WO2021000924A1

WO2021000924A1 - Self-cleaning antibacterial vitreous enamel panels

Info

Publication number: WO2021000924A1
Application number: PCT/CN2020/100027
Authority: WO
Inventors: Chung Kong Chau; Yong Fan; Man Lung Sham; Wai Keung LEUNG; Kai Fung LEUNG
Original assignee: Program Contractors Limited
Priority date: 2019-07-03
Filing date: 2020-07-03
Publication date: 2021-01-07
Also published as: CN113677641A

Abstract

A self-cleaning, hydrophilic, antibacterial, acid-resistant, glossy, and durable vitreous enamel panel includes a decarbonized metal substrate with at least a ground coat(20), a first layer enamel top coat(30), and a second layer enamel top coat(40) positioned sequentially over the metal substrate. The second layer enamel top coat(40) has more than one nano-modifiers, each in an amount of at least 0.1 weight percent of the frit. The nano-modifiers include zinc oxide, silver oxide, zirconium oxide. silicon dioxide, copper oxide, boric acid, aluminium oxide, magnesium oxide, calcium oxide, and titanium dioxide. The vitreous enamel panel has a water contact angle of less than approximately 20 degrees; the antibacterial effectiveness against E. coli and S. aureus of at least 99 percent or the antibacterial activity value of at least 2.0; and a gloss level between 80 and 95, even after multiple firings at 850℃ or higher.

Description

SELF-CLEANING ANTIBACTERIAL VITREOUS ENAMEL PANELS

Cross-reference to Related Applications:

This application claims priority from a U.S. provisional patent application number 62/870,073 filed on July 3 ^rd, 2019, and the disclosure of which is incorporated herein by reference in its entirety.

Field of the Invention:

The present invention relates to vitreous enamel panels in general and, more particularly, to vitreous enamel panels that are self-cleaning, hydrophilic, antibacterial, glossy, acid-resistant, and durable.

Background:

Vitreous enamel has been used in a wide variety of applications where hard, durable, scratch-resistant, and color-fast surfaces are needed. The term “vitreous enamel, ” as used herein, relates to a thin layer of oxide and/or glass materials fused by heat onto a substrate. Vitreous enamel includes coatings for appliances, architectural coatings, street signs, coatings for tunnel walls, rail stations, and other high-traffic public locations. In general, vitreous enamel is selected for easy cleaning and maintenance, long life, and non-flammability.

However, in many high-traffic locations that are congested with pedestrians, such as mass transit stations, the environment is conducive to the transmission of germs due to being touched or being in contact with droplets emitted by sneezing or coughing. In enclosed environments, the spreading of such germs to surfaces and from surfaces to other people is facilitated by surfaces which permit the growth of bacteria.

Therefore, there is a need in the art for improved vitreous enamel surfaces that resist the growth of bacteria. There is also a need for improved vitreous enamel surfaces that are self-cleaning, which further reduces the opportunity for growth of bacteria.

Summary of the Invention

In one aspect, the present invention provides a self-cleaning, hydrophilic, antibacterial, acid-resistant, glossy, and durable vitreous enamel panel. The present panel includes at least a metal substrate, an interface layer (or called ground coat) , a first layer of enamel (first layer enamel top coat) , and a second layer of enamel which can be an outermost layer enamel top coat of the panel. The first layer enamel top coat is positioned over the ground coat. A second layer enamel top coat is positioned over the first layer enamel top coat. A composition for forming the second layer enamel top coat includes a plurality of nano-modifiers as an antibacterial agent, a self-cleaning agent, and/or functional admixture, wherein each of the nano-modifiers is in an amount of at least 0.1 weight percent to the total weight of the frit. In one embodiment, the antibacterial agent is selected from zinc oxide, silver oxide, copper oxide, and boric acid. In other embodiment, the self cleaning agent is selected from silicon dioxide and titanium dioxide. In another embodiment, the functional admixture is selected from aluminium oxide, magnesium oxide, calcium oxide, and zirconium oxide. Each of the first and second compositions for forming the first and second layers of enamel top coat, respectively, further comprises a frit mixture including frit, silica sand, clay and water. The vitreous enamel panel has a low water contact angle of less than approximately 20 degrees, a gloss level (GU) at 60 degrees of 80-95, and the antibacterial effectiveness against E. coli and S. aureus is at least 99 percent, or the antibacterial activity value (R) is at least 2.0.

