U.S. patent application number 12/888019 was filed with the patent office on 2011-04-21 for glass plate for display device, plate glass for display device and production process thereof.
This patent application is currently assigned to Asahi Glass Company, Limited. Invention is credited to Shusaku AKIBA, Kazutaka Hayashi.
Application Number | 20110091704 12/888019 |
Document ID | / |
Family ID | 43879526 |
Filed Date | 2011-04-21 |
United States Patent
Application |
20110091704 |
Kind Code |
A1 |
AKIBA; Shusaku ; et
al. |
April 21, 2011 |
GLASS PLATE FOR DISPLAY DEVICE, PLATE GLASS FOR DISPLAY DEVICE AND
PRODUCTION PROCESS THEREOF
Abstract
A process for producing a plate glass for a display device
having a thickness of at most 1.5 mm by a float process, wherein
the plate glass comprises, as represented by mole percentage based
on the following oxides, from 67 to 75% of SiO.sub.2, from 0 to 4%
of Al.sub.2O.sub.3, from 7 to 15% of Na.sub.2O, from 1 to 9% of
K.sub.2O, from 6 to 14% of MgO and from 0 to 1.5% of ZrO.sub.2, has
a total content of SiO.sub.2 and Al.sub.2O.sub.3 of from 71 to 75%,
has a total content Na.sub.2O+K.sub.2O of Na.sub.2O and K.sub.2O of
from 12 to 20%, and has a content of CaO of less than 1% if
contained.
Inventors: |
AKIBA; Shusaku; (Chiyoda-ku,
JP) ; Hayashi; Kazutaka; (Chiyoda-ku, JP) |
Assignee: |
Asahi Glass Company,
Limited
Chiyoda-ku
JP
|
Family ID: |
43879526 |
Appl. No.: |
12/888019 |
Filed: |
September 22, 2010 |
Current U.S.
Class: |
428/220 ; 501/65;
501/66; 501/69; 501/70; 501/72 |
Current CPC
Class: |
C03C 3/085 20130101;
H05K 5/03 20130101; C03C 3/087 20130101; C03C 3/078 20130101 |
Class at
Publication: |
428/220 ; 501/70;
501/69; 501/72; 501/65; 501/66 |
International
Class: |
C03B 18/02 20060101
C03B018/02; C03B 27/00 20060101 C03B027/00; C03C 3/087 20060101
C03C003/087; C03C 3/085 20060101 C03C003/085; C03C 3/078 20060101
C03C003/078; C03C 3/089 20060101 C03C003/089; C03C 3/091 20060101
C03C003/091 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 20, 2009 |
JP |
2009-241524 |
Claims
1. A process for producing a plate glass for a display device
having a thickness of at most 1.5 mm by a float process, wherein
the plate glass comprises, as represented by mole percentage based
on the following oxides, from 67 to 75% of SiO.sub.2, from 0 to 4%
of Al.sub.2O.sub.3, from 7 to 15% of Na.sub.2O, from 1 to 9% of
K.sub.2O, from 6 to 14% of MgO and from 0 to 1.5% of ZrO.sub.2, has
a total content of SiO.sub.2 and Al.sub.2O.sub.3 of from 71 to 75%,
has a total content Na.sub.2O+K.sub.2O of Na.sub.2O and K.sub.2O of
from 12 to 20%, and has a content of CaO of less than 1% if
contained.
2. The process for producing a plate glass for a display device
according to claim 1, wherein the SiO.sub.2 content of the plate
glass is from 69 to 74%.
3. The process for producing a plate glass for a display device
according to claim 1, wherein the Al.sub.2O.sub.3 content of the
plate glass is at least 0% and less than 3%.
4. The process for producing a plate glass for a display device
according to claim 1, wherein the MgO content of the plate glass is
from 8 to 13%.
5. The process for producing a plate glass for a display device
according to claim 1, wherein the total content Na.sub.2O+K.sub.2O
of the plate glass is higher than 13.5%.
6. The process for producing a plate glass for a display device
according to claim 1, wherein when the plate glass contains at
least one component of CaO, SrO, BaO and ZrO.sub.2, the total
content of these four components is less than 1.5%.
7. The process for producing a plate glass for a display device
according to claim 1, wherein the B.sub.2O.sub.3 content of the
plate glass is less than 1% if contained.
8. The process for producing a plate glass for a display device
according to claim 1, wherein the temperature at which the
viscosity of the plate glass is 10.sup.2 dPas is at most
1,650.degree. C.
9. The process for producing a plate glass for a display device
according to claim 1, wherein the average linear expansion
coefficient of the plate glass at from 50 to 350.degree. C. is
higher than 86.times.10.sup.-7/.degree. C.
10. A plate glass for a display device having a thickness of at
most 1.5 mm, comprising, as represented by mole percentage based on
the following oxides, from 67 to 75% of SiO.sub.2, from 0 to 4% of
Al.sub.2O.sub.3, from 7 to 15% of Na.sub.2O, from 1 to 9% of
K.sub.2O, from 6 to 14% of MgO and from 0 to 1.5% of ZrO.sub.2,
having a total content of SiO.sub.2 and Al.sub.2O.sub.3 of from 71
to 75%, having a total content Na.sub.2O+K.sub.2O of Na.sub.2O and
K.sub.2O of from 12 to 20%, and having a content of CaO of less
than 1% if contained.
