CA2148072A1

CA2148072A1 - Multilayer polyolefin film containing recycle polymer for irradiated films

Info

Publication number: CA2148072A1
Application number: CA 2148072
Authority: CA
Inventors: Livio Buongiorno; Paolo Ciocca
Original assignee: Livio Buongiorno; Paolo Ciocca; W.R. Grace & Co.-Conn.; Cryovac, Inc.
Current assignee: Cryovac LLC
Priority date: 1994-04-28
Filing date: 1995-04-27
Publication date: 1995-10-29
Also published as: JPH0852781A; NZ270984A; US5928798A; BR9501861A; AU688863B2; US5605660A; AU1774495A; EP0679487A1

Abstract

A process for the manufacture of a multilayer cross-linked, heat-shrinkable, polyolefin film, said film having at least one inner layer comprising thermo-plastic polymer sandwiched between two outer layers comprised of thermoplastic polymer different from the thermoplastic polymer of said inner layer, comprising the steps of a) coextruding the materials into a tape;
b) cross-linking it;
c) converting said cross-linked tape into a heat-shrinkable film by orientation;
characterized in that scrap material produced in the manufacture or in the further processing to finished articles of cross-linked films of this same structure is incorporated by recycling it into said step a) in an amount up to 50% by weight of the total film weight.

Description

" 2l~8o72 ~ULTI-~AY~R POLYOLEFI~ FILM CONTAINING RECYCLE POLYMER
FROM CROSS-T.TNR~n FILMS

Field of the invention The present invention relates to a process of ma-nufacturing heat shrinkable films particularly to the recycling of film scraps in the manufacture of said films.
Background of the invention The manufacture of heat-shrinkable films is well known in the art.
As heat-shrinkable film, the expert in the field means a polymeric film which has the ability to shrink or, if restrained from shrinking, to generate shrink - tension within the film.
Heat-shrinkable films are well known in the art and their main field of application is package of food and non-food goods.
The term "film" identifies a flexible thermoplastic sheet with a typical thickness of from about 10 microns to about 150 micr~ns and preferably of from about 12 to about 100 microns. When a packaging film to be used as such in a packaging machine is meant, it will typically have a thickness of from about 10 to about 50 microns and preferably of from about 12 to about 35 microns, while when the film has first to be heat-sealed to itself, converted into a flexible thermoplastic container and then used in a packaging machine in the form of a bag or a pouch where the good to be packaged is introduced, it will have typically a ~hickness of from about 50 to about 150 microns and ~ , .
: ` t ::. ~ 2l~8o72 .! 2 preferably of from about 50 to about lOO microns.
Heat-shrinkable films typically have a multi-laye-red structure comprising olefinic polymers and/or co-polymers of various kind, and the terms "polymer" or "polymeric resin", as herein used, generally include homopolymers, copolymers, terpolymers, block polymers, graft polymer, random polymers and alternate polymers.
The manufacture of the above films may generally be accomplished by extrusion (for single layer films) or coextrusion (for multi-layer films) of thermoplastic resinous materials which have been heated to their flow or melting point from one extrusion or coextrusion die in, for example, either tubular or planar (sheet) form.
After a post-extrusion quenching to cool by well known systems the relatively thick extrudate is then reheated to a temperature within its orientation temperature range, generally below the crystalline melting point but above the second order transition temperature (glass transition point).
The terms "orientation" or "oriented" are used he-rein to generally describe the process step and resul-tant product characteristics obtainéd by stretching and immediately cooling a resinous thermoplastic polymeric material, which has been heated to an orientation tem-perature range so as to revise the molecular configura-tion of the material by physical alignment of the cry-stallites and/or molecules of the material in order to modify certain mechanical properties to the desired properties, for example shrink tension and orientation release stress.
The term "oriented" is also used herein inter-.. , ... . .. .. . , .. . . . .. ._ .

