Claims:We Claim:

1. A primer-less clear coating composition to coat the metal or metal alloy surfaces, particularly the automobile wheels, directly without the primer and/or base coat to provide adhesion as well as anticorrosion properties besides complying with performance tests like pencil hardness, weatherability resistance or flow/levelling and aesthetic tests like Crater/Cissing, recoatability or gloss; wherein the composition comprises
i. Acrylic Resins;
ii. Melamine Resin;
iii. Hindered amine light stabilizers (HALS);
iv. UV absorbers;
v. Levelling agents;
vi. Solvents;
vii. Conductivity Additives;
viii. Additive (a) - epoxy functional silane oligomer;
ix. Additive (b) - Silicone- and polyether-macromer-modified polyacrylate or Silicone- and polyether- modified polyacrylate; and
x. Additive (c) - solution of unmodified low molecular weight solid diglycidyl ether of bisphenol-A resin in xylene.
2. The coating composition as claimed in claim 1, wherein the solvents used are selected from alcohol such as methanol, ethanol, propanol or butanol; aromatic hydrocarbons such as o-xylene, p-xylene, m-xylene, mixed xylene, high solvency C9 aromatic fluid or ethylene glycol n-butyl ether acetate solvent.
3. The coating composition as claimed in claim 1, wherein the additive (a) used in the composition of the invention is 2 to 4 parts by weight of the composition.
4. The coating composition as claimed in claim 1, wherein the additive (a) i.e. epoxy functional silane oligomer has formula (I);

5. The coating composition as claimed in claim 1, wherein the additive (b) used in the composition of the invention is 0.11 to 0.22 parts by weight of the composition.
6. The coating composition as claimed in claim 1, wherein the additive (b) i.e. Silicone- and polyether-macromer-modified polyacrylate used in the composition has density (20° C) of 1.07 gm/ml, Non-volatile matter (10 min., 150°C): > 97 %, and Flash point: > 100 °C.
7. The coating composition as claimed in claim 1, wherein the additive (b) i.e. Silicone- and polyether- modified polyacrylate has density (20° C) of 1.07 gm/ml, Non-volatile matter (10 min., 150°C): > 96 %, and Flash point: > 100 °C.
8. The coating composition as claimed in claim 1, wherein the additive (c) used in the composition of the invention is 3 to 5 parts by weight of the composition.
9. The coating composition as claimed in claim 1, wherein the additive (c) i.e. solution of unmodified low molecular weight solid diglycidyl ether of bisphenol-A resin in xylene has Epoxy equivalent weight based on solids of 450 - 500 g/eq (ASTM D 1652-04), Viscosity @25°C of 8,000-13,000 cP (Brookfield viscosity) (ASTM D 2196-05), Non-volatile content of 74-76 % (ASTM D 1259-06), Epoxide Value of 2.00-2.22 (ASTM D 1652-04), Density @25°C of 1.07 g/cc (ASTM D 1475-98), Water content 0.5 % max. (ASTM E 203-01) and Flash point of 30°C (ASTM D 93).
10. The coating composition as claimed in any of the preceding claims, wherein the composition comprises: (i) 53.72 (parts by wt.) of Acrylic Resins; (ii) 18.91 (parts by wt.) of Melamine Resin; (iii) 0.91 (parts by wt.) of Hindered amine light stabilizers (HALS); (iv) 2.15 (parts by wt.) of UV absorbers; (v) 0.09 (parts by wt.) of Levelling agents; (vi) 14.93 to 19.04 (parts by wt.) of Solvents; (vii) 0.07 (parts by wt.) of Conductivity Additives; (viii) 2 to 4 (parts by wt.) of Additive (a) - epoxy functional silane oligomer; (ix) 0.11 to 0.22 (parts by wt.) of Additive (b) - Silicone- and polyether-macromer-modified polyacrylate or Silicone- and polyether- modified polyacrylate; and (x) 3 to 5 (parts by wt.) of Additive (c) - solution of unmodified low molecular weight solid diglycidyl ether of bisphenol-A resin in xylene.
11. A method of primer-less clear coating the metal or metal alloys surfaces, particularly the automobile wheels, directly without the primer and/or base coat to provide adhesion as well as anticorrosion properties besides complying with performance tests like pencil hardness, weatherability resistance or flow/levelling and aesthetic tests like Crater/Cissing, recoatability or gloss; wherein the method comprises
coating the metal or metal alloy surfaces directly with the coating composition as claimed in claim 1 followed by subjecting the coated metal or metal alloy surfaces to flash off for at least 8 to 10 minutes followed by baking at 140 to 160° C for at least 30 minutes.
12. The method as claimed in claim 11, wherein the metal or metal alloy surfaces are coated with the coating composition to achieve coating of at least 15 to 25 µ thickness.
13. The method as claimed in claim 11, wherein the baking step is carried out at 155° C for 30 minutes.
14. The method as claimed in claim 11, wherein the metal or metal alloy surfaces coated with the coating composition are air dried for 24 hours upon baking.

Dated this 29th day of December 2021

Dr. Shilpa Gharve
Patent Agent
(Reg. No. IN/PA 890)

, Description:Technical field of the invention:

The present invention is related to the field of metals or metal alloys coating.
Particularly, the present invention is related to the primer-less clear coating composition for metals or metal alloys, more particularly for automobile wheels.
The primer-less clear coating composition of the invention is applied as a coat on the metal or metal alloy surfaces, particularly all kinds of automobile wheels, directly without the primer and/or base coat. This coat provides adhesion as well as anticorrosion properties besides complies with performance tests like pencil hardness, weatherability resistance, flow/levelling, etc. and aesthetic tests like Crater/Cissing, recoatability, gloss, etc.
The present invention is also related to a method of primer-less clear coating of the metal or metal alloy surfaces, particularly all kinds of automobile wheels, directly without the primer and/or base coat to achieve adhesion as well as anticorrosion properties besides complying with performance tests like pencil hardness, weatherability resistance, flow/levelling, etc. and aesthetic tests like Crater/Cissing, recoatability, gloss, etc.

