JP2005049586A - Optical element, condensing backlight system, and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element capable of condensing and collimating incident light from a light source by arranging a specific phase difference layer between circular polarization type reflecting polarizers, and capable of suppressing transmission of incident light at a large angle to the normal direction, improving the front brightness, and reducing coloring. <P>SOLUTION: The optical element characterized in that at least three sheets of circular polarized light type reflection polarizers (a) in which the selectively reflected wavelength bands of polarized light are overlapping with each other; at least in one interlayer between the circular polarization type reflecting polarizer (a) and the circular polarization type reflecting polarizer (a), a layer (b) having an almost zero front phase difference (normal direction)but having a λ/8 or larger phase difference to incident light tilted by 30° or more to the normal direction is interlayed; and at least in one interlayer between the other circular polarization type reflecting polarizer (a) and the circular polarization type reflecting polarizer (a), they are laminated without interlaying a phase difference layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical element using a circularly polarized reflective polarizer. The present invention also relates to a condensing backlight system using the optical element, and further to a liquid crystal display device using the same.

  Conventionally, from the viewpoint of improving the visibility of a liquid crystal display device, in order to efficiently enter the light emitted from the light source into the liquid crystal display device, etc., a condensing element with a surface shape such as a prism sheet or a lens array sheet In general, a technique for condensing outgoing light in the front direction and improving luminance is used.

  However, in the case of condensing light using a condensing element having these surface shapes, a large difference in refractive index is necessary in principle, so that it is necessary to install it through an air layer. For this reason, there have been problems such as an increase in the number of parts, light loss due to unnecessary scattering, and surface contamination and contamination of foreign matters in the installation gap are easily visible.

  As a technique for improving the emission luminance of polarized light, an illumination system has been proposed in which a reflective layer is provided on the lower surface of the light guide plate and a reflective polarizer is provided on the emission surface side. The reflective polarizer here has a function of separating the light component of incident natural light into transmitted polarized light and reflected polarized light according to the polarization state.

  If a retardation plate controlled so that the phase difference value in the normal incidence direction and the phase difference value in the oblique incidence direction are specifically different is inserted between the polarizers, the angular distribution of transmitted light is restricted, and the absorption polarizer It is described that light is transmitted only in the vicinity of the front and that all of the peripheral light is absorbed (for example, see Patent Document 1 and Patent Document 2). If a reflective polarizer is used as the polarizer, light rays are transmitted only near the front surface and all peripheral light rays are reflected. If such a theory is used, it is possible to condense and collimate the light beam emitted from the backlight without causing absorption loss.

In a condensing system using such a reflective polarizer, the thin film layer that generates parallel light is several tens to several hundreds μm including the reflective polarizer, and is extremely thin compared to prism arrays and lens array sheets. Is easy to design. Moreover, since an air interface is not required, it can be used by being bonded together, which is advantageous in terms of handling. For example, a cholesteric liquid crystal polymer (thickness of about 10 μm) is used as a reflective polarizer, and a retardation film to be combined is also a liquid crystal polymer coating thin film (thickness of about 5 μm) and laminated with an adhesive layer (thickness of about 5 μm). For example, the film thickness can be reduced to 50 μm or less. If each layer is directly coated and produced so that the interface is eliminated, the layer can be further thinned.
Japanese Patent No. 2561483 Japanese Patent Laid-Open No. 10-321025

  The mechanism of simultaneous expression of light condensing property and luminance improvement using the reflective polarizer will be described below with an ideal model.

  Natural light emitted from the light source is separated into transmitted polarized light and reflected polarized light by the first reflective polarizer. Then, the transmitted polarized light has a phase difference of λ / 8 or more with respect to incident light having an incident front phase difference (normal direction) of substantially zero and incident with an inclination of 30 ° or more with respect to the normal direction. By the layer (hereinafter also referred to as C plate), light having an angle near the normal direction of the transmitted polarized light is transmitted as it is because it is polarized light transmitted by the second reflective polarizer. At an angle inclined from the normal direction, the polarization state changes due to the phase difference, and the polarization component reflected by the second reflective polarizer increases and is reflected. In particular, the light is effectively reflected when the phase difference is about λ / 2. The reflected polarized light undergoes a phase difference again and changes its polarization state to become polarized light that passes through the first reflective polarizer. Therefore, the first reflected polarized light is transmitted and returned to the light source unit. The light reflected by the first reflective polarizer and the light reflected by the second reflective polarizer are depolarized and bent in the direction of light by a diffuse reflector provided under the light source. A part of the returned light is repeatedly reflected until it becomes polarized light transmitted by the reflective polarizer in the vicinity of the normal direction, thereby contributing to improvement in luminance.

  When the circularly polarized light separation by the planar structure of the cholesteric liquid crystal phase is used as the reflective polarizer, the polarization conversion is performed by the C plate regardless of the azimuth angle. When the phase difference of the C plate with respect to the obliquely incident light is about λ / 2, the circularly polarized light is just opposite to the incident light.

  In the case where the C plate is a retardation layer that converts incident light incident at an angle of 30 ° with respect to the normal direction into reverse circularly polarized light, the transmitted light is substantially concentrated in a range of about ± 15 to 20 °. . However, only light incident at a specific angle receives the phase difference of λ / 2. Above or below this angle, the circularly polarized light is not completely opposite to the incident light. For this reason, when the light is condensed to this extent, the light incident at 50 ° or more with respect to the normal direction receives a phase difference of λ / 2 or more, and thus is not completely circularly polarized light opposite to the incident light, It becomes partially circularly polarized light and part of it is transmitted without being reflected. In particular, the more light is collected and collimated in the normal direction, the greater the amount of transmitted light that is incident at a larger angle with respect to the normal direction, and the front brightness is significantly reduced. When the viewing angle was greatly reduced, the coloring increased.

  For example, when the incident light is designed to be condensed and collimated at an angle within 30 ° with respect to the normal direction, most of the light incident at an angle of 50 ° or more with respect to the normal direction is Transmits without being reflected. For this reason, there has been a problem that the light reuse rate decreases, the luminance in the normal direction decreases, and coloring occurs when the viewing angle is greatly tilted with respect to the normal direction by the transmitted light.

  The present invention is an optical element in which a layer having a specific phase difference is arranged between circularly polarizing reflective polarizers, and incident light from a light source can be collected and collimated, and has a large angle with respect to the normal direction. It is an object of the present invention to provide an optical element that can suppress the transmission of light incident on the light source, improve the front luminance, and reduce coloring.

  Another object of the present invention is to provide a condensing backlight system using the optical element, and further to provide a liquid crystal display device.

  As a result of intensive studies to solve the above problems, the present inventors have found the following optical elements and have completed the present invention. That is, the present invention is as follows.

1. At least three circularly polarized reflective polarizers (a) in which the wavelength bands of selective reflection of polarized light overlap each other are laminated,
Between at least one layer of the circularly polarized reflective polarizer (a) and the circularly polarized reflective polarizer (a), the front phase difference (normal direction) is almost zero and tilted by 30 ° or more with respect to the normal direction. A layer (b) having a phase difference of λ / 8 or more with respect to the incident light incident thereon, and another circularly polarized reflective polarizer (a) and a circularly polarized reflective polarizer (a) An optical element characterized in that at least one of the layers is laminated without a retardation layer.

  2. Circularly polarized reflective polarizer (a) / retardation layer (b) / circularly polarized reflective polarizer (a) / circularly polarized reflective polarizer (a) are laminated in this order. 2. The optical element according to 1 above.

3. The circularly polarized reflective polarizer (a) / retardation layer (b) / circularly polarized reflective polarizer (a) / circularly polarized reflective polarizer (a) are stacked in the order of arrangement from the light source side. ,
The incident light incident at an angle of 30 ° or more with respect to the normal direction is polarized and separated from the light source by the first circular polarization type reflective polarizer (a), and then the first circular polarization type from the light source side. Sum of phase differences received before polarization separation by the reflective polarizer (a), the retardation layer (b), and the second circular polarization type reflective polarizer (a), or the first circular polarization type from the light source After being polarized and separated by the reflective polarizer (a), the first circularly polarized reflective polarizer (a), the retardation layer (b), and the second circularly polarized reflective polarizer (a) from the light source side. And the sum of the phase differences received by the third circularly polarized reflective polarizer (a) before being polarized and separated is λ / 4 + λ · n to 3λ / 4 + λ · n (where n is an integer of 0 or more). Adjusted to be, and
The incident light incident at an angle of 60 ° with respect to the normal direction is polarized and separated from the light source by the first circular polarization type reflective polarizer (a), and then the first circular polarization type reflection from the light source side. Sum of phase differences received before polarization separation by the polarizer (a), the retardation layer (b) and the second circularly polarized reflective polarizer (a), or the first circularly polarized reflection from the light source After being polarized and separated by the polarizer (a), the first circularly polarized reflective polarizer (a), the retardation layer (b), the second circularly polarized reflective polarizer (a), and The sum of the phase differences received before the third circularly polarized reflective polarizer (a) undergoes polarization separation is λ / 4 + λ · n to 3λ / 4 + λ · n (where n is an integer greater than or equal to 0). 2. The optical element according to 1 above, which is adjusted as described above.

4). The circularly polarized reflective polarizer (a) / circularly polarized reflective polarizer (a) / retardation layer (b) / circularly polarized reflective polarizer (a) are stacked in the order from the light source side. ,
The incident light incident at an angle of 30 ° or more with respect to the normal direction is polarized and separated from the light source by the first circular polarization type reflective polarizer (a), and then the first circular polarization type from the light source side. The sum of the phase differences received before the polarized light is separated by the reflective polarizer (a) and the second circularly polarized reflective polarizer (a), or the first circularly polarized reflective polarizer (a) from the light source After the polarization separation, the first circularly polarized reflective polarizer (a), the second circularly polarized reflective polarizer (a), the retardation layer (b) and the third circularly polarized light from the light source side. Is adjusted so that the sum of the phase differences received before polarization separation by the type reflective polarizer (a) is λ / 4 + λ · n to 3λ / 4 + λ · n (where n is an integer of 0 or more). ,And,
The incident light incident at an angle of 60 ° with respect to the normal direction is polarized and separated from the light source by the first circular polarization type reflective polarizer (a), and then the first circular polarization type reflection from the light source side. The sum of the phase difference received before the light is separated by the polarizer (a) and the second circularly polarized reflective polarizer (a), or polarized by the first circularly polarized reflective polarizer (a) from the light source After being separated, the first circularly polarizing reflective polarizer (a), the second circularly polarizing reflective polarizer (a), the retardation layer (b), and the third circularly polarizing type from the light source side. The sum of the phase differences received before the polarized light is separated by the reflective polarizer (a) is adjusted to be λ / 4 + λ · n to 3λ / 4 + λ · n (where n is an integer of 0 or more). 2. The optical element as described in 1 above.

