JPH0259702A - retardation plate - Google Patents

Abstract

PURPOSE:To obtain a composite polarizing plate used for a liquid crystal display body by uniaxially stretching a polycarbonate polymer film or sheet thereby forming the plate. CONSTITUTION:The polycarbonate polymer film or sheet which has the average value of the intrinsic viscosity [eta] ranging 0.35 to 0.7 and <=10% deviation width thereof is uniaxially stretched. The measured value of the retardation defined by the product of double refractive index and thickness of the formed film or sheet is in a 30 to 1,200nm range and the deviation width of the average value thereof is confined to <=7%. The composite polarizing plate which is less restricted at the time of making color display and is applicable to new applications including a liquid crystal display device is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Applications wt] The present invention relates to a retardation plate that can be applied to liquid crystal display devices and the like.

[Prior Art] A retardation plate is a film or sheet-like material having birefringence. Since the light transmitted through the retardation plate has different refractive indexes in two orthogonal directions, a phase difference occurs between the orthogonal rays after passing through the retardation plate.

As a retardation plate, there is a so-called 1/4 λ plate which has a function of producing a phase difference of 1/4 λ with respect to the wavelength λ of an incident light beam, which is currently commercially available and in practical use. This 1/
The 4λ plate is obtained by uniaxially stretching a cellulose acetate film. A 1/4λ plate becomes a circularly polarizing plate when attached at a 45 degree angle to the optical principal axis of a linear polarizing plate, and has an anti-glare function that cuts reflected light.
It is used in various anti-glare materials, including T-filters.

In addition to the above-mentioned cellulose-based resin, vinyl chloride-based resin (PTK
5-84477, JP-A-56-125702, etc.), polycarbonate resins (Japanese Patent Publication No. 41-121, etc.)
90, JP-A-56-130708, etc.), acrylonitrile resins (JP-A-66-130702, etc.), styrene resins (JP-A-56-125708, etc.), polyolefin resins (JP-A-56-125708, etc.) Showa 60-2450
Publication No. 2, etc.) have been proposed, but all of them are letterage.

This is a so-called 1/4 λ plate with a measured value of around 135 nm. Note that the letter silane value (R value) is expressed as the product of the thickness d of the film or sheet and the birefringence Δn of the film, that is, R=Δnxd.

On the other hand, JP-A-61-186987, JP-A-60-
As described in Japanese Patent No. 26822, a liquid crystal display device in which the twist angle of liquid crystal molecules is 90 degrees, and a pair of polarizing plates are arranged above and below a liquid crystal cell so that their absorption axes are perpendicular or parallel! Attempts have also been made to improve display quality by applying a retardation plate to TN type liquid crystal display devices (generally referred to as TN type liquid crystal display devices, which have been applied to watches, calculators, etc.).

Furthermore, in recent years, with the increase in display capacity and the demand for enlarged display screens, the twist angle of the axillary molecules has been increased to 90 degrees or more, that is,
130 to 270 degrees (generally referred to as STN type liquid crystal display devices). However, the black and white display that was possible with conventional TN type liquid crystal display devices, In this case, coloration occurs due to the birefringence of liquid crystal molecules, making it impossible to display black and white.-For example, the background color is yellow-green and the display color is dark blue.If the display device has such a hue, In order to solve this problem, for example, as described on page 84 of the October 1987 issue of Nikkei Micro Devices, polarized A method is shown in which an additional achromatic liquid crystal cell is added to the STN type liquid crystal cell as an optical compensation plate to solve the problem of coloring and enable black and white display.

[Problems to be Solved by the Invention] A method of adding another achromatic liquid crystal cell as an optical compensator to the STN type liquid crystal cell described above eliminates coloring and makes black and white display possible, but (1) it is expensive; is high and is less economical,
There are problems such as (2) weight and (8) thickness, and in addition to improving the display performance described above, it is required to solve these problems in combination.

It is theoretically conceivable to use a retardation plate instead of this achromatic liquid crystal cell, but with the conventional 174λ plate, (1) the retardage value does not match optically. (2
) The optical axis is not constant.

(8) Optical color unevenness is large and homogeneous black and white display cannot be achieved. (4) It is not possible to produce a good walk r+'T' IJ over a long length. For these reasons, it cannot be applied to new uses such as the above-mentioned liquid crystal display device.

