JPH0421526B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a sheet-like support for supporting separation membranes such as reverse osmosis membranes and ultrafiltration membranes. These membranes place a solution on one side and apply mechanical pressure to the solution to separate it into a concentrated solution and a permeate with a dilute solute concentration. The film is formed on a permeable sheet-like support and used in consideration of the workability of membrane and modularization. Of course, this separation membrane support needs to be able to permeate liquid more easily than the separation membrane itself, and currently polyester nonwoven fabric is used as this support, and dry and wet methods are available for manufacturing this nonwoven fabric. The surface properties, density, etc. are adjusted by heat rolling. As a separation membrane support, from the relationship of effective volume and price at the time of modularization, it is better to be thinner as long as it has the necessary characteristics.
g/m ² and a thickness of about 50 to 200 μm, there are large variations in thickness, air permeability (water permeability can be evaluated by air permeability), etc. Separation membranes are usually formed by casting a membrane material polymeric substance solution (hereinafter referred to as casting liquid) onto a support, but in the case of a dry method, the thickness of the deposited membrane is stable due to the above-mentioned variations in the support. Otherwise, the casting liquid may partially pass through the support and strike through. On the other hand, wet-processed nonwoven fabrics are made by mixing the main fibers and binder fibers with a slightly lower melting point, and are processed by hot rolling to improve surface properties, density, etc.
A common method is to adjust the strength, etc., and the uniformity of thickness, air permeability, etc. is sufficient as a separation membrane support, but the surface condition is not sufficient, that is, short fibers with a length of several mm or less are used. Because it is used as a raw material, there is a lot of fluffing, and if the processing strength of the hot roll is increased, the fluffing can be suppressed, but the surface density increases and the adhered film becomes easier to peel off.If the processing strength is weakened to the extent that the film does not peel off, There were drawbacks such as the raising of the fluff could not be suppressed, causing defects in the film, and the casting liquid could not be prevented from bleeding through. In addition, when the fibers used are made thicker and the processing strength is increased, the napping is suppressed and the opening and surface roughness are large, so the adhesion of the film is good, but depending on the processing conditions, the casting liquid may bleed through. If the sheet had the same basis weight and the fibers had the same length, the uniformity of the sheet tended to decrease due to a decrease in the absolute number of fibers. The present invention eliminates the above-mentioned drawbacks and provides a separation membrane support with a uniform layer, no napping, and good adhesion to the separation membrane. As shown in the figure, the surface layer 2, on which the separation membrane 1 is to be adhered, is made of thick fibers and has large openings and surface roughness, and the back layer 3 is made of thin fibers and is a dense layer with small openings. This is a separation membrane support made of a two-layer nonwoven fabric with layers thermally bonded together. Each layer can be made separately and integrated by hot roll processing, or the paper itself can be made into multilayer paper using a circular mesh paper machine or the like and then hot roll processed.
Furthermore, a sheet having a density gradient may be made by a well-known method. When polyester is used as the fiber, layer 2 contains fibers with a thickness of 2 to 10 denier and length of 3 to 50 mm, and layer 3 contains 30 to 80 main fibers with a thickness of 0.05 to 2 denier and a length of 3 to 50 mm. % and 70 to 20% of binder fibers such as copolymer fibers, composite fibers, and nonwoven fibers with a thickness of 1 to 5 denier and length of 3 to 20 mm, which have a slightly lower melting point, are used. The standard thickness is 2:8 to 8:2, and in addition to polyester, heat-fusible fibers such as polyamide, polyimide, polyvinyl chloride, and polyolefin (polypropylene, polyethylene) can also be used. Since the separation membrane support of the present invention uses thick fibers for the surface layer 2 and thin fibers for the back layer 3 as described above,
In manufacturing this by a wet method, a uniform sheet is made using a paper machine, and as shown in FIGS. By applying heat and pressure to fuse the outer surface of the surface layer 2, the outer surface of the surface layer 2 has a rough structure that suppresses naps and improves the adhesion of the separation membrane due to the anchoring effect.At the same time, the back layer 3 is made of cast The surface layer 2 has a dense structure through which liquid cannot pass through, and allows the casting liquid to appropriately penetrate into the support depending on the fiber material and the properties of the casting liquid.
The thickness and opening of the surface layer 3 can be adjusted. Also, basically based on the above idea, the fourth
As shown in the figure, the thin fiber layer 3 is replaced by the thick fiber layer 2, 2.
It is also possible to reduce the water flow resistance of the entire support by reducing the proportion of thin fiber layers that exhibit relatively high water flow resistance by creating a sanderch structure sandwiched between the supports.
By adopting a two-layer or multi-layer structure like this, even if a defect occurs in one layer, it can be compensated for by other layers, making it easy to maintain the overall quality at all times.Furthermore, it is easy to use with conventional wet method nonwoven fabric manufacturing equipment. It has the effect of being able to be produced at a low cost. Data comparing Comparative Examples 1 and 2 of conventional separation membrane supports made of nonwoven fabric and the separation membrane support made of a double layer of the present invention are shown on the next page.

【table】

[Table] Although the case where the separation membrane support of the present invention is produced by a wet method has been described above, it is clear that if the same product is obtained by a dry method, exactly the same effect can be obtained. However, if you try to manufacture a sheet with a basis weight of around 100g/ ^m2 with a multilayer structure,
The non-uniformity of the sheet described at the beginning has become even more serious, and a dry manufacturing method has not been established at present.

[Brief explanation of drawings]

The figures show examples of the present invention, FIG. 1 is a partially enlarged cross-sectional explanatory view of a separation membrane supported on a separation membrane support, and FIGS. 2 and 3 are production of the separation membrane support shown in FIG. 1. An explanatory diagram showing the method; FIG. 4 is a partially enlarged sectional explanatory diagram showing another example in which a separation membrane is attached to a separation membrane support;
FIG. 5 is an explanatory diagram showing a method for manufacturing the separation membrane support shown in FIG. 4. In the figure, 1 is a separation membrane, 2 and 3 are the front and back layers of the separation membrane support, 4 is a heat roll, and 5 is an elastic roll.

Claims (1)

[Claims] 1 Consists of a nonwoven fabric with a multilayer structure based on a double structure: a surface layer using thick fibers with large openings and surface roughness, and a back layer using thin fibers with small openings and a dense structure. A separation membrane support characterized by: