GALLEZ, Vincent, B. (Rue de Namur 20, Ottignies - Louvain La Neuve, B-1340, BE)
VOGELAERS, Nancy (Broekstraat 20, Leefdaal, B-3061, BE)
VAN DEN BOSSCHE, Linda (Dorpwest 141, Zwijndrecht, B-2070, BE)
GALLEZ, Vincent, B. (Rue de Namur 20, Ottignies - Louvain La Neuve, B-1340, BE)
VOGELAERS, Nancy (Broekstraat 20, Leefdaal, B-3061, BE)
CLAIMS
1. Extrusion lamination process on a continuous line comprising: a) supplying an OPP substrate layer; b) extruding a tie-layer in molten form between the OPP substrate and another layer onto the surface of the OPP substrate, in which the tie layer has a composition of a propylene based elastomer a heat of fusion of less than 75 J/g at its surface in contact with the OPP layer and is applied without the interposition at said surface of a primer applied from a primer diluent mixture.
2. Process according to Claim 1 in which the adhesive strength between the OPP substrate layer and the other layer is at least 0.4 N/15 mm, preferably at least 1 N/15 mm when applied at a weight of less than 15 g/m 2 .
3. Process according to Claim 1 or Claim 2 in which the composition of a propylene based elastomer in contact with the OPP substrate layer contains from 2 to 98 wt% of the propylene based elastomer and a balance of an ethylene based polymer or interpolymer.
4. Process according to any of the preceding claims in which the composition of a propylene based elastomer in contact with the OPP substrate layer contains from 5 to 70 wt% of a free radical produced ethylene based polymer, preferably an LDPE or an interpolymer of ethylene and a copolymerizable ester and/or acid group containing monomer, optionally at least partly neutralized.
5. Process according to any of the preceding claims in which the composition of a propylene based elastomer in contact with the OPP substrate layer contains from 5 to 80 wt% of a catalytically produced ethylene based interpolymer having a density of from 0.85 to 0.96 g/cm 3 .
6. Process according to any of claims 1 to 5 in which the composition of a propylene based elastomer in contact with the OPP substrate layer contains at least 30 wt%, preferably 50 wt%, of the propylene based elastomer and optionally from 5 to 40 wt% of a free radical produced low density ethylene based polymer, preferably an LDPE and/or an interpolymer of ethylene and a copolymerizable ester or acid group containing monomer, optionally at least partly neutralized.
7. Process according to any of claims 1 to 6 in which the composition of a propylene based elastomer in contact with the OPP substrate layer contains less than 50 wt% of the propylene based elastomer and at least 15 wt% of free radical produced low density ethylene based polymer, preferably an LDPE and/or an interpolymer of ethylene and a copolymerizable ester or acid group containing monomer, optionally at least partly neutralized, and at least 30 wt% of a linear ethylene based interpolymer having a density of from 0.85 to 0.96 g/cm 3 .
8. Process according to any of the preceding claims in which the composition of a propylene based elastomer in contact with the OPP substrate layer comprises an high crystallinity isotactic propylene based polymer having a melting peak above 140 0 C, optionally with a total heat of fusion above 60 0 C of less than 75
J/g.
9. Process according to any of the preceding claims in which the propylene based elastomer contains from 5 to 30 wt% of units derived from a comonomer, preferably ethylene.
10. Process according to any of the preceding claims in which the propylene based elastomer has an isotactic triad fraction of 70 % to 98 %.
11. Process according to any of the preceding claims in which the other layer is a polyamide (PA), polyethylene terephthalate (PET), metallised film, paper, metal foil, polyethylene or polypropylene.
12. Process according to any of the preceding claims in which the composition of propylene based elastomer in contact with the OPP substrate layer is also in contact with the other layer.
13. Process according to any of the preceding claims in which the other layer is a second OPP layer.
14. Process according to any of Claims 1 to 11 in which the composition of propylene based elastomer in contact with the OPP substrate layer is not in contact with the other layer and the tie layer comprises another coextruded composition extruded simultaneously, in which the composition not in contact with the OPP substrate contains no propylene based elastomer or, if it contains propylene based elastomer, contains 10wt% less than that in the layer in contact with the OPP substrate, said weight percent being based on the total weight of the polymer components of the respective layers.
15. Process according to Claim 14 in which the other layer is paper or a metal foil, such as aluminum foil, metallised OPP, metallised PET, PET or PA.
16. Extrusion coating process on a continuous line comprising: a) supplying an OPP substrate layer; b) extruding a coating-layer in molten form onto the OPP substrate, in which the coating layer has a composition of a propylene based elastomer a heat of fusion of less than 75 J/g at its surface in contact with the OPP layer and is applied without the interposition at said surface of a primer applied from a primer diluent mixture; and c) cooling the extrusion coated film.
17. Process according to Claim 16 in which the composition of a propylene based elastomer in contact with the OPP substrate layer contains from 2 to 98 wt% of the propylene based elastomer and of a balance of an ethylene based polymer or interpolymer.
18. Process according to Claim 16 or Claim 17 in which the composition of a propylene based elastomer in contact with the OPP substrate layer contains from 5 to 70 wt% of a free radical produced an ethylene based polymer, preferably an LDPE or an interpolymer of ethylene and a copolymerizable ester and/or acid group containing monomer, optionally at least partly neutralized.
19. Process according to any of the preceding claims 16 to 18 in which the composition of a propylene based elastomer in contact with the OPP substrate layer contains from 5 to 80 wt% of a catalytically produced ethylene based interpolymer having a density of from 0.85 to 0.96 g/cm 3 .
20. Process according to any of the preceding claims 16 to 19 which the composition of a propylene based elastomer in contact with the OPP substrate layer contains at least 30wt%, preferably at least 50 wt%, of the propylene based elastomer and optionally from 5 to 40 wt% of a free radical produced low density ethylene based polymer, preferably an LDPE and/or an interpolymer of ethylene and a copolymerizable ester or acid group containing monomer, optionally at least partly neutralized.
