JP2010224031A - Liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display element achieved in favorable display. <P>SOLUTION: The liquid crystal display element includes: a first substrate; a second substrate disposed opposite to the first substrate; a liquid crystal layer held between the first and second substrates and vertically aligned; a first sheet polarizer disposed on the surface at the opposite side to the liquid crystal layer in the first substrate; and a second sheet polarizer disposed in a cross Nicol state with the first sheet polarizer on the surface at the opposite side to the liquid crystal layer in the second substrate. The liquid crystal layer contains a host liquid crystal and a dichroic coloring matter uniformly dispersed in the host liquid crystal and exhibiting a blue color, and a content of the dichroic coloring matter in the liquid crystal layer is not lower than 0.001 wt.% and lower than 0.5 wt.% with respect to the host liquid crystal. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a liquid crystal display (LCD).

  A liquid crystal display element containing a dichroic dye in a liquid crystal layer is known (see, for example, Patent Document 1). Patent Document 1 describes an invention of a highly stable normally white mode reflective guest-host liquid crystal display element utilizing vertical alignment. According to this liquid crystal display element, bright display can be realized.

  In a transmissive liquid crystal display element, a polarizing plate is used to improve display contrast. In the case of a transmissive liquid crystal display element utilizing vertical alignment, it is difficult to obtain a sufficient black display with a parallel Nicol arrangement, and therefore a crossed Nicols polarizing plate arrangement is usually employed. In a vertical alignment type liquid crystal display element in which polarizing plates are arranged in crossed Nicols, black display is obtained when no voltage is applied, and white display is obtained when a voltage is applied. This is because the liquid crystal molecules are vertically aligned when no voltage is applied and horizontally aligned when a voltage is applied.

  Here, in the liquid crystal display element, the condition that no voltage is applied is a portion other than the so-called pixel that is not opposed to the electrode. For the pixel portion, the orientation of the liquid crystal is controlled by the OFF voltage and the ON voltage, and the transmittance is controlled. In a liquid crystal display element that performs duty driving, an OFF voltage is applied to the OFF portion, so that the liquid crystal molecules respond to such an extent that the transmittance is not greatly affected. For this reason, there is a slight difference in transmittance between the OFF state of the pixel portion and the no-voltage application state. Due to this difference, the phenomenon in which the OFF portion is visually recognized is called OFF segment appearance. Due to the appearance of the OFF segment, when the OFF voltage is applied, the OFF portion looks different from the background and is observed.

  By the way, the dichroic dye has a molecular structure similar to liquid crystal molecules, and can change the alignment state in synchronization with the movement of the liquid crystal. For this reason, when a vertically aligned liquid crystal cell to which a dichroic dye is added is observed without applying a polarizing plate, white (colorless and transparent) display is displayed when the voltage is OFF, and color (colored) display is displayed when the voltage is ON. Therefore, in a liquid crystal display element in which polarizing plates are arranged in a crossed Nicol arrangement in this liquid crystal cell, a black display equivalent to an element not containing a dichroic dye is obtained when the voltage is OFF. The brightness of the display is reduced as compared with an element that does not include the element. As a result, the display becomes dark and the contrast decreases.

  Further, when a dichroic dye is added, an increase in driving voltage of the element becomes a problem. For these reasons, adding a dichroic dye to a vertical alignment type liquid crystal display element in which polarizing plates are arranged in crossed Nicols has been considered as an undesirable treatment that leads to a reduction in display performance.

  It is known that a general vertical alignment type liquid crystal display element to which a dichroic dye is not added (for example, see Patent Document 2) also causes a display problem called yellowing. Yellowing is a phenomenon in which the white display is yellowish, and is noticeable when the viewing angle is changed and the liquid crystal display element is observed. It is particularly easy to observe in high duty driving.

  In order to suppress yellowing, an invention of a vertical alignment type liquid crystal display element in which a dichroic dye for color compensation is added to a liquid crystal layer is disclosed (for example, see Patent Document 3).

JP 10-31216 A JP 2005-234254 A Japanese Patent Laid-Open No. 10-282498

  An object of the present invention is to provide a liquid crystal display element capable of good display.

  According to one aspect of the present invention, a first substrate, a second substrate disposed opposite to the first substrate, and a vertically aligned liquid crystal layer sandwiched between the first and second substrates A first polarizing plate disposed on a surface of the first substrate opposite to the liquid crystal layer; and a first polarizing plate disposed on a surface of the second substrate opposite to the liquid crystal layer. A liquid crystal layer including a host liquid crystal and a dichroic dye exhibiting a blue color uniformly dispersed in the host liquid crystal, and the liquid crystal layer The liquid crystal display element in which the content of the dichroic dye in the layer is 0.001 wt% or more and less than 0.5 wt% with respect to the host liquid crystal is provided.

  According to the present invention, it is possible to provide a vertical alignment type liquid crystal display element capable of reducing the problem of yellowing and OFF seg appearance without impairing the transmittance, particularly the front ON transmittance, and enabling good display. .

