JP3808048B2 - Optical element, surface light source device using the same, and liquid crystal display device - Google Patents

Optical element, surface light source device using the same, and liquid crystal display device Download PDF

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Publication number
JP3808048B2
JP3808048B2 JP2003066855A JP2003066855A JP3808048B2 JP 3808048 B2 JP3808048 B2 JP 3808048B2 JP 2003066855 A JP2003066855 A JP 2003066855A JP 2003066855 A JP2003066855 A JP 2003066855A JP 3808048 B2 JP3808048 B2 JP 3808048B2
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Japan
Prior art keywords
light
optical element
wavelength
backlight
plate
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JP2003337337A (en
Inventor
和孝 原
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日東電工株式会社
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Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a bandpass filter type optical element capable of forming a surface light source device excellent in front directivity suitable for use in a liquid crystal display device, and in particular, light reaching the surface of the bandpass filter from the liquid crystal cell side. It is related with the optical element which can prevent that the reflected light of is visually recognized, and can suppress the fall of the display quality of a liquid crystal display device.
[0002]
[Prior art]
Surface light source devices such as EL (electroluminescence element) backlights, CCFL (cold cathode fluorescent tube) backlights, and LED (light emitting diode) backlights used in liquid crystal display devices usually have a peak at a specific wavelength. It is.
[0003]
Therefore, if a band pass filter (interference filter) that transmits light at a specific peak wavelength emitted from the backlight at the time of vertical incidence and reflects at the time of oblique incidence is arranged on the emission surface side of the backlight, the vertical incident light is Light that is transmitted but incident from an oblique direction is reflected without being transmitted, and parallel light can be made.
[0004]
The bandpass filter has a characteristic that non-parallel light rays are reflected without being absorbed and returned to the backlight side, unlike the conventional parallel light using a light shielding plate. Here, the reflected oblique incident light is returned to the backlight, re-reflected toward the band-pass filter, and only the front direction component of the re-reflected light is transmitted through the band-pass filter. Therefore, by the so-called light recycling effect in which the above operations are repeated, it is possible to obtain a surface light source device that increases the brightness of light in the front direction (vertical direction) that passes through the bandpass filter and emits parallel light with high efficiency. .
[0005]
Here, the wavelength characteristic of optical interference in the band-pass filter changes depending on the incident angle, that is, the wavelength selectively transmitted through the band-pass filter changes depending on the incident angle. The transmission center wavelength and the transmission wavelength width (half width) can be controlled. For example, if the transmission wavelength width (half-value width) is set narrow, the transmitted light is concentrated only in the vicinity of a very narrow front surface, and a surface light source device with high parallelism can be obtained.
[0006]
On the other hand, when the transmission wavelength width (half-value width) of the bandpass filter is set to be wide, it is possible to achieve a parallel degree that is about the same as when using a commercially available brightness enhancement prism sheet. Here, in the case of a prism sheet, in principle, it cannot be attached to a backlight or a liquid crystal cell in order to utilize the refraction of light at the air interface. However, when using a band-pass filter, unlike the prism sheet, an air interface is unnecessary, so it is possible to attach and integrate with a backlight or a liquid crystal cell. It has the feature that can be made easy. Furthermore, since the surface of the band-pass filter is smooth, it is possible to prevent the surface from being scratched by performing a hard coat treatment or the like, thereby making handling easier. On the other hand, in the prism sheet using the refraction at the surface, it is difficult to perform a scratch generation prevention process such as a hard coat process. Therefore, it can be said that the advantage of using the bandpass filter for the parallel light of the backlight is great.
[0007]
As an optical element using such a bandpass filter, for example, using cholesteric liquid crystal, it has been proposed in Japanese Patent Application Nos. 2001-60005 and 2000-281382, and has been made parallel (condensed). A surface light source device can be obtained.
[0008]
On the other hand, the band-pass filter used for the parallelization of the backlight is not limited to the one using the cholesteric liquid crystal, and includes, for example, a stack of vapor-deposited thin films having different refractive indexes, or a resin composition having different refractive indexes. Of course, it is also possible to use bandpass filters formed from thin film stacks, and by arranging these bandpasses on the exit surface side of the backlight, parallelization of the backlight and improvement of light utilization efficiency are achieved. It is possible.
[0009]
A bandpass filter formed from a laminate of the vapor-deposited thin film or a thin film made of a resin composition may have an advantage in heat resistance and chemical resistance compared to a bandpass filter using cholesteric liquid crystal. The above utility value is high.
[0010]
[Problems to be solved by the invention]
However, in a liquid crystal display device in which a band-pass filter formed from a laminated thin film made of a vapor deposition thin film or a resin composition is disposed on the light emission surface side of the backlight, the display surface side of the liquid crystal display device (that is, the backlight is disposed) The light incident from the direction opposite to the direction is reflected on the surface of the band-pass filter and is viewed as return light, which deteriorates the display quality of the liquid crystal display device.
[0011]
More specifically, as shown in FIG. 9, in the white display, the external light L1 incident from the display surface side of the liquid crystal display device passes through the polarizing plate 8, the liquid crystal cell 4, and the polarizing plate 3. The light reaches the filter 1, is reflected on the surface of the bandpass filter 1, and is visually recognized as the return light L2. Therefore, when the image around the liquid crystal display device is mirror-shaped, or when an anti-glare layer is provided on the surface of the polarizing plate 8, the mirror-reflected image diffuses and spreads in the anti-glare layer, or As a result, the reflected color of the band-pass filter 1 becomes visible, and the display quality of the liquid crystal display device is significantly deteriorated.
[0012]
The present invention has been made to solve such a problem of the prior art, and prevents the reflected light of the light reaching the surface of the bandpass filter from being visually recognized and suppresses the deterioration of the display quality of the liquid crystal display device. It is an object to provide an optical element that can be used.