21. Process according to any of the preceding claims 16 to 20 which the composition of a propylene based elastomer in contact with the OPP substrate layer contains less than 50 wt% of the propylene based elastomer and at least 15 wt% of free radical produced low density ethylene based polymer, preferably an LDPE and/or an interpolymer of ethylene and a copolymerizable ester or acid group containing monomer, optionally at least partly neutralized, and at least 30 wt% of a linear ethylene based interpolymer having a density of from 0.85 to 0.96 g/cm 3 .
22. Process according to any of the preceding claims 16 to 21 in which the propylene-based elastomer comprises an high crystallinity isotactic propylene based polymer having a melting peak above 140 0 C, optionally with a total heat of fusion above 60 0 C of less than 75 J/g.
23. Process according to any of the preceding claims 16 to 22 in which the propylene based elastomer contains from 5 to 30 wt% of units derived from a comonomer, preferably ethylene.
24. Process according to any of the preceding claims 16 to 23 in which the propylene based polymer has an isotactic triad fraction of 70 % to 98 %.
25. Process according to any of Claims 16 to 24 in which the composition of propylene based elastomer in contact with the OPP substrate layer is also in contact with the other layer also forms the outer surface of the extrusion coated film.
26. Process according to any of Claims 16 to 24 in which in which the composition of propylene based elastomer in contact with the OPP substrate layer does not form the outer surface of the extrusion coated film and the coating-layer comprises at least two layers that are extruded simultaneously, in which the composition not in contact with the OPP substrate contains no propylene based elastomer or, if it contains propylene based elastomer, contains 1 Owt% less than that in the layer in contact with the OPP substrate, said weight percent being based on the total weight of the polymer components of the respective layers.
27. Process according to Claim 26 in which the composition not in contact with the OPP substrate comprises an ethylene based polymer or interpolymer adapted for heat sealing to a polyethylene film layer.
28. Process for extrusion lamination or extrusion coating on a continuous line comprising: a) supplying an OPP substrate layer; b) extruding a composition comprising a propylene based elastomer as a tie-layer extruded in molten form onto the surface of the OPP substrate without the interposition of a primer applied from a primer diluent mixture and c) laminating or coating a further layer a to provide an adhesive strength between the substrate layer and the further layer of at least 0.4 N/15 mm, preferably at least 1 N/ 15 mm.
29. Composition for use as a tie-layer or heat seal layer in extrusion lamination or extrusion coating which composition contains from 2 to 98 wt% of a propylene-based elastomer and from 5 to 70 wt% of a free radical produced low density ethylene based polymer, preferably an LDPE or an interpolymer of ethylene and a copolymerizable ester and/or acid group containing monomer, optionally at least partly neutralized.
30. Composition according to Claim 29 which contains from 2 to 98 wt% of the propylene based elastomer and of a balance of an ethylene based polymer or interpolymer.
31. Composition according to Claim 29 or 30 which contains from 5 to 70 wt% of a free radical produced ethylene based polymer, preferably an LDPE or an interpolymer of ethylene and a copolymerizable ester and/or acid group containing monomer, optionally at least partly neutralized.
32. Composition according to any of the preceding claims 29 to 31 which contains from 5 to 80 wt% of a catalytically produced ethylene based interpolymer having a density of from 0.85 to 0.96 g/cm 3 .
33. Composition according to any of claims 29 to 32 which contains at least 30 wt%, preferably at least 50 wt%, of the propylene based elastomer and optionally from 5 to 40 wt% of a free radical produced low density ethylene based polymer, preferably an LDPE and/or an interpolymer of ethylene and a copolymerizable ester or acid group containing monomer, optionally at least partly neutralized.
34. Composition according to any of claims 29 to 33 which contains less than 50 wt% of the propylene based elastomer and at least 15 wt% of free radical produced low density ethylene based polymer, preferably an LDPE and/or an interpolymer of ethylene and a copolymerizable ester or acid group containing monomer, optionally at least partly neutralized, and at least 30 wt% of a linear ethylene based interpolymer having a density of from 0.85 to 0.96 g/cm 3 .
35. Composition according to any of the preceding claims 29 to 34 which comprises an high crystallinity isotactic propylene based polymer having a heat of fusion of over 100 J/g and low crystallinity propylene based polymer, providing in combination a heat of fusion of less than 70J/g.
36. Composition according to any of the preceding claims 29 to 35 in which the propylene based elastomer contains from 5 to 30 wt% of units derived from a comonomer, preferably ethylene.
37. Composition according to Claim 35 and/or Claim 36 in which low crystallinity based propylene based polymer has an isotactic triad fraction of 70 % to 98 %. |
PROCESS FOR EXTRUSION COATING AND LAMINATING
ORIENTED POLYPROPYLENE FILM, TIE-LAYER COMPOSITIONS
FOR SUCH A PROCESS AND MULTI-LAYER FILMS WITH LAYERS
BONDED BY SUCH TIE-LAYERS.
FIELD OF INVENTION
[0001] The invention relates to processes for producing multi-layer film structures, comprising an oriented polypropylene (OPP) film layer, by an extrusion process. The invention relates especially extrusion lamination and extrusion coating of OPP films. The invention also relates to compositions for use as a tie-layer in such processes and multi-layer films produced by such processes.
BACKGROUND
[0002] One general technique of producing multi-layer films starts with a previously formed layer and applying further layers to it. The starting layer may be formed by an earlier and separate extrusion or other film forming process. When the starting layer is a previously formed film, the process of combining it with other previously formed layers to form a multi-layer film is referred to as a lamination process. In the specific case where the bonding layer between two previously formed films is molten polymer extrudate, one refers to an extrusion lamination process. When a layer is applied in molten form extruded onto a previously formed film from a die, the process is referred to as a coating process.
[0003] In extrusion lamination, structures can be produced by laminating the previously formed base layers using an extruded, molten tie-layer, which acts to "tie" bond or adhere the layers together. It may be referred to as a tie-layer. In extrusion coating, the base layer may be previously formed by a simple extrusion process or may be in a form not available from simple extrusion such OPP, paper, aluminum etc. or other forms of film that have been specially processed after extrusion or calendering; and a coated layer or several coextrusion coated layers is or are extruded onto the base layer. The coated layer may be used to establish a
bond with other layers in later process steps such as heat sealing and can in this sense also be referred to as a tie-layer.
