JP2003294948A - Band filter and surface light source device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a band filter the pass band of which can easily be made narrower, and to provide a surface light source device superior in directivity to the front by using the band filter. <P>SOLUTION: The band filter is provided with a first reflective polarizer 21 which has a center wavelength λc of selective reflection and has selective reflectivity of a wavelength band width W and a second reflective polarizer 22 which is arranged on the first reflective polarizer 21 so as to have an approximately orthogonal relation to the first reflective polarizer and has a center wavelength λc' of selective reflection and has selective reflectivity of the wavelength band width W, and the center wavelength λc' of selective reflection of the second reflective polarizer 22 satisfies (λc-W)<λ c'<(λc+W)... and λc≠λc'. A surface light source device is provided with a surface light source 1 for emitting light like a surface and the band filter arranged on the exit face side of the surface light source 1. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention forms a surface light source device having excellent front directivity, and is applicable to obtain a liquid crystal display device having high brightness, and reflects (transmits) light in a specific wavelength band. The present invention relates to a bandpass filter and a surface light source device using the bandpass filter, and more particularly, to a bandpass filter capable of easily narrowing a band and a surface light source device using the bandpass filter.

[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, if a band-pass filter (interference filter) that transmits the light of a specific peak wavelength emitted from the backlight at the time of vertical incidence and reflects it at the time of oblique incidence is arranged on the side of the emission surface of the backlight, vertical incidence is achieved. Light is transmitted, but incident light from an oblique direction is reflected without being transmitted, and parallelization is possible.

According to the bandpass filter, unlike the conventional collimation using a light shielding plate, the non-parallel 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 operations are 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 determined by the bandpass filter. It can be controlled by the transmission center wavelength and the transmission wavelength width (half-value width). 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 facilitating handling of the entire device. It has a feature that it can be easily done. Further, since the surface of the bandpass filter is smooth, it is possible to prevent the occurrence of scratches on the surface by performing a hard coat treatment or the like, which makes handling easier. 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 band filter has a great advantage in making a backlight parallel light.

As such a bandpass filter, for example, a cholesteric liquid crystal is used, and Japanese Patent Application No. 2001-60 is used.
No. 005 and Japanese Patent Application No. 2000-281382, it is possible to obtain a surface light source device that is collimated (condensed).

As described above, in order to realize an ideal collimated backlight with a bandpass filter, a bandpass filter that transmits light of a specific peak wavelength of the backlight while reflecting light of other wavelengths is used. is necessary. For example, as shown in FIG. 7, the emission spectrum of a general CCFL backlight has red (610 nm) and green (54 nm).
5 nm) and blue (435 nm).

CCF having such an emission spectrum
To achieve ideal collimation for the L backlight, wavelengths longer than red, shorter than blue, longer than blue and shorter than green, and longer than green and shorter than red. A band-pass filter that cuts (reflects) the respective lights may be used. Where wavelengths longer than red,
A wavelength shorter than blue, a bandpass filter that cuts off each light having a wavelength longer than blue and shorter than green, for example, or a cholesteric liquid crystal layer having selective reflectivity in the same reflection wavelength band may be stacked orthogonally to each other,
It can be relatively easily prepared by repeatedly laminating high refractive index / low refractive index thin film layers by vacuum deposition or the like.

However, it is not easy to make a bandpass filter that reflects only light having a wavelength longer than green (545 nm) and shorter than red (610 nm), that is, a narrow band wavelength of about 50 nm. For example, when a cholesteric liquid crystal layer is used to create such a narrow band filter, the wavelength band width of selective reflection is the difference (Δn) between the ordinary and extraordinary ray refractive indices of the liquid crystal. Determined due to. However, the wavelength bandwidth is 50n
It is not easy to form a cholesteric liquid crystal layer having a small Δn of m or less, and the wavelength bandwidth is usually around 100 nm.

Further, in order to produce the narrow band filter by vacuum vapor deposition, a high refractive index layer and a low refractive index layer having a thickness of ¼ wavelength may be repeatedly laminated. In this case, the wavelength bandwidth of the bandpass filter is determined by the refractive index difference between the high refractive index layer and the low refractive index layer, and the smaller the refractive index difference, the narrower the wavelength bandwidth. However, if the refractive index difference is reduced, there is a problem that the number of layers required to obtain a sufficient reflectance for light having a wavelength in the wavelength band is significantly increased. For example, when the wavelength bandwidth is 50 nm, sufficient reflectance cannot be obtained unless the number of layers is increased to at least 30 layers, preferably 50 layers or more. Therefore, such a band-pass filter has a problem that it takes time and effort to make it and the cost rises.

