FR2935706A1 - Fluorinated polymer composition, used e.g. in pipe for conveying fluid pressure, comprises optionally plasticizer with fluoropolymer, shock modifying particles of core-shell type, and homopolymer or copolymer of vinylidene fluoride - Google Patents

Abstract

Fluorinated polymer composition (I), comprises optionally at least a compatible plasticizer with the fluoropolymer (1-6 (preferably 2-5) parts); shock modifying particles 4-10 (preferably 5-8 parts) of core-shell type that contains at least one inner layer with a soft polymer of glass transition temperature (T g) of less than -25[deg] C, preferably less than -60[deg] C and acrylic shell; and at least one homopolymer or copolymer of vinylidene fluoride (VDF) (make up to 100 parts), where the modifying particles have interparticle distance (D1) of at most 150 nm, preferably at most 100 nm. An independent claim is included for a flexible metal conduit with one or more elements metal and at least one layer comprising (I) and optionally one or more layers of a polymer material.

Description

FIELD OF THE INVENTION The present invention relates to a fluorinated polymeric composition for producing pipes or other articles capable of withstanding extremely severe operating conditions, such as those encountered in the offshore oil industry. It also relates to pipes and other shaped articles comprising at least one layer obtained from the fluoropolymer composition mentioned above. [The technical problem] The exploitation of oil deposits located at sea subjects the equipment and materials used to extreme conditions, and in particular the pipes or pipes used to convey the hydrocarbons thus extracted. Indeed, the hydrocarbons are generally transported at high temperature (up to 135 ° C.) and high pressure (for example 700 bar). During the operation of the installations, there therefore arise acute problems of mechanical resistance (resistance to pressure, friction), thermal and chemical materials used. Such pipes and pipes must in particular withstand hot oil, gas, surrounding salt water and mixtures of at least two of these products for periods of up to 20 years.

Typically, these pipes comprise a metal inner layer not waterproof oil and water, formed of a profiled metal strip, helically wound such as an interlocked strip. This metal inner layer, which gives shape to the pipe, is coated, generally by extrusion, with a polymer layer intended to provide sealing. Other protective and / or reinforcing layers such as metal fiber webs and rubbers may also be arranged around the sealed polymer layer.

For operating temperatures below 60 ° C, the polymer generally used is HDPE (high density polyethylene). For temperatures between 60 ° C and 90 ° C is commonly used polyamide; up to 90 ° C can also be used crosslinked polyethylene (PEX) when the pressure is not too important. For temperatures above 90 ° C, fluorinated polymers such as PVDF (polyvinylidene fluoride) or a copolymer of vinylidene fluoride (VDF) are generally used.

Fluorinated polymers and in particular polyvinylidene fluoride (PVDF) are known for their good thermal resistance, their chemical resistance, especially to solvents, their resistance to weather and radiation (UV, etc.), their impermeability to gases and to liquids and their quality of electrical insulators. They are used in particular for the manufacture of pipes or pipes, intended to convey hydrocarbons extracted from oil deposits located under the sea (offshore) or not (on-shore).

Other requirements are added to those indicated above, before or after the oil exploitation: thus, during their installation or dismantling (winding-winding), the pipes or pipes can undergo shocks, to which they must withstand varying temperatures depending on the installation depth of these pipes or ducts and can reach quite low values (for example -35 ° C), and significant deformations. Deformability of at least 7% (between the initial state and the deformation) is considered necessary to allow (un) winding not detrimental to the pipes. Finally, it is important that the properties of the pipes or ducts remain almost constant over time, to ensure a long life and possibly to allow their reuse.

In an attempt to cope with all these requirements in the short term and in the long term, various types of pipes have already been proposed, generally comprising one or more metal elements guaranteeing the mechanical rigidity, for example a spiral steel ribbon, as well as various layers based on polymeric compositions, in particular sealing the extracted fluids and seawater as well as the thermal shielding. These polymeric compositions may for example be based on polyethylene, but this choice limits the temperature of use of the pipes to at most 60 ° C. They may also be based on fluoropolymers such as PVDF (polyvinylidene fluoride), which allows a maximum temperature of use that can be higher; and confer excellent chemical resistance. However, PVDF is very rigid and for this reason homopolymers of VDF are often formulated or used in admixture with VDF copolymers to improve flexibility.

Finally, additional requirements arise during the manufacture of pipes or pipes. Thus, it is desirable that the implementation of the polymer compositions is as easy as possible, which imposes a viscosity suitable for the transformation process (typically extrusion). In particular, it is preferable that the composition used does not have a viscosity that is too low (for example a melt index measured under ASTM D-1238 (at 230 ° C. with 5 kg) less than 15 g / 10 min). The selection of a polymeric composition is therefore crucial to withstand without damage the conditions of manufacture, handling, laying of offshore flexible pipes containing them and also of good use. The construction of the hoses is complex. The juxtaposition of the polymeric layers and the metallic elements (carcass, spiral reinforcements, etc.) causes the polymer used to be subjected to locally triaxial stresses and deformations, in particular when the hoses are bent. This occurs cyclically during the various handling operations and laying of hoses. This is also the case when using these compositions, in particular for dynamic applications as for the constitution of hoses connecting the seabed to the surface (riser in English terminology) and which are subject to the swell. .

