JP2009271207A - Liquid crystal display element - Google Patents

Abstract

To realize a liquid crystal display element that further reduces the fluidity of liquid crystal so as not to cause a change in display, and improves the strength while maintaining the brightness and contrast of the display.
A liquid crystal display element in which a liquid crystal 12 is sandwiched between two transparent substrates 11 and 13 and a cell gap is maintained by spacer structures 41, 43, and 45 for bonding and fixing the two transparent substrates. The spacer structure includes a closed structure 41 having one opening corresponding to each pixel, and inner structures 43 and 45 provided in the closed structure 41.
[Selection] Figure 4

Description

  The present invention relates to a liquid crystal display element, and more particularly to a memory type liquid crystal display element.

  In recent years, electronic paper has been actively developed as a rewritable display device that can retain display contents even when the power is turned off. Electronic paper aims to realize ultra-low power consumption that enables memory display even when the power is turned off, a reflective display that is easy on the eyes and does not get tired, and a flexible and thin display body that is flexible like paper Research is ongoing. As application fields in which electronic paper is expected to be used, various application forms such as electronic books, sub-displays for mobile terminal devices, and display units for IC cards have been proposed.

  Various display systems have been proposed for electronic paper, and cholesteric liquid crystal is one of the effective systems for display electronic paper. Cholesteric liquid crystal has excellent characteristics such as semi-permanent display retention (memory property), vivid color display, high contrast, and high resolution.

  Cholesteric liquid crystals are sometimes referred to as chiral nematic liquid crystals, and by adding a relatively large amount (several tens of percent) of chiral additives (chiral materials) to nematic liquid crystals, the molecules of nematic liquid crystals are helical. It is a liquid crystal that forms a cholesteric phase.

  FIG. 1 is a diagram for explaining a state of a cholesteric liquid crystal. As shown in FIGS. 1A and 1B, the display element 10 using cholesteric liquid crystal has an upper substrate 11, a cholesteric liquid crystal layer 12, and a lower substrate 13. A cholesteric liquid crystal has a planar state that reflects incident light as shown in FIG. 1A and a focal conic state that transmits incident light as shown in FIG. The state is stably maintained even in the absence of an electric field.

  In the planar state, light having a wavelength corresponding to the helical pitch of the liquid crystal molecules is reflected. The wavelength λ at which the reflection is maximum is expressed by the following formula from the average refractive index n of the liquid crystal and the helical pitch p.

λ = n · p
On the other hand, the reflection band Δλ varies greatly depending on the refractive index anisotropy Δn of the liquid crystal.

  In the planar state, incident light is reflected, so that a “bright” state, that is, white can be displayed. On the other hand, in the focal conic state, by providing a light absorption layer under the lower substrate 13, light transmitted through the liquid crystal layer is absorbed, so that a "dark" state, that is, black can be displayed.

  As described above, in the planar state, light of a wavelength corresponding to the helical pitch of the liquid crystal molecules is reflected. Therefore, when the liquid crystal material and the chiral material are selected and the content of the chiral material is determined, blue (blue), green When a three-layer panel that selectively reflects each wavelength of (green) and red (red) is obtained and these are laminated, a color display element is obtained.

  Since the cholesteric liquid crystal element and the driving method thereof are described in, for example, Patent Document 1 and the like, detailed description thereof is omitted here. In this application, the description of Patent Document 1 is referred to.

  The liquid crystal display element holds a transparent substrate such as a glass substrate or a resin substrate at a predetermined interval (cell gap), and a liquid crystal material having predetermined characteristics is filled in the gap. In a liquid crystal display element, in order to realize a uniform cell gap, particles having a diameter corresponding to the cell gap, which is called a spacer, are dispersed on one substrate, and then the other substrate is bonded. In addition, a spacer structure having a height corresponding to the cell gap is formed on one transparent substrate, and the other substrate is bonded. Also in the cholesteric liquid crystal display element, a predetermined cell gap is realized by a spacer structure, and in particular, by forming an adhesive spacer structure and bonding and fixing the substrate, the predetermined cell gap is reduced. It is possible to maintain it stably.

