MXPA97006232A

MXPA97006232A - Thermoencogible films based on a copolimerolineal of ethylene with one or more alpha-olefi

Info

Publication number: MXPA97006232A
Application number: MXPA/A/1997/006232A
Authority: MX
Inventors: Perdomi Gianni; Cometto Claudio; Beccarini Enrico
Original assignee: Montell Technology Company Bv
Priority date: 1995-12-18
Filing date: 1997-08-15
Publication date: 1998-07-03

Abstract

Shrink films based on polyolefin compositions comprising: (i) a linear copolymer of ethylene with one or more alpha-olefins (LLDPE), (ii) a propylene copolymer having particular composition and characteristics, the films are characterized by good optical and mechanical properties and in particular by an alpha resistance to tearing

Description

THERMOENCOGIBLE FILMS ñ BASE OF AN ETHYLENE LINEAR COPOLIHERO WITH ONE OR MORE tt-QLEFINAS DESCRIPTIVE MEMORY This invention relates to heat shrinkable films based on polyolefin compositions comprising linear copolymers of ethylene with α-olefins having from 3 to 12 carbon atoms (LLPDE) and particular propylene copolymers, said polyolefin compositions having particular mechanical properties . The use of LLDPE in the production of single or multi-layer heat shrink films is well known in the art. Said films are normally produced by extrusion of the polymer, obtaining a primary film which is then oriented by stretching under temperature conditions such that molecular orientation exists without there being problems of tearing and rupture. The polymer used in the production of the film must therefore be sufficiently plastic to be stretched, within the temperature range in which the orientation procedure takes place, and at the same time strong enough to withstand the force of stretching. In addition, the temperature scale within which these two properties coexist should be as wide as possible, since narrow temperature scales would make it difficult to handle the stretching and orientation procedure. The orientation can be either in one direction or in two directions, usually perpendicular to one another (biaxial orientation). The biaxial orientation is generally carried out using, for example, the twin bubble or frame frame method. Once it has been oriented, the film has the ability - when subjected to a certain temperature - to shrink or exert a shrink force when the actual shrinkage is avoided, perfectly adhering in this way to the object that will be packed. In the case of single-layer films based on LLDPE or multilayer films in which the different layers consist essentially of LLDPE, it is usually necessary to entangle the film, at least partially, before subjecting it to the orientation procedure. , to give it the right mechanical properties to withstand the stretching force. The entanglement is usually effected by irradiating the film. As an alternative or in addition to the interlacing, the LLDPE is mixed with other polymers, such as ethylene / vinyl acetate (EVA) or VLDPE / ULDPE copolymers to obtain films having suitable mechanical properties and which are easy to work with. These techniques affect the economics of the production process and therefore the final cost of the film. Non-interlacing heat shrink films exclusively based on LDPE can only be produced when the LLDPE is a copolymer of ethylene with a higher α-olefin, for example 1-octene. With other olefins, for example 1-butene or hexene, the temperature necessary for the orientation is so close to the melting point of the polymer that in practice it is not possible to stretch the film, even at low speed, without any ruptures. in the movie isma. The patent of E.U.A. No. 4597920 describes a process for the production of heat shrinkable films in which the polyene used is a copolymer of ethylene with an α-olefin having 8-18 carbon atoms. The copolymer is characterized fjords different melting points that allow the production of films on a commercial basis without interlacing the polymer. However, the working regime is restricted, - it can be observed in fact from the examples that the film can only be stretched with good results at temperatures between 115 and 1 ° 0 ° C. In addition, LLDPEs modified with higher 1-octene or or-olefins have significantly higher costs than conventional LLDPEs modified with l-butene. Patent application EP-A -434322 discloses the use of mixtures of ethylene / l-hexene copolymers or ethylene / 1-ketene copolymers with significant amounts of LDPE. According to the description of the patent, the addition of LDPE