JP2006219811A - Method for controlling membrane forming stock solution and method for producing porous membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for controlling a membrane forming stock solution controlling fluctuation of composition in a specified range even using a dope obtained by solving at least two kind of polymers as a stock solution for membrane forming and to provide a method for producing porous membrane using the method for controlling the stock solution. <P>SOLUTION: The invention relates to the method for controlling the membrane forming stock solution comprising characterization of fluctuation of composition of the stock solution which contains the dope obtained by solving at least two kinds of polymers. The fluctuation of the composition is controlled by characterizing the fluctuation of the viscosity and the refractive index wherein the accuracy of measurement of the viscosity is preferably set within ±500 cP and the accuracy of measurement of the refractive index is preferably set within ±0.0002. The method for producing the porous membrane comprises wet forming of the stock solution controlled by the method, into the porous membrane, wherein stock solutions obtained by dissolving polyvinylidene fluoride or polyvinylpyrrolidone are preferably used. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for managing the composition of a film-forming stock solution that is a raw material for a polymer membrane, and a method for producing a porous membrane using the same.

  In recent years, due to increasing interest in environmental pollution and stricter regulations, water treatment using porous membranes with excellent separation integrity and compactness, for example, industrial wastewater by ultrafiltration and microfiltration, sewage wastewater, and purified water Such processing has attracted attention.

  As a method for producing such a porous membrane, a method of drawing a hollow fiber obtained by melt spinning a polymer, a method of utilizing a heat-induced phase separation phenomenon that occurs when a polymer solution dissolved at high temperature is cooled, a polymer A method utilizing a non-solvent induced phase separation phenomenon that occurs when a non-solvent is added to a solution is known. As a method for forming a film by non-solvent induced phase separation, a wet method or a dry wet method (hereinafter, both methods are collectively referred to as a wet method or a wet shaping) are known, and by using these methods, A porous membrane having a high filtration flow rate and good fractionation characteristics can be obtained (for example, Patent Documents 1 to 6).

  In the production of a porous film by a wet method, the porous structure changes depending on the film forming conditions such as the composition of a film forming solution composed of a polymer solution (hereinafter referred to as dope) in a good solvent, the composition of a coagulation bath, and the temperature These conditions greatly affect membrane properties such as filtration characteristics and fractionation characteristics. Therefore, as one of the important requirements for industrially producing a porous membrane having stable physical properties, appropriate management of fluctuations in the composition of the film forming stock solution can be mentioned.

When a dope in which one kind of polymer is dissolved in a solvent is used as a film-forming stock solution, it is possible to manage fluctuations in the composition of the film-forming stock solution, for example, by measuring its viscosity.
However, when a dope in which two or more types of polymers are dissolved is used as a film-forming stock solution in order to obtain a porous membrane with further excellent filtration characteristics and fractionation characteristics (for example, Patent Documents 7 to 9), Since the composition cannot be specified, it is difficult to manage the composition of the film forming solution only by measuring the viscosity.

As a method for specifying the composition of such a dope, for example, a method of determining the content of each polymer from a molecular weight distribution obtained by fractionating each polymer and measuring each molecular weight, an infrared absorption spectrum, NMR A method for obtaining the abundance ratio of each polymer in the dope from a peak or the like peculiar to each polymer obtained from measurement of a spectrum or the like can be mentioned. However, these methods require complicated operations for measurement and tend to have insufficient measurement accuracy, and are not appropriate methods for managing a film-forming stock solution.
JP-A 63-296939 JP-A-6-79150 JP-A-8-299770 JP-A-10-134793 JP 11-319522 A JP 2000-15066 A JP 2004-25066 A Japanese Patent Laid-Open No. 2004-25067 JP 2004-217900 A

  The present invention relates to a method for managing a film-forming stock solution that can identify fluctuations in the composition even when a dope in which two or more types of polymers are dissolved is used as a film-forming stock solution, and a method for producing a porous membrane using this method Is intended to provide.

  That is, the first gist of the present invention is a method for managing a film-forming stock solution, in which a composition variation of a film-forming stock solution composed of a dope in which two or more kinds of polymers are dissolved is specified from changes in viscosity and refractive index.

