U.S. patent application number 10/929726 was filed with the patent office on 2005-03-10 for precision press-molding preform, process for the production thereof, optical element and process for the production of the optical element.
This patent application is currently assigned to HOYA CORPORATION. Invention is credited to Fujiwara, Yasuhiro, Zou, Xuelu.
Application Number | 20050054511 10/929726 |
Document ID | / |
Family ID | 34225110 |
Filed Date | 2005-03-10 |
United States Patent
Application |
20050054511 |
Kind Code |
A1 |
Fujiwara, Yasuhiro ; et
al. |
March 10, 2005 |
Precision press-molding preform, process for the production
thereof, optical element and process for the production of the
optical element
Abstract
A precision press-molding preform for producing an optical
element for use in an imaging device using a CCD type or MOS type
solid image-sensing device, which is formed of a glass composition
containing, by mol %, 25 to 45% of P.sub.205, 0.5 to 10% of CuO, 0
to 10% of B.sub.20.sub.3, 0 to 10% of Al.sub.20.sub.3, 2 to 30% of
Li.sub.2O, 0 to 25% of Na.sub.2O, 0 to 15% of K.sub.2O, the total
content of Li.sub.2O, Na.sub.2O and K.sub.2O being 3 to 40%, 3 to
45% of BaO, 0 to 30% of ZnO, 0 to 20% of MgO, 0 to 20% of CaO, 0 to
20% of SrO, 0 to 10% of Bi.sub.2O.sub.3, 0 to 5% of
La.sub.2O.sub.3, 0 to 5% of Gd.sub.2O.sub.3 and 0 to 5% of
Y.sub.2O.sub.3, the total content of these components being at
least 98%, and a precision press-molding preform, which is formed
of a phosphate glass containing CuO, an alkali metal oxide, BaO and
ZnO and having a BaO content/ZnO content molar ratio (BaO/ZnO) of
greater than 1.
Inventors: |
Fujiwara, Yasuhiro; (Tokyo,
JP) ; Zou, Xuelu; (Tokyo, JP) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
1100 N GLEBE ROAD
8TH FLOOR
ARLINGTON
VA
22201-4714
US
|
Assignee: |
HOYA CORPORATION
Tokyo
JP
|
Family ID: |
34225110 |
Appl. No.: |
10/929726 |
Filed: |
August 31, 2004 |
Current U.S.
Class: |
501/45 ; 501/47;
501/48; 65/123 |
Current CPC
Class: |
C03C 3/17 20130101; C03B
7/12 20130101; C03B 11/122 20130101; Y02P 40/57 20151101 |
Class at
Publication: |
501/045 ;
065/123; 501/047; 501/048 |
International
Class: |
C03C 003/16; C03C
003/19; C03C 003/17 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 4, 2003 |
JP |
2003-312576 |
Claims
1. A precision press-molding preform, which is formed of a glass
composition comprising, by mol %, 25 to 45% of P.sub.2O.sub.5, 0.5
to 10% of CuO, 0 to 10% of B.sub.2O.sub.3, 0 to 10% of
Al.sub.2O.sub.3, 2 to 30% of Li.sub.2O, 0 to 25% of Na.sub.2O, 0 to
15% of K.sub.2O, the total content of Li.sub.2O, Na.sub.2O and
K.sub.2O being 3 to 40%, 3 to 45% of BaO, 0 to 30% of ZnO, 0 to 20%
of MgO, 0 to 20% of CaO, 0 to 20% of SrO, 0 to 10% of
Bi.sub.2O.sub.3, 0 to 5% of La.sub.2O3, 0 to 5% of Gd.sub.2O.sub.3
and 0 to 5% of Y.sub.2O.sub.3, the total content of these
components being at least 98%.
2. A precision press-molding preform as recited in claim 1, wherein
the glass composition has a BaO content/ZnO content molar ratio
(BaO/ZnO) of greater than 1.
3. A precision press-molding preform, which is formed of a
phosphate glass containing CuO, an alkali metal oxide, BaO and ZnO
and having a BaO content/ZnO content molar ratio (BaO/ZnO) of
greater than 1.
4. A precision press-molding preform as recited in claim 3, wherein
the phosphate glass contains, by mol %, 25 to 45% of
P.sub.2O.sub.5, 0.5 to 10% of cuO, 0 to 10% of B.sub.2O.sub.3, 0 to
10% of Al.sub.2O.sub.3, 3 to 40% of a total of Li.sub.2O, Na.sub.2O
and K.sub.2O, 3 to 45% of BaO and 0 to 30% of ZnO.
5. A precision press-molding preform as recited in claim 1 or 3,
wherein the glass, when it has a thickness of 1 mm, has, as
transmittance characteristics, an external transmittance of 80 to
90% at a wavelength of 400 nm, an external transmittance of 0.1 to
18% at a wavelength of 700 nm, an external transmittance of 1 to
30% at a wavelength of 1,200 nm and a maximum external
transmittance at a wavelength of 400 to 600 nm.
6. A process for the production of a precision press-molding
preform, which comprises separating a molten glass gob having a
predetermined mass from a molten glass and shaping the molten glass
gob into the precision press-molding preform recited in claim 1 or
3.
7. An optical element which is a precision press-molded product
from the precision press-molding preform recited claim 1 or 3.
8. An optical element which is a precision press-molded product
from that precision press-molding preform which is produced by the
process recited in claim 6.
9. An optical element which is a precision press-molded product and
is formed of a glass composition comprising, by mol %, 25 to 45% of
P.sub.2O.sub.5, 0.5 to 10% of CuO, 0 to 10% of B.sub.2O.sub.3, 0 to
10% of Al.sub.2O.sub.3, 2 to 30% of Li.sub.2O, 0 to 25% of
Na.sub.2O, 0 to 15% of K.sub.2O, the total content of Li.sub.2O,
Na.sub.2O and K.sub.2O being 3 to 40%, 3 to 45% of BaO, 0 to 30% of
ZnO, 0 to 20% of MgO, 0 to 20% of CaO, 0 to 20% of SrO, 0 to 10% of
Bi.sub.2O.sub.3, 0 to 5% of La.sub.2O.sub.3, 0 to 5% of
Gd.sub.2O.sub.3 and 0 to 5% of Y.sub.2O.sub.3, the total content of
these components being at least 98%.
10. An optical element which is a precision press-molded product
and is formed of a phosphate glass containing Cuo, an alkali metal
oxide, BaO and ZnO and having a BaO content/ZnO content molar ratio
(BaO/ZnO) of greater than 1.
11. An optical element as recited in claim 7, which is one of an
aspherical lens, a spherical lens, a lens array, an optical
low-pass filter and a diffraction grating, and has a near infrared
absorbing function.
12. A process for the production of an optical element, which
comprises heating the precision press-molding preform recited in
claim 1 or 3 and precision press-molding the preform by means of a
press mold.
13. A process for the production of an optical element, which
comprises heating that precision press-molding preform produced by
the process recited in claim 6 and precision press-molding the
preform by means of a press mold.
14. A process for the production of an optical element as recited
in claim 12, wherein the precision press-molding preform is
introduced into the press mold, and the preform and the press mold
are heated together for the precision press-molding.
15. A process for the production of an optical element as recited
in claim 12, wherein the precision press-molding preform is
pre-heated and then introduced into the press mold for precision
press-molding.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a precision press-molding
preform (a preform for precision press-molding) and a process for
the production thereof and also relates to an optical element and a
process for the production thereof. More specifically, the present
invention relates to a precision press-molding preform, the preform
being formed of a phosphate glass and being for an optical element
to be encased in an imaging device of a color VTR or digital camera
using a solid image sensing device of a CCD (Charge-Coupled Device)
type or MOS (Metal-Oxide-Semiconductor) type, and a process for the
production thereof. And, it also relates to various optical
elements formed from such preforms by precision press-molding,
particularly, an optical element having a near infrared absorbing
function, and a process for the production thereof.