Background of the invention:

Vehicle wheels are made of alloys, specifically aluminium or magnesium alloy. The wheels are exceptionally vulnerable part of the vehicle to damage as those are the lowest part of the vehicle. Wheels are always in contact with debris, water, oil or grease. Furthermore, the spokes of the wheels are literally inches away from the brakes. Hence, when the brake pads press against the rotors, the brake dust created can easily have adverse impact on the wheels. The wheels are susceptible to corrosion over a period of time. Especially in humid climatic conditions and adverse road conditions, a coating film of the wheels is susceptible to degradation due to damage, and therefore, the outer appearance of the wheels easily deteriorates or rust is likely to be formed due to the corrosion of the alloy. Therefore, the wheels are an exceptionally good candidate for the protection from corrosion and extreme weather. At the same time, they should have good aesthetic or cosmetic feature which increases the overall look or value of the vehicle. In the recent styling era, the painted wheels are mostly desired by the consumers.
The alloy wheels are subjected to chemical conversion treatment and then to coating for imparting an anticorrosive property, a cosmetic property, and weatherability. The coating is applied to the whole area or a part of the surface thereof. Usually, the wheels are coated with primer coat followed by the base coat and / or clear top coat to impart anticorrosive property, a cosmetic property, and weatherability properties.
Thus, there was research carried out to develop coatings and the method for forming a coating film having an anticorrosive, cosmetic and weatherability performance at a level enough for coping with such problems.
KR101428589 (B1) discloses the middle liquid paint composition for sputtering coating of an aluminium alloy wheel. This patent has a purpose of providing a middle liquid paint preventing the crack of a sputtering surface occurring when an existing paint is applied, improving an exterior levelling, and producing a wheel having an excellent brightness and various properties after finishing an acrylic powder topcoat process. The middle liquid paint composition comprising 45-65 wt. % (based on 55 % of solid contents) of an acryl or polyester resin solution, 15-35 wt. % (based on 60 % of solid contents) of a melamine resin solution, 1-15 wt. % (based on 65 % of solid contents) of an epoxy resin solution, 1-8 wt. % of an additive, and 5-25 wt. % of a solvent.
US2013313888 (A1) discloses the coating composition with the superior cosmetic property as well as an anticorrosive property much enough for preventing corrosion even in the use in an area where the coating film is susceptible to salt damage. The method for coating the aluminium wheel includes applying an anticorrosive coating composition onto the aluminium wheel, and thereafter applying a clear coating composition to form a transparent multilayer coating film. The anticorrosive coating composition contains an acrylic resin (1) having a weight average molecular weight of 50,000 to 140,000, a glass transition point of 20 to 50° C, a hydroxyl value of 10 to 50 mgKOH/g, an acid value of 10 to 40 mgKOH/g, and an epoxy resin (2) having an epoxy equivalent of 210 to 1,000 g/eq and contains the epoxy resin (2) in an amount of 5 to 20 parts by weight on the solid matter basis to 100 parts by weight of the solid matter of the acrylic resin (1).
JPH05209141 (A) provided the weather-resistant coating film composed of specific primer layer, base-coat layer and clear coat layer formed on an aluminium part, having excellent adhesivity, corrosion resistance and paintability and useful for the coating of aluminium parts such as car wheel. The primer layer consisting of an epoxy-polyester hybrid powder paint formed on an aluminium part. The base-coat layer composed of an acrylic high-solid metallic paint formed on the primer layer. The clear coat layer composed of an acrylic high-solid paint and formed on the base-coat layer.
KR20180131048 (A) disclosed the middle liquid glossy transparent coating composition for improving the corrosiveness of aluminium alloy D/C wheels. This composition includes a polyester resin, a melamine resin, and an epoxy resin as basic skeletons, and additives such as a levelling agent, a curing accelerator, a corrosion-preventing pigment and the like.
KR20170024834 (A) disclosed the middle liquid paint composition for sputtering coating of an aluminium alloy wheel. The middle liquid paint composition comprising: 35-60 wt. % (based on 55 % of solid contents) of an acryl solution or a polyester resin solution, 10-25 wt. % (based on 60 % of the solid contents) of a melamine resin solution, 1-15 wt. % (based on 65 % of the solid contents) of an epoxy resin solution, at least one of 1-7 wt. % of an organic pigment and 20-35 wt. % of a white pigment, 2-8 wt. % of an additive, 0.1-5.0 wt. % of a dispersant, and 5-25 wt. % of a solvent.
KR20170032747 (A) provided the middle layer paint composition for dry-plating, which is applied to a sputtering method, a dry-type method for producing high brightness automotive aluminium wheels. The intermediate layer paint composition comprising a polyurethane-based resin, a desiccant, a storage stabilizer, a levelling agent and a curing agent.
CN102167951 (A) disclosed an environment-friendly dual-curing vacuum coating primer special for an automobile wheel hub. This coating comprises the following components in percentage by mass: 25-35 % of NCO-containing polyurethane acrylate, 5-10 % of aliphatic polyurethane diacrylate, 5-10 % of phenolic epoxy acrylate, 10-20 % of aliphatic epoxy acrylate, 20-35 % of reactive diluent, 1-5 % of photoinitiator and 0.1-1 % of assistant.
We have come across prior arts where the wheels are always coated with multilayer coatings like primer coat, base coat and top or clear coat to achieve anticorrosive property, cosmetic property, and weatherability properties. Thus, prior arts require two or more coating compositions (inventories) and makes the method of coating laborious. We have not found any prior art reference to have single layer coating or primer-less clear coating to coat the automobile wheels directly without the primer and/or base coat to provide properties namely adhesion as well as anticorrosion properties besides complying with performance tests like pencil hardness, weatherability resistance, flow/levelling, etc. and aesthetic tests like Crater/Cissing, recoatability, gloss, etc.
There is need to develop the single layer coating or primer-less clear coating to coat the metal or metal alloy surfaces, particularly all kinds of automobile wheels, directly without the primer and/or base coat and still provides properties namely adhesion as well as anticorrosion properties besides complies with performance tests like pencil hardness, weatherability resistance, flow/levelling, etc. and aesthetic tests like Crater/Cissing, recoatability, gloss, etc.