[Means to solve the problem]

The present invention was completed as a result of repeated research in view of the above points, and is as follows.

That is, in the present invention, the average value of the intrinsic viscosity [η] is 0.86.
A film or sheet formed by uniaxially stretching a polycarbonate polymer film or sheet having a birefringence index (Δn) of 0.7 and a deviation width of 10% or less. The measured value of retardage carbon defined as the product of and thickness (d) is 30 to 1200 nm.
The present invention relates to a retardation plate which is within the range of 7% and whose average deviation is 7% or less, and a composite polarizing plate formed by laminating the retardation plate on a polarizing plate.

The retardation plate of the present invention is a novel retardation plate that has an appropriate retardage value that is constant in the longitudinal direction and is optically less uneven in color. Retardage value is 30-120
A range of 0 nm is used, preferably 20 nm.
It is adjusted in the range of 0 to 11000n. A more appropriate retardage value is selected depending on the specific application.

For example, the retardage value is 200 to 850.
For example, those in the range of 475 nm to 625 nm can be used for liquid crystal display devices.

In the present invention, the average intrinsic viscosity [η] of the polycarbonate polymer film or sheet used is 0.86 to 0.86.
7 Preferably, by specifying it in the range of 0.4 to 0.66, more preferably from 0.46 to 0.6, and adjusting the amplitude to 10% or less, preferably 7% or less, the longitudinal It has been discovered that a retardation plate that is directionally stable and optically extremely homogeneous can be obtained. Specifically, the average deviation of the retardation value of the retardation plate is 7%.
Below, preferably 6% or less, more preferably 5% or less, a retardation plate that is optically homogeneous over a long length can be obtained, and in particular, it has been devised to improve the display quality when used in a cross-crystal display device. It is what was done.

The polycarbonate resin used in the present invention is mainly
A straight polycarbonate or copolymerized polycarbonate having a bisphenol skeleton, and 4,4'
-Dihydroxydiphenylalkanes or their halogen-substituted products by the phosgene method or the transesterification method. 4.4'-Dihydroxydiphenylalkane or substituted products thereof are exemplified by 4,
4'-dihydroxydiphenylmethane, 4.4'-dihydroxydiphenylethane, 4゜4'-dihydroxydiphenylbutane, 4.4'-dihydroxydiphenyl-
2,2-propane, 8,8-dibromo-4,4'-dihydroxydiphenyl-2,2-propane, 8,8'-dichloro-4,4'-dihydroxydiphenyl-2,2-
Examples thereof include propane, 8,8',5,5'-tetrabromo-4°4'-dihydroxydiphenyl-2,2-propane, and the like.

Furthermore, blends of these polycarbonate resins with styrene resins and modified products thereof are also effective in the present invention.

In order to use these polycarbonate resins as a retardation plate, the polycarbonate resin is formed into a film or sheet by a known film forming method, such as a solvent casting method, a calendar method, or an extrusion method, and then stretched appropriately in the -axial direction. This is achieved by

In order to obtain an optically homogeneous retardation plate over a long length with a small fluctuation in the average value of retardage according to the present invention, the original film or sheet must have good thickness accuracy and be as optically homogeneous as possible. something is needed. It is undesirable for Gly lines to occur on the film or sheet during molding. Normally, when forming a film or sheet, minute orientations often occur, and it is important to reduce these minute orientations prior to stretching. Heat treatment is an effective method for reducing micro-orientation before stretching. In order to produce the retardation plate of the present invention, the film or sheet is heat-treated at a temperature equal to or higher than the heating deformation temperature before stretching. In the case of a polycarbonate film or sheet, if heat treatment is performed at a temperature of 130 to 200°C for about 6 minutes to a temperature of 0.1 before stretching, the birefringence of the original film or sheet will be less than lXl0-' and almost The result is a completely unoriented film or sheet.

A method for uniaxially stretching the raw film or sheet obtained in this way is a transverse stretching method using a tenter method.
Known uniaxial stretching methods such as axial stretching method, inter-roll compression stretching method, longitudinal-axial stretching method using rolls with different peripheral speeds, inter-roll compression stretching method, longitudinal-axial stretching method using rolls with different peripheral speeds, etc. It is possible to adopt ξ.

