JP2007212831A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device wherein an image having color balance the same as the color balance obtained when viewed from a direction parallel or orthogonal to a transmission axis of a dichroic polarizer can be displayed even when viewed from a direction oblique to the transmission axis of the dichroic polarizer which constitutes a liquid crystal panel. <P>SOLUTION: The liquid crystal display device is obtained by disposing a light source, a selected light reflective optical element wherein a lower limit λ<SB>L</SB>of a wavelength band reflecting a light ray made incident at 0° angle is longer than the wavelength λ<SB>R1</SB>of light showing the maximum light emission intensity in 600 to 700 nm wavelength band of light emitted by the light source and light made incident at 60° angle and having 600 to 700 nm wavelength has 20 to 80% average transmittance, a luminance enhancing element reflecting one polarized light ray of a visible light region wavelength and transmitting the other polarized light ray on the side near to a liquid crystal panel and the liquid crystal panel in this order. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device. More specifically, when observed from an orientation that is oblique to the transmission axis of the dichroic polarizer that constitutes the liquid crystal panel, and when observed from an orientation that is parallel or perpendicular to the transmission axis of the dichroic polarizer; The present invention relates to a liquid crystal display device capable of displaying an image with a similar color balance.

  The liquid crystal display device includes a light source, two dichroic polarizers, and a liquid crystal cell disposed between the dichroic polarizers. The light source balances blue light (wavelength 410 to 470 nm), green light (wavelength 520 to 580 nm), and red light (wavelength 600 to 660 nm), and emits white light. A cold cathode tube, a hot cathode tube, an LED ( Light emitting diode), EL (electroluminescence), and the like. In a liquid crystal display device, light from a light source is converted into linearly polarized light by a first dichroic polarizer. The linearly polarized light is converted into linearly polarized light whose phase is unchanged or inverted depending on the difference in voltage application or no voltage application in the liquid crystal cell. When the transmission axis of the first dichroic polarizer is perpendicular to the transmission axis of the second dichroic polarizer, the linearly polarized light whose phase is inverted in the liquid crystal cell is the second dichroic polarization. The linearly polarized light that is transmitted through the polarizer and has the same phase cannot pass through the second dichroic polarizer. In general, even in a liquid crystal cell that can invert the phase with respect to light incident from an incident angle of 0 degrees (that is, the phase is delayed by a half wavelength), the phase delay is just There is a tendency for distortion to occur because the wavelength cannot be halved. The degree of this distortion tends to vary depending on the wavelength. As a result, the color image when viewed from the front may be different from the color image when viewed from an oblique direction.

In addition, a brightness enhancement element may be used in a liquid crystal display device in order to improve brightness. In the brightness enhancement element, the reflection band of light incident from an oblique direction may be shifted to the shorter wavelength side than the reflection band of light incident from the front. Even with a brightness enhancement element that can reflect the entire visible light region with respect to light incident from the front, long-wavelength light (red light) may not be reflected with respect to light incident from an oblique direction.
For this reason, in general, in a liquid crystal display device, the hue of a color image when observed from the front may differ from the hue of the color image when observed from an oblique direction.
Further, even when observed from the same oblique direction, when observed at an azimuth angle oblique to the transmission axis of the dichroic polarizer constituting the liquid crystal panel, it is parallel to the transmission axis of the dichroic polarizer or The intensity of blue and green becomes weaker than when observed at an angle that is perpendicular to the direction, and the red becomes relatively strong, so the hue may be greatly different.

Until now, it has been strongly demanded to eliminate such a difference in hue depending on the observation angle, and various studies have been made to solve the above problems.
In Patent Document 1, a cholesteric liquid crystal layer having a selective reflection wavelength band at wavelengths λ1 to λ2 (λ1 <λ2) with respect to normal incident light is used, and the maximum wavelength λ0 of the emission spectrum of a light source used in combination. It has been proposed to arrange a collimator satisfying λ0 <λ1 in the backlight system. The collimator described in Patent Document 1 has a function of aligning light traveling at various angles with only light traveling in the vertical direction. Accordingly, light rays incident from an oblique direction are reflected by the collimator and are not transmitted. For this reason, the liquid crystal display device disclosed in Patent Document 1 may have a dark display screen, and the color tone when observed from an oblique direction is insufficient.

  Further, in Patent Document 2, it has a transmission characteristic with respect to incident light in the visible light region in the normal direction, has a reflection wavelength band in the infrared region, and has a reflection wavelength as the incident angle with respect to the normal direction increases. It has been proposed to arrange an infrared reflecting layer (B) whose band changes to the short wavelength side in an illumination device. Patent Document 2 discloses an infrared reflective layer (B) having a transmittance of light of 10% or less at a wavelength of 710 nm, 640 nm, or 610 nm at an incident angle of 45 degrees. Therefore, the red light incident obliquely is almost completely reflected or absorbed by the infrared reflection layer (B). For this reason, the liquid crystal display device disclosed in Patent Document 1 may have a dark display screen, and the color tone when observed from an oblique direction is insufficient.

JP 2002-169026 A JP 2004-309618 A

  The object of the present invention is when observed from an orientation that is oblique to the transmission axis of the dichroic polarizer constituting the liquid crystal panel, or from an orientation that is parallel or orthogonal to the transmission axis of the dichroic polarizer. It is an object of the present invention to provide a liquid crystal display device capable of displaying an image with the same color balance.