Objectives of the invention:

A primary objective of the present invention is to provide a primer-less clear coating composition for the metal or metal alloy surfaces, particularly all kinds of automobile wheels, directly without the primer and/or base coat.
Another objective of the present invention is to provide the primer-less clear coating composition for the metal or metal alloy surfaces, particularly all kinds of automobile wheels, directly without the primer and/or base coat, said coating achieves adhesion as well as anticorrosion properties besides complies with performance tests like pencil hardness, weatherability resistance, flow/levelling, etc. and aesthetic tests like Crater/Cissing, recoatability, gloss, etc.
Still another objective of the present invention is to provide the primer-less clear coating composition for the metal or metal alloy surfaces, particularly all kinds of automobile wheels, directly without the primer and/or base coat, thereby eliminating need of primer coat or base coat.
Still another objective of the present invention is to provide the primer-less clear coating composition for the metal or metal alloy surfaces, particularly all kinds of automobile wheels, directly without the primer and/or base coat, thereby reducing inventory like replacing two coating compositions namely primer coat and top coat by single coat composition thereby reducing cost, laborious efforts and energy consumption.
Yet another objective of the present invention is to provide the primer-less clear coating composition for the metal or metal alloy surfaces, particularly all kinds of automobile wheels, directly without the primer and/or base coat, said coating is efficient, economical and simple.
An additional objective of the present invention is to provide the method of primer-less clear coating of the metal or metal alloy surfaces, particularly all kinds of automobile wheels, directly without the primer and/or base coat, said method eliminates laborious task of multicoating and reduce inventory cost, energy, manpower and cycle time thereby making the method simple, economical and efficient.

Summary of the Invention:

The metal and metal alloy surfaces, particularly all kinds of automobile wheels are coated with the primer-less clear coating composition of the present invention eliminating the need of multilayer coating such as primer coat, and/or the base coat and top or clear coat to achieve adhesion as well as anticorrosion properties besides complying with performance tests like pencil hardness, weatherability resistance, flow/levelling, etc. and aesthetic tests like Crater/Cissing, recoatability, gloss, etc.
It is surprising to note that the additives namely (i) epoxy functional silane oligomer having formula (I);

Formula (I)
(ii) Silicone- and polyether-macromer-modified polyacrylate having density (20° C) of 1.07 gm/ml, Non-volatile matter (10 min., 150°C): > 97 %, and Flash point: > 100 °C or Silicone- and polyether- modified polyacrylate having density (20° C) of 1.07 gm/ml, Non-volatile matter (10 min.,150°C): > 96 %, and Flash point: > 100 °C and
(iii) solution of unmodified low molecular weight solid diglycidyl ether of bisphenol-A resin in xylene having Epoxy equivalent weight based on solids of 450 - 500 g/eq, Viscosity @25°C of 8,000 - 13,000 cP (Brookfield viscosity), Non-volatile content of 74 - 76 %, Epoxide Value of 2.00 - 2.22, Density @25°C of 1.07 g/cc, Water content 0.5 % max. and Flash point of 30°C;
if added in the clear coat composition comprising acrylic resin and melamine along with stabilizer, UV absorber, levelling agent, conductivity additive and solvent makes the composition useful to coat the alloy wheels without the multilayer coating such as primer coat, and/or the base coat and top or clear coat to achieve adhesion as well as anticorrosion properties besides complying with performance tests like pencil hardness, weatherability resistance, flow/levelling, etc. and aesthetic tests like Crater/Cissing, recoatability, gloss, etc.

It is found that the concentration of each of the three additives is tested to achieve primer-less clear coating composition of the invention including them at optimum concentration which contribute to achieve important properties like adhesion as well as anticorrosion properties besides complying with performance tests like pencil hardness, weatherability resistance, flow/levelling, etc. and aesthetic tests like Crater/Cissing, recoatability, gloss, etc. by replacing multiplayer coating system by single coating with the primer-less clear coating composition of the present invention directly to alloy wheels.

According to the invention, there is provided a primer-less clear coating composition to coat the metal or metal alloy surfaces, particularly the automobile wheels, directly without the primer and/or base coat to provide adhesion as well as anticorrosion properties besides complying with performance tests like pencil hardness, weatherability resistance, flow/levelling, etc. and aesthetic tests like Crater/Cissing, recoatability, gloss, etc., wherein the composition comprises
i. Acrylic Resins;
ii. Melamine Resin;
iii. Hindered amine light stabilizers (HALS);
iv. UV absorbers;
v. Levelling agents;
vi. Solvents;
vii. Conductivity Additives;
viii. Additive (a) - epoxy functional silane oligomer;
ix. Additive (b) - Silicone- and polyether-macromer-modified polyacrylate or Silicone- and polyether- modified polyacrylate; and
x. Additive (c) - solution of unmodified low molecular weight solid diglycidyl ether of bisphenol-A resin in xylene.
Typically, the solvents used are selected from alcohol such as methanol, ethanol, propanol, butanol, etc; aromatic hydrocarbons such as o-xylene, p-xylene, m-xylene, mixed xylene, high solvency C9 aromatic fluid or ethylene glycol n-butyl ether acetate solvent.
Typically, the additive (a) used in the composition of the invention is 2 to 4 parts by weight of the composition.
Typically, the additive (a) i.e. epoxy functional silane oligomer has formula (I);