TECHNICAL BACKGROUND
[0002] Conventionally, most of imaging devices of digital cameras
and digital VTR cameras use CCD and MOS solid image-sensing
devices. The optical system of such an image-sensing device
requires a filter optical element capable of cutting near infrared
light. In solid image-sensing devices, generally, the spectral
sensitivity, for example, of CCD extends from a visible light
region to the vicinity of 1,000 nm in a near infrared light region,
so that it is required to cut near infrared light for matching the
spectral sensitivity received through CCD to the counterpart of
human eyes. Otherwise, an image obtained comes to be reddish, and
no excellent image reproduction can be attained. For this purpose,
filter glasses for cutting near infrared light have been developed
and widely employed. For example, JP-A-4-104918 discloses a
phosphate glass and a fluorophosphate glass.
[0003] Meanwhile, as imaging devices are downsized in recent years,
it is strongly demanded to downsize image-sensing optical systems.
For coping with the downsizing, it is sufficient to decrease the
number of parts by using an optical element having a plurality of
optical functions. For example, a thinkable solution is to impart
one optical element with the above near infrared light cutting
function and the function of an optical low-pass filter that passes
light having a low spatial modulation frequency, or to impart one
optical element with the near infrared light cutting function and a
lens function.
[0004] Concerning lens functions as well, when the optical element
is an aspherical lens, excellent optical performances can be
obtained while using fewer parts as compared with an optical system
using a spherical lens alone.
[0005] However, the above low-pass filter and the above aspherical
lens have a problem that they cannot be produced highly
productively when an infrared-light-absorbing glass is mechanically
processed. For overcoming this problem, a near-infrared-absorbing
glass can be precision-press molded to produce an optical element
having the above multi-functions.
[0006] Since, however, a conventional near-infrared-absorbing glass
contains arsenic, a large amount of P.sub.2O.sub.5 or fluorine for
attaining a high transmittance at and around 400 nm, such a glass
is not suitable as a glass for precision press-molding.
[0007] Arsenic involves environmental problems due to its toxicity.
Further, it exhibits very high oxidizability, so that it may damage
the molding surface of a press mold used for the precision
press-molding and may make it impossible to use the mold
repeatedly.
[0008] Further, a glass containing a large amount of P.sub.2O.sub.5
has a problem that such a glass is poor in climate resistance. When
precision press-molding preforms are produced from such a glass and
stored, the surface state of the preforms is deteriorated, and the
preforms are no longer suitable as materials for producing optical
elements by precision press-molding.
[0009] The introduction of fluorine gives a glass having a lower
melting point and having an excellent transmittance. However, this
glass has the following problem. Since fluorine volatilizes when
the glass is melted, it is difficult to. stably produce preforms
one by one from the glass in a molten state, and such a glass is
not suitable for the precision press-molding. Therefore, no optical
element has been put to practical use that is produced from a glass
described in the above JP-A-4-104981.
DISCLOSURE OF THE INVENTION
[0010] It is an object of the present invention to provide a
precision press-molding preform, which overcomes the above defects
of conventional glasses, which is excellent in precision
press-moldability and durability and which enables the stable
production of an optical element having an excellent near infrared
absorbing function, etc., and a process for the production thereof,
and it is also another object of the present invention to provide
an optical element obtained from the above preform by precision
press-molding and a process for the production of the optical
element.
[0011] The present inventors have conducted a variety of
experiments for overcoming the above problems. As a result, it has
been found that when an alkali component and BaO are introduced
into a P.sub.2O.sub.5-containi- ng glass, the melting point of the
P.sub.2O.sub.5-containing glass can be decreased, and the
P.sub.2O.sub.5-containing glass can be imparted with excellent near
infrared absorption properties and sufficiently high climate
resistance, so that a glass composition suitable for precision
press-molding can be obtained. On the basis of this finding, the
present invention has been completed.
[0012] That is, the present invention provides;
[0013] (1) a precision press-molding preform, which is formed of a
glass composition comprising, by mol %, 25 to 45% of
P.sub.2O.sub.5, 0.5 to 10% of CuO, 0 to 10% of B.sub.2O.sub.3, 0 to
10% of Al.sub.2O.sub.3, 2 to 30% of Li.sub.2O, 0 to 25% of
Na.sub.2O, 0 to 15% of K.sub.2O, the total content of Li.sub.2O,
Na.sub.2O and K.sub.20 being 3 to 40%, 3 to 45% of BaO, 0 to 30% of
ZnO, 0 to 20% of MgO, 0 to 20% of CaO, 0 to 20% of SrO, 0 to 10% of
Bi.sub.2O3, 0 to 5% of La.sub.2O3, 0 to 5% of Gd.sub.2O.sub.3 and 0
to 5% of Y.sub.2O.sub.3, the total content of these components
being at least 98%,
[0014] (2) a precision press-molding preform as recited in the
above (1), wherein the glass composition has a BaO content/ZnO
content molar ratio (BaO/ZnO) of greater than 1,
[0015] (3) a precision press-molding preform, which is formed of a
phosphate glass containing CuO, an alkali metal oxide, BaO and ZnO
and having a BaO content/ZnO content molar ratio (BaO/ZnO) of
greater than 1,
[0016] (4) a precision press-molding preform as recited in the
above (3), wherein the phosphate glass contains, by mol %, 25 to
45% of P.sub.2O.sub.5, 0.5 to 10% of cuO, 0 to 10% of
B.sub.2O.sub.3, 0 to 10% of Al.sub.2O.sub.3, 3 to 40% of a total of
Li.sub.2O, Na.sub.2O and K.sub.2O, 3 to 45% of BaO and 0 to 30% of
ZnO,
[0017] (5) a precision press-molding preform as recited in the
above (1) or (3), wherein the glass, when it has a thickness of 1
mm, has, as transmittance characteristics, an external
transmittance of 80 to 90% at a wavelength of 400 nm, an external
transmittance of 0.1 to 18% at a wavelength of 700 nm, an external
transmittance of 1 to 30% at a wavelength of 1,200 nm and a maximum
external transmittance at a wavelength of 400 to 600 nm,
[0018] (6) a process for the production of a precision
press-molding preform, which comprises separating a molten glass
gob having a predetermined mass from a molten glass and shaping the
molten glass gob into the precision press-molding preform recited
in the above (1) or (3),
[0019] (7) an optical element which is a precision press-molded
product from the precision press-molding preform recited in the
above (1) or (3),
[0020] (8) an optical element which is a precision press-molded
product from that precision press-molding preform which is produced
by the process recited in the above (6),
[0021] (9) an optical element which is a precision press-molded
product and is formed of a glass composition comprising, by mol %,
25 to 45% of P.sub.2O.sub.5, 0.5 to 10% of CuO, 0 to 10% of
B.sub.2O.sub.3, 0 to 10% of Al.sub.2O.sub.3, 2 to 30% of Li.sub.2O,
0 to 25% of Na.sub.2O, 0 to 15% of K.sub.2O, the total content of
Li.sub.2O, Na.sub.2O and K.sub.2O being 3 to 40%, 3 to 45% of BaO,
0 to 30% of ZnO, 0 to 20% of MgO, 0 to 20% of CaO, 0 to 20% of SrO,
0 to 10% of Bi.sub.2O.sub.3, 0 to 5% of La.sub.2O.sub.3, 0 to 5% of
Gd.sub.2O.sub.3 and 0 to 5% of Y.sub.2O.sub.3, the total content of
these components being at least 98%,
[0022] (10) an optical element which is a precision press-molded
product and is formed of a phosphate glass containing CuO, an
alkali metal oxide, BaO and ZnO and having a BaO content/ZnO
content molar ratio (BaO/ZnO) of greater than 1,
[0023] (11) an optical element as recited in the above (7), which
is one of an aspherical lens, a spherical lens, a lens array, an
optical low-pass filter and a diffraction grating, and has a near
infrared absorbing function,
[0024] (12) a process for the production of an optical element,
which comprises heating the precision press-molding preform recited
in the above (1) or (3) and precision press-molding the preform by
means of a press mold,
[0025] (13) a process for the production of an optical element,
which comprises heating that precision press-molding preform
produced by the process recited in the above
[0026] (6) and precision press-molding the preform by means of a
press mold,
[0027] (14) a process for the production of an optical element as
recited in the above (12), wherein the precision press-molding
preform is introduced into the press mold, and the preform and the
press mold are heated together for the precision press-molding,
and
[0028] (15) a process for the production of an optical element as
recited in the above (12), wherein the precision press-molding
preform is pre-heated and then introduced into the press mold for
precision press-molding.
