WO1994015787A1

WO1994015787A1 - Multilayer film comprising polypropylene and polyethylene layers, method of fabrication and utilization for retractable covers

Info

Publication number: WO1994015787A1
Application number: PCT/FR1993/001320
Authority: WO
Inventors: Nathalie Debruyne; Christophe Le Roy; Vincent Hervais
Original assignee: Ecp Enichem Polymeres France
Priority date: 1992-12-31
Filing date: 1993-12-30
Publication date: 1994-07-21
Also published as: NO301465B1; FI943972A0; EP0627992A1; NO943205D0; FR2699856A1; FR2699856B1; JPH08500550A; FI943972A; KR950700172A; CA2131085A1; NO943205L

Abstract

The invention relates to a multilayer film comprising two external layers and at least one intermediary layer. For all the successive layers forming the film, it comprises at least once the succession of the three following layers; (A) layer comprising (a) at least one propylene homopolymer, and/or (b) at least one propylene/α-olefin copolymer; the binding layer (L) comprising (e) at least one ethylene/α-olefin copolymer; (B) layer comprising (c) at least one radical polymer of the ethylene (homopolymer of ethylene or copolymer of ethylene/polar comonomer), or (d) a mixture of at least one polymer such as defined in (c) with up to 20 % by weight of said radical polymer of ethylene, at least one linear copolymer of ethylene/α-olefin; the binding layer (L) being arranged between the layers (A) and (B), and, when the multilayer film comprises more than one layer of a given type (A), (B) and (L), the constituants of the different layers of the same type may be identical or different. Utilization in the field of retractable covers.

Description

MULTILAYER FILM HAVING POLYPROPYLENE AND POLYETHYLENE BASED LAYERS. ITS MANUFACTURING METHOD AND ITS USE FOR RETRACTABLE COVERS.

The present invention relates to a multilayer film comprising at least one layer (A), based on a homopolymer or copolymer of propylene, at least one layer (B), essentially based on a radical homopolymer or copolymer of ethylene, and at least one particular binder layer (L), disposed between two layers (A) and (B). Bi-layer films are known comprising a first layer of a composition based on a mixture of polypropylene and polyethylene and a second layer based on polyethylene, as well as bilayer films comprising two layers each of a composition based on polypropylene and polyethylene, the proportions of the two constituents being different from one layer to another. These bilayer films are not always satisfactory in applications where it is desired that one of the layers is predominantly polyethylene and the other, predominantly polypropylene, such as, for example, in the case of shrink wrapping for wrapping, such as described below. As illustrated by the Comparative Examples also appearing below, the bilayer films, comprising a layer based on radical polyethylene and a layer based on polypropylene, do not exhibit sufficient adhesion of these two layers, leading to unacceptable delamination on 'use. It is this problem of incompatibility between these two types of layers that the Applicant Company sought to resolve.

The solution which it proposes for this purpose, and which is the subject of the present invention, consists in providing, between two layers of the aforementioned type, a binder layer of a copolymer of ethylene and at least one alpha -olefin, which may be advantageously associated with a homopolymer and / or a copolymer of propylene. It has been observed - which will be shown by

Examples of the invention below - that the presence of this particular binder layer (L) makes it possible to obtain films having better adhesion of their constituent layers to each other.

In addition, after aging of the films according to the invention, the adhesion generally shows only a very small decrease in its original value (less than 10%).

For preferred compositions, it sometimes shows an increase in this value. The adhesion values between layers are also well balanced between the longitudinal direction (machine direction) and the transverse direction. Finally, it has been observed that the rupture which occurs during the measurement of the adhesion is of the cohesive type when the value of adhesion is high.

