JP2015045695A - Optical film and liquid crystal display device - Google Patents

Abstract

Disclosed is a C plate that is applied to optical compensation of an IPS liquid crystal display device, and a defect recognized by a white point on a display screen can be effectively avoided.
In an optical film 11 having at least a C plate (nx = ny <nz or nx = ny> nz) 7A, the C plate 7A is formed of a liquid crystal compound and is formed in one direction on a lower layer 12 of the C plate 7A. Rubbing traces extending to the surface are provided.
[Selection] Figure 2

Description

  The present invention relates to an optical film and a liquid crystal display device, and can be applied to, for example, an IPS liquid crystal display device (IPS-LCD).

  In recent years, IPS liquid crystal display devices have been widely applied to various display devices because they can ensure a wide viewing angle characteristic. Regarding this IPS liquid crystal display device, various devices have been proposed in Patent Document 1 and the like.

  However, the IPS liquid crystal display device has a drawback that light leakage occurs obliquely from the linear polarizing plate during black display, and as a result, a sufficient contrast ratio cannot be ensured. Optical compensation (phase difference compensation) in the IPS liquid crystal display device is a configuration that reduces this light leakage. Patent Document 2 discloses a configuration in which optical compensation is performed by a laminate of a + A plate and a + C plate.

  The C plate used for this type of optical compensation can be made of a liquid crystal compound. More specifically, it can be prepared by applying a coating liquid made of a polymerizable liquid crystal monomer, raising the temperature to the phase transition point, and then polymerizing by ultraviolet irradiation or the like to fix the alignment state of the liquid crystal.

  By the way, in the C plate, there is a defect that is recognized by a white spot on the display screen due to foreign matters contained in the coating liquid, surface foreign matters to be coated, and the like. If such a defect can be effectively avoided, the image quality of the image display device can be further improved.

US Pat. No. 3,807,831 JP-T 2006-520008

  The present invention has been made in view of such a situation, and it is possible to effectively avoid a defect recognized by a white point on a display screen with respect to a C plate applied to optical compensation or the like of an IPS liquid crystal display device. An object is to propose an optical film and a liquid crystal display device.

  The present inventor has conducted intensive research to solve the above-mentioned problems, and sets the stretching axis direction of the coating object or the extending direction of the rubbing trace to be parallel to the absorption axis or the transmission axis of the linear polarizing plate. As a result, the present invention has been completed.

    Specifically, the present invention provides the following.

  (1) In an optical film provided with at least a C plate (nx = ny <nz or nx = ny> nz), the C plate is formed of a liquid crystal compound and is rubbed in one direction on a lower layer of the C plate. Traces are provided. However, nx and ny (nx ≧ ny) are refractive indexes in the in-plane direction, and nz is a refractive index in the thickness direction.

  According to (1), the liquid crystal material around the foreign material is formed so that the liquid crystal material is arranged in one direction, which is an extension direction of the rubbing trace. As a result, the arrangement direction can be set to the absorption axis direction or the transmission axis direction of the linearly polarizing plate so that it cannot be recognized by the white spot on the display screen, and as a result, defects can be effectively avoided. .

  (2) An optical film arranged on a backlight side or an emission surface side of a liquid crystal cell, comprising a linearly polarizing plate and an optical compensation layer having at least a C plate (nx = ny <nz or nx = ny> nz). The C plate is formed of a liquid crystal compound, and the extending axis direction of the lower layer of the C plate or the extending direction of the rubbing trace is set to be parallel to the absorption axis or the transmission axis of the linearly polarizing plate. However, nx and ny (nx ≧ ny) are refractive indexes in the in-plane direction, and nz is a refractive index in the thickness direction.

  According to (2), the liquid crystal material around the foreign material is formed so that the liquid crystal material is arranged in one direction which is the extension axis direction of the lower layer or the rubbing trace. As a result, the arrangement direction can be set to the absorption axis direction or the transmission axis direction of the linearly polarizing plate so that it cannot be recognized by the white spot on the display screen, and as a result, defects can be effectively avoided. .

  (3) In a liquid crystal display device in which a liquid crystal cell is sandwiched between linearly polarizing plates on the backlight side and the emitting surface side arranged so that the absorption axis directions are orthogonal, the linearly polarizing plate on the emitting surface side or the backlight side and the linear polarizing plate At least a C plate (nx = ny <nz or nx = ny> nz) is disposed between the liquid crystal cell, the C plate is formed of a liquid crystal compound, and the stretching axis direction or rubbing trace of the lower layer of the C plate Is set to be parallel to the absorption axis or transmission axis of the linearly polarizing plate on the exit surface side. However, nx and ny (nx ≧ ny) are refractive indexes in the in-plane direction, and nz is a refractive index in the thickness direction.