-~ 2148~72 . ~

changeably with the term "heat-shrinkable". An oriented (i.e. heat-shrinkable) material will tend to return to its unstretched (unextended) dimension when heated to an appropriate elevated temperature.
In the basic process for manufacturing the film as above, the film, once extruded (or coextruded, whenever the case) and initially cooled by, for example, cascade water or chill roll quenching, is then reheated to within its orientation temperature range and oriented by stretching. When the stretching force is applied in one direction, uniaxial orientation results. When the stretching force is applied in two directions, biaxial orientation results. The stretching to orient may be accomplished in many ways such as for example by "blown bubble" techniques or "tenter framing". These processes _ . .
- are well-known to those skilled in the æ t and refer to orientation procedures whereby the material is stret-ched in the cross or transverse direction (TD) and/or in the longitudinal or machine direction (MD). After being stretched, the film is rapidly cooled while substantially retaining its stretched dimension and thus set or lock-in the oriented (aligned) molecular configuration.
After setting the stretch-oriented molecular con-figuration, the film may then be stored in rolls andutilized to tightly package a wide variety of items.
The a~ove general outline of manufacturing of films is not meant to be all inclusive, since such pro-cesses are well-known to the expert in the art. Exam-ples of these processes are disclosed in Italian patentn. 1163118 and US patent n. 4551380, both in the name ` `' 2148~72 .
.

of the applicant; said patents also refers to a number of documents relating to the prior art, for example US
Pat. Nos. 4,274,900; 4,229,241; 4,194,039; 4,188,443;
4,048,428; 3,821,182; 3,022,543.
Furthemore, when certain characteristics of the film are to be improved, the polymeric structure may be modified in a well-known way. In particular cases, cross-linking of the polymeric structure can be perfor-med, for example by irradiation or chemically. A gene-ral disclosure of cross-linking can be found, among others, in US patent n. 4,551,380, assigned to the ap-plicant, issued November 5, 1985.
Cross-linked multi-layered heat shrinkable films are there disclosed and claimed.
Generally, a considerable amount of scrap is gene-rated in the course of the manufacture of heat-shrinka-ble films, such scraps coming from trimming from roll ends, film breakages, filling custom orders requesting special width, or rolls out of specification. In the tenter frame biaxial orientation step, considerable scraps come also from trimming the film edges in the transversal dlrection.
Such amount of scraps represents an economical burden and a heavy environmental problem due to the wa-ste of plastic material.
A method of recycling coextruded scraps is di-sclosed in US patent n. 4,877,682, assigned to Amoco Corporation, issued October 31, 1989. This patent di-scloses laminates containing scraps and further disclo-ses articles of manufacture, particularly cookware. Thepatent relates to thermoplastic materials, which must 21~72 have particular characteristics as to stiffness and heat-resistance. Among the many exemplary layer mate-rials, polyolefins are cited, particularly crystalline polypropylene, crystalline polyethylene of low, medium, preferably high density. Crystalline polypropylene is said to be particularly preferred because of its high use temperature. The laminates herein disclosed must be capable of resisting deformation or deflection at cooking temperature. Therefore the background of this patent is distant from the one of the present invention which relates to heat-shrinkable films for pac~aging use.
The International Application WO 91/17886, in the name o E. I. Dupont De Nemours, published 28 November 1991, discloses a multi-layer heat-shrinkable polymeric film containing recycle polymer.
This document claims a process of coextruding a multi-layer heat-shrinkable film having at least a core layer of thermoplastic polymer sandwiched between two outer layers and coextruding recycle of said film into said core along with said thermoplastic polymer of said core. On p. 2, 1. 30, of WO 91/178~6 it is clearly sta-ted that radiation involved in making particular heat-shrinkable films prevents scrap from the film from being recycled by melt processing, e.g. extrusion. This teaching is repeated on p. 8, 1. 22, as the scrap must be melt processable, hence the original heat shrinkable film from which the scrap was obtained must be free of crosslinking, such as from radiation, which would pre-vent melt processing.

.. ~
:j 6 Definitions In the present description, unless specificallyset forth and defined or otherwise limited, the terms "polymer" or "polymer resin" generally include, but are not limited to, homopolymers, copolymers, such as, for example, block, graft, random and alternating copoly-mers, terpolymers etc. and blends and modifications thereof. Furthermore, unless otherwise specifically li-mited, the terms "polymer" or "polymer resin" shall in-clude all possible symmetrical structure of the mate-rial. These structures includes, but are not limited to, isotactic, syndiotactic and random symmetries.
The terms "melt flow" as used herein is the amount, in grams, of a thermoplastic resin which can be forced through a given orifice under a specified pres-sure and temperature within ten minutes, pursuant to ASTM D 1238-79. The term "melt flow index" as used he-rein is the amount, in grams, of a thermoplastic resin which can be forced through a given orifice under a specified pressure and temperature within ten minutes, pursuant to condition E of AST~ D 1238-79.
The terms "outer" or "outer layer" or "skin" or "skin layer" as used herein means a layer of a multi-layer film which comprises surface thereof .
The term "inner" or "inner layer" as used herein refers to a layer of a multi-layer film which is not a skin or outer layer of the film.
The term "core" or "core layer" as used herein re-fers to an inner layer of a multi-layer film having an odd number of layers wherein the same number of layers is present on either side of the core layer.

