U.S. patent application number 17/449829 was filed with the patent office on 2022-01-27 for glass plate and process for producing the same.
This patent application is currently assigned to AGC Inc.. The applicant listed for this patent is AGC Inc.. Invention is credited to Hiroyuki HIJIYA, Yutaka KUROIWA, Yusaku MATSUO, Tomonori OGAWA, Kazutaka ONO.
Application Number | 20220024803 17/449829 |
Document ID | / |
Family ID | |
Filed Date | 2022-01-27 |
United States Patent
Application |
20220024803 |
Kind Code |
A1 |
HIJIYA; Hiroyuki ; et
al. |
January 27, 2022 |
GLASS PLATE AND PROCESS FOR PRODUCING THE SAME
Abstract
A glass plate has a dielectric dissipation factor at 10 GHz of
tan .delta.A and a glass transition temperature of Tg.degree. C.
The glass plate satisfies (tan .delta.100-tan
.delta.A).gtoreq.0.0004, where tan .delta.100 is a dielectric
dissipation factor of the glass plate at 10 GHz after having been
heated to (Tg+50).degree. C. and then cooled to (Tg-150).degree. C.
at 100.degree. C./min.
Inventors: |
HIJIYA; Hiroyuki; (Tokyo,
JP) ; KUROIWA; Yutaka; (Tokyo, JP) ; ONO;
Kazutaka; (Tokyo, JP) ; OGAWA; Tomonori;
(Tokyo, JP) ; MATSUO; Yusaku; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
AGC Inc. |
Tokyo |
|
JP |
|
|
Assignee: |
AGC Inc.
Tokyo
JP
|
Appl. No.: |
17/449829 |
Filed: |
October 4, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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PCT/JP2020/015748 |
Apr 7, 2020 |
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17449829 |
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International
Class: |
C03C 3/087 20060101
C03C003/087; C03B 17/06 20060101 C03B017/06; C03C 4/14 20060101
C03C004/14 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 12, 2019 |
JP |
2019-076423 |
Jun 28, 2019 |
JP |
2019-120828 |
Nov 27, 2019 |
JP |
2019-214690 |
Claims
1. A glass plate having a dielectric dissipation factor at 10 GHz
of tan .delta.A and a glass transition temperature of Tg.degree.
C., wherein the glass plate satisfies (tan .delta.100-tan
.delta.A).gtoreq.0.0004, where tan .delta.100 is a dielectric
dissipation factor of the glass plate at 10 GHz after having been
heated to (Tg+50).degree. C. and then cooled to (Tg-150).degree. C.
at 100.degree. C./min.
2. The glass plate according to claim 1, having a relative
permittivity at 10 GHz of .epsilon.rA, wherein the glass plate
satisfies 0.95.ltoreq.(.epsilon.r100/.epsilon.rA).ltoreq.1.05,
where .epsilon.r100 is a relative permittivity of the glass plate
at 10 GHz after having been heated to (Tg+50).degree. C. and then
cooled to (Tg-150).degree. C. at 100.degree. C./min.
3. The glass plate according to claim 1, comprising a principal
surface with an area of 350 cm.sup.2 or larger.
4. The glass plate according to claim 1, having the dielectric
dissipation factor at 10 GHz of 0.009 or less.
5. The glass plate according to claim 1, having a relative
permittivity at 10 GHz of 6.8 or less.
6. The glass plate according to claim 1, wherein any two portions
separated from each other by 40 mm or more have a difference in
dielectric dissipation factor at 10 GHz of 0.0005 or less.
7. The glass plate according to claim 1, wherein any two portions
separated from each other by 40 mm or more have a difference in
relative permittivity at 10 GHz of 0.05 or less.
8. The glass plate according to claim 1, comprising from 30 to 85%
of SiO.sub.2 as represented by mol % based on oxides.
9. The glass plate according to claim 1, comprising, as represented
by mol % based on oxides, SiO.sub.2: from 57 to 70%,
Al.sub.2O.sub.3: from 5 to 15%, B.sub.2O.sub.3: from 15 to 24%,
provided that Al.sub.2O.sub.3+B.sub.2O.sub.3 is from 20 to 40%, and
Al.sub.2O.sub.3/(Al.sub.2O.sub.3+B.sub.2O.sub.3) is from 0.1 to
0.45, MgO: from 0 to 10%, CaO: from 0 to 10%, SrO: from 0 to 10%,
BaO: from 0 to 10%, Li.sub.2O: from 0 to 5%, Na.sub.2O: from 0 to
5%, and K.sub.2O: from 0 to 5%, provided that R.sub.2O (R is alkali
metal): from 0 to 5%.
10. The glass plate according to claim 1, comprising, as
represented by mol % based on oxides, SiO.sub.2: from 55 to 80%,
Al.sub.2O.sub.3: from 0 to 15%, provided that
SiO.sub.2+Al.sub.2O.sub.3 is from 55 to 90%, B.sub.2O.sub.3: from 0
to 15%, MgO: from 0 to 20%, CaO: from 0 to 20%, SrO: from 0 to 15%,
BaO: from 0 to 15%, provided that MgO+CaO is from 0 to 30%, and
MgO+CaO+SrO+BaO: from 0 to 30%, Li.sub.2O: from 0 to 20%,
Na.sub.2O: from 0 to 20%, and K.sub.2O: from 0 to 20%, provided
that R.sub.2O (R is alkali metal) is from 0 to 20%.
11. The glass plate according to claim 1 which is for use as a
substrate for a high-frequency device in which high-frequency
signals having a frequency of 3.0 GHz or higher are handled.
12. The glass plate according to claim 1 which is for use as a
window material.
13. A process for producing the glass plate according to claim 1,
comprising, in the following order, a melting/forming step of
melting raw materials for glass to obtain a molten glass and
forming the molten glass into a plate shape, a cooling step of
cooling the molten glass formed into the plate shape to a
temperature of (Tg-300).degree. C. or lower with respect to the
glass transition temperature Tg (.degree. C.) to obtain a glass
base plate, and a heat treatment step of heating the obtained glass
base plate from the temperature of (Tg-300).degree. C. or lower to
a temperature in a range of from (Tg-100).degree. C. to
(Tg+50).degree. C., without being heated to a temperature exceeding
(Tg+50).degree. C., and then cooling the glass base plate again to
(Tg-300).degree. C. or lower, wherein the heat treatment step is
conducted one or two or more times, each heat treatment step
extends until the temperature of the glass base plate exceeds
(Tg-300).degree. C., thereafter reaches a maximum temperature Temax
(.degree. C.) in the range of from (Tg-100).degree. C. to
(Tg+50).degree. C., and then declines again to (Tg-300).degree. C.
or lower, a total time period in which the temperature of the glass
base plate is in the range of from (Tg-100).degree. C. to
(Tg+50).degree. C. in a whole heat treatment step(s) is K (minutes)
or longer, the K being represented by the following formula (1)
using the maximum temperature Tmax (.degree. C.) of the glass base
plate in the whole heat treatment step(s), and each heat treatment
step satisfies the following formula (2), where t1 (minutes) is a
time period in each heat treatment step from a time when the
temperature of the glass base plate lastly begins to decline from
the maximum temperature Temax (.degree. C.) to a time when the
temperature of the glass base plate lastly passes (Tg-110).degree.
C.: K=[{(Tg+50)-Tmax}/10]+15 Formula (1)
{Temax-(Tg-110)}/t1.ltoreq.10 Formula (2).
14. The process for glass plate production according to claim 13,
wherein in each heat treatment step, the temperature of the glass
base plate which has first become lower than (Tg-110).degree. C.
after having declined from the maximum temperature Temax (.degree.
C.) does not exceed (Tg-110).degree. C. again.
15. The process for glass plate production according to claim 13,
wherein in each heat treatment step, if any two times in the step
which lie between the time when the temperature of the glass base
plate lastly begins to decline from the maximum temperature Temax
(.degree. C.) and the time when the temperature of the glass base
plate lastly passes (Tg-110).degree. C. are expressed by t2
(minutes) and t3 (minutes) and if t2<t3, then t2 and the t3 have
a difference in time therebetween of 1 minute or more, and if the
temperature of the glass base plate at t2 is expressed by Te2 and
the temperature of the glass base plate at t3 is expressed by Te3,
then Te2 and Te3 satisfy the following formula (3):
(Te2-Te3)/(t3-t2).ltoreq.10 Formula (3).
16. The process for glass plate production according to claim 13,
wherein in the cooling step, the molten glass is cooled from
(Tg+50).degree. C. to (Tg-100).degree. C. at an average cooling
rate exceeding 10.degree. C./min.
17. The process for glass plate production according to claim 13,
wherein in the cooling step, the molten glass is cooled at an
average cooling rate of from 10 to 1,000.degree. C./min.
Description
TECHNICAL FIELD
[0001] The present invention relates to a glass plate and a process
for producing the glass plate.
BACKGROUND ART
[0002] It has become usual to use appliances utilizing radio waves
(hereinafter referred to as "radio appliances"), such as radars and
portable telephones, in vehicles including motor vehicles and in
buildings. Especially in recent years, radio appliances utilizing
radio waves having frequencies in a high-frequency band (microwaves
to millimeter waves), more specifically a gigahertz frequency band,
e.g., 3-300 GHz range, have come to be intensively developed.
[0003] Circuit boards used in such radio appliances for
high-frequency applications (hereinafter referred to as
"high-frequency devices) generally employ insulating substrates
such as resin substrates, ceramic substrates, and glass substrates.
Such insulating substrates for use in high-frequency devices are
required to attain reductions in transmission loss due to
dielectric loss, conductor loss, etc., in order to ensure the
properties of high-frequency signals, such as the quality and
intensity thereof.
[0004] Meanwhile, glass plates for use as window materials for
vehicles, e.g., motor vehicles, and buildings have been required to
have a high visible-light transmittance and the ability to highly
shield ultraviolet light and solar radiation and be visually
satisfactory. Patent Literature 1 discloses an ultraviolet- and
infrared-absorbing glass constituted from a soda-lime silica glass
having a specific composition.
CITATION LIST
Patent Literature
[0005] Patent Literature 1: JP-A-2002-348143
SUMMARY OF INVENTION
Technical Problem
[0006] However, in view of the facts that millimeter-wave radars
are coming to be mounted in vehicles, e.g., motor vehicles, and
that electronic appliances are used in buildings, glass plates for
use as window materials for the vehicles and buildings are required
to attain reductions in propagation loss and transmission loss like
the insulating substrates of high-frequency devices.
[0007] Accordingly, an object of the present invention is to
provide a novel glass plate which is low in propagation loss and
transmission loss in a high-frequency band and is usable as the
substrates of high-frequency devices or as window materials, and to
provide a process for producing the glass plate.
Solution to Problem
[0008] The present invention relates to the following.
[0009] 1. A glass plate having a dielectric dissipation factor at
10 GHz of tan .delta.A and a glass transition temperature of
Tg.degree. C.,
[0010] wherein the glass plate satisfies (tan .delta.100-tan
.delta.A).gtoreq.0.0004, where tan .delta.100 is a dielectric
dissipation factor of the glass plate at 10 GHz after having been
heated to (Tg+50).degree. C. and then cooled to (Tg-150).degree. C.
at 100.degree. C./min.
[0011] 2. The glass plate according to 1 above having a relative
permittivity at 10 GHz of .epsilon.rA, wherein the glass plate
satisfies 0.95.ltoreq.(.epsilon.r100/.epsilon.rA).ltoreq.1.05,
where .epsilon.r100 is a relative permittivity of the glass plate
at 10 GHz after having been heated to (Tg+50).degree. C. and then
cooled to (Tg-150).degree. C. at 100.degree. C./min.
[0012] 3. The glass plate according to 1 or 2 above which has a
principal surface having an area of 350 cm.sup.2 or larger.
[0013] 4. The glass plate according any one of 1 to 3 above wherein
the dielectric dissipation factor at 10 GHz is 0.009 or less.
[0014] 5. The glass plate according to any one of 1 to 4 above
which has a relative permittivity at 10 GHz of 6.8 or less.
[0015] 6. The glass plate according to any one of 1 to 5 above
wherein any two portions separated from each other by 40 mm or more
have a difference in dielectric dissipation factor at 10 GHz of
0.0005 or less.
[0016] 7. The glass plate according to any one of 1 to 6 above
wherein any two portions separated from each other by 40 mm or more
have a difference in relative permittivity at 10 GHz of 0.05 or
less.
[0017] 8. The glass plate according to any one of 1 to 7 above
which includes from 30 to 85% of SiO.sub.2 as represented by mol %
based on oxides.
[0018] 9. The glass plate according to any one of 1 to 8 above
which includes, as represented by mol % based on oxides,
[0019] SiO.sub.2: from 57 to 70%,
[0020] Al.sub.2O.sub.3: from 5 to 15%,
[0021] B.sub.2O.sub.3: from 15 to 24%,
[0022] provided that Al.sub.2O.sub.3+B.sub.2O.sub.3 is from 20 to
40%, and
[0023] Al.sub.2O.sub.3/(Al.sub.2O.sub.3+B.sub.2O.sub.3) is 0.1 to
0.45,
[0024] MgO: from 0 to 10%,
[0025] CaO: from 0 to 10%,
[0026] SrO: from 0 to 10%,
[0027] BaO: from 0 to 10%,
[0028] Li.sub.2O: from 0 to 5%,
[0029] Na.sub.2O: from 0 to 5%,
[0030] K.sub.2O: from 0 to 5%, and
[0031] R.sub.2O (R=alkali metal) is from 0 to 5%.
[0032] 10. The glass plate according to any one of 1 to 8 above
which includes, as represented by mol % based on oxides,
[0033] SiO.sub.2: from 55 to 80%,
[0034] Al.sub.2O.sub.3: from 0 to 15%,
[0035] provided that SiO.sub.2+Al.sub.2O.sub.3 is from 55 to
90%,
[0036] B.sub.2O.sub.3: from 0 to 15%,
[0037] MgO: from 0 to 20%,
[0038] CaO: from 0 to 20%,
[0039] SrO: from 0 to 15%,
[0040] BaO: from 0 to 15%,
[0041] provided that MgO+CaO is from 0 to 30%, and
[0042] MgO+CaO+SrO+BaO: from 0 to 30%,
[0043] Li.sub.2O: from 0 to 20%,
[0044] Na.sub.2O: from 0 to 20%, and
[0045] K.sub.2O: from 0 to 20%,
[0046] provided that R.sub.2O (R=alkali metal) is from 0 to
20%.
[0047] 11. The glass plate according to any one of 1 to 9 above
which is for use as a substrate for a high-frequency device in
which high-frequency signals having a frequency of 3.0 GHz or
higher are handled.
[0048] 12. The glass plate according to any one of 1 to 8 and 10
above which is for use as a window material.