  The second gist of the present invention is a method for producing a porous membrane, which is wet-shaped using a membrane-forming stock solution managed by the above-described method.

  Even when a dope in which two or more kinds of polymers are dissolved is used as a film-forming stock solution by the method for managing a film-forming stock solution of the present invention, it is possible to easily identify the variation of the composition, and this management method is applied. By doing so, it becomes possible to industrially produce a porous membrane having stable physical properties.

The viscosity and refractive index of the film-forming stock solution (dope) vary depending on the solvent amount, polymer amount, polymer molecular weight, etc., but also vary depending on the measurement temperature, etc. It must always be kept constant.
In carrying out the present invention, the dope may be extracted from the production line of the porous membrane, and the viscosity and / or refractive index of the film-forming stock solution may be batch measured. In the production line for transferring the dope dissolving machine or dope, This viscosity and / or refractive index may be measured continuously. It is also possible to batch measure either viscosity or refractive index and measure the other continuously.

In the case of batch measurement, for example, the dope can be appropriately diluted as necessary in order to make the measured value easy to measure. In particular, in batch measurement, if the solvent volatilizes during measurement, the dope composition changes, which is not preferable. Therefore, the measurement temperature is preferably set to be equal to or lower than the boiling point of the solvent.
In addition, if bubbles are mixed in the dope, the dope is allowed to stand in the case of batch measurement, and a degasser is introduced into the production line in the case of continuous measurement. The measurement is preferably performed after defoaming.

  In the present invention, the viscosity can be measured using a falling ball viscometer, a capillary viscometer, a rotational viscometer, a tuning fork viscometer, or the like. In the case of using any type of rotational viscometer among a rotating cylinder type, a cone plate type, and a parallel plate type, the viscosity to be measured may be a steady flow viscosity or a viscosity obtained from dynamic viscoelasticity measurement.

  These viscometers can be appropriately selected in consideration of, for example, the dope viscosity and the ease of measurement. For example, the Brookfield viscometer, which is one of the rotary viscometers, is easy to measure, Since it is possible to select a spindle according to the viscosity, it is one of the preferred devices when measuring the viscosity by batch measurement.

  In the case of continuously measuring the viscosity, for example, when a vibrating body (viscosity sensor) is placed in a liquid and vibrated, the vibration amplitude of the sensor decreases as the liquid viscosity increases due to the viscosity resistance of the liquid. Commercially available ultrasonic viscometers for processes using on-line rheometers and online rheometers can be used. It is also possible to use a capillary viscometer utilizing the Hagen-Poiseule law.

  In the present invention, the viscosity measurement accuracy is preferably within ± 500 cP. This is because, when the measurement accuracy is within ± 500 cP, the composition fluctuation of the film forming stock solution tends to be accurately grasped. More preferably, it is within ± 100 cP.

In the present invention, the refractive index can be measured using a photorefractive critical angle detection method or the like.
When measuring the refractive index continuously, for example, use a commercially available process refractometer that utilizes the refraction of light generated at the interface between the small prism plane exposed at a part of the tip of the detector and the liquid to be measured. can do.

  In the present invention, it is preferable that the refractive index measurement accuracy be within ± 0.0002. This is because, when the measurement accuracy is within ± 0.0002, the composition fluctuation of the film-forming stock solution tends to be accurately grasped. More preferably, it is within ± 0.0001. The wavelength of light used for refractive index measurement is preferably D line.

As the membrane base polymer used in the method for producing a porous membrane of the present invention, polyolefin such as polyethylene and polypropylene, polysulfone, polyacrylonitrile, cellulose acetate, polyvinylidene fluoride, and the like are used.
Although the present invention is not limited by the membrane material, the polymer comprising polyvinylidene fluoride and / or polyvinylidene fluoride units and other monomer units is excellent in chemical resistance and heat resistance. It is suitably used as a material polymer.

  Also, as the membrane base polymer, it is possible to use a mixture of polymers of the same type and different average molecular weight, or two or more types of polymers, and when the membrane base polymer is polyvinylidene fluoride, the average molecular weight is 10 It is preferable to use a mixture in the range of 10,000 to 2,000,000 as appropriate. When the membrane substrate is polyvinylidene fluoride, it is preferable to form the membrane by a dry and wet method from the viewpoint of fractionation performance and water permeability.

