JP2005169960A - Wet coagulation molding apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an effective method for washing an endless belt and a coagulation process for reducing the amount of waste liquid in a wet coagulation molding process for a thin film-shaped article using the endless belt as a substrate. <P>SOLUTION: Part of the coagulation liquid of the thin film-shaped article is extracted, and the pretreated coagulation liquid is made to flow down on the endless belt, so that the washing of the belt and the control of a coagulation liquid state are materialized at the same time. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to a method and apparatus for wet coagulation molding of a polymeric porous material suitable for a base material of a thin film composite material. Among the apparatuses using an endless belt as a molded substrate, the substrate is coagulated with a molded product. The present invention relates to a wet coagulation molding method and apparatus in an apparatus introduced into the company.

  Conventionally, as a method for producing a sheet-like polymer porous material, 1) a method in which an inorganic salt powder is kneaded into a thermoplastic polymer and formed into a thin film, and then the inorganic salt is dissolved and extracted with a solvent. A method of physically creating small pores by stretching a thin film obtained by kneading 3), 3) making a polymer solution dissolved in a solvent (solvent) into a thin film, having compatibility with the solvent and the polymer A method is known in which a polymer material is agglomerated by bringing it into contact with another solvent (non-solvent) that does not dissolve the material and extracting and replacing the original solvent. However, in the methods 1) and 2), it is difficult to obtain a porous sheet having a fine pore size because the size pore size of the powder of inorganic salt or the like is restricted. As a method for obtaining a sheet, the method 3) is widely used.

  As an example of application by the method 3) above, fuel cells that have been attracting attention as a new power generation technology that is excellent in energy efficiency and environmental performance in recent years, especially polymer electrolyte fuel cell applications using polymer solid electrolyte membranes The development is expected. Generally, proton-conducting ion exchange resin membranes are used for polymer solid electrolyte membranes. However, in addition to proton conductivity, characteristics such as fuel permeation deterrence and mechanical strength to prevent hydrogen permeation of fuel are required. is there. As such a polymer solid electrolyte membrane, for example, a perfluorocarbon sulfonic acid polymer membrane into which a sulfonic acid group is introduced as represented by Nafion (trade name) manufactured by DuPont, USA is known.

  However, attempts have been made to reduce the film thickness as one of the measures for higher output and higher efficiency of the polymer electrolyte fuel cell. To reduce. As a result, it becomes difficult to realize an integrated manufacturing process of the polymer solid electrolyte membrane and the electrode. In addition, the dimensional change of the film is caused by fluctuations in heat and moisture content during power generation. In this case, there arises a problem that the polymer solid electrolyte membrane and the electrode are peeled off to deteriorate the power generation characteristics. Furthermore, reducing the film thickness has a problem in that the fuel permeation deterrence is lowered, leading to a decrease in electromotive force and a decrease in fuel utilization efficiency.

  Therefore, studies have been actively conducted to impregnate and composite a perfluorocarbon sulfonic acid polymer into a porous material in order to increase mechanical strength. In order to realize it as a composite material, it is very important that the porous substrate can be produced industrially stably and at a low cost.

  As a method for forming a thin film, in addition to a film forming method called a casting method in which a polymer solution is spread on a substrate using a doctor blade or the like, a method of extruding from a linear slit die or a circumferential slit die Any method of forming a solution into a film, such as a blow extrusion method, a sandwich method in which a polymer solution sandwiched between two substrates is pressed with a roller, or a spin coating method in which a dope is dropped on a rotating substrate and the substrate is rotated. Can be used.

  However, as an actual production process, a casting method using an endless belt as a molded substrate is widely used as a method that is relatively inexpensive and simple in terms of maintenance.

  A wet coagulation molding apparatus using the endless substrate is generally solidified by contact with a coagulation liquid after forming a solution. Usually, since the molded product is difficult to peel before solidification, the endless substrate is often guided into the coagulation tank together with the molded product and peeled off. Or after coagulation | solidification is advanced by spraying a coagulating liquid on an endless board | substrate, it is guide | induced into a water-washing tank with an endless board | substrate. In order to use the peeled endless substrate again as a molded substrate, it is necessary to clean and remove the remaining material of the molded product and the coagulating liquid, and a cleaning device is provided on the return path side of the endless belt.

