JP3830559B2 - Optical compensation film and liquid crystal display device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an optical compensation film used as a viewing angle compensation plate for an optical rotation mode twist nematic type liquid crystal display device.
[0002]
[Prior art]
In recent years, liquid crystal display elements have a great advantage of being thin and light and have low power consumption, and are therefore actively used in display devices such as personal computers, word processors, and portable electronic notebooks. Many principles of liquid crystal display elements have been proposed, but most of the liquid crystal display elements that are widely used at present use twisted nematic liquid crystal. Such display methods using liquid crystal are roughly classified into two methods, birefringence mode and optical rotation mode.
[0003]
The super twist nematic (STN) method, which is a birefringence mode, has a steep electro-optic characteristic and can be driven by a simple matrix, so it is supplied to the market at a relatively low price. Therefore, there is a problem that incident light that is linearly polarized becomes elliptically polarized light due to birefringence by the liquid crystal cell, and the display appears colored when viewed through a polarizing plate. Therefore, an F-STN system is proposed in which a retardation plate made of a stretched film or the like is interposed between the liquid crystal cell and the polarizing plate in order to return the elliptically polarized light after passing through the liquid crystal cell to a straight line to prevent coloring.
[0004]
On the other hand, the twisted nematic (TN) mode, which is an optical rotation mode, consists of a 90 ° twisted nematic liquid crystal, has a fast response speed of several tens of milliseconds, a high contrast ratio, and a good gradation display property. As a liquid crystal display element in which this switching element is provided for each pixel, it is used in applications requiring high definition and high speed such as liquid crystal televisions.
[0005]
However, even a TN liquid crystal display element combined with such a switching element has a problem that it has a viewing angle dependency that a contrast ratio changes depending on a viewing direction.
[0006]
Many methods for improving the viewing angle characteristics of TN liquid crystal display elements have been proposed. For example, in Japanese Patent Laid-Open No. 4-161928, a viewing angle characteristic is obtained by arranging a TN liquid crystal cell and an optical anisotropic element whose optical axis is substantially perpendicular to the display surface of the liquid crystal cell between two polarizing plates. A method for improving the above has been proposed. In addition, as an example more specifically proposed for such an optical anisotropic element, there is a description in the 16th Liquid Crystal Discussion Symposium Preliminary Proceedings P236. Here, the viewing angle characteristics are improved by arranging two TN liquid crystal cells and two uniaxial retardation films made of polycarbonate laminated so that the optical axes are orthogonal to each other between two polarizing plates. Proposed method. As a method for obtaining a film having an in-plane refractive index larger than the refractive index in the thickness direction, a method using an inorganic layered compound is disclosed as disclosed in JP-A-6-82797.
[0007]
The characteristics of the method of improving the viewing angle characteristics by using the retardation plate having the optical axis in the film thickness direction are the phase difference given by the liquid crystal cell to the light incident from the front with respect to the liquid crystal cell and the light incident from the oblique direction. Note that the phase difference given by the liquid crystal cell differs depending on the liquid crystal alignment in the liquid crystal cell, and this is the reason for determining the viewing angle characteristics. There is a place to compensate.
[0008]
On the other hand, a pixel division method has been proposed in which one pixel of a liquid crystal cell is divided into a plurality of pixels to improve viewing angle characteristics. Various methods have been proposed for dividing one pixel into a plurality of methods, such as a method using electric field control and a device using an alignment film. Furthermore, a method for further improving display quality by combining such a pixel-divided cell and an optical compensation film has been proposed.
[0009]
As described above, although optical characteristics for improving the viewing angle characteristics of the 90 ° TN system using an optical compensator have been disclosed, the optical characteristics and mass productivity of the optical compensation film are actually satisfied at the same time. At present, no film has been obtained.
[0010]
[Problems to be solved by the invention]
In the above-mentioned Japanese Patent Laid-Open No. 4-161928, the material and manufacturing method of the optical anisotropic element are not described in detail. Further, the method described in the above-mentioned 16th Liquid Crystal Discussion Symposium Preliminary Proceedings P236 uses two retardation films, and thus has a problem of loss of transmittance and cost. Furthermore, by biaxially stretching the film, it is difficult in the present process to obtain a film in which there is no optical axis in the film plane direction but there is an optical axis in the film thickness direction. It has the problem of being inferior. In addition, the method for forming an inorganic layered compound on a film as disclosed in JP-A-6-82279 has a problem that it is expensive.
[0011]
Furthermore, it is already known that a polymer resin is dissolved in an appropriate solvent and formed into a film by a casting method to apply a film excellent in transparency, smoothness, and optical uniformity to optical applications. It was difficult to obtain an optical compensation film having the optical characteristics of the present invention without adopting special cast film formation conditions that are problematic.
