CA1223514A - Carrier film backed with composite film - Google Patents
Carrier film backed with composite filmInfo
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- CA1223514A CA1223514A CA000440007A CA440007A CA1223514A CA 1223514 A CA1223514 A CA 1223514A CA 000440007 A CA000440007 A CA 000440007A CA 440007 A CA440007 A CA 440007A CA 1223514 A CA1223514 A CA 1223514A
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- layers
- layer
- composite film
- polyethylene
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Abstract
ABSTRACT OF THE DISCLOSURE
A multilayer film consists of a support film and a blown, coextruded composite film which is joined to the support films by means of an adhesive and is heat bonded into a tube.
The layers of the composite film consist of polyethylenes or polyethylene copolymers of different mechanical shock resistance.
at least one of the polyethylenes of polyethylene copolymers has a mechanical shock resistance of more than 100 cN. The composite film heat bonded into a tube, has two outer layers of corresponding material and thickness and two inner layers of corresponding material thickness. The inner layers are connected by heat bonding and the outer layers are connected to the inner layers by melt bonding.
A multilayer film consists of a support film and a blown, coextruded composite film which is joined to the support films by means of an adhesive and is heat bonded into a tube.
The layers of the composite film consist of polyethylenes or polyethylene copolymers of different mechanical shock resistance.
at least one of the polyethylenes of polyethylene copolymers has a mechanical shock resistance of more than 100 cN. The composite film heat bonded into a tube, has two outer layers of corresponding material and thickness and two inner layers of corresponding material thickness. The inner layers are connected by heat bonding and the outer layers are connected to the inner layers by melt bonding.
Description
~2~35~
The present invention relates to multi layer films consisting of a single- or multi-layer support film and a polyethylene or polyethylene copolymer composite film, which is joined to the support film by a lamination and whose layers are produced from polyethylene or polyethylene copolymers with mechanical shock resistances differing by at least 25 con, and of which at least one polyethylene or polyethylene copolymer has a mechanical shock resistance greater than 100 ON, as meat surged by ASTM D 1709-62.
1 (I
Multi layer films are known and used to a great extent, for example, in packaging foods. These films consist of a support film and a further single- or multi layer film, which is laminated to the support film. usually, the support film is heat-resistant, stretched biaxially and, if necessary, lacquered. Preferably, it is produced from regenerated cell-lose, polyester, polyamide, polypropylene or aluminum. It may also be formed from several individual films of the said mate-fiats. The support film forms the outer layer in the finished package and must therefore be readily printable.
The film, laminated on the support film, forms the inside of the finished package. This film, or in the case of composite film, at least the layer, of which the inside of the package will later on consist, must be readily heat-sealable and, of reasons of good process ability, have a low coefficient of friction so as to ensure good process ability on packaging machines.
For various areas of application, this film con-struction has, however, not yet proven to be satisfactory, especially because the puncture resistance, particularly for I
vacuum packaging, is notate adequate. Consequently, there may be serious failures, such as leaks which, for many foods, can lead to spoilage of the goods. It might seem obvious to . I. -- 1 I
compensate for the low puncture resistance by an increased film thickness. However, this is not possible because many packaging machines can process only films of a particular Max immune thickness. In the case of coffee packaging machines, this maximum thickness is 110 my Multi layer films of the aforementioned kind have therefore already been produced from support films and coed-trued polyethylene films, which are laminated on the support faultiness. The coextruded polyethylene composite films used con-I sit of two layers joined together by a melt bond, one officio usually consists of the copolymer of a polyethylene of sigh mechanical shock resistance, that is, great toughness, and the other of a normal polyethylene (homopolyethylene, LOPE, low density polyethylene). Either the polyethylene layer of high mechanical shock resistance or - and this is preferred - the LOPE layer is joined to the support film by a lamination. Although it was possible to increase the puncture resistance by means of this system, these multi layer films also have deficiencies, so that they cannot be used satisfac-.() gorily in all areas. It is a disadvantage of such a multi-layer film that it is insufficiently flat at elevated process-in temperatures, so that breakdowns occur frequently, espy-dally with packaging machines operating at high speed. The causes of this are, above all, the different coefficients of thermal expansion of the two layers of the composite film and the different film thicknesses of the two layers of the come posit film, so that these act like a bi-metal. This pie-nomenon occurs particularly strongly in a multi layer composite film, in which the polyethylene layer of high mechanical shock I resistance lies between the support layer and the LOPE layer.
On the other hand, if thy polyethylene layer of high mechanic eel shock resistance is used as lower layer, the LOPE layer being laminated to the support film, the rolling tendency of the multi layer film is admittedly reduced. however, because the surface of the polyethylene layer of high mechanical shock resistance is generally dull, there are processing difficult ties. The addition of lubricants to the polyethylene, from which this layer is produced, is possible but only within limp its because lubricants migrate into the other layers and reduce the strength of the lamination.
Owing to the fact that at least one layer of the lo coextruded composite film consists of a polyethylene or a polyethylene copolymer with a mechanical shock resistance greater than 100 con, the known film admittedly has a certain puncture resistance, which, however, is not yet adequate for many areas of application.
Laminated plastics, which consist of several wheat boiled" plastic films, are moreover known from the German Offenlegungsschrift 1,479,440. Rigid or semirigid plastic objects are formed from the laminated plastic by molding. It is noted that the object has a greater strength than a similar object produced from a single film of comparable thickness.
Moreover, express reference is made to the greater vertical load carrying capacity of containers.
Furthermore, composite films are known (Herman Offenlegungsschrift 1,966,466 and German Offenlegungsschrift
The present invention relates to multi layer films consisting of a single- or multi-layer support film and a polyethylene or polyethylene copolymer composite film, which is joined to the support film by a lamination and whose layers are produced from polyethylene or polyethylene copolymers with mechanical shock resistances differing by at least 25 con, and of which at least one polyethylene or polyethylene copolymer has a mechanical shock resistance greater than 100 ON, as meat surged by ASTM D 1709-62.
