Polyvinylidene fluoride for high purity water supply applications

Abstract

The present invention relates to a process for producing vinylidene fluoride polymer compositions with reduced levels of residual impurities (notably total oxidizable carbon (TOC) and fluoride ion F-). This improvement can be achieved in a cost-effective manner by a combination of polymer formulation and use of a washing step, in particular a dewatering extruder. The invention also relates to the use of such vinylidene fluoride polymers in high purity applications.

Description

TECHNICAL FIELD

[0001] The present invention relates to a process to produce a vinylidene fluoride polymer composition with reduced levels of residual impurities, notably total oxidizable carbon (TOC) and fluoride ions (F-). This improvement can be achieved in a cost effective manner by a combination of polymer formulation and use of a washing step, in particular a dewatering extruder. The present invention also relates to the use of such vinylidene fluoride polymers in high purity water supply applications. BACKGROUND

[0002] In the field of electronics, electronic components such as semiconductors are cleaned with ultra-pure water. This ultra-pure water is usually delivered by means of a distribution system comprising pipes, valves, connectors and bends made of vinylidene fluoride polymer ("PVDF" or "polyvinylidene fluoride" or "polyvinylidene fluoride polymer" or "polymer").

[0003] For these applications, there are very important requirements regarding the purity of the polymer used, since impurities present in the polymer can be released into the ultra-pure water.

[0004] However, during the manufacturing process of the polymer, impurities such as ions, metals or low molecular weight organic molecules are found to be trapped in the polymer.

[0005] Fluoropolymers are typically prepared by aqueous dispersion methods, which provide a suitable heat sink for controlling the heat of polymerization, and can produce high yields and high molecular weight. In order to obtain a stable dispersion or emulsion, a suitable surfactant or emulsifier must be used. Fluoro surfactants are typically used because they can produce stable particles and high molecular weight fluoropolymers. However, fluorinated surfactants commonly used in emulsion polymerization of fluoropolymers, such as ammonium or perfluoro sulfonate salts of perfluoro octanoic acid, are expensive and present environmental problems associated with bio-persistence. In addition, they can decompose during melt processing, adding an undesirable color to the polymer. Thus, it is desirable to reduce or minimize the amount of fluorinated surfactant retained within the final solid polymer product.

[0006] Some non-fluorinated surfactants can also be used to produce fluoropolymers. These surfactants do not have the same environmental problems as fluorinated surfactants, but they increase the total oxidizable carbon (TOC, also known as total organic carbon) content retained in the polymer. This is undesirable for the high purity water supply applications described above. In these cases, it is therefore desirable to reduce or minimize the amount of TOC due to non-fluorinated surfactants retained in the final solid polymer product.

[0007] Dehydrating extrusion has been used for emulsion polymers and combines the steps of coagulation, washing, dewatering and venting / de-aeration in a single, twin-screw extruder unit operation. The document EP 2548897 discloses the use of a dehydrating extruder with a steam coagulation step, providing an efficient means for separating the solid fluoropolymer from the aqueous dispersion or suspension, and the resulting fluoropolymer contains very low levels of fluorosurfactant.

[0008] However, the above-mentioned methods do not sufficiently remove impurities present in vinylidene fluoride polymers. Therefore, there is a real need for a process for producing vinylidene fluoride polymers that provides means to ensure more efficient removal of impurities, and in particular low molecular weight impurities, such as ionic or organic compounds (TOC). SUMMARY

[0009] The present invention first relates to a process for reducing TOC and ionic impurities, such as fluorides, during the polymerization, washing, drying and extrusion of vinylidene fluoride polymers, said process comprising the steps of:

[0010] a) polymerizing vinylidene fluoride monomers using less than 0.1 % by weight of fluorosurfactant, based on the weight of vinylidene fluoride monomers, and / or less than 5 % by weight of non-fluorosurfactant, to produce an aqueous polyvinylidene fluoride (PVDF) composition in the form of an emulsion;

[0011] b) feeding said aqueous PVDF composition into a finishing system in which coagulation, washing, drying and extrusion occur and can be obtained by a one-step dehydrating extrusion process, to produce a solid PVDF composition having a TOC level lower than 20000 pg / m 2 a TOC level of the polymer and lower than 10000 pg / m 2 a fluorine (F - ) ion level of the polymer.

