JP2005164957A - Circularly polarizing plate and liquid crystal display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizing plate which has excellent circularly polarization characteristics and a liquid crystal display element which makes light display in transmission mode and has a high contrast and small viewing angle dependency. <P>SOLUTION: The circularly polarizing plate comprises at least an optical anisotropic element composed of a polarizing plate and two or more optical anisotropic layers, and the optical anisotropic element includes a liquid crystal film (A) having a nematic hybrid alignment structure fixed. The circularly polarizing plate is characterized in that a relation of Rb=α×(Ra-1)+1 is satisfied and α is between 0.2 and 0.8, where Ra represents the ratio of indexes of double refraction of the liquid crystal film (A) at 450 and 590 nm light wavelengths respectively and Rb represents the ratio of indexes of double refraction of one of the remaining optical anisotropic layers at 450 and 590 nm light wavelengths. Further, provided is the liquid crystal display element equipped with the circularly polarizing plate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a circularly polarizing plate and a liquid crystal display device including the same.

  In recent years, the liquid crystal display element is expected to expand the market as a display of a portable information terminal device that can make the most of its thin and light features. Since portable electronic devices are usually battery-driven, it is an important issue to reduce power consumption. Therefore, as a liquid crystal display element for portable use, a reflective liquid crystal display element that does not use a backlight with high power consumption or does not always use it, and can be reduced in power consumption, thinned, and reduced in weight. Is attracting particular attention.

As a reflection type liquid crystal display element, a two-polarization type reflection type liquid crystal display element in which a liquid crystal cell is sandwiched between a pair of polarizing plates and a reflection plate is arranged outside is widely used for monochrome display. More recently, a single-polarization type reflective liquid crystal display element with a liquid crystal layer sandwiched between a polarizing plate and a reflector is in principle brighter and easier to color than the two-polarization plate type. Has been. In a reflection type liquid crystal display element of a single polarizing plate, a quarter wave plate is used for the retardation plate disposed between the polarizing plate and the liquid crystal cell in order to provide a substantially circular polarizing plate function. A normally white reflection type liquid crystal display element is realized by setting the thickness of the liquid crystal layer to about 1/4 wavelength (see, for example, Patent Document 1 and Patent Document 2). However, since these reflective liquid crystal display elements normally perform display using outside light, they have a drawback that the display becomes difficult to see when used in a dark environment.
As a technique for solving this problem, in a reflection type liquid crystal display element of a single polarizing plate, a transflective plate having a property of transmitting a part of incident light is used instead of a reflecting plate, and a backlight is used. A transflective liquid crystal display element provided has been proposed (see Patent Document 3). In this case, it can be used as a reflection type (reflection mode) using external light when the backlight is not lit, and as a transmission type (transmission mode) with the backlight lit in a dark environment.
JP-A-6-11711 WO 98/4320 pamphlet JP 10-206846 A

This single-polarizing plate type transflective liquid crystal display element is typified by one or a plurality of polycarbonates because, in the transmissive mode, it is necessary to make substantially circular polarized light incident on the liquid crystal cell through the transflective layer. It is necessary to arrange a circularly polarizing plate comprising a stretched polymer film and a polarizing plate between the transflective layer and the backlight. However, in the liquid crystal display element of the transmission mode, the problem of the viewing angle that the display color changes or the display contrast decreases when viewed obliquely due to the refractive index anisotropy of the liquid crystal molecules is essentially avoided. In the case of a circularly polarizing plate using a polymer stretched film, this viewing angle expansion is essentially difficult.
In particular, the image quality in the transmission mode is remarkably improved, and further improvement in contrast and improvement in color purity are desired.

  An object of the present invention is to provide a liquid crystal display element having good circular polarization characteristics, bright display in transmission mode, high contrast, and little viewing angle dependency.

  1st of this invention is a circularly-polarizing plate comprised at least from the optically anisotropic element which consists of a polarizing plate and two or more optically anisotropic layers, Comprising: The said optically anisotropic element fixed the nematic hybrid alignment structure. The ratio of the birefringence of the liquid crystal film (A) at a wavelength of 450 nm to the birefringence at 590 nm is Ra, and any one of the remaining optical anisotropic layers includes the liquid crystal film (A). When the ratio of the birefringence of the layer light at a wavelength of 450 nm to the birefringence at 590 nm is Rb, the relationship is Rb = α × (Ra−1) +1, and α at that time is 0.2-0. 8. It is related with the circularly-polarizing plate characterized by being 8.

The second aspect of the present invention relates to the circularly polarizing plate as described above, wherein the optically anisotropic element comprises at least a liquid crystal film (A) having a nematic hybrid alignment structure fixed and a polymer stretched film.
According to a third aspect of the present invention, the optically anisotropic element is composed of at least a liquid crystal film (A) having a nematic hybrid alignment structure fixed and a liquid crystal film (B) having a nematic alignment structure fixed. The present invention relates to the circularly polarizing plate described above.
According to a fourth aspect of the present invention, the liquid crystal film (A) is a liquid crystal film in which a liquid crystal material is nematic hybrid aligned in a liquid crystal state, and the alignment is glass-fixed by cooling from the state. It relates to the described circularly polarizing plate.
A fifth aspect of the present invention is characterized in that the liquid crystal film (A) is a liquid crystal film in which a liquid crystal material is nematic hybrid aligned in a liquid crystal state and the alignment is fixed by a crosslinking reaction by light or heat. This relates to a circularly polarizing plate.

