JP2020177168A - Display device - Google Patents

Abstract

To provide a display device including a polymer dispersion type liquid crystal layer with higher display quality.SOLUTION: A display device includes a first substrate, a second substrate facing the first substrate, a liquid crystal layer LC disposed between the first substrate and the second substrate and including a stripe polymer 30 and a liquid crystal molecule 31, and a light source that delivers light to the liquid crystal layer. In a spatial frequency spectrum obtained by two-dimensional Fourier transformation of a pattern of the stripe polymer 30 in a plan view about a first frequency component and a second frequency component, the contour of a region of 75% or more of the maximum value is elliptical in a plane defined by the first frequency component and the second frequency component.SELECTED DRAWING: Figure 3

Description

Embodiments of the present invention relate to display devices.

A display device including a light source, a pair of substrates including a pixel electrode and a common electrode, and a polymer-dispersed liquid crystal layer arranged between the substrates is known. For example, the polymer-dispersed liquid crystal layer contains streaky polymers and liquid crystal molecules.

In the polymer-dispersed liquid crystal layer, the inclination of the optical axis of the liquid crystal molecule with respect to the optical axis of the polymer can be controlled by rotating the liquid crystal molecule by the electric field between the pixel electrode and the common electrode. This makes it possible to control the degree of scattering of light from the light source for each pixel and display an arbitrary image on the display device.

Japanese Unexamined Patent Publication No. 2012-151081

In a display device provided with a polymer-dispersed liquid crystal layer, further improvement in display quality is required. Therefore, one of the purposes of the present disclosure is to provide a display device capable of improving display quality.

The display device in one embodiment is a liquid crystal that is arranged between the first substrate, the second substrate facing the first substrate, and the first substrate and the second substrate, and contains streaky polymers and liquid crystal molecules. It includes a layer and a light source that irradiates the liquid crystal layer with light. Further, in the spatial frequency spectrum obtained by performing a two-dimensional Fourier transform on the streaky polymer pattern in plan view with respect to the first frequency component and the second frequency component, the contour of a region of 75% or more of the maximum value is It is elliptical in the plane defined by the first frequency component and the second frequency component.

FIG. 1 is a plan view showing a schematic configuration of a display device according to an embodiment. FIG. 2 is a cross-sectional view showing an example of a configuration applicable to a display panel included in the display device. FIG. 3 is a schematic cross-sectional view for explaining the configuration of the liquid crystal layer included in the display device. FIG. 4 is a schematic cross-sectional view of a configuration applicable to the display device. FIG. 5 is a graph showing the relationship between the voltage applied to the liquid crystal layer and the degree of scattering (luminance) of the liquid crystal layer. FIG. 6A is a plan view of the polymer pattern contained in the liquid crystal layer. FIG. 6B is a spatial frequency spectrum obtained by performing a fast Fourier transform on the pattern of FIG. 6A. FIG. 7A is a plan view of the polymer pattern contained in the liquid crystal layer. FIG. 7B is a spatial frequency spectrum obtained by performing a fast Fourier transform on the pattern of FIG. 7A. FIG. 8A is a plan view of the polymer pattern contained in the liquid crystal layer. FIG. 8B is a spatial frequency spectrum obtained by performing a high-speed Fourier transform on the pattern of FIG. 8A. FIG. 9A is a plan view of the polymer pattern contained in the liquid crystal layer. FIG. 9B is a spatial frequency spectrum obtained by performing a fast Fourier transform on the pattern of FIG. 9A. FIG. 10 is a diagram showing an outline of an evaluation circle of a spatial frequency spectrum. FIG. 11A is a diagram showing a spatial frequency spectrum and an evaluation circle to be evaluated for hysteresis. FIG. 11B is a graph showing the results of measuring the degree of scattering (luminance) with respect to voltage for the liquid crystal layer containing the polymer of the spatial frequency spectrum shown in FIG. 11A. FIG. 12A is a diagram showing a spatial frequency spectrum and an evaluation circle to be evaluated for hysteresis. FIG. 12B is a graph showing the results of measuring the degree of scattering (luminance) with respect to voltage for the liquid crystal layer containing the polymer of the spatial frequency spectrum shown in FIG. 12A. FIG. 13A is a diagram showing a spatial frequency spectrum and an evaluation circle to be evaluated for hysteresis. FIG. 13B is a graph showing the results of measuring the degree of scattering (luminance) with respect to voltage for the liquid crystal layer containing the polymer of the spatial frequency spectrum shown in FIG. 13A. FIG. 14A is a diagram showing a spatial frequency spectrum and an evaluation circle to be evaluated for hysteresis. FIG. 14B is a graph showing the results of measuring the degree of scattering (luminance) with respect to voltage for the liquid crystal layer containing the polymer of the spatial frequency spectrum shown in FIG. 14A.

