CA2149097A1

CA2149097A1 - Microwaveable multilayer films with metal-like appearance

Info

Publication number: CA2149097A1
Application number: CA002149097A
Authority: CA
Inventors: Mario Paleari
Original assignee: Mario Paleari; W.R. Grace & Co.-Conn.; Cryovac, Inc.
Current assignee: Cryovac LLC
Priority date: 1994-05-11
Filing date: 1995-05-10
Publication date: 1995-11-12
Also published as: US5622780A; NZ272083A; AU694764B2; AU1793495A

Abstract

A microwaveable multilayer film with metal-like appearance, comprises at least a sealing layer, an inner layer, and an outer abuse layer, the film including from 0.05 to 2.5% by weight, based on the total weight of the film, of aluminum powder in finely divided form, dispersed in at least one layer selected from the inner and the outer abuse layers.

Description

: .
~14~9~97 "Mlcro~aveable multilayer films ~ith mctal-like appearance"
, * ~ .
FIELD OF TH~ INVENTION
This invention rclates to a micro~aveable ~u~tilayer ~ilm with metal-like appearance, and the use thereof for packaging food products and consumer articles More particularly, this inven~ion relates to a heat ;hrinkable or thermoformable, micro~aveable dnd multiLayer film ~i~h metal-like appearance, comprising at least a sealing layer, an inner layer, and an outer abuse layer, ~hich compri.es from about O OS to about 2 5Z by ~eight, based on ehe ueigh' of the overall fi~m, ot aLuminum powder in f;nely divided form, dispersed in at least one layer selected from the inner and the outer abuse layers.
~ACKGROU~D OF THF IN~ENTION
M~ltilayer laminates comprising an aluTinum foil or an aluminum metallized substrate and one or more thermoPlastic ~ilms have been known for a Lor)g time The advantages of aluminum are barrier to gasses and light, and a typica~ agreeab~e glossy metaLLic appearance.
HoweYer, it is impossible to use aluminul~ foil or aluminum metalli~ed substrates in shrinkab~e structures In turn, tnermoformation is possible only to a very limited eKtent excLusive~y when the metalLized substrate is a thermop~ast;c resin.
In addition, packages made from multilayer laminates comprising an aluminum foil or an aLuminum metallized substrate cannot be used in microwave ovens, o~ing to eLectrostatic discharges and electric arc formation ;n the oven.
Another drawback is the difficult~ to maintain a hi~h level ~1~9~97 Z

of barrier due to the formdtion of pin-holes particular~y when the package is submitted to abuse during handling and transportation A rurther dr~wback of aluminum foil is that there is a eonc rn about th recyclability and the inci~eration of che structures containing t D~-A-4 137 139 discloses a non-shrinkable and non-thermoformable thermop~astic film comPriSing from 0.1 to 6 by weight of a metal powder selected from the group consisting of aluminum, magnesi~m, zinc and manganese This film is used in the manu-facture of a laminate comprising an aluminum foil and has the aim of increasing the resistance o~ said alumirlum fsll to a~gressive agents US-A-4,985,300 describes a h at resistant microwave transparent base film which is first oriented and then coated with a lay r of microwave susceptor material The microwave susceptor matcrial ~hich is applied ;n a substantiallY
continuous layer by means of convent;onal coating methods such as vacuum deposition and solution coating, should not be so thick to completely prevent penetration of microwav energy to the interior of the packaged food but should be used in ~mount sufficient to cause the film to heat und r micro~ave cooking conditions to provide browing arld crisping of the surface whiLe providing a degree of microwave shieldin5 for the interior of the food to avoid its overcooking. The method of applying the microwave co~ting must be one which does n~t expose the heat shrinkabl fi~m to high temperatures; otherwis the film will shrink durlng processing The App~icants are not aware of any heat shrinkable or thermoformable, subçtantially microwave-transparent multilayer 21`49097 3 ~

film w-th metal-like appearance 08JECTS OF TH~ INVENTION
In acccrdance ~ith the above, a first object of this inverltion is to provide a heat-shrinkable or thermof~rmabLe microwaveab~e mwltilayer fil~ bith metal-like appear3nce A second object of this invention i5 to provide a heat-shrinkable or thermoformable gas-barrier, microwaveable, multilayer film with metal-like appearance __ A thlrd object of the present invention is t~ provide a tubular, heat-shrinkable, optionally gas barrier, microwaveable, multilayer film food casing ~ith metal-like appearance d -rourth object is to provide bags, pouches and tubings by heat-sea~ing to it~elf a heat-shrinkable, optiona~ly gas-barrier, microwaveabLe, mult;layer film with metal-like appearance Another object of this invention is to provide a package wherein an article is ~rapped and sealed or clipped into a shrunk, optionally barrier, microwaveable and multilaye~ filn -~ having metal-like appearance A ~urther object of this invention is to provide a package wherein an article is placed in a cavity obtained in a thermofcr~ed film and sealed under vacuum or a modified atmosphere either by disponing a substantially non-forTing web ov~r said cavity as a lid or br molding down upon and around the article a highly forning web These and other objects are achieved br th~ fi~ dlsclosed hereinbelc~
DEFINITIONS
Unless otherwise stated in .this descriPtion and in the claims, the fol~o~ing symboLs, terms and expressions have the meanings indicated hereinbelo~.
The e~pression "metallized substrate" neans a substrate, such as paper or a thermcplast;c film, coated with an almost monomolecular layer obtained by meta~lization under vacoum The term "film" means a flat and flexible material having a thickness of at least 5 microns, typically of ~rom 20 to 350 microns. As used here;n the term "film" is intended to mean also those fLat, thermoformable f~exible or rigid articles other~ise kno~n as "laminates"
The e~pression "heat shrinkable film" means an orien~ed film ~hich shrinks by at least 10X in dt ~east one direction at ~S~C .
The term "nicro~avcable" or "substantially microwave-transparent" means a structure capable of being crossed by at least 70X, preferably 80X of the microwaves generated by a micro~ave oven ~ithout negatively interfering therewith The term ~'thermofor~able film" means a film suitable to be used in a vacuum or compressed air forming or p~ug-assist vacuum or compressed air forming method In a vacuum or compressed air forming method, a thermoformable film is heated, for examPle, by a contact plate and sucked against the plate by applying ~ vacuum or pushed against the plate by means of COmpresSed air; once heated, the thermoformable film is pushed by atmospheric pressure or by compressed air or by applying a vacuum do~n into a preformed mold In a plug-assist vacuum or compressed air forming method, after the thermoformable film has been heated and sealed across a mold cavity, a plug shape similar to the mold shape impinges on the thermofofmable f;lm and, upon application of vacu~m, the termuformable film .. .. . .. ..

