WO2019062913A1

WO2019062913A1 - Water-borne coating composition, method of preparing the same, and substrate coated therewith

Info

Publication number: WO2019062913A1
Application number: PCT/CN2018/108638
Authority: WO
Inventors: Liguo LU; Qing Li; Long Huang
Original assignee: PPG Coatings Tianjin Co Ltd
Current assignee: PPG Coatings Tianjin Co Ltd
Priority date: 2017-09-30
Filing date: 2018-09-29
Publication date: 2019-04-04
Anticipated expiration: 2020-03-30
Also published as: CN107699085A

Abstract

Provided is a water-borne coating composition comprising a resin component, a passivation component and an electro-plated aluminum paste. Also provided is a method of preparing a water-borne coating composition, comprising: (1) mixing a resin component with an electro-plated aluminum paste and dispersing to form a pre-dispersed liquid (a); (2) adding a passivation component to the pre-dispersed liquid (a), stirring and dispersing to form a pre-dispersed liquid (b); and (3) adding water, optionally co-solvent and adjuvant to the pre-dispersed liquid (b) to form the water-borne coating composition. Further provided is a substrate coated with the water-borne coating composition.

Description

WATER-BORNE COATING COMPOSITION, METHOD OF PREPARING THE SAME, AND SUBSTRATE COATED THEREWITH

FIELD OF INVENTION

The present application relates generally to water-borne coating compositions and methods of preparing the same. In particular, the present application relates to water-borne electro-plated silver coating compositions for metallic substrates and methods of preparing the same. The present application further relates to substrates coated with such water-borne coating compositions.

BACKGROUND OF INVENTION

Currently, solvent-borne electro-plated silver coatings dominate the market of electro-plated silver coatings for metal substrates. Solvent-borne electro-plated silver coatings are generally prepared from electro-plated aluminum powders, resins, organic solvents, adjuvants, and the like. Generally, aluminum pigments comprising aluminum powders having particle size of about 6-16 μm and aluminum flake thickness between 18 nm and 50 nm are used as electro-plated aluminum powders. Such pigments have a variety of advantages, such as, high aspect ratio, dense color, chrome-plating effect, smoothness, denseness, good hiding capability, and ultra-thin thickness. However, solvent-borne electro-plated silver coatings have disadvantages, such as, low flash point, flammability, non-conductivity, VOC emissions, or the like.

There also exists a small amount of water-borne electro-plated silver coatings on the market. Water-borne electro-plated silver coatings have advantages of ease-to-clean, high flash point, and low pollution, etc. Aluminum particles and flakes in electro-plated aluminum paste are fine and thin in size, and have large specific surface areas, while aluminum itself is an active metal and can rapidly react with water at atmospheric temperature (2Al + 6H ₂O = 2Al (OH) ₃↓ + 3H ₂↑) ; thus, it is required to pre-treat electro-plated aluminum pastes prior to application in a water-borne system.

Currently, there are two main types of water-borne electro-plated silver coatings on the market. One is electro-plated silver coating encapsulated with fumed silica. The preparation principle and schematic diagram for this type of water-borne electro-plated silver coating are shown in Figure 1.

The characteristics of electro-plated silver coating encapsulated with fumed silica include: complicated preparation process and high production cost (about two or three times of common solvent-borne electro-plated aluminum pastes) of aluminum pigments, good water resistance, long storage period, but poor color effect.

The other is an electro-plated aluminum paste treated with mixed organophosphate resins, which has advantages of simple treatment process and moderate cost and disadvantages of short storage period in water and poor stability of aluminum paste.

At present, the problems that need to be solved in water-borne electro-plated silver coatings include, e.g., insufficient color brightness as compared with solvent-borne electro-plated silver coatings; short storage period; poor stability; and relatively high production cost.

Accordingly, there is a need in the art for water-borne electro-plated silver coatings having the following advantages: comparable color effect with respect to solvent-borne electro-plated silver coatings; long-term storage stability; and cost effectiveness.

SUMMARY OF THE INVENTION

The present application relates to water-borne coating compositions, comprising a resin component, a passivation component, and an electro-plated aluminum paste.

