U.S. patent application number 16/246255 was filed with the patent office on 2019-05-16 for liquid crystal display device, polarizing plate, and polarizer protection film.
This patent application is currently assigned to TOYOBO CO., LTD.. The applicant listed for this patent is TOYOBO CO., LTD.. Invention is credited to Kouichi MURATA, Mitsuharu NAKATANI, Yasushi SASAKI.
Application Number | 20190146280 16/246255 |
Document ID | / |
Family ID | 47176980 |
Filed Date | 2019-05-16 |
United States Patent
Application |
20190146280 |
Kind Code |
A1 |
MURATA; Kouichi ; et
al. |
May 16, 2019 |
LIQUID CRYSTAL DISPLAY DEVICE, POLARIZING PLATE, AND POLARIZER
PROTECTION FILM
Abstract
The invention provides a liquid crystal display device, as well
as a polarizer and a protective film suitable for the liquid
crystal display device. The liquid crystal display device comprises
a backlight light source, two polarizers, and a liquid crystal cell
disposed between the two polarizers; the backlight light source
being a white light-emitting diode light source; each of the two
polarizers comprising a polarizing film and protective films
laminated on both sides of the polarizing film; at least one of the
protective films being a polyester film having an
adhesion-facilitating layer; the polyester film having a
retardation of 3,000 to 30,000 nm; and the adhesion-facilitating
layer comprising a polyester resin (A) and a polyvinyl alcohol
resin (B).
Inventors: |
MURATA; Kouichi; (Tsuruga,
JP) ; NAKATANI; Mitsuharu; (Otsu, JP) ;
SASAKI; Yasushi; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOYOBO CO., LTD. |
Osaka |
|
JP |
|
|
Assignee: |
TOYOBO CO., LTD.
Osaka
JP
|
Family ID: |
47176980 |
Appl. No.: |
16/246255 |
Filed: |
January 11, 2019 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
14118169 |
Nov 15, 2013 |
10180597 |
|
|
PCT/JP2012/062477 |
May 16, 2012 |
|
|
|
16246255 |
|
|
|
|
Current U.S.
Class: |
349/69 ; 349/96;
359/488.01; 428/1.31; 428/1.33 |
Current CPC
Class: |
G02B 1/11 20130101; G02F
1/133611 20130101; G02F 2201/50 20130101; G02B 5/3033 20130101;
G02B 5/3083 20130101; C09K 2323/031 20200801; G02B 1/111 20130101;
G02F 1/133528 20130101; C09K 2323/035 20200801; G02F 2202/40
20130101; Y10T 428/105 20150115; Y10T 428/1041 20150115 |
International
Class: |
G02F 1/1335 20060101
G02F001/1335; G02B 1/111 20060101 G02B001/111; G02B 1/11 20060101
G02B001/11; G02B 5/30 20060101 G02B005/30 |
Foreign Application Data
Date |
Code |
Application Number |
May 18, 2011 |
JP |
2011-111441 |
Claims
1. A polarizer comprising a polarizing film and a protective film
laminated on the polarizing film, wherein the protective film is a
polyester film having an adhesion facilitating layer, wherein the
polyester film has an in-plane retardation of more than 3,000 nm
and 30,000 nm or less, and wherein the adhesion-facilitating layer
comprises a resin composition comprising a polyester resin (A) and
a polyvinyl alcohol resin (B).
2. The polarizer according to claim 1, wherein the in-plane
retardation is 7,350 nm or more and less than 10,000 nm.
3. The polarizer according to claim 2, wherein the polyester film
has a ratio in-plane of retardation to thickness-direction
retardation (Re/Rth) of 0.2 or more and 1.2 or less.
4. The polarizer according to claim 1, wherein the adhesion
facilitating layer further comprises a crosslinking agent.
5. The polarizer according to claim 4, wherein the crosslinking
agent is a melamine-based compound or an isocyanate-based
compound.
6. The polarizer according to claim 1, wherein the acid value of
the polyester resin (A) in the adhesion facilitating layer is 20
KOHmg/g or less.
7. The polarizer according to claim 1, wherein the degree of
saponification of the polyvinyl alcohol resin (B) in the adhesion
facilitating layer is 60 mol % or more and 85 mol % or less.
8. The polarizer according to claim 1, wherein the polyester film
has, on the surface opposite to the surface facing the polarizing
film, one or more layers selected from the group consisting of a
hard-coat layer, an antiglare layer, an antireflection layer, a
low-reflection layer, a low-reflection antiglare layer, and an
antireflection antiglare layer.
9. The polarizer according to claim 1, wherein the polarizer
further comprises a protective film that is a birefringence-free
film or a film selected from the group consisting of a triacetyl
cellulose film, an acrylic film, and a norbornene film and that is
laminated on the polarizing film opposite to the protective film
that is a polyester film.
10. A protective film comprising a polyester film that has an
adhesion-facilitating layer comprising a resin composition
comprising a polyester resin (A) and a polyvinyl alcohol resin (B),
and that has an in-plane retardation of more than 3,000 nm and
30,000 nm or less.
11. The protective film according to claim 10, wherein the in-plane
retardation is 7,350 nm or more and less than 10,000 nm.
12. The protective film according to claim 11, wherein the
polyester film has a ratio in-plane of retardation to
thickness-direction retardation (Re/Rth) of 0.2 or more and 1.2 or
less.
13. The protective film according to claim 10, wherein the adhesion
facilitating layer further comprising a crosslinking agent.
14. The protective film according to claim 13, wherein the
crosslinking agent is a melamine-based compound or an
isocyanate-based compound.
15. The protective film according to claim 10, wherein the acid
value of the polyester resin (A) in the adhesion facilitating layer
is 20 KOHmg/g or less.
16. The protective film according to claim 10, wherein the degree
of saponification of the polyvinyl alcohol resin (B) in the
adhesion facilitating layer is 60 mol % or more and 85 mol % or
less.
17. The protective film according to claim 10, wherein the
polyester film has, on the surface opposite to the surface facing
with the polarizing film, one or more layers selected from the
group consisting of a hard-coat layer, an antiglare layer, an
antireflection layer, a low-reflection layer, a low-reflection
antiglare layer, and an antireflection antiglare layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application is a continuation of co-pending U.S.
patent application Ser. No. 14/118,169, filed on Nov. 15, 2013,
which is the U.S. national phase of International Patent
Application No. PCT/JP2012/062477, filed May 16, 2012, which claims
the benefit of Japanese Patent Application No. 2011-111441, filed
on May 18, 2011, each of which is incorporated by reference in its
entirety herein.
TECHNICAL FIELD
[0002] The present invention relates to a liquid crystal display
device, a polarizer (polarizing plate), and a protective film. More
specifically, the present invention relates to a liquid crystal
display device that ensures high visibility and can be made
thinner, and to a polarizer and a protective film suitable for the
liquid crystal display device.
BACKGROUND ART
[0003] Polarizers used in liquid crystal display devices (LCDs)
generally have a structure in which a polarizing film obtained by
dyeing polyvinyl alcohol (PVA), etc., with iodine is sandwiched
between two protective films. Triacetyl cellulose (TAC) films are
commonly used as the protective films. Along with the recent trend
toward thinner LCDs, there is a demand for reducing the thickness
of the polarizers. However, when the thickness of a TAC film is
reduced, problems such as lower mechanical strength and higher
moisture permeability occur. Moreover, since TAC films are
relatively expensive, inexpensive alternative materials are
strongly desired.
[0004] To address this situation, there is a proposal to use
polyester films, which have relatively high durability despite
their thinness, in place of TAC films (PTL 1 to PTL 3).
[0005] TAC films, the surface of which is treated with alkali,
etc., have a very high affinity for hydrophilic adhesives and have
very high adhesion to polarizing films coated with a hydrophilic
adhesive. In contrast, polyester films have insufficient adhesion
to hydrophilic adhesives. In particular, this tendency is more
prominent in polyester films having orientation due to a stretching
treatment. Accordingly, PTL 2 and PTL 3 propose providing an
easy-bonding layer in a polyester film in order to improve the
adhesion of the polyester film to a polarizing film or a
hydrophilic adhesive applied to the polarizing film.
CITATION LIST
Patent Literature
[0006] PTL 1: JP2002-116320A
[0007] PTL 2: JP2004-219620A
[0008] PTL 3: JP2004-205773A
SUMMARY OF INVENTION
Technical Problem
[0009] As described above, polyester films are superior in
durability to TAC films; however, unlike TAC films, polyester films
have birefringence. Therefore, the use of polyester films as
protective films causes problematic lower image quality due to
optical distortion. That is, polyester films having birefringence
have a specific optical anisotropy (retardation); therefore, when
they are used as protective films, rainbow unevenness is observed
from an oblique direction, and image quality deteriorates. Hence,
PTL 1 to PTL 3 attempt to reduce the retardation by using
copolymerized polyester as the polyester. However, even such an
attempt has failed to completely prevent rainbow unevenness.
[0010] Furthermore, polyester films have a low affinity for water,
and polyester films having crystal orientation due to stretching
have an even lower affinity for water. On the other hand, the
polarizing film or an adhesive applied to the polarizing film
comprises a polyvinyl alcohol resin as a main component and has
high hydrophilicity. Due to the differences in their
characteristics, oriented polyester films and the polarizing film
or the adhesive have a low affinity for each other, making it
difficult to bond them firmly. For this reason, even the
adhesion-facilitating layers disclosed in Patent Documents 2 and 3
do not have sufficient adhesion, compared to triacetyl cellulose
films. Therefore, when a polarizer comprising conventional
orientated polyethylene terephthalate films as its protective films
was used as a display member for a long period of time, floating
and peeling occurred between the protective films and the
polarizing film, the change in the moisture content of the
polarizing film deteriorated polarization properties, and
visibility was lowered because of white spots, etc.
[0011] The present invention was made to solve these problems. An
object of the present invention is to provide a liquid crystal
display device that can be made thinner and that has improved
visibility, and a polarizer and a protective film suitable for the
liquid crystal display device.
Solution to Problem
[0012] The present inventors conducted intensive studies on the
mechanism of rainbow unevenness that occurs when using a polyester
film as a protective film. The results revealed that the rainbow
unevenness was attributable to the retardation of the polyester
film and the emission spectrum of the backlight light source.
Conventionally, fluorescent tubes, such as cold-cathode tubes and
hot-cathode tubes, are commonly used as backlight light sources of
liquid crystal display devices. The spectral distribution of
fluorescent lamps, such as cold-cathode tubes and hot-cathode
tubes, shows emission spectra having a plurality of peaks. These
discontinuous emission spectra are combined to provide a white
light source. In contrast, when a film having a high retardation
transmits light, transmission intensity varies depending on the
wavelength of the light. Accordingly, when the backlight light
source has discontinuous emission spectra, only light of a specific
wavelength is intensively transmitted, presumably leading to the
occurrence of rainbow unevenness.
[0013] Based on these findings, the present inventors conceived
that the above problems can be solved by using, in combination, a
specific backlight light source and a polyester film having a
specific retardation, and further using an adhesion-facilitating
layer having a specific binder composition. This idea has been
demonstrated, thereby leading to the completion of the present
invention.
[0014] That is, the present invention includes the following
inventions set forth in items (1) to (10) below: [0015] Item 1.
[0016] A liquid crystal display device comprising a backlight light
source, two polarizers, and a liquid crystal cell disposed between
the two polarizers,
[0017] wherein the backlight light source is a white light-emitting
diode light source,
[0018] wherein each of the two polarizers comprises a polarizing
film and protective films laminated on both sides of the polarizing
film,
[0019] wherein at least one of the protective films is a polyester
film having an adhesion-facilitating layer,
[0020] wherein the polyester film has a retardation of 3,000 to
30,000 nm, and
[0021] wherein the adhesion-facilitating layer comprises a
polyester resin (A) and a polyvinyl alcohol resin (B). [0022] Item
2.
[0023] The liquid crystal display device according to item 1,
wherein the protective film on the light-outgoing side of the
polarizing film of the polarizer disposed on the light-outgoing
side with respect to the liquid crystal cell is the polyester film
having an adhesion-facilitating layer. [0024] Item 3.
