Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-05-01
2003-10-14
Szekely, Peter (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C220S592160, C428S035700, C524S582000, C528S491000, C528S492000, C528S495000
Reexamination Certificate
active
06632874
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to polyolefin products such as polyethylene and polypropylene packaging materials for food and beverages. More particularly, this invention relates to reduction of aldehydes in polyolefins by incorporation of additives capable of reacting with these aldehydes.
BACKGROUND OF THE INVENTION
Polyolefins, particularly polyethylene and polypropylene, are utilized extensively across a wide range of industries in a variety of product forms, including fibers, films, and three-dimensional structures. A particularly important application for polyolefins is containers, especially for food and beverages. Polyolefin materials often are selected for use in food and beverage packages and closures because they are inexpensive, lightweight, easily modified, and impact resistant. Yet despite these advantages, polyolefins can have certain undesirable attributes. For example, they frequently contribute “off-taste” to packaged products, particularly sensitive products such as water. This off-taste commonly is referred to as a “plastic” off-taste. It would be highly desirable to reduce or eliminate this off-taste from products packaged in polyolefin materials.
One approach that has been taken to mitigate the off-taste problem in the non-polyolefin polymer polyethylene terephthalate (PET) is to incorporate additives that are scavengers for aldehydes that are produced by degradation of the PET itself during heat processing of the polymer. U.S. Pat. No. 4,837,115 to Igarashi discloses incorporating additives of amine-group terminated polyamides and amine-group containing small molecules into PET, wherein the additives selectively react with acetaldehyde (AA) that is generated in the PET. Igarashi teaches that the amine groups are effective because they can react with AA to form imines, where the amine nitrogen forms a double bond with the AA moiety. Igarashi teaches that essentially any amine is effective. Mills (U.S. Pat. Nos. 5,258,233; 5,650,469; and 5,340,884) and Long (U.S. Pat. No. 5,266,416) disclose the use of various polyamides, especially low molecular weight polyamides, while Turner and Nicely (PCT WO 97/28218) disclose the use of polyesteramides. These polyamides and polyesteramides are believed to react with AA in the same manner as described by Igarashi. While these AA scavengers are effective at reducing the AA content of melt-processed PET, they suffer from their own drawbacks. In particular, relatively high loadings of the polyamides are needed to effect significant AA reductions, and a significant yellowing of the PET occurs from incorporation of these amine-containing additives. This coloring is believed to be due to the inherent color of the imine group, which for most applications is undesirable because most polyolefin articles in use today are clear and uncolored.
U.S. Pat. No. 5,663,223 to Teumac discloses using a polymeric liner that includes inorganic sulfites or organic hydrazides as flavor protectant compounds. These compounds are added to scavenge oxygen that otherwise could react with the polymer or additives therein to form off-taste producing aldehydes. Incorporation of these compounds into polyolefins is difficult, however, because these protectant compounds have an extremely low thermal stability. Furthermore, these compounds may themselves contribute to an off-taste in sensitive products, and hydrazides react with aldehydes to form hydrazones, which often are highly colored. Such colors oftentimes are unwanted, as many applications require or desire that the polyolefin packaging be white or clear.
A simple and economical method is therefore needed for reducing aldehyde content in polyolefin products without using aldehyde-scavenging agents that impart an off-taste to products packaged in containers made from polyolefins or that impart a color to such polyolefin containers.
It is therefore an object of the present invention to provide methods for decreasing aldehyde content of products in contact with polyolefin packaging materials.
It is another object of the present invention to provide methods for decreasing aldehyde content in polyolefin materials without coloring the polyolefin materials and without creating another source of product off-taste.
It is a further object of the present invention to provide polyolefin packaging containers which provide a decreased aldehyde content of products contained therein.
SUMMARY OF THE INVENTION
Methods are provided for decreasing the aldehyde content in polyolefin materials by combining the polyolefin material with an organic additive compound that reacts with aldehydes to form water and a resulting organic compound. The organic additive compound comprises at least two hydrogen-substituted heteroatoms bonded to carbons of the organic additive compound such that the organic additive compound is reactive with aldehydes present in the polyolefin to form water and the resulting organic compound, which comprises an unbridged five- or six-member ring including the at least two heteroatoms. The resulting organic compound neither imparts an off-taste to food and beverage products in contact with the polyolefin nor discolors the polyolefin.
The organic additive compound can be added at relatively low levels to the polyolefin and still sufficiently decrease the aldehyde content of the polyolefin. The organic additive compound preferably is substantially thermally stable at the melt processing temperature of the polyolefin. Preferred organic additive compounds include anthranilamide, 3,4-diaminobenzoic acid, malonamide, tryptophan, and allantoin.
DETAILED DESCRIPTION OF THE INVENTION
It has been discovered that the off-taste from beverage and food products packaged in polyolefin materials is in fact largely due to the migration of C
8
through C
10
aldehydes from the polyolefin into the products, and that these aldehydes typically are the degradation products of various unsaturated additives used as processing aids in the polyolefins. These additives degrade chemically, thermally, or by photo-oxidation to yield these undesirable aldehydes. Examples of processing aid additives are erucic acid derivatives, such as erucamide, which often is used as a processing aid additive due to its efficacy and low cost. Although one might propose eliminating the processing aid additives as a solution to the aldehyde problem, the processing properties provided by the unsaturated additives are important and not readily duplicated. It thus is desirable to continue the use of unsaturated additives while simultaneously minimizing or eliminating the off-taste caused by their degradation. Methods therefore have been developed for substantially decreasing the aldehyde content of processed polyolefins by incorporating low levels of an organic additive compound into the polyolefin, such as during melt processing. The organic additive compound scavenges the aldehyde present in the polyolefin by chemically reacting with the aldehyde.
The Aldehyde-Containing Polyolefin
The present method is useful for removing aldehydes from a variety of polyolefin materials. In preferred embodiments, the polyolefin is polypropylene (PP) or polyethylene (PE). Other useful polymers include polyisoprene, polystyrene, poly(vinyl chloride), and poly(methylmethacrylate). The present method can be used with essentially any polyolefin polymer in which unsaturated additives have been incorporated.
Polyolefins, such as PP and PE, can be processed to form films, sheets, and three-dimensional articles, which can be used as or in packaging containers and closures. As part of the processing of the polyolefin, for example, melt-processing (e.g., extrusion and molding), processing aids typically are added to achieve favorable product properties and/or to improve ease of polymer processing. Representative types of processing aid additives include internal lubricants, external lubricants, and viscosity modifiers. Many of these processing aid additives are unsaturated compounds. Euramide, for example, often is added to polyethylene and po
Liu Linda Hsiaohua
Rule Mark
Shi Yu
Standish John V.
Sutherland & Asbill & Brennan LLP
Szekely Peter
The Coca-Cola Company
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