6th of this invention is related with the liquid crystal display element characterized by having the above-mentioned circularly-polarizing plate.
According to a seventh aspect of the present invention, there is provided a first substrate having a transparent electrode, a second substrate having a transflective electrode, and a liquid crystal layer having a liquid crystal layer sandwiched between the first substrate and the second substrate. A liquid crystal layer of the second substrate, comprising: a cell; and at least one phase difference compensation plate and one polarizing plate disposed on a surface opposite to the surface in contact with the liquid crystal layer of the first substrate. The present invention relates to a liquid crystal display element having at least the above-described circularly polarizing plate on a surface opposite to a surface in contact with.

  According to an eighth aspect of the present invention, there is provided a first substrate having a transparent electrode, a second substrate having a transflective electrode, and a liquid crystal layer having a liquid crystal layer sandwiched between the first substrate and the second substrate. A liquid crystal layer of the first substrate, comprising: a cell; and at least one phase difference compensation plate and one polarizing plate disposed on a surface opposite to the surface in contact with the liquid crystal layer of the second substrate. The present invention relates to a liquid crystal display element having at least the above-described circularly polarizing plate on a surface opposite to a surface in contact with.

  According to a ninth aspect of the present invention, there is provided a first substrate having a transparent electrode, a second substrate having a transflective electrode, and a liquid crystal layer having a liquid crystal layer sandwiched between the first substrate and the second substrate. The present invention relates to a liquid crystal display element comprising a cell and having at least the circularly polarizing plate described above on both sides of the liquid crystal cell.

  A tenth aspect of the present invention is a liquid crystal display element having at least an optically anisotropic layer (C) other than the circularly polarizing plate and the circularly polarizing plate, and fixing a nematic hybrid alignment structure constituting the circularly polarizing plate The ratio of the birefringence at a wavelength of 450 nm of the light of the liquid crystal film (A) to the birefringence at 590 nm is Ra, and the ratio of the birefringence of the optical anisotropic layer (C) at a wavelength of 450 nm to the birefringence at 590 nm. The present invention relates to a liquid crystal display element having a relationship of Rc = α × (Ra−1) +1 where α is 0.2 to 0.8.

The eleventh aspect of the present invention relates to the liquid crystal display element described above, wherein a twisted nematic mode is used as the liquid crystal layer.
A twelfth aspect of the present invention relates to the liquid crystal display element described above, wherein a super twisted nematic mode is used as the liquid crystal layer.
The thirteenth aspect of the present invention relates to the liquid crystal display element described above, wherein an ECB mode is used as the liquid crystal layer.
The fourteenth aspect of the present invention relates to the liquid crystal display element described above, wherein a HAN mode is used as the liquid crystal layer.
The fifteenth aspect of the present invention relates to the liquid crystal display element described above, wherein an OCB mode is used as the liquid crystal layer.
The sixteenth aspect of the present invention relates to the liquid crystal display element described above, wherein an IPS mode is used as the liquid crystal layer.
The seventeenth aspect of the present invention relates to the liquid crystal display element described above, wherein a VA mode is used as the liquid crystal layer.

The present invention is described in detail below.
The circularly polarizing plate of the present invention comprises at least an optically anisotropic element comprising a polarizing plate and two or more optically anisotropic layers. Although a plurality of optical anisotropic elements may be used, a single optical element can obtain sufficient optical characteristics.
The polarizing plate is not particularly limited as long as the object of the present invention can be achieved, and those usually used for liquid crystal display elements can be appropriately used. Specifically, iodine and / or dichroic dyes are applied to hydrophilic polymer films made of PVA such as polyvinyl alcohol (PVA) or partially acetalized PVA or partially saponified ethylene-vinyl acetate copolymer. A polarizing film formed by adsorbing and stretching a polarizing film, a polyene oriented film such as a dehydrated PVA product or a dehydrochlorinated polyvinyl chloride product can be used. A reflective polarizing film can also be used.

  The polarizing plate may be used alone, or may be provided with a transparent protective layer or the like on one or both sides of the polarizing film for the purpose of improving strength, improving moisture resistance, improving heat resistance, etc. good. Examples of the transparent protective layer include those obtained by laminating a transparent plastic film such as polyester or triacetyl cellulose directly or through an adhesive layer, a transparent resin coating layer, an acrylic or epoxy photocurable resin layer, and the like. . When these transparent protective layers are coated on both sides of the polarizing film, different protective layers may be provided on both sides.

The optically anisotropic element constituting the circularly polarizing plate of the present invention comprises at least a liquid crystal film (A) composed of two or more optically anisotropic layers and fixed with a nematic hybrid alignment structure, and is approximately 4 in the visible light region. It is an element having a phase difference of one wavelength.
The nematic hybrid alignment mentioned here refers to an alignment form in which the liquid crystal molecules are nematically aligned, and the angle between the director of the liquid crystal molecules and the film plane at this time is different between the upper surface and the lower surface of the film. Therefore, since the angle formed by the director and the film plane is different between the vicinity of the upper surface interface and the vicinity of the lower surface interface, the angle continuously changes between the upper surface and the lower surface of the film. I can say that.
In the film in which the nematic hybrid alignment state is fixed, the directors of the liquid crystal molecules are oriented at different angles at all positions in the film thickness direction. Therefore, the film no longer has an optical axis when viewed as a film structure.

