JP2003337337A - Optical element, surface light source device using the same and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element which can suppress reduction of display quality of a liquid crystal display device by preventing visual confirmation of reflected light of light arriving at the surface of a band-pass filter. <P>SOLUTION: The optical element 11 formed from a laminated body of thin films having refractive indices different from each other is provided with the band-pass filter 1 for selectively transmitting light emitted from a backlight 6, a polarizing plate 3 and a quarter-wave plate 2 disposed between the band- pass filter 1 and the polarizing plate 3 so as to prevent light made incident from the polarizing plate 3 side from being reflected by the band-pass filter 1 and emitted from the polarizing plate 3 side. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field 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, which is suitable for use in a liquid crystal display device, and more particularly,
The present invention relates to an optical element capable of preventing the reflected light of the light reaching the surface of a bandpass filter from the liquid crystal cell side from being visually recognized and suppressing the deterioration of the display quality of a liquid crystal display device.

[0002]

2. Description of the Related Art EL (electroluminescence element) backlights, CCFL (cold cathode fluorescent tube) backlights, LEDs (light emitting diodes) used in liquid crystal display devices.
A surface light source device such as a backlight usually has a peak at a specific wavelength.

Therefore, a bandpass filter (interference filter) that allows light having a specific peak wavelength emitted from a backlight to pass through when vertically incident, but reflects when obliquely incident
Is arranged on the emission surface side of the backlight, the vertically incident light is transmitted, but the incident light from an oblique direction is reflected instead of being transmitted, and parallelization becomes possible.

According to the bandpass filter, unlike the conventional parallel light conversion using a light shielding plate, non-parallel light rays are not absorbed but reflected, and returned to the backlight side. Here, the reflected obliquely incident light is returned to the backlight and re-reflected toward the band pass filter, and only the front direction component of the re-reflected light passes through the band pass filter. Therefore, due to the so-called light recycling effect in which the above operation is repeated, the brightness of light in the front direction (vertical direction) that passes through the bandpass filter is increased, and it is possible to obtain a surface light source device that emits parallel light with high efficiency. .

Here, the wavelength characteristic of the optical interference in the bandpass filter changes depending on the incident angle, that is, the wavelength selectively transmitted by the bandpass filter changes according to the incident angle. Therefore, the parallelism of the parallel light is It can be controlled by the transmission center wavelength and the transmission wavelength width (half-value width) of the bandpass filter. For example, when the transmission wavelength width (half-value width) is set to be narrow, the transmitted light is concentrated only in the vicinity of the front, which is extremely narrow, and thus a surface light source device having high parallelism can be obtained.

On the other hand, if the transmission wavelength width (half-value width) of the bandpass filter is set wide, it is possible to achieve parallelism of the same level as in the case of using a commercially available prism sheet for improving brightness. Here, in the case of a prism sheet, in principle, since it uses refraction of light at an air interface, it cannot be attached to a backlight or a liquid crystal cell. However, when a bandpass filter is used, unlike a prism sheet, an air interface is not required, so it is possible to attach it to a backlight or a liquid crystal cell and integrate it, thereby handling the entire device. It has the feature that it can be facilitated. Furthermore, since the surface of the bandpass filter is smooth,
By performing a hard coat treatment or the like, it is possible to prevent the occurrence of scratches on the surface, which makes it easier to handle. On the other hand, with a prism sheet that uses refraction on the surface, it is difficult to perform a scratch generation prevention process such as a hard coat process, so it can be said that the bandpass filter has a great advantage in making a backlight parallel light.

As an optical element using such a bandpass filter, for example, cholesteric liquid crystal is used, and Japanese Patent Application Nos. 2001-60005 and 2000-28 are used.
Proposed in No. 1382, parallelization (convergence)
It is possible to obtain a flat surface light source device.

On the other hand, the band-pass filter used for making the backlight parallel light is not limited to the one using the cholesteric liquid crystal, and for example, a stack of vapor-deposited thin films having different refractive indexes or resin compositions having different refractive indexes are used. It is, of course, possible to use a bandpass filter formed by stacking thin films made of materials, and by arranging these bandpass filters on the emission surface side of the backlight, the parallelization of the backlight and the light utilization efficiency It is possible to improve.

The band-pass filter formed by stacking the vapor-deposited thin film and the thin film made of the resin composition may have an advantage in heat resistance and chemical resistance as compared with the band-pass filter using the cholesteric liquid crystal. Yes, it has high practical utility value.

[0010]

However, in a liquid crystal display device in which a band-pass filter formed by laminating a vapor-deposited thin film or a thin film made of a resin composition is arranged on the emission surface side of a backlight, the display surface of the liquid crystal display device is Light incident from the side (that is, the direction opposite to the direction in which the backlight is arranged) is reflected by the surface of the bandpass filter and is visually recognized as return light, which causes a problem that the display quality of the liquid crystal display device is degraded. It was

More specifically, as shown in FIG. 9, during white display, 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. Reaches the bandpass filter 1, is reflected on the surface of the bandpass filter 1, and is visually recognized as return light L2.
Therefore, when the image around the liquid crystal display device is mirror-imaged, or when the surface of the polarizing plate 8 is provided with an anti-glare layer, the mirror-reflected image is diffused and spread by the anti-glare layer, or However, there is a problem in that a phenomenon such as the reflected color of the bandpass filter 1 being visible occurs and the display quality of the liquid crystal display device is significantly deteriorated.

The present invention has been made to solve the problems of the prior art, prevents the reflected light of the light reaching the surface of the bandpass filter from being visually recognized, and improves the display quality of the liquid crystal display device. It is an object to provide an optical element that can suppress the decrease.

