JP5632625B2 - VA liquid crystal display device - Google Patents

Description

  The present invention relates to a VA (Vertically Aligned) liquid crystal display device with improved front contrast.

In recent years, liquid crystal display devices have become increasingly high contrast (CR). In particular, the VA liquid crystal display device has an advantage that the CR in the normal direction (hereinafter referred to as “front CR”) is higher than other modes, and various research and developments have been conducted to further improve the advantage. It has been broken. As a result, in the past six years, the front CR of the VA liquid crystal display device has increased from about 400 to about 8000, about 20 times higher.
The front CR is an important characteristic that is an index of image sharpness, and a VA type LCD characterized by its high characteristic has become the mainstream of LCD panels today.

For example, there is a color filter on array (COA) structure as one means for increasing the transmittance (for example, Patent Documents 1, 2, and 3). According to the COA structure, since the aperture ratio can be increased, the transmittance during white display can be increased. At present, there is a high interest in environmental problems, and adopting a COA structure to improve the transmittance contributes to the reduction of power consumption and is preferable from the viewpoint of the environment.
By the way, the front CR is determined by two transmittances (white luminance and black luminance) at the time of white display and black display, and therefore cannot be achieved only by increasing the transmittance. Even if the transmittance at the time of white display can be increased, the transmittance at the time of black display also increases, so that a high CR cannot be achieved. In order to increase the front CR by adopting a structure capable of improving the transmittance during white display, it is important to suppress an increase in black transmittance due to the adoption of the structure.

  On the other hand, for a liquid crystal display device, it is important that not only the front CR is high, but also the CR in the oblique direction (hereinafter sometimes referred to as “viewing angle CR”) is high. As for the VA liquid crystal display device, various proposals have been made to adopt a retardation film as a technique for reducing light leakage that occurs in an oblique direction during black display (for example, Patent Document 4). In general, phase compensation films are arranged on the front and rear sides of the liquid crystal cell as the center, and the optical compensation is achieved by sharing the retardation required for optical compensation between the two retardation films. ing. Two methods are usually used for the combination of optical compensation. One method is a method in which the retardation film is equally allocated to the retardation films respectively arranged on the front side and the rear side, and there is an advantage that a single film can be used. The other method is a method in which a large phase difference is shared by the phase difference film disposed on one side, and is advantageous in terms of cost because optical compensation can be performed in combination with an inexpensive film. In the latter method, it has been practically common to share a large retardation with the retardation film disposed on the rear side. One reason is manufacturing cost. Regarding this reason, in Patent Document 5, when the cellulose acylate film of the present invention is used only for the protective film (between the liquid crystal cell and the polarizing film) of one polarizing plate, Either the observation side) or the lower polarizing plate (backlight side) may be used, and there is no functional problem, but if used as an upper polarizing plate, there is a need to provide a functional film on the observation side (upper side). Since there is a possibility that the production yield is lowered, it is considered that it is highly used as a lower polarizing plate and is considered to be a more preferred embodiment.

  Further, there is a demand for thinning the liquid crystal display device. In a thin liquid crystal display device, the internal temperature often rises excessively due to the heat of the backlight when used for a long time. In recent years, liquid crystal display devices have been used in various usage environments not only indoors but also outdoors for digital signage applications. Therefore, the liquid crystal display device is required to have a small variation in display characteristics due to changes in environmental humidity and temperature.

  Cellulose acylate is mainly used as the material constituting the retardation film. Polycarbonate and cyclic olefin resins can be used to reduce performance changes due to environmental humidity and temperature, but these materials are expensive. Therefore, a retardation film made of a polypropylene resin has been proposed as a material that is less expensive than polycarbonate or cyclic olefin resin and has a smaller performance change due to environmental humidity and temperature than cellulose acylate. By the way, since a polypropylene resin is a crystalline material, there is a problem that light scattering is large, a retardation film made of a polypropylene resin has a large haze, and the front CR of the liquid crystal display device is lowered.

JP 2005-99499 A JP 2005-258004 A JP 2005-3733 A JP 2006-184640 A [0265] column of JP-A-2006-241293

When this inventor tried to improve front CR by adopting a COA structure in a VA liquid crystal display device made of a polypropylene resin or containing a polypropylene resin, the improvement of the front CR cannot be achieved. all right. As a result of further investigation, the cause is partially due to the existence of a retardation film that contributes to the reduction of light leakage that occurs in the oblique direction during black display of the VA liquid crystal display device, that is, the improvement of the viewing angle CR. I understood it. In particular, when the COA structure is adopted in the VA type liquid crystal display device in which the retardation film having a large retardation is arranged on the rear side, which is the above-described general configuration, the front CR is not improved, but rather is lowered. I understood it. In the VA liquid crystal display device having a retardation film, it can be said that the problem of adopting the COA structure has not been known so far as far as the present inventors know.
That is, the present invention solves the problem of adopting the COA structure in a VA liquid crystal display device having a retardation film made of polypropylene resin or containing a polypropylene resin, which has not been conventionally known. Is an issue. Specifically, an object of the present invention is to provide a COA-structured VA liquid crystal display device using a retardation film made of a polypropylene resin or containing a polypropylene resin with improved front contrast. .
In addition, using a retardation film made of cellulose acylate, a front-side CR is superior to a conventional liquid crystal display device having a general configuration, and a retardation film made of a polypropylene resin or containing a polypropylene resin is used. It is an object of the present invention to provide a VA liquid crystal display device.
Another object of the present invention is to provide a liquid crystal display device that has good display characteristics and viewing angle characteristics, and that has reduced variations in display characteristics due to temperature and humidity.

  As a result of the study by the present inventor, when the COA structure is adopted in the VA liquid crystal display device in which the retardation film having a large retardation is arranged on the rear side, the front CR is not improved, and the COA structure is adopted. It was found that the front CR would rather be lower than what was not. As a result of various studies in order to solve this problem, the present inventor has found that the total Rth of the retardation films disposed on the rear side is within a predetermined range, the VA type liquid crystal display device adopting the COA structure. The knowledge that the front CR can be remarkably improved was obtained, and the present invention was completed.

  According to the present invention, it is possible to provide a VA liquid crystal display device using a retardation film having a high front contrast, made of a polypropylene resin, or containing a polypropylene resin.

It is a cross-sectional schematic diagram of an example of the VA-type liquid crystal display device of the present invention. It is a cross-sectional schematic diagram of an example of a VA type liquid crystal display device having a non-COA structure used for reference.

Hereinafter, the present invention will be described in detail. In the present specification, a numerical range represented by using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.
First, terms used in this specification will be described.
(Retardation, Re and Rth)
In the present specification, Re (λ) and Rth (λ) represent in-plane retardation (nm) and retardation in the thickness direction (nm) at wavelength λ, respectively. Re (λ) is measured by making light having a wavelength of λ nm incident in the normal direction of the film in KOBRA 21ADH or WR (manufactured by Oji Scientific Instruments). The standard wavelength of KOBRA is 550 nm.
When a sample such as a film to be measured is represented by a uniaxial or biaxial refractive index ellipsoid, Rth (λ) is calculated by the following method.
Rth (λ) is Re (λ), with the in-plane slow axis (determined by KOBRA 21ADH or WR) as the tilt axis (rotation axis) (if there is no slow axis, any in-plane film The light is incident at a wavelength of λ nm from the inclined direction in steps of 10 degrees from the normal direction to 50 degrees on one side with respect to the film normal direction of the rotation axis of KOBRA 21ADH or WR is calculated based on the measured retardation value, the assumed value of the average refractive index, and the input film thickness value.
In the above case, in the case of a film having a direction in which the retardation value is zero at a certain tilt angle with the in-plane slow axis from the normal direction as the rotation axis, retardation at a tilt angle larger than the tilt angle. The value is calculated by KOBRA 21ADH or WR after changing its sign to negative.
In addition, the retardation value is measured from the two inclined directions, with the slow axis as the tilt axis (rotation axis) (in the absence of the slow axis, the arbitrary direction in the film plane is the rotation axis), Rth can also be calculated from the following formula (X) and formula (XI) based on the value, the assumed value of the average refractive index, and the input film thickness value.

注記：
上記のＲｅ（θ）は法線方向から角度θ傾斜した方向におけるレターデーション値をあらわす。また、式中、ｎｘは面内における遅相軸方向の屈折率を表し、ｎｙは面内においてｎｘに直交する方向の屈折率を表し、ｎｚはｎｘ及びｎｙに直交する方向の屈折率を表す。ｄは膜厚を表す。

Note:
The above Re (θ) represents a retardation value in a direction inclined by an angle θ from the normal direction. In the formula, nx represents the refractive index in the slow axis direction in the plane, ny represents the refractive index in the direction orthogonal to nx in the plane, and nz represents the refractive index in the direction orthogonal to nx and ny. . d represents a film thickness.

In the case where the film to be measured cannot be expressed by a uniaxial or biaxial refractive index ellipsoid, that is, a film having no so-called optical axis, Rth (λ) is calculated by the following method.
Rth (λ) is from −50 degrees to +50 degrees with respect to the normal direction of the film, with Re (λ) being the in-plane slow axis (determined by KOBRA 21ADH or WR) and the tilt axis (rotating axis). In each of the 10 degree steps, light of wavelength λ nm is incident from the inclined direction and measured at 11 points. Based on the measured retardation value, the assumed average refractive index, and the input film thickness value, KOBRA 21ADH or WR is calculated.
In the above measurement, the assumed value of the average refractive index may be a value in a polymer handbook (John Wiley & Sons, Inc.) or a catalog of various optical films. Those whose average refractive index is not known can be measured with an Abbe refractometer. Examples of the average refractive index values of main optical films are given below:
Cellulose acylate (1.48), cycloolefin polymer (1.52), polycarbonate (1.59), polymethyl methacrylate (1.49), and polystyrene (1.59).
The KOBRA 21ADH or WR calculates nx, ny, and nz by inputting the assumed value of the average refractive index and the film thickness. Nz = (nx−nz) / (nx−ny) is further calculated from the calculated nx, ny, and nz.

In this specification, the values of Re (λ) and Rth (λ) such as Re (450), Re (550), Re (630), Rth (450), Rth (550), and Rth (630) are , Re and Rth are measured for three or more different wavelengths (for example, λ = 479.2, 546.3, 632.8, and 745.3 nm) by a measuring device, and calculated from these values. Specifically, these measured values are approximated by Cauchy's equation (up to the third term, Re = A + B / λ ² + C / λ ⁴ ), and values A, B, and C are obtained, respectively. From the above, Re and Rth at the wavelength λ can be plotted again, and Re (λ) and Rth (λ) at each wavelength λ can be obtained therefrom.

In the present specification, the “slow axis” of a retardation film or the like means a direction in which the refractive index is maximized. The “visible light region” means 380 nm to 780 nm. Moreover, in this specification, when there is no special mention about a measurement wavelength, a measurement wavelength is 550 nm.
Further, in this specification, numerical values, numerical ranges, and qualitative expressions (for example, “equivalent”, “equal”, etc.) indicating optical characteristics of each member such as a retardation region, a retardation film, and a liquid crystal layer are used. ) Is interpreted to indicate numerical values, numerical ranges and properties including generally allowable errors for liquid crystal display devices and members used therefor.

In this specification, the retardation film means a self-supporting film disposed between the liquid crystal cell and the polarizer. (It does not matter whether the retardation is large or small.) The retardation film, the retardation layer, and the retardation film are synonymous. The retardation region is a general term for a retardation film of one layer or two or more layers disposed between a liquid crystal cell and a polarizer.
In this specification, “front side” means the display surface side, and “rear side” means the backlight side. In this specification, “front” means a normal direction with respect to the display surface, and “front contrast (CR)” is calculated from white luminance and black luminance measured in the normal direction of the display surface. The viewing angle contrast (CR) is an oblique direction inclined from the normal direction of the display surface (for example, a direction defined by an azimuth angle direction of 45 degrees and a polar angle direction of 60 degrees with respect to the display surface). ) Means the contrast calculated from the white luminance and the black luminance measured.

