an oblique direction, the display is observed roughly in all azimuth directions. Furthermore, if the degree of occurrence of the disclination line is severe, there also arises a problem that the display quality depends on the viewing angle.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a liquid crystal display device that is excellent in viewing angle characteristics and capable of high-quality display.

  A liquid crystal display device according to the present invention includes a first substrate, a second substrate, a vertical alignment type liquid crystal layer provided between the first substrate and the second substrate, and a voltage for applying a voltage to the liquid crystal layer. A liquid crystal display device comprising: a voltage applying unit; and a plurality of picture elements each including the liquid crystal layer whose alignment state changes according to a voltage applied by the voltage applying unit, The liquid crystal layers in each of the first domain, the second domain, the third domain, and the fourth domain have different alignment directions of liquid crystal molecules located near the center in the thickness direction of the liquid crystal layer at least in a voltage application state. Includes four divided domains arranged in this order along a certain direction, and the first substrate has a regulating force to align the liquid crystal molecules of the liquid crystal layer in the first direction corresponding to the four divided domains. One second The second substrate having a region and a second region having a regulating force for aligning the liquid crystal molecules in a second direction opposite to the first direction and provided between the two first regions. Includes a third region having a regulating force for orienting the liquid crystal molecules in a third direction intersecting the first direction, and a third region having a regulating force for orienting the liquid crystal molecules in a fourth direction opposite to the third direction. And the boundary between the domains extends in a direction orthogonal to the arrangement direction of the domains, thereby achieving the above object.

  The first direction and the third direction are preferably orthogonal to each other.

  It is preferable that an angle formed by the first direction and the second direction, and the third direction and the fourth direction is in a range of 89 ° to 91 °.

  As described above, according to the present invention, a liquid crystal display device having excellent viewing angle characteristics and capable of high quality display is provided. Since the liquid crystal display device according to the present invention is excellent in response characteristics, high-quality moving image display can be realized.

  First, the configuration of a liquid crystal display device 100 according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 schematically shows one picture element of the liquid crystal display device 100.

  In the present specification, the region of the liquid crystal cell corresponding to the “picture element” that is the minimum unit of display is also referred to as “picture element” for simplicity. A picture element is defined by, for example, a picture element electrode in an active matrix type liquid crystal display device (for example, a TFT type liquid crystal display device) and a counter electrode facing the picture element electrode. In a simple matrix type liquid crystal display device, a striped column electrode (signal Electrode) and a row electrode (scanning electrode). In a plasma addressed liquid crystal display device, a picture element is defined by an intersection of a virtual electrode defined by a plasma channel and a column electrode facing the virtual electrode. The picture elements are typically arranged in a matrix composed of rows and columns, and constitute a display area.

  The liquid crystal display device 100 includes a first substrate (for example, a TFT substrate) 10, a second substrate (for example, a color filter substrate) 20, and a vertical alignment type liquid crystal layer provided between the first substrate 10 and the second substrate 20. 30. Between the first substrate 10 and the second substrate 20, electrode application means (not shown) for applying a voltage to the liquid crystal layer 30 is provided. In the present specification, a component for applying a voltage for display operation to a liquid crystal layer is referred to as a voltage applying unit, and not only an electrode pair in an active matrix type liquid crystal display device and a simple matrix type liquid crystal display device, but also a plasma address type. A combination of a virtual electrode and a column electrode of a liquid crystal display device is included.

  The vertical alignment type liquid crystal layer 30 is typically a vertical alignment film (not shown) in which a nematic liquid crystal material having a negative dielectric anisotropy is provided on the liquid crystal layer 30 side of the first substrate 10 and the second substrate. It is obtained by controlling the orientation. When no voltage is applied, the liquid crystal molecules 30a of the vertical alignment type liquid crystal layer 30 are substantially perpendicular (about 87 ° or more) to the surfaces of the vertical alignment films (the surfaces of the first substrate 10 and the second substrate 20). Oriented to When a voltage that generates an electric field in a direction perpendicular to the layer surface of the liquid crystal layer 30 is applied, a force that tilts the liquid crystal molecules 30a in a direction orthogonal to the direction of the electric field acts on the liquid crystal molecules 30a, causing the liquid crystal molecules 30a to collapse. At this time, the direction in which the liquid crystal molecules 30 a are tilted is determined by the alignment regulating force on the surfaces of the first substrate 10 and the second substrate 20. In FIG. 1, the liquid crystal molecules 30a are shown as cylinders, and the top or bottom surface of the liquid crystal molecules 30a is in front. FIG. 1 schematically shows a state in which a voltage for displaying a halftone is applied to the liquid crystal layer 30.

  The liquid crystal layer in each of the picture elements of the liquid crystal display device 100 of the present invention has at least a first domain D1 in which the alignment directions of the liquid crystal molecules located near the center in the thickness direction of the liquid crystal layer 30 are different from each other in a voltage applied state. , The second domain D2, the third domain D3, and the fourth domain D4 include four divided domains D arranged in this order along a direction (for example, a column direction). Typically, a picture element is a rectangle that is long in the column direction (vertical direction) and short in the row direction (horizontal direction), and in a color display device, the ratio of the lengths is about 3: 1. That is, red (R), green (G), and B (blue) columns are arranged side by side to form a pixel (color display pixel) having an aspect ratio of approximately 1: 1. Of course, the present invention is not limited to such a liquid crystal display device having a pixel arrangement, and the liquid crystal display device having various pixel arrangements is effective, and the dividing direction is not limited to the above example. For the sake of simplicity, an example will be described in which a vertically long picture element is divided in the column direction.

  In the liquid crystal display device of the present invention, each picture element is divided into a plurality of domains (including four divided domains) only along a certain direction (column direction is exemplified), and in the other directions Not divided. FIG. 1 shows a case where one picture element is occupied by one quadrant domain D, but the present invention is not limited to this, and may have additional domains, and two or more You may have 4 division domains.