  In the method for producing a porous membrane of the present invention, an additive polymer can be used in addition to the membrane base polymer. As the additive polymer, a water-soluble polymer is generally used, and examples thereof include polyethylene glycol and polyvinyl pyrrolidone. In particular, polyvinylpyrrolidone is preferable in terms of pore diameter control and film strength. Polyvinylpyrrolidone having a molecular weight in the range of 10,000 to 3,000,000 can be suitably used. Moreover, you may use the copolymer which has a vinylpyrrolidone unit and another monomer.

  As the solvent of the membrane forming stock solution used in the method for producing a porous membrane of the present invention, a solvent that is soluble in the above polymer is used, but when the membrane base polymer is polyvinylidene fluoride, dimethylformamide, dimethylacetamide , Dimethyl sulfoxide, dimethylacetamide and the like are used.

  When polyvinylidene fluoride is used as the film base polymer and polyvinylpyrrolidone is used as the additive polymer, dimethylacetamide is suitable as the solvent.

  The film-forming stock solution is preferably produced by dissolving the membrane base polymer and the additive polymer in a solvent. The concentration of the membrane base polymer is preferably in the range of 12 to 25% by mass. By setting the content to 12% by mass or more, voids tend not to be formed in the porous film. By setting the content to 25% by mass or less, the viscosity of the film-forming stock solution becomes a value suitable for film formation, and the productivity is increased. This is because tends to be favorable. The concentration of the additive polymer is preferably 1% by mass or more and more preferably 5% by mass or more as the lower limit. Moreover, it is preferable that an upper limit shall be 2 times or less of the density | concentration of a membrane base polymer.

In the method for producing a porous membrane of the present invention, it is preferable that the fluctuation range of the viscosity of the membrane forming stock solution with respect to the standard value is within ± 22%.
This is because, by making the fluctuation range of the viscosity of the membrane forming stock solution within ± 22%, in particular, using polyvinylidene fluoride as the membrane base polymer, polyvinylpyrrolidone as the additive polymer, and dimethylacetamide as the solvent, This is because in the case of adopting the above-described stock solution composition, it tends to be possible to produce a porous membrane having stable physical properties. More preferably, it is within ± 15%.
The standard value of the viscosity of the film-forming stock solution in the present invention is not particularly limited as long as it is a value within a range that allows film formation, and can be selected from the range of 500 to 150,000 cP, for example.

In the method for producing a porous film of the present invention, it is preferable that the fluctuation range of the refractive index of the film forming stock solution with respect to the standard value is within ± 0.07% of the standard value.
This is because the fluctuation range of the refractive index of the film forming stock solution is within ± 0.07%, in particular, polyvinylidene fluoride is used as the film base polymer, polyvinylpyrrolidone is used as the additive polymer, and dimethylacetamide is used as the solvent. In addition, when the above-described stock solution composition is employed, a porous membrane having stable physical properties tends to be produced. More preferably, it is within ± 0.03%.
The standard value of the refractive index of the film-forming stock solution in the present invention is not particularly limited as long as it is a dope value that can be formed into a film. For example, a value in the range of 1.4 to 1.5 is selected as a guide. can do.

The above-mentioned film-forming stock solution can be extruded from a predetermined nozzle and formed into a film by wet or dry-wet spinning. In order to achieve both filtration performance and fractionation performance, dry-wet spinning is preferable. When the porous membrane is a hollow fiber membrane, it is extruded from a tubular nozzle.
The extrusion temperature is preferably in the range of 20 to 40 ° C. This is because, within this temperature range, the viscosity of the film-forming stock solution becomes a region where spinning can be performed stably, and the production conditions tend to be excellent in productivity.

  The form of the porous membrane obtained by the present invention is not particularly limited and may be a flat membrane or a hollow fiber membrane, but from the viewpoint of miniaturization of the water treatment device, the hollow fiber membrane is Is preferred.

