U.S. patent application number 16/936533 was filed with the patent office on 2020-11-05 for crystallized glass of three-dimensional shape, chemically strengthened glass of three-dimensional shape, and method for producing crystallized glass of three-dimensional shape and chemically strengthened glass of three-dimensional shape.
This patent application is currently assigned to AGC Inc.. The applicant listed for this patent is AGC Inc.. Invention is credited to Kenji IMAKITA, Akio KOIKE, Qing LI, Eriko MAEDA.
Application Number | 20200346969 16/936533 |
Document ID | / |
Family ID | 1000005006117 |
Filed Date | 2020-11-05 |
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United States Patent
Application |
20200346969 |
Kind Code |
A1 |
LI; Qing ; et al. |
November 5, 2020 |
CRYSTALLIZED GLASS OF THREE-DIMENSIONAL SHAPE, CHEMICALLY
STRENGTHENED GLASS OF THREE-DIMENSIONAL SHAPE, AND METHOD FOR
PRODUCING CRYSTALLIZED GLASS OF THREE-DIMENSIONAL SHAPE AND
CHEMICALLY STRENGTHENED GLASS OF THREE-DIMENSIONAL SHAPE
Abstract
The present invention provides crystallized glass of
three-dimensional shape for easily producing chemically
strengthened glass of three-dimensional shape that resists damage
and has exceptional transparency. This crystallized glass of
three-dimensional shape: contains crystals; has light transmittance
in terms of a thickness of 0.8 mm of 80% or higher; and contains
45-74% SiO.sub.2, 1-30% Al.sub.2O.sub.3, 1-25% Li.sub.2O, 0-10%
Na.sub.2O, 0-5% K.sub.2O, a total of 0-15% of SnO.sub.2 and/or
ZrO.sub.2, and 0-12% P.sub.2O.sub.5, these amounts expressing the
oxide-based mass percentage.
Inventors: |
LI; Qing; (Tokyo, JP)
; IMAKITA; Kenji; (Tokyo, JP) ; KOIKE; Akio;
(Tokyo, JP) ; MAEDA; Eriko; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
AGC Inc. |
Chiyoda-ku |
|
JP |
|
|
Assignee: |
AGC Inc.
Chiyoda-ku
JP
|
Family ID: |
1000005006117 |
Appl. No.: |
16/936533 |
Filed: |
July 23, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2019/006907 |
Feb 22, 2019 |
|
|
|
16936533 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C03B 23/0252 20130101;
C03B 32/02 20130101; C03C 2204/00 20130101; C03C 4/0028 20130101;
C03C 10/0054 20130101; C03C 21/002 20130101; C03C 10/0027
20130101 |
International
Class: |
C03C 10/00 20060101
C03C010/00; C03C 4/00 20060101 C03C004/00; C03C 21/00 20060101
C03C021/00; C03B 32/02 20060101 C03B032/02; C03B 23/025 20060101
C03B023/025 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2018 |
JP |
2018-033693 |
Feb 8, 2019 |
JP |
2019-021896 |
Claims
1. A three-dimensionally shaped crystallized glass comprising a
crystal, the glass having a light transmittance of 80% or more in
terms of a thickness of 0.8 mm and comprising, in mass % on an
oxide basis: from 45 to 74% of SiO.sub.2; from 1 to 30% of
Al.sub.2O.sub.3; from 1 to 25% of Li.sub.2O; from 0 to 10% of
Na.sub.2O; from 0 to 5% of K.sub.2O; from 0 to 15% in total of
either one or more of SnO.sub.2 and ZrO.sub.2; and from 0 to 12% of
P.sub.2O.sub.5.
2. The three-dimensionally shaped crystallized glass according to
claim 1, comprising, in mass % on an oxide basis: from 58 to 74% of
SiO.sub.2; from 5 to 30% of Al.sub.2O.sub.3; from 1 to 14% of
Li.sub.2O; from 0 to 5% of Na.sub.2O; from 0 to 2% of K.sub.2O;
from 0.5 to 12% in total of either one or more of SnO.sub.2 and
ZrO.sub.2; and from 0 to 6% of P.sub.2O.sub.5.
3. The three-dimensionally shaped crystallized glass according to
claim 2, comprising, in mass % on an oxide basis: from 58 to 70% of
SiO.sub.2; from 15 to 30% of Al.sub.2O.sub.3; from 2 to 10% of
Li.sub.2O; from 0 to 5% of Na.sub.2O; from 0 to 2% of K.sub.2O;
from 0.5 to 6% of SnO.sub.2; from 0.5 to 6% of ZrO.sub.2; and from
0 to 6% of P.sub.2O.sub.5, in which Na.sub.2O+K.sub.2O is from 1 to
5%.
4. The three-dimensionally shaped crystallized glass according to
claim 1, comprising, in mass % on an oxide basis: from 45 to 70% of
SiO.sub.2; from 1 to 20% of Al.sub.2O.sub.3; from 10 to 25% of
Li.sub.2O; from 0 to 10% of Na.sub.2O; from 0 to 5% of K.sub.2O;
from 0 to 15% of ZrO.sub.2; and from 0 to 12% of
P.sub.2O.sub.5.
5. The three-dimensionally shaped crystallized glass according to
claim 1, comprising a .beta.-spodumene crystal.
6. The three-dimensionally shaped crystallized glass according to
claim 1, comprising a petalite crystal.
7. The three-dimensionally shaped crystallized glass according to
claim 1, comprising a lithium metasilicate crystal.
8. The three-dimensionally shaped crystallized glass according to
claim 1, having a Vickers hardness of 780 or more.
9. A three-dimensionally shaped chemically strengthened glass
having a compressive stress layer on a surface thereof, the glass
being a crystallized glass comprising a crystal, having a light
transmittance of 80% or more in terms of a thickness of 0.8 mm and
comprising, in mass % on an oxide basis: from 45 to 74% of
SiO.sub.2; from 1 to 30% of Al.sub.2O.sub.3; from 1 to 25% of
Li.sub.2O; from 0 to 10% of Na.sub.2O; from 0 to 5% of K.sub.2O;
from 0 to 15% in total of either one or more of SnO.sub.2 and
ZrO.sub.2; and from 0 to 12% of P.sub.2O.sub.5.
10. The three-dimensionally shaped chemically strengthened glass
according to claim 9, comprising, in mass % on an oxide basis: from
58 to 74% of SiO.sub.2; from 5 to 30% of Al.sub.2O.sub.3; from 1 to
14% of Li.sub.2O; from 0 to 5% of Na.sub.2O; from 0 to 2% of
K.sub.2O; from 0.5 to 12% in total of either one or more of
SnO.sub.2 and ZrO.sub.2; and from 0 to 6% of P.sub.2O.sub.5.
11. The three-dimensionally shaped chemically strengthened glass
according to claim 9, comprising, in mass % on an oxide basis: from
45 to 70% of SiO.sub.2; from 1 to 20% of Al.sub.2O.sub.3; from 10
to 25% of Li.sub.2O; from 0 to 10% of Na.sub.2O; from 0 to 5% of
K.sub.2O; from 0 to 15% of ZrO.sub.2; and from 0 to 12% of
P.sub.2O.sub.5.
12. The three-dimensionally shaped chemically strengthened glass
according to claim 9, comprising a .beta.-spodumene crystal.
13. The three-dimensionally shaped chemically strengthened glass
according to claim 9, comprising a lithium metasilicate
crystal.
14. The three-dimensionally shaped chemically strengthened glass
according to claim 9, having a Vickers hardness of 800 or more.
15. The three-dimensionally shaped chemically strengthened glass
according to claim 9, having a surface compressive stress of 600
MPa or more and a depth of the compressive stress layer of 80 .mu.m
or more.
16. A production method of a glass for chemical strengthening, the
method comprising: heating and crystallizing a glass comprising, in
mass % on an oxide basis: from 45 to 74% of SiO.sub.2; from 1 to
30% of Al.sub.2O.sub.3; from 1 to 25% of Li.sub.2O; from 0 to 10%
of Na.sub.2O; from 0 to 5% of K.sub.2O; from 0 to 15% in total of
either one or more of SnO.sub.2 and ZrO.sub.2; and from 0 to 12% of
P.sub.2O.sub.5; and bend-forming a resulting crystallized glass
under heating.
17. The production method of a glass for chemical strengthening
according to claim 16, wherein the glass comprises, in mass % on an
oxide basis: from 58 to 74% of SiO.sub.2; from 5 to 30% of
Al.sub.2O.sub.3; from 1 to 14% of Li.sub.2O; from 0 to 5% of
Na.sub.2O; from 0 to 2% of K.sub.2O; from 0.5 to 12% in total of
either one or more of SnO.sub.2 and ZrO.sub.2; and from 0 to 6% of
P.sub.2O.sub.5, in which Na.sub.2O+K.sub.2O is from 1 to 5%.
18. The production method of a glass for chemical strengthening
according to claim 16, wherein the glass comprises, in mass % on an
oxide basis: from 45 to 70% of SiO.sub.2; from 1 to 20% of
Al.sub.2O.sub.3; from 10 to 25% of Li.sub.2O; from 0 to 10% of
Na.sub.2O; from 0 to 5% of K.sub.2O; from 0 to 15% of ZrO.sub.2;
and from 0 to 12% of P.sub.2O.sub.5.
19. A production method of a chemically strengthened glass, the
method comprising chemically strengthening a glass for chemical
strengthening obtained by the method according to claim 16.
Description
TECHNICAL FIELD
[0001] The present invention relates to a three-dimensionally
shaped crystallized glass having high transparency and excellent
chemical strengthening properties, and relates to a production
method thereof. The present invention also relates to a
three-dimensionally shaped chemically strengthened glass and a
production method thereof.
BACKGROUND ART
[0002] A thin chemically strengthened glass having high-strength is
used as a cover glass of a display unit of a mobile device such as
cell phone and smartphone or as a cover glass of an in-vehicle
display member such as instrument panel and head-up display (HUD).
In such a display unit, a cover glass having a three-dimensional
shape (curved shape) is sometimes required so as to improve the
operability and visibility. The three-dimensionally shaped cover
glass is produced by a method in which a flat glass sheet is heated
and then subjected to bend-forming (sometimes referred to as
three-dimensional forming) using forming molds (see, Patent
Literature 1).
[0003] Patent Literature 2 discloses a lithium aluminosilicate
glass capable of being three-dimensionally formed and chemically
strengthened.
[0004] Patent Literature 3 discloses a chemically strengthened
crystallized glass.
CITATION LIST
Patent Literature
[0005] Patent Literature 1: International Publication
WO2014/167894
[0006] Patent Literature 2: JP-T-2013-520385 (the term "JP-T" as
used herein means a published Japanese translation of a PCT patent
application)
[0007] Patent Literature 3: JP-T-2016-529201
SUMMARY OF INVENTION
Technical Problem
[0008] The chemical strengthening properties of a crystallized
glass are greatly affected by a glass composition and a
precipitated crystal. Scratch resistance and transparency of the
crystallized glass are also greatly affected by a glass composition
and a precipitated crystal. In order to obtain a crystallized glass
excellent in both chemical strengthening properties and
transparency, the glass composition and precipitated crystal need
to be subtly adjusted.
[0009] The method for obtaining a three-dimensionally shaped
crystallized glass includes a method in which an amorphous glass is
bend-formed and then crystallized, a method in which an amorphous
glass is crystallized and then processed into a three-dimensional
shape by grinding or other methods, and a method in which an
amorphous glass is crystallized and then bend-formed.
