U.S. patent application number 16/153555 was filed with the patent office on 2019-02-07 for optical element and method for producing optical element.
The applicant listed for this patent is CANON KABUSHIKI KAISHA. Invention is credited to Keiko Abe, Tomonari Nakayama.
Application Number | 20190041551 16/153555 |
Document ID | / |
Family ID | 54548084 |
Filed Date | 2019-02-07 |
United States Patent
Application |
20190041551 |
Kind Code |
A1 |
Abe; Keiko ; et al. |
February 7, 2019 |
OPTICAL ELEMENT AND METHOD FOR PRODUCING OPTICAL ELEMENT
Abstract
An optical element having a substrate and a light-shielding film
on part of an outer portion of the substrate further contains a
coating on the light-shielding film, the coating containing a cured
mixture of a melamine or benzoguanamine resin, and a phenolic
resin, in proportions by mass of 1:5 to 7:5.
Inventors: |
Abe; Keiko; (Kawasaki-shi,
JP) ; Nakayama; Tomonari; (Yokohama-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CANON KABUSHIKI KAISHA |
Tokyo |
|
JP |
|
|
Family ID: |
54548084 |
Appl. No.: |
16/153555 |
Filed: |
October 5, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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14947910 |
Nov 20, 2015 |
10120107 |
|
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16153555 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 1/113 20130101;
G02B 1/118 20130101; G02B 1/11 20130101; G02B 27/0018 20130101;
G02B 1/14 20150115 |
International
Class: |
G02B 1/14 20150101
G02B001/14; G02B 27/00 20060101 G02B027/00; G02B 1/11 20150101
G02B001/11 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 27, 2014 |
JP |
2014-240621 |
Claims
1. A method for producing an optical element, the method
comprising: forming a light-shielding film on an outer portion of a
substrate; and forming a coating on a surface of the
light-shielding film, the coating containing a cured mixture of a
methylol melamine or methylol benzoguanamine resin, and a phenolic
resin, in proportions of 1:5 to 7:5.
2. The method according to claim 1, wherein the coating contains a
condensation product of the methylol melamine or methylol
benzoguanamine resin and the phenolic resin.
3. The method according to claim 2, wherein the coating contains a
condensation product of the benzoguanamine resin and the phenolic
resin.
4. The method according to claim 3, wherein the substrate is a
piece of glass.
5. The method according to claim 4, wherein the optical element is
a lens or a prism.
6. The method according to claim 1, further comprising: forming an
antireflection film on the substrate after the formation of the
coating, wherein the formation of the antireflection film involves
forming a film of aluminum oxide and making the film of aluminum
oxide in contact with water at a temperature of 40.degree. C. or
more and 100.degree. C. or less to give a surface of the film of
aluminum oxide a textured structure formed by crystals mainly of an
aluminum hydroxide or a hydrate of an aluminum oxide.
7. The method according to claim 6, further comprising: washing the
substrate with an alkaline solution before the formation of the
antireflection film.
8. An optical equipment comprising: a lens including the optical
element produced by the method defined in claim 1; or a prism
including the optical element produced by the method defined in
claim 1; or a reflector including the optical element produced by
the method defined in claim 1; or a diffraction grating including
the optical element produced by the method defined in claim 1.
9. A camera comprising a lens including the optical element
produced by the method defined in claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional of U.S. patent application
Ser. No. 14/947,910 filed Nov. 20, 2015, which claims the benefit
of Japanese Patent Application No. 2014-240621 filed Nov. 27, 2014,
each of which is hereby incorporated by reference herein in their
entirety.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The present invention relates to an optical element such as
a lens and a method for producing an optical element.
Description of the Related Art
[0003] Optical elements such as optical lenses have a
nontransparent film (a light-shielding film) on their outer portion
to prevent flares and ghosts. Optical elements such as optical
lenses also have an antireflection film to reduce surface
reflection and remove scattered light resulting from
reflection.
[0004] Japanese Patent Laid-Open Nos. 2011-145627 and 2013-24922
disclose optical elements. These optical elements, an example being
an optical lens, have a light-shielding film on their outer
portion, a protective coating on the light-shielding film, and an
antireflection film.
[0005] Japanese Patent Laid-Open No. 2010-54827 discloses a
protective coating. This protective coating contains at least one
of the following resins: epoxy, acrylic, imide, melamine, phenolic,
novolac, alkyd, maleic acid, and silicone resins. According to the
disclosure, this protective coating prevents dyes in a
light-shielding film, such as a black dye, from dissolving out of
the film.
[0006] The inventors found the optical elements disclosed in these
publications to be disadvantageous in that when they are used for a
long period of time under high-temperature and high-humidity
conditions, the light-shielding film changes its shade of color and
develops white spots. This disadvantage can be significant
particularly if the optical element is washed with an alkaline
aqueous solution after the attachment of the light-shielding film
and the protective coating.
[0007] The present invention provides an optical element that
maintains good appearance even through a long period of use under
high-temperature and high-humidity conditions despite washing with
an alkaline aqueous solution prior to the formation of an
antireflection film.