  The present inventor can obtain an image in which blue, green and red are well balanced when the liquid crystal display device disclosed in the above-mentioned patent document is observed from the front. I found out that there is a problem that sometimes the image becomes bluish. And this reason came to be thought that it is because the collimator or infrared reflection layer (B) used in the above-mentioned patent documents 1 and 2 blocks too much red light incident obliquely.

Therefore, the present inventor has a wavelength band (λ _L) longer than the wavelength λ _{R1 of the} light having the maximum emission intensity in the wavelength range of 600 to 700 nm of the light source on the side closer to the light source between the light source and the liquid crystal panel. has a band that reflects light incident angle of 0 degrees to [lambda] _H), the selective light reflective optical element average transmittance of light with a wavelength of 600~700nm is 80% or less 20% or more at an incident angle of 60 degrees When a brightness enhancing element that reflects one polarized light in the visible light region and transmits the other polarized light is provided on the side close to the liquid crystal panel, it transmits the dichroic polarizer constituting the liquid crystal panel. It has been found that even when observed from an orientation oblique to the axis, an image having the same color balance as that observed from an orientation parallel or perpendicular to the transmission axis of the dichroic polarizer can be displayed. Based on this knowledge, the present inventor further studied and completed the present invention.

Thus, according to the present invention,
(1) A light source, a selective light reflective optical element, a brightness enhancement element, and a liquid crystal panel are arranged in this order, and the selective light reflective optical element reflects a light beam having an incident angle of 0 degrees. The lower limit λ _L of the wavelength band is longer than the wavelength λ _{R1 of} light having the maximum emission intensity in the wavelength band of 600 to 700 nm in the light emitted from the light source, and the average transmission of the light of wavelength 600 to 700 nm at an incident angle of 60 degrees The liquid crystal display device has a rate of 20% or more and 80% or less, and the brightness enhancement element reflects one polarized light in a visible light region wavelength and transmits the other polarized light.
(2) The selective light reflective optical element further has an average transmittance of light having a wavelength of 600 to 700 nm at an incident angle of 0 degree of 60% or more, and an average of light having a wavelength of 600 to 700 nm at an incident angle of 0 degree. The liquid crystal display device according to (1), wherein the transmittance is larger than an average transmittance of light having a wavelength of 600 to 700 nm at an incident angle of 60 degrees.
(3) The liquid crystal display according to (1) or (2), wherein the selective light reflective optical element has an average transmittance of light having a wavelength of 600 to 700 nm at an incident angle of 60 degrees of 30% to 70%. apparatus.
Is provided.

  Conventional liquid crystal display devices are often reddish when observed obliquely. This is because the amount of red light when viewed from an oblique angle is relatively higher than the amount of blue and green light when compared to the light amount balance of blue, green, and red when viewed from the front. On the other hand, if the transmittance of light having a wavelength of 710 nm, 640 nm, or 610 nm incident obliquely as in Patent Documents 1 and 2 is 10% or less, the light quantity balance of blue, green, and red when observed from the front is reduced. As a result, the amount of red light when observed from an oblique direction is relatively low compared to the amounts of blue and green light. As a result, when the liquid crystal display device is observed obliquely, it tends to be bluish or dark.

  The liquid crystal display device of the present invention includes a selective light reflecting optical element that transmits light having a wavelength of 600 to 700 nm incident at an incident angle of 60 degrees in a range of 20% to 80%. The blue, green and red color balance can be adjusted to the same balance as the blue, green and red balance when viewed from the front. When the light adjusted in balance by the selective light reflecting optical element is incident on the brightness enhancement element, the two colors are also observed when observed from an oblique direction with respect to the transmission axis of the dichroic polarizer constituting the liquid crystal panel. A high-luminance image with the same color balance as that observed when viewed from an orientation parallel or perpendicular to the transmission axis of the transmissive polarizer can be displayed.

  In the liquid crystal display device of the present invention, a light source, a selective light reflecting optical element, a brightness enhancement element, and a liquid crystal panel are arranged in this order.

  The light source used in the present invention may be any light source that emits white light, and examples thereof include a cold cathode tube, a hot cathode tube, a light emitting diode, and electroluminescence. A reflector having a reflective metal film or a white film may be provided behind the light source in order to increase the light utilization efficiency.

The light emitted from the light source is sent to a selective light reflective optical element described later. In the present invention, a light diffusing element can be provided between the selective light reflective optical element and the light source in order to send light uniformly to the selective light reflective optical element. This light diffusing element is an element that scatters light from a light source to make diffused light in order to eliminate in-plane distribution of luminance. Specifically, a light diffusing material such as silicone beads dispersed in a transparent substrate (sometimes referred to as a light diffusing plate), or a light diffusing material applied to the surface of a transparent substrate (referred to as a light diffusing sheet) In some cases). As another aspect, a light guide plate may be used to make light from the light source uniform. The light guide plate is an element for receiving light from the light source on the side surface, guiding the light into the light source, and emitting the light to the front surface with uniform luminance.
Further, a prism sheet for collecting light scattered too much may be disposed between the light diffusing element or the light guide plate and the selective light reflecting optical element described later.

The selective light reflective optical element used in the present invention has a lower limit λ _L of a wavelength band for reflecting a light beam having an incident angle of 0 °, and has a maximum emission intensity in a wavelength band of 600 to 700 nm among light emitted from a light source. The average transmittance of light having a wavelength of 600 to 700 nm longer than the wavelength λ _R1 and an incident angle of 60 degrees is 20% or more and 80% or less.