When the strength of the resulting porous membrane is insufficient, a fiber reinforced porous membrane in which fibers are arranged in the porous membrane, or a braid reinforced porous membrane in which a membrane forming stock solution is applied to the braid is used. , The strength can be improved.
In the case of a fiber reinforced porous membrane, the fiber is discharged from the nozzle simultaneously with the film forming stock solution and then solidified. In the case of a braided cord reinforced porous membrane, the film forming stock solution is applied onto the braided string with a nozzle. These can be obtained by discharging and solidifying.
In addition, in order to improve the adhesion between the braid and the porous membrane, the film-forming stock solution may be applied after first impregnating the braid with a thin film-forming stock solution.

  As the coagulation liquid used at the time of film formation, an aqueous solution containing a solvent used for the spinning dope is preferable. The solvent concentration depends on the target porous structure and the type of solvent, but when dimethylacetamide is used, for example, it is preferably in the range of 1 to 50% by mass. The temperature of the coagulation bath is usually 90 ° C. or less, preferably 50 to 85 ° C.

  Further, the solvent contained in the porous membrane is washed following the solidification. It is effective to perform this washing in water as hot as possible.

In the case of using an additive polymer, it is preferable to remove it as much as possible using water washing, hot water washing, an oxidizing agent, a photocatalyst, or the like in order to improve water permeability. Here, as the oxidizing agent, sodium hypochlorite, ozone, or the like can be used. When an oxidizing agent or the like is used, it is preferably washed in hot water at 60 to 95 ° C.
The washed film is preferably dried and then wound on a bobbin or a bag.

  The porous membrane obtained by the present invention may be composed of a plurality of porous layers. For example, in the case of consisting of two porous layers, after forming and winding up the first porous film, the second porous layer is formed thereon to produce the porous film. Alternatively, after the first porous layer is solidified, the second porous layer may be continuously formed to produce the porous film.

  Hereinafter, the present invention will be described in more detail based on examples. The viscosity measurement and refractive index measurement in this example were performed by the following methods.

[Viscosity measurement]
Using a Brookfield type viscometer (Brookfield, programmable digital viscometer DV-II +), a 40 ° C. dope was put in a bottle with an inner diameter of 45 mm and a volume of 225 ml immersed in a constant temperature bath at 40 ° C., and the diameter was 27.4 mm. Spindle No. 4 was used to measure the viscosity at a rotation speed of 10 rpm. This measurement accuracy is ± 100 cP.

[Refractive index measurement]
Using a refractometer with a photorefractive critical angle detection method (Kyoto Electronics Industry Co., Ltd., refractometer RA-500N), set the dope at 40 ° C to a measurement temperature of 40 ° C so that no bubbles are generated. After confirming that the temperature of the measurement part was stable at 40 ° C., the refractive index (nD) of values up to the fourth decimal place was measured. This measurement accuracy is ± 0.0001.

<Example 1>
Polyvinylidene fluoride was used as the membrane base polymer, polyvinylpyrrolidone as the additive polymer, and N, N-dimethylacetamide (DMAc) as the solvent.
Polyvinyl fluoride is made of Atofina Japan's Kyner 301F and Kyner 9000LD as vinylidene, and polyvinyl pyrrolidone is K-90 made by ISP, with the composition (mass ratio) shown in Table 1 at 60 ° C. for 4 hours. The polymer was dissolved to prepare a dope.

  As can be seen from Table 1, it can be seen that the composition variation of the film forming stock solution can be detected by the viscosity and refractive index of the dope. If the composition of dope 1 is the standard composition, the viscosity of dope 2 is 28% larger than that of dope 1 and the refractive index is 0.08% larger than the refractive index of dope 1. Therefore, the composition of dope 2 is judged to be abnormal. can do. Further, although the refractive index of the dope 3 is the same as that of the dope 1, it can be determined that the viscosity is 30% smaller than that of the dope 1 and the composition of the dope 3 is also abnormal.

<Example 2>
Polyvinylidene fluoride was used as the membrane base polymer, and polyvinylpyrrolidone was used as the additive polymer to form a film by a dry and wet method. For polyvinylidene fluoride, Kyner 301F and Kyner 9000LD manufactured by Atofina Japan were used, and for polyvinylpyrrolidone (PVP), K-90 manufactured by ISP was used, and N, N-dimethylacetamide (DMAc) was used as a solvent.

