JPH0242406A - Phase difference plate and composite polarizing plate formed by using this plate and liquid crystal display device - Google Patents

Abstract

PURPOSE:To allow high-quality black and white display with high reliability by stretching a thermoplastic high-polymer film having specific characteristics, thereby forming the phase difference plate. CONSTITUTION:The film formed by uniaxially stretching the thermoplastic high-polymer film is used. The measured value of the retardation defined by the product of a double refractive index and thickness of the film is in a 30-1,200nm range and the color difference when measurement is made by disposing the film in such a manner that the optical axis thereof attains 45 deg. under crossed nicols is <=30. The phase difference plate which has the adequate retardation value, has optically less unequal colors and attains the black and white display of uniform quality is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a novel retardation plate, a composite polarizing plate using the same, and a liquid crystal display device.

C. Prior Art] A retardation plate is a film or sheet-like material having birefringence. Since the light that has passed 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 currently commercially available and in practical use, there is a so-called 17° λ plate which has the function of producing a phase difference of 1/4 λ with respect to the wavelength λ of an incident light beam. This conventional 1/4λ plate is made by uniaxially stretching a cellulose acetate film.

A 1/41 plate becomes a circularly polarizing plate when laminated at a 45 degree angle with respect to the optical axis of a linear polarizing plate.It has an anti-glare function that cuts reflected light, so it is used in various anti-glare materials including VDT filters. has been done.

In addition to the above-mentioned cellulose resins, vinyl chloride resins (PTK
(No. 84477, Japanese Unexamined Patent Publication No. 125702/1984)
, Glycarbonate-based tM fat (Special Publication No. 41-12190
(Japanese Patent Application Laid-Open No. 56-180703), acrylonitrile resin (Japanese Patent Application Laid-open No. 56-180702),
Styrene resin (Japanese Unexamined Patent Publication No. 125708/1983),
Polyolefin resins (Japanese Unexamined Patent Publication No. 60-24502) have been proposed, but all of them have a retardage value of around 185 nm, so-called 1/4λ.
It is a board. Note that the retardage value (hereinafter sometimes abbreviated as R value) is the product of the thickness (d) of the film or sheet and the birefringence (△n) of the film, that is, the opening/closing 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 on both sides of a liquid crystal cell so that their absorption axes are perpendicular or parallel! ! ! There has also been an attempt to improve display quality by applying a retardation plate between one polarizing plate and a liquid crystal cell in a liquid crystal display device (generally referred to as a TN type liquid crystal display device). Furthermore, in recent years, with the demand for increased display capacity and enlarged display screens, liquid crystal display devices (generally referred to as S 'I' N type liquid crystal display devices) in which the twist angle of liquid crystal molecules is approximately 180 to 270 degrees have been developed. was developed. In this STN type liquid crystal display device, coloring occurs due to birefringence of liquid crystal molecules, and black and white display cannot be performed. - For example, the background color is yellow-green and the display color is dark blue.

When a display device has such a hue, it is often subject to restrictions when performing color display such as multicolor or full color. In order to solve this problem, for example, as described in Nikkei Microdevice October 1987 issue, page 84, an additional achromatic liquid crystal cell is added to the STN type liquid crystal cell as an optical compensator to prevent coloring. resolved,
A method is shown to 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 (3) thickness, and in addition to improving the display performance described above, it is required to solve these problems in combination.

Although it is theoretically conceivable to use a retardation plate instead of this achromatic liquid crystal cell, with the conventional l/4λ plate, (1) the retardation value does not match optically. (2
) The optical axis is not constant.

(3) Optical color unevenness is large and homogeneous black and white display cannot be achieved. For these reasons, it cannot be applied to new uses such as the above-mentioned liquid crystal display device.

[Means for Solving the Problems] The present invention has been completed as a result of repeated research in view of the above points, and is as follows.

