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
2003-06-18
2004-06-01
Cheung, William (Department: 1713)
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...
C524S322000, C525S386000, C525S333700, C526S352000
Reexamination Certificate
active
06743845
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to oriented film of high density polyethylene, to compositions suitable for the preparation thereof, and to a process for its preparation.
2. Background Art
Polyethylene is available in numerous forms required of the various and distinct end uses for which it is destined. Polyethylene may be roughly divided into low density and high density grades. Within each grade, polyethylene may exhibit a variety of melt temperatures, melt flow ratios, melt viscosities, and the like. The physical properties of each type of polyethylene must be closely tailored to the specific end use; otherwise processing becomes problematic or even impossible. Thus, it is impossible, in general, to employ a polyethylene composition tailored for one type of processing in another type of processing. For example, low density polyethylene (LDPE) is widely used for preparation of films, and finds uses in such items as cargo wrap and plastic refuse bags. LDPE is relatively easy to formulate for such uses, and may contain numerous ingredients in addition to LDPE itself, i.e., pigments, UV absorbers, thermal stabilizers, plasticizers, lubricants, etc.
Oriented high density polyethylene (HDPE) is an altogether different product, and is formulated differently than its LDPE relative. By orienting HDPE, the strength and stiffness properties are markedly improved. As a result, stronger, and optionally thinner films may be prepared. The higher density and, in general, different physical properties of HDPE require different processing considerations, and orientation adds additional complexity. Oriented HDPE is generally extruded as a film, and water quenched. Films may also be chill roll cast, or blown and air quenched. The film is then uniaxially or biaxially stretched, optionally followed by annealing. The stretching operation takes place below the melt temperature, and may be termed a “hot stretch.” The stretching operation must take place without any substantial likelihood of breakage, as breakage requires that the entire orientation process be restarted, increasing process down-time and greatly increasing cost.
A variety of different types of HDPE may be successfully oriented as film, and such HDPE is commercially available. However, oriented film produced from such compositions is not necessarily optimal for certain applications, and thus improvements in HDPE oriented film are desirable. Moreover, up till now, solution processed HDPE has proven to be extremely difficult to prepare as oriented film. Solution-polymerized HDPE is prepared by polymerizing ethylene in solution, following which the solvent is removed and the polymer is pelletized. Solution-polymerized HDPE tends to stretch inconsistently, and thus the rate and/or amount of stretch must be decreased in order to orient the film without breaking, if orientation can be performed at all. Decreasing the amount of stretch generates a product having different and generally less desirable physical properties, while decreasing the rate of stretch results in increased production time and cost.
SUMMARY OF THE INVENTION
The present invention pertains to an HDPE composition containing a normally solid, long chain carboxylic acid having a melting point below the orientation temperature of the HDPE film. The compositions, even when employing solution-polymerized HDPE, have been found to stretch at commercially useful rates and stretch ratios without undue breakage. For HDPE which can be stretched without additives, adding long chain carboxylic acids lowers further the already low frequency of breakage occurring during commercial manufacturing processes, and may result in higher physical properties as a result of greater uniformity in the stretching operation.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
The HDPE used in the present invention is that conventionally recognized as HDPE by the skilled artisan, i.e., polyethylene homopolymers or copolymers having a density of from 0.94 to 0.965. In general, copolymeric HDPE contains 20 weight percent or less, particularly 10% by weight or less of copolymerizable comonomers. Suitable comonomers are well known in the art, with preferred comonomers being butene, hexene, and octene. The polyethylene may be made by conventional catalysts, i.e., of the Ziegler-Natta type, or may be made employing a wide variety of single site catalysts, for example STAR™ ethylene polymerization catalysts developed by EQUISTAR, Cincinnati, Ohio. Processes for preparing HDPE include all those in common use, including gas phase, slurry, and solution processes. Solution processed polyethylene is the preferred polyethylene in the present application. The resultant polyethylene, optionally including thermal and/or UV stabilizers, is commonly extruded and pelletized to form a polyethylene “raw material”.
The HDPE polyethylene raw material is extruded through a die into film. Prior to or while in the extruder, the HDPE raw material is compounded with any additional ingredients, generally including dyes and/or pigments, thermal and/or UV stabilizers, etc. These may be dosed into the extruder by themselves, or in master batches of HDPE containing larger than desired amounts of additives. Alternatively, master batches containing the desired ingredients may be mixed in the appropriate proportions with the HDPE raw material prior to entry into the extruder. The HDPE preferably contains no fillers, especially fillers which would cause disruption of the film such as the formation of voids.
In the present invention, the ability to stably orient extruded polyethylene films is induced or augmented by the addition of a small quantity of a normally solid carboxylic acid, one having a melting point below the film orientation temperature, preferably stearic acid, palmitic acid, or mixtures thereof, and most preferably, palmitic acid alone. Other low melting but normally solid fatty carboxylic acids may be used as well, one example being lignoceric acid. While the fatty carboxylic acids may contain ethylenic unsaturation, they must be normally solid, i.e. solid at 25° C. Thus, numerous common unsaturated fatty acids such as oleic acid, linoleic acid, and linolenic acid are not suitable for use herein, although they may find themselves useful as lubricants or plasticizers in very small amounts. The preferred fatty acids are saturated fatty acids, most preferably linear fatty acids such as occur in natural products, preferably natural products of vegetable origin.
The manner in which the normally solid, low melting fatty acid functions is not known with certainty. Without wishing to be bound to any particular theory, it is presently believed that the long chain fatty acids, having a structure similar to polyethylene, is able to be homogeneously dispersed in the polyethylene, where it functions to allow greater mobility between adjacent polyethylene polymer chains. The greater mobility is thought to reduce the inconsistencies otherwise associated with the orientation of polyethylene polymers.
The amount of solid, fatty acid is an amount effective to allow orientation without undue breakage, while maintaining desirable end properties. The actual amount is dependent to some degree on the particular HDPE, and thus may vary. However, the amount is virtually always less than 1% by weight (10,000 ppm), more preferably from about 200 ppm to 5,000 ppm, yet more preferably between 500 ppm and 3,000 ppm, and most preferably about 2,000 ppm, these weights in parts per million based on the sum of the weights of the polyethylene and the carboxylic acid in the finished composition. It should be noted that in addition to facilitating orientation, many of the properties of the oriented film are improved as well.
The solid, fatty acid is preferably supplied as a master batch, dispersed in the same or another HDPE. In certain circumstances, LDPE, LLDPE or other polyethylene homopolymers or copolymers may be introduced as well. Preferred master batches contain stearic acid or palmitic acid at a lev
Krohn James V.
Tate Richard F.
Cheung William
Equistar Chemicals L.P.
LandOfFree
Oriented high density polyethylene film, compositions and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Oriented high density polyethylene film, compositions and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Oriented high density polyethylene film, compositions and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3333831