WO2003040199A1

WO2003040199A1 - Heat-sealed easy-open packaging article containing highly branched homogeneous polyolefin

Info

Publication number: WO2003040199A1
Application number: PCT/US2002/035369
Authority: WO
Inventors: Blaine C. Childress; Ronald D. Moffitt
Original assignee: Cryovac, Inc.
Priority date: 2001-11-06
Filing date: 2002-11-04
Publication date: 2003-05-15

Abstract

A heat-sealed easy-open article has a film which is heat sealed to itself or another component of the article. The film has a heat seal layer containing a blend of a first polymer and a second polymer. The first polymer is a highly branched homogeneous polyolefin having at least 60 branches per 1000 methylene groups, and for every 100 branches that are methyl, about 4 to 20 ethyl branches, about 1 to 12 propyl branches, about 1-12 butyl branches, about 1 to 10 amyl branches, and about 1 to 20 hexyl or longer branches. The second polymer being present in an amount of at least 5 weight percent based on the weight of the blend. The second polymer having a glass transition temperature or melt temperature which is higher than the first polymer. The wherein the heat seal has a strength of from 5 to 75 percent of an ultimate seal strength formed by heat sealing to itself a corresponding film having a heat seal layer containing 100 percent of the second polymer.

Description

HEAT-SEALED EASY-OPEN PACKAGING ARTICLE CONTAINING HIGHLY BRANCHED HOMOGENEOUS POLYOLEFIN

Field of the Invention The present invention is directed to heat-sealed articles having easy-open heat seals. The invention is particularly directed to packaging articles, including flexible films as well as rigid packaging structures such as molded articles.

Background of the Invention In the packaging of an article for distribution and sale, it is important to provide a package which both protects the product and is attractive to consumers. Protection of the product, and attractiveness to consumers, can be accomplished in a wide variety of manners. However, it is often the case that in an effort to protect the product in a packaging article which is attractive to consumers, there is difficulty opening the package. The use of knives and other cutting devices is time-consuming and potentially dangerous. It would be desirable to provide a high quality package which both adequately protects the product while being easy to open. The goals of adequate protection and ease of openability are often at odds with each other.

Summary of the Invention

The present invention provides an easy-open heat-sealed article in which at least a portion of the heat seal contains a highly branched homogeneous polyolefin. This highly branched homogeneous polymer provides the seal layer with an easy-open character by lowering the seal strength of the heat seal formed using the seal layer. The strength of the heat seal is lowered at least 25 percent below the seal strength which would otherwise occur without the presence of the highly branched homogeneous polymer. It has been discovered that during heat sealing the highly branched homogeneous polymer imparts a lower seal strength because the branches of the polymer do not entangle to an extent other polyolefms exhibit. Rather, the individual branches of the highly branched polymer, though unusually numerous, are not long enough to generate a type of entanglement which results in seals having the strength exhibited by other relatively low melting polyolefms such as very low density polyethylene, linear homogeneous ethylene/alpha-olefm copolymer which are not "highly branched", long chain branched homogeneous ethylene/alpha-olefin copolymer which are not "highly branched", linear low density polyethylene, high density polyethylene, low density polyethylene, etc. Blends of the highly branched homogeneous polyolefms with other polymers can be used to produce an easy-open seal having a strength higher than can be produced if the seal layer is made of 100 percent highly branched homogeneous polyolefin.

As a first aspect, the present invention is directed to a heat-sealed easy-open article comprising a film heat sealed to itself or another component of the article. The film comprises a heat seal layer containing a blend of a first polymer and a second polymer. The first polymer is a highly branched homogeneous polyolefin having at least 60 branches per 1000 methylene groups, and for every 100 branches that are methyl, about 4 to 20 ethyl branches, about 1 to 12 propyl branches, about 1-12 butyl branches, about 1 to 10 amyl branches, and about 1 to 20 hexyl or longer branches. The second polymer is present in an amount of at least 5 weight percent based on the weight of the blend, the second polymer having a glass transition temperature or melt temperature which is higher than the first polymer. The heat seal has a strength of from 5 to 75 percent of an ultimate seal strength formed by heat sealing to itself a corresponding film having a heat seal layer containing 100 percent of the second polymer. Preferably, the heat seal has a strength of from about 10 to 70 percent of the ultimate seal strength, more preferably from 20 to 60 percent.

Preferably, the second polymer comprises at least one member selected from the group consisting of olefin homopolymer, olefin copolymer, olefin/unsaturated ester copolymer, olefin/unsaturated acid copolymer, ionomer, and olefin styrene copolymer. More preferably, the second polymer comprises at least one member selected from the group consisting of polyethylene, polypropylene, propylene/ethylene copolymer, ethylene/alpha-olefin copolymer, ethylene/vinyl acetate copolymer, ethylene/butyl acrylate copolymer, ethylene/acrylic acid copolymer, ethylene/methacrylic acid copolymer, and ethylene/styrene copolymer. More preferably, the second polymer comprises at least one member selected from the group consisting of high density polyethylene, low density polyethylene, linear low density polyethylene, very low density polyethylene, ultra low density polyethylene, and homogeneous ethylene/alpha- olefin copolymer. Preferably, the highly branched polymer is present in an amount of from about 1 to 75 percent, based on total weight of the blend; more preferably from 1 to 50 percent, more preferably from 1 to 40 percent, more preferably from 10 to 40 percent.

Preferably, the heat seal has a strength of from about 0.5 pounds per inch to about 7 pounds per inch; more preferably from 0.5 to 5 pounds per inch; more preferably from 1 to 3 pounds per inch.

