U.S. patent application number 12/234881 was filed with the patent office on 2009-01-15 for transparent substrate comprising a stack of thin layers for electromagnetic armour.
This patent application is currently assigned to SAINT-GOBAIN GLASS FRANCE. Invention is credited to Sylvain Belliot, Carinne Fleury, Estelle Mainpin.
Application Number | 20090015909 12/234881 |
Document ID | / |
Family ID | 34203512 |
Filed Date | 2009-01-15 |
United States Patent
Application |
20090015909 |
Kind Code |
A1 |
Fleury; Carinne ; et
al. |
January 15, 2009 |
TRANSPARENT SUBSTRATE COMPRISING A STACK OF THIN LAYERS FOR
ELECTROMAGNETIC ARMOUR
Abstract
A transparent substrate, especially made of glass, provided with
a thin-film multilayer (20) that includes three silver layers (Ag1,
Ag2, Ag3) and comprises, alternately on the substrate, a titanium
dioxide layer (21), a metal oxide layer (22), one of the silver
layers (Ag1, Ag2, Ag3) and a covering layer (23), characterized in
that: the metal oxide is zinc oxide; the covering layer (23) is a
sacrificial metal; and an antireflection layer (24) comprising at
least one metal oxide is deposited on the covering layer (23) for
the silver layer (Ag.sub.3) furthest away from the substrate.
Inventors: |
Fleury; Carinne; (Paris,
FR) ; Belliot; Sylvain; (Paris, FR) ; Mainpin;
Estelle; (Paris, FR) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
SAINT-GOBAIN GLASS FRANCE
Courbevoie
FR
|
Family ID: |
34203512 |
Appl. No.: |
12/234881 |
Filed: |
September 22, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10572286 |
Mar 16, 2006 |
7452603 |
|
|
PCT/FR04/02152 |
Aug 18, 2004 |
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12234881 |
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Current U.S.
Class: |
359/360 ;
428/637 |
Current CPC
Class: |
C03C 17/3644 20130101;
C03C 17/3676 20130101; H01J 2211/446 20130101; Y10T 428/12646
20150115; C03C 17/3618 20130101; H01J 17/16 20130101; C03C 17/3652
20130101; B32B 17/10174 20130101; C03C 17/3639 20130101; C03C
2217/73 20130101; H01J 5/02 20130101; B32B 2367/00 20130101; C03C
17/36 20130101; B32B 17/10018 20130101; H05K 9/0096 20130101; B32B
17/10761 20130101 |
Class at
Publication: |
359/360 ;
428/637 |
International
Class: |
G02B 1/10 20060101
G02B001/10; B32B 15/04 20060101 B32B015/04; G02B 5/26 20060101
G02B005/26 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 17, 2003 |
FR |
0310912 |
Claims
1. A transparent substrate, especially made of glass, provided with
a thin-film multilayer (20) that includes three silver layers (Ag1,
Ag2, Ag3) and comprises, alternately on the substrate, a titanium
dioxide layer (21), a metal oxide layer (22), one of the silver
layers (Ag1, Ag2, Ag3) and a covering layer (23), characterized in
that: the metal oxide is zinc oxide; the covering layer (23) is a
sacrificial metal; and an antireflection layer (24) comprising at
least one metal oxide is deposited on the covering layer (23) for
the silver layer (Ag.sub.3) furthest away from the substrate.
2. The substrate as claimed in claim 1, characterized in that the
thickness of each of the silver layers (Ag.sub.1, Ag.sub.2,
Ag.sub.3) is between 13 nm and 19 nm.
3. The substrate as claimed in claim 2, characterized in that the
thicknesses (e.sub.Ag1, e.sub.Ag2, e.sub.Ag3) of the respective
layers (Ag.sub.1, Ag.sub.2, Ag.sub.3) are identical, or else they
vary in a ratio of between 0.8 and 1.2 and are such that
e.sub.Ag1.ltoreq.e.sub.Ag3.ltoreq.e.sub.Ag2.
4. The substrate as claimed in one of claims 1 to 3, characterized
in that the titanium dioxide layer (21) as sublayer for the silver
layer (Ag.sub.1) closest to the substrate has a thickness of
between 10 and 20 nm, preferably between 10 and 15 nm, and the
titanium oxide layers (21) as sublayers for the other two silver
layers (Ag.sub.2, Ag.sub.3) have a thickness of between 35 and 55
nm, preferably between 40 and 50 nm.