1 (I
Multi layer films are known and used to a great extent, for example, in packaging foods. These films consist of a support film and a further single- or multi layer film, which is laminated to the support film. usually, the support film is heat-resistant, stretched biaxially and, if necessary, lacquered. Preferably, it is produced from regenerated cell-lose, polyester, polyamide, polypropylene or aluminum. It may also be formed from several individual films of the said mate-fiats. The support film forms the outer layer in the finished package and must therefore be readily printable.
The film, laminated on the support film, forms the inside of the finished package. This film, or in the case of composite film, at least the layer, of which the inside of the package will later on consist, must be readily heat-sealable and, of reasons of good process ability, have a low coefficient of friction so as to ensure good process ability on packaging machines.
For various areas of application, this film con-struction has, however, not yet proven to be satisfactory, especially because the puncture resistance, particularly for I
vacuum packaging, is notate adequate. Consequently, there may be serious failures, such as leaks which, for many foods, can lead to spoilage of the goods. It might seem obvious to . I. -- 1 I
compensate for the low puncture resistance by an increased film thickness. However, this is not possible because many packaging machines can process only films of a particular Max immune thickness. In the case of coffee packaging machines, this maximum thickness is 110 my Multi layer films of the aforementioned kind have therefore already been produced from support films and coed-trued polyethylene films, which are laminated on the support faultiness. The coextruded polyethylene composite films used con-I sit of two layers joined together by a melt bond, one officio usually consists of the copolymer of a polyethylene of sigh mechanical shock resistance, that is, great toughness, and the other of a normal polyethylene (homopolyethylene, LOPE, low density polyethylene). Either the polyethylene layer of high mechanical shock resistance or - and this is preferred - the LOPE layer is joined to the support film by a lamination. Although it was possible to increase the puncture resistance by means of this system, these multi layer films also have deficiencies, so that they cannot be used satisfac-.() gorily in all areas. It is a disadvantage of such a multi-layer film that it is insufficiently flat at elevated process-in temperatures, so that breakdowns occur frequently, espy-dally with packaging machines operating at high speed. The causes of this are, above all, the different coefficients of thermal expansion of the two layers of the composite film and the different film thicknesses of the two layers of the come posit film, so that these act like a bi-metal. This pie-nomenon occurs particularly strongly in a multi layer composite film, in which the polyethylene layer of high mechanical shock I resistance lies between the support layer and the LOPE layer.
On the other hand, if thy polyethylene layer of high mechanic eel shock resistance is used as lower layer, the LOPE layer being laminated to the support film, the rolling tendency of the multi layer film is admittedly reduced. however, because the surface of the polyethylene layer of high mechanical shock resistance is generally dull, there are processing difficult ties. The addition of lubricants to the polyethylene, from which this layer is produced, is possible but only within limp its because lubricants migrate into the other layers and reduce the strength of the lamination.
Owing to the fact that at least one layer of the lo coextruded composite film consists of a polyethylene or a polyethylene copolymer with a mechanical shock resistance greater than 100 con, the known film admittedly has a certain puncture resistance, which, however, is not yet adequate for many areas of application.
Laminated plastics, which consist of several wheat boiled" plastic films, are moreover known from the German Offenlegungsschrift 1,479,440. Rigid or semirigid plastic objects are formed from the laminated plastic by molding. It is noted that the object has a greater strength than a similar object produced from a single film of comparable thickness.
Moreover, express reference is made to the greater vertical load carrying capacity of containers.
Furthermore, composite films are known (Herman Offenlegungsschrift 1,966,466 and German Offenlegungsschrift
2,102,377), which are formed by folding together blown tubes with walls of at least two coextruded layers. In these come posit films, the inner layers are sealed together or melt bonded. As a result of the rotation of the blown film die, the molecules are oriented in crosswise directions in the folded
- 3 -'` ~L2;235~L~
walls I thy tube. Consequently, -the strength of the composite film ; on whole is more balanced and improved.
lo present invention provides a multi layer composite film of the aforementioned kind, which comprises a support and composite elm laminated on this support, has high puncture l-esist(lnce, lies flat even at elevated temperatures and, if Nazis, can slide well over metal on the side of -the composite film ol~pvsite the support film.
according to the present invention there is provided in I a multi layer film composed of a single or multi layer support film .l.~nlllil~al.ed to a composite film, the improvement which comprises said colllposite film briny formed from a folded coex-truded blown tube having at least two contiguous layers, one of which is an outernlost layer and the other of which is an innermost layer, the contacting surfaces of the outermost and innermost layers being Lusted to one another, and said innermost layer being lolled and heat-bonded upon itself, said tubes further having up to throw additional layers between -the outermost and innermost lulls, said additional layers and said outermost and innermost .>() layers beitlcJ different from one another and having mechanical shock resistances which differ by at least 25 con, a-t least one ox said innermost or outermost layers having a mechanical shock resistance greater than 100 con as measured by ASTM D 1709-62, Lowe outermost layers being selected from the group consisting of OLDIE having a melt index from 0.2 to 4 and LOPE having a melt index from 0.2 to 4 and the innermost layers briny sol-octet from the group consisting of LLDPE having a melt index prom 0.2 to 4, and LOPE having a melt index from 0.2 to 4, and polyeLIlylene/vinyl acetate copolymer.