In the liquid crystal film used in the present invention, the angle formed by the director and the film plane is usually 40 ° to 90 °, preferably 60 ° to 90 ° as an absolute value near one interface of the film. In the vicinity of the interface on the opposite side of the surface, the absolute value is usually 0 ° to 30 °, preferably 0 ° to 20 °, and the average tilt angle is usually 5 ° to It is in the range of 35 °, preferably 7 ° to 33 °, more preferably 10 ° to 30 °, and most preferably 13 ° to 27 °. When the average tilt angle is out of the above range, it is not desirable because there is a risk of a decrease in contrast when viewed from an oblique direction.
In addition, the average tilt angle as used in the field of this invention means the average value of the angle which the director of a liquid crystal molecule and the film plane in the film thickness direction of a liquid crystal film (A) form. The average tilt angle can be obtained by applying a crystal rotation method.

  The liquid crystal film (A) constituting the optical anisotropic element used in the present invention may be formed of any liquid crystal as long as the above nematic hybrid alignment state is fixed. I do not care. For example, after forming a low molecular liquid crystal material in a nematic hybrid alignment in a liquid crystal state, a liquid crystal film obtained by fixing the alignment by photocrosslinking or thermal crosslinking, or after forming a polymer liquid crystal material in a nematic hybrid alignment in a liquid crystal state, A liquid crystal film obtained by fixing the orientation to glass by cooling can be used. The liquid crystal film as used in the present invention does not ask whether the film itself exhibits liquid crystallinity, but means a film obtained by forming a liquid crystal material such as a low-molecular liquid crystal material or a polymer liquid crystal material into a film. To do.

  In addition, as the apparent retardation value in the plane when viewed from the normal direction of the liquid crystal film, in a film with nematic hybrid orientation, the refractive index in the direction parallel to the director (hereinafter referred to as ne) is perpendicular to the director. When the refractive index (hereinafter referred to as “no”) is different and the value obtained by subtracting “no” from “ne” is the apparent birefringence, the apparent retardation value is the difference between the apparent birefringence and the absolute film thickness. Is given as a product. This apparent retardation value can be easily obtained by polarization optical measurement such as ellipsometry.

  The optically anisotropic layer used in the present invention is not particularly limited as long as it is excellent in transparency and uniformity, but a polymer stretched film or an optical compensation film made of liquid crystal can be preferably used. As the polymer stretched film, uniaxial or biaxial composed of cellulose, polycarbonate, polyarylate, polysulfone, polyvinyl alcohol (PVA), polyacryl, polyether sulfone, cyclic olefin polymer, etc. A retardation film can be exemplified. Of these, polycarbonate is preferred from the viewpoint of cost and film uniformity.

  In addition, the optical compensation film made of liquid crystal is not particularly limited as long as it is a film that can utilize the optical anisotropy generated from the alignment state by aligning the liquid crystal. For example, known materials such as various optical functional films using nematic liquid crystal, discotic liquid crystal, smectic liquid crystal, or the like can be used. In particular, a liquid crystal film (B) having a nematic alignment structure fixed can be preferably used.

Hereinafter, the retardation value of the optically anisotropic element constituting the circularly polarizing plate of the present invention will be described.
When combined with one nematic hybrid aligned liquid crystal film (A) and one optical anisotropic layer, a quarter wave plate and a 550 nm birefringent light phase difference of 550 nm monochromatic light are approximately ¼ wavelength. Good circular polarization characteristics can be obtained by pasting together a half-wave plate whose phase difference of birefringent light in the monochromatic light is about ½ wavelength in a state where their slow axes intersect. . The retardation value of the quarter-wave plate is usually in the range of 70 nm to 180 nm, preferably 90 nm to 160 nm, particularly preferably 120 nm to 150 nm. The retardation value of the half-wave plate is usually in the range of 180 nm to 320 nm, preferably 200 nm to 300 nm, particularly preferably 220 nm to 280 nm. If the retardation range of the quarter-wave plate and the half-wave plate deviates from the above, unnecessary coloration may occur in the liquid crystal display.

The angle formed by the slow axis of the quarter-wave plate and the slow axis of the half-wave plate is usually 40 to 90 degrees, preferably 50 to 80 degrees, particularly preferably 55 to 75 on the acute angle side. It is a range of degrees.
The nematic hybrid oriented liquid crystal film (A) may be used for a quarter wavelength plate or a half wavelength plate.
When using a liquid crystal film (A) for a quarter-wave plate, using another optical anisotropic layer for the half-wave plate, and using a liquid crystal film (A) for a half-wave plate Any other optically anisotropic layer may be used for the quarter-wave plate.