  Hereinafter, the configuration of the four-divided domain D formed when a voltage is applied will be described with reference to FIGS. 2A to 2C together with FIG.

  2A indicates the alignment direction of the liquid crystal molecules 30a on the first substrate 10, and the arrow in FIG. 2B indicates the alignment direction of the liquid crystal molecules 30a on the second substrate 10, and FIG. The arrow c) indicates the alignment direction of the liquid crystal molecules 30a near the center in the thickness direction of the liquid crystal layer 30 (hereinafter referred to as “reference alignment direction” for simplicity). The reference orientation direction determines the viewing angle dependence of the domain. Each of the arrows shown in FIGS. 2A to 2C indicates the orientation direction (azimuth angle direction) when viewed along the normal direction from the substrate 20 side.

  The first substrate 10 has two first regions A1 having a regulating force to orient the liquid crystal molecules 30a in the first direction R1, and a regulating force to orient the liquid crystal molecules 30a in the second direction R2 opposite to the first direction R1. And a second region A2 provided between the two first regions A1. On the other hand, the second substrate 20 includes a third region A3 having a regulating force for aligning the liquid crystal molecules 30a in a third direction R3 intersecting the first direction R1, and a fourth direction opposite to the third direction R3. And a fourth region A4 having a regulating force to be oriented in R4.

  These regions (also referred to as “alignment regulation regions”) A1 to A4 having alignment regulating force can be formed by, for example, rubbing a vertical alignment film. The first direction R1 and the second direction R2 are parallel to the row direction, and the third direction and the fourth direction R4 are parallel to the column direction. That is, the rubbing process is performed on the first substrate 10 in two directions (antiparallel to each other), and the rubbing process is performed on the second substrate 20 in two directions (antiparallel to each other). Can be formed.

  As described above, the first region A1 / second region A2 / first region A1 are formed in this order along the column direction, and the third region A3 / fourth region A4 are arranged in this order. A quadrant domain D is formed by disposing the second substrate 20 formed along the line A as shown in FIG. 1 (and FIG. 2C). In other words, the first domain D1 is formed between the first region A1 and the third region A3, and the second domain D2 is formed between the second region A2 and the third region A3. The first substrate 10 is formed such that D3 is formed between the second region A2 and the fourth region A4, and the fourth domain D4 is formed between the other first region A1 and the fourth region A4. The second substrate 20 is disposed. The first direction R1 and the second direction R2 may be reversed from the illustrated example, and the third direction R3 and the fourth direction R4 may be reversed from the illustrated example. Further, the first substrate 10 and the second substrate 20 may be interchanged.

  The reference orientation directions of the four domains D1 to D4 in the quadrant domain D formed in this way are different from each other as shown in FIG. 1 and FIG. There are two types, twisted clockwise (D1 and D3) and counterclockwise (D2 and D4). The twist direction is a twist direction when viewed from the substrate 20 toward the substrate 10. Accordingly, the viewing angle dependency of each domain represented by the reference orientation direction is different from each other, and the viewing angle dependency of the liquid crystal display device 100 is averaged over all azimuth angle directions. In particular, as illustrated, when the first direction R1 and the third direction R3 are orthogonal to each other (inevitably, the second direction R2 and the fourth direction R4 are also orthogonal to each other), the viewing angle characteristics are more uniform. This is preferable. Further, as will be described later, the alignment of the liquid crystal molecules is stabilized, and the formation of disclination lines that are unstable and move with respect to the change of the electric field between the domains is suppressed or prevented. Further, from the viewpoint of alignment stability, the boundary between the domains (D1 to D4) (or the boundary between the alignment control regions (A1 and A2 and A3 and A4)) is preferably a direction orthogonal to the column direction. .

  Further, since the area ratio of each domain of the domains D1 to D4 affects the viewing angle characteristics of the entire display region, as illustrated, the first domain D1, the second domain D2, and the third domain D3 included in each picture element. It is preferable that the total area for each domain of the fourth domain D4 is equal to each other. Here, a case where one picture element is occupied by one quadrant domain D (substantially configured by only one quadrant domain D) is illustrated, and one quadrant domain D is illustrated. The areas of the first domain D1, the second domain D2, the third domain D3, and the fourth domain D4 are equal to each other. That is, as shown in FIG. 2A, the first substrate 10 has the first region A1 / second region A2 / first region A2 arranged in this order, and the area ratio is 1: 2: 1. In the second substrate 20, as shown in FIG. 2B, the third area A3 / the fourth area A4 are arranged in this order, and the area ratio is 2: 2. As a result, the first domain D1 / second domain D2 / third domain D3 / fourth domain D4 are arranged in this order, and a quadrant domain D having an area ratio of 1: 1: 1: 1 is formed. . Here, the area ratio is expressed in units of areas of the domains D1 to D4.

  The number of domains into which a picture element is divided can be appropriately set in consideration of the picture element size, display characteristics required for a liquid crystal display device, and the like. However, it is preferable to have at least one quadrant domain D (consisting of D1 to D4) in the picture element. When there are more domains, the four domains D1 to D4 are D1 / D2 / D3 / D4. It is preferable that the domains are formed according to this arrangement order (circularly) along the direction in which they are arranged in this order.

  For example, as shown in FIG. 3A, a first area A1 / second area A2 / first area A1 is formed on the first substrate 10 at an area ratio of 3: 4: 1. When the third region A3 / fourth region A4 / third region A3 are formed at an area ratio of 2: 4: 2, the first domain D1 / second domain D2 / third domain D3 / fourth domain D4 / first domain D1 is arranged in this order, and a domain having an area ratio of 2: 1: 3: 1: 1 is formed. Here, the area ratio is shown with the area of the second domain D2 as a unit.