  According to (3), the liquid crystal material around the foreign material is formed so that the liquid crystal material is arranged in one direction which is the extension axis direction of the lower layer or the rubbing trace. As a result, the arrangement direction can be set to the absorption axis direction or the transmission axis direction of the linearly polarizing plate so that it cannot be recognized by the white spot on the display screen, and as a result, defects can be effectively avoided. .

  ADVANTAGE OF THE INVENTION According to this invention, the fault recognized by the white point on a display screen can be effectively avoided regarding C plate applied to the optical compensation etc. of an IPS liquid crystal display device.

It is a figure which shows the liquid crystal display device which concerns on 1st Embodiment of this invention. It is a figure which shows the transfer film applied to the liquid crystal display device of FIG. It is a figure which shows the liquid crystal display device which concerns on 2nd Embodiment of this invention. It is a figure which shows the transfer film applied to the liquid crystal display device of FIG.

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

[First Embodiment]
FIG. 1 is a cross-sectional view showing a liquid crystal display device according to a first embodiment of the present invention. The liquid crystal display device 1 is an IPS liquid crystal display device, and is formed by disposing a liquid crystal display panel 3 on the front surface of a backlight 2. In FIG. 1, a symbol by arrows indicating the horizontal direction and the vertical direction, and a symbol by double circles indicating the depth direction indicate the absorption axis direction of the linearly polarizing plate and the slow axis directions of the liquid crystal cell and the retardation layer.

  The liquid crystal display panel 3 is provided with a liquid crystal cell 4 made of IPS liquid crystal. Here, the liquid crystal cell 4 is a liquid crystal having positive dielectric anisotropy (Δε> 0) or negative dielectric anisotropy (Δε> 0) between two glass substrates held so as to face each other. The liquid crystal molecules are horizontally aligned and formed. In the liquid crystal display panel 3, a linearly polarizing plate 5 is provided on the backlight side of the liquid crystal cell 4 by, for example, a pressure-sensitive adhesive layer (not shown). In the example shown in FIG. 1, as will be described later, an optical compensation layer is provided on the linear polarizing plates 8 and 9 on the exit surface side. Alternatively, an optical compensation layer can be provided on the linear polarizing plate 5 on the backlight side. However, from the viewpoint of sufficiently reducing light leakage during black display, it is more preferable to provide an optical compensation layer on the linear polarizing plates 8 and 9 on the exit surface side. The IPS liquid crystal is a liquid crystal display device in which liquid crystal molecules such as Super-IPS (Super-In-Plane-Switching) and FFS (Fringe-Field-Switching) are substantially horizontally aligned and driven by an applied voltage. All liquid crystals according to the above are included.

  Here, in the linear polarizing plate 5, a polarizer 5 </ b> B that is an optical functional layer serving as a linear polarizing plate is provided on a base material 5 </ b> A made of a transparent film, and a protective film 5 </ b> C is further provided. Here, as the base material 5A, various films having a small in-plane retardation can be applied. For example, a TAC (triacetylcellulose (so-called Z-TAC (registered trademark)) film, COP (cycloolefin polymer) system In order to reduce the phase difference, the base material 5A may be omitted, and the polarizer 5B is a film material made of, for example, polyvinyl alcohol (PVA). In addition, various transparent films can be applied as the protective film 5C.

  In the liquid crystal display panel 3, for example, an optical film 6 is disposed on the exit surface of the liquid crystal cell 4 by a pressure sensitive adhesive layer (not shown). The optical film 6 includes an optical compensation layer 7 for use in optical compensation, a polarizer 8, and a base material 9 that is a surface material. Here, in this embodiment, a transparent film such as TAC is applied to the base material 9, and an optical functional layer as a linear polarizing plate is provided in the same manner as the linear polarizing plate 5. In the optical film 6, a polarizer 8 is formed by this optical functional layer, and thereby, a linear polarizing plate on the exit surface side is configured by the base material 9 and the polarizer 8.

  In the liquid crystal display panel 3, the absorption axis directions of the pair of polarizers 8 and 5B sandwiching the liquid crystal cell 4 by the linear polarizing plates 8 and 9 on the emission surface side and the linear polarizing plate 5 on the backlight side are orthogonal to each other. Further, the slow axis direction of the liquid crystal cell 4 is configured to coincide with the absorption axis direction of the polarizer 5B or the absorption axis direction of the polarizer 8, and accordingly, the liquid crystal cell 4 corresponds to the voltage applied to the liquid crystal cell 4. And controlling the amount of transmitted light to display a desired image.

  The optical compensation layer 7 is disposed between the linear polarizing plate on the exit surface side and the liquid crystal cell 4, and in this embodiment, the + C plate 7A and the + A plate 7B are sequentially disposed from the liquid crystal cell 4 side. . The + A plate 7B is disposed so that the slow axis direction is orthogonal to the absorption axis direction of the polarizer 8 (so as to coincide with the slow axis direction of the IPS liquid crystal cell 4). Thereby, in this embodiment, light leakage is sufficiently reduced with a simple configuration. A biaxial plate (nx> ny> nz) may be provided instead of the + A plate 7B.

