U.S. patent application number 11/390307 was filed with the patent office on 2006-07-27 for process to produce a resin-cemented optical element.
This patent application is currently assigned to NIKON CORPORATION. Invention is credited to Akiko Miyakawa, Toru Nakamura, Masahito Suzuki.
Application Number | 20060163761 11/390307 |
Document ID | / |
Family ID | 26517398 |
Filed Date | 2006-07-27 |
United States Patent
Application |
20060163761 |
Kind Code |
A1 |
Miyakawa; Akiko ; et
al. |
July 27, 2006 |
Process to produce a resin-cemented optical element
Abstract
A process to produce a resin-cemented optical element having a
base member and a resin layer formed on the surface of the base
member and having a cured product of a photosensitive resin
composition. The resin layer has (1) a refractive index of 1.55 or
more, (2) a visible-light inner transmittance of 95% or more in a
100 .mu.m thick area, (3) a rate of hygroscopic dimensional change
of 0.4% or less, (4) a durometer hardness of HDD 70 or more, (5) a
gel percentage of 95% or more, (6) a glass transition temperature
of 95.degree. C. or above or (7) a rate of shrinkage on curing of
7% or less.
Inventors: |
Miyakawa; Akiko;
(Sagamihara-shi, JP) ; Nakamura; Toru;
(Kawasaki-shi, JP) ; Suzuki; Masahito;
(Kawasaki-shi, JP) |
Correspondence
Address: |
STAAS & HALSEY LLP
SUITE 700
1201 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Assignee: |
NIKON CORPORATION
Tokyo
JP
|
Family ID: |
26517398 |
Appl. No.: |
11/390307 |
Filed: |
March 28, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10031602 |
Jan 23, 2002 |
|
|
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PCT/JP00/04922 |
Jul 24, 2000 |
|
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11390307 |
Mar 28, 2006 |
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Current U.S.
Class: |
264/1.32 ;
264/1.36; 264/2.6 |
Current CPC
Class: |
Y10T 428/31601 20150401;
Y10T 428/31649 20150401; B29D 11/0073 20130101; B29L 2011/0016
20130101; B29C 43/18 20130101; B29D 11/00 20130101 |
Class at
Publication: |
264/001.32 ;
264/001.36; 264/002.6 |
International
Class: |
B29D 11/00 20060101
B29D011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 23, 1999 |
JP |
11-209345 |
Sep 27, 1999 |
JP |
11-271738 |
Claims
1. A process to produce a resin-cemented optical element, the
process comprising: a first exposure operation of irradiating a
photosensitive resin composition held between the surface of a base
member and a mold tool, to cure the composition to form a resin
layer; a mold release operation of mold-releasing the resin layer;
and a heating operation of heating the resin layer, in this
order.
2. A process to produce a resin-cemented optical element, the
process comprising: a first exposure operation of irradiating a
photosensitive resin composition held between the surface of a base
member and a mold tool, with heating to cure the composition to
form a resin layer; and a mold release operation of mold-releasing
the resin layer, in this order.
3. The process to produce a resin-cemented optical element
according to claim 2, wherein the heating in said first exposure
operation is carried out at a temperature of from 40.degree. C. to
130.degree. C.
4. A process to produce a resin-cemented optical element, the
process comprising: one or more exposure operations of irradiating
a photosensitive resin composition held between the surface of a
base member and a molding tool, to cure the composition to form a
resin layer; and at least one of said exposure operations being the
operation of irradiating the resin composition by light not
comprising light with a wavelength less than 300 nm.
5. The process to produce a resin-cemented optical element
according to claim 4, further comprising a mold release operation
of mold-releasing the resin layer; said operation of irradiating
the resin composition by the light not comprising light with a
wavelength of less than 300 nm being a first exposure operation
carried out before said mold release operation.
6. The process to produce a resin-cemented optical element
according to claim 4, further comprising a mold release operation
of mold-releasing the resin layer; said operation of irradiating
the resin composition by the light not comprising light with a
wavelength of less than 300 nm being a second exposure operation
carried out after said mold release operation.
7. The process to produce a resin-cemented optical element
according to claim 1, further comprising, after said mold release
operation, a second exposure operation of irradiating the resin
layer by light not comprising light with a wavelength of less than
300 nm.
8. The process to produce a resin-cemented optical element
according to claim 4, wherein the irradiation in the operation of
irradiation by the light not comprising light with a wavelength of
less than 300 nm is performed shutting out light with a wavelength
of less than 300 nm among light emitted from a light source.
9. The process to produce a resin-cemented optical element
according to claim 2, further comprising, after said mold release
operation, a heating operation of heating the resin layer.
10. The process to produce a resin-cemented optical element
according to claim 6, further comprising, after said second
exposure operation, a heating operation of heating the resin
layer.
11. The process to produce a resin-cemented optical element
according to claim 1, wherein the heating in said heating operation
is carried out at a temperature of from 40.degree. C. to
130.degree. C.
12. The process to produce a resin-cemented optical element
according to claim 1, wherein said resin composition comprises: a
polyfunctional (meth) acrylate; a polyfunctional urethane-modified
(meth) acrylate; and a photopolymerization initiator.
13. The process to produce a resin-cemented optical element
according to claim 2, further comprising, after said mold release
operation, a second exposure operation of irradiating the resin
layer by light not comprising light with a wavelength of less than
300 nm.
14. The process to produce a resin-cemented optical element
according to claim 5, further comprising, after said mold release
operation, a second exposure operation of irradiating the resin
layer by light not comprising light with a wavelength of less than
300 nm.
15. The process to produce a resin-cemented optical element
according to claim 9, wherein the heating in said heating operation
is carried out at a temperature of from 40.degree. C. to 130
C.degree..
16. The process to produce a resin-cemented optical element
according to claim 10, wherein the heating in said heating
operation is carried out at a temperature of from 40.degree. C. to
130 C.degree..
17. The process to produce a resin-cemented optical element
according to claim 2, wherein said resin composition comprises: a
polyfunctional (meth) acrylate; a polyfunctional urethane-modified
(meth) acrylate; and a photopolymerization initiator.
18. The process to produce a resin-cemented optical element
according to claim 4, wherein said resin composition comprises: a
polyfunctional (meth) acrylate; a polyfunctional urethane-modified
(meth) acrylate; and a photopolymerization initiator.
19. The process to produce a resin-cemented optical element
according to claim 5, further comprising, after said mold release
operation, a heating operation of heating the resin layer.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 10/031,602, filed Jan. 23, 2002, which has
been allowed. This application is based upon and claims priority
from U.S. patent application Ser. No. 10/031,602, filed Jan. 23,
2002, the contents being incorporated herein by reference, and
claims priority based on International Patent application no.
PCT/JP00/04922 filed Jul. 24, 2000 and Japanese patent application
nos. 11-209345 and 11-271738 respectfully filed Jul. 23, 1999 and
Sep. 27, 1999.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to a resin-cemented optical element
having a resin layer formed on the surface of a base member, a
process for its production, and an optical article having the
element.
[0004] 2. Description of Related Art
[0005] At present, optical elements are used in various fields.
Depending on the purpose for which they are used, it is difficult
to materialize required optical characteristics and so forth in
some cases in respect of conventional spherical lenses comprised
only of glass. Accordingly, resin-cemented optical elements
comprising a base member provided thereon with a cured resin layer
having a stated shape are attracting notice.
[0006] For example, in order to make optical elements such as
camera lenses compact and light-weight, it is important to lessen
the number of component lenses of an optical system. In order to
lessen the number of component lenses, it is effective that a
component part constituted of a plurality of spheric lenses is
replaced with one aspheric lens.
[0007] "Aspheric lens" is a generic term for lenses the curvature
of which is kept continuously different over the region extending
from the lens center toward the periphery. The use of aspheric
lenses at some part of optical systems enables considerable
reduction of the number of lenses necessary for the correction of
aberrations, compared with a case in which the optical system is
constituted only of spheric lenses. This can make the optical
system compact and light-weight. Also, the use of aspheric lenses
enables high-grade correction of aberrations which is difficult for
spherical lenses, and hence can bring about an improvement in image
quality.
[0008] Aspheric lenses having such superior characteristics have
not necessarily come into wide use. The greatest reason therefor
can be said to be a difficulty in working. Conventional aspheric
lenses make use of base members made of glass, and have only be
able to be produced by precisely polishing this glass, having
involved the problem of a high cost.
[0009] In recent years, however, techniques for producing
resin-cemented optical elements such as composite-type
aspherical-surface molding, plastic molding, and glass molding have
been put into practical use one after another, and it has become
possible to produce aspheric lenses at a low cost by these methods.
Thus, the aspheric lenses have rapidly come into wide use.