The present invention therefore firstly relates to a multilayer film comprising two external (surface) layers and at least one intermediate layer, characterized in that, for all the successive layers which compose it, it comprises at least once the succession of the following three layers: a layer (A), which comprises: (a) at least one homopolymer of propylene, and / or

(b) at least one copolymer of propylene and at least one alpha-olefin;

- a binder layer (L), which comprises:

(e) at least one copolymer of ethylene and at least one alpha-olefin, a layer (B), which comprises:

(c) at least one radical polymer of ethylene chosen from radical homopolymers of ethylene and radical copolymers of ethylene and of at least one polar comonomer, or

(d) a mixture of at least one radical polymer of ethylene as defined in point (c) above, with up to 20% by weight, relative to said radical polymer of ethylene, of at least at least one linear copolymer of ethylene and at least one alpha-olefin; the binder layer (L) being disposed between layers (A) and (B), when the multilayer film comprises more than one layer of a given type (A), (B) and (L), the constituents of the different layers of the same type which may be identical or different. The multilayer film according to the invention can constitute a complex structure comprising layers of a nature different from (A), (L) and (B). In the case where it only comprises layers (A), (L) and (B) (each of the layers A, L and B respectively being made up of the same polymer or else of different polymers, but of the same type), its two outer layers are of type (A) and / or (B). They can be of different types (A on the one hand, B, on the other hand) in a three-layer film or 7 layers; they are of the same nature (A or B) in a film with 5 or 9 layers.

Also included in the present invention are multilayer films in which a layer of a polymer of the same kind as that constituting at least one layer A and / or B is attached to said layer. Examples include multilayer films of type A '/ A / L / B, A / L / B / B' and A '/ A / L / B / B' in which the polymer constituting layer A 'is of the type (a) and / or (b), and the polymer constituting the layer B * is of the type (c) and / or (d). The same polymer can constitute the layers (A) and (A *). The same other polymer can constitute the layers (B) and (B ').

The binding layer (L) can further comprise:

(f) at least one homopolymer of propylene, and / or

(g) at least one copolymer of propylene and at least one alpha-olefin, the constituent (f) of said layer (L) and the constituent (a) of layer (A) possibly being identical or different, and the component (g) of said layer (L) and component (b) of layer (A) may be identical or different.

The binder layer (L) thus notably consists of a mixture of: 93 to 30% by weight, preferably 83 to 43% by weight, more preferably 78 to 53% by weight, of the component (e); and

7 to 70% by weight, preferably 17 to 57% by weight, even more preferably 22 to 47% by weight, of component (f) and / or (g).

The constituent (a) of a layer (A) is a homopolymer of propylene, obtained, for example, by polymerization using Ziegler type catalysts, and having in particular a density between 0.89 and 0.91, an index fluidity advantageously between 2 and 20 g / 10 min. about.

Components (b) and (g) may be the same or different. They each consist of at least one propylene copolymer, chosen from random, block and block copolymers of propylene and at least one alpha-olefin chosen from ethylene and C 1 -C 4 alpha-olefins. These copolymers can be obtained by copolymerization of propylene and of the selected comonomer (s) (preferably ethylene), in the presence of stereospecific Ziegler type catalysts, for example in suspension in a solvent or in phase liquid.

These copolymers advantageously have a density between 0.89 and 0.91, and a melt index advantageously between 3 and 20 g / 10 min.

Mention may in particular be made of crystalline copolymers of propylene and ethylene, having a degree of crystallinity (measured by X-ray diffraction) of at least about 40%, these crystalline copolymers being able to be isotactic or syndiotactic. An isotactic, random copolymer containing 85 to 99%, preferably 90 to 99%, in moles of propylene units, and 1 to 15%, preferably 1 to 10%, in moles of ethylene units, will advantageously be chosen. , whose melting point J (measured by differential enthalpy analysis according to standard NFT-51223) is between 130 and 150 "C, preferably between 130 and 140 ° C. Concerning the constituent (c) of a layer (B), by radical homopolymer of ethylene is meant a product obtained by polymerization of ethylene under high pressure

(generally 1000 to 4000 bars) and at high temperature (140 ° C to 350 ° C), in the presence of a free radical initiator (such as oxygen, peroxides and peresters); and, by radical copolymer of ethylene, is meant a product obtained, by a polymerization carried out under the same conditions as those which have just been indicated, of ethylene with at least one monomer copolymerizable with ethylene, such as , for example, carbon monoxide, ethylenically unsaturated carboxylic acids, esters derived from said acids and from an alcohol having from 1 to 8 carbon atoms, maleic anhydride, vinyl acetate, etc. In the context of the present invention, it is preferred to choose a radical homo- or copolymer of ethylene having a density of between approximately 0.910 and 0.940, in particular a density of between approximately 0.915 and 0.935, and a melt index included between about 0.15 and 20 dg / min.

