Method and apparatus for producing electrostatically polarized fibers

Abstract

The invention relates to a method and a device for producing electrostatically polarized fibers (33), in which a plurality of fibers (31) are produced from a polymer melt by means of a spinneret device (2) (S 1) and a polar liquid (4) is applied to the plurality of fibers (31) by means of a spray device to form a treatment aerosol (24) (S2), wherein with the application of the treatment aerosol the plurality of fibers (31) are formed into a plurality of polarized fibers (33) (S3), wherein the plurality of polarized fibers (33) are dried over a predetermined drying section (TS) (S4) and a circumference (U) of the plurality of polarized fibers (33) is stabilized over a predetermined stabilization section (ST).

Description

[0001] The invention relates to a method and a device for producing electrostatically polarized fibers.

[0002] The production of polarized fibers is known from the general state of the art.

[0003] DE 10 2022 000 777 A1 discloses a method and an apparatus for the production of electrostatically charged fibers, in particular for the production of an electret fiber structure, in which fibers are produced from a plastic and / or natural material, in which a polar liquid is atomized by means of a gaseous pressure medium to produce a treatment aerosol, and in which the fibers are treated with the treatment aerosol for electrostatic charging, wherein the atomization is carried out with a quotient of the volume flow of the polar liquid in liters per hour and the overpressure of the gaseous pressure medium in hectopascals of 0.004 to 0.008.

[0004] This method enables the passive dry production of electrostatically charged or polarized fibers, since the amount of polar liquid applied is limited and does not require active drying, for example by a heating device.

[0005] However, if larger quantities of polar liquid are required, subsequent active drying of the electrically charged fibers may be necessary. This active drying can, however, lead to a deterioration or reduction of the fiber polarization achieved with the polar liquid.

[0006] The object of the invention is therefore to provide a method for producing electrostatic fibers in which active drying is possible regardless of the amount of polar liquid without any deterioration of the resulting polarization.

[0007] It is further an object of the invention to provide a device for the production of electrostatic fibers in which active drying is possible regardless of the amount of polar liquid without any deterioration of the resulting polarization.

[0008] The problem with regard to the method is solved according to the invention with a method having the features according to claim 1.

[0009] According to one aspect of the invention, a method for producing electrostatically polarized fibers is provided, in which a plurality of fibers are produced from a polymer melt by means of a spinneret device and a polar liquid is applied to the plurality of fibers by means of a spray device to form a treatment aerosol, wherein with the application of the treatment aerosol the plurality of fibers are formed into a plurality of polarized fibers, wherein the plurality of polarized fibers are dried over a predetermined drying section and a circumference of the plurality of polarized fibers is stabilized over a predetermined stabilization section.

[0010] Drying and stabilizing a circumference means essentially maintaining a constant circumference across a multiple of threads. This achieves even and gentle drying without diminishing or eliminating the previously applied polarization through excessive heat.

[0011] Additives for charge stabilization can include fatty acids (e.g., distearylethylenediamide) or their salts (magnesium stearate), sterically hindered amines (e.g., Chimassorb 944), fluorine compounds or polymers, and combinations thereof, which can be added to the plastic material or the polymer melt.

[0012] According to a preferred embodiment of the method, the fibers are guided in a stabilized manner over a predetermined length in the stabilization section with a predetermined and constant circumference of the fiber circumference fanning and are heated at least section by section to a predetermined temperature, wherein the temperature has a maximum of the evaporation temperature of the polar liquid, so that the polarized fibers can be laid down as dried polarized fibers on a depositing belt.

[0013] In principle, increasing the distance between the spinneret assembly, which extrudes the majority of the fibers, and the depositing tray, on which the majority of the fibers are laid down, leads to fiber dispersal, resulting in less uniform fiber deposition and consequently reduced filtration efficiency. To prevent or mitigate this, the device underlying the invention is designed as a heating and spinning chamber for drying the fibers. It is intended to isolate the majority of the fibers from external influences (e.g., excitations from the spinning chamber) and to actively stabilize the chamber. This can be achieved by means of a predetermined stabilization section.

[0014] The process should make it possible to produce a polarized dry nonwoven fabric that can be laid down on a drying conveyor belt without a reduction in polarization.

[0015] According to a preferred embodiment of the process, the polarized fibers are drawn from a pale spinning nozzle with a tempered primary flow at a first primary temperature, mixed with a non-tempered secondary flow at a second secondary temperature, and dried and stabilized with a third tertiary temperature of a tertiary flow, wherein the primary temperature is greater than the secondary temperature and / or the tertiary temperature, and the tertiary temperature is less than 70°C.

