JP2006231847A - Regeneration method of fluorine resin film, and fluorine resin film obtained using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for regenerating a fluorine resin film used as a water treating film without incinerating or landfilling. <P>SOLUTION: The fluorine resin film is regenerated by the step of removing impurities contained in the fluorine resin film, the step of crushing the fluorine resin film after removing the impurities to make a fluorine resin, and the step of performing extrusion molding by supplying the fluorine resin after being crushed into an extruder while heating it near the melting temperature of the fluorine resin. Further, a part or the whole of the fluorine resin regenerated by this method is used to make the fluorine resin film. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to a method for regenerating a fluororesin film used for a water treatment membrane and a module.

  In general, a fluororesin has a remarkably high melting point, good chemical resistance, and a low coefficient of friction on the surface of the resin, so that it is widely used in various fields. For example, fluororesins used in heat-resistant wire coating materials, semiconductor manufacturing materials, electronic components, pipes, valves, etc. are difficult to handle because of the difficulty in handling the gas generated during thermal decomposition, and cannot be recycled. Until now, it was treated as industrial waste.

  In the field of water treatment, a method of obtaining drinking water by chlorination after rapid sand filtration has been generally used. However, for the purpose of removing the pathogenic protozoa Cryptosporidium having chlorine resistance, In recent years, the introduction of separation membranes has increased rapidly. In particular, a separation membrane made of a fluororesin has come to be frequently used because of the mechanical strength and chemical resistance of the membrane. Since the performance of the fluororesin membrane gradually deteriorates over a long period of use, it must be replaced with a new membrane module. As a result, the membrane module with degraded performance is discarded. The disposal of fluororesin membranes has been carried out until now, but as the amount of fluororesin membranes increases, the amount of waste becomes enormous and the impact on the environment is extremely high. It is expected to grow and become a major social problem in the future.

As a resin recycling method, a method in which a resin is dissolved in a solvent and then supplied to an extruder (Patent Document 1) and a method in which a fluorine resin is thermally decomposed by thermal decomposition (Patent Document 2) have been devised. Further, in order to recycle the resin, a method (Patent Document 3) of polishing the resin surface in order to remove impurities attached to the resin surface has been performed.
JP 2000-351869 A JP 2004-346000 A JP 2001-145920 A

  However, it is difficult to control the amount of the solvent when it is supplied to the extruder after being dissolved in the solvent, and it is difficult to remove the solvent contained in the resin after extrusion due to excessive heat in the extruder. is there. In addition, when chemical recycling is performed, if it is desired to regenerate the same resin before thermal decomposition, a multi-step complicated process is required, which increases production costs and increases the amount of carbon dioxide generated during production. Have problems. The resin powder generated by polishing for the purpose of removing impurities has a problem that it must be disposed of separately because it contains many impurities. An object of the present invention is to establish a method for regenerating a fluorine-based resin by avoiding the above-mentioned problems without being treated as industrial waste.

  The present invention for solving the above-described problems is characterized by the following configurations (1) to (5).

  (1) A method for regenerating a fluororesin film that regenerates a fluororesin that forms a fluororesin film used for water treatment without chemically changing the process, and removing impurities contained in the fluororesin film And crushing the fluororesin film after removing the impurities into a fluororesin; and heating the crushed fluororesin film near the melting point of the fluororesin in the extruder. A method for regenerating a fluororesin film, comprising a step of supplying and performing extrusion molding.

  (2) The method for regenerating a fluororesin film according to (1), wherein the fluororesin film is porous.

  (3) The method for regenerating a fluororesin film according to (1) or (2), wherein the fluororesin forming the fluororesin film is a resin made of polyvinylidene fluoride.

  (4) The method for regenerating a fluorine resin film according to any one of (1) to (3), wherein the fluorine resin film has a hollow fiber shape.

  (5) A fluororesin film obtained using a fluororesin regenerated by the fluororesin film regeneration method according to any one of (1) to (4) in part or in whole.

  According to the present invention, in a water treatment membrane whose membrane material is made of a fluororesin, the porous fluororesin is easy to remove impurities and has a high thermal conductivity so that it applies excessive heat. Therefore, the material can be easily recycled without changing the physical properties of the fluororesin. In particular, when the water treatment membrane is in the form of a hollow fiber, it can be continuously and stably regenerated, and contains almost no resin material other than the fluororesin. Regeneration to a low fluorine resin is possible.

The present invention relates to a method and a method for regenerating a fluororesin film without dissolving it in a solvent and without chemically changing the fluororesin film in a water treatment membrane and module in which the membrane material is made of a fluororesin. fluorine characterized by comprising the step of by fluoric supplied from resin film into the extruder while heating the fluorocarbon resin film was crushed with a step of crushing the step and the fluorine-based resin film to remove impurities perform extrusion This is a method for regenerating a resin film.

