Heat-curable powder coating composition

Abstract

The disclosure relates to a heat curable powder coating composition suitable for being cured at a temperature from 60 to 130 C. containing: a thermal initiation system and a resin system, wherein the reactivity of the thermal initiation system is such that the thermal initiation system provides a geltime between 2.5 and 1000 minutes at 60 C. in butane diol-dimethacrylate as measured according to DIN 16945 using 1 wt % of the thermal initiation system in 99 wt % of butane dioldimethacrylate, wherein the amount of thermal initiation system is chosen such that when the powder coating composition is applied to a substrate and cured at a temperature of 130 C. for 20 minutes.

Claims

1. A heat curable powder coating composition suitable for being cured at a temperature from 60 to 130 C. comprising: a thermal initiation system and a resin system; wherein the reactivity of the thermal initiation system is such that the thermal initiation system provides a geltime between 2.5 and 1000 minutes at 60 C. in butane diol-dimethacrylate as measured according to DIN 16945:1989-03 using 1 wt % of the thermal initiation system in 99 wt % of butane diol-dimethacrylate; and wherein the amount of thermal initiation system is chosen 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 50 acetone double rubs; and wherein the resin system comprises a resin and a co-crosslinker; and wherein the resin contains reactive unsaturations which are carbon carbon double bonds connected directly to an electron withdrawing group; and wherein the resin is a polyester; and wherein the co-crosslinker is chosen from the group of acrylates, methacrylates, vinylesters, vinylethers, vinyl amides, alkyn ethers, alkyn esters, alkyn amides, alkyn amines, propargyl ethers, propargyl esters, itaconates, enamines and mixtures thereof; and wherein the weight per unsaturation (WPU) of the co-crosslinker is higher than 150 and lower than 870 g/mole as determined using .sup.1H NMR; and wherein the weight per unsaturation in the resin system is between 100 and 1000 g/mole as determined using .sup.1H NMR; and wherein the powder coating composition is a one component system.

2. The composition according to claim 1, wherein the geltime is at least 6 minutes and less than 1000 minutes.

3. The composition according to claim 1, wherein the thermal initiation system comprises a peroxide.

4. The composition according to claim 3, wherein, the peroxide is any of the following initiators: peranhydrides, peroxydicarbonates.

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

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

7. The composition according to claim 1, wherein the thermal initiation system comprises hydroquinones or catechols.

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

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

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

11. The composition according to claim 10, wherein the resin has an acid value of less than 5 mg KOH per g resin.

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

13. The composition according to claim 12, wherein the resin has an acid value of less than 5 mg KOH per g resin.

14. 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.

15. The composition according to claim 1, wherein the weight per unsaturation of the co-crosslinker is higher than 150 g/mole and lower than 650 g/mole.

16. The composition according to claim 1, wherein the weight per unsaturation of the co-crosslinker is higher than 150 g/mole and lower than 630 g/mole.

17. The composition according to claim 1, wherein the weight per unsaturation of the resin is less than 1500 g/mole as determined using .sup.1H NMR.

18. The composition according to claim 1, wherein the weight per unsaturation of the resin is less than 1150 g/mole as determined using .sup.1H NMR.

19. The composition according to claim 1, wherein the weight per unsaturation of the co-crosslinker is higher than 150 g/mole and lower than 630 g/mole and wherein the weight per unsaturation of the resin is less than 1150 g/mole.

20. The composition according to claim 1, wherein the resin and the co-crosslinker are the same.

21. The composition according to claim 1, wherein the resin and the co-crosslinker are the same and the thermal initiation system comprises hydroquinones or catechols.

22. The composition according to claim 1, wherein the resin is a polyester based on fumaric acid, wherein the co-crosslinker is a vinylether and wherein the thermal initiation system comprises a perdicarbonate and a hydroquinone.

23. The composition according to claim 22, wherein the perdicarbonate is di(4-t-butylcyclohexyl)peroxydicarbonate or dimyristyl peroxydicarbonate, and wherein the hydroquinone is tert-butylhydroquinone or 2,3,5-trimethylhydroquinone.

24. The composition according to claim 1, wherein the resin is a polyester based on fumaric acid, wherein the co-crosslinker is a vinylether and wherein the thermal initiator is benzoyl peroxide.