[0016] Different air streams with varying temperatures and flow rates are provided for drawing off and drying the fibers. The primary stream is supplied at a predetermined pressure and temperature, allowing the polymer melt to be drawn off from the blow-drying die onto a deposit belt. A secondary stream, essentially at ambient temperature, is entrained by the primary stream, as is the case at the location of the electrically charged fiber production device.

[0017] A tertiary flow dries and stabilizes the majority of the threads. This tertiary flow maintains a specific temperature, allowing the threads to be dried without any deterioration of their polarization. This can be achieved over a predetermined length of drying section at a predetermined temperature. Temperatures above 70°C can reduce the polarization of the polarized fibers, thereby decreasing the filter effect and efficiency.

[0018] The deposited fibers form a fleece. This fleece made of charged fibers can be used, for example, for filters, especially respiratory filters.

[0019] The problem with regard to the device is solved according to the invention with a device having the features according to claim 4.

[0020] According to one aspect of the invention, a device for producing electrostatically polarized fibers is provided, comprising a spinneret device for forming fiber from a polymer melt, a spray device positioned downstream of the spinneret device for wetting the fibers with a polar liquid to form polarized fiber, and a stabilizing dryer device positioned downstream of the spray device for drying the polarized fiber and stabilizing the circumference of the polarized fiber.

[0021] The device resulting from the invention requires an installation space that increases the distance from the fiber exit of the spinneret assembly to a lay-up belt. The spinneret assembly can comprise an Exxon nozzle, a coaxial nozzle (e.g., from Biax Fiberfilm Inc.), a spunbond nozzle, and / or a solvent spinneret, hereinafter also generally referred to as a bleach spinneret.

[0022] A stabilizing dryer prevents, or at least reduces to an acceptable level, the fanning out of the majority of fibers, regardless of the large distance between the spinneret and the lay-up belt. Various configurations of the stabilizing dryer are possible for this purpose. The consolidated fibers or nonwovens produced with this system exhibit a similarly uniform fiber lay-up as consolidated fibers produced with a small distance between the fiber exit and the lay-up unit. However, gentle drying can be achieved without affecting the polarization.

[0023] According to a preferred embodiment of the device, the stabilizing dryer assembly comprises a stabilizing dryer shaft for guiding and stabilizing the polarized fibers and a dryer assembly for drying the polarized fiber, wherein the stabilizing dryer shaft surrounds the polarized fibers to be dried on at least two sides, and advantageously, the stabilizing dryer shaft essentially isolates the polarized fibers from the environment.

[0024] The stabilization shaft allows the fiber circumference to be kept constant while simultaneously drying the fibers gently, without impairing their polarization. Additionally, the stabilization dryer shaft is designed to isolate the fibers from environmental influences, so that essentially only a predetermined temperature and airflow can act upon them.

[0025] According to a further preferred embodiment of the device, the stabilizing dryer shaft has a stabilizing flow inlet by means of which the tertiary flow can be supplied for drying and stabilizing the polarized fiber, wherein the stabilizing flow inlet is designed as a through-opening for supplying the tertiary flow, and wherein the stabilizing shaft increases the distance between the spinneret device and a depositing belt for depositing dried polarized fibers.

[0026] The stabilizing dryer shaft has openings that direct the tertiary flow, such as heated air, towards the majority of fibers, thus stabilizing and keeping constant the circumference or width of the majority of fibers.

[0027] Additionally, the distance between the spinneret unit and a lay-down belt is increased to allow for gentle drying over a predetermined distance. The distance between the spinneret unit and the lay-down belt is greater than in a conventional device.

[0028] According to a particularly preferred embodiment of the device, the tempered tertiary flow can be adjusted to a predetermined temperature using the dryer device and to a predetermined flow using an air blowing device, wherein a flow angle can be adjusted by means of the air blowing device and / or by means of the stabilizing dryer shaft.

[0029] Additionally, the direction of the tertiary flow towards the fibers can be adjusted. For this purpose, the dryer unit is movable and / or adjustable, where movable means that the position of the dryer unit can be changed, and adjustable means that the dryer unit itself has, for example, a joint, so that the dryer unit can be moved flexibly.

[0030] Preferably, the temperature of the drying unit can be adjusted and / or its position relative to the majority of the fibers can be changed. This allows for setting an optimal drying distance.

