JP2006126557A - Polarizing and splitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarized light separating element which has as much a simple structure, as possible, while having small number of layers and further has high polarization and splitting effects. <P>SOLUTION: A single layer or multi layers of a thin film is deposited on a prism substrate of prism structure, having a groove of cross-sectional triangle shape. Then prism substrates manufactured on the same conditions are stuck together via a UV curing resin. Thereby the polarization and splitting element can have high polarization and splitting effects with few number of times of film-deposition, and consequently simplification of a manufacturing process is realized without lowering the optical characteristics. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polarization separation element that selectively transmits predetermined polarized light and selectively reflects other polarized light.

  Liquid crystal displays (LCDs) have lower power consumption and are smaller and thinner than CRTs (Cathode Ray Tubes) and are now available from small devices such as mobile phones, digital cameras, and PDAs. Various sizes are widely used, ranging from large-sized LCD TVs.

  The LCD device mainly includes a liquid crystal panel in which liquid crystal is sandwiched between glass plates, a polarizing plate, and a backlight device. Since the liquid crystal itself does not emit light like the fluorescent material of the cathode ray tube, it is necessary to provide a light source in the LCD device.

  FIG. 1 schematically shows an example of the configuration of the LCD device. As shown in FIG. 1A, in the case of a large display of 18 inches or more, a so-called direct type configuration is adopted in which a plurality of light sources 7 are installed directly below the liquid crystal panel 1 and a reflection plate 4 is provided to brighten the entire screen. . However, when this configuration is used, the apparatus becomes thick, so that it is not suitable for a notebook computer or a small liquid crystal television. Therefore, as shown in FIG. 1B, in the case of a small LCD device, an edge light type in which a light source 7 is placed beside the liquid crystal panel 1 and a light guide plate 5 and a reflection sheet 6 are used together is adopted.

  Regardless of which configuration is used, the optical film 2 is used to make the light 8 from the light source 7 uniform and improve the luminance.

  This optical film has a structure as shown in Patent Document 1 below, for example. FIG. 2 shows the structure of the optical film described in Patent Document 1.

JP 2004-78234 A

  In Patent Document 1, the prism surface of the substrate 11 having a prism structure with a right apex angle and the prism surface of the substrate 12 having the same structure as the substrate 11 are opposed to each other so that the peaks and valleys thereof coincide with each other. To place. A plurality of dielectric films are laminated in advance on the plane forming the oblique side of the prism structure surface of the substrate 11. Furthermore, an optical film is produced by bonding the substrate 11 and the substrate 12 on which the dielectric film is formed via the adhesive layer 15. The dielectric film is composed of a high refractive index material 13 and a low refractive index material 14 and is laminated in order.

  In the embodiment described in Patent Document 1, 28 layers of high refractive index material and low refractive index material are alternately laminated, and these dielectric films are formed by vapor deposition or sputtering.

  The optical film as described above transmits P-polarized light and reflects S-polarized light among incident light at the interface of the dielectric film. However, since the reflection coefficient of S-polarized light is not 1, some of the light passes through the interface of the dielectric film.

  The P-polarized light selectively transmitted by the optical film goes straight to the liquid crystal panel side and brightens the LCD device. However, since the S-polarized light transmitted to the substrate 12 side is not used effectively, the light intensity is lost, and the luminance is reduced.

  Therefore, the S-polarized light is returned to the substrate 11 side (backlight side), and the light is again directed toward the liquid crystal panel to be separated by polarization, and the P-polarized light is transmitted. By repeating this, the luminance can be improved.

  Further, by increasing the polarization separation effect by laminating dielectric films, S-polarized light can be reused efficiently. Since polarization separation occurs at the interface of the dielectric film, the polarization separation effect increases as the number of dielectric films between the substrates increases. Therefore, in order to improve the reflectance of S-polarized light, an optical film is produced by laminating multiple dielectric films.

