CA2012538C - Packaging film - Google Patents
Packaging filmInfo
- Publication number
- CA2012538C CA2012538C CA002012538A CA2012538A CA2012538C CA 2012538 C CA2012538 C CA 2012538C CA 002012538 A CA002012538 A CA 002012538A CA 2012538 A CA2012538 A CA 2012538A CA 2012538 C CA2012538 C CA 2012538C
- Authority
- CA
- Canada
- Prior art keywords
- layer
- film
- film according
- copolymer
- melt index
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/06—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material
- B32B27/08—Layered products comprising a layer of synthetic resin as the main or only constituent of a layer, which is next to another layer of the same or of a different material of synthetic resin
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B27/00—Layered products comprising a layer of synthetic resin
- B32B27/30—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers
- B32B27/304—Layered products comprising a layer of synthetic resin comprising vinyl (co)polymers; comprising acrylic (co)polymers comprising vinyl halide (co)polymers, e.g. PVC, PVDC, PVF, PVDF
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2323/00—Polyalkenes
- B32B2323/04—Polyethylene
- B32B2323/046—LDPE, i.e. low density polyethylene
Abstract
A multi-layer film useful in food packaging comprising a first core layer comprising VLDPE or LLDPE;
optionally a second core layer comprising VLDPE or LLDPE; two outer layers each comprising an ionomer; and further core layers between the first core layer and the outer layer and between the second core layer and the outer layer the further core layers comprising an olefin polymer or copolymer. The film may also include an oxygen barrier layer and may be oriented to provide a heat shrinkable film.
optionally a second core layer comprising VLDPE or LLDPE; two outer layers each comprising an ionomer; and further core layers between the first core layer and the outer layer and between the second core layer and the outer layer the further core layers comprising an olefin polymer or copolymer. The film may also include an oxygen barrier layer and may be oriented to provide a heat shrinkable film.
Description
r ~~~.~5~~
-.1-PACxAGZN
This invention relates to a packaging film and more particularly to a film useful in the packaging of food products, especiall}~ frozen meat.
Thermoplastic film, and especially films of polyolefin materials, have been used in the past to package various articles including perishable food products which require protection from the environment. The films should possess resistance to physical and environmental abuse during storage and distribution and should present an aesthetic and attractive appearance. Optical qualities such as high gloss, high clarity and low haze contribute to the aesthetic consumer appeal of products wrapped in such packaging materials. Good optical properties also permit adequate inspection of the packaged product during the distribu-tion cycle and by the end-user at the point of purchase.
Shrinkability may be imparted to a thermoplastic film by orientation of the film during its manufacture. This allows the film to shrink or, if restrained, to create shrink tension within the packaging film on exposure to heat, for example, in a hot water bath or by exposure to hot air. In a typical process manufactured film is stretched :Ln either the machine direction or perpendicular to the machine direction,, or both, i.e, in the longitudinal and transverse dirE:etions respectively, in varying ~1.238 ..z_ degrees to impart a desired clegree of shrinkability to the film upon subsequent heating. After this stretching operation the film ~is rapidly cooled to impart latent shrinkability to the resulting film. Shrinkable film provides a tight, smooth appearance to a product wrapped in such a film as well as some added toughness in order to provide abuse resistance. It is of course desirable that the film should have good optical properties after shrinking.
Bags made from heat shrinkable polymeric films have gained aceeptanee for packaging meat, particula~-ly fresh meat and processed meat. Bags made from the heat shrinkable film are supplied to a meat packer being sealed at one end with the other end open and ready to receive a meat product. After the cut of meat is placed in the bag, the' bag will normally be evacuated and the open end of the bag closed by heat sealing or by applying a metal clip. This process is advantageously carried out within a vacuum chamber where the evacuation and application of a clip or heat seal is done automatically. After the bag is removed from the chamber it is heat shrunk by applying heat for example by immersing the filled bag in a hot water bath or by conveying it through a hot air tunnel.
In the usual, distribution chain a whole primal or 'subprimal is packaged within such a shrink bag. The packaged meat will travel from a central slaughter house Where it has been packaged to a retail supermarket inhere the bag will be opened and the meat will be cut into portions for retail sale. Thus) the bags of this ~1.~~,~~
_;_ type must satisfy a number of requirements which are imposed both ,by the slaughter house or packing house and by the bag user.
Furthermore, the bag may be ~~Iaced on display for retail sale to a consumer. It is thereforEZ desirable to have an attractive package in which there has braen relatively complete shrinkage of the bag around the product so that the bag is not wrinkled and so that blood and juices are not trapped in any folds of the wrinkles. The films from which such bags are produced should therefore possess relatively high shrink as well as good optical properties particularly after shrinkage.