The Applicant has developed a composition which has interesting technical characteristics, namely in particular: 1. a change in volume during prolonged holding at a temperature of 130 ° C. of less than 10%; 2. a multiaxial fatigue strength resulting in a number of failure cycles (NCR)> 5000, preferably> 10000 according to the fatigue test described below; 3. a ductile-brittle Charpy shock transition temperature <-15 ° C; 4. Creep resistance when hot> 130 ° C at 6 MPa.

[The Prior Art] European Application EP 166385 discloses a fluorinated polymeric composition comprising a VDF-HFP copolymer containing from 5 to 10 mol% of HFP (hexafluoropropylene). This copolymer improves the flexibility of the pipes but is not suitable for low temperatures.

The French application FR 2,592,655 describes a composition based on polyvinylidene fluoride with improved resistance to contact with hydrocarbons by incorporation of the elastomer particles having the capacity to adsorb the hydrocarbons. Nothing is said about the quality of the dispersion of the particles in the composition, or the morphology of the particles or the nature of the acrylic bark.

The application EP 1342752 describes a fluorinated polymeric composition comprising at least one homo- or copolymer of PVDF, at least one fluorinated elastomer and optionally a plasticizer. Comparative examples describe fluorinated polymeric compositions where the fluoroelastomer is replaced by an acrylic elastomer of the core-shell type with acrylic bark. The composition is obtained by mixing with a single-screw extruder. Nothing is said about the quality of the dispersion nor about the nature of the acrylic bark. GB 2242906 discloses a fluorinated polymeric composition comprising a PVDF and a core-shell shock modifier comprising an elastomeric core and an acrylic shell. The composition does not include a plasticizer. There is no mention of any particular use of the composition.

EP 1541603 discloses a core-shell shock modifier comprising a shell based on a hydrophilic monomer. This impact modifier is incorporated in a thermoplastic polymer which may be a PVDF (rev.10). The proportion of impact modifier in the thermoplastic varies from 0.5 to 77%, preferably from 1 to 70% and even more preferably from 3 to 60%.

WO2006 / 045753 discloses a fluorinated polymeric composition comprising a VDF homopolymer a fluorinated thermoplastic copolymer and a plasticizer said composition at a ductile-brittle transition temperature of less than 5 ° C. The composition does not contain an impact modifier.

None of these documents describes or suggests the fluorinated polymeric composition according to the invention which are intended in particular for use in hydrocarbon or oil transport pipes.

[Brief description of the invention] More precisely, the present invention relates to a fluorinated polymeric composition comprising, for 100 parts of composition: • optionally from 1 to 6 parts, preferably from 2 to 5 parts, of at least a compatible plasticizer; From 4 to 10 parts, preferably from 5 to 8 parts of particles of a core-shell type impact modifier which comprises at least one inner layer of a soft polymer having a Tg <25 ° C, preferably <40 ° C and a bark based on a (meth) acrylic polymer; • the complement to 100 parts of at least one homopolymer or copolymer of VDF; characterized in that the impact modifier particles have an interparticular distance D1 of at most 150 nm, preferably at most 100 nm.

This composition can be used for the manufacture of: • pipes intended to convey a fluid under pressure and / or corrosive; • or hollow bodies intended to store a fluid under pressure and / or corrosive; • or a monolayer or multilayer film; • or to manufacture a sealing sheath of an offshore pipe. This composition does not have the disadvantages of the compositions of the prior art. [Figures] FIG. 1 represents scanning electron micrographs of the compositions which comprise a core-shell shock modifier: FIG. A (1 μm scale): corresponds to the composition of Example 3; Snapshot B (1 μm scale): corresponds to the composition of Example 2. FIG. 2 shows a sectional view of a flexible metal pipe comprising a layer of the composition 1 covering a metal carcass 3, all reinforced by a weave 2. FIG. 3 is a graph showing the ductile-fragile Charpy impact temperature of different compositions as a function of the interparticular distance D in nm.

FIG. 4 represents an axisymmetrical specimen intended for a tensile fatigue test making it possible to impose a triaxial stress field on the stressed material: the specimen comprises a longitudinal axis z, a curved notch of curvature radius R, a minimum diameter a and a maximum diameter d -.

