CA1240247A - Unbalanced oriented multiple layer film - Google Patents
Unbalanced oriented multiple layer filmInfo
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- CA1240247A CA1240247A CA000456179A CA456179A CA1240247A CA 1240247 A CA1240247 A CA 1240247A CA 000456179 A CA000456179 A CA 000456179A CA 456179 A CA456179 A CA 456179A CA 1240247 A CA1240247 A CA 1240247A
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Abstract
ABSTRACT OF THE DISCLOSURE
An unbalanced multiple layer polymeric film having good interfacial adhesions has a first molecularly oriented polymeric surface layer of nylon on one surface thereof, and a second molecularly oriented polymeric surface layer of a heat sealable ethylene-based polymer or copolymer on the other surface thereof. Films are disclosed having interior functional layers of EVOH and HDPE, along with adhesive polymers selected for good interfacial adhesion after orientation of the film in the machine direction.
Processes for making and orienting the films are also disclosed.
An unbalanced multiple layer polymeric film having good interfacial adhesions has a first molecularly oriented polymeric surface layer of nylon on one surface thereof, and a second molecularly oriented polymeric surface layer of a heat sealable ethylene-based polymer or copolymer on the other surface thereof. Films are disclosed having interior functional layers of EVOH and HDPE, along with adhesive polymers selected for good interfacial adhesion after orientation of the film in the machine direction.
Processes for making and orienting the films are also disclosed.
Description
lZ~Z47 The present Invention relates to an unbalanced multiple layer polymeric film having good Interfaclal adhesions.
There have been proposed a plurality of single and mull tlple layer sheet structures for packaging of products requlrlngslgnlflcant f unctlona I protection from transmission of gaseous materials Into or out of the package through the packaging film.
For example, various food type products require bafflers to transmission of oxygen, moisture, oils and the like. Numerous conventional single and multiple layer structures have been made to serve this end, with a moderate degree of success. Such structures Include, for example, Saran coated polypropylene, glasslne, and the like. It Is known to use multiple layer struck lures Into which may be Incorporated a separately formed layer of oriented polypropylene or oriented polyester, as well as lung-tonal baffler layers.
While such multiple layer films Incorporating an off-enter layer do provide certain Improvements, they require a mull tlpllclty of manùfacturlng steps which puts them at a competltlvecost disadvantage to simpler films. Advantageously, though, the functional baffler benefits of the multlplIclty of layers do pro-vlde overall Improved baffler functions.
Other desirable attributes of film packages, and par-tlcularly those used for packaging certain foods, are related to the appearance and feel of the package; which translates Into consumer perception of the package at the point of sale. Partly-ularly desirable perceived attributes are gloss and stiffness, and, In some cases transparency.
A highly desirable combination of attributes, then, Includes functional baffler properties to certain gaseous trays-mission, and perceived properties of glass, stiffness, and some-36 times transparency.
lZ4~247 Various attempts have been made to advantageously utile-laze the benefits of molecular orientation of films to achieve certain of the desirable properties. A serious problem In these developments has been that each different polymer has Its unique required set of healing and stretching conditions. Where certain comblnat I owns of layer compositions do not have overlapping con-dltlons conducive to molecular orientation of the multiple layer f I Imp additional provisions must be made for effecting the slimly-Tunis orientation of the plurality of layers. Absent these provisions, In previous attempts to orient multiple layer flimsy adjacent layers have developed undesirable stresses at layer Interfaces, and cohesive stresses within the layers themselves.
These stresses too often have manifested themselves In poor Inter layer adhesion at the layer Interfaces, and In cracking or hole development In one or more of the layers.
Mueller, US. Patent No. 4,188,443 Issued February 1980 handles this problem In a 5 layer film by selecting the compost-lions of the second and fourth layers such that they are above their melt temperature during the orientation process tool. 5 fine 43). While this mechanism Is successful In relieving the Interfaclal stresses of the orientation process, only 3 of the 5 layers may be truly molecularly oriented, and selection of mate-flat compositions for layers 2 and 4 may be severely limited by the molting temperature requirements.
Yamaha, US. Patent No. 4,261,~73 Issued April 1981 teaches a balanced 3 layer film, as In his EXAMPLE 10, wherein the outer layers are polyethylene terephthalate and the core layer Is EVE. Sheets of this film are preheated for a lengthy 5 minutes, apparently to reach steady state temperature throughout the film thickness, before the film Is stretched by drawing It Into a 'cup" shaped 124~Z~7 mold. Indeed, this process is more closely related to convent tonal thermoforming than to molecular orientation.
Mueller, US. Patent No. 4,194,039 issued March 28, 1980 to WAR. Grace & Co. teaches a balanced 3-layer film (got. 6 line 23) that is a combination of olefins and olefin blends. The film is made by a plurality of extrusion steps and orientation steps.
sornstein US. Patent No. 4,06~,296 issued December 20, 1977 to W. R. Grace & Co. teaches an oriented 3 layer film having EVE as the core layer. However, in Born stein's film it is crucial (got. 4 line 65) that one of the two outer layers be cross-linked, i.e. by irradiation.
In US. Patent No. 4,501,797 issued February 26, 1985 to American Can Company, there are disclosed four and five layer unbalanced oriented films and method of oriental lion. The films disclosed therein all had polypropylene as one surface layer, and no film was disclosed as having more than five layers.
The present invention provides a multiple layer packaging film material which may have up to seven layers, and including nylon as an outer layer thereof, the film being coo-nominally competitive to make, and having a combination of attributes including!, as functional physical properties, high barrier to gaseous transmission through the film, high inter-layer adhesion, and good tear strengths; and as available per-ceiled properties, high gloss, transparency, and stiffness.
Preferably the films are unbalanced in that conventional heat sealing equipment may be used to apply heat to the nylon side of the film, driving the heat through the film without undue distortion of the film to effect heat sealing of the layer on the opposite surface of the film. Such unbalanced films are readily adapted for use in conventional packaging equipment to , .
lZ~2~7 economically package a variety of products.
According to one aspect of the present invention there is provided an unbalanced multiple layer polymeric film wherein the interracial adhesion at each layer interface is at least 50 grams per inch width, the layers comprising, in order through the film: (a) a first molecularly oriented layer of nylon; (b) a second molecularly oriented layer whose compost-lion is selected from the group consisting of nylon, ethylene vinyl alcohol copolymer, and blends of nylon and ethylene vinyl alcohol copolymer; (c) a third molecularly oriented layer of nylon; (d) a fourth molecularly oriented polymeric adhesive layer having car boxy moieties in the polymeric struck lure; (e) a fifth molecularly oriented layer comprising a pot-ethylene or a blend of ethylene polymers; (f) a sixth mole-ocularly oriented polymeric adhesive layer having car boxy moieties in the polymeric structure; and (g) a seventh sealant layer.
In another aspect thereof the present invention pro-vises an unbalanced multiple layer polymeric film having two outer surfaces, and wherein the interracial adhesion at each layer interface is at least 50 grams per inch width, the layers comprising, in order through the film: (a) a first molecularly oriented layer of nylon; (b) a second molecularly oriented layer whose composition is selected from the group consisting of nylon, ethylene vinyl alcohol copolymer, and blends of nylon and ethylene vinyl alcohol copolymer; 5c) a third molecularly oriented layer of nylon; (d) a fourth mole-ocularly oriented polymeric adhesive layer having car boxy moieties in the polymeric structure; (e) a fifth molecularly oriented layer comprising a polyethylene or a blend of ethylene polymers; (f) a sixth molecularly oriented polymeric adhesive layer having car boxy moieties in the polymeric - pa -124~47 structure; and (g) a seventh heat sealant layer; orientation of said film having been accomplished by applying heat directly to each of said outer surfaces in different amounts, thus creating a temperature differential between said surfaces, and effecting said orientation during the existence of said temperature differential.
, - 3b -lZ41~ 47 The Inventors heroin have found that certain unbalanced multiple layer polymeric films can be molecularly oriented by proper choices of I ever structure I no and processing conditions to achieve a heat sealable, high baffler oriented f I Imp Illustra-live of f I Its of this Invention Is an unbalanced f I It where the layers are, In order; a first molecularly oriented layer of nylon, a second molecularly oriented layer whose composition Is selected from the group consisting of nylon, ethylene vinyl Alcoa hot copolymer (EVE) and blends of nylon and EVE, a third molecularly oriented adhesive layer, of nylon, a fourth Milwaukee-laxly oriented adhesive layer, a fifth molecularly oriented layer comprising a polyethylene or a blend of ethylene polymers, a sixth molecularly oriented adhesive layer, and a seventh mole-ularly oriented sealant layer. The fourth and sixth layers come pulse car boxy moieties In an ethylene based polymeric structure;
and most preferably, the composition of the fourth and sixth lay-ens Is modified medium density polyethylene (MMDPE) and the fifth layer comprises high density polyethylene (HYPE). Desirably the composition of the seventh layer Is chosen from the group con-slstlng of monomer, linear low density polyethylene (LLDPE), lowdenslty polyethylene (LOPE) and ethylene vinyl acetate copolymer (EVA) having up to 18 weight percent vinyl acetate (VA).
In a similar structure, the first, second, and third layers all comprise nylon and are effectively a single layer.
Under normal mlscroscoplc observation, the layer Interfaces Join-lung these three layers In this structure are nonexistent In any of the structures recited above, and In combine-lions thereof, cereal advantages are achieved wherein the second layer comprises an blend of nylon and EVE.