[0012]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and provides a band filter capable of easily narrowing the band, and the band filter An object of the present invention is to provide a surface light source device having excellent directivity when used.

[0013]

In order to solve such a problem, the inventors of the present invention have earnestly studied, and as a result, two reflection type polarizers having different selective reflection central wavelengths are selected as one reflection type polarizer. On the other hand, by arranging the other reflection-type polarizer in a substantially orthogonal relationship, and by further setting the difference between the selective reflection center wavelengths within a predetermined range, it is possible to create a narrow band filter very easily. The inventors have found that and completed the present invention. That is, according to the present invention, as described in claim 1, the first reflection-type polarizer having the selective reflection center wavelength λc and the wavelength bandwidth W having the selective reflection property and the first reflection-type polarizer are provided. A second reflective polarizer having a selective reflection central wavelength λc ′ and a selective reflection property of a wavelength bandwidth W, which are arranged so as to be substantially orthogonal to each other; Selective reflection center wavelength λ
c'provides a bandpass filter characterized by satisfying the following expressions (1) and (2). (Λc−W) <λc ′ <(λc + W) (1) λc ≠ λc ′ (2)

According to the first aspect of the invention, of the light incident on the bandpass filter, the first reflection-type polarizer causes the selective reflection band of the polarizer (a wavelength having a bandwidth W centered on the wavelength λc). Part of the light in the band (polarized light that matches the polarizer) will be reflected. Furthermore, of the light transmitted through the first reflective polarizer, by the second reflective polarizer,
Part of the light in the selective reflection band of the polarizer (the wavelength band having the bandwidth W centering on the wavelength λc ′) (polarized light that matches the polarizer) is reflected. Here, the first reflection-type polarizer and the second reflection-type polarizer are arranged so as to be substantially orthogonal to each other. Here, the orthogonal relationship means that when the first and second reflective polarizers are circular polarizers, one of them functions as a right circular polarizer and the other functions as a left circular polarizer. Means a relationship that plays.
Further, when the first and second polarizers are linear polarizers, it means that the polarization planes of the linearly polarized light reflected by the respective polarizers are orthogonal to each other. Therefore, regarding the light in the band where the selective reflection band of the first reflective polarizer and the selective reflection band of the second reflective polarizer overlap, whether the light incident on the bandpass filter is natural light or polarized light Regardless of whether or not, all will be reflected. According to the invention, the second
The selective reflection center wavelength λc ′ of the reflective polarizer of
By satisfying (2) and (2), an overlapping band is always generated, and the selective reflection center wavelength λc ′ is
It is possible to easily narrow the overlapping band, that is, the selective reflection band of the band filter, by adjusting the value within the range that satisfies the expressions (1) and (2).

Preferably, as described in claim 2, one of the first and second reflective polarizers selectively reflects right circularly polarized light and the other selectively reflects left circularly polarized liquid crystal. Formed by layers.

Alternatively, as described in claim 3, the first
And the second reflective polarizer is formed of a cholesteric liquid crystal layer having gyrations in the same direction,
1 / disposed between the first and second reflective polarizers
The configuration may further include a two-wave plate.

According to the third aspect of the invention, the first and second reflective polarizers have the turning properties in the same direction, and the half-wave plate is provided between the two polarizers. The same function as in the case where both polarizers are arranged so as to be orthogonal to each other is achieved. The turning property in the same direction means that right circularly polarized light or both left circularly polarized light is selectively reflected.

Further, as described in claim 4, the first and second reflective polarizers are formed by uniaxially stretching after laminating resins having birefringence and having different refractive indexes. However, the first and second reflective polarizers may be arranged so that their stretching directions are substantially orthogonal to each other.

