JP2005351944A - Translucent liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a translucent liquid crystal display wherein wide visual field angle characteristics can be obtained while contrast in a front direction is secured when a backlight is turned on. <P>SOLUTION: The tranlucent liquid crystal display constituted of at least a polarizing plate, a visual field angle improving film, a retardation film consisting of a liquid crystal film having a twisted structure, a light diffusion layer, an STN type liquid crystal display element having a semitransmission film, a λ/4 film, a polarizing plate and a backlight successively from a display side is characterized in that the visual field angle improving film has 400 to 600 nm product (Δn×d) of refractive index anisotropy Δn and thickness d and the delay phase axis of the visual field angle improving film is set in a direction coincident with or orthogonal to the absorption axis of the polarizing plate on the display side. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention provides an STN-type transflective liquid crystal display with a good viewing angle when a backlight is lit, which is provided with a specific viewing angle improving film between a display-side polarizing plate and a retardation film composed of a liquid crystal film having a twisted structure. Relates to the device.

In recent years, the application of liquid crystal display devices from calculators to word processors and personal computer displays has expanded due to the remarkable improvement in display performance due to the development of liquid crystal display technology. Furthermore, the market expansion expectation as a display of a portable information terminal device that can make the most of the thin and light features of a liquid crystal display device is increasing. As portable applications, high definition is rapidly progressing and high image quality is required.
A conventional transflective liquid crystal display device includes a pair of polarizing plates, a liquid crystal display element disposed between the pair of polarizing plates, and at least one sheet disposed between the polarizing plate and the liquid crystal display element. The liquid crystal display element includes a retardation film, a light diffusion layer disposed between the retardation film and the liquid crystal display element, and a semi-transmissive film in the liquid crystal display element or on the backlight surface side.
The liquid crystal display element is a semi-transmission only on a pair of glass substrates, a liquid crystal layer disposed between the glass substrates, a transparent electrode formed on each surface of the glass substrate on the liquid crystal layer side or the backlight surface side. A certain electrode and an alignment film formed on each surface of the both electrodes on the liquid crystal layer side are sandwiched.

Conventionally, TN (twisted nematic) type and STN (super twisted nematic) type liquid crystal display devices are mainly used.
The above-mentioned STN type liquid crystal display device generally has a structure in which a liquid crystal display element (liquid crystal cell) is sandwiched between a pair of polarizing plates. The transflective film is arranged outside the liquid crystal display element on the light surface side. In the STN liquid crystal display device, the twist angle of the liquid crystal molecules in the liquid crystal display element is set to 90 ° or more, and the setting angle of the transmission axis of the polarizing plate with respect to the elliptically polarized light generated by the birefringence effect of the liquid crystal display element is optimized. Therefore, rapid molecular orientation deformation accompanying voltage application can be reflected in the change in birefringence of the liquid crystal, and an electro-optical characteristic exhibiting a rapid optical change above the threshold can be realized.
In an STN liquid crystal display device, yellowish green or dark blue may occur as a display background color due to the birefringence of liquid crystal. In order to improve this coloring phenomenon, color compensation is performed by superimposing a liquid crystal cell for optical compensation or a retardation film formed of a polymer such as polycarbonate or a twisted retardation film on the display STN liquid crystal cell. Yes.

  As a problem of the STN liquid crystal display device, wide viewing angle is cited. The backlight system disposed on the lower side (back side) of the liquid crystal display device generally includes one or two prism sheets in order to improve the front luminance which is the luminance in the direction perpendicular to the display surface. Consists of including. Each time one prism sheet is positioned, the front luminance is improved. However, since the diffusion of light in the direction perpendicular to the longitudinal direction of the groove depends on the angle of the apex angle of the groove of the prism sheet, the viewing angle is narrow due to the structural effect of the groove formed in the prism sheet. Problem arises.