EFFECT OF THE INVENTION
[0029] According to the present invention, there can be provided a
precision press-molding preform which is excellent in precision
press-moldability and durability and which enables the stable
production of an optical element having an excellent near infrared
absorbing function, etc., and a process for the production
thereof.
[0030] According to the present invention, further, there can be
provided an optical element that is a precision press-molded
product from the above preform and a process for the production of
the optical element.
[0031] There can be therefore obtained various optical elements
such as an aspherical lens, a spherical lens, a lens array, etc.,
which have a near infrared light absorbing function, etc., so that
the optical system of a solid image-sensing device can be
constituted of fewer parts, which is effective for downsizing and
weight-decreasing of imaging devices. Further, since the above
optical elements can be produced by precision press-molding, there
can produced optical elements such as an aspherical lens, a lens
array, a lens with an optical low-pass filter, a microlens, etc.,
easily and at a low cost, which require labors and a cost when
produced by processing with a machine.
BRIEF DESCRIPTION OF DRAWINGS
[0032] FIG. 1 is a schematic cross-sectional view of a hot preform
float-shaping apparatus used in Example 1.
[0033] FIG. 2 is a schematic cross-sectional view of a precision
press-molding apparatus used in Examples.
[0034] FIG. 3 is a chart of an external transmittance curve of a
glass constituting a No. 9 preform in Example 1 when the glass has
a thickness of 1 mm.
PREFERRED EMBODIMENTS OF THE INVENTION
[0035] First, the precision press-molding preform (the preform for
precision press-molding) and the process for the production thereof
will be explained below.
[0036] [Precision Press-molding Preform and Process for the
Production Thereof]
[0037] The precision press-molding preform, provided by the present
invention, includes two embodiments, a preform I and a preform
II.
[0038] (Preform I)
[0039] The first precision press-molding preform (preform I),
provided by the present invention, is formed of a glass having a
composition comprising, by mol %, 25 to 45% of P.sub.2O.sub.5, 0.5
to 10% of CuO, 0 to 10% of B.sub.2O.sub.3, 0 to 10% of
Al.sub.2O.sub.3, 2 to 30% of Li.sub.2O, 0 to 25% of Na.sub.2O, 0 to
15% of K.sub.2O, the total content of Li.sub.2O, Na.sub.2O and
K.sub.20 being 3 to 40%, 3 to 45% of BaO, 0 to 30% of ZnO, 0 to 20%
of MgO, 0 to 20% of CaO, 0 to 20% of SrO, 0 to 10% of
Bi.sub.2O.sub.3, 0 to 5% of La.sub.2O.sub.3, 0 to 5% of
Gd.sub.2O.sub.3 and 0 to 5% of Y.sub.2O.sub.3, the total content of
these components being at least 98%,
[0040] Contents of glass components to be described hereinafter
represent contents by mol % unless otherwise specified.
[0041] Reasons for limitations of the contents of the glass
components will be explained as below.
[0042] P.sub.2O.sub.5 is a main component to constitute the network
structure of the glass and is essential for stable operations and
formation of the glass. When the content thereof is less than 25%,
the glass is degraded in thermal stability and is also degraded in
climate resistance. When it exceeds 45%, the viscosity of a molten
glass increases, so that it is difficult to introduce optional
components to be explained later, such as Bi.sub.2O.sub.3,
Nb.sub.2O.sub.5 and WO.sub.3. Further, it may not be possible to
carry out the procedure of hot preform shaping in which a molten
glass gob having a mass equivalent to one preform is separated from
a molten glass and shaped into a preform before the glass is
cooled. The content of P.sub.2O.sub.5 is therefore limited to 25 to
45%, and it is preferably in the range of 27 to 42%. The content of
P.sub.2O.sub.5 by mass % is preferably less than 65 mass %, more
preferably 60 mass % or less, still more preferably 59 mass % or
less.
[0043] CuO is an essential component that works as a main component
for imparting the above glass with the property of absorbing near
infrared light. When the content of CuO is less than 0.5%, there
may be obtained no sufficient property of absorbing near infrared
light. When it exceeds 10%, the glass may be degraded in
devitrification resistance. The content thereof is therefore
limited to 0.5 to 10%.
[0044] B.sub.2O.sub.3 is a component having the effect of improving
the glass in climate resistance when added in a small amount and
attaining low-dispersion of optical properties of the glass. When
the content thereof exceeds 10%, the glass transition temperature
greatly increases, and the durability thereof is greatly degraded.
The content of B.sub.2O.sub.3 is therefore limited to 0 to 10%. The
content thereof is preferably 8% or less, more preferably over 0%
but not more than 8%. The content of B.sub.2O.sub.3 by mass % is
more preferably 3 mass % or less, particularly preferably 2.5 mass
% or less.
[0045] Al.sub.2O.sub.3 has the effect of improving the glass in
climate resistance and water resistance when added in a small
amount. However, it may increase the melting temperature, may
promote the reducing reaction of Cu.sup.2+.fwdarw.Cu.sup.+ and may
attenuate the transmittance of the glass and the property of the
glass absorbing near infrared light. The content of Al.sub.2O.sub.3
is therefore limited to 0 to 10%. It is preferably 0 to 6%, still
more preferably over 0% but not more than 6%. The content of
Al.sub.2O.sub.3 by mass % is more preferably less than 10 mass %,
particularly preferably 9 mass % or less.
[0046] In the above glass composition, it is remarkably effective
to incorporate at least Li.sub.2O as an alkali metal oxide. The
reason therefor is that Li.sub.2O is a component effective for
decreasing the melting point and softening temperature of the
glass. For this purpose, at least 2% of Li.sub.2O is incorporated.
When the content thereof exceeds 30%, however, the glass
increasingly tends to devitrify and the liquidus temperature of the
glass may increase, so that the content of Li.sub.2O is limited to
the range of 2 to 30%. The content thereof is preferably in the
range of 5 to 25%.
[0047] For alleviating the devitrification tendency when Li.sub.2O
alone is incorporated as an alkali metal oxide R.sub.2O, it is
preferred to incorporate at least one member selected from
Na.sub.2O or K.sub.2O.
[0048] The content of Na.sub.2O is in the range of 0 to 25%,
preferably 0 to 20%, more preferably over 0% but not more than 20%.
The content of K.sub.2O is in the range of 0 to 15%, preferably 0
to 10%, more preferably over 0% but not more than 10%. The reason
therefor is that when the content of Na.sub.2O exceeds 25%, the
glass is degraded in durability and stability and that when the
content of K.sub.2O exceeds 15%, it is difficult to impart the
glass with a low melting point.
[0049] R.sub.2O (R=Li, Na or K) is an essential component that has
the effect of decreasing the glass transition temperature and the
liquid-phase viscosity of the glass and that imparts the glass with
thermal properties required for shaping a precision press-molding
preform. When a large amount of an alkali is incorporated, there is
produced an effect that the reduction of near infrared
light-absorbing Cu.sup.2+ into Cu.sup.+ (Cu.sup.2+.fwdarw.Cu.sup.+)
is suppressed. When the content of R.sub.2O is less than 3%, the
effect of suppressing the reducing reaction of
Cu.sup.2+.fwdarw.Cu.sup.+ is attenuated, the glass transition
temperature increases, and the viscosity of a molten glass during
hot preform shaping increases, so that there are caused
difficulties in press-molding and hot preform shaping. When the
total content of these components exceeds 40%, the glass is
degraded in climate resistance and thermal stability. The total
content of these components is therefore limited to 3 to 40%. The
total content thereof is preferably in the range of 5 to 36%, more
preferably over 5% but not more than 36%.