According to the present invention, as described in claim 5,
Also provided as a surface light source device comprising: a surface light source that emits light in a planar shape; and the bandpass filter according to any one of claims 1 to 4 that is disposed on an emission surface side of the surface light source. It

According to the invention of claim 5, a surface light source device having excellent frontal directivity can be obtained by transmitting light emitted from a surface light source such as an EL backlight or a CCFL backlight through a bandpass filter. it can.

[0021]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
FIG. 3 is a vertical cross-sectional view showing a schematic configuration of a surface light source device including a bandpass filter according to the embodiment of FIG. As shown in FIG. 1, a surface light source device 10 according to this embodiment includes a surface light source 1 that emits light in a planar shape, and a bandpass filter 2 that is arranged on the emission surface side of the surface light source 1.

The surface light source 1 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 in a planar manner to the bandpass filter 2. In addition to the so-called direct type as shown in FIG. 1, the surface light source 1 is also a so-called sidelight type in which a light source is arranged laterally and is configured to emit light in a planar manner via a light guide. Is also possible.

The bandpass filter 2 has a selective reflection center wavelength λc.
And a first reflection-type polarizer 21 having a selective reflection property with a wavelength bandwidth W, and the first reflection-type polarizer 21 and the first reflection-type polarizer 21 are overlapped with each other so as to be substantially orthogonal to each other, and have a selective reflection center. The second reflective polarizer 22 having a selective reflection property with a wavelength λc ′ (≠ λc) and a wavelength bandwidth W is provided.

Here, the reflective polarizers 21 and 22 constituting the bandpass filter 2 generally have a wavelength band that functions as a polarizer, and the selective reflection center wavelength and the wavelength bandwidth W are It can be controlled depending on the material properties of the polarizer and the manufacturing method.

As shown in FIG. 2, in this embodiment, the first
The reflective polarizer 21 is a circular polarizer (right circular photon) that transmits right circularly polarized light and reflects left circularly polarized light, while the second reflective polarizer 22 is the first reflective type. The circular polarizer is orthogonal to the polarizer 21, that is, a circular polarizer (left circular polarizer) that transmits left circularly polarized light and reflects right circularly polarized light.

Here, if the selective reflection center wavelength and the wavelength bandwidth of the second reflective polarizer 22 are the same as those of the first reflective polarizer 21, the selective reflection band (wavelength is Light in the reflection band width W centered on λc) is reflected regardless of whether the incident light (light emitted from the surface light source 1) is natural light or polarized light. In other words, it acts as a bandpass filter that reflects light having a wavelength λ in the range of λc−W / 2 ≦ λ ≦ λc + W / 2 (transmits light having a wavelength outside the range).

However, the selective reflection center wavelength λc ′ of the second reflective polarizer 22 according to this embodiment is different from the selective center wavelength λc of the first reflective polarizer 21 as described above. (Λc−W) <λc ′ <(λ
c + W) ... (1) is formed. Therefore, of the light that has entered the bandpass filter 2, the left-handed circularly polarized light in the selective reflection band (the wavelength band of the bandwidth W centering on the wavelength λc) of the polarizer 21 is converted by the first reflective polarizer 21. Will be reflected. Further, of the light transmitted through the first reflective polarizer 21 (which also includes right-handed circularly polarized light in the selective reflection band of the polarizer 21), the second reflective polarizer 22 causes Right circularly polarized light in the selective reflection band (wavelength band of bandwidth W centering on wavelength λc ′) of the child is reflected. Therefore, regarding the light in the band where the selective reflection band of the first reflective polarizer 21 and the selective reflection band of the second reflective polarizer 22 overlap, the light that has entered the bandpass filter 2 is natural light. All will be reflected regardless of whether it is polarized light or polarized light. Selective reflection center wavelength λ of the second reflective polarizer 22
Since c ′ is set within the range that satisfies the above equation (1), there is always an overlapping band, and
By adjusting the selective reflection central wavelength λc ′, it is possible to easily narrow the overlapping band, that is, the selective reflection band of the bandpass filter 2.

For example, the selective reflection band of the first reflective polarizer 21 is 500 to 600 nm (λc = 550 nm, W
= 100 nm), and the selective reflection band of the second reflective polarizer 22 is 550 to 650 n satisfying the above formula (1).
It is assumed that m (λc ′ = 600 nm, W = 100 nm). In this case, the wavelength band in which all the light is reflected is 550 to 600 nm where the selective reflection bands of both the polarizers 21 and 22 overlap, regardless of the polarization. That is, the reflective polarizers 21 and 22 having different selective reflection bands are simply included.
It is possible to narrow the selective reflection band of the band filter 2 as a whole by simply combining.

