The present invention concerns coating compositions for porcelain ware, in particular, anti-stain coating compositions for porcelain tableware, and a process for preparing thereof. The present invention also concerns a process for coating a porcelain ware, in particular a porcelain tableware selected among plates, bowls, cups, saucers, pitchers, teapots, coffeepots, mugs. The invention further relates to a coated porcelain ware, in particular, a coated porcelain tableware selected among plates, bowls, cups, saucers, pitchers, teapots, coffeepots, mugs, comprising at least one layer of a coating composition according to the invention.

Porcelain tableware is highly appreciated by people and can add value to simple everyday meals and formal dinners, making them enjoyable and unique. Thus, it is important to have perfect tableware.

Stains and coloration of porcelain tableware caused by, for example, food, sauces, or drinks such as tea or coffee may irreversibly damage the porcelain tableware and modify its appearance. In such cases, the classical cleaning techniques like washing with dishwashing products and water may prove to be inadequate in removing the coloration or the stains from the porcelain. Removal of the coloration and stains by abrasive potentially toxic chemicals is not advisable as it may damage the porcelain and be food unsafe.

Thus, there is a need for a new technique that is food safe and avoids efficiently the coloration and staining of porcelain ware while preserving the quality of the porcelain.

The present invention addresses this need through the provision of a coating composition comprising:

^B 2.5 to 7.5% by weight of aminoethylaminoisobutylmethylsiloxane, dimethyl siloxane copolymer, relative to the total weight of the composition;

¹⁸ 0,01 to 0.5% by weight of decani ethyl cyclopentasiloxane, relative to the total weight of the composition;

¹⁸ 0.1 to 1% by weight of octamethylcyclotetrasiloxane, relative to the total weight of the composition;

s 5 to 30%> by weight of a food grade alcohol selected from isopropanol or ethanol, relative to the total weight of the composition;

¹⁸ 0.1 to 1% by weight of acetic acid, relative to the total weight of the composition; and ^a up to 85% by weight of water, relative to the total weight of the composition. The coating of the invention is a food safe and food grade coating that can be used on porcelain tableware such as plates, bowls, cups, saucers, pitchers, teapots, coffeepots, mugs etc. without altering the porcelain.

The coating composition of the invention adds a completely new property to the porcelain ware onto which it is applied: it prevents the adhesion of stains and coloration to the porcelain ware (anti-stain property). Consequently, rinsing with water only or, if desired, washing by water and a mild dishwashing product will remove easily and efficiently coloration and stains caused by drinks, food, sauces etc. from the surface of a porcelain ware coated with a composition according to the invention. In addition to its anti-stain properties, the coating composition of the invention is further capable of preventing the adhesion of grease on the coated surfaces of the porcelain.

The coating composition of the invention adheres strongly to the surface of the porcelain surface and ensures a durable coating of the porcelain ware.

Although the coating composition of the invention is particularly adapted for porcelain ware, in particular, porcelain tableware such as plates, bowls, cups, saucers, pitchers, teapots, mugs etc., it may also be used for any porcelain surface where staining and coloration and food safety is an issue.

In an embodiment, the amount of aminoethylaminoisobutylmethylsiloxane, dimethylsiloxane copolymer in the coating composition of the invention is 3 to 7% by weight, preferably, 3.5 to 6.75% by weight, relative to the total weight of the composition.

In an embodiment, the amount of decamethylcyclopentasiloxane in the coating composition is 0.03 to 0.4% by weight, preferably, 0.05 to 0.38% by weight, relative to the total weight of the composition.

In an embodiment, the amount of octamethyicyclotetrasiioxane in the coating composition is 0.15 to 0.85% by weight, preferably, 0.25 to 0.75% by weight, relative to the total weight of the composition.

In an embodiment, the amount of the food grade alcohol selected from isopropanol or ethanol is 8 to 28% by weight, preferably, 10 to 25% by weight, relative to the total weight of the composition. The food grade alcohol is preferably isopropanol.

In an embodiment, the amount of acetic acid in the coating composition of the invention is 0.1 to 0.7%, preferably, 0.1 to 0.4% by weight, relative to the total weight of the composition. In an embodiment, the amount of water present in the coating compositions of the invention is 70 to 85% by weigh, preferably, 75 to 82% by weight relative to the total weight of the composition.

In a preferred embodiment, the coating composition comprises:

B 3.5 to 6.75% by weight of aminoethylaminoisobutylmethylsiloxane, dimethyl siloxane copolymer, relative to the total weight of the composition;

¹⁸ 0.05 to 0.38% by weight of decamethylcyclopentasiloxane, relative to the total weight of the composition;

¹⁸ 0.25 to 0.75% by weight of octamethylcyclotetrasiloxane, relative to the total weight of the composition;

¹⁸ 10 to 25%> by weight of isopropanol, relative to the total weight of the composition; ¹⁸ 0.1 to 0.4% by weight of acetic acid, relative to the total weight of the composition; and ¹⁸ 75 to 82% by weight of water, relative to the total weight of the composition.

