U.S. patent application number 09/991746 was filed with the patent office on 2002-05-30 for glass sheet intended to be thermally toughened.
This patent application is currently assigned to SAINT-GOBAIN GLASS FRANCE. Invention is credited to Bordeaux, Frederic, Duffrene, Lucas.
Application Number | 20020065187 09/991746 |
Document ID | / |
Family ID | 9523530 |
Filed Date | 2002-05-30 |
United States Patent
Application |
20020065187 |
Kind Code |
A1 |
Bordeaux, Frederic ; et
al. |
May 30, 2002 |
Glass sheet intended to be thermally toughened
Abstract
The subject of the invention is a glass sheet intended to be
thermally toughened, the matrix of which is of the silica-soda-lime
type, having an expansion coefficient .alpha. of greater than
100.times.10.sup.-7 K.sup.-1, a Young's modulus E of greater than
60 GPa and a thermal conductivity k of less than 0.9 W/m.K.
Inventors: |
Bordeaux, Frederic; (Bourg
la Reine, FR) ; Duffrene, Lucas; (Paris, FR) |
Correspondence
Address: |
PENNIE & EDMONDS LLP
1667 K STREET NW
SUITE 1000
WASHINGTON
DC
20006
|
Assignee: |
SAINT-GOBAIN GLASS FRANCE
|
Family ID: |
9523530 |
Appl. No.: |
09/991746 |
Filed: |
November 26, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09991746 |
Nov 26, 2001 |
|
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|
09403741 |
Feb 29, 2000 |
|
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Current U.S.
Class: |
501/67 ; 501/55;
501/65; 501/66; 501/72 |
Current CPC
Class: |
C03C 3/087 20130101 |
Class at
Publication: |
501/67 ; 501/66;
501/65; 501/72; 501/55 |
International
Class: |
C03C 003/076; C03C
003/089; C03C 003/091; C03C 003/093; C03C 003/078 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 2, 1998 |
FR |
FR 98/02493 |
Claims
1. A glass sheet intended to be thermally toughened, comprising a
silica-soda matrix, wherein said sheet has an expansion cofficient
.alpha. of greater than 100.times.10.sup.-7K.sup.-1, a Young's
modulus E of greater than 60 GPa and a thermal conductivity k of
less than 0.9 W/m.K.
2. The glass sheet of claim 1, wherein said sheet has a Poisson's
ratio of greater than 0.21.
3. The glass sheet of claim 2, wherein said sheet has a specific
heat of greater than 7.40 J/kg.K.
4. The glass sheet of claim 1, wherein said sheet has a specific
heat of greater than 7.40 J/kg.K.
5. The glass sheet of claim 1, wherein said sheet has a density of
greater than 2520 kg/m.sup.3.
6. The glass sheet of claim 1, wherein said sheet satisfies the
relationship:.alpha..multidot.E/K>8000.
7. The glass sheet of claim 1, wherein said matrix comprises, in
percentages by weight, the following constituents:
5 SiO.sub.2 45-69% Al.sub.2O.sub.3 0-14% CaO 0-22% MgO 0-10%
Na.sub.2O 6-24% K.sub.2O 0-10% BaO 0-12% B.sub.2O.sub.3 0-6% ZnO
0-10%
and satisfies the
relationships:Na.sub.2O+K.sub.2O>20%Na.sub.2O+K.sub.2-
O+CaO>27%.
8. The glass sheet of claim 1, wherein said matrix comprises, in
percentages by weight, the following constituents:
6 SiO.sub.2 45-69% Al.sub.2O.sub.3 0-14% CaO 0-22% MgO 0-10%
Na.sub.2O 6-24% K.sub.2O 0-10% BaO 0-12% B.sub.2O.sub.3 0-6% ZnO
0-10%
and satisfies the
relationships:Na.sub.2O+K.sub.2O>17%Na.sub.2O+K.sub.2-
O+CaO>35%.
9. The glass sheet of claim 1, wherein said matrix comprises, in
percentages by weight, at least one of Na.sub.2O and K.sub.2O in
amounts which satisfy the following
relationship:Na.sub.2O+K.sub.2O>17%.