[0010] According to the method in which an amorphous glass is
bend-formed and then crystallized, since a heat treatment is
performed after the forming, not only deformation is likely to
occur but also a dimensional change is caused at the time of
crystallization of the amorphous glass, thereby making it difficult
to obtain a desired shape. According to the method in which an
amorphous glass is crystallized and then processed into a
three-dimensional shape by grinding or other methods, the grinding
processing takes a long time and therefore the production
efficiency is low.
[0011] Then, it is preferable to crystallize an amorphous glass and
then perform bend-forming. However a crystallized glass generally
has a higher softening temperature, compared with an amorphous
glass, and thus bend-forming thereof is difficult. In addition,
when a transparent crystallized glass is heated at a high
temperature so as to bend-form the glass, crystals in the
crystallized glass are likely to grow excessively, thereby giving
rise to a problem such as reduction in transparency.
[0012] In consideration of these, an object of the present
invention is to provide a three-dimensionally shaped crystallized
glass for easily producing a three-dimensionally shaped chemically
strengthened glass that is scratch-resistant and has excellent
transparency.
[0013] In addition, an object of the present invention is to
provide a three-dimensionally shaped chemically strengthened glass
that is scratch-resistant and has excellent transparency, obtained
by chemically strengthening the three-dimensionally shaped
crystallized glass above.
[0014] Furthermore, an object of the present invention is to
provide a production method of a chemically strengthened glass that
is the three-dimensionally shaped crystallized glass above.
Solution to Problem
[0015] The present invention provides a three-dimensionally shaped
crystallized glass including a crystal, the glass having a light
transmittance of 80% or more in terms of a thickness of 0.8 mm and
including, in mass % on an oxide basis, from 45 to 74% of
SiO.sub.2, from 1 to 30% of Al.sub.2O.sub.3, from 1 to 25% of
Li.sub.2O, from 0 to 10% of Na.sub.2O, from 0 to 5% of K.sub.2O,
from 0 to 15% in total of either one or more of SnO.sub.2 and
ZrO.sub.2, and from 0 to 12% of P.sub.2O.sub.5.
[0016] In addition, the present invention provides a
three-dimensionally shaped chemically strengthened glass having a
compressive stress layer on a surface thereof, the glass being a
crystallized glass including a crystal, having a light
transmittance of 80% or more in terms of a thickness of 0.8 mm and
including, in mass % on an oxide basis, from 45 to 74% of
SiO.sub.2, from 1 to 30% of Al.sub.2O.sub.3, from 1 to 25% of
Li.sub.2O, from 0 to 10% of Na.sub.2O, from 0 to 5% of K.sub.2O,
from 0 to 15% in total of either one or more of SnO.sub.2 and
ZrO.sub.2, and from 0 to 12% of P.sub.2O.sub.5.
[0017] The present invention also provides a production method of a
glass for chemical strengthening, the method including heating and
crystallizing a glass including, in mass % on an oxide basis, from
45 to 74% of SiO.sub.2, from 1 to 30% of Al.sub.2O.sub.3, from 2 to
25% of Li.sub.2O, from 0 to 10% of Na.sub.2O, from 0 to 5% of
K.sub.2O, from 0 to 15% in total of either one or more of SnO.sub.2
and ZrO.sub.2, and from 0 to 12% of P.sub.2O.sub.5, and
bend-forming a resulting crystallized glass under heating.
[0018] Furthermore, the present invention provides a production
method of a chemically strengthened glass, including heating and
crystallizing a glass including, in mass % on an oxide basis, from
45 to 74% of SiO.sub.2, from 1 to 30% of Al.sub.2O.sub.3, from 2 to
25% of Li.sub.2O, from 0 to 10% of Na.sub.2O, from 0 to 5% of
K.sub.2O, from 0 to 15% in total of either one or more of SnO.sub.2
and ZrO.sub.2, and from 0 to 12% of P.sub.2O.sub.5, bend-forming a
resulting crystallized glass under heating, and thereafter,
chemically strengthening the glass.
Advantageous Effects of Invention
[0019] In the present invention, a three-dimensionally shaped
crystallized glass for easily producing a three-dimensionally
shaped chemically strengthened glass that is scratch-resistant and
has excellent transparency, is obtained.
[0020] In addition, the chemically strengthened glass of the
present invention is scratch-resistant, has excellent transparency,
and can be easily produced by chemically strengthening the
three-dimensionally shaped crystallized glass of the present
invention.
[0021] Furthermore, in the production method of the chemically
strengthened glass of the present invention, the
three-dimensionally shaped crystallized glass of the present
invention is obtained.
BRIEF DESCRIPTION OF DRAWINGS
[0022] FIG. 1 is a perspective diagram illustrating one example of
the shape of the three-dimensionally shaped glass of the present
invention.
[0023] FIG. 2 is a perspective diagram illustrating one example of
the shape of the three-dimensionally shaped glass of the present
invention.
[0024] FIG. 3 is a perspective diagram illustrating one example of
the shape of the three-dimensionally shaped glass of the present
invention.
[0025] FIG. 4 is a diagram illustrating one example of the X-ray
diffraction pattern of the crystallized glass.
[0026] FIG. 5 is a diagram illustrating one example of the X-ray
diffraction pattern of the crystallized glass.
[0027] FIG. 6 is a schematic diagram illustrating a test method of
bend formability for the crystallized glass; (a) of FIG. 6
illustrates the state before bending; and (b) of FIG. 6 illustrates
the state of being heated and thus bent.
DESCRIPTION OF EMBODIMENTS
[0028] The embodiments of the present invention are described
below. However, the present invention is not limited to the
embodiments described below. In the following drawings, members and
regions having the same actions may be described by assigning the
same symbols thereto, and duplicated descriptions thereof may be
omitted or simplified. In addition, the embodiments in the drawings
are schematically illustrated for clearly describing the present
invention and not always show the actual size or scale exactly.
[0029] In the present description, the numerical range expressed
using "to" is used in the meaning of including numerical values
described before and after it as the lower limit value and the
upper limit value.
[0030] In the present description, the "amorphous glass" and the
"crystallized glass" are collectively referred to as "glass".
[0031] In the present description, the "amorphous glass" means a
glass in which a diffraction peak indicating a crystal cannot be
observed by a powder X-ray diffraction method.
[0032] In the present description, the "crystallized glass" is a
glass obtained by heating the "amorphous glass" to precipitate a
crystal therein and means a glass containing a crystal.
[0033] In powder X-ray diffractometry, a region where 2.theta. is
from 10.degree. to 80.degree. is measured using CuK.alpha.
radiation, and when a diffraction peak appears, a precipitated
crystal is identified by, for example, a Hanawalt method.
[0034] In the present description, the "chemically strengthened
glass" means a glass having been subjected to a chemical
strengthening treatment, and the "glass for chemical strengthening"
means a glass before being subjected to a chemical strengthening
treatment.
[0035] Furthermore, in the present description, the "base
composition of a chemically strengthened glass" means a glass
composition of a glass for chemical strengthening. Unless an
immoderate ion exchange treatment is performed, a glass composition
of a part deeper than a depth of a compressive stress layer (DOL)
in a chemically strengthened glass is the same as the base
composition of the chemically strengthened glass.
[0036] In the present description, unless otherwise indicated, the
glass composition is expressed in mass % on an oxide basis, and
mass % is simply written as "%".
[0037] In the present description, the "substantially free of"
means that the content is not higher than a level of impurities
contained in raw materials or the like, i.e., the substance is not
intentionally added. In the present description, when the
"substantially free of a certain component" is stated, the content
of the component is specifically, for example, less than 0.1%.
[0038] In the present description, the "stress profile" means a
profile showing a compressive stress value by using a depth from a
glass surface as the variable. In the stress profile, the tensile
stress is expressed as a negative compressive stress.
[0039] The "compressive stress value (CS)" can be measured by
thinning a cross section of a glass and analyzing the thinned
sample with a birefringence imaging system. The birefringence
imaging system includes, for example, a birefringence imaging
system Abrio-IM manufactured by Tokyo Instruments, Inc. The value
can also be measured by use of scattered-light photoelasticity. In
this method, the CS can be measured by making light incident from a
surface of a glass and analyzing polarization of the scattered
light. The stress meter using scattered-light photoelasticity
includes, for example, a scattered-light photoelastic stress meter
SLP-1000 manufactured by Orihara Manufacturing Co., Ltd.
[0040] The "depth of compressive stress layer (DOL)" is a depth at
which the compressive stress value (CS) is zero.
[0041] In the following, the surface compressive stress at a depth
of DOL/4 is sometimes denoted by CS.sub.1, and the compressive
stress at a depth of DOL/2 is sometimes denoted by CS.sub.2.
[0042] In addition, the depth at which the compressive stress value
becomes CS/2 is denoted by DOL.sub.1, and m.sub.1 represented by
the following expression is taken as an inclination of the stress
profile from the glass surface to the depth DOL.sub.1.
m.sub.1=(CS-CS/2)/(0-DOL.sub.1)
[0043] m.sub.2 represented by the following expression is taken as
an inclination of the stress profile from the depth DOL/4 to the
depth DOL/2.
m.sub.2=(CS.sub.1-CS.sub.2)/(DOL/4-DOL/2)
[0044] m.sub.3 represented by the following expression is taken as
an inclination of the stress profile from the depth DOL/2 to the
depth DOL.
m.sub.3=(CS.sub.2-0)/(DOL/2-DOL)
[0045] In the present description, the "internal tensile stress
(CT)" means a tensile stress value at a depth corresponding to 1/2
of a sheet thickness t.
[0046] In the present description, the "light transmittance" means
an average transmittance of light at a wavelength of 380 nm to 780
nm.
[0047] In the present description, the "haze value" means a haze
value measured with a C illuminant according to JIS K3761:2000.
[0048] In the present description, the "Vickers hardness" is a
Vickers hardness (HV0.1) specified in JIS R1610:2003.
[0049] In addition, the "fracture toughness value" means an
indentation-fracture method (IF method) fracture toughness value
specified in JIS R1607:2010.
[0050] In the present description, the "three-dimensional shape"
means a shape obtained by bending a flat sheet. Incidentally, the
three-dimensional shape is not limited to a shape having a uniform
thickness as a whole but may be a shape having portions differing
in the thickness.
<Three-Dimensionally Shaped Crystallized Glass>
[0051] FIG. 1 is a perspective diagram illustrating one example of
the three-dimensionally shaped crystallized glass of the present
embodiment (hereinafter, sometimes referred to as "the present
three-dimensionally shaped glass"). In FIG. 1, a concave shape is
depicted, but the present three-dimensionally shaped glass may have
a convex shape. In FIG. 1, a glass having a flat sheet shape in the
central part is illustrated, but the present three-dimensionally
shaped glass may be curved as a whole. In addition, the present
three-dimensionally shaped glass may have a three-dimensional shape
composed of a plurality of R shapes as illustrated in FIG. 2 and
FIG. 3.
[0052] The present three-dimensionally shaped glass has high
transparency and therefore, is suitable for a cover glass, etc. in
the display part of a mobile terminal, etc. The light transmittance
in terms of a thickness of 0.8 mm of the present
three-dimensionally shaped glass is preferably 80% or more, because
the screen is viewed easily when used for a cover glass of a mobile
display, and is more preferably 85% or more, still more preferably
86% or more, particularly preferably 88% or more. The light
transmittance of the present three-dimensionally shaped glass in
terms of a thickness of 0.8 mm is preferably higher, but it is
usually 91% or less, or 90% or less. The light transmittance of 90%
is comparable to that of a general amorphous glass.