Certain novel aspects of the Invention also reside In a method of mulling an unbalanced, oriented, multiple layer polyp Merle film wherein the Interfaclal adhesion at each layer Inter-face Is at least 150 grams per Inch width, the film having a I
.
, ~24~24~
first polymeric surface layer of nylon on one surface thereof and a second polymeric surface layer of a heat sealable ethylene polymer, or copolymer on the other surface thereof. The novel method of orientation commences with the step of prattling each of the respective surfaces to separately preselected tempera-lures, the preselected temperature of the surface of the second surface layer being between 10F. and 60F. below the heat seal-lung temperature of the second surface layer, the preselected temperature of the surface of the first surface layer being between Sophie. and 230F. After the surfaces are preheated, the preheated film Is stretched, the stretched film Is annealed, and finally the annealed film Is cooled.
A particularly advantageous embodiment of the method Is one wherein the surfaces are heated by passing a continuous sheet of the film over a series of heated rollers. The sheet passes over the heated rollers In such a configuration that each roller contacts only one surface of the film, and the temperature Of each roller Is controlled so as to apply an appropriate tempera-lure to the surface so contacted. When the film surfaces reheated to the proper temperature, the film Is then stretch off-enter In the machining direction.
Preferably, the annealing Is done by application of heat to the nylon surface layer, since It Is less physically affected by the heat than the other surface layer.
The present Invention will be further Illustrated by way of the accompanying drawings, In which:-Figure 1 Is a cross-sectlon of a representative 7 layer film of the Invention; and Figure 2 Is an outline of a representative fine of pro-swizzling equipment for carrying out the orientation of multiple layer films of the Invention.
` Referring now to Figure 1, the overall film Is deslg-noted by the numeral 10. Layer 12 Is nylon. Layer 14 Is a bar-ruler layer of either nylon, EVE, or a blend of nylon and EVE.
Layer 16 Is nylon. Layer 18 Is an adhesive polymer. Layer 20 IS
an ethylene polymer or copolymer or a blend of ethylene polymers.
Layer 22 Is an adhesive polymer. Layer 24 Is a heat sealable layer which may be so I acted with substantial Independent Judge-mint, depending on Its adhesion requirements to the specific come position of layer 22 and the desired heat scaling temperature.
Referring now to Figure 2, the overall layout of the equipment and film Is designated 108. The layout Includes an unwind station 109 from which Is unwound a roll 112 of if It AYE.
The film first passes over a turning roll 114, from there to a f First preheat roll 116, and thence Is wound over a series of heated rolls 118, 120, 122, 124, 126 and 128. The f I It Is stretch oriented between rolls 120 and 122 as Indicated by the designation 110B for the stretched f I Imp The stretched film Is annealed on roll 130 and then cooled on roll 132. Finally, the 20 stretched film 110B Is wound up as a roll 134 on windup station 136.
Upon examination of the overall nature of the film hereinabove described, it Is seen that there are disclosed seven layer films having the combination of at least six layers, and In most cases, all seven of the layers molecularly oriented, and wherein dlsslmllar polymeric material structures :
- ~.24~7 - -are associated with the several layers. More specifically, not all the layers of the films of this invention need be derivatives of the same family, e.g. polyethylene, polypropylene, or even polyolefins. Further, the compositions of the several layers need not have similar melt flow properties 90 long as they are compatible for a coextrusion process. Neither is it necessary, and indeed it is not desired, that any of the layers melt during the orientation process, as melting of any given layer would preclude true molecular orientation of that layer. From the perspective of desired physical properties of the overall film, it is generally preferred that all the layers be molecularly oriented. For reasons of facilitating construction of some members of the family of films of the invention, the sealant layer may, or may not, be oriented. For example, in some cases it is preferred to coextrude all the layers of the film except the sealant layer, and to orient the so coextruded multiple layer film. After orientation, the sealant layer, erg. layer 24 is then added -- for example by solution coating, by extrusion coating, extrusion lamination, or by heat and pressure lamination of a previously formed film.
Other conventional means of adding a sealant layer to a separately formed film are also contemplated.
Definitions- Certain terms used herein require some elan-ligation as to the intended meaning in order to preclude possible confusion as to their significance.
Throughout this teaching, the films of the invention are described as being "unbalanced". Unbalanced refers to the relationships of physical and chemical properties of the polymers relative to the symmetry, or lack thereof, of the lo film cross-section. In a generally balanced film the properties will be at least similar as one progresses from the two outside surfaces of the film toward the center of the film cross-section. Referring to a seven layer balanced film, which could be represented by the structure shown in FIGURE 1 though it is not intended herein to represent that inventive films illustrated by FIGURE 1 are balanced), the outer layers such as 12 and 24 would have similar properties, and the next pair of layers such as 14 and 22 would have similar properties and so on. the similarities in a balanced film usually are both chemical, e.g. polymeric structure and composition; and physical, e.g. melting properties, rheology of fluid flow, heat seal temperature, vapor permeation rates and the like. In unbalanced films, and now referring to the inventive films represented by FIGURE 1, the outer layers, layers 12 and 24 are dissimilar in at least some properties, usually both chemical properties and physical properties. For example, layer 24 is usually an ethylene polymer or copolymer and has lower melting temperature and lower heat sealing temperature than the nylon of layer 12.
Layers 14 and 22 are normally not similar. their selection is based primarily on their individual functional purposes within the film, and not on their similarities to each other.
Layer 14 it a barrier layer. Layer 22 is an adhesive layer.
Like dissimilar comparisons can be made with the other corresponding pairs of film layers.
The term "car boxy moieties" refers to a plurality of functional group derivatives of carboxylic acids in the compound which include components such as Jo -o R - C - o - Al or O O
if if R - C - O - C - Al Illustrative of such car boxy structures are organic acids and acid salts, esters, and androids.
The term "molecularly oriented" refers to the rearrange-mint of polymeric film by any process which simultaneously reduces the film thickness and elongates its dimension in at least one direction; all while the film is in a heated, but unmelted state. Specifically, "molecular orientation"
does not include those processes that stretch the polymer when it is in a softened state, such as in blow-molding.
The phrase "heat sealing temperature" refers to that temperature, or range of temperatures at which films of certain polymers are susceptible to being sealed to themselves in face-to-face relationship by application of heat and pressure in conventionally known manner.
The term "annealing" refers to a step of temporarily holding a film at an elevated temperature under controlled levels of tension. This known process provides a degree of stability to a stretched film after it is cooled and improves performance characteristics.
Returning now to the invention in detail, layers 12 and 16 are advantageously nylon, and provide toughness and stiffness to the film. Nylon 6 is preferred. Modified nylon 6 has also been found particularly desirable. Where stiffness of the overall film structure is less important, nylon 666 may be used too Less preferred, but acceptable is nylon 12.
Toe crucial property of the nylon in all cases is its _ g _ 12~Z47 capability to be coextruded in a 3-layer sub-combination as layers 12, 14, and 16. Thus the desirable properties of layers 12 and 16 alone must be considered in view of the anticipated composition of layer 14. Layer 12 should exhibit thermal stability under heat sealing conditions, and may contain surface modifying additives, such as slip and anti-block agents.
Layer 14 serves as a barrier to transmission of oxygen through the film. Acceptable barrier layer materials are EYE, nylon, and blends of EVE and nylon. Preferred compositions are EVE. When blending is practiced, blends containing at least 50~ EVE are preferred to effect improved barrier to transmission of oxygen through the film.
The finally selected composition of layer 14 is at times a compromise between the better oxygen barrier provided by EVE, the lower cost attributed to a blend of nylon and EVE, and the still lower cost of plain nylon. Skipping, for the moment, over layer 18, let us deal next with layer 20.
The composition of layer 20 is chosen for one or more of the functions of (1) moisture barrier, and (2) physical strength in a relatively thick, economical layer. The preferred material for layer 20 is HYPE. HYPE provides an effective moisture vapor barrier at an economical cost.
Other alternative materials for layer 20 are medium density polyethylene (MOPE), LOPE, LLDPE and blends of LLDPE with MOPE or HYPE and blends of MOPE with HYPE. The moisture barrier properties and cost vary, depending on the polymer selected, and the thickness of layer 20.
Layer 24 is a heat sealable layer. Its preferred composition is Surly monomer which, in oriented form, has a heat sealing temperature of about 210F. Another acceptable lZ~247 composition Is LLDPE, why I ah has a higher heat scaling temperature of about 260F . Other acceptab I e compositions are LOPE and EVA
having up to 18 weight percent VA. Above 18% VA, the surface of layer 24 Is tacky and requires use of excessive amounts of slip and antl-block additives. Other conventionally heat sealable materials may be chosen for fulfilling specific f I I m design parameters. Slip and antl-block additives are commonly used with all the layer 24 compositions, In amounts of about 5% by weight of the layer composition, though higher percentages are contem-plated. A typical slip and antl-block agent Is sold as a concern-irate under the trademark COMPEL 8719-3 by Dupont Company.
The most common problem In producing oriented multiple layer films of the nature disclosed heroin Is serious reduction, or failure of adhesion at the layer Interfaces. In the struck lures disclosed heroin, the Interface most sensitive to adhesion problems Is the Interface between layers 22 and 24.
