U.S. patent application number 14/046933 was filed with the patent office on 2014-06-26 for strengthened glass and methods for making using differential time.
This patent application is currently assigned to Saxon Glass Technologies, Inc.. The applicant listed for this patent is Saxon Glass Technologies, Inc.. Invention is credited to Patrick K. Kreski.
Application Number | 20140178689 14/046933 |
Document ID | / |
Family ID | 50974974 |
Filed Date | 2014-06-26 |
United States Patent
Application |
20140178689 |
Kind Code |
A1 |
Kreski; Patrick K. |
June 26, 2014 |
STRENGTHENED GLASS AND METHODS FOR MAKING USING DIFFERENTIAL
TIME
Abstract
Chemically strengthened glass and a method for making utilizing
differential time are provided. The method includes providing a
substrate. The substrate includes a glass chemical structure. Host
alkali ions are situated in the chemical structure. The substrate
has a treatment-rich volume and a treatment-poor volume located as
opposed to each other in the substrate. The method also includes
providing an exchange medium including invading alkali ions having
an average ionic radius that is larger than an average ionic radius
of the host alkali ions. The method also includes applying the
exchange medium to a surface of the treatment-rich volume for a
period of time and applying the exchange medium to a surface of the
treatment-poor volume for a modified period of time. The method
also includes conducting ion exchange while applying the exchange
medium to produce the strengthened substrate.
Inventors: |
Kreski; Patrick K.; (Alfred
Station, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Saxon Glass Technologies, Inc. |
Alfred |
NY |
US |
|
|
Assignee: |
Saxon Glass Technologies,
Inc.
Alfred
NY
|
Family ID: |
50974974 |
Appl. No.: |
14/046933 |
Filed: |
October 5, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61710139 |
Oct 5, 2012 |
|
|
|
Current U.S.
Class: |
428/410 ;
65/30.14 |
Current CPC
Class: |
Y10T 428/315 20150115;
C03C 21/002 20130101 |
Class at
Publication: |
428/410 ;
65/30.14 |
International
Class: |
C03C 21/00 20060101
C03C021/00 |
Claims
1. A method for making a strengthened substrate, the method
comprising: providing a substrate characterized by having a glass
chemical structure including host alkali ions having an average
ionic radius situated in the glass chemical structure, and wherein
the substrate has dimensional volumes including a treatment-rich
volume and a treatment-poor volume located as opposed to each other
in the substrate; providing an exchange medium comprising invading
alkali ions having an average ionic radius that is larger than the
average ionic radius of the host alkali ions; applying the exchange
medium to a surface of the treatment-rich volume for a period of
time; applying the exchange medium to a surface of the
treatment-poor volume for a modified period of time, wherein the
modified period of time is longer than the period of time; and
conducting ion exchange while applying the exchange medium to
produce the strengthened substrate.
2. The method of claim 1, further comprising submerging the
substrate in a bath containing the exchange medium during the
period of time.
3. The method of claim 1, wherein at least one of the applying
steps is accomplished through submerging at least one of the
volumes in a bath containing the exchange medium.
4. The method of claim 1, wherein the period of time and the
modified period of time are continuous and end at the same point in
time.
5. The method of claim 1, wherein the substrate comprises a
variation in at least one of chemical composition and chemical
structure in the substrate.
6. The method of claim 5, wherein at least one of the chemical
composition and chemical structure in the treatment-poor volume is
different than in the treatment-rich volume.
7. The method of claim 1, wherein a time difference between the
period of time and the modified period of time occurs prior to
exposure of the treatment-rich volume to an exchange medium.
8. The method of claim 1, wherein a net bending moment about
mid-plane is about zero in the strengthened substrate.
9. The method of claim 1, wherein a compressive stress varies at
different locations of the strengthened substrate.
10. The method of claim 1, wherein at least one of the period of
time and the modified period of time is discontinuous.
11. The method of claim 1, wherein conducting ion exchange is
performed at a constant temperature during at least one of the
period of time and the modified period of time.
12. The method of claim 1, wherein conducting ion exchange is
performed at a variable temperature during at least one of the
period of time and the modified period of time.
13. The method of claim 1, wherein conducting ion exchange is
performed while applying about an equal temperature to the
treatment-poor volume and the treatment-rich volume.
14. The method of claim 1, wherein conducting ion exchange is
performed at an average temperature during the period of time that
is different from an average temperature utilized while conducting
ion exchange during the modified period of time.
15. The method of claim 1, wherein the exchange medium is one of a
liquid, a solid, a gas and mixtures thereof.
16. The method of claim 1, wherein the treatment-rich volume and
the treatment-poor volume are located as diametrically opposed in
the substrate.
17. The method of claim 1, wherein the method is one of a
continuous process and a batch process.
18. The method of claim 1, wherein the substrate comprises one of
alkali aluminosilicate glass and soda-lime silicate glass.
19. The method of claim 1, wherein the substrate is flat.
20. The method of claim 1, wherein the substrate has a width of
about 3.0 millimeters or less.
