Low temperature cure powder coating compositions

Patent metadata

Field	Value
Publication number	US-11104809-B2
Application number	US-201716314483-A
Country	US
Kind code	B2
Filing date	Jul 4, 2017
Priority date	Jul 4, 2016
Publication date	Aug 31, 2021
Grant date	Aug 31, 2021

Abstract

The invention relates to a powder coating composition for low temperature curing that can be used on temperature sensitive substrates and, despite of the low curing temperature, has excellent flow properties and forms a coating with excellent appearance and nevertheless also good mechanical and weathering properties. The invention also relates to an advantageous process for the manufacture of the powder coating composition. Said powder coating composition comprises a poly-acid functional polyester component A, a poly-epoxy functional component B, a poly-anhydride functional component C and a thermosetting curing catalyst D. The invention also relates to a polyester for use in the powder coating compositions according to the invention, in particular for durable powder coatings.

First claim

What is claimed is:

1. A powder coating composition for low temperature curing comprising:
a. a poly-acid functional polyester component A,
b. a poly-epoxy functional component B,
c. a poly-anhydride functional component C; and
d. a curing catalyst D,
wherein component A has an acid number (AV) of 20 to 50 mg KOH/g and a hydroxyl number (OHV) of less than 15 mg KOH/g, and
wherein component A is formed from one or more polyols and one or more poly-acid constituents wherein of the poly-acid constituents in the polyesters at least 60% are isophthalic acid and less than 20 wt % are terephthalic acid.

2. The powder coating composition of claim 1 , comprising one or more of the following characteristics:
a. component A has a number averaged molecular weight Mn, as determined with GPC, in the range between 1000-10000 g/mol,
c. component A comprises polyacid branching monomers comprising at least three carboxyl groups in an amount below 9 wt % relative to the weight of polyester component A,
d. component A comprises polyol branching monomers comprising at least three hydroxyl groups in an amount below 9 wt % relative to the weight of polyester component A or wherein component A comprises a combination of polyol and polyacid monomers in a total amount of these monomers below 9 wt %,
e. component A comprises branching monomers and has a polydispersity Mw/Mn in the range between 1.3 and 5,
f. component A has a polydispersity Mw/Mn in the range between 1.3 and 3.2,
g. the acid functionality of component A is 1.5-3.5, wherein functionality is defined as the average number of acid groups per molecule as calculated by Mn/(56100/AV),
h. component A has a DSC mid point Tg as determined at heating rate of 10° C./min in the range 40-80° C.

3. The powder coating composition according to claim 1 , comprising one or more of the following characteristics:
a. component B has a number averaged molecular weight Mn in the range between 100 1500 g/mol,
b. component B has an epoxy equivalent weight between 50 and 200 g/Eq,
c. the epoxy functionality of component B is 2.0-3.0,
d. component B is chosen from the group of polyfunctional epoxy-ester or polyfunctional epoxy-isocyanurates or combinations thereof,
e. component B is diglycidyl terephthalate, triglycidyl trimellitate or triglycidyl isocyanurate or combinations thereof,
f. at least 70 wt % of all components B in the composition have any of the above features.

4. The powder coating composition according to claim 1 , comprising one or more of the following characteristics:
a. component C has a number averaged molecular weight Mn, as determined with GPC, in the range between 300 and 6000 g/mol,
b. the anhydride functionality of the poly anhydride component C is 2 to 10.0,
c. component C is an aliphatic polyanhydride,
d. component C is one or more components selected from the group consisting of polysebacic polyanhydride, polyadipic polyanhydride, polyazelaic polyanhydride and polydodecandioic polyanhydride.

5. The powder coating composition according to claim 1 , wherein curing catalyst component D is selected from the group consisting of amines, phosphines, ammonium salts, phosphonium salts, blocked amine or phosphine catalysts, encapsulated catalysts and combinations thereof.