Nowadays, such aspheric lenses have come into wide use in camera
lenses and so forth.
[0010] The plastic molding is a method in which a resin is injected
into a mold with the desired aspherical shape to effect molding.
This method can enjoy a high productivity and a low cost. It,
however, has had problems that aspheric lenses thus produced have a
limit to their refractive index and moreover are inferior to glass
lenses in respect of figure tolerance and reliability.
[0011] The glass molding is a method in which a glass blank
material standing softened is shaped in a mold having the desired
aspherical shape. This method enables achievement of mass
productivity and high precision. It, however, has a limit to the
types of glass usable therefor. Moreover, it requires a relatively
high molding temperature, and may impose a great load on the mold.
Accordingly, how this load be reduced comes into question.
[0012] The composite-type aspherical-surface molding is a method in
which, using a mold having an aspherical shape, a resin layer
having the aspherical shape is provided on a spheric or aspheric
glass lens. This method can be said to be a method having both the
characteristics, i.e., the reliability the glass lens has and the
mass productivity the plastic molding has. In the present
specification, a lens produced by this composite-type
aspherical-surface molding is called a PAG lens. Conventional PAG
lenses have characteristic features that they can well be
mass-produced and are relatively inexpensive. They, however, have
problems such that, compared with aspheric lenses made of glass,
they have a restriction on the extent of designable aspheric
surface, have a low light transmittance, and may change in optical
performance depending on environment, resulting in a poor
reliability.
[0013] As the resin used in this composite-type aspherical-surface
molding, it may include thermoplastic resins and photosensitive
resins. In the case when aspheric lenses are produced, a method is
especially effective in which a composition of photosensitive resin
(photo-reactive resin) is made to adhere to the surface of a base
member, followed by irradiation with light such as ultraviolet
light to effect curing. However, when such a photosensitive resin
is used in the PAG lens resin layer, there is a problem that the
shape of the mold can not exactly be transferred especially in the
case of a PAG lens having a large extent of aspherical surface,
i.e., having a large resin thickness. This imposes a restriction on
designing.
[0014] Conventional PAG lenses also have a lower light
transmittance than glass lenses, and hence the employment of such
PAG lenses may possibly lead to a low transmittance of the whole
optical system. For this reason, the number of PAG lenses usable in
one optical system is usually limited to one or two.
[0015] Resin-cemented optical elements such as the PAG lenses also
have a problem that they may so greatly change in optical
performance depending on environment as to have a poor
weatherability. In order to improve the weatherability, it is
effective to enhance the degree of cure (degree of polymerization)
of the resin, and, in order to do so, it is effective to irradiate
the resin by a large amount of light so as to cure the resin
further. However, an increase in irradiation level results in a
decrease in light transmittance of the resin because of its
yellowing. Thus, it is difficult for any conventional techniques to
achieve both the improvement in light transmittance and the
improvement in weatherability of the resin-cemented optical
element.
SUMMARY OF THE INVENTION
[0016] An object of the present invention is to provide a superior
resin-cemented optical element having solved the above problems in
conventional PAG lenses, i.e. the problems on the restrictions on
optical performance and extent of designable aspherical surface,
the weatherability and so forth, and having a high light
transmittance (in particular, visible-light inner
transmittance).
[0017] With regard to the aspheric lens having a large extent of
aspherical surface, which has hitherto had insufficient optical
performance in respect of, e.g., transmittance and been moldable
with difficulty and producible only by costly methods, the present
inventors have made extensive studies from various points of view
in order to produce such an aspheric lens with ease and also to
achieve superior optical performance by the use of the aspheric
lens, and have discovered the following facts.
[0018] 1. Characteristics of Resin Layer:
[0019] As a method by which a resin is molded with greater ease
than conventional methods without damaging any optical performance
having ever been achieved, a method is available in which the resin
is made to have a higher refractive index. Namely, by the use of a
resin having a higher refractive index, the same effect of
aspherical surface as that achievable by the one having a large
extent of aspherical surface can be achieved in a smaller extent of
aspherical surface. Also, the lens having a small extent of
aspherical surface is obtainable in a better moldability than the
lens having a large extent of aspherical surface. Thus, it follows
that the moldability can be improved by making the refractive index
higher. More specifically, in order to make the effect of
aspherical surface higher without changing the shape of aspherical
surface, it is effective to make the resin have a higher refractive
index. In particular, a resin having a refractive index of 1.55 or
more enables the aspherical surface to be designed at a higher
freedom, so that an aspheric lens usable for various purposes can
be obtained.
[0020] Resins used in resin layers of conventional PAG lenses have
had a refractive index of about 1.50 on the whole. However, the use
of the resin having a refractive index of 1.55 or more enables the
resin layer to have a layer thickness thinner than that in
conventional cases. This not only makes the moldability higher, but
also allows the resin to be used in a small quantity, enabling
achievement of cost reduction.
[0021] It has also been ascertained that making the resin have a
larger refractive index makes the PAG lens have a higher
transmittance. This is because the difference in refractive index
between the resin constituting the PAG lens and the glass can be
made small, so that the light may less reflect at their interface.
Hence, the use of the resin having a high refractive index makes it
possible to use the PAG lens even in an aspheric lens required to
have a higher transmittance. Such a PAG lens having a high
transmittance contributes to the improvement of transmittance of
the whole optical system and to the prevention of flares.
[0022] What is most questioned in optical performance of resin is
the transmittance. In general, resin has lower transmittance than
glass, and hence PAG lenses often have a transmittance inferior to
the transmittance of aspheric lenses made only of glass. The
transmittance of resin may lower on account of two factors, the
scattering and absorption of light in the interior of the resin.
The scattering is caused when the resin does not have any uniform
compositional distribution to have refractive-index distribution at
some part, by minute bubbles formed in the resin, or by any
dot-like defects at the surface. As for the absorption, it arises
from the molecular structure itself of a resin-constituting
substance in some cases, but commonly in many cases it is
absorption due to impurities included in the course of synthesis of
the resin and a polymerization inhibitor previously added to the
resin, or it is absorption due to a photopolymerization initiator
and a reaction product thereof, or it is caused by any excess
irradiation at the time of curing.
[0023] Accordingly, in order to improve light transmittance, it is
important to remove impurities by purification as far as possible,
taking account of the resin's molecular structure carefully. In
addition, it is effective that a composition having a
polymerization inhibitor and a photopolymerization initiator in an
optimum state is polymerized under proper conditions for the
irradiation.
[0024] In consideration of the foregoing, the resin layer may have
an inner transmittance of 95% or more in a 100 .mu.m thick area,
where a PAG lens having optical characteristics good for practical
use can be obtained.
[0025] In the step of transferring the shape of aspherical surface
of a mold by the use of a photosensitive resin, the resin surface
may peel from the mold during the irradiation. Such a problem may
often occur. It has been ascertained that this relates closely to
the rate of shrinkage on curing of resin. The fact that the shape
of the mold can not exactly be transferred when a photosensitive
resin is used is due to the shrinkage on curing when the resin
cures. This shrinkage has a remarkable influence in the case of a
PAG lens having a great difference in the extent of aspherical
surface or the resin layer thickness. Here, the rate of shrinkage
on curing is the value that depends substantially on the
composition of the resin, and is an important property which
determines the moldability of resin in the molding for PAG
lenses.
[0026] Resin layers of PAG lenses have a difference of hundreds of
micrometers or more between the maximum layer thickness and the
minimum layer thickness. This difference in layer thickness of
resin layers has a tendency of becoming larger and larger with a
spread of the use of aspheric lenses hereafter. When a resin layer
having such a complicated shape is irradiated by light, a stress is
produced upon any abrupt shrinkage on curing to cause a difficulty
that the shape of the mold is not exactly transferred. The rate of
shrinkage on curing can readily be determined by measuring the
specific gravity of the resin before and after its curing. More
specifically, where the specific gravity before curing is
represented by a, and the specific gravity after curing by b, the
rate of shrinkage on curing can be calculated according to
{(b-a)/b}.times.100 (%).
[0027] Accordingly, resins having different rates of shrinkage on
curing have been compared and studied to examine in detail the
relationship between the rate of shrinkage on curing and the
frequency of occurrence of faulty shape transfer for each resin. As
the result, it has been ascertained that a resin having a rate of
shrinkage on curing of 7% or less can be molded after the shape of
aspherical surface without any problem. The use of such a resin
enables production of aspheric lenses in a better moldability and
in a superior production efficiency.
[0028] In order to control the rate of shrinkage on curing of the
resin in this way, it is effective not to make up the resin from
monomers, but to add also an oligomer having a relatively large
molecular weight so that the number of functional groups per unit
weight can be made small.
