A hydrophobic coating composition, a hydrophobic glass and a method thereof

Abstract

A hydrophobic coating composition for glass substrate is provided. The said hydrophobic coating composition comprising one or more silanol terminated siloxane polymer in the amount of from 3 to 9 wt%, at least one nonionic surfactant in the amount of from 0.5 to 5 wt%, at least one co-surfactant in the amount of from 0.1 to 2 wt%, 20 to 80 wt% of diluent, and 20 to 80 wt% of dispersion medium. The hydrophobic coating composition comprising silanol terminated siloxane polymer is free of any halogen containing compounds. The present disclosure further relates to a hydrophobic coated glass substrate and a method of making the hydrophobic glass substrate using the hydrophobic coating composition.

Description

[0001] A HYDROPHOBIC COATING COMPOSITION, A HYDROPHOBIC GLASS

[0002] AND A METHOD THEREOF

[0003] TECHNICAL FIELD

[0004] The present disclosure relates in general to a hydrophobic coating composition for glass substrates, a substrate comprising hydrophobic coating composition and a method thereof. More particularly to hydrophobic coating composition for glass substrates comprising silanol terminated siloxane polymer which is completely devoid of any halogen containing compounds.

[0005] BACKGROUND

[0006] Over a period glass is susceptible to deterioration when exposed to hot and humid climatic conditions. This is seen as loss of clarity caused due to haze development. Haze development is result of glass corrosion which detrimentally impacts the transparency and aesthetic appeal.

[0007] Silicate-based glasses are predominantly rich in alkali and alkaline earth metal elements. These elements are primarily added to reduce the viscosity of melt during glass production. They also lower the temperature requirements during float glass manufacturing process. However, these elements make silicate-based glass susceptible to atmospheric moisture attack. This means that when glass surface is exposed to atmospheric humidity for an extended duration, it experiences chemical transformation [ ai’ insight into atmospheric alteration of alkali-lime silicate glasses, Corrosion Science 122 (2017) 12-25], Migration of alkali and alkaline earth metal ions takes place from bulk of the glass-to-glass surface in presence of surface adsorbed water. This process is fairly slow and continues over long period of time. This is termed as Class 1 corrosion in glass. Excessive class 1 corrosion is said to have occurred when chemical transformation via cation exchange leads to change in localized refractive index creating hazy appearance. This is a permanent damage where aesthetic of the glass is lost with high haze generation and is termed as class 2 corrosion of glass.

[0008] This entire phenomenon of alteration of glass surface is termed as weathering of glass. It is more prominent in hot and humid climate as extend of atmospheric humidity will dictate the severity of weathering.

[0009] Ideal situation is to prevent initiation of class 1 corrosion on glass surface in first place. This can be achieved by eliminating direct contact of water with glass surface. However, glass surface is fundamentally hydrophilic in nature. High atmospheric humidity leads to higher adsorption of atmospheric moisture on the glass surface to an extent where water film is formed. Presence of surface water film facilitates process of class 1 corrosion. Here, H+ ion from water migrates inwards facilitating ion exchange reaction with alkali (Na+) and alkaline earth metal ions (Ca2+). These cations will migrate out and dissolve in water film. Further, atmospheric gases like CO2, NOx and SOx also get dissolved in water film. These dissolved gases act as anions like carbonate, sulphates and nitrates. When water film dries off due to atmospheric changes, cations combine with anions to form of salt crystals like sodium sulphate, sodium carbonate, calcium carbonate, etc. These are termed as weathering products. If not cleaned promptly, and heavy salt build-up is allowed, a layer of salt crust can form on surface [Influence of weather conditions on glass properties, Journal of the University of Chemical Technology and Metallurgy, 47, 4, 2012, 429-439],

[0010] These weathering products and localized crust impact clarity of glass. To eliminate the initiation of class 1 corrosion of glass, it is paramount to clean these weathering products periodically. It can be cleaned with periodic washing with water and soap solution or with water-alcohol solution, or with dilute acidic solutions.