11. The plate glass for a display device according to claim 10,
which has an Al.sub.2O.sub.3 content of at least 0% and less than
3%.
12. The plate glass for a display device according to claim 10,
which has a total content Na.sub.2O+K.sub.2O of higher than
13.5%.
13. The plate glass for a display device according to claim 10,
which has an average linear expansion coefficient at from 50 to
350.degree. C. of higher than 86.times.10.sup.-7/.degree. C.
14. A glass plate for a display device, obtained by chemically
tempering a glass plate having a thickness of at most 1 mm,
comprising, as represented by mole percentage based on the
following oxides, from 67 to 75% of SiO.sub.2, from 0 to 4% of
Al.sub.2O.sub.3, from 7 to 15% of Na.sub.2O, from 1 to 9% of
K.sub.2O, from 6 to 14% of MgO, and from 0 to 1.5% of ZrO.sub.2,
having a total content of SiO.sub.2 and Al.sub.2O.sub.3 of from 71
to 75%, having a total content Na.sub.2O+K.sub.2O of Na.sub.2O and
K.sub.2O of from 12 to 20%, and having a content of CaO of less
than 1% if contained.
15. A cover glass for a display device, comprising the glass plate
for a display device as defined in claim 14.
16. The cover glass according to claim 15, wherein the display
device is a mobile device.
17. The cover glass according to claim 15, wherein the display
device is a touch panel.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a glass plate for e.g. a
cover glass or a glass substrate of a display device, typically a
mobile device such as a cell phone or a personal digital assistance
(PDA) or a small display device such as a touch panel, a plate
glass used for production of such a glass plate, a process for
producing such a plate glass, a cover glass and a display
device.
[0003] 2. Discussion of Background
[0004] In recent years, for mobile devices such as cell phones and
PDA, use of a cover glass (protective glass) for protecting a
display and improving appearance, is increasing.
[0005] Weight reduction and thickness reduction are required for
such portable digital devices. Therefore, a cover glass used for
protecting a display is also required to be thin. However, if the
thickness of the cover glass is made to be thin, the strength is
lowered, and if a display device is dropped at a time of using or
carrying it, the cover glass itself may sometimes be broken.
Therefore, there is a problem that the cover glass cannot
accomplish the original object to protect display devices.
[0006] In order to solve the above problem, it is conceivable to
improve the strength of the cover glass, and as such a method, a
method to form a compressive stress layer on a glass surface is
commonly known.
[0007] As the method to form a compressive stress layer on a glass
surface, typical are an air quenching tempering method (physical
tempering method) wherein a surface of a glass plate heated to near
the softening point is quenched by air cooling or the like and a
chemical tempering method wherein alkali metal ions having a small
ion radius (typically Li ions or Na ions) on a glass plate surface
are exchanged with alkali ions having a larger ion radius
(typically K ions) by ion exchange at a temperature lower than the
glass transition point.
[0008] As mentioned above, the thickness of the cover glass is
required to be thin. If the air quenching tempering method is
applied to a thin glass plate, the temperature difference between
the surface and the inside tends not to arise, and it is thereby
difficult to form a compressive stress layer, and the desired
property of high strength cannot be obtained. Therefore, a cover
glass tempered by the latter chemical tempering method is usually
used.
[0009] As such a cover glass, glass having soda lime glass
chemically tempered is widely used (e.g. Patent Document 1).
[0010] SiO.sub.2--Al.sub.2O.sub.3--Na.sub.2O glass other than the
soda lime glass has also been proposed as a cover glass, and as a
process of such glass, a downdraw process or an overflow downdraw
process has been assumed (e.g. Patent Document 2). [0011] Patent
Document 1: JP-A-2007-11210 [0012] Patent Document 2:
JP-A-2009-57271
[0013] A cover glass or the like for a mobile device may have a
hole having a function as a speaker or the like, or it is preferred
to have a complicated shape in view of the design. Accordingly,
when a plate glass for a cover glass is processed to form a glass
plate for a cover glass, it is subjected to a complicated process
such as drilling or scribing a curve to be formed into a glass
plate having a final shape in many cases.
[0014] If chipping occurs when such a plate glass (so-called raw
plate glass) is processed, latent flaws are also formed at the same
time. Such chipping formed at the time of processing before
chemical tempering treatment has not conventionally been
problematic. However, in a case where a glass plate which has
remaining latent flaws which have been formed at the same time as
chipping by processing is chemically tempered, if the latent flaws
are so deep that they are beyond the compressive stress layer, the
improvement in the strength of the glass plate may be insufficient.
Further, if the latent flaws are present in an interior tensile
stress layer of glass, cracks may expand by themselves and the
glass may voluntarily break.
[0015] Further, in a case where chemical tempering treatment is
carried out while glass dust formed by chipping is attached to the
surface of the glass plate, only that portion is not tempered and
may cause a drawback such as a dent or warpage. That is, the
chipping may cause a product failure other than the latent flaws,
which may lead to a decrease in the strength.
[0016] Further, substrates before processing are getting larger so
as to improve the productivity, and may have a G4 (680.times.880)
size or a G5 (1100.times.1300) size.
