BACKGROUND OF THE INVENTION

Field of the Invention

The present invention includes matte textured polyester powder monocoat coating compositions that can be used to coat substrates, such as automobile bodies, and methods of coating such substrates.

SUMMARY OF THE INVENTION

The present invention includes matte textured polyester powder monocoat coating compositions that can be used to coat substrates, such as automobile bodies, and methods of coating such substrates with the matt textured polyester powder monocoat coating

compositions.

One of the differences between automobile body coatings and exterior trim coatings is durability. For many OEM body coating specifications, the expectation is that the coating will maintain appearance and functional film integrity for 5+ years in Florida exposure. For high quality exterior trim coatings, the requirements are not as stringent for duration of exposure and functional film integrity after exposure. For example, some OEM body coating requirements call for gloss retention of at least about 90% after 1 year of Florida exposure, at least about 80% after 3 years of Florida exposure, and at least about 65% after 5 years of Florida exposure. For exterior trim coatings, the related durability requirements are at least about 80% gloss retention after 1 year of Florida exposure, at least about 50% after 3 years of Florida exposure, and no requirement after 5 years of Florida exposure.

In one embodiment of the invention, a powder coating composition comprises a polyester resin, a UV light stabilizer, a matting agent, and a texturing additive, wherein the cured powder coating composition transmits less than about 0.1% of UV light at 290 nm and less than about 0.5% of UV light at 400 nm. The invention also includes methods of coating a substrate comprising applying a powder coating composition to the substrate and curing the powder coating composition.

DETAILED DESCRIPTION OF THE INVENTION

The present invention includes matte textured polyester powder monocoat coating compositions that can be used to coat substrates and methods of coating such substrates with the matte textured polyester powder monocoat coating compositions. The coated and cured powder coating compositions are matte, have a fine texture and satisfy automotive industry standards for UV transmission, chemical resistance and durability. In some embodiments, an electrocoat is applied to the substrate, and the powder coating compositions of the invention is applied over the electrocoat. Thus, the present invention also includes substrates coated with a dual-coat coating composition, the dual-coat coating composition having an electrocoat coated between the substrate and a powder coating composition of the present invention.

A powder coating composition of the present invention may comprise a polyester resin, a UV light stabilizer, a matting agent, and a texturing additive. Suitable polyester resins include, without limitation, a carboxyl functional polyester resin, a hydroxyl functional polyester resin, or a combination thereof.

In some embodiments, the polyester resin is present in an amount of from about 45 to about 75 wt% of the powder coating composition. For non-limiting example, the polyester resin may include a carboxyl functional polyester resin in an amount of from about 45 to about 75 wt% of the coating composition, a hydroxyl functional polyester resin in an amount of from about 45 to about 65 wt%, or a combination thereof.

In some embodiments, the powder coating composition includes one or more compounds that function as a curing agent or as a co-reacting resin. The curing agent or co- reacting resin may include, for non-limiting example, a hydroxyalkylamide, triglycidyl isocyanurate, a low epoxy equivalent weight (EEW) glycidyl methacrylate acrylic resin, such as a resin having an EEW of about 250 to about 400, a hydrogenated Bisphenol A epoxy resin, a uretedione-butanediol adduct, a polymeric aliphatic isocyanate, a multifunctional glycidyl ester, or a combination thereof. In some embodiments of the invention, the curing agent or co-reacting resin is present in an amount of from about 2 to about 35 wt% of the coating composition.

Suitable UV light stabilizers for use in the present invention include without limitation hydro xyphenyl benzotriazole, a hindered amine light stabilizer, an oxalanilide, a hydro xybenzophenone, a hydroxyphenyl-s-triazine, or a combination thereof. In some embodiments of the invention, the UV light stabilizer may be present in an amount of from about 0.1 to about 5 wt % of the powder coating composition, or from about 1 to about 3 wt% of the coating composition. The UV light stabilizer may be used to contribute to optimum weathering and UV transmission requirements.