25. The composition to claim 1, wherein the thermal initiation system comprises transition metal compounds of transition metals with atomic numbers from/equal to 21 up to/equal to 79.

26. The composition according to claim 1, wherein the thermal initiation system comprises transition metal compounds of Mn, Fe, Co or Cu.

27. The composition according to claim 1, wherein the thermal initiation system comprises metal salts or complexes or mixtures thereof of Mn, Fe, Co or Cu.

28. 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.

29. 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.

30. 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.

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

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

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 g/mole and lower than 630 g/mole and said co-crosslinker is chosen from the group of vinylethers, vinylesters and mixtures thereof.

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 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 g/mole and lower than 630 g/mole and said co-crosslinker is chosen from the group of vinylethers, vinylesters and mixtures thereof; and the thermal initiation system comprises an inhibitor.

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 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 g/mole 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 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 g/mole and lower than 630 g/mole and said co-crosslinker is a vinylether; and the thermal initiation system 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 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 g/mole and lower than 630 g/mole and said co-crosslinker is a vinylether.

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

43. 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 g/mole and lower than 630 g/mole and said co-crosslinker is a vinylether.

44. The composition according to claim 43, wherein the reactive unsaturations of the resin are based on fumaric acid and/or maleic acid.

45. 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 g/mole and lower than 630 g/mole and said co-crosslinker is a vinylether; and the thermal initiation system comprises an inhibitor.

46. The composition according to claim 45, wherein the reactive unsaturations of the resin are based on fumaric acid and/or maleic acid.

47. 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 g/mole and lower than 630 g/mole and said co-crosslinker is a vinylether; and the thermal initiation system comprises an inhibitor.

48. The composition according to claim 47, wherein the reactive unsaturations of the resin are based on fumaric acid and/or maleic acid.

49. 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.

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

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

52. The substrate according to claim 51, wherein the substrate is a heat-sensitive substrate.

53. The substrate according to claim 52, wherein the heat-sensitive substrate is wood.

54. The substrate according to claim 52, 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.

(2) Experimental Section

(3) Determination of Reactivity of Initiation Systems in Butane Diol-Dimethacrylate (BDDMA)

(4) The determination of reactivity of the initiating systems was performed by monitoring the curing of BDDMA by means of standard gel time equipment. The gel time (T.sub.gel or T.sub.60->70 C.) was determined by measuring the exothermic reaction according to the method of DIN 16945 section 6.2.2.2 when curing BDDMA at 60 C. with 1% of the initiation systems as indicated in table 2. The equipment used therefore was a Soform gel timer, with a Peakpro software package and National Instruments hardware; the water bath and thermostat used were respectively Haake W26, and Haake DL30.

(5) In table 2, the amount of transition metal compound (the accelerator) is indicated in mmol transition metal compound per kg BDDMA.

