FIELD OF INVENTION

The present invention relates generally to the field of the extrusion of thermoplastic polymers. More particularly, the invention relates to an extrusion assistant agent, that is to say an additive which makes it possible to reduce or eliminate the surface defects which appear when extruding a thermoplastic resin, in particular a polyolefin in the form of fibers. The extrusion aid agent according to the invention (or processing aid in the remainder of the application) contains thermoplastic fluoropolymers low viscosity and does not contain a synergist. The invention also relates to the use of the processing aid for extrusion in the form of single fibers or multi-filaments or nonwoven, and the extrusion process.

TECHNICAL BACKGROUND

During extrusion of polyolefins, flow irregularities and / or deposits may appear at the outlet of the die, which results in surface defects and sometimes the deterioration of mechanical properties of the extruded polyolefin. The addition of a processing aid in the polyolefin to be extruded to reduce these defects and even to eliminate them.

US 4013622 discloses the use of polyoxyethylene glycol (PEG) as a processing aid.

It is known to use as blowing agents fluoropolymers, as described in documents US 3125547 and US 4581406, which disclose the use of fluoro-elastomers.

Numerous documents describe the use of blowing agents consisting of fluoropolymers blended with synergists, and optionally other additives. The Applicant has already described in EP 1616907 the use of a mixture of at least one fluorinated polymer and at least one interfacial agent, such as processing aid for the extrusion of a polyolefin in the form of movie.

Documents US 4855360 and US 5587429 disclose the use of a fluoro elastomer in combination with a polyoxyalkylene to improve the conversion of hydrocarbon polymers.

However, it was found that the use of fluoroelastomers as extrusion agent fails to remove the extrusion defects of all types of polyolefins, especially those of low viscosity, having a melt index of at least 10 g / 10 min, preferably greater than 25 g / 10 min. Indeed, in this case the use of fluoroelastomers as extrusion agent does not give satisfactory results to eliminate or at least reduce the surface defects, because these compounds do not disperse evenly in the weight of said polyolefin.

There is therefore a need to prepare new blowing agents based on fluorinated polymers, which improve the extrusion of low viscosity polyolefins, especially in fiber form.

SUMMARY OF THE INVENTION

The invention firstly relates to a processing aid for polyolefin extrudable form of fibers, said processing aid comprises a polymer based on vinylidene fluoride (polymer referred to hereinafter "PVDF") having a thermoplastic character.

Typically, said PVDF has a viscosity less than 5 kP, preferably less than 1 kP, as measured at 232 ° C and 100s "1 using a capillary rheometer or a parallel plate rheometer. The PVDF according the invention has a molecular weight ranging from 5 000 to 200 000 Dalton as measured by steric exclusion chromatography.

Advantageously, the processing aid according to the invention is free of synergist. The term "synergist" is here comprises an interface agent (surfactant) which is an oligomer or a thermoplastic polymer is located in the liquid state or melted at the extrusion temperature and has a viscosity at the lower melt that of the polymer to be extruded and the additives used. Many synergists are used in combination with a fluorinated polymer to enhance the positive effects of the latter during extrusion of polyolefins.

It has now been found that the extrusion agent according to the invention provides good results during extrusion of polyolefins, such a pressure drop, an improved surface quality and an absence of deposits. The processing aid according to the invention is particularly effective in reducing or eliminating the extrusion defects likely to arise during the extrusion of low viscosity polyolefin having a melt index of at least 10 g / 10 min, preferably greater than 25 g / 10 min, preferably greater than 40 g / 10 min, measured according to ASTM 1238.

According to a second aspect, the invention relates to extruded fibers from a formulation comprising a polyolefin and the processing aid of the invention. These fibers are in the form of mono- or multi- filaments, or in the form of nonwoven materials. One of the advantages obtained by the processing aid of the invention is to allow to obtain good quality fibers from low viscosity polyolefins, for which the use of a fluoro-elastomer as extrusion (alone or in admixture with a synergist), does not give satisfactory results, due to its high viscosity and elasticity which prevent the homogeneous dispersion in the mass of the polyolefin.