[Detailed Description of the Invention] Tg is the glass transition temperature of a polymer measured by DSC according to ISO 11357-2: 1999. We also speak of the Tg of a monomer to designate the Tg of the homopolymer made from this monomer having a number average molecular weight Mn of at least 10,000 g / mol, obtained for example by radical polymerization of said monomer. Thus, it will be said that ethyl acrylate has a Tg of -24 ° C because the ethyl homopolyacrylate has a Tg of -24 ° C. All percentages are by weight unless otherwise indicated.

As regards the PVDF according to the invention, it is a homopolymer of vinylidene fluoride (VDF of formula CH2 = CF2) or a copolymer of PVDF, that is to say a copolymer of VDF comprising by weight at least 90% of VDF and at least one other monomer copolymerizable with VDF. The VDF content must be greater than 90%, or even better 95%, to ensure sufficient mechanical strength when hot (that is to say, a good resistance to creep at 130 ° C.).

The comonomer according to the invention may be a fluorinated monomer chosen, for example, 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). Preferably, the optional comonomer is chosen from chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), trifluoroethylene (VF3) and tetrafluoroethylene (TFE). The comonomer may also be an olefin such as ethylene or propylene. The preferred comonomer is HFP.

The melt index (ASTM D-1238, 230 ° C., 5 kg) of the PVDF should not exceed 15 g / 10 min, advantageously 3 g / 10 min and more preferably 1.5 g / 10 min, for to guarantee good properties of mechanical resistance. Preferably, the number of defects corresponding to head-to-tail or tail-tail sequences measured using the 19 F NMR should not exceed 6%, or even better, 4.5%.

A PVDF characterized by a polymer chain fraction of very high molar masses, fraction having a dynamic viscosity greater than 50 kPoise at 230 ° C under a shear rate of 100 s-1, is particularly suitable for this application. This PVDF is designated in the following by bimodal PVDF because on a size exclusion chromatography elution profile (GPC), a bimodal distribution is observed, the fraction of high masses being visible on the profile either in the form of a distribution. isolated or in the form of a shoulder of a distribution of chains of smaller masses. Having a fraction of high masses and a fraction of smaller masses makes it possible to obtain a good compromise between the impact resistance and the ability of the PVDF to be transformed by extrusion. The fraction of polymer chains is at least 10% by weight relative to PVDF and it is advantageously between 10 and 50% (it is the fraction relative to the total amount of PVDF, that is to say that for 10 to 50% of chains of very high mass there are respectively 90 to 50% of other chains). This PVDF has a very good impact resistance as well as a strongly pseudoplastic character (strong drop in viscosity with shear rate). This PVDF can be prepared by emulsion or suspension, for example according to the process described in EP 1279685. In a first step, a dispersion in water of VDF and of the optional comonomer (s) is carried out in the presence of a surfactant. surface (surfactant, colloidal agent), said dispersion being brought into contact with a non-organic initiator soluble in water capable of initiating the polymerization. In a second step, a portion of the PVDF having been formed in the first step, is added: (i) a chain transfer agent capable of propagating the polymerization, said polymerization is then initiated by a non-organic initiator soluble in the water or an organic initiator, or (ii) an organic initiator capable of also carrying chain transfer and optionally a water-soluble non-organic initiator. The principle of this process is based on the formation, at the beginning of polymerization, of a very high molecular weight fraction of polymer chains, produced without a transfer agent (or without a secondary reaction of transfer or termination type contributing to greatly limiting the chain length) and without initiator capable of inducing a transfer reaction. The reaction therefore starts without a transfer agent (CTA), and the first charge of CTA is injected at a conversion rate of the monomers, for example of the order of 5% by weight. The required dose of CTA can then be incrementally or continuously introduced, the total amount making it possible to adjust the average molar mass of the polymer. In the case of a single injection of transfer agent, the product obtained will show a bimodal distribution of the molar masses with a first distribution of very high mass and a second distribution of limited mass. The polymerization step after addition of the first dose of transfer agent can also be carried out under the effect of an organic initiator whose contribution to the transfer reactions will be more or less important. In the particular case of an organic initiator having a transfer effect sufficient to adjust the molecular weight, it is also possible to dispense with the transfer agent itself without changing the nature of the invention. In this case, the high mass fraction is still obtained during the first polymerization step in the presence of the non-organic initiator, and a second fraction of moderate molar mass is formed under the sole action of the organic initiator. Preferably, the size of the spherulites of this PVDF is between 0.5 and 4 μm.

Example of preparation of a bimodal PVDF In a 30 liter autoclave, 18.6 liters of deionized water and 50 g of perfluorinated anionic surfactant of C $ F17002NH4 type are introduced. The autoclave is closed and intermittently stirred mechanically, then it is degassed under vacuum, filled with nitrogen to 10 bar pressure, again degassed under vacuum, filled with VDF to 5 bar pressure, and finally degassed under vacuum one last time. The autoclave is then brought to 85 ° C. with mechanical stirring at 150 rpm and then filled with VDF to an absolute pressure of 85 bar. A 50 ml dose of 0.5% by weight aqueous solution of potassium persulfate is added all at once to start the reaction. The pressure is maintained at 85 bars by VDF continuous introduction. When 2.25 kg of VDF have been consumed, 250 ml of ethyl acetate (EA) and 70 ml of the same aqueous potassium persulfate solution are added.

