U.S. patent application number 12/149815 was filed with the patent office on 2008-09-11 for process for the production of glass molded article, optical element produced by the process, and method of treating glass.
This patent application is currently assigned to HOYA CORPORATION. Invention is credited to Kazutaka Hayashi, Hiroshi Kawazoe, Hiromasa Tawarayama, Xuelu Zou.
Application Number | 20080216514 12/149815 |
Document ID | / |
Family ID | 18800582 |
Filed Date | 2008-09-11 |
United States Patent
Application |
20080216514 |
Kind Code |
A1 |
Hayashi; Kazutaka ; et
al. |
September 11, 2008 |
Process for the production of glass molded article, optical element
produced by the process, and method of treating glass
Abstract
Provided are a process for the production of a precision
press-molded article having a high transmittance and a method of
treating a glass to color or decolor the glass, the process
comprising heat-treating a press-molded article containing at least
one selected from WO.sub.3, Nb.sub.2O.sub.5 or TiO.sub.2 in an
oxidizing atmosphere to produce a glass molded article, and the
method comprising heat-treating a colored glass containing at least
one oxide of WO.sub.3 and Nb.sub.2O.sub.5 in an oxidizing
atmosphere to decolor the glass, or heat-treating a glass
containing at least one oxide selected from WO.sub.3,
Nb.sub.2O.sub.5 or TiO.sub.2 in a non-oxidizing atmosphere to color
the glass.
Inventors: |
Hayashi; Kazutaka; (Tokyo,
JP) ; Tawarayama; Hiromasa; (Tokyo, JP) ; Zou;
Xuelu; (Tokyo, JP) ; Kawazoe; Hiroshi;
(Kanagawa, JP) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
HOYA CORPORATION
Tokyo
JP
|
Family ID: |
18800582 |
Appl. No.: |
12/149815 |
Filed: |
May 8, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10892206 |
Jul 16, 2004 |
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12149815 |
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09981237 |
Oct 18, 2001 |
6786064 |
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10892206 |
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Current U.S.
Class: |
65/32.3 |
Current CPC
Class: |
C03C 1/10 20130101; C03B
2215/66 20130101; C03B 32/00 20130101; C03C 3/21 20130101; C03C
3/16 20130101; C03C 4/02 20130101; C03B 11/005 20130101; C03B 11/08
20130101 |
Class at
Publication: |
65/32.3 |
International
Class: |
C03B 32/00 20060101
C03B032/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 23, 2000 |
JP |
2000-322765 |
Claims
1.-12. (canceled)
13. An optical element produced by the process of claim 16.
14. (canceled)
15. A method of treating a glass, which comprises heat-treating a
glass containing at least one oxide selected from WO.sub.3,
Nb.sub.2O.sub.5 or TiO.sub.2 in a non-oxidizing atmosphere to color
the glass.
16. A method of treating a glass, which comprises heat-treating a
colored phosphate glass containing at least one oxide of WO.sub.3
and Nb.sub.2O.sub.5 in an oxidizing dry atmosphere to decolor the
glass.
17. The method of claim 16, wherein the glass contains
Nb.sub.2O.sub.5.
18. The method of claim 16, wherein the glass is heat-treated at a
glass transition temperature of the glass or lower.
19. The method of claim 16, wherein the glass is an optical glass
having a refractive index (nd) of 1.6 or more and an Abbe's number
(vd) of 33 or less.
20. The method of claim 16, wherein the glass has a composition
containing, by mol%, 12 to 50 % of P.sub.2O.sub.5, 2 to 45 % of
WO.sub.3, 0 to 25 % of Nb.sub.2O.sub.5, 0 to 22 % of TiO.sub.2, 0
to 30% of Li.sub.2O, 0 to 33 % of Na.sub.2O, 0 to 25 % of K.sub.2O,
0 to 23 % of B.sub.2O.sub.3, 0 to 25 % of BaO and 0 to 20 % of ZnO
and having a WO.sub.3 and Nb.sub.2O.sub.5 total content of 45 mol%
or less.
21. The method of claim 20, wherein the glass contains, by mol%, 2
to 30 % of Li.sub.2O and 2 to 33 % of Na.sub.2O.
22. The method of claim 20, wherein the glass contains, by mol%, 5
to 25 % of Nb.sub.2O.sub.5, 1 to 22 % of TiO.sub.2, 0.5 to 23 % of
B.sub.2O.sub.3 and 1 to 25 % of BaO, and the glass has an alkali
metal oxide total content of 45 mol% or less, an alkaline earth
metal oxide and ZnO total content of 35 mol% or less.
23. The method of claim 20, wherein the glass contains 9 to 30 mol%
of Li.sub.2O.
24. The method of claim 16, wherein the glass contains 2,000 ppm or
less of each of Sb.sub.2O.sub.3 and As.sub.2O.sub.3.
25. The method of claim 17, wherein the glass contains 2,000 ppm or
less of each of Sb.sub.2O.sub.3 and As.sub.2O.sub.3.
26. The method of claim 20 wherein the glass contains 2,000 ppm or
less of each of Sb.sub.2O.sub.3 and As.sub.2O.sub.3.
27. The method of claim 16, wherein the glass is an optical
element, and the optical element is heat-treated.
28. The method of claim 17, wherein the glass is an optical
element, and the optical element is heat-treated.
29. The method of claim 18, wherein the glass is an optical
element, and the optical element is heat-treated.
30. The method of claim 20, wherein the glass is an optical
element, and the optical element is heat-treated.
31. The method of claim 16, wherein the glass is heat-treated in an
oxidizing dry atmosphere under the water vapor partial pressure of
5.times.10.sup.4 Pa or higher.
32. The method of claim 16, wherein the color degree of the glass
is controlled by changing the atmosphere for the heat-treatment.
Description
DETAILED DESCRIPTION OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a process for the
production of a glass molded article, an optical element produced
by the process, and a method of treating a glass. More
specifically, it relates to a process for efficiently producing a
transparent glass molded article by decoloring a press-molded
product, an optical element produced by the above production
process and a method of treating a glass, particularly, an optical
glass, for coloring and decoloring the glass.
[0003] 2. Prior Art of the Invention
[0004] In recent years, as a technique for mass-producing glass
optical elements such as aspherical lenses, increasing interests
are invited to a precision press-molding technique of press-molding
a glass material made of an optical glass with a mold having a
transfer molding surface having a reversal form of an optical
element as an end product thereby to obtain a high-precision
optical element without cutting and polishing after the
press-molding. In the above precision press-molding, press-molding
is carried out in a non-oxidizing atmosphere of nitrogen so that
the transfer molding surface is not oxidized at a high
temperature.
[0005] In the field of the above optical glass, there is a demand
for reversibly decolorable and colorable glasses. It is general
practice to incorporate an ion of a transition metal such as Fe or
Co, a colloid of cadmium sulfide, gold or silver, or a sulfide etc.
into a glass. In this practice, a glass can be only colored, and a
glass that is once colored cannot be rendered colorless or
transparent. As a glass that permits reversible control of the
color degree, there is known a so-called photochromic glass
obtained by incorporating silver chloride. This glass contains a
great number of fine particles that are dispersed or precipitated
in the glass.
