EP3083780A1 - Uninflammable pvdf film that is resistant to tearing at low temperatures - Google Patents

Abstract

The present invention relates to a fluorinated film possessing properties making it able to be used outside, especially in the agricultural field as a greenhouse film for animals. The film according to the invention is a monolayer polymer film comprising a polyvinylidene fluoride (PVDF) matrix, at least one impact modifier, the content by weight of the impact modifier varying between 2.5% and less than 40%, and a flame-retarding agent. According to one variant embodiment, the invention relates to a multilayer film comprising at least one layer of said fluorinated film and at least one unmodified PVDF layer.

Description

 PVDF FILM RESISTANT TO LOW DRYING

 TEMPERATURE AND NON-FLAMMABLE

The present invention relates to a fluorinated film having properties making it suitable for use outdoors, particularly in the field of breeding as cover films houses or shelters for livestock. The film according to the invention comprises a polyvinylidene fluoride matrix, at least one impact modifier and a flame retardant.

 In regions with a harsh climate, a minimum of protection should be offered to animals, especially during cold and wet seasons. The lack of protection against the wind can in particular have adverse consequences on the health status of the animals. Agricultural greenhouses are used to shelter livestock, protecting them from climatic elements. The cover of these greenhouses is translucent and generally made of glass, but also of plastic (for example: polyethylene film, semi-rigid PVC sheets) rigid or flexible, generally treated to withstand ultraviolet light. This film can be armed to increase its resistance to rips.

 In general, the films used for the roofs of livestock buildings must have multiple properties:

 - mechanical, such as: tear resistance in a temperature range of -20 ° C to + 60 ° C, creep resistance, drawability;

- optical, such as the partial transmission of visible light and the diffuse nature of the transmitted light;

 - chemical resistance, especially in environments rich in ammonia; durability: resistance to damp heat and cold; UV resistance; a high ability to reflect infrared rays from the sun during the day and from inside the building at night to ensure temperature stability within the building;

 - fire resistance;

 - anti-fog and anti-dust properties.

It is known to use fluorinated polymers, especially based on vinylidene fluoride, to manufacture monolayer films used for the manufacture of agricultural buildings (in the closed sense). Monolayer films based on PVDF (polyvinylidene fluoride) or copolymers VDF / HFP (vinylidene fluoride / hexafluoropropylene), obtained by jacket blowing or by the cast film technique, have good mechanical, optical, chemical resistance and durability properties, so that they are good candidates for the application of agricultural greenhouses. The tear resistance of these films, however, is insufficient, especially in the direction of extrusion (MD).

 WO 2011/121228 discloses multilayer fluorinated films comprising at least 3 layers, including a layer A in a first copolymer of vinylidene fluoride having a crystallization temperature TcA, and a layer B in a second copolymer of vinylidene fluoride having a crystallization temperature TcB, TcA being greater than TcB, layers A and B being alternate, layer A being placed on the outside and layer B between two layers A. The tear resistance of these films has been significantly improved, compared to known fluorinated films, however it remains insufficient at low temperature.

 It would therefore be desirable to have fluorinated films for application as a roof and / or facade of livestock buildings which, in addition to the general characteristics described above, have good tear resistance properties in a temperature range from - 20 ° C to + 60 ° C and leave partially light, contributing to the welfare of animals by a harmonious distribution of natural light, while having a good fire resistance.

It has now been found that by modifying a polyvinylidene fluoride polymer by adding a core-shell shock modifier, a significant improvement in the tear strength of the film, especially at low temperature, is obtained while maintaining a high level of stability. in the visible range compatible with the use of film as a film for agricultural buildings. On the other hand, the addition of a flame retardant gives good fire resistance properties, indispensable for use as a greenhouse film for animals.

One of the objects of the present invention consists of a PVDF monolayer film modified by addition of at least one heart-bar shock modifier ("coreshell") and also containing a flame-retardant agent.