In another aspect, the present invention provides a method for making the vitreous enamel panel of the present invention. The method includes pre-treating a metal substrate of the vitreous enamel panel including grease removal, rust removal and neutralization; coating an interface layer as a ground coat on both surfaces of the metal substrate which is decarbonized; drying the surfaces of the decarbonized metal plate; coating a first composition forming a first layer of enamel to provide a better enamel context and protection; subjecting the first composition to furnace for bonding to a metal substrate of the vitreous enamel panel including firing the first composition to 850 ℃ or higher; maintaining the temperature of furnace at 850 ℃ or higher for a first period of time; cooling the temperature of furnace to approximately room temperature inside the furnace; coating a second composition for forming a second layer of enamel including a plurality of nano-modifiers mixed thoroughly with other components in the second composition; subjecting the second composition to furnace for firing at 850 ℃ or higher; maintaining the temperature of furnace at 850 ℃ or higher for a second period of time; cooling the temperature of furnace to approximately room temperature inside the furnace to obtain the vitreous enamel panel with outermost surfaces. The steps of coating the layer enamel top coat forming composition, the firing and cooling cycle can be repeated until a desired outermost surface of the panel is formed.

In an embodiment, the metal substrate is a decarbonized steel substrate.

In another embodiment, each of the nano-modifiers being the anti-bacterial agent is in an amount of 0.1 to 15 weight percent to the weight of the frit in the composition. Preferably, the anti-bacterial agent is in a total amount of 0.1 to 10 weight percent to the weight of the frit of the composition. More preferably, the anti-bacterial agent is in a total amount of 5 to 8 weight percent to the weight of the frit of the composition.

In other embodiment, each of the nano-modifiers being the self-cleaning agent is in an amount of 0.1 to 5 weight percent.

In yet another embodiment, each of the nano-modifiers being the functional admixture is in an amount of 0.1 to 15 weight percent. Preferably, the functional admixture is in an amount of 0.1 to 10 weight percent. More preferably, the functional admixture is in an amount of 0.1 to 5 weight percent.

In one embodiment, the total weight percent of nano-modifiers in the second or subsequent composition for forming the outermost layer enamel top coat is about 7 to 10 %to the weight of the frit in the composition.

In an exemplary embodiment, the total weight percent of the nano-modifiers being the anti-bacterial agent selected from zinc oxide, silver oxide, copper oxide, and boric acid is about 5 to 8%, wherein about 60 to 95%of said anti-bacterial agent is zinc oxide.

In other embodiment, the ground coat has a thickness of approximately 80 μm or more.

In another embodiment, the drying of the ground coat is at about 70 ℃ for about 20 minutes.

In yet another embodiment, the first layer enamel top coat has a thickness of 80 ± 10 μm.

In one another embodiment, the firing of the first, second, and/or subsequent compositions in the furnace is from room temperature to about 850 ℃ or higher within about 20 minutes.

In other embodiment, the first or second period of time for maintaining the first, second, and/or subsequent compositions at a temperature of about 850 ℃ or higher is about 5 minutes in the furnace.

In another embodiment, the second or subsequent composition for forming the second, outmost layer enamel top coat is prepared by thoroughly mixing the frit mixture and the nano-modifiers of the present invention.

For example, to prepare a 20-kg batch of the second or subsequent composition, a minimum of about 120 minutes may be required; to prepare a 50-kg batch of the second or subsequent composition, a minimum of about 400 minutes may be required.

Brief Description of the Drawings:

FIG. 1 is a schematic depiction of a vitreous enamel panel according to an embodiment.

FIG. 2 depicts an example of how to prepare the vitreous enamel panel according to an embodiment of the present invention.

Detailed Description:

1. Vitreous Enamel Panel Overview

Turning to the drawings in detail, FIG. 1 schematically depicts a vitreous enamel panel according to one aspect of the present invention. The panel includes various layers of enamel coating on a metal substrate such as a steel substrate, with optional core and backing layers depending upon the application of the panel (e.g., thickness and rigidity requirements, how the panel is to be mounted to a wall or other surface, etc. ) . The base layer 10 is a steel sheet with a controlled low carbon content or no carbon content. By controlling the carbon content, the bonding of the subsequent enamel layers to the steel substrate is enhanced. The ground coat 20 includes glass frit and other metal oxides that increase the bonding between the steel and the enamel coating. For example, the ground coat may include cobalt and copper oxides that promote adhesion of the coating to steel. The cobalt and copper oxides can form alloys with iron and, in this manner, increase the adhesion of the subsequent enamel layers to the steel substrate. As used herein, the term “frit” relates to a glass or ceramic composition that has been fused, typically as a molten material, quenched (e.g., pouring the molten mixture into a water bath) , and granulated. When fired in an oxygen-containing atmosphere, a layer of iron oxide is formed on the steel surface which bonds with the oxides in the ground coat layer.

