Polyvinylidene fluoride for high-purity water supply applications

Abstract

This invention relates to residual impurities, particularly the total amount of oxidizable carbon (TOC) and the amount of fluoride ions F. - The present invention relates to a method for obtaining a vinylidene fluoride polymer composition with reduced [unclear]. Such improvements can be achieved in a cost-effective manner by combining polymer compounding and washing processes, particularly the use of a dewatering extruder. The present invention also relates to the application of such vinylidene fluoride polymers to high-purity applications.

Description

[Technical Field]

[0001] This invention relates to residual impurities, particularly the total amount of oxidizable carbon (TOC) and fluoride ions (F). - The present invention relates to a method for obtaining a vinylidene fluoride polymer composition with reduced amount. Such improvements can be achieved in a cost-effective manner by combining polymer compounding and washing processes, particularly the use of a dewatering extruder. The present invention also relates to the application of such vinylidene fluoride polymers to high-purity water supply applications. [Background technology]

[0002] In the field of electronics, electronic components such as semiconductors are cleaned with ultrapure water. This ultrapure water is typically transported by distribution systems equipped with tubes, valves, connectors, and elbows made of vinylidene fluoride polymer ("PVDF," or "polyvinylidene fluoride," or "vinylidene fluoride polymer," or "polymer").

[0003] Because impurities present in the polymer can be released into ultrapure water, the purity of the polymers used in these applications is a critical requirement.

[0004] However, it has been found that impurities such as ions, metals, or low molecular weight organic molecules are trapped within the polymer during the manufacturing process. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Fluoropolymers are generally produced by an aqueous dispersion method, which provides a suitable heat sink for controlling the polymerization heat and enables the production of high yields and high molecular weights. To obtain a stable dispersion or emulsion, a suitable surfactant or emulsifier must be used. Fluorine-based surfactants are commonly used because they can produce stable particles and high molecular weight fluoropolymers. However, fluorinated surfactants commonly used in the emulsion polymerization of fluoropolymers (e.g., ammonium perfluorooctanoate or perfluorosulfonate) are expensive and cause environmental problems regarding bioaccumulation. Furthermore, they may decompose during melt processing and add unwanted color to the polymer. Therefore, it is desirable to reduce or minimize the amount of fluorine-based surfactants remaining in the final solid polymer product. [[ID=​​​​​​​​​[Means for solving the problem]

[0008] The present invention relates, firstly, to a method for reducing ionic impurities such as TOC and fluorides during the polymerization, washing, drying, and extrusion of vinylidene fluoride polymers, a) A step of polymerizing vinylidene fluoride monomer using less than 0.1% by mass of a fluorinated surfactant and / or less than 5% by mass of a non-fluorinated surfactant based on the mass of vinylidene fluoride monomer to produce an emulsion-like aqueous polyvinylidene fluoride (PVDF) composition, b) The aqueous PVDF composition can be supplied to a finishing system that aggregates, washes, dries, and extrudes, and can be obtained by a one-step dehydration extrusion process, wherein the TOC amount according to SEMI F40 standards is 1 m³ of polymer. 2 The amount is less than 20,000 μg per unit, and the amount of fluoride ions (F - ) Amount of polymer 1m 2 The present invention relates to a method including a step of producing a solid PVDF composition having a content of less than 10,000 μg per unit.

[0009] In another aspect, the present invention relates to a method for reducing ionic impurities such as TOC and fluorides during polymerization, washing, drying and extrusion of a vinylidene fluoride polymer, comprising the steps of: a) producing an aqueous polyvinylidene fluoride (PVDF) composition by emulsion polymerization of vinylidene fluoride monomer in an aqueous medium in the presence of an inorganic initiator, using less than 0.01% by mass of a fluorinated surfactant and less than 2% by mass of a non-fluorinated surfactant based on the mass of vinylidene fluoride monomer; b) The aqueous PVDF composition is supplied to a finishing system for coagulation, washing, drying, and extrusion molding, and the amount of TOC measured according to SEMI F40 standards is measured per 1 m of polymer 2 The amount of fluoride (F) per unit is less than 20,000 μg and measured according to the SEMI F40 standard. - ) Ion content of polymer 1m 2 TOC amount and fluoride (F) that are less than 10,000 μg per unit -It relates to a process for producing a solid PVDF composition having an ion content. All steps of step b) can be realized in a single-step finishing system such as a dehydration extruder.

