Laminated wavelength plate, circular polarizing plate and liquid crystal display

A wavelength plate which shows little undesirable retardation in a specific wavelength range while substantially maintaining the function of 1/2 wavelength plate or 1/4 wavelength plate over the entire visible light range and a circular polarizing plate which shows little reflection at the interface and exhibits an anti-reflection effect over a wide wavelength range and an excellent thermal stability. A laminated wavelength plate comprising a plurality of oriented films giving a retardation having a wavelength half that of monochromatic light laminated with their optical axes crossing each other, wherein the dependence of the birefringence differences .DELTA.n.sub.1 and .DELTA.n.sub.2 of said oriented films on wavelength each satisfy the relationship .DELTA.n.sub.1 /.DELTA.n.sub.2 <1.05 based on light having wavelength of 400 nm (.DELTA.n.sub.1) and 550 nm (.DELTA.n.sub.2), a laminated wavelength plate comprising a plurality of oriented films laminated with their optical axes crossing each other, the dependence of the birefringence differences .DELTA.n.sub.1 and .DELTA.n.sub.2 of said oriented films on wavelength each satisfying the relationship .DELTA.n.sub.1 /.DELTA.n.sub.2 <1.05 based on light having wavelength of 400 nm (.DELTA.n.sub.1) and 550 nm (.DELTA.n.sub.2), wherein the oriented films used are those giving a retardation of 1/2 wavelength with respect to monochromatic light and those giving a retardation of 1/4 wavelength with respect to monochromatic light in combination, a circular polarizing plate comprising a laminate of the the laminated wavelength plate having a 1/4 wavelength plate and a polarizing plate, and a liquid crystal display comprising the circular polarizing plate.

FIELD OF THE INVENTION 
The present invention relates to a laminated wavelength plate which gives a 
predetermined retardation of 1/2 wavelength, 1/4 wavelength or the like 
over a wide wavelength range, a circular polarizing plate having an 
excellent durability which prevents reflection over a wide wavelength 
range, and a liquid crystal display having an excellent visual 
perceptibity. 
BACKGROUND OF THE INVENTION 
A 1/2 wavelength plate or 1/4 wavelength plate made of a single sheet of 
oriented film has heretofore been known. However, such a wavelength plate 
is disadvantageous in that its retardation differs from wavelength to 
wavelength, restricting the wavelength at which it can act as a 1/2 
wavelength plate or 1/4 wavelength plate to a specific value. In other 
words, a wavelength plate which acts as a 1/4 wavelength plate with 
respect to light having a wavelength of 550 nm cannot act as a 1/4 
wavelength plate with respect to light having a wavelength of 450 nm or 
650 nm. Therefore, when a circular polarizing plate obtained by bonding 
such a 1/4 wavelength plate to a polarizing plate is used as an 
anti-reflection filter for preventing reflection from the surface of 
display or the like, it cannot exert a sufficient anti-reflection effect 
with respect to light having a wavelength which is not 550 nm, 
particularly with respect to blue-based light. In this case, the display 
or the like looks blue. 
In this respect, the present inventors earlier proposed a laminated 
wavelength plate comprising a plurality of oriented films giving a 1/2 
wavelength or 114 wavelength laminated with their optical axes crossing 
each other (JP-A-5-100114 (The term "JP-A" as used herein means an 
"unexamined published Japanese patent application")). In accordance with 
this laminated wavelength plate, a predetermined phase difference such as 
1/2 wavelength and 1/4 wavelength can be given over a wide wavelength 
range. However, it was found that such a laminated wavelength plate gives 
an undesirable retardation in a specific wavelength range. It was also 
found that a circular polarizing plate made of such a laminated wavelength 
plate shows too great a reflection at the interface of layers to exhibit 
sufficient light shielding properties or undergoes a partial retardation 
change due to heat to give ununiform visual perceptibility. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a wavelength 
plate which shows little undesirable retardation in a specific wavelength 
range while substantially maintaining the function of 1/2 wavelength plate 
or 1/4 wavelength plate over the entire visible light range and a circular 
polarizing plate which shows little reflection at the interface and 
exhibits an anti-reflection effect over a wide wavelength range and an 
excellent thermal stability. 