The first top coat layer 30 is formed from a combination of glass frit with small amounts of clay and silica dioxide. Typically, pigments for color and other surface additives are reserved for the second top coat layer, 40. The second top coat layer 40 is formed from a combination of glass frit, small amounts of clay and silicon dioxide, along with the nano-modifiers as described herein in an amount of at least approximately 0.1 weight percent for each of the nano-modifiers, particularly an amount from 0.1 weight percent to approximately 15 weight percent, more particularly from 0.1 weight percent to approximately 10 weight percent, and the most particularly from 0.1 weight percent to approximately 5 weight percent. In an exemplary embodiment, the total amount of the anti-bacterial nano-modifiers is from 5 to no more 10 weight percent. More specifically, the amount of each of the anti-bacterial nano-modifiers is about 0.5 to 5.0 weight percent. Other optional nano-modifiers may be included to improve acid resistance, gloss, durability, and reduce the water contact surface angle.

In one aspect, a thermal stabilizer such as calcium phosphate may be added to improve the properties during firing.

In one aspect, the coated steel sheets may be fired in a single or multiple firing processes each at a temperature of over 850 ℃. For example, at least two top coats are separately fired each at a temperature of over 850 ℃. In the inventive vitreous enamel panels, the water contact surface angle has been reduced to the low value of below approximately 20 degrees, in some embodiments, as low as 16 degrees.. By providing such a low contact angle, water easily spreads out across the surface of the panel. That is, the panel surface becomes more hydrophilic. Through the increased water contact, the panels, when exposed to environmental water sources such as rain, become self-cleaning as the adhered water dissolved and removes surface dirt from the panels. In enclosed environments, the hydrophilic nature of the panels means that low amounts of water are needed to clean the panels.

Depending upon the application, the vitreous enamel panel may include an optional core, 50. The core may be selected from a variety of stiff, lightweight materials that add rigidity to the vitreous enamel panel. Examples of such materials include aluminum honeycomb structures and calcium silicate boards. A backing sheet 60 may be further included to protect the core and also to aid in placement of the panel on a wall, ceiling, or other structure.

2. Frit Compositions

In order to create enamel coatings on metal, the coating material, upon firing must have good fluidity and low surface tension so that it flows and fills in any minor surface imperfections. Because metal and glass/enamel have different coefficients of thermal expansion, it is important to try to match the metal coefficient of thermal expansion through careful selection of ingredients to prevent the enamel coating from cracking or peeling off the metal substrate. As the major ingredient in the coatings is the frit, frit selection must be carefully made to ensure coating adhesion.

A variety of frits may be selected for use in the vitreous enamel panels of the present invention. Typically frits are selected that are a combination of oxides, with the major ingredient being silica (SiO ₂) as a glass former, with various other ingredients selected to reduce the melting point such as boric oxide (B ₂O ₃) , sodium oxide (Na ₂O) , potassium oxide (K ₂O) , calcium oxide (CaO) , and lead oxide (PbO) , generally termed as “fluxes. ” As used herein, the term “flux” relates to a material that reduces the melting point and increases the flowability of the composition to which it is added. Durability, acid resistance, and scratch resistance may be imparted through nano-modifiers such as aluminum oxide (Al ₂O ₃) and zironium oxide (ZrO ₂) . In an exemplary embodiment, each of these nano-modifiers being the functional admixture is in an amount of 0.2 to 0.8 weight percent. Opacity (and the color white) may be achieved through the addition of titanium dioxide (TiO ₂) . In an exemplary embodiment, the amount of each of the self-cleaning nano-modifiers is about 0.2 to 1.0 weight percent to the weight of the frit of the composition.

Features of each of these frit materials are described below. Based on these properties, the variation of a particular frit ingredient to achieve more or less of that ingredient’s property is within the scope of the present invention.

Silica is the main glass former of the frit material. Silicon and oxygen combine to form a series of tetrahedral structures that create a low thermal expansion material that is durable. Boric oxide forms planar triangular structures of boron and oxygen and, when combined with silica, lowers its melting point while still retaining a strong network of bonded structures and low coefficient of thermal expansion. In this aspect, it may be seen as a glass-former as well as a flux. Boric oxide also increases corrosion resistance and durability.

