WO2017154680A1 - Liquid crystal display device - Google Patents

Abstract

This liquid crystal display device (100) is provided with a liquid crystal display panel (1) that comprises a first substrate (10), a second substrate (20) and a liquid crystal layer (30). The first substrate comprises a first electrode (11), which is provided in each pixel, and a second electrode (12) that generates, together with the first electrode, a transverse electric field in the liquid crystal layer. The second substrate comprises a third electrode (21) which generates, together with the first electrode and the second electrode, a vertical electric field in the liquid crystal layer. In a state where a transverse electric field is generated in the liquid crystal layer, liquid crystal molecules (31) in the liquid crystal layer are twist-aligned. The thickness d of the liquid crystal layer and the natural chiral pitch p of the liquid crystal layer satisfy the relational expression 1 ≤ p/d ≤ 3. The dielectric anisotropy ∆ε of a liquid crystal material contained in the liquid crystal layer is from 16 to 25 (inclusive).

Description

Liquid crystal display

The present invention relates to a liquid crystal display device.

In recent years, see-through displays have attracted attention as display devices for information displays and digital signage. In the see-through display, the background (the back side of the display panel) can be seen through, so that the information displayed on the display panel and the background can be superimposed. Therefore, the see-through display is excellent in appealing effect and eye catching effect. It has also been proposed to use a see-through display for a showcase or a show window.

When a liquid crystal display device is used as a see-through display, its light utilization efficiency is low. The low light use efficiency of the liquid crystal display device is caused by a color filter or a polarizing plate provided in a general liquid crystal display device. The color filter and the polarizing plate absorb light in a specific wavelength range and light in a specific polarization direction.

Therefore, it is conceivable to use a field sequential type liquid crystal display device. In the field sequential method, color display is performed by switching the color of light emitted from the illumination element to the liquid crystal display panel in a time-sharing manner. This eliminates the need for a color filter and improves the light utilization efficiency. However, in the field sequential method, high-speed response is required for the liquid crystal display device.

Patent Documents 1 and 2 disclose liquid crystal display devices having improved response characteristics by providing an electrode structure that can be generated by switching a vertical electric field and a horizontal electric field in a liquid crystal layer. In the liquid crystal display devices disclosed in Patent Documents 1 and 2, in one of the transition from the black display state to the white display state (rise) and the transition from the white display state to the black display state (fall), A vertical electric field is generated in the liquid crystal layer, and on the other hand, a horizontal electric field (fringe field) is generated in the liquid crystal layer. Therefore, the dielectric torque due to voltage application acts on the liquid crystal molecules both at the rising edge and the falling edge, so that excellent response characteristics can be obtained.

Also, Patent Document 3 proposes a liquid crystal display device that realizes high-speed response by applying an alignment regulating force due to an electric field to liquid crystal molecules at both rising and falling. In the present specification, a display mode realized by an electrode structure that can be generated by switching a vertical electric field and a horizontal electric field in a liquid crystal layer as disclosed in Patent Documents 1, 2, and 3, is referred to as an “on / on mode”. Call it.

However, according to the examination by the applicant of the present application, when an on / on mode liquid crystal display device is used for a see-through display, a problem of blurred background (double visibility) occurs and display quality deteriorates. I understood it.

Therefore, the present applicant has proposed a liquid crystal display device capable of preventing the occurrence of such a problem in Patent Document 4. Each pixel of the liquid crystal display device disclosed in Patent Document 4 has a black display state in which black display is performed in a state in which a vertical electric field is generated in the liquid crystal layer, and a white display in a state in which a horizontal electric field is generated in the liquid crystal layer. It is possible to switch and present the white display state in which is performed. Each pixel can also exhibit a transparent display state in which the back side of the liquid crystal display panel can be seen through when no voltage is applied to the liquid crystal layer, thereby blurring the background (recognized twice). The occurrence of the problem is prevented.

JP 2006-523850 A JP 2002-365657 A International Publication No. 2013/001979 International Publication No. 2014/136586

Patent Document 4 discloses a configuration in which liquid crystal molecules have homogeneous alignment and a configuration in which twist alignment is performed in a state where a horizontal electric field is generated in the liquid crystal layer (white display state). According to the inventor's study, in the latter configuration, as will be described in detail later, there is room for further improvement in response characteristics, but in that case, since the response characteristics and the contrast ratio are in a trade-off relationship, It was found that it is difficult to achieve both a further improvement in response characteristics and a high contrast ratio.

The present invention has been made in view of the above problems, and an object thereof is to achieve both excellent response characteristics and a high contrast ratio in an on / on mode liquid crystal display device in which liquid crystal molecules can take twist alignment. It is in.

A liquid crystal display device according to an embodiment of the present invention includes a liquid crystal display panel having a first substrate and a second substrate facing each other, and a liquid crystal layer provided between the first substrate and the second substrate, and a matrix. A liquid crystal display device having a plurality of pixels arranged in a shape, wherein the first substrate has a first electrode provided in each of the plurality of pixels, and a horizontal electric field applied to the liquid crystal layer together with the first electrode. And the second substrate is provided so as to face the first electrode and the second electrode, and applies a vertical electric field to the liquid crystal layer together with the first electrode and the second electrode. In a state where a third electric field is generated and a lateral electric field is generated in the liquid crystal layer, the liquid crystal molecules of the liquid crystal layer have a twist alignment, and the thickness d of the liquid crystal layer and the natural chirality of the liquid crystal layer The pitch p is 1 ≦ p Satisfy the relation d ≦ 3, dielectric anisotropy Δε of the liquid crystal material included in the liquid crystal layer is 16 to 25.

In one embodiment, the thickness d of the liquid crystal layer is 2.5 μm or more and 4.0 μm or less.

In one embodiment, the first substrate has a first alignment film on the surface on the liquid crystal layer side, the second substrate has a second alignment film on the surface on the liquid crystal layer side, and the second substrate The substrate has a dielectric layer between the third electrode and the second alignment film.

In one embodiment, the first substrate has a first alignment film on the surface on the liquid crystal layer side, the second substrate has a second alignment film on the surface on the liquid crystal layer side, and the second substrate The substrate does not have a dielectric layer between the third electrode and the second alignment film.

In one embodiment, each of the plurality of pixels has a black display state in which black display is performed in a state in which a vertical electric field is generated in the liquid crystal layer and a white display in a state in which a horizontal electric field is generated in the liquid crystal layer. A white display state to be performed and a transparent display state in which the back side of the liquid crystal display panel can be seen through when no voltage is applied to the liquid crystal layer can be switched and presented.

In one embodiment, the first electrode is provided on the second electrode through an insulating layer.

In one embodiment, the first electrode has at least one slit extending in a predetermined direction, and a liquid crystal molecule near the center in the thickness direction of the liquid crystal layer in a state where a lateral electric field is generated in the liquid crystal layer. Are oriented so as to be substantially parallel to or substantially orthogonal to the predetermined direction.

