FR2703624A1 - Heat shrinkable composite film, method of manufacture and use of the said film for the exterior packaging of articles - Google Patents

Abstract

The subject of the invention is a heat shrinkable composite film comprising a core layer and two outer or intermediate layers applied to each surface of the core layer, the said intermediate and outer layers being formed by one or more polyolefins, the flexural modulus of which is greater than 200 MPa, according to ASTM D 790, and the Vicat softening point of which is greater than 100 DEG C, according to ASTM D 1525, the said core layer being formed by a polymer, the flexural modulus of which is less than 400 MPa, according to ASTM D 790 and the Vicat softening point is less than 70 DEG C, according to ASTM D 1525, the said polymer being chosen in particular from polypropylenes having a high alpha-olefin content, polyolefin-based elastomeric materials or their blends. The invention also relates to a method of manufacturing the film and its use for the exterior packaging of articles.

Description

The present invention relates to a heat shrink composite film.

  table comprising a core layer consisting mainly of polyolefin elastomeric materials and two outer or intermediate layers applied to each surface of the core layer, said intermediate and outer layers being formed from one or more polyolefins whose flexural modulus is greater than 200 M Pa according to ASTM

  D 790 and whose melting point is greater than 1000 C according to ASTM D 1525.

  It also relates to a process for manufacturing such

  films and the use thereof for the overpackaging of articles.

  Heat shrinkable films generally consist of single or multi-layer structures based on polyolefins, of copolymer

  ethylene vinyl acetate, polyester or poly (vinyl chloride).

  The main characteristics of these heat-shrinkable films are appreciated by the measurement: shrinkage as a function of temperature, shrinkage force, resistance to propagation of the tear and to primed tear, optical characteristics and in particular the gloss and the

transparency.

  Poly (vinyl chloride) films have many qualities which make them easy to process because they

  tolerate varying thermal and running conditions.

  In fact, often the ovens used to shrink the film are poorly adjusted: either they are too hot and the films melt on the package to be packed or, in the case of flexible packages, the force of withdrawal of the film deforms the package or the oven is too cold or poorly ventilated, the film is then not shrunk or partially shrunk; either the temperature of the oven is correct but the duration of stay of the packaging in the oven is not sufficient and then the film is not

  retracted or partially retracted.

  In all the cases described above, the films in

PVC give satisfaction.

  In particular, PVC films can be shrunk over a wide range of temperatures and with a speed of passage through the oven which can vary appreciably, which gives them remarkable shrinking comfort. Their withdrawal force is also low enough to allow the packaging of deformable articles such as stationery (packets of letter envelopes) PVC films

  also have excellent optical qualities.

  However, we know that films based on poly (vinyl chloride) are often the subject of negative reactions from users,

  causes them to have an unpleasant odor during fusion sealing.

  In addition, harmful gases escape during the incineration of used films

  and, for ecological reasons, this drawback becomes unacceptable.

  Films based on poly (vinyl chloride) also have certain drawbacks during their use: they have a corrosive nature which is harmful to packaging machines and the surface yields are insufficient because the films of poly (vinyl chloride) have a density of 1.38 and a thickness generally greater than 12 micrometers

  which leads to high weights / m 2 and low areas per kilogram.

  This is why films based on polyolefins or the like tend more and more to replace films based on poly (vinyl chloride). Certain polyolefin structures have been described in particular in the following patents: French patent FR-A-2 521 907 describes a multilayer polyolefin film comprising a core layer based on linear polyethylene of low or medium density and two layers of skin comprising a mixture of low-ethylene ethylene-propylene copolymer and a propylene homopolymer, the layers of

  skin ensuring the mechanical strength and the optical qualities of the film.

  European patent EP-A-285 444 describes a composite stretched film comprising a core layer comprising a linear low density polyethylene or an ethylene propylene copolymer with a low ethylene content (2 to 6 96) and two external layers formed of a polyethylene linear low density or low-ethylene propylene copolymer

  ethylene These different layers are separated by two intermediate layers.

  diaries which are in particular based on a copolymer of ethylene vinyl acetate, ethylene butyl acrylate and a mixture of linear polyethylene

  low density in combination with the abovementioned copolymers.