[0006] Meanwhile, a P.sub.2O.sub.5--WO.sub.3-containing glass is
available as a glass suitable for the above precision
press-molding, and this glass is also highly useful as an optical
glass that exhibits high-refractivity high-dispersion properties.
When optical elements such as a lens made of a
P.sub.2O.sub.5--WO.sub.3-containing glass are produced by precision
press-molding, there is a problem that a glass that is transparent
before the press-molding is colored after the press-molding so that
the transparency of the optical glass decreases. The coloring
problem caused on a glass article by precision press-molding even
if a glass material for the precision press-molding is colorless
and transparent takes place not only in the
P.sub.2O.sub.5--WO.sub.3-containing glass but also in a
P.sub.2O.sub.5--Nb.sub.2O.sub.5-containing glass and a
P.sub.2O.sub.5--TiO.sub.2-containing glass.
[0007] Since the photochromic glass that is reversibly colorable
and decolorable contains a great number of fine particles dispersed
and precipitated in the glass, it has a problem that it causes
light scattering and is sometimes not suitable for use where
particularly high homogeneity is required.
[0008] The above problems can be all overcome by controlling the
color degree of a glass.
SUMMARY OF THE INVENTION
[0009] Under the circumstances, it is an object of the present
invention to provide a process for efficiently producing a
transparent glass molded article, particularly a precision
press-molded article having a high transmittance, an optical
element obtained by said process, and a treatment method of
effectively coloring and decoloring a glass, particularly, an
optical glass.
[0010] For achieving the above object, the present inventors have
made diligent studies and as a result found the following. A
P.sub.2O.sub.5--WO.sub.3-containing glass, a
P.sub.2O.sub.5--Nb.sub.2O.sub.5-containing glass and a
P.sub.2O.sub.5--TiO.sub.2-containing glass are colored because W
ion, Nb ion and Ti ion in the glasses are reduced due to exposure
to a non-oxidizing atmosphere when the glasses are precision
press-molded in a high-temperature state. Therefore, the
P.sub.2O.sub.5--WO.sub.3-containing glass, the
P.sub.2O.sub.5--Nb.sub.2O.sub.5-containing glass and the
P.sub.2O.sub.5--TiO.sub.2-containing glass are colored by exposing
the glasses to a non-oxidizing atmosphere (a more remarkable change
takes place in a reducing atmosphere) at a high temperature. On the
other hand, W ion, Nb ion and Ti ion are oxidized by exposing the
glasses to an oxidizing atmosphere in a high-temperature state, so
that the color degree can be decreased and, further, that the
above-colored glass can be decolored. And, it is difficult to
control the color degree by merely heating the glass, and the color
degree is greatly influenced by oxidizing and reducing atmospheres
to which the glass under heat is exposed.
[0011] The present invention has been completed on the basis of the
above findings.
[0012] That is, (1) according to the present invention, there is
provided a process for producing a glass molded article by
press-molding a glass under heat in a non-oxidizing atmosphere,
[0013] the process comprising press-molding a glass containing at
least one oxide selected from WO.sub.3, Nb.sub.2O.sub.5 or
TiO.sub.2, to prepare a glass molded article, and then
heat-treating the glass molded article in an oxidizing
atmosphere.
[0014] (2) According to the present invention, there is also
provided an optical element obtained by the above method.
[0015] (3) According to the present invention, there is further
provided a method of treating a glass, comprising heat-treating a
colored glass containing at least one oxide of WO.sub.3 and
Nb.sub.2O.sub.5 in an oxidizing dry atmosphere, to decolor the
glass.
[0016] (4) According to the present invention, there is still
further provided a method of treating a glass, comprising
heat-treating a glass containing at least one oxide selected from
WO.sub.3, Nb.sub.2O.sub.5 or TiO.sub.2 in a non-oxidizing
atmosphere, to color the glass.
BRIEF DESCRIPTION OF DRAWINGS
[0017] FIG. 1 is a spectrum showing one example of the relationship
between a heat treatment time period and a transmittance when a
glass is heat-treated in a nitrogen atmosphere.
[0018] FIG. 2 is a spectrum showing one example of the relationship
between a heat treatment time period and a transmittance when a
colored glass is heat-treated in atmosphere of air.
[0019] FIG. 3 is a spectrum showing one example of the relationship
between a heat treatment time period and a transmittance when a
glass colored during melting is heat-treated in atmosphere of
air.
PREFERRED EMBODIMENTS OF THE INVENTION
[0020] First, the process for the production of a glass molded
article, the method of treating a glass and the mechanism of
coloring and decoloring, in the present invention, will be
explained below.
[0021] It is considered that the following mechanism causes the
phenomenon of coloring and decoloring (discoloration) of a
WO.sub.3-containing phosphate glass that exhibits high refractivity
and high dispersion. When the above composition-based glasses
having different color degrees are measured for electron spin
resonance absorptions, it is found that a signal assigned to a
W.sup.5+ center and a signal assigned to an electron trap formed of
cation in glass increase with an increase in the color degree, and
it is therefore seen that the coloring is caused directly by the
formation of these reducing species. For increasing the color
degree, therefore, it is sufficient to reduce W ion in the glass,
and for decreasing the color degree, it is sufficient to oxidize W
ion. The coloring and decoloring based on the above mechanism
proceed reversibly. It is considered that the coloring and
decoloring phenomenon of Nb ion and Ti ion is also caused by a
similar mechanism.
[0022] The present invention aims at controlling the color degree
of not a glass in a molten state but a glass material that is
cooled at least to a temperature equivalent to, or lower than, a
softening point, such as a glass molded article or an optical
element. A glass in a molten state can be colored or decolored for
a relatively short period of time by adjusting an oxygen partial
pressure of a melting atmosphere. When oxygen is used as a carrier
for a redox reaction for changing the color degree of a glass
molded material, it takes a very long time since oxygen ion in the
glass has a very small diffusion coefficient. As a carrier for the
redox reaction, therefore, it is preferred to use hydrogen ion that
has a large diffusion coefficient in a glass. When hydrogen ion is
used as a carrier, a glass can be rapidly colored or decolored as
far as the internal center of the glass. Since a phosphate glass
shows a large diffusion coefficient of hydrogen ion in the glass,
it is suitable for a redox method using hydrogen ion as a carrier
as compared with any other glass.
[0023] The coloring treatment can be carried out by heating a glass
in a non-oxidizing atmosphere. The above redox reaction using a
hydrogen ion as a carrier is preferred since the treatment time
period can be decreased. Therefore, the above non-oxidizing
atmosphere preferably includes a nitrogen gas atmosphere, an inert
gas atmosphere and a reducing atmosphere such as an atmosphere
formed by adding water vapor to such a non-oxidizing atmosphere or
a hydrogen gas atmosphere. A mixture of nitrogen gas and an inert
gas and an atmosphere formed by adding water vapor to such an
atmosphere may be also used. When the above atmosphere is employed,
the coloring treatment time period can be decreased. A
non-oxidizing atmosphere containing water is characteristically
easier to handle than a hydrogen gas atmosphere, and a hydrogen gas
atmosphere has a characteristic feature that the coloring can be
carried out at a higher rate so that the coloring can be made for a
shorter period of time. The content of the water in the above
non-oxidizing atmosphere is preferably set such that water vapor in
the atmosphere has a partial pressure of 5.times.10.sup.4 Pa or
higher. In such a heat treatment, the reducing reaction on a glass
surface spreads into a glass, and, for example, the entire glass
having a thickness of several mm can be colored rapidly.
