U.S. patent application number 11/994448 was filed with the patent office on 2009-05-28 for polarizing plate with optical compensation layer and image display apparatus using the same.
This patent application is currently assigned to NITTO DENKO CORPORATION. Invention is credited to Yoshitsugu Kitamura, Katsunori Takada.
Application Number | 20090135343 11/994448 |
Document ID | / |
Family ID | 38067252 |
Filed Date | 2009-05-28 |
United States Patent
Application |
20090135343 |
Kind Code |
A1 |
Kitamura; Yoshitsugu ; et
al. |
May 28, 2009 |
POLARIZING PLATE WITH OPTICAL COMPENSATION LAYER AND IMAGE DISPLAY
APPARATUS USING THE SAME
Abstract
The polarizing plate with an optical compensation layer of the
present invention includes: a hardcoat layer; a polarizer; a first
optical compensation layer placed so that a slow axis thereof
intersects with an absorption axis of the polarizer; and a second
optical compensation layer placed so that a slow axis thereof
intersects with the absorption axis of the polarizer in the stated
order, wherein: the first optical compensation layer provides a
substantially 1/2 retardation with respect to a wavelength of
monochromatic light; the second optical compensation layer provides
a substantially 1/4 retardation with respect to a wavelength of
monochromatic light; and the hardcoat layer contains
urethaneacrylate, polyol (meth)acrylate, and (meth) acrylic polymer
having an alkyl group containing at least two hydroxyl groups. The
polarizing plate with an optical compensation layer of the present
invention may suitably be used for various image display
apparatuses (such as a liquid crystal display apparatus and a
self-luminous display apparatus).
Inventors: |
Kitamura; Yoshitsugu;
(Osaka, JP) ; Takada; Katsunori; (Osaka,
JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW, SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
NITTO DENKO CORPORATION
Ibaraki-shi, Osaka
JP
|
Family ID: |
38067252 |
Appl. No.: |
11/994448 |
Filed: |
November 24, 2006 |
PCT Filed: |
November 24, 2006 |
PCT NO: |
PCT/JP2006/323390 |
371 Date: |
January 2, 2008 |
Current U.S.
Class: |
349/96 ;
359/489.03 |
Current CPC
Class: |
G02F 2202/40 20130101;
G02F 1/133634 20130101; G02F 2201/50 20130101; G02F 1/13363
20130101; G02F 2413/12 20130101; G02F 2413/08 20130101; G02F
1/133528 20130101; G02F 1/133638 20210101; G02F 2413/13 20130101;
G02B 5/3033 20130101; G02F 2413/03 20130101; G02B 5/3083 20130101;
C09K 2323/035 20200801 |
Class at
Publication: |
349/96 ;
359/499 |
International
Class: |
G02F 1/13363 20060101
G02F001/13363; G02B 5/30 20060101 G02B005/30 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 28, 2005 |
JP |
2005-341547 |
Claims
1. A polarizing plate with an optical compensation layer,
comprising: a hardcoat layer; a polarizer; a first optical
compensation layer placed so that a slow axis thereof intersects
with an absorption axis of the polarizer; and a second optical
compensation layer placed so that a slow axis thereof intersects
with the absorption axis of the polarizer in the stated order,
wherein: the first optical compensation layer provides a
substantially 1/2 retardation with respect to a wavelength of
monochromatic light; the second optical compensation layer provides
a substantially 1/4 retardation with respect to a wavelength of
monochromatic light; and the hardcoat layer contains
urethaneacrylate, polyol(meth)acrylate, and (meth)acrylic polymer
having an alkyl group containing at least two hydroxyl groups.
2. The polarizing plate with an optical compensation layer
according to claim 1, wherein the polyol(meth)acrylate contained in
the hardcoat layer contains pentaerythritol triacrylate and
pentaerythritol tetraacrylate.
3. The polarizing plate with an optical compensation layer
according to claim 1, wherein the hardcoat layer has a thickness of
15 .mu.m to 50 .mu.m.
4. The polarizing plate with an optical compensation layer
according to claim 1, wherein the first optical compensation layer
contains a resin with an absolute value of a photoelastic
coefficient of 2.0.times.10.sup.-11 m.sup.2/N or less and has a
relationship of nx.sub.1>ny.sub.1=nz.sub.1 and an in-plane
retardation Re.sub.1 of 200 to 300 nm.
5. polarizing plate with an optical compensation layer according to
claim 1, wherein the second optical compensation layer contains a
resin with an absolute value of a photoelastic coefficient of
2.0.times.10.sup.-11 m.sup.2/N or less and has a relationship of
nx.sub.2>ny.sub.2=nz.sub.2 and an in-plane retardation Re.sub.2
of 90 to 160 nm.
6. The polarizing plate with an optical compensation layer
according to claim 1, wherein each of the first optical
compensation layer and the second optical compensation layer
comprises a stretched film obtained by uniaxially stretching a
polymer film containing a norbornene-based resin.
7. The polarizing plate with an optical compensation layer
according to claim 1, further comprising a protective layer on at
least one side of the polarizer.
8. The polarizing plate with an optical compensation layer
according to claim 1, wherein the polarizer, the first optical
compensation layer, and the second optical compensation layer are
placed via a pressure-sensitive adhesive layer.
9. The liquid crystal panel, comprising the polarizing plate with
an optical compensation layer according to claim 1, and a liquid
crystal cell.
10. The liquid crystal panel according to claim 9, wherein the
liquid crystal cell employs a TN mode, an ECB mode, or a VA
mode.
11. A liquid crystal display apparatus comprising the liquid
crystal panel according to claim 9.
12. An image display apparatus comprising the polarizing plate with
an optical compensation layer according to claim 1.
13. A liquid crystal display apparatus comprising the liquid
crystal panel according to claim 10.
Description
TECHNICAL FIELD
[0001] The present invention relates to a polarizing plate with an
optical compensation layer and an image display apparatus using the
same. More specifically, the present invention relates to a
polarizing plate with an optical compensation layer, which does not
require a cover plate, contributes to the reduction in thickness,
is excellent in abrasion resistance, moist heat resistance, and
viewing angle compensation, exhibits circularly polarized light in
a wide-band, prevents heat non-uniformity (heat fluctuation), and
suppresses light leakage in a black display, and an image display
apparatus using the polarizing plate with an optical compensation
layer.
BACKGROUND ART
[0002] As one of image display apparatuses, there is known a liquid
crystal display apparatus. Along with the technological innovations
including wide viewing angle, high definition, high-speed response,
and color reproducibility of the liquid crystal display apparatus,
the application of the liquid crystal display apparatus has also
been spread from a laptop computer and a monitor to a television, a
mobile telephone, and further to a personal digital assistant
(PDA). According to a basic configuration, the liquid crystal
display apparatus includes a liquid crystal cell in which a pair of
glass substrates each having a transparent electrode are opposed to
each other with a predetermined interval via spacers and a liquid
crystal material is sealed between the glass substrates, and
polarizing plates arranged on both sides of the liquid crystal
cell.
[0003] For example, in middle and small-sized liquid crystal
display apparatuses used in the mobile telephones and the PDAs, a
semi-transmissive reflection-type liquid crystal display apparatus
has been proposed in addition to a transmission-type liquid crystal
display apparatus and a reflection-type liquid crystal display
apparatus (for example, see Patent Documents 1 and 2). The
semi-transmissive reflection-type liquid crystal display apparatus
uses ambient light in a bright place in the same way as in the
reflection-type liquid crystal display apparatus, and enables a
display to be recognized visually with an internal light source
such as a backlight in a dark place. In other words, the
semi-transmissive reflection-type liquid crystal display apparatus
adopts a display system having both a reflection type and a
transmission type, and can switch between a reflection mode and a
transmission mode depending upon the lightness of the environment.
As a result, the semi-transmissive reflection-type liquid crystal
display apparatus can perform a clear display even in a dark
environment while reducing power consumption, so it is preferably
used in a display part of mobile equipment.
[0004] A specific example of the semi-transmissive reflection-type
liquid crystal display apparatus described above includes a liquid
crystal display apparatus, for example, in which a reflective film
obtained by forming a window portion for light transmittance in a
metal film such as aluminum is provided on an inner side of a lower
substrate, and the reflective film is allowed to function as a
semi-transmissive reflective plate. In the liquid crystal display
apparatus described above, in a reflection mode, outer light
incident from an upper substrate side passes through the liquid
crystal layer, is reflected from the reflective film on the inner
side of the lower substrate, passes through the liquid crystal
layer again, and is outgoing from the upper substrate side, thereby
contributing to a display. On the other hand, in a transmission
mode, light of a backlight incident from the lower substrate side
passes through the window portion of the reflective film, passes
through the liquid crystal layer, and is outgoing from the upper
substrate side, thereby contributing to a display. Thus, in a
reflective film formation region, an area where the window portion
is formed functions as a transmission display region, and the other
area functions as a reflection display region.
[0005] On the other hand, the liquid crystal display apparatus uses
an optical film made of various polymer materials as an optical
compensation layer for the purpose of enhancing image quality, as
well as a polarizing plate. The optical compensation layer is
selected appropriately based on the display mode (TN, VA, OCB, IPS,
ECB, etc.) of liquid crystal. As such an optical compensation
layer, for example, a uniaxially stretched film of a polymer film
is known.
[0006] In the above-mentioned conventional liquid crystal display
apparatus, a cover plate made of glass (thickness: about 0.5 mm) or
a thick plastic sheet is provided on an outer side of a polarizing
plate to prevent the damage of the polarizing plate. However, in
middle and small-sized liquid crystal display apparatuses required
to be reduced in thickness and weight, it is not preferred to
provide such a cover plate. Further, it can be assumed that the
middle and small-sized liquid crystal display apparatuses are used
under severe conditions (for example, high temperature and high
humidity), so moist heat resistance is also required.
Patent Document 1: JP 11-242226 A
Patent Document 2: JP 2001-209065 A
DISCLOSURE OF THE INVENTION
Problems to be Solved by the Invention
[0007] The present invention has been made in view of solving the
above-mentioned conventional problems, and an object of the present
invention is to provide a polarizing plate with an optical
compensation layer, which does not require a cover plate made of
glass or the like, contributes to the reduction in thickness, is
excellent in abrasion resistance, moist heat resistance, and
viewing angle compensation, exhibits circularly polarized light in
a wide band, prevents heat non-uniformity, and suppresses light
leakage in a black display, and an image display apparatus using
the polarizing plate with an optical compensation layer.
Means for Solving the Problems
[0008] According to one aspect of the invention, a polarizing plate
with an optical compensation layer is provided. The polarizing
plate with an optical compensation layer includes: a hardcoat
layer; a polarizer; a first optical compensation layer placed so
that a slow axis thereof intersects with an absorption axis of the
polarizer; and a second optical compensation layer placed so that a
slow axis thereof intersects with the absorption axis of the
polarizer in the stated order, wherein: the first optical
compensation layer provides a substantially 1/2 retardation with
respect to a wavelength of monochromatic light; the second optical
compensation layer provides a substantially 1/4 retardation with
respect to a wavelength of monochromatic light; and the hardcoat
layer contains urethaneacrylate, polyol (meth)acrylate, and (meth)
acrylic polymer having an alkyl group containing at least two
hydroxyl groups.
[0009] In one embodiment of the invention, the polyol(meth)acrylate
contained in the hardcoat layer contains pentaerythritol
triacrylate and pentaerythritol tetraacrylate.
[0010] In one embodiment of the invention, the hardcoat layer has a
thickness of 15 .mu.m to 50 .mu.m.
[0011] In one embodiment of the invention, the first optical
compensation layer contains a resin with an absolute value of a
photoelastic coefficient of 2.0.times.10.sup.-11 m.sup.2/N or less
and has a relationship of nx.sub.1>ny.sub.1=nz.sub.1 and an
in-plane retardation Re.sub.1 of 200 to 300 nm.
[0012] In one embodiment of the invention, the second optical
compensation layer contains a resin with an absolute value of a
photoelastic coefficient of 2.0.times.10.sup.-11 m.sup.2/N or less
and has a relationship of nx.sub.2>ny.sub.2=nz.sub.2 and an
in-plane retardation Re.sub.2 of 90 to 160 nm.
[0013] In one embodiment of the invention, each of the first
optical compensation layer and the second optical compensation
layer includes a stretched film obtained by uniaxially stretching a
polymer film containing a norbornene-based resin.
[0014] In one embodiment of the invention, the polarizer further
includes a protective layer on at least one side thereof.
[0015] In one embodiment of the invention, the polarizer, the first
optical compensation layer, and the second optical compensation
layer are placed via a pressure-sensitive adhesive layer.
[0016] According to another aspect of the invention, a liquid
crystal panel is provided. The liquid crystal panel includes the
polarizing plate with an optical compensation layer and a liquid
crystal cell.
[0017] In one embodiment of the invention, the liquid crystal cell
employs a TN mode, an ECB mode, or a VA mode.
[0018] According to still another aspect of the invention, a liquid
crystal display apparatus is provided. The liquid crystal display
apparatus includes the liquid crystal panel.
[0019] According to still another aspect of the invention, an image
display apparatus is provided. The image display apparatus includes
the polarizing plate with an optical compensation layer.
