Abstract:
Coating compositions are disclosed having a non-bisphenol A based film forming resin and an adhesion promoter resin. The coating compositions provide an alternate to epoxy resins that still allow melamine formaldehyde free cure, blush resistance, capability to retort and can withstand hard-to-hold beverages. In some embodiments, the coating compositions are used to coat substrates such as cans and packaging materials for the storage of food and beverages. Substrates can be coated by preparing an adhesion promoter composition by a method including mixing an epoxidized resin and a solvent to form a mixture, adding a phosphoric acid compound to the resulting mixture to form a phosphate ester, adding water to partially hydrolyze the phosphate ester, and adding a neutralizer to form the adhesion promoter resin, followed by blending the adhesion promoter resin with a non-bisphenol A based film forming resin to form a coating composition, and applying the coating composition to the substrate.

Description:
This application is the U.S. National Phase of PCT/EP2011/073935 filed on Dec. 23, 2011 and claims the benefit of U.S. Provisional Application No. 61/427,863 filed on Dec. 29,2010 and European Application No. 1154058.9 filed on Feb. 10, 2011, the entire contents of each of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to adhesion promoter resin compositions, coating compositions having the adhesion promoter resin compositions, methods of coating substrates with coating compositions, and substrates coated with coating compositions. 
     2. Description of Related Art 
     Coating compositions formed from epoxy resins have been used to coat packaging and containers for foods and beverages. Although the weight of scientific evidence, as interpreted by the major global regulatory food safety agencies in the US, Canada, Europe, and Japan, shows that the levels of bisphenol A consumers are exposed to with current commercial epoxy based coatings is safe, some consumers and brand owners continue to express concern, and a coating that does not contain bisphenol A or any other endocrine disruptor is desirable. 
     Many coating compositions that do not contain bisphenol A or any other endocrine disruptors have not achieved the performance of epoxy based coatings and have not been successfully used on a commercial basis in food and beverage coating compositions. Some drawbacks have been delamination, flavor acceptance in beer and blush performance in pasteurized or retorted hard-to-hold beverages. 
     Commonly-owned U.S. Pat. No. 4,522,961 describes coating compositions having an epoxy-acrylic copolymer and up to 50 wt % of a phosphated polymer. The examples of U.S. Pat. No. &#39;961 indicate that better results are obtained when the coating composition has a high amount of the epoxy-acrylic copolymer and a low amount of the phosphated polymer. Such results are obtained because the epoxy-acrylic copolymer has inherently good adhesion at such high levels. However, U.S. Pat. No. &#39;961 does not explain how to obtain a coating composition that has acceptable adhesion without using an epoxy-acrylic copolymer. 
     There is a need to produce coating compositions that do not contain bisphenol A or are substantially free of bisphenol A. The adhesion promoter resin compositions of the invention can be used in the preparation of coating compositions suitable, inter alia, as packaging coatings for food and beverage packaging and containers. 
     SUMMARY OF THE INVENTION 
     The present invention provides an alternate to epoxy resins that still allows melamine formaldehyde free cure, blush resistance, capability to retort and can withstand hard-to-hold beverages. The coating compositions of the invention can be made with a simple process, not requiring multiple polymers or processing stages to achieve the intended effect. 
     The present invention includes coating compositions and methods for forming coating compositions comprising a non-bisphenol A based film forming resin and an adhesion promoter composition. The present invention also includes methods of coating a substrate comprising: a) preparing an adhesion promoter composition by a method comprising: i) mixing an epoxidized resin and a solvent to form a mixture; ii) adding a phosphoric acid compound to the resulting mixture to form a phosphate ester; iii) adding water to partially hydrolyze the phosphate ester; and iv) adding a neutralizer to form the adhesion promoter resin; b) blending the adhesion promoter resin with a non-bisphenol A based film forming resin to form a coating composition; and c) applying the coating composition to the substrate. 
     In addition, the present invention includes coating compositions prepared by a method comprising: a) preparing an adhesion promoter composition by a method comprising: i) mixing an epoxidized resin and a solvent to form a mixture; ii) adding a phosphoric acid compound to the resulting mixture to form a phosphate ester; iii) adding water to partially hydrolyze the phosphate ester; and iv) adding a neutralizer to form the adhesion promoter resin; b) blending the adhesion promoter resin with a non-bisphenol A based film forming resin to form a coating composition. 
     Still further, the present invention includes cans and packaging coated by the methods and including the coating compositions of the present invention. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention includes substrates coated at least in part with a coating composition of the invention and methods for coating the substrates. The term “substrate” as used herein includes, without limitation, cans, metal cans, packaging, containers, receptacles, or any portions thereof used to hold, touch or contact any type of food or beverage. Also, the terms “substrate”, “food can(s)”, “food containers” and the like include, for non-limiting example, “can ends”, which can be stamped from can end stock and used in the packaging of beverages. 
     The present invention includes adhesion promoter resin compositions comprising a phosphoric acid compound, an epoxidized resin (which may be aliphatic or aromatic), or a combination thereof. The compositions may also include a solvent and a neutralizer. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is an SEM image of the surface morphology of a film formed according to Example 2A. 
         FIG. 2  is an SEM image of the surface morphology of a film formed according to Example 2B. 
         FIG. 3  is an SEM image of the surface morphology of a film formed according to Example 2C. 
         FIG. 4  is an SEM image of the surface morphology of a film formed according to Example 2D. 
         FIG. 5  is an SEM image of the surface morphology of a film formed according to Example 2E. 
     
