Coating Composition

Abstract

A coating composition for a food and/or beverage container comprising a polyester material, wherein the polyester material comprises the reaction product of; (a) 1,2-propanediol, (b) terephthalic acid, and (c) a molecular weight increasing agent,
characterized in that the polyester material has a number-average molecular weight (Mn) of at least 6,100 Da and a glass transition temperature (Tg) of at least 80 C.

Claims

1. A food and/or beverage container coated on at least a portion thereof with a coating composition comprising a polyester material, wherein the polyester material comprises the reaction product of a reaction mixture comprising; (a) 1,2-propanediol, (b) terephthalic acid, and (c) a molecular weight increasing agent, characterised in that the polyester material has a number-average molecular weight (Mn) of at least 6,100 Da and a glass transition temperature (Tg) of at least 80 C.

2. The food and/or beverage container according to claim 1, wherein the molecular weight increasing agent comprises a polyacid, a polyol or a combination thereof.

3. The food and/or beverage container according to claim 2, wherein the polyacid comprises maleic anhydride or itaconic acid or a combination thereof.

4. The food and/or beverage container according to either of claim 2, wherein the polyol comprises trimethylolpropane.

5. A food and/or beverage container coated on at least a portion thereof with a coating composition comprising a polyester material, wherein the polyester material comprises the reaction product of a one step process, the one step process comprising contacting (a) 1,2-propanediol, (b) terephthalic acid, and (c) a polyol molecular weight increasing agent, characterised in that the polyester material has a number-average molecular weight (Mn) of at least 6,100 Da and a glass transition temperature (Tg) of at least 80 C.

6. A food and/or beverage container coated on at least a portion thereof with a coating composition 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 1,2-propanediol, terephthalic acid, and a second step comprising contacting the polyester prepolymer with (c) a molecular weight increasing agent, characterised in that the polyester material has a number-average molecular weight (Mn) of at least 6,100 Da and a glass transition temperature (Tg) of at least 80 C.

7. The food and/or beverage container according to claim 1, wherein the coating composition is substantially free of bisphenol A (BPA) and derivatives thereof.

8. (canceled)

9. The food and/or beverage container according to claim 1, wherein the polyester material has a glass transition temperature (Tg) of about 80 C. to 120 C.

10. The food and/or beverage container according to claim 1, wherein the polyester material has a polydispersity index of 2 to 10.

11. The food and/or beverage container according to claim 1, wherein the polyester material has a critical entanglement molecular weight of the polyester material.

12. The food and/or beverage container according to claim 1, wherein the reaction mixture further includes a catalyst.

13. The food and/or beverage container according to claim 1, wherein the coating composition further comprises a solvent, a crosslinking agent, a catalyst, or a combination thereof.

14. The food and/or beverage container according to claim 1, wherein the polyester material is a branched polymer.

15. The food and/or beverage container according to claim 1, wherein the polyester material has an acid value expressed on solids of 2 to 5 mg KOH/g.

16. The food and/or beverage container according to claim 1, wherein the reaction mixture comprises a polyacid.

17. The food and/or beverage container according to claim 16, wherein the polyacid comprises maleic anhydride, itaconic acid, or a combination thereof.

Description

EXAMPLES

[0090] Preparation of Polyesters

Comparative Example 1

[0091] 1,2-Propanediol/Terephthalic Acid Polymer

[0092] A polyester material made without a molecular weight increasing agent was synthesised. 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. 3165.5 g 1,2-propanediol (PD), 6805.5 g terephthalic acid (TPA) and 5.06 g butyl stannoic acid (0.05% on charge) were added to the reaction vessel via a packed column and heated to 185 C. The reaction vessel was then heated to a maximum temperature of 230 C. and the contents were held at this temperature until the resin had reached clarity and had an acid value (AV) of <10. The reaction vessel was then cooled to 180 C. and a sample was taken in order to measure the hydroxyl value (OHV). The net OHV was adjusted to 8.63 with PD or TPA. The reaction vessel was then reheated to a maximum temperature of 230 C. and held at this temperature until an AV of 3 was achieved. The viscosity was monitored throughout using a CAP 2000+ viscometer and GPC. The resin was discharged from the reaction vessel at 210-220 C. in PTFE trays.

[0093] The characteristics of the polyester produced in comparative example 1 were determined and are shown in Table 1.

