FR2781789A1 - Transparent substrate, for plasma screens, flat high frequency lamps and building or aircraft glazing, is assembled with a thermoplastic film containing adjacent metal wires having different undulations - Google Patents

Abstract

A transparent substrate is assembled with a thermoplastic film containing a network of adjacent metal wires having different undulations. An Independent claim is also included for a plasma screen having the above substrate located on its front face. Preferred Features: The metal wires have periodic undulations with a period of 0.3-5 mm. The network may have two orientations which are approximately perpendicular to one another. The thermoplastic film contains an additive for filtering electromagnetic waves of 800-1000 (especially 830) nm wavelength. The substrate has a stack of layers, including a conductive silver layer, which are deposited directly on the substrate or on another plastic film. The layer stack comprises: (a) glass/SnO2/ZnO/Ag/Ti/SnO2/Si3N4; (b) glass/SnO2 and/or Si3N4/ZnO/Ag/ZnO/Si3N4/ZnO/Ag/ZnO/Si3N4; or (c) glass/SnO2/Ag/NiCr or Nb or Ti/SnO2//Ag/NiCr or Nb or Ti/SnO2. The metallic elements are connected to earth by a metal strip, placed against the network and connecting all the wires together, and a metal foil brazed to the entire periphery of the substrate. The substrate has a light transmission (TL) of \-60%, an IR transmission (TIR) of less than 50% at 800-1000 nm (especially less than 15% at 830 nm) and a light reflection (RL) of less than 10%.

Description

TRANSPARENT SUBSTRATE HAVING A NETWORK OF WIRES

  METALS AND USE OF SUCH A SUBSTRATE

  The present invention relates to a transparent substrate, in particular made of glass, assembled with at least one sheet of thermoplastic material, in particular polyvinyl butyral PVB, in which is

  inserted at least one network of corrugated metal wires.

  Although the invention is described more particularly with reference to an application for plasma screens, it is not however limited to

such an application.

  Such a screen essentially consists of two sheets of glass constituting the front and rear faces of the screen on which functional layers are deposited. These constitute in particular the

  electrodes, the dielectric, and the phosphors of the plasma screen.

  In normal use, the addressing signals of such an emissive screen, like all the broadcasting receivers and their associated devices existing to date, generate electromagnetic waves whose propagation, mainly through the front face of the screen, can be the source of very annoying disturbances,

  especially for equipment located nearby.

  Solutions have already been proposed in the past to annihilate, at least reduce, the propagation of these electromagnetic waves

generated by a plasma screen.

  These solutions all consist in having in front of the front face of the plasma screen a window which is both transparent and "metallized" for

  provide effective electromagnetic shielding.

  Thus a first type of window proposed consists of a PMMA substrate, one of the faces of which is covered with a stack of thin layers, the metallic functional layer of which is based on oxide.

indium (ITO).

  This solution is not fully satisfactory. Indeed, to achieve a sufficient level of electromagnetic shielding, it is necessary to have an electrical resistance per square of the above-mentioned ITO layer, to the point that the limits of industrial feasibility are reached, more particularly in terms of manufacturing costs . In addition, the light transmission coefficient TL of such

  window is not necessarily sufficient for certain types of plasma screen.

  Another type of window envisaged consists of a PMMA substrate on which is deposited, by a micro-lithography technique, a fine

metal grid.

  This window has many drawbacks. First of all, once placed in front of the front face of a plasma screen, it creates considerable visual disturbance for an observer looking at the plasma screen under a certain incidence. This visual discomfort results in particular from a moiré problem caused by the superposition of the grid on the

plasma screen pixels.

  In addition, fragile, it must be handled with care.

  Finally, its weight and rigidity give it a crippling arrow to

  the scale of dimensions of plasma screens.

  The object of the invention is then to overcome the aforementioned drawbacks and, therefore, to propose a window of the aforementioned type with improved properties, which in particular does not cause visual disturbance for a

  observer watching a plasma screen through it.

