WO1992012010A1 - Heat sealable multilayer polyolefinic film structures - Google Patents

Heat sealable multilayer polyolefinic film structures Download PDF

Info

Publication number
WO1992012010A1
WO1992012010A1 PCT/US1992/000221 US9200221W WO9212010A1 WO 1992012010 A1 WO1992012010 A1 WO 1992012010A1 US 9200221 W US9200221 W US 9200221W WO 9212010 A1 WO9212010 A1 WO 9212010A1
Authority
WO
WIPO (PCT)
Prior art keywords
layer
film structure
linear polyethylene
heat
heat seal
Prior art date
Application number
PCT/US1992/000221
Other languages
French (fr)
Inventor
Pak-Wing S. Chum
Kaelyn C. Koch
Original Assignee
The Dow Chemical Company
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Family has litigation
First worldwide family litigation filed litigation Critical https://patents.darts-ip.com/?family=24564988&utm_source=google_patent&utm_medium=platform_link&utm_campaign=public_patent_search&patent=WO1992012010(A1) "Global patent litigation dataset” by Darts-ip is licensed under a Creative Commons Attribution 4.0 International License.
Application filed by The Dow Chemical Company filed Critical The Dow Chemical Company
Priority to EP92904532A priority Critical patent/EP0566679B1/en
Priority to AU12316/92A priority patent/AU667802B2/en
Priority to DE69208646T priority patent/DE69208646T2/en
Publication of WO1992012010A1 publication Critical patent/WO1992012010A1/en

Links

Classifications

    • BPERFORMING OPERATIONS; TRANSPORTING
    • B32LAYERED PRODUCTS
    • B32BLAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00Layered products comprising a layer of synthetic resin
    • B32B27/06Layered 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
    • B32B27/08Layered 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
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B32LAYERED PRODUCTS
    • B32BLAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00Layered products comprising a layer of synthetic resin
    • B32B27/32Layered products comprising a layer of synthetic resin comprising polyolefins
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B32LAYERED PRODUCTS
    • B32BLAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2250/00Layers arrangement
    • B32B2250/24All layers being polymeric
    • B32B2250/242All polymers belonging to those covered by group B32B27/32
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B32LAYERED PRODUCTS
    • B32BLAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00Properties of the layers or laminate
    • B32B2307/30Properties of the layers or laminate having particular thermal properties
    • B32B2307/31Heat sealable
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B32LAYERED PRODUCTS
    • B32BLAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2307/00Properties of the layers or laminate
    • B32B2307/70Other properties
    • B32B2307/732Dimensional properties
    • B32B2307/734Dimensional stability
    • B32B2307/736Shrinkable
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B32LAYERED PRODUCTS
    • B32BLAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2323/00Polyalkenes
    • B32B2323/04Polyethylene
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B32LAYERED PRODUCTS
    • B32BLAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B2439/00Containers; Receptacles
    • B32B2439/70Food packaging
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10STECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S428/00Stock material or miscellaneous articles
    • Y10S428/91Product with molecular orientation
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10TTECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00Stock material or miscellaneous articles
    • Y10T428/24Structurally defined web or sheet [e.g., overall dimension, etc.]
    • Y10T428/24942Structurally defined web or sheet [e.g., overall dimension, etc.] including components having same physical characteristic in differing degree
    • Y10T428/24992Density or compression of components
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10TTECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00Stock material or miscellaneous articles
    • Y10T428/28Web or sheet containing structurally defined element or component and having an adhesive outermost layer
    • Y10T428/2813Heat or solvent activated or sealable
    • Y10T428/2817Heat sealable
    • Y10T428/2826Synthetic resin or polymer
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10TTECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00Stock material or miscellaneous articles
    • Y10T428/31504Composite [nonstructural laminate]
    • Y10T428/31725Of polyamide
    • Y10T428/31739Nylon type
    • Y10T428/31743Next to addition polymer from unsaturated monomer[s]
    • Y10T428/31746Polymer of monoethylenically unsaturated hydrocarbon
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10TTECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00Stock material or miscellaneous articles
    • Y10T428/31504Composite [nonstructural laminate]
    • Y10T428/31855Of addition polymer from unsaturated monomers
    • Y10T428/31909Next to second addition polymer from unsaturated monomers
    • Y10T428/31913Monoolefin polymer
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10TTECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00Stock material or miscellaneous articles
    • Y10T428/31504Composite [nonstructural laminate]
    • Y10T428/31855Of addition polymer from unsaturated monomers
    • Y10T428/31909Next to second addition polymer from unsaturated monomers
    • Y10T428/31913Monoolefin polymer
    • Y10T428/3192Next to vinyl or vinylidene chloride polymer

