JPH11160538A - Polarizing element, manufacture and display device thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing element which can be incorporated in a liquid crystal display device and is provided with the functions of both a linear polariz ing plate and a 1/4-wavelength plate. SOLUTION: A polarizing element consists of a polarizing layer 9 formed directly on a substrate 2. This polarizing layer 9 consists of filmed polymer liquid crystal 9a and dichroic pigment 9b dispersed therein. The polymer liquid crystal 9a includes liquid crystal to be oriented uniaxially in a specific direction, in a side chain. The diachronic pigment 9b shows absorbency for incident light different from between the long and short axes of a molecule. The long axis of molecule of the diachronic pigment 9b is arrayed in the specific direction in accordance with the uniaxial orientation of the polymer liquid crystal 9a and vibrating components included in the incident light are selectively absorbed, transmitted and converted into polarized light. The polarizing element is so filmed that the retardation becomes (2n+1).λ/4 and is provided with a function as a 1/4-wavelength plate. Where, λ is the wavelength of a visible range and (n) is zero or an integer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing element for converting incident light into linearly polarized light and a method for manufacturing the same. Further, the present invention relates to a display device using a polarizing element.

[0002]

2. Description of the Related Art Many polarizing elements used in a display device using a liquid crystal or the like as an electro-optical material have a structure as shown in FIG. A polarizing element is produced by adsorbing and dispersing polarizing particles on a polarizing substrate 101, sandwiched between supports 102 and fixed with an adhesive layer 103 in order to maintain the durability and mechanical strength. As a basic function, it is important for a polarizing element to exhibit a high polarizing function as well as to have excellent appearance characteristics and durability, to be easily processed as a component, and to be easy to use. In order to satisfy these functions, polarizers for display devices currently supplied on the market mainly use a halogen substance such as iodine or a dye as polarizing particles. As the polarizing substrate 101, a polyvinyl alcohol film is often used. A film of polyvinyl alcohol is stretched about 3 to 5 times in a certain direction between rollers rotating at different speeds. The stretched micelles of polyvinyl alcohol are arranged in the stretching direction, and the arranged film generates strong birefringence.

The above-mentioned polarizing element is generally supplied on the market as a polarizing plate. An adhesive is applied to one surface of the polarizing plate in advance. When incorporated in a display device, a polarizing plate is attached to the outer surface of a liquid crystal panel, which is a main component thereof, via an adhesive. It is necessary to perform this sticking work so that air bubbles and foreign matter are not caught between the panel and the polarizing plate.
This is a burden on the manufacturing process. Further, it is difficult to insert a conventional polarizing element into a liquid crystal panel. In the case of a reflection-type display device, it is not possible to realize this with a conventional polarizing plate, though it is preferable to incorporate a polarizing element inside from the viewpoints of efficiency of use of incident light and image quality.

[0004]

A display device using a built-in polarizing element in place of an external polarizing plate has been developed, and is disclosed in, for example, Japanese Patent Application Laid-Open No. 2-104315. The polarizing element is formed as a polarizing layer on a substrate. The polarizing layer is made of a polymer liquid crystal mixed with a dichroic dye, and has uniaxial anisotropy. As dichroic dyes, merocyanine dyes, styryl dyes, azomethine dyes, azo dyes and anthraquino dyes are used. As the polymer liquid crystal, it is desirable to use a thermotropic type in view of the fact that uniaxial orientation can be easily and satisfactorily imparted by a thermal process.
In order to maintain the developed uniaxial anisotropy for a long period of time, a thermotropic polymer liquid crystal having a glass transition temperature higher than the operating temperature of the display device is used. To form a polarizing layer, a polymer liquid crystal is dissolved in an appropriate solvent such as toluene or tetrahydrofuran, mixed with a dichroic dye, and then applied by a method such as vapor deposition, spin coating, roller coating, dipping, and then heat treatment. It only has to be dried. Dichroic dyes exhibit different absorbances for incident light on the long and short axes of the molecule. The dichroic dye has its long axis aligned with the uniaxial orientation of the polymer liquid crystal. Thus, the polarizing layer can selectively absorb and transmit the vibration component contained in the incident light and convert it into substantially linearly polarized light.

