Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From phenol – phenol ether – or inorganic phenolate
Reexamination Certificate
2000-07-14
2002-02-12
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From phenol, phenol ether, or inorganic phenolate
C528S179000, C528S190000, C528S193000, C528S194000, C528S211000, C528S219000, C528S274000, C528S302000, C528S361000, C528S365000, C524S186000, C524S366000, C524S379000, C427S207100, C428S480000, C264S239000, C264S331110
Reexamination Certificate
active
06346596
ABSTRACT:
FIELD
The present invention relates to gas barrier polymer compositions and methods of making and using same.
BACKGROUND
Plastics are finding increasing use as replacements for glass and metal containers in packaging. This trend can be attributed in part to the advantages presented by plastic packaging, including lighter weight, decreased breakage, and potentially lower costs. However, the use of plastics in the packaging industry presents some drawbacks. One drawback is that packaging plastics have relatively low gas barrier capabilities. Oxygen or carbon dioxide can readily pass through most of the plastic materials traditionally used in the packaging industry, including polycarbonates, polyesters, and polyolefins. Oxygen-sensitive substances, such as foods, beverages, medicines, or medical supplies, may be susceptible to oxidative degradation if packaged in these plastic materials. One goal of the plastic packaging industry has thus been to greatly reduce the gas permeability of packaging materials.
Another drawback associated with the use of plastics in the packaging industry is that widespread commercial acceptance of plastic in the bottling industry, particularly polyethylene terephthalate (PET), has created a significant environmental problem. PET bottles are typically not reused and accumulate in waste disposal facilities, because PET is very stable and not susceptible to biodegradation. Thus, another goal of the packaging industry has been the development of PET recycling methods.
Research in the packaging industry focuses on designing packaging materials with enhanced gas barrier properties that maintain the favorable cost and processing characteristics of PET and additionally, that can be recycled. Efforts to develop plastic packaging materials with improved gas barrier properties and favorable recyclability characteristics have been based on several general strategies.
A first general strategy involves developing new polymer blends, or modifying the chemical or physical properties of “parent” packaging materials, such as PET, polyethylene, polycarbonate, or polyester. For example, one gas-scavenging packaging material is made from a polyethylene graft copolymer and a polyamide. Another gas-scavenging packaging material is made from a blend of an aromatic condensation polymer (such as polyester or polycarbonate) and an oxygen scavenging polymer (such as nylon), in the presence of a trace amount of a transition metal catalyst like cobalt. A similar gas barrier polymer packaging material incorporates activating metals such as cobalt, magnesium, or manganese in a PET/polyamide admixture. Preparation of gas barrier packaging materials of this type involves heating a mixture of the polymer materials and the metal to produce an injection molded preform. A container with enhanced gas barrier properties is then fashioned from the preform. In each of the above examples, improved gas barrier properties are observed. However, activating metal incorporation in the packaging material formulations raises the issue of activating metal recapture at the recycling stage.
A second general strategy for improving gas barrier properties follows a multilayer packaging scheme. A gas barrier polymer composition is applied to a plastic packaging material that has limited gas resistance. In one approach, inner and outer layers of PET are used to surround a core layer of oxygen scavenging ethylene vinyl alcohol or polyketone. In a second approach, PET is coated with an aminoepoxy barrier coating material. In this second approach, the aminoepoxy barrier coating material may contain an inorganic filler; or alternatively, a polyvinyl alcohol or polysaccharide gas barrier film may contain the inorganic filler. The fillers retard gas permeation by blocking the pores of the film through which gas molecules would normally migrate.
Barrier coatings derived from 1,1-dichloroethene or ethylene vinyl alcohol have some disadvantages as well. For instance, they lose barrier properties upon exposure to water. In addition, packages made incorporating these materials do not stand up to the conditions required for pasteurization (heating under pressurized steam) and lose their adhesion properties. Disposal or recycling of the packages also poses environmental concerns, because of the presence of chloride atoms in the coating materials made from, for example, 1,1-dichloroethene.
In a hybrid strategy that combines aspects of each of the above-mentioned approaches, hydroxyfunctional polyesters serve either as PET substitutes or as barrier films. These polyesters have moieties derived from hydroxy functional aliphatic diacids and diglycidyl ethers or diglycidyl esters. The polyesters have gas resistance capabilities and are uncrosslinked. They are processable as thermoplastics useful for making films or molded or formed articles employing conventional injection molding techniques. However, the promise of substantial gas barrier properties has not proved out in practice for the hydroxy functional polyesters. The known hydroxyfunctional polyesters do not show superior barrier properties.
As a result, there remains a need in the packaging industry for the development of effective gas barrier polymer compositions. In particular, there remains a need to develop gas barrier polymer compositions from hydroxy functional aliphatic diacids and diglycidyl ethers with effective gas barrier properties. A further need is to develop polymers that have gas resistance qualities, and are processable and recyclable.
SUMMARY
These and other needs are met by the present invention, which is directed to gas barrier polymer compositions having high active hydrogen group densities. In a preferred embodiment, the invention is directed to active hydrogen containing polyesters that are substantially free of the degradation products derived from organic diacids containing active hydrogen groups.
In one aspect, the invention is directed to gas barrier polymer compositions that are the reaction product of diglycidyl ethers and organic diacids containing active hydrogen groups, and that are at least substantially free of degradation product polyesters. A preferred gas barrier polymer composition of the present invention is the polyester product of an active hydrogen containing organic diacid and a diglycidyl ether, which product is substantially free of moieties derived from the degradation of the active hydrogen containing organic diacid.
In another aspect, the invention is directed to a process for preparing gas barrier polymer compositions by combining organic diacids containing active hydrogen groups and diglycidyl ethers in the presence of an optional catalyst; wherein the pressure, temperature, time, and solvent parameters of the process are regulated to prevent degradation and subsequent incorporation of degradation products of organic diacids containing active hydrogen groups into the gas barrier polymer compositions.
In another aspect, the invention is directed to a coating formulation of the gas barrier polymer composition and a suitable carrier.
In a further aspect, the invention is directed to a method of making multilayer packaging materials or container preforms of at least one layer of a polymeric gas-permeable material and at least one layer of a gas barrier polymer composition of the invention.
In still another aspect, the invention is directed to a polymeric container useful in packaging oxygen sensitive substances, the container having at least one layer of a polymeric gas barrier material that contains a gas barrier polymer composition of the invention.
DEFINITIONS
The terms used in this specification have the meanings and preferred embodiments as provided unless otherwise specified.
The term “active hydrogen group” means a moiety that has labile hydrogen. Moieties known in the art that have labile hydrogen include, but are not limited to hydroxyl moieties, as well as primary and secondary amino moieties and thiol moieties.
The term “degradation product polyester” means a polyester obtained from the degradation products of a
Mallen Thomas R.
Stevenson Thomas A.
Acquah Samuel A.
Fish & Richardson P.C. P.A.
Valspar Corporation
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