BRPI0404121B1 - MULTIPLE LAYER FILM - Google Patents

Description

Patent Descriptive Report for "MULTIPLE LAYER FILM".

FIELD OF THE INVENTION The invention relates to co-extruded film shrink film structures and polyethylene blends used therefor.

Background of the Invention Collation shrinkage refers to the baling of bundled items using a heat shrinkable film. Glue shrinkage is used in a very wide variety of applications and notably for secondary packaging of food or beverages. Examples include metal cans and plastic bottles.

Typically, films are applied at room temperature and placed under a heat source to shrink. Appropriate performance characteristics in the shrink baling line include sufficient stiffness to allow the film to wrap correctly around the items to be wrapped, sufficient dimensional shrinkage to ensure a comfortable fit and a low coefficient of friction (COF). enough for packaging handling and handling. Films suitable for use with glue shrinkage should have a high thermal shrink force to ensure a firm fit and high tensile strength to withstand handling and misuse during transport.

In addition, the packaging should have excellent display properties including brightness (preferably at different angles to maximize appeal), turbidity (or "contact transparency") and transparency ("transparency seen through packaging").

Finally, the manufacturer of glue shrink films aims at low melt pressure properties and the ability to use low engine power, both allowing for higher production rates.

Although it is known to improve many of the above-mentioned properties individually, currently available structures do not combine all properties satisfactorily into a film having a size sufficiently thin to be commercially attractive.

Polyethylene is an attractive component for use in glue shrink film. Various types of polyethylenes are known in the art. Low density polyethylene ("LDPE") may be prepared under high pressure using free radical initiators and typically having a density in the range 0.916-0.940 g / cm3. LDPE is also known as "branched" or "heterogeneously branched" polyethylene due to the relatively large number of long chain extensions extending from the main structure of the main polymer. Polyethylene in the same density range, that is, 0.916 to 0.940 g / cm3, which is linear and does not contain large amounts of long chain branching, is also known; This "linear low density polyethylene" ("LLDPE") can be produced with conventional Ziegler-Natta catalysts or single site catalysts such as metallocene catalysts. Relatively higher density LDPE or LLDPE, typically in the range of 0.928 to 0.940 g / cm3, is sometimes referred to as medium density polyethylene ("MDPE") or linear medium density polyethylene (LMDPE). Polyethylenes having even higher density are high density polyethylenes ("HDPEs"), that is, polyethylenes having densities greater than 0.940 g / cm3, and are generally prepared with Ziegler-Natta catalysts, chromium catalysts or even single site catalysts. as metallocene catalysts. Very low density polyethylene ("VLDPE") is also known. VLDPEs can be produced by several different processes giving polymers with different properties, but can generally be described as polyethylenes having a density of less than 0.916 g / cm3, typically 0.890 to 0.915 g / cm3 or 0.900 to 0.915 g / cm3. US Patent 6,187,397 teaches a 3-layer co-extruded heat shrinkable film devoid of metallocene polyethylene. The patent teaches that prior art "high transparency" heat shrinkable polyethylene films are obtained by three-layer co-extrusion comprising a predominantly free radical (> 50 wt%) polyethylene core layer having a density 0.918 - 0.930, optionally with HDPE for stiffness, sandwiched between two layers of predominantly linear (80-90% by weight) metallocene polyethylene having a density of 0.918 - 0.927. US 6,340,532 describes shrink films made from "pseudo-homogeneous" linear low density polyethylene resins, preferably prepared with an advanced Ziegler Natta catalyst. Several deficiencies of "homogeneous" resins, ie metallocene resins, used in the prior art shrink films are discussed. US 6,368,545 teaches a high transparency multilayer blown co-extruded film prepared using special methods, wherein a film having a central HDPE core is described. US Patent Application No. 20020187360 is directed to a heat shrinkable co-extruded polyethylene film laminate having a relatively high melting core layer comprising a linear low density polyethylene (LLDPE) having a density of 0.910 - 0.930 g / cm3 and a very low density linear polyethylene (VLDPE) having a density of 0.880 - 0.915 g / cm3 sandwiched between two relatively higher melting surface layers comprising a linear low density polyethylene and a linear high density polyethylene. WO 01/44365 describes a homogeneous mixture of a metallocene catalyzed medium density polyethylene (mMDPE) with a low density polyethylene (LDPE) to produce blown films. The mixture may be coextruded between LDPE layers to produce blown films having, as taught in the reference, the good optical properties of LDPE and the good processing and mechanical properties of MDPE.

Additional patents of interest include US Patent No. 6,492,010, US Statutory Registration H2073, WO 95/00333 and EP 0597502. The high gloss obtained by metallocene polyethylenes is a very attractive property. However, film layers comprising metallocene polyethylene have a very high coefficient of friction in the absence of specific additives. These additives, in turn, decrease the desired optical properties in the gluing shrink films. A film exploiting the high gloss capacities of metallocene polyethylene, which can be produced effectively, and having the properties sought in a glue shrink film, is highly desirable. The present inventor has surprisingly found that an improved gluing shrink film can be obtained by a structure having a core layer comprising HDPE and film layers comprising metallocene polyethylene and optionally at least one of the HDPE or LDPE resins.

Summary of the Invention The invention is directed to a film structure having at least two layers: a layer comprising HDPE and the layer comprising a metallocene catalyzed polyethylene (hereinafter mPE), optionally further comprising at least one of HDPE or LDPE. The invention is further directed to a shrink-wrapped structure comprising shrinkage of the film wrapped around various items.

