FR2868769A1 - Glass plate with a metal deposit, resistant to colouration due to migration and/or reduction a metal specie, for use as an electronic substrate, notably for a range of screen applications - Google Patents

Abstract

Glass plate is designed to constitute a product in the form of a plate endowed with, one at least one surface, a metal deposit. The plate is resistant to colouration due to at least one metal specie Mn+> of the metal deposit. This specie, during fabrication and/or utilisation, is able to migrate in the glass, from at least part of its surface, and undergo a reduction to the specie Mo> responsible for the colouration. It incorporates, at least at the surface and on a surface sensitive to the colouration, a composition able to limit or block the migration and/or the reduction of the specie Mn+>. An independent claim is also included for: fabrication of the glass plate.

Description

GLASS PLATE FOR RECEIVING A METALLIC DEPATCH AND RESISTANT TO

  COLORING LIKELY TO BE CAUSED BY SUCH DEPAT

  The present invention relates to a glass plate intended to constitute a plate-shaped product provided on at least a part of at least one of its faces with a metal deposit, said plate being resistant to coloration due to metal deposition, manufacture and / or migrate into the at least one metal species Mn + of said species, under the conditions of use of the product, is susceptible to glass from its surface and then undergo a staining reduction.

  The undesirable coloring species in the species M responsible for the metal that can induce one are in particular Ag, Cu and Au.

  Such undesirable colorations appear, because of interactions between the glass components and these metallic species, either during the manufacturing processes of the products, more particularly when these treatments include heating steps promoting the migration of the species responsible for the coloring. unwanted in the glass, and also throughout the aging and use of the products, especially when the use involves high temperature and / or electron bombardment.

  Plate products having received a metallic deposit with risks of coloring the glass are referred to as substrates in the field of electronics. These include the faces of television screens, computer screens, in general, emissive screens, such as plasma screens (Plasma Display Panel), electroluminescent screens and cold cathode screens (Field Emission Display). ).

  Other products include flat lamps, graded index microlenses, and heated rear windows.

  The current emissive screens comprise a glass substrate on which very thin transparent layers of tin-indium mixed oxide (ITO) are deposited, and also thin layers, very thin, of silver, constituting a second network. electrodes, these electrodes being within a dielectric material.

  It is observed that these substrates tend to develop a yellow coloration which contributes to degrading the image quality, in particular by reducing its luminous intensity and by modifying its colors, and which gives the screen a dirty and not very presentable appearance. This phenomenon of yellowing is attributed to the fact that Ag + ions migrate into the glass where they are reduced in the form of Ag colloidal particles, which absorb light in the wavelength range of 390 to 420 nm.

  This discolouration may occur at different times: - during the production of the screen if it has been necessary to conduct a high temperature treatment, the temperature rise favoring the migration of Ag + ions; during use, for example, where the rise in temperature or electron bombardment will further promote coloration; by the normal aging of the screen, the Ag + ions migrating more over time, in particular when they are under tension.

  The same problems with screens arise with flat lamps, microlenses and rear glasses.

  There is therefore a need to have a glass plate as defined above, not exhibiting coloring, under the conditions of manufacture and use of the finished products, such as screens ...

  The present invention provides a solution to this problem.

  For this purpose, the glass plate according to the present invention is characterized in that it comprises at least on the surface and on at least one color-sensitive face a composition capable of limiting or blocking said migration and / or said reduction. Mn + species According to a particular characteristic of the glass plate according to the present invention, it may have been developed to present on the surface and on the face or faces sensitive to color and at least a depth on which Mn + species is likely to migrate, an amount of reducing agent capable of reducing the Mn + species which is at most equal to 1.40 × 10 -2 mol / cm 2, in particular at most equal to 7 × 10 -8 mole / cm 2 and advantageously at most equal to 3.5 × 10 -8 mol / cm 2 when the metal species Mn + is Ag +.

  The reducing agent is chosen from elements with multiple oxidation states such as Fe, S, Sn, Sb and mixtures of these elements. Preferably, Fe, S and / or Sn are chosen.

  The protocol for this measurement is as follows: On a glass sheet, a layer of metallic silver about 400 nm thick is deposited by sputtering. The sheet is then heated under air at 600 ° C for 1 hour, then treated with nitric acid to remove the surface silver layer.

  The profile of silver in the surface layer of glass is made by SIMS: it has a bump corresponding to the reduction of silver by the reducing agent. The amount of reducing agent, in moles per cm 2, is obtained by measuring the silver content integrated on the thickness of the glass corresponding to the silver bump.

