U.S. patent application number 14/708090 was filed with the patent office on 2015-08-27 for optical member, polyimide, method for manufacturing optical member, and method for producing polyimide.
The applicant listed for this patent is CANON KABUSHIKI KAISHA. Invention is credited to Tomonari Nakayama.
Application Number | 20150240031 14/708090 |
Document ID | / |
Family ID | 44170019 |
Filed Date | 2015-08-27 |
United States Patent
Application |
20150240031 |
Kind Code |
A1 |
Nakayama; Tomonari |
August 27, 2015 |
OPTICAL MEMBER, POLYIMIDE, METHOD FOR MANUFACTURING OPTICAL MEMBER,
AND METHOD FOR PRODUCING POLYIMIDE
Abstract
There is provided an optical member that can retain a high
antireflection effect on a substrate for a long time. The optical
member includes a laminated body that can reduce the reflection of
light formed on a substrate surface, wherein at least one layer of
the laminated body is a polyimide layer containing a polyimide
film, and the polyimide contains a repeating unit represented by
the following general formula (1), and a 1,4-cyclohexylene group in
the main chain of R.sub.2 in the general formula (1) contains 90%
by mole or more of a trans-1,4-cyclohexylene group: ##STR00001##
wherein R.sub.1 denotes a tetravalent organic group, and R.sub.2
denotes a divalent organic group having one or two or more
1,4-cyclohexylene groups in the main chain.
Inventors: |
Nakayama; Tomonari;
(Yokohama-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CANON KABUSHIKI KAISHA |
Tokyo |
|
JP |
|
|
Family ID: |
44170019 |
Appl. No.: |
14/708090 |
Filed: |
May 8, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13581098 |
Aug 24, 2012 |
|
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PCT/JP2011/054670 |
Feb 23, 2011 |
|
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14708090 |
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Current U.S.
Class: |
427/162 ;
525/436 |
Current CPC
Class: |
G02B 1/04 20130101; B05D
5/063 20130101; B05D 2505/50 20130101; C08G 73/106 20130101; G02B
1/04 20130101; C08G 73/10 20130101; G02B 1/118 20130101; C08G
73/1028 20130101; C08L 79/08 20130101; C08L 79/08 20130101; Y10T
428/24355 20150115 |
International
Class: |
C08G 73/10 20060101
C08G073/10; B05D 5/06 20060101 B05D005/06 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 26, 2010 |
JP |
2010-043332 |
May 26, 2010 |
JP |
2010-121000 |
Feb 3, 2011 |
JP |
2011-022042 |
Claims
1. A method for manufacturing an optical member including a
laminated body that can reduce the reflection of light formed on a
substrate surface, comprising: 1) purifying a diamine represented
by the following general formula (3) such that a 1,4-cyclohexylene
group in the main chain of R.sub.2 in the general formula (3)
contains 90% by mole or more of a trans-1,4-cyclohexylene group;
[Chem. 2] H.sub.2N--R.sub.2--NH.sub.2 (3) wherein R.sub.2 denotes a
divalent organic group having one or two or more 1,4-cyclohexylene
groups in the main chain, 2) producing a polyimide containing a
repeating unit represented by the following general formula (1) by
the reaction of the purified diamine with an acid dianhydride
represented by the following general formula (4) in a solvent;
##STR00018## wherein R.sub.1 denotes a tetravalent organic group,
##STR00019## wherein R.sub.1 and R.sub.2 are as described above, 3)
applying a solution containing the polyimide to the substrate or a
thin film formed on the substrate; and 4) drying and/or firing the
applied solution containing the polyimide at 100.degree. C. or more
and 250.degree. C. or less to form a polyimide layer.
2. The method for manufacturing an optical member according to
claim 1, further comprising: 5) applying a precursor sol of
aluminum oxide to the outermost surface of the laminated body; 6)
drying and/or firing the applied precursor sol of aluminum oxide at
100.degree. C. or more and 250.degree. C. or less to form an
aluminum oxide film; and 7) immersing the aluminum oxide film in
hot water to form a textured structure formed of plate crystals
containing 70% by mole or more of aluminum oxide.
3. A polyimide having a repeating unit represented by the following
general formula (1), wherein 90% by mole or more of a
1,4-cyclohexylene group in the general formula (1) has a trans
form: ##STR00020## wherein R.sub.1 denotes a tetravalent organic
group, and R.sub.2 denotes a divalent organic group having one or
two or more 1,4-cyclohexylene groups in the main chain.
4. The polyimide according to claim 3, further comprising a
repeating unit represented by the following general formula (2):
##STR00021## wherein R.sub.1 denotes a tetravalent organic group, n
denotes an integer in the range of 0 to 2, R.sub.3 to R.sub.10
independently denote a hydrogen atom, a halogen atom, a phenyl
group, or a linear or cyclic alkyl, alkenyl, or alkynyl group
having 1 to 6 carbon atoms, and R.sub.11 and R.sub.12 independently
denote a hydrogen atom or a linear or cyclic alkyl group having 1
to 6 carbon atoms.
5. The polyimide according to claim 3, further comprising a
repeating unit represented by the following general formula (5):
##STR00022## wherein R.sub.1 denotes a tetravalent organic group,
R.sub.11 to R.sub.14 independently denote a hydrogen atom, a phenyl
group, or an alkyl, alkenyl, or alkynyl group having 1 to 4 carbon
atoms, R.sub.11 to R.sub.14 may be the same or different, R.sub.15
and R.sub.16 independently denote a phenylene group or an alkylene
group having 1 to 4 carbon atoms, R.sub.15 and R.sub.16 may be the
same or different, and n denotes an integer in the range of 0 to
6.
6. A method for producing a polyimide, comprising: purifying a
diamine represented by the following general formula (3) such that
90% by mole or more of a 1,4-cyclohexylene group in the general
formula (3) has a trans form; [Chem. 6] H.sub.2N--R.sub.2--NH.sub.2
(3) wherein R.sub.2 denotes a divalent organic group having one or
two or more 1,4-cyclohexylene groups in the main chain, producing a
polyimide precursor by the reaction between the diamine represented
by the general formula (3) purified and an acid dianhydride
represented by the following general formula (4) in a solvent;
##STR00023## wherein R.sub.1 denotes a tetravalent organic group,
producing a polyimide by the imidization of the polyimide precursor
in a solvent; and isolating the polyimide by removing the
solvent.
7. The method for producing a polyimide according to claim 6,
wherein the polyimide precursor is produced by the reaction between
the diamine represented by the general formula (3) purified, a
diamine represented by the following general formula (12), and the
acid dianhydride represented by the general formula (4):
##STR00024## wherein R.sub.11 to R.sub.14 independently denote a
hydrogen atom, a phenyl group, or an alkyl, alkenyl, or alkynyl
group having 1 to 4 carbon atoms, R.sub.11 to R.sub.14 may be the
same or different, R.sub.15 and R.sub.16 independently denote a
phenylene group or an alkylene group having 1 to 4 carbon atoms,
R.sub.15 and R.sub.16 may be the same or different, and n denotes
an integer in the range of 0 to 6.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional of U.S. patent application
Ser. No. 13/581,098 filed Aug. 24, 2012, which is a national stage
entry of PCT/JP2011/054670 filed on Feb. 23, 2011, which claims
priority to Japanese Patent Application No. 2011-022042 filed Feb.
3, 2011, Japanese Patent Application No. 2010-121000 filed May 26,
2010, and Japanese Patent Application No. 2010-043332 filed Feb.
26, 2010, all of which are hereby incorporated by reference herein
in their entireties.
TECHNICAL FIELD
[0002] The present invention relates to an antireflective optical
member and a method for manufacturing the antireflective optical
member and, more particularly, to an optical member suitable to
stably achieve high antireflection performance from a visible
region to a near-infrared region for a long time, a polyimide, a
method for manufacturing the optical member, and a method for
producing the polyimide.
BACKGROUND ART
[0003] Polyimides are used in electronic components and electrical
machinery components because of their high heat resistance and
excellent electrical insulating properties. Transparent polyimides
having an aliphatic structure are used also in liquid crystal
display elements. However, the introduction of the aliphatic
structure to impart transparency to a polyimide can lower the heat
resistance and the mechanical characteristics of the polyimide.
Thus, a polyimide having high transparency, high heat resistance,
and excellent mechanical characteristics has been synthesized by
introducing a specific alicyclic structure (see PTL 1). A polyimide
having high transparency, high heat resistance, and excellent
mechanical characteristics has been synthesized by using a
substantially planar diamine, such as trans-1,4-cyclohexanediamine
(see PTL 2). However, use of trans-1,4-cyclohexanediamine made
polymerization difficult because of the formation of a salt during
polymerization. Thus, the formation of a salt must be reduced, for
example, by silylation of the diamine.
[0004] It is also known that a polyimide produced using
pyromellitic acid and 4,4'-methylenebis(aminocyclohexane) has high
transparency, high heat resistance, and excellent mechanical
characteristics (see PTL 3). However, the polyimide produced by
this method has low solubility. Thus, a film of the polyimide must
be manufactured by heat treatment of a film of a precursor, such as
polyamic acid, at high temperature. This causes problems, such as
thermal damage to a substrate and degradation of transparency
because of the yellow coloration of the polyimide. Thus, there is a
demand for a polyimide that is easy to synthesize, has high
transparency and heat resistance, and can be processed without
causing thermal damage to neighboring members.
[0005] In an antireflective structure having a periodic fine
structure having a pitch less than or equal to a wavelength in a
visible light region, it is known that the formation of a periodic
fine structure having an appropriate pitch and height results in
high antireflection performance in a wide wavelength range. A known
method for forming a periodic fine structure includes the
application of a film in which fine particles having a size less
than or equal to the wavelength are dispersed. In particular, it is
known that a textured structure formed of aluminum oxide boehmite
grown on a glass substrate has a high antireflection effect. This
textured structure formed of boehmite is produced by steam
treatment or hot-water immersion treatment of an aluminum oxide
film, for example, formed by a liquid phase method (a sol-gel
method) (see NPL 1). However, exposure to water vapor or hot water
can cause damage to the glass substrate.
[0006] It is known that polyimides can be transparent, have a
variable refractive index, and protect a glass substrate from
damage caused by water or water vapor (see PTL 4). However, it is
difficult to produce a polyimide that is easy to synthesize and has
high transparency and heat resistance. In order to manufacture a
low-reflectance optical member, there is a demand for an optical
thin film that has small variations in thickness and optical
properties.
[0007] A porous film that contains fine particles deposited on the
surface layer as an antireflection coating and a metal oxide or
halogenated metal layer formed by a method of growing boehmite on a
substrate are convenient and have high productivity and excellent
optical performance. On the other hand, the porous film and the
metal oxide or halogenated metal layer have low density and many
voids. Thus, water from the outside can easily reach the substrate,
often causing erosion of the substrate or the elution of substrate
components, such as alkali ions. Thus, there is a demand for a
thin-film material that can be applied between a porous film or a
boehmite film and a substrate to improve antireflection performance
and reduce damage to the substrate. Furthermore, there is a demand
for a high-performance antireflection-coated optical member without
cracking or film irregularities caused by a variation in film
thickness or optical properties resulting from the effects of heat
or water.
