Patent Application
20100323134
This invention relates to film structures useful in the manufacture of packaging, particularly packaging useful in the food industry.
Packaging films consist of multiple polyolefin film layers. Such laminates have many uses such as in the food industry for food packaging in the formation of various flexible pouches. Polyolefins are polyalkenes and the more common polyalkenes include polyethylene and polypropylene. Oriented polyolefin layers such as oriented polypropylene have also been advantageously used.
U.S. Patent Application 2003/0204001 Van Gelder et al. describes a plastic film blended with fragrance and a waxy fatty-acid amide.
Turnbull U.S. Pat. No. 4,487,801 describes a fragrance release pull apart sheet. In the example, aroma of Concord grapes was microencapsulated in a urea formaldehyde resin, and the capsules formed into a coating applied as a stripe down the middle of a paper.
Dobler U.S. Patent Application 2009/0050506 describes fragrance samplers and at column 1 provides an overview of Scentstrip™ magazine fragrance inserts using microcapsules bonded to paper.
Ashcraft et al. U.S. Pat. No. 5,249,676 describes a structure with a flavor burst comprising a laminated multilayer polymeric film. In Ashcraft's laminate the flavorant is applied in a selected area and released upon delamination of the laminate. Resealability is not contemplated, nor is there discussion of for example the present invention's security achievable with a rupturable web layer separate from the package lumen.
U.S. Patent Application 2006/0291756 Thomas et al. describes a web material where an active agent is selectively prepositioned so as to be in communication with the web compartment formed. A separate closure device is also added to the web. The Thomas system requires costly additional steps of positioning and inserting a closure device along with applying the active agent strip or layer so that it is in communication with the compartment formed from the web.
The present invention is a laminate and resultant package expressing an aroma burst. The laminate or package is comprised of a polyolefin sealing layer; a pressure sensitive adhesive layer and microcapsules containing an active core material, the microcapsules dispersed in a resealably tacky pressure sensitive adhesive layer; the pressure sensitive adhesive sandwiched between at least two layers by being disposed along substantially an entire surface of the polyolefin sealing layer and in continuous and direct contact with a second polyolefin layer opposing and coextensive with the polyolefin sealing layer. The microcapsules in the pressure sensitive adhesive layer having less tensile strength than the adhesive such that a fraction of the microcapsules rupture releasing core material such as an aroma or fragrance when the pressure sensitive adhesive layer is separated when the polyethylene and first polyolefin layers sandwiching the pressure sensitive adhesive are pulled apart. The adhesive layer is designed to split apart. The laminate polyolefin sealing layer can have a portion such as one or more edge areas that are sealed to itself or to a second laminate forming a lumen. Lumen for purposes hereof is intended to encompass chamber, pocket, pouch, baggie, package interior, container interior, cavity, interior volume, and interior space. All such terms are equivalent for purposes hereof. The lumen area is physically isolated from the pressure sensitive adhesive and microcapsule layer by a polyolefin layer until the polyolefin layer is ruptured.
Preferably the polyolefin sealing layer is a low density polyethylene, or even a polyolefin elastomer-modified polyethylene.
In one embodiment, the polyolefin layer opposing the sealing layer is a top layer of the laminate and is selected from films consisting of polypropylene, oriented polypropylene, biaxially oriented polypropylene polyethylene and elastomer-modified polyethylene. Optionally the laminate can include additional polyolefin layers or other substrates and preferably in addition one to eight additional polyolefin layers.
In a further embodiment a pouch can be made by heat sealing the sealing layers of two laminates.
In a yet further embodiment an article is made by heat sealing areas of the sealing layer of a laminate according to the invention to itself forming a fin seal and lumen area, or lap seal and lumen, or both types of seal and lumen or chamber for packaging contents.
In an alternate embodiment a laminate is disclosed comprised of a low density polyethylene sealing layer forming one side of said laminate; a pressure sensitive adhesive layer and microcapsules containing an active core material, the microcapsules dispersed in the pressure sensitive adhesive layer; the pressure sensitive adhesive sandwiched between at least two layers of the laminate by being disposed along substantially an entire surface of the low density polyethylene sealing layer and in continuous and direct contact with a first polyolefin layer opposing and coextensive with the low density polyethylene sealing layer, the first polyolefin layer forming an opposing side of the laminate. A pouch can be made by heat sealing the polyethylene sealing layers of two laminates according to this embodiment, or by overlapping and heat sealing the polyethylene sealing layer of the laminate to itself.