As for the linear polymer (s) of ethylene and at least one α-olefin entering the mixture defining the constituent (d) of a layer (B), it (s) is

(or are) constituted by at least one copolymer chosen in particular from ethylene copolymers:

- with at least one alpha-olefin having 3 to 12 carbon atoms; having a content of units derived from ethylene of at least 80 mol%; - having a density between 0.895 and 0.945; and having a melt index of between 0.1 and

8 g / 10 min., In particular between 0.1 and 4 g / 10 min.

The alpha-olefin used to prepare the copolymer (d) advantageously has from 3 to 12 carbon atoms, preferably from 3 to 8 carbon atoms. It is chosen, for example, from propylene, butene-1, methyl-4-pentene-1, hexene-1, octene-1 and their mixtures. These ethylene copolymers are prepared by copolymerization of ethylene with at least one of the alpha-olefins mentioned above, in the presence of catalytic systems of the Ziegler type, in solution, in emulsion, in gas phase or in the state hypercritical. Advantageously, copolymers obtained using a process consisting in copolymerizing ethylene and at least one alpha-olefin are used at a temperature between approximately 180 and 300 ° C., under a pressure comprised between approximately 300 and 2500 bars, preferably according to a method continuous, the residence time of the catalytic system in the copolymerization reactor being between 1 and 150 seconds. The content of the comonomer in the gas stream is adjusted as a function of the nature of the latter and of the density desired for the copolymer. Thus, to obtain these copolymers, a gas stream is polymerized containing from 30 to 50% by weight of approximately ethylene and from 50 to 70% of comonomer (s). One of those described in European Patent No. 32,339 is advantageously used as a catalyst. It is possible to operate in the presence of up to 2 mol% of a transfer agent, such as hydrogen, so as to obtain the desired fluidity index.

Furthermore, with regard to the content of linear copolymers of ethylene in the mixture (d), it may be indicated that a choice is made not to affect the optical properties of the radical polymers (c) too much, although it is increased thus the mechanical properties. The linear copolymer (s) of ethylene and at least one α-olefin entering the mixture defining the constituent (d) advantageously represents from 5 to 15% by weight of said ( or said radical polymer (s) of ethylene as the base of said mixture.

According to another characteristic of the present invention, the layer (A) can also comprise: (h) up to 20% by weight of said external layer (A) of at least one copolymer of ethylene and at least one C ₃ -CiL ₂ alpha-olefin, having a content of units derived from ethylene of at least 70 mol%.

The constituent (e) involved in the formation of the binder layer (L) is at least one copolymer chosen in particular from ethylene copolymers: with at least one alpha-olefin having 3 to 12 carbon atoms; containing at least 70 mole% of units derived from ethylene; - having a density between 0.860 and 0.930; having a degree of crystallinity, measured by X-ray diffraction, of at least 2%; and having a melt index of between 0.5 and 10 g / 10 min. For a more detailed description of the components (h) or (e) and (g), reference is made to the detailed description respectively of the linear ethylene copolymer entering into the composition of the mixture (d) and of the component (b). According to an embodiment of the present invention, according to which a layer (B) advantageously constitutes at least one outer layer and consists of the radical polymer (s) and the binder layer (L) only comprises the copolymer (e ), it is preferable that the latter has a density between 0.900 and 0.930.

The compositions of each layer (A), (B) and (L) of the film according to the invention can be prepared by any known means of mixing their constituents, for example, by mixing granules or powder, then, as the case may be. if necessary, mixing in the molten state of this mixture, then extrusion and regranulation. From these granules, the film is converted.

The films are obtained in a known manner, by using a coextrusion of the compositions in the molten state intended to form the layers (A), (B) and (L), through a flat die, or else to through a die comprising at least three concentric channels, opening in a circular air gap co-axial with said channels, in which case it is followed by a blowing of the tubular sheath formed, the compositions of each of the three layers each having a melt index in particular between 0.5 and 5 g / 10 min .