In a preferred embodiment, the film structure comprises a core layer comprising HDPE sandwiched by two layers of metallocene film. In a more preferred embodiment, at least one of said metallocene film layers further comprises at least one of HDPE or LDPE. It is an object of the present invention to provide various embodiments of the above inventions having unique properties, particularly with respect to optical, strength and processing properties, as well as performance in the resulting shrinkage structure.

Another object of the present invention is to provide a glue-wrapping film having proper performance in the shrinkage winding line. It is yet another object of the present invention to provide a shrinkage bonding film having properties suitable for handling abuse during transport. It is yet another object of the present invention to provide a shrink wrapped structure having attractive display properties at the point of sale.

These and other objects, aspects and advantages will become apparent with reference to the following detailed description, preferred embodiments, examples and appended claims.

Detailed Description In one embodiment, a film structure is provided having at least two layers. One layer, referred to herein as the first layer and in one embodiment as the core layer, comprises a high density polyethylene (hereinafter "HDPE") and the second layer, also referred to herein as at least one film layer, comprises a single site catalyzed polyethylene such as metallocene polyethylene or mPE.

As used herein, HDPE means polyethylene having a density greater than 0.940 g / cm3. The terms "high density polyethylene" polymer and "HDPE" polymer refer to an ethylene homopolymer or copolymer having a density greater than 0.940 g / cm. Polymers having more than two types of monomers, such as terpolymers , are also included in the term "copolymer" as used herein.

Comonomers which are generally usable to produce the HDPE copolymers usable in the present invention include alpha olefins such as C3 -C20 alpha olefins and preferably C3 -C12 alpha olefins. The alpha olefin comonomer may be linear or branched, and two or more comonomers may be used, if desired. Examples of suitable comonomers include C3 -C12 alpha olefins, and alpha olefins having one or more C1 -C3 alkyl extensions, or an aryl group. Specific examples include propylene; 3-methyl-1-butene; 3,3-dimethyl-1-butene; 1-pentene; 1-butene; 1-pentene with one or more methyl, ethyl or propyl substituents; 1-hexene; 1-hexene with one or more methyl, ethyl or propyl substituents; 1-heptene with one or more methyl, ethyl or propyl substituents; 1-decene; 1-dodecene; 1-octene with one or more methyl, ethyl or propyl substituents; 1-nonene with one or more methyl, ethyl or propyl substituents; 1-decene substituted with ethyl, methyl or dimethyl; 1-dodecene; and styrene. It should be appreciated that the list of comonomers above is simply illustrative, and is not intended to be limiting.

Preferred comonomers include propylene, 1-butene, 1-pentene, 4-methyl-pentene, 1-hexene, 1-octene and styrene. Other usable comonomers include polar vinyl, conjugated and unconjugated dienes, and acetylene and aldehyde monomers, which may be included in minor amounts in terpolymer compositions. Unconjugated dienes usable as comonomers are preferably straight chain hydrocarbon diolines or cycloalkenyl substituted alkenes having 6 to 15 carbon atoms. Suitable unconjugated dienes include, for example: (a) straight chain acyclic dienes such as 1,4-hexadiene and 1,6-octadiene; (b) branched chain acyclic dienes, such as 5-methyl-1,4-hexadiene; 3,7-dimethyl-1,6-octadiene; and 3,7-dimethyl-1,7-octadiene; (c) single ring alicyclic dienes such as 1,4-cyclohexadiene; 1,5-cyclooctadiene and 1,7-cyclododecadiene; (d) multi-ring alicyclic fused and attached ring dienes such as tetrahydroindene; norbomadiene; methyl tetrahydroindene; dicyclopentadiene (DCDP); bicyclo- (2,2,1) -hepta 2,5-diene, alkenyl, alkylidene, cycloalkenyl and cycloalkylidene norbornenes, such as 5-methylene-2-norbomene (NINB), 5-propenyl-2-norbomene, 5-isopropylidene 2-norbomene, 5- (4-cyclopentyl) -2-norbomene, 5-cyclohexylidene-2-norbomene and 5-vinyl-2-nor-bornene (VNB); and (e) cycloalkenyl substituted alkenes such as vinyl cyclohexene, allyl cyclohexene, vinyl cyclohekenene, 4-vinyl cyclohexene, allyl cyclodecene and vinyl cyclododecene. Of the typically unconjugated dienes used, preferred dienes are dicyclopentadiene, 1,4-hexadiene, 5-methylene-2-norbomene and 5-ethylidene-2-norbomene. Particularly preferred diolefins are 5-ethylidene-2-norbomene (ENB), 1,4-hexadiene, dicyclopentadiene (DCPD), norbornadiene and 5-vinyl-2-norbornene (VNB). The amount of comonomer used will depend on the desired density of the HDPE polymer and the specific comonomers selected, taking into account processing conditions such as temperature and pressure and other factors such as the presence or absence of telomeres and others, as may be apparent. one skilled in the art having the present disclosure.

In one embodiment, the HDPE polymer has a density greater than 0.940 g / cm3, preferably from about 0.940 g / cm3 to about 0.970 g / cm3, more preferably from about 0.955 g / cm3 to about 0.965 g / cm3. and most preferably from about 0.960 g / cm3 to about 0.965 g / cm3. The densities referred to herein are in accordance with ASTM D1505.