  In the LCD device, the power consumption of the backlight greatly affects the life of the LCD device. For example, in a large-sized liquid crystal television, 90% or more of it is the power consumption of the backlight. For this reason, not only lowering the power consumption of the backlight itself, but also improving the performance of the optical film to prevent a decrease in luminance, not only lowering the power consumption but also extending the life of the LCD device. .

  In order to obtain a polarization separation effect in a wide band using a structure in which a high refractive index material and a low refractive index material are repeatedly laminated as described in Patent Document 1 described above, several types of laminated dielectric films are combined. It is necessary and the number of layers reaches several tens of layers. When such a dielectric film is formed by a vacuum deposition method, it is difficult to control the film thickness and film quality.

  For example, as the number of layers increases, the shape of the prism apex portion and the valley bottom portion is lost. Further, since the film is formed on the inclined surface, problems such as a film thickness shift and a shift of the apex and valley positions are likely to occur. For these reasons, the polarization separation effect is reduced.

  Further, when the reactive sputtering method is used, the rate is 10 to 50 nm. Since it was slow at m / min, there was a problem in productivity.

  Therefore, not only from the aspect of optical characteristics but also from the viewpoint of production process, a polarization separation element (optical film) having a small number of layers and a structure as simple as possible is required.

  Therefore, an object of the present invention is to provide a polarization separation element having a small number of layers, a structure as simple as possible, and having a high polarization separation effect.

  In order to solve the above-mentioned problems, according to a first aspect of the present invention, there is provided a first prism substrate and a second prism substrate having a structure surface in which a groove having a triangular cross section formed with a dielectric film layer is continuously formed. The polarization separating element is characterized in that the respective crests and troughs face each other so that they coincide with each other, and an adhesive transparent resin is disposed and bonded between the first and second prism substrates.

  According to the present invention, it is possible to have a high polarization separation effect with a small number of film formation layers. For example, by forming and attaching three layers of dielectric films on the prism substrate, the upper and lower three layers and the adhesive layer can be combined to obtain a seven-layer dielectric film effect.

  Since the polarization separation element manufactured using this method requires half the number of times of forming the dielectric film, compared with the polarization separation element manufactured by the conventional method, the film formation accuracy of the dielectric film is increased. Therefore, the manufacturing process can be simplified without degrading the optical characteristics.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 3 is a cross-sectional view showing a configuration of a polarization beam splitting element manufactured by applying the present invention. This polarization separating element is constituted by a prism substrate denoted by reference numeral 21, a prism substrate denoted by reference numeral 22, and a dielectric multilayer film denoted by reference numeral 23.

  The prism substrate 21 has a prism structure with a groove having a triangular cross section, and is manufactured by injection molding or pressing a transparent resin. The prism substrate 22 is also made of the same transparent resin as the prism substrate 21.

  The prism substrates 21 and 22 are made of a transparent resin material that can transmit incident light from the backlight device. As a material for the prism substrate, a transparent resin having a relatively high refractive index is suitable, and a transparent material having a refractive index of about 1.5 to 1.9 such as polycarbonate (PC, n = 1.59), an acrylic resin, and an epoxy resin. Any resin can be used.

  The dielectric multilayer film 23 is formed on the prism structure surfaces of the prism substrate 21 and the prism substrate 22, and is formed of a dielectric film 23a made of a material having a higher refractive index than the other (hereinafter referred to as H as appropriate) A dielectric film 23b made of a material having a low rate (hereinafter referred to as L as appropriate) is laminated in three layers in the order of [HLH].

  As described above, the prism substrate 21 having the dielectric multilayer film 23 formed on the prism structure surface and the prism substrate 22 are arranged so that the respective prism structure surfaces face each other. And the prism substrate 22 are bonded so that the triangular cross-sectional valleys coincide with each other, whereby a polarization separation element is manufactured. The substrates are bonded by applying an ultraviolet curable resin to the bonding surface to form an adhesive layer 24 and irradiating with ultraviolet rays to cure.