Definitions

  • This invention relates to oriented multilayer, heat sealable thermoplastic film structures. More particularly, the invention relates to multilayer film structures which retain heat sealability even after irradiation.
  • irradiation is used in some instances to destroy micro-organisms in the wrapped product (e.g., in food sterilization) and to also prepare at least one component of the film for thermal shrinkage at a later time.
  • Multilayer film packaging has many requirements for both enduring the irradiation exposure and preparing part of the structure for subsequent shrinkage.
  • the package is a multilayer structure, with the different layers performing different functions.
  • the layers are made from thermoplastic polymers.
  • one layer may be a barrier layer (e.g., ethylene vinyl alcohol (EVOH)), the heat seal layer may be a polyethylene (e.g., linear low density polyethylene
  • HDPE high density polyethylene
  • Irradiation of multilayer film structures can be done by exposure to Cobalt 60 (gamma irradiation) or
  • the heat sealability of the heat seal layer often decreases (i.e., the intiation temperature of the heat sealing increases), especially when the heat seal layer is polyethylene, while the
  • the core layer and the heat seal layer 20 also cause the core layer and the heat seal layer to shrink, especially when the multilayer structure has been oriented (e.g., film). Controlled shrinkage of the core layer is desirable, but a narrower heat sealing 2c temperature range of the heat seal layer is not desirable.
  • USP 4,927,708 discloses an improvement in multilayer thermoplastic film having at least 5 layers wherein a core layer comprises a very low density polyethylene, intermediate layers adjacent each side of the core layer comprising a linear low density polyethylene and two outer layers each bonded to the respective intermediate layer comprising a very low density polyethylene.
  • the very low density polyethylene can have a density between 0.890 and 0.915 grams/cubic centimeter (g/cm 3 ).
  • USP 4,798,081 discloses a method and apparatus for analyzing a solution of a crystalline or semi-crystalline polymer sample (e.g., polyethylene).
  • the analysis includes temperature rising elution fractionation (TREF) which measures the degree of branching of select fractions of the polymer sample.
  • TEZ temperature rising elution fractionation
  • USP 4,755,419 discloses a 7-layer coextruded oriented film comprising a core layer of ethylene-vinyl alcohol copolymer.
  • two intermediate layers each comprising a polyamide
  • two outer layers each comprising a blend of polymeric materials and two layers each comprising an adhesive polymeric material.
  • the blend of polymeric materials are taken from the group consisting of (i) a blend of linear low density polyethylene, a linear medium density polyethylene and an ethylene vinyl acetate copolymer and (ii) a blend of an ethylene propylene copolymer and a polypropylene.
  • USP 4,724,185 discloses a coextruded multiple layer oriented film.
  • the core layer comprises a cross-linked blend of ethylene vinyl alcohol copolymer and polyamide.
  • Two cross-linked interior layers each comprising adhesive resins and two cross-linked outer layers each comprising a 3 component blend of linear low density polyethylene, linear medium density polyethylene and ethylene-vinyl acetate, are each included in the multiple layer film.
  • USP 4,668,752 discloses ethylene/Ci
  • the 5 ethylene copolymers have various properties, including a melt flow rate of from 0.01 to 200 g/10 minutes, a molecular weight distribution measured as Mw/Mn of 2.5 ⁇ Mw/Mn '- 10, a density of from 0.850 to 0.930 g/cm 3 , the amount of components having a degree of 0 branching of not more than 2/1000 carbons of not more than 10 percent by weight based on the ethylene copolymer and the amount of components having a degree of branching of at least 30/1000 carbons of not more c than 70 percent by weight based on the eth/lene copolymer.
  • the disclosure alleges that the ethylene copolymers made using this invention have excellent mechanical properties, optical properties, blocking resistance, heat resistance and low temperature heat sealability in a well balanced combination.
  • Tominari et al. do not specify how the ethylene/Ci-C20 alpha-olefin copolymers perform when exposed to irradiation, much less how they perform when in a multilayer structure that is exposed to irradiation.
  • USP 4,640,856 discloses multi-layer thermoplastic shrink film having improved shrink, toughness and barrier properties achieved by a substrate layer of very low density polyethylene and a gas barrier layer of vinylidene chloride copolymer or ethylene-vinyl alcohol.
  • the very low density polyethylene can have a density of less than 0.910 g/cm 3 and as low as 0.860 g/cm 3 or even lower, there is no disclosure as to the molecular weight distribution, nor 0 is there any reference to the short chain branching distribution of the substrate layer.
  • USP 4,352,849 discloses multilayer heat shrinkable packaging film comprising a core layer 5 consisting essentially of an ethylene-propylene copolymer blended with an ethylene-vinyl acetate copolymer and a skin or surface layer comprising an ethylene-propylene copolymer.
  • USP 4,064,296 (Bornstein et al. ) discloses a multi-layer packaging film having low oxygen permeability comprising two polymeric layers, at least one of which is cross-linked, and a layer between the c polymeric layers comprising a hydrolyzed ethylene vinyl acetate copolymer.
  • the two polymeric layers can comprise polyethylene, although the type of polyethylene is not specified.
  • a multilayer heat-sealable thermoplastic film structure has now been discovered that has improved heat seal performance after irradiation.
  • the novel multilayer film structure comprises at least one heat sealable outer layer (A) and at least one core layer
  • Layer (A) of the multilayer thermoplastic film structure comprises a first linear polyethylene characterized as having: pe - (a) a density from 0.88 grams/cubic centimeter
  • melt index measured as 12? from 2 grams/10 minutes to 20 grams/10 minutes
  • Layer (B) comprises a second linear polyethylene characterized as having: 5 (a) a density from 0.88 g/cm 3 , to 0.94 g/cm 3 ,
  • melt index measured as l2» from 0.05 grams/10 minutes to 5 gram/10 minutes
  • Figure 1 shows the preparative scale temperature rising elution fractionation apparatus used to determine the branching distribution in the polymer 15 fractions.
  • Figure 2 plots heat seal strength (measured in Newtons/inch) versus heat seal temperature (in °F) of three ultra low density polyethylene (ULDPE) resins made into film.
  • ULDPE ultra low density polyethylene
  • Figure 3 plots cross-link density (measured in percent gel) versus radiation dosage (in megarads) of two ULDPE resins made into film.
  • Figure 4 plots heat seal strength (measured in pt - Newtons/inch) versus heat seal temperature (in °F) of one ULDPE resin made into film after different levels of exposure to irradiation.
  • Figure 5 plots heat seal strength (measured in Newtons/inch) versus heat seal temperature (in °F) of 30 one ULDPE resin made into film after different levels of exposure to irradiation.
  • Figure 6 plots cross-link density (measured in percent gel) versus radiation dosage (in megarads) of one LLDPE resin made into film.
  • Figure 7 depicts one multilayer film structure of the present invention.
  • the multilayer structures of the present invention comprise at least one heat-sealable outer 5 layer and at least one core layer.
  • the multilayer structure can have many layers, but the heat-sealable layer of the present invention must be on at least one outer surface of the structure to take advantage of the ln improvement in heat seal characteristics.
  • Typical multilayer structures can be made using a coextruded blown or cast film process.
  • Figure 7 shows a multilayer structure of the present invention.
  • the structures of the film product can generally be described as an
  • layer A (18) is the heat sealable outer layer
  • layer B (19) is the core layer
  • layers D (20) and/or X (21) are a tie layer(s) and/or a barrier layer(s).
  • the core layer (19) can be adjacent to the heat seal layer, but does not have to
  • the multilayer film structure is comprised of from 2 to 20 layers, preferably from 2 to 7 layers.
  • the multilayer film structure can be irradiated pc - at any point during the process.
  • the heat- sealable outer layer and the core layer of the present invention can be coextruded, irradiated and subsequently laminated and oriented (i.e., stretched) to make the final multilayer film structure, so long as the heat- 30 sealable outer layer is on at least one outer surface of the structure.
  • the entire multilayer structure can be formed and oriented, and then subsequently irradiated.
  • the order of the steps of orientation and irradiation is not critical. Irradiation is preferably accomplished by using an electron beam (beta) irradiation device at a dosage level of from 0.5 megarad (Mrad) to 20 Mrad.
  • Thickness of the multilayer film structures can vary from 0.1 mil to 50 mils (.0025 mm to 1.3 mm), zz, preferably from 0.5 mils to 10 mils. (.013 mm to .25 mm).
  • the tie layer(s) and/or the barrier layer(s) are made from conventional thermoplastic polymers known to be useful for this purpose, especially polyolefinic 10 polymers.
  • Thermoplastic polymers useful as the tie layer(s) include ethylene acrylic acid interpolymers (e.g., U.S. Patent 4,599 * 392), ethylene methacrylic acid 15 interpolymers (e.g., U.S. Patent 4,248,990 and U.S.
  • Patent 4,252,924 succinic acid or succinic anhydride grafted polyolefins and blends with ungrafted polyolefins (e.g., U.S. Patents 4,684,576, 4,741,970 and 4,394,485), vinyl acetate interpolymers.
  • Thermoplastics e.g., U.S. Patents 4,684,576, 4,741,970 and 4,394,485), vinyl acetate interpolymers.
  • polymers useful for the barrier layer(s) include EV0H, polyvinyl chloride, polyvinylidene chloride, and nylon.
  • the heat-sealable outer layer and the core pt - layer of the present invention are fabricated from linear polyethylene.
  • Manufacture of linear polyethylene is disclosed, e.g., in U.S. Patent 4,076,698 and involves coordination catalysts of the "Ziegler” type or “Phillips” type and includes variations of the Ziegler 30 type, such as the Natta type. These catalysts may be used at very high pressures, but may also (and generally are) used at very low or intermediate pressures.
  • the products made by these coordination catalysts are generally known as "linear" polymers because of the substantial absence of branched chains of polymerized monomer units pendant from the main polymer "backbone.” It is these linear polymers to which the present invention pertains.
  • Linear low density polyethylene (LLDPE) and ultra low density polyethylene (ULDPE) typically have a density between about 0.88 g/cm 3 and about 0.94 g/cm 3 .
  • the density of the polyethylene is lowered by copolymerizing ethylene with minor amounts of an alpha, beta-ethylenically unsaturated alkene(s) having from 3 to 20 carbons per alkene molecule (e.g., ⁇ n 1-propene, 1-butene, 1-pentene, 4-methyl-l-pentene, 1- hexene, 1-octene, 1,9-decadiene and 1,7-octadiene) , preferably 4 to 8 carbon atoms (e.g., 1-butene, 1-hexene and 1-octene) and most preferably 8 carbons per alkene molecule (i.e., 1-octene).
  • the amount of the alkene e.g., ⁇ n 1-propene, 1-but
  • linear low density polyethylene is generally sufficient to cause the density of the linear low density polymer to be substantially in the same density range as LDPE, due to the alkyl side chains on the polymer molecule, yet the polymer remains in the "linear” classification; they are conveniently 0 referred to as "linear low density polyethylene.”
  • the density of the linear polyethylene useful in the heat sealable outer layer (A) in the present invention is from 0.88 g/cm 3 to 0.92 g/cm 3 , preferably from 0.89 g/cm 3 to 0.915 g/cm 3 .
  • the density of the linear polyethylene useful in the core layer (B) in the present invention is from 0.88 g/cm 3 to 0.94 g/cm 3 , preferably from 0.9 g/cm 3 to 0.93 g/cm 3 .
  • the molecular weight of the LLDPE useful in the present invention is indicated and measured by melt
  • the 12 of the linear polyethylene used in the heat sealable outer layer (A) can be as low as 0.5 grams/10 minutes, but is
  • the 12 of the linear polyethylene used in the core layer (B) can be from 0.05 g/10 minutes to 5 g/10 minutes, preferably from 0.2 g/10 minutes to 1 g/10 0 minutes.
  • the molecular weight distribution is indicated and measured by I-JO/12 according to ASTM D-1238, Conditions (N) (190°C/10 kilograms) and (E), 5 respectively.
  • the I10 I2 of the heat sealable outer layer (A) can be from 5 to 8, preferably from 6.5 to 8.
  • the I10/I2 of the core layer (B) can be from 8 to 30, preferably from 8 to 15.
  • Molecular weight distribution can be achieved by varying catalytic conditions, reactor 0 conditions or feed percentages.