Some embodiments will be described with reference to the drawings.
It should be noted that the disclosure is merely an example, and those skilled in the art can easily conceive of appropriate changes while maintaining the gist of the invention are naturally included in the scope of the present invention. In addition, the drawings may be represented schematically as compared with actual embodiments in order to clarify the description, but the drawings are merely examples and do not limit the interpretation of the present invention. In each figure, the reference numerals may be omitted for the same or similar elements arranged consecutively. Further, in the present specification and each figure, components exhibiting the same or similar functions as those described above with respect to the above-mentioned figures may be designated by the same reference numerals, and duplicate detailed description may be omitted.

FIG. 1 is a plan view showing a schematic configuration of a display device DSP according to the present embodiment. In the present embodiment, the first direction X, the second direction Y, and the third direction Z are orthogonal to each other, but they may intersect at an angle other than 90 degrees. The first direction X and the second direction Y correspond to the directions parallel to the main surface of the substrate constituting the display device DSP. The third direction Z corresponds to the thickness direction of the display device DSP. In the present embodiment, viewing the XY plane defined by the first direction X and the second direction Y is referred to as a plan view.

In the present embodiment, as an example of the display device DSP, a liquid crystal display device to which a polymer-dispersed liquid crystal (PDLC) is applied is disclosed. The display device DSP includes a display panel PNL, a wiring board 1, an IC chip 2 (drive circuit), and a plurality of light sources LS.

The display panel PNL includes a first substrate SUB1 (array substrate), a second substrate SUB2 (opposing substrate), a liquid crystal layer LC, and a seal SE. The first substrate SUB1 and the second substrate SUB2 are formed in a flat plate shape parallel to the XY plane and face each other in the third direction Z. The seal SE is formed in a loop shape, for example, and adheres the first substrate SUB1 and the second substrate SUB2. The liquid crystal layer LC is arranged between the first substrate SUB1 and the second substrate SUB2, and is sealed by the seal SE.

The display panel PNL has a display area DA for displaying an image and a frame-shaped peripheral area PA surrounding the display area DA. The seal SE is located in the peripheral region PA. The display area DA includes a plurality of pixels PX arranged in a matrix in the first direction X and the second direction Y.

As shown enlarged in FIG. 1, each pixel PX includes a switching element SW, a pixel electrode PE, and a common electrode CE. The switching element SW is composed of, for example, a thin film transistor (TFT) and is electrically connected to the scanning line G and the signal line S. The scanning line G is electrically connected to the switching element SW in each of the pixels PX arranged in the first direction X. The signal line S is electrically connected to the switching element SW in each of the pixels PX arranged in the second direction Y. The pixel electrode PE is electrically connected to the switching element SW. The common electrode CE is commonly provided for a plurality of pixel electrode PEs. The liquid crystal layer LC is driven by an electric field generated between the pixel electrode PE and the common electrode CE. The capacitance CS is formed, for example, between an electrode having the same potential as the common electrode CE and an electrode having the same potential as the pixel electrode PE.

As will be described later, the scanning line G, the signal line S, the switching element SW, and the pixel electrode PE are provided on the first substrate SUB1, and the common electrode CE is provided on the second substrate SUB2. The scanning line G extends to the peripheral region PA and is electrically connected to the wiring board 1 or the IC chip 2. The signal line S extends to the peripheral region PA and is electrically connected to the wiring board 1 or the IC chip 2.

The wiring board 1 is electrically connected to a terminal arranged at the extension portion Ex of the first board SUB1. The extending portion Ex corresponds to a portion of the first substrate SUB1 that does not face the second substrate SUB2. For example, the wiring board 1 is a flexible printed circuit board. The IC chip 2 is mounted on the wiring board 1. The IC chip 2 has, for example, a built-in display driver that outputs a signal necessary for displaying an image. The IC chip 2 may be mounted on the extension portion Ex.

