Coating composition for a food or beverage can

Abstract

A two component coating composition, suitable for coating onto a metal substrate, especially food and beverage cans, the coating composition comprising: a first component comprising an acrylic latex material; and a second component comprising a functional silane material.

Claims

1. A two component coating composition suitable for coating onto a metal substrate, the coating composition comprising: a first component comprising an acrylic latex material; and a second component comprising a functional silane material; wherein the acrylic latex material comprises an alkyl (meth)acrylate which comprises epoxy functionality.

2. The coating composition of claim 1, wherein the acrylic latex material comprises an aqueous emulsion of one or more acrylic polymers.

3. The coating composition of claim 1, wherein the acrylic latex material comprises an aqueous dispersion of an acrylic material in a core/shell arrangement.

4. The coating composition of claim 3, wherein the core is formed from a core mixture and the shell is formed from a shell mixture, and wherein the ratio of the core mixture (monomers and initiator) to shell mixture (monomers and initiator) is between about 20:80 and 90:10 by weight.

5. The coating composition of claim 1, wherein the latex material comprises an aqueous dispersion of an acrylic material with reactive functional groups and stabilized with an emulsifier or surfactant material.

6. The coating composition of claim 1, wherein the functional silane material comprises a silane material according to Formula I, or a polysiloxane polymer derived from one or more silane material according to Formula I:
(R.sup.1).sub.nSi(OR.sup.2).sub.mI wherein each R.sup.1 is independently selected from an epoxy functional optionally substituted alkyl group, each R.sup.2 independently represents H or an alkyl group n=1 to 3, m=1 to 3; and n+m=4.

7. The coating composition of claim 1, wherein the functional silane material comprises a silane material according to Formula 2, or a polysiloxane polymer derived from one or more silane material according to Formula 2:
((R.sup.3)HN(CH.sub.2).sub.3).sub.nSi(OR.sup.4).sub.m2 wherein each R.sup.3 is independently selected from H or an optionally substituted alkyl group, each R.sup.4 independently represents H or an alkyl group n=1 to 3, m=1 to 3; and n+m=4.

8. The coating composition of claim 1, wherein the functional silane material comprises an epoxy functional silane or an amino functional silane.

9. The coating composition of claim 1, wherein the coating composition comprises the acrylic latex material and the functional silane material in a ratio of latex solids to silane solids of between about 99:1 parts by wt to 1:99 parts by wt.

10. The coating composition of claim 1, wherein the functional silane material reduces the curing time in a two component coating composition as compared to a coating lacking the functional silane material.

11. The coating composition of claim 1, wherein the functional silane material reduces the curing temperature in a two component coating composition as compared to a coating lacking the functional silane material.

12. The coating composition of claim 1, wherein the alkyl (meth)acrylate comprises glycidyl methacrylate.

13. The coating composition of claim 6, wherein the functional silane material comprises -glycidyloxypropyl trialkoxysilane.

14. The coating composition of claim 7, wherein the functional silane material comprises -aminopropyl trialkoxysilane.

Description

EXAMPLES

(1) The following examples are intended to illustrate the invention and should not be construed as limiting the invention in any way.

Polymer Examples

(2) Core/shell latex emulsions were formed as follows.

Shell Polymer Example 1

(3) The ingredients of this shell polymer example are displayed in Table 1 below.

(4) TABLE-US-00001 TABLE 1 Item no Component Parts (by weight) 1 Propylene glycol mono methyl ether 6.00 2 Butyl glycol 11.88 3 Trigonox 42S* 0.50 4 Butyl glycol 3.00 5 Methacrylic acid 11.25 6 Ethyl acrylate 6.25 7 Styrene 7.50 8 Butyl glycol 1.00 9 Trigonox 42S* 0.25 10 Butyl glycol 1.50 11 Butyl glycol 0.50 12 De-ionized water 5.83 13 Dimethylethanolamine** 5.83 14 De-ionized water 38.73 *= tert-Butyl peroxy-3,5,5-trimethylhexanoate **= the amine used to neutralise the polymer
Process Method