The present application also relates to methods of preparing a water-borne coating composition, comprising: (1) mixing a resin component with an electro-plated aluminum paste and dispersing to form a pre-dispersed liquid (a) ; (2) adding a passivation component to the pre-dispersed liquid (a) , stirring and dispersing to form a pre-dispersed liquid (b) ; and (3) adding water, optionally co-solvent and adjuvant to the pre-dispersed liquid (b) to form water-borne coating composition.

The present application further relates to substrates coated with a water-borne coating composition comprising a resin component, a passivation component, and electro-plated aluminum paste.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic diagram showing a principle of preparing the existing water-borne electro-plated silver coatings encapsulated with fumed silica and the formed silvery aluminum flakes.

Figure 2 indicates schematic diagrams showing a dispersion formed after 1 hour standing of a passivated electro-plated aluminum paste mixed with water (a) , and a dispersion formed after 1 hour standing of an un-passivated electro-plated aluminum paste mixed with water (b) .

DETAILED DESCRIPTION

For the purposes of the following detailed description, it should be understood that the invention can employ various alternative modifications and step orders, unless clearly indicated to the contrary. In addition, other than in any operating examples, or where otherwise indicated, all numbers with reference to, e.g., quantities of ingredients as used in the description and claims, are to be understood as being modified by the term “about” in all instances. Accordingly, unless indicated to the contrary, the numerical parameters as set forth in the following specification and attached claims are approximate values that may vary depending upon the desired properties to be obtained by the present application. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the application are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard variation found in their respective testing measurements.

Also, it should be understood that any numerical range recited herein is intended to include all sub-ranges subsumed therein. For example, a range of “1 to 10” is intended to include all sub-ranges between (and including) the recited minimum value of 1 and the recited maximum value of 10, that is, having a minimum value equal to or greater than 1 and a maximum value of equal to or less than 10.

In the present application, the use of the singular includes the plural and the plural includes the singular, unless specifically stated otherwise. In addition, in the present application, the use of "or" means "and/or" unless specifically stated otherwise, even if "and/or" may be used explicitly in some cases. In addition, in the present application, "a" or "an" is used to mean "at least one" unless specifically stated otherwise. For example, "a" polymer, "a" coating composition, and the like refer to any one or more of these items. As described above, existing water-borne electro-plated silver coatings have disadvantages, such as, poor color effect, low storage stability, high production cost, and the like. The present application aims to provide novel water-borne electro-plated silver coating compositions which are prepared by special process to achieve excellent color effect, long-term storage stability and low production cost.

As used herein, the term “water-borne” refers to a coating composition including at least water in an amount of more than 50 wt%, based on the total solvent weight in the composition.

The water-borne electro-plated silver coating compositions according to the present application comprise a resin component. Suitable resin component for use in the present application is miscible with water, e.g., under vigorous stirring and/or in the presence of co-solvent, and the formed solution exhibits a transparent or translucent state. The resin component may comprise a resin or a mixture of different resins. Resins suitable for the present electro-plated silver coatings include, but are not limited to, acrylic resins, saturated or unsaturated polyester resins, polyurethane dispersions, acrylic emulsions, amino resins, and any mixtures of the foregoing resins. The resins may be thermosetting.

The resin component may be present in the coating composition in an amount of at least about 2 wt%, suitably at least about 3 wt%, such as at least about 4 wt%, and up to about 15 wt%, suitably up to about 10 wt%, even up to about 8 wt%, based on the total weight of the water-borne electro-plated silver coating composition. If the resin level is less than 2 wt%, it is likely to cause poor adhesion problem; and if the resin level is higher than 15 wt%, the color effect of the electro-plated aluminum paste might be negatively affected, for example, the metallic appearance might be lowered and the color might not be sufficiently bright.

Examples of commercially available resinous components include, but are not limited to, amino resins from INEOS, Taiwan Changchun Chemicals, Allnex, Taiwan Changxing Chemicals and the like; acrylic resins from Shuike Chemical, Mitsui Specialty Chemicals, Korea Daikin, Japan DIC, Arkema, Nuplex, DSM, Allnex, Beijing Comens New Materials, Shanghai Xinhua Resin, etc.; polyester resins from Neplex, DSM, Dow Chemical, Shuaike Chemical; polyurethane resins from Bayer and Henkel; and any mixture of the above resins.