It is a flowchart which shows the manufacturing method of the liquid crystal display element by an Example. It is the schematic of the liquid crystal display element by an Example. When, 3A and 3B are graphs showing the relationship between the drive voltage and the contrast ratio. When, When, When, 4A to 4D are graphs showing the relationship between the wavelength of light and the transmittance for ON display (bright display). When, When, When, 5A to 5D are graphs showing the relationship between the wavelength of light and the transmittance for OFF display (black display). When, When, When, 6A to 6D are graphs showing the relationship between the wavelength of light and the transmittance for background display. When, When, When, FIGS. 7A to 7D are graphs showing comparison results for the comparative sample and the first to third samples observed from the polar angle 30 ° direction of the optimum viewing direction. When, When, When, FIGS. 8A to 8D are graphs showing comparison results for the comparative sample and the first to third samples observed from the polar angle 50 ° direction of the optimum viewing direction, respectively. It is a graph which shows the relationship between a drive voltage and contrast ratio. When, When, When, 10A to 10D are graphs showing the relationship between the wavelength of light and the transmittance for ON display. When, When, When, FIGS. 11A to 11D are graphs showing the relationship between the wavelength of light and the transmittance for OFF display. When, When, When, 12A to 12D are graphs showing the relationship between the wavelength of light and the transmittance for background display. When, When, When, FIGS. 13A to 13D are graphs showing the comparison results for the comparative sample and the fourth to sixth samples, respectively, observed from the polar angle 30 ° direction of the optimal viewing direction. When, When, When, FIGS. 14A to 14D are graphs showing the comparison results for the comparative sample and the fourth to sixth samples observed from the polar angle 50 ° direction of the optimum viewing direction. The chromaticity diagram regarding a comparative sample and the 4th-6th sample is shown. It is a graph which shows the relationship between a drive voltage and contrast ratio. When, When, When, FIGS. 17A to 17D are graphs showing the relationship between the wavelength of light and the transmittance for ON display. When, When, When, 18A to 18D are graphs showing the relationship between the wavelength of light and the transmittance for OFF display. When, When, When, 19A to 19D are graphs showing the relationship between the wavelength of light and the transmittance for background display. When, When, When, 20A to 20D are graphs showing comparison results for the second comparative sample and the seventh to ninth samples observed from the polar angle 30 ° direction of the optimum viewing direction. When, When, When, FIGS. 21A to 21D are graphs showing the comparison results for the second comparative sample and the seventh to ninth samples, respectively, observed from the polar angle 50 ° direction of the optimal viewing direction.

  FIG. 1 is a flowchart illustrating a method for manufacturing a liquid crystal display device according to an embodiment.

  First, in step S101, two transparent substrates, for example, glass substrates are prepared, and a transparent electrode is formed on the glass substrate by, for example, ITO (Indium Tin Oxide). The transparent electrode is formed by etching an ITO film formed by vapor deposition or sputtering on a glass substrate into a desired ITO pattern by a photolithography process.

  In step S102, an insulating film is formed on each glass substrate on which the ITO pattern is formed by, for example, flexographic printing. The insulating film is formed in a portion corresponding to the display portion of the completed liquid crystal display element. The insulating film is not limited to printing, and can be formed by vapor deposition using a metal mask or sputtering. Note that the formation of the insulating film is not essential, but it is desirable to form it in order to prevent a short circuit between the upper and lower substrates of the liquid crystal display element.

  In step S103, a vertical alignment film having substantially the same pattern as the insulating film is formed on the insulating film. The alignment film is formed using, for example, a vertical alignment film material manufactured by Nissan Chemical Industries, Ltd., SE-1211. A known technique, for example, a method described in Patent Document 2 is used so that uniform monodomain alignment is realized.

  Next, in step S104, the alignment film is subjected to an alignment process by rubbing. The rubbing process is a process in which a cylindrical roll wound with a cloth is rotated at high speed and rubbed on the alignment film. By rubbing the alignment film, the liquid crystal molecules of the liquid crystal display element are uniaxially (unidirectional) Along). For example, the rubbing process is performed so that the alignment state between the upper and lower substrates is anti-parallel (anti-parallel).

  Note that the alignment treatment performed on the upper and lower substrates may be performed using a photo-alignment method, an ion beam alignment method, a plasma beam alignment method, an oblique deposition method, or the like instead of rubbing.

  By the processes of steps S101 to S104, two glass substrates (an upper substrate and a lower substrate) in which the patterned ITO electrode, the insulating film, and the alignment film subjected to the alignment process are formed in this order are obtained.

  In step S105, a sealant is printed. For example, ES-7500 manufactured by Mitsui Chemicals, Inc., which is a thermosetting sealant, is printed on one substrate by a screen printing method. This sealant contains several percent of glass fiber having a size of 3.9 μm. In addition, a sealing agent can also be apply | coated using a dispenser. Further, instead of thermosetting, a photo-curing sealant or a photo / heat combination curable sealant may be used.

  The sealing agent is a liquid crystal layer formed when a vacuum injection method is used, a predetermined pattern having an injection port, and when a liquid crystal drop injection method (One Drop Filling; ODF) is used, it is closed without an injection port. The printed pattern is printed.

  A conductive agent is further printed in a predetermined pattern on the substrate on which the sealing agent is printed. For example, the above-mentioned sealant ES-7500 contains 4.5% diameter, for example, several percent of plastic balls with gold plating such as Micropearl AU manufactured by Sekisui Chemical Co., Ltd. Print on screen.

  Further, a plastic ball having a diameter of 4 μm, for example, is sprayed as a gap control agent on the other substrate on which the sealant and the conductive agent pattern are not printed by a dry spraying method. Instead of plastic balls, straight spheres may be sprayed. It is preferable to use a gap control agent that has been subjected to a surface treatment so as not to disturb the alignment of the liquid crystal molecules.

  In step S106, the upper and lower substrates are bonded together. In a state where the upper and lower substrates are aligned, overlapped and pressed, the sealant is cured by heat treatment.

  Step S107 is a division process. The glass substrate is scratched with a scriber device, and empty cells of a predetermined shape and size are divided and formed by breaking.

  In step S108, liquid crystal is vacuum injected into the separately formed empty cells. The inventors of the present application injected the following four types of liquid crystal materials to prepare samples of four types of liquid crystal display elements.

  (A) Liquid crystal material having negative dielectric anisotropy (manufactured by Merck & Co., Inc.).

  (B) 0.15 wt% of a dichroic dye exhibiting a blue color (G-472 manufactured by Hayashibara Biochemical Laboratories) is added to the liquid crystal material manufactured by Merck Co., Ltd., and the liquid crystal phase is stirred. A liquid crystal material that is heated above the transition temperature and has its dye dissolved in the liquid crystal.