(1) A film or sheet formed by uniaxially stretching a thermoplastic polymer film or sheet, which has a retardage (Δn × The measured value of d) is in the range of 80 to 1200 nm, and the color difference (ΔE*) is 80 when measured with the optical axis of the film or sheetra placed under crossed nicols at 45 degrees. A retardation plate characterized by the following:

(2) A polymer film or sheet formed by stretching a thermoplastic polymer film or sheet in the uniaxial direction so that the neck-in rate is 10% or less, and which has a birefringence (
The measured value of retardation (△nXd) defined as the product of △n A retardation plate having a color difference (ΔE*) of 20 or less when measured by arranging it so that

(3) The α value defined by equation (1) is 1.0! The retardation plate according to claim wi1, which is the above.

RF α=100・・・・・・・・・・・・・・・・・・
...(1) Here RF: Sodium F ray (48
Retardation value measured at 6.1 nm).

RD: Retardage value measured with Natriu AD line (589, 8 nm).

(4) A composite polarizing plate obtained by laminating the retardation plate according to claim 1 on a polarizing plate.

(5) A liquid crystal display device in which the retardation plate according to claim 1 is laminated on one side of a liquid crystal cell, and a pair of polarizing plates are laminated to sandwich the retardation plate.

The retardation plate of the present invention relates to a new retardation plate that has appropriate retardage and n value and is optically less uneven in color.

The retardation value used is in the range of 30 to 1200 nm, preferably 200 to 10001 m.
is adjusted within the range of A more appropriate letter silane value is selected depending on the specific application. For example, retardation values in the range of 200 to 350 nm and those in the range of 475 to 6251 m can be exemplified for use in liquid crystal display devices.

In addition, in the present invention, when forming a retardation plate by stretching a thermoplastic film or sheet uniaxially, the retardation plate is placed under crossed Nicols so that its optical axis is at an angle of 45 degrees, and measurement is performed. It has been found that by controlling the color difference (ΔE*) to 80 or less, preferably 20 or less, an excellent retardation plate without optical color unevenness can be obtained.

The thermoplastic resin used in the retardation plate of the present invention satisfies the above characteristics when formed into a film or sheet, and has an average transmittance of 50% or more in the visible light wavelength range of 400 to 700 nm. It can be applied to the present invention without particular limitation as long as it shows preferably 80% or more, more preferably 85% or more.

Examples include polymethyl methacrylate, methyl methacrylate obtained by copolymerizing methyl methacrylate with other ethylene comonomers, poly(meth)acrylate resins such as copolymers, polystyrene, and styrene copolymers. Polystyrene resins such as styrene copolymers obtained by co-N-merging with other ethylene comonomers, acrylonitrile resins such as polyacrylonitrile and acrylonitrile copolymers, polyester resins such as polyethylene terephthalate and polyester copolymers. , polyamide resins such as nylon 6 and nylon 66, polyvinyl chloride resins such as polyvinyl chloride and vinyl chloride copolymers, polio-based materials such as polyethylene, polypropylene, ethylene copolymers, and propylene copolymers; At least one resin material selected from the group consisting of a transparent low-molecular compound such as a polymeric liquid crystal or a low-molecular liquid crystal, or a transparent inorganic compound blended with the resin described above is mentioned.

Preferred resins include polyester resins such as polyethylene terephthalate and polyester copolymers.
Polysulfone, polychloride In order to improve the display quality of a liquid crystal display device, the retardation plate of the present invention is a thermoplastic material having an α value defined by the following formula (1) of 1.00 or more, preferably 1.08 or more. Uses resin.

Here, RF: Retardation value measured with Thorium AF line (486, 1 nm) Rp: + Retardation value measured with Thorium D line (589, 8 nm) When the retardation plate is applied to an STN type liquid crystal display device The dependence of the display quality on the α value will be explained using an example.

When a birefringent body exists at 45 degrees with respect to the optical axis under parallel Nicols, the light transmittance (T) of the optical system is expressed by the following formula (2
).