(6) TABLE-US-00002 TABLE 2 Gel time Entry Initiation system (min) 1 Azo-bis-isobutyronitril (AIBN) 31 2 Di(4-t-butyl cyclohexyl) peroxy dicarbonate (Perkadox 16) 5.8 3 Dicetyl peroxy dicarbonate (Perkadox 24) 7 4 Dimyristyl peroxy dicarbonate (Perkadox 26) 4.3 5 Di decanoyl peroxide (Perkadox SE-10) 67 6 Dilauroyl peroxide (Laurox S) 90 7 Dibenzoyl peroxide (Luperox A98) 101 8 t-Amyl peroxy pivalate (Trigonox 125) 13 9 t-Butyl peroxy neoheptanoate (Trigonox 257) 11 10 Lauroyl peroxide (Luperox LP) 82 11 t-Butyl peroxy 2-ethylhexanoate (Trigonox 21) 131 12 Di-iso-butyrylperoxide (Trigonox 187-W26) <0.4 13 Cumyl peroxyneodecanoate (Trigonox 99-C75) 2 14 1,1,3,3-Tetramethyl butyl peroxyneodecanoate (Trigonox 423-C70) 2.2 15 1,1-Di-(t-butylperoxy)-3,3,5-trimethylcyclohexane (Trigonox 29 40B-GR) >1440 16 3,6,9-Triethyl-3,6,9-trimethyl triperoxonane (Trigonox 310) >1440 17 Di(t-butylperoxy isopropyl)benzene (Perkadox 14S) >1440 18 2,3-Dimethyl-2,3-diphenylbutane (Perkadox 30) >1440 19 Di-t-butylperoxide >1440 20 Cumylhydroperoxide >1440 21 Dicumylperoxide (Perkadox BC-FF) >1440 22 t-Butyl perbenzoate (Trigonox C) >1440 23 2,5-Dimethyl-2,5-di(t-butylperoxy)hexane >1440 24 Methylethylketone peroxide solution (Butanox M50) >1440 25 Acetylacetone peroxide solution (Trigonox 44B) >1440 26 Cyclohexanone peroxide solution (Cyclonox LE50) 1105 27 Dilauroylperoxide/N,N-diisopropanol-p-toluidine (equimolar amounts) 4.8 28 Dibenzoylperoxide/N-phenyldiethanolamine (equimolar amounts) 4.0 29 Dibenzoylperoxide/N,N-dimethyl-p-toluidine (equimolar amounts) 0.4 30 t-Butyl perbenzoate/Cu (1.0 mmol/kg) 11 31 Methylethylketone peroxide solution/Co (1.0 mmol/kg) 5 32 t-Butyl perbenzoate/Co (6.0 mmol/kg 5.2 33 Dicumylperoxide/Mn (3.0 mmol/kg)/ 41 pentaerythritoltetramercaptopropionate (1.3 mmol/kg) 34 Di(4-t-butyl cyclohexyl) peroxy dicarbonate/methylhydroquinone 9.2 (250 ppm) 35 Di(4-t-butyl cyclohexyl) peroxy dicarbonate/methylhydroquinone 11.9 (2000 ppm) 36 Dicetyl peroxy dicarbonate/methylhydroquione (500 ppm) 10.1 37 Dimyristyl peroxy dicarbonate/methylhydroquinone (250 ppm) 6.8 38 Dimyristyl peroxy dicarbonate/methylhydroquinone (2000 ppm) 8.6 39 t-Butyl perbenzoate/Co (6.0 mmol/kg)/t-butylhydroquinone (500 ppm) 11.6 40 t-Butyl perbenzoate/Co (12.0 mmol/kg)/t-butylhydroquinone (500 ppm) 7.9 41 t-Butyl peroxy 2-ethylhexanoate/Co (3.0 mmol/kg) 3.8 42 t-Butyl peroxy 2-ethylhexanoate/Cu (3.0 mmol/kg) 16.6 43 t-Butyl peroxy-2-ethylhexyl carbonate (Trigonox 117) >1440 44 t-Butyl peroxy-2-ethylhexyl carbonate/Co (3.0 mmol/kg) 28.3 45 t-Butyl peroxy-2-ethylhexyl carbonate/Cu (3.0 mmol/kg) 18.7 46 t-Amyl peroxy-2-ethylhexanoate (Trigonox 121) 88.6 47 t-Amyl peroxy-2-ethylhexanoate/Co (3.0 mmol/kg) 2.8 48 t-Amyl peroxy-2-ethylhexanoate/Cu (3.0 mmol/kg) 13.2 49 1,1-Di-(t-butylperoxy)-3,3,5-trimethylcyclohexane/Co (3.0 mmol/kg) >1440 50 1,1-Di-(t-butylperoxy)-3,3,5-trimethylcyclohexane/Co (6.0 mmol/kg) 1213

(7) This table clearly shows that multiple peroxides are suitable initiator systems according to the invention. Furthermore this table demonstrates that various relatively unreactive peroxides can be made more reactive with accelerators to gain reactivity in line with the invention (see for example entry 22 vs. entry 30). Furthermore this table shows that various reactive peroxides can be made less reactive with inhibitors in order to obtain a more suitable reactivity (see for example entry 4 vs. entry 38. Furthermore this table also shows that combinations of accelerators and inhibitors can be used for changing the reactivity (entry 39).