[0025] The liquid crystal display device according to item 1 or 2,
wherein the polyester film has a ratio of retardation to
thickness-direction retardation (Re/Rth) of 0.2 or more and 1.2 or
less. [0026] Item 4.
[0027] The liquid crystal display device according to any one of
items 1 to 3, wherein the polyester film has, on the surface
opposite to the surface in contact with the polarizing film, one or
more layers selected from the group consisting of a hard-coat
layer, an antiglare layer, an antireflection layer, a
low-reflection layer, a low-reflection antiglare layer, and an
antireflection antiglare layer. [0028] Item 5.
[0029] A polarizer for use in a liquid crystal display device
comprising a white light-emitting diode as a backlight light
source,
[0030] wherein the polarizer comprises a polarizing film and
protective films laminated on both sides of the polarizing
film,
[0031] wherein at least one of the protective films is a polyester
film having an adhesion-facilitating layer,
[0032] wherein the polyester film has a retardation of 3,000 to
30,000 nm, and
[0033] wherein the adhesion-facilitating layer comprises a
polyester resin (A) and a polyvinyl alcohol resin (B). [0034] Item
6.
[0035] The polarizer for use in a liquid crystal display device
comprising a white light-emitting diode as a backlight light source
according to item 5, wherein the polyester film has, on the surface
opposite to the surface in contact with the polarizing film, one or
more layers selected from the group consisting of a hard-coat
layer, an antiglare layer, an antireflection layer, a
low-reflection layer, a low-reflection antiglare layer, and an
antireflection antiglare layer. [0036] Item 7.
[0037] A protective film for use in a liquid crystal display device
comprising a white light-emitting diode as a backlight light
source,
[0038] wherein the film comprises a polyester film that has an
adhesion-facilitating layer comprising a polyester resin (A) and a
polyvinyl alcohol resin (B), and that has a retardation of 3,000 to
30,000 nm. [0039] Item 8.
[0040] The protective film for use in a liquid crystal display
device comprising a white light-emitting diode as a backlight light
source according to item 7, wherein the polyester film has a ratio
of retardation to thickness-direction retardation (Re/Rth) of 0.2
or more and 1.2 or less. [0041] Item 9.
[0042] The protective film for use in a liquid crystal display
device comprising a white light-emitting diode as a backlight light
source according to item 7 or 8, wherein the polyester film
comprises at least three or more layers, contains an ultraviolet
absorber in the layer other than the outermost layers, and has a
light transmittance at 380 nm of 20% or less. [0043] Item 10.
[0044] The protective film for use in a liquid crystal display
device comprising a white light-emitting diode as a backlight light
source according to any one of items 7 to 9, wherein the polyester
film has, on the surface opposite to the surface in contact with
the polarizing film, one or more layers selected from the group
consisting of a hard-coat layer, an antiglare layer, an
antireflection layer, a low-reflection layer, a low-reflection
antiglare layer, and an antireflection antiglare layer.
Advantageous Effects of Invention
[0045] The liquid crystal display device, polarizer, and protective
film of the present invention have an excellent adhesion between
the polarizing film and the protective films, allow the transmitted
light to have a spectrum approximated to that of the light source
at any observation angle, and ensure excellent visibility without
rainbow unevenness.
Description of Embodiments
[0046] In general, a liquid crystal panel comprises a back module,
a liquid crystal cell, and a front module in this order, starting
from the side opposing a backlight light source to the side on
which an image is displayed (i.e., the light-outgoing side). The
back module and the front module each ordinarily include a
transparent substrate, a transparent conductive film formed on the
surface of the transparent substrate on the liquid crystal cell
side, and a polarizer disposed on the opposite side. In this
regard, the polarizer in the back module is disposed on the side
opposing the backlight light source, and the polarizer in the front
module is disposed on the side on which an image is displayed
(i.e., the light-outgoing side).
[0047] The liquid crystal display device of the present invention
comprises, as components, at least a backlight light source, two
polarizers, and a liquid crystal cell disposed between the
polarizers. Furthermore, as long as visibility and the adhesion
between the polarizing film and the protective films are not
impaired, the liquid crystal display device may appropriately
comprise, in addition to the above components, other components,
such as a color filter, a lens film, an optical diffusion sheet,
and an antireflection film.
[0048] The structure of the backlight may be an edge-light system
comprising a light guide plate, a reflector, etc., as components,
or a direct under-light system; however, in the present invention,
it is necessary to use white light-emitting diodes (white LEDs) as
the backlight light source of the liquid crystal display device.
The white LEDs refer to organic light-emitting diodes (OLEDs), or
phosphor-based devices, that is, devices that emit white light by
the combined use of phosphors with light-emitting diodes using
compound semiconductors to emit blue light or ultraviolet light.
Among phosphors, white light-emitting diodes comprising
light-emitting devices obtained by the combined use of
yttrium-aluminum-garnet yellow phosphors with blue light-emitting
diodes using compound semiconductors are suitable as the backlight
light source of the present invention because of their continuous
and wide emission spectrum and excellent luminous efficiency.
Moreover, organic light-emitting diodes are also suitable because
of their continuous and wide emission spectrum. A continuous and
wide emission spectrum means that the emission spectrum is
continuous in the visible light range, and that there is no
wavelength at which the light intensity of the emission spectrum is
zero, at least in a wavelength region of 450 to 650 nm. The liquid
crystal display device of the present invention uses white LEDs,
which consume low power; therefore, it can attain the effect of
energy conservation.
[0049] In relation to this, a type of LED that utilizes the
combination of red-emitting, green-emitting, and blue-emitting LEDs
as a white light source (three-color LED system) has also been put
to practical use. However, this method is not preferred, because it
provides a narrow and discontinuous emission spectrum; therefore,
it is expected to be difficult to obtain the desired effect of the
present invention.
[0050] In addition, fluorescent tubes, such as cold-cathode tubes
and hot-cathode tubes, which have hitherto been widely used as
backlight light sources, only have a discontinuous emission
spectrum with peaks at specific wavelengths; therefore, it is
difficult to obtain the desired effect of the present
invention.
[0051] The polarizer has a structure in which a polarizing film
prepared by dyeing PVA, etc., with iodine is bonded between two
protective films. In the present invention, at least one of the
protective films, which constitute the polarizer, is a polyester
film having a specific range of retardation.
[0052] Although not wishing to be bound by any theory, the
mechanism for preventing the occurrence of rainbow unevenness by
the above structure is considered to be as follows.
[0053] When a polyester film having birefringent properties is
disposed on one side of the polarizing film, linearly polarized
light emitted from the polarizing film is disturbed when passing
through the polymer film. The transmitted light shows an
interference color specific to the retardation of the polymer film,
which is the product of the birefringence and the thickness
thereof. Accordingly, when cold-cathode tubes, hot-cathode tubes,
or the like that have a discontinuous emission spectrum are used as
the light source, the intensity of the transmitted light varies
depending on the wavelength, causing rainbow unevenness (refer to
pages 30 and 31 of Proceedings of the 15th Microoptics
Conference).
[0054] In contrast, white light-emitting diodes have a continuous
and wide emission spectrum in the visible light region. Therefore,
when focusing on the envelope curve shape of the interference color
spectrum of light transmitted through a birefringent material, a
spectrum similar to the emission spectrum of the light source can
be obtained by controlling the retardation of the polyester film.
It is thus considered that rainbow unevenness is not generated, and
visibility is significantly improved, because the envelope curve
shape of the interference color spectrum of the light transmitted
through the birefringent material becomes similar to the emission
spectrum of the light source.
[0055] As described above, since the present invention uses white
light-emitting diodes having a wide emission spectrum as the light
source, the envelope curve shape of the spectrum of the transmitted
light can be approximated to the emission spectrum of the light
source with only a relatively simple structure.
[0056] To attain the above effect, the polyester film used as the
protective film is preferably an oriented polyester film having a
retardation of 3,000 to 30,000 nm. If a polyester film having a
retardation of less than 3,000 nm is used as the protective film, a
strong interference color is presented when observed from an
oblique direction. This makes the envelope curve shape dissimilar
to the emission spectrum of the light source; therefore, excellent
visibility cannot be ensured. The lower limit of the retardation is
preferably 4,500 nm, more preferably 6,000 nm, still more
preferably 8,000 nm, and even more preferably 10,000 nm.
[0057] On the other hand, the upper limit of the retardation is
30,000 nm. A polyester film having a retardation of higher than
30,000 nm is not preferred. This is because the use of such a
polyester film cannot substantially attain the effect of further
improving visibility, while also leading to a considerable increase
in the thickness of the film. This reduces the handling ability of
the film as an industrial material.
[0058] The retardation of the polyester film can be determined by
measuring refractive indices in two mutually orthogonal directions
and thickness, or can also be determined using a commercially
available automatic birefringence analyzer, such as KOBRA-21ADH
(Oji Scientific Instruments).
[0059] In the present invention, at least one of the protective
films has the above specific retardation. The position of the
protective film having the specific retardation in the liquid
crystal display device is not particularly limited as long as
excellent visibility is obtained; however, it is preferable that
the protective film on the light source side of the polarizing film
of the polarizer disposed on the light source side of the liquid
crystal, or the protective film on the light-outgoing side of the
polarizing film of the polarizer disposed on the light-outgoing
side of the liquid crystal, be a polyester film having the specific
retardation. In particular, it is more preferable that the
protective film on the light-outgoing side of the polarizing film
of the polarizer disposed on the light-outgoing side of the liquid
crystal be a polyester film having the specific retardation. If the
polyester film is disposed in a position other than the
above-described positions, the polarization properties of the
liquid crystal cell may be changed. Since the polymer film of the
present invention cannot be used in a place for which polarization
properties are required, the polymer film of the present invention
is preferably used only in such a limited position.
[0060] The polarizer of the present invention has a structure in
which a polarizing film prepared by dyeing polyvinyl alcohol (PVA),
etc., with iodine is bonded between two protective films, at least
either of which has the above specific retardation. The other
protective film is preferably a birefringence-free film, typified
by TAC films, acrylic films, and norbornene films.
[0061] The polarizer used in the present invention can be provided
with various functional layers so as to prevent background
reflections, glare, scratches, and so on. Examples of such
functional layers include, but are not limited to, a hard-coat
layer, an antiglare (AG) layer, an antireflection (AR) layer, a
low-reflection (LR) layer, a low-reflection antiglare (LR/AG)
layer, and an antireflection antiglare (AR/AG) layer. Functional
layers are preferably provided on the surface of the polyester film
(the surface of the polyester film opposite to the surface in
contact with the polarizing film). Only one of these layers may be
formed on the polyester film, or a combination of two or more
layers may be laminated, as necessary.
[0062] When various functional layers are provided, it is
preferable to provide an adhesion-facilitating layer on the surface
of the oriented polyester film. In that case, in terms of
preventing the interference of reflected light, it is preferable to
adjust the refractive index of the adhesion-facilitating layer to
be close to the geometric mean of the refractive index of the
functional layers and the refractive index of the polyester film.
The refractive index of the adhesion-facilitating layer can be
adjusted by a known method, for example, by incorporating titanium,
zirconium, or other metal species into a binder resin, such as
polyester or polyurethane.
[0063] The polyester used in the present invention may be
polyethylene terephthalate or polyethylene naphthalate, but may
contain other copolymerization components. The resins of these
materials have excellent transparency, and also have excellent
thermal and mechanical properties. This makes it possible to easily
control the retardation by a stretching treatment. In particular,
polyethylene terephthalate is preferable, because it has high
intrinsic birefringence, and therefore can relatively easily
provide great retardation, even if the thickness of the film is
small.
[0064] In order to prevent degradation of the optical functional
dye, such as iodine dye, the film of the present invention
preferably has a light transmittance at a wavelength of 380 nm of
20% or less. The light transmittance at 380 nm is more preferably
15% or less, still more preferably 10% or less, and particularly
preferably 5% or less. When the above light transmittance is 20% or
less, the degradation of the optical functional dye caused by
ultraviolet light can be prevented. In addition, the transmittance
in the present invention is a value measured vertically with
respect to the plane of the film, and can be measured with a
spectrophotometer (e.g., Hitachi U-3500 spectrophotometer).
