JP2005266323A - Optical element, condensing backlight system and liquid crystal display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element with which incident light from a light source is condensed, made into parallel light by a polarizing element and transmission of light made incident in the normal direction with a large angle is suppressed. <P>SOLUTION: The optical element is an optical element X, in which a cholesteric liquid crystal polarizing element A which performs polarizing separation of the incident light and a cholesteric liquid crystal polarizing element B in the same spiral direction as that of A. In the two polarizing elements, an exit light distortion ratio is ≥0.5 to the incident light in the normal direction, a distortion ratio is ≤0.2 when inclined by 60° from the normal direction. In the optical element X having linear polarizing components of the exit light increase as making an incident angle larger in A, and the linear polarization components of the exit light which increases as making the incident angle larger have a linear polarization axis in the perpendicular direction to the normal direction of a polarizing element surface in B, the linear polarization components of the exit light as making the incident angle larger have the linear polarizing axis in the parallel direction to the normal direction of the polarizing element surface, a circularly polarized reflective polarizer C is further arranged in either one of two polarizing elements. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an optical element using a polarizing element. 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.

  Attempts have long been made to condense or collimate a diffuse light source using an optical film having a flat surface, or to control the transmittance only in a specific direction. As a typical example, there is a method of combining a bright line light source and a band pass filter (for example, Patent Document 1, Patent Document 2, Patent Document 3, Patent Document 4, Patent Document 5, Patent Document 6, Patent Document 7, (See Patent Document 8, Patent Document 9, etc.). In addition, a light source that emits bright lines, such as CRT and electroluminescence, and a method of concentrating and collimating light by arranging a band pass filter on a display device have been proposed (for example, Patent Document 10, Patent Document 11, Patent). (Refer to Literature 12, Patent Literature 13, Patent Literature 14 and the like).

  Further, a method combining polarization and phase difference has been proposed (see Patent Document 15). Other optical elements comprising a reflective polarizer, an optical rotatory plate, and a reflective polarizer have been proposed (see Patent Document 16, Patent Document 17, and Patent Document 18). Moreover, what uses the hologram material is proposed (refer patent document 19).

  However, in the method using the bright line spectrum as an optical film for imparting directivity to the diffused light source, the precision relating to the wavelength matching between the light source type and the bandpass filter is high, and the production is difficult. On the other hand, it is not a big problem with monochromatic light, but when it corresponds to the three primary colors, the color will be felt if the transmittance change of each color does not change at the same ratio depending on the incident angle. Therefore, the combination of the bright line light source and the bandpass filter requires precise matching between the light source wavelength and the bandpass filter, and the technical difficulty is high.

  For example, in Patent Document 13 and Patent Document 14, a reflection plate obtained by combining a left circular polarization separation plate and a right circular polarization separation plate, or a reflection obtained by arranging a half-wave plate between circular polarization separation plates in the same direction. Condensing light in the front direction using a plate. However, in this system, it is necessary to form a layer corresponding to each wavelength of the light source, and three sets of layers are necessary for colorization. This was complicated and expensive.

  In addition, when using polarized light and a phase difference, if the angle at which the light can be emitted is narrowed, a secondary transmission region tends to appear at a larger incident angle.

  In general, the optical path length increases when obliquely entering the phase difference plate, and the optical path length difference tends to increase as the optical path length increases. By combining this characteristic with a polarizer, a polarizing element having an angle dependency in transmittance as in Patent Document 15 can be manufactured. Such a polarizing element can change the transmittance according to the incident angle. For example, according to such a polarizing element, it is possible to increase the transmittance in the front direction and reduce the transmittance of oblique incident light.

  Furthermore, between the optical elements that separate circularly polarized light in the same direction, if a layer that does not have a phase difference in the front and gives a phase difference of ½ wavelength in the oblique direction is inserted, the oblique direction is totally reflected. Light is transmitted only in the direction (see Patent Document 20). However, in this method, if a condition for total reflection at a specific angle is set, there remains a problem that a region that transmits again at a larger incident angle occurs. As the incident angle increases, the optical path length increases and the phase difference received increases. For this reason, it has the property of transmitting again at an incident angle that receives a phase difference of 3/4 wavelength. For this reason, when the transmission characteristic only to the front face is narrowed down, a transmission component in an oblique direction is generated and a failure occurs.

  Patent Document 17, Patent Document 18, and Patent Document 19 are all about the problem of productivity reduction and area yield deterioration caused by laminating the reflective polarizer laminates for transflective reflector applications by shifting the angles. Can be produced by roll-to-roll by using an optical rotator to improve productivity. In such a general combination of a reflective polarizer, an optical rotatory plate, and a reflective polarizer, the angle dependency of the transmittance did not occur. In addition, it is difficult to control and manufacture a phase difference plate whose optical rotation characteristics change depending on the incident angle with a general optical material such as quartz or sucrose, or a laminated body of phase difference plates. there were.

  On the other hand, most of the hologram materials are expensive, soft and have poor mechanical properties, and there is a problem in long-term durability.

As described above, the conventional optical element has problems such as difficulty in fabrication, difficulty in obtaining the desired optical characteristics, and poor reliability.
JP-A-6-235900 Japanese Patent Laid-Open No. 2-158289 Japanese National Patent Publication No. 10-521525 US Pat. No. 6,307,604 German Patent Application Publication No. 3836955 German Patent Application No. 422028 European Patent Application Publication No. 578302 US Patent Application Publication No. 2002/34009 International Publication No. 02/25687 Pamphlet US Patent Application Publication No. 2001/521443 US Patent Application Publication No. 2001/516066 US Patent Application Publication No. 2002/036735 JP 2002-90535 A Japanese Patent Laid-Open No. 2002-258048 Japanese Patent No. 2561483 US Pat. No. 4,984,872 US Patent Application Publication No. 2003/63236 International Publication No. 03/27731 Pamphlet International Publication No. 03/27756 Pamphlet Japanese Patent Laid-Open No. 10-321025

  The present invention is an optical element that can condense and collimate incident light from a light source using a polarizing element, and can suppress transmission of light incident at a large angle with respect to the normal direction. The purpose is to provide.

  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 element and have completed the present invention. That is, the present invention is as follows.

1. A polarizing element (A) formed of cholesteric liquid crystal that emits incident light after being polarized and separated, and a polarizing element (B) formed of cholesteric liquid crystal having the same spiral direction as the polarizing element (A) are arranged. An optical element (X),
The polarizing element (A) and the polarizing element (B) are both
The outgoing light with respect to the incident light in the normal direction has a distortion rate of 0.5 or more,
The outgoing light with respect to the incident light that is inclined by 60 ° or more from the normal direction has a distortion rate of 0.2 or less,
The linearly polarized light component of the emitted light increases as the incident angle increases, and
In the polarizing element (A), the linearly polarized light component of the emitted light that increases as the incident angle increases has a polarization axis of linearly polarized light in a direction substantially orthogonal to the normal direction of the polarizing element surface.
The polarizing element (B) is an optical element in which the linearly polarized light component of the emitted light that increases as the incident angle increases has a polarization axis of linearly polarized light in a direction substantially parallel to the normal direction of the polarizing element surface. (X)
Furthermore, the circularly polarized reflective polarizer (C) is disposed on either side of the polarizing element (A) or the polarizing element (B).

  2. 2. The optical element according to 1 above, wherein the polarizing element (A) and the polarizing element (B) substantially reflect a non-transmission component of incident light.

  3. 3. The optical element as described in 1 or 2 above, wherein the thickness of the polarizing element (A) and the polarizing element (B) is 2 μm or more.

  4). 4. The optical element as described in any one of 1 to 3 above, wherein the polarizing bandwidth of the polarizing element (A) and the polarizing element (B) is 200 nm or more.

  5). 5. The optical element as described in any one of 1 to 4 above, wherein the circularly polarized reflective polarizer (C) is a cholesteric liquid crystal layer (C1).

  6). The circularly polarizing reflective polarizer (C) has a cholesteric liquid crystal layer (C1) and a layer (C2) in which the front phase difference (normal direction) is λ / 8 or less and the phase difference increases as the incident angle increases. 5. The optical element as described in any one of 1 to 4 above, characterized by comprising:

  7). 7. The optical element as described in 5 or 6 above, wherein the cholesteric liquid crystal (C1) has a reflection bandwidth of 200 nm or more.

  8). 5. The optical element as described in any one of 1 to 4 above, wherein the circularly polarized reflective polarizer (C) has a linearly polarized reflective polarizer (C3) and a quarter-wave plate (C4).

9. A quarter-wave plate (C4) has a direction in which the in-plane refractive index is maximum as an X axis, a direction perpendicular to the X axis as a Y axis, and a film thickness direction as a Z axis. When the refractive index is nx, ny, nz,
9. The optical element according to 8 above, wherein an Nz coefficient represented by Nz = (nx−nz) / (nx−ny) is −3 <Nz <4.

  10. The optical element according to 8 above, wherein the 10.1 / 4 wavelength plate (C4) includes a ½ wavelength plate (C41) and a ¼ wavelength plate (C42).

11. The half-wave plate (C41) has the X-axis as the direction in which the in-plane refractive index is maximum, the Y-axis as the direction perpendicular to the X-axis, and the Z-axis as the thickness direction of the film. When the refractive index is nx, ny, nz,
Nz coefficient represented by Nz = (nx−nz) / (nx−ny) is −1.5 <Nz <2,
The quarter-wave plate (C42) has an in-plane refractive index in the X-axis direction, a direction perpendicular to the X-axis in the Y-axis direction, and a film thickness direction in the Z-axis direction. Is nx, ny, nz,
11. The optical element as described in 10 above, wherein the Nz coefficient represented by Nz = (nx−nz) / (nx−ny) is −1.5 <Nz <2.

  12 The above-mentioned 1 characterized in that a quarter-wave plate (R) is arranged on the side where the circularly polarized reflective polarizer (C) is not arranged so that the emitted light from the light source side becomes linearly polarized light. The optical element in any one of -11.

  13. The optical element as described in 12 above, wherein the quarter-wave plate (R) is a broadband wavelength plate that functions as a substantially quarter-wave plate in the entire visible light region.

14. The quarter-wave plate (R) has an X-axis in the direction in which the in-plane refractive index is maximum, a Y-axis in the direction perpendicular to the X-axis, and nx, ny, and thickness d in the respective axial directions. (Nm)
14. The optical element as described in 13 above, wherein the front phase difference value at each wavelength in the light source wavelength band (420 to 650 nm): (nx−ny) × d is within ¼ wavelength ± 10%.

15. The quarter-wave plate (R) has a direction in which the in-plane refractive index is maximum as an X axis, a direction perpendicular to the X axis as a Y axis, and a film thickness direction as a Z axis. When the refractive index is nx, ny, nz,
15. The optical element according to any one of 12 to 14, wherein an Nz coefficient represented by Nz = (nx−nz) / (nx−ny) is −2.5 <Nz ≦ 1.

  16. A polarizing plate is arranged on the quarter wavelength plate (R) side so that the polarization axis direction of linearly polarized light obtained by transmission from the light source side is aligned with the polarization axis direction of the polarizing plate. 16. The optical element according to any one of 12 to 15 above.

  17. The optical element according to any one of the above 1 to 16, wherein each layer is laminated using a translucent adhesive or pressure-sensitive adhesive.

  18. 18. A condensing backlight system comprising at least a light source disposed on the optical element according to any one of 1 to 17 above.