  5. 5. The optical element according to any one of 1 to 4 above, wherein the selective reflection wavelengths of at least three circularly polarized reflective polarizers (a) overlap each other in a wavelength range of 550 nm ± 10 nm.

  6). 6. The optical element as described in any one of 1 to 5 above, wherein a cholesteric liquid crystal material is used as the circularly polarized reflective polarizer (a).

7. The retardation layer (b)
Fixed planar orientation of cholesteric liquid crystal phase having selective reflection wavelength region other than visible light region,
A fixed liquid crystal in a homeotropic alignment state;
A fixed discotic liquid crystal nematic phase or columnar phase alignment state,
A biaxially oriented polymer film,
An inorganic layered compound having negative uniaxiality and oriented and fixed so that the optical axis is in the normal direction of the surface, and
A film obtained from at least one polymer selected from the group consisting of polyamide, polyimide, polyester, poly (ether ketone), poly (amide-imide) and poly (ester-imide);
7. The optical element as described in any one of 1 to 6 above, which is at least one selected from the group consisting of:

  8). A λ / 4 plate is disposed on the circularly polarizing reflective polarizer (a) disposed on the viewing side (liquid crystal cell side) so that the transmitted light from the light source side becomes linearly polarized light. The optical element in any one of 1-7.

  9. 9. The polarizing plate is arranged on the λ / 4 plate side so that the axial direction of linearly polarized light obtained by transmission from the light source side is aligned with the transmission axis direction of the polarizing plate. Optical element.

  10. 10. The optical element according to any one of 1 to 9 above, wherein each layer is laminated using a light-transmitting adhesive or pressure-sensitive adhesive.

  11. A condensing backlight system, wherein at least a light source is disposed on the optical element according to any one of 1 to 10 above.

  12 12. A liquid crystal display device comprising at least a liquid crystal cell in the condensing backlight system according to 11 above.

  13. 13. A liquid crystal display device comprising the liquid crystal display device as described in 12 above, wherein a diffusion plate having no backscattering or depolarization is laminated on the liquid crystal cell viewing side.

  In the optical element of the present invention, at least three circularly polarized reflective polarizers (a) in which the wavelength bands of selective reflection of polarized light overlap each other are laminated. Between at least one layer of the circularly polarized reflective polarizer (a) and the circularly polarized reflective polarizer (a), the front phase difference is substantially zero and for obliquely incident light of various angles. And a phase difference layer (b) exhibiting a specific phase difference value is disposed, and at least one layer of the other circularly polarized reflective polarizer (a) and the circularly polarized reflective polarizer (a) is disposed between It is laminated without interposing a retardation layer.

  Such an optical element can totally reflect a part of light obliquely transmitted through the incident-side circularly polarized reflective polarizer (a) at various angles by the outgoing-side circularly polarized reflective polarizer (a). It becomes possible. By this effect, it is possible to suppress the transmission of light incident at a large angle with respect to the normal direction, and to form a collimation system that can improve the front luminance and the degree of polarization to reduce coloring. it can. That is, the liquid crystal display device in which the optical element is arranged on a backlight light source that is condensed and collimated can use light rays only in a high-quality region near the front.

  The optical element of the present invention is a parallel light system that can be easily designed to be thin. In particular, the optical element of the present invention is advantageous for thinning because at least one layer of the circularly polarized reflective polarizer (a) and the circularly polarized reflective polarizer (a) is laminated without a retardation layer. It is. Further, the optical element of the present invention can be used by being bonded, and is advantageous in terms of handling. A viewing angle widening system can be constructed by combining a condensing backlight source using these optical elements and a diffuser plate that has little backscattering and does not cause depolarization.

  A condensing backlight system using the optical element thus obtained can easily obtain a light source having a higher degree of parallelism than conventional ones. In addition, since collimated light with reflected polarized light that has essentially no absorption loss can be obtained, the reflected non-parallel light component returns to the backlight side, and only the parallel light component is extracted by scattering reflection or the like. The recycling is repeated, and a substantially high transmittance and high light utilization efficiency can be obtained.

  The present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of an optical element (A) in which three layers of circularly polarized reflective polarizers (a) are laminated. The optical element (A) in FIG. 1 has a normal phase difference (normal direction) between the first and second circularly polarizing reflective polarizers (a) from the bottom, and is normal. A layer (b) having a phase difference of λ / 8 or more with respect to incident light inclined at an angle of 30 ° or more with respect to the direction is disposed. On the other hand, the first and second circularly polarizing reflective polarizers (a) from the top are stacked without interposing the retardation layer (b). In the optical element (A) of FIG. 1, the side of the circularly polarized reflective polarizer (a) on either side may be the light source side.

  FIGS. 2 and 3 are examples in which the λ / 4 plate (B) is arranged on the optical element (A) so that the transmitted light from the light source side is linearly polarized light. The λ / 4 plate (B) is disposed on the side of the circularly polarized reflective polarizer (a) disposed on the viewing side (liquid crystal cell side).

  The number of circularly polarized reflective polarizers (a) is not particularly limited as long as it is 3 or more. Similarly, even when there are four or more sheets, it is possible to reduce the omission in the oblique direction. However, since other problems such as an increase in defects due to cost, required film thickness, and a large number of layers are likely to occur, the circularly polarizing reflective polarizer (a) is preferably limited to 3 to 5 layers. Is good. In consideration of the thickness, even when four or more circularly polarized reflective polarizers (a) are used, it is preferable that the retardation layer (b) is one.

(Circularly polarized reflective polarizer (a))
As the circularly polarized reflective polarizer (a), for example, a cholesteric liquid crystal material is used. It is desirable that total reflection is achieved with respect to light having a wavelength near 550 nm, which has high visibility from the viewpoint of improving luminance, and the selective reflection wavelengths of the reflective polarizers overlap at least in the wavelength region of 550 nm ± 10 nm. It is desirable. In the reflective polarizer (a), the center wavelength of selective reflection is determined by λ = np (where n is the refractive index of the cholesteric material and p is the chiral pitch). For obliquely incident light, the selective reflection wavelength is blue-shifted. Therefore, it is preferable that the overlapping wavelength region is wider. Further, it is more desirable that the reflection wavelength bands overlap in the visible light all-wavelength region 380 nm to 780 nm from the viewpoint of coloring and the viewpoint of RGB corresponding to a liquid crystal display device or the like. From this point of view, the reflective polarizers may be in exactly the same combination, or one may have reflection at all visible light wavelengths and the other may partially reflect.

  When the circularly polarized reflective polarizer (a) is a cholesteric material, the same concept can be used for different types (right-handed and left-handed), and if the front phase difference is tilted by λ / 2, the phase difference is zero or λ. A similar polarizer can be obtained, but this is not preferable because problems such as anisotropy and coloring due to the azimuth angle of the inclined axis occur. From such a viewpoint, combinations of the same types (right twists and left twists) are preferable.

  In the present invention, a suitable cholesteric liquid crystal constituting the circularly polarized reflective polarizer (a) may be used without any particular limitation. For example, a liquid crystal polymer exhibiting cholesteric liquid crystallinity at high temperature, a polymerizable liquid crystal obtained by polymerizing a liquid crystal monomer, and optionally a chiral agent and an alignment aid by irradiation with ionizing radiation such as an electron beam or ultraviolet light, or heat, A mixture etc. are mention | raise | lifted. The liquid crystallinity may be either lyotropic or thermotropic, but is preferably a thermotropic liquid crystal from the viewpoint of ease of control and ease of formation of a monodomain.

  The cholesteric liquid crystal layer can be formed by a method according to a conventional alignment process. For example, rayon is formed by forming a film of polyimide, polyvinyl alcohol, polyester, polyarylate, polyamide imide, polyether imide, etc. on a support substrate having a birefringence retardation as small as possible such as triacetyl cellulose or amorphous polyolefin. A liquid crystal polymer is developed on an alignment film rubbed with a cloth, an obliquely deposited layer of SiO, or an alignment film formed by stretching, and heated to a temperature higher than the glass transition temperature and lower than the isotropic phase transition temperature. Examples thereof include a method of forming a solidified layer in which the orientation is fixed by cooling to below the glass transition temperature in a state where the molecules are in a planar orientation to form a glass state.

  The liquid crystal polymer film is formed by, for example, thinning a solution of a liquid crystal polymer in a solvent by spin coating, roll coating, flow coating, printing, dip coating, casting film formation, bar coating, or gravure printing. It can be carried out by a method of developing a layer and drying it as necessary. As the solvent, for example, methylene chloride, cyclohexanone, trichloroethylene, tetrachloroethane, N-methylpyrrolidone, tetrahydrofuran and the like can be appropriately selected and used.

  In addition, a heating melt of a liquid crystal polymer, preferably a heating melt exhibiting an isotropic phase, is developed according to the above, and a thin layer is further developed and solidified while maintaining the melting temperature as necessary. can do. This method is a method that does not use a solvent. Therefore, the liquid crystal polymer can be developed even by a method that provides good hygiene in the working environment. In developing the liquid crystal polymer, a superposition method of a cholesteric liquid crystal layer through an alignment film can be adopted as necessary for the purpose of thinning.

  Furthermore, if necessary, these optical layers can be peeled off from the supporting substrate / orienting substrate used at the time of film formation and transferred to other optical materials for use.

  Further, as the circularly polarized reflective polarizer (a) of the present invention, a combination of a linearly polarized reflective polarizer and a λ / 4 plate can be used. One of these may be used, or two or more may be used. All may be a combination of a linearly polarized reflective polarizer and a λ / 4 plate.

  Linearly polarized reflective polarizers include grid polarizers, two or more multilayer thin film stacks of two or more materials having a difference in refractive index, vapor deposited multilayer thin films with different refractive indices used for beam splitters, birefringence, etc. Two or more birefringent layer multilayer thin film laminates made of two or more materials having a stretch, two or more bilayered resin laminates using two or more resins having birefringence, an axis orthogonal to linearly polarized light And the like that separate by reflecting / transmitting in the direction.

  For example, phase difference expression such as polyethylene naphthalate, polyethylene terephthalate, materials that generate phase difference by stretching such as polycarbonate, acrylic resin typified by polymethyl methacrylate, norbornene resin typified by JSR Arton, etc. A resin obtained by uniaxially stretching a small amount of resin alternately as a multilayer laminate can be used. Specific examples of the linearly polarized reflective polarizer include DBEF manufactured by 3M.