, ~ 2l48o72 The term "intermediate" or "intermediate layer" as used herein refers to an inner layer of a multi-layer film which is positioned between a core layer and an outer layer of said film.
The term "palindromic" film as used herein refers to a multi-layer film, the layer of which is substan-tially symmetrical. Examples of palindromic films would be film having the following layer configurations A/B/A, or A/B/B/A or A/B/C/B/A, etc. An example of a non-palindromic film is a A/B/C/A.
As used herein and unless otherwise spe~ifically indicated, the term "cross-linking" refers to either irradiating the extruded film as described in the de-tailed description of the invention or suitably additi-vating the polymers to be extruded so that the desired degree of cross-linking is achieved in the extruded film.
As used herein the term "polyolefin" refers to thermoplastic polymers obtained by polymerization or copolymerization of re?atively simple (C2-C12) olefins which may contain other comonomers wherein the olefin units are however present in higher amounts with re-spect to the other comonomers; including, but not limi-ted to, homopolymers, copolymers, terpolymers blends and modifications of such relatively simple olefins.
Are specifically included therein homopolymers such as polyethylene and polypropylene, copolymers such as propylene copolymers, ethylene-alpha-olefin copoly-mers, ethylene-vinyl-acetate copolymers, and ethylene-acrylate or ethylene-metacrylate copolymers.
The term "polyethylene" as used herein refers to a ~ . 21~8072 family of resins obtained by polymerizing the gas ethy-lene, C2H4. By varying the catalysts and methods of polymerization, properties such as density, melt index, crystallinity, degree of branching and molecular weight distribution can be regulated over wide ranges.
Polyethylenes having densities below about 0.925 g/cm3 are called low density polyethylenes (LDPE), those having densities ranging from about 0.926 g/cm3 to about 0.940 g/cm3 are called medium density polyethylene (MDPE) and those having densities ranging from about 0.941 g/cm3 to about 0.965 g/cm3~and over are called high density polyethylenes (HDPE).
The molecular structure of con~entional LDPE is highly branched. While conventional MDPE possess a mo-- 15 lecular structure which is branched, the degree of branching is less than that of conventional LDPE. The molecular structure of HDPE possesses little or no side branching.
The term "polypropylene" refers to a thermoplastic resin obtained by homopolymerizing propylene units ac-cording to known processes. The term "propylene copoly-mers" refers to a propylene copolymer with ethylene and/or butene-l wherein the propylene units are present in a higher amount than the ethylene and/or butene-l units. The term "ethylene-alpha-olefin copolymer" re-fers to a copolymer of ethylene with one or more (C4-C12)alpha-olefin preferably selected from the group comprising the linear copolymers or terpolymers of ethylene with l-butene, 4-methyl-1-pentene, l-hexene, and l-octene. In particular, as used, herein linear low density polyethylene (LLDPE) has a density usually in .

21~8~2 g the range of from about 0.915 gtcm3 to about 0.925 g/cm3; linear medium density polyethylene (LMDPE), as defined herein, has a density usually in the range of from about 0.926 g/cm3 to about 0.941 g/cm3; while very low density polyethylene, (VLDPE), as used herein, has a density lower than 0.915. The melt flow index of li-near low, medium and very low density polyethylenes ge-nerally ranges from between about 0.1 to about 10 grams for ten minutes, preferably from about 0.5 to about 3.0 grams for ten minutes. Linear low, medium and very low density polyethylene resins of this type arP commer-cially available or can be manufactured by known methods.
Said terms also include the so-called metallocene (or single-site or constraint-geometry) linear ' polyethylenes having a density within the above indica-ted ranges.
The term "ethylene vinyl acetate copolymer" (EVA) as used herein refers to a copolymer formed from ethy-lene and vinyl acetate monomers wherein the ethylenederived units in the copolymer are present in major amounts and the vinyl acetate derived units in the co-polymer are present in minor amounts.
As used herein, the term "ethylene-acrylate or ethylene-methacrylate copolymer" refers to the product obtained by copolymerization of ethylene with acrylate monomers of formula XO -- ~ -- C = CH2 wherein R is hydrogen or a methyl group 21~8072 and X is hydrogen, (Cl-C4)alkyl or a metal cation, preferably selected from Na+ and Zn++, wherein the ethylene units are present in a higher amount than the acrylate units.
All compositional percentages used herein are cal-culated on a "by weight" basis.
Density should be measured at 23C and in accor-dance with ASTM D 1505-68 (reapproved 1979).
Free shrink should be measured in accordance with ASTM D 2732.
Shrink tension and orientation release stress - should be measured in accordance with ASTM D 2838-81.
The tensile properties of the film should be mea-sured in accordance with ASTM D 882-81.
The elongation properties of the film should be measured in accordance with ASTM D 638.
The haze and luminous transmittance of the film should be measured in accordance with ASTM D 1003-61 (reapproved 1971).
The specular gloss of the film should be measured in accordance with ASTM D 2457-70 (reapproved 1977).
The tear propagation of the film should be measu-red in accordance with ASTM D 1938-67 (reapproved 1978).
The impact resistance of the film should be measu-red in accordance with ASTM D 3420-80. --One method of determining whether a material is "cross-linked" is to reflux the material in boiling to-luene or xylene, as appropriate, for forty (40) hours.
If a weight percent residue of at least 5 percent re-mains, then the material is deemed to bevcross-linked.