  Of course, domains arranged in the order of the fourth domain D4 / first domain D1 / second domain D2 / third domain D3 / fourth domain D4 may be formed, and further second domain D2 and third domain D3 may be formed. It may be formed. Further, two or more quadrant domains D may be formed so that the arrangement order of D1 to D4 is cyclic. In any case, in order to realize uniform viewing angle characteristics, the total area of each domain of the first domain D1, the second domain D2, the third domain D3, and the fourth domain D4 included in each picture element. Are preferably equal to each other.

  Here, with reference to FIG. 2 and FIG. 3, a preferred form of pixel division will be described in detail.

  As shown in FIGS. 2 and 3, the liquid crystal display device of the present invention has a quadrant domain D in the picture element, and the quadrant domain D includes the first region A1 and the first region A1 formed in the first substrate 10. The second region A2 is formed by the alignment regulating force between the third region A3 and the fourth region A4 formed on the second substrate 20.

  In the configuration shown in FIG. 2, the length along the column direction of the second region A2 of the first substrate 10 and the third region A3 and the fourth region A4 of the second substrate 20 is y, respectively. When the length in the column direction of each of the two first regions A1 provided on both sides in the column direction of the ten second regions A2 is y / 2, the second region A2 and the second substrate of the first substrate 10 20 fourth regions A4 are arranged so as to overlap each other in the column direction by y / 2. As a result, when the length in the column direction of each of the domains D1 to D4 is x, the relationship x = y / 2 is established. A satisfactory quadrant domain D is formed. If the length of the picture element in the column direction is P, one quadrant domain D is formed in one picture element, so that the relationship P = 4x = 2y is satisfied.

  In FIG. 2, since one picture element is shown, the length in the column direction of the first region A1 is shown as y / 2. However, the picture elements are regularly arranged in a matrix. The first area A1 of the picture element is preferably formed continuously with the first area A1 of the picture element adjacent in the column direction. In this case, the length in the column direction is about y (strictly (y / 2) × 2 + pixel distance) is formed, and a part (equivalent to y / 2) is arranged so as to belong to each picture element. The same applies to the description of other arrangements of the orientation restriction regions. For simplicity, the distance between the picture elements is ignored, and the length in the column direction of each of the orientation restriction regions A1 to A4 may be represented by “y”.

  When the above relationship is satisfied, the areas of the domains D1 to D4 are equal to each other, so that uniform viewing angle characteristics can be realized. Of course, as described above, even when a plurality of four equally divided domains are included in one picture element, the total area of each domain D1 to D4 in each picture element is equal to each other. If the relationship of = 2ny (n is a positive integer of 1 or more) is satisfied, uniform viewing angle characteristics can be realized. However, since the effect of stabilizing the alignment may not be obtained if the length of one domain is too small, the length y in the column direction of the alignment control regions A1 to A4 is preferably 10 μm or more, and 50 μm. It is still more preferable that it is above.

  In general, it is preferable that the areas of a plurality of domains included in a picture element are equal to each other, but this is not always necessary. For example, in the configuration shown in FIG. 3, the length in the column direction of the second region A2 and the fourth region A4 is y, and the two first regions A1 formed on both sides in the column direction of the second region A2 The length in the column direction is 3y / 4 and y / 4, respectively, and the length in the column direction of the two third regions A3 formed on both sides in the column direction of the fourth region A4 is y / 2. The second region A2 and the fourth region A4 are arranged so as to overlap by 3y / 4 in the column direction, and as a result, the second domain D2 formed in the overlapping region of the second region A2 and the fourth region A4 If the length in the column direction is x, the first domain D1 / second domain D2 / third domain D3 / fourth domain D4 are in this order, and the length in the column direction is 2x / x / 3x / x. A quadrant domain D is formed. Further, following D4, the column direction First domain D1 is formed the length of further of x.

  Looking at the entire picture element thus divided, the total length (proportional to the area) of the first domain D1 in the column direction is 3x (= 2x + x), which is equal to the length of the third domain D3 in the column direction. . On the other hand, the length of the second domain D2 in the column direction and the length of the fourth domain D3 in the column direction are both equal to x. As can be seen from FIG. 3C, the reference orientation directions of the first domain D1 and the third domain D3 are antiparallel to each other, and the reference orientation directions of the second domain D2 and the fourth domain D4 are also antiparallel to each other. . Accordingly, the viewing angle characteristics of the first domain and the third domain D3 are complementary to each other, and the viewing angle characteristics of the second domain D2 and the fourth domain D4 are complementary to each other. Accordingly, the first domain D1 and the third domain D3 and / or the second domain D2 and the fourth domain may be used for all of the first domain D1 to the fourth domain D4 even if the total area for each domain is not equal to each other. If the areas of D4 are equal to each other, sufficient viewing angle characteristics may be obtained.

  Next, the mechanism by which the alignment of the liquid crystal molecules in the quadrant domain D is stabilized will be described with reference to FIGS. 4A to 4D.

  4A to 4D schematically show the alignment state of the liquid crystal molecules 30a of the liquid crystal layer 30 when a voltage is applied in the liquid crystal display device 100 shown in FIGS. The alignment directions of the liquid crystal molecules 30a are shown when the display surface is observed along the display surface normal from the substrate 20 side. 4A shows the vicinity of the boundary between the first domain D1 and the second domain D2, FIG. 4B shows the vicinity of the boundary between the second domain D2 and the third domain D3, and FIG. 4C shows the third domain D3 and the fourth domain D4. FIG. 4D shows the vicinity of the boundary between the fourth domain D4 and the first domain D1. In the example shown in FIGS. 1 and 2, since one picture element is occupied by one quadrant domain D, the vicinity of the boundary shown in FIG. Between the picture elements belonging to the matching row). In the configuration shown in FIG. 3, it exists in the picture element (in the figure, the lowermost part of the picture element).