It is also important that the bag should be capable of physically surviving the pre>cess of being filled, evacuated, sealed, closed, heat shrunk,, boxed, shipped, unloaded and then stored for retail sale. This type of abuse rules out many polymeric films. A polymeric film having good toughness is required.
The bags must also be strong enough to survive the handling involved in moving packaged meat which may weigh 95 kg or more.
In particular, when the meat is pusaed into the bag its bottom seal must withstand the force of the impact.
The present invention provides a multi-layer film which has good toughness and relatively high shrink as well as good optical properties, such as clarity, after shrinkage. The multi-layer film may be produced in known manner, for example coextruded, and then oriented to provide a shrinkable film.
_q_ The present invention accordingly provides a multi-layer film comprising; (a) a core layer comprising an LLDPE or, preferably, a VLDPE; an optional second core layer comprising a YLDPE or, preferably an LLDPE; (b) two outer layers each comprising an ionomer; and (c) further core layers between the first core layer and the outer layer and between the second core layer and the o~:ter layer, the further core layers comprising an olefin polymer or copolymer.
The multi-layer film advantageously further comprises, preferably between the first and second core layers, an additional core layer, comprising an olefin polymer or copolymer.
In the olefin polymer or copolymer the olefin is preferably ethylene; an ethylene vinyl acetate copolymer is preferred. A modified polymer may be used to improve inter-ply adhesion.
An oxygen barrier layer, for example a polyvinylidene chloride (PV.DC) or an ethylene vinyl alcohol (EVOH) polymer or copolymer layer may also be included in the mufti~layer film, for examgle between the first and second core layers, The invention also provides a method of making a mufti-layer film which comprises coextruding (a) a first core layer comprising an LLIaPE or, preferably, a VLDPE;
optionally a second core la:,~er comprising a VLDPE or, preferably an LLDPE; (b) two outer layers each comprising an - ionomer; and (c) further core layers between the first core layer and the outer layer and between the second core layer and the outer layer, the fu~:cther core, layers comprising an olefin polymer or copolymer:; cooling the coextruded film;
and collapsing the cooled f:llm) 2~1.2538 The first and second core layers in the films according to the invention are generally f,ach 5 to 15 ~m thick. The outer layers are generally .each 8 to 35ym thick. The further core layers are generally 2 to 10 ~m thick.
The coextruded film may be irradiated, for example with ionising radiation such as high energy electrons, at a dosage of, for example 3 to '15 dad. Suc.h irradiation causes .cross-linking and is generally carried out before orientation of the film, When the film comprises a barrier layer which is a,poly-vinylidene chloride/polyvinyl chloride copolymer cross-linking by irradiation should take place prior to incorporation of the barrier layer in the film structure; it is known that such barrier materials are adversely affected, for example by dis-coloration, by irradiation.
When the film comprises a barrier layer which is an EVOH or a polyvinylidene chloride/methyl acrylate copolymer the whole multi-layer film may be irradiated.
In order to produce an oriented film the method of the invention further comprises heating the collapsed film to its orientation temperature range, optionally after irradiating the film, and stretching and orienting the heated film.
Orientation is done by racking or stretching the film at a racking rate of from about 2 to 5 times the original dimensions of the film in the longitudinal (machine) and trans-verse directions. To orient the film, e.g, in a blown. bubble process the cooled tube is heated to its orientation temperature rare, These ranges are well known for many polymeric materials '~01~538 _s_ and are generally below the melting point of the film.
Preferably films according to the invention are heated to from 85oC to 95oC and more preferably from 87oC to 92°C.
Although the dese:ription above concerning preparation of multi-layer :films relates principally to tubular coextrusion and straatching by the trapped bubble techni9ue other methods of manufacture are available such as eoextruding the mufti-Layer film through a slot die and then stretching the film by the use of tenter frames.
Oriented mufti-ltiyer films in aceordance.with the invention have good abuse resistance, goad optical properties, especially after shrinking, and good sealability:
making them especially suitaible for packaging food, especially frozen meat products. Carcasses may be imported frozen, as in the case of Nc~w Zealand lamb, or frozen after slaughter locally. The meat: is then cut while frozen and packaged in shrink bags for retail sale. Orientation of the mufti-Layer films provides toughness and improved (i.e.
seduced) oxygen permeability. The films also generally have a relatively low rnodulus of elasticity making them easier to process, for example in bag making, and have good processability at racking.