CITATION LIST
Patent Literature
[0008] PTL 1 Japanese Patent Laid-Open No. 2002-161136 [0009] PTL 2
Japanese Patent Laid-Open No. 2005-146072 [0010] PTL 3 Japanese
Patent Laid-Open No. 2007-313739 [0011] PTL 4 U.S. Patent
Application Publication 2008/0310026
Non Patent Literature
[0011] [0012] NPL 1 K. Tadanaga, N. Katata, and T. Minami:
"Super-Water-Repellent Al2O3 Coating Films with High Transparency",
J. Am. Ceram. Soc., 80[4], 1040-1042 (1997)
SUMMARY OF INVENTION
Technical Problem
[0013] In view of such background art, the present invention
provides an optical member that has a high antireflection effect on
a substrate for a long time and a method for manufacturing the
optical member. The present invention also provides a polyimide
that can retain transparency after processing into a membrane or
film, has a sufficiently high glass transition temperature, and is
soluble in organic solvents, and a method for producing the
polyimide.
Solution to Problem
[0014] An optical member that can solve the problems described
above includes a laminated body that can reduce the reflection of
light formed on a substrate surface, wherein at least one layer of
the laminated body is a polyimide layer containing a polyimide
film, and the polyimide contains a repeating unit represented by
the following general formula (1), and a 1,4-cyclohexylene group in
the main chain of R.sub.2 in the general formula (1) contains 90%
by mole or more of a trans-1,4-cyclohexylene group:
##STR00002##
[0015] wherein R.sub.1 denotes a tetravalent organic group, and
R.sub.2 denotes a divalent organic group having one or two or more
1,4-cyclohexylene groups in the main chain.
[0016] A method for manufacturing an optical member that can solve
the problems described above is a method for manufacturing an
optical member including a laminated body that can reduce the
reflection of light formed on a substrate surface, including
[0017] 1) purifying a diamine represented by the following general
formula (3) such that a 1,4-cyclohexylene group in the main chain
of R.sub.2 in the general formula (3) contains 90% by mole or more
of a trans-1,4-cyclohexylene group;
[Chem. 2]
H.sub.2N--R.sub.2--NH.sub.2 (3)
[0018] wherein R.sub.2 denotes a divalent organic group having one
or two or more 1,4-cyclohexylene groups in the main chain,
[0019] 2) producing a polyimide containing a repeating unit
represented by the following general formula (1) by the reaction of
the purified diamine with an acid dianhydride represented by the
following general formula (4) in a solvent;
##STR00003##
[0020] wherein R.sub.1 denotes a tetravalent organic group,
##STR00004##
[0021] wherein R.sub.1 and R.sub.2 are as described above,
[0022] 3) applying a solution containing the polyimide to the
substrate or a thin film formed on the substrate; and
[0023] 4) drying and/or firing the applied solution containing the
polyimide at 100.degree. C. or more and 250.degree. C. or less to
form a polyimide layer.
[0024] A polyimide that can solve the problems described above has
a repeating unit represented by the following general formula (1),
wherein 90% by mole or more of a 1,4-cyclohexylene group in the
general formula (1) has a trans form:
##STR00005##
[0025] wherein R.sub.1 denotes a tetravalent organic group, and
R.sub.2 denotes a divalent organic group having one or two or more
1,4-cyclohexylene groups in the main chain.
[0026] A method for producing a polyimide that can solve the
problems described above includes
[0027] purifying a diamine represented by the following general
formula (3) such that 90% by mole or more of a 1,4-cyclohexylene
group in the general formula (3) has a trans form;
[Chem. 6]
H.sub.2N--R.sub.2--NH.sub.2 (3)
[0028] wherein R.sub.2 denotes a divalent organic group having one
or two or more 1,4-cyclohexylene groups in the main chain,
[0029] producing a polyimide precursor by the reaction between the
diamine represented by the general formula (3) purified and an acid
dianhydride represented by the following general formula (4) in a
solvent;
##STR00006##
[0030] wherein R.sub.1 denotes a tetravalent organic group,
[0031] producing a polyimide by the imidization of the polyimide
precursor in a solvent; and
[0032] isolating the polyimide by removing the solvent.
[0033] The present invention can provide an optical member that can
retain a high antireflection effect on a substrate for a long time.
The present invention can also provide a method for manufacturing
the optical member. The present invention can also provide a
polyimide that can retain transparency after processing into a
membrane or film, has a sufficiently high glass transition
temperature, and is soluble in organic solvents, and a method for
producing the polyimide.
[0034] Further features of the present invention will become
apparent from the following description of exemplary embodiments
with reference to the attached drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0035] FIG. 1 is a schematic view of an optical member according to
an embodiment of the present invention.
[0036] FIG. 2 is a schematic view of an optical member according to
another embodiment of the present invention.
[0037] FIG. 3 is a graph illustrating the refractive index
distribution of an optical member according to an embodiment of the
present invention.
[0038] FIG. 4 is a schematic view of an optical member according to
an embodiment of the present invention.
[0039] FIG. 5 is a schematic view of an optical member according to
an embodiment of the present invention.
[0040] FIG. 6 is a graph showing the relationship between the
thickness of a polyimide thin film and a rate of increase in film
thickness due to the immersion of the film in hot water in Example
1 and Comparative Example 1.
[0041] FIG. 7 is a graph showing DSC measurements of crude DADCM
(4,4'-methylenebis(aminocyclohexane)) and purified DADCM in
examples.
DESCRIPTION OF EMBODIMENTS
[0042] The present invention will be described in detail below.
[0043] An optical member according to an embodiment of the present
invention includes a laminated body that can reduce the reflection
of light formed on a substrate surface, wherein at least one layer
of the laminated body is a polyimide layer containing a polyimide
film, and the polyimide contains a repeating unit represented by
the following general formula (1), and a 1,4-cyclohexylene group in
the main chain of R.sub.2 in the general formula (1) contains 90%
by mole or more of a trans-1,4-cyclohexylene group:
##STR00007##
[0044] wherein R.sub.1 denotes a tetravalent organic group, and
R.sub.2 denotes a divalent organic group having one or two or more
1,4-cyclohexylene groups in the main chain.
[0045] The polyimide can contain a repeating unit represented by
the following general formula (2):
##STR00008##
[0046] wherein R.sub.1 denotes a tetravalent organic group, n
denotes an integer in the range of 0 to 2, R.sub.3 to R.sub.10
independently denote a hydrogen atom, a halogen atom, a phenyl
group, or a linear or cyclic alkyl, alkenyl, or alkynyl group
having 1 to 6 carbon atoms, and R.sub.11 and R.sub.12 independently
denote a hydrogen atom or a linear or cyclic alkyl group having 1
to 6 carbon atoms.
[0047] FIG. 1 is a schematic view of an optical member according to
an embodiment of the present invention. In FIG. 1, the optical
member according to this embodiment of the present invention
includes a polyimide layer 2 containing a polyimide and a
low-refractive index layer 3 on a surface of a substrate 1 in this
order.
[0048] A laminated body 9 composed of the polyimide layer 2 and the
low-refractive index layer 3 can reduce the reflection of light on
the surface of the substrate 1. The polyimide layer is formed of a
polyimide alone or a polyimide and a component other than the
polyimide. The component other than the polyimide complements the
polyimide and is compatible with, can be mixed with, or can be
dispersed in the polyimide within the bounds of not impairing the
characteristics of the polyimide.
[0049] The formation of the polyimide layer 2 between the substrate
1 and the low-refractive index layer 3 can produce a higher
antireflection effect than the formation of the low-refractive
index layer 3 directly on the substrate 1. The thickness of the
polyimide layer 2 is 10 nm or more and 150 nm or less, preferably
20 nm or more and 80 nm or less, and depends on the refractive
index of the substrate. The polyimide layer 2 having a thickness
below 10 nm has little antireflection effect. The polyimide layer 2
having a thickness above 150 nm has a markedly reduced
antireflection effect.
[0050] The polyimide contained in the polyimide layer 2 has a
repeating unit represented by the following general formula
(1):
##STR00009##
[0051] wherein R.sub.1 denotes a tetravalent organic group, and
R.sub.2 denotes a divalent organic group having one or two or more
1,4-cyclohexylene groups in the main chain. Most of the
1,4-cyclohexylene group, more specifically, 90% by mole or more of
the 1,4-cyclohexylene group in the main chain of R.sub.2 can be a
trans-1,4-cyclohexylene group.
[0052] The divalent organic group having one or two or more
1,4-cyclohexylene groups in R.sub.2 in the polyimide can impart
transparency and a low refractive index to the polyimide without
lowering the heat resistance of the polyimide. Although an
aliphatic group in R.sub.2 in the polyimide can reduce the
refractive index of the polyimide, linear aliphatic groups or
alicyclic groups other than the 1,4-cyclohexylene group lower the
glass transition temperature of the polyimide. 1,4-cyclohexylene
can be directly bonded to the nitrogen atom of an imide ring in the
polyimide. The polyimide can contain a repeating unit represented
by the following general formula (2):
##STR00010##
[0053] wherein R.sub.1 denotes a tetravalent organic group, n
denotes an integer in the range of 0 to 2, R.sub.3 to R.sub.10
independently denote a hydrogen atom, a halogen atom, a phenyl
group, or a linear or cyclic alkyl, alkenyl, or alkynyl group
having 1 to 6 carbon atoms, and R.sub.11 and R.sub.12 independently
denote a hydrogen atom or a linear or cyclic alkyl group having 1
to 6 carbon atoms.
[0054] The polyimide may further have a repeating unit represented
by the following general formula (5).
##STR00011##
[0055] wherein R.sub.1 denotes a tetravalent organic group,
R.sub.11 to R.sub.14 independently denote a hydrogen atom, a phenyl
group, or an alkyl, alkenyl, or alkynyl group having 1 to 4 carbon
atoms, R.sub.11 to R.sub.14 may be the same or different, R.sub.15
and R.sub.16 independently denote a phenylene group or an alkylene
group having 1 to 4 carbon atoms, R.sub.15 and R.sub.16 may be the
same or different, and n denotes an integer in the range of 0 to
6.
[0056] The repeating unit represented by the general formula (5)
can improve the solubility of the polyimide. The repeating unit
represented by the general formula (5) can also improve the
adhesion of a film made of the polyimide.
[0057] A 1,4-cyclohexylene group can be introduced into R.sub.2 in
the polyimide by using a diamine represented by the following
general formula (3) having a 1,4-cyclohexylene group or a
derivative of the diamine as a monomer:
[Chem. 13]
H.sub.2N--R.sub.2--NH.sub.2 (3)
[0058] wherein R.sub.2 denotes a divalent organic group having one
or two or more 1,4-cyclohexylene groups in the main chain.
[0059] A diamine represented by the following general formula (6)
or a derivative thereof can be used as a monomer:
##STR00012##
[0060] wherein R.sub.3 to R.sub.10 independently denote a hydrogen
atom, a halogen atom, a phenyl group, or a linear or cyclic alkyl,
alkenyl, or alkynyl group having 1 to 6 carbon atoms, and R.sub.11
and R.sub.12 independently denote a hydrogen atom or a linear or
cyclic alkyl group having 1 to 6 carbon atoms.
[0061] Examples of the diamine having a 1,4-cyclohexylene group
include, but are not limited to, 1,4-cyclohexanediamine,
1,4-bis(aminomethyl)cyclohexane,
4,4'-methylenebis(aminocyclohexane),
4,4'-methylenebis(1-amino-2-methylcyclohexane),
2,2-bis(4-aminocyclohexyl)propane, 4,4'-bicyclohexylamine, and
.alpha.,.alpha.'-bis(4-aminocyclohexyl)-1,4-diisopropylcyclohexane.