When 9 kg of VDF has been consumed, 20 ml of aqueous persulfate solution are incorporated to maintain a conversion rate in the range of 1.5 to 3.5 kg / hour. When 9 kg of VDF have been consumed, the supply of VDF is stopped and the reaction is continued up to 42 bars of pressure, before lowering the temperature to 23 ° C and emptying the autoclave of the residual monomer.

This test makes it possible to produce 31.2 kg of a latex containing 39.5% solids, ie 12.3 kg of dry PVDF. The polymer fraction obtained before introduction of the transfer agent is 2.9 kg, or 23.6% of the total product formed. The melt index measured according to ISO-1133 at 230 ° C. under a load of 5 kg is 1.7 g / 10 min.

As regards the plasticizer according to the invention, this is generally described in Encyclopaedia of Polymer Science and Engineering, Wiley and Sons (1989), pages 568-569 and 588-593. The plasticizer must be compatible with PVDF. Preferably, to ensure good cold properties, it is a low temperature plasticizer that is to say a plasticizer that does not solidify at -30 ° C. The plasticizer may be selected from the plasticizers described in US 3541039 or US 4584215 and mixtures thereof.

By way of example, the plasticizer that may be used in the invention may be dibutyl sebacate (DBS of formula C4H9-COO- (CH2) 8-COO-C4H9), dioctyl phthalate (DOP) or NBSA (Nn). butyl-butylsulfonamide). High-performance plasticizers are also the polymeric polyesters such as those derived from adipic, azelaic or sebacic acids and diols, and mixtures thereof, provided however that their number-average molecular weight is at least about 1500, preferably at least 1800, and not exceeding about 5000, preferably less than 2500 g / mol. Polyesters of too high molecular weight lead to compositions of lower impact resistance. An adipic acid polyester of average molecular weight of 2050 g / mol sold by CIBA under the brand RHEOPLEX 904 may be used. A high performance plasticizer for the present invention is DBS which is easily incorporated with PVDF. As regards the impact modifier of the heart-shell type according to the invention, it comprises at least one inner layer made of a soft polymer and one bark based on an acrylic polymer (that is to say the outer layer also called acrylic bark). Acrylic polymer means polymers that contain methacrylic and / or acrylic monomers. The impact modifier is in the form of particles whose average diameter is at most 1 μm, preferably between 50 and 400 nm.

The soft polymer has a Tg <25 ° C, preferably <-40 ° C and preferably <60 ° C. It is obtained for example from at least one soft monomer having a Tg <-25 ° C, advantageously <-40 ° C and preferably <60 ° C, and optionally at least one other monomer copolymerizable with the monomer soft. The soft monomer may be for example butadiene or a (meth) acrylate of Tg <-25 ° C, advantageously <-40 ° C and preferably <60 ° C such as butyl acrylate, 2-ethylhexyl or octyl. The soft polymer may be for example a copolymer comprising butadiene and styrene whose weight content of butadiene is> 75%, a copolymer comprising butadiene and at least one low Tg (meth) acrylate, a copolymer comprising styrene and at least one minus one (meth) acrylate of low Tg. The main soft polymer inner layer has the main function of improving cold impact resistance. The weight content of the inner layer represents a content of 50 to 95% by weight of the particle

The bark based on an acrylic polymer comprises at least 75% by weight of methyl methacrylate (MMA) and optionally at least one other monomer polymerizable with MMA. The main function of the acrylic bark is to improve the compatibility of the impact modifier with the fluoropolymer, in particular the homopolymer or copolymer of VDF.

There are several morphologies for the impact modifier according to the invention. It may be a soft / hard impact modifier comprising a core of a soft polymer (the inner layer) having a Tg <-25 ° C, preferably <-40 ° C and preferably <-60 ° C , and an acrylic bark. Examples of this morphology can be found in US Pat. No. 3,264,373. It can also be a shock modifier of the hard / soft / hard type comprising a core made of a hard polymer having a Tg> 0 ° C., an intermediate layer made of a polymer. soft and acrylic bark. Advantageously, each of the layers of the impact modifier can optionally be crosslinked in order to preserve the integrity of the particles during their hot incorporation into the PVDF. For this purpose at least one crosslinking agent is used, which may for example be divinylbenzene or a polyethylene glycol di (meth) acrylate. The Applicant has found that in order to have a good compromise of properties of the composition, in particular a good cold impact resistance (that is to say a TDF <-15 ° C.), it is necessary that the particles are very well dispersed in the composition, i.e. the impact modifying particles have an interparticle distance of at most 150 nm, preferably at most 100 nm. This distance is determined according to the following protocol: 2D images are acquired by Transmission Electron Microscopy (TEM). A preliminary chemical marking of the particles is carried out so as to obtain a good contrast on the microscopy images, making it possible to differentiate the particles from the PVDF matrix in which they are dispersed. Using an image analysis software (ANALYSIS from ELOISE), these images are transformed into binary images, then labeled to detect each particle (either the core-bark particle or the aggregate of several particles). Then, the interparticle distance, defined as the distance to the nearest particle, is extracted by the Nearest Distance function of the image analysis software. An arithmetic average is performed on all the distances obtained on the image and also on 4 TEM snapshots to give the average interparticular distance (DI) of the analyzed product.