  (C) A liquid crystal material obtained by adding 0.30 wt% of G-472 to the above-mentioned liquid crystal material manufactured by Merck Co., Ltd., and dissolving it by the same method as in (b).

  (D) A liquid crystal material obtained by adding 0.45 wt% of G-472 to the liquid crystal material manufactured by Merck Co., Ltd. and dissolving it in the same manner as in (b).

  Hereinafter, the liquid crystal display elements injected with the liquid crystal materials (a), (b), (c), and (d) are referred to as a comparative sample, a first sample, a second sample, and a third sample, respectively.

  G-472 is a dichroic dye having an absorption peak wavelength of 620 nm and a dichroic ratio of 7.992 (about 8). In a normal dichroic dye, since the dichroic ratio is often 10 or more, it can be said that G-472 is a dye having a relatively low dichroic ratio.

  In step S109, the liquid crystal inlet is sealed with an end sealant.

  In step S110, chamfering and cleaning are performed. Chamfering is an operation of chamfering the corner of the cut surface of the terminal. Moreover, since glass dust adheres to a liquid crystal cell, it wash | cleans.

  Finally, in step S111, a polarizing plate is attached to the surface of the two glass substrates opposite to the liquid crystal layer. The two polarizing plates were arranged so that the transmission axes were orthogonal to each other (in crossed Nicols) and the transmission axis was at an angle of 45 ° with the rubbing direction. A power source is connected between the transparent electrodes of both substrates.

  FIG. 2 is a schematic view of a liquid crystal display element (liquid crystal display element according to the example) manufactured by the method for manufacturing a liquid crystal display element according to the example.

  The liquid crystal display device according to the embodiment includes an upper substrate 10, a lower substrate 20, and a vertical alignment liquid crystal layer 30 sandwiched between the substrates 10 and 20, which are disposed to face each other in parallel.

  The upper substrate 10 is formed on the upper glass substrate (transparent substrate) 11, the upper transparent electrode 12 formed on the upper glass substrate 11, the upper insulating film 13 formed on the upper transparent electrode 12, and the upper insulating film 13. The upper alignment film 14 is included. Similarly, the lower substrate 20 includes a lower glass substrate (transparent substrate) 21, a lower transparent electrode 22 formed on the lower glass substrate 21, and a lower insulating film 23 formed on the lower transparent electrode 22. And a lower alignment film 24 formed on the lower insulating film 23.

  The upper and lower transparent electrodes 12 and 22 are made of, for example, ITO. The liquid crystal display element is driven by a power source 40 connected between the electrodes 12 and 22.

  The upper and lower alignment films 14 and 24 are subjected to an anti-parallel alignment process, for example, by rubbing.

  The liquid crystal layer 30 is a vertically aligned liquid crystal layer. The liquid crystal molecules 30a are uniaxially aligned (along a direction parallel to the rubbing direction of the upper and lower substrates 10 and 20) and are uniformly monodomain aligned. In the liquid crystal layer 30, a dichroic dye exhibiting a blue color (absorbing a yellow wavelength) is uniformly dispersed.

  When a voltage is applied between the upper and lower transparent electrodes 12 and 22 by the power source 40, the alignment state of the liquid crystal molecules 30a and the dichroic dye existing therebetween changes. In the liquid crystal layer 30 of the figure, the alignment state of the liquid crystal molecules 30a and the dichroic dye when no voltage is applied is shown on the left side of the drawing, and the alignment state when the voltage is applied is shown on the right side of the drawing. .

  An upper polarizing plate 15 and a lower polarizing plate 25 are disposed on the surfaces of the upper substrate 10 and the lower substrate 20 opposite to the liquid crystal layer 30, respectively. Both polarizing plates 15 and 25 are such that the light transmission axis of the upper polarizing plate 15 and that of the lower polarizing plate 25 are orthogonal to each other (in crossed Nicols), and the light transmission axes are the upper and lower substrates. It arrange | positions so that the angle of 45 degrees may be made with respect to the rubbing direction of 10 and 20. Therefore, the liquid crystal display element according to the embodiment is a normally black type liquid crystal display element.

  The inventors of the present application evaluated the electro-optical characteristics of the liquid crystal display elements (first to third samples) according to the examples and the comparative sample. For the evaluation, a liquid crystal display element evaluation apparatus, LCD-5200, manufactured by Otsuka Electronics Co., Ltd. was used.

  First, the relationship between the drive voltage and the contrast was examined for the comparative sample and the first to third samples. Each sample was driven at 150 Hz, 1/4 duty, and 1/3 bias, and contrast was measured from the normal direction of the upper and lower substrates 10 and 20 of each sample.

  3A and 3B are graphs showing the relationship between the drive voltage and the contrast ratio. In each figure, the horizontal axis of the graph represents the drive voltage in the unit of “volt (V)”, and the vertical axis represents the contrast ratio. The curve connecting the crosses in FIG. 3A shows the relationship between the comparative samples. In addition, the curves connecting the black squares, the black diamonds, and the black triangles in FIG. 3B indicate the relationship between the first sample, the second sample, and the third sample, respectively.

  It can be seen that the contrast of the first to third samples to which the dye is added is higher than that of the comparative sample to which no dichroic dye is added. In particular, the contrast characteristics of the first sample with an added amount of dichroic dye of 0.15 wt% and the second sample with 0.30 wt% are excellent. Although this result was outside the range expected by the inventors of the present application, the black level at the time of OFF display (when the OFF voltage was applied) was effectively improved by the addition of the dye, and the sample with a small amount of the dye addition In the (first and second samples), it is considered that the white level lowering phenomenon at the ON display due to the addition of the dye did not appear remarkably. If the dichroic dye exhibiting a blue color is added to the host liquid crystal in an amount of 0.001 wt% or more, more preferably 0.01 wt% or more, the effect of improving the contrast can be obtained. Let's go.

