JPH113608A - Display element illumination method and liquid crystal display device - Google Patents

Abstract

(57) [Summary] [PROBLEMS] An illumination method for a display element capable of achieving a bright display without improving the light source luminance accompanying an increase in power consumption by improving light use efficiency, and a display brightness. Development of an excellent transmissive liquid crystal display. SOLUTION: A polarization control layer (2) for changing a vibration plane of linearly polarized light is provided on a light emission side of a light guide plate (1) for emitting incident light from a side surface from one of upper and lower surfaces, and the polarization control layer is provided. The degree of parallelism of the vibration plane of the linearly polarized light emitted from the light guide plate with respect to the transmission axis of the light guide plate side polarizing plate (3) provided in the transmission type display element (4) is increased, and the linearly polarized light is applied to the polarizer. A method for illuminating a display element to be incident, and a liquid crystal display device using the method. [Effect] The absorption loss by the polarizing plate can be suppressed, the display brightness of the display element can be improved by increasing the transmittance of the polarizing plate, and when the brightness is the same as before, the brightness of the light source can be reduced and the power consumption can be reduced. In addition, the battery life of a battery-powered display element such as a portable personal computer can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for illuminating a display element which can achieve a bright display with excellent light use efficiency, and a transmission type liquid crystal display device using the method.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal cell having polarizing plates on both sides is arranged on a light guide plate type light source comprising a light guide plate for emitting incident light from the side from one of the upper and lower surfaces,
There has been known a transmission type liquid crystal display device in which a compensating retardation plate for compensating optical characteristics due to birefringence of a liquid crystal cell is disposed between a polarizing plate and a liquid crystal cell as necessary. The arrangement angle based on the transmission axis and the like of the polarizing plate on the light guide plate side is determined based on the alignment direction of the liquid crystal.
5 degrees or -45 degrees.

However, 50% or more of the light incident on the polarizing plate on the light guide plate side from the light guide plate type light source is usually absorbed by the polarizing plate, and the absorption loss is large, the light utilization efficiency is inferior and the display of the liquid crystal display device is poor. There is a problem that hinders the improvement of brightness. It is possible to improve the brightness by improving the brightness of the light source, but in this case, the light source temperature also rises and optical distortion occurs in the polarizing plate, etc., in addition to the increase in power consumption. Display quality is likely to be reduced.

[0004]

SUMMARY OF THE INVENTION The present invention provides a method of illuminating a display device and a method of illuminating a display device capable of achieving a bright display without the necessity of improving a light source luminance accompanying an increase in power consumption by improving light use efficiency. It is an object of the present invention to develop a transmission type liquid crystal display device which is excellent in quality.

[0005]

According to the present invention, there is provided a light guide plate for emitting incident light from a side surface from one of upper and lower surfaces, to a light emitting side.
A polarization control layer that changes the vibration plane of linearly polarized light is provided, and through the polarization control layer, with respect to the transmission axis of the polarization plate on the light guide plate side provided in the transmission type display element, the vibration plane of the linearly polarized light emitted from the light guide plate. An object of the present invention is to provide a method for illuminating a display element, wherein the degree of parallelism is increased and linearly polarized light is made incident on the polarizing plate, and a liquid crystal display device using the method.

[0006]

According to the present invention, linearly polarized light having a high degree of parallelism with its transmission axis can be made incident on a polarizing plate, so that absorption loss due to the polarizing plate can be suppressed, and the transmittance of the polarizing plate can be increased. Even if the same light source as described above is used, the brightness of display on a display element such as a liquid crystal display device can be improved. When the brightness is the same as that of the related art, the brightness of the light source can be reduced, the power consumption can be reduced, and the battery life of a battery-powered display element such as a portable personal computer can be improved.

The above-mentioned effect is obtained when the light emitted from the light guide plate is converted into partially polarized light, and the linearly polarized light has an incident angle such as a Brewster angle of light obliquely incident on an interface of a medium having a different refractive index and a reflection condition. Contains more P-polarized light than S-polarized light,
Therefore, by controlling the vibration plane of the P-polarized light to make it easier to transmit through the polarizing plate, the light use efficiency can be improved.
The polarization plane including the elliptically polarized light emitted from the light guide plate and the polarization characteristics such as the ellipticity are converted through the polarization control layer, and are easily transmitted through the polarization plate on the light guide plate side, whereby absorption loss is suppressed and transmittance is reduced. This is considered to be due to the improvement in

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The illumination method according to the present invention is characterized in that a light guide plate that emits incident light from a side surface from one of upper and lower surfaces is provided on a light emission side.
A polarization control layer that changes the vibration plane of linearly polarized light is provided, and through the polarization control layer, with respect to the transmission axis of the polarization plate on the light guide plate side provided in the transmission type display element, the vibration plane of the linearly polarized light emitted from the light guide plate. This increases the degree of parallelism and causes the linearly polarized light to enter the polarizing plate.

