U.S. patent application number 14/184044 was filed with the patent office on 2014-06-19 for optical glass.
This patent application is currently assigned to OHARA INC.. The applicant listed for this patent is OHARA INC.. Invention is credited to Michiko Ogino, Masahiro Onozawa, Junko Suzuki.
Application Number | 20140171287 14/184044 |
Document ID | / |
Family ID | 40509056 |
Filed Date | 2014-06-19 |
United States Patent
Application |
20140171287 |
Kind Code |
A1 |
Suzuki; Junko ; et
al. |
June 19, 2014 |
OPTICAL GLASS
Abstract
There is provided an optical glass with a high refractive index
and a low dispersion having a refractive index (nd) of not less
than 1.75 and an Abbe's number (.nu.d) of not less than 35 where
the image formation characteristic is hardly affected by changes in
temperature of the using environment. SiO.sub.2, B.sub.2O.sub.3 and
La.sub.2O.sub.3 are contained as essential components and the ratio
of the constituting components are adjusted whereby an optical
glass in which a product of .alpha. and .beta. where .alpha. is an
average linear expansion coefficient at -30 to +70.degree. C. and
.beta. is an optical elasticity constant at the wavelength of 546.1
nm is not more than 130.times.10.sup.-12.degree.
C..sup.-1.times.nm.times.cm.sup.-1.times.Pa.sup.-1 is able to be
achieved.
Inventors: |
Suzuki; Junko;
(Sagamihara-shi, JP) ; Ogino; Michiko;
(Sagamihara-shi, JP) ; Onozawa; Masahiro;
(Sagamihara-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OHARA INC. |
Sagamihara-shi |
|
JP |
|
|
Assignee: |
OHARA INC.
Sagamihara-shi
JP
|
Family ID: |
40509056 |
Appl. No.: |
14/184044 |
Filed: |
February 19, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13676525 |
Nov 14, 2012 |
8691712 |
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14184044 |
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13155797 |
Jun 8, 2011 |
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13676525 |
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|
12100798 |
Apr 10, 2008 |
8003556 |
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13155797 |
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60976193 |
Sep 28, 2007 |
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Current U.S.
Class: |
501/78 |
Current CPC
Class: |
C03C 3/068 20130101 |
Class at
Publication: |
501/78 |
International
Class: |
C03C 3/068 20060101
C03C003/068 |
Claims
1. An optical glass comprising, by mass on oxide basis: SiO.sub.2
more than 1.0% and less than 12.0%, B.sub.2O.sub.3 8.0 to 35.0%,
the ratio of SiO.sub.2/B.sub.2O.sub.3 being more than 0 and less
than 0.6, and La.sub.2O.sub.3 25.0 to 50.0%, wherein the product of
.alpha..times..beta., where .alpha. is an average linear expansion
coefficient within -30.degree. C. to +70.degree. C. and .beta. is
an optical elasticity constant at the wavelength of 546.1 nm, is
not more than 130.times.10.sup.-12.degree.
C..sup.-1.times.nm.times.cm.sup.-1.times.Pa.sup.-1.
2. The optical glass according to claim 1, wherein the glass has
optical constants within the rages where the refractive index (nd)
is 1.75 to 2.00 and the Abbe's number (.nu.d) is 35 to 55.
3. The optical glass according to claim 1, wherein the glass
further comprises 0.0 to 40.0% of Gd.sub.2O.sub.3, 0.0 to 15.0% of
Y.sub.2O.sub.3, 0.0 to 15.0% of ZrO.sub.2, 0.0 to 25.0% of
Ta.sub.2O.sub.5, 0.0 to 18.0% of Nb.sub.2O.sub.5 and 0.0 to 10.0%
of WO.sub.3.
4. The optical glass according to claim 1, wherein the glass
further comprises 0.0 to 0.1% by mass of GeO.sub.2, 0.0 to 1.0% by
mass of Yb.sub.2O.sub.3, 0.0 to 1.0% by mass of Ga.sub.2O.sub.3,
and 0.0 to 1.0% by mass of Bi.sub.2O.sub.2 and the optical glass
does not contain a lead compound such as PbO and an arsenic
compound such as As.sub.2O.sub.2.
5. The optical glass according to claim 1, wherein the product of
.alpha..times..beta. is not more than 100.times.10.sup.-12.degree.
C..sup.-1.times.nm.times.cm.sup.-1.times.Pa.sup.-1.
6. The optical glass according to claim 1, wherein the product of
.alpha. and .beta. is not more than 90.times.10.sup.-12.degree.
C..sup.-1.times.nm.times.cm.sup.-1.times.Pa.sup.-1 .
7. The optical glass according to claim 1, wherein the ratio of
(Ta.sub.2O.sub.5+Nb.sub.2O.sub.5+WO.sub.3)/(Gd.sub.2O.sub.3+Y.sub.2O.sub.-
3) is more than 0.05 and less than 1.30.
8. The optical glass according to claim 1, wherein the glass
contains 0 to 5.0% of Li.sub.2O, 0 to 5.0% of Na.sub.2O, 0 to 5.0%
of K.sub.2O, 0 to 5.0% of Cs.sub.2O, 0 to 5.0% of MgO, 0 to 5.0% of
CaO, 0 to 5.0% of SrO, 0 to 5.0% of BaO, 0 to 3.0% of TiO.sub.2, 0
to 3.0% of SnO.sub.2, 0 to 3.0% of Al.sub.2O.sub.3, 0 to 5.0% of
P.sub.2O.sub.5, 0 to 10.0% of ZnO, 0 to 5.0% of Lu.sub.2O.sub.3, 0
to 3.0% of TeO.sub.2, 0 to 2.0% of Sb.sub.2O.sub.3, 0 to 3.0% of
F.
9. The optical glass according to claim 1, wherein the glass
contains less than 2.0% of ZnO.
10. The optical glass according to claim 1, wherein the glass
contains less than 3.5% of Y.sub.2O.sub.3.
11. The optical glass according to claim 1, wherein the ratio of
(ZrO+Ta.sub.2O.sub.5+Nb.sub.2O.sub.5)/(SiO+B.sub.2O.sub.3) is less
than 1.00.
12. The optical glass according to claim 1, wherein the glass
contains less than 3.5% of Y.sub.2O.sub.3, the ratio of
(ZnO+Y.sub.2O.sub.3)/La.sub.2O.sub.3 is more than 0 and less than
0.5 and the sum of ZrO+Nb.sub.2O.sub.5 is more than 5.0% and less
than 13.0%.
13. An optical glass, comprising, by mass on oxide basis: more than
1.0% and less than 10.0% of SiO.sub.2, 15.0 to 28.0% of
B.sub.2O.sub.3, 28.0 to 35.0% of La.sub.2O.sub.3, 25.0 to 35.0% of
Gd.sub.2O.sub.3, 5.0 to 9.0% of ZrO.sub.2 and 0.1 to less than 2.0%
of ZnO 0.0 to 6.0% of Ta.sub.2O.sub.5, 0.0 to 5.0% of
Nb.sub.2O.sub.5, 0.0 to 1.0% of Sb.sub.2O.sub.3, and 0.0 to less
than 1.0% by mass of Al.sub.2O.sub.3, wherein the sum of
ZrO+Nb.sub.2O.sub.5 is more than 5.0% to less than 13.0%, the glass
has optical constants within such ranges that the refractive index
(nd) is 1.78 to 1.83 and the Abbe's number (.nu.d) is 44 to 48 and
the product of .alpha..times..beta., where a is an average linear
expansion coefficient within -30.degree. C. to +70.degree. C., and
.beta. is an optical elasticity constant at the wavelength of 546.1
nm, is not more than 90.times.10.sup.12.degree.
C..sup.-1.times.nm.times.cm.sup.-1.times.Pa.sup.-1.
14. The optical glass according to claim 1, wherein the optical
glass is included in an optical element.
15. The optical glass according to claim 1, wherein the optical
element is prepared by a reheat press processing.
16. The optical glass according to claim 1, wherein the optical
glass is included in an optical instrument.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation application of U.S. patent
application Ser. No. 13/676,525 filed on Nov. 14, 2012 which is
continuation of U.S. patent application Ser. No. 13/155,797 filed
on Jun. 8, 2011 which is continuation of U.S. patent application
Ser. No. 12/100,798, filed on Apr. 10, 2008, which is a
nonprovisional application of U.S. Provisional Patent Application
No. 60/976,193, filed on Sep. 28, 2007, the entire contents of
which are incorporated herein by references.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an optical glass having a
high refractive index and a low dispersion where the refractive
index (nd) is not less than 1.75 and an Abbe's number (.nu.d) is
not less than 35 and also relates to an optical element such as
lens and prism prepared by utilizing this optical glass. More
particularly, it relates to an optical glass having a high
refractive index and a low dispersion which is suitable as prism
and projection lens of optical instruments represented by projector
and camera where a highly precise image formation characteristic
and also relates to an optical element and an optical instrument
prepared therefrom.
[0004] 2. Description of the Related Art
[0005] There is a very high demand for glass having a high
refractive index and a low dispersion as a material for optical
elements such as various kinds of lenses and, with regard to an
optical glass where a refractive index (nd) is not less than 1.75
and an Abbe's number (.nu.d) is not less than 35, various kinds of
glass compositions represented by Patent Documents 1 to 3 have been
known.
[0006] In recent years, there has been a progress in digitization
of optical instruments and making them precise and there has been a
demand of high properties for optical elements used for the
instruments for the reproduction (projection) such as a projector
and a projection TV as well as for instruments for taking pictures
such as digital camera and video camera. The properties are now not
only covering the characteristic such as refractive index, Abbe's
number and degree of coloration which have been demanded for
optical glass already but also covering little variation in the
characteristic under an actually using environment and little
environmental load during the manufacture of optical glass and the
processing of optical elements.
[0007] With regard to a change in image forming characteristic
under an actually using environment, it has been presumed to be as
follows that an optical element such as lens and prism is fixed by
a jig in optical instruments and, when temperature of the using
environment changes (such as a change in temperature in the box or
use under high temperature), thermal expansion of the optical
element is resulted and, due to the difference in its expansion
coefficient from that of the fixing jig, stress is resulted in the
optical element whereby double refraction is resulted in the
optical element and image forming characteristic changes.
[0008] As mentioned above, when the image formation characteristic
designed by optical constants such as a refractive index and an
Abbe's number obtained under predetermined temperature (mostly
around room temperature) is not achieved in the actual using
environment, there is a disadvantage that, upon the optical
designing, the using environment is to be predicted and the design
is to be conducted presuming the complicated variations in the
characteristic.
[0009] When there are components having a high environmental load
such as a lead (Pb) compound or an arsenic (As) compound at the
time of manufacturing the optical glass and processing of optical
elements, there is a disadvantage that special measures are
necessary for the prevention of diffusion of polluting substances
into air and water. Further, when a rare mineral resource
represented by tantalum (Ta) is used in large amounts, not only the
production cost becomes high but also cost and labor for recovery
of the source are necessary.
[0010] With regard to an optical glass with a high refractive index
and a low dispersion containing no components having high
environmental load in the glass composition, various glass
compositions represented by the patent gazettes 1 to 3 are
disclosed but no consideration has been done for changes in image
formation characteristic under an actually using environment.
[0011] Patent Document 1: JP-A-2005-306732
[0012] Patent Document 2: JP-A-2002-284542
[0013] Patent Document 3: JP-A-2004-161506
[0014] Patent Document 4: JP-A-56-160340
[0015] Patent Document 5: JP-A-52-14607
[0016] Under such circumstances, the an object of the invention is
to provide an optical glass having a high refractive index and a
low dispersion where the refractive index (nd) is not less than
1.75 and the Abbe's number (.nu.d) is not less than 35 which is
hardly affected by image formation characteristic by changes in
temperature of the using environment without the use of large
amounts of the components having high environmental load and the
rare mineral resources.
SUMMARY OF THE INVENTION
[0017] In order to achieve the above object, the present inventors
have repeatedly carried out intensive tests and studies and, as a
result, they have found that, when SiO.sub.2, B.sub.2O.sub.3 and
La.sub.2O.sub.2 are made to contain as essential components and
ratio of the constituting components is adjusted, an optical glass
having a high refractive index and a low dispersion by which the
product of .alpha. and .beta. (where .alpha. is an average linear
expansion coefficient within -30.degree. C. to +70.degree. C. and
.beta. is an optical elasticity constant at the wavelength of 546.1
nm) is able to be made not more than 130.times.10.sup.-12.degree.
C..sup.-1.times.nm.times.cm.sup.-1.times.Pa.sup.-1 is now able to
be prepared without the use of large amounts of components having a
high environmental load and rare mineral resources whereby the
above object is achieved and they have accomplished the invention.
The constitution will be shown as follows.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0018] (Constitution 1)
[0019] An optical glass which is characterized in that the product
of .alpha. and .beta. where .alpha. is an average linear expansion
coefficient within -30.degree. C. to +70.degree. C. and .beta. is
an optical elasticity constant at the wavelength of 546.1 nm is not
more than 130.times.10.sup.-12.degree.
C..sup.-1.times.nm.times.cm.sup.-1.times.Pa.sup.-1, SiO.sub.2 is
contained therein in an amount of more than 1.0% by mass and less
than 12.0% by mass on the basis of an oxide, B.sub.2O.sub.3 is
contained in an amount of 8.0 to 35.0% by mass, the ratio of
SiO.sub.2/B.sub.2O.sub.3 in terms of % by mass is more than 0 and
less than 0.6 and La.sub.2O.sub.3 is contained in an amount of 25.0
to 50.0% by mass.
[0020] (Constitution 2)
[0021] The optical glass according to the constitution 1, wherein
the glass has optical constants within the rages where the
refractive index (nd) is 1.75 to 2.00 and the Abbe's number (.nu.d)
is 35 to 55.
[0022] (Constitution 3)
[0023] The optical glass according to the constitution 1 or 2,
wherein the glass contains, on the basis of an oxide, 0.0 to 40.0%
by mass of Gd.sub.2O.sub.3, 0.0 to 15.0% by mass of Y.sub.2O.sub.3,
0.0 to 15.0% by mass of ZrO.sub.2, 0.0 to 25.0% by mass of
Ta.sub.2O.sub.5, 0.0 to 18.0% by mass of Nb.sub.2O.sub.5 and 0.0 to
10.0% by mass of WO.sub.3.
[0024] (Constitution 4)
[0025] The optical glass according to any of the constitutions 1 to
3, wherein the glass contains, on the basis of an oxide,
[0026] 0.0 to 0.1% by mass of GeO.sub.2 and/or
[0027] 0.0 to 1.0% by mass of Yb.sub.2O.sub.3 and/or
[0028] 0.0 to 1.0% by mass of Ga.sub.2O.sub.3 and/or
[0029] 0.0 to 1.0% by mass of Bi.sub.2O.sub.3
[0030] and does not contain a lead compound such as PbO and an
arsenic compound such as As.sub.2O.sub.3.
[0031] (Constitution 5)
[0032] The optical glass according to any of the constitutions 1 to
4, wherein the product of .alpha. and .beta. where .alpha. is an
average linear expansion coefficient within -30.degree. C. to
+70.degree. C. and .beta. is an optical elasticity constant at the
wavelength of 546.1 nm is not more than
100.times.10.sup.-12.degree.
C..sup.-1.times.nm.times.cm.sup.-1.times.Pa.sup.-1.
[0033] (Constitution 6)
[0034] The optical glass according to any of the constitutions 1 to
5, wherein the product of .alpha. and .beta. where .alpha. is an
average linear expansion coefficient within -30.degree. C. to
+70.degree. C. and .beta. is an optical elasticity constant at the
wavelength of 546.1 nm is not more than 90.times.10.sup.-12.degree.
C..sup.-1.times.nm.times.cm.sup.-1.times.Pa.sup.-1.
[0035] (Constitution 7)
[0036] The optical glass according to any of the constitutions 1 to
6, wherein the ratio of
(Ta.sub.2O.sub.5+Nb.sub.2O.sub.5+WO.sub.3)/(Gd.sub.2O.sub.3+Y.sub.2O.sub.-
3) in terms of % by mass based on the oxides is more than 0.05 and
less than 1.30.
[0037] (Constitution 8)
[0038] The optical glass according to any of the constitutions 1 to
7, wherein the glass contains
[0039] 0 to 5.0% of Li.sub.2O and/or
[0040] 0 to 5.0% of Na.sub.2O and/or
[0041] 0 to 5.0% of K.sub.2O and/or
[0042] 0 to 5.0% of Cs.sub.2O and/or
[0043] 0 to 5.0% of MgO and/or
[0044] 0 to 5.0% of CaO and/or
[0045] 0 to 5.0% of SrO and/or
[0046] 0 to 5.0% of BaO and/or
[0047] 0 to 3.0% of TiO.sub.2 and/or
[0048] 0 to 3.0% of SnO.sub.2 and/or
[0049] 0 to 3.0% of Al.sub.2O.sub.2 and/or
[0050] 0 to 5.0% of P.sub.2O.sub.5 and/or
[0051] 0 to 10.0% of ZnO and/or
[0052] 0 to 5.0% of Lu.sub.2O.sub.2 and/or
[0053] 0 to 3.0% of TeO.sub.2 and/or
[0054] 0 to 2.0% of Sb.sub.2O.sub.2 and/or
[0055] 0 to 3.0% of F
in terms of % by mass on the basis of an oxide.
[0056] (Constitution 9)
[0057] The optical glass according to any of the constitutions 1 to
8, wherein the glass contains less than 2.0% by mass of ZnO on the
basis of an oxide.
[0058] (Constitution 10)
[0059] The optical glass according to any of the constitutions 1 to
9, wherein the glass contains less than 3.5% by mass of
Y.sub.2O.sub.3 on the basis of an oxide.
[0060] (Constitution 11)
[0061] The optical glass according to any of the constitutions 1 to
10, wherein the ratio of
(ZrO.sub.2+Ta.sub.2O.sub.5+Nb.sub.2O.sub.5)/(SiO.sub.2+B.sub.2O.sub.3)
in terms of % by mass on the basis of an oxide is less than
1.00.
[0062] (Constitution 12)
[0063] The optical glass according to any of the constitutions 1 to
11, wherein the glass contains less than 3.5% by mass of
Y.sub.2O.sub.3 on the basis of an oxide, the ratio of
(ZnO+Y.sub.2O.sub.3)/La.sub.2O.sub.3 in terms of % by mass on the
basis of an oxide is more than 0 and less than 0.5 and the sum of
ZrO.sub.2+Nb.sub.2O.sub.5 in terms of % by mass is more than 5.0%
and less than 13.0%.
[0064] (Constitution 13)
[0065] An optical glass, characterized in that, the glass contains
more than 1.0% by mass and less than 10.0% by mass of
SiO.sub.2,
[0066] 15.0 to 28.0% by mass of B.sub.2O.sub.3,
[0067] 28.0 to 35.0% by mass of La.sub.2O.sub.3,
[0068] 25.0 to 35.0% by mass of Gd.sub.2O.sub.3,
[0069] 5.0 to 9.0% by mass of ZrO.sub.2 and
[0070] 0.1 to less than 2.0% by mass of ZnO and
[0071] 0.0 to 6.0% by mass of Ta.sub.2O.sub.5 and/or
[0072] 0.0 to 5.0% by mass of Nb.sub.2O.sub.5 and/or
[0073] 0.0 to 1.0% by mass of Sb.sub.2O.sub.3 and/or
[0074] 0.0 to less than 1.0% by mass of Al.sub.2O.sub.2
on the basis of an oxide where the sum of ZrO.sub.2+Nb.sub.2O.sub.5
is more than 5.0% by mass to less than 13.0% by mass, the glass has
optical constants within such ranges that the refractive index (nd)
is 1.78 to 1.83 and the Abbe's number (.nu.d) is 44 to 48 and the
product of .alpha. and .beta. where .alpha. is an average linear
expansion coefficient within -30.degree. C. to +70.degree. C. and
.beta. is an optical elasticity constant at the wavelength of 546.1
nm is not more than 90.times.10.sup.-12.degree.
C..sup.-1.times.nm.times.cm.sup.-1.times.Pa.sup.-1.
[0075] (Constitution 14)
[0076] An optical element such as lens and prism where the glass
mentioned in the constitutions 1 to 13 is a mother material.
[0077] (Constitution 15)
[0078] An optical element such as lens and prism which is prepared
by a reheat press processing of the glass mentioned in the
constitutions 1 to 14.
[0079] (Constitution 16)
[0080] An optical instrument such as camera and projector using the
optical element and the optical substrate material prepared by the
glass mentioned in claims 1 to 15.
[0081] As a result of adoption of the above-mentioned embodiments,
it is now possible to provide an optical glass having a high
refractive index and a low dispersion which is hardly affected by
image formation characteristic caused by changes in temperature
under the using environment and has a refractive index (nd) of not
less than 1.75 and an Abbe's number (.nu.d) of not less than
35.
[0082] The optical glass of the invention will be illustrated as
follows.
[0083] The optical glass according to the above constitution 1 is
characterized in that the product of .alpha. and .beta. where
.alpha. is an average linear expansion coefficient within
-30.degree. C. to +70.degree. C. and .beta. is an optical
elasticity constant at the wavelength of 546.1 nm is not more than
130.times.10.sup.-12.degree.
C..sup.-1.times.nm.times.cm.sup.-1.times.Pa.sup.-1 and the index of
.alpha..times..beta. shows changed amount of image formation
characteristic under the using environment. To be more specific, it
means that the more the average linear expansion coefficient
.alpha., the more the expansion rate (changes in volume) of an
optical element against the changes in temperature under the using
environment and, therefore, it means that a big thermal stress is
generated in an optical element fixed by a jig or the like. It also
means that the more the optical elasticity constant .beta., the
more the double refraction generated by the resulted thermal stress
and, in other words, it suggests that the less the
.alpha..times..beta., the less the changes in the image formation
characteristic under the using environment.
[0084] Incidentally, there is an advantage that, when the product
of .alpha. and .beta. is not more than 130.times.10.sup.-12.degree.
C..sup.-1.times.nm.times.cm.sup.-1.times.Pa.sup.-1, an image
formation characteristic desired upon an optical design is apt to
be achieved even when the temperature changes under an actually
using environment.
[0085] In order to achieve that the product of .alpha. and .beta.
is not more than 130.times.10.sup.-12.degree.
C..sup.-1.times.nm.times.cm.sup.-1.times.Pa.sup.-1 in the optical
glass having a high refractive index and a low dispersion, the
constitution 1 is characterized in that SiO.sub.2 is contained
therein in an amount of more than 1.0% by mass and less than 12.0%
by mass on the basis of an oxide, B.sub.2O.sub.3 is contained in an
amount of 8.0 to 35.0% by mass, the ratio of
SiO.sub.2/B.sub.2O.sub.3 in terms of % by mass is more than 0 and
less than 0.6 and La.sub.2O.sub.3 is contained in an amount of 25.0
to 50.0% by mass.
[0086] Now each of the components will be illustrated. An SiO.sub.2
component promotes stable formation of glass and has an effect of
suppressing the devitrification (production of crystalline
products) and cord (non-uniformity inside the glass) which are
unfavorable for optical glass. However, when it is contained too
much, a refractive index (nd) is apt to become small and an optical
elasticity constant .beta. is apt to significantly increase and, as
a result, a desired characteristic is hardly achieved. Therefore,
its upper limit is less than 12.0% by mass, more preferably 11.5%
by mass and, most preferably 11.0% by mass and the amount is
preferably more than 1.0% by mass, more preferably not less than
1.2% by mass and, most preferably, not less than 1.4% by mass.
Although the SiO.sub.2 component is able to be contained in any
material form, it is preferred to be introduced in a form of an
oxide (SiO.sub.2), K.sub.2SiF.sub.6 or Na SiF.sub.6.
[0087] A B.sub.2O.sub.3 component promotes a stable glass formation
the same as the SiO.sub.2 component does and it is an inevitable
component for achieving a small average linear expansion
coefficient. However, when its amount is too small, stable glass is
hardly resulted while, when its amount is too much, a refractive
index (nd) is apt to become small and an optical elasticity
constant .beta. tends to significantly increase whereby the desired
characteristic is hardly available. Its upper limit is preferably
35% by mass, more preferably 34% by mass and, most preferably, 33%
by mass while its lower limit is preferably 8.0% by mass, more
preferably 8.5% by mass and, most preferably, 9.0% by mass. The
B.sub.2O.sub.3 component is able to be contained therein in a
material form such as H.sub.3BO.sub.3, Na.sub.2B.sub.4O.sub.7,
Na.sub.2B.sub.4O.sub.7.10H.sub.2O or BPO.sub.4 and it is preferred
to be introduced in a form of H.sub.3BO.sub.3.
[0088] As a result of making the ratio of SiO.sub.2/B.sub.2O.sub.3
less than 0.6 in terms of % by mass, not only an effect of
increasing the fusing property of the material and the stability of
glass is achieved but also an effect of suppressing the increase of
an average linear expansion coefficient .alpha. is achieved. When
it exceeds the upper limit, it may happen that the average linear
expansion coefficient .alpha. increases and further that melted
residue (hardly-fusible crystals mostly containing SiO.sub.2) upon
fusion of the glass is generated whereby the productivity becomes
bad and the inner quality is badly affected. More preferred range
of % by mass is 0.03 to 0.59 and most preferred one is within a
range of 0.05 to 0.58.
[0089] In addition to the effect of enhancing the refractive index
and making the dispersion small (making the Abbe's number large),
the La.sub.2O.sub.3 component also has an action of making the
optical elasticity constant .beta. small. However, if it is
contained too much, glass becomes significantly unstable and is apt
to be devitrified. Accordingly, its upper limit is preferably 50%
by mass, more preferably 49.5% by mass and, most preferably, 49.0%
by mass while its lower limit is preferably 25% by mass, more
preferably 25.5% by mass and, most preferably, 26% by mass. The
La.sub.2O.sub.3 component is able to be contained therein in any
material form and it is preferred to be introduced thereinto in a
form of an oxide (La.sub.2O.sub.3) and a nitrate or a nitrate
hydride (La (NO.sub.3).sub.3.xH.sub.2O where x is any integer).
[0090] The optical glass according to the above constitution 2 is
characterized in having optical constants of such ranges where a
refractive index (nd) is 1.75 to 2.00 and an Abbe' s number (.nu.d)
is 35 to 55 and it is useful for various optical elements and
optical designs.
[0091] The above-mentioned optical constants are useful in an
optical design particularly because miniaturization of an optical
system is possible (The characteristic of a high refractive index
that a refractive index is not less than 1.75 is able to afford a
big refractive amount of light even in the case of a thin lens and
the low dispersing characteristic that the Abbe's number is not
less than 35 is able to make the shift of focus (chromatic
aberration) small even in the case of a single lens.).
[0092] In the optical glass of the above constitutions 1 and 2, a
Gd.sub.2O.sub.3 component gives an effect of making the refractive
index high and making the dispersion small the same as an
La.sub.2O.sub.3 component does but, when it is contained too much,
devitrification is apt to happen the same as in the case of the
La.sub.2O.sub.3 component. Accordingly, its upper limit is
preferably 40% by mass, more preferably 39% by mass and, most
preferably, 38% by mass . The Gd.sub.2O.sub.3 component is able to
be contained therein in any material form and it is preferred to be
introduced thereinto in a form of an oxide (Gd.sub.2O.sub.3) or a
fluoride (GdF.sub.3).
[0093] Although an Y.sub.2O.sub.3 has an effect of adjusting the
refractive index and the dispersion, there is a risk that the
desired optical constants are not achieved if it is contained too
much. Its upper limit is preferably 15% by mass, more preferably
14.5% by mass and, most preferably, 14.0% by mass. The
Y.sub.2O.sub.3 component is able to be contained therein in any
material form and it is preferred to be introduced thereinto in a
form of an oxide (Y.sub.2O.sub.3) or a fluoride (YF.sub.3).
[0094] Although there is no particular technical disadvantage if
the range is mentioned as above, its amount is preferred to be less
than 3.5% by mass when a production cost is taken into
consideration because Y.sub.2O.sub.3 is the rarest mineral resource
among the components which are able to achieve the characteristics
of a high refractive index and a low dispersion.
[0095] A ZrO.sub.2 component has an effect of enhancing the
refractive index (nd) and improving the resistance to
devitrification but, since the ZrO.sub.2 component is a hardly
fusing component, fusing at high temperature is forced in the
manufacture of glass if it is contained too much and the loss in
energy is apt to cause a problem. On the other hand, there are some
cases where an effect of suppressing the devitrification is
achieved when a predetermined amount is contained. Accordingly, its
upper limit is preferably 15% by mass, more preferably 13% by mass
and, most preferably, 12% by mass while its lower limit is
preferably 1% by mass, more preferably 2% by mass and, most
preferably, 3% by mass. When no devitrification is resulted in the
glass even if no ZrO.sub.2 component is added, the component may
not be added. The ZrO.sub.2 component is able to be introduced in
any material form and it is preferred to be introduced in a form of
an oxide (ZrO.sub.2) or a fluoride (ZrF.sub.4).
[0096] Since a Ta.sub.2O.sub.5 component has an effect of enhancing
the refractive index to stabilize the glass, it may be optionally
contained. However, the Ta.sub.2O.sub.5 component is a rare mineral
resource, has a high material price, is a hardly melting component
and forces a fusion at high temperature in the manufacture of glass
whereby it has a characteristic that not only production cost
increases but also an optical elasticity constant .beta. increases.
Accordingly, the upper limit of its content is preferably 25% by
mass. More preferred upper limit is 22% by mass and the most
preferred upper limit is 19% by mass. Although the Ta.sub.2O.sub.5
component is able to be introduced in any material form, it is
preferred to be introduced in a form of an oxide
(Ta.sub.2O.sub.5).
[0097] An Nb.sub.2O.sub.5 component has an effect of increasing the
refractive index and stabilizing the glass the same as a
Ta.sub.2O.sub.5 component does and it may be optionally contained
within a range of 0 to 18% by mass. However, the Nb.sub.2O.sub.5
component is a hardly melting component and forces a fusion at high
temperature in the manufacture of glass whereby it has a
characteristic that not only production cost increases but also an
optical elasticity constant .beta. increases. Accordingly, the
upper limit of its content is preferably 18% by mass. More
preferred upper limit is 16% by mass and the most preferred upper
limit is 14% by mass. Although the Nb.sub.2O.sub.5 component is
able to be introduced in any material form, it is preferred to be
introduced in a form of an oxide (Nb.sub.2O.sub.5).
[0098] A WO.sub.3 component has an effect of adjusting the
refractive index and the dispersion and of improving the resistance
of the glass to devitrification. However, when it is contained too
much, coloration of the glass is significant and transmittance
particularly in the visible to short wave regions (shorter than 500
nm) becomes low and that is not preferred. Accordingly, its upper
limit is preferably 10% by mass, more preferably 8% by mass and,
most preferably, 6% by mass. Although the WO.sub.3 component is
able to be introduced in any material form, it is preferred to be
introduced in a form of an oxide (WO.sub.3).
[0099] In the optical glass of the above constitution 4, a
GeO.sub.2 component may be optionally added within a range of 0.0
to 0.1% by mass for adjustment of the refractive index and for
adjustment of viscosity of the fused glass. However, sine it is a
rare mineral resource and is expensive, it is preferred not to be
contained at all. Although each of Yb.sub.2O.sub.3, Ga.sub.2O.sub.3
and Bi.sub.2O.sub.3 may be optionally added for adjustment of the
refractive index, it has a property of increasing the optical
elasticity constant .beta. and, therefore, its upper limit is 1.0%
by mass. However, since those components are also rare mineral
resources, more preferred upper limit is 0.5% by mass and, most
preferably, nothing is added at all. Each of GeO.sub.2,
Yb.sub.2O.sub.3, Ga.sub.2O.sub.3 and Bi.sub.2O.sub.3 components may
be introduced in any material form and it is preferred to be
introduced in a form of an oxide (GeO.sub.2, Yb.sub.2O.sub.3,
Ga.sub.2O.sub.3 and Bi.sub.2O.sub.3).
[0100] Since a lead compound such as PbO and an arsenic compound
such as As.sub.2O.sub.3 are components having high environmental
loads, it is preferred not to be contained at all except in the
case of unavoidable mixing-in.
[0101] In the optical glass according to the above constitutions 5
and 6, the product of .alpha. and .beta. is preferably not more
than 100.times.10.sup.-12.degree.
C..sup.-1.times.nm.times.cm.sup.-1.times.Pa.sup.-1 and, most
preferably, not more than 90.times.10.sup.-12.degree.
C..sup.-1.times.nm.times.cm.sup.-1.times.Pa.sup.-1 for utilizing in
optical elements of higher precision and higher definition.
[0102] When the value of .alpha..times..beta. is smaller, an image
forming characteristic in the actually using environment becomes
faithful to the optically designed value calculated on the basis of
the optical property near the room temperature and, therefore,
there is an advantage that it is not necessary to conduct a
complicated optical simulation with a presumption of various using
environments.
[0103] In the optical glass of the constitution 7, the ratio of
(Ta.sub.2O.sub.5+Nb.sub.2O.sub.5+WO.sub.3)/(Gd.sub.2O.sub.3+Y.sub.2O.sub.-
3) in terms of % by mass which is the ratio in terms of % by mass
of the total amount of Ta.sub.2O.sub.5, Nb.sub.2O.sub.5 and
WO.sub.3 having a strong effect of enhancing the dispersion to the
total amount of Gd.sub.2O.sub.3 and Y.sub.2O.sub.3 having an effect
of reducing the dispersion is made within a range of more than 0.05
and less than 1.30 whereby the desired Abbe's number (35 to 55) is
apt to be achieved, so the above range is preferred. More
preferably, it is within a range of 0.055 to 1.29 and, most
preferably, it is within a range of 0.06 to 1.28.
[0104] When the components within the mentioned range are contained
in the optical glass of the constitution 8, the characteristics
mentioned in the constitution 1 to 7 are able to be stably
achieved. Reasons for limitation of each component will be
illustrated as follows.
[0105] Since the alkali metal oxide components (Li.sub.2O,
Na.sub.2O, K.sub.2O and Cs.sub.2O) give an effect of enhancing the
fusing property of the glass, it may be optionally contained but,
when they are contained too much, it is apt to happen that an
average linear expansion coefficient a increases or a refractive
index lowers whereby the glass becomes unstable and undesired
phenomenon such as devitrification is resulted and, accordingly,
each of them is preferred to be made within a range of 0.0 to 5.0%
in terms of % by mass. More preferred upper limits are 4.5% for an
Li.sub.2O component, an Na.sub.2O component and a K.sub.2O
component and 4.0% for a Cs.sub.2O component . The most preferred
upper limit for an Li.sub.2O component is 2.0% and, with regard to
the components of Na.sub.2O, K.sub.2O and Cs.sub.2O, they are not
contained at all. Although the alkali metal oxide components may be
introduced in various forms such as a carbonate (Li.sub.2CO.sub.3,
Na CO.sub.3, K.sub.2CO.sub.3 and Cs CO.sub.3), a nitrate
(LiNO.sub.3, NaNO.sub.3, KNO.sub.3 and CsNO.sub.3), a fluoride
(LiF, NaF, KF and KHF.sub.2) and a complex salt (Na.sub.2SiF.sub.6
and K.sub.2SiF.sub.6), it is preferred to be introduced in a form
of a carbonate and/or a nitrate.
[0106] Alkali earth metal oxide components (MgO, CaO, SrO and BaO)
give an effect of adjusting the refractive index and the optical
elasticity constant of the glass and, therefore, they are able to
be optionally contained but, if they are contained too much,
desired optical constants (particularly, a refractive index) are
apt to be hardly achieved whereby each of them is preferred to be
contained within a range of 0.0 to 5.0% in terms of % by mass. More
preferred upper limit is 4.0% for the MgO component and the CaO
component and 4.5% for the SrO component and the BaO component. The
most preferred upper limit is that no MgO component is contained at
all and is 3.0% for the CaO component and 4.0% for the SrO
component and the BaO component. Although the alkali earth metal
oxide components may be introduced in various forms such as a
carbonate (MgCO.sub.3, CaCO.sub.3 and BaCO.sub.3), a nitrate
(Sr(NO.sub.3).sub.2 and Ba(NO.sub.3).sub.2) and a fluoride
(MgF.sub.2, CaF.sub.2, SrF.sub.2 and BaF.sub.2), it is preferred to
be introduced in a form of a carbonate and/or a nitrate and/or a
fluoride.
[0107] The TiO.sub.2 component is able to be optionally contained
for adjustment of a refractive index and an Abbe's number but, when
it is contained excessively, coloration of the glass is apt to
become significant and, particularly, transmittance of the visible
short wavelength (500 nm and shorter) tends to become bad.
Accordingly, its preferred upper limit is 3.0% by mass, the more
preferred upper limit is 2.5% by mass and the most preferred upper
limit is 2.0% by mass. Although the TiO.sub.2 component may be
introduced in any material form, it is preferred to be contained in
a form of an oxide (TiO.sub.2).
[0108] An SnO.sub.2 component gives an effect of suppressing the
oxidation of the fused glass and making it clear and of preventing
the worsening of transmittance to irradiation of light and,
therefore, it may be optionally contained. However, if it is
contained excessively, there is a risk of coloration of the glass
due to reduction of fused glass and of giving an alloy with the
fusing device (particularly, noble metal such as Pt). Its upper
limit is preferably 3.0% by mass, more preferably 2.0% by mass and,
most preferably, 1.0% by mass. Although the SnO.sub.2 component may
be introduced in any material form, it is preferred to be
introduced in a form of an oxide (SnO and SnO.sub.2) or a fluoride
(SnF.sub.2 and SnF.sub.4).
[0109] An Al.sub.2O.sub.2 component is able to give an effect of
enhancing the chemical durability of the optical glass and the
optical element and of improving the resistance of the fused glass
to devitrification and, therefore, it may be optionally contained.
However, if it is contained excessively, it is apt to happen that a
refractive index significantly lowers and an optical elasticity
constant becomes too big. Accordingly, its upper limit is
preferably 3.0% by mass, more preferably 2.0% by mass and, most
preferably, 1.0% by mass. Although the Al.sub.2O.sub.2 component
may be introduced in any material form, it is preferred to be
introduced in a form of an oxide (Al.sub.2O.sub.2), a hydroxide
(Al(OH).sub.2) or a fluoride (AlF.sub.2).
[0110] A P.sub.2O.sub.5 component gives an effect of improving the
fusing property of the glass and, therefore, it may be optionally
contained but, when it is contained too much, it is apt to happen
that resistance of glass to devitrification becomes significantly
bad and an optical glass having no devitrification is hardly
available. Accordingly, its upper limit is preferably 5.0% by mass,
more preferably 1.0% by mass and, most preferably, it is not
contained at all. Although the P.sub.2O.sub.5 component may be
introduced in any material form, it is preferred to be introduced
in a form of Al(PO.sub.3).sub.3, Ca(PO.sub.3).sub.2,
Ba(PO.sub.3).sub.2, BPO.sub.4 or H.sub.3PO.sub.4.