[0012] According to another aspect, the present invention relates to a process for reducing TOC and ionic impurities, such as fluorides, during the polymerization, washing, drying and extrusion of vinylidene fluoride polymers, said process comprising the steps of:

[0013] a) emulsion polymerizing vinylidene fluoride monomers in an aqueous medium in the presence of an inorganic initiator using less than 0.01 % by weight of fluorosurfactant and less than 2 % by weight of non-fluorosurfactant, based on the weight of vinylidene fluoride monomers, to produce an aqueous polyvinylidene fluoride (PVDF) composition;

[0014] b) feeding the aqueous PVDF composition into a finishing system in which coagulation, washing, drying and extrusion occur to produce a solid PVDF composition having a TOC level and a fluoride (F - ) ion level such that the TOC level is below 20000 pg / m 2 of polymer and the fluoride (F - ) ion level is below 10000 pg / m 2 of polymer as measured according to the SEMI F40 standard. All stages of step b) can be realized as a unique one-step finishing system, such as a dewatering extruder.

[0015] In some embodiments, the solid PVDF composition obtained by using the method according to the present application has a TOC level of below 20000 pg / m 2 of polymer and a fluoride (F 2 ) level of below 10000 pg / m - of the same polymer as determined by the test method SEMI F40. In some embodiments, the solid PVDF composition obtained by using the method according to the present application has a TOC level and a fluoride (F - ) level such that the TOC level is below 20000 pg / m 2 of polymer as measured by the test method SEMI F40 and the fluoride (F - ) level is below 10000 pg / m 2 of the same polymer as measured by the test method SEMI F40.

[0016] The present application further relates to a polyvinylidene fluoride composition having a TOC level of below 20000 pg / m 2 of polymer and a fluoride (F 2 ) level of below 10000 pg / m - of polymer. In some embodiments, the present application relates to a polyvinylidene fluoride composition having a TOC level and a fluoride (F - ) level such that the TOC level is below 20000 pg / m 2 of polymer as measured by the test method SEMI F40 and the fluoride (F - ) level is below 10000 pg / m 2 of polymer as measured by the test method SEMI F40.

[0017] According to certain embodiments, the above polyvinylidene fluoride polymer (or composition) is obtained according to the process detailed herein.

[0018] According to certain embodiments, the PVDF polymer (or composition) is in the form of pellets or powder.

[0019] The present application also relates to a fluid conveying component comprising or consisting of a PVDF polymer (or composition) as described above, or formed from a powder or pellets as described above.

[0020] The present application also relates to the use of the above component for conveying ultra-high purity water for cleaning electronic components.

[0021] The present application makes it possible to meet the needs set out above. More particularly, the present application provides an improved formulation and process which makes it possible to obtain a polyvinylidene fluoride polymer exhibiting excellent purity by allowing more efficient removal of impurities, and in particular organic compounds and fluoride anions, contained in the PVDF polymer, without reducing the mechanical properties of the PVDF polymer. This leads to obtaining a good quality PVDF polymer exhibiting good mechanical properties and having a high level of purity, thereby making it possible to limit the release of these impurities during the subsequent use of the product (for example during the use of a pipe or tubing made of a PVDF polymer according to the present application for conveying ultra-high purity water).

[0022] The term "ultra-high purity water" is understood to mean water having a maximum content of metal and anion impurities of 0.1 parts per billion (ppb) by weight, a total organic carbon (TOC) content of 10 ppb by weight or less, a non-volatile residue content of 0.1 parts per million (ppm) by weight or less, an electrical resistivity of 18 m Ω.cm or more at 25°C, and a level of reactive silica impurities of less than 1 ppb, according to standard SEMI F 63.

[0023] This is achieved by a combination of a specific polymerization formulation and the use of a finishing system allowing separate coagulation, washing, drying and extrusion processes, which are preferably intensified into a one-step dewatering extruder (such as a one-step twin-screw dewatering extruder) to produce a solid dry polyvinylidene fluoride composition having low levels of impurities from a water-based PVDF suspension or dispersion. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 represents a graph showing the TOC released into the leaching water after 1 or 2 weeks of leaching from various formulations and finishing processes processed according to the SEMI F40 protocol (limits determined by the SEMI F57-0.622 standard). DETAILED DESCRIPTION

[0025] According to a first aspect, the present invention relates to a process for reducing TOC and ionic impurities (notably F - ) during the polymerization, washing, drying and extrusion of vinylidene fluoride polymers, the process comprising the following steps:

[0026] a) polymerizing vinylidene fluoride monomers using less than 0.1% by weight, preferably less than 0.01% by weight, of fluorosurfactants and / or less than 5% by weight, or less than 2% by weight, of non-fluorosurfactants based on the weight of the vinylidene fluoride monomers, to produce an aqueous polyvinylidene fluoride (PVDF) composition in the form of an emulsion;

[0027] b) feeding the aqueous PVDF composition into a finishing system in which coagulation, washing, drying and extrusion occur and can be obtained by a one-step dewatering extrusion process, to produce a solid PVDF composition having a TOC level lower than 20000 pg / m 2 of polymer and a fluorine (F 2 ) ion level lower than 10000 pg / m - of polymer, as measured according to the SEMI F40 standard.