  Patent FR-A-2 635 312 describes a heat-shrinkable composite film comprising a core layer formed from a low-density polyethylene with a straight chain and / or from a copolymer of propylene and of one or more alpha-olefins and of two outer layers formed from a crystalline polypropylene copolymer and at least one

other alpha-olefin.

  However, these polyolefin structures are difficult to recycle because of the presence of a large proportion of low density polyethylene associated with the copolymers. Furthermore, films based on polyolefins have a high shrinkage coefficient which prohibits their use for the packaging of certain products. articles such as letter envelopes In addition, these films can only be shrunk in narrow and high temperature ranges, which requires strict control of these conditions and does not offer satisfactory shrinking comfort. The expression retraction comfort is understood in the present

  description being able to shrink the film in a wide range of

  temperatures and with running speeds that can vary within a

range.

  A film with low shrinkage force has been well developed in US Pat. No. 5,023,143, but this film is based on polyethylene and ethylene copolymer which makes it very soft, deformable and of good qualities.

insufficient optics.

  The films according to the present invention have excellent shrinking comfort and the properties of PVC films without having the disadvantages. A general object of the present invention is a heat-shrinkable composite film which has an improvement over the film already

described in the prior art.

  Its subject in particular is a heat-shrinkable composite film

  based on polyolefins having improved optical properties.

  Another object of the invention is to provide a film having excellent heat-sealability and improved shrinking comfort since they can be shrunk over a wide range of temperatures.

  with a wide variation in scroll speed in the oven.

  In the case of films according to the invention which contain only a small proportion of linear low density polyethylene, another object of the present invention is to provide films having properties

  similar to those of PVC while being recyclable.

  Another object of the present invention is to provide a thin composite film whose thickness is generally less than or equal to 15 micrometers. Other advantages of the composite film according to the present invention

  will appear in the description below.

  According to the invention, the heat-shrinkable composite film is characterized in that it comprises a core layer and two external or intermediate layers, said external and intermediate layers being formed from one or more polyolefins whose flexural modulus is greater than 200 M Pa according to ASTM D 790 and whose Vicat point is greater than 1000 C according to ASTM D 1525 and in that the core layer is formed from one or more polymers whose flexural modulus is less than 400 M Pa according to ASTM D 790 and whose Vicat point is less than 701 C according to ASTM D 1525, with the exception of the films explicitly described in French patent application NO 92 12706 of the Applicant, the core layer of which is made up in percentage by weight of: 94 % of an ethylene and propylene elastomer with flexural modulus M Pa and at a Vicat point of 551 C, 2 96% of a masterbatch with slip agents (erucamide), 4% of a polybutylene, and whose outer layers They are chosen by those made up as a percentage by weight of: 94% of a random 4% ethylene copolymer with a flexural modulus of 800 M Pa and a Vicat point of 1300, 2% of a masterbatch with slip agents (erucamide), 4,096 of a masterbatch of anti-blocking agent, 94% of an ethylene propylene copolymer (ethylene content 2%) at Vicat point of 1480 C and a module of 1350 M Pa and 6% d '' slip and anti-lock agents,

  94% of a polypropylene homopolymer having the characteristics

  following: Vicat point: 1550 C module: 2400 M Pa

  and 6% slip and anti-lock agents.

  According to the present description, the expression core layer is

  relating to a layer in a multilayer film which is sandwiched in the outer layers or intermediate layers The film may consist in particular of three layers, a core layer and two layers of skin or of five layers comprising an intermediate layer separating two layers of hearts themselves covered by two outer layers

or layers of skin.

  The ASTM standard is well known to those skilled in the art and is updated periodically. It is notably published in the

appropriate technical brochures.

  As will be understood from the description below, said

  layers for certain applications may include other polymers. It should be clear to those skilled in the art that said outer, intermediate or core layers, in addition to the polymer component, contain in the usual proportions the various well-known ingredients such as anti-blocking or sliding agents for the intermediate or outer layers and anti-slip agents for layers of

heart for example.

