U.S. patent application number 10/103987 was filed with the patent office on 2003-04-03 for glass plate and method for tempering a glass plate.
This patent application is currently assigned to ASAHI GLASS COMPANY LIMITED. Invention is credited to Akada, Shuichi, Kato, Yasumasa, Yoda, Kazushige.
Application Number | 20030061835 10/103987 |
Document ID | / |
Family ID | 26612722 |
Filed Date | 2003-04-03 |
United States Patent
Application |
20030061835 |
Kind Code |
A1 |
Yoda, Kazushige ; et
al. |
April 3, 2003 |
Glass plate and method for tempering a glass plate
Abstract
A method for tempering a glass plate having a thickness of from
2 to 3 mm, and having an average linear thermal expansion
coefficient of at least 88.times.10.sup.-7/.degree. C. at a
temperature of from 50 to 300.degree. C. and a softening point of
from 715 to 740.degree. C., which comprises quenching the glass
plate from an initial glass temperature of quenching at which the
viscosity is within a range of from 10.sup.9 to 10.sup.10 poise to
a temperature at which the viscosity is 10.sup.12 poise, so that
the heat transfer coefficient h (W/m.sup.2K) satisfies the
following formula (1), where t (mm) is a glass plate thickness:
h>4970.5-3149.9t+550.3t.sup.2 formula (1)
Inventors: |
Yoda, Kazushige; (Chita-gun,
JP) ; Kato, Yasumasa; (Yokohama-shi, JP) ;
Akada, Shuichi; (Yokohama-shi, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
ASAHI GLASS COMPANY LIMITED
TOKYO
JP
|
Family ID: |
26612722 |
Appl. No.: |
10/103987 |
Filed: |
March 25, 2002 |
Current U.S.
Class: |
65/114 |
Current CPC
Class: |
C03B 27/0413 20130101;
C03C 23/007 20130101; C03C 3/087 20130101; C03B 27/04 20130101 |
Class at
Publication: |
65/114 |
International
Class: |
C03B 027/04 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 30, 2001 |
JP |
2001-099201 |
Sep 26, 2001 |
JP |
2001-293601 |
Claims
What is claimed is:
1. A method for tempering a glass plate having a thickness of from
2 to 3 mm, and having an average linear thermal expansion
coefficient of at least 88.times.10.sup.-7/.degree. C. at a
temperature of from 50 to 300.degree. C. and a softening point of
from 715 to 740.degree. C., which comprises quenching the glass
plate from an initial glass temperature of quenching at which the
viscosity is within a range of from 10.sup.9 to 10.sup.10 poise to
a temperature at which the viscosity is 10.sup.12 poise, so that
the heat transfer coefficient h (W/m.sup.2K) satisfies the
following formula (1), where t (mm) is a glass plate thickness:
h>4970.5-3149.9t+550.3t formula (1)
2. A method for tempering a glass plate having a thickness of from
2 to 3 mm, and having an average linear thermal expansion
coefficient of at least 88.times.10.sup.-7/.degree. C. at a
temperature of from 50 to 300.degree. C. and a softening point of
from 715 to 740.degree. C., which comprises quenching the glass
plate from an initial glass temperature of quenching at which the
viscosity is within a range of from 10.sup.9 to 10.sup.10 poise to
a temperature at which the viscosity is 10.sup.12 poise, so that
the heat transfer coefficient h (W/m.sup.2K) satisfies the
following formula (2), where t (mm) is a glass plate thickness:
h>2123.6.multidot.t.sup.-1.4641 formula (2)
3. The method for tempering a glass plate according to claim 1,
wherein a glass plate having the following composition is
tempered:
11 SiO.sub.2 66.0-74.0 mass %, Al.sub.2O.sub.3 1.5-4.0 mass %, CaO
7.0-10.0 mass %, MgO 3.8-6.0 mass %, Na.sub.2O 12.6-14.6 mass % and
K.sub.2O 0.4-2.0 mass %,
in a total amount of these components of at least 96 mass %,
and
12 SiO.sub.2 + Al.sub.2O.sub.3 70.0-74.0 mass %, CaO + MgO
12.0-14.5 mass % and Na.sub.2O + K.sub.2O 13.5-15.5 mass %.