[0028] According to another aspect, the present invention relates to a process for reducing TOC and ionic impurities (notably F - ) during the polymerization, washing, drying and extrusion of vinylidene fluoride polymers, the process comprising the following steps:

[0029] a) emulsion polymerizing vinylidene fluoride monomers in an aqueous medium in the presence of an inorganic initiator using less than 0.01% by weight of fluorosurfactants and less than 2% by weight of non-fluorosurfactants based on the weight of the vinylidene fluoride monomers, to produce an aqueous polyvinylidene fluoride (PVDF) composition;

[0030] b) feeding the aqueous PVDF composition into a finishing system in which coagulation, washing, drying and extrusion occur to produce a solid PVDF composition having a TOC level and a fluorine (F - ) ion level such that the TOC level is lower than 20000 pg / m 2 of polymer as measured according to the SEMI F40 standard and the fluorine (F - ) ion level is lower than 10000 pg / m 2 of polymer as measured according to the SEMI F40 standard.

[0031] In the present text, the expression "measured according to SEMI F40" means that the TOC level and the fluoride ion level are measured by performing the procedure of the SEMI F40 standard once or twice, advantageously twice. In some embodiments, the TOC level and the fluoride ion level measured according to SEMI F40 are measured by performing the procedure of the SEMI F40 standard only once.

[0032] In particular, coagulation, washing, drying and extrusion can be carried out in a finishing system, either by a one-step process, in particular a one-step dewatering extrusion process, or a multi-step process.

[0033] According to various embodiments, the process comprises the following features, combined where applicable.

[0034] Unless otherwise stated, all percentages are percentages by weight and all molecular weights provided are weight average molecular weights.

[0035] The terms "PVDF" and "vinylidene fluoride polymer" and "vinylidene fluoride polymer" have the same meaning for the present invention.

[0036] The term "PVDF" as used herein encompasses a vinylidene fluoride (VDF) homopolymer or a copolymer of VDF and at least one other comonomer, wherein VDF preferably represents at least 50% by weight, more preferably at least 75% by weight, the comonomer(s) preferably being selected from the group consisting of chlorotrifluoroethylene, hexafluoropropylene, trifluoroethylene, fluoroethylene, perfluoromethylvinyl ether, perfluoroethylvinyl ether and tetrafluoroethylene.

[0037] Preferably, the PVDF is a polyvinylidene fluoride homopolymer and / or a copolymer of vinylidene fluoride and hexafluoropropylene (HFP), wherein the level of HFP is preferably less than or equal to 30% by weight.

[0038] Polymerization reaction (step a)

[0039] According to one embodiment, the polymerization reaction can occur in a batch, semi-batch or continuous polymerization process. The reactor is a pressurized polymerization reactor equipped with a stirrer and a thermal control device. The temperature of the polymerization can vary between 35 and 140°C, preferably between 35 and 125°C, more preferably between 35°C and 100°C. For PVDF polymerization, the pressure of the polymerization is generally between 1380 and 17300 kPa, but it can be higher if the equipment allows operation at higher pressure. The pressure is most conveniently between 3450 and 9000 kPa.

[0040] According to one embodiment, the vinylidene fluoride is polymerized in an aqueous medium to produce an aqueous polyvinylidene fluoride composition in the form of an emulsion using less than 0.1 % by weight, preferably less than 0.01 % by weight of fluorosurfactant based on the weight of the vinylidene fluoride monomer, and / or less than 5% by weight, or less than 2% by weight of non-fluorosurfactant, preferably less than 0.01 % by weight of non-fluorosurfactant in the emulsion polymerization process. More particularly, the vinylidene fluoride is polymerized in an aqueous medium to produce an aqueous polyvinylidene fluoride composition using less than 0.01 % by weight of fluorosurfactant and less than 2% by weight of non-fluorosurfactant, preferably less than 0.005 weight percent of non-fluorosurfactant based on the weight of the vinylidene fluoride monomer in the emulsion polymerization process.

[0041] According to one embodiment, the vinylidene fluoride is polymerized in the emulsion polymerization process without using any surfactant, which means that there is less than 0.001 % by weight and advantageously 0% by weight of surfactant, whether fluorosurfactant or non-fluorosurfactant.

[0042] In the emulsion polymerization process, the vinylidene fluoride can be polymerized with at least one comonomer, the comonomer being preferably selected from the group consisting of chlorotrifluoroethylene, hexafluoropropylene, trifluoroethylene, fluoroethylene, perfluoromethyl vinyl ether, perfluoroethyl vinyl ether and tetrafluoroethylene.

[0043] During the emulsion polymerization, the pH of the emulsion is preferably kept below 4.0.