[0050] BaO is a component for modifying the glass and is used for
adjusting various properties of the glass. Further, BaO has the
effect of improving the glass in climate resistance, so that it is
an essential component in the above glass composition. When the
content thereof exceeds 45%, it is no longer possible to obtain a
low-temperature softening property, and the liquidus temperature of
the glass may increase. When it is less than 3%, the desired
durability and climate resistance can be no longer obtained, and
the glass is very easily devitrified. The content of BaO is
therefore limited to 3 to 45%, and it is preferably in the range of
5 to 40%. The content of BaO by mass % is more preferably at least
8.5 mass %, still more preferably at least 11 mass %, yet more
preferably at least 13 mass %, particularly preferably at least
20.5 mass %.
[0051] Like BaO, ZnO is a component for modifying the glass and is
used for adjusting various properties of the glass. Particularly,
ZnO greatly contributes to a lower melting point of the glass. When
the content of ZnO exceeds 30%, ZnO causes the thermal stability of
the glass to decrease or causes the liquid-phase viscosity of the
glass to increase, so that the thermal properties that the glass
suitable as a glass for forming a precision press-molding preform
is required to have are completely impaired. The content of ZnO is
therefore limited to 0 to 30%. The content thereof is preferably 0
to 25%, more preferably over 0% but not more than 25%. The content
of ZnO by mass % is more preferably less than 20 mass %,
particularly preferably 16 mass % or less.
[0052] For improving the climate resistance of the preform and an
optical element to be obtained, preferably, the molar ratio of the
content of BaO to the content of ZnO (BaO/ZnO) is adjusted to a
value of greater than 1.
[0053] MgO, CaO and SrO are components to be used for adjusting the
durability and stability of the glass. When the content of each of
these components exceeds 20%, it may be no longer possible to
incorporate BaO that is incorporated for imparting the glass with
climate resistance, so that the content of each of these components
is limited to 0 to 20%. The content of each component is preferably
0 to 15%.
[0054] Bi.sub.2O.sub.3 is an optional component. When
Bi.sub.2O.sub.3 is incorporated in a small amount, however, it is
capable of not only improving the glass in stability but also
suppressing the reducing reaction of Cu.sup.2+.fwdarw.Cu.sup.+.
Particularly, when the content of P.sub.2O.sub.5 is relatively
large, the incorporation of Bi.sub.2O.sub.3 is very effective. When
a large amount of Bi.sub.2O.sub.3 is incorporated, however, the
absorption in a near infrared light region increases, and the
transmittance at a wavelength of 400 nm may therefore decrease. The
content of Bi.sub.2O.sub.3 is therefore limited to 0 to 10%. It is
preferably in the range of 0.1 to 10%, more preferably 0.1 to
5%.
[0055] La.sub.2O.sub.3, Gd.sub.2O.sub.3 and Y.sub.2O.sub.3 are
components that have the effect of improving the glass in climate
resistance and that can be incorporated as required. However, when
the content of each component exceeds 5%, it is difficult to obtain
the desired low-temperature softening property, and the
liquid-phase viscosity of the glass is liable to increase. The
content of each of the above components is therefore limited to 0
to 5%. Preferably, the content of each component is 0 to 4%.
[0056] In the above glass composition, for imparting the glass with
the above desired properties, the total content of the above
components is required to be at least 98%, and it is preferably
over 98%, more preferably at least 99%, still more preferably
100%.
[0057] In addition to the above components, 0 to 2% of
Yb.sub.2O.sub.3 may be incorporated, or 0 to 2% of Lu.sub.2O.sub.3
may be incorporated, for improving the glass in climate resistance.
Further, 0 to 2% of CeO.sub.2 may be incorporated as well.
[0058] For adjusting the optical properties of the glass,
Nb.sub.2O.sub.5 and WO.sub.3 may be incorporated in an amount of 0
to 2% each.
[0059] Further, when GeO.sub.2, SnO and Fe.sub.2O.sub.3 are
incorporated in such a small amount that the glass properties are
not impaired, they have the effect of suppressing the reducing
reaction of Cu.sup.2+.fwdarw.Cu.sup.+. When each of these
components is incorporated in an amount of over 2%, they promote a
reaction between a melting platinum crucible and the glass, and the
transmittance at 400 nm may be therefore possibly degraded.
Therefore, it is preferred to control the total content of these
components so that it is 2% or less, it is more preferred to
control the above total content so that it is less than 0.1 mass %,
and it is still more preferred to control the above total content
so that it is 0.01 mass % or less. When components in such a trace
amount are incorporated, these trace components need to be
uniformly mixed in the entire raw material, so that it is difficult
to formulate such a glass, and that it is difficult to melt a glass
having a constant composition. Further, GeO.sub.2 is an expensive
material, and desirably, none of GeO.sub.2, SnO and Fe.sub.2O.sub.3
is incorporated when priority is given to a cost and the
formulation problem.
[0060] In addition to the above components, Sb.sub.2O.sub.3 may be
incorporated as a refining agent. In the case, the content of
Sb.sub.2O.sub.3 based on the total content of the glass composition
excluding Sb.sub.2O.sub.3 is preferably 0 to less than 1 mass %,
more preferably 0 to 0.9 mass %. The content of Sb.sub.2O.sub.3 by
mol % is preferably 0 to 1 mol %, more preferably 0 to 0.9 mol
%.
[0061] Desirably, the above glass contains none of PbO,
As.sub.2O.sub.3 and fluorine. The reason therefor is as already
explained.
[0062] Further, Tl, Cd and Cr which are toxic should be precluded,
and it is also preferred to preclude an Ag oxide that may be
reduced to precipitate as a metal during precision press-molding in
a non-oxidizing atmosphere.
[0063] The above glass composition particularly preferably has a
co-presence of P.sub.2O.sub.5, CuO, B.sub.2O.sub.3,
Al.sub.2O.sub.3, Li.sub.2O, Na.sub.2O, K.sub.2O, BaO and ZnO, and a
glass composition in which the total content of these components is
100% is the most preferred.
[0064] A glass composition having a more preferred compositional
range from the above viewpoints can be obtained by combining the
preferred content ranges of the above components as required. One
embodiment of such a more preferred glass composition specifically
contains 27 to 42% of P.sub.2O.sub.5, 0.5. to 10% of CuO, over 0%
but not more than 8% of B.sub.2O.sub.3, over 0% but not more than
6% of Al.sub.2O.sub.3, 5 to 25% of Li.sub.2O, over 0% but not more
than 20% of Na.sub.2O, over 0% but not more than 10% of K.sub.2O,
the total content of Li.sub.2O, Na.sub.2O and K.sub.2O being over
5% but not more than 36%, 5 to 40% of BaO, over 0% but not more
than 25% of ZnO, the BaO content/ZnO content molar ratio being
greater than 1 ((BaO/ZnO)>1), 0 to 15% of MgO, 0 to 15% of CaO,
0 to 15% of SrO, 0 to 10% of Bi.sub.2O.sub.3, 0 to 4% of
La.sub.2O3, 0 to 4% of Gd.sub.2O.sub.3 and 0 to 4% of
Y.sub.2O.sub.3, the total content of these components being at
least 98%. Another embodiment of the above preferred glass
composition specifically contains 27 to 42% of P.sub.2O.sub.5, 0.5
to 10% of CuO, over 0% but not more than 8% of B.sub.2O.sub.3, over
0% but not more than 6% of Al.sub.2O.sub.3, 5 to 25% of Li.sub.2O,
over 0% but not more than 20% of Na.sub.2O, over 0% but not more
than 10% of K.sub.2O, the total content of Li.sub.2O, Na.sub.2O and
K.sub.2O being over 5% but not more than 36%, 5 to 40% of BaO, over
0% but not more than 25% of ZnO, 0 to 15% of MgO, 0 to 15% of CaO,
0 to 15% of SrO, 0.1 to 10% of Bi.sub.2O.sub.3, 0 to 4% of
La.sub.2O.sub.3, 0 to 4% of Gd.sub.2O.sub.3 and 0 to 4% of
Y.sub.2O.sub.3, the total content of these component being at least
98
[0065] (Preform II)
[0066] The second precision press-molding preform (preform II),
provided by the present invention, is formed of a phosphate glass
containing CuO, an alkali metal oxide, BaO and ZnO and having a BaO
content/ZnO content molar ratio (BaO/ZnO) of greater than 1.