The term "core layer" as used herein defines a layer in a mufti-layer film adhered on both sides to other layers.
The term "orientf~d" is used to define a.polymeric material which has been heai:ed and stretched to realign the molecular configuration, thee stretching being accomplished by a racking or a blown bubt>Ie process. A thermoplastic material stretched in one di.rectian only is uniaxial_ly oriented and a material strE~tched in a longitudinal as well as the transverse direction is oiaxially ariented.
k..
2~~.~5~8 -a-The term "racking" is used herein to define a well--known process for stretching coextruded and reheated mufti-layer film by means of teeter framing or a blown bubble process.
The terms "LLDPE" and "linear low density polyethylene" are used herein to describe copolymers of ethylene with one or more comonomers preferably selected from Cq-C10 olefins such as but-1-ene and octene in which the molecules of the copolymers comprise long chains with few sidechain branches or cross-link structures. This molecular structure is to be contrasted with conventional low density polyethylenes which are more highly branched than their counterparts. LLDPE may also be characterised by the low pressure, low temperature processes used to produce it. LLDPE as defined herein has a density which is usually in the range of about 0.916 g/cr to about 0.925 g/ec.
The term "VLDPE°' or "ver~~ low density polyethylene" as used herein refers to linear polyethylene copolymers having a density usually in the range of less than about 0.912 g/cc to about 0.860 g/cc. The terms '°EVA" and "ethylene vinyl aeetate copolymer" as used herein refer to a copolymer formed from ethylene and vinyl acetate monomers in which the ethylene-derived units in the copolymer are present in major amounts, preferably from about 60 to 98 percent by weight, and the vinyl acetate-derived units in the copolymer are present in minor amounts, preferably from about 2 to 40 percent by weight of the total.
a..
2~2538 The term "ionomer" as used herein is, for example, a copolymer of ethylene snd a vinyl monomer with an . , acid group usually an ethyl~enically unsaturated carboxylic acid, which is generally mono-basic, for example acrylic or methacrylic acid. It is to be understood that the term "ionomer" as used in this specification includes both the free acid and ionised form. The ionised form is preferable to the free acid form. The neutralising cation may be any suitable metal ion, for. example an alkali metal ion, such as sodium, a zinc ion or other multivalent metal ion. Suitable ionomers include those sold under the trademark Surlyn marketed by Du Pont. Preferably the ionomer has a relatively low melt index.
When the ionomers are used in their free acid ' form, the poly (ethylene-co-methacrylic acid:EMA) and poly (ethylene-eo-acrylic acid:EAA) are preferred.
The term "ethylene vinyl alcohol copolymer" or "EVOM" as used herein inclu~9es saponified or hydrolysed ethylene vinyl acetate copolymers, and referv to a vinyl alcohol copolymer having an ethylene comonomer. Such eopolymers are prepared by, far example, hydrolysing vinyl acetate copolymers or by chemical reaction with polyvinyl alcohol. The degree of hydrolysis is preferably at least SO
percent and more preferably at least 85 percent. The ethylene eomonomer is generally present in a range of about 15 to about 65 percent.
The term "polyvinylidene chloride" as used herein includes vinylidene chloride copolymers sueh as those sold under the brand name "Saran'~ by Dow Chemical Company of the Dnited States and which usually comprise at least 50 percent vinylidene chloride monomer with, as the comonomer, vinyl chloride or Methyl acrylate, or another suitable comonomer.
r 201.x:538 The total thickness of the mufti-layer films according to the invention will generally be in the range of 50 to 150 Ym thick. Although thicker films may be used they are more expensive. The films will usually be in the range of 70 to 110 ym thick, thicknesses of 70 to 5~0 ~m being particularly preferred.
It will be understood that the films should not be' so thin as to render them insufficiently resistant to damage during packaging of, for example bone-in meat cuts, nar so thick as to render them unnecessarily difficult to orient and to process.
It~ is to be understood that percentages in this specifi-cation, including the accomp,~nying claims, are calculated on .a "by weight" basis unless otherwise specified.
The following examples illustrate the invention.
i ~~'~01253~
FiXAMPLES
Examples of mufti-layer films according to the invention are given in the following Table in which:
(i) The thickness of each layer in ~m is given in parenthesis.
(ii) Ionomer I is Surlyn 1605, available from Du Pont; it is an ethylene/methacrylic acid copolymer comprising 15 percent of methacrylic acid, the cation being sodium.. It has a melt index of 2.8.