In the above-described method of illuminating a display element, for example, a phase difference plate is arranged on the light emission side of a light guide plate for emitting incident light from the side from one of the upper and lower surfaces, and a polarization plate is provided above the phase difference plate. A transmissive display element is arranged via the plate, and the angle between the transmission axis of the polarizing plate on the light guide plate side and the in-plane normal to the incident side surface of the light guide plate when the retardation plate is arranged. This can be done by placing it in the middle.

FIG. 1 exemplifies a liquid crystal display device which implements the above-mentioned illumination method. 1 is a light guide plate, 2 is a retardation plate, 3 is a polarizing plate on the light guide plate side, 4 is a transmission type liquid crystal cell, and the retardation plate 2
Is arranged such that its optical axis is located at the middle of the angle between the in-plane normal to the incident side surface of the light guide plate 1 and the transmission axis of the polarizing plate 3 on the light guide plate side. In the figure, 11 is a light source,
12 is a reflective layer, and 31 is a polarizing plate on the viewing side.

FIG. 2 exemplifies another liquid crystal display device implementing the above-mentioned illumination method. This uses the light guide plate 1 having the prism array layer 5 on the light emission side. In this case, the phase difference plate 2 is located above the prism array layer 5, the optical axis of which is perpendicular to the ridge line of the apex of the prism of the prism array layer 5, and the transmission axis of the polarizing plate 3 on the light guide plate side. It is arranged in a state located in the middle of the corner formed.

In the liquid crystal display device exemplified above, the light guide plate 1
Emits incident light from the light source 11 disposed on the side surface thereof from the upper surface via the bottom surface or the like, and the emitted light is reflected by the prism array layer 5.
In the case where there is, the light is transmitted and incident on the phase difference plate 2, then sequentially incident on the polarizing plate 3, the liquid crystal cell 4 and the viewing side polarizing plate 31, and the display light is emitted from the polarizing plate 31.

Accordingly, the above-described embodiments of FIGS. 1 and 2 use the retardation plate 2 as a polarization control layer for changing the plane of vibration of linearly polarized light. According to this, the vibration plane of linearly polarized light in the light emitted from the light guide plate 1 or the prism array layer 5 is converted when transmitting through the retardation plate 2 as a polarization control layer, and the optical characteristics of the retardation plate When the light is emitted from the retardation plate because the angle of the axis is set to the above-mentioned intermediate position, the light becomes linearly polarized light having a vibration surface having a high degree of parallelism with the transmission axis of the polarizing plate 3 on the light guide plate side. The absorption loss due to the plate 3 is suppressed, the transmittance increases, and the luminance of the transmissive liquid crystal display device improves.

As described above, in the present invention, the polarization control layer for changing the plane of oscillation of linearly polarized light controls the polarization state of light emitted from the light guide plate or the prism array layer, and absorbs light from the light guide plate side polarizing plate. It is intended to convert the light into light that is easily transmitted. Therefore, as the polarization control layer, an appropriate optical element capable of changing the vibration plane of linearly polarized light, such as a retardation plate or an optical rotator, can be used.

FIGS. 3 and 4 show a liquid crystal display device using the rotator 7 to implement the illumination method of the present invention.
In the liquid crystal display device illustrated in FIG. 3, an optical rotator 7 instead of the above-described retardation plate 2 is disposed above the light guide plate 6, and the optical rotator includes an in-plane normal to an incident side surface of the light guide plate 6 and An optical rotation angle of ± 10 degrees based on light having a wavelength of 550 nm with respect to the angle formed by the transmission axis of the polarizing plate 3 on the light guide plate side is used.

On the other hand, the liquid crystal display device illustrated in FIG. 4 uses a light guide plate 6 having a prism array layer 5 on the light emitting side. In this case, the optical rotator 7 is provided at the vertex of the prism in the prism array layer. With respect to the angle between the vertical line in the plane direction with respect to the ridge line and the transmission axis of the polarizing plate on the light guide plate side, one having an optical rotation angle in a range of ± 10 degrees based on light having a wavelength of 550 nm is used.

In the liquid crystal display device illustrated in FIGS. 3 and 4, the light guide plate 6 emits incident light from the light source 11 disposed on the side surface of the prism array layer 5 through the bottom surface or the like. If there is, after passing through it and entering the optical rotator 7, the polarizing plate 3, the liquid crystal cell 4, and the viewing side polarizing plate 31
And display light is emitted from the polarizing plate 31.