[0053] The haze value of the present three-dimensionally shaped
glass in terms of a thickness of 0.8 mm is preferably 1.5% or less,
more preferably 1.2% or less, still more preferably 1% or less, yet
still more preferably 0.8% or less, and most preferably 0.5% or
less. On the other hand, in the case where the haze can hardly be
reduced unless the crystallinity is reduced, in order to, e.g.,
increase the mechanical strength, the haze value of the present
three-dimensionally shaped glass in terms of a thickness of 0.8 mm
is preferably 0.05% or more, more preferably 0.1% or more.
[0054] The present three-dimensionally shaped glass is a
crystallized glass and therefore, the strength is high compared
with an amorphous glass. In addition, the Vickers hardness is
large, and the glass is scratch-resistant.
[0055] In order to enhance the abrasion resistance, the Vickers
hardness of the present three-dimensionally shaped glass is
preferably 680 or more, more preferably 700 or more, and still more
preferably 740 or more, yet still more preferably 780 or more,
particularly preferably 800 or more.
[0056] However, if the Vickers hardness is too large, the
processing may become difficult. Therefore, the Vickers hardness of
the present three-dimensionally shaped glass is preferably 1,100 or
less, more preferably 1,050 or less, still more preferably 1,000 or
less.
[0057] The crystallized glass (hereinafter, sometimes referred to
as "the present crystallized glass") constituting the present
three-dimensionally shaped glass contains crystals, and it is
preferable to contain a lithium aluminosilicate crystal or a
lithium silicate crystal. In the case of containing a lithium
aluminosilicate crystal or a lithium silicate crystal, these
crystals are also ion-exchanged during a chemical strengthening
treatment and therefore, high strength is obtained. Examples of the
lithium aluminosilicate crystal include a .beta.-spodumene crystal
and a petalite crystal. Examples of the lithium silicate crystal
include a lithium metasilicate crystal and a lithium disilicate
crystal.
[0058] In the case of increasing the strength after chemical
strengthening, it is preferable for the present crystallized glass
to contain a .beta.-spodumene crystal. In the case of improving the
transparency and formability while keeping the chemical
strengthening properties, it is preferable for the present
crystallized glass to contain a lithium metasilicate crystal.
[0059] The .beta.-spodumene crystal is represented by
LiAlSi.sub.2O.sub.6 and is a crystal showing diffraction peaks at
Bragg angles (2.theta.) of 25.55.degree..+-.0.05.degree.,
22.71.degree..+-.0.05.degree., and 28.20.degree..+-.0.05.degree. in
an X-ray diffraction spectrum.
[0060] FIG. 2 illustrates examples of X-ray diffraction patterns of
a crystallized glass (a glass for chemical strengthening)
containing a .beta.-spodumene crystal and a crystallized glass
(chemically strengthened glass) obtained by chemically
strengthening the crystallized glass above. In FIG. 2, the solid
line is an X-ray diffraction pattern measured for the crystallized
glass sheet before strengthening, and a diffraction line of the
.beta.-spodumene crystal indicated by black circles is observed in
FIG. 2. The broken line shows an X-ray diffraction pattern measured
for the crystallized glass (chemically strengthened glass) sheet
after chemical strengthening. It is considered that the positions
of diffraction peaks are shifted to the lower angle side by
chemical strengthening because the lattice spacing is increased due
to occurrence of ion exchange between small ions in the crystal and
large ions in the molten salt.
[0061] However, when the present inventors compared powder X-ray
diffraction patterns before and after chemical strengthening, such
a shift of a diffraction line was not observed. The reason therefor
is considered because a change in the lattice spacing due to a
chemical strengthening treatment occurs only in the vicinity of the
surface of the glass sheet and no change is caused in the internal
crystals by a chemical strengthening treatment.
[0062] In the crystallized glass containing a .beta.-spodumene
crystal, the surface compressive stress (CS) tends to be increased
by chemical strengthening, compared with a crystallized glass
containing other crystals. This may be because the crystal
structure of the .beta.-spodumene crystal is dense and therefore,
when ions in the precipitated crystal are substituted by larger ion
through an ion exchange treatment for chemical strengthening, the
compressive stress generated along with a change in the crystal
structure increases.
[0063] The .beta.-spodumene crystal is known to have a high crystal
growth rate. Therefore, in the crystallized glass containing a
.beta.-spodumene crystal, the crystals contained therein easily
growth and consequently, in many cases, such a glass has low
transparency and large haze value. However, since the present
three-dimensionally shaped glass contains a large number of
microcrystals, the transparency is high and the haze value is
small.
[0064] The lithium metasilicate crystal is represented by
Li.sub.2SiO.sub.3 and is a crystal showing diffraction peaks at
Bragg angles (2.theta.) of 26.98.+-.0.2, 18.88.+-.0.2, and
33.05.+-.0.2 in an X-ray diffraction spectrum. FIG. 3 illustrates
an example of the X-ray diffraction pattern of a crystallized glass
containing a lithium metasilicate crystal.
[0065] The crystallized glass containing a lithium metasilicate
crystal has a high fracture toughness value compared with an
amorphous glass, and intense fracture is difficult to occur even
when a large compressive stress is formed by chemical
strengthening. An amorphous glass capable of precipitating a
lithium metasilicate crystal may precipitate a lithium disilicate
crystal depending on the heat treatment conditions, etc., and when
a lithium metasilicate crystal and a lithium disilicate crystal are
contained at the same time, the transparency is reduced. Then, in
terms of enhancing the transparency, it is preferred that the
crystallized glass containing lithium metasilicate does not contain
lithium disilicate. The phrase "does not contain lithium
disilicate" as used herein means that in the above-described X-ray
diffractometry, a diffraction peak of a lithium disilicate crystal
is not observed.
[0066] In the case of lowering the bend-forming temperature, the
present crystallized glass preferably contains a petalite crystal
or a lithium metasilicate crystal. A crystallized glass containing
such a crystal has a low crystallization treatment temperature and
a low softening temperature and therefore, the forming temperature
tends to be easily lowered.
[0067] For increasing the mechanical strength, the crystallinity of
the present crystallized glass is preferably 10% or more, more
preferably 15% or more, still more preferably 20% or more,
particularly preferably 25% or more. On the other hand, for
enhancing the transparency, the crystallinity of the present
crystallized glass is preferably 70% or less, more preferably 60%
or less, particularly preferably 50% or less. A low crystallinity
is preferable also in terms of that bend-forming or the like is
easily performed by heating.
[0068] The crystallinity can be calculated from X-ray diffraction
intensity by a Rietveld method. The Rietveld method is described in
"Handbook of Crystal Analysis" edited by the "Handbook of Crystal
Analysis" Editing Committee of the Crystallographic Society of
Japan (published by Kyoritsu Shuppan Co., Ltd., 1999, pp.
492-499).
[0069] The average particle size of precipitated crystals in the
present crystallized glass is preferably 300 nm or less, more
preferably 200 nm or less, still more preferably 150 nm or less,
and particularly preferably 100 nm or less. The average particle
size of precipitated crystals can be calculated from powder X-ray
diffraction intensity by the Rietveld method.
[0070] The crystallized glass containing a .beta.-spodumene crystal
is also known to have a small thermal expansion coefficient. In the
case where the present crystallized glass contains
.beta.-spodumene, the average thermal expansion coefficient thereof
at 50.degree. C. to 350.degree. C. is preferably
30.times.10.sup.-7/.degree. C. or less, more preferably
25.times.10.sup.-7/.degree. C. or less, still more preferably
20.times.10.sup.-7/.degree. C. or less, and particularly preferably
15.times.10.sup.-7/.degree. C. or less. The average thermal
expansion coefficient at 50.degree. C. to 350.degree. C. is usually
10.times.10.sup.-7/.degree. C. or more.
[0071] On the other hand, in the case where the present
crystallized glass contains a lithium metasilicate crystal, the
average thermal expansion coefficient thereof at 50.degree. C. to
350.degree. C. is preferably 10.times.10.sup.-7/.degree. C. or
more, more preferably 11.times.10.sup.-7/.degree. C. or more, still
more preferably 12.times.10.sup.-7/.degree. C. or more, and
particularly preferably 13.times.10.sup.-7/.degree. C. or more. If
the thermal expansion coefficient is too large, cracking is likely
to occur during heat treatment. Accordingly, in the case where the
present crystallized glass contains a lithium metasilicate crystal,
the average thermal expansion coefficient thereof at 50.degree. C.
to 350.degree. C. is preferably 160.times.10.sup.-7/.degree. C. or
less, more preferably 150.times.10.sup.-7/.degree. C. or less,
still preferably 140.times.10.sup.-7/.degree. C. or less.
[0072] The fracture toughness value of the present crystallized
glass is preferably 0.8 MPam.sup.1/2 or more, more preferably 1
MPam.sup.1/2 or more. Within this range, fragments are less likely
to scatter upon breakage of the strengthened glass.
[0073] The Young's modulus of the present crystallized glass is
preferably 80 GPa or more, more preferably 86 GPa or more, still
more preferably 90 GPa or more, and particularly preferably 100 GPa
or more. When the Young's modulus is increased, fragments are less
likely to scatter upon breakage of the strengthened glass.
[0074] In the case where the present crystallized glass contains a
lithium aluminosilicate crystal, the glass preferably includes, in
mass % on an oxide basis, from 58 to 74% of SiO.sub.2, from 5 to
30% of Al.sub.2O.sub.3, from 1 to 14% of Li.sub.2O, from 0 to 5% of
Na.sub.2O, from 0 to 2% of K.sub.2O, from 0.5 to 12% in total of
either one or more of SnO.sub.2 and ZrO.sub.2, and from 0 to 6% of
P.sub.2O.sub.5.
[0075] In the composition above, it is more preferable to include
from 2 to 14% of Li.sub.2O, and it is also more preferred that the
total (Na.sub.2O+K.sub.2O) of the contents of Na.sub.2O and
K.sub.2O is from 1 to 5%.
[0076] In addition, it is more preferred that the glass includes
from 58 to 70% of SiO.sub.2, from 15 to 30% of Al.sub.2O.sub.3,
from 2 to 10% of Li.sub.2O, from 0 to 5% of Na.sub.2O, from 0 to 2%
of K.sub.2O, from 0.5 to 6% of SnO.sub.2, from 0.5 to 6% of
ZrO.sub.2, and from 0 to 6% of P.sub.2O.sub.5 and
Na.sub.2O+K.sub.2O is from 1 to 5%.
[0077] In other words, the present three-dimensionally shaped glass
is preferably a glass obtained by crystallizing an amorphous glass
having the composition above.
[0078] In the case where the present crystallized glass contains a
lithium silicate crystal, the glass preferably includes, in mass %
on an oxide basis, from 45 to 75% of SiO.sub.2, from 1 to 20% of
Al.sub.2O.sub.3, from 10 to 25% of Li.sub.2O, from 0 to 12% of
P.sub.2O.sub.5, from 0 to 15% of ZrO.sub.2, from 0 to 10% of
Na.sub.2O, and from 0 to 5% of K.sub.2O.
<Chemically Strengthened Glass>
[0079] The present three-dimensionally shaped glass is preferably
chemically strengthened. The three-dimensionally shaped chemically
strengthened glass of this embodiment (hereinafter, sometimes
referred to as "the present strengthened glass") obtained by
chemically strengthening the present three-dimensionally shaped
glass is described.
[0080] The surface compressive stress (CS) of the present
strengthened glass is preferably 600 MPa or more, because cracking
is hardly caused by deformation such as deflection. The surface
compressive stress of the present strengthened glass is more
preferably 800 MPa or more.
[0081] The depth of compressive stress layer (DOL) of the present
strengthened glass is preferably 80 .mu.m or more, because cracking
hardly occurs even when the surface is flawed. The DOL of the
present strengthened glass is preferably 100 .mu.m or more.
