Vacuum skin-pack film

Field of the invention

The presently disclosed subject matter relates generally to packaging films, more specifically to packaging films useful in vacuum skin packaging applications, method of making films, vacuum skin packages, method of making vacuum skin packages and using the same in vacuum skin packaging applications.

Background

Vacuum skin packaging (VSP) is a process well known in the art using a thermoplastic packaging material to enclose a food product. The vacuum skin packaging process is in one sense a type of thermoforming process in which an article to be packaged serves as the mold for a forming web.

An article may be placed on a rigid, semi-rigid or flexible bottom support, that can be flat or shaped, e.g., tray-shaped, bowl-shaped or cup-shaped (also called “bottom” or “lower” web), and the supported article is then passed to a chamber where a “top” or “upper” web is first drawn upward against a heated dome and then draped down over the article. The movement of the top web is controlled by vacuum and/or air pressure, and in a vacuum skin packaging arrangement, the interior of the container is vacuumized before final welding of the top web to the bottom film.

The distinguishing feature of a vacuum skin package is that the top heated film forms a tight skin around the article and is sealed to the part of the bottom support not covered by the article while in the thermoforming process, the top thermoplastic film is only sealed to the flange-like edges or rim of the bottom support using heated sealing bars or similar equipment.

Vacuum skin packages safely secure the article between the top web and the bottom support and can be opened by various methods.

One less desirable method requires the use of scissors, knives, or other cutting device.

Another method allows for manual opening by pulling apart the two parts, i.e. top and bottom, normally starting from a point like a corner of the package where the top web has purposely not been sealed to the bottom support. Packages that can be opened in this way are called “easy-to-open” or “EZO” packages.

An example of an easy-to-open (EZO) packaging mechanism can be based on the different chemical nature of the top and bottom film. The films of the top and bottom films are only partially compatible and consequently the seal fails when a transversal force is applied to the package at opening.

Vacuum skin packaging has become an increasingly attractive way of packaging several kinds of food, in particular fresh red meats. The final package presents a tight fitting, clear package, which protects the food article form the external environment.

However, the demands imposed on the packaging material used in vacuum skin packaging are particularly high, especially during the heating phase in the dome and the subsequent draping over the article.

Films suitable for VSP applications, for examples, have to stand the heating and stretching conditions within the vacuum chamber of the packaging machine without undergoing excessive softening and perforations. Heating the top web at too high temperatures can cause deformation of the bottom support once the top web is draped down onto the bottom support. In particular, in case of flanged rigid or semi-rigid bottom supports, the flange may result bent up after the packaging cycle, thus resulting in an unpleasant package.

Deformation of the bottom support is more and more frequent due to cost saving strategies that reduce gauge and thermal resistance of bottom supports.

It would then be convenient to heat the top web at temperatures lower than the typical temperatures conventionally used, not only to avoid deformation but also for energy savings.

Films used in other packaging applications, for instance packaging in bags or pouches or in tray lidding, may be not suitable for VSP applications, as they are not required to have the very high formability and thermal resistance that VSP films must have. Typically, films for bags, pouches or tray lidding are minimally or not formed under use.

Even more, films for bags, pouches or tray lidding are typically sealed with a hot sealing bar, which makes the seal stronger just for the direct mechanical pressure applied on the seal. On the contrary, films for VSP are generally required to form strong seals over much larger surfaces under milder conditions, namely under the action of temperature and differential air pressure alone, without application of any further mechanical pressure.

In other words, sealing performance of a VSP film—just for the peculiar draping and sealing all over the surface of the support not covered by the product under suction—is peculiar and more demanding than in other applications.

Additives for the top web are often used to aid in film processing, in particular slip agents that are known to act as lubricants.

Slip agents in fact reduce the resistance, known as film surface drag, which the films encounter when pulled across machine parts. This resistance, which is expressed as coefficient of friction (COF), is harmful to high speed film processing.

However, the addition of slip agents into thermoplastic films should be careful as slip agents may adversely affect both the interfacial bond and the strength of the heat seal. Furthermore, addition of too high amounts of slip agents—e.g. above a level of 750 ppm of erucamide—in the sealant layer was in general discouraged as the film may become too slippery to efficiently process.

