JP2841376B2 - Phase difference plate - Google Patents

Description

The present invention relates to a retardation plate applicable to a liquid crystal display device and the like.

[Conventional technology]

The retardation plate is a film or sheet having birefringence. Since the light transmitted through the phase difference plate has different refractive indices in two directions orthogonal to each other, a phase difference occurs between the orthogonal light after transmission.

As a retardation plate, there is a so-called 板 λ plate having a function of generating a 差 λ phase difference with respect to the wavelength λ of an incident light beam, which is currently commercially available and practically used. This 1 / 4λ plate is obtained by stretching a cellulose acetate film in a uniaxial direction. The 1 / 4λ plate becomes a circular polarizer when bonded at an angle of 45 degrees to the optical axis of the linear polarizer, and has an anti-glare function that cuts reflected light. Used in materials.

As the polymer material constituting the 1 / 4λ plate, in addition to the above-mentioned cellulose resin, a vinyl chloride resin (Japanese Patent Publication No.
JP-A-34477, JP-A-46-125702, etc.), polycarbonate-based resin (JP-B-41-12190, JP-A-56-125702)
No. 130708), acrylonitrile resins (Japanese
No. 56-130702), styrene resins (Japanese Patent Application Laid-Open No.
No. 5703), polyolefin-based resin (JP-A-60-2450)
No. 2) have been proposed, but all are so-called 1 / 4λ plates having a measured retardation of around 135 nm. The retardation value (R value) is a product of the thickness d of the film or sheet and the birefringence Δn of the film,
That is, R = Δn × d.

On the other hand, as described in JP-A-61-136937 and JP-A-60-26322, the twist angle of liquid crystal molecules is 90%.
A liquid crystal display device in which a pair of polarizing plates are arranged above and below a liquid crystal cell so that their absorption axes are orthogonal or parallel (generally referred to as a TN type liquid crystal display, which has been applied to watches, calculators, etc.) Attempts have also been made to improve the display quality by applying a retardation plate to the optical disk.

Furthermore, in recent years, with the increase in display capacity and the demand for enlargement of the display screen, the twist angle of liquid crystal molecules is 90 degrees or more, that is,
A liquid crystal display device having an angle of about 180 to 270 degrees has been developed (generally referred to as an STN type liquid crystal display device). But conventional T
In the STN-type liquid crystal display device, coloring caused by birefringence of liquid crystal molecules occurs, and black-and-white display cannot be performed in the STN-type liquid crystal display device. For example, the background color is yellow-green, and the display color is dark blue. If the display device has such a hue, there are many restrictions when performing color display such as multi-color and full-color.To solve this problem, for example, Nikkei Microdepises, October 1987 As described on page 84, the polarizing plate
There is disclosed a method of adding another achromatizing liquid crystal cell as an optical compensator to an STN type liquid crystal cell to solve coloring and to enable monochrome display.

[Problems to be solved by the invention]

The method of adding another achromatizing liquid crystal cell to the STN-type liquid crystal cell as an optical compensator eliminates coloring and enables monochrome display, but (1) is expensive and inferior in economy.
There are problems such as (2) heavy and (3) thick, and in addition to the improvement of the display performance described above, it is required to solve these problems together.

Although it is possible in principle to use a retardation plate instead of the achromatizing liquid crystal cell, a conventional 1 / 4λ plate (1) does not optically match the retardation value.
(2) The optical axis is not constant. (3) Uniform black and white display with large optical color unevenness is not achieved. (4) Production cannot be performed with high yield over a long length. For this reason, it cannot be applied to new uses such as the liquid crystal display device described above.

[Means for solving the problem]

The present invention has been completed as a result of repeated studies 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 0.35
It is in the range of dl / g to 0.7 dl / g and the swing width is 10
% Or less, which is a film or sheet formed by uniaxially stretching a polycarbonate-based polymer film or sheet having a birefringence (Δn) and a thickness (d), which is a measured value of a translation rate. Is in the range of 30 to 1200 nm, and the average amplitude is 7% or less. A retardation plate for an STN liquid crystal display device, and the retardation plate is laminated on a polarizing plate. Related to a compound polarizing plate.