[0082] In addition, the maximum depth (hereinafter, sometimes
referred to as "50 MPa depth") at which the compressive stress
value is 50 MPa or more is preferably 80 .mu.m or more, because
cracking hardly occurs even when the glass is dropped on a hard
surface such as asphalt. The 50 MPa depth is more preferably 90
.mu.m or more, and particularly preferably 100 .mu.m or more.
[0083] In the present strengthened glass, the inclination m.sub.1
of the stress profile from the glass surface to the depth DOL.sub.1
is preferably -50 MPa/.mu.m or less, more preferably -55 MPa/.mu.m
or less, and still more preferably -60 MPa/.mu.m or less. The
chemically strengthened glass is a glass having a compressive
stress layer formed in the surface. Since a tensile stress is
generated in a portion far from the surface, the stress profile
thereof has a negative inclination from the surface at a depth of
zero toward the inside. Accordingly, m.sub.1 is a negative value,
and when an absolute value thereof is large, a stress profile
having a large surface compressive stress CS and a small internal
tensile stress CT is obtained.
[0084] The inclination m.sub.2 of the stress profile from a depth
of DOL/4 to a depth of DOL/2 has a negative value. In order to
suppress scattering of fragments upon breakage of the strengthened
glass, the inclination m.sub.2 is preferably -5 MPa/.mu.m or more,
more preferably -3 MPa/.mu.m or more, and still more preferably -2
MPa/.mu.m or more. If m.sub.2 is too large, the 50 MPa depth is
reduced, and there is a concern that the drop strength to asphalt
may lack. In order to increase the 50 MPa depth, m.sub.2 is
preferably -0.3 MPa/.mu.m or less, more preferably -0.5 MPa/.mu.m
or less, and still more preferably -0.7 MPa/.mu.m or less.
[0085] In the present strengthened glass, the inclination m.sub.3
of the stress profile from a depth of DOL/2 to DOL has a negative
value. In order to suppress scattering of fragments upon breakage
of the strengthened glass, m.sub.3 is preferably -5 MPa/mm or more,
more preferably -4 MPa/.mu.m or more, still more preferably -3.5
MPa/.mu.m or more, and particularly preferably -2 MPa/.mu.m or
more. If the absolute value of m.sub.3 is too small, the 50 MPa
depth is reduced, and cracking is likely to occur when the glass is
flawed. In order to increase the 50 MPa depth, m.sub.3 is
preferably -0.3 MPa/.mu.m or less, more preferably -0.5 MPa/.mu.m
or less, and still more preferably -0.7 MPa/.mu.m or less.
[0086] The ratio m.sub.2/m.sub.3 of the inclination m.sub.2 to the
inclination m.sub.3 is preferably 2 or less, because deep DOL and
small CT are obtained. The ratio m.sub.2/m.sub.3 is more preferably
1.5 or less, and still more preferably 1 or less. In order to
prevent occurrence of cracks in an end face of the strengthened
glass, the ratio m.sub.2/m.sub.3 is preferably 0.3 or more, more
preferably 0.5 or more, and still more preferably 0.7 or more.
[0087] The internal tensile stress (CT) of the present strengthened
glass is preferably 110 MPa or less, because fragments are less
likely to scatter upon breakage of the strengthened glass. The CT
is more preferably 100 MPa or less, still more preferably 90 MPa or
less. On the other hand, when the CT is reduced, the CS is also
reduced, resulting in a tendency that sufficient strength is
difficult to be obtained. Therefore, the CT is preferably 50 MPa or
more, more preferably 55 MPa or more, and still more preferably 60
MPa or more.
[0088] The four point bending strength of the present strengthened
glass is preferably 900 MPa or more.
[0089] Here, the four point bending strength is measured using a
test piece of 40 mm.times.5 mm.times.0.8 mm under the conditions of
a lower span of 30 mm, an upper span of 10 mm and a cross head
speed of 0.5 mm/min. An average value of 10 test pieces is taken as
the four point bending strength.
[0090] The light transmittance and haze value of the present
strengthened glass are substantially the same as those of the
three-dimensionally shaped glass before chemical strengthening and
therefore, descriptions thereof are omitted. In addition, as with
the three-dimensionally shaped glass before chemical strengthening,
it is preferable for the present strengthened glass to contain a
.beta.-spodumene crystal.
[0091] The Vickers hardness of the present strengthened glass tends
to be larger than that of the three-dimensionally shaped glass
before strengthening.
[0092] The Vickers hardness of the present strengthened glass is
preferably 720 or more, more preferably 740 or more, still more
preferably 780 or more, and yet still more preferably 800 or more.
On the other hand, the Vickers hardness of the present strengthened
glass is usually 950 or less.
<Glass Composition>
[0093] Here, the glass composition of the present crystallized
glass is described. The composition of the present crystallized
glass is as a whole the same as the composition of the amorphous
glass before crystallization treatment.
[0094] In addition, the present strengthened glass is obtained by
chemically strengthening the present three-dimensionally shaped
glass composed of the present crystallized glass and unless an
immoderate ion exchange treatment is performed, the composition of
the present strengthened glass is as a whole the same as the
composition of the present crystallized glass described below.
[0095] The present crystallized glass includes, in mass % on an
oxide basis, from 45 to 74% of SiO.sub.2, from 1 to 30% of
Al.sub.2O.sub.3, from 1 to 25% of Li.sub.2O, from 0 to 10% of
Na.sub.2O, from 0 to 5% of K.sub.2O, from 0 to 15% in total of
either one or more of SnO.sub.2 and ZrO.sub.2, and from 0 to 12% of
P.sub.2O.sub.5.
[0096] In the case where the present crystallized glass contains a
lithium aluminosilicate crystal, the glass preferably includes, in
mass % on an oxide basis, from 58 to 74% of SiO.sub.2, from 5 to
30% of Al.sub.2O.sub.3, from 1 to 14% of Li.sub.2O, from 0 to 5% of
Na.sub.2O, from 0 to 2% of K.sub.2O, from 0.5 to 12% in total of
either one or more of SnO.sub.2 and ZrO.sub.2, and from 0 to 6% of
P.sub.2O.sub.5.
[0097] In the composition above, it is more preferable to include
from 2 to 14% of Li.sub.2O, and it is also more preferred that the
total (Na.sub.2O+K.sub.2O) of the contents of Na.sub.2O and
K.sub.2O is from 1 to 5%.
[0098] In addition, it is still more preferred that the glass
includes, in mass % on an oxide basis, from 58 to 70% of SiO.sub.2,
from 15 to 30% of Al.sub.2O.sub.3, from 2 to 10% of Li.sub.2O, from
0 to 5% of Na.sub.2O, from 0 to 2% of K.sub.2O, from 0.5 to 6% of
SnO.sub.2, from 0.5 to 6% of ZrO.sub.2, and from 0 to 6% of
P.sub.2O.sub.5 and Na.sub.2O+K.sub.2O is from 1 to 5%.
[0099] In the case where the present crystallized glass contains a
lithium silicate crystal, the glass preferably includes, in mass %
on an oxide basis, from 45 to 75% of SiO.sub.2, from 1 to 20% of
Al.sub.2O.sub.3, from 10 to 25% of Li.sub.2O, from 0 to 12% of
P.sub.2O.sub.5, from 0 to 15% of ZrO.sub.2, from 0 to 10% of
Na.sub.2O, and from 0 to 5% of K.sub.2O.
[0100] These preferable glass compositions are described below.
[0101] SiO.sub.2 is a component forming a network structure of the
glass. In addition, SiO.sub.2 is a component enhancing the chemical
durability, is a constituent component of a lithium aluminosilicate
crystal, and is also a constituent component of a lithium silicate
crystal. The content of SiO.sub.2 is 45% or more, preferably 50% or
more, and more preferably 55% or more. In the case of increasing
particularly the strength, the content of SiO.sub.2 is preferably
58% or more, more preferably 60% or more, and still more preferably
64% or more. On the other hand, if the content of SiO.sub.2 is too
large, the meltability decreases significantly. Therefore, the
content of SiO.sub.2 is 74% or less, preferably 70% or less, more
preferably 68% or less, and still more preferably 66% or less.
[0102] Al.sub.2O.sub.3 is a component effective in increasing the
surface compressive stress generated by chemical strengthening, and
is essential. Al.sub.2O.sub.3 is a constituent component of a
lithium aluminosilicate crystal. The content of Al.sub.2O.sub.3 is
1% or more, preferably 2% or more, more preferably 5% or more, and
still more preferably 8% or more. In the case of precipitating a
.beta.-spodumene crystal, the content of Al.sub.2O.sub.3 is more
preferably 15% or more, and still more preferably 20% or more. On
the other hand, if the content of Al.sub.2O.sub.3 is too large, the
devitrification temperature of the glass rises. The content of
Al.sub.2O.sub.3 is 30% or less, and preferably 25% or less. In
order to lower the forming temperature, the content of
Al.sub.2O.sub.3 is more preferably 20% or less, and still more
preferably 15% or less.
[0103] Li.sub.2O is a component forming a surface compressive
stress by the effect of ion exchange, is a constituent component of
a lithium aluminosilicate crystal and a lithium silicate crystal,
and is essential.
[0104] The content of Li.sub.2O is 1% or more, preferably 2% or
more, more preferably 4% or more. For increasing the precipitated
amount of lithium metasilicate crystal, the content of Li.sub.2O is
more preferably 10% or more, still more preferably 15% or more, and
particularly preferably 20% or more. In the case of lithium
metasilicate, the content of Li.sub.2O is preferably 25% or less,
more preferably 22% or less, and still more preferably 20% or less.
On the other hand, for precipitating a lithium aluminosilicate
crystal, the content of Li.sub.2O is preferably 14% or less, and in
the case of precipitating a .beta.-spodumene crystal, the content
is preferably 10% or less, more preferably 8% or less, and still
more preferably 6% or less.
[0105] In the case where the present crystallized glass contains a
.beta.-spodumene crystal, the content ratio
Li.sub.2O/Al.sub.2O.sub.3 of Li.sub.2O and Al.sub.2O.sub.3 is
preferably 0.3 or less, because the transparency is improved.
[0106] Na.sub.2O is a component improving the meltability of the
glass.
[0107] Although Na.sub.2O is not essential, the content of
Na.sub.2O in the present crystallized glass is preferably 0.5% or
more, and more preferably 1% or more. If the content of Na.sub.2O
is too large, a lithium aluminosilicate crystal or lithium silicate
crystal becomes difficult to be precipitated, or the chemical
strengthening properties are deteriorated. Therefore, the content
of Na.sub.2O in the present crystallized glass is preferably 15% or
less, more preferably 12% or less, and still more preferably 10% or
less. For precipitating a .beta.-spodumene crystal, the content of
Na.sub.2O is preferably 5% or less, more preferably 4% or less, and
still more preferably 3% or less.
[0108] As with Na.sub.2O, K.sub.2O is a component lowering the
melting temperature of the glass and may be contained. In the case
where the present crystallized glass contains K.sub.2O, the content
thereof is preferably 0.5% or more, and more preferably 1% or more.
For lowering the forming temperature, the content of K.sub.2O is
more preferably 1.5% or more, and still more preferably 2% or
more.
[0109] The total content Na.sub.2O+K.sub.2O of Na.sub.2O and
K.sub.2O is preferably 1% or more, and more preferably 2% or
more.
[0110] If the content of K.sub.2O is too large, the chemical
strengthening properties are deteriorated. Therefore, in the case
where the present crystallized glass contains K.sub.2O, the content
thereof is preferably 8% or less, more preferably 7% or less, still
more preferably 6% or less, and particularly preferably 5% or less.