[0011] In absence of routine cleaning and maintenance, heavy build-up of salt crust continues. As water film develops on glass surface especially during high humidity conditions, partial dissolution of salt will take place. This leads to increase in pH of water film. If pH exceeds 9, the chemical transformation via cation exchange is accelerated leading to aggressive depletion of alkali and alkaline earth metal ions from glass [Ch 29 Corrosion of Glass by B. Grambow, Uhlig’s Corrosion Handbook, 3rd Ed. 2011], This rapidly increases haze and will lead to class 2 corrosion of glass. This is permanent damage to glass clarity.

[0012] Use of zinc salt solution to protect the freshly manufactured glass surface during storage is well known. However, being water soluble, it is not a viable solution to protect glass during end application scenarios. For example, on facade, balustrades, railings, sun-roof, window, canopies, automotive wind shield, automotive side lites, automotive backlites, shower cubicles, partitions, etc. There is a need to have more robust solution to protect the glass surface from weathering.

[0013] US 7138186 B2 discusses about a hydrophobic coating and methods thereof. This involves four step process using chloro silane as active agent to form hydrophobic coating. This process also involves depositing anchor layer and crosslinking layer on top of the hydrophobic layer and requires very reactive reagents and strong process control.

[0014] US 7687150 B2 discusses a thermal barrier coating composition comprising functionally terminated siloxane including silanol terminated group which is dissolved in a crosslinking agent along with an optional filler materials. This composition is particularly used on a variety of substrates that are exposed to high temperatures which includes pipelines, engine parts including jet engine components. However, there is no hint or indication on protecting the glass weathering in this document.

[0015] US 6706798 B2 a water repellent coating composition comprising silanol terminated diorganopolysiloxane, a cross-linking agent, catalyst, silica, coupling agent, solvents and optionally silicone fluid. However, there is no hint or indication on protecting the glass weathering in this document.

[0016] Hence, primary requirements from weather protection coating for glass is to restrict water film build-up on glass surface by maintaining its water repellant properties in indoor & outdoor conditions. It should have UV resistance, resistance towards degradation due to high temperature and high humidity exposure and mechanically robustness.

[0017] The present invention discloses the formulation of hydrophobic protection coating especially for glass used in hot and humid conditions. It can be outdoor as well as indoor wet area application. Furthermore, hydrophobic coating composition of the present disclosure is environmentally friendly and easy to apply. Water-based coating and room temperature curing will have added advantages in terms of energy conservation and lower its carbon footprint.

[0018] OBJECT OF INVENTION

[0019] The main object of the present invention is to provide a hydrophobic coating composition for glass substrate, such that coating on glass substrate to improve durability and protection against weathering. Another object of the present invention is to provide a hydrophobic coating composition for glass substrate, such that coating demonstrates easy-to-clean property and is free of any halogen containing compounds. Further, another object of the present invention is to provide a hydrophobic coating composition for glass substrate, such that the coated transparent substrate is chemically durable, abrasion resistant, corrosion resistant and highly stable against ultraviolet degradation. Furthermore, another object of the present invention is a hydrophobic coating composition for glass substrate, such that composition is cured at room temperature, thus, overall reducing energy requirement for coating process and lowering its carbon footprint compared to temperature cured sol-gel coatings. SUMMARY OF THE DISCLOSURE

[0020] In one aspect of the present disclosure, a hydrophobic coating composition is disclosed. The said hydrophobic coating composition comprising one or more silanol terminated siloxane polymer in the amount of from 3 to 9 wt%, at least one nonionic surfactant selected from the group consisting of Cl 2- 14 alcohol ethoxylates in the amount of from 0.5 to 5 wt%, at least one co-surfactant in the amount of from 0.1 to 2 wt%, 20 to 80 wt% of alcohol diluent, and 20 to 80 wt% of water.

[0021] In one other aspect of the present disclosure, the hydrophobic coating composition having pH in the range from about 5 to 7.

[0022] In another aspect of the present disclosure, the hydrophobic coating composition is a microemulsion preferably, oil-in-water microemulsion. In yet another aspect of the present disclosure, the hydrophobic coating composition comprising one or more silanol terminated siloxane polymer is devoid of any halogen containing compounds.