[0013]
[Means for Solving the Problems]
  In order to solve such a problem, the present invention provides a band-pass filter that is formed from a thin film stack having different refractive indexes and selectively transmits light emitted from a backlight. The polarizing plate is disposed between the band pass filter and the polarizing plate so as to prevent light incident from the polarizing plate side from being reflected by the band pass filter and emitted from the polarizing plate side. The bandpass filter is formed by laminating thin films having different refractive indexes made of inorganic oxides, dielectrics or metal oxides by vacuum deposition, electron beam co-evaporation or sputtering. FormedAnd a half-wave plate disposed on a different axis between the polarizing plate and the quarter-wave plate.The optical element characterized by the above is provided.
[0014]
  Alternatively, the band-pass filter can be formed by laminating thin films made of resin compositions each having a different refractive index.
[0015]
  In this case, the resin composition isClaim 7As described in (1), it is possible to make a thin layer by monoaxial stretching or biaxial stretching after multilayer extrusion.
[0016]
  According to the first or second aspect of the present invention, light incident from the polarizing plate side (light transmitted through the polarizing plate becomes linearly polarized light) becomes circularly polarized light by transmitting through the quarter-wave plate, and the band It will reach the surface of the pass filter. The light reflected by the bandpass filter reverses the direction of rotation of the circularly polarized light and passes through the quarter-wave plate again, so that it becomes linearly polarized light whose polarization plane is orthogonal to the incident light. Therefore, the reflected light does not pass through the polarizing plate because the planes of polarization are orthogonal. Therefore, in the liquid crystal display device in which the optical element according to claim 1 or 2 is arranged on the light exit surface side of the backlight, the front directivity can be enhanced by the band pass filter of the optical element, and the display surface side (polarizing plate) It is possible to prevent the return light of the light incident from the side) from being visually recognized, and to suppress the deterioration of display quality. Further, according to the invention according to claim 1 or 2, unlike the case of using a semi-absorbing semi-transmitting material formed of a general pigment or dye to prevent return light, it transmits the optical element. There is an excellent advantage that the influence on the amount of transmitted light does not occur except for slight absorption by the quarter-wave plate. In addition, since the band-pass filter is essentially a filter that does not absorb light, even if the luminance of the backlight is increased, the band-pass filter does not transmit the heat of light absorption to the liquid crystal cell via the band-pass filter. There is also an advantage that it can be blocked by a filter.The optical element further includes a half-wave plate disposed on a different axis between the polarizing plate and the quarter-wave plate.
[0017]
  The quarter-wave plate is formed by stretching a resin film having birefringence anisotropy, and is formed by applying a thin film of a liquid crystal polymer or by cutting a crystalline material. Things can be used. In addition to the one optimized for light of a specific single wavelength, the quarter wavelength plate has a wide band by lamination with a half wavelength plate, or a phase difference in which the phase difference is controlled in the thickness direction. A plate or the like is used.
[0019]
  The narrow-band quarter-wave plate functions as a quarter-wave plate only for specific one-wavelength light, and a shift occurs for light on the longer wavelength side or shorter wavelength side than the specific wavelength. Thus, the function as a quarter-wave plate is gradually lost. Therefore, especially when the band-pass filter has a characteristic of transmitting light of a plurality of wavelengths (in this case, the reflection hue of the band-pass filter is neutral), the narrow-band quarter-wave plate is used for specific light. It functions only as a quarter-wave plate, and it is difficult to effectively prevent the return light of light incident from the display surface side (polarizing plate side) from being visually recognized.Claims 1 and 2According to the invention according to the present invention, by providing a half-wave plate between the polarizing plate and the quarter-wave plate, as is generally known, a broadband that can function in the entire visible light range. Since a quarter-wave plate (a combination of a quarter-wave plate and a half-wave plate) is obtained, it is effective for the return light to be visually recognized even when the reflection hue of the bandpass filter is neutral. Can be prevented.
[0020]
  Preferably,Claim 3As described above, the refractive index in the thickness direction of the quarter-wave plate and / or the half-wave plate is controlled so that the viewing angle characteristics are improved.
[0021]
  When the quarter-wave plate or the half-wave plate is a normal retardation plate, a phase difference is generated only in the in-plane direction. Since the transmission length of the incident light from is increased, the phase difference value is changed.Claim 3According to the invention, the refractive index in the thickness direction of the quarter-wave plate and / or the half-wave plate is controlled so as to improve the viewing angle characteristics, that is, controlled to produce a phase difference in the thickness direction, It is possible to give the same phase difference to the incident light from the oblique direction as the phase difference with respect to the normal incident light. The retardation value in the thickness direction can be controlled by stretching in the thickness direction, biaxial stretching, or orienting the liquid crystal material (designing molecules so as to cause a retardation in the thickness direction). .
[0022]
  Preferably,Claim 4As described above, the phase difference of the ¼ wavelength plate is set to a value corresponding to the reflected hue of the bandpass filter.
[0023]
  When the bandpass filter has a characteristic of transmitting light of a single wavelength, the reflected hue of the bandpass filter has a complementary color relationship with the light of the short wavelength.Claim 4According to the invention, the phase difference of the quarter-wave plate is set to a value corresponding to the reflected hue of the bandpass filter (the setting value is a complementary color relationship between the reflected hue and the transmission wavelength of the bandpass filter). Therefore, it is possible to effectively prevent the light of the reflected hue from being visually recognized as the return light.
[0024]
  The quarter wavelength plate and / or the half wavelength plate isClaim 5For example, it can be formed from a liquid crystal polymer material.
[0025]
  Preferably,Claim 6As described above, the optical element includes each member constituting the optical element (a band-pass filter, a quarter wavelength plate (including a half wavelength plate).), A polarizing plate) is adhered with a pressure-sensitive adhesive or an adhesive, respectively, so that the air interface is removed.
[0026]
  Although the optical element according to the present invention functions even if each member (band pass filter, ¼ wavelength plate (including a ½ wavelength plate may be included), polarizing plate) is arranged apart from each other, If handling of the entire optical element and reflection loss at the air interface are taken into consideration, it is desirable to attach and integrate them with an adhesive or an adhesive. For example, when the band-pass filter, the quarter wavelength plate, and the polarizing plate are arranged apart from each other, there are four air interfaces, and the reflection loss is about 4 (%) × 4 (surface) = Although 16% is generated, the presence of reflected light at the air interface slightly reduces the display quality.Claim 6When each member is attached as in the invention according to the invention, the reflection loss is substantially 0%, and the light transmittance and the display quality are improved.