[0004] The laminated layers for a laminated film or the base and coating layers for an extrusion coated film may not be compatible from an adhesion point of view, depending on the nature of the materials forming the layers. That is to say the materials are not inclined to bond together. In some cases no single tie-layer material is available that provides a satisfactory bond between the base and the other layers. To remedy poor bonding between the constituent layers and permit the combination of more disparate layers, a primer or an adhesive may be applied in a diluent of an organic solvent or emulsified in an aqueous diluent to one of the layers to be laminated or extrusion coated before the tie-layer is applied. Sufficient time must be allowed on a continuous line to allow the adhesive to be absorbed and the diluent to be removed by drying and this limits the line speeds and increases the costs. Furthermore the layer to be primed must be sufficiently porous to absorb the adhesive. Subsequent to the application of the adhesive, the ultimate structure can be formed by lamination or coating.
[0005] Ethylene based polymers are widely used as a tie-layer and applied in the molten state to combine different film layers of a multi-layer film structure. The low (120 0 C) melting point helps maintain the polymer in molten form in which conditions it can provide a satisfactory bond and high line speeds can be sustained. No solvent is present and there is no drying step in the application.
[0006] OPP is a low cost, highly transparent material that is for suitable for processing at high line speeds by virtue of its stiffness. OPP is widely used for laminate structures. However the OPP surface does not readily bond with generally available ethylene based polymers to provide the requisite strength of bond for many practical applications due to it lack of absorbency, surface smoothness and lack of surface polarity.
[0007] In many extrusion lamination and extrusion coating processes for OPP films therefore a primer is applied onto the OPP layer prior to the application of a polyethylene based tie-layer laminated in between OPP and another layer or coated to the layer of OPP film. The primer raises adhesion values between the laminated layers to around 0.4-0.8 N/15mm for a typical 12-15 g/m 2 polymer coating weight, which is sufficient to fulfill the requirements of most non-food packaging applications.
[0008] However a majority of primers available commercially are water-based so that the final structure may be sensitive to water and water vapor, limiting the usefulness of the film structures as far as outdoor applications are concerned.
Furthermore the primer may have a yellowing effect on the coated reels important in applications where transparency is desired. As with adhesive lamination, the use of a primer may limit the operational line speed on a continuous lamination line, especially with water based primers because the water or other medium used for applying the adhesive must be removed before the lamination can proceed further.
[0009] With the term "primer" in this specification is meant a polymeric material which contained oxygen and/or nitrogen atom containing moieties and is applied at low dry application weights of less than 1 g/m 2 in a removable diluent.
The primer increases the potential for reactive bonding of the tie-layer and provides a clean contaminant free surface to assist the wetting out of the molten extruded tie-layer and improve bonding at the chill roll. Chemical primers may be applied at low dry application weights, as low as 0.004 g/m 2 . Primers can be solvent based and include polyurethanes, polyethylene-imine, polyesters, organo- functional amines and polyamides.
[0010] Attempts to overcome the disadvantages of using primers have involved special OPP films coextruded before their orientation with a PE outer layer so as to provide good adhesion to other polyolefins film layers. However these special OPP films are expensive and are available in limited thicknesses and/or surface
finishes. OPP films have been subjected before their orientation to coextrusion with a coating of a high comonomer content ethylene acrylate copolymer as a tie layer but capital costs are increased because a coextrusion line has to be provided separate from a lamination line.
[0011] Propylene based elastomers with a relatively low melting point and decent extrusion processability are known from EPl 003814 (WOl 999/07788 and US6525157 and US6635715, incorporated herein by reference) describing the use of heterophase compositions. The compositions comprise up to 95% by weight of a first polymer semi-crystalline component and a second propylene-based elastomer polymer component in the form of a copolymer of propylene and a limited amount of ethylene. EP 1003814 contains no reference to the use of the composition or its ingredients in laminated structures. More details on propylene based elastomers are alsO set out in US20020004575. Production of a copolymer material of similar nature but using different types of single sited catalysts is described in WO2003/040201. The isotactic propylene sequences benefit adhesion and may lead to improved physical properties as compared to isotactic polypropylene blends with prior art ethylene propylene rubbers.
[0012] Applicants are aware of co-pending applications in which such elastomers have been used in film structures. US Serial Number 1 1/039090 (published as US2006-0159943 on 20 July 2006and incorporated for US purposes only) describes the use of such elastomers in a cling film. The elastomer forms the cling layer and is co-extruded with a thin flexible and stretchable no-cling layer. The structure is not a laminate. The propylene based elastomer is not applied in an extrusion lamination process.
[0013] US Serial Number 60/700896 (published on 25 January 2007 under WO2007/011460 and incorporated for US purposes only) on 19 July 2005, describes a film for surface protection having at least one base layer and a surface layer for removably adhering to a substrate comprising at least 40 wt% of an
elastomeric propylene-based polymer with a heat of fusion derived from isotactic propylene type crystallinity as determined by DSC of less than 40 J/g.
[0014] In addition in US Serial Number 60/700896 an ethylene-based polymer is disclosed in the form of an ethylene-alpha-olefin copolymer having a density of less than 0.91 g/cm 3 and/or an ethylene-vinyl ester copolymer having from 5 to 60 wt% of the ester derived units and/or optionally less than 40 wt% of a propylene based polymer having a heat of fusion of greater than 70 J/g. Again the propylene based elastomer is not applied in an extrusion lamination process onto a highly crystalline stiff, inert substrate.
[0015] US Serial Number 60/559369 (incorporated for US purposes only) on 02 April 2004 describes multi-layer films that are suitable for packaging and having improved sealing properties. A lower minimum sealing temperature may be used. A soft polymer may be blended in a core layer and a tie layer comprising the soft polymer. A sealable layer is provided on the side of the tie layer opposite the core layer.
[0016] WO2006/019544 published 13 July 2004 discloses a film of biaxially oriented polypropylene which contains 20 % or les of a tackifier resin as modifier to aid in printing etc. The resin modifier may be maleic anhydride modified. The examples 9 to 11 show extrusion coated structures
[0017] It is among the objects of the invention to provide a process that permits fast extrusion lamination or extrusion coating and reduces any restrictions in terms of substrate selection, processing speed arising from the need for primer solvent or diluent removal.