[0017] In a case where such a large substrate is processed, as the
one side tends to be long, formation of deep latent flaws is highly
possible. Further, as the substrate gets larger, it is heavier and
is likely to bend, and the probability of breakage from the latent
flaws tends to be high.
[0018] Accordingly, the probability of chipping is increased by the
increase in size of the substrate, and the breakage failure of
glass may be increased in the substrate processing step.
[0019] Such problems due to the chipping are more serious due to an
increase in the demand for a reduction in the thickness of a cover
glass accompanying need for weight saving of e.g. mobile devices.
That is, if the thickness of a cover glass is reduced form 2 mm to
1 mm, the strength is reduced to one quarter, and the
above-described problems are more serious.
[0020] Further, such a cover glass is suitably formed by a downdraw
process such as a downdraw process or an overflow downdraw method
in many cases, but such a method is not necessarily applicable to
mass production.
SUMMARY OF THE INVENTION
[0021] It is an object of the present invention to solve the above
problems.
[0022] The present invention provides a process (production process
of the present invention) for producing a plate glass for a display
device having a thickness of at most 1.5 mm by a float process,
wherein the plate glass comprises, as represented by mole
percentage based on the following oxides, from 67 to 75% of
SiO.sub.2, from 0 to 4% of Al.sub.2O.sub.3, from 7 to 15% of
Na.sub.2O, from 1 to 9% of K.sub.2O, from 6 to 14% of MgO and from
0 to 1.5% of ZrO.sub.2, has a total content of SiO.sub.2 and
Al.sub.2O.sub.3 of from 71 to 75%, has a total content
Na.sub.2O+K.sub.2O of Na.sub.2O and K.sub.2O of from 12 to 20%, and
has a content of CaO of less than 1% if contained.
[0023] Further, the present invention provides the above process
for producing a plate glass for a display device, wherein the
SiO.sub.2 content of the plate glass is from 69 to 74%.
[0024] Further, the present invention provides the above process
for producing a plate glass for a display device, wherein the
Al.sub.2O.sub.3 content of the plate glass is at least 0% and less
than 3%.
[0025] Further, the present invention provides the above process
for producing a plate glass for a display device, wherein the MgO
content of the plate glass is from 8 to 13%.
[0026] Further, the present invention provides the above process
for producing a plate glass for a display device, wherein the total
content Na.sub.2O+K.sub.2O of the plate glass is higher than
13.5%.
[0027] Further, the present invention provides the above process
for producing a plate glass for a display device, wherein when the
plate glass contains at least one component of CaO, SrO, BaO and
ZrO.sub.2, the total content of these four components is less than
1.5%.
[0028] Further, the present invention provides the above process
for producing a plate glass for a display device, wherein the
B.sub.2O.sub.3, content of the plate glass is less than 1% if
contained.
[0029] Further, the present invention provides the above process
for producing a plate glass for a display device, wherein the
temperature at which the viscosity of the plate glass is 10.sup.2
dPas is at most 1,650.degree. C.
[0030] Further, the present invention provides the above process
for producing a plate glass for a display device, wherein the
average linear expansion coefficient of the plate glass at from 50
to 350.degree. C. is higher than 86.times.10.sup.-7/.degree. C.
[0031] Further, the present invention provides a plate glass (plate
glass of the present invention) for a display device having a
thickness of at most 1.5 mm, comprising, as represented by mole
percentage based on the following oxides, from 67 to 75% of
SiO.sub.2, from 0 to 4% of Al.sub.2O.sub.3, from 7 to 15% of
Na.sub.2O, from 1 to 9% of K.sub.2O, from 6 to 14% of MgO and from
0 to 1.5% of ZrO.sub.2, having a total content of SiO.sub.2 and
Al.sub.2O.sub.3 of from 71 to 75%, having a total content
Na.sub.2O+K.sub.2O of Na.sub.2O and K.sub.2O of from 12 to 20%, and
having a content of CaO of less than 1% if contained.
[0032] Further, the present invention provides the plate glass for
a display device, which has an Al.sub.2O.sub.3 content of at least
0% and less than 3%.
[0033] Further, the present invention provides the plate glass for
a display device, which has a total content Na.sub.2O+K.sub.2O of
higher than 13.5%.
[0034] Further, the present invention provides the plate glass for
a display device, which has an average linear expansion coefficient
at from 50 to 350.degree. C. of higher than
86.times.10.sup.-7/.degree. C.
[0035] Further, the present invention provides a glass plate for a
display device, obtained by chemically tempering a glass plate
having a thickness of at most 1 mm, comprising, as represented by
mole percentage based on the following oxides, from 67 to 75% of
SiO.sub.2, from 0 to 4% of Al.sub.2O.sub.3, from 7 to 15% of
Na.sub.2O, from 1 to 9% of K.sub.2O, from 6 to 14% of MgO, and from
0 to 1.5% of ZrO.sub.2, having a total content of SiO.sub.2 and
Al.sub.2O.sub.3 of from 71 to 75%, having a total content
Na.sub.2O+K.sub.2O of Na.sub.2O and K.sub.2O of from 12 to 20%, and
having a content of CaO of less than 1% if contained.
[0036] Further, the present invention provides a cover glass (cover
glass of the present invention) for a display device, comprising
the above glass plate for a display device.