Another subject of the invention relates to a multilayer film comprising at least one modified PVDF layer as described above, and at least one layer of unmodified PVDF, that is to say a PVDF which contains neither a modified shock nor a flame retardant (hereinafter referred to as "PVDF layer"). According to one embodiment, this PVDF layer is located outside the multilayer film.

Another subject of the invention relates to the use of the films according to the invention as roofing materials for agricultural buildings, in particular as roofs and / or facades for greenhouses for animals.

 Other features and advantages of the invention will appear on reading the following description.

 According to a first aspect, the invention relates to a monolayer polymer film comprising a polyvinylidene fluoride (PVDF) matrix, at least one impact modifier and a flame retardant, in which the impact modifier mass ratio varies between 2.5% and less. 40%.

 Although achieving the desired mechanical properties, the addition of impact modifier in the films generally also has the consequence of making them flammable. The object of the invention therefore relates to the addition of a second flame retardant additive, which makes it possible to restore the fire resistance of the product while maintaining an improved tear resistance by the presence of impact modifiers. Several families of flame retardants can fulfill this role. By way of example, mention may be made of:

 halogenated flame retardants,

 phosphorus flame retardants, for example metal or organometallic salts of phosphonate,

 calcium tungstates, and

 aluminum silicates.

 Many of these compounds can be used simultaneously as a flame retardant. The ratio of the total amount of flame retardant to that of impact modifier is between 1/30 and 1/1, preferably between 1/15 and 1/7.

 The thickness of the film according to the invention is between 30 and 200 microns, preferably between 80 and 150 microns (inclusive).

According to one embodiment, the impact modifying rate is greater than 5% and less than or equal to 30% of the total weight of the film. Preferably, the level of impact modifier is greater than or equal to 10% and less than or equal to 30%. According to one embodiment, the monolayer film according to the invention consists of a PVDF matrix, at least one core-shell shock modifier and a flame retardant agent.

The PVDF matrix consists of a PVDF homopolymer or a copolymer prepared by copolymerization of vinylidene fluoride (VDF, CH ₂ = CF ₂ ) with a fluorinated comonomer chosen from: vinyl fluoride; trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro (alkyl vinyl) ethers such as perfluoro (methyl vinyl) ether (PMVE), perfluoro (ethyl vinyl) ether (PEVE) and perfluoro (propyl vinyl) ether (PPVE); perfluoro (1,3-dioxole); perfluoro (2,2-dimethyl-1,3-dioxole) (PDD).

 According to one embodiment, said matrix is made of PVDF homopolymer.

 According to another embodiment, said matrix consists of a VDF copolymer. Preferably, the fluorinated comonomer is chosen from chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), trifluoroethylene (VF3) and tetrafluoroethylene (TFE), and mixtures thereof.

 The comonomer is advantageously the HFP. Preferably, the copolymer comprises only VDF and HFP.

Preferably, the fluorinated copolymers are copolymers of VDF such as VDF-HFP containing at least 50% by weight of VDF, advantageously at least 75% by weight of VDF and preferably at least 80% by weight of VDF. These include for example in particular copolymers of VDF containing more than 75% of VDF and HFP supplement marketed by Arkema under the name Kynar Flex ^®. The core-shell shock modifier is, in one embodiment, in the form of fine particles having an elastomeric core (having a glass transition temperature of less than 25 ° C, preferably less than 0 ° C, more preferably less than -5 ° C, even more preferably less than -25 ° C), and at least one thermoplastic bark (comprising at least one polymer having a glass transition temperature greater than 25 ° C). The size of the particles is generally less than one micron and advantageously between 50 and 300 nm. As an example of a core, homopolymers of isoprene or butadiene may be mentioned, copolymers of isoprene with at most 30 mol% of a vinyl monomer and copolymers of butadiene with at most 30 mol% of a vinyl monomer. The vinyl monomer may be styrene, alkylstyrene, acrylonitrile or alkyl (meth) acrylate. Another family of cores consists of the homopolymers of an alkyl (meth) acrylate and the copolymers of an alkyl (meth) acrylate with at most 30 mol% of a monomer chosen from another (meth) ) alkyl acrylate and a vinyl monomer. The alkyl (meth) acrylate is advantageously butyl acrylate. According to one embodiment, the core of the impact modifier consists of 2-ethyl-exyl acrylate, which gives a gain in tear-resistance properties equivalent to the product based on butyl-acrylate.

