Powder composition

Abstract

There is described a powder coating composition suitable for food contact use comprising a mix of: (A) a first polyester that is amorphous and COOH functional being obtained from IPA and/or TPA and no more than 10 mole % neopentyl glycol (NPG); (B) a second optional COOH functional polyester obtained from analiphatic diacid and analiphatic diol, and (C) a curing agent that comprises functional groups reactable with the COOH of the polyester(s). The powders are suitable for coating the interior of metal cans especially those holding alcoholic beverages.

Claims

1. A powder coating composition comprising a binder and 0 mole % of neopentyl glycol, wherein the binder consists of a mixture of: (A) a first polyester that is amorphous and comprises at least one carboxy group; the first polyester having an acid number from 15 to 100 mg KOH/g, a glass transition temperature (Tg) from 45 C. to 80 C. and a viscosity from 5 to 15000 mPa.Math.s, said first polyester being obtained from: an acid component comprising: (a) a dicarboxylic acid component consisting of isophthalic acid, terephthalic acid and mixtures thereof; and (c) from 1 up to 18 mole % of polyacids comprising at least three carboxy groups; and a polyol component (b) consisting of propylene glycol; (b) a polyol component consisting of propylene glycol; and (B) optionally a second polyester that is amorphous and that comprises at least one carboxy group; the second polyester being obtained from an aliphatic diacid and an aliphatic diol, and (C) a curing agent that comprises functional groups reactable with carboxylic acid groups on the polyester(s) (A) and (B), which is at least one selected from the group consisting of an epoxy resin and a -hydroxyalkylamide hardener, wherein the binder consists essentially of amorphous polyesters.

2. The composition according to claim 1, in which the first polyester (A) has an acid number from 20 to 80 mg KOH/g.

3. The composition according to claim 1, wherein the binder consists of a mixture of said first polyester (A), said second polyester (B) and said curing agent (C).

4. The composition according to claim 1, in which the dicarboxylic acid component (a) is terephthalic acid, optionally in combination with isophthalic acid.

5. The composition according to claim 1, in which the dicarboxylic acid component (a) is isophthalic acid.

6. The composition according to claim 1, in which the second polyester (B) is obtained from: (a) a dicarboxylic acid component comprising, by mole % of total acid, (i) from 75 to 100 mole % of a first acid comprising at least one linear non-branched aliphatic diacid selected from the group consisting of: succinic acid, adipic acid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,12-dodecanedioic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid anhydrides thereof, and any mixtures thereof; and (ii) optionally from 0 to 25 mole % of a second acid selected from the group consisting of fumaric acid, maleic anhydride, phthalic anhydride, isophthalic acid, terephthalic acid, and any mixtures thereof; and (b) a polyol component comprising: an alcohol selected from the group consisting of: propyleneglycol, 2-methyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 1-ethyl-2-methyl-1,3-propanediol, 2-ethyl-2-methyl-1,3-propanediol, diethyleneglycol; 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, hydrogenated Bisphenol A; ethyleneglycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,14-tetradecanediol, 1,16-hexadecanediol, hydroxypivalate of neopentyl glycol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, hydrogenated Bisphenol A, and any mixtures thereof.

7. The composition according to claim 1, in which the first and/or second polyester is branched.

8. The composition according to claim 1, wherein the powder coating composition is a thermosetting powder coating composition comprising a binder system consisting of from 19 to 99 parts by weight of polyester (A), from 0 to 44.5 parts by weight of polyester (B), and from 1 to 65 parts by weight of the curing agent (C), wherein polyester (B) has a Tg of less than or equal to 50 C. and which comprises with respect to a total amount of acids, from 75 to 100 mol % of an aliphatic diacid and, with respect to a total amount of alcohols, from 75 to 100 mol % of an aliphatic diol different from neopentyl glycol.