[0012]
When a transparent film is used, if it is only the in-plane refractive index, it can be controlled by stretching, and a method for increasing the refractive index in the film thickness direction is also disclosed. As for the method of controlling the refractive index in the film thickness direction that is optically negative and required as a film for improving the viewing angle in the nematic mode, there is still no satisfactory method in terms of optical characteristics and mass productivity. It was the current situation.
[0013]
As described above, in the conventional optical compensation film, it is difficult to obtain an optical rotation mode twisted nematic type liquid crystal display device having the necessary characteristics as an optical compensator for improving the viewing angle characteristics with a single film. That is, the light transmittance at 550 nm of the measurement light is 80% or more, and the refractive index in the in-plane direction of the film measured with the measurement light 550 nm is nx (slow axis), ny (fast axis), and directions orthogonal to them. When the refractive index in the film thickness direction is nz and the film thickness is d (nm), the optical characteristics represented by R = (nx−ny) × d and K = (nz− (nx + ny) / 2) × d , 0 ≦ R <80 (nm) and −300 <K <−140 (nm), it was difficult to obtain an optical compensation film.
[0014]
The present invention solves such a problem, and in the optical rotation mode twisted nematic type liquid crystal display device having the above characteristics, an optical compensation film excellent in mass productivity capable of improving viewing angle characteristics with a single film, and An object is to provide a liquid crystal display device used.
[0015]
[Means for Solving the Problems]
  The optical compensation film of the present invention is an optical compensation film used as a viewing angle compensation plate for an optical rotation mode twisted nematic type liquid crystal display device, and has a refractive index in the in-plane direction measured with light having a wavelength of 550 nm of nx (slow retardation). Phase axis) and ny (fast axis), where nz is the refractive index in the film thickness direction perpendicular to them, and d (nm) is the film thickness, R = (nx−ny) × d and K In the optical compensation film, the optical characteristics represented by = (nz− (nx + ny) / 2) × d have the characteristics of 0 ≦ R <80 (nm) and −300 <K <−140 (nm),Formula (I)
[Chemical 3]
    (I)
(Where Y is
  Alternatively, a direct bond, R is H, and the substitution position of the rightmost CO group is the para-position or meta-position. When Y is a direct bond, the substitution position of the rightmost CO group is the para position. )
Polyarylate having a molecular weight of 20,000 or more in terms of polystyrene containing a repeating unit represented byTheCasting the solution onto the support, drying the film on the support until the solvent content is at least 20% by weight, and then peeling the film containing the solvent to support the film It consists of step 2 that is peeled off and dried while being transported, and is dried at an atmosphere temperature T1 (° C.) of 15 ≦ T1 ≦ 50 in step 1, and in step 2, an apparent resin glass containing a solvent. When the transition temperature is Tg ′ (° C.), the drying temperature is in the temperature range of (Tg′−50) ≦ T2 ≦ (Tg ′ + 50) until the solvent content is 5% by weight or more, and the solvent content is If it is less than 5% by weight, the temperature is continuously or sequentially increased in the temperature range of (Tg′−50) ≦ T3 ≦ (Tg ′ + 20) according to the transition of Tg ′ and dried.The film is formed by a solution casting method.
[0016]
Although some liquid crystal display devices using ferroelectric liquid crystals are also supplied, most of the current liquid crystal display devices are of a twisted nematic type. The optical compensation film in the present invention is used as a viewing angle compensator for a 90 ° twisted nematic liquid crystal cell which is a mode utilizing the optical rotation of liquid crystal.
[0017]
In the 90 ° twisted nematic mode, there are a normally white mode in which light is transmitted when no voltage is applied and a normally black mode in which a dark state is applied when no voltage is applied. In a 90 ° twisted nematic high-definition liquid crystal display device with a thin film transistor used in a liquid crystal television or a notebook type personal computer, the birefringence ΔnLC of the liquid crystal material and the cell gap d from the viewpoint of a wide viewing angle and high-speed response. The product ΔnLC · d with (μm) is determined at a relatively small value. Although the normally black mode has an advantage of low voltage driving, it is not so often used in current display devices due to low coloring and low contrast in the dark state, and many of the current display devices are normally white modes. The ΔnLC · d of the 90 ° twisted nematic cell that requires high quality is different in the normally white mode and the normally black mode, but is determined to be around 0.4 μm in the former and around 0.48 μm in the latter. . These are almost the same in the pixel division method in the 90 ° twisted nematic mode. Although ΔnLC has dispersion depending on the measurement wavelength, a value measured with light having a wavelength of 550 nm or the vicinity in which human visual sensitivity is the highest is often adopted.