[0062] The diamine having a 1,4-cyclohexylene group is generally
synthesized by the hydrogenation of an aromatic diamine. The
diamine synthesized contains a mixture of a trans-1,4-cyclohexylene
group and a cis-1,4-cyclohexylene group due to cis-trans
isomerization. For example, a diamine having one 1,4-cyclohexylene
group, such as 1,4-cyclohexanediamine, contains a mixture of a
structural isomer only having a trans form and a structural isomer
only having a cis form. A diamine having two 1,4-cyclohexylene
groups, such as 4,4'-methylenebis(aminocyclohexane), contains a
mixture of a structural isomer only having the trans form, a
structural isomer only having the cis form, and a structural isomer
(or stereoisomer) having one trans form and one cis form.
[0063] Thus, a polyimide synthesized using the diamine having a
1,4-cyclohexylene group described above without purification
contains both the trans-1,4-cyclohexylene group and the
cis-1,4-cyclohexylene group. The heat resistance and the mechanical
characteristics of the polyimide depend on the ratio of the
structural isomer having the trans form to the structural isomer
having the cis form.
[0064] The expression "most of the 1,4-cyclohexylene group in the
polyimide has the trans form" indicates that the 1,4-cyclohexylene
group in the polyimide skeleton has the trans form alone or a
mixture of the trans form and a small amount of cis form. The
polyimide in which most of the 1,4-cyclohexylene group has the
trans form has a higher glass transition temperature (Tg) than a
polyimide in which most of the 1,4-cyclohexylene group has the cis
form. Thus, a film made of the polyimide in which most of the
1,4-cyclohexylene group has the trans form has a higher
strength.
[0065] The polyimide layer 2 has a very small thickness of 100 nm
or less. A change as small as several nanometers in the thickness
of the polyimide layer 2 therefore results in deterioration of the
optical properties of an optical member according to an embodiment
of the present invention. Since a thin film having such a thickness
has a lower density than thin films having larger thicknesses, the
thin film absorbs water in the manufacturing process or in the
environment, causing an increase in film thickness and variations
in refractive index. This can cause uneven surface reflectance or
cracking of an optical member. In the case that most of the
1,4-cyclohexylene group in the polyimide has the trans form, the
polyimide having a thickness of 100 nm or less has smaller
variations in thickness or refractive index resulting from moisture
absorption. This causes smaller variations in the optical
properties of an optical member according to an embodiment of the
present invention. This is probably because the
trans-1,4-cyclohexylene group in the polyimide can be stacked on
top of each other and thereby prevent water intrusion.
[0066] The polyimide in R.sub.2 in which most of the
1,4-cyclohexylene group has the trans form is produced by using a
diamine only having the trans-1,4-cyclohexylene group as a monomer.
The diamine is produced by the purification of a mixture of
structural isomers. The diamine only having the
trans-1,4-cyclohexylene group can be isolated from a mixture of
structural isomers by the recrystallization of only a
high-crystallinity trans form in a solvent, distillation under
reduced pressure utilizing different boiling points of the isomers,
extraction or washing utilizing different solubilities of the
isomers in a particular solvent, or chromatography.
[0067] However, it is difficult to completely isolate the diamine
only having the trans-1,4-cyclohexylene group by these methods, and
a small amount of diamine having the cis-1,4-cyclohexylene group
remains. Thus, isolation conditions must be optimized or isolation
procedures must be repeatedly performed so that most of the
1,4-cyclohexylene group has the trans form.
[0068] It is desirable that the 1,4-cyclohexylene group in the main
chain of R.sub.2 in the general formula (1) contain 90% by mole or
more, preferably 93% by mole or more and 100% by mole or less, of
the trans-1,4-cyclohexylene group. More specifically, the trans/cis
ratio of the 1,4-cyclohexylene group in the polyimide may be at
least 9/1 (mol/mol). The trans/cis ratio lower than 9/1 results in
insufficient prevention of water intrusion and a marked increase in
film thickness. Thus, the trans/cis ratio of the 1,4-cyclohexylene
group in the diamine having the 1,4-cyclohexylene group
corresponding to the polyimide skeleton can also be at least 9/1
(mol/mol).
[0069] The polyimide is synthesized by the polyaddition reaction
between the diamine represented by the general formula (3) in which
most of the 1,4-cyclohexylene group has the trans form and the acid
dianhydride represented by the general formula (4) and a
dehydration condensation reaction (imidization reaction). Thus, the
type of tetravalent organic group of R.sub.1 in the general formula
(1) is determined in accordance with the type of the acid
dianhydride represented by the following general formula (4):
##STR00013##
[0070] wherein R.sub.1 denotes the tetravalent organic group.
[0071] The R.sub.1 can be a tetravalent organic group represented
by any of the following general formulae (7) to (11).
##STR00014##
[0072] Examples of the acid dianhydride used in the synthesis of
polyimides include, but are not limited to, aromatic acid
dianhydrides, such as pyromellitic acid anhydride, 3,3'-biphthalic
acid anhydride, 3,4'-biphthalic acid anhydride,
3,3',4,4'-benzophenonetetracarboxylic acid dianhydride,
3,3',4,4'-diphenylsulfonetetracarboxylic acid dianhydride,
4,4'-(hexafluoroisopropylidene)diphthalic acid anhydride, and
4,4'-oxydiphthalic acid dianhydride, and aliphatic acid
dianhydrides, such as meso-butane-1,2,3,4-tetracarboxylic acid
dianhydride, 1,2,3,4-cyclobutanetetracarboxylic acid dianhydride,
1,2,3,4-cyclopentanetetracarboxylic acid dianhydride,
1,2,4,5-cyclohexanetetracarboxylic acid dianhydride,
bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride,
bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic acid dianhydride,
bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic acid dianhydride,
5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic
anhydride, and
4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicar-
boxylic anhydride. In order to improve the solubility, coating
performance, and transparency of polyimides, the acid dianhydride
may be 3,3',4,4'-diphenylsulfonetetracarboxylic acid dianhydride,
4,4'-(hexafluoroisopropylidene)diphthalic acid anhydride,
meso-butane-1,2,3,4-tetracarboxylic acid dianhydride,
bicyclo[2.2.2]octane-2,3,5,6-tetracarboxylic acid dianhydride,
bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic acid dianhydride,
5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic
anhydride, or
4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicar-
boxylic anhydride.
[0073] In addition to the diamine in which most of the
1,4-cyclohexylene group has the trans form, one or more other
diamines may be used in the polymerization. In order to achieve
high adhesion to an inorganic substrate, such as glass, and a low
refractive index, a diamine represented by the general formula (12)
may be used.
##STR00015##
[0074] wherein R.sub.11 to R.sub.14 independently denote a hydrogen
atom, a phenyl group, or an alkyl, alkenyl, or alkynyl group having
1 to 4 carbon atoms, R.sub.11 to R.sub.14 may be the same or
different, R.sub.15 and R.sub.16 independently denote a phenylene
group or an alkylene group having 1 to 4 carbon atoms, R.sub.15 and
R.sub.16 may be the same or different, and n denotes an integer in
the range of 0 to 6.
[0075] Examples of the alkyl group having 1 to 4 carbon atoms
include, but are not limited to, a methyl group, an ethyl group, a
propyl group, an isopropyl group, a butyl group, an isobutyl group,
a sec-butyl group, and a tert-butyl group. Examples of the alkenyl
group include, but are not limited to, an ethenyl group and an
allyl group. Examples of the alkynyl group include, but are not
limited to, an ethynyl group and a propargyl group. Examples of the
alkylene group having 1 to 4 carbon atoms include, but are not
limited to, a methylene group, an ethylene group, an ethylidene
group, a propylene group, an isopropylidene group, and a butylene
group.
[0076] Specific examples of the diamine represented by the general
formula (12) include, but are not limited to, organosiloxane
diamines. Examples of the organosiloxane diamines include, but are
not limited to, diamines having a diorganosiloxane group, such as
1,3-bis(3-aminopropyl)tetramethyldisiloxane,
1,4-bis(3-aminopropyldimethylsilyl)benzene, and dimethylsiloxane
oligomers having an amino group at both ends.
[0077] Polyimides having an organosiloxane group through an
organosiloxane diamine have higher transparency, a lower refractive
index, and narrower optical dispersion than polyimides only having
a hydrocarbon group. Polyimides only having an organosiloxane group
are highly hydrophobic and have a low Tg because of their flexible
structure. Films formed of such polyimides are therefore brittle.
However, a combined use of a repeating unit having the
trans-1,4-cyclohexylene group and a repeating unit having the
organosiloxane group can provide a polyimide having a low
refractive index and narrow optical dispersion without lowering the
Tg of the polyimide. The combined use can also impart high
solubility in organic solvents to the polyimide. The ratio of the
amount of diamine represented by the general formula (12) to the
amount of diamine represented by the general formula (3) used in
the reaction described above may be 0.05 or more and 1 or less
(mol/mol). The ratio of the amount of acid dianhydride represented
by the general formula (4) to the total amount of diamine
represented by the general formula (3) and diamine represented by
the general formula (12) used in the reaction described above may
be 0.94 or more and 1.06 or less (mol/mol). If these ratios fall
outside these ranges, the polymerization proceeds insufficiently,
and an amino group or a carboxy group remains at an end of the
polyimide, possibly causing moisture absorption or coloring of the
polyimide.
[0078] Examples of a third diamine for use in the synthesis of the
polyimide other than diamines in which most of the
1,4-cyclohexylene group has the trans form include, but are not
limited to, aromatic diamines, such as m-phenylenediamine,
p-phenylenediamine, 3,4'-diaminodiphenylmethane,
4,4'-diaminodiphenylmethane,
4,4'-diamino-3,3'-dimethyldiphenylmethane, o-tolidine, m-tolidine,
4,4'-diaminobenzophenone, 1,1-bis(4-aminophenyl)cyclohexane,
3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether,
1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene,
2,2-bis[4-(4-aminophenoxyl)phenyl]propane,
4,4'-bis(4-aminophenoxy)biphenyl,
bis[4-(4-aminophenoxyl)phenyl]sulfone,
4,4'-bis(3-aminophenoxy)biphenyl,
bis[4-(4-aminophenoxyl)phenyl]sulfone,
9,9-bis(4-aminophenyl)fluorene,
9,9-bis(4-amino-3-methylphenyl)fluorene,
9,9-bis(4-amino-3-fluorophenyl)fluorene,
2,2-bis(4-aminophenyl)hexafluoropropane,
2,2-bis(3-aminophenyl)hexafluoropropane,
2,2-bis[4-(4-aminophenoxyl)phenyl]hexafluoropropane, and
2,2'-bis(trifluoromethyl)benzidine. Polyimides produced by the
copolymerization with a diamine having an aromatic group can have a
refractive index in the range of 1.5 to 1.7.
[0079] In particular, a combination with a diamine having a
1,4-cyclohexylene group and/or a diamine having an organosiloxane
group allows wide control of the refractive index. Thus,
4,4'-bis(3-aminophenoxy)biphenyl, 9,9-bis(4-aminophenyl)fluorene,
9,9-bis(4-amino-3-methylphenyl)fluorene, and
9,9-bis(4-amino-3-fluorophenyl)fluorene can be used.
[0080] Diamines having a linear or branched aliphatic group, such
as 1,4-diaminobutane, 1,5-diaminopentane, and
1,3-cyclohexanediamine unfavorably reduce the Tg of the
polyimide.
[0081] The refractive index ni of the polyimide layer 2, the
refractive index nb of the substrate 1, and the refractive index ns
of the low-refractive index layer 3 can satisfy the relationship of
nb.gtoreq.ni.gtoreq.ns. The refractive index ns of the
low-refractive index layer 3 may continuously increase from the top
toward the substrate. In this case, the refractive index ns of the
low-refractive index layer 3 is considered as the refractive index
on the substrate side. A diamine only having the
trans-1,4-cyclohexylene group may be used in combination with 90%
by mole or less of another diamine within the refractive index
range described above.
