U.S. patent application number 10/121259 was filed with the patent office on 2003-04-17 for thin film forming method, optical film, polarizing film and image display method.
This patent application is currently assigned to Konica Corporation. Invention is credited to Fukuda, Kazuhiro, Murakami, Takashi.
Application Number | 20030072891 10/121259 |
Document ID | / |
Family ID | 18976485 |
Filed Date | 2003-04-17 |
United States Patent
Application |
20030072891 |
Kind Code |
A1 |
Murakami, Takashi ; et
al. |
April 17, 2003 |
Thin film forming method, optical film, polarizing film and image
display method
Abstract
A method of forming a layer or layers are disclosed which
comprises the steps of transporting a substrate having a first
surface and a second surface on the side opposite the first surface
to a gap formed between a first electrode and a second electrode
opposing each other, the second surface having a coefficient of
kinetic friction of not more than 0.9; and subjecting the first
surface of the substrate to plasma discharge treatment to form the
layer at atmospheric pressure or at approximately atmospheric
pressure while supplying a reactive gas to the gap.
Inventors: |
Murakami, Takashi; (Tokyo,
JP) ; Fukuda, Kazuhiro; (Tokyo, JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN & CHICK, PC
767 THIRD AVENUE
25TH FLOOR
NEW YORK
NY
10017-2023
US
|
Assignee: |
Konica Corporation
26-2 Nishishinjuku 1-chome, Shinjuku-ku
Tokyo
JP
163
|
Family ID: |
18976485 |
Appl. No.: |
10/121259 |
Filed: |
April 12, 2002 |
Current U.S.
Class: |
427/569 ;
427/171; 427/255.28 |
Current CPC
Class: |
Y02T 50/60 20130101;
B05D 1/62 20130101; C23C 16/545 20130101; C23C 16/509 20130101 |
Class at
Publication: |
427/569 ;
427/255.28; 427/171 |
International
Class: |
C23C 016/00; B05D
003/12 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 25, 2001 |
JP |
127649/2001 |
Claims
What is claimed is:
1. A method of forming a layer or layers, the method comprising the
steps of: (a) transporting a substrate having a first surface and a
second surface on the side opposite the first surface to a gap
formed between a first electrode and a second electrode opposing
each other, the second surface having a coefficient of kinetic
friction of not more than 0.9; and (b) subjecting the first surface
of the substrate to plasma discharge treatment to form the layer at
atmospheric pressure or at approximately atmospheric pressure while
supplying a reactive gas to the gap.
2. A method of forming a layer or layers, the method comprising the
step of: subjecting the surface of a substrate, the substrate
having a thickness of from 10 to 60 .mu.m and having a tensile
strength of not less than 1.4.times.10.sup.2 N/mm.sup.2, to plasma
discharge treatment to form the layer at atmospheric pressure or at
approximately atmospheric pressure at a gap formed between a first
electrode and a second electrode opposing each other while
supplying a reaction gas to the gap.
3. A method of forming a first layer, the method comprising the
step of: subjecting the surface of a substrate or a second layer
provided on a substrate to plasma discharge treatment to form the
first layer at atmospheric pressure or at approximately atmospheric
pressure at a gap formed between a first electrode and a second
electrode opposing each other while supplying a reaction gas to the
gap, wherein the substrate has a moisture content of not more than
4% at 23.degree. C. and 80% RH.
4. A method of forming a first layer, the method comprising the
step of: subjecting the surface of a substrate or a second layer
provided on a substrate to plasma discharge treatment to form the
first layer at atmospheric pressure or at approximately atmospheric
pressure at a gap formed between a first electrode and a second
electrode opposing each other while supplying a reaction gas to the
gap, wherein the substrate has been stretched in the transverse
direction.
5. The method of claim 3 or 4, wherein the second layer provided on
the substrate is a hardened resin layer in which a monomer or an
oligomer each having an ethylenically unsaturated double bond has
been polymerized and hardened.
6. The method of any one of claims 1 through 5, wherein the
substrate is a cellulose ester film.
7. The method of claim 6, wherein the cellulose ester film
comprises a cellulose ester having a total acyl substitution degree
of from 2.55 to 2.95.
8. An optical film having a layer or layers formed according to the
method of claims 1 through 7.
9. A polarizing plate employing the optical film of claim 8 as the
protective film.
10. An image display employing the optical film of claim 8.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method of forming a layer
or layers on the surface of a substrate and an optical film
comprising the layer, and particularly to the method comprising
subjecting the surface of the substrate to plasma discharge
processing at atmospheric pressure or at approximately atmospheric
pressure to form the layer and an optical film having the layer
formed thereby. Further, the present invention relates to an
optical film used in a crystal liquid display, various displaying
devices, an organic EL display, a plasma display, and the like, a
polarizing plate employing the optical film, and an image display
employing the optical film or the polarizing plate.
BACKGROUND OF THE INVENTION
[0002] There have been proposed various techniques for
anti-reflection to increase transmittance and contrast or to
minimize undesired reflected images in a field such as an optical
lens, CRT, a liquid crystal displaying device of a computer or a
word processor, and the like. As technique for anti-reflection, a
technique is known which adjusts a refractive index and optical
thickness of a multilayer as an optical interference layer to an
appropriate value and reduces light reflection at the interface
between the multilayer layer and atmospheric air. Such a multilayer
is ordinarily composed of a layer of TiO.sub.2, ZrO.sub.2,
Ta.sub.2O.sub.5, and the like as a high refractive index layer, and
a layer of SiO.sub.2, MgF.sub.2, and the like as a low refractive
index layer, and these layers are layered according to a dry
coating method employing vacuum processing such as a spattering
method, a vacuum evaporation method or an ion plating method.
However, the vacuum processing, when materials to be processed are
of large size, requires a large-scale vacuum processing apparatus,
which is too expensive and time-consuming for evacuation, resulting
in lowering of productivity or incapability of continuous
production.
[0003] As another method for preparing an anti-reflection layer,
there is a method in which a metal alkoxide such as titanium
alkoxide or silicon alkoxide is coated on a substrate, dried and
heated to form a metal oxide layer on the substrate. However, this
method requires too high temperature such as 300.degree. C. as the
heating temperature, and may result in damage of the substrate. In
contrast, the method employing a relatively low temperature such as
100.degree. C. as the heating temperature, which is disclosed in,
for example, Japanese Patent O.P.I. Publication No 8-75904, is
time-consuming for the layer preparation. Both methods have
problem.
[0004] In order to solve the above problem regarding preparation
time and temperature, there is a proposal described in Japanese
Patent O.P.I. Publication No. 9-21902, in which an alkoxide of Ti,
Zr, Ta, or In and a compound having two or more acryloyl,
methacryloyl, allyl or vinyl groups in the molecule are used in
combination at a low temperature to prepare a high refractive index
material. There is disclosed in Japanese Patent O.P.I. Publication
No. 7-209503 an optical film coating composition comprising as a
main component a copolymer of an organosilicon compound having both
a polymerizable group such as vinyl group, an allyl group, an
acryloyl group or a methacryloyl group and a hydrolyzable group
such as an alkoxy group, with a polymerizable, unsaturated monomer,
which provides a layer with a binder resin component and an
inorganic component uniformly mixed in a molecular level. There is
further the description in this reference that the composition as
described above is coated and polymerized by being heated at
100.degree. C. for a long time or irradiated with ionizing
radiation to form a film.
[0005] Further, there is a technique disclosed in Japanese Patent
O.P.I. Publication Nos. 8-295846 and 9-220791, in which a
composition comprising active organometallic compounds and metal
oxides or silane compounds is hardened by heat or ionizing
radiation to prepare an anti-reflection layer. Further, there is
another technique disclosed in Japanese Patent O.P.I. Publication
Nos. 5-270864, 5-279598, 6-11602, 8-122501, 8-297201, 9-21902 and
9-25350, in which a composition comprising no active organometallic
compounds is hardened employing electron beam or ultraviolet ray as
ionizing radiation ray to prepare an anti-reflection layer.
However, there are the problems in these techniques that a part of
the organic components remains unreacted, and the remained
unreacted components vary with time. Therefore, the resulting
anti-reflection layer causes change in the refractive index, and
gradually loses an anti-reflection property.
[0006] As a method for solving the problems as described above, in
that use of a vacuum apparatus results in lowering of productivity
or an organic substance remains in the method in which a coated
metal oxide is hardened by application of energy, there is a method
as proposed in Japanese Patent O.P.I. Publication Nos. 11-133205,
2000-185362, 11-61406, 2000-147209, and 2000-121804, in which a
film having an antireflection property is formed by plasma
discharge processing under atmospheric pressure or under
approximately atmospheric pressure.
[0007] However, although an anti-reflection film can be formed in
only a small area according to the method proposed above, it is
difficult to form a uniform anti-reflection film on a wide and long
substrate, and it is extremely difficult to continuously form an
anti-reflection film with a constant refractive index and a
constant optical layer thickness.
SUMMARY OF THE INVENTION
[0008] An object of the invention is to provide a method of
manufacturing a uniform thin multiple layer on a substrate
continuously and at reduced cost and an optical film having on the
surface the layer formed according to the method.
[0009] Another object of the invention is to provide a polarizing
plate or an image display employing the optical film.
BRIEF EXPLANATION OF THE DRAWINGS
[0010] FIG. 1 shows a schematic drawing of one embodiment of a
plasma discharge apparatus used in the layer forming method of the
present invention.
[0011] FIG. 2 shows a schematic drawing of one embodiment of a
plasma discharge apparatus comprising a rotating electrode and a
fixed electrode useful for the layer forming method of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The above objects of the invention can be attained by the
following constitutions:
[0013] 1. A method of forming a layer or layers, the method
comprising the steps of (a) transporting a substrate having a first
surface and a second surface on the side opposite the first surface
to a gap formed between a first electrode and a second electrode
opposing each other, the second surface having a coefficient of
kinetic friction of not more than 0.9; and (b) subjecting the first
surface of the substrate to plasma discharge treatment to form the
layer at atmospheric pressure or at approximately atmospheric
pressure while supplying a reactive gas to the gap.
[0014] 2. A method of forming a layer or layers, the method
comprising the step of subjecting the surface of a substrate, the
substrate having a thickness of from 10 to 60 .mu.m and having a
tensile strength of not less than 1.4.times.10.sup.2 N/mm.sup.2, to
plasma discharge treatment to form the layer at atmospheric
pressure or at approximately atmospheric pressure at a gap formed
between a first electrode and a second electrode opposing each
other while supplying a reaction gas to the gap.
[0015] 3. A method of forming a first layer, the method comprising
the step of subjecting the surface of a substrate or a second layer
provided on a substrate to plasma discharge treatment to form the
first layer at atmospheric pressure or at approximately atmospheric
pressure at a gap formed between a first electrode and a second
electrode opposing each other while supplying a reaction gas to the
gap, wherein the substrate has a moisture content of not more than
4% at 23.degree. C. and 80% RH.
[0016] 4. A method of forming a first layer, the method comprising
the step of subjecting the surface of a substrate or a second layer
provided on a substrate to plasma discharge treatment to form the
first layer at atmospheric pressure or at approximately atmospheric
pressure at a gap formed between a first electrode and a second
electrode opposing each other while supplying a reaction gas to the
gap, wherein the substrate has been stretched in the transverse
direction.
[0017] 5. The method of item 3 or 4 above, wherein the second layer
provided on the substrate is a hardened resin layer in which a
monomer or an oligomer each having an ethylenically unsaturated
double bond has been polymerized and hardened.
[0018] 6. The method of any one of items 1 through 5 above, wherein
the substrate is a cellulose ester film.
[0019] 7. The method of item 6 above, wherein the cellulose ester
film comprises a cellulose ester having a total acyl substitution
degree of from 2.55 to 2.95.
[0020] 8. An optical film having a layer or layers formed according
to the method of any one of items 1 through 7.
[0021] 9. A polarizing plate employing the optical film of item 8
as the protective film.
[0022] 10. An image display employing the optical film of item 8
above.
[0023] The present invention will be explained below.
[0024] The present invention provides a method in which a layer or
layers with reduced layer thickness is formed on a substrate, the
method comprising the step of subjecting the surface of the
substrate to plasma discharge treatment at atmospheric pressure or
at approximately atmospheric pressure while supplying a reactive
gas to a gap formed between a first electrode and a second
electrode opposing each other, and provides an optical film with a
layer or layers formed according to the method.