[0029] It has also been found that the problem of weatherability
correlates with the rate of moisture absorption of resin. Resin
commonly has a higher rate of moisture absorption and also a lower
heat resistance than glass, and hence the former is inferior to the
latter in respect of the weatherability. Accordingly, the optical
performance of PAG lenses has been followed up throughout a year to
reveal that it varies seasonsably. It has been ascertained that
this is caused by the moisture absorption of resin according to
changes in moisture in environment. In an environment of high
humidity, the resin absorbs moisture to cause a volumetric change,
so that the optical performance may deteriorate.
[0030] Accordingly, resins having different rates of moisture
absorption have been compared and studied to determine resin
characteristics which are tolerable in practical use. As the
result, it has been discovered that the problem on the changes in
humidity can be solved when the rate of hygroscopic change in layer
thickness is controlled to be 0.4% or less. This enables production
of an aspheric lens having a durability strong enough to be usable
even in service environment which changes greatly. Also, in order
to make the resin have a low rate of moisture absorption, it is
effective to lower the content of hydrophilic groups such as
alkyleneoxy and isocyanate groups in the molecule.
[0031] As a result of evaluation on the weatherability of various
resins, it has also been found that the resin layer may have a
greatly poor weatherability when the resin has a low degree of
polymerization, and must be cured at a high rate in order to
achieve superior weatherability. Accordingly, as an index of the
degree of polymerization, gel percentage has been measured which is
determined from the weight ratio of dissolved things of cured resin
having been treated with a solvent under stated conditions. As the
result, it has been ascertained that a weatherability having no
problem in practical use can be achieved when this gel percentage
is 95% or more, and particularly preferably 96% or more.
[0032] The gel percentage is determined from a change in weight
observed when the component having dissolved in the solvent under
stated conditions is removed. Stated in detail, it is measured
under the following conditions.
[0033] That is, about 0.5 g of a resin cured product is dried in a
desiccator for about a day, and thereafter the mass of the dried
resin obtained is precisely measured. Next, this resin is immersed
in 70.degree. C. methyl ethyl ketone for 6 hours. Here, the methyl
ethyl ketone is changed for new one at intervals of 2 hours. The
resin having been immersed for 6 hours is heated at 100.degree. C.
for 2 hours, and then left in the desiccator for a day to make it
dry. Thereafter, the mass of the resin thus dried is precisely
measured. Here, where the mass of the initial resin is represented
by c, and the mass after immersion in methyl ethyl ketone by d, the
gel percentage is calculated according to (d/c).times.100 (%).
[0034] The cause of deterioration of the weatherability of resin is
that unreacted functional groups remain also after the molding.
Such unreacted functional groups may cause various side reaction
over a long period of time to cause the coloring of resin. In this
regard, the resin having a high gel percentage has less unreacted
functional groups. Hence, such a resin is considered to have
superior weatherability. In actual use, in order to provide a
sufficient weatherability, it is preferable for the resin to have
the gel percentage of 95% or more as stated above. In order to make
the gel percentage higher, it is effective to optimize the amount
of a photopolymerization initiator to be added and the level of
irradiation.
[0035] There has been an additional problem that conventional
resins for PAG lenses have a lower mar resistance than aspheric
lenses made of glass, and tend to be marred when handled in, e.g.,
the step of assembling lenses. It has been discovered that the use
of a resin having a durometer hardness of HDD 70 or more makes the
resin not become marred in usual handling. The use of such a resin
enables production of an aspheric lens having superior mar
resistance to make it possible to obtain an aspheric lens durable
to its use in service environment which tends to cause mars. This
broadens the scope in which the aspheric lens is applicable. Also,
in order to make the resin have such a higher hardness, it is
important that the amount of a photopolymerization initiator to be
added and the conditions for irradiation are optimized to cure the
resin sufficiently. It is also effective to add to components a
resin having a hard skeleton such as bisphenol-A skeleton.
[0036] The surfaces of resin layers of PAG lenses are usually
provided with anti-reflection coat. Such a anti-reflection coat is
formed by vacuum deposition or the like. If the resin has a low
heat resistance, the resin may expand when heated by radiation heat
at the time of this film formation, so that a coat layer harder
than the resin can not follow up the latter's changes in shape to
make the anti-reflection coat have cracks in some cases. Thus, the
resin used in PAG lenses is required to have properties not
causative of any changes even at high temperature.
[0037] Accordingly, in respect of some resins having different
glass transition points, how the resins cause cracks has been
compared and studied. As the result, it has been ascertained that a
resin having a glass transition temperature of 95.degree. C. or
above can keep cracks from occurring. Thus, the use of the resin
having such a property enables production of an aspheric lens
having various durabilities and, in addition thereto, having
superior reflection preventive performance and durable to more
various service environments. In order to make the glass transition
temperature higher, it is effective to use a polyfunctional
(meth)acrylate or a polyfunctional urethane (meth)acrylate as a
component of the resin. Here, the glass transition temperature can
be determined as the point of inflection of a curve showing
dimensional changes caused by heating, using TMA (thermomechanical
analysis), a type of thermal analysis.
[0038] On the basis of the new findings explained above, the
present invention provides an optical element comprising a base
member and a resin layer formed on the surface of the base member
and comprising a cured product of a photosensitive resin
composition. The resin layer is a resin layer having at least one
characteristic features of the following (1) to (7). The present
invention also provides an optical lens comprising this aspheric
lens, and provides an optical article having the optical lens.
Incidentally, the resin layer in the aspheric lens of the present
invention may preferably have at least two of any of these
characteristic features. [0039] (1) It has a refractive index of
1.55 or more. [0040] (2) It has a visible-light inner transmittance
of 95% or more in a 100 .mu.m thick area. [0041] (3) It has a rate
of hygroscopic dimensional change of 0.4% or less. [0042] (4) It
has a durometer hardness of HDD 70 or more. [0043] (5) It has a gel
percentage of 95% or more. [0044] (6) It has a glass transition
temperature of 95.degree. C. or above. [0045] (7) It has a rate of
shrinkage on curing of 7% or less (i.e., it is a cured product of a
resin composition having a rate of shrinkage on curing of 7% or
less.
[0046] In the case when the optical element of the present
invention is an aspheric lens, the shape of aspherical surface may
be formed on the side of convex surface, or may be formed on the
side of concave surface. In other words, the resin layer may be
formed on either of concave and convex sides of a base member
lens.
[0047] 2. Resin Composition:
[0048] Accordingly, studies have been made on resins preferable for
satisfying the above characteristics. As the result, what is
preferable as the resin layer in the optical element of the present
invention has been found to be a resin layer comprising a cured
product of a photosensitive resin composition containing:
[0049] (A) a polyfunctional (meth)acrylate;
[0050] (B) a polyfunctional urethane-modified (meth)acrylate;
and
[0051] (C) a photopolymerization initiator. The components (A) to
(C) may preferably be contained as chief components. Incidentally,
in the present specification, an acrylate and a methacrylate are
generically termed "(meth)acrylate".
[0052] The resin composition used in the optical element of the
present invention may preferably have a viscosity before
polymerization curing, of 50,000 cP or lower at room temperature.
If the resin composition has a viscosity higher than 50,000 cP, it
may have a poor operability and also may cause an increase in
defectives due to inclusion of bubbles.
[0053] In general, resins change in refractive index before and
after curing. Hence, in order to attain the desired refractive
index after curing, the composition of the resin must be determined
taking account of the changes in refractive index before and after
curing. Accordingly, in respect of the above resin composition,
changes in refractive index before and after curing have been
studied in detail. As the result, it has been ascertained that the
refractive index after curing comes to 1.55 or more when the
refractive index before curing is 1.52 or more. Thus, the
photosensitive resin composition in the present invention may
preferably have a refractive index before curing of 1.52 or
more.
[0054] In order for the resin composition to have the refractive
index of 1.52 or more before curing, the component-(A)
polyfunctional (meth)acrylate alone may be made to have a
refractive index of 1.53 or more. Such a polyfunctional
(meth)acrylate having a refractive index of 1.53 or more may
preferably be selected from those having two or more benzene ring
structures in one molecule.
[0055] As specific examples of the polyfunctional (meth)acrylate,
it may include bifunctional (meth)acrylates such as
di(meth)acrylate of
2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-propionate, ethylene
glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate,
propylene glycol di(meth)acrylate, polypropylene glycol
di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol
di(meth)acrylate, neopentyl glycol di(meth)acrylate,
di(meth)acrylate of an ethylene oxide addition product of bisphenol
A, di(meth)acrylate of a propylene oxide addition product of
bisphenol A, di(meth)acrylate of
2,2'-di(hydroxypropoxyphenyl)propane, di(meth)acrylate of
tricyclodecane dimethylol, and a di(meth)acrylic acid addition
product of 2,2'-di(glycidyloxyphenyl)propane.