  As a conventional endless belt cleaning device, scraper 20 is brought into contact with endless belt 10 as shown in FIG. 1 to scrape off deposits, or cleaning liquid is sprayed from nozzles onto endless belt as shown in FIG. After the deposits are washed off, a method of removing the adhering cleaning solution using the scraper 20 or the water absorption roll 21 alone or in combination is employed.

  The method of scraping off the deposit on the endless belt using a scraper is simple, but since the removal of the deposit is not complete, the arrangement of multiple stages of scrapers as described in Patent Document 1 As described in Patent Document 2, the scraper is disposed obliquely with respect to the direction of travel of the endless belt, thereby reducing the resistance of scraping of the deposit, and the retention of the deposit and the adhesion between the scraper and the endless belt. A method for improving the performance is described.

  The above-described method using a scraper, when an endless belt is used for transporting ores, foods, etc., simply scrapes the adhering portion, and the influence of frictional scratches due to contact of the scraper with the endless belt is not regarded as important. In the case of using the porous substrate molding apparatus as in the present invention, if there is a frictional flaw, the porosity and thickness unevenness of the porous material will be directly affected, which is not preferable in terms of product quality control.

Further, as shown in FIG. 3, a part of the conveyor belt 10 is bent by the guide roll 32 so as to be immersed in the cleaning tank 31, and the deposits are effectively removed by the cleaning liquid jet nozzle 34 without causing abrasion damage to the endless belt. A method that can be removed is described in Patent Document 3.
JP-A-7-215443 (pages 1 to 4 etc.) JP 2001-114417 (pages 1 to 6 etc.) Japanese Patent Laid-Open No. 7-277481 (pages 1 to 4 etc.)

  However, in the above method, at least one guide roll 32 is required at each of the tank inlet and outlet to guide the endless belt into the cleaning tank, and the guide roll contacts the surface of the endless belt. That is, although it is effective in peeling off the deposits in the cleaning tank, there is a possibility that the endless belt may be damaged when the surface of the endless belt comes into contact with the guide roll before removing the deposits. For this reason, it cannot be said that it is preferable in quality control to apply the above-mentioned method to a porous material molding apparatus.

  Furthermore, since the cleaning liquid becomes dirty over time, the removed deposits float or precipitate unless the cleaning liquid is frequently replaced. For the former, a reflow prevention effect is aimed at by giving a forced flow by the cleaning liquid injection nozzle 34 or the like. For the latter, precipitation is prevented by applying an upward flow by the cleaning liquid injection nozzle 35 installed in the cleaning tank in order to suppress precipitation. However, both are partial removal of deposits and are not complete. Moreover, not only a dead space is generated by installing the cleaning liquid injection nozzle 35 in the tank, but also maintainability is impaired.

  Furthermore, the state in which the structure as an endless belt is partially bent causes a reduction in the life of the belt due to repeated stress, which is disadvantageous in terms of maintenance when considering maintenance and belt replacement.

  In addition, an increase in the belt circumference increases the technical difficulty due to meandering adjustment, tension adjustment, etc., and the equipment becomes complicated.

  Then, waste liquid is generated by using the cleaning liquid, and the problem of waste liquid treatment cannot be avoided. Usually, in the process of obtaining a thin film by wet coagulation molding, a solvent that dissolves the polymer, a coagulation solvent, or a chemical solution for washing water is used. In many cases, the adhering liquid is mixed into the cleaning liquid by being immersed in the cleaning liquid, and the cleaning liquid cannot be drained as it is.