(5) The polymerisation was carried out using 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, stirred vessels for mixing and addition of monomers (a monomer tank) and free radical initiators (an initiator tank) were available and linked to the reaction vessel by pumps which could be used to control the addition rate. Items 1 and 2 were added to the reaction vessel and heated to 140 C. Whilst the vessel was heating to temperature items 3 and 4 were mixed in the initiator tank and items 5, 6 and 7 were mixed in the monomer tank. With the contents of the reactor maintained at a temperature of 139 to 140 C. the contents of the initiator tank and monomer tank were simultaneously added to the reactor at a constant rate over a period of 150 minutes. After the addition was completed the contents of the reactor were held at 139 to 140 C., then item 8 was added to the reactor from the monomer tank as a line wash. Items 9 and 10 were added to the initiator tank. After holding the reactor contents at 139-140 C. for 30 minutes 50% of the contents of the initiator tank (items 9 and 10) were added as rapidly as possible to the reactor and the temperature of the reactor held at 139 to 140 C. for a further 30 minutes. The remaining contents of the initiator tank were then added and item 11 added to the reactor via the initiator tank as a line wash. The contents of the reactor were then maintained at 139 to 140 C. for a further 90 minutes. The reactor contents were then cooled to 98 C., items 12 and 13 were mixed and the mixture was carefully added to the reactor over a period of 15 minutes. After thorough mixing of the contents of the reactor item 14 was added to produce a translucent or slightly hazy solution like material which was cooled to 25 C. and filtered ready for use in further polymerisation.

(6) The polymer obtained by the above example had the following characteristics:

(7) TABLE-US-00002 solids content 28.9% (180 C., 30 minutes 0.5 gm) viscosity 504 centipoise (Brookfield DVII pro viscometer spindle 3, 50 rpm @ 25 C.) acid value 69.6 (mgKOH/gm on total sample)

(8) This Shell polymer, also sometimes referred to as soap, can be used in various core/shell latex systems. One example is detailed in table 2.

Latex Example 1

(9) TABLE-US-00003 TABLE 2 Item Component Parts (by weight) 1 Shell polymer example 1.sup.1 25.38 2 De-ionized water 55.02 3 Styrene 6.80 4 Ethyl acrylate 9.54 5 Glycidyl methacrylate 1.32 6 Trigonox 21.sup.2 0.18 7 De-ionized water 1.68 8 Trigonox 21.sup.2 0.04 9 Trigonox 21.sup.2 0.04 .sup.1= the soap formed from the reaction components in Table 1, above .sup.2= the radical initiator = tert-Butyl peroxy-2-ethylhexanoate
Process Method

(10) Items 1 and 2 were placed in a reaction vessel equipped with heating, cooling, stirring and a simple reflux condenser. The vessel was also supplied with a nitrogen sparge to maintain an inert atmosphere and also attached were stirred addition tanks which could be employed to add unsaturated monomers and initiator. The mixture in the reaction vessel was heated to 85 C. and held at that temperature. Items 3 to 6 were mixed in a stirred addition tank and then added to the vessel over a period of 2 hours, whilst maintaining the temperature of the contents of the vessel at 85 C. After the addition was complete item 7 was added to the vessel via the stirrer addition tank as a line wash. The vessel was maintained at 85 C. for 30 minutes and then item 8 was added. The vessel was maintained at temperature for a further 1 hour before item 9 was added and the vessel was then maintained at 85 C. for a further 2 hours. Finally the contents of the vessel were cooled to 40 C and discharged with filtration prior to the use of this material, Latex example 1, in the preparation of coatings.

(11) The characteristics of the Latex produced in Latex example 1 were determined as follows:

(12) TABLE-US-00004 Solids content 25.4% (110 C., 60 minutes 0.5 gm) Viscosity 15 seconds (Ford 4 cup @25 C.) Particle size 167.4 nanometers (Z average value, determined with diluted sample using Malvern Zetasizer Nano ZS machine)

(13) The latex produced in this process is an example of a core shell latex dispersion, with a ratio of core to shell components of 73.3/26.7 wt %.

Coatings Examples

Preparation of Coatings

(14) Coatings were prepared from the Latex polymers as described below. The coatings were prepared as two parts, Part A and Part B, which are stored separately as stable components. The two parts are then mixed in weight ratios as outlined below prior to application of the coating.

(15) The tables below outline the components of each of the parts and also the mixture of the parts which make up the coating. All the quantities given in the tables are parts by weight.

(16) TABLE-US-00005 TABLE 3A Coating Coating Coating Components Example 1A Example 2A Example 3A Part A Latex Example 1.sup.1 85.92 82.29 0.00 Alberdingk AC 0.00 0.00 51.88 5503.sup.2 Deionized Water 13.36 16.83 47.08 BYK-307.sup.3 0.41 0.50 0.65 Optical Brightener.sup.4 0.10 0.12 0.13 BYK-024.sup.5 0.21 0.25 0.26 .sup.1= Core shell Latex from preparative example 1 .sup.2= Epoxy functional aqueous acrylic latex dispersion, commercially available from Alberdingk Boley GMBH, Krefeld Germany .sup.3= silicone wetting agent, commercially available from BYK-Chemie GmbH, Wesel, Germany .sup.4= Tinopal NFW Liq commercially available from BASF SE, Ludwigshafen, Germany .sup.5= silicone defoamer, commercially available from BYK-Chemie GmbH, Wesel, Germany

(17) Table 3A outlines the components of a composition which makes up part A which is the latex containing part of the two part coating. Each of the examples was made by adding the components in order, as in the table, to a vessel stirred with a high speed mixer at 25 C. Mixing was continued for 10 minutes after the addition of components was complete.