EFFECTS OF THE INVENTION
[0020] As described above, by allowing a hardcoat layer to contain
urethaneacrylate, polyol (meth)acrylate, and (meth) acrylic polymer
having an alkyl group containing at least two hydroxyl groups, a
polarizing plate with an optical compensation layer that does not
require a cover plate, contributes to the reduction in thickness,
and is excellent in abrasion resistance and moist heat resistance
can be obtained. It is presumed that, due to the presence of those
resins, the hardcoat layer has an excellent hardness, whereby
cracks, curls, and the deterioration in shrinkage on curing and in
flexibility are prevented. Thus, the hardcoat layer in the present
invention has excellent abrasion resistance and heat moist
resistance, so it can replace a cover plate made of glass or a
thick plastic sheet. The hardcoat layer in the present invention
(preferably having a thickness of 15 to 50 .mu.m) is remarkably
thinner than the above-mentioned glass (thickness: about 0.5 mm)
used in a liquid crystal display apparatus and the like, so the
hardcoat layer can greatly contribute to the reductions in
thickness and weight in a liquid crystal display apparatus and the
like.
[0021] Further, the absorption axis of the polarizer and the slow
axes of the first optical compensation layer (substantially a
.lamda./2 plate) and the second optical compensation layer
(substantially a .lamda./4 plate) are placed so as to intersect
with each other. Therefore, in a liquid crystal display apparatus,
particularly of a TN mode, an ECB mode, or a VA mode, a polarizing
plate with an optical compensation layer that has excellent viewing
angle compensation, exhibits circularly polarized light in a wide
band, and suppresses light leakage in a black display can be
obtained. Further, each of a first optical compensation layer and a
second optical compensation layer may have an absolute value of a
photoelastic coefficient in a predetermined range, so it can
suppress a change in a retardation value caused by shrinkage stress
during heating, and hence, heat non-uniformity can be prevented
satisfactorily.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] [FIG. 1] Parts (a) and (b) are schematic cross-sectional
views of a polarizing plate with an optical compensation layer
according to a preferred embodiment of the present invention.
[0023] [FIG. 2] An exploded perspective view of the polarizing
plate with an optical compensation layer according to a preferred
embodiment of the present invention.
[0024] [FIG. 3] A schematic cross-sectional view of a liquid
crystal panel used in a liquid crystal display apparatus according
to a preferred embodiment of the present invention.
[0025] [FIG. 4] Surface observation results of hardcoat layers in
Example 1 and Comparative Example 1 before and after measurement of
an abrasion resistance test.
[0026] [FIG. 5] Results of a moist heat resistance test of
polarizing plates with an optical compensation layer of Example 1
and Comparative Example 1.
DESCRIPTION OF SYMBOLS
[0027] 10 polarizing plate with an optical compensation layer
[0028] 11 hardcoat layer [0029] 12 polarizer [0030] 13 first
optical compensation layer [0031] 14 second optical compensation
layer [0032] 15 protective layer [0033] 16 third optical
compensation layer [0034] 20 liquid crystal cell [0035] 100 liquid
crystal panel
BEST MODE FOR CARRYING OUT THE INVENTION
Definitions of Terms and Symbols
[0036] Definitions of terms and symbols in the specification of the
present invention are described below.
[0037] (1) Symbols "nx" indicates a refractive index in a direction
providing a maximum in-plane refractive index (that is, a slow axis
direction), symbol "ny" indicates a refractive index in a direction
perpendicular to the slow axis in the plane (that is, a fast axis
direction), and symbol "nz" indicates a refractive index in a
thickness direction. Further, "ny=nz", for example, not only
indicates a case where ny and nz are exactly equal but also
indicates a case where ny and nz are substantially equal. In the
specification of the present invention, the phrase "substantially
equal" includes a case where ny and nz differ within a range
providing no effects on overall polarizing characteristics of a
polarizing plate with an optical compensation layer in practical
use. Similarly, "nx=ny", not only indicates a case where nx and ny
are exactly equal but also indicates a case where nx and ny are
substantially equal.
[0038] (2) The term "in-plane retardation Re" indicates an in-plane
retardation value of a film (layer) measured at 23.degree. C. by
using light of a wavelength of 590 nm. Re is obtained from an
equation Re=(nx-ny).times.d, where nx and ny represent refractive
indices of a film (layer) at a wavelength of 590 nm in a slow axis
direction and a fast axis direction, respectively, and d (nm)
represents a thickness of the film (layer).
[0039] (3) Thickness direction retardation Rth indicates a
thickness direction retardation value measured at 23.degree. C. by
using light of a wavelength of 590 nm. Rth is obtained from an
equation Rth=(nx-nz).times.d, where nx and nz represent refractive
indices of a film (layer) at a wavelength of 590 nm in a slow axis
direction and a thickness direction, respectively, and d (nm)
represents a thickness of the film (layer).
[0040] (4) The subscripts "1", "2", and "3" attached to a term or
symbol described in the specification of the present invention
represent a first optical compensation layer, a second optical
compensation layer, and a third optical compensation layer,
respectively.
[0041] (5) The term ".lamda./2 plate" indicates a plate having a
function of converting linearly polarized light having a specific
vibration direction into linearly polarized light having a
vibration direction perpendicular thereto, or converting
right-handed circularly polarized light into left-handed circularly
polarized light (or converting left-handed circularly polarized
light into right-handed circularly polarized light). The .lamda./2
plate has an in-plane retardation value of a film (layer) of about
1/2 with respect to a predetermined light wavelength (generally, in
a visible light region).
[0042] (6) The term ".lamda./4 plate" indicates a plate having a
function of converting linearly polarized light of a specific
wavelength into circularly polarized light (or converting
circularly polarized light into linearly polarized light). The
.lamda./4 plate has an in-plane retardation value of a film (layer)
of about 1/4 with respect to a predetermined light wavelength
(generally, in a visible light region).
[0043] A. Entire Configuration of a Polarizing Plate with an
Optical Compensation Layer
[0044] FIG. 1(a) is a schematic cross-sectional view of a
polarizing plate with an optical compensation layer according to a
preferred embodiment of the present invention. As shown in FIG.
1(a), a polarizing plate with an optical compensation layer 10
includes a hardcoat layer 11, a polarizer 12, a first optical
compensation layer 13, and a second optical compensation layer 14
in the stated order. The polarizer 12 and the first optical
compensation layer 13, and the first optical compensation layer 13
and the second optical compensation layer 14 are laminated
respectively via any suitable pressure-sensitive adhesive layer or
adhesive layer (not shown). FIG. 1(b) is a schematic
cross-sectional view of a polarizing plate with an optical
compensation layer according to another preferred embodiment of the
present invention. As shown in FIG. 1(b), the polarizing plate with
an optical compensation layer 10 of the present invention can
further include a third optical compensation layer 16 on a side of
the second optical compensation layer 14, which is opposite to the
first optical compensation layer 13, if required. Further, if
required, any suitable protective layer 15 may be provided on at
least one surface of the polarizer 12 (in FIG. 1, the protective
layers 15 are provided on both surfaces of the polarizer 12). The
entire thickness of the polarizing plate with an optical
compensation layer of the present invention is preferably 280 to
520 .mu.m, and more preferably 280 to 350 .mu.m.
[0045] B. Hardcoat Layer
[0046] The hardcoat layer 11 contains urethaneacrylate (A),
polyol(meth)acrylate (B), and a (meth)acrylic polymer (C) having an
alkyl group containing at least two hydroxyl groups. Hereinafter,
those materials (containing additives and the like, if required)
may be referred to as hardcoat layer-forming materials. Due to the
presence of those materials, the hardcoat layer has an excellent
hardness, whereby cracks and curls in the hardcoat layer can be
prevented. As a result, the hardcoat layer can have excellent
abrasion resistance and moist heat resistance, so the hardcoat
layer can replace a cover plate made of glass or the like. Further,
the hardcoat layer is remarkably thinner than the cover plate made
of glass or the like, so the hardcoat layer of the present
invention contributes to the reduction in thickness of the
polarizing plate with an optical compensation layer, and further
greatly contributes to the reduction in thickness and weight of the
entire liquid crystal display apparatus.
[0047] The thickness of the above hardcoat layer is appropriately
set depending upon the purpose. The thickness is preferably 15 to
50 .mu.m, more preferably 15 to 40 .mu.m, still more preferably 15
to 30 .mu.m, and particularly preferably 18 to 23 .mu.m. The
hardcoat layer can have a hardness of a certain degree or more (for
example, 4H or more in terms of the pencil hardness) due to the
thickness in those ranges, so the hardcoat layer can have excellent
abrasion resistance. Further, the hardness of a certain degree or
more can prevent cracks and curls in the hardcoat layer. Further,
since the hardcoat layer is remarkably thinner (for example, 1/10
or less) than a cover plate made of glass or the like, the hardcoat
layer can contribute to the reduction in thickness of the
polarizing plate with an optical compensation layer.
[0048] The above pencil hardness is preferably 4H or more, and
particularly preferably 5H or more. The pencil hardness is
preferably 8H or less although the upper limit thereof is not
limited. Because the pencil hardness is in those ranges, excellent
abrasion resistance can be obtained.
[0049] The abrasion resistance of the above hardcoat layer is
appropriately set depending upon the purpose. The abrasion
resistance can be based on difference in a haze value of a hardcoat
layer before and after an abrasion resistance test (descried later
in detail) by conducting the abrasion resistance test, for example.
The difference in a haze value is preferably 0 to 0.7, and more
preferably 0 to 0.5. Due to difference in the haze value in those
ranges, a practically excellent hardcoat layer that has excellent
abrasion resistance, excellent transparency and the like can be
obtained.
[0050] As the above urethaneacrylate (A), any suitable
urethaneacrylate is adopted. Urethaneacrylate preferably contains
(meth) acrylic acid and/or (meth)acrylate, polyol, and
diisocyanate. For example, urethaneacrylate produced by preparing
hydroxy(meth)acrylate having at least one hydroxyl group from
(meth)acrylic acid and/or (meth)acrylate and polyol, and allowing
hydroxy(meth)acrylate to react with diisocyanate is used. Those
components may be used alone or in a combination. Further, various
kinds of additives may be added depending upon the purpose. In this
specification, (meth)acrylic acid refers to acrylic acid and/or
methacylic acid, and the term "(meth)" has the meaning similar to
the above. In the case of using acrylic acid and methacrylic acid
together, the mixing ratio thereof is not particularly limited and
appropriately set depending upon the purpose.
[0051] As the (meth)acrylate, any appropriate (meth)acrylates may
be used. For example, alkyl (meth)acrylates such as methyl
(meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate,
isopropyl (meth)acrylate, and butyl (meth)acrylate, and cycloalkyl
(meth)acrylate such as cyclohexyl (meth)acrylate are mentioned.
[0052] The polyol is a compound having at least two hydroxyl
groups. As the polyol, any appropriate polyols may be used. For
example, ethylene glycol, 1,3-propylene glycol, 1,2-propylene
glycol, diethylene glycol, dipropylene glycol, neopentyl glycol,
1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, 1,9-nonanediol,
1,10-decane glycol, 2,2,4-trimethyl-1,3-pentanediol,
3-methyl-1,5-pentanediol, neopentyl glycol hydroxy pivalate,
cyclohexane dimethylol, 1,4-cyclohexanediol, spiroglycol,
tricyclode cane methylol, hydrogenated bisphenol A,
ethyleneoxide-added bisphenol A, propyleneoxide-added bisphenol A,
trimethylol ethane, tridimethylol propane, glycerine,
3-methylpentane-1,3,5-triol, pentaerythritol, dipentaerythritol,
tripentaerythritol, and glucoses are mentioned.
[0053] As the diisocyanate, any appropriate diisocyanates may be
used. For example, each diisocyanate of aromatic, aliphatic, or
alicyclic diisocyanates can be used. More specifically,
tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone
diisocyanate, 2,4-tolylene diisocyanate, 4,4-diphenyl diisocyanate,
1,5-naphthalene diisocyanate, 3,3-dimethyl-4,4-diphenyl
diisocyanate, xylene diisocyanate, trimethylhexamethylene
diisocyanate, 4,4-diphenylmethane diisocyanate, and hydrogenated
products thereof are mentioned.
[0054] The content of the urethaneacrylate (A) is appropriately set
depending upon the purpose. The content of the urethaneacrylate is
preferably 15 to 55 parts by weight, and more preferably 25 to 45
parts by weight with respect to 100 parts by weight of total resin
components (total of resin components A to C and additive resin
components) of the hardcoat layer-forming materials. When the
adding amount of the urethaneacrylate is in the above range, the
hardness and the flexibility are well balanced, and cracks and
curls can be prevented in a hardcoat layer. Further, a hardcoat
layer having adhesion with respect to the protective layer, the
polarizer, or the like, and having desired abrasion resistance
(hardness) can be obtained.
[0055] As the polyol (meth)acrylate (B), any appropriate polyol
(meth)acrylates may be used. More specifically, pentaerythritol
di(meth)acrylate, pentaerythritol tri(meth)acrylate,
pentaerythritol tetra(meth)acrylate, dipentaerythritol
hexa(meth)acrylate, and 1,6-hexanediol (meth)acrylate are
mentioned. Those components are used alone or in combination. In
addition, various additives may be added as required.
[0056] The polyol(meth)acrylate (B) preferably contains
pentaerythrytol triacrylate and pentaerythrytol tetraacrylate.
Pentaerythrytol triacrylate and pentaerythrytol tetraacrylate are
contained in any suitable state. For example, the
polyol(meth)acrylate (B) may be a copolymer or a mixture thereof.