The water-borne electro-plated silver coating compositions according to the present application comprise an electro-plated aluminum paste. The electro-plated aluminum paste may be prepared by any method known in the art. For example, the electro-plated aluminum paste for use in the coating composition according to the present application may be prepared by a method comprising: depositing an electro-plated aluminum film on a support via physical vapor deposition of pure aluminum (e.g, aluminum pieces or wires) in a near vacuum environment; removing the electro-plated aluminum film from the support by means of solvent soak, followed by collecting the aluminum film; pulverizing the aluminum film into aluminum flakes having appropriate size by stirring; and screening aluminum flakes having particle sizes within an appropriate range, thereby obtaining an electro-plated aluminum paste. Generally, the particle size of aluminum powder is ranging from about 6 to about 16 μm, and the aluminum flake thickness is between about 18 nm and about 50 nm.

The electro-plated aluminum paste may be present in the coating composition in an amount of at least 1%by weight, suitably at least 2%by weight, such as at least 3%by weight, and up to 10%by weight, suitably up to 8%by weight, even up to 6%by weight, based on the total weight of the water-borne electro-plated silver coating composition.

Examples of commercially available electro-plated aluminum pastes include, but are not limited to, electro-plated aluminum pastes from Silberline Effect Pigments, Eckart Effect Pigments, Toyo Aluminum, Taiyang Chemical, BASF, Schlenk, and other pigment companies.

The water-borne electro-plated silver coating compositions according to the present application further comprise a passivation component that is used for passivating the electro-plated aluminum paste to impart water and chemical resistances to aluminum surface. The passivation component may include strong oxidants including, but not limited to, one or a mixture of any two or more of the following: nitrates, chromates, molybdates, manganates, chlorates, bromates, persulphates and bismuthates. For example, the strong oxidants may include any one of nitrates, chromates, molybdates, manganates, chlorates, bromates, persulphates, and bismuthates, or a mixture of any two of the above oxidants, such as a mixture of bromates and chromates, a mixture of manganates and bromates, a mixture of manganates and chromates, a mixture of manganates and molybdates, a mixture of molybdates and chromates, a mixture of molybdates and bromates, and the like, at a weight ratio ranging from 9: 1 to 1: 9 (e.g., 8: 1, 7: 1, 6: 1, 5: 1, 4: 1, 3: 1, 2: 1, 1: 1, 1: 2, 1: 3, 1: 4.1: 5, 1: 6, 1: 7, or 1: 8) . More specifically, the passivation component may include an aqueous solution of any one of the above oxidants or any mixtures thereof.

The concentration of the aqueous solution of strong oxidants is critical to the formation of the water-borne electro-plated silver coating compositions according to the present application. The term "concentration" as used herein refers to a concentration by mass percentage, that is, a concentration represented by the mass percentage of the solute with respect to the total mass of the entire solution (i.e., water plus oxidant (s) ) . The concentration may not only meet the requirements of the water solubility of the oxidant, but also can achieve the passivation of the electro-plated aluminum paste, so as to impart water and chemical resistances to the aluminum surface.

The inventors have found that when the passivation component has an oxidant concentration in the range of 0.1 to 15%, it produces good passivation effect on the electro-plated aluminum paste, thereby imparting good water resistance. The oxidant may be present in a concentration of at least 0.1%, suitably at least 1%, suitably at least 2%, such as at least 5%, and up to 15%, suitably up to 12%, such as up to 10%, or even up to 8%.

The passivation component may be present in the coating composition in an amount ranging from about 0.1%to about 5%by weight, based on the total weight of the water-borne electro-plated silver coating composition. If the level of the passivation component exceeds the above range, it might adversely affect the coating composition, including, for example, producing an undesired chemical reaction between the passivation component and organic components in the composition, thereby affecting product performance. Excess passivation component may further cause precipitation of solids, and affect the behavior of product in use.