  This measurement expresses a quantity of reducing agent on the surface of the glass which must not be exceeded so that the Mn + ions do not have the possibility of being reduced to the point of causing an unacceptable coloration. A glass obtained by the Float process has, on its side which has been in contact with the tin bath, a higher content of reducing agent than on the opposite side. However, it will not be sufficient to simply apply the layer comprising the metal capable of migrating to this second side, less sensitive to coloring.

  It can also be emphasized that said amount of reducing agent according to the invention is that of glass as it is produced without an additional polishing step which would have made it possible to reach the surface layer having the desired amount of reducing agent.

  According to another particular characteristic of the glass plate according to the present invention, the latter is provided on the color-sensitive face (s) with a migration barrier layer of the Mn + species, on which continuous or discontinuous functional layers are adhere, and which is not likely to react chemically with said functional layers so as to deteriorate the properties thereof.

  In particular, the barrier layer may be chosen from layers based on metal oxide (s) such as SiO 2, SiOXCY (x = 0-2, y = 0-1, the terminals being excluded), SnO 2, SnO2: F, SnO2: Sb, ZrO2, Al2O3, MgO, ZnO, SnXZn, OZ (x and y each being a non-zero value; z = 2x + y) and TiO2, and the nitride (s) metal layers (s) such as SiN, TiN, Si3N4, AlN and mixtures of Si3N4 and AlN.

  Preferably, the barrier layer is non-conductive. Optionally, it is possible to apply on the barrier layer, before depositing the first functional layer, an additional layer of SiO 2, SiOC or Si 3 N 4 different from the barrier layer.

  As examples of functional layers, mention may be made of the antifouling layers of TiO 2 and the conductive layers of ITO, SnO 2: F, SnO: Sb and ZnO: Al.

  According to another particular characteristic of the present invention, the barium enters the alkaline earth metal content only in a limited proportion, that is to say in an amount such that the BaO content does not exceed 2. % by weight of the glass composition.

  According to yet another particular characteristic of the glass plate of the present invention, the latter comprises an alkali metal content under conditions ensuring a so-called mixed alkali effect. Preferably, the alkali metals are lithium, sodium and potassium. In particular, the alkali metals are sodium and potassium, present in the form of their corresponding oxides Na 2 O and K 2 O in molar quantities satisfying the following relationship: 0.35 <K 2 O / K 2 O + Na 2 O <0.65 In accordance with other particular characteristics of the glass plate according to the present invention, the latter has a weight content of alumina at most equal to 3% and / or a weight content of silica at least equal to 65%.

  In the case where the glass plate has a surface area sensitive to coloring, a composition different from that of the heart with the amount of reducing agent as indicated above, or is provided with a barrier layer, preferably, non-conductive, also as defined above, the surface layer capable of limiting or blocking the migration or reduction of the species Mn + preferably has a thickness of less than 100 μm, preferably less than 50 μm, especially less than 20} am.

  At least in the two cases just mentioned, the glass plate may have been made in the form of a ribbon obtained by floating on a bath of molten metal, such as a tin bath, the face of the the color-sensitive glass in the finished product being the opposite to that which has been in contact with the tin.

  According to yet another particular characteristic of the glass plate according to the present invention, the latter has a lower temperature of strain point corresponding to the temperature at which the glass has a viscosity of the order of 1014'5 poises which is greater than 550 ° C., in particular greater than 580 ° C.

  According to yet another particular characteristic of the glass plate according to the present invention, in the case where it has been elaborated on a tin bath, its composition is chosen to allow it to be produced under conditions which slow down the migration of Sn2 +. or H2 in the atmosphere side of glass ribbon. To do this, the H2 content of the N2 + H2 reducing atmosphere above the bath is lowered compared to normal working conditions to reduce the saturated vapor pressure of SnS and to limit the diffusion of H2 in the face. atmosphere. The temperature of the bath and that of the glass are also lowered compared to normal working conditions, the sulfate content of the glass being advantageously lowered relative to the normal working conditions to reduce the SnS content.

  In particular, at least one of the following conditions has been verified.

  - Viscosity of the glass corresponding to log ri = 3.5, at a temperature at most equal to 1230 C, preferably between 1180 and 1220 C (r) being expressed in dPa. $); bath temperature at most equal to 1220 C; casting temperature of glass on a tin bath of at most 1280 C; - H2 content in the bath atmosphere less than or equal to 7 by volume.

  According to other particular characteristics of the glass plate according to the present invention, the latter contains at least one element capable of coloring the glass in a complementary color of the risky color due to the diffusion of Mn +, for example Col +.