In one embodiment, the liquid crystal display device according to the present invention further includes an illumination element capable of switching and irradiating the liquid crystal display panel with a plurality of color lights including red light, green light, and blue light.

In one embodiment, the liquid crystal display device according to the present invention performs color display in a field sequential manner.

In one embodiment, the liquid crystal display panel does not have a color filter.

According to the embodiment of the present invention, it is possible to achieve both excellent response characteristics and a high contrast ratio in an on / on mode liquid crystal display device in which liquid crystal molecules can be twisted.

It is sectional drawing which shows typically the liquid crystal display device 100 by embodiment of this invention. 1 is a plan view schematically showing a liquid crystal display device 100 according to an embodiment of the present invention. 4 is a plan view showing an example of a specific wiring structure on the back substrate 10 of the liquid crystal display device 100. FIG. (A) And (b) is sectional drawing and the top view which show the orientation state of the liquid crystal molecule 31 in the black display state of the liquid crystal display device 100. FIG. (A) And (b) is sectional drawing and the top view which show the orientation state of the liquid crystal molecule 31 in the white display state of the liquid crystal display device 100. FIG. (A) And (b) is sectional drawing and the top view which show the orientation state of the liquid crystal molecule 31 in the transparent display state of the liquid crystal display device 100. FIG. 3 is a cross-sectional view showing an alignment state of liquid crystal molecules 31 in a halftone display state of the liquid crystal display device 100. FIG. It is sectional drawing which shows typically the liquid crystal display device 800 of a comparative example, (a) shows the state which is performing black display, (b) shows the state which is performing white display. It is a figure which shows typically a mode that double blur has generate | occur | produced. (A) And (b) is a graph which shows the result of having calculated the orientation state of the liquid crystal molecule 31 in a black display state by simulation, and shows the case where the natural chiral pitch p of the liquid crystal layer 30 is 45 μm and 5 μm, respectively. ing. When the natural chiral pitch p is changed to 45 μm, 30 μm, 15 μm, 10 μm, 9 μm, and 7.5 μm with the thickness d of the liquid crystal layer 30 being 3 μm (that is, p / d is 15, 10, 5, 3.3). It is a graph which shows the result of having calculated the response characteristic of a bag by simulation (when changing with 3, 2.5). It is sectional drawing which shows typically the liquid crystal display device 200 by embodiment of this invention. Response when the natural chiral pitch p is changed to 45 μm, 15 μm, and 7.5 μm with the thickness d of the liquid crystal layer 30 being 3 μm (that is, when p / d is changed to 15, 5, and 2.5). It is a graph which shows the result of having calculated the characteristic by simulation. (A) And (b) is a graph which shows the result of having calculated the orientation state of the liquid crystal molecule 31 in a black display state by simulation, and shows the cases where the dielectric anisotropy Δε of the liquid crystal material is 5 and 18, respectively. ing. (A) And (b) is a figure which shows the result of having calculated the orientation state of the liquid crystal molecule 31 at the time of black display by simulation, and shows the case where the dielectric anisotropy (DELTA) epsilon of a liquid crystal material is 15 and 16, respectively. ing. It is a graph which shows contrast ratio about the case where the overcoat layer is not provided, and the case where the overcoat layer is provided. It is a graph which shows the result of having calculated the response characteristic when changing a pixel from a white display state to a black display state by simulation, and the dielectric anisotropy Δε of the liquid crystal material is 10, 15, 16, 18, 20, and 25 Is shown.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment.

(Embodiment 1)
A liquid crystal display device 100 according to the present embodiment will be described with reference to FIGS. FIG. 1 is a cross-sectional view schematically showing the liquid crystal display device 100, and FIG. 2 is a plan view schematically showing the liquid crystal display device 100.

The liquid crystal display device 100 includes a liquid crystal display panel 1 and an illumination element 2 as shown in FIG. The liquid crystal display device 100 has a plurality of pixels arranged in a matrix. As will be described later, the liquid crystal display device 100 performs color display in a field sequential manner.

The liquid crystal display panel 1 includes a first substrate 10 and a second substrate 20 facing each other, and a liquid crystal layer 30 provided between the first substrate 10 and the second substrate 20. Hereinafter, of the first substrate 10 and the second substrate 20, the first substrate 10 that is relatively located on the back side is referred to as a “back substrate”, and the second substrate that is relatively located on the front side (observer side). The substrate 20 is referred to as a “front substrate”.

The back substrate 10 includes a first electrode 11 provided in each of a plurality of pixels, and a second electrode 12 that generates a lateral electric field in the liquid crystal layer 30 together with the first electrode 11. The first electrode 11 is provided on the second electrode 12 with the insulating layer 13 interposed therebetween. In other words, the second electrode 12 is provided below the first electrode 11 with the insulating layer 13 interposed therebetween. Hereinafter, of the first electrode 11 and the second electrode 12, the first electrode 11 positioned on the relatively upper side is referred to as “upper layer electrode”, and the second electrode 12 positioned on the lower side is referred to as “lower layer electrode”. " The lower layer electrode 12, the insulating layer 13, and the upper layer electrode 11 are supported by an insulating transparent substrate (for example, a glass substrate) 10a.

As shown in FIGS. 1 and 2, the upper layer electrode 11 includes a plurality of branch portions (comb teeth) 11b extending in a predetermined direction D and two branch portions adjacent to each other among the plurality of branch portions 11b. And at least one slit 11a located between 11b. Since at least one slit 11a extends in the direction D in which the plurality of branch portions 11b extend, the direction D is also referred to as “slit direction” below. Note that the numbers of the slits 11a and the branch portions 11b are not limited to the examples shown in FIGS. The width L of the branch portion 11b may be equal to or greater than the width S of the slit 11a (L ≧ S), or may be smaller than the width S of the slit 11a (L <S). The upper electrode 11 is made of a transparent conductive material (for example, ITO).

The lower layer electrode 12 does not have a slit. That is, the lower layer electrode 12 is a so-called solid electrode. The lower layer electrode 12 is made of a transparent conductive material (for example, ITO).

There are no particular restrictions on the material of the insulating layer 13. As a material of the insulating layer 13, for example, an inorganic material such as silicon oxide (SiO ₂ ) and silicon nitride (SiN _x ) or an organic material such as a photosensitive resin can be used.

The front substrate 20 has a third electrode (hereinafter referred to as “counter electrode”) 21 provided to face the upper layer electrode (first electrode) 11 and the lower layer electrode (second electrode) 12. The counter electrode 21 is supported by an insulating transparent substrate (for example, a glass substrate) 20a.

The counter electrode 21 generates a vertical electric field in the liquid crystal layer 30 together with the upper layer electrode 11 and the lower layer electrode 12. The counter electrode 21 is made of a transparent conductive material (for example, ITO).

A dielectric layer (overcoat layer) 22 is formed on the counter electrode 21 (between the counter electrode 21 and a second horizontal alignment film 24 described later). The overcoat layer 22 is provided to weaken a vertical electric field that is inevitably generated when a horizontal electric field is generated. As the material of the overcoat layer 22, an inorganic material such as silicon oxide (SiO ₂ ) or silicon nitride (SiN _x ) or an organic material such as a photosensitive resin can be used.