SUMMARY [0018] The invention has found that by incorporating an propylene based interpolymer in the tie-layer for extrusion lamination (between two substrate layers) or extrusion coating (onto one side of a substrate layer and on the other
side with a coating or without a coating) a strong bond can be formed with an OPP substrate without requiring use of an expensive primer which also slows the overall process.
[0019] The underlying concept referred to above can be employed similarly in extrusion lamination and extrusion coating. All that distinguishes those two processes is the additional second substrate used in the extrusion lamination process whereas the extrusion coating process relates to extruding one or more layers onto a single substrate, which may be followed in later manufacturing steps by the heat sealing to a second layer.
[0020] Generally the invention provides a process for extrusion lamination or extrusion coating on a continuous line comprising supplying an OPP substrate layer; extruding a composition comprising a propylene based elastomer as a tie- layer extruded in molten form onto the surface of the OPP substrate without the interposition of a primer applied from a primer diluent mixture and laminating. A further layer may be laminated or coating or not coated onto the earlier layers. If a further layer is laminated, an adhesive strength may be provided between the substrate layer and the other layer of at least 0.4 N/ 15 mm, preferably at least 1 N/15 mm for a coating weight of 12-15 g/m 2 and >=2N/15 mm for coatings of 25 g/m 2 . The measurement of adhesive strength is set hereinafter.
[0021] In a first aspect, the invention more specifically provides an extrusion lamination process on a continuous line comprising: a) supplying an OPP substrate layer; b) extruding a tie-layer in molten form between the OPP substrate and another layer onto the surface of the OPP substrate, in which the tie layer has a composition of a propylene based elastomer a heat of fusion of less than 75 J/g at its surface in contact with the OPP layer and is applied without the interposition at said surface of a primer applied from a primer diluent mixture.
[0022] The composition of propylene based elastomer in contact with the OPP substrate layer may also be in contact with the other layer. The lamination process may then essentially be a mono-extrusion lamination process whereby the composition constitutes essentially the whole of the tie layer. This process option may be useful to bond two OPP layers together or other materials that tend to bond to the same material. Alternatively the composition of propylene based elastomer in contact with the OPP substrate layer is not in contact with the other layer and the tie layer comprises another coextruded composition extruded simultaneously, in which the composition not in contact with the OPP substrate contains no propylene based elastomer or, if it contains propylene based elastomer, contains 10wt% less than that in the layer in contact with the OPP substrate, said weight percent being based on the total weight of the polymer components of the respective layers. In this way the tie layer overall can be adapted to bond optimally to each of the surfaces between which it is laminated and superior adhesive strengths may be obtained for certain laminate combinations having dissimilar bonding behavior. The lamination process is then essentially a coextrusion lamination process. In this laminates may be obtained of OPP and as the other layer, paper or a metal foil, such as aluminum foil, metallized OPP, metallized PET, PET or PA.
[0023] In a second aspect, the invention more specifically provides an extrusion coating process on a continuous line comprising: a) supplying an OPP substrate layer; b) extruding a coating-layer in molten form onto the OPP substrate, in which the coating layer has a composition of a propylene based elastomer a heat of fusion of less than 75 J/g at its surface in contact with the OPP layer and is applied without the interposition at said surface of a primer applied from a primer diluent mixture; and c) cooling the extrusion coated film.
[0024] Again this may take the form a mono-extrusion coating process or a coextrusion coating process. In the former case, the composition of propylene
based elastomer in contact with the OPP substrate layer is also in contact with the other layer and forms the outer surface of the extrusion coated film. In the latter case the composition of propylene based elastomer in contact with the OPP substrate layer does not form the outer surface of the extrusion coated film and the coating-layer comprises at least two layers that are extruded simultaneously, in which the composition not in contact with the OPP substrate contains no propylene based elastomer or, if it contains propylene based elastomer, contains 1 Owt% less than that in the layer in contact with the OPP substrate, said weight percent being based on the total weight of the polymer components of the respective layers. The composition not in contact with the OPP substrate comprises an ethylene based polymer or interpolymer adapted for example for heat sealing to a polyethylene film layer.
[0025A] A propylene-based elastomer is defined herein is an elastomeric polymer with a heat of fusion of the polymer as determined by DSC according to ASTM E 794 is less than 75 J/g. The heat of fusion as used herein is measured at a range of temperatures and the area under the melting peaks that are detected in that range of 140 0 C and below and generally 60 0 C or above. The area under the curve above 140 0 C, arising out of the optional presence of more crystalline fractions of polypropylene such as homopolymer, for example, are excluded for the purpose of determining the heat of fusion of the propylene based elastomer. The polymer is "propylene based" in the sense that the amount of propylene in the polymer is sufficient for propylene sequences to crystallize to give rise to a detectable heat of fusion. Preferably the polymers contain isotactic propylene sequences, interrupted by stereo or regio errors or by one or more units from a comonomer. Other properties of the propylene based elastomer reflect the total or average of the propylene based elastomer used in the process regardless of the location of the melting peaks.
[0025B] Figure 2 illustrates the principles for heat of fusion determination by reference to one component used in the examples PEE3, Vistamaxx VMX6202. The polymer sample is first molten, then cooled until solid and subsequently heat
at a rate of 5 or 10 0 C per minute or whatever speed will generate sharp enough delineation of the melting peak for the determination of the peak melting point and the heat of fusion. The polymer absorbs heat to re-crystallize at 17.14 0 C and then generates a peak between 40 and 110 0 C at 92.77 0 C. The area under any peak or curve above 140 0 C is not taken into consideration to determine the heat of fusion. In this case there is no melting peak above 140 0 C.
[0026] The composition of propylene based elastomer in contact with the OPP substrate layer may contain such a type and amount of the propylene based elastomer to provide the desired adhesive strength between the OPP and the selected material for the further layer or subsequent bonding. Generally these sealing strengths may be achieved using from 2 to 98 wt% of the propylene based elastomer.