[0049] 13. A process for producing the glass plate according to any
one of 1 to 12 above which includes, in the following order,
[0050] a melting/forming step in which raw materials for glass are
melted to obtain a molten glass and the molten glass is formed into
a plate shape,
[0051] a cooling step in which the molten glass formed into the
plate shape is cooled to a temperature of (Tg-300).degree. C. or
lower with respect to the glass transition temperature Tg (.degree.
C.) to obtain a glass base plate, and
[0052] a heat treatment step in which the obtained glass base plate
is heated from the temperature of (Tg-300).degree. C. or lower to a
temperature in a range of from (Tg-100).degree. C. to
(Tg+50).degree. C., without being heated to a temperature exceeding
(Tg+50).degree. C., and is then cooled again to (Tg-300).degree. C.
or lower,
[0053] wherein the heat treatment step is conducted one or two or
more times,
[0054] each heat treatment step extends until the temperature of
the glass base plate exceeds (Tg-300).degree. C., thereafter
reaches a maximum temperature Temax (.degree. C.) in the range of
from (Tg-100).degree. C. to (Tg+50).degree. C., and then declines
again to (Tg-300).degree. C. or lower,
[0055] a total time period in which the temperature of the glass
base plate is in the range of from (Tg-100).degree. C. to
(Tg+50).degree. C. in a whole heat treatment step(s) is K (minutes)
or longer, the K being represented by the following formula (1)
using the maximum temperature Tmax (.degree. C.) of the glass base
plate in the whole heat treatment step(s), and
[0056] each heat treatment step satisfies the following formula
(2), where t1 (minutes) is a time period in each heat treatment
from a time when the temperature of the glass base plate lastly
begins to decline from the maximum temperature Temax (.degree. C.)
to a time when the temperature of the glass base plate lastly
passes (Tg-110).degree. C.
K=[{(Tg+50)-Tmax}/10]+15 Formula (1)
{Temax-(Tg-110)}/t1.ltoreq.10 Formula (2)
[0057] 14. The process for glass plate production according to 13
above wherein in each heat treatment step, the temperature of the
glass base plate which has first become lower than (Tg-110).degree.
C. after having declined from the maximum temperature Temax
(.degree. C.) does not exceed (Tg-110).degree. C. again.
[0058] 15. The process for glass plate production according to 13
or 14 above wherein in each heat treatment step, if any two times
in the step which lie between the time when the temperature of the
glass base plate lastly begins to decline from the maximum
temperature Temax (.degree. C.) and the time when the temperature
of the glass base plate lastly passes (Tg-110).degree. C. are
expressed by t2 (minutes) and t3 (minutes) and if t2<t3,
then
[0059] t2 and the t3 have a difference in time therebetween of 1
minute or more, and
[0060] if the temperature of the glass base plate at t2 is
expressed by Te2 and the temperature of the glass base plate at t3
is expressed by Te3, then Te2 and Te3 satisfy the following formula
(3).
(Te2-Te3)/(t3-t2).ltoreq.10 Formula (3)
[0061] 16. The process for glass plate production according to any
one of 13 to 15 above wherein in the cooling step, the molten glass
is cooled from (Tg+50).degree. C. to (Tg-100).degree. C. at an
average cooling rate exceeding 10.degree. C./min.
[0062] 17. The process for glass plate production according to any
one of 13 to 16 above wherein in the cooling step, the molten glass
is cooled at an average cooling rate of from 10 to 1,000.degree.
C./min.
Advantageous Effects of Invention
[0063] The glass plate according to the present invention shows
little absorption of electromagnetic waves in a high-frequency band
and can attain a high transmittance. Furthermore, using this glass
plate in circuit boards makes it possible to provide practical
high-frequency devices, such as electronic devices, reduced in
propagation loss and transmission loss. Moreover, this glass plate,
when used as window materials for vehicles, e.g., motor vehicles,
and buildings, can propagate electromagnetic waves without causing
considerable attenuation, in the case where millimeter-wave radars
have been mounted in the vehicles or electronic appliances are used
in the buildings.
DESCRIPTION OF EMBODIMENTS
[0064] The present invention is described below in detail, but the
present invention is not limited to the following embodiments and
can be modified at will within the gist of the present invention.
Symbol "-" indicating a numerical range is used in the sense of
including the numerical values set force before and after the "-"
as a lower limit value and an upper limit value. Furthermore, "%"
indicating the composition of a glass plate shows a value as
represented by mol % based on oxides unless otherwise
indicated.
<Glass Plate>
[0065] The glass plate according to this embodiment has a
dielectric dissipation factor at 10 GHz of tan .delta.A and a glass
transition temperature of Tg.degree. C., and this glass plate,
after having been heated to (Tg+50).degree. C. and then cooled to
(Tg-150).degree. C. at 100.degree. C./min, satisfies the
relationship (tan .delta.100-tan .delta.A).gtoreq.0.0004, where tan
.delta.100 is a dielectric dissipation factor thereof.
[0066] The dielectric dissipation factor (hereinafter sometimes
referred to simply as "tan .delta.") of a glass plate is a value
represented by .epsilon.''/.epsilon.' using complex permittivity,
where .epsilon.' is relative permittivity and .epsilon.'' is
dielectric loss. The smaller the value of tan .delta., the lower
the absorption of electromagnetic waves in the frequency band and
the higher the attained transmittance.
[0067] In this description, dielectric dissipation factor and
relative permittivity are values measured at a measuring frequency
of 10 GHz by the method as provided for in IEC 61189-2-721
(2015).
[0068] In general, values of tan .delta. can be regulated by
changing the glass composition. However, the present invention is
based on a newly discovered method whereby values of tan .delta.
can be regulated without changing a glass composition. This makes
it possible to obtain a glass which has a smaller value of tan
.delta. than conventional glasses even when having the same
composition.
[0069] Glasses differing in density are obtained by using different
cooling rates in glass production. Specifically, a high cooling
rate results in a vitreous state having a low density (sparse),
while a low cooling rate results in a vitreous state having a high
density (dense). It has been discovered that the density of the
vitreous state correlates with the value of tan .delta. in a
high-frequency band.
[0070] That is, in the case where the vitreous state is dense and
has a high density, the glass plate can have an increased
transmittance for electromagnetic waves in a high-frequency band
(can be reduced in the absorption of the electromagnetic waves),
resulting in a smaller value of tan .delta. in the high-frequency
band. The term "high-frequency band" in this description is
intended to mean frequencies of usually not shorter than 3.0 GHz,
in particular, not shorter than 3.5 GHz, and actual tests were
performed at 10 GHz.
[0071] The glass plate according to this embodiment has a smaller
value of tan .delta.A in a high-frequency band than conventional
glass plates having the same composition. This can be assessed in
terms of the value of (tan .delta.100-tan .delta.A) described
above. Specifically, in the case where a glass plate having a
dielectric dissipation factor at 10 GHz of tan .delta.A is heated
to (Tg+50).degree. C. and then cooled to (Tg-150).degree. C. at
100.degree. C./min and when this glass plate thereafter has a value
of tan .delta.100 which is larger than the value of tan .delta.A
[(tan 1100-tan .delta.A).gtoreq.0], then the glass plate is deemed
to be a glass plate obtained through cooling conducted at a cooling
rate lower than 100.degree. C./min and has a high density and high
transparency.
[0072] Furthermore, in the case where the value of (tan
.delta.100-tan .delta.A) is 0.0004 or larger to satisfy the
relationship (tan .delta.100-tan .delta.A).gtoreq.0.0004, this
glass plate can be regarded as having a considerably smaller value
of tan .delta.A than conventional glass plates having the same
composition and as showing high transparency to electromagnetic
waves in a high-frequency band.
[0073] Although the tan .delta.A of the glass plate satisfies the
relationship (tan .delta.100-tan .delta.A).gtoreq.0.0004 as stated
above, the tan .delta.A preferably satisfies (tan .delta.100-tan
.delta.A).gtoreq.0.0005, more preferably satisfies (tan
.delta.100-tan .delta.A).gtoreq.0.0006, from the standpoint of
making the glass plate show higher transparency.
[0074] There is no particular upper limit on (tan .delta.100-tan
.delta.A). However, from the standpoint of shortening the
heat-treatment period to improve the production efficiency, the tan
.delta.A may satisfy (tan .delta.100-tan .delta.A).ltoreq.0.001, or
may satisfy (tan .delta.100-tan .delta.A).ltoreq.0.0008, or may
satisfy (tan .delta.100-tan .delta.A).ltoreq.0.0007, or may satisfy
(tan .delta.100-tan .delta.A).ltoreq.0.0006.
[0075] Any two portions of the glass plate which are separated from
each other by 40 mm or more have a difference in dielectric
dissipation factor tan .delta. at 10 GHz of preferably 0.0005 or
less, more preferably 0.0004 or less, still more preferably 0.0003
or less. In the case where the difference in dielectric dissipation
factor tan .delta. is 0.0005 or less, this glass plate can be
regarded as having a narrow in-plane distribution of dielectric
dissipation factor and can be regarded as a glass plate which had
evenness in cooling rate and is homogeneous. Such differences in
tan .delta. are hence preferred. The term "any two portions
separated from each other by 40 mm or more" means any two portions
lying on the same plane and separated by 40 mm or more.
[0076] There is no particular lower limit on the difference in
dielectric dissipation factor tan .delta. at 10 GHz between any two
portions of the glass plate which are separated from each other by
40 mm or more, but the difference may be 0.0001 or more.
[0077] It is preferable that the glass plate has a relative
permittivity .epsilon.rA at 10 GHz which satisfies the relationship
0.95.ltoreq.(.epsilon.r100/.epsilon.rA).ltoreq.1.05, where
.epsilon.r100 is a relative permittivity at 10 GHz of the glass
plate which has been heated to (Tg+50).degree. C. and then cooled
to (Tg-150).degree. C. at 100.degree. C./min. The value represented
by (.epsilon.r100/.epsilon.rA) is more preferably 0.98 or larger,
still more preferably 0.99 or larger, and is more preferably 1.03
or smaller, still more preferably 1.02 or smaller, especially
preferably 1.01 or smaller.
[0078] Unlike the tan .delta.A, the relative permittivity Fr of the
obtained glass plate has a substantially constant value even when
the glass plate has been produced using different cooling rates.
Because of this, a reduction in loss in high-frequency devices can
be attained without considerably changing the design of the
devices.
[0079] Any two portions of the glass plate which are separated from
each other by 40 mm or more have a difference in relative
permittivity .epsilon.rA at 10 GHz of preferably 0.05 or less, more
preferably 0.04 or less, still more preferably 0.03 or less. In the
case where the difference in relative permittivity .epsilon.rA is
0.05 or less, this glass plate is a homogeneous glass plate which
has a narrow in-plane distribution of relative permittivity and had
evenness in cooling rate. Such differences in .epsilon.rA are hence
preferred. Although there is no particular lower limit on the
difference in relative permittivity .epsilon.rA at 10 GHz between
any two portions of the glass plate which are separated from each
other by 40 mm or more, the difference may be 0.01 or more.
[0080] The glass plate having such properties can be advantageously
used as the substrates of high-frequency devices and as window
materials. The high-frequency devices are more preferably ones in
which high-frequency signals having a frequency of 3.0 GHz or
higher, in particular 3.5 GHz or higher, are handled.
[0081] The glass plate preferably includes SiO.sub.2 in an amount
of 30-85% as represented by mol % based on oxides. For use as a
substrate for high-frequency devices, the glass plate is more
preferably an alkali-free glass. For use as a window material, the
glass plate is more preferably a soda-lime glass.
[0082] Specific preferred glass compositions for the respective
applications are as follows.
[0083] In the case where the glass plate is for use as the
substrate of a high-frequency device, this glass plate more
preferably has the following composition as represented by mol %
based on oxides.
[0084] SiO.sub.2: from 57 to 70%,
[0085] Al.sub.2O.sub.3: from 5 to 15%,
[0086] B.sub.2O.sub.3: from 15 to 24%,
[0087] Al.sub.2O.sub.3+B.sub.2O.sub.3: from 20 to 40%,
[0088] Al.sub.2O.sub.3/(Al.sub.2O.sub.3+B.sub.2O.sub.3): from 0.1
to 0.45,
[0089] MgO: from 0 to 10%,
[0090] CaO: from 0 to 10%,
[0091] SrO: from 0 to 10%,
[0092] BaO: from 0 to 10%,
[0093] Li.sub.2O: from 0 to 5%,
[0094] Na.sub.2O: from 0 to 5%,
[0095] K.sub.2O: from 0 to 5%, and
[0096] R.sub.2O (R=alkali metal): from 0 to 5%.
[0097] Each component of the composition is explained below.
[0098] SiO.sub.2 is a network-forming substance. In the case where
the content thereof is 57% or higher, satisfactory glass-forming
ability and satisfactory weatherability can be attained and
devitrification can be inhibited. Such SiO.sub.2 contents are hence
preferred. The content of SiO.sub.2 is more preferably 58% or
higher, still more preferably 60% or higher, yet still more
preferably 61% or higher. Meanwhile, in the case where the content
of SiO.sub.2 is 70% or less, satisfactory glass meltability can be
attained; such SiO.sub.2 contents are hence preferred. The content
thereof is more preferably 68% or less, still more preferably 66%
or less, yet still more preferably 65% or less, especially
preferably 64% or less, most preferably 63% or less.
[0099] Al.sub.2O.sub.3 is a component effective in improving the
weatherability, improving the Young's modulus, inhibiting the glass
from suffering phase separation, reducing the coefficient of
thermal expansion, and so on. In the case where the content of
Al.sub.2O.sub.3 is 5% or higher, the effects of the inclusion of
Al.sub.2O.sub.3 are sufficiently obtained; such Al.sub.2O.sub.3
contents are hence preferred. The content of Al.sub.2O.sub.3 is
more preferably 6% or higher, still more preferably 7% or higher,
yet still more preferably 8% or higher. Meanwhile, in the case
where the content of Al.sub.2O.sub.3 is 15% or less, the glass has
satisfactory properties including meltability; such Al.sub.2O.sub.3
contents are hence preferred. The content thereof is more
preferably 14% or less, still more preferably 13% or less, yet
still more preferably 12% or less.
[0100] B.sub.2O.sub.3 is a component which improves the
meltability, and the content thereof is preferably 15% or higher.
B.sub.2O.sub.3 is also a component capable of lowering the
dielectric dissipation factor in a high-frequency range. Hence, the
content thereof is more preferably 16% or higher, still more
preferably 17% or higher, yet still more preferably 17.5% or
higher. Meanwhile, from the standpoint of obtaining satisfactory
chemical resistance, the content of B.sub.2O.sub.3 is preferably
24% or less, more preferably 23% or less, still more preferably 22%
or less.