Typically, the additive (b) used in the composition of the invention is 0.11 to 0.22 parts by weight of the composition.
Typically, the additive (b) i.e. Silicone- and polyether-macromer-modified polyacrylate used in the composition has density (20° C) of 1.07 gm/ml, Non-volatile matter (10 min.,150°C): > 97%, and Flash point: > 100 °C.
Typically, the additive (b) i.e. Silicone- and polyether- modified polyacrylate has density (20° C) of 1.07 gm/ml, Non-volatile matter (10 min.,150°C): > 96 %, and Flash point: > 100 °C.
Typically, the additive (c) used in the composition of the invention is 3 to 5 parts by weight of the composition.
Typically, the additive (c) i.e. solution of unmodified low molecular weight solid diglycidyl ether of bisphenol-A resin in xylene has Epoxy equivalent weight based on solids of 450 - 500 g/eq (ASTM D 1652-04), Viscosity @25°C of 8,000 - 13,000 cP (Brookfield viscosity) (ASTM D 2196-05), Non-volatile content of 74 - 76 % (ASTM D 1259-06), Epoxide Value of 2.00 - 2.22 (ASTM D 1652-04), Density @25°C of 1.07 g/cc (ASTM D 1475-98), Water content 0.5 % max. (ASTM E 203-01) and Flash point of 30°C (ASTM D 93).
Typically, the composition of the invention comprises: (i) 53.72 (parts by wt.) of Acrylic Resins; (ii) 18.91 (parts by wt.) of Melamine Resin; (iii) 0.91 (parts by wt.) of Hindered amine light stabilizers (HALS); (iv) 2.15 (parts by wt.) of UV absorbers; (v) 0.09 (parts by wt.) of Levelling agents; (vi) 14.93 to 19.04 (parts by wt.) of Solvents; (vii) 0.07 (parts by wt.) of Conductivity Additives; (viii) 2 to 4 (parts by wt.) of Additive (a) - epoxy functional silane oligomer; (ix) 0.11 to 0.22 (parts by wt.) of Additive (b) - Silicone- and polyether-macromer-modified polyacrylate or Silicone- and polyether- modified polyacrylate; and (x) 3 to 5 (parts by wt.) of Additive (c) - solution of unmodified low molecular weight solid diglycidyl ether of bisphenol-A resin in xylene.

According to the invention, there is also provided a method of primer less clear coating the metal or metal alloy surfaces, particularly the automobile wheels, directly without the primer and/or base coat to provide adhesion as well as anticorrosion properties besides complying with performance tests like pencil hardness, weatherability resistance, flow/levelling, etc. and aesthetic tests like Crater/Cissing, recoatability, gloss, etc., wherein the method comprises:
Coating the metal or metal alloy surfaces directly with the coating composition of the invention followed by subjecting the coated metal or metal alloy surfaces to flash off for at least 8 to 10 minutes followed by baking at 140 to 160 ° C for at least 30 minutes.
Typically, the metal or metal alloy surfaces are coated with the coating composition to achieve a coating of at least 15 to 25 µ thickness.
Typically, the baking step is carried out at 155° C for 30 minutes.
Typically, the metal or metal alloy surfaces coated with the coating composition are air dried for 24 hours upon baking.

Detailed Description of the invention:

The terms “a,” “an,” “the” and similar referents used in the context of describing the invention following claims are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein is intended merely to better illustrate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
Certain embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Of course, variations on these described embodiments will become apparent to those of ordinary skill in the art upon reading the description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the below-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
Specific embodiments disclosed herein can be further limited in the claims using consisting of or and consisting essentially of language. When used in the claims, whether as filed or added per amendment, the transition term “consisting of excludes any element, step, or ingredient not specified in the claims. The transition term “consisting essentially of limits the scope of a claim to the specified materials or steps and those that do not materially affect the basic and novel characteristic(s). Embodiments of the invention so claimed are inherently or expressly described and enabled herein.
The term “parts per wt.” used herein intends to cover parts per weight of the composition.

In the convention technique, the alloy wheels, particularly aluminium or magnesium alloy wheels are subjected to a pre-treatment followed by applying a primer coating and lastly applying a top or a clear coat followed by baking to achieve properties such as anti-corrosion, weatherability resistance, adhesion and aesthetic appearance. The top or clear coat is responsible for the aesthetic appearance and weatherability resistance while the primer coat is primarily responsible for anti-corrosion and adhesion. This coating method requires two separate coating compositions, one primer coat composition and second top coat composition. This conventional method and compositions involve two steps coatings, two coating compositions, more laborious efforts, cost for two separate compositions and two steps coating method, time, inventory, manpower, etc.
In conventional technique, two coat compositions used which are the primer coat composition used is N METAL PRIMER 21 imported from Japan and top coat composition is provided in table 1.

Table 1: Top coat formulation
Sr. No. Components Parts by weight of the composition
1 Acrylic Resin 53.72
2 Melamine 18.91
3 Stabilizer(s) 0.91
4 Absorber(s) 2.15
5 Levelling agent 0.09
6 Conductivity additive 0.07
7 Solvents 24.15

In order to achieve objectives like
1. reducing inventory like replacing two coating compositions namely primer coat and top coat by single coat composition thereby reducing cost, laborious efforts and energy consumption; and
2. eliminating multiple stage coating, particularly primer coating followed by base coat followed by top coat, thereby reducing manpower, energy, cost, and cycle time and thus increasing productivity;
without compromising properties and achieving the desired adhesion, anticorrosion, gloss, pencil hardness, weatherability resistance, desired flow/levelling, free from Crater/Cissing and desired recoatability test results;
the conventional clear coat composition is modified by adding additives namely
a) Additive (a) - the epoxy functional silane oligomer;
b) Additive (b) - the silicone- and polyether-macromer-modified polyacrylate or silicone- and polyether- modified polyacrylate; and
c) Additive (c) - the solution of unmodified low molecular weight solid diglycidyl ether of bisphenol-A resin in xylene.
at specific proportion.