[0025] The method according to item 1 above is a method in which a
layer or layers are formed on a substrate, the method comprising
the steps of (a) transporting a substrate having a first surface
and a second surface on the side opposite the first surface to a
gap formed between a first electrode and a second electrode
opposing each other, the second surface having a coefficient of
kinetic friction of not more than 0.9; and subjecting the first
surface of the substrate to plasma discharge treatment to form the
layer at atmospheric pressure or at approximately atmospheric
pressure while supplying a reactive gas to the gap. Hereinafter,
the second surface of the substrate opposite the first surface to
be subjected to plasma discharge treatment is referred to also as
the rear surface of the substrate. The plasma discharge treatment
described above is called an ordinary pressure plasma method or an
atmospheric pressure plasma method (hereinafter, the above plasma
discharge treatment at atmospheric pressure or approximately at
atmospheric pressure is also abbreviated as simply the plasma
discharge treatment). The method described above is a method in
which a layer or layers are formed on a substrate by subjecting the
surface of the substrate to plasma generated by electric discharge
at atmospheric pressure or approximately at atmospheric pressure at
a gap formed between opposing electrodes while supplying a reaction
gas to the gap. When the layer or layers are continuously formed on
a long substrate, this method, although the layer can be formed at
high speed, has problem in that unevenness of the layer thickness
is likely to be produced. An extensive study has been made in order
to solve this problem, and it has been found that unevenness of the
layer thickness is markedly minimized by controlling slidability of
the rear surface of the substrate opposite the surface on which the
layer is formed. That is, the present inventors have found that in
order to form a uniform layer on a substrate according to plasma
discharge treatment, it is preferable to form a layer or layers on
a substrate, by subjecting the first surface of the substrate to
plasma discharge treatment while transporting a gap between
opposing electrodes so that the second surface contacts the
electrode on one side, the second surface of the substrate being
opposite the layer to be formed and having a coefficient of dynamic
friction of not more than 0.9. The coefficient of dynamic friction
exceeding 0.9 often lowers smooth transportability, resulting in
unevenness of layer thickness. In the invention, the coefficient of
dynamic friction of not more than 0.9 provides stable
transportability whereby a layer or layers with a uniform layer
thickness can be obtained. The coefficient of dynamic friction is
preferably from 0.2 to 0.6 in forming a more uniform layer. The
substrate with a surface having a coefficient of dynamic friction
exceeding 0.9 is likely to zigzag on the electrode in contact with
the surface, resulting in undesired results that the substrate
undulates or wrinkles to cause unevenness.
[0026] The coefficient of dynamic friction herein referred to can
be obtained from measurements with respect to an interface formed
between two of the rear surface of the substrate contacting each
other. In order to obtain a desired coefficient of dynamic
friction, it is preferred that the substrate itself contains
particles or a particle-containing layer is provided on a substrate
to form a concavo-convex surface. The particulars will be explained
later.
[0027] Unevenness (irregularities) such as wrinkles or folds,
which, when the first surface of the substrate is subjected to
plasma discharge treatment particularly with the rear surface (of
the substrate) contacting a rotating electrode, have hitherto
occurred at a discharge section, are minimized by providing
particles on the rear surface of the substrate. Further, the
substrate with the rear surface having a coefficient of dynamic
friction falling within the claimed range restrains zigzag
transportation of the substrate on the rotating electrode, and
therefore, can continuously form a layer or layers on the substrate
over a long time, providing an optical film with high quality.
[0028] The method according to item 2 above is a method in which a
uniform layer can be formed on even a substrate with a small
thickness. The substrate with a small thickness had the problem
that wrinkles were likely to occur at plasma discharge treatment,
but it has been proved that a substrate with a thickness of from 10
to 60 .mu.m and having a tensile strength of not less than
1.4.times.10.sup.2 N/mm.sup.2, overcomes this problem. The tensile
strength of less than 1.4.times.10.sup.2 N/mm.sup.2 is undesirable
in that unevenness is likely to occur. Tensile strength of the
substrate in the invention is determined according to a method as
defined in JIS K7127-1989. In the invention, the tensile strength
of the substrate is measured employing a tensile tester TENSILON
RTA-100 produced by Olyentech Co., Ltd., provided that a substrate
cut to the same size as the specimen No. 1 as described in this JIS
is pulled at a tensile speed of 100 mm/min. In the invention, the
tensile strength of the substrate having a thickness of from 10 to
60 .mu.m is preferably not less than 1.4.times.10.sup.2 N/mm.sup.2,
more preferably not less than 1.45.times.10.sup.2 N/mm.sup.2, and
most preferably not less than 1.5.times.10.sup.2 N/mm.sup.2. It is
preferred that the tensile strength in the longitudinal
(mechanical) direction and that in the transverse direction of the
substrate both are preferably not less than 1.4.times.10.sup.2
N/mm.sup.2, and it is more preferred that in addition to the
aforementioned, the both tensile strengths of the substrate are
substantially the same. Typically, the tensile strength in the
transverse direction is within the range of preferably .+-.30%,
more preferably .+-.15%, and most preferably .+-.10%, of the
tensile strength in the longitudinal (mechanical) direction.
[0029] It is preferred that the substrate is brought into contact
with an electrode with a specific tension applied and subjected to
plasma discharge treatment to form a layer or layers on the
substrate, and use of the substrate having a tensile strength
falling within the range as claimed, even if the substrate is a
thin one, can form a uniform layer on the substrate surface,
providing an optical film with high quality.
[0030] The method according to item 3 above is a method comprising
the step of subjecting a substrate having a moisture content of not
more than 4% at 23.degree. C. and 80% RH to plasma discharge
treatment to form a layer or layers on the substrate surface. The
moisture content of the substrate is preferably 0.5 to 3%. The
present inventors have found that particularly when a cellulose
ester film having a moisture content of from 0.5 to 4% at
23.degree. C. and 80% RH is subjected to plasma discharge
treatment, a layer or layers with reduced unevenness of layer
thickness can be formed on the cellulose ester film surface. A
cellulose ester film ordinarily contains a small amount of
moisture. It is considered that when the moisture in a more than
necessary amount is released to a discharge section at plasma
discharge treatment, it plays any roll in causing unevenness of
layer thickness, although the reason is not clear. It has been
found that a substrate having a moisture content exceeding 4% at
23.degree. C. and 80% RH tends to produce unevenness of layer
thickness or increase haze, resulting in undesirable results. The
present invention can form a uniform layer with reduced unevenness
of layer thickness on a cellulose ester film having a moisture
content of from 0.5 to 4% at 23.degree. C. and 80% RH. The moisture
content of the cellulose ester film can be adjusted by varying the
total acyl substitution degree, kinds of an acyl group, kinds of
plasticizer contained in it or the content thereof.
[0031] Item 4 above comprises a method of subjecting a substrate,
for example, a cellulose ester film, which has been stretched in
the transverse direction, to plasma discharge treatment to form a
layer or layers with reduced unevenness of layer thickness on the
substrate surface. It has been found that a cellulose ester film
prepared according to a solution cast film manufacturing method is
contracted at a drying step, particularly in the transverse
direction, which is one of elements producing unevenness of layer
thickness at electric discharge treatment of the film. On the
contrary, it is considered that the cellulose ester film stretched
in the transverse direction can be brought into close contact with
an electrode due to its excellent flatness, and therefore,
treatment unevenness (unevenness of layer thickness) is difficult
to occur at plasma discharge treatment, resulting in formation of a
uniform layer. The cellulose ester film used in the optical film of
the invention is preferably a cellulose ester film stretched in the
transverse direction by a factor of not less than 1.03, and more
preferably a cellulose ester film stretched both in the transverse
direction by a factor of not less than 1.03, and in the mechanical
direction by a factor of not less than 1.03. Such a cellulose ester
film can provide an optical film having a layer or layers with
reduced unevenness of layer thickness.
[0032] Item 5 above comprises a method of providing, on a
substrate, a hardened resin layer formed by polymerizing a monomer
or an oligomer each having an ethylenically unsaturated double bond
as described later and hardened, and subjecting the resulting resin
layer to plasma discharge treatment to form a layer or layers with
reduced unevenness of layer thickness on the resin layer surface.
This method is especially effective for the substrate as recited in
item 3 or 4 above. The hardened resin layer is preferably hardened
by UV light irradiation.
[0033] As a method of forming a layer or layers with reduced
unevenness of layer thickness by plasma discharge treatment, the
methods of items 1 to 4 above are effective, but by a combination
thereof, an optical film having a more uniform layer can be
obtained (the method of item 8 above).
[0034] Next, the present invention will be explained in detail.
[0035] Examples of the substrate in the invention include a
cellulose ester film, a polyester film, a polycarbonate film, a
polystyrene film, a polyolefin film, a cellulose type film, and
other resin film. Examples of the cellulose ester film include
cellulose a diacetate film, a cellulose acetate butyrate film, a
cellulose acetate propionate film, a cellulose acetate phthalate
film, a cellulose triacetate film, and a cellulose nitrate film.
Examples of the polyester include polyethylene terephthalate,
polyethylene naphthalate, polybutylene naphthalate,
poly(1,4-dimethylenecyclohexylene) terephthalate, and a copolyester
comprising them as structural units. Examples of a polycarbonate
film include a bisphenol A polycarbonate film. Examples of a
polystyrene film include a syndiotactic polystyrene film. Examples
of a polyolefin film include a polyethylene film and a
polypropylene film. Examples of a polyvinyl alcohol type film
include a polyvinyl alcohol film and an ethylene vinyl alcohol
film. Examples of a cellulose type film include a cellophane film.
Examples of other resin film include a norbornene resin film, a
polymethylpentene film, a polyetherketone film, a polyimide film, a
polyethersulfone film, a polysulfone film, a polyetherketoneimide
film, a polyamide film, a fluorine-containing resin film, a nylon
film, a polymethyl methacrylate film, an acryl film, a polyarylate
film, and a polyvinylidene chloride film.
[0036] A film obtainable from an appropriate mixture of these film
materials can be used. For example, a film comprising commercially
available materials such as Zeonecks (produced by Nippon Zeon Co.,
Ltd.) or ARTON (produced by Nippon Gosei Gomu Co., Ltd.) can be
also used. The substrate suitable for the invention can be prepared
even from materials such as polycarbonate, polyacrylate,
polysulfone and polyethersulfone, each having a high specific
birefringence, by appropriately adjusting a solution casting
condition, a melt extrusion condition, or a stretching condition in
the transverse or mechanical direction. The substrate in the
invention is not specifically limited to those described above. The
substrate in the invention is preferably a cellulose ester film
(item 6 above).
[0037] The hardened resin layer may be a layer having various
functions, for example, an anti-glare layer or a clear hard coat
layer.
[0038] Of the films described above, the cellulose ester film is
especially preferably used as the substrate in the invention.
[0039] Next, cellulose ester, which is material of the cellulose
ester film especially preferably used as the substrate in the
invention, will be explained in detail.
[0040] The cellulose ester film in the invention is preferably a
film employing cellulose ester in which the hydrogens of the
hydroxyl groups of cellulose are substituted with 2.55 to 2.95 of
an acyl group, particularly an acyl group having a carbon atom
number of from 2 to 4. Examples of such a cellulose ester include
cellulose diacetate, cellulose triacetate, cellulose acetate
butyrate, and cellulose acetate propionate. Of these, cellulose
triacetate, cellulose acetate butyrate, and cellulose acetate
propionate are preferable. Of these preferable cellulose esters,
cellulose ester having an acetyl substitution degree of not less
than 1.6 is especially preferable. Raw materials for the cellulose
ester are not specifically limited, and include cotton lint, tree
pulp (derived from a coniferous tree or a broad-leaved tree) and
kenaf. These raw materials may be used in combination in an
arbitrary amount ratio. The cellulose ester is prepared by
esterifying cellulose raw materials with an acylating agent, for
example, an acid anhydride (acetic anhydride, propionic anhydride,
or butyric anhydride), in an organic acid such as acetic acid or an
organic solvent such as methylene chloride in the presence of a
protic catalyst such as sulfuric acid. A cellulose ester containing
different acid radicals can be prepared according to a method
described in Japanese Patent O.P.I. Publication No. 10-45804. The
acyl substitution degree of the cellulose ester can be measured
according to a method as defined in ASTM-817-96.
[0041] The number average molecular weight (Mn) of the cellulose
ester is preferably 70,000 to 250,000, in providing good mechanical
strength in a molded film, and an optimum dope viscosity, and more
preferably 80,000 to 15,000.
[0042] The cellulose ester film is manufactured according to a
method generally called a solution cast film manufacturing method
as described later. This method comprises the steps of casting a
dope (a cellulose ester solution) from a pressure die on a metal
support (hereinafter referred to also as simply a metal support)
for casting such as an endless metal belt support (for example, a
stainless steel belt) or a rotating metal drum support (for
example, a cast iron drum plated with chromium) to form a web (a
dope layer) on the metal support, peeling the web from the metal
support, and drying to manufacture a cellulose ester film.
[0043] The solvent used for preparing a cellulose ester dope is
preferably a solvent having an appropriate boiling point which is
capable of dissolving cellulose esters. Examples of the solvents
include methylene chloride, methyl acetate, ethyl acetate, amyl
acetate, acetone, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane,
cyclohexanone, ethyl formate, 2,2,2-trifluoroethanol,
2,2,3,3-tetrafluoro-1-propanol, 1,3-difluoro-2-propanol,
1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol,
1,1,1,3,3,3-hexafluoro-2-propanol,
2,2,3,3,3-pentafluoro-1-propanol, nitroethane,
1,3-dimethyl-2-imidazolidinone, and methyl actoacetate. Of these, a
halogenated organic compound such as methylene chloride, dioxolane
derivatives, methyl acetate, ethyl acetate and acetone are
preferred.
