WO2021171309A1

WO2021171309A1 - A heat treatable reflective coating and a coated article thereof

Info

Publication number: WO2021171309A1
Application number: PCT/IN2021/050175
Authority: WO
Inventors: Arun RAM MOHAN; Gowtham MANOHARAN
Original assignee: Saint-Gobain Glass France
Priority date: 2020-02-26
Filing date: 2021-02-24
Publication date: 2021-09-02

Abstract

The present disclosure provides a heat treatable reflective coating (110) that is deposited on a transparent substrate (102) comprising, a functional layer (104) comprising essentially of silicon and a protective layer (106) comprising essentially silica with carbonaceous material on a glass side surface (102a) of the transparent substrate (102); and an enamel layer (108) on a tin side surface (102b) of the transparent substrate (102). The transparent substrate (102) has increased light reflection and improved abrasion resistance and exhibits no visible scratches or defects post heat treatment. This disclosure also provides a method for depositing the disclosed coating and an article (100) which is coated with the heat treatable reflective coating (110).

Description

A HEAT TREATABLE REFLECTIVE COATING AND A COATED ARTICLE

THEREOF

FIELD OF THE INVENTION The present invention generally relates to a heat treatable coating on a transparent substrate. More particularly, the present invention relates to a heat treatable reflective coating on a glass and coated articles formed thereon, specifically for kitchen appliances having excellent light reflection and no visible scratches or defects post the heat treatment of the coated article. BACKGROUND

Generally, heat treatable reflective coatings include a transparent substrate comprising a reflective stack and an enamel layer. Heat treatable coatings are known in the art. For example, such coatings are widely used on glass in electronics, lighting, appliances, architectural, and display applications. Specifically, glass with heat treatable reflective coatings has found wide applications in home appliances. Reflective coatings deposited on the transparent glass substrate modulate the optical properties of the coated glass articles.

Tempering of such coated glasses for application in home / kitchen appliances is done by passing the coated glass through a series of hot ovens. It should be noted that the reflective coating should survive the tempering process and thereby retain their optical properties post the thermal treatment. For home appliances such as oven doors, refrigerator doors, lids for cookers used for food processing, top for gas stoves used in cooking or lids/closing aids for related appliances, the doors require to be reflective and further require enamel printing on the side opposite to the side provided with the reflective coating. The heat treatable reflective coating is provided on the glass substrate by an online chemical vapor deposition process known as CVD during the float glass manufacturing process. The enamel printing is provided on the glass side which is in contact with the molten tin bath during the float glass manufacturing process. The heat treatable reflective coating is deposited on the molten glass ribbon by an online chemical vapor deposition process to make the transparent glass substrate reflective. While printing enamel on the glass side, the reflective coating comes in contact with the conveyor belt and is pressed against it during printing. Post enamel printing, the reflective coating is again in contact with a series of mechanical rollers that convey the coated article to a dryer for drying the enamel. Following which, the enamel curing and the glass tempering processes happen simultaneously in a tempering furnace where the reflective coating is in contact with the rollers and the enamel faces the air side. During tempering, the coated article is exposed to heat and is taken back and forth in the furnace. The contact between the heat treatable reflective coating and the rollers can introduce scratch marks on the coated surface due to abrasion which becomes more visible on the coating post the tempering process. The visibility of such defects on the coating increases with the coating reflection.

Patent documents W02017/141052 Al, US 57981492, US 6 881 487 B2, W02010/011598 A2 disclose single layer CVD coatings and multilayer coating stacks for obtaining reflective glass articles. However, these documents do not cover the temperability of the coatings for home appliances. US 6 881 487 B2 does not discuss the impact of heat treatment of the proposed glass coating system when the coating side of the glass is in contact with the solid roller.

W02010/011598 A2 describes a single layer mixed oxide matrix coating made up of iron oxide, cobalt oxide and chromium oxide deposited on a transparent glass substrate by spray pyrolysis in the annealing lehr at a substrate temperature of 600 °C. This coating can be tempered for oven door application. However, spraying of a liquid solution containing chromium precursor poses environmental safety hazards during the spray process and further poses disposal hazard of the coated glass article. Referring to patent document US 2014/0267952 Al, provides abrasion resistant coatings which are interpenetrating layers of siloxane and diamond-like carbon are applied on glass substrates after chemical tempering of the substrate. These coatings find application in electronic devices. The purpose of these coatings is to protect the substrate surface from finger printing marks or scratches while handling the mobile devices. However, these coatings are not applicable for kitchen appliances that are subjected to thermal tempering as the temperature conditions are aggressive enough to destroy these coating.

US 6171646 B1 provides undoped tin oxide coating deposited on a glass substrate pyrolytically to increase the hardness and wear resistance of the glass. The roughness of the coating was reduced by polishing the coating with the alumina grains. The polished coating is sprayed with polyethylene solution to fill the gaps. Again this coating would not be useful for kitchen appliances as additional polymer coating (such as enamel) which come in contact with the rollers during tempering may cross-contaminate the coating leaving defects on the surface.