In one embodiment, the HDPE polymer may have a melt index of 0.01 to 45 g / 10 min as measured according to condition E of ASTM-1238. HDPE polymer may be produced using any conventional polymerization process such as a solution, a slurry, or a gas phase process, and a suitable catalyst such as chromium catalyst, a Ziegler-Natta catalyst or a metallocene catalyst. It is preferred that HDPEs used in the mixtures according to the present invention be produced using Ziegler-Natta catalysts.

Examples of suitable HDPEs usable in the present invention include HDPEs available from ExxonMobil Chemical Co., Houston, Texas, under the HD, HDA, HMA, HRA, HRP, HDZ or HYA series or under the trademark PAXON. Examples of HDPE include HYA800, gas phase produced, and HDZ222, produced by the stirred slurry process. Mixtures of two or more HDPE polymers and one or more HDPE polymers with one or more non-HDPE polymers are also contemplated. The first layer HDPE component (or, in the case of a three layer embodiment, the "core layer" HDPE component, described more fully below) must be present in an amount of from about 1 wt% to 50 wt% preferably between about 10 wt% and 50 wt%, more preferably between about 15 wt% and 45 wt%. The first layer (or, in one embodiment, core layer) should also comprise from about 99 wt% to 50 wt% LDPE, preferably from about 90 wt% to 50 wt%, more preferably from about from 85 wt% to 55 wt%, even more preferably from about 85 wt% to about 65 wt% LDPE. In a preferred embodiment, the first layer may also comprise another polyolefin, such as LLDPE (e.g., a trim blend). Suitable LDPE for use in the present invention is free radical initiated LDPE having a density in the range of 0.916 to 0.940 g / cm3, preferably 0.924 to 0.940 g / cm3. In one embodiment, the LDPE mixed with HDPE in the first layer or core layer has a density in the range of 0.916 to 0.935 g / cm3, more preferably 0.926 to 0.935 g / cm3. In another embodiment, LDPE mixed with HDPE in this layer has a density in the range of 0.916 to 0.927 g / cm3, and more preferably 0.921 to 0.926 g / cm3. Other embodiments include LDPEs having densities between any of the lower density limits specified at any of the higher density limits specified herein, for example 0.921 to 0.940 g / cm3 and 0.926 to 0.940 g / cm3. Preferred specific LDPEs are LD170BA and experimental types EX489BA and EX514BA. Also available from ExxonMobil Chemical Co., Houston, TX.

Additional polyolefins may be added, such as VLDPE, provided that the above mentioned weight% of HDPE and LDPE is found. Similarly, the mixture of HDPE and LDPE may include various additives, as discussed in more detail below. However, in one embodiment, it is preferred that the blend of HDPE and LDPE, comprising the first layer or core layer of the film structure, does not contain slip or antiblock additives. In a preferred embodiment, this layer does not contain any metallocene polyethylene. In another embodiment, mPE may be added, particularly where additional stiffness is required. The composition of this layer may further comprise polypropylene or may be without polypropylene. Other non-limiting examples of embodiments of the invention include combinations of the above-mentioned embodiments, such as the HDPE / LDPE blend of the invention, without slip or antiblock additives, without a metallocene polyethylene, and without polypropylene, a embodiment comprising a blend of HDPE LDPE of the invention without slip or antiblock additive, and with a metallocene polyethylene, and the like. The second layer of the film structure according to the present invention, which in one embodiment is a film layer around the core layer described above, comprises a single site catalyzed polyethylene such as metallocene polyethylene (mPE). In a preferred embodiment, mPE is a linear low density polyethylene (hereinafter "mLLDPE"). In another preferred embodiment, mPE is a VLDPE (hereinafter "mVLDPE") having a density between about 0.880 to 0.915 g / cm3. In the case where the HDPE component of the mixture is also a metallocene polyethylene, the second component of the invention must have an above mentioned mLLDPE or mVLDPE.

A "metallocene polyethylene" as used herein means a polyethylene produced by a metallocene catalyst. As used herein, the term "metallocene catalyst" is defined as at least one component of the metallocene catalyst containing one or more substituted or unsubstituted (Cp) cyclopentadienyl moieties in combination with a Group 4 transition metal , 5 or 6 (M).

Metallocene catalyst precursors generally require activation with an appropriate cocatalyst, or activator, to give an "active metallocene catalyst", that is, an organometallic complex with an unoccupied coordinating site that can coordinate, insert and polymerize olefins. Active catalyst systems generally include not only the metallocene complex, but also an activator such as an alumoxane or derivative thereof (preferably MAO), an ionizing activator, a Lewis acid, or a combination thereof. Alkylalumoxanes are additionally suitable as catalyst activators. The catalyst system is preferably supported on a vehicle, typically an inorganic chloride or oxide or a resinous material such as polyethylene. The prior art is provided with many examples of metallocene catalysts / systems for producing polyethylene. Non-limiting examples of metallocene catalysts and catalyst systems useful in the practice of the present invention include WO 96/11961; WO 96/11960; U.S. Patent Nos. 4,808,561; 5,017,714; 5,055,438; 5,064,802; 5,124,418; 5,153,157; 5,324,800; more recent examples are US Patent Nos. 6,380,122; and 6,376,410; and WO 01/98409, and references cited therein. Included within the definition of mPE resins, and more particularly mLLDPE resins, for the purpose of the present invention are polyethylene resins having a low polydispersity, as described, for example, in the above mentioned US Patent No. 6,492,010, i.e. a polydispersity produced by a catalyst described in various ways, such as single site, tight geometry, or metallocene catalyst, catalysts well known per se in the prior art. Preferred low polydispersity mPEs are mLLDPEs having a range density for LLDPEs, as described herein. Low polydispersity mLLDPE resins may be prepared from a partially crystalline polyethylene resin which is a polymer prepared with ethylene, preferably ethylene and at least one alpha-olefin monomer, for example a copolymer or terpolymer. The alpha olefin monomer generally has from about 3 to about 12 carbon atoms, preferably from about 4 to about 10 carbon atoms, and more preferably from about 6 to about 8 carbon atoms. The alpha olefin comonomer content is generally below about 30 weight percent, preferably below 20 weight percent, and more preferably from about 1 to about 15 weight percent. Examples of comonomers include propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-pentene, 4-methyl-1-pentene, 1-octene, 1-decene and 1-dodecene.