  When the dielectric film has a three-layer structure of [HLH], any refractive index of the resin material used for the adhesive layer can be used. However, when a material having a refractive index close to that of the dielectric film of a high refractive index material is used as the adhesive layer, the structure of the dielectric multilayer film is [HLHHHHLH]. Yes. In this case, polarization separation hardly occurs in the inner three layers (high refractive index material dielectric film-adhesion layer-high refractive index material dielectric film), and substantially [H-L-H-L- H] is considered to be the same as the five-layer structure.

  For this reason, it is more preferable to use a low refractive index material for the adhesive layer. Adhesives include UV curable acrylate resin (refractive index 1.50 to 1.51), UV curable epoxy resin (refractive index 1.46 to 1.57), UV curable fluorine adhesive (refractive index). In addition to an amorphous fluororesin or the like (refractive index of 1.34), a thermosetting epoxy-based or isocyanate-based adhesive can be used. Fluorine or the like may be added to control the refractive index. The refractive index should be relatively low, about 1.3, and the transmittance is desirably 95% or more.

  When this method is used, a low refractive index UV curable resin is thinly applied and bonded between the adhesive surfaces made of a dielectric film of a high refractive index material. It functions as a part of the body membrane layer. That is, an optical effect can be obtained by providing a difference in refractive index.

  On the other hand, in the optical film described in Patent Document 1, an adhesive is used to bond a prism substrate having a dielectric film formed in multiple layers and another prism substrate. Patent Document 1 describes that the refractive index of the adhesive used in the optical film should be matched as close as possible to the refractive index of the upper or lower prism substrate. That is, the adhesive does not give a polarization separation effect, and is optically configured to behave as a part of the substrate.

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

  A transparent resin having a refractive index of 1.71 is made of a prism surface having a prism vertical section of 90 °, a prism height of 25 μm, a prism pitch of 50 μm and a right-angled isosceles triangle, and the substrate is 10 mm long and 10 mm wide. A prism substrate is manufactured by injection molding so as to be a square.

A dielectric multilayer film is formed on the manufactured prism substrate. The dielectric multilayer film includes Nb ₂ O ₅ having a refractive index of 2.3 and SiO ₂ having a refractive index of 1.5 by Nb ₂ O ₅ —SiO ₂ —Nb ₂ O ₅ by reactive sputtering. It is manufactured by alternately laminating in the order of [HLH].

  Next, an adhesive is applied onto the prism substrate on which the dielectric multilayer film is formed, and the prism substrates are bonded together. After thinly applying an ultraviolet curable resin having a refractive index of 1.38, the ultraviolet curable resin surface is opposed to the prism surface of the prism substrate on which another dielectric film is formed so that the peaks and valleys coincide. And apply a load of 0.05N. Thereafter, the adhesive layer was cured by irradiating with ultraviolet rays for 20 seconds to produce a polarization separation element.

  The polarized light separating element transmits the P-polarized light as much as possible and reflects the S-polarized light as much as possible, thereby reducing the amount of light emitted from the backlight. That is, the reflectance of P-polarized light is required to be close to 0%, and the reflectance of S-polarized light is required to be close to 100%. Even though the P-polarized light is reflected, it is reused. However, if the S-polarized light is transmitted, it causes a decrease in luminance. Therefore, it is particularly important to improve the reflectance of the S-polarized light.

  By the above-described method, polarization separation elements of the following examples and comparative examples are manufactured.

<Example 1>
The polarization separating element A is formed by forming a three-layer dielectric film on a prism substrate and bonding the prism surfaces of the prism substrate through an adhesive layer, and the thickness of the dielectric film is asymmetric with the adhesive layer as the center. It is configured as follows. In addition, the dielectric multilayer film formed on the prism surface is formed by forming a high refractive index material Nb ₂ O ₅ on the prism substrate, and then applying a low refractive index SiO ₂ and a high refractive index material Nb ₂ O ₅ . By forming a film, a high refractive index material, a low refractive index material, and a high refractive index material ([H-L-H]) are formed from the prism substrate side, and the adhesive layer is similar to the polarization separation elements A and B. An ultraviolet curable resin having a refractive index of 1.38 is used. The entire structure of the polarized light separating element A is [HLHHLHLH]. Table 1 below shows the dielectric film material of the polarization separating element A and its thickness.