Optionally and in addition the laminate further comprises at least a second polyolefin layer disposed over the first polyolefin layer; the microcapsules in the pressure sensitive adhesive layer having less tensile strength than the adhesive such that a fraction of the microcapsules rupture releasing core material when the pressure sensitive adhesive layer is separated when the polyethylene and first polyolefin layers sandwiching the pressure sensitive adhesive are pulled apart.
In an alternate embodiment a container is disclosed comprising a first laminate heat sealed to a second laminate, the first laminate comprising at least one low density polyethylene sealing layer and a polyolefin layer, the second laminate being in the shape of a container, the polyethylene sealing layer forming a top surface of the container.
The second laminate comprises a low density polyethylene sealing layer; a pressure sensitive adhesive layer and microcapsules containing an active core material. The microcapsules are dispersed in the pressure sensitive adhesive layer. The pressure sensitive adhesive is sandwiched between two layers by being disposed along substantially an entire surface of the low density polyethylene sealing layer and in continuous and direct contact with a first polyolefin layer opposing and coextensive with the low density polyethylene sealing layer; and optionally at least a second polyolefin layer or other substrate disposed over or under the first polyolefin layer.
The microcapsules in the pressure sensitive adhesive layer are fashioned to have less tensile strength than the adhesive such that a fraction of the microcapsules rupture releasing core material such as aroma when the pressure sensitive adhesive layer is separated when the polyethylene and first polyolefin layers sandwiching the pressure sensitive adhesive are pulled apart when the first laminate is pulled from the second laminate.
In a yet further embodiment a container is disclosed comprising a first laminate and a second laminate, the first laminate comprising at least one low density polyethylene sealing layer and a polyolefin layer, the second laminate being in the shape of a container, the polyethylene sealing layer forming a top surface of the container.
The second laminate comprises a low density polyethylene sealing layer; a pressure sensitive adhesive layer and microcapsules containing an active core material, the microcapsules dispersed in the pressure sensitive adhesive layer; the pressure sensitive adhesive sandwiched between two layers by being disposed along substantially an entire surface of the low density polyethylene sealing layer and in continuous and direct contact with a first polyolefin layer opposing and coextensive with the low density polyethylene sealing layer; and at least a second polyolefin layer disposed over the first polyolefin layer; whereby the sealing layers of the first laminate and the second laminate can be heat sealed together to close the container.
In a yet further embodiment, disclosed is a package having an aroma burst, the package comprising a laminate comprised of a polyolefin sealing layer; a pressure sensitive adhesive layer and microcapsules containing an active core material, the microcapsules dispersed in a resealably tacky pressure sensitive adhesive layer; the pressure sensitive adhesive sandwiched between at least two layers by being disposed along substantially an entire surface of the polyolefin sealing layer and in continuous and direct contact with a second polyolefin layer opposing and coextensive with the polyolefin sealing layer; and the microcapsules in the pressure sensitive adhesive layer having less tensile strength than the adhesive such that a fraction of the microcapsules rupture releasing core material when the pressure sensitive adhesive layer is separated when the polyethylene and first polyolefin layers sandwiching the pressure sensitive adhesive are pulled apart, the laminate polyolefin sealing layer having a portion being sealed to itself or to a second laminate. The bond of the adhesive layer is less strong than the bond of the heat sealing layer when heat sealed to itself or another heat sealing layer. Therefore the adhesive layer preferentially separates first when the layers of the laminate are attempted to be pulled apart.
In the package according to this embodiment a lumen can be formed when the laminate is sealed to itself or to a second laminate, the pressure sensitive adhesive layer being isolated from the lumen by a continuous polyolefin layer until the polyolefin layer is ruptured.
In a further embodiment the heat sealable laminate of the invention is comprised of at least three layers comprising an oriented polypropylene film layer on one side of said laminate, and a polyolefin elastomer-modified polyethylene sealant film forming an opposing side of a laminate, an interior layer of said laminate comprising a resealable pressure sensitive adhesive layer and microcapsules containing an active core material, the microcapsules dispersed in the resealable pressure sensitive adhesive; the pressure sensitive adhesive layer sandwiched between the oriented polypropylene film layer and the polyolefin elastomer-modified polyethylene sealant film layers and substantially coextensive with the polypropylene film and polyethylene sealant film layers; the microcapsules in the pressure sensitive adhesive layer having less tensile strength than the adhesive such that a fraction of the microcapsules rupture releasing core material when the pressure sensitive adhesive layer is separated when the polyethylene sealant film layer and polypropylene film layers sandwiching the pressure sensitive adhesive are pulled apart.
