One component heat-curable powder coating composition

Abstract

The invention relates to a one component heat-curable powder coating composition comprising a resin containing reactive unsaturations and wherein all said reactive unsaturations are carbon carbon double bonds connected directly to an electron withdrawing group, a thermal initiation system comprising a transition metal catalyst and a peroxide, wherein the peroxide is chosen from the group of peroxyesters, mono-peroxycarbonates and mixtures thereof and a co-crosslinker chosen from the group of vinylethers, vinylesters, vinylamides, itaconates, enamines and mixtures thereof.

Claims

1. A one component heat curable powder coating composition comprising: (i) a polyester resin containing reactive unsaturations, the polyester resin having a weight per the reactive unsaturations (WPU) as determined using 1H-NMR which is higher than 250 and lower than 1500 g/mole, (ii) a thermal initiation system comprising (a) a transition metal catalyst and (b) a peroxide, wherein (a) the transition metal catalyst is selected from the group consisting of transition metal salts, transition metal complexes and mixtures thereof, wherein the transition metal is Mn, Fe, Co or Cu, and wherein (b) the peroxide is selected from the group consisting of peroxyesters, monoperoxycarbonates and mixtures thereof, and wherein the peroxide is represented by formula (1): ##STR00017## wherein R.sup.1, R.sup.2 and R.sup.3 each independently stand for an alkyl, and wherein X stands for R.sup.4 or for OR.sup.4, wherein R.sup.4 stands for an alkyl, an aryl or for an oligomer or polymer, and wherein the amount of peroxide is at least 10 mmol peroxide/Kg resin containing reactive unsaturations and co-crosslinker, and (iii) a co-crosslinker having a weight per unsaturation (WPU) as determined using 1H-NMR higher than 150 and lower than 870 g/mole, said crosslinker being chosen from the group consisting of vinylethers, vinyletherurethanes, vinylesters, vinylamides, itaconates, enamines and mixtures thereof, wherein all of the reactive unsaturations of the polyester resin are carbon-carbon double bonds connected directly to an electron withdrawing group and are reactive towards radicals generated by the peroxide, and wherein the thermal initiation system is present in an amount such that when the powder coating composition is applied to a substrate and cured at a temperature of 130 C. for 20 minutes, the resulting coating resists at least 70 acetone double rubs (ADR), wherein each ADR is a back and forward movement over a surface of the coating having a thickness of approximately 60 m using a cotton cloth drenched in acetone covering a hammer head having a weight of 980 grams and a contact surface area with the coating of 2 cm.sup.2.

2. The composition according to claim 1, wherein the resin has a WPU higher than 250 and less than 1150 g/mole.

3. The composition according to claim 1, wherein the resin has a WPU higher than 500 and less than 1500 g/mole.

4. The composition according to claim 1, wherein the resin has a WPU higher than 500 and less than 1150 g/mole.

5. The composition according to claim 1, wherein the co-crosslinker has a WPU higher than 150 and lower than 650 g/mole.

6. The composition according to claim 1, wherein the co-crosslinker has a WPU higher than 150 and lower than 630 g/mole.

7. The composition according to claim 1, wherein the resin has a hydroxyl value in the range of from 0 to 70 mg KOH per g resin.

8. The composition according to claim 1, wherein the reactive unsaturations of the resin are based on maleic acid, fumaric acid, itaconic acid, acrylic acid and/or methacrylic acid.

9. The composition according to claim 1, wherein the reactive unsaturations of the resin are based on maleic acid, fumaric acid, citraconic acid, itaconic acid, and/or mesaconic acid.

10. The composition according to claim 1, wherein the reactive unsaturations of the resin are based on fumaric acid and/or maleic acid.

11. The composition according to claim 1, wherein the reactive unsaturations of the resin are based on fumaric acid.

12. The composition according to claim 1, wherein the peroxide is t-butyl peroxybenzoate, t-butyl peroxy-2-ethyl hexanoate, t-amyl peroxy (2-ethyl) hexanoate or t-butyl peroxy-2-ethylhexyl carbonate.

13. The composition according to claim 1, wherein the transition metal is a Mn, Fe, or Cu salt or complex.

14. The composition according to claim 1, wherein the co-crosslinker is chosen from the group of vinylethers, vinylesters and mixtures thereof.