Further, the polymerization ratio, mixing ratio (content), etc.
thereof are set appropriately depending upon the purpose. For
example, in the case of using the polyol(meth)acrylate (B) as a
mixture, the content of pentaerythriol triacrylate is preferably 10
to 40 parts by weight, more preferably 15 to 35 parts by weight,
and particularly preferably 20 to 30 parts by weight with respect
to 100 parts by weight of the urethaneacrylate (A). The content of
pentaerythritol tetraacrylate is preferably 25 to 55 parts by
weight, more preferably 30 to 50 parts by weight, and particularly
preferably 35 to 45 parts by weight with respect to 100 parts by
weight of the urethaneacrylate (A). Due to the contents in those
ranges, a hardcoat layer having excellent hardness can be
obtained.
[0057] The content of the polyol(meth)acrylate (B) is preferably 70
to 180 parts by weight, and more preferably 100 to 150 parts by
weight with respect to 100 parts by weight of the urethaneacrylate
(A). When the polyol(meth)acrylate (B) is contained in parts by
weight in the above range with respect to the urethaneacrylate (A),
the shrinkage on curing of the hardcoat layer is small, curls in
the hardcoat layer can be prevented, and the degradation in
flexibility of the hardcoat layer can be suppressed. Further, when
the content of the polyol(meth)acrylate (B) is in the above range,
abrasion resistance (i.e., the difference in a haze value) can be
set in the above desired range (preferably 0 to 0.7, more
preferably 0 to 0.5), so a practically excellent hardcoat layer
that is excellent in a hardcoat property, i.e., a hardness and
abrasion resistance, and is excellent in transparency can be
obtained.
[0058] As the above (meth) acrylic polymer (C), the one having an
alkyl group containing at least two hydroxyl groups is used.
Specific examples thereof include a (meth) acrylic polymer having a
2,3-dihydroxypropyl group, and (meth)acrylic polymer having a
2-hydroxyethyl group and 2,3-dihydroxypropyl group.
[0059] The content of the above (meth) acrylic polymer (C) is
preferably 25 to 110 parts by weight, and more preferably 45 to 85
parts by weight with respect to 100 parts by weight of the
urethaneacrylate (A). When the content of the (meth) acrylic
polymer is in the above range, an excellent applying property can
be obtained, and curls in the hardcoat layer can be suppressed.
[0060] According to the present invention, due to containing the
above (meth)acrylic polymer (C), the shrinkage on curing of the
hardcoat layer is suppressed, and as a result, the occurrence of
curls is prevented. In terms of the production of a hardcoat layer
and the like, it is preferred that the occurrence of curls is
suppressed within 30 mm. By suppressing the occurrence of curls
within the range, workability and a production efficiency can be
enhanced further.
[0061] The above hardcoat layer-forming materials may have
inorganic fine particles and/or organic fine particles. The above
inorganic fine particles are not particularly limited, and examples
thereof include silicon oxide, titanium oxide, aluminum oxide, zinc
oxide, tin oxide, calcium carbonate, barium sulfate, talc, kaolin,
and calcium sulfate. The organic fine particles are not
particularly limited, and examples thereof include
polymethylmethacrylate acrylate resin powder, silicone-based resin
powder, polystyrene resin powder, polycarbonate resin powder,
acrylstyrene-based resin powder, benzoguanamine-based resin powder,
melamine-based resin powder, polyolefin-based resin powder,
polyester-based resin powder, polyamide resin powder,
polyimide-based resin powder, and polyethylene fluoride resin
powder. Fine particles that do not allow the hardcoat layer to
shrink on curing are preferred.
[0062] The above fine particles adjust the apparent refractive
index of the hardcoat layer depending upon the particle size,
content, and the like, so they can suppress a phenomenon called an
interference fringe in which reflected light of ambient light
exhibits a rainbow hue. Recently, for example, three band
fluorescent lamps, which have a strong emission intensity in a
particular wavelength and are characterized by allowing an object
to be recognized clearly, have increased greatly, and an
interference fringe appearing remarkably during the use of the
three band fluorescent lamps can be suppressed by using such fine
particles. Further, even in the case where the refractive index
changes between the hardcoat layer and the polarizer or the like
adjacent thereto, the degradation in display quality can be
suppressed by adjusting the apparent refractive index.
[0063] The shape of the above fine particles is not particularly
limited, and may have a spherical shape such as a bead shape or an
amorphous shape such as a powder shape. Those fine particles can be
selected alone or in combination for use. The average particle size
of the fine particles is set appropriately depending upon the
purpose. The average particle size is preferably 1 to 30 .mu.m, and
more preferably 2 to 20 .mu.m. Further, the ultra-fine particles
and the like may be dispersed or impregnated in the fine particles,
if required.
[0064] The content of the above fine particles is not particularly
limited, and can be set appropriately depending upon the purpose
and the particle size of the fine particles. For example, in the
case of providing an antiglare effect, the content of the fine
particles is preferably 2 to 60 parts by weight with respect to 100
parts by weight of the hardcoat layer-forming materials. Further,
in the case of providing an antiblocking property, the content of
the fine particles is preferably 1 to 50 parts by weight with
respect to 100 parts by weight of the hardcoat layer-forming
material.
[0065] The above ultra-fine particles have a function of adjusting
the apparent refractive index of the hardcoat layer in the same way
as in the above fine particles, as well as the function of
providing electrical conductivity. The particle size of the
ultra-fine particles is selected appropriately depending upon the
purpose, and is preferably 100 nm or less. The lower limit of the
ultra-fine particles is preferably 1 nm or more although not
particularly limited. As the ultra-fine particles, any suitable
ultra-fine particles are used. Preferably, the components (for
example, a metal oxide) similar to those of the above fine
particles are used. The ultra-fine particles may be used alone or
in a combination with the above fine particles. The compounding
ratio of the ultra-fine particles with the above fine particles or
the like is set appropriately depending upon the purpose.
[0066] The above hardcoat layer-forming materials can preferably
contain any suitable solvent. Due to the presence of the solvent in
the hardcoat layer-forming materials, the applying property of the
hardcoat layer-forming materials is enhanced. The concentration of
the solvent can be selected appropriately depending upon the
purpose. The content of the hardcoat layer-forming materials is
preferably 40 to 60 parts by weight, and more preferably 45 to 55
parts by weight with respect to 100 parts by weight of the solvent.
When the solvent is contained within those ranges, for example,
applying nonuniformity and drying nonuniformity can be suppressed,
and an excellent applying property can be obtained.
[0067] Specific examples of the solvent include methyl formate,
ethyl formate, n-pentyl formate, butyl formate, methyl acetate,
ethyl acetate, n-pentyl acetate, butyl acetate, isobutyl acetate,
methyl propionate, ethyl propionate, dibutyl ether, dimethoxy
methane, diethoxy ethane, propylene oxide, 1,4-dioxane,
1,3-dioxolane, 1,3,5-trioxane, tetra hydrofurane, acetone,
methylethyl ketone, diethyl ketone, dipropyl ketone, diisobutyl
ketone, cyclopentanone, cyclohexanone, methylcyclohexanone,
acetylacetone, diaceton alcohol, methyl acetoacetate, ethyl
acetoacetate, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol,
2-butanol, 2-methyl-2-butanol, 1-pentanol, cyclohexanol,
methylisobutyl ketone, 2-pentanone, 2-hexanone, 2-octanone, and
3-heptanone. Those solvents may be used alone or in a combination.
Preferably, the solvent is ethyl acetate and/or butyl acetate. The
content of those solvents is set appropriately depending upon the
purpose. For example, in the case of using ethylacetate, the
content of ethyl acetate is preferably 20 parts by weight or more,
more preferably 25 parts by weight or more, and particularly
preferably 30 to 70 parts by weight with respect to 100 parts by
weight of the total solvent. When the solvent contains ethyl
acetate in those ranges, applying nonuniformity and drying
nonuniformity caused by the volatilization rate of the solvent can
be suppressed. The mixing condition of the solvent and the hardcoat
layer-forming materials is set appropriately depending upon the
purpose. For example, the temperature is set appropriately
depending upon the purpose, and is preferably room temperature.
[0068] The above hardcoat layer-forming material may contain any
suitable leveling agent depending upon the purpose. The leveling
agent is preferably a fluorine-based or silicone-based leveling
agent, and more preferably a silicone-based leveling agent.
Examples of the silicone-based leveling agent include reactive
silicone, polydimethylsiloxane, polyether-denatured
polydimethylsiloxane, and polymethylalkylsiloxane. The reactive
silicone-based leveling agent and the siloxane-based leveling agent
are particularly preferred. The use of the reactive silicone-based
leveling agent imparts a sliding property to the surface, whereby
excellent abrasion resistance is maintained. Further, the use of
the siloxane-based leveling agent enhances the formability of the
hardcoat layer.
[0069] As the reactive silicone-based leveling agent, any
appropriate leveling agents may be used in accordance with purpose.
For example, agents having a siloxane bond, acrylate group, and
hydroxyl group are mentioned. Specific examples include:
(1) copolymer having a molar ratio of
(dimethylsiloxane/methyl):(3-acryloyl-2-hydroxypropoxypropyl
siloxane/methyl):(2-acryloyl-3-hydroxypropoxypropyl
siloxane)=0.8:0.16:0.04; (2) copolymer having a molar ratio of
dimethylsiloxane:hydroxylpropylsiloxane:6-isocyanate hexyl
isocyanurate:aliphatic polyester=6.3:1.0:2.2:1.0; and (3) copolymer
having a molar ratio of dimethylsiloxane:methylpolyethylene glycol
propylether siloxane having an acrylate at the
termial:methylpolyethylene glycol propylether siloxane having a
hydroxyl group at the terminal=0.88:0.07:0.05. Note that the molar
ratio of each component contained in those leveling agents may be
set appropriately in accordance with purpose.
[0070] The compounding amount of the leveling agent is set
appropriately depending upon the purpose. The compounding amount of
the leveling agent is preferably 5 parts by weight or less, and
more preferably 0.01 to 5 parts by weight with respect to 100 parts
by weight of the total resin components of the hardcoat
layer-forming materials.
[0071] When the above leveling agent is contained in the hardcoat
layer-forming materials in the case of using UV-light as a curing
means for the hardcoat layer-forming materials, the leveling agent
is bred on an air interface during preliminary drying and solvent
drying, and can prevent curing inhibition of a UV-curable resin,
caused by oxygen. As a result, a hardcoat layer having a sufficient
hardness even on the outermost surface can be obtained. Further,
the silicone-based leveling agent can also enhance abrasion
resistance since it provides a sliding property by being bred on
the surface of the hardcoat layer.
[0072] The above hardcoat layer-forming materials may have various
additives, if required, as long as the performance is not impaired.
Examples of the additives include a pigment, a filler, a
dispersant, a plasticizer, a UV-absorber, a surfactant, an
antioxidant, and a thixotropy agent. Those additives may be used
alone or in a combination.
[0073] The above hardcoat layer-forming materials may contain any
appropriate polymerization initiators as required, preferably
photopolymerization initiator. For example,
2,2-dimethoxy-2-phenylacetophenone, acetophenone, benzophenone,
xanthone, 3-methylacetophenone, 4-chlorobenzophenone,
4,4'-dimethoxybenzophenone, benzoinpropyl ether, benzyldimethyl
ketal, N,N,N',N'-tetramethyl-4,4'-diaminobenzophenone,
1-(4-isopropylphenyl)-2-hydroxy-2-methylpropane-1-one, and other
thioxanthone-based compounds are mentioned.
[0074] As a method of forming the above hardcoat layer, any
suitable method is adopted. Hereinafter, a typical formation
example of the hardcoat layer will be described, but the forming
method is not limited thereto. In order to form the hardcoat layer,
the urethaneacrylate (A), the polyol(meth)acrylate (B), and the
(meth)acrylpolymer (C) having an alkyl group containing at least
two hydroxyl groups (so-called hardcoat layer-forming materials)
are applied to any appropriate base material or the like, followed
by curing. The hardcoat layer-forming materials may be applied as a
solution dissolved in a solvent. In the case where the hardcoat
layer-forming materials are applied as a solution, it is preferred
to cure the materials after the solvent is dried.
[0075] As a method of applying the hardcoat layer-forming materials
to a base material, any suitable method is adopted, and for
example, applying methods such as fountain coating, die coating,
spin coating, spray coating, gravure coating, roll coating, and bar
coating can be used.
[0076] There is no particular limit to the curing means of the
hardcoat layer-forming materials. The curing means is preferably
ionizing radiation curing. For example, various kinds of active
energies can be used, and UV-light is preferably used. Examples of
an energy ray source include a high-pressure mercury lamp, a
halogen lamp, a xenon lamp, a metal halide lamp, a nitrogen laser,
an electron beam acceleration apparatus, and a radioactive element.
The metal halide lamp is preferred. The irradiation amount of the
energy ray source and the like are selected appropriately depending
upon the purpose. Preferably, the irradiation amount is 50 to 5,000
mJ/cm.sup.2 in terms of the accumulated exposure amount at a
UV-light wavelength of 365 nm. When irradiation amount is within
the range, curing can be performed sufficiently, and the hardcoat
layer can have a desired hardness and excellent transparency. The
hardcoat layer is formed through the above steps.
[0077] The above hardcoat layer may be subjected to various kinds
of surface treatments, if required. The surface treatment can
enhance the adhesiveness with respect to the base material,
protective layer, polarizer, or the like. As the surface treatment,
any suitable method can be adopted depending upon the purpose.
Examples of the surface treatment include a low-pressure plasma
treatment, a UV-light irradiation treatment, a corona treatment, a
flame treatment, an acid or alkali treatment. Further, the above
hardcoat layer may have an antiglare property, if required. As the
method of imparting an antiglare property, any suitable method is
adopted. For example, an antiglare property can be obtained by
using the above fine particles.