From a more mathematical point of view, we can define DI as well. For each particle i is defined the minimum distance among the distances between the particles i and the particles j in its vicinity. DI is then the average of each minimum distance. In other words, D1 = arithmetic average on particles (minimum between each particle i and particles j in its vicinity)

The good dispersion is obtained by using a shear mixing tool such as for example a BUSS extruder.

The Applicant has also found that the dispersion is improved (small interparticle distance = not agglomerates) when the acrylic bark is uniform. Uniform is understood to mean that the acrylic shell completely and completely covers the layer with which it is in contact, for example the soft core in the case of a soft / hard particle. EP 1541603 discloses a means for achieving such complete coverage, i.e., uniform acrylic bark. This means consists in using at least one hydrophilic monomer in the acrylic bark. By hydrophilic monomer is meant a monomer having a solubility of at least 6 g of monomer per 100 g of water at 25 ° C. As examples of hydrophilic monomers, mention may be made of hydroxyalkyl (meth) acrylates, (meth) acrylic acid, (meth) acrylic amides, especially 2-hydroxyethyl methacrylate (HEMA), 2-hydroxyethyl acrylate, hydroxypropylmethacrylate, 4-hydroxybutylacrylate, ethyl alpha-hydroxymethacrylate, glycidyl methacrylate, vinylpyrrolidone. The acrylic shell preferably comprises 99.5 to 80% MMA and 0.5 to 20% of at least one hydrophilic monomer. Another way is to graft on the surface of the layer in direct contact with the acrylic bark chemical functions that promote complete recovery. For example, a grafting agent such as diallyl maleate may be incorporated in said contacting surface. With regard to the fluorinated polymeric composition according to the invention, this comprises, for 100 parts of composition: • optionally from 1 to 6 parts, preferably from 2 to 5 parts, of at least one plasticizer; From 4 to 10 parts, preferably from 5 to 8 parts of particles of a core-shell shock modifier; • the complement to 100 parts of at least one PVDF; characterized in that the impact modifier particles have an average interparticle distance of at most 150 nm, preferably at most 100 nm.

Preferably, the complement is provided by a bimodal PVDF and optionally another PVDF. The other PVDF which is associated with the bimodal PVDF must be compatible with the bimodal PVDF, that is to say give a homogeneous mixture. It may be a homo- or copolymer PVDF.

The composition of the invention has good dimensional stability during prolonged use at high temperature, as well as high mechanical resistance to multiaxial fatigue and cold shock, especially in the unaged state. This compromise of properties is characterized more particularly by: 1. a change in volume during prolonged holding at a temperature of 130 ° C. of less than 10%; 2. a multiaxial fatigue strength resulting in a cycle failure number (NCR)> 5000, preferably> 10000 according to the fatigue test described below; 3. a ductile-brittle Charpy shock transition temperature <-15 ° C; 4. good creep resistance at 130 ° C. under a stress of 6 MPa min.

Test tubes Specimens for a tensile strength test are prepared from the polymer composition produced. The test pieces may be prepared by injection of the manufactured polymeric composition. Specimens may also be prepared by extrusion, for example extrusions of the strips or tubes followed by machining of the specimens. In particular, the specimens are cut in the circular thickness of a tube of the polymeric composition. Each specimen is axisymmetric to the longitudinal axis z and has a curved notch 5 of curvature radius R, a minimum radius a and a maximum diameter d. The specimen is defined by these three values ad and R. The relation between the minimum radius a and the radius of curvature a / R is from 0.05 to 10, preferably 0.2-1 and even more preferably 0.4-0. 6. The maximum diameter d is greater than 2 times the minimum radius a and preferably 10 is from 2a + R to 2a + 2R. In producing a test piece, the curvature radius R is 0.5 mm to 10 mm, preferably 3 mm to 5 mm and typically 4 mm; each test piece has a minimum radius a varying from 0.5 mm to 5 mm, preferably 1.5 mm to 2.5 mm and typically 2 mm; and the maximum diameter d is chosen from 2mm to 30mm, preferably 6mm to 10mm and typically 7mm.