[0027]
  The bandpass filter isClaim 8As described above, the band-pass filter laminate according to claim 1 or 2 may be pulverized into a scaly shape, and the pulverized piece may be embedded in a resin.
[0028]
  Preferably, the optical element isClaim 9As described in (1), a diffusion plate is further provided between the bandpass filter and the backlight.
[0029]
  Claim 9According to the invention according to the present invention, since the light that is obliquely incident on the bandpass filter and is reflected is scattered by the diffuser plate, a part of the scattered light (a component that enters perpendicularly to the bandpass filter) can be reused. The utilization efficiency of the light emitted from the backlight can be increased.
[0030]
  Preferably,Claim 10As described above, the surface of the diffusion plate on the side facing the backlight is formed to have an uneven shape.
[0031]
  When the diffusing plate and the backlight are arranged close to each other, Newton rings may be generated due to light interference in the gap between the diffusing plate and the backlight.Claim 10According to the invention, since the surface of the diffusion plate facing the backlight is formed to have an uneven shape, the generation of Newton rings can be suppressed and the quality of the backlight can be maintained. It is.
[0032]
  Preferably, the bandpass filter isClaim 11As described above, the substrate is formed from a base material and a thin film laminate laminated on the base material, and the base material has an in-plane phase difference of 30 nm or less between the light incident surface and the light emitting surface. In particular, as will be described later, when a so-called reflective polarizer is arranged between the bandpass filter and the backlight to increase the amount of transmitted light of the bandpass filter,Claim 11The base material of the band pass filter according to the present invention is preferable because it has a small phase difference. The in-plane retardation is more preferably 20 nm or less, and further preferably 10 nm or less.
[0033]
  Preferably, the bandpass filter isClaim 12As described above, a plurality of selective transmission wavelengths are set, and the incident angles at which reflection occurs at a predetermined ratio for the light of each wavelength are set to coincide with each other.
[0034]
  Claim 12According to the invention, it is possible to suppress a change in color tone due to a viewing angle in the liquid crystal display device by applying the optical element to the liquid crystal display device.
[0035]
  In the present invention,Claim 13As described above, the present invention is also provided as a surface light source device comprising: the optical element; and a backlight that emits light in a planar shape with respect to the optical element using a three-wavelength cold cathode tube as a light source. .
[0036]
  The present invention also provides:Claim 14A surface light source device comprising: the optical element; and a backlight that uses a light emitting diode as a light source, and emits planar light having a light emission wavelength of one or more types with respect to the optical element. Also provided as
[0037]
  Preferably,Claim 15A plurality of selective transmission wavelengths of the bandpass filter are set, and by adjusting the emission spectrum intensity of the light source of the backlight according to the transmittance at each selective transmission wavelength, The emitted light is neutralized in terms of visibility. That is, in other words, when the emitted light from the bandpass filter is viewed, the white light is adjusted to be visually recognized.
[0038]
  The present invention also provides:Claim 16As described above, the present invention is also provided as a surface light source device comprising the optical element and a backlight that uses the electroluminescence element as a light source and emits light in a planar shape with respect to the optical element.
[0039]
  Furthermore, the present invention providesClaim 17And a liquid crystal cell for illuminating the liquid crystal cellClaims 13 to 16And a liquid crystal display device comprising the surface light source device according to any one of the above.
[0040]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a longitudinal sectional view showing a schematic configuration of a liquid crystal display device including an optical element according to an embodiment of the present invention. As shown in FIG. 1, the liquid crystal display device 10 according to the present embodiment includes a backlight 6, a liquid crystal cell 7, and an optical element 11 that guides light emitted from the backlight 6 to the liquid crystal cell 7. The backlight 6 and the optical element 11 function as a surface light source device 12 that illuminates the liquid crystal cell 7.
[0041]
The optical element 11 includes a band pass filter (interference filter) 1 for selectively transmitting light emitted from the backlight 6, a quarter wavelength plate 2, and a polarizing plate 3. Furthermore, as a preferable aspect, the optical element 11 according to the present embodiment includes a half-wave plate 4 disposed between the polarizing plate 3 and the quarter-wave plate 2, the band-pass filter 1, and the backlight 6. And a diffusion plate 5 disposed between the two. In this embodiment, the entire optical element 11 is handled and reflection loss at the air interface is taken into consideration, and each member (diffuser plate 5, bandpass filter 1, quarter wavelength plate 2, half wavelength plate 4, The polarizing plate 3) is stuck and integrated with a pressure-sensitive adhesive or an adhesive.
[0042]
For example, the backlight 6 uses a light emitting diode, an electroluminescence element, or the like as a light source in addition to a three-wavelength cold cathode tube, and is configured to emit light in a planar shape with respect to the optical element. In addition to the so-called direct type as shown in FIG. 1, the backlight 6 is a so-called sidelight type in which a light source is arranged on the side and is emitted in a planar shape through a light guide. Is also possible.
[0043]
The quarter-wave plate 2 and the half-wave plate 4 constituting the optical element 11 are formed by stretching a resin film having birefringence anisotropy, and by applying a thin film of a liquid crystal polymer. And those formed by cutting a crystal material can be used.
[0044]
Here, in the optical element 11 according to the present embodiment, the quarter wave plate 2 is disposed between the bandpass filter 1 and the polarizing plate 3 so that the light incident from the polarizing plate 3 side is returned. It is possible to prevent the light from being visually recognized and suppress the deterioration of display quality. That is, as shown in FIG. 2, the light L1 incident from the polarizing plate 3 side (the light transmitted through the polarizing plate 3 becomes linearly polarized light) becomes circularly polarized light by passing through the quarter wavelength plate 2, The surface of the bandpass filter 1 is reached. The light L2 reflected by the bandpass filter 1 is reversed in the rotation direction of the circularly polarized light and is transmitted through the quarter wavelength plate 2 again, so that the light L2 becomes linearly polarized light whose polarization plane is orthogonal to the incident light L1. Therefore, the reflected light L2 does not pass through the polarizing plate 3 because the polarization planes are orthogonal. In this way, it is possible to prevent the return light from being visually recognized.