[0065] In order to adjust the transmittance of the film of the
present invention at a wavelength of 380 nm to 20% or less, it is
preferable to suitably control the type and concentration of the
ultraviolet absorber, and the thickness of the film. The
ultraviolet absorber used in the present invention is a known
substance. Examples of the ultraviolet absorber include organic
ultraviolet absorbers and inorganic ultraviolet absorbers; however,
organic ultraviolet absorbers are preferred in terms of
transparency. Specific examples of organic ultraviolet absorbers
include benzotriazole-based ultraviolet absorbers,
benzophenone-based ultraviolet absorbers, and cyclic imino
ester-based ultraviolet absorbers. These ultraviolet absorbers can
be used singly or in combination of two or more, as long as the
above range of absorbance can be obtained. When two or more
ultraviolet absorbers are used in combination, ultraviolet lights
of different wavelengths can be absorbed at the same time. Thus,
the ultraviolet absorption effect can be further improved.
Benzotriazole-based ultraviolet absorbers and cyclic imino
ester-based ultraviolet absorbers are particularly preferred in
terms of durability.
[0066] Examples of benzophenone-based ultraviolet absorbers,
benzotriazole-based ultraviolet absorbers, and acrylonitrile-based
ultraviolet absorbers include
2-[2'-hydroxy-5'-(methacryloyloxymethyl)phenyl]-2H-benzotriazole,
2-[2'-hydroxy-5'-(methacryloyloxyethyl)phenyl]-2H-benzotriazole,
2-[2'-hydroxy-5'-(methacryloyloxypropyl)phenyl]-2H-benzotriazole,
2,2'-dihydroxy-4,4'-dimethoxybenzophenone,
2,2',4,4'-tetrahydroxybenzophenone,
2,4-di-tert-butyl-6-(5-chlorobenzotriazol-2-yl)phenol,
2-(2'-hydroxy-3'-tert-butyl-5'-methylphenyl)-5-chlorobenzotriazole,
2-(5-chloro(2H)-benzotriazol-2-yl)-4-methyl-6-(tert-butyl)phenol,
2,2'-methylenebis(4-(1,1,3,3-tetramethylbutyl)-6-(2H-benzotriazol-2-yl)ph-
enol), etc. Examples of cyclic imino ester-based ultraviolet
absorbers include 2,2'-(1,4-phenylene)bis(4H-3,1-benzoxazin-4-one),
2-methyl-3,1-benzoxazin-4-one, 2-butyl-3,1-benzoxazin-4-one,
2-phenyl-3,1-benzoxazin-4-one, etc. However, ultraviolet absorbers
are not limited to these examples.
[0067] In addition to the ultraviolet absorber, various additives
other than catalysts can be added in the range where the effect of
the present invention is not impaired. Examples of such additives
include inorganic particles, heat-resistant polymer particles,
alkali metal compounds, alkaline earth metal compounds, phosphorus
compounds, antistatic agents, light-resistant agents, flame
retardants, heat stabilizers, antioxidants, anti-gelling agents,
surfactants, etc. Moreover, in order to achieve high transparency,
it is also preferable that the polyester film does not
substantially contain particles. "Not substantially contain
particles" indicates that, for example, in the case of inorganic
particles, the content of inorganic elements quantified by X-ray
fluorescence analysis is 50 ppm or less, preferably 10 ppm or less,
and particularly preferably not greater than the detection
limit.
[0068] In order to improve the adhesion of the polyester film to
the polarizing film or a polyvinyl alcohol resin layer (e.g., a
water-based adhesive) provided in one side or both sides of the
polarizing film, an adhesion-facilitating layer comprising a resin
composition containing a polyester resin (A) and a polyvinyl
alcohol resin (B) is laminated on at least one side of the
polyester film. The adhesion-facilitating layer may be famed on
both sides of the polyester film; or the adhesion-facilitating
layer may be formed on only one side of the polyester film, and a
coating layer of a different resin may be formed on the other side.
The polyester resin (A) imparts adhesion to the base film, while
the polyvinyl alcohol resin (B) imparts adhesion to the polarizing
film or water-based adhesive, thus ensuring excellent adhesion to
both layers.
[0069] The polyester resin (A) used in the adhesion-facilitating
layer of the present invention is a copolymer obtained by
polycondensation of a dicarboxylic acid component and a diol
component. Usable materials for the dicarboxylic acid component and
the diol component are described later. In terms of enhancing the
adhesion to the polyester film base, it is preferable to use, as
the dicarboxylic acid component of the polyester resin (A), a
dicarboxylic acid component whose structure and properties are
identical or similar to those of the dicarboxylic acid component in
the polyester film. Therefore, for example, when an aromatic
dicarboxylic acid is used as the dicarboxylic acid component of the
polyester film, it is preferable to use an aromatic dicarboxylic
acid as the dicarboxylic acid component of the polyester resin (A).
The most preferable aromatic dicarboxylic acid components are
terephthalic acid and isophthalic acid. Other aromatic dicarboxylic
acids may be added and copolymerized in an amount of 10 mol % or
less based on the total dicarboxylic acid component.
[0070] The material of the polyester resin (A) may be, but is not
limited to, a copolymer obtained by polycondensation of a
dicarboxylic acid component and a diol component; and a blended
resin thereof. Examples of the dicarboxylic acid component include
terephthalic acid, isophthalic acid, orthophthalic acid,
2,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid,
1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid,
diphenylcarboxylic acid, diphenoxyethanedicarboxylic acid,
diphenylsulfonecarboxylic acid, anthracenedicarboxylic acid,
1,3-cyclopentanedicarboxylic acid, 1,3-cyclohexanedicarboxylic
acid, 1,4-cyclohexanedicarboxylic acid, hexahydroterephthalic acid,
hexahydroisophthalic acid, malonic acid, dimethylmalonic acid,
succinic acid, 3,3-diethylsuccinic acid, glutaric acid,
2,2-dimethylglutaric acid, adipic acid, 2-methyladipic acid,
trimethyladipic acid, pimelic acid, azelaic acid, dimer acid,
sebacic acid, suberic acid, and dodecadicarboxylic acid. These may
be used singly or in combination of two or more.
[0071] Examples of the diol component constituting the polyester
resin (A) include ethylene glycol, propylene glycol, hexamethylene
glycol, neopentyl glycol, 1,2-cyclohexanedimethanol,
1,4-cyclohexanedimethanol, decamethylene glycol, 1,3-propanediol,
1,4-butanediol, 1,5-pentanediol, 1,6-hexadiol,
2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)sulfone.
These may be used singly or in combination of two or more.
[0072] Moreover, the glycol component of the polyester resin (A) is
preferably a combination of ethylene glycol and branched glycol. A
branched structure is considered to contribute to stress relaxation
in the adhesion-facilitating layer, resulting in excellent
adhesion. Examples of the branched glycol component include
2,2-dimethyl-1,3-propanediol, 2-methyl-2-ethyl-1,3-propanediol,
2-methyl-2-butyl-1,3-propanediol,
2-methyl-2-propyl-1,3-propanediol,
2-methyl-2-isopropyl-1,3-propanediol,
2-methyl-2-n-hexyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol,
2-ethyl-2-n-butyl-1,3-propanediol,
2-ethyl-2-n-hexyl-1,3-propanediol, 2,2-di-n-butyl-1,3-propanediol,
2-n-butyl-2-propyl-1,3-propanediol, and
2,2-di-n-hexyl-1,3-propanediol. These may be used singly or in
combination of two or more.
[0073] The lower limit of the molar ratio of the branched glycol
component to the total glycol component is preferably 10 mol %, and
particularly preferably 20 mol %. On the other hand, the upper
limit is preferably 80 mol %, more preferably 70 mol %, and
particularly preferably 60 mol %. If necessary, diethylene glycol,
propylene glycol, butanediol, hexanediol,
1,4-cyclohexanedimethanol, or the like, may be used in
combination.
[0074] The polyester resin (A) used in the present invention is
preferably a water-soluble or water-dispersible resin in terms of
the compatibility with the polyvinyl alcohol resin (B). In order to
make the polyester resin water-soluble or water-dispersible, it is
preferable to copolymerize a compound containing a hydrophilic
group, such as a sulfonic acid salt group or a carboxylic acid salt
group. In particular, dicarboxylic acid components having a
sulfonic acid salt group are preferable in terms of imparting
hydrophilicity while maintaining the acid value of the polyester
resin (A) at a low level and controlling reactivity with a
crosslinking agent. Examples of dicarboxylic acid components having
a sulfonic acid salt group include sulfoterephthalic acid,
5-sulfoisophthalic acid, 4-sulfonaphthaleneisophthalic
acid-2,7-dicarboxylic acid, 5-(4-sulfophenoxy)isophthalic acid, and
alkali metal salts thereof; among which 5-sulfoisophthalic acid is
preferred. The amount of the dicarboxylic acid component having a
sulfonic acid salt group is preferably 1 to 15 mol %, more
preferably 1.5 to 12 mol %, and even more preferably 2 to 10 mol %,
in the dicarboxylic acid component of the polyester resin (A). An
amount of the dicarboxylic acid component having a sulfonic acid
salt group equal to or greater than the above lower limit is
suitable for making the polyester resin water-soluble or
water-dispersible. An amount of the dicarboxylic acid component
having a sulfonic acid salt group equal to or less than the above
upper limit is suitable for adhesion to the polyester film
base.
[0075] When a crosslinking agent (C) is used in combination, as
described later, the polyester resin (A) preferably has a smaller
amount of carboxylic acid group, which is reactive with the
crosslinking agent (C). It is considered that the polyester resin
(A) having a smaller amount of carboxyl group reactive with the
crosslinking agent results in less reactivity with the crosslinking
agent, and consequently incompletely mixed with the polyvinyl
alcohol resin, whereby a domain structure formed by the crosslinked
polyvinyl alcohol resin is maintained. From such a viewpoint, the
acid value of the polyester resin (A) is desirably 20 KOHmg/g or
less, preferably 15 KOHmg/g or less, more preferably 10 KOHmg/g or
less, even more preferably 8 KOHmg/g or less, and still more
preferably 5 KOHmg/g or less. The acid value of the polyester resin
(A) can be theoretically determined from the results of component
analysis by a later-described titration method, NMR, or the
like.
[0076] In order to control the acid value of the polyester resin
(A) within the above range, it is preferable to reduce the amount
of carboxylic acid salt group that is introduced to make the resin
water-soluble or water-dispersible, to use hydrophilic groups other
than carboxylate groups, or to reduce the terminal carboxylic acid
concentration of the polyester resin. The terminal carboxylic acid
concentration of the polyester resin is preferably reduced by using
a polyester resin in which the terminal carboxylic acid group has
been modified, or using a polyester resin having a large number
average molecular weight. Accordingly, the number average molecular
weight of the polyester resin (A) is preferably 5,000 or more, more
preferably 6,000 or more, and even more preferably 10,000 or more.
It is also preferable to reduce the content of acid component(s)
having three or more carboxyl groups as a constituent component of
the polyester resin (A).
[0077] The glass transition temperature of the polyester resin (A)
is preferably, but is not limited to, 20 to 90.degree. C., and more
preferably 30 to 80.degree. C. A glass transition temperature equal
to or greater than the above lower limit is suitable for blocking
resistance, while a glass transition temperature equal to or less
than the above upper limit is suitable for adhesion to the
polyester film base.
[0078] The polyester resin (A) content of the adhesion-facilitating
layer is preferably 40 mass % or more and 90 mass % or less, more
preferably 45 mass % or more and 85 mass % or less, and even more
preferably 50 mass % or more and 80 mass % or less. A polyester
resin (A) content equal to or greater than the above lower limit is
suitable for adhesion to the polyester film base, whereas a
polyester resin (A) content equal to or less than the above upper
limit is suitable for adhesion to the polarizing film or
water-based resin.