[0024] On the other hand, in the treatment of decreasing the color
degree, the decoloring can be rapidly carried out by dissociating a
hydrogen ion out of a glass in the form of H.sub.2O. For example, a
colored glass is heated in an oxidizing atmosphere such as
atmosphere of air, to decolor the glass, whereby a colorless and
transparent glass can be obtained. The oxidizing atmosphere
includes an oxygen gas, a gas mixture containing an oxygen gas,
such as atmosphere of air. While an ozone gas may be used as an
oxidizing atmosphere, an oxygen gas, a gas mixture containing an
oxygen gas and atmosphere of air are more preferred. In the
treatment of decreasing the color degree, such as decoloring, the
color degree of the entire glass can be rapidly changed by
migration of a hydrogen ion as well. A phosphate glass is suitable
for the above treatment, since it shows a large diffusion
coefficient of a hydrogen ion. In the treatment of decreasing the
color degree of a glass, preferably, the partial pressure of water
vapor in the above atmosphere is adjusted to 10.sup.4 Pa or lower
for rapidly carrying out the decoloring treatment. More preferably,
the above partial pressure of water vapor is adjusted to
6.times.10.sup.3 Pa or lower.
[0025] The treatment rate of each of the coloring and the
decoloring can be increased by treatment at a high temperature. For
decreasing a deformation caused by the heat treatment, however, the
heating temperature for each of the coloring and the decoloring is
preferably set a temperature equivalent to, or lower than, the
softening point of a glass. For avoiding a change in form, further,
the heating temperature is preferably set at a temperature
equivalent to, or lower than, a glass transition temperature Tg.
For an article that is required to have high-precision form
accuracy such as a precision press-molded article or an optical
element, preferably, the heat treatment is carried out in a
temperature range in which the form accuracy of the article can be
maintained. For this purpose, the heating temperature is more
preferably adjusted to a "glass transition temperature Tg minus
10.degree. C." or lower, more preferably to a "glass transition
temperature minus 15.degree. C." or lower, still more preferably to
a "glass transition temperature Tg minus 25.degree. C." or lower,
and particularly preferably to a "glass transition temperature Tg
minus 30.degree. C." or lower.
[0026] The process for producing a transparent glass molded article
by decoloring a press-molded article, which process is a process
for the production of a glass molded article in the present
invention, will be explained below.
[0027] For protecting a molding surface of a press mold from an
oxidation at high temperatures during press-molding, there is
widely employed a method using, as a press-molding atmosphere, a
non-oxidizing atmosphere such as a nitrogen gas atmosphere, other
inert gas atmosphere or a gas mixture atmosphere containing a
nitrogen gas and an inert gas. In a precision press-molding method
in which a glass molded article can be directly obtained as an end
product such as an optical element without cutting or polishing or
the aspherical surface of an aspherical lens can be formed by
press-molding, the press-molding is carried out mostly in the above
atmosphere. Since the above press-molding is carried out at a
temperature higher than a glass transition temperature, a cation in
a glass is reduced to color the glass due to the already explained
mechanism. For an optical element such as a lens, a glass molded
article is required to have high transparency, so that it is
required to decolor the press-molded article. In the present
invention, a molded article is decolored by heating the glass
molded article in an oxidizing atmosphere such as atmosphere of
air, and it is particularly preferred to carry out the heat
treatment in a dry atmosphere. More preferably, the partial
pressure of water vapor in the atmosphere is adjusted to 10.sup.4
Pa or lower, and still more preferably, the partial pressure of the
water vapor is adjusted to 6.times.10.sup.3 Pa or lower. For
preventing deformation, the heating temperature is preferably a
temperature equivalent to, or lower than, a glass transition
temperature, more preferably "glass transition temperature minus
10.degree. C." or lower, still more preferably "glass transition
temperature minus 15.degree. C." or lower, yet more preferably
"glass transition temperature minus 25.degree. C." or lower,
particularly preferably "glass transition temperature minus
30.degree. C." or lower. The decoloring treatment may be carried
out such that annealing treatment of a press-molded article is
performed at the same time. The annealing treatment can remove
distortion of a glass and finely adjust a refractive index and an
Abbe's number.
[0028] The material of the molding surface of a press mold includes
silicon carbide (SiC), ultra hard alloys such as WC, hard carbon, a
noble metal and an alloy of a noble metal (e.g., platinum alloy).
Of these, SiC and hard carbon requires some expedient to take
against oxidation at high temperatures during press-molding.
[0029] In the process for the production of a glass molded article,
provided by the present invention, the following glasses can be
used. In the precision press-molding, a molding glass material is
molded in a state where it has a viscosity of 10.sup.6 to 10.sup.12
poise (10.sup.5 to 10.sup.11 PaS).
[0030] As described already, when a hydrogen ion having a large
diffusion rate in a glass is used as a carrier for a redox
reaction, the hydrogen ion makes it possible to carry out the rapid
coloring and decoloring of a glass. A phosphate glass exhibits a
large diffusion coefficient of a hydrogen ion and is suitable for
the above coloring and decoloring. Further, since oxidation and
reduction of W ion, Nb ion or Ti ion in a glass causes the color
degree of the glass, the method of the present invention can be
applied to glasses containing WO.sub.3, Nb.sub.2O.sub.5 and
TiO.sub.2. While the method of the present invention is suitable
for a phosphate glass, the present invention can be applied to a
silicate glass containing at least one oxide of WO.sub.3,
Nb.sub.2O.sub.5 and TiO.sub.2 so that a colored molded article can
be decolored and rendered colorless and transparent.
[0031] A high-quality P.sub.2O.sub.5--WO.sub.3-containing glass, a
P.sub.2O.sub.5--Nb.sub.2O.sub.5-containing glass and a
P.sub.2O.sub.5--TiO.sub.2-containing glass can be used as optical
glasses having high-refractivity and high-dispersion properties.
These optical glasses preferably have optical constants, a
refractive index (nd) of at least 1.6 and an Abbe's number (.nu.d)
of 33 or less, more preferably a refractive index (nd) of 1.6 to
1.9 and an Abbe's number (.nu.d) of 21 to 33, still more preferably
a refractive index (nd) of 1.65 to 1.86 and an Abbe's number
(.nu.d) of 22 to 32.5.
[0032] As a precision press-molding glass, all of the
P.sub.2O.sub.5--WO.sub.3-containing glass,
P.sub.2O.sub.5--Nb.sub.2O.sub.5-containing glass and
P.sub.2O.sub.5--TiO.sub.2-containing glass preferably have a glass
transition temperature (Tg) of 540.degree. C. or lower, more
preferably 530.degree. C. or lower, still more preferably
515.degree. C. or lower.
