EP0977666A1 - Couche de scellement constituee d'un polymere ethylene-styrene pour le conditionnement de liquides - Google Patents

Couche de scellement constituee d'un polymere ethylene-styrene pour le conditionnement de liquides

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Publication number
EP0977666A1
EP0977666A1 EP98916764A EP98916764A EP0977666A1 EP 0977666 A1 EP0977666 A1 EP 0977666A1 EP 98916764 A EP98916764 A EP 98916764A EP 98916764 A EP98916764 A EP 98916764A EP 0977666 A1 EP0977666 A1 EP 0977666A1
Authority
EP
European Patent Office
Prior art keywords
ethylene
film
volume
layer
overall
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP98916764A
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German (de)
English (en)
Inventor
Benjamin Andrew Smillie
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
DuPont Canada Inc
Original Assignee
DuPont Canada Inc
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Filing date
Publication date
Application filed by DuPont Canada Inc filed Critical DuPont Canada Inc
Publication of EP0977666A1 publication Critical patent/EP0977666A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
    • B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B1/00—Layered products having a non-planar shape
    • B32B1/08—Tubular products
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/34—Layered products comprising a layer of synthetic resin comprising polyamides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
    • B32B7/04—Interconnection of layers
    • B32B7/12—Interconnection of layers using interposed adhesives or interposed materials with bonding properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00—Properties of the layers or laminate
    • B32B2307/30—Properties of the layers or laminate having particular thermal properties
    • B32B2307/31—Heat sealable
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2439/00—Containers; Receptacles
    • B32B2439/70—Food packaging
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2597/00—Tubular articles, e.g. hoses, pipes

Definitions

  • This invention relates to the use of a film made from an ethylene/styrene polymer obtained by a single-site catalyst polymerization process, as a sealant layer in manufacturing packages, in particular, pouches for containing flowable materials, preferably liquids.
  • Packaging films include, for example films used to make fluid containing disposable pouches that may be manufactured on form and fill equipment employing either impulse or thermic sealing techniques; vacuum packages for irregular shaped products and for prepared meats, cheeses and the like; shrink wrapped poultry and skin packaging. While this invention has application to all forms of packaging, it is of particular value in the area of liquid packaging, namely for the manufacture of pouches for containing flowable materials.
  • Packaging machinery is being designed to operate at faster speeds all the time. The speeds of such machinery demands lower sealing temperatures and hence improved hot tack strength in films to be used to make packaging with such machines.
  • Hot tack strength is the ability of a film to seal under stress while still in a molten state. This property is one of the most critical in packaging applications where machines run at high speeds and sealing takes place between molten sealing components of a package, thereby placing the sealing components, and hence the seal under stress when the package is formed, filled and sealed.
  • SSC single site catalyst
  • metallocene metallocene
  • SSC single site catalyst
  • metallocene metallocene
  • SSC single site catalyst
  • metallocene metallocene polymers
  • Exxon is said to use mono- and bis-cyclopentadienyl metallocenes, while Dow's focus is on titanium cyclopentadienyl metallocenes, which it calls “constrained geometry catalysts”.
  • Exxon produces ethylene-butene and ethylene-hexene polymers, while Dow makes ethylene-octene polymers of the metallocene or SSC type.
  • Patent No. 5,382,630 issued January 17, 1995 to Stehling et al and WO
  • pouches for flowable materials wherein the sealant film is made from a SSC linear copolymer of ethylene and at least one C 4 -C 10 ⁇ - olefin. Blends of these SSC copolymers with at least one polymer selected from multi site catalyst linear copolymers of ethylene and at least one C 4 -C 10 ⁇ -olefin, a high pressure polyethylene and blends thereof.
  • the structure comprises an interposed layer of polyethylene having a thickness in the range of 5 to 20 microns and a density of at least 0.93 gm/cc and a melt index of from about 1 to 10 dg/minute, the at least one outer layer being a SSC or metallocene polyethylene/ ⁇ -olefin film which may have a density in the range of 0.88 to 0.93 gm/cc.
  • stiffening interposed layer The only requirements placed on the stiffening interposed layer are that it be of a particular thickness and density. These are greater in the stiffening layer than in the metallocene or SSC layer(s). This application indicates that the stiffening layer is included in order for the fluid containing pouch to function properly as a pouch from which fluid can be poured when the pouch is placed in a supporting container.
  • DUPONT CANADA INC. U.S. Patents Nos. 4,503, 102(Mollison) and
  • 4,521 ,437(Storms) disclose a polyethylene film for use in the manufacture in a form, fill and seal process of a disposable pouch for liquids such as milk.