Thus the prior art documents largely discuss the protection of either the optical coatings or the transparent glass substrate from vandalism or scratch or abrasion resistance. The performance of some of these coatings post processing, i.e., post heat treatment is not known especially when desired to be used for home appliances. The home appliances market which includes baking ovens needs a reflective surface that can be used as an oven door so that the edible contents inside the oven are not visible during food processing. The existing state of art neither address tempering of the substrate with the coating side in physical contact with the roller nor teaches durability of the glass substrate to withstand abrasion during enamel printing on the glass slide when the coating side is in physical contact with the roller or conveyer belt. Therefore, heat treatable coatings that have enhanced durability and abrasion resistance are significant.

There is a need for providing heat treatable reflective coatings for home / kitchen appliances, with improved light reflection, abrasion resistance and at the same time coatings that do not develop visible scratches or defects post the heat treatment of coated article. The present invention proposes such a heat treatable reflective coating and further addresses the drawbacks associated with the conventional reflective coatings on glass discussed earlier in the prior art references.

OBJECT OF THE INVENTION

The object of the present invention is to provide a heat treatable reflective coating on a transparent substrate, and also a method for depositing such a coating on the transparent substrate, such that the coating does not develop visible scratches or defects post the heat treatment of the transparent substrate, coated with the reflective coating.

Another object of the present invention is to provide a heat treatable reflective coating on one side of the transparent substrate, with improved light reflection and abrasion resistance while enamel printing on the other side of the transparent substrate. Yet another object of the present invention is to provide a heat treatable reflective coating on a transparent substrate, specifically for kitchen appliances like oven doors, such that the edible contents inside the oven are not visible. SUMMARY OF THE INVENTION

In an aspect, the present invention provides a heat treatable reflective coating deposited on a transparent substrate comprising, a functional layer comprising essentially silicon and a protective layer comprising silica with carbonaceous material on a glass side surface of the transparent substrate; and an enamel layer on a tin side surface of the transparent substrate. In another aspect, the present invention provides a method for depositing a heat treatable reflective coating on a transparent substrate during manufacturing of the transparent substrate in a float bath.

In yet another aspect, the present invention provides a coated article comprising a transparent substrate and a heat treatable coating formed over the transparent substrate. The coating comprises a functional layer and a protective layer deposited on the transparent substrate on a glass side surface; and an enamel layer on a tin side surface.

The other features of the present invention will be described in detail in conjunction with the accompanying drawings and the specific embodiments, but not limit the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings.

FIG. 1 illustrates a coated article 100 according to one embodiment of the present disclosure.

The use of the same reference symbols in different drawings indicates similar or identical items.

Skilled artisans appreciate that elements in the drawings 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 various embodiments of the disclosure. DETAILED DESCRIPTION

The following description, in combination with the figures, is provided to assist in understanding the teachings disclosed herein. The following discussion will focus on specific implementations and embodiments of the teachings. This discussion is provided to assist in describing the teachings and should not be interpreted as a limitation on the scope or applicability of the teachings.

Note that not all of the activities described in the general description or the examples are required, that a portion of a specific activity may not be required, and that one or more further activities may be performed in addition to those described. Still further, the order in which activities are listed is not necessarily the order in which they are performed.

The specification and illustrations of the embodiments described herein are intended to provide a general understanding of the structure of the various embodiments. The specification and illustrations are not intended to serve as an exhaustive and comprehensive description of all of the elements and features of systems that use the structures or methods described herein. Certain features, that are for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in a sub combination. Further, reference to values stated in ranges includes each and every value within that range. It will further be understood that no limitation of the scope of the disclosure is thereby intended, such alterations and further modifications in the disclosed composition, system, product and method, and such further applications of the principles of the disclosure therein being contemplated as would normally occur to one skilled in the art to which the disclosure relates.

The description in combination with the figures is provided to assist in understanding the teachings disclosed herein, is provided to assist in describing the teachings, and should not be interpreted as a limitation on the scope or applicability of the teachings.

As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having" or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a method, article, or apparatus that comprises a list of features is not necessarily limited only to those features but may include other features not expressly listed or inherent to such method, article, or apparatus. Further, unless expressly stated to the contrary, "or" refers to an inclusive-or and not to an exclusive-or.

The use of "a" or "an" is employed to describe elements and components described herein. This is done merely for convenience and to give a general sense of the scope of the invention. This description should be read to include one or at least one and the singular also includes the plural, or vice versa, unless it is clear that it is meant otherwise.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The materials, methods, and examples are illustrative only and not intended to be limiting. To the extent that certain details regarding specific materials and processing acts are not described, such details may include conventional approaches, which may be found in reference books and other sources within the manufacturing arts.

Reference throughout this specification to “one embodiment” “an embodiment” “alternate embodiment” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of such phrases throughout this specification may, but do not necessarily, all refer to the same embodiment.