[0044] Preferably, no acid is added in the medium in this emulsion polymerization process.

[0045] The reactor and contents are heated to the desired temperature and the vinylidene fluoride monomer, and optionally other materials such as, but not limited to, chain transfer agents, buffers or antifouling agents are added. Preferably, the amount of buffer used is less than 0.1 % by weight relative to the water introduced into the reactor. If a buffer is used, it is preferred that the buffer does not contain any metal ions. In some embodiments, no buffer is used. When the desired reaction pressure is reached, a free radical initiator is introduced to start the polymerization and the reaction is maintained.

[0046] After a given amount of monomer is fed, all feeds are stopped and the reaction is considered complete. Residual gases (containing unreacted monomers) are vented and the latex is recovered from the reactor.

[0047] In the polymerization process, the monomers, initiator, optional surfactants, and other materials can be all pre-charged prior to polymerization, fed continuously during polymerization, partially charged prior to polymerization and then charged during polymerization, or charged after polymerization has begun and proceeded for some time. The free radical initiator or mixture of initiators is a low TOC contributor, preferably an inorganic initiator, which is notably selected from the family of persulfates, including those examples bearing inorganic counterions such as ammonium, sodium, or potassium, preferably ammonium persulfate. These compounds are added at levels sufficient to maintain a sufficient rate of polymerization, typically in amounts of 10 ppm to 10,000 ppm, preferably 100 ppm to 2,000 ppm, and most preferably 150 ppm to 1,500 ppm, relative to the total monomers.

[0048] The polymerization process is preferably conducted in the absence of any fluorinated surfactant.

[0049] The optional surfactants of the present invention can be fluorinated, non-fluorinated, or mixtures thereof. As used herein, "fluorinated surfactant" and "fluorosurfactant" mean that the main surfactant chain contains at least one covalently bonded fluorine atom, while in the present invention, non-fluorinated surfactant means that there is no covalently bonded fluorine atom on the main chain.

[0050] Useful fluorosurfactants include, but are not limited to, salts of acids of the formula X(CF2) n COOM, where X is hydrogen or fluorine, M is an alkali metal, ammonium, a substituted ammonium (e.g., an alkylamine of 1 to 4 carbon atoms), or a quaternary ammonium ion, and n is an integer of 6 to 20; perfluoroalkanols of the formula X(CF2) n CH2OSO3M, where X and M are as described above; and sulfates of perfluoroalkanols of the formula CF3(CF2) n (CX2) m SO3M, where X and M are as described above; n is an integer of 3 to 7, and m is an integer of 0 to 2, for example, in potassium perfluorocetyl sulfonate.

[0051] Optional non-fluorosurfactants are surface active agents that do not contain any carbon-fluorine covalent bonds, and are ubiquitous to those skilled in the art, and are defined as molecular structures comprising a hydrophilic portion and a hydrophobic portion. These materials are widely used as cleaning agents and emulsion stabilizers, as they are able to reduce the surface tension of a liquid, typically water, via preferential segregation and molecular orientation at solid / liquid or gas / liquid interfaces. Examples of characteristics and physical properties of such materials can be found in: Handbook of Surfactants, 1991; and Critical Micelle Concentrations of Aqueous Surfactant Systems, P. Mukerjee and K. J. Mysels, United States Bureau of Standards Publication NSRDS-NBS 36, 1971. As such, all classes of surfactants are contemplated herein, including ionic (anionic and cationic), nonionic, polymeric, bio-based, zwitterionic, and those with specific structures such as gemini surfactants. Of particular interest are those known to be effective in vinylidene fluoride emulsion polymerization, such as those described in US8080621B2, US8158734B2, US8338518B2, US8765890B2, US9068071B2, US8697822B2, US7122610B2, and US9447256B2, primarily the classes of materials believed to be alkylene oxide polymers and alkylene oxide block copolymers and acid / ionizable group containing polymeric surfactants and alkyl sulfonate salts.

[0052] In one embodiment of the present invention, the total amount of surfactant used is less than 1% by weight relative to the water introduced into the reactor.

[0053] In one embodiment of the present invention, zero surfactant is added to the polymerization process.

[0054] The emulsion formed by the process of the present invention typically has a solids level of 5 to 65% by weight, preferably 10 to 55% by weight, as measured by drying the dispersion and gravimetrically. The PVDF particles in the dispersion have a particle size in the range of 30 to 600 nm, and preferably in the range of 100-350 nm, as measured by dynamic light scattering. The latex can be defined as stable when the particle diameter distribution is monodisperse around the average value of 100-350 nm.

[0055] The solids level in the stable emulsion produced in the present invention is greater than 24% by weight, preferably greater than 26% by weight, more preferably greater than 28% by weight, more preferably greater than 30% by weight and even more preferably greater than 32% by weight.