  • U.S. Patent No. 4,503,102 discloses pouches made from a blend of a linear ethylene copolymer of ethylene and a C 4 -C 10 ⁇ -olefin and an ethylene-vinyl acetate polymer copolymerized from ethylene and vinyl acetate.
  • the linear polyethylene copolymer has a density of from 0.916 to 0.930 g/cm 3 and a melt index of from 0.3 to 2.0 g/10 minutes.
  • the ethylene-vinyl acetate polymer has a weight ratio of ethylene to vinyl acetate from 2.2:1 to 24:1 and a melt index of from 0.2 to 10 g/10 minutes.
  • the blend disclosed in Mollison U.S. Patent No. 4,503,102 has a weight ratio of linear low density polyethylene to ethylene-vinyl acetate polymer of from 1.2:1 to 24: 1.
  • U.S. Patent No. 4,503,102 also discloses multilayer films having as a sealant film the aforementioned blend.
  • U.S. Patent No. 4,521,437 (Storms) describes pouches made from a sealant film which is from 50 to 100 parts of a linear copolymer of ethylene and octene- 1 having a density of from 0.916 to 0.930 g/cm 3 and a melt index of 0.3 to 2.0 g/10 minutes and from 0 to 50 parts by weight of at least one polymer selected from the group consisting of a linear copolymer of ethylene and a C 4 -C 10 - ⁇ - olefin having a density of from 0.916 to 0.930 g/cm 3 and a melt index of from 0.3 to 2.0 g/10 minutes, a high-pressure polyethylene having a density of from 0.916 to 0.924 g/cm 3 and a melt index of from 1 to 10 g/10 minutes and blends thereof.
  • the sealant film disclosed in U.S. Patent No. 4,521,437 is selected on the basis of providing (a) pouches with an M-test value substantially smaller, at the same film thickness, than that obtained for pouches made with film of a blend of 85 parts of a linear ethylene/butene-1 copolymer having a density of about 0.919 g/cm 3 and a melt index of about 0.75 g/10 minutes and 15 parts of a high pressure polyethylene having a density of about 0.918 g/cm 3 and a melt index of 8.5 g/10 minutes, or (b) an M(2)-test value of less than about 12% , for pouches having a volume of from greater than 1.3 to 5 litres, or (c) an M(1.3)- test value of less than about 5% for pouches having a volume of from 0.1 to 1.3 litres.
  • the M-, M (2)- and M (1.3)-tests are defined pouch drop tests for U.S. Patent No. 4,521,
  • metallocene polymers in the manufacture of films used to make fluid containing pouches.
  • These films are characterised as metallocene ultra low density linear polyethylene ("ULDPE") sold commercially as AFFINITY ® by Dow and described as a linear copolymer of ethylene with at least one ⁇ -olefin having from 3 to 10 carbon atoms, for example, the ULDPE may be selected from ethylene- 1-propylene, ethylene- 1-butene, ethylene- 1-pentene, ethylene-4-methyl- 1-pentene, ethylene- 1-hexene, ethylene-1-heptene, ethylene- 1-octene and ethylene- 1-decene copolymers, preferably ethylene- 1-octene copolymer.
  • metallocene polymers useful for making sealed articles comprising ethylene interpolymers having a CDBI of at least 50% and a narrow molecular weight distribution or a polymer blend comprising a plurality of said ethylene interpolymers as blend components.
  • Ethylene/styrene polymers can be prepared also using single-site or metallocene polymerization processes. These polymers may be alternating or pseudo-random. Examples of pseudo-random polymers are described in Dow's European Patent Application No. 416,815, the disclosures of which are incorporated herein by reference. Alternating ethylene/styrene copolymers (low styrene content) that have repeat sequences of ethylene/styrene/ethylene may be obtained through catalyst selection (Makromol). Chem., Macromol. Symp. 66, 203-214 (1993), at page 209).
  • Examples of other types of ethylene/ styrene polymers that are encompassed by this definition include those described in Idemitsu Kosan Co. LTD's Japanese Patent 08020605 A of January 23, 1996.
  • U.S. Patent No. 5,658,625 issued August 19, 1997 to Bradfute et al there is described a multilayer film that preferably may comprise outer polypropylene layers between which is an ethylene/styrene layer produced using single-site catalyst polymerization methods. This film is used primarily to produce shrink wrap packaging film.
  • the disclosures of all references mentioned in this description are incorporated herein by reference.
  • the present invention provides a sealant film for use in the manufacture of heat sealable film used to make pouches or bags for packaging various products, in particular food products where freshness, cost and film clarity are important properties.