  According to a first variant, the invention relates to films having a high modulus for an application where the use of thin films is possible (overpacking of rigid objects) These films having a

  satisfactory retraction comfort.

  According to this variant, the polyolefins forming the intermediate or external layers are based on polypropylene and have a flexural modulus between 750 M Pa and 2500 M Pa according to ASTM D 790 advantageously greater than or equal to 780 M Pa, and a higher Vicat point

  or equal to 1271 C according to ASTM D 1525.

  By the expression "propylene-based polyolefins" is meant that said layers mainly comprise in particular at height of

  at least 80%, and advantageously 90 06, one or more polypropylenes.

  Among the polymers forming the outer layer or intermediate layer suitable in the context of this variant, mention will be made

  especially polypropylene homopolymers obtained by polymer

  propylene with the appropriate catalysts, ethylene propylene copolymers with a low ethylene content (less than 10% and

  preferably 2 to 8%) or a mixture of such polymers.

  In known manner, these polymers are associated with weak

  quantities of slip and anti-blocking agents.

  Among the anti-blocking agents, mention may be made of silica and among the slip or plasticizing agents, mention may be made, for example, of stearamide or erucamide. Typically, these additives will be present in

  a proportion by weight not exceeding 0.5% relative to the total mixture.

  In order to further improve the retraction comfort, the polyolefins based on polypropylene forming the intermediate or external layers can be combined in a proportion of less than 30%, preferably between 5 and 20% by weight relative to the mixture, with a

  linear low density polyethylene.

  By the expression "mixture" is meant in this description

  all of the polymer components or additives forming the film.

  According to a second variant, the invention relates to a film

  presenting in addition to the comfort of retraction an excellent thermoscella-

  bility According to this variant, the polyolefins forming the intermediate or external layers are based on polypropylene and have a flexural modulus between 600 and 750 M Pa according to ASTM D 790 and a point

  Vicat between 120 and 1271 C according to ASTM D 1525.

  Preferably, the polyolefins based on polypropylene according to this second variant have a flexural modulus of between 620 and 720 M Pa. Generally the polyolefins based on polypropylene forming the intermediate or external layers according to this second variant are

  chosen from polypropylene homopolymers obtained by polymer

  sation of propylene with the appropriate catalysts, ethylene-propylene copolymers with a low ethylene content (less than 10% and

  preferably 2 to 8%) or a mixture of such polymers.

  As in the first variant, in order to further improve the retraction comfort, the polyolefins based on polypropylene forming the intermediate or external layers can be combined in a proportion of less than 30%, preferably between 5 and 20% by

  weight compared to the mixture, to a linear low density polyethylene.

  According to a third variant of the present invention, the polyolefins forming the outer and intermediate layers are formed from 1 to 30% of low-density radical polyethylene, 60 to 94% of linear low-density polyethylene, by weight relative to the mixture, and have a flexural modulus between 200 and 600 M Pa according to ASTM D 790

  and the Vicat point is between 100 and 1250 C according to ASTM D 1525.

  This third variant has the advantage of further improving the heat sealability of the film, which induces an increase in shrinkage at low temperature and an improvement in the resistance to tearing initiated. In a known manner, the polymers forming the core layer are associated with slip agents and with assistance in implementation such as

  polybutylene in a proportion not exceeding 6% by weight.

  According to a preferred variant, the core layer or intermediate layer will have a flexural modulus of less than 200 M Pa according to ASTM D

  790 and a Vicat point below 651 C according to ASTM D 1525.

  According to another preferred variant, the core layer will have a flexural modulus of less than 150 M Pa according to ASTM D 790 and a point

  Vicat less than 600 C according to ASTM D 1525.

  Generally the polymer forming the core layer is chosen from polypropylenes with a high alpha-olefin content, the materials

  polyolefin elastomers or mixtures thereof.

  In a preferred variant according to the invention, the polypropylene polymers with a high content of alpha-olefins comprise by weight 10 to 56 of alpha-olefins, preferably 20 to 40% and advantageously 30 to%. Among the alpha-olefins associated as comonomers in the polymers of the core layer, there may be mentioned 1-butene, 1-hexene,

  I-octene in particular and also ethylene.

