Coating Composition Comprising a Binder Formed from Polyester and a Phosphorus Acid

Abstract

Coating composition comprising a binder formed from polyester and a phosphorus acid A coating composition comprising a binder, the binder comprising a polyester material, wherein the polyester material comprises the reaction product of; (a) a polyacid, (b) a polyol and (c) a phosphorous acid, wherein the polyester material has a weight-average molecular weight (Mn) from about 1,000 Da to 25,000 Da and the polydispersity index (Mw/Mn) of the polyester material is from about to 10and characterised in that the polyester material is present in said binder composition in amounts of more than about 10 weight percent (wt %). The coating composition is useful for coating food and/or beverage containers.

Claims

1. A coating composition comprising a binder, the binder comprising a polyester material, wherein the polyester material comprises the reaction product of; (a) a polyacid, (b) a polyol and (c) a phosphorous acid, wherein the polyester material has a weight-average molecular weight (Mn) from about 1,000 Da to 25,000 Da; and wherein the polydispersity index (Mw/Mn) of the polyester material is from about 1 to 10; characterised in that the polyester material is present in said binder composition in amounts of more than about 10 weight percent (wt %).

2. A coating composition according to claim 1, wherein the polyacid comprises terephthalic acid, isophthalic acid, maleic anhydride, itaconic acid, 1,4-cyclohexane dicarboxylic acid, adipic acid, succinic acid, succinic anhydride, sebacic acid or a combination thereof.

3. A coating composition according to claim 2, wherein the polyacid comprises terephthalic acid, isophthalic acid, 1,4-cyclohexane dicarboxylic acid, maleic anhydride, itaconic acid or a combination thereof.

4. A coating composition according to claim 2, wherein the polyacid comprises 1,4-cyclohexane dicarboxylic acid, terephthalic acid, isophthalic acid, adipic acid, succinic acid, succinic anhydride, sebacic acid or a combination thereof.

5. A coating composition according to any preceding claim, wherein the polyol comprises ethylene glycol, 2-methyl-1,3-propanediol, 1, 2 propanediol, cyclohexanedimethanol (CHDM), trimethylol propane or glycerol or a combination thereof.

6. A coating composition according to any preceding claim, wherein the phosphorous acid comprises phosphoric acid.

7. A coating composition according to any preceding claim, wherein the ratio of (a):(b) ranges from 5:1 to 1:5

8. A coating composition according to any preceding claim, wherein the phosphorous acid is provided in amounts from 0.1 to 1.0 equivalents of phosphorous acid per hydroxyl equivalent of the polyester material.

9. A coating composition according to any preceding claim, wherein the polyester material has a weight-average molecular weight (Mw) from 1,500 Da to about 300,000 Da.

10. A coating composition according to any preceding claim, wherein the coating composition further comprises a crosslinking agent.

11. A coating composition comprising a binder, the binder comprising a polyester material, wherein the polyester material comprises the reaction product of a two step process, the two step process comprising: a first step comprising preparing a polyester prepolymer by contacting (a) a polyacid, (b) a polyol, and a second step comprising contacting the polyester prepolymer with (c) a phosphorous acid, wherein the polyester material has a weight-average molecular weight (Mn) from about 1,000 Da to 25,000 Da; and wherein the polydispersity index (Mw/Mn) of the polyester material is from about 1 to 10; characterised in that the polyester material is present in said binder composition in amounts of more than about 10 weight percent (wt %).

12. A coating composition according to claim 10, wherein the first reaction conditions include a temperature of between 100° C. and 250° C.

13. A coating composition according to claim 10 or claim 11, wherein the second reaction conditions include a temperature of between 90° C. and 200° C.

14. A coating composition according to any of claims 10 to 12, wherein the polydispersity index of the polyester material is from 0 to 5 units higher than the polydispersity index of the polyester prepolymer.

15. A coated article coated on at least a portion thereof with a coating composition according to any preceding claim.

16. A food or beverage container coated on at least a portion thereof with a coating composition according to any of claims 1 to 13.