  • Blends of polyethylenes can also be used. Such blends can be prepared by blending separate and discrete polyethylene polymers, or polymerizing the polyethylene polymer in-situ in multiple reactors, (e.g. the technique disclosed in U.S. Patent 3 * 914,342). It is important that the linear polyethylene(s) be well mixed when using discrete polymer blends.
  • Additives may be incorporated into the linear polyethylene to the extent that they do not interfere with the heat sealability of the outer layer and the shrinkability of the core layer after orientation and exposure to irradiation.
  • Short chain branching distribution (SCBD) of the polymer fractions of the polyethylene polymers useful in the heat seal layer and the core layer is measured according to the temperature rising elution fractionation (abbreviated herein as "TREF”) technique described herein and in U.S. Patent 4,798,081.
  • SCBD Short chain branching distribution
  • FIG. 1 A diagram of the TREF apparatus is shown in Figure 1.
  • the column (1) is 4 inches (10 cm) in diameter and 29 inches (74 cm) in length, a size easily capable of fractionating up to 20 grams of sample.
  • the column is packed with stainless steel shot (2) and heated by a circulating oil bath (3).
  • the entire apparatus is enclosed within a hood (not shown) to contain any solvent or heating oil vapors.
  • the column is constructed of 4 inch (10 cm) schedule 40 steel pipe. Legs of one inch (2.5 cm) angle iron were welded on the pipe to keep it in a vertical position. The end caps are welded on the pipe to prevent any solvent leakage into the oil system. A one inch (2.5 cm) hole is left in each end to allow for packing of the column and to accomodate a 1 inch MPT
  • the column is tightly packed with 0.028 inch (.07 cm) diameter stainless steel shot.
  • the interstitial volume of the column is approximately 1700 milliliters.
  • Stainless steel shot effectively prevents channeling and provides good heat transfer through the column.
  • the column temperature is regulated by a Haake N3B circulating bath controlled by a Haake PG-20 temperature programmer (4).
  • the oil used is Primol 355 mineral oil or a light silicon oil.
  • the 10 gallon (38 1) insulated bath (5) containing the column is galvanized steel.
  • the oil circulator injects oil at the bottom of this bath with the return from the top.
  • An air driven motor (6) is used for agitation of the large oil bath.
  • the solvent used is 1, 2, 4-trichlorobenzene (TCB) (12). It is pumped from a reservoir (7) into the bottom of the column through a preheating coil (8) located in the large bath. The solvent is pumped at a flow rate of approximately 40 ml/minute using a Fluid Metering, Inc. lab pump (9) designated RP-G-150 with a 2-SSY (3/8 inch or 0.95 cm) stainless steel pump head module. This pump allows control of flow rates from 1 to 100 milliliters/minute.
  • TCB 1, 2, 4-trichlorobenzene
  • Polymer samples (13) are loaded on the column utilizing a gravity flow method.
  • the sample is first dissolved in 1700 ml of TCB in a heated 5 liter flask (10).
  • the 130°C column is then loaded with the solution, also at 130°C.
  • One hundred milliliters of clean solvent is then heated and added to flush all transfer lines. These lines are heated with rheostat controlled heat tape (not shown).
  • the polymer sample (about 20 grams) is dissolved in 1700 ml of TCB in a heated 5 liter flask. Approximately 3 to 4 hours is required to carry out this step.
  • the column, the flask, and all transfer lines must be above 120°C to insure that no polymer is precipitated during the loading step.
  • a wash of fresh solvent is used to eliminate all polymer from the transfer lines. The amount of wash is dependent on the volume of the transfer lines (about 100 ml for this system).
  • the entire system must be brought back down to room temperature, with the rate of cooling being the most critical step in the fractionation procedure. The rates for this system are between 1°C and 2°C/hr.
  • a temperature recorder (15) equipped with a thermocouple (16) in the recirculating oil and a thermocouple (17) in the packed column is used to monitor the temperature changes.
  • the polymer selectively crystallizes allowing for efficient fractionation during the elution step. There is no solvent flow through the column during the cool- down step.
  • Elution of the polymer from the column is started at room temperature with a predetermined temperature rise rate. Solvent flows continuously during this step and fractions are collected over the desired change in temperature (5°C for this work).
  • the temperature rise rate used here is 6°C/hr.
  • the temperature rise can be achieved in two ways, stepwise or continuous. Solvent flow rates (40 ml/min) are chosen to achieve one interstitial column volume over the desired change in temperature. These rates result in a fraction collection every 50 minutes.
  • fractions are mixed about 1:1 with acetone and allowed to sit for at least one day to precipitate the polymer.
  • the polymer-TCB-acetone mixture is then added to a large separatory funnel, and allowed to sit for several minutes until the polymer rises to the top.
  • Branching content i.e., degree of branching
  • CH3/IOOO C methyls/1000 carbons
  • the polyethylene samples are prepared at a concentration of 0.25 grams of polyethylene in 50 milliliters of TCB. The volume injected is 100 microliters.
  • a Perkin-Elmer Infrared (IR) Model 760 is used to measure vinyl groups in the polymer chains.
  • the polymer is compression molded into a thin film and measured for thickness (target is approximately 0.1-0.3 mm thick).
  • the IR absorbancy spectrum is measured for each film and vinyl group content is calculated according to the following equation:
  • the vinyl groups/1000 carbons value obtained is inserted into the equation for determining corrected CH3/IOOO carbons for each polymer fraction as described earlier in Section D in this disclosure.
  • the first linear polyethylene suitable for use as the heat seal layer (A) in the present invention has a degree of branching less than or equal to 2 methyls/1000 carbons in 15 percent by weight or less, more preferably 10 percent by weight or less, of the linear polyethylene and a degree of branching equal to or greater than 25 methyls/1000 carbons in 25 percent by weight or less, more preferably 20 percent by weight or less, of the first linear polyethylene.
  • Example 1
  • This example demonstrates heat seal performance of three ULDPE Resins with different short chain branching distributions (SCBD).
  • ATTANE* 4002 ULDPE (labeled as Resin A), an ethylene/octene-1 copolymer made by The Dow Chemical
  • Resins A and B had similar short chain branching distributions but differed in I2 and I ⁇ o/l2«
  • Resin C had a "narrower" short chain branching distribution as compared to Resins A and B, as measured pc - using TREF, since about 8.5 percent (total weight basis) of Resin C had a degree of branching of less than or equal to 2 methyls /1000 carbons and about 18.5 percent (total weight basis) of Resin C had a degree of branching of greater than or equal to 25 methyls /1000
  • the fabrication conditions of the cast film are listed in Table 2.
  • the cast film samples were compared for heat seal performance and heat seal strength using an Instron peel test.
  • Film samples for heat seal testing were conditioned as described in ASTM E 171-82 (i.e., 73.4 +/- 3.6 °F (21-25°C), 50+/- 5 percent relative humidity) .
  • the heat seal tests were performed utilizing a heat sealer. A variety of equipment exists for this function, such as a Sentinel Heat Sealer, a Theller Precision Heat Sealer and a Packforsk Hot Tack Tester (made by Top Wave).
  • the conditions for sealing were typically 0.5 second dwell time, 40 psi (275 kPa) bar pressure. Both bars were heated.
  • One inch (2.5 cm) wide by six inch (15 cm) long strips were used for testing.
  • Resin C had a "narrower" SCBD and exhibited an improved heat seal performance (i.e., lower heat seal initiation temperature and higher seal strength at below 210°F) as compared to Resin A and Resin B.
  • Resin C is thus an example of this invention and can be used as a heat seal layer in a multilayer film structure.
  • This example demonstrates heat seal performance of electron beam irradiated ULDPE.
  • Resin B and Resin C were evaluated for heat seal performance and cross-link density (measured by percent gel) prior to and after electron beam irradiation.
  • An Energy Science Inc. Model EC 200 electron beam radiation machine was used for the radiation treatment.
  • the crosslink density indicates the resins' propensity for heat seal performance.
  • the cross-link densities of the resins before and after various doses of radiation treatment are illustrated in Figure 3 and the data are summarized in Table 4. As the data show, resin C can be exposed to about 5 megarads (Mrad) and still maintain a cross-link density of less than about 10 percent gel and thus is an example of this invention. Resin B reached a cross-link density of about 10 percent gel in less than about 3 Mrad exposure and is not an example of this invention for use in the heat seal layer.
  • Resin B heat seal performance deteriorated significantly.
  • Resin B achieved a heat seal strength of about 10 Newtons/inch (4 Newtons/cm) only after heat sealing at a temperature of about 215°F ( 102°C) or more.
  • This example demonstrates radiation crosslinking performance of LLDPE resins to be used for the core layer of the multi-layer film products with improved heat seal, orientation and shrink performance.
  • the blown film is made using a STERLING Blown Film Line. This line has a 3.5 inch (8.9 cm) diameter extruder, L/D of 30:1, an 8 inch (20 cm) diameter Western Polymer die with a 70 mil (1.8 mm) die gap, a STERLEX barrier type screw and Internal Bubble Cooling (IBC).
  • Film samples made from this resin were treated by electron beam radiation using an Energy Science Incorpoated electron beam radiation machine (Model EC200; 200 KeV) .
  • the treated polymer film was evaluated for propensity for thermal shrinkage by measuring percent gel (i.e., crosslink density) by the solvent extraction technique as described in Example 2.
  • This example demonstrates a two layer co ⁇ extruded film product having improved heat seal, crosslinking and orientation/shrink performance after irradiation to 3 Mrad.
  • a 1 mil (0.025 mm) thick 2-layer (A/B) co ⁇ extruded film sample was fabricated by the following blown film process:
  • Two layer blown films were prepared in accordance with this invention by fabrication on an Egan coextrusion blown film line equipped with a 2.5 inch (6.4 cm) diameter main extruder, a 1.5 inch (3.8 cm) skin layer extruder and a 2 layer single air ring cooled annular die.
  • the multilayer laminated film structure was an A/B configuration in which:
  • the "A-layer” was the heat seal layer and was extruded through the outer annular die as the outer layer.
  • the "A-layer” extruder was a 1.5 inch (3.8 cm) Egan having an L/D ratio of 20:1.
  • the extruder had four zones temperature control. This extruder was used to feed Resin C— to the outer layer. This layer was maintained at a thickness of approximately 0.15 mils (0.0038 mm).
  • the temperature profile of this extruder was as follows:
  • the polymer melt temperature was about 225°C.
  • the throughput rate was about 18 pounds/hour (8.2 kg/hr).
  • the "B-layer” is the support or core layer and was extruded through the inner annular die as the inside layer.
  • the "B-layer” extruder was a 2.5 inch (6.35 cm) Egan having a screw L/D ratio of 24:1. This extruder is used to feed Resin D to the middle annular die to form the inner layer at a throughput of about 110 pounds/hour (50 kg/hr) and at a melt temperature of about 225°C. The thickness of this layer is approximately 0.85 mils ( 0.022 mm).
  • the temperature profile of this extruder is as follows:
  • Resin C described in Example 2 was used to fabricate the heat seal layer and Resin D described in Example 3 was used to fabricate the other layer.
  • the thickness of the heat seal layer is approximately 15 percent of the total film thickness of about 1 mil (0.025 mm).
  • the film sample is irradiated at 3 Mrad using an Energy Science Incorporated electron beam radiation machine (Model EC200).
  • the total crosslink density of the film, measured as percent gel, after the radiation treatment was approximately 16 percent. At crosslink densities of between about 10 percent and about 25 percent, the film is known to have ideal performance for orientation and shrink applications. -32-
  • the heat seal performance (heat seal layer to heat seal layer) of this co-extruded crosslinked film was evaluated by the method described in Example 1.
  • Table 8 illustrates the heat seal strength of the heat seal layer of film before and after radiation treatment
  • the invention is particularly useful in heat- seal packaging of food, whereby the packaged food is exposed to irradiation for sterilization purposes.
  • the irradiation simultaneously strengthens the core layer and prepares it for shrinkage upon subsequent exposure to heat.
  • the heat seal initiation temperature of the heat seal layer is maintained after irradiation and the heat seal strength of the package is substantially maintained.

