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Novel polyethylene filmsRelated Patent Categories: Synthetic Resins Or Natural Rubbers -- Part Of The Class 520 Series, Natural Rubber Compositions Having Nonreactive Materials (dnrm) Other Than: Carbon, Silicon Dioxide, Glass Titanium Dioxide, Water, Hydrocarbon, Halohydrocarbon, Ethylenically Unsaturated Reactant Admixed With A Preformed Reaction Product Derived From: (a) At Least One Polycarboxylic Acid, Ester, Or Anhydride; (b) At Least One Polyhydroxy Compound; And (c) At Least One Fatty Acid Glycerol Ester, Or A Fatty Acid Or Salt Derived From A Naturally Occurring Glyceride, Tall Oil, Or A Tall Oil Fatty Acid, At Least One Solid Polymer Derived From Ethylenic Reactants Only, Polymer Mixture Of Two Or More Solid Polymers Derived From Ethylenically Unsaturated Reactants Only; Or Mixtures Of Said Polymer Mixture With A Chemical Treating Agent; Or Products Or Processes Of Preparing Any Of The Above MixturesNovel polyethylene films description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060036039, Novel polyethylene films. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] The present invention relates to copolymers of ethylene and alpha-olefins in particular to low density copolymers and also to novel films produced from said copolymer having improved properties in particular improved stretch and creep characteristics. [0002] In recent years there have been many advances in the production of polyolefin copolymers due to the introduction of metallocene catalysts. Metallocene catalysts offer the advantage of generally higher activity than traditional Ziegler catalysts and are usually described as catalysts which are single-site in nature. Because of their single-site nature the polyolefin copolymers produced by metallocene catalysts often are quite uniform in their molecular structure. For example, in comparison to traditional Ziegler produced materials, they have relatively narrow molecular weight distributions (MWD) and narrow Short Chain Branching Distribution (SCBD). [0003] Although certain properties of metallocene products are enhanced by narrow MWD, difficulties are often encountered in the processing of these materials into useful articles and films relative to Ziegler produced materials. In addition, the uniform nature of the SCBD of metallocene produced materials does not readily permit certain structures to be obtained. [0004] Recently a number of patents have published directed to the preparation of films based on low density polyethylenes prepared using metallocene catalyst compositions. [0005] WO 94/14855 discloses linear low density polyethylene (LLDPE) films prepared using a metallocene, alumoxane and a carrier. The metallocene component is typically a bis (cyclopentadienyl) zirconium complex exemplified by bis (n-butylcyclopentadienyl) zirconium dichloride and is used together with methyl alumoxane supported on silica The LLDPE's are described in the patent as having a narrow Mw/Mn of 2.5-3.0, a melt flow ratio (MFR) of 15-25 and low zirconium residues. [0006] WO 94/26816 also discloses films prepared from ethylene copolymers having a narrow composition distribution. The copolymers are also prepared from traditional metallocenes (eg bis (1-methyl, 3-n-butylcyclopentadienyl) zirconium dichloride and methylalumoxane deposited on silica) and are also characterised in the patent as having a narrow Mw/Mn values typically in the range 3-4 and in addition by a value of Mz/Mw of less than 2.0. [0007] However, it is recognised that the polymers produced from these types of catalyst system have deficiencies in processability due to their narrow Mw/Mn. Various approaches have been proposed in order to overcome this deficiency. An effective method to regain processability in polymers of narrow Mw/Mn is by the use of certain catalysts which have the ability to incorporate long chain branching (LCB) into the polymer molecular structure. Such catalysts have been well described in the literature, illustrative examples being given in WO 93/08221 and EP-A-676421. [0008] Furthermore, WO 97/44371 discloses polymers and films where long chain branching is present, and the products have a particularly advantageous placement of the comonomer within the polymer structure. Polymers are exemplified having both narrow and broad Mw/Mn, for example from 2.19 up to 6.0, and activation energy of flow, which is an indicator of LCB, from 7.39 to 19.2 kcal/mol (31.1 to 80.8kJ/mol). However, there are no examples of polymers of narrow Mw/Mn, for example less than 3.4, which also have a low or moderate amount of LCB, as indicated by an activation energy of flow less than 11.1kcal/mol (46.7kJ/mol). [0009] We have now found that it is possible to prepare copolymers of ethylene and alpha-olefins having narrow Mw/Ma and low or moderate amounts of LCB. These polymers are suitable for many applications which will be known to those skilled in the art, but in particular are advantageous for preparing films with an excellent balance of processing, optical and mechanical properties. [0010] In particular the present invention is particularly directed to stretch films with excellent cling properties and to blown films suitable for use for heavy duty sacks. [0011] Our copending application WO 00/68285 describes copolymers of ethylene and an alpha olefin having 3 to 10 carbon atoms, said copolymers having [0012] (a) a density in the range 0.900 to 0.940 [0013] (b) an apparent Mw/Mn of 2-3.4 [0014] (c) I.sub.21/I.sub.2 from 16 to 24 [0015] (d) activation energy of flow from 28 to 45 kJ/mol [0016] (e) a ratio Ea(HMW)/Ea(LMW) >1.1, and [0017] (f) a ratio g'(HMW)/g'(LMW) from 0.85 to 0.95. [0018] These copolymers may be used to prepare the full range of products normally manufactured from polyethylene copolymer products in the density range 0.900 to 0.940 kg/m.sup.3. Examples of applications for the copolymers include injection moulding, rotomoulding, extrusion into pipes, sheets, films, fibres, non-woven fabrics, cable coverings and other uses which will be known to those