The retardation plate of the present invention relates to a novel retardation plate which has an appropriate retardation value which is constant in the longitudinal direction and has little color unevenness optically. Retardation value is 30 ~ 1200nm
Are used, preferably from 200 to 1000 nm
Is adjusted to the range. A more appropriate retardation value is selected depending on the specific application. For example, a retardation value in the range of 200 to 350 nm, and 475
Those having a range of 625 nm can be exemplified for liquid crystal display devices.

In the present invention, the average value of the intrinsic viscosity [η] of the polycarbonate polymer film or sheet to be used is 0.35 to 0.7, preferably 0.4 to 0.65, more preferably 0.45 to 0.6.
It has been found that an optically extremely uniform retardation plate that is stable in the longitudinal direction can be obtained by regulating the amplitude to 10% or less, preferably 7% or less. . Specifically, the fluctuation width of the average retardation value of the retardation plate is 7% or less, preferably 6%,
More preferably, an optically uniform retardation plate having a length of 5% or less can be obtained over a long length, and is devised to improve display quality particularly when used in a liquid crystal display device.

The polycarbonate resin used in the present invention is mainly a straight-chain polycarbonate or a copolymerized polycarbonate having a bisphenol skeleton, and 4,4 ′
-Dihydroxydiphenylalkane or a halogen-substituted product thereof obtained by a phosgene method or a transesterification method. For example, 4,4'-dihydroxydiphenylalkane or a substituted product thereof is 4,4'-
Dihydroxydiphenylmethane, 4,4'-dihydroxydiphenylethane, 4,4'-dihydroxydiphenylbutane, 4,4'-dihydroxydiphenyl-2,2-propane, 3,3-dibromo-4,4'-dihydroxydiphenyl-
2,2-propane, 3,3'-dichloro-4,4'-dihydroxydiphenyl-2,2-propane, 3,3 ', 5,5'-tetrabromo-4,4'-dihydroxyphenyl-2,2 -Propane and the like.

Further, those obtained by blending a styrene resin and a modified product thereof with these polycarbonate resins are also effective in the present invention.

In order to make these polycarbonate-based resins into a retardation plate, the polycarbonate-based resins are formed into a film or sheet by a known film-forming means, that is, a solvent casting method, a calendar method, or an extrusion method, and then appropriately stretched in a uniaxial direction. Achieved by:

In order to obtain an optically uniform retardation plate over a small length having a small average deviation of the retardation of the present invention, the raw film or sheet has good thickness accuracy and is as optically uniform as possible. Things are needed. It is not preferable that a die line or the like is generated at the time of molding into a film or a sheet. Usually, when a film or sheet is formed, microscopic tendencies often occur, and it is important to reduce these microscopic orientations before stretching. Heat treatment is effective as a method for reducing micro-orientation before stretching. In order to produce the retardation film of the present invention, the film or sheet is subjected to a heat treatment at a temperature not lower than the heat deformation temperature before stretching. Polycarbonate film or sheet in the case of performing a heat treatment for about 0.1 to 5 minutes at a temperature of 130 to 200 ° C. before stretching, the birefringence of the raw film or sheet is
It becomes 1 × 10 ⁻⁴ or less, and almost completely becomes a non-oriented film or sheet.

The thus obtained raw film or sheet can be uniaxially stretched by a transverse uniaxial stretching method using a tenter method, a compression stretching method between rolls, a longitudinal uniaxial stretching method using rolls having different peripheral speeds, and a roll. A known uniaxial stretching method such as an inter-compression stretching method and a longitudinal uniaxial stretching method using rolls having different peripheral speeds can be employed.

In order to obtain a retardation plate having small optical unevenness in the present invention, a neck-in rate (100 × (AB) /) defined by a film width A before stretching and a film width B after stretching.
A) needs to be suppressed to 10% or less, preferably 5% or less, and more preferably to substantially zero. Therefore, the most effective stretching method in the present invention is a transverse uniaxial stretching method by a tenter method that does not substantially cause neck-in.