However, in order to obtain a display contrast sufficient for practical use by incorporating a polarizing layer in a display device, it is necessary to add a dichroic dye to the polymer liquid crystal at a relatively high concentration. Alternatively, when the concentration of the dichroic dye was reduced, it was necessary to increase the thickness of the polarizing layer. In any case, the amount of dichroic dye increases, and not only light absorption in the long axis direction but also light absorption in the short axis direction inevitably increases,
There is a problem that the brightness of white display is reduced.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems of the prior art, the following measures have been taken. That is, the polarizing element according to the present invention basically comprises a polymer formed into a film and a dye compounded therein. The polymer is a polymer liquid crystal containing a liquid crystal uniaxially oriented in a predetermined direction in a side chain. or,
The dye is a dichroic dye that exhibits different absorbances for the incident light on the major axis and the minor axis of the molecule. The dichroic dye has its major axis aligned in the predetermined direction in accordance with the uniaxial orientation of the polymer liquid crystal, and selectively absorbs and transmits the vibration component contained in the incident light to convert it into polarized light. As a characteristic feature, the polymer has a retardation of (2n + 1) · λ / 4.
(However, λ is a wavelength in the visible region, and n is zero or an integer.)
The film is formed such that

A polarizing element having such a configuration is manufactured by the following steps. First, a solution in which a polymer liquid crystal and a dichroic dye are dissolved in a solvent is prepared. Next, an orientation process is performed on the surface of the substrate along a predetermined direction. Further, the solution is applied on the substrate that has been subjected to the alignment treatment, and the film thickness is (2n + 1) · λ / 4.
(However, λ is a wavelength in the visible region, and n is zero or an integer.)
A coating film is formed such that Finally, the coating film is heat-treated to uniaxially orient the polymer liquid crystal in the predetermined direction and align the dichroic dyes according to the uniaxial orientation.

The present invention includes a display device having the above-described polarizing element. This display device is of a reflection type and is basically assembled using a pair of substrates. The first substrate is located on the incident side and has an electrode formed thereon. A polarizing plate is bonded to the first substrate. The second substrate is located on the reflection side, has electrodes formed thereon, and is joined to the first substrate via a predetermined gap. Liquid crystal is held in the gap between the two substrates. A polarizing layer is interposed between the second substrate and the liquid crystal. This polarizing layer is uniaxially oriented in a state where a dichroic dye is dispersed in a polymer liquid crystal, and is incorporated in a liquid crystal panel. As a characteristic feature, the polarizing layer is formed such that its retardation is (2n + 1) · λ / 4 (where λ is a visible region and n is zero or an integer). Correspondingly, the liquid crystal is optimally twist-oriented when the twist angle is in the range of 45 ° to 135 °. Preferably, the polarizing layer is arranged at α ° (0 °) from the direction of the uniaxial orientation.
(° <α ° <45 °) has a maximum absorption axis in a tilted direction, and the liquid crystal is optimized for a twist angle of 90 ° -α ° or 90 ° + α °. Preferably, the polarizing plate is arranged such that its transmission axis is parallel to the maximum absorption axis of the polarizing layer.

According to the present invention, a dichroic dye is dispersed in a uniaxially oriented polymer liquid crystal to obtain a function as a polarizing plate utilizing the anisotropy of light absorption. In addition, a function as a retardation plate utilizing uniaxial orientation of the polymer liquid crystal is simultaneously provided. In particular, by controlling the film thickness so that the retardation (product of the refractive index anisotropy and the film thickness) of the polymer liquid crystal is substantially λ / 4, a function as a quarter-wave plate is realized. doing. By incorporating a polarizing element having both functions of a linear polarizing plate and a quarter-wave plate into a liquid crystal display device, it is possible to improve display contrast without lowering the brightness of white display.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1A is a schematic cross-sectional view showing a basic configuration of the polarizing element according to the present invention.
As shown, the polarizing element according to the present invention is provided as a polarizing layer 9 formed directly on the substrate 2. The polarizing layer 9 basically includes a polymer liquid crystal 9a formed as a film and a dichroic dye 9b mixed therein. The polymer liquid crystal 9a contains a liquid crystal uniaxially oriented in a predetermined direction in a side chain. In the figure, the polymer liquid crystal 9a uniaxially oriented in a direction parallel to the paper is schematically represented by an ellipsoid. On the other hand, the dichroic dye 9b exhibits different absorbances for the incident light in the major axis and the minor axis of the molecule. In the dichroic dye 9b, the major axis of the molecule is aligned in a direction parallel to the paper surface according to the uniaxial orientation of the polymer liquid crystal 9a. With such a configuration, the polarizing layer 9 can selectively absorb and transmit the vibration component included in the incident light and convert it into substantially linearly polarized light. Note that a polymer liquid crystal 9a is disposed between the substrate 2 and the polarizing layer 9.
Is provided with a base orientation layer 22 for uniaxially orienting.

As a characteristic feature, the uniaxially oriented polymer liquid crystal 9a has a retardation of (2n + 1) · λ / 4.
(However, λ is a wavelength in the visible region, and n is zero or an integer.)
The film is formed such that Preferably, λ is 500 nm to 650 n at which the visibility is particularly high in the visible region.
The range of m is chosen. The retardation is polymer liquid crystal 9
It is given by the product of the refractive index anisotropy of a and the film pressure. The refractive index anisotropy is the difference between the refractive index in the uniaxial orientation direction of the polymer liquid crystal 9a and the refractive index in the direction perpendicular to the uniaxial direction. Generally, since the refractive index anisotropy is determined according to the material of the polymer liquid crystal 9a, the retardation is adjusted to (2n + 1) · λ / 4 by controlling the film thickness of the polymer liquid crystal 9a in an actual manufacturing process. And a function as a quarter-wave plate.

