JPH0318491B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing pleated modules. BACKGROUND ART Reverse osmosis, ultrafiltration, precision filtration, and other techniques are well known as techniques for treating liquids using semipermeable membranes for separation, and equipment is being introduced in various fields. By the way, the most important element that affects the performance of this processing equipment is the semipermeable membrane, which is a membrane-forming liquid (dope) in which a polymer substance is dissolved in a solvent and a swelling agent, and is used to coat a membrane such as a woven or non-woven fabric. Coating it on a support or spinning it into a hollow fiber using a double-hole spinneret,
A common method is to form a film by exposing it to air for a certain period of time and then gelling it in a coagulating liquid. The flat membrane or hollow fiber membrane produced in this way can be used as a flat membrane laminated type, a glue-wound type, a hollow fiber type,
It is used by molding into pleated modules, which are improved versions of cylindrical and glue-wound modules. Among these various types of modules, pleated modules (such as Utility Model Publication No. 55-33608) have the advantage of low flow resistance on the permeate side due to the short leaf length of the semipermeable membrane. It is known that it is suitable for many ultra-passage modules and large modules. The conventional manufacturing method for this pleated module is roughly as follows. (b) Heat-treat the preserved flat membrane according to the required grade. (b) Cut to a certain length. (c) The film is processed into pleated membranes using a pleating machine. (d) Handle the peaks and valleys of the pleats to set the crease. (e) Glue it to the square water collection pipe with adhesive. (f) Wrap the outer circumference with glass fiber impregnated with resin. FIG. 1 is a schematic diagram showing a part of the cross section of a membrane pleated by this manufacturing procedure, in which 1-1 is a support fabric such as polyester woven fabric, 2-2 is a semipermeable membrane, 3-3 is a spacer, A-a' is a pleat crest, and b is a pleat trough. Mountain part a- of pleated membrane in Fig. 1
In actual membranes, a' and valleys b are bent at acute angles due to handling, so when the membrane is observed under an electron microscope, minute cracks may be found in some areas. Since these cracks are only a small portion of the module's total membrane area and are only in the surface layer of the membrane, their effect on performance can be ignored in most cases, but water quality requirements have recently become particularly strict in some applications. It has become impossible to ignore it. The inventors of the present invention have arrived at the present invention as a result of intensive studies aimed at eliminating these slight cracks. The contents of the present invention will be explained in detail below. As mentioned above, when manufacturing pleated modules, the conventional method is to heat-treat a flat membrane, cut it, and apply it to a pleating machine to form pleats.The flat membrane used at this time has a moisture content of 40 to 85% Since it is in a gelatinous state, it appears to have considerable plasticity at first glance. Therefore, even when pleating is performed as described above, it appears that the pleats are formed without any problems from a macroscopic perspective, but the plasticity of the parts that undergo large deformations, such as the peaks and valleys of the pleated film, is poor. This will not be sufficient and will result in the minute cracks mentioned above. By the way, the flat membrane used for manufacturing this pleated module is manufactured through the following steps. That is, (a) a dope for casting is prepared by dissolving a polymer serving as a membrane material in a mixture of a solvent and a swelling agent. (b) After degassing the dope, it is cast onto a woven or nonwoven fabric in a constant casting atmosphere to a thickness of about 50 to 200 μm. (c) This is immersed in water for 30 minutes or more to dissolve the solvent and swelling agent into the water and form a hydrous gel-like film. (iv) This gel-like film is usually stored in a separate container of storage water (formalin water, etc.). During this film forming process, the solvent and swelling agent remain in the film and the film has sufficient plasticity only up to the middle of (c) above, and only traces remain at the pleating stage. It is normal for it to be stale. Therefore, the present inventors used a pleat folding machine to pleat the membrane in which the solvent and swelling agent remained in the membrane, that is, in the middle of the above (c), and then performed a heat treatment to set the grade. I tried that. As a result, it was possible to improve the inherent separation characteristics of the membrane and to obtain a pleated membrane without minute cracks in the peaks and valleys as shown in the photograph in FIG. The photograph in FIG. 3 shows the cracks in the peaks of a pleated membrane produced by the conventional method to which the method of the present invention is not applied. Note that in order to create a state in which the solvent remains in the membrane, there is a method of adjusting the immersion time in water after casting, but with this method, the concentration of the solvent and swelling agent in the membrane can be adjusted. Due to the difficulty of manufacturing and the complexity of managing the series of module manufacturing processes,
It is preferable to use the following method. In other words, a membrane in which almost no solvent or swelling agent is present is immersed in a storage solution containing a certain concentration of solvent or swelling agent, and then stored. This is a method of containing. According to this method, it is possible to arbitrarily control the concentration of the solvent and swelling agent in the membrane, and it is also possible to subject the membrane to the pleating process at any time. The total concentration of the solvent and swelling agent in the membrane used in the method of the present invention is 0.01 to 10%, preferably 0.1 to 5.0%. In addition, any type of solvent to be used can be used, as it has a plasticizing effect, as long as it dissolves the film. It would be safe to use the same swelling agent. It goes without saying that the present invention is applicable to any membrane material. Next, the effects of the present invention will be explained using Examples and Comparative Examples. Example 1 (a) A flat membrane made of cellulose acetate was prepared by the method described in Example 2 of Japanese Patent Publication No. 52-14235. (b) Cut the flat membrane created in (b) to a certain size,
It was immersed in a 3% formaldehyde aqueous solution (preservation solution) containing 1.0% acetone and 0.5% dioxane for 1 hour to impregnate it with acetone and dioxane. (c) The film of (b) was subjected to a pleating process using a pleating machine. (d) Place the pleated membrane created in (c) in warm water at 80℃ for 15 minutes.
After being heated for several minutes, it was attached to a vinyl chloride water collection pipe with adhesive. (e) The outer periphery was wrapped with resin-impregnated glass fiber filament and solidified. (F) The performance of two pleated membrane modules of the present invention, each having a membrane area of 6 m ² and having a diameter of 4 inches, prepared by the above method was measured under the following conditions.
I got a result like 1. Performance measurement solution: Salt is dissolved in ion-exchange resin treated water to a concentration of 3500 ppm, and the number of bacteria is 1x.
10 ³ pieces/ml, liquid with pyrogenic substance 100ng/ml Pressure: 40Kg/cm ² Water temperature: 25℃ Liquid feeding amount: 1m ³ /h