Preferably, the highly branched polyolefin has from about 60 to about 200 branches per 1000 methylene groups; more preferably, from about 60 to about 120 branches per 1000 methylene groups; more preferably, from about 70 to about 120 branches per 1000 methylene groups; more preferably, from about 80 to about 100 branches per 1000 methylene groups.

In one preferred embodiment, the article is an end-seal bag made from a seamless tubing, having an open top and a transverse heat seal across a bottom region of the bag, the heat seal being of the seal layer to itself. In another preferred embodiment, the article is a side-seal bag having a folded bottom edge, a first side seal, and a second side seal, the first and second side seals being heat seals of the heat seal layer to itself.

As a second aspect, the present invention is directed to a heat-sealed article comprising a film and a heat seal of the film to itself or another component of the article, the film comprising a heat seal layer containing a blend of (A) a highly branched polyolefin having at least 60 branches per 1000 methylene groups, and which contains for every 100 branches that are methyl, about 4 to 20 ethyl branches, about 1 to 12 propyl branches, about 1-12 butyl branches, about 1 to 10 amyl branches, and about 1 to 20 hexyl or longer branches, and (B) a second polymer comprising at least one member selected from the group consisting of polyamide, polyester (aliphatic and aromatic), polystyrene, polycarbonate, and polyurethane. The heat seal has a strength of from 5 to 75 percent of a seal strength of an ultimate seal strength formed by heat sealing to itself a corresponding film having a heat seal layer containing 100 percent of the second polymer. Preferably, the heat seal has a strength of from 1 to 6 pounds per inch.

As a third aspect, the present invention is directed to a packaged product comprisinga form-fill-and-seal package and a product within the package. The form- fill and seal package comprises a film heat sealed to itself in an upper transverse seal, a lower transverse seal, and a longitudinal seal. The film comprises a heat seal layer in accordance with the first aspect of the present invention. A fiowable product is within the package.

As a fourth aspect, the present invention is directed to a packaged product including a blister or clamshell package and a product within the package. The blister clamshell package comprises a film having a heat seal layer in accordance with the first aspect of the present invention.

As a fifth aspect, the present invention is directed to a container including an interior having at least two compartments separated by a peelable seal. The peelable seal is constructed from a film comprising a heat seal layer in accordance with the first aspect of the invention, except that the peelable seal has a seal strength of from 0.1 to 6 pounds per inch

Detailed Description of the Invention The ultimate seal strength of the second polymer is carried out as follows. The second polymer is compression molded at least 20°C above T_t into a monolayer film of about 5 mils. The second polymer is a single polymer if the second polymer in the blend is a single polymer, or is a blend of polymers in the relative proportions present in the blend with the highly branched polymer(s), but without the highly branched polymer. T_t is the highest transition temperature for the polymer or polymer blend as determined by the DSC second heat endotherm. Tt may correspond to either a melting temperature, T_m, or a glass transition temperature, T_g. The ultimate seal strength is obtained heat sealing this compression molded monolayer film to itself, using an impulse heat sealer operating under the following conditions: (A) A sealing temperature range of -10°C < T_seaι - T_t < 10°C (i.e., the sealing temperature is within a range which is plus or minus ten degrees C from T_t);

(B) A minimum heat sealing dwell time for the polymer or polymer blend is determined by the computed reptation time at the chosen heat sealing temperature. The reptation time at the melt reference temperature is determined as the reciprocal of the shear rate or angular frequency of a shear viscosity mastercurve of the polymer melt at which the shear viscosity has decreased to 80% of the zero-shear viscosity asymptote at the prescribed reference melt temperature; The heat sealing reptation time is shifted via time-temperature superposition to the prescribed heat sealing temperature; The heat sealing temperature and the melt reference temperature at which the measurement of shear viscosity is performed need not be the same temperature; and (C) A pressure of 40 psi. As used herein, the language: wherein the heat seal has a strength of from 5 to 75 percent of a seal strength of an ultimate heat seal formed by sealing to itself a corresponding film having a heat seal layer containing 100 percent of the second polymer refers to the seal strength of the heat seal in the article of the invention relative to the ultimate seal strength as described above. The ultimate seal strength is determined from a seal made using a corresponding film which is a monolayer film of identical thickness to the subject film and which has a composition which differs from the heat seal layer only in that it does not contain the highly branched homogeneous polymer. If the "second polymer" is just one polymer, then 100 percent of the corresponding film is this one "second polymer." However, if the "second polymer" is a blend of two or more polymers, 100 percent of the corresponding film is this same blend of two or more polymers. In either case, the corresponding film has a thickness which is the same as the thickness of the seal layer of the film containing the highly branched homogeneous polymer.