  As shown in FIGS. 4A to 4D, a dividing line DL is formed between adjacent different alignment regulation regions. In the four divided domains formed in the picture element of the liquid crystal display device of the present invention, the dividing line DL formed on one substrate (the first substrate 10 or the second substrate 20) is always the other substrate (first substrate). The two substrates 20 or the first substrate 10) are arranged so as to face one alignment regulating region. The dividing line DL between the first region A1 and the second region A2 formed on the first substrate 10 shown in FIG. 4A faces the third region A3 formed on the second substrate 20, A dividing line DL between the third region A3 and the fourth region A4 formed on the second substrate 20 shown in 4B faces the second region A2 formed on the first substrate 10. In addition, the division line DL between the second region A2 and the first region A1 formed on the first substrate 10 illustrated in FIG. 4C faces the fourth region A4 formed on the second substrate 20. The dividing line DL between the fourth region A4 and the third region A3 formed on the second substrate 20 shown in FIG. 4D faces the first region A1 formed on the first substrate 10.

  Since the alignment control regions A1 to A4 are arranged as described above, the liquid crystal molecules 30a positioned on the dividing line DL of one substrate are aligned under the influence of the alignment control force of the alignment control region of the other substrate. . The orientation regulating directions of the first region A1 and the second region A2 formed on the first substrate 10 and the orientation regulating directions of the third region A3 and the fourth region A4 formed on the second substrate 20 intersect each other. (Preferably orthogonal to each other). Further, in order for the liquid crystal molecules 30a to take a continuous alignment, the width W of the dividing line DL having a certain finite length depending on the continuum property of the liquid crystal is necessary. The size of the liquid crystal molecules 30a is small. Therefore, the width W of the dividing line DL is very small compared to the length (width) y in the column direction of the facing alignment control region.

  With the relationship as described above, the liquid crystal molecules 30a existing in the dividing line DL are unidirectionally aligned, even if the voltage applied to the liquid crystal layer is switched at high speed, from the facing alignment control region. As a result of being influenced by the flow effect of the liquid crystal, the position of the divided domain DL does not move, and a reverse tilt domain occurs in each of the domains D1 to D4. It does not occur. According to the present invention, the orientation of the divided domains is thus stabilized. In order to sufficiently obtain this stabilizing effect, the orientation regulating directions (R1 and R2) of the first region A1 and the second region A2, and the orientation regulating directions (R3 and R4) of the third region A3 and the fourth region A4 Is preferably in the range of about 89 ° to about 91 °, more preferably about 90 °.

  Since the liquid crystal display device 100 of the present invention includes the vertically aligned liquid crystal layer 30, it is preferable to perform display in a normally black mode (abbreviated as NB mode). When displaying in the NB mode, a display with a higher contrast ratio can be realized as compared with a conventional TN type NW mode liquid crystal display device.

  The viewing angle characteristics of the NB mode liquid crystal display device 100 including the vertical alignment type liquid crystal layer can be further improved by providing a polarizing plate and a phase difference compensation element as follows.

  A pair of polarizing plates (not shown) are arranged in a crossed Nicol state so as to face each other with the first substrate 10 and the second substrate 20 interposed therebetween, and the pair of polarizing plates and the first substrate 10 and the second substrate 20 A phase difference compensation element (not shown) is provided between at least one of the above. The slow axis of this retardation compensation element is in the layer surface of the liquid crystal layer 30 (parallel to the substrates 10 and 20), and the absorption axis of the polarizing plate disposed on the viewer side of the pair of polarizing plates ( What is necessary is just to arrange | position a phase difference compensation element so that it may orthogonally cross (perpendicular to a polarization axis). In particular, if a retardation compensation element is provided between both polarizing plates and the substrate, and the slow axis of each retardation compensation element is arranged so as to be orthogonal to the absorption axis of the closer polarizing plate, Viewing angle characteristics (polar angle (angle from display surface normal) dependency) in the 45 ° direction (azimuth angle direction) with respect to the absorption axis of the polarizing plate are greatly improved, and a good viewing angle in all directions. Characteristics can be obtained.

  Specifically, for example, the retardation of the liquid crystal layer 30 is set to 340 nm, and the slow axis of the phase difference compensation element is arranged between the pair of polarizing plates and the substrate so as to be orthogonal to the absorption axis of the closer polarizing plate, respectively. To do. At this time, the in-plane retardation Re (= df · (nx−ny)) of the phase difference compensation element is changed within a range of 0 to 50 nm, and the normal retardation Rth (= df · (nx−nz)) is changed within a range of 0 to 150 nm. When the contrast ratio in each viewing angle direction with polar angles of 40 ° and azimuth angles of 0 °, 45 °, 90 °, and 135 ° is measured, the results shown in FIGS. 5 and 6 are obtained. Here, df is the thickness of the phase difference compensation element, nx and ny are in-plane main refractive indexes, and nx is the main refractive index in the surface normal direction. Moreover, it has a relationship of nx> ny> nz.

  As is clear from FIGS. 5 and 6, the contrast ratio in the azimuth direction of 0 ° and 90 ° with respect to the absorption axis direction of the polarizing plate is constant regardless of the polar angle, but is 45 ° and 135 °. The contrast ratio in the azimuth direction of ° depends on the polar angle and shows a maximum value. When the value of the in-plane retardation Re is in the range of 36 nm to 43 nm and the value of the normal retardation Rth is in the range of 110 nm to 130 nm, a substantially isotropic contrast ratio can be realized in all directions. Further, the optimum values at this time are an in-plane retardation Re value of 39 nm and a normal retardation Rth value of 122 nm. Here, the optimum value of the retardation when the phase difference compensation element is provided on both sides of the liquid crystal layer has been described. However, when the phase difference compensation element is provided only on one side, the phase difference having the retardation twice the above value is provided. A compensation element may be used. As the liquid crystal layer, those having a retardation in the range of 250 nm to 400 nm can be suitably used.