4. The method for tempering a glass plate according to claim 3,
wherein a glass plate having the following composition is
tempered:
13 Al.sub.2O.sub.3 2.0-4.0 mass %, CaO + MgO 12.5-14.5 mass % and
CaO/MgO (mass ratio) = 1.7-2.2.
5. The method for tempering a glass plate according to claim 2,
wherein a glass plate having the following composition is
tempered:
14 SiO.sub.2 66.0-74.0 mass %, Al.sub.2O.sub.3 1.5-4.0 mass %, CaO
7.0-10.0 mass %, MgO 3.8-6.0 mass %, Na.sub.2O 12.6-14.6 mass % and
K.sub.2O 0.4-2.0 mass %,
in a total amount of these components of at least 96 mass %,
and
15 SiO.sub.2 + Al.sub.2O.sub.3 70.0-74.0 mass %, CaO + MgO
12.0-14.5 mass % and Na.sub.2O + K.sub.2O 13.5-15.5 mass %.
6. The method for tempering a glass plate according to claim 5,
wherein a glass plate having the following composition is
tempered:
16 Al.sub.2O.sub.3 2.0-4.0 mass %, CaO + MgO 12.5-14.5 mass % and
CaO/MgO (mass ratio) = 1.7-2.2.
7. The method for tempering a glass plate according to claim 3,
wherein the glass plate has at least one member selected from the
group consisting of Fe.sub.2O.sub.3, CoO, Se, NiO, Cr.sub.2O.sub.3,
MnO, V.sub.2O.sub.5, TiO.sub.2, CeO.sub.2, SnO, ZnO and SO.sub.3
added thereto.
8. The method for tempering a glass plate according to claim 5,
wherein the glass plate has at least one member selected from the
group consisting of Fe.sub.2O.sub.3, CoO, Se, NiO, Cr.sub.2O.sub.3,
MnO, V.sub.2O.sub.5, TiO.sub.2, CeO.sub.2, SnO, ZnO and SO.sub.3
added thereto.
9. The method for tempering a glass plate according to claim 1,
wherein the glass plate has a thickness of from 2 to 3 mm.
10. The method for tempering a glass plate according to claim 1,
wherein the glass plate is obtained by a float process.
11. The method for tempering a glass plate according to claim 1,
wherein the glass plate is used as a window glass for
automobiles.
12. A glass plate which has the following composition:
17 SiO.sub.2 66.0-74.0 mass %, Al.sub.2O.sub.3 2.0-4.0 mass %, CaO
7.0-10.0 mass %, MgO 3.8-6.0 mass %, Na.sub.2O 12.6-14.6 mass % and
K.sub.2O 0.4-2.0 mass %,
in a total amount of these components of at least 96 mass %,
and
18 SiO.sub.2 + Al.sub.2O.sub.3 70.0-74.0 mass %, CaO + MgO
12.5-14.5 mass %, Na.sub.2O + K.sub.2O 13.5-15.5 mass %, and
CaO/MgO (mass ratio) = 1.7-2.2.
13. The glass plate according to claim 12, which is obtained by
tempering a glass plate having the following composition:
19 Al.sub.2O.sub.3 2.0-4.0 mass %, CaO + MgO 12.5-14.5 mass % and
CaO/MgO (mass ratio) = 1.7-2.2.
14. The glass plate according to claim 12, which comprises SrO or
BaO instead of CaO.
15. The glass plate according to claim 12, which comprises SrO or
BaO instead of MgO.
16. The glass plate according to claim 12, which has at least one
member selected from the group consisting of Fe.sub.2O.sub.3, CoO,
Se, NiO, Cr.sub.2O.sub.3, MnO, V.sub.2O.sub.5, TiO.sub.2,
CeO.sub.2, SnO, ZnO and SO.sub.3 added thereto.
17. The glass plate according to claim 12, which has a thickness of
from 2 to 3 mm.
18. The glass plate according to claim 12, which is obtained by a
float process.
19. The glass plate according to claim 12, which is used as a
window glass for automobiles.
Description
[0001] The present invention relates to a glass plate capable of
being readily tempered by heat and a method for tempering it.
[0002] Conventionally, a glass plate made of general soda lime
silicate is used as a base plate for a tempered glass by heat. Such
a tempered glass is produced usually by quenching a base plate
after heating it to a predetermined initial glass temperature of
quenching. This quenching is carried out by blowing an air to the
heated glass plate in many cases.