The plurality of light sources LS are superimposed on the extension portion Ex. These light sources LS are arranged at intervals along the first direction X. Each light source LS includes, for example, a light emitting element that emits red light, a light emitting element that emits green light, and a light emitting element that emits blue light. As these light emitting elements, for example, a light emitting diode (LED) can be used, but the present invention is not limited to this example.

FIG. 2 is a cross-sectional view showing an example of a configuration applicable to the display panel PNL shown in FIG. The first substrate SUB1 includes a first transparent base material 10, insulating films 11 and 12, capacitive electrodes 13, a first alignment film 14, a switching element SW, and a pixel electrode PE. The first transparent base material 10 has a first surface 10A and a second surface 10B on the opposite side of the first surface 10A.

The switching element SW is arranged on the second surface 10B side. The insulating film 11 covers the switching element SW. Although the switching element SW is simplified in FIG. 2, the switching element SW actually includes a semiconductor layer and various electrodes. Further, the scanning line G and the signal line S shown in FIG. 1 are arranged between the first transparent base material 10 and the insulating film 11, but are not shown in FIG. The capacitive electrode 13 is arranged between the insulating films 11 and 12. The pixel electrode PE is arranged for each pixel PX between the insulating film 12 and the first alignment film 14. The pixel electrode PE is electrically connected to the switching element SW via the opening OP of the capacitance electrode 13. The pixel electrode PE faces the capacitance electrode 13 and forms the above-mentioned capacitance CS. The first alignment film 14 covers the pixel electrode PE.

The second substrate SUB2 includes a second transparent base material 20, a light-shielding layer 21, an overcoat layer 22, a second alignment film 23, and a common electrode CE. The second transparent base material 20 has a first surface 20A facing the first substrate SUB1 and a second surface 20B on the opposite side of the first surface 20A.

The light-shielding layer 21 and the common electrode CE are arranged on the first surface 20A side. For example, the light-shielding layer 21 faces the switching element SW, the scanning line G, and the signal line S. The common electrode CE is arranged over the plurality of pixels PX and faces the plurality of pixel electrodes PE in the third direction Z. Further, the common electrode CE covers the light-shielding layer 21. The common electrode CE has the same potential as the capacitance electrode 13. The overcoat layer 22 covers the common electrode CE. The second alignment film 23 covers the overcoat layer 22. The liquid crystal layer LC is arranged between the first alignment film 14 and the second alignment film 23, and is in contact with these alignment films 14, 23.

The first transparent base material 10 and the second transparent base material 20 are insulating substrates such as a glass substrate and a plastic substrate. The insulating film 11 is formed of a transparent insulating material such as silicon oxide, silicon nitride, silicon nitride or acrylic resin. In one example, the insulating film 11 includes an inorganic insulating film and an organic insulating film. The insulating film 12 is an inorganic insulating film such as silicon nitride. The capacitive electrode 13, the pixel electrode PE, and the common electrode CE are transparent electrodes formed of a transparent conductive material such as indium tin oxide (ITO) or indium zinc oxide (IZO). The first alignment film 14 and the second alignment film 23 are horizontal alignment films having an orientation regulating force substantially parallel to the XY plane. The orientation regulating force may be imparted by a rubbing treatment or a photoalignment treatment.

The configuration of the display panel PNL is not limited to the examples of FIGS. 1 and 2. For example, the first substrate SUB1 does not have to include the capacitive electrode 13. Further, the second substrate SUB2 does not have to include the light shielding layer 21.

FIG. 3 is a schematic cross-sectional view of the display panel PNL for explaining a configuration example of the liquid crystal layer LC. In the present embodiment, the liquid crystal layer LC has a streaky (network-like) polymer 30 and liquid crystal molecules 31. In one example, the polymer 30 is a liquid crystal polymer. The liquid crystal molecules 31 are dispersed in the gaps of the polymer 30. As shown in FIG. 3, the monomer 32 connected to the polymer 30 may be present.

In such a liquid crystal layer LC, for example, a liquid crystal monomer is injected between the first alignment film 14 and the second alignment film 23, and the liquid crystal monomer is oriented in a predetermined direction by the orientation restricting force of the alignment films 14 and 23. It can be obtained by irradiating with ultraviolet light. That is, the liquid crystal monomer is polymerized by ultraviolet light to form a streaky polymer 30.