` 2148072 , ---, 11 A procedure for determining whether a material is cross-linked is to reflux 0.4 g of the material in boi-ling toluene or another appropriate solvent, for exam-ple xylene, for twenty (20) hours. If no insoluble (gel) remains, the material may not be cross-linked.
However, this should be confirmed by the "melt-flow"
procedure below. If, after twenty (20) hours of re-fluxing insoluble residue (gel) remains the material is refluxed under the same conditions for another twenty (20) hours. If more than 5 weight percent remains upon conclusion of the second refluxing the material is con-sidered to be cross-linked. Preferably at least two re-plicates are utilized.
Another method whereby cross-linking and the de-gree of cross-linking can be determined is by ASTM D
~ 2765-68 (Reapproved 1978). Yet another method for de-termining whether a material is cross-linked is to de-termine the melt-flow of the material in accordance with ASTM D 1238-79 at 230C and while utilizing a 21,600 gram load. Materials having a melt flow of grea-ter than 75 grams for ten minutes are deemed non-cross-linked. This method should be utilized to confirm the "gel" method described above whenever the remaining in-soluble residue (gel content) is less than 5% by wei-ght, since some cross-linked materials will evidence a residual gel content of less than 5 weight percent. If the cross-linking is accomplished by irradiation of the film the amount of ionizing radiation which has been absorbed by a known film material can be calculated by comparing the weight percent of insoluble material (gel) remaining after refluxing the sample to the wei-.
, .~ _ . . . . . . . _ 21~8072 ght percent of gel remaining after refluxing standards of the same material which have been irradiated to dif-ferent known degrees. The experts in the field also re-cognize that a correlation exists between the amount of ionizing irradiation absorbed and the melt flow of ma-terial. Accordingly, the amount of ionizing irradiation which a material has absorbed may be determined by com-paring the melt flow of the material to the melt flow of the samples of the same material which have been ir-radiated to different known degrees.
The term "gauge" is a unit of measure applied tothe thickness of film or the layers thereof. 100 gauge is equal to 1 ml, which is one thousandth of an inch (1 inch = 2.54 cm).
A rad is the quantity of ionizing radiation that results in the absorption of 100 ergs of energy per gram of a radiated material, regardless of the source of the radiation (1 rad = 10 2 Gy). A megarad is 106 rads (MRad is the abbreviation for megarad).
Summary of the invention It has now been found a process for the manufac-ture of multi-layered heat-shrinkable cross-linked polyolefin films containing recycle scraps of the same film.
Particularly it has been found that, by recycling scraps of cross-linked multilayer heat-shrinkable polyolefin films in an inner layer of the same film, ~a film is obtained which has physical properties and packaging performances almost comparable to those of the virgin film.
In a general embodiment, the process of the pre-~ 21~8072 sent invention comprises the steps of:
a) coextruding a multilayer polyolefin film in the form of a "tape";
b) cross-linking it; and c) orienting said irradiated tape into a heat-shrinkable film, characterized in that scrap mate-rial produced in the manufacture or in the further processing to finished articles of cross-linked films of this same structure is recycled into said step a).
Objects of the present invention Accordingly, it is a general object of the present invention to provide a process for the manufacture of cross-linked heat-shrinkable polyolefin films compri-sing the recycling of scraps of said cross-linked film.
Another object of the present invention is to pro-vide a cross-linked heat-shrinkable polyolefin film suitable for packaging food and non-food goods.
A further object of the present invention is to provide packaging material, for example bags, pouches, comprising a film obtained according to the process he-rein disclosed.
The process according to the present invention provides several advantages when compared to the pro-cesses of prior art. Firstly, the present invention al-lows to recycle scraps of cross-linked films, which recycling was taught to be impossible by prior art.
Another advantage is in that the so obtained film has constant qualitative characteristics, comparable to the virgin film.
Both on-line and off-line recycling tecniques may .