[0003] In recent years, for weight saving of automobiles, it is
required to produce a window glass for automobiles with a further
thinner glass plate. However, if the thickness of the glass plate
is from 2 to 3 mm, it is required to greatly increase the degree of
quenching, and a conventional method can not be applied.
[0004] Accordingly, it is an object of the present invention to
provide a glass plate capable of being readily tempered even if it
has a thickness at a level of from 2 to 3 mm, and a method for
tempering a glass plate.
[0005] In order to overcome the above problem, the present
invention provides a method for tempering a glass plate having a
thickness of from 2 to 3 mm, and having an average linear thermal
expansion coefficient of at least 88.times.10.sup.-7/.degree. C. at
a temperature of from 50 to 300.degree. C. and a softening point of
from 715 to 740.degree. C., which comprises quenching the glass
plate from an initial glass temperature of quenching at which the
viscosity is within a range of from 10.sup.9 to 10.sup.10 poise to
a temperature at which the viscosity is 10.sup.12 poise, so that
the heat transfer coefficient h (W/m.sup.2K) satisfies the
following formula (1), where t (mm) is a glass plate thickness:
h>4970.5-3149.9t+550.3t.sup.2 formula (1)
[0006] Further, the present invention provides a method for
tempering a glass plate having a thickness of from 2 to 3 mm, and
having an average linear thermal expansion coefficient of at least
88.times.10.sup.-7/.degr- ee. C. at a temperature of from 50 to
300.degree. C. and a softening point of from 715 to 740.degree. C.,
which comprises quenching the glass plate from an initial glass
temperature of quenching at which the viscosity is within a range
of from 10.sup.9 to 10.sup.10 poise to a temperature at which the
viscosity is 10.sup.12 poise, so that the heat transfer coefficient
h (W/m.sup.2K) satisfies the following formula (2), where t (mm) is
a glass plate thickness:
h>2123.6.multidot.t.sup.-1.4641 formula (2)
[0007] The present invention further provides the above method for
tempering a glass plate, wherein a glass plate having the following
composition is tempered:
1 SiO.sub.2 66.0-74.0 mass %, Al.sub.2O.sub.3 1.5-4.0 mass %, CaO
7.0-10.0 mass %, MgO 3.8-6.0 mass %, Na.sub.2O 12.6-14.6 mass % and
K.sub.2O 0.4-2.0 mass %,
[0008] in a total amount of these components of at least 96 mass %,
and
2 SiO.sub.2 + Al.sub.2O.sub.3 70.0-74.4 mass %, CaO + MgO 12.0-14.5
mass % and Na.sub.2O + K.sub.2O 13.5-15.5 mass %.
[0009] The present invention further provides the above method for
tempering a glass plate, wherein a glass plate having the following
composition is tempered:
3 Al.sub.2O.sub.3 2.0-4.0 mass %, CaO + MgO 12.5-14.5 mass % and
CaO/MgO (mass ratio) = 1.7-2.2.
[0010] Further, the above glass plate preferably has a thickness of
from 2 to 3 mm. Further, the above glass plate is preferably one
produced by a conventional float glass process. Further, the above
glass plate is preferably used as a window glass for
automobiles.
[0011] Still further, the present invention provides a glass plate
which has the following composition:
4 SiO.sub.2 66.0-74.0 mass %, Al.sub.2O.sub.3 2.0-4.0 mass %, CaO
7.0-10.0 mass %, MgO 3.8-6.0 mass %, Na.sub.2O 12.6-14.6 mass % and
K.sub.2O 0.4-2.0 mass %,
[0012] in a total amount of these components of at least 96 mass %,
and
5 SiO.sub.2 + Al.sub.2O.sub.3 70.0-74.0 mass %, CaO + MgO 12.5-14.5
mass %, Na.sub.2O + K.sub.2O 13.5-15.5 mass %, and CaO/MgO (mass
ratio) = 1.7-2.2.
[0013] Now, the present invention will be described in detail with
reference to the preferred embodiments.