The coating composition according to the invention may further contain one or more additional components selected from known food safe and food grade additives for porcelain coating compositions. Examples of such additives are:

one or more viscosity modifiers or thickeners,

one or more dispersants,

one or more pigments,

one or more emulsifiers,

one or more dyes.

Any of the above additive types may be used alone or in admixture with each other and with other additives, if desired. Where one or more additives are present, the total amount of said additive(s) are 0.01 % by weight, relative to the total weight of the composition. Such additives are well known by a person skilled in the art.

The coating composition of the invention may be an ail-over coating meaning that it can completely cover the porcelain ware, or it may be partial meaning that it can only cover specific parts of the porcelain ware, for example the interior surface.

The coating composition of the invention is in the form of an aqueous colloidal emulsion in which the dispersed-phase particles have a diameter of less than 600 nm, preferably between I and 500 nm, more preferably between 20 to 450 nm as shown in Figures 2 and 3. In another aspect, the present invention provides a process for the preparation of a coating composition according to the present invention, comprising the steps of:

i) forming polymeric particles by mixing aminoethylamino isobutyl methyl siloxane, dimethylsiloxane copolymer, octamethylcyclotetrasiloxane, deeamethylcyclopentasiloxane in the presence of tetramethylammonium hydroxide as a catalyst;

ii) heating the resulting mixture at a temperature between 50 and 180°C, preferably between 60 and 150°C, still more preferably between 80 and 145°C;

iii) forming an aqueous emulsion by adding alcohol, acetic acid and water to the viscous liquid obtained in step (ii).

In step (i) other quaternary ammonium hydroxides may be used. Non limiting examples are tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, benzyl trimethylammonium hydroxide, benzyl triethylammomum hydroxide.

The viscous liquid obtained in step (ii) has a viscosity of generally less than 10

Pa.s (10,000 cP), for example less than 5 Pa.s (5,000 cP), at 25°C.

The dispersed-phase particles of the resulting emulsion have a diameter of less than 600 nm, preferably between 1 and 500 nm, more preferably between 20 to 450 nm.

The coating composition of the invention may be applied onto the porcelain ware during or after its production. According to an embodiment, the coating composition is applied to the porcelain ware after it's manufacture.

In yet still another aspect, the present invention provides a process for coating a porcelain ware, in particular a porcelain tableware selected among plates, bowls, cups, saucers, pitchers, teapots, coffeepots, mugs, comprising the steps of:

a) applying a coating composition according to the invention onto the surface of a porcelain ware, in particular a porcelain tableware selected among plates, bowls, cups, saucers, pitchers, teapots, coffeepots, mugs;

b) curing the resulting coated porcelain ware for 1 to 30 minutes, preferably for 1 to 15 minutes, more preferably for 1 to 5 minutes at a temperature ranging from 80 to 250 °C, preferably from 100 to 200° C.

Prior to applying the coating composition, the surface of the porcelain ware onto which the coating is to be applied may optionally be cleaned, for example, with a dry or wet cloth, or with an alcoholic solution such as an alcoholic solution of i sopropanol 99%, The application of the anti-stain coating composition of the invention may be done by any method known by a person skilled in the art and appropriate for coating of porcelain ware. The method is also selected taking into account the surface to be coated. The anti-stain coating composition of the invention can be applied uniformly onto the porcelain ware using a brush or a soft cloth.

The composition may also be applied by conventional spraying methods. Spraying can be done for example without the use of any air, only by using the pressure of the composition alone. An adapted pump pressurises the composition and forces a defined quantity of composition through a nozzle aperture at up to 25 MPa. During this process, the composition is diffused into a finely atomised spray jet. Spraying can also be done using a compressed air-driven spray where at the outlet of the nozzle, the composition is mixed with air. This atomizes the composition in very fine droplets to produce an extremely good spray pattern. A still another spraying method can be a low- pressure spraying using a high volume of air and low air pressure up to 0.07 bar.

The porcelain ware may also be coated by dip coating. Dip coating allows a complete coating of the porcelain ware. In dip coating process, the porcelain ware is immersed in the coating composition at a constant speed and remains therein for 1 to 20 minutes for example. The porcelain ware is then pulled up at a constant speed. The speed determines the thickness of the coating desired. Faster withdrawal gives thicker coating. The coating layer deposits itself on the porcelain ware while it is pulled up. Excess composition will drain from the surface of the porcelain ware. Usually, the coating is a thin layer of 50 nanometers or less.

The above-mentioned methods are well known by the skilled person in the art. Once the coating has been deposited on the porcelain ware, it is oven cured for 1 to 30 minutes, for example for 1 to 15 minutes, for example for 1 to 5 minutes, at a temperature ranging from 80 to 250°C, for example 100 to 200°C. Curing removes solvents and water present in the coating composition, and stabilizes the coating layer.