[0023] In another aspect of the present disclosure, a hydrophobic coated glass is disclosed. Said hydrophobic coated glass comprising a glass substrate with at least one of its two surfaces coated with the hydrophobic coating composition.

[0024] In yet another aspect of the present disclosure, a method of making a hydrophobic coated glass is disclosed. Said method involves cleaning a glass substrate having a first surface and a second surface, coating the hydrophobic coating composition on at least one surface of the glass substrate, drying the coated surface of the glass substrate at room temperature for about 1 minute or curing the coated surface at temperature of from 100 to 150 °C ; and washing with water to rinse off the surfactant from the surface to obtain a hydrophobic coated glass.

[0025] Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings.

[0026] BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Embodiments are illustrated by way of example and are not limited in the accompanying figures.

[0028] FIG. 1 illustrates a contact angle results for UV exposure test for coating on annealed and tempered glass in QUV, in accordance with one embodiment of the present disclosure. FIG. 2 illustrates a contact angle results for UV exposure test for coating on annealed and tempered glass in Ci4000 Weather-O-Meter, in accordance with one embodiment of the present disclosure.

[0029] FIG. 3 illustrates a contact angle results for UV exposure test for coating on air-side and tin-side of tempered glass in QUV, in accordance with one embodiment of the present disclosure.

[0030] FIG. 4 illustrates a contact angle results for UV exposure test for coating on air-side and tin-side of tempered glass in Ci4000 Weather-O-Meter, in accordance with one embodiment of the present disclosure.

[0031] FIG. 5 illustrates a contact angle results for high temperature test for coating applied on annealed and tempered glass, in accordance with one embodiment of the present disclosure.

[0032] FIG. 6 illustrates a weathering product on uncoated and coated annealed and tempered glass. Effect of scrubbing demonstrating easy-to-clean property of coating, in accordance with one embodiment of the present disclosure.

[0033] FIG. 7 illustrates a contact angle results for accelerated weathering test for coating applied on annealed and tempered glass, in accordance with one embodiment of the present disclosure.

[0034] FIG. 8 illustrates a contact angle results for abrasion test for coating applied on tempered glass. Abrasion test with sponge wipe as abrader in presence of water as cleaning agent for 5000 abrasion cycles and different abrasion load, in accordance with one embodiment of the present disclosure. Skilled artisans appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the invention.

[0035] DETAILED DESCRIPTION

[0036] As used herein, in every embodiment, it must be understood that the term ‘hydrophobic coating’ refers to a coating which when applied on a transparent substrate repels water.

[0037] The term ‘durability’, as used herein, refers to the increased chemical resistance, abrasion resistance, glass corrosion resistance and minimized UV degradation of the surface of the glass substrate coated with the hydrophobic coating.

[0038] The term ‘glass substrate’ or ‘transparent substrate’, as used herein, interchangeably, refers to a solid-like and transparent material that is used in numerous applications in our daily lives. As referred herein, the substrate is glass which is made from natural and abundant raw materials (sand, soda ash, limestone, boron-based compounds, alumina, etc.) that are melted at very high temperature to form a new material.

[0039] The term ‘silanol terminated siloxane-based polymers’, as used herein, very well known to a person skilled in the art, refers to medium and high viscosity hydroxyl terminated linear polydimethylsiloxane, also known as OH polymer.

[0040] The present disclosure provides a hydrophobic coating composition for substrates in hot and humid conditions. The said composition comprising at least one siloxane based active agent, at least one surfactant, at least one co-surfactant, a diluent and dispersing medium at select ratio. The said coating is inherently having low surface energy making it hydrophobic in nature.

[0041] The said hydrophobic coating composition prevents adsorption of water from atmospheric humidity and its spreading over glass surface. This limits the formation of continuous water film contrarily to water spreading readily on uncoated glass surface. This in turn restricts chemical transformation of glass via cation-exchange process reducing eventual weathering of glass surface and thus the coating acts like a physical barrier layer. However, coating will not limit the droplet condensation. This is like lotus-leaf effect where water can condense on the surface but not wet the surface.