[0056] It may also include as compounds preferred as the component
(A) in the present invention, e.g., trimethylolpropane
tri(meth)acrylate, pentaerythritol tri(meth)acrylate,
pentaerythrythol tetra(meth)acrylate, dipentaerythritol
hexa(meth)acrylate, tetramethylolmethane tetra(meth)acrylate,
tri(meth)acrylate of tris(hydroxyethyl)isocyanurate,
tri(meth)acrylate of tris(2-hydroxyethyl)isocyanurate,
tri(meth)acrylate of trimellitic acid, triallyltrimellitic acid,
and triallyl isocyanurate.
[0057] As a result of extensive studies, the present inventors have
discovered that a di(meth)acrylate represented by the following
Formula (1) is particularly preferred as the component (A). Of the
di(meth)acrylate represented by Formula (1), one having a molecular
weight of 1,000 or less is more preferred because of its large
refractive index. ##STR1## wherein R.sup.1 and R.sup.2 are each a
hydrogen atom or a methyl group, R.sup.3 and R.sup.4 are each a
hydrocarbon group having 2 to 4 carbon atoms, and m and n are each
an integer of 1 or more.
[0058] The component (A) may be constituted of one kind of
polyfunctional (meth)acrylate, or may be constituted of two kinds
or more. This component (A) has the function to enhance the
refractive index of the resin used in the optical element of the
present invention. Accordingly, the component (A) may preferably
have a refractive index before curing of 1.53 or more.
[0059] The polyfunctional (meth)acrylate having benzene rings tends
to have a large molecular weight. The one having too large a
molecular weight may make the resin have too high a viscosity. On
the other hand, the resin may have a low viscosity when the
structure (R.sup.3--O).sub.n and/or (R.sup.4--O).sub.m other than
the benzene rings in Formula (1) is/are large, but may also have a
low refractive index. Accordingly, polyfunctional (meth)acrylates
having various molecular weights have been compared and studied. As
the result, it has been ascertained that it is suitable for the
molecular weight to be 1,000 or less.
[0060] The component (A) may preferably be in a content of from 10
to 95% of the resin as weight percentage. If it is less than 10%,
the resin may have a refractive index less than 1.55. If it is more
than 95%, the resin may have a low environmental resistance.
[0061] The component (B) is a polyfunctional urethane-modified
(meth)acrylate. This is a compound composed chiefly of a
diisocyanate, a polyol and a hydroxy(meth)acrylate. Also, a
polyester diol may optionally be used. The component (B) may be
constituted of one kind of polyfunctional urethane-modified
(meth)acrylate, or may be constituted of two kinds or more.
[0062] The component-(B) polyfunctional urethane-modified
(meth)acrylate commonly has a low refractive index. In order for
the resin to have the refractive index of 1.52 or more after
mixing, the polyfunctional urethane-modified (meth)acrylate alone
may preferably be made to have a refractive index of 1.48 or more.
If the component (B) has a refractive index less than 1.48, the
resin layer may have a low refractive index.
[0063] As a result of extensive studies, the present inventors have
discovered that a compound represented by any of the following
Formulas (2) to (4) is particularly preferred as the component (B).
##STR2## wherein R.sup.5 and R.sup.6 are each a hydrogen atom or a
methyl group, R.sup.7 and R.sup.8 are each a hydrocarbon group
having 1 to 10 carbon atoms, R.sup.9 is an isocyanate residual
group, R.sup.10 is a polyol residual group or a polyester residual
group, and p is o0 or an integer of 10 or less. ##STR3## wherein
R.sup.11 is a hydrocarbon group having 1 to 10 carbon atoms, and
R.sup.12 is ##STR4## wherein R.sup.14, R.sup.15 and R.sup.18 are
each a hydrogen atom or a methyl group, and R.sup.17 is a
hydrocarbon group having 1 to 10 carbon atoms. ##STR5## wherein
R.sup.19 is a hydrocarbon group having 1 to 10 carbon atoms, and
R.sup.20 and R.sup.21 are each ##STR6## wherein R.sup.24, R.sup.25
and R.sup.26 are each a hydrogen atom or a methyl group, and
R.sup.27 is a hydrocarbon group having 1 to 10 carbon atoms.
[0064] R.sup.9 in Formula (2) may preferably contain an aliphatic
ring or an aromatic ring, taking account of the refractive index of
the component (B). Also, as in Formula (3), the (meth)acrylate may
be bonded to the isocyanate cyclic trimer. The (meth)acrylate in
Formulas (3) and (4) may be monofunctional or may be
polyfunctional.
[0065] The component (B) may preferably be in a content of from 5
to 80% of the resin as weight percentage. If it is less than 5%,
the resin may have a low environmental resistance. If it is more
than 80%, the resin may have so high a viscosity as to result in a
poor operability.
[0066] As the component-(C) photopolymerization initiator, any
known compound may be used. For example, substances of an
acetophenone type, a benzoin type, a benzophenone type, a thioxane
type and an acylphosphine oxide type may be used. In the present
invention, as the photopolymerization initiator, any one selected
from these may be used, or two or more of these may be used in
combination. If necessary, a photopolymerization initiator
auxiliary agent may further be added.
[0067] The component (C) may preferably be in an amount of from 0.1
to 5% of the resin as weight percentage. As long as it is within
this range, the resin can be cured at an appropriate curing rate
without any lowering of its properties.
[0068] In addition to the components (A) to (C) described above,
the photosensitive resin composition used in the present invention
may preferably further contain at least one additive selected
from:
[0069] (D) a monofunctional (meth)acrylate;
[0070] (E) a release agent;
[0071] (F) a silicon compound; and
[0072] (G) an epoxy (meth)acrylate.
[0073] The component-(D) monofunctional (meth)acrylate commonly has
a higher fluidity than other components, and hence it flows through
the interior of the resin layer also in the course of
polymerization reaction caused by irradiation, and has the effect
of keeping any internal stress from being produced. Concurrently
therewith, it has the effect of lessening unreacted functional
groups and making the gel percentage higher to improve the
weatherability of the optical element. Hence, the addition of the
component (D) enables the mold shape to be transferred in a higher
precision to provide an optical element having a surface with
higher precision.
[0074] As specific examples of the component (D), it may include
methyl(meth)acrylate, ethyl(meth)acrylate,
cyclohexyl(meth)acrylate, dicyclopentyl(meth)acrylate,
isobornyl(meth)acrylate, bornyl(meth)acrylate,
phenyl(meth)acrylate, halogen-substituted phenyl(meth)acrylate,
benzyl(meth)acrylate, .alpha.-naphthyl(meth)acrylate,
.beta.-naphthyl(meth)acrylate, and dicyclopentyloxyethyl acrylate.
Any one of these substances may used alone, or two or more selected
from these may be used in combination.
[0075] The component (D) may preferably be in an amount of from 0.1
to 30% of the resin as weight percentage. As long as it is within
this range, the fluidity of resin at the time of molding can be
ensured without any lowering of the properties of the resin.
[0076] The component-(E) release agent is used in order to weaken
the release-resisting force acting when a resin cured product is
released from the mold after the resin has been cured upon
irradiation. The addition of the component (E) enables the resin to
be prevented from sticking to the mold to remain even after a large
number of optical elements have been formed, and a much higher
figure tolerance can be achieved.
[0077] As this component (E), any known materials may be used. As
specific examples, it may include neutralizable or
non-neutralizable phosphate alcohols. As to the component (E), too,
any one of them may be used alone or two or more of them may be
used in combination.
[0078] The component (F) is a silicon compound. It has the effect
of smoothing the surface of the cured product to improve the mar
resistance or keep any defects from occurring. Hence, the addition
of the component (F) in a very small quantity makes the smoothness
of resin surface higher and brings about an improvement in mar
resistance, so that an optical element having a much higher
durability can be obtained.
[0079] In the present invention, a wide range of substances are
usable as the silicon compound. As specific examples of the
compound usable as the component (F), it may include
tetramethoxysilane, tetraethoxysilane,
.gamma.-methacryloxypropyltrimethoxysilane,
.gamma.-glycidyloxypropyltrimethoxysilane, and (meth)acrylates
having an Si--O linkage at some part of the backbone chain.
[0080] The component (F) may preferably be added in an amount of
from 0.001% by weight to 10% by weight. Its addition in an amount
less than 0.001% by weight can not be effective. Its addition in an
amount more than 10% by weight not only may provide no desired
refractive index, but also may cause faulty external appearance
such as milky-white.