  19. 19. A liquid crystal display device comprising at least a liquid crystal cell in the condensing backlight system according to the above 18.

  20. 20. A liquid crystal display device comprising the liquid crystal display device as described in 19 above, wherein a diffusion plate having no backscattering or depolarization is laminated on the liquid crystal cell viewing side.

  The optical element (Y) of the present invention is formed by a polarizing element (A) formed of cholesteric liquid crystal that emits polarized light by separating incident light, and a cholesteric liquid crystal having the same spiral direction as that of the polarizing element (A). And an optical element (X) in which the polarizing element (B) is disposed. Further, a circularly polarized reflective polarizer (C) is disposed on either side of the polarizing element (A) or the polarizing element (B) of the optical element (X). An example of a cross-sectional view of the optical element (Y) of the present invention is shown in FIG.

  The optical element (X) utilizes a unique phenomenon of the polarizing element (A) and the polarizing element (B). That is, in the optical element (X), when the incident angle is increased to a certain extent, the emitted light is linearly polarized, and even if the incident angle is further increased, the polarization axis direction of the linearly polarized light does not change, and the polarization state is kept constant. By utilizing the unique properties of the polarizing elements (A) and (B), the angle dependency of the emitted light is controlled to suppress the secondary transmission component at a large angle.

  In both of the polarizing element (A) and the polarizing element (B), the outgoing light with respect to the incident light in the normal direction has a distortion rate of 0.5 or more, and the vertical incident light or the incident angle close to the vertical incident is circular. Polarized light is emitted. Since the ratio of circularly polarized light increases as the distortion rate of outgoing light with respect to incident light in the normal direction increases, it is preferably 0.7 or higher, and more preferably 0.9 or higher. On the other hand, the outgoing light with respect to the incident light inclined at an angle of 60 ° or more from the normal direction has a distortion rate of 0.2 or less, and linearly polarized light is emitted at a deep incident angle. Since the ratio of linearly polarized light increases as the distortion rate of the outgoing light with respect to the incident light incident with an inclination of 60 ° or more from the normal direction, it is preferably 0.2 or less, more preferably 0.1 or less. Thus, the polarizing element (A) and the polarizing element (B) have a feature that the linearly polarized light component of the emitted light increases as the incident angle increases.

  In the polarizing element (A), the linearly polarized light component of the emitted light that increases as the incident angle increases has a polarization axis of linearly polarized light in a direction substantially orthogonal to the normal direction of the polarizing element surface. FIG. 1A shows that the outgoing light (e) transmitted through the polarizing element (A1) which is an optical surface (x-axis-y-axis plane) has different polarization components depending on the incident angle of the incident light (i). FIG. FIG. 1B is a conceptual diagram when the emitted light (e) is viewed from the z-axis direction. Note that, as shown in FIG. 3, (i) linearly polarized light, (ii) natural light, (iii) circularly polarized light, and (iv) elliptically polarized light.

  Emission light (e1): Emission light with respect to the incident light (i1) in the z-axis direction (normal direction) with respect to the polarizing element (A1), and is circularly polarized light.

  Outgoing light (e2), (e4): outgoing light with respect to incident light (i2), (i4) obliquely incident on the polarizing element (A1), and elliptically polarized light. The outgoing light (e2) is elliptically polarized light that exists on a plane including the z axis and the y axis and has an axis orthogonal to the plane. The outgoing light (e4) is elliptically polarized light that exists on a plane including the z-axis and the x-axis and has an axis orthogonal to the plane.

  Outgoing light (e3), (e5): outgoing light with respect to incident light (i3), (i5) obliquely incident on the polarizing element (A1) at a large angle, and linearly polarized light. The outgoing light (e3) is linearly polarized light that exists on a plane including the z-axis and the y-axis and has an axis orthogonal to the plane. The outgoing light (e5) is linearly polarized light that exists on a plane including the z-axis and the x-axis and has an axis orthogonal to the plane. Thus, the outgoing lights (e3) and (e5), which are linearly polarized light, have their polarization axes substantially perpendicular to the z-axis, that is, parallel to the optical surface (x-axis-y-axis plane). Yes.

  On the other hand, in the polarizing element (B), the linearly polarized light component of the emitted light that increases as the incident angle increases has a polarization axis of linearly polarized light in a direction substantially parallel to the normal direction of the polarizing element surface. . FIG. 2A shows that the outgoing light (e) transmitted through the polarizing element (B1) which is an optical surface (x-axis-y-axis plane) has different polarization components depending on the incident angle of the incident light (i). FIG. FIG. 2B is a conceptual diagram when the emitted light (e) is viewed from the z-axis direction.

  Emission light (e11): Emission light with respect to the incident light (i11) in the z-axis direction (normal direction) with respect to the polarizing element (B1) and circularly polarized light.

  Emission light (e12), (e14): Emission light with respect to incident light (i12), (i14) obliquely incident on the polarizing element (B1), and elliptically polarized light. The outgoing light (e12) is elliptically polarized light that exists on a plane including the z-axis and the y-axis and has an axis parallel to the plane. The outgoing light (e14) is elliptically polarized light that exists on a plane including the z-axis and the x-axis and has an axis parallel to the plane.

  Emission light (e13), (e15): Emission light with respect to incident light (i13), (i15) obliquely incident on the polarizing element (B1) at a large angle, and is linearly polarized light. The outgoing light (e13) is linearly polarized light that exists on a plane including the z-axis and the y-axis and has an axis parallel to the plane. The outgoing light (e15) is linearly polarized light that exists on a plane including the z-axis and the x-axis and has an axis parallel to the plane. Thus, the outgoing lights (e13) and (e15) which are linearly polarized light have their polarization axes substantially parallel to the z-axis, that is, orthogonal to the optical surface (x-axis-y-axis plane). Yes.

  The polarizing elements (A) and (B) are formed of a cholesteric liquid crystal layer. The reflection bandwidth of the polarizing element is preferably 200 nm or more. Conventionally, a cholesteric liquid crystal layer is supposed to transmit / reflect circularly polarized light regardless of the incident angle. See FIG. In fact, until now, in the single-pitch narrow-band cholesteric liquid crystal layer (a1), the emitted light has been circularly polarized regardless of the incident angle of the incident light. In the present invention, a cholesteric liquid crystal layer having a broadband selective reflection wavelength band finds out and utilizes a phenomenon in which linearly polarized light is transmitted when the incident angle of incident light is large as described above. That is, this phenomenon is not obtained in a single pitch cholesteric liquid crystal layer having a selective reflection function only at a specific wavelength, but is obtained only in a cholesteric liquid crystal layer in which the pitch length is changed over a wide band.

  In the past, when a cholesteric liquid crystal layer having a large birefringence is aligned to a thickness of several tens of μm (a2) by Takezoe (Jpn. J. Appl. Phys., 22, 1080 (1983)) It has been reported that incident light having a large angle is totally reflected and cannot be transmitted. See FIG. However, this document does not describe that incident light having a large incident angle is linearly polarized.

  The polarizing elements (A) and (B) having the above phenomenon are obtained, for example, by forming a cholesteric liquid crystal layer having a selective reflection wavelength band covering the entire visible light region by stacking cholesteric liquid crystal layers having different center wavelengths. be able to. See FIG. FIG. 6 shows a case where three layers of R (red wavelength region), G (green wavelength region), and B (blue wavelength region) are stacked. In addition, a cholesteric liquid crystal layer having a wider band by changing the twist pitch length in the thickness direction can be used. See FIG. Thus, the polarizing element having the above phenomenon may be a laminated product of cholesteric liquid crystal layers having a plurality of different selective reflection wavelength bands as shown in FIG. 6, and the pitch length is continuous in the thickness direction as shown in FIG. Any of the changing cholesteric liquid crystal layers can be used, and both have the same effect.

  The reason why the above phenomenon occurs is not clear. If the light is simply separated by the Brewster angle at the interface of the liquid crystal layer, linearly polarized light should be generated for a specific wavelength even in a single pitch cholesteric liquid crystal layer. Further, since there is no difference between the cholesteric liquid crystal layer laminate and the cholesteric liquid crystal layer whose pitch length continuously changes in the thickness direction, it is clear that there is no reflection effect due to the lamination interface. Therefore, it can be considered that the above phenomenon is that the cholesteric liquid crystal layer having a different wavelength band imparts a phase difference to the circularly polarized light separated when transmitted through the cholesteric liquid crystal layer and linearly polarized. Further, since the polarizing elements (A) and (B) are obtained when the twist pitch length of the cholesteric liquid crystal is discontinuous or has a pitch on the long wavelength side, the position of the cholesteric liquid crystal layer is obtained. It is thought that the angle dependency of the phase difference characteristic has an effect.

  In order for the above phenomenon to function effectively, a sufficiently wide selective reflection bandwidth is required, preferably 200 nm or more, more preferably 300 nm or more, and even more preferably 400 nm or more. Specifically, in order to cover the visible light region, it is necessary to cover the range of 400 to 600 nm. Since the selective reflection wavelength shifts to the short wavelength side according to the incident angle, the extended selective reflection wavelength band should be extended to the long wavelength side to cover the visible light range regardless of the incident angle. However, it is not limited to this.

  In order for the phenomenon of the polarizing element of the present invention to function effectively, the cholesteric liquid crystal layer is preferably sufficiently thick. In general, in the case of a cholesteric liquid crystal layer having a single pitch length, sufficient selective reflection can be obtained if the thickness is about several pitches (2 to 3 times the selective reflection center wavelength). If the selective reflection center wavelength is in the range of 400 to 600 nm, considering the refractive index of the cholesteric liquid crystal, it functions as a polarizing element if the thickness is about 1 to 1.5 μm. Since the cholesteric liquid crystal layer used in the polarizing element of the present invention has a reflection band in a wide band, the thickness is preferably 2 μm or more. The thickness is desirably 4 μm or more, more desirably 6 μm or more.

  In order to obtain the polarizing elements (A) and (B), it is also preferable to use a broadband cholesteric liquid crystal whose selective reflection band covers the visible light region. This is because the broadband cholesteric liquid crystal layer has a large thickness and can effectively impart a phase difference.

  In the polarizing elements (A) and (B), circularly polarized light is obtained from incident light in the front direction (normal direction), and linearly polarized light is emitted from incident light at a deep incident angle in a direction perpendicular or parallel to the normal line. To do. Therefore, if the selective reflection wavelength band is sufficiently extended to the long wavelength side, the reflectance in the visible light region does not change, and it can be visually recognized as a specular reflector having no color tone change.

  As shown in FIG. 14, the optical element of the present invention has an optical element (X) in which a polarizing element (A) and a polarizing element (B) are laminated. Note that either side of the polarizing element (A) or the polarizing element (B) can be the incident side. A circularly polarized reflective polarizer (C) is disposed on the incident side. The circularly polarized reflective polarizer (C) will be described later. 14 to 16 show examples in which the polarizing element (A) side is the incident side.

  The polarizing element (A) and the polarizing element (B) are formed of cholesteric liquid crystals having the same spiral direction. As will be described in detail later, as the polarizing element (A), the circularly polarized light having the same rotational direction as shown in FIG. 2 is used for the polarizing element (A1) that can obtain the circularly polarized light having the rotational direction as shown in FIG. The polarizing element (B1) from which is obtained is used. On the other hand, FIG. 9 shows a polarizing element (A2) that can obtain circularly polarized light in the rotation direction opposite to that of the polarizing element (A1) shown in FIG. 1 as the polarizing element (A). For such a polarizing element (A2), a polarizing element (B2) as shown in FIG. 10 is used. The polarizing element (B2) can obtain circularly polarized light in the rotation direction opposite to that of the polarizing element (B1).