As a conventional technique for solving this problem, there is a technique described in Patent Document 1 or Patent Document 2 below. In patent document 1, the said three-dimensional phase difference plate is utilized. In this technique, a polarizing plate is disposed on at least one side of a liquid crystal display device via at least one retardation film whose refractive index is set to nx>nz> ny. In Patent Document 2, a prism sheet whose upper surface is a prism surface and whose lower surface is a smooth surface is disposed on the back side of the liquid crystal display element, and a light diffusion plate is disposed on the opposite side of the backlight system of the liquid crystal display element. . The light whose traveling direction is aligned in a predetermined direction by the prism sheet is diffused in all directions by the light diffusing plate, and obtains image information with a certain degree of contrast and tone over a wide viewing angle range.
JP-A-5-157911 JP-A-6-194648

  An object of the present invention is to provide a transflective liquid crystal display device that can obtain a wide viewing angle characteristic while ensuring contrast in the front direction when a backlight is turned on.

As a result of intensive studies to solve the above problems, the present inventors have completed the present invention.
That is, the present invention is, in order from the display side, a polarizing plate, a viewing angle improving film, a retardation film composed of a liquid crystal film having a twisted structure, a light diffusion layer, an STN type liquid crystal display element having a semi-transmissive film, λ / 4 A transflective liquid crystal display device comprising at least a film, a polarizing plate and a backlight, wherein a product (Δn · d) of refractive index anisotropy Δn and thickness d of the viewing angle improving film is 400 nm to The present invention relates to a transflective liquid crystal display device having a range of 600 nm and a slow axis of a viewing angle improving film set in a direction coinciding with an absorption axis of a display side polarizing plate.

The present invention also includes, in order from the display side, a polarizing plate, a viewing angle improving film, a retardation film composed of a liquid crystal film having a twisted structure, a light diffusion layer, an STN type liquid crystal display element having a semi-transmissive film, and a λ / 4 film. A transflective liquid crystal display device comprising at least a polarizing plate and a backlight, wherein the product (Δn · d) of refractive index anisotropy Δn and thickness d of the viewing angle improving film is 400 nm to 600 nm. And a slow axis of the viewing angle improving film is set in a direction perpendicular to the absorption axis of the display-side polarizing plate.
The present invention also relates to the above-described transflective liquid crystal display device, wherein the refractive indexes nx, ny and nz in the three-dimensional direction of the viewing angle improving film have a relationship of nx>ny> nz.

Hereinafter, the present invention will be described in detail.
The transflective liquid crystal display device of the present invention includes a liquid crystal display element having a transflective film.
The liquid crystal display element has a pair of transparent substrates provided with electrodes, a layer of liquid crystal material inserted between them, and a semi-transmissive film. As the transparent substrate, one that aligns the liquid crystal substance in a specific alignment direction can be used. Specifically, a transparent substrate having a property of orienting the liquid crystal substance or a transparent substrate provided with an alignment film having a property of orienting the liquid crystal substance is used. By holding two transparent substrates having such a specific alignment direction so that the alignment directions are twisted, and forming a liquid crystal material layer between the transparent substrates, the liquid crystal material layer Can give a specific twist angle. Moreover, the electrode of a liquid crystal display element can be normally provided on the surface of the transparent substrate which touches the layer of a liquid crystal substance, and when a transparent substrate having an alignment film is used, it is provided between the transparent substrate and the alignment film. be able to. As the liquid crystal substance, various substances usually used for STN type liquid crystal display elements can be used.

  In the liquid crystal display element of the present invention, a voltage value of 2 or more is selected and a driving voltage is applied to the liquid crystal material layer. The voltage value of the two or more values is not particularly limited as long as it is an effective voltage value for performing liquid crystal display, and can be a voltage value before and after a sharp change in reflectance or transmittance occurs. . Thereby, the layer of the liquid crystal material can function as an active optical layer that provides display of bright achromatic colors and dark achromatic colors.