Here, the + C plate 7A has a characteristic represented by nx = ny <nz, where nx and ny are in-plane refractive indices and nz is a refractive index in the thickness direction. The -C plate is made of discotic liquid crystal, cholesteric liquid crystal composed of rod-like liquid crystal, or the like, and has optical characteristics represented by nx = ny> nz. On the other hand, the -A plate can apply a discotic liquid crystal, a retardation layer made of a negative uniaxial or positive biaxial stretched film, and the like, and has optical characteristics of nz>nx> ny.

For example, the following liquid crystal compounds can be applied to the rod-like liquid crystal compounds applicable to the C plate and the + A plate.

[Transfer for optical film]
FIG. 2 is a cross-sectional view showing a transfer film that is a transfer body for an optical film used for production of the optical film 6. In this embodiment, the transfer method is applied to the production of the optical film 6, and a laminate of the + C plate 7A, the + A plate 7B or the biaxial plate is set as a transfer layer used for transfer. Here, in the transfer method, for example, when a desired layer is formed on a base material, the layer is not directly formed on the base material, but can be peeled once on a releasable support. After forming the transfer body by laminating the layers, the layer formed on the support is finally placed on the base material (transfer base material) on which the layer is to be laminated according to the process, demand, etc. In this method, a desired layer is formed on the substrate by bonding and laminating, and then peeling and removing the support. In the example of this optical film, the substrate to be transferred is set to a laminate of the substrate 9 and the polarizer 8, and the laminate of the + C plate 7A and the + A plate 7B is transferred to the substrate to be transferred.

  Here, although various film materials can be applied to the support 12, from the viewpoint of inspecting the optical characteristics of the + C plate 7 </ b> B and + A plate 7 </ b> B, a transparent film with a small retardation or an in-plane optical axis is used. It is desirable that there is no significant change. For example, a cycloolefin polymer, an acrylic film, or a PET film with high in-plane optical axis uniformity can be applied. The transfer film 11 is a laminate of the + C plate 7A and + A plate 7B disposed on the support 12, and then the substrate 9 and the polarizer 8 are laminated to each other with an adhesive such as an ultraviolet curable resin. After the transfer layer made of the + C plate 7A and + A plate 7B is laminated, the support 13 is peeled off from the transfer layer, and the optical film 6 is produced.

  For this reason, after the transfer film 11 is coated on the support 12 with a coating solution for use in creating the + C plate 7A, the + C plate 7A is produced by drying and curing. Further, after the coating liquid to be used for creating the + A plate 7B is applied, the + C plate 7A is manufactured by dry curing.

  By the way, in the + C plate 7A created in this way, there is a possibility that a defect recognized by a white point on the liquid display screen may occur due to a foreign matter on the support 12, a foreign matter in the coating liquid, or the like. Therefore, in this embodiment, the surface of the support 12 is rubbed in advance, and rubbing traces that are line-shaped fine irregularities extending in one direction are formed on the surface of the support 12. The extending direction of the rubbing trace is set to be the transmission axis direction or the absorption axis direction of the linearly polarizing plates 9 and 8. The extending direction of the rubbing trace is more preferably matched with the absorption axis direction of the linearly polarizing plates 9 and 8.

  Therefore, when no rubbing trace is produced, a liquid crystal material arranged radially around the foreign matter is arranged by the foreign matter, and as a result, a defect is recognized. However, in this embodiment, the liquid crystal material around the foreign material is set so as to be aligned in the transmission axis direction or the absorption axis direction of the linear polarizing plates 9 and 8 due to the rubbing traces in the lower layer. As a result, in the transmitted light of the foreign substance portion, when displaying a black screen, it is emitted by linearly polarized light in a direction shielded by the linearly polarizing plates 8 and 9, thereby causing white spots on the display screen. Recognized drawbacks can be effectively avoided.

  According to the above configuration, the rubbing trace is provided in the lower layer of the + C plate, and the extending direction of the rubbing trace is set to the absorption axis direction or the transmission axis direction of the linearly polarizing plate, thereby causing white dots on the display screen. Recognized drawbacks can be effectively avoided.

[Second Embodiment]
In this embodiment, instead of rubbing traces on the lower layer of the + C plate, a stretched film made of, for example, polycarbonate having a large in-plane retardation is applied to the substrate provided on the lower layer of the + C plate. The direction is set to the absorption axis direction or the transmission axis direction of the linear polarizing plate. This embodiment has the same configuration as that of the first embodiment except that the configuration of this lower layer is different.