  The fluororesin film used in the present invention is preferably porous with countless micro-sized holes and gaps on the surface and inside thereof. Examples of the material of the fluororesin film include polytetrafluoroethylene, Tetrafluoroethylene-perfluorovinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, polyvinyl fluoride, trifluoroethylene chloride resin, tetrafluoroethylene resin, Examples thereof include a molten fluororesin composite agent. Among them, polyvinylidene fluoride is particularly preferable because it is melted at a low temperature during extrusion molding and is not easily thermally decomposed and is stable.

  The fluororesin may be used alone or as a composition with other resins. However, when other resins are used, it is better that the physical properties of the fluorinated resin after the regeneration are not significantly different from those before the regeneration. Therefore, the other resin contained in the fluorinated resin is 10% by mass or less in the fluorinated resin. Desirably, 5 mass% or less is more desirable. Therefore, membranes for water treatment include cylindrical membranes such as hollow fiber type, tubular type and monolith type, and spiral type, pleated type, disc type, flat membrane, etc. In addition to this, since a base material for supporting the membrane is used, it contains a large amount of resin materials other than fluororesin, which is not preferable for regeneration, and a hollow fiber type is preferable.

  The fluorine resin film regenerated by the present invention may be one actually used for water treatment or a non-standard product generated when producing a fluorine resin film.

  What is actually used for water treatment must be cleaned with chemicals such as acid or alkali, because organic and inorganic impurities contained in the raw filter water adhere to the surface and inside of the fluororesin membrane. If the membrane is porous, impurities adhering to the inside of the membrane can be easily dissolved by acid or alkali. As the acid, inorganic acids such as dilute hydrochloric acid, dilute sulfuric acid, phosphoric acid, nitric acid, and sodium hydrogen sulfite, and organic acids such as an aqueous oxalic acid solution and an aqueous citric acid solution can be used alone or as a mixture of two or more. As the alkali, an aqueous sodium hydroxide solution, an aqueous sodium hypochlorite solution, an aqueous sodium carbonate solution or the like can be used alone or as a mixture of two or more. In chemical cleaning, porous fluororesin membranes are immersed in acid or alkali aqueous solutions alone or alternately for a certain period of time, or acids and alkalis are circulated in the porous membrane module to remove impurities attached to the membrane. The method can be used.

  Fluorine resin films that were out of specification during the production of fluorine resin films may contain impurities such as various organic solvents, so rinse with water after washing with water-soluble organic solvents, etc. The removal process by this operation is required.

  The extrusion molding machine to which the present invention is applied is not particularly limited, and may be any of a single screw extruder, a twin screw extruder, and the like. In an extrusion molding machine, the fluorine resin is dissolved by rotating the screw in a cylinder whose temperature is controlled by a heater to dissolve the fluorine resin, and a regenerated fluorine resin is obtained from the nozzle of the extrusion molding machine. Can do.

  If the fluororesin film has a shape like a lump of resin, it is difficult to completely dissolve unless a temperature considerably higher than the melting point is applied in order to dissolve it to the inside of the fluororesin. Since the resin film can be easily dissolved in the vicinity of the melting point of the resin, the resin can be prevented from being chemically changed by excessive heating.

  The temperature for dissolving the fluororesin is preferably in the vicinity of the melting point of the fluororesin, and can be regenerated without causing a chemical change if the temperature is higher by about 20 ° C. than the melting point of the resin to be dissolved. The temperature is preferably 10 ° C. higher than the melting point of the resin.

  Methods for measuring the presence or absence of chemical changes due to thermal degradation of fluoropolymers include molecular weight distribution measurement, elemental analysis, melting point measurement, differential scanning calorimetry, heating weight loss analysis, nuclear magnetic resonance spectroscopy, infrared spectroscopy. Although it can be performed by ultraviolet spectroscopy or the like, it can also be confirmed by comparing the physical properties before and after the regeneration treatment after processing the regenerated fluororesin into the original shape. However, measurement errors occur regardless of which method is used, so molecular weight distribution measurement, elemental analysis, melting point measurement, differential scanning calorimetry, heating weight loss analysis, nuclear magnetic resonance spectroscopy, infrared spectroscopy In the analysis such as ultraviolet spectroscopy, the error is within 5%. When the regenerated fluororesin is processed into the original shape and the physical properties of the fluororesin before and after regeneration are compared, the error of about 10% changes chemically. It can be regarded as not.