" 21~9097 transfe~s to the mold surface Thermoforming is a popular method of packaging food Products The food product is Placed in the cavity obta~ned tn the thermoformed film and either a substant1ally non-forming web is disposed over the cavity as a l~d and the packages are sealed under vacuum or under mod~f~ed at~osphere according to conventional techni~ues, or a highly forming ~eb is moLded do~n upon and around the product and sealed against the thermoformed rigid supPort by differential air pressure using the ~acuum skin packaging technique Preferably, ho~ever, as used herein the term "thermoformable fiLm" is intended to refer to a rigid thermoformable sheet wnich is thermoformed by the above conventional methods, ~o provide a tray or an other~ise shaped rigid support.
The term "cook-in" means a packacJing materi~L structorally capabLe of uithstanding exposure to cook-in time-temperature conditions while containing a food product Cook-;n time-temperature conditions typically refer to a Lon~ sLo~
cooking, for example submersion in ~ater at 7û-8ûC for '-6 hour5 Submersion at 80C for 12 hours probably represents the Limi~ing case Under such conditions, a packaging mat~rial Droperly characteri2ed as cook-in viLL maintain seaL integrity and ~ill be delamination resistant. AdditionalLy, the packaging film is preferably heat shrinkable under these conditions so as to form a tightly fitting package In the present description, unless specificaLLy set forth or other~ise limited, the terms "polymer" or "polymer resin"
generalLy include, but are not Li~ited to, homopoLymers, copolymers, such as, for ex~mple, block, graft, random, and aLternating copolymers, terpolymers etc and bLends and modifications thereof Furthermorc, urless other~ise -sFeclfical(y limited, the terms "polymer" or "polymer reSin"
shaLl include all possible steric structure of the materidl These structure~ include but are not limited ~o, isotac~ic, syndiotactic, atactic and random arrangements.
The term "seaLing" Layer is intended to refer to a "skin" or "surface" layer that should be heat-sealable to itself wherein the term "skin" or "surface" layer means a layer of a multi~ayer 'ilm which comprtses a surfdce thereof _~ The term "inner" layer as used herein refers ~o an interior layer of a multilayer film which is not a skin ar surface layer nor a gas-barrier Layer.
The ter~ "o~ter abuse" Layer as used herein refers ~o the skin layer of a multilayer film uhich is ;ntended ~o be used as the outside abuse-resistant layer and not as the innermost heat-sealab~e larer The term "barrier" layer refers to a Layer of a polymer or Dolymer bLend relati~eLy impermeable to gas.
AS used herein the term "po~yolefin" refers to thermopl~stic polymers ebtained by polymerization or copolymer;zation of ~ relati~e~y simp~e (C2-C12) olefins ~hich may contain othe~
comonomers ~her-ein the oLefin units are however present in higher amounts with res~ect to th~ other c~mono~Frs; inc~uding, but not limited to, ho~opolymers, copolymers, terpolymers, blends and modifications of such rel~tiveLy ~impLe o-efins Polyo~efins s~ecifically incLuded therein are homopolymers such as Do(yethylene and polypropyLene, copolymers such as propylen~ copoLymers, ethykne-alpha-olefin copolymers either hetero~eneous or homogeneous, ethylene-vinyLacetate ccpolymers, and ethyLene-acryLate or ethylenemethacryLate copolymers.
The term "PolYethyLene" as used herein refers to a famiLy of ` ` 21~9097 reslns obtained by po(ymerizing the gas ethyLene, C2H4 ~y varying the catalysts and methods of polymerizat;on, properties such as density, melt inde~, crys~allinity, degree o~ branching and molecuLar ue;gh~ distribution can be regulated over wide ranges PolyethyLenes having densities belou about 0 925 g/cm are caLled Low density polyethyLenes ~OPE), those having censities rangir,~ from abrJut 0 926 g/cm to about 0 940 g/cm are calLed ~edium density poLyethy~ene (MDPE~ and those having densities ranging from about 0 941 g/cm3 to about 0.9~5 g/cm and over are called high density polyethyLenes (HDP~
The molecular structure of conventional L~PE is highly branched Whi~e conventionaL ~DPE possess a moLecular structure which is branched, the degree of branching is ~ess than that of conventional LDPE. The moLecular structure of HCPE possesses ~ittLe or no side branching The term "polypropylene" refers to a thermoplastic resin obtained by homopolymerizing pr~pylene units according to kno~
proces~es The term "propylene copolymers" refers to a propylene copo~ymer ~ith ethylene andtor butene-1 uherein the 3ropylene units are present in a higher amount than the ethylene andlor b~tene-1 un;ts.
AS used herein the expression "heterogeneous ethyLene-aLpha-olefin copoLymer" refers to polymerizat;on reaction products of ethylene with one or more alpha-o~efin comonomer5 containing from 4 to 8 carbon atoms, preferebLy selected from the group comprising linear copolymers or terpolymers of ethytene with one or more of butene-1, 4-methyl-pentene-1, hexene-1, or octene-1, characteri~ed by a relatively uide varat;on in mo~ecular weigh~ and composition distribution, ; e polymer .

.