  • heat sealable film used to make pouches or bags for packaging various products, in particular food products where freshness, cost and film clarity are important properties.
  • examples are fresh fruits, vegetables and liquids, such as milk and juice.
  • the invention provides a heat sealable multilayer film for use in manufacturing pouches for containing flowable materials wherein the pouches are in tubular form and have transversely heat sealed ends, said film comprising at least one layer comprising about 10% by volume of the overall film structure and is made from an ethylene-styrene copolymer obtained using a single site catalyst polymerization process and one or more of the following layers: (a) at least one interpolymer selected from interpolymers of ethylene and one or more C 3 - C 20 ⁇ -olefins made by polymerization processes using single- site catalyst, non-single-site catalyst and mixtures of such catalysts, and blends thereof, said interpolymers having a density in the range of about 0.87 to about 0.940 gm/cc and a melt index of from about 0.2 to about 20 dg/minute and comprising about 10 to about 90% by volume of the overall film structure; (b) at least one barrier layer selected from nylon polymers comprising about 5 to about
  • blends of polymers may be used, usually because of processability and/or economic requirements.
  • the blends that may be used herein are any of those which are known in the art and which have been described in any and all of the aforementioned patents and applications.
  • the ethylene/styrene copolymer layer preferably has a thickness of from about 25 to about 125 microns.
  • An example of a layer structure for a multilayer film comprises A/B/A layers, where each A layer is an ethylene/styrene copolymer layer and comprises at least 10% by volume of the overall film structure and B is selected from (a) to (d), and comprises about 50% to about 80% by volume of the overall film structure.
  • A is an ethylene/styrene copolymer and comprises at least about 10% by volume of the overall film structure: C is selected from (a), (b) and (d) and comprises about 5% to about 70% by volume of the overall film structure; and B is a co-extrudable adhesive having a thickness comprising about 5 to about 15% by volume of the overall film structure.
  • E/S copolymer layer provides a film with very low heat seal initiation temperatures. This allows for economies in manufacture of film, packages and bags that can be of importance to food producers.
  • films made from E/S polymers are stiffer at equivalent heat seal initiation compared to metallocene or Ziegler Natta ethylene/alpha olefin copolymers, and does not pose the handling problems of acid copolymer resins which are often used in these types of film structures.
  • the films are also tough and have good clarity.
  • the sealant film comprises a random copolymer of ethylene and styrene obtained by a single site catalyst polymerization process that may be characterized generally as follows: density range — about 0.93 to about 1.0 g/cm 3 ; melting point range — about 136°C(low styrene) to about 50°C (50 wt % styrene) or no melting point at styrene contents above 50 wt % ; melt index — about 0.3 to about 4 gm/10 min at 190°C; and molecular weight distribution — Mw/Mn about 2.0 to about 4.0 (narrow).
  • the copolymer comprises up to about 40 weight % styrene, most preferably from about 5 to about 40 weight % styrene. It may have a peak melting point of from about 110 to about 60°C and a melt index that is preferably less than about 4 dg/min.
  • the sealant film layer is combined with other polymers, copolymers or interpolymers, the choice of which depends upon the intended utility for the final film.
  • the final structure may be obtained by laminating, coextruding or blending.
  • the additional polymers may be made by single site or metallocene catalyst methods of polymerization or by conventional methods, such as those using Zeigler-Natta catalysts or by polymerization methods employing combinations of such catalysts.
  • the film structure may include linear low density polyethylene polymers which are well known in the art and are described in a large number of patents and patent applications, some of which have already been mentioned.
  • Such polymers are Novacor's SCLAIR ® 11L4 polyethylene - octene copolymer made by a Zeigler-Natta polymerization process.
  • a commercial example of a suitable metallocene resin is Exxon EXCEED ® 350D60 metallocene polyethylene - hexene copolymer.
  • a layer or resin that comprises ethylene vinyl alcohol may be used in the film structure.
  • a commercial example of such a resin is EVALCA ENAL ® LC-H101.
  • An alternative to this type of material is a polyamide that may be amorphous or crystalline.
  • Commercial examples include DuPont SELAR® PA 3426 an amorphous nylon resin or film or DuPont DARTEK ® F101, a nylon 6,6 film, or BASF ULRAMID ® B3 nylon 6 film.
  • Another alternative for this type of layer is a polyester film such as that sold by DuPont under the trademark SELAR ® PT 8307 or MYLAR ® polyester film.
  • Yet another choice of flavour/oxygen barrier is a polyvinylidene chloride, such as that sold commercially under the name MORTON SERFENE ® 546 PVDC adhesive.