In order to facilitate the precipitation of a lithium
aluminosilicate crystal, the content of K.sub.2O is preferably 2%
or less. In this case, if the total content Na.sub.2O+K.sub.2O of
Na.sub.2O and K.sub.2O is excessively large, there is a concern
that the transparency may be deteriorated. For enhancing the
transparency, the total content is preferably 5% or less, more
preferably 4% or less, and still more preferably 3% or less.
[0111] In the crystallized glass containing lithium metasilicate,
in order to satisfy both the chemical strengthening properties and
the precipitation of a lithium metasilicate crystal, the content of
K.sub.2O is preferably 4% or less, more preferably 3% or less, and
particularly preferably 2% or less.
[0112] Both ZrO.sub.2 and SnO.sub.2 are not essential but are a
component constituting a crystal nucleus at the time of
crystallization treatment, and it is preferable to contain either
one or more of these. In order to produce a crystal nucleus, the
total content SnO.sub.2+ZrO.sub.2 of SnO.sub.2 and ZrO.sub.2 is
preferably 0.5% or more, and more preferably 1% or more. In order
to form a large number of crystal nuclei and thereby enhance the
transparency, the total content is preferably 3% or more, more
preferably 4% or more, still more preferably 5% or more,
particularly preferably 6% or more, and most preferably 7% or more.
In order to precipitate lithium metasilicate, it is preferable to
contain ZrO.sub.2. In this case, the content of ZrO.sub.2 is
preferably 1% or more, more preferably 2% or more, still more
preferably 4% or more, particularly preferably 6% or more, and most
preferably 7% or more. Furthermore, in order to suppress
devitrification during glass melting, the SnO.sub.2+ZrO.sub.2 is
preferably 15% or less, and more preferably 14% or less. For making
a defect due to unmelted material difficult to occur in the glass,
the total content is preferably 12% or less, more preferably 10% or
less, still more preferably 9% or less, and particularly preferably
8% or less.
[0113] In the case of precipitating a .beta.-spodumene crystal, the
content of SnO.sub.2 is preferably 0.5% or more, more preferably 1%
or more, and still more preferably 1.5% or more. The content of
SnO.sub.2 is preferably 6% or less, because a defect due to an
unmelted material is difficult to occur in the glass, and the
content is more preferably 5% or less, still more preferably 4% or
less.
[0114] SnO.sub.2 is also a component enhancing the solarization
resistance. In order to suppress solarization, the content of
SnO.sub.2 is preferably 1% or more, and more preferably 1.5% or
more.
[0115] In the case of precipitating a .beta.-spodumene crystal, the
content of ZrO.sub.2 is preferably 0.5% or more, more preferably 1%
or more. In this case, if the content of ZrO.sub.2 exceeds 6%,
devitrification readily occurs during melting, and the quality of
the chemically strengthened glass may be deteriorated. The content
of ZrO.sub.2 is preferably 6% or less, more preferably 5% or less,
and still more preferably 4% or less.
[0116] In the crystallized glass containing lithium metasilicate,
for the precipitation of a lithium metasilicate crystal, the
ZrO.sub.2 content is preferably 1% or more, more preferably 2% or
more, still more preferably 4% or more, particularly preferably 6%
or more, and most preferably 7% or more. However, for suppressing
devitrification during melting, the content of ZrO.sub.2 is
preferably 15% or less, more preferably 14% or less, still more
preferably 12% or less, and particularly preferably 11% or
less.
[0117] In the case of precipitating a .beta.-spodumene crystal and
containing both SnO.sub.2 and ZrO.sub.2, in order to enhance the
transparency, the ratio SnO.sub.2/(SnO.sub.2+ZrO.sub.2) of the
SnO.sub.2 amount to the total amount of the both is preferably 0.3
or more, more preferably 0.35 or more, and still more preferably
0.45 or more.
[0118] On the other hand, in order to increase the strength, the
SnO.sub.2/(SnO.sub.2+ZrO.sub.2) is preferably 0.7 or less, more
preferably 0.65 or less, and still more preferably 0.60 or
less.
[0119] TiO.sub.2 serves as a component forming a crystal nucleus of
the crystallized glass and therefore may be contained. In the case
of precipitating a .beta.-spodumene crystal and containing
TiO.sub.2, the content thereof is preferably 0.1% or more, more
preferably 0.15% or more, and still more preferably 0.2% or more.
On the other hand, if the content of TiO.sub.2 exceeds 5%,
devitrification readily occurs during melting, and the quality of
the chemically strengthened glass may be deteriorated. Therefore,
the content is preferably 5% or less, more preferably 3% or less,
and still more preferably 1.5% or less.
[0120] In the case of precipitating a lithium metasilicate crystal
and containing TiO.sub.2, the content thereof is preferably 0.5% or
more, more preferably 0.1% or more, still more preferably 2% or
more, particularly preferably 3% or more, and most preferably 4% or
more. On the other hand, if the content of TiO.sub.2 exceeds 10%,
devitrification readily occurs during melting, and the quality of
the chemically strengthened glass may be deteriorated. Therefore,
the content is preferably 10% or less, more preferably 8% or less,
and still more preferably 6% or less.
[0121] In the case where Fe.sub.2O.sub.3 is contained in glass and
the glass contains TiO.sub.2, a composite called an ilmenite
composite is formed, and yellow or brown coloring is likely to
occur. Fe.sub.2O.sub.3 is normally contained as impurity in glass
and therefore, in order to prevent coloring, the content of
TiO.sub.2 is preferably 1% or less, more preferably 0.5% or less,
still more preferably 0.25% or less, and it is particularly
preferable that the glass is substantially free of TiO.sub.2.
[0122] P.sub.2O.sub.5 is not essential but has an effect of
encouraging phase separation of the glass and promoting the
crystallization and therefore, may be contained. In the case of
containing P.sub.2O.sub.5, its content is preferably 0.1% or more,
more preferably 0.5% or more, still more preferably 1% or more, and
particularly preferably 2% or more. In the case of precipitating a
lithium metasilicate crystal, the content of P.sub.2O.sub.5 is more
preferably 4% or more, still more preferably 5% or more, and
particularly preferably 6% or more. On the other hand, if the
content of P.sub.2O.sub.5 is large, acid resistance is
deteriorated. Accordingly, the content of P.sub.2O.sub.5 is 15% or
less, preferably 14% or less, more preferably 12% or less, still
more preferably 11% or less, yet still more preferably 10% or less,
particularly preferably 8% or less, and most preferably 7% or less.
In the case of a chemically strengthened glass containing a
.beta.-spodumene crystal, in order to make fragments less likely
scatter upon breakage, the content of P.sub.2O.sub.5 is preferably
6% or less, more preferably 5% or less, still more preferably 4% or
less, particularly preferably 3% or less, and most preferably 2% or
less. In the case of placing importance on the acid resistance, it
is preferable to be substantially free of P.sub.2O.sub.5.
[0123] B.sub.2O.sub.3 is a component enhancing the chipping
resistance and meltability of the glass for chemical strengthening
or the chemically strengthened glass and may be contained. Although
B.sub.2O.sub.3 is not essential, in the case of containing
B.sub.2O.sub.3, the content thereof is preferably 0.5% or more,
more preferably 1% or more, still more preferably 2% or more, for
enhancing the meltability. On the other hand, if the content of
B.sub.2O.sub.3 exceeds 5%, striae are generated during melting and
the quality of the glass for chemical strengthening is easily
deteriorated. Therefore, the content of B.sub.2O.sub.3 is
preferably 5% or less, more preferably 4% or less, still more
preferably 3% or less, and particularly preferably 1% or less. In
order to increase the acid resistance, it is preferable to be
substantially free of B.sub.2O.sub.3.
[0124] MgO is a component increasing the surface compressive stress
of the chemically strengthened glass, is a component suppressing
scattering of fragments upon breakage of the chemically
strengthened glass, and may be contained. In the case of containing
MgO, its content is preferably 0.5% or more, and more preferably 1%
or more. On the other hand, in order to suppress devitrification
during melting, the content of MgO is preferably 5% or less, more
preferably 4% or less, and still more preferably 3% or less.
[0125] CaO is a component enhancing the meltability of the glass
and may be contained so as to prevent devitrification during
melting and enhance the meltability while suppressing a rise in the
thermal expansion coefficient. In the case of containing CaO, the
content thereof is preferably 0.5% or more, and more preferably 1%
or more. On the other hand, in order to enhance the ion exchange
properties, the content of CaO is preferably 4% or less, more
preferably 3% or less, and particularly preferably 2% or less.
[0126] SrO is a component enhancing the meltability of the glass,
is also a component enhancing the refractive index of the glass to
make the refractive index of the residual glass phase after
crystallization close to the refractive index of the precipitated
crystal, thereby improving the light transmittance of the
crystallized glass. Therefore, SrO may be contained. In the case of
containing SrO, the content thereof is preferably 0.1% or more,
more preferably 0.5% or more, and still more preferably 1% or more.
On the other hand, if the content of SrO is too large, the ion
exchange rate decreases. Accordingly, the content of SrO is
preferably 3% or less, more preferably 2.5% or less, still more
preferably 2% or less, and particularly preferably 1% or less.
[0127] BaO is a component enhancing the meltability of the glass,
is also a component enhancing the refractive index of the glass to
make the refractive index of the residual glass phase after
crystallization close to the refractive index of the lithium
aluminosilicate crystal phase, thereby improving the light
transmittance of the crystallized glass. Therefore, BaO may be
contained. In the case of containing BaO, the content thereof is
preferably 0.1% or more, more preferably 0.5% or more, and still
more preferably 1% or more. On the other hand, if the BaO content
is too large, the ion exchange rate decreases. Accordingly, the
content of BaO is preferably 3% or less, more preferably 2.5% or
less, still more preferably 2% or less, and particularly preferably
1% or less.
[0128] ZnO is a component decreasing the thermal expansion
coefficient of the glass and increasing the chemical durability, is
also a component enhancing the refractive index of the glass to
make the refractive index of the residual glass phase after
crystallization close to the refractive index of the lithium
aluminosilicate crystal phase, thereby improving the light
transmittance of the crystallized glass. Therefore, ZnO may be
contained. In the case of containing ZnO, the content thereof is
preferably 0.5% or more, more preferably 1% or more, still more
preferably 1.5% or more, and particularly preferably 2% or more. On
the other hand, for suppressing devitrification during melting, the
content of ZnO is preferably 4% or less, more preferably 3% or
less, and still more preferably 2% or less.
[0129] All of Y.sub.2O.sub.3, La.sub.2O.sub.3, Nb.sub.2O.sub.5 and
Ta.sub.2O.sub.5 are effective in preventing fragments from
scattering upon breakage of the glass and may be contained so as to
increase the refractive index. In the case of containing these
components, the total
Y.sub.2O.sub.3+La.sub.2O.sub.3+Nb.sub.2O.sub.5 of the contents of
Y.sub.2O.sub.3, La.sub.2O.sub.3 and Nb.sub.2O.sub.5 is preferably
0.5% or more, more preferably 1% or more, still more preferably
1.5% or more, and particularly preferably 2% or more. Furthermore,
for the reason that the glass is less likely to devitrify during
melting, Y.sub.2O.sub.3+La.sub.2O.sub.3+Nb.sub.2O.sub.5 is
preferably 4% or less, more preferably 3% or less, still more
preferably 2% or less, and particularly preferably 1% or less.
