Anti-Staining Coating Composition

Abstract

A coating composition for a food or beverage container, the coating composition comprising an additive being operable to disrupt the chromophore of a colourant, upon absorption of the said colourant into the cured coating composition.

Claims

1. A metal food or beverage can comprising a food or beverage, wherein the can is coated on at least a portion of an internal surface with a coating derived from a coating composition comprising an additive comprising an unsaturated hydroxyl functional polybutadiene, wherein the polybutadiene reduces staining of the coating by chemical interaction with a chromophore in the food or beverage.

2. The metal food or beverage can of claim 1, wherein the polybutadiene is present in the composition in amount of 0.5-3 wt % based on total solids weight of the coating composition.

3. The metal food or beverage can of claim 1, wherein the polybutadiene has a number average molecular weight of less than 2,800 g/mol.

4. The metal food or beverage can of claim 1, wherein the coating is white.

5. The metal food or beverage can of claim 1, wherein the colorant comprises lycopene, alpha-carotene, beta-carotene, gamma carotene, lutein and/or zea xanthin.

6. The metal food or beverage can of claim 1, wherein the coating composition further comprises a resin.

7. The metal food or beverage can of claim 5, wherein the resin comprises a polyester resin.

8. The metal food or beverage can of claim 7, wherein the coating composition further comprises an amino group containing agent.

9. The metal food or beverage can of claim 1, wherein the food or beverage comprises a tomato product.

10. The metal food or beverage can of claim 1, wherein the composition comprises polybutadiene in an amount of 0.2-6 wt %, and further comprises a resin in an amount of 30-90 wt %, with wt % based on total solids.

11. The metal food or beverage can of claim 10, wherein the resin comprises polyester.

12. The metal food or beverage can of claim 10, wherein the resin comprises epoxy.

13. The metal food or beverage can of claim 10, wherein the resin comprises acrylic.

Description

EXAMPLE 1

[0085] The coating compositions as listed in table 1 were prepared as described below. All quantities given in the tables are shown in parts by weight.

TABLE-US-00001 TABLE 1 Control Item Item Coating Test coating Test coating Test coating Test coating no description composition composition 1 composition 2 composition 3 composition 4 1 Polyester A.sup.1 16.70 16.70 16.70 16.70 16.70 2 Tiona 595.sup.2 18.57 18.57 18.57 18.57 18.57 3 Solvesso 150 ND 1.00 1.00 1.00 1.00 1.00 4 Lanco Wax 0.20 0.20 0.20 0.20 0.20 TF1780EF.sup.3 5 Solution de 1.00 1.00 1.00 1.00 1.00 Lanoline 15% 6 Polyester A.sup.1 39.00 39.00 39.00 39.00 39.00 7 Uramex BF891.sup.4 9.36 9.36 9.36 9.36 9.36 8 Cycat 600.sup.5 0.10 0.10 0.10 0.10 0.10 9 Solvesso 150 ND 0.90 0.90 0.90 0.90 0.90 10 Xylène 0.27 0.27 0.27 0.27 0.27 11 XL480.sup.6 0.03 0.03 0.03 0.03 0.03 12 Xylène 0.15 0.15 0.15 0.15 0.15 13 Byk-088.sup.7 0.15 0.15 0.15 0.15 0.15 14 Dowanol PMA 3.83 3.83 3.83 3.83 3.83 15 Solvesso 150 ND 6.78 6.78 6.78 6.78 6.78 16 Poly Bd R20 LM.sup.8 0.98 17 Solvesso 150 ND 0.98 18 Poly Bd 605E.sup.9 0.98 19 Methoxypropanol 0.98 20 Poly Bd R45.sup.10 0.98 21 Solvesso 150 ND 0.98 22 Octa-Soligen 0.3 Calcium 5 .sup.11 23 Solvesso 150 ND 2.7 .sup.1= Polyester binder details of preparation described below. .sup.2= Titanium dioxide pigment commercially available from Millenium .sup.3= Micronized PTFE-Modified Polyethylene Wax commercially available from Lubrizol .sup.4= Melamin resin commercially available from Ineos .sup.5= Dodecylbenzylsulfonic acid solution commercially available from Cytec .sup.6= Amine resin modified acrylic copolymer commercially available from Cytec .sup.7= Defoamer commercially available from Byk-Chemie .sup.8,9,10= Polybutadiene grades commercially available from Cray Valley .sup.11 = Calcium bis(2-ethylhexanoate) commercially available from OMG Borchers