The selective light reflective optical element used in the present invention has a band for reflecting a light beam (hereinafter sometimes referred to as a reflection band). A solid line 30 in FIG. 1 indicates the wavelength dependence of the reflectance at an incident angle of 0 degree. Reflection band as shown by the solid line 30, a portion where the reflectance is greater than the other portion in (a wavelength range of between lambda _H from lambda _L) specific wavelength range. In FIG. 1, the reflectivity changes abruptly at the boundary between the reflection band and the non-reflection band, and the graph has a rectangular or trapezoidal shape. However, the reflectivity changes gradually, and the graph is gently like a parabola. It may have a chevron shape. Here, the lower limit λ _L and the upper limit λ _H of the reflection band are the shortest and the longest, respectively, among the wavelengths showing the reflectance that is ½ times the maximum reflectance in the reflection band.

FIG. 2 shows an example of an emission spectrum of a light source (light emitting diode) used in a liquid crystal display device. λ _R1 is the wavelength of light that exhibits the maximum emission intensity in the wavelength band of 600 to 700 nm in the light emitted from the light source.
The wavelength range of the band for reflecting the light beam of the selective light reflecting optical element varies depending on the incident angle. In the present invention, the lower limit λ _{L of the} wavelength band for reflecting light rays with an incident angle of 0 degrees is longer than the wavelength λ _R1 . For example, since λ _R1 is about 627 nm in the light source of FIG. 2, λ _L needs to be longer than 627 nm. The reflection band λ _L shown by the solid line 30 in FIG. 1 is about 680 nm. The width of the reflection band (difference between λ _H and λ _L ) is preferably 50 nm or more, particularly preferably 80 nm or more.

In the selective light reflective optical element used in the present invention, it is preferable that λ _L is longer than the wavelength λ _{R2 of} light that exhibits the maximum emission intensity in the wavelength band of 630 to 700 nm in the light emitted from the light source. By lambda _L becomes longer wavelengths can improve the color balance when the front observation, or it is possible to increase the value of the area ratio of the color reproduction range for the chromaticity region.

  The maximum reflectance of the reflection band at an incident angle of 0 degree is preferably 10% to 40%, more preferably 15% to 35%. When this maximum reflectance is in the above range, when the display screen of the liquid crystal display device of the present invention is observed obliquely, an image having the same color balance as that observed from the front can be obtained. When the reflectance exceeds the above range, the display image when observed from an oblique angle tends to be bluish. When the reflectance is less than the above range, the display image when observed from an oblique angle is likely to be reddish.

The selective light reflective optical element used in the present invention preferably has an average transmittance of light having a wavelength of 600 to 700 nm (hereinafter, sometimes referred to as “red light” for simplicity) at an incident angle of 0 degree, preferably 60%. Above, more preferably 70% or more. Furthermore, it is preferable that the average transmittance of red light at an incident angle of 0 degrees is larger than the average transmittance of red light at an incident angle of 60 degrees described later.
Light rays at a wavelength of 400 to 500 nm (hereinafter sometimes referred to as “blue light” for simplicity) and a wavelength of 500 to 600 nm (hereinafter sometimes referred to as “green light” for simplicity) at an incident angle of 0 degree. The transmittance can be appropriately selected in consideration of the light amount balance with respect to red light. The average transmittance of blue light and green light at an incident angle of 0 degree is preferably 60% or more, more preferably 70% or more. In the present specification, the average transmittance is an arithmetic average value of transmittance measured at a wavelength interval of 10 nm.

The reflection band is preferably shifted to the short wavelength side as the incident angle of light increases. Specifically, it is preferable that the reflection band includes the wavelength λ _R1 or λ _R2 at an incident angle of 60 degrees. By shifting the reflection band to the short wavelength side, the average transmittance of light having a wavelength of 600 to 700 nm at an incident angle of 60 degrees can be lowered. A broken line 31 in FIG. 1 indicates a reflection band at an incident angle of 60 degrees. In FIG. 1, the lower limit of the reflection band is about 610 nm.

  In the selective light reflective optical element used in the present invention, the average transmittance of light having a wavelength of 600 to 700 nm at an incident angle of 60 degrees is 20% or more and 80% or less, preferably 30% or more and 70% or less, more preferably 40. % To 60%. When the light transmittance is in the above range, the display image of the liquid crystal display device of the present invention can be made to have the same color balance in front and oblique observation. When the light transmittance is less than the above range, the display image when observed obliquely becomes bluish. When the light transmittance exceeds the above range, the display image when viewed from an oblique angle becomes reddish.

In the selective light reflective optical element used in the present invention, the average transmittance of blue light and green light at an incident angle of 60 degrees is preferably 60% or more, more preferably 70% or more.
The average transmittance of red light at an incident angle of 60 degrees is smaller than the average transmittance of blue light and green light at an incident angle of 60 degrees, specifically, the average of blue light and green light at an incident angle of 60 degrees. It is preferably 5 to 30% smaller than the transmittance.