21. An article of manufacture, the article comprising: a chemically
strengthened substrate characterized by having a glass chemical
structure including alkali ions situated in the glass chemical
structure wherein the substrate has dimensional volumes including a
treatment-rich volume including a rich surface of the substrate, a
treatment-poor volume including a poor surface of the substrate and
characterized by having a variation from the treatment-rich volume
in at least one of a chemical composition and a chemical structure,
and a bulk volume, within the substrate, adjacent at least one of
the treatment-rich volume and the treatment-poor volume, wherein a
concentration of metal in at least one of the treatment-poor volume
and the treatment-rich volume is .gtoreq.about 0.4 mol % higher
than a concentration of the metal in the bulk volume, wherein a
concentration of the metal is higher in the treatment-poor volume
than a concentration of the metal in the treatment-rich volume, and
wherein a concentration of alkali ions in a diffusion depth of at
least one of the treatment-rich volume and the treatment-poor
volume is .ltoreq.about 0.5 mol % higher than a concentration of
the alkali ions in the bulk volume.
22. The article of claim 21, wherein at least one of the
treatment-rich volume and the treatment-poor volume has a diffusion
depth of about 5 to 150 .mu.m.
23. The article of claim 21, wherein the chemically strengthened
glass substrate comprises greater than 50 mole % SiO.sub.2.
24. The article of claim 21, wherein the chemically strengthened
glass substrate comprises about 1 to 25 total mole % of
Li.sub.2O+Na.sub.2O+K.sub.2O in the diffusion depth, wherein the
diffusion depth is about 5 to 150 .mu.m.
25. An article of manufacture, the article comprising: a chemically
strengthened glass substrate made by a process including providing
a substrate characterized by having a glass chemical structure
comprising host alkali ions having an average ionic radius situated
in the glass chemical structure, and wherein the substrate has
dimensional volumes including a treatment-rich volume and a
treatment-poor volume located as opposed to each other in the
substrate; providing an exchange medium comprising invading alkali
ions having an average ionic radius that is larger than the average
ionic radius of the host alkali ions; applying the exchange medium
to a surface of the treatment-rich volume for a period of time;
applying the exchange medium to a surface of the treatment-poor
volume for a modified period of time, wherein the modified period
of time is longer than the period of time; and conducting ion
exchange while applying the exchange medium to produce the
strengthened substrate.
Description
PRIORITY
[0001] This application claims priority to U.S. Provisional
Application No. 61/710,139, entitled "Strengthened Glass and
Curvature Control" by Patrick K. Kreski filed on Oct. 5, 2012,
which is incorporated herein by reference in its entirety.
BACKGROUND
[0002] Chemical strengthening of glass, also called ion-exchange
strengthening or chemical tempering, is a technique to strengthen a
prepared glass article by increasing compression within the glass
itself. It generally involves introducing larger alkali ions into
the glass chemical structure, to replace smaller alkali ions
present in the structure. A common implementation of chemical
strengthening in glass occurs through the exchange of sodium ions,
having a relatively smaller ionic radius, with potassium ions,
having a relatively larger ionic radius by submerging a glass
substrate containing sodium ions in a bath containing molten
potassium salts.
[0003] Chemical strengthening is often utilized to increase
compression in order to increase strength, abrasion resistance,
and/or thermal shock resistance into a glass article. The increased
compression can be introduced to various depths in the glass and is
often implemented within a surface layer. Chemical strengthening is
commonly utilized for treating flat glass. But it may also be used
for treating non-flat glass articles, such as cylinders and other
shapes of greater geometric complexity.
[0004] Flat glass is commonly manufactured by a number of known
techniques. These include the float glass method and drawing
methods, such as the fusion down-draw method and the slot draw
method. However, a prepared flat glass article may have variations
in its chemical composition and/or structure at different locations
in the glass. For example, flat glass that is manufactured by the
float glass technique is often prepared by spreading softened glass
material on a molten metal surface such as tin. The glass is then
cooled to form a solid, flat glass. As a result, the prepared flat
glass often contains a greater amount of tin on the side that was
nearer the molten tin and the concentration of tin is commonly
greater near the surface of that side.
[0005] Chemical strengthening is often used to treat glass having
variations in chemical composition and/or structure at different
locations in the glass. The variations produce locations that are
treatment-rich or treatment-poor relative to each other for ion
exchange and/or compression development in chemical strengthening.
When chemical strengthening is used to treat such glass, the
introduced compressive stress is often not uniformly distributed.
This may introduce a bending moment and subsequent induced
curvature in a glass article treated by chemical strengthening,
particularly for glass articles having a width of less than 3 mm.
The induced curvature is often undesirable. Induced curvature is
especially problematic in manufacturing thin flat glass articles
according to manufacturing specifications that include the enhanced
physical properties associated with chemical strengthening, but
without induced curvature. For example, glass used in manufactured
electronic articles, such as displays for "smart" phones, often
requires glass that is uniformly flat and high in strength and
abrasion resistance.