Now that layers 16,20 and 24 have been defined, It Is appropriate to discuss adhesive polymer layers 18 and 2Z; for their selection can only be made In fight of the anticipated come positions selected for layers 16,20 and 24. For use as adhesive layers, the polymers must contain car boxy moieties and preferably contain functional group derivatives of carboxyllc colds and preferably anhydrlde derivatives. Moderate amounts of process experimentation are required with any new potential adhesive polymer In order to achieve acceptable levels of adhesion. This experimentation Is required because all acceptable adhesive polyp mews are modified oleflns, but not all modified oleflns are lung-tonally acceptable adhesive polymers In a given film structure when applied by one specific set of processing conditions.
The most successful adhesive polymer known to the Inventors for use In the preferred structure Is a modified medium density polyethylene sold by Mltsul Company under the trademark Adder NF500. NF500 retains minimum levels of adhesion of about lZ~4~
grooms per Inch width, and typical adhesion levels are around 300 grams per Inch. Other adhesives found acceptable with spew clflc compositions of layers 16,20 and 24 are modified low den-sty polyethylene.
In producing the oriented films of this Invention the selected polymers are first coextruded as a seven sometimes slicks layer film, and cooled, to yield a base film, unorlented. In coextruslon of the base film as, for Instance, a seven layer film, the melted polymer streams which subsequently form the seven layer film are first combined as three sub-comblnatlon melt streams as follows. Layers 12, 14 and 16 form one sub-comblna-lion. Layers 18, 20 and 22 form a second sub-comblnatlon. Layer 24 as a single stream Is the third sub-combinatlon. Particularly addressing the first and second sub-comblnatlon melt streams, It Is Important that the melt flow theological characteristics of the polymer streams within each sub-comblnatlon be compatible with each other to achieve acceptable coextruslve processing of the respective sub-comblnatlon to form the desired layers.
Preferably the nylon has a melt Index of about 9, and the HYPE
has a melt Index of about 3. The sub-comblnatlons are kept physically separated from each other up to and during formation of the sheetlike layer structuring of the Individual layers In each sub-comblnatlon. This physical separation of the sub-combinations permits separate control of the thermal envlronmentof each sub-comblnatlon. The sub-comblnatlons ' - 12 .
lz4~ ~47 are finally joined to form the seven layer film just before exiting the die. After exiting the die, the film is cooled.
While the cooled seven layer film may be immediately oriented in an in-line operation, it is entirely acceptable to wind up the film for subsequent orientation in a separate process such as the one outlined in FIGURE 2. Uniaxial orientation in the machine direction is generally preferred.
In understanding the process of the invention, it is significant to understand that the composition defined for sealant layer 24 responds to thermal stimuli at a sub-staunchly lower temperature than other layers of the film and particularly the layer 12. Significantly, the inventors have found that by applying heat to each surface separately, and at a temperature selected to be compatible with the orientation of the composition of that layer and all the interior layers, and by applying that heat to each surface for a moderate period of time, the multiple layer films of this invention may be oriented; and indeed, an unbalanced film hazing up to seven layers and wherein the several layers need not be derived from the same polymer family, can be molecularly oriented without necessarily incurring splitting, pin-holing, or softening of any one layer.
It is significant to note that, with the number of layers in the invention reaching as high as seven, selection ox the proper combination of polymers and layer thicknesses, compatible to simultaneous orientation, is a delicate task, requiring significant technical skill. With each considered increase in the number of layers to be simultaneously oriented, the complexity of selections of proper compositions and processing conditions is increased significantly. Thus, for example, layers 16, 18, and 20 are susceptible to trays-.
mission of heat from both surfaces ox the film -- those surfaces being on layers 12 and 24 -- and depending on the thickness and composition ox each layer, and the thickness of the overall film, the processing conditions, including temperatures, orientation ratios and line speeds are adjusted to achieve successful orientation.
Advantageously, as the amount of stretch achieved is increased, while maintaining adequate levels of inter layer adhesion, the desirable properties of the film are enhanced.
Disadvantageously, however, as the amount of stretch is increased, the adhesions at certain of the interfaces decreases. Thus, the selection of the best orientation ratio for any given film is dependent upon the specific film structure and the inter layer adhesion levels required by the intended end use of the film. For most packaging applications, interlocks adhesion levels must be at least 70 grams per inch width, as measured by ASTM D903. For films contemplated by this invention, and considering the adhesion levels required, satisfactory orientation ratios are normally between 2.~/1 and 4/1; with the preferred ratio being 3/1. The lower orientation ratios generally apply to structures having EVE
in layer 14 and wherein all the layers are simultaneously oriented. the higher orientation ratios are achieved wherein the layer (14) contains some nylon.
The heat applied to each of the surface layers, e.g. 12 and 24, is applied to the surface layers as they alternate contacting alternative ones of the temperature-controlled rolls.
As an illustration, consider the processing through equipment of FIGURE 2 of a typical film as in FIGURE 1, wherein layer 14 is EVE, layer 24 is Surly, and layer 20 ;24~3Z47 is HYPE. Layer thicknesses of this "typical structure" are given in following Table 1. The film Lola is unwound from unwind station lo at a speed of 60 to 80 feet per minute with the sealant layer 24 on the bottom surface of the film such that the sealant layer contacts the turning roll 114, which is kept at room temperature, or about 20C. The film then progresses to the first preheat roll 116 which is temperature controlled at a critical minimum temperature of at least awoke., and where layer 12 is against roll 116 lo and receives initial preheating. At the next preheat roll, ~18, which it temperature controlled at 70C, the sealant layer 24 contacts the preheat roll, and receives its initial direct-contact preheating. Layer 12 receives additional preheating at roll 120 which is temperature controlled at 90C. The film is then stretched between rolls 120 and 122.
This it accomplished by driving roll 122 faster than roll 120 and controlling the difference in drive speeds to effect the desired amount of stretch, hereinafter referred to as the orientation ratio -- that being the fractional ratio of the driving speeds of the rolls 120 and 122. In this illustration, then, typical machine speeds during and after stretching are on the order of 180 to 320 feet per minute.
After the film is stretched between rolls 120 and 122, it it designated lob, as shown between rolls 122 and 124.
Roll 124 is again temperature controlled, in this illustration at 90C., the same as roll 120. Roll 122 is temperature controlled at 70C., the same as roll 118. Rolls 126 and 128 are controlled at 80C~ The film is then annealed by contacting annealing roll 130, which roll is temperature controlled at 80C. After annealing, the film is cooled by chill roll 132 to less than 40~C., and is subsequently I '!Z4'7 wound up on a roll 134 at wind up station 136.
In terms of heating contact time, the film is in contact with preheat roll 116 for about 1.8-4 seconds, and rolls 118 and 120 for about 0.9-3.2 seconds each. Contact time on rolls 122, 124, 126, and 128 is about 0.3-0.8 seconds each.
Contact time on rolls 130 and 132 is about 0.6-1.0 second, Also significant to the process is good control of the film speed and contact on all rolls at all stages of the operation.
Thus nip rolls 140 are used at several locations along the processing line as shown in FIGURE 2.
As described briefly earlier herein, the layers which are primarily responsible for the physical properties of the film are layers 12, 14, 20 and 24. Layers 16, 18, and 22, on the other hand, serve primarily the functions of facilitating processing and providing inter layer adhesion. To meet the specific needs of a particular packaging use, the proportions of layers 12, 14, 20 and 24 can be adjusted somewhat; and usually the final structure is a compromise of properties which best meets the needs of the use while keeping the film cost competitive. Where stiffness is a major concern, the amount of layer 12, or layer 20, as a proportion of the film, is increased. Where oxygen barrier as measured by ASTM D-3985 is a concern, either the composition of layer 14 is adjusted or the amount of layer 14 is increased. Where water vapor transmission through the film, as measured by ASTM F-372 is a major concern, the amount of HYPE in layer 20 is increased.
Where the heat seal properties of the film are critical, or are particularly sensitive, for example because of the product willing operations, the amount of the heat seal layer 24 is increased, or its composition is adjusted.
Considering that the overall thickness of the film is lZ~UZ47 somewhat predetermined my the type of packaging contemplated, and by the cost limitations, and considering that some polymers in the structure are more expensive than others, and that minimum amounts of each layer are required for minimal layer functionality, there exists a generally defined range of proportions which is acceptable for each of the seven layers.
xpresse~ in terms of the percentage of the thickness of the overall film, for a 1.0 mix oriented film, the approximate minimum functional thickness of each layer is shown in Tale 1, along with examples of representative film structures.
_ .
Minimum Typical Heat Seal High WVTR Low Lever Thickness Structure Emphasis Barrier Cost _ _ 12 10% 20% I 10% 10%
14 5% 8% 7% 7% 5%1 16 3% 5% 3% 3%
18 5% 5% 5% 5%
20% 20% 20% 4%3 40~2 22 5% 5% 5% 5%
24 25% 37% 50% 30% 30~4 Total Thickness% 100% 100% 100% 100%
Represented 1. Nylon
There have been proposed a plurality of single and mull tlple layer sheet structures for packaging of products requlrlngslgnlflcant f unctlona I protection from transmission of gaseous materials Into or out of the package through the packaging film.
For example, various food type products require bafflers to transmission of oxygen, moisture, oils and the like. Numerous conventional single and multiple layer structures have been made to serve this end, with a moderate degree of success. Such structures Include, for example, Saran coated polypropylene, glasslne, and the like. It Is known to use multiple layer struck lures Into which may be Incorporated a separately formed layer of oriented polypropylene or oriented polyester, as well as lung-tonal baffler layers.