Generally, in order to achieved the desired slip effects and to avoid weakening of the seal strength, seal layers of prior art vacuum skin packaging films include slip agents in amount lower than 0.1% by weight with respect to the seal layer weight. US2006/210742AA1 (Cryovac) does not relate to VSP films but to retortable films for pouches manufactured by using vertical form-fill-seal machines.

WO02/43957A2 (Cryovac) does not relate to VSP films but to oriented, heat shrinkable films used for manufacturing bags and pouches for packaging liquid exuding products. This document faces the problem of sealing through contamination, which may result in weak seals and consequently package leaks. In order to improve sealability through contaminants, this document suggests the incorporation of high amount of slip agents in the seal layer of said films that would reduce the chemical affinity between the sealing resins and the contaminants and would allow the contaminant to be more easily squashed out or eliminated from the seal area. In both these documents, films are sealed with hot seal bars under the combined action of high temperatures and direct pressures on the seal areas.

Summary of the invention

The presently disclosed matter is an improvement on the above mentioned vacuum skin packaging by offering the addition of a slip agent at high loading to films used in the top film of vacuum skin packaging to reduce the sealing temperature needed to seal the package. The film and subsequent vacuum skin packaging using the film provide for a package that requires lower heating for sealing the package, which results in energy saving, and prevents the deformation of the bottom support, even with thin bottom supports. Surprisingly, the addition of anti-slip agent to the sealant layer at high loading (e.g. 3500 ppm), discouraged by the prior art, resulted in a decreased sealing temperature of the film without negatively affecting the processing (no excessive slippery) and the seal bond strength.

A first presently disclosed subject matter is thus directed to a non-oriented thermoplastic film suitable for use as a top film in vacuum skin packaging, said film comprising at least

an outer sealant layer a), comprising one or more sealable polymer(s) and one or more slip agent(s);

a second layer a′) adhered thereto, optionally comprising one or more sealable polymer(s) and one or more slip agent(s), wherein the total content of slip agent(s), in the outer sealant layer a) or in the outer sealant layer a) and in the second layer a′) adhered thereto, is greater than 0.10% by weight with respect to layer a) weight or to layer a) and second layer a′) total weight respectively.

A second presently disclosed subject matter is directed to a method of making a non-oriented thermoplastic film suitable for use as a top film in vacuum skin packaging, said method comprising

i) blending one or more sealable polymer(s) with one or more slip agent(s) to form an outer sealant layer a),

ii) optionally, blending one or more sealable polymer(s) with one or more slip agent(s) to form a second layer a′) to be adhered to the outer sealant layer a), wherein the outer sealant layer a) or the outer sealant layer a) together with the second layer a′) adhered thereto, comprise greater than 0.10% by weight of slip agent(s);

iii) coextruding the outer sealant layer a), the second layer a′) adhered thereto and, optionally, one or more of an outer abuse layer b), an inner bulk layer c), an inner tie layer d) or an inner barrier layer e) and

iv) optionally, cross-linking the film, thus providing the thermoplastic film suitable for use as a top film in vacuum skin packaging.

A third presently disclosed subject matter is directed to a vacuum skin package, comprising

a bottom support comprising a first outer sealant layer,

an article loaded on top of the bottom support, and

a top non-oriented thermoplastic film, according to the first disclosed subject matter, the film comprising a second outer sealant layer a), the top film substantially conforming with both an upper surface of the article and a portion of the bottom support not covered by the article, wherein the top film second outer sealant layer a) is sealed to the first outer sealant layer of the bottom support in the portion not covered by the article.

A fourth presently disclosed subject matter is directed to a method of manufacturing a vacuum skin package. The method includes providing a bottom support including a first outer sealant layer. The bottom support has preferably a thickness less than 800 microns. The method further includes placing an article on top of the bottom support. The method further includes providing a top non-oriented thermoplastic film over the bottom support having the article thereon. The top thermoplastic film is a film according to the first disclosed subject matter, the film comprising a second outer sealant layer a). The second outer sealant layer a) of the top film faces the bottom support. The top non-oriented film comprises at least an outer sealant layer a), comprising at least a sealable polymer and a second layer a′) adhered thereto, comprising at least the same or different sealable polymer, wherein the outer sealant layer a) or the outer sealant layer a) together with the second layer a′) adhered thereto, comprise greater than 0.10% by weight of a slip agent.