[0101] The total content of Al.sub.2O.sub.3 and
B.sub.2O.sub.3(Al.sub.2O.sub.3+B.sub.2O.sub.3) is more preferably
20% or higher, especially preferably 25% or higher, from the
standpoint of glass meltability. From the standpoint of heightening
the low-dielectric-loss characteristics of the glass plate while
maintaining the glass meltability, etc., the total content thereof
is preferably 40% or less, more preferably 37% or less, still more
preferably 35% or less, especially preferably 33% or less.
[0102] MgO is a component which increases the Young's modulus
without increasing the specific gravity, and can thereby heighten
the specific modulus. MgO hence is effective in mitigating the
problem of deflection and can improve the fracture toughness to
heighten the glass strength. Furthermore, MgO is a component which
improves the meltability also and can inhibit the glass from having
too low a coefficient of thermal expansion. Although MgO may not be
contained, the content of MgO, if it is contained, is preferably
0.1% or higher, more preferably 0.2% or higher, still more
preferably 1% or higher, yet still more preferably 2% or higher.
Meanwhile, from the standpoint of inhibiting the glass from having
an elevated devitrification temperature, the content of MgO is
preferably 10% or less, more preferably 9% or less, still more
preferably 8% or less, yet still more preferably 7% or less,
particularly preferably 6% or less, in particular 5% or less,
especially preferably 4% or less, most preferably 3% or less.
[0103] CaO is characterized by being next to MgO among the
alkaline-earth metals in heightening the specific modulus and by
not excessively lowering the strain point, and is a component which
improves the meltability like MgO. Furthermore, CaO is a component
characterized by being less prone to heighten the devitrification
temperature than MgO. Although CaO may not be contained, the
content of CaO, if it is contained, is preferably 0.1% or higher,
more preferably 0.2% or higher, still more preferably 0.5% or
higher, yet still more preferably 1% or higher, especially
preferably 2% or higher. Meanwhile, from the standpoints of
preventing the glass from having too high an average coefficient of
thermal expansion and of inhibiting the devitrification temperature
from increasing and thereby preventing the glass from devitrifying
when produced, the content of CaO is preferably 10% or less, more
preferably 8% or less, still more preferably 7% or less, yet still
more preferably 6% or less, particularly preferably 5% or less, in
particular 4% or less, especially preferably 3% or less.
[0104] SrO is a component which improves the meltability without
heightening the devitrification temperature of the glass. Although
SrO may not be contained, the content of SrO, if it is contained,
is preferably 0.1% or higher, more preferably 0.2% or higher, still
more preferably 0.5% or higher, yet still more preferably 1% or
higher, especially preferably 2% or higher. Meanwhile, from the
standpoint of inhibiting the average coefficient of thermal
expansion from becoming too high without increasing the specific
gravity, the content of SrO is desirably 10% or less, preferably 9%
or less, more preferably 8% or less, still more preferably 7% or
less, yet still more preferably 6% or less, particularly preferably
5% or less, in particular 4% or less, especially preferably 3% or
less, most preferably 2.5% or less.
[0105] BaO is a component which improves the meltability without
heightening the devitrification temperature of the glass. Although
BaO may not be contained, the content of BaO, if it is contained,
is preferably 0.1% or higher, more preferably 0.2% or higher, still
more preferably 1% or higher, especially preferably 2% or higher.
Meanwhile, from the standpoint that too high BaO contents result in
an increased specific gravity, a reduced Young's modulus, an
elevated relative permittivity, and too high an average coefficient
of thermal expansion, the content of BaO is preferably 10% or less,
more preferably 8% or less, still more preferably 5% or less, yet
still more preferably 3% or less.
[0106] ZnO is a component which improves the chemical resistance,
but is prone to separate out and may heighten the devitrification
temperature. Because of this, the content of ZnO is preferably 0.1%
or less, more preferably 0.05% or less, still more preferably 0.03%
or less, yet still more preferably 0.01% or less. Especially
preferably, the glass composition contains substantially no ZnO.
The term "containing substantially no ZnO" means that the content
thereof is, for example, less than 0.01%.
[0107] The molar ratio represented by
{Al.sub.2O.sub.3/(Al.sub.2O.sub.3+B.sub.2O.sub.3)} is preferably
0.1 or higher from the standpoint of enabling the glass to have
improved acid resistance and excellent evenness with inhibited
phase separation. From the standpoint of imparting an improved
Young's modulus, that molar ratio is more preferably 0.3 or higher,
still more preferably 0.33 or higher, yet still more preferably
0.35 or higher, especially preferably 0.38 or higher. Meanwhile,
from the standpoint of enabling the glass to attain a reduction in
dielectric loss in a range of high frequencies not lower than 10
GHz, preferably frequencies exceeding 30 GHz, that molar ratio is
preferably 0.45 or less, more preferably 0.4 or less, still more
preferably 0.35 or less, yet still more preferably 0.3 or less.
[0108] If the contents of Al.sub.2O.sub.3, MgO, CaO, SrO, and BaO
as represented by mol % based on oxides are respectively expressed
by [Al.sub.2O.sub.3], [MgO], [CaO], [SrO], and [BaO], then the
value represented by {[Al.sub.2O.sub.3]-([MgO]+[CaO]+[SrO]+[BaO])}
is preferably larger than -3, more preferably -2 or larger, still
more preferably -1 or larger, especially preferably -0.5 or larger,
from the standpoint of acid resistance. Meanwhile, from the
standpoint of inhibiting the glass from devitrifying, the value
represented by {[Al.sub.2O.sub.3]-([MgO]+[CaO]+[SrO]+[BaO])} is
preferably less than 2, more preferably 1.5 or less, still more
preferably 1.0 or less, especially preferably 0.5 or less.
[0109] The content molar ratio represented by {(SrO+BaO)/RO} is
preferably 0.64 or higher, more preferably 0.7 or higher, still
more preferably 0.75 or higher, especially preferably 0.8 or
higher, from the standpoints of lowering the surface
devitrification temperature and improving the glass production
efficiency. Meanwhile, from the standpoint of reducing the
raw-material cost in view of the fact that raw materials for SrO
and BaO are expensive, the molar ratio is preferably 0.85 or less,
more preferably 0.8 or less. The RO represents the total content of
MgO, CaO, SrO, and BaO.
[0110] R.sub.2O represents the total content of alkali metal
oxides. Examples of the alkali metal oxides include Li.sub.2O,
Na.sub.2O, K.sub.2O, Rb.sub.2O, and Cs.sub.2O. Since Rb.sub.2O and
Cs.sub.2O, among alkali metal oxides, are rarely contained in
glasses, R.sub.2O usually means the total content of Li.sub.2O,
Na.sub.2O, and K.sub.2O (Li.sub.2O+Na.sub.2O+K.sub.2O).
[0111] The glass composition may not contain alkali metal oxides.
However, inclusion of alkali metal oxides eliminates the need of
excessive raw-material purification and makes it possible to obtain
practical glass meltability and glass plate production efficiency
and to regulate the coefficient of thermal expansion of the glass
plate. Because of this, in the case where alkali metal oxides are
contained, the total content thereof (R.sub.2O) is preferably
0.001% or higher, more preferably 0.002% or higher, still more
preferably 0.003% or higher, especially preferably 0.005% or
higher. From the standpoint of enhancing the low-dielectric-loss
characteristics of the glass plate, the total content thereof is
preferably 5% or less, more preferably 3% or less, still more
preferably 1% or less, yet still more preferably 0.2% or less,
particularly preferably 0.1% or less, especially preferably 0.05%
or less.
[0112] The content of Li.sub.2O, as one of the alkali metal oxides,
is preferably from 0 to 5%, more preferably 0.1% or higher, still
more preferably 0.2% or higher, and is more preferably 4% or less,
still more preferably 3% or less. The content of Na.sub.2O is
preferably from 0 to 5%, more preferably 0.1% or higher, still more
preferably 0.2% or higher, and is more preferably 4% or less, still
more preferably 3% or less. The content of K.sub.2O is preferably
from 0 to 5%, more preferably 0.1% or higher, still more preferably
0.2% or higher, and is more preferably 4% or less, still more
preferably 3% or less.
[0113] Besides the components shown above, Fe may be contained in
order to reduce resistance values within a melting-temperature
range, e.g., the resistance value at 1,500.degree. C. In the case
where Fe is contained, the content thereof in terms of
Fe.sub.2O.sub.3 is preferably 0.01% or higher, more preferably
0.05% or higher. However, since too high Fe contents may result in
a decrease in visible-region transmittance, the content of Fe in
terms of Fe.sub.2O.sub.3 is preferably 1% or less, more preferably
0.5% or less, still more preferably 0.1% or less.
[0114] The .beta.-OH value, which is an index to the water content
of the glass, is preferably 0.05 mm.sup.-1 or higher, more
preferably 0.1 mm.sup.-1 or higher, still more preferably 0.2
mm.sup.-1 or higher, especially preferably 0.3 mm.sup.-1 or higher,
from the standpoint of attaining a reduced resistance value in a
temperature range where raw materials for glass are melted, for
example, at around 1,500.degree. C., to make the glass suitable for
melting by electric heating. Meanwhile, from the standpoint of
diminishing bubble defects in the glass, the .beta.-OH value is
preferably 1.0 mm.sup.-1 or less, more preferably 0.8 mm.sup.-1 or
less, still more preferably 0.6 mm.sup.-1 or less, especially
preferably 0.5 mm.sup.-1 or less.
[0115] The .beta.-OH value in this description is a value
determined by examining a glass sample for absorbance for light
having wavelengths of from 2.75 to 2.95 .mu.m and dividing a
maximum absorbance .beta..sub.max by the thickness (mm) of the
sample.
[0116] The glass composition may contain at least one component
selected from the group consisting of SnO.sub.2, Cl, and SO.sub.3
for improving the refinability of the glass plate. The total
content of these (SnO.sub.2+Cl+SO.sub.3) may be from 0.01 to 1.0
mass % with respect to the total content of SiO.sub.2,
Al.sub.2O.sub.3, RO, and R.sub.2O
(SiO.sub.2+Al.sub.2O.sub.3+RO+R.sub.2O) as represented by mass %
based on oxides, which is taken as 100%. The total content thereof
is preferably 0.80 mass % or less, more preferably 0.50 mass % or
less, still more preferably 0.30 mass % or less. Meanwhile, the
total content thereof is preferably 0.02 mass % or higher, more
preferably 0.05 mass % or higher, still more preferably 0.10 mass %
or higher.
[0117] The glass composition may contain at least one component
(hereinafter referred to as "minor component") selected from the
group consisting of Sc.sub.2O.sub.3, TiO.sub.2, ZnO.sub.2,
Ga.sub.2O.sub.3, GeO.sub.2, Y.sub.2O.sub.3, ZrO.sub.2,
Nb.sub.2O.sub.5, In.sub.2O.sub.3, TeO.sub.2, HfO.sub.2,
Ta.sub.2O.sub.5, WO.sub.3, Bi.sub.2O.sub.3, La.sub.2O.sub.3,
Gd.sub.2O.sub.3, Yb.sub.2O.sub.3, and Lu.sub.2O.sub.3 for improving
the acid resistance of the glass. However, in case where the
content of minor components is too high, the glass has reduced
evenness and is prone to suffer phase separation. Consequently, the
content of minor components, in terms of the total content thereof
as represented by mol % based on oxides, is 1.0% or less. Only one
of those minor components may be contained, or two or more thereof
may be contained.
[0118] The glass composition may be made to contain F for the
purposes of improving the meltability, lowering the strain point,
lowering the glass transition temperature, lowering the annealing
point, etc. However, from the standpoint of preventing the glass
from having an increased number of bubble defects, the content of F
is preferably 1 mass % or less with respect to the total content of
SiO.sub.2, Al.sub.2O.sub.3, RO, and R.sub.2O
(SiO.sub.2+Al.sub.2O.sub.3+RO+R.sub.2O) as represented by mass %
based on oxides, which is taken as 100%.
[0119] In the case where the glass plate is for use as a window
material, this glass plate more preferably has the following
composition as represented by mol % based on oxides.
[0120] SiO.sub.2: from 55 to 80%,
[0121] Al.sub.2O.sub.3: from 0 to 15%,
[0122] SiO.sub.2+Al.sub.2O.sub.3: from 55 to 90%,
[0123] B.sub.2O.sub.3: from 0 to 15%,
[0124] MgO: from 0 to 20%,
[0125] CaO: from 0 to 20%,
[0126] SrO: from 0 to 15%,
[0127] BaO: from 0 to 15%,
[0128] MgO+CaO: from 0 to 30%,
[0129] MgO+CaO+SrO+BaO: from 0 to 30%,
[0130] Li.sub.2O: from 0 to 20%,
[0131] Na.sub.2O: from 0 to 20%,
[0132] K.sub.2O: from 0 to 20%, and
[0133] R.sub.2O (R=alkali metal): from 0 to 20%.
[0134] Each component of the composition is explained below.
[0135] SiO.sub.2 and Al.sub.2O.sub.3 are components which
contribute to an improvement in Young's modulus and thereby make it
easy to ensure the strength required of window materials for use in
building applications, motor vehicle applications, etc.
[0136] From the standpoints of ensuring weatherability and
preventing the glass plate from suffering thermal cracking due to
too high an average coefficient of linear expansion, the content of
SiO.sub.2 is preferably 55% or higher, more preferably 57% or
higher, still more preferably 60% or higher, yet still more
preferably 63% or higher, particularly preferably 65% or higher,
especially preferably 68% or higher, most preferably 70% or higher.
Meanwhile, from the standpoints of preventing the glass from having
increased melt viscosity and of thereby facilitating the glass
production, the content of SiO.sub.2 is preferably 80% or less,
more preferably 78% or less, still more preferably 75% or less,
most preferably 74% or less.
[0137] Al.sub.2O.sub.3 is a component which is for ensuring
weatherability and which prevents the glass plate from suffering
thermal cracking due to too high an average coefficient of linear
expansion. Although Al.sub.2O.sub.3 may not be contained, the
content of Al.sub.2O.sub.3, if it is contained, is preferably 0.01%
or higher, more preferably 0.05% or higher, still more preferably
0.1% or higher. Meanwhile, from the standpoints of preventing the
glass from having increased melt viscosity so that the temperature
(hereinafter referred to as T2) at which the glass has a viscosity
of 10.sup.2 dPas and the temperature (hereinafter referred to as
T4) at which the glass has a viscosity of 10.sup.4 dPas are kept
low to facilitate the glass production and of making the glass
plate have satisfactory radio-wave transmission characteristics,
the content of Al.sub.2O.sub.3 is preferably 15% or less, more
preferably 10% or less, still more preferably 5% or less, yet still
more preferably 1% or less, especially preferably 0.5% or less.