[0013]

In order to solve such a problem, according to the present invention, as described in claim 1, the light emitted from a backlight is formed from a laminate of thin films having different refractive indexes. A bandpass filter for selectively transmitting, a polarizing plate, and the bandpass filter so as to prevent light incident from the polarizing plate side from being reflected by the bandpass filter and being emitted from the polarizing plate side. An optical element comprising: a quarter-wave plate disposed between the polarizing plate and the polarizing plate.

According to the invention of claim 1, the light incident from the polarizing plate side (the light transmitted through the polarizing plate becomes a linearly polarized light)
Is circularly polarized by passing through the quarter-wave plate and reaches the surface of the bandpass filter.
The light reflected by the bandpass filter has the circularly polarized light whose rotation direction is reversed and is transmitted through the quarter-wave plate again,
It becomes linearly polarized light whose polarization plane is orthogonal to that of the incident light. Therefore, the reflected light does not pass through the polarizing plate because the polarization planes thereof are orthogonal to each other. Therefore, in the liquid crystal display device in which the optical element according to claim 1 is arranged on the emission surface side of the backlight, by the bandpass filter of the optical element,
It is possible to improve the front directivity, prevent the return light of the light incident from the display surface side (polarizing plate side) from being visually recognized, and suppress the deterioration of the display quality. Further, according to the invention of claim 1, unlike the case where the returning light is prevented by using a semi-absorption and semi-transmission material formed of a general pigment or dye, the light transmitted through the optical element is There is an excellent advantage that the influence on the amount of transmitted light and the like does not occur except for slight absorption by the quarter-wave plate. Also,
Since the bandpass filter is essentially a filter that does not absorb light, even if the brightness of the backlight is increased, the heat of absorption of light does not transfer to the liquid crystal cell through the bandpass filter, It also has the advantage that it can be blocked.

The quarter-wave plate may be formed by stretching a resin film having birefringence anisotropy, or may be formed by applying a thin film of liquid crystal polymer or by cutting a crystalline material. It can be used. The 1/4 wavelength plate is optimized for light of a specific single wavelength, a broad band is formed by stacking with a 1/2 wavelength plate, and a retardation plate having a retardation controlled in the thickness direction. Are used.

[0016] Preferably, as described in claim 2, the optical element is provided between the polarizing plate and the quarter wavelength plate.
It further comprises a half-wave plate arranged on a different axis.

The narrow-band quarter-wave plate has a function as a quarter-wave plate only for light of a specific one wavelength, and has a function of a wavelength longer or shorter than the specific wavelength. A shift occurs and the function as the quarter-wave plate is gradually lost. Therefore, in particular, when the bandpass filter has a characteristic of transmitting light of a plurality of wavelengths (in this case, the reflection hue of the bandpass filter becomes neutral), the narrow band ¼ wavelength plate is used for specific light. Only only 1/4
It does not function as a wave plate, and it is difficult to effectively prevent the return light of the light incident from the display surface side (polarizing plate side) from being visually recognized. According to the second aspect of the present invention, by further providing the half-wave plate between the polarizing plate and the quarter-wave plate, as is generally known, the function in the entire visible light range is achieved. Since a broadband ¼ wavelength plate (combination of ¼ wavelength plate and ½ wavelength plate) that can be obtained is obtained, return light can be visually recognized even when the reflection hue of the bandpass filter is neutral. Can be effectively prevented.

Preferably, as described in claim 3, the refractive index in the thickness direction of the ¼ wavelength plate and / or the ½ wavelength plate is controlled so that the viewing angle characteristics are improved.

When the quarter-wave plate or the half-wave plate is an ordinary retardation plate, a phase difference is generated only in the in-plane direction, so that it functions as designed for vertically incident light. ,
Since the transmission length of incident light from an oblique direction increases, the phase difference value changes. According to the invention of claim 3, 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 characteristic is improved, that is, the phase difference is generated in the thickness direction. It is possible to give the same phase difference to the vertically incident light as to the incident light that is controlled and is oblique. The retardation value in the thickness direction can be controlled by stretching in the thickness direction, biaxial stretching, or by orienting the liquid crystal material (designing a molecule so as to cause a retardation in the thickness direction). .

Preferably, as described in claim 4, the phase difference of the quarter wavelength plate is set to a value corresponding to the reflection hue of the bandpass filter.

When the bandpass filter has a characteristic of transmitting light of a single wavelength, the reflection hue of the bandpass filter has a complementary color relationship with the light of the short wavelength. According to the invention of claim 4, the phase difference of the quarter-wave plate is set to a value corresponding to the reflection hue of the bandpass filter (the setting value is such that the reflection hue has a complementary color relationship with the transmission wavelength of the bandpass filter). Since it is easily calculated), it is possible to effectively prevent the light of the reflected hue from being visually recognized as return light.

The quarter-wave plate and / or the one-wave plate
The / 2 wave plate can be formed of a liquid crystal polymer material, for example, as described in claim 5.

[0023] Preferably, as described in claim 6, the optical element includes each member (band pass filter, quarter wave plate (half wave plate may be included) which constitutes the optical element. , A polarizing plate) are respectively attached by a pressure sensitive adhesive or an adhesive to form an air interface.

The optical element according to the present invention functions even if each member (band-pass filter, quarter-wave plate (may include half-wave plate), polarizing plate) is arranged apart from each other. However, considering the handling of the entire optical element and the reflection loss at the air interface, it is desirable to stick and integrate them with an adhesive or an adhesive. For example, when the bandpass filter, the quarter-wave plate, and the polarizing plate are arranged separately from each other, there are four air interfaces, and the reflection loss is about 4 (%) × 4 (plane) = 16% occurs and the display quality is slightly deteriorated due to the presence of reflected light at the air interface. However, when each member is attached as in the invention according to claim 6, the reflection loss is substantially reduced. It is 0%, which is effective in improving the light transmittance and the display quality.