  When using a circularly polarizing reflective polarizer (a), which is a combination of a linearly polarizing reflective polarizer and a λ / 4 plate, as an intermediate layer (for example, the second one from the backlight side when three are laminated) A λ / 4 plate is disposed on both sides of the linearly polarized reflective polarizer. When used for the lowermost layer (for example, the first one from the backlight side when three layers are stacked), the linearly polarized reflective polarizer and then the λ / 4 plate are arranged in this order from the backlight side. In the case of using the uppermost layer (for example, the third one from the backlight side when three layers are stacked), the λ / 4 plate and then the linearly polarized reflective polarizer are arranged in this order from the backlight side. In the case where a circularly polarized reflective polarizer (a) combining a linearly polarized reflective polarizer and a λ / 4 plate is used as the uppermost layer, as shown in FIG. 2, FIG. 3, FIG. 4, and FIG. It is not necessary to arrange the λ / 4 plate (B) on the optical element (A).

(Phase difference layer (b))
The retardation layer (b) disposed between the circularly polarized reflective polarizers (a) has a substantially zero retardation in the front direction. Since the front phase difference is intended to maintain vertically incident polarized light, it is desirable that the front phase difference be λ / 10 or less.

  The retardation layer (b) has a phase difference of λ / 8 or more with respect to incident light at an angle of 30 ° from the normal direction. For the retardation layer (b), λ / 2 is ideally effective. However, the circularly polarized reflective polarizer (a): the cholesteric liquid crystal layer itself has a phase difference. Therefore, the polarization state of the light transmitted by the circularly polarized reflective polarizer (a) changes depending on the C-plate-like birefringence of the reflective polarizer itself. Therefore, the phase difference of the C plate that is normally inserted is measured at that angle, and the value obtained by adding the phase difference between the circularly polarized reflective polarizer (a) through which incident light is transmitted and the C plate is about λ / 2. It is preferable to do so.

  In order to correct for these in consideration of the phase difference of the circularly polarized reflective polarizer (a) as described above, the phase difference layer (b) is used for incident light at an angle of 30 ° from the normal direction. Those having a phase difference of λ / 8 or more are used. The phase difference of the retardation layer (b) with respect to the obliquely incident light is appropriately adjusted according to the circularly polarized reflective polarizer (a).

  When the sum of the phase difference of the phase difference layer (b) with respect to the obliquely incident light and the phase difference received by the circularly polarized reflective polarizer (a) is about λ / 2, the circularly polarized light is just opposite to the incident light. Become. It is known that light obliquely incident on the reflective polarizer works as a retardation layer. (H. Takezone et al. JPN. J. Appl. Phys. 22, 1080 (1983)).

  The incident light from the oblique direction of the phase difference layer (b) is appropriately determined depending on the angle at which it is totally reflected so as to be efficiently polarized and converted. For example, in order to completely reflect the incident light incident at an angle of 60 ° with respect to the normal direction, the circularly polarized reflective polarizer (a) and the retardation layer (measured at an incident angle of 60 °) Control may be performed so that the total phase difference of b) is about λ / 2. However, in this case, since reflection near an incident angle of 30 ° is weakened, incident light near an incident angle of 30 ° is reflected by using the phase difference received by the other circularly polarized reflective polarizer (a). Control is performed so that the phase difference of the circularly polarized reflective polarizer (a) is about λ / 2 so as to be totally reflected.

  Preferred embodiments of the optical element of the present invention are as follows, for example. The case where the circularly polarized reflective polarizer (a) / retardation layer (b) / circularly polarized reflective polarizer (a) / circularly polarized reflective polarizer (a) are arranged in this order from the light source side. To do.

  In this case, for example, incident light incident at an angle of 30 ° or more with respect to the normal direction is polarized and separated from the light source by the first circularly polarizing reflective polarizer (a), and then from the light source side. The sum of the phase differences received by the first circularly polarized reflective polarizer (a), the retardation layer (b) and the second circularly polarized reflective polarizer (a) before being polarized and separated is λ / 4 + λ · n to 3λ / 4 + λ · n (where n is an integer of 0 or more). The incident light incident at an angle of 60 ° with respect to the normal direction is polarized and separated from the light source by the first circularly polarized reflective polarizer (a), and then the first circularly polarized light from the light source side. -Type reflective polarizer (a), retardation layer (b), second circularly polarized reflective polarizer (a), and third circularly polarized reflective polarizer (a) before being polarized and separated. Adjustment is made so that the sum of the phase differences becomes λ / 4 + λ · n to 3λ / 4 + λ · n (where n is an integer of 0 or more).

  In the above case, the incident light incident with an inclination of 30 ° or more with respect to the normal direction is polarized and separated from the light source by the first circularly polarizing reflective polarizer (a), and then from the light source side. Polarized by the first circularly polarized reflective polarizer (a), the retardation layer (b), the second circularly polarized reflective polarizer (a), and the third circularly polarized reflective polarizer (a) Adjustment is made so that the sum of the phase differences received before separation is λ / 4 + λ · n to 3λ / 4 + λ · n (where n is an integer of 0 or more). The incident light incident at an angle of 60 ° with respect to the normal direction is polarized and separated from the light source by the first circularly polarized reflective polarizer (a), and then the first circularly polarized light from the light source side. The sum of the phase differences received before polarization separation is performed by the type reflection polarizer (a), the retardation layer (b), and the second circular polarization type reflection polarizer (a) is λ / 4 + λ · n to 3λ / Adjustment is made so that 4 + λ · n (where n is an integer of 0 or more).

  Preferred embodiments of the optical element of the present invention are as follows, for example. The case where the circularly polarized reflective polarizer (a) / circularly polarized reflective polarizer (a) / retardation layer (b) / circularly polarized reflective polarizer (a) are arranged in this order from the light source side. To do.

  In this case, for example, the incident light incident with an inclination of 30 ° or more with respect to the normal direction is polarized and separated from the light source by the first circularly polarizing reflective polarizer (a), and then 1 from the light source side. The sum of the phase differences received before the first circularly polarized reflective polarizer (a) and the second circularly polarized reflective polarizer (a) undergo polarization separation is λ / 4 + λ · n to 3λ / 4 + λ · Adjustment is made so that n (where n is an integer of 0 or more). The incident light incident at an angle of 60 ° with respect to the normal direction is polarized and separated from the light source by the first circularly polarized reflective polarizer (a), and then the first circularly polarized light from the light source side. -Type reflective polarizer (a), the second circularly polarized reflective polarizer (a), the retardation layer (b), and the third circularly polarized reflective polarizer (a) are subjected to polarization separation. Adjustment is made so that the sum of the phase differences becomes λ / 4 + λ · n to 3λ / 4 + λ · n (where n is an integer of 0 or more).

  In the above case, the incident light incident with an inclination of 30 ° or more with respect to the normal direction is polarized and separated from the light source by the first circularly polarizing reflective polarizer (a), and then from the light source side. Polarized by the first circularly polarized reflective polarizer (a), the second circularly polarized reflective polarizer (a), the retardation layer (b), and the third circularly polarized reflective polarizer (a) Adjustment is made so that the sum of the phase differences received before separation is λ / 4 + λ · n to 3λ / 4 + λ · n (where n is an integer of 0 or more). The incident light incident at an angle of 60 ° with respect to the normal direction is polarized and separated from the light source by the first circularly polarized reflective polarizer (a), and then the first circularly polarized light from the light source side. The sum of the phase differences received before polarization separation is performed by the type reflection polarizer (a) and the second circular polarization type reflection polarizer (a) is λ / 4 + λ · n to 3λ / 4 + λ · n (where n Is an integer greater than or equal to 0).

  That is, when the circularly polarized reflective polarizer (a) has a phase difference, the total phase difference related to the circularly polarized reflective polarizer (a) and the retardation layer (b) is expressed as λ / By controlling so that it falls within the range of 4 + λ · n to 3λ / 4 + λ · n, obliquely incident light can be efficiently reflected, and even when the viewing angle is greatly reduced, the amount of transmitted light is reduced and coloring is controlled to be small. can do. That is, by controlling the incident light that is incident at an angle of 60 ° with respect to the normal direction, the incident light of about 40 to 80 ° with respect to the normal direction can be reflected well. In particular, incident light of about 50 to 60 ° can be well reflected. On the other hand, by controlling incident light that is incident at an angle of 30 ° or more with respect to the normal direction, incident light having an incident angle of about 10 to 50 ° with respect to the normal direction can be efficiently reflected. In particular, incident light of about 20 to 40 ° can be reflected well.

  Therefore, it is preferable to control the sum of the phase differences to be close to λ / 2. The total of the phase differences is preferably λ / 4 + λ · n to 3λ / 4 + λ · n, further 3λ / 10 to 7λ / 10, and more preferably 2λ / 5 to 3λ / 5.

  As described above, according to the optical element, incident light can be condensed and collimated in the normal direction, and the amount of transmitted light incident at a large angle with respect to the normal direction can be significantly reduced. As a result, the front luminance and the degree of polarization are improved, and coloring when the viewing angle is greatly tilted in the normal direction can be reduced.

  The material of the retardation layer (b) is not particularly limited as long as it has the above optical characteristics. For example, the planar alignment state of a cholesteric liquid crystal having a reflection wavelength other than the visible light region (380 nm to 780 nm), the homeotropic alignment state of a rod-like liquid crystal, the columnar alignment or nematic alignment of a discotic liquid crystal Examples include those used, negative uniaxial crystals oriented in the plane, and biaxially oriented polymer films. Moreover, the film obtained from the at least 1 sort (s) of polymer chosen from the group which consists of polyamide, a polyimide, polyester, poly (ether ketone), poly (amide-imide), and poly (ester-imide) is mention | raise | lifted. These films are obtained by applying a solution obtained by dissolving the polymer in a solvent to a substrate and performing a drying process. The substrate is preferably formed using a substrate having a dimensional change rate of 1% or less in the drying step. In addition, examples include nematic liquid crystal and discotic liquid crystal in which the alignment direction is fixed so that the alignment direction continuously changes in the thickness direction.

  In the C plate in which the planar alignment state of the cholesteric liquid crystal having a selective reflection wavelength other than the visible light region (380 nm to 780 nm) is fixed, it is desirable that the selective reflection wavelength of the cholesteric liquid crystal is not colored in the visible light region. Therefore, it is necessary that the selectively reflected light is not in the visible region. The selective reflection is uniquely determined by the cholesteric chiral pitch and the refractive index of the liquid crystal. Although the value of the center wavelength of selective reflection may be in the near-infrared region, it is more desirable to be in the ultraviolet region of 350 nm or less because it is affected by the optical rotation and a slightly complicated phenomenon occurs. The formation of the cholesteric liquid crystal layer is performed in the same manner as the formation of the cholesteric layer in the above-described reflective polarizer.

  The C plate with a fixed homeotropic alignment state is obtained by polymerizing a liquid crystalline thermoplastic resin or liquid crystal monomer exhibiting nematic liquid crystal properties at high temperature and, if necessary, an alignment aid by irradiation with ionizing radiation such as electron beams or ultraviolet rays or heat. A polymerizable liquid crystal or a mixture thereof is used. The liquid crystallinity may be either lyotropic or thermotropic, but is preferably a thermotropic liquid crystal from the viewpoint of ease of control and ease of formation of a monodomain. Homeotropic alignment is obtained, for example, by coating the birefringent material on a film on which a vertical alignment film (long-chain alkylsilane or the like) is formed, and expressing and fixing a liquid crystal state.