The semi-transmissive film is disposed inside or outside the liquid crystal display element. The semi-transmissive film is composed of a region having a reflective function (reflective layer) and a region having a transmissive function. The region having the reflective function becomes a reflective display portion that performs reflective display, and the region having the transmissive function performs transmissive display that performs transmissive display. It becomes a display part.
When the semi-transmissive film is installed inside the liquid crystal display element, it is installed adjacent to the electrode substrate on the side opposite to the display side. Further, the reflective layer of the semi-transmissive film can also have a function as an electrode of a liquid crystal display element.
Further, when the transflective film is installed outside the liquid crystal display element, it can be installed outside the liquid crystal display element on the backlight side of the liquid crystal display element.
The material of the semipermeable membrane is not particularly limited, and aluminum foil, silver foil, etc. can be preferably used. Moreover, an aluminum layer or a silver layer can be vacuum-deposited on a transparent glass transparent substrate by a vacuum deposition method to form a semi-transmissive film.

  In the transflective liquid crystal display device of the present invention, the polarizing plates are disposed on both sides of the liquid crystal display element. The polarizing plate used by this invention is not specifically limited, The general various thing which has an absorption axis can be used. However, in order to obtain a transflective liquid crystal display element with high reflectance, it is preferable to use a polarizing plate with high transmittance. Specifically, other support films such as a uniaxially stretched polyvinyl alcohol film (PVA), a halogen polarizing film made by arranging iodine molecules having a high degree of polarization in a certain direction, a polyvinyl alcohol film dyed with a direct dye, etc. Those sandwiched between can be used as a polarizing plate with high transmittance.

  A retardation film made of a liquid crystal film having a twisted structure used in the present invention (hereinafter also simply referred to as a retardation film) has an optically anisotropic axis and is optically anisotropic from one surface to the other surface. It means one having a twisted structure on its axis. Therefore, the retardation film referred to here has a characteristic equivalent to a plurality of layers having optical anisotropy, which are multilayered so that each optical anisotropic axis is twisted continuously, Similar to a normal TN liquid crystal cell or the like, it has a twist angle.

  The liquid crystal film having the twisted structure means a film having a structure in which a layer having an optical anisotropic axis is continuously twisted in one film. In general, the liquid crystal film can be obtained by forming a liquid crystalline material having twist characteristics into a film. Examples of liquid crystalline substances having torsional characteristics include optically positive uniaxiality regardless of the shape of liquid crystal molecules such as whether or not they are rod-like, and whether they are low or high molecular. Any liquid crystal compound or liquid crystal composition can be used. Specifically, a polymer liquid crystal having a unit that induces torsion, for example, a main chain type polymer liquid crystal such as polyester, polyamide, polycarbonate, and polyesterimide that exhibits liquid crystallinity, polyacrylate, polymethacrylate, polymalonate, and polysiloxane. A side chain type polymer liquid crystal or the like can be used. Of these, polyester is preferred because of its ease of synthesis, orientation, and glass transition point.

As the unit for inducing twist, optically active 2-methyl-1,4-butanediol, 2,4-pentanediol, 1,2-propanediol, 2-chloro-1,4-butanediol, 2-fluoro -1,4-butanediol, 2-bromo-1,4-butanediol, 2-ethyl-1,4-butanediol, 2-propyl-1,4-butanediol or derivatives thereof (for example, diacetoxy compounds, etc.) Units derived from derivatives) can be used. The diols may be either R-form or S-form, and may be a mixture of R-form and S-form.
In addition, the liquid crystal film said by this invention does not ask | require whether the said film itself exhibits liquid crystallinity. The liquid crystal film referred to in the present invention can be usually obtained by fixing the alignment state formed by the liquid crystalline substance as described above in the liquid crystal state by a method such as photocrosslinking, thermal crosslinking, or cooling.