10. The glass sheet of claim 1, wherein said matrix comprises, in
percentages by weight, the following constituents:
7 SiO.sub.2 45-69% Al.sub.2O.sub.3 0-14% CaO 0-22% MgO 0-10%
Na.sub.2O 6-24% K.sub.2O 0-10% BaO 0-12% B.sub.2O.sub.3 0-6% ZnO
0-10%
and satisfies the relationships: (a) Na.sub.2O+K.sub.2O>17%, and
(b) Na.sub.2O+K.sub.2O+CaO>29% when at least one of
Na.sub.2O>18%, K.sub.2O>5%, and Al.sub.2O.sub.3<3%.
11. The glass sheet of claim 9, wherein said matrix comprises, in
percentages by weight, at least one of TiO.sub.2 and
Al.sub.2O.sub.3 in amounts which satisfy the
relationship:TiO.sub.2+Al.sub.2O.sub.3<3%.
12. The glass sheet of claim 1, wherein said matrix comprises, in
percentages by weight, at least one of Na.sub.2O, K.sub.2O, CaO,
and Al.sub.2O.sub.3 in amounts which satisfy the following
relationships: (a) Na.sub.2O+K.sub.2O>17%, and (b)
Na.sub.2O+K.sub.2O+CaO>29% when at least one of
Na.sub.2O>18%, K.sub.2O>5%, and Al.sub.2O.sub.3<3%.
13. The glass sheet according to claim 1, wherein said sheet has a
thickness of less than 2.5 mm and is thermally toughened.
14. The glass sheet of claim 1, wherein said matrix comprises
Na.sub.2O and optionally one or more of K.sub.2O, CaO or
Al.sub.2O.sub.3 in amounts which satisfy the following
relationship:Na.sub.2O+K.sub.2O+CaO>29 wt %when at least one of
Na.sub.2O>18 wt %, K.sub.2O>5 wt %, and Al.sub.2O.sub.3<3
wt %.
15. The glass sheet of claim 1, wherein said matrix has a CaO
content of 10.4 to 22 wt %.
16. A glass sheet intended to be thermally toughened, comprising a
silica-soda matrix, wherein said sheet has an expansion cofficient
.alpha. of greater than 100.times.10.sup.-7K.sup.-1, a Young's
modulus E of greater than 60 GPa and a thermal conductivity k of
less than 0.9 W/m.K and said matrix has a SiO.sub.2 content of 45
to 65 wt %, wherein said matrix comprises Na.sub.2O and optionally
K.sub.2O in amounts which satisfy the following
relationship:Na.sub.2O+K.sub.2O>20wt %.
17. A glass composition comprising, in percentages by weight:
8 SiO.sub.2 45-69% Al.sub.2O.sub.3 0-14% CaO 0-22% MgO 0-10%
Na.sub.2O 6-24% K.sub.2O 0-10% BaO 0-12% B.sub.2O.sub.3 0-6% ZnO
0-10%,
wherein the glass has a viscosity .eta. in poise, a forming
temperature at which log .eta.=3.5, and a liquidus temperature
which is less than or equal to the forming temperature.
18. The glass composition of claim 17, wherein the liquidus
temperature is between 10.degree. C. and 30.degree. C. less than
the forming temperature.
19. The glass composition of claim 18, wherein the glass has an
expansion coefficient of greater than
100.times.10.sup.-7K.sup.-1.
20. The glass composition of claim 19, wherein the glass has a
Young's modulus of greater than 60 GPa.
21. The glass composition of claim 19, wherein the glass has a
thermal conductivity of less than 0.9 W/m.K.
Description
[0001] The invention relates to glass sheets intended to be
thermally toughened and more precisely to glass sheets intended to
be fitted into motor vehicles.
[0002] Although the invention is not limited to such applications,
it will be more particularly described with reference to the
production of thermally toughened thin glass sheets, i.e. those
having a thickness of less than 2.5 mm. This is because
motor-vehicle manufacturers are at the present time increasingly
tending to wish to limit the weight corresponding to the glazing,
while the glass area of the motor vehicles is increasing. A
reduction in the thickness of the glass sheets is therefore needed
in order to meet these new requirements.