  In addition, in FIG. 13, the conceptual diagram in which polarization changes with a wavelength plate is shown. F: fast axis, S: slow axis. Reference numerals 13-1 and 13-2 denote conversion from linearly polarized light to circularly polarized light using a quarter wave plate (R). Reference numerals 13-3 and 13-4 indicate conversion from circularly polarized light to linearly polarized light using a quarter wave plate (R). Reference numerals 13-5 and 13-6 denote axial or rotational conversion using a half-wave plate (R1).

  First, a case where the optical element (X) is arranged in the order of the polarizing element (A1) and the polarizing element (B1) will be described. The outgoing light from the polarizing element (A1) is as shown in FIG. 1, and the outgoing light from the polarizing element (B1) is as shown in FIG. The outgoing light transmitted in the order of the polarizing element (A1) and the polarizing element (B1) is shown in FIG.

  Emission light (e21): Present on the z-axis. The outgoing light (e1) is a light beam vertically transmitted through the polarizing element (B1). The outgoing light (e1) is circularly polarized light having the same rotation direction.

  Emission light (e22): Present on a plane including the z-axis and the y-axis. The outgoing light (e2) is a light beam obliquely transmitted through the polarizing element (B1). Although it is circularly polarized light in the same direction as the outgoing light (e21), it has a small value.

  Non-emitted light (e23): Present on a plane including the z-axis and the y-axis. Since the emitted light (e3) is shielded by the polarizing element (B1), it hardly transmits. This is because the outgoing light (e3) and the outgoing light (e13) have an orthogonal relationship between the axes of linearly polarized light.

  Emission light (e24): Present on a plane including the z-axis and the x-axis. The outgoing light (e4) is a light beam obliquely transmitted through the polarizing element (B1). Although it is circularly polarized light in the same direction as the outgoing light (e21), it has a small value.

  Non-emitted light (e35): Present on a plane including the z-axis and the x-axis. Since the outgoing light (e5) is shielded by the polarizing element (B1), it hardly transmits. This is because the outgoing light (e5) and the outgoing light (e15) are orthogonal to each other in the axis angle of the linearly polarized light.

  A case where the optical element (X) is arranged in the order of the polarizing element (A2) and the polarizing element (B2) will be described. The outgoing light transmitted only through the polarizing element (A2) is as shown in FIG. 9, and the outgoing light transmitted through only the polarizing element (B2) is as shown in FIG. The outgoing light transmitted in the order of the polarizing element (A2) and the polarizing element (B2) is shown in FIG.

  As shown in FIG. 9, the outgoing light transmitted only through the polarizing element (A2) is opposite in the axial direction and the rotational direction to the polarizing element (A1).

  Output light (e31): present on the z-axis. It is a light beam transmitted vertically through the polarizing element (A2). The outgoing light (e1) transmitted through the polarizing element (A1) is circularly polarized light whose rotational direction is opposite.

  Emission light (e32): Light rays obliquely transmitted through the polarizing element (A2). The outgoing light (e32) is elliptically polarized light having an axis orthogonal to the plane including the z axis and the y axis.

  Emission light (e33): Light that has passed through the polarizing element (A2) at a large incident angle. The outgoing light (e33) is linearly polarized light having an axis orthogonal to the plane including the z axis and the y axis.

  Emission light (e34): Light rays obliquely transmitted through the polarizing element (A2). The outgoing light (e34) is elliptically polarized light having an axis orthogonal to the plane including the z axis and the x axis.

  Emission light (e35): A light beam transmitted through the polarizing element (A2) at a large incident angle. The outgoing light (e35) is linearly polarized light having an axis orthogonal to the plane including the z axis and the x axis.

  As shown in FIG. 10, the emitted light that has passed through only the polarizing element (B2) is opposite in the axial direction and rotational direction to the polarizing element (B1).

  Emission light (e41): Present on the z-axis. It is a light beam vertically transmitted through the polarizing element (B2). The outgoing light (e11) transmitted through the polarizing element (B1) is circularly polarized light whose rotational direction is opposite.

  Emission light (e42): Light rays obliquely transmitted through the polarizing element (B2). The outgoing light (e42) is elliptically polarized light having an axis parallel to the plane including the z axis and the y axis.

  Emission light (e43): A light beam transmitted through the polarizing element (B2) at a large incident angle. The outgoing light (e43) is linearly polarized light having an axis parallel to the plane including the z axis and the y axis.

  Emission light (e44): Light rays obliquely transmitted through the polarizing element (B2). The outgoing light (e44) is elliptically polarized light having an axis parallel to the plane including the z axis and the x axis.

  Emission light (e45): Light that has passed through the polarizing element (B2) at a large incident angle. The outgoing light (e45) is linearly polarized light having an axis parallel to the plane including the z axis and the x axis.

  The emitted light that has passed through the polarizing element (A2) and the polarizing element (B2) in this order is shown in FIG.

  Emission light (e51): Present on the z-axis. The outgoing light (e31) is a light beam vertically transmitted through the polarizing element (B2). The outgoing light (e31) is circularly polarized light having the same rotation direction.

  Emission light (e52): exists on a plane including the z-axis and the y-axis. The outgoing light (e32) is a light beam obliquely transmitted through the polarizing element (B2). Although it is circularly polarized light in the same direction as the outgoing light (e51), it has a small value.

  Non-emitted light (e53): Present on a plane including the z-axis and the y-axis. The outgoing light (e33) is hardly transmitted because it is shielded by the polarizing element (B2). This is because the outgoing light (e33) and the outgoing light (e43) have an orthogonal relationship between the axes of linearly polarized light.

  Emission light (e54): exists on a plane including the z-axis and the y-axis. The emitted light (e34) is a light beam obliquely transmitted through the polarizing element (B2). Although it is circularly polarized light in the same direction as the outgoing light (e51), it has a small value.

  Non-emitted light (e55): Present on a plane including the z-axis and the x-axis. Since the outgoing light (e35) is shielded by the polarizing element (B2), it hardly transmits. This is because the outgoing light (e35) and the outgoing light (e45) are orthogonal to each other in the axis angle of the linearly polarized light.

  As shown in FIG. 8 or FIG. 11 above, according to the optical element (X), incident light in the vertical direction is emitted as circularly polarized light, but incident light incident in an oblique direction at a large angle cannot be transmitted. Moreover, since the polarizing element (A) and the polarizing element (B) are cholesteric liquid crystals, there is little absorption loss due to the polarization separation function by selective reflection, and all the light rays that could not be emitted can be reflected and recycled to the light source side. As a result, the emitted light can be efficiently extracted in the normal direction (vertical direction). If the polarization degree of the polarizing element (A) and the polarizing element (B) is sufficiently high, there is little absorption loss and the circularly polarized light can be extracted with high efficiency in the vertical direction. Further, since only the polarizing element (A) and the polarizing element (B) are disposed, and no retardation layer is required between them, the thickness can be reduced and the production is easy.

  In the optical element (X), incident light in the normal direction is emitted as circularly polarized light, and incident light incident in an oblique direction at a large angle cannot be transmitted. On the other hand, as shown in FIG. 8 or FIG. 11, circularly polarized light having a value smaller than that in the normal direction is emitted at a shallow angle close to the normal direction by obliquely incident light. Therefore, in order to collect light in the normal direction and improve the luminance, the circularly polarized light component emitted from the optical element (X) is increased in the normal direction, and the polarizing element (A) or the polarizing element (B) is shallow. Incident light incident at an angle is preferably shielded by increasing the linear polarization component. The optical element (Y) of the present invention increases the linearly polarized light component of incident light incident at a shallow angle close to the normal direction by making circularly polarized light incident on the optical element (X). The circularly polarized light component in the normal direction is increased by shielding and reflecting at. Therefore, in the present invention, the circularly polarized reflective polarizer (C) is arranged on the incident side of the optical element (X), and the luminance is further improved so that the circularly polarized light is incident on the optical element (X). .

  In the optical element (X), in the visible light region, it is difficult to align the axial directions of linearly polarized light with, for example, three wavelengths of R (610 nm), G (550 nm), and B (435 nm). Could cause problems. As in the optical element (Y) of the present invention, a circularly polarized reflective polarizer (C) is disposed on the incident side of the optical element (X), and circularly polarized light is incident on the optical element (X), thereby causing a color shift. Can be reduced.

  As described above, the incident light incident on the optical element (Y) of the present invention is emitted as circularly polarized light by the circularly polarized reflective polarizer (C) and then by the optical element (X). A quarter wave plate (R) can be arranged so as to be. See FIG. Circularly polarized light emitted from the optical element (X) can be converted into linearly polarized light by the quarter wavelength plate (R) (see FIGS. 13-3 and 4).

  FIG. 12 shows the circularly polarized light emitted from the polarizing element (A2) and the polarizing element (B2) as the optical element (X) in FIG. It shows a polarized state. In FIG. 8, the quarter-wave plate (R) is arranged on the circularly polarized light emitted from the polarizing element (A1) and the polarizing element (B1), which are the optical elements (X), and the emitted light is linearly polarized. In this case, linearly polarized light in a direction orthogonal to the linearly polarized light in FIG. 12 is obtained. In the following, FIG. 12 will be described.

  Emission light (e61): Present on the z-axis. The circularly polarized outgoing light (e51) is linearly polarized by the quarter-wave plate (R).

  Emission light (e62): exists on a plane including the z-axis and the y-axis. The circularly polarized outgoing light (e52) is linearly polarized by the quarter wavelength plate (R). The outgoing light (e62) has a smaller value than the outgoing light (e61).

  Non-emitted light (e63): Present on a plane including the z-axis and the y-axis. The non-emitted light (e63) is hardly emitted because it is shielded.

  Emission light (e64): Present on a plane including the z-axis and the x-axis. The circularly polarized outgoing light (e54) is linearly polarized by the quarter wave plate (R). The outgoing light (e64) has a smaller value than the outgoing light (e61).

  Non-emitted light (e65): Present on a plane including the z-axis and the y-axis. The non-emitted light (e65) is hardly emitted because it is shielded.

  Thus, what arrange | positioned the quarter wavelength plate (R) to the optical element (X) functions as an optical element which made the brightness improvement and condensing both compatible by arrange | positioning as a linearly polarizing element at the light source side of a liquid crystal display device. To do. The optical element (X) according to the present invention, which has essentially no absorption loss, reflects and recycles all light rays having an angle not incident on the liquid crystal display device to the light source side. This is because there is no exit and light is substantially condensed. In addition, since the optical element (Y) of the present invention makes circularly polarized light incident on the optical element (X) by the circularly polarized reflective polarizer (C), it is compared with the case where only the optical element (X) is used. In the normal direction and in the vicinity thereof, linearly polarized light is further condensed, while obliquely incident light has a great shielding effect even at a shallow angle close to the normal direction.

  That is, the optical element of the present invention has a high transmittance in the normal direction, a good shielding effect in the oblique direction, and no absorption loss in combination with the selective reflection characteristics of the cholesteric liquid crystal. Further, secondary transmission in an oblique direction and precise adjustment of wavelength characteristics are not required, and stable performance can be easily obtained. In addition, the problem of color shift can be reduced.

  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.