[0031] According to a preferred embodiment of the device, the stabilizing dryer shaft has a receiving opening with a drip protection plate and an outlet opening with a protective plate, which surround the dryer device at least partially, wherein an inlet circumference of the fibers from the receiving opening to an outlet circumference of the fibers can be stabilized to a predetermined circumference, in particular can be kept essentially constant.

[0032] To protect against, for example, fibers, dirt and melt, apertures are provided at the receiving and / or output openings.

[0033] The circumference of the fibers is essentially constant along the path from the receiving aperture to the output aperture, so that hardly any fanning out is noticeable.

[0034] According to a further preferred embodiment of the device, the stabilizing dryer shaft is movable and / or designed to be movable, so that the guidance of the tertiary flow and / or the temperature control of the tertiary flow according to a flow angle is adjustable and / or controllable.

[0035] The stabilizing dryer shaft can also be movable and / or designed to be movable, so that the flow and heat radiation can be optimally adjusted, enabling the gentlest and most complete drying possible without disturbing the polarization.

[0036] According to a particularly preferred embodiment of the device, the fibers can be deposited on a conveyor belt which is permeable to an intake flow, so that the polarized fibers can be deposited as a nonwoven fabric.

[0037] The discharge conveyor is a movable transport belt that guides the nonwoven fabric to a collection point where it can be gathered and transported away. On the side opposite the discharge area of ​​the conveyor belt, a suction device is provided that draws the nonwoven fabric against the conveyor belt.

[0038] The inventive method and the inventive device are explained in more detail below with reference to some exemplary embodiments of the inventive device and the inventive method and the accompanying figures.

[0039] They represent: Fig. 1 schematically a view of a first embodiment of a device according to the invention for producing electrically charged fibers, Fig. 2 schematic view of a second embodiment of a device according to the invention for producing electrically charged fibers, Fig. 3 schematic view of a third embodiment of a device according to the invention for producing electrically charged fibers, Fig. 4 schematically a view of a fourth embodiment of a device according to the invention for producing electrically charged fibers, and Fig. 5 a block diagram of a method according to the invention for producing electrically charged fibers.

[0040] Fig. Figure 1 schematically shows a device 1 for producing electrically charged fibers 33.

[0041] The device 1 for electrically charged fibers 33 has a spinneret assembly 2 for extruding a plurality of fibers 31 from a polymer melt 3. The plurality of fibers 31 are formed into polarized fibers 33 by means of a spraying device 4, which distributes a polar liquid 40.

[0042] The polymer melt 3 may contain additives for charge stabilization of fatty acids, such as distearylethylenediamide, or their salts, such as magnesium stearate, sterically hindered amines, such as Chimassorb 944, fluorine compounds or polymers in combination thereof.

[0043] The additives allow a polar liquid 40, in particular water, distributed by means of the spray device 4 to cause polarization or electrical charging of the fibers 31 to polarized fibers 33.

[0044] Furthermore, the device 1 has a stabilizing dryer unit 6 which allows the polarized fibers 33 to be dried and at the same time keeps the circumference U formed by the majority of fibers 33 essentially constant over the length of the stabilizing dryer unit 6.

[0045] The dried polarized fibers 34 are placed on a movable conveyor belt 10, with an aspiration flow 12 acting below the conveyor belt 10 on the opposite side to the depositing surface of the majority of fibers 33.

[0046] The intake flow 12 ensures a consolidation of the polarized threads 34 dried by means of the stabilizing dryer device 6 and can lead to fanned-out fibers 35 that form a nonwoven fabric 36 when laid down.

[0047] The spinneret assembly 2, as in Fig. Figure 1 shows a melt channel 21 through which the polymer melt 3 is guided.

[0048] The polymer melt 3 is drawn from the blow-drying die 20 via a compressed air channel 22. The compressed air channel 22 carries a so-called primary flow 23, which is a compressed air flow that can draw the polymer melt into fibers 31.

[0049] The primary flow 23 has a predetermined primary temperature T1, which essentially corresponds to the temperature of the polymer melt 3, so that excessively rapid cooling can be avoided.

[0050] The fibers 31 formed by the bleaching nozzle 20 are provided with the polarized liquid 40 by the spray device 40. The polarized liquid 40 causes the fibers 31 to become polarized fibers 33. Simultaneously, a secondary flow 5, hereinafter also referred to as a cold air flow, is entrained along with the polarized fibers 33.