5. The substrate as claimed in any one of the preceding claims,
characterized in that the zinc oxide layer (22) has a thickness of
greater than 15 nm.
6. The substrate as claimed in any one of the preceding claims,
characterized in that the sacrificial metal layer (23) is of
niobium (Nb), titanium (Ti) or zirconium (Zr).
7. The substrate as claimed in any one of the preceding claims,
characterized in that the sacrificial metal layer (23) has a
thickness not exceeding 2 nm.
8. The substrate as claimed in any one of the preceding claims,
characterized in that the antireflection layer (24) has a thickness
of between 25 and 50 nm, preferably between 25 and 35 nm.
9. The substrate as claimed in claim 8, characterized in that the
antireflection layer (24) includes at least one titanium dioxide
layer having a thickness of between 15 and 35 nm, preferably
between 20 and 30 nm.
10. The substrate as claimed in either of claims 8 or 9,
characterized in that the antireflection layer (24) includes a
titanium dioxide layer and another layer of a metal oxide that is
deposited on said titanium dioxide layer and has a thickness of
between 5 and 15 nm, preferably between 6 and 10 nm.
11. The substrate as claimed in claim 10, characterized in that the
metal oxide layer of the antireflection layer (24) is tin oxide
(SnO.sub.2) or silica nitride (Si.sub.3N.sub.4).
12. The substrate as claimed in any one of the preceding claims,
characterized in that it has a surface resistance not exceeding
1.OMEGA./.quadrature., preferably between 0.7 and 0.9
.OMEGA./.quadrature..
13. The substrate as claimed in any one of the preceding claims,
characterized in that it is made of toughened or untoughened glass,
or made of plastic.
14. An electromagnetic shielding filter comprising a substrate as
claimed in any one of the preceding claims, characterized in that
it has the following optical properties: a light transmission
factor T.sub.L of between 45 and 55%; a purity of less than 10% in
transmission; a light reflection R.sub.L of less than 5%,
preferably less than 4%; a predominantly violet-blue color in
reflection with a purity of less than 20%; a predominantly blue
color in transmission.
15. A display screen of the plasma display type incorporating, on
its front face, at least one substrate or filter as claimed in any
one of claims 1 to 14.
Description
[0001] The subject of the invention is a transparent substrate,
especially made of glass, which is coated with a thin-film
multilayer, comprising at least one metal layer, for
electromagnetic shielding.
[0002] The invention will be more particularly described for the
use of such a substrate in a plasma display screen; however, it is
not limited to such an application, it being possible for the
substrate to be inserted into any electromagnetic shielding
wall.
[0003] A plasma display screen comprises a plasma gas mixture (Ne,
Xe, Ar) trapped between two glass plates, and phosphors placed on
the internal face of the rear plate of the display. Ultraviolet
light radiation emitted by the plasma gas mixture during the plasma
discharge between the two glass plates interacts with the phosphors
on the internal face of the rear plate in order to produce the
visible light radiation (red, green or blue). A gas particle
deexcitation mechanism competes with the UV emission, which
generates infrared radiation between 800 and 1250 nm, the
propagation of which, mainly through the front face of the display,
may be the source of very troublesome interference, especially as
regards equipment located nearby and controlled by infrared, for
example by means of remote controls.
[0004] Moreover, like all electronic apparatus, plasma display
screens possess addressing systems or drivers that may generate
parasitic radiation which must not interfere with other devices,
such as microcomputers, mobile telephones, etc.
[0005] To eliminate, or at the very least attenuate, the
propagation of such radiation, one solution consists in placing
against the front face of the display a window, also called a
filter, which is both transparent and metallized in order to
provide electromagnetic shielding. This filter is, for example, a
transparent substrate coated with thin silver-based layers that
reflect the electromagnetic waves in the frequency range from 30
MHz to 1 GHz and infrared beyond 800 nm.
[0006] Thus, patent FR 2 641 272 proposes a substrate comprising a
reflective silver layer sandwiched between a transparent sublayer
that comprises at least one layer of a metal oxide, and a
transparent covering layer that comprises a layer of sacrificial
metal oxide, a zinc oxide layer, the thickness of which does not
exceed 15 nm, and an upper covering layer of a metal oxide.
