The invention relates to a method for end-sealing of hollow membrane filter fibers. During the method, one end of the hollow filter fibers is immersed in a low-viscosity hardening sealing material, preferably in glue filled in a container, to a given depth. After the sealing material solidifies, filter fibers with end seals are used to create membrane filter modules with a one-sided permeate head design.

In the chemical industry, membrane is a technological term. It denotes a technological barrier which, due to its selective permeability, enables the separation of the components of the materials to be processed mostly without chemical transformation. The essence of membrane separation or membrane filtration is that selective transport takes place through a membrane under the influence of some driving force. The membrane, which is the essence of the operation, is a partition wall that, due to its selective permeability, enables the separation of substances mostly without chemical transformation. The membrane serves as an intermediate phase when separating two phases and/or participates as an active or passive partition wall in the material transfer between the phases in contact with it. During the membrane separation operations, in contrast to the traditional filtration process, the supplied liquid is not flowed perpendicular to the filter medium, but parallel to the membrane (cross-flow), while a part of the components of the material to be filtered passes through the membrane under the influence of the driving force and leaves on the permeate side. The components retained by the membrane are enriched on the feed side of the membrane, this is the retentate or concentrate.

The application and construction of membranes is described in detail in the article entitled Membranos muveletek (Membrane Operations) by Katalin Belafine Bako and Nandor Nemestothy, which was published in 2020 by Pannon University and is available on the following website https://moodle2.mk.uni-pannon .hu/pluginfile.php/35982/mod_resource/content/0/Membr%C3%A1 nos%20m%C5%B 1veletek.pdf.

Membranes are increasingly used to solve separation problems in the food industry, healthcare, chemical industry, wastewater treatment, etc.

Patent application CN 10197266 describes a method for manufacturing a hollow fiber membrane module. The method comprises the following steps: the first ends of the equally long hollow fiber membrane yams are bundled by a conventional method, and preparing sealant in a container, immersing the second ends of the hollow fiber membrane yams in the sealant in the container in a depth of 2-15 mm.

A vacuum pump is coupled to he first ends of the membrane fibers of the membrane bundle, and the pressure is decreased by 500-1000 Pa inside the membrane fibers thereby the level of the sealant is increased. The vacuum is maintained till the sealant solidifies. Finally, the second ends of the membrane fibers are cut off by 5-20 mm so that the second ends remain sealed. In this solution, no auxiliary liquid, but a vacuum pump is used, which makes the procedure more complicated and more expensive.

The American patent No. US 9498753 B2 describes a method for sealing the free end of a hollow fiber membrane and for use in a filter module. According to the patent, one end of the membrane is immersed in a low-viscosity, light-curing adhesive and the adhesive is cured. The invention also covers the resulting sealed hollow fiber membrane, the diameter of which is only slightly larger than the diameter of the unsealed membrane.

US patent No. US 7,950,528 B2 relates to a through-one-end water collection type hollow fiber membrane and a method for manufacturing the same. According to the invention, an internal sealing part is formed in the hollow part of the membrane at its free end. The internal sealing part is surrounded by an external sealing part from its outer surface, so this solution aims to improve the efficiency of the entire sealing part. US Patent No. 8852438 B2 relates to a membrane filter device. The device contains a number of hollow membrane fibers standing free from each other. The device also contains a first header and a second header disposed in vertically spaced-apart relationship. Opposed ends of each fiber of the first header and the second header are sealingly secured, and all open ends of the fibers open to a permeate-discharging face of at least one header. The device further contains permeate collection means to collect the permeate, sealingly connected in open fluid communication with a permeatedischarging face of at least one of the headers; and means to withdraw said permeate. The fibers, the headers and the permeate collection means together form an integrated unit wherein the fibers are essentially vertically disposed and ends of the individual fibers are potted in closely spaced-apart relationship in cured resin at a fixed distance. In most known solutions, the fibers are individually immersed in glue, essentially an adhesive that binds to UV light, then illuminated, and depending on the viscosity and other physical properties of the glue, the glue penetrates the inner cavity of the fiber to a small extent, but mostly solidifies outside the end of the fibers in the form of a drop. This slightly increases the dimensions of the fiber. Furthermore, no auxiliary liquid is used in any of them.