Abstract

Multilayer thermoplastic film structures comprising at least one heat-sealable outer layer (A) and at least one core layer (B) are disclosed. Layer (A) has improved heat sealability after irradiation (e.g. electron beam). Layer (B) has improved shrinkage after irradiation. Layer (A) is a linear polyethylene having a melt index from 2 to 20 g/10 minutes, a density from 0.88 to 0.92 g/cm?3, a molecular weight distribution (I10?/I2?) from 5 to 8, a fraction of the polyethylene having a degree of branching less than or equal to 2 methyls/1000 carbons of not more than 15 percent by weight and a fraction of the polyethylene having a degree of branching greater than or equal to 25 methyls/1000 carbons of not more than 25 percent by weight of the polymer. Layer (B) is a linear polyethylene having a melt index from 0.05 to 5 g/10 minutes, a density from 0.88 to 0.94 g/cm?3 and a molecular weight distribution (I10?/I2?) from 8 to 30.

Description

Heat sealable multilayer polyolefinlc film structures.
This invention relates to oriented multilayer, heat sealable thermoplastic film structures. More particularly, the invention relates to multilayer film structures which retain heat sealability even after irradiation.
Many polymers have been developed which can withstand exposure to irradiation, often incorporating specific additives or antioxidants which prevent polymer degradation. Films and multilayer films made from these and other polymers are sometimes exposed to irradiation during processing or use. For example, irradiation is used in some instances to destroy micro-organisms in the wrapped product (e.g., in food sterilization) and to also prepare at least one component of the film for thermal shrinkage at a later time.
Multilayer film packaging has many requirements for both enduring the irradiation exposure and preparing part of the structure for subsequent shrinkage. Typically, the package is a multilayer structure, with the different layers performing different functions. Usually the layers are made from thermoplastic polymers. -2-
For example, one layer may be a barrier layer (e.g., ethylene vinyl alcohol (EVOH)), the heat seal layer may be a polyethylene (e.g., linear low density polyethylene
(LLDPE)), while still another type of polyethylene
(e.g., high density polyethylene (HDPE)) might be used 5 as the structural or core layer.
Irradiation of multilayer film structures can be done by exposure to Cobalt 60 (gamma irradiation) or
10 by electron beam (beta). When the entire multilayer film structure is irradiated, the heat sealability of the heat seal layer often decreases (i.e., the intiation temperature of the heat sealing increases), especially when the heat seal layer is polyethylene, while the
15 physical properties (e.g., strength) of the structural layer increase. Reduction in heat sealability causes lower heat seal strengths and narrower heat sealing temperature ranges. Exposure to irradiation, especially beta irradiation, and subsequent exposure to heat can
20 also cause the core layer and the heat seal layer to shrink, especially when the multilayer structure has been oriented (e.g., film). Controlled shrinkage of the core layer is desirable, but a narrower heat sealing 2c temperature range of the heat seal layer is not desirable.
Irradiation of the heat seal layer also results in higher heat seal initiation temperatures as well as 30 narrower heat seal temperature ranges. The narrow heat seal range of the heat seal layer can cause the wrapped product to become exposed to the external environment and contamination, thus negating the sterilizing effects of irradiation. USP 4,927,708 (Herran et al.) discloses an improvement in multilayer thermoplastic film having at least 5 layers wherein a core layer comprises a very low density polyethylene, intermediate layers adjacent each side of the core layer comprising a linear low density polyethylene and two outer layers each bonded to the respective intermediate layer comprising a very low density polyethylene. The very low density polyethylene can have a density between 0.890 and 0.915 grams/cubic centimeter (g/cm3). There is no disclosure as to the molecular weight distribution, nor is there any reference to the short chain branching distribution of any of the layers.
USP 4,798,081 (Hazlitt et al.) discloses a method and apparatus for analyzing a solution of a crystalline or semi-crystalline polymer sample (e.g., polyethylene). The analysis includes temperature rising elution fractionation (TREF) which measures the degree of branching of select fractions of the polymer sample.
USP 4,755,419 (Shah) discloses a 7-layer coextruded oriented film comprising a core layer of ethylene-vinyl alcohol copolymer. two intermediate layers each comprising a polyamide, two outer layers each comprising a blend of polymeric materials and two layers each comprising an adhesive polymeric material. The blend of polymeric materials are taken from the group consisting of (i) a blend of linear low density polyethylene, a linear medium density polyethylene and an ethylene vinyl acetate copolymer and (ii) a blend of an ethylene propylene copolymer and a polypropylene. USP 4,724,185 (Shah) discloses a coextruded multiple layer oriented film. The core layer comprises a cross-linked blend of ethylene vinyl alcohol copolymer and polyamide. Two cross-linked interior layers each comprising adhesive resins and two cross-linked outer layers each comprising a 3 component blend of linear low density polyethylene, linear medium density polyethylene and ethylene-vinyl acetate, are each included in the multiple layer film. 0
USP 4,668,752 (Tominari et al.) discloses ethylene/Ci|-C20 alpha-olefin copolymers which have new characteristics in regards to composition distribution, degree of branching, randomness and crystallinity. The 5 ethylene copolymers have various properties, including a melt flow rate of from 0.01 to 200 g/10 minutes, a molecular weight distribution measured as Mw/Mn of 2.5 ≤ Mw/Mn '- 10, a density of from 0.850 to 0.930 g/cm3, the amount of components having a degree of 0 branching of not more than 2/1000 carbons of not more than 10 percent by weight based on the ethylene copolymer and the amount of components having a degree of branching of at least 30/1000 carbons of not more c than 70 percent by weight based on the eth/lene copolymer. The disclosure alleges that the ethylene copolymers made using this invention have excellent mechanical properties, optical properties, blocking resistance, heat resistance and low temperature heat sealability in a well balanced combination. Tominari et al. do not specify how the ethylene/Ci-C20 alpha-olefin copolymers perform when exposed to irradiation, much less how they perform when in a multilayer structure that is exposed to irradiation. USP 4,640,856 (Ferguson et al.) discloses multi-layer thermoplastic shrink film having improved shrink, toughness and barrier properties achieved by a substrate layer of very low density polyethylene and a gas barrier layer of vinylidene chloride copolymer or ethylene-vinyl alcohol. The very low density polyethylene can have a density of less than 0.910 g/cm3 and as low as 0.860 g/cm3or even lower, there is no disclosure as to the molecular weight distribution, nor 0 is there any reference to the short chain branching distribution of the substrate layer.
USP 4,352,849 (Mueller) discloses multilayer heat shrinkable packaging film comprising a core layer 5 consisting essentially of an ethylene-propylene copolymer blended with an ethylene-vinyl acetate copolymer and a skin or surface layer comprising an ethylene-propylene copolymer.
0
USP 4,064,296 (Bornstein et al. ) discloses a multi-layer packaging film having low oxygen permeability comprising two polymeric layers, at least one of which is cross-linked, and a layer between the c polymeric layers comprising a hydrolyzed ethylene vinyl acetate copolymer. The two polymeric layers can comprise polyethylene, although the type of polyethylene is not specified.
0 USP 4,820,557 (Warren) discloses a packaging film comprising at least one layer of a linear copolymer of ethylene and an alpha-olefin with a density of about 0.935 g/cm3 or less and a low I10/I2 rati°« The film allegedly has better abuse resistance as compared with a film made with a linear ethylene/alpha-olefin copolymer having a comparatively higher Ϊ
Figure imgf000008_0001
va-lue- Warren is directed to use of polyethylene which has a narrow molecular weight distribution in order to improve abuse resistance of multilayer structures. Warren specifically teaches away from the use of polyethylene having a broad molecular weight distribution (i.e., higher I-]Q //I2 va-lues) in multilayer film structures.
In spite of these advances, a better balance of
10 heat seal and shrinkage properties of the overall structure is still needed before and after irradiation so that the overall integrity of the package is not lost after irradiation.
15 A multilayer heat-sealable thermoplastic film structure has now been discovered that has improved heat seal performance after irradiation. The novel multilayer film structure comprises at least one heat sealable outer layer (A) and at least one core layer
20 (B).
Layer (A) of the multilayer thermoplastic film structure comprises a first linear polyethylene characterized as having: pe- (a) a density from 0.88 grams/cubic centimeter
(g/cm3) to 0.92 g/cm3,
(b) a melt index, measured as 12? from 2 grams/10 minutes to 20 grams/10 minutes,
(c) a molecular weight distribution, measured 30 as Iιo/_E2- from 5 to 8, and wherein
(d) 15 percent by weight or less of said linear polyethylene has a degree of branching less than or equal to 2 methyls/1000 carbons, and (e) 25 percent by weight or less of said linear polyethylene has a degree of branching equal to or greater than 25 methyls/1000 carbons.
Layer (B) comprises a second linear polyethylene characterized as having: 5 (a) a density from 0.88 g/cm3, to 0.94 g/cm3,
(b) a melt index, measured as l2» from 0.05 grams/10 minutes to 5 gram/10 minutes,
(c) a molecular weight distribution, measured 10 as Iιo l2» from 8 to 30.
Figure 1 shows the preparative scale temperature rising elution fractionation apparatus used to determine the branching distribution in the polymer 15 fractions.
Figure 2 plots heat seal strength (measured in Newtons/inch) versus heat seal temperature (in °F) of three ultra low density polyethylene (ULDPE) resins made into film.
20
Figure 3 plots cross-link density (measured in percent gel) versus radiation dosage (in megarads) of two ULDPE resins made into film.
Figure 4 plots heat seal strength (measured in pt- Newtons/inch) versus heat seal temperature (in °F) of one ULDPE resin made into film after different levels of exposure to irradiation.
Figure 5 plots heat seal strength (measured in Newtons/inch) versus heat seal temperature (in °F) of 30 one ULDPE resin made into film after different levels of exposure to irradiation.
Figure 6 plots cross-link density (measured in percent gel) versus radiation dosage (in megarads) of one LLDPE resin made into film. Figure 7 depicts one multilayer film structure of the present invention.
The multilayer structures of the present invention comprise at least one heat-sealable outer 5 layer and at least one core layer. The multilayer structure can have many layers, but the heat-sealable layer of the present invention must be on at least one outer surface of the structure to take advantage of the ln improvement in heat seal characteristics. Typical multilayer structures can be made using a coextruded blown or cast film process. Figure 7 shows a multilayer structure of the present invention. The structures of the film product can generally be described as an
15 A/B/D/X multilayer structure wherein layer A (18) is the heat sealable outer layer, layer B (19) is the core layer and layers D (20) and/or X (21) are a tie layer(s) and/or a barrier layer(s). The core layer (19) can be adjacent to the heat seal layer, but does not have to
20 be. The multilayer film structure is comprised of from 2 to 20 layers, preferably from 2 to 7 layers.
The multilayer film structure can be irradiated pc- at any point during the process. For example, the heat- sealable outer layer and the core layer of the present invention can be coextruded, irradiated and subsequently laminated and oriented (i.e., stretched) to make the final multilayer film structure, so long as the heat- 30 sealable outer layer is on at least one outer surface of the structure. Conversely, the entire multilayer structure can be formed and oriented, and then subsequently irradiated. The order of the steps of orientation and irradiation is not critical. Irradiation is preferably accomplished by using an electron beam (beta) irradiation device at a dosage level of from 0.5 megarad (Mrad) to 20 Mrad.
Thickness of the multilayer film structures can vary from 0.1 mil to 50 mils (.0025 mm to 1.3 mm), zz, preferably from 0.5 mils to 10 mils. (.013 mm to .25 mm). The tie layer(s) and/or the barrier layer(s) are made from conventional thermoplastic polymers known to be useful for this purpose, especially polyolefinic 10 polymers.
Thermoplastic polymers useful as the tie layer(s) include ethylene acrylic acid interpolymers (e.g., U.S. Patent 4,599*392), ethylene methacrylic acid 15 interpolymers (e.g., U.S. Patent 4,248,990 and U.S.
Patent 4,252,924), succinic acid or succinic anhydride grafted polyolefins and blends with ungrafted polyolefins (e.g., U.S. Patents 4,684,576, 4,741,970 and 4,394,485), vinyl acetate interpolymers. Thermoplastic
20 polymers useful for the barrier layer(s) include EV0H, polyvinyl chloride, polyvinylidene chloride, and nylon.
The heat-sealable outer layer and the core pt- layer of the present invention are fabricated from linear polyethylene. Manufacture of linear polyethylene is disclosed, e.g., in U.S. Patent 4,076,698 and involves coordination catalysts of the "Ziegler" type or "Phillips" type and includes variations of the Ziegler 30 type, such as the Natta type. These catalysts may be used at very high pressures, but may also (and generally are) used at very low or intermediate pressures. The products made by these coordination catalysts are generally known as "linear" polymers because of the substantial absence of branched chains of polymerized monomer units pendant from the main polymer "backbone." It is these linear polymers to which the present invention pertains. Linear low density polyethylene (LLDPE) and ultra low density polyethylene (ULDPE) typically have a density between about 0.88 g/cm3 and about 0.94 g/cm3. The density of the polyethylene is lowered by copolymerizing ethylene with minor amounts of an alpha, beta-ethylenically unsaturated alkene(s) having from 3 to 20 carbons per alkene molecule (e.g., ιn 1-propene, 1-butene, 1-pentene, 4-methyl-l-pentene, 1- hexene, 1-octene, 1,9-decadiene and 1,7-octadiene) , preferably 4 to 8 carbon atoms (e.g., 1-butene, 1-hexene and 1-octene) and most preferably 8 carbons per alkene molecule (i.e., 1-octene). The amount of the alkene
15 comonomer is generally sufficient to cause the density of the linear low density polymer to be substantially in the same density range as LDPE, due to the alkyl side chains on the polymer molecule, yet the polymer remains in the "linear" classification; they are conveniently 0 referred to as "linear low density polyethylene." These polymers retain much of the strength, crystallinity, and toughness normally found in HDPE homopolymers of ethylene, but the higher alkene comonomers impart high r "cling" and "block" characteristics to extrusion or cast films and the high "slip" characteristic inherently found in HDPE is diminished.
The use of coordination-type catalysts for 0 copolymerizing ethylene with higher alkenes to make LLDPE and ULDPE copolymers having densities between about 0.88 g/cm3 and about 0.94 g/cm3 is disclosed variously in, e.g., U.S. 2,699,457; U.S. 2,846,425; U.S. 2,862,917; U.S. 2,905,645; U.S. 3,058,963; U.S. 4,076,698; and U.S. 4,668,752. The density of the linear polyethylene useful in the heat sealable outer layer (A) in the present invention is from 0.88 g/cm3 to 0.92 g/cm3, preferably from 0.89 g/cm3 to 0.915 g/cm3. The density of the linear polyethylene useful in the core layer (B) in the present invention is from 0.88 g/cm3to 0.94 g/cm3, preferably from 0.9 g/cm3 to 0.93 g/cm3.
The molecular weight of the LLDPE useful in the present invention is indicated and measured by melt
10 index according to ASTM D-1238, Condition (E) (i.e., 190°C/2.16 kilograms); also known as Iz - The 12 of the linear polyethylene used in the heat sealable outer layer (A) can be as low as 0.5 grams/10 minutes, but is
- preferably from 2 grams/10 minutes (g 10 minutes) to 20 g/10 minutes, more preferably from 3 g/10 minutes to 10 g/10 minutes. The 12 of the linear polyethylene used in the core layer (B) can be from 0.05 g/10 minutes to 5 g/10 minutes, preferably from 0.2 g/10 minutes to 1 g/10 0 minutes.
The molecular weight distribution is indicated and measured by I-JO/12 according to ASTM D-1238, Conditions (N) (190°C/10 kilograms) and (E), 5 respectively. The I10 I2 of the heat sealable outer layer (A) can be from 5 to 8, preferably from 6.5 to 8. The I10/I2 of the core layer (B) can be from 8 to 30, preferably from 8 to 15. Molecular weight distribution can be achieved by varying catalytic conditions, reactor 0 conditions or feed percentages. Blends of polyethylenes can also be used. Such blends can be prepared by blending separate and discrete polyethylene polymers, or polymerizing the polyethylene polymer in-situ in multiple reactors, (e.g. the technique disclosed in U.S. Patent 3*914,342). It is important that the linear polyethylene(s) be well mixed when using discrete polymer blends.
Additives, (e.g., anti-oxidants, pigments, hydrophobic and/or hydrophilic agents, etc.), may be incorporated into the linear polyethylene to the extent that they do not interfere with the heat sealability of the outer layer and the shrinkability of the core layer after orientation and exposure to irradiation.
Short chain branching distribution (SCBD) of the polymer fractions of the polyethylene polymers useful in the heat seal layer and the core layer is measured according to the temperature rising elution fractionation (abbreviated herein as "TREF") technique described herein and in U.S. Patent 4,798,081.
Experimental Procedure for Determining Short Chain Branching Distribution:
I. TREF Device Design
A diagram of the TREF apparatus is shown in Figure 1. The column (1) is 4 inches (10 cm) in diameter and 29 inches (74 cm) in length, a size easily capable of fractionating up to 20 grams of sample. The column is packed with stainless steel shot (2) and heated by a circulating oil bath (3). The entire apparatus is enclosed within a hood (not shown) to contain any solvent or heating oil vapors.
A. Column Construction
The column is constructed of 4 inch (10 cm) schedule 40 steel pipe. Legs of one inch (2.5 cm) angle iron were welded on the pipe to keep it in a vertical position. The end caps are welded on the pipe to prevent any solvent leakage into the oil system. A one inch (2.5 cm) hole is left in each end to allow for packing of the column and to accomodate a 1 inch MPT
