MXPA96003573A

MXPA96003573A - Polimeri films

Info

Publication number: MXPA96003573A
Application number: MXPA/A/1996/003573A
Authority: MX
Inventors: Thomas Alder Paul; Janine King Dawn
Original assignee: * Courtaulds Films
Priority date: 1994-12-23
Filing date: 1996-08-22
Publication date: 1998-01-01

Abstract

The present invention relates to a multi-layer polymeric film comprising a base layer of a propylene polymer, an intermediate layer without gaps on the base layer, and a heat-sealable polymer layer on the middle layer, the middle layer without hollows has internal cohesive strength less than the bond strength of the intermediate layer to either the base layer or the heat sealable layer and less than the internal cohesive forces either of the base layer or of the heat sealable layer of so that the film is released by breaking within the thickness of the intermediate layer instead of by delamination of the adjacent layers of the film.

Description

POLYMERIC FILMS FIELD OF THE INVENTION The present invention relates to polymeric films and more particularly to polyolefin films which form thermally releasable seals.

BACKGROUND OF THE INVENTION Heat-sealed polyolefin films which form detachable thermal seals have been proposed up to now, in which the films either split from one another or from a substrate to which they have been sealed with heat, when The thermal seal is removed by pulling or pulling. An example of such a heat-sealable film is disclosed in the patent W093 / 17863, the peeling ability that results either from a relatively weak thermal seal between the film and the substrate to which it has been fixed or by the delamination of a layer of the olefin polymer which forms the thermal seal of the other layers of which the film is constructed. The disadvantage of providing a detachment seal Ref. 22899 The part that starts or starts in the thermal seal between a polyolefin film and a substrate to which it has been sealed with heat is that the detachment capacity can be unpredictable. If the heat sealable layer of the film forming the removable seal forms a particularly strong bond with the substrate to which it has been heat sealed, the detachibility can be difficult, requiring a large force to separate the sealed surfaces. On the other hand, if the thermal seal is too weak, the seal can be broken before it is required, for example only by the forces involved in the handling of the packages that include the thermal seals. The detachability resulting from the delamination of a heat-sealable polymeric layer from the other layers of the film could be expected to be more predictable. However, such delamination requires a low interfacial bonding strength between the heat sealable layer of the film and the rest of the film, and this in turn tends to cause unpredictable results for the strength of the bond between the heat sealable layer and the substrates to which the film is thermosealed. In addition to these problems with the despicability of these prior art films, the same they do not provide good evidence of misuse. Films with indication of misuse that provide good evidence of misuse, however, have already been proposed up to now, including a polypropylene layer containing a relatively large amount of a particulate filler which induces microvacities during the biaxial stretching of the film during its manufacture. Instead of such films that start from substrates to which they have been thermally sealed or that are delaminated when their thermal seals are opened by pulling, the layer that includes the micro-voids is broken and separated by opening the parts of the layer that are to the left on both of the surfaces removed by detachment. Such films tend to provide predictable results since detachability is not a function of the ability of the layers to be separated from the substrates to which they have been heat-sealed, they do not depend on the low interfolding binding forces. which can lead to weak heat sealing with the substrates, and they show good evidence that the seals have been detached, that is, good evidence of misuse. However, such films have the inherent problem that they are opaque as a result of the present of a large number of micro-vaccines.