The material and structure for forming the reflective polarizers 21 and 22 are not particularly limited, but when the cholesteric liquid crystal layer is applied, it can be formed only by wet coating the cholesteric liquid crystal. Therefore, the reflective polarizers 21 and 22 of the present invention are most suitable. The cholesteric liquid crystal layer is not particularly limited as long as it exhibits a cholesteric liquid crystal property, and various compounds can be applied. For example, the cholesteric liquid crystal layer is formed of a liquid crystal polymer having various skeletons, which is a main chain type, a side chain type, or a composite type thereof showing cholesteric liquid crystal alignment.

The main chain type liquid crystal polymer is a condensation type polymer (for example, polyester type, polyamide type, etc.) having a structure in which mesogenic groups such as aromatic units are bonded.
Polymers such as polycarbonate type and polyester imide type) are applicable. As the aromatic unit to be a mesogen group, phenyl-based, biphenyl-based, and naphthalene-based ones can be applied, and these aromatic units are cyano groups,
It may have a substituent such as an alkyl group, an alkoxy group and a halogen group.

As the side chain type liquid crystal polymer, a polymer having a polyacrylate type, polymethacrylate type, polysiloxane type, polymalonate type main chain as a skeleton and having a mesogenic group composed of a cyclic unit or the like in the side chain is applicable. is there. Examples of the cyclic unit to be a mesogen group, for example,
Biphenyl-based, phenylbenzoate-based, phenylcyclohexane-based, azoxybenzene-based, azomethine-based, azobenzene-based, phenylpyrimidine-based, diphenylacetylene-based, diphenylpentoate-based, bicyclohexane-based, cyclohexylbenzene-based, terphenyl-based, etc. are applicable It is possible. The ends of these cyclic units may have a substituent such as a cyano group, an alkyl group, an alkoxy group, or a halogen group.

Further, the mesogenic group of any liquid crystal polymer may be bonded via a spacer portion which imparts flexibility. As such a spacer portion, a polymethylene chain, a polyoxymethylene chain or the like can be applied. The repeating number of the structural unit forming the spacer portion is appropriately determined according to the chemical structure of the mesogenic group, but the repeating unit of the polymethylene chain is 0 to 20, preferably 2 to 12, Repeating unit is 0 to 1
It is set to 0, preferably 1 to 3. The cholesteric liquid crystal polymer can be prepared by incorporating a low molecular weight chiral agent into the nematic liquid crystal polymer or introducing a chiral component into the polymer component.

The molecular weight of the liquid crystal polymer is not particularly limited, but it is preferable that the weight average molecular weight is about 2,000 to 100,000. When the weight average molecular weight of the liquid crystal polymer becomes large, the orientation property as a liquid crystal, especially the mono-domain formation when a rubbing orientation film or the like is interposed becomes poor, and the liquid crystal polymer tends to be difficult to form a uniform orientation state. Therefore, the weight average molecular weight of the liquid crystal polymer is more preferably 50,000 or less. Further, when the weight average molecular weight of the liquid crystal polymer is small, the film-forming property as the non-fluid layer tends to be poor. Therefore, the weight average molecular weight of the liquid crystal polymer is more preferably 2500 or more.

The glass transition temperature of the liquid crystal polymer is appropriately determined according to the application for which the liquid crystal polymer is used, but from the viewpoint of heat resistance of the base material, it is usually preferable to use a glass transition temperature of about 50 to 150 ° C. . The cholesteric liquid crystal layer is formed by applying a solution of the cholesteric liquid crystal polymer and drying it, or polymerizing a polymerizable cholesteric liquid crystal monomer with heat or light. Also,
The chiral component showing the cholesteric property of the cholesteric liquid crystal layer is a cholesteric liquid crystal polymer preparation step, or a cholesteric liquid crystal monomer polymerization step,
It is appropriately adjusted depending on the desired selective reflection band for the surface light source 3. Cholesteric liquid crystal layer is from 1 μm to 20
The thickness is preferably μm, more preferably 2 μm to 10 μm.