[0037] Further, the present invention provides the above cover
glass, wherein the display device is a mobile device.
[0038] Further, the present invention provides the above cover
glass, wherein the display device is a touch panel.
[0039] Further, the present invention provides a display device
comprising a display and a cover glass for protecting the display,
wherein the cover glass is the cover glass of the present
invention.
[0040] Further, the present invention provides a mobile device
comprising a display and a cover glass for protecting the display,
wherein the cover glass is the cover glass of the present
invention.
[0041] Still further, the present invention provides a touch panel
comprising a display and a cover glass for protecting the display,
wherein the cover glass is the cover glass of the present
invention.
[0042] According to the present invention, a thin plate glass for a
display device, with which chipping is less likely to occur at the
time of glass processing, and which is capable of chemical
tempering treatment, can be obtained. Further, it is possible to
produce such a thin plate glass by a float process.
[0043] Further, a glass plate and a cover glass for a display
device, with which a decrease in the strength due to chipping at
the time of glass processing before chemical tempering treatment is
less likely to occur, and the possibility of destruction of glass
by itself at the time of use is reduced, can be obtained.
[0044] Further, a mobile device and a touch panel comprising such a
cover glass can be obtained.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0045] The upper limit of the thickness of the glass plate for a
display device of the present invention is 1 mm, and the lower
limit is typically 0.2 mm in the case of a cover glass. If the
thickness is less than 0.2 mm, even though the chemical tempering
is carried out, a problem may arise from the viewpoint of the
strength for practical use. In a case where the glass plate is used
as a glass substrate, the thickness is typically at least 0.05
mm.
[0046] Of a commercially available chemically tempered product of
soda lime glass, the surface compressive stress was measured,
whereupon it was 555 MPa. Accordingly, the surface compressive
stress S of the glass plate for a display device of the present
invention is preferably at least 550 MPa. S is typically at most
800 MPa.
[0047] Further, for production of a cover glass, glass is usually
polished, and the size of abrasive grains used for first step
polishing is typically 100 .mu.m. By polishing using such abrasive
gains, microcracks having a depth of 40 .mu.m are considered to be
formed (Glass Engineering Handbook, edited by Masayuki Yamane et
al., first edition, Asakura Publishing Co., Ltd., Jul. 5, 1999, p.
397).
[0048] Accordingly, the depth t of the compressive stress layer of
the glass plate for a display device of the present invention is
preferably at least 40 .mu.m. Further, t is typically at most 70
.mu.m.
[0049] The glass plate for a display device of the present
invention is usually obtained by processing the plate glass of the
present invention e.g. by cutting, drilling or polishing to obtain
a glass plate, and chemically tempering the glass plate.
[0050] The chemical tempering method is not particularly restricted
as long as Na.sub.2O in the surface layer of the glass plate can be
ion exchanged with K.sub.2O in a molten salt, however, a method
may, for example, be mentioned wherein the glass plate is immersed
in a heated potassium nitrate (KNO.sub.3) molten salt.
[0051] The condition for forming a chemically tempered layer (a
surface compressive stress layer) having a desired surface
compressive stress on the glass plate varies depending on the
thickness of the glass plate, however, typically the glass plate is
immersed in a KNO.sub.3 molten salt at from 350 to 550.degree. C.
for from 2 to 20 hours. From the viewpoint of cost, the glass is
preferably immersed under a condition of at from 350 to 500.degree.
C. for from 2 to 16 hours, more preferably immersed for from 2 to
10 hours.
[0052] In a case where the above polishing is carried out, the
amount of polishing is preferably small from the viewpoint of the
production efficiency, and is usually at most 0.5 mm. Accordingly,
the thickness of the plate glass of the present invention is
considered to be at most 1.5 mm corresponding to the maximum
thickness of the glass plate for a display device of the present
invention, and is typically at most 1.3 mm.
[0053] The method for producing the plate glass of the present
invention is not particularly restricted. For example, the plate
glass is produced by mixing various raw materials in appropriate
amounts, heating the mixture to about 1,400 to 1,600.degree. C. to
melt it, then defoaming and homogenizing the melt by stirring or
the like, forming the melt into a plate shape by a well-known float
process, downdraw process or press method, annealing the plate
shape glass, and cutting it in a desired size. The plate glass of
the present invention is typically produced by the production
process of the present invention.
[0054] The glass of the plate glass produced by the production
process of the present invention will be referred to as the glass
of the present invention, and hereinafter the properties and the
composition of the glass will be described. The glass of the
present invention is the glass of the plate glass of the present
invention, and the glass of the above glass plate chemically
tempered to form a glass plate for a display device of the present
invention.
[0055] Since a float process is employed in the production process
of the present invention, usually a melting tank is used.
[0056] Accordingly, the temperature T.sub.2 at which the viscosity
of the glass of the present invention becomes 10.sup.2 dPas is
preferably at most 1,650.degree. C. If it exceeds 1,650.degree. C.,
it is difficult to melt glass, product defects such as stones tend
to form, or facility for melting glass may be expensive. It is
preferably at most 1,620.degree. C., typically at most
1,600.degree. C.
[0057] Further, the temperature T.sub.4 at which the viscosity of
the glass of the present invention becomes 10.sup.4 dPas is
preferably at most 1,190.degree. C. If it exceeds 1,190.degree. C.,
it is difficult to form glass. It is typically at most
1,180.degree. C.