[0081] The component-(G) epoxy (meth)acrylate provide the resin
appropriately with an adhesion attributable to the hydroxyl groups
formed upon cleavage of epoxy groups to afford the effect of
preventing the resin from coming off from the mold during the
irradiation. Hence, the addition of the component-(G) epoxy
(meth)acrylate in an appropriate quantity can prevent the resin
from coming off from the mold during UV irradiation. This is
effective especially when the PAG lens having a large extent of
aspherical surface is formed.
[0082] There are no particular limitations on the epoxy
(meth)acrylate to be used. For example, usable are addition
reaction products of an epoxy resin such as phenolic novolak epoxy
resin, bisphenol-A epoxy resin, glycerol polyglycidyl ether or 1-6
hexane diglycidyl ether with a monomer having a (meth)acrylic acid
or carboxylic acid group.
[0083] The component (G) may preferably be added in an amount of
from 1% by weight to 30% by weight. Its addition in an amount less
than 1% by weight can not be effective. Also, its addition in an
amount more than 30% by weight may provide so strong adhesion
between the mold and the resin as to make mold release
difficult.
[0084] 3. Exposure Step:
[0085] In the present invention, the photosensitive resin
composition capable of curing upon exposure is used to form the
resin layer. In order to improve the weatherability by curing the
resin to a higher degree of cure, the energy of light with which
the resin is irradiated at the time of curing must be made higher.
In conventional cases, the degree of cure is enhanced with an
increase in the level of irradiation, but resulting in a decrease
in light transmittance. The present inventors have examined the
relationship between the light transmittance of a resin and the
wavelength of the light applied to cure the resin. As the result,
they have discovered that irradiation by light with a wavelength of
300 nm or more can make the light transmittance higher than that in
conventional cases even when the level of irradiation is made
higher than that in conventional cases to cure the resin to a
higher degree.
[0086] Accordingly, the present invention provides a process for
producing a resin-cemented optical element, the process
comprising:
[0087] a first exposure step of irradiating a photosensitive resin
composition held between the surface of a base member and a mold,
by light with a wavelength of 300 nm or more to cure the
composition to form a resin layer; and
[0088] a mold release step of mold-releasing the resin layer; in
this order.
[0089] The irradiation by such light may also be performed at one
time, or may be done twice or more. In order to cure the resin to a
higher degree, it is effective to irradiate the resin-cemented
optical element additionally after mold release. In conventional
cases, however, such an additional irradiation has been considered
not preferable because an increase in irradiation level may make
the degree of cure higher but results in a lowering of light
transmittance. However, the present inventors have discovered that
the additional irradiation after mold release may also be made by
light with a wavelength of 300 nm or more and this enables the
resin to be further cured to a higher degree than the degree before
additional irradiation and at the same time enables the resin to be
more improved in light transmittance than that before such
irradiation.
[0090] Accordingly, the present invention provides a process for
producing a resin-cemented optical element, the process
comprising:
[0091] a first exposure step of irradiating a photosensitive resin
composition held between the surface of a base member and a mold,
to cure the composition to form a resin layer;
[0092] a mold release step of mold-releasing the resin layer;
and
[0093] a second exposure step of irradiating the resin layer by
light with a wavelength of 300 nm or more; in this order.
[0094] To perform this additional irradiation, a method may be
employed in which, e.g., a plurality of resin-cemented optical
elements having been released from the mold are put into an
exposure unit having a light source which radiates light with a
wavelength of 300 nm or more, and irradiate the resin-cemented
optical elements additionally at one time.
[0095] The mechanism is unclear as to the phenomenon that the
degree of cure of the resin is improved and the light transmittance
of the resin is also improved by setting to 300 nm or more the
wavelength of the light to which the resin is exposed. It, however,
can be presumed that, probably the light with a wavelength of 300
nm or more accelerates the curing reaction of the resin, without
destroying the chemical structure of the resin to cause absorption,
and hence the resin is cured to a higher degree and at the same
time a reaction initiator contained in the resin is thereby
consumed, so that the absorption of light that is inherent in the
reaction initiator may less occur.
[0096] As the light source used to irradiate the photosensitive
resin composition by light (usually, ultraviolet light is
preferred) to effect exposure to cure the composition, a metal
halide lamp, a high-pressure mercury lamp, a low-pressure mercury
lamp, a black light, a chemical lamp or the like may be used. Of
these, the metal halide lamp, the high-pressure mercury lamp and
the chemical lamp are preferred because they can emit light with a
wavelength of 300 nm or more in a good efficiency. It is also
preferable to shield the light with a wavelength of less than 300
nm by the use of a commercially available filter or the like.
[0097] There are no particular limitations on the atmosphere of
exposure. The exposure may be performed in air, in an atmosphere of
nitrogen, in an atmosphere of an inert gas or in vacuum, depending
on the properties of the photosensitive resin composition to be
used.
[0098] At the time of the exposure, the resin composition may also
be heated in order to accelerate its curing. When heated, it may
preferably be heated at a temperature of from 40.degree. C. to
130.degree. C. At a temperature lower than 40.degree. C., any
sufficient effect is not obtainable in some cases. At a temperature
higher than 130.degree. C., the resin may become too soft to retain
the desired shape of the resin layer.
[0099] In the present invention, when the irradiation is performed
a plurality of times, the same light source may be used, or a
different light source may be used each time. Also, its atmosphere
may be so changed such that the first irradiation is performed in
air and the second and subsequent irradiation in an atmosphere of
nitrogen.
[0100] The base member surface may also previously be subjected to
coupling treatment with a coupling agent so that the resin layer
can be made to adhere strongly to the base member.
[0101] 4. Heating Step:
[0102] In the present invention, the step of heating the resin
composition or resin cured product may preferably be provided in
the steps for producing the resin-cemented optical element. This
enables more improvement of the light transmittance of the resin
than that in conventional cases, and also enables the resin to be
cured to a higher degree to improve the weatherability.
[0103] This heating may be carried out at any time, and may
preferably be carried out after the resin composition has been
photo-cured and the cured product has been released from the mold
together with the base member. For example, a plurality of
resin-cemented optical elements having been released from the mold
may be put into an oven in one lot and heated at one time, thus the
heating can be carried out in a good productivity and at a low
cost.
[0104] Accordingly, the present invention provides;
[0105] (1) a process for producing a resin-cemented optical
element, the process comprising:
[0106] an exposure step of irradiating a photosensitive resin
composition held between the surface of a base member and a mold,
to cure the composition to form a resin layer;
[0107] a mold release step of mold-releasing the resin layer;
and
[0108] a heating step of heating the resin layer; in this order;
and
[0109] (2) a process for producing a resin-cemented optical
element, the process comprising:
[0110] an exposure step of irradiating a photosensitive resin
composition held between the surface of a base member and a mold,
with heating to cure the composition to form a resin layer; and
[0111] a mold release step of mold-releasing the resin layer; in
this order.
[0112] Incidentally, the mechanism is unclear as to the phenomenon
that the light transmittance and degree of cure of the resin are
improved by the heating. It, however, can be presumed that, the
heating accelerates the post-curing (a phenomenon that the curing
of photosensitive resin proceeds gradually also after exposure) of
the resin to enhance the degree of cure, and also, since in the
heating step the curing reaction proceeds, the chemical structure
of the resin is not destroyed by light and on the contrary any
slight absorption sources caused in the resin layer at the time of
curing are remedied on.
[0113] In this heating step, the heating temperature may preferably
be from 40.degree. C. to 130.degree. C. At a temperature lower than
40.degree. C., any sufficient effect is not obtainable in some
cases. At a temperature higher than 130.degree. C., the resin may
become too soft to retain the desired shape of the resin layer.
[0114] Between the mold release step and the heating step, the
second exposure step described previously may also be provided in
order to accelerate the curing reaction further and improve the
inner transmittance.
[0115] 5. Others:
[0116] The resin-cemented optical element of the present invention
may include, e.g., lenses, prisms and diffraction gratings. The
present invention can well be effective especially when applied to
aspheric lenses, and is especially suited for still cameras such as
an analog still camera and a digital still camera, and video
cameras, or interchangeable lenses for these, which are used in
various environments and whose optical systems are especially
required to be made compact and light-weight and to have good
optical characteristics.
[0117] As materials of the base member in the present invention,
any of glass, plastic and so forth may appropriately be selected as
long as they do not deform or change in properties as a result of
the heating in the heating step.
BRIEF DESCRIPTION OF THE DRAWINGS
[0118] FIG. 1 is a schematic illustration of a PAG lens according
to the present invention.
[0119] FIG. 2 is a schematic illustration of the step of feeding a
resin composition in a PAG lens production process.
[0120] FIG. 3 is a schematic illustration of an exposure step in
the PAG lens production process.