The primer-less clear coating composition of the invention is applied directly to coat the metal or metal alloy surfaces, particularly the automobile wheels, without the primer and/or base coat to provide adhesion as well as anticorrosion properties besides complying with performance tests like pencil hardness, weatherability resistance, flow/levelling, etc. and aesthetic tests like Crater/Cissing, recoatability, gloss, etc.
Typical primer-less clear coating composition of the invention comprises:
i. Acrylic Resins;
ii. Melamine Resin;
iii. Hindered amine light stabilizers (HALS);
iv. UV absorbers;
v. Levelling agents;
vi. Solvents;
vii. Conductivity additives;
viii. Additive (a) - epoxy functional silane oligomer;
ix. Additive (b) Silicone- and polyether-macromer-modified polyacrylate or silicone- and polyether- modified polyacrylate; and
x. Additive (c) solution of unmodified low molecular weight solid diglycidyl ether of bisphenol-A resin in xylene.

Typically, the acrylic resin used in the composition of the invention is 53.72 parts by wt. of the composition. The examples of acrylic resin used in the composition includes but not limited to ACR-461, DIANAL HR54, etc. The examples of the acrylic resins indicated here before are illustrative of the invention but not limitative of the scope thereof.
Typically, the melamine resin used in the composition of the invention is 18.91 parts by wt. of the composition. The example of the melamine resin used in the composition includes but not limited to SETAMINE US-138 BB-70, etc. The example of the melamine resin indicated herein is illustrative of the invention but intends to cover melamine resin having acid value of Max. 0.3 mg KOH/g (ISO: 3682), Colour APHA (Lico 200) of Max. 50 APHA (ISO: 6271), Non-Volatiles of 68 - 72 % (ISO: 3251), Viscosity (23°C at 100 s-1) of 1.1 - 1.7 Pa.s (ISO: 3219), Density 1.03 kg/dm3 (DIN 53217) and Flash point of 31 °C (ISO: 1523).
Typically, the Hindered amine light stabilizer (HALS) used in the composition of the invention is 0.91 parts by wt. of the composition. The example of the HALS used in the composition includes but not limited to Tinuvin® 292, etc. The example of the HALS indicated herein is illustrative of the invention but intends to cover basic pentamethylpiperidine derivative having molecular weight in the range of 370 to 509 g/mol, viscosity at 20 °C (68 °F) of ~ 450 mPa.s (DIN 53018/53019), density at 20 °C (68 °F) of 0.97 – 1.01 g/cm³ (DIN 51757) and flash point of 202 – 206 °C (396 – 403 °F) (DIN EN ISO 2719).
Typically, the UV absorbers used in the composition of the invention is 2.15 parts by wt. of the composition. The example of the UV absorbers used in the composition includes but not limited to hydroxyphenyl-triazine (HPT) UV absorbers such as TINUVIN ® 400 or benzotriazole-based UV absorbers such as Tinuvin® 384-2.
Typically, the levelling agent used in the composition of the invention is 0.09 parts by wt. of the composition. The example of the levelling agent used in the composition includes but not limited to acrylic based flow/levelling agents such as LEVELLER S_N.
Typically, the solvents used in the composition of the invention is 14.93 to 19.04 parts by wt. of the composition. Preferably, the solvents used in the composition of the invention is 16.06 parts by wt. of the composition. The example of the solvents used in the composition includes but not limited to aliphatic alcohol such as methanol, ethanol, propanol or butanol; aromatic hydrocarbon such as o-xylene, m-xylene, p-xylene and mixed xylene, high solvency C9 aromatic fluid such as Solvesso TM 100 or ethylene glycol n-butyl ether acetate such as Butyl Cellosolve TM Acetate solvent.
Typically, the conductivity additive used in the composition of the invention is 0.07 parts by wt. of the composition. The example of the conductivity additive used in the composition includes but not limited to solution of an alkylolammonium salt of an unsaturated acidic carboxylic acid ester such as BYK-ES 80 or halogen free cationic additive such as Efka® 6782.
Typically, the additive (a) used in the composition of the invention is 2 to 4 parts by wt. of the composition. Preferably, the additive (a) used in the composition of the invention is 3.58 parts by wt. of the composition.
Typically, example of the additive (a) namely the epoxy functional silane oligomer used in the composition includes but not limited to CoatOSil* MP 200.
Typically, the additive (b) used in the composition of the invention is 0.11 to 0.22 parts by wt. of the composition. Preferably, the additive (b) used in the composition of the invention is 0.18 parts by wt. of the composition.
Typically, the additive (b) namely Silicone- and polyether-macromer-modified polyacrylate has density (20° C) of 1.07 gm/ml, Non-volatile matter (10 min., 150°C): > 97 %, and Flash point: > 100 °C. The typical example of the Silicone- and polyether-macromer-modified polyacrylate includes but not limited to BYK 3568.
Typically, the additive (b) namely Silicone- and polyether- modified polyacrylate has density (20° C) of 1.07 gm/ml, Non-volatile matter (10 min., 150°C): > 96 %, and Flash point: > 100 °C. The typical example of the Silicone- and polyether- modified polyacrylate includes but not limited to BYK-LP X 24228.
Typically, the additive (c) used in the composition of the invention is 3 to 5 parts by wt. of the composition. Preferably, the additive (c) used in the composition of the invention is 4.48 parts by wt. of the composition.
Typically, the additive (c) namely solution of unmodified low molecular weight solid diglycidyl ether of bisphenol-A resin in xylene has Epoxy equivalent weight based on solids of 450-500 g/eq (ASTM D 1652-04), Viscosity @25°C of 8,000 - 13,000 cP (Brookfield viscosity) (ASTM D 2196-05), Non-volatile content of 74 - 76 % (ASTM D 1259-06), Epoxide Value of 2.00 - 2.22 (ASTM D 1652-04), Density @25°C of 1.07 g/cc (ASTM D 1475-98), Water content 0.5 % max. (ASTM E 203-01) and Flash point of 30°C (ASTM D 93).
The typical example of the solution of unmodified low molecular weight solid diglycidyl ether of bisphenol-A resin in xylene includes but not limited to EPOTEC YD 011X-75.
Number of experiments were carried out to derive the optimum concentration of Additive (a), Additive (b) and Additive (c) in the primer less clear coat composition of the invention. Upon preparing the various compositions by carrying out the experiments and checking the performance of coated wheels by using these compositions, the optimum concentration of the Additive (a), Additive (b) and Additive (c) are reported in table 2.
Typically, primer-less clear coating composition of the invention to coat the metal or metal alloy surfaces, particularly the automobile wheels, directly without the primer and/or base coat to provide adhesion as well as anticorrosion properties besides complies with performance tests like pencil hardness, weatherability resistance, flow/levelling, etc. and aesthetic tests like Crater/Cissing, recoatability, gloss, etc. is provided in table 2.