DETAILED DESCRIPTION OF THE INVENTION In accordance with the present invention there is provided a multilayer polymeric film comprising a base layer of a propylene polymer, an intermediate layer without voids or voids on the base layer, and a heat-sealable polymeric layer over the intermediate layer, the intermediate layer without voids or voids has a lower internal cohesive force than the bonding strength of the intermediate layer to either the base layer or the heat-sealable layer and less than the strength internal cohesive either of the base layer or of the heat sealable layer. It is generally preferred that the internal cohesive strength of the intermediate layer be less than that of the other layers in the film, and particularly smaller than that of either the base layer or the heat sealable layer to which it is attached, or the cohesive strength of the intermediate layer to any of these layers. The present invention provides heat sealable films which can be detached easily. In addition, particularly when the films are substantially transparent, they can be indicate where the detachment of the films occurred due to an increase in the opacity in these regions where the detachment has taken place. The detachibility results from the relatively weak internal cohesive force of the intermediate layer compared to that of the intermediate layer to any of the layers to which it is attached and which is weaker than the internal cohesive forces of the other layers of the layers. films, and particularly the layers to which it is attached or fixed directly. Furthermore, it is preferred that the internal cohesion of the intermediate layer be less than the strength of the thermal seal of the heat-sealable polymeric layer to the material to which it is optionally heat-sealed. Apart from the nature of the heat sealable polymer itself, this, of course, depends on the nature of the material to which the films are heat sealed and the conditions under which the sealing is carried out with heating. This may necessitate the selection of the composition of the intermediate layer to achieve an internal cohesive force of a sufficiently low value. The base layer can be a propylene homopolymer or a propylene copolymer with one or more aliphatic alkenes, for example ethylene and / or butene-1, and can be substantially clear or opaque. When the base coat or any other layer of the films of the present invention is opaque, the films will usually not provide evidence of indeterminate use after the thermal seals have become detached. In some cases, however, the opaque seals may show a reduction in the brightness of the outer layers of the films where the release has taken place. The intermediate layer is preferably a mixture of polymers in such a way that the mixture does not co-polymerize and that an interface will not be created within the inner layers. Such non-co-continuous structures are believed to fail by a mechanism whereby the fault propagates through the boundaries or boundaries of the domain between the components of the mixture, and this preferably occurs due to ductile or flexible failures. Accordingly, the intermediate layer will frequently lead to films of the present invention which have an increased darkening compared to the analogous films without the intermediate layer. Where substantially transparent films are required, it is preferred that this increase in darkening is not so great that the intermediate layer becomes essentially non-transparent, but an intermediate layer does not transpire.

This can be used when the films themselves are not going to be opaque. The intermediate layer is preferably a mixture or combination of a propylene polymer and an ethylene polymer. The propylene polymer is preferably a propylene homopolymer or a copolymer of propylene and ethylene having an ethylene content of not more than 2 percent by weight and more preferably not greater than 1 percent by weight with the remainder being essentially propylene polymerized The propylene polymer preferably has a high isotactic content, and especially greater than 95 weight percent. The ethylene polymer is preferably a copolymer of ethylene with at least one alpha-olefin, for example the copolymers of ethylene with propylene, butene-1 or 4-methylpentene-1. The ethylene polymers used in the mixture used for the intermediate layer are preferably the ethylene / butene-1 copolymers, optionally containing units derived from one or more other alpha-olefins, units derived from ethylene forming in each case the predominant of the copolymers. Particularly preferred are polymers containing from 80 to 95 weight percent of units derived from ethylene and 20 to 5 percent by weight by weight of units derived from butene-1 substantially without units derived from other olefins. A particularly preferred ethylene polymer contains about 90 weight percent of units derived from ethylene and about 10 weight percent of units derived from butene-1. The ratio or weight ratio of the propylene polymer to the ethylene polymer used for the intermediate layer will usually depend on the nature of the ethylene polymer itself. In general, the ratio or weight ratio of the propylene polymer to the ethylene polymer will be in the range from 70:30 to 30:70, and more particularly from 60:40 to 40:60. Mixtures or combinations containing approximately equal weights of an ethylene copolymer containing in the form of about 90 weight percent of ethylene and about 10 weight percent of butene-1 and a propylene homopolymer are especially preferred. In the formation of mixtures or combinations for the intermediate layer of the films of the present invention, care must be taken in the combination or mixing process since excessive work of the mixture can lead to the internal cohesive strength of the layers intermediates produced from it will increase to unacceptable levels so that the internal cohesive forces of the layer become too high for the detachment to take place within the intermediate layer. The mixture or combination must therefore be carried out to an extent necessary to lead to a substantially transparent intermediate layer without working the mixture or combination to a degree where the internal cohesion of the intermediate layer is increased to unacceptably high levels. To reduce the overload of the mixture, instead of forming a premix from the molten materials of the polymers for the intermediate layer and then using the premix as a feed to the extruder which is used to form the intermediate layer when the films are being manufactured, a mixture of pills of the individual polymers required in the intermediate layer can be fed to the extruder. The heat sealable layer can be made from a variety of heat sealable polymers that are known in the art to provide the cohesion of the heat sealable layer with the intermediate layer that is greater than the internal cohesion of the intermediate layer itself. Typically, the heat-sealable polymer may be selected from olefin copolymers, and more particularly from copolymers containing units derived from at least two of ethylene, propylene and butene-1. Particularly preferred are the heat sealable layers produced from propylene / ethylene copolymers and / or propylene / ethylene / butene-1 terpolymers. In general, it is preferred that the heat-sealable polymer used for the outer heat sealable layer be different from the copolymer component of the blend or combination used to form the intermediate layer. Where transparent films are required, it is generally preferred that the base layer of the films of the present invention have no gaps or voids, since this makes it possible for the peelable seals to provide an indication of detachment if other layers of the films are also substantially transparent. However, the base layer, and indeed other layers of the films of the present invention, if desired, may have voids or voids and / or be pigmented. If gap or void formation or pigmentation is used for any layer of the films of the present invention, it is preferred that this not be such that the release of the films occurs within the void or void layer, instead that is within the middle layer. The formation of voids or voids in the base layer can be effected by means known in the art. technique, in particular by the inclusion of an agent for the formation of voids, particulate, within the base layer and then biaxially orienting the film. The void or organic or inorganic voiding agents can be used, examples of void or organic voiding agents include polyesters, for example polyethylene terephthalate or polybutylene terephthalate, polyamides, for example, nylons , and examples of void or inorganic voiding agents include chalk, talc, barium sulfate and zinc sulphide. The base layer and / or the other layers of the films of the present invention can be pigmented, a preferred pigment is titanium dioxide. However, it is generally preferred that the intermediate layer with the relatively low internal cohesive force does not include a pigment. The films of the present invention may consist of the three layers specified above. However, they may include one or more additional layers on the surface of the base layer remote from the specified intermediate layer and the outer heat-sealable layer. Such other layers may be a single or single heat sealable layer, for example of a heat-sealable olefin polymer or copolymer, or the same can be combinations of two or more polymeric layers, example another intermediate layer when it is present on the other surface of the base layer and an associated heat sealable polymer layer thereon. The combination of the intermediate layer of a mixture or combination of polymers with a relatively low cohesive strength and the outer heat-sealable layer will usually form an inner surface of a heat-sealed package formed from the films of the present invention since this heat-sealable layer is the which will be used to form the thermal seals and by means of this will make it possible for the detachibility or detachibility of this intermediate layer to be exploited. The other surface of the films can therefore be selected to provide various effects. For example, they may include one or more additional layers, the outer surface of the films is preferably printable. If desired, the films of the present invention may include a metallized layer on the opposite side of the base layer from the combination of the polymer blend and the heat sealable layer. The films can also be used as a continuous roll of a laminate for another film which, for example, can be printable and / or include a metal layer.