  Furthermore, by setting the thickness of the liquid crystal layer 30 to 4 μm or less, a good response speed can be realized. Specifically, the sum of the time required for the transmittance to change from 0% to 90% (Ton in the NB mode) and the time required for the transmittance to change from 100% to 10% (Toff in the NB mode) Can be set to 16.6 msec or less. The thickness of the liquid crystal layer 30 is preferably in the range of 3 μm to 4 μm.

  Next, a method for manufacturing a liquid crystal display device according to the present invention will be described.

  As described above, the quadrant of the present invention includes two types of alignment control regions A1 and A2 formed on the first substrate 10 and two types of alignment control regions A3 and A4 formed on the second substrate 20. Formed by a combination of Further, the four orientation regulation regions are arranged in a certain order along the column direction. Accordingly, the first region A1 and the second region A2 extending along the row direction are alternately provided along the column direction on the surface of the first substrate 10 on the liquid crystal layer 30 side, and the liquid crystal layer 30 side of the second substrate 20 is provided. The third region A3 and the fourth region A4 extending in the row direction are alternately provided on the surface of the substrate along the column direction, and the first substrate 10 and the second substrate 20 are provided with the alignment control regions A1 to A4 in each picture element. Correspondingly, they may be bonded so as to have the above-described arrangement relationship. If the distance between the picture elements is ignored, the length in the column direction of each of the orientation regulation regions A1 to A4 is y. That is, the quadrants according to the present invention are formed in stripes so that the alignment control regions A1 to A14 are formed in parallel to the rows and penetrate through a plurality of picture elements constituting one row of the plurality of picture elements. Can be realized.

  An embodiment of a method for manufacturing a liquid crystal display device according to the present invention will be described with reference to FIGS.

  First, a substrate (for example, a glass substrate) 11 to be the first substrate 10 and the second substrate 20 is prepared. As shown in FIG. 5A, a vertical alignment film 12 is formed on the substrate 11 and rubbed in one direction. Here, an example of rubbing toward the front of the page is shown.

  Thereafter, as shown in FIG. 7B, a photosensitive resin layer 13 is formed so as to cover the entire surface of the alignment film 12 that has been subjected to the first rubbing treatment.

  The photosensitive resin layer 13 is patterned by exposing and developing using a predetermined photomask as shown in FIG. 7C. At this time, typically, strip-shaped openings 13a having a width y (for example, corresponding to the second region A2 or the fourth region A4) are provided in parallel at intervals of y + dy (dy is a distance between picture elements). At this time, the region covered with the photosensitive resin layer 13 includes, for example, a region that becomes the first region A1 or the third region A3. In this state, a second rubbing process is performed on the vertical alignment film 12 exposed in the opening 13a. The rubbing direction is opposite (antiparallel) to the first rubbing direction. If the picture element division pattern according to the present invention is adopted, it is only necessary to form stripes parallel to the row direction, so that there is no need to align the photomask in directions other than the division direction (column direction here). The advantage that it can be manufactured easily is also obtained.

  Thereafter, by peeling off the photosensitive resin layer 13, as shown in FIG. 7D, the first substrate 10 or the second substrate 20 can be obtained.

  In addition, each process of said description can be performed by a well-known method. Further, instead of the so-called split rubbing process described above, a known method such as a so-called mask rubbing process using a metal hard mask or a so-called photo-alignment process for controlling a pretilt angle by irradiating UV light from an oblique direction is used. Even if it is used, an equivalent result can be obtained.

  Maintaining a predetermined cell gap (corresponding to the thickness of the liquid crystal layer 30) with the first substrate 10 and the second substrate 20 obtained as described above facing the surface on which the vertical alignment film 13 is formed inside. A liquid crystal cell is obtained by bonding to each other via a spacer (for example, 3.5 μm). At this time, the division rubbing process is performed so that the areas subjected to the rubbing process in the antiparallel direction overlap each other in a predetermined arrangement relationship as described above (for example, the y / 2 widths overlap). The spacer is preferably provided in a dot shape in a region other than the picture element (for example, a region where a black matrix is formed) using a photosensitive resin or the like.

  A liquid crystal material is injected into the obtained liquid crystal cell. The retardation of the liquid crystal cell is preferably in the range of 250 nm to 400 nm. In order to make the thickness of the liquid crystal layer 4 μm or less, it is preferable to use one having a birefringence (Δn) of 0.07 or more. When such a liquid crystal layer is used, it is possible to obtain a liquid crystal display device with improved viewing angle characteristics and excellent response characteristics due to the above-described retardation compensation element.

  The step of injecting the liquid crystal material can be performed by a known method. However, after the liquid crystal material is injected, the liquid crystal cell is kept at a temperature equal to or higher than the Tni point (nematic-isotropic liquid transition temperature) of the liquid crystal material (preferably a temperature higher by 10 ° C. than the Tni point) for a certain time (for example, 10 minutes). ) It is preferable to hold above and then cool to room temperature (25 ° C.). The temperature decreasing rate is preferably 10 ° C./min or less, more preferably 10 ° C./hour or less. As described above, by performing the realignment treatment, it is possible to form a divided domain having a uniform alignment state over the entire display region.

<Example>
(Example 1)
A TFT type liquid crystal display device having the picture elements of the divided alignment pattern described in the above embodiment with reference to FIGS. 1 and 2 is manufactured. The division direction is the column direction, and one picture element region is substantially occupied by one quadrant domain. Since the basic configuration is the same as that of the above-described liquid crystal display device 100, the same reference numerals are used and detailed description thereof is omitted here.

  A well-known thing can be widely used for the TFT substrate used as the 1st board | substrate 10, and the color filter board | substrate used as the 2nd board | substrate 20, respectively. First, an example using the above-described divided rubbing method will be described with reference to FIG.