Sodium oxide, a material known to reduce the melting point as a conventional ingredient in soda-lime glass. In colored frits, sodium increases color responses to copper, cobalt, and iron based pigments. Potassium oxide is often used with sodium oxide to reduce the melting point. When used with lead oxide, bright colors may be formed when used with appropriate pigments.

Calcium oxide may increase hardness and scratch resistance of the resulting enamel while reducing the melting temperature. Lead oxide reacts with silica to form lead silicates that may increase the gloss of the resulting vitreous enamel panel. It also may enhance colors when used with pigments. The increased flowability of the frit due to lead oxide means that surface imperfections in the substrate are filled in so that the resulting surface is smooth and glossy. Lead oxide may also enhance acid and alkali resistance.

Al ₂O ₃ increases hardness and scratch resistance as well as durability. It also reacts with silica to form aluminosilicates which are strong and durable compounds. Zirconium oxide, a refractory material, may be used to increase hardness, scratch resistance and durability of the vitreous enamel panel. It may also be used as an opacifier. ZrO ₂ reduces the thermal expansion of the frit. TiO ₂ may also be used as an opacifier although it can also affect colors from pigments that include metals such as Cr, Mn, Fe, Co, Ni, and Cu.

Commercial glass frits are available that include some or all of these basic ingredients in varying ratios. For some applications where the use of lead is not desirable, lead-free frits are used.

3. Antibacterial Nano-modifiers:

As described above, one or both of the top coat layers includes one or more nano-modifiers in an amount greater than approximately 0.1 weight percent but no more than 15 weight percent to the weight of the frit of the composition. In one aspect, the total amount of the nano-modifiers in the composition for forming the outermost layer of enamel top coat may range between approximately 7 weight percent and approximately 10 weight percent to the weight of the frit of the composition. The amount for any individual agent may be as low as approximately 0.1 weight percent to the weight of the frit of the composition. In an embodiment, the antibacterial agent is a combination of antibacterial nano-modifiers. The anti-bacterial nano-modifiers may be selected from zinc oxide, silver oxide (Ag ₂O) , silver nitrate, silver carbonate, zirconium oxide, silicon dioxide, copper oxide (CuO) , calcium oxide (CaO) , and boric acid. In an exemplary embodiment, the antibacterial nano-modifiers are selected from silver oxide, copper oxide, zinc oxide and boric acid, in a total amount of approximately 5 to 8 weight percent to the total weight of the composition for forming the second layer enamel top coat, wherein about 60 to 95%of the anti-bacterial agents in the composition of the present invention is zinc oxide.

In one aspect, the one or more nano-modifiers may be added to the composition in the form of nanoparticles. By using nanoparticles, a small amount of additive may be widely dispersed throughout the vitreous enamel coating to further enhance the antibacterial activity. Other forms of the nano-modifiers are still possible, as long as the anti-bacterial properties are maintained after multiple firing of the coatings of the vitreous enamel panel. An antibacterial efficiency of the present panel is approximately 99 percent or the antibacterial activity value (R) is defined as 2.0 according to some embodiments of the present invention.

As described herein, an antibacterial activity index or value is calculated by dividing the number of bacteria present after 24 hours of cultivation onto a testing treated article/product (C) into the number of bacteria present after 24 hours of cultivation onto the corresponding untreated (without antimicrobial agent) article/product (B) , or any known method of calculating the antibacterial activity index to a skilled artisan in the art.

For example, an antibacterial activity index/value (R) of >2.0 (≥99%killing ratio) of a treated article with antimicrobial agent might be considered as antibacterial article/product.

The coatings may be spray coated onto the steel substrate. In one aspect the coated steel sheets may be fired in a single or multiple firing processes with top coats each at a temperature of about 850℃ or more. For example, the ground coat may be fired followed by firing of the two top coats, and the two top coats are separately fired. In general, the coatings are fired at a temperature of about 850℃ or more for a period of time between approximately 3 minutes and approxiamtely 7 minutes. More specifically, the coatings are maintained in the furnace for firing for approximately 5 minutes.

4. Self-cleaning Agent

A surface being regarded as “self-cleaning” is commonly dependent on its hydrophobicity or hydrophilicity. Whether cleaning aqueous or organic matter from a surface, water plays an important role in the self-cleaning process. Specifically, the contact angle of water on the surface is an important characteristic that helps determine the ability of a surface to self-clean. This angle is affected by the roughness of the surface and there are numerous models having been developed to describe the “stickiness” or wettability of a self-cleaning surface, e.g., Young’s model, Wenzel’s model, Cassie-Baxter’s model.