The various layers of the films of the present invention can usually be made to any desired thickness. However, it is generally preferred that the intermediate layer be at least 1.5 μm thick, so that it functions satisfactorily as an indicator of misuse. Although the intermediate layer may be 10 μm thick or more, it is preferably from 2 to 9 i? \ N or more, preferably from 3 to 7 l? m thick to impart the ability to show good evidence of misuse while at the same time not substantially reducing the mechanical properties of the films or increasing their darkening to unacceptable levels. The films according to the present invention can include various additives conventionally used in polypropylene films. For example, its outer layers will usually include at least one antiblocking or antiblocking agent which may be organic or inorganic, an example of an antiblocking or antiblocking agent which may be used is silica. The base layer may also contain one or more migratory additives which affect the properties of the films, examples of these being antistatic agents and slip agents.

The films according to the present invention can be produced by known methods, a preferred method is to coextrude the melted materials of the polymers for the respective layers, plus any additives, through a grooving punch to form a continuous roll of flat polymer which is then stretched in the extrusion direction and then transversely before it is rolled. If desired, either or both of the outer surfaces of the film can be subjected to a treatment to increase the surface energy of the films, for example the treatment with a corona arc discharge or the treatment with a flame. Such treatments are preferably carried out after the transverse stretching but before they are rolled up. The following Examples are given by way of illustration only. All percentages of the additives present are by weight of the respective layers in which they are present, and all percentages of the monomer contents of the various copolymers are by weight of the respective copolymers.

Example 1 A mixture of 50:50 weight percent of propylene homopolymer granules and granules of an ethylene / butene-1 copolymer (90 weight percent ethyl ene, 10 weight percent butene-1) were blended or combined using a Baker Perkins twin screw composition apparatus. The mixture is used to form a layer of a four-layer polymeric continuous roll as will now be described. The four-layer polymeric continuous roll was produced by co-extruding through a grooving punch a central layer of the polypropylene homopolymer, on one side of the core layer an intermediate layer of the above-described mixture of the polypropylene homopolymer and a copolymer of polypropylene. ethylene / butene-1, and two outer layers of a propylene / ethylene copolymer containing 4% by weight of ethylene, using the molten materials of the respective polymers. The continuous roll was cooled on a cooling roll and then stretched 4.5 times in the extrusion direction by passing it over a series of heating rolls rotating at different peripheral speeds. After this it is stretched 10 times in the transverse direction in a styrofoam. The resulting biaxially stretched film is hardens with heat, after which it is rolled on a roller or reel. The film had a total thickness of 35 Jim, the core or core layer is 27.2, the middle layer is 5 um, and each outer layer is 1.4 iim.

