Powder coatings based on branched oligoesters and triazole blocked polyisocyanates

Abstract

The present invention relates to powder coating compositions which can be cured at low temperatures. The powder coating compositions of the invention include a unique combination of a branched oligoester polyol and triazole blocked isocyanate cross-linking agent which when cured results in a coating binder with desirable hardness, flexibility, solvent resistance, corrosion resistance, weatherability and gloss.

Description

[0001] The present invention relates to powder coating compositions capable of curing at low temperatures in the presence or absence of catalysts. More particularly, the present invention relates to branched hydroxy-terminated oligoesters which, when crosslinked, provide improved low temperature cure properties even without the use of catalysts. background of the invention

[0002] Thermosetting powder coating compositions are well known in the art and are widely used as coatings for electrical appliances, bicycles, garden equipment, automotive parts, general metal parts, and the like. Thermosetting powders are composed of raw resin and one or more crosslinking agents (often called hardeners or curing agents). Common methods associated with powder coating technology include formulating the coating from solid components, mixing, dispersing the pigment (and other insoluble components) in the matrix of the main binder component, comminuting the formulation into a powder. To the ...

Examples

Embodiment 1

[0071] step 1

[0072] Reagent

weight

Neopentyl glycol (Eastman)

805g

1,6-Hexanediol (UBE)

161g

Terephthalic acid (Amoco)

1145g

Butyltin dihydroxide (Elf-Atochem)

2.1g

Antioxidant (Weston 618-General Electric)

4.6g

[0073] The mixture was heated slowly to 205°C and then processed at 240°C to a resin with an acid number of 4-7 mgKOH / g and an ICI cone and plate viscosity of 10-14 poise at 125°C. The hydroxyl value of the resin was measured to be about 130-140 mgKOH / g resin.

[0074] step 2

[0075] Fabrication of hydroxyl-terminated branched oligoesters

[0076] The above oligomer was cooled to 180°C and 153.5 g of trimellitic anhydride was added. The temperature was raised to 210-215°C over 50 minutes and the vacuum was slowly drawn down to a vacuum of 23-24 inches Hg. Response was monitored by periodically withdrawing samples and measuring acid number and ICI cone and plate viscosity at 200°C. Wh...

Embodiment 2

[0078] step 1

[0079] Reagent

weight

Neopentyl glycol (Eastman)

1396.99g

1,6-Hexanediol (UBE)

279.33g

Terephthalic acid (Amoco)

2048.14g

Butyltin dihydroxide (Elf-Atochem)

4.00g

Antioxidant (Weston 618-General Electric)

8.00g

[0080] The mixture was heated slowly to 205°C and then processed at 240°C to a resin with an acid number of 4-7 mgKOH / g and an ICI cone and plate viscosity of 10-14 poise at 125°C. The hydroxyl value of the resin was measured to be about 130-140 mgKOH / g resin.

[0081] step 2

[0082] Fabrication of hydroxyl-terminated branched oligoesters

[0083] The above oligomer was cooled to 180°C and 277.86 g of trimellitic anhydride was added. The temperature was raised to 210-215°C over 50 minutes and the vacuum was slowly drawn down to a vacuum of 23-24 inches Hg. Response was monitored by periodically withdrawing samples and measuring acid number and ICI cone and plate viscosity ...

Embodiment 3-6

[0085] Preparation of Powder Coatings

[0086] Example 3

[0087] All of the above ingredients are mixed together initially using a high speed mill such as a Welex mixer to obtain a homogeneous mixture. The resulting mixture was processed using a 200 rpm Buss PR-46 single screw extruder with a first zone temperature of 92°C and a second zone temperature of 140°C. The resulting melt was discharged on a pair of water-cooled extrusion rolls to roughly pulverize the output cooled sheet, which was then pulverized with a Brinkmann grinder or coffee mill and sieved through a 140 mesh screen.

[0001] The present invention relates to powder coating compositions capable of curing at low temperatures in the presence or absence of catalysts. More particularly, the present invention relates to branched hydroxy-terminated oligoesters which, when crosslinked, provide improved low temperature cure properties even without the use of catalysts. background of the invention

[0002] Thermosetting powder coating compositions are well known in the art and are widely used as coatings for electrical appliances, bicycles, garden equipment, automotive parts, general metal parts, and the like. Thermosetting powders are composed of raw resin and one or more crosslinking agents (often called hardeners or curing agents). Common methods associated with powder coating technology include formulating the coating from solid components, mixing, dispersing the pigment (and other insoluble components) in the matrix of the main binder component, comminuting the formulation into a powder. To the ...

Examples

Embodiment 1

[0071] step 1

[0072] Reagent

weight

Neopentyl glycol (Eastman)

805g

1,6-Hexanediol (UBE)

161g

Terephthalic acid (Amoco)

1145g

Butyltin dihydroxide (Elf-Atochem)

2.1g

Antioxidant (Weston 618-General Electric)

4.6g

[0073] The mixture was heated slowly to 205°C and then processed at 240°C to a resin with an acid number of 4-7 mgKOH / g and an ICI cone and plate viscosity of 10-14 poise at 125°C. The hydroxyl value of the resin was measured to be about 130-140 mgKOH / g resin.

[0074] step 2

[0075] Fabrication of hydroxyl-terminated branched oligoesters

[0076] The above oligomer was cooled to 180°C and 153.5 g of trimellitic anhydride was added. The temperature was raised to 210-215°C over 50 minutes and the vacuum was slowly drawn down to a vacuum of 23-24 inches Hg. Response was monitored by periodically withdrawing samples and measuring acid number and ICI cone and plate viscosity at 200°C. Wh...

Embodiment 2

[0078] step 1

[0079] Reagent

weight

Neopentyl glycol (Eastman)

1396.99g

1,6-Hexanediol (UBE)

279.33g

Terephthalic acid (Amoco)

2048.14g

Butyltin dihydroxide (Elf-Atochem)

4.00g

Antioxidant (Weston 618-General Electric)

8.00g

[0080] The mixture was heated slowly to 205°C and then processed at 240°C to a resin with an acid number of 4-7 mgKOH / g and an ICI cone and plate viscosity of 10-14 poise at 125°C. The hydroxyl value of the resin was measured to be about 130-140 mgKOH / g resin.

[0081] step 2

[0082] Fabrication of hydroxyl-terminated branched oligoesters

[0083] The above oligomer was cooled to 180°C and 277.86 g of trimellitic anhydride was added. The temperature was raised to 210-215°C over 50 minutes and the vacuum was slowly drawn down to a vacuum of 23-24 inches Hg. Response was monitored by periodically withdrawing samples and measuring acid number and ICI cone and plate viscosity ...

Embodiment 3-6

[0085] Preparation of Powder Coatings

[0086] Example 3

[0087] All of the above ingredients are mixed together initially using a high speed mill such as a Welex mixer to obtain a homogeneous mixture. The resulting mixture was processed using a 200 rpm Buss PR-46 single screw extruder with a first zone temperature of 92°C and a second zone temperature of 140°C. The resulting melt was discharged on a pair of water-cooled extrusion rolls to roughly pulverize the output cooled sheet, which was then pulverized with a Brinkmann grinder or coffee mill and sieved through a 140 mesh screen.