[0014] The glass plate to be used for the tempering method of the
present invention has an average linear thermal expansion
coefficient of at least 88.times.10.sup.-7/.degree. C. at a
temperature of from 50 to 300.degree. C. If the average linear
thermal expansion coefficient is lower than this, the glass plate
tends to be poor in readily tempering properties. It is preferably
at least 89.times.10.sup.-7/.degree. C., particularly preferably at
least 90.times.10.sup.-7/.degree. C. However, a glass having an
extremely high average linear thermal expansion coefficient has
significantly different physical properties such as a softening
point as compared with a conventionally used soda lime silicate
glass in many cases. Accordingly, it is necessary to change a
production process to use such a glass, such being impractical.
Practically, the upper limit of the average linear thermal
expansion coefficient at a temperature of from 50 to 300.degree. C.
is at a level of 92.times.10.sup.-7/.degree. C., particularly at a
level of 91.times.10.sup.-7/.degree. C.
[0015] Further, the glass plate to be used for the tempering method
of the present invention has a softening point of from 715 to
740.degree. C. Here, the softening point is defined as a
temperature measured by a test method as disclosed in JIS R3104. If
the softening point exceeds this range, it may be necessary to
change the existing production process. Particularly, in a case
where a ceramic paint which crystallizes by heating in a thermal
tempering step is used together, it may be necessary to employ a
composition of a ceramic paint which is different from a
conventional one, such as one which crystallizes at a temperature
different from a conventional one, in some cases, such being
disadvantageous. The softening point is preferably at least
720.degree. C., particularly preferably at least 725.degree. C.
Further, it is preferably at most 735.degree. C., particularly
preferably at most 730.degree. C.
[0016] Further, in the present invention, the glass plate is
quenched from an initial glass temperature of quenching at which
the viscosity is within a range of from 10.sup.9 to 10.sup.10
poise, to a temperature at which the viscosity is 10.sup.12 poise,
so that the heat transfer coefficient h (W/m.sup.2K) satisfies the
above formula (1) or (2), where t (mm) is a glass plate thickness.
Here, it is more preferred to satisfy the formula (2) than the
formula (1).
[0017] If the initial glass temperature of quenching is higher than
a temperature at which the viscosity is 10.sup.9 poise, the glass
plate is softened too much, whereby optical quality may not be
maintained. Preferably, the initial glass temperature of quenching
is at most a temperature at which the viscosity is 10.sup.9.3
poise. On the other hand, if the initial glass temperature of
quenching is lower than a temperature at which the viscosity is
10.sup.10 poise, the glass plate tends to be poor in readily
tempering properties. Preferably, the initial glass temperature of
quenching is at least a temperature at which the viscosity is
10.sup.9.7 poise.
[0018] Further, if the heat transfer coefficient at the time of
quenching does not satisfy the above formula (1) or (2), the glass
plate may not adequately be tempered.
[0019] The formulae (1) and (2) are obtained by calculating heat
transfer coefficients with which predetermined midplane tensile
residual stresses are caused when a glass plate having a
coefficient of linear thermal expansion of
90.times.10.sup.-7/.degree. C. is quenched from 660.degree. C., at
thicknesses of 2.25 mm, 2.5 mm and 2.8 mm, and fitting the obtained
respective heat transfer coefficients with a parabola, in
accordance with Narayanaswamy O.S., Journal of the American
Ceramics Society, vol. 61, No.3-4 (1978), 146-152. Here, the
predetermined midplane tensile residual stresses are 50 MPa with a
thickness of 2.8 mm, 51 MPa with a thickness of 2.5 mm and 54 MPa
with a thickness of 2.25 mm, and it can be assumed that the glass
plate is adequately tempered when such a midplane tensile residual
stress is caused.
[0020] Specifically, the glass plate of the present invention
preferably has the following composition:
6 SiO.sub.2 66.0-74.0 mass %, Al.sub.2O.sub.3 1.5-4.0 mass %, CaO
7.0-10.0 mass %, MgO 3.8-6.0 mass %, Na.sub.2O 12.6-14.6 mass % and
K.sub.2O 0.4-2.0 mass %,
[0021] in a total amount of these components of at least 96 mass %,
and
7 SiO.sub.2 + Al.sub.2O.sub.3 70.0-74.0 mass %, CaO + MgO 12.0-14.5
mass % and Na.sub.2O + K.sub.2O 13.5-15.5 mass %.
[0022] Now, the components and their upper and lower limits of the
above composition will be described below.