Table 2: Primer-less clear coating composition of the invention
Sr. No. Components Parts by weight of the composition
1 Acrylic Resins 53.72
2 Melamine Resin 18.91
3 Stabilizer(s) 0.91
4 UV Absorber(s) 2.15
5 Levelling agent (s) 0.09
6 Conductivity additive (s) 0.07
7 Solvents 14.93 to 19.04
8 Additive (a) -Epoxy functional silane oligomer 2 to 4
9 Additive (b) - Silicone- and polyether-macromer-modified polyacrylate or silicone- and polyether- modified polyacrylate 0.11 to 0.22
10 Additive (c) - Solution of unmodified low molecular weight solid diglycidyl ether of bisphenol-A resin in xylene 3 to 5

According to the invention there is also provided a method of primer-less clear coating of the metal or metal alloy surfaces, particularly the automobile wheels, directly without the primer and/or base coat to provide adhesion as well as anticorrosion properties besides complies with performance tests like pencil hardness, weatherability resistance, flow/levelling, etc. and aesthetic tests like Crater/Cissing, recoatability, gloss, etc.
Typically, the method of primer-less clear coating of the invention comprises applying the primer-less clear coating composition of the invention directly on metal or metal alloy surfaces, particularly the automobile wheel followed by baking.
The coated wheel was subjected to flash off for 8 to 10 minutes before subjecting to baking.
The baking step is carried out at 140 to 160°C for at least 30 minutes.
The alloy wheels are coated with primer-less clear coating to achieve a coating of thickness of 15 to 25 µ.
The alloy wheels coated with the primer-less clear coating composition of the invention are subjected to the tests after 24 hours of air drying of the baked coating, desired specification of the test results and results obtained thereof are illustrated in the table 3.

Table 3: Test Results
Sr. No. Test Description Desired specification of the test results Results of the coating of the invention
1 Degree of Dispersion by Hegman Gauge <=10 µ 10 µ
2 NVM (120°C / 1 Hr / 2 gm) 44 - 50% 46.00%
3 Viscosity FC#4 IS3944 @30°C 35 - 65 Sec 50 SEC
4 WPL at 30°c 0.93- 0.99 0.96
5 Thinner Intake (N 146) Max 35 % 30 %
6 ER @ Application Viscosity 300 - 1000 K Ohms 630 KOHM
7 Application Viscosity on FC#4 IS3944 @30°C 18±2 sec 16 sec
8 Appearance To be free from abnormalities like seed and craters Free From Seed and Craters
9 Adhesion 2 mm , 10 X 10 2x2mm, 100/100 Passes
10 Gloss @ 60º GH MIN 88 Units 92 UNITS
11 PENCIL HARDNESS (MITSUI) Min F-H H Passes
12 Crater/Cissing Test No cissing and craters No cissing and craters
13 Recoatability Test - Triple Bake 2x2mm, 100/100 Passes
14 CASS TEST -240HRS No blister, corrosion Passes

Thus, the primer-less clear coating composition for the metal or metal alloy surfaces, particularly all kinds of automobile wheels, directly without the primer and/or base coat achieves desired adhesion, anticorrosion, recoatability test, degree of dispersion (10 µ), gloss (92 Units), pencil hardness (H passes), weatherability resistance, appearance free from Seed and Craters, No Crater/Cissing, etc. Thus, the present invention eliminates multistep coats like primer coat, base coat and top or clear coat thereby reducing inventory cost and laborious efforts. Therefore, the primer-less clear coating is efficient, economic and simple. Similarly, to the coating composition of the invention, the method of primer-less clear coating of the metal or metal alloys surfaces, particularly all kinds of automobile wheels, directly without the primer and/or base coat eliminates laborious task of multicoating and reduces inventory cost, manpower, energy and cycle time simultaneously increasing productivity; thereby making the method of the invention simple and efficient.
The above invention can be illustrated with the below mentioned examples but not by way of limitations. In other words, exemplary illustrations of the operation of the present invention, the practice of its formulation of the compositions and the rendering of the disclosed method are described in the following examples. In addition to the preferred modes of operation, a practitioner of sufficient skill in the art will appreciate that the meets and bounds of the present invention are not limited by the specific instances described herein, rather are defined by the equivalents provided by the claims of the present invention.

Chemicals used
Chemicals Used Chemicals available under Trade name
Acrylic resin DIANAL HR54
Acrylic resin ACR-461
Melamine resin SETAMINE US-138 BB-70
Hindered amine light stabilizer (HALS) Tinuvin® 292
Hydroxyphenyl-triazine (HPT) UV absorber TINUVIN ® 400
Benzotriazole-based UV absorber Tinuvin® 384-2
Acrylic based flow/levelling agents LEVELLER S_N supplied by Nippon Paint, Japan
Solvents
n-butanol, Mixed xylene supplied by Reliance Industries Ltd., Solvesso TM 100 and Butyl Cellosolve TM Acetate
Conductivity additive Efka® 6782
Additive (a) - epoxy functional silane oligomer CoatOSil* MP 200
Additive (b) - Silicone- and polyether-macromer-modified polyacrylate or Silicone- and polyether- modified polyacrylate BYK 3568 or BYK-LP X 24228
Additive (c) - solution of unmodified low molecular weight solid diglycidyl ether of bisphenol-A resin in xylene EPOTEC YD 011X-75

EXAMPLE 1 (Primer-less clear coating composition A):

A primer-less clear coating composition of the invention was formulated according to table 4.