[0078] The above hardcoat layer may have an antireflection layer on
at least one side. When light strikes an object, the light repeats
a phenomenon of reflection from an interface of the object, and
absorption and scattering in the object, and then passes to a
reverse surface of the object. One of the factors of decreasing the
visibility of an image when the hardcoat layer is provided in an
image display apparatus or the like is the reflection of light at
an interface between the air and the hardcoat layer. The
antireflection layer reduces the surface reflection. By suppressing
light reflected at the surface of the hardcoat layer and the like,
for example, a display in a reflection-type liquid crystal display
apparatus becomes clearer. As the antireflection layer, any
suitable antireflection layer is adopted. Further, the
antireflection layer may be used as a single layer or as a laminate
of at least two layers. The lamination method is selected
appropriately depending upon the purpose. The antireflection layer
may contain a silane-based compound containing a fluorine group
and/or an organic compound containing a fluorine group, if
required. The purpose is to prevent the contamination resulted from
an outer environment.
[0079] The wavelength region of visible light that allows the above
antireflection layer to express an antireflection function is 380
to 780 nm, and the wavelength region with a particularly high
visibility is in a range of 450 to 650 nm. Generally, the
antireflection layer is designed so that the reflectance at a mean
wavelength of 550 nm is made minimum.
[0080] The thickness of the antireflection layer is set
appropriately depending upon the purpose. For example, the
thickness is 86 nm to 105 nm. The refractive index of the
antireflection layer is, for example, 1.2 to 1.8, although it may
vary depending upon the refractive index of a composition to be
used and the like.
[0081] As the method of forming the antireflection layer, any
suitable method is selected. For example, there is a method of
applying any suitable material for forming an antireflection layer
(herein after, referred to as "antireflection layer-forming
material") to the hardcoat layer by a dry method or a wet method,
followed by drying and curing. By using those methods, the
thickness of the antireflection layer becomes uniform, and an
excellent antireflection function can be obtained.
[0082] As the above antireflection layer-forming material, any
suitable material is selected. Examples of the material include a
resin-based material such as UV-curable acrylic resin, a hybrid
material in which inorganic fine particles such as colloidal silica
are dispersed in a resin, and a sol-gel material using metal
alkoxide such as tetraethoxysilane and titanium tetraethoxide. Each
material may use a fluorine group-containing compound for providing
the surface with an anti-contamination property. The antireflection
layer-forming material is preferably a material containing a large
amount of inorganic components, and more preferably a sol-gel
material. This is because such materials are excellent in abrasion
resistance. The sol-gel material can be used by being condensed
partially.
[0083] Further, an antireflection layer-forming material containing
a siloxane oligomer with a number average molecular weight of 500
to 10,000 in terms of the ethylene glycol conversion and a fluorine
compound having a fluoroalkyl structure and a polysiloxane
structure with a number average molecular weight of 5,000 to
100,000 in terms of the polystyrene conversion, described in JP
2004-167827 A, may be used.
[0084] The above antireflection layer-forming material may have any
suitable ultra-fine particles, if required. The structure of the
ultra-fine particles is selected appropriately depending upon the
purpose, and the ultra-fine particles are preferably hollow.
Further, the shape of the ultra-fine particles is selected
appropriately depending upon the purpose, and the ultra-fine
particles are preferably in a spherical shape. The average particle
size of the ultra-fine particles is selected appropriately
depending upon the purpose, and is preferably about 5 to 300 nm. As
the ultra-fine particles, any suitable material is selected
depending upon the purpose, and silicon oxide is used preferably.
If required, the ultra-fine particles may be treated with any
suitable coupling agent, and any suitable inorganic sol may be
added so as to enhance the film strength of the antireflection
layer.
[0085] The above antireflection layer-forming material may have a
dispersion of ultra-fine particles (for example, a dispersion of
the above silicon oxide ultra-fine particles in a hollow and
spherical shape) and any suitable matrix component. The matrix
component refers to a component capable of forming a coating film
on the surface of the hardcoat layer, and is selected for use
appropriately from a resin and the like that satisfy the conditions
such as the adhesion with respect to the hardcoat layer, a
hardness, and an applying property. Further, a hydrolysable organic
silicon compound or the like such as the above silicon oxide
ultra-fine particles may be used as the matrix component.
[0086] The above antireflection layer-forming material is prepared
by any suitable method. For example, the antireflection
layer-forming material can be prepared by mixing a dispersion of
the above ultra-fine particles with the above matrix component, and
diluting the mixture with any suitable organic solvent, if
required. For example, the weight ratio between the silicon oxide
ultra-fine particles and the matrix component of the above
antireflection layer-forming material is preferably in a range of
the silicon oxide ultra-fine particles:matrix=1:99 to 9:1. This is
because, by setting the weight ratio in such a range, the strength
of the antireflection layer satisfies practicability, and the
effect of adding the silicon oxide ultra-fine particles is likely
to be expressed.
[0087] As the method of forming the antireflection layer from the
antireflection layer-forming material, any suitable method is
adopted. For example, there is a method of applying the above
antireflection layer-forming material to the hardcoat layer,
followed by drying and curing. The applying method can be selected
appropriately depending upon the purpose.
[0088] The temperature for drying and curing the antireflection
layer-forming materials and the like for forming the above
antireflection layer is set appropriately depending upon the
purpose. The temperature is preferably 60 to 150.degree. C., and
more preferably 70 to 130.degree. C. Further, a drying and curing
time is set appropriately depending upon the purpose. The drying
and curing time is preferably 1 to 30 minutes, and more preferably
about 1 to 10 minutes. This is because drying and curing are
sufficient, and excellent productivity is obtained. A method of
performing drying and curing is selected appropriately depending
upon the purpose.
[0089] By subjecting the obtained antireflection layer to a heat
treatment, the antireflection layer having a higher hardness is
obtained. The temperature of the heat treatment is not particularly
limited, and is preferably 40 to 130.degree. C., and more
preferably 50 to 100.degree. C. The time of the heat treatment is
set appropriately depending upon the purpose. The time of the heat
treatment is preferably 1 minute to 100 hours. In order to further
enhance abrasion resistance, the heat treatment is performed for 10
hours or longer. As heating, a method using a hot plate, an oven, a
belt furnace, or the like is adopted appropriately.
[0090] The antireflection layer preferably has a laminate structure
of a titanium oxide layer and a silicon oxide layer. As a result,
the antireflection function can be expressed more greatly, and the
reflection in a wavelength region (380 to 780 nm) of visible light
can be further reduced uniformly.
[0091] The above hardcoat layer may have any suitable base
material, if required. The base material is used, for example, in
order to support a hardcoat layer-forming material to form a
hardcoat layer, or to enhance the self-supporting property of the
hardcoat layer. The base material is preferably a film that is
excellent in light transmittance of visible light (preferably, a
light transmittance of 90% or more) and transparency (preferably, a
haze value of 1% or less), and has less optical birefringence. As
the base material, any suitable base material is used depending
upon the purpose. Examples of the base material include films made
of transparent polymers, for example, a polyester-based polymer
such as polyethyleneterephthalate and polyethylenenaphthalate, a
cellulose-based polymer such as diacetyl cellulose and triacetyl
cellulose, a polycarbonate-based polymer, and an acrylic polymer
such as polymethylmethacrylate. The thickness of those films is set
appropriately depending upon the purpose, and is preferably 10 to
500 .mu.m, and more preferably 20 to 300 .mu.m. A protective layer
described later may also function as the base material.
[0092] The above base material may be treated appropriately
depending upon the purpose. For example, the reverse surface
(surface on an opposite side of the hardcoat layer formation
surface) of the base material may be subjected to a treatment for
preventing the occurrence of curls in the hardcoat layer. As this
treatment, any suitable treatment is adopted, and an example
thereof is a solvent treatment. This treatment cancels the force of
the hardcoat layer for being curled on the opposite side of the
base material surface, by providing the base material with the
property of being curled on the reverse surface side. Consequently,
the occurrence of curls in the entire hardcoat layer can be
prevented. A specific treatment method is performed by applying a
composition containing a solvent capable of dissolving the base
material or a solvent capable of swelling the base material by any
suitable method. For example, the composition is applied to the
reverse surface of the base material to be a wet film thickness
(film thickness before being dried) of preferably 1 to 100 .mu.m
and more preferably 5 to 30 .mu.m, with a gravure coater, a dip
coater, a reverse coater, an extrusion coater, or the like.
[0093] As the above solvent, any suitable solvent is used depending
upon the purpose. Examples of the solvent include benzene, toluene,
xylene, dioxane, acetone, methyl ethyl ketone,
N,N-dimethylformamide, methyl acetate, ethyl acetate,
trichloroethylene, methylene chloride, ethylene chloride,
tetrachloroethane, trichloroethane, and chloroform. Examples of the
solvent that does not dissolve the base material include methanol,
ethanol, n-propyl alcohol, i-propyl alcohol, and n-butanol. Those
solvents may be used alone or in a combination. The mixing ratio
(weight ratio) of the solvents is set appropriately depending upon
the purpose. For example, in the case of mixing the solvent capable
of dissolving the base material and/or solvent capable of swelling
the base material (A) with the solvent that does not dissolve the
base material (B), the mixing ratio there between is preferably
(A):(B)=10:0 to 1:9.
[0094] A transparent resin layer may be provided on the reverse
surface (the surface on an opposite side of the hardcoat layer
formation surface) of the base material for the same purpose as
that of the above solvent treatment. As the above transparent resin
layer, any suitable resin layer is adopted depending upon the
purpose. Examples of the transparent resin layer include those
which contain a thermoplastic resin, a radiation-curable resin, a
thermosetting resin, and other reactive resins as a main component.
The layer containing a thermoplastic resin as a main component is
preferred. A cellulose-based resin layer using diacetyl cellulose
or the like is more preferred.
[0095] C. Polarizer
[0096] Any suitable polarizers may be employed as the above
polarizer 12 depending on the purpose. Examples of the polarizer
include: a film prepared by adsorbing a dichromatic substance such
as iodine or a dichromatic dye on a hydrophilic polymer film such
as a polyvinyl alcohol-based film, a partially formalized polyvinyl
alcohol-based film, or an ethylene/vinyl acetate copolymer-based
partially saponified film and uniaxially stretching the film; and a
polyene-based orientated film such as a dehydrated product of a
polyvinyl alcohol-based film or a dehydrochlorinated product of a
polyvinyl chloride-based film. Of those, a polarizer prepared by
adsorbing a dichromatic substance such as iodine on a polyvinyl
alcohol-based film and uniaxially stretching the film is
particularly preferred in view of high polarized dichromaticity. A
thickness of the polarizer is not particularly limited, but is
generally about 1 to 80 .mu.m.
[0097] The polarizer prepared by adsorbing iodine on a polyvinyl
alcohol-based film and uniaxially stretching the film may be
produced by, for example: immersing a polyvinyl alcohol-based film
in an aqueous solution of iodine for coloring; and stretching the
film to a 3 to 7 times length of the original length. The aqueous
solution may contain boric acid, zinc sulfate, zinc chloride, or
the like as required, or the polyvinyl alcohol-based film may be
immersed in an aqueous solution of potassium iodide or the like.
Further, the polyvinyl alcohol-based film may be immersed and
washed in water before coloring as required.
[0098] Washing the polyvinyl alcohol-based film with water not only
allows removal of contamination on a film surface or washing away
of an antiblocking agent, but also prevents nonuniformity such as
uneven coloring or the like by swelling the polyvinyl alcohol-based
film. The stretching of the film may be carried out after coloring
of the film with iodine, carried out during coloring of the film,
or carried out followed by coloring of the film with iodine. The
stretching may be carried out in an aqueous solution of boric acid
or potassium iodide, or in a water bath.
[0099] D. Protective Layer
[0100] As shown in FIG. 1, any suitable protective layer 15 may be
provided on at least one surface of the above polarizer 12, if
required (In FIG. 1, the protective layers 15 are provided on both
surfaces of the polarizer 12). The protective layer may be a single
layer or include at least two layers. As the protective layer, any
suitable protective layer is used depending upon the purpose. For
example, any suitable film that can be used as the protective layer
of the polarizer can be adopted. Further, if required, the
protective layer may be subjected to a treatment capable of
preventing curls in the hardcoat layer.
[0101] Specific examples of a material to be included as a main
component of the film include: a cellulose-based resin such as
triacetyl cellulose (TAC); and a transparent resin such as a
polyester-based resin, a polyvinyl alcohol-based resin, a
polycarbonate-based resin, a polyamide-based resin, a
polyimide-based resin, a polyethersulfone-based resin, a
polysulfone-based resin, a polystyrene-based resin, a
polynorbornene-based resin, a polyolefin-based resin, an acrylic
resin, and an acetate-based resin. Other examples thereof include:
a thermosetting resin and a UV-curable resin such as an acrylic
resin, an urethane-based resin, an acrylurethane-based resin, an
epoxy-based resin, and a silicone-based resin. Still another
example thereof is a glassy polymer such as a siloxane-based
polymer. Further, a polymer film described in JP 2001-343529 A (WO
01/37007) may also be used. A material for the film may employ a
resin composition containing a thermoplastic resin having a
substituted or unsubstituted imide group on a side chain, and a
thermoplastic resin having a substituted or unsubstituted phenyl
group and nitrile group on a side chain, for example. A specific
example thereof is a resin composition containing an alternating
isobutene/N-methylmaleimide copolymer and an acrylonitrile/styrene
copolymer. The polymer film may be an extrusion molded product of
the resin composition described above, for example. TAC, a
polyimide-based resin, a polyvinyl alcohol-based resin, and a
glassy polymer are preferred. TAC is more preferred.