or LLDPE modified with 1-hexene (which can not be used as such in the production of heat shrinkable films) makes it possible to use the mixture obtained in the production of heat shrink films.; the mixture of LDPE with l-octene-modified LLDPE is claimed instead to allow the extrusion rate to be added and thus the productivity of the process. However, the work regime remains very restricted. Patent application WO 94/21726 discloses single-layer biorientated heat-shrink films obtained from polymer compositions comprising an ethylene / α-olefin copolymer. na, a polypnepca alloy (formed by a hetopofasic composition in which an amorphous ethylene / propylene copolymer is dispersed in a propylene matrix or copolymer) and / or a random copolymer of propylene with full e-t and possibly a crystallization inhibitor. According to the information reported in said patent application, the compositions described allow an adequate handling of the blowing and orientation phase in the twin bubble procedures. The preferred ethylene / cy-olefin copolymer is a LLDPE modified with 1-ooten; no examples are reported in which the LLDPE is modified with l-butene or 1-hexene. It has now been discovered that by using particular polymer compositions based on LLDPE it is possible to produce heat shrinkable films having very good mechanical properties (in some cases higher to those of the interlaced films) without using interlacing treatment and without encountering any problems during the orientation procedure. Surprisingly, it has in fact been observed that polyolefin compositions comprising particular LLDPE and propylene copolymers can be used in orientation processes without the problems of tearing or rupturing even when the LLDPE is formed by an ethylene / 1- copolymer. buteno The films of this invention are also characterized by a good set of optical and mechanical properties, in particular high tear resistance, which makes them particularly suitable for use on high speed packaging lines. The heat shrinkable films of this invention comprise a polyolefin composition containing: (i) from 80 to 100 parts by weight of an ethylene copolymer (LLDPE) with one or more C2 olefins of CH2 = CHR, wherein R is a hydrocarbon radical having 10 carbon atoms, said copolymer contains up to 20 mol% of α-olefin of CH 2 = CHR and has a density of at 0.88 and 0.945 g / cm 3; and (n) from 5 to 30 parts by weight of a copolymer of propylene with one or more w-olefins of CH2 = CHR *, wherein Ri is a hydrocarbon radical having from 2 to 10 carbon atoms, and possibly with ethylene, said copolymer contains from 60 to 98% by weight of units derived from propylene, from 2 to 40% by weight of units derived from the α-olefin of CH2 = CHRi, and from 0 to 10% by weight of derived units of ethylene, and having a fraction insoluble in xylene greater than 70%. The copolymer (i) is preferably present in amounts between 90 and 1 00 wt. In weight and has a density preferably below 0. 89 and 0. 94 g / crn3. You have preferentially these values are ent 0. 90 and 0. 935 The melt index (determined by the method ASTM D-1238, condition E) of the copolymer (i) has values that are usually between 0.1 and 10 g / 10 minutes, preferably between 0. 2 and 5 g / 10 minutes, more preferably between 0.2 and 3 and / 10 minutes. The α-olefin of CH2 = CHR can be selected, for example, from propylene, l-butene, 1-hexene, 1-octene and 4-methyl-l-pentene; l-butene or 1-hexene are preferably used. In the production of component (i) the of-olefmas of CH2 = CHR can also be used mixed. The copolymer (i) can be produced by copolirnepzation of ethylene with an or-olefin of CH2 = CHR, on the presence of a Ziegler-Natta type catalyst obtained from the reaction of an organometallic compound of a metal in the groups II and III of the periodic system with a catalytic component comprising a compound of a transition metal belonging to groups IV, V or VI of the periodic system. The transition metal compound is preferably supported on a solid support comprising a magnesium halide in an active form. Examples of catalysts that can be used in the production of the copolymer (a) are described in the patent of E.U.A. No. 4,218,339 and in the U.S. patent. No. 4,472,520, the description of which is included here for reference purposes. The catalysts can also be produced by the methods described in the U.S. Patents. Do not. . 48,221 and 4,803,251. Other examples of catalysts are described in patent applications EP-A-395083, EP-A-553805 and EP-A-553806.