If desired, one or more layers of the coating composition of the invention can be applied over the substrate with each layer being separately cured.

The coating process of the invention allows a complete coating meaning that the composition covers the porcelain ware on all of its surfaces, or a partial coating meaning that it can only cover specific parts of the porcelain ware, for example the interior surface. In still another aspect, the invention provides a coated porcelain ware, in particular, a coated porcelain tableware selected among plates, bowls, cups, saucers, pitchers, teapots, coffeepots, mugs, comprising at least one layer of a coating composition according to the invention.

The invention is illustrated with reference to the following non-limiting examples and Figures.

Figure 1 represents the Fourier Transform Spectroscopy (FTIR) analysis of a coating composition prepared according to Example 1.

Figures 2 and 3 represent the Transmission Electron Microscopy (TEM) image of a coating composition according to Example 1 where the diameter of the particles is between 20 to 450 nm.

Figure 4 shows the effectiveness of the anti-staining composition of the invention : when dipped into a bath of porcelain paint, the tile coated with the anti-stain composition of the invention does not change color while the non treated tile becomes green.

EXAMPLES

EXAMPLE 1: Preparation of a coating composition according to the invention

189 g of aminoethyianiinoisobutylmethylsiioxane, dimethyisiloxane copolymer (CAS No. 106842-44-8, commercialized by Meryer (Shanghai) Chemical Technology Co. Ltd.), 20 g of octamethylcyclotetrasiloxane (CAS No. 556-67-2, octamethylcyclotetrasiloxane 98% commercialized by Sigma Aldrich), 1 g of decamethylcyclopentasiloxane (CAS No. 541-02-6, decamethylcyciopentasiloxane 97% commercialized by Sigma Aldrich) and 1 g (3000ppm) of tetram ethyl ammonium hydroxide (tetramethylammonium hydroxide solution 25 wt.% in H ₂ 0 commercialized by Sigma Aldrich) were added to a 500 ml round bottom flask equipped with a stirrer, condenser, thermometer, strip head, heating mantle and nitrogen overgas. The mixture was stirred and heated to 80°C and held at that temperature for 10 hours. The temperature was then raised to 145°C for 2 hours. 210 g of a product was obtained. Gel permeation chromatography of the product revealed the presence of 85 wt.% of linear polysiloxanes and 15 wt.% cyclosiloxanes. The product had a viscosity of 2570 cP at 25°C measured with an Ubbeiohde viscosimeter in accordance with ASTM D 445-46T. An aqueous emulsion was next prepared by adding 2800 to 7000 g of isopropanol and 28 to 56 g of acetic acid to 210 g of the product obtained previously followed by the addition of 1 5000 g of distilled water. 28 kg of a coating composition according to the invention is obtained in this manner.

Figure 1 shows a FTIR spectrum of the coating composition prepared according to Example 1.

EXAMPLE 2: Preparation of a coating composition according to the invention

100 g of aminoethylaminoisobutylmethylsiloxane, dimethyl siloxane copolymer (CAS No. 106842-44-8), 1 g of octam ethyl cyclotetrasiloxane (CAS No. 556-67-2), 1 g of decamethylcyclopentasiloxane (CAS No. 541-02-6) and 0.5 g (BOOOppm) of tetramethylammonium hydroxide were added to a 500 ml round bottom flask equipped with a stirrer, condenser, thermometer, strip head, heating mantle and nitrogen overgas. The mixture was stirred and heated to 80°C and held at that temperature for 10 hours. The temperature was then raised to 145°C for 2 hours. 210 g of a product was obtained. Gel permeation chromatography of the product revealed the presence of 87.5 wt.% of linear polysiloxanes and 12.5 wt.% cyclosiloxanes. The product had a viscosity of 523 cp at 25°C measured with an Ubbeiohde viscosimeter in accordance with ASTM D 445-46T.

A solution/slurry was next prepared by adding 1500 to 3750 g of isopropanol and 15 to 30 g of acetic acid to 210 g of the product obtained previously followed by the addition of 15000 g of distilled water. 15 kg of a coating composition according to the invention is obtained in this manner.

EXAMPLE 3: Coating of a porcelain tableware with a composition according to the invention

A composition prepared according to example I was applied to the interior surface of a porcelain cup with a soft cloth with for approximately 5 minutes. The cup was then oven cured at a temperature of 180-200°C for 2 to 5 minutes.

EXAMPLE 4: Anti-staining property of the composition

The effectiveness of a coating composition according to invention was determined by spraying a composition prepared according to example 1 on the surface of a decorated white porcelain tile. The tile was then oven cured for 2 to 5 minutes at a temperature of 100 to 120°C. After letting it cool back to room temperature (20 + 5°C), the coated tile and a non treated decorated white tile (control) were both dipped the in a bath of green tile paint. The tiles remained inside the solution for a 2 to 3 seconds and then pulled up. As shown in Figure 4, the tile coated with the anti-stain composition of the invention does not chanse color while the non treated tile becomes green.