The method includes heating the top non-oriented thermoplastic film to a softening point to produce a softened, conformable top thermoplastic film. The method further includes evacuating the atmosphere from a region between the bottom support and the top thermoplastic film. The method even further includes draping a softened, conformable non-oriented top thermoplastic film over both an upper surface of the article and a portion of an upper surface of the bottom support not covered by the article. The method also includes sealing the first outer sealant layer to the second outer sealant layer a) in a region in which the first outer and second outer sealant layers come into direct contact with one another, by differential air pressure, without the bottom support undergoing substantial distortion as a result of the sealing of the first outer sealant layer of the bottom support to the second outer sealant layer a) of the top film. In particular, the method for manufacturing a vacuum skin package comprises the steps of: a. providing a bottom support including a first outer sealant layer; b. placing an article on top of the bottom support; c. providing a non-oriented top thermoplastic film including a second sealant layer a) according to the present invention—over the bottom support having the article thereon, wherein the second sealant layer a) of the top film faces the bottom support; d. heating the top thermoplastic film to a softening point to produce a softened, conformable top thermoplastic film; e. evacuating the atmosphere from a region between the bottom support and the top thermoplastic film; f. draping the softened, conformable top thermoplastic film over both an upper surface of the article and a portion of an upper surface of the bottom support not covered by the article; and g. sealing the first outer sealant layer to the second outer sealant layer a) in a region in which the first outer and second outer sealant layers come into direct contact with one another, by differential air pressure.

A fifth presently disclosed subject matter is directed to the use of the non-oriented thermoplastic film of the invention as a top thermoplastic film for vacuum skin packaging applications.

Figures

FIGS. 1A and 1B illustrate possible sealing defects of VSP products and outline the score in a formability test.

FIG. 2 illustrates possible sealing defect for circular bridging in VSP products.

FIG. 3 is a top view of the block used in the present implosion resistance test. The drawing is on scale, namely the proportion of the parts are kept, and the measures of the holes reported therein are the real dimensions in mm.

FIG. 4 (not to scale drawing) illustrates the preparation of the specimens for the measurement of the seal strength of the films of the invention and of comparative films as described in the present experimental section.

Detailed description

The presently disclosed subject matter is directed to a thermoplastic film wherein at least the outer sealant layer comprises a slip agent added at high loading and to vacuum skin packages that use the thermoplastic film as the top film. Definitions

While the following terms are believed to be well understood by one of ordinary skill in the art, the following definitions are set forth to facilitate explanation of the presently disclosed subject matter.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which the presently disclosed subject matter belongs.

Following long standing patent law convention, the terms “a”, “an”, and “the” refer to “one or more” when used in the subject application, including the claims. Thus, for example, reference to “a composition” includes a plurality of such compositions, and so forth.

Unless indicated otherwise, all numbers expressing quantities of components, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the instant specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the presently disclosed subject matter.

As used herein, the term “about”, when referring to a value or to an amount of mass, weight, time, volume, concentration, percentage, and the like can encompass variations of, and in some embodiments, ±20%, in some embodiments ±10%, in some embodiments ±5%, in some embodiments ±1%, in some embodiments ±0.5%, and in some embodiments ±0.1%, from the specified amount, as such variations are appropriated in the disclosed package and methods.

As used herein, the term “composition” refers to any solution, compound, formulation or mixture with at least two ingredients. The ingredients may be, for example, chemicals, substances, molecules, or compositions.

As used herein, the term “film” is used in a generic sense to include plastic web, regardless of whether it is a film or sheet. Films of and used in the present invention may have a thickness of up to 2000 microns or more.

As used herein, the phrase “a thermoplastic film suitable for use as a top film in vacuum skin packaging” and the like refer to a thermoplastic film which is suitable for use in a VSP process, namely a film able to stand heating and stretching conditions within the vacuum chamber of the packaging machine without undergoing perforations and excessive softening and, afterwards, able to tightly adhere to the surface of the support. Preferably, a film for use as a top film in VSP packaging is characterized by high implosion resistance, formability and sealability as defined and evaluated according to the present description.