[0042] In every embodiment of the present disclosure, the hydrophobic coating is formed by optimum ratio of siloxane based active agent surfactant, co-surfactant alcohol diluent and water. The hydrophobic coating can be coated in extremely thin layer and coating thickness can range between 100 nm to 10000 nm.

[0043] In every embodiment of the present disclosure, the hydrophobic coating composition having a pH between 5 and 7.

[0044] In every embodiment of the present disclosure, the siloxane-based protection coating was deposited on the glass from oil-in-water micro-emulsion. Micro-emulsions are thermodynamically stable consisting of micro-domains of oil in water with interfaces stabilized using surfactants. Most commonly, mixture of surfactant and co-surfactant is used. Nature of silicone oil defines the selection of other ingredients of microemulsions.

[0045] The active agent in every embodiment of the present disclosure is silanol terminated siloxane-based polymers like but not limited to silanol terminated dimethyl siloxanes [A], silanol terminated dimethyl diphenyl siloxanes copolymer [B], silanol terminated dimethyl aminopropylmethyl siloxane copolymer [C], silanol terminated dimethyl aminoethylaminopropylmethyl siloxane copolymer [D], Structure is as shown below,

[0046] In a specific embodiment, the active agent is preferably silanol terminated dimethyl aminoethylaminopropylmethyl siloxane copolymer [D] It is readily commercially available e.g Wacker Finish WR 1100LV from Wacker Chemie, , Variphob MS3000 from CHT and so on. It is widely known as fabric softener, textile and leather finishes. Recently, use of this chemical for non-porous surfaces like glass has been primarily for its anti-microbial property. Repeat unit ratio of dimethyl siloxane and aminoethyl aminopropyl methyl siloxane can be range from 85:15 to 99.99:0.01.

[0047] In a specific embodiment, the active agent is in form of viscous oil with viscosity in range between 800-7000 cps, preferably between 4000-7000 cps.

[0048] In a specific embodiment, the amine value for active agent can range between 4-10 mg of KOH / gm, preferably it should be between 7-10 mg of KOH / gm.

[0049] In a specific embodiment, average molecular weight of the active agent can range between 25000-35000, preferably between 27000-32000. The number average molecular weight should range between 10000-25000, preferably between 22000- 25000.

[0050] In a specific embodiment, the active having poly dispersity index ranging between 1.1- 2.1, preferably 1.2-1.4.

[0051] In a specific embodiment, the active having Silicon content in the range of 7-14, preferably 11-12.

[0052] In every embodiment of the present disclosure, stability of microemulsion depends on choice of surfactants. The choice of surfactants is also governed by the type of microemulsion to be formulated. Surfactants with low HLB (hydrophile-lipophile balance) ranging between 3-6 are preferred for water-in-oil emulsion whereas surfactants with high HLB ranging between 8-18 are preferred for oil-in-water emulsions. Typically, for microemulsions, combination of low HLB and high HLB surfactants are needed to attain good stability and shelf life.

[0053] In a specific embodiment, the surfactant is selected from the group comprising ethoxylated alcohols. Preferably, C12-C14-alcohol polyethylene glycol ether. More preferably, C12-C14-alcohol polyethylene glycol ether having 2 to 10 oxy ethylene units (2 to 10 EO).

[0054] In a specific embodiment, C12-C14-alcohol polyethylene glycol ether (8 EO) with high HLB of 13 was used in combination with C12-C14-alcohol polyethylene glycol ether (2 EO) with low HLB of 8. Surfactants are chosen such that their cloud point is above 60 degree C to ensure stability at room conditions.

[0055] In every embodiment of the present disclosure, in order to sufficiently lower the interfacial tension in microemulsions, co- surfactants are added.

[0056] In a specific embodiment, co- surfactants are primarily amphiphilic short-chain molecules e.g. short-chain alcohols. They bring down the surface tension close to zero in microemulsion. Carbon chain length ranging from C2-C10 facilitate interaction of short-chain alcohols with monolayers of surfactant molecules at interface enabling their packing. In a preferred embodiment, 1 -Heptanol 2-propyl is used as co-surfactant to achieve thermodynamically stable microemulsion.