  To do this, the subject of the invention is a transparent substrate, in particular made of glass, assembled with at least one sheet of thermoplastic material, in particular made of polyvinylbural PVB, into which is inserted a network of corrugated metal wires characterized in that two adjacent wires have different ripples. The solution according to the invention is an ideal compromise for

the intended application.

  On the one hand, the level of electromagnetic shielding reached

  thanks to the network of metallic wires is very satisfactory.

  On the other hand, the specific arrangement according to the invention not only does not harm the transparency of the substrate, but it also makes it possible, once said substrate positioned in front of the front face of the plasma screen, to avoid any discomfort. visual for an observer looking at the screen

through her.

  In particular, any moiré phenomenon likely to occur due to the superposition of the wires of the network on the pixels of the screen is avoided. Any risk of appearing on the surface of the screen,

  diffracted light is also discarded.

  In addition, before reaching its final destination, namely its positioning in front of the front face of a plasma screen, the substrate according to

  the invention is easy to handle without too much risk of damaging it.

  This is advantageous on the industrial level, in particular during the numerous operations carried out on the assembly lines of plasma screens. For reasons of manufacturing convenience, the undulations of the

  metal wires according to the invention are preferably periodic.

  Advantageously, the period of undulation of the metal wires is

between 0.3 mm and 5 mm.

  This range is advantageous insofar as it makes it possible both to ensure effective electromagnetic shielding and to be free from any moiré phenomenon likely to occur, whatever

  or the type of plasma screens for which the substrate is intended.

  So there is no need to take into account the structure on a case-by-case basis.

particular of the plasma screen.

  According to an advantageous characteristic of the invention, the network of wires has at least two orientations, preferably approximately perpendicular to each other. This characteristic of the network makes it possible not to have to worry, during assembly, of the orientation of the substrate according to the invention by

  compared to the electromagnetic field induced by the plasma screen.

  In other words, the mesh of the network makes it possible to avoid, for sure, any anisotropy of the electromagnetic shielding provided by the

substrate according to the invention.

  According to another advantageous characteristic of the invention, the sheet of thermoplastic material comprises at least one additive capable of filtering electromagnetic waves of wavelength between 800 and

  1000 nm, in particular equal to approximately 830 nm.

  Such an additive makes it possible to avoid the infrared wavelengths coming from the plasma screen, in particular those characteristic of the gas prevailing between the two faces of the screen such as Xenon, from disturbing

  infrared signals from remote controls.

  Very advantageously, the substrate according to the invention comprises a stack of thin layers comprising at least one

  conductive metal layer, of type Ag.

  By appropriately selecting the thickness of the metal layer as well as those of the other layers of the stack, the substrate according to the invention is thus given optical properties and

  which improve those already mentioned above.

  On the one hand, with a very low electrical resistance per square of the metallic layer, the electromagnetic shielding effect of the

substrate is further increased.

  On the other hand, with a transmission at very low infrared wavelengths, the risk of disturbing the signals of the

remotes is avoided.

  Anyone skilled in the art will in any case take care that the above-mentioned stack of thin layers does not in any case reduce the level of

transparency of the desired substrate.

  The stack of thin layers can, if desired, be deposited directly on the substrate or on another sheet of plastic,

  of the polyethylene terephthalate PET type.

  The stacks described in patent applications EP-A-0 678

  484 and EP-A-0 718 250 have been found to be particularly suitable.

  Advantageously, the stacking is as follows: Glass / SnO2 / ZnO / Ag / Ti / SnO2 / Si3N4 or: Glass / SnO2 and / or Si3N4 / ZnO / Ag / ZnO / Si3N4 / ZnO / Ag / ZnO / Si3N4 or: Glass / SnO2 / Ag / NiCr or Nb or Ti / SnO2 / Ag / NiCr or Nb or Ti / SnO2 These stacks have the advantage of being able to undergo heat treatments of the quenching, bending or laminating type without deteriorating. According to an additional characteristic of the invention, the substrate according to the invention comprises means for ensuring electrical contact

  between the metallic elements and their connection to ground.