Preferably, the sealant film is comprised of a mixture of polyolefin elastomer and a polyolefin plastomer, such as a polypropylene elastomer and a polyethylene sealant material
Desirably, the oriented polypropylene film is a biaxially oriented polypropylene film. The laminate can further comprise a barrier layer intermediate the oriented polypropylene layer and the polyethylene film layer. Preferably the barrier layer is comprised of EVOH.
More preferably the polypropylene polymer of the laminate is formed from a monomer represented by the formula H2C═CR1R2 wherein, independently, R1 may be H or a C2-C6 alkyl group, and R2 is H, a C2-C6 alkyl group, or a C(O)OR3 group wherein R3 is H or a C2-C6 alkyl group. Preferably the polyethylene sealant film of the laminate is comprised of low density polyethylene (LDPE), linear low density polyethylene (LLDPE), linear medium density polyethylene (LMDPE), linear very low density polyethylene (VLDPE), linear ultra low density polyethylene (ULDPE), metallocene linear low density polyethylene (MLLDPE), high density polyethylene (HDPE), Polyolefin Plastomer (PO), or mixtures thereof.
Desirably the polyolefin elastomer is present in the polyethylene sealant film in an amount of from about 1 to about 25 percent by weight. In this embodiment or any of the above embodiments, the laminate can further optionally include one or more, preferably one to eight, or even one to 16 or more additional layers intermediate the outer layers. The additional layers can comprise a layer selected from foil, nylon, polyvinylidene chloride, polyethylene terephthalate, oriented polypropylene, ethylene/vinyl acetate copolymers, paper, ethylene/acrylic acid copolymers, ethylene/methacrylic acid copolymers, EVOH, paper, and polyethylene.
The present invention relates to laminates useful as packaging materials and/or containers for goods. The laminates of the invention can efficiently and economically be fashioned into packaging, flexible containers and lids for rigid containers, reclosable plastic bags, storage containers, food containers, trash bags, flexible pouches, sandwich bags, and the like useful for packaging, storing, or extending the useful life of perishable items.
According to one embodiment, the invention discloses a laminate comprised of a polyethylene, preferably a low density polyethylene sealing layer. This layer advantageously lends itself to ease of heat sealing with itself or to another similar layer on a second laminate or a sealing layer on a container. The laminate, in addition to the low density polyethylene sealing layer also has a pressure sensitive adhesive layer along with microcapsules dispersed in the pressure sensitive adhesive layer.
The pressure sensitive adhesive layer is sandwiched between two layers by being disposed along substantially an entire surface of the low density polyethylene sealing layer. The pressure sensitive adhesive layer is also in continuous and direct contact with a first polyolefin layer opposing and coextensive with the low density polyethylene sealing layer. Optionally at least a second polyolefin layer can be disposed over the first polyolefin layer. The microcapsules in the sandwiched pressure sensitive layer are fashioned to have less tensile strength than the adhesive such that a fraction of the microcapsules rupture releasing core material from the microcapsules when the pressure sensitive adhesive layer is pulled apart or separated. This for example would occur when the polyethylene layer and first polyolefin layers sandwiching the pressure sensitive adhesive are pulled apart.
Since the microcapsules are dispersed throughout the pressure sensitive adhesive layer no prepositioning or separate insertion step is required.
Core material for purpose of the invention is the encapsulate and can include benefit agents such as fragrances, aromas, or materials providing a flavor burst or aroma. Preferably, the core material can be an active core material selected from perfumes, fragrances, aromas, essential oils, flavor enhancers, flavorants, or optionally the active core material can be any of the various active agents such as described in U.S. 2006/0291756 incorporated herein by reference. Active core materials can include freshness extenders, odor maskers, drying agents, gases, gas generators, inhibitors, indicators, or any beneficial material lending itself to delivery via microcapsule.
Although the invention is illustrated emphasizing an aroma burst achievable in food packaging, the invention is not to be construed as limited simply to aroma delivery, as evident from the above discussion of the various benefit agents able to be encapsulated and dispersed in the pressure sensitive adhesive of the laminate.
In a preferred aspect of the invention, as depicted in
Unlike in prior art constructions, the microcapsules containing an active core material are dispersed throughout the pressure sensitive adhesive layer. Further the pressure sensitive layer is sandwiched between the low density polyethylene sealing layer and the first polyolefin layer. The laminate core material therefore is always isolated from the interior of a formed package, bag or container by the polyethylene sealing layer or a polyolefin layer, until such time that the layer is deliberately ruptured.