According to another aspect, the invention relates to a fiber manufacturing process by extrusion of a polyolefin by means of the processing aid of the invention, said polyolefin having a melt index of at least 10 g / 10 min, preferably greater than 25 g / 10 min, preferably greater than 40 g / 10 min, said method comprising the steps of:

at. adding said processing aid in the formulation of polyolefin, and b. extrusion of the final formulation of polyolefin in the form of fibers.

EMBODIMENTS DESCRIPTION OF THE INVENTION

The invention is now described in more detail and not limited to the following description.

According to a first aspect, the invention relates to a processing aid for polyolefin extrudable form of fibers, said processing aid comprises a polymer based on vinylidene fluoride (PVDF) having a viscosity of less than 5 kP, preferably less 1 kP, and having a thermoplastic character.

According to one embodiment, said polymer is a PVDF homopolymer.

According to another embodiment, the PVDF is a copolymer of fluoride VDF and at least one other comonomer chosen from chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), trifluoroethylene (VF3), tetrafluoroethylene (TFE) and ethylene. Advantageously, the copolymer contains at least 75% VDF by weight, preferably at least 85 wt% VDF, which gives it a thermoplastic character.

These polymers may be obtained by known polymerization methods such as solution polymerization, emulsion or suspension. According to one embodiment, the PVDF is prepared by an emulsion process in the absence of fluorinated surfactant.

PVDF according to the invention are characterized by a low viscosity in the molten state, i.e. a viscosity of from 0.01 to less than 5 kP, preferably from 0.03 to 2.5 kp, preferably from 0.05 less than 1 kP and more preferably from 0.1 to 0.8 kP. The viscosity is measured at 232 ° C, at a shear gradient of 100 s "1 using a rheometer with a capillary rheometer or a parallel plate rheometer, according to ASTM D3825 standard. Both methods give similar results.

These PVDF have average molecular weights ranging from 5 kDa to 200 kDa, preferably 10 kDa to 100 kDa as measured by steric exclusion chromatography in DMF / LiBr 0.003M with PMMA as calibration standard. These low molecular weight PVDF can be obtained by using high levels of one or more chain transfer agents. According to one embodiment, chain transfer agents suitable for this purpose are chosen from:

short chain hydrocarbons such as ethane and propane,

esters such as ethyl acetate and diethyl maleate,

alcohols, carbonates, ketones,

Halocarbon and hydrohalocarbures such as chlorocarnures, hydrochlorocarbons, chlorofluorocarbons and hydrochlorofluorocarbons, organic solvents, when added to a polymerization reaction in emulsion or in suspension.

Other factors contributing to obtaining low molecular weight polymers are conducting the polymerization reaction at elevated temperatures, or the use of high initiator levels.

The PVDF used in the construction of the processing aid according to the invention are preferably homogeneous copolymers, this term meaning that they have uniform structures of chains in which the statistical distribution of the comonomer along the chain polymeric tightened.

This particular distribution of the comonomer distinguishes these polymers (so-called "homogeneous") of those called "heterogeneous" which are characterized by the fact that the polymer chains have an average content of comonomer distribution that is multimodal or spread; the heterogeneous PVDF therefore comprises polymer chains

rich in comonomer and chains comprising almost no or little comonomer. The applicant describes heterogeneous PVDF and extrusion agents containing in EP 1,976,927.

PVDF homogeneous copolymers are prepared by a process in a single step, wherein the VDF and comonomer are injected gradually maintaining a weight ratio of VDF / co mono constant mother.

One or more additives may be added to the PVDF described above to form the processing aid according to the invention. These additives are advantageously selected from primary antioxidants phenolic or phenolic hindered, and / or secondary components selected from phosphorus (phosphonites and / or phosphites). Amino can also be used but in general their use should be limited because of possible interactions with PVDF.

According to a second aspect, the invention relates to extruded fibers from a formulation comprising a polyolefin and the processing aid of the invention. These fibers are in the form of mono- or multi- filaments, or in the form of non-woven materials which are groups of randomly or directionally oriented fibers in the form of web, a web or a fiber mat. The diameters of these fibers range from 0.1 to 300 microns, preferably 0.5 to 5 microns (for non-woven), from 5 to 50 microns (for multi filaments), 50 to 300 microns (for mono-filaments). These diameters are indicative. These fibers are used in many fields such as textile (clothing, architecture, industrial) and filtration (air, liquids such as water or fuel).