6. The powder coating composition according to claim 1 consisting of:
a. between 40 and 97 wt. % of component A,
b. between 1 and 40 wt. % of component B,
c. between 0.1 and 10, wt. % of component C,
d. between 0.1 and 5 wt. % of component D,
e. optionally, up to 50 wt % powder coating additives,
f. less than 5 wt % volatile organic components,
wherein the wt % of A, B, C and D is expressed as the weight percentage of the total weight of components A, B, C and D and wt % of components e and f are expressed relative to total weight of the powder coating composition.

7. The powder coating composition according to claim 1 , wherein ratio R, defined as the ratio of moles of acid groups in components A and C to moles of epoxy groups in component B, is between 0.8 and 1.2.

8. The powder coating composition according to claim 1 , wherein the amount of curing catalyst component D is chosen to get a gel time of 200-800 seconds +/−40% determined at 140° C. on a composition having a ratio R of 0.95 wherein R is defined as the ratio of moles of acid groups in components A and C to moles of epoxy groups in component B.

9. The powder coating composition according to claim 1 in the form of a kit of parts comprising a Part 1 comprising component A and component C and a Part 2 comprising component B wherein Part 1 or 2 or both, comprise component D.

10. The powder coating composition according to claim 1 , wherein the poly-acid functional polyester A further has each of the following properties c.-e.:
c. has, in case of a branched polyester A, a polydispersity Mw/Mn, as determined with GPC, in the range between 1.3 and 5 or, in case of a linear polyester A, in the range between 1.3 and 3.5,
d. has a DSC mid-point Tg as determined at heating rate of 10° C./min in the range 40-80° C.,
e. has a number averaged molecular weight Mn, as determined with GPC, in the range between 2000 and 10000 gr/mol.

11. A process for the manufacture of a powder coating composition according to claim 1 comprising the steps of:
a. providing an acid functional polyester composition according to claim 10 comprising an acid functional polyester component A and a polyanhydride functional component C and crosslinking catalyst D,
b. adding and mixing polyepoxy component B and optional powder coating additives,
c. adding crosslinking catalyst D in step b and/or with the acid functional polyester composition,
d. cooling.

12. A process for coating a substrate comprising the steps of applying a layer of a powder coating composition of claim 1 on at least one surface of said substrate and heating the coated substrate to a temperature between 120 and 160° C. to thermally cure the coating thereon to form an adherent layer of the coating composition on the substrate.

13. The process of claim 12 wherein the substrate is a heat-sensitive substrate.

14. An article coated at least partially with a powder coating composition of claim 1 .

15. The process for the manufacture of powder coating composition according to claim 11 , wherein the acid functional polyester component A is formed in a 2 step process comprising the steps of:
a. polymerizing the polyacid and polyol at elevated temperatures between 100 and 250° C. while continuously distilling off water formed, optionally in the presence of a polyesterification catalyst,
b. determining the AV and the Net OHV and adding based on the measured Net OHV and AV a pre-calculated amount of polyacid and polyol to obtain after further polymerization a polyester having AV between 20 and 50 mg KOH/g and a OHV of less than 15 mg KOH/g.

Assignees

• Allnex Netherlands Bv

Inventors

• Weaver William
• Watson Robert
• Brinkhuis Richard Hendrikus Gerrit
• Bosma Martin
• Jones Paul
• White Steve
• Baxevanis Dimitrios
• Cavalieri Roberto

Classifications

• C09D167/03

  the dicarboxylic acids and dihydroxy compounds having the carboxyl - and the hydroxy groups directly linked to aromatic rings · CPC title

• C09D167/02 Primary

  Polyesters derived from dicarboxylic acids and dihydroxy compounds (C09D167/06 takes precedence) · CPC title

• C09D163/00

  Coating compositions based on epoxy resins; Coating compositions based on derivatives of epoxy resins · CPC title

• C09D5/03 Primary

  Powdery paints · CPC title

• C09D167/00

  Coating compositions based on polyesters obtained by reactions forming a carboxylic ester link in the main chain (based on polyester-amides C09D177/12; based on polyester-imides C09D179/08); Coating compositions based on derivatives of such polymers · CPC title