The main aspect of the present invention is to provide a heat treatable reflective coating on a transparent substrate, for application in home / kitchen appliances, more specifically in oven doors, refrigerator doors, lids for cookers used for food processing, top for gas stoves used in cooking, in which the s door is desired to have improved light reflection, abrasion resistance, and exhibits no visible scratches or defects post heat treatment.

“Heat treatable” in accordance with the present disclosure refers to thermal treatment involving heat strengthening and/or toughening processes and to other thermal processes during which the coated glass article reaches temperatures ranging between 600 °C to 750 °C.

Generally, in a float glass manufacturing process, a small amount of tin is absorbed by the glass that is in contact with the tin bath. This side of the glass is known as the “float or tin side” in accordance with the present disclosure, which is very well known to a person skilled in the art. The opposite side, which is not in contact with molten tin and in contact with float atmosphere (a mixture of nitrogen and hydrogen), is known as the “air side or glass side” which again is very well known to a person skilled in the art. FIG. 1 illustrates a coated article 100 according to one embodiment of the present disclosure. In accordance with the present invention the transparent substrate 102 in FIG. 1 comprises two surfaces, glass side 102a and tin side 102b. The glass side 102a is deposited with a heat treatable reflective coating 110 and the tin side 102b is provided with an enamel printing. The heat treatable reflective coating 110 is deposited on the glass side 102a by way of chemical vapor deposition method which is further detailed in the description.

Referring to FIG. 1, various embodiments of the heat treatable reflective coating 110 in accordance with the present disclosure are illustrated. The heat treatable reflective coating 110 is deposited on the transparent substrate 102 comprising a functional layer 104 and a protective layer 106. The functional layer 104 essentially comprises of silica and the protective layer 106 essentially comprises silica containing a carbonaceous material.

The coated article 100 in accordance with the present disclosure has a light reflection R_L ranging between 20% and 61% on the glass side 102a. In a preferred embodiment the light reflection of the coated article 100 is 35%.

In accordance with an embodiment the heat treatable reflective coating 110 has a thickness ranging between 15 nm and 70 nm. In a preferred embodiment the thickness of the heat-treatable reflective coating 110 is between 30nm and 55 nm.

In accordance with an embodiment the thickness of the functional layer 104 ranges between 19 and 35 nm. In a preferred embodiment the thickness of the functional layer 104 is between 25 and 32 nm. The functional layer 104 in accordance with the present invention comprises silicon predominantly, which is a mixture of silicon and silicon oxycarbide.

The functional layer 104 in accordance with the present disclosure comprises silicon, oxygen and carbon. The functional layer 104 essentially comprises silicon in the range of 30 to 50 atomic percentage. In a preferred embodiment silicon present in the functional layer 104 is 43 atomic percent. The functional layer 104 also comprises oxygen in the range of 35 to 45 atomic percentage, and carbon in the range of 6 to 10 atomic percentage. In a preferred embodiment oxygen and carbon is present in 41 atomic percent and 9 atomic percent, respectively.

The functional layer 104 in accordance with the present disclosure is a functional coating that makes the transparent substrate 102 provided with the heat treatable coating 110 to be reflective. The purpose of the functional layer 104 in accordance with the present invention is to prevent the contents / things on the tin side 102b of the transparent substrate 102 from being visible. Specifically, in home / kitchen appliances such as oven doors, it prevents the edible contents inside the oven from being visible. In accordance with an embodiment the thickness of the protective layer 106 ranges between 15 to 40 nm. In a preferred embodiment the thickness of the protective layer 106 is between 20 nm and 30 nm.

The protective layer 106 in accordance with the present invention comprises silica containing a carbonaceous material, which is preferably in the form of silicon oxycarbide. The protective layer 106 in accordance with the present disclosure comprises silicon, oxygen and carbon. The protective layer 106 essentially comprises carbon in the range of 10 to 20 atomic percentage. In a preferred embodiment carbon is present in 16 atomic percent. The protective layer 106 also comprises silicon in the range of 20 to 35 atomic percentage, and oxygen in the range of 45 to 60 atomic percentage. In a preferred embodiment silicon and oxygen is present in 24 atomic percent and 50 atomic percent, respectively.

The protective layer 106 in accordance with the present disclosure is a protective coating deposited on top of the functional layer 104 to enhance its mechanical durability. The protective layer 106 eliminates the use of a temporary sacrificial polymer coating commonly used in conventional coatings, that has to be applied before tempering to protect the reflective coating on glass. The heat treatable reflective coating 110 due to the presence of the protective coating 106 has improved mechanical durability during post processing of the transparent substrate 102 where the coating is in contact with the conveyor belts or rollers during the enamel printing, drying and tempering processes. The transparent substrate 102 further comprises an enamel layer 108 on the tin side surface 102b of the transparent substrate 102. In an embodiment the enamel layer 108 partially covers the circumferential area of the transparent substrate 102. In an alternate embodiment the enamel layer 108 can also cover the tin side 102b of the transparent substrate 102 completely. In an embodiment the heat treatable reflective coating 110 can be deposited on a transparent substrate 102 of varying thickness. The transparent substrate 102 in accordance with the present disclosure is selected from but not limited to a lacquered glass, a colored glass, a tinted glass, a laminated glass, a patterned glass, soda-lime-silica glass, borosilicate glass, alumino silicate glass, vycor, fused silica and vitreous silica or the like. In a preferred embodiment the transparent substrate 102 is soda lime glass.

