JPS6324111B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a tubular reinforced permeable membrane,
In particular, the present invention relates to a method for manufacturing a reinforced tubular permeable membrane for membrane separation operations that has high strength and is free from membrane defects.

Membrane separation operations using selectively permeable membranes such as ultrafiltration membranes and reverse osmosis membranes are already widely known, and are generally carried out by bringing the stock solution to be treated into contact with the membrane surface under pressure. In particular, in membrane treatment using reverse osmosis, the pressurizing force of the stock solution reaches several tens of kg/ ^cm2 , but as is well known, the thickness of the permeable membrane is 50 ~
Since the membrane itself has extremely low strength, with a thickness of only about 500μ, it is often used as a reinforced tubular membrane by using a nonwoven fabric tube as a reinforcing base material and forming a permeable membrane on its inner or outer surface.

In recent years, as membrane separation operations have been used in various fields, stricter physical and chemical properties have become required not only for the permeable membrane but also for the nonwoven fabric tube as a reinforcing base material. There is. For example, when alkali resistance is required, polyethylene or polypropylene nonwoven tubes are preferably used, but these have lower elastic modulus than polyester nonwoven fabrics and do not have sufficient compressive strength when used as nonwoven tubes. Therefore, when processing polyethylene or polypropylene nonwoven fabric into a tube as a permeable membrane reinforcing base material, a relatively thick nonwoven fabric with a thickness of 150 μm or more is preferably used.

Generally, a nonwoven fabric tube is made by winding a thermoplastic nonwoven fabric tape 1 in a spiral shape on a mandrel 2 while overlapping its side edges, as shown in FIGS. It is manufactured by heat welding under pressure using an ultrasonic horn 4. However, even if ultrasonic sealing is applied under sufficient pressure to eliminate the step difference in the overlapping portion 3, the joint portion 5 actually bends or bulges outward, as shown in FIG. 3, and caves in on the back side. are doing. This tendency is particularly noticeable when a thick nonwoven tape is used, or when a nonwoven tape made of rapidly melting polyethylene, polypropylene, or the like is used. The reason why the joint part of the overlapped part of the nonwoven tape is bent or raised is that immediately after the ultrasonic horn passes through the overlapped part, the overlapped part becomes flat due to the pressing force of the ultrasonic horn. Since the nonwoven fabric at the overlapped portion is still in a molten state, it will shrink and bend as it cools, causing the front surface to bulge and the back surface to cave in along the joint.

A tubular membrane using such a nonwoven fabric tube as a reinforcing base material has various drawbacks. For example, when a permeable membrane is formed on the inner surface of a nonwoven fabric pipe using a wet method, if there is a depression zone on the inner surface, air bubbles remain in the depression zone, resulting in membrane defects, and the film thickness becomes uneven. The membrane is easily damaged when large pressure is applied to the membrane surface.

The present invention was made to solve the various problems described above in manufacturing tubular membranes, and includes:
Using a non-woven fabric tape, a non-woven fabric tube with a flat surface without any protrusions or depressions in the overlapping portion is manufactured, and a film-forming liquid is applied to the inner or outer surface of the non-woven fabric tube,
The object of the present invention is to provide a method for manufacturing a tubular reinforced permeable membrane having excellent strength and no membrane defects by solidifying the membrane and forming the membrane by a so-called wet method.

The method for manufacturing a tubular reinforced permeable membrane according to the present invention involves overlapping the side edges of thermoplastic nonwoven fabric tapes having a thickness of 0.15 to 0.50 mm and an apparent porosity of 0.20 to 0.75, thermally welding this overlapping portion, and then While the welded part is in a fluid state under stress, the heat welded part is cooled while being pressed with a press plate to produce a nonwoven fabric tube in which the thickness of the joined part is 120% or less of the thickness of the nonwoven fabric tape, and It is characterized in that a membrane-forming liquid is applied to the inner or outer surface of the nonwoven fabric tube and solidified to form a permeable membrane.

The means for thermal welding is not particularly limited, and for example, ordinary electric heating seals using nichrome wire, high frequency heating seals, ultrasonic seals, etc. can be employed, and preferably ultrasonic seals are employed. Therefore, the case of ultrasonic sealing will be explained below.