πRr T= Tr x Tp x cos” -λ Tr: Transmittance Tp of birefringent material: Transmittance RY when two polarizing plates are arranged in parallel - Retardation silane (nm) of birefringent material λ: Wavelength of light (nm) The twist angle of the liquid crystal is approximately 200 degrees, and the product of the birefringence and thickness of the liquid crystal (△nxd) is approximately 8501 m. A pair of polarizing plates are placed in parallel on both sides of the liquid crystal cell. Placed in Nicol state,
And, between the upper polarizing plate and the liquid crystal cell, there is a distance of about 45 mm with respect to the polarization axis.
An STN type liquid crystal display device having a retardation plate (retardage of about 5501 m) is improved in display quality. In other words, the coloring disappears and the background color becomes white. The one with the clearest possible white background color is
This is preferable because it is excellent in display quality, and in equation (2), if the light transmittance is constant in the wavelength range of visible light, that is, if T=constant, the background color becomes completely white.

In formula (2), the conditions for T = constant are: The retardage, N, Re of the composite of the liquid crystal cell and the retardation plate is such that the value of R changes depending on the wavelength λ of the light, and the formula ( 4)
As shown in , if the R of the liquid crystal cell is compensated by the R of the retardation plate and T=constant in all wavelength ranges of visible light, the background color will be completely white and the display quality will be good.

The spectra of transmitted light of the STN liquid crystal display device when the value of α of the retardation plate was changed to 1.0O11,08,1,06 are shown in FIGS. 1 to 8. It can be seen that the larger the value of α, the closer the display becomes to perfect white εζ.

As is clear from the above description, the display quality will be better if the α value of the retardation plate used in the liquid crystal display is larger than 1.00, and preferably 1.08 or more. α
Thermoplastic polymers exhibiting a value of 1.08 or more, which is a preferable range, include polymer compounds containing an aromatic ring in the main repeating unit of the polymer, or polymers having polar groups such as halogen atoms and nitrile groups. Examples include molecular compounds. These polymer compounds include polymer compounds having aromatic rings such as polystyrenes, polyether sulfonos, polyether ether ketones, polyarylates, polyesters, polystyrenes, polycarbonates, and acrylonitrile polymers. Fluorine resins such as trifluoride-ethylene chloride polymer? Examples include vinyl chloride. Furthermore, modified products or mixtures of these polymer compounds can also be used as appropriate. Furthermore, even if the thermoplastic resin alone has an α value of 1.03 or less, the desired retardation plate of the present invention can be obtained by blending it with a low-molecular liquid crystal or polymer liquid crystal having a large α value. .

A method of using the above-mentioned thermoplastic polymer compound as a retardation plate will be described below. The retardation plate of the present invention is produced by forming the thermoplastic polymer into a raw film or sheet using a known film forming method, that is, a solvent casting method, a calendaring method, or an extrusion method, and then stretching the thermoplastic polymer appropriately in the axial direction. Manufactured by

In order to obtain a retardation plate with a constant optical axis and little optical color unevenness, the original film or sheet is required to have good thickness accuracy and be as optically homogeneous as possible. It is not preferable that die lines or the like occur on the film or sheet during molding. Normally, when forming a film or sheet, minute orientations often occur, and it is also a preferable method 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, heat treatment is performed at a temperature equal to or higher than the heating deformation temperature of the film or sheet before stretching.

When the heat treatment is performed, the birefringence of the original film or sheet becomes substantially 0, resulting in a nearly completely non-oriented film or sheet.

Methods for stretching the raw film or sheet obtained in this way in the uniaxial direction include a transverse-axial stretching method using a tenter method, an inter-roll compression stretching method, and a longitudinal-axial stretching method using rolls with different peripheral speeds. A known uniaxial stretching method can be employed.