[0044] A peeling tension at which the web is peeled from the metal
support is preferably not more than 250 N/m, and a transporting
tension at which the web is transported is preferably not more than
300 N/m, more preferably not more than 250 N/m, and still more
preferably 100 to 20 N/m. The peeled web is preferably dried at the
drying step while being stretched in the transverse direction by
applying a tension in a tenter, in that an optical film with high
durability comprising a metal oxide layer can be obtained.
[0045] The stretching magnification of the web in a tenter is
preferably 1.01 to 1.5. The stretching is preferably carried out
both in the transverse direction of the film and in the
longitudinal direction of the film biaxially). The residual solvent
of the web at the stretching is preferably 3 to 30% by weight, in
that a high durable metal oxide layer of an optical film can be
obtained.
[0046] The residual solvent content herein referred to is expressed
employing the following formula: Residual solvent content
(%)={(weight of web before heat treatment--weight of web after heat
treatment)/weight of web before heat treatment}.times.100
[0047] wherein the heat treatment represents heating the web at
115.degree. C. for one hour.
[0048] The cellulose ester film in the invention preferably
contains a plasticizer. The plasticizers are not specifically
limited, but the plasticizers include a phosphate plasticizer, a
phthalate plasticizer, a trimellitate plasticizer, a pyromellitate
plasticizer, a glycolate plasticizer, a citrate plasticizer, and a
polyester plasticizer. Examples of the phosphate plasticizer
include triphenyl phosphate, tricresyl phosphate, cresyldiphenyl
phosphate, octyldiphenyl phosphate, diphenylbiphenyl phosphate,
trioctyl phosphate, and tributyl phosphate. Examples of the
phthalate include diethyl phthalate, dimethoxyethyl phthalate,
dimethyl phthalate, dioctyl phthalate, dibutyl phthalate,
di-2-ethylhexyl phthalate, and butylbenzil phthalate. Examples of
the trimellitate plasticizer include tributyl trimellitate,
triphenyl trimellitate, and trimethyl trimellitate. Examples of the
pyromellitate plasticizer include tetrabutyl pyromellitate,
tetraphenyl pyromellitate, and tetraethyl pyromellitate. Examples
of a glycerin ester plasticizer include triacetin, and tributyrin.
Examples of the glycolate plasticizer include ethylphthalylethyl
glycolate, methylphthalylethyl glycolate, and butylphthalylbutyl
glycolate. Examples of other carboxylic acid esters include butyl
oleate, metylacetyl ricinolate, dibutyl sebacate, and various kinds
of trimellitic acid esters. Of these plasticizers, the phosphate
plasticizer and the glycolate plasticizer are preferable.
[0049] These plasticizers may be used singly or in combination.
[0050] The plasticizer content of the cellulose ester film is
preferably 1 to 30% by weight % based on weight of the cellulose
ester, in view of film properties or processability.
[0051] An ultraviolet (UV) absorbent used in the substrate in the
invention will be explained below. It is preferred that the
cellulose ester film in the invention contains a UV absorbent,
since an image display employing the cellulose ester film minimizes
deterioration occurring when it is placed outdoors.
[0052] The UV absorbent in the invention is preferably a UV
absorbent which has excellent absorption of ultraviolet light
having a wavelength of 370 nm or less, and has reduced absorption
of visible light having a wavelength of 400 nm or more. The UV
absorbents used in the invention include an oxybenzophenone
compound, a benzotriazole compound, a salicylic acid ester
compound, a benzophenone compound, a cyanoacrylate compound and a
nickel complex compound, but are not limited thereto.
[0053] Examples of the benzotriazole type UV absorbent include
2-(2'-hydroxy-5'-methylphenyl)-benzotriazole,
2-(2'-hydroxy-3',5'-di-tert- -butylphenyl)-benzotriazole,
2-(2'-hydroxy-3.sup.1-tert-butyl-5'-methylphe- nyl)-benzotriazole,
2-(2'-hydroxy-3',5'-di-t-butylphenyl)-5-chlorobenzotri- azole,
2-(2'-hydroxy-3.zeta.-(3",4",5",6"-tetrahydrophthalimidomethyl)-5'--
methylphenyl)-benzotriazole,
2,2-methylenebis(4-(1,1,3,3-tetramethylbutyl)-
-6-(2H-benzotriazole-2-yl)phenol),
2-(2'-hydroxy-3'-t-butyl-5'-methylpheny- l)-5-chlorobenzotriazole,
2-(2H-benzotriazole-2-yl)-6-(straight-chained or branched
dodecyl)-4-methylphenol, octyl-3-[3-t-butyl-4-hydroxy-5-(chloro--
2H-benzotriazole-2-yl)phenyl] propionate, and
2-ethylhexyl-3-[3-tert-butyl-
-4-hydroxy-5-(5-chloro-2H-benzotriazole-2-yl)phenyl] propionate.
TINUVIN 109, TINUVIN 171, and TINUVIN 326 (each produced by Ciba
Specialty Co., Ltd.) are commercially available, and preferably
used.
[0054] The benzophenone type UV absorbent is also one of UV
absorbents useful for the invention. Examples of the benzophenone
type UV absorbent include 2,4-dihydroxybenzophenone,
2,2'-dihydroxy-4-methoxybenzophenone,
2-hydroxy-4-methoxy-5-sulfobenzophenone, and bis
(2-methoxy-4-hydroxy-5-b- enzoylphenylmethane).
[0055] As UV absorbents preferably used in the optical film of the
invention, the benzotriazole or benzophenone type UV absorbent is
preferably used which has high transparency, and minimizes
deterioration of a polarizing plate or a liquid crystal. The
benzotriazole type UV absorbent is especially preferably used which
minimizes undesired coloration. UV absorbents are preferable, which
do not bleed out nor volatilize during cellulose ester film
manufacturing.
[0056] In the invention, particles as a matting agent are
preferably added to the substrate in order to adjust coefficient of
kinetic friction of the rear surface of the substrate,
[0057] The substrate useful for the invention, when it contains a
matting agent, can provide a good transportability or an easily
windable property. As a matting agent, particles with the smallest
possible particle size are preferable. The matting agent particles
include inorganic fine particles such as silicon dioxide, titanium
dioxide, aluminum oxide, zirconium oxide, calcium carbonate,
kaolin, talc, burned calcium silicate, hydrated calcium silicate,
aluminum silicate, magnesium silicate, and calcium phosphate, and
organic fine particles such as polymethacrylic acid-methylacrylate
resin powder, acrylstyrene resin powder, polymethylmethacrylate
resin powder, silicon resin powder, polystyrene resin powder,
polycarbonate resin powder, benzoguanamine resin powder, melamine
resin powder, polyolefin resin powder, polyester resin powder,
polyamide resin powder, polyimide resin powder and polyethylene
fluoride resin powder. The matting agent particles used in the
invention are not limited thereto, but is preferably cross-linked
polymer particles.
[0058] Of these matting agents, silicon dioxide is especially
preferable in adjusting a coefficient of kinetic friction or in
providing a reduced haze. The particles such as silicon dioxide
particles are often surface treated with an organic compound,
especially with a compound having a methyl group. Such surface
treated particles are preferable in giving a reduced haze to the
film. Examples of the organic compound used in the surface
treatment include halogenated silanes, alkoxysilanes (especially,
methylsilane), silazanes, and siloxanes.
[0059] The particle content of the substrate is preferably from
0.005 to 0.5% by weight, and more preferably from 0.05 to 0.4% by
weight, based on the substrate. The secondary particles of the
particles have an average particle size of preferably 0.005 to 1.0
.mu.m. The particles having a larger average particle size have a
high sliding property, and on the contrary, the particles having a
smaller average particle size have a good transparency. The primary
particles of the particles have an average particle size of
preferably not more than 20 nm, more preferably from 5 to 16 nm,
and most preferably 5 to 12 nm. It is preferred that these
particles are contained in the substrate so as to produce peaks of
0.01 to 1.0 .mu.m on the surface of the substrate. It is also
preferred that the number of peaks having a height of at least 0.1
.mu.m, which exist on the surface of the substrate, is from 10 to
500 per 1000 .mu.m.sup.2. The number of particles is preferably 5
to 500 per a 1000 .mu.m.sup.2 area of the substrate section which
represents 10 .mu.m (a depth from the surface of the
substrate).times.100 .mu.m (a length in the direction normal to the
depth direction) in the substrate section. The peak or particle
number as described above is determined by observing an electron
microscopic photograph of the surface or section of the
substrate.
[0060] Examples of the silicon dioxide particles include, for
example, Aerosil 200, 200V, 300, R972, R972V, R974, R202, R812,
OX50, or TT 600 (each produced by Nihon Aerosil Co., Ltd.), and are
preferably Aerosil 200V, R972, R972V, R974, R202 or R812. These
particles may be used as a mixture of two or more kinds thereof.
When two or more kinds of the particles are used, they may be mixed
at any amount ratio. Two matting agents different in kinds or
average particle size, for example, Aerosil 200V and R972 can be
used in a 200V to R972 amount ratio of from 0.1:99.9 to 99.9:0.01.
As zirconium oxide particles, commercially available products, for
example, Aerosil R976 and R811 each produced by Nihon Aerosil Co.,
Ltd., can be used.
[0061] Examples of the organic particles include silicon resin
particles such as Tospearl 103, 105, 108, 120, 145, 3210, or 240,
each produced by Toray Co., Ltd.
[0062] In the invention, the average primary particle size of the
particles in the invention is measured employing a transmission
type electron microscope. That is, the primary particle size of one
hundred particles is measured through the transmission type
electron microscope at a magnifying factor of 50,000 to 400,000,
and its average value is defined as the average primary particle
size.
[0063] The apparent specific gravity of the particles is preferably
70 g/liter, more preferably from 90 to 200 g/liter, and most
preferably from 100 to 200 g/liter. The particles of higher
apparent specific gravity are preferably used in preparing a
dispersion having a high concentration, improving a haze or
minimizing aggregates. Such particles are especially preferably
used in preparing the dope in the invention having a high solid
concentration.
[0064] The silicon dioxide particles having an average primary
particle size of not more than 20 nm and an apparent specific
gravity of not less than 70 g/liter can be prepared, for example,
by burning a mixture of hydrogen and a gaseous silicon
tetrachloride at 1,000 to 1,200.degree. C. in air. The apparent
specific gravity referred to in the invention is computed from the
following formula:
Apparent specific gravity (g/liter)=weight of silicon dioxide
particles (g)/volume of silicon dioxide particles (1)
[0065] wherein the volume of silicon dioxide particles is the
volume in which a certain amount of silicon dioxide particles are
put in a messcylinder and measured employing the messcylinder and
the weight of silicon dioxide particles is the weight of the
silicon dioxide particles put in the messcylinder.
[0066] As the methods of preparing a dispersion of the particles
useful for the invention and the method of adding the dispersion to
the dope, the following three are exemplified.
[0067] (Method A)
[0068] An organic solvent and the particles are mixed in a
disperser with stirring, and dispersed to obtain a dispersion of
the particles. The dispersion is added to a cellulose ester dope,
and stirred.
[0069] (Method B)
[0070] An organic solvent and the particles are mixed in a
disperser with stirring, and dispersed to obtain a dispersion of
the particles. Separately, a small amount of cellulose ester is
dissolved in an organic solvent with stirring, and added with the
above dispersion and stirred to obtain a particle addition
solution. The resulting particle addition solution is uniformly
mixed with a cellulose ester dope in an in-line mixer.
[0071] (Method C)
[0072] A small amount of cellulose ester is dissolved in a solvent
with stirring, added with particles, and dispersed in a disperser
to obtain a particle addition solution. The resulting particle
addition solution is mixed with a cellulose ester dope in an
in-line mixer.
[0073] The method A is preferred in that silicon dioxide particles
are effectively dispersed in a solvent, and the method C is
preferred in that dispersed silicon dioxide particles in a solvent
are difficult to be re-aggregated. The method B is more preferred
both in that silicon dioxide particles are effectively dispersed in
a solvent, and in that dispersed silicon dioxide particles in a
solvent are difficult to be re-aggregated.
[0074] (Dispersion Method)
[0075] When silicon dioxide particles are dispersed in a solvent to
obtain a silicon dioxide dispersion, the silicon dioxide
concentration of the dispersion is preferably 5 to 30% by weight,
more preferably 10 to 25% by weight, and most preferably 15 to 20%
by weight.
[0076] The content of silicon dioxide particles in the cellulose
ester film is preferably from 0.01 to 0.5 parts by weight, more
preferably from 0.05 to 0.2 parts by weight, and most preferably
from 0.08 to 0.12 parts by weight, based on 100 parts by weight of
cellulose ester. A higher content of the particles is superior in
coefficient of kinetic friction, and on the contrary, a lower
content of the particles is superior in lowering haze and
minimizing occurrence of aggregates.