[0102] A method of laminating the above protective layer on a
polarizer is selected appropriately depending upon the purpose. For
example, a pressure-sensitive adhesive layer may be used, or an
adhesive layer may be used. As described later, as the
pressure-sensitive adhesive layer, any suitable pressure-sensitive
adhesive is used depending upon the purpose. Any suitable adhesive
is used for the adhesive layer depending upon the purpose. Specific
examples of the adhesive layer include those which contain, as a
base polymer, an acrylic polymer, a silicone-based polymer,
polyester, polyvinyl alcohol, polyurethane, polyamide,
polyvinylether, a vinyl acetate/vinyl chloride copolymer, denatured
polyolefin, a rubber-based polymer such as an epoxy-based rubber, a
fluorine-based rubber, a natural rubber and a synthetic rubber, or
the like.
[0103] It is preferred that the above protective layer is
transparent and color less. Specifically, the thickness direction
retardation value is preferably -90 nm to +90 nm, more preferably
-80 nm to +80 nm, and most preferably -70 nm to +70 nm.
[0104] Any appropriate thickness can be adopted as the thickness of
the above film, as long as the above-mentioned preferable thickness
direction retardation is obtained. Specifically, the thickness of
the protective layer is preferably 5 mm or less, more preferably 1
to 500 .mu.m, still more preferably 20 to 300 .mu.m, and
particularly preferably 30 to 150 .mu.m.
[0105] The protective layer provided between polarizer 12 and the
hardcoat layer 11 can be subjected to hardcoat treatment,
antireflection treatment, anti-sticking treatment, antiglare
treatment, and the like, if required. More specifically, in the
case of using a (TAC) film for the protective layer, an alkali
saponification treatment is preferably used as a surface treatment.
The surface treatment is preferably performed in a cycle in which
the surface of a (TAC) film is soaked in an alkaline solution, and
thereafter, washed with water, followed drying. Examples of the
alkaline solution include a potassium hydroxide solution and a
sodium hydroxide solution, and the normal concentration of
hydroxide ions is preferably 0.1 N to 3.0 N, and more preferably
0.5 N to 2.0 N. The temperature of the alkaline solution is
preferably in a range of 25.degree. C. to 90.degree. C., and more
preferably in a range of 40.degree. C. to 70.degree. C. After that,
a water washing treatment and a drying treatment are conducted,
whereby surface-treated triacetyl cellulose can be obtained.
[0106] The protective layer may have the same role as that of the
base material for the above hardcoat layer. In this case, the base
material can be omitted, so a polarizing plate with an optical
compensation layer that is excellent in transmittance of visible
light and transparency, and that has less optical birefringence can
be obtained. Further, this case can contribute to the reduction in
thickness of the polarizing plate with an optical compensation
layer, and can omit the number of production steps, which can
enhance a production efficiency.
[0107] E. First Optical Compensation Layer
[0108] The above first optical compensation layer 13 is placed so
that a slow axis B thereof intersects with an absorption axis A of
the polarizer 12 (specifically, an angle .alpha. is defined) as
shown in FIG. 2. The angle .alpha. is preferably 10.degree. to
30.degree., more preferably 12.degree. to 27', and still more
preferably 14.degree. to 25.degree. in a counterclockwise direction
with respect to the absorption axis A of the polarizer 12.
[0109] The above first optical compensation layer 13 can function
as a .lamda./2 plate. The first optical compensation layer
functions as a .lamda./2 plate, whereby a retardation can be
adjusted appropriately regarding wavelength dispersion
characteristics (in particular, the wavelength range in which a
retardation departs from .lamda./4) of the second optical
compensation layer that functions as a .lamda./4 plate. An in-plane
retardation Re.sub.1 of the first optical compensation layer is
preferably 200 to 300 nm, more preferably 220 to 280 nm, and still
more preferably 230 to 270 nm. Further, the above first optical
compensation layer 13 has a refractive index profile of
nx.sub.1>ny.sub.1=nz.sub.1. Further, a thickness direction
retardation Rth.sub.1 is preferably 200 to 300 nm, more preferably
220 to 280 nm, and still more preferably 230 to 270 nm.
[0110] The thickness of the above first optical compensation layer
can be set so as to function as a .lamda./2 plate most suitably. In
other words, the thickness can be set so that a desired in-plane
retardation is obtained. Specifically, the thickness is preferably
30 to 70 .mu.m, more preferably 30 to 60 .mu.m, and particularly
preferably 30 to 50 .mu.m.
[0111] The above first optical compensation layer 13 can contain a
resin whose absolute value of a photoelastic coefficient is
preferably 2.0.times.10.sup.-11 m.sup.2/N or less, more preferably
2.0.times.10.sup.-13 to 1.0.times.10.sup.-11, and still more
preferably 1.0.times.10.sup.-12 to 1.0.times.10.sup.-11. If the
absolute value of the photoelastic coefficient is in such a range,
a change in retardation is unlikely to occur in the case where the
shrinkage stress during heating occurs. Thus, a first optical
compensation layer is formed by using a resin with such an absolute
value of a photoelastic coefficient, whereby heat nonuniformity of
an image display apparatus to be obtained can be prevented
preferably.
[0112] Typical examples of the resin capable of satisfying such a
photoelastic coefficient include a cyclic olefin-based resin and a
cellulose-based resin. The cyclic olefin-based resin is
particularly preferred. The cyclic olefin-based resin is a general
term for a resin prepared through polymerization of a cyclic olefin
as a monomer, and examples thereof include resins described in JP
1-240517 A, JP 3-14882 A, JP 3-122137 A, and the like. Specific
examples thereof include: a ring opened (co)polymer of a cyclic
olefin; an addition polymer of a cyclic olefin; a copolymer
(typically, a random copolymer) of a cyclic olefin, and an
.alpha.-olefin such as ethylene or propylene; their graft modified
products each modified with an unsaturated carboxylic acid or its
derivative; and hydrides thereof. A specific example of the cyclic
olefin includes a norbornene-based monomer.
[0113] Examples of the norbornene-based monomer include:
norbornene, its alkyl substitution and/or alkylidene substitution
such as 5-methyl-2-norbornene, 5-dimethyl-2-norbornene,
5-ethyl-2-norbornene, 5-butyl-2-norbornene,
5-ethylidene-2-norbornene, and their products each substituted by a
polar group such as halogen; dicyclopentadiene and
2,3-dihydrodicyclopentadiene; dimethano octahydronaphtalene, its
alkyl substitution and/or alkylidene substitution, and their
products each substituted by a polar group such as halogen, for
example, [0114]
6-methyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphtalene,
[0115]
6-ethyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphtalene,
[0116]
6-ethylidene-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphtalene,
[0117]
6-chloro-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphtalene,
[0118]
6-cyano-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphtalene,
[0119]
6-pyridyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphtalene,
and [0120]
6-methoxycarbonyl-1,4:5,8-dimethano-1,4,4a,5,6,7,8,8a-octahydronaphtalene-
; and a trimer of cyclopentadiene and a tetramer of
cyclopentadiene, for example, [0121]
4,9:5,8-dimethano-3a,4,4a,5,8,8a,9,9a-octa hydro-1H-benzoindene and
[0122] 4, 11:5,
10:6,9-trimethano-3a,4,4a,5,5a,6,9,9a,10,10a,11,11a-dodecahydro-1H-cyclop-
entaanthracene.
[0123] In the present invention, other ring-opening polymerizable
cycloolefins can be combined without impairing the purpose of the
present invention. Specific example of such cycloolefin includes a
compound having one reactive double-bond, for example,
cyclopentene, cyclooctene, and 5,6-dihydrodicyclopentadiene.
[0124] The cyclic olefin-based resin has a number average molecular
weight (Mn) of preferably 25,000 to 200,000, more preferably 30,000
to 100,000, and most preferably 40,000 to 80,000 measured through a
gel permeation chromatography (GPC) method by using a toluene
solvent. A number average molecular weight within the above ranges
can provide a resin having excellent mechanical strength, and
favorable solubility, forming property, and casting
operability.
[0125] In the case where the cyclic olefin-based resin is prepared
through hydrogenation of a ring opened polymer of a
norbornene-based monomer, a hydrogenation rate is preferably 90% or
more, more preferably 95% or more, and most preferably 99% or more.
A hydrogenation rate within the above ranges can provide excellent
heat degradation resistance, light degradation resistance, and the
like.
[0126] For the cyclic olefin-based resin (for example,
norbornene-based resin), various products are commercially
available. Specific examples of the resin include the trade names
"ZEONEX" and "ZEONOR" each manufactured by ZEON CORPORATION, the
trade name "Arton" manufactured by JSR Corporation, the trade name
"TOPAS" manufactured by TICONA Corporation, and the trade name
"APEL" manufactured by Mitsui Chemicals, Inc.
[0127] Any appropriate cellulose-based resin (typically an ester of
cellulose and acid) may be employed as the cellulose-based resin.
An ester of cellulose and fatty acid is preferred. Specific
examples of such cellulose-based resin include cellulose triacetate
(triacetylcellulose: TAC), cellulose diacetate, cellulose
tripropionate, and cellulose dipropionate. Cellulose triacetate
(triacetyl cellulose: TAC) is particularly preferred because it has
low birefringence and high transmittance. In addition, many
products of TAC are commercially available, and thus TAC has
advantages of availability and cost.
[0128] Specific examples of commercially available products of TAC
include the trade names "UV-50", "UV-80", "SH-50", "SH-80",
"TD-80U", "TD-TAC", and "UZ-TAC" each manufactured by Fuji Photo
Film CO., LTD., the trade name "KC series" manufactured by Konica
Minolta Corporation, and the trade name "Triacetyl Cellulose 80
.mu.m series" manufactured by Lonza Japan Corporation. Of those,
"TD-80U" is preferred because of excellent transmittance and
durability. In particular, "TD-80U" has excellent adaptability to a
TFT-type liquid crystal display apparatus.
[0129] The first optical compensation layer 13 is obtained by
stretching a film formed of the cyclic olefin-based resin or the
cellulose-based resin. Any appropriate forming method may be
employed as a method of forming a film from the cyclic olefin-based
resin or the cellulose-based resin. Specific examples thereof
include a compression molding method, a transfer molding method, an
injection molding method, an extrusion molding method, a blow
molding method, a powder molding method, an FRP molding method, and
a casting method. The extrusion molding method and the casting
method are preferred because a film to be obtained may have
enhanced smoothness and favorable optical uniformity. Forming
conditions may appropriately be set in accordance with the
composition or type of resin to be used, properties desired for the
first optical compensation layer, and the like. Many film products
of the cyclic olefin-based resin and the cellulose-based resin are
commercially available, and the commercially available films may be
subjected to the stretching treatment.
[0130] The stretching ratio of the above film can vary depending
upon the in-plane retardation value and thickness desired in the
first optical compensation layer, the kind of a resin to be used,
the thickness of a film to be used, the stretching temperature, and
the like. Specifically, the stretching ratio is preferably 1.1 to
3.0 times, more preferably 1.2 to 2.5 times, and particularly
preferably 1.3 to 2.4 times. By stretching a film with such a
ratio, a first optical compensation layer having an in-plane
retardation capable of exhibiting the effect of the present
invention appropriately can be obtained.
[0131] The stretching temperature of the above film can vary
depending upon the in-plane retardation value and thickness desired
in the first optical compensation layer, the kind of a resin to be
used, the thickness of a film to be used, the stretching ratio, and
the like. Specifically, the stretching temperature is preferably
130 to 150.degree. C., more preferably 135 to 145.degree. C., and
most preferably 137 to 143.degree. C. By stretching a film at such
a temperature, a first optical compensation layer having an
in-plane retardation capable of exhibiting the effect of the
present invention appropriately can be obtained.
[0132] Referring to FIGS. 1(a) and 1(b), the first optical
compensation layer 13 is placed between the polarizer 12 (or the
protective layer 15) and the second optical compensation layer 14.
As a method of placing the first optical compensation layer, any
suitable method can be adopted depending upon the purpose.
Typically, pressure-sensitive adhesive layers (not shown) are
provided on both sides of the above first optical compensation
layer 13, and the polarizer 12 (the protective layer 15 in the case
of FIG. 1) and the second optical compensation layer 14 are
attached thereto. By filling the gap between the respective layers
with the pressure-sensitive adhesive layers as such, whereby the
relationship between optical axes of the respective layers can be
prevented from being shifted and the respective layers can be
prevented from rubbing against each other to damage with each
other, when the layers are incorporated in an image display
apparatus. Further, interface reflection between the layers can be
reduced, and a contrast can also be enhanced when the layers are
used in an image display apparatus. Pressure-sensitive adhesive
layers to be used may be the same or different from each other.
[0133] The thickness of the above pressure-sensitive adhesive layer
can be set appropriately depending upon the use and the adhesive
strength. Specifically, the thickness of the pressure-sensitive
adhesive layer is preferably 1 .mu.m to 500 .mu.m, more preferably
5 .mu.m to 200 .mu.m, and most preferably 10 .mu.m to 100
.mu.m.
[0134] As the pressure-sensitive adhesive forming the above
pressure-sensitive adhesive layer, any suitable pressure-sensitive
adhesive can be adopted. Specific examples include a solvent-type
pressures-sensitive adhesive, a non-aqueous emulsion-type
pressure-sensitive adhesive, an aqueous pressure-sensitive
adhesive, and a hot-melt pressure-sensitive adhesive. A
solvent-type pressure-sensitive adhesive containing an acrylic
polymer as a base polymer is used preferably. This is because the
solvent-type pressure-sensitive adhesive exhibits appropriate
adhesive properties (wettability, cohesion, and adhesiveness) with
respect to the polarizer and the first optical compensation layer,
and is excellent in optical transparency, weather resistance, and
heat resistance. Further, the pressure-sensitive adhesive may
contain an appropriate additive depending upon the purpose.