[0067] In the preform II, P.sub.2O.sub.5, CuO, an alkali metal
oxide, BaO and ZnO exhibit the same activities and effects as those
in the above preform I. As explained already, a precision
press-molding preform is desirably formed of a glass that is
imparted with a low-temperature softening property and has
sufficient climate resistance. For this purpose, the molar ratio of
the content of BaO to the content of ZnO (BaO/ZnO) in the preform
II is determined to be greater than 1.
[0068] As an alkali metal oxide, it is preferred to incorporate
Li.sub.2O, it is more preferred to incorporate Li.sub.2O and
Na.sub.2O. Desirably, Li.sub.2O, Na.sub.2O and K.sub.2O are
incorporated, and these components are adjusted such that the total
content thereof is equivalent to the content of the alkali metal
oxide.
[0069] Like the preform I, further, it is preferred to incorporate
B.sub.2O.sub.3 or incorporate Al.sub.2O.sub.3.
[0070] In the preform II, similarly, the content of P.sub.2O.sub.5
is preferably in the range of 25 to 45%, more preferably 27 to 42%.
The content of P.sub.2O.sub.5 by mass % is more preferably 65 mass
% or less, still more preferably 60 mass % or less, yet more
preferably 59 mass % or less.
[0071] Like the preform I, similarly, the content of CuO is
preferably 0.5 to 10%.
[0072] Like the preform I, similarly, the content of B.sub.2O.sub.3
is preferably 0 to 10%. The content thereof is more preferably 8%
or less, still more preferably over 0% but not more than 8%. The
content of B.sub.2O.sub.3 by mass % is more preferably less than 3
mass %, particularly preferably 2.5 mass % or less.
[0073] Like the preform I, similarly, the content of
Al.sub.2O.sub.3 is preferably 0 to 10%. The content thereof is more
preferably 0 to 6%, still more preferably over 0% but not more than
6%. The content of Al.sub.2O.sub.3 by mass % is more preferably
less than 10 mass %, particularly preferably 9 mass % or less.
[0074] Like the preform I, similarly, the total content of
Li.sub.2O, Na.sub.2O and K.sub.2O is preferably 3 to 40%. The
content thereof is more preferably in the range of 5 to 36%, still
more preferably over 5 but not more than 36%.
[0075] Like the preform I, similarly, the content of Li.sub.2O is
preferably in the range of 2 to 30%, particularly preferably 5 to
25%.
[0076] Like the preform I, similarly, the content of Na.sub.2O is
preferably 0 to 25%. The content thereof is more preferably in the
range of 0 to 20%, still more preferably over 0% but not more than
20%.
[0077] Like the preform I, similarly, the content of K.sub.2O is
preferably in the range of 0 to 15%, more preferably 0 to 10%,
still more preferably over 0% but not more than 10%.
[0078] Like the preform I, similarly, the content of BaO is
preferably in the range of 3 to 45%, more preferably 5 to 40%. The
content of BaO by mass % is preferably 8.5 mass % or more, more
preferably 11 mass % or more, still more preferably 13 mass % or
more, particularly preferably 20.5 mass % or more.
[0079] Like the preform I, similarly, the content of ZnO is
preferably 0 to 30%. The content thereof is more preferably 0 to
25%, still more preferably over 0% but not more than 25%. The
content of ZnO by mass % is more preferably 20 mass % or less,
particularly preferably 16 mass % or less.
[0080] A glass composition having a more preferred compositional
range from the above viewpoints can be obtained by combining the
preferred content ranges of the above components as required. One
embodiment of such a more preferred glass composition specifically
contains 25 to 45% of P.sub.2O.sub.5, 0.5 to 10% of CuO, 0 to 10%
of B.sub.2O.sub.3, 0 to 10% of Al.sub.2O.sub.3, 3 to 40% of a total
of Li.sub.2O, Na.sub.2O and K.sub.2O, 3 to 45% of BaO and 0 to 30%
of ZnO.
[0081] In the preform II, the above glass composition particularly
preferably has a co-presence of P.sub.2O.sub.5, CuO,
B.sub.2O.sub.3, Al.sub.2O.sub.3, Li2O, Na.sub.2O, K.sub.2O, BaO and
ZnO as well, and a glass composition in which the total content of
these components is 100% is the most preferred.
[0082] In the preform II, Sb.sub.2O.sub.3 may be incorporated as a
refining agent as well. In this case, the content thereof is
preferably as discussed in the preform I. Further, preferably, the
above glass contains none of PbO, As.sub.2O.sub.3, fluorine, Tl,
Cd, Cr and an Ag compound for the same reasons as those explained
with regard to the preform I.
[0083] (Points Common to Preforms I and II)
[0084] Points common to the preforms I and II will be explained
below. The preforms I and II will be simply and collectively called
"preform" hereinafter.
[0085] In the present invention, desirably, the preform is formed
of a glass that absorbs near infrared light and has, as a
transmittance characteristic, an external transmittance of at least
80% at a wavelength of 400 nm when it has a thickness of 1 mm, for
obtaining a color-correcting optical element for a solid
image-sensing device (e.g., an image sensing device of CCD type
(Charge-Coupled-Device) or an image-sensing device of MOS type
(Metal-Oxide-Semiconductor)). More desirably, it is formed of a
glass having, as transmittance characteristics, an external
transmittance of 80 to 90% at a wavelength of 400 nm, an external
transmittance of 0.1 to 18% at a wavelength of 700 nm, an external
transmittance of 1 to 30% at a wavelength of 1,200 nm and a maximum
external transmittance at a wavelength of 400 to 600 nm when the
glass has a thickness of 1 mm.
[0086] The above external transmittance refers to a ratio of the
intensity of outgoing light to the intensity of incidence light
((outgoing light intensity/incidence light intensity).times.100),
when light is caused to vertically enter one of two plane-shaped
optically polished surfaces of a glass which surfaces are in
parallel with each other and is caused to exit from the other
surface.
[0087] In the wavelength region of 280 to 1,200 nm, the external
transmittance monotonously increases when and after the wavelength
becomes longer than 280 nm, and after the external transmittance
reaches 50%, it monotonously increases further to become a maximum
value. Then, the external transmittance monotonously decreases to
reach 50% again and decreases as well thereafter, and light in the
near infrared region is absorbed. And, a low transmittance is
maintained up to a wavelength of 1,200 nm. Therefore, it follows
that the wavelength region of 280 to 1,200 nm includes two
wavelengths at which the external transmittance becomes 50%. When a
longer wavelength of these is taken as .lambda.50, it is preferred
for obtaining an excellent color-correcting optical element for a
solid image-sensing device that .lambda.50 is in the range of 580
to 640 nm.
[0088] Further, the preform is preferably formed of a glass having
a refractive index (nd) of 1.52 to 1.7 and an Abbe's number (.nu.d)
in the range of 42 to 70.
[0089] For improving the precision press-moldability more, the
preform is preferably formed of a glass having a glass transition
temperature (Tg) of 560.degree. C. or lower, it is more preferably
formed of a glass having a glass transition temperature (Tg) of
500.degree. C. or lower, and it is still more preferably formed of
a glass having a glass transition temperature (Tg) of 450.degree.