  The vertical alignment film 12 having a thickness of 60 nm is formed on the TFT substrate and the color filter substrate using, for example, a polyimide-based vertical alignment film material (for example, JALS-682) manufactured by JSR. The vertical alignment film 12 is subjected to a uniaxial rubbing process (first time) in a predetermined direction, washed with pure water, and then a photosensitive film having a film thickness of 0.5 μm using a positive resist (for example, S1805) manufactured by Sibley. A resin layer 13 is formed.

  The photosensitive resin layer 13 is exposed through a photomask having a predetermined stripe pattern, for example, with a mask exposure apparatus manufactured by Dainippon Kaken Co., Ltd., with an exposure amount of 35 mJ (center wavelength: 365 nm). Thereafter, the photosensitive resin layer 13 is patterned by developing using, for example, an MP-DEV inorganic alkaline developer manufactured by Shibley, and the stripe-shaped openings 13a are formed.

  Thereafter, a second uniaxial rubbing process is performed on the vertical alignment film 12 exposed in the opening 13a of the photosensitive resin layer 13 in the direction opposite to the first time. Thereafter, the photosensitive resin layer 13 is peeled off using a peeling liquid (eg, a 10% aqueous solution of NaOH).

  Note that the first and second rubbing processes are preferably executed under the following conditions, for example. For example, YA-18-R manufactured by Yoshikawa Kogyo Co., Ltd. (hair leg 1.8 mm) is used as the rubbing cloth, and the push-in amount is 0.4 mm, the roller rotation speed is 300 mm / min, the stage speed is 100 mm / sec, and the number of times is 5 times. it can. This condition is a soft labin condition in which no rubbing streaks are generated, and it is preferable to carry out at a high rubbing density.

  When the photo-alignment process is used, for example, it is executed as follows.

  First, a vertical alignment film having a film thickness of 100 nm is formed on a TFT substrate and a color filter substrate using, for example, a vertical alignment film material RN-1338 manufactured by Nissan Chemical Industries.

This vertical alignment film is irradiated on the entire surface with polarized UV (center wavelength 313 nm) polarized using a dielectric mirror at a density of 1 J / cm ² . From the viewpoint of retention rate, the density of the UV irradiation light amount is preferably 1 J / cm ² or less. Thereafter, the polarized UV is irradiated from, for example, a 45 ° direction with respect to the normal line of the substrate according to a predetermined pattern through a quartz photomask. However, the irradiation direction of the polarized UV is not limited to 45 ° and may be inclined with respect to the normal line of the substrate (other than 0 ° and 90 °). When this method is used, the liquid crystal molecules are aligned in a direction orthogonal to the polarization direction of the polarized UV, so that the quadrant domain can be formed by changing the polarization direction of the polarized UV for each region.

  Thereafter, the TFT substrate and the color filter substrate are bonded so that the cell gap is 3.5 μm, and a liquid crystal material is injected into the obtained liquid crystal cell. As a liquid crystal material, for example, MJ001025 (Δn = 0.0916, Δε = −2.4, Tni = 80 ° C.), which is an Nn liquid crystal manufactured by Merck Co., is injected and sealed while heating the liquid crystal cell to about 60 ° C. . Thereafter, as a realignment treatment step, the liquid crystal cell is held in an oven set at about 120 ° C. for about 10 minutes, and then slowly cooled to room temperature (25 ° C.) at a temperature decrease rate of 10 ° C./hour.

  The pretilt angle of the liquid crystal molecules of the exemplified liquid crystal cell thus obtained was 88 °. As a result of various studies, it was found that the pretilt angle of the liquid crystal molecules is preferably 88 ° or more (<90 °) in order to stably form the divided domains. This is because the pretilt angle (that is, the development of the force that regulates the alignment direction) and the resistance to pure water cleaning, the solvent resistance of the resist, and the alkali developer resistance due to the alignment treatment (rubbing treatment, photo-alignment treatment, etc.). It is thought that this also depends on the chemical properties of the alignment film.

  Next, a polarizing plate and a phase difference compensation element are arranged in the obtained liquid crystal cell to produce an NB mode liquid crystal display device.

  Here, as the retardation compensation element, for example, a retardation compensation film (in-plane retardation 39 nm, normal retardation 122 nm) formed from a biaxially stretched film of norbornene resin or a liquid crystal polymer film is used. One sheet is arranged between each and the substrate.

  The viewing angle characteristics (equal contrast / contour) of the liquid crystal display device obtained as described above are shown in FIG. As is apparent from FIG. 8, a good display is realized over all 360 ° azimuth angles. Although not shown in FIG. 8, a display with a contrast ratio (CR) of 10 or more was realized in a range of polar angles ± 80 ° or more in all azimuth directions.

  Further, as shown in FIG. 9, the voltage-transmittance characteristic of this liquid crystal display device is steep and can display a good contrast ratio in the range of 2.5V to 6V. Further, it can be seen that the response time Ts of this liquid crystal display device is 13 msec, and the moving image display characteristics are excellent. The response time in the halftone display was 18 msec.

  Furthermore, the results of evaluating the gradation display characteristics of this liquid crystal display device are shown in FIGS. The polarities (angles from the normal line) dependence of transmittance in eight gradation display states in order from the black side are indicated by curves L1 to L8. FIG. 10 shows the result when the azimuth angle is 0 °, and FIG. 11 shows the result when the azimuth angle is 45 °.

  As is clear from the comparison between FIG. 10 and FIG. 11, it can be seen that the polar angle dependence of the transmittance is small in any azimuth angle direction, and the polar angle dependences in the bilateral angle directions are close to each other. Thus, it can be seen that the liquid crystal display device of this embodiment can achieve good display in all azimuth directions even in halftone display.

(Example 2)
In this embodiment, an example in which the present invention is applied to a plasma addressed liquid crystal display device (abbreviated as PALC) will be described.