  In order to stably supply the fluorine-based resin film into the extrusion molding machine, a step of crushing the fluorine-based resin film is required. In particular, in order to stably supply the fluorine-based resin film continuously, The fluororesin membrane is preferably in the form of a hollow fiber. For crushing fluorine-based resins, crushers and crushers such as ball mills, high-speed cutter mills, roll crushers, rotary cutters, and hydraulic cutters are usually used. In the case of crushing, since it is stretched and cannot be crushed well, it is preferable to use a uniaxial crusher, and it is particularly preferable to use a crushing means with a rotary cutter or a hydraulic cutting machine because it can be finely crushed. By treating the hollow fluororesin in these crushing steps, it can be introduced smoothly when supplied to the extruder, and the melting temperature of the fluororesin can be made uniform, which is preferable. The fluorinated resin obtained by regeneration can be used as a film for water treatment in addition to a coating material for heat-resistant wires, semiconductor manufacturing materials, electronic parts, pipes, valves, and the like.

  And, by using a part or all of the fluorine resin regenerated as described above to form a fluorine hollow fiber membrane, material recycling can be easily performed without changing the physical properties of the fluorine resin. is there.

The inner diameter and outer diameter of the hollow fiber membrane measured in the present invention were determined from a scanning electron micrograph of a broken section. A pure water permeation amount (m ³ / m ² · h) was produced by producing a miniature module having a length of 200 mm consisting of four hollow fiber membranes, substantially under conditions of a temperature of 25 ° C. and a filtration differential pressure of 16 kPa. The total pressure of pure water containing no solids is filtered for 30 minutes, and the permeation amount (m ³ ) is converted into a value per unit time (h) and effective membrane area (m ² ) as pressure (100 kPa) and did.

  The breaking strength and breaking elongation were measured 30 times using a tensile tester (TENSILON / RTM-100) (manufactured by Toyo Baldwin) by changing the sample at a pulling speed of 50 mm / min 30 times. The average was taken as the measured value.

[Example 1]
A polyvinylidene fluoride hollow fiber membrane (inner diameter 0.90 mm, outer diameter 1.42 mm, pure water permeation amount 3.7 m ³ ) manufactured for a polyvinylidene fluoride microfiltration hollow fiber membrane (manufactured by Toray Industries, Inc., model number HFM-2020) / (M ² · h), breaking strength 11.0 MPa, breaking elongation 97%) was washed with water and then dried by heating in a dryer heated to 120 ° C. for 3 hours to remove moisture. Next, the dried hollow fiber membrane was crushed into a length of 1 to 5 mm using a rotary cutter (manufactured by Nara Machinery Co., Ltd., model RCM-400). Next, the crushed hollow fiber membrane is put into a single-screw extruder (model number SLM50, manufactured by Hitachi Zosen), and the crushed hollow fiber membrane is melted while heating the cylinder part to 180 ° C. with a heater, and the screw is rotated. The molten resin was extruded. The extruded resin was gradually cooled at the nozzle portion and solidified to obtain a polyvinylidene fluoride resin. Using the obtained resin, a microfiltration hollow fiber membrane was produced again. The obtained hollow fiber membrane has an inner diameter of 0.82 mm, an outer diameter of 1.42 mm, a pure water permeation amount of 3.6 m ³ / (m ² · h), a breaking strength of 10.4 MPa, and a breaking elongation of 91%. It was confirmed that the product physical properties were satisfied.

[Comparative Example 1]
The same operation as in Example 1 was performed except that a polyacrylonitrile hollow fiber membrane was used instead of the polyvinylidene fluoride hollow fiber membrane. In order to heat and melt with an extrusion molding machine, the heater temperature was heated to 400 ° C., but the polyacrylonitrile hollow fiber membrane did not dissolve and could not be extruded.

[Comparative Example 2]
The same operation as in Example 1 was performed except that a cellulose acetate hollow fiber membrane was used instead of the polyvinylidene fluoride hollow fiber membrane. When the heater temperature was heated to 250 ° C. during melting with an extruder, the resin was dissolved, but part of the resin was oxidized and carbonized.

The present invention in the case of discarding the fluorine-based resin film which is used for water treatment, is preferably used as a method for reproducing resin without incineration or burial disposal.

Claims (5)

A method for regenerating a fluororesin film that regenerates a fluororesin that forms a fluororesin film used for water treatment without chemically changing, the step of removing impurities contained in the fluororesin film, A step of crushing the fluorine resin film after removing impurities to obtain a fluorine resin, and supplying the extruded fluorine resin into the extrusion machine while heating near the melting point of the fluorine resin. A method for regenerating a fluororesin film, comprising a step of molding. 2. The method for regenerating a fluorine resin film according to claim 1, wherein the fluorine resin film is porous. The method for regenerating a fluororesin film according to claim 1 or 2, wherein the fluororesin forming the fluororesin film is a resin made of polyvinylidene fluoride. The method for regenerating a fluorine resin film according to any one of claims 1 to 3, wherein the fluorine resin film has a hollow fiber shape. A fluorine-based resin film obtained by partially or entirely using a fluorine-based resin regenerated by the method for regenerating a fluorine-based resin film according to claim 1.