In the above, the vibrating plane of linearly polarized light of the light emitted from the light guide plate 6 or the prism array layer 5 is converted when passing through the optical rotator 7 as the polarization control layer, and the predetermined optical rotator is used as the optical rotator. When the light is emitted from the optical rotator, the light becomes a linearly polarized light having a vibration plane having a high degree of parallelism with the transmission axis of the polarizing plate 3 on the light guide plate side. The absorption loss due to the plate 3 is suppressed, the transmittance increases, and the luminance of the transmissive liquid crystal display device improves.

In the above description, the effect of improving the brightness based on the linearly polarized light has been described. However, the change in the optical characteristics such as the phase difference due to the polarization control layer affects light other than the linearly polarized light. It is considered that light other than linearly polarized light is converted into light that easily transmits through the polarizing plate via the polarization control layer and contributes to the improvement of the luminance of the device.

The illumination method of the present invention can be applied to an appropriate display element such as a transmission type liquid crystal cell in which linearly polarized light enters through a polarizing plate to achieve a display purpose, and is particularly preferably applied to a transmission type liquid crystal display device. can do. In general, a transmissive liquid crystal display device appropriately includes components such as a polarizing plate, a transmissive liquid crystal cell, a backlight, and a prism array layer including a prism sheet and the like, a diffusing plate, and a compensating retardation plate as necessary. It is formed by assembling a drive circuit. In the present invention, a light guide plate that emits incident light from the side surface from one of the upper and lower surfaces is used as a backlight, and a predetermined distance is provided between the light guide plate or the prism array layer on the light guide plate and the polarizing plate on the light guide plate side. There is no particular limitation except that a polarization control layer is provided, and a liquid crystal display device can be formed according to a conventional method.

As the light guide plate, an appropriate one having reflection layers 12 and 61 on the bottom surface as necessary as shown in the figure so that incident light from the side surface is emitted from one of the upper and lower surfaces is used. Those that can efficiently emit light without absorption are preferably used. (Cold, hot) A linear light source such as a cathode ray tube or a light source such as a light emitting diode is arranged on the side of a light guide plate, and the light transmitted through the light guide plate is diffused, reflected, diffracted or interfered by the light guide plate. An example is a light guide plate or the like known in a conventional transmissive liquid crystal display device that emits light to one side of the liquid crystal display device.

Incidentally, as a general light guide plate for emitting the internal transmission light to one side, a light-emitting surface of a transparent or translucent resin plate or a diffuser such as a dot-like or stripe-like diffuser is provided on the bottom surface thereof. And a structure in which an uneven structure, particularly an arrangement structure of fine prisms, is provided on the bottom surface of the resin plate. In the present invention, a light guide plate that emits light with large bias can be advantageously used.

The reflection layer provided on the bottom surface of the light guide plate as necessary is for the purpose of preventing transmission light reflection and light leakage, etc.
Formed as an appropriate reflection layer such as a diffuse reflection layer represented by an uneven surface or the like, a vapor deposition layer of aluminum or silver, a mirror reflection layer represented by a metal surface made of a resin plate or a metal foil provided with it, or the like. Good. The reflection layer may be provided in an appropriate form such as a coating layer or a coating layer on the bottom surface of the light guide plate or a reflection plate.

The prism array layer, which is disposed on the light guide plate as required, controls the direction of the light emitted from the light guide plate, and is perpendicular or nearly perpendicular to the light guide plate, which is advantageous for visual recognition of the liquid crystal display device. The purpose is to increase the amount of light emitted from the light source. The prism array layer can be provided in the form of a light guide plate by, for example, forming the light emitting surface of the light guide plate into an array structure of fine prisms, or separately from the light guide plate by attaching a prism sheet or the like. It can also be given as

The array direction of the prism array layers arranged on the light guide plate is arbitrary and is generally parallel or perpendicular to the incident side surface of the light guide plate. In the present invention, when the prism array layer is provided on the light guide plate, the arrangement angle and the optical rotation angle of the polarization control layer are determined not based on the light guide plate but on the ridge direction of the apex of the prism in the prism array layer.

When forming the light guide plate, appropriate auxiliary means such as a diffusion plate for equalizing light emission and a light source holder for guiding the light emitted from the light source to the side surface of the light guide plate are provided at predetermined positions as necessary. Layers or two or more layers can be arranged to form an appropriate combination. The position of the diffusion plate is generally between the light guide plate and the polarization control layer, and between the light guide plate and the prism array layer when a prism array layer is provided on the light guide plate, but is not limited thereto.