 The core of the core shell copolymer may be crosslinked in whole or in part. It suffices to add at least difunctional monomers during the preparation of the core, these monomers may be chosen from poly (meth) acrylic esters of polyols such as butylene di (meth) acrylate and trimethylolpropane trimethacrylate. Other difunctional monomers are, for example, divinylbenzene, trivinylbenzene, vinyl acrylate and vinyl methacrylate. The core may also be cross-linked by grafting or as a comonomer during the polymerization, unsaturated functional monomers such as unsaturated carboxylic acid anhydrides, unsaturated carboxylic acids and unsaturated epoxides. Mention may be made, for example, of maleic anhydride, (meth) acrylic acid and glycidyl methacrylate.

 The bark or barks are homopolymers of styrene, alkylstyrene or methyl methacrylate or copolymers comprising at least 70 mol% of one of these monomers and at least one comonomer selected from the other monomers above another alkyl (meth) acrylate, vinyl acetate and acrylonitrile. The bark may be functionalized by introducing, by grafting or as comonomer during the polymerization, unsaturated functional monomers such as unsaturated carboxylic acid anhydrides, unsaturated carboxylic acids and unsaturated epoxides. Mention may be made, for example, of maleic anhydride, (meth) acrylic acid and glycidyl methacrylate. The bark may be partially reticulated.

 According to one embodiment, the bark polymer is made of polystyrene or PMMA. There are also core-bark polymers with two barks, one made of polystyrene and the other outside PMMA.

Advantageously, the core represents, by weight, 70 to 98% of the core-shell polymer and the bark at 2%. All of these heart-shell shock modifiers are sometimes called soft / hard because of the elastomeric core. There are also other types of bark-like shock modifiers such as hard / soft / hard, that is to say they have in this order a hard heart, soft bark and hard bark. The hard parts may consist of the above soft / hard bark polymers and the soft part may consist of the above soft / hard core polymers. For example, those made in this order:

 A copolymer core of methyl methacrylate and ethyl acrylate,

A shell of copolymer of butyl acrylate and styrene,

 · A bark copolymer of methyl methacrylate and ethyl acrylate.

There are still other types of heart-bar shock modifiers such as hard (heart) / soft / hard. Compared to the previous ones, the difference comes from the outer bark "medium-hard" which consists of two barks: one intermediate and one outer. The intermediate bark is a copolymer of methyl methacrylate, styrene and at least one monomer selected from alkyl acrylates, butadiene and isoprene. The outer bark is a PMMA homopolymer or copolymer. For example, those made in this order:

 A copolymer core of methyl methacrylate and ethyl acrylate, a shell of butyl acrylate and styrene copolymer,

 · A shell of copolymer of methyl methacrylate, butyl acrylate and styrene,

• a bark copolymer of methyl methacrylate and ethyl acrylate. According to a preferred embodiment, the impact modifier contains a core consisting of butylene acrylate or butylene-co-butadiene acrylate or else 2-ethyl-exyl acrylate. The bark is formed of poly (methyl methacrylate) or copolymer of methyl methacrylate and another acrylic monomer. These include products from the DURASTRENGTH ^® range from ARKEMA. Other acrylic impact modifiers can be used such as the Paraloid ™ EXL range from Dow or the range of KANE ACE® on Kaneka.me KANE ACE ^® acrylic based Kaneka.

