Stock material or miscellaneous articles – Composite – Of polycarbonate
Reexamination Certificate
2002-04-01
2004-08-17
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of polycarbonate
C428S480000, C428S523000
Reexamination Certificate
active
06777088
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to barrier materials, curable coating compositions for forming such materials, and to packaging materials and/or containers including barrier materials.
BACKGROUND OF THE INVENTION
Plastics have found increasing use as replacements for glass and metal containers in packaging, especially of foods and beverages. The advantages of such plastic packaging includes lighter weight, decreased breakage (versus glass), resealability (versus most metal containers), and potentially lower costs. However, shortcomings in the gas-barrier properties of common packaging plastics, such as polyolefins, poly(ethylene terephthalate) (PET), and polycarbonates, present major disadvantages in the packaging of many foods and beverages.
Gases such as oxygen and carbon dioxide can readily permeate through most of the plastic materials commonly used by the packaging industry. Oxygen destroys the vitamin C present in fruit juices, and adversely effects the flavor of fruit juices and beer. Loss of carbon dioxide from carbonated beverages and beer results in the products going flat. Thus, the shelf life of beverages and foods in plastic containers is often much shorter than the shelf life of such products in traditional glass and metal containers. The problem is particularly acute in small packages designed for individual servings, since the greater surface-to-volume ratio of the smaller packages results in even shorter shelf life.
U.S. Pat. Nos. 5,008,137; 5,300,541; 5,637,365; 5,728,439; 5,840,825; and 5,902,643 all relate to gas barrier coatings formed by reacting polyepoxides and polyamines. U.S. Pat. No. 5,008,137 (Col 10/11-21) states “the thermoset barrier material will contain at least about four percent by weight amine nitrogen, preferably at least about seven percent by weight amine nitrogen and more preferably at least about nine percent by weight amine nitrogen. While not wishing to be bound by the present explanation, it is believed that greater levels of amine nitrogen in the barrier material contributes to lower gas permeabilities.” U.S. Pat. No. 5,300,541 at Col 2/6-13 states at least about seven percent by weight amine nitrogen is required, while exceptionally good barrier properties were found to be obtained at amine nitrogen contents of at least ten percent. The expression “amine nitrogen” is intended to exclude other nitrogen containing groups such as amides and urethanes. U.S. Pat. No. 5,637,365 discloses coatings where “the amine nitrogen content of these cured coatings may be less than seven percent, with good results being attainable a (sic) low as four percent or lower. The relatively lower amine content of the present invention generally has the advantage of less yellowing of the coating over time.”) (Col 2/27-33.)
U.S. Pat. Nos. 5,275,853; 5,464,924; and 5,962,093 are all related to thermoplastic barrier materials based on the chain extension of diglycidyl ethers with a monofunctional primary amine or a bis(secondary) diamine.
U.S. Pat. No. 6,346,596 B1 discloses a gas barrier polymer composition with active hydrogen functionality wherein the polymer is prepared by reacting a solution of organic diacid containing at least one active hydrogen group and diglycidyl ether in the presence of an optional catalyst.
U.S. application Ser. No. 10/062924 filed Jan. 31, 2002 discloses the acid catalyzed copolymerization of multifunctional epoxide compounds and water, preferably in the presence of a solvent, to produce higher molecular weight polyol products. Such polyols may be crosslinked with OH-reactive crosslinking agents, including amino resins such as melamine-formaldehyde resins, to yield crosslinked films exhibiting excellent properties such as high hardness and solvent resistance at relatively low bake temperatures.
SUMMARY OF THE INVENTION
The present invention provides a method for making a multilayer packaging material which reduces transmission of oxygen comprising
(a) providing a gas-permeable packaging material,
(b) providing a gas-barrier coating comprising a polymeric polyol made by copolymerizing a multifunctional epoxide resin and water in the presence of an amount of acid effective for polymerizing the epoxide resin and the water, the amount of water being sufficient to avoid gelation, and, optionally, a crosslinking agent for hydroxyl functionality, preferably an amino resin,
(c) applying the gas barrier coating over the gas-permeable packaging material to form a multilayer packaging material, and
(d) optionally heating the coated packaging material to effect crosslinking.
As another embodiment of the invention there is provided a multilayer packaging material comprising
(a) at least one layer of a gas-permeable material, preferably a polymeric plastic material, and
(b) at least one layer of a gas-barrier coating comprising a polymeric polyol made by copolymerizing a multifunctional epoxide resin and water in the presence of an amount of acid effective for polymerizing the epoxide resin and the water, the amount of water being sufficient to avoid gelation, the polymeric polyol optionally reacted with a crosslinking agent for hydroxyl functionality, preferably an amino resin. Preferably the gas-barrier coating affords an oxygen permeability constant of less than 2 Dow units when measured at 25° C. and 0% relative humidity.
Yet another and preferred embodiment of the invention affords a multilayer packaging material having at least one gas-permeable packaging material layer and at least one gas barrier material layer characterized in that the gas barrier material layer comprises the reaction product of
(a) a polymeric polyol made by copolymerizing the diglycidyl ether of bisphenol-A, the diglycidyl ether of bisphenol-F, the diglycidyl ether of hydroquinone, the diglycidyl ether of resorcinol or a mixture thereof and water in the presence of an ether solvent and an amount of superacid effective for polymerizing the diglycidyl ether and the water, the amount of water being sufficient to avoid gelation, and
(b) a crosslinking agent for hydroxyl functionality, preferably an amino resin crosslinking agent which is a melamine-formaldehyde resin, a urea-formaldehyde resin, a benzoguanamine-formaldehyde resin, a glycouril-formaldehyde resin, or an etherified derivative thereof.
Multifunctional epoxide resin-water copolymer compositions used in the barrier compositions comprise higher molecular weight polyols, or polymeric polyols, having a number average molecular weight (Mn) of at least about two times the molecular weight of the multifunctional epoxy resin from which they are prepared as measured by GPC using polystyrene calibration standards. The polymeric polyols will comprise glycol end groups and a repeat unit structure which contains two glycidyl units, primary and/or secondary alcohols.
When preferably formulated with suitable amino resin crosslinking agents, such as melamine formaldehyde resins, the polymeric polyols of Mn 500 to 5000, preferably 1000 to 3000, afford a composition which as a cured film or coating on a plastic packaging material substrate provide gas-barrier packaging materials.
The barriers substantially reduce the permeability of gases such as carbon dioxide and/or oxygen through polymeric packaging materials. The oxygen permeability constant (OPC) of the cured barrier composition itself will be less than 2 Dow units, preferably less than 1 and most desirably less than 0.3 Dow units.
DETAILED DESCRIPTION OF THE INVENTION
The oxygen permeability constant (OPC) of a material quantifies the amount of oxygen which can pass through a film or coating under a specific set of circumstances. It is often expressed in units of cubic centimeter-mil/100 square inches/atmosphere/day, a unit of measure referred to in the industry as Dow units. This is a standard unit of permeation measured as cubic centimeters of oxygen permeating through 1 mil (25.4 micron) thickness of a sample, 100 square inches (645 square centimeters) in area, over a 24 hour period, under a partial pressure differential of one atmosphere at spec
Dickenson John Bartram
Pepe Frank Ralph
Walker Frederick Herbert
Air Products and Chemicals Inc.
Dawson Robert
Feely Michael J.
Leach Michael
LandOfFree
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