The retardation plate as a polarization control layer is for converting polarization characteristics such as an ellipticity and an azimuth of incident polarized light. The azimuth conversion can be performed within a range of 2 ° according to the phase difference caused by the phase difference plate, where 角 is the angle between the polarization axis of the incident polarized light and the optical axis of the phase difference plate. In the case of linearly polarized light, when a phase difference of 位相 wavelength is given, the angle change of the polarization axis becomes maximum, and only the azimuth angle of the vibrating surface can be changed without changing the polarization state such as the ellipticity of the emitted light. it can.

Therefore, the mainstream direction of light transmission, that is, the in-plane normal direction to the incident side surface in the light guide plate, the vertical direction parallel to the prism array layer plane to the ridge line of the prism apex in the prism array layer, and the polarization plate on the light guide plate side. A retardation plate is arranged so that the optical axis is located at the center of the angle formed by the transmission axis, especially at the center, and the azimuth of polarized light is transmitted through the retardation plate to the transmission axis of the polarizing plate on the light guide plate side. By converting so as to be as parallel as possible, the absorption loss by the polarizing plate can be reduced and the transmittance can be increased. By the way, the angle between the oscillation plane of the linearly polarized light and the transmission axis of the polarizing plate is φ, and the intensity of the incident light is I
₀ , when the parallel transmittance is H ₀ , the intensity (I) of the emitted light can be obtained by I = I ₀ H ₀ cos ² φ according to Malus' law.

The retardation plate on which the polarization control layer is formed may be a retardation plate having an appropriate retardation, and is not particularly limited. The light emitted from the light guide plate or the prism array layer exhibits characteristics as partial polarization in which linearly polarized light is mixed with natural light, so that the polarization characteristics are prevented from being eliminated.
That is, mλ +
A retardation plate that provides a phase difference of λ / 2 (where m is an arbitrary integer and λ is a wavelength) is preferable.

When m is increased, m is preferably 0 because the wavelength range that does not conform to the above equation increases due to chromatic dispersion and the wavelength light that eliminates the polarization characteristic increases. Therefore, a retardation plate exhibiting a phase difference of .lambda. / 2 or in the vicinity thereof in a wide wavelength range is preferable, and from the point that the visible light of the liquid crystal display device is visible light, it is 400 to 700 nm, preferably 5 to 700 nm.
A phase difference plate exhibiting a phase difference of λ / 2 or in the vicinity thereof in the wavelength range of 00 to 580 mm,
A retardation plate exhibiting a phase difference of 0 to 300 nm is preferred.

The arrangement angle based on the optical axis of the phase difference plate can be appropriately determined according to the phase difference and the like. From the viewpoint of improving brightness, the angle of the optical axis of the phase difference plate is θ _R , the angle of the in-plane normal to the incident side surface of the light guide plate is θ _L , and the angle of the ridgeline direction of the prism apex of the prism array layer is θ _T. When the angle of the transmission axis of the polarizing plate on the light guide plate side is θ _P , the equation: θ = (θ _L +
theta _P) / relative 2 or _{(θ T + θ P) /} 2 is defined by theta, theta It is preferred _{that R} is in the range of 5 ° ±.

In particular, when the retardation plate gives a phase difference of λ / 2, as described above, the in-plane normal direction to the incident side surface of the light guide plate, and the ridge line of the prism apex in the light guide plate provided with the prism array layer. The arrangement in which the optical axis is positioned at the center (middle) of the angle between the transmission direction of the polarizing plate on the side of the light guide plate and the direction perpendicular to the plane of the light guide plate is preferable from the viewpoint of improving the luminance and the like.

In the above, it is preferable that the optical axis for determining the arrangement angle of the phase difference plate is a fast axis from the viewpoint of effective use of obliquely transmitted light. On the slow axis, the direction of the change in the optical axis of the phase difference plate and the direction of the change in the polarization axis of the polarizing plate with respect to the obliquely transmitted light are reversed, so that the obliquely transmitted light, and thus the transmission of the visible light when the liquid crystal display device is viewed obliquely, is transmitted through the polarizer. The rate may decrease.

Rather than increasing the transmittance by equalizing the amount of change in the optical axis of the retardation plate and the amount of change in the polarization axis of the polarizing plate, in particular, the formula:
Based on _{N z = (n x -n z} ) / (n x -n y) is defined by N _z, is preferably a retardation plate satisfying the relation 0 ≦ N _z ≦ 3. Note that _nx and _ny are the in-plane refractive indices of the retardation plate (where _nx ≧
_ny ) and _nz are refractive indexes in the thickness direction. When _Nz is outside the above range, the effect of increasing the transmittance of the obliquely transmitted light is poor.