[0010] In some embodiments, the solid PVDF composition obtained by using the method according to the present invention has a TOC content of less than 20,000 μg per 1 m of polymer and a fluoride ion (F 2 ) content of less than 10,000 μg per 1 m of polymer in the state of the extrusion molding part or the molding part, as determined by the test method SEMI F40. - ) amount per 1 m of polymer 2 is less than 10,000 μg. In some embodiments, the solid PVDF composition obtained by using the method according to the present invention has a TOC content of less than 20,000 μg per 1 m of polymer and a fluoride ion (F 2 ) content of less than 10,000 μg per 1 m of polymer in the same polymer form, as determined by the test method SEMI F40. - ) amount per 1 m of polymer 2 is less than 10,000 μg, and has a TOC content and a fluoride (F - ) ion content.

[0011] The present invention further relates to a polyvinylidene fluoride composition having a TOC content of less than 20,000 μg per 1 m of polymer and a fluoride ion (F 2 ) content of less than 10,000 μg per 1 m of polymer. In some embodiments, the present invention relates to a polyvinylidene fluoride composition having a TOC content of 20,000 μg per 1 m of polymer as determined by the test method SEMI F40 and a fluoride ion (F - ) content of less than 10,000 μg per 1 m of polymer as determined by the test method SEMI F40. 2 is less than 10,000 μg, and has a TOC content and a fluoride ion (F 2 ) content. - ) amount per 1 m of polymer 2 is less than 10,000 μg. - ) amount. [[ID=I]]

[0012] According to certain embodiments, the vinylidene fluoride polymer (or composition) described above is obtained by the method detailed herein.

[0013] According to certain embodiments, the PVDF polymer (or composition) is in the form of granules or powder.

[0014] The present invention also relates to a fluid transport component comprising or consisting of the above-mentioned PVDF polymer (or composition), or formed from the above-mentioned powder or granules.

[0015] The present invention also relates to the use of the above-mentioned components for transporting ultrapure water for cleaning electronic components.

[0016] The present invention makes it possible to satisfy the needs identified above. Specifically, it provides an improved formulation and method that makes it possible to obtain a vinylidene fluoride polymer exhibiting excellent purity without degrading the mechanical properties of the PVDF polymer, while more efficiently removing impurities contained in the PVDF polymer, particularly organic compounds and fluoride anions. This makes it possible to obtain a high-quality PVDF polymer with good mechanical properties and high purity. Furthermore, it is possible to limit the release of these impurities during the next use of this product (for example, when tubes or pipes made from the PVDF polymer according to the present invention are used for transporting ultrapure water).

[0017] The term "ultrapure water" is understood to refer to water with a maximum mass ratio of 0.1 ppb (parts per billion) of metallic and anionic impurities, a mass ratio of 10 ppb or less of total organic carbon (TOC), a mass ratio of 0.1 ppm or less of non-volatile residues, a resistivity of 18 MΩ·cm or more at 25°C, and a reactive silica impurity content of less than 1 ppb, which conforms to the SEMI F 63 standard.

[0018] This is achieved by combining a specific polymerization recipe with a finishing system that performs flocculation, washing, drying, and extrusion separately, and is preferably enhanced to a single-stage dehydration extruder (e.g., a single-stage twin-screw dehydration extruder) to produce a solid-dry polyvinylidene fluoride composition with low impurity content from an aqueous PVDF suspension or aqueous PVDF dispersion. [Brief explanation of the drawing]

[0019] [Figure 1] This figure shows a comparison of TOC release into leachate after 1 or 2 weeks of leaching from various formulations and finishing processes, performed according to the limit values ​​determined by the SEMI F40 protocol and the SEMI F57-0.622 standard. [Modes for carrying out the invention]

[0020] In a first embodiment, the present invention relates to the polymerization, washing, drying and extrusion of vinylidene fluoride polymers, and the removal of TOC and ionic impurities, particularly F - A method for reducing a) A step of polymerizing vinylidene fluoride monomer to produce an emulsion-like aqueous polyvinylidene fluoride (PVDF) composition using less than 0.1% by mass, preferably less than 0.01% by mass, of a fluorinated surfactant and / or less than 5% by mass or less than 2% by mass of a non-fluorinated surfactant, based on the mass of vinylidene fluoride monomer. b) The aqueous PVDF composition can be supplied to a finishing system that aggregates, washes, dries, and extrudes, and can be obtained by a one-step dehydration extrusion process, wherein the TOC amount according to SEMI F40 standards is 1 m³ of polymer. 2 The amount is less than 20,000 μg per unit, and the fluoride ion (F) is measured according to the SEMI F40 standard. - ) Amount of polymer 1m 2 The present invention relates to a method for producing a solid PVDF composition containing less than 10,000 μg per unit area.