9. The composition according to claim 1, wherein the binder consists of: (A) from 19.0 to 99.0 parts by weight of the first polyester; (B) from 44.5 to 0 parts by weight of the second polyester; and (C) from 1 to 65 parts by weight of the curing agent, all parts being based on a total weight of polyester resins and curing agents.

10. The composition according to claim 1, wherein the binder consists of: (A) from 24.5 to 95.5 parts by weight of the first polyester; (B) from 30.0 to 1.5 parts by weight of the second polyester; and (C) from 3 to 50 parts by weight of the curing agent, all parts being based on a total weight of polyester resins and curing agents.

11. The composition according to claim 1, wherein the polyacids (c) comprising at least three carboxy groups are selected from the group consisting of trimellitic acid, pyromellitic acid and their corresponding anhydrides.

12. The composition according to claim 1, wherein the binder consists of a mixture of the first polyester (A) and the curing agent (C).

13. A coated article obtained by a process comprising the steps of coating at least one surface of a substrate with the powder coating composition according to claim 1; and heating the coated substrate to thermally cure the coating thereon to form an adherent layer of the coating composition on the substrate.

14. The article according to claim 13, wherein the substrate is a metal can holding an alcoholic beverage.

15. The article according to claim 13, wherein the substrate is selected from metal sheets for food and/or beverage products.

16. The article according to claim 13, wherein the substrate is selected from metal containers for food and/or for beverage products.

17. The article according to claim 13, wherein an interior and/or exterior surface of the substrate are coated, and wherein the substrate is a food container coming into contact with alcohol.

18. The article according to claim 13, wherein at least an interior surface of the substrate is coated, and wherein the substrate is a metal can for holding an alcoholic beverage.

19. A process for coating substrates comprising the steps of coating at least one surface of a substrate with a powder coating composition according to claim 1; and heating the coated substrate to thermally cure the coating thereon to form an adherent layer of the coating composition on the substrate.

20. The process according to claim 19 wherein the substrate is selected from metal sheets for food and/or beverage products.

21. The process according to claim 19 wherein the substrate is selected from metal containers for food and/or for beverage products.

22. The process according to claim 19, wherein the interior and/or exterior of a food container coming into contact with alcohol is coated.

23. A powder coating composition comprising a binder and 0 mole % of neopentyl glycol, wherein the binder consists of a mixture of: (A) a first polyester that is amorphous and comprises at least one carboxy group; the first polyester having an acid number from 15 to 100 mg KOH/g, a glass transition temperature (Tg) from 45 C. to 80 C. and a viscosity from 5 to 15000 mPa.s, said first polyester being obtained from an acid component and a polyol component wherein: the acid component consists of: (a) a dicarboxylic acid component consisting of isophthalic acid, terephthalic acid and mixtures thereof; and (b) from 1 up to 18 mole% of polyacids comprising at least three carboxy groups; and the polyol component consists of propylene glycol; (B) optionally a second polyester that is amorphous and that comprises at least one carboxy group; the second polyester being obtained from an aliphatic diacid and an aliphatic diol, and (C) a curing agent that comprises functional groups reactable with carboxylic acid groups on the polyester(s) (A) and (B), which is at least one selected from the group consisting of an epoxy resin and a -hydroxyalkylamide hardener, wherein the binder consists essentially of amorphous polyesters.

Description

EXAMPLES

(1) The present invention will now be described in detail with reference to the following non limiting examples which are by way of illustration only.

Example 1: Synthesis of a Carboxylic Acid Group Containing Amorphous Polyester (A)

(2) Propyleneglycol (347.14 parts) are placed in a conventional four neck round bottom flask equipped with a stirrer, a distillation column connected to a water cooled condenser, an inlet for nitrogen and a thermometer attached to a thermoregulator.