The transverse uniaxial stretching by the tenter method generally includes three steps of 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 making the birefringence of the film or sheet substantially zero. The stretching step is the most important step for forming a retardation plate, and the conditions are different depending on the type and thickness of the polycarbonate resin, the target retardation of the retardation plate, etc. In order to obtain a retardation plate, it is important to perform uniform stretching, and for that, it is particularly essential to select a 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. When the stretching temperature is in a temperature range where the yield point appears due to the stress-strain, or less, the stretching is non-uniform, and the stretched product becomes uneven in thickness, and the deflection width and change rate of the retardation increase.

The stretching magnification 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 retardation, and the heat treatment temperature is from the stretching temperature or lower to around the heating deformation temperature. preferable.

The heating deformation temperature refers to a value measured at JIS K6735 18.6 kg f / cm ² .

The retardation in the present invention can be measured by a polarizing microscope, a spectrophotometer or the like, and the average value of the retardation () is determined as follows. A sample of 20 cm × 20 cm is sampled from the stretched film or sheet, and the average value of 16 points is calculated by uniformly selecting 16 points.
Similarly, sample 10 samples in the same manner as above at 20 m intervals in the longitudinal direction.
An individual sample is collected and the average value is measured, and the average value of the 10 points is further averaged to obtain a value. The value obtained by dividing the difference between the maximum value and the minimum value of the average value of these 10 points (expressed as a percentage)
Is the swing width.

The intrinsic viscosity [η] of the polycarbonate polymer film or sheet in the present invention is measured in the following manner by performing sampling at 10 places at intervals of 20 m in the same manner as described above. The resin is accurately weighed and dissolved uniformly in 100 cc of methylene chloride, and its specific viscosity ηsp is measured at a constant temperature of 30 ° C. using an Ostwald viscometer. Similarly, ηsp was measured by changing the solution concentration, and ηsp / c was plotted on a graph. When c → 0 according to the following equation, intrinsic viscosity [η]
Is found. Here, [η] ηsp / c = [η] + k [η] ² ck of the above 10 points: a constant that does not become a numerator c: The average value of the concentration is displayed as [η]. The difference between the maximum value and the minimum value of [η] at the above 10 points is [η].
(Expressed as a percentage).

The retardation plate according to the present invention may be used alone in a liquid crystal display device, or may be applied to a liquid crystal display device or the like by bonding to one surface of a polarizing plate to form a composite polarizing plate.

As the polarizing plate constituting the composite polarizing plate of the present invention, any polarizing plate can be used. As an example, a film made of polyvinyl alcohol or a derivative thereof is uniaxially stretched and oriented, and after adsorbing iodine or a dichroic dye as a polarizing element, a non-rotatory cellulose acetate film such as triacetic acid or cellulose is used. On both sides. Furthermore, a dichroic dye was blended with a hydrophobic resin such as a polyene-based polarizing plate or polyethylene terephthalate obtained by dehydrochlorination of a polyvinyl chloride film or dehydration treatment of a polyvinyl alcohol-based film, and uniaxially oriented. A polarizing plate of a type can be used. Above all, a polyvinyl alcohol film, adsorbing iodine or a dichroic dye, and a uniaxially-aligned polarizer and a cellulose-based film such as cellulose triacetate bonded on both sides as a protective film have polarizing properties. It is preferable from the viewpoint of hue characteristics.

The retardation plate of the present invention, and, using the polarizing plate, to form the composite polarizing plate of the present invention the optical axis of the polarizing plate and the optical axis of the retardation plate 15 to 75 degrees, preferably 30 to 60 degrees, More preferably, it is achieved by bonding using an adhesive or an adhesive in the range of 40 to 50 degrees.