When forming the cholesteric liquid crystal layer, an alignment film for aligning the cholesteric liquid crystal is used. As such an alignment film, for example, a thin film made of polyimide, polyvinyl alcohol, or the like is formed on a transparent substrate, and formed by rubbing it, a stretched film obtained by stretching a transparent film, a cinnamate skeleton or an azobenzene skeleton. Various alignment films can be used as long as the cholesteric liquid crystal can be aligned, for example, by irradiating the polymer or polyimide which it has with polarized ultraviolet light.

Although the first reflective polarizer 21 is a right circular polarizer and the second reflective polarizer 22 is a left circular polarizer in this embodiment, the present invention is not limited to this. Of course, the first reflective polarizer 21 may be a left circular polarizer and the second reflective polarizer 22 may be a right circular polarizer.

(Second Embodiment) Next, a second embodiment of the present invention will be described. FIG. 3 is a vertical cross-sectional view showing a schematic configuration of a surface light source device including a bandpass filter according to the second embodiment of the present invention. As shown in FIG. 3, the surface light source device 20 according to the second embodiment is also arranged on the emission surface side of the surface light source 3 and the surface light source 3 that emits light in a planar manner, as in the first embodiment. And a bandpass filter 4 that has been set. Also,
Similar to the first embodiment, the bandpass filter 4 includes a first reflective polarizer 41 having selective reflectivity with a selective reflection center wavelength λc and a wavelength bandwidth W and a first reflective polarizer 41. Centered on the selective reflection center wavelength λc '
A second reflective layer having a selective reflectance of (≠ λc) and a wavelength bandwidth W.
The reflective polarizer 42 of FIG. Here, the selective reflection center wavelength λc ′ of the second reflective polarizer 42 is (λc−W) <λc ′ <(λc + W), as in the first embodiment.
Is formed to satisfy.

However, in the band-pass filter 4 according to this embodiment, the first reflection type polarizer 41 and the second reflection type polarizer 42 are formed so as to have the turning properties in the same direction, and This is different from the first embodiment in that the half-wave plate 43 is arranged between the first reflective polarizer 41 and the second reflective polarizer 42. That is, in the present embodiment, both the first reflective polarizer 41 and the second reflective polarizer 42 are formed so as to selectively reflect right circularly polarized light or both selectively reflect left circularly polarized light. However, since the half-wave plate having the function of reversing the rotation direction of the circularly polarized light is provided between the both polarizers 41, 42, both the polarizers 41,
When 42 has an orthogonal relationship, substantially the same function (see FIG. 2) is achieved.

The ½ wavelength plate 43 is a birefringent film having a retardation delay corresponding to ½ wavelength of the visible light wavelength. The half-wave plate 43 is formed by stretching and orienting a polymer film, for example. The polymer film is not particularly limited, but a film that is optically transparent and has little alignment unevenness is preferably used. As such a polymer film, for example, polycarbonate, polyarylate, polysulfone, polyolefin-based, polyethylene terephthalate, polyethylene naphthalate, norbornene-based, acrylic-based, polystyrene-based, or cellulose-based is applicable. It is also possible to form by coating or impregnating a polymer film with the liquid crystal composition.

Also with the bandpass filter 4 according to the present embodiment, the light in the band where the selective reflection band of the first reflective polarizer 41 and the selective reflection band of the second reflective polarizer 42 overlap each other Regardless of whether the light incident on the bandpass filter 4 is natural light or polarized light, all the light is reflected and the overlapping band, that is, the selective reflection band of the bandpass filter 4 is easily narrowed. It is possible to

Further, the bandpass filter 4 according to the present embodiment.
For example, when the first and second reflective polarizers 41 and 42 are formed of cholesteric liquid crystal layers, it is not necessary to prepare a right-handed cholesteric liquid crystal layer and a left-handed cholesteric liquid crystal layer, respectively. Since it is sufficient to use one of them and change the selective reflection band of each cholesteric liquid crystal layer depending on the amount of the chiral agent added, there is an advantage that it can be prepared extremely easily.