The copolymer (n) is preferably present in amounts between 10 and 25 parts by weight. The copolymer (n) can be for example a propylene / cr-olefin copolymer of CH2 = CHR, containing from 70 to 95% by weight of units derived from propylene and from 5 to 30% by weight of units derived from the α-olefin CH2 = CHR1. Said copolymer is preferably a terpolymer of propylene with ethylene and α-olefin of CH2 = CHR1. In this case its content of propylene-derived units is between 80 and 98% by weight, preferably between 85 and 96% by weight, the content of units derived from ethylene is between 1 and 10% by weight, preferably between 2 and 7% by weight, and the content of units derived from the er-ole ina of CH2 = CHRi is between 1 and 10% by weight, preferably between 2 and 8% by weight. The content of the different components is determined by IR and PMN analysis. The α-olefin of CH2 = CHR * can be selected for example from l-butene, 1-hexene, 1-octene and 4-rnet? -1-pentene, and is preferably l-butene or 1-hexene. The msoluble fraction in xylene, determined by the method described below, is preferably greater than 80%, most preferably greater than 85%. The melting enthalpy of the copolymer (11) is generally greater than 50 3 / g, preferably greater than 60 3 / g, most preferably greater than 70 3 / g. The melting temperature of the copolymer (n) is less than 140 ° C and preferably between 120 and 140 ° C. The crystal number of the copolymer (ii) is generally more than 50%. The melt index (determined by the method ASTM D-1238, condition L) of the copolymer (i) has values which are generally between 1 and 1000, preferably between 2 and 100, rnu and preferably between 2 and 30. The copolymers di) they can conveniently produce using a highly ethereal catalyst, for example of the type described in the patent application EP-A-395083, the disclosure of which is included herein for the purposes of reference. The polyolefin compositions containing components (i) and (n) can be produced by mixing the components in the molten state, for example in a mixer having a high power of homogenization. Said polyolefin composition is preferably produced by a sequential polymerization process carried out in at least two stages in which, in any order, ethylene and one or more cf-olefins of CH2 = CHR are polyeneped in one step, obtaining a copolymer (i) containing up to 20 mol% of cx-olefma of CH2 = CHR and a density of between 0.88 and 0.945 g / cm3, and propylene, one or more α-olefms of CH2 = CHRi and possibly ethylene are polyenerated in another step, obtaining a copolymer (11) containing from 60 to 98% by weight of units derived from propylene, from 2 to 40% by weight. weight of units derived from the or-olefin of CH2 = CHRi and from 0 to 10% by weight of units derived from ethylene, and having a fraction insoluble in xylene of more than 70%. The polymerization is conveniently carried out in a gas phase, using fluidized bed reactors. Examples of procedures of this type and of products made by this method are described in international patent applications 10 93/03078 and UO 95/20009, the description of which is included herein for the purposes of reference. The heat shrink films of the invention may conveniently be produced using methods known in the art, such as the frame or twin bubble frame method. In the latter, the method includes the production of a primary tubular film by extruding the polymer components through an annular groove1. The primary film is calibrated and quickly cooled and then heated (by IR or hot air) and oriented in the longitudinal and transverse directions by blowing with compressed air (transverse orientation) and increasing the speed of the lifting roller (longitudinal orientation). The bioriented film is then rapidly cooled to stabilize the molecular orientation of the film. By this method it is possible to produce single-layer or multi-layer films in which the different layers can have the same composition or different compositions. A particular embodiment of the invention relates to single layer shrinkable films comprising polyolefin compositions containing components (i) and (11) as described above. In fact, it has been observed that by using said polyolefin compositions (particularly when these are produced directly by synthesis using a sequential polymerization process) it is possible to produce films having good optical and mechanical properties without interlacing the film, even when the copolymer (i) is a copolymer of ethylene with l-butene; this result is certainly surprising since it is known that to date copolymers of this type have not been used as essential components of non-interlaced heat shrink films, in view of the well-known problems of processing ability. Another embodiment of this invention relates to multi-layer heat shrink films, wherein at least one layer comprises polyolefin compositions containing components (i) and (n) as described above. For example, it is possible to produce three-layer films, with a AAA structure, in which all the layers are obtained from compositions containing components (i) and (n), or with a BAB structure, in which the layer in edio is obtained from compositions containing components (i) and (ii) and the outer layers are obtained from other olefin polymers, as reported in the patents EU 4532189, EP-A-586160 and EP-A-595252. The films of this invention, both co-or multilayer, are characterized by a good set of physical properties, in particular, optimum tear strength and improved processing ability compared to prior art films having a high degree of flexibility. similar structure. In fact, the film can be easily oriented without problems due to the instability of the bubble, on a scale of temperatures that is wider than the conventionally used temperatures, thus allowing to expand the framework. The weight scales described refer to the weight ratios of components (i) and di). As is known to those skilled in the art and as it can easily be ermined by routine tests, it is obviously also possible to add polymer components, additives (such as adhesion enhancers, stabilizers, antioxidants, anticorrosives, nucleating agents, auxiliary agents). processing, etc.) and organic and inorganic fillers that can give specific properties to the films of the invention. The films of this invention have wide applications in the packaging sector, particularly the packaging of small objects, food, etc. The following examples are given as illusions and do not restrict the invention.