Each of the polymer 30 and the liquid crystal molecule 31 has optical anisotropy or refractive index anisotropy. The responsiveness of the polymer 30 to the electric field is lower than the responsiveness of the liquid crystal molecule 31 to the electric field. For example, the orientation direction of the polymer 30 hardly changes regardless of the electric field between the pixel electrode PE and the common electrode CE. On the other hand, the orientation direction of the liquid crystal molecules 31 changes according to the electric field.

In FIG. 3, the liquid crystal molecule 31 shown by the solid line represents the orientation state when there is no potential difference between the pixel electrode PE and the common electrode CE (when no electric field is formed). Further, the liquid crystal molecule 31 shown by the broken line represents the orientation state when there is a potential difference between the pixel electrode PE and the common electrode CE (when an electric field is formed).

When no electric field is acting on the liquid crystal layer LC or the electric field is extremely weak, the optical axes of the polymer 30 and the liquid crystal molecule 31 are substantially parallel to each other. Therefore, the light incident on the liquid crystal layer LC is transmitted in the liquid crystal layer LC with almost no scattering. Hereinafter, such a state is referred to as a transparent state. Further, the voltage of the pixel electrode PE for realizing the transparent state is called a transparent voltage. The transparent voltage may be the same as the common voltage applied to the common electrode CE, or may be a voltage slightly different from the common voltage.

On the other hand, when a sufficient electric field is applied to the liquid crystal layer LC, the optical axes of the polymer 30 and the liquid crystal molecules 31 intersect with each other. Therefore, the light incident on the liquid crystal layer LC is scattered in the liquid crystal layer LC. Hereinafter, such a state is referred to as a scattering state. Further, the voltage of the pixel electrode PE for realizing the scattered state is called a scattered voltage. The scattered voltage is a voltage such that the potential difference from the common electrode CE is larger than the transparent voltage.

FIG. 4 is a schematic cross-sectional view showing an example of a configuration applicable to the display device DSP. The light source LS is arranged on the extending portion Ex and faces the side surface of the second substrate SUB2. However, the light source LS may be arranged in a place other than the extension portion Ex. Further, the light source LS may face the side surface of the first substrate SUB1 or may face the side surfaces of both the first substrate SUB1 and the second substrate SUB2.

As shown in FIG. 4, the light L1 emitted by the light source LS irradiates the side surface of the second substrate SUB2. The light L1 that has entered the inside of the display panel PNL from the side surface propagates inside the display panel PNL. In the vicinity of the pixel electrode PE (OFF in FIG. 4) to which the transparent voltage is applied, the light L1 is hardly scattered by the liquid crystal layer LC. Therefore, the light L1 hardly leaks from the first substrate SUB1 and the second substrate SUB2.

On the other hand, in the vicinity of the pixel electrode PE (ON in FIG. 4) to which the scattering voltage is applied, the light L1 is scattered by the liquid crystal layer LC. This scattered light is emitted from the first substrate SUB1 and the second substrate SUB2 and is visually recognized as a display image. It is also possible to realize a gradation expression of the degree of scattering (luminance) by defining the scattering voltage stepwise in a predetermined range.

In the vicinity of the pixel electrode PE to which the transparent voltage is applied, the external light L2 incident on the first substrate SUB1 or the second substrate SUB2 is transmitted through these substrates with almost no scattering. That is, when the display panel PNL is viewed from the second substrate SUB2 side, the background of the first substrate SUB1 side is visible, and when the display panel PNL is viewed from the first substrate SUB1 side, the second substrate SUB2 side is visible. The background is visible.

The display device DSP having the above configuration can be driven by, for example, a field sequential method. In this method, one frame period includes a plurality of subframe periods (fields). For example, if the light source LS includes red, green, and blue light emitting elements, one frame period includes red, green, and blue subframe periods.

During the red subframe period, the red light emitting element lights up and a voltage corresponding to the red image data is applied to each pixel electrode PE. As a result, a red image is displayed. Similarly, during the green and blue subframe periods, the green and blue light emitting elements are lit, and voltages corresponding to the green and blue image data are applied to the pixel electrode PEs, respectively. This will display green and blue images. The red, green, and blue images displayed in time division in this way are combined with each other and visually recognized by the observer as a multicolor display image.