Processes of microencapsulation are well known in the art. U.S. Pat. Nos. 2,730,456; 2,800,457; and 2,800,458 describe methods for capsule formation. Other useful methods for microcapsule manufacture are: U.S. Pat. Nos. 4,001,140; 4,081,376; and 4,089,802 describing a reaction between urea and formaldehyde; U.S. Pat. No. 4,100,103 describing reaction between melamine and formaldehyde in the presence of a styrenesulfonic acid. Microcapsules are also taught in U.S. Pat. Nos. 2,730,457 and 4,197,346. The more preferred process for forming microcapsules are from urea-formaldehyde resin and/or melamine formaldehyde resin as disclosed in U.S. Pat. Nos. 4,001,140; 4,081,376; 4,089,802; 4,100,103; 4,105,823; 4,444,699 or most preferably alkyl acrylate—acrylic acid copolymer capsules as taught in U.S. Pat. No. 4,552,811, each patent described is incorporated herein by reference to the extent each provides guidance regarding microencapsulation processes and materials.
In microencapsulation, small particles or droplets are surrounded by a coating, or embedded in a homogeneous or heterogeneous matrix and preferably surrounded by a coating, to give small capsules with many beneficial agents. Microencapsulation is a technique by which liquid droplets, oils, emulsions, solid particles or gaseous compounds are entrapped into thin films of a preferably food grade microencapsulating agent. The core may be composed of just one or several benefit agent ingredients and the wall may be single or multi-layered. The retention of the cores is governed by the core material's chemical functionality, charge distribution, rheology, solubility, polarity, size, osmotic pressure, and volatility, and the permeability of the wall which is further a function of variables including the composition, degree of cross-linking, porosity, solubility, thickness and porosity of the wall. The material inside the microcapsule is known as the core, internal phase, or fill, whereas the wall is the shell, coating, wall material, or membrane. Practically, the core may be a crystalline material, adsorbent particle, a suspension, an emulsion, a liquid, an oil, water, a suspension of solids, or a suspension of smaller microcapsules. Most microcapsules are small spheres with diameters comprised between a few micrometers and a few millimeters. The size and shape of formed microcapsules depend on the materials and methods used to prepare them. For purposes hereof microencapsulation can include such as: spray-drying, spray-cooling, spray-chilling, fluidized bed, air suspension coating, extrusion, centrifugal extrusion, freeze-drying, coacervation, rotational suspension separation, co-crystallization, and interfacial polymerization.
Common microencapsulation processes can be viewed as a series of steps. First, the core material which is to be encapsulated is emulsified or dispersed in a suitable dispersion medium. This medium is preferably aqueous but involves the formation of a polymer rich phase. Most frequently, this medium is a solution of the intended capsule wall material. The solvent characteristics of the medium are changed such as to cause phase separation of the wall material. The wall material is thereby contained in a liquid phase which is also dispersed in the same medium as the intended capsule core material. The liquid wall material phase deposits itself as a continuous coating about the dispersed droplets of the internal phase or capsule core material. The wall material is then solidified. This process is commonly known as coacervation.
Gelatin or gelatin-containing microcapsule wall material is well known. The teachings of the phase separation processes, or coacervation processes which are described in U.S. Pat. Nos. 2,800,457 and 2,800,458 are incorporated herein by reference. Uses of such capsules are described in U.S. Pat. No. 2,730,456. More recent processes of microencapsulation involve, and preferred herein, are the polymerization of urea and formaldehyde, monomeric or low molecular weight polymers of dimethylol urea or methylated dimethylol urea, melamine and formaldehyde, monomeric or low molecular weight polymers of methylol melamine or methylated methylol melamine, as taught in U.S. Pat. No. 4,552,811 is incorporated by reference. These materials are dispersed in an aqueous vehicle and the reaction is conducted in the presence of acrylic acid-alkyl acrylate copolymers
A method of encapsulation by a reaction between urea and formaldehyde or polycondensation of monomeric or low molecular weight polymers of dimethylol urea or methylated dimethylol urea in an aqueous vehicle conducted in the presence of negatively-charged, carboxyl-substituted, linear aliphatic hydrocarbon polyelectrolyte material dissolved in the vehicle, as taught in U.S. Pat. Nos. 4,001,140; 4,087,376; and 4,089,802 is incorporated by reference.
A method of encapsulating by in situ polymerization, including a reaction between melamine and formaldehyde or polycondensation of monomeric or low molecular weight polymers of methylol melamine or etherified methylol melamine in an aqueous vehicle conducted in the presence of negatively-charged, carboxyl-substituted linear aliphatic hydrocarbon polyelectrolyte material dissolved in the vehicle, is disclosed in U.S. Pat. No. 4,100,103, and is incorporated by reference.