[0006] For a thin, flat glass article, such as an article having
two major surfaces, the non-equivalence of interdiffusion of
invading alkali ions and/or compression generation properties
between the major surfaces of the flat glass substrate after
chemical strengthening commonly often has an effect, such that a
local force times the distance from the mid-plane of a glass
article is not equivalent when summed from the treatment-poor
surface to the mid-plane and from the rich surface to the
mid-plane. Thus the net bending moment about the mid-plane is
non-zero (i.e., there is a non-zero net bending moment of the
stress about the mid-plane). As a result, bending stresses are
generated. For glass articles of thin cross-section, these bending
stresses generate deflection of the glass article from flat. That
is, thin, chemically strengthened glasses manufactured by the float
process often exhibit measurable curvature after chemical
strengthening. The direction of curvature is often concave on the
poor surface and convex on the rich surface.
[0007] In recent years, various types of efforts have attempted to
overcome the problem of induced curvature that is associated with
the chemical strengthening of glass. One approach involves grinding
and polishing a prepared glass prior to chemical strengthening. The
grinding and polishing is performed to remove those parts of a
glass having a different chemical composition and/or structure. An
example of this approach is grinding and polishing a flat glass
made by the float method to remove the surface layer(s) containing
a significant amount of tin. However, grinding and polishing the
float glass introduces abrasions and may introduce other physical
defects, in addition to the added time and expense associated with
performing the grinding and polishing. Other approaches have
involved secondary chemical treatments of prepared glass done prior
to chemical strengthening. The secondary chemical treatments are
utilized in an attempt to address differences chemical composition
and/or structure at different locations in the glass. However
secondary chemical treatments can alter the physical properties of
the glass and otherwise degrade a glass produced through subsequent
chemical strengthening. Also, like grinding and polishing,
secondary chemical treatments involve the time and expense of an
extra processing step that is done prior to chemical
strengthening.
[0008] Given the foregoing, chemically strengthened glass and
methods for making chemically strengthened glass are desired in
which the strengthened glass has reduced induced curvature. It is
also desired that the strengthened glass not have the drawbacks
associated with grinding and polishing or secondary chemical
treatment(s) applied in prior methods associated with the chemical
strengthening of the glass. It is also desired that the
strengthened glass have the improved physical properties of
chemically strengthened glass, such as higher strength, higher
abrasion resistance, and/or higher thermal shock resistance.
SUMMARY
[0009] This summary is provided to introduce a selection of
concepts. These concepts are further described below in the
detailed description in conjunction with the accompanying drawings.
This summary is not intended to identify key features or essential
features of the claimed subject matter, nor is this summary
intended as an aid in determining the scope of the claimed subject
matter.
[0010] According to an implementation, a method for making a
strengthened substrate may include providing a substrate. The
substrate may be characterized by having a glass chemical
structure. The glass chemical structure may include host alkali
ions, having an average ionic radius, situated in the glass
chemical structure. The substrate may also have dimensional volumes
including a treatment-rich volume and a treatment-poor volume
located as opposed to each other in the substrate. The method may
also include providing an exchange medium. The exchange medium may
include invading alkali ions having an average ionic radius that
may be larger than the average ionic radius of the host alkali
ions. The method may also include applying the exchange medium to a
surface of the treatment-rich volume for a period of time. The
method may also include applying the exchange medium to a surface
of the treatment-poor volume for a modified period of time. The
modified period of time may be longer than the period of time. The
method may also include conducting ion exchange while applying the
exchange medium to produce the strengthened substrate.
[0011] According to another implementation, an article of
manufacture includes a chemically strengthened substrate. The
substrate may be characterized by having a glass chemical structure
including alkali ions situated in the glass chemical structure. The
substrate has dimensional volumes. The dimensional volumes may
include a treatment-rich volume including a rich surface of the
substrate. The dimensional volumes may also include a
treatment-poor volume including a poor surface of the substrate.
The treatment-poor volume may be characterized by having a
variation from the treatment-rich volume in one or more of a
chemical composition and a chemical structure. The dimensional
volumes may also include a bulk volume within the substrate. The
bulk volume may be adjacent one or more of the treatment-rich
volume and the treatment-poor volume. A concentration of metal in
one or more of the treatment-poor volume and the treatment-rich
volume may be .gtoreq.about 0.4 mole % higher than a concentration
of the metal in the bulk volume. A concentration of the metal may
be higher in the treatment-poor volume than a concentration of the
metal in the treatment-rich volume. A concentration of alkali ions
in a diffusion depth of one or more of the treatment-rich volume
and the treatment-poor volume may be .ltoreq.about 0.5 mole %
higher than a concentration of the alkali ions in the bulk
volume.
[0012] According to another implementation, an article of
manufacture includes a chemically strengthened glass substrate made
by a process. The process may include providing a substrate. The
substrate may be characterized by having a glass chemical structure
including host alkali ions having an average ionic radius situated
in the glass chemical structure. The substrate may have dimensional
volumes. The dimensional volumes may include a treatment-rich
volume and a treatment-poor volume. The two volumes may be located
as opposed to each other in the substrate. The process may also
include providing an exchange medium. The exchange medium may
include invading alkali ions having an average ionic radius that is
larger than the average ionic radius of the host alkali ions. The
process may include applying the exchange medium to a surface of
the treatment-rich volume for a period of time. The process may
include applying the exchange medium to a surface of the
treatment-poor volume for a modified period of time. The modified
period of time may be longer than the period of time. The process
may include conducting ion exchange while applying the exchange
medium to produce the strengthened substrate.