An example of the method of the present invention is illustrated in FIGS. 4 and 5. The nonwoven fabric tape 1 is wound spirally on a mandrel 2 with its side edges overlapping, and this overlapping portion 3 is thermally welded under pressure by an ultrasonic horn 4, and then this thermally welded portion is in a fluid state under stress. By cooling the heat-welded portion while pressing it with a press plate 6, a nonwoven fabric tube having a flat joint portion 5 as shown in FIG. 6 is obtained. In other words, the heat-welded part would contract and bend during the cooling process if it were not pressurized by the presser plate, but by cooling the heat-welded part while applying pressure with the presser plate, the heat-welded part can be forcibly bent. Cool while keeping it flat. Therefore, when the heat-welded part no longer has a fluid state under stress, cooling it while pressing it with a press plate has no effect.

As shown in FIG. 5, the push plate is a block with a rectangular cross section, and may be in line contact with the nonwoven fabric tube in one line, and as shown in FIG. 7, it has a groove with a V-shaped cross section. The block may have two or more lines in line contact with the nonwoven pipe, or the block may have grooves along the surface of the nonwoven pipe and have surface contact with the nonwoven pipe, as shown in FIG. It is sufficient that the heat-welded part after heat-welding can be cooled while being flatly pressurized. Furthermore, it is also possible to effectively cool the press plate by using a jacket type and allowing a cooling medium such as water to flow through the press plate.

The nonwoven fabric used in the present invention is polyester,
It is a nonwoven fabric made of a thermoplastic synthetic polymer such as polyamide, polyethylene, polypropylene, etc., and is particularly suitable for manufacturing pipes from a thick polyethylene or polypropylene nonwoven fabric as described above. The nonwoven fabric that can be suitably used in the method of the present invention has a thickness of 0.15 to 0.50 mm, preferably 0.18 to 0.35 mm. When the thickness is too small, the strength of the resulting nonwoven fabric tube is low;
This is because if it is too large, the stepped portion will be too high, making it difficult to obtain a nonwoven fabric tube with a flat joint. Further, when the basis weight of the nonwoven fabric is a (g/m ² ), the thickness is t (mm), and the density of the nonwoven fabric material polymer is ρ (g/cm ³ ), 1-(a/tρ)×10 ^- The apparent porosity defined by ³ is 0.20 to 0.75, preferably 0.25 to 0.60. Furthermore, the overlapping part of the side edges of the nonwoven tape has a width of 0.3 to 3
mm, preferably 0.5 to 2 mm. However, the nonwoven fabric used in the present invention is not limited to the above. Further, the nonwoven fabric can be made even stronger by stacking not only one layer but multiple layers.

According to the method of the present invention, as described above, it is possible to easily obtain a nonwoven fabric tube in which the bonded portion is substantially flat and the thickness of the bonded portion is 120% or less of the thickness of the nonwoven fabric tape. Therefore, when a permeable membrane is formed on the inner or outer surface of such a nonwoven fabric tube, the resulting reinforced permeable membrane has high strength and is free from membrane defects. Such a reinforced permeable membrane is used by being inserted into a porous support pipe such as a perforated stainless steel pipe or a porous FRP pipe, or used alone.

Examples of the present invention will be described below.

Example 1 A polypropylene nonwoven fabric with a thickness of 0.27 mm and an apparent porosity of 0.36 was made into a tape with a width of 27 mm, and this tape was spirally wound on a mandrel with a diameter of 12.0 mm with the width of the overlapping part being 1.5 mm, as shown in Fig. 8. As shown, after heat welding was performed at a speed of 4.0 m/min while pressing the overlapping parts with an ultrasonic horn with a frequency of 25 KHz,
Immediately, it was cooled while pressing a pressing plate to obtain a nonwoven fabric tube. The thickness of the joint of this nonwoven fabric tube was 0.29 mm, and the inner surface was almost flat.