SUMMARY OF THE INVENTION
[0008] An aspect of the invention provides an optical element. The
optical element has a substrate and a light-shielding film on part
of an outer portion of the substrate. There is a coating on the
light-shielding film. The coating contains a cured mixture of
melamine or benzoguanamine resin, and a phenolic resin, in
proportions by mass of 1:5 to 7:5.
[0009] Another aspect of the invention provides a method for
producing an optical element. The method includes forming a
light-shielding film on an outer portion of a substrate, forming a
coating on the surface of the light-shielding film, the coating
containing a cured mixture of methylol melamine or methylol
benzoguanamine resin, and a phenolic resin, in proportions of 1:5
to 7:5, and forming an antireflection film on the substrate after
the formation of the coating.
[0010] 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 THE DRAWINGS
[0011] FIG. 1 illustrates an example of an optical element
according to an embodiment of the invention.
[0012] FIGS. 2A to 2E illustrate exemplary methods by which the
optical elements of various Examples were produced.
DESCRIPTION OF THE EMBODIMENTS
[0013] The following describes some embodiments of the
invention.
Optical Element
[0014] An optical element according to an embodiment of the
invention can be applied to a structural element of optical
equipment, such as a lens, a prism, a reflector, and a diffraction
grating, preferably a lens or a prism.
[0015] The following describes an optical element according to an
embodiment of the invention applied to a lens with reference to
FIG. 1. As illustrated in FIG. 1, the optical element 1 has a
substrate 2 that has optically effective sections 2a and 2b and an
optically ineffective section 2c. There is a light-shielding film 3
on the optically ineffective section 2c of the substrate 2, with a
coating 4 on the light-shielding film 3. The light-shielding film 3
extends on part or all of the optically ineffective section 2c of
the optical element 1. The coating 4 may completely cover the
light-shielding film 3. The light-shielding film 3 is, in general
terms, a film an optical element has on its outer portion to
prevent flares and ghosts.
[0016] The optical element 1 according to this embodiment has an
antireflection film 5 on part of the optically effective sections
2a and 2b.
Substrate
[0017] The substrate 2 of the optical element according to this
embodiment can be a material such as a piece of glass, a glass
mirror, an optical lens, and a prism, preferably an optical lens or
a prism. Specific examples of glass include alkali-free glass and
alumina-silicate glass. Optical elements according to certain
embodiments of the invention can be used in optical equipment such
as cameras, binoculars, microscopes, and semiconductor exposure
devices.
[0018] The substrate 2 used in this embodiment can be in any shape
that can be eventually processed into the shape suitable for the
intended purpose of use, and can therefore have a two- or
three-dimensionally curved surface. Its thickness is not critical
and is usually 5 mm or less, although not limited to this.
Light-Shielding Film
[0019] The light-shielding film 3 of the optical element according
to this embodiment contains at least a coloring agent and a binder
resin. The light-shielding film 3 may optionally contain other
materials, such as inorganic fine particles.
[0020] The binder resin can be epoxy resin. The epoxy resin content
of the light-shielding film 3 can be 5.0% by mass or more and 60.0%
by mass or less, preferably 5.0% by mass or more and 40.0% by mass
or less. An epoxy resin content of less than 5.0% by mass leads to
low solvent resistance. An epoxy resin content of more than 60.0%
by mass leads to significant internal reflection.
[0021] The coloring agent in the light-shielding film 3 can be a
dye, a pigment, or a mixture of them. The dye can be any material
that absorbs visible light in the wavelength range of 400 nm to 700
nm and is soluble in any solvent. A single dye or a mixture of
multiple dyes, such as black, red, yellow, and blue ones, can be
used. The pigment can be any material that absorbs visible light in
the wavelength range of 400 nm to 700 nm. Examples of pigments that
can be used include carbon black, titanium black, and iron oxides.
The number-average particle diameter of the pigment can be 5 nm or
more and 200 nm or less. The use of a pigment with a number-average
particle diameter of less than 5 nm affects the stability of the
light-shielding paint. The use of a pigment with a number-average
particle diameter of more than 200 nm leads to significant internal
reflection in the light-shielding film.
[0022] The coloring agent content of the light-shielding film 3
according to this embodiment can be 5.0% by mass or more and 30.0%
by mass or less, preferably 10.0% by mass or more and 15.0% by mass
or less.
[0023] The light-shielding film 3 according to this embodiment may
optionally contain inorganic fine particles for adjusting its
refractive index. Ensuring that the difference in refractive index
(nd) between the substrate 2 and the light-shielding film 3 is 0.0
or more and 0.2 or less reduces internal reflection.
[0024] The inorganic fine particles may have a refractive index
(nd) of 2.2 or more. The number-average particle diameter of the
inorganic fine particles can be 5 nm or more and 1000 nm or less,
preferably 10 nm or more and 100 nm or less. The use of inorganic
fine particles with a number-average particle diameter of less than
5 nm affects the stability of the light-shielding paint, making the
paint more viscous and more likely to gel. The use of inorganic
fine particles with a number-average particle diameter of more than
1000 nm leads to the advantage of the prevention of white spots in
the light-shielding film being insufficient.
