DK148786B - BEARERLAG CONSISTING OF LIQUID - Google Patents

Description

in 148786

The present invention relates to a nonwoven fabric layer for supporting a semi-permeable membrane.

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It is known that semipermeable membranes are technologically weak and therefore require mechanical support in the form of a support member.

5 They are used, for example, in the form of hose and surface membranes in systems that operate according to the reverse osmosis principle and the ultrafiltration principle. The support can be done, for example, by using perforated pipes or hollowed-out plates, ie porous and relatively pressure-resistant support materials, for example in the form of PVC or special steel pipes or 10 sheets of plastic. Since the hole spacing or duct spacing of such support materials due to the often process-dependent high pressure (e.g. 1-140 bar) must be kept relatively large for the sake of mechanical strength, a porous, non-compressible drainage layer between the semipermeable membrane and the supporting element is used. lots like support teams.

Usually, semipermeable membranes consist of cellulose acetate. These are extruded in a layer thickness of approx. 100-200 µ on the porous support layer.

Following subsequent coagulation, the actual active membrane is formed at a thickness of 500 to 5000 Angstroms, 20 of which it is of particular importance for the later obtained permeation properties to obtain a smoothed layer thickness. The design of the support layer must therefore, as one of the important factors in this context, be given a very special importance.

It is already known to use support layers consisting of a textile surface layer, for example of a tissue, paper or nonwoven fabric. The results thus obtained have so far not been satisfactory. In particular, great difficulties arise due to the unavoidable irregularities in the micro-areas mentioned above. The structure of a tissue often appears in the surface of the highly sensitive membrane, which can lead to fine cracks and thus to the destruction of the membrane.

Paper of cellulose has little mechanical strength and is bacterially destroyed during use in a relatively short time. Paper with 100% synthetic composition and the required high mechanical strength cannot be made with the present technique.

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Therefore, they have switched to using nonwoven fabric. Nonwoven fabrics consisting of 100% synthetic, thermoplastic fibers, preferably of polyester or polypropylene fibers, which, after being manufactured in a dry manner, for example by winding or carding, are attached to a process known per se using heat and pressure. so far proved to be most suitable. Such nonwoven fabrics have extremely high wet strengths.

However, one major drawback of these dry-laid membranes is their irregular web formation, ie. an inadequate single-fiber distribution, as well as a rough nonwoven surface. In the case of transverse sheets, an irregular weight and thickness distribution follows the production width.

Some improvement in the weight and thickness distribution could be achieved by a combination of transverse and longitudinal webs and by a vaulting of the calender rolls. However, despite these measures, 15 are still available. over the production width, some irregularity, especially higher weight and inferior thickness in the marginal zones in comparison with the middle zone of the nonwoven fabric. This irregular nonwoven fabric thickness, upon subsequent coating with the membrane solution, causes an irregular membrane thickness, which results in irregular membrane properties. Since these irregular membrane properties cannot be accepted, a hitherto relatively wide rim zone must be discarded before or after coating the membrane. This, of course, leads to a significant costing of the overall membrane production.

Aerodynamically layered or spun webs exhibit a higher regularity in weight and thickness distribution over the production width, but their relatively irregular web formation due to an irregular single fiber solution or single fiber distribution also results in the subsequent coating with the membrane solution to relatively irregular 30 and thus to relatively irregular membrane properties.

The difficulty of the kind mentioned here has hitherto almost always been unavoidable, owing to the specific properties of the known textiles. Difficult detailed control measures as well as a very high rejection percentage have therefore had to be accepted and have led to a severe costing of these membranes.

German Patent Specification No. 1,142,924 discloses a method of producing a separator material for accumulators, whereby synthetic fibers by the wet method are combined into a fleece and then activated by treatment with a saline solution. However, with such a method, it is not possible to prepare a support layer for a semi-permeable membrane because the resulting material, in addition to an inappropriate internal structure, exhibits insufficient surface smoothness. Furthermore, as a result of 10 of the complicated fastening method, it was not possible to adapt the mechanical properties to the existing requirements.