[0111] A ZnO component has an effect of improving the fusing
property of the glass and also making an average linear expansion
coefficient a small and, therefore, it is able to be optionally
contained within a range of 0 to 10.0% by mass. Since it has a
property of significantly increasing the optical elasticity
constant .beta., a desired characteristic is apt to be hardly
available if it is contained excessively. The more preferred range
is less than 5.0% by mass and the most preferred range is less than
2.0% by mass. Preferably, the lower limit is 0.1% by mass. Although
the ZnO component may be introduced in any material form, it is
preferred to be introduced in a form of an oxide (ZnO) and/or a
fluoride (ZnF.sub.2).
[0112] An Lu.sub.2O.sub.3 component gives an effect of achieving a
high refractive index and a low dispersion the same as the
La.sub.2O.sub.3, Gd.sub.2O.sub.3 and Y.sub.2O.sub.3 components do
and, therefore, it is able to be optionally contained within a
range of 0 to 5.0% by mass. However, since it is a rare mineral
resource, it is not preferred to contain excessively. Its upper
limit is more preferably 3.0% by mass and, most preferably, it is
not contained at all. Although the Lu.sub.2O.sub.3 is able to be
introduced in any material form, it is preferred to be introduced
in a form of an oxide (Lu.sub.2O.sub.3).
[0113] A TeO.sub.2 component gives an effect of promoting the
clarifying action upon fusion of the glass and, therefore, it is
able to be optionally contained within a range of 0 to 3.0% by
mass. However, when it is contained excessively, coloration of the
glass is significant and transmittance is apt to become bad. More
preferred upper limit is 1.5% by mass and, most preferably, it is
not contained at all. Although the TeO.sub.2 component is able to
be introduced in any material form, it is preferred to be
introduced in a form of an oxide (TeO.sub.2).
[0114] An Sb.sub.2O.sub.3 has an effect as a defoaming agent for
glass and, therefore, it is able to be optionally contained within
a range of 0 to 2.0% by mass. However, when it is contained more
than the upper limit, there is a risk that an excessive foaming is
apt to happen upon fusion of the glass or it may form an alloy with
a fusing device (particularly a noble metal such as Pt) and,
therefore, it is preferred that more than the upper limit is not
contained. Although the Sb.sub.2O.sub.3 component may be introduced
in any material form, it is preferred to be introduced in a form of
an oxide (Sb.sub.2O.sub.3 and Sb.sub.2O.sub.5) or
Na.sub.2H.sub.2Sb.sub.2O.sub.7.5H.sub.2O.
[0115] An F component gives an effect of making the Abbe's number
big or making the optical elasticity constant .beta. small and,
therefore, it is able to be optionally contained within a range of
0 to 3.0% by mass. However, when it is contained in an amount of
more than the upper limit, there is a risk that a refractive index
becomes low and an average linear expansion coefficient a
increases. More preferred upper limit is 2.8% by mass and the most
preferred upper limit is 2.5% by mass. The F component is
introduced into the glass when the material form is introduced in a
form of a fluoride in the introduction of the above-mentioned
various kinds of oxides.
[0116] The expression of amount of each component used in this
specification on the basis of an oxide means % by mass of the
corresponding resulted oxide of each component to the total
component with a presumption that all of oxides, composite salts,
metal fluorides, etc. used as materials of the constituting
components of the glass of the invention are decomposed upon fusion
to convert into oxides and, in the case of a fluoride, mass of the
actually contained fluorine atoms to the mass of the resulting
oxide is expressed in terms of % by mass.
[0117] Various kinds of transition metal components such as V, Cr,
Mn, Fe, Co, Ni, Cu, Ag and Mo except Ti are colored even when each
of them is contained in small amount either solely or jointly
whereby absorption in the specific wavelength in visible region is
resulted. Therefore, in the case of an optical glass using the
wavelength of visible region, it is preferred that they are not
substantially contained. Further, there is a tendency that the use
of Pb, Th, Cd, Tl, As, Os, Be and Se components is decreasing as a
harmful chemical substance and it is necessary to take an action in
view of environmental measure not only in the manufacturing steps
for glass but also in processing steps and disposal after making
into a product. Consequently, it is preferred that those components
are not substantially contained when much importance is to be paid
to environmental influence.
[0118] In the optical glass of the above-mentioned constitution 11,
the ratio of the total amount of ZrO.sub.2, Ta.sub.2O.sub.5 and
Nb.sub.2O.sub.5 which are hardly-fusing component to the total
amount of SiO.sub.2 and B.sub.2O.sub.3 which are glass-forming
components, i.e.
(ZrO.sub.2+Ta.sub.2O.sub.5+Nb.sub.2O.sub.5)/(SiO.sub.2+B.sub.2O.sub.3)
is made less than 1.00 in terms of % by mass whereby there is
achieved an effect that there is no necessity of making the glass
fusing temperature significantly high and consumption of energy is
able to be reduced. When the above ratio is more than 1.00, since
each of Ta.sub.2O.sub.5 and Nb.sub.2O.sub.5 components is a rare
mineral resource, there is a risk that, the more the ratio, the
higher the material cost and further that the amount of the
glass-forming components becomes relatively small whereby glass
becomes unstable. Moreover, there is a risk that the relative
amount of ZrO.sub.2, Ta.sub.2O.sub.5 and Nb.sub.2O.sub.5 which
increase the optical elasticity coefficient becomes high and that
of B.sub.2O.sub.3 which has an effect of lowering the average
linear expansion coefficient a whereby the product of .alpha. and
.beta. increases. Thus, the above is not preferred for the
production of the desired optical glass cheaply.
[0119] In the optical glass of the above constitution 12, the
Y.sub.2O.sub.3 component which is the rarest mineral resource among
the components which are able to achieve the characteristics of the
high refractive index and the low dispersion is made less than 3.5%
by mass whereby an effect of reducing the manufacturing cost and
producing the glass in a stable and ever-lasting manner is able to
be achieved. Further the ratio of
(ZnO+Y.sub.2O.sub.2)/La.sub.2O.sub.2 in terms of % by mass is more
than 0 and less than 0.5 whereby an effect of stable formation of
an optical glass giving the desired production of .alpha. and
.beta. is able to be achieved. Furthermore, the sum of
ZrO.sub.2+Nb.sub.2O.sub.5 in terms of % by mass is more than 5.0%
and less than 13.0% whereby an effect of limiting the amount of the
hardly fusing components, suppressing the energy consumption and
providing an optical glass having an excellent resistance to
devitrification is able to be achieved.
[0120] In the optical glass of the above constitution 13, the range
of the constitution component ratio in the most suitable optical
glass among the above optical glass products of the above
constitutions 1 to 12 is made clear. To be more specific, the
composition of the glass is maintained to the following ones,
i.e.
[0121] more than 1.0% by mass and less than 10.0% by mass of
SiO.sub.2,
[0122] 15.0 to 28.0% by mass of B.sub.2O.sub.3,
[0123] 28.0 to 35.0% by mass of La.sub.2O.sub.3,
[0124] 25.0 to 35.0% by mass of Gd.sub.2O.sub.3,
[0125] 5.0 to 9.0% by mass of ZrO.sub.2 and
[0126] 0.1 to less than 2.0% by mass of ZnO and
[0127] 0.0 to 6.0% by mass of Ta.sub.2O.sub.5 and/or
[0128] 0.0 to 5.0% by mass of Nb.sub.2O.sub.5 and/or
[0129] 0.0 to 1.0% by mass of Sb.sub.2O.sub.3 and/or
[0130] 0.0 to less than 1.0% by mass of Al.sub.2O.sub.3
whereby there is an advantage that an optical glass in which
optical constants are within such ranges that the refractive index
(nd) is 1.78 to 1.83 and the Abbe's number (.nu.d) is 44 to 48 and
the product of .alpha. and .beta. where a is an average linear
expansion coefficient at -30.degree. C. to +70.degree. C. and
.beta. is an optical elasticity constant at the wavelength of 546.1
nm is not more than 90.times.10.sup.-12.degree.
C..sup.-1.times.nm.times.cm.sup.-1.times.Pa.sup.-1 is able to be
stably prepared. When the constituting components and the amounts
thereof are made within a ratio of the predetermined range as such,
the use of hardly fusing components and rare mineral resources is
suppressed to a minimum extent and production of an optical element
for the use of high precision and high definition where changes in
image forming characteristic under the using environment is little
is now possible without the use of the components having a high
load on environments.
[0131] As mentioned in the constitutions 14 to 16, the optical
glass mentioned in the above constitutions 1 to 13 is useful as a
mother material for the preparation of optical elements such as
lenses and prisms and, when the optical elements are utilized for
cameras and projectors, image formation and projection
characteristic with high precision and high definition are able to
be achieved.
[0132] Since the composition is expressed in terms of % by mass in
the glass composition of the invention, it is unable to be directly
expressed in terms of mol %. However, the composition of each of
the components in terms of mol % existing in the glass composition
satisfying various characteristics demanded in the invention has
almost the following values.
[0133] As to the range for the constitution 1, it is 2.0 to 25.0
mol % for SiO.sub.2, 25 to 65 mol % for B.sub.2O.sub.3, more than 0
to less than 0.7 in terms of the molar % ratio for
SiO.sub.2/B.sub.2O.sub.3 and 10 to 30 mol % for
La.sub.2O.sub.3.
[0134] As to the range for the constitution 3, it is 0 to 18 mol %
for Gd.sub.2O.sub.3, 0 to 10 mol % for Y.sub.2O.sub.3, 0 to 10 mol
% for ZrO.sub.2, 0 to 10 mol % for Ta.sub.2O.sub.5, 0 to 10 mol %
for Nb.sub.2O.sub.5 and 0 to 5 mol % for WO.sub.3.
