Single layered polypropylene containers and their use

Details Single layered polypropylene containers and their use Single layered polypropylene containers and their use

1999-03-05

2003-05-06

Nolan, Sandra M. (Department: 1772)

Stock material or miscellaneous articles

Hollow or container type article

Polymer or resin containing

C053S425000, C053S428000, C053S524000, C428S036600

Reexamination Certificate

active

06558764

ABSTRACT:

CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
FEDERALLY SPONSORED RESEARCH
Not Applicable
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to packaging for hygroscopic resin materials, and more particularly the invention relates to methods for packaging a hygroscopic resin composition wherein said method comprises packaging the composition into a mono-layer container comprising polypropylene resin and wherein the container has a wall thickness of between 0.25 mm and 0.6 mm. In a preferred embodiment, the composition comprises at least one polyamide resin or a compatibilized blend of polyphenylene ether resin and polyamide resin.
2. Brief Description of the Related Art
Many engineering resins such as polyurethane resin, polycarbonate resins, polyester resins, and polyamide resins as well as various blends containing these resins are hygroscopic to varying degrees and absorb moisture from the air. In manufacturing processes for the resins special handling precautions are necessary to minimize the water absorption. Often the resins are produced as small pellets that are packaged for shipment to a molder or converter into articles of commerce. The pellets are typically dried by the molder to reduce the level of absorbed water to very low levels to avoid issues such as material degradation and surface appearance issues. Unfortunately, if water is allowed to absorb throughout the thickness of the pellets, extremely long drying times are required for the water to migrate out from the pellet. Consequently manufacturers of such resins take special precautions to both minimize the water level that is packaged with the pellets and utilize packaging that allows very little moisture permeation. Resins may remain packaged for many months before being used so moisture pickup by the resins while packaged is highly likely to occur, this is however highly undesirable. Moreover, the packaging cost needs to be minimized since most packaging is discarded after a single use.
Conventional manufacturing processes for such resins often involve use of a compounding extruder to mix the resin with any additional components. The material typically exits the extruder through a die in the form of numerous strands which are in turn cooled in a water bath and chopped into pellets for packaging. By controlling the degree of cooling in the water bath and allowing the strands to dry any residual moisture before chopping into pellets, manufacturers can control the level of moisture in the pellets up to the packaging stage. In order to maintain the level of water very low, special packaging must be used that has a very low water permeation level. Conventional packaging is often a multi-layer structure, for example, a two-layer structure of an aluminum foil adhered to a second layer, often made from polyethylene or polyvinyl chloride. Three layer structures for packaging are also used wherein the aluminum foil layer is sandwiched between two plastic resin layers. These conventional packagings have sufficient moisture barrier properties to maintain very low water levels in the packaged resin materials, however, these packages require special handling for loading and sealing, are very expensive, and are not recycleable and must be landfilled or burned after a single use. Methods have been developed to avoid the multi-layer packaging and utilize more conventional single layer packaging. For example, single layer polyethylene bags having a thickness of 0.2 mm have been used to package polyamide resins. The low melting point of the polyethylene requires that the pellets be cooled to a low temperature before packaging to avoid having the packaging distort or have pellets of the resin adhere to the packaging. Special manufacturing equipment and/or modifications to the aforementioned strand cooling and chopping procedures are necessary to meet the temperature limitation of the polyethylene package and maintain a low moisture level in the pellets. With such known packaging it cannot be avoided that the moisture content of the resin increases too much over time, making it necessary to dry the resin before molding it.
It is therefore apparent that there continues to be a need for improved methods for packaging hygroscopic resins.
SUMMARY OF THE INVENTION
The invention relates to packaging for hygroscopic resin materials, and more particularly the invention relates to methods for packaging a hygroscopic resin composition wherein said method comprises packaging the composition into a mono-layer container comprising polypropylene resin and wherein the container has a wall thickness of between 0.25 mm and 0.6 mm. In a preferred embodiment, the composition comprises at least one resin of the group consisting of polyurethanes, polycarbonates, polyesters, and polyamides. These and other embodiments of the invention will become apparent as described herein.
DESCRIPTION OF THE DRAWINGS
Not applicable
DETAILED DESCRIPTION OF THE INVENTION
According to this invention, there is provided a packaging structure of a monolayer comprising polypropylene resin wherein the mono-layer is between 0.25 mm and 0.60 mm, preferably between 0.28 mm and 0.40 mm. The package structure is free of a metal layer, such as an aluminum foil layer. The packaging structure may vary widely in size, such as from vary small packages of a few grams of material to fairly large, for example, as a liner in a bulk package of 500 kg or more. After filling the package with the desired amount of material, the package can be sealed by conventional methods such as, for example, heat sealing or sealing with an adhesive. The package can be manufactured by methods known in the packaging art.
Although most any resin material may be packaged in accordance with the present invention, it is most useful for packaging hygroscopic resin materials. Such hygroscopic resin materials include any resin that needs to have a moisture pick-up below about 0.15 weight percent water, preferably below about 0.10 weight percent water after being packaged for about 180 days. This invention is especially useful for packaging polyurethanes, polycarbonates, polyesters, and polyamides as well as various blends and alloys containing at least one of the aforementioned resins.
In a preferred embodiment of the invention, the resin material comprises at least one polyamide resin. The polyamide containing resin may be a conventional polyamide resin, for example, nylon-6, nylon-6,6, nylon-12 or may be a filled polyamide containing, for example, glass fibers and/or mineral fillers. Alternatively, the polyamide resin may be a compatibilized blend of at least one polyamide and at least one second resin material such as, for example, an elastomer or a polyphenylene ether resin. In an especially preferred embodiment, the resin composition comprises a compatibilized blend of a polyphenylene ether resin and a polyamide resin.
Compatibilized blends of a polyphenylene ether resin and a polyamide resin are generally known in the art. These blends are typically made through reactive compounding techniques involving addition of a compatibilizing agent to compositions containing polyphenylene ether resin and polyamide resin. The compatibilizing agent is thought to result in reaction products between the polyphenylene ether resin and a polyamide resin and that these reaction products improve the compatibility between the polyphenylene ether resin and polyamide resin. The improved compatibility results in enhanced physical properties such as, for example, increased ductility. Illustrative compatibilizing agents for blends of polyphenylene ether resin and polyamide resin include citric acid, maleic anhydride, fumaric acid, malic acid as well as various derivatives of the foregoing.
The ratio of polyphenylene ether resin to polyamide resin can vary widely but is preferably adjusted so that the polyamide resin remains the continuous phase. Preferably the polyamide is at least about 40% by weight of the total resin composition. Increasing the level of the polyamide results in enhanced ductil

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