The above object of the present invention will become more apparent from 
the following detailed description and examples. 
The present invention provides a laminated wavelength plate comprising a 
plurality of oriented films giving a retardation having a wavelength half 
that of monochromatic light laminated with their optical axes crossing 
each other, wherein the dependence of the birefringence differences 
.DELTA.n.sub.1 and .DELTA.n.sub.2 of the oriented films on wavelength each 
satisfy the relationship .DELTA.n.sub.1 /.DELTA.n.sub.2 &lt;1.05 based on 
light having wavelength of 400 nm (.DELTA.n.sub.1) and 550 nm 
(.DELTA.n.sub.2), a laminated wavelength plate comprising a plurality of 
oriented films laminated with their optical axes crossing each other, the 
dependence of the birefringence differences .DELTA.n.sub.1 and 
.DELTA.n.sub.2 of said oriented films on wavelength each satisfying the 
relationship .DELTA.n.sub.1 /.DELTA.n.sub.2 &lt;1.05 based on light having 
wavelength of 400 nm (.DELTA.n.sub.1) and 550 nm (.DELTA.n.sub.2), wherein 
oriented film used are those giving a retardant of 1/2 wavelength with 
respect to monochromatic light and those giving a retardation of 1/4 
wavelength with respect to monochromatic light in combination, a circular 
polarizing plate comprising a laminate of the laminated wavelength plate 
having a 1/4 wavelength plate and a polarizing plate, and a liquid crystal 
display device comprising the circular polarizing plate. 
By laminating a plurality of oriented films giving a retardataion of 1/2 
wavelength or 1/4 wavelength with respect to monochromatic light with 
their optical axes crossing each other, the wavelength dispersion of 
retardation defined by the product (.DELTA.nd) of the birefringence 
difference (.DELTA.n) and the thickness (d) can be arbitrarily controlled, 
i.e., increased or decreased, making it possible to suppress the 
wavelength dispersion while controlling the entire phase difference to a 
predetermined value. Thus, a 1/2 wavelength plate or 1/4 wavelength plate 
which exhibits a predetermined phase difference over a wide wavelength 
range such as entire visible light range can be obtained. 
In this respect, the use of an oriented film the dependence of the 
birefringence differences .DELTA.n.sub.1 and .DELTA.n.sub.2 of which 
satisfies the relationship .DELTA.n.sub.1 /.DELTA.n.sub.2 &lt;1.05 based on 
light having wavelength of 400 nm (.DELTA.n.sub.1) and 550 nm 
(.DELTA.n.sub.2) makes it possible to obtain a wavelength plate which 
exhibits little undesirable retardation in a specific wavelength range but 
a desired retardation in a wide wavelength range such as visible light 
range. The use of a wavelength plate giving a retardation having a 
wavelength of 1/4 that of the wavelength plate makes it possible to obtain 
a circular polarizing plate useful, e.g., as wide range anti-reflection 
filter which can substantially inhibit the reflection of light in the 
visible range or the like. Further, by bonding a plurality of these 
wavelength plates with an adhesive layer having a refractive index 
difference of not more than 0.1 from that of these wavelength plates 
provided interposed therebetween, a circular polarizing plate which shows 
little reflection at the interface and exhibits an anti-reflection effect 
over a wide wavelength range and an excellent thermal resistance and other 
resistances can be obtained.

In the drawings, 1 and 3 indicate an oriented film giving a retardation of 
1/2 wavelength, 2 indicates an adhesive layer, 4 indicates an oriented 
film giving a retardation of 1/4 wavelength, 5 indicates a polarizing 
plate, and 6 indicates a 1/4 wavelength plate. 