[0025] The use of inorganic fine particles having a refractive
index (nd) of 2.2 or more will give the resulting light-shielding
film 3 a high refractive index, therefore helping to reduce
internal reflection. Examples of usable inorganic fine particles
having a refractive index (nd) of 2.2 or more include fine
particles of titanium oxide, zirconium oxide, aluminum oxide,
yttrium oxide, cadmium oxide, diamond, strontium titanate, and
germanium. In particular, titanium oxide and zirconium oxide have a
refractive index (nd) of 2.2 or more and 3.5 or less. When the
refractive index of the inorganic fine particles is less than 2.2,
the increase in the refractive index of the light-shielding film is
accordingly small. The difference in refractive index between the
substrate and the light-shielding film is therefore large, so that
internal reflection will not be sufficiently reduced.
[0026] The number-average particle diameter of the inorganic fine
particles having a refractive index (nd) of 2.2 or more can be 10
nm or more and 100 nm or less, preferably 10 nm or more and 20 nm
or less. Although the smaller the number-average particle diameter
of the inorganic fine particles with a refractive index (nd) of 2.2
or more is the better it would be, it is practically difficult to
disperse such particles to a number-average particle diameter of
less than 10 nm. The use of inorganic fine particles having a
number-average particle diameter of more than 100 nm leads to
likely occurrence of light scattering. Note that the number-average
particle diameter of the inorganic fine particles is based on the
actual size of particles in the light-shielding film. For example,
if the inorganic fine particles are in the form of aggregates,
their average particle diameter is based on the size of the
aggregates.
[0027] The amount of the inorganic fine particles in the
light-shielding film 3 according to this embodiment can be 5.0% by
mass or more and 40.0% by mass or less, preferably 10.0% by mass or
more and 15.0% by mass or less. The use of less than 5.0% by mass
inorganic fine particles in the light-shielding film 3 leads to the
increase in refractive index being so small that internal
reflection will be significant. The use of more than 40.0% by mass
inorganic fine particles in the light-shielding film 3 affects the
adhesion and durability of the film.
[0028] The light-shielding film 3 may optionally contain an
amine-based hardener as a curing agent for the epoxy resin. Any
known amine-based hardener can be used as long as intended
characteristics are given. Examples of amine-based hardeners that
can be used include linear aliphatic ones, polyamide-based ones,
alicyclic ones, and aromatic ones, as well as dicyandiamide, adipic
acid dihydrazide, and so forth. Any one of these can be used alone,
and it is also possible to use a mixture of two or more of
these.
[0029] The hardener content of the light-shielding film 3 can be
1.0% by mass or more and 25.0% by mass or less. A hardener content
of less than 1.0% by mass causes the degree of hardening of the
light-shielding film to be so low that the adhesion of the film to
the substrate is affected. A hardener content of more than 25.0% by
mass leads to low optical characteristics.
[0030] The light-shielding film 3 may optionally contain additives
unless its intended purpose is defeated. Examples of additives that
can be used include fungicides and oxidation inhibitors. The
additive content of the light-shielding film 3 according to this
embodiment can be 15.0% by mass or less, preferably 10.0% by
mass.
Coating on the Light-Shielding Film
[0031] The optical element 1 according to this embodiment has a
coating 4 on the light-shielding film 3, the coating 4 including
cured mixture of melamine or benzoguanamine resin, and a phenolic
resin.
[0032] The production of the melamine resin is as in reaction
formula (1) below. Melamine, an amino triazine compound, produces a
methylol melamine resin, and this methylol melamine resin is
crosslinked through heating.
##STR00001##
[0033] The production of the benzoguanamine resin is as in reaction
formula (2) below. Benzoguanamine, an amino triazine compound,
produces a methylol benzoguanamine resin, and this methylol
benzoguanamine resin is crosslinked through heating.
##STR00002##
[0034] Besides the melamine or benzoguanamine resin and the
phenolic resin, the coating 4 on the light-shielding film 3 may
optionally contain other materials, such as epoxy resin. The
phenolic resin can be any commonly used industrial phenolic resin,
preferably a resol resin, a type of thermally curable resins. Resol
resins are readily available in liquid form and easy to handle. The
phenolic resin may be liquid at the ordinary temperature, and may
contain a solvent to adjust its viscosity. Examples of commercially
available phenolic resins include Showa Denko SHONOL (registered
trademark), Sumitomo Bakelite SUMILITE RESIN (registered
trademark), and some phenolic resins available from DIC
Corporation.
[0035] The presence of a methylol resin in the coating 4 on the
light-shielding film makes this protective coating waterproof and
resistant to alkalis. As a thermally-activated crosslinking agent,
furthermore, the methylol resin is crosslinked when heated in the
presence of a hydroxy-bearing resin. This enhances the
waterproofness of the coating by increasing the crosslinking
density of the coating.
[0036] The coating 4 on the light-shielding film, containing
hydroxy-bearing resin(s) such as the phenolic resin and epoxy
resin, is highly flexible and firmly adheres to the light-shielding
film.