[0057] In a specific embodiment, co-surfactants are cationic co-surfactants. In a preferred embodiment, hexadecyl trimethyl ammonium bromide is used. It has very high HLB of 21. Addition of cationic co-surfactant improves the surface wettability on glass surface. In every embodiment of the present disclosure, the diluent is an alcohol. In a preferred embodiment, the alcohol diluent is 2-Propanol.

[0058] In a specific embodiment of the present disclosure, the dispersant medium is water.

[0059] In a specific embodiment of the present disclosure, the hydrophobic coating composition comprising one or more silanol terminated siloxane polymer in the amount of from 3 to 9 wt%.

[0060] In a specific embodiment of the present disclosure, the hydrophobic coating composition comprising at least one nonionic surfactant in the amount of from 0.5 to 5 wt.

[0061] In a specific embodiment of the present disclosure, the hydrophobic coating composition comprising at least one co-surfactant in the amount of from 0.1 to 2 wt%.

[0062] In a specific embodiment of the present disclosure, the hydrophobic coating composition comprising diluent in the amount of from 20 to 80 wt%.

[0063] In a specific embodiment of the present disclosure, the hydrophobic coating composition comprising dispersion medium in the amount of from 20 to 80 wt%.

[0064] Hydrophobic property is a surface phenomenon, especially in present disclosure. To ensure the durability of coating, hydrophobicity was evaluated. It is significant to understand that any change in hydrophobicity of the surface coated with the hydrophobic coating, after weathering test, abrasion test, chemical durability indicate that surface has been modified which in turn implies that hydrophobic property is altered. Generally, hydrophobicity of a surface is described with the term ‘contact angle’. The contact angle is also associated with determining the durability of the coated surface against chemicals. Thus, contact angle measurement was predominantly used as a technique to quantify the durability of coating. A contact angle > 90 degrees suggest presence of coating on the surface with uniform coverage. Decrease in contact angle below 90 degrees can be associated with non-uniform erosion of coating. Contact angle > 70 degree is generally accepted for glass in vertical applications like facade, balustrades, railings, windows, etc.

[0065] The coated glass substrate produced in accordance with the present disclosure imparts resistant to glass corrosion, abrasion resistant, chemically durable and UV degradation.

[0066] Advantageously said hydrophobic coating composition described in the present invention exhibits durability against abrasion as well as UV exposure by retaining its hydrophobic character. It additionally demonstrates easy-to-clean property. Also said hydrophobic coating composition is non-halogenated in nature. Formulation is cured at room temperature, thus, overall reducing energy requirement for coating process and lowering its carbon footprint compared to temperature cured sol-gel coatings.

[0067] Then hydrophobic coating in accordance with the present disclosure imparts Colourless, transparent (Haze < 1) and Sub-micron (thickness of 100-1000 nm) coating on the surface of the substrate and which does not impart mat as well as gloss finish.

[0068] The present disclosure also discloses a method of making a hydrophobic coated glass is provided. Said method involves cleaning a glass substrate having a first surface and a second surface, coating the hydrophobic coating composition comprising one or more silanol terminated siloxane polymer, at least one nonionic surfactant selected from the group consisting of Cl 2- 14 alcohol ethoxylates, at least one co-surfactant, alcohol diluent, and water at select ratio on at least one surface of the glass substrate, drying the coated surface of the glass substrate at room temperature for about 1 minute or curing the coated surface at temperature of from 100 to 150 °C, and washing with water to rinse off the surfactant from the surface to obtain a hydrophobic coated glass. In a preferred embodiment of the present disclosure, the coated surface is dried at room temperature to reduce energy requirement for coating process and lower its carbon footprint compared to temperature cured sol-gel coatings.

[0069] The present disclosure further discloses a hydrophobic coated glass comprising a glass substrate with at least one of its two surfaces coated with the hydrophobic coating composition.

[0070] In a specific embodiment of the present disclosure, the thickness of the hydrophobic coating on the glass substrate is 100 to 1000 nm.

[0071] In a preferred embodiment of the present disclosure, the thickness of the hydrophobic coating on the glass substrate is 100 to 500 nm.