Their disadvantage is that the filter modules consist of a large number of fibers, and the separate dipping and/or curing with a UV lamp requires a lot of work and time. In addition, the glue cannot penetrate the fiber to a sufficient depth and the glue cannot penetrate the membrane structure without pressure (there is no time for it), so the glue on the outside does not ensure a proper seal for a long term. Another problem is that the glue increases the cross-section of the end of the fiber, which makes it more difficult for impurities to be removed from the filter module, and it also partially blocks air evaporation. If the UV light-hardening glue penetrates very deeply into the inner cavity, it will not be exposed to enough UV light and will not bond. In this case, toxic substances may remain in the fiber, which may later enter the water to be filtered.

Our aim is to develop a manufacturing process that enables the simultaneous sealing of one end of a large number of filter fibers so that after sealing the filter fibers remain separable from each other and are also suitable for creating a single-sided suction head during the production of membrane filter modules.

It has been realized that if the filter fibers are immersed in a low-viscosity, one- or several-component adhesive sealing material, and a liquid with a lower specific weight than the sealing material is poured on top of the sealing material, due to the phenomenon of the communicating vessels, the sealing material pushes inside the membrane and hardens there. Then the auxiliary liquid with a lower specific weight can be removed, and then the external adhesive residue outside the fibers is cut off, so the fibers will become separate, but each one will be sealed one by one. Due to the low viscosity of the sealing material, the sealing material penetrates not only into the inner cavity, but also into the structure of the membrane filter, but does not affect its external geometry, or only to a negligible extent.

The present invention is a method for end-sealing of hollow membrane filter fibers. During the method, one end of the hollow filter fibers is immersed in a low-viscosity hardening sealing material, preferably in glue filled in a container, to a given depth. After the sealing material solidifies, filter fibers with end seals are used to create membrane filter modules with a one-sided permeate head design. The filter fibers are arranged in bundles to form their end seals, and then one end of the bundled filter fibers is immersed together into the liquid or gel state sealing material filled in the container to a maximum depth of 20 mm. An auxiliary liquid, with a specific weight lower than the specific weight of the sealing material is filled on the sealing material, which forces the sealing material to a certain extent into one end of the filter fibers. After solidification of the sealing material, the auxiliary liquid is removed and the bundled filter fibers are separated from the sealing material remaining in the container above the level of the solidified sealing material.

Advantageous embodiments of the present invention are described in the dependent claims.

The method according to the present invention will be described with reference to the accompanying drawings in which:

Figure 1 shows a side view section of the bundled filter fibers placed in the container, where one end of the filter fibers is filled with the sealing material and the auxiliary liquid is filled on the sealing material,

Figure 2 shows the top view of the bundled filter fibers placed in the container, one end of the filter fibers is filled with the sealing material and the auxiliary liquid is filled on the sealing material,

Figure 3 shows the side view section of the remaining adhesive material with the ends of the filter fibers where the bundled filter fibers are separated from the remaining adhesive material,

Figure 4 shows the top view of the already sealed, ready-to-use bundled filter fibers, and

Figure 5 is a perspective view of the bundled filter fibers, partially in section.

The membrane filter fiber 1 is designed in a known manner. It is based on a flexible structure made of polyester material made using a woven (braid) or knitted (knitting) process (similar to shoelaces). This structure is coated from the outside with plastic, the surface of which has micropores of 0.01 -0.03 micrometers.

Our method relates to the formation of end seals 2 of hollow, bundled filter fibers 6. During bundling, filter fibers 1 are cut to a given length and tied together. In this process, we can create membrane filter modules with a one-sided permeate head design (Figure 5). During the method, one end 3 of the hollow filter fibers 1 is immersed to a given depth in a low-viscosity, hardening, sealing material 5 filled in a container 4. The sealing material 5 is a one- or two-component adhesive preferably synthetic resin that solidifies independently of an external energy source. The sealing material 5 is advantageously a polyurethane, polyester or epoxy based synthetic resin. During the method, the filter fibers 1 are arranged in bundles to form their end seals 2. One end 3 of the bundled filter fibers 6 is immersed into the sealing material 5 filled in the container 4, which is still in liquid or gel state, to a maximum depth of 20 mm, then an auxiliary liquid 7 with a specific weight lower than the specific weight of the sealing material 5 is poured onto the sealing material 5. The auxiliary liquid 7 is a liquid that does not react with the sealing material 5. In this way, on the one hand, the sealing material 5 is forced into one end 3 of the filter fibers 1 to a given extent, and on the other hand, it is also ensured that the individual filter fibers 1 do not stick together, and that the end seal 2 does not increase the circumference of the filter fibers 1 at the end seal 2 (1., Figure 2). After solidification of the sealing material 5, the auxiliary liquid 7 is removed, and the bundled filter fibers 6 are separated from the sealing material 5 remaining in the container 4 above the level of the solidified sealing material 5 (Figures 3, 4).