In one embodiment, low polydispersity resins will have average molecular weights in the range of from about 20,000 to about 500,000, preferably from about 50,000 to about 200,000. Molecular weight is determined by commonly used techniques such as size exclusion chromatography or gel permeation chromatography.

In one embodiment, the low polydispersity polymer will have a molecular weight distribution, or polydispersity (Mw / Mn, "MWD") in the range of about 1 to about 4, preferably about 1.5 to about 4, more preferably from about 2 to about 4, and even more preferably from about 2 to about 3. These products are well known per se in the art and are discussed in U.S. Patent Nos. 5,907,942; 5,907,943; 5,902,684; 5,752,362; 5,814,399; and 5,749,202.

In one embodiment, the low polydispersity polymers thus produced generally have an excess crystalline content of at least 10 weight percent, generally in excess of at least 15 weight percent.

Preferred mLLDPE resins will be characterized by one or more of the above-mentioned embodiments, including preferred, most preferred, etc. As a non-limiting example, a preferred mLLDPE according to the present invention is characterized as having a molecular weight of from 20,000 to 500,000 and a polydispersity of from about 2 to about 4; Another preferred mLLDPE according to the present invention is characterized as having a polydispersity of from about 1 to about 4 and an excess crystalline content of at least 10% by weight.

Usable mLLDPE or low polydispersity polymers are available from, among others, the Dow Chemical Company and Exxon Chemical Company, which are producers of narrow geometry or single site catalyst polyethylenes. These resins are commercially available as ENHANCED POLYETHYLENE®, ELITE®, AFFINITY®, EXXACT® and EXCEED® polyethylene resins.

Also included in the definition of mLLDPE according to the present invention are bimodal resins produced by catalysts having at least one component, a tight geometry or single site catalyst which produces a low polydispersity polymer. Particularly preferred examples are bimodal resins having, as a component, a resin made using a tight, single-site metallocene catalyst and having a density in the LLDPE density range as described above. Bimodal resins are well known per se in the art.

In a more preferred embodiment, suitable usable mPE for the present invention includes metallocene LLDPE (mLLDPE) under the trademark Exceed, available from ExxonMobil Chemical Company, Houston, TX. Particularly preferred is Exceed® 1327CA polyethylene and Exceed® 1018CA polyethylene, both commercially available mLLDPEs with a C6 comonomer incorporated into them and produced in the gas phase.

In one embodiment, a suitable mixture for the second film layer or film layer (s) should comprise from about 100 wt% to 50 wt% mPE. Preferably, the mPE has a density range of from 0.910 to 0.940 g / cm3 and more preferably 0.915 to 0.940 g / cm3, even more preferably 0.921 to 0.934 g / cm3, even more preferably 0.925 to 0.929 g / cm3.

Optional components, in an amount no greater than 50% by weight, include LDPE and / or HDPE. Preferred LDPEs and HDPEs as far as the density ranges are as described elsewhere herein. Preferred embodiments are also preferably selected from the known or commercially available LDPEs or HDPEs discussed herein. In another preferred embodiment, LDPEs suitable for use in this second layer are free radical LDPEs having a density in the range of 0.916 to 0.940 g / cm3, preferably 0.924 to 0.940 g / cm3. In one embodiment, LDPE blended with HDPE in this layer has a density in the range of 0.916 to 0.940 g / cm3, more preferably 0.921 to 0.935 g / cm3. In another embodiment, LDPE mixed with HDPE in this layer has a density in the range of 0.916 to 0.927 g / cm3, and more preferably 0.921 to 0.926 g / cm3. Again, specific preferred examples of LDPEs are LD170BA and experimental types EX489BA and ΒΑ514ΒΑ, mentioned above. Mixtures of two or more LDPEs are contemplated. The LDPE used in this second layer, if present at all, may be the same or different than the LDPE used in the first layer. Particularly preferred HDPE in this second layer includes the available HDPEs from ExxonMobil Chemical Co., Houston, Texas under the HD, HDA, HMA, HRA, HRP, HDZ or HYA series or under the trademark PAXON, particularly HYA800 and HDZ222 discussed above. . Mixtures of two or more HDPE polymers in this layer are also contemplated.

Where HDPE is present in the second layer or film layer, it may be the same or different than HDPE in the first layer. Thus, the HDPE polymer has a density greater than 0.940 g / cm3. In a preferred embodiment, the HDPE in this layer has a density of from about 0.940 g / cm3 to about 0.970 g / cm3, more preferably from about 0.955 g / cm3 to about 0.965 g / cm3, and most preferably from about 0.950 g / cm3. 0.960 g / cm3 to about 0.965 g / cm3. This second layer may include various additives, as discussed in more detail below. However, it is preferred that this second layer, comprising mPE and optionally HDPE and / or LDPE, does not contain slip or antiblock additives.