  The selective light reflective optical element used in the present invention is not limited by its structure as long as the transmittance or reflectance characteristics change according to the incident angle as described above. The selective light reflecting optical element used in the present invention includes, for example, a multilayer thin film (for example, a cold filter) in which inorganic oxides having different refractive indexes are alternately deposited; a thin film in which thin films of resins having different refractive indexes are laminated; Infrared reflective film obtained by biaxially stretching a multilayer film of resins having different rates; An infrared reflective film obtained by uniaxially stretching two types of resin films having different refractive indexes, and laminated by orthogonalizing them A selective reflection band of a circularly polarized light reflector including a resin layer having cholesteric regularity in the infrared region; a laminate of right and left twisted products of the circularly polarized light reflector; cholesteric regularity in the same twist direction And two circularly polarized light reflection plates including a resin layer having a thickness of 2 are laminated via a half-wave plate; and a grid polarizer. Among these, the selective light reflective optical element including the circularly polarizing reflector including the resin layer having cholesteric regularity, the light reflected according to the incident angle as described above is either right-turn or left-turn. Of circularly polarized light and can be preferably used. In addition, the selective light reflective optical element including a film having a structure in which films having different refractive indexes are laminated, and the selective light reflective optical element including a grid polarizer have light reflected according to an incident angle as described above. , One of the two linearly polarized lights orthogonal to each other, and can be preferably used. The resin layer having cholesteric regularity is a resin layer having a structure in which the angle of the molecular axis of the resin is successively shifted (twisted) as it proceeds in the normal direction of the resin layer plane. .

  The brightness enhancement element used in the liquid crystal display device of the present invention reflects one polarization of visible light and transmits the other polarization (that is, separates into reflected light and transmitted light depending on the polarization state). is there. As the brightness enhancement element, the reflected light and the transmitted light are linearly polarized light (hereinafter sometimes referred to as a linearly polarized light separating film), and the reflected light and the transmitted light are circularly polarized light (hereinafter referred to as a circularly polarized light separating film). For example, many anisotropic polymer layers as disclosed in, for example, US Pat. No. 6,335,999, Japanese Patent Publication No. 9-506837, Japanese Patent Publication No. 10-511322, etc. A linearly polarized light separating film obtained by laminating, a circularly polarized light separating film using a resin layer having cholesteric regularity as disclosed in JP-A-6-235900 and JP-A-8-271731; A combination of / 4 wavelength plates may be mentioned. As a commercially available linearly polarized light separation film, for example, a multilayer film manufactured by 3M (trade name “D-BEF”) can be mentioned. As a combination of the circularly polarized light separating film and the quarter wavelength plate, for example, a brightness enhancement film (trade name “NIPOCS”) manufactured by Nitto Denko Corporation may be mentioned. In the combination of the circularly polarized light separating film and the quarter wavelength plate, when light is incident on the circularly polarized light separating film side, the reflected light becomes circularly polarized light and the transmitted light becomes linearly polarized light.

In the liquid crystal display device of the present invention, the aforementioned selective light reflecting optical element is disposed on the side closer to the light source, and the brightness enhancement element is disposed on the side closer to the liquid crystal panel described later.
The combination of the selective light reflective optical element and the brightness enhancement element is not particularly limited. Specific combinations include 1) a combination of a selective light reflective optical element that reflects linearly polarized light and a brightness enhancement element including a circularly polarized light separating film, and 2) a selective light reflective optical element that reflects circularly polarized light, and A combination with a brightness enhancement element comprising a circularly polarized light separating film, 3) a combination of a selective light reflective optical element reflecting circularly polarized light and a brightness enhancing element comprising a linearly polarized light separating film, and 4) a linearly polarized light There is a combination of a selective light reflecting optical element that reflects and a brightness enhancement element that includes a linearly polarized light separating film.

  1) When a selective light reflecting optical element that reflects linearly polarized light and a brightness enhancement element including a circularly polarized light separating film are combined, red light having an incident angle of 0 degrees is reflected by the selective light reflecting optical element. Instead, it is sent to the brightness enhancement element as it is and separated into right-handed circularly polarized light and left-handed circularly polarized light. Part of the obliquely incident red light is reflected by the selective light reflecting optical element, and the attenuated red light is sent to the brightness enhancement element, where it is separated into right-handed circularly polarized light and left-handed circularly polarized light Is done. Blue light and green light are transmitted through the selective light reflecting optical element as they are regardless of the incident angle, and are separated into right-handed circularly polarized light and left-handed circularly polarized light by the brightness enhancement element.

  The red light obliquely transmitted through the selective light reflecting optical element includes one linearly polarized light attenuated and the other linearly polarized light orthogonal thereto. In this aspect, when a quarter-wave plate is interposed between the selective light reflective optical element that reflects linearly polarized light and the brightness enhancement element including the circularly polarized light separation film, the selective light reflective optical element is transmitted. Linearly polarized light can be converted to circularly polarized light, and the separation efficiency in the circularly polarized light separation film can be increased. Moreover, by doing in this way, the thickness (the number of laminated thin films) of the selective light reflective optical element can be reduced (reduced).

  2) When a selective light reflective optical element that reflects circularly polarized light and a brightness enhancement element including a circularly polarized light separation film are combined, red light with an incident angle of 0 degrees is reflected by the selective light reflective optical element. Instead, it is sent to the brightness enhancement element as it is and separated into right-handed circularly polarized light and left-handed circularly polarized light. Part of the obliquely incident red light is reflected by the selective light reflecting optical element, and the attenuated red light is sent to the brightness enhancement element, where it is separated into right-handed circularly polarized light and left-handed circularly polarized light Is done. Blue light and green light are transmitted through the selective light reflecting optical element as they are regardless of the incident angle, and are separated into right-handed circularly polarized light and left-handed circularly polarized light by the brightness enhancement element. In this combination mode, it is preferable that the spiral rotation (twist) direction of the selective light reflective optical element that reflects circularly polarized light is opposite to the spiral rotation (twist) direction of the circularly polarized light separation film. In this way, it is possible to efficiently reduce obliquely transmitted red light.