[0023] SiO.sub.2 is a component to secure weather resistance, and
if it is less than 66.0 mass %, the weather resistance may
decrease. It is more preferably at least 67.0 mass %. Further, if
it exceeds 74.0 mass %, the viscosity tends to be high, and melting
may be difficult. It is more preferably at most 73.0 mass %,
particularly preferably at most 72.0 mass %.
[0024] Al.sub.2O.sub.3 is a component to secure weather resistance,
and if it is less than 1.5 mass %, the weather resistance may
decrease. It is more preferably at least 1.7 mass %, particularly
preferably at least 1.8 mass %. Further, if it exceeds 4.0 mass %,
the viscosity tends to be high, and melting may be difficult. From
this viewpoint, it is more preferably at most 3.5 mass %,
particularly preferably at most 3.3 mass %.
[0025] CaO is a component to improve melting ability of raw
materials, and if it is less than 7.0 mass %, the melting ability
may decrease. It is more preferably at least 7.4 mass %,
particularly preferably at least 8.4 mass %. Further, if it exceeds
10.0 mass %, the glass is likely to be devitrified, and stability
when formed into a float glass may decrease. It is more preferably
at most 9.8 mass %, particularly preferably at most 9.6 mass %.
[0026] MgO is a component to improve melting ability of raw
materials, and if it is less than 3.8 mass %, the melting ability
may decrease. It is more preferably at least 4.0 mass %,
particularly preferably at least 4.2 mass %. Further, if it exceeds
6.0 mass %, the glass is likely to be devitrified, and stability
when formed into a float glass may decrease. It is more preferably
most 5.8 mass %, particularly preferably at most 5.6 mass %.
[0027] Na.sub.2O is a component to improve melting ability of raw
materials, and if it is less than 12.6 mass %, the melting ability
may decrease. It is more preferably at least 12.8 mass %,
particularly preferably at least 13.0 mass %. Further, if it
exceeds 14.6 mass %, the weather resistance may decrease. It is
more preferably at most 13.8 mass %, particularly preferably at
most 13.6 mass %.
[0028] K.sub.2O is a component to improve melting ability of raw
materials, and if it is less than 0.4 mass %, the melting ability
may decrease. It is more preferably at least 0.5 mass %,
particularly preferably at least 0.9 mass %. Further, if it exceeds
2.0 mass %, the weather resistance may decrease, and the cost of
the glass plate tends to increase. It is more preferably at most
1.8 mass %, particularly preferably at most 1.6 mass %.
[0029] In the composition of the glass plate of the present
invention, the total amount of SiO.sub.2, Al.sub.2O.sub.3, CaO,
MgO, Na.sub.2O and K.sub.2O is preferably at least 96 mass %. If it
is less than this, physical properties depart from those of a
conventionally used soda lime silicate glass, and it may be
necessary to significantly change a production process of a
conventional glass plate.
[0030] Further, the total amount of SiO.sub.2 and Al.sub.2O.sub.3
is preferably at least 70.0 mass % so as to prevent lowering of the
softening point, and it is preferably at most 74.0 mass % so as to
prevent decrease in the coefficient of linear thermal expansion and
a resulting decrease in readily tempering properties. The total
amount of CaO and MgO is preferably at least 12.0 mass % so as to
prevent decrease in the coefficient of linear thermal expansion and
a resulting decrease in readily tempering properties, and
preferably at most 14.5 mass % so as to prevent lowering of the
softening point. The total amount of Na.sub.2O and K.sub.2O is
preferably at least 13.5 mass % so as to prevent decrease in the
coefficient of linear thermal expansion and a resulting decrease in
readily tempering properties, and preferably at most 15.5 mass % so
as to prevent lowering of the softening point.
[0031] Further, SrO or BaO may be used instead of CaO or MgO within
a range of not impairing the effects of the present invention.
Further, Li.sub.2O may be used instead of Na.sub.2O or K.sub.2O
within a range of not impairing the effects of the present
invention.
[0032] Further, to the glass plate of the present invention, as
e.g. a residual component of refining agents, coloring components
or components improving light transmission and absorption function,
Fe.sub.2O.sub.3, CoO, Se, NiO, Cr.sub.2O.sub.3, MnO,
V.sub.2O.sub.5, TiO.sub.2, CeO.sub.2, SnO, ZnO or SO.sub.3 may be
added within a range of not impairing the effects of the present
invention.