The liquid crystal layer LC is in a scattered state when a voltage similar to the common voltage is applied to the pixel electrode PE, and is in a transparent state when a voltage sufficiently different from the common voltage is applied to the pixel electrode PE. It may have the structure. Further, the display device DSP may have a configuration for displaying a monochromatic image.

As shown in FIG. 4, a cover member 40 made of, for example, glass may be arranged on the upper surface (second surface 20B) of the second substrate SUB2. In this case, the light source LS may or may not face the side surface of the cover member 40. Light from the light source LS may propagate inside the cover member 40.

Further, the first optical functional layer 41 may be provided on the upper surface of the cover member 40, and the second optical functional layer 42 may be provided on the lower surface (first surface 10A) of the first substrate SUB1. As these optical functional layers 41 and 42, for example, an ultraviolet light absorption layer or an antireflection layer can be applied. When an ultraviolet light absorbing layer is applied, deterioration of the liquid crystal layer LC due to ultraviolet light can be suppressed. When the antireflection layer is applied, it is possible to suppress the reflection of external light and improve the visibility of the image or the background. The optical functional layers 41 and 42 may include both an ultraviolet light absorbing layer and an antireflection layer.

FIG. 5 is a graph showing the relationship between the voltage applied to the liquid crystal layer LC and the degree of scattering (luminance) of the liquid crystal layer LC. The solid line curve C1 in the graph corresponds to the degree of scattering when the voltage applied to the liquid crystal layer LC is raised to a predetermined value. On the other hand, the broken line curve C2 in the graph corresponds to the degree of scattering when the voltage applied to the liquid crystal layer LC is lowered from the predetermined value.

In any of the curves C1 and C2, the higher the voltage, the higher the degree of scattering, and when the voltage becomes sufficiently large, the degree of scattering becomes saturated. From the viewpoint of display quality, it is preferable that the curves C1 and C2 match. However, in the example of FIG. 5, the curves C1 and C2 coincide with each other in the high voltage region, but in the low voltage region, the curve C2 has a larger degree of scattering than the curve C1 even at the same voltage. It is considered that such hysteresis of the response characteristic occurs because the responsiveness of the liquid crystal molecule 31 is lowered due to the orientation change in the vicinity of the polymer 30 when the voltage applied to the liquid crystal layer LC is lowered.

When the above hysteresis occurs, when the voltage of the pixel electrode PE is repeatedly switched between the transparent voltage and the scattering voltage, the liquid crystal molecules 31 are initially oriented (for example, FIG. 3) even when the transparent voltage is applied to the pixel electrode PE. Seizure may occur that does not completely return to the orientation shown by the solid line. When seizure occurs, the light from the light source LS is scattered even in the pixel PX that should be in the transparent state, and the display quality is deteriorated.

The inventor has found that the hysteresis depends on the shape of the polymer 30. That is, the hysteresis can be improved by optimizing the shape of the polymer 30. The shape of the polymer 30 can be analyzed, for example, by performing a two-dimensional Fourier transform (for example, a fast Fourier transform: FFT) on the pattern of the polymer 30 in a plan view.

The two-dimensional Fourier transform is a process of converting a spatial region consisting of pixel values constituting a pattern into a spatial frequency region. That is, the pattern of the polymer 30 in plan view has frequency components in the horizontal and vertical directions. In the two-dimensional Fourier transform, the pattern is Fourier transformed in the horizontal and vertical directions, and based on the result, a frequency spectrum representing the distribution of amplitude with respect to the frequency components in the horizontal and vertical directions is obtained. Hereinafter, patterns of some polymers 30 and a frequency spectrum obtained by performing a two-dimensional Fourier transform on these patterns will be illustrated.

6A to 9A are schematic views showing an enlarged pattern of the polymer 30 in a plan view. In any pattern, the white portion corresponds to the polymer 30. 6B to 9B are spatial frequency spectra obtained by performing a fast Fourier transform based on magnified photographs of the polymer 30 taken with a microscope, respectively. In FIGS. 6B to 9B, the horizontal axis is the first frequency component Fh (horizontal frequency component), and the vertical axis is the second frequency component Fv (vertical frequency component). For example, one of the first frequency component Fh and the second frequency component Fv is the frequency component in the first direction X, and the other is the frequency component in the second direction Y. However, the directions of these frequency components Fh and Fv are not limited to the first direction X and the second direction Y. The point where the axis of the first frequency component Fh and the axis of the second frequency component Fv intersect is (Fv, Fh) = (0,0), and the farther away from this point, the higher the frequency. The amplitude at each frequency component (Fh, Fv) is represented by the shade of color.