The specimen, thanks to its particular shape, has a triaxial stress field, representative of the stress conditions encountered by the polymer composition in a pressure sheath or an intermediate sheath or an outer sheath of offshore hose.

Fatigue test The fatigue test consists in stressing the specimens with a tensile fatigue test consisting of an elongation along the longitudinal axis z, with a sinusoidal signal of frequency ranging from 0.05 Hz to 5 Hz, preferably from 0.5 Hz to 2 Hz and typically 1 Hz, at a temperature ranging from -15 ° C to 23 ° C, preferably from -15 ° C to 5 ° C, preferably from -15 ° C to -5 ° C and typically from -10 ° C. The maximum elongation of the same tensile cycle is from 0.1 R to 1 R and preferably from 0.3 R to 0.4 R, expressed in relative dimension from the radius of curvature of the notch R. The minimum elongation of The same tensile cycle is 0 to 0.08 R and preferably 0.075 R to 0.08 R. The maximum elongation is chosen from 0.4 mm to 4 mm, preferably 1.2 mm to 1.6 mm and typically 1.4 mm.

The minimum elongation of the fatigue test is determined by the ratio between the minimum elongation and the maximum elongation of the cycle. This ratio is chosen from 0 to 0.8 and preferably from 0 to 0.5, and advantageously from 0.18 to 0.25 and is typically 0.21.

The result of the fatigue test is the number of failure cycles (NCR) of the test pieces. Different fluorinated compositions can be classified and compared from the results of this fatigue test: the greater the number of cycles to rupture, the better the polymeric composition.

The composition which has a number of cycles to failure (NCR) on average on several test specimens> 5000, and preferably> 10000. Several means that the number of measurements or specimens to calculate the average number of cycles to failure (NCR) is at least 2, preferably between 2 and 50, preferably between 5 and 40, and typically 10.25 The Applicant has found that the described test makes it possible to select a fluorinated polymeric composition that can be used in the manufacture of a flexible metal pipe (offshore pipe). It has therefore developed a method for selecting a fluorinated polymeric composition suitable for use in the field of offshore metal pipes. In this case, the term "fluorinated polymeric composition" is intended to mean a composition comprising predominantly at least one PVDF. This composition comprises at least 80% by weight of at least one PVDF, it may also optionally comprise at least one plasticizer and / or at least one impact modifier.

The composition according to the invention also preferably has the following properties: an elongation at the flow threshold cy> 9%; • elongation at break cr> 50%; • impact resistance at 23 ° C> 45 kJ / m2 (ISO 180-1982). The composition according to the invention may also comprise conventional additives chosen from mineral fillers, pigments, fibrous reinforcements, conductive fillers, etc. For example, it may be mica, alumina, talc, carbon black, fiber, glass and mixtures thereof. The composition is prepared by premixing the ingredients in the solid state (for example in the form of powders or granules) in the proportions indicated, and then subjecting the resulting mixture to a melt processing known to man. art. For example, the transformation may be carried out in an extruder or in a mixer.

Uses of the Composition The composition according to the invention is suitable for the manufacture of pipes subjected to severe use conditions in particular intended to convey a fluid under pressure and / or corrosive. These pipes comprise at least one layer comprising the composition of the invention. The composition may also be adapted for the manufacture of containers or hollow bodies intended to store a fluid under pressure and / or corrosive. A particular application is the transport or storage of hot hydrocarbons.

The composition according to the invention can be used to manufacture the flexible metal pipe sealing sleeves for extracting and / or transporting gas and / or hydrocarbons (offshore pipes). These lines must meet, among other things, the recommendations of API 17B (American Petroleum Institute Recommended Practice 17B). They are formed of a set of different layers each intended to allow the flexible pipe to support the service or handling constraints and the specific constraints related to their offshore use. These layers comprise in particular polymeric layers and reinforcing layers formed by windings of shaped wire, strip or son of composite material, but they may also comprise windings of various bands between the various layers of reinforcement, they include more particularly at least one internal sealing sheath or pressure sheath. Said sealing sheath may be the innermost element of the pipe (the pipe is then called smooth boron type) or be arranged around a carcass formed for example of the short-pitch winding of a stapled strip (The pipe is then called rough-boron type). Reinforcing layers formed by winding metal or composite wires are generally arranged around the pressure sheath.

Thus, the flexible metal conduits generally comprise one or more metal elements (or metal carcasses) guaranteeing the mechanical rigidity, for example a spiral steel ribbon, and at least one layer comprising the composition of the invention and optionally one or several layers of a polymeric material. These pipes can be made by extruding or coextruding the polymer layers and then inserting the metal element. The polymer layers can also be formed directly on the metallic element by the over-coating technique. Examples of flexible metal conduits can be found in US 5601893 or EP 0166385.