[0045]
In the present embodiment, the half-wave plate 4 is disposed between the polarizing plate 3 and the quarter-wave plate 2, but in this case, as shown in FIG. The combination of 2 and the half-wave plate 4 forms a broadband quarter-wave plate 13 that can function as a quarter-wave plate over the entire visible light range. Therefore, for example, even when the band-pass filter 1 has a characteristic of transmitting light of a plurality of wavelengths (in this case, the reflected hue of the band-pass filter 1 is neutral), the return light having a wide-band wavelength is visually recognized. Can be effectively prevented.
[0046]
The diffusion plate 5 constituting the optical element 11 is obliquely incident on the bandpass filter 1, the reflected light is scattered by the diffusion plate 5, and a part of the scattered light (perpendicularly to the bandpass filter 1). The component is reused to increase the utilization efficiency of the light emitted from the backlight 6. The diffusing plate 5 can be formed by a method of embedding fine particles having different refractive indexes in a resin or the like in addition to a plate having an irregular shape formed on the surface and having a function of diffusing light. Here, in particular, when the diffusing plate 5 and the backlight 6 are arranged close to each other, there is a possibility that Newton's ring may occur due to light interference in the gap between the diffusing plate 5 and the backlight 6. Since the diffusion plate 5 according to the present embodiment is formed so that the surface on the side facing the backlight 6 has an uneven shape, the generation of the Newton ring is suppressed and the quality of the backlight 6 is maintained. Is possible.
[0047]
The band-pass filter 1 constituting the optical element 11 has a refractive index different from each other, and two or more thin films that are designed and controlled with a thickness of about 1 to 1/8 of the wavelength of light to be transmitted are laminated on a transparent substrate. Is formed. As a result, reflection and interference between layers occur repeatedly, so that the designed specific wavelength is reflected or transmitted.
[0048]
Next, an example of the band pass filter 1 applicable in the present embodiment will be described.
[0049]
(1) When laminating thin films made of vapor deposition materials
TiO as a high refractive index material2, ZrO2As a low refractive index material, a metal oxide such as ZnS or a dielectric or a dielectric is used.2, MgF2, NaThreeAlF6, CaF2The band-pass filter 1 can be formed by using a metal oxide such as a dielectric or a dielectric and laminating materials having different refractive indexes on a transparent substrate by vapor deposition.
[0050]
(2) When laminating thin films made of a resin composition
For example, a high refractive index resin material such as a halogenated resin composition typified by polyethylene naphthalate, polyethylene terephthalate, polycarbonate, vinyl carbazole, brominated acrylate, a high refractive index inorganic material ultrafine particle embedded resin composition, and 3 Using a fluorine resin material typified by fluorine ethyl acrylate and the like and a low refractive index resin material such as acrylic resin typified by polymethyl methacrylate, these materials having different refractive indexes are laminated on a transparent substrate. Thus, the band pass filter 1 can be formed.
[0051]
It is also possible to form a band-pass filter by pulverizing the thin film laminate obtained in (1) and (2) into a scaly shape and embedding the crushed piece in a resin. Moreover, although there is no limitation in particular about the material of the transparent base material used by said (1) and (2), generally a polymer and glass material are used. Examples of the polymer include cellulose polymers such as cellulose diacetate and cellulose triacetate, polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, polyolefin polymers and polycarbonate polymers.
[0052]
A so-called reflective polarizer (polarization plane orthogonal to the polarization plane of the polarizing plate disposed on the backlight side of the liquid crystal cell 7) is provided between the bandpass filter 1 and the backlight 6 (in this embodiment, the diffusion plate 5). In the case of increasing the amount of light transmitted through the bandpass filter 1, the transparent base material may be cellulose triacetate, unstretched polycarbonate, unstretched polyethylene terephthalate having a small phase difference, or It is preferable to use a film such as a norbornene resin.
[0053]
Next, the setting of the selective transmission wavelength in the band pass filter 1 will be described in detail.
[0054]
The band-pass filter 1 according to the present embodiment exhibits a maximum transmittance at a wavelength corresponding to a peak wavelength in the emission spectrum of the backlight 6 (a wavelength indicating the maximum transmittance is referred to as a maximum transmission wavelength). The long wavelength side is set to have a reflection wavelength of 50% or more (wavelength at which the reflectance is 50% or more).
[0055]
Here, according to the difference between the reflection wavelength and the maximum transmission wavelength, the parallelism of the light transmitted through the bandpass filter 1 is different as will be described later, and the difference is arbitrarily set according to the purpose. Can do.
[0056]
That is, the reflection wavelength having a cut rate of 50% or more corresponding to the incident angle θ of the light to the band pass filter 1 is approximately derived by the following equation (1).
λ2 = λ1 × (1− (n0 / ne)2× sin2θ)1/2... (1)
Here, λ1 is a reflection wavelength value reflecting 50% or more of normal incident light, λ2 is a reflection wavelength value reflecting 50% or more of the incident angle θ, and n0 is a refractive index of the external medium (at the air interface). In this case, 1.0 represents the effective refractive index of the bandpass filter 1, and θ represents the incident angle.
[0057]
From the above formula (1), for example, with respect to the peak wavelength 545 nm in the emission spectrum of the backlight 6, the reflection wavelength λ1 = 555 nm, the effective refractive index of the bandpass filter 1 is ne = 2.0, and the air interface is left. In this case, the incident angle θ at which the reflection wavelength λ2 = 545 nm is approximately ± 22 degrees. That is, if the incident angle θ is in the range of about ± 22 degrees, a transmittance of 50% or more can be obtained (conversely, if the incident angle θ is out of the range of about ± 22 degrees, λ2 <545 nm. Therefore, the light having the peak wavelength of 545 nm of the backlight 6 that is longer than λ2 does not pass through the bandpass filter 1 by 50% or more). Similarly, when the reflection wavelength λ1 = 547 nm, the incident angle θ at which the reflection wavelength λ2 = 545 nm is about ± 10 degrees, and when the reflection wavelength λ1 = 5455.5 nm, the incident angle θ at which the reflection wavelength λ2 = 545 nm is It is about ± 5 degrees.