Thus the invention provides a coextruded composite film which is laminate don a support film, wherein the composite film so furled from a folded, two- to five-walled coextruded `' ~2~3S~
Lowe be, the inner layers of -the composite layers of -the come posit iamb being heat bonded and the outer layers being joined to the in r layers by melt ending The decisive importance of the inventive multi layer film figs in the symmetrical construction of the coextruded come posit film, which is laminated -to the support film. The Semite-rival construction, relative to the asymmetrical construction of the previously used two-layer composite films, causes the films lo lie slgllificantly flatter during processing, even at higher telllperal~lre differences.
The initially described bi-metal effect does not occur because the forces, which lead to the tendency of the film to roll to the one side or the other, have been mutually eliminated my the symmetrical construction. The puncture resistance is increased. The higher puncture resistance is explained partly by the heat bonding of the inner layers B, s'.
The composite film can be produced simply by blowing a multiwclll tube and folding the tube while heat bonding the inner flyers. Moreover, the surface of the outer walls forming the outer layers is reused with the surface of the inner walls of the blown lube which form the inner layers of -the composite film.
lJsincl float and pressure, the inner layers are heat bonded by IlleallS (> I` a pair of press rolls. As a result of the customary .~otati()ll of the blown film die during manufacture of the tube, tile orientation of the molecules between folded walls is crossed.
Conse~lllently, the strengths in the machine and cross directions are ecl-lalized to some extent. This leads to a further increase in puncture resistance.
Compared to previously known film constructions, which consist, for example, of a support film with an heat bonded single-layer polyethylene film, the advantage arises that, for the Salle thickness of composite films, a significantly higher I
:\ `
punctilio resistance is achieved or, for the same puncture no-distance the total -thickness of the composite film can be kept significantly lower, as a result of which a considerable savings of matcl-ial and great advantages on the processing machines are achieve The blown, coextruded tube preferably has two walls. it may however, also be advantageous for various areas of applique-lions to use three- to five-walled tubes and to heat bond -these to filmily composite films with six or ten layers. In this manner, I adclitlollal layers, of polyvinyl alcohol for example, with add-tonal functions (gas barrier) may be provided.
The finished, heat bonded, multi layer composite film is a~lvisa~)le pretreated electrically on one side by known procedures all Lyle fated on the single- or multi layer support film by pro-seeders, which are also known.
35~
seasides selecting a polyethylene or polyethylene copolymer of high mechanical shock resistance, which is also planned for the next state of the art, it is important for the purposes of the invention that raw materials, which heat bond well under pressure and heat, be used for the inner layers of the composite film. On the other hand, raw materials, which can readily be heat-sealed and which have a low coefficient of friction on metal, should be used for the outer layers.
Ethylene/vinyl acetate copolymers, with up to 30 lo weight percent of vinyl acetate, have proven to be preferably suitable for the production of layers of coextruded composite film. Copolymers with 3 to 10 weight percent of vinyl acetate and a melt index of 0.2 to 4.0 and preferably of 0.5 to 1.5 are regarded as especially suitable. These copolymers can be used as outer and inner layers. These polyethylene/vinyl act elate copolymers may contain lubricants or anti blocking agents, depending on whether they are to be used as outer or inner layers. The use of layers of ethylene/vinyl acetate copolymers as inner layers is preferred, because these types I of plastic can be interlocked well. On the other hand, because of their softness and poor frictional values on metal, as well as because of a certain odor of acetic acid, which increases with increasing vinyl acetate content, these mate-fiats are less suitable for producing the outer layers.
Nevertheless, their use as outer layer is possible if the aforementioned disadvantages are not of decisive significance and if, on the other hand, excellent heat sealing properties are important.
LLDPE (linear low density polyethylene), with a density of 0.918 to 0.945 and preferably of 0.922 to 0.930, is also especially suitable. The melt index of this polyethylene is of the order of 0.2 to 4Ø LLDPE with a melt index of 0.8 3519~
to 1.5 is especially preferred.
This group of polyethylene can be used with and without a lubricant and may, if necessary, contain silicate as anti-blocking agent. This raw material is preferably used in the outer layers as a material which is difficult to inter-lock. The mechanical shock resistance of LLDPE reaches peak values of 175 con, for which reason such an LLDPE is outstand-tingly suitable for the purpose of the invention.
An ethylene~methacrylic acid copolymer, cross linked with the ions of sodium or zinc, which is also known under the name of monomeric resin and which is manufactured by Dupont under the trademark of SURLY, is especially preferred. The mechanical shock resistance of monomeric resin, cross linked with sodium, is as high as 450 con; this material is preferred for producing the inner layers BOB'. Besides outstanding mechanical shock resistance, this raw material is also distinguished by very good interlocking properties, oil resistance and good extrudability.
~11 mechanical shock resistance data in this Apply-I cation is based on measurements carried out according to ASTMD ~709-62 with a drop height of 650 mm and a film thickness of I my For the purpose of the invention, it has proven to be advantageous to form the inner layers from ethylene or polyethylene copolymers with a higher mechanical shock nests-lance than that of the outer layers.
The preferred material for the outer layers and for the polyethylene with a lesser mechanical shock resistance is LOPE. It is easily accessible, has outstanding machine run-nine properties, good wear properties and is on the market in broad range of types, so that the outer layer of the coed-trued composite film, which is important for the heat-sealing his process and which forms the inner layer of the package in the finished package, can easily be matched to the requirements of suitable packaging machines. Usually, LOPE with a density of 0.918 to 0.934 and preferably of 0.922 to 0.928 and a melt index of 0.2 to 4.0 and preferably of 0.7 to 2.0 is used.
Composite films of the following construction are preferably employed:
l. The two outer layers consist of LOPE, to which anti-block-in and lubricant agents are added in the usual quantities.
lo The two inner layers consist of a polyethylene/vinyl acetate copolymer. Such a multi layer film is especially suitable for vacuum packaging coffee, has outstanding surface properties and, owing to the inner layers of polyethylene/vinyl acetate copolymers, has outstanding puncture resistance.