[0079] Examples of the polyvinyl alcohol resin (B) in the
adhesion-facilitating layer include, but are not limited to,
polyvinyl alcohol obtained by saponification of polyvinyl acetate;
derivatives thereof; saponified copolymer of vinyl acetate and a
monomer copolymerizable with vinyl acetate; modified polyvinyl
alcohol obtained by acetalization, urethanization, etherification,
grafting, or phosphorylation of polyvinyl alcohol; and the like.
Examples of the monomer include (anhydrous) maleic acid, fumaric
acid, crotonic acid, itaconic acid, (meth)acrylic acid, and other
unsaturated carboxylic acids, and esters thereof; ethylene,
propylene, and other .alpha.-olefins; (meth)allylsulfonic acid
(soda), sulfonic acid soda (monoalkyl malate), disulfonic acid soda
alkyl malate, N-methylolacrylamide, acrylamide alkyl sulfonic acid
alkali salts, N-vinylpyrrolidone, N-vinylpyrrolidone derivatives,
and the like. These polyvinyl alcohol resins may be used singly or
in combination of two or more.
[0080] Examples of the polyvinyl alcohol resin (B) used in the
present invention include vinyl alcohol-vinyl acetate copolymers,
vinyl alcohol-vinyl butyral copolymers, and ethylene-vinyl alcohol
copolymers; among which vinyl alcohol-vinyl acetate copolymers and
ethylene-vinyl alcohol copolymers are preferred. Although the
degree of polymerization of the polyvinyl alcohol resin (B) is not
limited, the degree of polymerization is preferably 3,000 or less,
in terms of the viscosity of the coating solution.
[0081] The copolymerization ratio of vinyl alcohol is represented
by the degree of saponification. The degree of saponification of
the polyvinyl alcohol resin (B) of the present invention is
preferably 60 mol % or more and 85 mol % or less, more preferably
65 mol % or more and 83 mol % or less, still more preferably 68 mol
% or more and 80 mol % or less, even more preferably 70 mol % or
more and less than 80 mol %, still even more preferably 71 mol % or
more and 78 mol % or less, and particularly preferably 73 mol % or
more and 75 mol % or less. When a crosslinking agent (C) is used in
combination, as described later, a degree of saponification of the
polyvinyl alcohol resin (B) equal to or greater than the above
lower limit facilitates the formation of a crosslinked structure
with the crosslinking agent (C). In contrast, a degree of
saponification of the polyvinyl alcohol resin (B) equal to or less
than (or below) the above upper limit enhances compatibility with
the polyester resin (A). The degree of saponification of the vinyl
alcohol resin can be determined by the alkali consumption required
for hydrolysis of copolymerization units, such as vinyl acetate, or
by composition analysis by NMR.
[0082] The polyvinyl alcohol resin (B) content of the
adhesion-facilitating layer is preferably 10 mass % or more and 60
mass % or less, more preferably 15 mass % or more and 55 mass % or
less, and even more preferably 20 mass % or more and 50 mass % or
less. A polyvinyl alcohol resin (B) content greater than the above
lower limit is suitable for adhesion to the polarizing film and
water-based resin, whereas a polyvinyl alcohol resin (B) content
less than the above upper limit is suitable for adhesion to the
polyester film base.
[0083] Examples of the crosslinking agent (C) include melamine-,
isocyanate-, carbodiimide, oxazoline-, and epoxy-based compounds,
but are not limited thereto as long as they are crosslinkable with
hydroxyl groups. In terms of the stability of the coating solution
over time, melamine-, isocyanate-, carbodiimide-, and
oxazoline-based compounds are preferred. Further preferred
crosslinking agents are melamine-based compounds and
isocyanate-based compounds that are preferably crosslinkable with
the hydroxyl group of the polyvinyl alcohol resin (B). This is
presumably because since carbodiimide-based crosslinking agents are
reactive with carboxyl groups, while melamine-based compounds or
isocyanate-based compounds are reactive with hydroxyl groups, these
compounds can more suitably form a crosslinked structure with the
polyvinyl alcohol resin (B), which has a hydroxyl group as a
functional group. In particular, isocyanate-based compounds are
preferred, because they are suitably crosslinked with the hydroxyl
group of the polyvinyl alcohol resin and have excellent
transparency. Further, a catalyst and the like may be appropriately
used, if necessary, in order to promote the crosslinking
reaction.
[0084] When the crosslinking agent (C) is used in combination, it
is preferable, as described above, to combine a polyester resin (A)
having an acid value of 20 KOHmg/g or less, a polyvinyl alcohol
resin (B) having a degree of saponification of 60 to 85 mol %, and
the crosslinking agent (C). Although not wishing to be bound by any
theory, the above combination is considered to enable the polyester
resin and the polyvinyl alcohol resin to more suitably form
individual domain units in the adhesion-facilitating layer, thereby
forming a phase separation structure, which is generally called a
sea-island structure. The separated structures of such domain units
are considered to more suitably ensure both the adhesion of the
domain formed by the polyester resin to the polyester film and the
adhesion of the domain formed by the polyvinyl alcohol resin to the
polyvinyl alcohol resin layer, without impairing both of these two
functions. The crosslinking agent (C) presumably promotes and
maintains the formation of the domain structure by crosslinking and
aggregating the polyvinyl alcohol resin (B).
[0085] Usable isocyanate compounds are low- and
high-molecular-weight diisocyanates, and trivalent or higher
polyisocyanates. Specific examples of isocyanate compounds include
aromatic diisocyanates, such as 2,4-tolylene diisocyanate,
2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate,
2,4'-diphenylmethane diisocyanate, 2,2'-diphenylmethane
diisocyanate, 1,5-naphthylene diisocyanate, 1,4-naphthylene
diisocyanate, phenylene diisocyanate, tetramethylxylylene
diisocyanate, 4,4'-diphenylether diisocyanate,
2-nitrodiphenyl-4,4'-diisocyanate,
2,2'-diphenylpropane-4,4'-diisocyanate,
3,3'-dimethyldiphenylmethane-4,4'-diisocyanate,
4,4'-diphenylpropanediisocyanate, and
3,3'-dimethoxydiphenyl-4,4'-diisocyanate; aromatic aliphatic
diisocyanates, such as xylylene diisocyanate; alicyclic
diisocyanates, such as isophorone diisocyanate,
4,4-dicyclohexylmethane diisocyanate, and
1,3-bis(isocyanatemethyl)cyclohexane; aliphatic diisocyanates, such
as hexamethylene diisocyanate and 2,2,4-trimethylhexamethylene
diisocyanate; and trimers of these isocyanate compounds. Other
examples are terminal isocyanate group-containing macromolecular
compounds obtained by reacting an excess amount of such an
isocyanate compound with a low-molecular-weight active hydrogen
compound, such as ethylene glycol, propylene glycol,
trimethylolpropane, glycerin, sorbitol, ethylenediamine,
monoethanolamine, diethanolamine, or triethanolamine; or with a
high-molecular-weight active hydrogen compound, such as polyester
polyols, polyether polyols, or polyamides. These may be used singly
or in combination of two or more.
[0086] A blocked isocyanate compound is also preferred as the
crosslinking agent (C). The addition of a blocked isocyanate
compound can more suitably improve the stability of the coating
solution over time.
[0087] A blocked isocyanate compound can be prepared by the
addition reaction of an aforementioned isocyanate compound and a
blocking agent using a known method. Examples of isocyanate
blocking agents include phenols, such as phenol, cresol, xylenol,
resorcinol, nitrophenol, and chlorophenol; thiophenols, such as
thiophenol and methylthiophenol; oximes, such as acetoxime,
methylethylketoxime, and cyclohexanone oxime; alcohols, such as
methanol, ethanol, propanol, and butanol; halogen-substituted
alcohols, such as ethylenechlorohydrin and 1,3-dichloro-2-propanol;
tertiary alcohols, such as t-butanol and t-pentanol; lactams, such
as .epsilon.-caprolactam, .delta.-valerolactam,
.gamma.-butyrolactam, and .beta.-propyllactam; aromatic amines;
imides; active methylene compounds, such as acetylacetone,
acetoacetic acid ester, and malonic acid ethyl ester; mercaptans;
imines; ureas; diaryl compounds; sodium bisulfite; and the
like.
[0088] Usable melamine compounds are those substituted with a
substituent --(CH.sub.2)n-O--R, wherein n is an integer of 1 to 3,
and R is C.sub.1-4 alkyl, preferably methyl. The number of
substituents of one melamine structure is preferably 3 to 6.
Specific examples of melamine compounds include the Sumitex Resin
series M-3, MK, M-6, M-100, and MC (produced by Sumitomo Chemical
Co., Ltd.), methylated melamine resins MW-22, MX-706, and MX-042
(produced by Sanwa Chemical Co., Ltd.), and the like.
[0089] The crosslinking agent (C) content of the
adhesion-facilitating layer is preferably 2 mass % or more and 50
mass % or less, more preferably 5 mass % or more and 40 mass % or
less, and even more preferably 8 mass % or more and 30 mass % or
less. A crosslinking agent (C) content equal to or greater than the
above lower limit is suitable for crosslink formation of the
polyvinyl alcohol resin, whereas a crosslinking agent (C) content
equal to or less than the above upper limit is suitable for
expression of the adhesion effect by the binder resin.
[0090] The mixing ratio (A)/(B) of the polyester resin (A) to the
polyvinyl alcohol resin (B) is preferably 0.8 to 5, more preferably
1 to 4, even more preferably 2 to 4, and particularly preferably
2.5 to 3.5, by mass ratio. An (A)/(B) ratio equal to or greater
than the above lower limit is suitable for adhesion to the
polyester film base, whereas an (A)/(B) ratio equal to or less than
the above upper limit is suitable for adhesion to the polarizing
film or water-based resin.
[0091] The mixing ratio ((A)+(B))/(C) of the polyester resin (A)
and the polyvinyl alcohol resin (B) to the crosslinking agent (C)
is preferably 2 to 50, more preferably 5 to 40, and even more
preferably 8 to 30, by mass ratio. An ((A)+(B))/(C) ratio equal to
or greater than the above lower limit is suitable for expression of
the adhesion effect by the binder resin component, whereas an
((A)+(B))/(C) ratio equal to or less than the above upper limit is
suitable for expression of the adhesion effect due to phase
separation.
[0092] Because of the above composition, the adhesion-facilitating
layer of the present invention has adhesion as high as that of
triacetyl cellulose to the polarizing film or water-based adhesive,
particularly when the polarizing film or water-based adhesive
comprises polyvinyl alcohol. More specifically, in an adhesion
test, described later, the area of the remaining polarizing film
after one peeling is preferably 80% or more, more preferably 90% or
more, even more preferably 95% or more, and most preferably
100%.
[0093] Further, as for the above adhesion, the remaining area after
5 continuous peelings and the remaining area after 10 peelings are
preferably as follows. The remaining area after 5 continuous
peelings is preferably 75% or more, more preferably 85% or more,
and even more preferably 95% or more. The remaining area after 10
continuous peelings is preferably 50% or more, more preferably 80%
or more, even more preferably 90% or more, still more preferably
93% or more, and particularly preferably 95% or more.
[0094] The adhesion-facilitating layer of the present invention may
contain known additives, such as surfactants, antioxidants,
catalysts, heat-resistant stabilizers, weathering stabilizers,
ultraviolet absorbers, organic lubricants, pigments, dye, organic
or inorganic particles, antistatic agents, and nucleating agents,
in the range where the effect of the present invention is not
impaired.
[0095] In a preferable embodiment of the present invention,
particles are added to the adhesion-facilitating layer so as to
improve the blocking resistance of the adhesion-facilitating layer.
In the present invention, examples of the particles to be added to
the adhesion-facilitating layer include inorganic particles of
titanium oxide, barium sulfate, calcium carbonate, calcium sulfate,
silica, alumina, talc, kaolin, clay, calcium phosphate, mica,
hectorite, zirconia, tungsten oxide, lithium fluoride, calcium
fluoride, or the like; and styrene, acrylic, melamine,
benzoguanamine, silicone, and other organic polymer particles.