  According to another particularly advantageous variant of the present invention, the core layer is formed of elastomeric material chosen from elastomers based on ethylene 50 to 70% propylene 30 to 50% diene derivative such as butadiene or a similar conjugated diene 3 to 5 % or the elastomers based on ethylene 10 to 80%, preferably 35 to 75%,

  propylene 20 to 90%, preferably 25 to 65%.

  According to one embodiment, the composite film will be formed from a three-layer sandwich structure, in particular according to the following proportions by weight: first outer layer, 2.5 to 35%, core layer, 30 to 95%,

  second outer layer, 2.5 to 35%.

  Generally, this film will have a thickness of between 12

  and 20 micrometers and preferably less than 10 micrometers.

  According to the present invention, the core layer provides elasticity and resistance to the propagation of the tear, primed or not, and to perforation. It also allows removal at low temperature with a

low withdrawal force.

  According to a particularly advantageous variant making it possible to provide an environmentally friendly film, the invention relates to a recyclable and / or incinerable composite film having a core layer as defined above with all the advantageous variants mentioned above, characterized in that '' it comprises two outer layers formed of one or more polypropylene-based polyolefins having a flexural modulus between 600 and 750 M Pa, preferably 620-720 M Pa according to ASTM D 790 and a Vicat point between 120 and 1271 C according to ASTM D 1525, in that said polyolefins are optionally combined in a proportion of less than 30% and preferably between 5 and 20% by weight relative to the mixture with a linear low density polyethylene and in that they are selected from polypropylene homopolymers, low-ethylene-propylene copolymers

  ethylene or a mixture of such polymers.

  The intermediate or external layers provide the optical properties (gloss, transparency), the heat seal properties and allow the obtaining of different surface states and make it possible to modify the mechanical characteristics of the films by correcting if

  necessary the weak characteristics of the core layer.

  The invention also relates to a method for producing films.

  heat-shrinkable composites according to the invention.

  The first stage consists in mixing the polymers and the additives for the various layers Then, one co-extrudes the layers to form a composite film This stage is followed by a bi-stretching preferably carried out by a bubble process provided with ovens

  infrared or heating cylinder preheating.

  It is also possible to carry out co-extrusion followed by a

bi-stretch flat.

  The invention also relates to the use of thin heat-shrinkable films as they have just been described above for the overpackaging of articles as diverse as paper products (books, envelopes), food (trays of eggs, vegetables etc), products

  household goods and boxes (games, cakes, chocolates, etc.).

  The composite films according to the invention are fully recyclable in the case of the absence of polyethylene and the fact that the film according to

  the invention then consists of an ethylenepropy-

  lene As standards relating to respect for the environment become more and more stringent, the treatment of the used film according to the invention makes it possible, at the outlet of the shredders, to recover products satisfying these standards and

thus allowing their recycling.

  The invention is illustrated by the examples below given by way of indication. The three-layer films are produced according to the well known bi-stretching process by double bubble process or a flat process like this.

  is described for example in patent FR-A 2,521,907.

Example I

  A composite film is produced having the following structure The two external layers are made up in percentage by weight of: 94% of a random copolymer with 4% of ethylene with modulus of

  bending of 800 M Pa and Vicat point of 130 'C.

  2% of a masterbatch with slip agents (erucamide),

  4% of a masterbatch of anti-blocking agent.

  The core layer consists of 94% by weight of an ethylene and propylene elastomer with 40% ethylene with a flexural modulus 100 M Pa and a Vicat point of 550 C. 2% of a masterbatch with agents slippery (erucamide)

4% of a polybutylene.

  The outer layers each have a thickness of 2.5 micro-

  meters while the core layer has a thickness of 8 micrometers.

Example II

  A film similar to that obtained in Example I has the following structure: The outer layers consist of 94% of an ethylene propylene copolymer (ethylene content 2%) at Vicat point of 1480 C and a

  1350 M Pa module and 6% slip and anti-lock agents.

  The inner layer is identical to that of Example I. The outer layers each have a thickness of 1.5 micrometers

  while the core layer has a thickness of 10 micrometers.