Control over the surface wettability is a critical aspect of self-cleaning surfaces. Both superhydrophobic and superhydrophilic surfaces have been used as self-cleaning materials.

Superhydrophobic surfaces can be created in a number of different ways including plasma or ion etching, crystal growth on a material surface, and nanolithography. All of these processes create nano-topographical features which imbue a surface with superhydrophobicity. The ultimate goal in developing superhydrophobic surfaces is to re-create the self-cleaning properties of the Lotus Leaf that has the inherent ability to repel all water in nature. The basis for superhydrophobic self-cleaning is the ability of these surfaces to prevent water from spreading out when in contact with the surface. This is reflected in a water contact angle nearing 180 degrees. Superhydrophobic self-cleaning surfaces also have low sliding angles which allows for water that is collected on the surface to easily be removed, commonly by gravity. While superhydrophobic surfaces are great for removing any water-based debris, these surfaces likely will not be able to clean away other types of fouling matter such as oil.

Superhydrophilicity allows for surfaces to clean away a wide variety of dirt or debris. This mechanism is very different than the aforementioned superhydrophobic surfaces. For superhydrophilic self-cleaning surfaces, cleaning occurs because water on the surface is able to spread out to a great degree (extremely low water contact angle) to get between any fouling debris and the surface to wash away the debris.

One of the most commonly used self-cleaning products, titanium dioxide, utilizes a unique self-cleaning mechanism that combines an initial photocatalytic step and subsequent superhydrophilicity. A titanium dioxide coating, typically on glass substrate, when exposed to UV light, will generate free electrons that will interact with oxygen and water in the air to create free radicals. These free radicals will in turn breakdown any fouling organic matter deposited on the surface of the glass. Titanium dioxide also changes the normally hydrophobic surface to a superhydrophilic surface. For example, when rainfall occurs, instead of water beading up on the window surface and instantly falling down the glass, rain drops will rapidly spread out on the hydrophilic surface. The water will then move down the surface of the window, as a film rather than a droplet, essentially acting like a squeegee to remove surface debris.

Other than superhydrophobic surface, a superhydrophilic surface could also result in a self-cleaning effect. Therefore, in the present invention, silicon dioxide and titanium dioxide are used as self-cleaning nano-modifiers because they both have hydrophilic or superhydrophilic properties when being incorporated into the enamel layer top coat forming composition.

Because titanium dioxide also has a photocatalyic effect, it provides extra self-cleaning function to the present panel by way of decomposing grease, dirt and organic compounds under exposure to light. Some studies revealed that silica has been mixed with titanium dioxide to prolong the photocatalytic activity of the titanim dioxide because silica can enhance the acidity of Si-O-Ti bonds at the SiO ₂-TiO ₂ interfaces, inducing greater amount of hydroxyl groups on the surface of the coated surface. However, only TiO ₂ anatase phase of the synthesized TiO ₂ develops below 500℃. When it is synthesized between 600 and 800℃, the anatase phase co-exists with rutile phase. When it is synthesized above 800℃, only the rutile phase is found. TiO ₂ at rutile phase may lose part of its photocatalytic properties, especially when it is not exposed to high band gap energy, i.e., UV light. In this regard, the present invention incorporates some other nano-modifiers in a higher ratio than other conventional enamel layer top coat to compensate the potential loss of self-cleaning properties due to the firing temperature of over 850℃ in the present invention. Specifically, the high ratio of zinc oxide in the antibacterial agent is used to contribute to the self-cleaning properties of present panel by lowering the required energy for excitation electron, leading to a lower band gap energy requirement for initiating the photocatalytic activity of the TiO ₂.

As described above, water contact angle is used to characterize surface wettability. A droplet of solvent, typically water for hydrophobic surfaces, is placed perpendicular to the surface. The droplet is imaged and the angle between the solid/liquid and liquid/vapor interfaces is measured. Samples are considered to be superhydrophobic when the contact angle is greater than 150 degrees. For drops to roll effectively on a superhydrophobic surface, contact angle hysteresis is an important consideration. Low levels of contact angle hysteresis will enhance the self-cleaning effect of a superhydrophobic surface.

In the present invention, the preferred water contact angle for the vitreous enamel panel outermost layer top coat is less than 20 degrees, and more preferably, equal to or less than 18 degrees. In one example, the water contact angle of the present panel can reach 16 degrees, leading to a very hydrophilic or nearly superhydrophilic surface.