In the present invention, in order to obtain a retardation plate with optically small color unevenness and small fluctuation in retardage, the neck-in rate (defined from the film width A before stretching and the film width B after stretching) ( toox(A-B)/A) to 1096
Below, it is necessary to suppress O to preferably 5% or less, and more preferably to substantially O. 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 includes three 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 to make the birefringence of the film or sheet substantially O. The stretching process is the most important process for producing a retardation plate, and processing conditions must be changed depending on the type and thickness of the thermoplastic resin used, the required retardation value, etc.

The heat treatment step after stretching is a useful step for improving the dimensional stability of the obtained stretched film or sheet and for improving the uniformity of the retard silane.

In the present invention, the average transmittance in the visible light wavelength range of 400 to 7 Q Q nm is defined as follows.

That is, 1) 400 to 70 using a spectrophotometer or spectrometer, etc.
Measure the transmittance every 10 nm in the range of 0 nm,
This is the average value of the transmittances of the 31 points obtained. Since this retardation plate is used for optical purposes, the average light transmittance is preferably as high as possible, usually 50% or more,
Preferably 80% or more is required.

The optical color unevenness referred to in the present invention is defined below as △E
*Can be displayed quantitatively.

In other words, L*, a*, b* (Dfi is JI
Measurement is performed using a spectrophotometer or spectrometer according to S-Z-8729 (Method for displaying object color using L*u*v* color system). The above L* a* for samples at n different locations
(ΔE*)i, j are calculated from b* using the following formula.

(△E*)i, j = (((ΔL*)i, j)2+((Δa*)i, j)2
+((△b*)i,j))1/.

Just △L*)i, j=(L*)i−(L*)j(△a*
)i, j=(a*)i −(a*)j(Δb*)i,
j=(b*)i-(b*)j1=1. ~n j = r ~ n i〆j The maximum value among these (ΔE*) i j is assumed to be ΔE*. It is preferable that the number of measurements n is large, but usually: 30cm
Ten samples are taken at random from the corner samples, measured, and calculated using the above formula. The smaller ΔE* is, the less optical color unevenness will occur, so it is preferable that it be as small as possible.

In the retardation plate of the present invention, the value of ΔE* needs to be 80 or less, preferably 20 or less.

The retardation plate thus obtained can be applied to new uses such as composite polarizing plates, liquid crystal display devices, and optical filters.

The retardation plate of the present invention can also be applied to liquid crystal display devices and the like 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, dichroic dyes are blended with hydrophobic resins such as polyene polarizing plates, polyethylene terephthalate, etc., obtained by dehydrochloric acid treatment of polyvinyl chloride films, or dehydration treatment of polyvinyl alcohol films, and oriented along the -axis. It is possible to use a similar type of polarizing plate. Among them,
A polyvinyl alcohol film that adsorbs iodine or dichroic dye and is laminated on both sides of a polarizer oriented on the -axis with a cellulose-based film such as cellulose triacetate as a protective film has excellent polarization characteristics and hue characteristics. Preferable from above.

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 80 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.

In addition, there are those in which the protective film on one side of the linear polarizing plate is removed and the retardation plate is bonded directly to the polarizer using an adhesive or adhesive, and those in which the protective film on one side of the linear polarizing plate is removed, and those with a hydrophobic polymer film without a protective film. The composite polarizing plate of the present invention also includes a structure in which a retardation plate is bonded to one side of a linear polarizing plate made of a combination of colored dyes using an adhesive or a pressure-sensitive adhesive. .

In the retardation plate of the present invention, the twist angle of the liquid crystal molecules is 90 degrees or more,
Specifically, the liquid crystal display device of the present invention is obtained by placing a pair of polarizing plates on one side of a liquid crystal cell at an angle of about 180 to 270 degrees and sandwiching them. At this time, the optical axis of the retardation plate and polarizing plate is 80 to 6
Good display quality can be achieved by bonding them at an angle of 0 degrees, preferably in the range of 40 to 60 degrees. Good display quality can be achieved by arranging the pair of polarizing plates so that their optical axes are perpendicular or nearly perpendicular, or parallel or nearly parallel.