Description

EXAMPLES

Preparation of Polyester Prepolymers

Prepolymer Example 1

[0107] The polymerisation was carried out in a reaction vessel equipped with heating, cooling, stirring and a reflux condenser. A sparge of nitrogen was applied to the reactor to provide an inert atmosphere. 1301 g ethylene glycol (EG), 1888.7 g 2-methyl-1,3-propanediol (MPD), 5976 g terephthalic acid (TPA), 664 g isophthalic acid (IPA), and 4.94 g butyl stannoic acid (0.05% on charge) were charged to a reactor and heated to about 170° C. via a packed column. This mixture was processed until there was approximately 1150 g of distillate and then 300 g of xylene was added, changing the distillation to azeotropic distillation. The mixture was further processed at a maximum reactor temperature of 230° C. until resin clarity was achieved and the acid value (AV) was less than 10. The reactor was cooled to 180° C. so that the net hydroxyl value (OHV) could be sampled and measured. The OHV was adjusted to 32.2 with MPD and the mixture was processed for 2 hours at 180° C. After this time, the OHV was sampled and measured again and further adjusted if required. When the OHV was 32.2 the reactor was reheated to distillation with a maximum temperature of 230° C. The process was allowed to continue until the AV was <1. The in-process viscosity was measured using a CAP-2000+ viscometer and GPC. The resin was discharged from the reactor at 200° C. into PTFE trays. The properties of the prepolymer are shown in Table 1.

Prepolymer Example 2

[0108] The polymerisation was carried out in a reaction vessel equipped with heating, cooling, stirring and a reflux condenser. A sparge of nitrogen was applied to the reactor to provide an inert atmosphere. 3813.8 g 1,2-propylene glycol (1,2PG), 3553.4 g terephthalic acid (TPA), 3681.9 g 1,4-cyclohexane dicarboxylic acid and 5.89 g 94 g butyl stannoic acid (0.05% on charge) were charged to a reactor and heated to about 165° C. via a packed column. The mixture was processed at a maximum reactor temperature of 230° C. and a maximum head temperature of 100° C. The reactor was cooled to 140° C. before 2.1 g 2-methylhydroquinone (0.3% on maleic anhydride) was charged to the reactor. After 10 minutes 701 g maleic anhydride was also added. The reactor was reheated to distillation at a maximum temperature of 200° C. 650 g xylene was then added to convert the reaction to azeotropic distillation. The mixture was processed until resin clarity was achieved and the AV was between 20 and 30. The reactor was then cooled to 140° C. so that the net hydroxyl value (OHV) could be sampled and measured. The OHV was adjusted to 6.1 with 1,2PG and the mixture was further processed for 2 hours at 180° C. After this time, the OHV was sampled and measured again and further adjusted if required. When the OHV was 6.1 the reactor was reheated to distillation with a maximum temperature of 200° C. The process was allowed to continue until the AV was between 5 and 6. The in-process viscosity was measured using a CAP-2000+ viscometer and GPC. The resin was discharged from the reactor at 190° C. into PTFE trays. The properties of the prepolymer are shown in Table 1.

[0109] Preparation of Polyesters

Comparative Example 3

[0110] Polymerisation was carried out in a reaction vessel equipped with heating, cooling, stirring and a reflux condenser. A sparge of nitrogen was applied to the reactor to provide an inert atmosphere. 3813.8 g 1,2-propylene glycol (1,2PG), 3553.5 g terephthalic acid (TPA), 3681.9 g 1,4-cyclohexane dicarboxylic acid and 5.89 g 94 g butyl stannoic acid (0.05% on charge) were charged to a reactor and heated to about 165° C. via a packed column. The mixture was processed at a maximum reactor temperature of 230° C. and a maximum head temperature of 100° C. The reactor was cooled to 140° C. before 2.1 g 2-methylhydroquinone (0.3% on maleic anhydride) was charged to the reactor. After 10 minutes 701 g maleic anhydride was also added. The reactor was reheated to distillation at a maximum temperature of 200° C. 650 g xylene was then added to convert the reaction to azeotropic distillation. The mixture was processed until resin clarity was achieved and the AV was between 20 and 30. The reactor was then cooled to 140° C. so that the net hydroxyl value (OHV) could be sampled and measured. The OHV was adjusted to 6.1 with 1,2PG and the mixture was further processed for 2 hours at 180° C. After this time, the OHV was sampled and measured again and further adjusted if required. When the OHV was 6.1 the reactor was reheated to distillation with a maximum temperature of 200° C. The process was allowed to continue until the AV was between 5 and 6. The in-process viscosity was measured using a CAP-2000+ viscometer and GPC. The resin was discharged from the reactor at 190° C. into PTFE trays. The properties of the polymer are shown in Table 1.

Example 4

[0111] The polymerisation was carried out in a reaction vessel equipped with heating, cooling, stirring and a reflux condenser. A sparge of nitrogen was applied to the reactor to provide an inert atmosphere. 250 g Solvesso 100 (available from Exxon-Mobil Chemical Company) was charged to a reactor and heated to 120° C. The prepolymer of example 1 was broken into small pieces and charged to the reactor over 1 hour with vigorous stirring to ensure the resin was fully dissolved. 13.64 g of phosphoric acid (85% solution) was charged to the reactor followed by 1 g demineralise water as a rinse. The reactor was heated to distillation to approximately 155° C. to remove the water distillate. The distillation process was continued at a temperature up to 172 ° C. The quantity of water distillate, AV and viscosity were monitored throughout. The properties of the polymer are shown in Table 1.