Examples of the additive include natural and synthetic resins, a
tackfier resin, a filler such as glass fibers, glass beads, metal
powder, and inorganic powder, a colorant, an antioxidant, and fine
particles having an optical diffusion property.
[0135] The pressure-sensitive adhesive layer is formed by any
suitable method. For example, any suitable solvent such as toluene
and ethyl acetate are used alone or mixed to produce a solvent.
Examples of the method include a method of dissolving or dispersing
a base polymer or a composition thereof in the solvent to prepare
about 10 to 40 parts by weight of a pressure-sensitive adhesive
solution, and flow-casting or applying the solution to the first
optical compensation layer or the like, thereby forming the
pressure-sensitive adhesive layer directly on the first optical
compensation layer and a method of transferring the
pressure-sensitive adhesive layer onto the first optical
compensation layer.
[0136] F. Second Optical Compensation Layer
[0137] The above second optical compensation layer 14 is placed so
that a slow axis C thereof intersects with the absorption axis A of
the polarizer 12 (specifically, an angle .beta. is defined) as
shown in FIG. 2. The angle .beta. is preferably 65 to 95.degree.,
more preferably 70 to 93.degree., and still more preferably 72 to
92.degree. in a counterclockwise direction with respect to the
absorption axis A of the polarizer 12.
[0138] The above second optical compensation layer 14 can function
as a .lamda./4 plate. According to the present invention, by
correcting the wavelength dispersion characteristics of the second
optical compensation layer that functions as a .lamda./4 plate with
the optical properties of the first optical compensation layer that
functions as a .lamda./2 plate, a circular polarization function
can be exhibited in a wide wavelength range. In one embodiment, the
above second optical compensation layer 14 can be a so-called
positive A plate that has a refractive index profile of
nx.sub.2>ny.sub.2=nz.sub.2. In another embodiment, the above
second optical compensation layer 14 can be a biaxial retardation
film that has a refractive index profile of
nx.sub.2>ny.sub.2>nz.sub.2. By using as the second optical
compensation layer 14 a biaxial retardation film that functions as
a .lamda./4 plate and has a refractive index profile of
nx.sub.2>ny.sub.2>nz.sub.2, the function of the .lamda./4
plate that is a uniaxial retardation film and the function of a
so-called negative C plate having a refractive index profile of
nx=ny>nz can be provided in one layer. Consequently, this can
greatly contribute to the reduction in thickness of the entire
polarizing plate with an optical compensation layer, while
compensating for the birefringence of a liquid crystal layer in a
liquid crystal cell of a VA mode effectively.
[0139] F-1. Second Optical Compensation Layer that is a Positive A
Plate
[0140] An in-plane retardation Re.sub.2 of the second optical
compensation layer that is a positive A plate is preferably 90 to
160 nm, more preferably 100 to 150 nm, and still more preferably
110 to 140 nm. Further, a thickness direction retardation Rth.sub.2
is preferably 90 to 160 nm, more preferably 100 to 150 nm, and
still more preferably 110 to 140 nm.
[0141] The thickness of the above second optical compensation layer
can be set so as to function most appropriately as a .lamda./4
plate. In other words, the thickness can be set so that a desired
in-plane retardation is obtained. Specifically, the thickness is
preferably 20 to 60 .mu.m, more preferably 30 to 50 .mu.m, and
particularly preferably 30 to 45 .mu.m.
[0142] The above second optical compensation layer can contain a
resin whose absolute value of a photoelastic coefficient is
preferably 2.0.times.10.sup.-11 m.sup.2/N or less, more preferably
2.0.times.10.sup.-13 to 1.0.times.10.sup.-11, and still more
preferably 1.0.times.10.sup.-12 to 1.0.times.10.sup.-11. When the
absolute value of a photoelastic coefficient is in such a range, in
the case where the shrinkage stress during heating occurs, a change
in retardation is unlikely to occur. Thus, by forming a second
optical compensation layer using a resin with such an absolute
value of a photoelastic coefficient, heat nonuniformity of an image
display apparatus to be obtained can be prevented satisfactorily
also in combination with the effect of the first optical
compensation layer.
[0143] Typical examples of resins capable of satisfying the
photoelastic coefficient as described above include an cyclic
olefin-based resin and a cellulose-based resin. The detail of the
cyclic olefin-based resin and the cellulose-based resin is as
described above.
[0144] An in-plane retardation Re.sub.2 of the second optical
compensation layer 14 can be controlled by changing the stretching
ratio and the stretching temperature of the above cyclic
olefin-based resin film and cellulose-based resin film. The
stretching ratio can vary depending upon the in-plane retardation
value and thickness desired in the second optical compensation
layer, the kind of a resin to be used, the thickness of a film to
be used, the stretching temperature, and the like. Specifically,
the stretching ratio is preferably 1.05 to 2.05 times, more
preferably 1.05 to 2 times, and most preferably 1.2 to 1.7 times.
By stretching a film with such a ratio, a second optical
compensation layer having an in-plane retardation capable of
exhibiting the effect of the present invention appropriately can be
obtained.
[0145] The stretching temperature can vary depending upon the
in-plane retardation value and thickness desired in the second
optical compensation layer, the kind of a resin to be used, the
thickness of a film to be used, the stretching ratio, and the like.
Specifically, the stretching temperature is preferably 130 to
150.degree. C., more preferably 135 to 145.degree. C., and most
preferably 137 to 143.degree. C. By stretching a film at such a
temperature, a second optical compensation layer having an in-plane
retardation capable of exhibiting the effect of the present
invention appropriately can be obtained.
[0146] F-2. Second Optical Compensation Layer that is a Biaxial
Retardation Film
[0147] An in-plane retardation Re.sub.2 of the second optical
compensation layer that is a biaxial retardation film is preferably
90 to 160 nm, more preferably 100 to 150 nm, and still more
preferably 110 to 140 nm. Further, a thickness direction
retardation Rth.sub.2 is preferably 100 to 300 nm, more preferably
120 to 280 nm, and still more preferably 140 to 260 nm.
[0148] A Nz coefficient of the above second optical compensation
layer is preferably 1.2 to 1.9, more preferably 1.3 to 1.9, still
more preferably 1.4 to 1.8, and particularly preferably 1.4 to 1.7.
In the case where the Nz coefficient is in the above ranges,
viewing angle properties can be enhanced. The Nz coefficient is
obtained by the following Expression (1).
Nz=(nx-nz)/(nx-ny) (1)
[0149] The above second optical compensation layer can contain a
resin whose absolute value of a photoelastic coefficient is
preferably 2.0.times.10.sup.-11 m.sup.2/N or less, more preferably
2.0.times.10.sup.-13 to 1.0.times.10.sup.-11, and still more
preferably 1.0.times.10.sup.-12 to 1.0.times.10.sup.-11. When the
absolute value of a photoelastic coefficient is in such a range, in
the case where the shrinkage stress during heating occurs, a change
in retardation is unlikely to occur. Thus, by forming a second
optical compensation layer using a resin with such an absolute
value of a photoelastic coefficient, heat nonuniformity of an image
display apparatus to be obtained can be prevented satisfactorily
also in combination with the effect of the first optical
compensation layer.
[0150] As the material forming the above second optical
compensation layer, the same material as that forming the second
optical compensation layer that is a positive A plate descried in
the item F-1 can be used.
[0151] The in-plane retardation and the thickness direction
retardation of the above second optical compensation layer can be
controlled by changing the stretching ratio and the stretching
temperature of a film formed of the above material. The stretching
ratio and the stretching temperature can vary depending upon the
in-plane retardation value, thickness direction retardation, and
thickness desired in the second optical compensation layer, the
kind of a resin to be used, the thickness of a film to be used, and
the like.
[0152] As the stretching method, a fixed-end biaxial stretching
method or a sequential biaxial stretching method can be preferably
adopted. In one embodiment of the fixed-end biaxial stretching,
stretching can be performed at a stretching temperature of
preferably 135 to 165.degree. C., more preferably 140 to
160.degree. C., and at a stretching ratio of preferably 2.8 to 3.2
times, more preferably 2.9 to 3.1 times. In one embodiment of the
sequential biaxial stretching, transverse stretching can be
performed at a stretching ratio of, for example, 1.17 to 1.57
times, preferably 1.22 to 1.52 times, and still more preferably
1.27 to 1.5 times, and then, longitudinal stretching can be
performed so as to cancel the shrinkage caused by the transverse
stretching, at a stretching temperature of preferably 130 to
150.degree. C., more preferably 135 to 145.degree. C., and still
more preferably 137 to 143.degree. C. According to such stretching
methods, a second optical compensation layer having an in-plane
retardation and a thickness direction retardation capable of
exhibiting the effect of the present invention appropriately can be
obtained.
[0153] Referring to FIG. 1, the second optical compensation layer
14 is placed on a side of the first optical compensation layer 13,
which is opposite to the polarizer 12. As the method of placing the
second optical compensation layer, any suitable method can be
adopted depending upon the purpose. Typically, a pressure-sensitive
adhesive layer (not shown) is provided on the first optical
compensation layer 13 side of the above second optical compensation
layer 14, and the first optical compensation layer 13 is attached
thereto. The detail of the pressure-sensitive adhesive layer is as
described above. The polarizing plate with an optical compensation
layer of the present invention can further include a third optical
compensation layer having a refractive index profile of
nx.sub.3=ny.sub.3>nz.sub.3 on a side of the second optical
compensation layer, which is opposite to the first optical
compensation layer, for example, in the case where the second
optical compensation layer is a .lamda./4 plate having a refractive
index profile of nx.sub.2>ny.sub.2=nz.sub.2. The third optical
compensation layer is as described later.
[0154] G. Third Optical Compensation Layer
[0155] The third optical compensation layer is a so-called negative
C plate having a refractive index profile of
nx.sub.3=ny.sub.3>nz.sub.3. When the third optical compensation
layer has such a refractive index profile, in particular, the
birefringence of a liquid crystal layer in a liquid crystal cell of
a VA mode can be compensated satisfactorily in combination with the
effect of the second optical compensation layer that has a
refractive index profile of nx.sub.2>ny.sub.2=nz.sub.2 and
functions as a .lamda./4 plate.
[0156] As described above, as used herein, "nx=ny" includes the
case where nx and ny are substantially equal to each other, as well
as the case where nx and ny are strictly equal to each other.
Therefore, the third optical compensation layer can have an
in-plane retardation and a slow axis. An in-plane retardation
Re.sub.3 that is practically allowable as a negative C plate is
preferably 0 to 20 nm, more preferably 0 to 10 nm, and still more
preferably 0 to 5 nm.
[0157] The above third optical compensation layer can be formed of
any suitable material as long as the above properties can be
obtained. One specific example of the third optical compensation
layer is a cholesteric alignment solidified layer. The "cholesteric
alignment solidified layer" refers to a layer in which constituent
molecules of the layer form a helical structure, a helical axis
thereof is aligned substantially perpendicular to a plane
direction, and an alignment state thereof is fixed. Thus, the
"cholesteric alignment solidified layer" includes the case where a
non-liquid crystal compound forms a pseudo structure like a
cholesteric liquid crystal phase, as well as the case where a
liquid crystal compound (preferably, nematic liquid crystal
compound) exhibits a cholesteric liquid crystal phase. For example,
the cholesteric alignment solidified layer can be formed by
twisting a liquid crystal material under the condition of
exhibiting a liquid crystal phase with a chiral agent to align the
liquid crystal material in a cholesteric structure (helical
structure), and subjecting the liquid crystal material to
polymerization or cross-linking under such a state, thereby fixing
the alignment (cholesteric structure) of the liquid crystal
material.
[0158] A specific example of the cholesteric alignment solidified
layer includes a cholesteric alignment solidified layer described
in JP 2003-287623 A.
[0159] A thickness direction retardation Rth.sub.3 of the
cholesteric alignment solidified layer is preferably 90 to 270 nm,
and more preferably 110 to 250 nm.
[0160] The thickness of the cholesteric alignment solidified layer
can be set to be any suitable value as long as the above desired
optical properties are obtained. In the case where the above third
optical compensation layer is a cholesteric alignment solidified
layer, the thickness thereof is preferably 1 to 5 .mu.m, and more
preferably 1.8 to 4.1 .mu.m. As described later, the cholesteric
alignment solidified layer can be attached to the second optical
compensation layer via an adhesive layer (thickness: 2 to 6 .mu.m),
so it can greatly contribute to the reduction in thickness of a
polarizing plate with an optical compensation layer.
[0161] Other specific examples of the above third optical
compensation layer include a film formed of a non-liquid crystal
material. The non-liquid crystal material is preferably a
non-liquid crystal polymer. Such a non-liquid crystal material
differs from a liquid crystalline material and may form a film
having optical uniaxial property of nx=ny>nz due to its property
regardless of alignment property of a substrate. Preferred examples
of the non-liquid crystal material include polymers such as
polyamide, polyimide, polyester, polyetherketone, polyamideimide,
and polyesterimide because those polymers have excellent heat
resistance, chemical resistance, and transparency, and high
rigidity. One kind of polymer may be used alone, or the polymers
may be used as a mixture of two or more kinds of polymers having
different functional groups such as a mixture of polyarylether
ketone and polyamide, for example. Of those polymers, polyimide is
particularly preferred because of high transparency, high alignment
property, and high stretching property.