The present invention relates to a VA liquid crystal display device having a COA structure. FIG. 1 is a schematic cross-sectional view of an example of the liquid crystal display device of the present invention, and FIG. 2 is a schematic cross-sectional view of a VA liquid crystal display device having a non-COA structure for reference.
1 includes a front side polarizer 26, a rear side polarizer 24, a liquid crystal layer 10 disposed between the front side polarizer 26 and the rear side polarizer 24, and a liquid crystal layer. 10 and the color filter layer 12 disposed between the rear polarizer 24, the rear phase difference region 20 disposed between the rear polarizer 24 and the color filter layer 12, and the front polarizer 26. A front-side retardation region 22 is provided between the liquid crystal layer 10 and the liquid crystal layer 10. In the liquid crystal cell LC of the VA liquid crystal display device shown in FIG. 1, the liquid crystal layer 10 is sandwiched between a front side substrate 18 and a rear side substrate 16, and the array member 14 and the color filter layer 12 are the same substrate, rear side. This is a liquid crystal cell having a COA structure disposed on the substrate 16. The liquid crystal cell LC may have a black matrix (not shown), and the position may be on the rear substrate 16 or the front substrate 18.

FIG. 2 is a schematic cross-sectional view of an example of a VA liquid crystal display device having a liquid crystal cell LC ′ having a non-COA structure as a reference example. In FIG. 2, the liquid crystal cell LC ′ includes a liquid crystal layer 50, a front side substrate 58 and a rear side substrate 56 that sandwich the liquid crystal layer 50, and a color filter layer 52 that is different from the array member 54. 58, a liquid crystal cell having a non-COA structure, which is disposed above.

In the VA liquid crystal display device of FIGS. 1 and 2, the cause of increasing the transmittance in the front direction during black display, that is, worsening the light leakage will be described.
In general, in a VA liquid crystal display device, the liquid crystal layer (10 or 50) is in a vertical alignment state during black display, and thus linearly polarized light that passes through the rear polarizer (24 or 64) and proceeds in the normal direction. Thereafter, even if it passes through the liquid crystal layer (10 or 50), its polarization state does not change, and in principle, it is absorbed by the absorption axis of the front polarizer (26 or 66). That is, in principle, it can be said that there is no light leakage in the normal direction during black display. However, the front transmittance at the time of black display of the VA liquid crystal display device is not zero. One reason for this is that liquid crystal molecules in the liquid crystal layer (10 or 50) are fluctuating, and light incident on the liquid crystal layer is known to be scattered to some extent by the fluctuations. The more the light that has entered the liquid crystal layer (10 or 50) contains only the linearly polarized light component that is absorbed by the absorption axis of the front polarizer (26 or 66), the greater the effect is. There is a tendency for leaks to increase. That is, as the phase difference of the phase difference region (20 or 60) arranged on the rear side is larger and converted to elliptically polarized light having a higher elliptical polarization rate, light leakage on the front due to this fluctuation can be reduced.

  However, as described above, as a result of the study by the present inventor, in addition to the fluctuation of the liquid crystal molecules in the liquid crystal layer, the position disposed between the rear-side polarizer (24 or 64) and the liquid crystal layer (10 or 50). It has been found that the retardation of the retardation film (20 or 60) is also due to this. When directional light from the backlight (28 or 68) passes through the rear polarizer (24 or 64) and enters the retardation film (20 or 60) from an oblique direction, a straight line is generated by the phase difference. Polarized light is converted to elliptically polarized light. This elliptically polarized light is diffracted and scattered by the array member (14 or 54) and the color filter layer (12 or 52) in the liquid crystal cell, and at least a part of the light becomes light traveling in the front direction. Since the elliptically polarized light includes a linearly polarized light component that cannot be blocked by the absorption axis of the front polarizer (26 or 66), light leaks in the front direction even during black display, causing a reduction in front CR. The optical phenomenon caused by passing through the array member (TFT array, etc.) or the color filter layer is, for example, that the surface of the array member or the color filter layer is not completely smooth and has some unevenness, Is due to the inclusion of scattering factors and the like. The influence of the optical phenomenon generated by passing through the array member and the color filter layer on the light leakage in the front direction is larger than the influence of the liquid crystal molecules in the liquid crystal layer described above.

Furthermore, as a result of intensive studies by the inventor, the optical phenomenon (diffraction and scattering, etc.) received when the light that has been elliptically polarized by passing through the retardation film passes through a predetermined member in the liquid crystal cell is It has been found that the aspect affecting the light leakage in the front direction differs depending on whether the light passes through the member before entering the liquid crystal layer or passes through the member after passing through the liquid crystal layer. 1 and 2, light passes through the array member (14 or 54) before entering the liquid crystal layer (10 or 50). On the other hand, in the COA structure shown in FIG. 1, light passes through the color filter layer (12) before passing through the liquid crystal layer (10). However, in the non-COA structure shown in FIG. ) And then the color filter layer (52).
In the array member and the color filter layer, if elliptically polarized light having a smaller elliptical polarization rate is incident, the influence of the optical phenomenon caused by passing through the member on the light leakage in the front direction is reduced.
Therefore, in order to reduce light leakage due to an optical phenomenon in the array member, elliptically polarized light having a smaller elliptical polarization rate may be incident. In the case of the COA structure, light leakage due to the optical phenomenon in the color filter layer is also reduced at the same time. it can.
In a member through which light passes before entering the liquid crystal layer, the elliptical polarization rate of the incident light is determined by the phase difference of the rear-side retardation region (20 or 60) that passes therethrough. On the other hand, the member that passes after entering the liquid crystal layer is determined by the phase difference of the liquid crystal layer in addition to the phase difference of the rear side phase difference region (20 or 60). Here, in the case of a liquid crystal display device for VA, in consideration of a switch for white display and black display, Δnd (550) of the liquid crystal layer (d is the thickness (nm) of the liquid crystal layer, and Δn (λ) is the liquid crystal layer. The refractive index anisotropy at the wavelength λ, and Δnd (λ) is the product of Δn (λ) and d) is set to about 280 to 380 nm. In the case of a non-COA structure, even if the phase difference in the rear side retardation region is set so that light leakage of the array member is reduced, the ellipticity increases conversely when passing through the liquid crystal. Light leakage due to optical phenomena caused by passing increases. The following table summarizes the phase difference in the rear side phase difference region (20 or 60), the tendency of the influence on the light leakage in the front direction by passing through each member, and the strength of the influence. .

  As shown in the above table, in the VA liquid crystal display device having a liquid crystal cell with a non-COA structure, when the retardation of the rear side retardation film (60) is lowered, the light in the front direction generated by the optical phenomenon by the array member (54) Leakage acts in a direction to reduce, while light leakage in the front direction caused by the optical phenomenon by the color filter layer (52) acts in an increasing direction; when the retardation of the rear side retardation film (60) is increased The light leakage in the front direction caused by the optical phenomenon by the array member (54) acts in an increasing direction, while the light leakage in the front direction caused by the optical phenomenon by the color filter layer (52) acts in a reducing direction; That is, there is a relationship in which both actions are canceled out. Therefore, in the non-COA structure, the level of the retardation of the rear side retardation film has little effect on the front CR, and in the VA liquid crystal display device of the non-COA structure, from the viewpoint of the front CR, the rear side retardation film There was no need to study the phase difference. That is, even if a high retardation is shared by the rear side retardation film, the problem of lowering the front CR does not become obvious, and as described above, considering the production cost, impact resistance and environmental resistance, the rear side A configuration in which a high retardation is shared by the retardation film has been put into practical use.

  Further, the retardation of the retardation film greatly affects the light leakage in the front direction due to the scattering factor in the retardation film. Therefore, there is an internal haze as a value indicating the amount of scattering of the retardation film. A retardation film made of a polypropylene-based resin tends to have high internal haze, but the contribution of the internal haze to the front CR varies depending on retardation values arranged on the rear side and the front side. For example, in order to increase the front CR of a liquid crystal cell having a COA structure, it is better to reduce the retardation of the rear retardation film. At this time, a retardation film having a high internal haze is used on the rear side. However, the decrease in front CR due to scattering in the rear film is reduced.

On the other hand, as shown in the above table, in the VA liquid crystal display device of FIG. 1 having a liquid crystal cell with a COA structure, when the phase difference in the rear phase difference region (20) is lowered, it is caused by an optical phenomenon caused by the array member (14). The light leakage in the front direction acts in a direction to reduce the light leakage, and also acts in a direction to reduce the light leakage in the front direction caused by the optical phenomenon by the color filter layer (12); conversely, the rear side retardation region (20 ) Increases, the light leakage in the front direction caused by the optical phenomenon by the array member (14) acts in an increasing direction, and the light leakage in the front direction caused by the optical phenomenon by the color filter layer (12) also occurs. Acts in an increasing direction. Therefore, even if the COA structure is adopted and the aperture ratio is enlarged, in the latter configuration, light leakage on the front side during black display increases due to an optical phenomenon caused by passing through the array member and the color filter layer. The front CR cannot be improved, but rather the front CR is lowered. This problem is a problem that has not been known so far as the present inventor knows.
It should be noted that the influence of the retardation in the rear side retardation region on the front CR is almost negligible in a low front CR liquid crystal display device. However, this influence cannot be ignored in order to further improve the front CR of a liquid crystal display device with a high front CR (for example, the front CR is 1500 or more) that has been provided in recent years. Further, in such a liquid crystal display device having a high front CR, the front CR difference due to the internal haze difference of the retardation film appears remarkably. The present invention is particularly useful for further improving the front CR when a retardation film made of a polypropylene resin or containing a polypropylene resin is used in a liquid crystal display device having a front CR of 1500 or more.

  As described above, the front CR improvement effect of the present invention is not the effect of increasing the aperture ratio by adopting a COA-structured liquid crystal cell, but making the rear side retardation region of the COA-structured liquid crystal cell have a low phase difference. This is because the scattering of polarized light entering the liquid crystal cell is reduced, and as a result, the front black luminance is lowered. The effect of the present invention can also be explained by the locus of the polarization on the Poincare sphere, assuming that the polarization state is substantially maintained after the polarized light incident on the liquid crystal cell is scattered by the internal members. On the other hand, conventionally, when polarized light is scattered, it was not thought that the polarization state is maintained. Therefore, the effect of the present invention that solves the reduction of the front CR due to scattering in the liquid crystal cell is effective on the Poincare sphere. What can be explained by the trajectory of polarization was unexpected.

By the way, not only the front CR but also the front color at the time of black display (front black color) is important as display characteristics of the liquid crystal display device. As a result of studies by the present inventor, the retardation (Re and Rth) of the rear side retardation region of the liquid crystal cell having the COA structure is so-called reverse wavelength dispersibility that the wavelength increases in the visible light region as the wavelength increases. When it is, it turned out that coloring to the specific color of a front black taste can be reduced. The reason for this can be considered in the same manner as the light leakage in the front direction of the liquid crystal display device described above. In other words, the stronger the inverse wavelength dispersion of the retardation in the rear side retardation region, the less the wavelength dependence of the elliptical polarization of the light incident obliquely from the light source (backlight) of the liquid crystal display device. The difference in the amount of leakage can be reduced, and coloring of a specific color with front blackness can be reduced.
Furthermore, as a result of studies by the present inventors, it has been found that a liquid crystal cell having a COA structure can reduce the front tint during black display compared to a liquid crystal cell having a non-COA structure. This is because in a liquid crystal cell having a non-COA structure, it is necessary to consider scattering on a member on the front side substrate, which is greatly affected by retardation of the liquid crystal layer. Light incident on the non-COA liquid crystal cell passes through the liquid crystal layer before being scattered by the member on the front substrate. Since the retardation of the liquid crystal layer, that is, Δnd (λ) exhibits forward dispersion (that the wavelength becomes smaller as the wavelength becomes longer), the elliptical polarization of light in the short wavelength region increases when passing through the liquid crystal layer. As a result, light in the blue region is more likely to leak. Therefore, a COA-structured liquid crystal cell that is less affected by scattering on the member on the front side substrate can reduce the front tint during black display compared to a non-COA-structured liquid crystal cell.
By setting the rear side retardation region of the liquid crystal cell having the COA structure to have a low phase difference and reverse wavelength dispersion, the front CR can be improved and the front tint during black display can be reduced.

  More specifically, when the rear side retardation region of the liquid crystal cell having a COA structure is made to have a low phase difference and reverse wavelength dispersion, similarly, the rear side retardation region has a low phase difference and a forward dispersion. Therefore, it is possible to reduce the front tint during black display.