  On the other hand, the temperature, concentration, etc. of the liquid in the coagulation tank through which the molded product passes along with the substrate or the molded product washing tank change over time. When this change over time is used as a coagulation tank, the influence on the coagulation process, such as the pore diameter and the porosity of the porous membrane, is large. Moreover, even when used as a cleaning tank, there is a possibility that the cleaning speed may be affected. In some cases, the cleaning time is insufficient, resulting in poor quality. As a result, production will be reduced by reducing the line speed, or new capital investment will be required.

  With respect to the temperature, it is necessary to adjust the temperature with a heating medium with a tank as a jacket structure, or to adjust the temperature with an external temperature controller by directly extracting the coagulation liquid. Concerning the concentration, it is necessary to add a concentration-adjusting liquid directly to the coagulation tank and simultaneously drain the coagulating solution, or provide a circulation line and add and adjust the concentration-adjusting liquid there. In either case, the facilities are large.

  As described above, separately installing the belt cleaning tank and the coagulation tank (or the cleaning tank) not only leads to an increase in equipment cost, but also causes a problem of waste liquid treatment.

  The present invention has been made in view of the above circumstances, and by extracting a part of the coagulation liquid and pre-treating the coagulation liquid onto the endless belt, the endless belt is cleaned, and the cleaning liquid is supplied to the coagulation tank. An object of the present invention is to provide a wet coagulation molding apparatus capable of controlling the state of the concentration, temperature, pH, and the like of the coagulating liquid by returning and circulating.

As a result of intensive studies to solve the above problems, the present inventors have finally completed the present invention.
That is, the present invention
(1) In the process of wet coagulation molding of a thin film using an endless belt as a substrate, the endless belt is washed, and at the same time, at least one of the concentration, temperature and hydrogen ion concentration (pH) of the coagulating liquid. A wet coagulation molding apparatus characterized by performing the above control.
(2) A wet coagulation molding apparatus characterized in that at least a part of the endless belt is immersed in the coagulation tank, and the coagulation liquid extracted from the coagulation tank is allowed to flow onto the endless belt.
(3) A wet coagulation molding apparatus characterized in that the temperature of the coagulation liquid is adjusted in the coagulation liquid circulation line, and the temperature of the entire liquid in the coagulation tank is controlled by circulation of the coagulation liquid.
(4) A wet coagulation molding apparatus characterized in that the pH is adjusted by adding a chemical in the coagulation liquid circulation line.
It is.

  By using the wet coagulation molding apparatus according to the present invention, it is possible to achieve both the cleaning of the endless belt, which is a belt molding substrate, and the control of the state of the coagulation liquid. As a result, the service life of the equipment can be extended, the cost of equipment can be reduced by combining the belt cleaning tank and the coagulation tank (or cleaning tank), and the amount of waste liquid can be reduced.

  The form of the thin film used in the present invention is not limited as long as it can be molded by casting a polymer in a solution on a substrate. For example, cellulose acetate, polysulfone, polycarbonate, polyvinyl alcohol, polyamide, Polyimide, polyvinylidene fluoride, polybenzoxazole, polybenzimidazole, precursors thereof, and mixtures thereof are suitable for base materials for composite membranes as polymer solid electrolyte membranes for polymer electrolyte fuel cells. The material is a polybenzazole polymer. Any solvent can be used as long as it can be removed by wet coagulation, and examples thereof include methanesulfonic acid, dimethylsulfuric acid, polyphosphoric acid, sulfuric acid, trifluoroacetic acid, or a combination of these solvents. A mixed solvent can also be used. Of these, methanesulfonic acid and polyphosphoric acid are particularly preferred.

  In the present invention, in the coagulation of an isotropic polybenzazole-based polymer solution, in addition to water vapor, methanesulfonic acid aqueous solution, phosphoric acid aqueous solution, glycerin aqueous solution, inorganic salt aqueous solution such as magnesium chloride aqueous solution, non-solvent (poor The solvent surface and the internal structure were controlled by selecting the solvent) and the solidification conditions. Particularly preferred solidification means are a method of solidifying by contacting with water vapor, a method of solidifying by contacting water vapor for a short time in the initial stage of solidification, then a method of solidifying by contacting with water, a method of solidifying by contacting with an aqueous methanesulfonic acid solution, etc. is there.

