JP2000042384A - Manufacturing method of sheet-like separation membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a sheet-like separation membrane having excellent separation performance free from membrane defects at a high speed and industrially stable continuously. SOLUTION: The present invention relates to a sheet in which a film-forming solution is applied on a porous substrate supported and conveyed by a rotating backing roll, and then the porous substrate is treated with a coagulating liquid to coagulate the sheet. The backing roll surface is coated with a fluororesin, and the discharge direction of the film forming solution is 45 ± 10 degrees with respect to a tangent passing through a coating position on the outer peripheral surface of the backing roll. Is applied by a die coater provided with a slit and a wiping edge in the range of (1).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a sheet-like separation membrane. More specifically, the present invention relates to a method for producing a sheet-like separation membrane which can be suitably used as a porous separation membrane such as an ultrafiltration membrane and a microfiltration membrane, or a support membrane for a reverse osmosis membrane.

[0002]

2. Description of the Related Art Separation membranes such as ultrafiltration membranes and microfiltration membranes are widely used in various fields such as production of ultrapure water, purification, concentration, sterilization, treatment of industrial wastewater and domestic wastewater in the pharmaceutical and food industries. Used. These separation membranes have various shapes such as a tubular shape, a hollow fiber shape, and a sheet shape. Of these, sheet-like separation membranes reinforced with a porous substrate such as woven or non-woven fabric can be formed even if the strength of the membrane material itself is low, so that cellulose acetate, polysulfone, polyacrylonitrile, ethylene vinyl alcohol Sheet-shaped separation membranes (porous separation membranes) using various membrane materials such as copolymers, polyvinyl chloride, polyamide, and polyimide are manufactured, and are used as modules of spiral type, plate & frame type, rotating flat type, etc. It is incorporated and used in a wide range of fields. Further, reverse osmosis membranes using the porous separation membrane thus obtained as a support membrane are also widely used.

[0003] The sheet-like separation membrane is usually manufactured by a film-forming method called a wet method or a dry-wet method. That is, a predetermined polymer is dissolved in a solvent, and a solution to which an additive such as a non-solvent or a swelling agent is added as required is applied or impregnated on a porous substrate. Then, if necessary, a part of the solvent is evaporated in the air, and at the same time, microphase separation is caused on the surface of the liquid film by the moisture in the atmosphere, and the sheet is further immersed in a coagulation bath to obtain a sheet-like separation membrane.

In such a method for producing a separation membrane, in order to apply a membrane-forming solution to a porous substrate, the porous substrate is supported by a backing roll, and an appropriate coater such as a fountain coater, a knife coater, or a comma coater is used. To apply. At this time, a part of the applied film forming solution leaches out to the back surface of the porous substrate such as a nonwoven fabric and adheres and accumulates on the surface of the backing roll, thereby causing bubbles, pinholes, streaks, thickness unevenness, etc. of the separation membrane. It may cause defects or cause a cutting accident of the substrate.

In order to solve such problems, conventionally, the density of a porous substrate is increased, the viscosity of a film-forming solution is increased, a film or the like is laminated on the back surface of the substrate, and the film is peeled off after the film is formed. Take measures such as applying the film forming solution without rotating the backing roll, and peeling the base material from the backing roll surface before the film forming solution leaches to the back surface of the base material by forming the film at high speed. However, none of these methods has yet achieved a sufficient effect.

That is, in the above-mentioned manufacturing method, the adhesive strength between the membrane and the substrate is weak, and the membrane is easily peeled off, and the water permeability is apt to be lowered. Further, in the production method, troubles due to displacement of the base material and the film or generation of wrinkles are likely to occur, and the film forming process becomes complicated and the cost increases.
In the production method, a predetermined effect can be obtained if a film of about several hundreds of meters is formed.However, in the case of a film of 1,000 m or more, a film-forming solution that has leached near the boundary surface where the substrate is separated from the backing roll accumulates, Furthermore, the above-mentioned defects and troubles are caused by gradually solidifying due to moisture in the air. In addition, while the method of manufacture is the most effective and efficient,
In general wet film forming, the coating thickness is 100 to 200 μm, which is a thick film coating, and the viscosity of the film forming solution is generally 1 to 300.
Because of poise and medium-high viscosity, bubbles are easily entrained in the film-forming solution, and the film-forming speed is limited to about 10 m / min, which is not a practical solution.

[0007]

SUMMARY OF THE INVENTION An object of the present invention has been made in view of the above-mentioned problems of the prior art, and a sheet-like separation membrane free from membrane defects is industrially stably and continuously produced. It is to provide a way to do it. In order to solve such a problem, the present inventors have made intensive studies, and as a result, have limited the application conditions of the film forming solution on the backing roll and performed the surface treatment of the backing roll, thereby leaching and adhering the film forming solution. With the knowledge that a sheet-like separation membrane having extremely few defects can be continuously and stably obtained, the present invention has been completed.