In the bandpass filter, as described in claim 7, thin films made of an inorganic oxide, a dielectric or a metal oxide having different refractive indexes are laminated by vacuum vapor deposition, electron beam co-evaporation or sputtering. Can be formed.

Alternatively, the bandpass filter can be formed by laminating thin films made of resin compositions having different refractive indexes as described in claim 8. In this case, the resin composition can be formed into a thin layer by uniaxially stretching or biaxially stretching after multilayer extrusion as described in claim 9.

In the bandpass filter, as described in claim 10, the laminated body of the bandpass filter according to any one of claims 7 to 9 is crushed into scales, and the crushed pieces are placed in a resin. It may be formed by embedding.

[0028] Preferably, the optical element is described in claim 11.
As described in 1 above, it further comprises a diffuser plate arranged between the band pass filter and the backlight.

According to the eleventh aspect of the invention, the light obliquely incident on the bandpass filter and reflected is scattered by the diffusion plate, and a part of the scattered light (a component incident perpendicularly to the bandpass filter). ) Can be reused, the use efficiency of the light emitted from the backlight can be improved.

Preferably, the surface of the diffusion plate facing the backlight is formed to have an uneven shape.

When the diffusing plate and the backlight are arranged close to each other, there is a possibility that Newton's rings may occur due to interference of light in the gap between the diffusing plate and the backlight. According to the invention of claim 12, since the surface of the diffusion plate facing the backlight is formed to have an uneven shape, the generation of Newton's rings is suppressed and the quality of the backlight is maintained. It is possible.

Preferably, the bandpass filter is
A thirteenth aspect of the invention is formed of a base material and a thin film laminated body laminated on the base material, and the base material has an in-plane retardation of a light incident surface and a light emission surface of 30 nm or less. Particularly, as 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, the base material of the bandpass filter according to claim 13 is The phase difference is small and suitable. The in-plane retardation is more preferably 20n
m or less, and more preferably 10 nm or less.

Preferably, the bandpass filter is
According to a fourteenth aspect, a plurality of selective transmission wavelengths are set and the incident angles at which light of each wavelength is reflected at a predetermined ratio are set to be the same.

According to the fourteenth aspect of the invention, by applying the optical element to a liquid crystal display device, it is possible to suppress a change in color tone depending on the viewing angle in the liquid crystal display device.

According to a fifteenth aspect of the present invention, it is provided with the optical element and a backlight that uses a three-wavelength cold cathode tube as a light source and emits light planarly toward the optical element. Is also provided as a surface light source device.

According to a sixteenth aspect of the present invention, the optical element and the light emitting diode are used as a light source, and a back light for emitting a planar light having an emission wavelength of one or more is emitted to the optical element. It is also provided as a surface light source device characterized by comprising a light.

Preferably, a plurality of selective transmission wavelengths of the bandpass filter are set, and the emission spectrum intensity of the light source of the backlight is adjusted according to the transmittance at each selective transmission wavelength. By doing so, the light emitted from the band-pass filter is sensitized to be neutralized. That is, in other words, when the light emitted from the bandpass filter is viewed, the light is adjusted to be viewed in white.

According to a eighteenth aspect of the present invention, there is provided the optical element, and a backlight that uses the electroluminescent element as a light source and emits light in a planar manner toward the optical element. Also provided as a surface light source device.

Furthermore, the present invention provides a liquid crystal cell as defined in claim 19 and a claim 1 for illuminating the liquid crystal cell.
A surface light source device according to any one of 5 to 18 is also provided as a liquid crystal display device.

[0040]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a vertical cross-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 the light emitted from the backlight 6 to the liquid crystal cell 7. The backlight 6 and the optical element 11 serve as a surface light source device 12 that illuminates the liquid crystal cell 7.

The optical element 11 includes a bandpass filter (interference filter) 1 for selectively transmitting the light emitted from the backlight 6, a quarter wavelength plate 2, and a polarizing plate 3. Furthermore, the optical element 11 according to the present embodiment is
As a preferred mode, the half-wave plate 4 arranged between the polarizing plate 3 and the quarter-wave plate 2 and the band-pass filter 1 are provided.
And a backlight 6 and a diffusion plate 5 disposed between the backlight 6 and the backlight 6. In the present embodiment, in consideration of handling of the entire optical element 11 and reflection loss at the air interface, each member (diffusion plate 5, bandpass filter 1, quarter wave plate 2,
The half-wave plate 4 and the polarizing plate 3) are attached and integrated by a pressure-sensitive adhesive or an adhesive.

The backlight 6 uses, for example, a light emitting diode, an electroluminescence element, and the like as a light source in addition to a three-wavelength cold cathode tube, and is configured to emit light planarly to an optical element. The backlight 6 may be a so-called direct-light type as shown in FIG. 1 or a so-called side-light type in which a light source is arranged laterally and a planar light is emitted through a light guide. Is also possible.

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 thin film coating of liquid crystal polymer. It is possible to use the one formed by cutting or the one formed by cutting the crystalline material.

Here, in the optical element 11 according to this embodiment, the quarter-wave plate 2 is arranged between the bandpass filter 1 and the polarizing plate 3, so that the light enters from the polarizing plate 3 side. It is said that it is possible to prevent the returning light of light from being visually recognized and to suppress the deterioration of display quality. That is, FIG.
As shown in, the light L1 incident from the polarizing plate 3 side (the light transmitted through the polarizing plate 3 becomes linearly polarized light) is
To be circularly polarized light and reach the surface of the bandpass filter 1. The light L2 reflected by the bandpass filter 1 has the circular polarization direction reversed,
By passing through the quarter-wave plate 2 again, the incident light L
1 means linearly polarized light whose planes of polarization are orthogonal to each other. Therefore, the reflected light L2 does not pass through the polarizing plate 3 because the polarization planes thereof are orthogonal to each other. In this way, it is possible to prevent the returning light from being visually recognized.