(Third Embodiment) Next, a third embodiment of the present invention will be described. FIG. 4 is a vertical cross-sectional view showing a schematic configuration of a surface light source device including a bandpass filter according to the third embodiment of the present invention. As shown in FIG. 4, the surface light source device 30 according to the third embodiment is also arranged on the emission surface side of the surface light source 5 and the surface light source 5 that emits light in a planar manner, as in the first embodiment. And a bandpass filter 6 that has been set. Also,
Similar to the first embodiment, the bandpass filter 6 includes a first reflection-type polarizer 61 having a selective reflection center wavelength λc and a wavelength bandwidth W having a selective reflection property, and the first reflection-type polarizer 61. Centered on the selective reflection center wavelength λc '
A second reflective layer having a selective reflectance of (≠ λc) and a wavelength bandwidth W.
The reflective polarizer 62 of FIG. Here, the selective reflection center wavelength λc ′ of the second reflective polarizer 62 is (λc−W) <λc ′ <(λc + W), as in the first embodiment.
Is formed to satisfy.

However, in the band-pass filter 6 according to this embodiment, after the first reflective polarizer 61 and the second reflective polarizer 62 are laminated with resins having birefringence and having different refractive indexes, respectively. This is different from the first embodiment in that it is uniaxially stretched and formed so that the refractive indexes in the stretching direction match. In other words, in the bandpass filter 6 according to this embodiment, the first and second reflective polarizers 61 and 62 are formed as reflective linear polarizers. In addition, the first reflective polarizer 61 and the second reflective polarizer 62 are arranged such that the stretching directions thereof are substantially orthogonal to each other. Therefore, the first reflective polarizer 61
And the second reflective polarizer 62 have an orthogonal relationship (each polarizer 6
The planes of polarization of the linearly polarized lights reflected by Nos. 1 and 62 are orthogonal to each other.

Also with the bandpass filter 6 according to the present embodiment, the light in the band where the selective reflection band of the first reflective polarizer 61 and the selective reflection band of the second reflective polarizer 62 overlap each other. Regardless of whether the light incident on the bandpass filter 6 is natural light or polarized light, all the light is reflected and the overlapping band, that is, the selective reflection band of the bandpass filter 6 is easily narrowed. It is possible to

The resin material for forming the first and second reflective polarizers 61, 62 according to the present embodiment is, for example, a high refractive resin material such as polyethylene naphthalate, polyethylene terephthalate, polycarbonate,
A halogenated resin composition typified by vinylcarbazole and brominated acrylate, a resin composition containing ultrafine particles of a high refractive index inorganic material can be used, and a low refractive index material typified by trifluoroethyl acrylate and the like. It is possible to use a fluororesin material, an acrylic resin represented by polymethylmethacrylate, or the like. The selective reflection band of each of the reflective polarizers 61 and 62 can be controlled to some extent by the refractive index of the resin material, the stretching conditions, and the like.

The characteristics of the present invention will be further clarified by showing Examples and Comparative Examples below.

Example 1 A triacetyl cellulose film having a thickness of 50 μm was used as a transparent film substrate, a polyvinyl alcohol layer having a thickness of 0.1 μm was formed on the substrate, and this was rubbed with a rayon cloth to form an alignment film. Formed. Next, a component monomer having a mesogenic group 0.0
A cholesteric liquid crystal polymer obtained by copolymerizing 88 mol and 0.010 mol of a component b monomer having an S-form chiral component is dissolved in cyclohexanone to prepare a liquid crystal solution, which is then applied to the alignment film by using a wire bar. Applied. Further, this was heated at 160 ° C. for 5 minutes and then cooled at room temperature to obtain a cholesteric liquid crystal solidified layer. The chemical formulas of the a-component monomer and the b-component monomer are as shown in the following (Chemical formula 1) and (Chemical formula 2), respectively.

[0049]

[Chemical 1]

[0050]

[Chemical 2]

Here, * in the above chemical formula indicates a chiral center, and the steric configuration of this portion is either the R configuration or the S configuration.

The cholesteric liquid crystal polymer obtained by copolymerizing the a-component monomer and the b-component monomer has a weight-average value obtained by copolymerizing the a-component monomer and the b-component monomer in the same bonding mode as the acrylic resin. It is a side chain type cholesteric liquid crystal polymer having a molecular weight of 80,000, a glass transition temperature of 180 ° C., and an isotropic phase transition temperature of 230 ° C.