The present invention relates to a physiologically harmless and, in the chemical, physical and thermal sense, to a large extent resilient carrier layer which avoids the above-mentioned disadvantages and which, in a relatively simple manufacturing process, ensures the production of a semi-permeable membrane with excellent regularity.

This carrier layer consists of a porous nonwoven fabric which is peculiar to the nonwoven fabric:. is a wet web fabric whose fibers in the surface layer are progressively compressed so that the surface is highly impregnated with thermoplastic binder fibers.

It has been found to be particularly advantageous if the carrier layer consists of binder fibers in admixture with non-binder fibers. The titer fibers used are conveniently in the range of 4-30 dtex, preferably at 6.8 dtex, and the titer fibers used are in the range 1-7 dtex, preferably between 1.3 and 3.3 dtex. For example, the carrier layer consists of 10-100% of binder fibers and 90-0% of non-binder fibers. Stretchy polyester fibers and / or polypropylene fibers are particularly suitable as binder fibers. The special use properties 30 can be modified in a very special way by the special properties of the non-bonding fibers used. Stretched polyester fibers and / or polyamidimide fibers and / or aromatic polyamide fibers have proven to be particularly suitable in this regard.

The carrier layer according to the invention is elucidated in the following:

The preparation of the carrier layer according to the invention is preferably carried out in a wide manner, for example in a layer thickness of 150 x 10 meters. The sedimentation method used in this manufacturing process leads to an asymmetrical structure of the formed web, whereby, in particular, in the contact surface area of the later formed membrane, an extremely fine-textured and flat surface which is highly impregnated with thermoplastic binder fibers is formed.

The regularity of the weight distribution and the thickness distribution over the production width is, by virtue of the method of production according to the wet-web method, significantly better than that of a web prepared according to the methods described above. By this method, weight and thickness variations over the production width of ± 1% can be obtained. The fleece image, ie. The single-fiber solution and the single-fiber distribution are substantially better in this process than in a dry-laid web. The fabric surfaces produced by the process of this invention are substantially smoother than the web surfaces of a dry layered web.

As for the mechanical properties, a far-reaching high isotropic strength can be obtained, which is of great importance for most applications.

The regularity and smoothness of the carrier herein is of great importance for the regularity of the membrane to be applied later. This results in a substantial simplification of the necessary control process and thus a surprisingly large reduction in production costs.

In particular, a particular advantage of the carrier layers of the present invention is that they can be made with specific properties that are within an extremely wide range. 1

Since, with this nonwoven fabric, a very regular membrane thickness can be obtained, a membrane with very

Claims (2)

148786 regular properties across the production path, which means that the full production width can be utilized. This allows a significantly more economical production of high quality semipermeable membranes. EXAMPLE A mixture of 50% unstretched polyester fibers with a titer of 6.8 dtex and a length of 12 mm and 50% of stretched polyester fibers with a titer of 1.3 dtex and a length of 6 mm is suspended in water. The solids content is 0.2%. The suspension is then passed to an inclined machine where the substance content is diluted to a solid content of 0.08%. The water is then sucked using vacuum through the sloping screen and the velocity of the slopes is adjusted so that a web with a surface weight of 174 g / m with a moisture content of 85% is deposited. The excess water is removed on a suction drum dryer by flowing hot air at a temperature of 140 ° C until a residual value of 10% is obtained. Immediately thereafter, the web is subjected to a calender consisting of a steel and a cotton roll with a diameter of 350 mm each, whereby the enriched surface of binder fibers is applied to the steel roll. The temperature of the steel roll was 20 215 ° C and the temperature of the cotton roll was 155 ° C. It was adjusted to a line pressure of 130 kg / cm and a speed of 3.5 m / minute. The surface of the resulting nonwoven fabric was very even and completely free of protruding fiber ends and loops. 25 1. Carrier layer for supporting a semi-permeable membrane, consisting of. of a porous nonwoven fabric bonded by self-bonding, characterized in that the nonwoven fabric is a nonwoven fabric whose fibers in the surface layer are progressively compressed so that the surface is highly impregnated with thermoplastic adhesive fibers.