[0013] The above summary is not intended to describe each
embodiment or every implementation. Further features, their nature
and various advantages are described in the accompanying drawings
and the following detailed description of the examples and
embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The accompanying drawings, which are incorporated in and
constitute a part of this specification, illustrate one or more
embodiments described herein and, together with the description,
explain these embodiments. In addition, it should be understood
that the drawings are presented for example purposes only. In the
drawings:
[0015] FIG. 1 is a flowchart illustrating an exemplary overview of
an implementation described herein;
[0016] FIG. 2 is a graph showing properties of exemplary
strengthened substrates made utilizing an exchange medium applied
to soda-lime silicate glass;
[0017] FIG. 3 is a graph showing properties of exemplary
strengthened substrates made utilizing an exchange medium applied
to sodium aluminosilicate glass; and
[0018] FIG. 4 is a flowchart illustrating an exemplary process for
making a strengthened substrate.
DETAILED DESCRIPTION
[0019] The following detailed description refers to the
accompanying drawings. The same reference numbers in different
drawings may identify the same or similar elements.
Overview
[0020] The present invention is useful for making chemically
strengthened glass, and has been found to be particularly
advantageous for making chemically strengthened glass having
reduced induced curvature. A chemically strengthened glass,
according to the principles of the invention, does not have the
drawbacks associated with grinding and polishing or secondary
chemical treatment(s) when done prior to chemical strengthening.
While the present invention is not necessarily limited to such
applications, various aspects of the invention are appreciated
through a discussion of various examples using this context.
[0021] FIG. 1 is flowchart illustrating an exemplary overview of an
implementation described herein. Assume that a glass substrate has
variations in its chemical composition and/or chemical structure at
different locations or "volumes" in the glass. One type of
variation has a chemical composition and/or chemical structure that
is more readily treated by chemical strengthening and is a
"treatment-rich" volume. Another type of variation has a chemical
composition and/or chemical structure that is less readily treated
by chemical strengthening and is a "treatment-poor" volume. The
term "treatment-rich volume" refers to a volume of a glass
substrate which exhibits faster alkali ion interdiffusion and/or
greater compression development during chemical strengthening
relative to a "treatment-poor volume" under equivalent chemical
strengthening conditions applied to the glass substrate. A volume
may occur at a surface of a substrate, or in a space or layer
beneath the surface. A treatment-rich volume or treatment-poor
volume may be a surface layer of a glass substrate in which the
diffusion of invading alkali ions extends to a given "diffusion
depth" from the surface, also called a penetration depth or a
diffusion layer. In chemical strengthening, a portion of the
diffusion depth is in compressive stress, called case depth. Case
depth is the width of the diffusion layer that is in compressive
stress in a specimen.
[0022] As shown in FIG. 1, at step 102, a glass substrate is
provided with the different volumes. At step 104, chemical
strengthening of the treatment-poor volume is performed for a
modified period of time that is longer than the period of time at
step 106, for chemical strengthening of the treatment-rich
volume.
[0023] While the exchange medium is applied to the different
volumes, chemical strengthening proceeds to produce a strengthened
substrate in which the induced curvature has been reduced or
nullified through the application of the exchange medium for the
different periods of time. Without wishing to be bound by any
particular theory, it appears that the longer time period in which
the exchange medium is applied to the treatment-poor volume offsets
the difference in ion-exchangeability between the treatment-rich
and treatment poor volumes, thus reducing or nullifying induced
curvature that may otherwise result from chemical strengthening of
the glass substrate.
[0024] For simplicity and illustrative purposes, the present
invention is described by referring mainly to embodiments,
principles and examples thereof. In the following description,
numerous specific details are set forth in order to provide a
thorough understanding of the examples. It is readily apparent
however, that the embodiments may be practiced without limitation
to these specific details. In other instances, some embodiments
have not been described in detail so as not to unnecessarily
obscure the description. Furthermore, different embodiments are
described below. The embodiments may be used or performed together
in different combinations.
[0025] The operation and effects of certain embodiments can be more
fully appreciated from the examples, as described below. The
embodiments on which these examples are based are representative
only. The selection of these embodiments to illustrate the
principles of the invention does not indicate that materials,
components, reactants, conditions, techniques, configurations and
designs, etc. which are not described in the examples are not
suitable for use, or that subject matter not described in the
examples is excluded from the scope of the appended claims or their
equivalents. The significance of the examples may be better
understood by comparing the results obtained therefrom with
potential results which may be obtained from tests or trials that
may be, or may have been, designed to serve as controlled
experiments and to provide a basis for comparison.
[0026] As used herein, the terms "based on", "comprises",
"comprising", "includes", "including", "has", "having" or any other
variation thereof, are intended to cover a non-exclusive inclusion.
For example, a process, method, article, or apparatus that
comprises a list of elements is not necessarily limited to only
those elements but may include other elements not expressly listed
or inherent to such process, method, article, or apparatus.