For example, the pattern of the polymer 30 can be adjusted by changing the characteristics of the liquid crystal layer LC before the polymerization, the exposure conditions of ultraviolet light at the time of the polymerization, the conditions at the heat treatment after the polymerization, and the like. By appropriately adjusting these, the polymer 30 having a desired pattern can be realized.

The patterns shown in FIGS. 6A to 9A can be created by taking a magnified photograph of the polymer 30 with a microscope, for example, and binarizing the photograph with a predetermined threshold value. The high-speed Fourier transform for obtaining the spatial frequency spectra of FIGS. 6B to 9B may be applied, for example, to the pattern of the polymer 30 in the region corresponding to one pixel PX. The size of this region (the size of one pixel PX) is, for example, 200 μm × 200 μm or 100 μm × 100 μm, but may be smaller or larger.

6A to 9A show the orientation regulation direction R (for example, the rubbing direction with respect to the alignment films 14 and 23) on which the orientation regulation force of the above-mentioned alignment films 14 and 23 acts, and the orthogonal direction P orthogonal to the orientation regulation direction R. It is indicated by an arrow. In FIGS. 6B to 9B, the directions corresponding to the orientation regulation direction R and the orthogonal direction P in the Fh-Fv plane defined by the frequency components Fh and Fv are indicated by arrows.

6B to 9B show the evaluation circle CR for quantitatively evaluating the spatial frequency spectrum. FIG. 10 is a diagram for explaining the outline of the evaluation circle CR. When determining the evaluation circle CR, first, in the spatial frequency spectrum, a spectrum of 75% or more of the maximum value of the amplitude is plotted on the Fh-Fv plane. Then, the circle obtained by connecting the plots having the highest frequency (the plot farthest from the origin O) in all directions passing through the origin O at (Fv, Fh) = (0,0) is referred to as the evaluation circle CR. To do. Such an evaluation circle CR corresponds to the contour of a region in which the amplitude is 75% or more of the maximum value in the Fh-Fv plane. The evaluation circle CR may be a perfect circle or an ellipse. If the contour does not have an exact perfect circle or ellipse, the evaluation circle CR may be an approximation of the contour to a perfect circle or ellipse. When the evaluation circle CR is elliptical, its long axis is defined as LX and its short axis is defined as SX.

In the pattern of FIG. 6A, the polymer 30 is irregularly distributed in all directions. Therefore, as shown in FIG. 6B, the spatial frequency spectrum is isotropic. The evaluation circle CR in this case is a substantially perfect circle.

In the pattern of FIG. 7A, the polymers 30 extend in the orientation control direction R and are aligned in the orthogonal direction P. As shown in FIG. 7B, the spatial frequency spectrum of such a pattern has a small spectrum width in the orientation regulation direction R and a large spectrum width in the orthogonal direction P. Therefore, the evaluation circle CR has an elliptical shape.

In the patterns of FIGS. 8A and 9A, the pitch of the polymer 30 in the orthogonal direction P is smaller than that of the pattern of FIG. 7A. The evaluation circle CR in this case is also elliptical, but the long axis LX of the evaluation circle CR is longer than that of FIG. 7A because the width of the spectrum in the orthogonal direction P is large as shown in FIGS. 8B and 9B.

In the patterns of FIGS. 8A and 9A, the pitches of the polymers 30 in the orthogonal direction P are equivalent. However, in the pattern of FIG. 8A, the polymer 30 continuously extends in the orientation regulating direction R, whereas in the pattern of FIG. 9A, the polymer 30 intermittently extends in the orientation regulating direction R. Due to this effect, the spatial frequency spectrum of FIG. 9B has a large width in the orientation regulation direction R. Therefore, the short axis SX of the evaluation circle CR of FIG. 9B is longer than the short axis SX of the evaluation circle CR of FIG. 8B.