Comparative Example 2

[0094] 1,2-Propanediol/Terephthalic Acid/Isophthalic Acid Polymer

[0095] A polyester material made with terephthalic acid and isophthalic acid was synthesised. 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. 3123.0 g 1,2-propanediol (PD), 6125.4 g terephthalic acid (TPA), 680.6 g isophthalic acid (IPA) and 5.06 g butyl stannoic acid (0.05% on charge) were added to the reaction vessel via a packed column and heated to 185 C. The reaction vessel was then heated to a maximum temperature of 230 C. and the contents were held at this temperature until the resin had reached clarity and had an acid value (AV) of 20-30. Then a small amount of xylene was added to the reaction vessel to convert the process to azeotropic distillation. The reaction vessel was then cooled to 180 C. and a sample was taken in order to measure the hydroxyl value (OHV). The net OHV was adjusted to 4 with PD or TPA. The reaction vessel was then reheated to a maximum temperature of 235 C. and held at this temperature until the in-process viscosity was >2000 Poise at 200 C. as measured with a CAP 2000+ viscometer. The resin was discharged from the reaction vessel at 210-220 C. in PTFE trays.

[0096] The characteristics of the polyester produced in comparative example 2 were determined and are shown in Table 1.

Comparative Example 3

[0097] 1,2-Propanediol/Terephthalic Acid/Cyclohexane Dimethanol/Cyclohexane Dicarboxylic Acid Polymer

[0098] A polyester material made with terephthalic acid, cyclohexane dimethanol and cyclohexane dicarboxylic acid was synthesised. 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. 1448.60 g 1,2-propanediol (PD) was added to the reaction vessel via a packed column followed by 2744.80 g 1,4-cyclohexane dimethanol (CHDM), which was previously warmed to melt. The contents were stirred to mix. 5.35 g butyl stannoic acid (0.05% on charge), 3271.3 g cyclohexane dicarboxylic acid (CHDA) and 3157.3 g terephthalic acid (TPA) were further added to the reaction vessel and heated to 160 C. The reaction vessel was then heated to a maximum temperature of 230 C. and the contents were held at this temperature until the resin had reached clarity and had an acid value (AV) of <15. Then a small amount of SOLVESSO 150 ND (available from Exxon-Mobil Chemical Company) was added to the reaction vessel to convert the process to azeotropic distillation. The reaction vessel was then cooled to 170 C. and a sample was taken in order to measure the hydroxyl value (OHV). The net OHV was adjusted 1 with CH DM and then reaction vessel was heated to 200 C. and held for 2 hours. The OHV was measured again and further adjustment with CHDM was made if required. The reaction vessel was then reheated to a temperature of 230 C. and held at this temperature until the in-process viscosity was 1500-1600 Poise at 200 C. as measured with a CAP 2000+ viscometer. The solids content of the resulting polymer was reduced to 90 wt % by adding SOLVESSO 150 ND to the reaction vessel. The resin was discharged from the reaction vessel at 210-220 C. in PTFE trays.

[0099] The characteristics of the polyester produced in comparative example 3 were determined and are shown in Table 1.

Example 1

[0100] 1,2-Propanediol/Terephthalic Acid/Trimethylolpropane (TMP) Branched Polymer

[0101] A polyester material using TMP as the chain increasing agent was synthesised. 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. 3010 g 1,2-propanediol (PD), 6805.5 g terephthalic acid (TPA), 135 g trimethylolpropane (TMP) and 5.06 g butyl stannoic acid (0.05% on charge) were added to the reaction vessel via a packed column and heated to 185 C. The reaction vessel was then heated to a maximum temperature of 230 C. and the contents were held at this temperature until the resin had reached clarity and had an acid value (AV) of <5. Then 675 g xylene was added to the reaction vessel to convert the process to azeotropic distillation. The reaction vessel was then cooled to 180 C. and a sample was taken in order to measure the hydroxyl value (OHV). The net OHV was adjusted to 1.43 with PD or TPA. The reaction vessel was then reheated to a maximum temperature of 235 C. and held at this temperature until the in-process viscosity was >3000 Poise at 220 C. as measured with a CAP 2000+ viscometer. The resin was discharged from the reaction vessel at 210-220 C. in PTFE trays.

[0102] The characteristics of the polyester produced in example 1 were determined and are shown in Table 1.