[0058] The devitrification temperature of the glass of the present
invention is preferably at most (T.sub.4+10.degree. C.). Otherwise,
if a glass is formed by a float process, devitrification will
occur, and it is difficult to form glass. It is more preferably at
most T.sub.4. Here, the devitrification temperature means the
maximum temperature at which devitrification precipitates when the
glass is maintained at that temperature for 15 hours.
[0059] The specific gravity of the glass of the present invention
is preferably at most 2.5. If it exceeds 2.5, weight reduction of a
display device may be insufficient.
[0060] The average linear expansion coefficient of the glass of the
present invention at from 50 to 350.degree. C. is preferably from
80.times.10.sup.-7 to 130.times.10.sup.-7/.degree. C., typically
higher than 86.times.10.sup.-7/.degree. C.
[0061] Now, the composition of the glass of the present invention
will be described by using contents represented by mole percentage
unless otherwise specified.
[0062] SiO.sub.2 is a component to constitute a glass matrix and is
essential. Further, it is a component to reduce chipping at the
time of glass processing. If the SiO.sub.2 content is less than
67%, stability of glass and weather resistance or chipping
resistance will be decreased. It is typically at least 69%. If the
SiO.sub.2 content exceeds 75%, the viscosity of glass will be
increased, and a melting property is remarkably lowered. It is
typically at most 74%.
[0063] Al.sub.2O.sub.3 is not essential but is a component to
improve the ion exchange performance and the chipping resistance
and may be contained up to 4%. If its content exceeds 4%, the
viscosity of the glass will be high, whereby homogeneous melting
will be difficult. It is typically less than 3% or less than 6 mass
%. In a case where Al.sub.2O.sub.3 is contained, its content is
preferably at least 1%.
[0064] If the total content SiO.sub.2+Al.sub.2O.sub.3 of SiO.sub.2
and Al.sub.2O.sub.3 exceeds 75%, the viscosity of the glass at high
temperature will be increased, whereby melting will be difficult.
It is typically at most 74%. If it is less than 71%, the chipping
resistance will be decreased. It is typically at least 72%.
[0065] Na.sub.2O is a component for forming a surface compressive
stress layer by ion exchange and improving the melting property of
the glass and is essential. If its content is less than 7%, it is
difficult to form a desired surface compressive stress layer by ion
exchange. It is typically at least 8%. If the Na.sub.2O content
exceeds 15%, the weather resistance will be decreased. It is
preferably at most 13%.
[0066] K.sub.2O is a component for improving the melting property
as well as for increasing the ion exchange rate in the chemical
tempering to obtain desired surface compressive stress and stress
layer depth, and is essential. If its content is less than 1%, the
melting property will be decreased, or the ion exchange rate will
be decrease. It is preferably at least 3%, typically at least 4%.
If the K.sub.2O content exceeds 9%, the weather resistance will be
decreased. It is preferably at most 7%, typically at most 6%.
[0067] If the total content Na.sub.2O+K.sub.2O of Na.sub.2O and
K.sub.2O is less than 12%, no desired ion exchange property will be
obtained. It is preferably at least 13%, typically higher than
13.5% or higher than 15.5 mass %. If Na.sub.2O+K.sub.2O exceeds
20%, the chemical durability of the glass such as weather
resistance will be low. It is preferably at most 18%, typically at
most 17%.
[0068] MgO is a component which may lower the ion exchange rate or
the chipping resistance, but is a component to improve the melting
property and is essential. If its content is less than 6%, the
viscosity will be increased, thus lowering the melting property. It
is preferably at least 8%, typically at least 10%. If it exceeds
14%, the glass tends to be devitrified. It is preferably at most
13%, typically at most 12%.
[0069] ZrO.sub.2 is not essential but may be contained up to 1.5%
so as to decrease the viscosity at high temperature or to increase
the surface compressive stress. If its content exceeds 1.5%,
ZrO.sub.2 may remain in the glass as stones. Further, the
resistance against chipping may be decreased. In a case where
ZrO.sub.2 is contained, its content is typically at least 0.2%.
[0070] The glass of the present invention essentially comprises the
above components, but may contain other component within a range
not to impair the object of the present invention. In a case where
such other component is contained, the total content of such
components is preferably at most 5%, typically at most 3%. Now, the
above other components will be explained.
[0071] ZnO may be contained for example up to 2% in order to
improve the melting property of the glass at high temperature in
some cases, but its content is preferably at most 1%. In a case
where the glass is produced by a float process, the content is
preferably at most 0.5%. If the content exceeds 0.5%, ZnO may be
reduced at the time of producing the glass by the float process,
and product defects may result. ZnO is typically not contained.
[0072] B.sub.2O.sub.3 may be contained for example up to less than
1% in order to improve the melting property at high temperature or
the glass strength in some cases. If its content is at least 1%, it
is difficult to obtain homogeneous glass, and to form glass, or the
chipping resistance may be decreased. B.sub.2O.sub.3 is typically
not contained.
[0073] Since TiO.sub.2 changes an oxidation reduction state of Fe
ions (Fe.sup.2+, Fe.sup.3+) present in the glass, whereby the
visible light transmittance changes, and the glass is stained, if
contained, the TiO.sub.2 content is preferably at most 1%, and
TiO.sub.2 is typically not contained.