As used herein, the phrase "highly branched polymer" refers to polymers such as those synthesized using transition metal catalysts such as the Ni(II) Dupont- Brookhart catalyst disclosed in, for example, U.S. Patent No. 5,880,241 to Brookhart et al. At least some of these polymers could be characterized as being "highly branched homogeneous polymers", which phrase is inclusive of both hyperbranched and dendritic chain structures. Dendrimers are monodisperse and perfectly branched, and the terminal groups are located on the surface of the molecule. They are synthesized by multi-step reactions requiring time-consuming purification, which generally precludes their commercial development. Hyperbranched polymers have a less regular structure, are not mono-disperse, and the functional groups are distributed throughout the molecule. See Chun-Yan Hong and Cai-Yuan Pan in Polymer, 42, 9385-9391 (2000), and M. Yamguchi and M. Takahashi Polymer, 42, 8665-8670 (2001), both of which are also hereby incorporated, in their entirety, by reference thereto. See also R.G. Larson, "Combinatorial Rheology of Branched Polymer Melts", Macromolecules 2001, Vol. 34, No. 13, 4556-4571, which is hereby incorporated, in its entirety, by reference thereto. The ethyl ene-based homogeneous hyperbranched polymers useful in the present invention all have highly branched structures, i.e., at least 60 branches per 1000 methylene groups. The branching may be only first degree branching, or can be up to second degree, or up to third degree, or up to fourth degree, or even higher than fourth degree branching. Preferably, the polymer has a branching within the range of from up to second degree to up to fourth degree. Second degree branching refers to "a branch on a branch", with the branches being distinguished from the main chain; third degree refers to "a branch on a branch on a branch", and so on.

The second polymer is inclusive of non-highly branched homogeneous copolymers, as well as highly branched homogeneous polymers having a branching level of less than 60 branches per 1,000 carbon atoms.

As used herein, the phrase "blister package" refers to the enclosing of articles in thermoformed, transparent "blisters" shaped to more or less fit the contours of the articles. The preformed blisters, usually slightly oversized to provide ample room, are made of thermoplastics such as vinyl, polystyrene, or cellulosic plastics. They are placed inverted in fixtures and loaded with the articles to be packaged, then cards coated with adhesive are applied and sealed to the flanges between and around the blisters by means of heat and pressure.

As used herein, the phrase "clamshell package" refers to a package produced using the modern version of the oldest form of blow molding: preheating two sheets of plastic, placing them between halves of a split mold, closing the mold, drawing the sheets against their respective mold surfaces by means of vacuum, then completing the forming with air pressure between the sheets. The modern process, mechanized and conveyorized, is superior to blow molding from a parison for very large parts and for those in which uniformity of wall thickness is important.

As used herein, the term "bag" is inclusive of L-seal bags, side-seal bags, end- seal bags, backseamed bags, and pouches. An L-seal bag has an open top, a bottom seal, one side-seal along a first side edge, and a seamless (i.e., folded, unsealed) second side edge. A side-seal bag has a an open top, a seamless bottom edge, with each of its two side edges having a seal therealong. An end-seal bag has an open top, seamless side edges, and a seal across the bottom of the bag. Although seals along the side and/or bottom edges can be at the very edge itself, (i.e., seals of a type commonly referred to as "trim seals"), preferably the seals are spaced inward (preferably 1/4 to 1/2 inch, more or less) from the bag side edges or bag bottom edge, and preferably are made using a impulse-type heat sealing apparatus, which utilizes a bar which is quickly heated and then quickly cooled. A backseamed bag is a bag having an open top, a seal running the length of the bag in which the bag film is either fin-sealed or lap-sealed, two seamless side edges, and a bottom seal along a bottom edge of the bag.

As used herein, the phrases "heat-shrinkable," "heat-shrink" and the like refer to the tendency of a film, generally an oriented film, to shrink upon the application of heat, i.e., to contract upon being heated, such that the size (area) of the film decreases if the film is not restrained when heated. Likewise, the tension of a heat-shrinkable film increases upon the application of heat if the film is restrained from shrinking. As a corollary, the phrase "heat-contracted" refers to a heat-shrinkable film, or a portion thereof, which has been exposed to heat such that the film or portion thereof is in a heat-shrunken state, i.e., reduced in size (unrestrained) or under increased tension (restrained). Preferably, the heat shrinkable film has a total free shrink (i.e., machine direction plus transverse direction), as measured by ASTM D 2732 (which is hereby incorporated, in its entirety, by reference thereto), of at least as 5 percent at 185°C, more preferably at least 7 percent, still more preferably, at least 10 percent, and, yet still more preferably, at least 20 percent. While heat shrinkability is preferred in some packaging applications where it is required by the customer or consumer, the heat shrinkability of the film structure is not a necessary requirement of the present invention since moderate heat shrinkage has little effect upon the heat sealing process. As used herein, the phrase "heterogeneous copolymer" refers to polymerization reaction products of relatively wide variation in molecular weight and relatively wide variation in composition distribution, i.e., typical polymers prepared, for example, using conventional Ziegler-Natta catalysts. Heterogeneous copolymers typically contain a relatively wide variety of chain lengths and comonomer percentages.

As used herein, the phrase "homogeneous polymer" refers to polymerization reaction products of relatively narrow molecular weight distribution and relatively narrow composition distribution, compared with heterogeneous polymers. In addition to possessing a narrower molecular weight distribution, homogeneous copolymers differ from heterogeneous copolymers in exhibiting a more even sequencing of comonomers within a chain, and a mirroring of sequence distribution in all chains. Homogeneous polymers have been prepared using metallocene, or other single-site type catalysis, rather than using Ziegler Natta catalysts.