  A PALC 200 shown in FIG. 12 includes a liquid crystal layer 230 and a plasma address substrate 210 and a color filter substrate 220 provided to face each other with the liquid crystal layer 230 interposed therebetween.

  The plasma address substrate 210 is formed of a plasma support substrate (eg, a glass substrate) 211, a dielectric sheet (eg, thin glass) 212, and a partition wall (eg, glass frit) provided between the plasma support substrate 211 and the dielectric sheet 212. 213), and a striped space surrounded by these is filled with ionizable gas, and this space constitutes the plasma channel 214. A cathode 215C and an anode 215A are formed in the plasma channel 214, and a voltage is applied to the gas in the plasma channel 214 to generate plasma discharge. The plasma channel 214 functions as, for example, a scanning line. The dielectric sheet 212 of the plasma substrate 210 is disposed on the liquid crystal layer 230 side, and a vertical alignment film 216 is provided on the surface of the liquid crystal layer 230 side.

  The color filter substrate 220 includes a transparent substrate (for example, a glass substrate) 222 having a color filter layer (not shown), a counter electrode 224, and a vertical alignment film 226 provided on the counter substrate 224. The counter electrode 224 is a striped electrode and is disposed so as to intersect the plasma channel 214. A region where these intersect each other constitutes a picture element. The counter electrode 224 functions as a signal line, for example.

  When a plasma discharge occurs in the plasma channel 214 due to the voltage applied between the cathode 215C and the anode 215A, the surface of the dielectric sheet 212 on the side of the plasma channel 214 becomes the potential of the cathode via the plasma channel 214 in a discharge state. Become. A surface (referred to as a lower surface) of the dielectric sheet 212 on the plasma channel 214 side functions as a virtual electrode. That is, a voltage between the lower surface (virtual electrode) of the dielectric sheet 212 and the counter electrode 224 is applied to the dielectric sheet 212 and the liquid crystal layer 230, and a voltage determined by the capacitance ratio is applied to the liquid crystal layer 230. Is done. Accordingly, the thinner the dielectric sheet 212 is, the higher the voltage applied to the liquid crystal layer 230 is. Further, in order to prevent deterioration of the liquid crystal material due to ultraviolet rays (wavelength: 250 nm to 350 nm) generated in the plasma channel 214, a material that blocks the ultraviolet rays is mixed in the dielectric sheet 212, or the dielectric sheet 212 It is preferable to apply to the surface.

  PALC200 is manufactured by a well-known method. In addition, the present invention can be applied to known PALCs other than those described above. Here, a PALC 200 having a quadrant domain for each picture element was manufactured in the same manner as in Example 1 using a dielectric sheet 212 having a thickness of 30 μm, 40 μm, and 50 μm.

  The voltage-transmittance characteristics of the obtained PALC 200 are shown in FIG. As is apparent from FIG. 13, each PALC 200 has a steep voltage-transmittance characteristic. The response time Ts was 16 msec when the thickness of the dielectric sheet 212 was 50 μm, and 10 msec when the thickness was 30 μm. It can be seen that both have a response speed that can be sufficiently applied to moving image display. As for the viewing angle characteristics, a display with a contrast ratio of 10 or more was realized in a range of polar angles of ± 70 ° or more in all azimuth directions.

  In addition, the orientation of the liquid crystal molecules was stable, and almost no disclination line was observed.

(Example 3)
As shown in FIG. 3, a liquid crystal display device was produced in the same manner as in Example 1 except that a plurality of domains (including the quadrant domain D) were formed in the picture element. FIG. 14 shows the viewing angle characteristics (equal contrast / contour) of the obtained liquid crystal display device.

  Compared with the viewing angle characteristics of the liquid crystal display device of Example 1 shown in FIG. 8, the azimuth angle dependence of the contrast ratio is slightly larger, but good display was realized in almost all azimuth directions. Further, the response speed was almost the same as that of the liquid crystal display device of Example 1, the alignment of the liquid crystal molecules was stable, and the occurrence of disclination lines was hardly observed.

(Comparative Example 1)
As shown in FIG. 15, a liquid crystal display device was produced in the same manner as in Example 1 except that a two-divided domain was formed in the picture element. Each picture element of the liquid crystal display device has only the first domain D1 and the third domain D3. That is, unlike the four-divided domain D of the liquid crystal display devices of the first and second embodiments, the second domain D2 and the fourth domain D4 are not formed in the picture element, and the first domain D1 and the third domain D3 Are adjacent to each other.

  FIG. 16 shows the viewing angle characteristics (equal contrast / contour) of the obtained liquid crystal display device. As is clear from the comparison between FIG. 16 and FIG. 8 and FIG. 14, the viewing angle characteristics of the liquid crystal display device of Comparative Example 1 are more dependent on the azimuth angle than the liquid crystal display devices of Example 1 and Example 2. The viewing angle is narrow in the range where good display can be realized. In addition, the alignment stability of the liquid crystal molecules is low, and the occurrence of disclination may be observed between the first domain D1 and the third domain D3.

  Furthermore, a 90 ° twisted TN liquid crystal display device having substantially the same configuration as that of the liquid crystal display device of Example 1 and without alignment division was produced, and the display characteristics were evaluated. However, as the alignment film, a horizontal alignment film (for example, AL4552) was used, and a nematic liquid crystal material (for example, MS90847) having positive dielectric anisotropy was used.

  The response time Ts speed of the obtained liquid crystal display device was 16 msec as in the case of the liquid crystal display device of Example 1, but the viewing angle dependency was large, and in particular, the color tone of color display greatly depended on the viewing angle and was good. The viewing angle range where a good display can be obtained was very narrow.