C. or lower. As described already, the precision press-molding of a
glass refers to a method in which a preform is molded under
pressure at a high temperature with a press mold having a cavity
having a predetermined form, to obtain a glass molded article
having an end product form or a form very close thereto and having
end product surface accuracy or surface accuracy very close
thereto. According to the precision press-molding, molded articles
having desired forms can be highly productively produced. It is
therefore present practice to produce various optical glass parts
such as a spherical lens, an aspherical lens, a diffraction
grating, etc., by precision press-molding. For obtaining an optical
element formed of a glass by precision press-molding, it is
naturally required to press-mold a preform at a high temperature as
described above, so that a press mold is exposed to high
temperatures and that high pressures are applied thereto. It is
therefore required to decrease the glass transition temperature of
the preform for preventing damage that a high-temperature
environment during the press-molding will cause a press mold itself
and a mold release film provided to an internal surface (molding
surface) of the mold. The preform of the present invention
satisfies the above requirements and enables excellent precision
press-molding.
[0090] For shaping the preform of the present invention from a
molten glass, it is preferred to improve the glass in
high-temperature stability. Particularly, for improving hot preform
shapeability, it is desired to decrease the liquidus temperature
(LT) of a glass for constituting the preform and bring the
viscosity of the glass at the liquidus temperature to a range
suitable for hot preform shaping. From the above viewpoint, it is
preferred to adjust the above liquidus temperature (LT) of a glass
to 900.degree. C. or lower. It is also preferred to shape a preform
from a glass that exhibits a viscosity of at least 4 dPa.multidot.s
at the liquidus temperature. The viscosity of the glass at a
liquidus temperature is preferably 4 to 100 dPa.multidot.s, more
preferably 5 to 100 dPa.multidot.s, still more preferably 10 to 50
dPa.multidot.s.
[0091] As a process for shaping a preform all the surfaces of which
are smooth and clean and have no scratches, a float-shaping process
is very effective, in which a molten glass is caused to flow out of
an outflow pipe, a molten glass gob equivalent to one preform is
separated and the molten glass gob is shaped into a preform while
it is caused to float by applying gas pressure to the molten glass
gob. Further, the preform can be shaped in a form of a body of
revolution such as a sphere or the like, which is advantageous for
precision press-molding. While the float shaping has the above
advantage, the viscosity of a glass at a liquidus temperature is
required to be at least 4 dPa.multidot.s as a high-temperature
working viscosity property of the glass that can be applied to the
floating shaping. When a glass has the above viscosity property,
all surfaces of a preform come to be formed by solidification of
the glass in a molten state, and such a glass is advantageous for
shaping the preform having free surfaces. When the viscosity of a
glass at a liquidus temperature exceeds 100 dPa.multidot.s, it is
attempted to increase the temperature further for decreasing the
viscosity to shape a preform, and in this case, glass components
are easily volatilized during the shaping, so that surface striae
are liable to occur.
[0092] A preform of which all the surfaces are formed by
solidification of a glass in a molten state or a preform of which
all the surfaces are formed of free surfaces is remarkably superior
as a precision press-molding preform, since all the surfaces are
smooth, clean and free of no microscope polishing marks as
explained already.
[0093] The method of separating a molten glass gob having a mass
equivalent to the mass of a preform from an outflowing molten glass
without using any cutting blade includes a method in which a molten
glass is caused to drop from an outflow pipe in the form of a
droplet, and a method in which a molten glass is caused to
continuously flow out of an outflow pipe, a lower end of the molten
glass flow is supported, a narrow portion is formed in a mid
portion of the molten glass flow and the support is removed to
separate a molten glass positioned below the narrow portion. The
former method is called a dropping method, and the later is called
a falling-separating method. In each method, when the viscosity of
an outflowing glass increases too excess, it is difficult to
separate a molten glass gob. On the other hand, when the viscosity
of a glass at the liquidus temperature thereof is less than 4
dPa.multidot.s, it may be difficult to employ the dropping method.
In both the dropping method and the falling-cutting method,
preferably, the flow rate of a molten glass from the outflow pipe
is adjusted to be constant, and the time interval of separating
molten glass gobs is adjusted to be constant, for stably producing
preforms having a constant mass each.
[0094] Further, concerning the water resistance of the glass for
constituting the preform, preferably, the mass loss of the glass in
a water resistance test (method of measuring an optical glass for
chemical durability (powder method) JOGISO06-1999) according to
Japan Optical Glass Industry Society Standard is 0.25 mass % or
less. Concerning the climate resistance, further, when a glass
having flat and optically polished surfaces that are in parallel
with each other is held in a clean constant-temperature
constant-humidity vessel having a temperature of 65.degree. C. and
a relative humidity of 90% for 7 days followed by transmitting of
white light through the optically polished surfaces of the glass,
preferably, the ratio of scattered light intensity/transmitted
light intensity (to be referred to as "haze value") is desirably
0.05 or less, more desirably 0.04 or less. It can be considered
that the scattered light intensity is obtained by deducting
transmitted light intensity from incidence light intensity.
[0095] When the rate of corrosion of the preform surface with water
drops or vapor and various chemical components in use environments
such as a gas, etc., or formation of a reaction product is large,
foreign matter is liable to be generated on the surface, and the
optical properties such as a transmittance are degraded. When a
coating such as an anti-reflection film or the like is formed on an
optical-function surface, the degradation of the surface condition
of an optical element can be prevented. When a preform is degraded
in surface condition, the preform is already a defective product.
The preform is therefore required to have the above chemical
durability.
[0096] The preform surface may be provided with a film for
improving lubricity between the preform surface and the surface of
a press mold during precision press-molding or a mold release film
for preventing adhesion of the preform to a press mold. Examples of
such films include a carbon-containing film and a self-assembled
monolayer. The carbon-containing film includes, for example, a
vapor-deposited carbon film and a hydrogenated carbon film.
Desirably, Such a film is formed on the entire surface of the
preform or on that surface of the preform which comes in contact
with a press mold.
[0097] The process for the production of a preform, provided by the
present invention, comprises separating a molten glass gob having a
constant mass from a molten glass and shaping the gob into the
above preform. Such a preform can be produced by a method in which
a homogenous optical glass block is formed, the block is cut after
a strain in the block is removed, the block is machine-processed
into the form of a preform and the surface thereof is optically
polished. However, the above method requires much labor and a large
cost and newly requires the step of machine-processing a preform
instead of replacing the machine-processing of an optical element
by precision press-molding, so that the industrial advantage of the
precision press-molding is reduced. In contrast, according to the
process for the production of a preform, provided by the present
invention, there can be highly productively provided preforms that
can be molded into optical elements having the property of
absorbing near infrared light by precision press-molding.
[0098] In the process for the production of a preform, provided by
the present invention, a molten glass is caused to flow out of an
outflow pipe made, for example, of a platinum alloy at a constant
rate, and preforms having high mass accuracy can be shaped by the
already explained dropping method or falling-cutting method. The
shaping of the preform by float-shaping is preferred as is already
explained.
[0099] The optical element and the process for the production
thereof will be explained below.
[0100] [Optical Element and Process for the Production Thereof]
[0101] The optical element of the present invention includes three
embodiments, a first optical element, a second optical element and
a third optical element.
[0102] The first optical element of the present invention is an
optical element produced by precision press-molding the above
preform or a preform produced by the above process for the
production of a preform.
[0103] The second optical element of the present invention is an
optical element that is a precision press-molded article and that
is formed of a glass having a composition comprising, by mol %, 25
to 45% of P.sub.2O.sub.5, 0.5 to 10% of CuO, 0 to 10% of
B.sub.2O.sub.3, 0 to 10% of Al.sub.2O.sub.3, 2 to 30% of Li.sub.2O,
0 to 25% of Na.sub.2O, 0 to 15% of K.sub.2O, the total content of
Li.sub.2O, Na.sub.2O and K.sub.2O being 3 to 40%, 3 to 45% of BaO,
0 to 30% of ZnO, 0 to 20% of MgO, 0 to 20% of CaO, 0 to 20% of SrO,
0 to 10% of Bi.sub.2O.sub.3, 0 to 5% of La.sub.2O.sub.3, 0 to 5% of
Gd.sub.2O.sub.3 and 0 to 5% of Y.sub.2O.sub.3, the total content of
these components being at least 98%.