<Example 2>
The polarization separating element B is formed by forming a three-layer dielectric film on a prism substrate, and bonding the prism surfaces of the prism substrate through an adhesive layer, and the thickness of the dielectric film is symmetrical about the adhesive layer. The configuration is the same as that of the first embodiment except for the above configuration. The entire structure of the polarization separation element B is [HLHHLHLH]. Table 2 below shows the dielectric film material of the polarization separation element B and its thickness.

<Example 3>
The polarization separation element C is formed by forming a three-layer dielectric film on a prism substrate, and bonding the prism surfaces of the prism substrate through an adhesive layer, and the dielectric film material and its thickness are the polarization separation of the second embodiment. Although it is the same as that of the element B, the thing with a refractive index of 1.6 is used for the ultraviolet curable resin for adhesion | attachment. The entire structure of the polarization separating element C is [HLHHLHLH]. Table 3 below shows the dielectric film material of the polarization separation element C and its thickness.

<Example 4>
The polarization separation element D is formed by forming a two-layer dielectric film on a prism substrate, and bonding the prism surfaces of the prism substrate through an adhesive layer, and the thickness of the dielectric film is symmetrical about the adhesive layer. It is configured as follows. In addition, the dielectric multilayer film formed on the prism surface is formed by depositing low refractive index SiO ₂ on the prism substrate, and then forming high refractive index material Nb ₂ O ₅ , so that the outside is low refractive. The refractive index material, the inner side being a high refractive index material ([LH]), and the adhesive layer is made of an ultraviolet curable resin having a refractive index of 1.38 similar to that of the polarization separation elements A and B. The entire structure of the polarization separation element D is [LHLHHL]. Table 4 below shows the dielectric film material of the polarization separation element D and its thickness.

<Comparative Example 1>
The polarization separation element E has a structure having a five-layer dielectric film manufactured by a conventionally known method. Table 1 below shows the dielectric film material of the polarization separation element B and its thickness.

  Table 6 below shows the reflectance of the P-polarized light and the S-polarized light when the polarization separation elements of Examples 1 to 4 and Comparative Example 1 produced in this way were used. Measurement is performed for each of the three primary colors of light, red R (650 nm), green G (550 nm), and blue B (450 nm), and the incident angle is 0 ° and 5 ° for each example and comparative example. The reflectance of was measured.

  From the measurement results shown in Table 6, when the incident angle of the polarization separation element of the comparative example is set to 5 °, the S-polarized reflectance is rapidly decreased on the short wavelength side, whereas the polarization separation film of each example is A broadband and stable reflectance can be obtained.

  The polarization separation film D has a low-refractive-index material on the outside and has a five-layer structure including two dielectric films and an adhesive layer. The entire structure is compared with a seven-layer structure (three layers above and below the dielectric film + adhesive layer). Although the typical reflectance is lowered, the manufacturing process is further shortened while maintaining a stable reflectance in a wide band.

[Evaluation]
The polarization separation characteristics of the polarization separation elements of Examples 1 to 4 and Comparative Example 1 described above were measured. In the measurement, the polarization separation element and the polarizing plate of each example are mounted on the white backlight unit, and the in-plane peak luminance is measured by rotating the spectrophotometer (V-500, manufactured by JASCO Corporation) by 180 °. . The luminance of the polarization separation element in each Example and Comparative Example calculated with the luminance when the polarization separation element was not used as 1 was defined as the luminance improvement rate.

[Evaluation results]
The brightness improvement rate of each example is as follows.

Example 1 1.7 times Example 2 1.6 times Example 3 1.5 times Example 4 1.4 times Comparative Example 1 1.2 times

  As described above, the polarization separation element A manufactured in Example 1 can have a wider band while having the same thickness as the polarization separation element E having a conventional five-layer structure. Further, there is little wavelength dispersion due to the incident angle, and high polarization separation characteristics can be maintained in the visible light region.