[0077] The organic solvents used in the dispersion are preferably
lower alcohols. Examples of the lower alcohols include methanol,
ethanol, propyl alcohol, isopropyl alcohol, and butanol. Solvents
other than the lower alcohols are not specifically limited, and
solvents used in the preparation of the cellulose ester dope are
preferred. ordinary dispersers may be employed. Dispersers are
mainly divided into two types; a media disperser and a medialess
disperser. Silicon dioxide particles are preferably dispersed by
the medialess disperser which results in decrease in haze. Cited as
medialess dispersers are a ball mill, a sand mill, a dyno mill, and
the like. As medialess dispersers, there are an ultrasonic type, a
centrifugal type, a high pressure type, and the like. In the
present invention, the high pressure type disperser is preferred.
The high pressure disperser is an device which generates special
conditions such as high shearing, high pressure, and the like by
passing a composition prepared by mixing particles with solvents
into a narrow pipe at a high speed. When the high pressure
disperser is used, the maximum pressure in the interior of a narrow
pipe having a diameter of for example, 1 to 2,000 .mu.m is
preferably at least 9.8 Mpa, and more preferably at least 19.6 Mpa.
Further, at the time, a disperser that allows a maximum attainable
speed of not less than 100 m/second as well as a heat transfer rate
of not less than 420 kJ/hour is preferred.
[0078] The high pressure dispersers as described above include an
ultra-high pressure disperser (with a trade name of Microfluidizer)
manufactured by Microfluidics Corporation, and Nanomizer
manufactured by Nanomizer Co. Listed as devices other than those
are Manton-Gaulin type high pressure disperser, for example,
Homogenizer manufactured by Izumi Food Machinery, UHN-01
manufactured by Sanwa Kikai Co., Ltd., and the like.
[0079] In the invention, the particles described above are
preferably contained in the cellulose ester film to be uniformly
distributed in the thickness direction. It is more preferable that
the particles are contained in the cellulose ester film to be
located near the surface of the film. For example, it is preferred
that two kinds of dopes are simultaneously cast on a support from a
single die by a co-extrusion method so that the dope containing
particles is arranged on the surface side, whereby haze is reduced
and coefficient of dynamic friction is lowered. Further, it is more
preferred that three kinds of dopes are simultaneously cast on a
support so that the two dopes containing particles are arranged on
both surface sides.
[0080] In the invention, particles as a matting agent are
preferably added to the substrate in order to adjust coefficient of
kinetic friction of the rear surface of the substrate.
[0081] When a backing coat layer is provided on the rear surface of
the substrate opposite the layer in the invention to be formed, the
back coating layer preferably contains particles and a binder resin
in order to adjust a coefficient of dynamic friction of the surface
of the backing coat layer. is preferably provided on the surface.
The coefficient of dynamic friction can be adjusted by the particle
size, addition amount or material of the particles added.
[0082] The particles in the back coating layer useful for the
invention include particles of inorganic compounds or organic
compounds. The kinds, particle size, apparent specific gravity or
dispersion methods of the particles are the same as those denoted
above in the particles contained in the substrate.
[0083] The content of the particles in the back coating layer is
preferably from 0.01 to 1 parts by weight, more preferably from
0.05 to 0.5 parts by weight, and most preferably from 0.08 to 0.2
parts by weight, based on 100 parts by weight of binder resin. A
higher content of the particles lowers coefficient of kinetic
friction, and on the contrary, a lower content of the particles
lowers haze and minimize occurrence of aggregates.
[0084] It is preferred that these particles are contained in the
backing layer so as to produce peaks of 0.01 to 1.0 .mu.m on the
surface of the backing layer. It is also preferred that the number
of peaks having a height of at least 0.1 .mu.m, which exist on the
backing layer, is from 10 to 500 per 1000 .mu.m.sup.2. The number
of particles is preferably 5 to 500 per a 1000 .mu.m.sup.2 area of
the section of the substrate with the backing layer which
represents 10 .mu.m (a depth from the backing layer surface) x 100
.mu.m (a length in the direction normal to the depth direction) in
the section of the substrate with the backing layer. The peak or
particle number as described above is determined by observing an
electron microscopic photograph of the surface of the backing layer
or an electron microscopic photograph of the section of the backing
layer and the substrate.
[0085] The organic solvent used for forming the back coating layer
is not specifically limited, but since the back coating layer can
provide an anti-curl property of the substrate, an organic solvent,
which is capable of dissolving or swelling the substrate or resin
used as material of the substrate, is effective. The solvent is
suitably selected in view of curling degree of substrate, kinds of
substrate materials, proportion of substrate materials or coating
amount.
[0086] The organic solvents used for forming the back coating layer
are not specifically limited, but include, for example, benzene,
toluene, xylene, dioxane, acetone, methyl ethyl ketone,
N,N-dimethylformamide, methyl acetate, ethyl acetate,
trichloroethylene, methylene chloride, ethylene chloride,
tetrachloroethane, trichloroethane, chloroform,
N-methylpyrrolidone, and 1,3-dimethyl-2-imidazolidinone. The
organic solvents, which do not dissolve a back coating layer
coating composition, include methanol, ethanol, n-propyl alcohol,
1-propyl alcohol, and n-butanol.
[0087] The coating methods of the back coating layer coating
composition include those employing a gravure coater, a dip coater,
a wire-bar coater, a reverse coater, and an extrusion coater, etc.
When the back coating layer is coated employing these coater, the
coating liquid thickness (also referred to as wet thickness) of the
layer is preferably from 1 to 100 .mu.m, and more preferably from 5
to 30 .mu.m.
[0088] Examples of the resin used in the back coating layer include
vinyl type homopolymers or copolymers such as vinyl chloride/vinyl
acetate copolymer, vinyl chloride resin, vinyl acetate resin, vinyl
acetate-vinyl alcohol copolymer, partially hydrolyzed vinyl
chloride/vinyl acetate copolymer, vinyl chloride/vinylidene
chloride copolymer, vinyl chloride/acrylonitrile copolymer,
ethylene/vinyl alcohol copolymer, chlorinated polyvinyl chloride,
ethylene/vinyl chloride copolymer, and ethylene/vinyl acetate
copolymer; cellulose ester resins such as cellulose nitrate,
cellulose acetate propionate, cellulose diacetate, cellulose
triacetate, cellulose acetate phthalate, and cellulose acetate
butyrate; copolymers of maleic acid or acrylic acid, copolymers of
acrylic esters, acrylonitrile/styrene copolymer, chlorinated
polyethylene, acrylonitrile/chlorinated ethylene/styrene copolymer,
methyl methacrylate/butadiene/styrene copolymer, acryl resin,
polyvinyl acetal resin, polyvinyl butyral resin,
polyesterpolyurethane resin, polyetherpolyurethane resin,
polycarbonatepolyurethane resin, polyester resin, polyether resin,
polyamide resin, amino resin, rubber resins such as
styrene/butadiene resin and butadiene/acrylonitrile resin, silicon
resin, fluorine containing resin polymethyl methacrylate, and a
copolymer of methyl methacrylate and methyl acrylate, but are not
limited thereto. The cellulose ester resins such as cellulose
diacetate and cellulose acetate propionate resin are
preferable.
[0089] The back coating layer described above can provide a
coefficient of dynamic friction of not more than 0.9.
[0090] The substrate used in the invention preferably has on the
substrate a hardened resin layer formed by polymerizing a
composition containing at least one ethylenically unsaturated
compound has been polymerized and hardening.
[0091] As the hardened resin layer formed by polymerizing a
composition containing an ethylenically unsaturated compound and
hardening, a hardened layer formed by hardening an active ray
hardenable resin or a heat-hardenable resin is preferably used, and
an active ray hardenable resin layer is more preferably used.
[0092] The active ray hardenable resin layer herein referred to
implies a layer containing, as a main component, a resin which
capable of being hardened by irradiation of active rays such as UV
light or electronic beam. Examples of the active ray hardenable
resin include an ultraviolet (hereinafter referred to also as UV)
ray hardenable resin or an electronic beam hardenable resin. The
active ray hardenable resin may be a resin which can be hardened by
active rays other than UV ray or electronic beam. The UV ray
hardenable resins include a UV ray hardenable acrylurethane resin,
a UV ray hardenable polyesteracrylate resin, a UV ray hardenable
epoxyacrylate resin, a UV ray hardenable polyolacrylate resin and a
UV ray hardenable epoxy resin. Examples thereof include
trimethylolpropane triacrylate, ditrimethylolpropane tetraacrylate,
pentaerythritol triacrylate, pentaerythritol tetraacrylate,
dipentaerythritol hexaacrylate or alkyl-modified dipentaerythritol
pentaacrylate.
[0093] The UV ray hardenable acrylurethane resins include those
prepared easily by reacting a polyesterpolyol with an isocyanate
monomer or its prepolymer and then reacting the resulting product
with an acrylate having a hydroxy group such as
2-hydroxyethylacrylate, 2-hydroxyethylmethacrylate (hereinafter,
acrylate also includes a methacrylate) or 2-hydroxypropylacrylate
(disclosed for example, in Japanese Patent O.P.I. Publication No.
59-151110/1984).
[0094] The UV ray hardenable polyesteracrylate resins include those
prepared easily by reacting a polyesterpolyol with
2-hydroxyethylacrylate or 2-hydroxypropylacrylate (disclosed for
example, in Japanese Patent O.P.I. Publication No.
59-151110/1984).
[0095] Examples of the UV ray hardenable epoxyacrylate resin
include those prepared by reacting an epoxyacrylate oligomer in the
presence of a reactive diluting agent and a photoinitiator
(disclosed for example, in Japanese Patent O.P.I. Publication No.
1-105738/1989).
[0096] The photoinitiators thereof include benzoine or its
derivative, or acetophenones, benzophenones, hydroxy benzophenones,
Michler's ketone, .alpha.-amyloxime esters, thioxanthones or their
derivatives. an oxime ketone derivative, a benzophenone derivative
or a thioxanthone derivative. These photoinitiators may be used
together with a photo-sensitizer. The above photoinitiators also
work as a photo-sensitizer. Sensitizers such as n-butylamine,
triethylamine and tri-n-butylphosphine can be used in
photo-reaction of epoxyacrylates.
[0097] The polymerizable monomers having one unsaturated double
bond in the molecule include methyl acrylate, ethyl acrylate, butyl
acrylate, benzyl acrylate, cyclohexyl acrylate, vinyl acetate, and
styrene. The polymerizable monomers having two unsaturated double
bonds in the molecule include ethylene glycol diacrylate, propylene
glycol diacrylate, divinylbenzene, 1,4-cyclohexane diacrylate,
1,4-cyclohexyldimethyl diacrylate, trimethylol propane triacrylate,
and pentaerythritol tetraacrylate.
[0098] Ultraviolet ray hardenable resins, which are available on
the market, include ADEKA OPTOMER KR-BY series: KR-400, KR-410,
KR-550, KR-566, KR-567, or BY-320B (each produced by Asahi Denka
Co., Ltd.); Koei Hard A-101-KK, A-101-WS, C-302, C-401-N, C-501,
M-101, M-102, T-102, D-102, NS-101, FT-102Q8, MAG-1-P20, AG-106, or
M-101-C, (each produced by Koei Kagaku Co., Ltd.); SEIKA BEAM PHC
2210 (S), PHC X-9 (K-3), PHC 2213, DP-10, DP-20, DP-30, P1000,
P1100, P1200, P1300, P1400, P1500, P1600, or SCR 900 (each produced
by Dainichi Seika Kogyo Co., Ltd.); KRM7033, KRM7039, KRM7130,
KRM7131, UVCRYL29201, or UVCRYL29202 (each produced by Daicel-UCB
Co., Ltd.); RC-5015, RC-5016, RC-5020, RC-5031, RC-5100, RC-5102,
RC-5120, RC-5122, RC-5152, RC-5171, RC-5180, or RC-5181 (each
produced by Dainippon Ink and Chemicals, Inc.); AUREX No. 340 Clear
(produced by Chugoku Toryo Co., Ltd.); SANRAD H-601 (produced by
Sanyo Chemical Industries, Ltd.); SP-1509 or SP-1507 (each produced
by Showa Kobunshi Co., Ltd.); RCC-15C (produced by Grace Japan Co.,
Ltd.); and ARONIX M-6100, M-8030, or M-8060 (produced by Toa Gosei
Co., Ltd.).
[0099] The active ray hardenable layer used in the invention can be
provided according to a conventional method. As a light source for
hardening the UV ray hardenable layer by photo hardening reaction
to form a hardened layer, any light source capable of emitting UV
rays can be used. Examples of the light source include a low
pressure mercury lamp, a medium pressure mercury lamp, a high
pressure mercury lamp, a super-high pressure mercury lamp, a carbon
arc lamp, a metal halide lamp, and a xenon lamp. Although the
exposure amount is varied depending on the kinds of light source,
it may be 20-10,000 mJ/cm.sup.2, and is more preferably 50-2,000
mJ/cm.sup.2. The sensitizer having an absorption maximum in the
range of from near-ultraviolet to visible wavelength is effectively
used.
[0100] The organic solvents for preparing a coating solution of a
UV ray hardenable resin layer can be suitably selected from for
example, hydrocarbons, alcohols, ketones, esters, glycols, other
solvents or a mixture thereof. An organic solvent is preferably
used which contains in an amount of preferably not more than 5% by
weight and more preferably 5 to 80% by weight, propylene glycol
monoalkyl (alkyl having 1 to 4 carbon atoms) ether or propylene
glycol monoalkyl (alkyl having 1 to 4 carbon atoms) ether
ester.