  • a suitable adhesive is an anhydride modified ethylene vinyl acetate, a commercial example is DuPont BYNEL ® 3800 series of co-extrudable adhesives.
  • This invention provides a film structure and a method of making it, as well as packages, preferably pouches for flowable materials, formed therefrom, wherein the sealing properties are substantially increased.
  • sealing properties is meant a substantially increased hot tack strength which is observable in such structures and which therefore allows the production of films and packaging products of greatly increased performance characteristics.
  • Other single site catalyst interpolymers may preferably be selected from interpolymers comprising ethylene and at least one C 4 - C 8 ⁇ -olefin, in particular butene, hexene, octene, n-methyl-pentane and combinations thereof.
  • polymers include the following: EXACT ® and EXCEED ® sold by Exxon and AFFINITY ® and EPE ® sold by Dow.
  • the more preferred density ranges for the single-site catalyst interpolymer may be from about 0.910 to about 0.960 gm/cc.
  • the other layers or resins may be selected, as stated previously from homopolymers, copolymers and terpolymers of ethylene. Especially preferred are interpolymers of ethylene and one or more C 3 - C ⁇ ⁇ -olefins, more preferably C 4 - C 10 most preferably C 4 - C 6 . In particular, butene, hexene, octene and n-methyl-pentane may be selected. Examples of commercially available materials include SCLAIR ® from Novacor, examples of ultra low density polyethylene materials are ATTANE ® and DOWLEX ® from Dow Chemical.
  • ethylene polymers may be used, with the only criteria being that the layer enhances the hot tack strength of the E/S polymer layer and it meets the intended application requirements.
  • Polymers that fall within this family include both single-site catalyst and multi-site catalyst ethylene polymers and interpolymers, the latter including, for example, Zeigler- Natta catalyst polymers.
  • hybrid polymers obtained using a process that involves a combination of multi-site and single-site catalysts are described in US Patent No. 5582923 issued December 10, 1996 to Kale et al, all of the disclosures of which are incorporated herein by reference.
  • This patent describes an ethylene polymer extrusion composition
  • an ethylene polymer extrusion composition comprising from about 80 to 95 percent, by weight of the total composition, of at least one ethylene/ ⁇ -olefin inte ⁇ olymer composition selected from the group consisting of a homogeneously branched linear ethylene polymer composition and a heterogeneously branched linear ethylene polymer composition, wherein the ethylene/ ⁇ -olefin polymer is characterized as having a density in the range of 0.85 g/cc to 0.940 g/cc and from about 5 to 20 percent, by weight of the total composition, of at least one high pressure ethylene polymer characterized as having a melt index, 12, less than 6.0g/10 minutes, density of at least 0.916 g/cc, a melt strength of at least 9 cN as determined using a Goettfert Rheotens unit at 190 °C, a Mw/Mn ratio of at least 7.0 and a bimodal molecular weight distribution
  • polyethylene homopolymers made by high pressure processes.
  • Commercial examples include ALATHONTM available from E.I. du Pont de Nemours and ethylene vinyl acetate polymers, examples of which are commercially available from E.I. du Pont de Nemours under the trade-mark EL VAX®.
  • a pouch for containing flowable materials which comprises a film as described previously.
  • the pouch may take the shape of a pillow, which requires support in a container to pour from it or it may be self-standing. In the latter instance, the pouch has a gusseted bottom that allows it to stand. Machines for manufacturing such pouches are well known in the art.
  • the film of this invention is a sealant film or as a component in a more complex multilayer structure.
  • Typical structures are those known in the art and which will suit the packaging application and still allow the benefits of the enhanced sealing properties of the metallocene or single-site catalyst ethylene/styrene copolymers.
  • this invention provides a process for making pouches filled with a flowable material, using a vertical form, fill and seal apparatus, in which process each pouch is made from a flat web of film by forming a tubular film therefrom with a longitudinal seal and subsequently flattening the tubular film at a first position and transversely heat sealing said tubular film at the flattened position, filling the tubular film with a predetermined quantity of flowable material above said first position, flattening the tubular film above the predetermined quantity of flowable material at a second position and transversely heat sealing said tubular film at the second position, the improvement comprising making the pouches from a flat web of film comprising a multilayer film as described above.
  • the pouch is sealed through its contents.
  • the seal is best produced using impulse sealing means.
  • Vertical form, fill and seal apparatus is used to make the pouches envisaged herein.
  • a flat web of film is unwound from a roll and formed into a continuous tube in a tube forming section by sealing the longitudinal edges together be either a lap seal or a fin seal.