In an embodiment the soda lime glass substrate 102 can be a tinted substrate or a clear substrate. The tint of the soda lime glass substrate 102 can be bronze in color with a transmission value of 60.4%, a* = 2.5 and b* = 4.6. In another embodiment the clear soda lime glass substrate 102 has a transmission value of 90%, a* = -0.9 and b* = 0.3. The soda lime glass substrate 102 can also be grey in color with a transmission value of 26%, a* = -4 and b* = -2.2 or green in color with a transmission of 91%, a* = -6.8 and b* = 0.4 or blue in color with transmission ranging from 40 % to 70%, a* = -1.8 and b* ranging from -3 to -30.

The coated article 100 with the heat treatable reflective coating 110 in accordance with the present disclosure has a light transmission percentage ranging between 20% and 73%. In a preferred embodiment the light transmission percentage of the coated article 100 is around 35 ± 4%.

The coated article 100 with the heat treatable reflective coating 110 in accordance with the present disclosure has a refractive index ranging between 2 and 5. In a preferred embodiment the refractive index of the coated article 100 is 3.5.

The heat treatable reflective coating 110 deposited on the transparent substrate 102 in accordance with the present disclosure can withstand abrasion between 50 and 500 cycles. In a preferred embodiment the heat treatable reflective coating 110 on the transparent substrate 102 can withstand up to 500 cycles of abrasion with CS-IOF wheels during taber test and the coating transmission changes by less than 3% over 500 cycles. The heat treatable reflective coating 110 which is deposited on the transparent substrate 102 is heat treated to a temperature ranging between 630 °C and 710 °C. In a preferred embodiment the temperature is between 670 °C and 690 °C. The coated article 100 with the heat treatable reflective coating 110 does not develop any visible scratch or defects post the heat treatment due to the presence of the protective coating 106 which protects the heat treatable reflective coating 110 in contact with the rollers during the heat treatment process from any abrasion defects.

Another aspect of the present invention is to provide a method for depositing the heat treatable reflective coating 110 on the transparent substrate 102 by way of chemical vapor deposition (CVD). The method for depositing the heat treatable reflective coating 110 on the transparent substrate 102 during manufacturing of the transparent substrate 102 comprises, providing two chemical vapor deposition beam assemblies during the float glass manufacturing process for the deposition of a functional layer 104 and a protective layer 106.

The two chemical vapor deposition beam assemblies comprise a gaseous mixture which is directed towards the transparent substrate 102. The first beam assembly is directed onto a glass side surface

102a of the transparent substrate 102 to deposit a functional layer 104, and the second beam assembly is directed onto the glass side surface 102a of the transparent substrate 102 coated with the functional layer 104 to deposit a protective layer 106, to form a heat treatable reflective coating 110 over the transparent substrate 102. In an embodiment the transparent substrate 102 is a molten float glass ribbon. The two chemical vapor deposition beam assemblies are used in a successive manner for the deposition of the coating on the molten glass ribbon in the float bath. These two beam assemblies are operated simultaneously and the deposition of the heat treatable reflective coating 110 is performed successively using the beams. The functional layer 104 is deposited when the molten glass ribbon is exposed to the gases from the first beam assembly. The protective layer 106 is deposited when the molten glass ribbon coated with the functional layer 104 is exposed to the gases from the second beam assembly. This deposition happens in a successive fashion. In accordance with the present disclosure the functional layer 104 essentially comprises of a composite coating predominantly rich in silicon and the protective layer 106 essentially comprises of a carbonaceous silica composite coating on the glass side surface 102a of the transparent substrate 102. The functional layer 104 and the protective layer 106 are deposited by a pyrolytic chemical vapor deposition process with a silicon containing compound, a hydrocarbon that acts as a radical scavenger and a diluent gas like argon or nitrogen.

The functional layer 104 is deposited on the molten glass ribbon by the pyrolytic chemical vapor deposition through the discharge of gases from the first beam assembly and the protective layer 106 is deposited on top of the functional layer 104 by pyrolytic chemical vapor deposition with the help of the second beam assembly located downstream of the first beam assembly. The composition of gases discharged on the top of the transparent substrate 102 is different in each of the two beam assemblies.

In an embodiment the silicon containing compound is a silane compound selected from but not limited to tetraethoxy silane Si(OC2H5)4, Silicon tetrachloride (SiCU) monochlorosilane (SiClfh), monosilane (SihL_t), disilane (S12H6) or trisilane (SnHx). In a preferred embodiment the source of silicon containing compound is monosilane (SihL_t).