[0037] The melamine or benzoguanamine resin content of the coating
4 on the light-shielding film can be 5.0% by mass or more and 100%
by mass or less, preferably 20.0% by mass or more and 60.0% by mass
or less. A melamine or benzoguanamine resin content of less than
5.0% by mass leads to the waterproofness and alkali resistance of
the coating being so low that the light-shielding film will be
likely to change its shade of color and develop white spots when
used for a long period of time under high-temperature and
high-humidity conditions. The phenolic resin content of the coating
4 on the light-shielding film can be 0% by mass or more and 95% by
mass or less, preferably 40% by mass or more and 80% by mass or
less.
[0038] The coating 4 on the light-shielding film includes a cured
mixture of melamine or benzoguanamine resin, and a phenolic resin.
The coating 4 can be a cured mixture of melamine or benzoguanamine
resin, and a phenolic resin, in proportions of 1:5 to 7:5 (the
melamine or benzoguanamine resin to the phenolic resin). The use of
the melamine resin or benzoguanamine resin in any proportion lower
than in this ratio leads to the crosslinking density of the resin
being so low that the waterproofness of the coating is affected. As
a result, a great change in the shade of color and many white spots
will be observed in the light-shielding film 3 after a reliability
study. The use of the phenolic resin in any proportion lower than
in this ratio leads to low adhesion between the coating 4 and the
light-shielding film 3. This also results in a great change in the
shade of color and many white spots being observed in the
light-shielding film 3 after a reliability study. The coating 4 may
be a condensation product of the melamine or benzoguanamine resin
and the phenolic resin.
Antireflection Film
[0039] The optical element 1 according to this embodiment can have
an antireflection film 5 on at least part of its optically
effective sections 2a and 2b. Examples of materials of which the
antireflection film 5 can be made include inorganic materials or
oxides such as zinc, aluminum, silicon, and titania, metal
fluorides such as magnesium fluoride, and polymers.
[0040] The antireflection film 5 may have a textured structure
formed by crystals mainly of an aluminum hydroxide or a hydrate of
an aluminum oxide on its surface. Such a film has great
antireflection capability.
[0041] Others
[0042] Besides these films and coating, the optical element 1
according to this embodiment may optionally have additional
functional films. For example, there may be a hard coating layer
that protects the film or coating therebeneath. There may be a
single or multiple layers of film between the substrate 2 and the
antireflection film 5 and/or the light-shielding film 3. This can
lead to enhanced antireflection capability and/or enhanced adhesion
to the substrate.
Method for Producing an Optical Element
Formation of a Light-Shielding Film
[0043] A method according to an embodiment of the invention for
producing an optical element includes forming a light-shielding
film 3 on an outer portion of a substrate 2.
[0044] The paint used to form the light-shielding film 3 according
to this embodiment (hereinafter referred to as "the light-shielding
paint") contains at least a coloring agent and a binder resin. The
binder resin can be epoxy resin. The light-shielding paint may
contain 10.0% by mass or more and 20.0% by mass or less epoxy
resin, 25.0% by mass or more and 35.0% by mass or less coloring
agent, e.g., a black dye, and 15.0% by mass or more and 25.0% by
mass or less excipient, such as filler. Besides these materials,
the light-shielding paint contains an organic solvent.
[0045] The light-shielding paint may optionally contain a hardener.
The hardener can be an amine-based hardener as a curing agent for
the epoxy resin. Any known amine-based hardener can be used,
examples including linear aliphatic ones, polyamide-based ones,
alicyclic ones, and aromatic ones, as well as dicyandiamide, adipic
acid dihydrazide, and so forth. Any one of these can be used alone,
and it is also possible to use a mixture of two or more of
these.
[0046] This embodiment may include adjusting the thickness of the
light-shielding film and/or the concentration and viscosity of the
light-shielding paint in order to make the paint easier to handle.
These can be done through the addition of organic solvent or epoxy
resin.
[0047] The light-shielding paint may contain at least one selected
from tar, pitch, dye, pigment, mica particles, and silica
particles.
[0048] The application of the light-shielding paint can be done
using any method deemed appropriate according to the shape of the
substrate and the position of the optically ineffective section,
examples including brush painting, spin coating, spray coating, and
dip coating.
[0049] Likewise, the curing of the light-shielding paint can be
done through a thermal process, and can also be done using any
other process that produces a cured product similar to that by a
thermal process. If a thermal process is used, the heating
conditions are selected according to the kind of the hardener and
the heat resistance of the substrate. For a light-shielding paint
that contains a hardener, the heating temperature can be 60.degree.
C. or more and 200.degree. C. or less, preferably 80.degree. C. or
more and 120.degree. C. or less, and the duration of heating can be
30 minutes or more and 20 hours or less, preferably 1 hour or more
and 4 hours or less.
Formation of a Coating on the Surface of the Light-Shielding
Film
[0050] The method according to this embodiment for producing an
optical element includes, after the formation of the
light-shielding film, applying a paint that includes a methylol
melamine or methylol benzoguanamine resin to the surface of the
light-shielding film to form a coating on the light-shielding
film.