While such multiple layer films Incorporating an off-enter layer do provide certain Improvements, they require a mull tlpllclty of manùfacturlng steps which puts them at a competltlvecost disadvantage to simpler films. Advantageously, though, the functional baffler benefits of the multlplIclty of layers do pro-vlde overall Improved baffler functions.
Other desirable attributes of film packages, and par-tlcularly those used for packaging certain foods, are related to the appearance and feel of the package; which translates Into consumer perception of the package at the point of sale. Partly-ularly desirable perceived attributes are gloss and stiffness, and, In some cases transparency.
A highly desirable combination of attributes, then, Includes functional baffler properties to certain gaseous trays-mission, and perceived properties of glass, stiffness, and some-36 times transparency.
lZ4~247 Various attempts have been made to advantageously utile-laze the benefits of molecular orientation of films to achieve certain of the desirable properties. A serious problem In these developments has been that each different polymer has Its unique required set of healing and stretching conditions. Where certain comblnat I owns of layer compositions do not have overlapping con-dltlons conducive to molecular orientation of the multiple layer f I Imp additional provisions must be made for effecting the slimly-Tunis orientation of the plurality of layers. Absent these provisions, In previous attempts to orient multiple layer flimsy adjacent layers have developed undesirable stresses at layer Interfaces, and cohesive stresses within the layers themselves.
These stresses too often have manifested themselves In poor Inter layer adhesion at the layer Interfaces, and In cracking or hole development In one or more of the layers.
Mueller, US. Patent No. 4,188,443 Issued February 1980 handles this problem In a 5 layer film by selecting the compost-lions of the second and fourth layers such that they are above their melt temperature during the orientation process tool. 5 fine 43). While this mechanism Is successful In relieving the Interfaclal stresses of the orientation process, only 3 of the 5 layers may be truly molecularly oriented, and selection of mate-flat compositions for layers 2 and 4 may be severely limited by the molting temperature requirements.
Yamaha, US. Patent No. 4,261,~73 Issued April 1981 teaches a balanced 3 layer film, as In his EXAMPLE 10, wherein the outer layers are polyethylene terephthalate and the core layer Is EVE. Sheets of this film are preheated for a lengthy 5 minutes, apparently to reach steady state temperature throughout the film thickness, before the film Is stretched by drawing It Into a 'cup" shaped 124~Z~7 mold. Indeed, this process is more closely related to convent tonal thermoforming than to molecular orientation.
Mueller, US. Patent No. 4,194,039 issued March 28, 1980 to WAR. Grace & Co. teaches a balanced 3-layer film (got. 6 line 23) that is a combination of olefins and olefin blends. The film is made by a plurality of extrusion steps and orientation steps.
sornstein US. Patent No. 4,06~,296 issued December 20, 1977 to W. R. Grace & Co. teaches an oriented 3 layer film having EVE as the core layer. However, in Born stein's film it is crucial (got. 4 line 65) that one of the two outer layers be cross-linked, i.e. by irradiation.
In US. Patent No. 4,501,797 issued February 26, 1985 to American Can Company, there are disclosed four and five layer unbalanced oriented films and method of oriental lion. The films disclosed therein all had polypropylene as one surface layer, and no film was disclosed as having more than five layers.
The present invention provides a multiple layer packaging film material which may have up to seven layers, and including nylon as an outer layer thereof, the film being coo-nominally competitive to make, and having a combination of attributes including!, as functional physical properties, high barrier to gaseous transmission through the film, high inter-layer adhesion, and good tear strengths; and as available per-ceiled properties, high gloss, transparency, and stiffness.
Preferably the films are unbalanced in that conventional heat sealing equipment may be used to apply heat to the nylon side of the film, driving the heat through the film without undue distortion of the film to effect heat sealing of the layer on the opposite surface of the film. Such unbalanced films are readily adapted for use in conventional packaging equipment to , .
lZ~2~7 economically package a variety of products.
According to one aspect of the present invention there is provided an unbalanced multiple layer polymeric film wherein the interracial adhesion at each layer interface is at least 50 grams per inch width, the layers comprising, in order through the film: (a) a first molecularly oriented layer of nylon; (b) a second molecularly oriented layer whose compost-lion is selected from the group consisting of nylon, ethylene vinyl alcohol copolymer, and blends of nylon and ethylene vinyl alcohol copolymer; (c) a third molecularly oriented layer of nylon; (d) a fourth molecularly oriented polymeric adhesive layer having car boxy moieties in the polymeric struck lure; (e) a fifth molecularly oriented layer comprising a pot-ethylene or a blend of ethylene polymers; (f) a sixth mole-ocularly oriented polymeric adhesive layer having car boxy moieties in the polymeric structure; and (g) a seventh sealant layer.
In another aspect thereof the present invention pro-vises an unbalanced multiple layer polymeric film having two outer surfaces, and wherein the interracial adhesion at each layer interface is at least 50 grams per inch width, the layers comprising, in order through the film: (a) a first molecularly oriented layer of nylon; (b) a second molecularly oriented layer whose composition is selected from the group consisting of nylon, ethylene vinyl alcohol copolymer, and blends of nylon and ethylene vinyl alcohol copolymer; 5c) a third molecularly oriented layer of nylon; (d) a fourth mole-ocularly oriented polymeric adhesive layer having car boxy moieties in the polymeric structure; (e) a fifth molecularly oriented layer comprising a polyethylene or a blend of ethylene polymers; (f) a sixth molecularly oriented polymeric adhesive layer having car boxy moieties in the polymeric - pa -124~47 structure; and (g) a seventh heat sealant layer; orientation of said film having been accomplished by applying heat directly to each of said outer surfaces in different amounts, thus creating a temperature differential between said surfaces, and effecting said orientation during the existence of said temperature differential.
, - 3b -lZ41~ 47 The Inventors heroin have found that certain unbalanced multiple layer polymeric films can be molecularly oriented by proper choices of I ever structure I no and processing conditions to achieve a heat sealable, high baffler oriented f I Imp Illustra-live of f I Its of this Invention Is an unbalanced f I It where the layers are, In order; a first molecularly oriented layer of nylon, a second molecularly oriented layer whose composition Is selected from the group consisting of nylon, ethylene vinyl Alcoa hot copolymer (EVE) and blends of nylon and EVE, a third molecularly oriented adhesive layer, of nylon, a fourth Milwaukee-laxly oriented adhesive layer, a fifth molecularly oriented layer comprising a polyethylene or a blend of ethylene polymers, a sixth molecularly oriented adhesive layer, and a seventh mole-ularly oriented sealant layer. The fourth and sixth layers come pulse car boxy moieties In an ethylene based polymeric structure;
and most preferably, the composition of the fourth and sixth lay-ens Is modified medium density polyethylene (MMDPE) and the fifth layer comprises high density polyethylene (HYPE). Desirably the composition of the seventh layer Is chosen from the group con-slstlng of monomer, linear low density polyethylene (LLDPE), lowdenslty polyethylene (LOPE) and ethylene vinyl acetate copolymer (EVA) having up to 18 weight percent vinyl acetate (VA).
In a similar structure, the first, second, and third layers all comprise nylon and are effectively a single layer.
Under normal mlscroscoplc observation, the layer Interfaces Join-lung these three layers In this structure are nonexistent In any of the structures recited above, and In combine-lions thereof, cereal advantages are achieved wherein the second layer comprises an blend of nylon and EVE.
Certain novel aspects of the Invention also reside In a method of mulling an unbalanced, oriented, multiple layer polyp Merle film wherein the Interfaclal adhesion at each layer Inter-face Is at least 150 grams per Inch width, the film having a I
.
, ~24~24~
first polymeric surface layer of nylon on one surface thereof and a second polymeric surface layer of a heat sealable ethylene polymer, or copolymer on the other surface thereof. The novel method of orientation commences with the step of prattling each of the respective surfaces to separately preselected tempera-lures, the preselected temperature of the surface of the second surface layer being between 10F. and 60F. below the heat seal-lung temperature of the second surface layer, the preselected temperature of the surface of the first surface layer being between Sophie. and 230F. After the surfaces are preheated, the preheated film Is stretched, the stretched film Is annealed, and finally the annealed film Is cooled.
A particularly advantageous embodiment of the method Is one wherein the surfaces are heated by passing a continuous sheet of the film over a series of heated rollers. The sheet passes over the heated rollers In such a configuration that each roller contacts only one surface of the film, and the temperature Of each roller Is controlled so as to apply an appropriate tempera-lure to the surface so contacted. When the film surfaces reheated to the proper temperature, the film Is then stretch off-enter In the machining direction.
Preferably, the annealing Is done by application of heat to the nylon surface layer, since It Is less physically affected by the heat than the other surface layer.
The present Invention will be further Illustrated by way of the accompanying drawings, In which:-Figure 1 Is a cross-sectlon of a representative 7 layer film of the Invention; and Figure 2 Is an outline of a representative fine of pro-swizzling equipment for carrying out the orientation of multiple layer films of the Invention.
` Referring now to Figure 1, the overall film Is deslg-noted by the numeral 10. Layer 12 Is nylon. Layer 14 Is a bar-ruler layer of either nylon, EVE, or a blend of nylon and EVE.
Layer 16 Is nylon. Layer 18 Is an adhesive polymer. Layer 20 IS
an ethylene polymer or copolymer or a blend of ethylene polymers.