The liquid crystal material contained in the liquid crystal layer 30 has positive dielectric anisotropy. That is, the liquid crystal layer 30 is formed from a positive liquid crystal material. Further, the liquid crystal material forming the liquid crystal layer 30 contains a chiral agent. 1 and 2 show the alignment direction of the liquid crystal molecules 31 of the liquid crystal layer 30. FIG. The alignment direction shown in FIGS. 1 and 2 is the alignment direction in a state where no voltage is applied to the liquid crystal layer 30.

The liquid crystal display panel 1 further includes a pair of horizontal alignment films 14 and 24 provided so as to face each other with the liquid crystal layer 30 interposed therebetween. One of the pair of horizontal alignment films 14 and 24 (hereinafter also referred to as “first horizontal alignment film”) 14 is formed on the surface of the back substrate 10 on the liquid crystal layer 30 side. The other of the pair of horizontal alignment films 14 and 24 (hereinafter also referred to as “second horizontal alignment film”) 24 is formed on the surface of the front substrate 20 on the liquid crystal layer 30 side.

Each of the first horizontal alignment film 14 and the second horizontal alignment film 24 is subjected to an alignment process, and alignment regulation for aligning the liquid crystal molecules 31 of the liquid crystal layer 30 in a predetermined direction (referred to as a “pretilt direction”). Have power. As the alignment process, for example, a rubbing process or an optical alignment process is performed.

In the pretilt direction defined by each of the first horizontal alignment film 14 and the second horizontal alignment film 24, the liquid crystal molecules 31 are twisted in a state where no voltage is applied to the liquid crystal layer 30 (a state where no electric field is generated). Is set to take. Specifically, the pretilt direction defined by each of the first horizontal alignment film 14 and the second horizontal alignment film 24 forms an angle of about 45 ° with respect to the slit direction D. Further, the pretilt direction defined by the second horizontal alignment film 24 forms an angle of 90 ° with respect to the pretilt direction defined by the first horizontal alignment film 14. Therefore, in a state where no voltage is applied to the liquid crystal layer 30, the liquid crystal molecules 31 have 90 ° twist alignment.

The liquid crystal display panel 1 further includes a pair of polarizing plates 15 and 25 provided to face each other with the liquid crystal layer 30 interposed therebetween. A transmission axis (polarization axis) 15a of one of the pair of polarizing plates 15 and 25 (hereinafter also referred to as “first polarizing plate”) and a transmission axis of the other (hereinafter also referred to as “second polarizing plate”) 25 ( As shown in FIG. 2, it is substantially orthogonal to the (polarization axis) 25a. That is, the first polarizing plate 15 and the second polarizing plate 25 are arranged in crossed Nicols. The transmission axes 15a and 25a of the first polarizing plate 15 and the second polarizing plate 25 are substantially parallel to or substantially parallel to the pretilt direction defined by the first horizontal alignment film 14 and the second horizontal alignment film 24, respectively. Orthogonal. Accordingly, the transmission axes 15 a and 25 a of the first polarizing plate 15 and the second polarizing plate 25 form an angle of about 45 ° with respect to the slit direction D.

The illumination element (sometimes called “backlight”) 2 is arranged on the back side of the liquid crystal display panel 1. The illumination element 2 can switch and irradiate the liquid crystal display panel 1 with a plurality of color lights including red light, green light, and blue light.

As the lighting element 2, for example, an edge light type backlight as shown in FIG. 1 can be used. The edge-light type backlight 2 includes a light source unit 2a and a light guide plate 2b. The light source unit 2a can emit a plurality of color lights including red light, green light, and blue light. The light source unit 2a includes, for example, a red LED, a green LED, and a blue LED as light sources. The light guide plate 2b guides the color light emitted from the light source unit 2a to the liquid crystal display panel 1.

The liquid crystal display device 100 performs color display by a field sequential method. Therefore, the liquid crystal display panel 1 does not have a color filter.

When a predetermined voltage is applied between the upper layer electrode 11 and the lower layer electrode 12 (that is, when a predetermined potential difference is given), a horizontal electric field (fringe field) is generated in the liquid crystal layer 30. The “lateral electric field” is an electric field including a component substantially parallel to the substrate surface. The direction of the transverse electric field generated by the upper layer electrode 11 and the lower layer electrode 12 is substantially orthogonal to the slit direction D.

On the other hand, when a predetermined voltage is applied between the counter electrode 21 and the upper layer electrode 11 and the lower layer electrode 12 (that is, when a predetermined potential difference is given), a vertical electric field is generated. The “longitudinal electric field” is an electric field whose direction is substantially parallel to the normal direction of the substrate surface.

The liquid crystal display device 100 has a configuration capable of controlling the strength of the horizontal electric field and the vertical electric field for each pixel. Typically, the liquid crystal display device 100 has a configuration capable of supplying different voltages for each pixel for each of the upper layer electrode 11 and the lower layer electrode 12. Specifically, both the upper layer electrode 11 and the lower layer electrode 12 are formed separately for each pixel, and each pixel includes a switching element (for example, a thin film transistor; not shown) electrically connected to the upper layer electrode 11. A switching element (for example, a thin film transistor; not shown) electrically connected to the lower layer electrode 12 is provided. A predetermined voltage is supplied to the upper layer electrode 11 and the lower layer electrode 12 via corresponding switching elements. The counter electrode 21 is formed as a single conductive film that is continuous over all the pixels. Accordingly, a common potential is applied to the counter electrode 21 in all the pixels.

FIG. 3 shows an example of a specific wiring structure on the back substrate 10. In the configuration shown in FIG. 3, each pixel is provided with a first TFT 16 </ b> A corresponding to the upper layer electrode 11 and a second TFT 16 </ b> B corresponding to the lower layer electrode 12.

The gate electrodes 16g of the first TFT 16A and the second TFT 16B are electrically connected to a gate bus line (scanning wiring) 17. Here, the portion of the gate bus line 17 that overlaps the channel regions of the first TFT 16A and the second TFT 16B functions as the gate electrode 16g. The source electrodes 16s of the first TFT 16A and the second TFT 16B are electrically connected to a source bus line (signal wiring) 18. Here, a portion branched from the source bus line 18 functions as the source electrode 16s. The drain electrode 16d of the first TFT 16A is electrically connected to the upper layer electrode 11. On the other hand, the drain electrode 16d of the second TFT 16B is electrically connected to the lower layer electrode 12. The wiring structure of the back substrate 10 is not limited to that illustrated in FIG.

In the liquid crystal display device 100 according to the present embodiment, each of the plurality of pixels generates a “black display state” in which black display is performed in a state where a vertical electric field is generated in the liquid crystal layer 30, and a horizontal electric field is generated in the liquid crystal layer 30. Switching between the “white display state” in which white display is performed and the “transparent display state” in which the back side (that is, the background) of the liquid crystal display panel 1 can be seen through when no voltage is applied to the liquid crystal layer 30 Can be presented.