Example III

  A film similar to that of Examples I and II is produced, comprising two outer layers consisting of 94% of a polypropylene homopolymer having the following characteristics Vicat point: 1550 C modulus: 2400 M Pa and 6% of slip agents and d 'antiblocking, and a core layer consisting of an ethylene propylene elastomer similar to that of Example I. The outer layers have a thickness of 1 micrometer and the

  core layer has a thickness of 10 micrometers.

  Example IV (comparative) Two composite films were produced according to Example 1 but by replacing the core layer with: a layer of linear low density polyethylene of thickness 9 μm (Example IV-1), the characteristics of which are as follows Vicat point: 100 OC module: 100 M Pa a layer of random copolymer with 4% ethylene of thickness 10 plm (example IV 2) whose characteristics are as follows: Vicat point: 130 'C module: 800 M Pa

Example V Results.

  The performances with regard to the free retraction at 80 and 1201 ° C., the withdrawal force in g / cm, the tear resistance initiated in Newton were compared for the films of Example IV and that of

  Example I The results are shown in the table below.

Ex 1 Ex IV-I Ex IV-2

s.m s t s m s t s m s t.

 C 12% 12% 11% 11% 6% 6%

Free retraction

 C 34% 38% 40% 40% 25% 25%

  Withdrawal force g / cm 32 35 32 38 38 42 Tear resistance 7 6 9.5 8 9.5 10 primed (N) Elongation at tear 796 6% 7% 5% 2% 2% rure primed Thickness (prm ) 13 14 15 sm (machine direction) st (cross direction) It can be seen from this table that the structures according to the invention are thinner and allow films having characteristics equivalent to multilayer films to be obtained on the basis of the layer of heart made of linear low density polyethylene which are difficult

  recyclable due to the heterogeneity of their structure.

  Furthermore, the films according to the invention have characteristics

  ticks clearly superior to films whose core layer is a random copolymer with 4% ethylene which, on the other hand, are recyclable.

Example VI

  A composite film is produced having the following structure The two outer layers are made up in percentage by weight of: 10% of a linear low density polyethylene, 82% of a random copolymer with 4% of ethylene with flexural modulus of 800 M Pa (ASTM D 790) and Vicat point 130 C (ASTM D

1525),

  3% of a masterbatch with slip agents (erucamide),% of a masterbatch of silica-based anti-blocking agent. The core layer is made up in percentage by weight of 96.5% of an elastomer of ethylene and propylene to 40% of ethylene with flexural modulus 100 M Pa and at Vicat point of 55 C and

  tensile strength of 5 M Pa (ASTM D 638).

  3.5% of a masterbatch of slip agents (erucamide).

  The outer layers each have a thickness of 2 micrometers

  while the core layer has a thickness of 10 micrometers.

  The film has the following characteristics: Characteristics Machine direction Direction through O Haze (%) ASTM 1003 A 3 3 Optics i gloss (o) ASTM D 529 85 115 115 Meca (Resistance (da N) ASTM 8 6 nics mm 2,882 t Elongation %) I 102 119 - Tear initiated N / pm 0.30 0.23 Thermo Elongation (%) 5.5 4.8 mechanical Withdrawal force (kg / cm 2) 15 13 Cohesion force (kg / cm 2) 8 9 Withdrawal at 120 C 31 35

(ASTM 1204) (9%)

Example VII

  A similar film is produced, the core layer of which is identical to that of Example VI and the outer layers of which have the following composition and characteristics: 10% linear low density polyethylene,% of a masterbatch of anti-blocking agents, 3% of a masterbatch of slip agents (erucamide), 82% of propylene ethylene to 6% ethylene random copolymer with a Vicat point of 1251 C and a flexural modulus of 700

M Pa.

  Comparative Example VIII The film obtained in Example VI is compared with two films of the prior art, one made of PVC, the other corresponding to the film presented in

Example IV 2

  The wrapped object is a packet of 20 sheets of Bristol paper 21 x 29.7 At each test, the packet is observed and it is given the following ratings: NR = Not Retracted RI = Retraction Incomplete RC = Correct Retraction TBR = Very Good EP shrinkage = Folded packaging FF = Melted Film A figurative illustration of the tables below is given in the

single figure appended.