(Comparative Example 2)
The liquid crystal display device of Comparative Example 2 is an ECB mode liquid crystal display device having four divided domains, and is the same as the liquid crystal display device of Example 1 except that a four divided domain D ′ is formed as shown in FIG. It is.

  The four-divided domain D ′ of the liquid crystal display device of Comparative Example 2 is different from the four-divided domain D of Example 1 shown in FIG. 2, and the four domains are formed by four alignment regulation regions formed on the respective substrates. Has been. That is, the boundaries of the four domains D′ 1, D′ 2, D′ 3, and D′ 4 coincide with the boundaries of the alignment control regions formed on both substrates. As a result, the alignment of the liquid crystal molecules became unstable, and a disclination line was generated between the four domains D'1, D'2, D'3 and D'4, and the display quality was lowered. Furthermore, the response time Ts was about 25 msec, which is longer than 16 msec of the liquid crystal display devices of the first and second embodiments, and was found to be unsuitable for moving image display.

  Further, in the process for forming the quadrant domain, it is necessary to perform the photolithography process (application of the photosensitive resin layer, exposure, development, and peeling) twice for each substrate in order to define the domain formation region. As a result, the manufacturing process became complicated and there was a concern about damage to the vertical alignment film.

  As described above, the present invention is useful for liquid crystal display devices for portable information terminals, personal computers, word processors, amusement equipment, educational equipment, television devices, and particularly, high viewing angle characteristics. Suitable for displaying quality.

It is sectional drawing which shows typically the liquid crystal display device 100 by embodiment of this invention. (A), (b), and (c) are the schematic diagrams for demonstrating the structure of the 4-partition domain D formed in the pixel of the liquid crystal display device 100. FIG. (A), (b), and (c) are the schematic diagrams for demonstrating the structure of the other divided domain formed in the pixel of the liquid crystal display device by embodiment. 4 is a schematic diagram for explaining a mechanism by which the alignment of liquid crystal molecules in the quadrant domain D is stabilized. FIG. 4 is a schematic diagram for explaining a mechanism by which the alignment of liquid crystal molecules in the quadrant domain D is stabilized. FIG. 4 is a schematic diagram for explaining a mechanism by which the alignment of liquid crystal molecules in the quadrant domain D is stabilized. FIG. 4 is a schematic diagram for explaining a mechanism by which the alignment of liquid crystal molecules in the quadrant domain D is stabilized. FIG. It is a graph which shows the in-plane retardation Re (= df * (nx-ny)) dependence of the phase difference compensation element of the contrast ratio of the liquid crystal display device by embodiment of this invention. It is a graph which shows the normal line retardation Rth (= df * (nx-nz)) dependence of the phase difference compensation element of the contrast ratio of the liquid crystal display device by embodiment of this invention. (A), (b), (c) and (d) is typical sectional drawing for demonstrating embodiment of the manufacturing method of the liquid crystal display device by this invention. 3 is an equal contrast contour showing viewing angle characteristics of the liquid crystal display device of Example 1. FIG. 3 is a graph showing voltage-transmittance characteristics of the liquid crystal display device of Example 1. FIG. 4 is a graph showing polar angle dependency (azimuth angle 0 ° direction) of gradation display characteristics of the liquid crystal display device of Example 1; 4 is a graph showing polar angle dependency (azimuth angle 45 ° direction) of gradation display characteristics of the liquid crystal display device of Example 1. FIG. 6 is a schematic cross-sectional view showing the structure of a PALC 200 of Example 2. FIG. 6 is a graph showing voltage-transmittance characteristics of the PALC 200 of Example 2. 10 is an equal contrast contour showing the viewing angle characteristic of the liquid crystal display device of Example 3. 6 is a schematic diagram for explaining a configuration of divided domains of the liquid crystal display device of Comparative Example 1. FIG. 4 is an equi-contrast contour showing the viewing angle characteristics of the liquid crystal display device of Comparative Example 1. 10 is a schematic diagram for explaining a configuration of divided domains in a liquid crystal display device of Comparative Example 2. FIG.

Explanation of symbols

10 First substrate 11 Substrate (glass substrate)
12 vertical alignment film 13 photosensitive resin layer 13a opening 20 second substrate 30 liquid crystal layer 30a liquid crystal molecule 100 liquid crystal display device 200 PALC
A1 1st area (orientation regulation area)
A2 2nd area (orientation regulation area)
A3 3rd area (orientation regulation area)
A4 4th area (orientation regulation area)
D 4 divided domain D1 1st domain D2 2nd domain D3 3rd domain D4 4th domain

Claims (3)

A first substrate; a second substrate; a vertical alignment type liquid crystal layer provided between the first substrate and the second substrate; a voltage applying means for applying a voltage to the liquid crystal layer; A plurality of picture elements each including the liquid crystal layer whose alignment state changes according to the voltage applied by the means,
The liquid crystal layer in each of the plurality of picture elements includes a first domain, a second domain, and a second domain in which the alignment directions of liquid crystal molecules located near the center of the thickness direction of the liquid crystal layer are different from each other at least in a voltage application state 3 domains and a 4th domain include a quadrant domain arranged in this order along a direction,
Corresponding to the four-divided domains, the first substrate has two first regions having a regulating force for aligning the liquid crystal molecules of the liquid crystal layer in the first direction, and the liquid crystal molecules are opposite to the first direction. And a second region provided between the two first regions, wherein the second substrate intersects the liquid crystal molecules with the first direction. A third region having a regulating force to orient in three directions, and a fourth region having a regulating force to orient the liquid crystal molecules in a fourth direction opposite to the third direction;
The boundary between the domains extends in a direction orthogonal to the arrangement direction of the domains.   The liquid crystal display device according to claim 1, wherein the first direction and the third direction are orthogonal to each other.   2. The liquid crystal display device according to claim 1, wherein an angle formed by the first direction and the second direction and the third direction and the fourth direction is in a range of 89 ° to 91 °.

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