[0072] In an embodiment of the present disclosure, the hydrophobic coated glass having contact angle of > 90°.

[0073] In an embodiment of the present disclosure, the hydrophobic coated glass having improved durability. In a preferred embodiment the hydrophobic coating on the glass substrate having improved durability of more than 5 years.

[0074] In an embodiment of the present disclosure, the hydrophobic coating on the glass substrate provides protection against weathering.

[0075] In an embodiment of the present disclosure, the hydrophobic nature of the coated glass surface demonstrates easy-to-clean property. In an embodiment of the present disclosure, the substrate can be transparent substrate or glass substrate, ceramic substrate and metal substrate. In a preferred embodiment, the substrate is glass substrate. Preferably, the hydrophobic coated glass substrate according to the present disclosure, may be used in exterior glasses such as architectural applications like balustrades, railings, windows glass, door glass and facade as well as automotive applications such as windshield, sidelite windows, backlites, may be used in interior glasses such as shower glass, kitchen shutters, glass furniture and mirror, may also be used in value added glasses such as frosted (acid etched, sand blasted or grit blasted) glass and glass with ceramic frit coating.

[0076] EXAMPLES

[0077] Example 1

[0078] Table 1:A Hydrophobic Coating Formulation

[0079] Preparation of hydrophobic coating formulation

[0080] To prepare the said coating formulation, the active agent was mixed with water and surfactants for 2 hour using overhead stirrer at 1000 rpm. Glacial acetic acid was added to mixture while stirring to adjust the pH between 5.5-6.5. Lastly, iso propyl alcohol was added to the mixture and was mixed for 5 minutes with stirring speed reduced to 400 rpm. To assess the stability of formulation, the coating formulation was placed in sealed container for 6 months under room condition and was observed to be stable with similar end properties for coating.

[0081] Stability of microemulsion was evaluated for particle size distribution. Said formulation of microemulsion is stable up to 6 months.

[0082] Preparation of hydrophobic coated glass

[0083] To apply the hydrophobic coating on the surface, non-porous surfaces like glass is cleaned with water and lint free tissue paper. Coating can also be applied on glasses cleaned with industrial brush washing machine. Coating volume of 7-10 ml / m2 was sprayed and wiped using lint free tissue paper.

[0084] Advantage for Example 1 is that this coating can be applied directly on surface without any pretreatment like priming, plasma treatment or corona treatment. This is, thus, one step process of coating application. Additional, advantage for Example 1 is applied coating will dry within 1 min at 30 degree C (under room conditions) eliminating need of high temperature curing as necessary for sol-gel coatings.

[0085] Excess coating has to be washed off with water leaving behind the coating layer which has reacted with glass. Excess coating leads to haze which after washing leads to clear transparent glass. Change from hydrophilic surface to hydrophobic surface can be evidently seen during washing. Lastly, coated surface is to be wipe with iso-propyl alcohol to remove traces of unreacted silicone. Wiping with iso propyl alcohol will result in clear coating. Coated glass is ready to use and test.

[0086] Terminal hydroxyl group in active agent are reactive in nature and chemically bind with hydroxyl group from freshly cleaned surfaces of substrate. Due to covalent bonding at terminal end, it significantly improves the durability to the coating. Presence of dimethyl siloxane as a repeat unit, this coating is naturally hydrophobic in nature. Thus, contact angle measurement was predominantly used as a technique to quantify the durability of coating. Minimum of 5 readings are taken across the surface to validate uniformity of coating upon exposure to various conditions. Contact angle > 90 degree suggest presence of coating on the surface with uniform coverage.

[0087] Weather resistance property:

[0088] Results obtained for disclosed formulation are discussed below.

[0089] Coating was applied on annealed as well as tempered glass substrate for UV resistance test. Evaluation was made using two different equipment viz. QUV from QLabs and Ci4000 Weather-O-Meter from Atlas Instruments with different conditions. For QUV, UVA 340nm light source was used with 0.55 W / m2 intensity and back panel temperature of 62 degree C. Whereas for Ci4000 Weather-O-Meter, broad spectrum UV source with wavelength of 300-400 nm was used. UV Intensity was 42 W / m2, with back panel temperature of 47 degree C, RH 40% and chamber temperature of 35 degree C.