According to another aspect, the invention relates to a fiber manufacturing process by extrusion of a polyolefin by means of the processing aid of the invention, said polyolefin having a melt index of at least 10 g / 10 min, preferably greater than

25 g / 10 min, preferably greater than 40 g / 10 min, said method comprising the steps of:

at. adding said processing aid in the formulation of polyolefin, and b. extrusion of the final formulation of polyolefin in the form of fibers.

The processing aid may be added to the final formulation in a prior compounding phase or dry blending during extrusion through the use of a masterbatch. In the latter case, the processing aid is diluted in a polyolefin formulation having the same viscosity as the formulation of polyolefin to be extruded.

The extrudable thermoplastic resin in the form of fibers can be a polyolefin, a styrene resin, a polyester or a polyamide / copolyamide.

The polyolefin is chosen from:

• a polyethylene, especially low density polyethylene (LDPE), high density (HDPE), linear low density (LLDPE), high density (UHDPE).

polypropylene, in particular an isotactic or syndiotactic polypropylene;

Without departing from the scope of the invention in the case of extruding a feed mixture of two or more polyolefins.

styrenic resin denotes a homopolystyrene or a styrene copolymer containing at least 50% by weight of styrene. It may be a crystal polystyrene, high impact polystyrene, an acrylonitrile-butadiene-styrene (ABS) or of a block copolymer, for example a copolymer comprising styrene and a diene.

The polyester may be, for example poly (ethylene terephthalate) (PET) or poly (butylene terephthalate) (PBT).

Polyamide and copolyamide may be for example a PA6, PA6.6, PA6.6 / 6,

PA6.10, PA12, PA10.10, PAU, this list is not restrictive.

The thermoplastic resin may be loaded that is to say contain organic or inorganic particles dispersed. The mineral filler may be for example a silica, an alumina, a zeolite, titanium oxide, sodium or potassium carbonate, hydrotalcite, talc, zinc oxide, magnesium oxide or calcium, diatomaceous earth or carbon black. It can be also an inorganic pigment. The organic particles may, for example those of an organic pigment or an antioxidant. The organic filler may be antioxidants, as well as UV absorbers, HALS, slip agent, antiblock agent, anti-fogging agent or anti-waterproofed.

In a particular case, the polyolefin is a polypropylene having a melt index of at least 10 g / 10 min, preferably greater than 25 g / 10 min, preferably greater than 40 g / 10 min, measured according to ASTM 1238 .

EXAMPLES

The following examples illustrate the invention without limiting it.

Example 1:

A high-pressure autoclave having an inner volume of 2 1 is charged with 1000 ml of deionized water and 0.6 g of surfactant Pluronic ® 31R1. The autoclave was purged with nitrogen with rapid stirring for 20 min. Closing the vent valve, is added 5.0 g of propane and heated up to 83 ° C. Then added about 140 g of vinylidene fluoride (VDF) to arrive at a pressure of 44.8 bar. While continuing to stir the contents of the autoclave were added 1% by weight of a potassium persulfate solution and 1% by weight of a sodium acetate solution (total solids rates of 2% by weight) at a flow rate of 3.0 ml / min until the pressure starts to fall, then the flow rate is decreased to 0.5 ml / min. The addition of VDF continues so as to maintain the pressure to 44.8 bar. When the amount of VDF added is 400 g, it stops the feeding VDF and initiator and the reaction was maintained at 83 ° C until the pressure drops below 20.68 bar; at this stage the autoclave is vented and cooled to room temperature. Is obtained 1.3 1 of a fluid white latex. The latex was dried at 110 ° C for 12h in an oven to obtain dry fragments. The latex has the following characteristics:

- particle size: 276 nm;

- solids content: 30.2% by weight;

- melt index: 0.4 kP (232 ° C, 100s 1 );

mass average molecular weight: 105.7 kDa as measured by steric exclusion chromatography in DMF / LiBr 0.02M with PMMA as a calibration standard, average molecular weight: 52.7 kDa;

melting point: 170.7 ° C as measured by differential scanning calorimetry (DSC) second heating cycle.