    
    
     In some embodiments of the invention, the solvent comprises 2-butoxyethanol, butanol, 2-hexoxyethanol, or other hydroxylated solvents, as well as combinations thereof. The solvent may be present in an amount from about 4:1 to about 1:4 based on weight of solvent to solids or from about 3:1 to about 1:3. 
     The neutralizer may comprise without limitation a tertiary amine, secondary amine, a primary amine, sodium hydroxide, potassium hydroxide, a carbonate, or a combination thereof. Suitable tertiary amines for use in the present invention include without limitation dimethyl ethanol amine, 2-dimethylamino-2-methylpropanol, tributylamine, and combinations thereof. In some embodiments, the neutralizer is present in an amount from about 0.25 to about 1.5 equivalents on the phosphoric acid compound or from about 0.75 to about 1.0. 
     The adhesion promoter resin composition of the present invention may also include without limitation a phosphated epoxidized oil, a phosphated epoxidized polybutadiene copolymer, a phosphated acrylic copolymer, a phosphated polyester, a phosphated copolymer containing a copolymerized phosphate monomer, an epoxy phosphate, a phosphated epoxy-acrylic copolymer, a mono-alkyl ester of the foregoing, a di-alkyl ester of the foregoing, or a combination thereof. In some embodiments, the adhesion promoter resin composition may be present in an amount from about 0.5 to about 10.0% to coating solids or from about 2.0 to about 7.0%. 
     The epoxidized resin of the present invention in some embodiments may include a mono- and diglycidyl ether of a diol (such as without limitation dipropylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, ethylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,4 butanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, and 1,6 hexanediol diglycidyl ether), a mono- or di-glycidyl ester of a diacid (such as without limitation a diglycidyl ester of hexahydrophthalic anhydride), epoxidized soyabean oil, a bisphenol A glycidyl ether, epoxidized polybutadiene, or a combination thereof. In some embodiments, the epoxidized resin may be present in an amount from about 10% to about 75 wt % of the coating composition or from about 20% to about 50 wt %. In some embodiments, the adhesion promoter composition further comprises water. 
     The present invention also includes methods of coating a substrate comprising: a) preparing a coating composition by a method comprising: i) mixing an epoxidized resin and a solvent to form a mixture; ii) adding a phosphoric acid compound to the resulting mixture to form a phosphate ester; iii) adding water to partially hydrolyze the phosphate ester; and iv) adding a neutralizer to form an adhesion promoter resin; b) blending the adhesion promoter resin with a non-bisphenol A based film forming resin to form a coating composition; and c) applying the coating composition to the substrate. In some embodiments, the phosphoric acid compound can be without limitation phosphoric acid, superphosphoric acid, polyphosphoric acid, P 2 O 5 , or a combination thereof. 
     The methods, the adhesion promoter resin compositions and the coating compositions described herein may include any of the features described throughout this application. The non-bisphenol A based film forming resin may be a conventional coating system that is typically used as a coating composition, such as a latex coating composition (including for example a styrene acrylic latex composition), a polyester coating composition, a polyolefin coating composition, a polyurethane coating composition, a polyacrylic coating composition, a polycarbonate coating composition, a polyurea coating composition, the coating compositions of any of commonly-owned published applications WO 2010/100122, WO 2010/100121 or WO 2010/097353, or a combination thereof. 
     In some embodiments, the adhesion promoter resin composition may be blended with the non-bisphenol A based film forming resin in an amount from about 0.5% to about 10% based on total polymer solids, or from about 2% to about 6% on total polymer solids. 
     In addition, the present invention includes coating compositions prepared by a method comprising: a) preparing an adhesion promoter composition by a method comprising: i) mixing an epoxidized resin and a solvent to form a mixture; ii) adding a phosphoric acid compound to the resulting mixture to form a phosphate ester; iii) adding water to partially hydrolyze the phosphate ester; and iv) adding a neutralizer to form the adhesion promoter resin; b) blending the adhesion promoter resin with a non-bisphenol A based film forming resin to form a coating composition. The methods, the adhesion promoter compositions and the coating compositions described herein may include the features described throughout this application. 
     Still further, the present invention includes substrates, such as cans and packaging, coated with the coating compositions and/or by the methods of the present invention. 
     The non-bisphenol A based film forming resins, the adhesion promoter resin compositions and the coating compositions of the invention can include conventional additives known to those skilled in the art, such as without limitation, additives to control foam, reduce equilibrium and dynamic surface tension, control rheology and surface lubricity. Amounts can vary depending on desired coating application and performance in any manner known to those skilled in the art. The adhesion promoter resin compositions can also include additives, such as without limitation, solution acrylics, siloxanes, water-borne polyesters, phenolics or other surface active materials. 