[0021] In another aspect, the present invention relates to the polymerization, washing, drying and extrusion of vinylidene fluoride polymers, and the removal of TOC and ionic impurities, particularly F - A method for reducing a) A step of producing an aqueous polyvinylidene fluoride (PVDF) composition by emulsion polymerization of vinylidene fluoride monomer in an aqueous medium in the presence of an inorganic initiator, using less than 0.01% by mass of a fluorinated surfactant and less than 2% by mass of a non-fluorinated surfactant based on the mass of vinylidene fluoride monomer. b) The aqueous PVDF composition is supplied to a finishing system for coagulation, washing, drying, and extrusion molding, and the amount of TOC measured according to SEMI F40 standards is measured per 1 m of polymer 2 The amount of fluoride ions (F) per unit is less than 20,000 μg and measured according to the SEMI F40 standard. - ) Amount of polymer 1m 2 TOC amount and fluoride (F) that are less than 10,000 μg per unit - This relates to a process for producing a solid PVDF composition having a certain amount of ions.

[0022] In this specification, unless otherwise specified, the expression "measured by SEMI F40" means that the TOC amount and fluoride ion amount were measured by performing the SEMI F40 standard procedure once or twice, preferably twice. In some embodiments, the TOC amount and fluoride ion amount measured by SEMI F40 are measured by performing the SEMI F40 standard procedure only once.

[0023] In particular, solidification, washing, drying, and extrusion can be carried out in a finishing system in a single-step process, especially a single-step dewatering extrusion process, or in a multi-step process.

[0024] According to various embodiments, the process includes the following features, which can be combined:

[0025] Unless otherwise specified, all percentages are mass percentages, and all molecular weights given are weight-average molecular weights.

[0026] In this invention, the terms "PVDF," "vinylidene fluoride polymer," and "vinylidene fluoride polymer" have the same meaning.

[0027] As used herein, the term "PVDF" includes a homopolymer of vinylidene fluoride (VDF), or a copolymer of VDF and at least one other comonomer, where VDF is preferably at least 50% by mass, more preferably at least 75% by mass, and the comonomer is preferably selected from chlorotrifluoroethylene, hexafluoropropylene, trifluoroethylene, vinyl fluoride, perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, and tetrafluoroethylene.

[0028] Preferably, the PVDF is a polyvinylidene fluoride homopolymer and / or a copolymer of vinylidene fluoride and hexafluoropropylene (HFP), where the amount of HFP is preferably 30% by mass or less.

[0029] Polymerization reaction (step a) According to one embodiment, the polymerization reaction may be carried out in a batch, semi-batch, or continuous polymerization process. The reactor is a pressurized polymerization reactor equipped with a stirrer and temperature control means. The polymerization temperature can vary in the range of 35 to 140°C, preferably 35 to 125°C, and more preferably 35 to 100°C. The polymerization pressure is typically in the range of 1380 to 17300 kPa for the polymerization of PVDF, but can be higher if the apparatus allows for operation at higher pressures. The pressure is most conveniently in the range of 3450 to 9000 kPa.

[0030] According to one embodiment, in an emulsion polymerization process, an emulsion-type aqueous polyvinylidene fluoride composition is produced by using less than 0.1% by mass, preferably less than 0.01% by mass, of a fluorinated surfactant and / or less than 5% by mass, or less than 2% by mass, preferably less than 0.01% by mass, of a nonfluorinated surfactant, based on the mass of vinylidene fluoride monomer. More specifically, in an emulsion polymerization process, an aqueous polyvinylidene fluoride composition is produced by polymerizing vinylidene fluoride in an aqueous medium using less than 0.01% by mass of a fluorinated surfactant and less than 2% by mass, preferably less than 0.005% by mass, of a nonfluorinated surfactant, based on the mass of vinylidene fluoride monomer.

[0031] According to one embodiment, vinylidene fluoride is polymerized in an emulsion polymerization process without using any surfactants. That is, the content of either a fluorinated surfactant or a non-fluorinated surfactant is less than 0.001% by mass, and preferably 0% by mass.