  A glass having the following composition corresponds to the present invention, the weight proportions of the constituents being the following: SiO 2 = 65-75% Al 2 O 3 - 0-3% ZrO 2 = 2-7% Na 2 O = 0-8% K 2 O = 2- 10% CaO = 3-10% MgO = 0-5% SrO = 3-12% BaO = 0-2% Other oxides 0-2 The present invention also relates to a method of manufacturing a glass plate resistant to staining by a molten tin bath floatation process, characterized in that the floating is carried out under the following conditions: viscosity of the glass corresponding to log r = 3.5, at a temperature at most equal to 1230 C, preferably between 1180 and 1220 C (r being expressed in dPa. $); bath temperature at most equal to 1220 C; casting temperature of glass on a tin bath of at most 1280 C; - H2 content in the bath atmosphere less than or equal to 7 by volume.

  The present invention also relates to the application of a glass plate as defined above or obtained by the process as defined above, to the manufacture of plate-shaped glass products which have received metallic deposits susceptible to generate a coloration during treatments especially at high temperature during their manufacture and / or during use due to interactions between the glass components in itself and these metals, in particular to the manufacture of emissive screens such as and plasma screens, electroluminescent displays and cold cathode screens, flat lamps, index gradient microlenses and rear automobile glasses.

  The following examples illustrate the present invention without, however, limiting its scope.

EXAMPLES 1 to 3

  These examples illustrate the effect of the glass casting temperature and the H2 content in the tin bath on the coloration of the final glass.

  Conventional silico-soda-lime glasses are produced in the form of a ribbon by floating on a tin bath under the conditions defined below. These glasses have the following chromatic coordinates L *, a * and b * measured for a thickness of 6 mm, under illuminant D65, taking the CIE 1931 colorimetric reference observer.

  Ex.l Ex. 2 Ex. 3 Temp. casting (C) 1269 1330 1330 H2 content (%) 6 0> 6 L * 94.7 94.5 94.5 a * -2.01 -2.44 -2.47 b * 5.59 6, 7.31 It is observed that the glasses of Examples 1 and 2 according to the invention have a lower value of b * than that of the glass of Example 3 (Comparative), which corresponds to a less significant yellow coloration. Reducing the glass casting temperature (Example 1) or the H2 content in the tin bath (Example 2) reduces the yellowing of the glass.

EXAMPLES 4 and 5

  These examples illustrate the barrier effect of a Si3N4 layer.

  On a conventional silico-soda-lime glass (SiO2 content: 70%) obtained by floating on a molten tin bath, a first layer of Si3N4 of thickness equal to 500 nm is deposited by magnetron sputtering and a second layer of silver 400 nm thick by sputtering (Example 4).

  Under the measuring conditions described in Examples 1 to 3, the glass has a value of b * equal to 0.73.

  By comparison, this same glass lacking layers of Si3N4 and silver (Example 5) has a value of b * equal to 10.95 corresponding to a strong yellow color. This demonstrates the significant barrier effect of the Si3N4 layer with respect to silver ion migration.

EXAMPLES 6 and 7

  These examples illustrate the influence of the composition of the glass on the content of reducing agent on the surface.

  On a glass sheet, a layer of metallic silver about 400 nm thick is deposited by sputtering. After treatment at 600 ° C. under air for 1 hour, the face carrying the silver deposit is treated with nitric acid.

  The glass according to the invention (Example 6) has the following composition, in weight: SiO 2 67.5 Al 2 O 3 0.5 ZrO 2 2.0 Na 2 O 4.0 K 2 O 8.0 CaO 9.0 SrO 9.0 The amount of The reducing agent measured by SIMS as previously indicated is 2.89 × 10 -8 mol / cm 2. This amount is equal to 1.40 × 10 -3 mol / cm 2 for a conventional silico-soda-lime glass obtained by floating on a molten tin bath treated under the same conditions (Example 7).

Claims (11)