     One or more coating compositions of the invention are applied to a substrate in some embodiments, such as for non-limiting example, cans, metal cans, packaging, containers, receptacles, can ends, or any portions thereof used to hold or touch any type of food or beverage. In some embodiments, one or more coatings are applied in addition to the coating composition of the present invention, such as for non-limiting example, a prime coat may be applied between the substrate and a coating composition of the present invention. 
     The coating compositions can be applied to substrates in any manner known to those skilled in the art. In some embodiments, the coating compositions are sprayed onto a substrate. When spraying, the coating composition contains, for non-limiting example, between about 10% and about 30% by weight polymeric solids relative to about 70% to about 90% water including other volatiles such as, without limitation, minimal amounts of solvents, if desired. For some applications, typically those other than spraying, the aqueous polymeric dispersions can contain, for non-limiting example, between about 20% and about 60% by weight polymer solids. Organic solvents are utilized in some embodiments to facilitate spray or other application methods and such solvents include, without limitation, n-butanol, 2-butoxy-ethanol-1, xylene, toluene, and mixtures thereof. In some embodiments, n-butanol is used in combination with 2-butoxy-ethanol-1. The coating compositions of the present invention are pigmented and/or opacified with known pigments and opacifiers in some embodiments. For many uses, including food use for non-limiting example, the pigment is titanium dioxide. The resulting aqueous coating composition is applied in some embodiments by conventional methods known in the coating industry. Thus, for non-limiting example, spraying, rolling, dipping, and flow coating application methods can be used for both clear and pigmented films. In some embodiments, after application onto a substrate, the coating is cured thermally at temperatures in the range from about 130° C. to about 250° C., and alternatively higher for time sufficient to effect complete curing as well as volatilizing of any fugitive component therein. 
     For substrates intended as beverage containers, the coating are applied in some embodiments at a rate in the range from about 0.5 to about 15 milligrams of polymer coating per square inch of exposed substrate surface. In some embodiments, the water-dispersible coating is applied at a thickness between about 1 and about 25 microns. 
     EXAMPLES 
     The invention will be further described by reference to the following non-limiting examples. It should be understood that variations and modifications of these examples can be made by those skilled in the art without departing from the spirit and scope of the invention. 
     Example 1 
     Preparation of Adhesion Promoter Composition 
     Phosphorylation Stage 
     A premix was prepared by adding 24.0 parts of epoxidized polybutadiene (Poly BD 600) and 34.2 parts of butyl cellosolve to a reaction flask and heated to 70° C. with medium stirring and a nitrogen blanket. The butyl cellosolve was used as a diluent solvent and also to buffer the reaction to prevent gellation. To this mixture was added a premix of 1.0 parts of superphosphoric acid (105% phosphoric acid) and 3.29 parts of butyl cellosolve. Superphosphoric acid was used since it is a concentrated form of an acid without water present to interfere with the oxirane ring reaction. The components were allowed to react and within five minutes the exothermic reaction reached 76° F. The temperature was then slowly raised to 120° F. over 20 minutes and held for 3 hours. As the reaction proceeded, mono-, di- and tri- esters formed and consumed most of the available acid groups on the acid. Samples were taken hourly and tested for acid number to monitor the reaction. Starting from a theoretical acid number of 43.6, the final acid number was 3.2. A final sample was also tested for the percent oxirane to check for any remaining oxirane groups. Starting from a theoretical oxirane of 3.5%, the final value was 0.22%. 
     Hydrolysis Stage 
     The batch was cooled to 97° F. and 3.36 parts of water was added to the flask and held for 2 hours. Reacting with water broke up any di- and tri- esters of phosphoric acid back to all mono-esters which is an effective form for adhesion to metal substrates. Samples were taken hourly and tested for acid number. The final acid number was 39.1. 
     Emulsion Stage 
     While holding at greater than 95° F., a premix of 0.96 parts of dimethyl ethanol amine and 2.88 parts of water was slowly added to the flask and held for 20 minutes to neutralize the acid. The heat was then turned off and 30.31 parts of water was added over 30 minutes to form the final emulsion. The batch was air-cooled to room temperature and checked for acid number and percent solids. The final values were 39.1 acid number and 26.3% solids. 
     Example 2 
     The following examples resulted in improved film appearance when using the adhesion promoter compositions of the present invention. 
     Example 2A 
     Control Coating 
     To 2415.3 g of a styrene acrylic latex (23.5% NV) was added 141.7 g of demineralized water, followed by a mixture of 349.41 g of butanol, 85.5 g of butyl cellosolve, 7.13 g of hexyl cellosolve, and 5.7 g of Surfynol 420, mixing well during addition. 
     Example 2B 
     Coating with Adhesion Promoter Composition 
     To 2342.8 g of a styrene acrylic latex (23.5% NV) was added 221.4 g of demineralized water and 68.4 g of the adhesion promoter composition from Example 1. Then, a mixture of 349.41 g of butanol, 59.45 g of butyl cellosolve, 7.13 g of hexyl cellosolve, and 5.7 g of Surfynol 420 was added, mixing well during addition. 
     Examples 2C-2E 
     Coating Modifications 
     To 3400.0 g of material from Example 2B was added the materials indicated in the table below, mixing well after addition. 
     