[Effect of the invention] The retardation plate or composite polarizing plate obtained in this way has good optical performance and can be heated to 80°C and 60°C.
"These products can pass the accelerated durability test at 0x90% RH. Therefore, the twist angle of liquid crystal molecules is 90%.
If the liquid crystal display device is used in a liquid crystal display device having a temperature of 180° to 270° or more, the liquid crystal display device of the present invention is highly reliable and has a high quality black and white display. In addition, it is also possible to apply it to optical filters for each dish.

[Example] The present invention will be explained below with reference to Examples. The present invention is not limited to these. In the measurement of the retardation value of the retardation plate in the examples, a Senarmont compensator (546 nm) attached to a polarizer Wi mirror was used, and a halogen lamp was used as the light source. ΔE* was measured and calculated using a spectrophotometer according to the method described above.

Note that the value of α of the retardation plate defined by formula (1) was determined by the following procedures (I) to (5) using an Atsube refractometer.

(L) Using sodium D line (589,8 nm) 1
．． N"ic, the refractive index nDI in the optical axis direction and the refractive index nD2 in the direction orthogonal thereto are measured, and the retardage is measured at 589.8 nm using the following equation (2).

Calculate the value RD.

R"" I nDI "D21 X d...
・・・・・・−・・・・・・(2) d: Thickness of retardation plate (n
m) Co., Ltd. Using sodium Fil (486, 1 nm), the apparent refractive index nF1 in the optical principal axis direction and the apparent refractive index np in the direction orthogonal to it! The actual refractive index NFI is determined by the following equations (3) and (4).
Calculate NF2.

Np2=PXsin[68°L-sin-'("Ax
5in(68°-5in-'(ri))]"-(4)P
L, 74 However, P is the refractive index of the main prism of the refractometer at 486.1 nm, and the value calculated using the following equation (5) was used.

= 1.7589 ・・・・・・・・・・・・
・・・・・・・・・・・・・・・・・・・・・・・・(5)
(I[D NFI , Npg (7) Using the value,
The retardation value RF measured at 486.1 nrn is calculated using the following equation (6).

RP= l Npt-Npg l X d...
・・・・・・・・・・・・・・・・・・(6) d: Thickness of retardation plate (nm) ([v) Using Rp and RoO values, α is calculated by equation (1). Calculate the value.

In addition, the linear polarizing plate in the embodiment is, for example, disclosed in Japanese Patent Application Laid-Open No. 1986-
It is produced by the method described in Japanese Patent No. 20008, in which iodine is uniaxially adsorbed and oriented as a dichroic dye 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 polycarbonate film (approximately 26,000 molecules per molecule) with a thickness of 800 ttm and a width of 800 m was preheated at a temperature of 190"C, and then horizontally uniaxially stretched by a tenter method at a temperature of 175"C to a thickness of approximately 200μm 1 width 45
A stretched film of 0 cm was obtained. The stretched film had light rays, and a retardation plate of the present invention with almost no optical color unevenness was obtained. This retardation plate was attached to one surface of a polarizing plate using an acrylic adhesive so that the optical axis was set at about 45 degrees to obtain a composite polarizing plate of the present invention. Furthermore, the twist angle of the liquid crystal molecules is approximately 200 degrees, and the △nXci of the liquid crystal is
When used by bonding via an adhesive between the liquid crystal cell of a liquid crystal display device with a wavelength of about 35 Q nm and the upper polarizing plate,
The liquid crystal display device of the present invention was obtained, which had a substantially monochrome display with a white background and a black display area, and had good display quality without any color unevenness such as a rainbow pattern.