  Further, unlike the conventional lens sheet and prism sheet, the optical element of the present invention does not require an air interface and can be used by being laminated with a polarizing plate or the like as a laminated integrated product, which is advantageous in terms of handling. It has a great effect on thinning. Because it does not have a regular structure that is visible like a prism structure, moiré is unlikely to occur, and the use of diffuser plates that reduce the total light transmittance and lower haze (generally the total light transmittance is improved) Has the advantage that it can be easily performed. Of course, there is no problem when used in combination with a prism sheet or the like. For example, it is preferable to use a combination in which condensing to a steep front is performed by a prism sheet, and a secondary transmission peak appearing at a large emission angle by the prism sheet is shielded by the optical element of the present invention.

  Further, in a conventional backlight device using only a prism sheet, the direction of the outgoing light peak tends to be biased away from the light source cold cathode tube. This is because a large number of light beams emitted obliquely from the light guide plate are emitted away from the light source cold cathode tube, and it is difficult to position the peak intensity in the vertical direction of the screen. On the other hand, when the optical element according to the present invention is used, the emission peak can be easily matched in the front direction.

  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.

  As described above, the polarizing elements (A) and (B) of the present invention can be formed of a cholesteric liquid crystal layer having a reflection bandwidth of 200 nm or more. The cholesteric liquid crystal layer can be formed by stacking cholesteric liquid crystal layers having a plurality of different selective reflection wavelength bands. Further, a cholesteric liquid crystal layer whose pitch length continuously changes in the thickness direction can be used. In order to control the emitted light as shown in the polarizing element (A) of FIGS. 1 and 9 or the polarizing element (B) of FIGS. 2 and 10, the cholesteric is controlled. A liquid crystal layer is selected as appropriate. The polarizing element (A) and the polarizing element (B) are the same in the spiral direction of the cholesteric liquid crystal.

  The difference in the axial direction of linearly polarized light of obliquely transmitted light such as the polarizing element (A) and the polarizing element (B) can be arbitrarily produced depending on the order of lamination of the cholesteric liquid crystal layers and the production method. In the case of a polarization splitting element with a general Brewster angle, the transmitted light in the oblique direction is uniquely defined, and only those having a linearly polarized light axis in a direction substantially parallel to the normal of the optical surface can be obtained. Absent.

  The selective reflection wavelength band of the polarizing element (A) and the polarizing element (B) includes at least 550 nm, preferably 100 nm or more, more preferably 200 nm or more, and further preferably 300 nm or more. The polarizing element (A) and the polarizing element (B) have the same direction of circularly polarized light transmitted in the front direction and the same selective reflection wavelength band can be used, but the selective reflection wavelength band is limited to this. Is not to be done.

(Laminated body of cholesteric liquid crystal layer)
In the case where the polarizing element is a laminate of cholesteric liquid crystal layers having a plurality of different selective reflection wavelength bands, each cholesteric liquid crystal layer appropriately includes a plurality of cholesteric liquid crystal layers so that the reflection bandwidth of the laminate is 200 nm or more. Select and stack.

  A suitable cholesteric liquid crystal layer 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, if necessary, a chiral agent and an alignment aid by irradiation with ionizing radiation such as an electron beam or ultraviolet light or heat, or a liquid crystal polymer thereof 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. An alignment film rubbed with a cloth or the like, an obliquely deposited layer of SiO, or a substrate using the surface properties of a stretched substrate such as polyethylene terephthalate or polyethylene naphthalate as an alignment film, or the above substrate surface is rubbed or bentara A substrate that has been processed with a fine polishing agent represented by the above and formed fine irregularities having fine alignment regulating force on the surface, or an alignment film that generates liquid crystal regulating force by light irradiation such as an azobenzene compound on the substrate film A liquid crystal polymer is applied on a suitable alignment film composed of a base material formed with Open and heat to above the glass transition temperature and below the isotropic phase transition temperature, and in a state where the liquid crystal polymer molecules are in a planar orientation, cool to below the glass transition temperature to form a solidified layer in which the orientation is fixed And how to do it. Further, the structure may be fixed by irradiation of energy such as ultraviolet rays or ion beams at the stage where the alignment state is formed.

  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. Examples of the solvent include chlorinated solvents such as methylene chloride, trichloroethylene, and tetrachloroethane; ketone-based solvents such as acetone, methyl ethyl ketone, and cyclohexanone; aromatic solvents such as toluene; cyclic alkanes such as cycloheptane; or N -Methyl pyrrolidone, tetrahydrofuran, etc. can be used suitably.

  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 or the like, a method of superimposing a cholesteric liquid crystal layer through an alignment film may be employed as necessary for the purpose of reducing the thickness. The cholesteric liquid crystal layer thus obtained can be used without being peeled off from the support substrate / alignment substrate used at the time of film formation and transferred to another optical material.

  Cholesteric liquid crystal layer stacking methods include the method of laminating a plurality of individually produced cholesteric liquid crystal layers with an adhesive or adhesive, the method of crimping after swelling or dissolving the surface with a solvent, etc., heat, ultrasonic waves, etc. The crimping method is given while adding. Moreover, after producing a cholesteric liquid crystal layer, methods, such as overlaying the cholesteric liquid crystal layer which has another selective reflection center wavelength on this layer, can be used.

(Production method of cholesteric liquid crystal layer covering visible light wavelength range)
Examples of a method for producing a cholesteric liquid crystal layer covering the visible light wavelength range include a method of irradiating the composition with an ionizing radiation such as an electron beam or an ultraviolet ray by the following method using a composition containing the same liquid crystal monomer as described above. . For example, a method using a difference in polymerization rate due to a difference in ultraviolet transmittance in the thickness direction (Japanese Patent Laid-Open No. 2000-95883), a method of forming a concentration difference in the thickness direction by extraction with a solvent (Japanese Patent No. 3062150) And a method of performing the second polymerization by changing the temperature after the first polymerization (US Pat. No. 6,057,008) and the like.

  In addition, a step of applying a liquid crystal mixture containing a polymerizable mesogenic compound (a) and a polymerizable chiral agent (b) to an alignment substrate, and a state in which the liquid crystal mixture is in contact with a gas containing oxygen from the substrate side A method of performing a polymerization and curing step by irradiating with ultraviolet rays, and increasing the difference in polymerization rate in the thickness direction due to inhibition of oxygen polymerization by irradiating ultraviolet rays from the substrate side (Japanese Patent Laid-Open No. 2000-139953) is preferably used. It is done.

  Regarding the method described in JP-A-2000-13953, a cholesteric liquid crystal layer having a wider reflection wavelength band can be obtained by the following method.

For example, in the ultraviolet polymerization step, the liquid crystal mixture is in contact with a gas containing oxygen at an ultraviolet irradiation intensity of 20 to 200 mW / cm ² at a temperature of 20 ° C. or higher for 0.2 to 5 seconds. The step (1) of irradiating ultraviolet rays from the alignment substrate side, the step (2) of heating the liquid crystal layer at 70 to 120 ° C. for 2 seconds or more in a state where the liquid crystal layer is in contact with the gas containing oxygen, and then In the state in which the liquid crystal layer is in contact with a gas containing oxygen, the step of irradiating with ultraviolet rays from the alignment substrate side at a temperature of 20 ° C. or higher and lower than the step (1) for 10 seconds or more. (3) Next, there is a method performed by the step (4) of irradiating ultraviolet rays in the absence of oxygen (Japanese Patent Application No. 2003-93963).

Further, in the ultraviolet polymerization step, the liquid crystal mixture is in contact with a gas containing oxygen, at a temperature of 20 ° C. or higher, an ultraviolet irradiation intensity of 1 to 200 mW / cm ² and a range of 0.2 to 30 seconds. Step (1) of irradiating ultraviolet rays from the alignment substrate side three times or more while lowering the ultraviolet irradiation intensity and lengthening the ultraviolet irradiation time each time the number of times of ultraviolet irradiation increases, and then in the absence of oxygen Then, there is a method performed by the step (2) of irradiating with ultraviolet rays (Japanese Patent Application No. 2003-94307).

Further, the ultraviolet polymerization step is carried out for 0.2 to 5 seconds at an ultraviolet irradiation intensity of 20 to 200 mW / cm ² at a temperature of 20 ° C. or higher in a state where the liquid crystal mixture is in contact with a gas containing oxygen. Step (1) of irradiating ultraviolet rays from the alignment substrate side, and then in a state where the liquid crystal layer is in contact with a gas containing oxygen, until it reaches a temperature higher than Step (1) and 60 ° C. or higher, A step (2) of irradiating with ultraviolet rays from the alignment substrate side for 10 seconds or more at a temperature rising rate of 2 ° C./second or lower with an ultraviolet irradiation intensity lower than that in step (1), and then irradiating with ultraviolet rays in the absence of oxygen. An example is a method performed in the step (3) (Japanese Patent Application No. 2003-94605).

  Furthermore, the following method can be used. In the following method, a cholesteric liquid crystal layer having a wide reflection wavelength band and good heat resistance can be obtained. For example, there is a method in which a liquid crystal mixture containing a polymerizable mesogenic compound (a), a polymerizable chiral agent (b) and a photopolymerization initiator (c) is subjected to ultraviolet polymerization between two substrates (Japanese Patent Application 2003). No. 4346, Japanese Patent Application No. 2003-4101). Further, there is a method in which a polymerizable ultraviolet absorber (d) is further added to the liquid crystal mixture and ultraviolet polymerization is carried out between two substrates (Japanese Patent Application No. 2003-4298). Also, a method of applying a liquid crystal mixture containing a polymerizable mesogenic compound (a), a polymerizable chiral agent (b), and a photopolymerization initiator (c) on an alignment substrate and subjecting it to ultraviolet polymerization in an inert gas atmosphere (Japanese Patent Application No. 2003-4406).

The ultraviolet polymerization step is performed for 0.1 to 5 seconds at a temperature of 70 ° C. or higher and an ultraviolet irradiation intensity of 10 to 200 mW / cm ^{2 in} a state where the liquid crystal mixture is in contact with a gas containing oxygen. , Ultraviolet ray irradiation (1), and then a step (2) of heat treatment at 70 ° C. or higher for 0.1 to 5 seconds in a state where the liquid crystal layer is in contact with a gas containing oxygen, After step (1) and step (2), the step can be carried out by step (3) of irradiating with ultraviolet rays in the absence of oxygen. Preferably, the step (1) and the step (2) are repeated a plurality of times, and then the step (3) of ultraviolet irradiation is performed (Japanese Patent Application No. 2004-71158).

  Moreover, as a manufacturing method of a polarizing element (B), the method of the said Japanese Patent Application No. 2003-93963 is preferable.

  The polymerizable mesogenic compound (a), polymerizable chiral agent (b) and the like that form the cholesteric liquid crystal layer will be described below. These materials are cholesteric liquid crystal layers whose pitch length is continuously changed in the thickness direction, and cholesteric to form a laminate. Any liquid crystal layer can be used.