FIG. 2B schematically shows a measurement system used for evaluating the optical characteristics of the polarizing layer 9 shown in FIG. The polarizing layer 9 is disposed on the reflecting plate 8, and the linear polarizing plate 4 is superposed thereon. Light was incident from the polarizing plate 4 side, and the reflected light intensity was measured while rotating the transmission axis (indicated by a double-headed arrow) of the polarizing plate 4.

(C) is a graph showing the measurement results. The horizontal axis shows the angle of the transmission axis of the polarizing plate 4, and the vertical axis shows the reflected light intensity. Note that the angle is set to 0 ° as a reference when the uniaxial orientation direction of the polarizing layer 9 and the transmission axis of the polarizing plate 4 match. In the graph, the curve indicates that the concentration of the dichroic dye 9b is 0%.
, The curve shows the case where the density is 8%, and the curve shows the case where the density is 10%. 0% concentration
In the case of, there is no function as a polarizing plate, and it functions as a simple quarter-wave plate. Therefore, as shown in the curve, the uniaxial orientation direction of the polymer liquid crystal 9a and the transmission axis of the
At an angle of °, the reflected light intensity is minimized. In this state, the linearly polarized light transmitted through the polarizing plate 4 becomes circularly polarized light after passing through the quarter-wave plate. The light reflected by the reflecting plate 8 becomes linearly polarized light when passing through the quarter-wave plate again. At this time, since the linear polarization direction of the reflected light is rotated by 90 ° with respect to the linear polarization direction of the incident light, the reflected light is almost absorbed by the polarizing plate 4. On the other hand, when the dichroic dye 9b is added at a sufficient concentration as shown by the curve, the polarizing layer 9
The function of the polarizing plate becomes dominant, and the angle of the polarizing plate 4 is 0 °
The absorption becomes maximum when. That is, since the transmission axis of the polarizing plate 4 coincides with the molecular long axis of the dichroic dye 9b, the incident linearly polarized light is almost absorbed. Generally, a p-type dichroic dye shows a large absorbance in the major axis direction and a small absorbance in the minor axis direction. Conversely, an n-type dichroic dye exhibits a small absorbance in the major axis direction and a large absorbance in the minor axis direction. In this example, a p-type dichroic dye 9b is used, and the absorption in the molecular long axis direction is large. However, there is some absorption in the direction of the minor axis of the molecule, and when the concentration of the dichroic dye 9b increases, the total amount of transmitted light decreases, and the screen becomes dark when applied to a display device.

As the added concentration of the dichroic dye 9b increases, the reflected light intensity characteristic shifts from a curve to a curve. The curve is located at the middle, and the addition concentration of the dichroic dye 9b is 8%. Incidentally, the retardation of the polarizing layer 9 is set to 150 nm. In the case of the curve, the function as a quarter-wave plate and the function as a polarizing plate are mixed, and the angle of the polarizing plate 4 at which the absorbance is minimized is α = ± 2.
It is located around 5 °. As is clear from the curve, the reflected light intensity at angles ± α is lower than the reflected light intensity at 0 °. Therefore, at angles ± α, absorption greater than that obtained by the dichroic dye 9b is obtained.
If the absorption at ± α is used for a display device, a practically sufficient black display can be obtained without extremely increasing the addition concentration of the dichroic dye 9b. That is, when the polarizing element according to the present invention is applied to a display device, a sufficiently dark black display can be obtained without impairing the brightness of the white display, and the display contrast can be improved as a whole.