[0056] Preferably, the composition obtained from the emulsion polymerization step has a pH lower than 4.0.

[0057] The vinylidene fluoride polymer to be purified comprises at least one impurity.

[0058] At least one impurity can originate from the medium and from the polymerization conditions of the monomers during the manufacture of the final PVDF polymer.

[0059] In one embodiment, the one or more impurities can be organic compounds, such as alcohols, aldehydes, carboxylic acids and / or esters and / or carbonates.

[0060] According to one embodiment, the one or more impurities are represented by organic compounds and ionic impurities, such as anions, preferably fluorine anions (F - ).

[0061] The amount of organic compound impurities can be determined by performing a measurement of the "Total Organic Carbon" (or TOC). Thus, the amount of organic compounds as well as the amount of fluorine anions is determined using the following standards. The preparation of the sample is performed according to the standard SEMI F40-0621, wherein 50 g of polymer is placed in a jar containing 100 ml of ultrapure water, which is then placed in an oven at 85°C for a period of 7 days. A second test of 7 days can be performed according to SEMI F40-0621 : upon completion of the first period of 7 days at 85°C in ultrapure water, the test fluid is drained and analyzed, the jar is replenished with 100 ml of fresh ultrapure water and then placed in an oven at 85°C for a second period of 7 days, and finally the test fluid is drained and analyzed. The organic compounds and the fluorine anions present in the washing water are then analyzed according to the standard test methods ASTM D4327 (for the measurement of fluorine anions) and ASTM D4779 and D5904 (for the measurement of organic compounds) after the 1stweek, and then after the 2ndweek. A control water sample, not exposed to any polymer, is used as a reference. The values obtained are then converted into pg / mg of polymer according to the standard SEMI C69-1015. The determination is preferably performed on polymer in the form of pellets, but can also be performed on polymer in the form of powder, pressed into parts. When the polymer is in the form of parts, in particular molded parts, one or more parts can be cut into pieces before the measurement is performed. 2 The equivalent. The determination is preferably performed on polymer in the form of pellets, but can also be performed on polymer in the form of powder, pressed into parts. When the polymer is in the form of parts, in particular molded parts, one or more parts can be cut into pieces before the measurement is performed.

[0062] The refining step (step b)

[0063] After polymerization, the PVDF emulsion, dispersion or suspension is pumped to a refining process to isolate the PVDF solids.

[0064] According to one embodiment, the refining process is a standard refining process, comprising the following steps:

[0065] i / coagulating and aerating the latex obtained by emulsion polymerization:

[0066] The latex (i.e. aqueous PVDF composition obtained by emulsion polymerization) is continuously fed to a device (e.g. a specialized rig) where the suspended latex particles agglomerate (flocculate) into larger aggregates. High speed agitation is ensured, and pressurized air is injected. At the outlet, a solid-like foam is obtained. The basic role of this unit is to produce floating PVDF polymer particles for the washing column operation.

[0067] ii / The washed latex (i.e. PVDF composition obtained in step i / ) is washed to remove residual molecules:

[0068] The agglomerated floes of aerated PVDF polymer are transported to a column where they are washed with co-current or counter-current deionized water. For example, the foam flocculate rises in the column and is discharged at the top or bottom with excess water, while the water containing impurities is removed at the bottom or top.

[0069] iii / The washed PVDF polymer is spray dried to produce a PVDF powder:

[0070] The washed foam is atomized in a nozzle by high pressure hot air. The flow is co-current and the temperature at the outlet is adjusted to achieve complete drying. Then, the purified PVDF polymer powder is ready for handling.

[0071] iv / The powder is extruded to form pellets:

[0072] The powder is fed into an extruder (in particular a twin-screw extruder). Due to the shear rate and temperature control, the PVDF polymer is melted and cut into pellets before a cooling step.

[0073] According to one embodiment, the finishing process is performed using a dewatering extruder. The dewatering extruder combines the steps of coagulation, washing, dewatering and degassing / venting in a single (preferably twin-screw) extruder unit operation.

[0074] The extruder and screws are of the same general type as described in the literature US 4,148,991. The preferred design is a counter-rotating non-intermeshing screw design. For production purposes, for example, the screws can have an outer diameter of 50 mm to 250 mm and a screw length of 35-80 times the screw diameter (35-80D), depending on the number of dewatering stages.

[0075] The extruder (e.g. twin-screw extruder) typically has an open forward-threaded screw design to transport the material towards the outlet of the screw. The exception to this are several "sealing" or "flow restrictor" sections which typically divide the extruder into 3-5 operating zones. These "sealing" or "flow restrictor" elements can be a) non-threaded elements, b) positively threaded elements, or c) counter-threaded elements.