[0033] The present invention can be suitably applied to the
above-explained P.sub.2O.sub.5--WO.sub.3-containing glass,
P.sub.2O.sub.5--Nb.sub.2O.sub.5-containing glass and
P.sub.2O.sub.5--TiO.sub.2-containing glass. A
P.sub.2O.sub.5--WO.sub.3-containing glass in particular is also
suitable as an optical glass having high-refractivity and
high-dispersion properties. As a composition that satisfies the
low-melting point property required of a precision press-molding
glass in addition to the high-refractivity and high-dispersion
properties, preferred is a glass having a composition containing,
by mol %, 12 to 50% of P.sub.2O.sub.5, 2 to 45% of WO.sub.3, 0 to
25% of Nb.sub.2O.sub.5, 0 to 22% of TiO.sub.2, 0 to 30% of
Li.sub.2O, 0 to 33% of Na.sub.2O, 0 to 25% of K.sub.2O, 0 to 23% of
B.sub.2O.sub.3, 0 to 25% of BaO and 0 to 20% of ZnO and having a
WO.sub.3 and Nb.sub.2O.sub.5 total content of 45 mol % or less.
[0034] P.sub.2O.sub.5 is a material for forming a network structure
of the glass, and it is also an essential component for increasing
the diffusion rate of a hydrogen ion to improve the coloring and
decoloring rate. When the content of P.sub.2O.sub.5 is less than 12
mol %, devitrification increasingly tends to take place, and a
glass may not be easily formed. When it exceeds 50 mol %, it is
difficult to introduce components such as WO.sub.3, etc., and the
glass is caused to have an increased glass transition temperature,
a low refractive index nd and an increased Abbe's number .nu.d. The
content of P.sub.2O.sub.5 is therefore preferably 12 to 50 mol
%.
[0035] WO.sub.3 is also an essential component, and it is a
component effective for imparting the glass with low-melting point,
high-refractivity and high-dispersion properties without using PbO
that exerts a large environmental load. It is also a component for
coloring and decoloring the glass by oxidation and reduction.
WO.sub.3 decreases the glass transition temperature and the sag
temperature like an alkali metal oxide and works to increase the
refractive index, and it also works to inhibit wettability between
the glass and a mold during press-molding so that it improves the
releasability of the glass from the mold. When the content of
WO.sub.3 is less than 2 mol %, the glass transition temperature and
sag temperature increase, and the glass is liable to cause foaming
during precision press-molding, and further, the effective coloring
may come to be no longer possible. When the content of WO.sub.3
exceeds 45 mol %, the viscosity of the glass at high temperature
decreases, and it is sometimes difficult to produce a preform to be
used in the precision press-molding. The content of WO.sub.3 is
therefore preferably 2 to 45 mol %.
[0036] Nb.sub.2O.sub.5 is an optional component that can be used
for imparting the glass with high-refractivity high-dispersion
properties without using PbO. However, the content of
Nb.sub.2O.sub.5 exceeds 25 mol %, it not only causes the glass
transition temperature and sag temperature to increases but also
decreases the glass stability and high-temperature meltability.
Further, the glass is liable to cause foaming during precision
press-molding. Like WO.sub.3, Nb.sub.2O.sub.5 is a component that
causes coloring of the glass and is therefore a component that is
an object of the coloring and decoloring treatment. The content of
Nb.sub.2O.sub.5 is therefore preferably 0 to 25 mol %.
[0037] As described above, WO.sub.3 and Nb.sub.2O.sub.5 are
components for causing reversible coloring and decoloring. However,
when the total content thereof exceeds 45 mol %, the decoloring is
difficult. When the glass is colored, the total content of WO.sub.3
and Nb.sub.2O.sub.5 is preferably at least 15 mol %.
[0038] TiO.sub.2 is a component for increasing the refractive index
and dispersion and improving the glass in anti-devitrification.
When the content thereof exceeds 22 mol %, the glass is sharply
degraded in anti-devitrification, and the glass transition
temperature, sag temperature and liquidus temperature sharply
increase. Like WO.sub.3 and Nb.sub.2O.sub.5, TiO.sub.2 is also a
component that causes the glass to be colored and is therefore a
component that is an object of the coloring and decoloring
treatment. Therefore, TiO.sub.2 may be added in an amount range of
from 0 to 22 mol %.
[0039] Li.sub.2O is a component for improving the glass in
anti-devitrification, decreasing the glass transition temperature,
sag temperature and liquidus temperature, and improving the glass
in high-temperature meltability. When the content thereof exceeds
30 mol %, the glass stability decreases, and it is difficult to
attain high-refractivity high-dispersion properties. The content of
Li.sub.2O is therefore preferably 0 to 30 mol %.
[0040] Na.sub.2O is also a component for improving the glass in
anti-devitrification, decreasing the glass transition temperature,
sag temperature and liquidus temperature and improving the glass in
high-temperature meltability. When the content thereof exceeds 33
mol %, the glass stability decreases, and it is difficult to attain
high-refractivity high-dispersion properties. The content of
Na.sub.2O is therefore preferably 0 to 33 mol %.
[0041] K.sub.2O is also a component for improving the glass in
anti-devitrification, decreasing the glass transition temperature,
sag temperature and liquidus temperature and improving the glass in
high-temperature meltability. When the content thereof exceeds 25
mol %, the glass stability decreases, and it is difficult to attain
high-refractivity high-dispersion properties. The content of
K.sub.2O is therefore preferably 0 to 25 mol %.
[0042] B.sub.2O.sub.3 is a component remarkably effective for
improving the meltability and homogeneity of the glass, and it is a
component that alters OH bondability inside the glass when added in
a small amount and which inhibits formation of bubbles of the glass
during press-molding. However, when the content thereof exceeds 23
mol %, the glass is liable to be unstable. The content of
B.sub.2O.sub.3 is therefore preferably 0 to 23 mol %.
[0043] BaO is a component for increasing the refractive index of
the glass and improving the glass in anti-devitrification, and it
is a component that works to decrease the liquidus temperature.
When a glass contains a large amount of WO.sub.3, BaO works as a
component that inhibits the irreversible coloring of the glass.
When the content thereof exceeds 25 mol %, the glass sometimes
comes to be unstable and poor in chemical durability. The content
of BaO is therefore preferably 0 to 25 mol %.
[0044] ZnO is a component for increasing the refractive index and
dispersion of the glass and decreasing the glass transition
temperature, sag temperature and liquidus temperature. However,
when the content thereof exceeds 20 mol %, the anti-devitrification
of the glass may decrease, and the liquidus temperature may
increase. Therefore, ZnO can be added in an amount range of from 0
to 20 mol %.
[0045] Of glasses having composition containing some components in
preferred amount ranges, a more preferred glass composition has an
Li.sub.2O content of 2 to 30 mol % and an Na.sub.2O content of 2 to
33 mol %.