A method of encapsulating by polymerizing urea and formaldehyde in the presence of gum Arabic as disclosed in U.S. Pat. No. 4,221,710 is incorporated by reference. This patent further discloses that anionic high molecular weight electrolytes can also be employed with the gum Arabic. Examples of the anionic high molecular weight electrolytes include acrylic acid copolymers. Specific examples of acrylic acid copolymers include copolymers of alkyl acrylate and acrylic acid including methyl acrylate-acrylic acid, ethyl acrylate-acrylic acid, butyl acrylate-acrylic acid and octyl acrylate-acrylic acid copolymers.
A method for preparing microcapsules by polymerizing urea and formaldehyde in the presence of an anionic polyelectrolyte and an ammonium salt of an acid as disclosed in U.S. Pat. Nos. 4,251,386 and 4,356,109 is incorporated by reference. Examples of the anionic polyelectrolytes include copolymers of acrylic acid. Examples include copolymers of alkyl acrylates and acrylic acid including methyl acrylate-acrylic acid, ethyl acrylate-acrylic acid, butyl acrylate-acrylic acid and octyl acrylate-acrylic acid copolymers.
The pressure sensitive adhesive is selected to be resealable, retaining tackiness when the pressure sensitive layer is separated, and preferably, able to repeatedly rupture or pull apart a portion of the microcapsules on each successive reopening of the package, bag or container providing for example a repeated aroma burst, depending on the active core selected for the microcapsules.
Pressure sensitive adhesive compositions are materials that will form a bond upon contacting the material to be adhered to. Adhesive compositions are considered resealable when the bond is able to be broken yet retains tack, preferably without significant damage to the substrate or layer and can be refastened with only moderate pressure and re-adhered. Pressure sensitive adhesives can include without limitation various acrylic adhesives styrene butadiene block copolymers, styrene isoprene block copolymers, acrylic acid esters, rubber adhesives, acrylic compounds of block copolymers, silicone adhesives, polysiloxanes, including combinations with elastomeric, non-elastomeric or thermoplastic compounds, tackifying resins, plasticizers, and modifying resins. A variety of pressure sensitive adhesives are described in U.S. Pat. Nos. 4,500,021; 3,239,478; 3,917,607 and Canadian Patent No. 1083745. Desirably, in some embodiments the adhesives can have an initial bond strength of from 50 to 400 grams per inch of width of adhesive, using a test such as PSTC-1 described in Example 2 of U.S. Pat. No. 4,500,021. Higher or lower bond strengths may be desirable depending on the application and tensile strength of the capsules and polyolefin layers. The above bond strengths although useful guides to selection, however are approximate and the skilled artisan can select appropriate pressure sensitive adhesives from the many commercially available and/or described in the above references, and adhesives with various bond strengths sold commercially such as Mactac™, (Stow, Ohio), Flexcon™ (Spencer, Mass.) Dow Corning (Milland, Mich.) 3M (St. Paul, Minn.), and Rohm and Haas.
In one aspect, the pressure sensitive adhesive layer is designed to be splittable. When the laminate layers are pulled apart the adhesive layer splits and in the process fractures a portion of the embedded microcapsules releasing their core material. The layers sandwiching the pressure sensitive adhesive layers preferably are barrier layers to passage of the core contents of the microcapsules, therefore the core materials provide a burst of release, such as aroma release before rupture of one of the barrier or polyolefin layers.
In
In
In
In
Unlike in
In
In
In a preferred embodiment, adhesive and capsule layer 12 would be designed to preferentially separate before sealing layers 13 separate from each other, thereby first fracturing some portion of microcapsules releasing aroma before a layer 13 is ruptured to provide access to the container contents. Layer 12 is preferably resealably tacky.
Seal 29 as shown in
The laminate of the present invention may be comprised of multiple layers coextruded or laminated, such as, for example, up to 8 layers, or even up to 16 or more layers, including one or more layers each of the polypropylene, polyethylene, and barrier layers such as EVOH or nylon layers.
Exemplary internal layers within the laminate include but are not limited to foil, nylon, polyvinylidene chloride, polyethylene terephthalate (PET), ethylene/vinyl acetate copolymers, paper, ethylene/acrylic acid copolymers, ethylene/methacrylic acid copolymers, EVOH, polyethylene, metalized polyethylene terephthalate, or oriented polypropylene (OPP), etc. The specific identity of such layers is not critical to the practice of the present invention, but may be determined based on the specific utility contemplated for the laminate.