DETAILED DESCRIPTION OF THE INVENTION 
The laminated wavelength plate according to the present invention comprises 
a plurality of oriented films giving a retardation having a wavelength 
half that of monochromatic light laminated with their optical axes 
crossing each other, wherein the dependence of the birefringence 
differences .DELTA.n.sub.1 and .DELTA.n.sub.2 of the oriented films on 
wavelength each satisfy the relationship .DELTA.n.sub.1 /.DELTA.n.sub.2 
&lt;1.05 based on light having wavelength of 400 nm (.DELTA.n.sub.1) and 550 
nm (.DELTA.n.sub.2). An embodiment of the laminated wavelength plate 
according to the present invention is shown in FIG. 1. Shown each at the 
reference numerals 1 and 3 is an oriented film giving a retardation of 1/2 
wavelength. Shown at the reference numeral 2 is a transparent adhesive 
layer. The laminated number of sheets of oriented films is arbitrary. In 
the light of light transmittance or the like, it is preferably from 2 to 
5. 
The angle of crossing of the optical axes of the various oriented films for 
the structure of 1/2 wavelength plate may be calculated by the following 
equation as a basic example. Supposing that the laminated number of sheets 
of oriented films is N and the angle of the polarizing direction of 
outcoming light transmitted by the wavelength plate from the polarizing 
direction of incident light as a reference (0.degree.) is .theta., the 
crossing angle .theta..sub.k of each of the various 1/2 wavelength films 
is determined by the equation: 
EQU .theta..sub.k =(2K-1).multidot..theta./2N 
wherein K is an integer of from 1 to N. 
On the other hand, another embodiment of the laminated wavelength plate 
according to the present invention comprises a plurality of oriented films 
laminated with their optical axes crossing each other, the dependence of 
the birefringence differences .DELTA.n.sub.1 and .DELTA.n.sub.2 of said 
oriented films on wavelength each satisfying the relationship 
.DELTA.n.sub.1 /.DELTA.n.sub.2 &lt;1.05 based on light having wavelength of 
400 nm (.DELTA.n.sub.1) and 550 nm ((.DELTA.n.sub.2), characterized in 
that the oriented films there used are those giving a retardation of 1/2 
wavelength with respect to monochromatic light and those giving a 
retardation of 1/4 wavelength with respect to monochromatic light in 
combination. An example of this laminated wavelength plate is shown in 
FIG. 2. Shown at the reference numeral 4 is an oriented film giving a 
retardation of 1/4 wavelength. 
In order to obtain a 1/4 wavelength plate, the following requirements must 
be satisfied. In other words, an oriented film giving a retardation of 1/2 
wavelength with respect to monochromatic light and an oriented film giving 
a retardation of 1/4 wavelength with respect to monochromatic light must 
be used. Further, the dependence of the birefringence differences 
.DELTA.n.sub.1 and .DELTA.n.sub.2 of these oriented films on wavelength 
each must satisfy the relationship .DELTA.n.sub.1 /.DELTA.n.sub.2 &lt;1.05 
based on light having wavelength of 400 nm (.DELTA.n.sub.1) and 550 nm 
(.DELTA.n.sub.2). Moreover, these oriented films must be laminated with 
their optical axes crossing each other. In this case, the laminated number 
of sheets of oriented films is arbitrary. In the light of light 
transmittance, the laminated number of sheets of oriented films is 
normally from 2 to 5. The position of the oriented film giving a 
retardation of 1/2 wavelength with respect to monochromatic light and the 
oriented film giving a retardation of 1/4 wavelength with respect to 
monochromatic light are arbitrary. 