(2.5 cm) x 1/4 inch (0.6 cm) tubing connection.
B. Column Packing
The column is tightly packed with 0.028 inch (.07 cm) diameter stainless steel shot. The interstitial volume of the column is approximately 1700 milliliters. Stainless steel shot effectively prevents channeling and provides good heat transfer through the column.
C. Heating System
The column temperature is regulated by a Haake N3B circulating bath controlled by a Haake PG-20 temperature programmer (4). The oil used is Primol 355 mineral oil or a light silicon oil. The 10 gallon (38 1) insulated bath (5) containing the column is galvanized steel. The oil circulator injects oil at the bottom of this bath with the return from the top. An air driven motor (6) is used for agitation of the large oil bath.
D. Solvent System
The solvent used is 1, 2, 4-trichlorobenzene (TCB) (12). It is pumped from a reservoir (7) into the bottom of the column through a preheating coil (8) located in the large bath. The solvent is pumped at a flow rate of approximately 40 ml/minute using a Fluid Metering, Inc. lab pump (9) designated RP-G-150 with a 2-SSY (3/8 inch or 0.95 cm) stainless steel pump head module. This pump allows control of flow rates from 1 to 100 milliliters/minute.
E. Column Loading System
Polymer samples (13) are loaded on the column utilizing a gravity flow method. The sample is first dissolved in 1700 ml of TCB in a heated 5 liter flask (10). The 130°C column is then loaded with the solution, also at 130°C. One hundred milliliters of clean solvent is then heated and added to flush all transfer lines. These lines are heated with rheostat controlled heat tape (not shown).
F. Fraction Collection
The column eluent (14) is collected in one gallon metal cans (11). Acetone is then added to the cans to precipitate the polymer. Fraction work-up will be discussed in a later section.
II. Fractionation Procedure and Column Operation
A. Loading the Column
The polymer sample (about 20 grams) is dissolved in 1700 ml of TCB in a heated 5 liter flask. Approximately 3 to 4 hours is required to carry out this step. The column, the flask, and all transfer lines must be above 120°C to insure that no polymer is precipitated during the loading step. After the polymer solution is deposited on the column, a wash of fresh solvent is used to eliminate all polymer from the transfer lines. The amount of wash is dependent on the volume of the transfer lines (about 100 ml for this system). After completing these steps, the entire system must be brought back down to room temperature, with the rate of cooling being the most critical step in the fractionation procedure. The rates for this system are between 1°C and 2°C/hr. A temperature recorder (15) equipped with a thermocouple (16) in the recirculating oil and a thermocouple (17) in the packed column is used to monitor the temperature changes. During the cooling step the polymer selectively crystallizes allowing for efficient fractionation during the elution step. There is no solvent flow through the column during the cool- down step.
B. Column Elution
Elution of the polymer from the column is started at room temperature with a predetermined temperature rise rate. Solvent flows continuously during this step and fractions are collected over the desired change in temperature (5°C for this work). The temperature rise rate used here is 6°C/hr. The temperature rise can be achieved in two ways, stepwise or continuous. Solvent flow rates (40 ml/min) are chosen to achieve one interstitial column volume over the desired change in temperature. These rates result in a fraction collection every 50 minutes.
Approximately 15 fractions are collected for each sample.
C. Fraction Work-Up
The fractions are mixed about 1:1 with acetone and allowed to sit for at least one day to precipitate the polymer. The polymer-TCB-acetone mixture is then added to a large separatory funnel, and allowed to sit for several minutes until the polymer rises to the top. -16-
The bulk of the solvent is then drained and more acetone added to wash the polymer. The acetone-polymer mixture is then vacuum filtered, and the resulting polymer sample dried in a vacuum oven at 8θ-90°C followed by weighing. These samples can then be directly used for 5 gel permeation chromatography, differential scanning calorimetry, and infrared analysis.
D. Branching Content Determination
10 Branching content (i.e., degree of branching) is calculated from CH3/IOOO C (methyls/1000 carbons) determination according to ASTM method D2238-68. A Beckman 4260 infrared spectrophotometer is employed, using films of approximately 0.15 mm thickness. A
15 correction for chain end methyl groups is necessary for accurately determining weight percent comonomer (e.g., 1-octene) incorporation. The correction is done according to the following equation:
Corrected CH3/IOOOC = Uncorrected CH3/IOOOC +Vinyl - 2800
1000 Mn
25 Comonomer incorporation can be determined from the following equation:
Wt.% octene = (Molecular Weight of 1-octene) (Corrected CH IOOOC) (100)
14000 + 84 (corrected CH3/IOOOC)
E. Molecular Weight Determination Number average molecular weight (Mn) is measured by using a Waters Model 150C Gel Permeation
Chromatograph. The measurements are made by dissolving polymer samples in hot, filtered, 1, 2, 4 trichlorobenzene (TCB). The GPC (Gel Permeation zz.
Chromatography) runs are made at 140°C in TCB. A flow rate of 1.0 ml/min is used and the columns used are 3
Polymer Laboratories 10 micron linear columns. Each column diameter is 7.5 mm and the column length is 30
10 cm. Column performance is typically around 30,000 plates/meter as determined using 0.02 grams eicosane in 50 milliliters of TCB. Columns are disposed of if the plate count is below 20,000 plates per meter. Column performance is also monitored using the multiplied
15 product of the spreading factor "σ" and the slope of the calibration curve "D". This value is typically around 0.081. Columns with values above 0.09 for the multiplied factor "Dσ" are not employed. The antioxidant butylated hydroxytoluene is added to the TCB
20 at a concentration of 250 parts per million. The system is calibrated using narrow molecular weight polystyrene standards. The following formula is used to transform polystyrene molecular weights to polyethylene molecular pc- weights:
Mw of polyethylene = (0.4316) (Mw of polystyrene)
30
The polyethylene samples are prepared at a concentration of 0.25 grams of polyethylene in 50 milliliters of TCB. The volume injected is 100 microliters. F. Infrared Determination of Vinyl Content
A Perkin-Elmer Infrared (IR) Model 760 is used to measure vinyl groups in the polymer chains. The polymer is compression molded into a thin film and measured for thickness (target is approximately 0.1-0.3 mm thick). The IR absorbancy spectrum is measured for each film and vinyl group content is calculated according to the following equation:
Vinyl Groups/ = IR Absorbance at A
1000 Carbons in the polymer chain (t) (k)
where: t=thickness k=0.970 and λ=909 cm"1.
The vinyl groups/1000 carbons value obtained is inserted into the equation for determining corrected CH3/IOOO carbons for each polymer fraction as described earlier in Section D in this disclosure.
The first linear polyethylene suitable for use as the heat seal layer (A) in the present invention has a degree of branching less than or equal to 2 methyls/1000 carbons in 15 percent by weight or less, more preferably 10 percent by weight or less, of the linear polyethylene and a degree of branching equal to or greater than 25 methyls/1000 carbons in 25 percent by weight or less, more preferably 20 percent by weight or less, of the first linear polyethylene. Example 1
This example demonstrates heat seal performance of three ULDPE Resins with different short chain branching distributions (SCBD).
5
ATTANE* 4002 ULDPE (labeled as Resin A), an ethylene/octene-1 copolymer made by The Dow Chemical
Company, having 12 = 3.3 grams/10 minutes, I10 I2 = 7 .1 and density of about 0.912 g/cm3 and ATTANE* 4001 ULDPE
10 (labeled as Resin B), also an ethylene/octene-1 copolymer made by The Dow Chemical Company, having I2 =
1.0 gram/10 minute, I10/I2 = 8.2 and density of about
0.912 g/cm3 and another ULDPE resin (labeled as Resin
C), also an ethylene/octene-1 copolymer, having I2 = 3-3
15 grams/10 minutes, I10/I2 = 7.7 and density of about
0.912 g/cm3 were made into single layer cast film and evaluated for heat seal performance. Each film sample was heat sealed and then tested for heat seal strength.
20 Resins A and B had similar short chain branching distributions but differed in I2 and Iιo/l2«
Resin C had a "narrower" short chain branching distribution as compared to Resins A and B, as measured pc- using TREF, since about 8.5 percent (total weight basis) of Resin C had a degree of branching of less than or equal to 2 methyls /1000 carbons and about 18.5 percent (total weight basis) of Resin C had a degree of branching of greater than or equal to 25 methyls /1000
30 carbons. The physical properties of the resins used in all of the experiments described herein (Resins A. B, C and D) are summarized in Table 1. TABLE 1 Resin Physical Properties
Figure imgf000022_0001
NM = Not Measured
Samples of single layer 1 mil thick films were fabricated from Resins A, B and C using a cast film line equipped with a MPM extruder with a 2 inch (5 cm) screw (L/D=24:l) a 12 inch (30 cm) cast film die and a MPM cast film take-up system with a 18 inch (46 cm) chrome plate chill roll and an air knife to cool the polymer melt. The fabrication conditions of the cast film are listed in Table 2.
TABLE 2 Fabrication Conditions for Samples
Figure imgf000023_0001
The cast film samples were compared for heat seal performance and heat seal strength using an Instron peel test. Film samples for heat seal testing were conditioned as described in ASTM E 171-82 (i.e., 73.4 +/- 3.6 °F (21-25°C), 50+/- 5 percent relative humidity) . The heat seal tests were performed utilizing a heat sealer. A variety of equipment exists for this function, such as a Sentinel Heat Sealer, a Theller Precision Heat Sealer and a Packforsk Hot Tack Tester (made by Top Wave). The conditions for sealing were typically 0.5 second dwell time, 40 psi (275 kPa) bar pressure. Both bars were heated. One inch (2.5 cm) wide by six inch (15 cm) long strips were used for testing. After sealing, the samples were conditioned at the ASTM conditions described above for about 24 hours. The heat seal tests were made using an Instron tensiometer at a constant crosshead speed of about 2 inches/minute (5 cm/minute) in a 90° "T-peel" mode. Three to five heat seal tests were made and tested. The results were averaged and are illustrated in Figure 2 and the data are summarized in Table 3.
Resin C had a "narrower" SCBD and exhibited an improved heat seal performance (i.e., lower heat seal initiation temperature and higher seal strength at below 210°F) as compared to Resin A and Resin B. Resin C is thus an example of this invention and can be used as a heat seal layer in a multilayer film structure.
TABLE 3 Heat Seal Strength of Resins A, B, AND C
Figure imgf000025_0001
Example 2
This example demonstrates heat seal performance of electron beam irradiated ULDPE.
Resin B and Resin C were evaluated for heat seal performance and cross-link density (measured by percent gel) prior to and after electron beam irradiation. An Energy Science Inc. Model EC 200 electron beam radiation machine was used for the radiation treatment. The crosslink density (percent gel in xylene, measured by ASTM method D-2765) indicates the resins' propensity for heat seal performance. The cross-link densities of the resins before and after various doses of radiation treatment are illustrated in Figure 3 and the data are summarized in Table 4. As the data show, resin C can be exposed to about 5 megarads (Mrad) and still maintain a cross-link density of less than about 10 percent gel and thus is an example of this invention. Resin B reached a cross-link density of about 10 percent gel in less than about 3 Mrad exposure and is not an example of this invention for use in the heat seal layer.
TABLE 4 Crosslink Density of Irradiated ULDPE (Resin B and Resin C)
Figure imgf000026_0001
The heat seal performance of Resin B and Resin C prior to and after the radiation treatment was evaluated by the method described in Example 1. The results are illustrated in Figures 4 and 5 and the data are summarized in Tables 5 and 6. The data illustrate that Resin C retained good heat seal performance (i.e., a broad temperature bonding window yielding good heat seal values) even after electron beam radiation treatment of up to about 4 Mrad of radiation dosage. As Figure 4 shows, after an irradiation exposure of about 4 Mrad, Resin C achieved a heat seal strength of about 10 Newtons/inch (4 Newtons/cm) or more at a heat seal temperature as low as about 195°F (91°C). Resin C is thus an example of this invention for use in the heat seal layer of a multilayer structure demonstrating good heat seal at low temperatures after irradiation.
However, for Resin B, heat seal performance deteriorated significantly. After about 4 Mrad irradiation dosage, Resin B achieved a heat seal strength of about 10 Newtons/inch (4 Newtons/cm) only after heat sealing at a temperature of about 215°F ( 102°C) or more.
TABLE 5 Heat Seal Strength of Resin C after Irradiation Treatment
Figure imgf000028_0001
TABLE 6 Heat Seal Strength of Resin B after Irradiation Treatment
Figure imgf000029_0001
Example 3
This example demonstrates radiation crosslinking performance of LLDPE resins to be used for the core layer of the multi-layer film products with improved heat seal, orientation and shrink performance.
An octene-1 LLDPE copolymer, labeled as Resin D, having 12 = 0.55 grams/10 minutes, I10 I2 = 2 and density of about 0.923 g/cm3 was fabricated into 1 mil (.025 mm) thick film using a blown film process. The blown film is made using a STERLING Blown Film Line. This line has a 3.5 inch (8.9 cm) diameter extruder, L/D of 30:1, an 8 inch (20 cm) diameter Western Polymer die with a 70 mil (1.8 mm) die gap, a STERLEX barrier type screw and Internal Bubble Cooling (IBC).
Film samples made from this resin were treated by electron beam radiation using an Energy Science Incorpoated electron beam radiation machine (Model EC200; 200 KeV) . The treated polymer film was evaluated for propensity for thermal shrinkage by measuring percent gel (i.e., crosslink density) by the solvent extraction technique as described in Example 2.
The results are illustrated in Figure 6 and the data are summarized and compared to Resin C in Table 7. The data show that resin D had an enhanced radiation crosslinking efficiency as compared to Resin C (data shown earlier in Example 2, Table 4). Resin D, having Ilθ/l2 of about 12, had a crosslink density at a dosage of about 3 Mrad of approximately 18 to 20 percent gel, whereas resin C does not attain a cross-link density of about 20 percent gel until exposure to about 7 Mrad. Resin D would, therefore, attain higher shrinkage at lower levels of irradiation than resin C, and is thus an example of this invention for use as a core layer in a multilayer structure.
TABLE 7
Crosslink Density of Resins C and D after Irradiation
Figure imgf000031_0001
Example 4
This example demonstrates a two layer co¬ extruded film product having improved heat seal, crosslinking and orientation/shrink performance after irradiation to 3 Mrad.
A 1 mil (0.025 mm) thick 2-layer (A/B) co¬ extruded film sample was fabricated by the following blown film process:
Two layer blown films were prepared in accordance with this invention by fabrication on an Egan coextrusion blown film line equipped with a 2.5 inch (6.4 cm) diameter main extruder, a 1.5 inch (3.8 cm) skin layer extruder and a 2 layer single air ring cooled annular die. The multilayer laminated film structure was an A/B configuration in which:
(I) The "A-layer" was the heat seal layer and was extruded through the outer annular die as the outer layer. The "A-layer" extruder was a 1.5 inch (3.8 cm) Egan having an L/D ratio of 20:1. The extruder had four zones temperature control. This extruder was used to feed Resin C— to the outer layer. This layer was maintained at a thickness of approximately 0.15 mils (0.0038 mm). The temperature profile of this extruder was as follows:
Figure imgf000032_0001
The polymer melt temperature was about 225°C. The throughput rate was about 18 pounds/hour (8.2 kg/hr).
(II) The "B-layer" is the support or core layer and was extruded through the inner annular die as the inside layer. The "B-layer" extruder was a 2.5 inch (6.35 cm) Egan having a screw L/D ratio of 24:1. This extruder is used to feed Resin D to the middle annular die to form the inner layer at a throughput of about 110 pounds/hour (50 kg/hr) and at a melt temperature of about 225°C. The thickness of this layer is approximately 0.85 mils ( 0.022 mm). The temperature profile of this extruder is as follows:
Figure imgf000033_0001
Resin C described in Example 2 was used to fabricate the heat seal layer and Resin D described in Example 3 was used to fabricate the other layer. The thickness of the heat seal layer is approximately 15 percent of the total film thickness of about 1 mil (0.025 mm). The film sample is irradiated at 3 Mrad using an Energy Science Incorporated electron beam radiation machine (Model EC200). The total crosslink density of the film, measured as percent gel, after the radiation treatment was approximately 16 percent. At crosslink densities of between about 10 percent and about 25 percent, the film is known to have ideal performance for orientation and shrink applications. -32-
The heat seal performance (heat seal layer to heat seal layer) of this co-extruded crosslinked film was evaluated by the method described in Example 1.
Table 8 illustrates the heat seal strength of the heat seal layer of film before and after radiation treatment
(3 Mrad). The film retained its excellent heat seal performance after the electron beam radiation treatment.
Table 8
Heat Seal Strength of the Heat Seal Layer of
Coextruded Film Samples before and after
Irradiation
10
15
20
Figure imgf000034_0001
25
30 This example illustrates that by using the resins disclosed in this invention for specific layers, a multi-layer film can be made, exposed to radiation and still maintain a combination of excellent core layer crosslinking performance and excellent heat seal layer performance.
The invention is particularly useful in heat- seal packaging of food, whereby the packaged food is exposed to irradiation for sterilization purposes. The irradiation simultaneously strengthens the core layer and prepares it for shrinkage upon subsequent exposure to heat. By using the present invention in the heat seal outer layer, the heat seal initiation temperature of the heat seal layer is maintained after irradiation and the heat seal strength of the package is substantially maintained.