In accordance with the present disclosure the hydrocarbon gas is used in this process as a radical scavenger. In a preferred embodiment the hydrocarbon gas is ethylene (C2H4), acetylene or propylene. In a most preferred embodiment the hydrocarbon gas is ethylene.

In an embodiment nitrogen (N2) is used as a preferred diluent to decrease the concentration of silicon containing species and hydrocarbon, thereby eliminating any powder formation.

In accordance with an embodiment the functional layer 104 which is deposited through the first beam comprises silane, ethylene and nitrogen. In a preferred embodiment the first beam comprises silane from 2% to 14%, ethylene from 10% to 20% and nitrogen from 80% to 90%. In a most preferred embodiment the first beam comprises silane from 7% to 10%, ethylene from ll% to 15% and balance nitrogen from 85% to 95%. In accordance with an embodiment the protective layer 106 which is deposited through the second beam comprises silane, ethylene and nitrogen. In a preferred embodiment the second beam comprises silane from 0.5% to 10%; ethylene from 5% to 20% and nitrogen from 70% to 85%. In a most preferred embodiment the second beam comprises silane from 0.5% to 4%, ethylene from 7% to 12% and nitrogen from 75% to 82%.

In an embodiment the intensity ratio of silicon to carbon in the heat treatable reflective coating 110 is in the range of 1% to 10%. In a preferred embodiment the intensity ratio of silicon to carbon is 2% to 6%.

In an embodiment the chemical vapor deposition beam assembly which is used for the deposition of the heat treatable reflective coating 110 is inserted preferably inside a tin bath. In another embodiment the beam assembly can also be inserted in the gap between the tin bath and the annealing lehr or in the very early part of the annealing lehr such that the suitable temperature of for the deposition of both the functional layer 104 and the protective layer 106 on the transparent substrate 102 is in the range of 600 °C and 750 °C. The transparent substrate 102 flows on the top of the tin bath from a furnace towards the annealing lehr. The float atmosphere is typically filled with nitrogen and hydrogen. In an embodiment the temperature for deposition of the functional layer 104 is in the range of 600 °C to 750 °C. In a preferred embodiment the temperature for deposition of the functional layer 104 is between 650 °C and 680 °C. As the transparent substrate 102 moves towards the annealing lehr, the protective layer 106 is deposited after the deposition of the functional layer 104 in the adjacent bay. In an embodiment the temperature for deposition of the protective layer 106 is in the range of 600 °C to 650 °C. In a preferred embodiment the temperature for deposition of the protective layer 106 is between 630 °C and 650 °C. Preferably, the transparent substrate 102 moves continuously through the float manufacturing chamber, such that the functional layer 104 and the protective layer 106 are deposited onto the transparent substrate 102 as it is moving in the float in a successive fashion through the chemical vapor deposition beam assemblies, at a lehr speed between 6 m per min and 20 m per min. In accordance with the present disclosure the deposition of the heat treatable reflective coating 110 can be performed by online or offline chemical vapor deposition. In a preferred embodiment, the deposition of the heat treatable reflective coating 110 is performed by online chemical vapor deposition. The heat treatable reflective coating 110 in accordance with the present disclosure can also be deposited on the transparent substrate 102 after the glass manufacture and in the cutting ribbon.

The transparent substrate 102 in accordance with the present invention is subjected to post processing operations, such as enamel printing, drying and tempering. The heat treatable reflective coating 110 in accordance with the present disclosure withstands abrasion during enamel printing on the glass slide 102a when the tin side is in physical contact with the roller or conveyer belt, and can be tempered with the tin side being in physical contact with the roller.

Conventionally, during the tempering of coated glass for architectural applications, the coating side always faces upwards in contact with air and the glass side faces downwards in contact with the metallic or a ceramic roller. A protective layer for protecting the coated surface from any abrasion during tempering is generally not necessary. Whereas while tempering glass articles intended to be used in home appliances, enamel is printed on the other side of the glass substrate and the side of the glass substrate coated with the reflective coating comes in contact with the roller.

For home appliances where the doors should be reflective, the enamel printing is on the tin side which is in contact with the molten tin during the float glass manufacturing process. The heat treatable reflective coating is deposited on the molten glass ribbon by an online chemical vapor deposition process to make the transparent glass substrate reflective. While printing enamel on the glass side, the coating is in contact with the conveyor belt and pressed against it. After enamel printing, the coating is in contact with mechanical rollers that convey the substrate to the dryer for drying the enamel. After enamel drying, the enamel curing and the glass tempering processes happens simultaneously in the tempering furnace where the coating is in contact with the rollers and the enamel is on the air side.

During tempering, the substrate is exposed to heat and it moves back and forth in the furnace. The coating is in contact with the rollers during tempering. Such contact introduces scratch marks on the coated surface that are more visible on the coating after tempering. The visibility of the defects increases with the coating reflection. These disadvantages are rectified with the heat treatable reflective coating 110 in accordance with the present invention.