[0018]
The optical anisotropy of such an optical compensation film is expressed by a three-dimensional refractive index nx, ny, nz. Here, nx and ny are the refractive indexes in the slow axis direction and the fast axis direction in the in-plane direction, respectively, and nz is the refractive index in the film thickness direction. The axes having refractive indexes of nx, ny, and nz are orthogonal to each other, and nx and ny are substantially parallel to the in-plane direction of the film. Depending on the film forming conditions, the nx, ny direction and the in-plane direction of the film may not be completely parallel, but here the angle formed is assumed to be within ± 10 °.
[0019]
When the three-dimensional refractive index is used, the values of R (nm) and K (nm) important for describing the anisotropy of the optical compensation film of the present invention are R = (nx−ny) × d, K, respectively. = (Nz− (nx + ny) / 2) × d. The R value is a value generally referred to as retardation measured with light incident from the vertical direction in the film plane, and thereby represents in-plane anisotropy. Further, since the K value is the difference between the refractive index in the film thickness direction and the average of the in-plane refractive indexes, the magnitude of anisotropy in the film thickness direction with respect to the in-plane direction can be expressed.
[0020]
Although the three-dimensional refractive index can be directly obtained by an Abbe refractometer or the like, the values used in the present invention are based on the incident angle dependency of retardation assuming that the film is optically a three-dimensional refractive index ellipsoid. The calculation method was adopted. That is, when the refractive indexes nx, ny, and nz are used,
[0021]
[Expression 1]
[0022]
[Expression 2]
[0023]
However, after determining the average refractive index n = (nx + ny + nz) / 3 of the optical compensation film by another method, the retardation R (θ) at the incident angle θ is measured by changing the incident angle, and the equation (1) Refractive indexes nx, ny, and nz are determined from equation (2). Δn (θ) is an apparent birefringence at an incident angle θ, and d is a film thickness (nm).
[0024]
Many methods for measuring retardation have been proposed. In the present invention, any principle can be used as long as the retardation value can be obtained accurately. However, the range of retardation that can be measured accurately varies depending on the measurement method. So be careful. Although the three-dimensional refractive index varies depending on the measurement wavelength, a value measured at a wavelength of 550 nm is used here.
[0025]
The effect of the optical compensation mechanism of the optical compensation film in the present invention is different between K and R. Since an actual film has both R and K values which are not 0, it may be difficult to completely separate the two effects. Here, the difference between the two values will be described.
[0026]
The effect of the K value, particularly when the K value takes a negative value, is optically positive with a large refractive index in the film thickness direction when the liquid crystal stands up in response to an electric field in a voltage applied state. An optical compensation film that is optically biaxial and negative with respect to the liquid crystal cell and has a smaller refractive index in the film thickness direction than that in the in-plane direction. Compensates and improves viewing angle characteristics.
[0027]
In addition, when the optical compensation film of the present invention is used in a 90 ° twisted nematic mode liquid crystal display device, not only the viewing angle compensation but also the driving voltage is reduced by optimizing the bonding angle between the R value and the liquid crystal cell and polarizing plate. Can be made. This is effective not only when a normal 90 ° twisted nematic liquid crystal cell is used but also when combined with a pixel division method cell. Particularly in the normally white mode, when a sufficient black level cannot be obtained due to the presence of liquid crystal that does not rise in the film thickness direction at a certain voltage, the black level at the front is compensated optically by the R value. Can be improved, that is, the drive voltage can be lowered.
[0028]
The optical anisotropy of the optical compensation film of the present invention needs to satisfy 0 ≦ R <80 (nm) and −300 <K <−140 (nm) measured with light having a wavelength of 550 nm.
[0029]
As described above, the high-quality 90 ° twisted nematic mode display device has its ΔnLC · d set to approximately 400 to 500 nm with the measurement light of 550 nm. This value is the K value of the liquid crystal cell when the liquid crystal is perfectly aligned in the voltage applied state, but the K value in the voltage applied state is smaller than this because it is not actually vertically aligned. It becomes. Normally, gradation display is also performed in the high-quality 90 ° TN mode, so optimization of the K value of the optical compensation film is not simple. However, as a result of considering the gradation display, if the K value range of the optical compensation film is in the range of −300 <K <−140 (nm), the viewing angle characteristics of the liquid crystal cell having the above-described ΔnLC · d It was found that the effect of improving When the K value deviates from this range, the compensation effect is reduced. Strictly speaking, it is preferable to optimize the K value within the above range according to the purpose by the value of ΔnLC · d.