In this respect, with reference to the structure in which a sheet of an 
oriented film giving a retardation of 1/4 wavelength is disposed on a 
laminated wavelength plate on the side thereof from which light comes out, 
the relationship between the angle of crossing of the optical axes of 
various oriented films and the direction (.theta.) of polarized light 
coming out from the various oriented films can be represented by the 
following equation. Supposing that the used number of oriented films 
giving a retardation of 1/2 wavelength is n (n-th oriented film is 
represented by .lambda./2(n)) and the laminating angle of .lambda./2(1, 2, 
. . . n) are .theta..sub.1, .theta..sub.2, . . . .theta..sub.n, 
Laminating angle=2 (.theta..sub.1 +.theta..sub.2 + . . . 
+.theta..sub.n-1)+.theta..sub.n 
Direction of polarized light coming out from various 
.lambda./2 plates=2 (.theta..sub.1 +.theta..sub.2 + . . . +.theta..sub.n) 
By laminating an oriented film giving a retardation of 1/4 wavelength on 
this structure at an angle of 45 degrees, circular polarization can be 
obtained. 
The above relationship will be set forth in the table below with reference 
to the structure comprising three sheets of oriented films giving a 
retardation of 1/2 wavelength (.lambda./2 (1, 2, 3)). .lambda./4 indicates 
an oriented film giving a retardation of 1/4 wavelength. 
______________________________________ 
Direction of polarized light 
coming out from 
wavelength 
Laminating angle 
plate 
______________________________________ 
/2 (1) .theta..sub.1 
2.theta..sub.1 
/2 (2) 2.theta..sub.1 + .theta..sub.2 
2(.theta..sub.1 + .theta..sub.2) 
/2 (3) 2(.theta..sub.1 + .theta..sub.2) + .theta..sub.3 
2(.theta..sub.1 + .theta..sub.2 + .theta..sub.3) 
/4 2(.theta..sub.1 + .theta..sub.2 + .theta..sub.3) 
Circular polarization 
______________________________________ 
The oriented film giving a retardation of 1/2 wavelength or 1/4 wavelength 
with respect to monochromatic light employable herein can be obtained, 
e.g., by orienting a high molecular film monoaxially, biaxially or in any 
other proper processes. The kind of the high molecular weight compound is 
not specifically limited. In practice, however, a high molecular weight 
compound having an excellent transparency is preferably used. Examples of 
such a high molecular weight compound include polycarbonate-based high 
molecular weight compounds, polyester-based high molecular weight 
compounds, polysulfone-based high molecular weight compounds, polyether 
sulfone-based high molecular weight compounds, polystyrene-based high 
molecular weight compounds, polyolefin-based high molecular weight 
compounds, polyvinyl alcohol-based high molecular weight compounds, 
cellulose acetate-based high molecular weight compounds, polyvinyl 
chloride-based high molecular weight compounds, polymethyl 
methacrylate-based high molecular weight compounds, polyacrylate-based 
high molecular -weight compounds, and polyamide-based high molecular 
weight compounds. 
Particularly preferred among these high molecular weight weight compounds 
are polyolefin-based high molecular weight compounds, especially cyclic 
olefin-based high molecular weight compounds, cellulose acetate-based high 
molecular weight compounds, and polymethyl methacrylate-based high weight 
molecular compounds in the light of ease of realization of the foregoing 
dependence of birefringence difference on wavelength, photoelastic 
coefficient, controllability of the difference in refractive index from 
the adhesive layer with which the oriented films are laminated, etc. 
The oriented film the dependence of the birefringence differences 
.DELTA.n.sub.1 and .DELTA.n.sub.2 of which on wavelength satisfies the 
relationship .DELTA.n.sub.1 /.DELTA.n.sub.2 &lt;1.05 based on light having 
wavelength of 400 nm (.DELTA.n.sub.1) and 550 nm (.DELTA.n.sub.2) can be 
obtained by controlling the orientation conditions or the like. In order 
to prevent the 1/2 wavelength plate or 1/4 wavelength plate from departing 
from their desired retardation properties, i.e., showing undesirable 
retardation in a specific wavelength range, particularly short wavelength 
range, the foregoing value of .DELTA.n.sub.1 /.DELTA.n.sub.2 is preferably 
from 0.95 to 1.04, more preferably from 0.97 to 1.03, particularly from 
0.98 to 1.02. 