(18) TABLE-US-00006 TABLE 3B Coating Coating Coating Components Example 1B Example 2B Example 3B Part B Epoxy-methoxy 100.00 20.00 0.00 silane.sup.6 Amino-ethoxy 0.00 0.00 21.55 silane.sup.7 Methoxypropanol 0.00 55.00 78.45 Acetone 0.00 25.00 0.00 .sup.6= Silquest A-187 commercially available from Momentive Performance Materials Albany, NY, USA .sup.7= Silquest A-1100 commercially available from Momentive Performance Materials Albany, NY, USA

(19) Table 3B outlines the components of a composition which makes up part B which is the functional silane containing part of the two part coating. Each of the examples was made by adding the components in order, as in the table, to a vessel stirred with a high speed mixer at 25 C. Mixing was continued for 10 minutes after the addition of components was complete.

(20) TABLE-US-00007 TABLE 3C Coating Coating Coating Components Example 1 Example 2 Example 3 Coating Coating Example 1A 97 Mixture Coating Example 2A 80 Coating Example 3A 77 Coating Example 1B 3 Coating Example 2B 20 Coating Example 3B 23

(21) Table 3C outlines the component parts and the amounts which are mixed to produce the final coatings. Thus Coating example 1 was prepared by mixing Coating example 1 A (part A or the latex part) with Coating example 1B (part B or the functional silane containing part) in the weight proportions as given in the table. Other examples were prepared by combining part A and part B as outlined in table 3C.

(22) Each of the Coating examples were made by adding component B to component A in a mixing vessel which was stirred with a high speed mixing blade at 500-1000 rpm at a temperature around 25 C. Mixing continued for 10 minutes after the addition was complete. After mixing each of the coatings was ready for use; stored at a temperature around 25 C. they remained in a useable state for around 50 hours.

(23) Using the solids contents as determined for the latex materials discussed above, the proportion of latex solids and silane solids in each of the example coatings was calculated:

(24) For coating example 1, the proportion of latex solids to silane solids by weight is 87.6 to 12.4. For coating example 2, the proportions of latex to silane solids by weight are 80.7 to 19.3 and for coating example 3, the latex to silane solids ratio is 80.3 to 19.7.

(25) Coating Application and Drying

(26) The Coatings from the coating examples outlined above and a commercial standard product were applied to a metal substrate, being a full aperture tinplate easy open end, such as those routinely used in food or beverage cans. The ends used were coated with clear, gold or white pigmented lacquer with print markings and had not been repair coated.

(27) The coatings were applied with an airless spray gun in a strip 5-25 mm wide over the score line on the easy open end.

(28) After application of the coatings the easy open ends were dried for one minute in a fan assisted oven at a temperature between 100 C. and 150 C. as outlined in tables 4 and 5 below. The drying process produces a cured film of the coating on the end which is tested, as outlined in the details below, to demonstrate the performance of the protective coating applied to the score line as a repair layer.

(29) Details of Methods for Testing Coatings

(30) The performance of the coatings are evaluated in the following ways:

(31) The coating is evaluated using a test for bubbles, blush, adhesion and yellowing. Details of how these tests are performed and evaluated are given below.

(32) Bubbles

(33) After application and curing the formation of bubbles is evaluated. This is done by examining the score line with a microscope looking particularly for bubbles and defects which are trapped within the film or in the coating metal interface. The evaluation is rated between 0 and 5. Rating grade 0 corresponds to no bubbles seen along the score line and grade 5 corresponds to bubbles covering all of the score line.

(34) Blush

(35) Blush is white colouration of the film caused by water penetration and entrapment. To assess the resistance to blush the coated ends are sterilised in an autoclave for 1 hour at 130 C. in water and in water plus 1% teepol (sodium dodecyl benzene sulphonate, detergent) (as detergent) and the film is observed.

(36) In the evaluation of the coating examples reported below the blush evaluation corresponds to sterilisation in the liquid phase (completely immersed in the solution) in water with 1% arylsulphosuccinate detergent for 1 hour at 130 C.

(37) After sterilisation the appearance of the film is rated between 0 and 5. Grade 0 corresponds to perfect film appearance with no discernable attack. Grade 5 corresponds to complete attack of the film across the whole of the score line.

(38) The industrial process for processing or sterilisation of cans containing various food stuffs often uses water which is treated with detergents such as arylsulphosuccinates. In some cases the industrial process can also use a 1% solution of Teepol in water. Hence, this test has particular relevance to the industrial use of the coatings that are under evaluation.