Example 2 A polyester copolymer film (PETG6768, Eastman Chemical Company) with a thickness of 400 μm% @ 800 m was preheated at a temperature of tab"c, and then
Transverse uniaxial stretching was carried out using a tenter method at a temperature of 0'C to obtain a stretched film with a thickness of about 250 μm and a width of 480 cm. The stretched film has a light transmittance of about 89% and an α value of about 1.
．． 06, a retardation plate of the present invention having an R value of 585 nm, ΔE* of 11.0, uniform quality, and almost no optical color unevenness was obtained. When applied to a liquid crystal display device in the same manner as in Example 1, a liquid crystal display device of the present invention having good display quality was obtained as in Example 1.

Example 8 After preheating, transverse uniaxial stretching was carried out using a tenter method at a temperature of 100"C to obtain a stretched film with a thickness of about 140 μm and a width of 540 m. It had a uniform quality of 8.0 and an optical color. A retardation plate of the present invention with almost no unevenness was obtained. This retardation plate was attached to one side of a polarizing plate using an acrylic adhesive so that the optical axis was approximately 45 degrees. A composite polarizing plate was obtained.This retardation plate was used by applying 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 approximately 180 degrees and the ΔnXd of the liquid crystal is approximately 950 nm. When the liquid crystal display device of the present invention was laminated with the liquid crystal display device used, the background color was white and the display area was black, resulting in an almost black and white display, and there was no color unevenness such as a rainbow pattern, and the liquid crystal display device of the present invention had good display quality.

Example 4 A polysulfone film (Sumilite FS-1200, manufactured by Sumitomo Bakelite) with a thickness of 150 Imms and a width of 800 m was preheated at a temperature of 280°C, and then heated to 21G”C.
Transverse uniaxial stretching was carried out using a tenter method at a temperature of about 75 μm in thickness and 600 μm in width to obtain a stretched film. 9.5
A retardation plate of the present invention was obtained which had a uniform quality and almost no optical color unevenness. When applied to a liquid crystal display device in the same manner as in Example 1, a liquid crystal display device of the present invention having good display quality was obtained as in Example 1.

Example 5 A polyethylene terephthalate film with a thickness of 200 μm and a width of 800 μm was preheated at a temperature of 210° C., and then horizontally uniaxially stretched using a tenter method at a temperature of 195”C to obtain a stretched film with a thickness of about 140 μm and a width of 480 cm with ΔE* The retardation plate of the present invention has a uniform quality of 12.8 and almost no optical color unevenness.This retardation plate is optically attached to one side of a polarizing plate using an acrylic adhesive. The composite polarizing plate of the present invention was obtained by pasting the plates so that their axes were at about 45 degrees.

Furthermore, the twist angle of the liquid crystal molecules in this retardation plate is approximately 220.
When used by pasting an adhesive between the liquid crystal cell and the upper polarizing plate of a liquid crystal display device in which the Δnxd of the liquid crystal is approximately 800 nm, the background color is white and the display area is black, almost black and white. A liquid crystal display device with good display quality without color unevenness such as a rainbow pattern was obtained.

As a comparative example, a retardation plate with a thickness of about 400 μm made of cellulose acetate (
When the α value was approximately 0.96 and the R value was approximately 525 nm) was applied to a liquid crystal display device in the same manner as in Example 1, Example 1
Compared to this, only a liquid crystal display device with inferior contrast could be obtained.

Comparative Example 2 Retardation plate (α
When applied to a liquid crystal display device in the same manner as in Example 1 (the R value was approximately 0.99 and the R value was approximately 610 nm), a liquid crystal display device with inferior contrast compared to Example 1 was obtained.

Example 6 75 wt % of polyvinyl chloride and 25 wt % of a polymeric liquid crystal compound represented by the following formula (7) were blended at 150° C. and then formed into a film of about 200 μm. Roll temperature 10
Compression stretching was performed between a pair of rolls at 0° C. and a linear pressure of 200 kQ/lyn to obtain a stretched film with a thickness of about 100 μm.