[0046] In the above glass composition having an Li.sub.2O content
of 2 to 30 mol % and an Na.sub.2O content of 2 to 33 mol %, a more
preferred composition contains, by mol %, 5 to 25% of
Nb.sub.2O.sub.5, 1 to 22% of TiO.sub.2 and 0.5 to 23% of
B.sub.2O.sub.3 and has a total alkali metal oxide content of 45 mol
% or less and an alkaline earth metal oxide and ZnO total content
of 35 mol % or less. In the above glass composition, a still more
preferred composition contains, by mol %, 14 to 45% of
P.sub.2O.sub.5, 5 to 40% of WO.sub.3, 5 to 23% of Nb.sub.2O.sub.5,
1 to 15% of TiO.sub.2, 5 to 27% of Li.sub.2O, 2 to 33% of
Na.sub.2O, 0 to 15% of K.sub.2O, 0.5 to 15% of B.sub.2O.sub.3, 0 to
23% of BaO and 0 to 17% of ZnO, and in this glass composition,
particularly preferred first composition and second composition are
as follows.
[0047] A first glass composition contains, by mol %, 17 to 30% of
P.sub.2O.sub.5, 5 to 25% of WO.sub.3, 5 to 23% of Nb.sub.2O.sub.5,
1 to 9% of TiO.sub.2, 5 to 22% of Li.sub.2O, 4 to 22% of Na.sub.20,
1 to 7% of K.sub.2O, 1 to 10% of B.sub.2O.sub.3, 2 to 23% of BaO, 1
to 10% of ZnO and 0 to 1% of Sb.sub.2O.sub.3. In the first glass
composition, a composition in which the total content of the above
components is at least 98 mol % is more preferred, a composition in
which the total content of the above components is at least 99 mol
% is still more preferred, and a composition in which the total
content of the above components is 100 mol % is particularly
preferred.
[0048] A second glass composition contains, by mol %, 17 to 30% of
P.sub.2O.sub.5, 5 to 25% of WO.sub.3, 5 to 23% of Nb.sub.2O.sub.5,
1 to 9% of TiO.sub.2, 5 to 22% of Li.sub.2O, 5 to 33% of Na.sub.20,
1 to 10% of B.sub.2O.sub.3, 0 to 23% of BaO and 0 to 1% of
Sb.sub.2O.sub.3. In the second glass composition, a composition in
which the total content of the above components is at least 98 mol
% is more preferred, a composition in which the total content of
the above components is at least 99 mol % is still more preferred,
and a composition in which the total content of the above
components is 100 mol % is particularly preferred.
[0049] The above first and second glass compositions are the most
preferred for obtaining optical glasses which accomplish the object
of the present invention, which have high-refractivity
high-dispersion properties, a refractive index (nd) of at least 1.6
and an Abbe's number (.nu.d) of 33 or less and further have
low-melting properties suitable for precision press-molding, a
glass transition temperature of 540.degree. C. or lower, and which
are stable as a glass.
[0050] In addition to the above components, SiO.sub.2, MgO, CaO,
SrO, Al.sub.2O.sub.3, Y.sub.2O.sub.3, La.sub.2O.sub.3,
Gd.sub.2O.sub.3, ZrO.sub.2, Ta.sub.2O.sub.5, Bi.sub.2O.sub.3,
TeO.sub.2, Cs.sub.2O and As.sub.2O.sub.3 may be added as optional
components. In this case, preferably, the content by mol % of each
component is as follows. The content of SiO.sub.2 is 0 to 5%, the
content of MgO is 0 to 25%, the content of CaO is 0 to 25%, the
content of SrO is 0 to 25%, the content of Al.sub.2O.sub.3 is 0 to
5%, the content of Y.sub.2O.sub.3 is 0 to 5%, the content of
La.sub.2O.sub.3 is 0 to 6%, the content of Gd.sub.2O.sub.3 is 0 to
6%, the content of ZrO.sub.2 is 0 to 6%, the content of
Ta.sub.2O.sub.5 is 0 to 6%, the content of Bi.sub.2O.sub.3 is 0 to
6%, the content of TeO.sub.2 is 0 to 6%, the content of Cs.sub.2O
is 0 to 6% and the content of As.sub.2O.sub.3 is 0 to 1%.
[0051] In the glass to be used in the present invention, for
improving the stability of the glass and attaining
high-refractivity high-dispersion properties, the total content of
Li.sub.2O, Na.sub.2O and K.sub.2O is preferably 45 mol % or less,
more preferably 10 to 45 mol %, still more preferably 12 to 43 mol
%.
[0052] In any one of the above preferred glass compositions, the
content of Li.sub.2O is desirably at least 9 mol %, more desirably
at least 10 mol %.
[0053] When the glass is colored in the present invention, the
total content of WO.sub.3 and Nb.sub.2O.sub.5 that serve for
coloring (particularly, reversible coloring) is preferably at least
15 mol %, and the total content of WO.sub.3, Nb.sub.2O.sub.5 and
TiO.sub.2 is preferably at least 25 mol %.
[0054] In a P.sub.2O.sub.5--WO.sub.3-containing glass that has not
yet been explained with regard to the above preferred compositions,
the content of Li.sub.2O is desirably 9 to 30 mol %, more desirably
10 to 30 mol %, for forming a glass that is suitable for precision
press-molding.
[0055] Further, the process for the production of a glass molded
article is suitable for producing a glass molded article formed of
a glass containing 2,000 ppm or less of each of Sb.sub.2O.sub.3 and
As.sub.2O.sub.3, more suitable for producing a glass molded article
formed of a glass containing 200 ppm or less of As.sub.2O.sub.3,
still more suitable for producing a glass molded article formed of
a glass containing no As.sub.2O.sub.3 and containing 1,000 ppm or
less of Sb.sub.2O.sub.3, and particularly suitable for producing a
glass molded article formed of a glass containing no
As.sub.2O.sub.3 and containing 500 ppm or less of Sb.sub.2O.sub.3.
While Sb.sub.2O.sub.3 and As.sub.2O.sub.3 are added as a refining
agent to a glass, they are strong oxidizing agents, so that they
work to prevent reduction of W ion, Nb ion and Ti ion. In
consideration for the environment, however, a glass having no
content of As.sub.2O.sub.3 or having a small content thereof, if
any, is desired, and such a glass is easily colorable since W ion,
Nb ion and Ti ion in the glass are reduced during precision
press-molding. On the other hand, Sb.sub.2O.sub.3 and
As.sub.2O.sub.3 are strong oxidizing agents and therefore oxidize
the molding surface of a press mold, so that it is one factor that
decreases the lifetime of the mold. Therefore, the content of each
of the Sb.sub.2O.sub.3 and As.sub.2O.sub.3 is decreased as
described above, and the process of the present invention is
applied. In this case, the lifetime of a press mold can be
lengthened while obtaining transparent press-molded articles.
[0056] According to the present invention, further, there is
provided a decolored optical element obtained by the above process
for the production of a glass molded article, provided by the
present invention. There is also provided a method of treating a
glass, which comprises heat-treating a colored glass containing at
least one oxide of WO.sub.3 and Nb.sub.2O.sub.5 in an oxidizing
atmosphere, to decolor the glass. And, there is further provided a
method of treating a glass, which comprises heat-treating a glass
containing at least one oxide selected from WO.sub.3,
Nb.sub.2O.sub.5 or TiO.sub.2 in a non-oxidizing atmosphere, to
color the glass.