Examples:

Table 1 below provides the key components according to various embodiments of the present invention with different combination of nano-modifiers in various concentrations (by weight percent) to formulate the composition for forming the second, outermost layer enamel top coat, and their respective antibacterial activity, water contact angle, and gloss level (GU) at 60 degrees of the final (outermost) top coat are provided in Table 2.

Table 1:

Table 2:

* An antibacterial activity index or value is calculated by dividing the number of bacteria present after 24 hours of cultivation onto a testing treated panel into the number of bacteria present after 24 hours of cultivation onto the corresponding untreated (without antimicrobial agent) panel, or any well known method of calculating the antibacterial activity index or value to a skilled artisan in the art;

** The gloss of a surface is described as the reflection of light from the surface that is independent of color; ASTM method D 523 uses the 60° geometry both for comparing surfaces and to determine whether the 20° or 85° geometry is warranted; the most common angle used by the coatings industry to break up the basic divisions of gloss is 60° from the perpendicular; to measure gloss reflectance, a single beam of light is deflected off the surface, at the prescribed angle, into a receptor. This receptor gauges the intensity of that light in gloss units. The higher the number of units, the shinier the surface.

As shown in Tables 1 and 2, samples 1 and 2, even they are added with high concentration of nano-modifiers, do not result in the desired performance, i.e., with low water contact angle and glossy coating. Sample 3 has a lower anti-bacterial and self-cleaning nano-modifier content, which results in a better water contact angle than those from samples 1 and 2, but it still has an unacceptable anti-bacterial performance. In this regard, sample 4 has been added with a higher content of one of the anti-bacterial nano-modifiers without changing the content of the remaining nano-modifiers, which results in a better anti-bacterial performance, but the surface of the coating is turned into more greenish and less glossy (and higher water contact angle than that of sample 3) . Analogously, increasing the content of another anti-bacterial nano-modifier in sample 5 does not result in an acceptable anti-bacterial performance, until the content of zinc oxide is increased in sample 6. In sample 6, the zinc oxide content is increased by almost half of that used in sample 5. To attempt to lower the dosage of other categories of nano-modifiers, sample 7 has been lowered with its self-cleaning nano-modifier content by half of that used in sample 6, which results in a poorer water contact angle. Among the performances of samples 1-7, it is provided that sample 6 has the most promising and outstanding result, and therefore the next step is to further improve the anti-bacterial performance while the water contact angle can remain more or less the same to exert the self-cleaning function. It is found that even further increasing the content of zinc oxide in the composition, the water contact angle is only slightly increased but still within the desirable range, while the anti-bacterial performance is almost double by increasing the concentration of zinc oxide by about two-third as compared to samples 6 and 7. With reference to these samples, it is provided that the composition of the present invention forming the outermost layer enamel top coat with anti-bacterial and self-cleaning properties is tunable within a certain category of nano-modifiers, and specifically one or more nano-modifiers within that category of nano-modifiers. One of those nano-modifiers which can be tuned to increase the anti-bacterial activity is zinc oxide. To balance the anti-bacterial property, self-cleaning property and gloss level of the final product, it appears that samples 6 and 8 are the two most promising compositions for forming the outermost layer enamel top coat in the present invention.

As above discussed, a higher ratio of zinc oxide is believed to enhance the self-cleaning properties of the present panel even after multiple firings of the panel over 850℃. From the preferred formulations set forth in Table 2, a ratio of at least 1: 3 between the self-cleaning nano-modifiers (TiO ₂ and SiO ₂) and zinc oxide is used.

Turning to the detail in FIG. 2, a method for preparing the self-cleaning, hydrophilic, antibacterial, acid-resistant, glossy, and durable vitreous enamel panel according to some embodiment of the present invention is provided. The method mainly includes the following steps:

s201: pre-treating a metal substrate of the vitreous enamel panel including grease removal, rust removal and neutralization to form a decarbonized metal substrate;

s202: coating an interface layer as a ground coat on both surfaces of the decarbonized metal substrate;

s203: drying the surfaces of the decarbonized metal plate;

s204: coating a first composition for forming a first layer of enamel to provide a better enamel context and protection;

s205: subjecting the first composition to furnace for bonding to the metal substrate of the vitreous enamel panel including firing to 850℃ or higher;

s206: maintaining the temperature of furnace at 850℃ or higher for a first period of time;

s207: cooling the temperature of furnace to approximately room temperature inside the furnace;