Hereinafter, the black display state, the white display state, and the transparent display state will be described in more detail with reference to FIGS. 4, 5, and 6.

4 (a) and 4 (b) show the alignment state of the liquid crystal molecules 31 in the black display state. In the black display state, a predetermined voltage is applied between the counter electrode 21, the upper layer electrode 11, and the lower layer electrode 12, and a vertical electric field is generated in the liquid crystal layer 30. In FIG. 4A, the electric lines of force at this time are schematically shown by broken lines.

In this black display state, the liquid crystal molecules 31 of the liquid crystal layer 30 are substantially perpendicular to the substrate surfaces (the surfaces of the rear substrate 10 and the front substrate 20) (that is, the liquid crystal molecules as shown in FIGS. 4A and 4B). Oriented (substantially parallel to the layer normal direction of layer 30). Note that the liquid crystal molecules 31 in the immediate vicinity of the first horizontal alignment film 14 and the second horizontal alignment film 24 are strongly affected by the alignment regulating force of the first horizontal alignment film 14 and the second horizontal alignment film 24, so that the substrate surface However, since these liquid crystal molecules 31 are substantially parallel or substantially orthogonal to the transmission axis 15 a of the first polarizing plate 15, they pass through the first polarizing plate 15. Almost no phase difference is given to the light incident on the liquid crystal layer 30, and the contrast ratio is hardly lowered.

5A and 5B show the alignment state of the liquid crystal molecules 31 in the white display state. In the white display state, a predetermined voltage is applied between the upper layer electrode 11 and the lower layer electrode 12, and a horizontal electric field (fringe field) is generated in the liquid crystal layer 30. In FIG. 5A, the electric lines of force at this time are schematically shown by broken lines.

In this white display state, as shown in FIGS. 5A and 5B, the liquid crystal molecules 31 of the liquid crystal layer 30 are substantially parallel to the substrate surface (that is, substantially perpendicular to the layer normal direction of the liquid crystal layer 30). ) Orient. More specifically, the liquid crystal molecules 31 in the vicinity of the first horizontal alignment film 14 and the liquid crystal molecules 31 in the vicinity of the second horizontal alignment film 24 are aligned so as to form an angle of about 90 °, and as a result, the liquid crystal layer 30 The liquid crystal molecules 31 in the vicinity of the center in the thickness direction are aligned so as to be substantially orthogonal to the extending direction (slit direction) D of the slit 11 a of the upper electrode 11. Therefore, the average alignment direction of the liquid crystal molecules 31 in the liquid crystal layer 30 is substantially orthogonal to the slit direction D (that is, approximately 45 with respect to the transmission axes 15a and 25a of the first polarizing plate 15 and the second polarizing plate 25). Make a corner of °).

6A and 6B show the alignment state of the liquid crystal molecules 31 in the transparent display state. In the transparent display state, no voltage is applied to the liquid crystal layer 30, and neither a vertical electric field nor a horizontal electric field is generated in the liquid crystal layer 30.

In this transparent display state, the liquid crystal molecules 31 of the liquid crystal layer 30 are twisted as shown in FIGS. 6 (a) and 6 (b). That is, the liquid crystal molecules 31 are aligned substantially parallel to the substrate surface (that is, substantially perpendicular to the layer normal direction of the liquid crystal layer 30). The liquid crystal molecules 31 in the vicinity of the first horizontal alignment film 14 and the liquid crystal molecules 31 in the vicinity of the second horizontal alignment film 24 are aligned so as to form an angle of about 90 °, and as a result, the liquid crystal layer 30 is centered in the thickness direction. The nearby liquid crystal molecules 31 are aligned so as to be substantially orthogonal to the slit direction D. Therefore, the average alignment direction of the liquid crystal molecules 31 in the liquid crystal layer 30 is substantially orthogonal to the slit direction D (that is, approximately 45 with respect to the transmission axes 15a and 25a of the first polarizing plate 15 and the second polarizing plate 25). Make a corner of °). Each pixel of the liquid crystal display device 100 has the highest light transmittance in this transparent display state (that is, in any of the black display state and the white display state).

It should be noted that each of the plurality of pixels of the liquid crystal display device 100 has a “halftone display” indicating luminance corresponding to a halftone as shown in FIG. 7 in addition to the above-described black display state, white display state, and transparent display state. A “state” may also be exhibited. In the halftone display state, a desired transmittance can be realized by adjusting the strength of the lateral electric field (fringe field) generated in the liquid crystal layer 30.

As described above, in the liquid crystal display device 100, when the information displayed on the liquid crystal display panel 1 and the background are overlapped, the pixel in the display area where the information is to be displayed has a black display state, a white display. A state or a halftone display state is exhibited, and pixels in other portions exhibit a transparent display state. These display states can be switched as follows, for example.

A typical driving circuit for a liquid crystal display device includes an 8-bit driver IC and generates an output voltage for 256 gradations (0 to 255 gradations). In a general liquid crystal display device, 0 gradation is assigned to a black display state, 1 to 254 gradations are assigned to a halftone display state, and 255 gradations are assigned to a white display state.

In the liquid crystal display device 100 of this embodiment, for example, 0 gradation is assigned to the black display state, 1 to 253 gradation is assigned to the halftone display state, 254 gradations are assigned to the white display state, and 255 gradations are assigned to the transparent display state. By assigning, switching between the black display state, the halftone display state, the white display state, and the transparent display state can be realized. Note that the transparent display state does not necessarily have to be assigned to 255 gradations, and any gradation may be assigned to the transparent display state. Similarly, in a case other than the exemplified 256 gradation display, a specific gradation may be assigned to the transparent display state.

As described above, since the liquid crystal display device 100 according to the present embodiment performs color display by the field sequential method, the liquid crystal display panel 1 does not need a color filter. Therefore, the light use efficiency is improved. In the liquid crystal display device 100, a vertical electric field is generated in the liquid crystal layer 30 in the black display state, and a horizontal electric field is generated in the liquid crystal layer 30 in the white display state. ) And a rise (transition from the black display state to the white display state), the dielectric torque due to voltage application can be applied to the liquid crystal molecules 31. Therefore, excellent response characteristics can be obtained.

Furthermore, in the liquid crystal display device 100 according to the present embodiment, each pixel can exhibit not only a black display state and a white display state but also a transparent display state in which no voltage is applied to the liquid crystal layer 30. By performing the background display in this transparent display state, it is possible to prevent the occurrence of the problem that the background is blurred (recognized twice). The reason why this problem (double blur) occurs in the liquid crystal display devices of Patent Documents 1 to 3 will be described below with reference to a liquid crystal display device of a comparative example.

FIGS. 8A and 8B show a state in which black display and a white display are performed in the liquid crystal display device 800 of the comparative example, respectively. The liquid crystal display device 800 of the comparative example has the same configuration as the liquid crystal display device shown in FIGS.