These particles may be used singly or in combination of two or
more.
[0096] The average particle diameter of the particles in the
adhesion-facilitating layer (average particle diameter based on the
number of particles measured by SEM; hereafter the same) is
preferably 0.04 to 2.0 .mu.m, and more preferably 0.1 to 1.0
.mu.m.
[0097] Inert particles having an average particle diameter of less
than 0.04 .mu.m result in insufficient formation of irregularities
on the film surface. Consequently, the handling properties of the
film, such as sliding properties and winding properties, may be
reduced, and processability during bonding may be lowered. Inert
particles having an average particle diameter of more than 2 .mu.m
are not preferred because they tend to easily drop out. The
particle concentration in the adhesion-facilitating layer is
preferably 1 to 20 mass %, and more preferably 5 to 15 mass %, in
the solid components.
[0098] In the present invention, the thickness of the
adhesion-facilitating layer can be suitably determined within the
range of 0.001 to 2 .mu.m; however, in order to achieve both
processability and adhesion, the thickness is preferably in the
range of 0.01 to 1 .mu.m, more preferably 0.02 to 0.8 .mu.m, and
even more preferably 0.05 to 0.5 .mu.m. When the thickness of the
adhesion-facilitating layer is less than 0.01 .mu.m, adhesion
becomes insufficient. When the thickness of the
adhesion-facilitating layer is more than 2 .mu.m, blocking may
occur.
[0099] In a general method for producing polyester films, for
example, non-oriented polyester obtained by melting a polyester
resin and extruding the molten resin into a sheet-like shape is
stretched in a longitudinal direction through the use of roll
velocity difference at a temperature higher than the glass
transition temperature, and then stretched in a transverse
direction with a tenter, followed by heat treatment.
[0100] The method for providing the adhesion-facilitating layer may
be a known method. Examples thereof include reverse-roll coating,
gravure coating, kiss coating, roll-brush coating, spray coating,
air-knife coating, wire-bar coating, pipe doctor method, and the
like. These methods can be used singly or in combination. The
adhesion-facilitating layer can be provided by applying the coating
solution to one side or both sides of an unstretched film or
uniaxially stretched film in the film production process.
[0101] The polyester film of the present invention may be a
uniaxially stretched film or a biaxially stretched film. However,
care should be taken when a biaxially stretched film is used as the
protective film, because no rainbow unevenness is observed when the
film is viewed from right above the film plane, whereas rainbow
unevenness may be observed when the film is viewed from an oblique
direction.
[0102] This phenomenon is caused by the following factors: The
biaxially stretched film has an index ellipsoid with different
refractive indices in the running direction, width direction, and
thickness direction, and there is a direction in which the
retardation is zero (the index ellipsoid looks like a perfect
circle) depending on the light transmission direction in the film.
Accordingly, when the screen of the liquid crystal display is
observed from a specific oblique direction, there may be a point at
which the retardation is zero. Centering on that point, rainbow
unevenness is generated in a concentric manner. When the angle
between the position right above the film surface (normal
direction) and the position at which rainbow unevenness is visible
is regarded as .theta., the angle .theta. becomes larger as the
birefringence in the film plane increases, and rainbow unevenness
is less likely to be visible. Since a biaxially stretched film
tends to have a lower angle .theta., a uniaxially stretched film,
in which rainbow unevenness is less likely to be visible, is
preferred.
[0103] However, a complete uniaxial (uniaxially symmetric) film is
not preferred, because mechanical strength in a direction
orthogonal to the orientation direction remarkably decreases. In
the present invention, it is preferable to have biaxiality (biaxial
symmetry) in a range where rainbow unevenness is not substantially
generated, or in a range where rainbow unevenness is not generated
within the range of the viewing angle required for liquid crystal
display screens.
[0104] As an indicator for determining the difficulty in visibility
of rainbow unevenness, there is a method of evaluating differences
in retardation (in-plane retardation) and thickness-direction
retardation (Rth). A thickness-direction phase difference indicates
the average of phase differences obtained by multiplying each of
two birefringence values .DELTA.Nxz and .DELTA.Nyz, when the film
is viewed from the thickness-direction cross-section, by the film
thickness d. The smaller the difference between the in-plane
retardation and the thickness-direction retardation, the higher the
isotropy of the action of birefringence depending on the
observation angle. Thus, the variation of retardation depending on
the observation angle is reduced. Accordingly, the occurrence of
rainbow unevenness depending on the observation angle is presumably
prevented.
[0105] The ratio of retardation to thickness-direction retardation
(Re/Rth) of the polyester film of the present invention is
preferably 0.2 or higher, more preferably 0.5 or higher, and still
more preferably 0.6 or higher. The greater the ratio of retardation
to thickness-direction retardation (Re/Rth), the higher the
isotropy of the action of birefringence, and the more the
occurrence of rainbow unevenness depending on the observation angle
is prevented. A complete uniaxial (uniaxially symmetric) film has a
ratio of retardation to thickness-direction retardation (Re/Rth) of
2.0. However, as described above, as the film becomes closer to a
complete uniaxial (uniaxially symmetric) film, mechanical strength
in a direction orthogonal to the orientation direction remarkably
decreases.
[0106] On the other hand, the ratio of retardation to
thickness-direction retardation (Re/Rth) of the polyester film of
the present invention is preferably 1.2 or less, and more
preferably 1.0 or less. In order to completely prevent the
occurrence of rainbow unevenness depending on the observation
angle, the above ratio of retardation to thickness-direction
retardation (Re/Rth) is not necessarily 2.0, but is sufficiently
1.2 or less. Moreover, even if the above ratio is 1.0 or less, it
is sufficiently possible to satisfy viewing-angle characteristics
required for liquid crystal display devices (right/left viewing
angle: about 180 degrees, and upper/lower viewing angle: about 120
degrees).
[0107] The film-forming conditions of the polyester film are
described in detail below. The temperature for stretching in the
longitudinal direction and the temperature for stretching in the
transverse direction are preferably 80 to 130.degree. C., and
particularly preferably 90 to 120.degree. C. The stretch ratio for
stretching in the longitudinal direction is preferably 1.0 to 3.5,
and particularly preferably 1.0 to 3.0. The stretch ratio for
stretching in the transverse direction is preferably 2.5 to 6.0,
and particularly preferably 3.0 to 5.5. In order to control the
retardation within the above range, it is preferable to control the
proportion of longitudinal stretch ratio and transverse stretch
ratio. An overly small difference between the longitudinal and
transverse stretch ratios is not preferred, because it is difficult
to make a difference in retardation. To increase the retardation,
it is also preferable to set the stretch temperature low. In the
subsequent heat treatment, the treatment temperature is preferably
100.degree. C. to 250.degree. C., and particularly preferably
180.degree. C. to 245.degree. C.
[0108] In order to suppress variations in retardation, the
thickness variation of the film is preferably low. Since the
stretch temperature and the stretch ratios have a great influence
on the film thickness variation, it is necessary to optimize the
film production conditions in terms of the thickness variation. In
particular, when the longitudinal stretch ratio is reduced to make
a difference in retardation, the longitudinal thickness variation
may deteriorate. Since there is an area in which the longitudinal
thickness variation significantly deteriorates in a specific range
of the stretch ratio, it is preferable to set the film production
conditions outside that range.
[0109] The film of the present invention preferably has a thickness
variation of 5.0% or less, more preferably 4.5% or less, still more
preferably 4.0% or less, and particularly preferably 3.0% or less.
The thickness variation of the film can be measured, for example,
as follows. A tape-like sample continuous in a longitudinal
direction (length: 3 m) is taken from the film, and the thickness
of the sample is measured in 100 points at a 1-cm pitch. The
thickness can be measured by using, for example, an electronic
micrometer (Miritoron 1240, produced by Seiko EM). The maximum
value (dmax), minimum value (dmin), and average value (d) of
thickness are determined from the measured values, and the
thickness variation (%) can be calculated by the following
formula:
Thickness variation (%)=((dmax-dmin)/d).times.100
[0110] As described above, it is possible to control the
retardation of the film in a specific range by appropriately
setting the stretch ratio, the stretch temperature, and the
thickness of the film. For example, the higher the stretch ratio,
the lower the stretch temperature, or the greater the thickness of
the film, the more likely will a large retardation be obtained. In
contrast, the lower the stretch ratio, the higher the stretch
temperature, or the smaller the thickness of the film, the more
likely will a small retardation be obtained. However, when the film
thickness is increased, the phase difference in the thickness
direction is likely to increase. It is therefore preferable to
appropriately set the film thickness in the range described later.
In addition to the control of retardation, it is necessary to
determine the final film production conditions in consideration of
physical properties, etc., required for processing.
[0111] The polyester film used in the present invention may have
any thickness, but preferably has a thickness in the range of 15 to
300 .mu.m, and more preferably 15 to 200 .mu.m. Even a film having
a thickness of lower than 15 .mu.m can, in principle, provide a
retardation of 3,000 nm or higher. In this case, however, the
mechanical properties of the film become significantly anisotropic.
This causes the film to, for example, tear or break, which
significantly reduces the practicality of the film as an industrial
material. The lower limit of the thickness is particularly
preferably 25 .mu.m. On the other hand, when the upper limit of the
thickness of the protective film exceeds 300 .mu.m, the polarizer
is overly thick, which is not preferred. The upper limit of the
thickness is preferably 200 .mu.m in terms of the practicality as a
protective film. The upper limit of the thickness is particularly
preferably 100 .mu.m, which is almost equivalent to the thickness
of a general TAC film. In order to control the retardation in the
range of the present invention in the above thickness range,
polyethylene terephthalate is preferred as the polyester used as
the film base.
[0112] As the method for mixing an ultraviolet absorber with the
polyester film of the present invention, known methods can be used
in combination. For example, a masterbatch is previously produced
by mixing a dried ultraviolet absorber with polymer starting
materials using a kneading extruder, and the masterbatch and the
polymer starting materials are mixed during the film
production.
[0113] In that case, the ultraviolet absorber concentration in the
masterbatch is preferably 5 to 30 mass % so as to uniformly
disperse and economically mix the ultraviolet absorber. Preferred
conditions for producing the masterbatch include the use of a
kneading extruder, and extrusion at a temperature equal to or
greater than the melting point of the polyester starting material
and equal to or lower than 290.degree. C. for 1 to 15 minutes. At a
temperature of 290.degree. C. or more, a large amount of
ultraviolet absorber is lost, and the viscosity of the masterbatch
is significantly reduced. For an extrusion time of 1 minute or
less, it is difficult to homogeneously mix the ultraviolet
absorber. At this point, a stabilizer, a color tone-controlling
agent, and an antistatic agent may be added, if necessary.
[0114] In the present invention, it is preferable that the film
have a multi-layered structure including at least three or more
layers, and that an ultraviolet absorber be added to the
intermediate layer(s) of the film. Such a three-layer film
containing an ultraviolet absorber in the intermediate layer can be
specifically produced in the following manner. Polyester pellets
are singly used for the outer layers. For the intermediate layer,
polyester pellets and a masterbatch containing an ultraviolet
absorber are mixed in a predetermined proportion, and then dried.
These are supplied into a known extruder for melt-lamination, and
extruded through a slit-shaped die into a sheet-like shape,
followed by cooling and solidification on a casting roll, thereby
forming an unstretched film. More specifically, film layers
constituting both outer layers and a film layer constituting the
intermediate layer are laminated by using two or more extruders, a
three-layer manifold, or a junction block (e.g., a junction block
having a square-shaped junction). A three-layered sheet is extruded
through a die and cooled on a casting roll, thereby forming an
unstretched film. In the invention, in order to remove foreign
substances, which cause optical defects, from the starting material
(i.e., polyester), it is preferable to perform high-precision
filtration during melt extrusion. The filtration particle size
(initial filtration efficiency: 95%) of a filtering medium used for
high-precision filtration of the molten resin is preferably 15
.mu.m or less. When the filtration particle size of the filtering
medium is more than 15 .mu.m, the removal of foreign substances
having a size of 20 .mu.m or more is likely to be insufficient.