Referring to FIG. 2, a method for forming the polarizing layer shown in FIG. 1A will be described in detail. First, the alignment step (A)
Is performed, and the surface of the insulating substrate 2 such as glass or quartz is oriented along a predetermined orientation direction. For example,
After a base alignment layer 22 made of a polyimide film or the like is formed on the surface of the substrate 2, the polyimide film may be rubbed along the alignment direction. In addition, the base alignment layer 2
Polyamic acid, polyvinyl alcohol, or the like can be used as 2 in place of polyimide. In some cases, the surface of the substrate 2 may be directly rubbed. Next, a film forming step (B) is performed. First, a solution in which the polymer liquid crystal 9a and the dichroic dye 9b are dissolved in a solvent is prepared in advance. This solution is applied on the substrate 2 which has been subjected to the orientation treatment, to form a coating film. At this time, the thickness of the coating film is adjusted so that the retardation of the polymer liquid crystal 9a becomes substantially λ / 4. Specifically, the polymer liquid crystal 9a and the dichroic dye 9b are dissolved in an appropriate solvent, and a predetermined thickness is applied to the surface of the substrate 2 which has been subjected to the alignment treatment by spin coating, wire coating or various printings. Apply with. As the solvent,
For example, cyclohexanone and methyl ethyl ketone (ME
A solution in which K) is mixed at a ratio of 8: 2 can be used. After applying the solution, heat and dry at a temperature sufficient to evaporate the solvent. Finally, a temperature treatment step (C) is performed.
The substrate 2 is once heated to a temperature equal to or higher than the transition point and then cooled to room temperature equal to or lower than the transition point, and the formed polymer liquid crystal 9a is aligned in the alignment direction to form the polarizing layer 9. In some cases, it is possible to obtain a desired uniaxial orientation by allowing the liquid crystal phase to stand for a certain period of time. As shown in the figure, the liquid crystal molecules contained in the polymer liquid crystal are in a random state during the film formation stage, but after the temperature treatment process, the liquid crystal molecules are aligned along the alignment direction, and the desired uniaxial alignment is obtained. Can be At the same time, the dichroic dye also becomes uniaxially oriented. In the example described above, the polymer liquid crystal already in a polymer state is dissolved in a solvent and applied to the substrate, but a material in a monomer state may be used instead. In this case, a polymer is obtained by uniaxially orienting in a monomer state and then irradiating with ultraviolet rays or the like to polymerize. When the viscosity of the liquid crystal in the monomer state is low, the dichroic dye can be directly dissolved in the liquid crystal without using a solvent, and the liquid crystal can be applied to a desired thickness on the substrate.

FIG. 3 shows specific examples of the polymer liquid crystal 9a, each of which has a side-chain type chemical structure. (I)
Indicates a polymer liquid crystal having biphenylbenzoate as a pendant entering a side chain. That is, side chains are bonded to the alkyl main chain at predetermined intervals (only one side chain is shown in the figure). The space length of this side chain is 6 in carbon number, but the present invention is not limited to this. Biphenyl benzoate is attached to the tip of this side chain as a pendant. (II) represents a side chain type polymer liquid crystal having methoxybiphenyl in addition to biphenylbenzoate as a pendant. The space length of the side chain to which methoxybiphenyl is bonded is 2 in carbon number, but the present invention is not limited to this. (III)
Shows a side chain type polymer liquid crystal having methoxyphenyl benzoate as a pendant. The side chain has a space length of 2 or 6 carbon atoms bonded to the main chain.
Types (I) and (II) are more excellent in solvent resistance than (III). Furthermore, the side chain type polymer liquid crystal shown by (IV) also shows good uniaxial orientation.

FIG. 4 shows a specific example of the dichroic dye 9b. In this example, the dyes A to E were mixed to prepare a black dichroic dye. Dye A alone exhibits blue color, and Dye B
Independently represents yellow, pigment C independently represents red, pigment D alone represents blue-violet, and pigment E independently represents blue. FIG. 5 shows the absorption spectrum of each dye. These dyes were mixed at a ratio of A: B: C: D: E = 2: 1: 1: 1: 1 to prepare a black dichroic dye. In order to evaluate the light absorption characteristics of this mixture, it was dissolved in a nematic liquid crystal having a negative dielectric anisotropy (manufactured by Merck) at a ratio of 3 wt%. This liquid crystal composition was sealed in a liquid crystal cell on which a vertical alignment film was formed.
The optical characteristics of this cell were measured using an instantaneous multi-photometric detector. FIG. 6 shows absorption spectra when 4.5 V and 0 V are applied. When the applied voltage is 0 V, the nematic liquid crystal is vertically aligned. In accordance with this, the dichroic dye is also vertically oriented. In this case, the incident light is hardly absorbed, and the absorbance is close to zero. On the other hand, when the applied voltage is 4.5 V, the liquid crystal shifts to the horizontal alignment, and the dichroic dye also changes to the horizontal alignment state accordingly. In this case, the absorbance for the incident light is greatly increased. In this example, the yellow pigment B, the red pigment C, the blue pigment E, the blue-violet pigment D, and the blue pigment A are mixed at a weight ratio of 1: 1: 1: 1: 2. In particular, a disazo blue dye E having a thienothiazole ring having a large extinction coefficient and a large dichroic ratio and a trisazo blue-violet dye D having a benzothiazole ring are used. Further, a disazo red dye C having a thienothiazole ring is also used. These dyes have a relatively high absorbance and a high dichroic ratio, as is apparent from FIG.