[0032] In the emulsion polymerization process, vinylidene fluoride can preferably be polymerized with at least one conomomer selected from chlorotrifluoroethylene, hexafluoropropylene, trifluoroethylene, vinyl fluoride, perfluoromethyl vinyl ether, perfluoroethyl vinyl ether, and tetrafluoroethylene.

[0033] It is preferable to maintain the pH of the emulsion below 4.0 during emulsion polymerization.

[0034] In this emulsion polymerization process, it is preferable not to add acid to the medium.

[0035] The reactor and its contents are heated to the desired temperature, and vinylidene fluoride monomer and, if necessary, other materials such as chain transfer agents, buffers, or antifouling agents are added. Preferably, the amount of buffer used is less than 0.1% by mass relative to the water added to the reactor. If a buffer is used, preferably it does not contain metal ions. In some embodiments, no buffer is used. Once the desired reaction pressure is reached, a radical initiator is added to start polymerization and maintain the reaction.

[0036] After supplying the predetermined amount of monomer, all supply is stopped and the reaction is considered complete. Residual gas (containing unreacted monomer) is discharged and the latex is recovered from the reactor.

[0037] In the polymerization process, monomers, initiators, optional surfactants, and other materials may be added all at once before polymerization, continuously during polymerization, partially before polymerization and then during polymerization, or added a certain time after polymerization has started. Radical initiators or mixtures of initiators have a low TOC contribution and are preferably inorganic initiators, particularly selected from the persulfate family, including those having inorganic counterions such as ammonium, sodium, or potassium, and preferably ammonium peroxodisulfate. These compounds are added in amounts sufficient to maintain a sufficient polymerization rate, typically 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.

[0038] The polymerization process is preferably carried out without the use of fluorinated surfactants.

[0039] Any surfactant of the present invention may be fluorinated, non-fluorinated, or a mixture thereof. In this specification, "fluorinated surfactant" and "fluorinated surfactant" mean that the main chain of the surfactant contains at least one covalently bonded fluorine atom, whereas a non-fluorinated surfactant in the present invention means that the main chain does not contain a covalently bonded fluorine atom.

[0040] Useful fluorinated surfactants include those with formula X(CF2) n Salts of acids represented by COOM (wherein X is hydrogen or fluorine, M is an alkali metal, ammonium, substituted ammonium (e.g., alkylamines having 1 to 4 carbon atoms), or quaternary ammonium ions, and n is an integer from 6 to 20); formula X(CF2) n Sulfate esters of polyfluoroalkanols represented by CH2OSO3M (wherein X and M are as described above); and formula CF3(CF2) n (CX2) m Salts of acids represented by SO3M (wherein X and M are as described above); where n is an integer from 3 to 7 and m is an integer from 0 to 2, such as potassium perfluorocetylsulfonate, but not limited to these.

[0041] Any non-fluorinated surfactant is defined as a surfactant that does not contain a carbon-fluorine covalent bond, is well known to those skilled in the art, and has a molecular structure containing both hydrophilic and hydrophobic parts. These substances are widely used as detergents and emulsifying stabilizers due to their ability to reduce the surface tension of liquids, often water, through selective separation and molecular orientation at solid / liquid or gas / liquid interfaces. Examples of the identity and physical properties of such substances can be found in the following literature: *Handbook of Surfactants* by M.R. Porter (Springer, New York, 1991); and *Critical Micelle Concentrations of Aqueous Surfactant Systems* by P. Mukerjee and K.J. Mysels (NSRDS-NBS 36, 1971). Accordingly, this specification covers all types of surfactants, including ionic (anionic and cationic), nonionic, polymeric, bio-based, zwitterionic, and gemini surfactants, and other surfactants with special structures. In particular, surfactants known to be effective in the emulsion polymerization of vinylidene fluoride, such as those listed below, are of interest. These are materials mainly classified as alkylene oxide polymers and alkylene oxide block copolymers, as well as polymeric surfactants and alkyl sulfonates containing acid / ionizable groups, as described in US8080621B2, US8158734B2, US8338518B2, US8765890B2, US9068071B2, US8697822B2, US7122610B2 ​​and US9447256B2.

[0042] In one embodiment of the present invention, the total amount of surfactant used is less than 1% by mass relative to the water introduced into the reactor.

[0043] In one embodiment of the present invention, no surfactant is added to the polymerization process.