[0051] The paint used to form the coating on the light-shielding
film (hereinafter referred to as "the coating paint") includes a
methylol melamine or methylol benzoguanamine. The coating paint
contains at least a methylol as a reaction product of an amino
triazine compound having two or more amino groups and formaldehyde.
The methylol can be of any kind, preferably a methylol that
contains a triazine ring and a methylol group in its structure,
such as a methylol melamine or methylol benzoguanamine.
[0052] The methylol can be liquid at the ordinary temperature, and
its properties may allow it to be easily cured through heating at
low temperatures. Examples of commercially available methylol
resins include NIKALAC MX-706 methylol melamine resin (Sanwa
Chemical) and NIKALAC BL-60 methylol benzoguanamine resin (Sanwa
Chemical).
[0053] The application of the paint that includes a methylol
melamine or methylol benzoguanamine can be done using any method
deemed appropriate according to the shape of the substrate and the
position of the optically ineffective section, examples including
brush painting, spin coating, spray coating, and dip coating.
[0054] The method according to this embodiment for producing an
optical element may include, after the application of the paint
that includes a methylol melamine or methylol benzoguanamine resin,
curing this paint to form a coating on the light-shielding film,
more specifically curing the methylol melamine to form a coating
that includes a melamine resin or curing the methylol
benzoguanamine to form a coating 4 that includes a benzoguanamine
resin.
[0055] The curing of the paint that includes a methylol melamine or
methylol benzoguanamine can be done through a thermal process, and
can also be done using any other process that produces a cured
product similar to that by a thermal process. If a thermal process
is used, the heating conditions are selected according to the kind
of the methylol and phenolic resins and the heat resistance of the
substrate. For the aforementioned methylol resin-based formulation,
the heating temperature can be 100.degree. C. or more and
250.degree. C. or less, preferably 140.degree. C. or more and
220.degree. C. or less.
Formation of an Antireflection Film
[0056] The method according to this embodiment for producing an
optical element includes, after the formation of the coating
through the application of the paint that includes a methylol
melamine or methylol benzoguanamine, forming an antireflection film
5 on the substrate 2. Examples of processes through which the
antireflection film can be formed include those that involve
heating in the air, such as liquid-phase processes, and those
performed under humid conditions, such as immersion in warm
water.
[0057] The formation of the antireflection film involves applying
paint for forming the antireflection film (hereinafter referred to
as the "antireflection paint") to at least part of the optically
effective sections 2a and 2b of the substrate 2 to form the
antireflection film 5. Methods such as spin coating, spray coating,
and dip coating can be used to apply the antireflection paint. The
antireflection paint may be applied unevenly to part of the
light-shielding film 3 and coating 4. Examples of ways to form a
film with antireflection capability from the antireflection paint
include forming a layer with a controlled refractive index or a
textured structure on the surface of the substrate.
[0058] The layer with a controlled refractive index can be formed
through, for example, the application of fine particles of a
material having a low refractive index, such as magnesium fluoride,
or the application of hollow particles of silicon oxide.
[0059] The antireflection film with a textured structure can be
formed on the substrate by, for example, applying an
aluminum-oxide- or aluminum-containing antireflection paint to the
surface of the substrate, fixing the material into a film through
heating, and then immersing the film in or bringing it into contact
with warm water or exposing the film to steam. For the heating
following the application of the paint, the heating temperature can
be 100.degree. C. or more and 220.degree. C. or less, and the
duration of heating can be 5 minutes or more and 24 hours or less.
The temperature of the warm water can be 40.degree. C. or more and
100.degree. C. or less, and the time of contact with the warm water
can be 5 minutes or more and 24 hours or less. Through the
immersion of the film in or contact with warm water or the exposure
of the film to steam, the aluminum component in the film dissolves
or separates out through reaction, creating a textured structure
formed by crystals mainly of an aluminum oxide, an aluminum
hydroxide, or a hydrate of an aluminum oxide on the surface. These
crystals are tabular, preferably boehmite crystals. These tabular
crystals, the end portions of which provide a fine-textured
structure, are positioned at a selected angle from the surface of
the substrate so that the fine-textured structure has a large
height and a small pitch. This textured structure provides
excellent antireflection capability by creating an ascending
gradient of refractive index from their interface with air to the
substrate.
[0060] The method according to this embodiment for producing an
optical element may further include washing the substrate 2 with an
alkaline solution between the formation of the coating on the
surface of the light-shielding film and the formation of the
antireflection film.
[0061] If the antireflection film is formed on the surface of the
substrate using a liquid-phase process, the entire lens may be
subjected to a washing process so that the surface of the substrate
should be clear of any dirt or foreign substance prior to the
formation of the antireflection film. The washing process involves
immersing the entire lens for 5 to 10 minutes in a cleaning liquid
which is a commercially available alkaline detergent diluted and
mixed with water to a concentration of 5% by volume to 10% by
volume and having an adjusted pH of 9 to 10. The entire lens is
then sonicated in purified water for 10 to 20 minutes and dried
with hot air at a temperature of 60.degree. C. for 5 to 10
minutes.