The water-borne electro-plated silver coating compositions according to the present application further comprise a solvent and a co-solvent. Water-borne coating compositions comprise primarily water as solvent, and a small amount of co-solvent may be contained. The main function of co-solvent is to improve the solubility of resins in the coating, improve the ease-to-apply, control volatilization speed of the coating, and improve the film quality of the coating, etc. The co-solvent may comprise alcohol solvents, ether solvents, ketone solvents, and the like. The solvents and the co-solvents may be present in the coating composition in an amount ranging from about 60%to about 90%by weight, based on the total weight of the water-borne electro-plated silver coating composition.

The water-borne electro-plated silver coating compositions according to the present application further comprise various additives/adjuvants which are known in the coatings art. The additives/adjuvants may comprise, but are not limited to, wetting and dispersing agents, anti-settling aids, anti-sagging aids, antioxidants, pH regulators, etc. The additive (s) , if present, is in an amount of 10 wt%or less based on the total weight of the water-borne electro-plated silver coating composition.

The water-borne electro-plated silver coating compositions according to the present application have excellent color effect, long-term storage stability, and economic advantages. These advantages and effects are achieved by use of specific elements and specific preparation processes. In particular, a specific concentration of aqueous strong oxidant solution made from inorganic strong oxidants (including any one of nitrates, chromates, molybdates, manganates, chlorates, bromates, persulfates and bismuthates or a mixture of any of the foregoing) is used as the passivating agent according to the present application. The aqueous oxidant solution may react with aluminum surfaces in the electro-plated aluminum paste to form a dense protective film, which prevents a reaction of water with aluminum, thereby providing the desired water resistance and color effect.

Therefore, the present application also provides methods of preparing a water-borne coating composition, comprising: (1) mixing a resin component with an electro-plated aluminum paste and dispersing to form a pre-dispersed liquid (a) ; (2) adding a passivation component to the pre-dispersed liquid (a) , stirring and dispersing to form a pre-dispersed liquid (b) ; and (3) adding water, optionally co-solvent and adjuvant to the pre-dispersed liquid (b) to form water-borne coating composition.

In embodiments, the passivation component may be added to the pre-dispersed liquid (a) in multiple steps. For example, the passivation component may be added to the pre-dispersed liquid (a) in two steps. In one embodiment of the present application, methods of preparing a water-borne coating composition, comprising: (1) mixing a resin component with an electro-plated aluminum paste and dispersing to form a pre-dispersed liquid (a) ; (2’) adding a portion of a passivation component to the pre-dispersed liquid (a) , stirring and dispersing to form a pre-dispersed liquid (b1) ; (2” ) adding the remaining portion of the passivation component to the pre-dispersed liquid (b1) , stirring and dispersing to form a pre-dispersed liquid (b2) ; and (3) adding water, optionally co-solvent and adjuvant to the pre-dispersed liquid (b2) to form water-borne coating composition.

In particular, the method may further comprise, prior to the steps (3) , a step of testing the water resistance comprising: taking out an appropriate amount of the pre-dispersed liquid, e.g., the pre-dispersed liquid (b) or (b2) , diluting it with an appropriate amount of co-solvent (e.g., including, but not limited to, isopropanol, ethanol, ethylene glycol butyl ether, propylene glycol methyl ether, acetone, dipropylene glycol methyl ether) (pre-dispersed liquid : co-solvent = 2～1) ; mixing the diluted pre-dispersed liquid with water at a weight ratio of 1: 3, visually observing the state of the electro-plated aluminum powders in the mixture; if the aluminum powder state does not change over one hour, it indicates that the passivation treatment is successful. When mixing with water in line with the aforesaid steps, un-passivated electro-plated aluminum powders would react with water instantaneously, resulting in change of aluminum powder state, and the aluminum powders go black and dark.