(8) Synthesis and Application of the Powder Coating

(9) TABLE-US-00003 TABLE 3 Chemicals Chemical name Commercial name Description or use Propylene glycol Monomer Neopentyl glycol Monomer Trimethylol propane Monomer Hydrogenated bis-phenol A Monomer Terephthalic acid Monomer Isophthalic acid Monomer Benzoic acid Monomer Fumaric acid Monomer Hydroxylbutyl vinylether Monomer Isophoronediisocyanate Monomer Ethylene carbonate 2,3-epoxy propyl neodecanoate Bis-(4-vinyl oxy butyl) URACROSS P3307 from DSM Co-crosslinker hexamethylenediurethane Di(4-tert-butylcyclohexyl) peroxy Perkadox 16 from Akzo Nobel Initiator dicarbonate Dimyristyl peroxy dicarbonate Perkadox 26 from Akzo Nobel Initiator Dilauroyl peroxide Laurox S from Akzo Nobel Initiator Dibenzoyl peroxide (BPO) Luperox A75 from Arkema Initiator Tert-butyl peroxybenzoate Trigonox C from Akzo Nobel Initiator Di-iso-butyrylperoxide Trigonox 187-W26 from AkzoNobel Initiator Cumyl peroxyneodecanoate Trigonox 99-C75 from AkzoNobel Initiator 1,1,3,3-tetramethyl butyl Trigonox 423-C70 from AkzoNobel Initiator peroxyneodecanoate Tert-butyl hydroquinone Inhibitor 2,3,5-trimethyl hydroquinone Inhibitor Cobalt Octoate (Co), also known as COMMET Cobalt Octoate from De Accelerator Cobalt bis(2-ethylhexanoate) Monchy International B.V. Titanium dioxide pigment Kronos 2310 from Kronos Pigment Byk-361 N from Byk Flow agent
Synthesis of Resins: General Procedure

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

(11) Resin Synthesis (Resin B)

(12) 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 4. Stirring was then applied and a light nitrogen flow was passed over the reaction mixture while the temperature was raised to 230 C. Subsequently, for the second step benzoic acid was added at a temperature of 140 C. followed by esterification at 230 C. When an acid value of less than approximately 8 mg KOH/g resin was reached, the reaction mixture was cooled to 160 C. Fumaric acid together with a small amount of radical inhibitor was added and esterified by increasing the temperature to 200 C. The final stage of the polyester preparation was carried out under reduced pressure.

(13) Resin Synthesis (Resin C, D, E, K)

(14) 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 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 benzoic acid, fumaric acid together with a small amount of a radical inhibitor was added at a temperature of 160 C. followed by esterification at 210 C. Esterification was followed by a step under reduced pressure to reach an acid value of approximately 5 mg KOH/g resin. 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 4 which chemical is used). The used amount was dependent on the acid value before addition.

(15) Resin Synthesis (Resin A, G, H, J)

(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 and terephthalic 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 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 till an acid value 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 4 which chemical is used). The used amount was dependent on the acid value before addition.

(17) Resin Synthesis (Resin F)

(18) 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 230 C. When an acid value of less than approximately 10 mg KOH/g resin was reached, the reaction mixture was cooled to 160 C. Itaconic acid together with a small amount of radical inhibitor was added and esterified by increasing the temperature to 220 C. The final stage of the polyester preparation was carried out under reduced pressure.

(19) Resin and Co-Crosslinker Analysis:

(20) 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.

(21) 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.

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

(23) $\mathrm{WPU}={\left[\frac{W_{\mathrm{pyr}}}{W_{\mathrm{resin}}}\frac{1}{{\mathrm{MW}}_{\mathrm{pyr}}}\frac{A_{c=c}/N_{c=c}}{A_{\mathrm{pyr}}/N_{\mathrm{pyr}}}\right]}^{-1}$
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).