[0033] As one measure indicating the readily tempering properties
of a glass plate, a difference between a temperature at which the
viscosity is 10.sup.9 poise and a temperature at which the
viscosity is 10.sup.12 poise (hereinafter referred to as "tempering
viscosity temperature difference") is mentioned. If the tempering
viscosity temperature difference is small, the readily tempering
properties tend to improve. Specifically, the tempering viscosity
temperature difference is preferably at most 100.degree. C.,
particularly preferably at most 95.degree. C. However, glass having
an extremely small tempering viscosity temperature difference tends
to have significantly different physical properties such as a
softening point as compared with conventionally used soda lime
silicate glass in many cases. Accordingly, it may be necessary to
change a production process to use such a glass, such being
impractical. Practically, the tempering viscosity temperature
difference is at least 90.degree. C.
[0034] In order to decrease the tempering viscosity temperature
difference, it is effective to increase the total amount of CaO and
MgO. On the other hand, if the total amount of CaO and MgO is
increased, the devitrification temperature may increase, and
stability in float forming may decrease. Further, the softening
point may also be lowered.
[0035] Taking the above points into consideration, the composition
of the glass plate of the present invention particularly preferably
satisfies the following conditions:
8 Al.sub.2O.sub.3 2.0-4.0 mass %, CaO + MgO 12.5-14.5 mass % and
CaO/MgO (mass ratio) = 1.7-2.2.
[0036] When the above conditions are satisfied, glass capable of
being readily tempered, having a relatively high softening point,
can be obtained, without substantially impairing stability in float
forming.
[0037] More preferably, the following conditions are satisfied:
9 Al.sub.2O.sub.3 2.5-4.0 mass %, CaO + MgO 13.0-14.5 mass % and
CaO/MgO (mass ratio) = 1.7-2.2.
[0038] The method for producing the glass plate of the present
invention is not particularly limited, but the glass plate can be
produced as follows for example. A blended material is continuously
supplied to a melter and heated to about 1,500.degree. C. by e.g.
heavy oil for vitrification. Then, this molten glass is refined,
and then formed into a glass plate having a predetermined thickness
by e.g. a float process. Then, this glass plate is cut into a
predetermined shape to produce the glass plate of the present
invention.
[0039] Then, the cut glass plate is subjected to a tempering
treatment. The tempering treatment is carried out, as mentioned
above, by heating the glass plate to a predetermined temperature
and then quenching it. Simultaneously with the heating for the
tempering treatment, bending or baking of a ceramic paint may be
carried out.
[0040] Now, the present invention will be explained in further
detail with reference to Examples. However, it should be understood
that the present invention is by no means restricted to such
specific Examples.
[0041] Using as materials silica sand, feldspar, dolomite, soda
ash, salt cake, ferric oxide, titanium oxide and cerium oxide, a
batch prepared so that an aimed composition as identified in Table
1 would be obtained was melted in a conventional type melter (an
atmosphere at an O.sub.2 concentration at a level of 2%), and the
molten glass was supplied to a small size float test apparatus
connected to the melter to produce a glass plate.
[0042] The compositions are shown in Table 1 together with physical
properties of the glass plates. Examples are all examples of the
present invention.