[0007] The silver layer preferably has a thickness of between 8 and
12 nm.
[0008] The metal oxide layer of the sublayer may be chosen from
several oxides and may be a mixture of several oxides. A preferred
example is a titanium dioxide layer and a tin oxide layer deposited
on said titanium dioxide.
[0009] The object of the sacrificial metal oxide is to protect the
silver layer from oxidation, in particular during its deposition
when this is carried out by the technique of sputtering. This is
because, if the silver were to be impaired, the coated substrate
would lose its low emissivity and its light transmission would be
greatly reduced. The sacrificial metal often preferred is titanium,
as it provides the silver with very effective protection against
oxidation and has the advantage of being easily oxidized, to form
an oxide of very low absorbency.
[0010] The zinc oxide layer serves as protection against the
penetration of oxygen into the lower layers and allows the
thickness of sacrificial metal to be reduced somewhat, this metal
then being more easily, more completely and more uniformly
oxidized. The above document requires a limited thickness for the
zinc oxide layer of 15 nm, in particular so as to give the layer
good light transmission properties.
[0011] However, such a substrate with a single metal layer is not
suitable for obtaining sufficient electromagnetic shielding, such
as to have a surface resistance of less than
1.8.OMEGA./.quadrature.. Furthermore, other patent applications
propose multilayers containing a plurality of metal layers, in
particular silver layers. However, it is known that increasing the
number of layers reduces the light transmission; a compromise
between thicknesses and types of layer must therefore be found in
order to achieve satisfactory light transmission.
[0012] The patent application published under WO 01/81262 proposes
a multilayer having two silver layers, with a thickness e.sub.1 in
the case of the silver layer closest to the substrate and a
thickness e.sub.2 for the other layer, a sacrificial metal oxide,
such as titanium oxide, being placed above each silver layer in
order to protect it. One example of a sequence is the following:
[0013]
substrate/Si.sub.3N.sub.4/ZnO/Ag/Ti/Si.sub.3N.sub.4/ZnO/Ag/Ti/ZnO/Si.sub.-
3N.sub.4.
[0014] To achieve a surface resistance of less than
1.8.OMEGA./.quadrature., while still maintaining a suitable light
transmission, the ratio of the thicknesses e.sub.1/e.sub.2 is
between 0.8 and 1.1, preferably between 0.9 and 1, and the total
thickness of the metal layers, e.sub.1+e.sub.2, is between 27.5 and
30 nm, preferably between 28 and 29.5 nm.
[0015] European patent application EP 1 155 816 discloses a
multilayer having three, or even four, silver layers with an
alternation of a titanium oxide layer and of a layer having a
refractive index of less than 2.4 at a wavelength of 550 nm, such
as for example zinc oxide or preferably silica nitride. The
thickness of the silver layer closest to the substrate and of that
furthest away is preferably equal to 0.5 to 1 times the thickness
of the other silver layer. An example of a sequence having a
surface resistance of 1.5.OMEGA./.quadrature., with a light
transmission of 67%, is given with three palladium-doped silver
layers each having a thickness of 16 nm. This sequence is the
following: [0016]
substrate/TiO.sub.x/SiN.sub.x/Ag/SiN.sub.x/TiO.sub.x/SiN.sub.x/Ag/-
SiN.sub.x/TiO.sub.x/SiN.sub.x/Ag/SiN.sub.x/TiO.sub.x.
[0017] However, it is always desirable for the properties of
existing solutions to be further improved, and thus obtain an even
more substantial reduction in surface resistance without degrading
the light transmission.
[0018] The object of the invention is therefore to find another
filter solution, especially for a plasma display screen, in order
to alleviate the problem of electromagnetic wave transmission,
while still achieving satisfactory optical properties.
[0019] According to the invention, the transparent substrate,
especially made of glass, provided with a thin-film multilayer that
includes three silver layers and comprises, alternately on the
substrate, a titanium dioxide layer, a metal oxide layer, one of
the silver layers and a covering layer, characterized in that:
[0020] the metal oxide is zinc oxide; [0021] the covering layer is
a sacrificial metal; and [0022] an antireflection layer comprising
at least one metal oxide is deposited on the covering layer for the
silver layer furthest away from the substrate.