Example 5

[0112] The polymerisation was carried out in a reaction vessel equipped with heating, cooling, stirring and a reflux condenser. A sparge of nitrogen was applied to the reactor to provide an inert atmosphere. 287.1 g Solvesso 100 (available from Exxon-Mobil Chemical Company) was charged to a reactor and heated to 120° C. The prepolymer of example 2 was broken into small pieces and charged to the reactor over 1 hour with vigorous stirring to ensure the resin was fully dissolved. 1.1 g of phosphoric acid (85% solution) was charged to the reactor followed by 1 g demineralise water as a rinse. The reactor was heated to distillation to approximately 163° C. to remove the water distillate. The distillation process was continued at a temperature up to 168 ° C. The quantity of water distillate, AV and viscosity were monitored throughout. The properties of the polymer are shown in Table 1.

Comparative Example 6

[0113] The polymerisation was carried out in a reaction vessel equipped with heating, cooling, stirring and a reflux condenser. A sparge of nitrogen was applied to the reactor to provide an inert atmosphere. 268.3 g Solvesso 150 ND (available from Exxon-Mobil Chemical Company) was charged to a reactor and heated to 120° C. 1008.6 g of the prepolymer of example 2 was broken into small pieces and charged to the reactor over 1 hour with vigorous stirring to ensure the resin was fully dissolved. 2.15 g of trimellitic anhydride (TMA) was charged to the reactor. The reactor was heated to distillation to approximately 184° C. to remove the water distillate. The distillation process was continued at a temperature up to 189° C. The quality of water distillate, AV and viscosity were monitored throughout. Resin samples were taken after 2.5 hours under these conditions to measure AV, viscosity and Mw/Mn. The remaining resin gelled in the reactor after a further 20 minutes of processing. The properties of the polymer sample 5 are shown in Table 1.

Comparative Example 7

[0114] Comparative example 6 was repeated except that the resin samples were taken after 3 hours. The properties of the polymer sample 5 are shown in Table 1.

TABLE-US-00001 TABLE 1 Properties of Prepolymers and Polymers Prepolymer Prepolymer Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Solids 97.1% 94.3% 94.3% 80.5% 79.3% 75 75 content.sup.1 Acid Value 0.4 5.6 4.5 8.0 4.4 4.5 4.3 (AV) Viscosity.sup.2 90 poise 885 poise 1890 poise 1440 poise 2730 poise 2070 poise 3450 poise Net hydroxyl 27.1 2.6 1.8 — — — — value (OHV) Gross OHV 27.5 8.2 6.3 — — — — Mn (GPC).sup.3 7,600 17,690 17,540 11,530 20,220 20,120 23,850 Mw (GPC).sup.3 14,470 44,430 60,230 22,300 81,800 125,700 149,300 Mw/Mn 1.904 2.512 3.434 1.935 4.045 6.247 6.260 Appearance Hard, brittle, Hard, brittle Hard, brittle Soft, light Soft, light Soft, light Soft, light pale yellow pale brown pale brown brown semi brown semi brown semi brown semi solid solid solid solid solid solid solid .sup.1Solids content was determined at 180° C. for 30 mins using 0.5 g resin samples diluted in 10 g dichloromethane. The measurements were taken in triplicate with the average value recorded. .sup.2Viscosity was measured on a CAP2000+ viscometer with the following settings; 180° C., spindle 6, 5 rpm, 20 seconds hold/40 seconds run, pumped 10 × 15 times. .sup.3The GPC was measure at high temperature using styrene as the reference.

[0115] Polymer example 4 is the reaction product of saturated prepolymer example 1 with phosphoric acid. Surprisingly, and as shown in Table 1, the number-average molecular weight (Mn) and weight-average molecular weight (Mw) of polymer example 4 have significantly increased compared to prepolymer example 1. However, there has been very little change in the polydispersity index (Mw/Mn).

[0116] Polymer example 5 is the reaction product of polyester prepolymer example 2 with phosphoric acid. Comparative example 3 was made using conventional methods for producing polyester polymers and has the same composition as prepolymer example 2. However, comparative example 3 has slightly lower Mn and a higher Mw compared to prepolymer example 2. As shown in Table 1, polymer example 5 has a significantly higher weight-average molecular weight (Mw) than the starting prepolymer example 2. However, there is only a slight increase in the polydispersity index (Mw/Mn) compared to that of comparative example 3.