15. The composition according to claim 1, wherein the co-crosslinker is a vinylether.

16. The composition according to claim 14, wherein the resin has an acid value of less than 10 mg KOH per g resin.

17. The composition according to claim 15, wherein the resin has an acid value of less than 10 mg KOH per g resin.

18. The composition according to claim 14, wherein the resin has an acid value of less than 5 mg KOH per g resin.

19. The composition according to claim 15, wherein the resin has an acid value of less than 5 mg KOH per g resin.

20. The composition according to claim 1, wherein the composition further comprises an inhibitor.

21. The composition according to claim 20, wherein the inhibitor is a hydroquinone or a catechol.

22. The composition according to claim 1, wherein the resin has a glass transition temperature of at least 40 C. as measured via DSC at a heating rate of 5 C./min.

23. The composition according to claim 1, wherein the resin has a glass transition temperature of at least 45 C. as measured via DSC at a heating rate of 5 C./min.

24. The composition according to claim 1, wherein the resin has a glass transition temperature of at least 40 and of at most 65 C. as measured via DSC at a heating rate of 5 C./min.

25. The composition according to claim 1, wherein the resin has a number average molecular weight in the range of from 1500 to 8000 Da.

26. The composition according to claim 1, wherein the resin has a number average molecular weight in the range of from 2100 to 4000 Da.

27. The composition according to claim 1, wherein the reactive unsaturations of the resin are based on maleic acid, fumaric acid, itaconic acid, acrylic acid and/or methacrylic acid, said resin has a hydroxyl value in the range of from 0 to 70 mg KOH per g resin and a number average molecular weight in the range of from 1500 to 8000 Da and a glass transition temperature of at least 40 C. as measured via DSC at a heating rate of 5 C./min; and the co-crosslinker has a WPU higher than 150 and lower than 630 g/mole and said co-crosslinker is chosen from the group of vinylethers, vinylesters and mixtures thereof.

28. The composition according to claim 27, wherein the reactive unsaturations of the resin are based on fumaric acid and/or maleic acid.

29. The composition according to claim 1, wherein the reactive unsaturations of the resin are based on maleic acid, fumaric acid, itaconic acid, acrylic acid and/or methacrylic acid, said resin has a hydroxyl value in the range of from 0 to 70 mg KOH per g resin and a number average molecular weight in the range of from 1500 to 8000 Da and a glass transition temperature of at least 40 C. as measured via DSC at a heating rate of 5 C./min; and the co-crosslinker has a WPU higher than 150 and lower than 630 g/mole and said co-crosslinker is chosen from the group of vinylethers, vinylesters and mixtures thereof; and the composition comprises an inhibitor.

30. The composition according to claim 29, wherein the reactive unsaturations of the resin are based on fumaric acid and/or maleic acid.

31. The composition according to claim 1, wherein the reactive unsaturations of the resin are based on maleic acid, fumaric acid, itaconic acid, acrylic acid and/or methacrylic acid, said resin has a hydroxyl value in the range of from 0 to 70 mg KOH per g resin and a number average molecular weight in the range of from 1500 to 8000 Da and a glass transition temperature of at least 40 C. as measured via DSC at a heating rate of 5 C./min; and the co-crosslinker has a WPU higher than 150 and lower than 630 g/mole and said co-crosslinker is a vinylether.

32. The composition according to claim 31, wherein the reactive unsaturations of the resin are based on fumaric acid and/or maleic acid.

33. The composition according to claim 1, wherein the reactive unsaturations of the resin are based on maleic acid, fumaric acid, itaconic acid, acrylic acid and/or methacrylic acid, said resin has a hydroxyl value in the range of from 0 to 70 mg KOH per g resin and a number average molecular weight in the range of from 1500 to 8000 Da and a glass transition temperature of at least 40 C. as measured via DSC at a heating rate of 5 C./min; and the co-crosslinker has a WPU higher than 150 and lower than 630 g/mole and said co-crosslinker is a vinylether; and the composition comprises an inhibitor.

34. The composition according to claim 33, wherein the reactive unsaturations of the resin are based on fumaric acid and/or maleic acid.