As used herein, the term “non-oriented” refers to films that had not been subjected to any orientation process, also known as “cast films”.

As used herein the term “orientation process” relates to stretching the coextruded tape or tube in at least one or in two perpendicular directions, typically the longitudinal or machine direction (MD) and the transverse or crosswise direction (TD), at a temperature higher than the highest Tg of the resins making up the film layers and lower than the highest melting point of at least one polymer of the film layers, namely at a temperature where the resins, or at least some of the resins, are not in the molten state.

As used herein, the term “non-oriented, non heat-shrinkable” film refers to a film which had not been oriented by stretching under temperature conditions, as indicated above. Upon subsequent reheating, the non-oriented, non heat-shrinkable film will not or will minimally shrink in seeking to recover its original dimensional state as an oriented, heat-shrinkable film does.

As used herein, the term “non heat-shrinkable” refers to a film having a free shrink percentage (at 160° C. in oil) in both the machine and transverse directions of less than 15%, preferably less than 10% or less than 5%. The terms “vacuum skin packaging” or “VSP” as used herein indicate a packaging process in which the article is packaged under vacuum and the space containing the article is evacuated from gases at packaging. The top flexible film is also referred to as “skin-forming” or “skin” film.

As used herein, the term “package” refers to packaging materials used in the packaging of an article.

As used herein, the term “homopolymer” refers to a polymer resulting from the polymerization of a single monomer, i.e., a polymer consisting essentially of a single type of repeating unit.

As used herein, the term “copolymer” refers to polymers formed by the polymerization reaction of at least two different monomers. The term copolymer also includes terpolymers.

As used herein, the term “sealable polymer” relates to thermoplastic polymers generally used as components of outer sealant layers of VSP films for their sealability under VSP conditions.

In particular, sealable polymers are characterized by a melting point lower than 180° C., preferably lower than 160° C., more preferably lower than 140° C., particularly preferably lower than 120° C. Preferably, the melting point is higher than 60° C. In case of amorphous polymer(s), sealable polymers are characterized by a glass transition temperature (Tg) lower than 120° C., preferably lower than 100° C., more preferably lower than 80° C. Tg and Tm can be measured according to ASTM D 3418 using a Differential Scanning calorimeter.

Preferred sealable polymers are polyolefins as herein below defined.

As used herein, the term “polyolefin” refers to any polymerized olefin, which can be linear, branched, cyclic, aliphatic, aromatic, substituted or unsubstituted. More specifically, included in the term “polyolefin” are homopolymers of olefin, copolymers of olefins, copolymers of an olefin and a non-olefinic comonomer copolymerizable with the olefin, such as vinyl monomers, modified polymers thereof, and the like. Specific examples include polyethylene homopolymer, polypropylene homopolymer, polybutene, ethylene/alpha-olefin copolymer, propylene/alpha-olefin copolymer, butene/alpha-olefin copolymer, ethylene-vinyl acetate copolymer (EVA), ethylene unsaturated ester copolymer and ethylene unsaturated acid copolymer [especially ethylene/butyl acrylate copolymer, ethylene/methyl acrylate, ethylene-acrylic acid copolymer (EAA), ethylene/methacrylic acid copolymer (EMAA)], modified polyolefin resins, ionomer resins, polymethylpentene, etc.