[0030]
On the other hand, the R value is preferably as small as possible for the purpose of viewing angle compensation only. Specifically, 0 ≦ R <20 (nm) is preferable. Even when 20 ≦ R <80 (nm), if the polarizing axis or absorption axis of the polarizing plate and the slow axis of the optical compensation film are set as parallel as possible, problems such as a decrease in front contrast can be prevented. be able to. Of course, even if 0 ≦ R <20 (nm), it is preferable that the polarization axis or absorption axis of the polarizing plate and the slow axis of the optical compensation film are as parallel as possible. In the case of R ≧ 80 (nm), even if the bonding angle is slightly shifted, problems such as a decrease in front contrast occur depending on the bonding angle, which is not preferable in productivity.
[0031]
Particularly in the normally white mode, when not only the viewing angle compensation but also the effect of reducing the driving voltage and improving the viewing angle characteristics by improving the front black level, R falls within the range of 20 ≦ R <80 (nm). It is preferable that there is. Below this range, the compensation effect is small and no further value is required. This also applies to the pixel division method if it is normally white. However, in this case, the bonding angle with the rubbing direction of the polarizing plate and the liquid crystal cell is important, and even if the R value is within the above range, the effect of lowering the driving voltage cannot be obtained unless it is optimized. It may cause a decrease in. If the R value is within the above range, the driving voltage reduction effect by optimizing the bonding angle can be obtained.
[0032]
In addition, the above three-dimensional refractive index has been described with respect to values measured with light having a wavelength of 550 nm. However, even a highly transparent resin such as that used in this application has wavelength dispersion of the three-dimensional refractive index. The matching of the birefringence wavelength dispersibility of the liquid crystal material and the retardation plate, which is a problem in the refraction mode, does not matter so much. That is, in this application, it is only necessary to optimize the three-dimensional refractive index and the bonding angle at 550 nm, which has the highest human visibility, and the influence of the three-dimensional refractive index wavelength dispersion of the resin is small. More specifically, when K and R values measured at 450 and 550 nm are K (450 nm), K (550 nm), R (450 nm), and R (550 nm), respectively, 0.90 <K (450 nm) / It is preferable that K (550 nm) <1.25, 0.90 <R (450 nm) / R (550 nm) <1.25, more preferably 0.95 <K (450 nm) / K (550 nm) <1. .10, 0.95 <R (450 nm) / R (550 nm) <1.10.
[0033]
In addition, the polarizing plate has an incident angle dependency of the degree of polarization. To compensate for this, a technique is disclosed in which a retardation film is bonded to the polarizing plate to compensate the incident angle dependency of the polarization characteristics. . A polarizing plate in which a retardation film that compensates for the polarization angle incidence angle dependency of the polarizing plate is bonded to the polarizing plate is used as a polarizing plate in the liquid crystal display device using the optical compensation film of the present invention. Also good.
[0034]
Furthermore, the optical compensation film of the present invention must be transparent. The haze is required to be 1% or less, and preferably 0.6% or less. Further, the transmittance needs to be 80% or more with a measuring light of 550 nm, and the transmittance is preferably 80% or more in the range of 400 to 700 nm. It is preferable to use a film that is not colored when observed with the human eye.
[0035]
Further, the film thickness is set in the range of 50 μm to 180 μm, and thickness unevenness is one of the causes of optical non-uniformity, so it is preferably within ± 5%, more preferably within ± 3%. is there.
[0036]
In order to produce an optical compensation film that satisfies these characteristics, it is important to select a resin and a film forming method. The optical compensation film of the present invention is produced by a solution casting method in terms of uniformity of optical properties. As a method for forming a transparent film, a melt extrusion method or the like is known as a known technique, but it is not a preferable method because of problems such as optical uniformity, foreign matter contamination, and generation of a gel substance.
[0037]
The solution casting method is a method in which a resin is dissolved in a solvent, cast on a flat substrate from a die, and dried to form a film. If it is soluble in the solvent, most of the resin can be formed into a film. . When the present inventors diligently examined the film forming conditions and the type of resin, the above-mentioned K and R values change to some extent depending on the film forming conditions. It was found that the selection of the resin is very important in order to obtain a product having a relatively large absolute value with high productivity. In other words, it is possible to increase the K value that brings the refractive index nz in the film thickness direction closer to the refractive indexes nx and ny in the in-plane direction by devising film forming conditions such as orientation relaxation by heat. It has been found that reducing nz and increasing the difference between nx and ny is difficult only by optimizing the solution casting film forming method, but can be easily controlled by selecting a resin.