Example 2

[0103] 1,2-Propanediol/Terephthalic Acid/Maleic Anhydride (MAN) Unsaturated Polymer

[0104] A polyester material using MAN as the chain increasing agent was synthesised. 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. 2687.3 g 1,2-propanediol (PD), 5350.3 g terephthalic acid (TPA) and 5.06 g butyl stannoic acid (0.05% on charge) were added to the reaction vessel via a packed column and heated to 185 C. The reaction vessel was then heated to a maximum temperature of 230 C. and the contents were held at this temperature until the resin had reached clarity and had an acid value (AV) of <5. The reaction vessel was cooled to 140 C. before 0.81 g 2-methyhydroquinone (0.3% on maleic anhydride) was added. After 10 minutes maleic anhydride (MAN) was added to the reaction vessel. After the addition was complete, 3046.3 g SOLVESSO 150 ND (available from Exxon-Mobil Chemical Company) was added to the reaction vessel to convert the process to azeotropic distillation. The reaction vessel was then reheated to a maximum temperature of 200 C. Once the AV was measured to be between 20-30, the reaction vessel was cooled to 180 C. and a sample was taken in order to measure the hydroxyl value (OHV). The net OHV was adjusted to 6.05 with PD or TPA. The reaction vessel was then reheated to a maximum temperature of 200 C. and held at this temperature until the in-process viscosity was about 1800 Poise at 200 C. as measured with a CAP 2000+ viscometer. The resin was reduced to 56.2% solids with approximately 2000 g SOLVESSO 100 (available from Exxon-Mobil Chemical Company) in the reaction vessel.

[0105] The characteristics of the polyester produced in example 2 were determined and are shown in Table 1.

[0106] Test Methods

[0107] Molecular Weight Determination: The number-average molecular weight and weight-average molecular weight were measured using gel permeation chromatography (also known as size exclusion chromatography) according to ASTM D6579-11.

[0108] Briefly, a Waters Corporation liquid chromatography system comprising a series of three size exclusion columns; 2PLgel 5 m MIXED-D columns (300 mm7.5 mm from Agilent Technologies) and 1PLgel 5 m 50 (300 mm7.5 mm from Agilent Technologies) and a UV detector tuned to 254 nm was used to conduct the experiments. The columns were first calibrated with polystyrene standards of known molecular weight (2348 kDa, 841.7 kDa, 327.3 kDa, 152.8 kDa, 60.45 kDa, 28.77 kDa, 10.44 kDa, 2.94 kDa, and 0.58 kDa where kDa=1000 Da=1000 g/mol). The standards were dissolved in unstabilised THF as mixtures of 4-6 molecular weight standards per sample. The standards were run under the same conditions as were used for the polyester material samples.

[0109] Samples were prepared by dissolving 0.01 g to 0.05 g of the polymer materials prepared according to comparative examples 1 and 2 and examples 1 and 2 above in 4 ml unstabilised tetrahydrofuran (THF). 20 l was injected for each run. The experiment was conducted at a flow rate of 0.9 ml/min and the system was maintained at a constant temperature of 22 C. throughout. Data were collected using Turbochrom 4 software from Perkin Elmer. The data were then processed using Turbochrom and Turbogel software from Perkin Elmer.

[0110] Glass Transition Temperature: The glass transition temperature of the polyester materials were measured according to ASTM D6604-00 (2013).

[0111] Briefly, the polymer samples were dissolved in tetrahydrofuran (THF) and then vacuum dried. 10 mg of the dried samples were placed in an aluminium pan in the differential scanning calorimeter along with an empty aluminium pan as the reference sample. A preliminary thermal cycle was performed from ambient temperature to 190 C. at a heating rate of 20 C./min. The temperature was then held isothermally at 200 C. for 10 minutes before being crash cooled to 60 C. with liquid nitrogen. The temperature was then held isothermally at this temperature (60 C.) for 13 minutes. Finally, the temperature of the sample was increased from 60 C. to 200 C. at a rate of 20 C./min and the heating curve was recorded.