Thus, the flexible metal conduits are manufactured by extruding a layer of the composition of the invention on a metal carcass, all resembling a large shower hose (see Fig. 2). The metal carcass is intended to take up the external pressure to avoid the phenomenon of collapse. Armor, consisting for example of metal son, is then wound to resume the internal pressure of the fluid. The nature of the fluid, the temperature and the pressure determine the choice of the polymer to make the pressure sheath. For the most severe applications, corresponding to high temperatures (> 110 ° C) and high pressures (> 500 bar), the composition of the invention has great advantages.

Finally, the composition according to the invention can also be used to make a film either monolayer or multilayer. The film can be prepared using the extrusion blow molding technique.

The composition used in the context of the present invention is prepared by melt blending of the various constituents in any mixing device, and preferably an extruder. The composition is most often recovered in the form of granules. The present invention will now be illustrated by examples of various compositions the use of which is the subject of the present invention.

Products used VDF-homopolymer: KYNAR 400: PVDF bimodal homopolymer marketed by ARKEMA VDF-HFP copolymer: KYNAR 2750: VDF-HFP copolymer (15% HFP weight), MFI = 3-4 g / 10 min (230 ° C., 5 kg) marketed by ARKEMA; KYNAR 2800: VDF-HFP copolymer (110/0 weight of HFP), MFI about 1 g / 10 min (230 ° C., 5 kg) marketed by ARKEMA DBS: dibutyl sebacate (plasticizer) Impact modifier: DURASTRENGTH D200: heart-bar shock modifier marketed by ARKEMA having a soft internal layer of Tg = -45 ° C. DURASTRENGTH D200L: heart-bark shock modifier marketed by ARKEMA having a soft internal layer of Tg = -46 ° C.

EXL 2650: shock modifier marketed by ROHM & HAAS having a soft internal layer of Tg = -76 ° C.

Characterization of shocks modifiers.

The measurement of the glass transition temperature (Tg) of the impact modifiers is done by DSC using a DSC 2920 TA instruments with the following protocol: 1 heats from -120 to 200 ° C at 20 ° C / min, then cooling: from 200 to -120 ° C at 20 ° C / min and 2nd heating: from -120 to 200 ° C at 20 ° C / min according to ISO 11357-2: 1999.

Preparation of the Compositions In the context of the numbered tests examples 1 to 6, which are either comparative or according to the invention, 6 separate compositions have been prepared.

The compositions were prepared using a BUSS extruder operating at a temperature of 200 to 220 ° C.

Table I Examples composition (% by weight) Polymer fluorine Plasticizer Shock modifier 1 (comp.) 95% 3% 2% KYNAR 400 DBS DURASTRENGTH D200 2 (comp.) 89% 3% 8% KYNAR 400 DBS DURASTRENGTH D200 3 (inv. ) 89.5% 3% 7.5% KYNAR 400 DBS DURASTRENGTH D200L 4 (inv.) 89.5% 3% 7.5% KYNAR 400 DBS PARALOID EXL 2650 (Comp.) 77% KYNAR 400 30 / o 0 + 20% KYNAR DBS 2750 6 (comp.) 74% KYNAR 400 0 0 + 20% KYNAR DBS 2800 Example 1 is a comparative example based on the composition described in EP884 5 358 using DURASTRENGTH D200. Examples 5 and 6 are comparative examples close to the composition described in WO2006 / 045753.

Preparation of specimens for fatigue test Specimens are cut in the circular thickness of an extruded tube.

Description of the material characterization methods Measurement of the ductile-brittle transition temperature (TDF) For measurement of the ductile-brittle temperature (TDF), measurements are made according to the Charpy shock test by following a protocol derived from the test of ISO 179 leA. This protocol has been adapted to be more severe than that of the standard in that the notch is made using a razor blade and therefore has a bottom radius of notch smaller than the value of 0 , 25 mm recommended in the standard. The thickness of the bars used is also greater than that of the bars recommended in the standard (6 or 7 mm typically against 4 mm). On 10 bars, we proceed by dichotomy in steps of 5 ° C to supervise the TDF. This corresponds to 50% brittle fracture. The impact velocity referenced is that recommended by ISO 179 leA.

Fatigue test This test consists in determining, for a given sample of polymer composition, the number of cycles to rupture (NCR), that is to say the number of cycles at the end of which the rupture of the sample occurs. The larger the NCR, the better the result of the fatigue test for the given sample. The test is carried out at a temperature of -10 ° C. on axisymmetric test pieces having a radius of curvature of notch of 4 mm (R4) and a minimum radius of 2 mm, using a servohydraulic dynamometer, for example of the type MTS 810. The distance between jaws is 10 mm. The test piece is subjected to a maximum elongation of 1.4 mm and a ratio between the minimum elongation and the maximum elongation of 0.21, which leads to a minimum elongation of 0.3 mm; with a sinusoidal signal having a frequency of 1 Hz. The result of the test is the average of the results obtained on 10 test pieces. The average found for 10 specimens corresponds to NCR (average number of cycles to rupture). Example: The composition of Example 4 has an NCR of 27800 on 10 test pieces tested. This means that there is an average of 27800 cycles before the test piece breaks.