EXAMPLES The indicated properties were determined by means of the following methods: Polymer composition: percentage by weight of the different monomers determined by I.R .; - Fraction insoluble in xylene: 2 g of the polymer are dissolved in 250 cm3 of xylene at 135 ° C with stirring. After 20 minutes the solution is allowed to cool, still stirring until the temperature reaches 25 ° C. After 30 minutes the precipitated insoluble polymer is separated by filtration. The solvent is removed from the solution by evaporation in a stream of nitrogen and the residue is vacuum dried at 80 ° C to a constant weight. In this way the percentage of polymer soluble in xylene at 25 ° C is calculated, and the percentage of polymer that is soluble is determined in this way; - Fusion enthalpy: ASTM D 3418-82; - Density: ASTM D 1505; - melting index E (MIÉ): ASTM D 1238, condition E; - melt index F (MIF): ASTM D 1238, condition F; - melt index L (MIL): ASTM ü 1238, condition L; - F / E: ratio between the melt index F and the melt index E: - Tear strength: ASTM D 1004 - Breakthrough alarm: ASTM D 882 - Burst strength: ASTM D 882 - Movement test fast: ASTM D 1709 / A - Turbidity: ASTM D 1003 Production of the film: general procedure The films were produced by the twin bubble method with the following steps. extrusion of the polymer composition in a worm extruder with peak temperatures of about 190-195 ° C; cooling of the primary tubular film at temperatures around 25 ° C; - heating the primary film in an oven with IR rays; - Bio-orientation with a stretch ratio of 6/6 longitudinal / transversal; - Cooling of the bioriented tubular film at room temperature.

EXAMPLE 1 A one layer film was produced using a polyolefin composition (i) + (ii) obtained directly in the polymerization process, operating in two gas phase reactors as described in the international patent application U) 0 95/20009 . The composition comprised 85% of an ethylene / 1-bu-t-ene copolymer [component (i)] and 15% of a propylene terpolymer (92.1%) with ethylene (2.3%) and l-butene (5.6%) ) with an insoluble fraction in xylene of more than 70% [component (n)]. The resulting composition had a HIE of 0.57 and a density of 0.9073. Operating as described in the general methodology for the production of the film, a 15 μm thick film was obtained whose characteristics are shown in Table L.