[0135] As to the range for the constitution 4, it is 0.0 to 0.1 mol
% for GeO.sub.2, 0.0 to 1.0 mol % for Yb.sub.2O.sub.3, 0.0 to 1.0
mol % for
[0136] Ga.sub.2O.sub.3 and 0.0 to 1.0 mol % for
Bi.sub.2O.sub.3.
[0137] As to the range for the constitution 7, the ratio in terms
of mol % for
(Ta.sub.2O.sub.5+Nb.sub.2O.sub.5+WO.sub.3)/(Gd.sub.2O.sub.3+Y.sub.2O.-
sub.3) is more than 0.03 and less than 1.25.
[0138] As to the range for the constitution 8, that in terms of mol
% is as follows.
[0139] 0 to 7.0% for Li.sub.2O,
[0140] 0 to 5.0% for Na.sub.2O,
[0141] 0 to 5.0% for K.sub.2O,
[0142] 0 to 3.0% for Cs.sub.2O,
[0143] 0 to 5.0% for MgO,
[0144] 0 to 5.0% for CaO,
[0145] 0 to 5.0% for SrO,
[0146] 0 to 5.0% for BaO,
[0147] 0 to 5.0% for TiO.sub.2,
[0148] 0 to 3.0% for SnO.sub.2,
[0149] 0 to 3.0% for Al.sub.2O.sub.3,
[0150] 0 to 3.0% for P.sub.2O.sub.5,
[0151] 0 to 7.0% for ZnO,
[0152] 0 to 2.0% for Lu.sub.2O.sub.3,
[0153] 0 to 1.0% for TeO.sub.2,
[0154] 0 to 1.0% of Sb.sub.2O.sub.3 and
[0155] 0 to 10% for F.
[0156] As to the range for the constitution 9, it is less than 5.0
mol % for ZnO.
[0157] As to the range for the constitution 10, it is less than 4.0
mol % for Y.sub.2O.sub.3.
[0158] As to the range for the constitution 11, the mol % ratio is
less than 0.8 for
(ZrO.sub.2+Ta.sub.2O.sub.5+Nb.sub.2O.sub.5)/(SiO.sub.2+B.sub.2O.sub.3).
[0159] As to the range for the constitution 12, it is less than 4.0
mol % for Y.sub.2O.sub.3, the mol % ratio is more than 0 and less
than 1.0 for (ZnO +Y.sub.2O.sub.3)/La.sub.2O.sub.3 and the mol %
sum is more than 5.0% and less than 13.0% for
(ZrO.sub.2+Nb.sub.2O.sub.5).
[0160] As to the range for the constitution 13, it is 3 to 22 mol %
for SiO.sub.2, 27 to 63 mol % for B.sub.2O.sub.3, 10 to 25 mol %
for La.sub.2O.sub.3, 6 to 15 mol % for Gd.sub.2O.sub.3, 4 to 10 mol
% for ZrO.sub.2, 0.1 to 2.0 mol % for ZnO, 0 to 5.0 mol % for
Ta.sub.2O.sub.5, 0 to 3 mol % for Nb.sub.2O.sub.5, 0 to 0.5 mol %
for Sb.sub.2O.sub.3 and 0 to less than 1.0 mol % for
Al.sub.2O.sub.3.
EXAMPLES
[0161] Now the invention will be illustrated in more detail by way
of the following Examples although the invention is not limited to
those Examples.
[0162] Tables 1 to 8 show glass composition, refractive index (nd),
Abbe's number (.nu.d), average linear expansion coefficient .alpha.
at -30 to +70.degree. C., optical elasticity coefficient .beta. at
the wavelength of 546.1 nm, product of .alpha. and .beta. and ratio
and sum of the amounts of various components for Examples (1 to 38)
which are suitable for the production of optical glass with a high
refractive index and a low dispersion where the refractive index
(nd) is not less than 1.75 and the Abbe's number (.nu.d) is not
more than 35 in which image formation characteristic is hardly
affected by changes in the temperature in the using
environment.
[0163] Table 9 shows glass compositions and various properties of
Comparative Examples (A to C) for known optical glass products.
[0164] In this table, Comparative Example A is Example 6 in
JP-A-2005-306732, Comparative Example B is Example 1 in
JP-A-2002-284542 and Comparative Example C is Example 7 in
JP-A-2004-161506. The refractive indexes (nd) and Abbe's numbers
(.nu.d) in the table are those mentioned in each of the above
gazettes.
[0165] For the optical glass prepared, its refractive index (nd),
Abbe's number (.nu.d), average linear expansion coefficient
(.alpha.) at -30.degree. to +70.degree. C. and optical elasticity
coefficient (.beta.) at the wavelength of 546.1 nm were measured as
follows.
[0166] (1) Refractive index (nd) and Abbe's number (.nu.d)
[0167] Measurements were conducted for the optical glass where the
temperature lowering rate with a gradual cooling was made
-25.degree. C/hour.
[0168] (2) Average linear expansion coefficient (a) at -30 to
+70.degree. C.
[0169] Measurement was conducted in accordance with the method
mentioned in the stipulations by the Japan Optical Glass Industry
Association (JOGIS 16-2003) (a method for the measurement of
average linear expansion coefficient of optical glass at about
ambient temperature). As a test piece, a sample of 50 mm length and
4 mm diameter was used.
[0170] (3) Optical elasticity constant (.beta.) at the wavelength
of 546.1 nm
[0171] An optical elasticity constant (.beta.) was determined in
such a manner that the shape of a sample was made into a disk of 25
mm diameter and 8 mm thickness after subjecting to a face-to-face
polishing, a compressing load was applied in the predetermined
direction, an optical path difference generated in the center of
the glass was measured and calculation was conducted according to
the formula .delta.=.beta..d.F. A super-high voltage mercury lamp
was used as a light source for the measurement at 546.1 nm. In the
above formula, optical path difference, glass thickness and stress
are given as .delta. (nm), d (cm) and F (Pa), respectively.
TABLE-US-00001 TABLE 1 % by mass 1 2 3 4 5 SiO.sub.2 2.62 2.60 2.60
2.60 2.60 B.sub.2O.sub.3 31.20 31.22 31.22 29.22 30.21
Al.sub.2O.sub.3 P.sub.2O.sub.5 Y.sub.2O.sub.3 11.70 10.70 10.70
10.70 1.75 La.sub.2O.sub.3 44.31 45.31 44.31 45.31 45.19
Gd.sub.2O.sub.3 Yb.sub.2O.sub.3 Lu.sub.2O.sub.3 1.00 TiO.sub.2
ZrO.sub.2 6.60 6.60 6.60 6.50 6.60 SnO.sub.2 TeO.sub.2 0.10
Nb.sub.2O.sub.5 1.62 1.62 1.62 1.62 2.71 Ta.sub.2O.sub.5 WO.sub.3
ZnO 0.90 0.90 0.90 0.90 0.90 MgO CaO SrO 1.00 1.00 1.00 1.00 1.00
BaO Li.sub.2O Na.sub.2O 1.00 K.sub.2O Cs.sub.2O Sb.sub.2O.sub.3
0.05 0.05 0.05 0.05 0.04 F 1.00 Total 100.00 100.00 100.00 100.00
100.00 .alpha. 62 62 62 64 62 .beta. 1.44 1.43 1.43 1.40 1.42
.alpha. .times. .beta. 89.28 88.66 88.66 89.60 88.04 nd 1.772 1.773
1.773 1.773 1.780 .nu.d 49.6 49.6 49.6 50.0 48.5
SiO.sub.2/B.sub.2O.sub.3 0.084 0.083 0.083 0.089 0.086
(Ta.sub.2O.sub.5 + Nb.sub.2O.sub.5 + 0.138 0.151 0.151 0.151 0.252
WO.sub.3)/(Gd.sub.2O.sub.3 + Y.sub.2O.sub.3) (ZrO.sub.2 +
Ta.sub.2O.sub.5 + 0.243 0.243 0.243 0.255 0.284
Nb.sub.2O.sub.5)/(SiO.sub.2 + B.sub.2O.sub.3) (ZnO +
Y.sub.2O.sub.3)/La.sub.2O.sub.3 0.284 0.256 0.262 0.256 0.258
ZrO.sub.2 + Nb.sub.2O.sub.5 8.22 8.22 8.22 8.12 9.31
TABLE-US-00002 TABLE 2 % by mass 6 7 8 9 10 SiO.sub.2 2.00 2.60
2.60 2.32 2.60 B.sub.2O.sub.3 29.00 29.20 29.20 27.87 28.20
Al.sub.2O.sub.3 P.sub.2O.sub.5 0.54 Y.sub.2O.sub.3 8.80 10.80 10.80
La.sub.2O.sub.3 29.49 47.06 45.06 39.02 45.06 Gd.sub.2O.sub.3 26.97
18.89 Yb.sub.2O.sub.3 Lu.sub.2O.sub.3 TiO.sub.2 0.50 ZrO.sub.2 6.71
6.60 6.60 6.66 6.60 SnO.sub.2 TeO.sub.2 0.05 0.04 Nb.sub.2O.sub.5
2.96 3.30 3.80 3.75 3.80 Ta.sub.2O.sub.5 2.28 WO.sub.3 0.50 ZnO
0.90 0.90 0.95 0.90 MgO CaO SrO 1.00 1.00 0.50 BaO Li.sub.2O 0.50
Na.sub.2O K.sub.2O 1.00 Cs.sub.2O Sb.sub.2O.sub.3 0.04 0.04 0.04 F
Total 100.00 100.00 100.00 100.00 100.00 .alpha. 60 61 61 61 61
.beta. 1.46 1.38 1.40 1.42 1.40 .alpha. .times. .beta. 87.60 84.18
85.40 86.62 85.40 nd 1.783 1.788 1.788 1.788 1.789 .nu.d 47.3 47.4
47.4 48.1 47.3 SiO.sub.2/B.sub.2O.sub.3 0.069 0.089 0.089 0.083
0.092 (Ta.sub.2O.sub.5 + Nb.sub.2O.sub.5 + 0.194 0.375 0.352 0.199
0.398 WO.sub.3)/(Gd.sub.2O.sub.3 + Y.sub.2O.sub.3) (ZrO.sub.2 +
Ta.sub.2O.sub.5 + 0.385 0.311 0.327 0.345 0.338
Nb.sub.2O.sub.5)/(SiO.sub.2 + B.sub.2O.sub.3) (ZnO +
Y.sub.2O.sub.3)/La.sub.2O.sub.3 0 0.206 0.260 0.024 0.260 ZrO.sub.2
+ Nb.sub.2O.sub.5 9.67 9.90 10.40 10.41 10.40
TABLE-US-00003 TABLE 3 % by mass 11 12 13 14 15 SiO.sub.2 2.60 2.30
2.00 2.00 2.00 B.sub.2O.sub.3 29.00 27.87 26.54 26.54 26.64
Al.sub.2O.sub.3 0.10 P.sub.2O.sub.5 Y.sub.2O.sub.3 12.86 5.40
La.sub.2O.sub.3 43.00 38.76 32.49 32.49 32.49 Gd.sub.2O.sub.3 13.50
26.98 26.97 26.97 Yb.sub.2O.sub.3 Lu.sub.2O.sub.3 TiO.sub.2
ZrO.sub.2 6.60 6.66 7.29 6.71 6.71 SnO.sub.2 TeO.sub.2
Nb.sub.2O.sub.5 3.80 3.38 3.56 2.96 3.56 Ta.sub.2O.sub.5 1.14 0.28
WO.sub.3 ZnO 1.10 0.45 1.00 2.00 1.00 MgO 0.50 CaO SrO 1.00 BaO
0.68 Li.sub.2O Na.sub.2O K.sub.2O Cs.sub.2O Sb.sub.2O.sub.3 0.04
0.04 0.04 0.05 0.05 F Total 100.00 100.00 100.00 100.00 100.00
.alpha. 61 60 61 61 63 .beta. 1.43 1.43 1.43 1.43 1.40 .alpha.