[0076] Purified vinylidene fluoride polymers

[0077] According to another aspect, the present application relates to a polyvinylidene fluoride composition having a TOC level lower than 20000 μg / m 2 of polymer and a fluoride (F 2 ) ion level lower than 10000 μg / m - of polymer, according to SEMI F40 standard.

[0078] According to another aspect, the present application relates to a polyvinylidene fluoride composition having a TOC level and a fluoride (F - ) ion level such that the TOC level is lower than 20000 μg / m 2 of polymer and the fluoride (F - ) ion level is lower than 10000 μg / m 2 of polymer, measured according to SEMI F40 standard.

[0079] According to various embodiments, the PVDF composition comprises the following features, in combination where applicable.

[0080] In one embodiment of the application, the TOC level in the PVDF composition is lower than 10000 μg / m 2 , preferably lower than 5000 μg / m 2 , according to SEMI F40 analytical standard. In one embodiment, the TOC level in the PVDF composition is such that the TOC level is lower than 10000 μg / m 2 , preferably lower than 5000 μg / m 2 of polymer, measured according to SEMI F40 standard, wherein the procedure of SEMI F40 standard is performed twice (i.e. measured in a second procedure).

[0081] In one embodiment of the application, the fluoride (F - ) ion level in the PVDF composition is lower than 5000 μg / m 2 , preferably lower than 2000 μg / m 2 , according to SEMI F40 analytical standard. In one embodiment, the fluoride (F - ) ion level in the PVDF composition is such that the fluoride (F - ) ion level is lower than 5000 μg / m 2 , preferably lower than 2000 μg / m 2 of polymer, measured according to SEMI F40 standard, wherein the procedure of SEMI F40 standard is performed twice (i.e. measured in a second procedure).

[0082] The PVDF composition can be in any suitable form, for example in the form of pellets, prills, or in the form of a powder, or in the form of a molded part, for example in its final form, and in particular in the form of a tube or pipe. Inventive feature of these articles is that they exhibit very low total organic carbon and fluoride extraction rates into ultra-high purity water.

[0083] In one embodiment of the application, the TOC level in the PVDF composition is higher than 1500 μg / m 2 polymer. In one embodiment, the TOC level in the PVDF composition is such that the TOC level measured according to the SEMI F40 standard, wherein the procedure of the SEMI F40 standard is performed twice, is higher than 1500 μg / m 2 polymer.

[0084] In one embodiment of the application, the F - ion level in the PVDF composition is higher than 500 μg / m 2 polymer. In one embodiment, the F - ion level in the PVDF composition is such that the F - ion level measured according to the SEMI F40 standard, wherein the procedure of the SEMI F40 standard is performed twice, is higher than 500 μg / m 2 polymer.

[0085] The content level of organic compounds and of fluoride anions is measured using the method as described above.

[0086] Preferably, the PVDF composition is a PVDF polymer (including its impurities, such as TOC and F - ion impurities as described above), i.e. consisting essentially of a PVDF polymer.

[0087] Thus, the PVDF polymer according to the application has a reduced content of impurities (without reducing the mechanical properties of the polymer), which makes it possible to subsequently limit the release of impurities, that is to say at the time of use of the product. The mechanical properties include for example the thermal degradation temperature, the melting temperature, the crystallization temperature, the weight loss at high temperature (for example 270°C), the crystallinity index, the tensile strength, the elongation at break and the elongation at yield.

[0088] In one embodiment of the application, the PVDF composition is a solid composition obtained by the process according to the application. This solid composition has a low level of water-soluble or water-immiscible impurities. The impurities notably include TOC and F - ion.

[0089] The extractable TOC of the extruded tubing is very low, 5 times lower than the current SEMI F57-0622 standard. The extractable fluoride ion of the extruded tubing is high at the 1st wash, but very low after the 2nd wash (8 times lower than the current SEMI F57-0622 standard).

[0090] The process for producing high purity PVDF of the present invention has several advantages over the reaction and finishing procedures in the art:

[0091] a) The PVDF produced has very low levels of water soluble or water miscible impurities, and in particular lower levels of TOC and F - ions;

[0092] b) Individual unit operations can replace a series of more complex operations;

[0093] c) The PVDF pellets can be produced without going through a powder stage.

[0094] d) Coagulation and separation can be performed without the use of a coagulant - resulting in a purer, less contaminated product.

[0095] The high purity PVDF according to the present invention can be particularly useful for the manufacture of components, in particular tubing, valves, connectors or elbows, for the delivery of very high purity water for cleaning electronic components, such as semiconductor compounds.

[0096] Examples

[0097] The following examples illustrate the present invention without any limitation thereto.