The R configuration of the above configuration acts as a left circular polarizer, and the S configuration thereof acts as a right circular polarizer. The selective reflection center wavelength of each of these polarizers is
It can be easily adjusted by adding a slight amount of S-form to the R-form liquid crystal polymer.

A reflective circular polarizer having a cholesteric liquid crystal layer having the following characteristics was prepared by the method described above. Right circular polarizer: selective reflection center wavelength λc = 560 nm, bandwidth W = 120 nm Left circular polarizer: selective reflection center wavelength λc ′ = 600 nm, bandwidth W = 120 nm

Each of these circular polarizers was adhered via an acrylic adhesive with the cholesteric liquid crystal layers facing each other to form a bandpass filter. FIG. 5 shows the transmission spectrum of the bandpass filter according to this example.

(Example 2) By the same method as in Example 1, a reflective circular polarizer having a cholesteric liquid crystal layer having the following characteristics was prepared. Right circular polarizer 1: selective reflection center wavelength λc = 560 nm, bandwidth W = 120 nm Right circular polarizer 2: selective reflection center wavelength λc ′ = 600 nm,
Bandwidth W = 120nm

Further, a half-wave plate formed by stretching a polycarbonate resin is prepared, and the cholesteric liquid crystal layer side of each circular polarizer faces the half-wave plate.
Both polarizers were attached via an acrylic adhesive to prepare a bandpass filter. The bandpass filter according to the present example has a transmission spectrum substantially similar to that of the first example.

Example 3 A multilayer linear laminate of resins having birefringence and different refractive indexes was uniaxially stretched to prepare a reflective linear polarizer. More specifically, 30 layers of polyethylene naphthalate / polymethyl methacrylate are laminated and then uniaxially stretched (stretching conditions are adjusted so that the refractive index in the stretching direction is the same for polyethylene naphthalate and polymethyl methacrylate). A reflective linear polarizer was prepared.

By adjusting the stretching conditions and the laminating conditions by the method described above, the film thickness of each layer was changed to prepare two types of reflective linear polarizers having the following characteristics. Linear polarizer 1: Selective reflection center wavelength λc = 540 nm, bandwidth W = 70 nm Linear polarizer 2: Selective reflection center wavelength λc ′ = 570 nm,
Bandwidth W = 70nm

The two linear polarizers were made to have the optical axes orthogonal to each other (the stretching directions were orthogonal to each other), and both polarizers were adhered via an acrylic adhesive to prepare a bandpass filter. It was confirmed that the bandpass filter obtained by this example has a narrow selective reflection band of about 540 to 570 nm.

(Comparative Example 1) By the same method as in Example 1, a reflective circular polarizer having the following selective reflection central wavelength and the same bandwidth and having the following characteristics was prepared, and thereby a bandpass filter was prepared. Right circular polarizer: selective reflection center wavelength λc = 600 nm, bandwidth W = 120 nm Left circular polarizer: selective reflection center wavelength λc ′ = 600 nm, bandwidth W = 120 nm

FIG. 6 shows the transmission spectrum of the bandpass filter according to this comparative example.

Comparative Example 2 By the same method as in Example 1, a reflection type circular polarizer having the following characteristics was prepared, and a bandpass filter was prepared accordingly. Right circular polarizer: selective reflection center wavelength λc = 500 nm, bandwidth W = 120 nm Left circular polarizer: selective reflection center wavelength λc ′ = 650 nm, bandwidth W = 120 nm That is, the bandpass filter of this comparative example has the above-described formula. (1)
Is not satisfied.

(Evaluation) As shown in FIG. 5, the bandpass filter of Example 1 is a band where the selective reflection bands of the reflection type polarizers orthogonal to each other overlap, that is, only 60 nm.
It has been found that it has a high reflectance only in the narrow band, and is easy to manufacture and easily realizes the narrow band. On the other hand, with the bandpass filter of Comparative Example 1, only the bandpass filter having the same selective reflection band as the conventional one was obtained. Further, in the bandpass filter of Comparative Example 2,
Only the selective reflection band where the transmittance was about 50% widened, and only the same characteristics as those obtained by combining circular polarizers having the same chiral center in parallel relationship were obtained.