The specific arrangement conditions of the optical anisotropic element made of the liquid crystal film (A) in the liquid crystal display element will be described. In explaining the more specific arrangement conditions, the upper and lower sides of the film surface of the liquid crystal film (A), the liquid crystal The tilt direction of the film (A) and the pretilt direction of the liquid crystal cell layer will be described below.
FIG. 1 shows the concept of the tilt angle and twist angle of liquid crystal molecules. FIG. 2 shows the concept of the alignment structure of the liquid crystal film constituting the second optical anisotropic element.
First, when the upper and lower sides of the liquid crystal film surface are respectively defined by the angles formed by the liquid crystal molecule director and the film plane in the vicinity of the film interface of the liquid crystal film (A), the angle formed by the liquid crystal molecule director and the film plane is the acute side. The surface that forms an angle of 40 to 90 degrees is defined as b-plane, and the surface that forms an angle of 0 to 30 degrees on the acute angle side is defined as c-plane.
When the c-plane is viewed from the b-plane of the compensation element through the liquid crystal film (A) layer, the angle formed by the liquid crystal molecule director and the projection component of the director on the c-plane is an acute angle and parallel to the projection component. This direction is defined as the tilt direction of the compensation element.

  Next, usually, at the cell interface of the liquid crystal cell layer, the driving low-molecular liquid crystal is not parallel to the cell interface but is inclined at a certain angle, which is generally referred to as a pretilt angle. A direction in which the angle formed by the projection component on the interface of the director is an acute angle and a direction parallel to the projection component of the director is defined as a pretilt direction of the liquid crystal cell layer (see FIG. 3).

The retardation wavelength dispersion of the optical anisotropic element constituting the circularly polarizing plate of the present invention will be described below.
When one nematic hybrid oriented liquid crystal film (A) and one optical anisotropic layer are combined, the ratio of the birefringence of the liquid crystal film (A) at a wavelength of 450 nm to the retardation Δnd at 590 nm (Δnd (450 nm) / Δnd (590 nm)) is Ra, and when the ratio of the birefringence of the optical anisotropic layer at a wavelength of 450 nm to the retardation at 590 nm is Rb, the relationship is Rb = α × (Ra−1) +1. In addition, by providing a relationship such that α at that time is 0.2 to 0.8, preferably 0.3 to 0.7, good circular polarization characteristics can be obtained. When α is out of the above range, unnecessary coloration may occur in the liquid crystal display or the contrast may be lowered.

The circularly polarizing plate of the present invention comprises at least the polarizing plate described above and an optically anisotropic element composed of two optically anisotropic layers including the liquid crystal film (A).
Furthermore, the circularly polarizing plate of the present invention includes a protective layer, an antireflection layer, an antiglare layer, a hard coat layer, an adhesive layer, an adhesive layer, a light diffusion layer, and a light diffusing adhesive, in addition to the polarizing plate and the optical anisotropic element. One or more layers may be included.

The present invention also relates to a liquid crystal display device comprising the above-described circularly polarizing plate of the present invention.
Generally, liquid crystal display elements include a polarizing plate, a liquid crystal cell, and, if necessary, a retardation compensation plate, a transflective layer, a light diffusion layer, a backlight, a front light, a light control film, a light guide plate, a prism sheet, and the like. Although comprised from a member, in the liquid crystal display element of this invention, there is no restriction | limiting in particular except the point which uses the above-mentioned circularly-polarizing plate of this invention. Further, the use position of the circularly polarizing plate is not particularly limited, and may be one or a plurality of places.

The liquid crystal cell is not particularly limited, and a general liquid crystal cell such as a liquid crystal layer sandwiched between a pair of transparent substrates provided with electrodes can be used.
The transparent substrate constituting the liquid crystal cell is not particularly limited as long as the liquid crystal material constituting the liquid crystal layer is aligned in a specific alignment direction. Specifically, a transparent substrate having the property of aligning the liquid crystal itself, a substrate itself lacking alignment ability, but a transparent substrate provided with an alignment film having the property of aligning liquid crystal, etc. Can also be used. Moreover, a well-known thing can be used for the electrode of a liquid crystal cell. Usually, it can be provided on the surface of the transparent substrate with which the liquid crystal layer is in contact, and when a substrate having an alignment film is used, it can be provided between the substrate and the alignment film.

The material exhibiting liquid crystallinity for forming the liquid crystal layer is not particularly limited, and examples thereof include various ordinary low-molecular liquid crystal substances, high-molecular liquid crystal substances, and mixtures thereof that can constitute various liquid crystal cells. In addition, a dye, a chiral agent, a non-liquid crystal substance, or the like can be added to these as long as liquid crystallinity is not impaired.
In addition to the electrode substrate and the liquid crystal layer, the liquid crystal cell may include various components necessary for forming various types of liquid crystal cells described later.

As liquid crystal cell methods, TN (Twisted Nematic) method, STN (Super Twisted Nematic) method, ECB (Electrically Controlled Birefringence) method, IPS (In-Plane Switching) method, VA (Vertical Alignment) method, OCB (Optically Compensated) Birefringence method, HAN (Hybrid Aligned Nematic) method, ASM (Axially Symmetric Aligned Microcell) method, halftone gray scale method, domain division method, display method using ferroelectric liquid crystal, antiferroelectric liquid crystal, etc. The method is mentioned.
Also, the liquid crystal cell driving method is not particularly limited, and a passive matrix method used for STN-LCDs, etc., and an active matrix method using active electrodes such as TFT (Thin Film Transistor) electrodes and TFD (Thin Film Diode) electrodes, Any driving method such as a plasma addressing method may be used.