  As the polymerizable mesogenic compound (a), those having at least one polymerizable functional group and having a mesogenic group composed of a cyclic unit or the like are preferably used. Examples of the polymerizable functional group include an acryloyl group, a methacryloyl group, an epoxy group, and a vinyl ether group. Among these, an acryloyl group and a methacryloyl group are preferable. Further, by using a compound having two or more polymerizable functional groups, a crosslinked structure can be introduced to improve durability. Examples of the cyclic unit serving as a mesogenic group include biphenyl, phenylbenzoate, phenylcyclohexane, azoxybenzene, azomethine, azobenzene, phenylpyrimidine, diphenylacetylene, diphenylbenzoate, and bicyclohexane. Cyclohexylbenzene, terphenyl and the like. In addition, the terminal of these cyclic units may have substituents, such as a cyano group, an alkyl group, an alkoxy group, a halogen group, for example. The mesogenic group may be bonded via a spacer portion that imparts flexibility. Examples of the spacer portion include a polymethylene chain and a polyoxymethylene chain. The number of repeating structural units forming the spacer portion is appropriately determined depending on the chemical structure of the mesogenic portion, but the repeating unit of the polymethylene chain is 0 to 20, preferably 2 to 12, and the repeating unit of the polyoxymethylene chain is 0 to 0. 10, preferably 1-3.

The molar extinction coefficient of the polymerizable mesogenic compound (a) is 0.1 to 500 dm ³ mol ⁻¹ cm ⁻¹ @ 365 nm, 10 to 30000 dm ³ mol ⁻¹ cm ⁻¹ @ 334 nm, and 1000 to 100,000 dm ^3. it is preferably a mol ^-1 m ^-1 @ 314nm. Those having the molar extinction coefficient have ultraviolet absorbing ability. Molar extinction coefficient is ^{0.1~50dm 3 mol -1 cm -1 @ 365nm} , a ^{50~10000dm 3 mol -1 cm -1 @ 334nm} , is 10000~50000dm ³ mol ^-1 cm ^-1 @ 314nm More preferred. Molar extinction coefficient is ^{0.1~10dm 3 mol -1 cm -1 @ 365nm} , a ^{1000~4000dm 3 mol -1 cm -1 @ 334nm} , at 30000~40000dm ³ mol ^-1 cm ^-1 @ 314nm More preferably. Molar extinction coefficient of ^{0.1dm 3 mol -1 cm -1 @ 365nm} , 10dm 3 mol -1 cm -1 @ 334nm, 1000dm 3 mol -1 cm -1 @ without stick 314nm smaller than sufficient polymerization rate difference It is difficult to increase the bandwidth. On the other ^{hand, 500dm 3 mol -1 cm -1 @} 365nm, 30000dm 3 mol -1 cm -1 @ 334nm, 100000dm 3 mol -1 cm -1 @ If 314nm greater than the polymerization curing to not proceed completely does not end There is. The molar extinction coefficient is a value measured from the absorbance at 365 nm, 334 nm, and 314 nm obtained by measuring the spectrophotometric spectrum of each material.

  The polymerizable mesogenic compound (a) having one polymerizable functional group is, for example, a general formula of the following chemical formula 1:

（式中、Ｒ₁〜Ｒ₁₂は同一でも異なっていてもよく、−Ｆ、−Ｈ、−ＣＨ₃、−Ｃ₂Ｈ₅または−ＯＣＨ₃を示し、Ｒ₁₃は−Ｈまたは−ＣＨ₃を示し、Ｘ₁は一般式（２）：
−（ＣＨ₂ＣＨ₂Ｏ）_a−（ＣＨ₂）_b−（Ｏ）_c−、を示し、Ｘ₂は−ＣＮまたは−Ｆを示す。但し、一般式（２）中のａは０〜３の整数、ｂは０〜１２の整数、ｃは０または１であり、かつａ＝１〜３のときはｂ＝０、ｃ＝０であり、ａ＝０のときはｂ＝１〜１２、ｃ＝０〜１である。）で表される化合物があげられる。

(In the formula, R _{1 to} R ₁₂ may be the same or different and represent —F, —H, —CH ₃ , —C ₂ H ₅ or —OCH ₃ , and R ₁₃ represents —H or —CH ₃ . X ₁ is represented by the general formula (2):
— (CH ₂ CH ₂ O) _a — (CH ₂ ) _b — (O) _c —, and X ₂ represents —CN or —F. In the general formula (2), a is an integer of 0 to 3, b is an integer of 0 to 12, c is 0 or 1, and when a = 1 to 3, b = 0 and c = 0. Yes, when a = 0, b = 1 to 12, and c = 0 to 1. ).

  Examples of the polymerizable chiral agent (b) include LC756 manufactured by BASF.

  The amount of the polymerizable chiral agent (b) is preferably about 1 to 20 parts by weight, preferably 3 to 7 parts by weight based on 100 parts by weight of the total of the polymerizable mesogenic compound (a) and the polymerizable chiral agent (b). The part is more suitable. The helical twisting force (HTP) is controlled by the ratio of the polymerizable mesogenic compound (a) and the polymerizable chiral agent (b). By setting the ratio within the above range, the reflection band can be selected so that the reflection spectrum of the obtained cholesteric liquid crystal film can cover the long wavelength region.

  The liquid crystal mixture usually contains a photopolymerization initiator (c). Various kinds of photopolymerization initiators (c) can be used without particular limitation. Examples thereof include Irgacure 184, Irgacure 907, Irgacure 369, Irgacure 651 and the like manufactured by Ciba Specialty Chemicals. The blending amount of the photopolymerization initiator is preferably about 0.01 to 10 parts by weight with respect to 100 parts by weight of the total of the polymerizable mesogenic compound (a) and the polymerizable chiral agent (b), and 0.05 to 5 parts by weight. The part is more suitable.

  As the polymerizable ultraviolet absorber (d), a compound having at least one polymerizable functional group and having an ultraviolet absorbing function can be used without any particular limitation. Specific examples of the polymerizable ultraviolet absorber (d) include RUVA-93 manufactured by Otsuka Chemical Co., and UVA935LH manufactured by BASF. The blending amount of the polymerizable ultraviolet absorber (d) is preferably about 0.01 to 10 parts by weight with respect to a total of 100 parts by weight of the polymerizable mesogenic compound (a) and the polymerizable chiral agent (b). 5 parts by weight is more preferred.

  In order to widen the bandwidth of the resulting cholesteric liquid crystal film, the mixture can be mixed with an ultraviolet absorber to increase the UV exposure intensity difference in the thickness direction. Further, the same effect can be obtained by using a photoreaction initiator having a large molar extinction coefficient.

  The mixture can be used as a solution. Solvents used in preparing the solution are usually halogenated hydrocarbons such as chloroform, dichloromethane, dichloroethane, tetrachloroethane, trichloroethylene, tetrachloroethylene, chlorobenzene, phenols such as phenol and parachlorophenol, benzene, toluene, Aromatic hydrocarbons such as xylene, methoxybenzene, 1,2-dimethoxybenzene, others, acetone, methyl ethyl ketone, ethyl acetate, tert-butyl alcohol, glycerin, ethylene glycol, triethylene glycol, ethylene bricol monomethyl ether, diethylene glycol Dimethyl ether, ethyl cellosolve, butyl cellosolve, 2-pyrrolidone, N-methyl-2-pyrrolidone, pyridine, triethylamine, te Rahidorofuran, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, can be used acetonitrile, butyronitrile, carbon disulfide, cyclopentanone, cyclohexanone and the like. The solvent to be used is not particularly limited, but methyl ethyl ketone, cyclohexanone, cyclopentanone and the like are preferable. Although the concentration of the solution depends on the solubility of the thermotropic liquid crystalline compound and the final film thickness of the cholesteric liquid crystal film, it cannot be generally stated, but it is usually preferably about 3 to 50% by weight.

  It should be noted that the exemplified alignment substrate can also be used when a cholesteric liquid crystal layer whose pitch length continuously changes in the thickness direction is produced. A similar method can be adopted as the orientation method.

(Circularly polarized reflective polarizer (C))
The case where the circularly polarized reflective polarizer (C) is laminated on the optical element (X) will be described below. As shown in FIG. 14A to 14D show specific modes. The circularly polarized reflective polarizer (C) may be disposed on either side of the polarizing element (A) or the polarizing element (B) in the optical element (X). In FIG. 14, the circularly polarized reflective polarizer (C) is arranged on the polarizing element (A) side, but in FIGS. 14A to 14D, it is arranged on the polarizing element (B) side. It is an example.

  For example, a cholesteric liquid crystal layer (C1) is used as the circularly polarized reflective polarizer (C). See FIG. The cholesteric liquid crystal layer (C1) preferably has the same spiral direction as the polarizing elements (A) and (B).

  The cholesteric liquid crystal layer (C1) preferably has a wide selective reflection bandwidth in order to function in the visible light region. The thickness is desirably 200 nm or more, more desirably 300 nm or more, and further desirably 400 nm or more. Specifically, it is preferable to cover a range of 400 to 600 nm. As the cholesteric liquid crystal layer (C1), the same ones as the polarizing elements (A) and (B) can be used. However, in the polarizing elements (A) and (B), as the incident angle increases due to the influence of the cholesteric liquid crystal layer, the linearly polarized light component increases, and thus circularly polarized light cannot be incident. Therefore, when the cholesteric liquid crystal layer (C1) having a reflection bandwidth of 200 nm or more is used, the front phase difference (normal direction) is λ / 8 or less, and the phase difference increases as the incident angle increases. It is preferable to use in combination with (C2). See FIG. By the retardation layer (C2), the normal direction is circularly polarized light, and substantially circularly polarized light can be transmitted even when the incident angle is increased. Examples of the retardation layer (C2) include a negative C-plate and a positive C-plate.

  Further, as the circularly polarized reflective polarizer (C), a linearly polarized reflective polarizer (C3) and a quarter wavelength plate (C4) can be used. See FIG. When the ¼ wavelength plate (C4) is used, circularly polarized light may become elliptically polarized light as the incident angle increases due to its Nz coefficient. For this reason, the Nz coefficient of the quarter wave plate (C4) is preferably close to 0.5. In general, the Nz coefficient of the quarter wave plate (C4) is preferably −1.5 <Nz <2 and more preferably 0 <Nz <1.

  One quarter wavelength plate (C4) can be used alone, or two or more wavelength plates can be used in combination. For example, a half-wave plate (C41) and a quarter-wave plate (C42) can be used. That is, by stacking the half-wave plate (C41) and the quarter-wave plate (C42), it can function as a quarter-wave plate. Refer to FIG. As a result, circularly polarized light can be transmitted at a wider viewing angle (circularly polarized light can be transmitted even when the incident angle is increased). At this time, the axis of the ½ wavelength plate (C41) is arranged so as to be substantially coaxial with the linearly polarized light reflection axis of the linearly polarized reflective polarizer (C3), and the ¼ wavelength plate (C42) is further arranged. Install at approximately 45 ° to the axis. In this case, the Nz coefficient of the half-wave plate (C41) is preferably 0.75, and the Nz coefficient of the quarter-wave plate (C42) is preferably close to 0.5. In general, the Nz coefficient of the half-wave plate (C41) is preferably −1.5 <Nz <2, more preferably 0 <Nz <1, and the Nz coefficient of the quarter-wave plate (C42). The coefficient is preferably -1 <Nz <2, more preferably 0 <Nz <1.5.

(Cholesteric liquid crystal layer (C1))
A suitable cholesteric liquid crystal may be used without any particular limitation. For example, a liquid crystal polymer exhibiting cholesteric liquid crystallinity at high temperature, or a polymerizable liquid crystal obtained by polymerizing a liquid crystal monomer and, if necessary, a chiral agent and an alignment aid by irradiation with ionizing radiation such as an electron beam or ultraviolet light or heat, or their 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.

  The cholesteric liquid crystal layer (C1) having a wide selective reflection bandwidth of 200 nm or more can be obtained by the same method as the polarizing elements (A) and (B).