35. The composition according to claim 1, wherein the reactive unsaturations of the resin are based on maleic acid, fumaric acid, itaconic acid, acrylic acid and/or methacrylic acid, said resin has a hydroxyl value in the range of from 0 to 70 mg KOH per g resin and an acid value of less than 10 mg KOH per g resin, and a number average molecular weight in the range of from 1500 to 8000 Da and a glass transition temperature of at least 40 C. as measured via DSC at a heating rate of 5 C./min; and the co-crosslinker has a WPU higher than 150 and lower than 630 g/mole and said co-crosslinker is a vinylether.

36. The composition according to claim 35, wherein the reactive unsaturations of the resin are based on fumaric acid and/or maleic acid.

37. The composition according to claim 1, wherein the reactive unsaturations of the resin are based on maleic acid, fumaric acid, itaconic acid, acrylic acid and/or methacrylic acid, said resin has a hydroxyl value in the range of from 0 to 70 mg KOH per g resin and an acid value of less than 5 mg KOH per g resin, and a number average molecular weight in the range of from 1500 to 8000 Da and a glass transition temperature of at least 40 C. as measured via DSC at a heating rate of 5 C./min; and the co-crosslinker has a WPU higher than 150 and lower than 630 g/mole and said co-crosslinker is a vinylether.

38. The composition according to claim 37, wherein the reactive unsaturations of the resin are based on fumaric acid and/or maleic acid.

39. The composition according to claim 1, wherein the reactive unsaturations of the resin are based on maleic acid, fumaric acid, itaconic acid, acrylic acid and/or methacrylic acid, said resin has a hydroxyl value in the range of from 0 to 70 mg KOH per g resin and an acid value of less than 10 mg KOH per g resin, and a number average molecular weight in the range of from 1500 to 8000 Da and a glass transition temperature of at least 40 C. as measured via DSC at a heating rate of 5 C./min; and the co-crosslinker has a WPU higher than 150 and lower than 630 g/mole and said co-crosslinker is a vinylether; and the composition comprises an inhibitor.

40. The composition according to claim 39, wherein the reactive unsaturations of the resin are based on fumaric acid and/or maleic acid.

41. The composition according to claim 1, wherein the reactive unsaturations of the resin are based on maleic acid, fumaric acid, itaconic acid, acrylic acid and/or methacrylic acid, said resin has a hydroxyl value in the range of from 0 to 70 mg KOH per g resin and an acid value of less than 5 mg KOH per g resin, and a number average molecular weight in the range of from 1500 to 8000 Da and a glass transition temperature of at least 40 C. as measured via DSC at a heating rate of 5 C./min; and the co-crosslinker has a WPU higher than 150 and lower than 630 g/mole and said co-crosslinker is a vinylether; and the composition comprises an inhibitor.

42. The composition according to claim 41, wherein the reactive unsaturations of the resin are based on fumaric acid and/or maleic acid.

43. A process for the preparation of a powder coating composition according to claim 1, comprising the steps of: (a) mixing the components of the powder coating composition to obtain a premix; (b) heating the premix to obtain an extrudate; (c) cooling down the extrudate to obtain a solidified extrudate; and (d) breaking the solidified extrudate into smaller particles to obtain the powder coating composition.

44. A process for coating a substrate comprising the following steps of: (1) applying a powder coating composition according to claim 1 to a substrate; and (2) heating the substrate.

45. A substrate that is fully or partially coated with a powder coating composition according to claim 1.

46. The substrate according to claim 45, wherein the substrate is a heat-sensitive substrate.

47. The substrate according to claim 46, wherein the heat-sensitive substrate is wood.

48. The substrate according to claim 46, wherein the heat-sensitive substrate is plastic.

Description

EXAMPLES

(1) The invention is explained in more detail with reference to the following non-limiting examples.