Hot creep The resistance to hot creep is evaluated by performing a temperature pulling test according to ISO 527 on new test pieces of the polymer composition, with a temperature conditioning of these test pieces of 20 min before the test. The threshold stress of these test pieces is measured at 130 ° C. for polymeric compositions based on homopolymers or copolymers of VDF. This stress corresponds to the maximum nominal tensile stress supported by the specimens before traction. The greater this stress, the better the creep resistance of the polymer. Table 2 Ex. Composition (% TDF NCR Resistance in DI (creep specimen: stress weight) [C] R4 - 1 Hz with threshold at [nm] -10 ° C) 130 ° C [MPa] 1 95% KYNAR 400 + -2,5 500 8,318 (comp.) 3% DBS + 2% D200 2 89% KYNAR 400 + (comp.) 3% DBS + 8% D200 - 2,500 7,256 (snapshot B) 89.5% KYNAR 400 + 3 (inv.) 3% DBS + 7.5% D200L -17 16500 8,106 (snapshot A) 89.5% KYNAR 400 + 4 (inv) 3% DBS + 7.5% EXL -32 27800 8 93 2650 5 77% KYNAR 400 + (comp.) 3% DBS + 20% -10,500 6 - KYNAR 2750 6 74% KYNAR 400 + (comp.) 6% DBS + 20% -15 4900 6 - KYNAR 2800 The comparison between Example 3 according to the invention and Comparative Example 2 shows the importance of the mean interparticular distance (ID) on the mechanical properties of the fluorinated polymeric composition, especially TDF and NCR.

Claims (15)

REVENDICATIONS1. A fluorinated polymeric composition comprising, per 100 parts by weight of composition: • optionally from 1 to 6 parts, preferably from 2 to 5 parts, of at least one plasticizer compatible with the fluorinated polymer; From 4 to 10 parts, preferably from 5 to 8 parts of particles of a core-shell shock modifier which comprises at least one inner layer of a soft polymer having a Tg <25 ° C, advantageously <-40 ° C and preferably <60 ° C and an acrylic bark; • the complement to 100 parts of at least one homopolymer or copolymer of VDF; characterized in that the impact modifier particles have an interparticular distance DI of at most 150 nm, preferably at most 100 nm. 2. Composition according to claim 1 characterized in that the complement is provided by a bimodal VDF homopolymer or copolymer and optionally another homopolymer or copolymer of VDF. 3. Composition according to one of claims 1 or 2 characterized in that the impact modifier is soft / hard type comprising a core of a soft polymer (the inner layer) having a Tg <25 ° C, preferably <-40 ° C and preferably <60 ° C, and an acrylic bark. 25 4. Composition according to any one of claims 1 to 3 characterized in that the acrylic shell completely and completely covers the layer with which is in contact. 5. Composition according to any one of claims 1 to 4 characterized in that the acrylic shell comprises at least one hydrophilic monomer. 6. Composition according to any one of claims 1 to 5 characterized in that the surface of the layer in direct contact with the acrylic shell comprises a grafting agent. 7. Composition according to any one of claims 1 to 6 characterized in that the plasticizer has a solidification temperature <-30 ° C. 15 8. Composition according to any one of claims 1 to 7 characterized in that the plasticizer is dibutyl sebacate, dibutyl phthalate, N-n-butyl-butylsulfonamide or a polymeric polyester derived from adipic, azelaic or sebacic acids having a number-average molecular weight of at least about 1500, preferably at least 1800, and not more than about 5000, preferably less than 2500 g / mol. 9. Use of the composition as defined in any one of claims 1 to 8 for the manufacture of: • pipes for conveying a fluid under pressure and / or corrosive • or hollow body for storing a fluid under pressure and / or corrosive; • or a monolayer or multilayer film. Pipe comprising at least one layer comprising the composition as defined in any one of Claims 1 to 8. Hollow body comprising at least one layer comprising the composition as defined in any one of claims 1 to 8. 12. Film comprising at least one layer comprising the composition as defined in any one of Claims 1 to 8. 13. Use of the composition according to any one of claims 1 to 8 to manufacture a sealing sheath of an offshore pipe. 14. Use of the composition according to any one of claims 1 to 8 for manufacturing a pipe for the extraction and / or transport of gas and / or hydrocarbons. 15. Flexible metal conduit comprising one or more metal elements and at least one layer comprising the composition according to any one of claims 1 to 8 and optionally one or more layers of a polymeric material. 20 25