[0130] The total content
Y.sub.2O.sub.3+La.sub.2O.sub.3+Nb.sub.2O.sub.5+Ta.sub.2O.sub.5 of
Y.sub.2O.sub.3, La.sub.2O.sub.3, Nb.sub.2O.sub.5 and
Ta.sub.2O.sub.5 is preferably 0.5% or more, more preferably 1% or
more, still more preferably 1.5% or more, and particularly
preferably 2% or more. Furthermore, for the reason that the glass
is less likely to devitrify during melting,
Y.sub.2O.sub.3+La.sub.2O.sub.3.+-.Nb.sub.2O.sub.5+Ta.sub.2O.sub.5
is preferably 4% or less, more preferably 3% or less, still more
preferably 2% or less, and particularly preferably 1% or less.
[0131] In addition, CeO.sub.2 may be contained. CeO.sub.2 is
effective in oxidizing glass. In the case of containing a large
amount of SnO.sub.2, CeO.sub.2 may inhibit SnO.sub.2 from being
reduced to SnO that is a coloring component, thereby suppressing
coloring. In the case of containing CeO.sub.2, the content thereof
is preferably 0.03% or more, more preferably 0.05% or more, and
still more preferably 0.07% or more. In the case of using CeO.sub.2
as an oxidizer, if the content of CeO.sub.2 is too large, the glass
is readily colored. Therefore, for enhancing the transparency, the
content of CeO.sub.2 is preferably 1.5% or less, and more
preferably 1.0% or less.
[0132] Furthermore, as long as the attainment of desired chemical
strengthening properties is not impeded, a coloring component may
be added. Preferable examples of coloring components include
Co.sub.3O.sub.4, MnO.sub.2, Fe.sub.2O.sub.3, NiO, CuO,
Cr.sub.2O.sub.3, V.sub.2O.sub.5, Bi.sub.2O.sub.3, SeO.sub.2,
Er.sub.2O.sub.3, and Nd.sub.2O.sub.3.
[0133] The content of the coloring components is preferably 1% or
less in total. In the case of increasing the light transmittance of
the glass, it is preferable that the glass is substantially free of
these components.
[0134] In addition, SO.sub.3, a chloride, a fluoride, etc. may be
appropriately contained as a refining agent at the time of glass
melting. It is preferable not to contain As.sub.2O.sub.3. In the
case of containing Sb.sub.2O.sub.3, the content thereof is
preferably 0.3% or less, more preferably 0.1% or less, and most
preferably nil.
<Production Method of Glass for Chemical Strengthening>
[0135] The production method of a glass for chemical strengthening
of this embodiment is a production method of a glass for chemical
strengthening including heating and crystallizing an amorphous
glass and bend-forming the resulting present crystallized glass
under heating. The present three-dimensionally shaped glass can be
produced by the production method of a glass for chemical
strengthening of the present invention.
[0136] In addition, the production method of a chemically
strengthened glass of this embodiment is a production method of a
chemically strengthened glass including heating and crystallizing
an amorphous glass, bend-forming the resulting present crystallized
glass under heating, and thereafter chemically strengthening the
glass. The three-dimensionally shaped chemically strengthened glass
of this embodiment is obtained by the production method of a
chemically strengthened glass of this embodiment.
(Production of Amorphous Glass)
[0137] The amorphous glass can be produced, for example, by the
following method. Note that the following production method is an
example of producing a sheet-like chemically strengthened
glass.
[0138] Glass raw materials are prepared to obtain a glass having a
desired composition, and heated and melted in a glass melting
furnace. After that, the molten glass is homogenized by bubbling,
stirring, addition of a refining agent, etc., then formed into a
glass sheet with a predetermined thickness by a known forming
method, and annealed. Alternatively, the molten glass may be formed
into a sheet by a method in which the molten glass is formed into a
block, annealed, and then cut.
[0139] Examples of the forming method of the sheet-like glass
include a float process, a press process, a fusion process, and a
down draw process. Particularly in the case of producing a
large-size glass sheet, a float process is preferred. In addition,
a continuously forming method other than a float process, for
example, a fusion process or a down draw process, is also
preferred.
(Crystallization Treatment)
[0140] A crystallized glass is obtained by heat-treating the
amorphous glass obtained by the procedure above.
[0141] The heating treatment is preferably a two-step heating
treatment in which the temperature is raised from room temperature
to a first treatment temperature, followed by holding for a given
time, and then raised to a second treatment temperature higher than
the first treatment temperature, followed by holding for a given
time. The heating treatment is also preferably a three-step heating
treatment in which the temperature is raised from room temperature
to a first treatment temperature, followed by holding for a given
time, then raised to a second treatment temperature higher than the
first treatment temperature, followed by holding for a given time,
and further raised to a third treatment temperature higher than the
second treatment temperature, followed by holding for a given
time.
[0142] In the case of the two-step heating treatment, the first
treatment temperature is preferably within a temperature range at
which the crystal nucleation rate increases in the glass
composition, and the second treatment temperature is preferably
within a temperature range at which the crystal growth rate
increases in the glass composition. In addition, the holding time
at the first treatment temperature is preferably long enough to
produce a sufficient number of crystal nuclei. When a large number
of crystal nuclei are produced, the size of each crystal is reduced
and consequently a crystallized glass having high transparency is
obtained.
[0143] The first treatment temperature is, for example, from 550 to
800.degree. C., and the second treatment temperature is, for
example, from 850 to 1,000.degree. C. The first treatment
temperature is held for 2 to 10 hours, and the second treatment
temperature is then held for 2 to 10 hours.
[0144] The crystallized glass obtained by the procedure above is
ground and polished as necessary, to form a crystallized glass
sheet. In the case where the crystallized glass sheet is cut into a
predetermined shape and size or chamfered, cutting or chamfering is
preferably performed before applying a chemical strengthening
treatment, because a compressive stress layer is formed also on the
end face by the later chemical strengthening treatment.
(Bend-Forming)
[0145] As for the bend-forming method, any method can be selected
from existing bend-forming methods such as self-weight forming
method, vacuum forming method and press forming method. Two or more
kinds of bend-forming methods may be used in combination.
[0146] The self-weight forming method is a method in which a glass
sheet is placed on a forming mold and the glass sheet is heated,
then made to fit the forming mold by gravity to be bend-formed into
a predetermined shape.
[0147] The vacuum forming method is a method in which a glass sheet
is placed on a forming mold and after the periphery of the glass
sheet is sealed, a space between the forming mold and the glass
sheet is depressurized to apply a differential pressure between the
front and back surfaces of the glass sheet so as to perform
bend-forming. On this occasion, a pressure may be supplementarily
applied to the upper surface side of the glass sheet.
[0148] The press forming is a method in which a glass sheet is
placed between forming molds (upper mold and lower mold) and the
glass sheet is heated and bend-formed into a predetermined shape by
applying a press load between the upper and lower molds.
[0149] In any case, the glass is deformed by applying a force while
the glass is heated.
[0150] The bend-forming (thermal bending) temperature is, for
example, from 700 to 1,100.degree. C., and preferably from 750 to
1,050.degree. C. In view of dimension accuracy, the thermal bending
temperature is preferably high relative to the maximum temperature
of the crystallization treatment because thermal deformation
readily occurs. The difference between the maximum temperature of
the crystallization treatment and the thermal bending temperature
is preferably 10.degree. C. or more, and more preferably 30.degree.
C. or more. On the other hand, if the thermal bending temperature
is too high relative to the crystallization treatment temperature,
the light transmittance may be deteriorated by the bend-forming.
Accordingly, the difference between the maximum temperature of the
crystallization treatment and the thermal bending temperature is
preferably 120.degree. C. or less, more preferably 100.degree. C.
or less, still more preferably 90.degree. C. or less, and
particularly preferably 60.degree. C. or less.
[0151] The decrease of light transmittance by bend-forming is
preferably 3% or less, more preferably 2% or less, still more
preferably 1.5% or less, and particularly preferably 1% or
less.
[0152] In addition, for keeping the transparency of the final glass
high, a higher light transmittance before thermal bending is
advantageous, and the light transmittance in terms of a thickness
of 0.8 mm is preferably 85% or more, more preferably 87% or more,
and particularly preferably 89% or more.
(Chemical Strengthening Treatment)
[0153] The chemical strengthening treatment is a treatment in which
a glass is brought into contact with a metal salt by a method of,
for example, immersing the glass in a metal salt (e.g., potassium
nitrate) melt containing a metal ion having a large ionic radius
(typically, Na ion or K ion), and a metal ion having a small ionic
radius (typically Na ion or Li ion) in the glass is thereby
replaced by a metal ion having a large ionic radius (typically Na
ion or K ion for Li ion, and K ion for Na ion).
[0154] In order to increase the rate of the chemical strengthening
treatment, it is preferable to use "Li--Na exchange" of replacing
Li ion in the glass by Na ion. Furthermore, in order to form a
large compressive stress by ion exchange, it is preferable to use
"Na--K exchange" of replacing Na ion in the glass by K ion.
[0155] Examples of the molten salt for performing the chemical
strengthening treatment include a nitrate, a sulfate, a carbonate,
and a chloride. Among these, examples of the nitrate include
lithium nitrate, sodium nitrate, potassium nitrate, cesium nitrate,
and silver nitrate. Examples of the sulfates include lithium
sulfate, sodium sulfate, potassium sulfate, cesium sulfate, and
silver sulfate. Examples of the carbonate include lithium
carbonate, sodium carbonate, and potassium carbonate. Examples of
the chloride include lithium chloride, sodium chloride, potassium
chloride, cesium chloride, and silver chloride. One of these molten
salts may be used alone, or a plurality of kinds thereof may be
used in combination.
[0156] The treatment conditions such as time and temperature of the
chemical strengthening treatment may be appropriately selected
while taking into account the glass composition, the kind of molten
salt, etc.
[0157] The present strengthened glass is preferably obtained, for
example, by the following two-step chemical strengthening
treatment.
[0158] First, the present three-dimensionally shaped glass is
immersed in an Na ion-containing metal salt (e.g., sodium nitrate)
at approximately from 350 to 500.degree. C. for approximately from
0.1 to 10 hours. This causes ion exchange between Li ion in the
present three-dimensionally shaped glass and Na ion in the metal
salt, and for example a compressive stress layer having a surface
compressive stress of 200 MPa or more and a depth of compressive
stress layer of 80 .mu.m or more can thereby be formed. If the
surface compressive stress introduced by this treatment exceeds
1,000 MPa, it is difficult to increase DOL while keeping CT low in
the finally obtained present strengthened glass. Accordingly, the
surface compressive stress introduced by this treatment is
preferably 900 MPa or less, more preferably 700 MPa or less, and
still more preferably 600 MPa or less.
[0159] Next, the glass after the treatment above is immersed in a K
ion-containing metal salt (e.g., potassium nitrate) at
approximately from 350 to 500.degree. C. for approximately from 0.1
to 10 hours. A large compressive stress is consequently generated,
for example, in a portion at a depth of about 10 .mu.m or less of
the compressive stress layer formed in the previous treatment.
[0160] According to such a two-step treatment, a favorable stress
profile with a surface compressive stress of 600 MPa or more is
likely to be obtained.
[0161] The glass may be immersed in the K ion-containing metal salt
after the glass is first immersed in the Na ion-containing metal
salt and then held at 350 to 500.degree. C. in the atmosphere for 1
to 5 hours. The holding temperature is preferably from 425 to
475.degree. C., and more preferably from 440 to 460.degree. C.
[0162] Holding at a high temperature in the atmosphere allows Na
ions introduced inside the glass from the metal salt by the first
treatment to thermally diffuse in the glass, leading to formation
of a more favorable stress profile.
[0163] Alternatively, instead of holding in the atmosphere after
immersion in an Na ion-containing metal salt, the glass may be
immersed in a metal salt containing Na ion and Li ion (for example,
a mixed salt of sodium nitrate and lithium nitrate) at 350 to
500.degree. C. for 0.1 to 20 hours.