.times. .beta. 87.23 85.80 87.23 87.23 88.20 nd 1.789 1.796 1.799
1.800 1.801 .nu.d 47.3 47.0 46.3 47.0 46.7 SiO.sub.2/B.sub.2O.sub.3
0.090 0.083 0.075 0.075 0.075 (Ta.sub.2O.sub.5 + Nb.sub.2O.sub.5 +
0.295 0.239 0.132 0.120 0.132 WO.sub.3)/(Gd.sub.2O.sub.3 +
Y.sub.2O.sub.3) (ZrO.sub.2 + Ta.sub.2O.sub.5 + 0.329 0.371 0.380
0.349 0.360 Nb.sub.2O.sub.5)/(SiO.sub.2 + B.sub.2O.sub.3) (ZnO +
Y.sub.2O.sub.3)/La.sub.2O.sub.3 0.325 0.151 0.031 0.062 0.031
ZrO.sub.2 + Nb.sub.2O.sub.5 10.40 10.04 10.85 9.67 10.27
TABLE-US-00004 TABLE 4 % by mass 16 17 18 19 20 SiO.sub.2 2.15 2.00
2.04 2.00 7.49 B.sub.2O.sub.3 26.54 26.54 26.54 26.54 17.71
Al.sub.2O.sub.3 P.sub.2O.sub.5 Y.sub.2O.sub.3 5.00 La.sub.2O.sub.3
32.49 32.45 32.99 32.48 29.81 Gd.sub.2O.sub.3 26.98 27.00 26.97
15.98 31.06 Yb.sub.2O.sub.3 Lu.sub.2O.sub.3 TiO.sub.2 ZrO.sub.2
6.71 6.72 6.72 6.71 7.04 SnO.sub.2 0.60 TeO.sub.2 Nb.sub.2O.sub.5
4.09 2.96 3.69 2.96 Ta.sub.2O.sub.5 2.28 2.28 2.25 WO.sub.3 ZnO
1.00 1.00 1.00 MgO CaO SrO BaO 3.00 Li.sub.2O Na.sub.2O K.sub.2O
Cs.sub.2O 1.00 Sb.sub.2O.sub.3 0.04 0.05 0.05 0.05 0.04 F Total
100.00 100.00 100.00 100.00 100.00 .alpha. 59 60 61 61 65 .beta.
1.48 1.42 1.41 1.41 1.30 .alpha. .times. .beta. 87.32 85.20 86.01
86.01 84.50 nd 1.803 1.804 1.804 1.805 1.806 .nu.d 45.9 46.6 46.6
46.5 47.4 SiO.sub.2/B.sub.2O.sub.3 0.081 0.075 0.077 0.075 0.423
(Ta.sub.2O.sub.5 + Nb.sub.2O.sub.5 + 0.152 0.194 0.137 0.250 0.072
WO.sub.3)/(Gd.sub.2O.sub.3 + Y.sub.2O.sub.3) (ZrO.sub.2 +
Ta.sub.2O.sub.5 + 0.376 0.419 0.364 0.419 0.369
Nb.sub.2O.sub.5)/(SiO.sub.2 + B.sub.2O.sub.3) (ZnO +
Y.sub.2O.sub.3)/La.sub.2O.sub.3 0.031 0 0.030 0.133 0.034 ZrO.sub.2
+ Nb.sub.2O.sub.5 10.80 9.68 10.41 9.67 7.04
TABLE-US-00005 TABLE 5 % by mass 21 22 23 24 25 SiO.sub.2 7.49 7.51
7.52 7.52 7.50 B.sub.2O.sub.3 17.71 18.33 18.02 17.94 17.76
Al.sub.2O.sub.3 P.sub.2O.sub.5 Y.sub.2O.sub.3 3.00 La.sub.2O.sub.3
29.81 32.41 31.75 31.34 29.71 Gd.sub.2O.sub.3 31.06 31.66 31.52
31.45 31.08 Yb.sub.2O.sub.3 Lu.sub.2O.sub.3 TiO.sub.2 ZrO.sub.2
7.04 7.06 7.07 7.07 7.05 SnO.sub.2 0.60 TeO.sub.2 Nb.sub.2O.sub.5
1.98 1.32 0.99 Ta.sub.2O.sub.5 2.25 1.75 2.63 5.25 WO .sub.3 ZnO
1.00 1.00 1.00 1.01 1.00 MgO CaO 0.60 SrO BaO Li.sub.2O Na.sub.2O
K.sub.2O Cs.sub.2O Sb.sub.2O.sub.3 0.04 0.05 0.05 0.05 0.05 F Total
100.00 100.00 100.00 100.00 100.00 .alpha. 64 64 63 64 63 .beta.
1.36 1.29 1.32 1.26 1.37 .alpha. .times. .beta. 87.04 82.56 83.16
80.64 86.31 nd 1.812 1.814 1.816 1.816 1.816 .nu.d 47.4 46.6 46.6
46.6 46.6 SiO.sub.2/B.sub.2O.sub.3 0.423 0.410 0.417 0.419 0.422
(Ta.sub.2O.sub.5 + Nb.sub.2O.sub.5 + 0.066 0.063 0.097 0.115 0.169
WO.sub.3)/(Gd.sub.2O.sub.3 + Y.sub.2O.sub.3) (ZrO.sub.2 +
Ta.sub.2O.sub.5 + 0.369 0.350 0.397 0.420 0.487
Nb.sub.2O.sub.5)/(SiO.sub.2 + B.sub.2O.sub.3) (ZnO +
Y.sub.2O.sub.3)/La.sub.2O.sub.3 0.134 0.031 0.031 0.032 0.034
ZrO.sub.2 + Nb.sub.2O.sub.5 7.04 9.04 8.39 8.06 7.05
TABLE-US-00006 TABLE 6 % by mass 26 27 28 29 30 SiO.sub.2 7.49 2.43
5.17 1.94 2.38 B.sub.2O.sub.3 17.96 24.96 20.66 24.64 24.02
Al.sub.2O.sub.3 P.sub.2O.sub.5 Y.sub.2O.sub.3 1.50 1.50
La.sub.2O.sub.3 31.81 38.46 37.63 41.88 42.90 Gd.sub.2O.sub.3 31.05
17.57 21.31 16.34 12.26 Yb.sub.2O.sub.3 Lu.sub.2O.sub.3 TiO.sub.2
ZrO.sub.2 7.04 6.63 6.80 6.50 5.57 SnO.sub.2 TeO.sub.2 0.100
Nb.sub.2O.sub.5 3.00 4.98 3.63 5.55 7.40 Ta.sub.2O.sub.5 2.92 4.24
2.92 WO .sub.3 0.60 3.00 ZnO 1.00 0.50 0.51 1.00 MgO CaO SrO BaO
Li.sub.2O Na.sub.2O K.sub.2O Cs.sub.2O Sb.sub.2O.sub.3 0.05 0.05
0.05 0.05 0.05 F Total 100.00 100.00 100.00 100.00 100.00 .alpha.
63 62 63 64 62 .beta. 1.34 1.36 1.29 1.34 1.31 .alpha. .times.
