Planarisation of a coating

Abstract

Methods are disclosed for planarisation of a coated glass substrate by deposition of a silazane based layer thereon. Coated substrates according to the invention exhibit improved properties in terms of reduced roughness, lower haze and higher visible light transmission and the coated surface may be exposed to the external environment, for example as surface 1 or surface 4 of a double glazing unit. The resulting smooth surface is less susceptible to marking and scratch damage, and offers enhanced surface energy (improved hydrophobicity).

Claims

1. A method of planarising a surface of a coating on a glass pane comprising: providing a glass pane that is directly or indirectly coated on a major surface thereof with a rough underlayer, and depositing at least one layer based on one or more silazane or polysilazane on said underlayer; wherein the method further comprises partially or completely converting the at least one layer based on one or more silazane or polysilazane to at least one layer based on silica and/or an organo silica, and wherein the rough underlayer comprises at least one layer based on a transparent conductive coating (TCC), wherein the TCC is a transparent conductive oxide (TCO), and wherein the TCO is one or more of fluorine doped tin oxide (SnO.sub.2:F), zinc oxide doped with aluminium, gallium or boron (ZnO:Al, ZnO:Ga, ZnO:B), indium oxide doped with tin (ITO), cadmium stannate, ITO:ZnO, ITO:Ti, In.sub.2O.sub.3, In.sub.2O.sub.3ZnO (IZO), In.sub.2O.sub.3:Ti, In.sub.2O.sub.3:Mo, In.sub.2O.sub.3:Ga, In.sub.2O.sub.3:W, In.sub.2O.sub.3:Zr, In.sub.2O.sub.3:Nb, In.sub.2-2xM.sub.xSn.sub.xO.sub.3 with M being Zn or Cu, ZnO:F, Zn.sub.0.9Mg.sub.0.1O:Ga, (Zn,Mg)O:P, ITO:Fe, SnO.sub.2:Co, In.sub.2O.sub.3:Ni, In.sub.2O.sub.3:(Sn,Ni), ZnO:Mn, and/or ZnO:Co, and wherein each layer of the at least one layer based on a TCC has a thickness of at least 20 nm, but at most 600 nm, and wherein a surface of the at least one layer based on silica and/or an organo silica has an arithmetical mean height of the surface value, Sa, of at most 3 nm, and wherein after depositing the layer based on one or more polysilazane or silazane, and/or after partially or completely converting the layer based on one or more polysilazane or silazane to at least one layer based on silica and/or an organo silica, said pane exhibits a haze value measured in accordance with the ASTM D 1003-61 standard of from 0.2% to 1.0%.

2. The method according to claim 1, wherein said polysilazane or silazane is comprised of a perhydropolysilazane, a polymethylsilazane and/or a polydimethylsilazane.

3. The method according to claim 1, wherein the polysilazane or silazane is a polysilazane, and the polysilazane has a number average molecular weight of 1000 to 200,000 g/mol.

4. The method according to claim 1, wherein said at least one layer based on one or more polysilazane or silazane is deposited by spin coating, slot die coating, spraying, roller coating, dipping, and/or printing.

5. The method according to claim 1, wherein said conversion comprises treating the pane with heat after depositing the layer based on one or more polysilazane or silazane.

6. The method according to claim 5, wherein said heat treatment comprises heating the pane at at least 100 C., but at most 700 C.

7. The method according to claim 6, wherein said heat treatment further comprises heating the pane at said temperature for at least 30 min, but at most 4 hr.

8. The method according to claim 6, wherein said heat treatment further comprises heating the pane to said temperature over a period of at least 20 min.

9. The method according to claim 1, wherein said conversion comprises treating the pane with UV and/or IR radiation treatment which comprises exposing said layer based on one or more polysilazane or silazane to UV and/or IR radiation for at least 3 min, but at most 1 hr.

10. The method according to claim 1, wherein said at least one layer based on silica and/or an organo silica has a thickness of at least 10 nm, but at most 400 nm.

11. The method according to claim 10, wherein said at least one layer based on silica and/or an organo silica has a thickness of at least 100 nm.