10TABLE 1 Examples 1 2 3 4 5 6 7 8 9 *1 88 92 89 90 90 90 90 92 91
*2 725 720 726 724 722 725 721 710 727 SiO2 71.3 69.1 70.5 69.9
68.5 69.5 68.2 69.1 68.5 Al2O3 1.6 2.5 1.7 2.5 1.8 2.1 3.1 1.8 3.1
CaO 7.7 8.2 8.2 8.4 8.4 8.8 8.4 9.4 8.5 MgO 4.4 4.4 4.4 4.0 4.2 4.4
4.8 4.1 4.4 Na2O 13.3 13.9 12.9 13.9 13.7 13.3 13.5 13.8 13.5 K2O
0.9 1.1 1.5 0.5 0.8 1.1 1.1 1.0 1.2 Subtotal 99.15 99.15 99.15
99.15 97.35 99.15 99.05 99.22 99.15 SO3 0.24 0.24 0.24 0.24 0.10
0.24 0.24 0.21 0.24 Fe2O3 0.50 0.50 0.50 0.50 0.60 0.50 0.60 0.51
0.50 TiO2 0.14 0.14 0.14 0.14 0.40 0.14 0.14 0.01 0.14 CeO2 0.00
0.00 0.00 0.00 1.50 0.00 0.00 0.00 0.00 Total 100.0 100.0 100.0
100.0 100.0 100.0 100.0 100.0 100.0 SiO2 + Al2O3 72.9 71.6 72.2
72.4 70.3 71.6 71.3 70.9 71.6 RO 12.1 12.6 12.6 12.4 12.6 13.2 13.2
13.5 12.9 R2O 14.2 15.0 14.4 14.4 14.5 14.4 14.6 14.8 14.7 CaO/MgO
1.75 1.86 1.86 2.10 2.00 2.00 1.75 2.30 1.93 T(log .eta. = 9) 656
653 657 655 662 656 659 651 658 T(log .eta. = 12) 561 560 562 562
569 563 566 559 565 *3 95 93 95 93 93 93 93 92 93 T(log .eta. = 4)
1034 1021 1032 1026 1033 1024 1028 1042 1027 *4 991 1002 1007 1008
985 1025 1031 1030 1026 *5 43 19 25 18 48 -1 -3 12 1 *1:
Coefficient of linear thermal expansion *2: Softening point *3:
Tempering viscosity temperature difference *4: Devitrification
temperature *5: Difference (float formability)
[0043] In Table 1, the coefficient of linear thermal expansion is
an average linear thermal expansion coefficient at a temperature of
from 50 to 300.degree. C. as measured in accordance with JIS R3102,
and the unit is .times.10.sup.-7/.degree. C. Further, the softening
point was measured in accordance with JIS R3104, and the unit is
.degree. C. The unit of each component is mass %. Here, the values
were obtained by extrapolation except for Examples 5 and 6.
[0044] T(log .eta.=4), T(log .eta.=9) and T(log .eta.=12) in Table
1 are temperatures at which the viscosity is 10.sup.4 poise,
10.sup.9 poise and 10.sup.12 poise, respectively, and the unit is
.degree. C. They were calculated from a viscosity curve prepared
based on a temperature at which the viscosity was from 10.sup.2 to
10.sup.5 poise as measured by a rotating-cylinder method, and a
softening point as measured in accordance with JIS R3104. Further,
the devitrification temperature was measured by examining presence
or absence of devitrification by observation with an optical
microscope after a glass plate sample heated in an electric furnace
maintained at various temperatures was quenched, and the unit is
.degree. C.
[0045] The readily tempering properties were evaluated from a
difference between a temperature at which the viscosity was
10.sup.9 poise and a temperature at which the viscosity was
10.sup.12 poise, and shown in the column "tempering viscosity
temperature difference" in Table 1. It can be said that the readily
tempering properties are high when the tempering viscosity
temperature difference is at most 100.degree. C., and the readily
tempering properties are particularly high when it is at most
95.degree. C.
[0046] The stability in float forming was evaluated from a
difference between a devitrification temperature and a temperature
at which the viscosity was 10.sup.4 poise, and shown in the column
"difference (float formability)" in Table 1. When the temperature
at which the viscosity was 10.sup.4 poise is the same as or higher
than the devitrification temperature, float forming can stably be
carried out.
[0047] Then, the glass as identified in Example 8 of Table 1 was
formed into a glass plate of 1,350.times.550 mm with a thickness of
2.5 mm, and quenched for tempering from 640.degree. C. at a heat
transfer coefficient of 648 W/m.sup.2K.
[0048] The obtained tempered glass plate was subjected to a test
wherein the position of point 3 was fractured, in accordance with
JIS R3212, whereupon the number of roughest fragments was from 63
to 142, and an adequate tempering was confirmed.
[0049] As mentioned above, according to the glass plate and the
method for tempering it of the present invention, a glass plate
which is a thin glass plate having a thickness at a level of from 2
to 3 mm, and which has a degree of tempering which is by no means
inferior to a conventional glass plate of at least 3 mm, can be
obtained. Such a tempered glass plate is useful as e.g. a glass
plate for vehicles such as automobiles and trains and further for
buildings.
[0050] The entire disclosures of Japanese Patent Application No.
2001-099201 filed on Mar. 30, 2001 and Japanese Patent Application
No. 2001-293601 filed on Sep. 26, 2001 including specifications,
claims and summaries are incorporated herein by reference in their
entireties.
* * * * *