Further, in this embodiment, the polarizing plates 3 and 1/4
The half-wave plate 4 is arranged between the half-wave plate 2 and the wave plate 2, but in this case, as shown in FIG.
By combining with the two-wave plate 4, 1 /
Broadband quarter-wave plate 1 capable of functioning as a four-wave plate
3 is formed. Therefore, for example, even when the bandpass filter 1 has a characteristic of transmitting light of a plurality of wavelengths (in this case, the reflection hue of the bandpass filter 1 becomes neutral), the return light having a wavelength of a wide band is visually recognized. Can be effectively prevented.

The diffuser 5 constituting the optical element 11 obliquely enters the bandpass filter 1, and the reflected light is scattered by the diffuser 5 and a part of the scattered light (perpendicular to the bandpass filter 1). It is provided in order to improve the utilization efficiency of the light emitted from the backlight 6 by reusing the component incident on the. The diffusing plate 5 can be formed by a method of embedding fine particles having different refractive indexes in a resin, in addition to the diffusing plate 5 having an uneven surface so as to have a function of diffusing light. Here, particularly when the diffuser plate 5 and the backlight 6 are arranged close to each other, there is a possibility that Newton's rings may occur due to interference of light in the gap between the diffuser plate 5 and the backlight 6. Diffusion plate 5 according to the present embodiment
Since the surface facing the backlight 6 is formed to have an uneven shape, the generation of the Newton's rings is suppressed and the quality of the backlight 6 can be maintained.

The bandpass filter 1 constituting the optical element 11 has two different thin films on the transparent base material, each having a different refractive index and a design and controlled thickness of about 1/8 of the wavelength of light to be transmitted. It is formed by stacking the above.
This causes reflection and interference to be repeated between the layers, and has a characteristic of reflecting or transmitting a designed specific wavelength.

Next, an example of the bandpass filter 1 applicable in this embodiment will be described.

(1) When Laminating Thin Films Made of Evaporation Materials Metal oxides and dielectrics such as TiO ₂ , ZrO ₂ and ZnS are used as high refractive index materials, and SiO _{2 is} used as low refractive index materials.
Forming the bandpass filter 1 by using metal oxides or dielectrics such as MgF ₂ , Na ₃ AlF ₆ , CaF _{2 and the} like, and stacking materials having different refractive indexes on a transparent substrate by vapor deposition. You can

(2) When laminating a thin film made of a resin composition For example, polyethylene naphthalate, polyethylene terephthalate, polycarbonate, vinylcarbazole,
A halogenated resin composition represented by brominated acrylate, a high refractive index resin material such as a high refractive index inorganic material ultrafine particle embedded resin composition, a fluororesin material represented by trifluoroethyl acrylate, or a polyresin The bandpass filter 1 can be formed by using a low-refractive-index resin material such as an acrylic resin typified by methyl methacrylate, and laminating materials having different refractive indexes on a transparent substrate.

It is also possible to form the bandpass filter by crushing the thin film laminate obtained in the above (1) and (2) into scales and embedding the crushed pieces in resin. . The material of the transparent substrate used in the above (1) and (2) is not particularly limited, but a polymer or glass material is generally used. Examples of the polymer include cellulose-based polymers such as cellulose diacetate and cellulose triacetate, polyester-based polymers such as polyethylene terephthalate and polyethylene naphthalate, and polyolefin-based or polycarbonate-based polymers.

It should be noted that a so-called reflective polarizer (a polarization plane of a polarizing plate arranged on the backlight side of the liquid crystal cell 7) is orthogonal to between the bandpass filter 1 and the backlight 6 (diffusion plate 5 in this embodiment). To reflect light that has a polarization plane
And to increase the amount of transmitted light of the bandpass filter 1, a film of cellulose acetate having a small phase difference, unstretched polycarbonate, unstretched polyethylene terephthalate, or norbornene resin is used as the transparent substrate. It is preferably used.

Next, the setting of the selective transmission wavelength in the bandpass filter 1 will be described in detail.

Bandpass filter 1 according to the present embodiment
Indicates the maximum transmittance at a wavelength corresponding to the peak wavelength in the emission spectrum of the backlight 6 (the wavelength indicating the maximum transmittance is referred to as the maximum transmission wavelength), while the cut rate is 50% or more on the longer wavelength side than the maximum transmission wavelength. Is set to have a reflection wavelength (wavelength at which the reflectance is 50% or more).

Here, as will be described later, the parallelism of the light passing through the bandpass filter 1 differs depending on the difference between the reflection wavelength and the maximum transmission wavelength, and the difference is arbitrarily set according to the purpose. Can be set.

That is, the reflection wavelength with a cut rate of 50% or more according to the incident angle θ of light on the bandpass filter 1 is approximately derived by the following equation (1). λ2 = λ1 × (1- (n0 / ne) ² × sin ² θ) ^1/2 (1) where λ1 is the value of the reflected wavelength that reflects 50% or more of the vertically incident light, and λ2 is the incident wavelength. The value of the reflection wavelength that reflects 50% or more of the light of the angle θ, n0 is the refractive index of the external medium (1.0 in the case of the air interface), ne is the effective refractive index of the bandpass filter 1, and θ is The incident angles are shown respectively.