More particularly, homogeneous ethylene/alpha-olefin copolymers may be characterized by one or more processes known to those of skill in the art, such as molecular weight distribution (Mw/Mn), Mz Mn, composition distribution breadth index (CDBI), and narrow melting point range and single melt point behavior. The molecular weight distribution (Mw/Mn), also known as polydispersity, may be determined by gel permeation chromatography. The homogeneous ethylene/alpha- olefin copolymers useful in this invention generally has (Mw Mn) of less than 2.7; preferably from about 1.9 to 2.5; more preferably, from about 1.9 to 2.3. The composition distribution breadth index (CDBI) of such homogeneous ethylene/alpha- olefin copolymers will generally be greater than about 70 percent. The CDBI is defined as the weight percent of the copolymer molecules having a comonomer content within 50 percent (i.e., plus or minus 50%) of the median total molar comonomer content. The CDBI of linear polyethylene, which does not contain a comonomer, is defined to be 100%. The Composition Distribution Breadth Index (CDBI) is determined via the technique of Temperature Rising Elution Fractionation (TREF). CDBI determination clearly distinguishes the homogeneous copolymers (narrow composition distribution as assessed by CDBI values generally above 70%) from VLDPEs available commercially which generally have a broad composition distribution as assessed by CDBI values generally less than 55%. The CDBI of a copolymer is readily calculated from data obtained from techniques known in the art, such as, for example, temperature rising elution fractionation as described, for example, in Wild et. al., J. Poly. Sci. Poly. Phys. Ed., Vol. 20, p.441 (1982). Preferably, homogeneous ethylene/alpha-olefin copolymers have a CDBI greater than about 70%, i.e., a CDBI of from about 70% to 99%. In general, the homogeneous ethylene/alpha- olefin copolymers also exhibit a relatively narrow melting point range, in comparison with heterogeneous copolymers. Preferably, the homogeneous ethylene/alpha-olefin copolymers exhibit an essentially singular melting point characteristic, with a peak melting point (Tm), as determined by Differential Scanning Calorimetry (DSC), of from about 60°C to 110°C. Preferably the homogeneous ethylene/alpha-olefin copolymer has a DSC peak Tm of from about 80°C to 100°C. As used herein, the phrase "essentially single melting point" means that at least about 80%, by weight, of the material corresponds to a single Tm peak at a temperature within the range of from about 60°C to 110°C, and essentially no substantial fraction of the material has a peak melting point in excess of about 115°C, as determined by DSC analysis. DSC measurements are made on a Perkin Elmer System 7 Thermal Analysis System. Melting information reported are second melting data, i.e., the sample is heated at a programmed rate of 10°C./min. to a temperature below its critical range. The sample is then reheated (2nd melting) at a programmed rate of 10°C/min. The presence of higher melting peaks is detrimental to film properties such as haze, and compromises the chances for meaningful reduction in the seal initiation temperature of the final film. A homogeneous ethylene/alpha-olefin copolymer can, in general, be prepared by the copolymerization of ethylene and any one or more alpha-olefin. Preferably, the alpha-olefin is a C₃-C₂₀ alpha-monoolefin, more preferably, a C -C₁₂ alpha-monoolefin, more preferably, a C₄-C₈ alpha-monoolefin, and still more preferably, a Cβ-Cs alpha- monoolefin. Still more preferably, the alpha-olefin comprises at least one member selected from the group consisting of butene-1, hexene-1, and octene-1, i.e., 1-butene, 1-hexene, and 1-octene, respectively. Most preferably, the alpha-olefin comprises hexene-1 and/or octene-1.

Processes for preparing and using homogeneous polymers are disclosed in U.S. Patent No. 5,206,075, U.S. Patent No. 5,241,031, and PCT International Application WO 93/03093, each of which is hereby incorporated by reference thereto, in its entirety. Further details regarding the production and use of homogeneous ethylene/alpha-olefin copolymers are disclosed in PCT International Publication Number WO 90/03414, and PCT International Publication Number WO 93/03093, both of which designate Exxon Chemical Patents, Inc. as the Applicant, and both of which are hereby incorporated by reference thereto, in their respective entireties.

Still another genus of homogeneous ethylene/alpha-olefin copolymers is disclosed in U.S. Patent No. 5,272,236, to LAI, et. al., and U.S. Patent No. 5,278,272, to LAI, et. al., both of which are hereby incorporated by reference thereto, in their respective entireties. Each of these patents disclose substantially linear homogeneous long chain branched ethylene/alpha-olefin copolymers produced and marketed by The Dow Chemical Company.

Yet another genus of homogeneous polymers, including both homopolymers and copolymers, is disclosed in U.S. Patent No. 5,880,241 to Brookhart et al. These homogeneous polymers exhibit the narrow molecular weight distribution of homogeneous polymers such as the metallocene catalyzed ethylene/alpha-olefin copolymers. However, the homogeneous polymers of Brookhart et al have a higher level of branching than the metallocene catalyzed ethylene/alpha-olefin copolymers. In addition to including both homopolymers and copolymers, the polymers disclosed in Brookhart et al include nonpolar polymers as well as polar polymers. Highly branched homogeneous ethylene homopolymers are particularly preferred polymers for use in the article and packaged product of the present invention.

As used herein, the phrase "ethylene/alpha-olefin copolymer", and "ethylene/alpha-olefin copolymer", refer to such materials as linear low density polyethylene (LLDPE), and very low and ultra low density polyethylene (NLDPE and ULDPE); and homogeneous polymers such as metallocene catalyzed polymers such as EXACT^® resins obtainable from the Exxon Chemical Company, and TAFMER^® resins obtainable from the Mitsui Petrochemical Corporation. All these materials generally include copolymers of ethylene with one or more comonomers selected from C₄ to C₁₀ alpha-olefin such as butene-1 (i.e., 1-butene), hexene-1, octene-1, etc. in which the molecules of the copolymers comprise long chains with relatively few side chain branches or cross-linked structures. This molecular structure is to be contrasted with conventional low or medium density polyethylenes which are more highly branched than their respective counterparts. The heterogeneous ethylene/alpha-olefins commonly known as LLDPE have a density usually in the range of from about 0.91 grams per cubic centimeter to about 0.94 grams per cubic centimeter. Other ethylene/alpha-olefin copolymers, such as the long chain branched homogeneous ethylene/alpha-olefin copolymers available from the Dow Chemical Company, known as AFFINITY^® resins, are also included as another type of homogeneous ethylene/alpha-olefin copolymer useful in the present invention.