(Neck-in rate 2%) The stretched film has a light transmittance of about 87%, an α value of about 1.06, an R value of about 240 nm, and a ΔE
* was 17.8, and the retardation plate of the present invention with little optical color unevenness was obtained.

Example 7 Consisting of a uniform blend of polycarbonate (molecular weight approximately 16,000) and styrene/maleic anhydride copolymer (styrene/maleic anhydride (weight ratio) = 92/8) at a weight ratio of 80:20. Thickness 200μm 1 width 800
After preheating the transparent film at a temperature of 180° C., transverse uniaxial stretching was performed using a tenter method at a temperature of 155”C to obtain a stretched film with a thickness of approximately 185 μm and a width of 515 wg. The value is approximately 1.05
, R value was about 460 nm, Δ, A* was 8.8, and the retardation plate of the present invention was obtained which had uniform quality and almost no optical color unevenness. This retardation plate was attached to a polarizing plate using an acrylic adhesive so that their optical axes were at about 45 degrees to obtain a composite polarizing plate of the present invention. When applied to a liquid crystal display device in the same manner as in Example 1, a liquid crystal display device of the present invention having good display quality was obtained as in Example 1.

Example 8 A polymethyl methacrylate film (extruded film of Sumipex MMO manufactured by Sumitomo Chemical ■- ■) with a thickness of approximately 220 nm% and a width of 800 m was
After preheating at 0°C, transverse uniaxial stretching was performed at 80''C using a tenter method to obtain a stretched film with a thickness of about 150 μm and a width of about 440 m.

This stretched film has an R value of approximately 5701 m%, an E* value of 7.2, a light transmittance of approximately 9096, and an α value of approximately 1.0.
In Example No. 1, a good retardation plate was obtained which exhibited uniform quality and almost no optical color unevenness.

Example 9 A 60 μm thick low density polyethylene (Sumikasen F208-1 manufactured by Sumitomo Chemical) film was compressed and stretched between a pair of rolls at a roll temperature of 100°C and a linear pressure of 250 bJ/cm. A stretched film with a diameter of 15 μm and a neck-in rate of 3% was obtained.

The resulting stretched film has an R value of approximately 680 nm and a ΔE*
The value is 14.4, the light transmittance is about 86%, and the α value is about 1.
．． A good retardation plate was obtained which exhibited uniform quality in OO and almost no optical color unevenness.

Example 10 Using the same raw material polysulfone film as in Example 4,
After preheating at 215[deg.] C., the film was stretched longitudinally and longitudinally between rolls having different circumferential speeds to obtain a stretched film with a thickness of about 70 [mu]m and a neck-in rate of 6%.

This stretched film has a light transmittance of about 88% and an R value of about 6.
A good retardation plate with a wavelength of 60 nm and ΔE* of 16.0, showing uniform quality and almost no optical color unevenness, was obtained.

Example 11゜The retardation plate obtained in Examples γ to 10 was prepared so that the twist angle of the liquid crystal molecules was about 200 and the △nXd of the liquid crystal molecules was about 850.
When used by bonding between the liquid crystal cell and the upper polarizing plate of a liquid crystal display device using an adhesive, the display showed an almost monochrome display with a white background and a black display area, with no rainbow-like color unevenness. (
A liquid crystal display device with good display quality was obtained. Among them, excellent display quality was obtained when a retardation plate having an α value of 1.03 or more was used.

Comparative Example 8 In Example 10, stretching was carried out by increasing the distance between the rolls of the longitudinal-axial stretching device to obtain a stretched film with a thickness of about 80 μm. (Neck-in rate: 80%) The stretched film had a light transmittance of about 88% and an R value of about 720 nm, but ΔE* was 82.4, and only a retardation plate with large optical color unevenness was obtained. I couldn't. When this retardation plate was applied to the same liquid crystal display device as in Example 11, color unevenness such as a rainbow pattern was large, and the display quality was rather deteriorated.