Examples 2-6: PVDF homopolymers

A high-pressure autoclave having an inner volume of 352.4 1 was charged with 149.3 1 deionized water and 720 g of fluorinated surfactant Capstone ® FS-10 (30% solution by weight). The autoclave was purged with nitrogen; Closing the vent valve was added ethyl acetate (CTA) and heated to 83 ° C. Is then added vinylidene fluoride (VDF) to arrive at a pressure of 44.8 bar. While continuing to stir the contents of the autoclave were rapidly added 3.629 kg of a first potassium persulfate solution to 1.65% by weight and a second solution of sodium acetate 1.65% by weight (total solids rate: 3.3%). Following a short induction stage, the initiator solution is added continuously at a flow rate 0.227 to 1.361 kg / h. The addition of VDF continues so as to maintain the pressure to 44.8 bar. When the amount of VDF added is 96.162 kg, it stops the feeding VDF and initiator and the reaction was maintained at 83 ° C until the pressure drops below 20.68 bar; at this stage the autoclave is vented and cooled to room temperature. About 272.156 kg of white latex fluid is obtained. The latex is diluted to 20% by weight and spray-dried. The latex has the following features shown in Table 1:

- particle size: about 300 nm;

mass of solids ratio: 30%;

melt index measured at 232 ° C, 100s "1 using a capillary rheometer or a parallel plate rheometer;

melting point: Measured by differential scanning calorimetry (DSC) second heating cycle.

Examples 7 and 8: A copolymer VDF / HFP

A high-pressure autoclave having an inner volume of 352.4 1 was charged with 156.49 1 of deionized water and 66 g of surfactant Pluronic ® 31R1. The autoclave was purged with nitrogen; Closing the vent valve was added ethyl acetate and heated to 83 ° C. While continuing to stir the contents of the autoclave were rapidly added 8.3 kg of hexafluoropropylene (HFP) and VDF was then added to reach a pressure of 44.8 bar. While continuing to stir the contents of the autoclave was rapidly added 2.95 kg of a first potassium persulfate solution to 1% by weight and a second solution of sodium acetate to 1% by weight (rate total solids: 2%). Following a short induction stage, the initiator solution is added continuously at a flow rate 0.227 to 1.361 kg / h. The addition of HFP and VDF continues so as to maintain the pressure to 44.8 bar. When the amount of VDF added reaches 7.484 kg and the amount of HFP to 2.042 kg (9.526 kg in total), the feed is stopped by VDF, HFP and initiator and the reaction was maintained at 83 ° C until the pressure drops below 20.68 bar; at this stage the autoclave is vented and cooled to room temperature. Approximately 24.95 kg of white latex fluid obtained (the solid content is 33%). The latex is diluted to 20%) by weight and spray-dried to obtain a white powder.

Its characteristics are presented in Table 1 ( "n / a" means "not determined".

The mass HFP content of the copolymer was determined by magnetic resonance spectroscopy ( 19 F NMR).

Melt rheology wt%

Load CTA Index fluidity

(kp, @ 100s " \ Tf in the HFP

Ex. g CTA / kg VDF ou kP, @100s"
230 ° C, plates e / Kg (VDF + HFP) 230 ° C, capillary (° C) parallel copolymer)

2 23,6 1 ,2 1 ,2 170,6 - 3 28,3 0,7 0,62 171 ,4 - 4 35,4 0,4 0,25 171 ,4 - 5 47,2 0, 1 0, 1 1 171 ,8 - 6 76,0 <0, 1 0,04 172,4 - 7 12,4 4,0 n/d 123,9 17,4

8 15,7 1 ,7 n/d 123,9 17,6

Table 1

example 9

Granules of a PVDF homopolymer medium viscosity: 3-4 kP are incorporated by twin screw extrusion at 5% by weight in a type of polypropylene Sabic ® PP 511 A, MFI 25 g / 10 min at 230 ° C, 2.16 kg. This masterbatch, which is in the form of granules, is then tested as an agent to help the implementation according to the protocol described below:

extrusion at 230 ° C on an extruder Collin screw 30 mm in diameter, L / D = 25 with a capillary die of 0.5 mm diameter and a length of 10mm;

after 15 minutes of extrusion said masterbatch is introduced in an amount of 1% by mass.