Examples

Synthesis and Application of the Powder Coating

(2) TABLE-US-00002 TABLE 2 Chemicals Commercial Description or Chemical name Structure name use Propylene glycol Monomer Neopentyl glycol Monomer Trimethylol propane Monomer Hydrogenated Monomer bis-phenol A Terephthalic acid Monomer lsophthalic acid Monomer Fumaric acid Monomer Hydroxylbutyl Monomer vinylether lsophoronediisocyanate Monomer Ethylene carbonate Monomer 2,3-epoxy propyl Monomer neodecanoate Dimyristyl peroxy dicarbonate Perkadox 26 from Akzo Nobel Initiator Dilauroyl peroxide 0 Laurox S from Akzo Nobel Initiator Dibenzoyl peroxide (BPO) Luperox A75 from Arkema Initiator Tert-butyl peroxybenzoate Trigonox C from Akzo Nobel Initiator Tert-butyl peroxy-2- ethyl hexanoate Trigonox 21-S from AkzoNobel Initiator Tert-amyl peroxy (2- ethyl) hexanoate Trigonox 121 from AkzoNobel Initiator Tert-butyl peroxy-2- ethylhexyl carbonate Peroxan BEC from Perkan Initiator Dicumyl peroxide Perkadox BC- FF from AkzoNobel Initiator Tert-butyl Inhibitor hydroquinone Cobaltbis(2- COMMET Accelerator ethylhexanoate), also Cobalt Octanoate known as Cobalt from De Monchy octanoate International B.V. Octa Soligen Accelerator Manganese 10 from OMG Borchers Harcat copper Accelerator naphthenate Iron acetate Accelerator Byk -361 N Flow agent from Byk
Synthesis of Resins: General Procedure

(3) The chemicals used in the following examples are described in table 2.

(4) Resin Synthesis (Resin A)

(5) A reaction vessel fitted with a thermometer, a stirrer and a distillation device, was filled with a tin catalyst and the monomers for the first step (all the (poly)alcohols and terephthalic acid) as listed in table 3. Stirring was then applied and a light nitrogen flow was passed over the reaction mixture while the temperature was raised to 220 C. Subsequently, for the second step fumaric acid together with a small amount of radical inhibitor was added at a temperature of 180 C. followed by esterification at 220 C. When an acid value of less than approximately 15 mg KOH/g resin was reached, the reaction mixture was cooled to 205 C. The third stage of the polyester preparation was carried out under reduced pressure at 205 C. till an acid value of approximately 5 mg KOH/g resin was reached. The acid value of the resin was brought below 5 mg KOH/g resin via reaction of the remaining acid-groups of the resin with an epoxy or an alkylene carbonate group (see table 3 which chemical is used). The used amount was dependent on the acid value before addition.

(6) Resin Synthesis (Resin B)

(7) A reaction vessel fitted with a thermometer, a stirrer and a distillation device, was filled with a tin catalyst and the monomers for the first step (all the (poly)alcohols and terephthalic acid) as listed in table 3. Stirring was then applied and a light nitrogen flow was passed over the reaction mixture while the temperature was raised to 220 C. Subsequently, for the second step fumaric acid together with a small amount of radical inhibitor was added at a temperature of 180 C. followed by esterification at 205 C. When an acid value of less than approximately 30 mg KOH/g resin was reached, the third stage of the polyester preparation was carried out under reduced pressure at 205 C. till an acid value of approximately 5 mg KOH/g resin was reached. The acid value of the resin was brought below 5 mg KOH/g resin via reaction of the remaining acid-groups of the resin with an epoxy (see table 3 which chemical is used). The used amount was dependent on the acid value before addition.

(8) Resin and Co-Crosslinker Analysis:

(9) Glass transition temperature (Tg) measurements (inflection point) and melting temperature measurements were carried out via differential scanning calorimetry (DSC) on a Mettler Toledo, TA DSC821, in N.sub.2 atmosphere and at a heating rate of 5 C./min. Viscosity measurements were carried out at 160 C., on a Rheometric Scientific CT 5 (Rm 265) apparatus (Mettler Toledo). A 30 mm spindle was used. The applied shear-rate was 70 s.sup.1. The acid and hydroxyl values of the resins were determined titrimetrically according to ISO 2114-2000 and ISO 4629-1978, respectively.

(10) The weight per unsaturation (WPU) was determined via .sup.1H-NMR on a 300 MHz Varian NMR-spectrometer using pyrazine as internal standard. Recorded spectra were analyzed in full with ACD software and peak areas of all peaks were calculated.