EXAMPLES
[0115] The present invention will hereinafter be described more
specifically by way of Examples; however, the present invention is
not limited to the Examples described below. The present invention
can be put into practice after appropriate modifications or
variations within a range meeting the gist of the present
invention, all of which are included in the technical scope of the
present invention. In the following Examples, the methods for the
evaluation of physical properties are as follows: [0116] (1) Glass
Transition Temperature
[0117] The glass transition temperature was measured according to
JIS K7121 using a differential scanning calorimeter (DSC6200,
produced by Seiko Instruments Inc.). The temperature of a resin
sample (10 mg) was raised at a rate of 20.degree. C./min in a
temperature range of 25 to 300.degree. C., and an extrapolated
glass transition initiation temperature obtained from the DSC curve
was defined as the glass transition temperature. [0118] (2) Number
Average Molecular Weight
[0119] A resin (0.03 g) was dissolved in 10 ml of tetrahydrofuran,
and the number average molecular weight was measured by using a
GPC-LALLS (low angle laser light scattering) photometer LS-8000
(produced by Tosoh Corporation; tetrahydrofuran solvent; reference:
polystyrene) and columns (Shodex KF-802, 804, and 806, produced by
Showa Denko K.K.) at a column temperature of 30.degree. C. at a
flow rate of 1 ml/min. [0120] (3) Resin Composition
[0121] A resin was dissolved in heavy chloroform, and .sup.1H-NMR
analysis was performed using a nuclear magnetic resonance (NMR)
spectrometer (Gemini 200, produced by Varian) to determine the
molar percent ratio of each composition by the integration ratio.
[0122] (4) Acid Value
[0123] A sample (solids content: 1 g) was dissolved in 30 ml of
chloroform or dimethylformamide, and titrated with a 0.1 N
potassium hydroxide/ethanol solution using phenolphthalein as an
indicator to determine the amount (mg) of KOH required to
neutralize carboxyl groups per gram of the sample. [0124] (5)
Degree of Saponification
[0125] The amount of residual acetate groups (mol %) of polyvinyl
alcohol resin was quantified using sodium hydroxide according to
JIS-K6726, and the obtained value was defined as the degree of
saponification (mol %). The measurement was repeated three times on
the same sample, and the average of the obtained values was used as
the degree of saponification (mol %). [0126] (6) Retardation
(Re)
[0127] Retardation is a parameter defined by the product
(.DELTA.Nxy X d) of the anisotropy (.DELTA.Nxy=|Nx-Ny|) of
refractive indices in two mutually orthogonal directions on a film
and the film thickness d (nm), and is a scale indicating optical
isotropy or anisotropy. The anisotropy (.DELTA.Nxy) of refractive
indices in two directions is obtained by the following method. The
directions of orientation axes of a film were determined using two
polarizers, and the film was cut into a 4 cm.times.2 cm rectangle
so that the direction of the orientation axis was orthogonal to
either side of the rectangle. The cut piece was used as a sample
for measurement. The sample was measured for the refractive indices
(Nx and Ny) in two mutually orthogonal directions and the
refractive index (Nz) in the thickness direction by the use of an
Abbe refractometer (NAR-4T available from Atago Co., Ltd.). Then,
the absolute value (|Nx-Ny|) of the difference between the
refractive indices in two directions was defined as the anisotropy
(.DELTA.Nxy) of the refractive indices. The film thickness d (nm)
was measured using an electric micrometer (Millitron 1245D,
available from Feinpruf GmbH), and was converted to nm units. The
retardation (Re) was determined by the product (.DELTA.Nxy.times.d)
of the anisotropy (.DELTA.Nxy) of the refractive indices and the
film thickness d (nm). [0128] (7) Thickness-Direction Retardation
(Rth)
[0129] Thickness-direction retardation is a parameter indicating
the average of retardation obtained by multiplying two
birefringence values .DELTA.Nxz (=|Nx-Nz|) and .DELTA.Nyz
(=|Ny-Nz|) when viewed from a film-thickness direction
cross-section, by a film thickness d. The refractive indices Nx,
Ny, and Nz, and the film thickness d (nm) were determined in the
same manner as in the measurement of retardation, and the average
value of (.DELTA.Nxz.times.d) and (.DELTA.Nyz.times.d) was
calculated to determine the thickness-direction retardation (Rth).
[0130] (8) Light Transmittance at Wavelength of 380 nm
[0131] Using a spectrophotometer (U-3500, produced by Hitachi,
Ltd.), the light transmittance of each film at a wavelength of 300
to 500 nm was measured using the air space as standard, and the
light transmittance at a wavelength of 380 nm was determined.
[0132] (9) Observation of Rainbow Unevenness
[0133] The polyester film of the present invention was bonded to
one side of a polarizing film comprising PVA and iodine so that the
absorption axis of the polarizing film was vertical to the main
orientation axis of the polyester film. A TAC film (produced by
Fujifilm Corporation; thickness: 80 .mu.m) was bonded to the
opposite side, thereby producing a polarizer. The obtained
polarizer was placed on the light-outgoing side of a liquid crystal
display device (having a polarizer comprising two TAC films as
protective films on the light source side of the liquid crystal
cell) that employed, as a light source, white LEDs (NSPW500CS,
available from Nichia Corporation) having light-emitting devices
obtained by the combined use of yttrium-aluminum-garnet yellow
phosphors with blue light-emitting diodes, so that the polyester
film was disposed on the light-outgoing side. The polarizer of the
liquid crystal display device was visually observed from the front
direction and an oblique direction, and the occurrence of rainbow
unevenness was determined as follows. In Comparative Example 5, a
backlight light source using cold-cathode tubes as the light source
was used in place of the white LEDs.
[0134] ++: no formation of rainbow unevenness observed from any
direction
[0135] +: partial, very light rainbow unevenness observed from an
oblique direction
[0136] -: clear rainbow unevenness observed from an oblique
direction [0137] (10) Tear Strength
[0138] The tear strength of each film was measured according to JIS
P-8116 using an Elmendorf tearing tester (produced by Toyo Seiki
Seisaku-sho, Ltd.). The tear direction was parallel to the
orientation axis direction of the film, and the results were
evaluated as follows. The orientation axis direction was measured
by a molecular orientation analyzer (MOA-6004, produced by Oji
Scientific Instruments).
[0139] +: Tear strength was 50 mN or more.
[0140] -: Tear strength was less than 50 mN. [0141] (11) PVA
Adhesion
[0142] A polyvinyl alcohol aqueous solution (PVA117, produced by
Kuraray Co., Ltd.) adjusted to a solids content of 5 mass % was
applied to the surface of the adhesion-facilitating layer of the
protective film using a wire bar so that the thickness of the dried
polyvinyl alcohol resin layer was 2 .mu.m, and dried at 70.degree.
C. for 5 minutes. In order to facilitate determination, red dye was
added to the polyvinyl alcohol aqueous solution. The produced film,
which was the subject of evaluation, was attached to a 5-mm-thick
glass plate, to which a double-sided tape had been attached, so
that the surface of the film opposite to the surface coated with
the polyvinyl alcohol resin layer was in contact with the
double-sided tape. Then, 100 grid cuts penetrating the polyvinyl
alcohol resin layer to reach the protective film were made using a
cutter guide with space intervals of 2 mm. Subsequently, an
adhesive tape (Cellotape (registered trademark) CT-24, produced by
Nichiban Co., Ltd.; 24 mm width) was bonded to the grid cut
surface. Air remaining in the interface during the bonding was
pushed out using an eraser to completely bond to each other, and
then the adhesive tape was swiftly peeled off vertically. This
operation was conducted once, five times, and ten times. The number
of grids in which the polyvinyl alcohol resin layer was not peeled
was counted, and used as the PVA adhesion. More specifically, when
the PVA layer was not peeled at all, the PVA adhesion rate was 100;
whereas when the entire PVA layer was peeled, the PVA adhesion rate
was 0. Accordingly, for example, when peeling is observed in five
grids, the PVA adhesion rate is 95. Grids in which partial peeling
occurred were also counted as having peeled.
Production of Adhesion-Facilitating Layer Components Polymerization
of Polyester Resin
[0143] Dimethyl terephthalate (194.2 parts by mass), 184.5 parts by
mass of dimethyl isophthalate, 14.8 parts by mass of
dimethyl-5-sodium sulfoisophthalate, 233.5 parts by mass of
diethylene glycol, 136.6 parts by mass of ethylene glycol, and 0.2
parts by mass of tetra-n-butyl titanate were placed in a stainless
steel autoclave equipped with a stirrer, a thermometer, and a
partial reflux condenser, and transesterification was performed at
a temperature of 160 to 220.degree. C. for 4 hours. Subsequently,
the temperature was raised to 255.degree. C., and the pressure of
the reaction system was gradually reduced. The reaction was then
performed at a reduced pressure of 30 Pa for an hour and a half,
thereby obtaining a copolymerized polyester resin (A-1). The
obtained copolymerized polyester resin (A-1) was light yellow and
transparent. The reduced viscosity of the copolymerized polyester
resin (A-1) was 0.70 dl/g. The glass transition temperature
measured by DSC was 40.degree. C.
[0144] Copolymerized polyester resins (A-2) and (A-3) having
different compositions were obtained in the same manner as
described above. Table 1 shows the compositions (mol % ratio;
measured by .sup.1H-NMR) and other properties of these
copolymerized polyester resins.
TABLE-US-00001 TABLE 1 A-1 A-2 A-3 Dicarboxylic Terephthalic acid
49 49 97 acid component Isophthalic acid 48 48 -- (mol %)
Trimellitic acid -- -- -- 5-sodium 3 3 3 sulfoisophthalate Glycol
Ethylene glycol 40 50 20 component Diethylene glycol 60 -- -- (mol
%) Neopentyl glycol -- 50 -- Propanediol -- -- 79
Trimeethylolpropane -- -- 1 Physical Glass transition 40 65 75
properties temperature (.degree. C.) Number average 20 15 8
molecular weight (.times. 1,000 MW) Acid value 2 4 6 (KOH mg/g)
Preparation of Polyester Aqueous Dispersion
[0145] The polyester resin (A-1) (30 parts by mass) and 15 parts by
mass of ethylene glycol n-butyl ether were placed in a reactor
equipped with a stirrer, a thermometer, and a reflux condenser, and
the mixture was heated to 110.degree. C. and stirred to dissolve
the resin. After the resin was completely dissolved, 55 parts by
mass of water was gradually added to the polyester solution while
stirring. After addition, the solution was cooled to room
temperature while stirring, thereby preparing a milky-white
polyester aqueous dispersion (Aw-1) having a solids content of 30
mass %. Aqueous dispersions (Aw-2) and (Aw-3) were prepared in the
same manner as described above using the polyester resins (A-2) and
(A-3) in place of the polyester resin (A-1).
Preparation of Polyvinyl Alcohol Aqueous Solution
[0146] Water (90 parts by mass) was placed in a container equipped
with a stirrer and a thermometer, and, while stirring, 10 parts by
mass of polyvinyl alcohol resin having a degree of polymerization
of 500 (produced by Kuraray) (B-1) was gradually added. After
addition, the solution was heated to 95.degree. C., while stirring,
to dissolve the resin. After dissolution, the solution was cooled
to room temperature while stirring, thereby preparing a polyvinyl
alcohol aqueous solution (Bw-1) having a solids content of 10 mass
%. Aqueous solutions (Bw-2) to (Bw-6) were prepared in the same
manner as described above using polyvinyl alcohol resins (B-2) to
(B-6) in place of the polyvinyl alcohol resin (B-1). Table 2 shows
the degree of saponification of the polyvinyl alcohol resins (B-1)
to (B-6).