In addition, in embodiments, this second layer or film layer may include or exclude one or more of the following: additional polyolefins such as VLDPE or polypropylene, glidants or antiblockers, and the like. Multilayer film forming techniques are well known to those skilled in the art and the prior art provides several examples; see, for example, WO 01/98409. Any of these techniques may be used to form the multilayer films of the present invention, but coextrusion is more preferred, offering the greatest advantage of the invention over glue shrinkage film structures. Molded films are also considered, particularly where at least one film layer, as more fully described below, comprises polypropylene.

Although those skilled in the art will appreciate that the thickness of the layers may be adjusted based on the desired end use, one of the surprising aspects of the present invention is that the composition of the layers of the present invention provides multilayer films having the properties suitable for gluing shrinkage. while being thin enough to be commercially attractive.

Thus, according to one embodiment of the invention, the first layer comprising HDPE, as described above, and the second layer comprising mPE, are coextruded to form a multilayer film as the glue shrink film. In the structure involved with the preferred gluing shrinkage, the second layer comprising metallocene polyethylene is in the outer layer with the first layer comprising HDPE in contact with the shrinkage wrapped items.

In one embodiment, the film according to the invention consists essentially of the first layer comprising HDPE and the second layer comprising mPE. In a more preferred embodiment, the first layer is about 30 microns thick and the second layer is about 5 microns thick.

In another embodiment, the first layer comprising HDPE described above is a core layer between two film layers, at least one of which is the second layer comprising mPE described above. The two film layers may be the same or different, provided that at least one is the second layer as described above comprising mPE. In this embodiment, it is preferred that both film layers also comprise mPE.

As used herein, the term "film layer" means that the layer is the outer layer of the structure. Thus, in a three layer structure there are two film layers and a core layer, sandwiched by the film layers. This structure will be called A / B / A, wherein layer A means a film layer corresponding to the second layer comprising mPE above and layer B means the core layer corresponding to the first layer described above. It will be recognized that layers A, however, need not be identical.

In yet another embodiment, the structure includes the layer comprising HDPE without a metallocene polyethylene component, and a layer comprising a mixture comprising metallocene polyethylene and HDPE. Optionally, the layer comprising HDPE without a metallocene polyethylene component is sandwiched between two film layers comprising mLLDPE, wherein at least one of the film layers further comprises HDPE. The film layers in any of these "film and core" (or A / B / A) embodiments may be the same or different.

Additional film layers are contemplated, for example, between one or both of A / B, for example, as bonding layers. However, in the preferred embodiment, core layer B comprises HDPE and film layers A comprise mPE (i.e. corresponding to one of the first layers and two of the second layers, respectively, described above). The final film comprising the A / B / A structure may be symmetrical or may be asymmetrical.

In a more detailed embodiment, the film according to the present invention comprises the A / B / A structure, wherein the film layers A, which may be the same or different, each independently comprise an mPE having a density in the range. about 0.910 to 0.940 g / cm3, preferably 0.915 to 0.940 g / cm3, and optionally an HDPE, preferably having a density between about 0.940 and 0.970 g / cm3, more preferably 0.955 to about 0.965 g / cm3, and more preferably. from about 0.960 to about 0.965 g / cm3, and core layer B comprises an HDPE, preferably having a density between about 0.940 and 0.970 g / cm3, more preferably 0.955 to about 0.965 g / cm3, and more preferably. from about 0.960 to about 0.965 g / cm3, and an LDPE, preferably having a density in the range of 0.916 to 0.935 g / cm3, more preferably 0.921 to 0.930 g / cm3. Where HDPE exists in one or both of the film layers, HDPE in each layer is independently selected and may be the same or different from the other layer and / or the core layer.

In this preferred A / B / A structure, it is more preferred that core layer B comprises 60-90 wt.%, More preferably 70-80 wt.% LDPE, and 40-10 wt.% HDPE, more preferably 30. And 20% by weight, and that the film layers A are each independently selected from 80-100% by weight, preferably 85-95% by weight of mPE, and 20-0% by weight of HDPE, more preferably 15-30%. 5% by weight. In a preferred embodiment, the A / B / A structure is symmetrical with respect to composition and thickness. In another embodiment, the A / B / A structure is no thicker than 50 microns and more preferably about 40 microns thick or less.

In another embodiment, in a structure comprising A / B / A layers according to the present invention, the film layers A each independently comprise at least one mLLDPE resin and at least one LDPE resin, and the core B comprises at least one LDPE resin and at least one HDPE resin. One or more additional layers may be present between the film layers and the core, and the structure may be asymmetric or symmetrical, so that, for example, one embodiment includes a structure consisting of layer A, bonding layer, layer B bonding layer, layer A, a structure consisting of layer A, bonding layer, layer B, layer A and the like. A preferred embodiment where the structure consists essentially of a layer A, a layer B, layer A having a total thickness of 50 microns ± 10 microns (2 mils), the layers being in the ratio, respectively, of about 15 : 70: 15. In another preferred embodiment, layers A comprise from about 99 to about 80 wt.%, Preferably from about 98 to about 90 wt.% MLLDPE and from about 1 to about 20 wt. about 2 to about 10% by weight of LDPE. In another preferred embodiment, layer B comprises from about 90 to about 50% by weight, preferably from about 85 to about 55% by weight, more preferably from about 85 to about 75% by weight. LDPE, and from about 10 to about 50 wt%, preferably from about 15 to about 45 wt%, more preferably 15 to about 25 wt% HDPE. Additional preferred embodiments include combinations of the aforementioned embodiments, preferred embodiments and the most preferred embodiment, as well as the preferred and most preferred densities for each of the prospective polyethylenes in this layer, as described in the appropriate sections herein. Each of the aforementioned layers may independently include or exclude additional ingredients such as slip or antiblocking agents and / or additional polyolefins such as polypropylene and / or VLDPEs. A particularly advantageous embodiment as an A / B / A structure as described in this paragraph, wherein one of the layers A does not contain polypropylene and one of the layers A contains polypropylene. In a structure surrounded by a preferred gluing shrinkage, the layer having the polypropylene may be in contact with at least one item involved a gluing shrinkage.