Further, unless expressly stated to the contrary, "or" refers to an
inclusive or and not to an exclusive or. For example, a condition A
or B is satisfied by any one of the following: A is true (or
present) and B is false (or not present), A is false (or not
present) and B is true (or present), and both A and B is true (or
present). Also, use of the "a" or "an" is employed to describe
elements and components. This is done merely for convenience and to
give a general sense of the description. This description should be
read to include one or at least one and the singular also includes
the plural unless it is obvious that it is meant otherwise.
[0027] The meaning of abbreviations and certain terms used herein
is as follows: "mm" means millimeter(s), ".mu.m" means
micrometer(s) or micron(s), "g" means gram(s), "mg" means
milligram(s), ".mu.g" means microgram(s), "L" means liter(s), "mL"
means milliliter(s), "cc" means cubic centimeter(s), "cc/g" means
cubic centimeters per gram, "mol" means mole(s), "mmol" means
millimole(s), "wt %" means percent by weight and "mol %" means
percent by mole.
Exemplary Substrate Glasses
[0028] As used herein a "glass substrate" may comprise any kind of
ion-exchangeable glass. Examples of such glass include soda-lime
silicate glass, alkali aluminosilicate glass or alkali
aluminoborosilicate glass, though other glass compositions are
contemplated including glasses where glass forming components are
free of silica, such as boron oxide (borate), phosphorus oxide
(phosphate), aluminum oxide (aluminate), etc. As used herein, "ion
exchangeable" means that a glass is capable of exchanging alkali
ions located in the glass structure of the glass (i.e., "host
alkali ions"), such as at or near the surface of the substrate,
with larger alkali ions (i.e., "invading alkali ions") from an
exchange medium that may be a liquid, solid or gas. An "ion
exchange rate" refers to an amount of invading ions entering a
substrate over a period of time. A glass may have chemical
composition and/or chemical structure variations at different
locations or "volumes" in the glass. An example of chemical
composition variation is an excess of metal, such as metal ions or
other forms of metal and may include a metal species, such as tin
or lead. An example is metal that remains in a flat glass made by a
float glass method, such as tin. An example of chemical structure
variation is the presence of an element in the glass in which the
element may have different valences throughout different volumes,
such as tin present in Sn.sup.2+ and Sn.sup.4+ valences in the
different volumes. In this example, the different forms of tin form
different chemical structures in the different volumes.
[0029] Exemplary embodiments of substrate glasses include silicate
glasses, such as soda-lime silicate glass or sodium aluminosilicate
glass that includes alumina, at least one alkali metal and, in some
embodiments, greater than 50 mol % SiO.sub.2, in other embodiments
at least 58 mol % SiO.sub.2, and in still other embodiments at
least 60 mol % SiO.sub.2.
Exemplary Strengthened Glasses
[0030] Exemplary embodiments of chemically strengthened glasses
include soda-lime silicate glass and sodium aluminosilicate glass
which are strengthened, such as, in potassium nitrate salt baths.
Chemical strengthening may be performed at various temperatures,
such as at temperatures above about 400.degree. C., preferably
about 430.degree. C., and with ion exchange durations of about 1-24
hours. The zone of compressive stress occurs, for example, within a
diffusion depth of about 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100
or 125 to about 150 .mu.m of a surface of a substrate glass.
According to an exemplary embodiment, compressive stress in a
strengthened glass is greatest at a surface (i.e., a "surface
compression") of the glass and the level of compressive stress
follows a gradient extending downward from the surface through a
case depth in the strengthened glass. In exemplary embodiments, the
amount of surface compression may be up to about 800 MPa or higher
in strengthened soda-lime silicate glass and up to about 1200 MPa
or higher in aluminosilicate glass. In some exemplary embodiments,
surface compression is about 200-650 MPa in strengthened soda-lime
silicate glass and about 300-850 MPa in aluminosilicate glass. In
other exemplary embodiments, surface compression is about 400-600
MPa in strengthened soda-lime silicate glass and about 600-800 MPa
in aluminosilicate glass.
[0031] In some exemplary embodiments, a strengthened silicate
glass, such as soda-lime silicate glass or sodium aluminosilicate
glass comprises alumina, at least one alkali metal and, in some
embodiments, greater than 50 mol % SiO.sub.2, in other embodiments
at least 58 mol % SiO.sub.2, and in still other embodiments at
least 60 mol % SiO.sub.2. In these embodiments, a
Li.sub.2O+Na.sub.2O+K.sub.2O total mol %, such as in a volume
associated with a diffusion depth, is at least about 1, 2, 5, 7 or
8-10 mol % and .ltoreq.25 mol %, preferably .ltoreq.20 mol %, and
more preferably .ltoreq.about 2, 5, 7, 8, 10, 12, 15 or 16-18 mol
%.
[0032] In another exemplary embodiment, an alkali aluminosilicate
glass comprises, consists essentially of, or consists of: 60-75 mol
% SiO.sub.2; 5-15 mol % Al.sub.2O.sub.3; 0-12 mol % B.sub.2O.sub.3;
8-21 mol % Na.sub.2O; 0-8 mol % K.sub.2O; 0-15 mol % MgO; and 0-3
mol % CaO. In these embodiments, such as in a volume associated
with a diffusion depth, a Li.sub.2O+Na.sub.2O+K.sub.2O total mol %
is at least about 1, 2, 5, 7 or 8-10 mol % and .ltoreq.25 mol %,
preferably .ltoreq.20 mol %, and more preferably .ltoreq.about 2,
5, 7, 8, 10, 12, 15 or 16-18 mol %.