       
         
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Example 
                 Material 
                 Amount 
               
               
                   
                   
               
             
             
               
                   
                 C 
                 solution acrylic 1   
                  2.9 g 
               
               
                   
                 D 
                 polyester 2   
                 71.8 g 
               
               
                   
                 E 
                 Z-6070 silane 
                 17.0 g 
               
               
                   
                   
                 Z-6124 silane 
                 17.0 g 
               
               
                   
                   
               
               
                   
                   1 an acid-functional solution acrylic flow modifier 
               
               
                   
                   2 an aqueous polyester dispersion 
               
             
          
         
       
     
     Example 2F 
     Coating Testing 
     Material from Examples 2A-2E above were sprayed onto two-piece beverage cans and evaluated for performance.
         Spray: cans with 125 mg/can film weight evaluated via enamel rater.   Seltzer Delamination: cans sprayed at 100 mg/can film weight, enamel rated and then filled with seltzer water. Evaluated for surface delamination; 0=no delamination, 10=severe delamination   Cans filled with Gatorade and retorted for 60 min at 250 F and evaluated for blush, color pick-up and drop and damage.   Blush: 0=no whitening, 5=opaque white   Color: 0=no color, 5=significant color   Drop and Damage by enamel rating after drop onto wedge.       

                                                                                   Seltzer           Drop and       Example   Spray   delamination   Blush   Color   Damage                                2A   3.0   8   0   0   42.6       2B   1.5   0   0   0   9.4       2C   2.1   0   0   0   20.3       2D   5.5   0   0   0   14.9       2E   2.9   0.5   0   0   13.3                    
Surface Morphology:
 
     Below are SEM pictures of the film surface morphology of the Examples 2A-2E. Smooth surfaces with limited pits are desired. 
     Example 3 
     Coating with Adhesion Promoter Composition 
     With nitrogen passed throughout, butyl dioxitol and 89.9% phosphoric acid were charged and heated to 70° C. To the mixture, a premix of a diglycidyl ester of hexahydrophthalic anhydride and butyl dioxitol were added over 180 minutes at 70-75° C. The resulting mixture was held for 60 minutes until an acid number of 35 mg KOH/gram was obtained. Next, a mixture of deionized water and butyl dioxitol were added and the mixture was heated to 140-142° C. The mixture was held for 60 minutes and sampled for an acid number of 71 mg KOH/gram. The resulting mixture was cooled to 95° C. and dimethylethanolamine was added. The batch was allowed to exotherm to 100° C. and it was held for 30 minutes at 90-100° C. The weight percentages were: 
     