These were mixed with Kyner 301F / Kyner 9000LD / K-90 / DMAc at a mass ratio of 12/8/10/70 to prepare a film-forming stock solution 1 serving as a film substrate. Further, in order to enhance the adhesion between the membrane substrate and the braid that increases the strength of the porous membrane, Kyner 301F / Kyner 9000LD / K-90 / DMAc is mixed at a mass ratio of 3/2 / 2.5 / 95, Film-forming stock solution 2 was prepared.
Using a tubular nozzle kept at 30 ° C., a polyester multifilament braid is introduced, a film-forming stock solution 2 is applied thereon, and a film-forming stock solution 1 is applied onto the film-forming stock solution 2 applied to the braid. Then, it was discharged from a nozzle and introduced into a coagulation bath having a DMAc concentration of 5% by mass set at 80 ° C. to obtain a braid reinforced porous layer having an outer diameter of 2.3 mm and an inner diameter of 1 mm.

Subsequently, the braided reinforcing porous layer is introduced into a tubular nozzle kept at 30 ° C., glycerin is applied as an internal coagulating liquid on the porous layer, and the film-forming solution 1 is further applied on the glycerin. Then, it was discharged from a nozzle and introduced into a coagulation bath set at 80 ° C. to obtain a braid reinforced composite porous layer.
The braided reinforcing composite porous layer was desolvated in hot water for 1 minute, then immersed in 50000 mg / L sodium hypochlorite aqueous solution, washed in hot water for 10 minutes, and dried at 90 ° C. for 10 minutes. A braid reinforced composite porous hollow fiber membrane having an outer diameter of 2.8 mm and an inner diameter of 1 mm was obtained.

  At this time, the viscosity and refractive index of the film-forming stock solution 1 serving as the membrane substrate of the porous membrane are 59000 to 79000 cP (69000 ± 10000 cP (± 14%)), and the refractive index is 1.4325 to 1.4333 ( It was managed in the range of 1.4329 ± 0.0004 (± 0.03%). In addition, the viscosity and refractive index were extracted from the dissolver after completion of dissolution of the film-forming stock solution 1, and batch measurement was performed. Various physical properties of the porous hollow fiber membrane produced by managing the membrane-forming stock solution as described above are as shown in Table 2, and those satisfying predetermined performance such as water permeability and bubble point were obtained.

<Comparative Example 1>
As a result of film formation in the same manner as in Example 2 except that the viscosity and refractive index of the film-forming stock solution 1 serving as the membrane substrate of the porous film were not controlled, the fractionation performance was inferior in a certain production lot (low A porous hollow fiber membrane (bubble point) was obtained. Table 2 shows the physical properties of the obtained porous hollow fiber membrane.
The viscosity and refractive index of the film-forming stock solution of this production lot were measured. As a result, the refractive index variation was small (approximately 0.03% smaller than the standard value), but the viscosity variation was large (approximately 40% smaller than the standard value), and the composition abnormality of the film forming stock solution was confirmed. Was suggested.

Claims (8)

A method for managing a film-forming stock solution, wherein the composition fluctuation of a film-forming stock solution composed of a dope in which two or more kinds of polymers are dissolved is specified from changes in viscosity and refractive index. The method for managing a film-forming stock solution according to claim 1, wherein the viscosity measurement accuracy is within ± 500 cP. The method for managing a film-forming stock solution according to claim 1 or 2, wherein the measurement accuracy of the refractive index is within ± 0.0002. The manufacturing method of the porous membrane which wet-forms using the film-forming stock solution managed by the method in any one of Claims 1-3. The manufacturing method of the porous membrane of Claim 4 using the film forming stock solution in which the polymer which consists of a polyvinylidene fluoride and / or a polyvinylidene fluoride unit and another monomer unit melt | dissolved. The method for producing a porous film according to claim 4 or 5, wherein a film-forming stock solution in which polyvinylpyrrolidone is dissolved is used. The method for producing a porous membrane according to any one of claims 4 to 6, wherein the fluctuation range of the viscosity of the membrane-forming stock solution is within ± 22%. The method for producing a porous film according to any one of claims 4 to 7, wherein the fluctuation range of the refractive index of the film-forming stock solution is within ± 0.07%.