Layer 22 Is an adhesive polymer. Layer 24 Is a heat sealable layer which may be so I acted with substantial Independent Judge-mint, depending on Its adhesion requirements to the specific come position of layer 22 and the desired heat scaling temperature.
Referring now to Figure 2, the overall layout of the equipment and film Is designated 108. The layout Includes an unwind station 109 from which Is unwound a roll 112 of if It AYE.
The film first passes over a turning roll 114, from there to a f First preheat roll 116, and thence Is wound over a series of heated rolls 118, 120, 122, 124, 126 and 128. The f I It Is stretch oriented between rolls 120 and 122 as Indicated by the designation 110B for the stretched f I Imp The stretched film Is annealed on roll 130 and then cooled on roll 132. Finally, the 20 stretched film 110B Is wound up as a roll 134 on windup station 136.
Upon examination of the overall nature of the film hereinabove described, it Is seen that there are disclosed seven layer films having the combination of at least six layers, and In most cases, all seven of the layers molecularly oriented, and wherein dlsslmllar polymeric material structures :
- ~.24~7 - -are associated with the several layers. More specifically, not all the layers of the films of this invention need be derivatives of the same family, e.g. polyethylene, polypropylene, or even polyolefins. Further, the compositions of the several layers need not have similar melt flow properties 90 long as they are compatible for a coextrusion process. Neither is it necessary, and indeed it is not desired, that any of the layers melt during the orientation process, as melting of any given layer would preclude true molecular orientation of that layer. From the perspective of desired physical properties of the overall film, it is generally preferred that all the layers be molecularly oriented. For reasons of facilitating construction of some members of the family of films of the invention, the sealant layer may, or may not, be oriented. For example, in some cases it is preferred to coextrude all the layers of the film except the sealant layer, and to orient the so coextruded multiple layer film. After orientation, the sealant layer, erg. layer 24 is then added -- for example by solution coating, by extrusion coating, extrusion lamination, or by heat and pressure lamination of a previously formed film.
Other conventional means of adding a sealant layer to a separately formed film are also contemplated.
Definitions- Certain terms used herein require some elan-ligation as to the intended meaning in order to preclude possible confusion as to their significance.
Throughout this teaching, the films of the invention are described as being "unbalanced". Unbalanced refers to the relationships of physical and chemical properties of the polymers relative to the symmetry, or lack thereof, of the lo film cross-section. In a generally balanced film the properties will be at least similar as one progresses from the two outside surfaces of the film toward the center of the film cross-section. Referring to a seven layer balanced film, which could be represented by the structure shown in FIGURE 1 though it is not intended herein to represent that inventive films illustrated by FIGURE 1 are balanced), the outer layers such as 12 and 24 would have similar properties, and the next pair of layers such as 14 and 22 would have similar properties and so on. the similarities in a balanced film usually are both chemical, e.g. polymeric structure and composition; and physical, e.g. melting properties, rheology of fluid flow, heat seal temperature, vapor permeation rates and the like. In unbalanced films, and now referring to the inventive films represented by FIGURE 1, the outer layers, layers 12 and 24 are dissimilar in at least some properties, usually both chemical properties and physical properties. For example, layer 24 is usually an ethylene polymer or copolymer and has lower melting temperature and lower heat sealing temperature than the nylon of layer 12.
Layers 14 and 22 are normally not similar. their selection is based primarily on their individual functional purposes within the film, and not on their similarities to each other.
Layer 14 it a barrier layer. Layer 22 is an adhesive layer.
Like dissimilar comparisons can be made with the other corresponding pairs of film layers.
The term "car boxy moieties" refers to a plurality of functional group derivatives of carboxylic acids in the compound which include components such as Jo -o R - C - o - Al or O O
if if R - C - O - C - Al Illustrative of such car boxy structures are organic acids and acid salts, esters, and androids.
The term "molecularly oriented" refers to the rearrange-mint of polymeric film by any process which simultaneously reduces the film thickness and elongates its dimension in at least one direction; all while the film is in a heated, but unmelted state. Specifically, "molecular orientation"
does not include those processes that stretch the polymer when it is in a softened state, such as in blow-molding.
The phrase "heat sealing temperature" refers to that temperature, or range of temperatures at which films of certain polymers are susceptible to being sealed to themselves in face-to-face relationship by application of heat and pressure in conventionally known manner.
The term "annealing" refers to a step of temporarily holding a film at an elevated temperature under controlled levels of tension. This known process provides a degree of stability to a stretched film after it is cooled and improves performance characteristics.
Returning now to the invention in detail, layers 12 and 16 are advantageously nylon, and provide toughness and stiffness to the film. Nylon 6 is preferred. Modified nylon 6 has also been found particularly desirable. Where stiffness of the overall film structure is less important, nylon 666 may be used too Less preferred, but acceptable is nylon 12.
Toe crucial property of the nylon in all cases is its _ g _ 12~Z47 capability to be coextruded in a 3-layer sub-combination as layers 12, 14, and 16. Thus the desirable properties of layers 12 and 16 alone must be considered in view of the anticipated composition of layer 14. Layer 12 should exhibit thermal stability under heat sealing conditions, and may contain surface modifying additives, such as slip and anti-block agents.
Layer 14 serves as a barrier to transmission of oxygen through the film. Acceptable barrier layer materials are EYE, nylon, and blends of EVE and nylon. Preferred compositions are EVE. When blending is practiced, blends containing at least 50~ EVE are preferred to effect improved barrier to transmission of oxygen through the film.
The finally selected composition of layer 14 is at times a compromise between the better oxygen barrier provided by EVE, the lower cost attributed to a blend of nylon and EVE, and the still lower cost of plain nylon. Skipping, for the moment, over layer 18, let us deal next with layer 20.
The composition of layer 20 is chosen for one or more of the functions of (1) moisture barrier, and (2) physical strength in a relatively thick, economical layer. The preferred material for layer 20 is HYPE. HYPE provides an effective moisture vapor barrier at an economical cost.
Other alternative materials for layer 20 are medium density polyethylene (MOPE), LOPE, LLDPE and blends of LLDPE with MOPE or HYPE and blends of MOPE with HYPE. The moisture barrier properties and cost vary, depending on the polymer selected, and the thickness of layer 20.
Layer 24 is a heat sealable layer. Its preferred composition is Surly monomer which, in oriented form, has a heat sealing temperature of about 210F. Another acceptable lZ~247 composition Is LLDPE, why I ah has a higher heat scaling temperature of about 260F . Other acceptab I e compositions are LOPE and EVA
having up to 18 weight percent VA. Above 18% VA, the surface of layer 24 Is tacky and requires use of excessive amounts of slip and antl-block additives. Other conventionally heat sealable materials may be chosen for fulfilling specific f I I m design parameters. Slip and antl-block additives are commonly used with all the layer 24 compositions, In amounts of about 5% by weight of the layer composition, though higher percentages are contem-plated. A typical slip and antl-block agent Is sold as a concern-irate under the trademark COMPEL 8719-3 by Dupont Company.
The most common problem In producing oriented multiple layer films of the nature disclosed heroin Is serious reduction, or failure of adhesion at the layer Interfaces. In the struck lures disclosed heroin, the Interface most sensitive to adhesion problems Is the Interface between layers 22 and 24.
Now that layers 16,20 and 24 have been defined, It Is appropriate to discuss adhesive polymer layers 18 and 2Z; for their selection can only be made In fight of the anticipated come positions selected for layers 16,20 and 24. For use as adhesive layers, the polymers must contain car boxy moieties and preferably contain functional group derivatives of carboxyllc colds and preferably anhydrlde derivatives. Moderate amounts of process experimentation are required with any new potential adhesive polymer In order to achieve acceptable levels of adhesion. This experimentation Is required because all acceptable adhesive polyp mews are modified oleflns, but not all modified oleflns are lung-tonally acceptable adhesive polymers In a given film structure when applied by one specific set of processing conditions.
The most successful adhesive polymer known to the Inventors for use In the preferred structure Is a modified medium density polyethylene sold by Mltsul Company under the trademark Adder NF500. NF500 retains minimum levels of adhesion of about lZ~4~
grooms per Inch width, and typical adhesion levels are around 300 grams per Inch. Other adhesives found acceptable with spew clflc compositions of layers 16,20 and 24 are modified low den-sty polyethylene.
In producing the oriented films of this Invention the selected polymers are first coextruded as a seven sometimes slicks layer film, and cooled, to yield a base film, unorlented. In coextruslon of the base film as, for Instance, a seven layer film, the melted polymer streams which subsequently form the seven layer film are first combined as three sub-comblnatlon melt streams as follows. Layers 12, 14 and 16 form one sub-comblna-lion. Layers 18, 20 and 22 form a second sub-comblnatlon. Layer 24 as a single stream Is the third sub-combinatlon. Particularly addressing the first and second sub-comblnatlon melt streams, It Is Important that the melt flow theological characteristics of the polymer streams within each sub-comblnatlon be compatible with each other to achieve acceptable coextruslve processing of the respective sub-comblnatlon to form the desired layers.
Preferably the nylon has a melt Index of about 9, and the HYPE
has a melt Index of about 3. The sub-comblnatlons are kept physically separated from each other up to and during formation of the sheetlike layer structuring of the Individual layers In each sub-comblnatlon. This physical separation of the sub-combinations permits separate control of the thermal envlronmentof each sub-comblnatlon. The sub-comblnatlons ' - 12 .
lz4~ ~47 are finally joined to form the seven layer film just before exiting the die. After exiting the die, the film is cooled.