(24) TABLE-US-00004 TABLE 4 Synthesis and properties of the resins used Resin no. A B C D E F G H J K Amount Amount Amount Amount Amount Amount Amount Amount Amount Amount Monomers (mole %) (mole %) (mole %) (mole %) (mole %) (mole %) (mole %) (mole %) (mole %) (mole %) Propylene glycol 46.6 46.6 46.6 46.6 48.2 46.6 Neopentylglycol 52.1 48.9 52.1 47.9 Trimethylol propane 1.4 1.4 1.4 1.4 3.7 3.7 3.4 1.4 Benzoic acid 7.6 7.6 7.6 7.6 7.6 Terephthalic acid 26.7 25.4 25.4 25.4 25.4 24.7 36.9 37.5 38.5 34.5 Fumaric acid 21.3 19.0 19.0 19.0 19.0 11.1 10.9 9.9 9.9 Itaconic acid 22.7 Ethylene carbonate X X X X X X X 2,3-epoxy propyl X neodecanoate Resin characterization Weight per unsaturation 502 493 493 493 493 481 1008 1028 999 995 (WPU) (theoretical) Weight per unsaturation 518 530 537 554 654 758 995 1130 1170 1061 (WPU) (measured with NMR) Mn (theoretical) 2134 2203 2203 2203 2203 2144 2225 2723 2521 2294 Hydroxyl value (mg KOH/g) 44.9 12.8 17.7 18.7 20.2 68.0 38.5 42.7 53.2 17.2 Acid value (mg KOH/g) 1.2 6.5 1.8 2.3 3.0 3.1 1.5 3.1 1.5 1.6 Tg ( C.) 38.4 43.2 39.2 38.0 38.1 24.2 49.6 46.5 51.9 47.3 Viscosity at 160 C. (Pa .Math. s) 5.1 4.0 5.3 3.0 2.5 3.2 12.7 21.2 33.3 4.6
Synthesis of Vinyl Ether Based Co Crosslinkers: General Procedure
Method to Determine Presence of Free-NCO.

(25) 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.

(26) Co-Crosslinker Synthesis (II)

(27) A reaction vessel fitted with a thermometer and a stirrer, was filled with an isocyanate as listed in table 5. Stirring was then applied and a light nitrogen flow was passed over the reaction mixture while the temperature was kept below 15 C. Subsequently, a vinylether as listed in table 5 was dosed such that the reaction mixture was kept below 15 C. during addition. After all vinylether was dosed, the temperature was raised to 65 C. and a tin catalyst was added. The alcohol as listed in table 5 was dosed while the temperature was kept below 75 C. After all alcohol was dosed the temperature was set at 105 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 raised to 115 C. and vacuum (0.1 bar) was applied to remove all volatiles. After vacuum the content of the vessel was discharged.

(28) Co-Crosslinker Synthesis (III/IV/V)

(29) 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, terephthalic or isophthalic acid) as listed in table 5. 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 and a tin catalyst as listed in table 5 were added at a temperature of 100 C. Subsequently, an isocyanate as listed in table 5 was dosed such that the reaction mixture was kept below 100 C. during addition. After all isocyanate was dosed, the temperature was kept or set at 105 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 raised to 115 C. and vacuum (0.1 bar) was applied to remove all volatiles. After vacuum the content of the vessel was discharged.

(30) TABLE-US-00005 TABLE 5 Synthesis and properties of the co-crosslinker Co-crosslinker I II III IV V Type Vinylether Vinylether Vinylether Vinylether Vinylether urethane urethane urethane urethane urethane Amount Amount Amount Amount Amount (mole %) (mole %) (mole %) (mole %) (mole %) Hydroxyl butyl vinyl 42.9 28.4 28.5 22.0 ether Isophorone 42.9 28.4 28.5 22.0 diisocyanate Hydrogenated 14.3 bisphenol A Neopentylglycol 28.7 14.3 33.6 Trimethylol 14.3 propane Terephthalic acid 14.4 22.4 Isophthalic acid 14.3 Commercially URACROSS available from DSM P3307 Resins Co-crosslinker characterization Mn (theoretical) 400 1149 1009 1152 1272 Weight per 204 383 504 576 630 unsaturation in g/mole (WPU) (theoretical) Weight per 210 386 532 623 870 unsaturation in g/mole (WPU) as measured using 1H NMR Phase Crystalline Amorphous Amorphous Amorphous Amorphous Tm or Tg ( C.) Tm = 90 C. Tg = 30 C. Tg = 24 C. Tg = 41 C. Tg = 36 C. Hydroxyl value (mg n.d. 6.4 9.0 1.0 1.3 KOH/g) Acid value (mg n.d. 0.4 1.0 0.5 0.1 KOH/g) Viscosity at 160 C. n.d. 1.2 0.8 3.9 1.8 (Pa .Math. s)
Preparation of the Powder Coating Composition, Application and Analysis:

(31) 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 20 minutes in a convection oven (Heraeus UT 6120). The applied coating layer thickness was approximately 60 m.