[0057] The above treatment methods are preferably applied to a
glass containing P.sub.2O.sub.5 in particular.
[0058] In the present invention, the color degree can be locally
changed by local contact to an atmosphere during the heat treatment
or local heating. When such a treatment method is employed, a
desired color pattern or a desired distribution of the color degree
can be obtained. In the above method, a desired pattern
corresponding to information to be recorded can be recorded in a
glass, and the above information can be stored in the glass.
Therefore, the above glass material can be used as an optical
storage material.
[0059] Further, since the refractive index changes to a slight
extent depending upon the color degree, a refractive index
distribution type optical element such as a GRIN lens can be
produced.
[0060] In the present invention, since a tungsten-containing
phosphate glass contains no fine particles that constitute
light-scattering sources, unlike a photochromic glass containing
fine particles such as fine particles of a metal halide, the light
scattering loss is remarkably small as compared with a photochromic
glass, and a low-loss optical element can be produced.
[0061] As explained above, the process and the method of the
present invention are suitable for an optical glass, and are
particularly suitable for a glass containing no lead.
EXAMPLES
[0062] 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.
[0063] Tables 1, 2, 3 and 4 show compositions, optical properties
and thermal properties of glasses that were treated for coloring
and decoloring in Examples. All of these glasses are optical
glasses and are suitable for precision press-molding.
Example 1
[0064] A glass having a composition 1 shown in Table 1 (22.8 mol %
of P.sub.2O.sub.5, 15.2 mol % of WO.sub.3, 15.9 mol % of
Nb.sub.2O.sub.5, 10.1 mol % of Li.sub.2O, 9.7 mol % of Na.sub.2O,
2.5 mol % of K.sub.2O, 16.2 mol % of BaO and 7.6 mol % of
B.sub.2O.sub.3) was prepared by melting at 1,100.degree. C. After
gradually cooled, the glass had a yellowish color. The glass had
properties as shown in Table 1. The glass was formed into a sheet
having a thickness of 2 mm by cold working, and the glass having a
sheet form was heat-treated in a nitrogen gas atmosphere at
560.degree. C. As the time period of the heat treatment increased,
circumferential areas of the glass began to turn blackish purple
and the entire glass was colored in several tens minutes. FIG. 1
shows a change of a transmittance spectrum with the passage of the
heat treatment time. As shown in FIG. 1, the minimum transmittance
was controlled to be 62% by controlling the heat treatment time
period.
[0065] Glasses having compositions 2 to 28 shown in Tables 1 to 6
were successfully colored by heat treatment in a nitrogen gas
atmosphere.
[0066] Further, when the atmosphere for the heat treatment in this
Example was changed from the nitrogen gas atmosphere to a
non-oxidizing gas or reducing gas atmosphere such as a hydrogen gas
atmosphere, a gas mixture atmosphere of hydrogen gas and nitrogen
gas or a gas mixture atmosphere of hydrogen gas and an inert gas,
the glasses were also colored. Further, when water vapor was added
to the above atmospheres, the glasses were also colored.
[0067] After the above heat treatment, no change was found in the
glass compositions.
Example 2
[0068] The colored glass obtained by heat treatment in a nitrogen
gas atmosphere for 36 minutes in Example 1 was heat-treated under
atmosphere of air at 480.degree. C. FIG. 2 shows a change of a
transmittance spectrum in the heat treatment under atmosphere of
air. With an increase in the time period of the heat treatment, the
glass colored in blackish purple came to be lighter in color. After
4 hours, the glass came to be nearly colorless.
[0069] The glasses having compositions 2 to 28, which were treated
for coloring in Example 1, were similarly heat-treated under
atmosphere of air, whereby the color degrees of the glasses were
decreased and the glasses were decolored and rendered transparent.
After the heat treatment, further, no change was found in the glass
compositions. When the atmosphere for the heat treatment is altered
as described above, the reversible coloring and decoloring can be
performed.
Example 3
[0070] A glass having a composition containing, by mol %, 23.9% of
P.sub.2O.sub.5, 19.8% of WO.sub.3, 14.8% of Nb.sub.2O.sub.5, 4.9%
of TiO.sub.2, 15.2% of Li.sub.2O, 5.8% of Na.sub.2O, 2.5% of
K.sub.2O, 11.1% of BaO and 2.5% of B.sub.2O.sub.3 was prepared by
melting at 1,100.degree. C. The obtained glass had a blackish blue
color. The glass was formed into a sheet having a thickness of 2 mm
by cold working, and the glass having a sheet form was heat-treated
under atmosphere of air at 515.degree. C. As the time period of the
heat treatment increased, the blackish blue color of the glass came
to be lighter. FIG. 3 shows a change of a transmittance spectrum in
the heat treatment under atmosphere of air. As shown in FIG. 3, the
minimum transmittance was controlled to be in the range of from 64%
to 80% by carrying out the heat treatment for a period of time up
to 6 hours.
[0071] There was found no change that was caused on the glass
composition by the above heat treatment.
Example 4
[0072] A glass having a composition 16 containing, by mol %, 24.0%
of P.sub.2O.sub.5, 11.0% of WO.sub.3, 19.0% of Nb.sub.2O.sub.5,
5.0% of TiO.sub.2, 12.0% of Li.sub.2O, 9.0% of Na.sub.2O, 2.0% of
K.sub.2O, 7.0% of ZnO, 8.0% of BaO and 3.0% of B.sub.2O.sub.3 was
hot-formed into an ellipsoidal material having a diameter of
approximately 10 mm and a height of approximately 6 mm, and the
ellipsoidal material was cooled to prepare a preform. The preform
was colorless and transparent. The preform was re-heated in a
nitrogen gas atmosphere and also precision press-molded into a
convex meniscus lens having a diameter of approximately 17 mm with
a mold made of SiC. The glass after the molding had the color of
black. The thus-molded article was heat-treated in atmosphere of
air at 480.degree. C. which was lower than the glass transition
temperature Tg 516.degree. C. of the glass by approximately
30.degree. C., whereby the glass molded article was decolored and a
colorless and transparent convex meniscus lens was obtained. There
was found no change that was caused on the molded article by the
heat treatment, and the molded article maintained its form
accuracy.
[0073] For preventing the fusion of the glass and the mold during
the press-molding, there may be used a preform having a surface
formed of a carbon film. When the carbon-film-applied preform is
used, the carbon film remains on the surface of the molded article
after the precision press-molding, and the remaining carbon film
can be oxidized and removed by heat treatment in the above
atmosphere of air or an oxidizing atmosphere.
[0074] Glasses having compositions 1 to 15 and 17 to 28 were formed
into convex meniscus lenses by precision press-molding in the same
manner as that described above, and the lenses were heat-treated at
a temperature lower than their glass transition temperatures by
approximately 30.degree. C., to give colorless and transparent
convex meniscus lenses.