In the present invention, in order to obtain a retardation plate with small optical unevenness, the film width A before stretching and the film width B after stretching are
The neck-in rate defined as (100x(A-B)/
It is necessary to suppress A) to 10% or less, preferably 6% or less, and more preferably substantially 0. Therefore, the most effective stretching method in the present invention is a transverse uniaxial stretching method using a tenter method that does not substantially cause neck-in.

Transverse uniaxial stretching by the tenter method generally consists of eight steps: a preheating step, a stretching step, and a heat treatment step. The preheating step is useful because it has the same role as the heat treatment step of reducing the birefringence of the film or sheet to substantially zero. The stretching process is the most important process for making a retardation plate, and although conditions vary depending on the type of polycarbonate resin, thickness, and target retardation size of the retardation plate, the present invention has minimal optical unevenness. In order to obtain a retardation plate, it is important to carry out uniform stretching, and therefore it is essential to select the stretching temperature under appropriate conditions.

The stretching temperature needs to be higher than the temperature at which the apparent yield point disappears in the stress-strain curve of the tensile test. If the stretching temperature is in the range where the yield point appears on the stress-strain curve or below, the stretching will be uneven, resulting in uneven thickness of the stretched product, resulting in letterage,
The amplitude and rate of change of the current will increase.

The stretching ratio is not particularly limited, but is about 1.2 to 6 times, preferably about 1.2 to 4.0 times.

The heat treatment step after stretching is a useful step for improving the dimensional stability of the obtained stretched film or sheet and improving the uniformity of the letter silane, and the heat treatment temperature ranges from below the stretching temperature to around the heat distortion temperature. is preferred.

The heating deformation temperature is JISK678518.6kgf.
It refers to the value measured at /-.

The retardation in the present invention can be measured using a polarizing microscope, a spectrophotometer, etc., and the average value (R) of the retardation can be determined as follows. A sample of 20cWIX20 is taken from the stretched film or sheet, and the average value of the 16 points measured at 16 equally selected points is calculated. Similarly, take 10 samples in the same manner as above at intervals of 20 m in the longitudinal direction and measure the average value.
Let R be the value obtained by further averaging the average value of 0 points. Further, the value (expressed as a percentage) obtained by dividing the difference between the maximum value and the minimum value of the average values of these 10 points by R is defined as the amplitude of the fluctuation.

Further, the intrinsic viscosity [η] of the polycarbonate polymer film or sheet in the present invention is measured in the following manner by sampling at 10 locations at 20 m intervals in the same manner as above. Accurately weigh the resin, dissolve it uniformly in IQQcc methylene chloride, and measure 30% using an Ostwald viscometer.
Its specific viscosity ηsp is measured at a constant temperature of °C. By changing the liquid concentration at several points, ηsp is measured in the same way, ηSi)/c is plotted on the graph, and the limiting viscosity [η] is determined when C → O is determined by the following formula. Here, the above 10 points [η
] ηsp/c = [η] 10k [η] Secret: The average value of the average values independent of the molecular weight is displayed as [η]. Furthermore, the amplitude is the difference between the maximum and minimum values of [η] at the 10 points above.
) divided by the average value (expressed as a percentage). Therefore, the amplitude of vibration includes variations in measured values.

The retardation plate of the present invention may be used alone in a liquid crystal display device, or can be applied to a liquid crystal display device etc. by laminating it on one side of a polarizing plate to form a composite polarizing plate.

Any polarizing plate can be used as the polarizing plate constituting the composite polarizing plate of the present invention. - For example, a film made of polyvinyl alcohol or a derivative thereof is uniaxially stretched and oriented, iodine or dichroic dye is adsorbed as a polarizing element, and then a non-optically active cellulose film such as cellulose triacetate is formed. is pasted on both sides.

Furthermore, a dichroic dye is blended with a hydrophobic resin such as a polyene polarizing plate, polyethylene terephthalate, etc. obtained by desalination rll of a polyvinyl chloride film or a dehydration treatment of a polyvinyl alcohol film. An axially oriented polarizing plate or the like can be used. Among them, a polyvinyl alcohol film that adsorbs yotsudine or dichroic dye, and is laminated on both sides with a cellulose film such as cellulose triacetate as a protective film to a polarizer oriented along the - axis. , preferred from the viewpoint of polarization characteristics and hue characteristics.