In addition, reducing the phase difference region on the rear side of the liquid crystal cell having a COA structure contributes not only to the front-side CR but also to the contrast in the oblique direction (hereinafter sometimes referred to as “viewing angle CR”). To do. For example, even if a liquid crystal cell having a COA structure is employed, neither the front CR nor the viewing angle CR can be improved if the rear phase difference region has a high phase difference as in the prior art. That is, this viewing angle CR improvement effect of the present invention is also an effect brought about by reducing the light leakage that fluctuates due to the polarized light incident on the liquid crystal cell. By adopting a liquid crystal cell with a COA structure, the aperture ratio is increased. This effect cannot be obtained only by
Further, this is distinguished from the effect of improving the viewing angle CR by the front side retardation region that compensates for the polarization axes of the pair of polarizing plates being deviated from the orthogonal arrangement by the front side retardation region described later.
As with the front CR improvement effect, the viewing angle CR improvement effect of the present invention is also assumed to be on the Poincare sphere, assuming that the polarization state that is incident on the liquid crystal cell is substantially maintained after being scattered by the internal members. This can also be explained by the locus of polarization. On the other hand, as described above, conventionally, when the polarized light is scattered, it was not considered to maintain the polarization state, so the effect of the present invention that solves the reduction of the front CR due to scattering in the liquid crystal cell, What can be explained by the trajectory of polarized light on the Poincare sphere was unexpected.

As a result of intensive studies by the present inventor, the rear side retardation region (20 in FIG. 1) through which light passes before entering the liquid crystal cell having the COA structure is represented by the following formula (I).
(I): | Rth (550) | ≦ 90 nm
Surprisingly, it has been found that the above problems can be solved by satisfying the above. As long as the phase difference of the entire retardation region that passes through before the light enters the liquid crystal cell LC having the COA structure satisfies the above-described formula (I), the light incident from the oblique direction is then converted into an array member in the liquid crystal cell. 14 and the color filter layer 12 are scattered or diffracted to become light traveling in the normal direction, and even if affected by fluctuations of liquid crystal molecules in the liquid crystal layer, light leakage in the front direction during black display As compared with a VA liquid crystal display device that employs a liquid crystal cell having a non-COA structure, the front CR can be remarkably improved. In addition, a polypropylene resin compared to a liquid crystal display device that applies a compensation method that shares a large retardation on the rear side, which is common as a conventional compensation method, and that includes a cellulose acylate phase difference film. The front CR of a liquid crystal display device comprising a retardation film comprising or comprising a polypropylene resin can be improved. The effect of the present invention is an effect that cannot be obtained only by adopting the COA structure and enlarging the aperture ratio. The COA structure is adopted, and the rear side retardation region satisfies the above formula (I). This is an effect obtained for the first time.

Other members (for example, black matrix) not shown in FIG. 1 are the same as the color filter layer and the array member described above. That is, the member through which light passes before entering the liquid crystal layer is the same as the non-COA structure array member in the above table, and the member through which light passes after entering the liquid crystal layer has the non-COA structure color filter in the above table It becomes the same as a member.
As described above, the incident light polarization state dependence of light leakage at the time of black display due to the optical phenomenon in the color filter, black matrix, and array member shows the same tendency, but the contribution of the black matrix is relatively Since it is small, the position of the black matrix in the liquid crystal display device with the COA structure may be anywhere in the liquid crystal cell, but it is preferably located between the rear-side polarizer and the liquid crystal layer in order to obtain a high front CR.

  The rear side retardation region 20 in FIG. 1 may have a single-layer structure or a laminate composed of two or more layers. In an embodiment having a single layer structure, the layer needs to satisfy the formula (I), and in an embodiment of a laminate of two or more layers, the laminate needs to satisfy the formula (I) as a whole.

The front side retardation region 22 in FIG. 1 may also have a single-layer structure or a laminate composed of two or more layers. It is preferable that the front side phase difference region 22 has a phase difference that contributes to the improvement of the viewing angle CR, since not only the effect of the present invention, that is, the improvement of the front CR, but also the viewing angle CR can be achieved. As described above, Δnd (λ) of the liquid crystal layer of the liquid crystal cell LC is generally about 280 to 380 nm. However, a preferable range of retardation of the front side retardation region 22, particularly Rth, is the rear side. The phase difference varies depending on the retardation of the retardation region 20 and the value of Δnd (λ) of the liquid crystal layer. In order to improve the oblique CR, various combinations of the front side phase difference region and the rear side phase difference region with respect to Δnd (λ) of the liquid crystal layer are described in various publications, for example, Japanese Patent Nos. 3282986 and 3666666. No. 3556159 and the like, and can be referred to. From this point of view, the front side retardation region 22 has the following formulas (III) and (IV):
(III): 30 nm ≦ Re (550) ≦ 90 nm
(IV): 150 nm ≦ Rth (550) ≦ 500 nm
It is preferable to satisfy In order to satisfy the above characteristics, the front side retardation region 22 may be composed of, for example, one or two or more biaxial polymer films, or one or two or more biaxial films. The polymer film may be included. Further, the front side retardation region 22 may include one sheet or two or more uniaxial polymer films.

  Note that Δnd (550) of the VA liquid crystal cell is generally about 280 to 380 nm, in order to make the transmittance during white display as high as possible. On the other hand, when Δnd (550) is 280 nm or less, white luminance slightly decreases with a decrease in Δnd (550), but since the cell thickness d decreases, the liquid crystal display device is excellent in high-speed response. If the first retardation region on the rear side has a low retardation, the feature of the present invention that a high front CR is obtained as a result of less light leakage in the front direction is the liquid crystal display of any Δnd (550). It is also effective in the apparatus.

In one aspect of the present invention, the rear side retardation region (20 in FIG. 1) is represented by the following formula (II):
(II): | Re (550) | ≦ 100 nm
Satisfied. Even if a retardation film having a high Re is disposed on the rear side, the effect of the present invention can be obtained as long as Rth satisfies the above formula (I). On the other hand, when a retardation film having a certain amount of Re is arranged on the rear side, it is necessary to strictly align the axis with respect to the optical axis of other members, such as the relationship with the absorption axis of the rear-side polarizer. Will. When the rear side retardation region as a whole has a low Re and satisfies the above formula (II), one or more retardation films used as the rear side retardation region are incorporated in the liquid crystal display device. At this time, it is preferable because axis alignment and the like are facilitated.

  Furthermore, another effect of the present invention is reduction of “circle unevenness”. “Circle unevenness” refers to a phenomenon in which when a liquid crystal panel is exposed to a high-temperature and high-humidity atmosphere and then brought into a black display state, an annular light leak occurs on the panel. Details are described in JP-A No. 2007-187841. One reason for this is that the liquid crystal cell substrate on the backlight side (ie, the rear substrate 16 in FIG. 1) is warped when exposed to a high temperature and high humidity atmosphere. In the COA structure, since the color filter layer is arranged in addition to the array member on the rear substrate, the warp hardly occurs even when heated, and as a result, the circle unevenness can be reduced.

  As described above, by adopting the COA structure, it is possible to reduce the circle unevenness to some extent. As a result of investigations by the present inventors, it has been found that circle unevenness is also affected by the optical characteristics of the rear side retardation region, and can be reduced as Rth of the rear side retardation region is reduced. From the viewpoint of circle unevenness, the thickness of the retardation film arranged in the rear side retardation region (20 in FIG. 1) is preferably thinner, specifically, the thickness is preferably about 2 to 100 μm, About 2 to 60 μm is more preferable, and about 2 to 40 μm is more preferable.

In FIG. 1 again, “COA” of the COA structure of the liquid crystal cell LC in FIG. 1 is an abbreviation for color filter on array, and a structure in which a color filter is formed on an active matrix substrate is called a COA structure. . Initially, the COA structure was only for forming a color film on a normal TFT substrate, but recently, in order to improve display characteristics, a pixel electrode is formed on the upper side of the color film, and a small hole called a contact hole is formed. A structure in which the pixel electrode and the TFT are connected to each other is generally used. Any structure may be used in the present invention. In the COA structure, the thickness of the color filter layer is thicker than that of a conventional color film layer (about 1 to 2 μm), and generally about 2 to 4 μm. This is to suppress parasitic capacitance generated between the end of the pixel electrode and the wiring. The color filter layer of the liquid crystal display device of the present invention preferably has a thickness of about 2 to 4 μm, but is not limited to this range. Further, in manufacturing a liquid crystal cell having a COA structure, it is necessary to pattern the pixel electrode on the color filter layer, and resistance to an etching solution or a stripping solution is required. For this purpose, a color filter material (colored photosensitive composition) whose film thickness is adjusted to be thick is used, but a two-layer structure of color filter layer + overcoat layer formed of a normal color filter material may be used. Any configuration may be used in the present invention.
The COA structure is also described in JP-A-2007-240544, JP-A-2004-163979, etc. in addition to the above-mentioned Patent Documents 1 and 2, and any configuration is adopted in the present invention. Can do.

  Further, the color filter of the liquid crystal display device of the present invention has a plurality of different colors (for example, three primary colors of red, green, and blue light, transparent, Yellow, cyan, etc.). There are various preparation methods, for example, using a coloring material (organic pigment, dye, carbon black, etc.) to prepare a colored photosensitive composition (which may be colorless) called a color resist. In general, a layer is formed by coating on a substrate, and a pattern is formed by photolithography. There are also various methods for applying the colored photosensitive composition on the substrate. For example, the spin coater method is employed in the initial stage, and the slit & spin type coater method is employed from the viewpoint of liquid saving. The slit coater method is generally adopted. Other methods include roll coating, bar coating, and die coating. In recent years, after forming a pattern called a separation wall by photolithography, a pixel color is also formed by an inkjet method. In addition, methods using a combination of a colored non-photosensitive composition and a photosensitive positive resist, a printing method, an electrodeposition method, and a film transfer method are known. The color filter used in the present invention may be produced by any method.

  There are no particular restrictions on the material for forming the color filter. As the coloring material, any of dyes, organic pigments, inorganic pigments and the like can be used. Dyes have been studied because of the demand for higher contrast, but in recent years, organic pigment dispersion technology has advanced, and breakdown pigments that have been finely crushed by the salt milling method, finer pigments by the build-up method, etc. Used for contrast. Any coloring material may be used in the present invention.

  In FIG. 1, all or part of the rear-side retardation region 20 and the front-side retardation region 22 may function as protective films for the rear-side polarizer 24 and the front-side polarizer 26, respectively. Although omitted in FIG. 1, the rear polarizer 24 has a functional film such as a protective film, an antifouling film, an anti-reflection film, an anti-glare film, and an anti-static film on the surface on the backlight 28 side. Similarly, the front-side polarizer has a functional film such as a protective film, an antifouling film, an anti-reflection film, an anti-glare film, or an anti-static film on its display surface side surface. You may do it.

By the way, as described above, in the case of a method of optical compensation by sharing a large retardation on one side, a film having a large retardation is generally arranged on the rear side, but as in the present invention. It is considered that the yield rate as a polarizing plate is improved by arranging on the front side. The reason will be explained.
Since a film with a large retardation requires a process of stretching at a high magnification, it is difficult to widen compared to an inexpensive film that can be produced without adding many additives to the film and a film with a small retardation. . In a normal liquid crystal display device, a horizontally long liquid crystal cell is used, and the absorption axis of the front-side polarizer is arranged in the horizontal direction (left-right direction), and the absorption axis of the rear-side polarizer is arranged in the vertical direction (up-down direction). It is common. Furthermore, in industrial production, a polarizer and a retardation film are generally bonded by roll-to-roll. Considering that the polarizing plate produced by this manufacturing method is bonded to the liquid crystal cell, it is possible to use the width direction of the polarizing plate with high efficiency by arranging a film having a large retardation on the front side, that is, The yield increases. When a retardation film having a small retardation is arranged on the rear side as in the present invention, such a film can be easily produced as a wide film, and the yield is further increased by combining with a wide polarizer. it can. As a result, the amount of the polarizing plate to be discarded can be reduced.