Example 2 A five-layer polymeric film is produced in a manner similar to that described in Example 1, an intermediate layer of the composition described in Example 1 is co-extruded between each outer layer and the core or core layer. The resulting film had a total thickness of 35 Xm, the core or core layer was 22.2 ü, the intermediate layers were both 5 iva, and each outer layer was 1.4 lira.

Example 3 A five-layer polymeric film was produced as described in Example 2, but using a mixture or combination of 60 weight percent of the propylene homopolymer and 40 weight percent of the ethylene / butene-1 copolymer.

The respective film layers, of the resulting film, were as given in Example 2.

Example 5 A continuous five-layer polymeric roll was produced by co-extruding through a grooving punch, a central core layer of the propylene homopolymer containing various additives, with an intermediate layer on a surface of the core layer consisting of the above mixture , an outer layer on this intermediate layer is a terpolymer of propylene, ethylene and butene-1 (4% weight of ethylene, 6% weight of butene-1, 90% weight of propylene), and another intermediate layer on the other surface of the core layer consisting of a propylene homopolymer, with an outer layer on this intermediate layer consisting of a propylene / ethylene copolymer (4% by weight of ethylene, 96% by weight of propylene) containing 15% by weight of titanium dioxide and 0.1% weight of silica. A 50:50 ratio per mixture of granules of the propylene homopolymer and granules of an ethylene / butene-1 copolymer (90% weight of ethylene, 10 weight percent of butene-1 was used as the feed for the extruder producing the intermediate layers, the additives of the The core layer consisted of 10.76% by weight of titanium dioxide (average particle size of 0.1 μm), bis-ethoxylated sebaceous amine, erucamide, and glyceryl mono-stearate. The continuous roll was cooled on a cooling roll and then stretched 4.5 times in the extrusion direction by passing it over a series of heating rolls rotating at different peripheral speeds. After this it is stretched 10 times in the transverse direction in a stripping furnace. The resulting biaxially stretched film is hardened with heat, and then treated with a corona arc discharge on the outer surface consisting of the propylene / ethylene copolymer containing titanium dioxide, after which it is wound into a roll or reel. The movie had a total thickness of 40 JÁJ? , the core layer is 27.2 mt, the intermediate layer of the polymeric mixture is 7 mm, and the middle layer of the propylene homopolymer is 3mt thick. Both of the outer layers were 1.4 U m thick. This film is opaque as a result of titanium dioxide in the core layer and an outer layer, but the core layer had no gaps or voids.

Example 6 A five-layer film according to the present invention was produced as described in Example 5, except that the additives in the core layer consisted of 3% by weight of calcium carbonate (average particle size of 3.5 μm) , 4% by weight of titanium dioxide, bis-ethoxylated sebaceous amine, erucamide and glyceryl monostearate. The respective layers of the finished film were as given in Example 5. This film was opaque due to the presence of titanium dioxide in the core and in an outer layer, the core layer of this film is also provided with voids or empty as a result of the presence of calcium carbonate.

Example 7 A five layer film similar to that of Example 5 was produced using the same polymers and additives for the respective layers except that the additives in the core layer consisted of 17.1% by weight of titanium dioxide (average particle size of 0.1 m ), plus sebaceous amine bis-ethoxylate, erucamide, and glyceryl mono-stearate. The film produced a total thickness of 50 Tm, the core layer was 29.2 μm thick, the two intermediate layers were each 9 thick, and the two outer layers were each 1.4 μm thick.

Example 8 A five layer film similar to that of Example 5 was produced using the same polymers and additives for the respective layers, except that the intermediate layer immediately below the outer layer containing the titanium dioxide consisted of the propylene homopolymer, and the additives of the core layer consisted of 14.2% by weight of titanium dioxide (average particle size 0.1 μm). .m), more bis-ethoxylated sebaceous amine, erucamide, and glyceryl monostearate. The film produced a total thickness of 50 μm, the core layer was 35.2 Lm thick, the intermediate layers formed of the polymeric mixture was 9 LL thick, and the middle layer of the propylene homopolymer was 3 μm thick . The two outer layers were each 1.4 lm thick.