[0023] According to one feature, the thickness of each of the
silver layers is between 13 nm and 19 nm. The thicknesses
(e.sub.Ag1, e.sub.Ag2, e.sub.Ag3) of the three respective layers
(Ag.sub.1, Ag.sub.2, Ag.sub.3) are identical, or else they vary in
a ratio of between 0.8 and 1.2 and are such that
e.sub.Ag1.ltoreq.e.sub.Ag3.ltoreq.e.sub.Ag2.
[0024] According to another feature, the titanium dioxide layer as
sublayer for the silver layer (Ag.sub.1) closest to the substrate
has a thickness of between 10 and 20 nm, preferably between 10 and
15 nm, and the titanium oxide layers as sublayers for the other two
silver layers (Ag.sub.2, Ag.sub.3) have a thickness of between 35
and 55 nm, preferably between 40 and 50 nm.
[0025] Preferably, the zinc oxide layer has a thickness of greater
than 15 nm.
[0026] Advantageously, the sacrificial metal layer is of niobium,
titanium or zirconium, and has a thickness not exceeding 2 nm.
[0027] According to another feature, the antireflection layer has a
thickness of between 25 and 50 nm, preferably between 25 and 35 nm.
Advantageously, this antireflection layer includes at least one
titanium dioxide layer having a thickness of between 15 and 35 nm,
preferably between 20 and 30 nm, and may also include another layer
of a metal oxide that is deposited on said titanium dioxide layer
and has a thickness of between 5 and 15 nm, preferably between 6
and 10 nm. This metal oxide layer is preferably tin oxide
(SnO.sub.2) or silicon nitride (Si.sub.3N.sub.4).
[0028] With such features, the substrate according to the invention
has a surface resistance not exceeding 1.OMEGA./.quadrature.,
preferably between 0.7 and 0.9 .OMEGA./.quadrature..
[0029] The substrate may be made of toughened or untoughened glass,
or made of plastic.
[0030] It will be advantageous to use such a substrate in an
electromagnetic shielding filter, applied for example to a display
screen of the plasma display type. This filter therefore comprises
a substrate provided with the multilayer of the invention, together
with one or more functional plastic sheets (for example with
pigments or dyes) and/or another transparent substrate, optionally
coated with an antireflection layer, so as to have the following
optical properties: [0031] a light transmission factor T.sub.L of
between 45 and 55%; [0032] a purity of less than 10% in
transmission; [0033] a light reflection R.sub.L of less than 5%,
preferably less than 4%; [0034] a predominantly violet-blue color
in reflection with a purity of less than 20%; [0035] a
predominantly blue color in transmission.
[0036] Other features and advantages of the invention will now be
described with regard to the appended drawings, in which:
[0037] FIG. 1 illustrates a first embodiment of an electromagnetic
shielding filter;
[0038] FIG. 2 illustrates a second embodiment of an electromagnetic
shielding filter; and
[0039] FIG. 3 illustrates schematically the multilayer of the
invention.
[0040] It should firstly be pointed out that the proportions
relating to the various dimensions, especially thicknesses, of the
elements of the invention have not been drawn to scale in the
figures so that they are easier to read.
[0041] FIG. 1 illustrates a first example of an embodiment of the
transparent structure 1 intended to be joined to the front face of
a plasma display in order to form an optical and electromagnetic
shielding filter.
[0042] The structure 1 comprises a first transparent substrate 10,
which for example is of the glass type but which could, as a
variant, be made of plastic, intended to be placed on the same side
as the display, a thin-film multilayer 20 according to the
invention, which is placed on the internal face of the substrate
10, facing the inside of the structure, a second substrate 30 of
the glass type, which is joined to the first substrate, facing the
multilayer 20, by means of a plastic film 40, such as a PVB film.
This functional plastic film may advantageously include a mineral
pigment or an organic dye so as to filter the orange color of
wavelength centered on 590 nm. The reader may refer for further
details about the plastic film or alternative embodiments of the
structure to French patent application FR 03/04636.
[0043] The external faces of the substrates 10 and 30 to the
outside of the structure are preferably provided with an
antireflection coating 50.