EXAMPLE 2 A one layer film was produced using a polyolefin composition (i) + (ii) obtained directly in the polymerization process, operating in two gas phase reactors as described in the international patent application UO 95/20009. The composition comprised 85% ethylene / 1-butene copolymer [component (i)] and 15% of a propylene terpolymer (92.1%) with ethylene (2.3%) and l-butene (5.6%) with a more soluble fraction in xylene of more than 70% and a MIL of 13.2 [component (ii) l. The resulting composition had a MIE of 1.06 and a density of 0.910. Operating with or described in the general methodology for the production of the film, a film of 15 urn thickness was obtained whose characteristics are shown in the table L.

EXAMPLE 3 (comparison) For comparison purposes, a film of μm thickness (GRACE MR) was characterized and compared with the films of this invention »The results are shown in table 1.

EXAMPLE 4 A one layer film was produced using a polymer composition comprising: 50% by weight of a polyolefin composition (i) + di) obtained directly in the polymerization process and with a MIE of 1 and a density of 0.901 comprising 85% of an ethylene / l-butene copolymer [coinpone + e (i)] and 15% of a propylene terpolymer (90.8% ep) with ethylene (2.7% ep) and l-butene (6.5% ep) with a insoluble fraction in xylene of more than 70% and one MIL of 13 [component di)]; 25% by weight of an ethylene / 1 -exene copolymer with a MIE of 0.8 and a density of 0.921 marketed by Sabic under the name SABIC 6821N; 25% by weight of a copolymer of ethylene / 1-ketene with an NIE of 1 and a density of 0.923 marketed by Eni chern under the name FG 308. The 15-gauge film was obtained by operating in accordance with procedure of Example 1 and its characteristics are shown in Table 1.

Claims

NOVELTY OF THE INVENTION CLAIMS

1. - A heat-shrinkable film comprising a polyolefin composition containing: (i) from 80 to 100 parts by weight of an ethylene copolymer with one or more α-olefins of CH2 = CHR, wherein R is a hydrocarbon radical having from 1 to 10 carbon atoms, said copolymer contains up to 20 mol% of cx-olefin of CH2-CHR and has a density between 0.88 and 0.945 g / cm3; and (11) from 5 to 30 parts by weight of a copolymer of propylene with one or more w-olefins of CH2 = CHRi, wherein R * is a hydrocarbon radical having from 2 to 10 carbon atoms, and possibly with ethylene, said copolymer contains from 60 to 98% by weight of units derived from propylene, from 2 to 40% by weight of units derived from the -olefi a of CH2"-CHRi, and from 0 to 10% by weight of derived units of ethylene, and having a fraction insoluble in xylene of more than 70%

2. The heat shrinkable film according to claim 1, wherein the copolymer (11) contains from 70 to 95% by weight of units derived from propylene and from 5 to 30% by weight of units derived from the α-olefin of CH2 = CHRi, said copolymer (11) with a more soluble fraction in xylene of more than 80%

3. The heat shrinkable film according to the claim l, in which the copolymer (ii) contains from 80 to 98% by weight of units derived from propylene, from 1 to 10% by weight of ades derived from the α-olefin of CH2 = CHRi and from 1 to 10% by weight of units derived from ethylene, said copolymer di) with a fraction insoluble in xylene of more than 80%.

4. The heat shrinkable film according to claim 1, wherein said pol-olefin composition contains from 90 to 100 parts by weight of said copolymer (1) and from 10 to 25 parts by weight of said copolymer (11). .

5. The heat shrinkable film according to one or more of the preceding claims, wherein the CH2-CHR O-olefme is selected from propylene, 1-butene, 1-pentene, 4-methyl-1-pentene, hexene and 1-octene, and the o-olefin of CH2 = CHR1 is selected from l-butene, 1-pentene, 4-me + il-l-pentene, l-hexene and 1-octene.