  However, in the case of the selective reflection type cholesteric liquid crystal display element used in flexible electronic paper, if an external force is generated by bending the display element or pressing the surface, or if a change in temperature distribution occurs, Causes the liquid crystal to flow. When such liquid crystal flow occurs, there arises a problem that the display changes due to the disorder of the alignment state displaying the image. In general, when the liquid crystal flows, a phase (planar state) with high directivity and high reflectance appears, so that the display phase disappears and the display contrast decreases.

  In order to solve such a problem, Patent Document 2 describes a configuration in which a cross-shaped spacer structure is provided between four adjacent pixels to restrict the flow of liquid crystal. 2A and 2B are diagrams showing the spacer structure described in Patent Document 2, in which FIG. 2A is a perspective view, FIG. 2B is a plan view, and FIG. 2C is an enlarged view of the spacer structure 31. is there. As shown in FIG. 2C, a part of the wall of the spacer structure 31 is thick in order to increase the stability of adhesion to the substrate. In a liquid crystal display element having a simple matrix structure, a plurality of strip electrodes extending in two directions different by 90 degrees are formed on two opposing substrates, and a pixel is formed at an intersection of the strip electrodes. As shown in FIGS. 2A and 2B, in the spacer structure 31, one straight line portion is located between the lower strip electrodes 15 of the lower substrate, and the other straight line portion is not shown. It arrange | positions so that it may be located between the upper strip electrodes of an upper board | substrate. Accordingly, each pixel 16 is surrounded by four spacer structures 31, and four openings are formed between the adjacent spacer structures 31. As a result, the flow of the liquid crystal is limited, so that a change in display can be reduced.

  However, even if the spacer structure of FIG. 2 described in Patent Document 2 is provided, the fluidity of the liquid crystal in the flexible electronic paper cannot be sufficiently reduced, and further reduction of the fluidity of the liquid crystal is required. It was. Therefore, Patent Document 3 describes a liquid crystal display element in which the fluidity of liquid crystal is further reduced by providing a closed structure having one opening so as to surround a pixel. FIG. 3 is a plan view of the spacer structure described in Patent Document 3. As shown in FIG. The spacer structure 32 forms a single small opening 33 that surrounds the pixels 16 and connects each pixel 16 to a liquid crystal injection path 34 extending in the vertical direction. Thereby, the fluidity of the liquid crystal in the pixel 16 is greatly limited, and a change in display due to a change in external force or temperature distribution can be reduced.

International Publication WO2007 / 110949A1 International Publication WO2007 / 007394A1 International Publication WO2008 / 023416A1

  However, even in the spacer structure shown in FIG. 3 described in Patent Document 3, there is still a problem that the fluidity of the liquid crystal is insufficiently reduced and the display is changed.

  Further, in FIG. 3, the spacer structure 32 occupies a larger area than the pixel area, and there is a problem that the brightness of the display is lowered and the contrast is lowered accordingly. In order to solve this problem, it is necessary to reduce the wall thickness of the spacer structure 32. In this case, the pixels are surrounded by the spacer structure 32 having a thin wall, and an external force is applied to the display surface. If it is done, there is a problem that the spacer structure 32 is destroyed.

  An object of the present invention is to realize a liquid crystal display element that further reduces the fluidity of the liquid crystal so as not to cause a change in display, and has improved strength while maintaining display brightness and contrast.

  The dot matrix type display element of the present invention includes a spacer structure for bonding and fixing two transparent substrates, a closed structure corresponding to each pixel having one opening, and an inner portion provided in the closed structure. And a structure.

  It is desirable that the inner structure has a shape that divides the interior surrounded by the closed structure into a subspace connected to one opening through a small subopening.