[0164] Immersion in the metal salt containing Na ion and Li ion
causes ion exchange between Na ion in the glass and Li ion in the
metal salt to form a more favorable stress profile, thereby
improving the drop strength to asphalt.
[0165] In the case of performing such a two-step or three-step
strengthening treatment, in view of production efficiency, the
total treatment time is preferably 10 hours or less, more
preferably 5 hours or less, and still more preferably 3 hours or
less. On the other hand, in order to obtain a desired stress
profile, the total treatment time needs to be 0.5 hours or more,
and more preferably 1 hour or more.
[0166] The three-dimensionally shaped chemically strengthened glass
of the present embodiment obtained in the above-described manner is
useful particularly as a cover glass used, for example, in a mobile
device such as cell phone and smartphone. The glass is also useful
for a cover glass of a display device not intended to be portable,
such as television, personal computer and touch panel. The glass is
also useful as a cover glass of, for example, an interior
decoration of a car, an airplane, etc.
EXAMPLE
[0167] The present invention is described below by referring to
Examples, but the present invention is not limited thereto.
[0168] Glass raw materials of each of Glasses 1 to 8 were prepared
to give a glass composition shown by mass % on an oxide basis in
Table 1, and weighed so that 800 g of a glass can be obtained.
Subsequently, the mixed glass raw materials were put in a platinum
crucible, charged into an electric furnace at 1,500 to
1,700.degree. C., melted for about 5 hours, degassed, and
homogenized.
[0169] The obtained molten glass was cast into a mold, held for 1
hour at a temperature 30.degree. C. higher than the glass
transition point, and then cooled down to room temperature at a
rate of 0.5.degree. C./min to obtain a glass block.
(Glass Transition Point)
[0170] Based on JIS R1618:2002, a thermal expansion curve was
obtained using a thermal dilatometer (TD5000SA made by Bruker AXS
GmbH.) by setting the temperature riserate to 10.degree. C./min. In
addition, a glass transition point Tg [unit: .degree. C.] was
determined from the obtained thermal expansion curve. The results
are shown in Table 1. In the Table, the blank indicates
unevaluated.
TABLE-US-00001 TABLE 1 Glass 1 Glass 2 Glass 3 Glass 4 Glass 5
Glass 6 Glass 7 Glass 8 SiO.sub.2 65.4 62.9 66.1 73.6 59.5 57.7
53.8 51.2 Al.sub.2O.sub.3 22.4 22.4 21.0 7.6 2.0 2.0 7.2 8.7
Li.sub.2O 4.3 4.3 1.9 11.2 18.4 18.5 18.1 17.4 Na.sub.2O 2.0 2.0
0.5 1.6 2.0 5.6 4.4 1.9 K.sub.2O 0.0 0.0 0.0 0.0 2.0 0.0 0.8 1.9
ZrO.sub.2 2.3 2.3 4.8 3.7 10.1 10.1 9.9 9.5 SnO.sub.2 2.1 2.1 0.0
0.0 0.0 0.0 0.0 0.0 P.sub.2O.sub.5 1.5 3.0 0.0 2.1 5.9 6.0 5.8 5.6
B.sub.2O.sub.3 0.0 0.0 0.0 0.2 0.0 0.0 0.0 0.0 Y.sub.2O.sub.3 0.0
0.0 0.0 0.0 0.0 0.0 0.0 3.9 SrO 0.0 1.0 0.0 0.0 0.0 0.0 0.0 0.0 MgO
0.0 0.0 5.7 0.0 0.0 0.0 0.0 0.0 Tg 739 714 453 440 460 471
Ex. 1 to Ex. 14 and Ex. 16 to Ex. 19
[0171] The obtained glass block was processed into a sheet of
approximately 60 mm.times.60 mm.times.1.5 mm and heat-treated under
the conditions shown in Table 2 or 3 to obtain a crystallized glass
(Ex. 1 to Ex. 14, and Ex. 16 to Ex. 19). In the column of
crystallization treatment of Tables, when two-step treatment
conditions are described, this means that the glass sheet was held
at the temperature and for the time shown in the upper stage and
then held at the temperature and for the time shown in the lower
stage. For example, when 750.degree. C. 4 h is written in the upper
stage and 920.degree. C. 4 h is written in the lower stage, this
means that the glass sheet was held at 750.degree. C. for 4 hours
and then held at 920.degree. C. for 4 hours. In addition, when
three-step treatment conditions are described, this means that the
glass sheet was held at the temperature and for the time shown in
the upper stage, then held at the temperature and for the time
shown in the middle stage, and furthermore held at the temperature
and for the time shown in the lower stage.
[0172] The obtained crystallized glass was evaluated for the
density, Young's modulus, thermal expansion coefficient,
precipitated crystal, Vickers hardness, fracture toughness value,
light transmittance, and bend formability as follows. In addition,
chemical strengthening treatment was performed and the
strengthening properties were evaluated. The results are shown in
Table 2 or 3. The blank in the Table indicates unmeasured.
(Density)
[0173] The density [unit: g/cm.sup.3] was measured by the
Archimedes method after processing by minor polishing into a
thickness of 0.8 mm.
(Young's Modulus)
[0174] The Young's modulus [unit: GPa] was measured by an
ultrasonic method after processing by mirror polishing into a
thickness of 0.8 mm.
(Thermal Expansion Coefficient)
[0175] A thermal expansion curve was obtained using a thermal
dilatometer (TD5000SA manufactured by Bruker AXS GmbH.) by setting
the temperature rise rate at 10.degree. C./min. In addition, an
average linear thermal expansion coefficient [unit:
.times.10.sup.-7/.degree. C.] at 50.degree. C. to 350.degree. C.
was measured from the obtained thermal expansion curve.
(Precipitated Crystal)
[0176] Powder X-ray diffraction was measured under the following
conditions to identify the precipitated crystal (main crystal). In
addition, crystallinity (degree of crystallinity) [unit: %] and
crystal grain size (crystal size) [unit: nm] were calculated using
a Rietveld method. In the Tables, .beta.SP stands for a
.beta.-spodumene crystal, P stands for a petalite crystal, LD
stands for lithium disilicate, LS stands for lithium metasilicate,
and .beta.Q stands for .beta.-quartz.
[0177] Measurement apparatus: SmartLab manufactured by Rigaku
Corporation
[0178] X-Ray: CuK.alpha. radiation
[0179] Measurement Range: 20=from 10.degree. to 80.degree.
[0180] Speed: 10.degree./min
[0181] Step: 0.02.degree.
(Light Transmittance)
[0182] After processing by mirror polishing into a thickness of 0.8
mm, an average transmittance (transmittance before forming,
transmittance after forming) [unit: %] for light at a wavelength of
380 to 780 nm was measured before the later-described bend
formability test and after the test with a configuration using, as
a detector, an integrating sphere unit for a spectrophotometer
(LAMBDA950 manufactured by PerkinElmer, Inc.), and the difference
therebetween was also calculated.
(Vickers Hardness)
[0183] The Vickers hardness was measured by pressing an indenter
under a load of 100 gf for 15 seconds by use of a Shimadzu
micro-Vickers hardness tester (HMV-2 manufactured by Shimadzu
Corporation). Incidentally, the Vickers hardness was measured in
the same manner also after the later-described chemical
strengthening treatment (Vickers hardness before strengthening,
Vickers hardness after strengthening).
(Fracture Toughness Value)
[0184] Based on JIS R1607:2010, a fracture toughness value after a
chemical strengthening treatment (fracture toughness value after
strengthening) was determined by an indentation fracture method (IF
method) using a Vickers hardness tester (FLC-50V manufactured by
Future-Tech Corp.). Indentation was performed under a load of 3 kgf
in an atmosphere at a temperature of 22.degree. C. and a relative
humidity of 40%. The indentation length was measured in the same
atmosphere 20 minutes after the indentation. Measurement was
performed at 10 points for each sample, and an average value was
calculated and taken as the fracture toughness value [unit:
MPam.sup.1/2].
(Bend Formability)
[0185] A high alumina insulating firebrick (BAL-99 manufactured by
Isolite Insulating Products Co., Ltd.) was processed to prepare two
supporting bricks 1 and one loading brick 3, each having a rod
shape of 20 mm.times.20 mm.times.120 mm. Supporting bricks 1 were
placed in parallel at an interval of 40 mm in an electric furnace,
and the loading brick 3 was also placed in the same electric
furnace, followed by preheating.
[0186] The obtained crystallized glass was processed into 60
mm.times.10 mm.times.0.8 mm, and both surfaces of 60 mm.times.10 mm
were mirror-polished. In an electric furnace kept at a bending
temperature shown in Table 2 or 3, as illustrated in (a) of FIG. 6,
the crystallized glass sheet 2 was put on two supporting bricks 1,
the loading brick 3 (weight: 85 g) was put on the crystallized
glass sheet 2, and these were held for 10 minutes. After the elapse
of 10 minutes, the loading brick 3 was removed from the surface of
the crystallized glass sheet 2, and the crystallized glass sheet 2
was taken out from the electric furnace and cooled. Thereafter, the
deformation amount h (bend-deformation amount) of the crystallized
glass, as illustrated in (b) of FIG. 6, was measured. In Tables,
"-" means that the glass was scarcely deformed and the deformation
amount could not be measured.
(Bend Formability 2)
[0187] With respect to Ex. 16 to Ex. 19, a bend-forming test
described below was separately performed.
[0188] First, carbon-made concave mold and convex mold which were
designed for forming a curved surface having a curvature radius of
6.0 mm, a bending angle of 70.5.degree. and a bending depth of 4.0
mm were prepared. And then the crystallized glass sheet was placed
near the center of the glass contact surface of the concave
mold.
[0189] Subsequently, preheating, deformation and cooling were
performed using a forming device. Incidentally, the preheating was
performed at a temperature at which the crystallized glass has an
equilibrium viscosity of about 10.sup.18 Pas. The deformation was
performed by moving the convex mold downward at a temperature at
which the crystallized glass has an equilibrium viscosity of about
10.sup.11.5 Pas, followed by pressing the glass with 2,000 N at a
maximum.
[0190] By the treatment above, the crystallized glasses of all of
Ex. 16 to Ex. 19 were formed into a three-dimensional shape having
a curvature radius of 2,000 mm.
[0191] The above-described test indicated that the crystallized
glasses of Ex. 16 to Ex. 19 can be formed into a desired shape.
<Chemical Strengthening Treatment>
[0192] The obtained crystallized glass was subjected to a chemical
strengthening treatment under the following conditions.
[0193] In Ex. 1 to Ex. 8, the glass was immersed in a molten salt
of sodium nitrate at 450.degree. C. for 30 minutes, then immersed
in a molten salt of potassium nitrate at 450.degree. C. for 30
minutes, thereby performing chemical strengthening.
[0194] In Ex. 9 to Ex. 11, the glass was immersed in a lithium
sulfate-potassium sulfate mixed salt (in which the mass ratio
between the lithium sulfate and potassium sulfate was 90:10) at
740.degree. C. for 240 minutes, thereby performing chemical
strengthening.
[0195] In Ex. 12 to Ex. 14, the glass was immersed in sodium
nitrate at 430.degree. C. for 2 hours, then immersed in potassium
nitrate at 430.degree. C. for 2 hours, thereby performing chemical
strengthening.
[0196] In Ex. 16 to Ex. 19, the glass was immersed in sodium
nitrate at 450.degree. C. for 3 hours, then immersed in potassium
nitrate at 450.degree. C. for 1 hour, thereby performing chemical
strengthening.