From the above formula (1), for example, for the peak wavelength 545 nm in the emission spectrum of the backlight 6, the reflection wavelength λ1 = 555 nm, the bandpass filter 1
If the effective refractive index of is set to ne = 2.0 and the air interface is left, the incident angle θ becomes the reflection wavelength λ2 = 545 nm.
Is about ± 22 degrees. That is, the incident angle θ is about ±
If it is within the range of 22 degrees, it is possible to obtain a transmittance of 50% or more (on the contrary, if the incident angle θ is outside the range of about ± 22 degrees, then λ2 <545 nm, which is on the longer wavelength side than λ2. The light having the peak wavelength of 545 nm of the backlight 6 does not pass through the bandpass filter 1 by 50% or more). Similarly, the reflection wavelength λ1 = 547n
where m is the incident angle θ at which the reflection wavelength λ2 = 545 nm
Is about ± 10 degrees, and when the reflection wavelength λ1 = 545.5 nm, the incident angle θ at which the reflection wavelength λ2 = 545 nm is about ± 5 degrees.

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 is set. Can be controlled freely.

When there are a plurality of peak wavelengths in the emission spectrum of the backlight 6, the same setting may be made for each wavelength. For example, in the case of the backlight 6 using a three-wavelength cold cathode tube as a light source, it 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. 1 reflection wavelength λ1
You can set. Specifically, in 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 color. It becomes degree. That is, regardless of the color, it is possible to control the parallelism of the light passing through the bandpass filter 1 within a range of ± 10 degrees from the front.

The maximum transmittance for each wavelength in the bandpass filter 1 can be changed by designing the film quality. To adjust the color tone of the transmitted light, the fluorescent light of each color of the light source forming the backlight 6 is adjusted. Adjusting the blending amount of the body, making the backlight 6 adapted to the maximum transmittance for each wavelength, or supplying the light source (plural light emitting diodes) forming the backlight 6 to each light emitting diode By adjusting the electric power, it is possible to make the emission spectrum intensity of the backlight 6 suitable for the maximum transmittance for each wavelength.

[0061]

[Examples] Hereinafter, by showing Examples and Comparative Examples,
The characteristics of the present invention will be further clarified.

Example 1 Twenty layers of dielectric thin films made of ZrO ₂ / SiO ₂ were laminated, and as shown in FIG.
The center wavelength showing the maximum transmittance is 545 nm, and the half width is about 1
A bandpass filter having a thickness of 0 nm was produced. A glass plate having a thickness of 0.4 mm was used as the base material to be the adherend.

For the bandpass filter, a wavelength of 5
A backlight using a three-wavelength cold cathode tube having a maximum emission line spectrum at 45 nm as a light source was arranged. Such a backlight was colored green and had a characteristic that emitted light was condensed within a range of ± 14 degrees from the front as shown in FIG. 4 (b).

The bandpass filter of this embodiment has a wavelength of 5
It reflects light other than in the vicinity of 45 nm. Therefore,
When this bandpass filter is placed 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 causes the liquid crystal cell to enter. The transmitted light may reach the bandpass filter, be reflected on the surface of the bandpass filter, and the reflected light may be visually recognized. Therefore, a quarter-wave plate for preventing reflection is arranged between the bandpass filter and the polarizing plate. In this embodiment, however, it is necessary to prevent reflection in the entire visible light range except the wavelength near 545 nm. Therefore, in the present embodiment, the broadband quarter wave plate (1/4 wave plate and 1/2 wave plate) is used.
A combination of wave plates) was used.

More specifically, the relationship between the axial angles as shown in FIG. 10 (the half-wave plate and the quarter-wave plate shown in FIG. 10) is used.
(The long side direction of the wave plate corresponds to the stretching axis of each wave plate.)
Then, a phase difference value of 1 between the bandpass filter and the polarizing plate.
40 nm quarter wavelength plate and 1/270 nm phase difference value 270 nm
The two-wave plate and the two-wave plate are laminated and arranged. Here, the retardation plate (1
NRF film (retardation value 140 nm, 270 nm) manufactured by Nitto Denko Corporation is used as the / 4 wavelength plate and the 1/2 wavelength plate, and SEG1465D manufactured by Nitto Denko Corporation is used as the polarizing plate.
U was used. In addition, in FIG. 10, since the bandpass filter itself does not have a polarization characteristic, the bonding angle is not particularly specified. Furthermore, the phase difference value and the bonding angle shown in FIG. 10 are examples, and the values are not limited to these values.

According to the optical element having the above-described structure, 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 transmitting through the broadband ¼ wavelength plate. , Will reach the surface of the bandpass filter. The light reflected by the bandpass filter has its rotation direction of circularly polarized light reversed, and again passes through the broadband quarter-wave plate to become linearly polarized light whose polarization plane is orthogonal to that of the incident light. Therefore, the reflected light is prevented from being absorbed and visually recognized by the polarizing plate because the polarization planes thereof are orthogonal to each other. In particular, in the present embodiment, since the quarter-wave plate having a wide band is used, the reflected light due to the strong incident light is not visually recognized, and the window of strong external light enters or the fluorescent light of indoor lighting. Even in a use environment where a light image was reflected, the reflected light was not colored and visually recognized.

Example 2 Twenty layers of dielectric thin films made of ZrO ₂ / SiO ₂ were laminated, and as shown in FIG.
A short-wavelength transmission type bandpass filter (dichroic color filter) having a half-value wavelength of 580 nm was manufactured.
A glass plate having a thickness of 0.4 mm was used as the base material to be the adherend.

As shown in FIG. 5A, a backlight having a monochromatic cold-cathode tube having a maximum emission line spectrum at a wavelength of 545 nm as a light source was arranged for the dichroic color filter.