  Here, specific numbers will be described. In general, the width of the retardation film is approximately 1100 mm, 1300 mm, 1500 mm, 2000 mm, and 2500 mm, and the thickness of the film is approximately 25 μm, 40 μm, and 80 μm. The length of the roll around which the film is wound is approximately 2500 m and 4000 m. On the other hand, the screen size of the VA liquid crystal display device is 20 inches, 32 inches, 40 inches, 42 inches, 52 inches, 68 inches, etc., for television use. As an example, when 42 inches, which are currently shipped, are considered to be 42 inches (standard 4: 3), the screen width is 853 mm (42 inches wide 16: 9 is 930 mm), and the screen height is 640 mm (42 inches wide is 523 mm). In the conventional method in which a film having a large retardation is arranged on the rear side, for example, a retardation film having a width of 1300 mm or 1500 mm can take only one retardation film for a screen in the width direction. In the present invention, since a film having a large retardation is disposed on the front side, for example, even if the retardation film has a width of 1300 mm or 1500 mm, it suffices if the screen height can be taken in the width direction of the retardation film. The retardation film for two screens can be taken in the width direction, and productivity is nearly doubled. The size of TVs increases year by year. For example, 65 inches (standard) has a screen width of 991 mm and a screen height of 1321 mm. However, although only one retardation film for a screen can be taken in the width direction, as in the present invention, two retardation films for a screen can be taken in the width direction in the front side arrangement. Furthermore, since the 68-inch (wide) screen has a screen width of 1505 mm and a screen height of 846 mm, a productivity almost twice as high can be expected.

  The mode of the VA type liquid crystal display device of the present invention may be any mode, specifically, MVA (Multi-domain Vertical Alignment) type, PVA (Patterned Vertical Alignment) type, optical alignment type (Optical Alignment), and Any of PSA (Polymer-Sustained Alignment) may be used. Details of these modes are described in JP-A-2006-215326 and JP-T-2008-538819. A high front contrast can be obtained with a photo-alignment type or PSA. The effect shown in the present invention is further enhanced by applying it to a panel exhibiting high contrast.

  The effect of improving the front contrast of the present invention can be further improved by adjusting the angle profile of the light emitted from the backlight. Specifically, when a backlight having a higher light collecting property is used, the absolute value of the front contrast is increased, so that the increase in the absolute value of the front CR shown in the present invention is also increased. The light collecting index is represented by, for example, a ratio I (0 °) / I (45 °) of the outgoing light intensity I (45 °) at a polar angle of 45 degrees with respect to the outgoing light intensity I (0 °) at the front. The larger the value, the stronger the light collection. As a backlight having a high light collecting property, it is desirable to provide a prism film (prism layer) having a light collecting function between the diffusion film and the liquid crystal panel. This prism film collects the light emitted from the light exit surface of the light guide plate and diffused by the diffusion film with high efficiency on the effective display area of the liquid crystal panel. A liquid crystal display device equipped with a general direct type backlight has, for example, a color filter sandwiched between a transparent substrate and a polarizing plate at the top, a liquid crystal panel composed of a liquid crystal layer, and a backlight on the lower surface side. It has been. A brightness enhancement film (Brightness Enhancement Film: BEF), which is a registered trademark of 3M USA, is a representative example. BEF is a film in which unit prisms having a triangular cross section are periodically arranged in one direction on a film substrate, and the prism has a size (pitch) larger than the wavelength of light. The BEF collects light from “off-axis” and directs this light to the viewer “on-axis” or “recycle”. To do. Patent documents that disclose that a luminance control member having a repetitive array structure of prisms represented by BEF is adopted for a display include Japanese Patent Publication No. 1-37801, Japanese Patent Laid-Open No. Hei 6-102506, and Special Tables. Many examples are known as exemplified in Japanese Patent Laid-Open No. 10-506500.

  It is also desirable to use a lens array sheet in order to improve the light collecting property. The lens array sheet has a lens surface in which a plurality of unit lenses formed in a convex shape at a predetermined pitch are two-dimensionally arranged. A lens array sheet in which the opposite side of the lens surface is a flat surface and a light reflecting layer for reflecting light rays on the non-light-condensing surface region of the lens is formed on the flat surface is preferable. Further, a lenticular lens surface in which a plurality of convex cylindrical lenses formed at a predetermined pitch are arranged in parallel, and a side opposite to the lens surface is a flat surface, and the convex surface has the convex surface. A lens array sheet in which a light reflecting layer for reflecting light beams in the longitudinal direction is formed on the non-light-condensing surface region of the cylindrical lens is also preferable. Further, for example, a lenticular lens array sheet in which unit lenses composed of cylindrical curved surfaces are arranged in one plane in a plane, or a dome-shaped curved surface having a bottom surface shape such as a circle, a rectangle, or a hexagon. A lens array sheet in which unit lenses are two-dimensionally arranged in a plane can also be used. Regarding these lens array sheets, JP-A-10-241434, JP-A-2001-201611, JP-A-2007-256575, JP-A-2006-106197, JP-A-2006-208930, JP-A-2007-213035, And can be referred to in JP-A 2007-41172.

  The present invention is also effective in a display mode in which the color reproduction range is widened by adjusting the emission light spectrum of the backlight and the transmission spectrum of the color filter. Specifically, it is desirable to use a white backlight in which a red LED, a green LED, and a blue LED are mixed and mixed as the backlight. Moreover, it is preferable that the half value width of the emitted light peak of red LED, green LED, and blue LED is small. In the case of LED, the half-value wavelength width is as small as about 20 nm as compared with CCFL, and the peak wavelength is R (red) is 610 nm or more, G (green) is 530 nm, and B (blue) is 480 nm or less. The color purity of the light source itself can be increased.

  Further, it has been reported that the color reproducibility is further improved by suppressing the spectral transmittance of the color filter as small as possible except for the peak wavelength of the LED, and the NTSC ratio is 100%. For example, there is description in JP-A-2004-78102. The red color filter desirably has a small transmittance at the peak positions of the green LED and the blue LED, the green color filter desirably has a small transmittance at the peak position of the blue LED and the red LED, and the blue color filter has a red color. It is desirable that the transmittance at the peak position of the LED and the green LED is small. Specifically, both of these transmittances are desirably 0.1 or less, more preferably 0.03 or less, and still more preferably 0.01 or less. The relationship between the backlight and the color filter is described in, for example, Japanese Patent Application Laid-Open No. 2009-192661, and can be referred to.

  It is also preferable to use a laser light source for the backlight in order to widen the color reproduction range. The peak wavelengths of the red, green, and blue laser light sources are preferably 430 to 480 nm, 520 to 550 nm, and 620 to 660 nm, respectively. The backlight of the laser light source is described in JP2009-14892A, and can be referred to.

Hereinafter, various members used in the VA liquid crystal display device of the present invention will be described in detail.
1. Rear side retardation region and front side retardation region In the present invention, the entire retardation layer of one layer or two or more layers disposed between the rear side polarizer and the color filter layer in the VA type liquid crystal cell, This is referred to as “rear phase difference region”. The rear side phase difference region as a whole satisfies the above formula (I). It is preferable that the above formula (II) is further satisfied.

  In the present invention, the whole of one or more retardation layers disposed between the front polarizer and the liquid crystal layer in the VA type liquid crystal cell is referred to as a “front retardation region”. The front side phase difference region preferably has a phase difference that contributes to the improvement of the viewing angle CR in relation to the whole and the phase difference of the rear side phase difference region. Specifically, it is preferable that the front side retardation region satisfies the above formulas (III) and (IV).

  There are no particular restrictions on the material of each layer constituting the rear side retardation region and the front side retardation region. The retardation region satisfying the formulas (I) and (II) or the retardation region satisfying the formulas (III) and (IV) can be constituted by one or more biaxial films. It can also be configured by combining two or more uniaxial films, such as a combination of a C plate and an A plate. Of course, it can also be configured by combining one or more biaxial films and one or more uniaxial films. From the viewpoint of cost reduction, it is preferable that one of the rear-side retardation region and the front-side retardation region is constituted by one film, and more preferably both are constituted by one film.

In any of the above aspects, the chromatic dispersion of the in-plane retardation Re of the rear side and front side retardation regions exhibits so-called reverse dispersion in which the wavelength becomes larger as the wavelength becomes longer in the visible light region. Is preferred. That is, it is preferable that Re (450) <Re (550) <Re (630) is satisfied. The reason for this is that if the Re in the phase difference region is inverse wavelength dispersive, the optical wavelength is optimized at the center wavelength of about 550 nm in the visible light region, and there is a tendency to be optimized over the entire visible light region. Most preferably, Re is reversely dispersible, and it is also preferred that it be constant regardless of wavelength. The same applies to Rth in the rear-side retardation region, and it is preferable that Rth exhibits reverse wavelength dispersion or is constant regardless of the wavelength in the visible light region. More preferred is reverse wavelength dispersion. For example, for Rth, the following two expressions | Rth (450) | / | Rth (550) | ≦ 1 and 1 ≦ | Rth (630) | / | Rth (550) |
Is equivalent to satisfying
When the retardation of the rear side retardation region is other than forward wavelength dispersibility (reverse wavelength dispersibility or constant regardless of wavelength), compared to the mode of forward wavelength dispersibility, the front blackish bluish This is preferable because it can be reduced.
As described above, the effect of the reverse phase dispersion in the rear side phase difference region is the improvement effect of the front blackness (the reduction effect of the front bluish when displaying black), while the front side position. The effect of the phase difference region having the reverse wavelength dispersion is the improvement of the viewing angle characteristics such as the viewing angle CR improvement and the improvement effect of the viewing angle tint (the effect of reducing the tint in the oblique direction during black display). is there. That is, if the rear side phase difference region has a low phase difference and reverse wavelength dispersion, and the front side phase difference region satisfies the formulas (III) and (IV) and is reverse wavelength dispersion, the front CR and the viewing angle. Both CR are improved, and the front blackness and the viewing angle blackness are both good liquid crystal display devices.

In order to obtain a higher front CR, the internal haze of the retardation film constituting the rear side and front side retardation regions is preferably lower, specifically, 2.0% or less is preferable, and 0.6 % Or less is more preferable, and 0.2% or less is more preferable. Haze is an index representing the transparency of a retardation film, and is a physical property measured in accordance with JIS K-6714. The smaller the haze, the more transparent the film.
The haze of the film is caused by the influence of scattering caused by the surface state of the film and the scattering factor (crystal state, etc.) inside the film. However, in the liquid crystal display device, the film surface state is filled with an adhesive or the like. It does not contribute to lowering the front CR of the device. Therefore, in order to evaluate the scattering inside the film that contributes to the reduction of the front CR of the liquid crystal display device, an index called internal haze is used.
In this specification, the measuring method of the internal haze of a retardation film is as follows. For the measurement, a retardation film sample of 40 mm × 80 mm was prepared, and a method according to JIS K-6714 was performed using a haze meter (NDH-2000, manufactured by Nippon Denshoku Industries Co., Ltd.) in an environment of 25 ° C. and 60% RH. Measured in The internal haze is the haze value of the blank excluding the measurement film from the haze value measured by putting dimethyl phthalate, which is a liquid having substantially the same refractive index as the polypropylene resin, and the film to be measured into a quartz glass container. Excluded value.
In the case of a cellulose acylate film, the internal haze is measured using liquid paraffin having substantially the same refractive index as that of the cellulose acylate film.

  The present invention relates to a liquid crystal display device having a COA structure using a retardation film, wherein a material constituting the rear side and / or front side retardation region is made of a polypropylene resin or contains a polypropylene resin. In the present invention, the reduction in front CR, which has been a problem by using a film made of a polypropylene resin or containing a polypropylene resin, is improved, and fluctuations in optical compensation ability due to changes in temperature and humidity are compared with the conventional one. A liquid crystal display device with reduced power consumption is provided. As a result, the liquid crystal display device having the retardation film of the present invention is characterized in that it exhibits good display characteristics and viewing angle characteristics and has small variations in display characteristics due to temperature and humidity.

  The retardation film comprising the polypropylene resin of the present invention or containing the polypropylene resin preferably contains one or more of the polypropylene resins as a main component. If necessary, an additive described later may be contained. The polypropylene resin can be selected from propylene homopolymers. Moreover, it can select from the copolymer obtained by copolymerizing the monomer copolymerizable with propylene with propylene. However, it is preferable that propylene is the main monomer, and the amount of the comonomer to be copolymerized is smaller than that of propylene, for example, 20% by mass or less, preferably 10% by mass or less. The lower limit is not particularly limited (of course, it may be 0% by mass), but in order for the characteristics to be affected by the copolymerization of the comonomer, 1% by mass or more of comonomer will be necessary.

