JP2012173590A - Liquid crystal display and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display including a plurality of effective display regions whose switching characteristics are different from each other, and a method of easily manufacturing the liquid crystal display.SOLUTION: In a liquid crystal display including a plurality of effective display regions, the spacer area density of a predetermined effective display region is made small and the thickness of a liquid crystal layer is made thin.

Description

  The present invention relates to a liquid crystal display element including a plurality of effective display areas having different switching characteristics, and a manufacturing method thereof.

  The liquid crystal display element applies a voltage to the liquid crystal layer sandwiched between the opposing substrates, thereby controlling the alignment of the liquid crystal molecules constituting the liquid crystal layer and changing the retardation. The display state is switched in combination with the plate. Liquid crystal display devices are known to have slower switching characteristics than other display devices, especially in low-temperature environments. Switching is performed by reducing the thickness of the liquid crystal layer or lowering the viscosity of the liquid crystal layer. Methods for improving the characteristics have been proposed.

  FIG. 10 is a plan view schematically showing an in-vehicle information display unit using a liquid crystal display element. The in-vehicle information display unit 10 includes effective display areas 11a and 11b. For example, the seven-segment display areas 12a to 12c that display vehicle speed information in the effective display area 11a and the temperature information in the vehicle in the effective display area 11b are displayed. 7-segment display areas 12d and 12e. In such an in-vehicle information display unit 10, the speed information displayed in the effective display area 11 a needs to immediately follow the speed change of the vehicle for the safety of the driver and the passenger.

  Thus, there are cases where it is desired to improve at least the switching characteristics of the effective display area 11a in the information display unit 10. In this case, a method of arranging different liquid crystal display elements having different switching characteristics in the effective display region 11a and the effective display region 11b in parallel can be considered. However, in this method, there is a possibility that the boundary portion of these liquid crystal display elements can be visually recognized, so that there is room for improvement in appearance quality. Further, in one liquid crystal display element, a method of providing a resin or the like between opposing substrates corresponding to the effective display region 11a and reducing the thickness of the liquid crystal layer located in the region can be considered (for example, Patent Document 1). . However, this method is not very preferable from the viewpoint of production efficiency because the number of steps for forming a resin or the like between the opposing substrates increases.

Japanese Patent No. 4105437

  An object of the present invention is to provide a liquid crystal display element including a plurality of effective display regions having different switching characteristics, and a method for easily manufacturing the liquid crystal display element.

  According to one aspect of the present invention, a pair of substrates with electrodes that define a first effective display region and a second effective display region, and a pair of substrates, the opposing distance between the pair of substrates is set. A plurality of spacers having different area densities in the first effective display region and the second effective display region, and arranged in a peripheral portion between the pair of substrates, and partitioning the opposing region of the pair of substrates There is provided a liquid crystal display element including a sealing material to be sealed and a liquid crystal layer filled in an opposing region of the pair of substrates and having different thicknesses in the first effective display region and the second effective display region. .

  According to another aspect of the present invention, step a) forming an electrode for defining a first effective display region and a second effective display region on the surface of the pair of substrates; and step b) the pair of substrates Forming a plurality of spacers having a uniform height on the surface of at least one of the substrates on which the electrodes are formed with different area densities in the first effective display region and the second effective display region. And c) a step of forming a sealing material on a peripheral portion of the surface of one of the pair of substrates on which the electrodes are formed; and a step d) the pair of substrates sandwiching the spacer and the sealing material. A step of forming an empty cell in which the facing distance between the pair of substrates in the first effective display area is different from the facing distance between the pair of substrates in the second effective display area; and step e) A process for enclosing liquid crystal in the empty cell. When a method of manufacturing a liquid crystal display device comprising, are provided.

  A liquid crystal display device including a plurality of effective display areas having different switching characteristics is provided.