[0003] With regard to the thermal toughening of these glass sheets,
and more particularly in order to produce the side windowpanes of
motor vehicles, the requirements of European Regulation No. 43,
relating to the homologation of safety glazing and of the materials
for glazing intended to be fitted into motor vehicles and their
trailers, have to be met. According to this regulation, the
constraints on toughening must be such that the glazing, in the
event of it breaking, does so into a number of fragments which,
over any 5.times.5 cm square, is neither less than 40 nor greater
than 350 (the latter number being increased to 400 in the case of
glazing having a thickness of less than or equal to 2.5 mm). Again
according to these requirements, no fragment must be greater than
3.5 cm.sup.2, except possibly in a strip 2 cm in width around the
periphery of the glazing and within a 7.5 cm radius around the
point of impact, and there must not be any elongate fragment of
greater than 7.5 cm.
[0004] Conventional toughening plants, especially the devices for
bending and toughening glass sheets, by making them run along a
roller conveyor having a profile that is curved in the direction in
which the glass sheets run, allow 3.2 mm thick glass sheets to be
toughened according to European Regulation No. 43 completely
satisfactorily.
[0005] The abovementioned techniques are known, especially from
French Patents FR-B-2,242,219 and FR-B-2,549,465 and consist in
making the glass sheets, heated in a horizontal furnace, run
between two layers of rollers--or other rotating elements--arranged
with a curvilinear profile and passing through a terminal
toughening zone. In order to produce side windowpanes, sunroofs or
other glazing articles, especially of cylindrical shape, the layers
consist of, for example, right cylindrical rods arranged with a
circular profile. The layers may also consist of elements giving
the glazing a secondary curvature, such as conical elements or else
those of the diabolo type or barrel type. This technique allows a
very high production capacity since, on the one hand, the glass
sheets do not have to be widely spaced, it being possible for one
glass sheet to enter the forming zone without any problem while the
treatment of the previous sheet has yet to be completed and, on the
other hand, if the length of the rollers so allow, two or three
glass sheets side by side may be treated simultaneously.
[0006] The running speed of the glass plates or sheets is at least
10 cm/s and is about 15 to 25 cm/s. The speed normally does not
exceed 30 cm/s in order to allow sufficient toughening time.
[0007] When the thickness of the glass sheets decreases, and in
order to meet the same toughening standards, the heat-exchange
coefficient must be greatly increased. To do this, it is possible
to increase the blowing power of the toughening devices. Such
modifications entail, on the one hand, major investment and, on the
other hand, higher operating costs. Moreover, the increase in the
blowing power may impair the optical quality of the glass sheets
and/or their flatness.
[0008] The inventors were thus tasked with the mission of producing
glass sheets toughened according to European Regulation No. 43,
having a thickness of less than 2.5 mm on standard toughening
plants of the type described above.
[0009] Thus, the object of the invention is to provide a glass
sheet intended to be thermally toughened, the intrinsic properties
of which lead to results in the case of thicknesses of less than
2.5 mm but are equivalent to those usually obtained in the case of
thicknesses of greater than 3 mm, with the same cooling
devices.
[0010] This object is achieved by a glass sheet intended to be
thermally toughened, the matrix of which is of the silica-soda-lime
type and has an expansion coefficient .alpha. of greater than
100.times.10.sup.-7K.sup.-1- , a Young's modulus E of greater than
60 GPa and a thermal conductivity k of less than 0.9 W/m.K.
[0011] Such properties actually give the glass sheet the
possibility of being thermally toughened according to European
Regulation No. 43 when this sheet has a thickness of less than 2.5
mm.
[0012] According to a preferred embodiment of the invention, the
glass sheet has a Poisson's ratio of greater than 0.21.
[0013] The elastic modulus and the Poisson's ratio are determined
by the following test: a glass test piece having the dimensions
100.times.10 mm.sup.2 and a thickness of less than 6 mm is
subjected to 4-point bending, the outer supports of which are
separated by 90 mm and the inner supports by 30 mm. A strain gauge
is adhesively bonded to the centre of the glass plate. The
principal displacements (in the length of the plate and in its
width) are calculated therefrom. The applied stress is calculated
from the applied force. The relationships between stress and
principal displacements allow the elastic modulus and the Poisson's
ratio to be determined.
[0014] Also preferably, the specific heat of the glass sheet is
greater than 740 J/kg.K.