[0058]
In this way, by setting the maximum transmission wavelength of the bandpass filter 1 (the peak wavelength in the emission spectrum of the backlight 6) and the reflection wavelength λ1, the parallelism of the light transmitted through the bandpass filter 1 can be freely set. Can be controlled.
[0059]
In addition, when there are a plurality of peak wavelengths in the emission spectrum of the backlight 6, the same setting may be performed for each wavelength. For example, the backlight 6 using a three-wavelength cold cathode tube as a light source often has a peak wavelength of 435 nm for blue light, 545 nm for green light, and 610 nm for red light, and a bandpass filter corresponding to each peak wavelength. The reflection wavelength λ1 of 1 may be set. Specifically, in the case of the above example, if the reflection wavelength λ1 is set to 436.6 nm for blue light, 547 nm for green light, and 612.3 nm for red light, the incident angle θ is about ± 10 regardless of the color. Degree. That is, it is possible to control the parallelism of the light transmitted through the bandpass filter 1 within a range of ± 10 degrees from the front regardless of the color.
[0060]
Further, the maximum transmittance for each wavelength in the bandpass filter 1 can be changed by designing the film quality, but in order to adjust the color tone of the transmitted light, the composition of the phosphors of the respective colors of the light source forming the backlight 6 The amount of light is adjusted, the backlight 6 is adapted to the maximum transmittance for each wavelength, or the power supplied to each light emitting diode of the light source (a plurality of light emitting diodes) forming the backlight 6 is adjusted. By doing so, it is possible to make the emission spectrum intensity of the backlight 6 suitable for the maximum transmittance for each wavelength.
[0061]
【Example】
Hereinafter, the features of the present invention will be further clarified by showing examples and comparative examples.
[0062]
(Example 1)
ZrO2/ SiO2As shown in FIG. 4A, a band-pass filter having a central wavelength indicating the maximum transmittance of 545 nm and a half-value width of about 10 nm was produced. A glass plate having a thickness of 0.4 mm was used as the substrate serving as an adherend.
[0063]
A backlight using a three-wavelength cold cathode tube having a maximum emission line spectrum at a wavelength of 545 nm as a light source was disposed for the band-pass filter. Such a backlight has a green coloration, and has a characteristic that the emitted light is condensed within a range of ± 14 degrees from the front as shown in FIG. 4B.
[0064]
The bandpass filter of the present embodiment reflects light other than the wavelength near 545 nm. Therefore, when this band pass filter is disposed between the polarizing plate attached to the backlight side of the liquid crystal cell and the backlight, when white display is performed, external light incident from the display surface side of the liquid crystal display device is liquid crystal. There is a possibility that the reflected light may be visually recognized by passing through the cell and reaching the bandpass filter and being reflected by the surface of the bandpass filter. Therefore, a quarter-wave plate for preventing reflection is disposed between the band-pass filter and the polarizing plate. In this embodiment, it is necessary to prevent reflection in the entire visible light region other than the vicinity of the wavelength of 545 nm. Therefore, in this example, a broadband quarter wave plate (a combination of a quarter wave plate and a half wave plate) was used.
[0065]
More specifically, the relationship between the axial angles as shown in FIG. 10 (the long side direction of the half-wave plate and the quarter-wave plate shown in FIG. 10 corresponds to the extending axis of each wave plate). Thus, a quarter-wave plate having a retardation value of 140 nm and a half-wave plate having a retardation value of 270 nm were laminated and disposed between the bandpass filter and the polarizing plate. Here, an NRF film (phase difference value 140 nm, 270 nm) manufactured by Nitto Denko Corporation is used as a retardation plate (1/4 wavelength plate and 1/2 wavelength plate), and SEG1465DU manufactured by Nitto Denko Corporation is used as a polarizing plate. Using. In FIG. 10, the band pass filter itself does not have polarization characteristics, and therefore the bonding angle is not particularly defined. Furthermore, the phase difference value and the bonding angle shown in FIG. 10 are examples, and are not limited to these values.
[0066]
According to the optical element having the above configuration, the external light incident from the polarizing plate side (the light transmitted through the polarizing plate becomes linearly polarized light) becomes circularly polarized light by passing through the broadband quarter-wave plate, and the bandpass. The surface of the filter will be reached. The light reflected by the bandpass filter reverses the direction of rotation of the circularly polarized light and passes through the broadband quarter-wave plate again to become linearly polarized light whose plane of polarization is orthogonal to the incident light. Therefore, the reflected light is absorbed by the polarizing plate and prevented from being visually recognized because the planes of polarization are orthogonal. In particular, in the present embodiment, since the configuration uses a quarter-wave plate with a wide band, reflected light due to strong incident light is not visually recognized. Even in a usage environment in which a lamp image is reflected, the reflected light is not colored and visually recognized.
[0067]
(Example 2)
ZrO2/ SiO2As shown in FIG. 5A, a short-wavelength transmission bandpass filter (dichroic color filter) having a half-value wavelength of 580 nm was fabricated. A glass plate having a thickness of 0.4 mm was used as the substrate serving as an adherend.
[0068]
For the dichroic color filter, as shown in FIG. 5A, a backlight using a monochromatic cold-cathode tube having a maximum emission line spectrum at a wavelength of 545 nm as a light source is disposed.
[0069]
When the emission spectrum of the backlight is limited to a single specific wavelength (545 nm) and the reflection band of the dichroic color filter is limited to the long wavelength side as in this embodiment, the reflected color of the dichroic color filter is Since it is colored, it is possible to obtain a sufficient antireflection effect by preventing the reflection around the wavelength band having this reflection hue (red color tone in this embodiment). From this point of view, in this embodiment, a polycarbonate single-layer retardation plate (NRF film manufactured by Nitto Denko Corporation) is used as a quarter-wave plate between the dichroic color filter and the polarizing plate attached to the backlight side of the liquid crystal cell. , Phase difference value 150 nm). This retardation value exhibits an antireflection effect for light having a wavelength in the vicinity of 600 nm indicating red coloring.