[0117] Furthermore, polymer example 4 and polymer example 5 were prepared at much lower reaction temperatures and significantly reduced process times than typically required in traditional polyester preparations of similar Mw polymers.

[0118] Comparative examples 6 and 7 are the reaction product of polyester prepolymer example 2 with trimellitic anhydride. As shown in Table 1, comparative examples 6 and 7 have an increased polydispersity index (Mw/Mn) compared to that of the inventive examples.

[0119] Preparation of Coatings

[0120] Comparative Coating Compositions 1-2 and 5-8

[0121] 550 g of the solid prepolymer prepared in example 1 was dissolved in 387.4 g SOLVESSO 100 (available from Exxon-Mobil Chemical Company), 85.9 g 1-methoxy-2-propanol and 172.3 g propylene carbonate preheated to 80-90° C. to form Resin A. Resin A therefore contains no phosphorous acid.

[0122] Comparative coating compositions 1-2 and 5-8 were then prepared using Resin A as outlined in Tables 2 and 3.

[0123] Coating Compositions 3-4 and 9-12

[0124] 1220 g of the solid polyester polymer prepared in example 4 was dissolved in 421.4 g SOLVESSO 100 (available from Exxon-Mobil Chemical Company), 146.6 g 1-methoxy-2-propanol and 294.3 g propylene carbonate preheated to 80-90° C. to form Resin B. Resin B therefore contains phosphorous acid.

[0125] Coating compositions 3-4 and 9-12 were then prepared using Resin B as outline in Tables 2 and 3.

[0126] Comparative Coating Compositions 13-16

[0127] 450 g of the solid polyester polymer prepared in comparative example 3 was dissolved in 192.5 g of SOLVESSO 100, 192.5 g SOLVESSO 150ND (naphthalene depleted grade of SOLVESSO 150 also available from Exxon-Mobile Chemical Company), 165.0 g of RHODIASOLV RPDE (available from Rhodia Inc.) preheated to 80-90° C. to form Resin C. Resin C therefore contains no phosphoric acid.

[0128] Coating compositions 17-20 were then prepared using Resin C as outlined in Table 4.

[0129] Coating Compositions 17-20

[0130] 950 g of the solid polyester polymer prepared in example 5 was dissolved in 286.2 g of SOLVESSO 150ND, 245.7 g of RHODIASOLV RPDE preheated to 80-90° C. to form Resin D. Resin D therefore contains phosphoric acid.

[0131] Coating compositions 17-20 were then prepared using Resin D as outlined in Table 4.

[0132] The coatings were assessed according to the following tests:

[0133] Test Panel Preparation: The coating compositions were applied onto 0.22 mm tinplate panels using a wire wound bar coater to give a 5-6 g/sqare metre dried coating weight. The coated panels were transferred to a laboratory box oven for 10 minutes at 190° C.

[0134] MEK Rub Test: The number of reciprocating rubs required to remove the coating was measured using a ball of cotton wool soaked in methyl ethyl ketone (MEK).

[0135] Wedge Bend Test: A 10cm×4cm coated panel was bent on a 6 mm steel rod to form a U-shaped strip 10 cm long and 2 cm wide. The U-shaped strip was then placed onto a metal block with a built in tapered recess. A 2 kg weight was dropped onto the recessed block containing the U-shaped strip from a height of 60 cm in order to from a wedge. The test piece was then immersed in a copper sulphate (CuSO.sub.4) solution acidified with hydrochloric acid (HCI) for 2 minutes, followed by rinsing with tap water. The sample was then carefully dried by blotting any residual water with tissue paper. The length of coating without any fracture was measured. The result was quoted in mm passed. The wedge bends were tested in triplicate and the average value was quoted.

[0136] Acid Retort Wedge Bend Test: Wedge bend test pieces were prepared as described above and placed in a high temperature resistant glass jar filled with a solution of 3% acetic acid and 2% salt dissolved in de-ionized water. The immersed wedge bends were sterilized for 1 hour at 130° C. in an autoclave. Immediately after sterilization the wedge bends were taken out of the acid solution, rinsed in tap water and dried with a paper tissue. A strip of Scotch 610 tape was firmly placed along the entire length of the wedge bend with any air bubbles trapped underneath the tape removed to ensure good contact with the coating. The tape was then quickly peeled off to remove any coating that had no longer adhered to the metal substrate as a result of the acid sterilization. The taped wedge bend was then immersed in acidified copper sulphate solution, rinsed, dried and graded in the same way as in the Wedge Bend Test.