  As a C plate using discotic liquid crystal, a discotic liquid crystal material having a negative uniaxial property such as a phthalocyanine or triphenylene compound having an in-plane molecular spread as a liquid crystal material, a nematic phase or a columnar phase is used. It is expressed and fixed. Examples of the negative uniaxial inorganic layered compound are detailed in JP-A-6-82777.

  C plate using biaxial orientation of polymer film is a method of biaxially stretching a polymer film having positive refractive index anisotropy in a balanced manner, a method of pressing a thermoplastic resin, and cutting out from a parallel oriented crystal. It is obtained by a method.

  Each of the retardation layers (b) may be composed of one retardation plate, and two or more retardation plates can be laminated and used so as to have a desired retardation.

(Lamination of each layer)
The layers may be stacked, but it is desirable to stack the layers using an adhesive or a pressure-sensitive adhesive from the viewpoints of workability and light utilization efficiency. In that case, the adhesive or pressure-sensitive adhesive is transparent, has no absorption in the visible light region, and the refractive index is desirably as close as possible to the refractive index of each layer from the viewpoint of suppressing surface reflection. From this viewpoint, for example, an acrylic pressure-sensitive adhesive can be preferably used. Each layer is separately formed into a monodomain in the form of an alignment film, etc., and sequentially laminated by a method such as transfer to a translucent substrate, an alignment film or the like for alignment without providing an adhesive layer, etc. It is also possible to form each layer as appropriate and form each layer directly in sequence.

  In each layer and (viscous) adhesive layer, particles are added to adjust the degree of diffusion as necessary to give isotropic scattering, UV absorbers, antioxidants, leveling during film formation A surfactant or the like can be appropriately added for the purpose of imparting property.

(Condensing backlight system)
It is desirable to dispose a diffuse reflector on the lower side of the light guide plate as the light source (on the side opposite to the liquid crystal cell arrangement surface). The main component of the light beam reflected by the collimating film is an oblique incident component, and is regularly reflected by the collimating film and returned to the backlight direction. Here, when the regular reflection property of the reflector on the back side is high, the reflection angle is preserved, and the light cannot be emitted in the front direction and becomes lost light. Accordingly, it is desirable to dispose a diffuse reflector in order to increase the scattering reflection component in the front direction without preserving the reflection angle of the reflected return beam.

  It is desirable to install an appropriate diffuser plate between the optical element (A: collimating film) of the present invention and the backlight source (D). This is because the light reuse efficiency is increased by scattering the incident and reflected light rays in the vicinity of the backlight light guide and scattering a part thereof in the vertical incident direction. The diffusion plate can be obtained by a method such as embedding fine particles having different refractive indexes in a resin in addition to a surface irregularity shape. This diffusing plate may be sandwiched between the optical element (collimating film) and the backlight, or may be bonded to the collimating film.

  When a liquid crystal cell with an optical element (collimating film) bonded is placed close to the backlight, Newton's rings may occur in the gap between the film surface and the backlight. The occurrence of Newton's ring can be suppressed by disposing a diffusion plate having surface irregularities on the light guide plate side surface of the control film). Moreover, you may form the layer which served as the uneven | corrugated structure and the light-diffusion structure on the surface itself of the optical element (collimating film) in this invention.

(Liquid crystal display device)
The optical element is preferably applied to a liquid crystal display device in which polarizing plates are arranged on both sides of the liquid crystal cell, and the optical element is applied to the polarizing plate side of the light source side surface of the liquid crystal cell. For example, it is applied as shown in FIG. 4 and 5, only the polarizing plate (C) on the side surface of the light source is shown as the liquid crystal panel.

  Further, as shown in FIG. 4, the optical element (A) is laminated on the polarizing plate (C) via the λ / 4 plate (B). The λ / 4 plate (B) changes the circularly polarized light emitted from the optical element (A) into linearly polarized light and enters the polarizing plate (C). As the optical element of the present invention, a λ / 4 plate (B) and a polarizing plate (C) bonded in advance can be used.

  By laminating a diffusion plate that does not have backscattering and depolarization on the liquid crystal cell viewing side on the liquid crystal display device combined with the above-mentioned collimated backlight, light with good display characteristics near the front is diffused. The viewing angle can be enlarged by obtaining uniform and good display characteristics within the entire viewing angle.

  The viewing angle widening film used here is a diffusion plate that does not substantially have backscattering. The diffusion plate can be provided as a diffusion adhesive material. The location is on the viewing side of the liquid crystal display device, but it can be used either above or below the polarizing plate. However, it is desirable to provide a layer as close to the cell as possible, such as between the polarizing plate and the liquid crystal cell, in order to prevent the deterioration of the contrast due to the influence of the blur of the pixel or the like or the slight remaining backscattering. In this case, a film that does not substantially eliminate polarized light is desirable. For example, a fine particle dispersion type diffusion plate as disclosed in JP-A Nos. 2000-347006 and 2000-347007 is preferably used.

  When the viewing angle widening film is located outside the polarizing plate, the collimated light beam is transmitted from the liquid crystal layer to the polarizing plate, so that in the case of the TN liquid crystal cell, it is not necessary to use a viewing angle compensating retardation plate. In the case of an STN liquid crystal cell, it is only necessary to use a retardation film in which only the front characteristics are well compensated. In this case, since the viewing angle widening film has an air surface, it is possible to adopt a type based on a refraction effect due to the surface shape.

  On the other hand, when a viewing angle widening film is inserted between the polarizing plate and the liquid crystal layer, it becomes a diffused light at the stage where it passes through the polarizing plate. In the case of a TN liquid crystal, it is necessary to compensate for the viewing angle characteristics of the polarizer itself. In this case, it is necessary to insert a retardation plate for compensating the viewing angle characteristics of the polarizer between the polarizer and the viewing angle widening film. In the case of STN liquid crystal, it is necessary to insert a phase difference plate for compensating the viewing angle characteristics of the polarizer in addition to the front phase difference compensation of STN liquid crystal.

  In the case of a viewing angle widening film having a regular structure inside, such as a conventional microlens array film or hologram film, a microlens included in a black matrix of a liquid crystal display device or a conventional parallel light conversion system of a backlight Moire was likely to occur due to interference with a fine structure such as an array / prism array / louver / micromirror array. However, the collimated film in the present invention has no regular structure in the plane, and there is no regular modulation of the emitted light, so there is no need to consider compatibility with the viewing angle widening film and the arrangement order. Accordingly, the viewing angle widening film is not particularly limited as long as it does not cause interference / moire with the pixel black matrix of the liquid crystal display device, and the options are wide.

  In the present invention, it is a light scattering plate as described in JP-A-2000-347006 and JP-A-2000-347007, which has substantially no backscattering as a viewing angle widening film and does not cancel polarization. A haze of 80% to 90% is preferably used. In addition, a hologram sheet, a microprism array, a microlens array, or the like can be used as long as it does not form interference / moire with the pixel black matrix of the liquid crystal display device even if it has a regular structure inside.

(Other materials)
Note that the liquid crystal display device is manufactured by appropriately using various optical layers and the like according to a conventional method.

  As the λ / 4 plate, an appropriate retardation plate is used according to the purpose of use. The λ / 4 plate can control two or more kinds of retardation plates to control optical characteristics such as retardation. As the retardation plate, a birefringent film formed by stretching a film made of an appropriate polymer such as polycarbonate, norbornene resin, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene, other polyolefins, polyarylate, polyamide, Examples thereof include an alignment film made of a liquid crystal material such as a liquid crystal polymer, and an alignment layer of the liquid crystal material supported by the film. In general, the thickness of the λ / 4 plate is preferably 0.5 to 200 μm, and more preferably 1 to 100 μm.

  A retardation plate that functions as a λ / 4 plate in a wide wavelength range such as a visible light region is, for example, a retardation layer that functions as a λ / 4 plate for light-colored light having a wavelength of 550 nm and a retardation that exhibits other retardation characteristics. It can be obtained by a method of superimposing a layer, for example, a retardation layer functioning as a λ / 2 plate. Therefore, the retardation plate disposed between the polarizing plate and the brightness enhancement film may be composed of one or more retardation layers.

  In general, a polarizing plate having a protective film on one side or both sides of a polarizer is generally used.

  The polarizer is not particularly limited, and various types can be used. Examples of the polarizer include hydrophilic polymer films such as polyvinyl alcohol film, partially formalized polyvinyl alcohol film, and ethylene / vinyl acetate copolymer partially saponified film, and two colors such as iodine and dichroic dye. Examples thereof include polyene-based oriented films such as those obtained by adsorbing volatile substances and uniaxially stretched, polyvinyl alcohol dehydrated products and polyvinyl chloride dehydrochlorinated products. Among these, a polarizer composed of a polyvinyl alcohol film and a dichroic material such as iodine is preferable. The thickness of these polarizers is not particularly limited, but is generally about 5 to 80 μm.

  A polarizer obtained by dyeing a polyvinyl alcohol film with iodine and uniaxially stretching it can be produced, for example, by dyeing polyvinyl alcohol in an aqueous solution of iodine and stretching it 3 to 7 times the original length. If necessary, it can be immersed in an aqueous solution such as potassium iodide which may contain boric acid, zinc sulfate, zinc chloride and the like. Further, if necessary, the polyvinyl alcohol film may be immersed in water and washed before dyeing. In addition to washing the polyvinyl alcohol film surface with dirt and anti-blocking agents by washing the polyvinyl alcohol film with water, it also has the effect of preventing unevenness such as uneven coloring by swelling the polyvinyl alcohol film. is there. Stretching may be performed after dyeing with iodine, or may be performed while dyeing, or may be performed with dyeing after iodine. The film can be stretched in an aqueous solution of boric acid or potassium iodide or in a water bath.

  As a material for forming the transparent protective film provided on one side or both sides of the polarizer, a material excellent in transparency, mechanical strength, thermal stability, moisture shielding property, isotropy and the like is preferable. For example, polyester polymers such as polyethylene terephthalate and polyethylene naphthalate, cellulose polymers such as diacetyl cellulose and triacetyl cellulose, acrylic polymers such as polymethyl methacrylate, styrene such as polystyrene and acrylonitrile / styrene copolymer (AS resin) -Based polymer, polycarbonate-based polymer and the like. In addition, polyethylene, polypropylene, polyolefins having a cyclo or norbornene structure, polyolefin polymers such as ethylene / propylene copolymers, vinyl chloride polymers, amide polymers such as nylon and aromatic polyamide, imide polymers, sulfone polymers , Polyether sulfone polymer, polyether ether ketone polymer, polyphenylene sulfide polymer, vinyl alcohol polymer, vinylidene chloride polymer, vinyl butyral polymer, arylate polymer, polyoxymethylene polymer, epoxy polymer, or the above Polymer blends and the like are also examples of polymers that form the transparent protective film. The transparent protective film can also be formed as a cured layer of thermosetting or ultraviolet curable resin such as acrylic, urethane, acrylurethane, epoxy, and silicone.