[0038]
In the present invention, the selection of the resin is determined by the plane orientation parameter Z. That is, it is necessary that Z ≧ 0.0065. The method for determining this Z is shown below.
1. The solvent is methylene chloride, and the resin is dissolved to prepare a solution having a concentration of 4.0 g / dl (gram / deciliter).
2. 1. The solution is cast on a glass substrate by spin coating to form a resin thin film. As spin coating conditions, 0.5 g was dropped on a glass substrate at a temperature of 20 ° C., rotated at 4000 rpm for 30 seconds, and then stopped by providing a deceleration period of 3 seconds. A well-cleaned glass substrate is used, and a retardation of less than 0.1 nm is used in the range from 0 ° to 50 ° oblique incidence with the normal incidence angle of the glass substrate being 0 °. The measurement wavelength is 550 nm.
3. 2. The film thickness d (nm) of the resin thin film on the glass substrate is measured. The points to be measured are as follows. Then, three different points within the spot diameter of the light subjected to retardation measurement are measured, and the average value is adopted.
4). The direction perpendicular to the glass substrate is set to 0 °, and the x and y axes orthogonal to each other in the glass substrate plane are arbitrarily set. In the case of an oblique incidence of 50 ° in the plane including the x and y axes and orthogonal to the glass substrate The retardation (nm) is measured and the respective values are defined as Rx (50 °) and Ry (50 °). The wavelength of the measurement light is 550 nm.
5). Using the values measured in 3 and 4, the plane orientation parameter Z is defined as Z = | (Rx (50 °) + Ry (50 °)) | / (2d).
[0039]
If the plane orientation parameter Z thus defined is used, the orientation in the film thickness direction inherent to the resin, that is, the ease of decreasing nz (as described above in the optical compensation film of the present invention, compared to nx, ny). Therefore, it is preferable that nz is small. If this method is used, it is possible to express the ease of surface orientation of the resin in the solution casting method, and the selection of the resin is an important factor for obtaining the target K value, and the resin is selected using Z. be able to.
[0040]
In this case, the measurement method requires that the resin thin film has a thickness of about 100 to 600 nm and R (50 °) is about 1 to 5 nm. As a method for measuring the film thickness, a stylus type surface shape measuring method or an optical method is preferable, and as a phase difference measuring method, the Senarmon method or polarization modulation method which is a quenching position detecting method is preferable. The film thickness measurement of the resin thin film in the present invention is a trade name “alpha-step200” manufactured by Tencor Instruments Japan, which is a stylus type surface shape measuring apparatus, and the polarization modulation method is used for the phase difference measurement. The product name “M-150” manufactured by JASCO Corporation was used.
[0041]
In addition, it is preferable that the spot diameter at the time of phase difference measurement is 7 mm or less in diameter on a glass substrate in the state of perpendicular incidence. Since the retardation of the glass substrate is measured together with the retardation of the resin thin film, it is necessary to satisfy the above condition, and it is preferable that the retardation is as small as possible.
[0042]
As the film forming conditions of the solution casting method for forming the optical compensation film in the present invention, the solution is cast on a support such as a casting drum or a casting belt, and the solvent content is at least 20% by weight or less. Solution casting consisting of Step 1 of drying the film on the support until it is, and Step 2 of peeling the film containing the solvent, and then drying while transporting the film such as a tenter dryer from the support. In the method, the atmosphere temperature T1 (° C.) in the step 1 is dried at 15 ≦ T1 ≦ 50, and in the step 2, the apparent glass transition temperature of the resin containing the solvent is Tg ′ (° C.). In this case, the drying temperature is within the temperature range of (Tg′−50) ≦ T2 ≦ (Tg ′ + 50) until the solvent content is 5% by weight or more, and when the solvent content is less than 5% by weight ( g'-50) ≦ T3 ≦ (Tg it is necessary to dry continuously or sequentially raised in accordance with the transition of the '+ 20) its Tg in the temperature range of'. Since the viscosity of the solution concentration varies depending on the resin used, it must be changed each time, but the concentration is set between 3 wt% and 30 wt%. Moreover, although it changes with required R values, it is preferable that the tension concerning the film which arises in a drying process is the range of 0.5-5 kg / square cm.
[0043]
The amount of the solvent remaining in the film needs to be 1% by weight or less, and more preferably 0.5% by weight or less. The drying time in the film forming method is determined by the final film residual solvent amount. The method for measuring the residual solvent amount is determined by a dry weight method, a nuclear magnetic resonance spectrum method, or the like.