[0138] The total content of SiO.sub.2 and
Al.sub.2O.sub.3(SiO.sub.2+Al.sub.2O.sub.3) is preferably from 55 to
90% from the standpoint of obtaining a satisfactory radio-wave
transmittance. From the standpoints of ensuring weatherability and
preventing the average coefficient of linear expansion from
becoming too high, the total content thereof is more preferably 57%
or higher, still more preferably 60% or higher, yet still more
preferably 65% or higher, especially preferably 70% or higher, most
preferably 72% or higher. Meanwhile, from the standpoint of keeping
the T2 and the T4 low to render the glass easy to produce, the
total content thereof is more preferably 85% or less, still more
preferably 80% or less, yet still more preferably 78% or less,
especially preferably 75% or less.
[0139] B.sub.2O.sub.3 is a component which improves the meltability
and glass strength and heightens the radio-wave transmittance.
Meanwhile, B.sub.2O.sub.3 is a component which makes alkali
elements prone to volatilize during melting/forming, leading to a
decrease in glass quality. In addition, too high contents thereof
reduce the average coefficient of linear expansion to render the
glass difficult to physically strengthen. Because of these, the
content of B.sub.2O.sub.3 is preferably 15% or less, more
preferably 10% or less, still more preferably 8% or less, yet still
more preferably 5% or less, particularly preferably 3% or less,
especially preferably 1% or less. Most preferably, the glass
composition contains substantially no B.sub.2O.sub.3. The
expression "containing substantially no B.sub.2O.sub.3" means that
the glass composition does not contain B.sub.2O.sub.3 except for
the case where B.sub.2O.sub.3 has come into the glass as an
unavoidable impurity.
[0140] MgO is a component which accelerates the melting of the raw
materials for glass and improves the weatherability. Meanwhile,
from the standpoint of preventing devitrification to heighten the
radio-wave transmittance, the content of MgO is preferably 20% or
less, more preferably 15% or less, still more preferably 8% or
less, yet still more preferably 4% or less, especially preferably
1% or less, most preferably 0.5% or less. MgO may not be
contained.
[0141] CaO, SrO, and BaO are components which lower the dielectric
dissipation factor of the glass and can improve the meltability of
the glass. One or more of these may be contained.
[0142] CaO may not be contained. However, in the case where CaO is
contained, the content thereof is preferably 3% or higher, more
preferably 6% or higher, still more preferably 8% or higher, yet
still more preferably 10% or higher, especially preferably 110% or
higher, from the standpoints that CaO reduces the dielectric loss
of the glass to thereby improve the radio-wave transmittance and
that CaO can further bring about an improvement in meltability
(decreases in T2 and T4). Meanwhile, from the standpoints of
avoiding an increase in the specific gravity of the glass and
enabling the glass to retain the strength and low brittleness, the
content of CaO is preferably 20% or less. From the standpoint of
lower brittleness, the content thereof is more preferably 15% or
less, still more preferably 14% or less, yet still more preferably
13% or less, especially preferably 12% or less.
[0143] The content of SrO is preferably 15% or less, more
preferably 8% or less, still more preferably 3% or less, yet still
more preferably 1% or less, from the standpoints of avoiding an
increase in the specific gravity of the glass and enabling the
glass to retain the strength and low brittleness. Especially
preferably, the glass composition contains substantially no SrO.
The expression "containing substantially no SrO" means that the
glass composition does not contain SrO except for the case where
SrO has come into the glass as an unavoidable impurity.
[0144] The content of BaO is preferably 15% or less, more
preferably 5% or less, still more preferably 3% or less, yet still
more preferably 2% or less, especially preferably 1% or less, from
the standpoints of avoiding an increase in the specific gravity of
the glass and enabling the glass to retain the strength and low
brittleness. Most preferably, the glass composition contains
substantially no BaO. The expression "containing substantially no
BaO" means that the glass composition does not contain BaO except
for the case where BaO has come into the glass as an unavoidable
impurity.
[0145] The total content of MgO, CaO, SrO, and BaO
(MgO+CaO+SrO+BaO) may be 0% (none of these is contained). However,
from the standpoint of lowering the glass viscosity during
production to lower the T2 and T4 or from the standpoint of
heightening the Young's modulus, the total content thereof is
preferably higher than 0%, more preferably 0.5% or higher, still
more preferably 5% or higher, yet still more preferably 8% or
higher, especially preferably 10% or higher, most preferably 11% or
higher. Meanwhile, from the standpoint of improving the
weatherability, the total content thereof is preferably 30% or
less, more preferably 17% or less, still more preferably 16% or
less, yet still more preferably 15% or less, especially preferably
14% or less, most preferably 13% or less.
[0146] Furthermore, from the standpoint of avoiding a trouble in
which devitrification occurs during glass melting or during forming
and this results in a decrease in glass quality, the total content
of MgO and CaO (MgO+CaO) is preferably 30% or less, more preferably
25% or less, still more preferably 20% or less, yet still more
preferably 15% or less, especially preferably 13% or less. The
total content thereof may be 0% (neither is contained). However,
from the standpoint of preventing the glass from having too high
viscosity during melting/forming and from thereby becoming
difficult to produce, the total content thereof is preferably 1% or
higher, more preferably 2% or higher, still more preferably 5% or
higher, yet still more preferably 8% or higher, especially
preferably 10% or higher.
[0147] Li.sub.2O is a component which improves the meltability of
the glass and is also a component which renders the glass apt to
have an increased Young's modulus, thereby contributing to an
improvement in glass strength. Although Li.sub.2O may not be
contained, the inclusion thereof makes chemical strengthening
possible and is sometimes effective in heightening the radio-wave
transmittance. Because of this, the content of Li.sub.2O, if it is
contained, is preferably 0.1% or higher, more preferably 1% or
higher, still more preferably 2% or higher, yet still more
preferably 3% or higher, especially preferably 4% or higher.
Meanwhile, too high Li.sub.2O contents might result in
devitrification or phase separation during glass production to make
the production difficult. Hence, the content thereof is preferably
20% or less, more preferably 16% or less, still more preferably 12%
or less, yet still more preferably 8% or less, especially
preferably 7% or less, most preferably 6.5% or less.
[0148] Na.sub.2O and K.sub.2O are components which improve the
meltability of the glass, and incorporating at least either of the
two in an amount of 0.1% or larger makes it easy to regulate the T2
to 1,750.degree. C. or lower and the T4 to 1,350.degree. C. or
lower. Meanwhile, too low total contents of Na.sub.2O and K.sub.2O
might make the glass unable to have an increased average
coefficient of linear expansion and to be thermally strengthened.
Furthermore, by the inclusion of both Na.sub.2O and K.sub.2O, the
weatherability can be improved while maintaining the meltability.
There are cases where the inclusion thereof is effective also in
heightening the radio-wave transmittance.
[0149] Although Na.sub.2O may not be contained, the inclusion
thereof renders chemical strengthening possible, besides having the
effects shown above. Because of this, the content thereof is
preferably 0.1% or higher, more preferably 1% or higher, still more
preferably 3% or higher, yet still more preferably 5% or higher,
especially preferably 6% or higher. Meanwhile, from the standpoint
of preventing the glass plate from having too high an average
coefficient of thermal expansion to become prone to suffer thermal
cracking, the content of Na.sub.2O is preferably 20% or less, more
preferably 16% or less, still more preferably 14% or less, yet
still more preferably 12% or less, especially preferably 10% or
less, most preferably 8% or less.
[0150] Although K.sub.2O may not be contained, the inclusion
thereof produces the effects shown above. Because of this, the
content thereof is preferably 0.1% or higher, more preferably 0.9%
or higher, still more preferably 2% or higher, yet still more
preferably 3% or higher, especially preferably 4% or higher.
Meanwhile, from the standpoint of preventing the glass plate from
having too high an average coefficient of thermal expansion to
become prone to suffer thermal cracking and from the standpoint of
preventing the weatherability from decreasing, the content of
K.sub.2O is preferably 20% or less, more preferably 16% or less,
still more preferably 14% or less, yet still more preferably 12% or
less, especially preferably 10% or less, most preferably 8% or
less. Also from the standpoint of radio-wave transmittance,
regulating the content of K.sub.2O so as to be within that range
makes it possible to obtain a high radio-wave transmittance.
[0151] As described above, by regulating the contents of Na.sub.2O
and K.sub.2O to values within those ranges, the average coefficient
of thermal expansion can be regulated to a desired value to render
the glass plate suitable for use as window materials which
satisfactorily match with other members, e.g., black ceramics and
interlayers.
[0152] R.sub.2O represents the total content of alkali metal
oxides. Since Rb.sub.2O and Cs.sub.2O, among alkali metal oxides,
are rarely contained in glasses, R.sub.2O usually means the total
content of Li.sub.2O, Na.sub.2O, and K.sub.2O
(Li.sub.2O+Na.sub.2O+K.sub.2O).
[0153] Alkali metal oxides, although the glass composition may not
contain these, are components which lower the glass viscosity
during glass production to lower the T2 and the T4. Because of
this, the total content of alkali metal oxides, if these are
contained, is preferably higher than 0%, more preferably 1% or
higher, still more preferably 5% or higher, yet still more
preferably 6% or higher, particularly preferably 8% or higher, in
particular 10% or higher, especially preferably 11% or higher, most
preferably 12% or higher. Meanwhile, from the standpoint of
improving the weatherability, the total content thereof is
preferably 20% or less, more preferably 19% or less, still more
preferably 18.5% or less, yet still more preferably 18.0% or less,
especially preferably 17.5% or less, most preferably 17.0% or
less.
[0154] In the case where the glass composition contains one or more
alkali metal oxides, it is preferable that Na.sub.2O is contained,
and the molar ratio represented by (Na.sub.2O/R.sub.2O) is more
preferably 0.01 or higher and is more preferably 0.98 or less, from
the standpoint of sufficiently obtaining the effect of lowering the
dielectric dissipation factor. That molar ratio is still more
preferably 0.05 or higher, yet still more preferably 0.1 or higher,
particularly preferably 0.2 or higher, especially preferably 0.3 or
higher, most preferably 0.4 or higher. Meanwhile, that molar ratio
is still more preferably 0.8 or less, yet still more preferably 0.7
or less, especially preferably 0.6 or less, most preferably 0.55 or
less.
[0155] In the case where the glass composition contains one or more
alkali metal oxides, it is also preferable that K.sub.2O is
contained, and the molar ratio represented by (K.sub.2O/R.sub.2O)
is more preferably 0.01 or higher and is more preferably 0.98 or
less, from the standpoint of sufficiently obtaining the effect of
heightening the radio-wave transmittance. That molar ratio is still
more preferably 0.05 or higher, yet still more preferably 0.1 or
higher, particularly preferably 0.2 or higher, especially
preferably 0.3 or higher, most preferably 0.4 or higher. Meanwhile,
that molar ratio is still more preferably 0.8 or less, yet still
more preferably 0.6 or less, especially preferably 0.55 or
less.
[0156] It is preferable, from the standpoint of heightening the
radio-wave transmittance, that the product (R.sub.2O.times.MgO,
%.sup.2) of the total content of alkali metal oxides (R.sub.2O, %)
and the content of MgO (%) is made small. (R.sub.2O.times.MgO) is
preferably 100%.sup.2 or less, more preferably 80%.sup.2 or less,
still more preferably 66%.sup.2 or less, yet still more preferably
60%.sup.2 or less, particularly preferably 50%.sup.2 or less,
especially preferably 40%.sup.2 or less, most preferably 30%.sup.2
or less. Meanwhile, from the standpoint of improving the efficiency
of glass production, that product is preferably 1%.sup.2 or larger,
more preferably 3%.sup.2 or larger, still more preferably 5%.sup.2
or less.
[0157] ZrO.sub.2 is a component which lowers the glass viscosity
during melting to accelerate the melting and improves the heat
resistance and chemical durability. Meanwhile, too high contents
thereof may result in an increase in liquidus temperature. Because
of this, the content of ZrO.sub.2 is preferably 5% or less, more
preferably 2.5% or less, still more preferably 2% or less, yet
still more preferably 1% or less, especially preferably 0.5% or
less. Most preferably, the glass composition contains substantially
no ZrO.sub.2. The expression "containing substantially no
ZrO.sub.2" means that the glass composition does not contain
ZrO.sub.2 except for the case where ZrO.sub.2 has come into the
glass as an unavoidable impurity.
[0158] The total content of some of the components described above
which is represented by
(SiO.sub.2+Al.sub.2O.sub.3+MgO+CaO+SrO+BaO+Li.sub.2O+Na.sub.2O+K.sub.2O)
is preferably 85% or higher, more preferably 88% or higher, still
more preferably 90% or higher, yet still more preferably 92% or
higher, particularly preferably 95% or higher, especially
preferably 98% or higher, most preferably 99.5% or higher, from the
standpoint that such values of that total content not only make it
possible to produce the glass plate from easily available raw
materials for glass but also make it easy to ensure the
weatherability of the glass plate. That total content may be 100%,
and is more preferably 99.9% or less in view of cases where a
colorant, a refining agent, etc. are added to the glass plate.
[0159] The glass composition may contain at least one component
selected from the group consisting of SnO.sub.2, Cl, and SO.sub.3
for improving the refinability of the glass plate. The total
content of these (SnO.sub.2+Cl+SO.sub.3) may be from 0.01 to 1.0
mass % with respect to the total content of the main components
SiO.sub.2, Al.sub.2O.sub.3, RO, and R.sub.2O
(SiO.sub.2+Al.sub.2O.sub.3+RO+R.sub.2O) as represented by mass %
based on oxides, which is taken as 100%. The total content thereof
is preferably 0.80 mass % or less, more preferably 0.50 mass % or
less, still more preferably 0.30 mass % or less. Meanwhile, the
total content thereof is preferably 0.02 mass % or higher, more
preferably 0.05 mass % or higher, still more preferably 0.10 mass %
or higher.
[0160] In the case where the glass plate is for use as substrates
for high-frequency devices, preferred examples of the glass
transition temperature Tg, T2, T4, devitrification temperature,
Young's modulus, acid resistance, alkali resistance, coefficient of
expansion (average coefficient of expansion), strain point,
density, plate thickness, and principal-surface area of the glass
plate are as follows.
[0161] The glass transition temperature Tg is preferably
580.degree. C. or higher, more preferably 600.degree. C. or higher,
from the standpoint of preventing the substrate from deforming in
high-frequency device production steps. Meanwhile, from the
standpoint of easily producing the glass plate, the Tg is
preferably 750.degree. C. or lower, more preferably 720.degree. C.
or lower. Values of glass transition temperature Tg are measured in
accordance with JIS R 3103-3:2001.
[0162] The T2 is preferably 1,950.degree. C. or lower, more
preferably 1,700.degree. C. or lower, from the standpoint of easily
producing the glass plate. Meanwhile, from the standpoint of
reducing the convection of the molten glass to make the
glass-melting apparatus less apt to be damaged, the T2 is
preferably 1,500.degree. C. or higher.