The term “ethylene copolymer” is used herein to refer to ethylene/alpha-olefin copolymers. Ethylene/alpha-olefin copolymers generally include copolymers of ethylene and one or more comonomers selected from alpha-olefins having from 4 to 12 carbon atoms, such as 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene and the like. “Ethylene-alpha-olefin copolymer” and “ethylene/alpha olefin copolymer”, refer to such heterogeneous materials as linear low density polyethylene (LLDPE), and very low and ultra low density polyethylene (VLDPE and ULDPE); and homogeneous polymers such as metallocene-catalyzed EXACT™ linear homogeneous ethylene/alpha olefin copolymers resins obtainable from Exxon Chemical Company and TAFMER™ linear homogeneous ethylene-alpha olefin copolymer resins obtainable from Mitsui Petrochemical Corporation. All these materials generally include copolymers of ethylene with one or more comonomers selected from C.sub.4 to C.sub.10alpha-olefins 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 structure. This molecular structure is to be contrasted with conventional low or medium density polyethylenes, which are more highly branched than their respective counterparts. Ethylene/alpha-olefin copolymers generally have a density in the range of from about 0.86 g/cm.sup.3 to about 0.94 g/cm.sup.3. The term linear low density polyethylene (LLDPE) is generally understood to include that group of ethylene/alpha-olefin copolymers which fall into the density range of about 0.915 g/cm.sup.3 to about 0.94 g/cm.sup.3 and particularly about 0.915 g/cm.sup.3 to about 0.925 g/cm.sup.3. Sometimes linear polyethylene in the density range from about 0.926 g/cm.sup.3 to about 0.94 g/cm.sup.3 is referred to as linear medium density polyethylene (LMDPE). Lower density ethylene/alpha-olefin copolymers may be referred to as very low density polyethylene (VLDPE) and ultra-low density polyethylene (ULDPE). Ethylene/alpha-olefin copolymers may be obtained by either heterogeneous or homogeneous polymerization processes. 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.

As used herein, the term “ionomer” (Io) refers to the ionized or partially ionized form of a copolymer of ethylene with a copolymerisable ethylenically unsaturated carboxylic acid monomer selected from acrylic acid and methacrylic acid wherein the neutralizing cation can be any suitable metal ion, e.g. an alkali metal ion, a zinc ion, or other multivalent metal ions.

As used herein, the term “polyamides” includes aliphatic homo- or co-polyamides commonly referred to as e.g. polyamide 6, polyamide 69, polyamide 610, polyamide 612, polyamide 11, polyamide 12, polyamide 6/12, polyamide 6/66, polyamide 66/610, modifications thereof and blends thereof. Said term also includes crystalline or partially crystalline, aromatic or partially aromatic, polyamides, such as polyamide 6I/6T or polyamide MXD6.

As used herein, the term “polyesters” refers to polymers obtained by the polycondensation reaction of dicarboxylic acids with dihydroxy alcohols. Suitable dicarboxylic acids are, for instance, terephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid and the like. Suitable dihydroxy alcohols are for instance ethylene glycol, diethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol and the like. Examples of useful polyesters include poly(ethylene 2,6-naphtalate), poly(ethylene terephthalate), and copolyesters obtained by reacting one or more dicarboxylic acids with one or more dihydroxy alcohols, such as PETG which is an amorphous co-polyesters of terephthalic acid with ethylene glycol and 1,4-cyclohexanedimethanol.

As used herein, the phrase “directly adhered” or “directly adhering”, as applied to film layers, is defined as adhesion of the subject film layer to the object film layer, without a tie layer, adhesive, or other layer there between.

As used herein “contiguous”, when referred to two layers, is intended to refer to two layers that are directly adhered one to the other. In contrast, as used herein, the word “between”, as applied to a film layer expressed as being between two other specified layers, includes both direct adherence of the subject layer to the two other layers it is between, as well as lack of direct adherence to either or both of the two other layers the subject layer is between, i.e., one or more additional layers can be imposed between the subject layer and one or more of the layers the subject layer is between.

As used herein, the term “extrusion” is used with reference to the process of forming continuous shapes by forcing a molten plastic material through a die, followed by cooling. Immediately prior to extrusion through the die, the relatively high viscosity polymeric material is fed into a rotating screw of variable pitch, i.e., an extruder, which forces the polymeric material through the die.

As used herein, the term “coextrusion” refers to the process of extruding two or more materials through a single die with two or more orifices arranged so that the extrudates merge and weld together into a laminar structure before chilling, i.e. quenching.

As used herein, the phrase “outer layer” or “skin layer” refer to any film layer having only one of its principal surfaces directly adhered to another layer of the film.

As used herein, the phrase “inner layer” refers to any layer having both its surfaces directly adhered to another layer of the film.

As used herein, the terms “core”, and “core layer” refer to any inner layer, which has a primary function other than serving as an adhesive or compatibilizer for adhering two layers to one another.