In some embodiments of the invention, a powder coating composition having a UV light stabilizer satisfies UV transmission targets for automotive body coatings. For non- limiting example, a cured coating composition of the invention may transmit less than about 0.1% of UV light at 290 nm and less than about 0.5% of UV light at 400 nm.

The powder coating compositions of the invention can include a matting agent in some embodiments which may provide a matte appearance to the cured powder coating composition, such as when the cured coating composition exhibits a 60° gloss of less than about 10. The matting agent may include, without limitation, barium sulfate, magnesium silicate, silicon dioxide, alumino silicates, such as without limitation anhydrous sodium potassium alumino silicate, alkali alumino silicate ceramic microspheres, alumino silicate glass microspheres or flakes, polyolefin waxes in combination with the salt of an organic anion, polymeric wax additives, or a combination thereof. The matting agent may contribute to good dispersion and handling of the texturing additive and/or to contribute to restrict the flow of the coating composition. In some embodiments of the invention, the matting agent is present in an amount of from about 0.1 to about 40 wt% of the coating composition.

In some embodiments, the powder coating composition includes a texturing additive to provide a texture to the cured coating, such as when the cured coating composition exhibits a rough, rippled or sandy appearance, as opposed to a smooth or orange peel appearance. The texturing additive may include, for non-limiting example, polytetrafluoroethylene powder, PTFE/polyethylene wax mixtures, PTFE/talc mixtures, or a combination thereof. The polytetrafluoroethylene powder may be present in an amount of from about 0.05 to about 0.5 wt% of the coating composition, or from about 0.1 to about 0.2 wt% of the coating composition. In some embodiments, the polytetrafluoroethylene powder is a granular powder having a particle size of from about 5 to about 600 microns in average particle size, and alternatively from about 5 to about 25 microns in average particle size.

The powder coating compositions of the invention may be applied over an electrocoat to protect the electrocoat from UV degradation. The powder coating compositions may have a non-uniform thickness with hills and valleys, and the coated powder coating compositions can have a measured film thickness (when measuring the top of the hills) of about 35 to about 200 μηι or about 50 to about 100 μιη in some embodiments. In some coating compositions of the invention, the valley:hill thickness ratio is about 1:3 or from about 1:4 to about 1:2. A measured film thickness within the range of the present invention helps prevent UV light from penetrating through the valleys of the coating and reaching the underlying electrocoat. As a result, the thickness of the powder coating composition contributes to the stability of the underlying electrocoat. In addition, the UV light stabilizer that may be present in the powder coating composition also contributes to the stability of the underlying electrocoat, although the UV light stabilizer may have little or no benefit to the powder coating composition itself.

The powder coating compositions of the invention may also include additives, such as without limitation, pigments, degassing agents, antioxidants, fillers, flow aids, catalysts, or a combination thereof.

Pigments for use in powder coating compositions of the invention include, for non- limiting example, titanium dioxide, iron oxide (yellow, brown, red, black), carbon black and organic pigments. These pigments can be added in conventional amounts known to those in the art.

A degassing agent can be added to the composition to allow any volatile material present to escape from the film during baking. Benzoin is a degassing agent and when used in some embodiments can be present in amounts from about 0.05 to about 0.8 wt% of the coating composition.

Suitable antioxidants include, without limitation, phenolic, phosphite, phosphonite and lactone-type antioxidants, such as octadecyl-3-(3,5-Di-tert-butyl-4-hydroxyphenyl)- propionate and pentaerythritol tetrakis (3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate, as well as combinations thereof. In some embodiments, the antioxidants are present in an amount of from about 1 to about 3 wt% of the powder coating composition.