Further, in the light of satisfaction of the desired dependence of 
birefringence difference on wavelength, reduction of deviation of 
retardation from desired value in a specific wavelength range, prevention 
of coloring due to change of viewing angle, etc., an oriented film 
satisfying the relationship 0.ltoreq.Nz.ltoreq.1 is preferably used 
wherein Nz is (n.sub.x -n.sub.z)/(n.sub.x -n.sub.y) in which n.sub.x is 
the maximum in-plane refractive index, n.sub.y is the refractive index 
perpendicular to n.sub.x and n.sub.z is the vertical refractive index. 
Accordingly, the foregoing relationship means n.sub.y .ltoreq.n.sub.z 
.ltoreq.n.sub.x. If it is necessary to control the vertical refractive 
index of an oriented film, a high molecular film may be oriented while a 
heat-shrinkable film is being bonded thereto. 
The circular polarizing plate according to the present invention is a 
laminate of the foregoing laminated wavelength plate having a 1/4 
wavelength plate and a polarizing plate. An example of this circular 
polarizing plate is shown in FIG. 3. Shown at the reference numerals 2, 5 
and 6 are a transparent adhesive layer, a polarizing plate and a laminated 
wavelength plate, respectively. The circular polarizing plate can be 
formed by laminating the polarizing plate 5 with the laminated wavelength 
plate 6 at the foregoing laminating angle. During this process, the 
direction of the transmission axis of the polarizing plate can be changed 
by 90 degrees to change the direction of circular polarization (clockwise 
or counterclockwise circular polarization). 
The circular polarizing plate can be formed by any proper polarizing plate. 
The polarizing plate employable herein is not specifically limited. In 
practice, however, a polarizing plate obtained by a process which 
comprises allowing a film of a high molecular weight compound such as 
polyvinyl alcohol-based or partially-formalated polyvinyl alcohol-based 
compound and ethylene-vinyl acetate copolymer-based partially-saponified 
compound to adsorb iodine and/or two-tone dye, and then orienting the film 
or a polarizing film made of an oriented polyene film such as dehydration 
product of polyvinyl alcohol and dehydrochlorination product of polyvinyl 
chloride may be used. 
The thickness of the polarizing film is normally from 5 to 80 .mu.m but is 
not limited thereto. The polarizing plate may comprise a polarizing film 
coated with a transparent protective layer or the like on one or both 
sides thereof. Such a transparent protective layer may have various 
purposes such as reinforcing the polarizing film, improving the heat 
resistance of the polarizing film and protecting the polarizing film 
against moisture or the like. The transparent protective layer may be 
formed as a resin coating layer or resin film laminating film. It may also 
comprise a particulate material for dispersion or surface roughening 
incorporated therein. 
The circular polarizing plate preferably comprises one or both of an 
anti-reflection layer and a glare protection layer provided on one or both 
sides thereof for the purpose of preventing surface reflection or like 
purposes. The anti-reflection layer may be properly formed as a coherent 
layer such as fluorine-based polymer coating layer and multi-layer 
evaporated metal layer. 
The glare protection layer may be formed by any proper method which allows 
the surface of the circular polarizing plate to scatter reflected light. 
Examples of such a method include a method which comprises spraying and 
fixing a particulate material with a binder onto the surface of the 
circular polarizing plate, a method which comprises embossing, 
sandblasting or etching the surface of the circular polarizing plate to 
provide the surface of the circular polarizing plate with a fine 
unevenness, a method which comprises coating the surface of the circular 
polarizing plate with a transparent resin containing a particulate 
material to provide the surface of the circular polarizing plate with a 
fine unevenness, and a combination thereof. 