6. The heat shrinkable film according to claim 1, wherein said polyolefin composition is produced by a sequential polling process carried out in at least two steps in which, in any order, ethylene and one or more or-olefins of CH2 = CHR are poly erized in one step, obtaining a copolymer (i) containing up to 20 mol% of α-olefin of CH2 = CHR and a density between 0.88 and 0.945 g / cm3 , and propylene, one or more or-olefins of CH2 = CHR1 and possibly et full are polymerized in another step, obtaining a copolymer (ii) containing from 60 to 98% by weight of units derived from propylene, from 2 to 40% by weight of units derived from the α-olefin of CH2 = CHR * and from 0 to 10% by weight of units derived from ethylene, and having an insoluble fraction in xylene of more than 70%.

7. The heat shrinkable film according to claim 6, wherein the copolymer di) contains from 70 to 95% by weight of units derived from propylene, from 5 to 30% by weight of units derived from the α-olefin of CH2 = CHR1, said copolymer (ii) has a more soluble fraction in xylene of more than 80%.

8. The heat shrinkable film according to claim 6, wherein the copolymer (i) contains from 80 to 98% by weight of units derived from propylene, from 1 to 10% by weight of units derived from the or-olefin. of CH2 = CHRi and from 1 to 10% by weight of units derived from ethylene, said co-polar (ii) has a fraction insoluble in xylene of more than 80%.

9. The shrinkable film according to any of claims 7 and 8, in which the O-olefin of CH2-CHR is l-butene and the α-olefin of CH2 = CHR * is 1-butene.

10. A heat-shrinkable film of a layer comprising a polyolefin composition containing: (i) from 80 to 100 parts by weight of a copolymer of ethylene with one or more α-olefins of CH2 = CHR, wherein R is a hydrocarbon radical having 10 carbon atoms, said copolymer contains up to 20 mol% of or-olefin of CH2 = CHR and has a density between 0.88 and 0.945 g / cm3; and (n) from 5 to 30 parts by weight of a propylene copolymer with one or more CI- ^ CHRi of-olefms, wherein R * is a hydrocarbon radical having from 2 to 10 carbon atoms, and possibly with ethylene, said copolymer contains from 60 to 98% by weight of units derived from propylene, from 2 to 40% by weight of units derived from the α-olefin of CH2 = CHR, and from 0 to 10% by weight of units derived from ethylene, and having a more soluble fraction in xylene of more than 70%.

11. A heat-shrinkable film of a layer comprising a polyolefin composition produced by a sequential polymerization process as described in claim 6.

12. The heat shrinkable film according to claim 11, wherein the -ole of CH2 = CHR is J -butene and the α-ole ina of CH2 = CHR1 is l-butene. 13, - A terribly shrinkable film of multiple layers. wherein at least one layer comprises a polyolefin composition containing: (1) from 80 to 100 parts by weight of a copolymer of ethylene with one or more α-olefins of CH2 = CHR, wherein R is a radical of hydrocarbon having from 1 to 10 carbon atoms, said copolymer contains up to 20 mol% of of-olefma of CH 2 = CHR and has a density of between 0.88 and 0.945 g / cm 3; and (11) from 5 to 30 parts by weight of a copolymer of propylene with one or more or-olefins of CH2 = CHRi, wherein Ri is a hydrocarbon radical having from 10 carbon atoms, and possibly with ethylene, said copolymer contains from 60 to 98% by weight of units derived from propylene, from 2 to 40% by weight of units derived from the of-olefin of CH2 = CHR1, and from 0 to 10% by weight of units derived from ethylene, and that it has a fraction insoluble in xylene of more than 70%. 14. A multilayer shrinkable film comprising a polyolefin composition produced by a sequential polymerization process as described in claim 6. 15. The heat shrinkable film according to claim 14, wherein the α-olefin of CH2 = CHR is 1-butene and the α-olefin of CH2 = CHRi is l-butene.