The retardation plate forming the polarization control layer may be composed of one or more retardation layers for the purpose of controlling the retardation. The superposition of two or more retardation layers having different phase differences, or the superposition of the same or different retardation layers with the optical axes crossing each other is effective in expanding the wavelength range to be converted into the target polarization characteristic. It is.

As the retardation plate or the retardation layer forming the retardation plate, an appropriate one exhibiting birefringence can be used. Incidentally, examples thereof include a film obtained by appropriately stretching a polymer film uniaxially or biaxially, and a retardation film formed of a liquid crystal polymer film or the like. Examples of the polymer film include polycarbonate, polyester, polysulfone, polyethersulfone, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene and other polyolefins, cellulose acetate-based polymers, polyvinyl chloride, polyarylate, and polyamide. And a film made of transparent plastic.

A retardation plate generally exhibits wavelength dispersion peculiar to the material thereof. Generally, the shorter the wavelength, the larger the retardation. However, in the present invention, the retardation plate having a low chromatic dispersion, particularly, A retardation plate exhibiting reverse dispersion is preferred.

The optical rotator as the polarization control layer is for converting the polarization characteristics such as the azimuth angle of the incident polarized light by utilizing the optical rotatory power. Can be converted by rotating only the azimuth without changing the state of polarization. The conversion of the azimuth angle by the optical rotator can be expressed as the optical rotation angle θ, and the angle between the polarization axis of the incident polarized light and the transmission axis of the light guide plate side polarizing plate is defined as η, where the rotation direction of the polarization axis is the positive direction. , N · 180 degrees <
An optical rotator having an optical rotation angle satisfying θ <n · 180 degrees + 2η (n is an arbitrary integer) can be used. An optical rotator having an optical rotation angle of θ = n · 180 degrees + η is preferable from the viewpoint of improvement in luminance and the like. Further, from the viewpoint of suppressing chromatic dispersion, those having a small n, especially 0 are preferable.

In order to form a liquid crystal display device, an in-plane normal to the incident side surface of the light guide plate, or a flat surface with respect to the ridge line of the apex of the prism in the prism array layer in the light guide plate in which the prism array layer is arranged, for the purpose of improving the brightness. Direction, and the angle between the transmission axis of the polarizing plate on the light guide plate side,
Optical rotators that exhibit an optical rotation angle in the range of ± 10 degrees based on light having a wavelength of 550 nm are preferably used.

The optical rotator may be made of an appropriate material exhibiting optical rotatory power. Examples thereof include a low molecular weight liquid crystal and a high molecular weight liquid crystal, or a combination thereof. A liquid crystal that is preferable from the viewpoint of optical rotation and the like has a twisted nematic structure.

The optical rotator composed of a liquid crystal is, for example, a cell type in which a low molecular liquid crystal layer is sandwiched between transparent substrates such as a film, a mode in which a layer composed of a high molecular weight liquid crystal or a liquid crystal polymer is supported by a transparent substrate, a liquid crystal polymer film And appropriate forms such as a form in which these forms are overlapped in an appropriate combination. The liquid crystal polymer film can be obtained, for example, by a method in which a liquid crystal polymer layer is formed on a substrate provided with a release coat and the layer is separated from the substrate.

As the transparent substrate, for example, a film made of a plastic such as triacetyl cellulose, polyvinyl alcohol, polyimide, polyarylate, polyester, polycarbonate, polysulfone, polyether sulfone, or epoxy resin, or a glass plate may be used. Can be used.

The liquid crystal layer can be formed by a method according to a conventional alignment treatment. By the way, as an example, a liquid crystal is formed on a suitable alignment film made of a film of polyimide or polyvinyl alcohol formed on a base material and rubbed with a rayon cloth or the like, or an obliquely deposited layer of SiO ₂ or the like. There is a method of expanding. The development is a bar coater and spinner,
The coating can be performed by a suitable coating machine such as a roll coater or a gravure printing method.

In the case of a high-molecular liquid crystal or a liquid crystal polymer, the liquid crystal is developed on an alignment film, and then heated to a temperature equal to or higher than the glass transition temperature and lower than the isotropic phase transition temperature to align the liquid crystal. To form a solidified layer in which the orientation is fixed by cooling to a glass state.

The development of high-molecular liquid crystal or liquid crystal polymer is as follows.
It can be carried out as a solution by a heat melting method or a solvent. Examples of the solvent include methylene chloride and cyclohexanone, trichloroethylene and tetrachloroethane,
Appropriate materials such as N-methylpyrrolidone and tetrahydrofuran can be used. Upon development, a method of superimposing a liquid crystal layer via an alignment film, if necessary, can be adopted.

