Annealed low emissivity coating

IS 2 174 891 T3

DESCRIPTION

Low-E multi-layer coating.

Field of the invention

The present invention relates generally to the art of low-emissivity multilayer coatings, and more particularly to the art of low-emissivity coatings of the general metal oxide / silver / metal oxide configuration.

Background of the invention

Gillery US Patent No. 4,610,771 describes low emissivity and high transmittance multi-layer coatings comprising zinc oxide / silver / zinc oxide-tin deposited by bombardment of the cathode.

Gillery US Patent Nos. 4,834,857 and 4,902,580 disclose a low-emissivity, high-transmittance enhanced neutral coating comprising an infrared reflective metal layer between layers of anti-reflective metal oxide where a high-index neutral metal oxide is deposited. of refraction between the antireflective metal oxide layer and the infrared reflective metal layer.

US Patent No. 4,898,789 to Finley describes a low-emissivity film for automotive heat load reduction comprising a first layer of anti-reflective metal oxide, a first infrared reflective layer, a first primer layer, a second layer anti-reflective metal oxide, a second infrared reflective metal layer, a second primer layer and a third anti-reflective metal oxide layer.

US Patent No. 4,898,790 to Finley describes a metal oxide / silver / metal oxide type low emissivity film for high temperature processing such as bending, blueing or laminating, in which a primer layer between the layer Infrared reflective metal and the anti-reflective metal oxide layer comprises a metal layer and a metal oxide layer.

US Patent No. 5,050,295 to Finley discloses a method of producing a low-emissivity coating comprising bombarding a first layer of cincestane oxide, bombarding a second layer of titanium, bombarding a third layer of silver, bombarding a fourth layer of titanium, bombarding a fifth layer of zinc-tin oxide, bombarding a sixth layer of titanium oxide and then heating the glass to a temperature where the titanium layers are oxidized but the silver is protected from oxidation.

Compendium of the invention

The present invention as defined in the claims provides an improvement in multi-layer bombardment low-emissivity coatings, by thermally processing the coated substrate at temperatures below the substrate torsion point, soda-calsolice glass. The present invention maximizes the mechanical and chemical durability and optimizes the solar energy and ooptic properties of low-emissivity bombardment films comprising one or more infrared reflective metal films between two or more antireflective metal oxide films. The thermic processing at temperatures below the torsion point of the glass is sufficient to temper the infrared reflective metal, eg silver, and the metal oxide layers to optimize the chemical and mechaonic durability of the coating. Brief description of the figure

Figure 1 illustrates the effect of tempering on the properties of two coated articles according to the present invention. The coated articles were placed in a storage oven at 100 ° F (approximately 538 ° C) for the indicated time periods. Figure shows the effect of tempering on the sheet resistance of the coated article, measured in ohms per square, as a function of the tempering period. Figure 1b shows the effect of tempering on the emissivity of the coated article. Figure 1c illustrates the effect of tempering on torsional strength, evaluated as described herein. Figure 1d illustrates the effect of tempering on the light transmission of the coated article.

Figure 2 illustrates the effects of tempering on the properties of an article coated with a double layer of silver in accordance with the present invention. These coated items were placed in a storage oven at 850 F (454 ° C) for the indicated time periods. Figure 2a shows the effect of tempering on the laminate resistance of the coated article, measured in ohms per square. Figure 2b shows the effect of tempering on light transmittance. Figure 2c shows the effect of tempering on emissivity. Figure 2d shows the effect of tempering on the torsional strength of the coating. Figure 2e illustrates the temperature of the sample as a function of time in the oven.

Description of preferred embodiments

A stack of low emissivity multilayer thin films made up of the general layer sequence of metal oxide / silver / metal primer / metal oxide / silver / metal primer / metal oxide / protective overcoat is preferably deposited by magnetroon bombardment as described above. previously described.

The present invention provides a novel method for maximizing the chemical and mechanical efficacy and durability of such low emissivity coated glass substrates. The ooptic, mechanical and chemical properties of a coating based on the above sequence of layers can be significantly improved if the coated substrate is heated to moderate to high temperatures for a short period of time for coating tempering. The results of the tempering of the thermal processing of the coating after its deposition results in the elimination or reduction of mechaonic and chemical stresses within the coating layers or at the interfaces. These stresses, which result in a shorter-lasting coating, as well as a coating with higher strength and emissivity, can be the result of structural defects, such as dot and boundary defects within the coating layer.

ES 2 174 891 T3 silver, or the presence of more reactive metal layers, for example titanium, together with the oxide of other metals, for example zinc or tin.

By heating to eliminate or reduce structural defects and chemical reactions, tempering results in more mechanically and chemically stable layers and interfaces. In order to avoid the introduction of permanent stresses into the glass substrate, the maximum temperature used for this purpose will remain below the temperature of the torsion point of the glass substrate, for example, 940 ° F (504 ° C) for a clear soda-lime-salice glass. The preferred temperature range for this application is between approximately 600^°F (315^°C) and the twist point of the substrate, more preferably about 700 to 850^°F (approximately 371 to 454^°C). Heating to anneal the coating can be carried out by any means such as convective, conductive, radiative, inductive, or combinations thereof. Various apparatus such as a temper, furnace or muffle can be used. Alternatively, the coating can be tempered by heating the coated article while still in the coating chamber, preferably by either inductive or radiative means. Tempering can be carried out even after the deposition of the metal layer (s) prior to the deposition of the final oxide layer (s). Preferably, the coated article can be heated to a low oxygen partial pressure.