In general, the ethylene/alpha-olefin copolymer comprises a copolymer resulting from the copolymerization of from about 80 to 99 weight percent ethylene and from 1 to 20 weight percent alpha-olefin. Preferably, the ethylene/alpha-olefin copolymer comprises a copolymer resulting from the copolymerization of from about 85 to 95 weight percent ethylene and from 5 to 15 weight percent alpha-olefin.

As used herein, the phrase "very low density polyethylene" refers to heterogeneous ethylene/alpha-olefin copolymers having a density of 0.915 g/cc and below, preferably from about 0.88 to 0.915 g/cc. As used herein, the phrase "linear low density polyethylene" refers to, and is inclusive of, both heterogeneous and homogeneous ethylene/alpha-olefin copolymers having a density of at least 0.915 g/cc, preferably from 0.916 to 0.94 g/cc. As used herein, the phrases "inner layer" and "internal layer" refer to any layer, of a multilayer film, having both of its principal surfaces directly adhered to another layer of the film.

As used herein, the phrase "outer layer" refers to any film layer of film having less than two of its principal surfaces directly adhered to another layer of the film. The phrase is inclusive of monolayer and multilayer films. In multilayer films, there are two outer layers, each of which has a principal surface adhered to only one other layer of the multilayer film. In monolayer films, there is only one layer, which, of course, is an outer layer in that neither of its two principal surfaces are adhered to another layer of the film. As used herein, the phrase "inside layer" refers to the outer layer of a multilayer film packaging a product, which is closest to the product, relative to the other layers of the multilayer film.

As used herein, the phrase "outside layer" refers to the outer layer, of a multilayer film packaging a product, which is furthest from the product relative to the other layers of the multilayer film. Likewise, the "outside surface" of a bag is the surface away from the product being packaged within the bag.

As used herein, the term "adhered" is inclusive of films which are directly adhered to one another using a heat seal or other means, as well as films which are adhered to one another using an adhesive which is between the two films. Although the films used in the sealed article according to the present invention can be monolayer films or multilayer films, the sealed article comprises at least two films laminated together. Preferably, the sealed article is comprised of films which together comprise a total of from 2 to 20 layers; more preferably, from 2 to 12 layers; and still more preferably, from 4 to 12 layers. In general, the multilayer film(s) used in the present invention can have any total thickness desired, so long as the film provides the desired properties for the particular packaging operation in which the film is used, e.g. abuse-resistance (especially puncture-resistance), modulus, seal strength, optics, etc. Various multilayer structures can be used in the formation of the first heat- shrinkable film according to the invention. Given below are some examples of preferred combinations in which letters are used to represent film layers. Although only 1 through 3 -layer embodiments are provided here for illustrative purposes, the multilayer films of the invention also can include more layers, as follows:

"A" represents a highly branched homogeneous polyolefin homopolymer or copolymer; "B" represents a heterogeneous ethylene/alpha-olefin copolymer having a density greater than about 0.915 g/cm³. "C" represents a homogeneous ethylene/alpha-olefin copolymer having a density of less than about 0.915 g/cm³. "D" represents a polymer comprising at least one member selected from the group consisting of polyolefin, polystyrene, polyamide, polyester, and polyurethane. "X" represents a layer comprising an ethylene/alpha-olefin copolymer having a density greater than about 0.915 g/cm³, as described in the description of the first component. "Y" represents a layer containing a second component comprising heterogeneous ethylene/alpha-olefin copolymer having a density of less than about 0.915 g cm³, as described in the description of the second component.

"Z" represents a layer comprising at least one member selected from the group consisting of polyolefin, polystyrene, polyamide, polyester, and polyurethane, as described in the description of the second layer. The film may be a monolayer film comprising (1) A and B, or (2) A, B, & C. Some preferred two layer films are represented in Table II, below. Table II

Some preferred three layer films include: X / Y / X; X / Y / Z; Y / X / Y; Y / X / Z; X / Z / Y; A+ B / Z / C; A+C / Z / B; and, B+C / Z / A. In any one of these multilayer structures, a plurality of layers may be formed of the same or different modified compositions and one or more tie-layers added. Examples

The purpose of these examples is to demonstrate the effect of adding highly branched hyperbranched polymers to base heat sealing polymers on the ultimate heat seal strength of the polymer blend. Resin blends comprising a homogeneous hyperbranched polyethylene incorporating at least 60 branches per 1,000 carbon atoms with the base heat sealing polymers were prepared using (a) Exxon Exact 3132, a single- site catalyzed, homogeneous, linear poly(ethylene-co-l-hexene) copolymer (MI = 1.2 g/10 min ASTM D-1238, Condition 2.16/190, p = 0.900 g/cm³) and (b) Fina Z9450 ethylene-propylene copolymer (MFR = 5.0 ASTM D-1238, Condition 2.16/230, p = 0.89 g/cm³ ). The respective virgin base heat sealing polymers and polymer blends were compression molded into films approximately 5 mils in thickness. The resulting films were cut into strips and heat sealed on a Sencorp Systems impulse heat sealer. Blend Preparation Procedure