[0082] The amount of the third diamine may be 50% by mole or less
of the total amount of diamine represented by the general formula
(3) and/or diamine represented by the general formula (12) and the
third diamine used in the reaction described above. The amount of
the third diamine larger than 50% by mole may result in low
transparency or an excessively high refractive index.
[0083] A method for manufacturing an optical member according to an
embodiment of the present invention is a method for manufacturing
an optical member including a laminated body that can reduce the
reflection of light formed on a substrate surface. This method
includes
[0084] 1) purifying a diamine represented by the following general
formula (3) such that a 1,4-cyclohexylene group in the main chain
of R.sub.2 in the general formula (3) contains 90% by mole or more
of a trans-1,4-cyclohexylene group,
[Chem. 18]
H.sub.2N--R.sub.2--NH.sub.2 (3)
[0085] wherein R.sub.2 denotes a divalent organic group having one
or two or more 1,4-cyclohexylene groups in the main chain,
[0086] 2) producing a polyimide containing a repeating unit
represented by the following general formula (1) by the reaction of
the purified diamine with an acid dianhydride represented by the
following general formula (4) in a solvent,
##STR00016##
[0087] wherein R.sub.1 denotes a tetravalent organic group,
##STR00017##
[0088] wherein R.sub.1 and R.sub.2 are as described above,
[0089] 3) applying a solution containing the polyimide to the
substrate or a thin film formed on the substrate, and
[0090] 4) drying and/or firing the applied solution containing the
polyimide at 100.degree. C. or more and 250.degree. C. or less to
form a polyimide layer.
[0091] The method for manufacturing an optical member according to
an embodiment of the present invention may further include
[0092] 5) applying a precursor sol of aluminum oxide to the
outermost surface of the laminated body,
[0093] 6) drying and/or firing the applied precursor sol of
aluminum oxide at 100.degree. C. or more and 250.degree. C. or less
to form an aluminum oxide film, and
[0094] 7) immersing the aluminum oxide film in hot water to form a
textured structure formed of plate crystals mainly composed of
aluminum oxide.
[0095] A method for producing a polyimide according to an
embodiment of the present invention will be described below.
[0096] In the synthesis of a polyimide, a diamine having one or two
or more 1,4-cyclohexylene groups represented by the general formula
(3) is purified by the method described above to produce a diamine
in which most of the 1,4-cyclohexylene group has the trans form.
The resulting diamine is reacted with an acid dianhydride
represented by the general formula (4) in a solvent to produce a
polyamic acid solution. In addition to the diamine in which most of
the 1,4-cyclohexylene group has the trans form, a diamine
represented by the general formula (12) and/or the third diamine,
such as an aromatic diamine, may also be reacted with an acid
dianhydride represented by the general formula (4) in a solvent to
produce a polyamic acid solution. The imidization of the resulting
polyamic acid in a solution yields a polyimide. The polyimide may
be isolated by removing the solvent.
[0097] The ratio of the amount of acid dianhydride represented by
the general formula (4) to the amount of diamine used in the
reaction described above can be 0.94 or more and 1.06 or less
(mol/mol).
[0098] The solvent for use in the synthesis of the polyimide may be
any solvent that can dissolve the polyamic acid and the polyimide,
for example, an aprotic polar solvent, such as
N,N-dimethylformamide, N,N-dimethylacetamide, or
N-methyl-2-pyrrolidone.
[0099] The imidization converts the polyamic acid into the
polyimide by cyclodehydration. The imidization may be performed by
heating at 25.degree. C. or more and 120.degree. C. or less in the
presence of a tertiary amine, such as pyridine or triethylamine,
and acetic anhydride or by azeotrope with xylene at 150.degree. C.
or more.
[0100] After the polyimide synthesis, the polyimide solution may be
directly used in the latter process. Alternatively, the polyimide
solution may be poured into a poor solvent to precipitate a
polyimide powder, which is filtered off, dried, and dissolved in a
solvent again. In the latter case, precipitation in an alcohol can
remove unreacted monomers and various chemicals used in the
imidization. The polyimide solution or the isolated polyimide
powder may be dried at 50.degree. C. or more and 150.degree. C. or
less in the atmosphere or under reduced pressure to remove the
solvent.
[0101] The imidization rate of the polyimide is preferably 90% or
more, more preferably 93% or more and 99% or less. The imidization
rate lower than 90% tends to result in an increase in the water
absorption rate of the polyimide, causing variations in film
thickness or refractive index.
[0102] A polyimide soluble in organic solvents according to an
embodiment of the present invention may be dissolved again in an
organic solvent before use. Examples of the organic solvent
include, but are not limited to, ketones, such as 2-butanone,
methyl isobutyl ketone, cyclopentanone, and cyclohexanone; esters,
such as ethyl acetate, n-butyl acetate, ethylene glycol monomethyl
ether acetate, propylene glycol monomethyl ether acetate, ethyl
lactate, and .gamma.-butyrolactone; ethers, such as
tetrahydrofuran, dioxane, diisopropyl ether, dibutyl ether,
cyclopentyl methyl ether, and diglyme; aromatic hydrocarbons, such
as toluene, xylene, and ethylbenzene; chlorinated hydrocarbons,
such as chloroform, methylene chloride, and tetrachloroethane; and
others, such as N-methylpyrrolidone, N,N-dimethylformamide,
N,N-dimethylacetamide, dimethyl sulfoxide, and sulfolane.
[0103] In particular, a polyimide soluble in organic solvents
according to an embodiment of the present invention may be
dissolved in at least two solvents selected from
N,N-dimethylacetamide, cyclopentanone, cyclohexanone, propylene
glycol monomethyl ether acetate, ethyl lactate, and
.gamma.-butyrolactone at a concentration of 5% by weight or
more.
[0104] It is desirable that a repeating unit having the
trans-1,4-cyclohexylene group in the repeating unit represented by
the general formula (1) in a polyimide according to an embodiment
of the present invention be 25% by mole or more and 90% by mole or
less, preferably 30% by mole or more and 95% by mole or less, of
all the repeating units of the polyimide. At less than 25% by mole,
the refractive index cannot be reduced without lowering the Tg of
the polyimide. At more than 90% by mole, an organosiloxane group
cannot be sufficiently introduced.
[0105] It is desirable that a repeating unit having an
organosiloxane group represented by the general formula (5) in a
polyimide according to an embodiment of the present invention be 5%
by mole or more and 50% by mole or less, preferably 10% by mole or
more and 40% by mole or less, of all the repeating units of the
polyimide. Within these ranges, the refractive index and the
optical dispersion of the polyimide can be markedly reduced, and
the solubility of the polyimide in organic solvents can be
improved.
[0106] A method for forming a polyimide layer 2 according to an
embodiment of the present invention will be described below.
[0107] In the formation of the polyimide layer 2 using a polyimide
synthesized as described above, a solution containing the
synthesized polyimide is applied to a substrate or a thin film
formed on the substrate and is dried or fired at 100.degree. C. or
more and 250.degree. C. or less.
[0108] A polyimide solution produced in the polyimide synthesis may
be directly used in the formation of the polyimide layer 2.
Alternatively, the polyimide solution may be poured into a poor
solvent to precipitate a polyimide powder, which is filtered off,
dried, and dissolved in a solvent again. In the latter case,
reprecipitation in an alcohol can remove unreacted monomers and
various chemicals used in the imidization.
[0109] Examples of the solvent in which the precipitated polyimide
powder is to be dissolved include, but are not limited to, ketones,
such as 2-butanone, methyl isobutyl ketone, cyclopentanone, and
cyclohexanone; esters, such as ethyl acetate, n-butyl acetate,
ethylene glycol monomethyl ether acetate, propylene glycol
monomethyl ether acetate, ethyl lactate, and .gamma.-butyrolactone;
ethers, such as tetrahydrofuran, dioxane, diisopropyl ether,
dibutyl ether, cyclopentyl methyl ether, and diglyme; aromatic
hydrocarbons, such as toluene, xylene, and ethylbenzene;
chlorinated hydrocarbons, such as chloroform, methylene chloride,
and tetrachloroethane; and others, such as N-methylpyrrolidone,
N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide,
and sulfolane. Furthermore, alcohols, such as 1-butanol, methyl
cellosolve, and methoxypropanol may also be used.
[0110] It is desirable that the polyimide be soluble in organic
solvents.
[0111] The polyimide solution can be applied by a known method,
such as dipping, spin coating, spraying, printing, or flow coating,
or a combination thereof.
[0112] The drying and/or firing of the polyimide solution is
principally performed to remove the solvent. The polyimide solution
can be heated for approximately five minutes to two hours. The
polyimide solution may be heated by light, radiation, or
electromagnetic wave irradiation using a circulating hot-air oven,
a muffle furnace, infrared rays, or a microwave.
[0113] It is desirable that the polyimide content of a polyimide
layer according to an embodiment of the present invention be 70% by
weight or more, preferably 80% by weight or more and 100% by weight
or less.
[0114] The polyimide layer 2 may contain a component other than the
polyimide provided that the component does not impair the optical
properties, transparency, heat resistance, and water-fastness of
the polyimide. The amount of component other than the polyimide is
less than 20 parts by weight per 100 parts by weight of the
polyimide. Twenty parts by weight or more of the component other
than the polyimide may impair the transparency, the film strength,
and the film thickness uniformity of the polyimide.
[0115] Examples of the component other than the polyimide include,
but are not limited to, silane coupling agents and phosphates for
improving adhesion; thermosetting resins, photocurable resins, and
cross-linkers, such as epoxy resin, melamine resin, and acrylic
resin, for improving the solvent resistance of the polyimide layer
2; and small amounts of inorganic fine particles, such as
SiO.sub.2, TiO.sub.2, ZrO.sub.2, SiO.sub.2, ZnO, MgO, and
Al.sub.2O.sub.3, for controlling the refractive index or the film
hardness of the polyimide. It is desirable that the amount of
component other than the polyimide be 30% by weight or less,
preferably 0% by weight or more and 20% by weight or less.
[0116] The low-refractive index layer 3 formed on the polyimide
layer 2 may have a refractive index of 1.4 or less and may be
composed of a metal oxide, a metal halide, or a fluoropolymer. The
low-refractive index layer 3 formed of a porous layer mainly
composed of silicon oxide, magnesium fluoride, or a fluorinated
acrylic polymer or a layer having a fine textured structure mainly
composed of silicon oxide, aluminum oxide, or a transparent polymer
can have a higher antireflection effect.
[0117] An optical member according to an embodiment of the present
invention may have a textured structure on the outermost surface of
the laminated body. The textured structure may be formed of plate
crystals mainly composed of aluminum oxide.
[0118] FIG. 2 is a schematic view of an optical member according to
another embodiment of the present invention. In FIG. 2, the optical
member according to this embodiment of the present invention
includes a polyimide layer 2 and a layer 4 having a fine textured
structure, on a surface of a substrate 1 in this order. The
outermost surface has a fine textured structure 5.
[0119] The fine textured structure 5 of the layer 4 having a fine
textured structure in a laminated body 9 can be formed of plate
crystals of aluminum oxide. The plate crystals of aluminum oxide
refer to plate crystals deposited and grown on a surface layer of a
film mainly composed of aluminum oxide by immersing the film into
hot water to peptize the surface layer.