  • This tube is pulled vertically towards a filling station and is then collapsed across a transverse cross section of the tube, the position of which section coincides with a sealing device below a filling station.
  • a transverse heat seal is made at the section providing an air and liquid tight seal across the tube.
  • the material to be packaged enters the tube above the transverse seal; the tube drops a predetermined distance under the influence of gravity on its load.
  • the sealing device is operated again, and a second transverse seal is made together with a cut through the tube and often through the material placed in the pouch.
  • the pouch which has an elongate pillow shape is formed, filled and sealed in a rapid sequence of steps.
  • Examples of typical liquid packaging apparatus used for this type of manufacture are made by Hayssen, Thimonnier and Prepac.
  • the term "flowable materials" as used herein encompasses materials which flow under gravity or which may be pumped. Gaseous materials are not included in this definition.
  • the flowable materials include liquids, for example, milk, water, fruit juice, oil; emulsions, for example, ice cream mix and soft margarine; pastes, for example, meat pastes, peanut butter; preservers, for example, jams, pie fillings, marmalade; jellies; doughs; ground meat, for example, sausage meat; powders, for example, gelatine powders, detergents; granular solids, for example, nuts, sugar; and like materials.
  • the pouch of the present invention is particularly useful for liquid foods, for example, milk.
  • the resins used to make the film of this invention are preferably coextruded in known ways, although other suitable methods may be used, such as those involving laminates, coatings and the like. When blends are used, these may be made by blending the components, prior to or at the time of extrusion, and just prior to remelting in the extruder. A film extruder may be used and the film made using known techniques. An example of a blown film process is found in Canadian Patent No. 460,963 issued November 8, 1949 to Fuller. Canadian Patent No. 893,216 issued February 15, 1972 to Bunga et al describes a preferred method using an external or internal cooling mandrel in the blown film process.
  • Additives known to those skilled in the art, such as anti-block agents, slip additives, UV stabilisers, pigments and processing aids may be added to the polymers from which the pouches of the present invention are made. Typically these may comprise up to 5% by weight of total resin components, although as previously indicated, when the additional additives and other components reach this proportion, it is important to be sensitive to the desired hot tack strength enhancement for the structure.
  • the film of this invention may be used in packaging applications where sealing properties, particularly where hot tack strength is important.
  • a monolayer film may be made from a copolymer of ethylene and styrene (E/S) when high oxygen transmission rates combined with low moisture vapor transmission rates are required, such as for the packaging of fresh fruits and vegetables.
  • E/S ethylene and styrene
  • An example of such a package would be that used to package prepared salads for sale in supermarkets and similar retail outlets.
  • the film would usually be from about 10 to about 50 microns in thickness.
  • a thicker film would be required for packaging foods with a higher bulk density since these thin films would have insufficient yield strength.
  • This structure comprises a three layer film of A/B/A, where A is the E/S copolymer layer which may range from about 5 to about 25 microns in thickness.
  • Layer B may be either of linear low density polyethylene polymer or high density polyethylene ranging in thickness of from about 25 to about 50 microns.
  • This structure has application as a packaging film requiring low heat seal initiation temperature and a high degree of abuse resistance (higher modulus, higher tear strength and hence puncture resistance). The core layer provides these characteristics. When the styrene content is appropriately adjusted, the use of an adhesive layer may be avoided.
  • This coextruded five layer film structure comprises A/B/C/B/A, where A is the E/S layer as described above, but the B layers are co-extrudable adhesive, for example BYNEL ® adhesive, which may be from about 5 to about 15 microns thick.
  • the C layer may be a linear low density polyethylene or high density polyethylene polymer film ranging in thickness of from about 25 to about 50 microns.
  • the C layer may also be an oxygen/flavour barrier layer.
  • a layer or resin that comprises ethylene vinyl alcohol may be used in the film structure.
  • a commercial example of such a resin is EVALCA EVAL ® LC-H101.
  • polyamide which may be amo ⁇ hous or crystalline.
  • Commercial examples include DuPont SELAR ® PA 3426 an amo ⁇ hous nylon resin or film or DuPont DARTEK ® F101, a nylon 6,6 resin or film, or BASF ULRAMID ® B3 nylon 6 resin or film.
  • Another alternative for this type of layer is a polyester film or resin such as that sold by DuPont under the trademark SELAR ® PT 8307 or MYLAR ® polyester film.
  • Yet another choice of flavour/oxygen barrier is a polyvinylidene chloride, such as that sold commercially under the name MORTON SERFENE ® 546 PVDC adhesive.