(iii) Ionomer 7 is Surlyn 1601, available from Du Pont; it is an ethylene/methacrylic acid copolymer comprising 10 percent of methacrylic acid, the= can on being sodium. It has a melt index of 1.3. ' (iv) LLDPE1 is a linear low density polyethylene having a density of 9.20 g/cc an~~ a melt index of 1.
(v) LLDPE2 is a linear low density polyethylene having a density of 9.17 and a melt index of 2.3.
(vi) EVA, is a standard E11A comprising 18~ vinyl acetate and having a melt index of 2Ø
The films were produced by a conventional tubular co-extrusion technique in which, after extrusion the tube formed was cooled and flattened. The resulting tape was fed through a hot water bath) at a temperature of 87-89o C; on leaving the bath the tube was inflated and blown to give a wall thickness in the blown tube of about 70 Vim. This °'trapped bubble'° technique is known in the art. The film was then rapidly cooled to set the e~rientation and rolled up to give the desired oriented mufti-layer film.
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t0 P fe F.o i -~2-In relation to the comparison film the films according to the invention all had good optical properties (those of the comparison were adjudged fa:ir); their abuse resistance was as good as, or slightly better i:.han, the comparison film; their processability was good, that of the comparison film being poor.
The actual thickness in ym of each film (the nominal thickness,being 70 Vim) and the percentage free shrink in the . longitudinal (L) and transverse (T) directions are, given in the following Table.
Film Thickness Shrink dactua l T
) L
Comparison 61 33 q5 2 6q 33 qq Comparison 77 Comparison 90 Comparison 72 33 7 73 3'9 42 r.,
-.1-PACxAGZN
This invention relates to a packaging film and more particularly to a film useful in the packaging of food products, especiall}~ frozen meat.
Thermoplastic film, and especially films of polyolefin materials, have been used in the past to package various articles including perishable food products which require protection from the environment. The films should possess resistance to physical and environmental abuse during storage and distribution and should present an aesthetic and attractive appearance. Optical qualities such as high gloss, high clarity and low haze contribute to the aesthetic consumer appeal of products wrapped in such packaging materials. Good optical properties also permit adequate inspection of the packaged product during the distribu-tion cycle and by the end-user at the point of purchase.
Shrinkability may be imparted to a thermoplastic film by orientation of the film during its manufacture. This allows the film to shrink or, if restrained, to create shrink tension within the packaging film on exposure to heat, for example, in a hot water bath or by exposure to hot air. In a typical process manufactured film is stretched :Ln either the machine direction or perpendicular to the machine direction,, or both, i.e, in the longitudinal and transverse dirE:etions respectively, in varying ~1.238 ..z_ degrees to impart a desired clegree of shrinkability to the film upon subsequent heating. After this stretching operation the film ~is rapidly cooled to impart latent shrinkability to the resulting film. Shrinkable film provides a tight, smooth appearance to a product wrapped in such a film as well as some added toughness in order to provide abuse resistance. It is of course desirable that the film should have good optical properties after shrinking.
Bags made from heat shrinkable polymeric films have gained aceeptanee for packaging meat, particula~-ly fresh meat and processed meat. Bags made from the heat shrinkable film are supplied to a meat packer being sealed at one end with the other end open and ready to receive a meat product. After the cut of meat is placed in the bag, the' bag will normally be evacuated and the open end of the bag closed by heat sealing or by applying a metal clip. This process is advantageously carried out within a vacuum chamber where the evacuation and application of a clip or heat seal is done automatically. After the bag is removed from the chamber it is heat shrunk by applying heat for example by immersing the filled bag in a hot water bath or by conveying it through a hot air tunnel.
In the usual, distribution chain a whole primal or 'subprimal is packaged within such a shrink bag. The packaged meat will travel from a central slaughter house Where it has been packaged to a retail supermarket inhere the bag will be opened and the meat will be cut into portions for retail sale. Thus) the bags of this ~1.~~,~~
_;_ type must satisfy a number of requirements which are imposed both ,by the slaughter house or packing house and by the bag user.
Furthermore, the bag may be ~~Iaced on display for retail sale to a consumer. It is thereforEZ desirable to have an attractive package in which there has braen relatively complete shrinkage of the bag around the product so that the bag is not wrinkled and so that blood and juices are not trapped in any folds of the wrinkles. The films from which such bags are produced should therefore possess relatively high shrink as well as good optical properties particularly after shrinkage.
It is also important that the bag should be capable of physically surviving the pre>cess of being filled, evacuated, sealed, closed, heat shrunk,, boxed, shipped, unloaded and then stored for retail sale. This type of abuse rules out many polymeric films. A polymeric film having good toughness is required.