  These means preferably comprise at least one metal strip placed against the network and connecting all of the wires.

between them.

  More preferably, the means comprise at least one

  metallic foil, advantageously brazed to said substrate.

  Advantageously, the metallic foil extends over the entire

around the substrate.

  With such a ground connection structure, it is freed, during the mounting of the substrate according to the invention on the front face of

  the plasma screen, to use other elements, such as an absorbent gasket.

  Advantageously, the substrate comprises at least one anti-reflective coating. This will preferably be deposited on the outer face of the substrate. When you want to increase the minimum contrast of the plasma screen,

  the substrate according to the invention is preferably dyed in its mass.

  To arrange the substrate according to the invention in front of the front face of the plasma screen, it is possible, as desired, to leaf directly through the substrate on the front face by means of the sheet of thermoplastic material or to assemble with another transparent substrate, in particular glass, and arrange the assembly using an appropriate mechanical structure

  at a distance of a few millimeters from the front face.

  The previously defined substrate is remarkable in that it has a light transmission TL of at least 60% and a transmission in the wavelengths X of infrared TIR, in particular those between 800 and 1000 nm less than 50% , preferably

  less than 15% for those equal to 830 nm.

  It is also remarkable in that it presents a reflection

luminous RL less than 10%.

  Finally, it is remarkable in that it attenuates electromagnetic waves of frequency between 80 and 800 MHz of a

value at least equal to 30 dB.

  The invention also relates to a plasma screen incorporating

  minus a previously described substrate, disposed on the face of said screen.

  Preferably, the metallic elements of the substrate are connected

to the mass of said screen.

  The invention is applicable to the production of high frequency flat lamps, glazing for buildings such as those intended to equip air traffic control towers or computer rooms,

  aircraft glazing of the aircraft cockpit type.

  Other details and advantageous characteristics will emerge below.

  after reading the description of illustrative examples but not

  limiting of the invention made with reference to the figures which represent: o figures 1 and the: an exploded view and a partial view of a substrate according to the invention a figure 2: a schematic representation of a measurement chain of electromagnetic attenuation produced by a Faraday cage incorporating substrates in accordance with the invention; o Figure 3: a schematic representation of the mounting of substrates according to the invention on a Faraday cage of the type shown in Figure 2; o Figures 4a to 4d: the curves representative of the measurement results

  electromagnetic attenuation performed on various substrates.

  First, it should be noted that, for the sake of clarity, the proportions

  relative between the different elements are not respected.

  Figure 1 shows an exploded view of a substrate 1 according to the invention. It consists of two glass sheets 2, 3 assembled together by means of a PVB sheet 4 of thickness approximately equal to

0.76 mm, in a manner known per se.

  The face of the glass sheet 2 in contact with the PVB sheet 4 comprises on almost all of its surface a stack of layers

  thin 21 including at least one conductive silver layer.

  The characteristics of this stack will be detailed below.

  Over the entire periphery of this glass sheet 2 extends a brazed metallic foil 22 and a part 221 of which is intended to ensure the

  mass recovery, in particular on the Faraday cage described above.

  The metallic foil 22 is in contact with the aforementioned silver conductive layer by means of a copper adhesive 23. The outer face of the glass sheet 3, that is to say that which is not

  not in contact with the PVB sheet 4, is provided with an anti-

  reflections 31, such as those described in patent application EP-A-0 728 712.

  The PVB sheet 4, for its part, comprises a network of corrugated metal wires 41 inserted within it. In addition to this network 41, a band is deposited

  metallic 42 connecting together all the metallic wires.

  FIG. 1a is a partial enlarged view of the network of corrugated metal wires 41. In this figure, it can be seen that two adjacent wires

  410, 411 have different undulations.