Blends of the highly branched hyperbranched polyethylene (HBP) resins previously prepared and numbered as batch runs 63653 and 63654 each had a weight- average molecular weight, Mw, of 122,000 and total branching levels of 81 and 82 branches per 1,000 carbon atoms, respectively. Blend series #1 constituted HBP 63653 blended into Fina Z9450 at weight percents of 0, 12.5, 25.0, and 50.0. Similarly, blend series #2 was prepared by blending HBP 63654 into Exxon Exact 3132 at weight percents of 0, 12.5, 25.0, and 50.0 as well. The HAAKE Rheocord 90 torque rheometer with the Rheomix 600 mixing bowl attachment and standard roller blades operating at 100 rpm and a mixing bowl temperature of 200°C was used to mix all blends. Approximately 40 grams of each blend were removed from storage in a nitrogen atmosphere box and were compounded for 8 minutes before the polymer mixture was removed from the mixing chamber. A nitrogen purge was used to blanket the contents of the mixing chamber during the entire eight-minute compounding cycle. The resulting polymer blobs extracted from the mixing bowl were reground for subsequent compression molding. The ground samples were returned to the nitrogen atmosphere box until the material was ready to be compression molded into films. Compression Molding Procedure for Films

Polymer films comprising the various blends were compression molded using a Carver Model CMG 302H-12-ASTM hydraulic press. The compression mold assembly employed was characterized by the following six-part bottom-to-top stacked arrangement: (1) a 6" x 6" x 0.125" 304 stainless steel plate, (2) a 6" x 6" sheet of 3.4 mil thick PTFE coated aluminum foil (Caroplast, Inc., T303 PTFE/Aluminum TriFoil tape, P/N 70201666), (3) a mold shim formed by cutting a square frame with an internal opening of dimensions 4" x 4" with 1" borders along each side of the mold shim from a sheet of the same PTFE coated aluminum foil, (4) 2.0 grams of each item for each blend series were evenly sprinkled over the opening of the mold shim, (5) a second 6" x 6" sheet of 3.4 mil thick PTFE coated aluminum foil, and finally (6) a second 6" x 6" x 0.125" 304 stainless steel plate capped the mold assembly. The completed mold assembly was placed between the plates of the hydraulic press and press operation was activated. Hydraulic press operating conditions for each blend were automatically sequenced via a pre-programmed standard ASTM D 1928-96 Procedure C heating, compression molding, and cooling protocol. Following compression molding, film samples were manually cut into 4-inch long by 0.724-inch wide strips using the metal ruler as a cutting template. Shear Rheologv Characterization

Resin discs, 50 mm in diameter, and approximately 2 mm thick were prepared for each resin sample according to ASTM D 1928-96, Procedure C. Discs free of included air bubbles were easily produced for all subject resins using the prescribed molding conditions. Each disc formed was placed between the plates of a 50 mm diameter parallel plate fixture of a Rheometric Scientific, Inc. RMS-800 Mechanical Spectrometer and the plate spacing was adjusted to 1.500 mm. Any rejected melt squeezed beyond the plate edge during gap adjustment was removed with a spatula. The copolymers and polymers comprising blend series #1 and #2 follow the Cox-Merz rule, and consequently dynamic mechanical testing of the melt was employed to measure the melt rheological properties of the blend systems. A dynamic strain low enough to ensure a stable linear viscoelastic response yet high enough to ensure an accurate transducer response was imposed on the sample to ensure as the frequency of oscillation was varied from 0.01 rad/sec to 100 rad/sec at logarithmically-spaced intervals of five points per decade. Typically a dynamic strain in the range of 1 percent to 10 percent is adequate to meet testing requirements for most polymers, especially polyolefin homopolymers, copolymers, and polymer blends. However, the linear viscoelastic range for melt testing can be easily determine using the dynamic strain sweep test. Dynamic frequency sweeps were performed at each of three melt temperatures usually spaced at 10°C to 20°C intervals upward from about 10°C above the peak melting point or glass transition. For polyethylene homopolymers, copolymers, and polymer blends a temperature range extending from 180 °C to 140 °C in 20°C increments is used to minimize sample thermal degradation, and to facilitate the construction of a shear viscosity master curve. In this experiment, Exxon Exact 3132 and Fin Z9450 were analyzed over temperature range from 180 °C to 140 °C in 20°C increments. The parallel plate fixture was initially zeroed at the highest experiment melt temperature, and a thermal expansion coefficient of 2.5 Dm °C was specified for the parallel plate fixture to account for the change in plate spacing with temperature, as recommended by Rheometric Scientific, Inc. The employed testing procedure complies with ASTM D 4440.

The data for the complex shear viscosity (η^*), the loss (G" ) and storage moduli (G ' ) obtained from frequency sweeps at the three melt temperatures were collapsed into a master curve, with each frequency sweep referenced through time-temperature superposition to the data obtained at the highest melt temperature. Time-temperature superposition was accomplished using the Rheometric Scientific Orchestrator^® Version 6.4.4 rheological analysis software operating in the horizontal shift mode. An Arrhenius fit of the resulting shift factors for each melt temperature provided an estimate of the flow activation energy. The following table summarizes the Cross Model parameters for Exxon Exact 3132 and Fina Z9450.