  The transflective layer is not particularly limited, and metals such as aluminum, silver, gold, chromium and platinum, alloys containing them, oxides such as magnesium oxide, dielectric multilayer films, liquid crystals exhibiting selective reflection, or these The combination of these can be illustrated. These reflective layers may be flat or curved. Further, the transflective layer is a surface that has been processed to have a diffusive shape, such as a concavo-convex shape, that has diffuse reflectivity, a layer that has electrodes on the electrode substrate opposite to the viewer side of the liquid crystal cell, a reflective layer It is also possible to make a part of light pass through a process such as reducing the thickness of the film or making a hole, or a combination thereof.

The light diffusion layer is not particularly limited as long as it has a property of diffusing incident light isotropically or anisotropically. For example, it may be composed of two or more regions, with a difference in refractive index between the regions, or with surface irregularities. Examples of the two or more regions having a refractive index difference between the regions include those in which particles having a refractive index different from that of the matrix are dispersed in the matrix. The diffusion layer may itself be adhesive.
Further, the total light transmittance of the light diffusion layer is preferably 50% or more, and particularly preferably 70% or more. Further, the haze value of the light diffusion layer is usually 10 to 95%, preferably 40 to 90%, and more preferably 60 to 90%.

The backlight, front light, light control film, light guide plate, and prism sheet are not particularly limited, and known ones can be used.
The liquid crystal display element of the present invention can be provided with other constituent members in addition to the constituent members described above. For example, by attaching a color filter to the liquid crystal display element of the present invention, a color liquid crystal display element capable of performing multicolor or full color display with high color purity can be manufactured.

  The liquid crystal display element in the present invention includes a liquid crystal cell in which a liquid crystal layer is sandwiched between a pair of transparent substrates having electrodes, and a transflective layer (having electrodes) installed behind the liquid crystal layer as viewed from the observer. The circularly polarizing plate may be closer to the viewer than the liquid crystal layer than the transflective layer as viewed from the viewer. It may be on the back or on both sides of the liquid crystal layer.

Examples of the liquid crystal display device having the above configuration include the following modes. In addition, the board | substrate which has a transflective electrode said by this invention is the meaning including not only the board | substrate which has a transflective electrode but the case where it comprises from a translucent reflective layer and a transparent substrate provided with an electrode. is there.
(1) a first substrate having a transparent electrode, a second substrate having a transflective electrode, a liquid crystal cell having a liquid crystal layer sandwiched between the first substrate and the second substrate, A surface having at least one retardation compensation plate and one polarizing plate disposed on a surface opposite to the surface of the first substrate in contact with the liquid crystal layer, and a surface of the second substrate in contact with the liquid crystal layer; Is a liquid crystal display device having at least the circularly polarizing plate of the present invention on the opposite surface.
(2) a first substrate having a transparent electrode, a second substrate having a transflective electrode, a liquid crystal cell having a liquid crystal layer sandwiched between the first substrate and the second substrate, A surface having at least one retardation compensation plate and one polarizing plate disposed on a surface opposite to the surface of the second substrate in contact with the liquid crystal layer, and a surface of the first substrate in contact with the liquid crystal layer; Is a liquid crystal display device having at least the circularly polarizing plate of the present invention on the opposite surface.
(3) a first substrate having a transparent electrode, a second substrate having a transflective electrode, and a liquid crystal cell having a liquid crystal layer sandwiched between the first substrate and the second substrate. A liquid crystal display device having at least the circularly polarizing plate of the present invention on both sides of the liquid crystal cell.

When the circularly polarizing plate is disposed only on the viewer side, at least one retardation compensation plate and a polarizing plate are disposed behind the transflective layer as viewed from the viewer, and the circularly polarizing plate is In the case where it is disposed only behind the transflective layer as viewed from the viewer side, at least one retardation compensation plate and a polarizing plate are disposed closer to the viewer side than the liquid crystal layer.
The circularly polarizing plate is preferably behind the transflective layer as viewed from the observer, and particularly preferably on both sides of the liquid crystal layer.
In this type of liquid crystal display element, it is possible to use both a reflection mode and a transmission mode by installing a backlight at the end.

As the retardation compensation plate, a polymer stretched film or an optical compensation film made of liquid crystal can be preferably used. In particular, a film using two stretched polymer films and / or two optical compensation films made of liquid crystal is desirable because a good display can be obtained.
The polymer stretched film may be uniaxial or biaxial composed of cellulose, polycarbonate, polyarylate, polysulfone, polyvinyl alcohol (PVA), polyacryl, polyether sulfone, cyclic olefin polymer, etc. A retardation film can be exemplified. In addition, the optical compensation film made of liquid crystal is not particularly limited as long as it is a film that can utilize the optical anisotropy generated from the alignment state by aligning the liquid crystal, for example, nematic liquid crystal, discotic liquid crystal, smectic liquid crystal. Well-known optical compensation films such as various optical functional films using the above and the like.
In addition, it can be said that the liquid crystal display element is preferably provided with a diffusion layer outside the liquid crystal cell or using a diffuse reflective semi-transmissive reflection layer as an electrode of the liquid crystal cell because it provides good display characteristics.