Further, in the present invention, the selective light that reflects the circularly polarized light by interposing the half-wave plate between the selective light reflective optical element that reflects the circularly polarized light and the brightness enhancement element including the circularly polarized light separation film. The same result as described above can be obtained by making the spiral rotation (twist) direction of the reflective optical element the same as the spiral rotation (twist) direction of the circularly polarized light separation film.
The spiral rotation direction is a twist direction of molecules in the resin layer having cholesteric regularity which is a main component of the selective light reflecting optical element or the circularly polarized light separation film, and the rotation direction is the method shown in the embodiment. Can be measured.

  3) When a selective light reflective optical element that reflects circularly polarized light and a brightness enhancement element including a linearly polarized light separating film are combined, red light with an incident angle of 0 degrees is reflected by the selective light reflective optical element. Instead, it is sent to the brightness enhancement element as it is and separated into two orthogonal linearly polarized light. Part of the obliquely incident red light is reflected by the selective light reflecting optical element, and the attenuated red light is sent to the brightness enhancement element, where it is separated into two orthogonal linearly polarized lights. Blue light and green light are transmitted through the selective light reflecting optical element as they are regardless of the incident angle, and are separated into two linearly polarized lights orthogonal to each other by the brightness enhancement element.

  The red light transmitted obliquely through the selective light reflecting optical element includes one circularly polarized light attenuated and the other circularly polarized light having a different rotational direction. In this aspect, when a quarter wavelength plate is interposed between the selective light reflective optical element that reflects circularly polarized light and the brightness enhancement element including the linearly polarized light separation film, the selective light reflective optical element is transmitted. Circularly polarized light can be converted into linearly polarized light, and the separation efficiency in the linearly polarized light separation film can be increased. Moreover, by doing in this way, the thickness (the number of laminated thin films) of the selective light reflective optical element can be reduced (reduced), and luminance unevenness can be further reduced.

  4) When a selective light reflective optical element that reflects linearly polarized light and a brightness enhancement element including a linearly polarized light separating film are combined, red light with an incident angle of 0 degrees is reflected by the selective light reflective optical element. Instead, it is sent to the brightness enhancement element as it is and separated into two orthogonal linearly polarized light. Part of the obliquely incident red light is reflected by the selective light reflecting optical element, and the attenuated red light is sent to the brightness enhancement element, where it is separated into two orthogonal linearly polarized lights. Blue light and green light are transmitted through the selective light reflecting optical element as they are regardless of the incident angle, and are separated into two linearly polarized lights orthogonal to each other by the brightness enhancement element.

  The red light transmitted obliquely through the selective light reflecting optical element includes one linearly polarized light attenuated and the other linearly polarized light orthogonal thereto. In this combination mode, it is preferable that the transmission axis of the selective light reflective optical element that reflects linearly polarized light and the transmission axis of the linearly polarized light separating film are arranged so as to be orthogonal. In this way, it is possible to efficiently reduce obliquely transmitted red light. The transmission axis of the selective light reflecting optical element is an axis in a direction perpendicular to one linearly polarized light attenuated by the selective light reflecting optical element, and the transmission axis of the linearly polarized light separating film is a linearly polarized light. It is the axis in the direction parallel to the linearly polarized light that is transmitted through the separation membrane.

  Further, in the present invention, the selective light that reflects linearly polarized light by interposing a half-wave plate between the selective light reflective optical element that reflects linearly polarized light and the brightness enhancement element including the linearly polarized light separation film. The same result as described above can also be obtained by making the transmission axis of the reflective optical element and the transmission axis of the linearly polarized light separating film parallel to each other.

  When the selective light reflective optical element and the brightness enhancement element are used in combination, if they are stacked, an air layer between the elements is eliminated, and unnecessary reflection and interference at the interface can be reduced. A resin having cholesteric regularity by using the above-described selective light reflective optical element on a transparent substrate for laminating a resin layer having cholesteric regularity that can be preferably used when manufacturing a circularly polarized light separation film The layer can be directly laminated on the selective light reflective optical element, and the liquid crystal display device can be made thin.

The liquid crystal panel used in the present invention is composed of two linear polarizers and a liquid crystal cell arranged between the linear polarizers.
The linear polarizer transmits one of two linearly polarized lights that intersect at right angles. For example, a hydrophilic polymer film such as a polyvinyl alcohol film or an ethylene vinyl acetate partially saponified film adsorbed a dichroic substance such as iodine or a dichroic dye and uniaxially stretched, the hydrophilic polymer film Examples include uniaxially stretched and dichroic substances adsorbed, and polyene oriented films such as polyvinyl alcohol dehydrated products and polyvinyl chloride dehydrochlorinated products. Other examples include a polarizer having a function of separating polarized light such as grid polarizer and multilayer polarizer into reflected light and transmitted light. Of these, a polarizer containing polyvinyl alcohol is preferred.