The bags must also be strong enough to survive the handling involved in moving packaged meat which may weigh 95 kg or more.
In particular, when the meat is pusaed into the bag its bottom seal must withstand the force of the impact.
The present invention provides a multi-layer film which has good toughness and relatively high shrink as well as good optical properties, such as clarity, after shrinkage. The multi-layer film may be produced in known manner, for example coextruded, and then oriented to provide a shrinkable film.
_q_ The present invention accordingly provides a multi-layer film comprising; (a) a core layer comprising an LLDPE or, preferably, a VLDPE; an optional second core layer comprising a YLDPE or, preferably an LLDPE; (b) two outer layers each comprising an ionomer; and (c) further core layers between the first core layer and the outer layer and between the second core layer and the o~:ter layer, the further core layers comprising an olefin polymer or copolymer.
The multi-layer film advantageously further comprises, preferably between the first and second core layers, an additional core layer, comprising an olefin polymer or copolymer.
In the olefin polymer or copolymer the olefin is preferably ethylene; an ethylene vinyl acetate copolymer is preferred. A modified polymer may be used to improve inter-ply adhesion.
An oxygen barrier layer, for example a polyvinylidene chloride (PV.DC) or an ethylene vinyl alcohol (EVOH) polymer or copolymer layer may also be included in the mufti~layer film, for examgle between the first and second core layers, The invention also provides a method of making a mufti-layer film which comprises coextruding (a) a first core layer comprising an LLIaPE or, preferably, a VLDPE;
optionally a second core la:,~er comprising a VLDPE or, preferably an LLDPE; (b) two outer layers each comprising an - ionomer; and (c) further core layers between the first core layer and the outer layer and between the second core layer and the outer layer, the fu~:cther core, layers comprising an olefin polymer or copolymer:; cooling the coextruded film;
and collapsing the cooled f:llm) 2~1.2538 The first and second core layers in the films according to the invention are generally f,ach 5 to 15 ~m thick. The outer layers are generally .each 8 to 35ym thick. The further core layers are generally 2 to 10 ~m thick.
The coextruded film may be irradiated, for example with ionising radiation such as high energy electrons, at a dosage of, for example 3 to '15 dad. Suc.h irradiation causes .cross-linking and is generally carried out before orientation of the film, When the film comprises a barrier layer which is a,poly-vinylidene chloride/polyvinyl chloride copolymer cross-linking by irradiation should take place prior to incorporation of the barrier layer in the film structure; it is known that such barrier materials are adversely affected, for example by dis-coloration, by irradiation.
When the film comprises a barrier layer which is an EVOH or a polyvinylidene chloride/methyl acrylate copolymer the whole multi-layer film may be irradiated.
In order to produce an oriented film the method of the invention further comprises heating the collapsed film to its orientation temperature range, optionally after irradiating the film, and stretching and orienting the heated film.
Orientation is done by racking or stretching the film at a racking rate of from about 2 to 5 times the original dimensions of the film in the longitudinal (machine) and trans-verse directions. To orient the film, e.g, in a blown. bubble process the cooled tube is heated to its orientation temperature rare, These ranges are well known for many polymeric materials '~01~538 _s_ and are generally below the melting point of the film.
Preferably films according to the invention are heated to from 85oC to 95oC and more preferably from 87oC to 92°C.
Although the dese:ription above concerning preparation of multi-layer :films relates principally to tubular coextrusion and straatching by the trapped bubble techni9ue other methods of manufacture are available such as eoextruding the mufti-Layer film through a slot die and then stretching the film by the use of tenter frames.
Oriented mufti-ltiyer films in aceordance.with the invention have good abuse resistance, goad optical properties, especially after shrinking, and good sealability:
making them especially suitaible for packaging food, especially frozen meat products. Carcasses may be imported frozen, as in the case of Nc~w Zealand lamb, or frozen after slaughter locally. The meat: is then cut while frozen and packaged in shrink bags for retail sale. Orientation of the mufti-Layer films provides toughness and improved (i.e.
seduced) oxygen permeability. The films also generally have a relatively low rnodulus of elasticity making them easier to process, for example in bag making, and have good processability at racking.
The term "core layer" as used herein defines a layer in a mufti-layer film adhered on both sides to other layers.
The term "orientf~d" is used to define a.polymeric material which has been heai:ed and stretched to realign the molecular configuration, thee stretching being accomplished by a racking or a blown bubt>Ie process. A thermoplastic material stretched in one di.rectian only is uniaxial_ly oriented and a material strE~tched in a longitudinal as well as the transverse direction is oiaxially ariented.
k..