[0090] Figure 1 and 2, clearly highlights the stability of coating against UV light irrespective of UV exposure conditions employed. Also, no significant change is observed in contact angle even after 1000 hours of continuous UV exposure for both the conditions and for both annealed and tempered glass substrates. Contact angle remained above 90 degree maintaining its hydrophobic nature, which demonstrate resistance of coating against UV degradation.

[0091] Similar promising results were obtained when coating is applied on air side and tin- side of tempered glass and was tested for UV resistance.

[0092] Figure 3 clearly highlights the stability of coating against UV light irrespective of surface characteristics and UV exposure conditions employed. No significant change is observed in contact angle even after 1000 hours of continuous UV exposure for both coating applied on air-side and tin-side when exposed in QUV.

[0093] Coating applied on air-side continues to display splendid results even in severe conditions presented in Ci4000 Weather-O-Meter. However, minor drop in contact angle for coating applied on tin-side was observed as seen from Figure 4. This is expected as tin-side has significantly less concentration of surface -OH groups. This leads to high concentration of unanchored terminal silanol groups to surface which then are susceptible to UV degradation. Nonetheless, contact angle remains above 85 degrees after exposure for 1000 hours. This demonstrates that coating can be applied on both air-side and tin-side of glass while maintaining its performance and displaying resistance against UV degradation.

[0094] High temperature test was carried out at 55 degree C in convection oven to assess the stability of coating towards very high ambient temperatures. This test was carried out for both coating applied on annealed and tempered glass. Contact angles remained above 85 degree for both the samples even after 1700+ hours at 55 degree C, as seen from Figure 5. This exemplifies the thermal stability of coating. Table 2: Haze Value for Coated and Uncoated Glass substrate

[0095] Table 2 discloses corresponding haze values signifying the weather resistance property, according to Example. For accelerated weathering conditions mimicking hot and humid atmosphere, test was carried out 55 degree C at RH 95% in HCP 240 Humidity chamber from Memmert. This test was carried out for both coating applied on annealed and tempered glass. Surface of coated glass was evaluated by observing under microscope along with contact angles measurements being carried out over the duration of exposure. First sign of weathering products was observed at 1750 hours exposure. Interestingly, significantly less concentration of weathering products was observed on coated glass after 1750 hours as compared to uncoated reference glass which showed the high weathered products on surface within 336 hours (refer Figure 6). After measuring the contact angle, coated glass surface was scrubbed with water and microfiber cloth. The cleaned surface was re-examined under microscope. Astonishingly surface was completely cleaned, and the contact angle was also regained to 85 degree + for both the samples. Test was continued till 2080 hours at which point, no evident weathering product were observed under microscope while contact angle was also maintained as evident from Figure 7. This convincingly concludes that disclosed formulation in Example 1 provides weathering resistance to glass surface irrespective of annealed or tempered nature of glass.

[0096] Haze values observed for annealed and tempered samples in Figure 6 and Figure 7 are shown in table 2. Uncoated glass develops excessive haze within 336 hours due to salt formation on surface, also evident from Figure 6. It is evident that coating restricts water film on glass surface, thus, reducing ionic migration from glass to outward surface. This lowers the development of haze as compared to uncoated glass. Whereas coated glass with five-times higher exposure duration, developed lower haze -47% which can be further removed completely.

[0097] Durability against abrasion is key property as it will be used to gauge the behavior of coating during regular maintenance cleaning during end use. Accordingly, coated tempered glass was evaluated for 5000 abrasion cycles in presence of water as cleaning medium using sponge wipe as abrader and under normal load of 400 g and 1000 g loads. From Figure 8, It is quite evident that coating is robust towards abrasion and maintains the contact angle ~90 degree even after 5000 abrasion cycles under 1000 g load.

[0098] Inventive examples to support technical significance have been provided: weather resistant property in terms of coating stability against UV exposure, contact angle above 900maintaining its hydrophobic nature, stability of coating towards very high ambient temperatures, durability against abrasion and lowered development of haze values.