TABLE-US-00002 TABLE 2 Properties of coating compositions from Resin A and Resin B with varying amounts of phosphoric acid as a catalyst Comparative Comparative Coating 1 Coating 2 Coating 3 Coating 4 Resin A 71.7 71.5 — — Resin B — — 69.6 69.5 Phenolic* 13.4 13.4 13.4 13.4 Catalyst** — 1.6 — 1.6 BYK 310*** 0.1 0.1 0.1 0.1 1-methoxy-2- 14.8 13.4 16.9 15.5 propanol Total 100 100 100 100 MEK Rubs 1 2 38 38 Wedge Bend 0 83 96 98 *Phenodur PR516 (previously available from CYTEC Industries Inc. now available from ALLNEX USA Inc. under the same trade name) **Solution of ortho-phosphoric acid in 1-methoxy-2-propanol prepared by mixing 5.88 g of 85% strength ortho-phosphoric acid (available from most suppliers of fine chemicals) in 94.12 g 1-methoxy-2-propanol ***BYK 310 is available from BYK-Chemie GmbH

TABLE-US-00003 TABLE 3 Properties of coating compositions from Resin A and Resin B with varying amounts of phenolic resin Comparative Comparative Comparative Comparative Coating 5 Coating 6 Coating 7 Coating 8 Coating 9 Coating 10 Coating 11 Coating 12 Resin A 79.5 71.5 59.6 51.0 — — — — Resin B — — — — 77.4 69.6 58.0 49.7 Phenolic* 7.4 13.4 22.3 28.6 7.4 13.4 22.3 28.7 Catalyst** 1.6 1.6 1.6 1.6 1.6 1.6 1.6 1.6 BYK 310*** 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 1-methoxy-2- 11.4 13.4 16.5 18.7 15.0 16.9 19.6 21.6 propanol Total 100 100 100 100 100 100 100 100 MEK Rubs 2 2 37 193 4 38 >200 >200 Wedge Bend 12 83 65 53 94 96 95 83 *Phenodur PR516 (previously available from CYTEC Industries Inc. now available from ALLNEX USA Inc. under the same trade name) **Solution of ortho-phosphoric acid in 1-methoxy-2-propanol prepared by mixing 5.88 g of 85% strength ortho-phosphoric acid (available from most suppliers of fine chemicals) in 94.12 g 1-methoxy-2-propanol ***BYK 310 is available from BYK-Chemie GmbH

TABLE-US-00004 TABLE 4 Properties of coating compositions from Resin C and Resin D with varying amounts of phenolic resin Comparative Comparative Comparative Comparative Coating 13 Coating 14 Coating 15 Coating 16 Coating 17 Coating 18 Coating 19 Coating 20 Resin C 82.4 73.9 61.2 52.3 Resin D — — — — 82.0 73.4 60.6 51.7 Phenolic* 7.7 13.7 22.7 29.1 7.8 14.0 23.1 29.5 Catalyst** 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 BYK 310*** 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 1-methoxy-2- 6.8 9.2 12.8 29.1 7.0 9.5 13.1 15.6 propanol Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 Wedge Bend 94 90 84 75 94 96 95 83 Acid Retort 6 33 18 26 77 74 58 56 Wedge Bend *Phenodur PR516 (previously available from CYTEC Industries Inc. now available from ALLNEX USA Inc. under the same trade name) **Solution of ortho-phosphoric acid in 1-methoxy-2-propanol prepared by mixing 5.88 g of 85% strength ortho-phosphoric acid (available from most suppliers of fine chemicals) in 94.12 g 1-methoxy-2-propanol ***BYK 310 is available from BYK-Chemie GmbH

[0137] The results in Tables 2 and 3 show that the coating compositions comprising Resin A (coatings 3-4 and 9-12), i.e. those comprising polyester material that contains phosphorous acid, display higher MEK rubs and significantly better wedge bend performance than the comparative coating compositions comprising Resin B (comparative coatings 1-2 and 5-8), i.e. those comprising polyester material that does not contain phosphorous acid.

[0138] Results with varying amount of phenolic in the coating composition as shown in Table 3 further demonstrates the superior performance of Resin B (Coatings 13-16) compared to Resin A (Coatings 9-12).

[0139] One requirement for coating compositions is the ability to withstand retort conditions after fabrication of the coated substrate into, for example, food and/or beverage containers. Retort conditions may comprise temperatures of up to 130° C. and acidic media. As shown in Table 4, the coating compositions according to the present invention (coatings 17-20) show an improved adhesion performance after retort in 3% acetic acid and 1% salt solution compared to the comparative coating compositions (comparative coatings 13-16).

[0140] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0141] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

[0142] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0143] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.