Examples of comonomers copolymerized with propylene include ethylene and α-olefins having 4 to 20 carbon atoms. Specific examples of the α-olefin include the following.
1-butene, 2-methyl-1-propene (above C ₄ ); 1-pentene, 2-methyl-1-butene, 3-methyl-1-butene (above C ₅ ); 1-hexene, 2-ethyl- 1-butene, 2,3-dimethyl-1-butene, 2-methyl-1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 3,3-dimethyl-1-butene ₆ ); 1-heptene, 2-methyl-1-hexene, 2,3-dimethyl-1-pentene, 2-ethyl-1-pentene, 2-methyl-3-ethyl-1-butene (above C ₇ ); 1-octene, 5-methyl-1-heptene, 2-ethyl-1-hexene, 3,3-dimethyl-1-hexene, 2-methyl-3-ethyl-1-pentene, 2,3,4-trimethyl- 1-pentene, 2-propyl-1-pentene, 2,3 Diethyl-1-butene (or C _8); 1-nonene (C _9); 1-decene (C _10); 1-undecene (C _11); 1-dodecene (C _12); 1-tridecene (C ₁₃₎ 1-tetradecene (C ₁₄ ); 1-pentadecene (C ₁₅ ); 1-hexadecene (C ₁₆ ); 1-heptadecene (C ₁₇ ); 1-octadecene (C ₁₈ ); 1-nonadecene (C ₁₉ ) and the like.

  Preferred among the α-olefins are α-olefins having 4 to 12 carbon atoms, specifically 1-butene, 2-methyl-1-propene; 1-pentene, 2-methyl-1- Butene, 3-methyl-1-butene; 1-hexene, 2-ethyl-1-butene, 2,3-dimethyl-1-butene, 2-methyl-1-pentene, 3-methyl-1-pentene, 4- Methyl-1-pentene, 3,3-dimethyl-1-butene; 1-heptene, 2-methyl-1-hexene, 2,3-dimethyl-1-pentene, 2-ethyl-1-pentene, 2-methyl- 3-ethyl-1-butene; 1-octene, 5-methyl-1-heptene, 2-ethyl-1-hexene, 3,3-dimethyl-1-hexene, 2-methyl-3-ethyl-1-pentene, 2,3,4-trimethyl-1-pen Ten, 2-propyl-1-pentene, 2,3-diethyl-1-butene; 1-nonene; 1-decene; 1-undecene; 1-dodecene and the like. From the viewpoint of copolymerizability, 1-butene, 1-pentene, 1-hexene and 1-octene are preferable, and 1-butene and 1-hexene are more preferable.

  The copolymer may be a random copolymer or a block copolymer. Preferred copolymers include propylene / ethylene copolymers and propylene / 1-butene copolymers. In the propylene / ethylene copolymer and the propylene / 1-butene copolymer, the ethylene unit content and the 1-butene unit content are, for example, 616 of “Polymer Analysis Handbook” (published by Kinokuniya, 1995). Infrared (IR) spectrum measurement can be performed by the method described on the page.

  From the viewpoint of improving the transparency and workability of the retardation film, it is preferable to use a random copolymer obtained by random copolymerization of an arbitrary unsaturated hydrocarbon with propylene as a main monomer. Of these, a copolymer with ethylene is preferred. When making a copolymer, it is advantageous that unsaturated hydrocarbons other than propylene have a copolymerization ratio of about 1 to 10% by mass, and a more preferable copolymerization ratio is 3 to 7% by mass. It is preferable that the amount of units of unsaturated hydrocarbons other than propylene be in the above-mentioned range since the workability and transparency of the film are improved without drastically reducing the heat resistance due to the lowering of the melting point of the resin. In addition, when setting it as the copolymer of two or more types of comonomers, and a polypropylene, it is preferable that the total content of the unit derived from all the comonomers contained in the copolymer is the said range.

  The polypropylene resin used in the present invention has a melt flow rate (MFR) measured at a temperature of 230 ° C. and a load of 21.18 N in accordance with JIS K-7210 of 0.1 to 200 g / 10 minutes. Preferably, it is 0.5 to 50 g / 10 min. By using a polypropylene resin having an MFR in this range, a uniform film can be obtained without imposing a large load on the extruder.

  The polypropylene resin can be produced by a method of homopolymerizing propylene using a known polymerization catalyst or a method of copolymerizing propylene and another copolymerizable comonomer. As a known polymerization catalyst, for example, a Ti—Mg catalyst comprising a solid catalyst component containing magnesium, titanium and halogen as essential components; a solid catalyst component containing magnesium, titanium and halogen as essential components; And a catalyst system in combination with a third component such as an electron-donating compound, if necessary, and a metallocene catalyst.

  Among these catalyst systems, a combination of an organic aluminum compound and an electron donating compound with a solid catalyst component containing magnesium, titanium and halogen as essential components is preferable. Examples of the organoaluminum compounds include triethylaluminum, triisobutylaluminum, a mixture of triethylaluminum and diethylaluminum chloride, tetraethyldialumoxane, etc .; and examples of electron donating compounds include cyclohexylethyldimethoxysilane, tert -Butylpropyldimethoxysilane, tert-butylethyldimethoxysilane, dicyclopentyldimethoxysilane and the like are included.

  On the other hand, examples of solid catalyst components containing magnesium, titanium and halogen as essential components include catalysts described in JP-A-61-218606, JP-A-61-287904, JP-A-7-216017, and the like. Examples of metallocene catalysts include the catalyst systems described in Japanese Patent No. 2587251, Japanese Patent No. 2627669, Japanese Patent No. 2668732, and the like.

  The polypropylene resin can be produced by various methods. For example, solution polymerization using an inert solvent typified by hydrocarbon compounds such as hexane, heptane, octane, decane, cyclohexane, methylcyclohexane, benzene, toluene, xylene, bulk polymerization using a liquid monomer as a solvent, gas It can be produced by a gas phase polymerization method in which the monomer is polymerized as it is. Polymerization by these methods may be carried out batchwise or continuously.

  The stereoregularity of the polypropylene resin may be any of isotactic, syndiotactic, and atactic. In the present invention, it is preferable to use a syndiotactic or isotactic polypropylene resin from the viewpoint of heat resistance and crystallinity in the resin.

  In the present invention, it is preferable to use a film containing a polypropylene-based resin as a main raw material as a retardation film. However, the film contains one kind selected from various additives as long as the effects of the present invention are not impaired. The above may be added. Examples of the additive include an antioxidant, an ultraviolet absorber, an antistatic agent, a lubricant, a nucleating agent, an antifogging agent, and an antiblocking agent. Antioxidants include, for example, phenolic antioxidants, phosphorus antioxidants, sulfur antioxidants, hindered amine light stabilizers, etc., and, for example, a phenolic antioxidant mechanism in one molecule A composite antioxidant having a unit having a phosphorus-based antioxidant mechanism can also be used. Examples of the UV absorber include UV absorbers such as 2-hydroxybenzophenone and hydroxyphenylbenzotriazole, and benzoate UV blockers. The antistatic agent may be polymer type, oligomer type or monomer type. Examples of the lubricant include higher fatty acid amides such as erucic acid amide and oleic acid amide, higher fatty acids such as stearic acid, and salts thereof. Examples of the nucleating agent include sorbitol nucleating agents, organophosphate nucleating agents, and polymer nucleating agents such as polyvinylcycloalkane. As the anti-blocking agent, fine particles having a spherical shape or a shape close thereto can be used regardless of inorganic type or organic type. A plurality of these additives may be used in combination.

  Polypropylene resin can be formed by any method (hereinafter, the film after film formation is referred to as “raw film”). This raw film is transparent and has substantially no in-plane retardation. For example, a polypropylene system having substantially no in-plane retardation by extrusion molding from molten resin, solvent casting method in which a resin dissolved in an organic solvent is cast on a flat plate, and the solvent is removed to form a film. A resin raw film can be obtained.

  An example of a method for producing a raw film by extrusion is as follows. A polypropylene resin is melt-kneaded by rotation of a screw in an extruder and extruded from a T die into a sheet. The temperature of the molten sheet to be extruded is about 180 to 300 ° C. If the temperature of the molten sheet at this time is lower than 180 ° C., the spreadability is not sufficient, the thickness of the resulting film becomes non-uniform, and there is a possibility that the film has phase difference unevenness. Further, when the temperature exceeds 300 ° C., the resin is easily deteriorated or decomposed, and bubbles may be generated in the sheet or carbides may be contained. The extruder may be a single screw extruder or a twin screw extruder. For example, in the case of a single screw extruder, L / D, which is the ratio of the screw length L to the diameter D, is about 24 to 36, the screw groove space volume in the resin supply unit, and the screw groove space volume in the resin metering unit The compression ratio, which is the ratio (the former / the latter), is about 1.5 to 4, and a screw such as a full flight type, a barrier type, and a type having a Maddock type kneading portion can be used. From the viewpoint of suppressing deterioration and decomposition of the polypropylene resin and uniformly melting and kneading, a barrier type screw having an L / D of 28 to 36 and a compression ratio of 2.5 to 3.5 is used. preferable. Moreover, in order to suppress deterioration and decomposition | disassembly of polypropylene resin as much as possible, it is preferable to make the inside of an extruder into nitrogen atmosphere or a vacuum. Furthermore, in order to remove the volatile gas generated by the deterioration or decomposition of the polypropylene resin, it is also preferable to provide an orifice of 1 mmφ to 5 mmφ at the tip of the extruder to increase the resin pressure at the tip of the extruder. Increasing the resin pressure at the tip of the extruder at the orifice means increasing the back pressure at the tip, thereby improving the stability of extrusion. The diameter of the orifice to be used is more preferably 2 mmφ or more and 4 mmφ or less.

The T-die used for extrusion preferably has no fine steps or scratches on the surface of the resin flow path, and its lip is plated or coated with a material having a low coefficient of friction with the molten polypropylene resin. Further, a sharp edge shape with a lip tip polished to 0.3 mmφ or less is preferable. Examples of the material having a small friction coefficient include tungsten carbide type and fluorine type special plating. By using such a T-die, it is possible to suppress the generation of eyes and simultaneously suppress the die line, so that a resin film having excellent appearance uniformity can be obtained. In the T-die, the manifold has a coat hanger shape and preferably satisfies the following condition (1) or (2), and more preferably satisfies the condition (3) or (4).
When the lip width of the T die is less than 1500 mm: length in the thickness direction of the T die> 180 mm (1)
When the lip width of the T die is 1500 mm or more: length of the T die in the thickness direction> 220 mm (2)
When the lip width of the T die is less than 1500 mm: Length in the height direction of the T die> 250 mm (3)
When the lip width of the T die is 1500 mm or more: Length in the height direction of the T die> 280 mm (4)
By using a T die that satisfies the above conditions, the flow of the molten polypropylene resin inside the T die can be adjusted, and the lip portion can be extruded while suppressing thickness unevenness. An original film having excellent and more uniform retardation can be obtained.

  From the viewpoint of suppressing the extrusion fluctuation of the polypropylene resin, it is preferable to attach a gear pump via an adapter between the extruder and the T die. In addition, it is preferable to attach a leaf disk filter to remove foreign substances in the polypropylene resin.

  The molten sheet extruded from the T-die is between a metal cooling roll (also referred to as a chill roll or a casting roll) and a touch roll including an elastic body that presses and rotates in the circumferential direction of the metal cooling roll. A desired film can be obtained by clamping and solidifying by cooling. In this case, the touch roll may be one in which an elastic body such as rubber is directly on the surface, or may be one in which the surface of the elastic body roll is covered with an outer cylinder made of a metal sleeve. When using a touch roll in which the surface of the elastic roll is covered with an outer cylinder made of a metal sleeve, the molten sheet of polypropylene resin is directly sandwiched between the metal cooling roll and the touch roll for cooling. On the other hand, in the case of using a touch roll whose surface is an elastic body, a biaxially stretched film of a thermoplastic resin can be interposed between the molten sheet of polypropylene resin and the touch roll for sandwiching.

  When the molten sheet of polypropylene resin is sandwiched between the cooling roll and the touch roll as described above and cooled and solidified, both the cooling roll and the touch roll have their surface temperatures lowered, and the molten sheet is rapidly cooled. I need to do it. Specifically, the surface temperature of both rolls is adjusted to a range of 0 ° C. or higher and 30 ° C. or lower. When these surface temperatures exceed 30 ° C., it takes time to cool and solidify the molten sheet, so that the crystal component in the polypropylene resin grows, and the resulting film is inferior in transparency. The surface temperature of the roll is preferably less than 30 ° C, more preferably less than 25 ° C. On the other hand, when the surface temperature of the roll is less than 0 ° C., condensation occurs on the surface of the metallic cooling roll, and water droplets adhere to the surface, which tends to deteriorate the appearance of the film.