In certain embodiments, the coated article 100 is subjected to a tempering step subsequent to deposition of the coating. The heat treatable reflective coating 110 survives exposure to the high temperatures required for tempering a glass substrate, such as a soda-lime glass substrate intended for interior, kitchen or architectural applications.

The coated article 100 with the heat treatable reflective coating 110 thus formed in accordance with the disclosed method has a light reflection (R_L) ranging between 20 % and 61% on the glass side 102a. It can pass up to 500 cycles during the taber abrasion with CS-IOF wheels where the transmission of the coated transparent substrate 102 changes by less than 3%, and exhibits no visible scratches or defects post heat treatment.

Yet another aspect of the present invention is to provide an article which is coated with the heat treatable reflective coating 110 in accordance with the present disclosure. The coated article 100 comprises a transparent substrate 102 and a heat treatable reflective coating 110 formed over the transparent substrate 102. The heat treatable reflective coating 110 comprises a functional layer 104 and a protective layer 106 deposited on the transparent substrate 102, using chemical vapor deposition method.

In accordance with the present disclosure the functional layer 104 essentially comprises of a coating rich in silicon and the protective layer 106 essentially comprises of silica containing carbonaceous material on a glass side 102a of the transparent substrate 102. The heat treatable reflective coating 110 in accordance with the present disclosure comprises an enamel layer 108 on a tin side surface 102b of the transparent substrate 102.

The coated article 100 has wide application in home / kitchen appliances, specifically in food processing appliances. In a preferred embodiment the coated article 100 is used as doors for kitchen appliances. The home appliances market which includes baking ovens need a reflective surface that can be used as an oven door so that the edible contents inside the oven are not visible during food processing. The home appliance or food processing appliance in accordance with the present disclosure possesses a closed cavity with a plurality of walls. At least one wall of the home appliance or food processing appliance comprises the reflective heat treatable coated article in accordance with the present disclosure. The closed cavity of home appliance or food processing appliance in accordance with the present invention is an oven, and specifically an oven door.

Although the heat treatable reflective coating 110 and method for depositing the same and the coated article 100 formed thereon are described herein in connection with interior applications and more specifically within a kitchen environment including oven doors, lids for cookers used for food processing, top for gas stoves used in cooking; the coating can be implemented for a wide variety of automotive and architectural applications, or any combination thereof, as desired.

The present invention is further disclosed by the following examples, which are intended for purposes of illustration and not limitation.

EXAMPLES

The following examples are provided to explain and illustrate the preferred embodiments of the heat treatable reflective coating of the present invention and do not in any way limit the scope of the invention as described and claimed:

Inventive Example 1:

Inventive example 1 discloses a double layer coating deposited by pyrolytic chemical vapor deposition on top of the molten glass ribbon inside the float. A first coater deposits a reflective coating on top of the glass ribbon. The concentration of silicon precursor and electron-donating hydrocarbon precursor in the gas phase discharged from coater 1 is in ranging between 1 to 12 % and 7 to 13% respectively. The temperature of the glass ribbon is between 650 °C and 700 °C during the deposition of the Layer 1 which is the reflective layer by the first coater. The temperature for the deposition of reflective Layer 1 is between 665 °C and 690 °C. The second layer denoted as Layer 2 is a protective layer deposited by pyrolytic chemical vapor deposition, on top of the reflective coating denoted as Layer 1 , by a second coater which is located downstream of the first coater. The protective coating Layer 2 is deposited on the substrate which is in the form of a molten glass ribbon inside the float. The concentration of silicon precursor and the electron donating hydrocarbon precursor in the gas phase discharged by the second coater for the deposition of the protective Layer 2 is between 1.1% to 6.8% and 3.8% to 14% respectively. The temperature of the glass ribbon for the deposition of Layer 2 is between 600 °C and 650 °C. The temperature for the deposition of Layer 2 that acts as a protective layer is between 630 °C and 650 °C. The silicon precursor is monosilane. The silicon precursor used is not restricted to monosilane. Chlorinated silane gases like dichlorosilane and tetrachlorosilane can also be used. The hydrocarbon precursor that acts as an electron donor can preferably be ethylene. It can also be propylene or acetylene.

The coating reflection of Inventive samples in accordance with the disclosure was measured by the spectrophotometer to be 31.8%. Both a* and b* values measured on the glass side were found to be negative. However, the values were not significantly large enough to result in blue colored reflection. The coating appeared more neutral. Alkali test was conducted by dipping the coated article in a IN solution of sodium hydroxide. The coated substrate remained immersed in the solution. The coating was found to withstand the aggressive alkaline environment for a minimum time period of 170 minutes. The coating described in this example can be deposited on clear substrate and any tinted soda lime glass substrate that would appear bronze, or blue or green by transmission without any coating.

Following the same procedure, samples of Inventive Examples 2-7 were also prepared using varying percentages of silicon precursor and the electron donating hydrocarbon in Layer 1 and Layer 2, in accordance with the present disclosure. Light transmission and reflectance values of all the samples were measured and are presented in table 1.

Table 1 describes Optical Properties of the Pyrolytic CVD Coatings on Glass Substrate.