[0098] Comparison of the purity of the leach water after 1 week and 2 weeks (SEMI F40 protocol, limits determined from SEMI F57-0622 standard).

[0099] Figure 1 The graph showing the comparison of the TOC released into the leach water after 1 week and 2 weeks from various formulations and processes is represented, where the symbols are as follows:

[0100] - Leach results for tubing made from PVDF suspensions

[0101] - To represent the leaching results from pipes made from a PVDF emulsion polymerization with a formulation as described in EP2548897B examples 7-10 using fluorosurfactant containing formulations and a one step finishing process dehydrating extruder (hereinafter "old formulation"). The detailed description of the process is made in examples 7-10. The first step is to make PVDF by emulsion polymerization using C4-C12 perfluoroalkane sulfonate surfactant. The emulsion is then introduced into a counter-rotating non-intermeshing twin-screw extruder with a screw outer diameter of 30 mm and a total screw length of 78 diameters (2.3368 m). The extruder configuration is described in EP2548897B examples 7-10. The extruder barrel surface and screws are made of high nickel alloy metal. High purity DI water is used for all process streams. The molten PVDF polymer is discharged from the extruder into a strand die. The PVDF polymer strand is placed in a water bath and cut into pellets. Figure 1 The detailed description of the process is made in examples 7-10. The first step is to make PVDF by emulsion polymerization using C4-C12 perfluoroalkane sulfonate surfactant. The emulsion is then introduced into a counter-rotating non-intermeshing twin-screw extruder with a screw outer diameter of 30 mm and a total screw length of 78 diameters (2.3368 m). The extruder configuration is described in EP2548897B examples 7-10. The extruder barrel surface and screws are made of high nickel alloy metal. High purity DI water is used for all process streams. The molten PVDF polymer is discharged from the extruder into a strand die. The PVDF polymer strand is placed in a water bath and cut into pellets.

[0102] - The detailed description of the process is made in examples 7-10. The first step is to make PVDF by emulsion polymerization using C4-C12 perfluoroalkane sulfonate surfactant. The emulsion is then introduced into a counter-rotating non-intermeshing twin-screw extruder with a screw outer diameter of 30 mm and a total screw length of 78 diameters (2.3368 m). The extruder configuration is described in EP2548897B examples 7-10. The extruder barrel surface and screws are made of high nickel alloy metal. High purity DI water is used for all process streams. The molten PVDF polymer is discharged from the extruder into a strand die. The PVDF polymer strand is placed in a water bath and cut into pellets.

[0103] - The detailed description of the process is made in examples 7-10. The first step is to make PVDF by emulsion polymerization using C4-C12 perfluoroalkane sulfonate surfactant. The emulsion is then introduced into a counter-rotating non-intermeshing twin-screw extruder with a screw outer diameter of 30 mm and a total screw length of 78 diameters (2.3368 m). The extruder configuration is described in EP2548897B examples 7-10. The extruder barrel surface and screws are made of high nickel alloy metal. High purity DI water is used for all process streams. The molten PVDF polymer is discharged from the extruder into a strand die. The PVDF polymer strand is placed in a water bath and cut into pellets.

[0104] Figure 1 It is shown that by using the formulation described in this document as step a / with one step b / finishing process, significantly lower TOC levels are observed compared to previous formulations with the same finishing step or PVDF resins with a suspension process. This is true for both types of finishing processes. In particular, after 2 weeks of leaching, the TOC is reduced by almost 5 times compared to the emulsion previous formulation values, ending in a very low TOC concentration.

[0105] F - Reduction in leaching time course

[0106] Table 1 below shows the evolution of fluoride concentration into water after 1 and 2 weeks of leaching, and the calculation of the fluoride reduction rate between week 1 and week 2. Results were obtained by using the SEMI F40 method on tubing extruded from the PVDF pellet samples, and are expressed in pg / m2. 2 In one embodiment, the samples in the last column of Table 1 are prepared using a polymerization process as in US2435537A or US3193539A.

[0107]

[0108] Table 1

[0109] This table shows the huge improvement of the F- residual after 2 weeks of leaching with the "new" formulation (described as step a / in this document) compared to the "old" formulation (as described in prior art EP2548897). - This reduction is valuable for both the two-step refining process.

[0110] This improvement is achieved thanks to the better kinetics of fluoride transfer into the leaching water with the "new" formulation compared to the "old" formulation and the suspension PVDF. This is especially true for the one-step refining results.