Comparative Example 4 A polyester copolymer film with a thickness of 250μ (same as in Example 2) was used, and with the same stretching device as in Comparative Example 8, 11
Uniaxial stretching was performed at 0°C to obtain a stretched film of 170μ.

(neck-in rate: 40%), the stretched film had a light transmittance of about 89% and an R value of about 490 nm, but ΔE* was 84.5, and only a retardation plate with large optical color unevenness was obtained. I couldn't.

When this retardation plate was applied to the same liquid crystal display device as in Example 11, color unevenness such as a rainbow pattern was large, and the display quality was rather deteriorated.

Example 12 The same polycarbonate film as in Example 1 was preheated at a temperature of 185°C, and then horizontally uniaxially stretched at a temperature of 17δ°C by a tenter method to obtain a stretched film with a thickness of about 160 μm and a width of 560 mm. The stretched film has uniform quality with a light transmittance of about 91%, an α value of about 1.06, an R dip of about 885 nm, and a ΔA* of 9.8.
A retardation plate of the present invention with almost no optical color unevenness was obtained.

When applied to a liquid crystal display device in the same manner as in Example 6, an almost monochrome display with a white background and a black display area was obtained, and a liquid crystal display device with good display quality without color unevenness such as a rainbow pattern was obtained. Ta.

Example 13 A polycarbonate film (molecular weight 26,000) with a thickness of 200/(rn 1N800 wm) was preheated at a temperature of 190°C, and then transversely uniaxially stretched by a tenter method at a temperature of 175°C. C
Heat treatment was performed for 2 minutes. The stretched film has a light transmittance of about 91%, an α value of about 1.06, and an R value of about 60 nm.
, ΔE* was 18.1, the retardation plate of the present invention had uniform quality and almost no optical color unevenness.

[Brief explanation of the drawing]

The twist angle of the liquid crystal is about 200 degrees, and the value of △nXd of the liquid crystal is about 850 nm.A pair of polarizing plates are arranged in a parallel Nicol state on both sides of the liquid crystal cell, and an R is placed between the upper polarizing plate and the liquid crystal cell. In an STN liquid crystal display device configured with a retardation plate with a value of about 650 nm, the α value of the retardation plate is set to 1.
．． Transmitted light spectrum (background color) when changed to 00 (Fig. 1), 1.08 (Fig. 2), and 1.06 (Fig. 8)
shows. λ (nm) Figure 1 (nm) Figure 2 λ (nm) Figure 3

Claims (5)

[Claims] (1) A film or sheet formed by uniaxially stretching a thermoplastic polymer film or sheet, which has retardation (Δn×d) defined as the product of birefringence (Δn) and thickness (d). is in the range of 80 to 1200 nm, and the color difference (ΔE^*) is 80 or less when the film or sheet is placed under crossed Nicols with its optical principal axis at 45 degrees. A retardation plate characterized by: (2) A polymer film or sheet formed by stretching a thermoplastic polymer film or sheet in the uniaxial direction so that the neck-in rate is 10% or less, and which has a birefringence (
The measured value of retardation (Δn x d) defined as the product of Δn) and thickness (d) is in the range of 200 to 1000 nm, and the optical principal axis of the film or sheet is placed under crossed Nicols at 45 degrees. A retardation plate having a color difference (△E^*) of 20 or less when measured by arranging it so that (3) The retardation plate according to claim 1, wherein the α value defined by formula (1) is 1.00 or more. α=(R_F)/(R_D)…………(1) where R_F: retardation value measured with sodium F line (486.1 nm). R_D: Retardation value measured with sodium D line (589.8 nm). (4) A composite polarizing plate obtained by laminating the retardation plate according to claim 1 on a polarizing plate. (5) A liquid crystal display device in which the retardation plate according to claim 1 is laminated on one side of a liquid crystal cell, and a pair of polarizing plates are laminated to sandwich the retardation plate.