[0044] The emulsion formed by the process of the present invention generally has a solid content of 5 to 65% by mass, preferably 10 to 55% by mass, when the dispersion is dried and measured by gravimetric analysis. The PVDF particles in the dispersion have a particle diameter in the range of 30 to 600 nm, preferably 100 to 350 nm, as measured by dynamic light scattering. If the particle size distribution is monodisperse with an average value around 100 to 350 nm, the latex can be defined as stable.

[0045] The solid content of the stable emulsion produced by the present invention is more than 24% by mass, preferably more than 26% by mass, more preferably more than 28% by mass, even more preferably more than 30% by mass, and most preferably more than 32% by mass.

[0046] Preferably, the composition obtained from the emulsion polymerization process has a pH of less than 4.0.

[0047] The purified vinylidene fluoride polymer contains at least one type of impurity.

[0048] At least one type of impurity may arise during the production of the final PVDF polymer, originating from the medium and monomer polymerization conditions.

[0049] In one embodiment, one or more impurities may be organic compounds such as alcohols, aldehydes, carboxylic acids, and / or esters, and / or carbonates.

[0050] According to one embodiment, at least one impurity is an organic compound and an ionic impurity, such as an anion, preferably a fluoride ion (F - ) and so on.

[0051] The amount of organic compound impurities can be measured by determining the "total organic carbon" (TOC). Therefore, the amounts of organic compounds and fluoride anions are determined using the following standards. Sample preparation is performed according to SEMI F40-0621, with 50 g of polymer placed in a bottle containing 100 mL of ultrapure water, and then kept in an oven at 85°C for 7 days. A 7-day secondary test can be performed according to SEMI F40-0621. After the first 7 days in ultrapure water at 85°C, the test solution is drained and analyzed. The bottle is refilled with 100 mL of new ultrapure water and kept in an oven at 85°C for another 7 days. Finally, the test solution is drained and analyzed. Organic compounds and fluoride anions present in the wash water (after the first week and the following second week) are analyzed according to the standard test methods of ASTM D4327 for fluoride anion measurement and ASTM D4779 and D5904 for organic compound measurement. A control water sample not exposed to the polymer is used as a reference. The obtained values ​​are expressed in μg / m³ according to the SEMI C69-1015 standard. 2 It is converted to an equivalent. The measurement is preferably performed on a polymer in granular form, but it may also be performed on a polymer in powder form that has been subjected to pressure on a part. If the polymer is in the form of a part (especially a molded part), it is possible to cut one or more parts into fragments before performing the measurement.

[0052] Finishing process (process b) After polymerization, the PVDF emulsion, PVDF dispersion, or PVDF suspension is pumped to a finishing process to separate the solid PVDF.

[0053] In one embodiment, the finishing process is a standard finishing process and includes the following steps. i. Coagulate and aerate the latex obtained by emulsion polymerization: Latex (i.e., an aqueous PVDF composition obtained by emulsion polymerization) is continuously supplied to the apparatus (e.g., a rig), and the suspended latex particles are agglomerated (flocculated) to form larger aggregates. The mixture is stirred at high speed, and pressurized air is injected. Solid foam is obtained at the outlet. The basic role of this unit is to generate floating PVDF polymer particles for washing column operations. ii. Wash the latex (i.e., the PVDF composition obtained in step i) to remove any residual molecules: The aerated PVDF polymer flocs are transported to a column, where they are washed with deionized water in the same or reverse flow. For example, foam flocs rise in the column and are discharged from the top or bottom along with excess water. Meanwhile, water containing impurities is removed from the bottom or top. iii. The washed PVDF polymer is spray-dried to produce PVDF powder: The washed foam is atomized using high-temperature, high-pressure air in the nozzle. The flow is synchronized, and the outlet temperature is controlled to achieve complete drying. After this, the purified PVDF polymer powder is ready for processing. iv. Extrude the powder to form pellets: The powder is supplied to an extruder (especially a twin-screw extruder). By controlling the shear rate and temperature, the PVDF polymer is melted and cut into pellets before the cooling process.

[0054] According to one embodiment, the finishing process is carried out using a dewatering extruder. The dewatering extruder combines the processes of coagulation, washing, dewatering, and degassing in a single, preferably twin-screw extruder unit operation.

[0055] This extrusion machine and screw are of the same general type as those described in U.S. Patent No. 4,148,991. A preferred design is an anti-meshing shaft design with opposite rotations. For production purposes, for example, the screw outer diameter may be 50 mm to 250 mm, and the screw length may be 35 to 80 times the screw outer diameter (35 to 80D) depending on the number of dewatering stages.