[0070]
It should be noted that the quarter-wave plate and the polarizing plate can exhibit an antireflection effect if they are laminated with the quarter-wave plate extending axis inclined at 45 degrees with respect to the absorption axis of the polarizing plate. Here, SEG1465DU manufactured by Nitto Denko Corporation was used as the polarizing plate.
[0071]
As shown in FIG. 5B, the distribution of the emitted light from the optical element having the above configuration is condensed within a range of about ± 30 from the front direction and exposed to strong external light incident from the polarizing plate side. Even when the liquid crystal display device is in the white display state, the coloring caused by the reflected light is not visually recognized.
[0072]
(Example 3)
TiO2/ SiO2As shown in FIG. 6 (a), 21 thin films are laminated by vapor deposition, and have a high transmittance with respect to the three wavelengths of the emission spectrum of the three-wavelength bright-line cold cathode tube, and reflect light of other wavelengths. A bandpass filter (interference filter) was prepared. A PET film (Lumirror manufactured by Toray Industries Inc., thickness 75 μm) was used as a substrate to be an adherend.
[0073]
When the band-pass filter is used, the light emitted from the backlight having the three-wavelength bright-line cold-cathode tube as a light source is reflected at about ± 20 degrees from the vertical direction and has a light collecting characteristic that returns to the backlight side. .
[0074]
In the case of using a bandpass filter that transmits light of three wavelengths and reflects light in other wavelength bands as in the present embodiment, the antireflection function is broadened in the same manner as in the first embodiment so that visible light is visible. It is necessary to prevent reflection throughout the entire area. From this point of view, in the present embodiment as well, in the same manner as in the first embodiment, a broadband quarter-wave plate for preventing reflection is provided between the bandpass filter and the polarizing plate attached to the backlight side of the liquid crystal cell. It was set as the structure to arrange. As in Example 1, as a retardation plate (1/4 wavelength plate and 1/2 wavelength plate), an NRF film (retardation value 140 nm, 270 nm) manufactured by Nitto Denko Corporation was used, and as a polarizing plate, Nitto Denko SEG1465DU was used.
[0075]
The distribution of the emitted light from the optical element having the above configuration and the antireflection effect are the same as those in Example 1, and has a light condensing property of about ± 30 degrees from the front direction and a strong external incident from the polarizing plate side. Even when exposed to light, when the liquid crystal display device is in the white display state, a reflected image caused by the reflected light from the bandpass filter was not visually recognized.
[0076]
(Example 4)
20 layers of polyethylene naphthalate (PEN) / polymethyl methacrylate (PMMA) thin films were alternately laminated by a feed block method under thickness control, and this laminate was biaxially stretched. The stretching temperature was about 140 ° C., and the stretching ratio was about 4 times in the TD direction and about 3 times in the TM direction.
[0077]
A short wavelength transmission type bandpass filter having reflection characteristics in a band of 650 nm to 900 nm in a total of 100 layers by laminating five stretched 20-layer films obtained as described above. It adjusted so that it might function as (dichroic color filter).
[0078]
The dichroic color filter produced as described above has a reflectance of 50% or more at a wavelength of 635 nm. With respect to such a dichroic color filter, a backlight having an AlGaInP-based high-intensity LED whose light emission spectrum has a center wavelength of 630 nm as a light source is disposed. Moreover, the quarter wavelength plate and polarizing plate to be used and their arrangement were the same as in Example 2.
[0079]
The distribution of the emitted light from the optical element having the above configuration was almost the same as in Example 2. In addition, when the liquid crystal display device is in the white display state, the coloring caused by the reflected light from the dichroic color filter was not visually recognized.
[0080]
(Example 5)
Fluorine acrylate resin (LR202B manufactured by Nissan Chemical Co., Ltd.) having a refractive index of about 1.40 as a low refractive index material, and acrylate resin containing inorganic high refractive index ultrafine particles (JSR) having a refractive index of about 1.71 as a high refractive index material. Short-wavelength transmission type bands as shown in FIG. 7, each of which is laminated on a base material (TAC film (TD-TAC) manufactured by Fuji Film Co., Ltd.) by multilayer thin film coating. A pass filter (dichroic color filter) was produced. The half-value wavelength of such a dichroic color filter was about 580 nm.
[0081]
Multilayer thin film coating uses a micro gravure coater, dried at 90 ° C. for 1 minute, and then subjected to ultraviolet polymerization (illuminance: 50 mW / cm2× 1 second), and repeatedly overcoating the next coating film on the cured coating film. Since the filter thus obtained had insufficient uniformity of in-plane transmission spectral characteristics, it was decided to select and use a region having good characteristics for the corresponding wavelength region.
[0082]
A backlight using a three-wavelength cold cathode tube having a maximum emission line spectrum at a wavelength of 545 nm as a light source was disposed for the dichroic color filter. Moreover, the quarter wave plate and the polarizing plate were arrange | positioned similarly to Example 2. FIG.
[0083]
The distribution of the emitted light from the optical element having the above configuration is condensed within a range of ± 40 degrees from the front, and the same antireflection effect as that of the second embodiment is obtained, and the liquid crystal display device is in a white display state. In addition, the coloring caused by the reflected light was not visually recognized.
[0084]
(Example 6)
Fluorine acrylate resin (LR202B manufactured by Nissan Chemical Co., Ltd.) having a refractive index of about 1.40 as a low refractive index material, and acrylate resin containing inorganic high refractive index ultrafine particles (JSR) having a refractive index of about 1.71 as a high refractive index material. Short-wavelength transmission type bands as shown in FIG. 8 by laminating 21 layers on the base material (TAC film (TD-TAC) manufactured by Fuji Film Co., Ltd.) by multilayer thin film coating. A pass filter (dichroic color filter) was produced. The transmission wavelength of such a dichroic color filter exists in three regions of 435 nm, 545 nm, and 610 nm, and corresponds to each RGB color in the emission spectrum of a general cold cathode tube.