[0074] Li.sub.2O is a component to lower the strain point whereby
stress tends to be relaxed, and as a result, a stable surface
compressive stress layer cannot be obtained. Therefore, glass
preferably contains no Li.sub.2O. Even if Li.sub.2O is contained,
its content is preferably less than 1%, more preferably at most
0.05%, particularly preferably less than 0.01%.
[0075] Further, at the time of chemical tempering treatment,
Li.sub.2O sometimes elutes into a molten salt such as KNO.sub.3,
and if the chemical tempering treatment is carried out with a
molten salt containing Li, the surface compress stress is
remarkably lowered. That is, the present inventors chemically
tempered the glass of the after-mentioned Example 20 by using
KNO.sub.3 containing no Li, KNO.sub.3 containing 0.005 mass % of
Li, KNO.sub.3 containing 0.01 mass % of Li and KNO.sub.3 containing
0.04 mass % of Li under the condition of 450.degree. C. for 6
hours, and as a result, they found that the surface compressive
stress was remarkably lowered even by the molten salt containing
0.005 mass % of Li. Therefore, from the above viewpoint, no
Li.sub.2O is preferably contained.
[0076] CaO improves the melting property at high temperature or
makes the glass be hardly devitrified, and thus may be contained up
to less than 1%. If its content is at most 1%, the ion exchange
rate or the chipping resistance will be decreased.
[0077] SrO may be contained as the case requires, but its content
is preferably less than 1% if contained since it has a high effect
of lowering the ion exchange rate as compared with MgO and CaO.
[0078] BaO has the highest effect of lowering the ion exchange rate
among alkaline earth metal oxides, and thus it is preferred that no
BaO is contained, or its content is less than 1% even if
contained.
[0079] In a case where SrO or BaO is contained, their total content
is preferably at most 1%, more preferably less than 0.3%.
[0080] In a case where at least one of CaO, SrO, BaO and ZrO.sub.2
is contained, the total content of these four components is
preferably less than 1.5%. If it is at least 1.5%, the ion exchange
rate may be decreased. Typically it is at most 1%.
[0081] As a refining agent at the time of melting glass, SO.sub.3,
a chloride or a fluoride may appropriately be contained. However,
in order to increase the visibility of display devices such as a
touch panel, it is preferred to reduce contamination of impurities
such as Fe.sub.2O.sub.3, NiO or Cr.sub.2O.sub.3 having an
absorption in a visible light range in raw materials as far as
possible, and the content of each of them is preferably at most
0.15%, more preferably at most 0.05% as represented by mass
percentage.
EXAMPLES
[0082] Now, the present invention will be described in further
detail with reference to Examples. However, it should be understood
that the present invention is by no means restricted to such
specific examples.
[0083] In Examples 1 to 12 and 20 to 22 shown in Tables 1 to 3,
commonly used glass raw materials such as oxides, hydroxides,
carbonates and nitrates were properly selected so as to have
compositions as represented by mole percentage shown in columns of
SiO.sub.2 to K.sub.2O, weighed to obtain 400 g of glass, and in
addition, although not shown in the above-mentioned compositions,
sodium sulfate corresponding to 0.2 mass % as calculated as
SO.sub.3 was added to the raw materials, and the raw materials were
mixed. Then, the raw material mixture was put in a platinum
crucible, the platinum crucible was put in a resistance heat type
electric furnace at 1,600.degree. C., the raw material mixture was
melted for 3 hours, refined, homogenized and cast into a mold, and
annealed at a predetermined temperature to obtain a glass block.
The glass block was cut and polished and finally both surfaces were
mirror polished to obtain a plate form glass having a size of 40
mm.times.40 mm.times.0.9 mm in thickness.
[0084] In Example 23 shown in Table 3, a separately prepared soda
lime glass was used, and in Examples 13 to 19 shown in Tables 2 and
3, such melting of glass and the like is not carried out.
[0085] Examples 1 to 19 are examples of the present invention, and
Examples 20 to 23 are comparative examples.
[0086] Further, compositions as represented by mass percentage
corresponding to the compositions as represented by mole percentage
shown in Tables 1 to 3 are shown in Tables 4 to 6.
[0087] Of the obtained glass, the glass transition point Tg (unit:
.degree. C.), the temperature T2 (unit: .degree. C.) at which the
viscosity becomes 10.sup.2 dPas, the temperature T4 (unit: .degree.
C.) at which the viscosity becomes 10.sup.4 dPas, the specific
gravity .rho., the average linear expansion coefficient .alpha.
(unit: -7/.degree. C.) at from 50 to 350.degree. C., and the
devitrification temperature Td (unit: .degree. C.) are shown.
[0088] Values with * are values obtained by calculation from the
composition or estimated values, and the same applies to other
measurement data such as the after-mentioned F. Further, the
devitrification temperature was to be measured by whether the glass
held at a certain temperature (X.degree. C.) for 15 hours was
devitrified or not, and if the glass was not devitrified at
X.degree. C., the result is represented by Td<X.
[0089] Further, the crack 50% start load F (unit: kg) of each glass
was measured as follows by using a Vickers hardness tester.