[0015] According to an advantageous embodiment of the invention the
glass sheet has a density of greater than 2520 kg/cm.sup.3 and
preferably greater than 2550 kg/m.sup.3.
[0016] Again preferably, the glass sheet according to the invention
satisfies the following relationship:
.alpha..multidot.E/K>8000
[0017] The glass matrices of the glass sheets according to the
invention are advantageously chosen from among matrices having, in
percentages by weight, the following constitutes:
1 SiO.sub.2 45-69% Al.sub.2O.sub.3 0-14% CaO 0-22% MgO 0-10%
Na.sub.2O 6-24% K.sub.2O 0-10% BaO 0-12% B.sub.2O.sub.3 0-6% ZnO
0-10%.
[0018] The glass compositions proposed above have the advantage in
particular of being able to be melted and converted into glass
ribbon on float-type plants, at temperatures close to those adopted
for the manufacture of conventional silica-soda-lime glass.
[0019] The compositions are actually chosen to have a temperature
corresponding to the viscosity .eta., expressed in poise, such that
log .eta.=2 is less than 1500.degree. C. in order to allow melting
under standard conditions. Moreover, the compositions according to
the invention have a sufficient difference between the forming
temperature of the glass and its liquidus temperature; this is
because, in the technology of float glass in particular, it is
important for the liquidus temperature of the glass to remain equal
to or less than the temperature corresponding to the viscosity,
expressed in poise, such that log .eta.=3.5. Advantageously, this
difference is at least from 10.degree. C. to 30.degree. C.
[0020] The SiO.sub.2 content must not exceed 69%; above this, the
melting of the batch and the refining of the glass require high
temperatures which cause the furnace refractories to undergo
accelerated wear. Below 45%, the glasses according to the invention
are insufficiently stable. Advantageously, the SiO.sub.2 content is
greater than 53%.
[0021] Alumina acts as a stabilizer; this oxide helps to increase
the strain-point temperature. The Al.sub.2O.sub.3 content must not
exceed 14%, or else melting becomes too difficult and the
high-temperature viscosity of the glass increases unacceptably.
[0022] The glass compositions according to the invention may also
include the oxide B.sub.2O.sub.3. In this case, the B.sub.2O.sub.3
content does not exceed 6% as, above this value, the volatilization
of the boron in the presence of alkali metal oxides during
production of the glass may become significant and lead to
corrosion of the refractories. Furthermore, higher B.sub.2O.sub.3
contents impair the quality of the glass. When B.sub.2O.sub.3 is
present in the glass composition with a content of greater than 4%,
the Al.sub.2O.sub.3 content is advantageously greater than 10%.
[0023] The influence of the other oxides on the ability of the
glasses according to the invention to be melted and floated on a
metal bath, as well as on their properties, is as follows: the
alkali metal oxides, and more particularly Na.sub.2O and K.sub.2O,
make it possible to keep the melting point of the glasses according
to the invention and their high-temperature viscosity within
acceptable limits. To do this, the sum of the contents of these
alkali metal oxides remains greater than 11% and preferably greater
than 13%.
[0024] The alkaline-earth metal oxides introduced into the glasses
according to the invention also have the effect of reducing the
melting point, as well as the high-temperature viscosity of the
glasses. The sum of the contents of these oxides is at most 6% and
preferably greater than 8%. Above approximately 28%, the tendency
of the glasses to devitrify may increase to levels incompatible
with the process of floating them on a metal bath.
[0025] The glass compositions may furthermore contain colorants,
especially for applications of the motor-vehicle window type; these
may especially be oxides of iron, of chronium, of cobalt, of
nickel, of selenium, etc.
[0026] According to a first embodiment of the invention, the glass
sheet according to the invention is such that its matrix comprises,
in percentages by weight, the abovementioned constitutes and
satisfies the relationships:
Na.sub.2O+K.sub.2O>20%
Na.sub.2O+K.sub.2O+CaO>27%.
[0027] According to a second embodiment of the invention, the glass
matrix satisfies the relationships:
Na.sub.2O+K.sub.2O>17%
Na.sub.2O+K.sub.2O+CaO>35%.
[0028] According to other embodiments according to the invention,
the glass matrix satisfies the relationships:
Na.sub.2O+K.sub.2O>17%
Na.sub.2O+K.sub.2O+CaO>29% when Na.sub.2O>18% and/or
K.sub.2O>5% and/or Al.sub.2O.sub.3<3%.