According to another embodiment, the impact modifier contains an acrylate-polysiloxane copolymer core and a hard resin bark. In this case, the heart is a flexible rubber-like material prepared by polymerizing one or more vinyl monomers in the presence of a rubber-like polymer obtained from monomers such as alkyl acrylates or alkyl methacrylates, wherein the alkyl group contains 2 to 10 carbon atoms. Polyfunctional monomers such as divinylbenzene, ethylene dimethacrylate, triallyl cyanurate, or triallyl isocyanurate may be added during the polymerization as crosslinking agents. The rubber-like polymer thus obtained is combined with a rubber containing polysiloxane. The elastomers thus prepared contain at least 20% by weight of rubber-like polymer, preferably at least 40% by weight. Examples of this type of impact modifier are rubber-based graft copolymers prepared by graft copolymerization of a composite rubber with at least one vinyl monomer, wherein the composite rubber comprises from 5 to 95% by weight of a rubber based on polysiloxane and 5 to 95% by weight of a polyacryl (meth) acrylate rubber. The particle size of these impact modifiers varies between 0.01 and 1 micron. Preferably, this type of impact modifier consists of a copolymer core of polysiloxane and butyl acrylate surrounded by a bark of poly (methyl methacrylate). Products of this type are marketed by Mitsubishi Rayon under the reference Metablen ^® S-2001.

According to another embodiment, the impact modifier is composed of a poly (organosiloxane) core and a thermoplastic resin bark. The organic groups of the poly (organosiloxane) cores are preferably alkyl or vinyl radicals containing between 1 and 18 carbons, advantageously between 1 and 6 carbons, or substituted aryl radicals or hydracarbones. The poly (organosiloxane) contains one or more of these groups. The siloxanes have a variable degree of functionahsation which defines the degree of crosslinking of the poly (organosiloxane). Preferably, the average degree of functionahsation is between 2 and 3 thus forming a partially crosslinked core. The bark is formed of polymers or copolymers derived from monomers such as acrylates or alkyl methacrylate, acrylonitrile, styrene, vinylstyrene, vinylpropionate maleimide, vinyl chloride, ethylene, butadiene, isoprene and chloroprene. Preferably, the bark is composed of styrene or acrylate or alkyl methacrylate, the alkyl having between 1 and 4 carbons. The fraction of the core represents between 0.05 and 90% by weight of the particles, preferably between 60 and 80% by weight. The particle size is between 10 and 400 nm. This shock modifier can also be in the form of a heart surrounded by 2 successive barks. The description of the core and the outer bark remains identical to that of the silicone shock modifiers with a single bark previously presented. The intermediate bark consists of a poly (organosiloxane) different from that of the heart but chosen from the same family of composition. Preferably, this type of impact modifier consists of a polydimethyl siloxane core and a poly (methyl methacrylate) bark. The Genioperl® range of Silicone Waker can be cited as an example.

 According to one embodiment, the monolayer film according to the invention comprises an additive reflecting infrared radiation. This additive may be a titanium oxide or a mixed compound such as a mother-of-pearl constituted in its center of mica and covered with a layer of titanium oxide. Metal alloys can also be used as infrared reflectors. They contain two or more of the following: iron, chromium, cobalt, aluminum, manganese, antimony, zinc, titanium, magnesium. Preferably, this alloy consists of two elements: cobalt and aluminum, or it is a ternary alloy of cobalt, chromium and aluminum.

 According to another embodiment, the monolayer film according to the invention further comprises at least one additive chosen from:

 mattifying agents,

 opacifying agents,

 acrylic homopolymers or copolymers,

 plasticizers chosen preferably from dibutyl sebacate, dioctyl phthalate, N-n-butylsulfonamide and polymeric polyesters such as those derived from the combination of adipic, azelaic or sebacic acid and diols. Combinations of these compounds may also be used. The films according to the invention have the particularity of combining a high resistance to cold tear with a fire resistance equivalent to that of PVDF.

 According to one embodiment, the film according to the invention comprises a VDF / HFP copolymer matrix (the compound Al in the examples), an impact modifier having a poly (methyl methacrylate) bark (30%) containing cores of polydimethylsiloxane (70%), and 2% by weight of calcium tungstate as flame retardant.