[0085]
Multilayer thin film coating uses a micro gravure coater, dried at 90 ° C. for 1 minute, and then subjected to ultraviolet polymerization (illuminance: 50 mW / cm2× 1 second), and repeatedly overcoating the next coating film on the cured coating film. Since the filter thus obtained had insufficient uniformity of in-plane transmission spectral characteristics, it was decided to select and use a region having good characteristics for the corresponding wavelength region.
[0086]
A backlight using a three-wavelength cold-cathode tube having an emission line spectrum at each wavelength as a light source is arranged for the dichroic color filter corresponding to the three wavelengths. Further, as in Example 1, a retardation plate and a polarizing plate were disposed.
[0087]
The distribution of the emitted light from the optical element having the above configuration is condensed within a range of ± 30 degrees from the front, and the same antireflection effect as that of the first embodiment is obtained, and the liquid crystal display device is in the white display state. In addition, the reflection image caused by the reflected light from the dichroic color filter was never visually recognized.
[0088]
(Example 7)
A bandpass filter was produced in the same manner as in Example 3. For such a bandpass filter, a retardation plate and a polarizing plate were disposed in the same manner as in Example 1. In this example, as the retardation plate, an NRZ film (retardation values 140 nm and 270 nm manufactured by Nitto Denko Corporation) was used. Nz coefficient is 0.5) for both. Since the NRZ film is a retardation film in which the change in retardation value in the thickness direction is controlled, by using this film, the phase difference equivalent to the phase difference with respect to the vertical incident light can be obtained even for the incident light from the oblique direction. It is possible to grant. Therefore, a sufficient antireflection effect can be achieved even for incident light that deviates significantly from the vertical direction.
[0089]
According to the optical element having the above configuration, even in an environment where bright oblique incident light such as a window is present, when the liquid crystal display device is in a white display state, a reflected image caused by the reflected light from the bandpass filter is not displayed. I didn't see it.
[0090]
(Example 8)
A bandpass filter was produced in the same manner as in Example 3. Although a retardation plate and a polarizing plate were arranged for such a bandpass filter, in this example, the retardation plate to be used was produced by precision coating with a slit coater of a liquid crystal polymer (LC242 manufactured by BASF).
[0091]
Specifically, 1% by weight of a photoinitiator (Irg184 manufactured by Ciba-Gaigi Co., Ltd.) was added to the liquid crystal polymer to prepare a cyclopentane solution (corresponding to 20% by weight). This solution was coated on a substrate with a wire bar so that the thickness when dried was equivalent to 1.2 μm, dried at 90 ° C. × 2 minutes, and then irradiated with ultraviolet light (10 mW / cm2× 2 minutes), a retardation plate having a retardation value of about 140 nm was produced. Similarly, a retardation plate having a retardation value of about 270 nm was produced by coating so that the thickness was about 2.5 μm. If these retardation plates are laminated in the same manner as in Example 1, it functions as a broadband quarter-wave plate and thus has an antireflection function in the visible light region.
[0092]
In this example, the surface of the bandpass filter with an alignment film was used as the substrate on which the liquid crystal polymer was applied. The alignment film was formed by spin-coating a 2% by weight aqueous solution of PVA (Poval manufactured by Kuraray Co., Ltd.) on the surface of the bandpass filter and drying, followed by rubbing with a cotton rubbing cloth. A liquid crystal retardation plate having a retardation value equivalent to 140 nm is formed on the alignment film of such a bandpass filter by the above-described method, and a 2 wt% aqueous solution of PVA (Kuraray Co., Ltd.) is spin-coated thereon. After applying and drying, rubbing treatment was performed with a cotton rubbing cloth. Here, the rubbing direction was set to 62.5 degrees between the first rubbing direction and the second rubbing direction so as to coincide with the arrangement of FIG. 10 described in the first embodiment (shown in FIG. 10). The long side direction of the phase difference plate corresponds to the rubbing direction). On the alignment film formed by such rubbing treatment, a liquid crystal retardation plate having a retardation value equivalent to 270 nm was formed by the method described above. Further thereon, a polarizing plate was arranged so as to coincide with the arrangement of FIG. 10 in Example 1.
[0093]
In the optical element according to this example, the total thickness of the retardation plate was within about 5 μm. This can be reduced to a thickness of 1/10 or less compared to the thickness (about 50 μm) of a quarter-wave plate formed of a polycarbonate stretched film, and it has been found that this contributes to thinning of the surface light source device. The antireflection effect is equivalent to that of Example 3, and when the liquid crystal display device is in a white display state, a reflection image caused by the reflected light from the bandpass filter was not visually recognized.
[0094]
(Comparative example)
A three-wavelength cold-cathode tube having a single peak wavelength at a light source wavelength of 545 nm is formed by using a band-pass filter formed by stacking 20 layers of dielectric thin films, having a center wavelength of maximum transmission of 545 nm and a half-value width of 10 nm. Light was emitted from the backlight as the light source toward the bandpass filter. The distribution of the light emitted from the bandpass filter was condensed within a range of ± 14 degrees from the front, as in Example 1, but the liquid crystal display using the bandpass filter and the backlight as a surface light source device. When the device displayed white, the surrounding image was reflected as a mirror image on the bandpass filter, and this was visually recognized, thereby degrading the display quality.
[0095]
In the examples and comparative examples described above, the reflection wavelength band is measured by the instantaneous multi-photometry system MCPD2000 manufactured by Otsuka Electronics Co., Ltd., and the spectroscopic ellipso M220 manufactured by JASCO Corporation is transmitted and reflected by the thin film characteristics. The spectrophotometer U4100 manufactured by Hitachi, Ltd. is used for the evaluation of the spectral characteristics, DOT3 manufactured by Murakami Color Co., Ltd. is used for the characteristics evaluation of the polarizing plate, and the birefringence measuring apparatus manufactured by Oji Scientific Instruments is used for the measurement of the retardation value. For KOBRA21D, Ez contrast manufactured by ELDIM was used for measurement of viewing angle characteristics (contrast, color tone, luminance).