  Since the surface state of the metal cooling roll used is transferred to the surface of the polypropylene resin film, there is a possibility that the thickness accuracy of the resulting polypropylene resin film may be lowered if the surface is uneven. . Therefore, it is preferable that the surface of the metal cooling roll is in a mirror surface state as much as possible. Specifically, the roughness of the surface of the metal cooling roll is preferably 0.3 S or less, more preferably 0.1 S to 0.2 S, expressed in the standard sequence of the maximum height. .

  As for the touch roll forming the nip portion with the metal cooling roll, the surface hardness of the elastic body is 65 to 80 as a value measured by a spring type hardness test (A type) defined in JIS K-6301. It is preferable that there is, more preferably 70-80. By using a rubber roll having such a surface hardness, it becomes easy to maintain a uniform linear pressure applied to the molten sheet, and a bank of the molten sheet (resin pool) is provided between the metal cooling roll and the touch roll. ) Can be easily formed into a film.

  The pressure (linear pressure) when sandwiching the molten sheet is determined by the pressure for pressing the touch roll against the metal cooling roll. The linear pressure is preferably 50 N / cm or more and 300 N / cm or less, and more preferably 100 N / cm or more and 250 N / cm or less. By setting the linear pressure within the above range, it becomes easy to produce a polypropylene resin film while maintaining a constant linear pressure without forming a bank.

  When a biaxially stretched film of a thermoplastic resin is sandwiched between a metallic cooling roll and a touch roll together with a molten sheet of polypropylene resin, the thermoplastic resin constituting the biaxially stretched film is strong with the polypropylene resin. Any resin may be used as long as it is not heat-sealed, and specific examples include polyester, polyamide, polyvinyl chloride, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, and polyacrylonitrile. Among these, polyesters that have little dimensional change due to humidity, heat, and the like are most preferable. In this case, the thickness of the biaxially stretched film is usually about 5 to 50 μm, preferably 10 to 30 μm.

  In this method, the distance (air gap) from the lip of the T die to the pressure between the metal cooling roll and the touch roll is preferably 200 mm or less, and more preferably 160 mm or less. The molten sheet extruded from the T-die is stretched from the lip to the roll, and orientation tends to occur. By shortening the air gap as described above, a film having a smaller orientation can be obtained. The lower limit of the air gap is determined by the diameter of the metal cooling roll to be used, the diameter of the touch roll, and the tip shape of the lip to be used, and is usually 50 mm or more.

  The processing speed when producing a polypropylene resin film by this method is determined by the time required for cooling and solidifying the molten sheet. When the diameter of the metal cooling roll to be used is increased, the distance at which the molten sheet is in contact with the cooling roll becomes longer, so that production at a higher speed is possible. Specifically, when a 600 mmφ metal cooling roll is used, the processing speed is about 5 to 20 m / min at the maximum.

  The molten sheet sandwiched between the metal cooling roll and the touch roll is cooled and solidified by contact with the roll. And after slitting an edge part as needed, it is wound up by a winder and becomes a film. Under the present circumstances, in order to protect the surface until it uses a film, you may wind up in the state which bonded the surface protection film which consists of another thermoplastic resin to the single side | surface or both surfaces. When a molten sheet of polypropylene resin is sandwiched between a metal cooling roll and a touch roll together with a biaxially stretched film made of a thermoplastic resin, the biaxially stretched film is used as one surface protective film. You can also.

The raw film produced by the above method or the like can be used as a retardation film as it is. Moreover, it can also be used as a retardation film after performing any one of the following treatments or two or more of them.
<Extension processing>
In order to express the retardation of the raw film, a stretching process can be performed. A film exhibiting biaxial birefringence by biaxial stretching can be used as the retardation film. The stretching ratio is about 1.1 to 10 times in the direction in which the optical axis is developed (the direction in which the stretching ratio is large and becomes the slow axis), in the longitudinal direction and the transverse direction (stretching direction). The direction can be appropriately selected according to the required phase difference value from a range of about 1.1 to 7 times in the direction in which the magnification is small and becomes the fast axis. The optical axis may be developed in the lateral direction of the film, or the optical axis may be developed in the longitudinal direction.

<Easy adhesion treatment>
Adhesiveness with the optically anisotropic layer formed on the surface of the retardation film made of the polypropylene resin or containing the polypropylene resin, or an alignment film formed as desired In order to improve this, it is preferable to perform an easy adhesion treatment. By performing this treatment, even when exposed to high heat and high humidity, peeling with other optical films, polarizers, liquid crystal cells and the like hardly occurs, and heat resistance is improved. As the easy adhesion treatment, corona discharge treatment or atmospheric pressure plasma treatment is preferred. Corona discharge treatment is also roughly classified into atmospheric pressure plasma treatment, but here, what directly exposes the workpiece to the plasma region by corona discharge is called corona discharge treatment, and the plasma region and the surface of the workpiece are separated. This is called atmospheric pressure plasma treatment. Although corona treatment has many industrial practical examples and is low in cost, it has a demerit that physical damage on the surface of the treatment body is large. On the other hand, there are relatively few practical examples of atmospheric pressure plasma treatment, and the cost is higher than that of corona treatment, but there is an advantage that the treatment body surface is less damaged and treatment intensity can be set relatively high. Therefore, the preferable processing method may be selected from the relationship between the damage of the polymer film to be used and the improvement level of the adhesiveness after the processing.

The treated surface of the film subjected to these treatments becomes hydrophilic. As an indication of hydrophilization, the contact angle of water on the treated surface may be used. Specifically, the contact angle of water on the treated surface is preferably 55 ° or less, and more preferably 50 ° or less. When the contact angle of water on the treated surface is within the above range, the adhesiveness with the optically anisotropic layer and the alignment film formed thereon is improved, and defects such as peeling are less likely to occur. Although there is no restriction | limiting in particular about a lower limit, It is preferable to set so that a polymer film may not be damaged. The contact angle can be measured according to JIS R-3257 (1999). In the corona discharge treatment and the atmospheric pressure plasma treatment, treatment conditions are determined so that the contact angle is in the above range. The processing conditions to be varied include applied voltage, frequency, atmospheric gas type, processing time, etc. in any processing method.
For details of these treatments, see Polymer Surface Modification (Modern Editorial Company), p. 88- Basics and applications of polymer surfaces (bottom) (Chemical Doujin) 31--Principles / characteristics of atmospheric pressure plasma and polymer film / glass substrate surface modification technology (Technical Information Association), etc. are described respectively, and the contents thereof can be referred to.

《Dust removal process》
The surface of the film, particularly the surface subjected to corona discharge treatment or atmospheric pressure plasma treatment (hereinafter sometimes referred to as “treated surface”) is preferably subjected to dust removal treatment before forming a layer thereon. The dust removal method is not particularly limited. Ultrasonic dust removal using ultrasonic waves is preferred. Ultrasonic dust removal is described in detail in JP-A-7-333613 and can be referred to.
Moreover, when forming the alignment film mentioned later, it is preferable to perform a dust removal process after performing the rubbing process on the surface of the alignment film.

<Swelling treatment>
When a coating layer such as a liquid crystal composition is formed on the film, the coating solvent in the coating composition of the layer formed adjacent to the film causes the film to swell to some extent, thereby It is also possible to improve adhesion. Specifically, the adhesiveness can be preferably improved without causing whitening of the coating layer by using a solvent in which a solvent capable of swelling the film and a solvent that does not swell are mixed at a predetermined ratio.

  There are no particular restrictions on the materials constituting the rear side and front side phase difference regions other than the polypropylene resin. Various polymer films such as cellulose acylate, polycarbonate polymer, polyester polymer such as polyethylene terephthalate and polyethylene naphthalate, acrylic polymer such as polymethyl methacrylate, polystyrene, acrylonitrile / styrene copolymer (AS resin), etc. Styrene polymers and the like can be used. Also, vinyl chloride polymers, amide polymers such as nylon and aromatic polyamide, imide polymers, sulfone polymers, polyether sulfone polymers, polyether ether ketone polymers, polyphenylene sulfide polymers, vinylidene chloride polymers, vinyl Select one or more polymers from alcohol polymers, vinyl butyral polymers, arylate polymers, polyoxymethylene polymers, epoxy polymers, or polymers mixed with the above polymers, and use them as the main component. A film can be produced and used for producing the rear side and front side retardation regions in a combination satisfying the above characteristics.

  Further, the retardation layer constituting the rear side and front side retardation regions may be a layer formed by fixing the alignment state after setting the liquid crystal composition to a desired alignment state, or It may be a laminate having a polymer film that supports the layer together with the layer. In the latter embodiment, the polymer film can be used as a protective film for a polarizer. Examples of the liquid crystal that can be used for producing the retardation layer constituting the front side retardation region include various liquid crystals such as a rod-like liquid crystal, a disk-like liquid crystal, and a cholesteric liquid crystal.

2. Polarizer There is no particular limitation on the polarizer disposed on the front side and the rear side. A commonly used linear polarizing film can be used. The linear polarizing film is manufactured by Optiva Inc. And a polarizing film comprising a binder and iodine or a dichroic dye is preferable. The iodine and the dichroic dye in the linearly polarizing film exhibit polarizing performance by being oriented in the binder. It is preferable that the iodine and the dichroic dye are aligned along the binder molecule, or the dichroic dye is aligned in one direction by self-assembly such as liquid crystal. Currently, commercially available polarizers are made by immersing a stretched polymer in a solution of iodine or dichroic dye in a bath and allowing iodine or dichroic dye to penetrate into the binder. Is common.

3. Protective film It is preferable that the protective film is bonded to both surfaces of the front-side polarizer and the rear-side polarizer. However, the protective film disposed on the liquid crystal cell side constitutes a part of the rear side retardation region and the front side retardation region, respectively, and the former is required to satisfy the above formula (I). The The latter also constitutes a part of the front-side retardation region, and depending on the mode, it is required to show optical characteristics that contribute to the improvement of the viewing angle CR alone or in combination with other layers.

  There is no restriction | limiting in particular about the protective film arrange | positioned on the outer side of a front side polarizer and a rear side polarizer. Various polymer films can be used. This is the same as the example of the polymer film that can constitute the front side retardation region. For example, cellulose acylates (eg, films of cellulose acetate, cellulose propionate, cellulose butyrate, etc.), polyolefins (eg, norbornene polymers, polypropylene), poly (meth) acrylates (eg, polymethyl methacrylate) Examples thereof include, but are not limited to, films mainly composed of polycarbonate, polyester, or polysulfone. Commercially available polymer films ("Fujitac TD80UL" (manufactured by Fujifilm) for cellulose acylates), Arton (manufactured by JSR), ZEONOR (manufactured by ZEON Corporation) and the like for norbornene polymers can also be used.