21~8~7~

be used in the process according to the present inven-tion.
Detailed description of the invention The present invention relates to a process of ma-nufacturing heat-shrinkable multi-layer cross-linked polyolefin films characterized in that one or more of the inner layers of said films contain recycle cross-linked polyolefin scraps.
The process of the present invention is a conven-tional process of manufacturing heat-shrinkable multi-layered polyolefin films, as disclosed in the ~above ci-ted prior art.
Every method of recycling scraps available in the art is suitable for the process of the invention.
According to the invention, the multilayered film - is composed of at least three layers comprising one core layer sandwiched between two outer layers. The film can be a palindromic film, with the two outer layers one equal to the other, or can be asymmetric with the two outer layers different one from the other.
When a number of layers of more than three layers is pro~ided in the film, the core layer is herein in-tended as the central core of the multi-layered struc-ture.
In a typical embodiment of the present invention the process begins by blending, if and as necessary, the raw materials (i.e. the polymeric resins) in the proportions and ranges according to the desired film.
The resins are usually purchased from a supplier in pellet form and can be blended in anyone of a number of commercially available blenders as is well known in the 214807~

art. During the blending process any conventional addi-tives and/or agents which are desired to be utilized are also incorporated. The additives may be incor-porated by utilizing a masterbatch containing small percentages of the additives.
Additives which can conventionally be used include anti-fog, antioxidant, antistatic, slip and anti-block agents, thermal stabilizers, U.V. stabilizers, organic and inorganic pigments, and the like agents. Preferred anti-block agents are diatomaceous silica (SiO2, which is available for example from Mc Cullogh Benton, Inc.) and synthetica silica such as those manufactured and marketed by W.R. Grace Davison Division under the trade name Syloid or Sylobloc. A preferred slip agent is eru-camide (available from Humko Chemical). Other slipagen~s such as steraramide (available from ~umko Chemi-cal), behenamide N,N'-diolleylethylenediamine (available from Glyco Chemical) may be utilized. A preferred an-tioxidant and thermal stabilizing agent is tetrakis tmethYlene 3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propio-nate~methane (available from Ciba-Geigy). Suitable an-tifo~ agents are polyoxyethylene sorbitan esters, gly-cerol fatty acid esters, and polyoxyethylene alkyl esters such as those commercially available under the trade names Atmer. Preferred antistatic agents are polyoxyethylene amines (such as Atmer 163) or polyoxyethylene fatty alchols (e.g. Atmer 178).
The resins and applicable additives and/or agents are then fed to the hoppers of extruders which feed a coextrusion die. Depending on the structural architec-ture of the multi-layer film, the number of extruders 21~8~72 will be determined by the expert in the field. When ex-truding through a round die, the materials are coextru-ded as a relatively thick tube or "tape" which has an initial diameter and thickness dependent upon the dia-meter and die gap of the coextrusion die. If desired, aine mist of a silicone or anti-fog spray may be appli-cated to the interior of the freshly extruded tubolar material to further improve processability of the tubu-lar material, as disclosed, for example in E~-A-0071349. The final diameter and thickness of the tubu-lar film is dependent upon the racking ratio, i.e. the stretching ratio. As an alternative to tubular coextru-sion, slot dies, could be used to coextrude the mate-rial in sheet (or tape) form. Well-known single or multi-layer extrusion coating processes could also be utilized, if desired. Exemplary of this method is US
pat. N. 3,741,253.
When cross-linking is achieved chemically a suita-ble amount of cross-linking agents (e.g. peroxides~ is added to the polymers to be extruded and no specific additional step is required.
When, according to a preferr~`d embodiment of the invention, cross-linking is achieved by irradiation, said step is carried out after extrusion by bomb æ ding the film in its "tape" or unexpanded tubing or sheet form with high-energy electrons from an accelerator.
Irradiation may be accomplished by the use of high-energy radiation using electrons, which is the prefer-red radiation, but X-rays, gamma rays, beta rays, etc.
can also be used. The electron irradiation source can be a Van der Graaf electron accelerator, e.g. one ope-. . ; , -- - . . .