As used herein, the phrase “tie layer” refers to any inner layer having the primary purpose of adhering two layers to one another.

As used herein, the phrase “bulk layer” refers to any inner layer having the primary purpose to improve the mechanical properties. For example, a bulk layer improves the abuse or puncture resistance of the film or just to provide the desired thickness.

As used herein, the phrases “seal layer”, “sealing layer”, “heat-seal layer”, and “sealant layer”, refer to an outer layer of a film or of a bottom support involved in a sealing step in the manufacture of a vacuum skin package.

As used herein the term “barrier layer” refers to a gas barrier layer or, preferably, to an oxygen-barrier layer, and it is used to identify layers or structures characterized by an Oxygen Transmission Rate (evaluated at 23° C. and 0% R. H. according to ASTM D-3985 and measured through using an OX-TRAN instrument by Mocon) of less than 500 cm.sup.3/m.sup.2/day atm. Suitable thermoplastic materials that would provide such gas-barrier properties are PVDC, polyamides, EVOH, polyesters, and blends thereof, preferably EVOH.

As used herein, PVDC is any vinylidene chloride copolymer wherein a major amount of the copolymer comprises vinylidene chloride and a minor amount of the copolymer comprises one or more unsaturated monomers copolymerisable therewith, typically vinyl chloride, and alkyl acrylates or methacrylates (e.g. methyl acrylate or methacrylate) and the blends thereof in different proportions. Generally, a PVDC barrier layer will contain plasticisers and/or stabilizers as known in the art. As used herein, EVOH is the saponified product of ethylene-vinyl ester copolymers, generally of ethylene-vinyl acetate copolymers, wherein the ethylene content is typically comprised between 20 and 60% by mole and the degree of saponification is generally higher than 85% preferably higher than 95%.

As used herein, the term “thermoplastic starch” or “TPS” means a native starch or a starch derivative that has been rendered destructured and thermoplastic by treatment with one or more plasticizers, with at least one plasticizer still remaining. Thermoplastic starch compositions are well known and disclosed in several patents, for example: U.S. Pat. Nos. 5,280,055; 5,314,934; 5,362,777; 5,844,023; 6,214,907; 6,242,102; 6,096,809; 6,218,321; 6,235,815; 6,235,816; and 6,231,970.

As used herein the term “bottom support” means the bottom part of the VSP package onto which the article is accommodated and onto which the top film is sealed for the part that is not covered by the article. The bottom support can be flat or shaped, i.e. tray-shaped, rigid, semi-rigid or flexible. The bottom support may be a bottom in-line thermoformed or an off-line pre-made tray, optionally perforated.

As used herein, the term “seal” refers to any seal of a first region of a bottom support surface to a second region of a top film surface, wherein the seal is formed by heating the regions to at least their respective seal initiation temperatures. The heating can be provided by anyone or more of a wide variety of manners, such as using a heated bar, hot air, infrared radiation, heated dome, etc. For example, heating during a VSP process is generally performed on the top film only, and is commonly done by contacting the top film with a heated dome. The top film is fully heated while held by suction in contact with the heated ceiling and walls of the dome, while typically the bottom support is only heated indirectly, by the heated top film when draped onto it.

As used herein, the term “sealing temperature” refers to the temperature of the dome of the VSP equipment, onto which the top film is applied by suction and by which it is heated during VSP cycle.

As used herein the terms “easy-to-open” or “EZO” or “easy opening” blend or layer relate to a polymer blend or a layer comprising said polymer blend which easily fail when contrary forces are applied to.

As used herein, the term “easy opening package” means a package showing an opening force, measured by using the method described herein, of from 150 to 900 g/2.54 cm, preferably 250 to 800 g/2.54 cm, even more preferably 300 to 700 g/2.54 cm.

As used herein, the phrase “cohesive failure” refers to any system where the easy opening feature is achieved by internal rupture of a layer, which during opening of the package breaks along a plane parallel to the layer itself.

As used herein, the terms “cohesive failure blend” or “frangible blend” relate to a blend of polymers having a different chemical nature. The polymers are only partially compatible and consequently the material fails when a transversal force is applied to.