Further, the protective film on one side of the linear polarizing plate is removed, and the retardation plate is directly adhered to the polarizer using an adhesive or an adhesive. One side of a linear polarizing plate composed of a combination of chromatic dyes, a configuration in which a retardation plate is adhered using an adhesive, or an adhesive or the like is also included in the scope of the composite polarizing plate of the present invention. .

[Effects of the Invention] The retardation plate or the composite polarizing plate thus obtained has good optical performance and at the same time 80 ° C and 60 ° C.
Since it can pass the durability promotion test at × 90% RH, it can be used for new uses such as a liquid crystal display.

 An example in which the present invention is applied to a liquid crystal display is shown below.

(1) If a retardation plate is placed above the upper polarizing plate of a TN type liquid crystal display device in which the twist angle of liquid crystal molecules is 90 degrees, there is no rainbow pattern etc. when viewed through polarized sunglasses from any direction. The display quality is significantly improved as compared with the case where a conventional elliptically polarizing plate is used.

(2) By disposing a retardation plate below the upper polarizer of the TN type liquid crystal display device where the twist angle of the liquid crystal molecules is 90 degrees, the interference side of the liquid crystal phase can be eliminated uniformly over a large screen. Display quality can be significantly improved.

(3) In an STN type liquid crystal display device in which the twist angle of liquid crystal molecules is 180 to 270 degrees, coloring occurs due to birefringence of the liquid crystal layer. The phase difference plate of the present invention is stuck between the upper polarizing plate or lower polarizing plate and the liquid crystal cell of the STN liquid crystal display device so that the optical axis thereof is in the range of 30 to 60 degrees, preferably 40 to 50 degrees. By matching, the display quality becomes good. By arranging the optical axes of the pair of polarizing plates in an orthogonal or nearly orthogonal state, or in a parallel or nearly parallel state, black-and-white display is possible, and display quality is improved.

〔Example〕

Hereinafter, the present invention will be described with reference to examples. The present invention is not limited to these. In the examples, the retardation value of the retardation plate was measured using a Senarmon compensator (546 nm) provided for a polarizing microscope, and a halogen lamp was used as a light source. The linear polarizing plate in the examples is one obtained by uniaxially adsorbing iodine as a dichroic dye on polyvinyl alcohol, prepared by a method described in, for example, JP-A-61-20003. If necessary, a transparent non-rotating polymer film such as cellulose oxyacetate is bonded as a protective film.

Example 1 As a raw film, a transparent polycarbonate film having a thickness of 200 μm and a length of 300 m having a [η] of 0.553 d / g and a runout of 4.2% was used as a tenter facility (2 m width × 9 m) of Hirano Metal Co., Ltd. Long) to perform uniaxial transverse stretching. The raw film is heated to 190 ° C in the preheating step, and the birefringence of the raw film is set to 0.3 × 10 ^-4. This was performed to obtain a stretched film having a thickness of about 110 μm. The stretched film had a length of 550 nm, a run-out width of 4.0% in the longitudinal direction, and a retardation plate having a long optical length and little optical unevenness was obtained. This retardation plywood was attached to one surface of a polarizing plate using an acrylic pressure-sensitive adhesive so that the optical axis was about 45 degrees, to obtain a composite polarizing plate. In addition, the twist angle of the liquid crystal molecules
When used between the liquid crystal cell of the liquid crystal display device at 200 degrees and the upper polarizing plate, the background color is white, the display portion is almost black and white, and almost black and white display is possible. A liquid crystal display of display quality was obtained.