FIG. 7 is a schematic partial sectional view showing a reflection type liquid crystal display device incorporating a polarizing layer according to the present invention.
This display device is a normally white type, and displays white when no voltage is applied and black when voltage is applied.
The figure shows a state where no voltage is applied. This display device has a panel structure in which a first substrate 1 located on the incident side and a second substrate 2 located on the reflecting side are joined to each other via a predetermined gap. A polarizing plate 4 is bonded to the first substrate 1. On the inner surface of the second substrate 2, a light reflection layer 8 is formed.
A liquid crystal 3 is held in a gap between the two substrates 1 and 2. A polarizing layer 9 is interposed between the liquid crystal 3 and the light reflecting layer 8.
In some cases, a protective layer may be provided between the liquid crystal 3 and the polarizing layer 9. This protective layer is made of, for example, a transparent fluororesin film or an acrylic resin film. The polarizing layer 9 is uniaxially oriented with the dichroic dye 9b dispersed in the polymer liquid crystal 9a. In the figure, the uniaxial orientation is taken parallel to the paper. The polarizing layer 9 has a retardation of (2n +
1) It is formed so as to be λ / 4. Here, λ is a wavelength in the visible region, and n is zero or an integer. Liquid crystal 3
Uses a twisted nematic liquid crystal that is optimally twisted in a twist angle range of 45 ° to 135 °. The polarizing layer 9 has a maximum absorption axis in a direction inclined by α ° from the direction of the uniaxial orientation. As described with reference to FIG. 1C, α is in the range of 0 ° to 45 °, for example, 25 °.
It is about. In accordance with this, the twist angle of the twisted nematic liquid crystal 3 is optimized to 90 ° −α ° or 90 ° + α °. In the case of the normally white mode, the polarizing plate 4 on the incident side is arranged so that its transmission axis is parallel to the maximum absorption axis of the polarizing layer 9.

The incident light becomes polarized light after passing through the polarizing plate 4, and becomes polarized light whose polarization axis is rotated after passing through the liquid crystal 3. The polarized light is reflected by the light reflecting layer 8 via the polarizing layer 9 and becomes polarized light. The polarized light passes through the liquid crystal 3 and becomes a polarized light whose polarization axis is rotated.

FIG. 8 schematically shows the polarization directions of the respective polarized lights through the double-headed arrows. In the figure, polymer liquid crystal 9a
And the dichroic dye 9b is schematically represented by an ellipsoid. These molecular major axes are represented by 9x. In addition, the liquid crystal 3 has a left-handed twist angle of 90 ° -α °. The transmission axis of the polarizing plate 4 is set parallel to the maximum absorption axis of the polarizing layer 9. In other words, the transmission axis of the polarizing plate 4 is
It intersects the molecular long axis 9x of a by α °. As described above, the direction of α ° is the maximum absorption axis of the polarizing layer 9 and is shifted from the molecular major axis 9x. Therefore, the polarization direction of the polarized light that has passed through the polarizing plate 4 is inclined by α ° with respect to the molecular major axis 9x. The polarization axis is 90 ° while passing through the liquid crystal 3.
Rotate by -α °. Accordingly, the polarization axis of the polarized light is orthogonal to the molecular major axis 9x and parallel to the maximum transmission axis of the polarizing layer 9. Accordingly, the polarized light passes through the polarizing layer 9 without being absorbed, and is reflected by the light reflecting layer 8 to become polarized light. The polarization axis is 90 ° -α while passing through the liquid crystal 3.
Rotate by ° and become polarized. As shown in the figure, since the polarization axis of the polarized light coincides with the transmission axis of the polarizing plate 4, it passes through as it is, and a white display is obtained.

FIG. 9 shows a voltage application state of the present display device. As shown, the liquid crystal 3 shifts from twist alignment to vertical alignment in response to an applied voltage. As in FIG.
The polarization state in the display device is represented by.

FIG. 10 is a plan view showing each polarized light or the like shown in FIG. The polarized light that has passed through the polarizing plate 4 becomes polarized light without being affected by the liquid crystal 3 in the vertical alignment state and reaches the polarizing layer 9. The polarized light coincides with the maximum absorption axis of the polarizing layer 9 and is largely absorbed. The polarized light is reflected by the light reflection layer 8 and becomes polarized light. The polarized light rotates 2α ° during the reciprocation of the polarizing layer 9 due to the function as a quarter-wave plate. This polarized light passes through the liquid crystal 3 as it is and becomes polarized light. Since the polarization direction of the polarized light intersects the transmission axis of the polarizing plate 4 by 2α, it is absorbed. As described above, in the present invention, the incident light is absorbed by the dichroic dye 9 b and also absorbed by the polarizing plate 4. In other words, both the function of the polarizing layer 9 as a polarizing plate and the function as a quarter-wave plate substantially completely absorb the incident light and obtain a substantially perfect black display. Accordingly, it is not necessary to increase the concentration of the dichroic dye 9b as in the related art, and unnecessary absorption in white display can be suppressed.

FIG. 15 is a schematic plan view showing the polarization direction of a display device employing a normally black mode. The liquid crystal is left-handed and the twist angle is set to 90 ° -α °. The transmission axis of the polarizing plate is set so as to be orthogonal to the molecular long axis 9x. In other words, the transmission axis of the polarizing plate coincides with the transmission axis of the polarizing layer. When no voltage is applied, black is displayed, and when voltage is applied, white is displayed. FIG. 15 shows a state where no voltage is applied. The linearly polarized light transmitted through the polarizing plate is turned by the twisted liquid crystal to suppress the optical rotation by 90 ° -α °. The polarization direction of the polarized light coincides with the maximum absorption axis of the polarizing layer. The polarized light is rotated by 2α ° while being absorbed while passing through the polarizing layer twice, and becomes polarized light.
The polarized light is again rotated by the liquid crystal, becomes finally polarized light, and is absorbed by the polarizing plate.