[0044]
The solvent is not particularly limited, but a known one can be used as long as the resin such as methylene chloride and dioxolane is dissolved and there is no problem in film forming property.
[0045]
In order to obtain the required R and K values, the conditions are set more finely within these ranges, but in order to obtain the target K value, the resin with the plane orientation parameter Z ≧ 0.0065 Must be used. There is a correlation between the plane orientation parameter Z defined in the present invention and the K value of the film.
[0046]
In a normal solution casting method that does not involve a stretching step, the K value is negatively large at a relatively early stage in which the solution is cast on a support and the solvent evaporates, and nz becomes nx, ny due to orientation relaxation in the drying step. Get closer to. Therefore, it is difficult to obtain −300 nm <K <−140 nm when the plane orientation parameter does not satisfy the above condition. The K value is negative and the absolute value tends to increase as the plane orientation parameter increases, but when the K value becomes smaller than −300 nm, the drying temperature is set higher within the above range in the film forming process, It can be controlled by relaxing the orientation. In the region where the plane orientation parameter is smaller than 0.0065, it is difficult to obtain the K value in the above range under the conditions of the casting film forming method, and a special condition inferior in productivity and a stretching process are added. The need arises.
[0047]
  The plane orientation parameter Z is greatly influenced by the skeleton and molecular weight of the resin. If the molecular skeleton is the same, the higher the molecular weight, the larger the Z tends to be. As a result of examining many resins, it was found that those having a polyarylate skeleton have a relatively large Z value. The following structural formula(2)(7) to the optical compensation film of the present inventionTreeThe oil skeleton is shown. These may be single polymers, copolymers or blends. In the following structures, it is preferable that the molecular weight is large, but if the molecular weight is too large, a problem may occur in the film-forming property, etc., so it is necessary to consider the film-forming property.is there. Structural formulaIn (2) and (3), the molecular weight is preferably 20,000 or more in terms of polystyrene. Further, from the viewpoint of heat resistance, the glass transition point temperature of the optical compensation film is preferably 130 ° C. or higher.
[0049]
[Chemical 2]
[0050]
[Chemical Formula 3]
[0051]
[Formula 4]
[0052]
[Chemical formula 5]
[0053]
[Chemical 6]
[0054]
[Chemical 7]
[0055]
[referenceExample 1]
  A polycarbonate resin having a repeating structure represented by the structural formula (1) and having a polystyrene equivalent molecular weight of 67,000 is dissolved in methylene chloride to prepare a 15% by weight solution, which is cast on a casting belt support from a die, and contains a solvent. A solution comprising Step 1 of drying the film on the support until the content is at least 18% by weight, and then Step 2 of peeling the film containing the solvent and drying the film while transporting the film with a tenter dryer In the casting method, the atmosphere temperature T1 (° C.) in step 1 is dried within a range of 18 ≦ T1 ≦ 35. In step 2, the apparent glass transition temperature of the resin containing the solvent is Tg ′ (° C.). The drying temperature is within the temperature range of (Tg′−10) ≦ T2 ≦ (Tg ′ + 20) until the solvent content is 5% by weight or more. Content is less than 5 wt% and dried by continuously or sequentially raised in accordance with the transition of 'its Tg in the temperature range of (+ 20 (Tg'-20) ≦ T3 ≦ Tg)'. The characteristics of the obtained film were K = −150 nm and R = 50 nm. In determining the R and K values, a product name “M-150” manufactured by JASCO Corporation was used for phase difference measurement, and an Abbe refractometer product name “2T” manufactured by Atago Co., Ltd. was used for measurement of the average refractive index. The haze was 0.3%, the residual solvent amount was 0.3% by dry weight method, and the film thickness was 85 μm using an electronic micrometer. On the other hand, the plane orientation parameter was measured by the above-described method using this resin, and Z = 0.068.
[0056]
【Example1]
  A 19% by weight solution is prepared by dissolving a polyarylate resin having a repeating structure of the structural formula (2) and having a molecular weight of 22,000 in terms of polystyrene in methylene chloride.referenceA film was formed by the solution casting method under the same conditions as in Example 1.referenceAs a result of measurement in the same manner as in Example 1, the properties of the obtained film were K = −250 nm and R = 20 nm. The haze was 0.3%, the residual solvent amount was 0.3% by dry weight method, and the film thickness was 90 μm using an electronic micrometer. On the other hand, when the plane orientation parameter was measured using this resin, Z was 0.0099.
