Process for the improvement of the abrasion resistance features and the chemical inertia of transparent thin coatings

Abstract: A process for the improvement of the durability features of a thin transparent coating deposited under vacuum by means of a physical vapour deposition method on a transparent substrate surface such as glass, consists in the deposition of one thin transparent layer of ZrO 2-x or Zr transparent alloy oxides or a combination of transparent alloys containing ZrO 2-x. The process is realized according to a physical vapour deposition method that could be the same as the one utilized for the deposition of the base coating, and the protective layer does not alter considerably the spectrophotometry features.

Description: The present invention relates to a process for the improvement of the durability features of a thin transparent coating, according to the preamble of claim 1. Products provided with superficial coatings (from now on called coating) made up of one or more thin layers which, thanks to their electromagnetic radiation and/or electric conductivity features, find increasing applications in fields such as, for example, automotive and architectural glass have been realized for years on an industrial basis by using different technologies; (by means of a physical vapour deposition: RF sputtering, magnetron sputtering, thermal evaporation, electron gun evaporation and by means of chemical vapour deposition: pyrolysis, cvd, sol-gel). The origin of success of such products has a twofold nature. With coating application on transparent substrates (such as, for example, glass), the interference phenomena can be exploited, typical of the wave-like processes, in order to modify during the spectral visible range UV-VIS-NIR-FIR (that is from 0.28 µm to 100 µm) the substrate response when compared to the electromagnetic radiation affecting it, and arrange, if necessary , a base which is no longer electrically insulated. This allows to consider at the same time both the different aesthetic and chromatic needs, to realize products able to satisfy the numerous requests for solar control, energy savings (thermal transmission reduction), the improvement of the visual and environmental comfort in buildings and automobiles, the deterioration reduction of interior materials, surface defrosting, etc. Naturally there exists a great difference between products present on the market, both on the basis of the durability and services features. Furthermore the increasing development of glazings is separating in a clear-cut manner the products realized by the application of various technologies. So the coatings obtained by means of physical vapour deposition proved to be incompatible with some recent applications. In particular coatings, so-called reflective, based on the usage of materials such as for example Steel (SSt), Titanium (Ti), Chromium (Cr), Tin (Sn) and/or related oxides, nitrides and oxide nitrides are not generally suitable for use on ventilated panes (it deals with curtain walls realized with glass coated with coating, in particular monolithic glass and used more frequently in buildings). The reason for this is tied to the general problem of the long term instability of the coatings realized by physical vapour deposition when they are used directly in contact with the environment. Similarly, in case of products intended for the automotive market, the reduced resistance features to the abrasion does not consent the installation as monolithic glass covered by a coating, particularly monolithic on movable parts (movable sunroofs, roll-down windows). EP-A-0,530,676 and JP-A- 05 294 674 disclose a transparent substrate protected by a complex two-layered structure containing zirconium oxide and having an increased overall thickness. EP-A-0,331, 201, JP-A 03 112 883 and JP-A- 04 182 239 disclose a transparent substrate having a protective layer made of an amorphous oxide based on a mixture of Zirconium-Boron or Zirconium-Silica. JP-A- 01 208 344 discloses a transparent weatherable plate having a protective layer obtainable from a wide range of metal oxides. The object of the present invention is that of overcoming the above mentioned inconveniences. The invention, as characterized by the claims, solves the problem of the usage of glass provided with thin coatings applied by means of physical vapour deposition directly in contact with the environment, for example ventilated panes, and/or in severe abrasion conditions, for example as movable glazings for cars. A further scope of the present invention is that of improving the durability of said coatings without considerably altering the spectrophotometric features. The present invention is based on the discovery that the abrasion resistance features and coating chemical inertia applied by physical vapour deposition utilizing materials consisting of SSt, (AISI 316 or similar), Ti, Cr, their oxides, nitrides and/or oxide nitrides, can be improved by applying on them, continuously, an external protective layer having appropriate features. The innovation deals with an overall general methodology that allows both the "brand new" design of new coatings, and the improvement of coatings already