[0163] The T4 is preferably 1,350.degree. C. or lower, more
preferably 1,300.degree. C. or lower, from the standpoint of
protecting the production apparatus. Meanwhile, from the standpoint
that a decrease in the quantity of heat carried into the forming
apparatus by the glass results in the necessity of increasing the
quantity of heat to be inputted to the forming apparatus, the T4 is
preferably 1,100.degree. C. or higher.
[0164] Values of T2 and T4 are measured with a rotary
high-temperature viscometer.
[0165] The devitrification temperature is preferably 1,350.degree.
C. or lower, more preferably 1,300.degree. C. or lower, from the
standpoint that in glass-plate forming, such devitrification
temperatures enable the members of the forming apparatus to have
lowered temperatures and hence prolonged lives. Meanwhile, although
there is no particular lower limit on devitrification temperature,
the devitrification temperature may be 1,000.degree. C. or higher,
or may be 1,050.degree. C. or higher. The devitrification
temperature is determined by placing particles of a crushed glass
on a dish made of platinum, heat-treating the glass particles for
17 hours in electric furnaces having constant temperatures,
examining the heat-treated sample with an optical microscope to
determine a highest temperature which has resulted in crystal
precipitation in the surface and inside of the glass and a lowest
temperature which has not resulted in crystal precipitation, and
taking an average of the highest and the lowest temperatures as the
devitrification temperature.
[0166] The Young's modulus is preferably 50 GPa or higher, more
preferably 55 GPa or higher, from the standpoint that such values
of Young's modulus are effective in reducing the amount in which
the glass plate deflects when used in high-frequency device
production steps. Although there is no particular upper limit on
Young's modulus, the Young's modulus may be 100 GPa or less. Values
of Young's modulus are measured with an ultrasonic-pulse Young's
modulus meter.
[0167] The term "acid resistance" means the amount of glass
components extracted per unit surface area when the glass plate is
immersed in an aqueous acid solution (6 wt % HNO.sub.3+5 wt %
H.sub.2SO.sub.4; 45.degree. C.) for 170 seconds. The extraction
amount indicating the acid resistance is preferably 0.05 g/cm.sup.2
or less, more preferably 0.03 g/cm.sup.2 or less, from the
standpoint of preventing the glass surfaces from being roughened
when cleaned with an acid solution. Although there is no particular
lower limit on extraction amount, the extraction amount may be
0.001 g/cm.sup.2 or larger.
[0168] The term "alkali resistance" means the amount of glass
components extracted per unit surface area when the glass plate is
immersed in an aqueous alkali solution (1.2 wt % NaOH; 60.degree.
C.) for 30 minutes. The extraction amount indicating the alkali
resistance is preferably 0.10 g/cm.sup.2 or less, more preferably
0.08 g/cm.sup.2 or less, from the standpoint of preventing the
glass surfaces from being roughened when cleaned with an alkali
solution. Although there is no particular lower limit on extraction
amount, the extraction amount may be 0.001 g/cm.sup.2 or
larger.
[0169] As the coefficient of expansion, use is made of values of
the average coefficient of thermal expansion measured with a
thermodilatometer in the temperature range of from 50 to
350.degree. C. The average coefficient of thermal expansion is
preferably 20.times.10.sup.-7 (K.sup.-1) or higher, more preferably
25.times.10.sup.-7 (K.sup.-1) or higher, from the standpoint of
more suitably regulating the difference in thermal expansion
coefficient between the glass plate and each of other members in
configuring, for example, a semiconductor package as a
high-frequency device. Meanwhile, the average coefficient of
thermal expansion is preferably 60.times.10.sup.-7 (K.sup.-1) or
less, more preferably 50.times.10.sup.7 (K.sup.1) or less.
[0170] The strain point is preferably 500.degree. C. or higher,
more preferably 550.degree. C. or higher, from the standpoint of
heat resistance. Meanwhile, from the standpoint of facilitating
relaxation, the strain point is preferably 800.degree. C. or lower.
Values of strain point are measured in accordance with JIS R 3103-2
(2001).
[0171] The density is preferably 2.8 g/cm.sup.3 or less from the
standpoint of making the glass plate lightweight. Although there is
no particular lower limit on density, the density may be 2.0
g/cm.sup.3 or higher. Values of density are determined by the
Archimedes method.
[0172] The plate thickness is preferably 0.05 mm or larger, more
preferably 0.1 mm or larger, still more preferably 0.3 mm or
larger, from the standpoint of ensuring the strength required of
substrates. Meanwhile, from the standpoints of thickness reduction,
size reduction, improvement in production efficiency, etc., the
plate thickness is preferably 2.0 mm or less, more preferably 1.5
mm or less, still more preferably 1.0 mm or less, yet still more
preferably 0.7 mm or less, especially preferably 0.5 mm or
less.
[0173] In the case where the glass plate is for use as the
substrate of a high-frequency device, the area of each principal
surface of the glass plate is preferably 80 cm.sup.2 or larger,
more preferably 350 cm.sup.2 or larger, still more preferably 500
cm.sup.2 or larger, yet still more preferably 1,000 cm.sup.2 or
larger, even still more preferably 1,500 cm.sup.2 or larger, and
especially preferably 2,000 cm.sup.2 or larger, 2,500 cm.sup.2 or
larger, 3,000 cm.sup.2 or larger, 4,000 cm.sup.2 or larger, 6,000
cm.sup.2 or larger, 8,000 cm.sup.2 or larger, 12,000 cm.sup.2 or
larger, 16,000 cm.sup.2 or larger, 20,000 cm.sup.2 or larger, and
25,000 cm.sup.2 or larger in order of increasing preference.
Meanwhile, the area of the principal surface of the substrate is
usually preferably 5,000,000 cm.sup.2 or less. Even when having
such a large area, this glass plate has a narrow in-plane
distribution of dielectric dissipation factor and is homogeneous.
Because of this, the glass plate is suitable for use in producing
large-area high-frequency devices and in windows for transmitting
high-frequency waves, etc., unlike conventional glass plates. The
area of the principal surface of the substrate is more preferably
100,000 cm.sup.2 or less, still more preferably 80,000 cm.sup.2 or
less, yet still more preferably 60,000 cm.sup.2 or less, especially
preferably 50,000 cm.sup.2 or less, particularly preferably 40,000
cm.sup.2 or less, most preferably 30,000 cm.sup.2 or less.
[0174] In the case where the glass plate is for use as window
materials, preferred examples of the glass transition temperature
Tg, T2, T4, devitrification temperature, Young's modulus, acid
resistance, alkali resistance, coefficient of expansion (average
coefficient of expansion), strain point, density, plate thickness,
and principal-surface area of the glass plate are as follows.
Methods for determining these properties are the same as those used
for determining the properties in the case of the use as substrates
for high-frequency devices.
[0175] The glass transition temperature Tg is preferably
500.degree. C. or higher, more preferably 520.degree. C. or higher,
from the standpoint of performing glass bending. Meanwhile, the Tg
is preferably 620.degree. C. or lower, more preferably 600.degree.
C. or lower, from the standpoint of performing strengthening by air
chilling.
[0176] The T2 is preferably 1,550.degree. C. or lower, more
preferably 1,480.degree. C. or lower, from the standpoint of easily
producing the glass plate. Meanwhile, from the standpoint of
reducing the convection of the molten glass to make the
glass-melting apparatus less apt to be damaged, the T2 is
preferably 1,250.degree. C. or higher.
[0177] The T4 is preferably 1,200.degree. C. or lower, more
preferably 1,100.degree. C. or lower, from the standpoint of
protecting the production apparatus. Meanwhile, from the standpoint
that a decrease in the quantity of heat carried into the forming
apparatus by the glass results in the necessity of increasing the
quantity of heat to be inputted to the forming apparatus, the T4 is
preferably 900.degree. C. or higher.
[0178] The devitrification temperature is preferably 1,100.degree.
C. or lower, more preferably 1,000.degree. C. or lower, from the
standpoint that in glass-plate forming, such devitrification
temperatures enable the members of the forming apparatus to have
lowered temperatures and hence prolonged lives. Meanwhile, although
there is no particular lower limit on devitrification temperature,
the devitrification temperature may be 900.degree. C. or
higher.
[0179] The Young's modulus is preferably 50 GPa or higher, more
preferably 55 GPa or higher, from the standpoint of attaining a
reduced deflection amount. Although there is no particular upper
limit on Young's modulus, the Young's modulus may be 100 GPa or
less.
[0180] The acid resistance is such that the extraction amount shown
above is preferably 0.1 g/cm.sup.2 or less, more preferably 0.05
g/cm.sup.2 or less, from the standpoint of preventing the glass
surfaces from being roughened when cleaned with an acid solution.
Although there is no particular lower limit on extraction amount,
the extraction amount may be 0.001 g/cm.sup.2 or larger.
[0181] The alkali resistance is such that the extraction amount
shown above is preferably 0.20 g/cm.sup.2 or less, more preferably
0.10 g/cm.sup.2 or less, from the standpoint of preventing the
glass surfaces from being roughened when cleaned with an alkali
solution. Although there is no particular lower limit on extraction
amount, the extraction amount may be 0.001 g/cm.sup.2 or
larger.
[0182] As the coefficient of thermal expansion, use is made of
values of the average coefficient of thermal expansion within the
temperature range of from 50 to 350.degree. C. The average
coefficient of thermal expansion is preferably 60.times.10.sup.-7
(K.sup.-1) or higher, more preferably 70.times.10.sup.-7 (K.sup.-1)
or higher, from the standpoint of facilitating strengthening by air
chilling. Meanwhile, from the standpoint that too high average
coefficients of thermal expansion result in poor thermal shock
resistance, the average coefficient of thermal expansion is
desirably 130.times.10.sup.-7 (K.sup.-1) or less, preferably
110.times.10.sup.-7 (K.sup.-1) or less.
[0183] The strain point is preferably 450.degree. C. or higher,
more preferably 500.degree. C. or higher, from the standpoint of
heat resistance. Meanwhile, from the standpoint of facilitating
relaxation, the strain point is preferably 700.degree. C. or lower.
Values of strain point are measured in accordance with JIS R 3103-2
(2001).
[0184] The density is preferably 2.8 g/cm.sup.3 or less from the
standpoint that too high densities make the glass plate too heavy
and difficult to handle in conveyance. Although there is no
particular lower limit on density, the density may be 2.0
g/cm.sup.3 or higher.
[0185] The plate thickness is preferably 1.0 mm or larger, more
preferably 1.5 mm or larger, from the standpoint of ensuring the
rigidity required of window materials. Meanwhile, from the
standpoint of weight reduction, the plate thickness is preferably
6.0 mm or less, more preferably 5.0 mm or less.
[0186] In the case where the glass plate is for use as a window
material, the area of each principal surface of the glass plate is
preferably 350 cm.sup.2 or larger, more preferably 500 cm.sup.2 or
larger, still more preferably 1,000 cm.sup.2 or larger, even still
more preferably 1,500 cm.sup.2 or larger, and especially preferably
2,000 cm.sup.2 or larger, 2,500 cm.sup.2 or larger, 3,000 cm.sup.2
or larger, 4,000 cm.sup.2 or larger, 6,000 cm.sup.2 or larger,
8,000 cm.sup.2 or larger, 12,000 cm.sup.2 or larger, 16,000
cm.sup.2 or larger, 20,000 cm.sup.2 or larger, and 25,000 cm.sup.2
or larger in order of increasing preference.
[0187] Meanwhile, the area of the principal surface of the window
material is usually 6,000,000 cm.sup.2 or less. Even when having
such a large area, this glass plate has a narrow in-plane
distribution of dielectric dissipation factor and is homogeneous.
Because of this, the glass plate is suitable for use in producing
large-area high-frequency devices and in windows for transmitting
high-frequency waves, etc., unlike conventional glass plates. Since
too large principal-surface areas are undesirable from the
standpoint of ensuring the homogeneity of the glass plate, the area
of the principal surface of the window material is more preferably
100,000 cm.sup.2 or less, still more preferably 80,000 cm.sup.2 or
less, yet still more preferably 60,000 cm.sup.2 or less, especially
preferably 50,000 cm.sup.2 or less, particularly preferably 40,000
cm.sup.2 or less, most preferably 30,000 cm.sup.2 or less.
[0188] It is preferable that both the tan .delta.A and the
.epsilon.rA are small. By configuring the glass plate so as to have
such values of tan .delta.A and .epsilon.rA, the glass plate is
rendered applicable to large-area high-frequency devices, windows
for transmitting high-frequency waves, etc. unlike conventional
glass plates. The tan .delta.A is preferably 0.009 or less, more
preferably 0.008 or less, 0.007 or less, 0.006 or less, and 0.005
or less in order of increasing preference, still more preferably
0.004 or less, especially preferably 0.0035 or less, particularly
preferably 0.003 or less, most preferably 0.0025 or less.
[0189] There is no particular lower limit on tan .delta.A. However,
from the standpoint of actually producing the glass plate, the tan
.delta.A is 0.0001 or larger, more preferably 0.0004 or larger,
still more preferably 0.0006 or larger, yet still more preferably
0.0008 or larger, most preferably 0.001 or larger. The .epsilon.rA
is preferably 6.8 or less, more preferably 6.5 or less, 6.0 or
less, 5.5 or less, 5.2 or less, and 4.9 or less in order of
increasing preference, still more preferably 4.7 or less,
especially preferably 4.5 or less, particularly preferably 4.4 or
less, most preferably 4.3 or less.
[0190] There is no particular lower limit on .epsilon.rA. However,
from the standpoint of actually producing the glass plate, the
.epsilon.rA is 3.5 or higher, more preferably 3.6 or higher, still
more preferably 3.7 or higher, especially preferably 3.8 or higher,
particularly preferably 3.9 or higher, most preferably 4.0 or
higher.
<Process for Producing Glass Plate>
[0191] The process of glass plate production according to this
embodiment includes, in the following order: a melting/forming step
in which raw materials for glass are melted to obtain a molten
glass and the molten glass is formed into a plate shape; a cooling
step in which the molten glass formed into the plate shape is
cooled to a temperature of (Tg-300).degree. C. or lower with
respect to the glass transition temperature Tg (.degree. C.) to
obtain a glass base plate; and a heat treatment step in which the
obtained glass base plate is heated from the temperature of
(Tg-300).degree. C. or lower to a temperature in a range of from
(Tg-100).degree. C. to (Tg+50).degree. C., without being heated to
a temperature exceeding (Tg+50).degree. C., and is then cooled
again to (Tg-300).degree. C. or lower.
[0192] The heat treatment step is conducted one, two, or three or
more times.
[0193] Each heat treatment step extends until the temperature of
the glass base plate exceeds (Tg-300).degree. C., thereafter
reaches a maximum temperature Temax (.degree. C.) in a range of
from (Tg-100).degree. C. to (Tg+50).degree. C., and then declines
again to (Tg-300).degree. C. or lower.