The samples were further subjected to post production processing where each sample underwent each one of the following steps

Each sample was enamel printed on the glass side such that the coating was in contact with the conveyor belt and pressed against it when the enamel was poured over the screen and printed against the glass substrate.

After enamel printing, the sample is conveyed into the dryer with the help of the metallic rollers that may or may not be wrapped with Kevlar. The wet enamel was facing the air side and the coating was in contact with the roller mentioned above.

The samples are loaded into the tempering furnace such that the enamel dried surface is facing the air side and the coating is in contact with the rollers that oscillate during tempering. INFERENCE:

The samples prepared in accordance with the present invention having a double layered heat treatable reflective coating showed the appearance of the reflective coating are negative suggesting that the coating appears blue in color, deposited by Inventive Example 3 after heat treatment. The alkali test showed that etching in harsh chemical environment has not occurred, thereby increasing its durability. The coated transparent substrate was heat treated successfully with the coating stack deposited by Inventive Example 3 without any defects/scratches visible to the naked eye.

TABER TEST

Taber Test was performed on, Reflective coated article and double layer heat treatable reflective coating deposited by Inventive Example 3 in clear and bronze substrate. The abrasion test was conducted in the Taber 5135 Abrader tester. For comparison, CS-IOF wheels were used for the abrasion tests. The transmission of the coating sample was measured after every 50 cycles. The test was repeated for a total of 500 cycles and the transmission values were measured. The change in transmission was calculated. The change in transmission value is less than 3% for Inventive Example 3 and greater than 5% for reflective coated article indicating a better resistance to abrasion. The better resistance of Example 3 to abrasion was found to be due to the higher deposition temperature (630 °C - 680 °C) of the online coating process as opposed to the spray pyrolysis process in reflective coated article that happens in the annealing lehr at a temperature less than 625 °C.

INFERENCE:

It is clear from the above results in Table 2 that the Inventive Example 3 in accordance with the present invention exhibits excellent abrasion resistance. The average light transmissions remain substantially constant over 500 cycles. T_L % after 500 cycles is less than 3% for the inventive coating in accordance with the present disclosure, thereby indicating that the heat treatable reflective coating in accordance with the present invention is highly abrasion resistant.

Inventive Example 8:

Following the same procedure of Inventive Examples 1-7, sample of Inventive Example 8 was also prepared using varying percentages of silicon precursor and the electron donating hydrocarbon in Layer 1 and Layer 2, in accordance with the present disclosure, as shown in Table 5. Light transmission and reflectance values of all the samples were measured and are presented in table 3 and 4.

Further, Taber abrasion experiments were performed for Reflective coated article (Comparative Examples 1 to 4) and double layer heat treatable reflective coating (Inventive Example 8) on a rotating wheel abrader Abraser 5135 Taber Industries. The taber test is conducted on coated glass to evaluate the mechanical durability of the products. The 100 mm by 100 mm coated glass is placed on the sample rotation stage with the coating facing upward. A pair of CS-IOF Taber wheels, each 1.27 cm in thickness and 5.08 cm in diameter, come in contact with the coating on the glass surface. A contact load of 500 g is applied by the pair of abrasive wheels on the coated surface. The sample stage rotates at a speed of 60 rpm forcing the abrasive wheels to rotate in the opposite direction and abrade the coating surface. A single rotation of sample stage is called a Taber cycle. The abrasive wheel was refreshed according to standard prescriptions between different samples. The visible light transmission was measured by the Haze meter according to ASTM D1003 in the abraded area before and after Taber. The transmission values are tabulated in Table 3 and Table 4.

Comparative Examples 1 to 4:

The comparative examples propose a single layer reflective coating with varying percentages of silicon precursor, the electron donating hydrocarbon in Layer

Table 3:

For comparison, the Table 4 below shows the change in transmission values measured for Inventive Examples 1 to 6:

Table 5, as produced below indicates the percentages of components in Layer 1 & 2 of Inventive Example 8; and the percentages of components in Layer 1 alone which were used for comparison (Comparative Examples 1 to 4) over the Inventive Examples.

INFERENCE:

It is clear from the above results in Table 3 and 4 that the Inventive Examples in accordance with the present invention exhibits excellent abrasion resistance. The average light transmissions remain substantially constant over 500 cycles. T_L % after 500 cycles is less than 4% for the inventive coating in accordance with the present disclosure, thereby indicating that the heat treatable reflective coating in accordance with the present invention is highly abrasion resistant.