That is, according to the present invention, a film-forming solution is applied onto a porous substrate supported and transported by the outer periphery of a rotating backing roll, and then the porous substrate is treated with a coagulating liquid to coagulate. In a wet film forming method for a separation membrane, the backing roll surface is coated with a fluororesin, and the discharge direction of the film forming solution is 45 ± 10 degrees with respect to a tangent passing through a coating position on the outer peripheral surface of the backing roll. An object of the present invention is to provide a method for producing a sheet-like separation membrane, wherein the coating is performed by a die coater provided with a slit and a wiping edge.

[0009]

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1 is a schematic view showing a specific example of a production apparatus used in the method for producing a sheet-like separation membrane of the present invention. The porous base material 1 is unwound from the base material unwinding section 2 and is sent to the rotating backing roll 7 via the transport rolls 3, 4, 5, and 6. Here, the surface of the backing roll 7 is preferably coated with a fluororesin. As the porous substrate 1, any known woven fabric or nonwoven fabric conventionally used as a reinforcing material for a separation membrane may be used. As the backing roll 7 rotates, the porous substrate 1 moves while being supported by the outer peripheral surface thereof.

On the outer surface of the porous substrate 1 supported by the backing roll 7, a predetermined coater 8 for discharging a film forming solution is arranged to apply the film forming solution. Here, the application of the film forming solution by the coater 8 is performed when the discharge direction of the film forming solution is 45 ± 10 with respect to a tangent passing through the coating position on the outer peripheral surface of the backing roll.
Perform at an angle of degrees. Outside this range, stable film formation cannot be achieved.

FIG. 2 shows a specific example of a coater 8 preferably used for applying such a film forming solution.
1, a slit 22 having a predetermined discharge angle and a wiping edge 23 are provided. That is, when the film forming solution is applied using this die coater, the film forming solution is discharged from the slit 22 at an angle of approximately 45 degrees with respect to a tangent passing through the coating amount on the backing roll 7 and is applied onto the substrate 1. Is done. Next, the coating surface of the solution is smoothed by the wiping edge 23, and the coating 9 having a uniform thickness is formed on the substrate 1. Here, the width of the slit 22 can be adjusted by the plate 24, but is preferably 0.5 to 3 mm.
It is set considerably wider than a general die coater. The width of the gap between the wiping edge surface and the substrate surface can be appropriately adjusted depending on the coating thickness of the film forming solution, but is usually preferably 100 to 200 μm.

As described above, when a special die coater as shown in FIG. 2 is used, continuity can be achieved without adhering the film-forming solution to the backing roll surface at a film-forming speed of usually 20 m / min or more. Thus, it is possible to stably produce a sheet-like separation membrane having a very good membrane surface free from defects.

When the amount of the film-forming solution leached and adhered to the back surface of the substrate is large due to the properties of the film-forming solution and the characteristics of the substrate, it is preferable that the guide roll is also subjected to a fluorine coating treatment, more preferably. It is desirable to use a non-contact turn roll. Further, when there is a possibility that the solvent removal may become insufficient due to the high-speed film formation, it is desirable to perform warm water cleaning and suction cleaning using a vacuum roll.

The membrane-forming solution may be a solution obtained by dissolving a polymer known in the art for producing a separation membrane in a good solvent. The porous substrate 1 on which the film 9 formed by the film forming solution supplied by the coater 8 is formed is separated from the surface of the backing roll 7 and is introduced into a coagulation water tank 10 filled with a coagulation liquid to remove the solvent and coagulate to form a film. Is formed. Next, the porous base material is provided with a first washing tank 11 and a second washing tank 1.
2 and the residual solvent is washed away with water and finally taken up by the take-up unit 13.

[0015]

The present invention will be described more specifically with reference to the following examples.

Example 1 17 parts by weight of polysulfone (P3500, manufactured by Amoco) were added to 83 parts by weight of dimethylformamide, heated (80 ° C.) and dissolved, and then filtered and defoamed to prepare a membrane forming solution. . Polyester nonwoven fabric (basis weight 70 g / m ² , thickness 100 μm, width 500 mm) as porous substrate
Was used. Using the film-forming apparatus shown in FIG. 1 and the fountain coater shown in FIG.
The coating was performed on the nonwoven fabric under the conditions of a coating thickness of 130 μm, a width of 450 mm, and a film formation speed of 20 m / min.