(3) The flask contents are heated, while stirring under nitrogen, to a temperature of circa 130 C. at which point 760.35 parts of isophthalic acid, 45.67 parts of trimellitic anhydride and 2.00 parts of n-butyltintrioctoate are added. The heating is continued gradually to a temperature of 230 C. Water is distilled from the reactor from 180 C. on. When distillation under atmospheric pressure stops, a vacuum of 50 mm Hg is gradually applied. After three hours at 230 C. and 50 mm Hg, following characteristics are obtained:

(4) TABLE-US-00001 AN 46.4 mg KOH/g Brfld.sup.175 C. (cone/plate) 7590 mPa .Math. s Tg (DSC, 20/min) 70 C.

Example 2: Synthesis of a Carboxylic Acid Group Containing Amorphous Polyester (A)

(5) 2-Ethyl 2-butyl 1,3-propanediol (504.16 parts), terephthalic acid (471.22 parts) of and of n-butyltintrioctoate (2.00 parts) were charged to a reaction vessel, in the same manner as described in Example 1. The temperature of the reaction mixture was gradually increased to 220 C. under a nitrogen atmosphere. The mixture was stirred and held at 220 C. until an acid value of below 5 mg KOH/g was obtained. The reaction mixture was then cooled to 170-190 C. followed by the addition of 118.92 parts of trimellitic anhydride. The temperature was maintained for about two hours until a polyester with following characteristics was obtained:

(6) TABLE-US-00002 AN 73.5 mg KOH/g Brfld.sup.175 C. (cone/plate) 5590 mPa .Math. s Tg (DSC, 20/min) 57 C.

Example 3: Synthesis of a Carboxylic Acid Group Containing Amorphous Polyester (B)

(7) According to the procedure described in Example 1, 397.34 parts of propyleneglycol, 764.86 parts of adipic acid, 21.20 parts of trimellitic anhydride and 2.00 parts of n-butyltintrioctoate are put into reaction until a polyester with following characteristics is obtained:

(8) TABLE-US-00003 AN 22.2 mg KOH/g Brfld.sup.100 C. (cone/plate) 1100 mPa .Math. s Tg (DSC, 20/min) 45 C.

Examples 4 to 7: Synthesis of Amorphous Polyester (A)

(9) According to the procedure of examples 1 the polyesters of examples 4, 5 and 7, having the compositions as in table 1, were prepared. On the other hand, the polyester of example 6 was prepared accordingly the procedure of example 2.

(10) For all the examples of table 1, 2.00 parts of n-butyltintrioctoate were introduced as the polycondensation catalyst.

(11) TABLE-US-00004 TABLE 1 Ex. 4 Ex. 5 Ex. 6 Ex. 7 Terephthalic 378.65 560.78 549.87 Acid Isophthalic 163.52 786.29 90.28 Acid Trimellitic 46.93 18.84 105.28 17.58 Anhydride 2-Ethyl 2-Butyl 521.86 1,3- Propanediol Propylene- 355.18 glycol 2-Methyl 1,3- 300.54 342.27 Propanediol Diethylene 33.39 glycol AN, mg 48.2 29.2 69 28.5 KOH/g Brookfield 5130.sup.(200 C.) 9800.sup.(175 C.) 7250.sup.(175 C.) 6600.sup.(200 C.) viscosity, mPa .Math. s Tg (DSC: 55 74 52 49 20 C./min)

(12) The polyester of example 1 and 2 and 4 to 7 are then formulated to a powder accordingly to the white paint formulation as mentioned below.

(13) White Paint Formulation

(14) TABLE-US-00005 Binder 69.06 Kronos 2310 29.60 Modaflow P6000 0.99 Benzoin 0.35

(15) The powders are prepared first by dry blending of the different components and then by homogenisation in the melt using a PRISM 16 mm L/D 15/1 twin screw extruder at an extrusion temperature of 85 C. The homogenised mix is then cooled and ground in an Alpine. Subsequently the powder is sieved to obtain a particle size between 10 and 110 m. The powder thus obtained is deposited on cold rolled steel with a thickness of 0.5 mm, and aluminium panels with a thickness of 0.6 mm, by electrostatic deposition using the GEMAVolstatic PCG 1 spray gun. At a film thickness of about 30 m, the panels are transferred to an air-ventilated oven, where curing proceeds for a 18 minutes at a temperature of 200 C. The paint characteristics for the finished coatings obtained from the different amorphous polyesters (A) optionally combined with the amorphous polyester (B) of Example 3, as illustrated in this invention, are reproduced in the table 2 and table 3.