Evaluation / Film Test Each of the above films was heat-sealed to itself, the heat-sealed layer having an intermediate layer of a polymer blend below which is used to form the thermal seal. The thermal seals were formed at a temperature of 130 ° C under a load of 96.5 kN / m (14 psi) for a period of 1 second. After cooling, the seals were removed by hand pulling. In all cases, the originally transparent heat-sealed areas were completely peeled off and turned white where the seals have been removed by pulling. The evaluation of the seals detached from Examples 1 to 4 by scanning electron microscopy revealed that in all cases the seals failed due to rupture of the intermediate layer immediately below the sealable layer with heat-sealed heating, within the thickness of the intermediate layer . The sealing with heating of the other surface of the respective films to itself gave thermal seals which were satisfactorily detached in the case of Examples 5, 6 and 8. However, in the case of the other Examples, where one layer inter-media was not present below the heat-sealable layer used to form the thermal seal, the films themselves tear or the thermal seals themselves delaminate. In a comparison test in which a three-layer film is produced as described in Example 1 but without the intermediate layer, seal failure occurred by tearing the film itself, through the thickness of the core layer .

It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates.

Having described the invention as above, property is claimed as contained in the following

Claims

R E I V I N D I C A C I O N S

1. A multilayer polymer film, characterized in that it comprises a base layer of a propylene polymer, an intermediate layer without voids or voids on the base layer, and a heat sealable polymer layer on the intermediate layer, the intermediate layer without voids or voids has a internal cohesive force less than the bonding strength of the intermediate layer to either the base layer or the heat-sealable layer and less than the internal cohesive forces of either the base layer or the heat-sealable layer.

2. A film according to claim 1, characterized in that the base layer comprises a propylene homopolymer.

3. A film according to any of the preceding claims, characterized in that the intermediate layer comprises a mixture of a propylene polymer and an ethylene polymer.

4. A film according to claim 3, characterized in that the ethylene polymer contains units derived from at least one alpha-olefin additional .

5. A film according to any of claims 2 to 4, characterized in that the ethylene polymer has at least 50 weight percent of units derived from ethylene and not more than 50 weight percent of units derived from one or more alpha- olefins.

6. A film according to any of claims 2 to 5, characterized in that the ethylene polymer has at least 75 weight percent of units derived from ethylene and not more than 25 weight percent of units derived from one or more alpha- olefins.

7. A film according to claim 5 or claim 6, characterized in that the alpha-olefin is at least propylene and butene-1.

8. A film according to any of claims 5 to 7, characterized in that the ethylene polymer is an ethylene / butene-1 copolymer.

9. A film according to claim 8, characterized in that the ethylene polymer contains from 80 to 95 weight percent of units derived from ethylene and from 20 to 5 weight percent of units derived from butene-1 substantially without units derived from the propylene.

10. A film according to claim 9, characterized in that the ethylene polymer contains about 90 weight percent of units derived from ethylene and about 10 weight percent of units derived from butene-1.

11. A film according to any of claims 3 to 10, characterized in that the propylene polymer in the mixture is a propylene homopolymer or a propylene copolymer and not more than 2 weight percent ethylene.

12. A film according to any of claims 3 to 11, characterized in that the mixture comprises from 70 to 30 weight percent of a propylene polymer and from 30 to 70 weight percent of the ethylene polymer.

13. A film according to claim 12, characterized in that the mixture comprises from 60 to 40 weight percent of the propylene polymer and from 40 to 60 weight percent of the ethylene polymer.

14. A film according to any of the preceding claims, characterized in that the heat-sealable polymeric layer comprises a copolymer containing units derived from at least two of ethylene, propylene and butene-1.

15. A film according to claim 14, characterized in that the heat-sealable polymeric layer comprises a propylene / ethylene copolymer of a propylene / ethylene / butene-1 terpolymer.

16. A film according to any of the preceding claims, characterized in that it has at least one additional polymeric layer on the opposite side of the base layer from the intermediate layer and the heat sealable layer.

17. A film according to any of the preceding claims, characterized in that It is substantially transparent.

18. A film according to any of claims 1 to 16, characterized in that it is opaque.

19. A film according to claim 18, characterized in that the base layer has gaps or voids and / or contains a pigment.

20. A film according to claim 16, characterized in that at least one of the at least one additional polymer layer on the opposite side of the base layer contains a pigment.