[0057]
【Example2]
  In the structural formula (3), a polyallylate having a repeating structure of m: n = 37: 63 (mol%) and having a polystyrene equivalent molecular weight of 27000 and a polycarbonate copolymer resin are dissolved in methylene chloride to prepare a 20 wt% solution. AndreferenceA film was formed by the solution casting method under the same conditions as in Example 1.referenceAs a result of measurement in the same manner as in Example 1, the properties of the obtained film were K = -190 nm and R = 8 nm. The haze was 0.3%, the residual solvent amount was 0.3% by dry weight method, and the film thickness was 92 μm using an electronic micrometer. On the other hand, when the plane orientation parameter was measured using this resin, Z was 0.0074.
[0058]
[Comparative Example 1]
  A 10% by weight solution is prepared by dissolving a triacetyl cellulose resin having a molecular weight in terms of polystyrene of 20000 in methylene chloride.referenceA film was formed by the solution casting method under the same conditions as in Example 1.referenceAs a result of measurement in the same manner as in Example 1, the properties of the obtained film were K = −40 nm and R = 5 nm, and those satisfying the object of the present invention were not obtained. The haze was 0.3%, the residual solvent amount was 0.4% by weight by the dry weight method, and the film thickness was 89 μm using an electronic micrometer. On the other hand, when the plane orientation parameter was measured using this resin, Z = 0.014.
[0059]
【Example3]
  For the liquid crystal material, a product name “ZLI4792” manufactured by Merck Co., Ltd., which is doped with a small amount of chiral agent, is used. A liquid crystal display device was created by installing it in Mary White mode. When a backlight was placed on the opposite side of the observation side and evaluated by transmission, the voltage required to obtain a contrast of 50 or more due to luminance at the front was 4.6 V or more. In addition, eight-gradation display was performed, and a viewing angle range with relatively little gradation inversion, black crushing, white blanking, etc. and a contrast of 10 or more was measured, and 10 °, 10 °, and 25 ° in the vertical and horizontal directions, respectively. 25 °.
[0060]
  Next example1The optical compensation film formed in (1) was placed between the observation-side polarizing plate and the liquid crystal cell in the same manner in accordance with the slow axis of the film and the rubbing direction on the observation side of the liquid crystal cell. The voltage required to obtain a contrast of 50 or more due to luminance at the front is 4.6 V or more. In addition, eight-gradation display was performed, and a viewing angle range with relatively little gradation inversion, black crushing, white blanking, etc. and a contrast of 10 or more was measured, and 10 °, 10 °, and 40 ° in the vertical and horizontal directions, respectively. 40 °. In particular, the change in color tone due to the use of the optical compensation film was not a problem.
[0061]
【Example4]
  referenceExample except that the optical compensation film formed in Example 1 was used3In the same manner as described above, the effect of the optical compensation film was evaluated by viewing angle. The voltage required to obtain a contrast of 50 or more due to luminance at the front is 4.6 V or more. In addition, eight-gradation display was performed, and a viewing angle range with relatively little gradation reversal, black crushing, white blanking, etc. and a contrast of 10 or more was measured, and 10 °, 10 °, and 30 ° in the vertical and horizontal directions, respectively. 30 °. In particular, the change in color tone due to the use of the optical compensation film was not a problem.
[0062]
[Comparative Example 2]
  Example except that the optical compensation film formed in Comparative Example 1 was used3In the same manner as described above, the effect of the optical compensation film was evaluated by viewing angle. The voltage required to obtain a contrast of 50 or more due to luminance at the front is 4.6 V or more. In addition, eight-gradation display was performed, and a viewing angle range with relatively little gradation inversion, black crushing, white blanking, etc. and a contrast of 10 or more was measured, and 10 °, 10 °, and 25 ° in the vertical and horizontal directions, respectively. 25 °, and the effect of the optical compensation film was not confirmed.
[0063]
【Example5]
  Example3Using the liquid crystal cell created in Step 1, the backlight side polarizing plate polarization axis and the backlight side liquid crystal cell rubbing direction were each 45 °, the observation side polarizing plate polarization axis and the observation side liquid crystal cell rubbing direction were 135 ° each,referenceThe optical compensation film formed in Example 1 was bonded between the observation-side polarizing plate and the liquid crystal cell so that the slow axis of the optical compensation film was 150 °, and a normally white liquid crystal display device was produced.3Evaluation was performed in the same manner as above. The voltage required to obtain a contrast of 50 or more due to luminance at the front is 3.8 V or more. In addition, eight-gradation display was performed, and a viewing angle range with relatively little gradation reversal, black crushing, white blanking, etc. and a contrast of 10 or more was measured, and 10 °, 10 °, and 30 ° in the vertical and horizontal directions, respectively. 30 °. Low drive voltage and viewing angle compensation effect were confirmed. In particular, the change in color tone due to the use of the optical compensation film was not a problem.