2. The two outer layers consist of LLDPE, and the inner layer consists of a polyethylene/vinyl acetate copolymer. This variation has an even higher puncture resistance and can, moreover, be thermoformed.
3. The two outer layers consist of a polyethylene/vinyl I) acetate copolymer; the two inner layers consist of an ethyl lene/methacrylate copolymer, cross linked with sodium ions.
This film has outstanding puncture resistance and is portico-laxly suitable for thermoforming. This film is preferably used for packaging meat, cheese and nuts.
Films based on polyamide, polyester, polypropylene or regenerated cellulose, which are unstretched or stretched biaxially and applied with an adhesive, and which, if nieces-spry, are additionally laminated with aluminum foil, are used as support film - just as they will be in the next state of I the art.
For packaging which is not thermoformed, such as that used, for example, for vacuum packaging coffee, the total g US
thickness of known multi layer films is approximately 100 em, of which approximately 15 to 25 my is due to the support film, which optionally consists of two layers. The usual thicknesses of laminated films, which are not thermoformed, are approximately 25 to 100 m and generally 50 to 75 m.
It is not possible to produce the individual layers of coed-trued composite film with average thicknesses less than 10 Jo m.
Preferably, the thickness of the outer layer amounts to 1/2 to 4/5 of the total thickness of the coextruded compost tie or of the interlocked tube; up to 1/2 of the total thick-news than remains for the total thickness of the inner layers.
The total thickness of the composite film falls within the range of at least 40,~m to no more than 500 em, the preferred thickness range being 70 to 100 m for films which are not thermoformed, while thermoformed film have a higher thickness, the preferred range lying between 80 and 2501~m.
The inventive, multi layer films can be used in wide areas of the packaging industry. However, they have proven to I be especially suitable for vacuum packaging, which is subject to the danger of puncturing, and moreover for: thermoformed vacuum packaging, especially for meat products, cheese and nuts, those with a support film of unstretched polyamide, as well as a coextruded`composite film with outer layers of polyethylene/vinyl acetate copolymers and inner layers of ethylene/methacrylic acid copolymers, cross linked with metal ions, not thermoformed vacuum packaging, especially for coffee and similar oxygen-sensitive products, those with a support film or polyester film, laminated with aluminum, metallized or PVDC-lacquered (PVDC = polyvinylidene chloride) and stretched polyester or polyamide film, as well as a coextruded composite film with outer layers of an ethylene/vinyl acetate fZ3S~'l copolymer and inner layers of ethylene/methacrylic acid copolymer, cross linked with sodium ions, or outer layers ALA' of LLDPE and inner layers B, B ' of ethylens/vinyl acetate copolymer.
A description of embodiments of the invention by means of Figs 1 to 3 follows:
Fig. 1 shows a schematic representation of a two-walled coextruded blown tube in cross section;
Fig. 2 shows a cross section of a composite film, formed from the tube of Fig. 1 by interlocking the inner layers; and Fig. 3 shows an inventive multi layer film in schematic form, in which the composite film, shown in Fig. 2, is laminated on a single-layer support film or polyamide.
The outer and inner layers of the coextrusion tube 1 are labeled A and B, respectively, in Fig. 1.
Fig. 2 shows composite film 1', produced by inter-locking. Layers A, A' are joined at 3 by melt bonding to layers BOB'.
I The inner layers B, B ' are interlocked along line 4.
The I' ~35~
side Al which an electrical pretreatment was carried out before i 11g is Noel red 2 .
In Fig. 3, a polyamide support film, which is laminate with adhesive S to interlocked composite film 1', is numbered 6.
aye Two-wallecl, blown, coextruded tubes with walls of different thickness are produced for preparing multi layer vacuum thermoforminc~ film. The blown tube is subsequently heat bonded.
The outer layers I, A' of this four-layer composite iamb consist lo of polyethylene copolymer with 4.2 weigh-t percent of vinyl ace-tare, a mechallical shock resistance of 145 con and a melt index of 0.8. The two inner layers B, B' consist of a polyethylene/
metllacl~ylic acid copolymer, which is cross linked with sodium ions end has a mechanical shock resistance of 450 con and a melt index of 1.4. The total thickness of the two outer layers A, A' amulets to 2/3 and the total thickness of the two inner layers B, B' to 1/3 of the -total thickness of the heat bonded tube. In a series ox experiments, heat bonded tubes with the above-describ-Ed eollstruction and total thicknesses of 80, 100, 120, 140, 160, 0, 200, 220 and 240 m were produced.
'file float bonded tubes were laminated with support films old unstl-etcl~ed polyamide 6, the thickness of the support film Bunnell Lyle the thickness of the heat bonded tube.
One of the above described, inventive, multi layer films, with a total thickness of 240 em, was compared with a known thermos forming film in a comparative packaging experiment, in which curved, finely minced port sausages were packaged. The known therllloEorlllincJ film had a total thickness of 300 em and consisted of a 100 em unstretched polyamide film and Jo of a two-layer composite film of polyethylene copolymer with 8 weight percent of vinyl acetate, which was joined by inter-locking to the polyamide film and each of whose individual layers was 100 em thick. In spite of the fact that the thickness was reduced by 60~m and that the vinyl acetate con-tent was lower, the inventive, multi layer film had better thermoforming properties (shown especially by a cleanly drawn out trough) and fewer puncture leaks than the known film.