  The characteristics of these wires will be presented below. Various examples have been produced in accordance with the substrate 1 previously described for each of which the nature and characteristics of both the stack of thin layers 21 and the network of metallic wires 41 have

been changed.

EXAMPLE 1 (COMPARATIVE)

  By way of comparative example, a substrate was made up of two sheets of standard bare silica-soda-lime glass assembled by

o10 a single PVB sheet.

EXAMPLE 2

  The stack of thin layers 21 has the following sequence Glass / SnO2 / ZnO / Ag / Ti / SnO2 / Si3N4 Table 1 below groups together the thicknesses e of each of the

layers in nanometers (nm).

TABLE 1

  Glass e (nm) SnO2 17 ZnO 15 Ag 12 Ti 2 SnO2 20 Si3N4 20 The network of metal wires 41 has a single orientation approximately parallel to the longitudinal edges of the rectangular substrate. Each of the metal wires 410, 411 is made of tungsten, has a diameter of the order of 24 μm and an electrical resistance of the order of Q / m. The undulation period of each wire 410, 411 is between

1.4 and 2.6 mm.

  Two adjacent wires 410, 411 are separated from one another by

distance of the order of 1.6 mm.

  In addition, two adjacent wires have corrugations offset from each other by at least 1.2 mm in the direction perpendicular to the orientation of the network previously defined so that by superimposing them in this direction , there is an offset of

non-zero phase.

EXAMPLE 3

  The stack of layers 21 has the following sequence Glass / SnO2 / ZnO / Ag / ZnO / Si3N4 / ZnO / Ag / ZnO / Si3N4 Table 2 below groups together the thicknesses e of each of the

layers in nanometers (nm).

TABLE 2

  Glass e (nm) SnO2 21 ZnO 21 Ag 9 ZnO I 16 Si3N4 I 57 ZnO 16 Ag 10 ZnO 20 Si3N4 18 The network of metallic wires 41 has the same characteristics as that of Example 2, the nature and arrangement of the son 410, 411 remaining

identical.

EXAMPLE 4

  The stack of layers 21 has the same characteristics as that

  of Example 3, the layers having the same thicknesses.

  The wire network 41 has only one orientation, approximately

  parallel to the longitudinal edges of the substrate.

  Each of the metal wires 410, 411 is made of enameled copper, has a diameter of the order of 30 µm and an electrical resistance of the order of Q / m. The undulation period of each wire is between 0.5 and

0.75 mm.

  Two adjacent wires 410, 411 are separated from each other by a distance of the order of 0.5 mm. In addition, similar to the previous examples, two adjacent wires have their corrugations offset from each other by at least 0.25 mm in the direction perpendicular to the orientation of the network. EXAMPLE 5 The stack of thin layers 21 has the same characteristics

as in example 2.

  The wire network 41 has approximately two orientations

  perpendicular to each other and to the edges of the substrate.

  Each of the metal wires 410, 411 is made of tungsten, has a diameter of the order of 24 μm and an electrical resistance of the order of Q / m. The undulation period of each wire is between 1.4 and

2.6 mm.

  Similarly to the previous examples, the undulations of two adjacent wires 410, 411 are offset by at least 1.6 mm according to a

given orientation of the network.

  The network 41 therefore has a sinusoid mesh structure

phase shifted.

  Each mesh of network 41 has an area of the order of 5 to

6 mm2.

EXAMPLE 6

  The stack of thin layers 21 has the same characteristics

as in Example 3.

  The network of wires 41 is arranged analogously to that of

Example 5.

  The glass 2 on which the stack of thin layers 21 is deposited is a mass-colored glass, called TSA3 +, conforming to It

  the teaching of patent EP-A-0 644 164.

  Spectrophotometric measurements of each of the relative substrates

  in examples 1 to 5 were carried out.