Polyester A Preparation

[0086] A reaction vessel was set up for manufacture of a polyester using fusion and azeotropic distillation. The vessel was equipped with a stirrer, nitrogen sparge, packed column, condenser, separator and return from the separator. Ethylene glycol 74 gm, Neopentyl glycol 665 gm, 1,4-cyclohexane dimethylol 338 gm, isophthalic acid 862 gm, terephthalic acid 754 gm and butylstannoic acid 1.14 gm were charged to the reactor. The mixture was then heated and when the glycols had melted the stirrer was started, heating was continued until distillation began at 166 deg C., the reactor temperature was steadily increased to a maximum of 245 deg C. whilst maintaining a steady rate of distillation. When the reaction mixture became clear, at acid value 17.8 mg KOH/gm, a sample was taken and tested for net Hydroxyl value. The net Hydroxyl value, 6.55 mg KOH/gm in this preparation, was adjusted to 7 to 8 mg KOH/gm. The separator was filled with Xylene and water and Solvesso150 (Naphthalene depleted) aromatic hydrocarbon solvent was added to the reactor. Reaction was then continued under azeotropic distillation at a reaction temperature around 210 deg C. The reaction was continued until the acid value of the samples from the reactor had decreased to below 2 mgKOH/gm and a viscosity (tested by solution at 33% solids in Solvesso 150 ND/Propylene glycol methyl ether acetate 1/1) had reached 9 to 14 poise at 25 deg C., The final sample, for this batch, as measured was acid value 1.54 mg KOH/gm and solution viscosity 13.3 poise at 25 C. The reaction mixture was cooled and dissolved in Solvesso 150 (naphthalene depleted) 1694 gm and propylene glycol methyl ether acetate 2156 gm. The final polyester solution had the characteristics of solids content 35.3% (0.5 gm 150 deg C. 60 min) viscosity 14.7 poise at 25 deg C. Acid value 1.7 mg KOH/gm (on solids) and Mn 16349, Mw 37125 by GPC using polystyrene standards.

Coating Preparation

[0087] Coating compositions 1 to 4 and the control composition were prepared in a vessel equipped with stirring system at ambient temperature. While item 1 was under slow agitation, item 2 was added to create a paste. Then stirring speed was increased until approximately 3000 to 5000 rpm until complete pigment dispersion. Fineness of grind was checked and particles size had to be fewer than 10 microns. Under stirring, items 3, 4, 5, 6 and 7 were added in this order. Then premix 8-9, premix 10-11, premix 12-13 were prepared separately and added in the mixture under mixing at 1500 rpm. Viscosity is finally adjusted with items 14 and 15.

[0088] When mixing, basic rules of mixing as known in the art are respected, the dispersion or mixing blade size used is about ⅓ of the diameter of the mixing pot.

[0089] The additives shown as items 16-17, 18-19, 20-21 and 22-23 were prepared as premixes and added to the coating compositions in 1 to 4 in order to test the additive effect on the staining properties of the coating compositions.

[0090] The coatings produced from the control composition and compositions 1 to 4 outlined above were applied to tinplate or TFS metal panels.

[0091] The coatings were applied with a roller coater to stick to industrial application system or a bar coater if no coating device is available. Applied film weight is between 14 and 18 gsm for single coat application or between 7 and 10 gsm per layer for two coats application in case of aggressive food.

[0092] After application, the coatings were dried for 10 minutes in a fan assisted oven at a temperature of 200° C. Drying process produces a white cured film of each coating which is tested, as outlined in the details below, to demonstrate the performance of the protective coating applied to this panel.