[0121] FIG. 4 is a schematic illustration of a heating step in the
PAG lens production process.
[0122] FIG. 5 is a schematic illustration of an exposure step in a
PAG lens production process.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0123] The present invention is specifically described below by
giving Examples. The present invention is by no means limited to
these Examples.
[0124] In the following Examples, the resin layer is irradiated by
light (ultraviolet light) on the side of the base member, and a
metal mold made of a metal is used as the mold. In the present
invention, however, the mold is by no means limited to it. For
example, a mold comprised of a transparent material such as glass
may also be used as the mold. When such a transparent material is
used as the mold, the resin composition can be cured by irradiation
on the side of the mold, and hence the base member need not be
transparent. On the other hand, when an opaque material such as a
metal is used as the mold as in the following Examples, a
light-transmissive material must be used as the base member because
it is necessary to irradiate the photosensitive resin composition
on the side of the base member. Accordingly, in the following
Examples, a glass lens is used as the base member.
[0125] In the following Examples, the value at a wavelength of 380
nm was used as the inner transmittance, where the order of
fluctuations of the inner transmittance value did not reverse.
EXAMPLE 1
[0126] In this Example, first a resin composition (photosensitive
resin composition) was prepared which was obtained by mixing the
following components (A) to (C). Next, this composition was coated
on a glass base, followed by curing to form a resin layer to
produce a PAG lens.
[0127] Component (A): 80 parts of di(meth)acrylate of Formula (1)
wherein m +n is 3.
[0128] Component (B): 19.5 parts of urethane-modified
di(meth)acrylate of Formula (2).
[0129] Component (C): 0.5 part of an acetophenone type
photopolymerization initiator.
[0130] The refractive index of this resin composition before curing
was 1.535, and the viscosity thereof at room temperature was 3,500
cP.
[0131] This resin composition was poured into a base mold made of
glass, and then irradiated by light of a high-pressure mercury lamp
for 2 minutes to form a rectangular colorless transparent block of
2 mm thick. Concerning this block, its refractive index after
curing was measured to find that it was 1.556. Its durometer
hardness was also measured to find that it was HDD 78.
[0132] Its inner transmittance in a 100 .mu.m thick area was
further calculated using data of spectral transmittance of a molded
product different in thickness to reveal that the transmittance was
97% for the light with a wavelength of 380 nm.
[0133] Next, the glass transition temperature Tg was examined on a
molded product of 2 mm thick. The Tg was determined as the point of
inflection of a curve showing dimensional changes caused by
heating, using TMA (thermomechanical analysis), a type of thermal
analysis. As the result, the Tg was 97.degree. C.
[0134] Next, using a molded product of 2 mm thick, the rate of
hygroscopic dimensional change before and after moisture absorption
was examined. More specifically, the initial dimension of the
molded product was measured in an environment of 25.degree. C./50%
RH, and thereafter put into a thermo-hygrostat for 24 hours which
was kept at 50.degree. C./90% RH, to cause the molded product to
absorb moisture. Thereafter, its dimensions were measured again in
the environment of 25.degree. C./50% RH to determine their change
rate. As the result, the rate of hygroscopic dimensional change was
0.35%.
[0135] The gel percentage was determined in the following way:
About 0.5 g of the resin cured product was dried in a desiccator
for about a day, and thereafter the mass of the dried resin
obtained was precisely measured. Next, this resin was immersed in
70.degree. C. methyl ethyl ketone for 6 hours. Here, the methyl
ethyl ketone was changed for new one at intervals of 2 hours. The
resin having been immersed for 6 hours was heated at 100.degree. C.
for 2 hours, and then left in the desiccator for a day to make it
dry. Thereafter, the mass of the resin thus dried was precisely
measured. Here, where the mass of the initial resin was represented
by c, and the mass after immersion in methyl ethyl ketone by d, the
gel percentage was calculated to be 97% according to the
expression: (d/c).times.100 (%).
[0136] The rate of shrinkage on curing was calculated using
measurements of specific gravity before and after curing. As the
result, the rate of shrinkage on curing was 5.5%.
[0137] In this Example, a PAG lens was produced in the following
way. First, as shown in FIG. 2, a resin composition 21 was dropped
on the concave surface of a glass base member 10. As shown in FIG.
3, the glass base member 10 on which the resin composition was
dropped was, with its upside down, pressed against a convex
aspherical-surface metal mold 32 to press and spread the resin
composition 21 into the desired shape. Thereafter, the resin
composition was irradiated by ultraviolet rays 33 for 2 minutes by
means of a high-pressure mercury lamp (not shown) to cure the resin
composition 21. After the resin composition 21 was cured, the cured
product was released from the mold to obtain a PAG lens 12 as shown
in FIG. 1, comprising the glass base member 10 having on its
surface a resin layer 11.
[0138] Here, the glass base member 10 used in this Example was 40
mm in diameter, and its side on which the resin was to be dropped
was previously subjected to silane coupling treatment to improve
the adhesion of glass to the resin layer 11.
[0139] The resin layer of the PAG lens 12 obtained in this Example
has a greatly aspherical shape in a maximum thickness of 800 .mu.m
and a minimum thickness of 100 .mu.m. Even though the resin layer
was molded in such a greatly aspherical shape, the desired
aspherical shape stood transferred exactly to the resin layer
without any coming-off of the resin from the metal mold during the
molding.
[0140] On the PAG lens thus obtained, a anti-reflection coat (not
shown) was formed by vacuum deposition. As the result, a PAG lens
having both good external appearance and good performance was
producible without causing any difficulties such as cracking. A
heat resistance test was made on the PAG lens having this
anti-reflection coat. As the result, even though it was left in an
environment of 70.degree. C. for 24 hours, any change in external
appearance was not seen at all.
[0141] A weatherability test was also made using a carbon
fadometer. The change in transmittance at 380 nm after the
weatherability test was 0.5% or less in terms of the inner
transmittance in a 100 .mu.m thick area. This is value not
problematic at all in practical use.
EXAMPLE 2
[0142] In this Example, a PAG lens was produced in the same manner
as in Example 1 except that the urethane-modified
hexa(meth)acrylate of Formula (3) was used as the component (B) of
the resin composition.
[0143] Physical properties of the resin composition before curing
and of the resin after curing which were measured in the same
manner as in Example 1 are shown in Table 1. TABLE-US-00001 TABLE 1
Example 1 2 3 4 5 6 7 Before Refractive 1.535 1.531 1.532 1.525
1.529 1.529 1.530 curing: index Viscosity at 3500 4500 2000 3000
3500 3500 3500 room temperature (cP) After Refractive 1.556 1.552
1.556 1.551 1.555 1.555 1.556 curing: index Durometer HDD78 HDD82
HDD80 HDD80 HDD79 HDD79 HDD80 hardness Transmittance 97 98 98 98 98
98 98 (100 .mu.m thickness) Glass 97 101 100 99 100 100 100
transition temperature (.degree. C.) Hygroscopic 0.35 0.30 0.35
0.30 0.35 0.35 0.35 dimensional change (%) Gel 97 98 98 98 98 98 98
percentage (%) Shrinkage on 5.5 6.0 6.0 5.0 6.0 6.0 6.0 curing
(%)
[0144] Next, a PAG lens was produced using an aspherical-surface
metal mold in the same manner as in Example 1. As the result, the
desired aspherical shape stood transferred exactly to the resin
layer without any coming-off of the resin from the mold during the
molding.
[0145] On the surface of the resin layer of the PAG lens thus
obtained, a anti-reflection coat was further formed by vacuum
deposition. As the result, a PAG lens having both good external
appearance and good performance was producible without causing any
difficulties such as cracking in the anti-reflection coat. A heat
resistance test was made on the PAG lens having this
anti-reflection coat. As the result, even though it was left in an
environment of 70.degree. C. for 24 hours, any change in external
appearance was not seen at all.
[0146] The same good results as those in Example 1 were also
obtained in the weatherability test made using a carbon
fadometer.
EXAMPLE 3
[0147] In this Example, a PAG lens was produced in the same manner
as in Example 1 except that the urethane-modified
tetra(meth)acrylate of Formula (4) was used as the component (B) of
the resin composition. As the result, the desired aspherical shape
had exactly been transferred to the resin layer without any
coming-off of the resin from the mold during the molding. Physical
properties of the resin composition before curing and of the resin
after curing which were measured in the same manner as in Example 1
were as shown in Table 1.
[0148] On the surface of the resin layer thus obtained, a
anti-reflection coat was further formed in the same manner as in
Example 1. As the result, a PAG lens having both good external
appearance and good performance was obtained, and the results of
its heat resistance test were also as good as those in Example
1.