2~~.~5~8 -a-The term "racking" is used herein to define a well--known process for stretching coextruded and reheated mufti-layer film by means of teeter framing or a blown bubble process.
The terms "LLDPE" and "linear low density polyethylene" are used herein to describe copolymers of ethylene with one or more comonomers preferably selected from Cq-C10 olefins such as but-1-ene and octene in which the molecules of the copolymers comprise long chains with few sidechain branches or cross-link structures. This molecular structure is to be contrasted with conventional low density polyethylenes which are more highly branched than their counterparts. LLDPE may also be characterised by the low pressure, low temperature processes used to produce it. LLDPE as defined herein has a density which is usually in the range of about 0.916 g/cr to about 0.925 g/ec.
The term "VLDPE°' or "ver~~ low density polyethylene" as used herein refers to linear polyethylene copolymers having a density usually in the range of less than about 0.912 g/cc to about 0.860 g/cc. The terms '°EVA" and "ethylene vinyl aeetate copolymer" as used herein refer to a copolymer formed from ethylene and vinyl acetate monomers in which the ethylene-derived units in the copolymer are present in major amounts, preferably from about 60 to 98 percent by weight, and the vinyl acetate-derived units in the copolymer are present in minor amounts, preferably from about 2 to 40 percent by weight of the total.
a..
2~2538 The term "ionomer" as used herein is, for example, a copolymer of ethylene snd a vinyl monomer with an . , acid group usually an ethyl~enically unsaturated carboxylic acid, which is generally mono-basic, for example acrylic or methacrylic acid. It is to be understood that the term "ionomer" as used in this specification includes both the free acid and ionised form. The ionised form is preferable to the free acid form. The neutralising cation may be any suitable metal ion, for. example an alkali metal ion, such as sodium, a zinc ion or other multivalent metal ion. Suitable ionomers include those sold under the trademark Surlyn marketed by Du Pont. Preferably the ionomer has a relatively low melt index.
When the ionomers are used in their free acid ' form, the poly (ethylene-co-methacrylic acid:EMA) and poly (ethylene-eo-acrylic acid:EAA) are preferred.
The term "ethylene vinyl alcohol copolymer" or "EVOM" as used herein inclu~9es saponified or hydrolysed ethylene vinyl acetate copolymers, and referv to a vinyl alcohol copolymer having an ethylene comonomer. Such eopolymers are prepared by, far example, hydrolysing vinyl acetate copolymers or by chemical reaction with polyvinyl alcohol. The degree of hydrolysis is preferably at least SO
percent and more preferably at least 85 percent. The ethylene eomonomer is generally present in a range of about 15 to about 65 percent.
The term "polyvinylidene chloride" as used herein includes vinylidene chloride copolymers sueh as those sold under the brand name "Saran'~ by Dow Chemical Company of the Dnited States and which usually comprise at least 50 percent vinylidene chloride monomer with, as the comonomer, vinyl chloride or Methyl acrylate, or another suitable comonomer.
r 201.x:538 The total thickness of the mufti-layer films according to the invention will generally be in the range of 50 to 150 Ym thick. Although thicker films may be used they are more expensive. The films will usually be in the range of 70 to 110 ym thick, thicknesses of 70 to 5~0 ~m being particularly preferred.
It will be understood that the films should not be' so thin as to render them insufficiently resistant to damage during packaging of, for example bone-in meat cuts, nar so thick as to render them unnecessarily difficult to orient and to process.
It~ is to be understood that percentages in this specifi-cation, including the accomp,~nying claims, are calculated on .a "by weight" basis unless otherwise specified.
The following examples illustrate the invention.
i ~~'~01253~
FiXAMPLES
Examples of mufti-layer films according to the invention are given in the following Table in which:
(i) The thickness of each layer in ~m is given in parenthesis.
(ii) Ionomer I is Surlyn 1605, available from Du Pont; it is an ethylene/methacrylic acid copolymer comprising 15 percent of methacrylic acid, the cation being sodium.. It has a melt index of 2.8.
(iii) Ionomer 7 is Surlyn 1601, available from Du Pont; it is an ethylene/methacrylic acid copolymer comprising 10 percent of methacrylic acid, the= can on being sodium. It has a melt index of 1.3. ' (iv) LLDPE1 is a linear low density polyethylene having a density of 9.20 g/cc an~~ a melt index of 1.
(v) LLDPE2 is a linear low density polyethylene having a density of 9.17 and a melt index of 2.3.