  Next, the inventors of the present application varied the viewing angle direction (observation angle, polar angle) for ON display (bright display) of the comparative sample and the first to third samples, and changed the light wavelength and transmittance. I investigated the relationship. The viewing angle direction (observation angle, polar angle) was changed in the optimum viewing direction, which is the direction in which yellowing is most noticeable.

  4A to 4D are graphs showing the relationship between the wavelength of light and the transmittance for ON display (bright display). The horizontal axis of each graph represents the wavelength of light in the unit “nm”, and the vertical axis represents the transmittance in the unit “%”. The display methods of the comparative sample and the first to third samples are the same as those in FIGS. 3A and 3B. For example, the cross-curved curve indicates the relationship between the light wavelength and the transmittance for the comparative sample. Indicates. FIG. 4A shows an observation result from the polar angle 0 ° direction (substrate normal direction). 4B, 4C, and 4D show observation results from polar angles of 15 °, 30 °, and 50 °, respectively.

  Reference is made to FIG. In observation from the polar angle 0 ° direction, substantially the same wavelength-transmittance characteristics are obtained in the comparative sample and the first sample. Although the dye molecules are inclined with respect to the vertical alignment together with the liquid crystal molecules, it is understood that almost no color is observed when the addition amount is 0.15 wt%. In the second sample with the dye addition amount of 0.30 wt%, a decrease in light transmittance is observed, and in particular, the transmittance of light having a wavelength of 550 nm to 600 nm absorbed by the dye is low. In the third sample in which the dye addition amount is 0.45 wt%, the light transmittance is reduced in all wavelength regions. In order to realize a bright display, it is preferable that the amount of dye added is less than 0.5 wt%, and more preferably 0.45 wt% or less. Addition of 0.5 wt% or more of dye is considered undesirable.

  Reference is made to FIG. In the observation from the polar angle of 15 °, compared to the observation from the polar angle of 0 ° (FIG. 4 (A)), the wavelength dependence of the light transmittance starts to appear for the comparative sample, which is bluer than other colors. A tendency for the transmittance to become lower, that is, the beginning of yellowing is observed.

  The light transmittance of the first sample is lower than that of the comparative sample. In particular, a difference occurs in the light transmittance at a wavelength of 550 nm to 600 nm absorbed by the dye. However, from the viewpoint of color balance, it can be considered that the first sample is better than the comparative sample.

  Although both the second and third samples can be considered to have achieved a good color balance, the light transmittance is almost the same as the measurement result from the polar angle 0 ° direction shown in FIG. It is falling.

  Reference is made to FIGS. 4C and 4D. In the observation from the polar angle 30 ° direction and the 50 ° direction, the wavelength dependence of the light transmittance is more remarkable for the comparative sample than in the case shown in FIGS. The tendency of the transmittance of the film to become low, that is, yellowing is clearly recognized. As described above, yellowing is a phenomenon that deteriorates display quality. In particular, in the optimal viewing direction that is a relatively bright direction, it is considered to be less preferable than a decrease in brightness.

  The light transmittance of the first sample is even lower than that of the comparative sample. The decrease in light transmittance is particularly significant in the wavelength region of 550 nm or more. However, from the viewpoint of color balance, the first sample is considered to be much better than the comparative sample.

  Both the second and third samples are considered to have achieved a very good color balance, but the light transmittance is reduced at the same rate as the measurement results shown in FIGS. 4 (A) and 4 (B). .

  Subsequently, the inventors of the present application examined the relationship between the wavelength of light and the transmittance by changing the viewing angle direction variously for the OFF display (black display) of the comparative sample and the first to third samples. The viewing angle direction was changed in the optimal viewing direction.

  5A to 5D are graphs showing the relationship between the wavelength of light and the transmittance for OFF display (black display). The horizontal axis of each graph represents the wavelength of light in the unit “nm”, and the vertical axis represents the transmittance in the unit “%”. The display methods of the comparative sample and the first to third samples are the same as those in FIGS. 3 (A) and 3 (B) and FIGS. 4 (A) to 4 (D). FIG. 5A shows an observation result from the polar angle 0 ° direction. FIGS. 5B, 5C, and 5D show observation results from polar angles of 15 °, 30 °, and 50 °, respectively.

  Reference is made to FIGS. In observation from the polar angle 0 ° direction and the 15 ° direction, there is almost no difference in the wavelength-transmittance characteristics of the comparative sample and the first to third samples. Since it is a vertical alignment type liquid crystal display element, it is considered that there is no significant difference in observation from the substrate normal direction and a direction close thereto.

  Reference is made to FIGS. In the observation from the direction where the polar angle is 30 ° or more, the difference due to the addition of the dye is clearly recognized, and it can be seen that the light transmittance decreases as the addition amount increases.

  Further, the inventors of the present application varied the viewing angle direction for the background display of the comparative sample and the first to third samples (display of the region where the transparent electrodes 12 and 22 are not formed), and the wavelength and transmission of the light. The relationship with rate was examined. The viewing angle direction was changed in the optimal viewing direction.

  6A to 6D are graphs showing the relationship between the wavelength of light and the transmittance for background display. The horizontal axis of each graph represents the wavelength of light in the unit “nm”, and the vertical axis represents the transmittance in the unit “%”. The display methods of the comparative sample and the first to third samples are the same as those in FIGS. 3A, 3B, 4A to 4D, and 5A to 5D. FIG. 6A shows an observation result from the polar angle 0 ° direction. FIGS. 6B, 6C, and 6D show observation results from polar angles of 15 °, 30 °, and 50 °, respectively.

  Reference is made to FIGS. 6A and 6B. In the observation from the polar angle 0 ° direction and the 15 ° direction, there is almost no difference in the wavelength-transmittance characteristics of the comparative sample and the first to third samples as in the case of OFF display.