  Moreover, the polymer film described in JP-A-2001-343529 (WO01 / 37007), for example, (A) a thermoplastic resin having a substituted and / or unsubstituted imide group in the side chain, and (B) a substitution in the side chain And / or a resin composition containing an unsubstituted phenyl and a thermoplastic resin having a nitrile group. A specific example is a film of a resin composition containing an alternating copolymer composed of isobutylene and N-methylmaleimide and an acrylonitrile / styrene copolymer. As the film, a film made of a mixed extruded product of the resin composition or the like can be used.

  Although the thickness of a protective film can be determined suitably, generally it is about 1-500 micrometers from points, such as workability | operativity, such as intensity | strength and handleability, and thin layer property. 1-300 micrometers is especially preferable, and 5-200 micrometers is more preferable.

  Moreover, it is preferable that a protective film has as little color as possible. Therefore, Rth = [(nx + ny) / 2−nz] · d (where nx and ny are the main refractive index in the plane of the film, nz is the refractive index in the film thickness direction, and d is the film thickness). A protective film having a retardation value in the film thickness direction of −90 nm to +75 nm is preferably used. By using a film having a thickness direction retardation value (Rth) of −90 nm to +75 nm, the coloring (optical coloring) of the polarizing plate caused by the protective film can be almost eliminated. The thickness direction retardation value (Rth) is more preferably −80 nm to +60 nm, and particularly preferably −70 nm to +45 nm.

  As the protective film, a cellulose polymer such as triacetyl cellulose is preferable from the viewpoints of polarization characteristics and durability. A triacetyl cellulose film is particularly preferable. In addition, when providing a protective film in the both sides of a polarizer, the protective film which consists of the same polymer material may be used by the front and back, and the protective film which consists of a different polymer material etc. may be used. The polarizer and the protective film are usually in close contact with each other through an aqueous adhesive or the like. Examples of the water-based adhesive include an isocyanate-based adhesive, a polyvinyl alcohol-based adhesive, a gelatin-based adhesive, a vinyl-based latex, a water-based polyurethane, and a water-based polyester.

  The surface of the transparent protective film to which the polarizer is not adhered may be subjected to a hard coat layer, an antireflection treatment, an antisticking treatment, or a treatment for diffusion or antiglare.

  The hard coat treatment is applied for the purpose of preventing scratches on the surface of the polarizing plate. For example, a transparent protective film with a cured film excellent in hardness, sliding properties, etc. by an appropriate ultraviolet curable resin such as acrylic or silicone is used. It can be formed by a method of adding to the surface of the film. The antireflection treatment is performed for the purpose of preventing reflection of external light on the surface of the polarizing plate, and can be achieved by forming an antireflection film or the like according to the conventional art. Further, the anti-sticking treatment is performed for the purpose of preventing adhesion with an adjacent layer.

  Anti-glare treatment is applied for the purpose of preventing external light from being reflected on the surface of the polarizing plate and obstructing the visibility of the light transmitted through the polarizing plate. For example, roughening by sandblasting or embossing. It can be formed by imparting a fine concavo-convex structure to the surface of the transparent protective film by an appropriate method such as a method or a compounding method of transparent fine particles. Examples of the fine particles to be included in the formation of the surface fine concavo-convex structure include a conductive material made of silica, alumina, titania, zirconia, tin oxide, indium oxide, cadmium oxide, antimony oxide, or the like having an average particle diameter of 0.5 to 50 μm. Transparent fine particles such as inorganic fine particles, organic fine particles composed of a crosslinked or uncrosslinked polymer, etc. may be used. When forming a surface fine uneven structure, the amount of fine particles used is generally about 2 to 50 parts by weight, preferably 5 to 25 parts by weight, based on 100 parts by weight of the transparent resin forming the surface fine uneven structure. The antiglare layer may also serve as a diffusion layer (viewing angle expanding function or the like) for diffusing the light transmitted through the polarizing plate to expand the viewing angle.

  The antireflection layer, antisticking layer, diffusion layer, antiglare layer, and the like can be provided on the transparent protective film itself, or can be provided separately from the transparent protective film as an optical layer.

  A retardation plate is laminated on a polarizing plate as a viewing angle compensation film and used as a wide viewing angle polarizing plate. The viewing angle compensation film is a film for widening the viewing angle so that an image can be seen relatively clearly even when the screen of the liquid crystal display device is viewed from a slightly oblique direction rather than perpendicular to the screen.

  As such a viewing angle compensation retardation plate, a birefringent film that has been biaxially stretched or stretched in two orthogonal directions, a bidirectionally stretched film such as a tilted orientation film, and the like are used. Examples of the inclined alignment film include a film obtained by bonding a heat shrink film to a polymer film and stretching or / and shrinking the polymer film under the action of the contraction force by heating, and a film obtained by obliquely aligning a liquid crystal polymer. Can be mentioned. The viewing angle compensation film can be appropriately combined for the purpose of preventing coloring or the like due to a change in viewing angle based on a phase difference caused by a liquid crystal cell or increasing the viewing angle for good viewing.

  Also, from the viewpoint of achieving a wide viewing angle with good visibility, an optically compensated phase difference in which a liquid crystal polymer alignment layer, in particular an optically anisotropic layer composed of a discotic liquid crystal polymer gradient alignment layer, is supported by a triacetylcellulose film. A plate can be preferably used.

  In addition to the above, the optical layer laminated in practical use is not particularly limited. For example, one or more optical layers that may be used for forming a liquid crystal display device such as a reflective plate or a transflective plate are used. Can do. In particular, a reflective polarizing plate or a semi-transmissive polarizing plate in which a reflecting plate or a semi-transmissive reflecting plate is further laminated on an elliptical polarizing plate or a circular polarizing plate can be given.

  A reflective polarizing plate is a polarizing plate provided with a reflective layer, and is used to form a liquid crystal display device or the like that reflects incident light from the viewing side (display side). Such a light source can be omitted, and the liquid crystal display device can be easily thinned. The reflective polarizing plate can be formed by an appropriate method such as a method in which a reflective layer made of metal or the like is attached to one surface of the polarizing plate via a transparent protective layer or the like as necessary.

  Specific examples of the reflective polarizing plate include those in which a reflective layer is formed by attaching a foil or vapor-deposited film made of a reflective metal such as aluminum on one surface of a protective film matted as necessary. In addition, the protective film may contain fine particles to form a surface fine concavo-convex structure and a reflective layer having a fine concavo-convex structure thereon. The reflective layer having the fine concavo-convex structure has an advantage that incident light is diffused by irregular reflection to prevent directivity and glaring appearance and to suppress unevenness in brightness and darkness. Moreover, the protective film containing fine particles also has an advantage that incident light and its reflected light are diffused when passing through it and light and dark unevenness can be further suppressed. The reflective layer with a fine concavo-convex structure reflecting the surface fine concavo-convex structure of the protective film is transparently protected by an appropriate method such as a vapor deposition method such as a vacuum deposition method, an ion plating method, a sputtering method, or a plating method. It can be performed by a method of attaching directly to the surface of the layer.

  The reflective plate can be used as a reflective sheet in which a reflective layer is provided on an appropriate film according to the transparent film, instead of the method of directly imparting to the protective film of the polarizing plate. Since the reflective layer is usually made of metal, the usage form in which the reflective surface is covered with a protective film, a polarizing plate or the like is used to prevent a decrease in reflectance due to oxidation, and thus the long-term sustainability of the initial reflectance. More preferable is the point of avoiding the additional attachment of the protective layer.

  The semi-transmissive polarizing plate can be obtained by using a semi-transmissive reflective layer such as a half mirror that reflects and transmits light with the reflective layer. A transflective polarizing plate is usually provided on the back side of a liquid crystal cell, and displays an image by reflecting incident light from the viewing side (display side) when a liquid crystal display device is used in a relatively bright atmosphere. In a relatively dark atmosphere, a liquid crystal display device or the like that displays an image using a built-in light source such as a backlight built in the back side of the transflective polarizing plate can be formed. In other words, the transflective polarizing plate is useful for forming a liquid crystal display device of a type that can save energy of using a light source such as a backlight in a bright atmosphere and can be used with a built-in light source even in a relatively dark atmosphere. It is.

  Further, the polarizing plate may be formed by laminating a polarizing plate and two or three or more optical layers, like the above-described polarization separation type polarizing plate. Therefore, a reflective elliptical polarizing plate or a semi-transmissive elliptical polarizing plate in which the above-mentioned reflective polarizing plate or transflective polarizing plate and a retardation plate are combined may be used.

  The elliptical polarizing plate and the reflective elliptical polarizing plate are obtained by laminating a polarizing plate or a reflective polarizing plate and a retardation plate in an appropriate combination. Such an elliptical polarizing plate can be formed by sequentially laminating them in the manufacturing process of the liquid crystal display device so as to be a combination of a (reflective) polarizing plate and a retardation plate. An optical film such as an elliptically polarizing plate is advantageous in that it can improve the production efficiency of a liquid crystal display device and the like because of excellent quality stability and lamination workability.

  The optical element of the present invention can be provided with an adhesive layer or an adhesive layer. The pressure-sensitive adhesive layer can be used for adhering to a liquid crystal cell and also used for laminating optical layers. When adhering the optical films, their optical axes can be set at an appropriate arrangement angle in accordance with the target retardation characteristics.

  It does not restrict | limit especially as an adhesive agent or an adhesive. For example, acrylic polymer, silicone polymer, polyester, polyurethane, polyamide, polyvinyl ether, vinyl acetate / vinyl chloride copolymer, modified polyolefin, epoxy-based, fluorine-based, natural rubber, synthetic rubber and other rubber-based polymers Can be appropriately selected and used. In particular, those excellent in optical transparency, exhibiting appropriate wettability, cohesiveness, and adhesive pressure-sensitive adhesive properties and excellent in weather resistance, heat resistance and the like can be preferably used.

  The adhesive or pressure-sensitive adhesive can contain a crosslinking agent according to the base polymer. Examples of adhesives include natural and synthetic resins, in particular, tackifier resins, glass fibers, glass beads, metal powders, other inorganic powders, fillers, pigments, colorants, and antioxidants. An additive such as an agent may be contained. Further, it may be an adhesive layer containing fine particles and exhibiting light diffusibility.