[0101] The coating solution of the ultraviolet ray hardenable resin
composition can be coated through the coaters described above. The
wet coating thickness is preferably 0.1 to 30 .mu.m, and more
preferably 0.5 to 15 .mu.m.
[0102] The ultraviolet ray hardenable resin composition, while or
after coating or drying, is irradiated with ultraviolet rays, and
the irradiation time is preferably from 0.5 seconds to 5 minutes,
and more preferably from 3 seconds to 3 minutes, in view of
hardening efficiency or workability.
[0103] The hardened resin layer can contain inorganic or organic
fine particles in order to prevent blocking or to increase
anti-scratch resistance. The fine particles include those as
denoted in the matting agent above. These particles have an average
particle size of preferably from 0.005 to 1 .mu.m, and more
preferably from 0.01 to 0.1 .mu.m.
[0104] The content of the particles in the ultraviolet ray
hardenable resin composition is preferably 0.1 to 10 parts by
weight based on the 100 parts by weight of ultraviolet ray
hardenable resin composition.
[0105] The UV ray hardened resin layer may be a clear hard coat
layer with a center-line surface roughness Ra of 1 to 50 nm, or an
anti-glare layer with a center-line surface roughness Ra of 0.1 to
1 .mu.m, the center-line surface roughness Ra being defined in JIS
B0601. According to the invention, these resin layers can be
subjected to plasma treatment to form a layer or layers on the
surface thereof, and as described above, a uniform layer can be
formed on the uneven surface of the substrate. The layer is
preferably used as for example, an optical interference layer of a
low reflection laminate comprised of a high refractive index layer,
a medium refractive index layer or a low refractive index layer.
The method according to the invention is preferable in that a
uniform layer can be formed on the surface of an anti-glare layer
with a center-line surface roughness Ra of 0.1 to 0.5 .mu.m.
[0106] The substrate in the invention or the substrate in the
invention having a coated layer thereon has a retardation Ro in
planes of preferably 0 to 1000 nm as an optical property, and a
retardation R.sub.t in the thickness direction of preferably 0 to
300 nm as an optical property. Herein, R.sub.0 (450) implies a
retardation in planes based on the measurement of the three
dimensional refractive indices measured through a 450 nm light, and
R.sub.0 (600) implies a retardation in planes based on the
measurement of the three dimensional refractive indices measured
through a 600 nm light.
[0107] The plasma discharge treatment at atmospheric pressure or at
approximately atmospheric pressure in the method of the invention,
whereby a layer or layers are formed, are carried out employing the
following plasma discharge apparatus.
[0108] Regarding a layer or layers forming apparatus used in the
method of the present invention, examples of the plasma discharge
apparatus useful for the present invention will be shown below, but
the present invention is not limited thereto.
[0109] FIG. 1 shows a schematic drawing of one embodiment of a
plasma discharge apparatus used in the layer forming method of the
present invention. In FIG. 1, the plasma discharge apparatus
comprises a pair of rotating electrodes 10A and 10B being connected
through voltage applying members 82 and 81, respectively, to a
power supply 80. The rotating electrodes 10A and 10B transport a
substrate, which are preferably in a roll form or in an endless
belt form. The electrodes of FIG. 1 are roller electrodes. A gap
formed between the paired electrodes is a space where discharge is
carried out, and a substrate F can be introduced. The gap between
the paired electrodes provides a discharge section 50. The gap is
maintained at atmospheric pressure or at approximately atmospheric
pressure. A reaction gas G is supplied from a reaction gas supply
section 30 to the gap where the surface of a substrate F is
subjected to plasma discharge treatment. The substrate F, unwound
from a supply spool (not illustrated) or transported from the
previous process, is transported through a guide roller 20 to the
rotating electrode 10A rotating in the transporting direction to be
in contact with it, and passes through the discharge section 50,
whereby a layer or layers are formed on the surface of the
substrate F. The substrate F delivered from the discharge section
50 is allowed to make a U-turn around U-turn rollers 11A, 11B, 11C
and 11D, transported to the rotating electrode 10B to be in contact
with it, which is rotating in the opposite direction of the
rotating electrode 10A, and allowed to again pass through the
discharge section 50, where the surface of the substrate F is
further subjected to plasma discharge treatment, and another layer
is again formed on the layer formed previously. The reaction gas G,
which has been used for discharge treatment, is exhausted from a
gas exhaust port 40 as waste gas G'. In FIG. 1, the formed layer is
not illustrated. The substrate F' having a formed layer on the
surface is transported to the next process or to an uptake spool
(not illustrated) through a guide roller 21. Accordingly, the
substrate reciprocates at the discharge section 50 in contact with
the rotating electrodes 10A and 10B. Although not illustrated, the
devices such as the rotating electrodes 10A and 10B, guide rollers
20 and 21, U-turn rollers 11A through 11D, the reaction gas supply
section 30, and the gas exhaust port 40 are preferably accommodated
in a discharge vessel whereby the devices are segregated from the
outside. Although also not illustrated, the rotating electrodes 10A
and 10B have a structure in which their temperature is adjusted by
a circulated temperature-controlled medium.
[0110] FIG. 2 shows a schematic drawing of another embodiment of a
plasma discharge apparatus. FIG. 2 shows one example of the plasma
discharge apparatus comprising a rotating electrode and a fixed
electrode useful for the layer forming method of the invention. In
FIG. 2, the plasma discharge apparatus comprises a rotating
electrode 110 and plural fixed electrodes 111 arranged to oppose
the rotating electrode. A substrate F from a supply spool (not
illustrated) or the previous process is transported to the rotating
electrode through a guide roller 120 and a nip roller 122, and
further transported in synchronism with the rotation of the
rotating electrode 110 while contacting the rotating electrode 110.
A reaction gas G generated in a gas generation device 131 is
introduced through a gas supply pipe 130 into a plasma discharge
section 150 at atmospheric pressure or at approximately atmospheric
pressure where a layer or layers are formed on the substrate
surface facing the fixed electrodes. The power supply 180, which is
capable of applying voltage for plasma generation, is connected to
the rotating electrode 110 and the fixed electrodes 111 through
voltage applying members 181 and 182. The rotating electrode 110,
the fixed electrodes 111 and the discharge section 150 are covered
with a plasma discharge vessel 190 and segregated from the
exterior. Waste gas G' is exhausted from a gas exhaust port 140
arranged at a lower portion of the discharge section. The substrate
F' subjected to the plasma discharge treatment is transported to
the next process or to an uptake spool (not illustrated) through a
nip roller 123 and a guide roller 121. A Blade 124 is provided to
contact the nip roller 122 arranged at the inlet of the substrate F
in order to prevent air accompanied by substrate F from entering
the discharge section, and a blade 125 is provided to contact the
nip roller 123 arranged at the outlet of the substrate F' in order
to prevent the reaction gas G or waste gas G' from escaping from
the discharge section. Although not illustrated, the rotating
electrode 110 and fixed electrodes 111 have a structure in which
their temperature is adjusted by a circulated
temperature-controlled medium.
[0111] As described above, it is preferable in the invention that
the substrate is subjected to plasma discharge treatment while
transporting the substrate in contact with the rotating electrode,
whereby a layer or layers are formed on the substrate surface.
[0112] The surface of the rotating electrode, which is in contact
with the substrate being transported, is required to have a high
smoothness. The surface of the rotating electrode has a maximum
surface roughness (Rmax) of preferably not more than 10 .mu.m, more
preferably not more than 8 .mu.m, and most preferably not more than
7 .mu.m. Herein, the maximum surface roughness refers to that in
the surface roughness defined in JIS B 0601.
[0113] The surface of the electrodes used in the invention is
preferably covered with a solid dielectric substance, and it is
also preferable that a conductive base metal such as metal is
covered with a solid dielectric substance. Examples of the solid
dielectric substance include a plastic such as
polytetrafluoroethylene or polyethylene terephthalate, a metal
oxide such as glass, silicon dioxide, aluminum oxide
(Al.sub.2O.sub.3), zirconium oxide (ZrO.sub.2), titanium oxide
(TiO.sub.2), and a complex oxide such as barium titanate. It is
especially preferable that the coverage is carried out by thermally
spraying ceramic on the base metal, and sealing the ceramic layer
with inorganic materials. Herein, examples of the conductive base
metal such as metal include silver, platinum, stainless steel,
aluminum, and iron, and of these, stainless steel is preferable in
view of processability. Materials for lining include silicate
glass, borate glass, phosphate glass, germanate glass, tellurite
glass, aluminate glass, and vanadate glass. Among these, borate
glass is preferably used in view of processability.
[0114] In the invention, the electrodes have a structure capable of
being optionally heated or cooled with a heating or cooling source
in the interior. When the electrodes are in the form of a belt,
they can be cooled with cooled air from the rear side. When the
electrodes are rotating electrodes in the form of roll, it is
preferable that the outer surface temperature of the electrodes or
the temperature of the substrate is controlled by supplying a
medium to the interior of the electrodes. As the medium, insulating
materials such as distilled water and oil are preferably used.
Although the temperature, at which the substrate is treated, is
different due to treatment conditions, it is preferably from room
temperature to 200.degree. C., and more preferably from room
temperature to 120.degree. C. It is necessary that the substrate be
treated not to produce unevenness of the temperature of the
substrate.
[0115] In the invention, the gap distance between the electrodes is
determined in view of the thickness of the solid dielectric
substance, applied voltage or frequency, or an object of employing
plasma. In the opposing electrodes described above, when an
electrode on only one side has a solid dielectric substance or
electrodes on both sides thereof have solid dielectric substances,
the minimum gap distance between the electrode and the dielectric
substance in the former or the minimum gap distance between the
dielectric substances in the latter is preferably from 0.5 to 20
mm, and more preferably 1.+-.0.5 mm, in that uniform plasma is
generated.
[0116] In the invention, a mixed gas generated in a gas generation
device is introduced from a reaction gas supply port in a
controlled amount into a plasma discharge section between the
opposing electrodes. The concentration or amount of the reaction
gas is adjusted as necessary, but the gas is preferably supplied to
the discharge section at a rate sufficient to meet the transporting
speed of the substrate. The gas supply amount or discharging
conditions are preferably set to form a layer or layers employing
substantially all the amount of the gas supplied to the discharge
section.
[0117] In order to prevent ambient air from entering into a
discharge section or to prevent the reaction gas from escaping from
the discharge section, the electrodes and the transporting
substrate are preferably segregated from the outside by being
surrounded with a cover. In the invention, the pressure in the
discharge section is maintained at atmospheric pressure or at
approximately atmospheric pressure. Herein, the approximately
atmospheric pressure herein referred to implies a pressure of 20
kPa to 110 kPa. In order to obtain the effects of the invention,
the pressure is preferably 93 kPa to 110 kPa.
[0118] In the plasma discharge apparatus useful for the invention
comprising electrodes opposing each other, it is preferable that in
order to generate stable plasma, voltage is applied to the
electrode on one side connected to the power supply to generate
plasma, and the electrode on the other side is grounded.
[0119] Voltage applied to the electrodes by a high frequency power
supply is properly determined. For example, the voltage may be 0.5
to 10 kV, the frequency applied may be 1 kHz to 150 MHz, and the
wave shape may be a pulse shape or a sine curve shape.
Particularly, a frequency of from less than 100 kHz to 50 MHz
provides a preferable discharge section (discharge space).
[0120] The discharge density at the discharge section is preferably
from 5 to 1000 W.multidot.min./m.sup.2, and more preferably from 50
to 500 W.multidot.min./m.sup.2.
[0121] The plasma discharge section is preferably covered with for
example, a vessel of pyrex glass, but a vessel of metal may be used
if insulation from the electrodes is secured. For example, the
vessel may be a vessel of aluminum or stainless steel laminated
with a polyimide resin or of aluminum or stainless steel thermally
sprayed with ceramic to produce an insulation layer on the surface.
The reaction gas is suitably supplied to the plasma discharge
section or the waste gas is suitably exhausted by surrounding the
sides of the discharge section, the rotating electrodes or the
transporting section of the substrate with a protective
material.
[0122] The reaction gas used in the method of the invention of
forming a layer or layers will be explained below.
[0123] The reaction gas for forming a layer or layers according to
the method of the invention preferably contains inert gas. That is,
the reaction gas preferably contains a mixed gas of inert gas with
a reactive gas described later. The inert gas herein referred to
implies an element belonging to group XVIII in the periodic table,
and is typically helium, neon, argon, krypton, xenon, or radon. In
the invention, helium or argon is preferably used, and argon is
more preferably used. The inert gas content of the reaction gas is
preferably not less than 90% by volume, in obtaining a stable
plasma, and more preferably from 90 to 99.99% by volume.
[0124] The inert gas is used for producing a stable plasma. The
reaction gas is ionized or radicalized in the plasma, and is
accumulated or adhered on the substrate to form a layer or layers
on the substrate surface.