In order to form the composite polarizing plate of the present invention using the retardation plate and polarizing plate of the present invention, the optical axis of the polarizing plate and the optical axis of the retardation plate are set at 15 to 75 degrees, preferably 30 to 60 degrees, More preferably, this is achieved by bonding at an angle of 40 to 50 degrees using a pressure-sensitive adhesive or an adhesive.

Even more straight! I: A structure in which the protective film on one side of the polarizing plate is removed and the retardation plate is bonded directly to the polarizer using an adhesive or adhesive, or a hydrophobic polymer film and two-color without a protective film. Also included within the scope of the composite polarizing plate of the present invention is a linearly polarizing plate made of a combination of polarizing dyes, with a retardation plate attached to one side using an adhesive or a pressure-sensitive adhesive.

〔Effect of the invention〕

The retardation plate or composite polarizing plate obtained in this way has good optical performance and at the same time
Since it can pass the accelerated durability test at ℃ x 90% R1, it can be used for new applications such as liquid crystal display applications.

An example of application to a liquid crystal display is shown below.

(1) If a retardation plate is placed above the polarizing plate of a TN type liquid crystal display device in which the twist angle of U-product molecules is 90 degrees, a rainbow pattern can be seen from any direction when viewed through polarized sunglasses. The display quality is significantly improved compared to the case of using a conventional elliptically polarizing plate.

(2) If a retardation plate is placed below the upper polarizing plate of a TNg liquid crystal display in which the twist angle of the liquid crystal molecules is 90 degrees, interference colors in the liquid crystal layer can be uniformly eliminated over a large screen. , display quality is significantly improved.

(8) S in which the twist angle of liquid crystal molecules is 130 to 270 degrees
In a TN type liquid crystal display device, coloration occurs due to birefringence of the liquid crystal layer. The retardation plate of the present invention is attached between the upper polarizing plate or the lower polarizing plate and the liquid crystal cell of an STN crystal display device so that its optical axis is in the range of 30 to 60 degrees, preferably 40 to 50 degrees. By combining these values, display quality can be improved. By arranging the pair of polarizing plates so that their optical axes are perpendicular or nearly perpendicular, or parallel or nearly parallel, black-and-white display is possible and display quality is improved.

[Example] The present invention will be explained below with reference to Examples. The present invention is not limited to these. The retardage and n values of the retardation plates in the Examples were measured using a Senarmont compensator (546 nm) attached to a polarizing AM mirror, and a halogen lamp was used as the light source. The linearly polarizing plate in the example was prepared by, for example, the method described in JP-A-61-20008, in which iodine as a dichroic dye was uniaxially adsorbed and aligned on polyvinyl alcohol. If necessary, a transparent non-optically active polymer film such as cellulose triacetate is laminated as a protective film.

Example 1 A transparent polycarbonate film with a thickness of 200 μm and a length of 300 m with an [η] of 0.558 and a swing width of 4.2% was used as a raw film in a tenter equipment made by Hirano Metal (2 m width x 9, Transverse uniaxial stretching was carried out using a long film.

The original film was heated to 190°C in the preheating process to make the birefringence of the original film 0.8X10, and then stretched 1.8 times horizontally uniaxially at 170°C in the stretching process.
Heat treatment was performed at 0° C. to obtain a stretched film with a thickness of about 110 μm.

The stretched film had an R of 650 nm and a fluctuation width of 4.0% in the longitudinal direction, and a retardation plate with little optical unevenness over a long length was obtained. This retardation plate was attached to one side of a polarizing plate using an acrylic adhesive so that the optical axis was at about 45 degrees to obtain a composite polarizing plate. Furthermore, when this retardation plate is used by adhering it between the liquid crystal cell and the upper polarizing plate of a liquid crystal display device in which the twist angle of the liquid crystal molecules is 200 degrees, it is possible to create an almost monochrome display with a white background and a black display area. Thus, a liquid crystal display device with good display quality without rainbow pattern color unevenness was obtained.