  • Monolayer Film Structure In this instance, the E/S layer may be laminated to a polyethylene or barrier layer film as described above. The laminating methods are well known in the art and would be apparent to those skilled in the art.
  • a one litre Hoke cylinder was charged with toluene (450 ml), styrene (50ml) and polymethyl aluminoxane (PMAO) (4 ml, 7.9 wt% Al in toluene).
  • a second smaller Hoke cylinder was loaded with a 5 ml toluene solution of 0.06 mole of [(C 5 Me 4 )Si(Me) 2 NC(Me) 3 ]TiCl 2 .
  • a one litre autoclave was assembled and evacuated. The toluene, styrene, and PMAO solution was added to the autoclave and heated to 90°C. The catalyst solution was added to the autoclave along with 180 psig of ethylene.
  • Example 2 A one litre Hoke cylinder was charged with toluene (380 ml), styrene
  • a one litre Hoke cylinder was charged with toluene (350 ml), styrene (150 ml) and PMAO (4 ml, 7.9 wt% Al in toluene).
  • a second smaller Hoke cylinder was loaded with a 5 ml toluene solution of 0.06 mole of [(C 5 Me 4 )Si(Me) 2 NC(Me) 3 ]TiCl 2 .
  • a one litre autoclave was assembled and evacuated. The toluene, styrene and PMAO solution was added to the autoclave and heated to 90 °C . The catalyst solution was added to the autoclave along with 180 psig of ethylene.
  • a one litre Hoke cylinder was charged with toluene (100 ml), styrene (400 ml) and PMAO-IP (3 ml, 9.7 wt% Al in toluene).
  • a second smaller Hoke cylinder was loaded with a 5 ml toluene solution of 0.06 mole of [(C 5 Me 4 )Si(Me) 2 NC(Me) 3 ]TiCl 2 .
  • a one litre autoclave was assembled and evacuated. The toluene, styrene, and PMAO solution was added to the autoclave and heated to 90°C. The catalyst solution was added to the autoclave along with 180 psig of ethylene.
  • the four experimental resin were ground into a coarse powder and then compression moulded into sheets.
  • the compression moulding conditions were as follows: Upper and lower platen temperature had a setpoint temperature of 150°C. Thirteen to fifteen grams of ground resin sample was placed between two TEFLON ® sheets with a third 0.005" thick TEFLON ® sheet with 9.25" by 9.75" opening acting as a frame to contain the sample. The powder was preheat at 150°C for 3 minutes at 1 ton of pressure after which it was pressed for another 4 minutes at 20 tonnes of pressure. After the four minutes the sample was cooled at 36°C per min down to 75 °C at which time the press opened and the sample was removed. Generally the samples were 0.009 to 0.012" thick.
  • Comparative resin sample A was SCLAIR ® 8107 polyethylene (sold by Nova Chemicals) was selected because it had a similar melt index to the ethylene styrene copolymers.
  • Test Results on two blown film samples made from commercially available polyethylene resins were also included for comparison pu ⁇ oses. The two films were made from a Nova Chemicals, Octene lldpe grade called SCLAIR ® HL4b and a Dow Octene polyethylene plastomer called AFFINITY ® PL 1880. The films were blown using a 3/4" diameter, 24/1 L/D extruder with a 1" diameter annular film die and 0.065" die gap. The films were labelled Comp Film B and Comp Film C respectively.
  • This test method consists of heating or cooling the test material at a controlled rate in a controlled atmosphere and comparing the areas under the crystallization exotherm or fusion endotherm of the test material against the respective areas obtained by the similar treatment of a well-characterized standard.
  • Elmendorf Tear Resistance Properties were measured according to ASTM D1922.
  • the Elmendorf Tear value is used to estimate a films resistance to propagating a tear.
  • the film is intentionally notched to initiate the place on the film where tearing will occur.
  • the test measures the difficulty to continue or propagate the tear.
  • the cut-through horizontal seal area often has notches or nicks left in the film from which tears will propagate during handling and or shipping.
  • the Elmendorf Tear test is a useful predictor of how well the area of horizontal seal (which is a cut through seal) will stand up to this abuse. Higher Elmendorf Tear values are preferred. Summary of Test Method
  • the force in grams required to propagate tearing across a film or sheeting specimen is measured using a precisely calibrated pendulum device. Acting by gravity, the pendulum swings through an arc, tearing the specimen from a precut slit. The specimen is held on one side by the pendulum and on the other side by a stationary member. The loss in energy by the pendulum is indicated by a pointer. The scale indication is a function of the force required to tear the specimen.