[0125] The reaction gas in the invention can contain various kinds
of reactive gases, whereby a layer or layers having various
functions can be formed on the surface of the substrate.
[0126] Employing for example, an organic fluorine-containing
compound or a silicon compound as a reactive gas, a low refractive
index layer of an anti-reflection layer can be formed. Further,
employing an organometallic compound comprising Ti, Zr, In, Sn, Zn,
Ge, Si, or another metal, a metal oxide or metal nitride layer can
be formed which functions as a medium or high refractive index
layer of an anti-reflection layer, a conductive layer or an
anti-static layer. Employing an organic fluorine-containing
compound, an anti-stain layer or a low refractive index layer can
be formed, and employing a silicon compound, a gas barrier layer or
a low refractive index layer can be formed. The method according to
the invention is especially preferably used in order to prepare an
anti-reflection layer which is a multiple layer prepared by
laminating a high or medium refractive index layer and a low
refractive index layer alternately.
[0127] The thickness of the layer formed according to the invention
is preferably in the range of 1 nm to 1000 nm.
[0128] When the layer in the invention is formed on the surface of
the substrate described above according to the invention, the
thickness of the layer is provided on the substrate surface so that
the thickness deviation from the average thickness falls within the
range of preferably .+-.8%, more preferably .+-.5%, and still more
preferably .+-.1%.
[0129] As the organic fluorine-containing compound used in the
reactive gas useful for the invention, a fluorocarbon gas or a
fluorohydrocarbon gas is preferably used. Examples of the organic
fluorine-containing compound include a fluorocarbon compound such
as tetrafluorocarbon, hexafluorocarbon, tetrafluoroethylene,
hexafluoropropylene, or octafluorocyclobutane; a fluorohydrocarbon
compound such as difluoromethane, tetrafluoroethane,
tetrafluoropropylene, trifluoropropylene or octafluorocyclobutane;
a halide compound of a fluorohydrocarbon compound such as
monochlorotrifluoromethane, monochlorodifluoromethane, or
dichlorotetrafluorobutane; and fluorinated compounds of alcohols,
acids or ketones. These compounds may be used singly or as a
mixture of two or more kinds thereof. Examples of the
fluorohydrocarbon gas include difluoromethane, tetrafluoroethane,
tetrafluoropropylene, and trifluoropropylene, and further include a
halide compound of a fluorohydrocarbon compound such as
monochlorotrifluoromethane, monochlorodifluoromethane, or
dichlorotetrafluorobutane and fluorinated compounds of alcohols,
acids or ketones, but are not limited thereto. These compounds may
have an ethylenically unsaturated group in the molecule. These
compounds may be used singly or as a mixture of two or more kinds
thereof. When the organic fluorine-containing compound is used in
the reaction gas useful for the invention, the content of the
organic fluorine-containing compound in the reaction gas is
preferably 0.01 to 10% by volume, and more preferably 0.1 to 5% by
volume, in that a uniform layer is formed on the substrate by the
plasma discharge treatment.
[0130] When the organic fluorine-containing compound in the
invention is gas at ordinary temperature and ordinary pressure, it
can be used as it is in the reaction gas, wherein the method of the
invention can be carried out most easily. When the organic
fluorine-containing compound in the invention is liquid or solid at
ordinary temperature and ordinary pressure, it may be used as gas,
in which it is gasificated by heating or under reduced pressure, or
in the form of solution, in which it is dissolved in an appropriate
solvent.
[0131] As the silicon compound for the reactive gas useful for the
invention, for example, an organometallic compound such as
dimethylsilane or tetramethylsilane; a metallic hydride such as
monosialne or disilane; a metal halide such as dichlorosilane,
trichlorosilane or silicon tetrafluoride, an alkoxysilane such as
tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane,
dimethyldiethoxysilane, methyltrimethoxysilane or
ethyltriethoxysilane; or an organosilane is preferably used, but is
not limited thereto. Another compound may be added to the reaction
gas to modify or control layer properties. When the above silicon
compound as the reactive gas is used in the reaction gas, the
content of the silicon compound in the reaction gas is preferably
0.01 to 10% by volume, and more preferably 0.1 to 5% by volume, in
that a uniform layer is formed on the substrate by the plasma
discharge treatment.
[0132] The organometallic compounds as the reactive gas useful for
the invention are not specifically limited, but include a compound
of metal such as Al, As, Au, B, Bi, Sb, Ca, Cd, Cr, Co, Cu, Fe, Ga,
Ge, Hg, In, Li, Mg, Mn, Mo, Na, Ni, Pb, Pt, Rh, Se, Si, Sn, Ti, Zr,
Y, V, W, or Zn, which are preferably used. In order to form a high
refractive index layer as an antireflection layer, the titanium
compound is preferably used. As the above described titanium
compound, for example, an organometallic amino compound such as
tetradimethylamino titanium, a metallic hydride such as titanium
tetrahydride or dititanium hexahydride, a metal halide such as
titanium dichloride, titanium trichloride or titanium
tetrachloride, or a metal alkoxide such as titanium tetraethoxide,
titanium tetrapropoxide or titanium tetrabutoxide is preferably
used. The titanium compound used in the invention is not limited
thereto. As the silicon compound or organometallic compound, a
metal hydride compound or a metal alkoxide compound is preferably
used in view of handling, and the metal alkoxide compound is more
preferably used, since it is not corrosive and does not generate
harmful gas. When the organometallic compound is used in the
reaction gas useful for the invention, the content of the
organometallic compound in the reaction gas is preferably 0.01 to
10% by volume, and more preferably 0.1 to 5% by volume, in that a
uniform layer is formed on the substrate by the plasma discharge
treatment.
[0133] When the silicon compound or titanium compound is introduced
into the discharge section, it may be any of gas, liquid or solid
at ordinary temperature and ordinary pressure. When it is gas at
ordinary temperature and ordinary pressure, it can be used as it
is, and when it is liquid or solid at ordinary temperature and
ordinary pressure, it can be used as gas, in which it is gasified
by heating, under reduced pressure or ultrasonic wave application.
When the silicon compound or titanium compound is gasified by
heating, and used, a metal alkoxide such as tetraethoxysilane or
titanium tetraisopropoxide, which has a boiling point at ordinary
temperature or ordinary pressure of not more than 200.degree. C.,
is suitably used in order to form a layer or layers of a low
reflection laminate. The above metal alkoxide may be diluted with
another organic solvent. The solvents include an organic solvent
such as methanol, ethanol, n-hexane or a mixture thereof.
[0134] The reaction gas further containing hydrogen in an amount of
0.1 to 10% by volume can markedly increase hardness of the layer
formed on the substrate.
[0135] Examples of the optical film of the invention include, for
example, an optical film in which a low refractive index layer and
a high refractive index layer are laminated to form an
anti-reflection layer or an optical film in which a conductive
layer or an anti-static layer is formed.
[0136] In the invention, a multiple layer can be continuously
formed on a substrate employing plural plasma discharging
apparatuses in the invention, whereby an optical film can be
obtained, which has a multiple layer without unevenness. For
example, when an optical film is prepared which has an
anti-reflection layer on a substrate, a high refractive index layer
with a refractive index of 1.6 to 2.3 and a low refractive index
layer with a refractive index of 1.3 to 1.5 are continuously and
effectively provided on a substrate. The low refractive index layer
is preferably a fluorine-containing compound-containing layer
formed by plasma discharging in the gas containing a
fluorine-containing compound, or a silicon dioxide-containing layer
formed by plasma discharging in the gas containing an organic
silicon compound such as an alkoxysilane. The high refractive index
layer is preferably a metal oxide-containing layer formed by plasma
discharging in the gas containing an organometallic compound, for
example, a titanium oxide-containing layer or a zirconium
oxide-containing layer. The layer in the invention is not limited
to these layers, and the structure of the layer is not limited to
that of these layers. For example, the outermost layer can be
subjected to plasma discharging treatment under atmospheric
pressure or approximately atmospheric pressure in the presence of a
reaction gas containing a fluorine-containing organic compound gas
to form an anti-stain layer.
[0137] The method of the invention can form a multiple layer
without unevenness and provide an optical film with a uniform
layer. Thus, the present invention can provide an optical film with
a layer or layers having various functions.
[0138] An anti-static layer or conductive layer may be a layer with
a thickness of 0.1 to 2 .mu.m comprising metal oxide fine particles
or conductive fine particles of a cross-linkable cationic polymer,
or a conductive substance-containing layer comprising a metal oxide
such as tin oxide or zinc oxide produced by plasma discharging
treatment at atmospheric pressure or at approximately atmospheric
pressure.
[0139] The optical film of the invention is useful especially for a
polarizing plate protective film, and a polarizing plate can be
prepared according to a conventional method employing the optical
film. The optical film has a layer or layers with high uniformity
and is preferably applied to various image displays which provide
excellent displaying properties.
EXAMPLES
[0140] The invention will be detailed according to the following
examples, but is not limited thereto.
Example 1
[0141] This example 1 relates to items 4, 6, 7, and 8.
1 Preparation of Dope A (Dope composition A) Methylene chloride 370
kg Ethanol 70 kg Cellulose acetate propionate (acetyl 100 kg
substitution degree: 2.0, propionyl substitution degree: 0.8)
Ethylphthalylethylglycolate 7 kg TINUVIN 326 1 kg
[0142] The acyl substitution degree of the cellulose ester was
measured according to the method as defined in ASTM-D817-96.
[0143] The organic solvents of the above dope composition A was
incorporated in a sealed vessel, added with the other components,
and stirred while heating to obtain a solution. The resulting
solution was cooled to a temperature to be cast on a support,
allowed to stand overnight, defoamed, and filtered employing an
Azumi Roshi No. 244 produced by Azumi Roshi Co., Ltd. to obtain
Dope A.
[0144] Preparation of Cellulose Acetate Propionate Film
[0145] A cellulose acetate propionate film was prepared according
to a solution cast film manufacturing method. Dope A was uniformly
cast at a dope temperature of 35.degree. C. on a 30.degree. C.
endless stainless steel belt support to form a web. The web was
dried until it could be peeled from the support, and then was
peeled from the stainless steel belt support. At peeling, the
residual solvent amount of the web was 35% by weight. The peeled
web was dried at 90.degree. C. in a tenter while being stretched in
the transverse direction by a stretching magnification as shown in
Table 1, and further dried in a dry zone of 120.degree. C. while
transported by rollers. Thus, cellulose ester films 1 and 2 each
having a thickness of 70 .mu.m, a width of 1.3 m, and a length of
2000 m were prepared, and designated as substrate samples 1 and 2,
respectively. Cellulose ester film 1C was prepared in the same
manner as in cellulose ester film 1, except that stretching was not
carried out, and was designated as substrate sample 1C.
[0146] Preparation of Optical Film
[0147] Employing the plasma discharge apparatus shown in FIG. 2, a
thin titanium oxide layer (a high refractive index layer) was
formed on substrate samples 1, 2 and 1C. Thus, optical film samples
1, 2 and 1C were obtained.
[0148] As a rotating electrode, a roll electrode with a solid
dielectric substance was prepared, in which a stainless steel
jacket roll base metal having the function of adjusting temperature
by circulated water was covered with a 1 mm thick alumina layer by
means of thermal spraying of ceramic, coated with an organic
solvent solution of tetramethoxysilane, dried, hardened by
irradiation of ultraviolet rays to carry out sealing treatment, and
further subjected to vertical specular polish for finish. A fixed
electrode with a solid dielectric substance was prepared in the
same manner as in the roll electrode above. The roll electrode and
fixed electrode were arranged as shown in FIG. 2. The gap between
both electrodes was 1.5 mm.+-.0.1 mm. The power supply used to
generate discharge plasma was a high frequency power supply
JRF-1000 produced by Nihon Denshi Co. Ltd. Plasma discharge
treatment was carried out at 13.56 MHz and at a discharge density
of 300 W.multidot.min/m.sup.2. The rotating electrode was rotated
by means of a driving device, and the circumferential speed thereof
was synchronized with the transporting speed of the substrate
sample.
[0149] Employing the following reaction gas composition for forming
a high refractive index layer, optical film samples 1, 2 and 1C
having a thin titanium oxide layer were continuously prepared from
substrate samples 1, 2 and 1C, respectively.
[0150] The evaluation results thereof are shown in Table 1.
2 (Composition for forming a high refractive index layer) Inert
gas: argon 99.4% by volume Reactive gas: tetraisopropoxytitanium
0.1% by volume vapor (150.degree. C. liquid was bubbled with argon
gas) Hydrogen gas 0.5% by volume (Visual observation evalution)
[0151] The samples were cut into a width of 1.3 m and a length of
50 cm, and the rear surface thereof was subjected to light
absorbing treatment employing a black spray to form a light
absorption layer. Reflection of light of a fluorescent lamp from
the surface of the samples opposite the light absorption layer was
visually observed, and evaluated for unevenness of the layer
according to the following criteria:
[0152] A: No unevenness was observed.
[0153] B: Slight unevenness was observed.
[0154] C: Unevenness was observed.
[0155] D: Apparent unevenness was observed.