According to another embodiment, the film according to the invention comprises a PVDF homopolymer matrix, an impact modifier having a poly (methacrylate) bark. methyl) (30%) contain polydimethyl-siloxane cores (70%), and 2% by weight calcium tungstate as flame retardant.

 According to another embodiment, the film according to the invention comprises a VDF / HFP copolymer matrix (the compound Al in the examples), an impact modifier containing a partially crosslinked butyl polyacrylate core (90% by weight) and a bark consists of a copolymer of methyl methacrylate and ethyl acrylate (10%), and 3% of calcium tungstate as flame retardant.

 According to another embodiment, the film according to the invention comprises a VDF / HFP copolymer matrix (the compound Al in the examples), an impact modifier containing a partially crosslinked butyl polyacrylate core (90% by weight) and a bark is composed of a copolymer of methyl methacrylate and ethyl acrylate (10%), and 2% by weight of benzyl penta-brominated polyacrylate as flame retardant.

According to a second aspect, the invention relates to a multilayer film comprising at least one layer of the described monolayer film and at least one other layer of PVDF. By "PVDF layer" is meant a layer consisting of a PVDF homopolymer or a copolymer prepared by copolymerization of vinylidene fluoride (VDF, CH ₂ = CF ₂ ) with a fluorinated comonomer chosen from: vinyl fluoride; trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro (alkyl vinyl) ethers such as perfluoro (methyl vinyl) ether (PMVE), perfluoro (ethyl vinyl) ether (PEVE) and perfluoro (propyl vinyl) ether (PPVE); perfluoro (1,3-dioxole); perfluoro (2,2-dimethyl-1,3-dioxole) (PDD).

 In the case of a multilayer film, the overall thickness is between 30 and 200 microns. According to one embodiment, the multilayer film consists of a central layer of PVDF modified with a core - shell shock modifier and containing a flame retardant, and two outer layers of PVDF. These may have the same structure, or they may have different structures.

 The distribution of the thicknesses as a percentage of the final thickness of the structure is as follows: modified PVDF layer: 20%> - 95%>, unmodified PVDF layer: 5% - 80%), ie for example for a total thickness 30 microns and a 70/30 distribution: modified PVDF layer: 21 microns and unmodified PVDF layer: 9 microns.

In another aspect, the invention relates to the methods of preparing films described above. PVDF / impact modifier / flame retardant mixtures are obtained by melt compounding techniques known to those skilled in the art, such as BUSS or twin screw. The films are then obtained by jacket blowing or by the technique of cast film, these techniques advantageously making it possible to obtain films of large widths. The films can be extruded at a temperature between 200 and 280 ° C. The inflation rate should be between 1.2 and 4, preferably between 1.5 and 3. The stretching ratio should be between 2 and 15, preferably between 5 and 10.

 According to another aspect, the invention relates to the use of the monolayer film or multilayer film comprising at least one layer of said monolayer film, as material for the manufacture of films for roofs and / or facades of buildings, particularly agricultural buildings such as livestock buildings. These films then have the advantage of having improved durability combined with good resistance to deformation and fire.

The following examples illustrate the invention without limiting it. formulations

 The compounds are produced according to the rules of the art in a twin-screw corotative extruder. The films are then made by flat extrusion at 220 ° C. using a flat die with a gap of 1 mm, and stretched by a calendrette to adjust the thickness of the product to the desired target (100 μιη).

Study materials

Matrix:

 Al: VDF / HFP copolymer having a melt flow rate (MFR) of 7 g / 10min (5kg, 230 ° C), a melting temperature (Tf) of 142 ° C and a Young's modulus of 650 MPa at 23 ° C., measured according to ISO 178. The Tf was measured by DSC or differential scanning calorimetry during a rise in temperature at a rate of 10 ° C./min. The melt index is measured according to ISO 1133.