  Velocity of the belt carrying the package through the shrinking oven (m / min) FILMS ^ (Fih "example IV 2) Templratre of the shrinking oven (C) 80, _________ 110 130 160 j1 70 180 Ri Ri N RI Ri NR NR NR NR NR NR NR NR NR RI RI RI NR NR NR NR EP EP EP EP EP RC RI EP EP EP EP EP RC RC EP EP EP EP EP RC TBR FF FF FF FF FF EP EP FILMS B (Rms PVC wire) Oven temperature retraction (C)

-80 110 130 160 170 180

  Velocity of taps 2 RC TIR TBR TBR FF FF carrying the package 4 RC TIR TIR TBR TBR FF FF or through the 6 Rl RC TIR TBR TBR TBR FF crazy retraction 8 NR RC TBR TBR TBR TIR FF (m / min) 10 NR Ri RC TIBR TR TIR FF

12 NR RI RC TBR MI TBR FF

  14 NR Ri Ri RC TBR TBR FF m l FLMS (example VI) Temprotue of the shrink oven (OC)

80 110 130 160 170 180

  Velocity of the carpet 2 NR Ri TI TBR TIBR FF carrying the bag 4 NR RI TR TIR TBR FF through the 6 NR R 1 T TI TBR FF for retraction 8 NR Ri C TR TIR TIR FF (m / ran) 10 NR Rl C TIR TBR TIR FF

12 NR RI C TIR TR TBR IR

14 NR Ri C TIR TIR TBR TB R

Example IX

  A film similar to Example VI is produced, the core layer of which is identical to that of Example VI and the outer layers of which have the following composition and characteristics: 2% masterbatch with slip agents (erucamide) 4% of a masterbatch of anti-blocking agents% of free radical low density polyethylene 79% of linear low density polyethylene with a flexural modulus of 140 M Pa and a Vicat softening point of 1000 C. This film leads to an improvement in the heat sealability of the film and an increase in low temperature shrinkage and a

  improved resistance to tearing.

Claims (18)