While the cooled seven layer film may be immediately oriented in an in-line operation, it is entirely acceptable to wind up the film for subsequent orientation in a separate process such as the one outlined in FIGURE 2. Uniaxial orientation in the machine direction is generally preferred.
In understanding the process of the invention, it is significant to understand that the composition defined for sealant layer 24 responds to thermal stimuli at a sub-staunchly lower temperature than other layers of the film and particularly the layer 12. Significantly, the inventors have found that by applying heat to each surface separately, and at a temperature selected to be compatible with the orientation of the composition of that layer and all the interior layers, and by applying that heat to each surface for a moderate period of time, the multiple layer films of this invention may be oriented; and indeed, an unbalanced film hazing up to seven layers and wherein the several layers need not be derived from the same polymer family, can be molecularly oriented without necessarily incurring splitting, pin-holing, or softening of any one layer.
It is significant to note that, with the number of layers in the invention reaching as high as seven, selection ox the proper combination of polymers and layer thicknesses, compatible to simultaneous orientation, is a delicate task, requiring significant technical skill. With each considered increase in the number of layers to be simultaneously oriented, the complexity of selections of proper compositions and processing conditions is increased significantly. Thus, for example, layers 16, 18, and 20 are susceptible to trays-.
mission of heat from both surfaces ox the film -- those surfaces being on layers 12 and 24 -- and depending on the thickness and composition ox each layer, and the thickness of the overall film, the processing conditions, including temperatures, orientation ratios and line speeds are adjusted to achieve successful orientation.
Advantageously, as the amount of stretch achieved is increased, while maintaining adequate levels of inter layer adhesion, the desirable properties of the film are enhanced.
Disadvantageously, however, as the amount of stretch is increased, the adhesions at certain of the interfaces decreases. Thus, the selection of the best orientation ratio for any given film is dependent upon the specific film structure and the inter layer adhesion levels required by the intended end use of the film. For most packaging applications, interlocks adhesion levels must be at least 70 grams per inch width, as measured by ASTM D903. For films contemplated by this invention, and considering the adhesion levels required, satisfactory orientation ratios are normally between 2.~/1 and 4/1; with the preferred ratio being 3/1. The lower orientation ratios generally apply to structures having EVE
in layer 14 and wherein all the layers are simultaneously oriented. the higher orientation ratios are achieved wherein the layer (14) contains some nylon.
The heat applied to each of the surface layers, e.g. 12 and 24, is applied to the surface layers as they alternate contacting alternative ones of the temperature-controlled rolls.
As an illustration, consider the processing through equipment of FIGURE 2 of a typical film as in FIGURE 1, wherein layer 14 is EVE, layer 24 is Surly, and layer 20 ;24~3Z47 is HYPE. Layer thicknesses of this "typical structure" are given in following Table 1. The film Lola is unwound from unwind station lo at a speed of 60 to 80 feet per minute with the sealant layer 24 on the bottom surface of the film such that the sealant layer contacts the turning roll 114, which is kept at room temperature, or about 20C. The film then progresses to the first preheat roll 116 which is temperature controlled at a critical minimum temperature of at least awoke., and where layer 12 is against roll 116 lo and receives initial preheating. At the next preheat roll, ~18, which it temperature controlled at 70C, the sealant layer 24 contacts the preheat roll, and receives its initial direct-contact preheating. Layer 12 receives additional preheating at roll 120 which is temperature controlled at 90C. The film is then stretched between rolls 120 and 122.
This it accomplished by driving roll 122 faster than roll 120 and controlling the difference in drive speeds to effect the desired amount of stretch, hereinafter referred to as the orientation ratio -- that being the fractional ratio of the driving speeds of the rolls 120 and 122. In this illustration, then, typical machine speeds during and after stretching are on the order of 180 to 320 feet per minute.
After the film is stretched between rolls 120 and 122, it it designated lob, as shown between rolls 122 and 124.
Roll 124 is again temperature controlled, in this illustration at 90C., the same as roll 120. Roll 122 is temperature controlled at 70C., the same as roll 118. Rolls 126 and 128 are controlled at 80C~ The film is then annealed by contacting annealing roll 130, which roll is temperature controlled at 80C. After annealing, the film is cooled by chill roll 132 to less than 40~C., and is subsequently I '!Z4'7 wound up on a roll 134 at wind up station 136.
In terms of heating contact time, the film is in contact with preheat roll 116 for about 1.8-4 seconds, and rolls 118 and 120 for about 0.9-3.2 seconds each. Contact time on rolls 122, 124, 126, and 128 is about 0.3-0.8 seconds each.
Contact time on rolls 130 and 132 is about 0.6-1.0 second, Also significant to the process is good control of the film speed and contact on all rolls at all stages of the operation.
Thus nip rolls 140 are used at several locations along the processing line as shown in FIGURE 2.
As described briefly earlier herein, the layers which are primarily responsible for the physical properties of the film are layers 12, 14, 20 and 24. Layers 16, 18, and 22, on the other hand, serve primarily the functions of facilitating processing and providing inter layer adhesion. To meet the specific needs of a particular packaging use, the proportions of layers 12, 14, 20 and 24 can be adjusted somewhat; and usually the final structure is a compromise of properties which best meets the needs of the use while keeping the film cost competitive. Where stiffness is a major concern, the amount of layer 12, or layer 20, as a proportion of the film, is increased. Where oxygen barrier as measured by ASTM D-3985 is a concern, either the composition of layer 14 is adjusted or the amount of layer 14 is increased. Where water vapor transmission through the film, as measured by ASTM F-372 is a major concern, the amount of HYPE in layer 20 is increased.
Where the heat seal properties of the film are critical, or are particularly sensitive, for example because of the product willing operations, the amount of the heat seal layer 24 is increased, or its composition is adjusted.
Considering that the overall thickness of the film is lZ~UZ47 somewhat predetermined my the type of packaging contemplated, and by the cost limitations, and considering that some polymers in the structure are more expensive than others, and that minimum amounts of each layer are required for minimal layer functionality, there exists a generally defined range of proportions which is acceptable for each of the seven layers.
xpresse~ in terms of the percentage of the thickness of the overall film, for a 1.0 mix oriented film, the approximate minimum functional thickness of each layer is shown in Tale 1, along with examples of representative film structures.
_ .
Minimum Typical Heat Seal High WVTR Low Lever Thickness Structure Emphasis Barrier Cost _ _ 12 10% 20% I 10% 10%
14 5% 8% 7% 7% 5%1 16 3% 5% 3% 3%
18 5% 5% 5% 5%
20% 20% 20% 4%3 40~2 22 5% 5% 5% 5%
24 25% 37% 50% 30% 30~4 Total Thickness% 100% 100% 100% 100%
Represented 1. Nylon
2. LOPE
3. HYPE
4. EYE% VA
In the structures shown in Table 1, layers 12 and 16 are nylon in all structures. Layer 14 is EVE or nylon-EVOH
blend except as noted. Layers 18 and 22 are car boxy modified medium density polyethylene. Layer 20 is any of the 124~
polyethylene except as noted. Layer 24 is Surlyn/ionomer with by weight slip anti-block additive concentrate, except as noted.
In light of the foregoing description of the several layers, it is seen that the structures of Table 1 are illustrative only, and that additional specific structures are contemplated by the foregoing description. For example, different minimum layer thicknesses may be defined for films of a different thickness or for films made by a different process, i.e. extrusion coating layer 24. As the composition and proportions of the various layers are changed, processing parameters must likewise be changed. Particularly sensitive are the temperatures of rolls 118, 120, 122, and 124. For example, in the Table 1 structure labeled "High ~VTR Barrier", the increased amount of layer 20 HYPE as a proportion of the film requires that more heat be applied to that layer during the orientation process. Since layer 24 is sensitive, as a heat sealable layer, to increased amounts of heat, the higher heat required by layer 20 cannot be supplied through layer 24, but must, rather, be supplied through layers 12-18.
Thus, when high proportions of HYPE are used in layer 20, the temperature must be increased in the preheating rolls which contact layer 12. Specifically, the temperature of rolls 120 and 124 is typically raised to 110C., rather than the more typical 90C., to achieve successful orientation.
The temperature of roll 116 may also be raised.
The limitations on applying heat through layer 24 are functionally determined by the temperature at which polymer material from layer 24 sticks to one or more of the rolls which-it contacts, and particularly rolls 118 and 122.
Typically acceptable temperatures for rolls 118 and 122 are 70 -85 C.
In designing a specific process: run, temperatures on rolls 118 and 122 are held as high as possible without incurring sticking ox layer 24. The temperatures of rolls 120 and 124 are then adjusted to provide at least the minimal amount of heat to encourage successful orientation of the film structure.
A typical temperature range for the first preheat roll to contact layer 12, namely roll 116, is 70 to 100C.
Rolls 120 and 124 typically operate within the range of 90 to 110C.
Rolls 126 and 128 are optional in the processing line.
When used, they are typically held at about kiwi the preferred functional nature of rolls 126 and 128 being such that they are held at the maximum temperature possible without having layer 24 stick.
The annealing roll 140 is also held at about 80C.
The following structures are specific examples of films of this invention. A slash line represents a layer surface. The percentage numbering in each example represents the percentage of the thickness of that layer compared to the thickness of the entire film.