[0093] Typical staining conditions were reproduced with 2 tests: the panels were immersed in a tomato solution for discovering the immediate effect of the lycopene colourant contained in tomatoes on the white coatings, and the panels were also processed into cans and filled with the tomato solution, the cans were then stored for discovering the longer term effect of the lycopene colourant of tomatoes on the white coatings.

[0094] The tomato solution was prepared by mixing double concentrate tomato puree with water in ratio 3:1.

[0095] In the first test, the coated panels were immersed partially in this solution for 30 min at 115° C.

[0096] In the second test, the cans were filled with the tomato solution as described above, heated for 30 minutes at 115 C, then stored 2 weeks at 70° C. They were opened after these two weeks.

[0097] Staining was evaluated first with a visual check and then using colorimetric measurement. [0098] Visual check  Coloration was observed just after processing of the panels or the opening of the cans. Grade 0 corresponds to no coloration change, coating is still white, and grade 5 corresponds to high staining level, coating is yellowed/reddish (color pick up is yellow when little color pick up and more reddish when more color pick up) [0099] Colorimetric check  In order to get more details about staining, measurements were made on the panels and cans using a spectrophotometer CEILAB system (SP64 commercially available from X-Rite). Parameters used are explained in table 2 below:

TABLE-US-00002 TABLE 2 Standard Measuring Color difference Illuminant Type Observers Geometrics model D65 10° D8i Delta-E CMC(2:1)

[0100] In the CIELAB system, measurements are expressed as three coordinates: L*, a* and b*. L* represents the lightness of the color: L*=0 yields black and L*=100 indicates diffuse white. a* is the position between red and green: a negative value indicates green while a positive value indicates red. b* is the position between yellow and blue: a negative value indicates blue and a positive value indicates yellow.

[0101] Staining caused by tomatoes is mainly red and yellow. Therefore, it is detected by positive values of a* and b*. All test coatings were measured in comparison to a standard coating which is the same coating composition comprising the relevant additive but without any exposure to tomato solution or processing. The results are expressed as an observed Da value that is the difference between the a* value for the standard coating and the a* value for test coatings. The lower the value, the more similar the standard coating and the tested coating were, therefore the more unstained the tested coating appears after exposure to the lycopene colourant derived from the tomatoes.

[0102] The control and the test coating compositions were prepared, applied and dried as outlined in the preceding descriptions. The coated panels obtained were then tested. Evaluation results are compiled in table 3 below.

TABLE-US-00003 TABLE 3 Control Test Test Test Test coating coating coating coating coating composition composition 1 composition 2 composition 3 composition 4 Staining visual evaluation 4 1 3 2 2 Da value (colorimetric 2,36 0,6 1,53 1,1 1,34 measurement)

[0103] Results in table above show that the control composition which comprises no additive is very sensitive to tomato staining. All test coating compositions 1 to 4 comprising an additive have a positive effect in staining reduction.

[0104] After visual checking, coating compositions 1, 3 and 4 are the most interesting coating compositions tested. Colorimetric measurement is a precise method that can separate these three close results. From the colorimetric results, it appears that the additive within coating compositions 1 and 3 is the most efficient in reducing staining.

[0105] Hydroxyl terminated polybutadiene was the additive used in coating compositions 1 and 3, this additive is more efficient for reducing staining than the epoxidized polybutadiene used as an additive in coating composition 4 and the Octa-soligen Calcium 5 used as an additive in coating composition 2. The polybutadiene additive used in coating composition 1 has a lower molecular weight than that used in coating composition 2. This could provide a better reactivity to the additive, and therefore cause a better reaction with the double bond of the chromophore of the lycopene colourant to occur. This could explain the better reduction in staining observed in coating composition 1 when compared to coating composition 3. On this basis, it seems that low molecular weight hydroxyl terminated polybutadiene, as used in coating composition 1, is the best additive with which to reduce staining of coating compositions for use in food or beverage containers such as cans. In particular, these results show that the specific additive Poly Bd® R20 LM is an optimal additive to reduce staining in coating compositions.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.