The auxiliary liquid 7 is preferably paraffin oil. Of course, the auxiliary liquid 7 can be any liquid which, on the one hand, has a lower specific weight than the specific weight of the sealing material 5, and on the other hand, does not enter into any chemical reaction with the sealing material 5.

During the formation of the end seal 2 according to our method, it is advantageous if the filter fibers 1 are immersed in the sealing material 5 for a maximum of 10 mm before the auxiliary liquid 7 is filled, and then the auxiliary liquid 7 is filled into the container 4. Afterwards, the filter fibers 1 are immersed in the sealing material 5 to a maximum depth of 20 mm. In this case, the outer side of the filter fibers 1 will be less coated with the sealing material 5, because it is prevented by the auxiliary liquid 7. At the same time, it will be deep enough so that the end of the filter fiber 1 remains below the level of the sealing material 5. This is achieved even if, due to the hydrostatic pressure generated by the auxiliary fluid 7, the sealing material 5 has already penetrated inside the filter fiber 1 , and because of this, the level of the sealing material 5 in the container 4 has decreased.

During the procedure the following steps are made. The filter fibers 1 cut to the given length are bundled, thus preparing the bundled filter fibers 6. The sealing material 5 is filled in the container. If it is multi-component, it is in already mixed state. After that, the ends of the bundled filter fibers 6 are immersed (for example 7 mm deep) into the sealing material 5. The auxiliary liquid 7 is slowly poured on top of the sealing material 5. After that, the bundled filter fibers 6 are immersed deeper, approx. 10-20 mm deep into the sealing material 5. Due to its hydrostatic pressure, the auxiliary liquid 7 forces a part of the sealing material 5 inside the filter fibers 1 . Then, of course, the level of the sealing material 5 will be lower than before the auxiliary liquid 7 was applied to the adhesive. The outer side of the filter fibers 1 is surrounded by the auxiliary liquid 7 and does not allow the sealing material 5 to cover it. This ensures that the filter fibers 1 can be separated later. After solidification of the sealing material 5, the auxiliary liquid 7 is removed. The bundled filter fibers 6 fixed in the sealing material 5 are taken out of the container 4. The bundled filter fibers 6 are cut directly above the level of the sealing material 5 or a few millimeters above the level of the sealing material 5. Thus, the filter fibers 1 and one of their ends 3 are already separate. At the same time, the sealing material 5 introduced into them seals the ends of the filter fibers 1 .

In the case of a suction system, the bundled filter fibers 6 prepared in this way must be immersed in the liquid to be cleaned. The open fiber ends of the bundled filter fibers 6 are connected to the suction side of the pump. As a result, a vacuum is created in the filter fibers 1 through the open fiber ends, and the clean liquid flows into the fiber through the small pores on the outer superficies of the filter fibers 1 , and the dirt remains outside. Contamination can be removed with a counter flow.

In a pressurized system, the bundled filter fibers 6 are surrounded by a closed shell. In this case, the filter consists of a filtrate outlet, a filter space de-aerate hole, and an inlet-cleaning hole. This latter opening serves for the introduction of air in the cleaning cycle, and of the purified liquid in normal operation.

The use of the bundled filter fibers 6 formed with end seals 2 in different filter systems will not be described in more detail, considering that this must be within knowledge of a person skilled in the art.

The advantage of our invention is that the filter fibers become more suitable for mass production, a large number of filter fibers can be produced simultaneously in one step, no manual labor is required, regardless of the number and size of the fibers. Specifically, less adhesive is required. The level of the adhesive/sealing material that enters the filter fiber can be limited by the level of the upper auxiliary liquid, i.e. , how deep the sealing/adhesive material should go into the cavity. Deeper penetration into the inner part of the filter fiber can be provided. The sealing material has a longer time to set, so its penetration into the spongy membrane structure is better. The glue sets completely on all parts, even on parts blocked from light. The geometry of the filter fiber does not change, so pollutants are more easily removed from the formed module, or aeration also cleans more effectively. Depending on the hardness of the glue, even a flexible sealing can be created, which also does not cause damage in the superficies of the filter fiber. It is cheaper to use glue that solidifies without the use of an external energy source. The labor required for its production is lower. The auxiliary liquid can be used several times. The filter fibers according to the method of the present invention are equally suitable for the production of filters consisting of membrane fibers with or without a carrier. Furthermore, the amount of adhesive flowing into one end of the filter fiber can be controlled together with the level of the auxiliary liquid and the degree of immersion of the filter fiber.