  As a method for forming a thin film, in addition to a film forming method called a casting method in which a polymer solution is spread on a substrate using a doctor blade or the like, a method of extruding from a linear slit die or a circumferential slit die Any method of forming a solution into a film, such as a blow extrusion method, a sandwich method in which a polymer solution sandwiched between two substrates is pressed with a roller, or a spin coating method in which a dope is dropped on a rotating substrate and the substrate is rotated. Can be used. Preferred film forming methods suitable for the purpose of the present invention are the casting method and the sandwich method. For the substrate of the casting method and the substrate of the sandwich method, various porous materials are preferably used as the substrate for the purpose of controlling the void structure of the support film during solidification, in addition to a glass plate, a metal plate, a resin film, etc. be able to. In addition, the substrate can be easily applied to a continuous process by one-pass or endless.

  In the present invention, in the molding apparatus using the endless belt, a part of the coagulation liquid is extracted from the coagulation tank by a pump and is allowed to flow down from the coagulation tank to the outside of the coagulation tank. The remaining material of the molded product can be washed away. Thereafter, the coagulating liquid is drained with a scraper made of polytetrafluoroethylenete. Moreover, when liquid draining is insufficient, drying can be completed by blowing air or heating air.

  The place for extracting the coagulation liquid from the coagulation tank is appropriately selected depending on the specific gravity of the solvent and the apparatus configuration. However, when the specific gravity of the solvent is heavy relative to the coagulation liquid, it is desirable to extract from the lower surface of the coagulation tank. On the other hand, when the specific gravity of the solvent is lighter than the coagulation liquid, it is more efficient to extract it from the upper part of the coagulation tank.

  As a method for circulating the coagulating liquid, a method of circulating in the counterflow direction with respect to the substrate moving direction (withdrawing from the downstream side and flowing down from the upstream side) is preferable. The amount of circulation is selected each time depending on the system conditions, but is preferably 2 to 20 times per hour for the capacity of the coagulated water tank. In addition, in the case of the amount of circulation which satisfy | fills the frequency | count of replacement | exchange 5 to 8 times per hour, it can circulate, suppressing the fluctuation | variation in the water level of a liquid level, and is more preferable.

  The extracted coagulating liquid may be acidic or alkaline due to the solvent of the coagulated molded product, and particularly in the case of the application example of the present invention, since the coagulating liquid is acidic, it flows down to the endless belt as it is. This will accelerate the corrosion of the metal endless belt. Therefore, after adjusting the pH of the extracted coagulation liquid with an appropriate agent, the acid coagulation liquid adhering to the belt surface can be washed away efficiently by flowing down the belt, and as a result, the life of the belt can be improved. it can. In addition, as a hydrogen ion concentration for suppressing corrosion, it is 3-9 in pH, Preferably, it is 5-7 in pH.

  In addition, by filtering the extracted coagulation liquid using the pump discharge pressure before flowing down onto the belt, it is possible to prevent the residue of the molded product in the coagulation tank and foreign matter such as contamination from reattaching to the belt. be able to. As a result of the circulation of the liquid in the tank, the waste in the entire coagulation tank can be removed. The material of the endless belt should be selected as appropriate depending on the properties of the coagulation liquid, but a metal mesh made of SUS316L and having an opening of about 40 μm is suitable.

  Also, before the extracted coagulated liquid flows down on the belt, the temperature of the coagulated liquid flowing down by the heat exchanger is raised by 5 to 50 ° C., preferably 20 to 50 ° C., thereby removing the deposits from the belt. Can be improved. Moreover, the temperature fluctuation with time in the coagulation tank can be relaxed.

  As for the flow-down method of the coagulation liquid for washing off the deposits, it is possible to promote the peeling of the deposits by increasing the pressure with a pump and forcibly spraying it. It is not preferable because there is a risk of corrosion of workers and damage to workers. A method of smoothly flowing down on the belt in a laminar flow state and completely removing with a scraper is preferable. The amount of flow down onto the belt is appropriately determined by the system, but it is appropriate to secure a flow rate about three times as high as the linear velocity relative to the belt moving speed.