Further, the present invention is a liquid crystal display element having at least an optically anisotropic layer (C) other than the circularly polarizing plate of the present invention and the circularly polarizing plate, wherein the nematic hybrid alignment structure constituting the circularly polarizing plate is fixed. The ratio of the birefringence of the liquid crystal film (A) at a wavelength of 450 nm to the birefringence at 590 nm is Ra, and the ratio of the birefringence of the optically anisotropic layer (C) at a wavelength of 450 nm to the birefringence at 590 nm. The liquid crystal display element has a relationship of Rc = α × (Ra−1) +1 when Rc, and α at that time is 0.2 to 0.8, preferably 0.3 to 0.7.
The application and type of the optically anisotropic layer (C) are not particularly limited, but one example is the retardation compensator. The optically anisotropic layer (C) used for the retardation compensation plate may be one sheet or two or more sheets. When two or more sheets are used, each value may be the same or different as long as α is in the range of 0.2 to 0.8, preferably 0.3 to 0.7. May be.
As the optically anisotropic layer (C), a polymer stretched film or an optical compensation film made of liquid crystal can be preferably used. The polymer stretched film may be uniaxial or biaxial composed of cellulose, polycarbonate, polyarylate, polysulfone, polyvinyl alcohol (PVA), polyacryl, polyether sulfone, cyclic olefin polymer, etc. A retardation film can be exemplified. In addition, the optical compensation film made of liquid crystal is not particularly limited as long as it is a film that can utilize the optical anisotropy generated from the alignment state by aligning the liquid crystal, for example, nematic liquid crystal, discotic liquid crystal, smectic liquid crystal. Well-known optical compensation films such as various optical functional films using the above and the like.

  The circularly polarizing plate of the present invention has good circular polarization characteristics. By using the circularly polarizing plate of the present invention, a liquid crystal display element having a bright display in the transmission mode, high contrast, and little viewing angle dependency can be obtained.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these. The retardation Δnd in this example is a value at a wavelength of 550 nm unless otherwise specified. In addition, the ratio of retardation at a wavelength of 450 nm and retardation at 590 nm is defined as a D value [D value = Δnd (450 nm) / Δnd (590 nm)] and will be described.

(Example 1)
The outline of the transflective liquid crystal display element of the present invention will be described with reference to FIG. 4, and the configuration of Example 1 will be described with reference to FIG.
As shown in FIG. 4, the second substrate 7 is provided with a transflective electrode 6 made of a material having a high reflectance such as Al, the counter electrode 4 is provided on the first substrate 3, and the transflective electrode is provided. A liquid crystal layer 5 made of a liquid crystal material exhibiting positive dielectric anisotropy is sandwiched between 6 and the counter electrode 4. The retardation compensation plate 2 and the polarizing plate 1 are provided on the opposite surface of the first substrate 3 on the side where the counter electrode 4 is formed, and the surface of the second substrate 7 on which the transflective electrode 6 is formed. The circularly polarizing plate 12 composed of the optical anisotropic element 8 and the polarizing plate 9 is provided on the opposite side. A backlight 10 is provided on the back side of the polarizing plate 9.

The liquid crystal film (A) 15 in which the nematic hybrid alignment with an average tilt angle in the film thickness direction of 28 degrees is fixed and the liquid crystal film (B) 16 in which the nematic alignment is fixed are prepared, as shown in FIG. An ECB-type transflective liquid crystal display element was manufactured in the arrangement.
The liquid crystal cell 11 used was homogeneously aligned using ZLI-1695 (manufactured by Merck) as the liquid crystal material. The thickness of the liquid crystal layer was 5.0 μm, the pretilt angle between the two interfaces of the liquid crystal layer was 2 degrees, and the Δnd of the liquid crystal cell was about 310 nm.

  A polarizing plate 1 (thickness: about 180 μm; SQW-862 manufactured by Sumitomo Chemical Co., Ltd.) is disposed on the viewer side (upper side of the figure) of the liquid crystal cell 11, and the phase difference is between the polarizing plate 1 and the liquid crystal cell 11. As the compensation plate 2, polymer stretched films 13 and 14 made of a uniaxially stretched polycarbonate film were disposed. Δnd of the stretched polymer film 13 was approximately 250 nm, and Δnd of the stretched polymer film 14 was approximately 113 nm.

In addition, as an optically anisotropic element, a liquid crystal film (A) 15 having a nematic hybrid alignment and a liquid crystal film (B) 16 having a nematic alignment fixed are arranged behind the liquid crystal cell 11 as viewed from the observer, and further on the back side. A polarizing plate 9 was disposed. Δnd of the liquid crystal film (A) 15 having the hybrid nematic alignment structure fixed was 100 nm, the D value was 1.12, Δnd of the liquid crystal film (B) 16 was 265 nm, and the D value was 1.06. When α is obtained from this D value, 0.5 is obtained.
The absorption axes of the polarizing plates 1 and 9, the slow axes of the polymer stretched films 13 and 14 and the liquid crystal film (B) 16, the pretilt direction of both interfaces of the liquid crystal cell 11, and the tilt direction of the liquid crystal film (A) 15 are shown in FIG. It arrange | positioned on the conditions described in.