A preferred barrier material comprises an ethylene/vinyl alcohol (EVOH) copolymer. EVOH generally has an ethylene content of from 15-70 mol %, preferably from 25-55 mol %, which has a degree of hydrolysis for the vinyl ester moiety of from 85-99%, and preferably 95% or greater. If the ethylene content of the EVOH copolymer is greater than about 70 mol %, the gas barrier properties exhibited thereby are diminished, as is also exhibited if the degree of hydrolysis is less than about 95%.
For purposes of the present invention, the term barrier layer is intended to mean that the layer is impermeable to gases or liquids. In particular, the layer is impermeable to oxygen or to core contents contained in the microcapsules.
The EVOH copolymer may further be copolymerized with comonomers such as but not limited to propylene, butylene, unsaturated carboxylic acid (such as methacrylic acid, an ester of an unsaturated carboxylic acid (such as methyl(meth)acrylate), vinylpyrrolidone, etc. Such additional monomers may be present in amounts which do not otherwise disadvantageously affect the desired gas barrier properties of the EVOH film.
It is also within the scope of the present invention to employ two or more types of EVOH polymers in the EVOH film, as well as various conventional additives such as heat stabilizers, UV light absorbers, sealant enhancers, antioxidants, coloring agents, fillers, etc., in amounts which do not affect the desired properties of the EVOH layer.
EVOH polymers are well known in the art and commercially readily available. See, for example, U.S. Pat. Nos. 3,510,464; 3,560,461; 3,847,845; 3,595,740; and 3,585,177, which describe well-known methods for the production of such polymers.
The polyolefin sealing layer usually refers to an outer or inner film or inner layer, or layers, involved in the sealing of the film to itself, another film layer of the same or another film, and/or another article which is not a film. In general, the sealing layer is a layer of any suitable thickness, that provides for the sealing of the film laminate to itself or another layer. The phrase can refer to the interior surface film layer of a package, as well as supporting layers of the interior surface of the sealing layer. The inside layer frequently also serves as a food contact layer in the packaging of foods. In general, sealing layers employed include polyolefins such as linear low density polyethylene, very low density polyethylene, homogeneous polymers such as metallocene catalyzed ethylene/alpha-olefin copolymer, etc.), polypropylene homopolymers and copolymers, polyamide, polyester (e.g., polyethylene terephthalate glycol), ethylene/ester copolymer (e.g., ethylene/vinyl acetate copolymer), ionomer, and functional equivalents thereof. More specifically, the sealant layer may comprise one or more materials or for purposes hereof a blend of a sealant enhancing composition, such sealant enhancing compositions being selected from various blends including any of the foregoing polyolefins and/or including one or more thermoplastic resins and additives inclusive of: polyolefins polymerized by using a single-site catalyst or metallocene catalyst inclusive of linear low-density polyethylene and very low-density polyethylene; conventional types of ethylene-olefin copolymers inclusive of “LLDPE” and “VLDPE” in terms of generally accepted abbreviations; ethylene-vinyl acetate copolymer (“EVA”), ethylene-methacrylic acid copolymer (“EMAA”), ethylene-methacrylic acid-unsaturated aliphatic carboxylic acid copolymer, low-density polyethylene, ionomer resin (“10 (resin)”), ethylene-acrylic acid copolymer, ethylene-methyl acrylate copolymer (“EMA”), and ethylene-butyl acrylate copolymer (“EBA”). Such a preferred class of sealable resins may be termed as an ethylene copolymer, typically a copolymer of a major amount (i.e., more than 50 wt. %) of ethylene with a minor amount (i.e., less than 50 wt. %, preferably up to 30 wt. %) of a vinyl monomer copolymerizable with ethylene selected from the group consisting of alpha-olefins having 3 to 8 carbon atoms, and unsaturated carboxylic acids and unsaturated esters of carboxylic acids having up to 8 carbon atoms, inclusive of acrylic acid, methacrylic acid, acrylate esters, methacrylate esters and vinyl acetate, or an acid-modified product of the ethylene copolymer (preferably modified with up to 3 wt. % of an unsaturated carboxylic acid). It is also possible to use a thermoplastic resin, such as polypropylene resin, polyester resin or aliphatic nylon. The sealable resin may preferably have a melting point of up to about 135° C., or even up to about 150° C. It is also possible to use blends with other additives including at least one species of a sealable resin within an extent of preferably not impairing the transparency of the resultant film or a sealed product thereof. The respective layers may be of any suitable thickness, as the thickness of the respective layers is not critical to practice of the present invention. By way of example, the thickness of the individual film layers in the laminate may range from about 1 μm to about 150μ, and more preferably, from about 7 μm to about 100μ. However, any suitable thickness may be employed with advantage.