.beta. 84.42 84.32 81.27 85.76 81.22 nd 1.819 1.819 1.825 1.826
1.834 .nu.d 45.5 44.7 44.7 43.4 42.6 SiO.sub.2/B.sub.2O.sub.3 0.417
0.097 0.250 0.079 0.099 (Ta.sub.2O.sub.5 + Nb.sub.2O.sub.5 + 0.116
0.414 0.369 0.523 0.750 WO.sub.3)/(Gd.sub.2O.sub.3 +
Y.sub.2O.sub.3) (ZrO.sub.2 + Ta.sub.2O.sub.5 + 0.394 0.530 0.568
0.453 0.602 Nb.sub.2O.sub.5)/(SiO.sub.2 + B.sub.2O.sub.3) (ZnO +
Y.sub.2O.sub.3)/La.sub.2O.sub.3 0.031 0.052 0.014 0.000 0.058
ZrO.sub.2 + Nb.sub.2O.sub.5 10.04 11.61 10.43 12.05 12.97
TABLE-US-00007 TABLE 7 % by mass 31 32 33 34 35 SiO.sub.2 2.82 7.39
4.61 6.43 5.89 B.sub.2O.sub.3 23.38 14.96 17.67 11.67 12.46
Al.sub.2O.sub.3 P.sub.2O.sub.5 Y.sub.2O.sub.3 3.00 1.33
La.sub.2O.sub.3 43.92 39.99 41.96 42.11 40.00 Gd.sub.2O.sub.3 8.17
15.38 12.08 13.54 15.38 Yb.sub.2O.sub.3 1.00 Lu.sub.2O.sub.3
TiO.sub.2 0.50 0.30 ZrO.sub.2 6.54 5.99 6.27 6.00 5.99 SnO.sub.2
0.50 0.33 TeO.sub.2 Nb.sub.2O.sub.5 6.27 1.00 3.14 0.50 1.00
Ta.sub.2O.sub.5 5.85 14.69 12.27 15.82 17.38 WO.sub.3 ZnO 1.90 1.00
MgO CaO SrO 0.30 BaO Li.sub.2O Na.sub.2O 0.50 K.sub.2O 0.50
Cs.sub.2O Sb.sub.2O.sub.3 0.05 0.10 0.07 0.10 F Total 100.00 100.00
100.00 100.00 100.00 .alpha. 62 62 64 65 67 .beta. 1.31 1.38 1.31
1.31 1.33 .alpha. .times. .beta. 81.22 85.56 83.84 85.15 89.11 nd
1.835 1.847 1.859 1.878 1.881 .nu.d 42.7 42.7 41.8 41.2 40.7
SiO.sub.2/B.sub.2O.sub.3 0.121 0.494 0.261 0.551 0.473
(Ta.sub.2O.sub.5 + Nb.sub.2O.sub.5 + 1.085 1.020 1.276 1.098 1.195
WO.sub.3)/(Gd.sub.2O.sub.3 + Y.sub.2O.sub.3) (ZrO.sub.2 +
Ta.sub.2O.sub.5 + 0.712 0.970 0.973 1.233 1.328
Nb.sub.2O.sub.5)/(SiO.sub.2 + B.sub.2O.sub.3) (ZnO +
Y.sub.2O.sub.3)/La.sub.2O.sub.3 0.068 0.000 0.000 0.077 0.025
ZrO.sub.2 + Nb.sub.2O.sub.5 12.81 6.99 9.41 6.50 6.99
TABLE-US-00008 TABLE 8 % by mass 36 37 38 SiO.sub.2 6.39 5.92 6.42
B.sub.2O.sub.3 11.96 12.50 11.65 Al.sub.2O.sub.3 P.sub.2O.sub.5
Y.sub.2O.sub.3 1.33 La.sub.2O.sub.3 39.99 40.47 42.02
Gd.sub.2O.sub.3 15.39 15.46 13.51 Yb.sub.2O.sub.3 Lu.sub.2O.sub.3
TiO.sub.2 0.25 ZrO.sub.2 5.99 6.03 5.99 SnO.sub.2 0.50 0.50
TeO.sub.2 Nb.sub.2O.sub.5 1.00 1.00 0.50 Ta.sub.2O.sub.5 18.68
17.62 15.59 WO .sub.3 2.19 ZnO 0.65 MgO CaO SrO BaO Li.sub.2O
Na.sub.2O K.sub.2O Cs.sub.2O Sb.sub.2O.sub.3 0.10 0.10 0.10 F Total
100.0 100.0 100.0 .alpha. 66 68 67 .beta. 1.30 1.32 1.34 .alpha.
.times. .beta. 85.80 89.76 89.78 nd 1.883 1.883 1.883 .nu.d 40.8
40.8 40.7 SiO.sub.2/B.sub.2O.sub.3 0.534 0.474 0.551
(Ta.sub.2O.sub.5 + Nb.sub.2O.sub.5 + 1.279 1.204 1.245
WO.sub.3)/(Gd.sub.2O.sub.3 + Y.sub.2O.sub.3) (ZrO.sub.2 +
Ta.sub.2O.sub.5 + 1.399 1.338 1.233 Nb.sub.2O.sub.5)/(SiO.sub.2 +
B.sub.2O.sub.3) (ZnO + Y.sub.2O.sub.3)/La.sub.2O.sub.3 0 0.016
0.032 ZrO.sub.2 + Nb.sub.2O.sub.5 6.99 7.03 6.49
TABLE-US-00009 TABLE 9 Comp. Comp. Comp. % by mass Ex. A Ex. B Ex.
C SiO.sub.2 6.70 1.00 6.00 B.sub.2O.sub.3 10.80 24.00 34.50
Al.sub.2O.sub.3 P.sub.2O.sub.5 Y.sub.2O.sub.3 3.80 2.18
La.sub.2O.sub.3 41.80 40.68 30.00 Gd.sub.2O.sub.3 9.60 12.68
Yb.sub.2O.sub.3 Lu.sub.2O.sub.3 TiO.sub.2 ZrO.sub.2 5.20 6.00 5.00
SnO.sub.2 TeO.sub.2 Nb.sub.2O.sub.5 1.30 7.75 Ta.sub.2O.sub.5 15.90
WO.sub.3 ZnO 4.50 5.75 22.00 MgO CaO 2.00 SrO BaO 0.50 Li.sub.2O
0.20 Na.sub.2O K.sub.2O Cs.sub.2O Sb.sub.2O.sub.3 0.20 F Total
100.0 100.4 100.0 .alpha. 71 67 51 .beta. 1.28 1.50 2.55 .alpha.
.times. .beta. 90.88 100.50 130.05 nd 1.88 1.834 1.783 .nu.d 40.9
42.7 47.7 SiO.sub.2/B.sub.2O.sub.3 0.620 0.042 0.174
(Ta.sub.2O.sub.5 + Nb.sub.2O.sub.5 + 1.284 0.522
WO.sub.3)/(Gd.sub.2O.sub.3 + Y.sub.2O.sub.3) (ZrO.sub.2 +
Ta.sub.2O.sub.5 + 1.280 0.550 0.123 Nb.sub.2O.sub.5)/(SiO.sub.2 +
B.sub.2O.sub.3) (ZnO + Y.sub.2O.sub.3)/La.sub.2O.sub.3 0.199 0.195
0.733 ZrO.sub.2 + Nb.sub.2O.sub.5 6.50 13.75 5.00
[0172] All of the glass products in accordance with the invention
mentioned in Tables 1 to 8 were prepared in such a manner that
common materials for optical glass such as the corresponding oxide,
hydroxide, carbonate, nitrate, fluoride, hydroxide, metaphosphate,
etc. as the materials for each component were used, weighed and
mixed in a predetermined ratio, poured over into a platinum
crucible, fused for 3 to 4 hours at the temperature range of 1,200
to 1,400.degree. C. in an electric furnace depending upon the
easiness of the fusion of the glass composition, stirred for making
uniform, lowered down to an appropriate temperature, placed in a
metal mold or the like and gradually cooled.
[0173] It has been found that, as shown in Tables 1 to 8, all of
the preferred Examples of the invention are able to achieve the
desired optical constants and the product .alpha..times..beta.. On
the contrary, in the Comparative Examples shown in Table 9,
Comparative Example 1 is able to achieve a relatively small
.alpha..times..beta. but, as compared with Examples 36 to 38 where
the optical constants are similar, the mass % ratio of
SiO.sub.2/B.sub.2O.sub.3 exceeds 0.6 whereby an average linear
expansion coefficient a becomes big and the product
.alpha..times..beta. is more than 90.times.10.sup.-12.degree.
C..sup.-1.times.nm.times.cm.sup.-1.times.Pa.sup.-1. In Comparative
Example B, abundant ZnO is contained and, therefore, the optical
elasticity constant .beta. becomes large and the product
.alpha..times..beta. exceeds 100.times.10.sup.-12.degree.
C..sup.-1.times.nm.times.cm.sup.-1.times.Pa.sup.-1 as compared with
Examples 30 to 32 where the optical constants are similar. Besides
that, amount of SiO.sub.2 is small and the mass % ratio of
SiO.sub.2/B.sub.2O.sub.3 is less than 0.05 and, therefore,
resistance of the glass against devitrification is not sufficient
and, when the glass is cast, crystals are generated nearly on the
whole surface of the glass. In Comparative Example C, amount of ZnO
is significantly large and the mass % ratio of
(ZnO+Y.sub.2O.sub.3)/La.sub.2O.sub.3 is as big as 0.733 and,
therefore, the optical elasticity constant .beta. increases and the
product .alpha..times..beta. exceeds 130.times.10.sup.-12.degree.
C..sup.-1.times.nm.times.cm.sup.-1.times.Pa.sup.-1.
[0174] When the glass products of the Examples mentioned in Tables
1 to 8 were subjected to a cold processing or a reheat press
processing, no problem such as devitrification was resulted but
they were able to be stably made into various lens and prism
forms.
[0175] When the lens or the prism prepared as such was installed in
a camera or a projector and an image formation characteristic was
confirmed, the image formation characteristic which is expected by
an optical design utilizing the optical constants obtained at room
temperature was reproducible even upon operations at high
temperature (about 50 to 70.degree. C.).
[0176] Although the invention was illustrated in detail hereinabove
for an object of exemplification, it will be understood that
the
[0177] Examples are merely for an object of exemplification and
that various modifications are able to be carried out by persons
skilled in the art without deviating from the idea and scope of the
invention.
[0178] In accordance with the invention, there is provided an
optical glass with a high refractive index and a low dispersion
having a refractive index (nd) of not less than 1.75 and an Abbe's
number (.nu.d) of not less than 35 where the image formation
characteristic is hardly affected by changes in temperature of the
using environment and, when the optical glass is used, lenses and
prisms for image projecting (reproducing) instruments such as
projectors and picture-taking devices such as highly precise camera
are able to be stably manufactured.
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