_ - 8 prepared for example, using conventional ~iegler-~atta 'catalr5t5. Such po~ymers typically contairl a rc~atively wide variety of chain lengths and comono0er percentage~.
As used herein the term "VLDPE" or the expression "very lo~
density polyethylene" refer to a heterogeneous copalymel of ethylene with one or more (C4-C8)-alpha-o kfin having a density c 0 ~1S g/cc Typically the density of such a ~LDPE will be of from about 0 8~ g/cc to abou~ 0 915 g/cc, and preferab~y of from about 0 9G0 ~/cc to about 0 15 g/cc.
As used herein the term "LLDPE" or the expres~ion "linear lo~ density polyethylene" refer ~o a heterogeneous copolymer of ethylene and one or more (C4-C ~alpha-olefin havin~ a density of from about 0 915 g/cc to about 0 925 g/cc.
As used herein the term "~MDP~" or the expression "linear Tediun density polyethylene" refer to a heterogeneous copolymer of ethy~ene and one or more tC4-C8)-alpha-olefin having a d~nsity in the range of from about 0 926 to about 0.940 g/cc The meLt flo~ index of linear low, medium and very low density polyethylenes generally ranges from between about 0 1 to about lG grams for ten minutes, preferably from abou~ 0 5 to about 3.0 grams for ten minutes ~inear lo~, medium and very lo~ density polyethylene resins of this type are commercial~Y
avaible or can be manufactured by kno~n mcthods As used herein Lhe expression "homogeneous ethylene-alpha-olefin copolr~ers" refers to polymerisation re~ction products having a relatively narro~ molecular weight distribution and relative~y narro~ composition di~Lribution Such po~ymers exhibit a rel~tively even sequencing of comonomers ~ithin a chain, the mirroring of sequence distribution in all ch~ins and the 5i~i larity of length of all chains, and are typicaL~y - . . . . -,_ 214~097 prepared us;ng metallocene or other single site type catalysts More particularly homogeneous ethylene-alPha-olefin copo~ymers ~ay be characterized by one or more methods known ~o those skilled in the art such as molecular weight distrib~tion (M /M ), or composition distribution breadth inde~ ~CD~I) The ~ n molecular ~eight distribution also known as polydispersity ~ay be determined by gel permeation chromatography. The homogeneous ethylene-aLpha-~lefin copolymers useful in the presen~ in~ention generally have a ~M /M ) of less than a~out 3 preferably less than about 2 7 and even more pre~erably comprised between about 1 9 and about 2.5. The CDaI of such homogeneous ethylene-alpha-olefin copolymer will generally be grater than about 60 percent The CDBI is defined as the percent of the copolymer ~olecules having a comonomer content within SO percent (i e plus or minus 50%) of the median total molar comonome~ content The CDBI of a polyethylene homopoly~er ~hich does not contain a comonomer is defined to be 100X The CDBI is determined via the technique of Temperature Rising ElutiQn Fractionation ~TREF~ as described f~r istance by Wild et al in J PoLy Sci. Polr Phys Ed 20 p 441 (1982) Preferab~y the homogeneous ethylene-alpha-ole~in copolymers have a CDB~ greater than about 65 and more preferably greater than 70X. ExamPles of processes for preparing homo~eneous ethyLen~-alpha-olefin copolymers are disclosed in US-A-5 206 075 US-A-5 Z41~031~ and W0-A-93~303.
Further details regard;ng the production of homogeneous ethylene-alpha-olefin copolymers are d;sclosed in W0-A-9003414 Another genus of homogeneous ethyLene-alpha-olefin copolymers is disclosed in US-A-5 272 236 and US-A-5 Z78 Z7Z
The term "ethy~ene vinyl aeetate copolymer" (EVA) as used - .. ~ -21~9097 `_ - 1a-herein refers to a coPolymer formed from ethylene and vinyl acetate monomer~ wherein the ethylene derived units in the cooolymer are pre6ent in major amounts and the viny~ acetate derived units ;n the copolymer are present irt mirlor amounts A5 used herein, the term "ethylene-acrylate or ethylene-methacrylate copolymer" refers to the ~roduct obtained by copolymerization of ethylene with acrylate l~onomers of formula R
XO - C - C = CH
O - .
wherein R is hydrogen or methyl group and X is hydrogen, (C1-C4~alkyl or a metal cation, preferably selected from Na and Zn , wherein the ethylene units are present in a h;gher amount than the acrYlate units The term ~'modified polyolefin" means polyolefin as defined above characterized by the presence of functional groups such as ketone, carboxylic acid and/or anhydryde grOups, these last groups being preferred.
The ~erm "ethylene~vinyL a koho~ copolymer" or "EVOH" means a hydrolyzed EVA copolymer-, preferably hydrolyzed to a degree of at least 50~, more preferably at least 99% The moleX of ~inyl acetate is generally at least 25X, preferably at least 29%, highcr proportions of vinyl acetate and hi~her degree of hydrolysis giving improved barrier properties The term "PVDC", as used herein, refers to a vinyl;dene chloride coPolymer wherein a major amount of the copolymer rompr-ses vinylidene chLoride amd a minor amount of the copo~ymer comprises one or more unsaturated monomers copolymer;sable therewith Examples of unsaturated mono~crs 214gO97 copolymerisable with the vinyLidene chloride are vinyl chLoride, acrylonitrile, and alkyt acrylates.
The term "polycarbonate" essentially ref~rs to linear thermoplastic polyesters of carbonic acid ~ith aliphatic, cycloaliphatic or aromatic dihydroxy compounds.
rhe term ~polyester~ generally refers to heterochain polymeric compounds possessing a plurality of carboxylate ester groups as components of their sketetal structures, and as used herein said term refers Lo ring-containing polyesters and co-polyesters, such as poly(ethylene terephthalate), poly-~ehylene 2,5-dimethyl terephthalate~, po~y(1,4-cyclohexylene ~
terephthalate), and the like esters par~icularly those ~ith a high degree of crystallinity.
The term "polystyrene" rerefs ~o -~hose polymers ~hich are obtainable by po~ymerisation of styrene or styrene derivatives, e.g. diviny~benzene, vinyltoluene, and a~pha-methylstyrene, or co-polymerisation of the above ~onomers with other vinyl co-monomers e.g. bu~adiene, acrylonitrile-, methyl methacrylate, maLe;c anhydride, and the like comonomers, as we~l as to the rubber-modified poLystyrenes (impact-resistant polystyrenes).
The term "poLyamide" means high moLecular weight polymers having amide linkages along the molecular chain, and refers more specifically to synthetic polyamides such as various nylons The polya~ides may contain a small amount of a nucleating agent such as talc.
SUMMARY OF THE INVENTION
It has now been found that incorporat;on of from about 0.05 to about 2.S% by weight based on the ~eight of the overall f;lm of al~minum powder into one or more layers selected from the inner and the outer abuse ~ayers of a heat-shrinkab~e or a 21~9097 `_ thermoformable, multilayer structure, compr;sing at least a sealing ~ayer, an inner layer, and an outer abuse layer, results in a structure which has an agreeable 0etal-like appearance, further characterized by the fact that the structure maintains its basic properties, sealability, mechanical properties and shrinkability or thermoformability, respectively and, when it contains a gas-barrier layer, also its gas barrier properties, and can be easily microwaved.
Therefore this invention relates to a nicrowaveable muLtilayer film with metal-like appearance, comprising at least a sealing layer, an inner layer, and an outer abuse layer, ~haracterized in that from about 0.05 to about 2 SX by weight based on the weight of the o~erall film of alu~inum powder in finely divided form is dispersed in one or more layers selected from the inner and the outer abuse layers According to a preferred embodiment of the present invention said aluminum powder is dispersed in the inner layer(s) Tipycally, the aluminium powder has a small particle size Typical particle size distributions of suitablc aluminium powders are e g 90~ less than 20 microns and SOX less than 10 microns, preferably 90% less than 18 microns and 5ûX less than 7 microns, even more preferably 9~ ~ess than 15 microns and 50X less than 6 microns, to allow a fine dispersion thereof into the resin Preferably the film w;ll comprise from about 0 1 to about Z 0 by weight of aluminium pawder, more preferably from about 0.1 to about 1 5 and even more preferably from about 0.15 to about 1X
Advantageously the film ~ill also comprise, in adtition to the aluminium powder, up to abo~t ZX, preferably up to about - - - .;, - - .