  Further, since the inner structure is further provided in the space surrounded by the closed structure, the fluidity of the liquid crystal in the space surrounded by the closed structure can be reduced. In particular, if an internal structure having a shape that divides the interior surrounded by the closed structure into a subspace connected to one opening through a small subopening is provided, the liquid crystal in the space surrounded by the closed structure is provided. The fluidity of can be further reduced.

  As described in Patent Document 3, by providing a closed structure having one opening so as to surround a pixel, the fluidity of liquid crystal between the inside and outside of the pixel is greatly reduced. However, the change in the display is also affected by the change in the display phase due to the fluidity of the liquid crystal in the pixel, and the liquid crystal in the pixel is simply provided by providing a closed structure surrounding the pixel. The fluidity could not be reduced sufficiently, and this affected the change in display. On the other hand, according to the present invention, since the fluidity of the liquid crystal in the space surrounded by the closed structure can be reduced, the change in display can be greatly reduced. Note that according to the present invention, not only the fluidity of the liquid crystal within the space surrounded by the closed structure can be reduced, but also the fluidity of the liquid crystal between the inside and outside of the pixel can be further reduced.

  Since the inner structure is further provided in the space surrounded by the closed structure, the external force applied to the surface of the liquid crystal display element is distributed to the closed structure and the inner structure. Thereby, it becomes harder to be destroyed than the closed structure and the internal structure, and accordingly, the thickness of the wall can be reduced and the brightness and contrast of the display can be improved.

  Hereinafter, an embodiment in which the present invention is applied to a full-color cholesteric liquid crystal display device in which flexible cholesteric liquid crystal display elements are laminated will be described. The full-color cholesteric liquid crystal display device is described in detail in Patent Documents 1 to 3 and the like. Since it is widely known, the description of the full-color cholesteric liquid crystal display device is omitted here. The cholesteric liquid crystal display element of this embodiment is different from the conventional example in the shape of an adhesive spacer structure that bonds two substrates with a predetermined cell gap. Hereinafter, different parts will be described.

  The cholesteric liquid crystal display element of the embodiment is made of a polycarbonate substrate having a thickness of 100 μm, and a plurality of strip electrodes made of an IZO transparent conductive film are formed on the surface of each substrate. The strip electrode on the upper substrate and the strip electrode on the lower substrate are arranged to face each other in a direction orthogonal to each other, and are passively driven.

  FIG. 4 is a diagram illustrating a planar shape of the spacer structure in the embodiment. As shown in FIG. 6, pixels are formed at the intersections of the strip-shaped transparent electrodes of the upper strip-shaped electrode 14 and the lower strip-shaped electrode 15. The spacer structure is a triple square thin wall surface provided corresponding to each pixel, and the outermost wall surface 41 has a small opening 42. The wall surface 43 inside the wall surface 41 has a small opening 44. Further, the wall surface 45 inside the wall surface 43 has a small opening 46. Therefore, the space 49 surrounded by the wall surface 45 is connected to the space 48 between the wall surface 45 and the wall surface 43 through the small opening 46. Similarly, the space 48 is connected to a space 47 between the wall surface 43 and the wall surface 41 through a small opening 44. The space 47 is connected to the space 50 between the pixels through a small opening 42.

  Two sides of the outermost wall surface 41 are located between the adjacent upper strip electrodes 14 and the adjacent lower strip electrodes 15. A space 50 is formed between adjacent outermost wall surfaces 41, that is, between pixels, and a space 47 of each pixel is connected to a space 50 between the pixels via a small opening 42. This space 50 is connected between pixels, and an injection opening connected to the space 50 is provided on the side of the display element (panel). After the inside of the panel is in a vacuum state, the liquid crystal is injected by immersing the opening in cholesteric liquid crystal and opening it to the atmosphere.