FIG. 11 is a schematic partial sectional view showing a specific configuration example of a display device having a polarizing layer built therein. This display device is assembled using a pair of substrates 1 and 2.
The first substrate 1 is located on the incident side and has a transparent electrode 6 formed thereon. The second substrate 2 is located on the reflection side, has a transparent electrode 11 formed thereon, and is joined to the first substrate 1 via a predetermined gap. A twisted nematic liquid crystal 3 is held in a gap between the two substrates 1 and 2. Polarizing layer 9
Are interposed between the second substrate 2 and the twisted nematic liquid crystal 3. The polarizing layer 9 is not externally mounted but is built in the liquid crystal panel. The polarizing layer 9 is one in which a dichroic dye is dispersed in a polymer liquid crystal and is uniaxially oriented. The retardation is substantially set at λ / 4.

This display device is of a so-called active matrix type, in which a counter electrode 6 is formed entirely on the substrate 1 side. On the substrate 2 side, the pixel electrode 11 with the polarizing layer 9 interposed
And a switching element for driving the same are integrally formed. In this example, this switching element is formed by the thin film transistor 13. Pixel electrode 11 and thin film transistor 1
Reference numerals 3 are electrically connected to each other via a contact hole 23 opened in the polarizing layer 9. This contact hole 23
Can be precisely formed by patterning the polarizing layer 9 by photolithography and etching.
In this structure, since the liquid crystal 3 is directly held by the counter electrode 6 and the pixel electrode 11, a signal voltage can be applied efficiently.

A polarizing plate 4 is attached to the outer surface of the first substrate 1. The transmission axis of the polarizing plate 4 is set so as to coincide with the maximum absorption axis of the polarizing layer 9. The liquid crystal 3 uses a nematic liquid crystal twist-aligned by the upper and lower alignment layers 7 and 12. That is, the twisted nematic liquid crystal 3 twists 90 ° -α ° between the upper and lower substrates 1 and 2 and has a positive dielectric anisotropy. The helical pitch of the twisted nematic liquid crystal 3 is designed to satisfy Morgan's requirements. That is, the helical pitch is set sufficiently long with respect to the wavelength of the incident light. A color filter 5 is formed on the inner surface of the upper substrate 1 so as to correspond to the pixel electrode 11. A flattening film 5a is interposed between the color filter 5 and the counter electrode 6. The color filter 5 may be formed on the lower substrate 2 instead of the upper substrate 1. A light reflecting layer 8 having a diffusivity is formed on the lower substrate 2. In addition, the light reflection layer 8 may have a mirror-reflective property. In this case, it is preferable to provide a light diffusion layer on the upper substrate 1.

The reflection type display device according to this embodiment is of a so-called active matrix type, and a thin film transistor 13 is formed on the lower substrate 2 as a switching element for driving each pixel electrode 11, for example. The thin film transistor 13 has a bottom gate structure, and a gate electrode 14, a gate insulating film 15, and a semiconductor thin film 1 in this order from the bottom.
6, the stopper 17 is laminated. An interlayer insulating film 18 is formed so as to cover the thin film transistor 13. A source electrode 19 and a drain electrode 20 are formed thereon by patterning, and the thin film transistor 13 is formed through a contact hole opened in the interlayer insulating film 18.
Is electrically connected to The light reflection layer 8 is formed on the interlayer insulating film 18. This light reflection layer 8 is formed of a pixel electrode 11
And the pixel is subdivided for each pixel.
It has the same potential as 0. The light reflecting layer 8 has an uneven light scattering surface, and realizes a display screen called a so-called white paper. A flattening layer 21 is formed so as to fill the unevenness of the thin film transistor 13 and the light reflecting layer 8. A base alignment layer 22 is formed on the flattening layer 21.
It is used for uniaxially aligning a polymer liquid crystal formed thereon. The pixel electrode 11 is electrically connected to the corresponding drain electrode 20 of the thin film transistor 13 through a contact hole 23 provided through the polarizing layer 9 and the planarizing layer 21.