and 1A and 1B are schematic cross-sectional views of a liquid crystal display element including a plurality of effective display regions having different spacer arrangement densities. FIG. 2 is a block diagram showing a manufacturing flow of a liquid crystal display element including a plurality of effective display areas having different spacer arrangement densities. and 3A and 3B are a schematic plan view of the first photomask used in the spacer forming step, and a plane observation photograph of the empty cell in which the spacer is manufactured using the first photomask. and 4A and 4B are a schematic plan view of the second photomask used in the spacer forming step, and a plane observation photograph of the empty cell in which the spacer is manufactured using the second photomask. and 5A and 5B are a schematic plan view of a third photomask used in the spacer formation step, and a plane observation photograph of an empty cell in which a spacer is manufactured using the third photomask. and 6A and 6B are a schematic plan view of the fourth photomask used in the spacer formation step, and a plane observation photograph of the empty cell in which the spacer is manufactured using the fourth photomask. FIG. 7 is a graph showing the spacer area density dependence of the liquid crystal layer thickness. 8A and 8B are schematic cross-sectional views of a liquid crystal display element including a plurality of effective display regions having different spacer area densities and further combining a polarizing plate, a retardation plate, and the like. FIG. 9 is a schematic cross-sectional view of a liquid crystal display element including a plurality of effective display areas having different spacer area densities, in which liquid crystal layers having different viscosities are filled in each area. FIG. 10 is a plan view schematically showing an in-vehicle information display unit using a liquid crystal display element.

  FIG. 1A is a cross-sectional view showing a part of the configuration of a liquid crystal display element studied by the present inventors. The liquid crystal display element 10 is disposed between a pair of substrates 1a and 1b, a pair of substrates 1a and 1b, a plurality of spacers 2 that hold a substrate facing distance (a facing distance between the pair of substrates 1a and 1b), and a pair of substrates. And a liquid crystal layer 4 that fills the substrate facing region and a sealing material 3 that divides the substrate facing region (the facing region of the pair of substrates 1a and 1b). It is. The pair of substrates 1a and 1b includes upper and lower electrodes 6a and 6b disposed on the surfaces of the upper and lower substrates 5a and 5b, and the alignment films 7a and 6b disposed so as to cover the glass substrates 5a and 5b, the electrodes 6a and 6b and the spacer 2, respectively. 7b. The display areas 12a to 12d are defined as areas where the electrodes 6a and 6b overlap with the liquid crystal layer 4 interposed therebetween, and the effective display areas 11a and 11b are defined as areas where a plurality of display areas 12a and 12b and display areas 12c and 12d are arranged. The Here, as shown in FIG. 1A, the present inventors have determined that the area density of spacers (referred to as spacers 2a) in the effective display area 11a (spacer occupation area ratio per unit area in the substrate plane) is the effective display area 11b. The liquid crystal display element 10 having a smaller area density than the spacer (referred to as the spacer 2b) in FIG.

  FIG. 1B is a cross-sectional view schematically showing a liquid crystal display element studied by the present inventors. When the spacers 2 are uniformly arranged between the pair of substrates 1a and 1b, the substrate facing pressure applied to each spacer 2 (the pressure for maintaining the facing distance between the pair of substrates 1a and 1b) is uniform. The compressive displacement of the spacer 2 is considered to be uniform within the substrate surface. For example, in the effective display area 11a, the arrangement density of spacers 2a (the number of spacers per unit area) is reduced, and the spacer area density is made smaller than a predetermined value. At this time, it is considered that the substrate facing pressure per spacer 2a is larger than the substrate facing pressure per spacer 2b, and the compression displacement of the spacer 2a is larger than the compression displacement of the spacer 2b. That is, as shown in FIG. 1B, the substrate facing distance is shorter in the effective display area 11a (substrate facing distance d1) than the effective display area 11b (substrate facing distance d2), and correspondingly, the substrate facing area is filled. The thickness of the liquid crystal layer 4 is also considered to be thinner in the effective display area 11a than in the effective display area 11b. In general, the switching characteristics of a liquid crystal display element are faster when the liquid crystal layer is thin, and are slower when the liquid crystal layer is thick. Therefore, it is considered that an effective display region 11a having relatively fast switching characteristics and a slow effective display region 11b are realized in the liquid crystal display element 10. For convenience, the change in the liquid crystal layer thickness is exaggerated in FIG. 1B.

  The present inventors produced a plurality of liquid crystal display elements having different spacer shapes and arrangement densities, and evaluated the dependency of the liquid crystal layer thickness on the spacer area density.

  FIG. 2 is a block diagram showing a manufacturing flow of a vertical alignment type liquid crystal display device manufactured by the present inventors. Hereinafter, a method for manufacturing a liquid crystal display element manufactured by the present inventors will be described with reference to FIGS.

  The electrode-formed substrate forming step 21 will be described. ITO films are formed on the upper and lower glass substrates 5a and 5b, and upper and lower ITO electrodes 6a and 6b having desired patterns are formed by a photolithography process and an etching process. Note that a black mask and an insulating film may be formed on the glass substrate surface as necessary.