[0056] Extruders (such as twin-screw extruders) generally have an open forward-flight shaft design to transport material to the shaft exit. Exceptions to this are several "seal" or "restrictor" sections that divide the extruder into typically 3 to 5 operating zones. These "seal" or "restrictor" elements are either a) non-flight elements, b) forward-flight elements, or c) reverse-flight elements.

[0057] Purified vinylidene fluoride polymer In another aspect, the present invention relates to a polymer whose TOC content according to the SEMI F40 analytical standard is repeatable twice. 2 The amount is less than 20,000 μg per unit, and the amount of fluoride ions (F - ) Amount of polymer 1m 2 This invention relates to a polyvinylidene fluoride composition containing less than 10,000 μg per unit area.

[0058] In another aspect, the present invention relates to the amount of TOC measured by the SEMI F40 standard in polymer 1 m 2 The amount of fluoride ions (F) per unit is less than 20,000 μg and measured according to the SEMI F40 standard. - ) Amount of polymer 1m 2 TOC amount and fluoride ions (F) are less than 10,000 μg per unit. - This relates to a polyvinylidene fluoride composition having an amount of ).

[0059] According to various embodiments, the PVDF composition includes the following features, which can be combined:

[0060] In one embodiment of the present invention, the TOC content in the PVDF composition according to the SEMI F40 analysis standard is 10,000 μg / m³ 2 Less than 5000 μg / m² is preferred. 2 It is less than. In one embodiment, the TOC content in the PVDF composition is determined by performing the SEMI F40 procedure twice, and the TOC content measured by the SEMI F40 standard (i.e., the value measured in the second procedure) is 10,000 μg / m³. 2Less than 5000 μg / m² is preferred. 2 It is less than.

[0061] In one embodiment of the present invention, the PVDF composition contains F according to the SEMI F40 analytical standard. - The ion content is 5000 μg / m³. 2 Less than 2000 μg / m² is preferred. 2 It is less than. In one embodiment, the procedure of the SEMI F40 standard is performed twice, and the F in the PVDF composition measured according to the SEMI F40 standard is measured. - The ion concentration (i.e., the value measured in the second procedure) is 5000 μg / m². 2 Less than 2000 μg / m² is preferred. 2 It is less than.

[0062] The PVDF composition may be in any suitable form, such as granules, pellets, powder, or molded parts, for example, in the final form, particularly in the form of tubes or pipes. A feature of these products of the present invention is that the amount of total organic carbon and fluoride extracted into ultrapure water is very small.

[0063] In one embodiment of the present invention, the amount of TOC in the PVDF composition is, polymer 1m 2 It is more than 1500 μg per unit. In one embodiment, the TOC amount in the PVDF composition measured by the SEMI F40 standard, after performing the procedure of the SEMI F40 standard twice, is 1 m of polymer 2 It is more than 1500 μg per unit.

[0064] In one embodiment of the present invention, F in the PVDF composition - The amount of ions is, polymer 1 m 2 More than 500 μg per unit. In one embodiment, F in the PVDF composition - The amount of ions was measured according to the SEMI F40 standard by performing the SEMI F40 standard procedure twice in the PVDF composition. - The amount of ions is, polymer 1m 2 It is more than 500 μg per unit.

[0065] The content of organic compounds and fluoride anions is measured using the method described above.

[0066] Preferably, the PVDF composition is a PVDF polymer (TOC and F as described above). - It contains impurities such as ionic impurities, and is essentially composed of PVDF polymer.

[0067] Therefore, the PVDF polymer according to the present invention reduces the impurity content (without degrading the mechanical properties of the polymer). This makes it possible to limit the release of impurities when the product is used. Mechanical properties include, for example, thermal decomposition temperature, melting point, crystallization temperature, mass loss at high temperatures (e.g., 270°C), degree of crystallinity, tensile strength, elongation at break, and elongation at yield point.

[0068] In one embodiment of the present invention, the PVDF composition is a solid composition obtained by the method of the present invention. This solid composition contains small amounts of water-soluble or water-immiscible impurities. The impurities are particularly TOC and F - Contains ions.

[0069] The amount of TOC extracted from extruded pipes is very low, about one-fifth of the current SEMI F57-0622 standard. The amount of fluoride ions extracted from extruded pipes is high during the first wash, but becomes very low after the second wash (about one-eighth of the current SEMI F57-0622 standard).