[0162] A specific example of the above polyimide and a specific
example of a method of forming the third optical compensation layer
include a polymer and a method of producing an optical compensation
film described in JP 2006-98849 A.
[0163] In the case where the third optical compensation layer is a
film formed of the above non-liquid crystal material, a thickness
direction retardation Rth.sub.3 thereof is preferably 220 to 320
nm, and more preferably 240 to 300 nm.
[0164] In the case where the third optical compensation layer is a
film formed of the above non-liquid crystal material, a thickness
thereof is preferably 1 to 10 .mu.m, and more preferably 2 to 4
.mu.m.
[0165] Still another specific example of the above third optical
compensation layer includes a polymer film containing a
norbornene-based resin or the like. As the polymer film containing
a norbornene-based resin, a polymer film formed of a
norbornene-based resin (for example, "ZEONEX" (trade name) and
"ZEONOR" (trade name) manufactured by Zeon Corporation) described
in the above item E or the like can be used. By subjecting such a
polymer film to, for example, biaxial stretching, a third optical
compensation layer having desired optical properties can be
obtained.
[0166] In the case where the third optical compensation layer is a
polymer film containing a norbornene-based resin, a thickness
direction retardation Rth.sub.3 thereof is preferably 160 to 290 nm
and more preferably 180 to 270 nm.
[0167] In the case where the third optical compensation layer is a
polymer film containing a norbornene-based resin, a thickness
thereof is preferably 10 to 80 .mu.m, and more preferably 20 to 50
.mu.m.
[0168] By subjecting the above polymer film to, for example,
sequential biaxial stretching, a third optical compensation layer
having an in-plane retardation and a thickness direction
retardation capable of exhibiting the effect of the present
invention appropriately can be obtained. In one embodiment of
sequential biaxial stretching, longitudinal stretching can be
performed at a stretching ratio of preferably 1.17 to 1.37 times,
more preferably 1.22 to 1.32 times, and then, transverse stretching
can be performed at a stretching ratio of preferably 1.27 to 1.47
times, more preferably 1.32 to 1.42 times, at a stretching
temperature of preferably 155 to 195.degree. C., more preferably
165 to 185.degree. C.
[0169] Still another specific example of the above third optical
compensation layer includes a laminate having the above cholesteric
alignment solidified layer and a polymer film layer containing a
cellulose-based resin such as triacetyl cellulose (TAC). As the
polymer film layer containing a cellulose-based resin, the polymer
film (for example, "TD-80U" (trade name) manufactured by FUJIFILM
Corporation) described in the above item E or the like can be
used.
[0170] In the case where the third optical compensation layer is
the above laminate, a thickness direction retardation Rth.sub.3 is
preferably 120 to 320 nm, and more preferably 140 to 300 nm.
[0171] In the case where the third optical compensation layer is
the above laminate, a thickness thereof is preferably 15 to 80
.mu.m, and more preferably 35 to 60 .mu.m.
[0172] As the method of laminating the cholesteric alignment
solidified layer and the polymer film layer, any suitable method
can be adopted. Specifically, for example, a liquid crystal
composition containing a liquid crystal material and a chiral agent
is applied to a polymer film, the liquid crystal material is
aligned in a cholesteric structure on the film, and the alignment
thereof is fixed, whereby a laminate can be formed. Further, for
example, there are a method of transferring the above cholesteric
alignment solidified layer onto a polymer film layer, and a method
of attaching a cholesteric alignment solidified layer formed
previously on a base material to a polymer film layer via an
adhesive layer (typically, an isocyanate-based adhesive layer). The
thickness of the adhesive layer is preferably 1 to 10 .mu.m, and
more preferably 2 to 6 .mu.m.
[0173] Referring to FIG. 1(b), the third optical compensation layer
16 is placed on a side of the second optical compensation layer 14,
which is opposite to the first optical compensation layer 13. As
the method of placing the third optical compensation layer, any
suitable method can be adopted depending upon the purpose. For
example, in the case where the third optical compensation layer is
formed of a cholesteric alignment solidified layer, the third
optical compensation layer can be attached to the second optical
compensation layer via an isocyanate-based adhesive layer (not
shown) having a thickness of 2 to 6 .mu.m. Further, for example, in
the case where the third optical compensation layer is formed of a
resin film, the same means as that of the method of placing the
second optical compensation layer can be used.
[0174] H. Other Structural Components
[0175] The polarizing plate with an optical compensation layer of
the present invention may be provided with other optical layers. As
the other optical layers, any appropriate optical layers may be
employed in accordance with the purpose and the types of image
display apparatus. Specific examples thereof include a liquid
crystal film, a light scattering film, a diffraction film, and
another optical compensation layer (retardation film).
[0176] The polarizing plate with the optical compensation layer of
the present invention may further include a pressure-sensitive
adhesive layer or adhesive layer as an outermost layer on at least
one side thereof. In this way, the polarizing plate includes the
pressure-sensitive adhesive layer or adhesive layer as an outermost
layer, to thereby facilitate lamination with another member (for
example, a liquid crystal cell) and prevent peeling off of the
polarizing plate from another member. Any appropriate materials may
be used as the material for forming the pressure-sensitive adhesive
layer. Specific examples of the pressure-sensitive adhesive are
described above. Any appropriate materials may be used as the
material for forming the adhesive layer. Specific examples of the
adhesive layer are described above.
[0177] Preferably, a material having excellent moisture absorption
property or excellent heat resistance is used for preventing
foaming or peeling due to moisture absorption, degradation in
optical properties due to difference in thermal expansion or the
like, warping of the liquid crystal cell, and the like.
[0178] For practical use, a surface of the pressure-sensitive
adhesive layer or adhesive layer is covered by any appropriate
separator to prevent contamination until the polarizing plate is
actually used. The separator may be formed by a method of providing
a release coat on any appropriate film by using a releasing agent
such as a silicone-based, long chain alkyl-based, or fluorine-based
releasing agent, molybdenum sulfide, or the like as required.
[0179] Each of the layers of the polarizing plate with an optical
compensation layer of the present invention may be subjected to
treatment with a UV absorbing agent such as a salicylic ester-based
compound, a benzophenone-based compound, a benzotriazole-based
compound, a cyanoacrylate-based compound, a nickel complex
salt-based compound, or the like, to thereby impart UV absorbing
property.
[0180] I. Method of Producing a Polarizing Plate with an Optical
Compensation Layer
[0181] The polarizing plate with an optical compensation layer of
the present invention can be produced by laminating each of the
above layers via the above adhesive layer or pressure-sensitive
adhesive layer. As laminating means, any suitable means can be
adopted as long as the angles (the above angles .alpha. and .beta.)
formed by the optical axes of the respective layers are in the
above range. For example, the polarizer, the first optical
compensation layer, and the second optical compensation layer, and
in the case of placing the third optical compensation layer, the
third optical compensation layer are punched to a predetermined
size, and the directions thereof are adjusted so that the above
angles .alpha. and .beta. are in a desired range, whereby they can
be laminated via a pressure-sensitive adhesive or an adhesive. By
laminating two particular optical compensation layers in such a
particular positional relationship, light leakage in a black
display of (in particular, a reflection type or a semi-transmissive
type) liquid crystal display apparatus of a TN mode, an ECB mode,
or a VA mode can be prevented remarkably. A slow axis is not
expressed basically in the third optical compensation layer 16, so
the precise position adjustment with respect to the absorption axis
of the polarizer 12 is not required.
[0182] J. Applications of Polarizing Plate with an Optical
Compensation Layer
[0183] The polarizing plate with the optical compensation layer of
the present invention may suitably be used for various image
display apparatuses such as a liquid crystal display apparatus and
a self-luminous display apparatus. Specific examples of applicable
image display apparatuses include a liquid crystal display
apparatus, an EL display, a plasma display (PD), and a field
emission display (FED). In the case where the polarizing plate with
the optical compensation layer of the present invention is used for
a liquid crystal display apparatus, the polarizing plate with the
optical compensation layer is useful for prevention of light
leakage in black display and for compensation of viewing angle. The
polarizing plate with the optical compensation layer of the present
invention is preferably used for a liquid crystal display apparatus
of TN mode, ECB mode, or VA mode, and is particularly preferably
used for a reflection-type, transmission-type, or semi-transmissive
liquid crystal display apparatus of TN mode, ECB mode, or VA mode.
In the case where the polarizing plate with the optical
compensation layer of the present invention is used for an EL
display, the polarizing plate with the optical compensation layer
is useful for prevention of electrode reflection.
[0184] As an example of the image display apparatus of the present
invention, a liquid crystal display apparatus will be described. As
the driving mode of the liquid crystal display apparatus, any
suitable driving mode is adopted. A cell of a TN, ECB, or VA mode
is preferred. Examples of the TN mode include a twisted nematic
(TN) type and a super-twisted nematic (STN) type. The TN mode has a
high response speed, and is mostly used in liquid crystal monitors
of a laptop PC and inexpensive liquid crystal monitors. The
electrically controlled birefringence effect mode (ECB) exhibits a
colored display without using a color filter. The VA mode is widely
adopted for liquid crystal televisions, mobile telephones, and the
like. Further, the liquid crystal display apparatus may be a
reflection type or a semi-transmissive type. The polarizing plate
with an optical compensation layer of the present invention may be
provided on a viewer side or a backlight side of a liquid crystal
cell, or on both sides thereof without any limit. For example, a
third optical compensation layer in the case where the polarizing
plate with an optical compensation layer having a third optical
compensation layer is placed on both sides (i.e. the viewer side
and the backlight side of a liquid crystal cell) preferably has
about a half of the thickness direction retardation value of a
third optical compensation layer in the case where the polarizing
plate with an optical compensation layer having a third optical
compensation layer is placed on only one side of the liquid crystal
cell.
[0185] FIG. 3 is a schematic cross-sectional view of a liquid
crystal panel according to a preferred embodiment of the present
invention. Herein, a liquid crystal panel for a reflection type
liquid crystal display apparatus of a TN mode will be described. A
liquid crystal panel 100 has a liquid crystal cell 20, a
retardation plate 30 placed on an upper side of the liquid crystal
cell 20, and a polarizing plate 10 placed on an upper side of the
retardation plate 30. As the retardation plate 30, any suitable
retardation plate can be adopted depending upon the purpose and the
alignment mode of the liquid crystal cell. The retardation plate 30
can be omitted depending upon the purpose and the alignment mode of
the liquid crystal cell. The above polarizing plate 10 is a
polarizing plate with an optical compensation layer of the present
invention. When the polarizing plate with an optical compensation
layer of the present invention is used as the polarizing plate 10,
the retardation plate 30 can be omitted. The liquid crystal cell 20
includes a pair of glass substrates 21, 21', and a liquid crystal
layer 22 as a display medium placed between the substrates. A
reflective electrode 23 is provided on the liquid crystal layer 22
side of a lower substrate 21'. A color filter (not shown) is
provided on the upper substrate 21. An interval (cell gap) between
the substrates 21, 21' is controlled by spacers 24.
[0186] For example, in the case of the TN mode, liquid crystal
molecules in the liquid crystal layer 22 are aligned so as to shift
a polarization axis by 90.degree. under no voltage application in
the liquid crystal display apparatus 100. In such a state, incident
light only in one direction transmitted by the polarizing plate 10
is twisted by 90.degree. by the liquid crystal molecules and is
reflected by the reflective electrode 23 as it is. The light is
twisted by 90.degree. by the liquid crystal molecules in the liquid
crystal layer 22 again and is output from the polarizing plate 10.
Thus, under no voltage application, the liquid crystal display
apparatus 100 expresses a white display (normally white mode). On
the other hand, when a voltage is applied to the liquid crystal
display apparatus 100, the alignment of the liquid crystal
molecules in the liquid crystal layer 12 changes. As a result, the
light reflected from the reflective electrode 23 is absorbed by the
polarizing plate 10, whereby a black display is expressed. Such
switching of a display is performed for each pixel using active
elements, whereby an image is formed.
[0187] The application of the liquid crystal panel, the liquid
crystal display apparatus, and the like of the present invention is
not particularly limited. The liquid crystal panel and the liquid
crystal display apparatus can be suitably applied for various use
in: office automation (OA) devices such as a personal computer
monitor, a laptop personal computer, and a copying machine;
portable devices such as a cellular phone, a watch, a digital
camera, a personal digital assistance (PDA), and a portable game
machine; home appliances such as a video camera, a liquid crystal
television, and a microwave; on-vehicle devices such as a back
monitor, a car navigation system monitor, and a car audio; display
device such as a commercial information monitor; security device
such as a surveillance monitor; and nursing care and medical
devices such as a nursing monitor and a medical monitor.
[0188] Particularly preferably, the liquid crystal panel, the
liquid crystal display apparatus, and the like of the present
invention are preferably used for mobile products such as portable
devices, on-vehicle devices, and the like.
[0189] Hereinafter, the present invention will be more specifically
described by examples. However, the present invention is not
limited to the examples. Methods of measuring characteristics in
the examples are as described below.
[0190] (1) Measurement of a Thickness
[0191] The thickness was measured with a microgauge-type thickness
meter manufactured by Mitsutoyo Corporation. The thickness of a
hardcoat film in which a hardcoat layer is provided on a
transparent film base material was measured, and the thickness of
the base material was subtracted from the obtained thickness to
calculate the film thickness of the hardcoat layer.
[0192] (2) Measurement of Pencil Hardness
[0193] The hardcoat layer was placed on a glass plate so that the
base material side of the hardcoat layer faced the glass plate, and
the surface of the hardcoat layer was tested in accordance with a
pencil hardness test (load: 500 g) described in JIS K-5400.