A2: PVDF homopolymer of melt index of 0.14 g / 10 min (5 kg, 230 ° C.) and melting point 168 ° C. Shock modifier:

Bl: Durastrength ^® D380 acrylic impact modifier from Arkema, in the form of core-shell particles 250 nm in diameter. 90% of partially cross-linked butyl polyacrylate forms the core of the particles. The bark (10%>) consists of a copolymer of methyl methacrylate and ethyl acrylate.

B2: acrylic impact modifier Durastrangth ^® D200 from Arkema formed of polybutyl acrylate core partially crosslinked (70%>) surrounded by methyl methacrylate copolymer bark and ethyl acrylate (30%).

B3: Heart-bark particles of Genioperl ^® P52 from Waker. Poly (methyl methacrylate) barks (30%) contain polydimethyl-siloxane cores (70%).

Plasticizer:

C: Dibutyl sebacate

Fireproof:

 D1: penta-brominated benzyl polyacrylate FR-1025 from the company ICL D2: calcium tungstate in powder form from Chem-Met.

The tests performed are as follows:

Characterization of the fire resistance: the film is placed on a vertical support and is ignited by a flame calibrated according to the UL94 standard. The flame is placed 10 mm below the bottom end of the film and is maintained for 5s. The flame persistence time, the area burned and the presence of inflamed drop are noted. 5 test pieces are analyzed for each sample. Characterization of the resistance to cold tearing: a film of thickness 100 μιη is supported by a frame so as to stretch it by applying a tension of IN. A conical 980 g striker is released from a height of 230 mm and pierces the sample. Depending on the rupture profile of the film (long crack propagated in the film or localized stretching), the fragile or ductile nature of the deformation can be estimated. This test is performed at different temperatures to estimate the ductile / brittle transition temperature of the products. Example 1 Cold Puncture Resistance of Reference Formulations Without Flame Retardant

 As illustrated in Examples 1 to 7 in Table 1 above, the most influencing parameter on puncture resistance of the films is in the shock modifier incorporated in the formulation. Its mass fraction and its nature directly impact the ductile or fragile nature of the deformation after cold impact.

 Comparison of Examples 5 and 8 as well as 7 and 9 shows that a matrix change of a VDF / HFP copolymer for a PVDF homopolymer has only a limited effect on the perforation behavior of the film.

The presence of plasticizer in the mixture allows a slight improvement of the ductile behavior of the film at low temperature but its effect is limited as shown by the lack of property noted between Examples 10 and 11 and 12 and 13. The change in nature of the Shock modifier in these last 2 examples also causes a significant evolution of the ductile-brittle transition.

Table 1 Example 2: Fire resistance and maintains mechanical properties

 Table 2

* The value of 5890 mm ² corresponds to the combustion of the entire analyzed sample

The results obtained are shown in Table 2. These results show that the addition of 2% or 3% flame retardant (ie a ratio of 2/15 or 1/5 with the amount of impact modifier) in the film formulation makes it possible to restore the fire resistance of the film to a level equivalent to that of the pure matrix.

 The intrinsic fire resistance of the films is degraded by the presence of the impact modifying particles which are dispersed in the sample, as illustrated in Examples 1 to 5. The addition of specific flame retardants in the film formulation makes it possible to simultaneously achieve high fire resistance of the film and a low temperature brittle ductile transition temperature as shown in Examples 14-17.