[0027] Provided sufficient propylene-based elastomer is used for the desired bond strength, other polymeric components may be present. The composition of propylene based elastomer in contact with the OPP substrate layer may contain from 5 to 70 wt% of a free radical produced low density ethylene based polymer, preferably an LDPE or an interpolymer of ethylene and a copolymerizable ester and/or acid group containing monomer, optionally at least partly neutralized, such as an EVA (ethylene vinyl acetate) or EAA (ethylene acrylic acid). The at least partially neutralized acid copolymers are also known as ionomers. As an alternative or in combination, a more linear, less branched polymeric component may also be present such as from 5 to 80 wt% of a catalytically produced ethylene based interpolymer having a density of from 0.85 to 0.96 g/cm 3 . All densities herein are in g/cm 3 and determined by ASTM D 1505 for the ethylene based polymers. With ethylene based polymer is meant that sufficient ethylene derived units are present in the polymer chain to prevent the formation of crystalline regions except those that are of the polyethylene type and that no measurable crystallinity can be observed due the crystallization of stereoregular higher alpha- olefins.
[0028] In one variant, the composition of propylene based elastomer in contact with the OPP substrate layer may be of a composition containing at least 30 wt%, or at least 50 wt% of the propylene based elastomer and optionally from 5 to 40 wt% of a free radical produced low density ethylene based polymer, preferably an LDPE and/or an interpolymer of ethylene and a copolymerizable ester or acid group containing monomer, optionally at least partly neutralized. In another variant the composition of propylene based elastomer in contact with the OPP substrate layer may be of a composition containing less than 50 wt% of the propylene based elastomer and at least 15 wt% of free radical produced low density ethylene based polymer, preferably an LDPE and/or an interpolymer of ethylene and a copolymerizable ester or acid group containing monomer, optionally at least partly neutralized, and at least 30 wt% of a linear ethylene based interpolymer having a density of from 0.85 to 0.96 g/cm 3 .
[0029] The propylene-based elastomer itself may be a polymer with a narrow molecular weight distribution and composition distribution. However the propylene-based elastomer contains may contain some isotactic propylene based polymer having a heat of fusion of over 100 J/g or a melting peak above 140 0 C.
[0030] Control over the heat of fusion may be exercised by varying the amount of a comonomer in the propylene-based elastomer. Suitably the propylene based elastomer contains from 5 to 30 wt% of units derived from a comonomer such as ethylene or butene-1, preferably ethylene.
[0031] The process may be performed in different ways as indicated previously within the general concept. Suitably the tie layer is combined simultaneously with the OPP layer and the further layer. The manner of application of the further layer can vary. In a lamination variant the further layer is applied as an already solid film layer, which may be an aluminum foil or paper or a solidified thermoplastic material. In another variant of the process the further layer is applied by a coating process in a molten state.
[0032] By suitable adjustment if the process line, high line speeds may be reached to yield if a multi-layer film structure in which the constituent layers are firmly bonded together without application of primer and drying of the primer.
[0033] The multi-layer film structures produced may comprise at least one OPP layer, preferably from a propylene homopolymer, in contact with the tie layer. A laminate may be formed comprising a layer from a polyamide, paper, or metal foil in contact with the tie layer.
[0034] In a second aspect of the invention there is provided a composition for use as a tie-layer in extrusion lamination or extrusion coating which composition contains from 2 to 98 wt% of a propylene-based elastomer and from 5 to 70 wt% of a free radical produced low density ethylene based polymer, preferably an LDPE or an interpolymer of ethylene and a copolymerizable ester and/or acid group containing monomer, optionally at least partly neutralized. The composition may have the different components and ranges of proportion of the components, as indicated above in connection with the process.
[0035] In a third aspect there is provided a multi-layer structure comprising an OPP substrate layer; a tie-layer of a composition comprising a propylene based elastomer in direct contact with the surface of the OPP substrate without the presence of a primer a further layer a to provide an adhesive strength between the substrate layer and the further layer of at least 0.4 N/15 mm.
DETAILS OF INVENTION
[0036] Propylene based elastomeric polymers may be produced A) by random polymerization processes leading to polymers having randomly distributed irregularities in stereoregular propylene propagation or B) by propylene based copolymers in which the propylene derived units are arranged in blocky fashion and may alternate with ethylene derived units also arranged in a more blocky, non-random fashion.
[0037] The term "elastomeric polymer" indicates that the heat of fusion of the polymer as determined by DSC is less than 75 J/g as discussed preciously. Generally the elastomer will have a melting point as determined by DSC below 105 0 C when considering the range of 0 0 C or 20 (twenty) 0 C to 140 (one hundred and forty) 0 C. Other peaks may additionally be present above 140 0 C. This is in contrast to homopolymers or propylene copolymers that lack a melting peak below 105 0 C or even below 14O 0 C or atactic polymers containing propylene derived units, which lack recovery from elastic deformation. The polymers and compositions described herein can be characterized in terms of their melting points (Tm) and heats of fusion, which properties can be influenced by the presence of comonomers or steric irregularities that hinder the formation of crystallites by the polymer chains. The melting points and heats of fusion and crystallization transitions in propylene based polymers are determined herein by Differential Scanning Calorimetry (DSC) based on ASTM E-793-89, E-794-89.
[0038] The test method involves heating or cooling the polymer at a controlled rate in a controlled atmosphere (N2) in the region of fusion or crystallization. Around 6+1 mg of the sample is weighed and introduced in an aluminum pan. A cover is placed on the pan and sealed with the appropriate press. The weight is recorded together with the sample information. The sample is scanned while heating to 210° C at 10° C/min. If it is desired to determine crystallization parameters this may be followed by holding the sample for 2 min at 210° C (higher temperature and longer time is sometimes required), cooling to 0° C at 10° C/min, holding at 0° C for 1 min and reheating to 190° C at 10° C/min.