The thickness of the three-layer film, depending on its use, is generally between 15 and 500 μm, each of the layers (A), (B) and (L) having a thickness ranging from 5 μm to 300 μm. The present invention also relates to the use of a multilayer film as defined above, more particularly in its simplest form of three-layer film, in the field of shrinkable covers, for example for wrapping on pallets of products contained in envelopes of polyethylene, at least one layer (A) of said multilayer film constituting an external layer and being in contact with said polyethylene envelopes, thus avoiding sticking of the cover to the envelopes.

In the nonlimiting examples given below by way of illustration of the invention (as well as in the general description above), the characteristics of the copolymers and the results of the measurements were obtained as follows: the molar contents in units constituent of polymers: by infrared spectroscopy; - densities: according to standard ASTM D-1505; the fluidity indices, expressed in g / 10 min. : according to standard ASTM D-1238 under the conditions: (E) (190 ° C., 2.16 kg) for polymers of ethylene; and

(L) (230 ° C, 2.16 kg) for propylene polymers; The peel strength evaluation tests were carried out as follows:

We use a LHOMARGY blood pressure monitor. The sample to be tested is, after having started the peeling, placed in the tensiometer so that each of the primers is clamped by one of the two jaws. A 90 ° peeling angle between on the one hand each of the outer layers and, on the other hand, the rest of the sample is maintained during peeling. The width of the sample is 15 mm. The tensile test (peeling phase) is carried out at a speed of 300 mm / min. The measurements were carried out on days 0 and 14, after storage at room temperature. In the examples below, the sample was taken in the longitudinal direction (machine direction).

In the following examples, the following polymers and copolymers were used (denoted by the capital letter A, B or L, depending on whether they are part of the layers (A), (B) or (L), this letter being followed by the lower case letter corresponding to the constituent described above, then a serial number): Abl or Lgl: random copolymer of propylene, marketed under the name "ELTEX PKS 409". Aal or Lfl: homopolymer of propylene, sold under the name "VESTOLENE P 6000"; Ab2 or Lg2: block copolymer of propylene, sold under the name "HOSTALENE PPR 1042"; Bel: radical homopolymer of ethylene, density 0.924 and melt index 0.80, marketed under the name "RIBLENE

FF 30 "by the company ECP - ENICHEM POLYMERES FRANCE S.A.; Lel: copolymer of ethylene and butene-1, at

89% by mole of ethylene and 11% by mole of butene-1, of density 0.910 and of melt index 0.9, marketed under the name "CLEARFLEX FG B0" by the Company

ECP - ENICHEM POLYMERES FRANCE S.A.;

Le2 (or Ahl): terpolymer of ethylene, propylene and butene-1, having a density of 0.881 and a melt index of 1.2, sold under the name "CLEARFLEX CH GO" by the company ECP - ENICHEM POLYMERES FRANCE SA;

Le3: terpolymer of ethylene (88 mol%), propene and butene-1, density 0.898, and melt index 0.8, sold under the name "CLEARFLEX FF DO" by the company ECP - ENICHEM POLYMERES FRANCE SA;

Le4: copolymer of ethylene (96 mol%) and butene-1, density 0.920, and melt index 1.0, sold under the name "FLEXIRENE FG 20" by the company ECP - ENICHEM POLYMERES FRANCE SA In the examples, the percentages are given by weight unless otherwise indicated.

Examples 1 to 3 (Comparatives)

B / A type bilayer film

A bilayer film B / A was produced by coextrusion, the thicknesses of the outer layers (B) and (A) being 30 μm and 20 μm respectively. The results of the adhesion test are reported in Table 1 below:

Table 1

Examples 4 to 7

Bcl / Lel type three-layer films + x% Lgl / Abl

Three-layer films of the above type were produced by coextrusion, the thicknesses of the layers (B), (L) and (A) being 30 μm, 10 μm and 20 μm respectively. The constituents of layer (L) were dry mixed for extrusion. The layer (A) constitutes, as in all the examples, the layer facing the outside of the sheath during the extrusion-blowing.

The results of the adhesion test are reported in Table 2 below.