[0044] FIG. 2 illustrates a second example of an embodiment of the
structure 1, which in this case comprises a substrate 10 one of the
faces of which, intended to be on the opposite side from the
observer, is provided with the thin-film multilayer 20, and a
substrate 60 made of plastic, such as PET, which is intended to be
placed on the same side as the display and is joined to the
substrate 10, facing the multilayer 20, by means of a plastic film
40, such as a PVB film, which may advantageously incorporate other
functionalities as described above in the first embodiment. The
external face of the substrate 10, to the outside of the structure,
is preferably provided with an antireflection coating 50.
[0045] The invention therefore relates to the multilayer 20
deposited on a substrate, such as the substrate 10. This multilayer
includes three metallic silver layers, Ag.sub.1 being the layer
closest to the substrate, Ag.sub.2 being the central layer and
Ag.sub.3 being the one furthest away, the function of which is to
reflect the electromagnetic waves having a frequency between 30 MHz
and 1 GHz and infrared waves beyond 800 nm.
[0046] The multilayer includes, deposited alternately on the
substrate, a titanium dioxide layer 21, a layer 22 of a metal
oxide, consisting of zinc oxide, one of the silver layers Ag.sub.1,
Ag.sub.2 or Ag.sub.3, and a layer 23 of a sacrificial metal
coating. Deposited on top of the sacrificial metal layer 23, which
is deposited on the silver layer Ag.sub.3 furthest from the
substrate, is an antireflection layer 24 consisting of at least one
metal oxide.
[0047] The thickness of each of the silver layers Ag.sub.1,
Ag.sub.2 and Ag.sub.3 is between 13 nm and 19 nm. The thicknesses
e.sub.Ag1, e.sub.Ag2 and e.sub.Ag3 of the respective layers
Ag.sub.1, Ag.sub.2 and Ag.sub.3 may be identical or they may vary
in a ratio of between 0.8 and 1.2 and are such that
e.sub.Ag1.ltoreq.e.sub.Ag3.ltoreq.e.sub.Ag2. The imbalance in layer
thicknesses is preferential, so as to lower the light reflection
while maintaining the same surface resistance.
[0048] The titanium oxide layer 21 as sublayer for the silver layer
Ag.sub.1 close to the substrate has a thickness of between 10 and
20 nm, preferably between 10 and 15 nm.
[0049] The titanium oxide layers 21 as sublayers for the other two
silver layers Ag.sub.2 and Ag.sub.3 have a thickness of between 35
and 55 nm, preferably between 40 and 50 nm.
[0050] The zinc oxide layer 22 preferably has a thickness of
greater than 15 nm, for example 16 or 18 nm.
[0051] The sacrificial metal layer 23 is of niobium, titanium or
zirconium, preferably titanium, and has a thickness of at most 2
nm, for example 1.5 nm.
[0052] This sacrificial metal layer makes it possible to protect
the silver against oxidation, and to improve its resistivity.
Although the presence of titanium may degrade the light
transmission, it does allow an even lower surface resistance to be
obtained, while maintaining a sufficiently correct light
transmission. The compromise to be found between the optical
properties of the filter and its shielding properties is provided
by giving preference to shielding, while still maintaining good
optical properties. Thus, with the sequence of the invention based
on three silver layers, the surface resistance drops to
0.8.OMEGA./.quadrature., instead of 1.5 according to the prior art,
which not only meets Class A of European Standard EN 55022, dealing
with what are called "consumer" products, but also Class B, dealing
with special products of the home-cinema type.
[0053] The antireflection layer 24 for the silver layer Ag.sub.3
remote from the substrate has a thickness of between 25 and 50 nm,
preferably between 25 and 35 nm. It comprises at least titanium
dioxide with a thickness of between 15 and 35 nm, preferably
between 20 and 30 nm.
[0054] Advantageously, deposited on top of the titanium dioxide of
this antireflection layer is another metal oxide, of small
thickness, between 5 and 15 nm, and preferably between 6 and 10 nm.
This metal oxide is, for example, tin oxide (SnO.sub.2) or silica
nitride (Si.sub.3N.sub.4)--which helps to improve the purity of the
colors in reflection and in transmission.
[0055] All the layers of the multilayer are deposited on the
substrate by the known technique of sputtering.