[0149] The same good results as those in Example 1 were also
obtained in the weatherability test made using a carbon
fadometer.
EXAMPLE 4
[0150] In this Example, a resin composition was prepared by mixing
as the component (A) 80 parts of the di(meth)acrylate of Formula
(1), as the component (B) 14.5 parts of the urethane-modified
di(meth)acrylate of Formula (2), as the component (C) 0.5 part of
an acetophenone type photopolymerization initiator and as the
component (D) 5 parts of methyl(meth)acrylate. Using this
composition, a PAG lens was produced. As the result, the desired
aspherical shape had exactly been transferred without any
coming-off of the resin from the metal mold during the molding.
Physical properties of the resin composition before curing and of
the resin after curing which were measured in the same manner as in
Example 1 were as shown in Table 1.
[0151] On the surface of the resin layer thus obtained, a
anti-reflection coat was further formed in the same manner as in
Example 1. As the result, a PAG lens having both good external
appearance and good performance was obtained, and the results of
its heat resistance test were also as good as those in Example
1.
[0152] The same good results as those in Example 1 were also
obtained in the weatherability test made using a carbon
fadometer.
EXAMPLE 5
[0153] In this Example, a photosensitive resin composition was
prepared by mixing as the component (A) 80 parts of the
di(meth)acrylate of Formula (1), as the component (B) 19 parts of
the urethane-modified di(meth)acrylate of Formula (2), as the
component (C) 0.5 part of an acetophenone type photopolymerization
initiator and as the component (E) 0.5 part of a non-neutralizable
phosphate alcohol. Using this composition, a PAG lens was produced.
As the result, the desired aspherical shape had exactly been
transferred without any coming-off of the resin from the metal mold
during the molding.
[0154] In particular, when the resin of this Example was used, much
better releasability than that in Examples 1 to 4 was achievable,
and the resin did not adhere to the mold even when a large number
of PAG lenses were continuously formed. As the result, the time
taken for cleaning the mold was reduced to half or less, bringing
about an improvement in production efficiency.
[0155] Physical properties of the resin composition before curing
and of the resin after curing which were measured in the same
manner as in Example 1 were as shown in Table 1.
[0156] On the surface of the resin layer of the PAG lens thus
obtained, a anti-reflection coat was further formed in the same
manner as in Example 1. As the result, like Example 1, a PAG lens
having both good external appearance and good performance was
obtained, and the results of its heat resistance test were also as
good as those in Example 1.
[0157] The same good results as those in Example 1 were also
obtained in the weatherability test made using a carbon
fadometer.
EXAMPLE 6
[0158] In this Example, a photosensitive resin composition was
prepared by mixing as the component (A) 80 parts of the
di(meth)acrylate of Formula (1), as the component (B) 19 parts of
the urethane-modified di(meth)acrylate of Formula (2), as the
component (C) 0.5 part of an acetophenone type photopolymerization
initiator and as the component (F) 0.5 part of
y-methacryloxypropyltrimethoxysilane. Using this composition, a PAG
lens was produced. As the result, the desired aspherical shape had
exactly been transferred without any coming-off of the resin from
the metal mold during the molding. As a result of microscopic
observation of the resin surface of the PAG lens of this Example,
the surface was found to be very smooth. Also, though in the PAG
lenses of Examples 1 to 5 microscopic defects of few .mu.m or less
in diameter were slightly present at their surfaces, such defects
were not seen at all in the PAG lens of this Example.
[0159] Physical properties of the resin composition before curing
and of the resin after curing which were measured in the same
manner as in Example 1 were as shown in Table 1.
[0160] On the surface of the resin layer thus obtained, a
anti-reflection coat was further formed in the same manner as in
Example 1. As the result, like Example 1, a PAG lens having both
good external appearance and good performance was obtained, and the
results of its heat resistance test were also as good as those in
Example 1.
[0161] The same good results as those in Example 1 were also
obtained in the weatherability test made using a carbon
fadometer.
EXAMPLE 7
[0162] In this Example, a photosensitive resin composition was
prepared by mixing as the component (A) 70 parts of the
di(meth)acrylate of Formula (1), as the component (B) 19 parts of
the urethane-modified di(meth)acrylate of Formula (2), as the
component (C) 0.5 part of an acetophenone type photopolymerization
initiator and as the component (G) 10.5 parts of bisphenol-A
epoxyacrylate. Using this composition, a PAG lens was produced. As
the result, the desired aspherical shape had exactly been
transferred without any coming-off of the resin from the metal mold
during the molding. Physical properties of the resin composition
before curing and of the resin after curing which were measured in
the same manner as in Example 1 were as shown in Table 1.
[0163] It was also tested to form fifty PAG lenses continuously by
using an aspherical-surface metal mold having a difference of as
large as 900 .mu.m between the maximum resin thickness and the
minimum resin thickness. As the result, any faulty molding did not
occur at all. Then, the like test was made using the resins of
Examples 1 to 6. As the result, the lenses produced using the
resins of Examples 1 to 6 were on the level of no problem in
practical use, but faulty molding that the resin came off from the
mold during the irradiation by ultraviolet light occurred at a rate
of one or two lenses in the fifty lenses for each Example. Thus,
the resin of this Example was found to be especially superior.
[0164] On the surface of the resin layer thus obtained, a
anti-reflection coat was further formed in the same manner as in
Example 1. As the result, like Example 1, a PAG lens having both
good external appearance and good performance was obtained, and the
results of its heat resistance test were also as good as those in
Example 1.
[0165] The same good results as those in Example 1 were also
obtained in the weatherability test made using a carbon
fadometer.
EXAMPLE 8
[0166] In this Example, a PAG lens was produced using the same
photosensitive resin composition as that in Example 1 and using a
glass lens of 40 mm in diameter as the base member.
[0167] More specifically, the same photosensitive resin composition
21 as that in Example 1 was dropped on the concave surface of a
glass base member 10 subjected previously to silane coupling
treatment to improve its adhesion to the resin. The glass base
member 10 was, with its upside down, pressed against a convex
aspherical-surface metal mold 32 to press and spread the resin
composition 21 into the desired shape. Thereafter, the resin
composition was irradiated by ultraviolet rays 33 by means of a
high-pressure mercury lamp (not shown) to cure the resin
composition 21, and the cured product was released from the mold 32
to obtain a PAG lens.
[0168] At the time of the exposure, the irradiation light was
measured with an illuminance meter manufactured by EYEGRAPHICS CO
LTD., having the sensitivity center at 365 nm, to find that the
irradiation energy was 1,800 mJ/cm.sup.2. Also, at the time of the
exposure, as shown in FIG. 4, irradiation by infrared light 41 was
performed through the glass base member 10 by means of an infrared
lamp to heat the whole of the resin composition 21 and the mold 32
to 60.degree. C.
[0169] The PAG lens thus obtained had the same good optical
characteristics and weatherability as those in Example 1. Also, a
plurality of PAG lenses having resin layers in different thickness
were produced in the same manner as in this Example, and their
spectral transmittances were measured. From the measurements
obtained, the 100 .mu.m thick inner transmittance was calculated to
find that it was 98%. Also, the gel percentage of a resin cured
product obtained by curing the resin composition in the same manner
as in this Example was determined in the same manner as in Example
1 to find that it was 98%. The results are shown in Table 2.
[0170] As can be seen from these results, the introduction of the
heating step into the resin-cemented optical element production
steps can bring about an improvement in light transmittance of the
resin layer and also an improvement in its gel percentage.
TABLE-US-00002 TABLE 2 Exaple 8 Exaple 9 Exaple 10 Exaple 11
Exposure The first Wavelength not not 300 nm or not step: time of
irradiation selected selected more selected (before light mold
Irradiation 1800 1800 3000 1800 release): light energy
(mJ/cm.sup.2) Heating at yes no no no the time of exposure The
Wavelength undone undone undone 300 nm or second of irradiation
more time light (after Irradiation 3000 mold light energy release):
(mJ/cm.sup.2) Heating at no the time of exposure Heating step:
Heating no yes no no after curing Inner transmittance (%): 98 98 98
98 Gel percentage (%): 98 98 98 98
EXAMPLE 9
[0171] A PAG lens was produced in the same manner as in Example 8
except that in this Example the resin composition was not heated at
the time of exposure and, after the cured product was released from
the metal mold, it was put into an oven and heated at 70.degree. C.
for 24 hours.
[0172] The PAG lens thus obtained had the same good optical
characteristics and weatherability as those in Example 8. Also, the
inner transmittance and gel percentage determined in the same
manner as in Example 8 in respect of the PAG lens and resin cured
product in this Example were both 98%. The results are shown in
Table 2.