[0065]

As described above, according to the present invention, of the light incident on the bandpass filter, the first reflection type polarizer causes the selective reflection band of the polarizer (centered around the wavelength λc). Part of the light in the wavelength band of the bandwidth W) (polarized light that matches the polarizer) will be reflected. Further, of the light transmitted through the first reflective polarizer, the light of the selective reflection band (the wavelength band having a bandwidth W centered on the wavelength λc ′) of the polarizer is converted by the second reflective polarizer. A part (polarized light that matches the polarizer) will be reflected. here,
The first reflective polarizer and the second reflective polarizer are arranged so as to be substantially orthogonal to each other.
Therefore, regarding the light in the band where the selective reflection band of the first reflective polarizer and the selective reflection band of the second reflective polarizer overlap, whether the light incident on the bandpass filter is natural light or polarized light Regardless of whether or not, all will be reflected. According to the present invention, the selective reflection center wavelength λc ′ of the second reflective polarizer is (λc−W) <λc ′ <(λc
+ W) ... (1) and λc ≠ λc ′ ... (2)
By satisfying the condition (1) and (2), an overlapping band is always generated, and by adjusting the selective reflection center wavelength λc ′ within a range that satisfies the expressions (1) and (2), the overlapping band, that is, a bandpass filter It is possible to easily narrow the selective reflection band of.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view showing a schematic configuration of a surface light source device including a bandpass filter according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating a function of the bandpass filter illustrated in FIG.

FIG. 3 is a vertical cross-sectional view showing a schematic configuration of a surface light source device including a bandpass filter according to a second embodiment of the present invention.

FIG. 4 is a vertical cross-sectional view showing a schematic configuration of a surface light source device including a bandpass filter according to a third embodiment of the present invention.

FIG. 5 shows a transmission spectrum of the bandpass filter according to the first embodiment of the present invention.

FIG. 6 shows a transmission spectrum of a bandpass filter according to Comparative Example 1 of the present invention.

FIG. 7 shows an emission spectrum of a general CCFL backlight.

[Explanation of symbols]

1, 3, 5 ... Surface light source 2, 4, 6 ... Band filter 10, 20, 30 ... Surface light source device 21, 41, 61 ... First reflective polarizer 22, 42, 62 ... Second reflective polarized light Child 43 ... 1/2 wave plate

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G02F 1/1335 520 G02F 1/1335 520 1/13357 1/13357 1/139 1/139 F term (reference) 2H048 FA04 FA15 FA22 2H049 BA03 BA05 BA06 BA42 BB03 BC22 2H088 GA03 HA03 HA11 HA18 HA21 HA28 JA09 KA05 MA20 2H091 FA01Z FA07Z FA14Z FA41Z FA44Z FA45Z FC22 GA06 HA07 LA30

Claims (5)

[Claims] 1. A selective reflection center wavelength λc and a wavelength bandwidth W
And a first reflection-type polarizer having a selective reflection property, and the first reflection-type polarizer and the first reflection-type polarizer are arranged so as to be substantially orthogonal to each other, and have a selective reflection center wavelength λ.
c ′ and a second reflective polarizer having selective reflectivity with a wavelength bandwidth W, and the selective reflection center wavelength λc ′ of the second reflective polarizer is
A bandpass filter satisfying the following expressions (1) and (2). (Λc−W) <λc ′ <(λc + W) (1) λc ≠ λc ′ (2) 2. The first and second reflective polarizers are each formed of a cholesteric liquid crystal layer that selectively reflects right circularly polarized light and the other selectively reflects left circularly polarized light. The bandpass filter according to claim 1. 3. The first and second reflective polarizers are formed by a cholesteric liquid crystal layer having a turning property in the same direction, and are arranged between the first and second reflective polarizers. Done 1 /
The bandpass filter according to claim 1, further comprising a two-wave plate. 4. The first and second reflective polarizers are formed respectively by uniaxially stretching after laminating resins having birefringence and having different refractive indexes, respectively. The band-pass filter according to claim 1, wherein the two reflective polarizers are arranged so that their respective stretching directions are substantially orthogonal to each other. 5. A surface light source, comprising: a surface light source that emits light in a planar shape; and the bandpass filter according to any one of claims 1 to 4, which is disposed on the light emitting surface side of the surface light source. apparatus.