As described above, the characteristics of the pattern of the polymer 30 in the plan view appear in the evaluation circle CR. In the present embodiment, the value obtained by dividing the length of the major axis LX in the evaluation circle CR by the length of the minor axis SX (LX / SX) is used as the evaluation value of the pattern of the polymer 30. As an example, the evaluation value of the evaluation circle CR in FIG. 6B is 1.0, the evaluation value of the evaluation circle CR in FIG. 7B is 2.0, and the evaluation value of the evaluation circle CR in FIG. 8B is 2.8. , The evaluation value of the evaluation circle CR in FIG. 9B is 2.4.

Next, the relationship between the evaluation circle CR and hysteresis will be described. 11A to 14A are diagrams showing the spatial frequency spectrum and the evaluation circle CR to be evaluated for hysteresis. 11B to 14B are graphs showing the results of measuring the degree of scattering (luminance) with respect to voltage for the liquid crystal layer LC containing the polymer 30 having the spatial frequency spectrum shown in FIGS. 11A to 14A. The solid line curve C1 in the graph corresponds to the degree of scattering when the voltage applied to the liquid crystal layer LC is raised to a predetermined value. On the other hand, the broken line curve C2 in the graph corresponds to the degree of scattering when the voltage applied to the liquid crystal layer LC is lowered from the predetermined value.

In the spatial frequency spectrum of FIG. 11A, the evaluation value (LX / SX) of the evaluation circle CR is 1.9. In this case, as shown in FIG. 11B, the curves C1 and C2 are slightly deviated in the low voltage region.

In the spatial frequency spectrum of FIG. 12A, the evaluation value of the evaluation circle CR is 2.7. In the spatial frequency spectrum of FIG. 13A, the evaluation value of the evaluation circle CR is 3.7. In the spatial frequency spectrum of FIG. 14A, the evaluation value of the evaluation circle CR is 4.4. In these cases, as shown in FIGS. 12B to 14B, the curves C1 and C2 are hardly displaced.

As shown in FIG. 6B, when the evaluation circle CR is a substantially perfect circle (when the evaluation value is 1.0), the curves C1 and C2 deviate more than in FIG. 11B. Therefore, even in the spatial frequency spectrum of FIG. 11A having an evaluation value of 1.9, the hysteresis is improved as compared with the case where the evaluation value is 1.0. This is because, as shown in FIG. 6A, in a complicated pattern in which the polymer 30 extends not only in the orientation control direction R but also in the orthogonal direction P thereof, the movement of the liquid crystal molecules 31 in the vicinity of the polymer 30 is inhibited by the polymer 30. It is thought to be caused.

As the evaluation value increases from 1.0, the deviation of the curves C1 and C2 decreases as shown in FIGS. 11B and 12B. From this result, it can be seen that the hysteresis can be improved by defining the pattern of the polymer 30 so that the evaluation circle CR has an elliptical shape. As an example, it is preferable to determine the pattern of the polymer 30 so that the evaluation value is 1.1 or more.

Further, when the evaluation value is 1.9, there is still a deviation of the curves C1 and C2, so that the evaluation value is larger than 1.9, for example, 2.0 or more shown in FIG. 7B. It is preferable to determine the pattern of the polymer 30.

If the evaluation value is too large, the distance between the polymers 30 arranged in the orthogonal direction P becomes remarkably narrow, which may affect the display quality. Therefore, it is preferable to determine the pattern of the polymer 30 so that the evaluation value is 6.0 or less. Since the pattern with the evaluation value of 4.4 shown in FIG. 14A exhibits good response characteristics as shown in FIG. 14B, it is more preferable to determine the pattern of the polymer 30 so that the evaluation value is 4.5 or less. ..

By adjusting the pattern of the polymer 30 as described above, the occurrence of hysteresis or seizure can be suppressed, and the display quality of the display device DSP provided with the polymer-dispersed liquid crystal layer LC can be improved. Further, in the display device DSP in which the background can be visually recognized as in the present embodiment, the visibility of the background can be improved by suppressing hysteresis or seizure.

From the viewpoint of increasing the degree of scattering of the liquid crystal layer LC to which the voltage is applied, it is preferable that the direction in which the streaky polymer 30 extends and the direction in which the light axis emitted by the light source LS are orthogonal to each other in a plan view. The direction of the optical axis of the light emitted by the light source LS coincides with, for example, the second direction Y shown in FIG. In order to realize such a polymer 30, the orientation regulation direction R of each of the alignment films 14 and 23 may be parallel to the first direction X. When the direction in which the polymer 30 extends and the direction of the optical axis of the light source LS coincide with each other, in the spatial frequency spectra shown in FIGS. 7B to 9B and 11B to 14B, the direction of the long axis LX is the light source. It corresponds to the direction of the optical axis of LS.