[0120] As illustrated in FIG. 3, the refractive index of the layer
4 having a fine textured structure may continuously increase from
the top toward the substrate in a linear (a) or curved (b or c)
manner. The layer 4 having a refractive index that continuously
increases from the top toward the substrate has a higher
reflectance-reduction effect than a plurality of layers in which
the refractive index increases layer by layer from the top.
[0121] The fine textured structure is formed of crystals mainly
composed of an oxide of aluminum, a hydrate of an oxide of
aluminum, or a hydroxide of aluminum. The textured structure is
preferably formed of crystals containing 70% by mole or more, more
preferably 90% by mole or more, of an oxide of aluminum, a hydrate
of an oxide of aluminum, or a hydroxide of aluminum. These crystals
are herein referred to as plate crystals. In particular, the plate
crystals can be formed of boehmite. Since the textured structure 5
having fine ridges is formed of plate crystals, the plate crystals
are disposed at a particular angle with respect to the substrate
surface to increase the height and reduce the intervals of the fine
ridges. An oxide of aluminum, a hydroxide of aluminum, and hydrates
of these compounds are herein collectively referred to as aluminum
oxide. One or more oxide layers formed of aluminum oxide alone or
70% by mole or more, preferably 90% by mole or more, of aluminum
oxide and ZrO.sub.2, SiO.sub.2, TiO.sub.2, ZnO, or MgO are
hereinafter referred to as a layer mainly composed of aluminum
oxide.
[0122] In FIG. 4, a substrate 1, such as a plate, a film, or a
sheet, has a flat surface. It is desirable that plate crystals be
disposed such that the average of the angles 81 between the slopes
6 of the plate crystals and the substrate surface is 45.degree. or
more and 90.degree. or less, preferably 60.degree. or more and
90.degree. or less.
[0123] In FIG. 5, a substrate 1 has a two-dimensionally or
three-dimensionally curved surface. It is desirable that plate
crystals be disposed such that the average of the angles .theta.2
between the slopes 7 of the plate crystals and the tangent line 8
of the substrate surface is 45.degree. or more and 90.degree. or
less, preferably 60.degree. or more and 90.degree. or less. If the
angles .theta.1 and .theta.2 are more than 90.degree., their
supplementary angles are considered as the angles .theta.1 and
.theta.2.
[0124] The thickness of the layer 4 having a fine textured
structure is preferably 20 nm or more and 1000 nm or less, more
preferably 50 nm or more and 1000 nm or less. The thickness of the
layer 4 having a fine textured structure in the range of 20 to 1000
nm results in effective antireflection performance of the fine
textured structure, eliminates the possibility of reduction in the
mechanical strength of the fine ridges, and provides advantages in
the manufacturing costs of the fine textured structure. The
thickness of the layer 4 having a fine textured structure in the
range of 50 to 1000 nm can further improve antireflection
performance.
[0125] The surface density of the fine ridges is also important and
can be represented by the average surface roughness Ra' and the
surface area ratio Sr, which is defined later. The average surface
roughness Ra' can be determined by applying the measurement of
center-line average roughness to the surface. The average surface
roughness Ra' is 5 nm or more, preferably 10 nm or more, more
preferably 15 nm or more and 100 nm or less. The surface area ratio
Sr is 1.1 or more, preferably 1.15 or more, more preferably 1.2 or
more and 3.5 or less.
[0126] One of methods for evaluating the fine textured structure is
the observation of the fine textured surface with a scanning probe
microscope. The average surface roughness Ra' and the surface area
ratio Sr can be determined through this observation. As mentioned
above, the average surface roughness Ra' (nm) can be determined by
three-dimensionally applying the measurement of center-line average
roughness Ra defined in JIS B 0601 to a surface to be measured. The
average surface roughness Ra' refers to "the average of the
absolute values of deviations of specified planes from the
reference plane" and is expressed by the following equation
(1):
[ Math . 1 ] ##EQU00001## Ra ' = 1 S 0 .intg. Y B Y T .intg. X L X
R F ( X , Y ) - Z 0 X Y ( 1 ) ##EQU00001.2##
[0127] wherein
[0128] Ra': average surface roughness (nm);
[0129] S.sub.0: the area of a surface to be measured, on the
assumption that the surface is flat,
|XR-X.sub.L|.times.|Y.sub.T-Y.sub.B|;
[0130] F(X,Y): a height at a point of measurement (X,Y), wherein X
denotes the x-coordinate, and Y denotes the y-coordinate;
[0131] X.sub.L to X.sub.R: the range of the surface to be measured
on the x-coordinate;
[0132] Y.sub.B to Y.sub.T: the range of the surface to be measured
on the y-coordinate; and
[0133] Z.sub.0: the average height of the surface to be
measured.
[0134] The surface area ratio Sr can be determined by Sr=S/S.sub.0
wherein S.sub.0 denotes the area of a surface to be measured, on
the assumption that the surface is flat, and S denotes the actual
surface area of the surface to be measured. The actual surface area
of the surface to be measured is determined as described below.
First, the surface to be measured is divided into minute triangles
defined by adjacent three data points (A, B, and C). The area
.DELTA.S of each of the minute triangles is then determined
utilizing a vector product.
.DELTA.S(.DELTA.ABC)=[s(s-AB)(s-BC)(s-AC)]0.5, wherein AB, BC, and
AC denote the lengths of their respective sides. s.ident.0.5
(AB+BC+AC)]. The surface area S is the sum total of .DELTA.S's.
When the surface density of the fine ridges is such that Ra' is 5
nm or more and Sr is 1.1 or more, the textured structure can
exhibit antireflection. Ra' of 10 nm or more and Sr of 1.15 or more
result in a higher antireflection effect. When Ra' is 15 nm or more
and Sr is 1.2 or more, the fine textured structure is actually
useful. When Ra' is 100 nm or more and Sr is 3.5 or more, however,
scattering due to the textured structure predominates over the
antireflection effect, resulting in poor antireflection
performance.
[0135] In the case that the layer 4 having a fine textured
structure is mainly composed of aluminum oxide, a metal film made
of metallic Al alone or a metal film made of metallic Al and
metallic Zn or metallic Mg is formed on the polyimide layer 2.
Immersion in hot water at 50.degree. C. or more or exposure to
water vapor forms the textured structure 5 on the metal surface by
hydration, dissolution, and reprecipitation. Likewise, hot-water
immersion or water vapor exposure of a layer mainly composed of
aluminum oxide formed on a layer 2 mainly composed of organic resin
can also precipitate the fine textured structure 5 on the surface.
The layer mainly composed of aluminum oxide can be formed by a
known gas phase method, such as chemical vapor deposition (CVD) or
physical vapor deposition (PVD), a known liquid phase method, such
as a sol-gel method, or a known hydrothermal synthesis using an
inorganic salt. In such a method involving the formation of plate
crystals of aluminum oxide, an amorphous aluminum oxide layer may
remain under the textured structure 5 in the layer 4 having a fine
textured structure.
[0136] A gel film formed by the application of a sol-gel coating
liquid containing aluminum oxide can be treated with hot water to
grow alumina plate crystals. This method can form a uniform
antireflection layer on a large-area or nonplanar substrate.
[0137] The raw material of the gel film formed by the application
of a sol-gel coating liquid containing aluminum oxide contains an
Al compound alone or an Al compound and at least one compound
selected from Zr, Si, Ti, Zn, and Mg compounds. Metal alkoxides and
salt compounds, such as chlorides and nitrates, may be used as the
raw materials for Al.sub.2O.sub.3, ZrO.sub.2, SiO.sub.2, TiO.sub.2,
ZnO, and MgO. In particular, metal alkoxides may be used as
ZrO.sub.2, SiO.sub.2, and TiO.sub.2 raw materials because of their
excellent film-forming properties.
[0138] Examples of the aluminum compound include, but are not
limited to, aluminum ethoxide, aluminum isopropoxide,
aluminum-n-butoxide, aluminum-sec-butoxide, aluminum-tert-butoxide,
and aluminum acetylacetonate, oligomers thereof, aluminum nitrate,
aluminum chloride, aluminum acetate, aluminum phosphate, aluminum
sulfate, and aluminum hydroxide.
[0139] Specific examples of the zirconium alkoxide include, but are
not limited to, zirconium tetramethoxide, zirconium tetraethoxide,
zirconium tetra-n-propoxide, zirconium tetraisopropoxide, zirconium
tetra-n-butoxide, and zirconium tetra-t-butoxide.
[0140] The silicon alkoxide may be represented by the general
formula Si(OR).sub.4. R's may be the same or different lower alkyl
groups, such as a methyl group, an ethyl group, a propyl group, an
isopropyl group, a butyl group, and an isobutyl group.
[0141] Examples of the titanium alkoxide include, but are not
limited to, tetramethoxytitanium, tetraethoxytitanium,
tetra-n-propoxytitanium, tetraisopropoxytitanium,
tetra-n-butoxytitanium, and tetraisobutoxytitanium.
[0142] Examples of the zinc compound include, but are not limited
to, zinc acetate, zinc chloride, zinc nitrate, zinc stearate, zinc
oleate, and zinc salicylate, particularly zinc acetate and zinc
chloride.
[0143] Examples of the magnesium compound include, but are not
limited to, magnesium alkoxides, such as dimethoxymagnesium,
diethoxymagnesium, dipropoxymagnesium, and dibutoxymagnesium,
magnesium acetylacetonate, and magnesium chloride.
[0144] The organic solvent may be any organic solvent that does not
induce the gelation of the raw materials described above, such as
alkoxides. Examples of the organic solvent include, but are not
limited to, alcohols, such as methanol, ethanol, 2-propanol,
butanol, pentanol, ethylene glycol, and ethylene
glycol-mono-n-propyl ether; aliphatic or alicyclic hydrocarbons,
such as n-hexane, n-octane, cyclohexane, cyclopentane, and
cyclooctane; aromatic hydrocarbons, such as toluene, xylene, and
ethylbenzene; esters, such as ethyl formate, ethyl acetate, n-butyl
acetate, ethylene glycol monomethyl ether acetate, ethylene glycol
monoethyl ether acetate, and ethylene glycol monobutyl ether
acetate; ketones, such as acetone, methyl ethyl ketone, methyl
isobutyl ketone, and cyclohexanone; ethers, such as
dimethoxyethane, tetrahydrofuran, dioxane, and diisopropyl ether;
chlorinated hydrocarbons, such as chloroform, methylene chloride,
carbon tetrachloride, and tetrachloroethane; and aprotic polar
solvents, such as N-methylpyrrolidone, dimethylformamide,
dimethylacetamide, and ethylene carbonate. Among the solvents
described above, alcohols can provide particularly excellent
solution stability.
[0145] Among the alkoxide raw materials, aluminum, zirconium, and
titanium alkoxides have particularly high reactivity to water and
are abruptly hydrolyzed by the action of moisture in the air or the
addition of water, producing turbidity and precipitation in the
solution. Aluminum salt compounds, zinc salt compounds, and
magnesium salt compounds are difficult to dissolve in organic
solvents and provide low solution stability. To avoid these
problems, a stabilizer may be added to stabilize the solution.