TABLE-US-00002 TABLE 2 B-1 B-2 B-3 B-4 B-5 B-6 Saponification 88 83
79 74 70 67 degree (mol %)
Polymerization of Blocked Polyisocyanate Crosslinking Agent
[0147] A polyisocyanate compound comprising hexamethylene
diisocyanate as a starting material and having an isocyanurate
structure (100 parts by mass; Duranate TPA, produced by Asahi Kasei
Chemicals Corp.), 55 parts by mass of propylene glycol monomethyl
ether acetate, and 30 parts by mass of polyethylene glycol
monomethyl ether (average molecular weight: 750) were placed in a
flask equipped with a stirrer, a thermometer, and a reflux
condenser tube, and maintained in a nitrogen atmosphere at
70.degree. C. for 4 hours. Thereafter, the temperature of the
reaction mixture was reduced to 50.degree. C., and 47 parts by mass
of methylethylketoxime was added dropwise. The infrared spectrum of
the reaction mixture was measured, and it was confirmed that no
absorption of isocyanate group was observed. Thus, a blocked
polyisocyanate aqueous dispersion (C-1) having a solids content of
75 mass % was obtained.
Production of Protective Film Components
Polyester X
[0148] The temperature of an esterification reaction vessel was
raised, and when the temperature reached 200.degree. C., 86.4 parts
by mass of terephthalic acid and 64.6 parts by mass of ethylene
glycol were put in the vessel. While stirring the mixture, 0.017
parts by mass of antimony trioxide, 0.064 parts by mass of
magnesium acetate tetrahydrate, and 0.16 parts by mass of
triethylamine were added as catalysts. Subsequently, the pressure
and temperature were raised, and pressure esterification was
performed at a gauge pressure of 0.34 MPa at 240.degree. C. Then,
the pressure in the esterification reaction vessel was returned to
normal pressure, and 0.014 parts by mass of phosphoric acid was
added. Further, the temperature was raised to 260.degree. C. over
15 minutes, and 0.012 parts by mass of trimethyl phosphate was
added. Subsequently, after 15 minutes, dispersion was performed
with a high-pressure disperser. After 15 minutes, the obtained
esterification reaction product was transferred to a
polycondensation reaction vessel, and a polycondensation reaction
was performed at 280.degree. C. under reduced pressure. After
completion of the polycondensation reaction, filtration was
performed using a Naslon filter (95% cut size: 5 .mu.m). The
resultant was extruded through a nozzle into a strand shape, cooled
and solidified with cooling water, which had been previously
filtered (pore size: 1 .mu.m or less), and cut into pellets. The
obtained polyethylene terephthalate resin had an intrinsic
viscosity of 0.62 dl/g, and did not substantially contain inert
particles and internally deposited particles (hereafter abbreviated
as "PET (X)").
Polyester Y
[0149] A dried ultraviolet absorber
2,2'-(1,4-phenylene)bis(4H-3,1-benzoxazin-4-one) (10 parts by mass)
and 90 parts by mass of particle-free PET (X) (intrinsic viscosity:
0.62 dl/g) were mixed, and a kneading extruder was used to obtain a
polyethylene terephthalate resin (Y) containing the ultraviolet
absorber (hereafter abbreviated as "PET (Y)").
Example 1
[0150] The following coating components were mixed to prepare a
coating solution in which the mass ratio of the polyester resin (A)
to the polyvinyl alcohol resin (B) was 70/30. The polyester aqueous
dispersion used was the aqueous dispersion (Aw-1) of polyester
resin having an acid value of 2 KOHmg/g. The polyvinyl alcohol
aqueous solution used was the aqueous solution (Bw-4) of polyvinyl
alcohol having a degree of saponification of 74 mol %.
[0151] Water: 40.61 mass %
[0152] Isopropanol: 30.00 mass %
[0153] Polyester aqueous dispersion (Aw-1): 11.67 mass %
[0154] Polyvinyl alcohol aqueous solution (Bw-4): 15.00 mass %
[0155] Blocked isocyanate crosslinking agent (C-1): 0.67 mass %
[0156] Particles (silica sol with an average particle diameter of
100 nm; solids content: 40 mass %): 1.25 mass %
[0157] Catalyst (organic tin compound; solids content: 14 mass %):
0.3 mass %
[0158] Surfactant (silicon-based; solids content: 10 mass %): 0.5
mass %
[0159] As the starting materials for the protective film
intermediate layer, 90 parts by mass of particle-free PET (X) resin
pellets and 10 parts by mass of ultraviolet absorber-containing PET
(Y) resin pellets were vacuum-dried (1 Torr) at 135.degree. C. for
6 hours, and then supplied to an extruder 2 (for the intermediate
layer II). Further, PET (X) was dried by a standard method,
supplied to extruders 1 (each for the outer layer I and the outer
layer III), and melted at 285.degree. C. These two polymers were
each filtered through a filtering medium of a stainless steel
sintered body (nominal filtering accuracy: 10 .mu.m-particle 95%
cut), laminated by two types of three-layered junction blocks, and
extruded through a die into a sheet-like shape. The resulting sheet
was cooled and solidified by winding the sheet around a casting
drum having a surface temperature of 30.degree. C. by an
electrostatic casting method, thereby forming an unstretched film.
At this time, the discharge of each extruder was adjusted so that
the thickness ratio of layer I, layer II, and layer III was
10:80:10.
[0160] Then, the above-prepared coating solution was applied to
both sides of the unstretched PET film by reverse-roll coating so
that the amount of dried coating was 0.12 g/m.sup.2, followed by
drying at 80.degree. C. for 20 seconds.
[0161] The unstretched film, on which a coating layer had been
formed, was guided to a tenter stretching machine. While holding
the edges of the film with clips, the film was guided to a hot-air
zone with a temperature of 125.degree. C., and stretched 4.0 times
in the width direction. Subsequently, while maintaining the width
of the film stretched in the width direction, the film was treated
at a temperature of 225.degree. C. for 30 seconds, and further
subjected to 3% relaxation treatment in the width direction. Thus,
a uniaxially oriented PET film having a thickness of about 50 .mu.m
was obtained.
Example 2
[0162] A uniaxially oriented PET film having a thickness of about
100 .mu.m was obtained in the same manner as in Example 1, except
that the coating solution was applied to one side of the
unstretched PET film, and that the thickness of the unstretched
film was changed.
Example 3
[0163] A biaxially oriented PET film having a thickness of about 50
.mu.m was obtained in the same manner as in Example 1, except that
the unstretched film was heated to 105.degree. C. using heated
rolls and an infrared heater, and that the film was then stretched
1.5 times in the running direction by rolls having different
peripheral speeds, and then stretched 4.0 times in the width
direction.
Example 4
[0164] A biaxially oriented PET film having a thickness of about 50
.mu.m was obtained in the same manner as in Example 3, except that
the unstretched film was stretched 2.0 times in the running
direction and 4.0 times in the width direction.
Example 5
[0165] A biaxially oriented PET film having a thickness of about 75
.mu.m was obtained in the same manner as in Example 3, except that
the unstretched film was stretched 3.3 times in the running
direction and 4.0 times in the width direction.
Example 6
[0166] A uniaxially oriented PET film having a thickness of about
50 .mu.m was obtained in the same manner as in Example 1, except
that the ultraviolet absorber-containing PET resin (Y) was not used
in the intermediate layer. The obtained film did not have rainbow
unevenness, but had high light transmittance at 380 nm, which may
degrade the optical functional dye.
Example 7
[0167] A uniaxially oriented PET film having a thickness of about
100 .mu.m was obtained in the same manner as in Example 3, except
that the unstretched film was stretched 4.0 times in the running
direction and 1.0 times in the width direction. The obtained film
had a retardation of 3,000 nm or more. Although the visibility was
excellent, the mechanical strength was slightly inferior.
Example 8
[0168] A biaxially oriented PET film having a thickness of about
250 .mu.m was obtained in the same manner as in Example 3, except
that the unstretched film was stretched 3.5 times in the running
direction and 3.7 times in the width direction. The obtained film
had a retardation of 4,500 nm or more; however, the Re/Rth ratio
was less than 0.2, and thus, very slight rainbow unevenness was
observed when the film was viewed from an oblique direction.
Example 9
[0169] A uniaxially oriented PET film having a thickness of about
75 .mu.m was obtained in the same manner as in Example 1, except
that the unstretched film was stretched 1.0 times in the running
direction and 3.5 times in the width direction.
Example 10
[0170] A uniaxially oriented PET film having a thickness of about
275 .mu.m was obtained in the same manner as in Example 1, except
that the thickness of the unstretched film was changed.
Example 11
[0171] A uniaxially oriented PET film was obtained in the same
manner as in Example 1, except that the polyester aqueous
dispersion was changed to the aqueous dispersion (Aw-2) of
polyester resin having an acid value of 4 KOHmg/g.
Example 12
[0172] A uniaxially oriented PET film was obtained in the same
manner as in Example 1, except that the polyester aqueous
dispersion was changed to the aqueous dispersion (Aw-3) of
polyester resin having an acid value of 6 KOHmg/g.
Example 13
[0173] A uniaxially oriented PET film was obtained in the same
manner as in Example 1, except that the polyvinyl alcohol aqueous
solution was changed to the aqueous solution (Bw-3) of polyvinyl
alcohol having a degree of saponification of 79 mol %.
Example 14
[0174] A uniaxially oriented PET film was obtained in the same
manner as in Example 1, except that the polyvinyl alcohol aqueous
solution was changed to the aqueous solution (Bw-2) of polyvinyl
alcohol having a degree of saponification of 83 mol %.
Example 15
[0175] A uniaxially oriented PET film was obtained in the same
manner as in Example 1, except that the following coating
components were mixed, and that the mass ratio of the polyester
resin (A) to the polyvinyl alcohol resin (B) was changed to
60/40.
[0176] Water: 37.28 mass %
[0177] Isopropanol: 30.00 mass %
[0178] Polyester aqueous dispersion (Aw-1): 10.00 mass %
[0179] Polyvinyl alcohol aqueous solution (Bw-4): 20.00 mass %
[0180] Blocked isocyanate crosslinking agent (C-1): 0.67 mass %
[0181] Particles (silica sol with an average particle diameter of
100 nm; solids content: 40 mass %): 1.25 mass %
[0182] Catalyst (organic tin compound: solids content: 14 mass %):
0.3 mass %
[0183] Surfactant (silicon-based; solids content: 10 mass %): 0.5
mass %
Example 16
[0184] A uniaxially oriented PET film was obtained in the same
manner as in Example 1, except that the following coating
components were mixed, and that the mass ratio of the polyester
resin (A) to the polyvinyl alcohol resin (B) was changed to
80/20.
[0185] Water: 43.95 mass %
[0186] Isopropanol: 30.00 mass %
[0187] Polyester aqueous dispersion (Aw-1): 13.33 mass %
[0188] Polyvinyl alcohol aqueous solution (Bw-4): 10.00 mass %
[0189] Blocked isocyanate crosslinking agent (C-1): 0.67 mass %
[0190] Particles (silica sol with an average particle diameter of
100 nm; solids content: 40 mass %): 1.25 mass %
[0191] Catalyst (organic tin compound; solids content: 14 mass %):
0.3 mass %
[0192] Surfactant (silicon-based; solids content: 10 mass %): 0.5
mass %
Example 17
[0193] A uniaxially oriented PET film was obtained in the same
manner as in Example 1, except that the following coating
components were mixed, and that the mass ratio of the polyester
resin (A) to the polyvinyl alcohol resin (B) was changed to
50/50.
[0194] Water: 33.95 mass %
[0195] Isopropanol: 30.00 mass %
[0196] Polyester aqueous dispersion (Aw-1): 8.33 mass %
[0197] Polyvinyl alcohol aqueous solution (Bw-4): 25.00 mass %
[0198] Blocked isocyanate crosslinking agent (C-1): 0.67 mass %
[0199] Particles (silica sol with an average particle diameter of
100 nm; solids content: 40 mass %): 1.25 mass %
[0200] Catalyst (organic tin compound; solids content: 14 mass %):
0.3 mass %
[0201] Surfactant (silicon-based; solids content: 10 mass %): 0.5
mass %
Example 18
[0202] A uniaxially oriented PET film was obtained in the same
manner as in Example 1, except that the formulation of the coating
solution was changed as follows.