In a further comparison experiment, one of the JO inventive multi layer films described in Example 1, with a total thickness of 360 MU m, was compared with a conventional, multi layer film with layers of polyamide/LDPE/LDPE/polyamide/
LOPE and a total thickness of 365 em. The known multi layer film was combined from two polyamide/polyethylene composite films by melt extrusion with polyethylene into a five-layer film. Such films are used for packing long-keeping sausages, which are known under the name of "Pfefferblock". Equally Good production results were achieved in spite of the slightly reduced total thickness. The actual advantage, however, lies I in the fact that the inventive film requires a significantly lower production effort, namely only one laminating process instead of the three of the previous film.
Example 2:
The multi layer films used consist of a rnetallized 12 my polyester film as support material and three different composite films, which are produced by extrusion blow molding and heat bond of the tubes so formed.
I: The two outer layers ALA' of the composite film consist of LOPE with a mechanical shock resistance of 86 con and a melt I index of 2.0; the two inner layers BOB' consist of polyethy-lene/vinyl acetate copolymer containing 5 weight percent of vinyl acetate, and have a mechanical shock resistance of 150 ON and a melt index of 2Ø
II: The two outer layers consist of LLDPE with a mechanical shock resistance of 175 con and a melt index of lo the two inner layers are similar to those described under I.
III: The two outer layers AYE consist of a polyethylene copolymer containing 3 weight percent of vinyl acetate, and have a mechanical shock resistance of 150 con and a melt index of 2.0 The two inner layer Bus' consist of a polyethy-lene/methacrylic acid copolymer, cross linked with sodium lo ions, and have a mechanical shock resistance of 450 con and a melt index of 1.4.
The total thickness of the composite film in all three variations amounted to 85 Jo m, of which 2/3 was due to the outer layers ALA' and l/3 to the inner layers BOB'. The total thickness, including the adhesive and the support film, was Lomb.
As comparison material, a metallized polyester film was laminated as support film with a 85/~ m polyethylene LOPE film. This film, including the adhesive, had a total I thickness of 100~ m.
In packaging experiments, in which coffee was vacuum packed into 250 g packages on a spike wheel machine, the inventive films resulted in a significantly lower leakage rate.
Example 3:
In a further experiment, in which coffee was vacuum packed into 250 and 500 g vacuum packages on a bag forming, filling and sealing machine, the films, described in the lot-lowing, were used and compared.
An inventive, multi layer film consisted of a Buicks-ally stretched 15 m polyamide film laminated with a 12 Jo m aluminum foil, and of a coextruded four-layer composite film, s .
3 So which was produced by heat bonding a tube and whose outer layers ALA' consisted ox LOPE with a mechanical shock nests-lance of 86 con and a melt index of 0.8 and whose inner layers B, B ' consisted of a polethylene/vinyl acetate copolymer, whose vinyl acetate content was 5 weight percent and which had a mechanical shock resistance of 150 con and a melt index of 2Ø
The thickness of the two outer layers ALA' together amounted to 50 my that of the inner layers BY together to 25 m.
The finished, laminated multi layer film had a total, thickness lo of 105,~1 m.
A conventional film was used for comparison. It consisted of the same support material as that described above and of a 75,u m LOPE film with a mechanical shock resistance of 86 con and a melt index of 0.8. The total thickness, including the adhesive, amounted -to 105 m.
In a packaging experiment in which coffee was vacuum packed, a 40% lower leakage rate was achieved with the invent live film.
I
I
walls I thy tube. Consequently, -the strength of the composite film ; on whole is more balanced and improved.
lo present invention provides a multi layer composite film of the aforementioned kind, which comprises a support and composite elm laminated on this support, has high puncture l-esist(lnce, lies flat even at elevated temperatures and, if Nazis, can slide well over metal on the side of -the composite film ol~pvsite the support film.
according to the present invention there is provided in I a multi layer film composed of a single or multi layer support film .l.~nlllil~al.ed to a composite film, the improvement which comprises said colllposite film briny formed from a folded coex-truded blown tube having at least two contiguous layers, one of which is an outernlost layer and the other of which is an innermost layer, the contacting surfaces of the outermost and innermost layers being Lusted to one another, and said innermost layer being lolled and heat-bonded upon itself, said tubes further having up to throw additional layers between -the outermost and innermost lulls, said additional layers and said outermost and innermost .>() layers beitlcJ different from one another and having mechanical shock resistances which differ by at least 25 con, a-t least one ox said innermost or outermost layers having a mechanical shock resistance greater than 100 con as measured by ASTM D 1709-62, Lowe outermost layers being selected from the group consisting of OLDIE having a melt index from 0.2 to 4 and LOPE having a melt index from 0.2 to 4 and the innermost layers briny sol-octet from the group consisting of LLDPE having a melt index prom 0.2 to 4, and LOPE having a melt index from 0.2 to 4, and polyeLIlylene/vinyl acetate copolymer.
Thus the invention provides a coextruded composite film which is laminate don a support film, wherein the composite film so furled from a folded, two- to five-walled coextruded `' ~2~3S~
Lowe be, the inner layers of -the composite layers of -the come posit iamb being heat bonded and the outer layers being joined to the in r layers by melt ending The decisive importance of the inventive multi layer film figs in the symmetrical construction of the coextruded come posit film, which is laminated -to the support film. The Semite-rival construction, relative to the asymmetrical construction of the previously used two-layer composite films, causes the films lo lie slgllificantly flatter during processing, even at higher telllperal~lre differences.
The initially described bi-metal effect does not occur because the forces, which lead to the tendency of the film to roll to the one side or the other, have been mutually eliminated my the symmetrical construction. The puncture resistance is increased. The higher puncture resistance is explained partly by the heat bonding of the inner layers B, s'.
The composite film can be produced simply by blowing a multiwclll tube and folding the tube while heat bonding the inner flyers. Moreover, the surface of the outer walls forming the outer layers is reused with the surface of the inner walls of the blown lube which form the inner layers of -the composite film.
lJsincl float and pressure, the inner layers are heat bonded by IlleallS (> I` a pair of press rolls. As a result of the customary .~otati()ll of the blown film die during manufacture of the tube, tile orientation of the molecules between folded walls is crossed.