90 minutes after introduction of the masterbatch, a pressure drop of about 10 bar and an improved surface appearance are observed.

example 10

Copolymer granules VDF / HFP homogeneous (mass content of HFP 18-20%, medium viscosity: 0.4-0.5 kP) are incorporated by twin screw extrusion at 5% by weight in a polypropylene type Sabic ® PP 511A, MFI 25 g / 10 min at 230 ° C, 2.16 kg. This masterbatch, which is in the form of granules, is then tested as an agent to help the implementation according to the protocol described below:

extrusion at 230 ° C on an extruder Collin screw 30 mm in diameter, L / D = 25 with a capillary die of 0.5 mm diameter and a length of 10mm;

after 15 minutes of extrusion said masterbatch is introduced in an amount of 1% by mass.

90 minutes after introduction of the masterbatch, a pressure drop of about 20 bar and an improved surface appearance are observed.

example 11

PVDF pellets from the synthesis example 5 (viscosity about 0.11 kP) are incorporated by twin screw extrusion at 5% by weight in a polypropylene type Sabic ® PP 511A, MFI 25 g / 10 min at 230 ° C, 2.16 kg. This masterbatch, which is in the form of granules, is then tested as an agent to help the implementation according to the protocol described below:

- extrusion at 230 ° C on an extruder Collin screw 30 mm in diameter, L / D = 25 with a capillary die of 0.5 mm diameter and a length of 10mm;

after 15 minutes of extrusion said masterbatch is introduced in an amount of 1% by mass.

90 minutes after introduction of the masterbatch, a pressure drop of about 15 bar and an improved surface appearance are observed.

CLAIMS

Processing aid for polyolefin extrudable form of fibers, said processing aid comprises a polymer based on vinylidene fluoride (PVDF) having a viscosity of less than 5 kP, a molecular weight ranging from 5 to 200 kDa as measured by chromatography size exclusion, and having a thermoplastic character, the viscosity being measured at 232 ° C, at a shear gradient of 100 s "1 in accordance with ASTM D3825.

processing aid according to claim 1 wherein said PVDF is a homopolymer PVDF.

processing aid according to claim 1 wherein said PVDF is a copolymer comprising vinylidene fluoride (VDF) and at least one other comonomer chosen from chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), trifluoroethylene (VF3 ), tetrafluoroethylene (TFE) and ethylene, said copolymer containing at least 75% VDF by weight.

processing aid according to one of the preceding claims wherein said PVDF has a viscosity of less than 1 kP.

processing aid according to one of the preceding claims wherein said PVDF has a molecular weight ranging from 10 to 100 kDa as measured by steric exclusion chromatography.

processing aid according to one of claims 3 to 5 wherein said PVDF is a homogeneous copolymer.

7. extrusion Agent according to one of the preceding claims for extruding a polyolefin having a melt index of at least 10 g / 10 min, preferably greater than 25 g / 10 min, preferably greater than 40 g / 10 min when measured at 230 ° C and 2.16 kg (ASTM 1238).

8. extrusion agent according to claim 7 characterized in that said polyolefin is polypropylene.

9. extrusion Agent according to one of the preceding claims characterized in that it is free of synergist.

10. extruding Agent according to one of the preceding claims comprising an additive selected from antioxidants.

11. Fibers extruded from a formulation comprising a polyolefin and a processing aid according to any one of claims 1 to 10.

12. Fibers according to claim 11 characterized in that said polyolefin has a melt index of at least 10 g / 10 min, preferably greater than 25 g / 10 min, preferably greater than 40 g / 10 min.

13. Fibers according to one of Claims 11 and 12, said fibers of mono or multi filaments.

14. Fibers according to one of Claims 11 and 12, said fibers being in the form of oriented fiber groups to form nonwoven materials.

15. A method of extruding a polyolefin in the form of fibers, by means of a processing aid according to any one of claims 1 to 10, said polyolefin having a melt index of at least 10 g / 10 min, preferably greater than 25 g / 10 min, preferably greater than 40 g / 10 min, said method comprising the steps of:

at. adding said processing aid in polyolefin formulation, and b. extrusion of the final formulation in the form of polyolefin fibers.

16. The method of claim 15, wherein in step a) consists in adding said extrusion by compounding agent in the formulation of polyolefin.

17. The method of claim 15, wherein in step a) said blowing agent is initially diluted in a polyolefin formulation having the same viscosity as the formulation of polyolefin to be extruded to form a masterbatch which is added in a second stage, said polyolefin formulation.