  FIG. 5 is a diagram illustrating a manufacturing process of the cholesteric liquid crystal display element of the embodiment, the left side shows a common substrate on which a common electrode is formed, and the right side shows a segment substrate on which a segment electrode is formed. Basically, either the common board or the segment board can be used as the upper board or the lower board, but here the lower board is the common board and the upper board is the segment board, and the lower board is a spacer. The description will be made assuming that a structure is formed.

  Transparent conductive film layers 14 and 15 are formed on the upper substrate 11 and the lower substrate 13, respectively.

  Resist layers 51 and 52 are applied on the transparent conductive film layers 14 and 15, respectively.

  The resist layers 51 and 52 are each patterned corresponding to the shape of the strip electrode by photolithography or the like.

  Etching is performed on the patterned resist layers 51 and 52 to process the transparent conductive film layers 14 and 15 into strip-shaped electrodes.

  When the patterned resist layers 51 and 52 are peeled off, the patterned transparent conductive film layers (band electrodes) 14 and 15 appear.

  The steps up to here are the same for the upper substrate 11 and the lower substrate 13.

  An insulating film 53 is formed on the upper substrate 11 so as to cover the patterned strip electrode 14. Thereby, the upper substrate 11 is completed.

  A negative resist 54 for the wall surface of the spacer structure is applied on the lower substrate 13 so as to cover the patterned strip electrode 15.

  Exposure is performed using a photomask 55 that transmits the portion to be left as the wall surface of the spacer structure.

  When the surface of the lower substrate 13 is developed, the portion corresponding to the wall surface of the spacer structure of the negative resist 54 is cured, and the other portions are removed, so that the wall surface of the spacer structure is formed when baked. Further, a seal 56 is formed around the panel. The seal 56 may be formed using the negative resist 54 for the wall surface.

  Thus, the lower substrate 13 is completed.

  Next, the upper substrate 11 is inverted and aligned so that the strip electrode 14 of the upper substrate 11 and the strip electrode 14 of the lower substrate 13 are orthogonal to each other, and the insulating film 53 is formed on the negative resist 54 for the wall surface of the spacer structure. The insulating film 53 is adhered by curing the wall-surface negative resist 54 in contact with each other.

  FIG. 5 shows a manufacturing process when the wall surface of the spacer structure is formed of a negative resist. However, the wall surface of the spacer structure can be formed of a positive resist. FIG. 6 is a diagram showing a manufacturing process when a positive resist is used.

  The manufacturing process of the upper substrate when the positive resist is used and the manufacturing process until the patterned strip electrode 15 is formed on the lower substrate 13 are the same as when the negative resist is used.

  A positive resist 63 for the wall surface of the spacer structure is applied on the lower substrate 13 so as to cover the patterned strip electrode 15.

  The portion left as the wall surface is exposed using a photomask 65 that does not transmit.

  When the surface of the lower substrate 13 is developed, a portion corresponding to the wall surface of the spacer structure of the positive resist 63 remains, and the other portions are removed. At this time, the positive resist 63 is not cured.

  A granular spacer 64 having a diameter corresponding to the cell gap is dispersed. At this time, the spacer 64 may be scattered on the positive resist 63. Further, a seal 56 is formed around the panel.

  Thus, the lower substrate 13 is completed.

  Next, the upper substrate 11 is inverted and aligned so that the strip electrode 14 of the upper substrate 11 and the strip electrode 15 of the lower substrate 13 are orthogonal to each other, and the insulating film 53 forms the positive resist 63 for the wall surface of the spacer structure. Laminate to touch. At this time, when the upper substrate 11 is pressed against the lower substrate 13, the spacers 64 on the positive resist 63 are embedded in the uncured positive resist 63. In this manner, the wall-surface positive resist 63 is cured and the insulating film 53 is adhered in a state in which the distance between the substrates becomes the cell gap by the spacer 64.

  As mentioned above, although the manufacturing process of the cholesteric liquid crystal display element of embodiment was demonstrated, it cannot be overemphasized that there can be various modifications in a manufacturing process.