Comparative Example 1 A nonwoven fabric tube was obtained in exactly the same manner as in Example 1 except that the press plate was not used. As shown in FIG. 3, the bonded portion of this nonwoven fabric tube was raised on the surface side, the height of the bump was 0.25 mm, and the thickness of the bonded portion including the raised height was 0.52 mm.

Example 2 A polyethylene nonwoven fabric with a thickness of 0.20 mm and an apparent porosity of 0.60 was made into a tape with a width of 27 mm, and this tape was spirally wound on a mandrel with a diameter of 12.2 mm with the width of the overlapping part being 1.0 mm. As shown, while pressing the overlapping part with an ultrasonic horn,
After heat welding was carried out at a speed of 10 minutes, it was immediately cooled while pressing a press plate. The resulting nonwoven fabric tube had a thickness of 0.20 mm at the joint, the same as the original nonwoven fabric tape, and the back surface of the joint was completely flat.

Comparative Example 2 A nonwoven fabric tube was obtained in exactly the same manner as in Example 2 except that the press plate was not used. The joint portion of this nonwoven fabric tube was bent toward the surface side as shown in FIG. 3, and the thickness of the joint portion including the raised portion was 0.27 mm.

Example 3 A nonwoven fabric tape for the inner layer was wound on a mandrel, and a nonwoven fabric tape for the outer layer was wound thereon, thereby manufacturing a nonwoven fabric tube by winding the tape in two layers at the same time.

That is, a polypropylene nonwoven fabric with a thickness of 0.17 mm and an apparent porosity of 0.52 is made into a tape with a width of 27 mm, and this tape is spirally wound as an inner layer on a mandrel with a diameter of 12 mm, with a width of 1.5 mm at the overlapping part, and an ultrasonic horn is applied. The overlapping portions were pressed and heat-welded, and immediately cooled by pressing a pressing plate in the method shown in FIG. On this polypropylene non-woven tape, polyethylene adhesive is applied in many dots to a thickness of 0.23 mm.
mm, apparent porosity 0.45, width 28 mm polypropylene non-woven tape as the outer layer, heated to 140°C and spirally wound to form an overlapping part of 1.2 mm wide, and press the overlapping part with an ultrasonic horn. heat welded while heating, immediately cooled by the method shown in Figure 8,
A nonwoven tube with two nonwoven layers was fabricated. The average thickness of this non-woven tube is
The diameter was 0.40 mm at the joint, and both the inner and outer surfaces were flat.

Example 4 In this example, a permeable membrane was formed on the inner surface of the nonwoven fabric tube obtained in each of the above Examples and Comparative Examples to produce a reinforced tubular membrane, and the bubble point or membrane properties after pressurization were evaluated.

Reinforced tubular membranes 1a and 1b 17 parts by weight of polysulfone (Udel polysulfone P-1700 manufactured by Union Carbide Co., Ltd.) and 83 parts by weight of N-methylpyrrolidone were added to the inner surface of the nonwoven fabric tube obtained in Example 1.
A reinforced tubular membrane 1a was produced by applying a membrane-forming solution consisting of parts by weight to a thickness of 200 μm, and then immersing it in ice water to solidify it. A polysulfone permeable membrane was formed on the inner surface of the nonwoven fabric tube obtained in Comparative Example 1 in exactly the same manner, and a reinforced tubular membrane 1 was obtained.
I made b.

Each reinforced tubular membrane was inserted into a perforated stainless steel tube with an inner diameter of 13.0 mm, and the inner pressure was increased to 10 Kg/cm ² while circulating water. Next, the reinforced tubular membrane was extracted from the stainless steel tube, one end of each was closed, and air was pressurized from the other end in water to measure the pressure at which bubbles were generated from the tube surface (bubble point).Membrane 1a
In the case of the membrane 1b, no bubbles were generated even at a pressure of 2.5 Kg/cm ² , whereas in the case of the membrane 1b, the pressure was 0.1 Kg/cm ² . After measuring the bubble point, we observed the joint in detail.
No abnormality was observed in the reinforced tubular membrane 1a, but cracks were found in the reinforced tubular membrane 1b.