The retardation film used in the present invention preferably has a temperature compensation effect in which the product (Δn3 · d3) of the refractive index anisotropy Δn3 and the thickness d3 of the optical anisotropic body changes depending on the temperature. . This is because even if the ambient temperature changes, the color development does not change, and a liquid crystal display element capable of displaying excellent black and white can be provided. In this case, the change due to the temperature of Δn3 · d3 is the temperature of the product (Δn1 · d1) of the refractive index anisotropy Δn1 and the thickness d1 of the liquid crystal material layer in the liquid crystal display element used for driving. It is desirable that the change due to
Furthermore, the retardation film used in the present invention preferably has different optical anisotropy dispersion depending on the wavelength. This is because a transflective display device that further improves the achromatic color can be provided.
The retardation film is provided between the polarizing plate disposed on the display side and the liquid crystal display element.

The viewing angle improving films used in the transflective liquid crystal display device of the present invention have different refractive indexes in the three-dimensional direction, and the main refractive indexes in the three-dimensional direction are nx, ny, and nz, and the directions included in the plane. If the refractive index is nx, ny (nx> ny) and the refractive index in the thickness direction is nz, the refractive index in the three directions is set to nx>nz> ny. As such a film, for example, a three-dimensional retardation film having a retardation value of 400 to 600 nm made of polycarbonate manufactured by Sumitomo Chemical Co., Ltd. or Nitto Denko Corporation can be used.
The viewing angle improving film is provided between the display-side polarizing plate and the retardation film, and is set so that its slow axis is parallel or orthogonal to the absorption axis of the polarizing plate.

In the transflective liquid crystal display device of the present invention, a light diffusion layer is further disposed between the retardation film and the liquid crystal display element.
Here, the light diffusion layer means a layer having the property of diffusing incident light isotropically or anisotropically, and diffuses light emitted from the liquid crystal display element by being reflected by the reflective layer of the semi-transmissive film. It has the function to do.
The light diffusing layer may be formed from a plastic sheet, a plastic film, a plastic substrate, a substrate other than plastic, etc. exhibiting light diffusibility, and has a refractive index different from that of the matrix in the adhesive matrix. It may be a sheet-like product or a film-like product having dispersed self-supporting particles. The sheet, film, substrate, or the like may be self-supporting or may not have self-supporting. When it does not have self-supporting property, it may be held on a film having a self-supporting property or a transparent substrate by some means, and the light diffusibility as a whole is not impaired. Further, on the retardation film, a compound or composition capable of forming a light diffusing layer is applied by means such as melt coating or solution coating, and if necessary, it is subjected to some treatment such as electric field, magnetic field, polarized light irradiation, A light diffusion layer may be formed. However, it is necessary to carry out so that the film strength of the retardation film is not lowered during melt coating or solution coating.

  The light diffusing layer having adhesive properties is an acrylic adhesive, rubber adhesive, silicon adhesive, ethylene-vinyl acetate copolymer adhesive, urethane adhesive, vinyl ether adhesive, polyvinyl alcohol adhesive, In a matrix composed of a polyacrylamide pressure-sensitive adhesive and a mixed pressure-sensitive adhesive thereof, for example, organic fine particles such as polystyrene fine particles and polymethacrylic acid fine particles having an average particle diameter of 0.5 to 5 μm, silica, alumina, titania, zirconia Examples include inorganic fine particles such as tin oxide, indium oxide, cadmium oxide, and antimony oxide, hollow fine particles enclosing gas, and microcapsules enclosing a liquid dispersed therein. Among these, an acrylic pressure-sensitive adhesive is preferable as a matrix because it is excellent in transparency, weather resistance, heat resistance and the like. When the adhesive light diffusing layers are superimposed, the individual adhesive light diffusing layers can be appropriately combined of the same type or different types.

  Any known material can be used as the acrylic pressure-sensitive adhesive. For example, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, t-butyl group, isobutyl group, amyl group, isoamyl group, hexyl group, heptyl group, cyclohexyl group, 2-ethylhexyl group, octyl Acrylic acid having a linear or branched alkyl group having 1 to 18 carbon atoms such as a group, isooctyl group, nonyl group, isononyl group, decyl group, undecyl group, lauryl group, tridecyl group, tetradecyl group, stearyl group, octadecyl group And a pressure-sensitive adhesive mainly composed of an acrylic polymer using one or more acrylic acid alkyl esters composed of esters of methacrylic acid.