As in this embodiment, the emission spectrum of the backlight is limited to a single specific wavelength (545 nm),
When the reflection band of the dichroic color filter is limited to the long wavelength side, since the reflection color of the dichroic color filter is colored, the wavelength band having this reflection hue (red tone in this embodiment) is centered. If the antireflection is performed, a sufficient antireflection effect can be obtained. From this point of view, in the present embodiment, a polycarbonate single-layer retardation plate (NRF film manufactured by Nitto Denko Corporation) was 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 150n
m) was placed. This phase difference value is 60 which indicates reddish coloring.
The effect of preventing reflection of light having a wavelength near 0 nm is exhibited.

The antireflection effect can be obtained by stacking the quarter-wave plate and the polarizing plate with the stretching axis of the quarter-wave plate inclined by 45 degrees with respect to the absorption axis of the polarizing plate. .
Here, as the polarizing plate, SEG1465 manufactured by Nitto Denko Corporation
DU was used.

As shown in FIG. 5B, the distribution of the light emitted from the optical element having the above-described structure is condensed within a range of about ± 30 from the front direction, and the strong external light incident from the polarizing plate side is incident. Even when exposed to light, coloring caused by reflected light was not visually recognized when the liquid crystal display device was in a white display state.

(Example 3) Twenty-one thin films of TiO ₂ / SiO ₂ were laminated by vapor deposition, and as shown in FIG.
A bandpass filter (interference filter) having a high transmittance for three wavelengths of the emission spectrum of the wavelength emission line type cold cathode fluorescent lamp and reflecting light of other wavelengths was produced. As a base material to be adhered, a PET film (Lumirror manufactured by Toray,
A thickness of 75 μm) was used.

When the bandpass filter is used, the light emitted from the backlight having the three-wavelength bright line type cold cathode fluorescent lamp as a light source is reflected at about ± 20 degrees from the vertical direction and returns to the backlight side. Had.

As in this embodiment, light of three wavelengths is transmitted,
When a bandpass filter that reflects light in other wavelength bands is used, it is necessary to broaden the antireflection function to prevent reflection in the entire visible light, as in the first embodiment. From this point of view, also in the present embodiment, similarly to the first embodiment, a broadband quarter-wave plate for antireflection is provided between the bandpass filter and the polarizing plate mounted on the backlight side of the liquid crystal cell. It is configured to be placed. In addition, Example 1
Phase difference plate (1/4 wave plate and 1/2 wave plate)
As an NRF film manufactured by Nitto Denko (retardation value 14
0 nm, 270 nm) and SEG1465DU manufactured by Nitto Denko Corporation was used as the polarizing plate.

The distribution and the antireflection effect of the light emitted from the optical element having the above-described structure are the same as those of the first embodiment, and the light collecting ability is about ± 30 degrees from the front direction and the light is incident from the polarizing plate side. Even when exposed to the strong external light, when the liquid crystal display device was in the white display state, the reflected image due to the reflected light from the bandpass filter was not visually recognized.

Example 4 Polyethylene naphthalate (PEN) / polymethylmethacrylate (PMMA)
20 thin films were laminated by the feed block method while alternately controlling the thickness, and this laminated body was biaxially stretched. The stretching temperature is about 140 ° C., and the stretching ratio is about 4 times in the TD direction.
About 3 times in the M direction.

By laminating five stretched products of the 20-layer laminated film obtained as described above, a laminated product having a total of 100 layers is obtained, which is a short wavelength transmissive type having reflection characteristics in the wavelength band of 650 nm to 900 nm. It was adjusted to function as a bandpass filter (dichroic color filter).

The dichroic color filter manufactured as described above had a reflectance of 50% or more at a wavelength of 635 nm. For such a dichroic color filter, a backlight using an AlGaInP-based high-luminance LED having a center wavelength of the emission spectrum of 630 nm as a light source was arranged. Also, use 1 /
The four-wave plate, the polarizing plate, and their arrangement were set to the same conditions as in Example 2.

The distribution of the light emitted from the optical element having the above structure was almost the same as that of the second embodiment. Further, when the liquid crystal display device was in the white display state, the coloring due to the reflected light from the dichroic color filter was not visually recognized.

Example 5 A fluorine-based acrylate resin (LR202B manufactured by Nissan Chemical Industries, Ltd.) having a refractive index of about 1.40 was used as the low refractive index material, and a refractive index of about 1.40 was used as the high refractive index material.
71 acrylate resin containing inorganic high refractive index ultrafine particles (J
(SR Desolite) is used as the base material (Fuji Film TAC film (TD-TAC)).
By laminating 18 layers by multilayer thin film coating, a short wavelength transmission type bandpass filter (dichroic color filter) as shown in FIG. 7 was produced. The half-value wavelength of such a dichroic color filter was about 580 nm.

The multilayer thin film coating was carried out by using a micro gravure coater, followed by drying at 90 ° C. for 1 minute and then curing by ultraviolet polymerization (illuminance 50 mW / cm ² × 1 second), and the following coating film was formed on the cured coating film. Overcoating of the coating film was repeated. Since the uniformity of the in-plane transmission spectral characteristics of the filter thus obtained was insufficient, it was decided to select and use a region having good characteristics in the relevant wavelength range.

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 arranged for the dichroic color filter.
Also, as in Example 2, a quarter wavelength plate and a polarizing plate were arranged.

The distribution of the light emitted from the optical element having the above-described structure 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 displays white. In the state, coloring due to reflected light was not visually recognized.