The degree of polarization of the linear polarizer used in the present invention is not particularly limited, but is preferably 98% or more, more preferably 99% or more. The average thickness of the linear polarizer is preferably 5 to 80 μm.
The pair of linear polarizers are arranged with the liquid crystal cell sandwiched so that their polarization transmission axes are parallel or perpendicular. The linear polarizer may change its polarization performance due to moisture absorption. In order to prevent this, a protective film is usually bonded to both sides of the linear polarizer. The protective film bonded to the linear polarizer on the viewing side may be provided with an antireflection layer, an antifouling layer, an antiglare layer and the like. In addition, it is preferable that the transmission axis of the linear polarizer on the incident side is parallel to the transmission axis of the brightness enhancement element. The transmission axis of the brightness enhancement element is an axis in a direction parallel to the linearly polarized light when the polarized light transmitted through the brightness enhancement element is linearly polarized light.

In the present invention, a retardation film can be provided between the linear polarizer on the incident side and the liquid crystal cell for viewing angle compensation. The retardation Re in the in-plane direction and the retardation Rth in the thickness direction of the retardation film vary depending on the design of the liquid crystal display device, but usually Re is appropriately selected from the range of about 0 to 300 nm and Rth of about −300 to 300 nm. Is done. Incidentally, Re is slow axis direction of the refractive indices n _x in the plane of the _film, the slow axis and the direction of the refractive index perpendicular in the plane n _y in the _plane, the refractive index in the thickness direction of the film n _z, the average thickness of the film is taken as _{T w, (n x -n y} ) is a value defined by × _{T w,} Rth _{is, (((n x + n} y) / 2) -n _z )) is a value defined by _Tw .

A liquid crystal cell is filled with a liquid crystal substance between two glass substrates provided with transparent electrodes facing each other with a gap of several μm, and a voltage is applied to this electrode to change the alignment state of the liquid crystal and pass through this. The amount of light to be controlled is controlled.
The liquid crystal cell is classified according to a method (operation mode) for changing the alignment state of the liquid crystal substance. For example, a TN (Twisted Nematic) type liquid crystal cell, a STN (Super Twisted Nematic) type liquid crystal cell, or a HAN (Hybrid Alignment Nematic) type. Examples thereof include a liquid crystal cell, an IPS (In Plane Switching) type liquid crystal cell, a VA (Vertical Alignment) type liquid crystal cell, an MVA (Multiple Vertical Alignment type liquid crystal cell), and an OCB (Optical Compensated Bend) type liquid crystal cell.

  The liquid crystal display device of the present invention includes a reflective element, a light diffusing element, a prism sheet, a quarter wavelength plate, a half wavelength plate, a viewing angle, in addition to a light source, a selective light reflecting optical element, a brightness enhancement element, and a liquid crystal panel. A compensation film, an antireflection film, an antiglare film, or the like may be disposed.

  FIG. 3 is a diagram showing a configuration of an example of the liquid crystal display device of the present invention. As shown in FIG. 3, the backlight unit BL including the reflecting plate 20, the light source (light emitting diode) 19 and the light diffusing plate 18, the selective light reflecting optical element 17, the brightness enhancing element 16, and the liquid crystal panel P are arranged in this order. Yes. When the light from the light source enters the selective light reflective optical element at an incident angle of 0 degree, each of blue, green, and red light is transmitted as it is. As the incident angle increases, a part of the red light is reflected, and the light transmittance of the red light decreases. At an incident angle of 60 degrees, the average transmittance of light having a wavelength of 600 to 700 nm is adjusted to 20% or more and 80% or less. As a result, the balance of the red light with respect to the blue light and the green light is adjusted, and an image with the same color balance can be displayed in the front and oblique observation.

  The present invention will be described in more detail with reference to examples and comparative examples, but the present invention is not limited to the following examples. Parts and% are based on weight unless otherwise specified.

The evaluation methods performed in this example are as follows.
(1) Retardation Re and Rth
Under the conditions of a temperature of 20 ° C. and a humidity of 60%, using a phase difference measuring device (manufactured by Oji Scientific Instruments Co., Ltd., KOBRA), in light of a wavelength of 550 nm, 10 points are measured at equal intervals in the width direction of the phase difference film, The average value of Re and Rth is calculated.
(2) Measurement of spiral direction of resin layer having cholesteric regularity Light from xenon lamp (product name “L2173” manufactured by Hamamatsu Photonics) is incident on selective light reflecting optical element, and is a quarter wavelength plate (Product name “AQWP05M-630” manufactured by THORLABS, Inc.) and a polarizing plate (product name “PO-30-2” manufactured by Chuo Seiki Co., Ltd.) through a spectroscope (manufactured by Soma Optics, product name “S -2600 "). Observation was carried out while changing the angle of the axis of slow propagation of the quarter-wave plate with respect to the transmission axis of the polarizing plate (observed from the spectroscope side, and counterclockwise as positive). When the transmitted light intensity at 720 nm, which is substantially the center of the reflection band, is minimum at 45 degrees, it indicates that right circularly polarized light is reflected, and the spiral of the resin layer having cholesteric regularity is right-handed. Conversely, if it is minimized at -45 degrees, the helix is left-handed.
The brightness enhancement element including the circularly polarized light separation film was measured in the same manner as described above at 550 nm, which is approximately the center of the reflection band, and whether the rotation direction of the spiral was right-handed or left-handed was measured.

Production Example 1
(Preparation of selective light reflective optical element 1)
An optically isotropic film (trade name “ZEONOR FILM ZF14” manufactured by ZEON Corporation, thickness 100 μm) made of a norbornene-based polymer is plasma-treated so that the wetting index is 56 dyne / cm. The material was obtained.
An alignment film composition comprising 5 parts of polyvinyl alcohol and 95 parts of water was applied to one side of the transparent substrate and dried to form a film. Next, the film was rubbed with a felt roll in a direction parallel to the longitudinal direction of the transparent substrate to obtain an alignment film having an average thickness of 0.1 μm.