  The spacer forming step 22 will be described. The lower glass substrate 5a on which the ITO electrode 6a is formed is coated with an ultraviolet-sensitive transparent resin (manufactured by Osaka Organic Chemical Co., Ltd.) with a thickness of about 4.5 μm using a slit coater, and prebaked at 90 ° C. for 30 seconds on a hot plate. I do. An ultraviolet exposure process is performed at a light intensity of about 200 mJ / cm through a photomask having a predetermined pattern, which will be described later, and a development process is performed with a TMAH (tetramethylammonium hydroxide) 0.04 wt% aqueous solution. After removing the TMAH aqueous solution by washing or the like, post-baking is performed at 200 ° C. for 60 minutes in a clean oven to form the spacer 2. The spacer 2 may be formed on the glass substrate 5b or on both the glass substrates 5a and 5b. Further, a spin coater may be used for applying the ultraviolet photosensitive transparent resin. Furthermore, the spacer 2 is preferably a translucent resin.

  The alignment film forming step 23 will be described. On the glass electrode 5a and the glass electrode 5b on which the spacer 2 having a uniform height with a predetermined pattern is formed, alignment films 7a and 7b having vertical alignment are applied by a flexographic printing method. Pre-bake at 90 ° C. for 15 minutes and host bake at 180 ° C. for 30 minutes in a clean oven. The glass substrates 5a and 5b on which the vertical alignment films 7a and 7b are formed are rubbed using a cotton rubbing cloth. The rubbing process was performed under the condition that the pretilt angle of the completed vertically aligned liquid crystal display element was about 89.9 °. Further, as the alignment treatment, an alignment method other than the rubbing treatment, for example, a photo alignment treatment method may be used. Furthermore, the alignment process should just be given to at least one board | substrate. Through the above steps, a pair of substrates 1a and 1b is completed.

  The bonding process 24 and the liquid crystal sealing process 25 will be described. The thermosetting sealing material 3 is applied in a desired pattern to one of the pair of substrates 1a and 1b. The pair of substrates 1a and 1b are bonded together so as to sandwich the sealing material 3 and the spacer 2, and the sealing material 3 is cured by thermocompression to complete an empty cell. Note that the pair of substrates were bonded so that the direction of the rubbing treatment performed in the previous step was antiparallel. Thereafter, a liquid crystal material (manufactured by Merck) with Δε <0 is injected into the empty cell by vacuum injection, sealed, and annealed at 120 ° C. for 60 minutes. Through the above steps, a vertical alignment type liquid crystal display element is completed.

  3A and 3B are a schematic plan view of the first photomask used in the spacer forming step, and a plane observation photograph of an empty cell in which a spacer is manufactured using the first photomask. As shown in FIG. 3A, the first photomask 31 has a pattern in which rectangular openings 31a are periodically arranged in four directions. The rectangular openings 31a are arranged with a side width W of 10 μm and a pitch P of 0.1 mm. The planar shape of the spacer 2 actually produced using the first photomask was substantially circular as shown in the region surrounded by the solid line in FIG. 3B, for example. Moreover, it was confirmed that the cross-sectional shape of the spacer 2 is a taper shape. In addition, for example, a “<”-shaped pattern 6 surrounded by a broken line in FIG. 3B is a pattern of an ITO electrode formed on a glass substrate.

  4A and 4B are a schematic plan view of the second photomask used in the spacer formation step, and a plane observation photograph of an empty cell in which a spacer is manufactured using the second photomask. As shown in FIG. 4A, the second photomask 32 has a pattern in which cross-shaped openings 32a are periodically arranged in four directions. The cross-shaped opening 32a has a width W of 10 μm, a length L of 0.1 mm, and a pitch P of 0.29 mm. The planar shape of the spacer 2 actually produced using the second photomask was a cross shape with rounded corners as shown in the region surrounded by the solid line in FIG. 4B, for example. Moreover, it was confirmed that the cross-sectional shape of the spacer 2 is a taper shape. For example, a rectangular pattern 6 surrounded by a broken line in FIG. 4B is an ITO electrode pattern formed on a glass substrate.

  5A and 5B are a schematic plan view of a third photomask used in the spacer formation step, and a plane observation photograph of an empty cell in which a spacer is manufactured using the third photomask. As shown in FIG. 5A, the third photomask 33 is a pattern in which rectangular openings 33a and 33b extending in directions orthogonal to each other are periodically arranged so as not to overlap each other. The rectangular openings 33a and 33b are arranged with a width W of 10 μm, a length L of 0.2 mm, an interval S of 0.09 mm, and a pitch P of 0.29 mm. The planar shape of the spacer 2 actually produced using the third photomask was a rectangular shape with rounded corners as shown in the region surrounded by the solid line in FIG. 5B, for example. Moreover, it was confirmed that the cross-sectional shape of the spacer 2 is a taper shape. For example, the inclined rectangular pattern 6 surrounded by the broken line in FIG. 5B is an ITO electrode pattern formed on the glass substrate.