[0075] Sb.sub.2O.sub.3 was added to each of the above compositions
1 to 28 to obtain glasses having an Sb.sub.2O.sub.3 content of 100
ppm, 200 ppm, 500 ppm and 1,000 ppm, and the glasses were similarly
press-molded to obtain molded articles. Thus-obtained molded
articles were heat-treated under atmosphere of air to give
colorless and transparent optical elements.
[0076] The glass molded article that can be produced is not limited
to a convex meniscus lens, and colorless and transparent lenses
having any form can be produced regardless of a spherical lens and
an aspherical lens.
Example 5
[0077] A mask made of aluminum in a desired pattern was formed on
the surface of each of colorless sheet-shaped glasses made of
glasses having compositions 1 to 28 shown in Tables 1 to 6, and the
sheet-shaped glasses were heated in a reducing atmosphere having an
elevated water vapor partial pressure, whereby each sheet-shaped
glass was colored in a pattern corresponding to a pattern of
opening portions of the mask. Further, a mask made of aluminum in a
desired pattern was formed on the surface of each of colored
sheet-shaped glasses made of glasses having the compositions 1 to
28, and the sheet-shaped glasses were heated in atmosphere of air,
whereby regions discolored in a pattern corresponding to a pattern
of opening portions of the mask were formed on/in each sheet-shaped
glass.
[0078] In the above treatment, regions having different color
degrees were formed with the mask. Further, other local heating,
for example, local irradiation with laser light, was carried out,
whereby the color degree was changed on heated portions alone.
[0079] Since a colored pattern can be formed as described above, a
colored pattern corresponding to information to be stored can be
recorded on the glass, and the recorded information can be read on
the basis of the above colored pattern. The above glass can be
therefore used as an optical storage material, and the above
coloring and decoloring methods can be applied to writing
information on/in the optical storage material and erasing
information.
[0080] Further, since the above coloring and decoloring proceed on
the basis of diffusion of a carrier of a redox reaction, a
distribution of the color degree in the depth direction from the
glass surface can be formed by a method of adjusting the heat
treatment time period, or the like. Further, a distribution of the
color degree can be formed by providing the interior of the glass
with a temperature distribution during heat treatment.
[0081] Further, since the refractive index changes depending upon a
change in the color degree, the present invention can be applied to
optical storage using a change in refractive index, and a
refractive index distribution type optical element such as a GRIN
lens having a refractive index distribution can be also produced by
providing a distribution of the color degree.
[0082] When it is required to color a glass as a whole, the glass
is press-molded in the non-oxidizing atmosphere explained in the
above Examples, whereby a colored glass molded material can be
obtained. When the above glass molded material is locally treated
for coloring or decoloring or subjected to the formation of a
distribution of the color degree, the above optical storage
material or the above refractive index distribution type optical
element can be also produced.
[0083] When a silicate glass containing TiO.sub.2 was treated in
the same manner as in Examples 1 to 5, the silicate glass gave the
same effects although the coloring and decoloring rate thereof
differed. It is considered that silicate glasses containing
WO.sub.3 and Nb.sub.2O.sub.5 other than TiO.sub.2 can give the same
effects.
TABLE-US-00001 TABLE 1 Composition 1 2 3 4 5 P.sub.2O.sub.5 22.8
23.6 18.1 25.0 23.0 WO.sub.3 15.2 15.7 20.6 6.0 17.5
Nb.sub.2O.sub.5 15.9 16.5 16.2 23.0 17.5 (A) 31.1 32.2 36.8 29.0
35.0 TiO.sub.2 0.0 0.0 0.0 0.0 0.0 (B) 31.1 32.2 36.8 29.0 35.0
Li.sub.2O 10.1 13.1 12.9 12.0 12.0 Na.sub.2O 9.7 7.4 7.3 10.0 9.0
K.sub.2O 2.5 2.6 2.6 3.0 2.0 (C) 22.3 23.1 22.8 25.0 23.0 ZnO 0.0
0.0 0.0 0.0 6.0 BaO 16.2 16.7 16.5 16.0 8.0 (D) 16.2 16.7 16.5 16.0
14.0 B.sub.2O.sub.3 7.6 4.4 5.8 5.0 5.0 GeO.sub.2 0.0 0.0 0.0 0.0
0.0 Ta.sub.2O.sub.5 0.0 0.0 0.0 0.0 0.0 Total 100.0 100.0 100.0
100.0 100.0 Tg (.degree. C.) 511 510 493 516 486 nd 1.80963 1.81467
1.85328 1.82159 1.83865 .nu.d 26.6 26.4 24.8 25.6 24.1
TABLE-US-00002 TABLE 2 Composition 6 7 8 9 10 P.sub.2O.sub.5 22.0
22.4 24.2 20.0 24.0 WO.sub.3 34.2 13.0 20.0 10.0 12.0
Nb.sub.2O.sub.5 13.5 18.6 15.0 20.0 18.0 (A) 47.7 21.6 35.0 30.0
30.0 TiO.sub.2 0.0 5.2 5.0 5.0 5.0 (B) 47.7 26.8 40.0 35.0 35.0
Li.sub.2O 0.0 12.5 15.3 12.0 12.0 Na.sub.2O 13.7 13.0 5.8 10.0 9.0
K.sub.2O 14.2 2.6 2.5 3.0 2.0 (C) 21.5 28.1 23.6 25.0 23.0 ZnO 0.0
0.0 0.0 0.0 5.0 BaO 0.0 11.2 10.8 15.0 10.0 (D) 0.0 11.2 10.8 15.0
15.0 B.sub.2O.sub.3 2.4 1.5 1.4 5.0 3.0 GeO.sub.2 0.0 0.0 0.0 0.0
0.0 Ta.sub.2O.sub.5 0.0 0.0 0.0 0.0 0.0 Total 100.0 100.0 100.0
100.0 100.0 Tg (.degree. C.) 539 510 515 508 503 nd 1.80025 1.84764
1.85023 1.85952 1.84264 .nu.d 23.3 23.6 23.3 23.7 23.7
TABLE-US-00003 TABLE 3 Composition 11 12 13 14 15 P.sub.2O.sub.5
24.0 24.0 24.0 23.6 15.0 WO.sub.3 11.0 12.0 12.0 20.8 17.7
Nb.sub.2O.sub.5 19.0 18.0 18.0 4.7 3.5 (A) 30.0 30.0 30.0 25.5 21.2
TiO.sub.2 5.0 4.5 5.0 3.4 7.7 (B) 35.0 34.5 35.0 28.9 28.9