Conse~lllently, the strengths in the machine and cross directions are ecl-lalized to some extent. This leads to a further increase in puncture resistance.
Compared to previously known film constructions, which consist, for example, of a support film with an heat bonded single-layer polyethylene film, the advantage arises that, for the Salle thickness of composite films, a significantly higher I
:\ `
punctilio resistance is achieved or, for the same puncture no-distance the total -thickness of the composite film can be kept significantly lower, as a result of which a considerable savings of matcl-ial and great advantages on the processing machines are achieve The blown, coextruded tube preferably has two walls. it may however, also be advantageous for various areas of applique-lions to use three- to five-walled tubes and to heat bond -these to filmily composite films with six or ten layers. In this manner, I adclitlollal layers, of polyvinyl alcohol for example, with add-tonal functions (gas barrier) may be provided.
The finished, heat bonded, multi layer composite film is a~lvisa~)le pretreated electrically on one side by known procedures all Lyle fated on the single- or multi layer support film by pro-seeders, which are also known.
35~
seasides selecting a polyethylene or polyethylene copolymer of high mechanical shock resistance, which is also planned for the next state of the art, it is important for the purposes of the invention that raw materials, which heat bond well under pressure and heat, be used for the inner layers of the composite film. On the other hand, raw materials, which can readily be heat-sealed and which have a low coefficient of friction on metal, should be used for the outer layers.
Ethylene/vinyl acetate copolymers, with up to 30 lo weight percent of vinyl acetate, have proven to be preferably suitable for the production of layers of coextruded composite film. Copolymers with 3 to 10 weight percent of vinyl acetate and a melt index of 0.2 to 4.0 and preferably of 0.5 to 1.5 are regarded as especially suitable. These copolymers can be used as outer and inner layers. These polyethylene/vinyl act elate copolymers may contain lubricants or anti blocking agents, depending on whether they are to be used as outer or inner layers. The use of layers of ethylene/vinyl acetate copolymers as inner layers is preferred, because these types I of plastic can be interlocked well. On the other hand, because of their softness and poor frictional values on metal, as well as because of a certain odor of acetic acid, which increases with increasing vinyl acetate content, these mate-fiats are less suitable for producing the outer layers.
Nevertheless, their use as outer layer is possible if the aforementioned disadvantages are not of decisive significance and if, on the other hand, excellent heat sealing properties are important.
LLDPE (linear low density polyethylene), with a density of 0.918 to 0.945 and preferably of 0.922 to 0.930, is also especially suitable. The melt index of this polyethylene is of the order of 0.2 to 4Ø LLDPE with a melt index of 0.8 3519~
to 1.5 is especially preferred.
This group of polyethylene can be used with and without a lubricant and may, if necessary, contain silicate as anti-blocking agent. This raw material is preferably used in the outer layers as a material which is difficult to inter-lock. The mechanical shock resistance of LLDPE reaches peak values of 175 con, for which reason such an LLDPE is outstand-tingly suitable for the purpose of the invention.
An ethylene~methacrylic acid copolymer, cross linked with the ions of sodium or zinc, which is also known under the name of monomeric resin and which is manufactured by Dupont under the trademark of SURLY, is especially preferred. The mechanical shock resistance of monomeric resin, cross linked with sodium, is as high as 450 con; this material is preferred for producing the inner layers BOB'. Besides outstanding mechanical shock resistance, this raw material is also distinguished by very good interlocking properties, oil resistance and good extrudability.
~11 mechanical shock resistance data in this Apply-I cation is based on measurements carried out according to ASTMD ~709-62 with a drop height of 650 mm and a film thickness of I my For the purpose of the invention, it has proven to be advantageous to form the inner layers from ethylene or polyethylene copolymers with a higher mechanical shock nests-lance than that of the outer layers.
The preferred material for the outer layers and for the polyethylene with a lesser mechanical shock resistance is LOPE. It is easily accessible, has outstanding machine run-nine properties, good wear properties and is on the market in broad range of types, so that the outer layer of the coed-trued composite film, which is important for the heat-sealing his process and which forms the inner layer of the package in the finished package, can easily be matched to the requirements of suitable packaging machines. Usually, LOPE with a density of 0.918 to 0.934 and preferably of 0.922 to 0.928 and a melt index of 0.2 to 4.0 and preferably of 0.7 to 2.0 is used.
Composite films of the following construction are preferably employed:
l. The two outer layers consist of LOPE, to which anti-block-in and lubricant agents are added in the usual quantities.
lo The two inner layers consist of a polyethylene/vinyl acetate copolymer. Such a multi layer film is especially suitable for vacuum packaging coffee, has outstanding surface properties and, owing to the inner layers of polyethylene/vinyl acetate copolymers, has outstanding puncture resistance.
2. The two outer layers consist of LLDPE, and the inner layer consists of a polyethylene/vinyl acetate copolymer. This variation has an even higher puncture resistance and can, moreover, be thermoformed.
3. The two outer layers consist of a polyethylene/vinyl I) acetate copolymer; the two inner layers consist of an ethyl lene/methacrylate copolymer, cross linked with sodium ions.
This film has outstanding puncture resistance and is portico-laxly suitable for thermoforming. This film is preferably used for packaging meat, cheese and nuts.
Films based on polyamide, polyester, polypropylene or regenerated cellulose, which are unstretched or stretched biaxially and applied with an adhesive, and which, if nieces-spry, are additionally laminated with aluminum foil, are used as support film - just as they will be in the next state of I the art.