existing in the market. In both cases the disturbance introduced by the external protective film is reduced to the point that it can be considered inside the production tolerances. It has surprisingly been found that a thin film made up of zirconium oxide, in particular ZrO 2-x (x<<1), or formed by transparent alloy oxides containing Zr selected from the group consisting of Zr-Al, Zr-Ti, Zr-SSt, Zr-Cr or formed by a combination these transparent oxides deposited continuously on an underlying coating provides enough protection to pass the standardized durability tests fixed by the international standards that deal with abrasion resistance, to chemical attacks (SO 2 , NaCl, etc.) and to atmospheric agents (condense) proving the advantage to utilize such coatings in contact with the environment and/or as parts in motion. Furthermore it has surprisingly been found that the thickness of the protective layer deposited according to the process object of the present invention, such as to allow the wanted protection, turns out to be included between 2x10 -3 µm and 8x10 -3 µm. Therefore, the above specified object is achieved by a process according to annexed claim 1. A protective layer having such reduced thicknesses, does not on the one hand influence considerably on the main spectrophotometric features of the underlying coating such as transmission (TUV) and ultraviolet reflection, the light transmission (TL) and energetic (TE), light reflection (RL) and energetic (RE), the dominating wave length λ D , excitation purity (Pe), emissivity, on the other hand it can be easily deposited, for example with the magnetron sputtering method, on a traditional system used for coating architectural or automotive glass sheets. In accordance with the process described above, is also part of the present invention, a glass sheet according to the preamble of annexed claim 6 and having a protective layer applied on the base coating continuously , it consists of a ZrO 2-x (x<<1) thin layer, or Zr alloys transparent oxides selected from the group of Zr-Al, Zr-Ti, Zr-SSt, Zr-Cr, or a combination of transparent oxides thereof and makes up an effective thicknesses barrier between 2x10 -3 m and 8x10 -3 µm. Layers having such thicknesses can be easily deposited, for example, by magnetron sputtering starting with Zr metal targets or with Zr alloys. In this case the sputtering will be of the reactive type, having its deposition in an appropriately oxidized environment so as to obtain a practically stoichiometric oxide (x <<1). It is emphasized that, as experts in the field well-know, other techniques, in addition to the magnetron sputtering, can be utilized to put into practice the present invention. Some examples are thermal evaporation, evaporation by electronic gun, RF sputtering. The application of an additional film on an existing coating generally involves a variation of the characteristic parameters of the original coating which should not be neglected. For the case in question the protective layer according to the present invention implies a minimum variation of the characteristic parameters of the base coating. This matter is a direct consequence of the possibility to utilize the protective external layers according to the present invention very thin thicknesses that turn out to have a factor of 10 2 below the wave length of the visible radiation. This way the differences turn out to be almost independent from the coating to be protected (more precisely from the refraction index of the material that makes up the most external layer of the coating to be protected). Therefore such disturbance falls within the production tolerances in case the process object of the present invention wants to be used in order to improve the durability features of an item already in production. The present invention allows to improve the resistance to abrasion features, the chemical attacks and the coating atmospheric agents for electromagnetic radiation control in the intervals UV-VIS-NIR-FIR (that is in the interval from 0.28 µm to 100 µm) minimizing also the variation of the main spectrophotometry characteristics such as transmission/ultraviolet reflection/luminous/energetic, dominant wave length, excitation purity, emissivity. The characteristics of the invention will turn out to be more evident after considering the following realization examples of the invention, given merely as non-limiting examples. The deposition system utilized is a classical magnetron sputtering system "G series" from AIRCO Inc. made up of three vacuum chambers and nine cathodes, able to coat glass sheets having a size up to 2100 x 3210 mm 2 . In general before beginning the process the vacuum chambers are pumped down to reach a pressure below 5x10 -6 Torr. During sputtering, such value is preferably included between 0,133 Pa (1x10 -3 Torr) and 0,667 Pa (5x10 -3 Torr). The power applied to the cathode is normally brought to a maximum (according to the size of the cathode and of the target material fusing point) to lower as much as possible the machine's cycle time. Test sheets have been coated measuring 700 x 700 mm 2 and 2100 x 3210 mm 2. EXAMPLE 1 In this comparative example the realization of a traditional