The operation of the display device will be described with reference to FIG. FIG. 11 shows a state where no voltage is applied. When external light enters the upper substrate 1 in this state, the external light is first converted into linearly polarized light by the polarizing plate 4. However, in the case of the reflection type, a polarizing plate 4 having a low degree of polarization may be used intentionally in order to increase the brightness. At this time, the external light is converted into elliptically polarized light instead of linearly polarized light. When the linearly polarized light enters the twisted nematic liquid crystal 3, the linearly polarized light rotates due to its optical rotation in the state where no voltage is applied, and advances to the polarizing layer 9. Since the linearly polarized light coincides with the transmission axis of the polarizing layer 9, the linearly polarized light passes therethrough and reaches the light reflecting layer 8. That is, the present embodiment is of a normally white mode, in which almost all of the incident light is transmitted. The linearly polarized light transmitted through the polarizing layer 9 is reflected by the light reflecting layer 8 and emitted out of the panel through a path opposite to that at the time of incidence.

FIG. 12 shows a voltage application state of the present display device. As the applied voltage is increased, the optical rotation of the twisted nematic liquid crystal 3 is gradually lost. When a voltage higher than the threshold is sufficiently applied, the liquid crystal molecules 3a shift to the vertical alignment, and the optical rotation almost disappears. Therefore, the light transmitted through the upper polarizing plate 4 reaches the lower polarizing layer 9 as it is. Since the polarization direction of the transmitted light coincides with the maximum absorption axis of the polarizing layer 9,
Almost completely absorbed.

Finally, a method of manufacturing the reflective display device shown in FIG. 11 will be described in detail with reference to FIGS. First, in the step (A) of FIG. 13, a thin film transistor 13 is placed on an insulating substrate 2 made of glass, quartz, or the like.
Are formed integrally. Specifically, after a gate electrode 14 made of a high-melting-point metal film or the like is formed by patterning, a silicon oxide film or a silicon nitride film is deposited by CVD or the like to form a gate insulating film 15. A semiconductor thin film 16 made of polycrystalline silicon or the like is formed thereon, and is patterned in an island shape according to the element region of the thin film transistor 13. A stopper 17 is provided thereon so as to match the gate electrode 14. Using the stopper 17 as a mask, an impurity is implanted into the semiconductor thin film 16 by ion doping or ion implantation to form a bottom-gate thin film transistor 13. This thin film transistor 13 is covered with an interlayer insulating film 18 made of PSG or the like.

In step (B), after opening a contact hole in the interlayer insulating film 18, aluminum or the like is sputtered and patterned into a predetermined shape to process the source electrode 19 and the drain electrode 20. At this time, the light reflection layer 8 is formed at the same time. In the region where the light reflection layer 8 is to be formed, irregularities are formed in advance as a base.
Has light scattering properties, and a so-called white paper display appearance can be obtained. Further, a flattening layer 21 made of an acrylic resin or the like is formed so as to fill the unevenness of the thin film transistor 13 and the light reflection layer 8. A rubbing treatment is applied thereon by applying a polyimide resin, and a base alignment layer 22 is provided. A polarizing layer 9 made of a mixture of a uniaxially oriented polymer liquid crystal and a dichroic dye is formed thereon with a predetermined thickness. Specifically, a solution in which a polymer liquid crystal and a dichroic dye are dissolved is formed on the base alignment layer 22. The polymer liquid crystal is a material capable of performing a phase transition between a nematic liquid crystal phase on a high temperature side and a glass solid phase on a low temperature side at a predetermined transition point. For example, the polymer liquid crystal is in a glassy state at room temperature, and is preferably a main chain type or a side chain type having a phase transition point at 100 ° C. or higher. After the polymer liquid crystal and the dichroic dye are dissolved in an organic solvent, the base alignment layer 2 is formed by spin coating.
2 with a predetermined thickness. In addition, you may apply by using dipping or screen printing etc. instead of spin coating. Thereafter, the substrate 2 is heated once to a transition point or higher, and then cooled to a room temperature lower than the transition point, and the formed polymer liquid crystal is aligned in the alignment direction to form the polarizing layer 9. The thickness of the polarizing layer 9 is such that the retardation is substantially λ /
4 is formed.

In step (C), a photoresist 10 is applied so as to cover the entire surface of the polarizing layer 9. As a coating method, spin coating or screen printing can be used. Proceeding to step (D), the photoresist 10 is exposed and developed to form a window 10
a is provided.

In step (E) of FIG. 14, etching is performed using the patterned photoresist 10 as a mask, and a contact hole 23 penetrating through the polarizing layer 9, the underlying alignment layer 22, and the planarizing layer 21 is opened. Here, dry etching in which oxygen plasma or the like is applied is employed. Proceeding to step (F), the used photoresist 10
Is removed, a transparent conductive film made of ITO or the like is formed on the polarizing layer 9, patterned into a predetermined shape, and processed into the pixel electrode 11. The pixel electrode 11 is connected to the drain electrode 20 of the thin film transistor 13 through the contact hole 23.
Electrical connection.

Finally, the process proceeds to step (G), where an organic alignment layer 12 is formed on the pixel electrode 11 and the polarizing layer 9. That is, a horizontal alignment agent is continuously applied on the pixel electrode 11 and on the polarizing layer 9 exposed between the pixel electrodes 11 and rubbed to form the alignment layer 12. Finally, although not shown, the upper substrate on which the counter electrode, the color filter, and the alignment layer are formed in advance is bonded to the lower substrate 2 via a predetermined gap, and if the nematic liquid crystal is injected into this gap, the reflection will occur. The type display device is completed.