[0203] Water: 40.87 mass %
[0204] Isopropanol: 30.00 mass %
[0205] Polyester aqueous dispersion (Aw-1): 11.67 mass %
[0206] Polyvinyl alcohol aqueous solution (Bw-4): 15.00 mass %
[0207] Melamine crosslinking agent (C-2) (Nikalac MX-042, produced
by Sanwa Chemical Co., Ltd.; solids content: 70%); 0.71 mass %
[0208] Particles (silica sol with an average particle diameter of
100 nm; solids content: 40 mass %): 1.25 mass %
[0209] Surfactant (silicon-based; solids content: 10 mass %): 0.5
mass %
Example 19
[0210] A uniaxially oriented PET film was obtained in the same
manner as in Example 1, except that the polyvinyl alcohol aqueous
solution was changed to the aqueous solution (Bw-5) of polyvinyl
alcohol having a degree of saponification of 70 mol %.
Example 20
[0211] A uniaxially oriented PET film was obtained in the same
manner as in Example 1, except that the polyvinyl alcohol aqueous
solution was changed to the aqueous solution (Bw-6) of polyvinyl
alcohol having a degree of saponification of 67 mol %.
Example 21
[0212] A uniaxially oriented PET film was obtained in the same
manner as in Example 1, except that the formulation of the coating
solution was changed as follows.
[0213] Water: 40.33 mass %
[0214] Isopropanol: 30.00 mass %
[0215] Polyester aqueous dispersion (Aw-1): 11.67 mass %
[0216] Polyvinyl alcohol aqueous solution (Bw-2): 15.00 mass %
[0217] Oxazoline crosslinking agent (C-3) (Epocros WS-500, produced
by Nippon Shokubai Co., Ltd.; solids content: 40 mass %): 1.25 mass
%
[0218] Particles (silica sol with an average particle diameter of
100 nm; solids content: 40 mass %): 1.25 mass %
[0219] Surfactant (silicon-based; solids content: 10 mass %): 0.5
mass %
Example 22
[0220] A uniaxially oriented PET film was obtained in the same
manner as in Example 1, except that the polyvinyl alcohol aqueous
solution was changed to the aqueous solution (Bw-1) of polyvinyl
alcohol having a degree of saponification of 88 mol %.
Example 23
[0221] A uniaxially oriented PET film was obtained in the same
manner as in Example 1, except that the following coating
components were mixed without mixing a crosslinking agent.
[0222] Water: 41.58 mass %
[0223] Isopropanol: 30.00 mass %
[0224] Polyester aqueous dispersion (Aw-1): 11.67 mass %
[0225] Polyvinyl alcohol aqueous solution (Bw-4): 15.00 mass %
[0226] Particles (silica sol with an average particle diameter of
100 nm; solids content: 40 mass %): 1.25 mass %
[0227] Surfactant (silicon-based; solids content: 10 mass %): 0.5
mass %
Example 24
[0228] An antiglare layer was provided on the surface of the
uniaxially oriented polyester film of Example 2 opposite to the
surface having a coating layer. Similar to Example 2, no rainbow
unevenness was observed from any direction; thus, an excellent
result was obtained.
Comparative Example 1
[0229] A biaxially oriented PET film having a thickness of about 38
.mu.m was obtained in the same manner as in Example 3, except that
the unstretched film was stretched 3.6 times in the running
direction and 4.0 times in the width direction. The obtained film
had a low retardation, and rainbow unevenness was observed when the
film was viewed from an oblique direction.
Comparative Example 2
[0230] A uniaxially oriented PET film having a thickness of about
10 .mu.m was obtained in the same manner as in Example 1, except
that the thickness of the unstretched film was changed. The
obtained film was very easy to tear and had no body. Therefore,
this film could not be used as the protective film. Moreover,
retardation was low, and rainbow unevenness was observed.
Comparative Example 3
[0231] A uniaxially oriented PET film was obtained in the same
manner as in Example 1, except that the following coating
components were mixed, and that the mass ratio of the polyester
resin (A) to the polyvinyl alcohol resin (B) was changed to
100/0.
[0232] Water: 50.62 mass %
[0233] Isopropanol: 30.00 mass %
[0234] Polyester aqueous dispersion (Aw-1): 16.66 mass %
[0235] Blocked isocyanate crosslinking agent (C-1): 0.67 mass %
[0236] Particles (silica sol with an average particle diameter of
100 nm; solids content: 40 mass %): 1.25 mass %
[0237] Catalyst (organic tin compound; solids content: 14 mass %):
0.3 mass %
[0238] Surfactant (silicon-based; solids content: 10 mass %): 0.5
mass %
Comparative Example 4
[0239] A uniaxially oriented PET film was obtained in the same
manner as in Example 1, except that the following coating
components were mixed, and that the mass ratio of the polyester
resin (A) to the polyvinyl alcohol resin (B) was changed to
0/100.
[0240] Water: 17.28 mass %
[0241] Isopropanol: 30.00 mass %
[0242] Polyvinyl alcohol aqueous solution (Bw-4): 50.00 mass %
[0243] Blocked isocyanate crosslinking agent (C-1): 0.67 mass %
[0244] Particles (silica sol with an average particle diameter of
100 nm; solids content: 40 mass %): 1.25 mass %
[0245] Catalyst (organic tin compound; solids content: 14 mass %):
0.3 mass %
[0246] Surfactant (silicon-based; solids content: 10 mass %): 0.5
mass %
Comparative Example 5
[0247] The same procedure as in Example 1 was carried out, except
that cold-cathode tubes were used as the light source of the liquid
crystal display device.
TABLE-US-00003 TABLE 3 Running- Width- Observation Thickness
direction direction Re Rth Re/Rth of rainbow Tear (.mu.m) stretch
ratio stretch ratio Nx Ny Nz (nm) (nm) ratio unevenness strength
Ex. 1 50 1.0 4.0 1.593 1.697 1.513 5177 6602 0.784 ++ + Ex. 2 100
1.0 4.0 1.594 1.696 1.513 10200 13233 0.771 ++ + Ex. 3 50 1.5 4.0
1.608 1.686 1.508 3915 6965 0.562 + + Ex. 4 50 2.0 4.0 1.617 1.681
1.502 3215 7341 0.438 + + Ex. 5 75 3.3 4.0 1.640 1.688 1.498 3570
12480 0.286 + + Ex. 6 50 1.0 4.0 1.593 1.697 1.513 5177 6602 0.784
++ + Ex. 7 100 4.0 1.0 1.735 1.570 1.520 16500 13250 1.245 ++ - Ex.
8 250 3.5 3.7 1.660 1.687 1.522 6750 37875 0.178 + + Ex. 9 75 1.0
3.5 1.580 1.678 1.525 7350 7800 0.942 ++ + Ex. 10 275 1.0 4.0 1.593
1.697 1.513 28476 36314 0.784 ++ + Ex. 11 50 1.0 4.0 1.593 1.697
1.513 5177 6602 0.784 ++ + Ex. 12 50 1.0 4.0 1.593 1.697 1.513 5177
6602 0.784 ++ + Ex. 13 50 1.0 4.0 1.593 1.697 1.513 5177 6602 0.784
++ + Ex. 14 50 1.0 4.0 1.593 1.697 1.513 5177 6602 0.784 ++ + Ex.
15 50 1.0 4.0 1.593 1.697 1.513 5177 6602 0.784 ++ + Ex. 16 50 1.0
4.0 1.593 1.697 1.513 5177 6602 0.784 ++ + Ex. 17 50 1.0 4.0 1.593
1.697 1.513 5177 6602 0.784 ++ + Ex. 18 50 1.0 4.0 1.593 1.697
1.513 5177 6602 0.784 ++ + Ex. 19 50 1.0 4.0 1.593 1.697 1.513 5177
6602 0.784 ++ + Ex. 20 50 1.0 4.0 1.593 1.697 1.513 5177 6602 0.784
++ + Ex. 21 50 1.0 4.0 1.593 1.697 1.513 5177 6602 0.784 ++ + Ex.
22 50 1.0 4.0 1.593 1.697 1.513 5177 6602 0.784 ++ + Ex. 23 50 1.0
4.0 1.593 1.697 1.513 5177 6602 0.784 ++ + Ex. 24 100 1.0 4.0 1.594
1.696 1.513 10200 13233 0.771 ++ + Comp. 38 3.6 4.0 1.649 1.680
1.497 1178 6365 0.185 - + Ex. 1 Comp. 10 1.0 4.0 1.591 1.698 1.513
1070 1318 0.812 - - Ex. 2 Comp. 50 1.0 4.0 1.593 1.697 1.513 5177
6602 0.784 ++ + Ex. 3 Comp. 50 1.0 4.0 1.593 1.697 1.513 5177 6602
0.784 ++ + Ex. 4 Comp. 50 1.0 4.0 1.593 1.697 1.513 5177 6602 0.784
- + Ex. 5 Polyvinyl alcohol resin (B) 380-nm light Polyester resin
(A) Saponification Cross- PVA adhesion transmittance Acid value
degree linking 1 5 10 (%) Type (KOHmg/g) Type (mol %) A/B agent
peeling peeling peeling Ex. 1 8.5 A-1 2 B-4 74 70/30 C-1 100 100
100 Ex. 2 1.0 A-1 2 B-4 74 70/30 C-1 100 100 100 Ex. 3 8.5 A-1 2
B-4 74 70/30 C-1 100 100 100 Ex. 4 8.5 A-1 2 B-4 74 70/30 C-1 100
100 100 Ex. 5 2.5 A-1 2 B-4 74 70/30 C-1 100 100 100 Ex. 6 79.0 A-1
2 B-4 74 70/30 C-1 100 100 100 Ex. 7 1.0 A-1 2 B-4 74 70/30 C-1 100
100 100 Ex. 8 0.4 A-1 2 B-4 74 70/30 C-1 100 100 100 Ex. 9 2.5 A-1
2 B-4 74 70/30 C-1 100 100 100 Ex. 10 0.3 A-1 2 B-4 74 70/30 C-1
100 100 100 Ex. 11 8.5 A-2 4 B-4 74 70/30 C-1 100 99 97 Ex. 12 8.5
A-3 6 B-4 74 70/30 C-1 100 99 98 Ex. 13 8.5 A-1 2 B-3 79 70/30 C-1
100 100 99 Ex. 14 8.5 A-1 2 B-2 83 70/30 C-1 100 98 91 Ex. 15 8.5
A-1 2 B-4 74 60/40 C-1 100 100 96 Ex. 16 8.5 A-1 2 B-4 74 80/20 C-1
100 100 100 Ex. 17 8.5 A-1 2 B-4 74 50/50 C-1 100 100 94 Ex. 18 8.5
A-1 2 B-3 79 70/30 C-2 100 99 93 Ex. 19 8.5 A-1 2 B-5 70 70/30 C-1
100 100 99 Ex. 20 8.5 A-1 2 B-6 67 70/30 C-1 100 100 98 Ex. 21 8.5
A-1 2 B-2 83 70/30 C-3 93 84 53 Ex. 22 8.5 A-1 2 B-1 88 70/30 C-1
89 69 41 Ex. 23 8.5 A-1 2 B-4 74 70/30 -- 87 22 4 Ex. 24 1.0 A-1 2
B-4 74 70/30 C-1 100 100 100 Comp. 15.0 A-1 2 B-4 74 70/30 C-1 100
100 100 Ex. 1 Comp. 56.0 A-1 2 B-4 74 70/30 C-1 100 100 100 Ex. 2
Comp. 8.5 A-1 2 -- -- 100/0 C-1 0 0 0 Ex. 3 Comp. 8.5 -- -- B-4 74
0/100 C-1 0 0 0 Ex. 4 Comp. 8.5 A-1 2 B-4 74 70/30 C-1 100 100 100
Ex. 5
INDUSTRIAL APPLICABILITY
[0248] The liquid crystal display device, polarizer, and protective
film of the present invention are very highly industrially
applicable, because the use of them results in an excellent
adhesion and contributes to thinner LCDs and lower cost, without
reduction in visibility caused by rainbow unevenness.
* * * * *