  In addition, the light diffusing layer having adhesiveness is, for example, a petroleum resin, a rosin resin, a terpene resin, a synthetic petroleum resin, a phenol resin, a xylene resin, and an alicyclic group as long as the effects of the present invention are not impaired. Tackifiers such as petroleum petroleum resins, coumarone indene resins, styrene resins, dicyclopentadiene resins, softeners such as phthalate esters, phosphate esters, chlorinated paraffins, polybutenes, polyisobutylenes, and other various fillers Appropriate additives such as an anti-aging agent and a crosslinking agent can be blended.

  Examples of the light diffusing layer having no adhesiveness include a plastic sheet, a film, and a substrate in which particles having a refractive index different from that of the matrix are dispersed in a resin matrix. Specifically, polyimide, polyamideimide, polyamide, polyetherimide, polyetheretherketone, polyetherketone, polyketonesulfide, polyethersulfone, polysulfone, polyphenylenesulfide, polyphenyleneoxide, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate. Inorganic fine particles, organic fine particles, and gases as exemplified above for phthalate, polyacetal, polycarbonate, polyarylate, acrylic resin, polyvinyl alcohol, polystyrene, polyurethane, polyethylene, polypropylene, cellulose plastics, epoxy resin, phenol resin, etc. Plastic film substrate in which encapsulated hollow fine particles, microcapsules enclosing liquid, etc. are dispersed Etc. can be mentioned.

The thickness of the light diffusion layer is not particularly limited, but is usually 10 μm or more and 500 μm or less.
Further, the total light transmittance of the light diffusion layer is preferably 50% or more, and particularly preferably 70% or more. Furthermore, the diffusion transmittance of the light diffusion layer is usually 5 to 99%, preferably 50 to 99%.

In the transflective liquid crystal display device of the present invention, a λ / 4 film is disposed between the backlight-side polarizing plate and the liquid crystal display element.
In the present invention, the λ / 4 film refers to a film having a function of giving a phase difference of approximately ¼ wavelength to light passing through the liquid crystal material layer.
The λ / 4 film used in the present invention is not particularly limited as long as it has such a function, and examples thereof include a twist alignment film and a nematic alignment film made of various liquid crystal materials. Moreover, the film which consists of transparent polymers, such as polyester polymers, such as a polyethylene terephthalate and a polyethylene naphthalate, cellulose polymers, such as a diacetyl cellulose and a triacetyl cellulose, an acrylic polymer, such as a polycarbonate polymer and a polymethylmethacrylate, is mentioned. Styrene polymers such as polystyrene and acrylonitrile / styrene copolymers, polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure, olefin polymers such as ethylene / propylene copolymers, vinyl chloride polymers, nylon and aromatic polyamides, etc. A film made of a transparent polymer such as an amide polymer may also be mentioned. Furthermore, imide polymers, sulfone polymers, polyether sulfone polymers, polyether ether ketone polymers, polyphenylene sulfide polymers, vinyl alcohol polymers, vinylidene chloride polymers, vinyl butyral polymers, arylate polymers, polyoxymethylene polymers Examples thereof include a film made of a transparent polymer such as a polymer, an epoxy-based polymer, and a blend of the above polymers. In addition, if these films have a function as a λ / 4 film, the same or different laminates of the films can be used as the films.

  In the transflective liquid crystal display device of the present invention, the twist angle θ1 of the liquid crystal material molecules from the display side polarizing plate to the backlight side polarizing plate in the liquid crystal material layer in the liquid crystal display element is in the range of + 200 ° to + 270 °. It is in. When the twist angle is less than + 200 °, there is little change in the liquid crystal state when time-division driving is performed at a high duty ratio that requires a steep change in transmittance. Moreover, when it exceeds +270 degrees, hysteresis tends to occur. In this specification, the + direction and − direction of the angle mean the rotation direction of the relative angle, and the counterclockwise direction from the display side polarizing plate to the backlight side polarizing plate is +. If the clockwise direction is +, conversely, if the clockwise direction is +, the counterclockwise direction is-. However, both are included in the scope of the present invention and the same effect can be obtained. Can do.