  The adhesive and the pressure-sensitive adhesive are usually used as an adhesive solution having a solid content concentration of about 10 to 50% by weight in which a base polymer or a composition thereof is dissolved or dispersed in a solvent. As the solvent, an organic solvent such as toluene or ethyl acetate or a solvent such as water can be appropriately selected and used.

  The pressure-sensitive adhesive layer and the adhesive layer can be provided on one side or both sides of a polarizing plate or an optical film as an overlapping layer of different compositions or types. The thickness of the pressure-sensitive adhesive layer can be appropriately determined according to the purpose of use and adhesive force, and is generally 1 to 500 μm, preferably 5 to 200 μm, particularly preferably 10 to 100 μm.

  For the exposed surface such as the adhesive layer, a separator is temporarily attached and covered for the purpose of preventing contamination until it is put to practical use. Thereby, it can prevent contacting an adhesion layer in the usual handling state. As the separator, except for the above thickness conditions, for example, a suitable thin leaf body such as a plastic film, rubber sheet, paper, cloth, non-woven fabric, net, foam sheet, metal foil, laminate thereof, and the like, silicone type or Appropriate ones according to the prior art, such as those coated with an appropriate release agent such as a long mirror alkyl type, fluorine type or molybdenum sulfide, can be used.

  In the present invention, each layer such as the optical element and the adhesive layer is made of an ultraviolet absorber such as a salicylic acid ester compound, a benzophenol compound, a benzotriazole compound, a cyanoacrylate compound, or a nickel complex compound. What gave the ultraviolet absorptivity by systems, such as a processing system, may be used.

  EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples, but the present invention is not limited to these examples.

  Note that the front phase difference is defined by the direction in which the in-plane refractive index is maximized as the X axis, the direction perpendicular to the X axis as the Y axis, and the thickness direction of the film as the Z axis, and the refractive index in each axial direction as nx, As ny and nz, the refractive index nx, ny and nz at 550 nm were measured by an automatic birefringence measuring device (manufactured by Oji Scientific Instruments, automatic birefringence meter KOBRA21ADH), and the thickness d (nm) of the retardation layer. From the above, the front phase difference: (nx−ny) × d was calculated.

  The phase difference when measured with an inclination of 30 ° with respect to the normal direction can be measured by the automatic birefringence measuring apparatus. The tilt phase difference is: (nx−ny) × d at the time of tilt. The automatic birefringence measuring apparatus can measure an incident angle from 0 to 50 °. The phase difference value at an incident angle of 60 ° is a value calculated from fitting. In addition, the phase difference value at an incident angle of 60 ° related to the circularly polarized reflective polarizer (a) was converted separately. The phase difference value at an incident angle of 30 ° was also determined by the same method as that at the incident angle of 60 °.

  The reflection wavelength band was determined by measuring the reflection spectrum with a spectrophotometer (manufactured by Otsuka Electronics Co., Ltd., instantaneous multi-photometry system MCPD-2000), and having a reflection wavelength band having half the maximum reflectance.

Example 1
(Circularly polarized reflective polarizer (a))
As the circularly polarized reflective polarizer (a), a broadband cholesteric liquid crystal layer having a reflection wavelength band of 400 to 800 nm was used. When the phase difference of the broadband cholesteric liquid crystal layer was measured, the phase difference when the incident light was measured by tilting by 30 ° with respect to the light having a wavelength of 550 nm was 100 nm.

The phase difference of the cholesteric liquid crystal layer having a center wavelength of 370 nm was measured with a spectroscopic ellipsometer (manufactured by JASCO Corporation, M-220). From the phase difference, Cauchy's formula: phase difference = a + bλ ² + c / λ ⁴ was approximated to obtain the wavelength dispersion of the refractive index (see FIG. 7). Up to this point, the device has automatically calculated.

Next, the change in the pitch interval of the broadband cholesteric liquid crystal layer having a reflection wavelength band of 400 to 800 nm was obtained from the result of the cross-sectional TEM (see FIG. 8). The width (Δλ) of the selective reflection region at a wavelength of 550 nm is 48 nm when calculated from Δλ = 2λ (Ne−No) / (Ne + No). Ne: 1.685, No: 1.545. Therefore, since 550 nm ± 24 nm is reflected, if this portion is applied to the pitch number in FIG. p / 2 is obtained from λ (center wavelength) = (Ne + No) × p / 2, and it can be seen from FIG. p: Cholesteric pitch (μm). When the pitch interval of the 32nd to 36th layers is added, it becomes 0.30 μm. Since the thickness of the cholesteric liquid crystal layer is 6 μm, 6−0.3 = 5.7 μm works as a retardation plate. From FIG. 9, when light having a wavelength of 950 nm is incident on the cholesteric liquid crystal layer at an incident angle of 60 °, a phase difference of 172 nm is received (measured with a spectroscopic ellipsometer). From the result of the chromatic dispersion shown in FIG. 7, the refractive index prescribed value at a wavelength of 550 nm is 1.061, the refractive index prescribed value at a wavelength of 950 nm is 0.709, and a phase difference of 172 nm is received at a wavelength of 950 nm. × 1.061 / 0.709 = 257.4 nm (calculated from Y = 110.75 × ^−0.7367 ). Although it receives a phase difference of about 260 nm at a wavelength of 550 nm, it does not work as a phase difference where there is a reflection wavelength and a pitch interval. Among them, the phase difference plate that acts as a retardation plate is 5.7 μm in the cholesteric liquid crystal layer 6 μm. Therefore, the phase difference received by the light having a wavelength of 550 nm from the cholesteric liquid crystal layer is retardation (nm) = 260 nm × 5.70 / 6 = 247 nm, It becomes. That is, when light having a wavelength of 550 nm is incident at an incident angle of 60 °, a phase difference of about 250 nm is received.

(C plate layer)
Next, a photopolymerizable nematic liquid crystal monomer (manufactured by BASF, LC242), a chiral agent (manufactured by BASF, LC756), a photoinitiator (manufactured by Ciba Specialty Chemicals, Irgacure 907) and a solvent (toluene) are selectively reflected at center wavelengths. The coating liquid prepared and adjusted so as to be 350 nm was coated on a commercially available polyethylene terephthalate film using a wire bar so that the thickness after drying was 4 μm, and the solvent was dried. Thereafter, the temperature was raised once to the isotropic transition temperature of the liquid crystal monomer, and then gradually cooled to form a layer having a uniform alignment state. The obtained film was irradiated with UV to fix the orientation state and obtain a C plate layer (negative). When the retardation of the C plate was measured, the front retardation was 2 nm and the thickness direction retardation was 220 nm with respect to light having a wavelength of 550 nm. The phase difference when the incident light was measured by tilting by 30 ° was 35 nm. Further, the phase difference when the incident light was measured by tilting by 60 ° was 75 nm.

(Optical element (A))
The circularly polarized reflective polarizer (a) was placed on the backlight side with the surface having a selective reflection band on the long wavelength side facing down. On top of this, a circularly polarizing reflective polarizer (a) was laminated with an adhesive having a thickness of 5 μm on the surface having a selective reflection band on the long wavelength side. Further, the two C plates were laminated with an adhesive having a thickness of 5 μm. The two C-plate laminate had a phase difference of 70 nm when measured by tilting incident light by 30 °. Further, the phase difference when measured by tilting the incident light by 60 ° was 150 nm. The laminate of the two C plate layers was used as a retardation layer (b). Further on this, a circularly polarized reflective polarizer (a) is laminated with an adhesive having a thickness of 5 μm on the long wavelength side, and an optical element (A) is laminated. Obtained.

  The incident light incident at an angle of 60 ° with respect to the normal direction is polarized and separated from the light source by the first circular polarization type reflective polarizer (a), and then the first circular polarization type reflection from the light source side. The sum of the phase differences received by the polarizer (a) and the second circularly polarized reflective polarizer (a) is 250 nm and is adjusted to be λ / 4 to 3λ / 4. ing.

  The incident light incident at an angle of 30 ° with respect to the normal direction is polarized and separated from the light source by the first circularly polarized reflective polarizer (a), and then the first circularly polarized light reflected from the light source side. Phase difference received by the polarizer (a), the second circularly polarized reflective polarizer (a), the retardation layer (b), and the third circularly polarized reflective polarizer (a) before being polarized and separated. Is 270 nm and is adjusted to be λ / 4 to 3λ / 4.

  A polycarbonate retardation plate (λ / 4 plate) having a front retardation of 130 nm was laminated with an adhesive having a thickness of 5 μm. The axial direction of the linearly polarized light obtained by transmission and the transmission axis direction of the backlight side polarizing plate (manufactured by Nitto Denko Corp., SEG1425DU) of the liquid crystal display device are arranged so as to be a condensing and collimating system. . FIG. 4 is a configuration diagram of the first embodiment. In FIG. 4, the retardation layer (b) is a two-layer laminate of C plates. The λ / 4 plate is (B), the backlight side polarizing plate is (C), and the backlight is (D).

Comparative Example 1
A broadband cholesteric liquid crystal layer similar to that in Example 1 was used as the circularly polarizing reflective polarizer (a). The same C plate layer as in Example 1 was used.

  The circularly polarized reflective polarizer (a) was placed on the backlight side with the surface having a selective reflection band on the long wavelength side facing down. On top of this, the two C plates were laminated with an adhesive having a thickness of 5 μm. The laminate of the two C plate layers was used as a retardation layer (b). Further on this, a circularly polarized reflective polarizer (a) is laminated with an adhesive having a thickness of 5 μm on the long wavelength side, and an optical element (A ′). Got.

  A polycarbonate retardation plate (λ / 4 plate) having a front retardation of 130 nm was laminated with an adhesive having a thickness of 5 μm. The axial direction of the linearly polarized light obtained by transmission and the transmission axis direction of the backlight side polarizing plate (manufactured by Nitto Denko Corp., SEG1425DU) of the liquid crystal display device are arranged so as to be a condensing and collimating system. . In FIG. 6, the block diagram of the comparative example 1 is shown. In FIG. 6, the retardation layer (b) is a two-layer laminate of C plates. The λ / 4 plate is (B), the backlight side polarizing plate is (C), and the backlight is (D).

(Evaluation)
The following evaluation was performed about the said condensing and parallel light system. A light table was used for the backlight, and this was evaluated using EZ Contrast (manufactured by ELDIM) for coloring with respect to the viewing angle according to the luminance viewing angle characteristics and chromaticity diagram.

The luminance viewing angle characteristic represents the relationship of luminance (cd / cm ² ) with respect to when the viewing angle from the front (0 °) is tilted, and from this, the luminance when viewed from an arbitrary angle can be known.

  Further, the chromaticity diagram shows the relationship of how colors are added when the viewing angle is changed, and the color when viewed from an arbitrary angle can be understood. The greater the distance traveled by the lines connected, the more colored.