In yet another embodiment, which may be a modification of any of the foregoing embodiments, the second layer or at least one of the film layers comprises an mLLDPE, an HDPE and an LDPE.

In yet another embodiment, the structure comprises a film layer comprising an mPE according to the present invention, a core layer comprising HDPE according to the present invention and a second film layer comprising polypropylene.

In a preferred embodiment, one or more of the layers of the multilayer film structure according to the invention may have certain additives, such as thermal stabilizers, but in this embodiment, each of the multilayer compositions must specifically exclude slip or antiblock additives. . Suitable additives include: fillers such as silica, talc, and others; antioxidants (e.g. prevented phenolics such as IRGANOX® 1010 or IRGANOX® 1076 available from Ciba-Geigy); phosphites (e.g. IRGAFOS® 168, available from Ciba-Geigy); anti-adhesion additives and antistatic additives; adhesion promoting agents, such as polybutenes, terpene resins, aliphatic and aromatic hydrocarbon resins, alkali metal and glycerol, hydrogenated stearates and rosin; UV stabilizers; thermal stabilizers; release agents; antistatic agents; pigments; colorants; dyes; waxes; and others.

Any mixture required to produce the layer compositions according to the present invention may be formed using conventional methods and equipment, such as dry blending of the individual components and subsequently melt blending in a blender, or blending the components together directly in a blender. , such as a Banbury mixer, a Haake mixer, a Brabender internal mixer, or a twin or single screw extruder including a combined extruder and side arm extruder used directly downstream of a polymerization process or prior to film extrusion. . Examples In the following examples, three layer films, A / B / A according to the invention and comparative films were produced in a commercially available extruder from Winmoller & Holscher. The co-extruded structures were symmetrical, having an inner core of 30 microns thick and two layers of film, each 5 microns thick. The machine conditions were as follows: (a) die diameter: 250 mm; (b) matrix range: 1.4 mm; (c) burst ratio: 3.0; (d) core extruder adapter temperature: 200 ° C; (e) adjusting extruder temperature adjustment on film: 190 ° C; (f) matrix temperature: 200 ° C.

The various products used in the examples in Table 2 are identified below in Table 1: Table 1 Continued ... 1 Commercially Available from ExxonMobil 2 Developing Versions. Enhanced versus commercially available as LD170BA. 3 ASTM D-1238, condition E (2.16 kg load, 190 ° C) Films having a thickness of 40 microns were formed using the compositions given in table 2. Examples 2-3, 5-6, 8-9 are examples of the present invention having film layers comprising mPE and HDPE, and core layers comprising HDPE. Examples 11-12, 14-15 and 17-20 are examples of the present invention having film layers comprising mPE but not HDPE, with core layers comprising HDPE. The other examples are for comparison purposes. The results of various tests performed are given in table 3.

Turbidity is the total turbidity measured according to ASTM D1003; 60 ° brightness angle and 20 ° brightness angle are both measured according to ASTM D2457; Transparency is measured according to ASTM D1746; Elmendorf tear values are both measured according to ASTM D1922; thermal force values are both measured according to ASTM D2838-95, set temperature: 190 ° C; relative 1% secant modulus and 10% production deviation are both measured according to ASTM D882. Thermal strength is measured based on ASTM D2838-95 procedure A using a Retramat test apparatus supplied by Pro-demat S.A.

Table 2 Continued ...

Table 3 Continued ... Various advantages can be seen in the present invention according to the examples. For example, the melt pressure of the extruder in the core drops when HDPE types are used in the core as compared to LLDPE types (examples 2-3, 5-6, 8-9,11-12,14-15,17 -20 versus 1.4, 7,10,13,16,22).

In the case of films comprising metallocene polyethylene and LDPE and the core comprising HDPE (examples 11-12,14-15,17-21), the values of 1% secant MD and TD modulus are significantly higher than in the case of that there is no HDPE in the core layer (examples 10,13,16, 22). Among other aspects, the 1% secant modulus provides a possible downward calibration measure using these films. The higher the secant modulus at 1%, the lower the caliber (film thickness) required to provide the same benefit. Increased tensile strength, when measured by 10% production deviation, is also a benefit that opens up possibilities for downward calibration. A thinner material having the same stiffness and strength (and thus a lower cost) is in high demand.

Likewise, films comprising the metallocene polyethylene and HDPE blends sandwiching a core comprising HDPE (examples 2-3, 5-6 and 8-9) had a 1% secant modulus relative to the examples having non-HDPE containing cores (examples 1,4 and 7).

Furthermore, as is apparent from an inspection of the optical properties, the increase in strength and / or downward calibration that accompanies the presence of HDPE in the core and / or film is not significantly offset by a loss of transparency or gloss values. Of course, it is particularly noteworthy that the 20 ° and 60 ° brightnesses are quite similar to the examples according to the present invention, particularly with respect to examples having HDPE in both the core and films with respect to examples having HDPE in the film, but not. in the core. A slight difference in brightness of 20 ° and 60 ° is important for display purposes, ie the angle of compliance is not important. In Table 3, for example, it can be seen that the difference in brightness values of 20 ° and 60 ° is about 0.1%, which is negligible. Typically for the examples of the present invention differences of 2% are observed.