In the transflective liquid crystal display device of the present invention, the product (Δn1 · d1) of the refractive index anisotropy Δn1 and the thickness d1 of the liquid crystal material layer in the liquid crystal display element is in the range of 700 nm to 1000 nm. If Δn1 · d1 is less than 700 nm, the change in the state of the liquid crystal when a voltage is applied is small. On the other hand, if it exceeds 1000 nm, viewing angle characteristics and responsiveness deteriorate.
In the transflective liquid crystal display device of the present invention, the twist angle θ5 from the display side polarizing plate to the backlight side polarizing plate of the slow axis of the retardation film, the refractive index anisotropy Δ of the retardation film The product (Δn3 · d3) of n3 and thickness d3 preferably has the following range.
θ5 = −155 ° to −420 °
Δn3 · d3 = 200 to 700 nm
As described above, by setting θ5 and θ1 to values in a specific range, and Δn1 · d1 and Δn3 · d3 to values in a specific range, good contrast can be realized.

In the transflective liquid crystal display device of the present invention, the ratio of the retardation change corresponding to the change in the elevation angle in the slow axis direction of the viewing angle improving film is expressed by the coefficient Nz = (nx -Nz) / (nx-ny), and a viewing angle improving film in which Nz = 0.3 when the wavelength λ is 633 nm can be realized with a retardation value of 400 to 600 nm.
By providing between the display side polarizing plate and the retardation film so that the slow axis of the viewing angle improving film is parallel or orthogonal to the absorption axis of the polarizing plate disposed on the display side of the driving liquid crystal display element. Thus, it is possible to realize a good viewing angle characteristic in the transmission mode, which cannot be realized only by the retardation film.

  The relationship between the angles described above will be specifically described with reference to FIG. 1. In FIG. 1, 1 is a polarizing plate, 2 is a viewing angle improving film, 3 is a retardation film composed of a liquid crystal film having a twisted structure, 4 Is a light diffusing layer, 5A is a liquid crystal material layer (translucent film, transparent substrate with electrodes not shown), 6 is a λ / 4 film, 7 is a polarizing plate, and 8 is a backlight. Yes. The orientation direction 51 on the surface on the polarizing plate 1 side of the liquid crystal material layer 5A and the orientation direction 52 on the surface on the λ / 4 film 6 side form an angle θ1. The direction 21 of the slow axis on the surface on the polarizing plate 1 side of the viewing angle improving film 2 forms an angle θ3 with the absorption axis 11 of the polarizing plate 1. The direction 31 of the slow axis on the surface of the retardation film 3 on the polarizing plate 1 side and the direction 32 of the slow axis on the surface on the light diffusion layer 4 side form an angle θ5. Further, the absorption axis 11 of the polarizing plate 1 and the direction 31 of the slow axis on the surface of the retardation film 3 on the polarizing plate 1 side form an angle θ4, and the absorption axis 11 of the polarizing plate 1 and the liquid crystal material layer 5A. An angle θ2 is formed with the orientation direction 51 on the surface of the polarizing plate 1 side.

FIGS. 2A and 2B show the positional relationship when these are viewed from the polarizing plate 1 side toward the backlight 8 side as a plan view using the same symbols. In FIGS. 1 and 2, θ1 to θ7 are all rotated counterclockwise from the polarizing plate 1 toward the backlight 8, that is, relatively rotated in the same direction for convenience of explanation. In the type liquid crystal display device, the rotation direction of θ1 is always opposite to θ5.
The transflective liquid crystal display device of the present invention includes two polarizing plates, a viewing angle improving film, a retardation film composed of a liquid crystal film having a twisted structure, a light diffusion layer, an STN liquid crystal display element having a transflective film, λ / 4 film and a backlight are provided as essential constituent members, but other constituent members may be provided in addition to these. For example, a color transflective liquid crystal display device capable of multi-color or full-color display with high color purity can be obtained by further including a color filter.

  Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples.

(Example 1)
An STN type transflective liquid crystal display device schematically shown in FIG. 3 was prepared. As shown in FIG. 3, the liquid crystal display element 5 includes a pair of opposed transparent substrates 5D, a transparent electrode 5B provided on the inner surface thereof, a porous metal electrode 5C functioning as a semi-transmissive film, There are provided an alignment film 5F and a color filter 9 which are printed thereon and subjected to an alignment process. A liquid crystal material is sealed in a space defined by the alignment film 5F and a sealant 5E formed by printing around the transparent substrate to form a liquid crystal material layer 5A. ZLI-2293 (manufactured by Merck) was used as the liquid crystal material, and the liquid crystal material layer 5A was aligned in a predetermined direction by adjusting the alignment processing direction of the alignment film 5F, and twisted to θ1 = + 240 °. The product Δn1 · d1 of the refractive index anisotropy Δn1 of the liquid crystal material in the liquid crystal display element 5 and the thickness d1 of the liquid crystal material layer 5A was about 850 nm.

The polarizing plate 1 is arranged on the display surface side (the upper side in the figure) of the liquid crystal display element 5 so that the absorption axis thereof is horizontal, while the polarizing plate 7 is arranged on the back side of the liquid crystal display element 5 (the lower side in the figure). did. A viewing angle improving film 2 is disposed between the polarizing plate 1 and the liquid crystal display element 5, a retardation film 3 is disposed between the viewing angle improving film 2 and the liquid crystal display element 5, and the retardation film 3 and the liquid crystal display. Between the elements 5, a light diffusion sheet IDS-21 (total light transmittance 91.1%, haze degree 51.6) manufactured by Dai Nippon Printing Co., Ltd. is disposed as the light diffusion layer 4, and the polarizing plate 7 on the back side. A λ / 4 film 6 is disposed between the liquid crystal display element 5 and the liquid crystal display element 5. A backlight 8 was installed outside the back side polarizing plate 7. The product Δn2 · d2 of the refractive index anisotropy Δn2 and the thickness d2 of the viewing angle improving film 2 was about 450 nm. The product Δn3 · d3 of the refractive index anisotropy Δn3 and the thickness d3 of the retardation film 3 was approximately 720 nm, and θ5 = −180 °. Further, the slow axis of the viewing angle improving film 2 was matched with the absorption axis of the polarizing plate 1 (θ3 = 0). Further, the angle from the absorption axis of the polarizing plate 1 to the slow axis on the surface of the retardation film 3 on the polarizing plate 1 side is θ4−θ3 = + 15 °, and the light diffusion of the liquid crystal material layer 5A from the absorption axis of the polarizing plate 1 The angle to the orientation direction on the layer side surface was θ2 = −65 °. The slow axis of the λ / 4 film 6 was an angle θ6 = + 45 ° with respect to the alignment axis of the liquid crystal material layer 5A on the λ / 4 film 6 side. The absorption axis of the polarizing plate 7 on the backlight side was an angle θ7 = + 90 ° with respect to the slow axis of the λ / 4 film 6.
A driving voltage was applied to the liquid crystal display device from a driving circuit (not shown) to the transparent electrode 5B and the metal electrode 5C under backlight lighting, and the viewing angle characteristics were subjected to sensory evaluation. As a result, the reversal direction disappeared. Also, a human face was displayed on the device, and the sensory evaluation was performed centering on the liquid crystal display device at a position where the displayed face was 0 degrees from the front and laid from 50 degrees to 80 degrees. As a result, there was no orientation in which the hair turned white.