12. The method according to claim 1, wherein after depositing the layer based on one or more polysilazane or silazane, and/or after partially or completely converting the layer based on one or more polysilazane or silazane to at least one layer based on silica and/or an organo silica, said pane exhibits a haze of at most 0.6%.

13. The method according to claim 1, wherein the underlayer further comprises at least one further layer, wherein said at least one further layer is based on an oxide of a metal or of a metalloid, selected from the group consisting of SiO.sub.2, SnO.sub.2, TiO.sub.2, silicon oxynitride and/or aluminium oxide.

14. The method according to claim 13, wherein each layer of the at least one further layer based on an oxide of a metal or of a metalloid has a thickness of at least 10 nm, but at most 50 nm.

15. The method according to claim 1, wherein the underlayer further comprises at least one further layer, wherein said at least one further layer is based on SiO.sub.2, SnO.sub.2, TiO.sub.2, silicon oxynitride and/or aluminium oxide.

16. The method according to claim 1, wherein the underlayer comprises, in sequence from the glass pane: a lower anti-reflection layer; a silver-based functional layer; and at least one further anti-reflection layer.

17. The method according to claim 1, wherein the method further comprises depositing at least one overlayer on the at least one layer based on one or more polysilazane or silazane and/or based on silica and/or an organo silica.

18. The method according to claim 1, wherein the at least one silazane or polysilazane comprises a polysilazane, and the polysilazane has a density of 0.5 to 1.5 g/cm.sup.3.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be further described by way of the following specific embodiments, which are given by way of illustration and not of limitation, with reference to the accompanying drawings in which:

(2) FIG. 1 is a graph that shows Arithmetical Mean Height of the Surface Values, Sa, vs. silica layer thickness for several comparative coated glass panes and a number of coated glass panes according to the present invention prepared using the precursor PHPS;

(3) FIG. 2 is a graph that shows Arithmetical Mean Height of the Surface Values, Sa, vs. organo silica layer thickness for a comparative reference coated glass pane and a number of coated glass panes according to the present invention prepared using the precursor PDMS; and

(4) FIG. 3 is a graph that shows percentage haze values vs. silica layer thickness for a comparative reference coated glass pane and a number of coated glass panes according to the present invention prepared using the precursor PHPS.

DETAILED DESCRIPTION OF THE INVENTION

Examples

(5) Samples of NSG TEC (RTM) 15 (glass (thickness=3.2 mm)/tin oxide (25 nm)/silicon dioxide (25 nm)/fluorine doped tin oxide (340 nm)) glass (sample size=75 mm75 mm) were used in all examples.

(6) Examples according to the invention were prepared by spin coating samples with perhydropolysilazane (PHPS) or polydimethylsilazane (PDMS).

(7) PHPS or PDMS solution was mixed with dibutylether (DBE) using a range of dilutions as shown below in Table 1:

(8) TABLE-US-00001 TABLE 1 Concentration and dilution of solutions of PHPS or PDMS in DBE, and corresponding PHPS or PDMS layer thicknesses obtained. Concentration of Dilution of PHPS or PDMS PHPS or PDMS PHPS:DBE Film Thickness (% by volume) or PDMS:DBE (nm) 7.6 1:12.2 21.7 9.7 1:9.34 26.1 15.8 1:5.33 40.2 18.9 1:4.30 46.5 32.3 1:2.10 83.8 37.3 1:1.68 97.7 48.7 1:1.054 132.7 55.7 1:0.795 153.2

(9) The spin coating process parameters were:

(10) TABLE-US-00002 Coating solution dispense volume ca. 2 ml Spin speed 2000 rpm Acceleration 1000 rpm/sec.

(11) The samples were then cured for 1 hr at 500 C. (involving ca. 1 hr heat up to the desired temperature, 1 hr hold at said temperature, and ca. 8 hr of cooling down to room temperature) to provide an outer layer of silica (from a PHPS precursor) or organo silica (from a PDMS precursor).

(12) Comparative examples were prepared by depositing a 20-150 nm thick SiO.sub.2 layer on a number of samples of TEC 15 via chemical vapour deposition (CVD).