Water resistance test is highly important to the preparation of the coating compositions according to the present application. Water in the step (3) cannot be added to the pre-formed dispersion of the coating composition, e.g., the pre-dispersed liquid (b) or (b2) , until the water resistance test is passed. Otherwise, the coating composition is likely to be damaged due to the rapid reaction between water and aluminum. If the pre-formed dispersion of the water-borne electro-plated silver coatings is irreversibly damaged, the raw materials used in the previous steps would have to be discarded. After the water resistance test is passed, adjuvants and water are added to the pre-dispersed liquid, e.g, (b) or (b2) , to prepare the final coating composition according to the present application.

The resin component can be dispersed with water, optionally co-solvent and adjuvant prior to mixing with the electro-plated aluminum paste. As used herein, “disperse/dispersed/dispersing” can be carried out by any suitable dispersion technology known in the art, such that, e.g., the resin component and the electro-plated aluminum paste are fully mixed, or the passivation component and the pre-dispersed liquid are fully contacted.

For example, in the step (1) , dispersing the resin component and the electro-plated aluminum paste for 15 minutes to 2 hours, or 30 minutes to 1.5 hours; in the step (2’) dispersing the pre-dispersed liquid (a) and a portion of the passivation component for 3 to 5 hours; in the step (2”) , dispersing the pre-dispersed liquid (b1) and the remaining of the passivation component for 2 to 3 hours. In embodiments of the present application, the dispersion followed by standing overnight (about 12 hours) .

Figure 2 indicates schematic diagrams showing a dispersion formed after 1 hour standing of a passivated electro-plated aluminum paste mixed with water (a) , and a dispersion formed after 1 hour standing of an un-passivated electro-plated aluminum paste mixed with water (b) (the tested electro-plated aluminum paste: Eckart L-56161 electro-plated aluminum powders, particle size: 8-12 μm, aluminum flake thickness: 20-30 nm) . It can be seen that in Fig. 2 (a) , the passivated electro-plated aluminum paste forms a uniform and stable dispersion in the aqueous solution, indicating that the aluminum surfaces have been passivated, and do not further react with water; and in Fig. 2 (b) , after mixing the aluminum powders in the untreated silver-plated aluminum paste react rapidly with water, and float on the surface of the solution.

The method of preparing the water-borne electro-plated silver coating composition according to the present application requires controlling the process steps and time. The time of mixing and dispersing the electro-plated aluminum paste and the passivation component is important to the storage time of the formed coating product, that is, the longer the mixing and dispersing time, the longer the storage time. Although not bound by any theory, it is believed that the electro-plated aluminum paste must be fully contacted with the passivation component so as to effectively form a protective film on the surface of the aluminum powders, thereby achieving excellent water resistance and color effect. Otherwise, in the case of non-fully (or partially) contacted, there may leave a partial of uncovered aluminum surface within the electo-plated aluminum paste which would react with water then result in poor water resistance and color effect of the coating composition. The “fully contacted” effect may be accomplished by common technical means in the art, such as vigorous mixing, longtime mixing, etc.

The co-solvents used in the preparation of the water-borne electro-plated silver coating composition according to the present application comprise, but are not limited to, ethanol, acetone, ethylene glycol butyl ether, diethylene glycol methyl ether, dimethylethanolamine, any mixtures thereof or the like. The adjuvants used in the preparation of the water-borne electro-plated silver coating composition according to the present application comprise, but are not limited to, wetting and dispersing agents, anti-settling aids, leveling agents, antifoaming agents, adhesion promoters, pH regulators, any mixtures thereof or the like.

In addition, it is desirable to control the pH of the water-borne electro-plated silver coating composition according to the present application such that the whole system is in a weakly alkaline environment, thereby enhancing the stability of the electro-plated aluminum paste and extending the storage time of the whole coating composition. This weakly alkaline environment can be achieved, for example, by using an adjuvant such as dimethylethanolamine or the like.

The water-borne electro-plated silver coating compositions according to the present application are applied by any standard coating methods in the art, such as electrocoating, spraying, electrostatic spraying, dipping, roll coating, brush coating, etc., and then cured to form a coating layer. The water-borne electro-plated silver coatings according to the present application may be sprayed to a thickness of 1-3 μm to provide excellent color effect, brightness and appearance.