[0194] A total time period in which the temperature of the glass
base plate is in the range of from (Tg-100).degree. C. to
(Tg+50).degree. C. in the whole heat treatment step(s) is K
(minutes) or longer, the K being represented by the following
formula (1) using the maximum temperature Tmax (.degree. C.) of the
glass base plate in the whole heat treatment step(s).
[0195] Each heat treatment step satisfies the following formula
(2), where t1 (minutes) is a time period in the step from a time
when the temperature of the glass base plate lastly begins to
decline from the maximum temperature Temax (.degree. C.) to a time
when the temperature of the glass base plate lastly passes
(Tg-110).degree. C.
K=[{(Tg+50)-Tmax}/10]+15 Formula (1)
{Temax-(Tg-110)}/t1.ltoreq.10 Formula (2)
[0196] Thus, the glass plate described above under <Glass
Plate> is obtained.
(Melting/forming Step)
[0197] In the melting/forming step, which is a step for melting raw
materials for glass to obtain a molten glass and forming the molten
glass into a plate shape, conventionally known methods can be used
without particular limitations. One example of the step is shown
below.
[0198] Raw materials for glass are prepared so as to result in a
desired composition of the glass plate. The raw materials are
continuously introduced into a melting furnace and heated to
preferably about 1,450 to 1,750.degree. C. to obtain a molten
glass.
[0199] Usable as the raw materials are oxides, carbonates,
nitrates, sulfates, hydroxides, halides such as chlorides, etc. In
the case where the melting and refining steps include a step in
which the molten glass comes into contact with platinum, fine
platinum particles are sometimes released into the molten glass and
undesirably come as a foreign substance into the glass plate being
obtained. Use of raw-material nitrates has the effect of inhibiting
the inclusion of platinum as a foreign substance.
[0200] Usable as the nitrates are strontium nitrate, barium
nitrate, magnesium nitrate, calcium nitrate, etc. It is more
preferred to use strontium nitrate. With respect to the particle
size of the raw materials, use can suitably be made of raw
materials ranging from a raw material composed of particles which
have a large particle diameter of several hundred micrometers but
do not remain undissolved to a raw material composed of particles
which have a small particle diameter of about several micrometers
and which neither fly off when conveyed nor aggregate to form
secondary particles. It is also possible to use granules. The water
content of each raw material can be suitably regulated in order to
prevent the raw material from flying off. The melting conditions
regarding .beta.-OH value and the degree of oxidation-reduction of
Fe (redox [Fe.sup.2+/(Fe.sup.2++Fe.sup.3+)]) can be suitably
regulated.
[0201] Next, a refining step for removing bubbles from the obtained
molten glass may be conducted. In the refining step, a method of
degassing by depressurization may be used, or degassing may be
conducted by heating the molten glass to a temperature higher than
the temperature used for melting the raw materials. SO.sub.3 or
SnO.sub.2 may be used as a refining agent.
[0202] Preferred SO.sub.3 sources are sulfates of at least one
element selected from Al, Li, Na, K, Mg, Ca, Sr, and Ba. More
preferred are sulfates of alkali metals. Of these, Na.sub.2SO.sub.4
is especially preferred because this sulfate is highly effective in
enlarging bubbles and shows satisfactory initial solubility. Also
sulfates of alkaline-earth metals may be used. Of these,
CaSO.sub.4.2H.sub.2O, SrSO.sub.4, and BaSO.sub.4 are more preferred
because these sulfates are highly effective in enlarging
bubbles.
[0203] As a refining agent in the method of degassing by
depressurization, it is preferred to use a halogen such as Cl or
F.
[0204] Preferred Cl sources are chlorides of at least one element
selected from Al, Mg, Ca, Sr, and Ba. More preferred are chlorides
of alkaline-earth metals. Of these, SrCl.sub.2.6H.sub.2O and
BaCl.sub.2.2H.sub.2O are especially preferred because these
chlorides are highly effective in enlarging bubbles and have low
deliquescence.
[0205] Preferred F sources are fluorides of at least one element
selected from Al, Na, K, Mg, Ca, Sr, and Ba. More preferred are
fluorides of alkaline-earth metals. Of these, CaF.sub.2 is still
more preferred because this fluoride is highly effective in
enhancing the meltability of raw materials for glass.
[0206] Tin compounds represented by SnO.sub.2 evolve O.sub.2 gas in
glass melts. In glass melts, SnO.sub.2 is reduced to SnO at
temperatures not lower than 1,450.degree. C. to evolve O.sub.2 gas
and thereby function to grow the bubbles. In producing glass
plates, raw materials for glass are melted by heating to about
1,450 to 1,750.degree. C. and, hence, the bubbles in the glass melt
are more effectively enlarged.
[0207] Next, a forming step is conducted in which the molten glass,
preferably the molten glass from which bubbles have been removed in
the refining step, is formed into a plate shape to obtain a glass
ribbon.
[0208] In the forming step, use can be made of a known method for
forming a glass into a plate shape, such as a float process in
which a molten glass is poured onto a molten metal, e.g., tin, and
thereby formed into a plate shape to obtain a glass ribbon, an
overflow downdraw process (fusion process) in which a molten glass
is caused to flow downward from a trough member, or a slit downdraw
process in which a molten glass is caused to flow down through a
slit.
[0209] The molten glass may be subjected as such to the subsequent
cooling step without being formed into a plate shape.
(Cooling Step)
[0210] The molten glass obtained in the forming step is cooled to a
temperature of (Tg-300).degree. C. or lower with respect to the
glass transition temperature Tg (.degree. C.) to obtain a glass
base plate. For this cooling, any desired average cooling rate can
be employed without particular limitations thereon. For example,
from the standpoint of preventing the glass from devitrifying, the
average cooling rate is preferably 10.degree. C./min or higher,
more preferably 40.degree. C./min or higher. Meanwhile, from the
standpoint of preventing the glass from coming to have a strain
therein in the cooling step, the average cooling rate is preferably
1,000.degree. C./min or less, more preferably 100.degree. C./min or
less. An average cooling rate from (Tg+50).degree. C. to
(Tg-100).degree. C. is preferably higher than 10.degree. C./min,
more preferably 15.degree. C./min or higher.
[0211] The term "average cooling rate", in the case where the
center and edge portions of the glass plate differ in cooling rate,
means an average value determined from refractive indexes. The
cooling rates of the center and the edge portions can be determined
by measuring the respective refractive indexes.
(Heat Treatment Step)
[0212] After the cooling step, a heat treatment step is conducted
in which the obtained glass base plate is heated from the
temperature of (Tg-300) .degree. C. or lower to a temperature in
the range of from (Tg-100).degree. C. to (Tg+50).degree. C.,
without being heated to a temperature exceeding (Tg+50).degree. C.,
and is then cooled again to (Tg-300).degree. C. or lower. This heat
treatment step may be conducted only once or may be conducted two
or three or more times.
[0213] Each heat treatment step extends until the temperature of
the glass base plate exceeds (Tg-300).degree. C., thereafter
reaches a maximum temperature Temax (.degree. C.) in a range of
from (Tg-100).degree. C. to (Tg+50).degree. C., and then declines
again to (Tg-300).degree. C. or lower.
[0214] In each heat treatment step, the heating rate from above the
(Tg-300).degree. C. to the range of from (Tg-100).degree. C. to
(Tg+50).degree. C. is not particularly limited. Before the
temperature of the glass base plate reaches the range of from
(Tg-100).degree. C. to (Tg+50).degree. C., the glass base plate may
be repeatedly heated and cooled or may be held at a certain
temperature.
[0215] The total time period in which the temperature of the glass
base plate is in the range of from (Tg-100).degree. C. to
(Tg+50).degree. C. in the whole heat treatment step(s) is K
(minutes) or longer, the K being represented by the following
formula (1) using the maximum temperature Tmax (.degree. C.) of the
glass base plate in the whole heat treatment step(s).
K=[{(Tg+50)-Tmax}/10]+15 Formula (1)
[0216] In the case where the heat treatment step is conducted two
or more times, the total time period in which the temperature of
the glass base plate is in the range of from (Tg-100).degree. C. to
(Tg+50).degree. C. is the sum of the time period in the first heat
treatment step when the temperature of the glass base plate is in
the range of from (Tg-100).degree. C. to (Tg+50).degree. C. and the
time period in the second and any succeeding heat treatment steps
when the temperature of the glass base plate is in the range. In
the case where the total time period in which the temperature of
the glass base plate is in the range of from (Tg-100).degree. C. to
(Tg+50).degree. C. is K (minutes) or longer, an improvement in
radio-wave transparency is attained.
[0217] The total time period in which the temperature of the glass
base plate is in the range of from (Tg-100).degree. C. to
(Tg+50).degree. C. is preferably (K+5) minutes or longer, more
preferably (K+10) minutes or longer. Although there is no
particular upper limit thereon, that total time period is
preferably (K+60) minutes or shorter, more preferably (K+45)
minutes or shorter, still more preferably (K+30) minutes or
shorter, from the standpoint of heightening the production
efficiency.
[0218] So long as the total time period in which the temperature of
the glass base plate is in the range of from (Tg-100).degree. C. to
(Tg+50).degree. C. is K (minutes) or longer, the glass base plate
is not particularly limited in temperature profile. That is, the
glass base plate may be repeatedly heated and cooled in one heat
treatment step so that, for example, the glass base plate is heated
to a temperature in the range of from (Tg-100).degree. C. to
(Tg+50).degree. C., subsequently cooled to a temperature higher
than (Tg-300).degree. C. but lower than (Tg+50).degree. C., and
then heated again to a temperature in the range of from
(Tg-100).degree. C. to (Tg+50).degree. C. Moreover, the glass base
plate may be held at a certain temperature.
[0219] Although the lower limit of that temperature range is
(Tg-100).degree. C. from the standpoint of improving the radio-wave
transparency, the lower limit is preferably (Tg-90).degree. C. or
higher, more preferably (Tg-80).degree. C. or higher. Furthermore,
although the upper limit of that temperature range is
(Tg+50).degree. C. from the standpoint of preventing the glass from
deforming, the upper limit is preferably (Tg+40).degree. C. or
lower, more preferably (Tg+35).degree. C. or lower.
[0220] Each heat treatment step satisfies the following formula
(2), where t1 (minutes) is a time period in each heat treatment
step from a time when the temperature of the glass base plate
lastly begins to decline from the maximum temperature Temax
(.degree. C.) to a time when the temperature of the glass base
plate lastly passes (Tg-110).degree. C. In the case where the heat
treatment step is conducted only once, the Temax (.degree. C.) is
the same as the Tmax (.degree. C.). In the case where the heat
treatment step is conducted two or more times, the highest
temperature of the two or more values of Temax (.degree. C.) is the
Tmax (.degree. C.).
{Temax-(Tg-110)}/t1.ltoreq.10 Formula (2)
[0221] The glass base plate can have various temperature profiles,
examples of which include: the aforementioned case where the glass
base plate is heated to a temperature in the range of from
(Tg-100).degree. C. to (Tg+50).degree. C., subsequently cooled to a
temperature higher than (Tg-300).degree. C. but lower than
(Tg+50).degree. C., and then heated again to a temperature in the
range of from (Tg-100).degree. C. to (Tg+50).degree. C.; the case
where the glass base plate is heated and cooled in the temperature
range of from (Tg-100).degree. C. to (Tg+50).degree. C. and thereby
undergoes temperature changes; and the case where the glass base
plate is held at a certain temperature in the temperature range of
from (Tg-100).degree. C. to (Tg+50).degree. C.
[0222] In such various temperature profiles, the expression "the
time when the temperature of the glass base plate lastly begins to
decline from the maximum temperature Temax (.degree. C.)", in the
case where the temperature of the glass base plate reaches the
maximum temperature Temax (.degree. C.) only once, means this time.
In the case where the temperature of the glass base plate reaches
the maximum temperature Temax (.degree. C.) two or more times, that
expression means the last of the times of reaching the Temax
(.degree. C.). Furthermore, in the case where the glass base plate
is held for a certain time period at the maximum temperature Temax
(C), that expression means the last time when the holding ends.
[0223] The same applies also to the time when the temperature of
the glass base plate lastly passes (Tg-110).degree. C. That is,
after the time when the temperature of the glass base plate has
lastly begun to decline from the maximum temperature Temax
(.degree. C.) and before the temperature thereof declines to
(Tg-300).degree. C. or lower, the glass base plate may be
repeatedly heated and cooled or may be held at a certain
temperature. In the case where the temperature of the glass base
plate passes (Tg-110).degree. C. only once before declining to
(Tg-300).degree. C. or lower, the expression "the time when the
temperature of the glass base plate lastly passes (Tg-110).degree.
C." means that time when the temperature of the glass base plate
passes (Tg-110).degree. C. In the case where the temperature of the
glass base plate passes (Tg-110).degree. C. at one time, thereafter
rises again to above (Tg-110).degree. C., and then declines again,
that expression means the time when the temperature of the glass
base plate passes (Tg-110).degree. C. during the final cooling.
Moreover, in the case where the glass base plate is held at
(Tg-110).degree. C. for a certain time period, that expression
means the last time when the holding ends.
[0224] Temperature profiles in the heat treatment step other than
those described above are not particularly limited.
[0225] In each heat treatment step, it is preferable from the
standpoint of shortening the production steps that the temperature
of the glass base plate which has first become lower than
(Tg-110).degree. C. after having declined from the maximum
temperature Temax (.degree. C.) does not exceed (Tg-110).degree. C.
again.
[0226] It is also preferable that in each heat treatment step, if
any two times in the step which lie between the time when the
temperature of the glass base plate lastly begins to decline form
the maximum temperature Temax (.degree. C.) and the time when the
temperature of the glass base plate lastly passes (Tg-110).degree.
C. are expressed by t2 (minutes) and t3 (minutes) and if t2<t3,
then the t2 and the t3 have a difference in time therebetween of 1
minute or more, and if the temperature of the glass base plate at
the t2 is expressed by Te2 and the temperature of the glass base
plate at the t3 is expressed by Te3, then the Te2 and the Te3
satisfy the following formula (3).
(Te2-Te3)/(t3-t2).ltoreq.10 Formula (3)
[0227] Formula (3) indicates that the cooling rate at the time t1
is not too high. In the case where the relationship of formula (3)
is satisfied, a sufficient heat treatment period can be ensured.
Such heat treatment step is hence preferred.
[0228] The value represented by (Te2-Te3)/(t3-t2) is more
preferably 9 or smaller, still more preferably 8 or smaller.
Although there is no particular lower limit thereon, that value may
be 0.1 or larger from the standpoint of preventing the glass plate
production from requiring too long a period.