(13) Roughness Data (Arithmetical Mean Height of the Surface Values, Sa) was obtained in accordance with ISO 25178 using atomic force microscopy. Percentage haze values were measured in accordance with the ASTM D 1003-61 standard.

(14) FIGS. 1 and 2 show the planarising effect of coating an underlayer with perhydropolysilazane (PHPS) or polydimethylsilazane (PDMS, MQ70) respectively followed by curing of the outer coatings to form a silica layer or an organo silica layer respectively.

(15) In FIG. 1, several data points lie on the y-axis of the graph which are comparative reference samples, i.e. samples of TEC 15 with no further coatings. All of the other samples, apart from those represented by data series B, are comparative and are samples of TEC 15 that have been coated with silica using atmospheric pressure CVD.

(16) Comparative data series A represents samples of TEC 15 that were coated with silica on a 6 inch (15 cm) atmospheric pressure thermal CVD coater using Di-t-butoxydiacetoxysilane (DBDAS) as the silica precursor (apart from the reference sample shown on the y-axis). Silica coatings were deposited onto NSG TEC 15 at 650 C., typically using a DBDAS gas phase concentration of 0.4%, oxygen at 0.223 mol/min and a nitrogen carrier flow of up to 11 l/min.

(17) Data series B represents samples according to the invention that were prepared as detailed above using PHPS as the silica precursor layer (apart from the reference sample shown on the y-axis). Curve E is a best fit through data series B.

(18) Comparative data series C represents samples of TEC 15 that were coated with silica on an atmospheric pressure thermal CVD coater using SiCl.sub.4 in EtOAc. Silica coatings were deposited onto an NSG TEC 15 substrate held at between 580 C. and 650 C., typically using flows of 0.5-2 l/min of nitrogen through a SiCl.sub.4 bubbler, 2 l/min O.sub.2, 3-7 l/min N.sub.2 carrier gas, 100-300 l/min of EtOAc. Deposition times ranged from 15 to 120 seconds.

(19) Comparative data series D represents samples of TEC 15 that were coated with silica on an atmospheric pressure thermal CVD coater using SiH.sub.4 (apart from the reference samples shown on the y-axis). The samples were subsequently polished to varying degrees (hence the presence of more than one data point at each thickness of silica) using a polishing brush (Standard, V3106, V3107 or V3109 supplied by Botech) and a liquid polishing medium containing an abrasive suspension of alumina (Acepol AL alumina slurry by Aachener Chemische Werke, diluted to 10% by volume). The best results were achieved by impregnating the brushes with a silicon carbide or aluminium oxide abrasive. During polishing, the brush was lowered until contact was just made with the exposed coating layer, such that the tips of the brush bristles were providing the majority of the contact between brush and coating.

(20) In FIG. 2, data series A represents samples according to the invention that were prepared as detailed above using PDMS as the organo silica precursor layer.

(21) Comparative reference data point B represents a sample of TEC 15 with no further coatings.

(22) FIGS. 1 and 2 illustrate that silica and organo silica coatings that were derived from PHPS and PDMS coatings respectively exhibit substantial planarising effects when assessed against comparative examples. Furthermore, from FIG. 1 it can be seen that samples bearing silica coatings of 100 nm thickness or more that are derived from PHPS coatings exhibit extremely high planarity. FIG. 2 shows that correspondingly high levels of planarity are exhibited by all four of the samples bearing organo silica coatings (thicknesses of 250 nm or 750 nm) that are derived from PDMS coatings.

(23) In FIG. 3, data point A represents a reference sample of TEC 15 with no further coatings. Data series B and C represent samples that were analysed for haze levels 1 year after production and immediately after production respectively. The samples for series B and C were prepared as detailed above using PHPS as the silica precursor layer. FIG. 3 shows that the use of PHPS as a precursor layer enables the provision of a silica coated glass pane that exhibits very low haze in comparison with the reference sample. Moreover these low levels of haze are maintained over time.

(24) The invention is not restricted to the details of the foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.