A light guide plate side of a display element such as a transmission type liquid crystal cell;
And if necessary, as a polarizing plate arranged on the viewing side,
An appropriate one may be used without any particular limitation. Generally, a polarizing film is used. Examples thereof include a film stretched by adsorbing iodine and / or a dichroic dye on a hydrophilic polymer film such as a polyvinyl alcohol-based, partially formalized polyvinyl alcohol-based, or ethylene-vinyl acetate copolymer-based partially saponified product. And polyene oriented films such as dehydration products of polyvinyl alcohol and dehydrochlorination products of polyvinyl chloride.

In particular, a film obtained by adsorbing iodine and / or a dichroic dye on a hydrophilic polymer film can be preferably used from the viewpoint of the degree of polarization and the like. The thickness of the polarizing film is usually 5 to 80
μm, but is not limited to this. The polarizing plate used is
A polarizing film in which one or both surfaces are covered with a transparent protective layer or the like may be used. Further, the transparent protective layer may have a fine uneven structure on the surface due to the attachment or inclusion of fine particles.

The fine particles may have, for example, an average particle size of 0.
01-50 μm, especially 0.1-20 μm, especially 0.2-1
Suitable inorganic particles such as silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide and the like having a conductive property of 0 μm, and organic fine particles such as a crosslinked or uncrosslinked polymer. Can be used.

The liquid crystal display device can be formed by assembling the respective components in a predetermined arrangement state, but the assembling order is not particularly limited. For example, an assembling method for each component, a plurality of components, Can be formed by an appropriate method such as an assembling method using a unit obtained by laminating in advance.

The components forming the liquid crystal display device may be simply placed on top of each other to be easily separated,
It may be bonded and integrated via an adhesive layer. In the case where the arrangement angle of the optical axis is a problem, such as a phase difference plate or a rotator serving as a polarization control layer and a polarizing plate on the light guide plate side, it is preferable to bond and integrate them in order to prevent displacement.

Further, even when components such as the phase difference plate and the light guide plate are formed of a plurality of separation materials, they can be formed in advance as an integrated adhesive. The bonding and integration through the bonding layer is also effective in preventing reflection loss at each interface, preventing deterioration of display quality by preventing foreign matter from entering the interface, and the like.

As the adhesive layer, an appropriate one can be used. An adhesive layer is preferable from the viewpoint of simplicity of the bonding treatment and the like. For forming the pressure-sensitive adhesive layer, a pressure-sensitive adhesive using an appropriate polymer such as an acrylic polymer, a silicone-based polymer, polyester, polyurethane, polyether, or synthetic rubber can be used. From the viewpoint of preventing reflection loss, it is preferable that the refractive index is an intermediate value of an object to be bonded.

The liquid crystal cell in the transmission type liquid crystal display device of the present invention includes, for example, a twist nematic liquid crystal, a super twist nematic liquid crystal, a non-twist type liquid crystal, a guest-host type liquid crystal in which a dichroic substance is dispersed in a liquid crystal, or A transmission type using an appropriate liquid crystal such as a ferroelectric liquid crystal may be used, and an appropriate driving method of the liquid crystal may be used.

In forming a liquid crystal display device, as described above, for example, a prism array layer made of a prism sheet or the like, a diffusion plate or an antiglare layer provided on a polarizing plate on the viewing side, an antireflection film, a protective layer or a protective plate, or One or more layers of an appropriate optical element such as a compensation retardation plate provided between the liquid crystal cell and the polarizing plate on the viewing side or / and the backlight side can be arranged at an appropriate position.

Since the above-mentioned prism array layer is intended to control the light emission direction, it can be arranged at an appropriate position such as the upper surface of the polarizing plate on the viewing side. When two or more prism array layers are arranged, it is preferable to arrange the array so that the upper and lower layers are in an intersecting state, such as orthogonal, from the viewpoint of leveling the emission direction.

Since the diffusion plate is intended to diffuse light and to homogenize luminance and to expand the direction of light emission, etc., the diffusion plate may be appropriately provided on the upper surface of the light guide plate or the upper surface of the viewing side polarizing plate. One or two or more layers can be arranged at a position. As the diffusion plate, an appropriate one such as a transparent film having a diffusion structure by an appropriate method such as a fine uneven structure exemplified by the transparent protective layer of the polarizing plate can be used, and any known diffusion plate can be used. Further, the compensating retardation plate can be obtained as a stretched film or the like according to the above retardation plate for the purpose of compensating birefringence by a liquid crystal cell or the like and preventing coloration of display.