The liquid crystal display device 800 includes an array substrate 810 and a counter substrate 820, and a liquid crystal layer 830 provided therebetween. The array substrate 810 includes a glass substrate 810a, a lower layer electrode 812, an insulating layer 813, and a pair of comb electrodes (upper layer electrodes) 817 and 818 stacked in this order on the glass substrate 810a. On the other hand, the counter substrate 820 includes a glass substrate 820a and a counter electrode 821 formed on the glass substrate 820a.

The liquid crystal layer 830 includes liquid crystal molecules 831 having positive dielectric anisotropy. In the liquid crystal display device 800, the liquid crystal molecules 831 of the liquid crystal layer 830 are in a vertical alignment state when no voltage is applied.

In the liquid crystal display device 800 of the comparative example, when black display is performed, a predetermined voltage is applied between the counter electrode 821, the lower layer electrode 812, and the upper layer electrode (a pair of comb electrodes) 817 and 818 (for example, A potential of 7 V is applied to the counter electrode 821 and a potential of 14 V is applied to the lower layer electrode 812 and the upper layer electrodes 817 and 818), and a vertical electric field is generated in the liquid crystal layer 830. As a result, the liquid crystal molecules 831 are aligned substantially perpendicular to the substrate surface as shown in FIG.

In the liquid crystal display device 800 of the comparative example, when white display is performed, a predetermined voltage is applied between the pair of comb electrodes 817 and 818 (for example, a potential of 0 V is applied to one comb electrode 817, A potential of 14V is applied to the other comb electrode 818), and a horizontal electric field is generated in the liquid crystal layer 830. Thereby, as shown in FIG. 8B, the liquid crystal molecules 831 are aligned with respect to the normal direction of the substrate surface.

When the liquid crystal display device 800 of the comparative example is simply used for a see-through display, when performing a see-through display, that is, a display in which the background can be seen through, white display in which the light transmittance of the pixel is high. Will be done in the state. However, since the state for performing white display is a state in which the liquid crystal molecules 830 are aligned by applying a voltage to the liquid crystal layer 830, the refractive index is distributed within the pixel. Therefore, the light L from the back side is scattered due to this refractive index distribution (that is, the traveling direction of the light L changes; see FIG. 8B), and the background is blurred. As a result, as shown in FIG. 9, the background is visually recognized by the observer V who observes the background BG via the see-through display STDP.

Thus, when see-through display is performed in a white display state in which a voltage is applied to the liquid crystal layer, double blurring occurs. On the other hand, in the liquid crystal display device 100 according to the present embodiment, background display (see-through display) is performed with pixels in a state where no voltage is applied to the liquid crystal layer 30 (transparent display state). An observer who observes the background sees the background clearly. Therefore, occurrence of double blurring is prevented and the quality of the see-through display is improved.

As already described, the liquid crystal display device of Patent Document 4 discloses a configuration in which liquid crystal molecules are twisted in a state where a horizontal electric field is generated in the liquid crystal layer, and this configuration further improves response characteristics. There is room for it. However, in that case, since the response characteristic and the contrast ratio are in a trade-off relationship, it is difficult to achieve a further improvement in the response characteristic and a high contrast ratio.

On the other hand, the liquid crystal display device 100 of the present embodiment is excellent in both response characteristics and contrast ratio by having the configuration described below. A more specific description will be given below.

First, the inventor of the present application studied to further improve the response characteristics by reducing the ratio p / d of the natural chiral pitch p of the liquid crystal layer 30 to the thickness d of the liquid crystal layer 30. As a result, it was found that when p / d is reduced, the response characteristic is improved, but the contrast ratio is lowered.

10A and 10B show the cases where the natural chiral pitch p of the liquid crystal layer 30 is 45 μm and 5 μm (in each case, the dielectric anisotropy Δε of the liquid crystal material is 4.9). The result of having calculated the orientation state of the liquid crystal molecule 31 in the black display state (that is, the state in which the vertical electric field is generated in the liquid crystal layer 30) by simulation is shown. 10A and 10B, the horizontal axis indicates the position of the liquid crystal molecule 31 in the thickness direction of the liquid crystal layer 30, and the vertical axis indicates the magnitude of the azimuth angle and polar angle in the alignment direction of the liquid crystal molecule 31. It is the graph which took (angle). The position of 0 μm on the horizontal axis corresponds to the interface between the back substrate 10 and the liquid crystal layer 30, and the position of 3.2 μm corresponds to the interface between the front substrate 20 and the liquid crystal layer 30 (that is, the thickness of the liquid crystal layer 30). Is 3.2 μm). As for the azimuth, the angle in the 3 o'clock direction when the display surface is regarded as a clock face is 0 °, and the counterclockwise direction is the positive direction.

First, pay attention to the azimuth. As shown in FIGS. 10A and 10B, in any case, at the interface between the back substrate 10 and the liquid crystal layer 30 (0 μm position), the orientation angle of the liquid crystal molecules 31 is 45 °. The liquid crystal molecules 31 are aligned substantially parallel to the absorption axis (substantially orthogonal to the transmission axis 15a) of the polarizing plate 15 on the back substrate 10 side. This is because the liquid crystal molecules 31 are strongly subjected to the alignment regulating force of the first horizontal alignment film 14. Further, at the interface between the front substrate 20 and the liquid crystal layer 30 (at a position of 3.2 μm), the azimuth angle of the alignment direction of the liquid crystal molecules 31 is −45 °, and the liquid crystal molecules 31 are the polarizing plate 25 on the front substrate 20 side. Oriented substantially parallel to the absorption axis (substantially orthogonal to the transmission axis 25a). This is because the liquid crystal molecules 31 are strongly subjected to the alignment regulating force of the second horizontal alignment film 24. Furthermore, at the center (position of 1.6 μm) in the thickness direction of the liquid crystal layer 30, the azimuth angle in the alignment direction of the liquid crystal molecules 31 is 0 °, and the liquid crystal molecules 31 are approximately the absorption axes of the polarizing plates 15 and 25. It is oriented in a direction that forms an angle of 45 °.

Next, pay attention to the polar angle. As shown in FIGS. 10A and 10B, in any case, in the vicinity of the center in the thickness direction of the liquid crystal layer 30 (position of 1.0 μm to 2.2 μm), the alignment direction of the liquid crystal molecules 31 is increased. The polar angle is 90 °, and the liquid crystal molecules 31 are aligned substantially perpendicular to the substrate surfaces of the back substrate 10 and the front substrate 20. This is because the liquid crystal molecules 31 are subjected to the alignment regulating force by the vertical electric field. However, in any case, the polar angle of the alignment direction of the liquid crystal molecules 31 is substantially 0 ° at the interface between the back substrate 10 and the liquid crystal layer 30 and the interface between the front substrate 20 and the liquid crystal layer 30. This is because the liquid crystal molecules 31 are strongly subjected to the alignment regulating force of the first horizontal alignment film 14 and the second horizontal alignment film 24.