  Nematic liquid crystal compound (BASF, trade name “LC242”) 100 parts, chiral agent (BASF, trade name “LC756”) 3.46 parts, photopolymerization initiator (Ciba Specialty Chemicals, product) (Name "Irgacure 907") and 3.21 parts of surfactant (product name "KH-40", manufactured by Seimi Chemical Co., Ltd.) 0.11 part are dissolved in 160 parts of methyl ethyl ketone, and a CD / made of polyfluoroethylene having a pore diameter of 2 μm A liquid crystal coating solution (polymerizable composition) was prepared by filtration using an X syringe filter.

On the alignment film, a liquid crystal coating solution was applied to a dry thickness of 3.76 μm and dried at 100 ° C. for 5 minutes. Subsequently, ultraviolet rays were irradiated at 150 mJ / cm ² to form a resin layer having cholesteric regularity, and a selective light reflective optical element 1 was obtained.
When the cross section of the selective light reflective optical element 1 was observed with a scanning electron microscope (SEM), the helical pitch (helical pitch) of the cholesteric resin layer was 470 nm.

  White light obtained by collimating light from a xenon lamp (product name “L2173”, manufactured by Hamamatsu Photonics Co., Ltd.) with a lens is incident on the selective light reflecting optical element 1 at an incident angle of 0 degree, and the light reflectance is measured by a spectroscope. (Trade name “S-2600”, manufactured by Soma Optical Co., Ltd.). The reflection band at an incident angle of 0 degrees was 690 nm to 850 nm, and the average transmittance of light having a wavelength of 600 to 700 nm at an incident angle of 0 degrees was 88%. Next, the collimated white light was incident at an incident angle of 60 degrees, and the light transmittance was measured in the same manner. The transmittance at a wavelength of 610 nm at an incident angle of 60 degrees was 50%. The average transmittance of light having a wavelength of 600 to 700 nm at an incident angle of 60 degrees was 59% (0.67 times the average transmittance of light having a wavelength of 600 to 700 nm at an incident angle of 0 degrees). The cholesteric resin layer of the selective light reflecting optical element 1 had a right-handed twist in the rotational direction of the spiral.

Production Example 2
(Preparation of retardation film 2A)
A 100 μm thick optically isotropic film (trade name “Zeonor Film ZF14”, manufactured by Nippon Zeon Co., Ltd.) made of a norbornene-based polymer is stretched at a stretching temperature of 138 ° C. and a longitudinal stretching ratio using a tenter stretching machine. Simultaneous biaxial stretching was performed at 1.41 times and a transverse draw ratio of 1.41 times.
One side of the stretched film was subjected to corona discharge treatment at an output of 0.8 kW using a high frequency transmitter (high frequency power supply AGI-024 manufactured by Kasuga Denki Co., Ltd.), the film surface tension was set to 0.072 N / m, and the thickness was 50 μm. A retardation film 2A was obtained.
The average values of Re and Rth of the obtained retardation film 2A were Re = 70 nm and Rth = 215 nm.

Production Example 4
(Production of polarizer)
A 75 μm thick PVA film (manufactured by Kuraray Co., Ltd., Vinylon # 7500) was attached to the chuck and immersed in an aqueous solution of 0.2 g / l iodine and 60 g / l potassium iodide at 30 ° C. for 240 seconds. Subsequently, it was immersed in an aqueous solution having a composition of boric acid 70 g / l and potassium iodide 30 g / l and uniaxially stretched 6.0 times. Finally, it was dried at room temperature for 24 hours to obtain a polarizer having an average thickness of 30 μm and a polarization degree of 99.97%.

Example 1
(Preparation of protective film)
One side of a triacetylcellulose film (trade name “KC8UX2M” manufactured by Konica Minolta Co., Ltd.) was coated with 25 ml / m ^{2 of} an isopropyl alcohol solution of 1.5 N potassium hydroxide and dried at 25 ° C. for 5 seconds. The film was washed with running water for 10 seconds and then dried by blowing air at 25 ° C. to obtain a protective film.

(Preparation of exit-side polarizing plate 4A and incident-side polarizing plate 5A)
The said protective film was bonded together on both surfaces of the polarizer obtained in manufacture example 4 using the polyvinyl alcohol-type adhesive agent, and the output side polarizing plate 4A was produced. At this time, the saponification surface of the protective film was made to face the polarizer.
In addition, the protective film is bonded to one surface of the polarizer obtained in Production Example 4 and the retardation film 2A obtained in Production Example 2 is bonded to the other surface in the same manner as described above, so that the incident-side polarized light is bonded. A plate 5A was produced. At this time, the saponification-treated surface of the protective film was made to face the polarizer, and the corona-treated surface of the retardation film 2A was made to face the polarizer. Further, the polarization transmission axis of the polarizer and the in-plane slow axis of the retardation film were made parallel.