In addition, examples according to the invention uniformly demonstrate higher Elmendorf tear values (higher number being as measured from highest tear strength) and higher thermal force (as a measure of holding force when wrapped around shrinkage around the items). grouped by collation). Example 23 A film having a 50 micron thick A / B / A structure with a thickness ratio of 15:70:15, respectively, was produced on a commercial Maachi® coextrusion line. Layers A consisted of about 95 wt% Exceed 1327CA and about 5 wt% LD514. Layer B consisted of about 80 wt% LD514BA and about 20 wt% HDZ222.

Example 24 A film identical to the above except that HDZ222 was replaced by LD514 was produced in the same way.

A comparison of examples 23 and 24 illustrates that a combination of an mLLDPE and LDPE as the film layer, in this particular case, results in a COF reduction of about 15%, a modest increase in brightness, and a reduction in turbidity. 10.4 in Example 24 to 5.9 in Example 23. The invention is described above with reference to numerous specific embodiments and examples. Many variations will be apparent to those skilled in the art in light of the detailed description above. All of these obvious variations are within the full scope of the appended claims.

A preferred embodiment is a multilayer structure having at least one first layer comprising HDPE and at least a second layer, different from said first layer comprising a metallocene polyethylene; Also more preferred embodiments may be combined where appropriate, as may be recognized by one of skill in the art having the present disclosure without undue experimentation: wherein said metallocene polyethylene is an mLLDPE; wherein said first layer further comprises LDPE in the amount of at least 50% by weight based on the composition of the first layer; wherein said second layer further comprises at least one additional polyolefin selected from the group consisting of HDPE, LDPE, and mixtures thereof, in the amount of from 0.1 wt% to 50 wt%; wherein said first layer comprising HDPE is a core layer, said second layer comprising a metallocene polyethylene is a film layer, and further comprising a second film layer; wherein said first layer comprising HDPE is a core layer, said second layer comprising a metallocene polyethylene is a film layer, and further comprising a second film layer, said second film layer comprising a metallocene polyethylene, which may be the same or different from the first film layer; wherein said first layer comprising HDPE is a core layer, said second layer comprising a metallocene polyethylene is a film layer, and further comprising a second film layer, said second film layer comprising an mLLDPE; wherein said first film layer comprising HDPE is a core layer, said second layer comprising a metallocene polyethylene is a film layer, and further comprising a second film layer, said second film layer comprising an mLLDPE and further comprising at least one additional polyolefin selected from the group consisting of HDPE, LDPE, and mixtures thereof, in the amount of from 0.1 wt% to 50 wt%; wherein said second film comprises an mLLDPE and further comprises a polyolefin selected from HDPE, LDPE, and mixtures thereof, in the amount of from 0.1 wt% to 50 wt%; wherein none of the layers contain slip or antiblock additives; any one of three or more layer structures, wherein the total thickness is 70 microns or less, 60 microns or less, 50 microns or less, preferably 40 microns or less, or even more preferably wherein said first layer comprising HDPE has a thickness of about 40 microns or less, preferably 30 microns or less and each of said layers has a thickness of about 10 microns or less, preferably 5 microns or less; and preferably wherein the ratio of the layers in structure A / B / A described herein is in the range of, respectively, (15 ± 5): (70 ± 10): (15 ± 5), wherein the structure is symmetrical or asymmetric with respect to one or more of the compositions, dimensions, additional layers, and others, for example, wherein the composition of the film layers is identical or different, wherein there are additional layers, such as bonding layers, between neither, one or both. A / B interfaces, where the ratio of A / B / A layers is 15:70:15, 20/70/10, etc.

Another preferred embodiment is a film comprising an A / B / A structure, wherein the A layers are film layers, which may be the same or different, each independently selected from a mixture comprising an mPE having a density of from about 0.910 to 0.940 g / cm3, preferably 0.915 to 0.940 g / cm3, and optionally an HDPE, which, if present, preferably has a density between about 0.940 and 0.970 g / cm3, more preferably 0.955 to about 0.965 g / cm3, and more. preferably from about 0.960 to about 0.965 g / cm3, and / or optionally an LDPE, which, if present, preferably has a density of from about 0.924 to about 0.940 g / cm3, or about 0.916 to about 0.935 g. / cm3, or about 0.926 to about 0.935 g / cm3, or about 0.916 to about 0.927 g / cm3, or about 0.921 to about 0.926 g / cm3, or about 0.925 g / cm3 to about 0.930 g / cm3, 0.916 to 0.940 g / cm3, or about 0.924 to 0.935, and other embodiments including LDPEs having densities of any of the lower density limits specified in any of the higher density limits specified herein, for example 0.921 to 0.940 g / cm3, or 0.926 to 0.940 g / cm3, or 0.925 to 0.935 g / cm3 and B is a core layer comprising a mixture comprising an HDPE, preferably having a density between about 0.940 and 0.970 g / cm3, more preferably 0.955 to about 0.965 g / cm3, and more preferably from about 0.960 to about 0.965. g / cm3, and an LDPE, preferably having a density in the range of 0.916 to 0.935 g / cm3, more preferably 0.925 to 0.930 g / cm3, and also including density ranges described above for one or more film layer (s) and Also more preferred embodiments of this A / B / A structure, wherein the core layer B comprises 60-90 wt.%, more preferably 70-80 wt.% LDPE and 40-10 wt.% HDPE, more preferably 30. -20% by weight, and A film layers are each independently 80-100 wt.%, preferably 85-95 wt.% mPE, and 20-0 wt.% HDPE, LDPE, and mixtures thereof, more preferably 15-5 wt.%; and a more preferred embodiment of any of the above embodiments wherein said layers A and layer B, when formed into a co-extruded A / B / A structure having a total thickness of less than 60 microns or less than 50 microns. have a 1% MD secant modulus of at least 335 mPa, preferably 400 mPa, more preferably 500 mPa, and a 1% TD secant modulus of at least 335 mPa, preferably 400 mPa, more preferably 500 mPa, and even more. preferably 600 mPa, secant modulus values measured according to ASTM D882; and also any of the above embodiments, wherein layers A and layer B, when formed into a co-extruded A / B / A structure having a total thickness of less than 50 microns, have a brightness difference of 20 ° and 60 ° of 2% or less, the brightness values measured according to ASTM D2457.