Li.sub.2O 9.0 12.0 16.0 0.0 0.0 Na.sub.2O 12.0 7.0 10.0 22.1 19.7
K.sub.2O 2.0 2.0 2.0 5.5 1.0 (C) 23.0 21.0 28.0 27.6 20.7 ZnO 7.0
6.5 5.0 0.0 0.0 BaO 8.0 11.0 5.0 4.5 4.0 (D) 15.0 17.5 10.0 4.5 4.0
B.sub.2O.sub.3 3.0 3.0 3.0 4.9 22.0 GeO.sub.2 0.0 0.0 0.0 10.5 9.4
Ta.sub.2O.sub.5 0.0 0.0 0.0 0.0 0.0 Total 100.0 100.0 100.0 100.0
100.0 Tg (.degree. C.) 507 508 486 494 479 nd 1.84817 1.85050
1.84151 1.70266 1.72277 .nu.d 23.27 23.7 23.3 32.3 26.5
TABLE-US-00004 TABLE 4 Composition 16 17 18 19 20 21 P.sub.2O.sub.5
24.0 13.6 16.5 14.8 20.7 27.1 WO.sub.3 11.0 16.6 23.0 18.7 31.5
16.4 Nb.sub.2O.sub.5 19.0 6.0 6.4 5.1 9.7 7.4 (A) 30.0 22.6 29.4
23.8 41.2 23.8 TiO.sub.2 5.0 9.4 10.1 20.9 6.0 2.7 (B) 35.0 32.0
39.5 44.7 47.2 36.5 Li.sub.2O 12.0 0.0 0.0 0.0 0.0 12.5 Na.sub.2O
9.0 20.2 21.7 20.7 25.8 28.9 K.sub.2O 2.0 17.0 4.0 1.1 4.8 0.0 (C)
23.0 37.2 25.7 21.8 30.6 41.4 ZnO 7.0 0.0 6.6 0.0 0.0 0.0 BaO 8.0
2.5 0.0 4.2 0.0 0.0 (D) 15.0 2.5 6.6 4.2 0.0 0.0 B.sub.2O.sub.3 3.0
9.9 6.7 4.7 0.0 5.0 GeO.sub.2 0.0 4.8 5.0 9.8 0.0 0.0
Ta.sub.2O.sub.5 0.0 0.0 0.0 0.0 1.5 0.0 Total 100.0 100.0 100.0
100.0 100.0 100.0 Tg (.degree. C.) 507 404 494 532 511 435 nd
1.84521 1.70035 1.79765 1.84190 1.82682 1.69127 .nu.d 23.3 29.1
23.7 22.7 22.3 31.27
TABLE-US-00005 TABLE 5 Composition 22 23 24 25 26 P.sub.2O.sub.5
24.0 24.0 24.0 24.0 23.5 WO.sub.3 8.0 7.0 8.0 7.0 7.8
Nb.sub.2O.sub.5 18.0 19.0 18.0 19.0 16.4 (A) 26.0 26.0 26.0 26.0
24.2 TiO.sub.2 6.0 6.0 6.0 6.0 5.9 (B) 32.0 32.0 32.0 32.0 30.1
Li.sub.2O 22.0 19.5 18.0 18.8 15.3 Na.sub.2O 11.0 11.5 11.0 11.2
14.2 K.sub.2O 2.0 2.0 2.0 2.0 2.0 (C) 35.0 33.0 31.0 32.0 31.5 ZnO
3.0 2.0 5.0 2.0 2.9 BaO 3.0 6.0 5.0 6.0 9.1 (D) 6.0 8.0 10.0 8.0
12.0 B.sub.2O.sub.3 3.0 3.0 3.0 4.0 2.9 GeO.sub.2 0.0 0.0 0.0 0.0
0.0 Ta.sub.2O.sub.5 0.0 0.0 0.0 0.0 0.0 Total 100.0 100.0 100.0
100.0 100.0 Tg (.degree. C.) 467 476 473 478 471 nd 1.82121 1.82694
1.82688 1.82668 1.80546 .nu.d 24.00 24.00 23.97 24.02 25.43
TABLE-US-00006 TABLE 6 Composition 27 28 P.sub.2O.sub.5 23.7 23.8
WO.sub.3 7.6 7.8 Nb.sub.2O.sub.5 16.2 16.0 (A) 23.8 23.8 TiO.sub.2
5.9 5.9 (B) 29.7 29.7 Li.sub.2O 19.3 19.7 Na.sub.2O 11.2 10.8
K.sub.2O 2.0 2.0 (C) 32.5 32.5 ZnO 2.9 2.9 BaO 7.9 8.1 (D) 10.8
11.0 B.sub.2O.sub.3 3.4 2.9 GeO.sub.2 0.0 0.0 Ta.sub.2O.sub.5 0.0
0.0 Total 100.0 100.0 Tg (.degree. C.) 466 465 nd 1.80558 1.80591
.nu.d 25.46 25.48
Notes to Tables 1 to 6:
[0084] (A) shows a total content of WO.sub.3 and Nb.sub.2O.sub.5,
(B) shows a total content of WO.sub.3, Nb.sub.2O.sub.5 and
TiO.sub.2, (C) shows a total content of Li.sub.2O, Nb.sub.2O.sub.5
and K.sub.2O, and (D) shows a total content of ZnO and BaO. Each
content and each total content are shown by mol %.
[0085] Tg shows a glass transition temperature, nd shows a
refractive index, and .nu.d shows an Abbe's number.
EFFECT OF THE INVENTION
[0086] According to the present invention, there can be provided
the method of controlling the color degree of a glass containing
WO.sub.3, Nb.sub.2O.sub.5 or TiO.sub.2, particularly a phosphate
glass.
[0087] Particularly, a glass colored by press-molding the above
glass having high-refractivity and high-dispersion properties and
having usefulness as an optical glass in a non-oxidizing atmosphere
can be decolored by a remarkably simple method, and a colorless and
transparent glass molded article can be produced. The above term
"colorless and transparent" means that the color degree and
transmittance of a glass molded article in a visible light region
satisfy requirements that lenses as optical elements are required
to satisfy. In the precision press-molding, the method of
press-molding in a non-oxidizing atmosphere is effective for
improving the lifetime of a mold and preventing the fusion of a
glass and a mold. It is therefore inevitable to heat the above
glass in a non-oxidizing atmosphere, and a colored glass molded
article is obtained.
[0088] According to the present invention, however, the colored
glass can be decolored, and the present invention can overcome the
coloring problem of a molded article that is a problem in precision
press-molding a glass containing WO.sub.3, Nb.sub.2O.sub.5 or
TiO.sub.2, particularly a phosphate glass.
[0089] According to the present invention, further, the color
degree of a glass can be locally changed by local heat-treatment of
the glass or by bringing part of the glass to an atmosphere during
heat treatment, so that a desired colored pattern or a desired
color degree distribution can be formed on/in the glass. According
to the above method, the glass can be used as an optical storage
material. Further, a refractive index distribution is also formed
depending upon the distribution of the color degree, so that a
refractive index distribution type optical element can be produced
by forming a desired color degree distribution in the glass.
[0090] FIG. 1
[0091] Transmittance, After melting, wavelength (nm)
[0092] A change in transmittance spectrum in heat treatment in
N.sub.2 atmosphere
[0093] FIG. 2
[0094] Transmittance, After melting, wavelength (nm)
[0095] A change in transmittance spectrum in heat treatment of
colored glass in atmosphere of air
[0096] FIG. 3
[0097] Transmittance, After melting, wavelength (nm)
[0098] A change in transmittance spectrum of a glass colored during
melting when the glass is heat-treated in atmosphere of air.
* * * * *