[0104] The optical element is formed of the above glass for the
same reasons as those explained with regard to the preform I.
[0105] The third optical element of the present invention is an
optical element that is a precision press-molded product and that
is formed of a phosphate glass containing CuO, an alkali metal
oxide, BaO and ZnO and having a BaO content/ZnO content molar ratio
(BaO/ZnO) of greater than 1.
[0106] The optical element is formed of the above glass for the
same reasons as those explained with regard to the preform II.
[0107] It is desirable that any one of the above optical elements
desirably should have the property of absorbing near infrared
light, so that they desirably have the light transmittance property
that the preforms I and II have.
[0108] The above optical element includes, for example, an
aspherical lens, a spherical lens, a lens array, a microlens, an
optical low-pass filter, a diffraction grating, and the like. It
may be an optical element having composite functions such as an
aspherical lens having an optical low-pass filter function, a
spherical lens having an optical low-pass filter function or a lens
with a diffraction grating.
[0109] Further, having the function of absorbing near infrared
light, the above optical element is effective as a color-correcting
optical element for a solid image-sensing device such as a CCD type
image-sensing device or MOS type image-sensing device.
[0110] The optical element surface may be provided with a
multi-layered film or a single-layered film such as an
anti-reflection film.
[0111] The process for the production of an optical element,
provided by the present invention, will be explained below. The
process for the production of an optical element, provided by the
present invention, comprises heating the above preform or a preform
produced by the process for the production of a preform and
precision press-molding it with a press mold. The optical element
of the present invention can be obtained by the above production
process.
[0112] The press mold in a high-temperature state is handled in a
non-oxidizing gas atmosphere. That is because it is required to
prevent damage that is to be caused on the molding surface of the
press mold by oxidation. The molding surface of the press mold is
provided with a mold release film for preventing the adhesion of
the glass to the mold. The mold release film can be selected from a
carbon film, a noble metal alloy film such as a platinum alloy film
or a noble metal film. When the film is damaged by oxidation, there
is caused a problem that the adhesion of a glass takes place in a
damaged portion or that the surface accuracy of an optical element
is degraded. The precision press-molding is carried out in the
atmosphere of a non-oxidizing gas such as nitrogen, a mixture gas
of nitrogen and hydrogen, argon or other inert gas, whereby the
above problem can be prevented.
[0113] The material for the press mold can be selected from known
materials, and it can be selected from a refractory material such
as a refractory metal, silicon carbide, or the like.
[0114] The process for the production of an optical element
includes two embodiments. The first embodiment of the process
comprises introducing a precision press-molding preform into a
press mold and heating the preform and the press mold together to
carry out precision press-molding. The second embodiment of the
process comprises introducing a pre-heated precision press-molding
preform into a press mold and precision press-molding it. The first
embodiment requires many press molds for mass-producing optical
elements since the preform and the press mold are heated together.
However, the preform and the press mold are in a thermal
equilibrium state or in a state close thereto, so that
high-accuracy precision press-molding can be carried out. The
second embodiment of the present invention enables the
mass-production of optical elements with a relatively small number
of press molds. While these two embodiments of the process have a
common point in that high-accuracy optical elements can be
obtained, it can be decided which one of the two embodiments should
be employed depending upon whether or not priority is given to
higher accuracy or depending upon whether or not priority is given
to an improvement in mass-productivity with a smaller number of
molds.
[0115] In the first embodiment of the process, preferably, the
press mold and the preform are together heated to a temperature at
which the glass shows a viscosity of 10.sup.8 to 10.sup.12
dPa.multidot.s. Further, desirably, the press mold and a molded
product are cooled to a temperature at which the glass shows
viscosity of at least 10.sup.12 dPa.multidot.s, more preferably at
least 10.sup.14 dPa.multidot.s, still more preferably at least
10.sup.16 dPa.multidot.s, before the molded product is taken out of
the press mold.
[0116] In the second embodiment of the process, desirably, the
molded product is taken out of the press mold after the viscosity
of the press-molded glass reaches 10.sup.12 dPa.multidot.s or more.
Further, preferably, the preform is heated while it is caused to
float, and the preform is introduced to the press mold. Desirably,
the preform is introduced into the press mold after the preform is
pre-heated until the glass shows, preferably, a viscosity of
10.sup.9 dPa.multidot.s or lower, more preferably a viscosity of
10.sup.5.5 to 10.sup.9 dPa.multidot.s. Further, it is desirable to
start the cooling of the glass simultaneously with the initiation
of the pressing or at some time during the pressing. The
temperature for heating the press mold is preferably adjusted to a
temperature at which the glass constituting the preform shows a
viscosity of 10.sup.9 to 10.sup.12 dPa.multidot.s. In the second
embodiment of the process, however, it is desirable that the
temperature for heating the preform should be higher than the
temperature for heating the press mold.
[0117] The molded product taken out of the press mold is annealed
as required, and when the preform surface has a film provided, the
film is removed.
[0118] Further, the molded product is processed for centering and
edging as required, and various optical elements such as the
optical element of the present invention having the property of
absorbing near infrared light can be produced without carrying out
the mechanical processing of the form of an optical-function
surface.
EXAMPLES
[0119] The present invention will be explained more in detail with
reference to Examples hereinafter, while the present invention
shall not be limited by these Examples.
Example 1
[0120] Oxides, carbonates, sulfates, nitrates, phosphates,
fluorides, hydroxides, etc., as raw materials for a glass were
weighed in an amount of 250 to 300 g so as to obtain a glass
composition having a predetermined amount ratio shown in Table 1,
and these materials were fully mixed to obtain a formulated batch.
The formulated batch was placed in a platinum crucible and melted
in air with stirring at a temperature of 900 to 1,100.degree. C.
for 1 to 4 hours. After melted, a clarified and homogenized molten
glass was cast into a 40.times.70.times.15 mm carbon mold and
gradually cooled to a temperature around the glass transition
temperature thereof, and immediately thereafter, the glass is
placed in an annealing furnace and annealed around the glass
transition temperature for about 1 hour to allow the glass to be
cooled to room temperature. The thus-obtained optical glass was
observed through an optical microscope to show no precipitation of
a crystal.
[0121] Table 2 shows external transmittances (T400, T700 and T1200)
at 400 nm, 700 nm and 1,200 nm, a maximum external transmittance
(Tmax), .lambda.50 and a glass transition temperature (Tg) of the
above glass had.
[0122] For properties shown in Table 2, measurements were made as
follows.
[0123] (1) Glass transition temperature (Tg) and sag temperature
(Ts)
[0124] A sample was measured with a thermo-mechanical analyzer
supplied by Rigaku Denki K.K. at a temperature elevation rate of
4.degree. C./minute.
[0125] (2) External transmittance (T400, T1200, T700 and
.lambda.50)
[0126] A polished glass having a thickness of 1.0.+-.0.1 mm was
measured for spectral transmittances (including a surface
reflection loss) in a wavelength region of 280 nm to 1,200 nm.
Concerning transmittances, T400, T700 and T1200 in Table 2 stand
for transmittances at wavelengths of 400 nm, 700 nm and 1,200 nm,
respectively, and .lambda.50 stands for a wavelength at which the
external transmittance reaches 50% on the longer wavelength side in
the above wavelength region.