Chemical Stability Test

IN sodium hydroxide solution is prepared by adding 40 g of sodium hydroxide in 1 Litre of deionized water. The solution is maintained at a temperature of 60 °C. The coated glass substrate was immersed in the solution so that the reflective coated surface is in contact with the alkali solution. It is periodically withdrawn from the solution for a very short duration of time for visual examination. Any degradation to the coating surface by chemical attack could be visually observed by the decrease in coating reflection. The duration of alkali test for which the coating is retained on the glass surface is reported. At the end of the alkali test, the coating is completely etched from the glass surface making the glass transparent. List of Elements 00 - Coated article 02 - Transparent substrate 04 - Functional layer 06 - Protective layer 08 - Enamel layer 10 - Heat treatable reflective coating

Claims

We Claim:

1. A heat treatable reflective coating (110) deposited on a transparent substrate (102) comprising, a functional layer (104) comprising essentially silicon and a protective layer (106) comprising essentially silica containing carbonaceous material on a glass side surface (102a) of the transparent substrate (102); and an enamel layer (108) on a tin side surface (102b) of the transparent substrate (102), wherein the transparent substrate (102) coated with the heat treatable reflective coating (110) has a light reflection (RL) ranging between 20% and 61% on the glass side (102a); and wherein the transparent substrate (102) has abrasion resistance up to 500 cycles, and exhibits no visible scratches or defects post heat treatment.

2. The heat treatable reflective coating (110) as claimed in claim 1, wherein the enamel layer (108) partially covers the circumferential area or completely covers the entire area of the tin side surface (102b) of the transparent substrate (102).

3. The heat treatable reflective coating (110) as claimed in claim 1, wherein the functional layer (104) comprising silicon predominantly is a mixture of silicon and silicon oxycarbide and the protective layer (106) comprising silica with carbonaceous material is in the form of silicon oxycarbide.

4. The heat treatable reflective coating (110) as claimed in claim 1, wherein the functional layer (104) comprises silicon in the range of 30 at% to 50 at%, oxygen in the range of 35 at% to 45 at%, and carbon in the range of 6 at% to 10 at%.

5. The heat treatable reflective coating (110) as claimed in claim 1, wherein the protective layer (106) comprises silicon in the range of 20 at% to 35 at%, oxygen in the range of 45 at% to 60 at%, and carbon in the range of 10 at% to 20 at%.

6. The heat treatable reflective coating (110) as claimed in claim 1, wherein the transparent substrate (102) is heat treated to a temperature ranging between 630 °C and 700 °C.

7. The heat treatable reflective coating (110) as claimed in claim 1 has a thickness ranging between 30 nm and 60 nm.

8. The heat treatable reflective coating (110) as claimed in claim 1, wherein the thickness of the functional layer (104) ranges between 20 and 40 nm.

9. The heat treatable reflective coating (110) as claimed in claim 1, wherein the thickness of the protective layer (106) ranges between 15 to 25 nm.

10. The heat treatable reflective coating (110) as claimed in claim 1, wherein the coating is deposited on the transparent substrate (102) by chemical vapor deposition method.

11. A method for depositing a heat treatable reflective coating (110) as claimed in claim 1, on a transparent substrate (102) comprising the steps of providing a transparent substrate (102), providing two chemical vapor deposition beam assemblies comprising a gaseous mixture towards the transparent substrate (102), directing a first beam onto a glass side surface (102a) of the transparent substrate (102) to deposit a functional layer (104), directing a second beam onto a glass side surface (102a) of the transparent substrate (102) over the functional layer (104) to deposit a protective layer (106) and form a heat treatable reflective coating (110) over the transparent substrate (102), printing an enamel layer (108) on a tin side surface (102b) of the transparent substrate (102), wherein the functional layer (104) comprising essentially silicon and a protective layer (106) comprising essentially silica containing carbonaceous material on the glass side surface (102a) of the transparent substrate (102).

12. The method as claimed in claim 11, wherein the functional layer (104) is deposited through the first beam comprising silane from 2% to 14%, ethylene from 10% to 20% and nitrogen from 80% to 90%.

13. The method as claimed in claim 11, wherein the protective layer (106) is deposited through the second beam comprising silane from 0.5% to 10%; ethylene from 5% to 20% and nitrogen from 70% to 85%.

14. The method as claimed in claim 11, wherein the temperature for deposition of the functional layer (104) is in the range of 600 to 750 °C.

15. The method as claimed in claim 11, wherein the temperature for deposition of the protective layer (106) is in the range of 600 to 680 °C.

16. The method as claimed in claim 11, wherein the transparent substrate (102) is a float glass ribbon.

17. A coated article (100) comprising a transparent substrate (102) and a heat treatable coating (110) as claimed in claim 1 comprising, a functional layer (104) comprising essentially predominantly a mixture of silicon and silicon oxycarbide and a protective layer (106) comprising silica containing carbonaceous material on a glass side surface (102a) of the transparent substrate (102); and an enamel layer (108) on a tin side surface (102b) of the transparent substrate (102).

18. The coated article (100) as claimed in claim 17, wherein the light transmission percentage of the transparent substrate (102) ranges between 20% and 70%.

19. The coated article (100) as claimed in claim 17, wherein the refractive index of the transparent substrate (102) ranges between 2.5 and 4.5.

20. A door for home appliances or food processing appliances comprising the reflective heat treatable coated article as claimed in any of the preceding claims.

21. The door as claimed in claim 20, wherein the home appliance or food processing appliance is an oven.