The water-borne electro-plated silver coating compositions according to the present application may be applied to various substrates as known in the industrial field. Preferably, the substrates are metal substrates, including, but not limited to, aluminum alloys, aluminum products, stainless steel, copper, and iron, etc. The metal substrates particularly refer to aluminum hub, automobile body/part, building, billboard, etc.

EXAMPLES

The following examples are provided to further illustrate the application. However, it should not be construed as limiting the application to the details of the examples. Unless otherwise indicated, all parts and percentages in the following examples and throughout the specification are based on weight. Unless otherwise indicated, all the procedures are performed at an atmospheric pressure and temperature.

Example 1. Preparation of the resin component

50 g of a water-borne acrylic resin (SK6517 resin, Shanghai Shuike) was mixed with 4 g of an organic amine (DMEA, BASF) , and pre-dispersed for 30 minutes to form a pre-dispersion. Then, 16 g of a water-soluble amino resin (MR-603LF (13g) &MR-627 (3g) , Changchun Chemicals) , 3 g of a water-soluble polyester resin (SK9080A resin, Shanghai Shuai) and 2 g of adjuvants (BYK-333 (1 g) , BYK; SURFYNOL 104E (1 g) , Gas Chemicals) were added to the pre-dispersed liquid, vigorously mixed and dispersed for about 30 to 40 minutes. Then, 15 g of a co-solvent (ethylene glycol butyl ether, INEOS) and 10 g of water were added under stirring, and the mixture was stirred for about 30 to 50 minutes to obtain a resin intermediate (apre-dispersion of the resin component) .

Example 2. Preparation of the water-borne electro-plated silver coating composition

5 g of the resin intermediate as prepared in Example 1 and 4 g of electro-plated aluminum powders (L-56161, Eckart) were pre-dispersed for 30 minutes to form a pre-dispersion. 10 g of a co-solvent (acetone: ethylene glycol butyl ether = 1: 1) , 0.5 g of a passivation component (manganate: bromate = 1: 9, concentration of 5%in aqueous solution) , and 0.5 g of a wetting and dispersing agent (BYK333, BYK) were added to the pre-dispersion, vigorously dispersed for 3 to 5 hours, and stood overnight (about 12 hours) . Then, 0.2 g of a passivation component (manganate: bromate = 1: 9, concentration of 5%in aqueous solution) was added to the mixture, vigorously stirred, and stood overnight (about 12 hours) . Next, 10 g of isopropyl alcohol (Shell Petroleum) and 5 g of diethylene glycol methyl ether (Dow Chemical) were added and stirred for 2 hours. Then, the resultant mixture was tested for water resistance by the following procedures: An appropriate amount of sample was taken out, diluted with ethylene glycol monomethyl ether. The diluted sample was mixed with water at a weight ratio of 1: 3. The state of the electro-plated aluminum powders in the mixture was visually observed. After the test was passed, 0.5 g of an anti-settling agent (BYK-420, BYK) , 0.5 g of an anti-sagging agent (AQ-633E, DSB) , and 64.8 g of de-ionized water were added to the mixture to prepare the water-borne electro-plated silver coating composition according to the present application.

Example 3. Preparation and assessment of coating layer

3.1. Color appearance

Two samples of the water-borne electro-plated silver coating prepared above (each 300 g) were weighed. One was stored at -30℃ for 7 days (-30℃ x 7 days) , and the other was stored at 40℃ for 30 days (40℃ x 30 days) . Then, the samples were stored at room temperature for additional one day. Then, two samples were re-stirred and compared with a standard sample. If the samples stored under conditions of -30℃ x 7 days and 40℃ x 30 days exhibit significant difference from the standard sample, the samples fail the storage test. If no change is observed in the appearance or the aluminum power state of the test samples, the samples pass the storage test.

Remarks: The standard sample is a reference sample prepared under the same conditions prior to storage.

3.2. Color effect

Sample panels were respectively prepared from the samples stored at -30℃ x 7 days and 40℃ x 30 days according to the following procedures:

Aluminum alloy substrate→ pretreatment (polishing, cleaning then drying) → black or gray primer powder (PPG, product name: PCFC90203F) → 170℃ x 20 min → cooling → spraying the water-borne electro-plated silver coating → standing for 5 min → 170℃ x 10 min →cooling → clear powder (PPG, product name: PCC10103) .