Additional preferred embodiments of any of the above may include films having one or more performance parameters indicated above in the experimental section, and may also include films having additional layers, such as A / B / C / D / E, wherein the layers A and E, which may be the same or different, corresponding to the composition described above for film layer A in structure A / B / A or where A corresponds to layer A and E corresponds to a layer comprising polypropylene, the composition C corresponds to the composition described above for core layer B in structure A / B / A, and B and D, which may be the same or different, correspond to layers which may be selected from, without limitation, bonding layers, of reprocessed material and, in a preferred embodiment, additional layers having the composition corresponding to layer B in structure A / B / A described above.

In one embodiment, the structure comprising A / B / A, as described herein, does not contain an oxygen barrier layer in the structure. However, one of the particularly beneficial uses of glue shrinkage comprising the A / B / A layers according to the present invention is to overcoat having a primary oxygen barrier layer, e.g. perishable items such as meat. Typical primary oxygen barriers are discussed in WO 95/00333 described above as vinylidene chloride copolymer, and may also include ethylene vinyl alcohol copolymers (EVOH copolymers).

Other preferred embodiments are co-extruded films, heat shrinkable films, cast films, blown films, and glue shrinkage structures according to any of the preceding embodiments (including preferred embodiments, more preferred embodiments, etc.).

Trade names used herein are indicated by a ® symbol or ® symbol, indicating that names may be protected by certain trademark rights, for example, they may be registered trademarks in various jurisdictions. All patents and patent applications, test procedures (such as ASTM methods, and others) and other documents cited herein are incorporated by reference to the extent that the description is not inconsistent with this invention and in all jurisdictions in which this incorporation is incorporated. is allowed.

Claims (11)

Multilayer film, characterized in that it comprises an A / B / A structure, wherein the A layers are film layers, which may be the same or different, each independently selected from a layer comprising an mPE having a single layer. 0.910 to 0.940 g / cm3 or a mixture of an mPE and HDPE or LDPE, and layer B is a core layer comprising a mixture comprising an HDPE and an LDPE, wherein the HDPE in said layer B has a density of between 0.940 and 0.970 g / cm3, wherein LDPE has a density of about 0.916 to 0.940 g / cm3, wherein said layers A and layer B, when formed into a co-extruded A / B / A structure having a thickness less than 70 microns, have a 1% MD secant module of at least 335 mPa and a 1% TD secant module of at least 335 mPa, both measured according to ASTM D882. Film according to claim 1, characterized in that at least one of said layers A further comprises HDPE and / or LDPE, said LDPE being preferably in an amount of 1 to 20% by weight and more preferably of 2%. at 10% by weight, said HDPE having a density between 0.940 and 0.970 g / cm3 and preferably a density between 0.960 to 0.965 g / cm3. Film as defined in claim 1, characterized in that said mPE has a density of 0.915 to 0.940 g / cm3 and is preferably an mLLDPE. Film as defined in claim 1, characterized in that the HDPE in said layer B has a density of 0.960 to 0.965 g / cm3. Film as defined in claim 1, characterized in that said LDPE has a density of 0.925 to 0.935 g / cm3. Film according to claim 1, characterized in that said layers A and layer B, when formed into a co-extruded A / B / A structure having a total thickness of less than 50 microns, have a modulus 1% MD secant of at least 400 mPa and 1% TD secant module of at least 400 mPa, both measured according to ASTM D882. Multilayer film according to claim 6, characterized in that it has a 1% MD drying module of at least 500 mPa and a 1% TD drying module of at least 500 mPa, preferably 800 mPa, measured. according to ASTM D882. Multilayer film according to claim 1, characterized in that the core layer B comprises 70-80 wt% LDPE, 30-20 wt% HDPE, and film layers A are each independently selected from a mixture comprising 85-95 wt% mPE and 15-5 wt% HDPE. Multilayer film according to claim 1, characterized in that said layers A and layer B, when formed into a co-extruded A / B / A structure having a total thickness of less than 50 microns, has a difference in brightness of 20 ° and 60 ° of 2% or less, measured brightness values according to ASTM D2457. Multilayer film according to claim 1, characterized in that it further comprises at least one layer between at least one of said A / B layers, said at least one layer selected from the group consisting of a bonding layer. a layer of reprocessed material and a layer selected from the mixtures comprising an HDPE and an LDPE. Film, characterized in that it is heat shrinkable, co-extruded as defined in claim 1.