For packaging which is not thermoformed, such as that used, for example, for vacuum packaging coffee, the total g US
thickness of known multi layer films is approximately 100 em, of which approximately 15 to 25 my is due to the support film, which optionally consists of two layers. The usual thicknesses of laminated films, which are not thermoformed, are approximately 25 to 100 m and generally 50 to 75 m.
It is not possible to produce the individual layers of coed-trued composite film with average thicknesses less than 10 Jo m.
Preferably, the thickness of the outer layer amounts to 1/2 to 4/5 of the total thickness of the coextruded compost tie or of the interlocked tube; up to 1/2 of the total thick-news than remains for the total thickness of the inner layers.
The total thickness of the composite film falls within the range of at least 40,~m to no more than 500 em, the preferred thickness range being 70 to 100 m for films which are not thermoformed, while thermoformed film have a higher thickness, the preferred range lying between 80 and 2501~m.
The inventive, multi layer films can be used in wide areas of the packaging industry. However, they have proven to I be especially suitable for vacuum packaging, which is subject to the danger of puncturing, and moreover for: thermoformed vacuum packaging, especially for meat products, cheese and nuts, those with a support film of unstretched polyamide, as well as a coextruded`composite film with outer layers of polyethylene/vinyl acetate copolymers and inner layers of ethylene/methacrylic acid copolymers, cross linked with metal ions, not thermoformed vacuum packaging, especially for coffee and similar oxygen-sensitive products, those with a support film or polyester film, laminated with aluminum, metallized or PVDC-lacquered (PVDC = polyvinylidene chloride) and stretched polyester or polyamide film, as well as a coextruded composite film with outer layers of an ethylene/vinyl acetate fZ3S~'l copolymer and inner layers of ethylene/methacrylic acid copolymer, cross linked with sodium ions, or outer layers ALA' of LLDPE and inner layers B, B ' of ethylens/vinyl acetate copolymer.
A description of embodiments of the invention by means of Figs 1 to 3 follows:
Fig. 1 shows a schematic representation of a two-walled coextruded blown tube in cross section;
Fig. 2 shows a cross section of a composite film, formed from the tube of Fig. 1 by interlocking the inner layers; and Fig. 3 shows an inventive multi layer film in schematic form, in which the composite film, shown in Fig. 2, is laminated on a single-layer support film or polyamide.
The outer and inner layers of the coextrusion tube 1 are labeled A and B, respectively, in Fig. 1.
Fig. 2 shows composite film 1', produced by inter-locking. Layers A, A' are joined at 3 by melt bonding to layers BOB'.
I The inner layers B, B ' are interlocked along line 4.
The I' ~35~
side Al which an electrical pretreatment was carried out before i 11g is Noel red 2 .
In Fig. 3, a polyamide support film, which is laminate with adhesive S to interlocked composite film 1', is numbered 6.
aye Two-wallecl, blown, coextruded tubes with walls of different thickness are produced for preparing multi layer vacuum thermoforminc~ film. The blown tube is subsequently heat bonded.
The outer layers I, A' of this four-layer composite iamb consist lo of polyethylene copolymer with 4.2 weigh-t percent of vinyl ace-tare, a mechallical shock resistance of 145 con and a melt index of 0.8. The two inner layers B, B' consist of a polyethylene/
metllacl~ylic acid copolymer, which is cross linked with sodium ions end has a mechanical shock resistance of 450 con and a melt index of 1.4. The total thickness of the two outer layers A, A' amulets to 2/3 and the total thickness of the two inner layers B, B' to 1/3 of the -total thickness of the heat bonded tube. In a series ox experiments, heat bonded tubes with the above-describ-Ed eollstruction and total thicknesses of 80, 100, 120, 140, 160, 0, 200, 220 and 240 m were produced.
'file float bonded tubes were laminated with support films old unstl-etcl~ed polyamide 6, the thickness of the support film Bunnell Lyle the thickness of the heat bonded tube.
One of the above described, inventive, multi layer films, with a total thickness of 240 em, was compared with a known thermos forming film in a comparative packaging experiment, in which curved, finely minced port sausages were packaged. The known therllloEorlllincJ film had a total thickness of 300 em and consisted of a 100 em unstretched polyamide film and Jo of a two-layer composite film of polyethylene copolymer with 8 weight percent of vinyl acetate, which was joined by inter-locking to the polyamide film and each of whose individual layers was 100 em thick. In spite of the fact that the thickness was reduced by 60~m and that the vinyl acetate con-tent was lower, the inventive, multi layer film had better thermoforming properties (shown especially by a cleanly drawn out trough) and fewer puncture leaks than the known film.
In a further comparison experiment, one of the JO inventive multi layer films described in Example 1, with a total thickness of 360 MU m, was compared with a conventional, multi layer film with layers of polyamide/LDPE/LDPE/polyamide/
LOPE and a total thickness of 365 em. The known multi layer film was combined from two polyamide/polyethylene composite films by melt extrusion with polyethylene into a five-layer film. Such films are used for packing long-keeping sausages, which are known under the name of "Pfefferblock". Equally Good production results were achieved in spite of the slightly reduced total thickness. The actual advantage, however, lies I in the fact that the inventive film requires a significantly lower production effort, namely only one laminating process instead of the three of the previous film.
Example 2:
The multi layer films used consist of a rnetallized 12 my polyester film as support material and three different composite films, which are produced by extrusion blow molding and heat bond of the tubes so formed.
I: The two outer layers ALA' of the composite film consist of LOPE with a mechanical shock resistance of 86 con and a melt I index of 2.0; the two inner layers BOB' consist of polyethy-lene/vinyl acetate copolymer containing 5 weight percent of vinyl acetate, and have a mechanical shock resistance of 150 ON and a melt index of 2Ø
II: The two outer layers consist of LLDPE with a mechanical shock resistance of 175 con and a melt index of lo the two inner layers are similar to those described under I.