  Table 3 below indicates the value of the light transmission level TL in percentages, the value of the light reflection level RL also in percentages as well as the values of the energy transmission level T800, T83o and Tlooo at wavelengths.

  respectively equal to 800, 830 and 1000 nm.

  It is specified that the measurements of RL and TL were made with reference to

i0 the illuminant D6s5.

TABLE 3

  Examples TL (%) RL (%) T8oo T83 TTiooo

1 92.1 3.6 73.8 72.7 61.4

i

2 72.3 9.9 40.4 36.0 24.2

3 78.1 4.6 49.1 43 17.0

4 f 75.7 2.9 41.2 35.5 14.2

75.1 9.8 1 41.7 38.1 23.7

6 63.8 4.5 11.3 9.8 2.8

  In addition, electromagnetic attenuation measures have been

  produced for each of the substrates relating to examples 1 to 5 above.

  Figure 2 is a schematic representation of the electromagnetic attenuation measurement chain produced by a Faraday cage incorporating the substrates according to the invention. This measurement chain consists of a transmission assembly 6, a reception assembly 7 and

  a Faraday cage 8 having an opening shown in FIG. 3.

  The transmission assembly 6 consists of a synthesizer 61 connected to

  an amplifier 62 itself connected to an antenna 63.

  The reception assembly 7 consists of an antenna 71 connected to a

spectrum analyzer 72.

  The attenuation measurement is carried out on the principle of a double weighing in accordance with the GAMT 20 standard: [first of all a reference is made by placing the transmit 63 and receive 71 antennas opposite one of the other, on either side of the opening of the Faraday cage 8 equipped with the substrate 1 relating to Comparative Example 1 at a distance d; [the level received using the spectrum analyzer 72 corresponding to NdB is then noted, for each predetermined frequency; [a measurement is then made by equipping the opening of the cage with the substrate for which the performance is to be measured, the distance d and the relative position between the two antennas 63, 71 remaining unchanged; [we then note at the same frequencies as those used for the

  references the level received at the spectrum analyzer 72 corresponding to N'dB.

  The electromagnetic attenuation for the substrate conforms to

  the invention considered is then given by the value (N - NIdB.

  Figure 3 is a schematic representation of the mounting of substrates according to the invention in the opening of the Faraday cage 8. This opening 9 is provided at its periphery with a metal frame

  fixed to the Faraday cage 8 by means of bolts 11.

  The mounting of substrates in accordance with the invention is carried out using an aluminum tape 12 comprising an adhesive part, which also extends around the periphery of the frame while being held thereon by

  through the aforementioned bolts.

  It is specified that the substrates comprising a network of unidirectional wires 41 are mounted in the opening of the Faraday cage of

  so that said array extends vertically.

  It is also specified that the substrate relating to example 5, that is to say

  say the one with the two-way wire network is mounted so

  one orientation of the network is horizontal and the other is vertical.

  During all the measurements, it is ensured that the antennas -3 and

  71 are placed in the same plane.

  The measurements were carried out successively: [in magnetic field H then in electric field E;

  [in vertical antenna polarization (1) then horizontal (2).

  The curves representing the results of attenuation measurement of the substrates relating to Examples 2 to 5 in accordance with the invention with respect to the substrate of Example 1 (reference) are shown in FIGS. 4a to 4d which are respectively relating to: FIG. 4a: magnetic field measurements in vertical polarization Hl; o Figure 4b: magnetic field measurements in horizontal position H2; o figure 4c: measurements in electric field in vertical position E1;

  o Figure 4d: measurements in electric field in horizontal position E2.

  On reading Table 3 relating to spectrophotometric measurements 0 0 and curves representative of the results of measurement of electromagnetic attenuation of substrates 2 to 5, it is clear that the substrates in accordance with the invention exhibit levels of optical and electromagnetic performance quite made compatible with an application for plasma screens more particularly for use as a "front-filter" since: o they all have an average attenuation of at least 30 dB whatever the polarization of the wave; o they have a transmission in the wavelengths of the infrared sufficiently low to suppress the interference of the elements of the screen, in particular of the gas prevailing inside it, with the signals emitted by the remote controls; o they have a transparency that is more than enough not to interfere

the vision of an observer.