s208: coating a second composition for forming a second layer of enamel including more than one nano-modifiers mixed thoroughly with other components in the second composition,

wherein the nano-modifiers include zinc oxide (ZnO) , silver oxide (Ag ₂O) , zirconium oxide (ZrO ₂) , silicon dioxide (SiO ₂) , copper oxide (CuO) , boric acid (H ₃BO ₃) , aluminum oxide (Al ₂O ₃) , magnesium oxide (MgO) , calcium oxide (CaO) , and/or titanium dioxide (TiO ₂) ;

s209: subjecting the second composition to furnace at 850℃ or higher;

s210: maintaining the temperature of furnace at 850℃ or higher for a second period of time; and

s211: cooling the temperature of furnace to approximately room temperature inside the furnace;

Optionally steps (s208) to (s211) can be repeated (represented by a dotted line with an arrow) until the vitreous enamel panel with desirable outermost surfaces is obtained.

In an embodiment, the metal substrate is a decarbonized steel substrate.

In another embodiment, each of the nano-modifiers being the anti-bacterial agent is in an amount of 0.1 to 15 weight percent to the weight of the frit in the composition. Preferably, the anti-bacterial agent is in a total amount of 0.1 to 10 weight percent to the weight of the frit in the composition. More preferably, the anti-bacterial agent is in a total amount of 5 to 8 weight percent to the weight of the frit in the composition.

In other embodiment, each of the nano-modifiers being the self-cleaning agent is in an amount of 0.1 to 5 weight percent to the weight of the frit in the composition.

In yet another embodiment, each of the nano-modifiers being the functional admixture is in an amount of 0.1 to 15 weight percent to the weight of the frit in the composition. Preferably, the functional admixture is in an amount of 0.1 to 10 weight percent to the weight of the frit in the composition. More preferably, the functional admixture is in an amount of 0.1 to 5 weight percent to the weight of the frit in the composition.

In one embodiment, the total weight percent of nano-modifiers in the second or subsequent composition for forming the outermost layer enamel top coat is about 7 to 10 %to the weight of the frit in the composition, and the remaining is the frit mixture.

In yet another embodiment, the first layer enamel has a thickness of 80 ± 10 μm.

According to an exemplary embodiment of the present invention, the vitreous enamel panel as-prepared by the present method has a water contact angle of less than 20 degrees, a gloss level at 60 degrees of 80 to 95, and an antibacterial activity value against E. coli and S. aureus of at least 2.0.

The foregoing description of the present invention has been provided for the purposes of illustration and descirption of various embodiments. It is not intended to be exhaustive or to limit the invention to the precise forms described. Many modifications and variations will be apparent to the practioner skilled in the art. The scope of the invention is set forth in the appended claims.

Claims

[Rectified under Rule 91, 06.08.2020]

A self-cleaning, hydrophilic, antibacterial, acid-resistant, glossy, and durable vitreous enamel panel comprising:

a decarbonized metal substrate;

a ground coat positioned over the decarbonized metal substrate;

a first layer enamel top coat positioned over the ground coat;

a second layer enamel top coat positioned over the first layer enamel top coat, the second layer enamel top coat comprising more than one of the following nano-modifiers in an amount of at least 0.1 weight percent for each of the nano-modifiers: zinc oxide (ZnO) , silver oxide (Ag ₂O) , zirconium oxide (ZrO ₂) , silicon dioxide (SiO ₂) , copper oxide (CuO) , boric acid (H ₃BO ₃) , aluminum oxide (Al ₂O ₃) , magnesium oxide (MgO) , calcium oxide (CaO) , and titanium dioxide (TiO ₂) ,

wherein the nano-modifiers being an anti-bacterial agent are selected from zinc oxide, silver oxide, copper oxide and boric acid in an amount of approximately 5 to 8 weight percent, wherein about 60 to 95%of the anti-bacterial nano-modifiers is zinc oxide, and