Claims

Claims:
1. A multilayer heat-sealable thermoplastic film structure having improved heat seal performance after electron beam irradiation, said film structure comprising at least one heat-sealable outer layer (A) and at least one core layer (B), wherein layer (A) comprises a first linear polyethylene characterized as having:
(a) a density from 0.88 g/cm3 to 0.92 g/cm3,
(b) a melt index, measured as 12? from 2 g/10 minutes to 20 g/10 minutes,
10 (c) a molecular weight distribution, measured as Iιo/l2» from 5 to 8, and wherein
(d) 15 percent by weight or less of said first linear polyethylene has a degree of branching less than or equal to 2 methyls/1000 carbons, and
15 (e) 25 percent by weight or less of said first linear polyethylene has a degree of branching equal to or greater than 25 methyls/1000 carbons, and wherein layer (B) comprises a second linear polyethylene characterized as having:
20 (f) a density from 0.88 g/cm3 to 0.94 g/cm3,
(g) a melt index, measured as l2» from 0.05 g/10 minutes to 5 g/10 minutes, and
(h) a molecular weight distribution, measured pc- as Iιo/l2> from 8 to 30.
2. The film structure of Claim 1 wherein layer (A) is adjacent to layer (B).
3. A linear polyethylene for use as layer (A) in the film structure of Claim 1.
4. The linear polyethylene of Claim 3 wherein the linear polyethylene is a copolymer of ethylene and 1-octene.
5. The linear polyethylene of Claim 3 wherein the linear polyethylene is a copolymer of ethylene and 1-hexene.
6. A linear polyethylene for use as layer (B) in the film structure of Claim 1.
7. The linear polyethylene of Claim 6 wherein the linear polyethylene is a copolymer of ethylene and 1-octene.
8. The linear polyethylene of Claim 6 wherein the linear polyethylene is a copolymer of ethylene and 1-hexene.
9. The film structure defined by Claim 1 which has been electron beam irradiated from 0.5 Mrad to 20 Mrad to form an irradiated film structure.
10. The irradiated film structure of Claim 9 wherein the heat-sealable outer layer (A) has a cross¬ link density of less than 10 percent gel after 5 Mrad radiation dosage or less.
11. The irradiated film structure of Claim 9 wherein the heat-sealable outer layer (A) has a cross¬ link density of less than 10 percent gel after 4 Mrad radiation dosage.
r-
12. The irradiated film structure of Claim 9 wherein the layer (B) has a cross-link density of at least 30 percent gel after 5 Mrad radiation dosage or less.
10 13. The irradiated film structure of Claim 9 wherein the layer (B) has a cross-link density of at least 20 percent gel after 4 Mrad radiation dosage.
14. The irradiated film structure of Claim 9
15 which has been subsequently heat sealed to form an irradiated and heat sealed film structure.
15. The irradiated and heat sealed film 0 structure of Claim 14 wherein said film structure has a heat seal strength of at least 10 Newtons/inch (3-9 N/cm) at a heat seal temperature of at least 195°F
(91°C) after electron beam irradiation of 4 Mrad.
5 16. The irradiated and heat sealed film structure of Claim 15 wherein the heat seal temperature is 200°F
(93°C) or less.
0
PCT/US1992/000221 1991-01-10 1992-01-07 Heat sealable multilayer polyolefinic film structures WO1992012010A1 (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
EP92904532A EP0566679B1 (en) 1991-01-10 1992-01-07 Heat sealable multilayer polyolefinic film structures
AU12316/92A AU667802B2 (en) 1991-01-10 1992-01-07 Heat sealable multilayer polyolefinic film structures
DE69208646T DE69208646T2 (en) 1991-01-10 1992-01-07 HOT SEALABLE MULTILAYER FILMS MADE OF POLYOLEFINES