1 nylon 6/EVOH/Nylon 6/NF500/LDPE/NF500/Surlyn/
B
20% 8% 5% 5% 20% 5% 37%
2 nylon 6/EVOH/Nylon 6/NF500/LDPE/NF500/Surlyn/
20% 8% 5% 5% 20% 5% 37%
3 nylon 6*/NF500/HDPE/NF500/LLDPE/
33% 5% 20% 5% 37%
10 4 95% Syrian nylon 6/EVOH/Nylon 6/NF500/HDPE/NF500/ 5% Compel 8719-3/
20% 8% 5% 5% 20% 5% 37%
95% Syrian .
nylon 6/EVOH/Nylon 6/NF500/HDPE/NF500/ 5% Compel 8719-3/
10% 8% 3% 5% 32% 5% 37%
6 95% Syrian 1601 nylon 6/EVOH/Nylon 6/NF500/HDPE/NF500/ 5% Compel 8719 3/
10% 8% 3% 5% 50% 5% 1g%
20 7 nylon 6/EVOH/Nylon 6/chemplex/HDpE/chemplex/95% 1601B
2467** A 2467** B 5% 8719-3/
20% I 5% 20% 5% 37%
8 Lyon 6*/NF500/HDPE/NF500/SurIyn/
Thus represents 3 nylon streams which lose their Interfaclal Identify when they are Joined.
Y*Chemplex 2467 Is a trademark for an adhesive polyolefln polymer available from Complex Company, Roiling Meadows, Illinois.
Table 2 shows slgnlflcant measurements and properties of the above eight example films, which films were made according to the disclosed process principles, and oriented In the with-machine direction.
, . ; . I, Table 2 . _ Thickness, mulls, Interfaclal* Strength WVTR
Example Stretch After Adhesion ASSUME D-1922 90% RHO
No. Ratio orientation inch width MD CUD 100F.
1 3.0 1.4 AIL CONS 60 1~9 No 2 3.6 1.4 B:350 92-216 106 No PA 3.5 1.5 B:242 No No 0.57 3B 4.0 1.4 Blue No No 0.63 3C 4,5 1.3 B:175 I No 0.64 4 3.0 1.5 C:343 64-236 134 0.72 3.0 1.6 C:263 No No 0.38 6 3.0 1.6 C:305 No No 0.30 7 3.0 1. 2 A: 106 NO. NO Owe B:42-146 8 3.0 1. 5 B:262 477 83 0.77 L _ I _ *All layers could not be separated (CONS) except those noted NO = Data not available Surprising data are seen in the MD Tear Strengths of Examples 2 and 4. During the MD tear tests, which are performed according to ASTM D-1922, it is observed that the tear is initiated in the machine direction at a moderate level of force. During propagation of the tear, the tear direction changes, of its own accord, to a diagonal direction and the force required to continue the tearing process increases substantially, as seen by the data in Table 2, Examples 2 and 4. Indeed, in both cases the final MD tear strength exceeds the CUD tear strength, a highly unusual property in a uniaxially oriented film.
Thus it is seen that the invention provides a multiple layer packaging film material which has up to seven layers, including nylon as an outer layer thereof. The film is lZ4~3Z47 economically competitive to make by coextrusion and sub-sequent orientation of the entire cross-section thickness of the film all at one time. it has a combination of desirable attributes including, as functional physical properties, high inter layer adhesion, good tear strengths, and high barrier to gaseous transmission through the film; and as available perceived properties, high gloss, transparency, and stiffness.
on the examples illustrated herein, the film has been lo oriented so that layer 24 it on the bottom of the film and thus made the first roll contact at roll 114, while layer 12 has been up, first contacting a roll at roll 116. The invention may likewise be practiced with the film inverted, so that lazes 24 is up and layer 12 is down. In this event, roll temperatures are adjusted accordingly, for the layers contacted. Advantageously, annealing roll 130 it then operated at a higher temperature of 115C. or move, desirably improving the heat-set characteristics of the film,
In the structures shown in Table 1, layers 12 and 16 are nylon in all structures. Layer 14 is EVE or nylon-EVOH
blend except as noted. Layers 18 and 22 are car boxy modified medium density polyethylene. Layer 20 is any of the 124~
polyethylene except as noted. Layer 24 is Surlyn/ionomer with by weight slip anti-block additive concentrate, except as noted.
In light of the foregoing description of the several layers, it is seen that the structures of Table 1 are illustrative only, and that additional specific structures are contemplated by the foregoing description. For example, different minimum layer thicknesses may be defined for films of a different thickness or for films made by a different process, i.e. extrusion coating layer 24. As the composition and proportions of the various layers are changed, processing parameters must likewise be changed. Particularly sensitive are the temperatures of rolls 118, 120, 122, and 124. For example, in the Table 1 structure labeled "High ~VTR Barrier", the increased amount of layer 20 HYPE as a proportion of the film requires that more heat be applied to that layer during the orientation process. Since layer 24 is sensitive, as a heat sealable layer, to increased amounts of heat, the higher heat required by layer 20 cannot be supplied through layer 24, but must, rather, be supplied through layers 12-18.
Thus, when high proportions of HYPE are used in layer 20, the temperature must be increased in the preheating rolls which contact layer 12. Specifically, the temperature of rolls 120 and 124 is typically raised to 110C., rather than the more typical 90C., to achieve successful orientation.
The temperature of roll 116 may also be raised.
The limitations on applying heat through layer 24 are functionally determined by the temperature at which polymer material from layer 24 sticks to one or more of the rolls which-it contacts, and particularly rolls 118 and 122.
Typically acceptable temperatures for rolls 118 and 122 are 70 -85 C.
In designing a specific process: run, temperatures on rolls 118 and 122 are held as high as possible without incurring sticking ox layer 24. The temperatures of rolls 120 and 124 are then adjusted to provide at least the minimal amount of heat to encourage successful orientation of the film structure.
A typical temperature range for the first preheat roll to contact layer 12, namely roll 116, is 70 to 100C.
Rolls 120 and 124 typically operate within the range of 90 to 110C.
Rolls 126 and 128 are optional in the processing line.
When used, they are typically held at about kiwi the preferred functional nature of rolls 126 and 128 being such that they are held at the maximum temperature possible without having layer 24 stick.
The annealing roll 140 is also held at about 80C.
The following structures are specific examples of films of this invention. A slash line represents a layer surface. The percentage numbering in each example represents the percentage of the thickness of that layer compared to the thickness of the entire film.
1 nylon 6/EVOH/Nylon 6/NF500/LDPE/NF500/Surlyn/
B
20% 8% 5% 5% 20% 5% 37%
2 nylon 6/EVOH/Nylon 6/NF500/LDPE/NF500/Surlyn/
20% 8% 5% 5% 20% 5% 37%
3 nylon 6*/NF500/HDPE/NF500/LLDPE/
33% 5% 20% 5% 37%
10 4 95% Syrian nylon 6/EVOH/Nylon 6/NF500/HDPE/NF500/ 5% Compel 8719-3/
20% 8% 5% 5% 20% 5% 37%
95% Syrian .
nylon 6/EVOH/Nylon 6/NF500/HDPE/NF500/ 5% Compel 8719-3/
10% 8% 3% 5% 32% 5% 37%
6 95% Syrian 1601 nylon 6/EVOH/Nylon 6/NF500/HDPE/NF500/ 5% Compel 8719 3/
10% 8% 3% 5% 50% 5% 1g%
20 7 nylon 6/EVOH/Nylon 6/chemplex/HDpE/chemplex/95% 1601B
2467** A 2467** B 5% 8719-3/
20% I 5% 20% 5% 37%
8 Lyon 6*/NF500/HDPE/NF500/SurIyn/
Thus represents 3 nylon streams which lose their Interfaclal Identify when they are Joined.
Y*Chemplex 2467 Is a trademark for an adhesive polyolefln polymer available from Complex Company, Roiling Meadows, Illinois.
Table 2 shows slgnlflcant measurements and properties of the above eight example films, which films were made according to the disclosed process principles, and oriented In the with-machine direction.
, . ; . I, Table 2 . _ Thickness, mulls, Interfaclal* Strength WVTR
Example Stretch After Adhesion ASSUME D-1922 90% RHO
No. Ratio orientation inch width MD CUD 100F.
1 3.0 1.4 AIL CONS 60 1~9 No 2 3.6 1.4 B:350 92-216 106 No PA 3.5 1.5 B:242 No No 0.57 3B 4.0 1.4 Blue No No 0.63 3C 4,5 1.3 B:175 I No 0.64 4 3.0 1.5 C:343 64-236 134 0.72 3.0 1.6 C:263 No No 0.38 6 3.0 1.6 C:305 No No 0.30 7 3.0 1. 2 A: 106 NO. NO Owe B:42-146 8 3.0 1. 5 B:262 477 83 0.77 L _ I _ *All layers could not be separated (CONS) except those noted NO = Data not available Surprising data are seen in the MD Tear Strengths of Examples 2 and 4. During the MD tear tests, which are performed according to ASTM D-1922, it is observed that the tear is initiated in the machine direction at a moderate level of force. During propagation of the tear, the tear direction changes, of its own accord, to a diagonal direction and the force required to continue the tearing process increases substantially, as seen by the data in Table 2, Examples 2 and 4. Indeed, in both cases the final MD tear strength exceeds the CUD tear strength, a highly unusual property in a uniaxially oriented film.