wherein the vitreous enamel panel has a water contact angle of less than approximately 20 degrees, a gloss level at 60 degrees between 80 and 95, and an antibacterial activity value against E. coli and S. aureus of at least 2.0 after multiple firings of the first and second layer enamel top coats at 850℃ or higher for at least 5 minutes.
The self-cleaning, hydrophilic, antibacterial, acid-resistant, glossy, and durable vitreous enamel panel of claim 1, further comprising a core positioned adjacent to the decarbonized metal substrate.
The self-cleaning, hydrophilic, antibacterial, acid-resistant, glossy, and durable vitreous enamel panel of claim 2, further comprising a backing sheet positioned adjacent to the core.
The self-cleaning, hydrophilic, antibacterial, acid-resistant, glossy, and durable vitreous enamel panel of claim 2, wherein the core comprises a calcium silicate board.
The self-cleaning, hydrophilic, antibacterial, acid-resistant, glossy, and durable vitreous enamel panel of claim 2, wherein the core comprises an aluminum honeycomb structure.
The self-cleaning, hydrophilic, antibacterial, acid-resistant, glossy, and durable vitreous enamel panel of claim 1, wherein each of the first and second layer enamel top coat further comprises frit, silica sand, clay and water.
The self-cleaning, hydrophilic, antibacterial, acid-resistant, glossy, and durable vitreous enamel panel of claim 1, wherein the nano-modifiers are in a total amount of about 7 to 10 weight percent of the second layer enamel top coat.
The self-cleaning, hydrophilic, antibacterial, acid-resistant, glossy, and durable vitreous enamel panel of claim 1, wherein the water contact angle of the vitreous enamel panel is about 18 degrees or less.
The self-cleaning, hydrophilic, antibacterial, acid-resistant, glossy, and durable vitreous enamel panel of claim 1, wherein the vitreous enamel panel has an anti-bacterial activity value against E. coli and S. aureus is at least 2.0.
The self-cleaning, hydrophilic, antibacterial, acid-resistant, glossy, and durable vitreous enamel panel of claim 1, wherein the decarbonized metal substrate is a decarbonized steel substrate.
The self-cleaning, hydrophilic, antibacterial, acid-resistant, glossy, and durable vitreous enamel panel of claim 1, wherein the ground coat has a thickness of at least 80 μm.
A method for preparing the self-cleaning, hydrophilic, antibacterial, acid-resistant, glossy, and durable vitreous enamel panel according to claim 1, the method comprising:

a) pre-treating a metal substrate of the vitreous enamel panel including grease removal, rust removal and neutralization to form a decarbonized metal substrate;

b) coating an interface layer as a ground coat on both surfaces of the decarbonized metal substrate;

c) drying the surfaces of the decarbonized metal plate;

d) coating a first composition for forming a first layer of enamel to provide a better enamel context and protection;

e) subjecting the first composition to furnace for bonding to the metal substrate of the vitreous enamel panel including firing to 850℃ or higher;

f) maintaining the temperature of furnace at 850℃ or higher for a first period of time;

g) cooling the temperature of furnace to approximately room temperature inside the furnace;

h) coating a second composition for forming a second layer of enamel including more than one of the following nano-modifiers which are mixed thoroughly with other components in the second composition: zinc oxide (ZnO) , silver oxide (Ag ₂O) , zirconium oxide (ZrO ₂) , silicon dioxide (SiO ₂) , copper oxide (CuO) , boric acid (H ₃BO ₃) , aluminum oxide (Al ₂O ₃) , magnesium oxide (MgO) , calcium oxide (CaO) , and titanium dioxide (TiO ₂) ;

i) subjecting the second composition to furnace at 850℃ or higher;

j) maintaining the temperature of furnace at 850℃ or higher for a second period of time;

k) cooling the temperature of furnace to approximately room temperature inside the furnace; and optionally repeating steps (h) to (k) , until the vitreous enamel panel with desirable outermost surfaces is obtained.
The method of claim 14, wherein the ground coat has a thickness of at least 80 μm.
The method of claim 14, wherein the first layer enamel top coat has a thickness of about 80 ± 10 μm.
The method of claim 14, wherein each of the nano-modifiers is from 0.1 to 15 weight percent.
The method of claim 17, wherein the total amount of the nano-modifiers is about 7 to 10 weight percent in the second composition.
The method of claim 17, wherein the total amount of the nano-modifiers being an anti-bacterial agent is about 5 to 8 weight percent, and wherein about 60%to 95%of the anti-bacterial agent is zinc oxide.
The method of claim 14, wherein the temperature of the furnace for the first and second layer enamel top coat formation is approximately at 850℃.
The method of claim 14, wherein the first or second period of time for maintaining the first or second composition in the furnace is about 5 minutes.
The method of claim 14, wherein the drying of the ground coat is carried out at about 70℃ for about 20 minutes prior to coating the first composition for forming the first layer enamel top coat.
The method of claim 14, wherein the vitreous enamel panel has a water contact angle of approximately 18 degrees or less, , and an anti-bacterial activity value against E. coli and S. aureus of at least 2.0.