1X, e.g. up to about 0.1Z by ~eight, based on the overall ~eight of the film, cf mica platelets disperset in the same l~rer~s~ as the a~ini~m po~der.
The Layer(s) ccmprising alumini~m Dowder may fur~her coTprise titani~m dioxide in an amount up to about 8X, pref~rably ùp to abo~t 4%, e.g. up to about ZX br ~eigh~ ~assd an the ~eight of the overalL ftLm.
According to a preferred enbodi~ent of the ~resen~ ;nven~ion ho~ev~r, ~ica platelets and titanium dioxide ars preferably dispersed in ~he same larer~Q) as the aluninium po~der in the for~ of titanium dioxid~-coated ~ica Dlatelets. In s~ch a case the amount of titanium dioside-co~ed m;ca may be up to ~bo~t 15X by ~eight, based on the weight of ~he o~erall fiLm.
Peeferably said ~mount 1s comprised in the range of fro~ aoout 1X to about 1~X b~ weight The addition of mica pl~telets co~ted ~th a smooth, thin and uniform ~ayer of titæ~ium dioxide in fact enhances t~
sparkLing effect proYided b~ the aluminiu~ Po~der thus greatly impr~ving the fi~ appearance. The particle si2e range of these tit~nium dioxide-coated mica parr1cles is generalLy up ~o 2a ~icrons and preferably up to 15 ~icrons. ~hile the Dar~icLe slze r3nge determine the ~eralL, str~ct~red gLitter or sa~in ~heen effect, the thickness of the t~tanium dioxide coating ~ay prod~ce di~feren~ perLescent cDlors, from siLver through yel~o~, red, ~rd blue, ~o gree~, Sa;d perlescent p1gments are a~aiLable for ~nstance fron The ~earl Corporation ~LJ.S.~
A~ternati~e~, if a metalLizet color different from siLver is desired, it can ~lso b- obtainad by the use - in addition to ~he aluminium po~der and the titaniu~ dio~1de-coated mica pla~elet~ providing for the si Lyer color - of a conventional .. . . . . . .

2i490~7 org~nic pigment in suitable proportions. Typically said organic Pl9ments may be present in an amo~nt of up to about 2 5% by weight based on the wei3ht of the overall film. As an example the addition sf a suitable combination of yellow and reb organic pigments ~ives a gold-like appearance to an otheruise silver-like structure According to a preferred embodiment the heat-shrinkable, or thermoformable, micro~aveable, multilayer film of this invention comprises a gas-barrier layer Additional layers such as tie layers or bulk layers may aLso be present A typiral structure of a heat-shrinkable fi~m according to the present invention ~ill comprise a seal~ng layer, an inner layer, an optional gas-barrier layer and an outer abuse layer;
a first tie layer between the inner and the barrier layer and a second tie layer between the barr;er and the outer abuse layer~
may a~s~ be present The sealing layer used in the heat-shrinkable film of the present invention may be any conventional heat-sea~able layer Such a layer may for example comprise an e~hylene-propylene copolymer, an ethylene-butene-propylene terpolymer, ~L~PE, LLDPE, homogeneous ethylene-alpha-olefins, ethylene vinyL
acetate copolymer, a ionomer (for exa~ple Surlyn ), ethylene acrylic acid copolymer~ ethylene methacrylic acid copolymer, ethylene bu~yl acrylate ~opolymer, ethylene-alkyl acrylate-maleic anhydride terpolymer and the like polymers In a preferred embodimerlt, an ethylene-propylene copolymer, an ethy~ene-butene-propylene terpolymer, or a VLDPE
heat-sea~able layer is used The ou~er abuse reSistant la~er in the heat-shrinkable film of the present invention may be any conventional type of such - - - .