III: The two outer layers AYE consist of a polyethylene copolymer containing 3 weight percent of vinyl acetate, and have a mechanical shock resistance of 150 con and a melt index of 2.0 The two inner layer Bus' consist of a polyethy-lene/methacrylic acid copolymer, cross linked with sodium lo ions, and have a mechanical shock resistance of 450 con and a melt index of 1.4.
The total thickness of the composite film in all three variations amounted to 85 Jo m, of which 2/3 was due to the outer layers ALA' and l/3 to the inner layers BOB'. The total thickness, including the adhesive and the support film, was Lomb.
As comparison material, a metallized polyester film was laminated as support film with a 85/~ m polyethylene LOPE film. This film, including the adhesive, had a total I thickness of 100~ m.
In packaging experiments, in which coffee was vacuum packed into 250 g packages on a spike wheel machine, the inventive films resulted in a significantly lower leakage rate.
Example 3:
In a further experiment, in which coffee was vacuum packed into 250 and 500 g vacuum packages on a bag forming, filling and sealing machine, the films, described in the lot-lowing, were used and compared.
An inventive, multi layer film consisted of a Buicks-ally stretched 15 m polyamide film laminated with a 12 Jo m aluminum foil, and of a coextruded four-layer composite film, s .
3 So which was produced by heat bonding a tube and whose outer layers ALA' consisted ox LOPE with a mechanical shock nests-lance of 86 con and a melt index of 0.8 and whose inner layers B, B ' consisted of a polethylene/vinyl acetate copolymer, whose vinyl acetate content was 5 weight percent and which had a mechanical shock resistance of 150 con and a melt index of 2Ø
The thickness of the two outer layers ALA' together amounted to 50 my that of the inner layers BY together to 25 m.
The finished, laminated multi layer film had a total, thickness lo of 105,~1 m.
A conventional film was used for comparison. It consisted of the same support material as that described above and of a 75,u m LOPE film with a mechanical shock resistance of 86 con and a melt index of 0.8. The total thickness, including the adhesive, amounted -to 105 m.
In a packaging experiment in which coffee was vacuum packed, a 40% lower leakage rate was achieved with the invent live film.
I
I
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a multilayer film composed of a single or multi-layer support film laminated to a composite film, the improve-ment which comprises said composite film being formed from a folded coextruded blown tube having at least two contiguous layers, one of which is an outermost layer and the other of which is an innermost layer, the contacting surfaces of the outermost and innermost layers being fused to one another, and said innermost layer being folded and heat-bonded upon itself, said tubes further having up to three additional layers between the outermost and innermost layers, said additional layers and said outermost and innermost layers being different from one another and having mechanical shock resistances which differ by at least 25 cN, at least one of said innermost or outermost layers having a mechanical shock resistance greater than 100 cN
as measured by ASTM D 1709-62, the outermost layers being sel-ected from the group consisting of LLDPE having a melt index from 0.2 to 4 and LDPE having a melt index from 0.2 to 4 and the innermost layers being selected from the group consisting of LLDPE having a melt index from 0.2 to 4, and LDPE having a melt index from 0.2 to 4, and polyethylene/
vinyl acetate copolymer.
as measured by ASTM D 1709-62, the outermost layers being sel-ected from the group consisting of LLDPE having a melt index from 0.2 to 4 and LDPE having a melt index from 0.2 to 4 and the innermost layers being selected from the group consisting of LLDPE having a melt index from 0.2 to 4, and LDPE having a melt index from 0.2 to 4, and polyethylene/
vinyl acetate copolymer.
2. The multilayer film of claim 1 wherein the inner-most layer of the composite film has the higher mechanical shock resistance.
3. The multilayer film of claim 1 wherein the poly-ethylene or polyethylene copolymer of the innermost layer of the composite film has a mechanical shock resistance of 120 to 460 cN
and the polyethylene or polyethylene copolymer of the outermost layer has a mechanical shock resistance of 60 to 175 cN.
and the polyethylene or polyethylene copolymer of the outermost layer has a mechanical shock resistance of 60 to 175 cN.
4. In a method for vacuum packaging wherein a multi-layer film composed of a support film and a composite film are used, the improvement which comprises said composite film being the film of claim 1 and wherein the total thickness of the com-posite film falls within the range of 60 to 100 µm of which not more than 4/5 and not less than 1/2 is due to the outermost layer.
5. In a method for packaging using a multilayer film composed of a support film laminated to a composite film as a thermoforming film, the improvement which comprises said com-posite film being the film of claim 1 and wherein the total thickness of the composite film falls within the range of 60 to 400 µm of which not more than 4/5 and not less than 1/2 is due to the outermost layer.
6. The multilayer film of claim 1 wherein at least one of the additional layers is formed from polyvinyl alcohol.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000440007A CA1223514A (en) | 1983-10-28 | 1983-10-28 | Carrier film backed with composite film |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000440007A CA1223514A (en) | 1983-10-28 | 1983-10-28 | Carrier film backed with composite film |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1223514A true CA1223514A (en) | 1987-06-30 |
Family
ID=4126405
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000440007A Expired CA1223514A (en) | 1983-10-28 | 1983-10-28 | Carrier film backed with composite film |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1223514A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5288531A (en) * | 1991-08-09 | 1994-02-22 | The Dow Chemical Company | Pouch for packaging flowable materials |
-
1983
- 1983-10-28 CA CA000440007A patent/CA1223514A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5288531A (en) * | 1991-08-09 | 1994-02-22 | The Dow Chemical Company | Pouch for packaging flowable materials |
| US5364486A (en) * | 1991-08-09 | 1994-11-15 | The Dow Chemical Company | Pouch for packaging flowable materials |
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