  In addition, the polarization separating element B of Example 2 can simplify the manufacturing process by bonding two prism substrates fabricated under the same conditions, and can achieve substantially the same polarization separation as the polarization separating element A. Has characteristics.

  The polarization separation element C of Example 3 is somewhat difficult to obtain a polarization separation effect because the refractive index of the adhesive layer is higher than that of the polarization separation element B, but a sufficiently stable polarization separation characteristic is obtained in a wide band, Since the two prism substrates manufactured under the same conditions are bonded together, the manufacturing process can be simplified.

  Since the polarization separation element D of Example 4 has two dielectric films formed on the prism substrate, the polarization separation effect is somewhat difficult to obtain compared to the polarization molecular elements A, B, and C. Since the film has two layers, the manufacturing process can be simplified.

  The embodiment of the present invention has been specifically described above, but the present invention is not limited to the above-described embodiment, and various modifications based on the technical idea of the present invention are possible.

  For example, a polarization separation element having a three-layer dielectric multilayer film in which a prism substrate having a single-layer dielectric film formed thereon is bonded via an adhesive layer may be used. When this polarized light separating element is used, the manufacturing process can be further shortened.

  Further, the number of dielectric films is not limited to an odd number, and may be a structure having an even number of dielectric films. For example, a polarization separation element having three layers of dielectric films on one prism substrate and two layers of dielectric films on the other prism substrate and a six-layer dielectric multilayer film together with an adhesive layer may be used. Also in this case, care must be taken so that a structure in which a high refractive index material and a low refractive index material are alternately laminated is obtained.

  Furthermore, the numerical values given in the above-described embodiment are merely examples, and different numerical values may be used as necessary.

  The polarization separation element as described above is effective in using more light from the backlight device more efficiently and improving the luminance in the LCD device, such as a liquid crystal television, a digital camera, a mobile phone, a PDA, etc. Used in liquid crystal display devices.

  By using the polarization separation element to which the present invention is applied, the power consumption of the backlight device can be reduced, leading to a longer life of the LCD device.

It is a basic diagram which shows an example of a structure of LCD apparatus. It is a basic diagram which shows an example of the polarization separation element produced with the conventional method. It is sectional drawing which shows the structure of the polarization splitting element to which this invention is applied. It is a basic diagram which shows one Example to which this invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Liquid crystal panel 2 ... Optical film 3 ... Diffusing plate 7 ... Light source 11 ... Prism substrate 12 ... Prism substrate 13 ... High refractive index material 14 ... Low refractive index Material 15: Adhesive layer 21 ... Prism substrate 22 ... Prism substrate 23 ... Dielectric multilayer film 23a ... High refractive index material 23b ... Low refractive index material 24 ... Adhesive layer

Claims (9)

The first and second prism substrates having a structure surface in which a groove having a triangular cross section formed with a dielectric film layer is continuously formed are opposed to each other so that their crests and troughs coincide with each other,
A polarization separating element, wherein an adhesive transparent resin is disposed and bonded between the first and second prism substrates.   2. The polarization separation element according to claim 1, wherein the first and second dielectric film layers formed on the first and second prism substrates have substantially the same structure.   3. The polarization separation element according to claim 2, wherein each of the first and second dielectric film layers is formed by laminating the same material in the same order.   3. The polarization separation element according to claim 2, wherein each of the first and second dielectric film layers is formed by laminating the same material with the same thickness in the same order.   The polarization separation element according to claim 2, wherein the first and second dielectric film layers are formed by forming one or more thin films. The dielectric film layer is made of a high refractive index material and a low refractive index material,
6. The polarization separation element according to claim 5, wherein a high refractive index material and a low refractive index material are alternately formed on the prism substrate.   The polarization separation element according to claim 1, wherein the refractive index of the adhesive layer has a difference of 0.2 or more from the refractive index of the dielectric film on the adhesive surface.   The polarization separation element according to claim 7, wherein the adhesive layer is made of a material having a lower refractive index than the dielectric film on the adhesive surface.   The polarization separation element according to claim 6, wherein the adhesive layer has a refractive index of 1.7 or less.

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