In order to avoid disintegration of silver through agglomeration resulting from exposure to oxygen plasma during bombardment deposition of metal oxide layers, or agglomeration during post-heating process, the thickness range of the layers of primer, which are preferably deposited as metals, will preferably be between 1-2.5 nm (10 and 25 Angstroms), with a more preferred range of 1.5-2nm (15 to 20 Angstroms). In the preferred coating design, the barrier layer from the above reaction consists of a reactive metal such as titanium for high transmissivity applications, e.g., 75 percent at a higher visible transmittance, or less reactive metals for lower visible transmittance applications, or a combination thereof.

Heating of the film, preferably using convective heat transfer as in an oven or muffle or, both, convection and radiation of the glass substrate in a temper, results in partial oxidation of the primer layer, tempering of defects in the silver layer, which contribute to the bombardment of electrons and light, as well as the growth of silver grains. All of these effects result in an increase in the visible transmission of the coated article, as well as a measurable reduction in sheet resistance and emissivity. The extent of variations in the above chemical and phasic properties can be controlled by a combination of maximum temperature and temper duration, as well as film design, eg alteration of primer coat tack. These variations result in the control of the final transmission, emissivity and degradation coefficient of the coated article. Although it is possible to provide a coating with adequate mechanical durability without tempering, the tempering process of the present invention provides a wide process window and a significant improvement in the chemical durability of the coating.

In the following examples, an amorphous zinc stannate layer is used as the metal oxide dielectric layer. The examples illustrate the effect of the maximum sample temperature, as well as the tempering time, on the observed properties. The maximum temperature of the furnace, muffle or annealer can be higher than the maximum desired temperature of the substrate to minimize the time required to anneal the coating. Depending on the heating apparatus and method, a wide range of times and temperatures may be employed to produce the tempered coatings according to the present invention, which will be further understood from the descriptions of the specific examples that follow.

Example 1

A low-emissivity coating was produced comprising eight contiguous layers deposited separately on an Airco ILS1600 dc magnetroanic deposition system with a base pressure of no more than 0.67 Pa (5 x 10^-6 Torr). All layers were deposited at 4 millitorr of total working gas pressure. The process consisted of multiple, sequential passes of a 12 x 12 x 0.9 inch (30.5 x 30.5 x 0.23 centimeter) plate of clear float lime glass at a line speed of 120 inches. (30.5 x 30.5 x 0.23 centimeter) of a clear buoyant lime glass at a line speed of 120 inches (3.05 meters) per minute under active cataodic bombardment targets. All metallic layers were deposited in pure argon; The zinc stannate layers and the titanium oxide overcoat were deposited in gaseous mixtures of 65 percent oxygen - 35 percent argoan and 50 percent oxygen - 50 percent argoan, respectively.

The coating consisted of a zinc stannate first anti-reflective layer deposited at 4.7 amps and 1.8 kilowatts (kW) in 4 passes; a first layer of infrared reflective silver deposited at 1.10 amps and 0.4 kW in one pass; a first layer of titanium metal primer deposited at 1.60 apms and 0.55 kW in one pass; a second anti-reflective layer of zinc stannate deposited at 4.7 apms and 1.8 kW in 10 passes; a second layer of infrared reflective silver deposited at 1.6 amps and 0.6 kW in one pass; a second layer of titanium metal primer deposited at 1.64 amps and 0.55 kW in one pass; a third anti-reflective layer of zinc stannate deposited at 4.62 amps and 1.8 kW in 4 passes; and finally, a protective layer of titanium oxide deposited at 12.46 amps and 6.0 kW in 3 passes. The coated glass plate was cut into multiple 2 x 12 inch (5 x 30.5 centimeter) parallel sections.

ES 2 174 891 T3 to its leading edge. The cut sections were then heated in a storage oven at 1000 ° F (about 538 ° C) for various time intervals.

The properties of the tempered coated glass of this invention are shown in Figure

1. Sheet resistance, emissivity, and transmittance of visible light were measured using conventional measurement methods. Another property measured relates to the shear resistance of the coating, which is an important characteristic of low-emissivity coatings. Shear strength determines the mechanical durability of the coating which is critical during transport of the coated glass. The method used here for the evaluation of the shear strength consists of the application of 20 successive blows of a fabric moistened with deionized water against the coated surface of the glass, followed by the visual examination of the test area. If a coating shows no signs of shear, including only visible scratches, then it receives a maximum score. Coatings showing uniform shear and delamination at any interface of the multi-layer coating within the test area receive a failure score. Other levels of effectiveness receive intermediate scores. In Figure 1c, subjective numerical grades are provided for shear strength. This method of characterizing the durability of the coating has been found to correlate well with the field efficiency of the coating. Clearly, all the measured properties of the coating improve with the resistance time of the sample in the storage oven. For all the tempering periods shown in Figure 1, the sample temperature is below that of the oven and within the transition of the time-temperature curve shown in Figure 2e.