Table 4: Primer-less clear coating composition A
Sr. No. Components Parts by weight of the composition
1 Acrylic Resin - DIANAL HR54 16.88
2 Acrylic Resin - ACR-461 36.84
3 Melamine - SETAMINE US-138 BB-70 18.91
4 Stabilizer - Tinuvin® 292 0.91
5 UV Absorber - TINUVIN ® 400 0.36
6 UV Absorber - Tinuvin® 384-2 1.79
7 Levelling agent - LEVELLER S_N 0.09
8 Conductivity additive - Efka® 6782 0.07
9 Solvent – N-Butanol 2.80
10 Solvent - Mixed xylene 2.24
11 Solvent - Solvesso TM 100 7.13
12 Solvent - Butyl Cellosolve TM Acetate 3.72
13 Epoxy functional silane oligomer - CoatOSil* MP 200 3.58
14 Silicone- and polyether-macromer-modified polyacrylate - BYK 3568 0.18
15 Solution of unmodified low molecular weight solid diglycidyl ether of bisphenol-A resin in xylene - EPOTEC YD 011X-75 4.48

The coating composition was prepared by mixing all the components in given specific proportions mentioned in table 4. The primer-less clear coating composition was applied on the aluminium wheel directly without the primer and/or base coat. The thickness of the coating was found to be 20 µ. The coated wheel was subjected to flash off for 8 to 10 minutes. The coated wheel was subjected to baking at 155° C for 30 minutes. The wheels coated with the primer-less clear coating composition A of the invention were subjected to the tests after 24 hours of air drying of the baked coating. The test results are illustrated in table 9.

EXAMPLE 2 (Primer-less clear coating composition B):

The primer-less clear coating composition of the invention was formulated according to table 4, except Silicone- and polyether-macromer-modified polyacrylate - BYK 3568, Silicone- and polyether-modified polyacrylate - BYK-LP X 24228 was used.
The coating composition B was prepared by mixing all the components in given specific proportions mentioned in table 4. The primer-less clear coating composition B was applied on the aluminium wheel directly without the primer and/or base coat. The thickness of the coating was found to be 20 µ. The coated wheel was subjected to flash off for 8 to 10 minutes. The coated wheel was subjected to baking at 155° C for 30 minutes. The wheels coated with the primer-less clear coating composition B of the invention were subjected to the tests after 24 hours of air drying of the baked coating. The test results are illustrated in the table 9.

Comparative Example 1 (Clear Coating composition C):

A clear coating composition was formulated according to table 5.

Table 5: Clear coating composition C
Sr. No. Components Parts by weight of the composition
1 Acrylic Resin - DIANAL HR54 16.88
2 Acrylic Resin - ACR-461 36.84
3 Melamine - SETAMINE US-138 BB-70 18.91
4 Stabilizer - Tinuvin® 292 0.91
5 UV Absorber - TINUVIN ® 400 0.36
6 UV Absorber - Tinuvin® 384-2 1.79
7 Levelling agent - LEVELLER S_N 0.09
8 Conductivity additive - Efka® 6782 0.07
9 Solvent – N-Butanol 3.00
10 Solvent - Mixed xylene 7.00
11 Solvent - Solvesso TM 100 10.00
12 Solvent - Butyl Cellosolve TM Acetate 4.15

The clear coating composition was prepared by mixing all the components in given specific proportions mentioned in table 5. The clear coating composition was applied on the aluminium wheel directly without the primer and/or base coat. The thickness of the coating was found to be 20 µ. The coated wheel was subjected to flash off for 8 to 10 minutes. The coated wheel was subjected to baking at 155° C for 30 minutes. The wheels coated with the clear coating composition C were subjected to the tests after 24 hours of air drying of the baked coating. The test results are illustrated in table 9.

Comparative Example 2 (Coating composition D):

The coating composition D was formulated according to table 6.

Table 6: Coating composition D
Sr. No. Components Parts by weight of the composition
1 Acrylic Resin - DIANAL HR54 16.88
2 Acrylic Resin - ACR-461 36.84
3 Melamine - SETAMINE US-138 BB-70 18.91
4 Stabilizer - Tinuvin® 292 0.91
5 UV Absorber - TINUVIN ® 400 0.36
6 UV Absorber - Tinuvin® 384-2 1.79
7 Levelling agent - LEVELLER S_N 0.09
8 Conductivity additive - Efka® 6782 0.07
9 Solvent – N-Butanol 3.00
10 Solvent - Mixed xylene 5.00
11 Solvent - Solvesso TM 100 8.00
12 Solvent - Butyl Cellosolve TM Acetate 4.57
13 Epoxy functional silane oligomer - CoatOSil* MP 200 3.58

The coating composition D was prepared by mixing all the components in given specific proportions mentioned in table 6. The coating composition D was applied on the aluminium wheel directly without the primer and/or base coat. The thickness of the coating was found to be 20 µ. The coated wheel was subjected to flash off for 8 to 10 minutes. The coated wheel was subjected to baking at 155° C for 30 minutes. The wheels coated with the coating composition D were subjected to the tests after 24 hours of air drying of the baked coating. The test results are illustrated in table 9.

Comparative Example 3 (Coating composition E):

The coating composition E was formulated according to table 7.