[0033] In yet another embodiment, an alkali aluminosilicate glass
substrate comprises, consists essentially of, or consists of: 60-70
mol % SiO.sub.2; 6-14 mol % Al.sub.2O.sub.3; 0-15 mol %
B.sub.2O.sub.3; 0-15 mol % Li.sub.2O; 0-20 mol % Na.sub.2O; 0-10
mol % K.sub.2O; 0-15 mol % MgO; 0-10 mol % CaO; 0-5 mol %
ZrO.sub.2; 0-2 mol % SnO.sub.2; 0-1 mol % CeO.sub.2; wherein about
1, 2, 5, 7, 8, or 10-12 mol
%.ltoreq.Li.sub.2O+Na.sub.2O+K.sub.2O.ltoreq.about 2, 5, 7, 8, 10,
12, 15 or 16-20 mol %, such as in a volume associated with a
diffusion depth, and 0 mol %.ltoreq.MgO+CaO.ltoreq.15 mol %.
[0034] In one example embodiment, sodium ions in the substrate
glass are replaced by potassium ions from a molten bath, though
other alkali metal ions having a larger atomic radius, such as
rubidium or cesium, may replace smaller alkali metal ions in the
glass. Similarly, other alkali metal salts such as, but not limited
to, nitrates, sulfates, halides, and the like may be used in the
ion exchange process.
[0035] In another example embodiment, a chemically-strengthened
glass substrate can have a surface compressive stress of about 200
MPa or more, e.g., about 300, 400, 500, 600, 700, 800, 900, 1000 or
1500 MPa or more, a case depth of about 5 .mu.m or more (e.g.,
about 5, 10, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80,
85, 90, 95, 100 .mu.m or more) and a diffusion depth of about 5
.mu.m or more (e.g., about 5, 10, 20, 25, 30, 35, 40, 45, 50, 55,
60, 65, 70, 75, 80, 85, 90, 95, 100, 125 or 150 .mu.m or more).
[0036] In another example embodiment, a chemically-strengthened
glass substrate can have a higher amount of metal in at least one
surface volume or layer, such as a treatment-rich volume or a
treatment-poor volume, than in a bulk volume adjacent these surface
volumes. A concentration of metal in at least one of the
treatment-poor volume and the treatment-rich volume may be
.gtoreq.about 0.4, 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, 6.0, 8.0,
10.0, 12.0, 15.0, 20 or 25 mol % higher than a concentration of the
metal in the bulk volume. According to an embodiment, a
concentration of metal in the treatment-poor volume is higher than
a concentration of the metal in a treatment-rich volume. A common
example of strengthened glass with variant metal concentrations in
the different volumes is chemically strengthened glass made from a
flat glass substrate prepared using a float glass process utilizing
tin.
[0037] In another example embodiment, a chemically-strengthened
glass substrate may have an average concentration of alkali ions
(e.g. invading alkali ions and host alkali ions) that is the same
or different in a diffusion depth of a surface volume than in an
adjacent volume, such as a bulk volume. The surface volume may be a
treatment-rich volume or a treatment-poor volume in the
strengthened glass. The average concentration of alkali ions may be
the same or different from an average concentration of alkali ions
in the adjacent volume, such as a bulk volume. In one example
embodiment, the average concentration of alkali ions in the
diffusion depth of the surface volume is .ltoreq.to about 0.5 mol %
higher than a concentration of the alkali ions in the bulk volume.
In other embodiments, the average concentration of alkali ions in
the diffusion depth of the surface volume is .ltoreq.to about 0.4,
0.3, 0.2, 0.0.1 or 0.05 mol % higher, equal to or less than a
concentration of the alkali ions in the bulk volume adjacent the
surface volume.
Exemplary Exchange Mediums
[0038] Exemplary embodiments of a liquid exchange medium which may
be utilized in chemical strengthening include liquid molten salt
baths. The molten liquid baths include invading alkali ions having
an average ionic radius in the alkali metal ion of the molten salt
that is larger than an average ionic radius of host alkali metal
ions in the substrate glass prior to ion exchange. A common example
of a liquid molten salt bath includes potassium nitrate with
potassium as the invading alkali ion to replace sodium and/or
lithium host ions in the substrate glass.
[0039] Mixed salt blends of invading alkali ions may also be used
as liquid exchange mediums. These blends may include salts of
different alkali metals, preferably different alkali metal
nitrates. A nitrate melt blend may include at least two different
alkali ions, for example Na and K, or as well Na and Rb. But it is
also possible that three or four different alkali metals are
included. Rb ions or Cs ions may be used in chemical strengthening.
The method according to the embodiment offers the option to
effectively incorporate invading alkali ions into a treated glass
article having ionic radii that are significantly larger than the
radii of host alkali ions, such as lithium or sodium ions.