(Example 2)
A liquid crystal display device similar to that of Example 1 was prepared except that the slow axis of the viewing angle improving film 2 was set to an angle θ3 = + 90 ° with respect to the absorption axis of the display-side polarizing plate 1, and a driving voltage was applied under backlight lighting. Was applied, and the viewing angle characteristics were subjected to sensory evaluation. As a result, the reversal direction disappeared. Also, a human face was displayed on the device, and the sensory evaluation was performed centering on the liquid crystal display device at a position where the displayed face was 0 degrees from the front and laid from 50 degrees to 80 degrees. As a result, there was no orientation in which the hair turned white.

(Comparative Example 1)
A liquid crystal display device similar to that of Example 1 was prepared except that the viewing angle improving film was not used, and a driving voltage was applied under backlight lighting, and the viewing angle characteristics were subjected to sensory evaluation. As a result, a negative / positive inversion phenomenon occurred between 0-90 °. As a result, it was found that good viewing angle characteristics were not achieved. In addition, the face of a person was displayed in the same manner as in Examples 1 and 2, and the sensory evaluation was performed centering on the liquid crystal display device at a position where the displayed face was set to 0 degrees from the front and laid from 50 degrees to 80 degrees therefrom. As a result, when viewed from the 2 o'clock to 3 o'clock direction on the watch, the hair turned white.

It is the schematic explaining the position and angle relationship of each structural member in the liquid crystal display device of this invention. It is a top view explaining the angle relationship of the slow axis direction of the absorption axis of the polarizing plate in the liquid crystal display device of this invention, the orientation direction of a liquid-crystal substance layer, a viewing angle improvement film, retardation film, and (lambda) / 4 film. FIG. 2 is an elevational cross-sectional view schematically showing the apparatus of Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polarizing plate 2 Viewing angle improvement film 3 Retardation film 4 Light diffusion layer 5 Liquid crystal display element 5A Liquid crystal substance layer 5B Transparent electrode 5C Porous metal electrode 5D Transparent substrate 5E Sealing agent 5F Alignment film 6 λ / 4 film 7 Polarizing plate 8 Backlight 9 Color filter 11 Absorption axis of polarizing plate 21 Slow axis on surface of polarizing film 1 of viewing angle improvement film 31 Slow axis on surface of polarizing film on side of polarizing plate 1 32 Retardation film The slow axis 51 on the surface of the liquid crystal display element side 51 The orientation direction of molecules of the liquid crystal material on the surface of the liquid crystal material layer on the polarizing plate 1 52 The orientation of molecules of the liquid crystal material on the surface of the liquid crystal material layer on the backlight side Direction 61 Slow axis on the surface of the liquid crystal material layer side of λ / 4 film 71 Absorption axis of polarizing plate 7

Claims (3)

  In order from the display side, a polarizing plate, a viewing angle improving film, a retardation film composed of a liquid crystal film having a twisted structure, a light diffusion layer, an STN type liquid crystal display element having a semi-transmissive film, a λ / 4 film, a polarizing plate, a back A transflective liquid crystal display device comprising at least light, wherein the product (Δn · d) of refractive index anisotropy Δn and thickness d of the viewing angle improving film is in the range of 400 nm to 600 nm, A transflective liquid crystal display device, characterized in that the slow axis of the viewing angle improving film is set in a direction coinciding with the absorption axis of the display-side polarizing plate.   In order from the display side, a polarizing plate, a viewing angle improving film, a retardation film composed of a liquid crystal film having a twisted structure, a light diffusion layer, an STN type liquid crystal display element having a semi-transmissive film, a λ / 4 film, a polarizing plate, a back A transflective liquid crystal display device comprising at least light, wherein the product (Δn · d) of refractive index anisotropy Δn and thickness d of the viewing angle improving film is in the range of 400 nm to 600 nm, And a slow axis of the viewing angle improving film is set in a direction perpendicular to the absorption axis of the display side polarizing plate. 3. The transflective liquid crystal display device according to claim 1, wherein refractive indexes nx, ny and nz in the three-dimensional direction of the viewing angle improving film have a relationship of nx>ny> nz.

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