  Reference is made to FIGS. 6C and 6D. In the observation from the direction where the polar angle is 30 ° or more, a difference due to the addition of the dye is recognized, and it can be seen that the light transmittance decreases as the addition amount increases.

  Finally, the inventors of the present application compared the wavelength-transmittance characteristics of the background display and the display when the OFF voltage is applied (OFF display) for the comparative sample and the first to third samples.

  FIGS. 7A to 7D are graphs showing comparison results for the comparative sample and the first to third samples observed from the polar angle 30 ° direction of the optimum viewing direction. 8A to 8D are graphs showing those observed from the polar angle 50 ° direction of the optimum viewing direction. The horizontal axis of each graph represents the wavelength of light in the unit “nm”, and the vertical axis represents the transmittance in the unit “%”. The curve connecting the black squares shows the relationship between the light wavelength and the transmittance for the background display. The curve connecting the black diamonds shows the relationship between the two relating to the OFF display.

  Reference is made to FIGS. It can be seen that the sample with a larger amount of dye added has a smaller difference in light transmittance (brightness) between the background display and the OFF display.

  8A to 8D are comparatively referred to. The difference in light transmittance (brightness) between the two displays is clearly smaller in the sample to which the dye is added (first to third samples) than in the sample to which no dye is added (comparative sample). In particular, the difference is small in the third sample, and it can be seen that an excellent display in which OFF segment appearance is suppressed can be realized.

  From these facts, it is understood that the OFF seg appearance when the liquid crystal display element is observed from an oblique direction, particularly from a deep polar angle direction, is reduced by the addition of a dye. It should be noted that OFF seg appearance can be further reduced by increasing the amount of dye added.

  Next, the inventors of the present application newly prepared three types of liquid crystal display element samples by changing the dichroic dye added to the liquid crystal material. A dichroic dye having an absorption peak wavelength of 550 nm and a dichroic ratio of 14.8 (about 15), which is blue, manufactured by Hayashibara Biochemical Laboratories Co., Ltd., was added. It can be said that the material has a medium dichroic ratio.

  The dichroic dye was added to the liquid crystal material constituting the liquid crystal layer of the comparative sample in an amount of 0.15 wt%, and heated to a temperature higher than the phase transition temperature of the liquid crystal while stirring to prepare a fourth sample. Similarly, fifth and sixth samples added with 0.30 wt% and 0.45 wt% were produced. And about the 4th-6th sample, the electro-optical characteristic was evaluated using the liquid crystal display element evaluation apparatus by the Otsuka Electronics Co., Ltd. and LCD-5200.

  First, the relationship between drive voltage and contrast was examined. Each sample was driven at 150 Hz, 1/4 duty, and 1/3 bias, and contrast was measured from the normal direction of the upper and lower substrates 10 and 20 of each sample.

  FIG. 9 is a graph showing the relationship between the drive voltage and the contrast ratio. The horizontal axis of the graph represents the drive voltage in the unit “volt (V)”, and the vertical axis represents the contrast ratio. Curves connecting black squares, black diamonds, and black triangles indicate the relationship between the fourth sample, the fifth sample, and the sixth sample, respectively.

  It can be seen that the contrast of the fourth to sixth samples to which the dye was added is higher than that of the comparative sample without the dichroic dye added as shown in FIG. In particular, the contrast characteristics of the fourth sample with 0.15 wt% dichroic dye addition and the fifth sample with 0.30 wt% are excellent. Although this result was outside the range expected by the inventors of the present application, the black level during OFF display was effectively improved by the addition of the dye, and in the fourth and fifth samples where the dye addition amount was small. This is probably because the decrease in white level during ON display due to the addition of a dye did not appear remarkably. If the dichroic dye exhibiting a blue color is added to the host liquid crystal in an amount of 0.001 wt% or more, more preferably 0.01 wt% or more, the effect of improving the contrast can be obtained. Let's go.

  Next, the inventors of the present application examined the relationship between the wavelength of light and the transmittance by changing the viewing angle direction (observation angle, polar angle) variously for the ON display of the comparative sample and the fourth to sixth samples. . The viewing angle direction (observation angle, polar angle) was changed in the optimum viewing direction, which is the direction in which yellowing is most noticeable.

  10A to 10D are graphs showing the relationship between the wavelength of light and the transmittance for ON display. The horizontal axis of each graph represents the wavelength of light in the unit “nm”, and the vertical axis represents the transmittance in the unit “%”. The display methods of the comparative sample and the fourth to sixth samples are the same as those in FIGS. 3 (A) and 9. FIG. 10A shows an observation result from the polar angle 0 ° direction (substrate normal direction). FIGS. 10B, 10C, and 10D show observation results from polar angles of 15 °, 30 °, and 50 °, respectively.

  Reference is made to FIG. As described above, when observed from the polar angle 0 ° direction, the comparative sample and the first sample have almost the same wavelength-transmittance characteristics, but the comparative sample and the fourth sample have wavelength-transmittance. There is a difference in characteristics, and in the fourth sample, the light transmittance is reduced even when the addition amount is 0.15 wt%. This will be the effect of the dichroic ratio of the added dichroic dye. Since the dichroic ratio of the dichroic dye added to the fourth sample is larger than that of the dye added to the first sample, even when the voltage is turned on and the liquid crystal molecules and the dye molecules are tilted, even from the normal direction. It is considered that the absorption of the dye was observed and the transmittance was lowered. In the fifth sample with 0.30 wt% dye addition and the sixth sample with 0.45 wt%, the light transmittance is further reduced, and in particular, the transmittance of light having a wavelength of 550 nm to 600 nm absorbed by the dye is low. .

  Reference is made to FIGS. Even when observed from an inclined angle, the light transmittance of the fourth sample is lower than that of the comparative sample. However, this is mainly in the wavelength range of 550 nm or more, and from the viewpoint of color balance, it can be considered that the fourth sample is better than the comparative sample. Although it can be considered that both the fifth and sixth samples achieve a better color balance, the light transmittance is reduced at a rate almost the same as the measurement result from the polar angle 0 ° direction.