(Chemical Strengthening Properties)
[0197] A stress value was measured using a surface stress meter
FSM-6000 manufactured by Orihara Manufacturing Co., Ltd. and a
measuring device SLP1000 utilizing scattered-light photoelasticity
manufactured by Orihara Manufacturing Co., Ltd., and a compressive
stress value CS [unit: MPa] on the glass surface, a depth DOL
[unit: .mu.m] at which the compressive stress value becomes zero,
an internal tensile stress (CT) [unit: MPa], and a maximum depth
(50 MPa depth) [unit: .mu.m] at which the compressive stress value
is 50 MPa or more, were read out. In addition, m.sub.1 represented
by the following expression was determined from the depth DOL.sub.1
at which the compressive stress value is CS/2.
m.sub.1=(CS-CS/2)/(0-DOL.sub.1)
[0198] m.sub.2 represented by the following expression was
determined from the compressive stress CS.sub.1 at the depth DOL/4
and the compressive stress CS.sub.2 at the depth DOL/2.
m.sub.2=(CS.sub.1-CS.sub.2)/(DOL/4-DOL/2)
[0199] m.sub.3 represented by the following expression was
determined from the compressive stress CS.sub.2 at the depth
DOL/2.
m.sub.3=(CS.sub.2-0)/(DOL/2-DOL)
[0200] These results are shown in Table 2 or 3. In the Table, the
blank indicates unmeasured.
TABLE-US-00002 TABLE 2 Ex. 1 Ex . 2 Ex. 3 Ex. 4 Ex. 5 Glass Glass 1
Glass 1 Glass 1 Glass 1 Glass 1 Crystallization 750.degree. C.
750.degree. C. 750.degree. C. 750.degree. C. 750.degree. C.
treatment 4 h 4 h 4 h 4 h 4 h 920.degree. C. 920.degree. C.
920.degree. C. 900.degree. C. 880.degree. C. 4 h 4 h 4 h 4 h 4 h
Density 2.492 2.492 2.492 Young's modulus 88 88 88 Thermal
expansion 12 12 12 coefficient Main crystal .beta.SP .beta.SP
.beta.SP .beta.SP .beta.SP Degree of crystallinity 25 25 25 Crystal
size 55 55 55 Transmittance before 87.3 87.3 87.3 87.3 88.2 forming
Bending temperature 1000.degree. C. 900.degree. C. 1100.degree. C.
1000.degree. C. 1000.degree. C. Transmittance after 85.7 86.5 76.8
85.0 83.1 forming Difference in 1.6 0.8 10.5 2.3 5.1 transmittance
before and after forming Bend-deformation amount 1.2 mm -- more
than 10 mm 1.5 mm -- Vickers hardness before 780 780 780
strengthening Vickers hardness after 830 830 830 strengthening
Fracture toughness value 1.2 1.2 1.2 after strengthening CS 1135
1135 1135 DOL 110 110 110 CT 65 65 65 m.sub.1 -104 -104 -104
m.sub.2 -4.0 -4.0 -4.0 m.sub.3 -3.0 -3.0 -3.0 50 MPa Depth 95 95 95
Ex. 6 Ex. 7 Ex. 8 Ex. 9 Ex. 10 Glass Glass 2 Glass 2 Glass 2 Glass
3 Glass 3 Crystallization 750.degree. C. 750.degree. C. 750.degree.
C. 750.degree. C. 750.degree. C. treatment 4 h 4 h 4 h 4 h 4 h
900.degree. C. 900.degree. C. 900.degree. C. 920.degree. C.
920.degree. C. 4 h 4 h 4 h 4 h 4 h Density 2.48 2.48 2.48 2.9
Young's modulus 86 86 86 98 98 Thermal expansion 12 12 12
coefficient Main crystal .beta.SP .beta.SP .beta.SP .beta.Q .beta.Q
Degree of crystallinity 73 73 73 Crystal size 120 120 120
Transmittance 89.4 89.4 89.4 83.0 83.0 before forming Bending
temperature 950.degree. C. 1000.degree. C. 1100.degree. C.
1000.degree. C. 900.degree. C. Transmittance 88.6 86.8 72.3 80.0
79.6 after forming Difference in 0.8 2.6 17.1 3 3.4 transmittance
before and after forming Bend-deformation amount 1.1 mm 10 mm 15 mm
1.5 mm -- Vickers hardness before 730 730 730 strengthening Vickers
hardness after 820 820 820 1040 strengthening Fracture toughness
value 1.2 1.2 1.2 1 after strengthening CS 1200 1200 1200 590 DOL
120 120 120 50 CT m.sub.1 -104 -104 -104 m.sub.2 -4.0 -4.0 -4.0
m.sub.3 -3.0 -3.0 -3.0 50 MPa Depth 95 95 95
TABLE-US-00003 TABLE 3 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 16 Ex. 17
Ex. 18 Ex. 19 Glass Glass 3 Glass 4 Glass 4 Glass 4 Glass 5 Glass 6
Glass 7 Glass 8 Crystallization 750.degree. C. 540.degree. C.
540.degree. C. 540.degree. C. 550.degree. C. 550.degree. C.
550.degree. C. 550.degree. C. treatment 4 h 4 h 4 h 4 h 2 h 2 h 2 h
2 h 920.degree. C. 600.degree. C. 600.degree. C. 600.degree. C.
700.degree. C. 710.degree. C. 710.degree. C. 730.degree. C. 4 h 4 h
4 h 4 h 2 h 2 h 2 h 2 h 710.degree. C. 710.degree. C. 710.degree.
C. 4 h 4 h 4 h Density 2.59 2.61 2.66 Young's modulus 98 105 105
105 104 106 105 Thermal expansion 134 131 131 123 coefficient Main
crystal .beta.Q P, L D P, LD P, LD LS LS LS LS Degree of
crystallinity 23 Crystal size 20 Transmittance 83.0 91.0 91.0 91.0
90.1 90.6 90.4 before forming Bending temperature 1100.degree. C.
800.degree. C. 750.degree. C. 900.degree. C. 710.degree. C.
Transmittance 71.1 89.9 90.9 29.1 90.0 after forming Difference in
11.9 2.1 0.1 61.9 0.1 transmittance before and after forming
Bend-deformation amount more than 10 mm 5 mm -- more than 10 mm 5
mm Vickers hardness 604 before strengthening Vickers hardness after
730 801 823 strengthening Fracture toughness value 0.8 after
strengthening CS 500 630 750 900 760 DOL 130 140 126 CT m.sub.1
m.sub.2 m.sub.3 50 MPa Depth
Ex. 15
[0201] A glass sheet composed of Glass 1 was bent at 1,000.degree.
C. in the same manner as in Ex. 1 and then crystallized under the
same crystallization conditions as in Ex. 1. As a result,
deformation was again caused, and the glass sheet retuned to the
same flat sheet shape as the tray used for the crystallization
treatment. This result indicates that the method of performing
bend-forming after crystallization makes it easy to retain a
desired shape.
[0202] Ex. 1 to Ex. 3 were crystallized glasses obtained by
crystallizing glass sheets composed of Glass 1 under the same
crystallization conditions, in which a .beta.-spodumene crystal was
the main crystal.
[0203] In Ex. 1, sufficiently high CS and DOL were obtained after
chemical strengthening.
[0204] In Ex. 2, since the bending temperature was not sufficiently
high, the bend-deformation amount was reduced.
[0205] In Ex. 3, since the bending temperature was too high, the
transparency was reduced.
[0206] It is therefore understood that in the case of producing the
crystallized glass of to the present invention, the bend-forming
temperature must be appropriately adjusted.
[0207] Ex. 4 and Ex. 5 were the same as Ex. 1 except that the
second treatment temperature in the two-step heating treatment
(crystallization treatment) is low, and the change in transparency
due to bending treatment was increased, compared with Ex. 1. It is
thought that since crystallization before bending treatment was
insufficient, the change in transmittance at the time of bending
treatment was increased.
[0208] Ex. 6 to Ex. 8 were crystallized glasses obtained by
crystallizing glass sheets composed of Glass 2 under the same
crystallization conditions, in which a .beta.-spodumene crystal was
the main crystal.
[0209] In Ex. 6, not only sufficiently high CS and DOL were
obtained after chemical strengthening but also the transmittance
before thermal bending was as high as 89% or more. Consequently,
when thermal bending was performed by reducing the difference
between the maximum temperature of the crystallization treatment
and the thermal bending temperature, a high transmittance of 88% or
more was finally achieved. In addition, a sufficiently large
bend-deformation amount was obtained.
[0210] In Ex. 7, the transmittance before thermal bending was
similarly as high as 89% or more. Therefore even when a large
bend-deformation amount was obtained by increasing the difference
between the maximum temperature of the crystallization treatment
and the thermal bending temperature, a high transmittance of 86% or
more was finally achieved.
[0211] In Ex. 8, since the bending temperature was too high, the
transmittance was reduced.
[0212] Ex. 9 to Ex. 11 were crystallized glasses obtained by
crystallizing glass sheets composed of Glass 3 under the same
crystallization conditions, in which .beta.-quartz was the main
crystal.
[0213] When Ex. 9 is compared with Ex. 1 and Ex. 6, the change in
transmittance due to the bend-forming treatment was slightly large
in Ex. 9.
[0214] Ex. 12 to Ex. 14 were crystallized glasses obtained by
crystallizing glass sheets composed of Glass 4 under the same
crystallization conditions, and were crystallized glasses
containing a petalite crystal.
[0215] When Ex. 12 is compared with Ex. 13 and Ex. 14, since the
bending temperature was not sufficiently high in Ex. 13, the
bend-deformation amount was reduced.
[0216] In Ex. 14, since the bending temperature was too high, the
transparency was reduced.
[0217] It is therefore understood that in the case of processing
the crystallized glass, the bend-forming temperature must be
appropriately adjusted.
[0218] In Ex. 12, since the bending temperature was appropriate, a
sufficiently large deformation amount was obtained by bend-forming
after crystallization and moreover the change in transparency was
small.
[0219] When Ex. 12 is compared with Ex. 1 and Ex. 6, the amount of
change by bend forming was large in Ex. 12 which was a crystallized
glass containing a petalite crystal, and bending thereof was
easy.
[0220] However, since the compressive stress value (CS) was low and
Kc after strengthening was small in Ex. 12, Ex. 1 and Ex. 6 which
were crystallized glasses containing a .beta.-spodumene crystal
were superior in view of strength.
[0221] Ex. 16 to Ex. 19 were crystallized glasses obtained by
crystallizing glass sheets composed of Glass 5 to Glass 8,
respectively, and all were crystallized glasses containing a
lithium metasilicate crystal.
[0222] A crystallized glass containing a lithium metasilicate
crystal is characterized in that not only sufficiently high CS and
DOL are obtained after chemical strengthening but also the
transmittance before thermal bending is high. It is seen that when
forming is performed at an appropriate bending temperature as in
Ex. 16, a sufficiently large deformation amount is obtained and at
the same time, the change in transparency can be suppressed.
[0223] While the present invention has been described in detail and
with reference to specific embodiments thereof, it is apparent to
one skilled in the art that various changes and modifications can
be made therein without departing from the spirit and scope of the
present invention. The present application is based on a Japanese
patent application filed on Feb. 27, 2018 (Japanese Patent
Application No. 2018-33693) and a Japanese patent application filed
on Feb. 8, 2019 (Japanese Patent Application No. 2019-21896), the
entireties of which are incorporated by reference. In addition, all
the references cited herein are incorporated as a whole.
REFERENCE SIGNS LIST
[0224] 1 Supporting brick [0225] 2 Crystallized glass sheet [0226]
3 Loading brick
* * * * *