  Hereinafter, the present invention will be specifically described with reference to the drawings.

  4 and 5 are examples of diagrams showing the outline of the endless belt type molding apparatus of the present invention.

  Each part will be described in detail below. First, as shown in FIG. 4, a polymer 13 is continuously supplied onto a continuous substrate composed of a metal endless belt 10 and drums 11 and 12, and formed into a thin film with a constant thickness via a doctor blade 14. . After initial solidification by passing the humidification zone 15 provided on the moving steel belt, the solidification is completed and washed in the coagulation tank 16. Alternatively, after coagulation is completed in the humidification zone, cleaning may be performed in the coagulation tank 16. Further, the solidification may be performed by putting it in the coagulation tank 16 without a humidification zone immediately after molding.

  FIG. 5 is an example of an outline of an endless belt type molding apparatus configured such that the endless belt substrate 10 circumscribes a total of four rolls of the drums 11 and 12 and the guide rolls 26 (two).

  Next, the belt cleaning apparatus will be described with reference to FIG. The coagulation liquid is continuously extracted from the lower surface of the coagulation tank 16 by the pump 17 and is allowed to flow down from the nozzle 19 onto the endless belt 10 through the filtration device 18. The scraper 20 is used to peel off the deposits that could not be removed, and the coagulation liquid is scraped off. Furthermore, you may blow off coagulating liquid using the air blow nozzle 22 (not shown). Furthermore, after heating air with the heating apparatus 23 (not shown), you may air blow and complete drying.

  Further, the pH adjusting device 28, the heat exchanger 29, and the concentration adjusting liquid adding device 30 are used in any combination after the filtering device 18 to adjust the pH, temperature, and concentration of the circulating liquid.

  Examples of the present invention are shown below, but the present invention is not limited to these Examples.

Example 1
Methanesulfonic acid (purity 99.5% by weight) was added to a dope containing 14% by weight of a polyparaphenylene cis benzobisoxazole polymer with IV = 24 dL / g in polyphosphoric acid and diluted to obtain polyparaphenylene cisbenzobisoxazole. An isotropic solution with a concentration of 1% by weight was prepared. This solution was manufactured by Hastelloy (trade name) on an endless belt having a width of 400 mm, a circumferential length of 7000 mm, and a thickness of 0.5 mm with a doctor blade having a molding width of 300 mm and a clearance of 300 μm, and continuously at a temperature of 25 ° C. and a relative humidity. The 80% humidification zone was passed through with a residence time of 3 min. Subsequently, the molded product was introduced into a coagulation tank having a liquid temperature of 25 ° C. together with an endless belt to complete coagulation. The formed film was peeled off in a coagulation tank, washed with water and wound up. After the film is peeled off, the endless belt exits the coagulation tank and then flows down the coagulation liquid extracted from the lower part of the coagulation tank at 2 L / min to remove the molding residue and scrape the coagulation liquid with a polytetrafluoroethylene scraper. I took it.

Example 2
The same method as in Example 1 was used except that the material of the endless belt was SUS316.

Example 3
The method was the same as Example 1 except that the coagulation liquid extracted from the lower part of the coagulation tank was adjusted to pH 6 with sodium hydroxide and then flowed down onto the endless belt.

Example 4
The method was the same as Example 2 except that the coagulation liquid extracted from the lower part of the coagulation tank was adjusted to pH 6 with sodium hydroxide and then flowed down onto the endless belt.

Example 5
The same procedure as in Example 1 was performed, except that the coagulation liquid extracted from the lower part of the coagulation tank was treated with a filtration device using a wire mesh having a mesh size of 40 μm and then allowed to flow down onto an endless belt.

Example 6
The method was the same as Example 1 except that the coagulation liquid extracted from the lower part of the coagulation tank was adjusted to 40 ° C. with a heat exchanger and then allowed to flow down onto an endless belt.