  Subsequently, the inventors of the present application examined the relationship between the wavelength of light and the transmittance by changing the viewing angle direction for the OFF display of the fourth to sixth samples. The viewing angle direction was changed in the optimal viewing direction.

  FIGS. 11A to 11D are graphs showing the relationship between the wavelength of light and the transmittance for OFF display. The horizontal axis of each graph represents the wavelength of light in the unit “nm”, and the vertical axis represents the transmittance in the unit “%”. The display methods of the comparative sample and the fourth to sixth samples are the same as those in FIGS. 10 (A) to 10 (D). FIG. 11A shows an observation result from the polar angle 0 ° direction. 11B, 11C, and 11D show observation results from polar angles of 15 °, 30 °, and 50 °, respectively.

  Reference is made to FIGS. 11A and 11B. In observation from the polar angle 0 ° direction and the 15 ° direction, there is almost no difference in the wavelength-transmittance characteristics of the comparative sample and the fourth to sixth samples. Since it is a vertical alignment type liquid crystal display element, it is considered that there is no significant difference in observation from the substrate normal direction and a direction close thereto.

  Reference is made to FIGS. 11C and 11D. In the observation from the direction where the polar angle is 30 ° or more, there is a difference due to the addition of the dye, and there is a slight tendency that the light transmittance of the OFF display decreases as the addition amount increases, but the dye is added. Then, it can be seen that the light transmittance is uniformly low.

  Furthermore, the inventors of the present application examined the relationship between the wavelength of light and the transmittance by changing the viewing angle direction variously for the background displays of the fourth to sixth samples. The viewing angle direction was changed in the optimal viewing direction.

  12A to 12D are graphs showing the relationship between the wavelength of light and the transmittance for background display. The horizontal axis of each graph represents the wavelength of light in the unit “nm”, and the vertical axis represents the transmittance in the unit “%”. The display methods of the comparative sample and the fourth to sixth samples are the same as those in FIGS. 10 (A) to 10 (D). FIG. 12A shows an observation result from the polar angle 0 ° direction. 12B, 12C, and 12D show observation results from polar angles of 15 °, 30 °, and 50 °, respectively.

  Reference is made to FIGS. In the observation from the polar angle 0 ° direction and the 15 ° direction, there is almost no difference in the wavelength-transmittance characteristics of the comparative sample and the fourth to sixth samples, as in the case of OFF display.

  Reference is made to FIGS. In the observation from the direction where the polar angle is 30 ° or more, a difference due to the addition of the dye is observed, and the light transmittance tends to decrease as the addition amount increases. As can be seen, the transmittance is low.

  Finally, the inventors of the present application compared the wavelength-transmittance characteristics of the background display and the OFF display for the comparative sample and the fourth to sixth samples.

  FIGS. 13A to 13D are graphs showing the comparison results for the comparative sample and the fourth to sixth samples, respectively, observed from the polar angle 30 ° direction of the optimal viewing direction. 14A to 14D are graphs showing those observed from the polar angle 50 ° direction of the optimum viewing direction. The horizontal axis of each graph represents the wavelength of light in the unit “nm”, and the vertical axis represents the transmittance in the unit “%”. The curve connecting the black squares shows the relationship between the light wavelength and the transmittance for the background display. The curve connecting the black diamonds shows the relationship between the two relating to the OFF display.

  Reference is made to FIGS. It can be seen that the sample with a larger amount of added dye has a smaller difference in light transmittance (brightness) between the background display and the OFF display. However, the difference is large when compared with the first to third samples.

  Reference is made to FIGS. The difference in light transmittance (brightness) between the two displays is clearly smaller in the sample to which the dye was added (fourth to sixth samples) than in the sample to which no dye was added (comparative sample). The effect of reducing the difference in light transmittance between the two displays due to the addition of the dye does not greatly depend on the added amount of the dye, and the fourth sample with the added amount of 0.15 wt% and the sixth sample with the added amount of 0.45 wt%. An almost equivalent effect is observed with the sample.

  From the measurement results for the fourth to sixth samples, it is understood that the OFF seg appearance when the liquid crystal display element is observed from an oblique direction, particularly from a deep polar angle direction, is reduced by the addition of a dye.

  In addition, in FIG. 15, the chromaticity diagram regarding a comparative sample and the 4th-6th sample is shown. The display methods of the comparative sample and the fourth to sixth samples are the same as those in FIGS. 10 (A) to 10 (D). Compared with the comparative sample, the fifth and sixth samples clearly have a small change in chromaticity depending on the viewing angle. The fourth sample also has a smaller viewing angle dependency of the chromaticity change than the comparative sample.

  Moreover, the dichroic dye added to the fourth to sixth samples causes a color shift. If this is utilized, the color tone of the white display of a liquid crystal display element can be controlled by addition of a pigment. In the case of this pigment material, the color tone changes to the violet (red) side, and the yellowish color that tends to be disliked by the user of the liquid crystal display element changes. By selecting the pigment, it is possible to match the user's preference for the color.

  Subsequently, the inventors of the present application differed in the liquid crystal material constituting the liquid crystal layer and the dichroic dye added to the liquid crystal material, and further provided four types of liquid crystal display element samples (second comparative sample and seventh sample). To 9th sample).

  The liquid crystal material used is the same as the comparative sample and the first to sixth samples in that the dielectric anisotropy made by Merck is negative. Further, a dichroic dye having a blue absorption peak wavelength of 600 nm and a dichroic ratio of 15.1 (about 15) manufactured by Hayashibara Biochemical Laboratories Co., Ltd. was added to the liquid crystal material. The dichroic ratio of this dichroic dye is medium.