Example 2 As a raw film, a transparent polycarbonate film with a thickness of 200 μm and a length of 300 m, with [η] of 0.485 and a width of 6.4%, was subjected to horizontal uniaxial stretching using the same tenter equipment as in Example 1. Ta. The raw film is heated to 190''C in the preheating process, and the birefringence of the raw film is set to 0.
After the film was made into 2X10, it was stretched 1.7 times horizontally uniaxially at 172°C in the stretching process, and heat treated at 140"C to obtain a stretched film with a thickness of about 120 μm. The stretched film had an R of a o o We obtained a retardation plate with a longitudinal deflection width of 5.6% in nm and little optical unevenness over a long length.This retardation plate was bonded to one side of the polarizing plate using an acrylic adhesive. A composite polarizing plate was obtained by pasting the optic axis at approximately 45 degrees.Furthermore, this retardation plate was adhered between the liquid crystal cell and the upper polarizing plate of a liquid crystal display device in which the twist angle of the liquid crystal molecules is 200 degrees. When used by bonding with an agent, a nearly monochrome display with a white background and a black display area was possible, and a liquid crystal display device with good display quality without rainbow pattern color unevenness was obtained.

Example 8 As a raw film, a transparent polycarbonate film with a thickness of 200 μm and a length of 300 m, which has an [η] of 0.585 and a swing width of 6.7%, was transferred to a pressure roll facility (diameter 2
Compression stretching was carried out along the longitudinal axis using a film with a length of 60 cm and a surface length of 700 cm. The original film was passed through a 160°C in a heating oven and stretched 1.6 times in the longitudinal direction to a thickness of about 125μ.
A stretched film of m (neck-in rate 8%) was obtained. The stretched film had an R of 920 nm and a longitudinal deflection width of 6.4%, yielding a retardation plate with little optical unevenness over a long length. This retardation plate was attached to one side of a polarizing plate using an acrylic adhesive so that the optical axis was at about 45 degrees to obtain a composite polarizing plate. Furthermore, when this retardation plate was attached via an adhesive between the liquid crystal cell and the upper polarizing plate of a liquid crystal display device in which the twist angle of the liquid crystal molecules is 200 degrees, the background color was white and the display area was black. A liquid crystal display device with good display quality was obtained, with almost black-and-white display possible and no rainbow-like color unevenness.

Comparative Example 1 [71] Mo 0.545. A stretched film having a thickness of about 110 μm was obtained by carrying out the same procedure as in Example 1 except that a polycarbonate raw film having a deflection width of 10.5% was used. The stretched film had an R of 5401 m and a sagging width in the longitudinal direction of 16.9%, and compared to Example 1, only a retardation plate with inferior homogeneity was obtained.

Comparative Example 2 A stretched film with a thickness of about 120 μm was obtained in the same manner as in Example 2, except that a polycarbonate raw film with [η] of 0.498 and a deviation width of 11.2% was used. Ta. The stretched film had an R of 830 mm and a deflection width in the longitudinal direction of 18.5%, and compared to Example 2, only a retardation plate with inferior homogeneity was obtained.

Comparative Example 8 A stretched film with a thickness of about 120 μm was obtained in the same manner as in Example 8, except that a polycarbonate raw film with [η] of 0.582 and a deflection width of 10.8% was used. . The stretched film had an R of 895 mm% and a deflection width in the longitudinal direction of 14.2%, and compared to Example 8, only a retardation plate with inferior homogeneity was obtained.

Procedural amendment (voluntary) 1. Display of incidents 1988 Patent Application No. 212121 2, Title of Invention retardation plate 3゜ 4゜ person who makes corrections Relationship with the incident address name representative implantation teenager

Claims (2)

[Claims] (1) Formed by uniaxially stretching a polycarbonate polymer film or sheet with an average value of intrinsic viscosity [η] in the range of 0.85 to 0.7 and a fluctuation width of 10% or less A film or sheet that is
The measured value of retardation defined as the product of birefringence (Δn) and thickness (d) is in the range of 30 to 1200 nm, and the average value fluctuation is 7% or less. Retardation plate. (2) A composite polarizing plate obtained by laminating the retardation plate according to claim 1 on a polarizing plate.