[0146] Examples of the stabilizer include, but are not limited to,
.beta.-diketone compounds, such as acetylacetone,
dipivaloylmethane, trifluoroacetylacetone, hexafluoroacetylacetone,
benzoylacetone, and dibenzoylmethane; .beta.-ketoester compounds,
such as methyl acetoacetate, ethyl acetoacetate, allyl
acetoacetate, benzyl acetoacetate, iso-propyl acetoacetate,
tert-butyl acetoacetate, iso-butyl acetoacetate, 2-methoxyethyl
acetoacetate, and 3-keto-methyl-n-valerate; and alkanolamines, such
as monoethanolamine, diethanolamine, and triethanolamine. The molar
ratio of the stabilizer to alkoxide or a salt compound can be
approximately one. After the addition of the stabilizer, a catalyst
can be added to promote part of reactions to form a desired
precursor. Examples of the catalyst include, but are not limited
to, nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid,
acetic acid, and ammonia. Examples of a method for applying the
sol-gel coating liquid to form a film include, but are not limited
to, known methods, such as dipping, spin coating, spraying,
printing, and flow coating, and combinations of these methods.
[0147] The application of the sol-gel coating liquid is preferably
followed by heat treatment at 100.degree. C. or more and
230.degree. C. or less, more preferably 120.degree. C. or more and
200.degree. C. or less. Although a higher heat-treatment
temperature results in a greater density of the film, a
heat-treatment temperature higher than 230.degree. C. may cause
damage, such as deformation, to the substrate. The heating time
depends on the heating temperature and may be 10 minutes or
more.
[0148] The gel film after drying or heat-treatment is immersed in
hot water to precipitate plate crystals mainly composed of aluminum
oxide, forming fine ridges on the outermost surface. Immersion in
hot water peptizes the surface layer of the gel film containing
aluminum oxide and elutes part of the components of the gel film.
Owing to difference in hot-water solubility between hydroxides,
plate crystals mainly composed of aluminum oxide are deposited and
grown on the surface layer of the gel film. The temperature of hot
water can range from 40.degree. C. to 100.degree. C. The hot-water
treatment time may range from approximately 5 minutes to 24
hours.
[0149] In the hot-water treatment of a gel film containing aluminum
oxide as the main component and an oxide, such as TiO.sub.2,
ZrO.sub.2, SiO.sub.2, ZnO, or MgO, as a different component,
crystallization is related to difference in hot-water solubility
between the components. Unlike the hot-water treatment of a film
formed of aluminum oxide alone, therefore, the ratios of the
inorganic components can be altered to control the size of plate
crystals. This allows the shape of fine ridges formed of the plate
crystals to be widely controlled within the range described above.
Use of ZnO as an accessory component allows eutectic
crystallization with aluminum oxide. This allows further wide
control of refractive index, thereby achieving excellent
antireflection performance.
[0150] Examples of the material of the substrate 1 include, but are
not limited to, glass, resin, glass mirrors, and resin mirrors.
Representative examples of the resin substrate include, but are not
limited to, films and formed products made of thermoplastic resins,
such as polyester, cellulose triacetate, cellulose acetate,
poly(ethylene terephthalate), polypropylene, polystyrene,
polycarbonate, polysulfone, polyacrylate, polymethacrylate, ABS
resin, poly(phenylene oxide), polyurethane, polyethylene,
polycycloolefin, and poly(vinyl chloride); and cross-linked films
and cross-linked formed products made of various thermosetting
resins, such as unsaturated polyester resin, phenolic resin,
cross-linking polyurethane, cross-linking acrylic resin, and
cross-linking saturated polyester resin. Specific examples of the
glass include, but are not limited to, non-alkali glass and
aluminosilicate glass. A substrate for use in the present invention
may be any substrate, such as a plate, a film, or a sheet, that can
have a shape for each intended use and may be a substrate having a
two- or three-dimensionally curved surface. The thickness of the
substrate is generally, but is not limited to, 5 mm or less.
[0151] An optical transparent member according to an embodiment of
the present invention may further include another functional layer.
For example, a hard coat layer may be disposed on the layer having
a fine textured structure to improve the film hardness. A water
repellent layer, for example, formed of fluoroalkylsilane or
alkylsilane may be formed to prevent the adhesion of dirt. An
adhesive layer or a primer layer may be formed to improve the
adhesion between the substrate and the polyimide layer.
EXAMPLES
[0152] The present invention will be further described in the
following examples. However, the present invention is not limited
to these examples. Optical films having fine ridges prepared in
examples and comparative examples were evaluated as described
below.
(1) Purification of 4,4'-methylenebis(aminocyclohexane)
[0153] Hexane was gradually added under reflux to 200 g of
4,4'-methylenebis(aminocyclohexane) (hereinafter referred to as
DADCM, manufactured by Tokyo Chemical Industry Co., Ltd.).
4,4'-methylenebis(aminocyclohexane) was completely dissolved in
hexane. After heating was completed, the solution was left to stand
for several (two to four) days at room temperature (20.degree. C.
to 25.degree. C.). A precipitate was filtered off and dried under
vacuum to yield 61 g of white purified DADCM in a solid state.
.sup.1H-NMR spectrum showed that the DADCM contained 95% by mole of
trans-1,4-cyclohexylene group.
[0154] .sup.1H-NMR (DMSO-d.sub.6); .delta.0.83 (2H, m), .delta.0.97
(2H, q), .delta.1.18 (2H, m), .delta.1.60 (2H, d), .delta.1.69 (2H,
d), .delta.2.05 (2H, s), .delta.2.42 (2H, m), .delta.3.30 (4H,
b)
(2) Synthesis of Polyimides 1 to 8
[0155] A total of 0.012 mol of diamine (1) (purified DADCM or crude
DADCM), diamine (2), and diamine (3) were dissolved in
N,N-dimethylacetamide (hereinafter referred to as DMAc). 0.012 mol
of acid dianhydride was added to the diamine solution while the
diamine solution was cooled with water. DMAc was used in such an
amount that the total mass of the diamines and the acid dianhydride
was 20% by weight.
[0156] This solution was stirred at room temperature for 15 hours
to cause polymerization reaction. After the solution was diluted
with DMAc to 8% by weight, 7.4 ml of pyridine and 3.8 ml of acetic
anhydride were added. The solution was stirred at room temperature
for one hour. The solution was stirred in an oil bath at a
temperature in the range of 60.degree. C. to 70.degree. C. for four
hours. The polymerization solution was poured into methanol or a
methanol/water mixed solvent for reprecipitation. A polymer thus
reprecipitated was removed and was washed several times in methanol
or a methanol/water mixed solvent. The polymer was dried under
vacuum at 100.degree. C. to yield a white to light yellow polyimide
powder. The imidization rate was determined by measuring the
residual amount of carboxy group from a .sup.1H-NMR spectrum. Table
1 shows the compositions of polyimides 1 to 8.
TABLE-US-00001 TABLE 1 Trans-1,4- cyclohexylene Acid content
Imidization Polyimide dianhydride Diamine (1) (% by mole) Diamine
(2) Diamine (3) Yield % rate % Polyimide 1 TDA(1.0) Purified 95
PAM-E(0.1) -- 92 96 DADCM(0.9) Polyimide 2 TDA(1.0) Crude 47
PAM-E(0.1) -- 90 95 DADCM(0.9) Polyimide 3 TDA(1.0) Purified 95
BAPB(0.3) PAM-E(0.1) 94 98 DADCM(0.6) Polyimide 4 TDA(1.0) Crude 47
BAPB(0.3) PAM-E(0.1) 93 98 DADCM(0.6) Polyimide 5 BDA(1.0) Purified
95 PAM-E(0.1) -- 85 95 DADCM(0.9) Polyimide 6 BDA(1.0) Crude 47
PAM-E(0.1) -- 81 95 DADCM(0.9) Polyimide 7 6FDA(1.0) Purified 95
PAM-E(0.1) --- 89 96 DADCM(0.9) Polyimide 8 6FDA(1.0) Crude 47
PAM-E(0.1) -- 89 95 DADCM(0.9)
(Note 1)
[0157] TDA:
4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-dicar-
boxylic anhydride
[0158] BDA: meso-butane-1,2,3,4-tetracarboxylic acid
dianhydride
[0159] DADCM: 4,4'-methylenebis(aminocyclohexane)
[0160] PAM-E: dimethylsiloxane oligomer in which both ends were
modified with amine
[0161] BAPB: 4,4'-bis(4-aminophenoxy)biphenyl
[0162] 6FDA: 4,4'-(hexafluoroisopropylidene)diphthalic acid
anhydride
(Note 2)
[0163] Values in parentheses for acid dianhydride and diamines
represent the molar ratio of these compounds charged.
(Note 3)
[0164] The trans-1,4-cyclohexylene group in the purified
4,4'-methylenebis(aminocyclohexane) accounted for 95% by mole of
the 1,4-cyclohexylene group in the purified
4,4'-methylenebis(aminocyclohexane).
(3) Preparation of Polyimide Solutions 1 to 9 and 11 to 13
[0165] 2.0 to 4.0 g of a powder of each of the polyimides 1 to 8
was dissolved in 96 to 98 g of a cyclopentanone/cyclohexanone mixed
solvent to prepare polyimide solutions 1 to 9 and 11 to 13.
(4) Preparation of Polyimide Solutions 10 and 14
[0166] 2.0 g of a powder of polyimide 1 or 2 and 0.3 g of melamine
resin (trade name: Nikalac MX-706, manufactured by Nippon Carbide
Industries Co., Inc.) were dissolved in 997 g of a
cyclopentanone/cyclohexanone mixed solvent to prepare polyimide
solutions 10 and 14. Table 2 shows the polyimide solutions
prepared.
TABLE-US-00002 TABLE 2 Cross- Solid Polyimide solution Polyimide
linker content % Polyimide solution 1 Polyimide 1 -- 2% Polyimide
solution 2 Polyimide 1 -- 3% Polyimide solution 3 Polyimide 1 -- 4%
Polyimide solution 4 Polyimide 2 -- 2% Polyimide solution 5
Polyimide 2 -- 3% Polyimide solution 6 Polyimide 2 -- 4% Polyimide
solution 7 Polyimide 3 -- 2% Polyimide solution 8 Polyimide 5 -- 2%
Polyimide solution 9 Polyimide 7 -- 2% Polyimide solution 10
Polyimide 1 MX-706 2% Polyimide solution 11 Polyimide 4 -- 2%
Polyimide solution 12 Polyimide 6 -- 2% Polyimide solution 13
Polyimide 8 -- 2% Polyimide solution 14 Polyimide 2 MX-706 2%
(5) Preparation of Aluminum Oxide (Alumina (Al.sub.2O.sub.3))
Sol
[0167] 22.2 g of Al(O-sec-Bu).sub.3, 5.86 g of ethyl 3-oxobutanate,
and 4-methyl-2-pentanol were stirred until the mixture became
homogeneous. 1.62 g of 0.01 M diluted hydrochloric acid dissolved
in a 4-methyl-2-pentanol/1-ethoxy-2-propanol mixed solvent was
gradually added to the Al(O-sec-Bu).sub.3 solution and was stirred
for a short time. The solvent was finally adjusted so as to contain
49.3 g of 4-methyl-2-pentanol and 21.1 g of 1-ethoxy-2-propanol.
The solution was stirred in an oil bath at 120.degree. C. for
another three hours or more to prepare a precursor sol of aluminum
oxide.
(6) Cleaning of Substrate
[0168] Various glass substrates having a diameter of approximately
30 mm and a thickness of approximately 2 mm, both surfaces of each
of which were polished, were ultrasonically cleaned with an
alkaline detergent and isopropyl alcohol (IPA) and were dried in an
oven.
(7) Measurement of Reflectance
[0169] Reflectance was measured with an absolute reflectometer
(USPM-RU, manufactured by Olympus Co.) at a wavelength in the range
of 400 to 700 nm at an incident angle of 0.degree..
(8) Measurement of Film Thickness and Refractive Index
[0170] The film thickness and the refractive index were measured
with a spectroscopic ellipsometer (VASE, manufactured by J. A.