3 TABLE 1 Optical Substrate Unevenness film sample Stretching
(Visual sample No. magnifi- observa- No. used cation tion) Example
1 1 1 1.05 B 2 2 1.10 A 1C 1C -- D
[0156] (Results)
[0157] It has been confirmed that the method according to the
invention forms a layer or layers with reduced film unevenness.
Example 2
[0158] This example 2 relates to items 2, 6, 7, and 8.
4 Preparation of Dope B (Dope composition B) Methylene chloride 380
kg Ethanol 40 kg Cellulose triacetate (acetyl 100 kg substitution
degree: 2.92) Triphenyl phosphate 11 kg Silicon dioxide particles
0.12 kg (particle size: 0.01 .mu.m) TINUVIN 326 1 kg
[0159] The organic solvents of the above dope composition B was
incorporated in a sealed vessel, added with the other components,
and stirred while heating to obtain a solution. The resulting
solution was cooled to a temperature to be cast on a support,
allowed to stand overnight, defoamed, and filtered employing an
Azumi Roshi No. 244 produced by Azumi Roshi Co., Ltd. to obtain
Dope B.
[0160] Preparation of Cellulose Triacetate Film
[0161] A cellulose triacetate film was prepared according to a
solution cast film manufacturing method. Dope B was uniformly cast
at a dope temperature of 35.degree. C. on a 25.degree. C. endless
stainless steel belt support to form a web. The web was dried until
it could be peeled from the support, and then was peeled from the
stainless steel belt support. At peeling, the residual solvent
amount of the web was 70% by weight. The peeled web was dried at
90.degree. C. in a tenter while being stretched in the transverse
direction by a stretching magnification of 1.03 and 1.10, and
further dried in a dry zone of 120.degree. C. while transported by
rollers. Thus, cellulose ester films 3 and 4 each having a
thickness of 60 .mu.m were prepared, and designated as substrate
samples 3 (stretched at a stretching magnification of 1.03) and 4
(stretched at a stretching magnification of 1.10), respectively.
Cellulose ester film 3C was prepared in the same manner as in
cellulose ester film 3, except that at peeling of the web, the
residual solvent amount of the web was 20% by weight, and was
designated as substrate sample 3C.
[0162] Preparation of an Optical Film
[0163] Employing the plasma discharge apparatus shown in FIG. 2, a
thin titanium oxide layer (a high refractive index layer) was
formed on substrate samples 3, 4 and 3C in a similar manner as in
Example 1. Thus, optical film samples 3, 4 and 3C having a thin
titanium oxide layer were prepared from substrate samples 3, 4 and
3C, respectively.
[0164] The evaluation results thereof are shown in Table 2.
[0165] (Measurement of Tensile Strength)
[0166] Tensile strength was measured according to a method as
defined in JIS K7127-1989. The tensile strength of the substrate
sample obtained above was measured employing a tensile tester
TENSILON RTA-100 produced by Olyentech Co., Ltd., provided that a
substrate cut to the same size as specimen No. 1 as described in
this JIS was pulled at a tensile speed of 100 mm/min. The
measurement was made with respect to the mechanical direction (MD
direction) and the transverse direction (TD direction) of the
substrate sample.
[0167] (Evaluation of Variation of Layer Thickness in the TD
Direction)
[0168] Optical film samples 3 and 4 formed a uniform layer without
unevenness, as compared with optical film sample 3C.
[0169] The spectral reflectance of the high refractive index layer
was measured under the condition of a 5.degree. regular reflection
through a spectrophotometer TYPE U-4000 (produced by Hitachi
Seisakusho Co., Ltd.). In order to prevent light reflection at the
rear surface of the substrate sample opposite the viewer side, the
rear surface of the sample was surface-roughened, and subjected to
light absorbing treatment employing a black spray to form a light
absorption layer. Reflectance of the resulting sample was measured
employing light with a wavelength of from 400 nm through 700 nm.
The thickness of the high refractive index layer was computed from
the reflection spectrum obtained above. The thickness of each of
ten points in the TD direction on the high refractive index layer
at an interval of 10 cm was measured, and the average of the layer
thickness and deviation from the average in the TD direction were
determined.
[0170] (Visual Observation Evaluation of Wrinkle Unevenness)
[0171] The samples were cut into a width of 1.3 m and a length of
50 cm, and subsequently, the rear surface thereof was subjected to
light absorbing treatment employing a black spray to form a light
absorption layer. Reflection of light of a fluorescent lamp from
the surface of the samples opposite the light absorption layer was
visually observed, and evaluated for wrinkle-like unevenness
according to the following criteria:
[0172] A: No wrinkle-like unevenness was observed.
[0173] B: Slight wrinkle-like unevenness was observed.
[0174] C: Wrinkle-like unevenness was partly observed.
[0175] D: Apparent wrinkle-like unevenness was observed.
5 TABLE 2 Wrinkle- *Average like of layer uneven- Optical Tensile
thickness ness film Substrate strength (Devia- (Visual sample
sample (N/mm.sup.2) tion) observa- No. No. MD/TD (nm) tion) Example
3 3 150/151 80 (.+-.2) B 2 4 4 160/157 80 (.+-.1) A 3C 3C 130/125
80 (.+-.10) D Symbol "*" represents the average layer thickness in
the TD direction of the high refractive index layer and a deviation
from the average.
[0176] (Results)
[0177] It has been proved that the optical film samples 3 and 4 in
the invention had a tensile strength of not less than 1.4.times.10
N/mm.sup.2 produced no wrinkle-like unevenness, and minimized
variation of layer thickness, judging from the measurement of
spectral reflectance.
Example 3
[0178] This example 3 relates to items 3, 6, 7, and 8.
6 Preparation of Dope C (Dope composition C) Methylene chloride 440
kg Ethanol 35 kg Cellulose triacetate (acetyl 100 kg substitution
degree: 2.86) Ethylphthalylethyl glycolate 15 kg TINUVIN 326 0.5 kg
TINUVIN 109 0.5 kg
[0179] The organic solvents of the above dope composition C was
incorporated in a sealed vessel, added with the other components,
and stirred while heating to obtain a solution. The resulting
solution was cooled to a temperature to be cast on a support,
allowed to stand overnight, defoamed, and filtered employing an
Azumi Roshi No. 244 produced by Azumi Roshi Co., Ltd. to obtain
Dope C.
[0180] Preparation of cellulose triacetate film
[0181] A cellulose triacetate film was prepared according to a
solution cast film manufacturing method. Dope C was uniformly cast
at a dope temperature of 35.degree. C. on a 30.degree. C. stainless
steel belt support to form a web. The web was dried until it could
be peeled from the support, and then was peeled from the stainless
steel belt support. At peeling, the residual solvent amount of the
web was 40% by weight.
[0182] The peeled web was dried at 90.degree. C. in a tenter while
being stretched in the transverse direction by a stretching
magnification of 1.05, and further dried in a dry zone of
120.degree. C. while transported by rollers. Thus, cellulose ester
film S having a thickness of 50 .mu.m was prepared, and designated
as substrate sample 5. Cellulose ester film 5C was prepared in the
same manner as in cellulose ester film 5, except that Dope C
contained 4 kg of ethylphthalylethyl glycolate instead of 15 kg of
ethylphthalylethyl glycolate, and was designated as substrate
sample 5C.
[0183] Preparation of an Optical Film
[0184] Employing the plasma discharge apparatus shown in FIG. 2, a
thin titanium oxide layer (a high refractive index layer) was
formed on substrate samples 5 and SC in a similar manner as in
Example 1. Thus, optical film samples 5 and 5C having a thin
titanium oxide layer was prepared from substrate samples 5 and 5C,
respectively.
[0185] The evaluation results thereof are shown in Table 3.
[0186] (Visual Observation Evaluation)
[0187] The optical samples 5 and 5C were processed and evaluated
for unevenness of the layer in the same manner as in Example 1.
[0188] (Haze)
[0189] Haze was measured according to JIS K7105.
[0190] (Measurement of Moisture Content)
[0191] The substrate sample was cut into a size of 10 cm.times.10
cm, allowed to stand at 23.degree. C. and 80% RH for 48 hours, and
weighed. The weight of the resulting sample was W.sub.2.
Subsequently, this sample was dried at 120.degree. C. for 45
minutes, and weighed, and the weight thereof was W.sub.1. The
moisture content of the sample was obtained from the following
formula:
Moisture content (%)={(W.sub.2-W.sub.1)/W.sub.1}.times.100
[0192]
7 TABLE 3 Optical film Substrate Moisture Unevenness sample sample
content Haze (Visual No. No. (%) (%) observation) Example 3 5 5 3.0
0.0 B 5C 5C 4.1 0.3 C
[0193] It has been proved that the optical film sample 5 employing
cellulose ester film sample 5 (substrate sample 5) having a
moisture content of 3.0% by weight of the invention provides a low
haze, and reduced unevenness, as compared with optical film sample
5C.
Example 4
[0194] This example 4 relates to items 1, 5, 6, 7, and 8.
8 Preparation of dope D (Dope composition D) Ethanol 35 kg AEROSIL
200 V 0.3 kg Methylene chloride 440 kg Cellulose triacetate (acetyl
100 kg substitution degree: 2.89) Triphenyl phoshate 10 kg
Ethylphthalylethyl glycolate 5 kg TINUVIN 326 0.5 kg TINUVIN 109
0.5 kg
[0195] The organic solvents of the above dope composition D was
incorporated in a sealed vessel, added with the other components,
and stirred while heating to obtain a solution. The resulting
solution was cooled to a temperature to be cast on a support,
allowed to stand overnight, defoamed, and filtered employing an
Azumi Roshi No. 244 produced by Azumi Roshi Co., Ltd. to obtain
dope D.
[0196] Preparation of Cellulose Triacetate Film
[0197] A cellulose triacetate film was prepared according to a
solution cast film manufacturing method. Dope D was uniformly cast
at a dope temperature of 35.degree. C. on a 30.degree. C. stainless
steel belt support to form a web. The web was dried until it could
be peeled from the support, and then was peeled from the stainless
steel belt support. At peeling, the residual solvent amount of the
web was 40% by weight.
[0198] The peeled web was dried at 85.degree. C. in a tenter while
being stretched in the transverse direction by a stretching
magnification of 1.06, and further dried in a dry zone of
120.degree. C. while transported by rollers. Thus, cellulose ester
film 6 having a thickness of 50 .mu.m and containing a matting
agent (AEROSIL 200V) was prepared, and designated as substrate
sample 6. Tensile strengths with respect to the mechanical
direction (MD direction) and the transverse direction (TD
direction) of the sample were both not less than 150 N/mm.sup.2. In
the above preparation of the cellulose ester film 6, the surface of
the cellulose ester film facing the stainless steel belt surface
was designated as surface B, and the surface of the film opposite
the surface B was designated as surface A. Cellulose ester film 6C
was prepared in the same manner as in cellulose ester film 6,
except that Dope D did not contain AEROSIL 200V, and was designated
as substrate sample 6C.
[0199] Preparation of Substrate Sample Coated with a Layer Such as
a Back Coating Layer
[0200] The following coating composition (1) was extrusion coated
on the surface A of substrate sample 6 to give a wet thickness of
13 .mu.m, and dried at 80.degree. C. to form a back coating layer.
The following coating composition (2) was extrusion coated on the
surface B of substrate sample 6 to give a wet thickness of 13
.mu.m, dried in a drying zone of 80.degree. C., and subjected to
ultraviolet light irradiation at 110 mJ/cm.sup.2 to form a clear
hard coating layer with a dry thickness of 3 .mu.m and a center
line average surface roughness (R.sub.a) of 12 nm. Thus, substrate
sample 7 was obtained.
[0201] Substrate sample 8 was prepared in the same manner as in
substrate sample 7, except that the following coating composition
(3) was used instead of coating composition (2) to form an
anti-glare layer with a dry thickness of 3 .mu.m.
[0202] The coating compositions (1), (2), and (3) used in the
preparation of the above substrate samples 7 and 8 and the
preparation method of coating composition (3) are shown below.
9 {Coating composition (1) (Back coating layer coating
compostition)} Acetone 30 parts by weight Ethyl acetate 45 parts by
weight Isoprophyl alcohol 10 parts by weight Cellulose diacetate
0.6 parts by weight 2% Silicon dioxide particle acetone 0.04 parts
by weight dispersion {Coating composition (2) (Clear hard coating
layer coating compostition)} Dipentaerythritol hexacrylate monomer
60 parts by weight Dipentaerythritol hexacrylate dimmer 20 parts by
weight Dipentaerythritol hexacrylate trimer 20 parts by weight or
its polymer higher than the trimer Diethoxybenzophenone 4 parts by
weight Ethyl acetate 45 parts by weight Methyl ethyl ketone 45
parts by weight Isopropyl alcohol 60 parts by weight Preparation of
Coating composition (3) (Anti-glare coating layer coating
composition) Ethyl acetate 45 parts by weight Methyl ethyl ketone
45 parts by weight Isopropyl alcohol 60 parts by weight Silycia 431
(average particle size: 2 parts by weight 2.5 .mu.m, produced by
Fuji Silysia Chemical Co., Ltd.) AEROSIL 200 V (average particle
size: 5 parts by weight 12 nm)
[0203] The above composition was stirred in a high speed stirrer TK
Homomixer, (produced by Tokushu Kika Kogyo Co., Ltd.) and further
dispersed in a collision type disperser Mantongorin (produced by
Gorin Co., Ltd.), and then added with the following Uv hardenable
solution to obtain a coating composition (3).