rated, for example at about 2,000,000 volts, with a power output of about 500 watts. Alterna~ively, there can be employed other sources of high energy electrons such as the General Electric 2,000,000 volt resonant transformer or the corresponding 1,000,000 volt, 4 ki-lowatt, resonant transformer. The voltage can be adju-sted to appropriate levels which may be, for example, 1,000,000 or 2,000,000 or 3,000,000 or 6,000,000 or hi-gher or lower. Other apparatus for irradiating films are known to those expert in the field. The irradiation is usually carried out at between 1 megarad and 12 me-garad. Preferably irradiation is carried out at between about 1 and about 6 MRad. Most preferably between about 1 and about 4 MRad. Irradiation can conveniently be - 15 carried out at room temperature, although higher and lower temperatures, as for example, from 0C to 60C
may be employed.
In the next step, the film is reheated to its orientation temperature range and oriented with a well-known orienting technique. For example, the heated filmis inflated, by application of internal air pressure, into a bubble thereby transforming the narrow tape with thick walls into a wide film with thin walls of the de-sired film thickness and width. This process is someti-mes referred as "trapped bubble technique" or"rac~ing". The degree of inflation and subsequent stretching is often referred to as the "racking ratio"
or "stretching ratio". After stretching, the tubular film is then collapsed into a superimposed lay-flat configuration and wound into rolls often referred to as "mill rolls".

Films scraps, which, as seen before, may be gene-rated at different stages of the overall process, are gathered, suitably comminuted and recycled. Film scrap can be recycled in any and in more than one of the in-ner layers of the original film structure or innerlayer(s) of recycle film can be newly formed in the recycle containing film by dedicating one or more ex-truders to melt process the recycle scrap and coextrude the recycle layer(s) along with the coextrusion of the original multilayer structure.
The amount of film scrap in the recycle~ layerts) may range from 5 to 100% by weight of the layer(s) to-tal weight.
The proportion of the scrap multilayer cross-linked film which may globally be incorporated into the :- inner layer(s) is however up to about 50% by weight over the film total weight.
In case of a three layer original structure, in one preferred embodiment, scrap is recycled into the 2Q core layer, blended with virgin core polymer in amounts generally up to 75Z of the core overall weight, prefe-rably up to 50% and more preferably up to 35%.
In an alterantive preferred embodiment two inter-mediate layers, between the core and the outer layers are formed entirely of recycle scrap by dedicating one or two additional extruders to the melt processing of said recycle scrap and giving rise to an increase in the overall number of layers from 3 of the virgin structure to 5 in the recycle-containing one.
In this case the core layer may also contain part of cross-linked film scrap blended with virgin polymer.