[0229] In a final heat treatment step, if an average cooling rate
of the center of the glass base plate and an average cooling rate
of an edge portion of the glass base plate in cooling from the
maximum temperature Temax (.degree. C.) to (Tg-300).degree. C. or
lower are respectively expressed by VC (.degree. C./min) and VE
(.degree. C./min), then the ratio represented by VC/VE is
preferably as close to 1 as possible, because such values of the
ratio make it possible to obtain a homogeneous glass plate.
Specifically, that ratio is preferably 0.8 or larger, more
preferably 0.9 or larger, and is preferably 1.2 or less, more
preferably 1.1 or less, most preferably 1.
[0230] The glass base plate which has been cooled to
(Tg-300).degree. C. or lower in the heat treatment step is
successively cooled to room temperature (e.g., 50.degree. C. or
lower), thereby obtaining the glass plate according to this
embodiment.
[0231] Conditions for the cooling to room temperature are not
particularly limited. For example, the average cooling rate from
(Tg-300).degree. C. to 50.degree. C. is preferably 0.5.degree.
C./min or higher and is preferably 50.degree. C./min or less.
Meanwhile, natural cooling may be conducted without performing
temperature control.
[0232] The process for glass plate production is not limited to the
embodiment described above, and modifications, improvements, etc.
within ranges where the object of the present invention is
achievable are included in the present invention.
[0233] For example, in producing a glass plate, a molten glass may
be formed into a plate shape using a press forming method in which
the glass is directly formed into a plate shape. After the glass
plate has been obtained, this glass plate can be subjected to any
desired treatments, processing, etc., such as, for example,
strengthening by air chilling, chemical strengthening, and
polishing.
[0234] In the melting of raw materials for glass and in refining,
use may be made of not only a melting tank made of a refractory but
also a crucible (hereinafter referred to as "platinum crucible")
made of platinum or an alloy including platinum as a main
component, as a melting tank and/or a refining tank.
[0235] In a melting step in the case of using a platinum crucible,
raw materials are prepared so as to result in the composition of a
glass plate to be obtained, and the platinum crucible containing
the raw materials is heated in an electric furnace preferably to
about 1,450.degree. C. to 1,700.degree. C. A platinum stirrer is
inserted thereinto to stir the contents for from 1 to 3 hours,
thereby obtaining a molten glass.
[0236] In a forming step in steps for glass plate production using
the platinum crucible, the molten glass may be poured, for example,
onto a carbon plate or into a mold to form the molten glass into a
plate shape or a block shape.
[0237] By using the thus-obtained glass plate as the substrate of a
high-frequency device, the propagation loss of high-frequency
signals can be reduced to improve the properties, e.g., quality and
intensity, of the high-frequency signals. Because of this,
substrates constituted of this glass plate are suitable for use in
high-frequency devices in which high-frequency signals of 3.0 GHz
or higher are handled. The substrates are suitable also for use in
high-frequency devices in which signals in various high-frequency
bands are handled, such as signals having frequencies of 3.5 GHz or
higher, 10 GHz or higher, 30 GHz or higher, 35 GHz or higher,
etc.
[0238] The high-frequency devices are not particularly limited.
Examples thereof include high-frequency devices (electronic
devices) such as semiconductor devices for use in communication
appliances such as portable telephones, smartphones, portable
digital assistants, and Wi-Fi appliances, surface acoustic wave
(SAW) devices, radar components such as radar transceivers, and
antenna components such as liquid-crystal antennas.
[0239] Besides being suitable for those applications, this glass
plate is suitable also for use as window materials for vehicles,
e.g., motor vehicles, and buildings. This is because there are
cases where those high-frequency devices in which high-frequency
signals are handled are disposed in vehicles like millimeter-wave
radars. Furthermore, there are frequently cases where
high-frequency devices are used in buildings like communication
appliances and base stations. Because of this, the glass plate is
exceedingly useful in reducing the propagation loss of
high-frequency signals in the window materials.
[0240] In the case where the glass plate is to be used as a window
material, this glass plate, besides being a glass plate formed into
a flat-plate shape by, for example, a float process or a fusion
process, may be a bent glass plate obtained by forming the
flat-plate-shaped glass plate into a curved shape by gravitational
forming, press forming, etc. The glass plate can be deformed at
will before use in accordance with where the glass plate is to be
disposed.
[0241] The glass constituting the glass plate is not particularly
limited to soda-lime glass, aluminosilicate glass, alkali-free
glass, etc., and an appropriate glass can be selected in accordance
with applications. Furthermore, the glass may be a strengthened
glass having a compression stress layer in the glass surfaces and a
tensile stress layer in an inner portion of the glass. As the
strengthened glass, use can be made of either a chemically
strengthened glass or a glass strengthened by air chilling
(physically strengthened glass).
EXAMPLES
[0242] The present invention is described in greater detail below
by referring to Examples, but the present invention is not limited
to these Examples.
Examples 1 to 4
[0243] Raw material for glass were put in a platinum crucible so as
to result in the composition which is Composition 1 shown in Table
1, and were melted by heating at 1,650.degree. C. for 3 hours in an
electric furnace, thereby obtaining a molten glass. In the melting,
a platinum stirrer was inserted into the platinum crucible and the
contents were stirred therewith for 1 hour to homogenize the glass.
The molten glass was poured onto a carbon plate and thereby formed
into a plate shape (melting/forming step).
[0244] Thereafter, the plate-shaped molten glass was introduced
into an electric furnace having a temperature of about
(Tg+50).degree. C. and the temperature was maintained for 1 hour.
Thereafter, the glass was cooled to room temperature .degree. C. at
an average cooling rate of 1.degree. C./min to obtain glass base
plates (cooling step).
[0245] Subsequently, the glass base plates were heated to
630.degree. C. at 10.degree. C./min and held at 630.degree. C. for
the time periods shown in Table 2 in the row "Holding period
(min)". Thereafter, the glass base plates were cooled in the
electric furnace from 630.degree. C. to (Tg-300).degree. C. at the
average cooling rates shown in Table 2 and then allowed to cool
naturally to room temperature, thereby obtaining glass plates (heat
treatment step). Examples 1 to 3 are Examples according to the
present invention, and Example 4 is Comparative Example.
[0246] The obtained glass plates were examined for the following
properties by the methods shown below.
[0247] The results thereof are shown in Tables 1 and 2 together
with the composition. In Table 1, each blank in the composition
indicates that the raw material had not been added on purpose, and
each of the blanks regarding the properties indicates that the
property was not determined.
[Glass Transition Temperature Tg (.degree. C.)]
[0248] Glass transition temperature was measured with a
thermodilatometer (Model TD5000SA, manufactured by MAC Corp.) in
accordance with JIS R 3103-3:2001.
[T2, T4 (.degree. C.)]
[0249] Each glass was examined for viscosity to calculate T2 and
T4. Specifically, a rotary high-temperature viscometer (RVM-550,
manufactured by OPT Corp.) was used to determine the viscosity of
the glass in accordance with ASTM C965-96 (2002). MIST717a was used
as a reference to correct the viscosity of the glass, and the T2
and the T4 were calculated therefrom.
[Devitrification Temperature]
[0250] Devitrification temperature was determined by placing
particles of a crushed glass on a dish made of platinum,
heat-treating the glass particles for 17 hours in electric furnaces
having constant temperatures, examining the heat-treated sample
with an optical microscope (Model ME600, manufactured by Nikon
Corp.) to determine a highest temperature which had resulted in
crystal precipitation in the surface and inside of the glass and a
lowest temperature which had not resulted in crystal precipitation,
and taking an average of the highest and the lowest temperatures as
the devitrification temperature.
[Young's Modulus]
[0251] Young's modulus was measured with an ultrasonic-pulse
Young's modulus meter (38DL-PAUS, manufactured by Olympus Co.,
Ltd.) in accordance with JIS R 1602 (1995).
[Acid Resistance]
[0252] Acid resistance was determined by immersing a glass sample
in an aqueous acid solution (6 wt % HNO.sub.3+5 wt %
H.sub.2SO.sub.4; 45.degree. C.) for 170 seconds and evaluating the
amount of glass components extracted per unit surface area
(mg/cm.sup.2).
[Alkali Resistance]
[0253] Alkali resistance was determined by immersing a glass sample
in an aqueous alkali solution (1.2 wt % NaOH; 60.degree. C.) for 30
minutes and evaluating the amount of glass components extracted per
unit surface area (mg/cm.sup.2).
[Average Coefficient of Thermal Expansion]
[0254] The coefficient of thermal expansion within the temperature
range of from 50 to 350.degree. C. was measured with a TMA (Model
TD5000SA, manufactured by MAC Corp.) in accordance with JIS R 3102
(1995). An average of the resultant coefficients of linear
expansion at 50-350.degree. C. was determined as the average
coefficient of thermal expansion.
[Strain Point]
[0255] Strain point was measured in accordance with JIS R 3103-2
(2001).
[Density]
[0256] Density was determined in accordance with JIS Z 8807
(2012).
[Dielectric Dissipation Factor Tan .delta.]
[0257] The dielectric dissipation factor tan .delta.A at 10 GHz of
an obtained glass plate was measured with a resonator for 10 GHz
(resonator for 10 GHz manufactured by OWED Company) by an SPDR
method in accordance with IEC 61189-2-721 (2015).
[0258] Furthermore, the glass plate was heated to (Tg+50).degree.
C. and cooled to (Tg-150).degree. C. at 100.degree. C./min, and was
then examined for dielectric dissipation factor tan .delta.100 at
10 GHz in the same manner.
[0259] In Table 2, ".DELTA. tan .delta." indicates the value of
(tan .delta.100-tan .delta.A).
[Relative Permittivity .epsilon.r]
[0260] The relative permittivity .epsilon.rA at 10 GHz of an
obtained glass plate was measured with a resonator for 10 GHz
(resonator for 10 GHz manufactured by OWED Company) by an SPDR
method in accordance with IEC 61189-2-721 (2015).
[0261] Furthermore, the glass plate was heated to (Tg+50).degree.
C. and cooled to (Tg-50).degree. C. at 100.degree. C./min, and was
then examined for relative permittivity .epsilon.r100 at 10 GHz in
the same manner.
TABLE-US-00001 TABLE 1 Compo- Compo- Compo- Compo- Compo- Compo-
Compo- sition sition sition sition sition sition sition 1 2 3 4 5 6
7 Composition SiO.sub.2 83.3 73.9 62.0 61.9 66.1 67.0 67.2 (mol %)
Al.sub.2O.sub.3 1.4 8.0 8.5 11.3 11.0 6.5 B.sub.2O.sub.3 11.3 23.0
21.1 7.8 10.0 19.5 MgO 0.1 4.0 0.2 5.1 2.0 0.5 CaO 11.6 2.0 0.2 4.5
9.0 5 SrO 0.8 7.0 5.2 1.0 0.5 BaO 0.2 1.1 Li.sub.2O Na.sub.2O 4.0
7.2 0.8 K.sub.2O 0.05 7.2 Tg (.degree. C.) 580 547 633 625 710 705
650 T2 (.degree. C.) 1437 1626 1656 1645 1745 T4 (.degree. C.) 1030
1231 1243 1275 1296 Devitrification 890 1270 1280 1266 temperature
(.degree. C.) Young's modulus 63 59 59 76 73 58 (GPa) Acid
resistance 0.0027 0.013 0.017 (g/cm.sup.-2) Alkali resistance 0.06
0.031 0.026 (g/cm.sup.-2) Average coefficient 38 101 31 35 38 34 31
of thermal expansion (10.sup.-7/.degree. C.) Strain point (.degree.
C.) 520 513 563 563 670 667 Density (g/cm.sup.3) 2.5 2.49 2.3 2.41
2.5 2.4 2.2
TABLE-US-00002 TABLE 2 Composition 1 Example 1 Example 2 Example 3
Example 4 Tmax (.degree. C.) 630 630 630 630 Temax (.degree. C.)
630 630 630 630 Holding period (min) 1550 210 75 30 Average cooling
rate (.degree. C./min) 0.1 1 10 500 .epsilon.r100 4.49 4.49 4.49
4.49 tan.delta.100 0.0062 0.0062 0.0062 0.0062 .epsilon.rA 4.51
4.47 4.46 4.42 tan.delta.A 0.0044 0.0050 0.0056 0.0066
.DELTA.tan.delta. 0.0018 0.0012 0.0006 -0.0004
.epsilon.r100/.epsilon.rA 1.00 1.00 1.01 1.02 t1 (min) 1600 160 16
0.32 Value of K in formula (1) 15 15 15 15 Value of left side of
formula (2) 0.10 1.0 10.0 500.0
Examples 5 to 8
[0262] Glass plates were obtained in the same manner as in Example
1, except that raw materials for glass were used so as to result in
the composition shown as Composition 2 in Table 1, that in the
subsequent heat treatment step, the glass base plates were heated
to 597.degree. C. at 10.degree. C./min and held at 597.degree. C.
for the time periods shown in Table 3 in the row "Holding period
(min)", and that the glass base plates were cooled in the electric
furnace to (Tg-300).degree. C. at the average cooling rates shown
in Table 3. Examples 5 to 7 are Examples according to the present
invention, and Example 8 is Comparative Example.
[0263] The obtained glass plates were examined for the properties
under the same conditions as in Example 1. The results thereof are
shown in Tables 1 and 3 together with the composition.
TABLE-US-00003 TABLE 3 Composition 2 Example 5 Example 6 Example 7
Example 8 Tmax (.degree. C.) 597 597 597 597 Temax (.degree. C.)
597 597 597 597 Holding period (min) 1550 210 75 30 Average cooling
rate (.degree. C./min) 0.1 1 10 500 .epsilon.r100 6.74 6.74 6.74
6.74 tan.delta.100 0.0093 0.0093 0.0093 0.0093 .epsilon.rA 6.63
6.67 6.72 6.76 tan.delta.A 0.0078 0.0083 0.0088 0.0096
.DELTA.tan.delta. 0.0015 0.001 0.0005 -0.0003
.epsilon.r100/.epsilon.rA 1.02 1.01 1.00 1.00 t1 (min) 1600 160 16
0.32 Value of K in formula (1) 15 15 15 15 Value of left side of
formula (2) 0.10 1.0 10.0 500.0
Examples 9 to 12
[0264] Glass plates were obtained in the same manner as in Example
1, except that raw materials for glass were used so as to result in
the composition shown as Composition 3 in Table 1, that in the
subsequent heat treatment step, the glass base plates were heated
to 653.degree. C. at 10.degree. C./min and held at 653.degree. C.
for the time periods shown in Table 4 in the row "Holding period
(min)", and that the glass base plates were cooled in the electric
furnace to (Tg-300).degree. C. at the average cooling rates shown
in Table 4. Examples 9 to 11 are Examples according to the present
invention, and Example 12 is Comparative Example.
[0265] The obtained glass plates were examined for the properties
under the same conditions as in Example 1. The results thereof are
shown in Tables 1 and 4 together with the composition.