Table 2

Example 4 5 6 7

% of Lgl in the 0 20 30 50 layer L

0 day grip 5.87 6.28 6.57 6.77 N / 15 mm

14 days 7.31 5.69 6.47 6.77

Examples 8 to 14

Bcl / Le2 + x% Lgl / Abl type three-layer films

The procedure was as in Examples 4 to 7 to prepare the three-layer films of the above type; the adhesion results are reported in Table 3. Table 3

Examples 15 and 16

Bcl / Le3 + x% Lgl / Abl type three-layer films

The procedure was as in Examples 4 to 7 to prepare the three-layer films as defined above. The adhesion results are reported in Table 4.

Examples 17 and 18

Bcl / Le4 + x% Lgl / Abl type three-layer films

Table 4

Examples 19 to 28

Bcl / Le + x% Lfl / Aal type three-layer films

The procedure was as in Examples 4 to 7 to prepare the three-layer films as defined above. The adhesion results are reported in Table 5.

Table 5

Adhesion N / 15 mm

Example Layer L

0 d. 14 d.

19 Le2 3.73 4.32

20 Le2 + 30% Lfl 4.02 6.09

21 Le3 6.09 8.63 bootable but difficult

22 Le3 + 30% Lfl impelable primable, impelable

23 Lel 4 3.63

24 Lel + 20% Lfl 7.26 8.83

25 Lel + 30% Lfl 6.77 8.34

26 Lel + 50% Lfl 7.60 8.83

27 Le4 7.7 4.7

28 Le4 + 30% Lfl bootable but 8.14 impelable

Examples 29 to 34

Three-layer films of the Bcl / Le + x% Lg2 / Ab2 type

The procedure was as in Examples 4 to 7 to prepare the three-layer films as defined above. The adhesion results are reported in Table 6. Table 6

Adhesion N / 15 mm

Example Layer L

0 d. 14 d.

29 Le3 6.28 5.49 hardly difficult

30 Le3 + 30% bootable Lg2; bootable; impelable impelable

31 Lel 6.67 5.69

32 Lel + 20% Lg2 6.47 6.87

33 Lel + 30% Lg2 7.75 7.36

34 Lel + 50% Lg2 7.11 7.75

Examples 35 and 36

Bcl / Le2 + x% Lgl / Abl + y% Ahl type three-layer films

Three-layer films of the above type were produced, the binder layer being obtained as in Examples 4 to 7. Layer A is also obtained after dry mixing of the granules. The thicknesses of the successive layers B, L and A are respectively 20 μm, 10 μm and 30 μm.

The adhesion values for each of the films produced are given in Table 7.

Table 7

Example 35 36

Layer L Le2 Le2 + 5% Lgl

Layer A Abl + 5% Ahl Abl + 5% Ahl

0 d. 2.8 3.2

Adhesion N / 15 mm

14 d. 1.6 2.0

Claims

1 - Multilayer film comprising two external layers and at least one intermediate layer, characterized in that, for all the successive layers which compose it, it comprises at least once the succession of the following three layers: a layer (A), which includes:

(a) at least one homopolymer of propylene, and / or

(b) at least one copolymer of propylene and at least one alpha-olefin; a binder layer (L), which comprises: (e) at least one copolymer of ethylene and at least one alpha-olefin, a layer (B), which comprises: (c) at least one radical polymer of l ethylene chosen from radical homopoly eres of ethylene and radical copolymers of ethylene and of at least one polar comonomer, or (d) a mixture of at least one radical polymer of ethylene as defined in point (c) above, with up to 20% by weight, relative to said radical polymer of ethylene, of at least one linear copolymer of ethylene and of at least one alpha-olefin; the binder layer (L) being disposed between layers (A) and (B), when the multilayer film comprises more than one layer of a given type (A), (B) and (L), the constituents of the different layers of the same type which may be identical or different. 2 - Multilayer film according to claim 1, characterized in that its two outer layers are of the type (A) and / or (B).

3 - Multilayer film according to claim 2, characterized in that it is of the three-layer type A / L / B. 4 multilayer film according to one of claims 1 to 3, characterized in that the binder layer (L) comprises, in addition to the constituent (e): (f) at least one homopolymer of propylene, and / or

(g) at least one copolymer of propylene and at least one alpha-olefin, the constituent (f) of said layer (L) and the constituent (a) of layer (A) possibly being identical or different, and the component (g) of said layer (L) and component (b) of layer (A) can be identical or different.