(39) Adhesion

(40) Film adhesion after sterilisation with water with 1% teepol (sodium dodecyl benzene sulphonate, detergent) for 1 hour at 130 C. is also checked. The coating is crosshatched and checked for removal with tape (3M 610 type tape). Grade 0 corresponds to good adhesion with no removal of coating and grade 5 to complete loss of adhesion as seen by complete removal of the coating with the tape.

(41) Yellowing

(42) To check yellowing the coating is applied on ends which are coated with white enamel and sterilized in water with 1% teepol (sodium dodecyl benzene sulphonate, detergent) for 1 hour at 130 C. Grade 0 corresponds to no yellowing and grade 5 to a high yellowing level.

(43) Results of Testing of Coating Examples

(44) The standard product and coating examples were prepared, applied and dried as outlined in the preceding descriptions. The coated ends obtained were then tested no later than 3 hours after completion of the drying process. The results of the testing and evaluation of the ends are compiled in Table 4. It should also be noted that for each coating ends were cured at three different temperatures (105 C., 120 C. and 150 C.) as outlined in the table.

(45) TABLE-US-00008 TABLE 4 Adhesion Film curing after temperature Bubbles Blush sterilisation Yellowing Standard from 105 C. 0 4 0 1 PPG (epoxy 120 C. 0 3 0 1 based solvent- 150 C. 0 2 0 1 borne product).sup.1 Coating 105 C. 0 2 0 0 Example 1 120 C. 0 2 0 0 150 C. 0 2 0 0 Coating 105 C. 0 1 0 0 Example 2 120 C. 0 1 0 0 150 C. 0 1 0 0 Coating 105 C. 0 1 0 0 Example 3 120 C. 0 1 0 0 150 C. 0 1 0 0 .sup.1= PPG 2982-803/A + PPG 2982-804/A mix 1:1

(46) The results in table 4 show that the standard product has poor blush performance particularly where the curing temperature used is low (105 C. and 120 C.). This is expected for the standard; in commercial production using products such as the standard employed here, the repaired easy open ends are held at a temperature around 22 C. for a period at least 24 hours to fully develop resistance properties. All of the coating examples under study at all of the temperatures show a better level of performance than the standard and have been shown to develop a good level of performance immediately after oven drying, with no need to age the coating. This offers an advantage, particularly in process costs, for the products under study compared to the standard.

(47) Tables 5 below shows the results of tests on ends which have been stored at a temperature of 19 and 22 C. for 24 hours after oven drying. This storage or ageing process is applied in commercial use of the standard coating which is known not to develop its full performance immediately after drying. Tests were made for the standard and the coating examples under study after this storage time and the results should be compared to those in table 4

(48) TABLE-US-00009 TABLE 5 Adhesion Film curing after temperature Bubbles Blush sterilisation Yellowing Standard from 105 C. 0 2 0 1 PPG (epoxy 120 C. 0 1 0 1 based solvent- 150 C. 0 1 0 1 borne product).sup.1 Coating 105 C. 0 2 0 0 Example 1 120 C. 0 2 0 0 150 C. 0 2 0 0 Coating 105 C. 0 1 0 0 Example 2 120 C. 0 1 0 0 150 C. 0 1 0 0 Coating 105 C. 0 1 0 0 Example 3 120 C. 0 1 0 0 150 C. 0 1 0 0 .sup.1= PPG 2982-803/A + PPG 2982-804/A mix 1:1

(49) The results in table 5 when compared to those in table 4 show that the performance of the standard has changed and reached a good level of performance. This change was as expected for the commercial standard product. Whereas for all the coating examples under study the test results in table 4, immediately after cure, are the same as the results in table 5, after 24 hours ageing. The results in table 5 of all the coating examples under test are comparable with the standard.

(50) In all of the examples under study the film is transparent and is colourless, as indicated by a score of 0 in the yellowing test, whereas the standard is known to be slightly yellowish, as indicated by a score of 1 in the yellowing test, giving the repair some visibility. Hence, the coatings under study offer another desirable advantage over the current commercial standard product, particularly where the ends are precoated with a pigmented white coating or colourless lacquer.

(51) Thus in summary, it can be seen from the examples above that a coating composition made in accordance with the present invention provides a water based coating with lower volatile organic content (VOC), requires a lower curing temperature, does not need to be stored (or aged) to produce the desired protection performance and produces less yellowing compared to the current commercial standard product. Furthermore, it can be seen from the examples presented that in common with the current commercial standard product the coating composition made in accordance with the present invention provides a two component coating with a workable life (after mixing of the components) of at least 12 hours, can be applied with airless spray equipment and provides sufficient protection to resist corrosion to the exposed metal score line which it has been applied to repair.

(52) 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.

(53) 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.

(54) 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.

(55) 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.