TiN x coating and of the same product protected is described, according to the present invention, with 5.10 -3 µm of ZrO 2-x . The system has been equipped with six Ti targets in the first two coating zones, and with one Zr target on the third chamber. Base product Power = 6 x 52 KW Pressure = 0,267 Pa (N 2 ) / 0,267 Pa (N 2 ) / 0,267 Pa (N 2 ) [1 µ = 1x10 -3 Torr; 0,267 Pa = 2 µ] Speed = 190 cm/minute Protected product Power = 6 x 52 + 50 KW Pressure = = 0,267 Pa (N 2 ) / 0,267 Pa (N 2 ) / 0,267 Pa (O 2 ) [1 µ = 1x10 -3 Torr; 0,267 Pa = 2 µ] Speed = 190 cm/minute EXAMPLE 2 In this example a comparison is made between a traditional SSt (AISI 316) TiN x type coating and of the same product protected, according to the present invention, with 5.10 -3 µm of ZrO 2-x . The system has been equipped with a SSt target in the first chamber, three Ti targets in the second coating zone, and one Zr target in the third chamber. Base product Power = 6 + 3 x 55 KW Pressure = 0,267 Pa (Ar) / 0,267 Pa (N 2 ) / 0,267 Pa (N 2 ) [1 µ = 1x10 -3 Torr; 0,267 Pa = 2 µ] Speed = 228 cm/minute Protected product Power = 6 + 3 x 55 + 65 KW Pressure = 0,267 Pa (Ar) / 0,267 Pa (N 2 ) / 0,267 Pa (O 2 ) [1 µ = 1x10 -3 Torr; 0,267 Pa = 2 µ] Speed = 228 cm/minute EXAMPLE 3 In this comparative example the realization of a traditional TiN x coating and the same protected product is described, according to the present invention, with a 5.10 -3 µm thick ZrO 2-x layer. The system has been equipped with three Ti targets in the second coating zone, and with one Zr target in the third chamber. Base product Power = 3 x 40 KW Pressure = 0,267 Pa (N 2 ) / 0,267 Pa (N 2 ) / 0,267 Pa (N 2 ) [1 µ = 1x10 -3 Torr; 0,267 Pa = 2 µ] Speed = 210 cm/minute Protected product Power = 3 x 40 + 60 KW Pressure = 0,267 Pa (N 2 ) / 0,267 Pa (N 2 ) / 0,267 Pa (O 2 ) [1 µ = 1x10 -3 Torr; 0,267 Pa = 2 µ] Speed = 210 cm/minute EXAMPLE 4 In this example the realization of a traditional SSt (AISI 316) / TiO 2-x type coating and of the same product protected is compared, according to the present invention, with a 5.10 -3 µm layer of ZrO 2-x . The system has been equipped with a SSt target in the first chamber, two Ti targets in the second coating zone, and one Zr target in the third chamber. Base product Power = 6 + 2x41 KW Pressure = 0,267 Pa (Ar) / 0,267 Pa (O 2 ) / 0,267 Pa (N 2 ) [1 µ = 1x10 -3 Torr; 0,267 Pa = 2 µ] Speed = 216 cm/minute Protected product Power = 6 + 2x41+60 KW Pressure = 0,267 Pa (Ar) / 0,267 Pa (O 2 ) / 0,267 Pa (O 2 ) [1 µ = 1x10 -3 Torr; 0,267 Pa = 2 µ] Speed = 216 cm/minute The results are shown on Table 1. As shown on Table 1, for each different type the standard coatings have been considered (identified on the table with the initials TQ) and the same protected with a 5.10 -3 µm thick ZrO 2-x (x<<1) layer. As shown by the measurements reported on this table, the variation of all spectrophotometry parameters are sufficiently reduced therefore the products are considered the same from the aesthetic and functional point of view. In fact the variations, both in transmission and reflection, of the dominant wave length λ D are included in the range of ± 2 nm and the variations of the TE energetic transmission are included within 2 points, therefore the competent man considers them to be included in the normal production tolerances. Let's still remember that the application of the protective film object of the present invention does not alter in any way the emissivity value of the base coating, since, even though it deals with a dielectric type film, the relationship between the wave length of the thermal radiation being considered and the thickness of the protective film is around 10 -3 µm. The products have then been subject to the following normalized tests: Abrasion test (EN1096) (Table 2) The scope of this test is to simulate (utilizing equipment that consents to apply on the coating, by means of a normalized felt, a constant pressure for a fixed number of cycles during the straight-line forward/back motion at a 1 Hz frequency of the same felt) the coating deterioration following mechanical actions of the abrasive type similar to those undergone by the product ready for use, such as, for example, cleaning, leaching, washing, rubbing of the parts in rubber, etc. There are two reference thresholds for the pair (N o of cycles, load), which correspond for example to the specifications supplied by the automobile manufactures for applications both inside and outside the automobile. Such values are respectively (200 cycles, 0.04N/mm 2 ) and (2000 cycles, 0.07N/mm 2 ). The favourable level of durability reached with the solution which is object of the present invention (5000 cycles in the both cases mentioned above), the behaviour has also been analyzed with a load of 0.09N/mm 2 which has given in the same way favourable results at 5000 cycles. ABRASION TEST RESULTS (EN 1096) 0,04 N / mm 2 0,07 N/mm 2 0,09 N/mm 2 300 cycles 800 cycles 5000 cycles 5000 cycles TiN X (1) TQ RUINED 50Å GOOD GOOD SSt/TiN X TQ RUINED 50Å GOOD GOOD TiN X (2) TQ RUINED 50Å GOOD GOOD SSt/TiO 2-x TQ RUINED 50Å GOOD GOOD NOTE Visual opinions have been reported since the variation of the spectrophotometry parameters turned