[0056] In the table below, we given give five examples (Ex 1 to Ex
5) of the multilayer 20 of the invention. Provided in the table are
the thicknesses (in nm) of each layer and, for each multilayer
joined to a substrate 10, the values of the light transmission
T.sub.L (in %), the light reflection R.sub.L (in %), the purity in
transmission p.sub.e in T (in %), the purity in reflection p.sub.e
in R (in %), the dominant wavelengths in transmission and in
reflection, respectively .lamda..sub.d in T and .lamda..sub.d in R
(in nm) and the surface resistance R.sub.surf (in
.OMEGA./.quadrature.).
[0057] These five examples make it possible to achieve suitable
shielding less than 1 .OMEGA./.quadrature..
[0058] In the case of examples 1, 2 and 5, the silver layers are
the same and equal to 15 nm; the zinc oxide thicknesses are
different, with a thickness of less than 15 nm, exactly equal to 10
nm in the case of example 5. For each example, the thickness of the
titanium dioxide layers is fixed so as to optimize the optical
properties of the multilayer.
[0059] The results show that, for examples 1 and 2 which have
larger zinc oxide thicknesses than example 5 (from 6 to 8 nm and
higher), the light transmission, contrary to what might be expected
as regards the prior art, remains substantially the same and even
slightly better in the case of example 1 with a zinc oxide
thickness of 18 nm, and the reflection has the advantage, in the
case of examples 1 and 2, of being lower than in the case of
example 5, thereby making it possible for the display to be
illuminated less brightly and aggressively for the observer.
[0060] Examples 3 and 4 provide a comparison, with unequal
thicknesses as regards the silver layers, with, in the case of
example 4, an antireflection layer 25 based on SnO.sub.2. It may be
seen that the imbalance has the advantage of reducing the light
reflection but has the drawback of increasing the purity in
transmission and in reflection; the addition of the antireflection
layer helps to overcome this drawback and thus obtain a purity in
transmission equivalent or substantially equivalent to that of
examples 1, 2 and 5, and to reduce the purity in reflection
compared with that of example 3.
TABLE-US-00001 Ex 1 Ex 2 Ex 3 Ex 4 Ex 5 TiO.sub.2 12 12 12 12 13
ZnO 18 16 16 16 10 Ag.sub.1 15 15 13.5 13.5 15 Ti 1.5 1.5 1.5 1.5
1.6 TiO.sub.2 43 43 43 43 48 ZnO 18 16 16 16 10 Ag.sub.2 15 15 16.5
16.5 15 Ti 1.5 1.5 1.5 1.5 1.5 TiO.sub.2 43 43 43 43 48 ZnO 18 16
16 16 10 Ag.sub.3 15 15 15 15 15 Ti 1.5 1.5 1.5 1.5 1.5 TiO.sub.2
25 25 25 25 25 SnO.sub.2 0 0 0 7 0 T.sub.L in % 62 61 62 65 61
R.sub.L in % 5.8 5.0 4.7 4.7 6 p.sub.e in T (%) 5 6 9 6 5
.lamda..sub.d in T (nm) 500 490 496 499 500 p.sub.e in R (%) 30 20
50 40 30 .lamda..sub.d in R (nm) -555 -560 -553 -547 -555
R.sub.surf (.OMEGA./.quadrature.) 0.8 0.8 0.8 0.8 0.8
[0061] Thus, by controlling the deposition of the silver and
dielectric layers and the thicknesses formulated according to the
invention, and also by the use of metal protection layers, the
filter obtained with reference to FIG. 1 or FIG. 2 has the
following properties: [0062] a surface resistance of less than 1
.OMEGA./.quadrature.; [0063] a light transmission factor T.sub.L of
between 45 and 55%; [0064] a purity in transmission of less than
10%; [0065] a light reflection R.sub.L of less than 5%, preferably
less than 4%; [0066] a predominantly violet-blue color in
reflection with a purity of less than 20%; and [0067] a
predominantly blue color in transmission.
[0068] The electromagnetic shielding filter using the substrate of
the invention may be applied to a display screen, in particular a
plasma display. It provides very good performance as regards
shielding (the surface resistance being less than
1.OMEGA./.quadrature.), and it consequently blocks especially
infrared with a transmission at 900 nm that does not exceed 1%.
This filter also provides good visibility--a light transmission
factor between 45 and 55%--and improves the contrast of the
display.
* * * * *