As used herein, the phrases “opening strength” or “opening force” refer to the force required to open the package measured according to the method described in the experimental section of the present description.

As used herein, the phrase “differential air pressure” refers to the difference in pressure between the atmospheric pressure outside and the vacuum inside the package.

As used herein, the term “gel content” refers to the content of gel material within a polymeric material. The gel content is related to the extent of cross-linking within a polymeric material. The gel content is expressed as a relative percent (by weight) of the polymer having formed insoluble carbon-carbon bonds between polymers and may be determined by the method described in the experimental part. All compositional percentages used herein are presented on a “by weight” basis, unless designated otherwise.

As used herein the abbreviation “mic.” refers to microns.

Although the majority of the above definitions are substantially as understood by those of skill in the art, one or more of the above definitions can be defined hereinabove in a manner differing from the meaning as ordinarily understood by those of skill in the art, due to the particular description herein of the presently disclosed subject matter. The Disclosed Thermoplastic Film

The presently disclosed non-oriented thermoplastic film suitable for use as a top film in vacuum skin packaging, comprises at least

an outer sealant layer a), comprising one or more sealable polymer(s) and one or more slip agent(s);

a second layer a′) adhered thereto, optionally comprising one or more sealable polymer(s) and one or more slip agent(s), wherein the total content of slip agent(s), in the outer sealant layer a) or in the outer sealant layer a) and in the second layer a′) adhered thereto, is greater than 0.10% by weight with respect to layer a) weight or to layer a) and second layer a′) total weight respectively.

The outer sealant layer a) of the present films comprises at least “a sealable polymer”, namely a polymer generally used for sealing purpose in the art of VSP films, typically at least a polyolefin characterized by low Tg and/or Tm values.

Suitable sealable polymers for the heat-sealable layer may be ethylene homo- or co-polymers, like LDPE, ethylene/alpha-olefin copolymers, ethylene/acrylic acid copolymers, ethylene/methacrylic acid copolymers, ethylene/vinyl acetate copolymers or ionomers.

Preferred materials for the heat-sealable layer are LDPE, ethylene/alpha-olefin copolymers, ionomers, ethylene-vinyl acetate copolymers and blends thereof, more preferred ionomers, LDPE, ethylene/alpha-olefin copolymers, most preferred ionomers and LLDPE.

The sealant layer may comprise a polyolefin.

The sealant layer may comprise 80% to lower than 100%, preferably 80 to 99.9% by weight of a polyolefin. In some embodiments, the sealant layer may comprise 90% to 95% of a polyolefin. In further embodiments, the sealant layer may comprise 93% of a polyolefin.

The polyolefin, may have a density of less than about 0.94 g/cm.sup.3. The polyolefin may be a low-density polyethylene with a density of 0.91 g/cm.sup.3 to 0.925 g/cm.sup.3. The polyolefin may be a linear low-density polyethylene with a density of 0.900 g/cm.sup.3 to 0.94 g/cm.sup.3. In some embodiments, the sealant layer may have 93% by weight of a linear low-density polyethylene.

Examples of suitable resins for the outer layer a) are ethylene-propylene copolymer VERSIFY 3000 (DOW), ethylene-vinyl acetate copolymer ESCORENE ULTRA FL00909 (Exxon Mobil), low-density polyethylene such as LD259 or LD158BW (Exxon Mobil), very low-density polyethylene QUEO 2M131 Borealis , linear low-density polyethylene (LLDPE) as Exceed 4518PA by Exxon Mobil or ionomer Surlyn 1702 (DuPont).

Preferably, layer a) comprises at least 50%, 60%, 70%, 80%, 90%, 95%, 99% or 99.9% by weight with respect to the layer a) weight of one or more of the above sealable polymers.

The outer sealant layer comprises at least a slip agent.

Slip agents preferably included in the outer sealant layer a) of the film of the present invention are, for example, non-ionic surfactants and other well-known lubricating agents.

In particular, the slip agent may be selected from amides, carboxylic acids and their admixtures.

Amides which are preferred are the amides of carboxylic acids having at least five carbon atoms, such as behenamide, linolenamide, arachidamide, ricinolamide, palmitamide, myristamide, linoleamide, lauramide, capramide, perlargonamide, caprylamide, oleamide, stearamide, N,N′-ethylene bisoleamide, and the most preferred slip agent, erucamide and the like, and their admixtures.