The powder coating compositions of the invention may include one or more catalysts to accelerate the cure or otherwise catalyze the system to enhance the properties of the coating composition. Suitable catalysts include without limitation accelerated phenolic resins, alkyl ammonium salts, such as tetra butyl ammonium bromide, tetra butyl ammonium chloride, tetra butyl ammonium iodide and benzyltriethylammonium chloride, quaternary ammonium and phosphonium salts, phosphines, imidazoles, such as 2-methyl imidazole and 2-heptadecylimidazole, metal salts, 2,4-diamino-6 (2-methylimidazolyl-(l))-ethyl-s-triazine, tin salts, such as dibutyl tin dilaurate, ethyltriphenyl phosphonium acetate,

triphenylphosphine, or a combination thereof. In some embodiments, the catalyst is present in an amount of from about 0.05 to about 1.5 wt% of the coating composition.

The powder coating compositions of the present invention are suitable for application to substrates, such as, without limitation, automotive bodies. However, it is also possible to apply the coating compositions to carbon, wood, glass, polymers, plastics and other substrates.

Application of the above described powder coating compositions can be accomplished by any known techniques, such as, without limitation, electrostatic spray or fluidized bed. EXAMPLES

The invention will be further described by reference to the following non-limiting examples. It should be understood that variations and modifications of these examples can be made by those skilled in the art without departing from the spirit and scope of the invention.

Example 1

Coating Compositions A through C were prepared by ensuring that the ingredients listed were (1) Physically mixed under dry, non- molten conditions, i.e. in the solid state and without substantial melting of the components being mixed by use of a bladed mixer, whereby the combined ingredients were generally uniformly distributed throughout the resulting mixture. (2) Melt-mixed under conditions in which the mixture was generally in a liquid condition, although some components of the mixture could have been present as suspended or dispersed solids or could have been dissolved rather than molten. Melt mixing was accomplished by the use of a twin screw extruder at elevated temperature. (3) Cooled by passing through a pair of chill rolls. (4) Discharged into a mill where it was ground into small particles. (5) Sieved for further particle size classification.

The compositions of Coating Compositions A through C are shown in the table below. In this table the components are listed in parts by weight.

¹ Carboxyl Polyester Resin A with an acid number of 25, a Tg of 60 °C ² Carboxyl Polyester Resin B with an acid number of 55, a Tg of 61 °C

³ PTFE powder with average particle size of 15 μιτι.

⁴ Barium Sulfate with mean particle size of 2.5 - 3 μιτι.

⁵ Aluminum Oxide with an average primary particle size of 13 nm.

⁶ Magnesium Silicate with a median particle size of 2 - 3 μιτι.

⁷ Aluminum Trihydrate with a median particle size of 10 μm.

⁸ Silicon Dioxide with a median particle size of 10 μm.

Compositions A through C were coated, cured and evaluated for various properties. The evaluation results are shown in the following table.

When viewing Composition A as the standard, the table above illustrates that the hydroxyphenyl benzotriazole light stabilizer in Composition C has a greater benefit on UV transmission compared to the increased amount of carbon black in Composition B.

Example 2

Coating Compositions 1 through 16 were prepared using the technique described in Example 1. The compositions of Coating Compositions 1 through 16 is shown in the table below. In this table the components are listed in parts by weight.

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¹ Carboxyl Polyester Resin A with an acid number of 25, a Tg of 60 °C

² Carboxyl Polyester Resin B with an acid number of 55, a Tg of 61 °C

³ Levelling additive.

⁴ PTFE powder with average particle size of 15 μm.

⁵ Barium Sulfate with mean particle size of 2.5 - 3 μm.

⁶ Aluminum Oxide with an average primary particle size of 13 nm.

⁷ Magnesium Silicate with a median particle size of 2 - 3 μm.

⁸ Aluminum Trihydrate with a median particle size of 10 μm.

⁹ Silicon Dioxide with a median particle size of 10 μm.

The following table and graph illustrates SAE J1961 EMMAQUA ^® accelerated outdoor weathering testing data for Compositions 1- 16 above.

As shown in Example 2, the presence of a UV light stabilizer has little effect on the color retention of the powder coating composition. However, as noted above, the UV light stabilizer may contribute to the stability of the underlying electrocoat.