Reinforced tubular membranes 2a and 2b A film-forming solution consisting of 25 parts by weight of cellulose acetate (E-3983 manufactured by Eastman Kodak), 30 parts by weight of formamide, and 45 parts by weight of acetone was applied to the inner surface of the nonwoven fabric tube obtained in Example 2. After coating 250μ, it is immersed in ice water to solidify to form a film, and then heat-treated by circulating 80℃ hot water inside the tube for 30 minutes to form a reinforced tubular membrane 2a.
was produced. A reinforced tubular membrane 2b was produced from the nonwoven fabric tube obtained in Comparative Example 2 in exactly the same manner.

Each reinforced tubular membrane was inserted into a porous FRP pipe with an inner diameter of 13.0 mm, and the pressure was 50 Kg/ while circulating water at a temperature of 25°C.
^cm2 for 30 min to consolidate the membrane, then 0.50 wt%
When a saline solution was supplied at a pressure of 42Kg/ ^cm2 ,
The reinforced tubular membrane 2a has a water permeability of 1.02 m ³ /m ² ·day and a salt removal rate of 90.3%, and the reinforced tubular membrane 2b has a water permeability of 1.50.
m ³ /m ² ·day, the salt removal rate was 65.3%.

Each of the reinforced tubular membranes subjected to the reverse osmosis experiment was immersed in water with one end closed, air was pressurized from the other end, and the bubble point was measured.
While the reinforced tubular membrane 2b had a pressure of 0.1 Kg/cm ² , no bubbles were generated in the reinforced tubular membrane 2a even under a pressure of 3.0 Kg/cm ² . After the valve point measurement, each tubular membrane was cut open and the inner surface was observed, and no abnormality was observed in the reinforced tubular membrane 2a.
In addition to cracks with a length of 4 to 5 mm, pinholes were observed in the reinforced tubular membrane 2b in areas containing air bubbles.

Reinforced Tubular Membrane 3a Using the nonwoven fabric tube obtained in Example 3, a polysulfone membrane was produced in exactly the same manner as in the case of the reinforced tubular membrane 1a. After pressurizing this reinforced tubular membrane 3a at a pressure of 10 Kg/cm ² for 2 hours while circulating water at 40° C., the valve point was measured and found to be 3.2 Kg/cm ² . Separately, the reinforcing tubular membrane 3a was inserted into a perforated stainless steel pipe with an inner diameter of 13.0 mm, and while water at 40°C was being circulated,
After pressurizing at a pressure of Kg/cm ² for 2 hours, the joint was closely observed, but no defects were observed.

[Brief explanation of drawings]

Fig. 1 is a front view showing a general manufacturing method for non-woven fabric pipes, Fig. 2 is a sectional view showing an example of thermal welding of overlapping parts, and Fig. 3 is a cross-sectional view showing an example of heat welding of the overlapping parts, and Fig. 3 is a diagram showing a joint part of non-woven fabric pipes obtained by a conventional method. 4 is a front view showing an example of the method for producing a nonwoven fabric tube according to the present invention, FIG. 5 is a cross-sectional view thereof, and FIG. 6 is a cross section showing a joint of a nonwoven fabric tube obtained by the method of the present invention. 7 and 8 are cross-sectional views showing other examples of the method for manufacturing a nonwoven fabric tube according to the present invention. 1... Nonwoven tape, 3... Overlapping portion, 5...
...joint part, 6...push plate.

Claims (1)

[Claims] 1. Thickness 0.15 to 0.50 mm and apparent porosity 0.20 to 0.75
The side edges of the thermoplastic nonwoven fabric tapes having the same properties are overlapped, and after heat welding this overlapped part, while the heat weld part is in a fluid state under stress, the heat weld part is cooled while being pressed with a press plate. , manufacturing a non-woven fabric tube whose joint part has a thickness of 120% or less of the thickness of the non-woven fabric tape, and applying a membrane-forming liquid to the inner or outer surface of the non-woven fabric tube and coagulating it to form a permeable membrane. A method for manufacturing a tubular reinforced permeable membrane. 2. The method for producing a tubular reinforced permeable membrane according to claim 1, wherein the thermoplastic nonwoven tape is made of polyethylene or polypropylene.