[0039] For all the materials one or several peaks may be recorded during the heating step. The crystallized propylene sequences in the polymer give rise to a detectable heat of fusion. The polymer contrasts in this respect with known elastomeric polymers based on ethylene and propylene in which the heat of fusion can be attributed to ethylene derived polymer sequences. The initially scan during the heating to 210° C at 10° C/min provide:
1) The Tm (melting peak) and δHf (heat of fusion) for the first heating. The subsequent scans can provide the Tc (crystallization peak) and the δHc (heat of crystallization) for the cooling step. The total area under the curve between the two integration limits of 20 0 C to 140 0 C give the heat of fusion (δHf) referred to in the Claims and the Examples. For PP homopolymer δHfl00%=208 J/g. This value can be used to calculate the crystallinity in % if desired. For the invention, the temperature of the melting peak decreases with co-monomer content.
[0040] The heat of fusion as defined herein preferably ranges from a lower limit of 1.0 J/g, or 1.5 J/g, or 3.0 J/g, or 4.0 J/g, or 6.0 J/g, or 7.0 J/g, to an upper limit of 30 J/g, or 40 J/g, or 50 J/g, or 60 J/g. Upper and lower range limits may be combined. Here and everywhere else, any lower range end may be combined with an upper range end to provide alternative ranges. If the heat of fusion is too high or not enough of the propylene based elastomer is present, the polymer may not be sufficiently adhesive. If the heat of fusion is too low may not process stably during extrusion. The heat of fusion can be reduced by using additional comonomer, higher polymerization temperatures and/or a different catalyst providing reduced levels of steric constraints and favoring more propagation errors for propylene insertion.
[0041] The propylene-derived units of the propylene elastomer having the stated heat of fusion previously set out, may at the same time have an isotactic triad fraction of about 65 % to about 99 %. Advantageously the propylene-derived units of the propylene elastomer have an isotactic triad fraction of 70 % to 98 %. In still another embodiment, the propylene-derived units of the propylene elastomer have an isotactic triad fraction of 75 % to 97%. Upper and lower range limits may be combined. If the triad tacticity is too high, the level of stereo-irregular disruption of the chain is too low and the material may not be compatible and sufficiently flexible for its purpose in a tie layer. If the triad tacticity is too low, the bonding strength may be too low. The "triad tacticity" of the polymers described herein can be determined from a 13 C nuclear magnetic resonance (NMR) spectrum of the polymer as described in U.S. Patent No. 5,504,172, and
U.S. Patent No. 6,642,316, column 6, lines 38 through column 9, line 18, which patents are hereby incorporated by reference in their entirety for US purposes.
CONTROL OF RANDOM POLYMER STRUCTURE [0042] The triad tacticity and tacticity index of the propylene based elastomer may be controlled by the catalyst influencing the stereoregularity of propylene placement, the polymerization temperature according to which stereoregularity can be reduced by increasing the temperature and by the type and amount of a comonomer which tends to disrupt reduce the level of longer propylene derived sequences.
[0043] Preferably the propylene based elastomer contains at least some comonomer, such as an ethylene or alpha-olefin, in order to facilitate control of the structure. Preferably the comonomer comprises substantially ethylene which can aid in achieving economic polymerization conditions by raising the molecular weight and/or permitting a raising of the polymerization temperature. Generally the combined amount of the ethylene and/or alpha-olefin in the propylene based elastomer varies from 5 to 30 wt% %, preferably from 10 to 20 wt% and especially from 12 to 20 wt%. Other suitable ranges of the ethylene and/or other alpha-olefin include 5-20 wt%, 5-15 wt%, 5.5-10.5 wt%, 6-10 wt%, 8-10 wt% and 8.5-10 wt%. Too much comonomer will reduce the crystallinity provided by the crystallization of stereoregular propylene derived sequences to the point where the material lacks strength; too little and the material will be too crystalline.
[0044] The comonomer content and sequence distribution of the polymers can be measured using 13 C nuclear magnetic resonance (NMR) by methods well known to those skilled in the art. Comonomer content of discrete molecular weight ranges can be measured using methods well known to those skilled in the art, including Fourier Transform Infrared Spectroscopy (FTIR) in conjunction with samples by GPC, as described in Wheeler and Willis, Applied Spectroscopy, 1993, vol. 47, pp. 1128-1130. For a propylene ethylene copolymer containing greater than 75 wt% propylene, the comonomer content (ethylene content) of such
a polymer can be measured as follows: A thin homogeneous film is pressed at a temperature of about 150°C or greater, and mounted on a Perkin Elmer PE 1760 infrared spectrophotometer. A full spectrum of the sample from 600 cm "1 to 4000 cm "1 is recorded and the monomer weight percent of ethylene can be calculated according to the following equation: Ethylene wt% = 82.585 - 11 1.987X +
30.045X 2 , where X is the ratio of the peak height at 1155 cm "1 and peak height at either 722 cm " or 732 cm "1 , whichever is higher. For propylene ethylene copolymers having 75 wt% or less propylene content, the comonomer (ethylene) content can be measured using the procedure described in the Wheeler and Willis.
Reference is made to US20020004575 published 10 January 2002 whose test methods were also fully applicable for the various measurements referred to in this specification and claims and which contains more details on GPC measurements, the determination of ethylene content by NMR and the DSC measurements.
[0045] The propylene based elastomer may be functionalized for example using maleic anhydride and may also contain some polyenes to facilitate such functionalization and/or a cross-linking reaction.
[0046] The catalyst may also control the stereoregularity in combination with the comonomer and the polymerization temperature. The catalyst should however be capable of a level of stereoregular placement, generally by suitable chirality of the single site catalyst. The polymer can be prepared using any single sited catalyst. Such a catalyst may be a transition metal complex generally containing a transition metal Groups 3 to 10 of the Periodic Table; and at least one ancillary ligand that remains bonded to the transition metal during polymerization. Preferably the transition metal is used in a reduced cationic state and stabilized by a cocatalyst or activator.
[0047] The ancillary ligand may be a structure capable of forming a π bond such a cyclopentadienyl type ring structure (See EP 129368, EP284708, Rieger
EP 1070087 and US6559262). The ancillary ligand may also be a pyridinyl or amide ligand (See WO2003/040201). The transition metal is preferably of Group 4 of the Periodic table such as titanium, hafnium or zirconium, which is used in polymerization in the d mono-valent cationic state and has one or two ancillary ligands as described in more detail hereafter. The important features of such catalysts for coordination polymerization are the ligand capable of abstraction and that ligand into which the ethylene (olefinic) group can be inserted.