21~9097 layer, for example an ethylene vinyl acetate copolymer, ionomer ~e.g. Surlyn ~, polyamide, V~0PE, ll~PE, r,r EMAA layer- ~n a particularly preferred embodiment the outer abuse layer is an ethylene-vinyl aGetate copolymer or a polyamide layer.
It ~ill be understood that blends of resins may be used in place of individw l re~ins in the various layers of the films of the inventionr Darticularly in the sealing and outer abuse layers.
ln the heat-shrinkab1e film according to the present invention, rhe inner layer which must be present, may for example be an ethylene-vinyl acetate copolymer, ethylene-butyl acry~ate copolymer, an ethylene-methacrylate copolymer, an ~LDPE, Gr a ~LDPE. In a preferred ewbodiment said inner layer is an ethylene-vinyl acetate copolymer, an LL31~E or VLUP~
layer. Additional inner layers may be present which may comprise the same or different polymers.
6as-barrier layers are typically EVOH or P~C layers ~herein said layers comprise EVOH, optionally blended with polyamtdes, or PVDC, as defined above.
When t~o adjacent layers do not bond satisfactorily each other, adhesive or tie layers are generalL~ employed. Said tie layers may comprise for exampLe a modified polyolefin, such as a modified ethylene-vinyl acetate copolymer ~herein the modifying agent is maleic anhydride The f;lm according to the present inver,tion ~ay be ;rradiated with high enersy electrons up to 16 Mrad in order to cause cross-linking and improve the mechanical properties thereof.
More prefer~bly the leveL of radiat;on is of from about 1 to about 12 Mrad 21~9097 Example of shrinkable films which may benefit from this invention by incorporating aluminum powder, preferably ~ith mica and titanium dioxide, in an inner cr in the outer abuse layer(s) are disclosed in e g US-A-4 469 742, US-A-~ 6~0 856, EP-A-3 217 252, EP-A-~ Z51 77~, EP-0 }6~ 808, EP-0 485 847 and European ?atent application ~283C555 6, the contents of which are incor~orated herein by reference.
A ~ypical structure of a thermoformable film according to the present invention will comprise a sealing layer, an inner Layer, optional~y a gas-barrier layer and an outer abuse layer Also in this case tie layers may be present as uell as additionaL layers with specific ~urPoses, such as layers ai~ed at orovinding an easy opening af the package, or additional inner layers to incre~se the oulk of the structure or improve its mechanical properties In such general thermoformab~e structure, the sealing layer may be any conventional heat-sealable layer as defined above, and preferably an EVA or an LDPE or a ionomer layer; the outer abuse-resistant layer may be for instance a polyolefin, e g EVA or HDPE or LDPE or polypropylene, a ionomer, a polycarbonate, a polyamide, a p~lystyrene, a Polyester; the inner layer ~h1ch in the preferred embodiment is used to im~art the desired rigidity to the thermoformable structure is generally based on polystyrene, polyester, or polypropylene The gas-barrier layer, if present, is as ~efined for the heat-shr;nkable structure and preferably EVOH In some cases, i e ~hem the inner layer comPrises a polyester ~nd is s~fficient~y th;ck, the structure ~ill have gas-barrier propert;es even ;n the absence of a separate gas-barrier layer.
The multilayer fi~ms of the present ;nvention can be -- .
- . . .
- - - - . . -. . - . . .

- 214gO97 produced by ronventional proceSSes which conprise co-extrud~ng the various resins through different extruders and passing the extrudate through a die, either round or flat, where the ldyers are joined and form a total coextrusion. ~he multilayer ~elt structure then exits the die lips and is cooled down. It may be desiderable to cross-link the structure to improve abuse or puncture-rcsiStance and other physical characteristics thereof and ~hen a heat-shrinkable fiLm ;s desired it 1S necessary to orient it either monoaxiaLly or, preferably, biaxially.
Processwise, cross-linking is preferably accomplished by irradiation with high energy elecerons usins apparatuses well known to those of skill in the art. The irradi~tion is usually carried out at a dosage up to about 16 MRad, eypically between about 1 MRad and about 1Z MRad. Alternatively cross-linking can be achieved by means of irradiation ~ith U~ radiation, X-rays, beta-particles and the like or che~ically throt,gh utilisation of peroxides.
Orientation, when requ;red, may be effected by the bubble technique when the extrusion is done through a round die or by tenterframe when the extrusion is done through a flat die. in the former case Lhe extruded tubular tape which is obtained by q~enching the melt structure exiting the die is collapsed, optionally cross-linked, and then passed through a hot water bath and, as it leaves the ho~ water, it is inrlated and blown into thin tub;ng In the latter case the melt sheet which exits the ~lat die is cooled down by calendering or quenched by using a chill roLL or other known means, it is optionally cross-linked, and is then heated by passing over a heating zone and oriented by stretching it either ~ono-axially or biaxially and in this latter case eit~er sequential~y or simultaneously.

- -, . .

214909~

Alternatively instead of using the full coextrusion method the structures ot the present invention can be manufactured by conventional extrusion coating or la~ination. ~n the former case one or more layers of the structure are e~truded or co-extruded first tthe substrate), optionally cross-linked, and then coated by extruding or c~-cxtruding the remaining layers thereonto In the latter case, two or more p~rtial structures, which may optionally be crsss-linked, are couDled by lamination typically using conventional adhesives, to form the desired end str~cture.
In order to get the structures according to the 1nventian, the aluminum powder oP~ionally mixed with mica plateLets, and/or ,iO2 or titanium dioxide-coated mica platelets, of the suitdble particle sizes and in the suitably selected amounts are carefully and uniformely disperded into the resin(s) of the suitably selected inner and/or outer abuse layer(s). This is preferably done by blending the resin with a so-called masterbatch, a concentrate of the above ingredients dispersed typically in the sa~e resin. This blending step c~n be carried out before or during extrusion. The masLerbatches are prepared by conventional ~echniques that typically in~olve griding the resin used as the masterbatch base, mixing it ~ith all. the other ingredients in powdered form using highly viScous liquids such as mineral oils, fatty acids, and fatty alcohols or waxes as dispersants, extruding through a die having a large number of holes using a double scre~ extruder and pelletizing the thus obtained strands.
The masterbatch optionally contains also a minor portion of antiblocking ~gents, such as silicon d;oxide, to prevent sticking effects.

. - . .

21~gO97 Furthermore it may contain also minor amounts of o~her conventional additives such as antioxidi~ers, stabiCizers, and the like additives, if necessary or advisable Said masterbatches ~ill typica~ly comprise from about Z to about 15~, ~referably from about 3 to about 1~%, of aluminium powder In a preferred embodiment said masterbatches will a~so comprise mica and/or titanium dioxide or titan;um dioxide-coated ~ica platelet5 in an overall amount of from about 20 to about 60%, pre~erably from about 30 to about 5ûX.
The microwaveable multilayer film with metal-like appearance of this invention may be used according to conventional techniques When the film of ~his invention is heat-shrinkable, it is wrapped around an article, or said article is introduced into a receptacle formed from sa;d film, such as a tubular casing, a pou_ch or a bag, the rece~tacle is vacuumi~ed if necessary, the open end(s) of the receptacle are sealed or clipped and the package is shrunk When the ~ilm of this invention is thermof~r-nable, it is vacuum or compressed air formed, an article or a food product is placed in the cavity thus obtained and eith~r a substantially non-forming web is disposed over the cavity and the package is sealed under vacuum or under modified atmosphere or a highly forming web is moulded down upon and around the product and sealed against the thermoformed rigid support aRIEF DESCRIPTION OF THE DRA~JING
Fig. 1 is a cross sectional view of a preferred embodiment of this invention consisting of a four ~ayered heat shrinkable barrier micro~aveable film having meta~-like apPearanCe , . . . - . . .