[0062] Having a coating that includes a methylol melamine or
methylol benzoguanamine thereon, the light-shielding film 3
produced in the method according to this embodiment for producing
an optical element maintains good appearance through a long period
of use under high-temperature and high-humidity conditions even if
having been washed with an alkali.
EXAMPLES
[0063] The following describes certain aspects of the invention in
detail by providing examples. No aspect of the invention is limited
to these examples.
[0064] Examples and Comparative Examples below involved the
following measurements and evaluations.
Appearance after a Reliability Study Under High-Temperature and
High-Humidity Conditions
[0065] The lenses of Examples and Comparative Examples were
subjected to a reliability study under high-temperature and
high-humidity conditions, where the lenses were held at a
temperature of 60.degree. C. and a humidity of 90% for 1000 hours.
After the study, visual evaluation was performed on the appearance
of the light-shielding film as viewed from the optically effective
section 2a side.
[0066] The evaluation of appearance consisted of two components,
"the shade of color" and "the number of white spots." The following
describes the assessment of "the shade of color" and "the number of
white spots."
Shade of Color
[0067] The interface between the light-shielding film 3 with the
coating 4 and the substrate of the lens was photographed from the
optically effective section 2a side using a Canon EOS 70D
single-lens reflex camera. On ImageJ image processing program, a
15-mm.sup.2 area was cut out of the obtained image within an image
region corresponding to the light-shielding film 3 and clear of any
dirt or debris. The cropped image was binarized, and the binary
image was used to determine the value of brightness, which is
herein referred to as "the shade of color." The greater (closer to
255) the value is, the worse the shade of color is. The criteria
for the evaluation of the shade of color were as follows.
[0068] A: The shade of color is 0 or more and 50 or less.
[0069] B: The shade of color is more than 50 and 80 or less.
[0070] C: The shade of color is more than 80 and 255 or less.
The Number of White Spots
[0071] The interface between the light-shielding film 3 with the
coating 4 and the substrate of the lens was photographed from the
optically effective section 2a side using an EOS 70D single-lens
reflex camera (Canon). On ImageJ image processing program, a
15-mm.sup.2 area was cut out of the obtained image within an image
region corresponding to the light-shielding film 3 and clear of any
dirt or debris. The cropped image was binarized, and white spots,
i.e., pixels with a value of brightness of 128 or more, were
counted on the binary image. The criteria for the evaluation of the
number of white spots were as follows.
[0072] A: The number of white spots was 0 or more and 50 or
less.
[0073] B: The number of white spots was 50 or more and 200 or
less.
[0074] C: The number of white spots was more than 200.
Example 1
[0075] In Example 1, the substrate was a lens made of optical glass
(Ohara L-BAL43). Paint for forming the light-shielding film (a
light-shielding paint; Canon Chemicals GT-7) was applied to the
optically ineffective section of the lens as illustrated in FIG.
2A. With the lens slowly rotated on the turntable 6 in FIG. 2A, the
light-shielding paint was applied using a brush 7. The applied
paint was dried at room temperature for 2 hours and heated at a
temperature of 120.degree. C. for 3 hours to form a light-shielding
film 3.
[0076] Paint for forming a coating 4 on the surface of the
light-shielding film (coating paint) was then prepared as follows.
Forty grams of a resol phenolic resin (Showa Denko SHONOL BKM-2620)
was dissolved in a solvent mixture of 40 g of
1-methoxy-2-acetoxypropane and 40 g of 1-ethoxy-2-propanol through
stirring with a mechanical stirrer at room temperature. The
obtained resin solution was mixed and stirred to uniformity with
11.3 g of a methylol resin solution containing an amino triazine
compound as raw material for a methylated melamine resin (Sanwa
Chemical NIKALAC MX-706 (a solid content of 70.6% by mass)). The
obtained solution was used as the coating paint.
[0077] As illustrated in FIG. 2B, the lens with the formed
light-shielding film 3 was slowly rotated on the turntable 6 while
the coating paint was applied with a brush 7. The application of
the coating paint was in such a manner that the entire
light-shielding film should be coated. The applied paint was dried
at room temperature for 1 hour and heated at a temperature of
150.degree. C. for 3 hours to form a coating 4 on the
light-shielding film 3.
[0078] The entire lens was then immersed for 5 to 10 minutes in a
cleaning liquid which was a commercially available alkaline
detergent diluted with water to a concentration of 5% by volume to
10% by volume. The entire lens was then sonicated in purified water
for 10 to 20 minutes and dried with hot air at a temperature of
60.degree. C. for 5 to 10 minutes.