[0048] The manner of activation of the single site catalyst can vary. Alumoxane and preferably methyl alumoxane can be used suitably in an amount to provide a molar aluminum to metallocene ratio of from 1 : 1 to 20,000: 1. Higher molecular weights can be obtained using non-or weakly coordinating anion activators (NCA) derived and generated in any of the ways amply described in published patent art such as EP 277004, EP 426637, EP426638 and many others. The non- coordinating anion can be a Group 10-14 complex wherein boron or aluminum is the charge-bearing atom shielded by ligands, which may be halogenated, and especially perfluorinated. Preferably tetra-aryl-substituted Group 10-14 non- carbon element-based anion, especially those that are have fluorine groups substituted for hydrogen atoms on the aryl groups, or on alkyl substituents on those aryl groups. The non-coordinating anion may be used in approximately equimolar amounts relative to the transition metal complex, such as at least 0.25, preferably 0.5, and especially 0.8 and such as no more than 4, preferably 2 and especially 1.5. Further options are described in U.S6048950; WO1998/27154; US6448358; US6265212, US5198401 and US5391629.
[0049] The polymerization reaction is conducted by reacting monomers in the presence of a catalyst system described herein at a temperature of from O 0 C to 200 0 C for a time of from 1 second to 10 hours. Preferably homogeneous conditions are used such as a continuous solution process or a bulk polymerization process with excess monomer used as diluent. Preferably the continuous process uses some form of agitation to reduce concentration differences in the reactor and maintain steady state polymerization conditions. The heat of the polymerization
reaction is preferably removed by cooling of the polymerization feed and allowing the polymerization to heat up to the polymerization, although internal cooling systems may be used.
OTHER GENERAL CHARACTERISTICS
[0050] The polymer preferably has an MFR of 0.5 to 200, especially from 1 to 100 or more especially 1 to 75 or 1 to 50. Upper and lower range limits may be combined. The term "MFR" as used herein stands for "Melt Flow Rate" and is used to characterize polymers, components and compositions. The units for "MFR" are grams per 10 minutes and the test to be herein for determining MFR is set forth in any version and condition set forth in ASTM- 1238 that uses 2.16 kg at 230 0 C with a 1 minute preheat on the sample to provide a steady temperature for the duration of the experiment. This data expressed as dg of sample extruded per minute is indicated as MFR. In an alternative procedure, the test is conducted in an identical fashion except at a temperature of 19O 0 C. This data is referred to as MI@190°C. Where the MFR is so low as to defy measurement under these conditions, molecular weight may be determined using Mooney.
[0051] A molecular weight distribution M w /M n (MWD), sometimes referred to as a "polydispersity index" (PDI), within the range having an upper limit of 40, or 20, or 10, or 5, or 4.5, and a lower limit of 1.5, or 1.8, or 2.0. The various molecular weight characteristics (e.g., Mw and Mn) and molecular weight distribution Mw/Mn (MWD) of the polymer components (or polymers) described herein can be measured in accordance with the procedures disclosed in U.S. Patent No. 6,525,157, column 5, lines 1-44, which patent is hereby incorporated by reference in its entirety for US purposes.
BLEND COMPONENTS
[0052] The propylene based elastomer can conveniently be blended with other polymers to obtain compositions which permit primer free operation but retain some of the benefits in adhesion, processability including line speed, and ultimate laminate properties enjoyed by prior art laminate structures.
[0053] The propylene based elastomer may contain some isotactic polypropylene (homopolymer or some form of interpolymer) with a peak melting point above 140 0 C that is produced as a side reaction in the polymerization process and which may be present to improve the stability of the pellet form of the propylene based elastomer most useful in extrusion processes and which may benefit the physical properties. To the extent such a propylene based semi- crystalline polymer is present in the form in which it is sold by a manufacturer and is present in any pelletized form, the polymer is treated as part of the propylene based elastomer.
[0054] Where appropriate further minor amounts of propylene based semi- crystalline polymer may be added to improve the physical properties associated with higher crystallinity.
[0055] The propylene based elastomer may be part of a composition or blend also containing a highly branched ethylene based polymer produced by a free radical process. This may be in the form of an LDPE having a density of from 0.91 to 0.93 g/cm 3 and an MI of from 0.1 to 50. Such LDPE's are highly branched and permit stable operation at high line speeds through more shear-thinning and higher melt strength. This may also be in the form of an ethylene based polymer further including units derived from a copolymerizable acid or ester containing from 3 to 30 wt% of the comonomer. Preferably this is in the form of an ethylene vinyl acetate. Presence of the polar groups may assist in adhesion to certain layers to be laminated.
[0056] The propylene based elastomer may be part of a blend also containing a linear ethylene based polymer produced by a catalytic Ziegler-Natta type polymerization processes, including single site, especially metallocene catalyzed processes. Such linear polymers preferably contain an alpha-olefin comonomer having from 3 to 10 carbon atoms in amounts such as to provide a density of from
0.85 to 0.92 g/cm 3 . The presence of such polymer can provide additional benefits in the processing and the properties of the ultimate laminate produced.
[0057] Adding propylene based elastomers such as propylene-ethylene elastomers (PEE) to the polymeric extrudate for oriented films of isotactic polypropylene provides good adhesion onto unprimed conventional OPP film substrate in extrusion lamination and extrusion or coextrusion coating. Depending on the base polyolefin selected, high transparency, low seal initiation temperature and overall good sealing performances are achieved. Also thermal lamination onto printed and /or lacquered surfaces may be facilitated. Blends composition of Propylene-Ethylene Elastomers (PEE) with isotactic propylene crystallinity (Versify™, Vistamaxx™) and Exact™ plastomers based enables to achieve high adhesion onto conventional OPP substrate without the need to use a primer. Also, addition of PEE in HEVA (high vinyl acetate EVA) provides adhesion onto OPP at least as high as adhesion of conventional HEVA coated onto primed OPP.