Woollam Japan Co., Inc.) at a wavelength in the range of 380 to 800
nm.
(9) Observation of Substrate Surface
[0171] A substrate surface treated with Pd/Pt was observed with a
field emission scanning electron microscope (FE-SEM) (S-4800,
manufactured by Hitachi High-Technologies Co.) at an accelerating
voltage of 2 kV.
Example 1
[0172] A polished and cleaned surface of glass A mainly composed of
La.sub.2O.sub.5 and having an nd of 1.77 and a .nu.d of 50 was
spin-coated with a proper amount of polyimide solution 1, 2, or 3
at 3000 to 4000 rpm. The substrate was dried at 200.degree. C. for
60 minutes to form a film made of the polyimide 1 synthesized from
purified DADCM on the substrate.
[0173] The thickness and the refractive index of the film of the
polyimide 1 were measured by ellipsometry. After the film of the
polyimide 1 was immersed in hot water at 80.degree. C. for 20
minutes, the thickness and the refractive index of the film were
measured again. FIG. 6 shows the rate of increase in film thickness
due to the immersion in hot water as a function of the initial film
thickness. The rate of increase in film thickness due to the
hot-water treatment of the film having an initial thickness of 100
nm or more ranged from 0.32% to 0.34%. The rate of increase in film
thickness due to the hot-water treatment of the film having an
initial thickness in the range of 40 to 50 nm ranged from 0.6% to
0.69%.
Comparative Example 1
[0174] The same procedures as Example 1 were performed except that
the polyimide solutions 1, 2, and 3 were replaced with the
polyimide solutions 4, 5, and 6 and that a layer was formed of the
polyimide 2 synthesized from crude DADCM.
[0175] FIG. 6 shows the rate of increase in film thickness due to
immersion in hot water as a function of the initial film thickness.
The rate of increase in film thickness due to the hot-water
treatment of the film having an initial thickness of 100 nm or more
ranged from 0.36% to 0.4%. The rate of increase in film thickness
due to the hot-water treatment of the film having an initial
thickness in the range of 40 to 50 nm ranged from 0.74% to 0.93%.
Thus, the rate of increase in film thickness due to moisture
absorption during the hot-water treatment was higher than that of
the film of the polyimide 1.
Examples 2 to 5
[0176] A polished and cleaned surface of glass A mainly composed of
La.sub.2O.sub.5 and having an nd of 1.77 and a .nu.d of 50 was
spin-coated with a proper amount of polyimide solution 7, 8, 9, or
10 at 3000 to 4000 rpm. The substrate was dried at 200.degree. C.
for 60 minutes to form a film made of the polyimide 3, 5, or 7
synthesized from purified DADCM or a film made of the polyimide 1
and a cross-linker on the substrate.
[0177] The thickness and the refractive index of each of the
polyimide films were measured by ellipsometry. After the polyimide
films were immersed in hot water at 80.degree. C. for 20 minutes,
the thickness and the refractive index of each of the films were
measured again. Table 3 shows the rate of increase in film
thickness due to the immersion in hot water relative to the initial
film thickness.
Comparative Examples 2 to 5
[0178] The same procedures as Examples 2 to 5 were performed except
that the polyimide solutions 7 to 10 were replaced with the
polyimide solutions 11 to 14 and that a film was formed of the
polyimide 4, 6, or 8 synthesized from crude DADCM or the polyimide
2 and a cross-linker.
[0179] Table 3 shows the rate of increase in film thickness due to
immersion in hot water relative to the initial film thickness. The
rates of increase in film thickness due to hot-water treatment were
higher than those of Examples 2 to 5.
TABLE-US-00003 TABLE 3 Rate of increase in Film Refractive film
thickness due Cross- thickness index to hot water Polyimide linker
(nm) (550 nm) treatment % Example 1 Polyimide 1 -- 42 1.56 0.68
Example 2 Polyimide 3 -- 43 1.60 0.50 Example 3 Polyimide 5 -- 43
1.53 0.75 Example 4 Polyimide 7 -- 43 1.55 0.55 Example 5 Polyimide
1 MX-706 44 1.56 0.57 Comparative Polyimide 2 -- 44 1.56 0.93
example 1 Comparative Polyimide 4 -- 42 1.60 0.81 example 2
Comparative Polyimide 6 -- 41 1.53 1.01 example 3 Comparative
Polyimide 8 -- 40 1.55 0.85 example 4 Comparative Polyimide 2
MX-706 46 1.56 0.84 example 5
Examples 6 and 7
[0180] A polished and cleaned surface of glass A mainly composed of
La.sub.2O.sub.5 and having an nd of 1.77 and a .nu.d of 50 was
spin-coated with a proper amount of polyimide solution 1 or 7 at
3000 to 4000 rpm. The substrate was dried at 200.degree. C. for 60
minutes to form a film made of the polyimide 1 or 3 synthesized
from purified DADCM on the substrate. The thickness and the
refractive index of each of the polyimide films were measured by
ellipsometry. After the polyimide films were left to stand at
60.degree. C. and 90% RH for 250 hours, the thickness and the
refractive index of each of the films were measured again. Table 4
shows the rate of increase in film thickness due to high
temperature and high humidity relative to the initial film
thickness.
Comparative Examples 6 and 7
[0181] The same procedures as Examples 6 and 7 were performed
except that the polyimide solutions 1 and 7 were replaced with the
polyimide solutions 4 and 11 and that a layer was formed of the
polyimide 2 or 4 synthesized from crude DADCM.
[0182] Table 4 shows the rate of increase in film thickness due to
high temperature and high humidity relative to the initial film
thickness. The rates of increase in film thickness due to high
temperature and high humidity were higher than those of Examples 6
and 7.
TABLE-US-00004 TABLE 4 Rate of increase in Film Refractive film
thickness due Cross- thickness index to hot water Polyimide linker
(nm) (550 nm) treatment % Example 6 Polyimide 1 -- 43 1.56 2.60
Example 7 Polyimide 3 -- 43 1.60 2.65 Comparative Polyimide 2 -- 43
1.56 3.42 example 6 Comparative Polyimide 4 -- 42 1.60 3.39 example
7
Example 8
[0183] A polished and cleaned surface of glass A mainly composed of
La.sub.2O.sub.5 and having an nd of 1.77 and a .nu.d of 50 was
spin-coated with a proper amount of polyimide solution 1 at 3000 to
4000 rpm. The substrate was dried at 200.degree. C. for 60 minutes
to form a film made of the polyimide 1 synthesized from purified
DADCM on the substrate.
[0184] The substrate on which the film of the polyimide 1 was
formed was spin-coated with a proper amount of precursor sol of
aluminum oxide at 4000 rpm for 20 seconds and was fired in a
circulating hot-air oven at 200.degree. C. for 120 minutes. Thus,
the film of the polyimide 1 was coated with an amorphous aluminum
oxide film. The substrate was then immersed in hot water at
80.degree. C. for 20 minutes and was dried at 60.degree. C. for 15
minutes.
[0185] The FE-SEM observation of the film surface showed the
presence of fine ridges formed of random complicated plate crystals
mainly composed of aluminum oxide.
[0186] Table 5 shows the absolute reflectance of the optical film
on the glass A. The resulting antireflection-coated glass substrate
had an absolute reflectance of 0.2% or less at a wavelength in the
range of 450 to 650 nm. There was no detachment and crack
observed.
Example 9
[0187] The same procedures as Example 8 were performed except that
the glass A was replaced with glass B mainly composed of TiO.sub.2
and having an nd of 1.78 and a .nu.d of 26.
[0188] The absolute reflectance of the optical film on the glass B
was measured. The resulting antireflection-coated glass substrate
had an absolute reflectance of 0.2% or less at a wavelength in the
range of 450 to 650 nm. There was no detachment and crack
observed.
Comparative Example 8
[0189] The same procedures as Example 8 were performed except that
the polyimide solutions 1 was replaced with the polyimide solution
4 and that a layer was formed of the polyimide 2 synthesized from
crude DADCM.
[0190] Although there was no detachment and crack observed, the
absolute reflectance of an optical film on glass A at a wavelength
in the range of 450 to 650 nm varied between 0.2% and 0.3%.
Comparative Example 9
[0191] The same procedures as Example 9 were performed except that
the polyimide solution 1 was replaced with the polyimide solution 4
and that a layer was formed of the polyimide 2 synthesized from
crude DADCM.
[0192] The absolute reflectance of an optical film on glass B at a
wavelength in the range of 450 to 650 nm varied between 0.2% and
0.3%. Furthermore, cracking was observed in a surrounding area.
TABLE-US-00005 TABLE 5 Absolute reflectance Obser- Cross- (450~
vation Substrate Polyimide linker 550 nm) on film Example 8 Glass A
Polyimide 1 -- <0.2% Good (nd = 1.77) Example 9 Glass B
Polyimide 1 -- <0.2% Good (nd = 1.78) Comparative Glass A
Polyimide 2 -- 0.2~0.3% Uneven example 8 (nd = 1.77) color
Comparative Glass B Polyimide 2 -- 0.2~0.3% Crack example 9 (nd =
1.78)
[0193] Examples in which the solubility and the glass transition
temperature of polyimides were measured will be described
below.
(10) Purification of 4,4'-methylenebis(aminocyclohexane)
[0194] Hexane was gradually added under reflux to 200 g of
4,4'-methylenebis(aminocyclohexane) (hereinafter referred to as
DADCM, manufactured by Tokyo Chemical Industry Co., Ltd.).
4,4'-methylenebis(aminocyclohexane) was completely dissolved in
hexane. After heating was completed, the solution was left to stand
in a refrigerator for several days. A precipitate was filtered off
and dried under vacuum to yield 61 g of white purified DADCM in a
solid state.
[0195] .sup.1H-NMR (DMSO-d.sub.6); .delta.0.83 (2H, m), .delta.0.97
(2H, q), .delta.1.18 (2H, m), .delta.1.60 (2H, d), .delta.1.69 (2H,
d), .delta.2.05 (2H, s), .delta.2.42 (2H, m), .delta.3.30 (4H,
b)
(11) DSC Measurement of 4,4'-methylenebis(aminocyclohexane)
[0196] The melting points of crude DADCM and purified DADCM were
measured with a differential scanning calorimeter (hereinafter
referred to as a DSC, manufactured by Seiko Instruments Inc., trade
name DSC 200) at a heating rate of 10.degree. C./min. FIG. 7 shows
the results. .DELTA.Q denotes the amount of heat, Exo. denotes
exothermic, and Endo. denotes endothermic.
(12) Gas Chromatography of 4,4'-methylenebis(aminocyclohexane)
[0197] The isomer contents of crude DADCM and purified DADCM were
measured with a GC/MS system (manufactured by Agilent Technologies,
trade name 6890N network GC) equipped with a GC column
(manufactured by Agilent Technologies, trade name HP-35). Peaks
assigned to a trans-trans isomer, a trans-cis isomer, and a cis-cis
isomer were observed in ascending order of retention time. From the
areas of these peaks, the trans content (% by mole) of the
1,4-cyclohexylene group was calculated by the following equation:
Trans content=([trans-trans isomer peak area]+[trans-cis isomer
peak area]/2)/[total peak area of three isomers].
(13) Synthesis of Polyimides 9 to 22
[0198] A total of 0.012 mol of diamine (1) (purified DADCM or crude
DADCM), diamine (2), and diamine (3) (organosiloxane diamine) were
dissolved in N,N-dimethylacetamide (hereinafter referred to as
DMAc). 0.012 mol of acid dianhydride was added to the diamine
solution while the diamine solution was cooled with water. DMAc was
used in such an amount that the total mass of the diamines and the
acid dianhydride was 20% by weight.