Example 6 A fluorine-based acrylate resin (LR202B manufactured by Nissan Chemical Co., Ltd.) having a refractive index of about 1.40 was used as the low refractive index material, and a refractive index of about 1.40 was used as the high refractive index material.
71 acrylate resin containing inorganic high refractive index ultrafine particles (J
(SR Desolite) is used as the base material (Fuji Film TAC film (TD-TAC)).
Twenty-one layers were laminated on the above by multilayer thin film coating to prepare a short wavelength transmission type bandpass filter (dichroic color filter) as shown in FIG. The transmission wavelength of such a dichroic color filter is 435 nm and 545 n.
It exists in three regions of m and 610 nm and corresponds to each color of RGB in the emission spectrum of a general cold cathode tube.

The multilayer thin film coating was carried out by using a micro gravure coater, followed by drying at 90 ° C. for 1 minute and then curing by ultraviolet polymerization (illuminance 50 mW / cm ² × 1 second), and the following coating film was formed on the cured coating film. Overcoating of the coating film was repeated. Since the uniformity of the in-plane transmission spectral characteristics of the filter thus obtained was insufficient, it was decided to select and use a region having good characteristics in the relevant wavelength range.

With respect to the dichroic color filter corresponding to the three wavelengths, a backlight using a three-wavelength cold cathode tube having a bright line spectrum at each wavelength as a light source is arranged.
Further, as in the case of Example 1, a retardation plate and a polarizing plate were arranged.

The distribution of the light emitted from the optical element having the above-mentioned structure is condensed within a range of ± 30 degrees from the front, and the same antireflection effect as that of Example 1 is obtained, and the liquid crystal display device displays white. In the state, the reflected image due to the reflected light from the dichroic color filter was not visually recognized.

Example 7 A bandpass filter was manufactured in the same manner as in Example 3. A retardation plate and a polarizing plate were arranged for the bandpass filter in the same manner as in Example 1, but in this example, as the retardation plate, an NRZ film manufactured by Nitto Denko Corporation (retardation values 140 nm and 270 nm) was used. ,
Both Nz coefficients used 0.5). Since the NRZ film is a retardation film in which the change in retardation value in the thickness direction is controlled, by using it, a retardation equivalent to that for vertically incident light can be obtained even for incident light from an oblique direction. It is possible to give. Therefore, a sufficient antireflection effect can be achieved even for incident light that is largely deviated from the vertical direction.

According to the optical element having the above-described structure, even when the liquid crystal display device is in the white display state, it is caused by the reflected light from the bandpass filter even in an environment such as a window where bright oblique incident light exists. The reflected image was not visible.

Example 8 A bandpass filter was prepared in the same manner as in Example 3. Although a retardation plate and a polarizing plate are arranged for such a bandpass filter, in the present embodiment, the retardation plate used is a liquid crystal polymer (L manufactured by BASF Corporation).
It was produced by precision coating with a slit coater of C242).

Specifically, with respect to the liquid crystal polymer,
A photoreaction initiator (Irg184 manufactured by Ciba-Geigy Co., Ltd.) was added at 1% by weight to prepare a cyclopentane solution (corresponding to 20% by weight). This solution was coated on a base material with a wire bar so that the thickness when dried was equivalent to 1.2 μm, and 90 ° C. × 2
After drying in minutes, UV irradiation (10 mW / cm ² × 2
By doing so, 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 applying the coating so that the thickness was about 2.5 μm. If these retardation plates are laminated in the same manner as in Example 1, they function as a broadband quarter-wave plate.
It has an antireflection function in the visible light range.

In this example, the surface of the bandpass filter with the 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 wt% aqueous solution of PVA (Poval by Kuraray Co., Ltd.) on the surface of the bandpass filter, drying it, and then rubbing it with a cotton rubbing cloth. On the alignment film of such a bandpass filter, a phase difference value of 14 is obtained by the method described above.
A liquid crystal retardation film of 0 nm is formed, and further,
A 2% by weight aqueous solution of PVA (Poval manufactured by Kuraray Co., Ltd.) was spin-coated, dried, and then rubbed with a cotton rubbing cloth. Here, the rubbing direction was set such that the angle formed by the first and second rubbing directions was 62.5 degrees so as to match the arrangement of FIG. 10 described in Example 1 (shown in FIG. 10). The long side direction of the retardation plate corresponds to the rubbing direction). On the alignment film formed by such a rubbing treatment, a liquid crystal retardation plate having a retardation value of 270 nm was formed by the method described above. Further, a polarizing plate was arranged on this so as to match the arrangement of FIG. 10 in Example 1.

In the optical element according to this example, the total thickness of the retardation plate was within about 5 μm. Since this can be reduced to 1/10 or less of the thickness (about 50 μm) of the quarter-wave plate formed of the stretched film made of polycarbonate, it has been found that it contributes to the thinning of the surface light source device. The antireflection effect was equivalent to that of Example 3, and when the liquid crystal display device was in the white display state, the reflected image resulting from the reflected light from the bandpass filter was not visually recognized.

(Comparative Example) 20 dielectric thin films were laminated to form a central wavelength of maximum transmission of 545 nm and a half width of 1
A bandpass filter with 0 nm is used, and the light source wavelength is 5
Light was emitted toward the band pass filter from a backlight having a three-wavelength cold cathode tube having one peak wavelength at 45 nm as a light source. 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 a liquid crystal display using the bandpass filter and the backlight as a surface light source device. When displaying white, the device reflected the surrounding image as a mirror image on the bandpass filter, and this was visually recognized to deteriorate the display quality.

In the examples and comparative examples described above, the instantaneous multi-photometric system MCPD2000 manufactured by Otsuka Electronics Co., Ltd. was used for the measurement of the reflection wavelength band, and the spectroscopic ellipso M220 manufactured by JASCO Corporation was used for the evaluation of the thin film characteristics. , The spectrophotometer U4 manufactured by Hitachi, Ltd. is used to evaluate the spectral characteristics of transmission and reflection.
100 is used for evaluating the characteristics of the polarizing plate, which is manufactured by Murakami Color Co., Ltd.
3 for measuring the phase difference value, Oji Scientific Instrumen
The birefringence measuring device KOBRA21D manufactured by ts is used for measuring the viewing angle characteristics (contrast, color tone, brightness) by ELDIM.
The Ez contrast manufactured by the company was used.