- 20 ~

Fig ~ is a cross sectional view of a further preferred embodiment of this inven~ion consisting of a fi~e ~ayer barrier microwaveable thermoformab~e structure having ~etal-iike appearance.
~SC~IPT~ON OF THE PREFERRED El~aODIMENTS
Referring ~o Fig 1, which is a sectional vieu o a fnur ~ayered prPferred embodiment of this ir,vention, it is seen that .his e~bodiment comprises sealant layer ~, inner layer 2, barrier Layer 3 and outer abuse layer 4. Suitable tie layer(s) S and/or S' may be present to improve adhesion when desired Prefera~ly, the sealant layer 1, of the film Com~r~ses a ~ropylene sopolymer e.g. a propylene-ethylene copolymer or propylene-ethylene-butene terpolymer wherein the monomers ratio is of from 98 2 to 90 1C as per cen~ by ~eight, an ethylene-alky~ acry~ate-ma~eic anhydride terPolymer or a VLDPE.
The inner layer Z, is preferably made of EVA wherein the monomers ratio is of from 7~:3~ to 95:S as per cent by weight, LLDPE or VLDPE
In a preferred embodiment, this inner ~ayer 2 will Compfise from about ~ 1 to about 1 5% by ~eight calculated on the ~eight ~f the overall structure (~/w) of aluminum powderr up to about G 1X ~u/u) of mica platclets and/or up to about 2X of titanium dioxide, or up to abou~ 6X by weight of titanium dioxide-coated mica platelets Typically, the th;ckness of the inner layer 2 is of from about 20% ~o about 60Z of the total thlckness nf the fiLm, and preferably from about ZS to about 40Y.
The bar~;er layer 3 is made o~ PVDC or, preferab~y of EVOH
The outer abuse layer 4, is preferably made of EVA ~herein the monomers ratio ;s of from 70 30 to 7:3 as per cenc by - - - , . . . -.

~ 21 --~ei ght .
The outer ab~se Layer 4 may also be made of a coPoLya~ide 6~12 ~caproLactam-lauro~ac~am) vh~rein the monomers ra~io i~ o~
from 4Q:60 to 70:30 as per cent by weight.
The preferred embodiment o~ Fig. 1, may fu-ther co~prise two 3dhesive layers 5 and S', other~ise kno~n a~ tie layers, pr~f~rably ~ade af modified ~YA or modifird ~LDPE type of resins rhe first tie layer S is lnterposed ~et~een the inner layer and the barri~r ld~er; ~hile the second tie layer 5' is interposed bet~een the barrier layer 3 and the outer abuse layer 4.
Advantageously, th~ ~o~al s~ructure or onlf some layer~
therecf are cr~ss-Linked ~y rad1at10n ~1~h high ~nergy elec~rons~
Referring to Fig. 2, ~his embodiment co~prises sealant Layer 6, inn~r layer 7, barrier Layer 8, another inner a~er ~, and an outer ab~se layer 1o~ Suit2ble tie layers 11, 12, 13, 14 may be presen~, if neceSs~r~ to irprove adhesion In this embodimenl, sealant layer 6 prsferably comprises E~A, LDPE or a ionGmer The inner layers 7 and 9, ~hich may be equJl or different, comprise poLyester or polystyrene resins; an aluminum powder and o~ionally ~i~a, and/or titanium dioxide, ;s added to a~
least one inner la~er 7 and 9, in the amounts indica~ed a~ove.
More prefera~ly, 1nnee lsyers 7 and 9 are eq~al and the alu~in~ po~der ar,t optionally mica, a~d~or tltaniu~ dioxite, 15 added ~o both inner layer~ 7 and 9.
The barrier layer 8 ~ilL prefera~ly comprtse EVOH
The aute- abuse ayer 'lO preferably comprises polypropy~ene, - ~ ~
- - .:

.

2 1 g 9 0 9 7 - 22 ~

pslyamide, po~ycarbonate, ionome~, or po~yester.
In the case of thermoformabLe structures, ~hich are ~n~ra~ly much thicker than the heae-shrinkable one~, ~he thickness of the co~bined inn~r layers 7 ant 9 ~ay range from about 25 ~o abous 80% of the totaL thickness.
r~is invention ~ay be further understoo~ ~y reference to the foLlo~ing specific eYamPLes~
E XA~IPL E
A fi!m havi~g the follo~ing structure uas fully coextruted, lrradiated to ~ 5 ~rad and ori~mted (stretching ratio: Z.8 in machine direction and 3.15 ir cross-direct1cn) ~Ith the ~ir ~ubble ;echnique. This film is suitabLe for ecok-in packages~
FiLm Structure - Sealing layer, thickness 13 microns approximately, prcpylene copolrmer (prop~Lene/ethylene/butene 94i4~2 as X
weight~, ~FI = S.O 9/10', d = 0 90~ g/nl ; Melting P~int -128-132C (DSC)-- Inner La~er, thickness ZZ ~icro~s approxi~atel~, EUA ~VA = 12X by ~eight~, MF2 : 2.5 ~l10', d- 0.933 g~
MeLting Point = 96C ~SC).
- rie ~ayer~ thickn~ss 4 m;cron5 aPProximateLy, modified EVA (~A = 28X by ueight~ containing e~hylenel propylene/dienx resin ~ByneL cxa 30~Z, D~P~n~
- earrier layer, thickness 4 microns, approxim~tely, EVOH (ethylene con~en~ ~ ~bous 44% by ~eight~, MFI = 5 5 9/1~', d c 1.140 gJml ; Melting Point 166C (DSC).
- Tie ~ayer, t~ickness ~ ~icrons approximateLy, ~odified ~VA (VA = 28~ by ~eight) contain~n~ eth~Len~
proprLene/diene resin.
- Outer abuse ~ayer, th;ckne55 6 micr~s appr~ximate~y, . .