Examples of the foregoing particulate material include finely divided 
grains of inorganic material which may be electrically conductive such as 
silica, calcium oxide, alumina, titania, zirconia, tin oxide, indium 
oxide, cadmium oxide and antimony oxide having an average grain diameter 
of from 0.5 to 20 .mu.m, and finely divided grains of crosslinked or 
uncrosslinked organic material made of proper polymer such as polymethyl 
methacrylate and polyurethane. These particulate materials may be used 
singly or in combination of two or more thereof. 
The various layers constituting the laminated wavelength plate or circular 
polarizing plate such as oriented film and polarizing plate may be 
disposed separately from each other. However, some or whole of these 
layers may be fixed to each other to inhibit reflection by adjusting the 
interlayer refractive index, inhibit deviation in the optical system or 
inhibit the contamination by foreign matters such as dust. Fixing may be 
carried out by the use of a proper material such as transparent adhesive. 
The kind of the adhesive to be used is not specifically limited. Taking 
into account the requirement that the constituent members should undergo 
no change in optical properties, an adhesive which requires neither high 
temperature process during curing or drying in the bonding step nor 
prolonged period of time for curing or drying is desirable. From this 
standpoint of view, an adhesive layer is preferably used. 
The transparent adhesive layer may be formed by any proper polymer such as 
acrylic polymer, silicone-based polymer, polyester, polyurethane, 
polyether and synthetic rubber. Particularly preferred among these 
polymers is acrylic adhesive in the light of optical transparency, 
adhesiveness, weathering resistance, etc. 
In the light of inhibition of reflection at the interface of layers or the 
like, the adhesive layer which is preferably used herein exhibits a 
refractive index which differs from that of the object to which it is 
bonded such as oriented film by not more than 0.1, preferably not more 
than 0.08, particularly not more than 0.06. The adjustment of the 
refractive index of the adhesive layer can be carried out by selecting the 
kind of the base polymer used or blending a refractive index modifier. As 
such a refractive index modifier there may be used any proper material 
such as polymer having a higher or lower refractive index than the base 
polymer. 
Further, the adhesive layer is preferably used also because its 
viscoelasticity can relax internal stress developed in the laminate due to 
heat to exert an excellent effect of inhibiting photoelastic deformation. 
The adhesive layer which is preferably used particularly for the purpose 
of inhibiting photoelastic deformation should exert an excellent effect of 
relaxing stress. In particular, an adhesive layer having a relaxation 
elasticity of from 2.times.10.sup.5 to 1.times.10.sup.7 dyne/cm.sup.2, 
particularly from 2.times.10.sup.6 to 8.times.10.sup.6 dyne/cm.sup.2, is 
desirable. The adhesive layer to be optionally provided for the purpose of 
bonding an adherend such as liquid crystal cell to one or both surfaces of 
the laminated wavelength plate or circular polarizing plate is preferably 
such an adhesive layer for the foregoing reasons. 
The laminated wavelength plate or circular polarizing plate as 1/2 
wavelength plate or 1/4 wavelength plate of the present invention can be 
used for various purposes such as anti-reflection filter, glare protection 
filter and liquid crystal projector. In general, a liquid crystal display 
device is formed, e.g., by properly assembling a polarizing plate, a 
liquid crystal cell, and optionally a back light, a reflector, a phase 
difference compensator, etc., and then incorporating a driving circuit 
into the assembly. In the present invention, the method of forming a 
liquid crystal display device is not specifically limited except that the 
foregoing laminated wavelength plate or circular polarizing plate is used. 
Thus, a liquid crystal display device can be formed according to any 
conventional methods. 
In this respect, the circular polarizing plate acts as a circular 
polarization forming plate which emits circularly polarized light from the 
laminated wavelength plate as mentioned above when natural light enters 
the device on the polarizing plate side but acts as a linear polarization 
forming plate which linearly polarizes circularly polarized light which 
has entered the device on the laminated wavelength plate side to generate 
linearly polarized light which then enters the polarizing plate. 