(vi) EVA, is a standard E11A comprising 18~ vinyl acetate and having a melt index of 2Ø
The films were produced by a conventional tubular co-extrusion technique in which, after extrusion the tube formed was cooled and flattened. The resulting tape was fed through a hot water bath) at a temperature of 87-89o C; on leaving the bath the tube was inflated and blown to give a wall thickness in the blown tube of about 70 Vim. This °'trapped bubble'° technique is known in the art. The film was then rapidly cooled to set the e~rientation and rolled up to give the desired oriented mufti-layer film.
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t0 P fe F.o i -~2-In relation to the comparison film the films according to the invention all had good optical properties (those of the comparison were adjudged fa:ir); their abuse resistance was as good as, or slightly better i:.han, the comparison film; their processability was good, that of the comparison film being poor.
The actual thickness in ym of each film (the nominal thickness,being 70 Vim) and the percentage free shrink in the . longitudinal (L) and transverse (T) directions are, given in the following Table.
Film Thickness Shrink dactua l T
) L
Comparison 61 33 q5 2 6q 33 qq Comparison 77 Comparison 90 Comparison 72 33 7 73 3'9 42 r.,
Claims (23)
1. A multi-layer film comprising: (a) a first core layer comprising an LLDPE or a VLDPE; (b) two outer layers each comprising an ionomer; and (c) at least one further core layer between the first core layer and the outer layer and between a second core layer and the outer layer, the further core layer comprising an olefin polymer or copolymer.
2. A film according to claim 1 in which the first core layer comprises a VLDPE.
3. A film according to claim 1 or 2 which further comprises a second core layer comprising a VLDPE or LLDPE.
4. A film according to claim 1, 2 or 3 in which the second core layer comprises an LLDPE.
5. A film according to any one of claims 1 to 4 which further comprises one additional core layer comprising an olefin polymer or copolymer between the first and second core layers.
6. A film according to claim 5 in which the olefin in the olefin polymer or copolymer is ethylene.
7. A film according to claim 5 or 6 in which the olefin polymer or copolymer is an ethylene vinyl acetate copolymer.
8. A film according to any one of claims 1 to 7 which further comprises an oxygen barrier layer.
9. A film according to claim 8 in which the oxygen barrier layer is a polyvinylidene chloride or ethylene vinyl alcohol polymer or copolymer.
10. A film according to any one of claims 1 to 9 in which the first and second core layers are from 5 to 15 µm thick.
11. A film according to any one of claims 1 to 10 in which the outer layers are from 8 to 35 µm thick.
12. A film according to any one of claims 1 to 11 in which the further core layers are from 2 to 10 µm thick.
13. A film according to any one of claims 1 to 12 whose total thickness is from 50 to 150 µm.
14. A film according to any one of claims 1 to 13 whose total thickness is from 70 to 90 µm.
15. A film according to any one of claims 1 to 14 in which the ionomer is an ethylene/methacrylic acid copolymer which comprises, as the neutralising cation, sodium.
16. A film according to claim 15 in which the ionomer has a low melt index.
17. A film according to any one of claims 1 to 16 which has been irradiated by ionising radiation.
18. A film according to any one of claims 1 to 17 which has been oriented.
19. A film according to claim 1 comprising (i) a layer of ethylene/methacrylic acid copolymer comprising 15% of methacrylic acid and having a sodium cation and a melt index of 2.8 or an ethylene/methacrylic acid copolymer comprising 10% of methacrylic acid and having a sodium cation and a melt index of 1.3;
(ii) a layer of ethylene vinyl acetate copolymer comprising 18% vinyl acetate and having a melt index of 2.0;
(iii) a layer of a very low density polyethylene, or a linear low density polyethylene having a density of 9.20 g/cc and a melt index of 1 or a linear low density polyethylene having a density of 9.17 and a melt index of 2.3;
(iv) if required, a layer of an ethylene vinyl acetate copolymer comprising 18% vinyl acetate and having a melt index of 2.0;
(v) a layer of a very low density polyethylene, or a linear low density polyethylene having a density of 9.20 g/cc and a melt index of 1 or a linear low density polyethylene having a density of 9.17 and a melt index of 2.3;
(vi) a layer of an ethylene vinyl acetate copolymer comprising 18% vinyl acetate and having a melt index of 2.0;
and (vii) a layer of ethylene/methacrylic acid copolymer comprising 15% of methacrylic acid and having a sodium cation and a melt index of 2.8 or an ethylene/methacrylic acid copolymer comprising 10% of methacrylic acid and having a sodium cation and a melt index of 1.3.