EXAMPLES
[0058] The following polymers were used in the examples:
Table 1
I) ASTM D 3418
2) Vinyl acetate comonomer
3) Methyl acrylate
4) N/A=not applicable
5) Acrylic acid
[0059] The monomer content of the Exact grades is determined using LNMR (liquid state NMR and are accurate to ± 2%. The reported values are these
calculated for the typical density - melt index combination using a multiple regression model to fit all experimental values.
[0060] The methods for determining the octene-1 contents are described in F.Cavagna, Macromolecules 1981, 14, page 215 and in H.N.Cheng, Polym.
Comm. 1984, 25, 99 and in Polymer, Volume 25, Issue 4, April 1984, pages 441- 446 by Keiichiro Kimura, Dakae Yuasa and Yasumitsu Maru.
[0061] The coating was performed by extrusion coating and or lamination in which a molten polymer web (mostly polyethylene) serves as a tie or coating layer with the OPP substrate without the aid of a primer.
[0062] All structures were produced on pilot extrusion lamination and coating line. The materials were extrusion coated or laminated on the equipment shown in Figure 1. Unwind station 2 supplied one of the OPP webs to be laminated. An optional corona treatment can be performed at the treatment station 4. Extruder 6 supplied molten polymer for the tie-layer between the films from unwind station 2 and another layer of OPP film or another substrate supplied from a roller 8. The laminated film structure passes over the chill roll 10 and is then advanced over reels generally indicated at 12 to the winding station 14.
A series of tests were done in extrusion lamination between two OPP films (examples 1 and 2) on machinery as described above. The OPP substrate was pretreated by a corona treatment. The coating conditions included: 100 m/min line speed, a 295°C temperature setting , 50 rpm screw speed for 25 g/m 2 coating weight, 25 rpm for 12 g/m2 .
[0063] Another set of tests were made in extrusion coating onto 1 OPP substrate (examples 3-7). Coating conditions: 15 g/m 2 coating weight, 150 m/min line speed, corona pretreated substrate, a 240 °C temperature setting for the HEVA based blend, 280 °C for the Exact based blend.
Additional tests were made in mono-extrusion coating, in coextrusion coating snd in extrusion lamination. In all experiments at least one substrate was an OPP film. Other substrates include paper, aluminum foil and OPP film.
[0064] The following blends served as the connecting polyethylene based layer:
Table 2
[0065] For examples 1 and 2, two webs of commodity OPP films were laminated in an extrusion lamination process (e.g. EM Bicor 20MB400, coating applied on the outer layer). Two coating weights were applied for Example 2: 25 g/m 2 and 12 g/m 2 at 100 m/min line speed, and 295 0 C set temperature. Example 1 was applied at 25 g/m 2 .
[0066] Adhesion was measured using standard T-peel test based on ASTM Dl 876 but modified in the following respects: As to condition 4.1.1, instead of
machine and loading range being selected so that the maximum load of the specimens falls between 15% and 85% of the upper limit of the loading range, a Zwick apparatus is used having a load cell of 200N (Zwickl) or 500N (Z wick 2), which is higher than the 15% and 85% of the maximum forces measured, that are only around 5 N max. As to condition 5.2 instead of cutting the bonded panels into 25 mm (1 inch) wide test specimens, the test specimens are 15mm wide. Instead of applying condition 5.3 and testing at least 10 specimens for each adhesive 4 samples are tested with a supplemental check of any outliers. Instead of applying condition 7.1 and applying the load at a constant speed of 254 mm/min or 10 inch/min, a peel speed of 100 mm/min is used. Instead of determining the peel resistance over at least a 127mm or 5 inch length of the bond line after the initial peak, as required by condition 7.3, 90 mm as standard is used or longer if the resistance varies significantly.
Values as high as 13 N/15 mm were obtained for Example 1 at 25g/m 2 and 10.5 N/15mm for Example 2 at 25 gm 2 . Example 2 had 6 N/15mm at 12 g/m 2 . For example 1 & 2, cohesive failure was observed.
[0067] For Examples 3 to 7 the Vistamaxx™ lean (meaning a reduced content of the PEE component) blends were mono-extrusion coated onto commodity OPP film (12 micron thick, clear, HB302-39 from H.S. industry). One coating weight was applied: 15 g/m 2 at 150 m/min. line speed, set temperature function of the base resin. Example 5 showed high chill-roll sticking (due possibly to the chill roll surface not being cooled down enough) which may have an impact on the adhesion. In such configuration, ones tries to optimize the processability and adhesion requirements with the specific sealing performances (often low temp seal initiation, sealing though contamination,...) of the coated polymer used as the sealing layer.
As reference, typical adhesion value for commercial structures coated onto primed OPP is 0.4 -0.8 N/15mm.
Further examples were completed using the same equipment and process with the following results:
MONO-EXTRUSION COATING: 25 g/m 2 polymer onto OPP:
POLYMER f S) COATING LAYER:
Propylene based elastomer blended with low density polyethylene and plastomer:
Table 3
This demonstrates that already with 5 wt% of the propylene based elastomer, adhesion is improved; and that lower density plastomers blend more homogeneously to permit extrusion into thin layers.
COATING LAYER:
Propylene based elastomer blended with ethylene vinyl acetate polymer
Table 4
Issues may arise with film sticking to rolls but good adhesion.
** The chill roll sticking issue can be solved by the use of additives.
COEXTRUSION COATING:
Total coating weight of 25 g/m 2 polymer onto OPP of which the OPP contact tie- layer represents 1/3 of the total coating weight:
Table 5
Excellent adhesion is obtained even at low coating temperature (235 C) using 30% VM 6200.
MONO-EXTRUSION LAMINATION: 25 and 12 g/m 2 polymer melt between OPP and Kraft paper
Table 6
This shows that a high VMX6202 levels can be used as a tie layer between paper and OPP foil.
CO-EXTRUSION LAMINATION: total tie layer weight of 25 and 12 g/m 2 polymers melt between OPP and aluminum foil of which the VMX contaiing layer is 2/3 of the toal tie-layer weight.
Table 7
Outstanding adhesion and interlayer adhesion were obtained by coextruding an acid copolymer with a VMX 6202 rich blend, even at very thin coating weight. Co-extrusion-lamination of polymer melt between OPP and OPP.
Table 8
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