[0051] The secondary flow 5 essentially has a secondary temperature T2. The secondary temperature T2 essentially corresponds to the ambient temperature in which the device 1 for producing electrically charged or polarized fibers 33 is positioned. The secondary temperature T2 is lower than the primary temperature T1 of the primary flow 23.

[0052] Subsequently, the polarized fibers 33 are dried and stabilized with the stabilizing dryer unit 6 to form dried polarized fibers 34 until they are placed on the depositing conveyor belt 10.

[0053] The stabilizing dryer unit 6 has a stabilizing dryer shaft 60 in which the polarized fibers 33 can be guided.

[0054] The stabilizing dryer shaft 60 extends at least on both sides of the polarized fibers 33 and surrounds them in the yarn feed direction to the discharge conveyor 10, so that substantially complete drying of the polarized fibers 33 can be carried out. In addition, a tertiary flow 7 is provided in the stabilizing dryer shaft 60, which stabilizes and dries the polarized fibers 33 from the previously applied polar liquid 40.

[0055] The tertiary flow 7 is heated by means of a dryer device 61 with a tertiary temperature T3.

[0056] The dryer unit 61 can be a heating unit capable of heating the ambient air to a desired tertiary temperature T3.

[0057] The tertiary temperature T3 is essentially smaller than the primary temperature T1, but larger than the secondary temperature T2.

[0058] The tertiary temperature T3 is intended to dry and gently warm the polarized fibers 33. Excessive heating can lead to a reduction or, in the worst case, a loss of polarization in the polarized fibers 33. A loss of polarization would impair the filtering effect of the nonwoven fabric 36.

[0059] The function of the stabilizing dryer shaft 60 is also to prevent the polarized fibers 33 from expanding or fanning out during drying.

[0060] Additionally, the stabilizing dryer device 6 can be designed with a stabilizing dryer shaft 60, which can both isolate the polarized fibers 33 from external influences and actively manipulate the external influences, in particular the tertiary flow 7 as well as the temperature of the tertiary flow, namely the tertiary temperature T3.

[0061] The tertiary flow T3 can be controlled or regulated by means of an air blowing device 8. Experience can be incorporated via a control system for the device 1, so that simply controlling the air blowing device 8 may be sufficient.

[0062] Additionally, for redundancy and / or to facilitate the easy exchange of new products, additional sensors can be provided in the stabilizing dryer unit 6, so that control of both the tertiary temperature T3 and the tertiary flow 7 via the dryer unit 61 and the blowing unit 8 is possible.

[0063] The stabilizing dryer device 6 has a receiving opening 63 and an outlet opening 64. Between the receiving opening 63 and the outlet opening 64, the tertiary temperature T3 and tertiary flow 7 are applied to polarizing thread 33 via a drying section TS and a stabilizing section ST, so that the inlet circumference UE of the polarized threads 33 at the receiving opening 63 can be kept essentially constant up to the outlet opening 64 with an outlet circumference UA.

[0064] The stabilizing dryer shaft 60 has a drip protection panel 65 at the receiving opening 63 and a protective panel 66 at the output opening 64.

[0065] The drip protection screen 65 is intended in particular to capture the polar liquid 40 originating from the spray device 4 and, if necessary, to direct it to a pot protection collection device 67, thereby preventing the polar liquid 40 from dripping onto the conveyor belt 10.

[0066] The drip protection device 67 is designed to intercept both polar liquid and dripping polymer melt 3, so that the consolidated fibers 36 placed on the conveyor belt 10 cannot be contaminated with it.

[0067] The drip protection collection device 67 can be configured as a collection device for trapping dirt. Additionally, the drip protection collection device 67 can also include appropriate draining and suction devices for removing polar liquid 40 and / or polymer melt 3. The drip protection collection device 67 is positioned away from the stabilizing dryer shaft 60.

[0068] A one-sided positioning of the drip protection collection device to protect consolidated fibers 36 on the depositing belt 10 to form a nonwoven, as in Fig. 1, Fig. 2, Fig. 3 to Fig. As shown in point 4, that is also possible.

[0069] The protective shield 66 at the outlet opening 64 is primarily intended to shield the dryer unit 61 and may be shaped accordingly so that any outflows of the primary flow 23, the secondary flow 5, and the tertiary flow 7 can escape unhindered without any flow stagnation. That is, the distance between the outlet opening 64 and the discharge conveyor 10 is large enough to prevent flow stagnation.