21~8072 In still another alternative embodiment, in the recycle-containing structure the core layer can be splitted into two layers and in between a new layer en-tirely composed of recycle scrap can be coextruded.
5Also in this case recycle scrap can also be added in the other inner layers blended with virgin polymer.
Analogously, in the case of films containing more than three layers, film scrap may be recycled in one or more inner layers, in percent by weight of from 5 to 10100% of the weight of the layer(s~ and/or additional layer(s) of film scrap can be formed up to a m~x;ml~m total recycle of about 50% of the film weight.
Preferably, in the case of a five layer film structure, the film scrap will be recycled in the core 15and/or in the two intermediate layers in a balanced amount. For recycling, scraps are either pre-blended with the virgin material of the inner layer(s) or di-rectly added into the selected extruders.
The scrap material which may be added up to a ma-20ximum amount of 50% w/w of the total structure, is pre-ferably added up to 35% and more preferably up to 25%
of the total structure.
The process of the present invention is generally applicable to multi-layers heat-shrinkable cross-linked 25polyolefin films.
Examples of said films may be found in EP-A-0 561 428, published 22.09.93, United States patent n.
4,551,380, published November 5, 1985, all in the name of the applicant; United States patent n. 4,865,902 as-30signed to E.I. Du Pont de Nemours and Company. In the above films the outer layers are main~y composed of low 21~8072 density polyethylene, medium density polyethylene, high density polyethylene, linear low density polyethylene, linear medium density polyethylene, very low density polyethylene, ethylenevinyl acetate copolymers or of 5blends thereof.
Description of the preferred embodiments.
According to the process of the present invention, a heat-shrinkable film was manufactured recycling scraps of the same film in the core of the manufactured film.
Particularly, the process of the present invention is applied to an oriented, heat-sealable, cross-linked, multi-layer film comprising:
a core layer, consisting essentially of a LLDPE;
15and two outer layers each comprising a three component blend of (1) a LLDPE, (2) a LMDPE, (3) an EVA copoly-mer.
This multi-layer film is disclosed in US patent n.
4~S51J38O~ issued November 5, 1985 and assigned to the 20applicant.
A more preferred embodiment is represented by em-bodiments I, II and III, disclosed in the above US
4,551,380; embodiment II being the most preferred he-reln.
25A standard ~ilm (Film A) was prepared according to embodiment II of the disclosure of US patent n.
4,551,880. Said film was irradiated at an average MRad of about 2.0 i 0.5 MR.
Estrusions were~carried out to incorporate recy-30cled Film A scraps in the standard structure. The scraps were pelletized and blended off-line with the 21~8~72 virgin core polymer.
Accordingly, four films containing scraps were prepared: the first containing 10X of recycled scraps in the core (referred to as Film B); the second con-taining 5X of recycled scraps in the core (referred toas Film C) the third containing 10% of recycled scraps in the skin (referred to as comparative Film D); the fourth containing 5% of recycled scraps in the skin (referred to as comparative Film E). Each of the four films was prepared with a thickness of 15 and 19 ~um, respectively.
The four films were examined as to their optical properties in comparison with standard film A
(hereinafter abbreviated as STD).
- 15 The results are shown in the following Table 1.

214~07~

:~: ~ o ~ . ~
m W

H
o U

H ~c.v ~ ~` O
o C.) O U
~O U
Il _ ~rl W q~
~ ~¢ UI~ Ul U~ ~ U I ~

21~07~
. --As shown in the above table, only Film B and Film C, namely the films containing recycled scraps in their core layer, have good optical properties, suitable for use in packaging for display purposes.
An evaluation of the shrink quality of the films was performed. The evaluation was carried out on packs made with a Gramegna semiauto L-sealer. The packs were shrunk in a Sitma tunnel at different temperatures. The samples were compared to STD which showed a good shrink quality at 180C.
The following tests were carried out only on Film B and Film C.
A physical characterization was carried out. Ta-bles 2 and 3 report the qualitative results.

Physical evaluation Film BlFilm C (15 micron) vs STD
Modulus: Both are similar and higher than STD.
Tensile strength: Similar to STD.
Elon~ation: Higher than STD.
Tear properties: Tear propagation and initiation resi-stance are higher than STD.
Kinetic coefficient of friction: Lower for film to film conditions and (Dynamic) equivalent for film to metal conditions.
Trim seal strength: STD stress conditions: similar to STD. High stress conditions:
higher than STD.

~1~8~72 FILM B/FILM C (19 micron) vs STD
Modulus: Similar to STD.
Tensile strength: Similar for L direction and sli-ghtly lower for T direction than STD.
Elongation: Slightly lower than STD.
Tear properties: Tear propagation is quite similar to STD.
Tear initiation is lower in both directions for Film B. Film C is equivalent in TD and slightly lower in LD.
Free shrink: No significant difference.
Shrink tension: LD: higher than STD;
TD: slightly higher for Film C.
Optics: Haze and gloss are similar to STD
Tack: No tack was detected for all the structures.
Kinetic coefficient of friction: Both film to film and film to me-(Dynamic) tal conditions are similar to STD
Trim seal strength: Considering STD and high stress conditions, the results are hi-gher than STD.
The above results show that the physical proper-ties of the films obtained according to the present in-vention have physical properties comparable to STD.
The sealability was evaluated on a Pulsar hot bar sealer at the following conditions:

214807~
. 25 sealing time 0.5 sec sealing pressure 2.0 bar set 1.5 bar actual Results are summarized in the following Table 4 FILM CODE SEAL BEHAVIOUR
( C) STICK SEAL MELT