EXAMPLE 10
[0173] A PAG lens was produced in the same manner as in Example 8
except that in this Example the resin composition was not heated at
the time of exposure and, at the time of the exposure, as shown in
FIG. 5 an ultraviolet-transmitting filter "UV-32" (51),
manufactured by HOYA Corporation, was fitted to a high-pressure
mercury lamp (not shown) to shut out light 54 with a wavelength of
less than 300 among light 52 from the light source so that only
light 53 with a wavelength of 300 nm or more was applied as
irradiation light 55. This irradiation light 55 was measured in the
same manner as in Example 8 to find that the irradiation energy was
3,000 mJ/cm.sup.2.
[0174] The PAG lens thus obtained had the same good optical
characteristics and weatherability as those in Example 8. Also, the
inner transmittance and gel percentage determined in the same
manner as in Example 8 in respect of the PAG lens and resin cured
product in this Example were both 98%. The results are shown in
Table 2.
[0175] As can be seen from these results, the irradiation by light
with a wavelength of 300 nm or more at the time of the curing of
the resin layer can make the gel persentage of the resin layer
higher and also can improve the light transmittance of the resin
layer, even under the irradiation at a higher energy than that in
conventional cases.
EXAMPLE 11
[0176] A PAG lens was produced in the same manner as in Example 8
except that in this Example the resin composition was not heated at
the time of exposure and, after the cured product was released from
the metal mold, it was put into a large-sized ultraviolet
irradiation unit to further perform additional irradiation by means
of a high-pressure mercury lamp to make second-time exposure
treatment. At the time of this additional irradiation, an
ultraviolet-transmitting filter UV-32, manufactured by HOYA
Corporation, was fitted to the high-pressure mercury lamp so that
only the light with a wavelength of 300 nm or more was applied. The
irradiation light in this additional irradiation was measured with
an illuminance meter manufactured by EYEGRAPNICS CO., LTD., having
the sensitivity center at 365 nm, to find that the irradiation
energy was 3,000 mJ/cm.sup.2.
[0177] The PAG lens thus obtained had the same good optical
characteristics and weatherability as those in Example 8. Also, the
inner transmittance and gel percentage determined in the same
manner as in Example 8 in respect of the PAG lens and resin cured
product in this Example were both 98%. The results are shown in
Table 2.
[0178] As can be seen from these results, the additional
irradiation by light with a wavelength of 300 nm or more after the
mold release can improve the light transmittance of the resin layer
and also can make its gel percentage higher.
EXAMPLE 12
[0179] A PAG lens was produced in the same manner as in Example 11
except that in this Example, at the time of the first-time
exposure, too, the ultraviolet-transmitting filter 51 was fitted to
the high-pressure mercury lamp (not shown) in the same manner as in
Example 10 to filter the irradiation light 55 so that only the
light 53 with a wavelength of 300 nm or more was applied. This
irradiation light was measured in the same manner as in Example 8
to find that the irradiation energy was 1,800 mJ/ cm.sup.2.
[0180] The PAG lens thus obtained had the same good optical
characteristics and weatherability as those in Example 8. Also, the
inner transmittance and gel percentage determined in the same
manner as in Example 8 in respect of the PAG lens and resin cured
product in this Example were both 98%. The results are shown in
Table 3.
[0181] As can be seen from these results, the irradiation by light
with a wavelength of 300 nm or more at the time of the curing of
the resin layer and the additional irradiation by light with a
wavelength of 300 nm or more after the mold release can improve the
light transmittance of the resin layer and also can make its gel
percentage higher. TABLE-US-00003 TABLE 3 Exaple Exaple Exaple 12
13 14 Exposure The first Wavelength 300 nm 300 nm not step: time of
irradiation or more or more selected (before light mold Irradiation
1800 1800 1800 release): light energy (mJ/cm.sup.2) Heating at no
no no the time of exposure The Wavelength 300 nm 300 nm not second
of irradiation or more or more selected time light (after
Irradiation 3000 3000 3000 mold light energy release):
(mJ/cm.sup.2) Heating at no no no the time of exposure Heating
step: Heating no yes no after curing Inner transmittance (%): 98 98
91 Gel percentage (%): 98 98 98
EXAMPLE 13
[0182] A PAG lens was produced in the same manner as in Example 12
except that in this Example, after the second-time exposure, the
cured product was put into an oven and heated at 70.degree. C. for
24 hours.
[0183] The PAG lens thus obtained had the same good optical
characteristics and weatherability as those in Example 8. Also, the
inner transmittance and gel percentage determined in the same
manner as in Example 8 in respect of the PAG lens and resin cured
product in this Example were both 98%. The results are shown in
Table 3.
[0184] As can be seen from these results, the introduction of the
heating step in the resin-cemented optical element production
steps, the irradiation by light with a wavelength of 300 nm or more
at the time of the curing of the resin layer and the additional
irradiation by light with a wavelength of 300 nm or more after the
mold release can improve the light transmittance of the resin layer
and also can make its gel percentage higher.
EXAMPLE 14
[0185] A PAG lens was produced in the same manner as in Example 11
except that in this Example, after the second-time exposure, too,
the wavelength of the irradiation light was not selected without
fitting any ultraviolet-transmitting filter 51 to the high-pressure
mercury lamp (not shown).
[0186] The PAG lens thus obtained had optical characteristics and
weatherability of no problem in practical use like those in Example
8. Also, the inner transmittance and gel percentage determined in
the same manner as in Example 8 in respect of the PAG lens and
resin cured product in this Example were as shown in Table 3. In
this Example, the gel percentage of the resin layer was 98%, which
did not differ from the result in Example 11, but the inner
transmittance was as low as 91% because the light for the
additional irradiation made after mold release comprised the light
with a wavelength of less than 300 nm.
POSSIBILITY OF INDUSTRIAL APPLICATION
[0187] According to the production process of the present
invention, a resin-cemented optical element can be provided which
has a resin layer having a high light transmittance and also has
superior weatherability. Hence, the optical characteristics and
reliability of the resin-cemented optical element can be improved.
This enables resin-cemented optical elements to be mounted on one
optical system in a larger number than ever.
[0188] In the optical element of present invention, the resin used
in the resin layer also has a refractive index of 1.55 or more
after curing, and hence the light by no means reflect greatly at
the interface between the base member and the resin layer even when
the base member has a high refractive index. Hence, an optical
element having superior optical characteristics in respect of
interference fringes can be obtained. Also, since the resin layer
has a refractive index of 1.55 or more, the resin layer may be
formed in a smaller thickness than a case in which resins having
low refractive index are used as in conventional cases. Hence,
according to the present invention, an optical element having
better optical performance than that in conventional cases can be
obtained with ease.
[0189] According to the present invention, since for example the
transmittance has been improved, a light optical element can be
obtained. Thus, the application of the present invention to the PAG
lens enables formation of sharp images which have been difficult
for conventional lenses to form.
[0190] According to the present invention, since the resin layer
can also be formed in a small thickness and the difference between
the maximum layer thickness value and minimum layer thickness value
can be made small, the moldability for resin-cemented optical
elements can be improved. Hence, it can be made to cause less
defectives, bringing about an improvement in production
efficiency.
[0191] In the present invention, since the resin layer of the
resin-cemented optical element can be formed in a smaller thickness
than conventional ones and in addition thereto the resin having a
low moisture absorption is used, the shape of the resin may less
change with time even in an environment of high humidity, and hence
an optical element can be obtained which can maintain high
performance over a long period of time.
[0192] Since also a higher refractive index than conventional one
can be achieved when the present invention is applied to PAG
lenses, the number of lenses of a lens group consisting of a
plurality of lenses in combination can be made smaller. This
enables production of light-weight optical articles and achievement
of cost reduction.
[0193] Moreover, since the resin used in the resin layer in the
optical element of the present invention has a higher light
transmittance than those conventionally used, and also has a small
rate of hygroscopic dimensional change, a high gel percentage, a
high glass transition temperature and a small rate of shrinkage on
curing, the PAG lens having a large extent of aspherical surface
which has ever been impossible to mold can be molded with ease.
[0194] Moreover, on account of the characteristics such as light
transmittance, moisture absorption and rate of shrinkage on curing,
an optical element can be produced which has superior optical
performance even when the resin layer has a large thickness.
[0195] Furthermore, according to the present invention, an optical
element also having superior environmental properties can be
provided because of the use of the resin having glass transition
temperature at the specific value.
[0196] In view of the foregoing, the optical element of the present
invention is especially suited for still cameras such as an analog
still camera and a digital still camera, and video cameras, or
interchangeable lenses for these, which are used in various
environments and whose optical systems are especially required to
be made compact and light-weight and to have good optical
characteristics.
* * * * *