In the present invention, components such as a retardation plate, an optical rotator, a polarizing plate, a light guide plate, a prismatic layer, and other diffusion plates and an adhesive layer, which form a display device such as a liquid crystal display device, are used. For example, salicylic acid ester compounds,
Ultraviolet ray absorbing ability can be provided by a method of treating with an ultraviolet absorbent such as a benzophenol compound, a benzotriazole compound, a cyanoacrylate compound, or a nickel complex compound.

[0058]

【Example】

Example 1 A side surface of a light guide plate having a thickness of 5 mm made of polymethyl methacrylate having a reflective layer made of an Al vapor-deposited layer provided on the back surface has a diameter of 4 mm.
After placing a cold cathode tube with a thickness of 2 mm and surrounding the side surface of the light guide plate and the cold cathode tube with an aluminum vapor-deposited film, a phase difference of 265 nm made of polycarbonate is provided on the upper surface of the light guide plate through an acrylic adhesive layer having a thickness of 20 μm. , N _{z of} about 1.0, and a TN type liquid crystal cell having a polarizing plate adhered to both sides thereof via a 20 μm-thick acrylic adhesive layer was adhered thereon to obtain a liquid crystal display device. .

In the above retardation plate, since the transmission axis of the polarizing plate on the light guide plate side is arranged at 45 degrees with respect to the in-plane normal of the incident side surface of the light guide plate, its fast axis is in this plane. It was arranged at an angle of 22.5 degrees with respect to the normal line. The TN type liquid crystal cell is of a normally white type in which the transmission axes of the polarizing plates on both sides are orthogonal.

[0060] In Example 2 a phase difference is 210 nm, except that N _z was used about 1.0 phase difference plate, to obtain a liquid crystal display device according to Example 1.

Example 3 A liquid crystal display device was obtained in the same manner as in Example 1 except that the retardation plate was arranged based on the slow axis (stretch axis).

Embodiment 4 A prism sheet is arranged between a light guide plate and a phase difference plate so that the ridge line of the apex of the prism is parallel to the incident side direction of the light guide plate, and the phase difference plate is arranged based on the slow axis. Is
A liquid crystal display device was obtained according to Example 1.

[0063] In Example 5 the phase difference is 265 nm, except that N _z was used about 2.5 phase difference plate, to obtain a liquid crystal display device according to Example 4.

Example 6 A liquid crystal display device according to Example 1, except that an optical rotator made of a liquid crystal polymer film having a TN (twisted nematic) structure and having an optical rotation angle of 22.5 degrees was used instead of the phase difference plate. I got

Example 7 A liquid crystal display device according to Example 4, except that an optical rotator made of a liquid crystal polymer film having a TN (twisted nematic) structure and having an optical rotation angle of 22.5 degrees was used instead of the phase difference plate. I got

Comparative Example 1 A liquid crystal display device was obtained in the same manner as in Example 1 except that the retardation plate was not provided.

Comparative Example 2 A liquid crystal display device was obtained in the same manner as in Example 4 except that the retardation plate was not provided.

Reference Test In the case where a polarizing plate is provided on a light source composed of a light guide plate according to the embodiment, the transmission axis of the light guide plate is the in-plane normal direction of the incident side surface of the light guide plate (main light guide direction), and the prism sheet is provided. It was arranged so as to be in the direction of the ridgeline of the prism apex (prism direction) or in a direction orthogonal thereto, and the front (screen vertical direction) luminance at the center of the light guide plate when the backlight was turned on was examined. The measurement was performed in a dark room using a color difference meter (manufactured by Minolta, CS-100).

The results are shown in Table 1.

[Table 1]

From Table 1, it can be seen that the front luminance is different depending on the arrangement angle of the transmission axis of the polarizing plate. If there is no prism sheet, the main light guiding direction (in-plane normal direction of the incident side surface); It can be seen that the direction orthogonal to (the ridgeline direction of the prism apex) has higher luminance than their perpendicular direction, and that there is a light bias in that direction based on the transmittance of the polarizing plate. Such deviation was confirmed on the entire exit surface of the light guide plate.

Evaluation Test The liquid crystal display device obtained in each of Examples and Comparative Examples was viewed from the front and obliquely in an unselected state when the backlight was turned on on the viewing side.
The luminance in the direction of 5 degrees was examined. The results are shown in Table 2.

[0072]

[Table 2]

From Table 2, it can be seen that the front luminance was improved by about 12% in Examples 1, 3, and 6 and by about 9% in Example 2 when no prism sheet was provided. When a prism sheet is provided, the front luminance is improved by about 18% in Examples 4 and 7 and about 15% in Example 5 with respect to Comparative Example 2. Examples 1 and 3,
From the comparison between 4 and 5, it can be seen that, for obliquely transmitted light, arranging the retardation plate based on the fast axis is advantageous from the viewpoint of improving luminance.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an example of a liquid crystal display device.