<Corrosion rate>
The object (endless belt) before and after the test was weighed, and the weight loss was converted to the weight per unit area and unit time.

  In each of Examples 1 to 6, the adhesion residue of the solidified molded product could be neatly peeled off.

  In Example 4, in comparison with Example 2, as shown in Table 1, there was an effect of reducing the corrosion rate of the belt. That is, the life of the belt could be improved. However, in the comparison between Examples 1 and 3, since the material of the belt is Hastelloy (trade name) having corrosion resistance, the degree of corrosion was small and no difference was observed. Although it is desirable to use a material having high corrosion resistance as the material of the belt, in reality, the cost is very high, and the corrosion-resistant material is often difficult to obtain because it uses a rare metal. Therefore, it is preferable to use a general-purpose material as much as possible.

  In Example 5, it was possible to suppress the reattachment of the adhesion residue peeled off to the belt, and as a result, it was possible to suppress the accumulation of the adhering matter in the scraper and to improve the maintenance frequency to 1/3.

  In Example 6, as compared with Example 1, it was possible to confirm the effect of improving the peelability of the adhesion residue by improving the cleaning effect due to the temperature rise.

  Furthermore, since the dedicated tank cleaning tank and the coagulation tank (or cleaning tank) are combined, the need for a new cleaning liquid is eliminated, resulting in a reduction in the amount of waste liquid and a reduction in running cost. In addition, as the initial cost, no additional equipment such as cleaning liquid supply equipment and storage equipment is required, so that equipment costs can be reduced. Although the effect cannot be generally stated, in the case of the present embodiment, it corresponds to about 5 to 10% of the entire equipment. The effect is even greater when running costs are included. As a result, the effect as a fuel cell application in which significant cost reduction is essential is great.

  Although described in the embodiments, the present invention is not limited to the above-mentioned examples as a matter of course, and can be carried out with appropriate modifications within a range that can be adapted to the above-mentioned purpose. Included in the technical scope.

  By using the wet coagulation molding apparatus of the present invention, there are advantages in terms of quality stabilization and low manufacturing costs in terms of continuous production of thin-film products, and it can be used in a wide range of application fields such as energy, food, and industrial materials. It is important to contribute to the industry.

Example of conventional endless belt cleaning mechanism Example of conventional endless belt cleaning mechanism Example of conventional endless belt cleaning mechanism An example of an overall outline of an endless belt forming apparatus according to the present invention An example of an overall outline of an endless belt forming apparatus according to the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 10: Endless belt 11: Drum 12: Drum 13: Polymer 14: Doctor blade 15: Humidification zone 16: Coagulation tank 17: Pump 18: Filtration apparatus 19: Nozzle 20: Scraper 21: Water absorption roll 22: Air blow nozzle 23: Heating apparatus 24: Winding machine 25: Belt drive motor 26: Guide roll 27: pH meter 28: pH adjusting device 29: Heat exchanger 30: Concentration adjusting liquid adding device 31: Washing tank 32: Guide roll 33: Guide roll 34: Cleaning liquid Injection nozzle 35: Cleaning liquid injection nozzle 36: Drain port

Claims (4)

In the process of wet coagulation molding of thin-film products using an endless belt as a substrate, the endless belt is cleaned, and at the same time, at least one of the concentration, temperature and hydrogen ion concentration (pH) of the coagulating liquid is controlled. Wet coagulation molding apparatus characterized by performing.   2. The wet coagulation molding apparatus according to claim 1, wherein at least a part of the endless belt is immersed in the coagulation tank, and the coagulation liquid extracted from the coagulation tank is allowed to flow down onto the endless belt.   3. The wet coagulation molding apparatus according to claim 1, wherein the temperature of the coagulation liquid is adjusted in the coagulation liquid circulation line, and the temperature of the entire liquid in the coagulation tank is controlled by circulation of the coagulation liquid.   4. The wet coagulation molding apparatus according to claim 1, wherein the pH is adjusted by adding a chemical in the coagulation liquid circulation line.

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