[0035]

As described above, according to the present invention,
A dichroic dye is dispersed in uniaxially oriented polymer liquid crystal to form a polarizing layer. Further, the thickness of the polarizing layer is set so that the retardation is substantially λ / 4.
With such a configuration, the polarizing layer functions as a linear polarizing plate and also functions as a quarter-wave plate. By incorporating a polarizing layer having both functions into a liquid crystal display device, almost perfect black display can be obtained without impairing the brightness of white display, and the display contrast can be remarkably improved as compared with the related art. In particular, it is possible to obtain a black display that is equal to or more than the light absorption ability of the dichroic dye.

[Brief description of the drawings]

FIG. 1 is a schematic view showing the structure and characteristics of a polarizing element according to the present invention.

FIG. 2 is a process chart showing a method for manufacturing a polarizing element according to the present invention.

FIG. 3 is a chemical structure diagram showing a specific example of a polymer liquid crystal used in the polarizing element according to the present invention.

FIG. 4 is a chemical structure diagram showing a specific example of a dichroic dye used in the polarizing element according to the present invention.

FIG. 5 is a graph showing light absorption characteristics of a dichroic dye.

FIG. 6 is a graph showing light absorption characteristics of a dichroic dye.

FIG. 7 is a partial cross-sectional view showing a basic configuration of a reflective display device incorporating a polarizing element according to the present invention.

FIG. 8 is a schematic diagram for explaining the operation of the display device shown in FIG. 7;

9 is a partial cross-sectional view showing a voltage application state of the display device shown in FIG.

FIG. 10 is a schematic diagram for explaining the operation of the display device shown in FIG. 9;

FIG. 11 is a partial cross-sectional view showing a specific configuration example of a reflective display device incorporating a polarizing element according to the present invention.

FIG. 12 is a partial cross-sectional view showing a specific configuration example of a reflective display device incorporating a polarizing element according to the present invention.

FIG. 13 is a process chart showing a method for manufacturing a reflective display device.

FIG. 14 is a process chart showing a method for manufacturing a reflective display device.

FIG. 15 is a schematic view showing another embodiment of the reflection type display device according to the present invention.

FIG. 16 is a schematic view showing the structure of a conventional polarizing plate.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Substrate, 3 ... Twisted nematic liquid crystal, 4 ... Polarizing plate, 6 ... Counter electrode, 8
..Light reflecting layers, 9 polarizing layers, 11 pixel electrodes,
13: thin film transistor, 22: base alignment layer

Claims (5)

[Claims] 1. A polarizing element comprising a film-formed polymer and a dye compounded therein, wherein the polymer includes liquid crystal uniaxially oriented in a predetermined direction, and the dye includes an incident light. Provided with dichroism exhibiting different absorbances for light with the long axis and short axis of the molecule, the long axis of the molecule is aligned in the predetermined direction according to the uniaxial orientation of the liquid crystal, and included in the incident light Selectively absorbs and transmits the vibration component to be converted into polarized light, and the polymer has a retardation of (2n + 1) · λ.
/ 4 (where λ is a wavelength in the visible region, and n is zero or an integer). 2. A step of preparing a solution in which a polymer liquid crystal and a dichroic dye are dissolved in a solvent; a step of aligning the surface of the substrate along a predetermined direction; A step of applying a solution to form a coating film such that the retardation is (2n + 1) · λ / 4 (where λ is a wavelength in the visible region, and n is zero or an integer); Performing a uniaxial alignment of the polymer liquid crystal in the predetermined direction and aligning the dichroic dyes in accordance with the uniaxial alignment. 3. A first substrate positioned on the incident side, a polarizing plate bonded to the first substrate, a second substrate positioned on the reflecting side and bonded to the first substrate via a predetermined gap, A display device comprising: a liquid crystal held in a gap between both substrates; and a polarizing layer interposed between the second substrate and the liquid crystal, wherein the polarizing layer is formed by adding a dichroic dye to a polymer liquid crystal. It is uniaxially oriented in a dispersed state, and its retardation is (2n + 1) · λ / 4 (where λ is the wavelength in the visible region, n
Wherein the liquid crystal is optimally twisted in a twist angle range of 45 ° to 135 °. 4. The polarizing layer according to claim 1, wherein the direction of the uniaxial orientation is α °.
(0 ° <α ° <45 °) has a maximum absorption axis in a tilted direction, and the liquid crystal has a twist angle of 90 ° −α ° or 90 ° +
The display device according to claim 3, wherein the display device is optimized to α °. 5. The display device according to claim 4, wherein the polarizing plate is disposed such that a transmission axis thereof is parallel to a maximum absorption axis of the polarizing layer.