[0040] Exemplary embodiments of a solid exchange medium which may
be utilized in chemical strengthening include semi-solid pastes
that may be applied to a surface of a glass substrate. The paste
includes invading alkali ions from a source such as a salt and at
least one rheological agent, such as clay, to suspend the ions in
the solid exchange medium. Kaolin is a common example of a
rheological agent which may utilized in making a solid exchange
medium. The viscosity of a paste made with kaolin may be modified
with water and other additives to suit an application by which the
paste is applied to a glass substrate. Water content of a paste may
be evaporated prior to application as a solid exchange medium
utilizing a raised high temperature, such as greater than
120.degree. C. Another example of a rheological agent is
aluminosilicate fiber. Other clays and rheological agents are also
contemplated.
[0041] In addition to liquid and solid exchange mediums, gas
exchange mediums are also contemplated.
EXAMPLES
[0042] The following examples demonstrate methods of making
chemically strengthened glass utilizing differential time
methodology.
Example 1
[0043] Example 1 demonstrates the preparation of a chemically
strengthened soda-lime silicate glass having a reduced induced
curvature. Reference is made to graph 200 in FIG. 2 in the example.
Graph 200 shows a differential time of exchange methodology. A
pre-treatment time for applying an exchange medium to the surface
of a treatment-poor volume is given in hours on the abscissa.
Peak-to-valley deflection for a flat glass having 50 mm width is
given in microns on the ordinate. Note that for this example, an
ideal flatness, (i.e., a nearly zero of induced curvature) is
crossed between 3.0 hours and 3.5 hours, as shown by the data
plotted in graph 200.
[0044] Sample preparation: Soda-lime silicate glass coupons, 50
mm.times.50 mm across and 0.4 mm width, were cut from a mother
sheet formed by a tin float glass process. The treatment-poor
volume surface on the coupons was manually coated with a uniform
layer of KNO.sub.3-containing paste as a solid exchange medium. The
paste composition was 2 parts distilled water, 1 part New Zealand
China clay (premium grade), and 1 part KNO.sub.3 (technical grade)
by weight. The wet weight of paste applied was 4.0 grams. Water was
dried from the applied paste by heating the coupons in a drying
oven at about 100.degree. C. for several hours. After drying the
pastes on the coupons, separate coupons were processed in air at
440.degree. C. for the following lengths of pre-treatment time:
0.5, 1.0, 1.5, 2.0, 2.25, 2.5, 2.75, 3.0, 3.5, and 4.0 hours.
Pre-treatment time represents the differential time between the
modified period of time and the period of time.
[0045] After the pre-treatment with the paste exchange medium, the
coupons were submerged for 24 hours in a liquid exchange medium, a
bath of molten KNO.sub.3 held at 440.degree. C. The paste on the
treatment-poor surface was not removed prior to the submerged
treatment and was adherent throughout the submerged treatment, and,
following submerged treatment and cooling, was removed by rinsing
with water. A minimum of two coupons were examined for each
parameter.
[0046] Results: Coupon deflection after processing was determined
from surface profiles measured using a non-contact optical
profiler. Deflection is the peak-to-valley height determined along
a line drawn between opposite edge mid-points of the square coupon.
Deflection versus pre-treatment time is given in graph 200. A
positive deflection measurement in graph 200 indicates convex
curvature of the treatment-rich volume surface. A negative
deflection measurement indicates concave curvature of the
treatment-rich surface.
[0047] For commercial purposes, such as for utilization in personal
electronic devices and flat panel displays, an acceptable
deflection is about 0.1% of the linear span--corresponding to 50
microns for a 50 mm span. In graph 200, pre-treatment times of
2.25, 2.5, 2.75, 3.0 and 3.5 hours produced a deflection less than
the 50 micron parameter in this example. An ideal flat was crossed
between 3.0 and 3.5 hours. At 2.75 hours, the average deflection
measured was 21.8 microns (treatment-rich side convex), average
surface compression was 486 MPa for the rich surface and 397 MPa
for the poor surface, average case depth was 26.1 micron for the
rich surface and 26.8 micron for the poor surface.
[0048] Sample coupons, which did not have any pre-treatment by
paste exchange medium applied to the poor surface, but otherwise
underwent equivalent processing in the liquid exchange medium had
an average deflection measurement of 116.3 micron (rich side
convex), an average surface compression of 489 MPa for the rich
surface and 417 MPa for the poor surface, and average case depth of
25.8 microns on the rich surface and 24.7 microns on the poor
surface. The average deflection of the coupons which did not have
any pre-treatment by paste exchange medium is represented by the
horizontal dashed line appearing above 100 microns deflection in
graph 200.
Example 2
[0049] Example 2 demonstrates the preparation of a chemically
strengthened sodium aluminosilicate glass having a reduced induced
curvature. Reference is made to graph 300 in FIG. 3 in the example.
Graph 300 shows a differential time of exchange methodology. A
pre-treatment time for applying an exchange medium to the surface
of a treatment-poor volume is given in minutes on the abscissa.
Peak-to-valley deflection for a flat glass having 50 mm width is
given in microns on the ordinate. Note that for this example, an
ideal flatness, (i.e., a nearly zero of induced curvature) is
crossed near 14 minutes, as shown by the data plotted in graph
300.