  6A and 6B are a schematic plan view of a fourth photomask used in the spacer formation step, and a plane observation photograph of an empty cell in which a spacer is manufactured using the fourth photomask. As shown in FIG. 6A, the fourth photomask 34 has a pattern in which line-shaped openings 34a are periodically arranged. The line-shaped openings 34a are arranged with a line width W of 10 μm and a pitch P of 0.29 mm. The planar shape of the spacer 2 actually produced using the fourth photomask was a line shape as shown in the region surrounded by the solid line in FIG. 6B, for example. In addition, the cross-sectional shape of the spacer 2 was estimated to be a tapered shape having a bottom side of about 20 μm and an upper side of about 10 μm. For example, a rectangular pattern 6 surrounded by a broken line in FIG. 6B is an ITO electrode pattern formed on a glass substrate.

  The present inventors produce a plurality of liquid crystal display elements having different spacer sizes and arrangement pitches in addition to the liquid crystal display elements having the spacers described above, and measure the retardation of the liquid crystal display elements. Thus, the liquid crystal layer thickness was estimated. The retardation is a parameter representing the phase difference of the polarization component of light, and is determined by the product of the liquid crystal layer thickness and the birefringence of the liquid crystal material constituting the liquid crystal layer.

  FIG. 7 is a graph showing the spacer area density dependence of the liquid crystal layer thickness. The horizontal axis represents the spacer area density (spacer occupation area ratio per unit area in the substrate plane), and the vertical axis represents the liquid crystal layer thickness (μm). From this graph, it can be seen that when the spacer area density is about 0.035 or less, the liquid crystal layer thickness significantly increases from about 3.2 μm to about 4.2 μm as the spacer area density increases. On the other hand, when the spacer area density is larger than about 0.035, the liquid crystal layer thickness is about 4.2 μm, and it can be seen that the increase in the liquid crystal layer thickness accompanying the increase in the spacer area density is not noticeable. According to further studies by the present inventors, it has been found that when the spacer area density is about 6%, the liquid crystal layer thickness is about 4.3 μm, and the liquid crystal layer thickness is almost saturated.

  From the above results, it was found that in this example, the liquid crystal layer thickness can be controlled by adjusting the spacer area density in the range where the spacer area density is about 0.035 or less. For example, in a liquid crystal display element including a first effective display region and a second effective display region, the spacer area density in the first effective display region is about 0.035 or less, and the spacer area in the second effective display region is By setting the density higher than about 0.035, it is possible to obtain a liquid crystal display element in which the liquid crystal layer thickness is thinner in the first effective display area than in the second effective display area, that is, the switching characteristics are faster. In addition, a liquid crystal display element including a plurality of regions having different spacer area densities can be manufactured by simply forming a spacer using a photomask including a plurality of regions having different opening patterns as compared with a conventional manufacturing method. It is possible to manufacture easily without increasing. Note that the error of the liquid crystal layer thickness in the conventional liquid crystal display element is about ± 0.1 μm, and it cannot be said that a sufficient difference in switching characteristics is realized with such a difference in liquid crystal layer thickness. The difference in the liquid crystal layer thickness is preferably at least twice the error of the liquid crystal layer thickness in a general liquid crystal display element, more preferably at least 0.5 μm.

  8A and 8B are schematic cross-sectional views of a liquid crystal display element including a plurality of effective display regions having different spacer area densities and further combining a polarizing plate, a retardation plate, and the like. Since liquid crystal display elements including a plurality of effective display regions having different spacer area densities have different liquid crystal layer thicknesses, retardation may be different in each region. In this case, as shown in FIG. 8A, a common polarizing plate 41 is disposed in each region on the observation surface side, and polarizing plates 42a and 42b having different absorption axis directions in each region are disposed on the other surface side. It is preferable to arrange the light shielding member 43 between the plates 42a and 42b by black ink printing or the like. With such a configuration, it is considered that deterioration in appearance quality such that a boundary portion of each region is visually recognized when viewed from the observation surface side is suppressed. Further, as shown in FIG. 8B, a common polarizing plate 41, 44 is disposed in each region on the observation surface side and the other surface side, and a phase difference plate 45 for changing the phase difference of the polarization component of light on the other surface side. Even with the arrangement, it is considered that deterioration in appearance quality is suppressed such that the boundary of each region is visually recognized when viewed from the observation surface side. Note that it is preferable to use a retardation film containing a polymerizable compound disclosed in Japanese Patent Application Laid-Open No. 2004-231638 as the retardation plate 45 because the difference in thickness between the regions is not noticeable.