TABLE-US-00001 TABLE 1 Characteristics of Polyester Comparative Examples 1-3 and Examples 1-2 Comparative Comparative Comparative Example 1 Example 2 Example 3 Example 1 Example 2 Solids content 93-97% 90.0% 72.2% 58.6%.sup. Acid Value (AV)/ 7.2 11.2 6.5 9.3 5.01 mg KOH/g Viscosity/Poise 445 @ 200 C. >2000 @ 200 C. ~1600 @ 200 C. >3000 @ 200 C. ~1800 @ 200 C. Net hydroxyl value 4.3 7.7 3.1 2.9 5.31 (OHV)/mg KOH/g Gross OHV/mg 11.5 3.5 3.4 6.4 10.32 KOH/g Mn (GPC)/Da 6,000 5,408 11,310 8,358 7,205 Mw (GPC)/Da 14,050 50,300 80,930 31,560 Mw/Mn 2.60 4.45 9.68 4.38 Tg/ C. 89.5 82.1 67 C. 95.4 89.0 Appearance Hard pale Clear light Hard pale Pale Soft pale yellow golden brown yellow yellow yellow solid solid solid solid solid .sup.Following dilution with SOLVESSO 100 in the reactor

[0112] The results show that when the PD/TPA polyester material is made without the addition of a molecular weight increasing agent, as in comparative examples 1 and 2, it had proven difficult to achieve Mn above 6,000 Da. Further, when isophthalic acid is added as a monomer component a slight reduction in Tg was observed. Higher Mn polyester materials can be prepared by the incorporation of other polyol and polyacid, as in comparative example 3, but resulted in a significant reduction in polymer Tg. However, upon the addition of a molecular weight increasing agent according to the invention, it is possible to increase the Mn to above about 6,100 Da, while maintaining a high Tg.

[0113] Preparation of Coatings

Comparative Coating Examples 1-6

[0114] 2750 g of the polyester prepared in comparative polyester example 1 was added to 1687.5 g SOLVESSO 150 ND (available from Exxon-Mobil Chemical Company) and 562.5 g 2-butoxyethanol. The coating compositions were then formulated as outlined in Table 2.

Comparative Coating Examples 7-9

[0115] 2500 g of the polyester prepared in comparative polyester example 3 was added to 2500.0 g SOLVESSO 100 (available from Exxon-Mobil Chemical Company). The coating compositions were then formulated as outlined in Table 3.

Coating Examples 10-15

[0116] 2432 g of the polyester prepared in polyester example 1 was added to 1743 g SOLVESSO 150 ND (available from Exxon-Mobil Chemical Company) and 825 g dibasic ester. The coating compositions were then formulated as outlined in Table 4.

Coating Examples 16-18

[0117] 8350 g of the polyester prepared in polyester example 2 was added to 433 g SOLVESSO 150 ND (available from Exxon-Mobil Chemical Company) and 2090 g dibasic ester. The coating compositions were then formulated as outlined in Table 5.

[0118] The properties of the coatings were tested via the following methods. Results are shown in Tables 2-7. The lactic acid sterilisation test was only performed on comparative coatings 7-9 and coatings 10-18, which are shown in Tables 6 and 7, respectively.

[0119] Test Methods

[0120] Test Panel Preparation: The coating samples were applied onto 0.22 mm tinplate using a wire wound bar coater to give a 5-6 g/square metre dried coating weight. The coated panels were transferred to a laboratory box oven for 10 minutes at 190 C.

[0121] 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).

[0122] Wedge Bend Test: A 10 cm4 cm 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 (HCl) 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.

[0123] Lactic acid sterilisation: This test is used to determine if the coatings are compatible for use in food and/or beverage containers. The coated panels were half immersed in a deionised water solution comprising 1% lactic acid inside a Kilner jar and sterilised for 1 hour at 130 C. in an autoclave. After this time, the coated panels were quickly removed whilst still hot and rinsed whilst under cold water. The portion of the coated panel immersed in lactic acid and the portion exposed to the vapour, which was produced during the sterilisation process, were assessed separately for extent of damage. Four aspects were graded; [0124] (A) Coating surface damage (visual assessment; 0=no damage/defect, 5=severe damage/defect) [0125] (B) Extent of blushing wherein the coating turns hazy due to water trapped in the coating (visual assessment; 0=no damage/defect, 5=severe damage/defect) [0126] (C) Substrate corrosion (visual assessment; 0=no damage/defect, 5=severe damage/defect) [0127] (D) % coating adhesion loss (assessed by making a cross hatch on the coating and taping with Scotch 610 tape; % of coating after taping)