(Phase difference layer (C2))
The retardation layer (C2) is preferably substantially zero because the front phase difference is intended to maintain vertically incident polarized light, and the front phase difference is preferably λ / 8 or less, more preferably λ / 10 or less. It is desirable to be.

  The phase difference layer (C2) generates a phase difference with respect to incident light inclined from the normal direction. For incident light from an oblique direction, it is determined as appropriate depending on the angle at which it is totally reflected so as to be efficiently polarized and converted. For example, in order to achieve total reflection at an angle of about 60 ° from the normal line, the phase difference when measured at 60 ° may be determined to be about λ / 4.

  The material of the retardation layer (C2) 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.

(Linear polarization reflection type polarizer (C3))
As the linearly polarized light reflection type polarizer (C3), a grid type polarizer, a multilayer thin film laminate of two or more layers made of two or more materials having a difference in refractive index, and a deposited multilayer thin film having different refractive indexes used for a beam splitter, etc. , Two or more birefringent layer multilayer thin film laminates made of two or more materials having birefringence, two or more resin laminates using two or more resins having birefringence, stretched linearly polarized light For example, it may be separated by reflecting / transmitting in an orthogonal axial 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 light reflective polarizer (C3) include 3M DBEF, Nitto Denko PCF, and the like.

  The selective reflection wavelength bandwidth of the linearly polarized light reflection type polarizer (C3) is desirably 200 nm or more, more desirably 300 nm or more, and further desirably 400 nm or more, like the polarizing elements (A) and (B). Specifically, in order to cover the visible light region, it is preferable to cover the range of 400 to 600 nm. To cover the visible light range regardless of the incident angle, the selective reflection wavelength band shifts to the short wavelength side according to the incident angle, so it is desirable to set the extended selective reflection wavelength band mainly to the long wavelength side. Is not limited.

  The polarizing elements (A) and (B) and the linearly polarized reflective polarizer (C3) have a selective reflection wavelength band of at least 550 nm, preferably 100 nm or more, more preferably 200 nm or more, more preferably 300 nm or more. It is preferable to have

(¼ wavelength plate (C4))
As a quarter wave plate (C4), for example, polyethylene naphthalate, polyethylene terephthalate, polycarbonate, norbornene resin typified by JSR Arton, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene and other polyolefins, polyarylate, Those obtained by uniaxially stretching a resin film such as polyamide, those obtained by improving the viewing angle characteristics by biaxially stretching, or those in which the nematic alignment state of the rod-like liquid crystal is fixed can be used. The same applies to the half-wave plate (C41) and the quarter-wave plate (C42).

(¼ wave plate (R))
Examples of the material of the quarter-wave plate (R) include the same materials as the quarter-wave plate (C4). The quarter-wave plate (R) is preferably a broadband wavelength plate having phase difference characteristics that function as a substantially quarter-wave plate in the entire visible light range in order to align the optical characteristics of each color and suppress coloring. . This is because if the change in the retardation value for each wavelength is too large, a difference occurs in the polarization characteristics for each wavelength, which affects the shielding performance for each wavelength and is colored and visually recognized. Such a quarter-wave plate (R) has an X-axis in the direction in which the in-plane refractive index is maximum, a Y-axis in a direction perpendicular to the X-axis, and nx, ny, and thickness d (in the respective axial directions). nm), the front phase difference value at each wavelength in the light source wavelength band (420 to 650 nm): (nx−ny) × d is preferably within ¼ wavelength ± 10%. The variation of the phase difference value within the light source wavelength band is preferably small, desirably within ± 7%, and more desirably within ± 5%. The front phase difference value is preferably about 100 to 180 nm, more preferably 110 to 150 nm.

  Such a quarter wavelength plate (R) can provide a phase difference corresponding to a quarter wavelength regardless of the wavelength of incident light by controlling different wavelength lamination characteristics by different axis lamination of different kinds of retardation plates or molecular design.

  A wider functioning wavelength band is better, but at least when the emission center wavelength of the light source is a cold cathode tube, blue is located at about 435 nm, green is at 545 nm, and red is at around 610 nm. Since light is emitted with a value width, it is desirable that the characteristics of the quarter wave plate (R) function within a range of at least about 420 nm to 650 nm. Polyvinyl alcohol is representative as a material of a retardation plate having such characteristics, and as a material designed for molecular use for optics, a norbornene-based resin film represented by JSR Arton or Nippon Zeon Zeonore, Examples include Teijin Pure Ace WR.

  Further, it is more desirable that the quarter wavelength plate (R) functions as a quarter wavelength plate for obliquely incident light. Generally, a phenomenon occurs in which the phase difference value changes due to an increase in the optical path length of the quarter wave plate with respect to an obliquely incident light beam, and deviates from the originally obtained phase difference value. In order to prevent this, it is preferable to use a quarter-wave plate (R) that controls the retardation in the thickness direction and reduces the change in phase difference with respect to the change in angle. As a result, a phase difference equivalent to that of the vertically incident light can be imparted to the obliquely incident light.

  In general, an Nz coefficient is used as a control coefficient for the retardation value in the thickness direction. The Nz coefficient is defined by taking the direction in which the in-plane refractive index is maximum 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. , Nz = (nx−nz) / (nx−ny). In order to give a phase difference value equivalent to that of the normal incident light to the incident light from the oblique direction, −2.5 <Nz ≦ 1 is preferable. More preferably, −2 <Nz ≦ 0.5. A typical example of the retardation plate that has been controlled in the thickness direction is a NRZ film manufactured by Nitto Denko. Note that the method as shown in Patent Document 17 cannot prevent the secondary transmission in the oblique direction. This is because it is impossible to achieve both the development of the phase difference in the oblique direction and the suppression of the increase in the phase difference in the oblique direction. This is the advantage of the present invention.

  The quarter-wave plate (R) 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. The thickness of the quarter-wave plate (R) is usually preferably from 0.5 to 200 μm, particularly preferably from 1 to 100 μm.

  In addition, a linearly polarized light reflection type polarizer (C3) can be further laminated on the quarter wavelength plate (R). Refer to FIG.

(Lamination of each layer)
The optical element of the present invention can be used not only in the optical path but also in a bonded state. This is because the air interface is not required because the transmittance is controlled not by the surface shape but by the polarization characteristics of the optical element.

  The layers are preferably laminated using an adhesive or a pressure-sensitive adhesive from the viewpoint 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 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.

  The light condensing characteristic according to the present invention can control light condensing in the front direction even with a diffusing surface light source such as a direct type backlight or an inorganic / organic EL element.

  It is desirable to install an appropriate diffusion plate (D) between the optical element (Y) of the present invention and the backlight source (L). 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 diffusion plate may be sandwiched between the optical element (Y) and the backlight, or may be bonded to the optical element (Y).

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

(Liquid crystal display device)
The optical element (Y) is suitably applied to a liquid crystal display device in which polarizing plates (P) are arranged on both sides of a liquid crystal cell (LC), and the optical element (Y) is a polarizing plate on the side of a light source of the liquid crystal cell. Applied to the (P) side. In FIG. 16, a polarizing plate (P) is laminated on a polarizing element (B) via a quarter-wave plate (R).

  FIG. 17 to FIG. 20 illustrate liquid crystal display devices. A reflector (RF) is also shown along with the light source (L). FIG. 17 shows a case where a direct type backlight (L) is used as the light source (L). FIG. 18 shows a case where a sidelight type light source (L) is used for the light guide plate (S). FIG. 19 shows a case where a planar light source (L) is used. FIG. 20 shows a case where a prism sheet (Z) is 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 by 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.

  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 elliptically polarizing plate or the reflective elliptical polarizing plate is 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. Each measurement is as follows.

  (Reflection wavelength band): The reflection spectrum was measured with a spectrophotometer (manufactured by Otsuka Electronics Co., Ltd., instantaneous multi-photometry system, MCPD-3000) to obtain a reflection wavelength band having a reflectance half of the maximum reflectance.

  (Distortion rate): In order to evaluate the distortion rate of the polarizing element, the transmission spectrum of the sample was measured with an instantaneous multiphotometer (MCPD-3000 manufactured by Otsuka Electronics Co., Ltd.). When natural light is projected and the sample is installed perpendicularly to the projected light (measurement of outgoing light from the front), and when the sample is installed at an angle of 60 ° from the vertical direction (measurement of 60 ° outgoing light) About each, the state of the light which permeate | transmitted them was measured with the polarizing plate arrange | positioned at the output side, and the transmission spectrum when a polarizing plate was rotated 10 degree | times was measured. As the polarizing plate, a Sigma-Optical Gram Thompson prism polarizer was used (extinction ratio of 0.00001 or less). The distortion rate was obtained from the following calculation formula. Strain rate = minimum transmittance / maximum transmittance.

  (Phase difference): The retardation of the wave plate is determined by taking the direction in which the in-plane refractive index is maximum 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. The refractive indexes nx, ny, and nz at 550 nm were measured with an automatic birefringence measuring device (manufactured by Oji Scientific Instruments, automatic birefringence meter KOBRA21ADH), where the refractive indexes were nx, ny, and nz. From the thickness d (nm), the front phase difference: (nx−ny) × d was calculated. Further, the Nz coefficient was calculated.

  UV irradiator: UVC321AM1 manufactured by USHIO INC. Was used.

  In addition, Nitto Denko's acrylic adhesive material (NO.7): 25 micrometers in thickness was used for lamination | stacking.

Example 1
(Polarizing element (A))
Prepare 95.4 parts by weight of monofunctional mesogenic compound (manufactured by Takasago International Corporation, L42), 4.6 parts by weight of bifunctional polymerizable chiral agent (LC756 made by BASF) and 233 parts by weight of solvent (cyclopentanone). A coating solution (solid content 30 wt%) was prepared by adding 5 wt% of a photopolymerization initiator (Ciba Specialty Chemicals, Irgacure 369) to the blended solution. The coating solution was cast on a stretched PET film (alignment substrate) using a wire bar so that the thickness after drying was 10 μm, and the solvent was dried at 100 ° C. for 2 minutes. The obtained film was subjected to UV irradiation at 50 mW / cm ² for 0.5 seconds in an air atmosphere at 100 ° C. from the PET substrate side as a step (1). Next, as step (2), heat treatment was performed in an air atmosphere at 100 ° C. for 2 seconds. Further, steps (1) and (2) were repeated. Thereafter, as step (3), UV irradiation was performed from the liquid crystal layer side at 60 mW / cm ² for 30 seconds in a nitrogen atmosphere at 50 ° C. to obtain a cholesteric liquid crystal layer having a selective reflection band of 420 to 900 nm. This was made into the polarizing element (A1-1).

  The polarizing element (A1-1) had a distortion rate in the front direction of 0.76 and a distortion rate in the 60 ° inclination direction of 0.10. Outgoing light transmitted through the polarizing element (A1-1) is linearly polarized light with a large incident angle, and the linearly polarized light is polarized in a direction substantially parallel to the normal direction (front) of the polarizing element surface. Had an axis.