(Production of liquid crystal display device A)
On a backlight unit having a light source having an emission spectrum shown in FIG. 2, a selective light reflective optical element 1, a brightness enhancement film made of a linearly polarized light separation film (product name “DBEF-D400” manufactured by 3M), Incident side polarizing plate 5A, VA mode liquid crystal cell (thickness 2.74 μm, positive dielectric anisotropy, birefringence difference Δn = 0.09884 at a wavelength of 550 nm, pretilt angle 90 degrees), and outgoing side polarizing plate 4A Were stacked in this order to produce a liquid crystal display device A having the structure shown in FIG. At this time, it arrange | positioned so that the phase difference film 2A of the incident side polarizing plate 5A might face a liquid crystal cell. In addition, the polarization transmission axis of the exit-side polarizer and the polarization transmission axis of the entrance-side polarizer are made perpendicular to each other.
When the chromaticity change according to the observation angle of the obtained liquid crystal display device A was visually evaluated, as shown in Table 1, the display image of the liquid crystal display device A has an azimuth (left and right) parallel to the polarization transmission axis of the incident side polarizer. ), Azimuth (vertical) perpendicular to the polarization transmission axis of the incident side polarizer, and +45 degrees obliquely with respect to the polarization transmission axis of the incident side polarizer (counterclockwise from the polarization transmission axis of the incident side polarizer is positive) )) And an angle of −45 degrees obliquely were observed in the range of incident angles of 0 to 80 degrees, but almost no change in chromaticity was observed.

Example 2
(Production of liquid crystal display device B)
The observation angle was the same as in Example 1 except that a brightness enhancement film including a circular polarization separation film (manufactured by Nitto Denko Corporation, trade name “NIPOCS”) was used instead of the brightness enhancement film composed of a linearly polarized light separation film. The chromaticity change due to was visually evaluated. In the display image of the liquid crystal display device B, as shown in Table 1, almost no change in chromaticity was observed in the range of incident angles from 0 to 80 degrees in the top and bottom, left and right, +45 degrees, and -45 degrees orientations of the display screen. . Note that the brightness enhancement film including the circularly polarized light separation film had a spiral left-handed.

Comparative Example 1
An unstretched film made of a norbornene-based polymer (manufactured by Nippon Zeon Co., Ltd., trade name “Zeonor film ZF14”, thickness 100 μm) is light having a wavelength of 600 to 700 nm when collimated white light is incident at an incident angle of 0 degree. The average transmittance was 90%. The average transmittance of light with a wavelength of 600 to 700 nm when collimated white light is incident at an incident angle of 60 degrees is 82% (0.91 times the average transmittance of light with a wavelength of 600 to 700 nm at an incident angle of 0 degrees) )Met. The unstretched film is a film having no selective reflection band.
A liquid crystal display device C was produced in the same manner as in Example 1 except that this unstretched film was used in place of the selective light reflective optical element 1 used in Example 1. As shown in Table 1, the obtained liquid crystal display device C is observed in any direction when viewed from the range of incident angles from 0 to 80 degrees in the vertical and horizontal directions, +45 degrees, and -45 degrees of the display screen. The image was light red throughout.

Comparative Example 2
A liquid crystal display device D configured as shown in FIG. 4 was prepared in the same manner as in Example 1 except that the order of the selective light reflective optical element 1 and the brightness enhancement film was reversed.
As shown in Table 1, the obtained liquid crystal display device D is vertically and horizontally when observed from a range of incident angles of 0 to 80 degrees in the top and bottom, left and right, +45 degrees, and -45 degrees orientation of the display screen. Almost no change in chromaticity was observed, but in the + 45 ° and −45 ° azimuth directions, the entire image was light red.

The meanings of ○ △ × in the table are as follows.
A: Almost no change in chromaticity was observed in the polar angle range of 0 to 80 degrees.
Δ: Mildly light red.
X: A light red color was exhibited.

It is a figure which shows an example of the reflective zone | band of a selective-light reflective optical element. It is a figure which shows an example of the emission spectrum of a light source. It is a figure which shows the structural example of the liquid crystal display device of this invention (Example). 10 is a diagram illustrating a configuration example of a liquid crystal display device of Comparative Example 2. FIG.

Explanation of symbols

10: Protective film 11: Linear polarizer (viewing side or emitting side)
12: Liquid crystal cell 13: Biaxial optical anisotropic film (viewing angle compensation film)
14: Protective film 15: Linear polarizer (incident side)
P: Liquid crystal panel 16: Brightness improving element 17: Selective light reflecting optical element 18: Light diffusing plate 19: Light emitting diode (light source)
20: Reflector BL: Backlight unit 30: Reflection band at an incident angle of 0 degrees 31: Reflection band at an incident angle of 60 degrees

Claims (3)

A light source, a selective light reflecting optical element, a brightness enhancement element, and a liquid crystal panel are arranged in this order,
In the selective light reflecting optical element, the lower limit λ _{L of the} wavelength band for reflecting the light beam with the incident angle of 0 ° is the wavelength λ _{R1 of the} light having the maximum emission intensity in the wavelength band of 600 to 700 nm among the light emitted from the light source. The average transmittance of light having a wavelength of 600 to 700 nm at an incident angle of 60 degrees is 20% or more and 80% or less,
The brightness enhancement element reflects one polarization in the visible light region wavelength and transmits the other polarization.
Liquid crystal display device.   The selective light reflective optical element further has an average transmittance of light having a wavelength of 600 to 700 nm at an incident angle of 0 degree of 60% or more and an average transmittance of light having a wavelength of 600 to 700 nm at an incident angle of 0 degree. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is larger than an average transmittance of light having a wavelength of 600 to 700 nm at an incident angle of 60 degrees. The liquid crystal display device according to claim 1, wherein the selective light reflective optical element has an average transmittance of light having a wavelength of 600 to 700 nm at an incident angle of 60 degrees of 30% to 70%.

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