Example 2 As a raw film, a transparent polycarbonate film having a thickness of 200 μm and a length of 300 m with [η] of 0.485 dl / g and a run-out width of 5.4% was uniaxially stretched in the same tenter equipment as in Example 1. Was. 190 ° C in pre-heating process for raw film
Then, the birefringence of the raw film was adjusted to 0.2 × 10 ^-4, and the film was stretched uniaxially 1.7 times at 172 ° C. in the stretching step and heat-treated at 140 ° C. to obtain a stretched film of about 120 μm. Was. The stretched film had a thickness of 300 nm, a run-out width in the longitudinal direction of 5.6%, and a retardation plate having little optical unevenness over a long length was obtained. This retardation plywood was attached to one surface of a polarizing plate using an acrylic pressure-sensitive adhesive so that the optical axis was about 45 degrees, to obtain a composite polarizing plate. Furthermore, when this retardation plate was bonded and used between a liquid crystal cell of a liquid crystal display device having a liquid crystal molecule twist angle of 200 degrees and an upper polarizing plate via an adhesive, the background color was white and the display portion was black. Almost black and white display became possible, and there was no color unevenness such as a rainbow pattern, and a liquid crystal display device with good display quality was obtained.

Example 3 As a raw film, a transparent polycarbonate film having a thickness of 200 μm and a length of 300 m with [η] of 0.585 dl / g and a run-out of 5.7% was applied to a pressure roll facility (diameter 260 mm, surface length 7).
(00 mm). The raw film is preheated to 160 ° C. in a preheating oven, and the birefringence of the raw film is set to 0.4 × 10 ^−4, and then passed between pressure rolls at 168 ° C. and stretched 1.6 times in one longitudinal axis. A stretched film having a thickness of about 125 μm (neck-in rate: 3%) was obtained. The stretched film had a length of 920 nm, a run-out width of 5.4% in the longitudinal direction, and provided a retardation plate having little optical unevenness over a long length. This retardation plywood was adhered to one surface of a polarizing plate using an acrylic pressure-sensitive adhesive so that the optical axis was about 45 degrees, to obtain a composite polarizing plate. Furthermore, when this retardation plate was pasted and used via an adhesive between the liquid crystal cell of the liquid crystal display device and the upper polarizing plate where the twist angle of the liquid crystal molecules was 200 degrees,
Almost black and white display with white background and black display section is possible,
There was no color unevenness such as a rainbow pattern, and a liquid crystal display device with good display quality was obtained.

Comparative Example 1 A stretched film having a thickness of about 110 µ was obtained in the same manner as in Example 1, except that a raw polycarbonate film having [η] of 0.545 dl / g and a run-out width of 10.5% was used.
The stretched film has a run width of 540 nm and a length of 1 mm.
It was 6.9%, and only a retardation plate having poor homogeneity as compared with Example 1 was obtained.

Comparative Example 2 A stretched film having a thickness of about 120 μm was obtained in exactly the same manner as in Example 2, except that an original polycarbonate film having [η] of 0.493 d / g and a run-out width of 11.2% was used.
The stretched film has a width of 330 nm and a run-out width of 1 mm.
It was 8.5%, and only a retardation plate having lower homogeneity than that of Example 2 was obtained.

Comparative Example 3 A stretched film having a thickness of about 120 μm was obtained in exactly the same manner as in Example 3, except that a raw polycarbonate film having [η] of 0.582 d / g and a run-out width of 10.3% was used.
The stretched film has a length of 895 nm and a run-out width of 1 in the longitudinal direction.
It was 4.2%, and only a retardation plate having lower homogeneity than that of Example 3 was obtained.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-189804 (JP, A) JP-A-61-6604 (JP, A) JP-A-61-210303 (JP, A) JP-A-63-189804 43949 (JP, A) JP-A-63-142057 (JP, A) JP-A-56-130703 (JP, A) JP 8-30806 (JP, B2) WO 87/5920 (WO, A1) ( 58) Field surveyed (Int.Cl. ⁶ , DB name) G02B 5/30

Claims (2)

(57) [Claims] An average value of the intrinsic viscosity [η] is from 0.35 dl / g to 0.1.
A film or sheet formed by uniaxially stretching a polycarbonate polymer film or sheet having a range of 7 dl / g and a runout of 10% or less, and having a birefringence (Δn) The measured value of the retardation defined by the product of the thickness (d) is in the range of 30 to 1200 nm, and the average value of the variation is 7% or less. Retarder. 2. A compound polarizing plate obtained by laminating the retardation plate according to claim 1 on a polarizing plate.