[0096]
【The invention's effect】
The liquid crystal display device in which the optical element according to the present invention is arranged on the light exit surface side of the backlight can improve the front directivity by the band pass filter of the optical element and is incident from the display surface side (polarizing plate side). It is possible to prevent the return light from being visually recognized, and to suppress the deterioration in display quality.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a schematic configuration of a liquid crystal display device including an optical element according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram for explaining that the return light is prevented from being visually recognized by the ¼ wavelength plate shown in FIG. 1;
FIG. 3 is an explanatory diagram for explaining that the return light is prevented from being visually recognized even by the combination of the quarter-wave plate and the half-wave plate shown in FIG. 1;
FIG. 4 is a diagram illustrating the spectral characteristics of the bandpass filter and the light source and the distribution of the emitted light in the first embodiment.
FIG. 5 is a diagram illustrating spectral characteristics of a bandpass filter and a light source and a distribution of emitted light in Example 2.
FIG. 6 is a diagram illustrating spectral characteristics of a bandpass filter and a light source according to the third embodiment.
FIG. 7 is a graph showing transmission spectral characteristics of a bandpass filter in Example 5.
FIG. 8 is a graph showing transmission spectral characteristics of a bandpass filter in Example 6.
FIG. 9 is a diagram for explaining a situation in which reflected light of light reaching the surface of the bandpass filter is visually recognized in a conventional liquid crystal display device.
FIG. 10 is an explanatory diagram showing an example of a stacked state of a polarizing plate, a half-wave plate, and a quarter-wave plate according to Example 1 of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Band pass filter 2 ... 1/4 wavelength plate 3 ... Polarizing plate
4 ... 1/2 wavelength plate 5 ... Diffusion plate 6 ... Backlight
DESCRIPTION OF SYMBOLS 7 ... Liquid crystal cell 10 ... Liquid crystal display device 11 ... Optical element 12 ... Surface light source device
13 ... Broadband quarter wave plate

Claims (17)

  1. A band pass filter that is formed from a laminate of thin films each having a different refractive index, and selectively transmits light emitted from the backlight;
    A polarizing plate;
    A quarter wavelength disposed between the bandpass filter and the polarizing plate so as to prevent light incident from the polarizing plate side from being reflected by the bandpass filter and emitted from the polarizing plate side. With a board,
    The band-pass filter, an inorganic oxide, the respective refractive index different thin film made of dielectric or metal oxide, a vacuum deposition, is formed by laminating the electron beam co-evaporation or sputtering, the said polarizing plate 1 / An optical element , further comprising a half-wave plate disposed on a different axis between the four-wave plate .
  2. A band pass filter that is formed from a laminate of thin films each having a different refractive index, and selectively transmits light emitted from the backlight;
    A polarizing plate;
    A quarter wavelength disposed between the bandpass filter and the polarizing plate so as to prevent light incident from the polarizing plate side from being reflected by the bandpass filter and emitted from the polarizing plate side. With a board,
    The bandpass filter is formed by laminating thin films made of resin compositions each having a different refractive index, and is arranged at a half wavelength between the polarizing plate and the quarter wave plate. An optical element further comprising a plate .
  3. The optical element according to claim 1, wherein a refractive index in a thickness direction of the ¼ wavelength plate and / or the ½ wavelength plate is controlled so that viewing angle characteristics are improved.
  4. The optical element according to any one of claims 1 to 3, characterized in that setting the phase difference of the quarter wavelength plate to a value corresponding to the reflection color of the band-pass filter.
  5. The optical element according to any one of claims 1 to 4 , wherein the quarter-wave plate and / or the half-wave plate is formed of a liquid crystal polymer material.
  6. The stuck by respective adhesive or bond the members constituting the optical element, the optical element according to claim 1, characterized in that the removal of the air interface 5.
  7.   The optical element according to claim 2, wherein the resin composition is thinned by monoaxial stretching or biaxial stretching after multilayer extrusion.
  8. The band-pass filter from claim 1, characterized in that the stack of band-pass filter according to claim 1 or 2 crushed into flakes, and the pulverized pieces were formed by embedding in a resin 8. The optical element according to any one of 7 .
  9. The optical element according to any one of claims 1 to 8, characterized by further comprising the placed diffusion plate between the backlight and the band-pass filter.
  10. The optical element according to claim 9 , wherein a surface of the diffusion plate facing the backlight has an uneven shape.
  11. The band-pass filter is formed of a base material and a thin film laminate laminated on the base material, and the base material has an in-plane retardation of a light incident surface and an output surface of 30 nm or less. the optical element according to claim 1, wherein 10.
  12. The band-pass filter from claim 1, characterized in that selected transmission wavelength with which a plurality of sets, the incident angle at which reflection occurs at a predetermined rate for the light of each wavelength is set so as to coincide respectively The optical element according to any one of 11 .
  13. 13. A surface light source device comprising: the optical element according to claim 1; and a backlight that uses a three-wavelength cold cathode tube as a light source and emits light in a planar shape with respect to the optical element. .
  14. 13. An optical element according to claim 1, and a backlight that uses a light emitting diode as a light source and emits planar light having a light emission wavelength of at least one type with respect to the optical element. A surface light source device.
  15. A plurality of selective transmission wavelengths of the bandpass filter are set, and the emission light from the bandpass filter is viewed by adjusting the emission spectrum intensity of the light source of the backlight according to the transmittance at each selective transmission wavelength. 15. The surface light source device according to claim 13 , wherein the surface light source device is neutralized in terms of sensitivity.
  16. 13. A surface light source device comprising: the optical element according to claim 1; and a backlight that uses the electroluminescence element as a light source and emits light in a planar shape with respect to the optical element.
  17. A liquid crystal display device comprising: a liquid crystal cell; and the surface light source device according to claim 13 for illuminating the liquid crystal cell.
JP2003066855A 2002-03-14 2003-03-12 Optical element, surface light source device using the same, and liquid crystal display device Expired - Fee Related JP3808048B2 (en)

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