Thus it is seen that the invention provides a multiple layer packaging film material which has up to seven layers, including nylon as an outer layer thereof. The film is lZ4~3Z47 economically competitive to make by coextrusion and sub-sequent orientation of the entire cross-section thickness of the film all at one time. it has a combination of desirable attributes including, as functional physical properties, high inter layer adhesion, good tear strengths, and high barrier to gaseous transmission through the film; and as available perceived properties, high gloss, transparency, and stiffness.
on the examples illustrated herein, the film has been lo oriented so that layer 24 it on the bottom of the film and thus made the first roll contact at roll 114, while layer 12 has been up, first contacting a roll at roll 116. The invention may likewise be practiced with the film inverted, so that lazes 24 is up and layer 12 is down. In this event, roll temperatures are adjusted accordingly, for the layers contacted. Advantageously, annealing roll 130 it then operated at a higher temperature of 115C. or move, desirably improving the heat-set characteristics of the film,
Claims (15)
1. An unbalanced multiple layer polymeric film wherein the interfacial adhesion at each layer interface is at least 50 grams per inch width, the layers comprising, in order through the film:
(a) a first molecularly oriented layer of nylon;
(b) a second molecularly oriented layer whose composition is selected from the group consisting of nylon, ethylene vinyl alcohol copolymer, and blends of nylon and ethylene vinyl alcohol copolymer;
(c) a third molecularly oriented layer of nylon;
(d) a fourth molecularly oriented polymeric adhesive layer having carboxy moieties in the polymeric structure;
(e) a fifth molecularly oriented layer comprising a polyethylene or a blend of ethylene polymers;
(f) a sixth molecularly oriented polymeric adhesive layer having carboxy moieties in the polymeric structure; and (g) a seventh sealant layer.
(a) a first molecularly oriented layer of nylon;
(b) a second molecularly oriented layer whose composition is selected from the group consisting of nylon, ethylene vinyl alcohol copolymer, and blends of nylon and ethylene vinyl alcohol copolymer;
(c) a third molecularly oriented layer of nylon;
(d) a fourth molecularly oriented polymeric adhesive layer having carboxy moieties in the polymeric structure;
(e) a fifth molecularly oriented layer comprising a polyethylene or a blend of ethylene polymers;
(f) a sixth molecularly oriented polymeric adhesive layer having carboxy moieties in the polymeric structure; and (g) a seventh sealant layer.
2. An unbalanced multiple layer film as in Claim 1 wherein said seventh sealant layer is molecularly oriented.
3. An unbalanced film as in Claim 1 wherein said first, second, and third layers all comprise nylon and are effectively a single layer.
4. An unbalanced film as in Claim 1 wherein the compositions of the polymers in said fourth and sixth layers comprise medium density polyethylene.
5. An unbalanced film as in Claim 1 wherein the composition of said fifth layer comprises high density polyethylene.
6. An unbalanced multiple layer film as in Claim 1 wherein the composition of said sealant layer is chosen from the group consisting of ionomer, linear low density polyethylene, low density polyethylene, and ethylene vinyl acetate copolymer having up to 18 weight percent vinyl acetate.
7. An unbalanced, molecularly oriented, multiple layer film wherein the interfacial adhesion at each layer interface is at least 150 grams per inch width, the layers comprising, in order through the film:
(a) a first layer of nylon;
(b) a second layer whose composition is selected from the group consisting of nylon, ethylene vinyl alcohol copolymer, and blends of nylon and ethylene vinyl alcohol copolymer;
(c) a third layer of nylon;
(d) a fourth adhesive layer whose composition is a medium density polyethylene having carboxy moieties in the polymeric structure;
(e) a fifth layer whose composition comprises high density polyethylene and, optionally, additives such as color concentrates and processing aids;
(f) a sixth adhesive layer whose composition is a medium density polyethylene having carboxy moieties in the polymeric structure; and (g) a seventh sealant layer.
(a) a first layer of nylon;
(b) a second layer whose composition is selected from the group consisting of nylon, ethylene vinyl alcohol copolymer, and blends of nylon and ethylene vinyl alcohol copolymer;
(c) a third layer of nylon;
(d) a fourth adhesive layer whose composition is a medium density polyethylene having carboxy moieties in the polymeric structure;
(e) a fifth layer whose composition comprises high density polyethylene and, optionally, additives such as color concentrates and processing aids;
(f) a sixth adhesive layer whose composition is a medium density polyethylene having carboxy moieties in the polymeric structure; and (g) a seventh sealant layer.
8. A method of making an unbalanced, oriented, multiple layer polymeric film from a previously formed unoriented film having a first polymeric surface layer of nylon on one surface thereof and a second polymeric surface layer of a heat seal-able ethylene-based polymer or copolymer on the other surface thereof, the method-comprising the steps of: (a) pre-heating each of said surfaces to separately pre-selected temperatures, the pre-selected temperature of the surface of said second surface layer being between 10°F. and 60°F. below the heat sealing temperature of said second surface layer, the pre-selected temperature of the surface of said first surface layer being between 150°F. and 230°F.; (b) stretching the pre-heated multiple layer film; (c) annealing the stretched film;
and (d) cooling the annealed film.
and (d) cooling the annealed film.
9. An unbalanced multiple layer polymeric film hav-ing two outer surfaces, and wherein the interfacial adhesion at each layer interface is at least 50 grams per inch width, the layers comprising, in order through the film: (a) a first molecularly oriented layer of nylon; (b) a second molecularly oriented layer whose composition is selected from the group consisting of nylon, ethylene vinyl alcohol copolymer, and blends of nylon and ethylene vinyl alcohol copolymer; (c) a third molecularly oriented layer of nylon; (d) a fourth mole-cularly oriented polymeric adhesive layer having carboxy moi-eties in the polymeric structure; (e) a fifth molecularly ori-ented layer comprising a polyethylene or a blend of ethylene polymer;s (f) a sixth molecularly oriented polymeric adhesive layer having carboxy moieties in the polymeric structure; and (g) a seventh heat sealant layer; orientation of said film having been accomplished by applying heat directly to each of said outer surfaces in different amounts, thus creating a tem-perature differential between said surfaces, and effecting said orientation during the existence of said temperature dif-ferential.
10. An unbalanced multiple layer film as in claim 9 wherein said seventh sealant layer is molecularly oriented.
11. An unbalanced film as in claim 1 wherein said first, second, and third layers all comprise nylon and are effectively a single layer.
12. An unbalanced film as in claim 1 wherein the compositions of the polymers in said fourth and sixth layers comprise medium density polyethylene.
13. An unbalanced film as in claim 1 wherein the composition of said fifth layer comprises high density polyethylene.
14. An unbalanced multiple layer film as in claim 1 wherein the compositions of said sealant layer is chosen from the group consisting of ionomer, linear low density polyethy-lene, low density polyethylene, and ethylene vinyl acetate copolymer having up to 18 weight percent vinyl acetate.
15. An unbalanced molecularly oriented multiple layer film having two outer surfaces, and wherein the interfa-cial adhesion at each layer interface is at least 150 grams per inch width, the seven sequential layers comprising, in order through the film: (a) a first layer of nylon; (b) a second layer whose compositions is selected from the group consisting of nylon, ethylene vinyl alcohol copolymer, and blends of nylon and ethylene vinyl alcohol copolymer; (c) a third layer of nylon; (d) a fourth adhesive layer whose compo-sition is a medium density polyethylene having carboxy moi-eties in the polymeric structure; (e) a fifth layer whose com-position comprises high density polyethylene; (f) a sixth adhesive layer whose composition is a medium density polyethy-lene having carboxy moieties in the polymeric structure; and (g) a seventh heat sealant layer; orientation of said film having been accomplished by applying heat directly to each of said outer surfaces in different amounts, thus creating a tem-perature differential between said surfaces, an effecting said orientation during the existence of said temperature dif-ferential.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000456179A CA1240247A (en) | 1984-06-08 | 1984-06-08 | Unbalanced oriented multiple layer film |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000456179A CA1240247A (en) | 1984-06-08 | 1984-06-08 | Unbalanced oriented multiple layer film |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1240247A true CA1240247A (en) | 1988-08-09 |
Family
ID=4128064
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000456179A Expired CA1240247A (en) | 1984-06-08 | 1984-06-08 | Unbalanced oriented multiple layer film |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1240247A (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2010009245A3 (en) * | 2008-07-18 | 2010-04-29 | Alcan Packaging Flexible France | Polyamide structures for the packaging of moisture containing products |
| US9498936B2 (en) | 2003-03-07 | 2016-11-22 | Coveris Flexibles Us Llc | Multilayer barrier structures, methods of making the same and packages made therefrom |
| US9498937B2 (en) | 2003-03-07 | 2016-11-22 | Coveris Flexibles Us Llc | Multilayer structures, packages, and methods of making multilayer structures |
-
1984
- 1984-06-08 CA CA000456179A patent/CA1240247A/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US9498936B2 (en) | 2003-03-07 | 2016-11-22 | Coveris Flexibles Us Llc | Multilayer barrier structures, methods of making the same and packages made therefrom |
| US9498937B2 (en) | 2003-03-07 | 2016-11-22 | Coveris Flexibles Us Llc | Multilayer structures, packages, and methods of making multilayer structures |
| WO2010009245A3 (en) * | 2008-07-18 | 2010-04-29 | Alcan Packaging Flexible France | Polyamide structures for the packaging of moisture containing products |
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