Preferably, the slip agent is a fatty acid amide, more preferably an unsaturated fatty acid amide. The fatty acid amide may be selected from erucamide, oleamide, stearamide and combinations thereof. The fatty acid amide may be erucamide. Most preferably, it is erucamide.

Suitable amides are commercially called amide waxes.

Carboxylic acids which are useful slip agents include those having at least four carbon atoms, for example, butyric, caproic, caprylic, capric, lauric, lauroleic, myristic, myristoleic, pentadecanoic, palmitic, palmitoleic, margaric, stearic, oleic, linoleic, linolenic, ricinoleic, 2,3-dihydroxystearic, 12-hydroxystearic, behenic, eleostearic, arachidic, 2-ecosenoic, 2,4-eicosadienoic, 2-docosenoic, 2-tetracosenoic, 2,4,6-tetracosatrienoic and the like.

The outer sealant layer a) and, optionally, the second layer a′) adhered thereto may contain one or more of the above mentioned slip agent(s).

The total content of slip agent in the outer sealant layer a) or in the outer sealant layer a) and in the second layer a′) adhered thereto, is preferably greater than 0.15%, 0.20%, 0.25%, 0.30%, 0.33% by weight with respect to layer a) weight or to layer a) and second layer a′) total weight respectively.

The total content of slip agent in the outer sealant layer a) or in the outer sealant layer a) and in the second layer a′) adhered thereto, is preferably lower than 1.5%, 1.0%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5% by weight with respect to layer a) weight or to layer a) and second layer a′) total weight respectively

The total content of slip agent, preferably erucamide, in the outer sealant layer a) or in the outer sealant layer a) and in the second layer a′) adhered thereto may range from 0.10% to 1.5%, preferably from 0.15 to 1.0%, more preferably from 0.15 to 0.8%, from 0.2 to 0.8% %, from 0.25 to 0.5% %, even more preferably from 0.3 to 0.4% by weight with respect to layer a) weight or to layer a) and second layer a′) total weight respectively.

In further embodiments, the total content of slip agent in the outer sealant layer a) or in the outer sealant layer a) and in the second layer a′) adhered thereto may be of 0.35 wt % of slip agent, preferably of erucamide.

In preferred embodiments, the slip agent is contained only in the outer sealant layer a) of the thermoplastic film of the present invention, more preferably the slip agent is not present in any other layer of the film.

In other embodiments, part of the slip agent is contained in the second layer a′) adhered to the outer sealant layer a).

Preferably, the second layer a′) comprises less than 70%, 60%, 50%, 40%, 30%, 20%, 10% or 5% of the total amount of slip agent, most preferably all the slip agent is contained in the outer seal layer a).

When the slip agent is also contained in the second layer a′), it may contribute to lowering the sealing initiation temperature of the outer seal layer a) by migrating into the outer seal layer a) or by preventing the slip agents back migration from the first outer seal layer a) to the same second layer a′).

The outer sealant layer a) may have a thickness from 2 mic. to 20 mic. In some embodiments, the sealant layer may have a thickness of a range from 2 mic. to 15 mic., preferably from 2 mic. to 12 mic., more preferably from 5 mic. to 10 mic. In further embodiments, the outer sealant layer may have a thickness of 8 mic. The outer sealant layer may have a thickness of 10 mic.

The present film comprises at least a second layer a′) adhered to the outer sealant layer a).

The second layer a′) adhered to the outer sealant layer a) may be an outer abuse layer b), an inner bulk layer c), an inner tie layer d) or an inner barrier layer e) as described herein below.

When comprising the slip agent, the second layer a′) also comprises one or more sealable polymer(s) as defined for the outer sealant layer a) above. In such a case, the second layer a′) may comprise the same or different sealable polymer(s) of the outer sealant layer a); preferably, the second layer a′) has the same composition of the outer sealant layer a).

An outer abuse layer b) is the layer of the non-oriented film that will be in contact with the heated dome of the vacuum chamber in the VSP process.

The description continues in the full USPTO document.