[0090] Further, the above plate form glass was polished by #1000
abrasive grains for 300 .mu.m or more, and then polished by cerium
oxide so that the surface would be a mirror surface. Then, to
remove the strain by processing on the mirror polished surface, the
glass was heated to Tg+50.degree. C. by a resistant heat type
electric furnace and held at the temperature for one hour, and then
cooled to room temperature at a rate of 0.5.degree. C./min. The
temperature was increased at such a temperature-raising rate that
the temperature reached Tg in one hour.
[0091] Using samples subjected to the above treatment, the
incidence of cracks was measured. That is, in the air, at a
temperature of from 20 to 28.degree. C. under a humidity of from 40
to 75%, while the load of the Vickers hardness tester was changed
step by step from 0.025 kg, 0.05 kg, 0.1 kg, 0.2 kg, 0.3 kg, 0.5
kg, 1 kg to 2 kg, Vickers indenters were pressed at 10 points at
each bad, and the number of cracks formed from four corners of the
indentation among the maximum of 40 was counted. The load at which
20 cracks were formed was read from a graph and regarded as the
crack 50% start load F.
[0092] F is preferably at least 0.2 kg, more preferably at least
0.6 kg.
[0093] In Examples 5 and 20 to 23, a scribing test was carried out
by using GLASS SCRIBER manufactured by JOYO ENGINEERING CO., LTD.,
and the chipping start load f (unit: N) was measured as
follows.
[0094] A measurement sample for the scribing test was prepared in
the same manner as the above sample for measurement of F.
[0095] In the scribing test, using a 130.degree. diamond wheel
cutter, while the load was changed step by step from 8.6 N to 26.6
N, scribing was carried out on the sample, whereupon the incidence
of chipping was evaluated. The minimum load at which the chipping
occurs was regarded as the chipping start load f.
[0096] In glass in Example 5 as an example of the present invention
in which the above F is so large as 0.86 kg, chipping occurred for
the first time at a high load of 15.8 N, whereas in glass in each
of Examples 20 to 23 which are comparative examples in which F was
so small as from 0.03 to 0.13 kg, chipping occurred at a load so
low as 12.2 N. Thus, it is found that incidence of chipping is
evaluated by the crack 50% start load.
[0097] The plate form glass in each of Examples 1 to 12, 20 and 23
was chemically tempered as follows. That is, the chemical tempering
treatment was carried out by immersing such glass in a KNO.sub.3
molten salt at 400.degree. C. for 10 hours. Of each glass, the
surface compressive stress S (unit: MPa) and the depth t (unit:
.mu.m) of the compressive stress layer were measured by a surface
stress meter FSM-6000 manufactured by Orihara Seisakusho
Corporation. The results are shown in columns in Tables. As evident
from Tables, the glass in each of Examples of the present invention
has a surface compressive stress of at least 550 MPa and a stress
layer depth of at least 40 .mu.m, and thus it is found that a
desired compressive stress layer is formed.
TABLE-US-00001 TABLE 1 Ex. 1 2 3 4 5 6 7 8 9 SiO.sub.2 69.6 71.1
71.0 71.7 71.3 71.3 71.6 70.9 67.9 Al.sub.2O.sub.3 3.0 2.0 2.0 2.0
2.0 2.0 2.0 2.0 3.3 MgO 12.0 11.5 11.0 10.5 10.4 11.8 11.8 10.6
12.8 CaO 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 SrO 0.03 0.03 0.03
0.03 0.03 0.03 0.03 0.03 0.03 BaO 0.02 0.02 0.02 0.02 0.02 0.02
0.02 0.02 0.02 ZrO.sub.2 0.5 0.5 1.0 0.5 0.5 0.5 0.5 1.5 1.2
Na.sub.2O 8.7 8.6 8.7 9.7 10.8 8.6 8.6 8.7 8.8 K.sub.2O 5.9 5.9 5.9