FIG. 6 shows the contrast ratio from all directions, with the ratio of transmittance (white display) / (black display) of white display 0V and black display 6V when the backlight is lit (transmission mode). Yes. The contrast ratio at the front at this time was 454.
FIG. 7 shows the viewing angle characteristics of the transmissivity in the left-right direction when displaying 6 gradations from white display 0 V to black display 6 V when the backlight is lit (transmission mode).
FIG. 8 shows the viewing angle characteristics of the transmissivity in the vertical direction when displaying 6 gradations from white display 0V to black display 6V when the backlight is lit (transmission mode).
6 to 8 show that the viewing angle characteristic is particularly good in the transmission mode.

(Comparative Example 1)
A liquid crystal film (B) 17 having a fixed nematic alignment is prepared, and instead of the liquid crystal film (B) 16 having a fixed nematic alignment disposed on the back side of the liquid crystal cell 11, a liquid crystal film (B) 17 is formed. A liquid crystal display element similar to that of Example 1 was produced except that the arrangement was performed under the conditions described in FIG. The liquid crystal film (B) 17 had a Δnd of 265 nm and a D value of 1.13. Since the D value of the liquid crystal film (A) 15 was 1.12, α at this time was 1.1.

FIG. 9 shows the contrast ratio from all directions, with the ratio of transmittance (white display) / (black display) of white display 0V and black display 6V when the backlight is lit (transmission mode). Yes. The contrast ratio at the front at this time was 412.
FIG. 10 shows the viewing angle characteristics of the transmissivity in the left-right direction when displaying 6 gradations from white display 0 V to black display 6 V when the backlight is lit (transmission mode).
FIG. 11 shows the viewing angle characteristics of the transmittance in the vertical direction when 6 gradations are displayed from white display 0 V to black display 6 V when the backlight is lit (transmission mode).
As for the viewing angle characteristics, it can be seen that a wide viewing angle characteristic is obtained as in the first embodiment.
However, in Example 1, the front contrast is 454, which is about 10% higher than that of 412 in Comparative Example 1.

(Comparative Example 2)
A liquid crystal film (B) 18 having a fixed nematic alignment is prepared, and instead of the liquid crystal film (A) 15 having a fixed nematic alignment disposed on the back side of the liquid crystal cell 11, a liquid crystal film (B) 18 is formed. A liquid crystal display element similar to that of Example 1 was produced except that the arrangement was performed under the conditions described in FIG. The liquid crystal film (B) 18 had a Δnd of 100 nm and a D value of 1.06. Since the D value of the liquid crystal film (B) 16 was 1.06, α at this time was 1.

FIG. 12 shows the contrast ratio from all directions, with the ratio of the transmittance (white display) / (black display) of white display 0V and black display 6V when the backlight is lit (transmission mode). Yes. The contrast ratio at the front at this time was 421.
FIG. 13 shows the viewing angle characteristics of the transmissivity in the left-right direction when displaying 6 gradations from white display 0 V to black display 6 V when the backlight is lit (transmission mode).
FIG. 14 shows the viewing angle characteristics of the transmissivity in the vertical direction when 6 gradations are displayed from 0 V for white display to 6 V for black display when the backlight is lit (transmission mode).
Examples 1 and 2 and Comparative Example 1 are compared with respect to viewing angle characteristics.

Comparing the omnidirectional isocontrast curves in FIG. 6 and FIG. 12, the case of Example 1 using the liquid crystal film (A) 15 having a hybrid nematic structure is a comparative example using the liquid crystal film (B) 18. It can be seen that the viewing angle characteristics are greatly improved as compared with the case of 2.
In addition, comparing the horizontal and vertical gradation characteristics, which are disadvantages in the transmission mode, in FIGS. 7 and 8 and FIGS. 13 and 14, the reversal characteristics are greatly improved by using a liquid crystal film having a hybrid nematic structure. I understand that
In Example 1, it can be seen that the front contrast is 454, which is about 10% higher than that of Comparative Example 1 412.

It is a conceptual diagram for demonstrating the tilt angle and twist angle of a liquid crystal molecule. It is a conceptual diagram of the orientation structure of the liquid crystalline film which comprises a 2nd optically anisotropic element. It is a conceptual diagram explaining the pretilt direction of a liquid crystal cell. It is sectional drawing which represented typically the transflective liquid crystal display element of Claim 7 of this invention. 4 is a plan view showing an angular relationship among an absorption axis of a polarizing plate, a pretilt direction of a liquid crystal cell, a slow axis of a polymer stretched film, and a tilt direction of a liquid crystal film in Example 1. FIG. It is a figure which shows contrast ratio when the transflective liquid crystal display element in Example 1 is seen from all directions. It is a figure which shows the viewing angle characteristic of the transmittance | permeability of the left-right direction when the transflective liquid crystal display element in Example 1 displays 6 gradations from 0V to 6V. It is a figure which shows the viewing angle characteristic of the transmittance | permeability of an up-down direction when the transflective liquid crystal display element in Example 1 displays 6 gradations from 0V to 6V. It is a figure which shows contrast ratio when the transflective liquid crystal display element in the comparative example 1 is seen from all directions. It is a figure which shows the viewing angle characteristic of the transmittance | permeability of the left-right direction when the transflective liquid crystal display element in the comparative example 1 displays 6 gradations from 0V to 6V. It is a figure which shows the viewing angle characteristic of the transmittance | permeability of the up-down direction when the transflective liquid crystal display element in the comparative example 1 displays 6 gradations from 0V to 6V. It is a figure which shows contrast ratio when the transflective liquid crystal display element in the comparative example 2 is seen from all directions. It is a figure which shows the viewing angle characteristic of the transmittance | permeability of the left-right direction when the transflective liquid crystal display element in the comparative example 2 displays 6 gradations from 0V to 6V. It is a figure which shows the viewing angle characteristic of the transmittance | permeability of the up-down direction when the transflective liquid crystal display element in the comparative example 2 displays 6 gradations from 0V to 6V.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,9: Polarizing plate 2: Phase difference compensation plate 3: 1st board | substrate 4: Counter electrode 5: Liquid crystal layer 6: Transflective electrode 7: 2nd board | substrate 8: Optical anisotropic element 10: Backlight 11: Liquid crystal cell 12: Circularly polarizing plate 13, 14: Polycarbonate 15: Liquid crystal film (A)
16: Liquid crystal film (B)