(32) Acetone Double Rubs

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

(34) Preparation of the Powder Coating Composition

(35) The ratio resin: co-crosslinker is chosen 1:1 on mole unsaturation. The amount of initiator in the initiation is based on the total weight of the resin system (e.g. x mole initiator per kg resin system; the resin system for purposes of the amount of initiator and inhibitor is defined as 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 and pigment is calculated in wt % of the total powder coating composition. In all powder coating compositions, 0.8 wt % of flow agent is used, unless indicated differently.

Example 1

(36) TABLE-US-00006 TABLE 6 Influence of the choice of initiation system on the processing in the extruder and on the cure of the powder coating composition. Exp-# comparative comparative comparative comparative 1.1 1.2 1.3 example 1.1 example 1.2 example 1.3 example 1.4 Resin B D C C C C C Co-crosslinker I I I I I I I Initiation system Initiator Perkadox 26 Laurox S Trigonox C Trigonox 187 Trigonox 99 Trigonox 423 Trigonox C 88.3 mmol/ 88.3 mmol/ 88.3 mmol/ 88.3 mmol/ 88.3 mmol/ 88.3 mmol/ 88.3 mmol/ kg kg kg kg kg kg kg Inhibitor Tert-butyl Tert-butyl hydro- hydro- quinone quinone 250 ppm 500 ppm Accelerator Co 6 mmol/kg Extrusion Ok Ok Ok Gel Gel Gel Ok T.sub.>50 ADR 70 80 70 150 ( C.) T.sub.>70 ADR 80 90 70 160 ( C.) Reactivity 6.3 90 11.6 <0.4 2 2.2 >1440 initiation system in BDDMA (min)

(37) As can be seen from table 6, the initiation systems that showed a reactivity in BDDMA as measured with the BDDMA test as described herein is from 2.5 to 1000 min can be used as initiation systems to cure a powder coating composition.

(38) It is also shown that by the selection of the initiation system within the reactivity ranges as claimed, the powder coating composition can be cured to an acceptable level at relatively low temperatures, that is T.sub.>50 ADR (the curing temperature necessary to obtain at least 50 ADR for the coating) is below 130 C. Also, the T.sub.>70 ADR (the curing temperature necessary to obtain at least 70 ADR for the coating) is below 130 C.

Example 2

(39) Different Initiation Systems

(40) TABLE-US-00007 TABLE 7 Different initiation systems. Exp-# 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 Resin B B B D E E G G G Co- I I I I I I I I I crosslinker Initiation system Initiator Perk. 26 Perk. 16 BPO Laurox S Perk. 16 BPO BPO Perk. 26 Perk. 26 82.0 mmol/ 82.0 mmol/ 82.0 mmol/ 82.0 mmol/ 82.0 mmol/ 82.0 mmol/ 82.0 mmol/ 82.0 mmol/ 82.0 mmol/ kg kg kg kg kg kg kg kg kg Inhibitor Tert-butyl 2,3,5- 2,3,5- Tert-butyl Tert-butyl hydro- trimethyl trimethyl hydro- hydro- quinone hydro- hydro- quinone quinone 250 ppm quinone quinone 250 ppm 500 ppm 250 ppm 250 ppm Accelerator T.sub.>50 ADR 70 75 90 80 75 90 80 80 90 ( C.) T.sub.>70 ADR 80 80 100 90 80 100 90 90 100 ( C.) Reactivity 6.3 7.7 101 90 7.7 101 101 6.3 8.7 initiation system in BDDMA (min)

(41) As can be seen from the above table 7, different initiation systems can be used in the powder coating compositions of the present invention. Also, the resin system may be varied and therefore different resin and co-crosslinker combinations may be employed.

(42) The results from table 7 also show that the amount of inhibitor used in the initiation system may be varied.

Example 3

(43) Use of Additives

(44) TABLE-US-00008 TABLE 8 The influence of the use of additives (pigment and flow agent) in the powder coating composition of the invention. Exp-# 3.1 3.2 3.3 Resin B B B Co-crosslinker I I I Initiator BPO BPO BPO 37.2 37.2 37.2 mmol/kg mmol/kg mmol/kg Pigment (Kronos 2310) 33.3 wt % Flow agent (Byk-361 N) 0.8 wt % 0.8 wt % T.sub.>50 ADR ( C.) 85 85 85 T.sub.>70 ADR ( C.) 90 90 90

(45) As can be seen from table 8, the powder coating composition may comprise additives without affecting the cure temperature needed to obtain an acceptable cure (T.sub.>50 ADR remains less than 130 C.).