10 (UV hardenable solution) Dipentaerythritol hexacrylate monomer
60 parts by weight Dipentaerythritol hexacrylate dimmer 20 parts by
weight Dipentaerythritol hexacrylate trimer 20 parts by weight or
its polymer higher than the trimer Diethoxybenzophenone 4 parts by
weight
[0204] Preparation of an Optical Film
[0205] Employing a plasma discharge apparatus shown in FIG. 2, a
titanium oxide layer (a high refractive index layer) was formed on
the surface B of substrate samples 6 and 6C, on the clear hard coat
layer of substrate sample 7, and on the anti-glare layer of
substrate sample 8 in a similar manner as in Example 1. Thus,
optical film samples 6, 6C, 7, and 8 were prepared from substrate
samples 6, 6C, 7, and 8, respectively.
[0206] The resulting samples were evaluated according to the
following methods. The results are shown in Table 4.
[0207] (Measurement of Coefficient of Dynamic Friction)
[0208] The resulting substrate sample was cut to a size of 100
mm.times.200 mm to obtain a first piece, and to a size of 750
mm.times.100 mm to obtain a second piece. The second piece was
superposed on the first piece so that the outermost surfaces on the
opposite side of the layer to be formed (the rear surfaces of the
substrate sample 6 or the back coating layers of the substrate
sample 7 or 8) contact each other, and the resulting composite was
placed on a fixed horizontal plate. A foamed rubber-covered load
with a weight of 200 g was put on the resulting material, adhered
to the upper piece, and pulled with a force F in the horizontal
direction. Force F (kg), with which the load begins moving, was
measured, and coefficient of dynamic friction (.mu.) was obtained
from the following formula:
F=.mu..times.W
[0209] wherein W (kg) represents weight of the load, and F (kg)
represents force with which the load begins moving. Evaluation of
variation of layer thickness in the MD direction
[0210] The spectral reflectance of the high refractive index layer
was measured under the condition of a 5.degree. regular reflection
through a spectrophotometer TYPE U-4000 (produced by Hitachi
Seisakusho Co., Ltd.). In order to prevent light reflection at the
rear surface of the substrate samples opposite the viewer side, the
rear surface of the sample was surface-roughened, and subjected to
light absorbing treatment employing a black spray to form a light
absorption layer. Reflectance of the resulting sample was measured
employing light with a wavelength of from 400 nm to 700 nm. The
thickness of the high refractive index layer was computed from the
reflection spectrum obtained above. Layer thickness of each of ten
points in the MD direction on the high refractive index layer at an
interval of 30 cm was measured, and the average of the layer
thickness and deviation from the average were determined.
11 TABLE 4 Clear *Average of hard Anti- layer Back coat glare
Coeffi- thickness in Optical Sub- coating layer layer cient of the
MD film strate layer (Sur- (Sur- dynam- direction sample sample
(Sur- face face ic (Deviation) No. No. face A) B) B) friction (nm)
Ex- 6 6 No Yes No 0.7 80 (.+-.5) am- 7 7 Yes Yes No 0.4 80 (.+-.2)
ple 4 8 8 Yes No Yes 0.4 80 (.+-.2) 6C 6C No Yes No 1.10 80
(.+-.10) Symbol "*" represents the average layer thickness in the
MD direction of the high refractive index layer and a deviation
from the average.
[0211] (Results)
[0212] The substrate sample 6 itself contained a matting agent. The
substrate sample 7 had a matting agent-containing back coating
layer on the surface A and a clear hard coating layer on the other
surface B. The substrate sample 8 had a matting agent-containing
back coating layer on the surface A and an anti-glare layer on the
other surface B. Each of the substrate samples 6, 7, and 8 had a
coefficient of dynamic friction of not more than 0.9. The substrate
samples 6, 7, and 8 were subjected to plasma discharge treatment to
obtain optical film samples 6, 7 and 8, respectively. The resulting
optical film samples 6, 7 and 8 provided uniform layer thickness
without variation of layer thickness in the MD direction.
12 Comparative example 1 Preparation of Dope E (Dope composition E)
Methylene chloride 440 kg Ethanol 35 kg Cellulose triacetate
(acetyl 100 kg substitutioin degree: 2.86) Triphenyl phosphate 8 kg
TINUVIN 326 0.5 kg TINUVIN 328 0.5 kg
[0213] The organic solvents of the above dope composition E was
incorporated in a sealed vessel, added with the other components,
and stirred while heating to obtain a solution. The resulting
solution was cooled to a temperature to be cast on a support,
allowed to stand overnight, defoamed, and filtered employing an
Azumi Roshi No. 244 produced by Azumi Roshi Co., Ltd. to obtain
Dope E.
[0214] Preparation of Cellulose Triacetate Film
[0215] A cellulose triacetate film was prepared according to a
solution cast film manufacturing method. Dope E was uniformly cast
at a dope temperature of 35.degree. C. on a 30.degree. C. endless
stainless steel belt support to form a web. The web was dried until
it could be peeled from the support, and then was peeled from the
stainless steel belt support. At peeling, the residual solvent
amount of the web was 20% by weight. The peeled web was dried in a
dry zone of from 90 to 120.degree. C. while transported by rollers.
Thus, cellulose ester film 7 having a thickness of 70 .mu.m, and
designated as substrate sample 9.
[0216] Preparation of an Optical Film
[0217] Employing a plasma discharge apparatus shown in FIG. 2, a
thin titanium oxide layer (a high refractive index layer) was
formed on substrate sample 9 in a similar manner as in Example 1.
Thus, optical film sample 9 having a thin titanium oxide layer was
prepared from substrate sample 9.
[0218] The resulting substrate sample was evaluated according to
the followings and the results are shown in Table 5.
[0219] (Evaluation)
[0220] Visual observation evaluation for unevenness of the layer
was carried out in the same manner as in Example 1, tensile
strength and variation of layer thickness in the TD direction were
measured and wrinkle unevenness was observed in the same manner as
in Example 2, haze and moisture content were obtained in the same
manner as in Example 3, and coefficient of dynamic friction and
variation of layer thickness in the MD direction were measured in
the same manner as in Example 4. The results are shown in Table
5.
13 TABLE 5 Visual obser- *Average of Opti- Mois- vation layer cal
Sub- Coeffi- Tensile ture Wrinkle- thickness film strate cient of
strength con- like (Deviation) sample sample dynamic MD/TD Haze
tent uneven- Uneven- (nm) No. No. friction (N/mm.sup.2) (%) (%)
ness ness MD TD Comparative 9 9 1.10 130/122 0.3 5 D D 80 80
example 1 (.+-.10) (.+-.13) Symbol "*" represents the average layer
thickness in the MD and TD directions of the high refractive index
layer and a deviation from the average.
[0221] As is apparent from Table 7, Optical film sample No. 9
(comparative), which employed an unstretched cellulose ester film,
had a thickness of 70 .mu.m, and had a tensile strength of
1.3.times.10.sup.2 N/mm2, a moisture content of 5% by weight, and a
coefficient of dynamic friction of 1.10, falling outside the scope
of the invention, provided apparent unevenness and a great
variation of layer thickness.
Example 5 and Comparative Example 2
[0222] Optical film samples 7 and 8 of example 4, and optical film
sample 9 of comparative example 1 were subjected to plasma
discharge treatment to form a low refractive index layer (with a
layer thickness of 95 nm and a refractive index of 1.46) on the
high refractive index layer in the same manner as in Example 1,
except that the following reaction gas composition for forming a
low refractive index layer was used instead of the reaction gas
composition for forming a high refractive index layer. Thus,
polarizing plate protective films 10, 11, and 12 was obtained from
optical film samples 7, 8 and 9, respectively.
14 (Composition for forming a low refractive index layer) Inert
gas: argon 98.2% by volume Reactive gas: tetramethoxysilane 0.3% by
volume vapor (bubbled with argon gas) Hydrogen gas 1.5% by
volume
[0223] Employing polarizing plate protective films 10, 11, and 12,
polarizing plates 1, 2, and 3 were prepared. Preparation of
polarizing plate Employing polarizing plate protective films 10,
11, and 12, polarizing plate samples 1 through 3 were prepared
according to the following procedures, and evaluated.
[0224] 1. Preparation of Polarizing Film
[0225] A 120 .mu.m thick polyvinyl alcohol film was uniaxially
stretched (at 110.degree. C. by a factor of 5). The resulting film
was immersed for 60 seconds in an aqueous solution comprised of
0.075 g of iodine, 5 g of potassium iodide, and 100 g of water,
further immersed at 68.degree. C. in an aqueous solution comprised
of 6 g of potassium iodide, 7.5 g of boric acid, and 100 g of
water, washed with water, and dried. Thus, a polarizing film was
obtained.
[0226] 2. Preparation of Polarizing Plate
[0227] The polarizing film obtained above and each of polarizing
plate protective films 10, 11, and 12 were laminated to obtain a
polarizing plate sample according to the following procedures 1 to
5.
[0228] Procedure 1
[0229] The polarizing plate protective film was cut to obtain two
specimens with a size of 30 cm (in the mechanical
direction).times.18 cm (in the transverse direction). The resulting
specimens were immersed in an aqueous 2 mol/liter sodium hydroxide
solution at 60.degree. C. for 90 seconds, washed with water, and
dried. The low refractive index layer of the resulting materials
was laminated with a peelable protective film. Thus, two polarizing
plate protective film samples were obtained.
[0230] Procedure 2
[0231] The polarizing film obtained above was cut into a size of 30
cm (in the mechanical direction).times.18 cm (in the transverse
direction), and immersed in a polyvinyl alcohol adhesive (with a
solid content of 2% by weight) for 1 to 2 seconds to form an
adhesive layer.
[0232] Procedure 3
[0233] The excessive adhesive of the adhesive layer on the
polarizing film prepared in Procedure 2 was softly removed. The one
polarizing plate protective film sample was laminated onto one
surface of the resulting polarizing film and further, the other
polarizing plate protective film sample was laminated onto the
other surface of the polarizing film through the adhesive layer
(with the low refractive index layers arranged outwardly). Thus,
laminate sample was obtained.
[0234] Procedure 4
[0235] Pressure was applied through a hand roller to the laminate
sample with a polarizing film and a polarizing plate protective
film sample obtained in the Procedure 3 to remove foams or
excessive adhesive from the ends of the laminate sample. The
pressure applied by the hand roller was from 20 to 30 N/cm.sup.2,
and the roller speed was 2 m/min.
[0236] Procedure 5
[0237] The sample obtained in the Procedure 4 was dried at
80.degree. C. for 2 minutes in a dryer. Thus, polarizing plate
samples 1 through 3 were prepared employing polarizing plate
protective film samples 10, 11, and 12, respectively. (Preparation
of liquid crystal display panel sample)
[0238] The polarizing plate on the viewer side of the liquid
crystal cell of a commercially available display panel (a color
liquid crystal display MultiSync LCD1525J TYPE LA-1529HM, produced
by NEC Co., Ltd.) was peeled. Subsequently, each of the polarizing
plate samples 1 through 3 was superposed on the liquid crystal cell
so that their polarizing direction was in accordance with the
original one to obtain liquid crystal display panel samples 1, 2
and 3, respectively.
[0239] The polarizing plate samples 1 through 3 and liquid crystal
display panel samples 1, 2 and 3 were visually observed, and
evaluated for unevenness according to the following criteria:
[0240] A: No unevenness was observed.
[0241] B: Slight unevenness was observed.
[0242] C: Unevenness was observed.
[0243] D: Apparent unevenness was observed.
[0244] The results are shown in Table 6.
15 TABLE 6 Polarizing Liquid Polar- plate Optical Uneven- crystal
Uneven- izing protective film ness display ness plate film sample
(Visual panel (Visual sample sample No. No. obser- sample obser-
No. used used vation) No. vation) Example 1 10 7 A 1 A 5 2 11 8 A 2
A Compara- 3 12 9 D 3 D tive example 2 Inv.: Inventive, Comp.:
Comparative
[0245] As is apparent from Table 6, the liquid crystal panel
samples 1 and 2 (Inventive) employing polarizing plate samples 1
and 2 in the invention provided no unevenness, exhibiting an
excellent displaying property, as compared with the liquid crystal
panel sample 3 (comparative) employing polarizing plate sample 12.
The liquid crystal panel sample 3 provided apparent unevenness.
EFFECTS OF THE INVENTION
[0246] The present invention provides a method of manufacturing a
uniform thin multiple layer on a substrate continuously and at
reduced cost according to plasma discharge at atmospheric pressure
or at approximately atmospheric pressure, an optical film having on
the surface the layer formed according to the method, and a
polarizing plate or an image display employing the optical
film.
* * * * *