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US07/639,648 US5089321A (en) 1991-01-10 1991-01-10 Multilayer polyolefinic film structures having improved heat seal characteristics
US639,648 1991-01-10

Publications (1)

Publication Number Publication Date
WO1992012010A1 true WO1992012010A1 (en) 1992-07-23

Family

ID=24564988

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/US1992/000221 WO1992012010A1 (en) 1991-01-10 1992-01-07 Heat sealable multilayer polyolefinic film structures

Country Status (9)

Country Link
US (1) US5089321A (en)
EP (1) EP0566679B1 (en)
AU (1) AU667802B2 (en)
CA (1) CA2100360A1 (en)
DE (1) DE69208646T2 (en)
ES (1) ES2083736T3 (en)
MX (1) MX9200093A (en)
NZ (1) NZ241252A (en)
WO (1) WO1992012010A1 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5916692A (en) * 1995-09-01 1999-06-29 Manuli Stretch S.P.A. Multilayer polyethylene film

Families Citing this family (104)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB8914703D0 (en) * 1989-06-27 1989-08-16 Dow Europ Sa Bioriented film
US5272236A (en) * 1991-10-15 1993-12-21 The Dow Chemical Company Elastic substantially linear olefin polymers
US6172173B1 (en) 1991-01-18 2001-01-09 The Dow Chemical Company Silica supported transition metal catalyst
US6747113B1 (en) 1991-01-18 2004-06-08 The Dow Chemical Company Silica supported transition metal catalyst
JP2890334B2 (en) * 1991-07-15 1999-05-10 株式会社新川 Tape transport device
US5250612A (en) * 1991-10-07 1993-10-05 The Dow Chemical Company Polyethylene films exhibiting low blocking force
US5674342A (en) 1991-10-15 1997-10-07 The Dow Chemical Company High drawdown extrusion composition and process
US5395471A (en) 1991-10-15 1995-03-07 The Dow Chemical Company High drawdown extrusion process with greater resistance to draw resonance
US5562958A (en) * 1991-10-15 1996-10-08 The Dow Chemical Company Packaging and wrapping film
US5582923A (en) 1991-10-15 1996-12-10 The Dow Chemical Company Extrusion compositions having high drawdown and substantially reduced neck-in
US5525695A (en) * 1991-10-15 1996-06-11 The Dow Chemical Company Elastic linear interpolymers
US5530065A (en) * 1992-01-07 1996-06-25 Exxon Chemical Patents Inc. Heat sealable films and articles made therefrom
JP3326873B2 (en) * 1992-07-22 2002-09-24 住友化学工業株式会社 Packaging film
EP0597502B1 (en) * 1992-11-13 2005-03-16 Cryovac, Inc. Heat shrinkable films containing single site catalyzed copolymers
US5883188A (en) * 1993-04-28 1999-03-16 The Dow Chemical Company Paintable olefinic interpolymer compositions
US5424362A (en) * 1993-04-28 1995-06-13 The Dow Chemical Company Paintable olefinic interpolymer compositions
US7316833B1 (en) 1993-06-24 2008-01-08 Penchiney Emballage Flexible Europe Multi-layer thermoplastic films and packages made therefrom
CA2166188A1 (en) * 1993-06-24 1995-01-05 John P. Eckstein Improved structures of polymers made from single site catalysts
US6645641B2 (en) 1993-06-24 2003-11-11 Pechiney Plastic Packaging, Inc. Structures of polymers made from single site catalysts
US6270867B1 (en) 1993-06-24 2001-08-07 Pechiney Plastic Packaging, Inc. Structures of polymers made from single site catalysts
NZ285222A (en) * 1994-04-20 1997-05-26 Dow Chemical Co Polymers of linear ethylenepolymers grafted with silane crosslinkers, use as weatherstrips, cable coating and fiber
US5416148B1 (en) * 1994-09-09 1999-03-02 Dow Chemical Co Blends of polycarbonate and ethylene polymers
US5792534A (en) 1994-10-21 1998-08-11 The Dow Chemical Company Polyolefin film exhibiting heat resistivity, low hexane extractives and controlled modulus
US7153909B2 (en) * 1994-11-17 2006-12-26 Dow Global Technologies Inc. High density ethylene homopolymers and blend compositions
US6506866B2 (en) * 1994-11-17 2003-01-14 Dow Global Technologies Inc. Ethylene copolymer compositions
US6287613B1 (en) 1994-12-12 2001-09-11 Cryovac Inc Patch bag comprising homogeneous ethylene/alpha-olefin copolymer
EP0819149A1 (en) * 1995-04-07 1998-01-21 The Dow Chemical Company Blends of polycarbonate and linear ethylene polymers
US5824718A (en) * 1995-04-20 1998-10-20 The Dow Chemical Company Silane-crosslinkable, substantially linear ethylene polymers and their uses
US5795941A (en) * 1995-10-03 1998-08-18 The Dow Chemical Company Crosslinkable bimodal polyolefin compositions
US6723398B1 (en) 1999-11-01 2004-04-20 Dow Global Technologies Inc. Polymer blend and fabricated article made from diverse ethylene interpolymers
US5705539A (en) * 1995-12-11 1998-01-06 Shell Oil Company Curing polyketones with high energy radiation
US5670586A (en) * 1995-12-11 1997-09-23 Shell Oil Company Polyketones with enhanced tribological properties
HUP9900394A3 (en) * 1996-01-22 2000-08-28 Dow Chemical Co Polyolefin elastomer blends exhibiting improved properties
US5993922A (en) * 1996-03-29 1999-11-30 Cryovac, Inc. Compositions and methods for selectively crosslinking films and improved film articles resulting therefrom
JPH09309926A (en) * 1996-05-17 1997-12-02 Dow Chem Co:The Production of ethylene copolymer
ZA976110B (en) 1996-07-12 1999-01-11 Dow Chemical Co Elastomers processes for their manufacture and articles made from these elastomers
ZA977909B (en) 1996-09-04 1999-03-03 Dow Chemical Co Compositions comprising a substantially random interpolymer of at least one alpha-olefin and at least one vinylidene aromatic monomer or hindered aliphatic vinylidene monomer
US6812289B2 (en) 1996-12-12 2004-11-02 Dow Global Technologies Inc. Cast stretch film of interpolymer compositions
AR012582A1 (en) 1997-04-14 2000-11-08 Dow Global Technologies Inc POLYMERIC COMPOSITIONS OF IMPROVED ELONGATION AND ADHESIVE FORMULATIONS OF HOT MELTING INCLUDING SUCH COMPOSITION
KR20010024534A (en) * 1997-10-17 2001-03-26 그래햄 이. 테일러 Compositions of interpolymers of alpha-olefin monomers with one or more vinyl or vinylidene aromatic monomers
US6323285B1 (en) 1998-01-09 2001-11-27 The Dow Chemical Company Heteromorphic polymer compositions
EP0982362A4 (en) 1998-03-10 2002-03-06 Mitsui Chemicals Inc Ethylene copolymer composition and use thereof
CN1143908C (en) 1998-03-11 2004-03-31 陶氏化学公司 Fibers made from alpha-olefin/vinyl or vinylidene aromatic and/or hindered cycloaliphatic or aliphatic vinyl or vinylidene interpolymers
AR018359A1 (en) * 1998-05-18 2001-11-14 Dow Global Technologies Inc HEAT RESISTANT ARTICLE, CONFIGURED, IRRADIATED AND RETICULATED, FREE FROM A SILANAN RETICULATION AGENT
US6709742B2 (en) 1998-05-18 2004-03-23 Dow Global Technologies Inc. Crosslinked elastic fibers
WO1999064501A1 (en) 1998-06-11 1999-12-16 The Dow Chemical Company Elastic films made from alpha-olefin/vinyl aromatic and/or aliphatic or cylcoaliphatic vinyl or vinylidene interpolymers
US6045882A (en) * 1998-07-16 2000-04-04 Viskase Corporation Multilayer thin plastic film, useful for shrink overwrap packaging
AU2375000A (en) * 1999-12-21 2001-07-03 H.B. Fuller Licensing And Financing Inc. Method of packaging a thermoplastic composition with a film having a low complexviscosity and corresponding packaged article
US6482532B1 (en) 2000-06-07 2002-11-19 Dow Global Technologies Inc. Easy tear non-halogenic food wrap
ATE284790T1 (en) * 2000-07-31 2005-01-15 Reynolds Metals Co PLASTIC CASE WITH SELF-ADHESIVE LAYER
US6559230B2 (en) 2000-09-29 2003-05-06 Dupont Dow Elastomers L.L.C. Thermosetting ethylene/alpha-olefin composition and safety glass interlayer film made from the composition
JP2004515664A (en) * 2000-12-11 2004-05-27 ダウ グローバル テクノロジーズ インコーポレイティド Thermal bonding cloth and manufacturing method thereof
WO2002053374A1 (en) 2001-01-02 2002-07-11 Dow Global Technologies Inc. Peelable seal and method of making and using same
JP2004531629A (en) * 2001-06-22 2004-10-14 エクソンモービル・ケミカル・パテンツ・インク Ultra-low density polyethylene or linear low density polyethylene as impact modifier made by metallocene
ATE301163T1 (en) 2001-08-17 2005-08-15 Dow Global Technologies Inc BIMODAL POLYETHYLENE COMPOSITION AND ARTICLES THEREOF
CA2457430C (en) * 2001-08-31 2011-10-18 Dow Global Technologies Inc. Multimodal polyethylene material
AU2003218113A1 (en) * 2002-03-11 2003-09-29 Dow Global Technologies Inc. Stretch fabric with improved chemical resistance and durability
EP1860214B1 (en) 2002-03-11 2009-04-29 Dow Global Technologies Inc. Reversible, heat-set, elastic fibers, and method of making and articles made from same
TWI336334B (en) * 2002-03-11 2011-01-21 Dow Global Technologies Inc Reversible, heat-set, elastic fibers, and method of making and articles made from same
AU2003222274A1 (en) * 2002-03-12 2003-09-29 Dow Global Technologies Inc. Linear ethylene/vinyl alcohol and ethylene/vinyl acetate polymers and process for making same
US20060046048A1 (en) * 2003-02-04 2006-03-02 Mridula Kapur Film layers made from polymer blends
ES2606780T3 (en) * 2003-06-10 2017-03-27 Dow Global Technologies Llc Film layers produced from polymer blends of ethylene
US7147930B2 (en) * 2003-12-16 2006-12-12 Curwood, Inc. Heat-shrinkable packaging films with improved sealing properties and articles made thereof
US8273826B2 (en) * 2006-03-15 2012-09-25 Dow Global Technologies Llc Impact modification of thermoplastics with ethylene/α-olefin interpolymers
WO2005097493A2 (en) * 2004-03-26 2005-10-20 Ipg Technologies, Inc. Silicone-free multilayer olefinic shrink film
JP5128955B2 (en) * 2004-12-03 2013-01-23 ダウ グローバル テクノロジーズ エルエルシー Kibe fiber plastic composite material
DE602005020688D1 (en) 2004-12-17 2010-05-27 Dow Global Technologies Inc RHEOLOGY-MODIFIED POLYETHYLENE COMPOSITIONS
US7326753B2 (en) 2005-02-08 2008-02-05 Momentive Performance Materials Inc. Process for the production of crosslinked polymer employing low VOC-producing silane crosslinker and resulting crosslinked polymer
WO2006101926A2 (en) 2005-03-17 2006-09-28 Dow Global Technologies Inc. Interpolymers of ethylene/alpha-olefins blends and profiles and gaskets made therefrom
WO2006127717A1 (en) * 2005-05-24 2006-11-30 Chevron Phillips Chemical Co Lp An integrated on-line two-dimensional method and device for synchronized analytical temperature rising elution fractionation and gel permeation chromatography
DE102005035705A1 (en) * 2005-07-27 2007-02-01 Boehringer Ingelheim Pharma Gmbh & Co. Kg pharmaceutical blister
CN101356225B (en) * 2006-05-02 2012-04-04 陶氏环球技术有限责任公司 High-density polyethylene compositions, method of making the same, articles made therefrom, and method of making such articles
EP2076565B1 (en) 2006-10-23 2010-06-02 Dow Global Technologies Inc. Polyethylene compositions, methods of making the same, and articles prepared therefrom
CN101490163A (en) * 2007-05-02 2009-07-22 陶氏环球技术公司 High-density polyethylene compositions, method of making the same, injection molded articles made therefrom, and method of making such articles
WO2009042602A1 (en) * 2007-09-28 2009-04-02 Dow Global Technologies Inc Thermoplastic olefin composition with improved heat distortion temperature
EP2052857A1 (en) * 2007-10-22 2009-04-29 Dow Global Technologies Inc. Multilayer films
CN101778707B (en) * 2008-01-29 2014-05-21 陶氏环球技术有限责任公司 Polyethylene compositions, method of producing the same, articles made therefrom, and method making the same
WO2009105938A1 (en) 2008-02-29 2009-09-03 Dow Global Technologies Inc. Oriented films comprising ethylene/α-olefin block interpolymer
EP2254920B1 (en) * 2008-03-13 2011-11-09 Dow Global Technologies LLC Long chain branched (lcb), block or interconnected copolymers of ethylene in combination with one other polymer
US20110318514A1 (en) * 2009-02-06 2011-12-29 Dow Global Technologies, Llc Ethylene-based polymers and compositions, method of making the same and articles prepared therefrom
EP2470340B1 (en) 2009-08-28 2019-09-25 Dow Global Technologies LLC Rotational molded articles, and method of making the same
CN102906320A (en) 2010-03-19 2013-01-30 陶氏环球技术有限责任公司 Bicomponent fibers
US8631940B2 (en) 2010-09-07 2014-01-21 Nova Chemical (International). SA Plastic dumpster
US8875937B2 (en) 2010-09-07 2014-11-04 Nova Chemicals (International) S.A. Plastic dumpster
JP5972887B2 (en) 2010-10-29 2016-08-17 ダウ グローバル テクノロジーズ エルエルシー Polyethylene-based drawn monofilaments and drawn strips and methods for their preparation
CN104812826B (en) 2012-09-28 2018-03-20 陶氏环球技术有限责任公司 Composition, band prepared therefrom and composite pipe and the method for preparing composite pipe
CN104812818B (en) 2012-09-28 2017-08-08 陶氏环球技术有限责任公司 Composition, connector, the method for improving bonding between two or more devices for trandfer fluid and the system for trandfer fluid
US20140134910A1 (en) 2012-11-09 2014-05-15 The Procter & Gamble Company Combination of Elastomeric Film Composition and Adhesive for a Stretch Laminate
US8859094B2 (en) 2012-11-09 2014-10-14 The Procter & Gamble Company Combination of elastomeric film composition and adhesive for a stretch laminate
CA2809402C (en) 2013-03-12 2021-02-09 Nova Chemicals Corporation Multilayer film prepared from high impact strength polyethylene and blends of ziegler natta catalyzed and high pressure low density polyethylenes
CN105307615B (en) 2013-06-20 2019-04-19 宝洁公司 With the absorbent article for activating friendly lamilate
MX370854B (en) 2013-09-30 2020-01-08 Dow Global Technologies Llc A process for increasing the melt strength of a polyethylene resin, a masterbatch composition and a polymeric composition.
JP2017538004A (en) * 2014-12-01 2017-12-21 ダウ グローバル テクノロジーズ エルエルシー Shrink film and manufacturing method thereof
MX2017016268A (en) * 2015-06-30 2018-04-20 Dow Global Technologies Llc Multi-layered films oriented in the machine direction and articles comprising the same.
PL3214005T3 (en) * 2016-03-04 2019-08-30 Tetra Laval Holdings & Finance S.A. A welding promoting element for a closure of an opening device
EP3469032A1 (en) 2016-06-13 2019-04-17 Acatechol, Inc. Ionic polymers and their use as wet-adhesives and coatings
US20180186543A1 (en) 2016-12-29 2018-07-05 Dow Global Technologies Llc Packaging Article with Three-Dimensional Loop Material
US20180186546A1 (en) 2016-12-29 2018-07-05 Dow Global Technologies Llc Packaging with Three-Dimensional Loop Material
US20180186544A1 (en) 2016-12-29 2018-07-05 Dow Global Technologies Llc Process for Packaging Article with Three-Dimensional Loop Material
EP3409614A1 (en) 2017-05-31 2018-12-05 Dow Global Technologies Llc Flexible container with three-dimensional random loop material
EP3409615A1 (en) 2017-05-31 2018-12-05 Dow Global Technologies Llc Packaging with three-dimensional loop material
EP3505680B1 (en) 2017-12-28 2022-08-24 Dow Global Technologies Llc Artificial turf system
KR102571139B1 (en) 2018-06-08 2023-08-28 사빅 에스케이 넥슬렌 컴퍼니 피티이 엘티디 Ethylene polymer mixture, process for producing the same, and a molded article using the same
CA3053597A1 (en) 2018-09-10 2020-03-10 Nova Chemicals Corporation Recycable package with fitment