5 - Multilayer film according to claim 4, characterized in that the binder layer (L) consists of a mixture of:

93 to 30% by weight of the constituent (e); and

7 to 70% by weight of component (f) and / or (g).

6 - Multilayer film according to claim 5, characterized in that the binder layer (L) consists of a mixture of:

83 to 43% (preferably 78 to 53%) by weight of the constituent (e); and

17 to 57% (preferably 22 to 47%) by weight of component (f) and / or (g). 7 - Multilayer film according to one of claims 1 to 6, characterized in that the constituent (e) is at least one copolymer chosen from copolymers of 1 • ethylene: with at least one alpha-olefin having 3 to 12 atoms of carbon ; containing at least 70 mole% of units derived from ethylene; having a density between 0.860 and 0.930; having a degree of crystallinity at least equal to 2%; and - having a melt index of between 0.5 and 10 g / 10 min.

8 - Multilayer film according to one of claims 1 to 7, characterized in that the constituent (b) and, when it is present, the constituent (g) each consist of a random, block or block copolymer of propylene and at least one alpha-olefin chosen from ethylene and C 1 -C 4 alpha-olefins _/ having a content of units derived from propylene of between 85% and 99% by moles.

9 - Multilayer film according to one of claims 1 to 8, characterized in that the layer (A) further comprises:

(h) up to 20% by weight thereof of at least one copolymer of ethylene and of at least one C ₃ -C ₁₂ alpha-olefin having a content of units derived from ethylene at least 70 mol%. 10 - Multilayer film according to one of claims 1 to 9, characterized in that the radical homo- and copolymers of ethylene as constituents (c) have a density between 0.910 and

0.940, especially between 0.915 and 0.935, and a melt index between 0.15 and 20 g / 10 min., The copolymers being obtained by copolymerization of ethylene with at least one comonomer chosen from carbon monoxide, ethylenically unsaturated carboxylic acids, esters derived from said acids and from an alcohol having from 1 to 8 carbon atoms, maleic anhydride and vinyl acetate.

11 - Multilayer film according to one of claims 1 to 10, characterized in that a linear ethylene copolymer entering the mixture defining component (d) is a copolymer chosen from ethylene copolymers : with at least one alpha-olefin having 3 to 12 carbon atoms; having a content of units derived from ethylene of at least 80 mol%; having a density between 0.895 and 0.945; and having a melt index of between 0.1 and 8 g / 10 min., in particular between 0.1 and 4 g / 10 min.

12 - Multilayer film according to one of claims 1 to 11, characterized in that the (or) linear copolymer (s) of ethylene and at least one α-olefin entering the defining mixture the component (d) represents (s) from 5 to 15% by weight of said radical polymer (s) of ethylene as the base of said mixture.

13 - Multilayer film according to claims 1 to 12, characterized in that the constituent (e) is a copolymer of ethylene and an α-olefin having a density between 0.900 and 0.930, when the layer (B) comprises, as sole constituent, only at least one radical polymer of ethylene (c). 14 - Process for manufacturing a multilayer film as defined in one of claims 1 to 13, characterized in that it comprises the coextrusion of the compositions in the molten state intended to form the layers (A), ( L) and (B), through a flat die, or else through an annular die in which case the coextrusion is followed by blowing the tubular sheath formed, the compositions of each of the layers each having a melt index in particular between 0.5 and 5 g / 10 min.

15 - Method according to claim 14, characterized in that one prepares a composition intended to form a layer (A), (B) and (L), in the case where it comprises at least two constituents, by mixing said constituents, for example by mixing granules or powders, then, if necessary, mixing in the molten state of this mixture, then extrusion and regranulation.

16 - Use of a multilayer film as defined in one of claims 1 to 13, in the field of shrinkable covers, in particular for wrapping on pallets of products contained in polyethylene envelopes, at least one layer (A) of said multilayer film constituting an outer layer and then being in contact with said polyethylene envelopes.