The sample panels prepared by this process were compared with a standard panel. No obvious difference was visually observed in the appearance of the panels. The result shows that the color effect was not adversely affected after storage at -30℃ x 7 days and 40℃ x 30 days. The samples passed the test.

3.3. Adhesion test

Sample panels were respectively prepared from the samples stored at -30℃ x 7 days and 40℃ x 30 days according to the following procedure and tested for adhesion.

Aluminum alloy substrate → pretreatment (polishing, cleaning then drying) → black or gray primer powder (PPG, product name: PCFC90203F) → 170℃ x 20 min → cooling →spraying the water-borne electro-plated silver coating according to the present application →standing for 5 min → 170℃ x 10 min → cooling (taking sample for testing the adhesion of primer powder + electro-plated silver coating) → clear powders (PPG, product name: PCC10103) → spraying the water-borne electro-plated silver coating of the present application → standing for 5 min → 170℃ x 10 min → clear powders (PPG, product name: PCC10103) (taking sample for testing the adhesion of primer powder + electro-plated silver coating + clear powders) →spraying the water-borne electro-plated silver coating of the present application → standing for 5 min → 170℃ x 10 min → cooling (taking sample for testing the adhesion of primer powder +electro-plated silver coating + clear powders + electro-plated silver coating) → clear powders (PPG, product name: PCC10103) → spraying the water-borne electro-plated silver coating →standing for 5 min → 170℃ x 10 min → clear powders (PPG, trade name: PCC10103) (taking sample for testing the adhesion primer powder + electro-plated silver coating + clear powders +electro-plated silver coating + clear powders) .

10 x 10 lines were scratched with an NT blade on the sample surfaces (total one hundred of 1 mm ² squares, the lines should be deep to the substrate) , which were kept as flat as possible (by keeping the blade sharp) . 3M Scotch tape (No. 4-1000) was adhered to the sample surface and pressed compact with an eraser so that the tape was in full contact with the test surface, followed by standing for 3 minutes. The tape was quickly torn in the direction of 90 degrees. The test surface was visually inspected and rated according to ISO standards.

ISO rating standards

0-rating: 5B

Smooth cutting edges, no peeling.

1-rating: 4B

A little coating peeling present at intersections of incisions, but not more than 5%of cross-cutting area being affected.

2-rating: 3B

Coating peeling present at intersections of incisions or along edges of incisions, more than 5%, but not more than 15%of cross-cutting area being affected.

3-rating: 2B

Part or all of coating peeling in large fragments along edges of cutting, and/or from different portions of grids, more than 15%, but not more than 35%of cross-cutting area being affected.

4-rating: 1B

Coating peeling in large fragments along edges of cutting, and/or some grids peeling as whole, more than 35%, but not more than 65%of cross-cutting area being affected.

5-rating: 0B

A piece of coating peeling at intersections of incisions or along edges of incisions, more than 65%of cross-cutting area being affected.

Typically, coating systems to be used in hubs require a test result of 4B or above.

Table 1. Results of Adhesion Test

Remarks: Dry film thickness of primer powder: 90-120 μm.

Dry film thickness of electro-plated silver coating: 3-5 μm.

Dry film thickness of clear powder: 90-120 μm.

3.4. Water soaking test

Sample pieces were prepared by using the electro-plated silver coating samples stored under conditions of -30℃ x 7 days and 40℃ x 30 days in accordance with the following procedure, respectively.

Aluminum alloy substrate → pretreatment (polishing, cleaning then drying) → black or gray primer powder (PPG, product name: PCFC90203F) → 170℃ x 20 min → cooling →spraying the water-borne electro-plated silver coating → standing for 5 min → 170℃ x 10 min → cooling → clear powder (PPG, product name: PCC10103) .

The sample pieces were immersed in water bath at a constant temperature of 60℃, and taken out after 48 hours. It was visually observed that no bubble was attached to the sample pieces; the color did not change or whiten; the coating film did not soften; and the adhesion was not lost. It indicated that the sample pieces passed the test.