TABLE-US-00002 TABLE 2 Comparative coating compositions 1-6 and test results Comparative Comparative Comparative Comparative Comparative Comparative Coating 1 Coating 2 Coating 3 Coating 4 Coating 5 Coating 6 Comparative 72.7 64.9 53.5 73.8 66.6 55.8 polyester example 1 Phenolic 1* 9 16 26.3 Phenolic 2** 7.5 13.5 22.7 Phenolic 3*** Catalyst.sup. 4.4 4.4 4.4 4.4 4.4 4.4 BYK 310.sup. 0.1 0.1 0.1 0.1 0.1 0.1 SOLVESSO 10.4 11 11.8 14.2 15.3 17 150 ND 2-butoxyethanol 3.5 3.7 3.9 Propylene 14.2 15.3 17 carbonate Total 100 100 100 100 100 100 MEK Rubs 2 2 13 3 5 11 Wedge Bend 0 7 0 74 70 53

TABLE-US-00003 TABLE 3 Comparative coating compositions 7-9 and test results Comparative Comparative Comparative Coating 7 Coating 8 Coating 9 Comparative polyester 79.2 71.6 60.1 example 3 Phenolic 1* 7.0 12.7 21.4 Phenolic 2** Phenolic 3*** Catalyst.sup. 2.4 2.4 2.4 BYK310.sup. 0.1 0.1 0.1 SOLVESSO 100 11.3 13.2 16.0 2-butoxyethanol Propylene carbonate Total 100 100 100 MEK Rubs 1 1 2 Wedge Bend 90 90 85

TABLE-US-00004 TABLE 4 Coating compositions 10-15 and test results Coating 10 Coating 11 Coating 12 Coating 13 Coating 14 Coating 15 Polyester 82.4 73.9 61.2 77.7 69.6 57.6 example 1 Phenolic 1* 7.7 13.7 22.7 Phenolic 2** Phenolic 3*** 7.7 13.8 22.9 Catalyst.sup. 3.1 3.1 3.1 3.1 3.1 3.1 BYK 310.sup. 0.1 0.1 0.1 0.1 0.1 0.1 SOLVESSO 6.8 9.2 12.8 11.3 13.3 16.2 150 ND Total 100 100 100 100 100 100 MEK Rubs 6 15 22 4 170 >200 Wedge Bend 91 92 88 87 79 67

TABLE-US-00005 TABLE 5 Coating compositions 16-18 and test results Coating 16 Coating 17 Coating 18 Polyester example 2 78.8 70.9 58.9 Phenolic 1* 7.5 13.4 22.3 Phenolic 2** Phenolic 3*** Catalyst.sup. 3.1 3.1 3.1 BYK 310.sup. 0.1 0.1 0.1 SOLVESSO 10.5 12.5 15.5 150 ND Total 100 100 100 MEK Rubs 3 4 15 Wedge Bend 86 92 80 *Phenodur PR516/B60 from Cytec Industries Inc. **Bakelite PF 6535LB from Hexion Speciality Chemicals ***BDP2201 from Bit Rez Ltd. .sup.5 weight % of o-phosphoric acid in 1-methoxy-2-propanol .sup.From BYK-Chemie

TABLE-US-00006 TABLE 6 Results of lactic acid sterilisation test on comparative coatings 7-9 Comparative Comparative Comparative Coating 7 Coating 8 Coating 9 Vapour A 3.5 3 0 B 3 1 0 C 0 0 0 D 5% 5% 5% Immersed A 5.5 5.5 2 B 4 3 1 C 0 0 0 D 5% 5% 5%

TABLE-US-00007 TABLE 7 Results of lactic acid sterilisation tests on coatings 10-18 Coating Coating Coating Coating Coating Coating Coating Coating Coating 10 11 12 13 14 15 16 17 18 Vapour A 3 0 0 3 0 0 0 0 0 B 2 1 1 1 1 1 1 1 1 C 0 0 0 0 0 0 0 0 0 D 0% 0% 0% 5% 5% 5% 5% 5% 5% Immersed A 2 2 2 0 0 0 2 2 0 B 4 3 2 4 3 3 3 2 1 C 0 0 0 0 0 0 0 0 0 D 5% 5% 5% 5% 5% 5% 5% 5% 5%

[0128] The results show that there is more attack on the coating surface by lactic acid when a polyester material with a lower Tg, as in comparative coating examples 7 and 8, is used.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] 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.