  The present invention will be described more specifically with reference to the following examples. The materials, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

1. Preparation of Films 1 to 12 (1) Production of Film 1 A propylene / ethylene random copolymer (Sumitomo Noblen W151, manufactured by Sumitomo Chemical Co., Ltd.) containing about 5% by mass of an ethylene unit was added to a single-screw melt extruder using a T-die. Extrusion was carried out at a melting temperature of 230 ° C. using a melt extrusion molding machine in which R (550) = 1.1 nm and Rth (550) = 1.3 nm. Thereafter, both the front and back surfaces of the raw film were subjected to corona discharge treatment and used as film 1. The internal haze of film 1 was 0.3.
(2) Production of film 2 After obtaining a polypropylene original film in the same manner as film 1, the film was sequentially biaxially stretched in the order of longitudinal stretching at a stretching ratio of 1.3 times and transverse stretching at a stretching ratio of 2.8 times. A transparent film with (550) = 100 nm and Rth (550) = 59 nm was obtained. Thereafter, both the front and back surfaces of this transparent film were subjected to corona discharge treatment and used as film 2. The internal haze of film 2 was 0.3.
(3) Production of film 3 After obtaining a polypropylene original film in the same manner as film 1, the film was sequentially biaxially stretched in the order of longitudinal stretching at a stretching ratio of 1.45 and transverse stretching at a stretching ratio of 1.45. A transparent film with (550) = 2 nm and Rth (550) = 90 nm was obtained. Thereafter, both the front and back surfaces of the transparent film were subjected to corona discharge treatment and used as a film 3. The internal haze of film 3 was 0.3.
(4) Production of film 4 After obtaining a polypropylene raw film in the same manner as film 1, the film was sequentially biaxially stretched in the order of longitudinal stretching at a stretching ratio of 1.5 times and transverse stretching at a stretching ratio of 1.5 times. A transparent film with (550) = 2 nm and Rth (550) = 95 nm was obtained. Thereafter, both the front and back surfaces of the transparent film were subjected to corona discharge treatment and used as a film 4. The internal haze of film 4 was 0.3.
(5) Production of film 5 After obtaining a polypropylene original film in the same manner as film 1, the film was sequentially biaxially stretched in the order of longitudinal stretching at a stretching ratio of 1.7 times and transverse stretching at a stretching ratio of 2.7 times. A transparent film having (550) = 85 nm and Rth (550) = 165 nm was obtained. Thereafter, both the front and back surfaces of the transparent film were subjected to corona discharge treatment and used as a film 5. The internal haze of film 5 was 0.3.
(6) Production of film 6 After obtaining a polypropylene raw film in the same manner as the film 1, the film was sequentially biaxially stretched in the order of longitudinal stretching at a stretching ratio of 1.6 times and transverse stretching at a stretching ratio of 2.5 times. A transparent film with (550) = 30 nm and Rth (550) = 160 nm was obtained. Thereafter, both the front and back surfaces of the transparent film were subjected to corona discharge treatment and used as a film 6. The internal haze of film 6 was 0.3.
(7) Production of film 7 After obtaining a polypropylene original film in the same manner as the film 1, the film was successively biaxially stretched in the order of longitudinal stretching at a stretching ratio of 2.5 and transverse stretching at a stretching ratio of 3.5. A transparent film with (550) = 60 nm and Rth (550) = 250 nm was obtained. Thereafter, both the front and back surfaces of this transparent film were subjected to corona discharge treatment, and used as film 7. The internal haze of film 7 was 0.3.
(8) Preparation of Film 8 A commercially available cellulose acylate film, trade name “Z-TAC” (manufactured by FUJIFILM Corporation) was prepared and used as film 8. Re (550) and Rth (550) of the film 8 were Re (550) = 0.7 nm, Rth (550) = 0.5 nm, and the internal haze was 0.1.
(9) Preparation of Film 9 A commercially available cellulose acylate film, trade name “Fujitac TD80UL” (manufactured by Fuji Film) was prepared and used as film 9. Re (550) and Rth (550) of the film 9 were Re (550) = 1.1 nm, Rth (550) = 47 nm, and the internal haze was 0.1.
(10) Production of Film 10 Cellulose acylate having the kind of acyl group and the substitution degree shown in the following table was prepared. This was carried out by adding sulfuric acid (7.8 parts by mass with respect to 100 parts by mass of cellulose) as a catalyst, adding carboxylic acid as a raw material for the acyl substituent, and carrying out an acylation reaction at 40 ° C. At this time, the kind and substitution degree of the acyl group were adjusted by adjusting the kind and amount of the carboxylic acid. Moreover, it age | cure | ripened at 40 degreeC after acylation. Further, the low molecular weight component of the cellulose acylate was removed by washing with acetone. In the table, Ac is an acetyl group, and CTA means cellulose triacetate (a cellulose ester derivative in which an acyl group is composed only of an acetate group).

(Cellulose acylate solution)
The following composition was placed in a mixing tank, stirred to dissolve each component, further heated to 90 ° C. for about 10 minutes, and then filtered through a filter paper having an average pore size of 34 μm and a sintered metal filter having an average pore size of 10 μm.
―――――――――――――――――――――――――――――――――
Cellulose acylate solution ――――――――――――――――――――――――――――――――――
CTA in the following table 100.0 parts by mass Triphenyl phosphate (TPP) 7.8 parts by mass Biphenyl diphenyl phosphate (BDP) 3.9 parts by mass Methylene chloride 403.0 parts by mass Methanol 60.2 parts by mass ――――――――――――――――――――――――――――――

(Matting agent dispersion)
Next, the following composition containing the cellulose acylate solution prepared by the above method was charged into a disperser to prepare a mat agent dispersion.
――――――――――――――――――――――――――――――――――
Matting agent dispersion ――――――――――――――――――――――――――――――――――
Silica particles having an average particle size of 16 nm (Aerosil R972, manufactured by Nippon Aerosil Co., Ltd. 2.0 parts by mass methylene chloride 72.4 parts by mass methanol 10.8 parts by mass cellulose acylate solution 10.3 parts by mass ―――――――――――――――――――――――――――

(Additive solution)
Next, the following composition containing the cellulose acylate solution prepared by the above method was put into a mixing tank and dissolved by stirring while heating to prepare an additive solution.
―――――――――――――――――――――――――――――――――
Additive solution ―――――――――――――――――――――――――――――――――
Retardation expression agent (1) 20.0 parts by mass Methylene chloride 58.3 parts by mass Methanol 8.7 parts by mass Cellulose acylate solution 12.8 parts by mass ――――――――――――――― ―――――――――――――――――

100 parts by mass of the cellulose acylate solution, 1.35 parts by mass of the matting agent dispersion, and an additive solution in an amount such that the addition amount of the retardation developer (1) in the cellulose acylate film is 10 parts by mass. Were mixed to prepare a dope for film formation. The addition ratio of the additive is shown in parts by mass when the amount of cellulose acylate is 100 parts by mass.
Here, abbreviations of the additives and plasticizers in the table and the above are as follows.
CTA: cellulose triacetate,
TPP: triphenyl phosphate,
BDP: biphenyl diphenyl phosphate.

  The above dope was cast using a band casting machine. The film stripped from the band with the residual solvent amount described in the following table is stretched in the longitudinal direction at the stretch ratio described in the following table in the section from stripping to the tenter, and then stretched in the table below using the tenter The film was stretched in the width direction at a magnification, and immediately after transverse stretching, the film was removed from the tenter after shrinking (relaxing) in the width direction at the magnification described in the following table, and a cellulose acylate film was formed.

The cellulose acylate film thus produced was used as the film 10.
Re (550) and Rth (550) of the film 10 were Re (550) = 3 nm, Rth (550) = 95 nm, and the internal haze was 0.1.

(11) Production of Film 11 A film except that the cellulose acylate shown in the following table was used, the addition amount of the retardation developer (1) was changed as shown in the following table, and the stretching treatment was carried out under different stretching conditions. In the same manner as in Example 10, a cellulose acylate film was prepared. This film was used as film 11. Re (550) and Rth (550) of the film 11 were Re (550) = 85 nm, Rth (550) = 165 nm, and the internal haze was 0.1.
In addition, about the abbreviation of the following additive and plasticizer, it is synonymous with the above.

(12) Production of Film 12 Film except that the cellulose acylate shown in the following table was used, the addition amount of the retardation enhancer (1) was changed as shown in the following table, and the stretching treatment was carried out under different stretching conditions. In the same manner as in Example 10, a cellulose acylate film was prepared. This film was used as film 12. Re (550) and Rth (550) of the film 12 were Re (550) = 61 nm, Rth (550) = 208 nm, and the internal haze was 0.1. In addition, about the abbreviation of the following additive and plasticizer, it is synonymous with the above.

2. Preparation of Polarizing Plate A polyvinyl alcohol (PVA) film having a thickness of 80 μm is dyed by dipping in an aqueous iodine solution having an iodine concentration of 0.05% by mass at 30 ° C. for 60 seconds, and then boric acid having a boric acid concentration of 4% by mass. While being immersed in an aqueous solution for 60 seconds, the film was longitudinally stretched 5 times the original length and then dried at 50 ° C. for 4 minutes to obtain a polarizing film having a thickness of 20 μm.
Among the films shown in the above table, the film containing cellulose acylates was immersed in an aqueous sodium hydroxide solution at 55 mol C at 1.5 mol / liter, and then the sodium hydroxide was sufficiently washed away with water. Then, after being immersed in a diluted sulfuric acid aqueous solution at 0.005 mol / liter at 35 ° C. for 1 minute, it was immersed in water to sufficiently wash away the diluted sulfuric acid aqueous solution. Finally, the sample was thoroughly dried at 120 ° C.
A polarizing plate having a protective film on both surfaces was prepared by sandwiching a polarizing film between any two of the films (films 1 to 12) and using an adhesive. In addition, about the cellulose acylate type | system | group film, the polyvinyl-type adhesive was used, and about the other film, it bonded with the polarizer using the acrylic adhesive. The combinations are shown in Table 11 below.
In addition, in the following table | surface, the film which attached | subjected "* 1" means the retardation film used as a polarizing plate protective film arrange | positioned further on the display surface side outer side from a polarizing film, and the film which attached "* 2" Means a retardation film used as a polarizing plate protective film disposed between the liquid crystal cell and the polarizing film, and the film marked with “* 3” is disposed further outside the polarizing film than the polarizing film. It means a retardation film used as a polarizing protective film. Any table below is synonymous.
In addition, about the films 2, 5-7, 11, and 12, the in-plane slow axis was bonded in parallel with the transmission axis of the polarizer. The films 1, 3, 4, and 8 to 10 were bonded so that the in-plane slow axis was perpendicular to the transmission axis of the polarizer. Moreover, about the film which has an easily bonding layer, it bonded together by making the easily bonding layer into the surface side of a polarizer.

3. Preparation and Evaluation of VA Type Liquid Crystal Display (1) Preparation of VA Type Liquid Crystal Cells 1 to 3 In this example, when forming a color filter on the TFT, an organic developer CD2000 (manufactured by FUJIFILM Electromaterials) ) Was used.
(1) -1 Preparation of VA liquid crystal cell 1 A TFT element was produced on a glass substrate, and a protective film was further formed on the TFT element.
Subsequently, a composition prepared as described in Examples 17, 18 and 19 described in JP-A-2009-144126 was used as the colored photosensitive composition on the protective film, respectively, and Special Table 2008- A color filter on array (COA) substrate was produced according to the process described in Example 9a described in [0099] to [0103] of Japanese Patent No. 516262. However, the concentration of the pigment in the colored photosensitive resin composition of each pixel is halved and the coating amount is adjusted so that the black pixel is 4.2 μm and the red, green, and blue pixels are all 3.5 μm. did. Further, after forming a contact hole in the color filter, an ITO (Indium Tin Oxide) transparent pixel electrode electrically connected to the TFT element was formed on the color filter. Next, according to Example 1 of Japanese Patent Application Laid-Open No. 2006-64921, a spacer was formed in a portion corresponding to the upper part of the partition wall (black matrix) on the ITO film.
Separately, a glass substrate on which an ITO transparent electrode was formed was prepared as a counter substrate, the COA substrate and the transparent electrode of the counter substrate were each patterned for the PVA mode, and an alignment film made of vertical polyimide was further provided thereon. .
After that, a UV curable resin sealant is applied by a dispenser method at a position corresponding to a black matrix outer frame provided around the RGB pixel group of the color filter, and a liquid crystal for PVA mode is dropped, and the counter substrate and After bonding, the bonded substrate was irradiated with UV, and then heat treated to cure the sealant. A liquid crystal cell was thus produced.
Subsequently, Δnd (550) of the produced liquid crystal cell was measured using AXOSCAN manufactured by AXOMETRICS and the attached software, and those having Δnd (550) of 295 nm were selected and used as the liquid crystal cell 1.

  The backlight used in the liquid crystal panel “KDL-40V5” manufactured by Sony was used as the light source of the liquid crystal cell 1, and the light source was disposed on the COA substrate side.

(1) -2 Preparation of VA liquid crystal cell 2 A TFT element was produced on a glass substrate, and a protective film was further formed on the TFT element. Subsequently, after forming a contact hole in the protective film, an ITO transparent electrode electrically connected to the TFT element was formed on the protective film to produce an array substrate.
As the colored photosensitive composition, compositions prepared as described in Examples 17, 18 and 19 described in JP-A-2009-144126 were used, respectively, and [0099] to [ [0103] A color filter substrate was prepared according to the process described in Example 9a.
An ITO transparent electrode is formed by sputtering on the produced color filter substrate, and then in accordance with Example 1 of Japanese Patent Application Laid-Open No. 2006-64921, a portion corresponding to the upper part of the partition wall (black matrix) on the ITO film is formed. A spacer was formed.
The transparent electrodes of the prepared array substrate and color filter substrate were each patterned for the PVA mode, and an alignment film made of vertical polyimide was further provided thereon.
After that, a UV curable resin sealant is applied by a dispenser method to a position corresponding to the outer periphery of the black matrix provided around the RGB pixel group of the color filter, and a PVA mode liquid crystal is dropped, and the array substrate and After the substrates were bonded together and irradiated with UV, the sealant was cured by heat treatment. A liquid crystal cell was thus produced.
Subsequently, Δnd (550) of the produced liquid crystal cell was measured using AXOSCAN manufactured by AXOMETRICS and the attached software, and those having Δnd (550) of 295 nm were selected and used as the liquid crystal cell 2.