As described above, all display devices that can be appropriately designed and implemented by those skilled in the art based on the display devices described as the embodiments of the present invention also belong to the scope of the present invention as long as the gist of the present invention is included.

Within the scope of the idea of the present invention, those skilled in the art can come up with various modifications, and it is understood that these modifications also belong to the scope of the present invention. For example, for each of the above-described embodiments, those skilled in the art appropriately add, delete, or change the design of components, or add, omit, or change the conditions of the process of the present invention. As long as it has a gist, it is included in the scope of the present invention.

In addition, with respect to other actions and effects brought about by the aspects described in each embodiment, those that are clear from the description of the present specification or those that can be appropriately conceived by those skilled in the art are naturally understood to be brought about by the present invention. Will be done.

The display device obtained from the present embodiment will be illustrated below.
[1]
1st board and
The second substrate facing the first substrate and
A liquid crystal layer arranged between the first substrate and the second substrate and containing streaky polymers and liquid crystal molecules,
With the pixel electrodes arranged on the first substrate or the second substrate,
With the common electrode arranged on the first substrate or the second substrate,
A light source for irradiating the liquid crystal layer with light is provided.
In the spatial frequency spectrum obtained by performing a two-dimensional Fourier transform on the streaky polymer pattern with respect to the first frequency component and the second frequency component in a plan view, the contour of a region of 75% or more of the maximum value is the first. A display device that is elliptical in a plane defined by a frequency component and the second frequency component.
[2]
The value obtained by dividing the length of the long axis of the elliptical contour by the length of the short axis is 1.1 or more.
The display device according to the above [1].
[3]
The value obtained by dividing the length of the long axis of the elliptical contour by the length of the short axis is 2.0 or more.
The display device according to the above [2].
[4]
The value obtained by dividing the length of the long axis of the elliptical contour by the length of the short axis is 6.0 or less.
The display device according to any one of the above [1] to [3].
[5]
The value obtained by dividing the length of the long axis of the elliptical contour by the length of the short axis is 4.5 or less.
The display device according to the above [4].
[6]
The light source irradiates the side surface of the first substrate or the second substrate with light.
The display device according to any one of the above [1] to [5].
[7]
The direction of the long axis corresponds to the direction of the optical axis of the light emitted by the light source.
The display device according to any one of the above [1] to [6].

DSP ... Display device, PNL ... Display panel, SUB1 ... 1st substrate, SUB2 ... 2nd substrate, LC ... Liquid crystal layer, LS ... Light source, DA ... Display area, PX ... Pixel, PE ... Pixel electrode, CE ... Common electrode, 30 ... polymer, 31 ... liquid crystal molecule, CR ... evaluation circle, LX ... major axis of evaluation circle, SX ... minor axis of evaluation circle.

Claims (7)

1st board and
The second substrate facing the first substrate and
A liquid crystal layer arranged between the first substrate and the second substrate and containing streaky polymers and liquid crystal molecules,
A light source for irradiating the liquid crystal layer with light is provided.
In the spatial frequency spectrum obtained by performing a two-dimensional Fourier transform on the streaky polymer pattern with respect to the first frequency component and the second frequency component in a plan view, the contour of a region of 75% or more of the maximum value is the first. A display device that is elliptical in the plane defined by the frequency component and the second frequency component. The value obtained by dividing the length of the long axis of the elliptical contour by the length of the short axis is 1.1 or more.
The display device according to claim 1. The value obtained by dividing the length of the long axis of the elliptical contour by the length of the short axis is 2.0 or more.
The display device according to claim 2. The value obtained by dividing the length of the long axis of the elliptical contour by the length of the short axis is 6.0 or less.
The display device according to any one of claims 1 to 3. The value obtained by dividing the length of the long axis of the elliptical contour by the length of the short axis is 4.5 or less.
The display device according to claim 4. The light source irradiates the side surface of the first substrate or the second substrate with light.
The display device according to any one of claims 1 to 5. The direction of the long axis corresponds to the direction of the optical axis of the light emitted by the light source.
The display device according to any one of claims 2 to 5.

Images