[Table] In addition, the measurement of salt concentration is converted from electrical conductivity,
The number of bacteria was determined by the direct counting method after culturing in a standard perspective medium, and the concentration of pyrogenic substances was determined by the pyrodic method. Comparative Example 1 Except that (b) and (d) in Example 1 were not carried out, and immediately after carrying out (b), the membrane was cut into the same membrane area as in Example 1 and then heat-treated in 80°C hot water for 15 minutes. The same procedure as in Example 1 was carried out, and the results shown in Table 1 were obtained. From the above results, the method of the present invention does not change the water permeation rate, bacteria removal rate, and pyrogenic substance removal rate, but
There was a large difference in the salt removal rate, and it is clear that the present invention produced an effect that was consistent with the observation results of the photographs in Figures 2 and 3. Example 2 (a) A flat membrane made of modified polyacrylonitrile was prepared with reference to Example 1 of Japanese Patent Publication No. 49-122479. (b) Cut the flat membrane created in (b) to a certain size,
DMF by immersion in a 3% formaldehyde aqueous solution containing 2.0% DMF and 0.5% dioxane for 1 hour.
Impregnated with dioxane. (c) The film of (b) was subjected to a pleating process using a pleating machine. (d) The pleated membrane prepared in (c) was heat-treated in 70°C hot water and then adhered to the water collection pipe with adhesive. (e) The outer periphery was wrapped with resin-impregnated glass fiber filament and solidified. (F) The performance of two pleated membrane modules of the present invention, each having a membrane area of 6 m ² and having a diameter of 4 inches, prepared by the above method was measured under the following conditions, and the results shown in Table 2 were obtained. Performance measurement solution: Dextran T-70 dissolved in ion exchange resin treated water to a concentration of 1000 ppm, bacterial count: 1 x ¹⁰³ /ml, pyrogenic substance: 100n
Liquid pressure with g/ml: 5Kg/cm ² Water temperature: 25℃ Liquid feeding amount: 1m ³ /h

[Table] Comparative Example 2 After carrying out (a) without carrying out (b) and (d) in Example 2, the membrane was cut to the same area as in Example 2 and then heated at 70°C.
The same procedure as in Example 2 was carried out except that the sample was heat-treated in warm water for 15 minutes, and the results shown in Table 2 were obtained. From the above results, even in the conventional module, the number of bacteria in the permeated water was 0 cells/ml, and the pyrogenic substance concentration was the same as the present invention's <0.01ng/ml, so it was found that the pyrogenic substance was generated in the conventional module. It is clear that the fissures in the pleat ridges are not hole-like fissures penetrating in the film thickness direction, but only in the membrane surface.

[Brief explanation of the drawing]

Figure 1 is an enlarged schematic diagram of the pleat ridges of a pleated membrane, Figure 2 is a 300x magnified electron micrograph of the fissures in the crests of a pleated membrane manufactured by the conventional method, and Figure
3 is the peak part of the pleated membrane manufactured according to the present invention.
This is an electron micrograph magnified 300 times.

Claims (1)

[Claims] 1. When processing a separation semipermeable membrane into a module, it is possible to process the membrane with the solvent and swelling agent remaining in the membrane after membrane formation, or to process the membrane without any residual solvent or swelling agent. It is immersed in a swelling agent aqueous solution to impregnate the solvent and swelling agent, and the total content of the solvent and swelling agent is 0.01 to 10% with respect to the membrane material.
A method for manufacturing a module, which comprises molding the semipermeable membrane in a state where it is imparted with plasticity. 2. The method for manufacturing a module according to claim 1, which comprises performing a heat treatment at a temperature of 50 to 90°C after forming the separation semipermeable membrane.