out to be irrelevant. RUINED = almost total removal of the coating Kesternich test (DIN50018, EN1096) Table 3) This test, fit for the behaviour evaluation of products exposed to highly polluted environments, consists in submitting the coating to repeated exposures into SO 2 saturated atmospheres. As reference it is reminded that the CEN standardization for architectural applications (TC129 "Glass in buildings" WG6 "Coated glazings for windows") anticipates, in the specific case the use of external coating, the exceeding of a number of cycles equal to at 1/10 concentration of SO 2 when compared to the one utilized. The parameters reported on the above mentioned table, that is ΔY, ΔC and ΔE, are related to the Lab-Hunter system and represent respectively the light transmission or reflection variation, the chromatic variation and the total color variation, when compared to the untreated sample (TQ). The test results show that the TQ samples deteriorate within 1 - 2 days, while those protected (apart from a case where the deterioration takes place after 4 days) alterations cannot be distinguished not even after 6 or 12 days. Condense test (EN1096) (Table 4) With this test it is evaluated the possible deterioration of the product caused by condense water formed on the coating after processing. Also in this case as a reference point the values provided by the CEN normalization (see above) can be used that, for external applications, anticipates 500hrs of exposure at a temperature of a 40°C (10°C less when compared to the conditions used here). The parameters reported on the above table, that is ΔY, ΔC and ΔE, are related to the Lab-Hunter system and represent respectively the light transmission or reflection variation, the chromatic variation or the total color variation, when compared to the untreated TQ sample. The examination of the test results shows that TQ samples deteriorate after 1000 hours of tests, while those protected did not show any alteration even after 2500 hours.

Claims: A process for the improvement of the durability of a transparent coating made up of one or more layers deposited on a surface of a transparent substrate, said transparent coating having an outer layer formed under vacuum by a physical vapour deposition method utilising materials consisting of stainless steel, titanium, chromium, their oxides, nitrides and/or oxide nitrides, said transparent coating controlling the transparent substrate spectrophotometric properties with respect to a radiation of wavelength from 0.28 µm to 100 µm, characterised in that it comprises a step of depositing under vacuum by a physical vapour deposition method only one transparent protective dielectric layer on said transparent coating, said transparent protective dielectric layer being made of materials consisting of zirconium oxide, or transparent oxides of zirconium alloys of a group comprising zirconium-aluminium, zirconium-titanium, zirconium-stainless steel, zirconium chromium alloys, and having a thickness in a range from 2x10 -3 µm to 8x10 -3 µm. Process according to claim 1, wherein said transparent protective dielectric layer is made of zirconium oxide ZrO 2-x (x<<1). Process according to claim 1, wherein said transparent protective dielectric layer has a thickness of 5.10 -3 µm. Process according to claim 1, wherein said transparent protective dielectric layer is deposited under vacuum immediately after said transparent coating to be protected by using the same physical vapour deposition method as in said transParent coating, and in the same deposition system. Process according to claim 4, wherein said physical vapour deposition method is a magnetron sputtering method, a thermal evaporation method, an evaporation by electronic gun method or a radio frequency sputtering method. Glass sheet equipped with a transparent coating made up of one or more layers deposited on a surface of a transparent substrate, said transparent coating having an outer layer formed under vacuum by a physical vapour deposition method utilising materials consisting of stainless steel, titanium, chromium, their oxides, nitrides and/or oxide nitrides, said transparent coating controlling the transparent substrate spectrophotometric properties with respect to a radiation of wavelength from 0.28 µm to 100 µm, characterised by one outer transparent protective dielectric layer deposited on said outer layer by a process according to any claim from 1 to 5. Glass sheet according to claim 6, wherein said transparent protective dielectric layer has such a thickness resulting in a 10 2 factor below the wave length of the visible radiation. Use of at least one glass sheet according to claims 6 or 7, wherein said transparent protective dielectric layer is directly in contact to the atmosphere. Use of at least one glass sheet according to claims 6 or 7 as an architectural ventilated pane. Use of at least one glass sheet according to claims 6 or 7 as a movable automotive glazing.

Inventors: BOLOGNESE LITTERIO, GAGLIARDI GIOVANNI, BOLOGNESE, LITTERIO, GAGLIARDI, GIOVANNI
Applicants: SIV SOC ITALIANA VETRO, SOCIETA' ITALIANA VETRO - SIV - S.P.A.
Application year: 1996
Main classification: C03C17
IPC codes: C23C14, C03C17