[0079] On the turntable 6 in FIG. 2C, the lens having the
light-shielding film 3 and the coating 4 on the light-shielding
film was spun at 3000 rpm for 30 seconds for spin coating with a
drop of an aluminum-oxide- or aluminum-containing paint applied to
near the center of the concavity of the optically effective section
2b. Subsequently, the lens was heated at a temperature of
210.degree. C. for 3 hours. The heated lens was immersed in a warm
water bath 8 at a controlled temperature of 65.degree. C. or more
and 85.degree. C. or less as illustrated in FIG. 2D. This produced
the lens illustrated in FIG. 2E, a lens having its optically
effective section coated with an antireflection film 5 that had a
textured structure formed by crystals mainly of a hydroxide of
aluminum or a hydrate of an aluminum oxide.
[0080] As presented in the Table, the lens of Example 1 was grade A
for both the shade of color and the number of white spots in the
appearance evaluation.
Example 2
[0081] In Example 2, the coating 4 was formed in the same way as in
Example 1 except that the quantity of the coating paint, a methylol
resin solution containing an amino triazine compound as raw
material for a methylated melamine resin (Sanwa Chemical NIKALAC
MX-706 (a solid content of 70.6% by mass)), was 22.6 g. Then the
same procedure as in Example 1 was followed, yielding a lens having
its optically effective section coated with an antireflection film
5.
[0082] As presented in the Table, the lens of Example 2 was grade A
for both the shade of color and the number of white spots in the
appearance evaluation.
Example 3
[0083] In Example 3, the coating 4 was formed in the same way as in
Example 1 except that the quantity of the coating paint, a methylol
resin solution containing an amino triazine compound as raw
material for a methylated melamine resin (Sanwa Chemical NIKALAC
MX-706), was 45.3 g. Then the same procedure as in Example 1 was
followed, yielding a lens having its optically effective section
coated with an antireflection film 5.
[0084] As presented in the Table, the lens of Example 3 was grade A
for both the shade of color and the number of white spots in the
appearance evaluation.
Example 4
[0085] In Example 4, the coating 4 was formed in the same way as in
Example 1 except that the quantity of the coating paint, a methylol
resin solution containing an amino triazine compound as raw
material for a methylated melamine resin (Sanwa Chemical NIKALAC
MX-706), was 79.4 g. Then the same procedure as in Example 1 was
followed, yielding a lens having its optically effective section
coated with an antireflection film 5.
[0086] As presented in the Table, the lens of Example 4 was grade A
for both the shade of color and the number of white spots in the
appearance evaluation.
Example 5
[0087] In Example 5, the coating paint was prepared as follows.
Forty grams of a novolac phenolic resin (Showa Denko SHONOL
BRG-557) was dissolved in a solvent mixture of 40 g of
1-methoxy-2-acetoxypropane and 40 g of 1-ethoxy-2-propanol through
stirring with a mechanical stirrer at room temperature. The
obtained resin solution was mixed and stirred to uniformity with
22.6 g of a methylol resin solution containing an amino triazine
compound as raw material for a methylated melamine resin (Sanwa
Chemical NIKALAC MX-706 (a solid content of 70.6% by mass)). Except
for the use of this solution as the coating paint, the same
procedure as in Example 1 was followed to produce a lens.
[0088] As presented in the Table, the lens of Example 5 was grade A
for both the shade of color and the number of white spots in the
appearance evaluation.
Example 6
[0089] In Example 6, the coating paint was 22.6 g of a methylol
resin solution containing an amino triazine compound as raw
material for a methylated benzoguanamine resin (Sanwa Chemical
NIKALAC BL-60 (a solid content of 70.6% by mass)). Except for this,
the coating 4 was formed in the same way as in Example 1. Then the
same procedure as in Example 1 was followed, yielding a lens having
its optically effective section coated with an antireflection film
5.
[0090] As presented in the Table, the lens of Example 6 was grade A
for the shade of color but grade B for the number of white spots in
the appearance evaluation.
Example 7
[0091] In Example 7, the paint specified below was used to form the
light-shielding paint.
[0092] The main ingredient of the light-shielding paint was
prepared as follows. First, 42.9 g of propylene glycol monomethyl
ether, a dispersant, and 14.3 g of fine particles of titania (a
refractive index (nd) of 2.2 or more) were dispersed in a bead mill
(Kotobuki Industries ULTRA APEX MILL) using 50-.mu.m diameter
beads, yielding 57.2 g of slurry containing titania fine particles
with a number-average particle diameter of 20 nm. Then 57.2 g of
the bead-milled slurry, 21 g of epoxy resin A, 1 g of a coupling
agent, 13 g of a coloring agent, and 40 g of propylene glycol
monomethyl ether were individually weighed into a ball mill pot.
Five 20-mm diameter magnetic balls were then put into the ball mill
pot. Titanium oxide (Tayca MT-05) was used as inorganic fine
particles having a refractive index (nd) of 2.2 or more. The epoxy
resin A was a condensation polymer of 4,4'-isopropylidenediphenol
and 1-chloro-2,3-epoxypropane (Mitsubishi Chemical EPIKOTE 828),
and the coupling agent was an epoxy silane coupling agent
(Shin-Etsu Silicone KBM 403). The formulated paint and magnetic
balls in the ball mill pot were stirred on a roll coater for 48
hours. In this way, the main ingredient of the light-shielding
paint was obtained.