  10 and 11 show a comparison between Example 1 and Comparative Example 1. FIG. FIG. 10 is a comparison of luminance viewing angle characteristics, and it can be seen that Example 1 can suppress the amount of transmitted light incident at a large angle with respect to the normal direction as compared with Comparative Example 1. Further, in Example 1, the front luminance was improved as compared with Comparative Example 1. FIG. 11 is a chromaticity diagram when the incident angle is increased in order from the normal direction, and it can be seen that the moving distance of the point in Example 1 is smaller than that in Comparative Example 1. This point represents the color at each incident angle, and the greater the coloring, the greater the distance that the point moves as the color changes. From this, it can be seen that coloring is reduced in Example 1, and coloring is severe in Comparative Example 1.

Example 2
(Circularly polarized reflective polarizer (a))
A broadband cholesteric liquid crystal layer similar to that in Example 1 was used as the circularly polarizing reflective polarizer (a).

(C plate layer)
Next, a photopolymerizable nematic liquid crystal monomer (manufactured by BASF, LC242), a chiral agent (manufactured by BASF, LC756), a photoinitiator (manufactured by Ciba Specialty Chemicals, Irgacure 907) and a solvent (toluene) are selectively reflected at center wavelengths. The coating liquid prepared and adjusted so as to be 350 nm was coated on a commercially available polyethylene terephthalate film using a wire bar so that the thickness after drying was 4 μm, and the solvent was dried. Thereafter, the temperature was raised once to the isotropic transition temperature of the liquid crystal monomer, and then gradually cooled to form a layer having a uniform alignment state. The obtained film was irradiated with UV to fix the orientation state and obtain a C plate layer (negative). When the retardation of the C plate was measured, the front retardation was 2 nm and the thickness direction retardation was 220 nm with respect to light having a wavelength of 550 nm. The phase difference when the incident light was measured by tilting by 30 ° was 35 nm. Further, the phase difference when the incident light was measured by tilting by 60 ° was 75 nm.

(Optical element (A))
The circularly polarized reflective polarizer (a) was placed on the backlight side with the surface having a selective reflection band on the long wavelength side facing down. On top of this, a circularly polarizing reflective polarizer (a) was laminated with an adhesive having a thickness of 5 μm on the surface having a selective reflection band on the long wavelength side. Further, the four C plates were laminated with an adhesive having a thickness of 5 μm. The laminate of four C plates had a phase difference of 140 nm when the incident light was measured by tilting it by 30 °. Further, the phase difference when the incident light was measured by tilting by 60 ° was 300 nm. The laminate of the four C plate layers was used as a retardation layer (b). Further on this, a circularly polarized reflective polarizer (a) is laminated with an adhesive having a thickness of 5 μm on the long wavelength side, and an optical element (A) is laminated. Obtained.

  The incident light incident at an angle of 60 ° with respect to the normal direction is polarized and separated from the light source by the first circular polarization type reflective polarizer (a), and then the first circular polarization type reflection from the light source side. The sum of the phase differences received by the polarizer (a) and the second circularly polarized reflective polarizer (a) is 250 nm and is adjusted to be λ / 4 to 3λ / 4. ing.

  The incident light incident at an angle of 30 ° with respect to the normal direction is polarized and separated from the light source by the first circularly polarized reflective polarizer (a), and then the first circularly polarized light reflected from the light source side. Phase difference received by the polarizer (a), the second circularly polarized reflective polarizer (a), the retardation layer (b), and the third circularly polarized reflective polarizer (a) before being polarized and separated. Is 340 nm and is adjusted to be λ / 4 to 3λ / 4.

  A polycarbonate retardation plate (λ / 4 plate) having a front retardation of 130 nm was laminated with an adhesive having a thickness of 5 μm. The axial direction of the linearly polarized light obtained by transmission and the transmission axis direction of the backlight side polarizing plate (manufactured by Nitto Denko Corp., SEG1425DU) of the liquid crystal display device are arranged so as to be a condensing and collimating system. . The block diagram of Example 2 is as FIG. In FIG. 4, the retardation layer (b) is a four-layer laminate of C plates. The λ / 4 plate is (B), the backlight side polarizing plate is (C), and the backlight is (D).

Comparative Example 2
A broadband cholesteric liquid crystal layer similar to that of Example 2 was used as the circularly polarized reflective polarizer (a). The same C plate layer as in Example 2 was used.

  The circularly polarized reflective polarizer (a) was placed on the backlight side with the surface having a selective reflection band on the long wavelength side facing down. On top of this, the four C plates were laminated with an adhesive having a thickness of 5 μm. The laminate of the four C plate layers was used as a retardation layer (b). Further on this, a circularly polarized reflective polarizer (a) is laminated with an adhesive having a thickness of 5 μm on the long wavelength side, and an optical element (A ′). Got.

  A polycarbonate retardation plate (λ / 4 plate) having a front retardation of 130 nm was laminated with an adhesive having a thickness of 5 μm. The axial direction of the linearly polarized light obtained by transmission and the transmission axis direction of the backlight side polarizing plate (manufactured by Nitto Denko Corp., SEG1425DU) of the liquid crystal display device are arranged so as to be a condensing and collimating system. . In FIG. 6, the block diagram of the comparative example 2 is shown. In FIG. 6, the retardation layer (b) is a four-layer laminate of C plates. The λ / 4 plate is (B), the backlight side polarizing plate is (C), and the backlight is (D).

(Evaluation)
The same evaluation as described above was performed on the condensing and collimating system. 12 and 13 show a comparison between Example 2 and Comparative Example 2. FIG. FIG. 12 is a comparison of luminance viewing angle characteristics, and it can be seen that the transmission amount of light incident at a large angle with respect to the normal direction can be suppressed in Example 2 as compared with Comparative Example 2. Further, in Example 2, the front luminance was improved as compared with Comparative Example 2. FIG. 13 is a chromaticity diagram when the incident angle is increased in order from the normal direction, and it can be seen that the moving distance of the point in Example 2 is smaller than that in Comparative Example 2. This point represents the color at each incident angle, and the greater the coloring, the greater the distance that the point moves as the color changes. From this, it can be seen that coloring is reduced in Example 2, and coloring is severe in Comparative Example 2.

Example 3
(Circularly polarized reflective polarizer (a))
A broadband cholesteric liquid crystal layer similar to that in Example 1 was used as the circularly polarizing reflective polarizer (a).

(C plate layer)
Transparent polyimide [6FDA-TFMD] was dissolved in a solvent, applied to a substrate so that the thickness after drying was 10 μm, and the solvent was dried to obtain a C plate layer (negative) having a thickness of 10 μm. When the retardation of the C plate was measured, the front retardation was 2 nm and the thickness direction retardation was 400 nm with respect to light having a wavelength of 550 nm. The phase difference when the incident light was measured by tilting by 30 ° was 60 nm. Further, the phase difference when the incident light was measured by tilting by 60 ° was 140 nm.

(Optical element (A))
The circularly polarized reflective polarizer (a) was placed on the backlight side with the surface having a selective reflection band on the long wavelength side facing down. On top of this, a circularly polarizing reflective polarizer (a) was laminated with an adhesive having a thickness of 5 μm on the surface having a selective reflection band on the long wavelength side. Further, the two C plates were laminated with an adhesive having a thickness of 5 μm. The two C-plate laminate had a phase difference of 120 nm when measured by tilting incident light by 30 °. Further, the phase difference when the incident light was measured by tilting by 60 ° was 280 nm. The laminate of the two C plate layers was used as a retardation layer (b). Further on this, a circularly polarized reflective polarizer (a) is laminated with an adhesive having a thickness of 5 μm on the long wavelength side, and an optical element (A) is laminated. Obtained.

  The incident light incident at an angle of 60 ° with respect to the normal direction is polarized and separated from the light source by the first circular polarization type reflective polarizer (a), and then the first circular polarization type reflection from the light source side. The sum of the phase differences received by the polarizer (a) and the second circularly polarized reflective polarizer (a) is 250 nm and is adjusted to be λ / 4 to 3λ / 4. ing.

  The incident light incident at an angle of 30 ° with respect to the normal direction is polarized and separated from the light source by the first circularly polarized reflective polarizer (a), and then the first circularly polarized light reflected from the light source side. Phase difference received by the polarizer (a), the second circularly polarized reflective polarizer (a), the retardation layer (b), and the third circularly polarized reflective polarizer (a) before being polarized and separated. Is 320 nm, and is adjusted to be λ / 4 to 3λ / 4.

  A polycarbonate retardation plate (λ / 4 plate) having a front retardation of 130 nm was laminated with an adhesive having a thickness of 5 μm. The axial direction of the linearly polarized light obtained by transmission and the transmission axis direction of the backlight side polarizing plate (manufactured by Nitto Denko Corp., SEG1425DU) of the liquid crystal display device are arranged so as to be a condensing and collimating system. . The block diagram of Example 3 is as FIG. In FIG. 4, the retardation layer (b) is a four-layer laminate of C plates. The λ / 4 plate is (B), the backlight side polarizing plate is (C), and the backlight is (D).

Comparative Example 3
A broadband cholesteric liquid crystal layer similar to that in Example 3 was used as the circularly polarized reflective polarizer (a). Further, the same C plate layer as in Example 3 was used.

  The circularly polarized reflective polarizer (a) was placed on the backlight side with the surface having a selective reflection band on the long wavelength side facing down. On top of this, the four C plates were laminated with an adhesive having a thickness of 5 μm. The laminate of the four C plate layers was used as a retardation layer (b). Further on this, a circularly polarized reflective polarizer (a) is laminated with an adhesive having a thickness of 5 μm on the long wavelength side, and an optical element (A ′). Got.

  A polycarbonate retardation plate (λ / 4 plate) having a front retardation of 130 nm was laminated with an adhesive having a thickness of 5 μm. The axial direction of the linearly polarized light obtained by transmission and the transmission axis direction of the backlight side polarizing plate (manufactured by Nitto Denko Corp., SEG1425DU) of the liquid crystal display device are arranged so as to be a condensing and collimating system. . In FIG. 6, the block diagram of the comparative example 3 is shown. In FIG. 6, the retardation layer (b) is a two-layer laminate of C plates. The λ / 4 plate is (B), the backlight side polarizing plate is (C), and the backlight is (D).

(Evaluation)
The same evaluation as described above was performed on the condensing and collimating system. 14 and 15 show a comparison between Example 3 and Comparative Example 3. FIG. FIG. 14 is a comparison of luminance viewing angle characteristics, and it can be seen that Example 3 can suppress the amount of transmitted light incident at a large angle with respect to the normal direction, as compared with Comparative Example 3. Further, in Example 3, the front luminance was improved as compared with Comparative Example 3. FIG. 15 is a chromaticity diagram when the incident angle is increased in order from the normal direction, and it can be seen that the moving distance of the point in Example 3 is smaller than that in Comparative Example 3. This point represents the color at each incident angle, and the greater the coloring, the greater the distance that the point moves as the color changes. From this, it can be seen that coloring is reduced in Example 3, and coloring is severe in Comparative Example 3.