Accordingly, the circular polarizing plate according to the present 
invention can be applied to a liquid crystal display as the foregoing 
circular polarization forming plate or linear polarization forming plate. 
The former function as circular polarization forming plate is useful as 
anti-reflection filter for inhibiting the surface reflection of liquid 
crystal display or the like. The latter function as linear polarization 
forming plate, if used in combination with a back light provided with a 
circular polarization forming plate made of cholesteric liquid crystal or 
the like, is useful for the formation of a system for enhancing the 
brightness of liquid crystal display device. In the formation of such a 
liquid crystal display device, any proper optical elements may be provided 
such as light diffuser, anti-glare layer, prism sheet, anti-reflection 
layer, protective layer and protective plate provided on the polarizing 
plate on the viewing side, retardation compensator provided between the 
liquid crystal cell and the polarizing plate on the viewing side and/or 
back light side and prism sheet and other light path controllers provided 
on the back light. 
The various parts constituting the laminated wavelength plate, circular 
polarizing plate or liquid crystal display according to the present 
invention such as oriented film, polarizing plate, adhesive layer, light 
diffuser and retardation compensator may be provided with ultraviolet 
absorbing properties as provided by treatment with an ultraviolet 
absorbing agent such as salicylic acid ester-based compound, 
benzophenol-based compound, benzotriazole-based compound, 
cyanoacrylate-based compound and nickel complex salt-based compound. 
Further, the liquid crystal display according to the present invention 
preferably have various constituent parts integrally fixed with an 
adhesive layer provided interposed therebetween. 
The present invention will be further described in the following examples, 
but the present invention should not be construed as being limited 
thereto. 
Reference Example 1 
A cyclic polyolefin film (hereinafter "ARTON", produced by JSR) having a 
refractive index of 1.51 and a thickness of 100 .mu.m was subjected to 50% 
orientation at a temperature of 175.degree. C. Thus, a .lambda./2 oriented 
film having .DELTA.n.sub.1 /.DELTA.n.sub.2 of 1.025 and Nz of 1 which 
gives a retardation of 1/2 wavelength with respect to light having a 
wavelength of 550 nm based on birefringent light was obtained. 
Reference Example 2 
A cyclic polyolefin film having a refractive index of 1.51 and a thickness 
of 100 .mu.m was subjected to 25% orientation at a temperature of 
175.degree. C. Thus, a .lambda./4 oriented film having .DELTA.n.sub.1 
/.DELTA.n.sub.2 of 1.025 and Nz of 1 which gives a retardation of 1/4 
wavelength with respect to light having a wavelength of 550 nm based on 
birefringent light was obtained. 
Reference Example 3 
A polycarbonate film having a refractive index of 1.59 and a thickness of 
50 .mu.m was subjected to 5% orientation at a temperature of 150.degree. 
C. Thus, a .lambda./2 oriented film having .lambda.n.sub.1 /.DELTA.n.sub.2 
of 1.16 and Nz of 1 which gives a retardation of 1/2 wavelength with 
respect to light having a wavelength of 550 nm based on birefringent light 
was obtained. 
Reference Example 4 
A polycarbonate film having a refractive index of 1.59 and a thickness of 
50 .mu.m was subjected to 2.5% orientation at a temperature of 150.degree. 
C. Thus, a .lambda./4 oriented film having .DELTA.n.sub.1 /.DELTA.n.sub.2 
of 1.16 and Nz of 1 which gives a retardation of 1/4 wavelength with 
respect to light having a wavelength of 550 nm based on birefringent light 
was obtained. 
EXAMPLE 1 
Two sheets of the .lambda./2 oriented films obtained in Reference Example 1 
were laminated with their optical axes (orientation axes) crossing each 
other at an angle of 45 degrees and an acrylic adhesive having a 
refractive index of 1.47 provided interposed therebetween to obtain a 1/2 
wavelength plate according to the present invention. 