  As mentioned above, although this invention was demonstrated along the Example, this invention is not limited to these. For example, the spacer is not limited to the shape and pattern shown in the embodiments. In the embodiments, the vertical alignment type liquid crystal display element has been described. However, the alignment state of the liquid crystal layer is not limited thereto.

  FIG. 9 shows a liquid crystal display element including effective display regions 11a and 11b having different spacer area densities, and partition walls 46a and 46b partitioning each region between a pair of substrates 1a and 1b. It is a schematic sectional drawing of the liquid crystal display element with which layers 4a and 4b are filled. In general, the switching characteristics of a liquid crystal display element increase when the viscosity of the liquid crystal layer is low, and decrease when the viscosity is high. Therefore, it is considered that the switching characteristics of the region can be further improved by filling the substrate facing region where the spacer area density is small and the liquid crystal layer thickness is thin with a liquid crystal layer having low viscosity. In such a liquid crystal display element in which each region is partitioned by a partition wall, a liquid crystal layer having a different alignment state, for example, a twisted nematic liquid crystal or a super twisted nematic liquid crystal may be filled in each region.

  It will be apparent to those skilled in the art that other various modifications, improvements, combinations, and the like are possible.

1 Substrate with electrodes,
2 spacers,
3 Sealing material,
4 Liquid crystal layer,
5 glass substrate,
6 electrodes,
7 Alignment film.

Claims (9)

A pair of substrates with electrodes defining a first effective display area and a second effective display area;
A plurality of spacers disposed between the pair of substrates, maintaining a facing distance between the pair of substrates, and having different area densities in the first effective display region and the second effective display region;
A sealing material that is disposed at a peripheral portion between the pair of substrates, and defines a facing region of the pair of substrates;
A liquid crystal layer filled in an opposing region of the pair of substrates and having different thicknesses in the first effective display region and the second effective display region;
A liquid crystal display element comprising:   2. The liquid crystal display element according to claim 1, wherein the liquid crystal layer located in the first effective display area and the liquid crystal layer located in the second effective display area are different in thickness by 0.5 μm or more.   The liquid crystal display element according to claim 1, wherein the spacer disposed in the first effective display area and the spacer disposed in the second effective display area have different planar shapes.   The liquid crystal display element according to claim 1, wherein the spacer is a translucent resin. Furthermore, a partition is provided between the pair of substrates to partition the first effective display area and the second effective display area,
The liquid crystal layer includes: a first liquid crystal layer filled in the first effective display area; and a second liquid crystal layer filled in the second effective display area;
The liquid crystal display element according to claim 1, wherein the first liquid crystal layer and the second liquid crystal layer have different viscosities.   The liquid crystal display element according to claim 5, wherein the first liquid crystal layer and the second liquid crystal layer have different natural alignment states.   Further, different polarizing plates are disposed outside the one of the pair of substrates in the first effective display region and the second effective display region, and a light shielding member is disposed between the polarizing plates. Item 7. The liquid crystal display element according to any one of items 1 to 6. Step a) forming an electrode that defines a first effective display region and a second effective display region on a pair of substrate surfaces;
Step b) A plurality of spacers having a uniform height are provided between the first effective display region and the second effective display region on the surface of the pair of substrates on which the electrodes are formed. Forming with different area densities;
Step c) forming a sealing material on a peripheral portion of a surface of the pair of substrates on which the electrodes of the one substrate are formed;
Step d) The pair of substrates are bonded to each other with the spacer and the sealing material interposed therebetween, and the opposing distance between the pair of substrates in the first effective display region and the pair of substrates in the second effective display region Forming empty cells with different facing distances;
Step e) enclosing a liquid crystal in the empty cell;
A method for producing a liquid crystal display element comprising:   In the step b), the spacer applies a photosensitive resin to a surface of one of the pair of substrates on which the electrode is formed, and performs an exposure process and a development process using a photomask on the photosensitive resin. The manufacturing method of the liquid crystal display element of Claim 8 formed by performing.