[0127] Glasses Nos. 1 to 16 and 18 in Tables 1 and 2 had a haze
value of less than 0.04 (less than 4%), and a glass No. 17 had a
haze value of 0.05 to 0.065 (5% to 6.5%)
1 TABLE 1 Glass composition (mol %) Li.sub.2O + BaO/ No.
P.sub.2O.sub.5 CuO B.sub.2O.sub.3 Al.sub.2O.sub.3 Li.sub.2O
Na.sub.2O K.sub.2O Na.sub.2O + K.sub.2O BaO ZnO ZnO MgO CaO SrO
Bi.sub.2O.sub.3 Gd.sub.2O.sub.3 Total 1 34.5 2.50 2.5 1.0 10.0 10.0
4.5 24.5 20.0 12.5 1.6 2.5 0.0 0.0 0.0 0.0 100.0 2 34.5 2.50 2.5
1.0 10.0 10.0 4.5 24.5 20.0 10.0 2.0 5.0 0.0 0.0 0.0 0.0 100.0 3
34.5 2.50 2.5 1.0 10.0 10.0 4.5 24.5 20.0 5.0 4.0 10.0 0.0 0.0 0.0
0.0 100.0 4 34.5 2.50 2.5 1.0 10.0 10.0 4.5 24.5 20.0 12.5 1.6 0.0
2.5 0.0 0.0 0.0 100.0 5 34.5 2.50 2.5 1.0 10.0 10.0 4.5 24.5 20.0
10.0 2.0 0.0 5.0 0.0 0.0 0.0 100.0 6 34.5 2.50 2.5 1.0 10.0 10.0
4.5 24.5 20.0 5.0 4.0 0.0 10.0 0.0 0.0 0.0 100.0 7 34.5 2.50 2.5
1.0 10.0 10.0 4.5 24.5 20.0 12.5 1.6 0.0 0.0 2.5 0.0 0.0 100.0 8
34.5 2.50 2.5 1.0 10.0 10.0 4.5 24.5 20.0 10.0 2.0 0.0 0.0 5.0 0.0
0.0 100.0 9 34.5 2.50 2.5 1.0 10.0 10.0 4.5 24.5 20.0 10.0 2.0 0.0
5.0 0.0 0.0 0.0 100.0 10 34.5 2.50 2.5 1.0 10.0 10.0 4.5 24.5 21.5
8.5 2.5 0.0 5.0 0.0 0.0 0.0 100.0 11 34.5 2.50 1.0 1.0 10.0 10.0
4.5 24.5 20.0 11.5 1.7 0.0 5.0 0.0 0.0 0.0 100.0 12 34.5 2.50 2.5
0.0 10.0 10.0 4.5 24.5 20.0 10.0 2.0 0.0 5.0 0.0 0.0 1.0 100.0 13
34.5 2.50 2.5 1.0 10.0 10.0 4.5 24.5 20.0 5.0 4.0 5.0 5.0 0.0 0.0
0.0 100.0 14 34.5 2.50 2.5 1.0 10.0 7.5 2.0 19.5 20.0 10.0 2.0 0.0
10.0 0.0 0.0 0.0 100.0 15 36.0 2.50 1.0 1.0 10.0 10.0 2.0 22.0 20.0
10.0 2.0 0.0 7.5 0.0 0.0 0.0 100.0 16 36.0 2.50 1.0 1.0 10.0 10.0
4.5 24.5 20.0 10.0 2.0 0.0 5.0 0.0 0.0 0.0 100.0 17 36.0 2.50 1.5
0.0 12.4 10.4 4.0 26.8 23.0 9.5 2.4 0.0 0.0 0.0 0.7 0.0 100.0 18
37.9 2.60 1.8 1.8 5.4 0.0 0.0 5.4 36.1 3.6 10.0 7.2 3.6 0.0 0.0 0.0
100.0 (Note 1) Li.sub.2O + Na.sub.2O + K.sub.2O stands for a total
content of these three components. (Note 2) BaO/ZnO stands for a
value obtained by dividing a BaO content expressed by mol % with a
ZnO content expressed by mol %.
[0128]
2 TABLE 2 Properties No. GTT(.degree. C.) T400(%) Tmax(%)
.lambda.50(nm) T700(%) T1200(%) 1 355 86.8 89.2 596 2.3 9.3 2 363
86.9 89.1 596 2.2 8.5 3 381 85.7 87.8 594 1.9 9.4 4 352 86.7 89.2
598 2.5 9.7 5 355 86.4 88.5 597 2.4 9.5 6 368 86.3 88.9 597 2.4 9.1
7 354 87 89.3 597 2.4 9.6 8 357 86.1 88.3 597 2.4 9.7 9 355 86.4
88.5 597 2.4 9.5 10 358 86.6 88.9 597 2.2 8.8 11 349 86.6 88.8 598
2.4 9.1 12 354 86.7 88.9 597 2.3 9.1 13 374 86.7 88.9 594 2.1 8.4
14 379 87 89.1 595 2.2 9.1 15 350 87.3 89.2 603 3.3 10.4 16 343
87.5 89.3 603 3.2 9.4 17 327 86.4 89.2 605 3.5 10.3 18 487 86.7
88.7 621 11.6 21.5 GTT = Glass transition temperature
[0129] It is seen from Table 2 that the optical glasses in Examples
have properties excellent as a material for precision press-molding
for producing near infrared light absorbing elements.
[0130] FIG. 1 is a schematic cross-sectional view of a hot preform
float-shaping apparatus, and the glasses shown in Tables 1 and 2
were shaped into spherical preforms having diameters of 2 to 30 mm
by a dropping method using the hot preform float-shaping apparatus
shown in FIG. 1. The thus-obtained preforms had a mass accuracy of
within .+-.1%. In this manner, spherical preforms having
predetermined masses of 5 to 600 mg can be produced. In FIG. 1,
numeral 21 indicates a molten glass, 22 indicates a glass droplet,
and 23 indicates a preform shaping mold.
[0131] Further, a molten glass gob is separated by a
falling-cutting method and floating-shaped into a preform, whereby
there can be produced the preform that has a predetermined mass of
100 mg to 10 g with a mass accuracy of within .+-.2%.
[0132] Preforms shaped in the above manner had all the surfaces
formed by solidification of a glass in a molten state, and the
preforms were formed of free surfaces. In this manner, there were
produced spherical preforms and preforms having a form close to an
ellipsoid of revolution having one axis of symmetrical
revolution.
Example 2
[0133] FIG. 2 shows a schematic cross-sectional view of a precision
press-molding apparatus. A preform 4 that was obtained in the same
manner as in Example 1 was placed between a lower mold member 2 and
an upper mold member 1 of the precision press-molding apparatus
shown in FIG. 2, and the atmosphere in a quartz tube 11 was
replaced with a nitrogen atmosphere. A heater 12 was electrically
powered to heat the quartz tube 11 internally. The temperature of
the heater 12 was set such that the temperature inside a press mold
was higher than the sag temperature of the glass by 20 to
60.degree. C., and while the temperature was maintained, a pressing
rod 13 was caused to move downward to press the upper mold member
1, so that the preform in the mold was precision press-molded. The
molding pressure was adjusted to 8 MPa, and the molding time period
was adjusted to 30 seconds. After the pressing, the molding
pressure was decreased, and while the mold product was in a state
where it was in contact in the lower mold member 2 and the upper
mold member 1, the molded product was gradually cooled to a
temperature lower than the glass transition temperature by
30.degree. C. Then, the molded product was sharply cooled to room
temperature and then taken out of the mold. Aspherical lenses
obtained from the preforms in Example 1 in the above manner were
highly accurate optical lenses. FIG. 3 shows a chart of external
transmittance of the glass constituting the preform No. 9 in
Example 1 when the glass had a thickness of 1 mm. In FIG. 2,
numeral 3 indicates a sleeve, 9 indicates a supporting rod, 10
indicates a support bed, and 14 indicates a thermocouple.
[0134] Industrial Utility
[0135] The precision press-molding preform, provided by the present
invention, is excellent in precision press-moldability and
durability and enables the stable production of various optical
elements such as an aspherical lens, a spherical lens, a lens
array, and the like which have the property of excellently
absorbing near infrared light.
* * * * *