Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
1998-06-05
2002-08-13
Wilson, D. R. (Department: 1713)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S910000, C524S570000, C524S587000, C525S211000, C525S240000
Reexamination Certificate
active
06432496
ABSTRACT:
FIELD OF THE INVENTION
This invention relates High Density Polyethylene (HDPE) films having improved barrier properties. More particularly, the invention relates to HDPE films containing hydrocarbon resins having improved moisture barrier, and the process of making said films.
BACKGROUND OF THE INVENTION
Polyolefins are plastic materials useful for making a wide variety of valued products due to their combination of stiffness, ductility, barrier properties, temperature resistance, optical properties, availability, and low cost.
The use of terpene and hydrogenated hydrocarbon resins as modifiers for polypropylene (PP) converted into oriented film is well known. Some of the attributes assigned to the use of low molecular weight resin products in polypropylene films, include good optical properties, improved processing when making oriented films, better sealing characteristics, and desirable mechanical properties and converting characteristics.
The use of hydrocarbon resins (HCR) for improving the moisture barrier properties of oriented polypropylene is also well known. The effectiveness of resin for improving barrier properties is expected to be highly dependent on the characteristics of the PP itself. These characteristics include the degree of crystallinity of the PP, the compatibility of the resin with the polypropylene amorphous regions and the amorphous region's glass transition.
Additionally, it has been generally known that high levels of hydrocarbon resin were required to cause substantial improvements in barrier properties of polypropylene film, typically in the range 5% to 25% by weight. However, adding resin at these levels typically embrittles non-oriented PP film to an excessive degree. In oriented polypropylene (OPP) film, the orientation imparted to the polymer offsets the negative effect of the resin on ductility, so that films with good mechanical properties can be produced at the high loadings of hydrocarbon resin required to impart improvements in barrier properties.
Because of differences between ethylene polymers and polypropylene in crystallinity level, glass transition temperature, and amorphous character (linear vs. branched aliphatic structure), the effects of hydrocarbon resins in polyethylene films can not be strictly predicted based on analogy with oriented polypropylene films. Additionally, because most polyethylene films possess a relatively low degree of molecular orientation as compared to OPP films, the ability to incorporate hydrocarbon resins in polyethylene films at an effective level without ruining mechanical properties is an area of concern.
High density polyethylene (HDPE) is nominally a linear homopolymer of ethylene containing few branch points in the polymer chain. As a result of its regular structure, HDPE is a highly crystalline material with a peak crystalline melting point typically around 135° C. Various types of HDPE are characterized by the density of the material, which ranges typically from 0.940 to 0.965 (g/cc). Density is a measure of the crystallinity developed by the HDPE material, where higher density relates to higher the level of crystallinity developed by the polymer. Mechanical properties and barrier properties are strongly influenced by the degree of crystallinity developed in the HDPE polymer.
Typical uses are in the production of blow molded containers such as milk bottles, molded articles, lightweight consumer bags and trash bags, and various types of film products.
One example of a HDPE film product is the inside liner used to package cereal products. In this and similar packaging applications, superior barrier properties of the HDPE, relative to non-oriented PP or low density PE films, is a very positive attribute of the HDPE film. One type of barrier property refers to preventing the permeation of moisture either in or out of the packaged food product.
The need exists for a method for a method for the incorporation of various hydrocarbon resins into high density polyethylene polymers (HDPE). The need also exists for films which possess superior barrier properties and still retain desirable mechanical properties such that the films can be used for packaging film applications where improved barrier properties of these films have value. Additionally, the need exists for a highly efficient process for producing films of HDPE modified with hydrocarbon resin. It has been found that by adding various types of hydrocarbon resins to HDPE polymer to form a blend, and forming a film from the blend, a superior packaging film can be produced with improved moisture barrier properties than films produced from the HDPE polymer by itself. These improved barrier films have value in packaging applications where a reduced rate of moisture loss (or gain) increases the shelf life of the packaged material. In the opposite sense, by improving the barrier properties of the HDPE film the thickness of the film used to package a material may be reduced, lowering the amount of packaging material required, and, as a result, reducing the amount of refuse derived from packaging film.
SUMMARY OF THE INVENTION
A polyethylene film comprising about 3% to about 25% by weight of a resin and about 97% to about 75% by weight of a polyethylene. The resin has a weight average molecular weight Mw of less than about 10,000 Daltons, as determined using size exclusion chromatography (SEC) using polystyrene as a standard. Resins of Mw less than 5,000 Daltons being preferred, for example resins having Mw of at least about 500 Daltons to about 2,000 Daltons being most preferred. The polyethylene has a density in the range from about 0.940 to about 0.970 g/cc, as measured at 23° C. according to ASTM D1505. Barrier properties improve as density or crystallinity of the, preferably from about 0.940 to about 0.965 g/cc. Preferably, the film comprises about 3% to about 15% of the hydrocarbon resin.
The resin further comprises hydrocarbon resin derived by thermally polymerizing olefin feeds rich in dicyclopentadiene (DCPD). Alternatively, the resin may be hydrocarbon resin derived from the polymerization of a C9 hydrocarbon feed stream. Either of the above hydrocarbon resins may be either fully or partially hydrogenated.
Alternatively, the hydrocarbon resin may be resin derived from polymerization of pure monomers, wherein the pure monomers are selected from the group consisting of such as styrene, a-methylstyrene, 4-methylstyrene and vinyltoluene.
Alternatively, the resin may be produced from terpene olefins.
The polyethylene film may comprises a cast film or an oriented film. If the polyethylene film comprises an oriented film, it may comprise a monoaxial or biaxial oriented film. The biaxially oriented film may be produced through a blown film process or through a tenter frame orientation process.
The invention also relates to a masterbatch for the production of polyethylene films, its preparation and the use of the masterbatch wherein the masterbatch comprises a resin and an ethylene polymer wherein the resin has a weight average molecular weight Mw of less than about 10,000 Daltons, as determined using size exclusion chromatography (SEC) using polystyrene as a standard. Resins of Mw less than 5,000 Daltons being preferred, for example resins having Mw of at least about 500 Daltons to about 2,000 Daltons being most preferred. The ethylene polymer has a density in the range from about 0.87 to about 0.965, as measured at 23° C. according to ASTM D1505. The masterbatch further comprises about 2% to about 25% by weight ethylene polymer and about 98% to about 75% by weight resin. Preferably, the masterbatch comprises about 70 to about 80% by weight resin.
The invention also relates to a process of producing a polyethylene film comprising the steps of a) blending a polyethylene with a resin to form a blend, and b) extruding the blend to form a film. The film comprises about 3% to about 25% by weight of a resin and about 97% to about 75% by weight of a polyethylene wherein the resin has a weight average molecular weight Mw of less than about 10,000 Daltons, as det
Boshears B. J.
Eastman Chemical Company
Graves, Jr. Bernard J.
Wilson D. R.
LandOfFree
High density polyethylene films with improved barrier... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High density polyethylene films with improved barrier..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High density polyethylene films with improved barrier... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2972125