Claims (17)

  A circularly polarizing plate comprising at least an optical anisotropic element comprising a polarizing plate and two or more optical anisotropic layers, the optical anisotropic element comprising a liquid crystal film (A) having a nematic hybrid alignment structure fixed thereto The ratio of the birefringence of the liquid crystal film (A) at a wavelength of 450 nm to the birefringence at 590 nm is Ra, and the light of one of the remaining optical anisotropic layers at a wavelength of 450 nm. Rb = α × (Ra−1) +1 when the ratio of the birefringence to the birefringence at 590 nm is Rb, and α at that time is 0.2 to 0.8. A circularly polarizing plate.   2. The circularly polarizing plate according to claim 1, wherein the optically anisotropic element includes at least a liquid crystal film (A) having a nematic hybrid alignment structure fixed thereon and a polymer stretched film.   The circularly polarized light according to claim 1, wherein the optically anisotropic element comprises at least a liquid crystal film (A) having a nematic hybrid alignment structure fixed and a liquid crystal film (B) having a nematic alignment structure fixed. Board.   4. The liquid crystal film according to claim 1, wherein the liquid crystal film (A) is a liquid crystal film in which a liquid crystal material is nematic hybrid aligned in a liquid crystal state, and the alignment is glass-fixed by cooling from the state. Circular polarizing plate.   The circle according to any one of claims 1 to 3, wherein the liquid crystal film (A) is a liquid crystal film in which a liquid crystal material is nematic hybrid aligned in a liquid crystal state and the alignment is fixed by a crosslinking reaction by light or heat. Polarizer.   A liquid crystal display element comprising the circularly polarizing plate according to claim 1.   A first substrate having a transparent electrode, a second substrate having a transflective electrode, a liquid crystal cell having a liquid crystal layer sandwiched between the first substrate and the second substrate, and the first substrate It comprises at least one retardation compensation plate and one polarizing plate installed on a surface opposite to the surface in contact with the liquid crystal layer of the substrate, and is opposite to the surface in contact with the liquid crystal layer of the second substrate. A liquid crystal display element comprising at least the circularly polarizing plate according to any one of claims 1 to 5 on a surface.   A first substrate having a transparent electrode, a second substrate having a transflective electrode, a liquid crystal cell having a liquid crystal layer sandwiched between the first substrate and the second substrate, and the second substrate The apparatus includes at least one retardation compensation plate and one polarizing plate disposed on a surface opposite to the surface in contact with the liquid crystal layer of the substrate, and is opposite to the surface in contact with the liquid crystal layer of the first substrate. A liquid crystal display element comprising at least the circularly polarizing plate according to any one of claims 1 to 5 on a surface.   A first substrate having a transparent electrode; a second substrate having a transflective electrode; and a liquid crystal cell having a liquid crystal layer sandwiched between the first substrate and the second substrate. A liquid crystal display element comprising at least the circularly polarizing plate according to any one of claims 1 to 5 on both sides of the cell.   A liquid crystal display element having at least an optically anisotropic layer (C) in addition to the circularly polarizing plate according to any one of claims 1 to 5 and the circularly polarizing plate, and constituting the circularly polarizing plate. The ratio of the birefringence of light at a wavelength of 450 nm to the birefringence at 590 nm of the liquid crystal film (A) having a fixed nematic hybrid alignment structure is represented by Ra, and the birefringence of the light of the optical anisotropic layer (C) at a wavelength of 450 nm. A liquid crystal display element having a relationship of Rc = α × (Ra−1) +1, where α is 0.2 to 0.8, where Rc is the birefringence ratio at 590 nm. .   The liquid crystal display element according to claim 7, wherein a twisted nematic mode is used as the liquid crystal layer.   The liquid crystal display element according to claim 7, wherein a super twisted nematic mode is used as the liquid crystal layer.   The liquid crystal display element according to claim 7, wherein an ECB mode is used as the liquid crystal layer.   The liquid crystal display element according to claim 7, wherein a HAN mode is used as the liquid crystal layer.   The liquid crystal display element according to claim 7, wherein an OCB mode is used as the liquid crystal layer.   The liquid crystal display element according to claim 7, wherein an IPS mode is used as the liquid crystal layer. The liquid crystal display element according to claim 7, wherein a VA mode is used as the liquid crystal layer.

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