[0064]
【Example6]
  The rubbing direction of the alignment film on the backlight side substrate is 45 ° and 225 °, the rubbing direction of the alignment film on the observation side substrate is 135 ° and 315 °, respectively, and one pixel is divided into two. A pixel alignment division cell was prepared in which the rubbing direction of the backlight-side substrate was 45 ° and the rubbing direction of the observation-side alignment film was 135 °, and similarly 225 ° and 315 ° were aligned. Examples of liquid crystal materials3The same was used. The twist angle was 90 ° and the pretilt angle was 3 °. A normally white liquid crystal display device was prepared by pasting together the polarizing axis of the backlight side polarizing plate at 45 ° and the polarizing axis of the observation side polarizing plate at 135 °.3And evaluated in the same manner. The voltage required to obtain a contrast of 50 or more due to luminance at the front is 5 V or more. In addition, eight-gradation display was performed, and a viewing angle range with relatively little gradation reversal, black crushing, white blanking, etc. and a contrast of 10 or more was measured, and 30 °, 30 °, 40 ° in the vertical and horizontal directions, respectively. 40 °.
[0065]
  In addition, between the observation side polarizing plate and the liquid crystal cell of this liquid crystal display device,3Example of bonding the optical compensation film formed in step 1 so that the slow axis is 150 °3And evaluated in the same manner. The voltage required to obtain a contrast of 50 or more due to luminance at the front is 4.5 V or more. In addition, eight-gradation display was performed, and a viewing angle range with relatively little gradation reversal, black crushing, white blanking, etc. and a contrast of 10 or more was measured, and 30 °, 30 °, 45 ° in the vertical and horizontal directions, respectively. 45 °. The low driving voltage and viewing angle compensation effect were also confirmed in the pixel-aligned divided cells. In particular, the change in color tone due to the use of the optical compensation film was not a problem.
[0066]
【The invention's effect】
The present invention relates to an optical compensation film used as a viewing angle compensation plate having characteristics of 0 ≦ R <80 (nm) and −300 <K <−140 (nm), which is used in an optical rotation mode twisted nematic liquid crystal display device. In view of the above, it is possible to provide a viewing angle compensator having high quality and excellent productivity by using a film formed by a solution casting method using a polymer resin having a specified plane orientation parameter. It has such an effect.
[0067]
Furthermore, in an optical rotation mode twisted nematic type liquid crystal display device using such an optical compensation film of the present invention as a viewing angle compensation plate, it has been difficult to obtain optical characteristics that have been difficult to obtain by using a plurality of uniaxially stretched retardation films. Since it can be obtained by using only one optical compensation film, a low-cost liquid crystal display device can be obtained with high productivity.

Claims (3)

An optical compensation film used as a viewing angle compensator for an optical rotation mode twisted nematic type liquid crystal display device having the following formula (I)
(I)
(Where Y is
Alternatively, a direct bond, R is H, and the substitution position of the rightmost CO group is the para-position or meta-position. When Y is a direct bond, the substitution position of the rightmost CO group is the para position. )
A polyarylate having a molecular weight of 20,000 or more in terms of polystyrene containing the repeating unit represented by is cast on a support, and a film is formed on the support until the solvent content is at least 20 wt% or less. It consists of Step 1 for drying, and Step 2 for peeling the film containing the solvent, and then peeling the film from the support and drying it while transporting. In step 2, assuming that the glass transition temperature of the apparent resin due to the inclusion of the solvent is Tg ′ (° C.), the drying temperature is (Tg′−) until the solvent content is 5% by weight or more. 50) ≦ T2 ≦ (Tg ′ + 50), and if the solvent content is less than 5% by weight, the transition of the Tg ′ occurs in the temperature range of (Tg′−50) ≦ T3 ≦ (Tg ′ + 20). Continuously or together An optical compensation film obtained by forming a film by sequentially warmed solution casting method of drying, the membrane plane direction of the refractive index measured with light having a wavelength of 550nm and nx (slow axis) ny (fast axis), where the refractive index in the film thickness direction that is orthogonal to them is nz, and the film thickness is d (nm), R = (nx−ny) × d and K = (nz− An optical compensation film in which the optical characteristics represented by (nx + ny) / 2) × d are 0 ≦ R <80 (nm) and −300 <K <−140 (nm). The repeating unit (I) of the polyarylate is represented by the following formula (I) -1
(I) -1
The optical compensation film of claim 1 is.   An optical rotation mode twist nematic type liquid crystal display device using the optical compensation film according to claim 1 as a viewing angle compensation plate.