[0070] As in Fig. As shown in Figure 1, the dried polarized fibers 34 become fanned-out fibers 35 when deposited onto the depositing belt 10, before being formed into consolidated fibers 36 by the suction flow 12, which can form a nonwoven fabric.

[0071] Fig. 2 and Fig. Figure 3 shows exemplary embodiments of the device 1 for producing electrically charged fibers, in particular the stabilizing dryer device 6.

[0072] The stabilizing dryer shaft 60 is movable in such a way that the tertiary flow 7 flows over a flow angle β (see Fig. 1) can be directed towards the polarized fibers 33. For this purpose, the stabilizing dryer device 6 can have a stabilizing dryer shaft 60, which is located on both sides of the polarized fibers 33, as for example in Fig. 2 towards the bleaching nozzle 20 is foldable and / or as in Fig. As shown in Figure 3, the stabilizing dryer shaft 60 can be pivoted across its opening width in the direction of the storage belt 20.

[0073] This allows, for example, the tertiary flow 7 to be controlled via a predetermined flow angle β (see Fig. 1) towards the polarized fibers 33.

[0074] In Fig. Figure 4 shows a further embodiment of the device 1 for producing polarized fibers 33. The stabilizing dryer unit 6 has a stabilizing dryer shaft 60 which is movable via a centrally arranged hinge connection, so that an opening enlargement is possible above and below the polarized fibers 33 both transversely to the blowing die 20 and transversely to the depositing belt 10.

[0075] This ensures optimal flow of the tertiary flow 7, enabling optimal drying of the polarized fibers 33 without restricting and / or deteriorating the polarization.

[0076] Fig. Figure 5 shows a block diagram of the essential process steps of the process for producing a polarized thread. In a first step S1, fibers 31 are formed from a polymer melt 3 by a spinneret device 2.

[0077] The spinneret device 2 can have a blowing spinneret 20, through which the polymer melt 2 can be formed into fibers 31.

[0078] In a second step S2, the fibers 31 produced with the spinneret device 2 are sprayed with a polar liquid 40, forming a treatment aerosol which is applied to the fiber 31 by means of the spray device 4.

[0079] In a third step S3, a polarized fiber 33 is formed by spraying or applying the treatment aerosol to the fibers 31.

[0080] In a fourth step S4, the fibers 33, previously wetted with the treatment aerosol, are dried via a predetermined drying section TS. Additionally, the circumference of the fibers 33 is stabilized via a predetermined stabilization section ST in step S4. The drying section TS and the stabilization section ST are integrated into the stabilizing dryer unit 6.

[0081] Stabilized here means that the majority of fibers 33 are held to a predetermined circumference U and do not fan out too much.

[0082] In a fifth step S5, the fibers 33 are guided in a stabilized manner over a predetermined length in the stabilization section ST with a predetermined constant circumference U in the fiber circumference fanning.

[0083] In a sixth step S6, the previously applied polar liquid 40 is subjected to evaporation by applying a predetermined temperature, in particular a tertiary temperature T3, by the dryer device 61, whereby the tertiary temperature T3 acts particularly gently on the polarized fibers 33, so that no depolarization can occur.

[0084] The dryer 61 can include electrically operated heating coils. The tertiary temperature T3 that can be generated with the dryer 61 is advantageously less than 70 °C. A temperature greater than 70 °C can reduce the applied charge on the polarized fiber 33 and decrease the filtration efficiency of the nonwoven fabric 36. Reference symbol list: 1 Device for producing electrically charged fibers 10 Filing belt 12 Intake flow 14 Outflow 2 spinneret assembly 20 Pale spinning nozzle 21 Melt channel 22 Compressed air duct 23 Compressed air flow / Primary flow 3 Polymer melt 31 fiber 33 polarized fiber 34 dried polarized fiber 35 fanning fiber 36 consolidated fiber, nonwoven 4 Spray device 40 polar liquid 5 Secondary flow; cold air flow 6 Stabilizing dryer unit 60 Stabilizing dryer shaft 61 Dryer unit 62 Stabilizing flow access 63 Reception opening 64 Exit opening 65 Drip protection cover 66 Protective cover 67 Drip collection device 7 Tertiary flow; heating flow; stabilizing flow 8 Blowing device ST stabilization section TS drying section T1 Primary temperature T2 Secondary temperature T3 Tertiary temperature U Scope U Input scope Ua initial scope β Flow angle QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2022 000 777 A1

[0003]

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