[0194] (3) Measurement of Abrasion Resistance
[0195] The value with respect to the degree of abrasion resistance
of the hardcoat layer was measured in accordance with the following
test contents. First, a hardcoat layer was cut into a size of 150
mm.times.50 mm to produce a sample. The sample was placed on a
glass plate, and an initial haze value was obtained. Then, Steel
Wool #0000 was attached uniformly to the smooth cross-section of a
cylinder with a diameter of 25 mm, and reciprocated on the surface
of the sample 200 times and 1000 times at a load of 1.5 kg and a
rate of about 100 mm per second. After that, the haze value of the
hardcoat layer after the test was obtained by the above method. The
value obtained by subtracting the initial haze value from the haze
value after the test was defined as an index for abrasion
resistance. A hardcoat layer whose surface is liable to be damaged
has a larger index.
[0196] (4) Measurement of a Retardation Value
[0197] The refractive index of the optical compensation layer was
obtained by measuring each refractive index of nx, ny, and nz with
an automatic birefringence measuring device (manufactured by Oji
Scientific Instruments, an elliptical polarizing plate measurement
mode, .lamda.=590 nm of automatic birefringence measuring device
KOBRA-31PEW).
[0198] (5) Evaluation of Moist Heat Resistance
[0199] A retardation value under humidity was obtained by cutting a
polarizing plate with an optical compensation layer into a size
with a width of 25 mm and a length of 100 mm to produce a sample,
attaching the sample to a glass plate so that air, foreign matter,
and the like are not mixed, and measuring the retardation of the
resultant sample using an automatic birefringence measuring device
KOBRA31PRW (elliptical polarizing plate measurement mode)
manufactured by Oji Scientific Instruments. The sample was allowed
to stand for 500 hours under the condition of 60.degree. C. and 95%
RH, and thereafter, the retardation value thereof was measured. The
change amount of the retardation before and after the
humidification was defined as an index for moist heat
resistance.
EXAMPLE 1
Production of a Hardcoat Layer
[0200] First, 100 parts of urethane acrylate composed of
pentaerythritol-based acrylate and hydrogenated xylenediisocyanate
as urethane acrylate (herein after, referred to as A component), 49
parts of dipentaerythritol hexaacrylate (herein after, referred to
as B1 component), 41 parts of pentaerythritol tetraacrylate (herein
after, referred to as B2 component), and 24 parts of
pentaerythritol triacrylate (herein after, referred to as B3
component) as polyol (meth)acrylate (herein after, referred to as B
component), and 59 parts of a (meth) acrylic polymer having
2-hydroxyethyl group and 2,3-dihydroxypropyl group as a
(meth)acrylic polymer having an alkyl group containing at least two
hydroxyl groups (herein after, referred to as C component) were
added. Then, 3 parts of a polymerization initiator (Irgacure 184)
and 0.5 parts of a reactive leveling agent were mixed with respect
to those total resin components, whereby a solid content of a
hardcoat layer-forming material was produced. The solid content was
diluted with a mixed solvent in which butyl acetate and ethyl
acetate were mixed in a ratio (weight ratio) of 46:54 (54 parts by
weight of ethyl acetate with respect to 100 parts by weight of an
entire solvent) so that the concentration of the solid content
became 50%, whereby a hardcoat layer-forming material was prepared.
The above reactive leveling agent is a copolymer obtained by
copolymerizing dimethylsiloxane, hydroxypropylsiloxane,
6-isocyanatehexyl isocyanurate, and aliphatic polyester at a molar
ratio of 6.3:1.0:2.2:1.0.
[0201] The above hardcoat layer-forming material was applied to a
triacetylcellulose (TAC) film (manufactured by FUJIFILM
Corporation, thickness: 80 .mu.m, refractive index: 1.48) with a
bar coater, followed by heating at 100.degree. C. for one minute,
whereby a coating film was dried. After that, the film was cured by
irradiation of UV-light at an integrated light amount of 300
mJ/cm.sup.2 with a metal halide lamp, whereby a hardcoat layer was
formed. The thickness of the obtained hardcoat layer was 20 .mu.m
and the pencil hardness thereof was 4H. Further, the surface
observation results before and after the measurement of an abrasion
resistance test of the obtained hardcoat layer are shown in FIG. 4
together with the results in Comparative Example 1.
[0202] (Production of Polarizer)
[0203] A commercially available polyvinyl alcohol (PVA) film
(VF-PS, manufactured by KURARAY CO., LTD.) was colored in an
aqueous solution containing iodine and then uniaxially stretched
about 6 times between rolls of different speed ratios in an aqueous
solution containing boric acid, whereby a continuous polarizer
(having a thickness of 30 .mu.m) was obtained. As a protective
layer, a commercially available TAC film (manufactured by FUJIFILM
Corporation, having a thickness of 80 .mu.m) was stuck to one side
of the polarizer using a PVA-based adhesive. The polarizer was
punched into a size of 20 cm (longitudinal).times.30 cm (lateral).
At this time, the polarizer was punched so that the absorption axis
of the polarizer was in a longitudinal direction.
[0204] (Production of a First Optical Compensation Layer)
[0205] A long norbornene-based resin film (Zeonor (trade name)
manufactured by Zeon Corporation, thickness: 40 .mu.m, photoelastic
coefficient: 3.10.times.10.sup.-12 m.sup.2/N) was stretched
uniaxially by 2.25 times at 140.degree. C., whereby a long film for
a first optical compensation layer. The thickness of the film was
35 .mu.m, and the in-plane retardation Re.sub.1 thereof was 260 nm.
The film was punched into a size of 20 cm (longitudinal).times.30
cm (lateral). At this time, the film was punched so that the slow
axis was in a longitudinal direction.
[0206] (Production of a Second Optical Compensation Layer)
[0207] A long norbornene-based resin film (Zeonor (trade name)
manufactured by Zeon Corporation, thickness: 40 .mu.m, photoelastic
coefficient: 3.10.times.10.sup.-12 m.sup.2/N) was stretched
uniaxially by 1.52 times at 140.degree. C., whereby a long film for
a second optical compensation layer. The thickness of the film was
35 .mu.m, and the in-plane retardation Re.sub.2 thereof was 140 nm.
The film was punched into a size of 20 cm (longitudinal).times.30
cm (lateral).
[0208] (Production of a Polarizing Plate with an Optical
Compensation Layer)
[0209] The hardcoat layer, the polarizer, the first optical
compensation layer, and the second optical compensation layer
obtained in the above were laminated in this stated order. Herein,
they were laminated so that the respective slow axes of the first
optical compensation layer and the second optical compensation
layer were at 15.degree. and 75.degree. in a counterclockwise
direction with respect to the absorption axis of the polarizer. The
base material (TAC film that is to be a protective layer finally)
side of the hardcoat layer was laminated on the polarizer using a
PVA-based adhesive. The side of the polarizer where the hardcoat
layer was not laminated and the first optical compensation layer,
and the first optical compensation layer and the second optical
compensation layer were laminated using an acrylic
pressure-sensitive adhesive (thickness: 20 .mu.m). Finally, the
laminate was punched into a size of 4.0 cm (longitudinal).times.5.3
cm (lateral), whereby a polarizing plate with an optical
compensation layer as shown in FIG. 1(a) was obtained.
[0210] The results of the moist heat resistance test of the
obtained polarizing plate with an optical compensation layer are
shown in FIG. 5 together with the results of Comparative Example
1.
EXAMPLE 2
[0211] First, 100 parts by weight of urethane acrylate (herein
after, referred to as A1 component) composed of
pentaerythritol-based acrylate and isophorone diisocyanate as an A
component, 59 parts by weight of a B1 component, 37 parts by weight
of a B2 component, and 15 parts by weight of a B3 component as B
components, 26 parts by weight of a (meth) acrylic polymer having a
2-hydroxyethyl group and a 2,3-dihydroxypropyl group as a C
component, and 2 parts by weight of a polymerization initiator
(Irgacure 184) with respect to the total resin components were used
to produce a hardcoat layer in the same way as in Example 1. The
thickness of the obtained hardcoat layer was 20 .mu.m, and the
pencil hardness thereof was 4H. A polarizing plate with an optical
compensation layer was produced in the same way as in Example 1,
except for using the obtained hardcoat layer.
EXAMPLE 3
[0212] A hardcoat layer was produced in the same way as in Example
1, except for using 100 parts by weight of the A1 component as an A
component, 38 parts by weight of the B1 component, 40 parts by
weight of the B2 component, and 16 parts by weight of the B3
component as B components, 30 parts by weight of a (meth) acrylic
polymer having a 2-hydroxyethyl group and a 2,3-dihydroxypropyl
group as a C component, and 3.5 parts by weight of a polymerization
initiator (mixture of 1 part by weight of Irgacure 184 and 2.5
parts by weight of 2,4,6-trimethylbenzoinphenylphosphin oxide) with
respect to the total resin components. The thickness of the
obtained hardcoat layer was 20 .mu.m, and the pencil hardness
thereof was 4H. A polarizing plate with an optical compensation
layer was produced in the same way as in Example 1, except for
using the obtained hardcoat layer.
COMPARATIVE EXAMPLE 1
[0213] A urethane-acrylic hardcoat material (conventional hardcoat
material for a liquid crystal display apparatus) manufactured by
Nippon Paper Co., Ltd. was applied to a triacetylcellulose (TAC)
film (manufactured by FUJIFILM Corporation, thickness: 80 .mu.m,
refractive index: 1.48) with a bar coater so that the thickness
became 5 mm, followed by heating at 100.degree. C. for one minute,
whereby a coating film was dried. After that, the coating film was
irradiated with UV-light at an integrated light amount of 300
mJ/cm.sup.2 with a metal halide lamp, whereby a hardcoat layer was
formed. The thickness of the hardcoat layer was 5 .mu.m, and the
pencil hardness thereof was 3H. Further, the surface observation
results before and after the measurement of an abrasion resistance
test of the obtained hardcoat layer are shown in FIG. 4 together
with the results in Example 1.
[0214] A polarizing plate with an optical compensation layer was
produced in the same way as in Example 1 except for using the above
hardcoat layer. The results of the moist heat resistance test of
the obtained polarizing plate with an optical compensation layer
are shown in FIG. 5 together with the results of Example 1.
COMPARATIVE EXAMPLE 2
[0215] A hardcoat layer was produced in the same way as in
Comparative Example 1 except for applying the material so that the
thickness of the hardcoat layer to be obtained became 20 .mu.m. As
a result, the hardcoat layer was curled largely, which was not able
to be used practically.
EXAMPLE 4
[0216] First, 54 parts of tetraalkoxysilane, 23 parts of a silane
coupling agent having a fluoroalkyl structure and polysiloxane
structure, and 23 parts of hollow spherical silicon oxide
ultra-fine particles with a diameter of 60 nm, which was made
hydrophobic by a surface treatment using a silane coupling agent
having an acrylic group were dispersed in a mixed solvent of
isopropyl alcohol/butyl acetate/methylisobutylketone (54/14/32
(parts by weight)), and the concentration of a solid content was
adjusted to 2.0% by weight, whereby an antireflection layer-forming
material was obtained.
[0217] The obtained antireflection layer-forming material was
applied to the hardcoat layer (opposite surface with respect to the
adjacent TAC film) obtained in Example 1. The antireflection
layer-forming material was applied with a die coater so that a
thickness of an antireflection layer is 100 nm. The material was
dried and cured by heating at 120.degree. C. for 3 minutes, whereby
an antireflection layer (refractive index: 1.38) was formed. A
polarizing plate with an optical compensation layer was produced in
the same way as in Example 1, except for using the hardcoat layer
with such an antireflection layer formed thereon.
EXAMPLE 5
[0218] A polarizing plate with an optical compensation layer was
produced in the same way as in Example 1 except for using, as a
second optical compensation layer, a biaxial retardation film
obtained by stretching a norbornene-based resin film (Arton (trade
name) manufactured by JSR, thickness: 100 .mu.m, photoelastic
coefficient: 5.00.times.10.sup.-12 m.sup.2/N) at 150.degree. C.
three times by fixed-end biaxial stretching (fixed in a
longitudinal direction, and stretched three times in a lateral
direction). The thickness of the biaxial retardation film thus used
was 50 .mu.m, the in-plane retardation Re.sub.2 thereof was 140 nm,
and the thickness direction retardation Rth.sub.2 thereof was 170
nm.
[0219] [Evaluation]
[0220] From the results shown in FIG. 4, the damages in the
abrasion resistance test are remarkably smaller in Example 1 than
in Comparative Example 1. From this, it is understood that the
polarizing plate with an optical compensation layer of the present
invention is remarkably excellent in abrasion resistance, compared
with the conventional polarizing plate with an optical compensation
layer. Further, from the results shown in FIG. 5, in Example 1, the
change amount of a retardation after the elapse of 500 hours is
about 0.5 (nm), where as the change amount of a retardation in
Comparative Example 1 is about 1.3 (nm). When the change amount of
a retardation is larger than about 1 (nm), the decrease in
practical display properties is recognized. The polarizing plate
with an optical compensation layer of the present invention has the
change amount of a retardation smaller than 1 (nm), so it has moist
heat resistance properties in which the decrease in display
properties is not recognized even during the use under high
temperature and high humidity. This is conceived to be caused by
the properties of the hardcoat layer used in the present
invention.
INDUSTRIAL APPLICABILITY
[0221] The polarizing plate with an optical compensation layer of
the present invention may suitably be used for various image
display apparatuses (such as a liquid crystal display apparatus and
a self-luminous display apparatus).
* * * * *