[0096]

In the liquid crystal display device in which the optical element according to the present invention is arranged on the emission 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 suppress the deterioration of the display quality.

[Brief description of drawings]

FIG. 1 is a vertical cross-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 a diagram showing the quarter wave plate shown in FIG.
It is explanatory drawing explaining that visual recognition of return light is prevented.

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.

FIG. 4 is a diagram showing spectral characteristics of a bandpass filter and a light source in Example 1, and distribution of emitted light.

FIG. 5 is a diagram showing spectral characteristics of a bandpass filter and a light source and distribution of emitted light in the second embodiment.

FIG. 6 is a diagram showing spectral characteristics of a bandpass filter and a light source in the third embodiment.

FIG. 7 is a diagram showing transmission spectral characteristics of a bandpass filter according to a fifth embodiment.

FIG. 8 is a diagram showing transmission spectral characteristics of a bandpass filter according to a sixth embodiment.

FIG. 9 is a diagram illustrating a situation in which reflected light of light reaching the surface of a bandpass filter is visually recognized in a conventional liquid crystal display device.

FIG. 10 is an explanatory diagram showing an example of a laminated state of a polarizing plate, a half-wave plate, and a quarter-wave plate according to the first embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Bandpass filter 2 ... 1/4 wavelength plate 3 ... Polarizing plate 4 ... 1/2 wavelength plate 5 ... Diffusion plate 6 ... Backlight 7 ... Liquid crystal cell 10 ... Liquid crystal display device 11 ... Optical element
12 ... Surface light source device 13 ... Broadband quarter wave plate

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G02F 1/13357 G02F 1/13357 // F21Y 103: 00 F21Y 103: 00 F term (reference) 2H048 GA04 GA05 GA12 GA15 GA24 GA61 2H049 BA02 BA06 BA07 BA42 BB03 BB51 BB63 BB66 BC22 2H091 FA05Z FA08Z FA10Z FA11Z FA42Z FA44Z FA45Z FB02 FB06 FC02 FC08 FC09 FD06 LA16

Claims (19)

[Claims] 1. A band-pass filter for selectively transmitting light emitted from a backlight, which is formed of a laminated body of thin films each having a different refractive index, a polarizing plate, and light incident from the polarizing plate side. An optical device comprising a quarter-wave plate arranged between the bandpass filter and the polarizing plate so as to prevent the light from being reflected by the bandpass filter and emitted from the polarizing plate side. element. 2. The optical element according to claim 1, further comprising a half-wave plate arranged on a different axis between the polarizing plate and the quarter-wave plate. 3. The ¼ to improve the viewing angle characteristics.
The optical element according to claim 2, wherein the refractive index in the thickness direction of the wave plate and / or the half wave plate is controlled. 4. The optical element according to claim 1, wherein the phase difference of the quarter-wave plate is set to a value corresponding to the reflection hue of the bandpass filter. 5. The quarter-wave plate and / or the half-wave plate
The optical element according to any one of claims 2 to 4, wherein the wave plate is formed of a liquid crystal polymer material. 6. The optical element according to claim 1, wherein each member constituting the optical element is adhered by an adhesive or an adhesive to remove an air interface. 7. The bandpass filter is formed by stacking thin films made of an inorganic oxide, a dielectric or a metal oxide, each having a different refractive index, by vacuum deposition, electron beam co-deposition or sputtering. The optical element according to any one of claims 1 to 6, which is characterized in that. 8. The optical element according to claim 1, wherein the bandpass filter is formed by laminating thin films made of resin compositions having different refractive indexes. 9. The resin composition, after multi-layer extrusion,
The optical element according to claim 8, wherein the optical element is thinned by uniaxial stretching or biaxial stretching. 10. The bandpass filter according to claim 7.
7. The laminate of the bandpass filter according to any one of claims 1 to 9 is crushed into scales, and the crushed pieces are embedded in a resin to form a scaly piece. Optical element. 11. The optical element according to claim 1, further comprising a diffusion plate arranged between the bandpass filter and the backlight. 12. The optical element according to claim 11, wherein a surface of the diffusion plate facing the backlight has an uneven shape. 13. The bandpass filter is formed of a base material and a thin film laminated body laminated on the base material, and the base material has an in-plane retardation of a light incident surface and a light emitting surface of 30 nm.
The optical element according to any one of claims 1 to 12, wherein: 14. The bandpass filter is characterized in that a plurality of selective transmission wavelengths are set, and that incident angles at which light of each wavelength is reflected at a predetermined ratio are matched with each other. Claims 1 to 1
The optical element according to any one of 3 above. 15. An optical element according to any one of claims 1 to 14, and a backlight that uses a three-wavelength cold cathode tube as a light source and emits light in a planar manner toward the optical element. Surface light source device. 16. An optical element according to any one of claims 1 to 14, and a backlight that uses a light emitting diode as a light source and emits planar light having an emission wavelength of one or more to the optical element. A surface light source device comprising: 17. A 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, 17. The surface light source device according to claim 15 or 16, characterized in that the emitted light of (1) is neutralized in terms of visibility. 18. An optical element according to any one of claims 1 to 14, and a backlight that uses an electroluminescent element as a light source and planarly emits light to the optical element. Surface light source device. 19. A liquid crystal display device comprising: a liquid crystal cell; and the surface light source device according to claim 15 for illuminating the liquid crystal cell.