TABLE-US-00004 TABLE 4 Composition 3 Example 9 Example 10 Example
11 Example 12 Tmax (.degree. C.) 653 653 653 653 Temax (.degree.
C.) 653 653 653 653 Holding period (min) 1550 210 75 30 Average
cooling rate (.degree. C./min) 0.1 1 10 500 .epsilon.r100 4.36 4.36
4.36 4.36 tan.delta.100 0.0029 0.0029 0.0029 0.0029 .epsilon.rA
4.34 4.35 4.36 4.37 tan.delta.A 0.0018 0.0022 0.0025 0.0032
.DELTA.tan.delta. 0.0011 0.0007 0.0004 -0.0003
.epsilon.r100/.epsilon.rA 1.00 1.00 1.00 1.00 t1 (min) 1300 130 13
0.26 Value of K in formula (1) 15 15 15 15 Value of left side of
formula (2) 0.10 1.0 10.0 500.0
Examples 13 to 16
[0266] Glass plates were obtained in the same manner as in Example
1, except that raw materials for glass were used so as to result in
the composition shown as Composition 4 in Table 1, that in the
subsequent heat treatment step, the glass base plates were heated
to 675.degree. C. at 10.degree. C./min and held at 675.degree. C.
for the time periods shown in Table 5 in the row "Holding period
(min)", and that the glass base plates were cooled in the electric
furnace to (Tg-300).degree. C. at the average cooling rates shown
in Table 5. Examples 13 to 15 are Examples according to the present
invention, and Example 16 is Comparative Example.
[0267] The obtained glass plates were examined for the properties
under the same conditions as in Example 1. The results thereof are
shown in Tables 1 and 5 together with the composition.
TABLE-US-00005 TABLE 5 Composition 4 Example 13 Example 14 Example
15 Example 16 Tmax (.degree. C.) 675 675 675 675 Temax (.degree.
C.) 675 675 675 675 Holding period (min) 1550 210 75 30 Average
cooling rate (.degree. C./min) 0.1 1 10 500 .epsilon.r100 4.86 4.86
4.86 4.86 tan.delta.100 0.0032 0.0032 0.0032 0.0032 .epsilon.rA
4.83 4.84 4.86 4.88 tan.delta.A 0.0022 0.0025 0.0028 0.0034
.DELTA.tan.delta. 0.0010 0.0007 0.0004 -0.0002
.epsilon.r100/.epsilon.rA 1.01 1.00 1.00 1.00 t1 (min) 1600 160 16
0.32 Value of K in formula (1) 15 15 15 15 Value of left side of
formula (2) 0.10 1.0 10.0 500.0
Examples 17 to 20
[0268] Glass plates were obtained in the same manner as in Example
1, except that raw materials for glass were used so as to result in
the composition shown as Composition 5 in Table 1, that in the
subsequent heat treatment step, the glass base plates were heated
to 760.degree. C. at 10.degree. C./min and held at 760.degree. C.
for the time periods shown in Table 6 in the row "Holding period
(min)", and that the glass base plates were cooled in the electric
furnace to (Tg-300).degree. C. at the average cooling rates shown
in Table 6. Examples 17 to 19 are Examples according to the present
invention, and Example 20 is Comparative Example.
[0269] The obtained glass plates were examined for the properties
under the same conditions as in Example 1. The results thereof are
shown in Tables 1 and 6 together with the composition.
TABLE-US-00006 TABLE 6 Composition 5 Example 17 Example 18 Example
19 Example 20 Tmax (.degree. C.) 760 760 760 760 Temax (.degree.
C.) 760 760 760 760 Holding period (min) 1550 210 75 30 Average
cooling rate (.degree. C./min) 0.1 1 10 500 .epsilon.r100 5.45 5.45
5.45 5.45 tan.delta.100 0.0063 0.0063 0.0063 0.0063 .epsilon.rA
5.42 5.44 5.44 5.46 tan.delta.A 0.0044 0.005 0.0056 0.0067
.DELTA.tan.delta. 0.0019 0.0013 0.0007 -0.0004
.epsilon.r100/.epsilon.rA 1.01 1.00 1.00 1.00 t1 (min) 1600 160 16
0.32 Value of K in formula (1) 15 15 15 15 Value of left side of
formula (2) 0.10 1.0 10.0 500.0
Examples 21 to 24
[0270] Glass plates were obtained in the same manner as in Example
1, except that raw materials for glass were used so as to result in
the composition shown as Composition 6 in Table 1, that in the
subsequent heat treatment step, the glass base plates were heated
to 760.degree. C. at 10.degree. C./min and held at 760.degree. C.
for the time periods shown in Table 7 in the row "Holding period
(min)", and that the glass base plates were cooled in the electric
furnace to (Tg-300).degree. C. at the average cooling rates shown
in Table 7. Examples 21 to 23 are Examples according to the present
invention, and Example 24 is Comparative Example.
[0271] The obtained glass plates were examined for the properties
under the same conditions as in Example 1. The results thereof are
shown in Tables 1 and 7 together with the composition.
TABLE-US-00007 TABLE 7 Composition 6 Example 21 Example 22 Example
23 Example 24 Tmax (.degree. C.) 755 755 755 755 Temax (.degree.
C.) 755 755 755 755 Holding period (min) 1550 210 75 30 Average
cooling rate (.degree. C./min) 0.1 1 10 500 .epsilon.r100 5.14 5.14
5.14 5.14 tan.delta.100 0.0053 0.0053 0.0053 0.0053 .epsilon.rA
5.18 5.17 5.16 5.12 tan.delta.A 0.0033 0.0040 0.0047 0.0058
.DELTA.tan.delta. 0.0020 0.0013 0.0006 -0.0005
.epsilon.r100/.epsilon.rA 0.99 0.99 1.00 1.00 t1 (min) 8650 865
86.5 1.73 Value of K in formula (1) 15 15 15 15 Value of left side
of formula (2) 0.10 1.00 10.00 500.00
Examples 25 to 28
[0272] Glass plates were obtained in the same manner as in Example
1, except that raw materials for glass were used so as to result in
the composition shown as Composition 7 in Table 1, that in the
subsequent heat treatment step, the glass base plates were heated
to 700.degree. C. at 10.degree. C./min and held at 700.degree. C.
for the time periods shown in Table 8 in the row "Holding period
(min)", and that the glass base plates were cooled in the electric
furnace to (Tg-300).degree. C. at the average cooling rates shown
in Table 8. Examples 25 to 27 are Examples according to the present
invention, and Example 28 is Comparative Example.
[0273] The obtained glass plates were examined for the properties
under the same conditions as in Example 1. The results thereof are
shown in Tables 1 and 8 together with the composition.
TABLE-US-00008 TABLE 8 Composition 7 Example 25 Example 26 Example
27 Example 28 Tmax (.degree. C.) 700 700 700 700 Temax (.degree.
C.) 700 700 700 700 Holding period (min) 1550 210 75 30 Average
cooling rate (.degree. C./min) 0.1 1 10 500 .epsilon.r100 4.54 4.54
4.54 4.54 tan.delta.100 0.0051 0.0051 0.0051 0.0051 .epsilon.rA
4.51 4.52 4.53 4.55 tan.delta.A 0.0032 0.0038 0.0044 0.0055
.DELTA.tan.delta. 0.0019 0.0013 0.0007 -0.0004
.epsilon.r100/.epsilon.rA 1.01 1.00 1.00 1.00 t1 (min) 8100 810 81
1.62 Value of K in formula (1) 15 15 15 15 Value of left side of
formula (2) 0.10 1.00 10.00 500.00
Examples 29 to 31
[0274] Raw materials for glass were used so as to result in the
composition shown as Composition 4 in Table 1, and a plate-shaped
molten glass was obtained using a glass melting tank and a forming
apparatus (melting/forming step).
[0275] Thereafter, the plate-shaped molten glass which had been
700.degree. C. was cooled to room temperature with an annealing
apparatus at an average cooling rate of 50.degree. C./min to obtain
glass base plates having a size of 37 cm.times.47 cm and a
thickness of 1.1 mm (cooling step).
[0276] Subsequently, glass plates were obtained in the same manner
as in Example 1, except that the glass base plates were heated to
the temperatures Tmax (.degree. C.) shown in Table 9 at 10.degree.
C./min, held at the temperatures Tmax (.degree. C.) for the time
periods shown in Table 9 in the row "Holding period (min)", and
cooled in the electric furnace to (Tg-300).degree. C. at the
average cooling rates shown in Table 9. Examples 29 to 31 are
Examples according to the present invention.
[0277] The temperature of the electric furnace was regulated so
that if the average cooling rate of the center of each glass base
plate and the average cooling rate of an edge portion thereof were
respectively expressed by VC (.degree. C./min) and VE (.degree.
C./min), then the ratio represented by VC/VE was 1.1 or less. The
term "edge portion of the glass base plate" means a position which
is at a distance of 10 cm from an edge of the glass base plate.
[0278] The obtained glass plates were examined for relative
permittivity and dielectric dissipation factor under the same
conditions as in Example 1. An approximately central portion of
each plate and four portions near the corners were thus examined
and maximum values and minimum values of those properties were
recorded. The results thereof are shown in Table 9.
[0279] Furthermore, minimum values of .DELTA. tan .delta. and
maximum values of .epsilon.r100/.epsilon.rA are shown in Table 9.
Table 9 further shows: the difference in tan .delta.A between two
portions which differed most in tan .delta.A among the
approximately central portion of the plate and the four portions
near the corners; and the difference in .epsilon.rA between two
portions which differed most in .epsilon.rA among those five
portions.
TABLE-US-00009 TABLE 9 Composition 4 Example 29 Example 30 Example
31 Tmax (.degree. C.) 675 675 625 Temax (.degree. C.) 675 675 625
Holding period (min) 15 10 30 Average cooling rate (.degree.
C./min) 1 10 10 Maximum vallue of .epsilon.r100 4.86 4.87 4.87
Minimum value of .epsilon.r100 4.85 4.85 4.85 Maximum value of
tan.delta.100 0.0033 0.0033 0.0033 Minimum value of tan.delta.100
0.0032 0.0032 0.0032 Maximum value of .epsilon.rA 4.85 4.86 4.86
Minimum value of .epsilon.rA 4.84 4.85 4.85 Maximum value of
tan.delta.A 0.0026 0.0028 0.0028 Minimum value of tan.delta.A
0.0024 0.0027 0.0026 Minimum value of .DELTA.tan.delta. 0.0006
0.0004 0.0004 Maximum value of .epsilon.r100/.epsilon.rA 1.00 1.00
1.00 Maximum value of difference in 0.0002 0.0001 0.0002
tan.delta.A between any two portions Maximum value of difference in
0.01 0.01 0.01 .epsilon.rA between any two portions t1 (min) 785
78.5 73.5 Value of K in formula (1) 15 15 20 Value of left side of
formula (2) 1.0 10.0 10.0
Examples 32 to 34
[0280] Raw materials for glass were used so as to result in the
composition shown as Composition 6 in Table 1, and a plate-shaped
molten glass was obtained using a glass melting tank and a forming
apparatus (melting/forming step).
[0281] Thereafter, the plate-shaped molten glass which had been
800.degree. C. was cooled to room temperature with an annealing
apparatus at an average cooling rate of 800.degree. C./min to
obtain glass base plates having a size of 37 cm.times.47 cm and a
thickness of 1.1 mm (cooling step).
[0282] Subsequently, glass plates were obtained in the same manner
as in Example 1, except that the glass base plates were heated to
the temperatures Tmax (.degree. C.) shown in Table 10 at 10.degree.
C./min, held at the temperatures Tmax (.degree. C.) for the time
periods shown in Table 10 in the row "Holding period (min)", and
cooled in the electric furnace to (Tg-300).degree. C. at the
average cooling rates shown in Table 10. Examples 32 to 34 are
Examples according to the present invention.
[0283] The temperature of the electric furnace was regulated so
that if the average cooling rate of the center of each glass base
plate and the average cooling rate of an edge portion thereof were
respectively expressed by VC (.degree. C./min) and VE (.degree.
C./min), then the ratio represented by VC/VE was 1.1 or less. The
term "edge portion of the glass base plate" means a position which
is at a distance of 10 cm from an edge of the glass base plate.
[0284] The obtained glass plates were examined for relative
permittivity and dielectric dissipation factor under the same
conditions as in Example 1. An approximately central portion of
each plate and four portions near the corners were thus examined
and maximum values and minimum values of those properties were
recorded. The results thereof are shown in Table 10.
[0285] Furthermore, minimum values of .DELTA. tan .delta. and
maximum values of .epsilon.r100/.epsilon.rA are shown in Table 10.
Table 10 further shows: the difference in tan .delta.A between two
portions which differed most in tan .delta.A among the
approximately central portion of the plate and the four portions
near the corners; and the difference in .epsilon.rA between two
portions which differed most in .epsilon.rA among those five
portions.
TABLE-US-00010 TABLE 10 Composition 6 Example 32 Example 33 Example
34 Tmax (.degree. C.) 625 725 695 Temax (.degree. C.) 625 725 695
Holding period (min) 20 10 30 Average cooling rate (.degree.
C./min) 1 10 10 Maximum value of .epsilon.r100 5.13 5.13 5.13
Minimum value of .epsilon.r100 5.12 5.12 5.12 Maximum value of
tan.delta.100 0.0057 0.0057 0.0057 Minimum value of tan.delta.100
0.0056 0.0056 0.0056 Maximum value of .epsilon.rA 5.16 5.17 5.16
Minimum value of .epsilon.rA 5.15 5.15 5.15 Maximum value of
tan.delta.A 0.0048 0.0050 0.0051 Minimum value of tan.delta.A
0.0047 0.0048 0.0050 Minimum value of .DELTA.tan.delta. 0.0008
0.0006 0.0005 Maximum value of .epsilon.r100/.epsilon.rA 1.00 1.00
1.00 Maximum value of difference in 0.0001 0.0002 0.0001
tan.delta.A between any two portions Maximum value of difference in
0.01 0.02 0.01 .epsilon.rA between any two portions t1 (min) 735.0
83.5 80.5 Value of K in formula (1) 28 18 21 Value of left side of
formula (2) 1.00 10.00 10.00
[0286] While the invention has been described in detail and with
reference to specific embodiments thereof, it will be apparent to
one skilled in the art that various changes and modifications can
be made therein without departing from the spirit and scope
thereof. This application is based on a Japanese patent application
filed on Apr. 12, 2019 (Application No. 2019-76423), a Japanese
patent application filed on Jun. 28, 2019 (Application No.
2019-120828), and a Japanese patent application filed on Nov. 27,
2019 (Application No. 2019-214690), the entire contents thereof
being incorporated herein by reference. All the references cited
here are incorporated herein as a whole.
* * * * *