, - . . . ... .. - .

21~9097 -- Z3 ~

~VA ~VA = 6.57~ by ~eight), MfI ~ 2.5 g~10', d 0.926 g~mL;
r~le~ting Point = tO3C (DSC).
The metaL-like appearanc~ ua~ ob~ained by incorpora~ing into the fi Lm for~ing compoC;t;cn of the inner layer 30X ~Jw~ of a masterbatch co~rising about 3Z ~w/~ of ~l~minum po~der in finely-divided form, less than lX of mica par~ic~es and a~out 9X ~X~) of titanium oxite ~w/w) in E~ A = 6%~ pLus mino~
a~ounes of siLicon dioxide 3nd ~isoersant ao~itives ~uch as ~a~es and fatty actds.
The amcunt of aluminu~ po~de- uas about 0.33X of the ~otal ei ght of ~he f i lm.
~XAMPL~ Z
A sec~nd fi lnl 1.12S rnanufactured as described in Example above except that the a~ount of the masterbatch added to the fi lm forming compositicn of ths irnar laysr ~as 40X Cw~w) in~ead of 3ûX.
The amaun~ of aluminum ~o~der ~as about 0.44X of the tot~l ~eight of the film.
EXAMP~E 3 A t~iro film ~as manufactured as described in Examp~e 1 abo~e except tha~ the amount of the maste-batch adted to the fi~ forming composition of the inner Layer ~as 50% (~
i nstead cf 30X.
~ he amount of a~u~inum po~der was about 0.55X of the total leight of the film.
EXA~IPLE 4 A fourth filT ~as Tanufactured as descr;bed in ~Aample 2 ab~ve except that the poLy~er of the abu~a Layer ~s a m~lon 6tlZ copoLymer containing 6a% of laurolac~am instead of E~A.
The amoUrlt of aluminum pol-der uas about 0.5ZX of the total ~eight of the ~iLm.
tOMPARATI~ ~XA~E 1 A conventional ~aminatC comprisi~g an alu~inum ~oil ~as manufactured accortimg to c~n~entional tcchni~es.

~he str~cture of the lam1nate was as fslLo~s First ~ayer, thickness 50 ~icrons aP~ro~imatel~, LLDF'~ ~d = ~.915 g/ml - MFI about 2 9/1~, Second layer, thickness Z3 microno app~simatel~, lonc~er (21nc salt) Thir~ layer, thickness 9 micr~ns approxi~ately, Aluminum ~oil;

Fo~rth L~r, thickness 15 microns approximatety, LGPE ~d - 0.~18 g~ml - MFI 5 9/1~'), Flfth layer, ~hickncss 12 microns appr~ximatel~, Polytethylene terepht~lat~ coated uith 4.4X (~/~) of a polyuretha~e primer.

C~MP~RATI~ ~XA~F'~E 2 A con~/en~ional laminate compri5ing a me~all-zed substrate ~as manufactored according to con~entional techniques.
The struc~ure of the laninate ~as as follo~s:
Firs~ ~ayer, thic~ness 70 m~cro~s appro~imate-~, LLDPF (d = ~.915 g/m~ - MFI about 2 9~1~'), second layer, th~ckness 1~ micro~S approsimatel~, ~3PE (d = 0.~18 g~mL - ~FI 5 9/1û'), Third la~er, thickness t2 ~icronS aPpro~imately, Poly(eth~lene terephthala~e~ coat~d ~ith 4.4Z ~w~w) of a poLyurethane primer; and c~ated ~nder vacu~m with a layer of aLomin~m par~ic~es.
COMPARATIvE TESTS
ALum;n~m percentage was tested ~ X-Ra~ fl~orrascence and 2149(~7 X-Ray diffraction~
Shri~k percentage ~as tes~ed according ~o A5TM D 2372 i~
~oth ~ongitudinaL t~) and transverse ~T) d1rec~ions.
Gloss ~as testet according ~o AST~ D Z457-~0.
~x~gen gas DerTeability was tested a~cording to AS~M D 3985.
Micro~aveability ~as tested lith a mic,o~ave oven BOSCH ~G
82C, po~er 720 ~, opera~ing wi~ 4 level~ ~f po~er t1~4, 2/4, 3l4, ~uL- oo~er).
The results are sho~n in ~able ~.
_ _ TA~LE I ___ I Co-llparative rest I E~am~le ~ m~Le_ _ Z 1 3 IL 1 1 l_ 2 I Z. A- ~inner layer) 1 0~9 1 1 2 i 1.5 1 1.2 1 laO I 150 1 I X Al totaL. I 0~33 1 0.4~ l Q,~ 1 0.52 1 1~.5 1 0 3 1 I X 5hrink 1 1 1 1 1 1 1 I at 85aC (L) I Z2 1 21 1 20 i23 1~0 IN0 ~ ~hri nk 3t 85aC (T) 1 33 ¦ 32 ¦ ~Q ¦3~ ¦~0 INO
0, permeabi Lity m~da~s.sqm ~ar 1 10 1 1G I 10 110 IC 5 1 5 G~oss 1 78 ,! 7~ J ?5 185 1 1û9_1 ~155 1 I X U.V. abso~ptior- 1~99 _1~99 1:~99 1>99 1 >99 1 > 99 1 Microwavsability 1 ~ES ¦ YES I YES I YES ¦ N~ ¦ NO ¦
~XAMPLE 5 A ther~oformable ft~m ~aving the struc~Jrt indicated be~oY
~a~ ful-y coextr~ded on a flat Line to an over~L thickness of abo~t Z8~ microns and then thermoformed by ~he v~cuu~ formin~
method:
- SeaLing layer~ thi~kness 15 microns approximateLy, - 26 ~