[0070] The present invention provides several advantages over conventional reaction and finishing processes for producing high-purity PVDF. a) The PVDF produced contains very small amounts of water-soluble or water-miscible impurities, especially very small amounts of TOC and F - Ion charge. b) A single unit operation can replace a series of complex operations. c) PVDF pellets can be manufactured without going through the powder stage. d) Coagulation and separation can be performed without the use of coagulants, resulting in a purer and less contaminated product.

[0071] The high-purity PVDF according to the present invention may be particularly used in the manufacture of tubes, valves, connectors, or elbows for transporting ultrapure water used to clean electronic components (such as semiconductor compounds). [Examples]

[0072] The following examples illustrate the present invention without limiting it. The purity of the leachate after one and two weeks will be compared (limit values ​​determined by the SEMI F40 protocol and SEMI F57-0622 standard).

[0073] Figure 1 compares the amount of TOC released into leachate from various formulations and processes after one week and two weeks, with the following symbols used.

[0074] [ka]

[0075] This shows the leaching results from a PVDF suspension pipe.

[0076] [ka]

[0077] This shows the leaching results from PVDF emulsion polymer pipes using a formulation with a fluorine-based surfactant and a one-step finishing process dewatering extruder (hereinafter referred to as "old formulation") as described in Examples 7-10 of EP2548897B. A detailed explanation of the process is given in Examples 7-10. The first step is to produce PVDF by emulsion polymerization using a C4-C12 perfluoroalkanesulfonate surfactant. This emulsion is then fed into an asymmetrically rotating, non-meshing twin-screw extruder with an outer diameter of 30 mm and a total screw length of 78 mm (2.3368 m). The configuration of the extruder is shown in Figure 1 of EP2548897B. The barrel surface and screws of the extruder are made of high-nickel alloy. High-purity DI water was used throughout the entire process. The molten PVDF polymer is discharged from the extruder to a strand die. The PVDF polymer strands are cut into pellets in a water bath.

[0078] [ka]

[0079] The following shows the leaching results from a PVDF emulsion pipe of the formulation according to the present invention (hereinafter, the description of step a above, in which a dewatering extrusion molding machine is used in finishing step b, is referred to as the "new formulation"). The first step is to obtain PVDF by emulsion polymerization using ammonium peroxodisulfate solution as an initiator, without using any surfactants. Subsequently, the emulsion was fed into a non-meshing twin-screw extrusion molding machine with the same configuration as in the previous example. The barrel surface and screws of the extrusion molding machine are made of high-nickel alloy. High-purity DI water was used throughout the entire process. The molten PVDF polymer was discharged from the extrusion molding machine to a strand die. The PVDF polymer strands were cooled in a water bath and cut into pellets.

[0080] [ka]

[0081] This shows the leaching results obtained in a standard multi-stage finishing process (finishing step b) using a PVDF emulsion pipe with the formulation of step a described herein. In this case, the polyvinylidene fluoride emulsion is treated in a conventional separation process consisting of filtration, coagulation by mechanical shear, washing with water, decantation, spray drying, and pelletization by extrusion, without the use of any surfactants, using the same formulation as in the previous example. High-purity DI water was used throughout the entire process.

[0082] Figure 1 shows that by using the formulation of step a described herein in a single finishing process b, a significantly lower TOC level is observed compared to a previous formulation with PVDF resin using the same finishing or suspension process. This applies to two types of finishing processes. In particular, after leaching at 2 weeks, the TOC level decreased to almost one-fifth of the value of the previous emulsion formulation, ultimately resulting in a very low TOC concentration.

[0083] F as the leaching time progresses - decrease Table 1 below shows the changes in fluoride concentration in water one and two weeks after leaching, and the calculated fluoride reduction rate between weeks 1 and 2. The results were measured using the SEMI F40 method on pipes extruded from PVDF pellet samples, and the values ​​were μg / m³. 2 This is shown as follows. In one embodiment, the polymerization process described in US2435537A or US3193539A is used to prepare the samples in the last column of Table 1.

[0084] [Table 1]

[0085] This table compares the residual F content in the leachate after two weeks of leaching with the "old" formulation (described in Prior Art EP2548897). - However, this has been significantly improved by the “new” formulation of step a described herein. This reduction is beneficial for both finishing processes of step b.