(11) The weight resin per mole unsaturation was calculated with the following formula:

(12) $\mathrm{WPU}={\left[\frac{W_{\mathrm{pyr}}}{W_{\mathrm{resin}}}\frac{1}{{\mathrm{MW}}_{\mathrm{pyr}}}\frac{A_{c=c}/N_{c=c}}{A_{\mathrm{pyr}}/N_{\mathrm{pyr}}}\right]}^{-1}$
W.sub.pyr and W.sub.resin are weights pyrazine (is internal standard) and resin, respectively, expressed in the same units. MW.sub.pyr is molecular weight pyrazine (=80 gr/mole). A.sub.CC is the peak area for hydrogens attached to the carbon carbon double bonds of the reactive unsaturations (CC component) in the resin; N.sub.CC is the number of hydrogens of that particular CC component. A.sub.pyr is the peak area for pyrazine and N.sub.pyr is the number of hydrogens (=4).

(13) TABLE-US-00003 TABLE 3 Synthesis and properties of the resins used Resin no. A B Amount Amount Monomers (mole %) (mole %) Propylene glycol 34.8 Neopentylglycol 47.9 Trimethylol propane 3.7 0.5 Terephthalic acid 37.5 44.4 Fumaric acid 10.9 20.2 Ethylene carbonate X 2,3-epoxy propyl neodecanoate X Resin characterization Weight per unsaturation (WPU) 1028 502 (theoretical) Weight per unsaturation (WPU) 1130 536 (measured with NMR) Mn (theoretical) 2723 2612 Hydroxyl value (mg KOH/g) 42.7 43.8 Acid value (mg KOH/g) 3.1 1.3 Tg ( C.) 46.5 48.1 Viscosity at 160 C. (Pa .Math. s) 21.2 7.6
Synthesis of Vinyl Ether Based Co Crosslinkers: General Procedure
Method to Determine Presence of Free-NCO.

(14) An FT-IR spectra was recorded on a Varian Excalibur apparatus equipped with an ATR (Golden Gate) accessories. A characteristic peak for free NCO can be found at 2250 cm.sup.1. Presence of a peak at this position refers to free NCO groups.

(15) Co-Crosslinker Synthesis (I)

(16) A reaction vessel fitted with a thermometer, a stirrer and a distillation device, was filled with a tin catalyst and the monomers for the first step (all the (poly)alcohols, isophthalic acid) as listed in table 4. Stirring was then applied and a light nitrogen flow was passed over the reaction mixture while the temperature was raised to 220 C. Subsequently, for the second step a vinylether as listed in table 4 and a tin catalyst were added at a temperature of 120 C. Subsequently, an isocyanate as listed in table 4 was dosed such that the reaction mixture was kept below 120 C. during addition. After all isocyanate was dosed, the temperature was kept or set at 120 C. and maintained at this temperature for approximately half an hour. Next, n-butanol was added until all free NCO had reacted (measured using FT-IR as described above). The temperature was kept at 120 C. and vacuum (0.1 bar) was applied to remove all volatiles. After vacuum the content of the vessel was discharged.

(17) TABLE-US-00004 TABLE 4 Synthesis and properties of the co-crosslinker I Vinylether urethane Co-crosslinker Amount Type (mole %) Hydroxyl butyl vinyl ether 28.5 Isophorone diisocyanate 28.5 Hydrogenated bisphenol A 14.3 Neopentylglycol 14.3 Isophthalic acid 14.3 Co-crosslinker characterization Mn (theoretical) 1152 Weight per unsaturation in g/mole (WPU) 576 (theoretical) Weight per unsaturation in g/mole (WPU) 623 (determined using .sup.1H NMR) Phase Amorphous Tm or Tg ( C.) Tg = 41 C. Hydroxyl value (mg KOH/g) 1.0 Acid value (mg KOH/g) 0.5 Viscosity at 160 C. (Pa .Math. s) 3.9
Preparation of the Powder Coating Composition, Application and Analysis:

(18) The compositions of the tested powder coating composition are given in the tables below. The components were extruded at 60 C. using a Prism Twin Screw extruder (200 rpm, torque >90%). The extrudate was grinded and sieved; the sieving fractions smaller than 90 microns were used as a powder coating composition. The powder coating compositions were applied with a corona powder application spray gun on an aluminum ALQ panel and cured at various temperatures for 15 minutes in a convection oven (Heraeus UT 6120). The applied coating layer thickness was approximately 60 m.