[0093] The coloring agent was a mixture of a black dye, a red dye,
two yellow dyes, and a blue dye. The black dye was Orient Chemical
Industries VALIFAST BLACK 1821, the red dye was Orient Chemical
Industries VALIFAST RED 3320, the yellow dyes were Orient Chemical
Industries OIL YELLOW 129 and VALIFAST YELLOW 3108, and the blue
dye was Orient Chemical Industries VALIFAST BLUE 1605.
[0094] Then 132.2 g of the main ingredient of the light-shielding
paint was stirred with 1.9 g of amine-based hardener A and 1 g of a
hardening catalyst on a roll coater for 30 minutes. The amine-based
hardener A, an aliphatic amine-based hardener, was Adeka
Corporation's ADEKA HARDENER EH 6019, and the hardening catalyst A
was 2,4,6-tris(diaminomethyl)phenol. Except for the use of this
paint as the light-shielding paint, the same procedure as in
Example 1 was followed to produce a lens.
[0095] As presented in the Table, the lens of Example 7 was grade A
for both the shade of color and the number of white spots in the
appearance evaluation.
Comparative Example 1
[0096] In Comparative Example 1, the same procedure as in Example 1
was followed to produce a lens, but after the formation of the
light-shielding film 3 in the same way as in Example 1, no coating
was formed on the surface of the light-shielding film.
[0097] As presented in the Table, the lens of Comparative Example 1
was grade C for both the shade of color and the number of white
spots in the appearance evaluation.
Comparative Example 2
[0098] In Comparative Example 2, the coating paint was prepared as
follows. Forty grams of a resol phenolic resin (Showa Denko SHONOL
BKM-2620) was dissolved in a solvent mixture of 40 g of
1-methoxy-2-acetoxypropane and 40 g of 1-ethoxy-2-propanol through
stirring with a mechanical stirrer at room temperature, and the
resulting solution was directly used as the coating paint. Except
for the use of this solution as the coating paint, the same
procedure as in Example 1 was followed to produce a lens.
[0099] As presented in the Table, the lens of Comparative Example 2
was grade B for the shade of color and grade C for the number of
white spots in the appearance evaluation.
Comparative Example 3
[0100] In Comparative Example 3, the coating paint was prepared
through the dissolution of 22.6 g of a methylol resin solution
containing an amino triazine compound as raw material for a
methylated melamine resin (Sanwa Chemical NIKALAC MX-706) in a
solvent mixture of 40 g of 1-methoxy-2-acetoxypropane and 40 g of
1-ethoxy-2-propanol through stirring with a mechanical stirrer at
room temperature. Except for the use of this solution as the
coating paint, the same procedure as in Example 1 was followed to
produce a lens.
[0101] As presented in the Table, the lens of Comparative Example 3
was grade B for the shade of color and grade C for the number of
white spots in the appearance evaluation.
TABLE-US-00001 TABLE Appearance Coating on the light-shielding film
after a reliability Light- Melamine or study shielding Methylol
Additional benzoguanamine The film resin resin resin to phenolic
number Main Mass Mass resin ratio Shade of white ingredient
Material [g] Material [g] (by mass) of color spots Example 1 GT-7
Methylol 11.3 Resol 40 1:5 A A melamine resin resin Example 2 GT-7
Methylol 22.6 Resol 40 2:5 A A melamine resin resin Example 3 GT-7
Methylol 45.3 Resol 40 4:5 A A melamine resin resin Example 4 GT-7
Methylol 79.4 Resol 40 7:5 A A melamine resin resin Example 5 GT-7
Methylol 22.6 Novolac 40 2:5 A A melamine resin resin Example 6
GT-7 Methylol 22.6 Resol 40 2:5 A B benzoguanamine resin resin
Example 7 Dyes Methylol 22.6 Resol 40 2:5 A A melamine resin resin
Comparative GT-7 None -- None -- -- C C Example 1 Comparative GT-7
None -- Resol 40 -- B C Example 2 resin Comparative GT-7 Methylol
22.6 None -- -- B C Example 3 melamine resin
Overall Review
[0102] Examples 1 to 7 demonstrated that if an optical element has
a coating including a cured mixture of melamine or benzoguanamine
resin, and a phenolic resin, on its light-shielding film, the
light-shielding film experiences little change in its shade of
color and develops few white spots during a reliability study.
[0103] Optical elements according to an aspect of the invention,
having their optically ineffective section shielded by a film
nontransparent to the spectrum of wavelengths to be used with them
and partially or completely protected by a coating suitable for the
prevention of damage to the appearance of the nontransparent film,
can be used as an optical element such as a lens, and also as an
optical system or optical equipment incorporating such an optical
element.
Advantages
[0104] An aspect of the invention provides an optical element that
has a coating including a melamine or benzoguanamine resin on a
nontransparent film. This coating improves the waterproofness and
alkali resistance of the nontransparent film, allowing the optical
element to maintain good appearance even through a long period of
use under high-temperature and high-humidity conditions.
[0105] 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.
* * * * *