(16) In these tables: Column 1 and 8: indicate the identification number of the formulation Column 2: indicates the type (example) and weight percentage of the amorphous polyester (A) relative to the total amount of polyester (A)+(B) Column 3: indicates the type (example) and weight percentage of the polyester (B) relative to the total amount of polyester (A)+(B) Column 4: indicates the weight percentage of resins (A) & (B) present in the binder Column 5: indicates the type of the hardener having functional groups being reactive with the polyesters' (A) and (B) carboxylic acid groups where: GT7004=Bisphenol-A type epoxy-resin, type n=3 (Huntsman) XL552=Primid XL552 (EMS)=N,N,N,N-tetrakis-(2-hydroxyethyl)-adipamide Column 6: indicates the weight percentage of the hardener present in the binder Column 7: indicates the 60 gloss, measured according to ASTM D523 Column 9: indicates the direct/reverse impact strength according to ASTM D2794. The highest impact which does not crack the coating is recorded in kg.Math.cm. Column 10: indicates the Erichsen slow embossing according to ISO 1520. The highest penetration which does not crack the coating is recorded in mm. Column 11: indicates the weight percentage of crosslinking catalyst (hexadecyltrimethylammonium bromide) relative to the binder (=(A)+(B)+Hardener) Column 12: indicates the number of twofold rubbing movements (to and fro) with a cotton pad impregnated with MEK, which does not detrimentally affect the appearance of the surface of the cured film. The pressure applied is as when erasing a pencil mark with a pencil eraser. Column 13: classification value for the cross-cut adhesion on cold rolled steel and aluminium respectively, by tape test according to ASTM D3359 according to which 5B: the edges of the cuts are completely smooth; none of the squares of the lattice is detached 4B: small flakes of the coating are detached at intersections; less than 5% of the area is affected 3B: small flakes of the coating are detached along edges and at intersections of cuts; the area affected is 5 to 15% of the lattice 2B: the coating has flaked along the edges and on parts of the squares; the area affected is 15 to 35% of the lattice 1B: the coating has flaked along the edges of cuts in large ribbons and whole squares have detached; the area affected is 35 to 65% of the lattice 0B: flaking and detachment worse than grade 1

(17) TABLE-US-00006 TABLE 2 polyester polyes- % Hard- % Gloss Powder (A) ter (B) A + B ener Hardener 60 Example 8 Ex. 1-100 91 XL552 9 96 Example 9 Ex. 1-100 60 GT7004 40 96 Example 10 Ex. 2-100 50 GT7004 50 94 Example 11 Ex. 4-100 91 XL552 9 93 Example 12 Ex. 4-100 60 GT7004 40 98 Example 13 Ex. 5-100 95 XL552 5 97 Example 14 Ex. 5-95 Ex. 3-5 95 XL552 5 94 Example 15 Ex. 6-100 50 GT7004 50 93 Example 16 Ex. 7-100 70 GT7004 30 96

(18) TABLE-US-00007 TABLE 3 % MEK DI/RI Erichsen crosslinking resis- Adhesion Powder (kg .Math. cm) (mm) catalyst tance Al/Steel Example 8 160/160 8.4 100 5B/5B Example 9 180/200 8.7 0.3 120 5B/5B Example 10 200/200 8.8 0.3 150 5B/5B Example 11 200/200 9.0 110 5B/5B Example 12 200/200 8.7 0.3 130 5B/5B Example 13 120/140 8.3 100 4B/4B Example 14 200/200 8.5 100 5B/5B Example 15 180/180 8.4 0.3 140 5B/4B Example 16 200/180 8.6 0.3 120 5B/5B