(19) Acetone Double Rubs

(20) Acetone double rubs (ADR) were carried out as described herein to determine the curing.

(21) Within the framework of the invention, an acceptable cure is defined as the ability of a powder coating composition cured for 15 minutes to withstand at least 50 acetone double rubs (ADR), more preferably at least 70 acetone double rubs. The cure temperature (in C.) at which the powder coating composition can withstand at least 50 ADR or at least 70 ADR is defined herein as the T.sub.>50 ADR, respectively T.sub.>70 ADR for purposes of the invention, this temperature is less than 130 C.
Preparation of the Powder Coating Composition

(22) The ratio resin: co-crosslinker is chosen 3:2 on mole unsaturation. The amount of initiator in the thermal initiation system is based on the total weight of the resin system (e.g. x mole initiator per kg resin system; The resin system is the resin containing the reactive unsaturations plus the co-crosslinker excluding the usual powder coating composition additives, like pigments, fillers etc.). The amount of inhibitor in the initiation system is based on the total weight of the resin system. The amount of accelerator in the initiation system is based on the total weight of the resin system (e.g. x mole accelerator per kg resin system). The amount of flow agent is calculated in wt % of the total powder coating composition. In all powder coating compositions 0.8 wt % flow agent is used, unless indicated differently.

Example 1

(23) TABLE-US-00005 TABLE 5 Influence of the choice of peroxide on the cure of the powder coating composition. Exp-# comparative comparative comparative comparative 1.1 1.2 1.3 1.4 example 1.5 example 1.6 example 1.7 example 1.8 Resin A A A A A A A A Co-crosslinker I I I I I I I I Initiation system Initiator Trigonox Trigonox Trigonox Peroxan Perkadox Laurox Luperox Perkadox C 21-S 121 BEC 26 S A75 BC-FF 92.0 92.0 92.0 92.0 92.0 92.0 92.0 92.0 mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg Chemical name Tert-butyl Tert-butyl Tert-amyl Tert-butyl Dimyristyl Dilauroyl Dibenzoyl Dicumyl peroxy- peroxy- peroxy peroxy-2- peroxy peroxide peroxide peroxide benzoate 2-ethyl (2-ethyl) ethylhexyl dicarbonate hexanoate hexanoate carbonate Inhibitor Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl hydro- hydro- hydro- hydro- hydro- hydro- hydro- hydro- quinone quinone quinone quinone quinone quinone quinone quinone 500 ppm 500 ppm 500 ppm 500 ppm 500 ppm 500 ppm 500 ppm 500 ppm Accelerator Co Co Co Co Co Co Co Co 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg Extrusion Ok Ok Ok Ok Gel Ok Ok Ok T.sub.>50 ADR ( C.) 100 90 80 120 120 C. 120 >130 C. T.sub.>70 ADR ( C.) 100 100 80 120 >130 C. 130 >130 C.

(24) As can be seen from the above table 5, the use of peresters and monopercarbonates, preferably of peresters results in a coating that can be cured to an acceptable level if cured for 15 minutes at a relatively low temperature (below 130 C.), whereas the use of other peroxides results in coatings that cannot be cured to an acceptable level at these low temperatures.

(25) These experiments were conducted with a resin having a WPU of 1130; in case a resin with a lower WPU is used with a similar initiation system (the peroxide+transition metal catalyst and optionally an inhibitor), T.sub.>50 ADR will be lower.