Example 4
A broadband cholesteric liquid crystal layer similar to that in Example 1 was used as the circularly polarizing reflective polarizer (a). The same C plate layer as in Example 1 was used.

  The circularly polarized reflective polarizer (a) was placed on the backlight side with the surface having a selective reflection band on the long wavelength side facing down. On top of this, the two C plates were laminated with an adhesive having a thickness of 5 μm. On top of this, a circularly polarizing reflective polarizer (a) was laminated with an adhesive having a thickness of 5 μm on the surface having a selective reflection band on the long wavelength side. Further on this, a circularly polarized reflective polarizer (a) is laminated with an adhesive having a thickness of 5 μm on the long wavelength side, and an optical element (A) is laminated. Obtained.

  The incident light incident at an angle of 60 ° with respect to the normal direction is polarized and separated from the light source by the first circular polarization type reflective polarizer (a), and then the first circular polarization type reflection from the light source side. The sum of the phase differences received before the polarization separation is performed by the polarizer (a), the retardation layer (b) and the second circularly polarized reflective polarizer (a) is 400 nm, and λ / 4 to 3λ / It is adjusted to be 4.

  The incident light incident at an angle of 30 ° with respect to the normal direction is polarized and separated from the light source by the first circularly polarized reflective polarizer (a), and then the first circularly polarized light reflected from the light source side. Phase difference received by the polarizer (a), the retardation layer (b), the second circularly polarized reflective polarizer (a), and the third circularly polarized reflective polarizer (a) before being polarized and separated. Is 270 nm and is adjusted to be λ / 4 to 3λ / 4.

  A polycarbonate retardation plate (λ / 4 plate) having a front retardation of 130 nm was laminated with an adhesive having a thickness of 5 μm. The axial direction of the linearly polarized light obtained by transmission and the transmission axis direction of the backlight side polarizing plate (manufactured by Nitto Denko Corp., SEG1425DU) of the liquid crystal display device are arranged so as to be a condensing and collimating system. . FIG. 5 shows a configuration diagram of the fourth embodiment. In FIG. 5, the retardation layer (b) is a two-layer laminate of C plates. The λ / 4 plate is (B), the backlight side polarizing plate is (C), and the backlight is (D).

(Evaluation)
The same evaluation as described above was performed on the condensing and collimating system. 16 and 17 show a comparison between Example 4 and Comparative Example 1. FIG. FIG. 16 is a comparison of luminance viewing angle characteristics, and it can be seen that Example 4 can suppress the transmission amount of light incident at a large angle with respect to the normal direction as compared with Comparative Example 1. Further, in Example 4, the front luminance was improved as compared with Comparative Example 1. FIG. 17 is a chromaticity diagram when the incident angle is increased in order from the normal direction, and it can be seen that the moving distance of the point in Example 4 is smaller than that in Comparative Example 1. This point represents the color at each incident angle, and the greater the coloring, the greater the distance that the point moves as the color changes. From this, it can be seen that coloring is reduced in Example 4, and coloring is severe in Comparative Example 1.

It is an example of sectional drawing of the optical element of this invention. It is an example of sectional drawing of the optical element of this invention. It is an example of sectional drawing of the optical element of this invention. It is an example of sectional drawing of the liquid crystal display device of this invention. It is an example of sectional drawing of the liquid crystal display device of this invention. 6 is a cross-sectional view of a liquid crystal display device of Comparative Example 1. FIG. It is a graph which shows the refractive index wavelength dispersion characteristic of a circularly polarized light-type reflective polarizer (cholesteric liquid crystal layer). It is a graph which shows the pitch change of a circularly polarized light type | mold reflective polarizer (cholesteric liquid crystal layer). It is a graph in order to convert the phase difference with respect to the incident angle of a circularly polarized light-type reflective polarizer (cholesteric liquid crystal layer). 6 is a graph showing luminance viewing angle characteristics of Example 1 and Comparative Example 1. 3 is a graph showing chromaticity diagrams of Example 1 and Comparative Example 1. 6 is a graph showing luminance viewing angle characteristics of Example 2 and Comparative Example 2. 6 is a graph showing chromaticity diagrams of Example 2 and Comparative Example 2. 10 is a graph showing luminance viewing angle characteristics of Example 3 and Comparative Example 3. 6 is a graph showing chromaticity diagrams of Example 3 and Comparative Example 3. 6 is a graph showing luminance viewing angle characteristics of Example 4 and Comparative Example 1. 6 is a graph showing chromaticity diagrams of Example 4 and Comparative Example 1.

Explanation of symbols

A, A ′ optical element a circularly polarized reflective polarizer b retardation layer B λ / 4 wavelength plate C polarizing plate D backlight

Claims (13)

At least three circularly polarized reflective polarizers (a) in which the wavelength bands of selective reflection of polarized light overlap each other are laminated,
Between at least one layer of the circularly polarized reflective polarizer (a) and the circularly polarized reflective polarizer (a), the front phase difference (normal direction) is almost zero and tilted by 30 ° or more with respect to the normal direction. A layer (b) having a phase difference of λ / 8 or more with respect to the incident light incident thereon, and another circularly polarized reflective polarizer (a) and a circularly polarized reflective polarizer (a) An optical element characterized in that at least one of the layers is laminated without a retardation layer.   Circularly polarized reflective polarizer (a) / retardation layer (b) / circularly polarized reflective polarizer (a) / circularly polarized reflective polarizer (a) are laminated in this order. The optical element according to claim 1. The circularly polarized reflective polarizer (a) / retardation layer (b) / circularly polarized reflective polarizer (a) / circularly polarized reflective polarizer (a) are stacked in the order of arrangement from the light source side. ,
The incident light incident at an angle of 30 ° or more with respect to the normal direction is polarized and separated from the light source by the first circular polarization type reflective polarizer (a), and then the first circular polarization type from the light source side. Sum of phase differences received before polarization separation by the reflective polarizer (a), the retardation layer (b), and the second circular polarization type reflective polarizer (a), or the first circular polarization type from the light source After being polarized and separated by the reflective polarizer (a), the first circularly polarized reflective polarizer (a), the retardation layer (b), and the second circularly polarized reflective polarizer (a) from the light source side. And the sum of the phase differences received by the third circularly polarized reflective polarizer (a) before being polarized and separated is λ / 4 + λ · n to 3λ / 4 + λ · n (where n is an integer of 0 or more). Adjusted to be, and
The incident light incident at an angle of 60 ° with respect to the normal direction is polarized and separated from the light source by the first circular polarization type reflective polarizer (a), and then the first circular polarization type reflection from the light source side. Sum of phase differences received before polarization separation by the polarizer (a), the retardation layer (b) and the second circularly polarized reflective polarizer (a), or the first circularly polarized reflection from the light source After being polarized and separated by the polarizer (a), the first circularly polarized reflective polarizer (a), the retardation layer (b), the second circularly polarized reflective polarizer (a), and The sum of the phase differences received before the third circularly polarized reflective polarizer (a) undergoes polarization separation is λ / 4 + λ · n to 3λ / 4 + λ · n (where n is an integer greater than or equal to 0). The optical element according to claim 1, wherein the optical element is adjusted as follows. The circularly polarized reflective polarizer (a) / circularly polarized reflective polarizer (a) / retardation layer (b) / circularly polarized reflective polarizer (a) are stacked in the order from the light source side. ,
The incident light incident at an angle of 30 ° or more with respect to the normal direction is polarized and separated from the light source by the first circular polarization type reflective polarizer (a), and then the first circular polarization type from the light source side. The sum of the phase differences received before the polarized light is separated by the reflective polarizer (a) and the second circularly polarized reflective polarizer (a), or the first circularly polarized reflective polarizer (a) from the light source After the polarization separation, the first circularly polarized reflective polarizer (a), the second circularly polarized reflective polarizer (a), the retardation layer (b) and the third circularly polarized light from the light source side. Is adjusted so that the sum of the phase differences received before polarization separation by the type reflective polarizer (a) is λ / 4 + λ · n to 3λ / 4 + λ · n (where n is an integer of 0 or more). ,And,
The incident light incident at an angle of 60 ° with respect to the normal direction is polarized and separated from the light source by the first circular polarization type reflective polarizer (a), and then the first circular polarization type reflection from the light source side. The sum of the phase difference received before the light is separated by the polarizer (a) and the second circularly polarized reflective polarizer (a), or polarized by the first circularly polarized reflective polarizer (a) from the light source After being separated, the first circularly polarizing reflective polarizer (a), the second circularly polarizing reflective polarizer (a), the retardation layer (b), and the third circularly polarizing type from the light source side. The sum of the phase differences received before the polarized light is separated by the reflective polarizer (a) is adjusted to be λ / 4 + λ · n to 3λ / 4 + λ · n (where n is an integer of 0 or more). The optical element according to claim 1.   5. The optical element according to claim 1, wherein the selective reflection wavelengths of at least three circularly polarized reflective polarizers (a) overlap each other in a wavelength range of 550 nm ± 10 nm.   The optical element according to any one of claims 1 to 5, wherein a cholesteric liquid crystal material is used as the circularly polarized reflective polarizer (a). The retardation layer (b)
Fixed planar orientation of cholesteric liquid crystal phase having selective reflection wavelength region other than visible light region,
A fixed liquid crystal in a homeotropic alignment state;
A fixed discotic liquid crystal nematic phase or columnar phase alignment state,
A biaxially oriented polymer film,
An inorganic layered compound having negative uniaxiality and oriented and fixed so that the optical axis is in the normal direction of the surface, and
A film obtained from at least one polymer selected from the group consisting of polyamide, polyimide, polyester, poly (ether ketone), poly (amide-imide) and poly (ester-imide);
The optical element according to claim 1, wherein the optical element is at least one selected from the group consisting of:   A λ / 4 plate is arranged on the circularly polarized reflective polarizer (a) arranged on the viewing side (liquid crystal cell side) so that the transmitted light from the light source side becomes linearly polarized light. Item 8. The optical element according to any one of Items 1 to 7.   9. The polarizing plate is disposed on the λ / 4 plate side so that an axial direction of linearly polarized light obtained by transmission from the light source side and a transmission axis direction of the polarizing plate are aligned. Optical elements.   Each layer was laminated | stacked using the translucent adhesive agent or adhesive, The optical element in any one of Claims 1-9 characterized by the above-mentioned.   A condensing backlight system comprising at least a light source disposed on the optical element according to claim 1.   A liquid crystal display device comprising at least a liquid crystal cell in the condensing backlight system according to claim 11.   13. A liquid crystal display device according to claim 12, wherein a diffusion plate having no backscattering and depolarization is laminated on the liquid crystal cell viewing side.

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