  • Density by Buoyancy Displacement was measured according to ASTM D792. For polymers synthesized from the same monomers, density is a useful predictor of monomer concentration. In the case of an ethylene styrene copolymer, density increases with increasing styrene content. Summary of Test Method
  • Tensile properties at 20"/min XHS including Tensile Yield, Yield at Break, Elongation at Break and 2% Secant Modulus were determined according to ASTM D882.
  • Tensile properties predict toughness and stiffness of the polymer.
  • the seal must have sufficient strength to resist bursting during the manufacture and filling of the package and downstream abuse.
  • the three values of tensile yield, yield at break and elongation at break predict the toughness of the seal area. Having high tensile yield and high yield at break without a good elongation (preferred +400%) is not a sufficient condition for a good seal layer. Low elongation values indicate the polymer would fail in a brittle mode when the seal layer is stressed.
  • High tensile yield values are generally preferred because the film can be pulled at higher speeds (which induces more film tension) without undesirable stretching of the film. Also a higher tensile yield gives the package better burst strength.
  • the secant modulus is a reflection of film stiffness. A stiffer film can allow down gauging in some applications.
  • a rectangular shaped piece of film 1 inch wide and 6 inches long is gripped at each end, the grips are separated by 4 inches.
  • one grip moves away from the other stationary grip at a constant speed of 20 inches per minute.
  • the resistance or force applied to the grip by the film is measured continuously as a function of the displacement of the jaw, from the start of the test until the film breaks (test end).
  • Tensile Yield, Yield at Break, Elongation at Break and 2% Secant Modulus for the test film can be calculated.
  • Melt Index at 190°C and 2.160 kg load was measured according to ASTM
  • melt index is commonly used in the plastics industry to estimate the rheological properties of the polymer melt. That is, how the polymer will respond to the stresses induced by melting the polymer, pumping the polymer and then blowing the polymer into a thin film. In the melt index test, the resistance of the molten polymer to flow is measured under a constant stress. Polymers with very little resistance to flow have high melt indices. Polymers with a low of resistance to flow have low melt indices. For polymers that will be used to extrusion blow thin films, melt indices in the 1.0 range are commonly used with polydispersity indices from 2 to 5. When the melt index drops below 0.5, the film will have surface roughening, sometimes called "melt fracture".
  • the melt fracture reduces the clarity of the film and ease of heat sealing.
  • the melt index is greater than 5, there may be problems with establishing and maintaining a uniform film gauge around the process.
  • Summary of Test Method Melt Index was measured at 190°C with a 2.160 kg. load. In this test, a plunger pushes the molten polymer through a capillary die under a constant load (force). After the plunger has travelled a specified distance under constant load, the rate of polymer extrusion from the die is determined. The rate of flow (in grams/ 10 minutes) is reported at the melt index.
  • the Kayeness Melt Viscosity was measured at 190°C and 46/s shear rate using a 15/1 L/D orifice with a 0.04" diameter opening according to ASTM procedure D3835.
  • Kayeness viscosity is a more elaborate predictor of polymer rheology compared to a melt index test. In this test the polymer is subjected to four different shear rates and an estimate of the polymer melt viscosity at each shear rate is measured.
  • An ideal polymer for extrusion blowing into a thin film would have a very large viscosity or resistance to flow at low shear rates. This is because low shear is typical of the polymer melt just as it exits the die.
  • the polymer viscosity should be as low as possible to minimize power consumption. Summary of Test Method
  • Kayeness Melt Viscosity was measured at 190°C and 46/s shear rate using a 15/1 L/D orifice with a 0.04 inch diameter opening according to ASTM procedure D3835.
  • a plunger pushes the molten polymer through a capillary die at several pre-selected speeds. The speed, at which the plunger pushes the polymer through the capillary die, is used to estimate the shear rate at the wall of the capillary. The force required to maintain the plunger at that constant speed is continuously recorded and can be used to calculate the shear stress and apparent melt viscosity at the specified melt temperature and shear rate.
  • Styrene content in each sample was determined by Proton Nuclear Magnetic
  • Figure 1 is a representation of a plot of moles of styrene, final melting point of the films tested and Hm (endotherm on melting);
  • Figure 2 is a representation of a plot of Elmendorf Tear, final melting point of the films tested and tensile elongation;
  • Figure 3 is a representation of a plot of Secant Modulus and final melting point of the films tested. DETAILED DESCRIPTION OF THE DRAWINGS Preferred Composition for Seal Layer
  • the ethylene styrene polymers defined by Examples 2 and 3 have superior stiffness to Comp Film C.