[0029] According to the latter embodiments and when the oxide
TiO.sub.2 is present in the matrix, the latter furthermore
satisfies the relationship:
TiO.sub.2+Al.sub.2O.sub.3<3%.
[0030] All the glass matrices described according to these various
embodiments allow the production of glass sheets having a thickness
of less than 2.5 mm and advantageously greater than 1.6 mm, which
may be thermally toughened in accordance with European Regulation
No. 43 on toughening devices originally intended for toughening
glass with a thickness of 3.15 mm.
[0031] The advantages afforded by the glass compositions according
to the invention will be better appreciated with the help of the
examples presented below.
[0032] Various glass compositions in accordance with the invention
were melted and converted into a glass ribbon according to the
invention. There are 6 of these compositions (numbered from 1 to
6). The composition T is a control composition, corresponding to
standard glass for motor-vehicle windows, which may be thermally
toughened in accordance with European Regulation No. 43 when it is
in the form of a glass sheet with a thickness of 3.15 mm.
[0033] These various compositions are given in the table below:
2 TABLE 1 SiO.sub.2 Al.sub.2O.sub.3 CaO MgO Na.sub.2O K.sub.2O BaO
T 71.3 0.6 9.6 4.1 13.6 0.3 0 1 67.1 2.1 8.5 0.1 16.0 5.1 0.1 2
63.59 0.45 13.19 0.07 21.75 0.01 0 3 63.22 2.45 13.40 0.1 17.5 2.65
0 4 64.8 2.0 10.4 0.5 17.4 4.9 0 5 64.0 2.0 10.4 0.5 16.3 4.8 2 6
65.0 1.0 14.1 0 18.9 1.0 0
[0034] The various properties of the glasses indicated above are
given in the following table:
3 TABLE 2 T 1 2 3 4 5 6 Expansion 90 11 12 12 12 12 12 coefficient
6 8 0 2 0 0 (10.sup.-7 K.sup.-1) Young's modulus 70 68 70 70 68 68
69 (GPa) Thermal 1 0.8 0.8 0.8 0.8 0.8 0.8 Conductivity 5 7 3 6 3 5
(W/m. K) Specific heat 85 85 87 85 85 84 86 (J/kg. K) 5 2 2 7 7 3 1
Density 25 25 26 26 26 27 26 (kg/m.sup.3) 80 60 60 48 26 31 70
Poisson's 0.2 0.2 0.2 0.2 0.2 0.2 0.2 ratio 2 2 3 3 3 3 3
[0035] It has been demonstrated that these glasses can be melted
and that they can be for the most part converted using the float
process.
[0036] When testing these glass compositions, it is apparent that
they can be melted under completely conventional conditions and
even at temperatures well below those of the control composition T.
These temperature differences make it possible to envisage a
reduction in energy costs.
[0037] On the other hand, if it appears that the forming ranges,
i.e. the differences between the temperature corresponding to a
viscosity .eta., expressed in poise, such that log .eta.=3.5 and
the liquidus temperature, are narrower in the case of the
compositions according to the invention; however, they are
sufficient to guarantee good-quality forming.
[0038] It is also apparent that the initial toughening temperature
is markedly lower in the case of the glasses according to the
invention; this also leads to energy cost reductions and to less
rapid wear of the furnaces.
[0039] The final table given below shows the thicknesses of the
glass sheets which have been toughened in accordance with European
Regulation No. 43.
4 TABLE 3 T 1 2 3 4 5 6 Thickness (mm) 3.1 2.5 2.4 2.3 2.4 2.4 2.4
5 0 0 5 0 5 5
[0040] It is therefore clearly apparent that the glass sheets
produced from the compositions according to the invention allow
so-called "safety" thermal toughening for thicknesses of less than
2.5 mm using the standard devices which limit the said toughening
to a thickness of 3.15 mm when the glass is of the composition
T.
[0041] Moreover, the optical quality of the glass sheets according
to the invention, having a thickness of less than 2.5 mm and
thermally toughened, is quite comparable to that of glass sheets
having a thickness of 3.15 mm produced from the control composition
T.
* * * * *