Table 1 Cross Model parameters for Exxon Exact 3132 and Fina Z9450

For steady-shear flow, the Cross Model yields the following form:

where η is the shear rate and temperature-dependent shear viscosity, 770 is the zero- shear viscosity at the reference temperature T_r, λo is the Cross Model relaxation time, b is the Cross Model exponent, γ is the shear rate, and a is the time-temperature superposition shift factor which establishes how the flow master curve shifts as a function of temperature. For dynamic shear, the Cross Model takes the following form:

"o^ai (2)

[l + fa_{τ 0}ω)^b ]

where ω is the angular frequency of the applied strain. The time-temperature superposition shift factor is determined by an Arrhenius relationship

where EA is the flow activation energy, R is the gas constant, and -Tis the system temperature that can be different or the same as the reference temperature, T_r , at which the parameters 770 and λo are determined. Generally, the Cross Model exponent, b, is considered to be a constant over a wide range of temperatures and shear rates. For polymers or polymer blends that follow the Cox-Merz rule, flow master curves obtained by steady-shear viscometry [Equation (1)] are equivalent with that gained by dynamic mechanical experiments [Equation (2)]. Under such conditions we have

Equation (3) is obeyed for most polyolefin systems. Once steady shear or dynamic shear melt rheological data have been obtained, the parameters ηo , o , b, and E are usually determined by a non-linear least squares fit of the data. In the present case, Rheometric Scientific, Inc. Orchestrator Version 6.4.4 data analysis software was used to perform the regression analyses for parameter determination. The reptation time, λ_mp, at the peak heat sealing temperature is defined by the equation

where aχ_s is taken at the peak heat seal temperature, T_s , in °C.

For example, the data for Exxon Exact 3132 in Table 1 can be used to compute the

reptation time for a heatseal peak temperature, T_s , of 96°C. In this case we had:

T_s = 98°C E_A = 6.39 kcal/mol R = 0.001987 kcal/mol K T_r = 180°C

λo = 0.0651 sec b = 0.617

The time-temperature superposition shift factor at the peak heat seal temperature was

a_{T s} = exp 6.39 kcal / mol 1 1 \

= 4.80

0.001987 kcal / mol - K \ 98°C + 273.16 180°C + 273.16

The reptation time, λ_rep, at the peak heat sealing temperature, T_s , was λ_rep = 4^1/06U (0.0651 sec)( 4.80) = 3.01 sec = 3 sec

Thus, the minimum required heat sealing dwell time is 3 sec to reach the ultimate heat seal strength for Exxon Exact 3132. Performing similar computations for Fina Z9450, the reptation time defining the minimum heat sealing dwell time was found to be 11.0 sec at 129°C (264 °C). Heat Sealing Experiments

Heat sealing experiments were conducted using a Sencorp Systems, Inc. Model 12AS/1 impulse sealer. The measured DSC second heat melting points for Exxon Exact 3132 and Fina Z9450 were 96°C and 129°C, respectively. Reptation times as functions of temperature for Exxon Exact and Fina Z9450 were determined from Cross Model fits of the shear viscosity master curves to estimate the minimum time required for the heat sealing dwell time. Each blend series was heat sealed with a peak sealing temperature corresponding to the DSC second heat melting temperature of the virgin base heat sealing polymer to ensure that the ultimate heat seal strength for the virgin base heat sealing polymer was attained. The heat sealing conditions employed for the two heat sealing resin systems were:

Table 2 Operating conditions for the Sencorp Systems impulse sealer

*Note: Film thickness measurements using a digital micrometer indicated that film samples produced using the prescribed molding assembly and the ASTM D 1928-90, Procedure C compression molding protocol, gave an average of 5.5 mils with a range of + 0.7 mils for blend series #1 and #2.

**Note: The value in parentheses was the impulse sealer temperature setpoint required to achieve the indicated actual peak heat seal temperature as measured with a hand-held digital thermometer (Omega Engineering, Inc. Model HH201 A, K thermocouple). The t-peel heat seal strength was measured in accordance with ASTM F88-00. Sample Conditioning

All heat sealed film strips were conditioned according to ASTM D 618-00, Procedure A, for 24 hours at 50% relative humidity and 23°C. Heat Sealing Results

The results of the heat sealing experiments yielding the ultimate heat seal strengths according to Cryovac Method E-013-1 are shown in Table 3 for blend series #1 and in Table 4 for blend series #2. Table 3

T-peel heat seal strengths for Fina Z9450 / HBP 63653 binary blends as a function of composition.

Table 4

T-peel heat seal strengths for Exxon Exact 3132 / HBP 63654 binary blends as a function of composition.

All subranges of all ranges disclosed herein are hereby expressly disclosed. All ASTM procedures referred to herein are hereby incorporated, in their entireties, by reference thereto. Although the present invention has been described in connection with the preferred embodiments, it is to be understood that modifications and variations may be utilized without departing from the principles and scope of the invention, as those skilled in the art will readily understand. Accordingly, such modifications may be practiced within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. A heat-sealed easy-open article comprising a film heat sealed to itself or another component of the article, the film comprising a heat seal layer containing a blend of a first polymer and a second polymer, the first polymer being a highly branched homogeneous polyolefin having at least 60 branches per 1000 methylene groups, and for every 100 branches that are methyl, about 4 to 20 ethyl branches, about 1 to 12 propyl branches, about 1-12 butyl branches, about 1 to 10 amyl branches, and about 1 to 20 hexyl or longer branches, and the second polymer being present in an amount of at least 5 weight percent based on the weight of the blend, the second polymer having a glass transition temperature or melt temperature which is higher than the first polymer, wherein the heat seal has a strength of from 5 to 75 percent of an ultimate seal strength formed by heat sealing to itself a corresponding film having a heat seal layer containing 100 percent of the second polymer.