(ii) a layer of ethylene vinyl acetate copolymer comprising 18% vinyl acetate and having a melt index of 2.0;
(iii) a layer of a very low density polyethylene, or a linear low density polyethylene having a density of 9.20 g/cc and a melt index of 1 or a linear low density polyethylene having a density of 9.17 and a melt index of 2.3;
(iv) if required, a layer of an ethylene vinyl acetate copolymer comprising 18% vinyl acetate and having a melt index of 2.0;
(v) a layer of a very low density polyethylene, or a linear low density polyethylene having a density of 9.20 g/cc and a melt index of 1 or a linear low density polyethylene having a density of 9.17 and a melt index of 2.3;
(vi) a layer of an ethylene vinyl acetate copolymer comprising 18% vinyl acetate and having a melt index of 2.0;
and (vii) a layer of ethylene/methacrylic acid copolymer comprising 15% of methacrylic acid and having a sodium cation and a melt index of 2.8 or an ethylene/methacrylic acid copolymer comprising 10% of methacrylic acid and having a sodium cation and a melt index of 1.3.
20. A method of making a multi-layer film which comprises coextruding (a) a first core layer comprising an LLDPE or a VLDPE; optionally a second core layer comprising a VLDPE or LLDPE; (b) two outer layers each comprising an ionomer; and (c) further core layers between the first core layer and the outer layer and between the second core layer and the outer layer the further core layers comprising an olefin polymer or copolymer; cooling the coextruded film; and collapsing the cooled film.
21. A method according to claim 20 which further comprises heating the collapsed film to its orientation temperature range, and stretching and orienting the heated film.
22. A method according to claim 20 or 21 in which the film is cross-linked by irradiation prior to orientation.
23. A method according to claim 20 wherein the collapsed film is in the form of a tube which is subsequently fed through a hot water bath at a temperature of 87-89°C, subsequently inflated and blown to give a wall thickness in the blown tube of about 70 µm and is then cooled to set orientation of said film.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8912202A GB2233934B (en) | 1989-05-26 | 1989-05-26 | Packaging film |
| GB8912202.2 | 1989-05-26 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2012538A1 CA2012538A1 (en) | 1990-11-26 |
| CA2012538C true CA2012538C (en) | 1999-10-19 |
Family
ID=10657441
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002012538A Expired - Fee Related CA2012538C (en) | 1989-05-26 | 1990-03-19 | Packaging film |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPH0334852A (en) |
| AU (1) | AU634546B2 (en) |
| CA (1) | CA2012538C (en) |
| GB (1) | GB2233934B (en) |
| NZ (1) | NZ233716A (en) |
| ZA (1) | ZA903807B (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA2061198A1 (en) * | 1991-02-14 | 1992-08-15 | Michael A. Jar | High abuse ionomer bag |
| FR2887801B1 (en) * | 2005-07-01 | 2007-09-07 | Bollore Sa | FILM WITH SEVERAL LAYERS |
| ES2530226T3 (en) | 2008-07-15 | 2015-02-27 | Dow Global Technologies Llc | Reticulated films and articles prepared from them |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA2015629C (en) * | 1989-05-08 | 1996-07-09 | Seizo Kobayashi | Laminate |
| DE68920315T2 (en) * | 1989-06-24 | 1995-06-01 | Dow Chemical Co | Multilayer film. |
-
1989
- 1989-05-26 GB GB8912202A patent/GB2233934B/en not_active Expired - Lifetime
-
1990
- 1990-03-19 CA CA002012538A patent/CA2012538C/en not_active Expired - Fee Related
- 1990-05-17 NZ NZ233716A patent/NZ233716A/en unknown
- 1990-05-17 ZA ZA903807A patent/ZA903807B/en unknown
- 1990-05-23 AU AU55790/90A patent/AU634546B2/en not_active Ceased
- 1990-05-24 JP JP2135141A patent/JPH0334852A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| GB8912202D0 (en) | 1989-07-12 |
| GB2233934A (en) | 1991-01-23 |
| ZA903807B (en) | 1991-03-27 |
| CA2012538A1 (en) | 1990-11-26 |
| AU634546B2 (en) | 1993-02-25 |
| GB2233934B (en) | 1992-12-23 |
| AU5579090A (en) | 1990-11-29 |
| JPH0334852A (en) | 1991-02-14 |
| NZ233716A (en) | 1994-03-25 |
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| Date | Code | Title | Description |
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| EEER | Examination request | ||
| MKLA | Lapsed |