  A sample in which no dichroic dye was added to the liquid crystal layer was used as a second comparative sample. In addition, 0.15 wt% of the dichroic dye is added to the liquid crystal material constituting the liquid crystal layer of the second comparative sample, and the mixture is heated and dissolved above the phase transition temperature of the liquid crystal while stirring to prepare a seventh sample. did. Similarly, eighth and ninth samples added with 0.30 wt% and 0.45 wt% were produced.

  In producing the second comparative sample and the seventh to ninth samples, a vertical alignment film different from the comparative sample and the first to sixth samples was used. A vertical alignment film that easily obtains a pretilt angle close to 90 ° even when rubbing is used. In addition, when forming a liquid crystal cell, the thickness of the cell can be reduced by using a sealant containing several percent of 4.2 μm glass fiber and spraying 4.25 μm diameter plastic balls as a gap control agent. It was thicker than the comparative sample and the first to sixth samples. Further, a polarizing plate with a viewing angle compensation plate (optical compensation plate) was attached to the liquid crystal cell.

  The inventors of the present application also evaluated the electro-optical characteristics of the second comparative sample and the seventh to ninth samples using a liquid crystal display element evaluation apparatus, LCD-5200, manufactured by Otsuka Electronics Co., Ltd.

  First, the relationship between the drive voltage and the contrast was examined for the second comparative sample and the seventh to ninth samples. Each sample was driven at 150 Hz, 1/64 duty, 1/9 bias, and contrast was measured from the normal direction of the upper and lower substrates 10 and 20 of each sample.

  FIG. 16 is a graph showing the relationship between the drive voltage and the contrast ratio. The horizontal axis of the graph represents the drive voltage in the unit “volt (V)”, and the vertical axis represents the contrast ratio. The curve connecting the crosses indicates the relationship between the second comparative samples. Further, curves connecting black squares, black diamonds, and black triangles indicate the relationship between the seventh sample, the eighth sample, and the ninth sample, respectively.

  The contrast of the seventh to ninth samples to which the dye is added is higher than that of the second comparative sample to which no dichroic dye is added. In particular, the contrast characteristics of the seventh sample with 0.15 wt% dichroic dye addition and the eighth sample with 0.30 wt% are excellent. Although this result was outside the range expected by the inventors of the present application, the black level at the time of OFF display (when the OFF voltage was applied) was effectively improved by the addition of the dye, and the sample with a small amount of the dye addition In the (seventh and eighth samples), it is considered that the above-described phenomenon of lowering the white level during ON display due to the addition of the dye did not appear remarkably. If the dichroic dye exhibiting a blue color is added to the host liquid crystal in an amount of 0.001 wt% or more, more preferably 0.01 wt% or more, the effect of improving the contrast can be obtained. Let's go.

  Next, the inventors of the present application varied the viewing angle direction (observation angle, polar angle) for the ON display (bright display) of the second comparative sample and the seventh to ninth samples, and changed the light wavelength and transmittance. I investigated the relationship with. The viewing angle direction (observation angle, polar angle) was changed in the optimum viewing direction, which is the direction in which yellowing is most noticeable.

  FIGS. 17A to 17D are graphs showing the relationship between the wavelength of light and the transmittance for ON display. The horizontal axis of each graph represents the wavelength of light in the unit “nm”, and the vertical axis represents the transmittance in the unit “%”. The display methods of the second comparative sample and the seventh to ninth samples are the same as those in FIG. 16, for example, a curved line connecting the crosses indicates the relationship between the wavelength of light and the transmittance for the second comparative sample. FIG. 17A shows an observation result from the polar angle 0 ° direction (substrate normal direction). FIGS. 17B, 17C, and 17D show observation results from polar angles of 15 °, 30 °, and 50 °, respectively.

  Reference is made to FIG. In the observation from the polar angle 0 ° direction, substantially the same wavelength-transmittance characteristics are obtained in the second comparative sample to which no dye is added and the seventh to ninth samples to which the dye is added.

  Reference is made to FIGS. In observation from any of the polar angle 15 ° direction, 30 ° direction, and 50 ° direction, there is no significant difference in wavelength-transmittance characteristics between the second comparative sample and the seventh sample. On the other hand, the transmittance of the eighth and ninth samples is slightly lower than that of the second comparative sample. However, there is almost no difference in the short wavelength (blue) region, and a slight decrease in transmittance is observed on the long wavelength (red) region side, so that the eighth and ninth samples are preferable displays with good yellowing suppression (good) It can be seen that a color balance can be realized. It is understood that a good display can be realized in the liquid crystal display element in which the dye addition amount is 0.45 wt% or less.

  Subsequently, the inventors of the present application examined the relationship between the wavelength of light and the transmittance by changing the viewing angle direction variously for the OFF display (black display) of the second comparative sample and the seventh to ninth samples. The viewing angle direction was changed in the optimal viewing direction.

  18A to 18D are graphs showing the relationship between the wavelength of light and the transmittance for OFF display. The horizontal axis of each graph represents the wavelength of light in the unit “nm”, and the vertical axis represents the transmittance in the unit “%”. The display methods of the second comparative sample and the seventh to ninth samples are the same as those in FIG. FIG. 18A shows an observation result from the polar angle 0 ° direction. 18B, 18C, and 18D show observation results from polar angles of 15 °, 30 °, and 50 °, respectively.

  Reference is made to FIGS. 18A and 18B. In observation from the polar angle 0 ° direction and the 15 ° direction, there is almost no difference in the wavelength-transmittance characteristics of the second comparative sample and the seventh to ninth samples. Since it is a vertical alignment type liquid crystal display element, it is considered that there is no significant difference in observation from the substrate normal direction and a direction close thereto.

  Reference is made to FIGS. 18C and 18D. Even in the observation from the direction where the polar angle is 30 ° or more, the significant difference in the wavelength-transmittance characteristics depending on the presence or absence of the dye and the amount added is larger as in the case of the comparative sample and the first to sixth samples. Absent.