2. The heat-sealed easy-open article according to Claim 1, wherein the second polymer comprises at least one member selected from the group consisting of olefin homopolymer, olefin copolymer, olefin/unsaturated ester copolymer, olefin/unsaturated acid copolymer, ionomer, and olefin styrene copolymer.

3. The heat-sealed easy-open article according to Claim 2, wherein the second polymer comprises at least one member selected from the group consisting of polyethylene, polypropylene, propylene/ethylene copolymer, ethylene/alpha-olefin copolymer, ethylene/vinyl acetate copolymer, ethylene/butyl acrylate copolymer, ethylene/acrylic acid copolymer, ethylene/methacrylic acid copolymer, and ethylene/styrene copolymer.

4. The heat-sealed easy-open article according to Claim 3, wherein the second polymer comprises at least one member selected from the group consisting of high density polyethylene, low density polyethylene, linear low density polyethylene, very low density polyethylene, ultra low density polyethylene, and homogeneous ethylene/alpha-olefm copolymer.

5. The heat-sealed easy-open article according to Claim 2, wherein the highly branched polymer is present in an amount of from about 1 to 75 percent, based on total weight of the blend.

6. The heat-sealed easy-open article according to Claim 1, wherein the heat seal has a strength of from about 0.5 pounds per inch to about 7 pounds per inch.

7. The heat-sealed easy-open article according to Claim 1, wherein the heat seal has a strength of from about 1 pound per inch to about 3 pounds per inch.

8. The heat-sealed easy-open article according to Claim 1, wherein the highly branched polyolefin has from about 60 to about 200 branches per 1000 methylene groups.

9. The heat-sealed easy-open article according to Claim 8, wherein the highly branched polyolefin has from about 60 to about 120 branches per 1000 methylene groups.

10. The heat-sealed easy-open article according to Claim 9, wherein the highly branched polyolefin has from about 70 to about 120 branches per 1000 methylene groups.

11. The heat-sealed easy-open article according to Claim 10, wherein the highly branched polyolefin has from about 80 to about 100 branches per 1000 methylene groups.

12. The sealed easy-open article according to Claim 1, wherein the article is an end-seal bag made from a seamless tubing, having an open top and a transverse heat seal across a bottom region of the bag, the heat seal being of the seal layer to itself.

13. The sealed easy-open article according to Claim 1, wherein the article is a side-seal bag having a folded bottom edge, a first side seal, and a second side seal, the first and second side seals being heat seals of the heat seal layer to itself.

14. A heat-sealed article comprising a film and a heat seal of the film to itself or another component of the article, the film comprising a heat seal layer containing a blend of (A) a first polymer which is a highly branched homogeneous polyolefin having at least 60 branches per 1000 methylene groups, and for every 100 branches that are methyl, about 4 to 20 ethyl branches, about 1 to 12 propyl branches, about 1-12 butyl branches, about 1 to 10 amyl branches, and about 1 to 20 hexyl or longer branches; and (B) a second polymer being present in an amount of at least 5 weight percent based on the weight of the blend, the second polymer having a glass transition temperature or melt temperature which is higher than the first polymer, the second polymer comprising at least one member selected from the group consisting of polyamide, polyester (aliphatic and aromatic), polystyrene, polycarbonate, and polyurethane; wherein the heat seal has a strength of from 5 to 75 percent of a seal strength of an ultimate seal strength formed by heat sealing to itself a corresponding film having a heat seal layer containing 100 percent of the second polymer.

16. The sealed article according to Claim 15, wherein the heat seal has a strength of from 1 to 6 pounds per inch.

17. A packaged product comprising:

(A) a form-fill-and-seal package comprising a film heat sealed to itself in an upper transverse seal, a lower transverse seal, and a longitudinal seal, the film comprising a heat seal layer containing a highly branched polyolefin having at least 60 branches per 1000 methylene groups, and which contains for every 100 branches that are methyl, about 4 to 20 ethyl branches, about 1 to 12 propyl branches, about 1-12 butyl branches, about 1 to 10 amyl branches, and about 1 to 20 hexyl or longer branches, wherein the heat seal has a strength of from 5 to 75 percent of a seal strength of an ultimate heat seal formed by heat sealing to itself a corresponding film having a heat seal layer containing 100 percent of the second polymer; and (B) a flowable product within the package.

18. A packaged product comprising:

(A) a blister or clamshell package comprising a heat seal of the film to itself or another component, the film comprising a heat seal layer containing a highly branched polyolefin having at least 60 branches per 1000 methylene groups, and which contains for every 100 branches that are methyl, about 4 to 20 ethyl branches, about 1 to 12 propyl branches, about 1-12 butyl branches, about 1 to 10 amyl branches, and about 1 to 20 hexyl or longer branches, wherein the heat seal has a strength of from 5 to 75 percent of a seal strength of an ultimate heat seal formed by heat sealing to itself a corresponding film having a heat seal layer containing 100 percent of the second polymer; and

(B) a product within the package.

19. A container including an interior having at least two compartments separated by a peelable seal, the peelable seal being constructed from a film comprising a heat seal layer containing a highly branched polyolefin having at least 60 branches per 1000 methylene groups, and which contains for every 100 branches that are methyl, about 4 to 20 ethyl branches, about 1 to 12 propyl branches, about 1-12 butyl branches, about 1 to 10 amyl branches, and about 1 to 20 hexyl or longer branches, wherein the peelable seal has a seal strength of from 0.1 to 6 pounds per inch