       
         
               
               
               
             
               
               
               
             
           
               
                   
               
               
                 MATERIAL 
                 WEIGHT 
                 WEIGHT PERCENTAGE 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Butyl dioxitol 
                 262.01 
                 26.20% 
               
               
                 Phosphoric acid (89.9%) 
                 64.80 
                 6.48% 
               
               
                 Epalloy 5200 
                 441.76 
                 44.18% 
               
               
                 Butyl dioxitol 
                 115.18 
                 11.52% 
               
               
                 Deionized water 
                 24.09 
                 2.41% 
               
               
                 Butyl dioxitol 
                 38.17 
                 3.82% 
               
               
                 Dimethylethanolamine 
                 53.99 
                 5.40% 
               
               
                   
               
             
          
         
       
     
     The resulting composition was analyzed for its solid content, viscosity and acid value. The results were: 
     
       
         
               
               
               
             
           
               
                   
               
               
                 SOLIDS CONTENT 
                 VISCOSITY 
                 ACID VALUE 
               
               
                   
               
             
             
               
                 60.2% 
                 9 poise at 25° C. 
                 110 mg KOH/gram solids 
               
               
                   
               
             
          
         
       
     
     Example 4 
     Three coating compositions were prepared by cold mixing the components and evaluated after application onto aluminum can stock as shown in the table below. The coating composition in the first column was prepared using a standard aromatic epoxy phosphate without an adhesion promoter of the invention. The coating composition in the second column was prepared using a non-epoxy adhesion promoter at an addition level of 2.2% of the total solids content. The coating composition in the third column was prepared using a non-epoxy adhesion promoter at an addition level of 1.1% of the total solids content. 
     
       
         
               
               
               
               
             
               
               
               
               
             
           
               
                   
               
               
                   
                   
                 Weight % 
                   
               
               
                   
                   
                 Full level 
                 Half level 
               
               
                   
                   
                 of adhesion 
                 of adhesion 
               
               
                 Component 
                 Standard 
                 promoter 
                 promoter 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Polyester 
                 53 
                 53 
                 53 
               
               
                 Dimethylethanolamine 
                 0.9 
                 0.9 
                 0.9 
               
               
                 Adhesion promoter 
                 0 
                 2.2 
                 1.1 
               
               
                 Epoxy phosphate 
                 2 
                 0 
                 0 
               
               
                 BYK333 surfactant 
                 0.2 
                 0.2 
                 0.216 
               
               
                 Drewplus 210-694 
                 0.2 
                 0.2 
                 0.2 
               
               
                 defoamer 
               
               
                 2-butoxy ethanol 
                 0.2 
                 0.2 
                 0.2 
               
               
                 Synocryl 811S vinyl 
                 1 
                 1 
                 1 
               
               
                 polymer 
               
               
                 Cymel 3745 crosslinker 
                 15 
                 15 
                 15 
               
               
                 Wax 
                 2.3 
                 2.3 
                 2.3 
               
               
                 Water 
                 25.2 
                 25 
                 26.1 
               
               
                   
               
             
          
         
       
     
                                                                           60° gloss                   IBO   122-131   120-128   117-124       Overstove   118-123   104-109   103-106       Altek slip       Deco   0.04-0.05   0.03-0.04   0.03-0.04       IBO   0.06-0.07   0.04-0.05   0.04-0.05       Overstove   0.09-0.10   0.05-0.06   0.05-0.06       MEK       Deco   16-19   19-26   25-28       IBO   100+   100+   100+       Overstove   100+   100+   100+       Wedge bend     88%     90%     92%       % non breakdown       Pencil hardness       IBO   &gt;7H    &gt;7H   &gt;7H       Overstove   6H   &gt;7H   &gt;7H       Blush resistance       Joy 95° C./30′   0-1    0    0       Water    0    0    0       Calsberg   0-1    0    0                    202 neck adhesion   Neck   SW   Neck   SW   Neck   SW               Joy 95° C./30′   0   0   0   0   0   0       Water boil 10′   0   0   0   0   0   0       Carlsberg 60° C./30′   0   0   0   0   0   0                    
The data above shows that the addition of a non-epoxy adhesion promoter at addition levels of 1.1 and 2.2% of total solids give adhesion performance equivalent to that of coatings formulated with a standard aromatic epoxy phosphate.