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0100247A2 (en) * 1982-06-03 1984-02-08 Norsolor S.A. Compositions of cured ethylene/alpha-olefine copolymers, process for their preparation and their use in the manufacture of electric cables
US4668752A (en) * 1983-10-21 1987-05-26 Mitsui Petrochemical Industries, Ltd. Linear ethylene copolymer
US4820557A (en) * 1987-09-17 1989-04-11 W. R. Grace & Co.-Conn. Thermoplastic packaging film of low I10 /I2
US4927708A (en) * 1987-04-10 1990-05-22 W. R. Grace & Co.-Conn. Flexible stretch/shrink film

Family Cites Families (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4064296A (en) * 1975-10-02 1977-12-20 W. R. Grace & Co. Heat shrinkable multi-layer film of hydrolyzed ethylene vinyl acetate and a cross-linked olefin polymer
US4352849A (en) * 1981-03-26 1982-10-05 W. R. Grace & Co. Coextruded, heat-shrinkable, multi-layer, polyolefin packaging film
US4798801A (en) * 1983-10-11 1989-01-17 Phillips Petroleum Company Production of methane by anaerobic fermentation of waste materials
US4640856A (en) * 1985-04-29 1987-02-03 W. R. Grace & Co., Cryovac Div. Multi-layer packaging film and receptacles made therefrom
US4724185A (en) * 1985-09-17 1988-02-09 W. R. Grace & Co., Cryovac Div. Oxygen barrier oriented film
US4755419A (en) * 1986-03-21 1988-07-05 W. R. Grace & Co., Cryovac Div. Oxygen barrier oriented shrink film
US4963419A (en) * 1987-05-13 1990-10-16 Viskase Corporation Multilayer film having improved heat sealing characteristics

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0100247A2 (en) * 1982-06-03 1984-02-08 Norsolor S.A. Compositions of cured ethylene/alpha-olefine copolymers, process for their preparation and their use in the manufacture of electric cables
US4668752A (en) * 1983-10-21 1987-05-26 Mitsui Petrochemical Industries, Ltd. Linear ethylene copolymer
US4927708A (en) * 1987-04-10 1990-05-22 W. R. Grace & Co.-Conn. Flexible stretch/shrink film
US4820557A (en) * 1987-09-17 1989-04-11 W. R. Grace & Co.-Conn. Thermoplastic packaging film of low I10 /I2

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5916692A (en) * 1995-09-01 1999-06-29 Manuli Stretch S.P.A. Multilayer polyethylene film

Also Published As

Publication number Publication date
CA2100360A1 (en) 1992-07-11
DE69208646D1 (en) 1996-04-04
NZ241252A (en) 1994-12-22
AU1231692A (en) 1992-08-17
MX9200093A (en) 1992-07-01
EP0566679A1 (en) 1993-10-27
EP0566679B1 (en) 1996-02-28
AU667802B2 (en) 1996-04-18
DE69208646T2 (en) 1996-08-22
US5089321A (en) 1992-02-18
ES2083736T3 (en) 1996-04-16

Similar Documents

Publication Publication Date Title
EP0566679B1 (en) Heat sealable multilayer polyolefinic film structures
AU721206B2 (en) Multilayer oxygen-barrier packaging film
AU611166B2 (en) Thermoplastic multi-layer packaging film and bags made therefrom
AU673081B2 (en) Puncture resistant heat shrinkable film containing narrow molecular weight ethylene alpha olefin
CA1300078C (en) Cook-in shrink film
US7588830B2 (en) Heat shrinkable films containing single site catalyzed copolymers
EP0087080B1 (en) Laminate film
JP3794698B2 (en) Heat-shrinkable films containing single-site catalyzed copolymers with long chain branching
EP0744285B1 (en) Multilayer oxygen barrier packaging film
US7147930B2 (en) Heat-shrinkable packaging films with improved sealing properties and articles made thereof
AU652244B2 (en) Produce packaging film
EP0562496B1 (en) Multilayer stretch/shrink film
CA1337287C (en) Meat adherable cook-in shrink film
EP1193052A1 (en) New heat-shrinkable multi-layer thermoplastic film and container obtained therefrom
CN112469567B (en) Multilayer thermoplastic film with improved puncture resistance
Warren et al. Thermoplastic packaging film of low I 10/I 2
CA2359323A1 (en) Heat-shrinkable, irradiated, polyethylene mono-layer film

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A1

Designated state(s): AU BR CA FI JP KR

AL Designated countries for regional patents

Kind code of ref document: A1

Designated state(s): AT BE CH DE DK ES FR GB GR IT LU MC NL SE

DFPE Request for preliminary examination filed prior to expiration of 19th month from priority date (pct application filed before 20040101)
WWE Wipo information: entry into national phase

Ref document number: 2100360

Country of ref document: CA

WWE Wipo information: entry into national phase

Ref document number: 1992904532

Country of ref document: EP

WWP Wipo information: published in national office

Ref document number: 1992904532

Country of ref document: EP

WWG Wipo information: grant in national office

Ref document number: 1992904532

Country of ref document: EP

WWW Wipo information: withdrawn in national office

Ref document number: 1992904532

Country of ref document: EP