EXAMPLE 2 
A sheet of the .lambda./2 oriented film obtained in Reference Example 1 and 
a sheet of the .lambda./4 oriented film obtained in Reference Example 2 
were laminated with their optical axes crossing each other at an angle of 
62.5 degrees and an acrylic adhesive having a refractive index of 1.47 
provided interposed therebetween to obtain a 1/4 wavelength plate 
according to the present invention. A polarizing film (NPF-HEG1425DUAG30, 
produced by NITTO DENKO CORP.) was then laminated on the 1/4 wavelength 
plate thus obtained with the optical axis of the .lambda./4 oriented film 
and the transmission axis of the polarizing film crossing each other at an 
angle of 80 degrees and the foregoing acrylic adhesive provided interposed 
therebetween to obtain a circular polarizing plate according to the 
present invention. 
Comparative Example 1 
A 1/2 wavelength plate was obtained in the same manner as in Example 1 
except that the .lambda./2 oriented film obtained in Reference Example 3 
was used. 
Comparative Example 2 
A circular polarizing plate was obtained in the same manner as in Example 2 
except that the .lambda./2 oriented film and .lambda./4 oriented film 
obtained in Reference Examples 3 and 4 were used. 
Comparative Example 3 
A circular polarizing plate was obtained in the same manner as in Example 2 
except that the .lambda./2 oriented film and .lambda./4 oriented film 
obtained in Reference Examples 1 and 4 were used. 
Evaluation test 
Wide band properties of 1/2 wavelength plate: 
The 1/2 wavelength plates obtained in Example 1 and Comparative Example 1 
were each disposed between polarizing plates which were arranged in a 
cross Nicol fashion. Under these conditions, these 1/2 wavelength plates 
were examined for spectrum in transmission mode. The 1/2 wavelength plate 
was disposed in such an arrangement that the optical axis of two sheets of 
.lambda./2 oriented films were 22.5 degrees and 67.5 degrees, 
respectively, with respect to the transmission axis of the polarizing 
plate on the incoming side. 
The results are shown in FIG. 4 (Example 1) and FIG. 5 (Comparative Example 
1). These results show that Example 1 gives almost flat retardation 
properties and high transmittance values over a wavelength range as wide 
as from 400 to 700 nm while Comparative Example 1 exhibits low 
transmittance values at a wavelength as short as from 400 to 450 nm. 
Wide band properties of anti-reflection effect: 
The circular polarizing plates obtained in Example 2 and Comparative 
Example 2 were placed on a mirror. Under these conditions, these circular 
polarizing plates were examined for spectrum in reflection mode. The 
results are shown in FIG. 6 (Example 2) and FIG. 7 (Comparative Example 
2). These results show that Example 2 exhibits a good light shielding 
effect and hence almost flat properties over a wavelength range as wide as 
from 400 to 700 nm while Comparative Example 2 shows a peak reflectance 
value in the vicinity of 430 nm, demonstrating that a bluish light is 
leaked, and high reflectance values as a whole due to reflection at the 
interface of the adhesive layer. Heat resistance of circular polarizing 
plate: 
The circular polarizing plates obtained in Example 2 and Comparative 
Examples 2 and 3 were bonded to a glass plate with an acrylic adhesive 
layer provided interposed therebetween. The laminate was then heated to a 
temperature of 70.degree. C. The laminate was then placed on a reflector 
and examined for coloring and color unevenness (color uniformity) of 
reflected light while being kept at the same temperature. 
The results are set forth in the table below. 
______________________________________ 
Comparative 
Comparative 
Example 2 Example 3 2 
______________________________________ 
Coloring None Observed Observed 
Color Observed 
Observed 
unevenness 
______________________________________ 
While the invention has been described in detail and with reference to 
specific embodiments thereof, it will be apparent to one skilled in the 
art that various changes and modifications can be made therein without 
departing from the spirit and scope thereof.