Claims

We Claim:

1. A hydrophobic coating composition for glass substrates, comprising: a. one or more silanol terminated siloxane polymer in the amount of from 3 to 9 wt%; b. at least one nonionic surfactant selected from the group consisting of Cl 2- 14 alcohol ethoxylates in the amount of from 0.5 to 5 wt%; c. at least one co-surfactant in the amount of from 0.1 to 2 wt%; d. 20 to 80 wt% of alcohol diluent; and e. 20 to 80 wt% of water, wherein the said composition having pH in range from about 5 to 7.

2. The hydrophobic coating composition as claimed in claim 1, wherein the said composition is a microemulsion.

3. The hydrophobic coating composition as claimed in claim 2, wherein the microemulsion is oil-in-water micro-emulsion.

4. The hydrophobic coating composition as claimed in claim 1 , wherein the silanol terminated siloxane polymer is free of halogen containing compounds.

5. The hydrophobic coating composition as claimed in claim 1 , wherein the silanol terminated siloxane polymer is selected from the group consisting of silanol terminated dimethyl siloxanes, silanol terminated dimethyl diphenyl siloxanes copolymer, silanol terminated dimethyl aminopropylmethyl siloxane copolymer or silanol terminated dimethyl aminoethylaminopropylmethyl siloxane copolymer.

6. The hydrophobic coating composition as claimed in claim 1 , wherein the silanol terminated siloxane polymer having viscosity in range between 800-7000 cps, preferably between 4000-7000 cps.

7. The hydrophobic coating composition as claimed in claim 1 , wherein the silanol terminated siloxane polymer having an average molecular weight of between 25000 and 35000, preferably from 27000 to 32000.

8. The hydrophobic coating composition as claimed in claim 1 , wherein the silanol terminated siloxane polymer having Polydispersity index ranging between 1.1 to 2.1, preferably 1.2 to 1.4.

9. The hydrophobic coating composition as claimed in claim 1 , wherein the silanol terminated siloxane polymer having Silicon content in the range of 7 tol4, preferably 11 to 12.

10. The hydrophobic coating composition as claimed in claim 1, wherein the nonionic surfactant is preferably Cl 2- 14 alcohol ethoxylates having 2 to 10 oxy ethylene units.

11. The hydrophobic coating composition as claimed in claim 1 , wherein the cosurfactant is selected from the group consisting of short-chain alcohols or cationic surfactant.

12. The hydrophobic coating composition as claimed in claim 11, wherein the short-chain alcohol is 2-Propyl-l -heptanol.

13. The hydrophobic coating composition as claimed in claim 11, wherein the cationic surfactant is Hexadecyltrimethylammonium bromide.

14. The hydrophobic coating composition as claimed in claim 1, wherein the alcohol diluent is 2-Propanol.

15. The hydrophobic coating composition as claimed in claim 1, wherein the composition further comprising pH adjuster.

16. The hydrophobic coating composition as claimed in claim 15, wherein the pH adjuster is Glacial acetic acid.

17. A method of making a hydrophobic coated glass comprising the steps of: cleaning a glass substrate having a first surface and a second surface; coating the hydrophobic coating composition as claimed in claim 1 on at least one surface of the glass substrate; drying the coated surface of the glass substrate at room temperature for about 1 minute or curing the coated surface at temperature of from 100 to 150 °C ; and washing with water to rinse off the surfactant from the surface to obtain a hydrophobic coated glass.

18. The method of making a hydrophobic coated glass as claimed in claim 17, wherein the step of coating the hydrophobic coating composition on the glass substrate is done by spraying or wiping technique using lint free tissue paper.

19. A hydrophobic coated glass comprising a glass substrate with at least one of its two surfaces coated with the hydrophobic coating composition as claimed in claim 1.

20. The hydrophobic coated glass substrate as claimed in claim 19, wherein the hydrophobic coating has a thickness ranging between 100 to 500 nm.

21. The hydrophobic coated glass substrate as claimed in claim 19, wherein the hydrophobic coated glass having contact angle of > 90°.

22. The hydrophobic coated glass substrate as claimed in claim 19, wherein the hydrophobic coated glass having improved durability.