  1 - Glass plate intended to constitute a product in the form of a plate provided on at least a part of at least one of its faces with a metal deposit, said plate being resistant to coloration due to at least one metal species Mn + of said metal deposit, which species, under the conditions of manufacture and / or use of the product, is likely to migrate into the glass from its surface and then undergo a reduction in the species M responsible for the coloring, characterized by the fact that it comprises, at least on the surface and on at least one color-sensitive face, a composition capable of limiting or blocking said migration and / or said reduction of the species Mn +, said plate having been developed to present in surface and on the surface or faces sensitive to coloration and at least to a depth on which the Mn + species is likely to migrate, an amount of reducing agent capable of reducing the species Mn + which is at most equal to 1.40 x 10- 'mole / cm2 when the metal species Mn + is Ag +, and / or the barium only entering the alkaline earth metal content in a limited proportion, the content BaO not exceeding 2% by weight of the glass composition, and / or said plate having an alkali metal content under conditions ensuring a so-called mixed alkali effect, and / or said plate has a weight content of alumina at most equal to 3%, and / or a silica content by weight of at least 65%, and / or said plate containing at least one element capable of coloring the glass in a color complementary to the risky color due to the diffusion of Mn + , for example Col'-, and / or the weight proportions of the constituents of said plate being as follows: SiO2 = 65-75% Al2O3 = 0-3% ZrO2 = 2-7% Na2O = 0-8% K2O = 2- 10% CaO = 3-10% MgO = 0-5% SrO = 3-12% BaO = 0-2% Other oxides 0-2%.   2 - Plate according to claim 1, characterized in that the reducing agent is selected from multiple oxidation state elements such as Fe, S, Sn, Sb and mixtures of these elements.   3 - Plate according to one of claims 1 and 2, characterized in that said amount of reducing agent is at most equal to 7 x 10- $ mole / cm 2, in particular at most equal to 3.5 x 10- $ mol / cm2.   4 - Plate according to one of claims 1 to 3,   characterized in that it is provided on the color-sensitive face (s) with a migration-barrier layer of the Mn + species, on which continuous or discontinuous functional layers are able to adhere, and which is not susceptible to to react chemically with said functional layers so as to deteriorate the properties thereof.   Plate according to claim 4, characterized in that the barrier layer is chosen from layers based on metal oxide (s) such as SiO 2, SiOXCy (x = 0-2, y = 0-1; the limits being excluded), SnO2r SnO2: F, SnO2: Sb, ZrO2, Al2O3, MgO, ZnO, Sn, ZnyOZ (x and y being a non-zero value, z = 2x + y) and TiO2, and the layers based on of metal nitride (s) such as SiN, TiN, Si3N4r A1N and mixtures of Si3N4 and AlN.   6 - Plate according to claim 4, characterized in that the layer is non-conductive.   7 - Plate according to claim 1, characterized in that the alkali metals are lithium, sodium and potassium.   8 - Plate according to claim 7, characterized in that the alkali metals are sodium and potassium, present in the form of their corresponding oxides Na2O and K20 in molar amounts satisfying the relationship: 0.35 <K20 / K20 + Na2O <0,65 9 - Plate according to one of claims 1 to 8, characterized in that a surface layer capable of limiting or blocking the migration or reduction of the species or species has a thickness less than 100 pm, preferably less than 50 pm, especially less than 20 pm.   - Plate according to one of claims 1 to 9, characterized in that it was developed in the form of a ribbon obtained by floating on a bath of molten metal, such as a tin bath, the face color-sensitive glass in the finished product being the opposite to that which has been in contact with the tin at least in the case of a glass as defined in one of claims 1 to 3.   11 - Plate according to one of claims 1 to   10, characterized in that it has a lower annealing temperature greater than 550 C.   12 - Plate according to one of claims 10 or   11, said plate having been elaborated on a tin bath, characterized in that its composition is chosen to allow it to be produced under conditions which slow down the migration of Sn 2 + or H 2 in the glass ribbon face, the H2 content of the reducing atmosphere of N2 + H2 above the bath being lowered from normal working conditions to reduce the saturated vapor pressure of SnS and the temperature of the bath and that of the glass being lowered compared to normal working conditions, the sulfate content of the glass being advantageously lowered relative to the normal working conditions to reduce the SnS content.   13 - Plate according to claim 12, characterized in that at least one of the following conditions has been verified: viscosity of the glass corresponding to log r) = 3.5, at a temperature at most equal to 1230 C, preferably between 1180 and 1220 C; - bath temperature at most equal to 1220 C; - pouring temperature of the glass on tin bath of at most 1280 C; H2 content in the bath atmosphere less than or equal to 7 by volume.   14 - Process for the production of a color-resistant glass plate, as defined in one of Claims 1 to 13, by a method of floating on a molten tin bath, characterized in that one drives floating under the following conditions: glass viscosity corresponding to log = 3.5, at a temperature at most equal to 1230 C, preferably between 1180 and 1220 C; - bath temperature at most equal to 1220 C; - pouring temperature of the glass on tin bath of at most 1280 C; H2 content in the bath atmosphere less than or equal to 7 by volume.   - Application of the glass plate as defined in one of claims 1 to 13 or obtained by the process as defined in claim 14, to the production of plate-shaped glass products which have received metal deposits likely to to generate a coloration during treatments, especially at high temperature during their manufacture and / or during use due to interactions between the components of the glass itself and these metals, in particular the manufacture of emissive screens such as plasma screens, electroluminescent screens and cold cathode screens, flat lamps, index gradient microlenses and rear automobile glasses.