Claims

A monolayer polymer film comprising a polyvinylidene fluoride (PVDF) matrix, at least one core - shell shock modifier and a flame retardant, wherein the impact modifier mass ratio ranges from 2.5% to less than 40%.  2. The film of claim 1 wherein the mass modifier impact modifier is greater than 5% and less than or equal to 30%.  3. Film according to one of claims 1 and 2 wherein the ratio of the amount of flame retardant relative to that impact modifier is between 1/30 and 1/1, preferably between 1/15 and 1/7.  4. Film according to one of claims 1 to 3 wherein the PVDF matrix consists of a PVDF homopolymer or a copolymer prepared by copolymerization of vinylidene fluoride with a fluorinated comonomer selected from: vinyl fluoride; trifluoroethylene; chlorotrifluoroethylene, 1,2-difluoroethylene; tetrafluoroethylene; hexafluoropropylene; perfluoro (alkyl vinyl) ethers chosen from perfluoro (methyl vinyl) ether, perfluoro (ethyl vinyl) ether (PEVE) and perfluoro (propyl vinyl) ether; perfluoro (1,3-dioxole); and perfluoro (2,2-dimethyl-1,3-dioxole).  5. Film according to one of claims 1 to 4 wherein the impact modifier contains an elastomeric core and at least one thermoplastic bark.  6. Film according to claim 5 wherein the core is composed of poly (organosiloxane) bearing one or more radicals selected from alkyl or vinyl radicals having 1 to 18 carbons, aryl radicals and substituted hydrocarbons. The film of claim 5 wherein the core comprises a polymer selected from homopolymers of isoprene or butadiene, copolymers of isoprene with at most 30 mole percent of a vinyl monomer and copolymers of butadiene. with not more than 30 mol% of a vinyl monomer, homopolymers of an alkyl (meth) acrylate and copolymers of an alkyl (meth) acrylate with not more than 30 mol% of a monomer selected from another alkyl (meth) acrylate and a vinyl monomer, the vinyl monomer being styrene, alkylstyrene, acrylonitrile, butadiene or isoprene. 8. The film of claim 6 wherein the bark is formed of polymers or copolymers derived from monomers selected from alkyl acrylates or methacrylates, alkyl having between 1 and 4 carbons, acrylonitrile, styrene, vinylstyrene, vinyl propionate maleimide, vinyl chloride, ethylene, butadiene, isoprene and chloroprene.  9. Film according to one of claims 5 or 7 wherein said core is crosslinked in whole or in part by means of an at least difunctional monomer selected from poly (meth) acrylic polyols, divinylbenzene, trivinylbenzene, vinyl acrylate and vinyl methacrylate, or by means of an unsaturated functional monomer selected from unsaturated carboxylic acid anhydrides, unsaturated carboxylic acids and unsaturated epoxides.  The film of claim 5 wherein the core is a flexible rubber-like material combined with a polysiloxane-containing rubber, said flexible rubber being prepared by polymerizing one or more vinyl monomers in the presence of a rubber-like polymer obtained from alkyl acrylates or alkyl methacrylates, wherein the alkyl group contains from 2 to 10 carbon atoms.  11. Film according to one of claims 5, 7, 9 or 10 wherein the bark or barks are homopolymers of styrene, an alkylstyrene or methyl methacrylate or copolymers comprising at least 70 mol% of one of these previous monomers and at least one comonomer selected from the remaining monomers, another alkyl (meth) acrylate, vinyl acetate and acrylonitrile.  12. The film as claimed in any one of the preceding claims, having a thickness of between 30 and 200 microns, preferably between 80 and 150 microns.  13. Film according to any one of the preceding claims, said film comprising at least one additive chosen from: matting agents, opacifying agents, acrylic homo or copolymers, plasticizers and infrared radiation reflecting agents chosen from oxides of titanium, pearlescent pigments based on mica and titanium oxide and metal alloys. A film according to any one of the preceding claims wherein the flame retardant is selected from halogenated flame retardants, phosphorus flame retardants, calcium tungstates, and aluminum silicates. A multilayer film comprising at least one layer of a film according to any one of claims 1 to 14 and at least one layer of PVDF.  16. The film of claim 15 consisting of an inner layer according to one of claims 1 to 14 and two outer layers of PVDF, said outer layers having the same or different structure.  17. Use of the film according to one of claims 1 to 14 or the film according to one of claims 15 or 16 as a material for the manufacture of films for roofs and / or facades of buildings, including agricultural buildings such as buildings breeding.