Subsequently, along the thickness direction of the liquid crystal layer 30 (from the back substrate 10 side toward the center in the thickness direction of the liquid crystal layer 30 or from the front substrate 20 side toward the center in the thickness direction of the liquid crystal layer 30. Note the change in orientation direction.

When the natural chiral pitch p of the liquid crystal layer 30 is 45 μm, as shown in FIG. 10A, after the polar angle in the alignment direction of the liquid crystal molecules 31 becomes sufficiently large, the azimuth angle starts from 45 ° or −45 °. Start to change. That is, in the region where the polar angle of the alignment direction of the liquid crystal molecules 31 is small (near the interface between the back substrate 10 and the liquid crystal layer 30 and near the interface between the front substrate 20 and the liquid crystal layer 30), the liquid crystal molecules 31 Oriented substantially parallel to the absorption axes of 15 and 25. Therefore, light leakage due to the liquid crystal molecules 31 in the vicinity of the back substrate 10 and the front substrate 20 does not occur, and good (that is, sufficiently low brightness) black display can be performed.

On the other hand, when the natural chiral pitch p of the liquid crystal layer 30 is 5 μm, the azimuth is 45 ° before the polar angle in the alignment direction of the liquid crystal molecules 30 becomes sufficiently large as shown in FIG. It starts to change from -45 °. That is, in the region where the polar angle of the alignment direction of the liquid crystal molecules 31 is small (near the interface between the back substrate 10 and the liquid crystal layer 30 and near the interface between the front substrate 20 and the liquid crystal layer 30), the liquid crystal molecules 31 are polarized. The plates 15 and 25 are oriented in a direction shifted from the absorption axis. This is presumably because the amount of the chiral agent added is larger when the natural chiral pitch p is 5 μm than when the natural chiral pitch p is 45 μm. For this reason, light leaks due to the liquid crystal molecules 31 in the vicinity of the rear substrate 10 and the front substrate 20, and the luminance in the black display state is increased. Accordingly, the contrast ratio is lowered.

Thus, when the natural chiral pitch p is reduced, that is, when p / d is reduced, the contrast ratio is lowered.

In the liquid crystal display device 100 of the present embodiment, the ratio p / d of the natural chiral pitch p of the liquid crystal layer 30 to the thickness d of the liquid crystal layer 30 is 1 or more and 3 or less. That is, the thickness d of the liquid crystal layer 30 and the natural chiral pitch p of the liquid crystal layer 30 satisfy the relationship 1 ≦ p / d ≦ 3.

According to the study of the present inventor, when p / d is 3 or less, when the pixel is changed from the black display state to the white display state (that is, the voltage applied to the liquid crystal layer 30 is switched from the vertical electric field to the horizontal electric field). It was found that the response speed can be improved sufficiently.

In FIG. 11, when the natural chiral pitch p is changed to 45 μm, 30 μm, 15 μm, 10 μm, 9 μm, and 7.5 μm with the thickness d of the liquid crystal layer 30 being 3 μm (that is, p / d is 15, 10, 5). 3 shows a result of calculating response characteristics (relationship between time and normalized luminance) by simulation. The simulation conditions are as shown in Table 1 below.

From FIG. 11, it can be seen that the smaller the natural chiral pitch p, that is, the smaller the p / d, the more the response speed is improved (the response characteristic is improved), and the p / d is 3 or less. It can be seen that sufficiently high response characteristics can be obtained.

If p / d is too small, the twist angle of the liquid crystal molecules 31 during white display may exceed 90 °, which may cause a decrease in transmittance. From the viewpoint of suppressing such a decrease in transmittance, p / d is preferably 1 or more.

Further, in the liquid crystal display device 100 of this embodiment, the dielectric anisotropy Δε (@ 20 ° C., 1 kHz) of the liquid crystal material included in the liquid crystal layer 30 is 16 or more. Generally, as the dielectric anisotropy Δε increases, the dielectric torque due to the electric field acting on the liquid crystal molecules 31 increases. That is, the alignment regulating force by the electric field is strengthened. According to the study of the inventor of the present application, when the dielectric anisotropy Δε of the liquid crystal material is 16 or more, in the black display state, in the vicinity of the back substrate 10 and the counter substrate 20 (however, the first horizontal alignment film 14 and the second horizontal alignment film). It was found that the polar angle in the alignment direction of the liquid crystal molecules 31 (except in the vicinity of the alignment film 24) can be sufficiently increased. Therefore, when the dielectric anisotropy Δε of the liquid crystal material is 16 or more, the occurrence of light leakage at the time of black display can be suppressed, and a high contrast ratio can be realized. Further, since the dielectric anisotropy Δε of the liquid crystal material is 16 or more, an effect of further improving the response speed when the pixel is changed from the black display state to the white display state can be obtained.

Note that if the dielectric anisotropy Δε of the liquid crystal material is too large, the rotational viscosity coefficient γ may increase and the response speed may decrease. Therefore, the dielectric anisotropy Δε of the liquid crystal material is preferably 25 or less.

The thickness d of the liquid crystal layer 30 is not limited, but the response speed improves as the thickness d of the liquid crystal layer 30 decreases. From the viewpoint of response speed, the thickness d of the liquid crystal layer 30 is preferably 4.0 μm or less. If the thickness d of the liquid crystal layer 30 is too small, the yield of the liquid crystal display panel 1 may be reduced. From the viewpoint of yield, the thickness d of the liquid crystal layer 30 is preferably 2.5 μm or more.

As already described, in the liquid crystal display device 100 of the present embodiment, a liquid crystal material having a dielectric anisotropy Δε of 16 or more is used. As the liquid crystal material having such a high dielectric anisotropy Δε, for example, a cyclohexanedimethyl derivative (represented by the following formula (1)) disclosed in JP-A-7-126205 is added to a nematic liquid crystal material. The liquid crystal material can be used. In the formula (1), R ₁ represents an alkyl group having 1 to 12 carbon atoms, X ₁ and X ₃ represent a hydrogen atom or a halogen atom, and X2 represents a halogen atom or a cyano group. For reference, the entire disclosure of Japanese Patent Laid-Open No. 7-126205 is incorporated herein by reference. Of course, materials other than the liquid crystal materials illustrated here may be used.

(Embodiment 2)
A liquid crystal display device 200 according to the present embodiment will be described with reference to FIG. FIG. 12 is a cross-sectional view schematically showing the liquid crystal display device 200. Hereinafter, the liquid crystal display device 200 will be described focusing on differences from the liquid crystal display device 100 according to the first embodiment.

The liquid crystal display device 200 is implemented in that the front substrate (second substrate) 20 does not have a dielectric layer (overcoat layer) between the counter electrode (third electrode) 21 and the second horizontal alignment film 24. This is different from the liquid crystal display device 100 of the first embodiment. That is, the liquid crystal display device 200 has a configuration in which the overcoat layer 22 in the liquid crystal display device 100 of Embodiment 1 is omitted.