(46) The compositions with additives were applied both on an aluminum substrate (ALQ panel) and on an oak veneer substrate. The coated substrates were cured for 25 minutes at 100 C. and a good cure was obtained as the coatings could withstand 100 ADR. This example therefore shows that the powder coating compositions of the invention are particularly suitable for coating of heat-sensitive substrates such as wood.

Example 4

(47) Itaconic Acid Based Polyester Resin

(48) TABLE-US-00009 TABLE 9 Itaconic acid based polyester resin used both as resin and as co-crosslinker. Exp-# 4.1 4.2 Resin F F Co-crosslinker I Initiator BPO BPO 61.3 mmol/kg 61.3 mmol/kg T.sub.>50 ADR ( C.) 120 100 T.sub.>70 ADR ( C.) 130 110 Reactivity initiator in BDDMA 101 101 (min)

(49) As can be seen from table 9, the itaconic acid based polyester resin can homopolymerize and thus the resin and the co-crosslinker may be the same.

Example 5

(50) Different Co-crosslinkers

(51) TABLE-US-00010 TABLE 10 Different co-crosslinkers. Exp-# 5.1 5.2 5.3 5.4 Resin D D D D Co-crosslinker III I II IV Initiator Laurox S Laurox S BPO BPO 85.3 85.3 85.3 85.3 mmol/kg mmol/kg mmol/kg mmol/kg Theoretical 504 204 383 580 WPU co- crosslinker State co- Amorphous Crystalline Amorphous Amorphous crosslinker Tg or Tm of Tg = 24 C. Tm = 90 C. Tg = 30 C. Tg = 41 C. the co- crosslinker T.sub.>50 ADR ( C.) 85 80 95 110 T.sub.>70 ADR ( C.) 90 90 100 115

(52) As can be seen from table 10, different co-crosslinkers may be used in the powder coating composition of the present invention. Also, both amorphous and crystalline co-crosslinkers may be employed.

Example 6

(53) Influence of the WPU of the Resin System, the WPU of the Resin and the WPU of the Co-crosslinker on the Curing Temperature Needed to Get an Acceptable Powder Coating

(54) TABLE-US-00011 TABLE 11 Influence of the WPU Exp-# comparative 6.1 6.2 6.3 example 6.1 Resin B K H J Co-crosslinker I II I V Initiator BPO BPO BPO BPO Theoretical WPU co-crosslinker 204 383 204 630 Actual WPU co-crosslinker 1210 286 210 870 Actual WPU resin 530 1061 1130 1170 WPU resin system 367 722 667 900 (calculated from theoretical WPU co- crosslinker and the actual WPU of the resin) Actual WPU resin system 370 724 670 1020 T.sub.>50 ADR ( C.) 90 115 115 150 T.sub.>70 ADR ( C.) 100 120 120 160

(55) As can be seen from the above table 11, the WPU of the resin system as determined using .sup.1H NMR (actual WPU) needs to be below 1000, preferably below 900. Furthermore, it is preferred that the WPU of the resin as determined using .sup.1H NMR (actual WPU) is below 1170 and/or the WPU of the co-crosslinker as determined using .sup.1H NMR (actual WPU) is below 870 g/mol, preferably 630 g/mole.

Example 7

(56) Effect of the Amount of Initiation System Used

(57) TABLE-US-00012 TABLE 12 Effect of the amount of initiation system used. Exp-# 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 7.9 Resin C C C C C C C C C Co-crosslinker I I I I I I I I I Initiator BPO 1.5 2.8 5.7 11.4 23.0 37.2 88.7 175.2 262.8 (mmol/kg) T.sub.>50 ADR >160 >160 140 115 100 85 80 80 80 ( C.) T.sub.>70 ADR >160 >160 150 120 105 90 90 85 85 ( C.)

(58) As can be seen from table 12, the person skilled in the art can easily determine using routine experimentation the minimum amount of initiation system required to cure a powder coating composition to an acceptable degree (T.sub.>50 ADR ( C.) is below 130 C.).