  As in this embodiment, instead of rubbing traces, the stretching axis direction of a member such as a lower layer base material may be set to the absorption axis direction or the transmission axis direction of the linear polarizing plate, as in the first embodiment. An effect can be obtained.

[Second Embodiment]
3 and 4 are cross-sectional views showing a liquid crystal display device and a transfer film according to the second embodiment of the present invention in comparison with FIG. 1 and FIG. In the liquid crystal display device 21, the + A plate 7B is omitted, and the optical compensation layer 7 is produced only by the + C plate 7A. As a result, the transfer film 31 includes a transfer layer only by the + C plate 7A. This embodiment has the same configuration as that of the first embodiment except that the configuration relating to the optical compensation layer 7 and the transfer layer is different.

  According to this embodiment, even when optical compensation is performed using only the + C plate 7A, it is possible to effectively avoid the defect recognized by the white point on the display screen as in the first embodiment.

[Third Embodiment]
In this embodiment, the optical film 6 shown in FIG. 1 is produced using a transfer film made only of the + C plate 7A shown in FIG. More specifically, in this embodiment, after the + A plate 7B is arranged on the linearly polarizing plates 9 and 8 by the transfer method, the + C plate 7A is further arranged by the transfer method. Alternatively, the + C plate 7A may be disposed by a transfer method after the transparent film on which the + A plate 7B is disposed is disposed on the optical function layer 8. Alternatively, a + C plate 7A is placed on a transparent film on which the + A plate 7B is placed by a transfer method to produce a laminate of the + A plate 7B and the + C plate 7A. You may make it stick together.

  According to this embodiment, even when the transfer film of only the + C plate is used and optical compensation is performed by the laminate with the + A plate 7B, the same effect as that of the first embodiment can be obtained.

Other Embodiment
As mentioned above, although the specific structure suitable for implementation of this invention was explained in full detail, this invention can change the structure of the above-mentioned embodiment variously in the range which does not deviate from the meaning of this invention.

  That is, in the above-described embodiment, the case where the optical compensation is performed using the + C plate has been described. However, the present invention is not limited to this, and the present invention can be widely applied to the case where the optical compensation is performed using the −C plate.

  Further, in the above-described embodiment, the case where the optical compensation layer is manufactured using the laminate of the + C plate and the + A plate, and the case where the optical compensation layer is manufactured using only the + C plate have been described. The present invention can also be widely applied to the case where an optical compensation layer is manufactured using a laminate other than the above.

  Further, in the above-described embodiment, the case where an optical film is produced by a transfer method has been described. However, the present invention is not limited to this, and the present invention can be widely applied to the case where an optical film is produced by directly laminating a C plate or the like. Can do.

  In the above-described embodiment, the case where the optical compensation is performed using the C plate has been described. However, the present invention is not limited to this, and can be widely applied to various optical films using the C plate.

DESCRIPTION OF SYMBOLS 1, 21 Liquid crystal display device 2 Backlight 3 Liquid crystal display panel 4 Liquid crystal cell 5 Linear polarizing plate 5A Base material 5B Polarizer 5C Protective film 6 Optical film 7 Optical compensation layer 7A + C plate 7B + A plate 11, 31 Transfer film 12 Support body

Claims (3)

In an optical film comprising at least a C plate (nx = ny <nz or nx = ny> nz),
The C plate is formed of a liquid crystal compound,
An optical film in which a rubbing trace extending in one direction is provided on a lower layer of the C plate.
However, nx and ny (nx ≧ ny) are refractive indexes in the in-plane direction, and nz is a refractive index in the thickness direction. In the optical film disposed on the backlight side or the emission surface side of the liquid crystal cell,
A linear polarizing plate;
An optical compensation layer having at least a C plate (nx = ny <nz or nx = ny> nz),
The C plate is formed of a liquid crystal compound;
The optical film set so that the extending | stretching axis direction of the lower layer of the said C plate, or the extending direction of a rubbing trace may become in parallel with the absorption axis or transmission axis of the said linearly-polarizing plate.
However, nx and ny (nx ≧ ny) are refractive indexes in the in-plane direction, and nz is a refractive index in the thickness direction. In a liquid crystal display device in which a liquid crystal cell is sandwiched between linearly polarizing plates on a backlight side and an emission surface side that are arranged so that the absorption axis directions are orthogonal,
At least a C plate (nx = ny <nz or nx = ny> nz) is disposed between the linear polarizing plate on the emission surface side or the backlight side and the liquid crystal cell,
The C plate is formed of a liquid crystal compound,
A liquid crystal display device, wherein an extending axis direction of a lower layer of the C plate or an extending direction of rubbing traces is set to be parallel to an absorption axis or a transmission axis of the linearly polarizing plate on the emission surface side.
However, nx and ny (nx ≧ ny) are refractive indexes in the in-plane direction, and nz is a refractive index in the thickness direction.

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