Also in the liquid crystal display device 200 of the present embodiment, the ratio p / d of the natural chiral pitch p of the liquid crystal layer 30 to the thickness d of the liquid crystal layer 30 is 1 or more and 3 or less. That is, the thickness d of the liquid crystal layer 30 and the natural chiral pitch p of the liquid crystal layer 30 satisfy the relationship of 1 ≦ p / d ≦ 3.

When p / d is 3 or less, the response speed when the pixel is changed from the black display state to the white display state (that is, when the voltage applied to the liquid crystal layer 30 is switched from the vertical electric field to the horizontal electric field) is sufficiently high. Can improve.

In FIG. 13, when the natural chiral pitch p is changed to 45 μm, 15 μm, and 7.5 μm with the thickness d of the liquid crystal layer 30 being 3 μm (that is, p / d is changed to 15, 5, and 2.5). ) Response characteristics (relationship between time and normalized luminance) by simulation. For reference, FIG. 13 also shows response characteristics when the natural chiral pitch p is 45 μm and an overcoat layer is provided. The simulation conditions are as shown in Table 2 below.

From FIG. 13, it can be seen that as the natural chiral pitch p becomes smaller (that is, as p / d becomes smaller), the response speed improves (response characteristics improve), and p / d becomes 3 or less. It can be seen that sufficiently high response characteristics can be obtained.

If p / d is too small, the twist angle of the liquid crystal molecules 31 during white display may exceed 90 °, which may cause a decrease in transmittance. From the viewpoint of suppressing such a decrease in transmittance, p / d is preferably 1 or more.

Further, in the liquid crystal display device 200 of the present embodiment, since the dielectric anisotropy Δε of the liquid crystal material included in the liquid crystal layer 30 is 16 or more, the liquid crystal molecules 31 in the vicinity of the back substrate 10 and the counter substrate 20 in the black display state. The polar angle in the orientation direction can be made sufficiently large.

14A and 14B show a black display state (that is, the natural chiral pitch p of the liquid crystal layer 30 is 5 μm in each case) when the dielectric anisotropy Δε of the liquid crystal material is 5 and 18. The result of having calculated the orientation state of the liquid crystal molecule 31 in the state where the vertical electric field is generated in the liquid crystal layer 30 by simulation is shown. 14A and 14B, the horizontal axis indicates the position of the liquid crystal molecules 31 in the thickness direction of the liquid crystal layer 30, and the vertical axis indicates the magnitudes of the azimuth and polar angles in the alignment direction of the liquid crystal molecules 31. It is the graph which took (angle). The position of 0 μm on the horizontal axis corresponds to the interface between the back substrate 10 and the liquid crystal layer 30, and the position of 3.2 μm corresponds to the interface between the front substrate 20 and the liquid crystal layer 30 (that is, the thickness of the liquid crystal layer 30). d is 3.2 μm). As for the azimuth, the angle in the 3 o'clock direction when the display surface is regarded as a clock face is 0 °, and the counterclockwise direction is the positive direction.

When the dielectric anisotropy Δε of the liquid crystal material is 5, as shown in FIG. 14A, the azimuth angle is changed from 45 ° or −45 ° before the polar angle in the alignment direction of the liquid crystal molecules 31 becomes sufficiently large. It starts to change. That is, in the region where the polar angle of the alignment direction of the liquid crystal molecules 31 is small (near the interface between the back substrate 10 and the liquid crystal layer 30 and near the interface between the front substrate 20 and the liquid crystal layer 30), the liquid crystal molecules 31 are polarized. The plates 15 and 25 are oriented in a direction shifted from the absorption axis. For this reason, light leaks due to the liquid crystal molecules 31 in the vicinity of the rear substrate 10 and the front substrate 20, and the luminance in the black display state is increased. Accordingly, the contrast ratio is lowered.

On the other hand, when the dielectric anisotropy Δε of the liquid crystal material is 18, as shown in FIG. 14B, the azimuth is 45 ° after the polar angle in the alignment direction of the liquid crystal molecules 31 becomes sufficiently large. It begins to change from -45 °. That is, in the region where the polar angle of the alignment direction of the liquid crystal molecules 31 is small (near the interface between the back substrate 10 and the liquid crystal layer 30 and near the interface between the front substrate 20 and the liquid crystal layer 30), the liquid crystal molecules 31 Oriented substantially parallel to the absorption axes of 15 and 25. Therefore, light leakage by the liquid crystal molecules 31 in the vicinity of the back substrate 810 and the front substrate 20 does not occur, and good (that is, luminance is sufficiently low) black display can be performed.

Thus, when the dielectric anisotropy Δε of the liquid crystal material is 16 or more, the occurrence of light leakage during black display can be suppressed, and a high contrast ratio can be realized. Further, according to the study of the present inventor, when the dielectric anisotropy Δε of the liquid crystal material is less than 16, disclination may occur during black display, and light leakage due to disclination may occur. I understood it. FIGS. 15A and 15B show the results of calculating the alignment state of the liquid crystal molecules 31 during black display by simulation for the cases where the dielectric anisotropy Δε of the liquid crystal material is 15 and 16. FIG.

When the dielectric anisotropy Δε of the liquid crystal material is 15, as shown in FIG. 15A, there is a region where the liquid crystal molecules 31 are aligned so as not to match the alignment of the liquid crystal molecules 31 in other regions. And disclination occurs. On the other hand, when the dielectric anisotropy Δε of the liquid crystal material is 16, as shown in FIG. 15B, no disclination occurs and the liquid crystal molecules 31 are uniformly aligned.

Thus, when the dielectric anisotropy Δε of the liquid crystal material is 16 or more, the occurrence of disclination is suppressed, which also contributes to the realization of a high contrast ratio.

Note that if the dielectric anisotropy Δε of the liquid crystal material is too large, the rotational viscosity coefficient γ may increase and the response speed may decrease. Therefore, the dielectric anisotropy Δε of the liquid crystal material is preferably 25 or less.

Further, in the liquid crystal display device 200 of the present embodiment, the front substrate 20 does not have an overcoat layer between the counter electrode 21 and the second horizontal alignment film 24. When the overcoat layer 22 is provided as in the liquid crystal display device 100 of Embodiment 1, the vertical electric field that is inevitably generated when the horizontal electric field is generated can be weakened. Can be strengthened. However, since the overcoat layer 22 is provided, the action of the vertical electric field is weakened. Therefore, the vertical electric field cannot be sufficiently applied to the liquid crystal layer 30 during black display, and the luminance in the black display state cannot be sufficiently lowered. On the other hand, as in the present embodiment, since no overcoat layer is provided between the counter electrode 21 and the second horizontal alignment film 24, a vertical electric field is sufficiently applied to the liquid crystal layer 30 during black display. Therefore, the contrast ratio can be further improved.

FIG. 16 shows contrast ratios when the overcoat layer is not provided and when the overcoat layer is provided. FIG. 16 is a graph in which the horizontal axis represents the natural chiral pitch p of the liquid crystal layer 30 and the vertical axis represents the contrast ratio. Here, the thickness d of the liquid crystal layer 30 is 3.2 μm.

FIG. 16 shows that the contrast ratio is remarkably increased by omitting the overcoat layer.