Next, the film-forming solution was coagulated by immersion in a coagulation water bath (25 ° C.). Further, the film was introduced into a water washing tank, and the residual solvent in the film was washed with water and removed. Then, the film was wound up by a winding section to obtain a sheet-like separation membrane (thickness: 150 μm). When the amount of pure water permeated through the membrane was measured under the conditions of a pressure of 2 kgf / cm ² ,
m ³ / m ² · day. The film surface of this film had no defects observable to the naked eye, and was in an extremely good film surface state.
In addition, the number of pinhole-shaped latent defects (hereinafter, abbreviated as pinholes) of 50 μm or more that can be observed under transmitted light is 2 / m ²
And very few. Further, the bubble point of the film wetted with water was measured to confirm the presence / absence of a defect in detail. As a result, it was 10 kgf / cm ² or more, and it was confirmed that the film was substantially free from defects. In addition, about 2000m continuous under the above conditions
It was confirmed that there was no contamination on the backing roll surface due to leaching of the film forming solution from the nonwoven fabric, and that the film could be formed stably.

[Examples 2 to 4] A film was formed in the same manner as in Example 1 except that the film forming speed was changed to 50 m / min, 70 m / min and 100 m / min. A separation membrane was manufactured. As shown in Table 1, it was confirmed that a separation membrane having no defect and having an extremely good film surface and having no pinholes can be manufactured even at a film formation speed of about 10 times that in the related art.

Comparative Example 1 A sheet-like separation membrane was produced in the same manner as in Example 1, except that the coater was a commonly used fountain coater and the slit width was 0.3 mm. . As shown in Table 1, the membrane surface was good, but many pinholes were observed, and the bubble point was as low as ¹ to 5 kgf / cm ² , suggesting that the separation membrane was defective.

Comparative Example 2 A film was formed in the same manner as in Example 1 except that the backing roll was a metal roll used in a normal film forming apparatus and the film forming speed was 5 m / min. A state separation membrane was manufactured. From the initial stage of film formation, a film forming solution leached from the nonwoven fabric adhered to the surface of the backing roll, and a film was formed on the back surface of the nonwoven fabric on the obtained separation membrane.

As shown in Table 1, the obtained separation membrane had numerous crater-like irregularities on the membrane surface, and many pinholes were observed. Therefore, the bubble point is 0.5kgf / cm
^It was as low as ² , suggesting that the separation membrane clearly contained defects. On the other hand, the amount of permeated water was low in spite of the influence of membranes formed on both sides of the nonwoven fabric or many defects.

[0022]

[Table 1] ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Film forming speed Number of pinholes Film surface state Bubble Point Pure water flow rate (m / min) (pieces / m ² ) (kgf / cm ² ) (m ³ / m ² · day) ━━━━━━━━━━━━━━━━━━━ ━━━━━━━━━━━━━━━━━ Example 1 20 2 good> 10 21 〃 250 3 good> 10 22 〃370 1 good> 10 21 ４ 4 1003 good> 10 23比較 Comparative Example 1 20 Many (> 400) Good 1 to 5 21 〃 25 Many (> 400) Many irregularities * 0.513 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ ━ Note) *: Crater-like unevenness Measurement pressure of pure water permeated water: 2 kgf / cm ²

[0023]

According to the method for producing a sheet-like separation membrane of the present invention, a film can be stably and continuously produced even with a low-density porous substrate, which has conventionally been difficult to produce. Since the film formation speed can be dramatically improved, it is possible to mass-produce a sheet-like separation membrane having excellent separation performance at low cost.

[Brief description of the drawings]

FIG. 1 is a schematic view showing one specific example of a membrane forming apparatus used in the method for producing a sheet-like separation membrane of the present invention.

FIG. 2 is a schematic view showing a specific example of a coater used for applying a film forming solution in the method for producing a sheet-like separation membrane of the present invention.

[Description of Signs] 1: Porous substrate 2: Substrate unwinding section 3, 4, 5, 6: Conveyance roll 7: Backing roll 8: Coater 9: Coating 10: Coagulation water tank 11: First washing tank 12: 2nd washing tank 13: Winding unit 21: Die body 22: Slit 23: Wiping edge 24: Plate

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D006 GA03 GA06 GA07 MA03 MA06 MA31 MC48X MC62X NA04 NA18 NA46 NA50 NA51 NA52 NA73 PA01 PB02 PC02 PC11 PC42 4D075 AC02 AC29 AC93 CA48 DA04 DA25 DC30 EA05

Claims (1)

[Claims] 1. A wet-type separation membrane in which a film-forming solution is applied on a porous substrate supported and conveyed by an outer periphery of a rotating backing roll, and then the porous substrate is treated with a coagulating liquid to coagulate. In the film forming method, the backing roll surface is coated with a fluororesin, and the discharge direction of the film forming solution is within a range of 45 ± 10 degrees with respect to a tangent passing through a coating position on the outer peripheral surface of the backing roll. A method for producing a sheet-like separation membrane, wherein the coating is performed by a die coater provided with a wiping edge.