Film B 15/~m 115 120 150 Film B l9/~m 120 125 175 - Film C 15/ym 115 120 150 Film C l9/~m 120 125 175 The heat seal range for MR 15 and 19 micron is 125-165C.
The shrink range was evaluated using cardboard boxes packed on a Gramegna semiauto L-sealer.
The packs were then shrunk in a Sitma tunnel at different temperatures.
The samples were compared with ST~.
Film Code Shrink Range (C) Burnt Through (C) Film B 15lym150-200 210 Film B l9/ym150-210 220 Film C 15/ym150-200 210 Film C l9/~m150-210 220 STD 15/~m 140-200 210 STD l9/~m 150-210 220 The results show no significant difference among 214807~

the formulations evaluated, the shrink range is wider for 19 micron films (60C vs 50C).
The packaging appearance was evaluated on the sam-ples packed as described above.
The samples were compared to STD which showed "good" shrink qualities.
At 180C, no difference was noticed between the experimental formulations and STD.
As to optical properties after shrink, STD perfor-med slightly better than Film B and Film C, which ap-peared to be less glossy.
The samples tested performed similarly to STD, with respect to the trim sealing properties, heat seal range and shrink range.
From the above results, it can be seen that the process of the present invention allows to obtain heat shrinkable irradiated films containing recycle scrap of the same film. The film obtainable from the process he-rein disclosed has physical and packaging characteri-stics which make it comparable to standard films.
Therefore, packaging materials comprising a film obtainable by the process herein disclosed are within the frame of the present invention.
It should be understood that the detailed de-scription and specific examples which indicate the pre-sently preferred embodiments of the invention are given by way of illustration only, since various changes and modifications within the spirit and scope of the inven-tion will become apparent to those of ordinary skill in the art upon review of the above detailed description and examples.

Claims

CLAIMS for the Contracting States: AT, BE, CH, LI, DE, DK, ES, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE.

1. A process for the manufacture of a multilayer cross-linked, heat-shrinkable, polyolefin film, said film having at least one inner layer comprising thermo-plastic polymer sandwiched between two outer layers comprised of thermoplastic polymer different from the thermoplastic polymer of said inner layer, comprising the steps of a) coextruding the materials into a tape;
b) cross-linking it;
c) converting said cross-linked tape into a heat-shrinkable film by orientation;
characterized in that scrap material produced in the manufacture or in the further processing to fini-shed articles of cross-linked films of this same structure is incorporated by recycling it into said step a) in an amount up to 50% by weight of the total film weight.

2. A process according to claim 1, characterized in that said film scraps are incorporated into the inner layer(s).

3. A process according to claims 1-2, characterized in that said film scraps are recycled in an amount up to 35% by weight of the film structure.

4. A process according to claims 1-3, characterized in that said film scraps are recycled in an amount up to 25% by weight of the film structure.

5. A process according to claims 1-3, characterized in that said film scraps are recycled in an amount up to about 10% by weight of the film structure.

6. A process according to claims 1-5, characterized in that the cross-linking step b) is carried out by ir-radiation at between 1 megarad and 12 megarad.

7. A process according to claims 1-6, characterized in that the outer layers of the coextruded cross-linked film are essentially composed of LDPE, MDPE, HDPE, LL-DPE, LMDPE, VLDPE, EVA or of blends thereof.

8. A process according to claims 1-7, characterized in that the coextruded cross-linked film has the fol-lowing structure:
a core layer, consisting essentially of a LLDPE and two surface layers each comprising a three component blend of (1) a linear low-density polyethylene, (2) a linear medium density polyethylene and (3) an ethylene vinyl acetate copolymer.

9. A process according to claim 8, characterized in that said film has a three layer structure comprising:
a first surface layer essentially consisting of about 50% by weight of linear low density polyethylene having a density of about 0.920 g/cm3; about 25% by weight of linear medium density polyethylene having a density of about 0.935 g/cm3; about 25% by weigth of ethylene vinyl acetate copolymer having from about 3.3 to about 4.1% vinyl acetate derived units and a density of from about 0.9232 to about 0.9250 g/cm3;
a core layer essentially consisting of 100% by weight of linear low density polyethylene having a density of about 0.920 g/cm3;
a second surface layer essentially consisting of about 50% by weight of linear low density polyethylene having a density of about 0.920 g/cm3; about 25% by weight of linear medium density polyethylene having a density of about 0.935 g/cm3; about 25% by weigth of ethylene vinyl acetate copolymer having from about 3.3 to about 4.1% vinyl acetate derived units and a density of from about 0.9232 to about 0.9250 g/cm3.

10. A process according to claims 1-9, characterized in that conventional additives and/or agents are incor-porated into the thermoplastic polymer materials to be coextruded in step a).

11. A multilayer, cross-linked, heat-shrinkable film obtainable by the process of claims 1-10.

12. A packaging material comprising a film according to claim 11.