Further, by omitting the overcoat layer, a vertical electric field can be sufficiently applied to the liquid crystal layer 30 during black display. Therefore, when the pixel is changed from the white display state to the black display state (that is, to the liquid crystal layer 30). The response speed when the applied voltage is switched from the horizontal electric field to the vertical electric field is also improved. FIG. 17 shows the result of calculating the response characteristics (relationship between time and normalized luminance) when the pixel is changed from the white display state to the black display state by simulation. FIG. 17 shows the case where the dielectric anisotropy Δε of the liquid crystal material is 10, 15, 16, 18, 20, and 25. The simulation conditions are as shown in Table 3 below.

17 that the response characteristics are sufficiently improved when the overcoat layer is omitted and the dielectric anisotropy Δε of the liquid crystal material is 16 or more.

Thus, by omitting the overcoat layer, it is possible to further improve the contrast ratio and to improve the response characteristics when the pixel is changed from the white display state to the black display state. In addition, if an overcoat layer is provided, there is a possibility that image sticking due to the accumulation of electric charge in the overcoat layer may occur, but the occurrence of such image burn-in can be prevented by omitting the overcoat layer. This improves reliability.

In the configuration in which the natural chiral pitch p of the liquid crystal layer 30 is large (specifically, the configuration in which p / d greatly exceeds 3), if the overcoat layer is omitted, the pixel is changed from the black display state to the white display state. Since the response characteristics at the time of transition are too low, the overcoat layer could not be omitted. On the other hand, the overcoat layer is omitted by adopting a configuration in which the natural chiral pitch p of the liquid crystal layer 30 is small (specifically, a configuration in which p / d is 3 or less) as in the present embodiment. And the effects described above can be obtained.

The thickness d of the liquid crystal layer 30 is not limited, but the response speed improves as the thickness d of the liquid crystal layer 30 decreases. From the viewpoint of response speed, the thickness d of the liquid crystal layer 30 is preferably 4.0 μm or less. If the thickness d of the liquid crystal layer 30 is too small, the yield of the liquid crystal display panel 1 may be reduced. From the viewpoint of yield, the thickness d of the liquid crystal layer 30 is preferably 2.5 μm or more.

(Other embodiments)
In the description so far, the case where the liquid crystal molecules 31 near the center in the thickness direction of the liquid crystal layer 30 are aligned so as to be substantially orthogonal to the slit direction D in a state where a horizontal electric field is generated in the liquid crystal layer 30 has been exemplified. However, the embodiment of the present invention is not limited to this configuration.

Further, in the present embodiment, a see-through display that performs color display by a field sequential method is exemplified, but the embodiment of the present invention is not necessarily limited to this. Embodiments of the present invention can be widely used in an on / on mode liquid crystal display device in which liquid crystal molecules can have twist alignment.

According to the embodiment of the present invention, it is possible to achieve both excellent response characteristics and a high contrast ratio in an on / on mode liquid crystal display device in which liquid crystal molecules can be twisted.

The liquid crystal display device according to the embodiment of the present invention is suitably used as a see-through display.

DESCRIPTION OF SYMBOLS 1 Liquid crystal display panel 2 Illumination element 2a Light source unit 2b Light guide plate 10 1st board | substrate (back substrate)
10a Transparent substrate 11 First electrode (upper layer electrode)
11a Slit 11b Branch-shaped part 12 2nd electrode (lower layer electrode)
DESCRIPTION OF SYMBOLS 13 Insulating layer 14 1st horizontal alignment film 15 1st polarizing plate 15a Transmission axis of 1st polarizing plate 16A 1st TFT
16B 2nd TFT
17 Gate bus line 18 Source bus line 20 Second substrate (front substrate)
20a Transparent substrate 21 Third electrode (counter electrode)
22 Dielectric layer (overcoat layer)
24 Second horizontal alignment film 25 Second polarizing plate 25a Transmission axis of second polarizing plate 30 Liquid crystal layer 31 Liquid crystal molecule 100, 100A, 200 Liquid crystal display device

Claims (10)

1. A liquid crystal display panel having a first substrate and a second substrate facing each other, and a liquid crystal layer provided between the first substrate and the second substrate;
   A liquid crystal display device having a plurality of pixels arranged in a matrix,
   The first substrate includes a first electrode provided in each of the plurality of pixels, and a second electrode that generates a lateral electric field in the liquid crystal layer together with the first electrode,
   The second substrate includes a third electrode that is provided to face the first electrode and the second electrode, and generates a vertical electric field in the liquid crystal layer together with the first electrode and the second electrode,
   In a state where a horizontal electric field is generated in the liquid crystal layer, the liquid crystal molecules in the liquid crystal layer take a twist alignment,
   The thickness d of the liquid crystal layer and the natural chiral pitch p of the liquid crystal layer satisfy the relationship 1 ≦ p / d ≦ 3,
   The liquid crystal display device, wherein the liquid crystal material included in the liquid crystal layer has a dielectric anisotropy Δε of 16 or more and 25 or less.
2. 2. The liquid crystal display device according to claim 1, wherein a thickness d of the liquid crystal layer is 2.5 μm or more and 4.0 μm or less.
3. The first substrate has a first alignment film on the surface on the liquid crystal layer side,
   The second substrate has a second alignment film on the surface on the liquid crystal layer side,
   The liquid crystal display device according to claim 1, wherein the second substrate has a dielectric layer between the third electrode and the second alignment film.
4. The first substrate has a first alignment film on the surface on the liquid crystal layer side,
   The second substrate has a second alignment film on the surface on the liquid crystal layer side,
   The liquid crystal display device according to claim 1, wherein the second substrate does not have a dielectric layer between the third electrode and the second alignment film.
5. Each of the plurality of pixels is
   A black display state in which black display is performed in a state where a vertical electric field is generated in the liquid crystal layer;
   A white display state in which a white display is performed in a state where a horizontal electric field is generated in the liquid crystal layer;
   5. The liquid crystal display device according to claim 1, wherein the liquid crystal display device can be switched between a transparent display state in which a back side of the liquid crystal display panel can be seen through when no voltage is applied to the liquid crystal layer.
6. 6. The liquid crystal display device according to claim 1, wherein the first electrode is provided on the second electrode via an insulating layer.
7. The first electrode has at least one slit extending in a predetermined direction;
   The liquid crystal molecules near the center in the thickness direction of the liquid crystal layer in a state where a lateral electric field is generated in the liquid crystal layer, are aligned so as to be substantially parallel to or substantially orthogonal to the predetermined direction. The liquid crystal display device according to any one of 1 to 6.
8. The liquid crystal display device according to any one of claims 1 to 7, further comprising an illumination element capable of switching and irradiating the liquid crystal display panel with a plurality of color lights including red light, green light, and blue light.
9. The liquid crystal display device according to any one of claims 1 to 8, wherein color display is performed by a field sequential method.
10. 10. The liquid crystal display device according to claim 1, wherein the liquid crystal display panel does not have a color filter.

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