The present invention also encompasses those embodiments where one or more of the films which comprise the laminate are oriented in one or more of the transverse or machine directions. For instance, non-oriented polyethylene and/or polypropylene films can be coated onto oriented polyethylene and/or polypropylene (or polyolefin) layers.
The laminate of the present invention can be formed by any suitable method. Exemplary methods which are suitable for formation of the laminate include extrusion, co-extrusion, extrusion coating, adhesive lamination, extrusion lamination, blowing and casting.
Optionally, the adhesive seal layer is comprised of a polyolefin elastomer as one component, in admixture with a heat-sealable polyethylene polymer. The polyethylene sealant polymer may be, for example, a polyethylene plastomer, or a polyethylene sealant material, or a combination of the two.
Preferably, the polyolefin elastomer comprises a polymer wherein the ethylene monomers are polymerized with an alpha-olefin having from 4 to 10 carbon atoms such that the resulting polymer composition has a narrow molecular weight distribution (Mw/Mn), homogeneous branching and controlled long chain branching. Suitable alpha-olefins include, but are not limited to, 1-octene, 1-butene, 1-hexene and 4-methyl-pentene.
Exemplary polymers include those which are known in the art as “metallocene”, “constrained geometry” or “single-site” catalyzed polymers such as those described in U.S. Pat. No. 5,472,775; U.S. Pat. No. 5,451,450; U.S. Pat. No. 5,539,124; and U.S. Pat. No. 5,554,775.
The metallocene process generally uses a metallocene catalyst which is activated, i.e. ionized, by a co-catalyst. Examples of metallocene catalysts include bis(n-butylcyclopentadienyl)titanium dichloride, bis(n-butylcyclopentadienyl)zirconium dichloride, bis(cyclopentadienyl)scandium chloride, bis(indenyl)zirconium dichloride, bis(methylcyclopentadienyl)titanium dichloride, bis(methylcyclopentadienyl)zirconium dichloride, cobaltocene, cyclopentadienyltitanium trichloride, ferrocene, hafnocene dichloride, isopropyl(cyclopentadienyl,-1-flourenyl)zirconium dichloride, molybdocene dichloride, nickelocene, niobocene dichloride, ruthenocene, titanocene dichloride, zirconocene chloride hydride, zirconocene dichloride, among others.
Numerous other metallocene catalysts, single site catalysts, constrained geometry catalysts and/or comparable catalyst systems are known in the art; see for example, The Encyclopedia of Chemical Technology, Kirk-Othemer, Fourth Edition, vol. 17, Olefinic Polymers, pp. 765-767 (John Wiley & Sons 1996).
The polyethylene sealant layer may comprise with advantage a combination of one or more of the polyethylene components (such as a low density polyethylene (LDPE), linear low density polyethylene (LLDPE), linear medium density polyethylene (LMDPE), linear very low density polyethylene (VLDPE), linear ultra low density polyethylene (ULDPE), metallocene linear low density polyethylene (MLLDPE), high density polyethylene (HDPE), or the like), together with a polyethylene plastomer.
When used in combination, typical weight ratios of the polyethylene component and the polyethylene plastomer range from 95:5 to 5:95, although the particular ratio is not critical. The amount of plastomer which is present is determined by the contemplated end use. That is, the presence of higher amounts of the plastomer in the polyethylene film will decrease the initiation temperature of the film for purposes of bonding, but may also detract from the physical properties exhibited by the film. It is thus desirable to provide sufficient plastomer to achieve a desired balance of physical properties.
As taught in commonly assigned Ser. No. 61/202,651 filed Mar. 23, 2009, in an alternate embodiment it has also been found to be useful to incorporate polypropylene plastomer into polyethylene sealing layers in order to enhance the compatibility of the sealing layer to polypropylene during bonding. The polypropylene plastomer may be used in conjunction with a polyethylene plastomer, or separately therefrom, upon admixture with the polyethylene sealing layer.
When so used, the polypropylene plastomer will generally be present in the polyethylene sealing layer in an amount of from about 1 to about 25% by weight, although the amount may vary depending upon the desired properties desired for the laminate.