[0086] This improvement is achieved because the "new" formulation has superior dynamic properties of fluoride transfer to leachate compared to the "old" formulation and suspended PVDF. This is particularly true for the results of a single-stage finishing process.

Claims

1. During the polymerization, washing, drying, and extrusion of PVDF polymers, the total amount of oxidizable carbon (TOC) and fluoride ions (F) － A method for reducing ionic impurities such as ), a) A step of producing an aqueous PVDF composition by emulsion polymerization of vinylidene fluoride monomer in an aqueous medium in the presence of an inorganic initiator, using less than 0.01% by mass of a fluorinated surfactant and less than 2% by mass of a non-fluorinated surfactant based on the mass of vinylidene fluoride monomer. b) The aqueous PVDF composition is supplied to a finishing system for agglomeration, washing, drying, and extrusion molding, and the amount of TOC measured according to the SEMI F40 standard is measured per 1 m of polymer. ２ The amount of fluoride ions (F) per unit is less than 20,000 μg and measured according to the SEMI F40 standard. － ) Amount of polymer 1 m ２ TOC amount and fluoride ions (F) that are less than 10,000 μg per unit － A process for producing a solid PVDF composition having the following quantity: Methods that include...

2. The method according to claim 1, wherein aggregation, washing, drying and extrusion are performed in the finishing system in a single step, particularly a single-step dehydration extrusion process, or a multi-step process.

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

0.

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

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

6. The method according to any one of claims 1 to 5, wherein sodium peroxodisulfate, ammonium peroxodisulfate, or potassium peroxodisulfate is used as the initiator, in an amount of 100 ppm to 10,000 ppm, preferably 250 ppm to 2,000 ppm, most preferably 500 ppm to 1,500 ppm, relative to the total amount of monomers, and preferably the initiator is ammonium peroxodisulfate.

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

8. The method according to any one of claims 1 to 7, wherein step b) includes the following finishing process: i. A step of agglomerating and aerating the aqueous PVDF composition obtained by emulsion polymerization. ii A step to wash the PVDF composition obtained in step i and remove residual molecules. iii A process of spray-drying the washed PVDF polymer to produce PVDF powder. iv. A step of extruding the powder to form pellets.

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

10. The solid PVDF composition has a TOC amount measured according to the SEMI F40 standard of less than 10,000 μg per 1 m of polymer ２ where the SEMI F40 standard procedure is carried out twice, and the fluoride (F － - ２ ) ion amount is less than 5,000 μg per 1 m of polymer, and the method according to any one of claims 1 to 9 having a TOC amount and a fluoride ion (F － - ) amount

11. The solid PVDF composition, when measured according to the SEMI F40 standard, has a TOC amount of polymer 1 m ２ The amount is less than 5000 μg per unit, and the procedure according to the SEMI F40 standard is performed twice, and the polymer is 1 m ２ The method according to any one of claims 1 to 10, having a TOC amount greater than 1500 μg per unit.

12. The solid PVDF composition, when measured according to the SEMI F40 standard, has a TOC amount of polymer 1 m ２ The amount is less than 2000 μg per unit, and the procedure according to the SEMI F40 standard is performed twice, and the polymer is 1 m ２ Fluoride ions (F) greater than 500 μg per unit － The method according to any one of claims 1 to 11, having the quantity of )

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

15. TOC amount measured according to SEMI F40 standard per 1 m of polymer ２ The amount of fluoride ions (F) per unit is less than 20,000 μg and measured according to the SEMI F40 standard. － ) Amount of polymer 1 m ２ TOC amount and fluoride ions (F) that are less than 10,000 μg per unit － A polyvinylidene fluoride composition having an amount of ).

16. TOC amount measured according to SEMI F40 standard per 1 m of polymer ２ Less than 10,000 μg per unit, with a preference for polymer 1 m ２ The PVDF composition according to claim 15, wherein the amount is less than 5000 μg and greater than 1500 μg per unit, and the procedure according to the SEMI F40 standard is performed twice.

17. Fluoride ions (F) measured according to the SEMI F40 standard － ) Amount of polymer 1 m ２ Less than 5000 μg per unit, with a preference for polymer 1 m ２ The PVDF composition according to claim 15 or 16, wherein the amount is less than 2000 μg and greater than 500 μg, and the procedure according to the SEMI F40 standard is performed twice.

18. A PVDF composition according to any one of claims 15 to 17, comprising a VDF copolymer, preferably a VDF / HFP copolymer.

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

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

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

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