  In addition, once placed in front of the face of a plasma screen, the substrates in accordance with the invention in no way hamper an observer

looking at the plasma screen.

  In particular, any moiré problem such as that mentioned in

preamble is avoided.

Claims (17)

  1. Transparent substrate, in particular made of glass, assembled with at least one sheet of thermoplastic material, in particular made of polyvinyl butyral (PVB), into which is inserted at least one network of corrugated metal wires, characterized in that two adjacent wires have different undulations . 2. Substrate according to claim 1, characterized in that the   corrugations of the metal wires are periodic.   3. Substrate according to claim 2, characterized in that the   corrugation period of the metal wires is between 0.3 and 5 mm.   4. Substrate according to one of claims 1 to 3, characterized in that   that said network has at least two orientations, preferably   approximately perpendicular to each other.   5. Substrate according to any one of the preceding claims,   characterized in that said sheet of thermoplastic material comprises at least one additive capable of filtering electromagnetic waves of wavelength k between 800 and 1000 nm, in particular equal to about 830 nm.   6. Substrate according to any one of the preceding claims,   characterized in that it comprises a stack of layers comprising   at least one conductive metallic layer, of the silver type.   7. Substrate according to claim 6, characterized in that said stack of thin layers is deposited directly on the substrate or on another sheet of plastic, of the type polyethylene terephthalate (PET).   8. Substrate according to claim 6 or 7, characterized in that the stack is as follows: Glass / SnO2 / ZnO / Ag / Ti / SnO2 / Si3N4 or: Glass / SnO2 and / or Si3N4 / ZnO / Ag / ZnO / Si3N4 / ZnO / Ag / ZnO / Si3N4 or: Glass / SnO2 / Ag / NiCr or Nb or Ti / SnO2 / Ag / NiCr or Nb or Ti / SnO2   9. Substrate according to any one of the preceding claims,   characterized in that it includes means for ensuring contact   between the metallic elements and their connection to ground.   10. Substrate according to claim 9, characterized in that the means for ensuring electrical contact comprise at least one metal strip disposed against the network and connecting all of the wires between them.   1 1. Substrate according to claim 9 or 10, characterized in that the means for ensuring the electrical contact comprise at least one   metallic foil, advantageously brazed to said substrate.   12. Substrate according to claim 11, characterized in that the   metallic foil extends over the entire periphery of the substrate.   13. Substrate according to any one of the preceding claims,   characterized in that it comprises at least one anti-reflective coating.   14. Substrate according to any one of the preceding claims,   characterized in that it is tinted in its mass.   15. Substrate according to any one of the preceding claims,   characterized in that it is further assembled to another substrate transparent, especially in glass.   16. Substrate according to any one of the preceding claims,   characterized in that it has a TL light transmission of at least 60% and a transmission in the wavelengths of the TIR infrared, in particular those between 800 and 1000 nm, of less than 50%,   preferably less than 15% for those equal to 830 nm.   17. Substrate according to any one of the preceding claims,   characterized in that it has a light reflection RL of less than%.   18. Substrate according to any one of the preceding claims,   characterized in that it attenuates electromagnetic waves of frequency   between 80 and 800 MHz with a value at least equal to 30 dB.   19. Plasma screen incorporating at least one substrate according to one   any one of claims 1 to 18 disposed on the front face of said   screen. 20. Plasma screen according to claim 19, characterized in that the metallic elements of the substrate are connected to the ground of said screen. 21. Application of the substrate according to any one of   Claims 1 to 18 to the production of high-level flat lamps   frequencies, of glazing for buildings such as those intended to equip air traffic control towers or glazing calculator rooms   aeronautical aircraft cockpit type.