3.5. Excessive baking test

Sample pieces were prepared by using the electro-plated silver coating samples placed under conditions of -30℃ x 7 days and 40℃ x 30 days in line with the following procedures.

Aluminum alloy substrate → pretreatment (polishing, cleaning then drying) → black gray primer powder (PPG, product name: PCFC90203F) → 170℃ x 20 min → cooling → spraying the water-borne electro-plated silver coating → standing for 5 min → 170℃ x 10 min →cooling → clear powder (PPG, product name: PCC10103) .

The sample pieces were baked in an oven at 180 ℃ for 2 hours. Then, the sample pieces were removed, dried, and tested for adhesion. No adhesion loss or appearance change was visually observed, indicating that the sample pieces passed the test.

Example 4. Performance comparisons of the water-borne electro-plated silver coating compositions according to the present application with commercially available water-borne electro-plated silver coating compositions.

4.1. In this example, the water-borne electro-plated silver coating according to the present application was compared with an existing water-borne electro-plated silver coatings treated with phosphate resin (referred to as "phosphate water-borne electro-plated silver coating" ) and an existing SO ₂-encapsulated water-borne electro-plated silver coating based on the performance tests as provided in Table 2. The results are shown in Table 2.

Table 2. Performance comparison of the coatings according to the present application with commercially available coatings

4.2. 10 g of each of the water-borne electro-plated silver coating prepared in accordance with the present application, the phosphate electro-plated silver coating, and the SO ₂-encapsulated water-borne electro-plated silver coating were weighed, and diluted with water to a 10%aqueous solution. The solutions were stored for a time period as listed in Table 3. The results are shown in Table 3.

Table 3. Testing Results of Storage Stability of Coatings

It can be seen from the results as shown the above tables that the water-borne electro-plated silver coating composition according to the present application exhibits superior comprehensive performances as compared with the existing water-borne electro-plated silver coating compositions. The coating compositions according to the present application have excellent color effect, long-term storage stability, and low production cost.

Having described the specific aspects of the invention, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention. The appended claims are intended to cover all such variations and modifications.

Claims

A water-borne coating composition, comprising a resin component, a passivation component and an electro-plated aluminum paste.
The water-borne coating composition of claim 1, wherein the resin component comprises an acrylic resin, a saturated or unsaturated polyester resin, a polyurethane dispersion, an acrylic emulsion, an amino resin and any mixture thereof.
The water-borne coating composition of claim 1, wherein the passivation component comprises an aqueous solution of an oxidant.
The water-borne coating composition of claim 3, wherein the oxidant is selected from the group consisting of nitrates, chromates, molybdates, manganates, chlorates, bromates, persulfates, bismuthates and any mixture thereof.
The water-borne coating composition of claim 3, wherein the aqueous solution of the oxidant has a concentration ranging from 0.1 to 15%.
The water-borne coating composition of claim 1, wherein the passivation component is present in the coating composition in an amount of 0.1 to 5wt%based on the total weight of the water-borne coating composition.
A method of preparing a water-borne coating composition, comprising:

(1) mixing a resin component with an electro-plated aluminum paste and dispersing to form a pre-dispersed liquid (a) ;

(2) adding a passivation component to the pre-dispersed liquid (a) , stirring and dispersing to form a pre-dispersed liquid (b) ; and

(3) adding water, optionally co-solvent and adjuvant to the pre-dispersed liquid (b) to form water-borne coating composition.
The method of claim 7, the passivation component is added to the pre-dispersed liquid (a) in multiple steps.
The method of claim 7 or 8, further comprising testing for water resistance prior to step (3) .
A coated substrate, comprising:

(1) a substrate,

(2) a water-borne coating composition applied to at least a portion of the substrate, wherein the water-borne coating composition comprises a resin component, a passivation component and an electro-plated aluminum paste.
The coated substrate of claim 10, wherein the substrate comprises a metallic substrate.
The coated substrate of claim 11, wherein the metallic substrate is selected from the group consisting of aluminum alloys, aluminum, stainless steel, copper, and iron.