Example 2 Initiation Systems without Cobalt

(26) TABLE-US-00006 TABLE 6 Different initiation systems without cobalt. Exp-# comparative comparative comparative comparative comparative comparative comparative comparative example 2.1 example 2.2 example 2.3 example 2.4 example 2.5 example 2.6 example 2.7 example 2.8 Resin A A A A A A A A Co-crosslinker I I I I I I I I Initiation system Initiator Trigonox Trigonox Trigonox Peroxan Perkadox Laurox Luperox Perkadox C 21-S 121 BEC 26 S A75 BC-FF 92.0 92.0 92.0 92.0 92.0 92.0 92.0 92.0 mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg Chemical name Tert-butyl Tert-butyl Tert-amyl Tert-butyl Dimyristyl Dilauroyl Dibenzoyl Dicumyl peroxy- peroxy-2-ethyl peroxy peroxy- peroxy peroxide peroxide peroxide benzoate hexanoate (2-ethyl) 2-ethylhexyl dicarbonate hexanoate carbonate Inhibitor Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl hydro- hydro- hydro- hydro- hydro- hydro- hydro- hydro- quinone quinone quinone quinone quinone quinone quinone quinone 500 ppm 500 ppm 500 ppm 500 ppm 500 ppm 500 ppm 500 ppm 500 ppm Accelerator Extrusion Ok Ok Ok Ok Gel Ok Ok Ok T.sub.>50 ADR ( C.) >130 >130 >130 >130 120 >130 >130 T.sub.>70 ADR ( C.) >130 >130 >130 >130 >130 >130 >130

(27) As can be seen from the results present in table 6 and table 5, by comparing examples 1.1, 1.2, 1.3 and 1.4 with respectively 2.1, 2.2, 2.3 and 2.4, a transition metal catalyst, for example cobalt is required to ensure sufficient cure at a temperature of below 130 C. for 15 minutes in case a perester or monopercarbonate is used in the powder coating composition of the invention.

Example 3 Amount of Peroxide Needed to Ensure Sufficient Cure

(28) TABLE-US-00007 TABLE 7 Different amounts of Trigonox C. Exp-# 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 Resin B B B B B B B B Co-crosslinker I I I I I I I I Initiation system Initiator Trigonox Trigonox Trigonox Trigonox Trigonox Trigonox Trigonox Trigonox C C C C C C C C 3.8 9.2 18.4 36.8 55.2 73.6 92.0 184.0 mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg Chemical name Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl peroxy- peroxy- peroxy- peroxy- peroxy- peroxy- peroxy- peroxy- benzoate benzoate benzoate benzoate benzoate benzoate benzoate benzoate Inhibitor Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl hydro- hydro- hydro- hydro- hydro- hydro- hydro- hydro- quinone quinone quinone quinone quinone quinone quinone quinone 500 ppm 500 ppm 500 ppm 500 ppm 500 ppm 500 ppm 500 ppm 500 ppm Accelerator Co Co Co Co Co Co Co Co 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg T.sub.>50 ADR ( C.) >130 >130 110 110 100 90 90 80 T.sub.>70 ADR ( C.) >130 >130 110 110 100 90 90 90

(29) As can be seen from the above table 7, the optimal amount of perester or monopercarbonate can easily be determined by the person skilled in the art.

Example 4 Amount of Cobalt Needed to Ensure Sufficient Cure

(30) TABLE-US-00008 TABLE 8 Different amounts of cobalt Exp-# 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 Resin B B B B B B B B B Co-crosslinker I I I I I I I I I Initiation system Initiator Trigonox Trigonox Trigonox Trigonox Trigonox Trigonox Trigonox Trigonox Trigonox C C C C C C C C C 73.6 73.6 73.6 73.6 73.6 73.6 73.6 73.6 73.6 mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg Chemical name Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl peroxy- peroxy- peroxy- peroxy- peroxy- peroxy- peroxy- peroxy- peroxy- benzoate benzoate benzoate benzoate benzoate benzoate benzoate benzoate benzoate Inhibitor Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl Tert-butyl hydro- hydro- hydro- hydro- hydro- hydro- hydro- hydro- hydro- quinone quinone quinone quinone quinone quinone quinone quinone quinone 500 ppm 500 ppm 500 ppm 500 ppm 500 ppm 500 ppm 500 ppm 500 ppm 500 ppm Accelerator Co Co Co Co Co Co Co Co 0.5 1.0 1.5 2.0 3.0 4.5 6.0 12.0 mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg mmol/kg T.sub.>50 ADR ( C.) >130 120 100 100 100 90 90 90 90 T.sub.>70 ADR ( C.) >130 120 100 100 100 90 90 90 90

(31) As can be seen from the above table 8, the person skilled in the art can easily determine using routine experimentation the optimal amount of transition metal catalyst.