  • the stiffness of the ethylene styrene films has been shown in terms of the 2% secant modulus.
  • the ethylene styrene copolymers have 2% secant modulus values of 15000 to 27000 psi. Those values are 2 to 4 times higher than the 6600 psi secant modulus measured on Comp Film C that had a melting point of 102 °C. This substantial improvement in stiffness over Comp film C, permits downgauging and easier processing on high speed filling machines with ethylene styrene compositions of Examples 2 and 3.

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Abstract

L'invention concerne l'utilisation d'un film multicouche thermoscellable pour la fabrication de sacs pouvant contenir des matériaux fluides. Les sacs, de forme tubulaire, ont des extrémités thermoscellées transversalement. Le film comprend au moins une couche représentant 10 % en volume environ de la structure totale du film et constituée d'un copolymère éthylène-styrène obtenu par un procédé de polymérisation utilisant un catalyseur monosite, et une ou plusieurs des couches suivantes: (a) au moins un interpolymère choisi parmi les interpolymères d'éthylène et d'une ou plusieurs α-oléfines C3-C20 obtenus par des procédés de polymérisation utilisant un catalyseur monosite, un catalyseur non monosite et des mélanges desdits catalyseurs, et les mélanges desdits interpolymères, ces derniers ayant une densité comprise entre 0,87 et 0,940 g/cm3 environ et un indice de fluage compris entre 0,2 et 20 dg/min. environ, et représentant 10 à 90 % en volume environ de la structure totale du film; (b) au moins une couche de protection choisie parmi les polymères de nylon, représentant 5 à 30 % en volume environ de la structure totale du film; les polymères de polyéthylène téréphtalate, représentant 5 à 15 % en volume environ de la structure totale; le nylon amorphe, représentant 5 à 30 % en volume environ de la structure totale; l'alcool éthylène vinylique, représentant 5 à 25 % en volume environ de la structure totale; (c) au moins une couche de liaison représentant 5 à 15 % en volume environ de la structure totale et choisie parmi les polymères de polyacétate d'éthylène vinyle, les copolymères d'acide éthylénique, les ionomères ou les copolymères d'éthylène fonctionnalisés anhydres; et (d) au moins un homopolymère d'éthylène haute pression.
EP98916764A 1997-05-02 1998-04-29 Couche de scellement constituee d'un polymere ethylene-styrene pour le conditionnement de liquides Withdrawn EP0977666A1 (fr)

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US4551797P 1997-05-02 1997-05-02
US45517P 1997-05-02
US6466298A 1998-04-23 1998-04-23
US64662 1998-04-23
PCT/CA1998/000424 WO1998050230A1 (fr) 1997-05-02 1998-04-29 Couche de scellement constituee d'un polymere ethylene-styrene pour le conditionnement de liquides

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7700707B2 (en) 2002-10-15 2010-04-20 Exxonmobil Chemical Patents Inc. Polyolefin adhesive compositions and articles made therefrom
US8071687B2 (en) 2002-10-15 2011-12-06 Exxonmobil Chemical Patents Inc. Multiple catalyst system for olefin polymerization and polymers produced therefrom

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8697164B2 (en) 2011-04-18 2014-04-15 Dole Fresh Vegetables, Inc. Commercial lettuce packaging in the field
US20140120377A1 (en) * 2011-06-30 2014-05-01 Dupont Teijin Films U.S. Limited Partnership Dimensionally stable multi-layer polyester films

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Publication number Priority date Publication date Assignee Title
CA2166188A1 (fr) * 1993-06-24 1995-01-05 John P. Eckstein Structures polymeriques ameliorees, obtenues a partir de catalyseurs de types metallocenes
US5658625A (en) * 1994-05-25 1997-08-19 W.R. Grace & Co.-Conn. Film containing alpha-olefin/vinyl aromatic copolymer

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9850230A1 *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US7700707B2 (en) 2002-10-15 2010-04-20 Exxonmobil Chemical Patents Inc. Polyolefin adhesive compositions and articles made therefrom
US8071687B2 (en) 2002-10-15 2011-12-06 Exxonmobil Chemical Patents Inc. Multiple catalyst system for olefin polymerization and polymers produced therefrom
US8088867B2 (en) 2002-10-15 2012-01-03 Exxonmobil Chemical Patents Inc. Multiple catalyst system for olefin polymerization and polymers produced therefrom
US8957159B2 (en) 2002-10-15 2015-02-17 Exxonmobil Chemical Patents Inc. Multiple catalyst system for olefin polymerization and polymers produced therefrom

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CA2288865A1 (fr) 1998-11-12
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