Again, the amount of the polypropylene plastomer and/or polyethylene plastomer which is employed in admixture with the polyethylene sealing component to form the sealing film will depend to a certain extent upon the desired end use of the laminate, since not only will the presence of the polypropylene plastomer will enhance the compatibility for purposes of bonding to the oriented polypropylene layer, but the presence of the plastomer will change the physical properties of the polyethylene film.
Polyolefin elastomers are typically copolymers of propylene and ethylene. Such elastomers are available from Mitsui under various product designations, as well as under the trademark NOTIO™, and from Exxon under various product designations as well as under the trademark VISTAMAXX™.
The polyolefin elastomer/polyethylene polymer blend which forms an outer layer of the laminate may be formed by in any suitable manner known to those skilled in the art including blown or cast extrusion or co-extrusion, or extrusion coating. The polyolefin elastomer will generally comprise from 1 to 50% by weight of the total mixture in order to enable the desired advantages to be achieved, preferably from about 5 to 25% by weight.
The laminate of the present invention may be used in a number of applications. The laminate finds particular utility in the packaging art, such as multilayer packaging consisting of shrink films and barrier shrink applications, packages formed via form/fill/seal steps, packaging for foods, liners, etc.
Unless otherwise indicated, all measurements herein are on the basis of weight and in the metric system. All references cited herein are expressly incorporated herein by reference.
A four layer coextrusion laminate similar to that depicted in
The laminate lends itself to use with various types and processes of microcapsule formation. Although illustrated with a polyalkyl acrylate wall, the invention is not limited to one particular type of wall. Various other microcapsule walls such as gelatin, urea formaldehyde, melamine formaldehyde, gelatin gum arabic, polyacrylate and the like can be successfully employed.
MF/PAA wall
Peppermint oil core
Volume weighted mean capsule size—11 μm
A melamine formaldehyde and polyalkyl acrylate microcapsule is preparable according to the process of U.S. Pat. No. 4,552,811 incorporated herein by reference. A first mixture is prepared by dispersing alkyl acrylate-acrylic acid copolymer in water and adjusted to be slightly acidic. Peppermint oil is emulsified into the first mixture. The ingredients to form the capsule wall material are prepared as follows: 9 grams of a corresponding capsule wall material copolymer pre-polymer (butylacrylate-acrylic acid copolymer) and 90 grams of water are combined and adjusted to pH 5.0. To this mixture is added 28 grams of a partially methylated methylol melamine resin solution. This mixture is added to the peppermint oil-in-water emulsion. High speed blending is used to achieve a particle size from 10 to 20 microns. The temperature of the mixture is gradually raised to at least 65 degrees Centigrade, and maintained at this temperature for 8 hours with continuous stirring to initiate and complete encapsulation. To form the acrylic acid-alkyl acrylate copolymer capsule wall, the alkyl group can be selected from any of ethyl, propyl, butyl, amyl, hexyl, cyclohexyl, 2-ethylhexyl, or other alkyl groups having from one to about sixteen carbons, preferably one to eight carbons. The microcapsules are blended with the PSA material.
During extrusion, the laminate was wound into a tube about 14″ (25.56 cm) wide. After extrusion the laminate was formed into a package by heat sealing edge areas of LDPE layer 13 to itself by applying heat to edge areas along the periphery of outside HDPE layer 10. A package/pouch was formed. Upon opening of the resultant package/pouch by pulling apart the heat sealed portion of the film laminate splits along the PSA layer. First, this exposes the PSA layer which is tacky and provides a method to reseal the package by pressing the package back together along the broken seal by pressing the split apart PSA layer back together. Opening also breaks some of the microcapsules in the PSA layer which allows the peppermint oil to diffuse giving an aroma burst. Secondly, in the process of opening, the LDPE layer 13 on one side of the package can be torn through for content access. If the package is resealed by pressing it back together and then pulled open again more capsules are broken resulting in a further aroma burst. This process can be repeated several times (10 to 20).
20% PSA+capsules Capsules were 1% of the layer by weight and contained spearmint essential oil as a core material
PSA—Bostik M550 (Wauwatosa, Wis.) resealable adhesive.
The principles, preferred embodiments, and modes of operation of the present invention have been described in the foregoing specification. The invention which is intended to be protected herein, however, is not to be construed as limited to the particular form disclosed, since these are to be regarded as illustrative rather than restrictive. While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.
All documents cited in the specification herein are, in relevant part, incorporated herein by reference for all jurisdictions in which such incorporation is permitted. The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that such publication is prior art or that the present invention is not entitled to antedate such publication by virtue of prior invention. To the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.