  1 heat-shrinkable composite film characterized in that it comprises a core layer and two external or intermediate layers applied to each surface of the core layer, said external and intermediate layers being formed from one or more polyolefins whose flexural modulus is greater than 200 M Pa according to ASTM D 790 and whose Vicat point is greater than 100 C according to ASTM D 1525, said core layer being formed from one or more polymers whose flexural modulus is less than 400 M Pa according to ASTM D 790 and the Vicat point is less than 70 C according to ASTM D 1525, with the exception of films in which the core layer is made up as a percentage by weight of:  94% of an ethylene and propylene elastomer with a flexural modulus 100 M Pa and at a Vicat point of 55 C, 2% of a masterbatch with slip agents (erucamide), 4% of a polybutylene, and whose layers external are chosen by those made up as a percentage by weight of: 94% of a random 4% ethylene copolymer with a flexural modulus of 800 M Pa and a Vicat point of 130, 2% of a masterbatch with slip agents (erucamide), 4% of a masterbatch of anti-blocking agent, 94% of an ethylene propylene copolymer (ethylene content 2%) at Vicat point of 148 C and a module of 1350 M Pa and 6% d '' slip and anti-lock agents,   94% of a polypropylene homopolymer having the characteristics   following characteristics: Vicat point: 155 C module: 2400 M Pa   and 6% slip and anti-lock agents.   2 composite film according to claim 1, characterized in that the polyolefins forming the intermediate or external layers are based on polypropylene and have a flexural modulus between 750 M Pa and 2500 M Pa according to ASTM D 790 and a higher Vicat point or equal to 127 C according to ASTM D 1525.   3 Composite film according to claim 2, characterized in that the polyolefins forming the intermediate or external layers have a   flexural modulus greater than or equal to 780 M Pa.   4 composite film according to one of claims 2 or 3,   characterized in that the polyolefins forming the intermediate or external layers are chosen from polypropylene homopolymers, ethylene propylene copolymers with a low ethylene content or a mixture such polymers.   Composite film according to one of claims 2 to 4,   characterized in that the polypropylene-based polyolefins forming the intermediate or external layers are combined in a proportion of less than 30%, preferably between 5 and 20% by weight per   compared to blending with a linear low density polyethylene.   6 composite film according to claim 1, characterized in that   the polyolefins based on polypropylene forming the intermediate layers   diaries or external have a flexural modulus between 600 and 750 M Pa, preferably 620-720 M Pa according to ASTM D 790 and a Vicat point included   between 120 and 1271 C according to ASTM D 1525.   7 composite film according to claim 6, characterized in that the polypropylene-based polyolefins are combined in a proportion of less than 30% and preferably between 5 and 20% by weight.   compared to blending with linear low density polyethylene.   8 Composite film according to claim 6 or 7, characterized in that the polypropylene-based polyolefins forming the intermediate or external layers are chosen from polypropylene homopolymers, ethylene-propylene copolymers with a low content of   ethylene or a mixture of such polymers.   9 composite film according to claim 1, characterized in that the polyolefins forming the intermediate or external layers are formed from 1 to 30% of free radical low density polyethylene, 60 to 94 96 of linear low density polyethylene, by weight relative to the mixture, and have a flexural modulus between 200 and 600 M Pa according to ASTM D 790   and a Vicat point between 100 and 1250 C according to ASTM D 1525.   Composite film according to one of claims 1 to 9,   characterized in that the polymer forming the core layer has a flexural modulus of less than 200 M Pa according to ASTM D 790 and a Vicat point   less than 650 C according to ASTM D 1525.   Il Composite film according to claim 10, characterized in that the polymer forming the core layer has a flexural modulus less than 150 M Pa according to ASTM D 790 and a Vicat point less than 60 'C according to ASTM D 1525.   12 Composite film according to one of claims 1, 10 or 11,   characterized in that the polymer forming the core layer is chosen from polypropylenes with a high content of alpha-olefins, the materials   polyolefin elastomers or mixtures thereof.   13 Composite film according to claim 12, characterized in that the polypropylenes with a high content of alpha-olefins comprise   weight 10 to 50% of alpha-olefins, preferably 20 to 40%.   14 Composite film according to one of claims 12 or 13,   characterized in that the alpha-olefins are chosen from ethylene,   1-butene, 1-hexene, 1-octene.   Composite film according to claim 12, characterized in that the elastomers are chosen from those having the following composition by weight: ethylene 50 to 70% propylene 30 to 50% diene derivative such as butadiene or a similar conjugated diene 3 to 5% or the elastomers based on ethylene 10 to 80%, preferably 35 to 75%,   propylene 20 to 90%, preferably 25 to 65%.   16 Recyclable and / or incinerable composite film according to one of the   Claims 10 to 15, characterized in that it comprises two layers   external formed from one or more polypropylene-based polyolefins having a flexural modulus between 600 and 750 M Pa, preferably 620-720 M Pa according to ASTM D 790 and a Vicat point between 1200 and   1270 C according to ASTM D 1525, in that said polyolefins are optionally-   Lely associated in a proportion of less than 30% and preferably between 5 and 20% by weight relative to the mixture with a linear low density polyethylene and in that they are chosen from polypropylene homopolymers, ethylene-propylene copolymers at   low ethylene content or a mixture of such polymers.   17 Composite film according to one of claims 1 to 16,   characterized in that it is formed from a three-layer sandwich structure in the following proportions by weight: first outer layer, 2.5 to 35%, core layer, 30 to 95 9, second outer layer, 2.5 to 35%, and in that preferably it has a thickness of between 12 and 20 micrometers,   advantageously less than 10 micrometers.   18 Use of the films according to one of claims 1 to 17,   for the overpacking of articles chosen in particular from products   stationers, food or household products.   19 Process for producing heat-shrinkable composite film   and recyclable according to one of claims 1 to 17, characterized in that   mixes the polymers and additives of the various layers then in that one co-extrudes said layers to form a composite film,   this step being followed by a bi-stretch.