(Polarizing element (B))
A solution containing 96.2 parts by weight of a monofunctional mesogen compound (manufactured by Takasago International Corporation, L42), 3.8 parts by weight of a bifunctional polymerizable chiral agent (LC756 made by BASF) and a solvent (cyclopentanone). A coating liquid (solid content 30% by weight) was prepared by adding 3% by weight of a photopolymerization initiator (Ciba Specialty Chemicals, Irgacure 907) to the solid content. The coating solution was cast on a stretched PET film (alignment substrate) using a wire bar so that the thickness after drying was 8 μm, and the solvent was dried at 100 ° C. for 2 minutes. The obtained film was irradiated with UV at 100 mW / cm ² for 0.6 seconds in an air atmosphere at 40 ° C. from the PET substrate side. Subsequently, it heated at 90 degreeC for 2 minute (s), and also UV irradiation was performed for 20 second at 6 mW / cm < ² > at 90 degreeC by air atmosphere. Thereafter, UV irradiation was performed at 60 mW / cm ² for 30 seconds from the liquid crystal layer side in a nitrogen atmosphere to obtain a cholesteric liquid crystal layer having a selective reflection band of 550 to 1100 nm. This was made into the polarizing element (B1-1).

  The polarizing element (B1-1) had a distortion rate in the front direction of 0.96 and a distortion rate in the 60 ° inclination direction of 0.02. Outgoing light transmitted through the polarizing element (B1-1) is linearly polarized light when the incident angle is large, and the linearly polarized light is polarized in a direction substantially parallel to the normal direction (front) of the polarizing element surface. Had an axis.

(Circularly polarized reflective polarizer (C))
Creation of a cholesteric liquid crystal layer (C1).
A solution containing 94.7 parts by weight of a monofunctional mesogen compound (manufactured by Takasago International Corporation, L42), 5.3 parts by weight of a bifunctional polymerizable chiral agent (LC756 made by BASF) and a solvent (cyclopentanone). A coating liquid (solid content 30% by weight) was prepared by adding 3% by weight of a photopolymerization initiator (Ciba Specialty Chemicals, Irgacure 907) to the solid content. The coating solution was cast on a stretched PET film (alignment substrate) using a wire bar so that the thickness after drying was 7 μm, and the solvent was dried at 100 ° C. for 2 minutes. The obtained film was subjected to first UV irradiation at 40 mW / cm ² for 1.2 seconds in an air atmosphere at 40 ° C. from the PET side. Subsequently, the second UV irradiation was performed at 4 mW / cm ² for 60 seconds while the temperature was increased to 90 ° C. at a temperature increase rate of 3 ° C./second in an air atmosphere. Next, 3rd UV irradiation was performed at 60 mW / cm ² for 10 seconds from the PET side under a nitrogen atmosphere, thereby obtaining a cholesteric liquid crystal layer having a selective reflection band of 425 to 900 nm. This was designated as a cholesteric liquid crystal layer (C1).

  The cholesteric liquid crystal layer (C1) had a distortion rate in the front direction of about 0.99 and a distortion rate in the 60 ° tilt direction of about 0.10. Outgoing light transmitted through the cholesteric liquid crystal layer (C1) has a large incident angle and is linearly polarized light. The linearly polarized light has a polarization axis substantially perpendicular to the normal direction (front) of the polarizing element surface. Had.

Preparation of positive C plate (C2).
Ethyl acetate in ethyl acetate and 2% isopropyl alcohol (trade name Colcoat P, Colcoat Co., Ltd.) as a sol solution for anchor coating on a plastic film made of polyethylene terephthalate (made by Toray Industries, Inc., thickness 50 μm) Made by gravure roll coating. Subsequently, it heated at 130 degreeC for 30 second, and formed the transparent glassy polymer film (0.08 micrometer).

上記の化２（式中の数字はモノマーユニットのモル％を示し、便宜的にブロック体で表示している、重量平均分子量５０００）に示される側鎖型液晶ポリマー５重量部、ネマチック液晶層を示す光重合性液晶化合物（ＢＡＳＦ社製，ＰａｌｉｏｃｏｌｏｒＬＣ２４２）２０重量部および光重合開始剤（チバスペシャルティケミカルズ社製，イルガキュア９０７）５重量％（対光重合性液晶化合物）をシクロヘキサノン７５重量部に溶解した溶液を、フィルム基材に設けたアンカーコート層上に、バーコーティングにより塗工した。次いで、８０℃で２分間加熱し、その後室温まで一気に冷却することにより、前記液晶層をホメオトロピック配向させ、かつ配向を維持したままガラス化しホメオトロピック配向液晶層を固定化した。さらに、固定化したホメオトロピック配向液晶層に紫外線を照射することによりホメオトロピック配向液晶フィルム（厚み３μｍ）を形成した。

5 parts by weight of a side chain type liquid crystal polymer represented by the above chemical formula 2 (the number in the formula represents the mol% of the monomer unit and is expressed in block form for convenience), and the nematic liquid crystal layer. 20 parts by weight of a photopolymerizable liquid crystal compound (BASF, Paliocolor LC242) and 5% by weight of a photopolymerization initiator (Ciba Specialty Chemicals, Irgacure 907) (photopolymerizable liquid crystal compound) were dissolved in 75 parts by weight of cyclohexanone. The solution was applied by bar coating on the anchor coat layer provided on the film substrate. Subsequently, the liquid crystal layer was heated at 80 ° C. for 2 minutes and then cooled to room temperature all at once, whereby the liquid crystal layer was homeotropically aligned and vitrified while maintaining the alignment to fix the homeotropically aligned liquid crystal layer. Furthermore, a homeotropic alignment liquid crystal film (thickness 3 μm) was formed by irradiating the fixed homeotropic alignment liquid crystal layer with ultraviolet rays.

  The optical retardation of the film was measured with an automatic birefringence measuring apparatus. The measurement light was incident on the sample surface vertically or obliquely, and the homeotropic alignment was confirmed from the chart of the optical phase difference and the incident angle of the measurement light. In homeotropic alignment, the phase difference (front phase difference) in the direction perpendicular to the sample surface is almost zero. When the phase difference was measured obliquely in the slow axis direction of the liquid crystal layer, it was judged that the homeotropic alignment was obtained because the phase difference value increased as the incident angle of the measurement light increased.

  Two positive C plates (C2) were laminated, and this was laminated on a cholesteric liquid crystal layer (C1) to produce a circularly polarized reflective polarizer (C).

(Performance evaluation)
With respect to the polarizing element (B), the distortion rate (however, the outgoing light with respect to the incident light incident with an inclination of 30 ° from the normal direction) was measured. The distortion factor of the polarizing element (B) was 65. Further, when the polarizing element (B) and the circular polarizing reflective polarizer (C) were combined (incident from the circular polarizing reflective polarizer (C) side), the distortion rate was 15. Thus, it can be seen that the linearly polarized light component is considerably increased even at a shallow angle (incident angle of 30 °) from the normal direction by combining the circularly polarized reflective polarizer (C).

(Optical element (Y))
The polarizing element (A1-1) and the polarizing element (B1-1) were laminated to obtain an optical element (X1). This was designated as Reference Example 1. As shown in FIG. 14B, the circularly polarized reflective polarizer (C) was laminated on the polarizing element (B1-1) side of the optical element (X1) to obtain an optical element (Y1). This was designated Example 1.

<Characteristic evaluation>
Optical element (X1): Reference example 1 and optical element (Y1): Example 1 was placed on a diffusion light source, and emitted light was measured. The polarizing element (B1-1) side in the optical element (X1) was disposed so as to be on the light source side. A light table KLV7000 made by Hakuba was used as the light source device (diffuse light source). Luminance and chromaticity when tilted with respect to the vertical direction and the normal direction were measured with a viewing angle measuring device ELDIM, Ez-Contrast.

  FIG. 21 shows luminance viewing angle characteristics. From FIG. 21, it can be seen that light is collected in the normal direction in Example 1 as compared with Reference Example 1. This is because the linearly polarized light component at a shallower angle increases in Example 1, and thus the amount of light reflected when the incident angle increases is increased. FIG. 22 shows a chromaticity diagram. In Example 1, it can be seen that the moving distance of the point is smaller than that in Reference Example 1 (this point represents the color at each incident angle, and the larger the color, the more the color changes. The travel distance will increase). From this, it can be seen that in Example 1, coloring is reduced compared to Comparative Example 1.

Example 2
(Circularly polarized reflective polarizer (C))
As the circularly polarizing reflective polarizer (C), a ½ wavelength plate (C41) is arranged coaxially with the reflection axis direction of the linearly polarized light of the linearly polarizing reflective polarizer (C3), and a ¼ wavelength plate (C42) is provided. ) Was installed at 45 ° to this axis. As the linearly polarized reflective polarizer (C3), DBEF manufactured by 3M was used. A polycarbonate retardation film (front retardation 270 nm, Nz coefficient = 0.75) was used as the half-wave plate (C41). A polycarbonate retardation film (front retardation 130 nm, Nz coefficient = 0.5) was used as the quarter-wave plate (C42).

(Optical element (Y))
The same polarizing element (A1-1) and polarizing element (B1-1) as used in Example 1 were used. The polarizing element (A1-1) and the polarizing element (B1-1) were laminated to obtain an optical element (X1). As shown in FIG. 14D, the circularly polarized reflective polarizer (C) was laminated on the polarizing element (B1-1) side of the optical element (X1) to obtain an optical element (Y2). This was designated Example 2.

<Characteristic evaluation>
The optical element (X1): Reference Example 1 and the optical element (Y2): Example 2 were placed on a diffusion light source, and the emitted light was measured. The polarizing element (B1-1) side in the optical element (X1) was disposed so as to be on the light source side. A light table KLV7000 made by Hakuba was used as the light source device (diffuse light source). The brightness and chromaticity when tilted with respect to the vertical direction and the normal direction were measured with a viewing angle measuring device ELDIM, Ez-Contrast.

  FIG. 23 shows luminance viewing angle characteristics. FIG. 23 shows that light is collected in the normal direction in Example 2 as compared with Reference Example 1. This is because the linearly polarized light component at a shallower angle increases in Example 1, and thus the amount of light reflected when the incident angle increases is increased. FIG. 24 shows a chromaticity diagram. In Example 2, it can be seen that the moving distance of the point is smaller than that in Comparative Example 1 (this point represents the color at each incident angle, and the larger the color, the more the color changes. The travel distance will increase). From this, it can be seen that in Example 2, coloring is reduced compared to Comparative Example 1.

Example 3
(Optical element (Y))
The same polarizing element (A1-1) and polarizing element (B1-1) as used in Example 1 were used. The polarizing element (A1-1) and the polarizing element (B1-1) were laminated to obtain an optical element (X1). Further, as shown in FIG. 14D, the circularly polarized reflective polarizer (C) used in Example 2 is laminated on the polarizing element (B1-1) side of the optical element (X1) to stack the optical element (Y2 )

  Further, as shown in FIG. 15A, the circularly polarized reflective polarizer (C) used in Example 2 was laminated on the polarizing element (A1-1) side of the optical element (X1). This was designated as Example 3.

<Characteristic evaluation>
Optical element (X1): The optical elements obtained in Reference Example 1 and Example 3 were placed on a diffusion light source, and the emitted light was measured. The polarizing element (B1-1) side in the optical element (X1) was disposed so as to be on the light source side. A light table KLV7000 made by Hakuba was used as the light source device (diffuse light source). The luminance from vertically above and the luminance when tilted with respect to the normal line direction were measured with a viewing angle measuring device ELDIM, Ez-Contrast.

  FIG. 25 shows luminance viewing angle characteristics. FIG. 25 shows that light is collected in the normal direction in Example 3 as compared with Reference Example 1. This is because the linearly polarized light component at a shallower angle increases in Example 1, and thus the amount of light reflected when the incident angle increases is increased.