[0199] This solution was stirred at room temperature for 15 hours
to cause polymerization reaction. After the solution was diluted
with DMAc to 8% by weight, 7.4 ml of pyridine and 3.8 ml of acetic
anhydride were added. The solution was stirred at room temperature
for one hour. The solution was stirred in an oil bath at a
temperature in the range of 60.degree. C. to 70.degree. C. for four
hours. The polymerization solution was poured into methanol or a
methanol/water mixed solvent for reprecipitation. A polymer thus
reprecipitated was removed and was washed several times in methanol
or a methanol/water mixed solvent. The polymer was dried under
vacuum at 100.degree. C. to yield a white to light yellow polyimide
powder. The imidization rate was determined by measuring the
residual amount of carboxy group from a .sup.1H-NMR spectrum.
(14) Evaluation of Solubility
[0200] 1.0 g of a powder of each of the polyimides 9 to 22 was
added to 4 g each of five solvents: N,N-dimethylacetamide
(hereinafter referred to as DMAc), N-methyl-2-pyrrolidone
(hereinafter referred to as NMP), .gamma.-butyrolactone,
cyclopentanone, and cyclohexanone to examine solubility. Table 7
shows the results, in which "Good" indicates soluble at room
temperature, "Fair" indicates soluble by heating, and "Poor"
indicates insoluble even by heating.
(15) Measurement of Glass Transition Temperature (Tg) of
Polyimide
[0201] An aluminum pan filled with a polyimide powder was heated in
the DSC from room temperature to 300.degree. C. at 20.degree.
C./min to measure the glass transition temperature of the
polyimide. Table 8 shows the results.
(16) Measurement of Refractive Index
[0202] A polished surface of glass A having an nd of 1.77 and a
.nu.d of 50 was spin-coated at 3000 to 4000 rpm with a proper
amount of solution in which 4.0 g of a powder of each of the
polyimides 9 to 22 was dissolved in 96 g of a
cyclopentanone/cyclohexanone mixed solvent. The substrate was dried
at 200.degree. C. for 60 minutes to form a film of each of the
polyimides 9 to 22 having a thickness of approximately 100 nm.
[0203] The refractive index of the polyimide film on the substrate
was measured with a spectroscopic ellipsometer (VASE, manufactured
by J. A. Woollam Japan Co., Inc.) at a wavelength in the range of
400 to 700 nm. Table 7 shows the refractive index (550 nm) and Abbe
number (.nu.d) obtained from the refractive index.
Examples 10 to 16
[0204] As shown in Table 6, the polyimides 9 to 15 were synthesized
by the method described above using purified DADCM.
TABLE-US-00006 TABLE 6 Acid Trans-1,4-cyclohexylene Imidization
Powder Example Polyimide dianhydride Diamine (1) content (% by
mole) Diamine (2) Diamine (3) Yield % rate % properties Example 10
Polyimide 9 TDA(1.0) Purified 97 PAM-E(0.1) 92 96 White powder
DADCM(0.9) Example 11 Polyimide 10 TDA(1.0) Purified 97 BAPB(0.3)
PAM-E(0.1) 94 98 White powder DADCM(0.6) Example 12 Polyimide 11
BDA(1.0) Purified 97 PAM-E(0.1) 85 95 White powder DADCM(0.9)
Example 13 Polyimide 12 BDA(1.0) Purified 97 PAM-E(0.2) 87 96 White
powder DADCM(0.8) Example 14 Polyimide 13 B4400(1.0) Purified 97
PAM-E(0.1) 85 95 Light yellow DADCM(0.9) powder Example 15
Polyimide 14 6FDA(1.0) Purified 97 PAM-E(0.1) 89 96 White powder
DADCM(0.9) Example 16 Polyimide 15 DSDA(1.0) Purified 97 PAM-E(0.1)
84 97 Light yellow DADCM(0.9) powder Comparative Polyimide 16
TDA(1.0) Crude 70 PAM-E(0.1) 90 95 Light yellow example 10
DADCM(0.9) powder Comparative Polyimide 17 TDA(1.0) Crude 70
BAPB(0.3) PAM-E(0.1) 93 98 Light yellow example 11 DADCM(0.6)
powder Comparative Polyimide 18 BDA(1.0) Crude 70 PAM-E(0.1) 81 95
Yellow powder example 12 DADCM(0.9) (sticky) Comparative Polyimide
19 BDA(1.0) Crude 70 PAM-E(0.2) 85 95 Yellow powder example 13
DADCM(0.8) (sticky) Comparative Polyimide 20 B4400(1.0) Crude 70
PAM-E(0.1) 84 96 Yellow powder example 14 DADCM(0.9) (sticky)
Comparative Polyimide 21 6FDA(1.0) Crude 70 PAM-E(0.1) 89 95 Yellow
powder example 15 DADCM(0.9) (sticky) Comparative Polyimide 22
DSDA(1.0) Crude 70 PAM-E(0.1) 79 97 Yellow powder example 16
DADCM(0.9) (Note 1) TDA:
4-(2,5-dioxotetrahydrofuran-3-yl)-1,2,3,4-tetrahydronaphthalene-1,2-d-
icarboxylic anhydride BDA: meso-butane-1,2,3,4-tetracarboxylic acid
dianhydride DADCM: 4,4'-methylenebis(aminocyclohexane) PAM-E:
dimethylsiloxane oligomer in which both ends were modified with
amine BAPB: 4,4'-bis(4-aminophenoxy)biphenyl B4400:
5-(2,5-dioxotetrahydrofury1)-3-methy1-3-cyclohexene-1,2-dicarboxyli-
c anhydride 6FDA: 4,4'-(hexafluoroisopropylidene)diphthalic acid
anhydride DSDA: 3,3',4,4'-diphenylsulfonetetracarboxylic acid
dianhydride (Note 2) Values in parentheses for acid dianhydride and
diamines represent the molar ratio of these compounds charged.
(Note 3) The trans content (% by mole) represents the mole
percentage of the trans-1,4-cyclohexylene group in the diamine 1
(DADCM).
[0205] The purified DADCM used as a monomer was obtained by
recrystallization of commercial DADCM. .sup.1H-NMR spectrum and gas
chromatography proved almost complete isolation of a trans-trans
structural isomer. Table 6 shows the trans content measured by gas
chromatography before and after purification. As illustrated in
FIG. 7, the DSC measurement of purified DADCM also showed one
endothermic peak at a temperature in the range of approximately
70.degree. C. to 71.degree. C. probably assigned to the melting of
the trans-trans structural isomer.
[0206] The polyimides 9 to 15 synthesized were white to light
yellow powders and were soluble in DMAc and NMP at room temperature
and soluble in cyclopentanone, if necessary, by heating. Table 7
shows the results.
TABLE-US-00007 TABLE 7 Solubility Example Polyimide DMAc NMP
.gamma.-butyrolactone Cyclopentanone Cyclohexanone Example 10
Polyimide 9 Good Good Good Good Good Example 11 Polyimide 10 Good
Good Good Good Fair Example 12 Polyimide 11 Good Good Poor Fair
Fair Example 13 Polyimide 12 Good Good Good Good Good Example 14
Polyimide 13 Good Good Good Good Good Example 15 Polyimide 14 Good
Good Poor Good Fair Example 16 Polyimide 15 Good Good Poor Good
Fair Comparative Polyimide 16 Good Good Good Good Good example 10
Comparative Polyimide 17 Good Good Good Good Good example 11
Comparative Polyimide 18 Good Good Fair Fair Fair example 12
Comparative Polyimide 19 Good Good Good Good Good example 13
Comparative Polyimide 20 Good Good Good Good Good example 14
Comparative Polyimide 21 Good Good Fair Good Good example 15
Comparative Polyimide 22 Good Good Poor Good Fair example 16 (Note
1) DMAc: N,N-dimethylacetamide NMP: N-methyl-2-pyrrolidone
[0207] The DSC measurement of the polyimide clearly showed the
presence of Tg. A polyimide produced using 0.1 molar equivalent of
the organosiloxane diamine (PAM-E) had a Tg as high as 200.degree.
C. or more, which was comparable to the Tg of a polyimide produced
by copolymerization with an aromatic diamine (BAPB). A polyimide
produced using 0.2 molar equivalent of PAM-E had a Tg as high as
190.degree. C.
[0208] The refractive index measurement showed that some of the
polyimides had a low refractive index below 1.55 and a high Abbe
number in the range of 27 to 45. The isolation of the trans form
did not cause a change in refractive index or an increase in Abbe
number. Table 8 shows the results.
TABLE-US-00008 TABLE 8 Refractive Comparative Refractive Example
Polyimide Tg/.degree. C. index vd example Polyimide Tg/.degree. C.
index vd Example 10 Polyimide 9 228 1.565 38 Comparative Polyimide
16 212 1.564 37 example 10 Example 11 Polyimide 10 227 1.61 28
Comparative Polyimide 17 215 1.610 28 example 11 Example 12
Polyimide 11 211 1.538 43 Comparative Polyimide 18 199 1.539 43
example 12 Example 13 Polyimide 12 190 1.525 45 Comparative
Polyimide 19 150-170* 1.525 45 example 13 Example 14 Polyimide 13
226 1.542 40 Comparative Polyimide 20 180-210* 1.541 40 example 14
Example 15 Polyimide 14 220 1.557 27 Comparative Polyimide 21
180-200* 1.557 28 example 15 Example 16 Polyimide 15 230 1.601 27
Comparative Polyimide 22 218 1.600 27 example 16 (Note 1) *No
distinct Tg was observed.
Comparative Examples 10 to 16
[0209] The same procedures as Examples 10 to 16 were performed
except that polyimides 16 to 22 were synthesized using crude
DADCM.
[0210] DSC measurement showed that crude DADCM had three broad
endothermic peaks probably assigned to the melting of cis-cis,
cis-trans, and trans-trans structural isomers.
[0211] The polyimides 9 to 15 synthesized in Examples 10 to 16 were
white or light yellow powders, whereas the polyimides 16 to 22
synthesized in Comparative Examples 10 to 16 were light yellow or
yellow polyimides. In particular, the polyimides 18 to 21 were
yellow sticky polyimide powders. Although the polyimides 16 to 22
had solubility in .gamma.-butyrolactone substantially equivalent to
or higher than the solubility of the polyimides 9 to 15, the
polyimides 16 to 22 had a 12.degree. C. or more lower Tg than the
polyimides 9 to 15. In particular, the polyimides 19 to 21 had
broad and indistinct Tg's.
[0212] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all such modifications and
equivalent structures and functions.
INDUSTRIAL APPLICABILITY
[0213] Optical members according to embodiments of the present
invention can be applied to transparent substrates having any
refractive index, have an excellent antireflection effect on
visible light, and excellent long-term weatherability. Thus,
optical members according to embodiments of the present invention
can be used in various displays for use in word processors,
computers, television sets, plasma display panels, and the like;
optical members, such as polarizers for liquid crystal displays,
and sunglass lenses, prescription glass lenses, viewing lens for
cameras, prisms, fly-eye lenses, toric lenses, various optical
filters, and sensors made of various optical lens materials and
transparent plastics; imaging optical systems, optical systems for
observation, such as binoculars, and projection optical systems for
use in liquid crystal projectors, using these optical members;
various optical lenses, such as scanning optical systems, for use
in laser-beam printers; and optical members, such as covers for
various measuring instruments and windowpanes for automobiles and
trains.
* * * * *