  Further, the inventors of the present application examined the relationship between the light wavelength and the transmittance by changing the viewing angle direction in various ways for the background display of the second comparative sample and the seventh to ninth samples. The viewing angle direction was changed in the optimal viewing direction.

  19A to 19D are graphs showing the relationship between the wavelength of light and the transmittance for background display. The horizontal axis of each graph represents the wavelength of light in the unit “nm”, and the vertical axis represents the transmittance in the unit “%”. The display methods of the second comparative sample and the seventh to ninth samples are the same as those in FIG. FIG. 19A shows an observation result from the polar angle 0 ° direction. 19B, 19C, and 19D show observation results from polar angles of 15 °, 30 °, and 50 °, respectively.

  Reference is made to FIGS. 19A and 19B. In the observation from the polar angle 0 ° direction and the 15 ° direction, there is almost no difference in the wavelength-transmittance characteristics of the second comparative sample and the seventh to ninth samples, as in the case of OFF display.

  Reference is made to FIGS. 19C and 19D. Even in the observation from the direction where the polar angle is 30 ° or more, the significant difference in the wavelength-transmittance characteristics depending on the presence or absence of the dye and the amount added is larger as in the case of the comparative sample and the first to sixth samples. Absent.

  Finally, the present inventors compared the wavelength-transmittance characteristics of the background display and the OFF display for the second comparative sample and the seventh to ninth samples.

  20A to 20D are graphs showing comparison results for the second comparative sample and the seventh to ninth samples observed from the polar angle 30 ° direction of the optimum viewing direction. FIGS. 21A to 21D are graphs showing those observed from the polar angle 50 ° direction of the optimum viewing direction. The horizontal axis of each graph represents the wavelength of light in the unit “nm”, and the vertical axis represents the transmittance in the unit “%”. The curve connecting the black squares shows the relationship between the light wavelength and the transmittance for the background display. The curve connecting the black diamonds shows the relationship between the two relating to the OFF display.

  Reference is made to FIGS. In the second comparative sample and the seventh sample, there is almost no difference in light transmittance (brightness) between the background display and the OFF display. In the eighth and ninth samples, the difference is smaller than in the second comparative sample and the seventh sample.

  Reference is made to FIGS. First, as shown in FIG. 21 (A), in the second comparative sample with no dye added, there is not much difference between the average value of the light transmittance of the background display and that of the OFF display. However, it can be seen that there is a difference in color between the background display and the OFF display because the dependency of the light transmittance on the wavelength is different. On the other hand, as shown in FIGS. 21 (B) to (D), in the seventh to ninth samples to which the dye is added, the difference in dependency of light transmittance depending on the wavelength is smaller than in the second comparative sample. . For this reason, the difference in color between the background display and the OFF display is reduced. In particular, in the seventh sample, it is understood that a good display with improved OFF segment appearance can be realized. Also in the seventh to ninth samples, as in the case of the fourth to sixth samples, the effect of reducing the difference in light transmittance between the background display and the OFF display due to the addition of the dye is not large in the added amount of the dye. Independently, it can be said that the seventh sample with the addition amount of 0.15 wt% can have an effect equal to or higher than that of the ninth sample with the addition amount of 0.45 wt%.

  Also from the measurement results for the seventh to ninth samples, it was found that the OFF seg appearance when the liquid crystal display element was observed from an oblique direction, particularly a deep polar angle direction, was reduced by the addition of the dye. It was also found that the effect of reducing the OFF seg appearance does not increase as the amount of added dye increases.

    As mentioned above, although this invention was demonstrated along the Example, this invention is not limited to these.

  For example, if the dichroic dye added to the liquid crystal material has an absorption wavelength peak of not less than 500 nm and not more than 650 nm, the same effects as in the examples can be obtained.

  In the examples, dyes having dichroic ratios of about 8 and 15 were used, but dichroic dyes having a dichroic ratio of 20 or less could be preferably used.

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

  It can be used for all types of liquid crystal displays such as in-vehicle displays, display for games, mobile phone / DSC displays, audio displays, personal computer monitor displays, liquid crystal TV displays, and mobile TV displays. In particular, it can be suitably used for character display such as in-vehicle audio display, in-vehicle heat control display, and character / dot matrix mixed display.

DESCRIPTION OF SYMBOLS 10 Upper substrate 11 Upper glass substrate 12 Upper transparent electrode 13 Upper insulating film 14 Upper alignment film 15 Upper polarizing plate 20 Lower substrate 21 Lower glass substrate 22 Lower transparent electrode 23 Lower insulating film 24 Lower alignment film 25 Lower Polarizing plate 30 Liquid crystal layer 30a Liquid crystal molecule 40 Power source 50 Light source

Claims (5)

A first substrate;
A second substrate disposed opposite to the first substrate;
A vertically aligned liquid crystal layer sandwiched between the first and second substrates;
A first polarizing plate disposed on a surface of the first substrate opposite to the liquid crystal layer;
On the surface of the second substrate opposite to the liquid crystal layer, the first polarizing plate and a second polarizing plate arranged in crossed Nicols,
The liquid crystal layer includes a host liquid crystal and a dichroic dye exhibiting a blue color uniformly dispersed in the host liquid crystal
The liquid crystal display element in which the content of the dichroic dye in the liquid crystal layer is 0.001 wt% or more and less than 0.5 wt% with respect to the host liquid crystal.   2. The liquid crystal display element according to claim 1, wherein the content of the dichroic dye in the liquid crystal layer is 0.01 wt% or more and 0.45 wt% or less with respect to the host liquid crystal.   The liquid crystal display element according to claim 1, wherein the liquid crystal layer is monodomain aligned.   The liquid crystal display element according to claim 1, wherein the absorption wavelength peak of the dichroic dye is 500 nm or more and 650 nm or less.   The dichroic ratio of the said dichroic dye is 20 or less, The liquid crystal display element of any one of Claims 1-4.

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