Claims

1. A method for reducing total oxidizable carbon (TOC) and ionic impurities such as fluorine (F - ) ions during polymerization, washing, drying, and extrusion of PVDF polymers, comprising the steps of: a) emulsion polymerizing a vinylidene fluoride monomer in an aqueous medium in the presence of an inorganic initiator using less than 0.01 % by weight of fluorosurfactant and less than 2 % by weight of non-fluorosurfactant based on the weight of the vinylidene fluoride monomer, to produce an aqueous PVDF composition; b) feeding the aqueous PVDF composition into a finishing system in which coagulation, washing, drying and extrusion occur to produce a solid PVDF composition having a TOC level and a Fluorine (F - ) ion level such that the TOC level is below 20000 pg / m 2 of polymer and the Fluorine (F - ) ion level is below 10000 pg / m 2 of polymer as measured according to the SEMI F40 standard.

2. The process according to claim 1, wherein coagulation, washing, drying and extrusion are carried out by a one-step process, in particular a one-step dewatering extrusion process, or a multi-step process in a finishing system.

3. The method of claim 1 or 2, wherein, The aqueous PVDF composition produced in step a) has a pH lower than 4.

0.

4. The process according to any one of claims 1 to 3, wherein the emulsion polymerization in step a) is carried out without addition of an acid.

5. The process according to any one of claims 1 to 4, wherein step a) is a batch, semi-batch or continuous emulsion polymerization process.

6. The process according to any one of claims 1 to 5, wherein sodium persulfate, ammonium persulfate or potassium persulfate is used as initiator at a level of 100 ppm to 10,000 ppm, preferably 250 ppm to 2,000 ppm, and most preferably 500 ppm to 1,500 ppm, relative to the total monomers, preferably the initiator is ammonium persulfate.

7. The process according to any one of claims 1 to 6, wherein no surfactant is used in step a).

8. The process according to any one of claims 1 to 7, wherein step b) is a finishing process comprising the following steps: i / coagulating and aerating the aqueous PVDF composition obtained by emulsion polymerization; ii / washing the PVDF composition obtained in step i / to remove residual molecules; iii / spray-drying the washed PVDF polymer to produce a PVDF powder; iv / extruding the powder to form pellets.

9. The process according to any one of claims 1 to 7, wherein step b) is a finishing process carried out using a dewatering extruder.

10. The method according to any one of claims 1 to 9, wherein the solid PVDF composition has a TOC level and fluorine (F) - The ion levels resulted in a TOC level below 10,000 μg / m³ as measured according to the SEMI F40 standard. 2 The polymer, wherein the procedure according to the SEMI F40 standard is performed twice, and the fluorine (F) is measured according to the SEMI F40 standard. - Ion levels below 5000 μg / m 2 polymer.

11. The method of any one of claims 1 to 10, wherein, The solid PVDF composition has a TOC level such that the TOC level is below 5000 μg / m 2 polymer and above 1500 μg / m 2 polymer, wherein the procedure of the SEMI F40 standard is performed twice.

12. The method of any one of claims 1 to 11, wherein the solid PVDF composition has a fluorine (F - ) ion level such that the TOC level measured according to the SEMI F40 standard is below 2000 μg / m 2 and above 500 μg / m 2 polymer, wherein the procedure of the SEMI F40 standard is performed twice.

13. The process according to any one of claims 1 to 12, wherein the solid PVDF composition comprises a VDF copolymer, preferably a VDF / HFP copolymer.

14. The process according to any one of claims 1 to 13, wherein the emulsion polymerization in step a) is carried out in a reactor, and wherein the amount of buffer used in the emulsion polymerization is less than 0.1 % by weight relative to the water introduced in the reactor, preferably the buffer does not contain any metal ions, and preferably no buffer is used.

15. A polyvinylidene fluoride composition having a TOC level and a fluorine (F - ) ion level such that the TOC level is less than 20000 pg / m 2 of polymer and the fluorine (F - ) ion level is less than 10000 pg / m 2 of polymer as measured according to the SEMI F40 standard.

16. The PVDF composition according to claim 15, wherein the TOC level is below 10000 pg / m 2 , preferably below 5000 pg / m 2 , and above 1500 pg / m 2 polymer, wherein the procedure of the SEMI F40 standard is performed twice.

17. The PVDF composition according to any one of claims 15 or 16, wherein the level of Fluorine (F - ) ions is below 5000 μg / m 2 , preferably below 2000 μg / m 2 , and above 500 μg / m 2 polymer, wherein the procedure of the SEMI F40 standard is performed twice.

18. The PVDF composition according to any one of claims 15 to 17, wherein the PVDF composition comprises a VDF copolymer, preferably a VDF / HFP copolymer.

19. The PVDF composition according to any one of claims 15 to 18, in the form of pellets.

20. An article comprising, or consisting of, or formed from, the PVDF composition according to any one of claims 15 to 18, or the pellets according to claim 19.

21. Use of the article according to claim 20 for delivering ultrapure water for cleaning electronic components.

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