Comparative Example 1
(Polarizing element (A))
Five kinds of cholesteric liquid crystal polymers having selective reflection center wavelengths of 350 nm, 450 nm, 550 nm, 700 nm, and 850 nm were prepared. The cholesteric liquid crystal polymer was prepared by polymerizing a liquid crystal mixture in which the ratio of a polymerizable mesogen compound (LC242 manufactured by BASF) and a polymerizable chiral agent (LC756 manufactured by BASF) was adjusted and mixed.

  Each liquid crystal mixture was made into a 30 wt% solution dissolved in cyclopentanone, and then a solution was prepared by adding a reaction initiator (Ciba Specialty Chemicals, Irgacure 907, 3 wt% to the mixture). .

The coating solution was cast on a stretched PET film (alignment substrate) using a wire bar so that the thickness after drying was 8 μm, and the solvent was dried at 100 ° C. for 2 minutes. The obtained film was subjected to UV irradiation at 60 mW / cm ² for 30 seconds in an air atmosphere at 40 ° C. from the cholesteric liquid crystal side. Thereafter, each layer was laminated to obtain a cholesteric liquid crystal layer having a selective reflection band in a wide band.

  The obtained cholesteric liquid crystal layer had a distortion rate in the front direction of about 0.95 and a distortion rate in the 60 ° tilt direction of about 0.20. Outgoing light transmitted through the cholesteric liquid crystal layer has a large incident angle and is linearly polarized light. The linearly polarized light has a polarization axis substantially perpendicular to the normal direction (front) of the polarizing element surface. Was.

Comparative Example 2
Two cholesteric liquid crystal layers obtained in Comparative Example 1 were laminated and used.

<Characteristic evaluation>
The optical element obtained in Example 3 and the cholesteric liquid crystal layer obtained in Comparative Examples 1 and 2 were placed on a diffusion light source, and the emitted light was measured. The optical element obtained in Example 3 was disposed so that the polarizing element (B1-1) side of the optical element (X1) was on the light source side. A light table KLV7000 made by Hakuba was used as the light source device (diffuse light source). The luminance from vertically above and the luminance when tilted with respect to the normal line direction were measured with a viewing angle measuring device ELDIM, Ez-Contrast.

  FIG. 26 shows luminance viewing angle characteristics. FIG. 26 shows that light is collected in the normal direction in Example 3 as compared with Comparative Examples 1 and 2. This is because the linearly polarized light component at a shallower angle increases in Example 1, and thus the amount of light reflected when the incident angle increases is increased.

It is a conceptual diagram which shows the polarization-axis direction of the emitted light which permeate | transmitted the polarizing element (A1). It is a conceptual diagram which shows the polarization axis direction of the emitted light at the time of seeing FIG. 1 (A) from the normal line direction of a polarizing element (A1). It is a conceptual diagram which shows the polarization axis direction of the emitted light which permeate | transmitted the polarizing element (B1). It is a conceptual diagram which shows the polarization axis direction of the emitted light at the time of seeing FIG. 2 (A) from the normal line direction of a polarizing element (B1). It is a conceptual diagram explaining a polarization component etc. It is a conceptual diagram which shows the polarization separation by the conventional cholesteric liquid crystal layer. It is a conceptual diagram which shows the polarization separation by the conventional cholesteric liquid crystal layer. It is a conceptual diagram which shows the polarization separation by a polarizing element (A) and (B). It is a conceptual diagram which shows the polarization separation by a polarizing element (A) and (B). It is a conceptual diagram which shows the polarization-axis direction of the emitted light which permeate | transmitted the polarizing element (A1) and then the polarizing element (B1). It is a conceptual diagram which shows the polarization-axis direction of the emitted light which permeate | transmitted the polarizing element (A2). It is a conceptual diagram which shows the polarization-axis direction of the emitted light which permeate | transmitted the polarizing element (B2). It is a conceptual diagram which shows the polarization axis direction of the emitted light which permeate | transmitted the polarizing element (A2) and then the polarizing element (B2). It is a conceptual diagram which shows the polarization axis direction of the emitted light which permeate | transmitted the optical element (X) of this invention, and then the quarter wavelength plate (R). It is a conceptual diagram which shows conversion of the polarization seed | species by a wavelength plate. It is an example of sectional drawing of the optical element (Y) of this invention. It is an example of sectional drawing of the optical element (Y) of this invention. It is an example of sectional drawing of the optical element (Y) of this invention. It is an example of sectional drawing of the optical element (Y) of this invention. It is an example of sectional drawing of the optical element (Y) of this invention. It is an example of sectional drawing at the time of laminating | stacking a quarter wavelength plate (R) on the optical element (Y) of this invention. It is an example of sectional drawing at the time of laminating | stacking the quarter wavelength plate (R) on the optical element (Y) of this invention, and also laminating | stacking a circular-polarization-type reflective polarizer (C). It is an example of sectional drawing at the time of laminating | stacking a quarter wavelength plate (R) and a polarizing plate (P) on the optical element (Y) of this invention. It is an example of sectional drawing of the liquid crystal display device using the optical element (Y) of this invention. It is an example of sectional drawing of the liquid crystal display device using the optical element (Y) of this invention. It is an example of sectional drawing of the liquid crystal display device using the optical element (Y) of this invention. It is an example of sectional drawing of the liquid crystal display device using the optical element (Y) of this invention. It is a figure showing the luminance viewing angle characteristic of the optical element of Example 1 and Reference Example 1. It is a figure showing the chromaticity diagram of the optical element of Example 1 and Reference Example 1. It is a figure showing the luminance viewing angle characteristic of the optical element of Example 1 and Reference Example 1. It is a figure showing the chromaticity diagram of the optical element of Example 2 and Reference Example 1. It is a figure showing the luminance viewing angle characteristic of the optical element of Example 3 and Reference Example 1. It is a figure showing the luminance viewing angle characteristic of the optical element of Example 3 and Comparative Examples 1 and 2.

Explanation of symbols

A Polarizing element B Polarizing element having the same spiral direction as A i Incident light e Emission light C Circularly polarized reflective polarizer C1 Cholesteric liquid crystal layer C2 Phase difference layer C3 Linearly polarized reflective polarizer C4 1/4 wavelength plate R 1 / 4 wavelength plate X optical element Y optical element P polarizing plate D diffuser plate L light source LC liquid crystal cell

Claims (20)

A polarizing element (A) formed of cholesteric liquid crystal that emits incident light after being polarized and separated, and a polarizing element (B) formed of cholesteric liquid crystal having the same spiral direction as the polarizing element (A) are arranged. An optical element (X),
The polarizing element (A) and the polarizing element (B) are both
The outgoing light with respect to the incident light in the normal direction has a distortion rate of 0.5 or more,
The outgoing light with respect to the incident light that is inclined by 60 ° or more from the normal direction has a distortion rate of 0.2 or less,
The linearly polarized light component of the emitted light increases as the incident angle increases, and
In the polarizing element (A), the linearly polarized light component of the emitted light that increases as the incident angle increases has a polarization axis of linearly polarized light in a direction substantially orthogonal to the normal direction of the polarizing element surface.
The polarizing element (B) is an optical element in which the linearly polarized light component of the emitted light that increases as the incident angle increases has a polarization axis of linearly polarized light in a direction substantially parallel to the normal direction of the polarizing element surface. (X)
Furthermore, the circularly polarized reflective polarizer (C) is disposed on either side of the polarizing element (A) or the polarizing element (B).   The optical element according to claim 1, wherein the polarizing element (A) and the polarizing element (B) substantially reflect a non-transmission component of incident light.   The optical element according to claim 1 or 2, wherein the polarizing element (A) and the polarizing element (B) have a thickness of 2 µm or more.   The optical element according to any one of claims 1 to 3, wherein the polarizing bandwidth of the polarizing element (A) and the polarizing element (B) is 200 nm or more.   The optical element according to claim 1, wherein the circularly polarizing reflective polarizer (C) is a cholesteric liquid crystal layer (C1).   The circularly polarizing reflective polarizer (C) has a cholesteric liquid crystal layer (C1) and a layer (C2) in which the front phase difference (normal direction) is λ / 8 or less and the phase difference increases as the incident angle increases. The optical element according to claim 1, wherein the optical element is provided.   The optical element according to claim 5 or 6, wherein the cholesteric liquid crystal (C1) has a reflection bandwidth of 200 nm or more.   The optical element according to claim 1, wherein the circularly polarized reflective polarizer (C) includes a linearly polarized reflective polarizer (C3) and a quarter-wave plate (C4). The quarter-wave plate (C4) has an in-plane refractive index in the X-axis direction, a direction perpendicular to the X-axis in the Y-axis direction, and a film thickness direction in the Z-axis direction. Is nx, ny, nz,
The optical element according to claim 8, wherein an Nz coefficient represented by Nz = (nx−nz) / (nx−ny) is −3 <Nz <4.   The optical element according to claim 8, wherein the quarter-wave plate (C4) includes a half-wave plate (C41) and a quarter-wave plate (C42). The half-wave plate (C41) has an in-plane refractive index in the X-axis direction, a direction perpendicular to the X-axis as a Y-axis, and a film thickness direction as a Z-axis. Is nx, ny, nz,
Nz coefficient represented by Nz = (nx−nz) / (nx−ny) is −1.5 <Nz <2,
The quarter-wave plate (C42) has an in-plane refractive index in the X-axis direction, a direction perpendicular to the X-axis in the Y-axis direction, and a film thickness direction in the Z-axis direction. Is nx, ny, nz,
The optical element according to claim 10, wherein an Nz coefficient represented by Nz = (nx−nz) / (nx−ny) is −1.5 <Nz <2.   The quarter-wave plate (R) is arranged on the side where the circularly polarized reflective polarizer (C) is not arranged so that the emitted light from the light source side becomes linearly polarized light. The optical element in any one of 1-11.   The optical element according to claim 12, wherein the quarter-wave plate (R) is a broadband wavelength plate that functions as a substantially quarter-wave plate in the entire visible light region. The quarter-wave plate (R) has a maximum in-plane refractive index in the X-axis, a direction perpendicular to the X-axis in the Y-axis, and a refractive index in each axial direction of nx, ny, and thickness d (nm). )
14. The optical element according to claim 13, wherein a front phase difference value (nx−ny) × d at each wavelength in the light source wavelength band (420 to 650 nm) is within ¼ wavelength ± 10%. The quarter-wave plate (R) has an X-axis as the direction in which the in-plane refractive index is maximum, a Y-axis as a direction perpendicular to the X-axis, and a Z-axis as the thickness direction of the film. Is nx, ny, nz,
The optical element according to claim 12, wherein an Nz coefficient represented by Nz = (nx−nz) / (nx−ny) is −2.5 <Nz ≦ 1.   The polarizing plate is arranged on the quarter wavelength plate (R) side so that the polarization axis direction of linearly polarized light obtained by transmission from the light source side and the polarization axis direction of the polarizing plate are aligned. The optical element according to any one of claims 12 to 15.   The optical element according to claim 1, wherein each layer is laminated using a translucent adhesive or pressure-sensitive adhesive.   A condensing backlight system comprising at least a light source disposed on the optical element according to claim 1.   19. A liquid crystal display device comprising at least a liquid crystal cell in the condensing backlight system according to claim 18. 20. A liquid crystal display device according to claim 19, wherein a diffusion plate having no backscattering or depolarization is laminated on the liquid crystal cell viewing side.

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