skilled in the art. are particularly suitable for the production of films and sheets prepared using traditional methods well known in the art. Examples of such methods are film blowing, film casting and orientation of the partially crystallised product. The films exhibit good processability, improved optical and mechanical properties and good heat sealing properties. [0019] WO 00/68285 described blown films from such copolymers having haze ranging from 3 to 20, dart impact >100 g and hexane extractables in the range 0.1-1.5%. Such films also exhibited a MD tear strength in the range 106-210 g/25 .mu.m. [0020] The application of polyethylene films in stretch wrapping has been considerably enhanced by the use of linear low density polyethylene (LLDPE) type products. When formed into a film for stretch wrap application, LLDPE products typically combine a high extensibility with good mechanical properties to provide a wrapping or collation function to be achieved in an economic and effective manner. In this respect, LLDPE has significant advantages over LDPE which, due to both its behaviour in extension and its mechanical performance, is not normally regarded as a product of choice for stretch wrapping applications. [0021] Application of stretch wrap films may be either by hand or by machine. The film may be either wrapped directly onto the article or articles to be packaged, or it may undergo a pre-stretching operation prior to wrapping. Pre-stretching typically enhances the mechanical property of the film and provides a more effective packaging and more efficient coverage for a given unit mass of film. Hence the response of the film to either a pre-stretch or the stretch applied during wrapping is an important parameter affecting film performance. In particular for a given film width and thickness the efficiency with which an object is wrapped is affected by the degree to which the film can be thinned during the stretching and the loss of film width which may occur at the same time. The resistance to sudden impact events, puncture by sharp objects and the ability to maintain a tension sufficient to maintain the package in the desired shape and configuration are also important parameters. [0022] A further requirement in many stretch wrapping applications is that the film displays a certain degree of adhesive or cling behaviour enabling a firm closure of the package to be achieved without resort to use of additional securing measures such as straps, glues or heat sealing operations. For monolayer films, such adhesion may be provided by the intrinsic film properties or by using a "cling" additive in the film formulation. An example of a cling additive which is widely used is poly(isobutene) (PIB) which term is taken to include polybutenes produced from mixed isomers of butene. For multi-layer films, it is relatively easy to provide one or more surface layers which are specifically formulated to provide cling. In general this method allows a more flexible approach to film manufacture as choice of product for the main body of the film may be made on the basis of mechanical performance and the surface layers can be specially formulated for adhesion. Those skilled in the art will appreciate the multiplicity and flexibility of the choices of possible film structures. [0023] A further requirement for the film producer is that the fabrication of the film is made as easy as possible by the use of polyethylenes having processing characteristics which allow film extrusion to be carried out as easily as possible. The use of a product of lower molecular weight or broader molecular weight distribution provides easier processability, but normally at the expense of a reduction in mechanical performance of the film. Similarly the use of products such an LDPE containing long chain branches (LCB) may assist processability but at the expense of stretchability in the subsequent wrapping process. [0024] We now found that a particularly advantageous combination of film properties may be obtained by producing a stretch film from the novel copolymers described in the aforementioned WO 00/68285. The films have a particularly advantageous combination of properties, combining high impact resistance with easy processability and good performance in stretch wrapping and when combined with polyisobutene as a cling enhancer, the films show a particularly advantageous control of cling force. [0025] Thus according to the present invention there is provided a stretch film comprising a cling additive in amount >0.5% and having [0026] (a) dart impact of >450 g [0027] (b) MD tear strength of >190 g/25 .mu.m [0028] (c) MD elongation at break of >450% [0029] said film comprising a copolymer of ethylene and an alpha-olefin having from 3 to 10 carbons atoms, said copolymer having [0030] (a) a density in the range 0.900 to 0.940 [0031] (b) an apparent Mw/Mn of 2-3.4 [0032] (c) I.sub.21/I.sub.2 from 16 to 24 [0033] (d) activation energy of flow from 28 to 45 kJ/mol [0034] (e) a ratio Ea(HMW)/Ea(LMW) >1.1, and [0035] (f) a ratio g'(HMW)/g'(LMW) from 0.85 to 0.95. [0036] The preferred stretch films according to the present are those having a dart impact of >600 g and most preferably >1100 g. [0037] The preferred films show an elongation of >500%. [0038] The cling additive may be present in amount >2% and most preferably in amount of greater than or equal to 4%. [0039] The preferred cling additive is polyisobutene (PIB). Continue reading about Novel polyethylene films... Full patent description for Novel polyethylene films Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Novel polyethylene films patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Novel polyethylene films or other areas of interest. ### Previous Patent Application: Thermoplastic molding compositions Next Patent Application: Thermoplastic elastomer compositions Industry Class: Synthetic resins or natural rubbers -- part of the class 520 series ### FreshPatents.com Support Thank you for viewing the Novel polyethylene films patent info. 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