~hyLene-~in~L acetate copo~ymer (9~ vin~ zcetate units) - rie layer, thic~ne~s 8 microns appro~imate~y, ~odified eth~ene-~inyl acetate c~poL~mer - Inner layer, thic~ness 100 microns appro~imatelY, 8-emds of poL~styrenes - Tie layer, th;ckness 8 micronS approxi~ately, modified eth~lene-vinyL acetate co~olyner - 9arrier layer, th;ckness 6 microns 3ppro~imately, E~OH ~eth~lene cortent = a~out 44X ~y ~e1ght) - Tie ~a~er, thickness 8 ~icrons approximateLr, mod1fied eth~lene-vinyl acetate cGpcLymer - Inner layer, thickness 100 microns appro~imately, aLencls cf polystyrenes - Ti~ layer, thickness ~ microns approximately, modified eth~lene-viny~ acotate copol~mer - Outer abuse Layer, thickness 25 micro~s a~Proximatel~, Po~y~ cyclohe~ylene terephthala~e~
The metaL-Like ~ppearance uas ob~aine~ by i~or~orating into each of the two inner layers SX CuJu) of a nasterbatch having the same composition as in Examp~e 1.
The a~ount of aluminum pouder ~as therefore aoout ~.lX by ~eight of the ~ota~ structure ~he structure ~ho~ed eo bc fu~y ~icrc~aveabLe.
~xAMPLE 6 The sa~e fiLm as that of E~amp~e 1 ~DS manufact~red and ~he silver~ e appearance was o~tained b~ incorporating jnto the fiLm forming comPosit1on of the 1nner layer 30X ~u/~) af a ma5t~rbatch co~prising about 3X ~Ju) of al~m1num powder (partic~e size distribution: 9~Z l.eS5 than 18 micron5, SO~ less ~han 7 ~icrons~ an~ ~bou~ ,az of t;tani4~ dio~ide-coated mica 21~9097 ~ Z7 ~

~latelets (particle size: less than t5 microns~, in EVa ~VA =
6X) plu~ minor amounts of dispersa~t additives.
The a~ount of a~uminu~ P wder ~as about ~.33X by ~et~ht o~
the total ~eight of the film.
Shrink, ~arrier and aptical properties ot the ob~ained structure ~ere comparable tcl those reported in TabL~ ~ for the fiLm af sample l.
Als~, the structure sho~ed to be fulLy microuaveable.
E~AMPL~ 7 A tubular ~ilm hav~ng subYtantiall~ ~he same s~r~cturs as that describ~d in cxample 6 ~h~re, ho~ever, the sealing layer ~as made cf an ionomer inStea~ of a propylene copoLymer, the averall thickness was 80 mtcrons ano the ;hickness of the inner l~yer ~as 24 microns, Yas ~ul~y cae~truded, irradiated ~o abou~
4 MRad ant biaxiall~ oriented.
A gold-like appearance ~as obtained b~ lncorparating into the film forming co~position of the inner layer 25X t~w~ of a master~atch conprising about 6X of aluminum po~der (particle size distribution: 90X Less than 18 ~icrons, and 50% less than 7 microns~, about 4~X af titanium dio~ide-coated mica plalelets having a particle si~Q af less than 15 microns, and about 3X o~
a blend of rallow and red organic pigments in EVA tV~ = 6X~
plus rinor amount5 of silicon dioxide a~d dispersant additives.
The 3mount of aluminum ~as about 0.5~ b~ ~eight of the total ueight of the film.

' , ' . ~ ' , :

, -.

Claims

1. A microwaveable multilayer film with metal-like appearance, comprising at least a sealing layer, an inner layer, and an outer abuse layer, characterized in that it comprises from about 0.05 to about 2.5%
by weight, based on the total weight of the film, of aluminum powder in finely divided form, dispersed in at least one layer selected from the inner and the outer abuse layers.

2. A film according to claim 1, characterized in that the film further comprises a gas barrier layer.

3. A film according to claim 1, characterized in that the film comprises from about 0.1 to about 1.5% by weight of aluminum powder.

4. A film according to claim 1, characterized in that the film further comprises up to about 2% by weight, based on the total weight of the film, of mica platelets, dispersed in the same at least one layer as the aluminum powder.

5. A film according to claim 1, characterized in that the film further comprises up to about 8% by weight, based on the total weight of the film, of titanium dioxide, dispersed in the same at least one layer as the aluminum powder.

6. A film according to claim 1, characterized in that the film further comprises up to about 15% by weight, based on the total weight of the film, of titanium dioxide-coated mica platelets, dispersed in the same at least one layer as the aluminum powder.

7. A film according to claim 6, characterized in that the amount of titanium dioxide-coated mica platelets is of from 1 to 10% by weight.

8. A film according to claim 6, characterized in that the particle size of the titanium dioxide-coated mica platelets is less than 20 microns.

9. A film according to claim 6, characterized in that the film further comprises up to 2.5% by weight, based on the weight of the overall structure, of one or more organic pigments, dispersed in the same at least one layer as the aluminum powder.

10. A film according to claim 1, characterized in that said film is heat-shrinkable.

11. A film according to claim 10, characterized in that the aluminum powder is incorporated into the inner layer.

12. A film according to claim 11, characterized in that the inner layer comprises ethylene vinyl acetate copolymer.

13. A film according to claim 10 characterized in that the film is cross-linked.

14. A film according to claim 1, characterized in that said film is thermoformable.

15. A film according to claim 14, characterized in that said film is rigid.

16. A method of packaging an article comprising:
a) forming a receptacle from a microwaveable, multilayer, heat-shrinkable film with a metal-like appearance, the film comprising at least a sealing layer, an inner layer, and an outer abuse layer, and from about 0.05 to about 2.5% by weight, based on the total weight of the film, of aluminum powder in finely divided form, dispersed in at least one layer selected from the inner and the outer abuse layers, the receptacle having open ends;
b) introducing said article into said receptacle;
c) closing the open ends of said receptacle; and d) shrinking the package.

17. The method of claim 16 wherein, between steps b) and c), the receptacle is vacuumized.

18. A method of packaging an article comprising:
a) thermoforming a microwaveable, multilayer thermoformable film with a metal-like appearance to form a cavity, the film comprising at least a sealing layer, an inner layer, and an outer abuse layer, and from about 0.05 to about 2.5% by weight, based on the total weight of the film, of aluminum powder in finely divided form, dispersed in at least one layer selected from the inner and the outer abuse layers;
b) placing the article in the cavity;
c) disposing a web over the article; and d) closing the package.

19. The method of claim 18 wherein a substantially non-forming web is disposed over the cavity, and the package is sealed.

20. The method of claim 18 wherein a forming web is moulded down upon and around the article and sealed against the cavity.