Comparative Example A

A low emissivity coating comprising 10 layers was prepared as in Example 1 except that a very thin layer of titanium oxide was deposited on top of the first and second layers of titanium metal primer. These layers, each approximately 0.9 nm (9 Angtroms) thick, were deposited into a gaseous mixture of 65 percent oxygen - 35 percent argon at 6.4 amps and 3 kW in one pass. The relatively low bombardment power level for the titanium oxide was selected in order to allow only a slow coverage of the outer metallic primer layer and, consequently, to facilitate its effective oxidation by the intense oxidation plasma that is in contact with her. The desired conversion of the majority of the last metal layer to be oxidized was confirmed by in situ measurement of the coating transmission immediately before and after the deposition of the previous titanium oxide layers, which showed a large increase after the stage. oxidation. As a result of the above conversion, the sample as deposited exhibits an appreciable improvement in transmission, sheet strength and emissivity over the unheated coated glass of Example 1, that is, prior to tempering. However, until further heat treatment, its shear strength remains very low, comparable to that of the unheated coated glass of the previous example, that is, before tempering. These examples illustrate the critical role of post-tempering in providing the coating with its superior qualities. The oxidation of the titanium primer layers, for example, by plasma oxidation, is insufficient to maximize the durability and effectiveness of the coating without the tempering process of the present invention. Example 2

An eight-layer coating as described in Example 1 was deposited on 69 x 41 x 0.09-inch (175 x 104 x 0.23 centimeter) clear float glass plates in an 84-inch (213-centimeter) zone seven. centimeters) of an Airco in-line coater. The coating consists of a first anti-reflective layer of zinc stannate deposited at 28 nm (280 Angstroms); a first layer of infrared reflective silver deposited at 11.3 nm (113 Angstroms); a first layer of titanium metal primer deposited at 24 Angstroms; a second anti-reflective layer of zinc stannate deposited at 75 nm (750 Angstroms), a second layer of infrared reflective silver deposited at 15 nm (150 Angstroms) a second layer of titanium metal primer deposited at 2.4 nm (24 Angstroms) ); a third anti-reflective layer of zinc stannate deposited at 24 nm (240 Angstroms); and finally a protective layer of titanium oxide deposited at 4.8 nm (48 Angstroms). The fully coated glass plates were then post-heated in an in-line Cattin quencher to approximately 800 to 900 ° F (approximately 427 to 482 ° C). Numerous heated plates corresponding to a typical roll shape were then packed onto a steel frame and transported over 1,920 km (1,200 miles) between production and inspection sites. All plates were free of the typical defects of less mechanically durable coatings, incurring shear marks and scratches due to material contact between sheets and relative slippage of adjacent glass plates. Additionally, for more than eight months of storage, from winter to autumn, the plates from this group of samples remained free of environmentally induced defects (eg, isolated "summer spots" that are frequently observed due to heat exposure. and humid weather) without the aid of any additional protection other than a loose plastic cover. Sheet strength, transmittance, emissivity, and shear strength were measured as in Example 1. The properties of the tempered coated glass of this example are shown in Figure 2.

Two fully coated plates, one heated and the other without any heat treatment, were measured for residual stresses (ie, surface compression and central tension) in the glass. Both samples showed levels of temper within acceptable limits with no significant differences between the two.

It is 2 plates. Thus, the tempering of the coating did not deteriorate the glass substrate.

Example 3

Sections were cut from the coated glass plates of Example 2 prior to heating in the temper and were instead heat treated in a storage oven that had been pre-heated to 850 ° F (approximately 454 ° C). Different tempering times were used in order to determine the optimal heating pattern at a maximum furnace temperature of 850^°F (approximately 454^°C). An examination of the property versus tempering time curves suggests a range of 2 to 6 minutes, with a preferred range of 3 to 5 minutes, and mine preferably 4 minutes of tempering. Excessive tempering periods at or above high oven temperatures can result in deterioration of the coating and are not preferred. My oven temperatures are low, for example 700^°F (approximately 371^°C), can be used but are less desirable since longer tempering periods are necessary to optimize coating properties. Coated samples were optimally tempered

891 T3 8 for 4.5 minutes in an oven pre-heated to 850^°F (454^°C) and were subjected to various tests to determine the chemical durability of the tempered coating. The accelerated tests included immersion of the samples in acidic, basic and saline solutions, exposure to high humidity and temperature (Cleveland Condensation Chamber) and the shear resistance test described above. The temper coating of the present invention passed all of these tests, whereas an untempered coating with the same eight-layer configuration failed the sodium chloride immersion, Cleveland moisture, and wet shear tests.

The above examples are offered to illustrate the present invention. The time and temperature of the tempering stage can be varied within a wide range depending on the configuration of the coating, composition and thickness of the layers, and particularly on the type and condition of the oven or temper. The scope of the present invention is defined by the following claims.