FIG. 2 is a cross-sectional view of another example of a liquid crystal display device.

FIG. 3 is a cross-sectional view of yet another example of a liquid crystal display device.

FIG. 4 is a cross-sectional view of another example of a liquid crystal display device.

[Explanation of symbols]

 1, 6: light guide plate 11: light source 12, 61: reflective layer 2: retardation plate 3, 31: polarizing plate 4: liquid crystal cell 5: prism array layer 7: optical rotator

Continued on the front page (51) Int.Cl. ⁶ Identification code FI G02F 1/1335 530 G02F 1/1335 530

Claims (10)

[Claims] 1. A polarization control layer for changing a vibration plane of linearly polarized light is provided on a light emission side of a light guide plate for emitting incident light from a side surface from one of upper and lower surfaces, and a transmission type display is provided via the polarization control layer. With respect to the transmission axis of the polarizing plate on the light guide plate side provided in the element,
A method for illuminating a display element, comprising: increasing the parallelism of a vibrating surface of linearly polarized light emitted from a light guide plate so that the linearly polarized light is incident on the polarizing plate. 2. A light guide plate for emitting incident light from a side surface from one of upper and lower surfaces, a retardation plate disposed on the light exit side, and a transmission type disposed above the retardation plate via a polarizing plate. At least a liquid crystal cell, so that the optical axis is located in the middle of the angle between the in-plane normal to the incident side surface of the light guide plate and the transmission axis of the polarizing plate on the light guide plate side. A liquid crystal display device which is arranged. 3. A light guide plate which emits incident light from a side surface from one of upper and lower surfaces and has a prism array layer on the light emission side, a retardation plate disposed above the prism array layer, and the retardation plate At least a transmissive liquid crystal cell disposed above a polarizing plate via a polarizing plate, wherein the retardation plate has a vertical line perpendicular to the ridge line of the apex of the prism in the prism array layer, and a polarizing plate on the light guide plate side. A liquid crystal display device, wherein the optical axis is located in the middle of the angle between the transmission axis and the transmission axis. 4. The method according to claim 2, wherein the angle of the optical axis of the phase difference plate is θ _R , the angle of the in-plane normal to the incident side surface of the light guide plate is θ _L , and the ridge direction of the prism apex of the prism array layer. When the angle is θ _T and the angle of the transmission axis of the polarizing plate on the light guide plate side is θ _P , the formula: θ = (θ _L + θ _P ) / 2 or (θ _T +
θ _P) / 2 θ _R with respect to theta defined by is in the range of ± 5 degrees liquid crystal display device. 5. The liquid crystal display device according to claim 2, wherein the retardation of the retardation plate is 200 to 300 nm based on light having a wavelength of 550 nm. 6. The liquid crystal display device according to claim 2, wherein an optical axis for determining an arrangement angle of the phase difference plate is a fast axis. 7. The method of claim 2-6, when the phase difference plate has its plane refractive index n _x, n _y (provided that n _x ≧ n _y), the refractive index in the thickness direction and n _z, wherein _{: N z = (n x -n} z) / (n
Based on N _z defined by _x -n _y), the liquid crystal display device is to satisfy 0 ≦ N _z ≦ 3. 8. A light guide plate for emitting incident light from a side surface from one of upper and lower surfaces, a rotator disposed on the light exit side, and a transmission type liquid crystal cell disposed above the rotator via a polarizing plate. Wherein the optical rotator has an angle of ± 10 based on light having a wavelength of 550 nm with respect to the angle formed by the in-plane normal to the incident side surface of the light guide plate and the transmission axis of the polarizing plate on the light guide plate side.
A liquid crystal display device showing an optical rotation angle in a range of degrees. 9. A light guide plate which emits incident light from a side surface from one of upper and lower surfaces and has a prism array layer on the light emission side, an optical rotator arranged above the prism array layer,
At least a transmission type liquid crystal cell disposed above the optical rotator with a polarizing plate interposed therebetween, wherein the optical rotator has a vertical line perpendicular to the ridge line of the apex of the prism in the prism array layer, and a light guide plate side. A liquid crystal display device having an optical rotation angle within a range of ± 10 degrees based on light having a wavelength of 550 nm with respect to an angle formed by a transmission axis of a polarizing plate. 10. The liquid crystal display device according to claim 2, wherein the phase difference plate or the optical rotator is bonded and integrated with the polarizing plate on the light guide plate side.