  FIG. 7 is a diagram illustrating a modification of the wall shape of the spacer structure of the cholesteric liquid crystal display element of the embodiment.

  In the example of FIG. 7A, the outermost wall surface 41 of FIG. 4 is provided inside the same square wall surface 71 and a cross wall surface formed by intersecting wall surfaces 73 and 74 is provided. One end of the wall surface 71 is connected to the wall surface 71, the other end of the wall surface 73 forms a small opening 75 with respect to the small opening 72 of the wall surface 71, and the wall surface 74 is a small opening between the wall surface 71. 76 is formed. The pixel structure is divided into four closed regions by the spacer structure having such a shape, and the four closed regions are connected by a small opening.

  7B, the outermost wall surface 41 of FIG. 4 is placed inside the same square wall surface 81, two wall surfaces extending from the lower side portion having the opening 82 of the wall surface 81, and the lower side And a single wall surface 83 extending from the upper side facing the portion toward the opening 82. The wall surface 83 forms a small opening 85 with respect to the small opening 82 of the wall surface 81, and the wall surface 84 forms a small opening 86 between the wall surface 81. The pixel structure is divided into four closed regions by the spacer structure having such a shape, and the four closed regions are connected by a small opening.

  The pixel structure is divided into a plurality of sub-regions by the spacer structure of FIGS. 4 and 7 described above, and not only the fluidity of the liquid crystal in the pixel is decreased, The fluidity of the liquid crystal outside the pixel is reduced. Further, the external force applied to the surface of the liquid crystal display element is dispersed in the closed structure and the internal structure. Thereby, it becomes harder to be destroyed than the closed structure and the internal structure, and accordingly, the thickness of the wall can be reduced and the brightness and contrast of the display can be improved. Needless to say, the shape of the spacer structure may have various modifications.

  As mentioned above, although embodiment of this invention was described, it cannot be overemphasized that this invention is not limited to this and various modifications are possible. For example, in the embodiment, an example in which cholesteric liquid crystal is used has been described. However, since the fluidity of other liquid crystals can be reduced by the spacer structure of the present invention, a liquid crystal display element that maintains display for a long time using memory characteristics If it is effective.

  As for the shape of the spacer structure, it is obvious to those skilled in the art to select an optimum shape according to the specification.

FIG. 1 is a diagram illustrating a bistable state (planar state and focal conic state) of a cholesteric liquid crystal. FIG. 2 is a view showing a conventional example of a spacer structure. FIG. 3 is a view showing another conventional example of the spacer structure. FIG. 4 is a diagram illustrating the spacer structure according to the embodiment. FIG. 5 is a diagram illustrating a manufacturing process of the liquid crystal display element of the embodiment. FIG. 6 is a diagram illustrating another manufacturing process of the liquid crystal display element of the embodiment. FIG. 7 is a diagram illustrating a modification of the spacer structure according to the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Display element 11 Upper substrate 12 Liquid crystal layer 13 Lower substrate 14 Upper strip electrode 15 Lower strip electrode 17 Light absorption layer 41, 43, 45 Wall surface 42, 44, 46 of spacer structure Opening

Claims (5)

A liquid crystal display element in which a cell gap is maintained by a spacer structure that sandwiches liquid crystal between two transparent substrates and adheres and fixes the two transparent substrates,
The said spacer structure is provided with the closed structure which has one opening part corresponding to each pixel, and the inner structure provided in the said closed structure, The liquid crystal display element characterized by the above-mentioned.   The liquid crystal display element according to claim 1, wherein the inner structure divides an interior surrounded by the closed structure into a subspace connected to the one opening through a small subopening.   The liquid crystal display element according to claim 1, wherein a plurality of the internal structures are formed in the closed structure.   The internal structure has a cross shape, and a space in the closed structure is divided into four subspaces by the cross-shaped internal structure. The liquid crystal display element as described.   The liquid crystal display element according to claim 1, wherein the inner structure has a plurality of walls alternately extending in a comb shape from the closed structure.

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