Table 7: Coating composition E
Sr. No. Components Parts by weight of the composition
1 Acrylic Resin - DIANAL HR54 16.88
2 Acrylic Resin - ACR-461 36.84
3 Melamine - SETAMINE US-138 BB-70 18.91
4 Stabilizer - Tinuvin® 292 0.91
5 UV Absorber - TINUVIN ® 400 0.36
6 UV Absorber - Tinuvin® 384-2 1.79
7 Levelling agent - LEVELLER S_N 0.09
8 Conductivity additive - Efka® 6782 0.07
9 Solvent – N-Butanol 3.00
10 Solvent - Mixed xylene 7.00
11 Solvent - Solvesso TM 100 9.82
12 Solvent - Butyl Cellosolve TM Acetate 4.15
13 Silicone- and polyether-macromer-modified polyacrylate - BYK 3568 0.18

The coating composition E was prepared by mixing all the components in given specific proportions mentioned in table 7. The coating composition E was applied on the aluminium wheel directly without the primer and/or base coat. The thickness of the coating was found to be 20 µ. The coated wheel was subjected to flash off for 8 to 10 minutes. The coated wheel was subjected to baking at 155° C for 30 minutes. The wheels coated with the coating composition E were subjected to the tests after 24 hours of air drying of the baked coating. The test results are illustrated in table 9.

Comparative Example 4 (Coating composition F):

The coating composition F was formulated according to table 8.

Table 8: Coating composition F
Sr. No. Components Parts by weight of the composition
1 Acrylic Resin - DIANAL HR54 16.88
2 Acrylic Resin - ACR-461 36.84
3 Melamine - SETAMINE US-138 BB-70 18.91
4 Stabilizer - Tinuvin® 292 0.91
5 UV Absorber - TINUVIN ® 400 0.36
6 UV Absorber - Tinuvin® 384-2 1.79
7 Levelling agent - LEVELLER S_N 0.09
8 Conductivity additive - Efka® 6782 0.07
9 Solvent – N-Butanol 3.00
10 Solvent - Mixed xylene 5.00
11 Solvent - Solvesso TM 100 7.10
12 Solvent - Butyl Cellosolve TM Acetate 4.57
13 Solution of unmodified low molecular weight solid diglycidyl ether of bisphenol-A resin in xylene - EPOTEC YD 011X-75 4.48

The coating composition F was prepared by mixing all the components in given specific proportions mentioned in table 8. The coating composition F was applied on the aluminium wheel directly without the primer and/or base coat. The thickness of the coating was found to be 20 µ. The coated wheel was subjected to flash off for 8 to 10 minutes. The coated wheel was subjected to baking at 155° C for 30 minutes. The wheels coated with the coating composition F were subjected to the tests after 24 hours of air drying of the baked coating. The test results are illustrated in table 9.


Table 9: Comparative test results
Test Description Desired test results Results of Primer-less clear coating composition A Results of Primer-less clear coating composition B Results of clear coating composition C Results of coating composition D Results of coating composition E Results of coating composition F
Degree of Dispersion by Hegman Gauge (ASTM D1210) <=10 µ 10 µ 10 µ 10 µ 10 µ 10 µ 10 µ
NVM (120°C / 1 Hr / 2 gm) (ASTM D2369) 44 - 50% 46.00% 46.00% 39.5 % 42.7 % 39.7 % 43 %
Viscosity FC#4 IS3944 @30°C (ASTM D 1200) 35 - 65 Sec 50 SEC 50 SEC 40 SEC 43 SEC 40 SEC 44 SEC
WPL at 30°c (ASTM D 1475) 0.93- 0.99 0.96 0.96 0.97 0.96 0.97 0.96
Thinner Intake (N 146) ASTM D 1200 Max 35 % 30 % 30 % 20 % 23 % 21% 24 %
ER @ Application Viscosity (ASTM D 5682) 300 - 1000 K Ohms 630 KOHM 630 KOHM 700 KOHM 680 KOHM 710 KOHM 650 KOHM
Application Viscosity on FC#4 IS3944 @30°C (ASTM D 1200) 18±2 sec 16 sec 16 sec 16 sec 16 sec 16 sec 16 sec
Appearance To be free from abnormalities like seed and craters Free From Seed and Craters Free From Seed and Craters Inferior Inferior Free From Seed and Craters Inferior
Adhesion 2 mm, 10 X 10
(ASTM 3359) 2x2mm, 100/100 Passes Passes Fail Pass Fail Fail
Gloss @ 60º GH
(ASTM D 523) MIN 88 Units 92 UNITS 92 UNITS 91 -92 UNITS 91 -92 UNITS 91 -92 UNITS 91 -92 UNITS
PENCIL HARDNESS (MITSUI) (ASTM 3363) Min F-H H Passes H Passes H Pass H Pass H Pass H Pass
Crater/Cissing Test No cissing and craters No cissing and craters No cissing and craters Fail Pass Pass Pass
Recoatability Test - Triple Bake (ASTM 3359) 2x2mm, 100/100 Passes Passes Fail Pass Fail Fail
CASS TEST -240HRS
(ASTM B368) No blister, corrosion Passes Passes Fail Fail Fail Fail
QUV Weatherability resistance -300 hrs (ASTM-G154) Gloss retention > 85 % 90 - 92 % 90 - 92 % 94 - 95% 90 -91 % 90 - 92 % 90 - 92 %
Flow & Levelling Smooth Pass Inferior Inferior Inferior Pass Inferior

According to the comparative results as illustrated in table 9, the primer-less clear coating compositions A and B of the invention demonstrated excellent adhesion and anti-corrosion properties apart of other performance properties like pencil hardness, weatherability resistance, flow and levelling, etc. and aesthetic properties like appearance, gloss, Crater/Cissing test, recoatability test, etc over the compositions C, D, E and F. These properties of the compositions of the present invention permits to coat the metal or metal alloy including automobile wheels directly without a need of primer coat and base coat and thus contribute towards technical advancement. Besides technical advancement, it will reduce inventory cost, manpower, energy, laborious efforts and the number of coating steps. This will also increase productivity of painted wheels. Thus, the composition will be economical. The method of coating of metal or alloys including vehicle wheels will be simple, economical, less time consuming and efficient.