5.2 4.6 5.4 5.1 5.9 5.7 Si + Al 72.6 73.1 73.0 73.7 73.3 73.3 73.6
72.9 71.2 Tg 582 572 572 560 548 576 574 582 603 T2 1600* 1589 1602
1600* 1569 1601* 1604* 1600* 1580* T4 1164* 1154 1164 1153* 1127
1159* 1161* 1166* 1158* .rho. 2.451 2.443 2.456 2.440 2.440 2.437
2.436 2.469 2.483 S 595 551 576 569 598 574 578 601 665 t 48 51 48
46 45 44 43 47 39 .alpha. 94 92 90 94 96 90 87 89 89 Td <1160
<1160 <1160 <1150 <1050 <1150 <1150 <1160
<1150 F 1.3 1.2 0.51 0.46 0.86 0.91 1.2 0.33 0.27 f -- -- -- --
15.8 -- -- -- --
TABLE-US-00002 TABLE 2 Ex. 10 11 12 13 14 15 16 17 18 SiO.sub.2
67.2 68.8 68.7 69.8 71.6 74.8 75.0 75.0 75.0 Al.sub.2O.sub.3 3.9
2.7 2.9 2.9 2.0 0 0 0 0 MgO 13.5 13.0 12.5 11.9 10.5 10.5 8.9 6.8
6.6 CaO 0.3 0.3 0.8 0.3 0 0 0 0 0 SrO 0.03 0.03 0.03 0 0 0 0 0 0
BaO 0.02 0.02 0.02 0 0 0 0 0 0 ZrO.sub.2 0.7 0.7 0.7 0.5 0.5 0 0 0
0 Na.sub.2O 8.7 8.7 8.7 8.7 10.9 9.9 15.0 12.6 15.0 K.sub.2O 5.7
5.7 5.6 5.9 4.6 4.7 1.1 5.6 3.4 Si + Al 71.1 71.5 71.6 72.7 73.6
74.8 75.0 75.0 75.0 Tg 603 585 587 582* 547* 556* 540* 500* 500* T2
1586 1584 1580* 1599* 1575* 1600* 1559* 1594* 1571* T4 1160 1155
1150* 1163* 1131* 1139* 1086* 1122* 1095* .rho. 2.474 2.464 2.467
2.45* 2.44* 2.41* 2.41* 2.41* 2.41* S 660 626 628 595* 614* 600*
748* 550* 661* t 40 42 40 49* 46* 53* 45* 64* 58* .alpha. 90 89 89
94* 96* 87* 91* 99* 99* Td <1150 <1150 <1150 <1160*
<1050* -- -- -- -- F 0.28 0.33 0.38 0.9* 0.86* 1* 1* 1* 1* f --
-- -- -- 15.8* -- -- -- --
TABLE-US-00003 TABLE 3 Ex. 19 20 21 22 23 SiO.sub.2 69.9 64.5 67.8
67.3 72 Al.sub.2O.sub.3 2.5 6.0 2.7 1.7 1.1 B.sub.2O.sub.3 0 0 3.0
0.1 0 MgO 13.6 11.0 10.4 15.0 5.5 CaO 0 0 0 0 8.6 SrO 0 0 0 0 0 BaO
0 0 0 0 0 ZrO.sub.2 0 2.5 0 0 0 Na.sub.2O 7.7 12.0 12.0 9.9 12.6
K.sub.2O 6.3 4.0 4.0 6.0 0.2 Si + Al 72.4 70.5 70.5 69.0 73.1 Tg
598* 620 548* 555* 588 T2 1600* 1575 1508* 1479* 1510 T4 1163* 1168
1052* 1060* 1052 .rho. 2.43* 2.525 2.427* 2.467* 2.49 S 550* 946
765* 540* 713 t 56* 34 56* 58* 10 .alpha. 87* 91 89* 94* 86 Td --
<1140 -- -- -- F 0.8* 0.13 0.03 0.13 0.12 f -- 12.2 12.2 12.2
12.2
TABLE-US-00004 TABLE 4 Ex. 1 2 3 4 5 6 7 8 9 SiO.sub.2 68.1 69.9
69.3 68.8 70.4 70.3 70.3 70.7 65.9 Al.sub.2O.sub.3 5.0 3.3 3.3 3.3
3.3 3.3 3.3 3.4 5.5 MgO 7.8 7.6 7.2 6.9 6.9 6.9 7.8 7.8 8.3 CaO 0.3
0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 SrO 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1
0.05 BaO 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.05 ZrO.sub.2 1.0 1.0 2.0
3.0 1.0 1.0 1.0 1.0 2.4 Na.sub.2O 8.7 8.8 8 8 8.7 9.9 11.0 8.8 8.8
8.8 K.sub.2O 9.0 9.1 9.0 8.9 8.0 7.1 8.3 7.9 8.6
TABLE-US-00005 TABLE 5 Ex. 10 11 12 13 14 15 16 17 18 SiO.sub.2
65.5 67.5 67.3 68.3 70.5 75.2 76.4 74.0 74.8 Al.sub.2O.sub.3 6.4
4.5 4.8 4.8 3.4 0 0 0 0 MgO 8.8 8.6 8.2 7.8 6.9 7.1 6.1 4.5 4.4 CaO
0.3 0.3 0.7 0.3 0 0 0 0 0 SrO 0.1 0.1 0.1 0 0 0 0 0 0 BaO 0.1 0.1
0.1 0 0 0 0 0 0 ZrO.sub.2 1.4 1.4 1.4 1.0 1.0 0 0 0 0 Na.sub.2O 8.8
.8 8.8 8.8 11.0 10.3 15.8 12.9 15.4 K.sub.2O 8.7 8.8 8.7 9.0 7.1
7.4 1.7 8.7 5.3
TABLE-US-00006 TABLE 6 Ex. 19 20 21 22 23 SiO.sub.2 69.2 60.9 66.7
67.1 72.8 Al.sub.2O.sub.3 4.2 9.6 4.6 2.8 1.9 B.sub.2O.sub.3 0 0
3.4 0.1 0 MgO 9.0 7.0 6.9 10.1 3.7 CaO 0 0 0 0 8.1 SrO 0 0 0 0 0
BaO 0 0 0 0 0 ZrO.sub.2 0 4.8 0 0 0 Na.sub.2O 7.9 11.7 12.2 10.2
13.1 K.sub.2O 9.7 5.9 6.2 9.4 0.3
[0098] The present invention is applicable to a cover glass of a
display device, its production, etc.
[0099] The entire disclosure of Japanese Patent Application No.
2009-241524 filed on Oct. 20, 2009 including specification, claims
and summary is incorporated herein by reference in its
entirety.
* * * * *