[0050] Sample preparation: Sodium aluminosilicate glass coupons, 50
mm.times.50 mm across and 0.56 mm width, were cut from a mother
sheet formed by a tin float glass process. The treatment-poor
volume surface on the coupons was manually coated with a uniform
layer of KNO.sub.3-containing paste as a solid exchange medium. The
paste composition was 2 parts distilled water, 1 part UNIFRAX
FIBERFRAX 7000 aluminosilicate fiber, and 1 part KNO.sub.3
(technical grade) by weight. The wet weight of paste applied was
4.0 grams. Water was dried from the applied paste by heating the
coupons in a drying oven at .about.100.degree. C. for several
hours. After drying the pastes on the coupons, separate coupons
were processed in air at 450.degree. C. for the following lengths
of pre-treatment time: 12, 13, 14, 15, and 16 minutes.
Pre-treatment time represents the differential time between the
modified period of time and the period of time.
[0051] After the pre-treatment with the paste exchange medium, the
coupons were submerged for 2 hours in a bath of molten KNO.sub.3
held at 450.degree. C. The paste on the treatment-poor surface was
not removed prior to the submerged treatment and was adherent
throughout the submerged treatment, and, following the submerged
treatment and cooling, was removed by rinsing with water. A minimum
of two coupons were examined for each parameter.
[0052] Results: Coupon deflection after processing was determined
from surface profiles measured using a non-contact optical
profiler. Deflection is the peak-to-valley height determined along
a line drawn between opposite edge mid-points of the square coupon.
Deflection versus pre-treatment time is given in graph 300. A
positive deflection measurement in graph 300 indicates convex
curvature of the treatment-rich volume surface. A negative
deflection measurement indicates concave curvature of the
treatment-rich surface.
[0053] For commercial purposes, such as use in personal electronic
devices and flat panel displays, acceptable deflection is about
0.1% of the linear span--corresponding to 50 micron for a 50 mm
span. In graph 300, pretreatment times produced deflection less
than the 50 micron parameter in this example. An ideal flat was
crossed near 14 minutes. At 14 minutes, average deflection was -2.5
micron (treatment-rich side concave), average surface compression
was 846 MPa for the rich surface and 824 MPa for the poor surface,
average case depth was 40.2 micron for the rich surface and 40.8
micron for the poor surface.
[0054] Sample coupons, which did not have any pre-treatment by
paste exchange medium applied to the poor surface and did not
undergo a pre-treatment, but otherwise underwent equivalent
processing in the liquid exchange medium, had an average deflection
measurement of 35.5 micron (treatment-rich side convex), average
surface compression was 862 MPa for the rich surface and 845 MPa
for the poor surface, and average case depth was 40.4 micron on the
rich surface and 35.5 micron on the poor surface. The average
deflection of the coupons which did not have any pre-treatment by
paste exchange medium is represented by the horizontal dashed line
appearing above 30 microns deflection in graph 300.
[0055] FIG. 4 is flowchart illustrating an exemplary process for
making a strengthened substrate.
[0056] At step 402, a glass substrate is provided having different
volumes, such as a "treatment-rich" volume and a "treatment-poor"
volume in the glass structure including host alkali ions. The glass
may be soda-lime silicate glass or aluminosilicate glass. The
volumes may be located, for example, as opposed to each other in
the substrate, and according to an embodiment, may be diametrically
opposed. The glass substrate may have variations in the different
volumes, such as a variation in chemical composition and/or
chemical structure. An example of a variation in chemical
composition is an amount of tin situated in different volumes of
the glass. An example of a variation in chemical structure is the
presence of tin in different valences, Sn.sup.2+ and Sn.sup.4+ in
different volumes of the glass. A variation in chemical composition
and/or chemical structure in the treatment-poor volume may
distinguish it from the treatment-rich volume.
[0057] At step 404, an exchange medium including invading alkali
ions is applied to a surface of the treatment-poor volume at a
first temperature ("T1" in the figure) for first period of time
("P1" in the figure).
[0058] At step 406, the glass substrate is submerged in a liquid
exchange medium including invading alkali ions at a second
temperature ("T2" in the figure) for second period of time ("P2" in
the figure). The second temperature (T2) may be the same or
different from the first temperature (T1). In an embodiment, the
submerging immediately follows the end of the first time period
(P1). In another embodiment, the submerging follows a break after
the end of the first time period (P1) when the exchange medium
applied in Step 404 is removed from contact with the glass
substrate. According to an embodiment, a net bending moment is
about zero, in a fully strengthened substrate after the liquid
exchange medium has been applied.
[0059] Although described specifically throughout the entirety of
the disclosure, the representative examples have utility over a
wide range of applications, and the above discussion is not
intended and should not be construed to be limiting. The terms,
descriptions and figures used herein are set forth by way of
illustration only and are not meant as limitations. Those skilled
in the art recognize that many variations are possible within the
spirit and scope of the principles of the invention. While the
examples have been described with reference to the figures, those
skilled in the art are able to make various modifications to the
described examples without departing from the scope of the
following claims, and their equivalents.
* * * * *