  The backlight used in the KDL-40V5 was used as the light source of the liquid crystal cell 2, and the light source was disposed on the array substrate side.

(1) -3 Preparation of VA liquid crystal cell 3 A liquid crystal cell of a liquid crystal panel “KDL-52W5” manufactured by Sony Corporation was prepared. This liquid crystal cell is a VA type liquid crystal cell having a COA structure. This was used as the liquid crystal cell 3.
When Δnd of the liquid crystal cell 1 was measured using AXOSCAN manufactured by AXOMETRIC and the attached software, Δnd (550) was 295 nm.

(2) Calculation of the member contrast of the front side substrate and the rear side substrate of each liquid crystal cell The member contrast of the rear side substrate and the front side substrate of the liquid crystal cell is the total of the various members formed on each substrate and each substrate. This means the contrast. Examples of the member include various members such as a color filter, a black matrix, an array member (such as a TFT array), a protrusion on the substrate, a common electrode, and a slit.
Two substrates forming each liquid crystal cell, that is, a front side substrate and a rear side substrate were separated, and each substrate was washed with ethanol. Subsequently, the front side board (including the front side board and all the members formed on the board) and the rear side board (including the rear side board and all the members formed on the board) The contrast was calculated by the following method.
A front side substrate prepared by disposing a polarizing plate (HLC2-2518, manufactured by Sanlitz) on a backlight of a liquid crystal panel “LC-32GH5” manufactured by SHARP, and disassembling each liquid crystal cell thereon, or The rear substrate was attached to a rotating stage (SGSP-120YAW, manufactured by Sigma Kogyo Co., Ltd.) and arranged in parallel with the polarizing plate on the light source at an interval of 2 mm. At this time, the wiring of the TFT array on the substrate and the lattice pattern of the black matrix were arranged so as to coincide with the polarization axis of the polarizing plate. Furthermore, a polarizing plate (HLC2-2518, manufactured by Sanlitz) attached to the rotary stage is arranged so that the distance between the polarizing plates is 52 mm, and a measuring instrument (BM5A, manufactured by TOPCON) is used. In a dark room, the luminance values of black display and white display in the normal direction were measured, and front contrast A (white luminance / black luminance) was calculated. Here, when the polarizing plate is rotated, the luminance value when the luminance value is the lowest is set as the luminance value for black display, and the luminance value when the polarizing plate is further rotated by 90 degrees is set as the luminance value for white display.
Next, in the above-described form, the front contrast B was calculated by measuring the luminance values of the black display and the white display of only the polarizing plate with the front substrate or the rear substrate removed.
In order to eliminate the influence of the front contrast B of the polarizing plate on the front contrast A, the member contrast was calculated by the following formula.
Member contrast = 1 / (1 / front contrast A-1 / front contrast B)
Further, for each liquid crystal cell, the ratio of the member contrast between the front substrate and the rear substrate (front substrate member contrast / rear substrate member contrast) was calculated. The liquid crystal cell 1 was 48.2 and the liquid crystal cell 2 was 0. The liquid crystal cell 3 was 13.5.

(3) Production of VA liquid crystal display device Any of the three types of liquid crystal cells produced above (liquid crystal cell 1 with COA structure, liquid crystal cell 2 with non-COA structure, and liquid crystal cell 3 with COA structure "KDL-52W5") Was selected, and a polarizing plate was bonded to the outer surfaces of both substrates in the combinations shown in the following table to produce a VA liquid crystal display device. The polarizing plates were bonded with the absorption axes orthogonal to each other.

(4) Evaluation of VA type liquid crystal display device The following evaluation was performed about each produced liquid crystal display device.
(4) -1 Measurement of front contrast ratio Using a measuring instrument (BM5A, manufactured by TOPCON), the brightness values of black display and white display in the panel normal direction are measured in a dark room, and the front contrast (white brightness / black) is measured. (Luminance) was calculated.
At this time, the distance between the measuring instrument and the panel was set to 700 mm.
Subsequently, the front contrast ratio was calculated by the following formula based on the front contrast ratio in the reference form.
Front contrast ratio = front contrast in the embodiment / front contrast in the reference form In the liquid crystal display device using the liquid crystal cell 1 or 2, the reference form is the liquid crystal display device of the comparative example 1, and the liquid crystal cell 3 is used. The liquid crystal display device was the liquid crystal display device of Comparative Example 7. The front contrast was 3500 in Comparative Example 1 and 3200 in Comparative Example 7.
(4) -2 Viewing angle contrast (contrast in diagonal direction)
Using a measuring instrument (BM5A, manufactured by TOPCON), in a dark room, the luminance values of black display and white display in three directions of polar angle direction 60 degrees from the front of the apparatus and azimuth angle directions 0 degrees, 45 degrees, and 90 degrees And the viewing angle contrast (white luminance / black luminance) was calculated to evaluate the viewing angle characteristics of the liquid crystal display device.
○: All viewing angle contrasts are 60 or more and light leakage cannot be recognized. Δ: The minimum value of viewing angle contrast is less than 60 and 30 or more. The minimum contrast value is less than 30, and large light leakage is recognized and unacceptable.
The column showing the viewing angle contrast evaluation results in the table below shows the average results of the above three directions evaluated according to the above criteria.
(4) -3 Durability Evaluation Each liquid crystal display device was continuously lit for 7 days. Thereafter, using a measuring instrument (BM5A, manufactured by TOPCON), viewing angle contrast was measured in a dark room at a polar angle direction of 60 degrees and an azimuth angle direction of 45 degrees from the front of the apparatus. The viewing angle contrast before and after continuous lighting was compared, and the durability was evaluated according to the following criteria.
○: Difference in viewing angle contrast is less than 10 (light leakage after continuous lighting is slight and acceptable)
X: Difference in viewing angle contrast is 10 or more (a large light leakage is recognized after continuous lighting and is not allowed)

The results are shown in the table below.

From the above results, all of the VA liquid crystal display devices according to the embodiments of the present invention in which the retardation film satisfying the above formula (I) is disposed between the rear polarizer and the liquid crystal cell having the COA structure have a front contrast. I can understand that it is expensive. Specifically, the front CR of Examples 1 to 3 and the front CR of Comparative Examples 3 to 5 having the same configurations as those of Examples 1 to 3 except that a liquid crystal cell having a non-COA structure is included. Thus, it can be understood that the VA liquid crystal display device of the present invention is far superior to the non-COA structure VA liquid crystal display device in terms of the front CR.
Further, referring to Comparative Examples 2 and 6, these are liquid crystal display devices having the same configuration except that the liquid crystal cell has a COA structure or a non-COA structure, and the relationship between Example 1 and Comparative Example 3, Example 2 and Comparative Example 4 and the same relationship as Example 3 and Comparative Example 5. However, in Comparative Example 2, Rth (550) in the rear side phase difference region is 95 nm, and the formula (I) | Rth (550) | ≦ 90 nm is not satisfied. Therefore, the front CR is equivalent to that in Comparative Example 6. is there. From this, it is clear that the effect of the present invention can be obtained only when the COA structure is adopted and the rear side phase difference region satisfies the above formula (I).
Moreover, although the liquid crystal display devices of Examples 1 to 5 have a retardation film made of a polypropylene resin, the front CR is superior to Comparative Example 1 which is a conventional general configuration. Can understand. Further, comparing Examples 3 to 5 with Comparative Example 8, the liquid crystal display device having a retardation film made of polypropylene resin has a small change in viewing angle CR due to a change in retardation film characteristics during continuous lighting, and durability. It can be understood that it is excellent. That is, it can be seen that the liquid crystal display device of the present invention is excellent in terms of durability in addition to the front CR.
Further, when comparing Examples 3 to 5, the retardation region made of the polypropylene resin on the front side and the rear side in Example 3 is changed to a cellulose acylate phase difference film on the front side as in Example 4. However, when the rear side is changed to a cellulose acylate phase difference film as in Example 5, the improvement rate of the front CR becomes higher. This is because the polarization state before scattering greatly affects the amount of light leakage in the front direction due to scattering in the retardation film forming the retardation region. That is, as in the third embodiment, when the phase difference in the rear side phase difference region is larger than that in the front side, the ellipticity in the polarization state of the light from the light source is the one before the incident on the front side phase difference region. Therefore, even in the same internal haze (scattering amount), the contribution to the front CR reduction is greater in the front phase difference region. Therefore, as in Example 4, the front CR improvement rate is greater when the front side retardation region is changed to a cellulose acylate retardation region having a lower internal haze. From this result, when applying a phase difference region having a high internal haze, such as a phase difference film made of polypropylene resin or containing polypropylene resin, the phase difference shared between the front side and the rear side is small. It is preferable to apply this method. In the case of the present invention, it is preferable to apply a retardation region made of a polypropylene resin or including a polypropylene resin on the rear side.

  In the above embodiment, as the outer protective film on the front side and the rear side, a film 9, that is, a commercially available TAC film is used, but as the outer protective film on the front side and / or the rear side, for example, Even for cellulose acylate films, other cellulose acylates (eg, films of cellulose propionate, cellulose butyrate, etc.), polyolefins (eg, norbornene polymers), poly (meth) acrylic acid esters (eg, Polymethylmethacrylate), polycarbonate, polyester, or polysulfone as a main component will provide the same effect, and other commercially available polymer films (for Norbornene polymers, Arton (manufactured by JSR), Zeonore) (Made by Nippon Zeon) etc.) Will effect can be obtained.

Reference example:
In Example 6, a VA liquid crystal display device produced in the same manner as in Example 6 was also evaluated in the same manner except that the film 3 was used instead of the film 7 as the front side retardation film. As a result, the front contrast ratio was 121%, which was as high as in the example, and the durability evaluation was good, but the viewing angle contrast was low. The reason for this is considered that the optical characteristics of the film 3 used as the front-side retardation film were insufficient to compensate for the viewing angle characteristics of the VA liquid crystal display device.

  The following table shows the results of evaluating the front tint during black display.

DESCRIPTION OF SYMBOLS 10 Liquid crystal layer 12 Color filter layer 14 Array member 16 Rear side board | substrate 18 Front side board | substrate 20 Rear side phase difference area | region 22 Front side phase difference area | region 24 Rear side polarizer 26 Front side polarizer 28 VA type of backlight unit LC COA structure Liquid crystal cell PL1 Rear polarizing plate PL2 Front polarizing plate

Claims (2)

Front side polarizer, rear side polarizer, liquid crystal layer disposed between front side polarizer and rear side polarizer, and color filter layer and array disposed between the liquid crystal layer and rear side polarizer A color filter-on-array structure having members on the same substrate, and one or more retardation layers disposed between the rear-side polarizer and the color filter layer as a whole , The whole of one or more retardation layers arranged between the rear-side polarizer and the color filter layer is referred to as “rear-side retardation region”), and the following formula (I)
(I): | Rth (550) | ≦ 90 nm
(However, Rth (λ) means retardation in the thickness direction (nm) at wavelength λnm),
One or two or more retardation layers disposed between the front-side polarizer and the liquid crystal layer (hereinafter, one or two layers disposed between the front-side polarizer and the liquid crystal layer) The whole of the above retardation layer is referred to as “front side retardation region”).
(III): 30 nm ≦ Re (550) ≦ 90 nm
(IV): 150 nm ≦ Rth (550) ≦ 500 nm
Satisfied,
The front-side retardation region or the rear-side retardation region is composed of a polypropylene resin, or a VA-type liquid crystal display device which comprises a polypropylene resin, VA type is front contrast is 1500 or more Liquid crystal display device. The rear side phase difference region has the following formula (II)
(II): Re (550) ≦ 100 nm
2. The VA liquid crystal display device according to claim 1, wherein Re (λ) means in-plane retardation (nm) at a wavelength of λ nm.

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