Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2003-02-12
2004-05-04
Cameron, Erma (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S392000, C427S393500, C427S421100
Reexamination Certificate
active
06730361
ABSTRACT:
BACKGROUND
Coating solutions and coated materials of various kinds are used in the packaging industry. Some coatings serve to protect the exterior layer while some coatings serve as a barrier protecting the contents from contamination by the package itself. In other instances, the coatings are used as decorations or as advertisements. Each coating presents specific requirements at production in order to meet the demand of its intended use. For example, exterior packaging coatings need to be abrasion resistant and if messages are incorporated, the coatings should maintain the properties needed to communicate the information to the intended audience. In some instances, the packaging coating for the exterior of the package should be adaptable to accept other coatings. Other requirements are presented depending on the intended use of the package, such as image retention, weather resistance, and information dissemination.
Interior packaging coatings present other requirements for container packaging. Depending on its intended use, the coated package may be required to meet certain stringent requirements. For example, drug containers must meet very stringent requirements in order to prevent contamination of the drugs. As another example, containers that are used to package edible items such as food, beer and beverage must meet exacting standards. These requirements generally include excellent cure, excellent adhesion of the coating, blush resistance, retort resistance and corrosion resistance.
Most coatings are not formulated to meet these stringent requirements. For example, an automotive coating composition, while useful on a car, may not be useful as a coating for a food or beverage packaging container. It is a fair conclusion, therefore, that not all coatings can be used on package containers for food items.
Another consideration for food and beverage package coatings is cost. An effective coating should be cost effective while meeting the high performance requirements for food and beverage container coatings.
From the foregoing, it will be appreciated that what is needed in the art is a low cost, high performance coating that is easy to make and apply. Such coatings and methods for preparing and applying the same are disclosed and claimed herein.
SUMMARY
In one embodiment, this invention relates to novel methods of coating a packaging container. The method of the present invention includes the steps of providing a coating composition having a crosslinkable polyester-polyurethane polymer. The crosslinkable polyester-polyurethane polymer of the present invention preferably comprises at least two carbamate sites. The coating composition preferably also includes a crosslinker.
A suitable method of the present invention includes the steps of: coating on a generally planar substrate; curing the composition; and forming the substrate into a container (e.g., a packaging container) or a portion of a container.
In another preferred embodiment, this invention also relates to a coating composition including a crosslinkable polyester-polyurethane polymer having at least two carbamate sites, a crosslinker, and at least one adjuvant such as a carrier, a lubricant, a pigment, a rheological control agent, a flow control agent, or a combination thereof.
Another embodiment of the present invention includes a coated package comprising a substrate, a cured coating produced from a composition including a crosslinkable polyester-polyurethane polymer that has at least two carbamate sites, a crosslinker, and at least one adjuvant such as a carrier, a lubricant, a pigment, a rheological control agent, a flow control agent, or a combination thereof.
DETAILED DESCRIPTION
The present invention provides a novel method of coating a packaging container substrate using a crosslinkable coating composition. In addition, the present invention provides a new packaging coating and compositions usable in the food packaging industry.
The coating composition of the present invention preferably comprises a crosslinkable polyester-polyurethane polymer, a crosslinker, and may optionally further comprise at least one adjuvant such as: lubricants, pigments, rheological control agents, flow control agents, and solvents. A catalyst may also be utilized to enhance the cure of the coating composition. The coating composition of the present invention provides one or more features such as: excellent film integrity on applied packages, excellent ability to accept pigmentation, desired chemical stability, enhanced corrosion resistance, and/or required sterilization resistance.
Suitable crosslinkable polyester-polyurethane polymers (“PE-PU polymer”) may be formed by reacting a polyester intermediate (“PE intermediate”) with a polyisocyanate compound. Preferred PE-PU polymers of the present invention comprise two or more carbamate sites per polymer chain. Such carbamate sites are preferably suitable for crosslinking of the PE-PU polymer by crosslinkers, such as amino resins, phenolic resins, and/or blocked isocyanates.
In one embodiment, the PE intermediate is a hydroxy functional polyester containing hydroxy end groups and the polyisocyanate compound is an organic polyisocyanate. Suitable hydroxy functional polyesters include, for example, the reaction product of (i) a diol of the formula HOROH, where R is an aliphatic, cycloaliphatic, or aromatic hydrocarbon radical that has, preferably between 2 and 40 carbon atoms, more preferably between 2 and 20 carbon atoms, and most preferably between 2 and 12 carbon atoms; and (ii) a dicarboxylic acid of the formula R′(COOH)
2
, or an anhydride of such an acid, where R′ is an aliphatic, cycloaliphatic, or aromatic hydrocarbon radical having preferably 4 to 50 carbon atoms, more preferably 4 to 45 carbon atoms, and most preferably 4 to 40 carbon atoms.
Suitable PE-PU polymers of the present invention have a number average molecular weight (“M
n
”) of at least 5,000, preferably between 5,000 and 35,000, more preferably between 7,000 and 20,000, and most preferably between 9,000 and 15,000. Suitable PE-PU polymers of the present invention have a weight average molecular weight (“M
w
”) of at least 10,000, preferably between 10,000 and 40,000, more preferably between 14,000 and 30,000, and most preferably between 18,000 and 25,000.
Suitable PE-PU polymers of the present invention have a glass transition temperature (“T
g
”) of at least about 0° C., preferably at least about 50° C., more preferably between about 50° C. and 80° C., and most preferably between about 60° C. and 70° C.
Suitable PE-PU polymers of the present invention have a hydroxyl number (OH#) of less than about 5 mg/g, and preferably between 0 and 1 mg/g. The hydroxyl number of a hydroxyl-containing polymer of the present invention is determined by methods as are known in the art such as described in ASTM E-222-00, Test Method C.
The PE-PU polymers in the coating composition of the present invention are preferably present in an amount between about 10 and 100 weight percent, more preferably between about 50 and 100 weight percent, most preferably between about 70 and 95 weight percent of the coating composition.
As previously mentioned, suitable PE-PU polymers may be formed by reacting a polyester intermediate (“PE intermediate”) with a polyisocyanate compound.
Suitable PE intermediates for use in the present invention include medium molecular weight, linear, hydroxy functional polyesters. Preferred PE intermediates have a number average molecular weight between about 1,000 and 10,000, more preferably between about 2,000 and 10,000, most preferably between about 4,000 and 8,000. The weight average molecular weight of the PE intermediates is preferably between about 2,000 and 25,000, more preferably between about 5,000 and 25,000, and most preferably between about 10,000 and 20,000. Preferably the hydroxyl number (OH#) of the PE intermediate is between 10 and 100, more preferably between 15 and 85, and most preferably between 20 and 50. Preferred PE intermediates have a glass transition temperature (“T
g
”) of
Goodwin Ronald L.
Parekh Girish G.
Paulson Gregory M.
Cameron Erma
Essien Michael A.
Larkin Hoffman Daly & Lindgren Ltd.
Valspar Sourcing Inc.
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