Meltblown spinning - Independent control of air and polymer temperatures

Abstract

The meltblown system includes a die including a die inlet end that receives molten polymer from a polymer source, a cavity downstream from the die inlet end through which the molten polymer flows, and a die outlet end that receives the molten polymer from the cavity and delivers it to an outlet orifice at the die outlet end. A fluid supply includes channels for delivering fluid to the die outlet end to draw fibers formed from the molten polymer emerging from the die outlet end. The fluid supply supplies fluid at a temperature T2 that is different from a temperature T1 of the molten polymer in the cavity, and the meltblown system is configured to independently maintain the molten polymer in the cavity at temperature T1 during operation.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Application No. 63 / 491,137 (filed March 20, 2023), the disclosure of which is incorporated herein by reference in its entirety.

[0002] The present invention relates to a meltblown process and the apparatus associated with that process. [Background technology]

[0003] As used herein, "meltblown" refers to a process in which synthetic fibers, such as microfibers and nanofibers (i.e., fibers with micrometer- or nanometer-sized cross-sectional features, e.g., fibers with diameters or cross-sectional dimensions of 0.5 micrometers or less, or from about 50 nanometers to about 300 nanometers), are formed by extruding a polymer melt through a small nozzle or orifice and surrounding it with a high-velocity air stream (e.g., air). The formed fibers are randomly deposited upon emerging from the orifice of the meltblown device to form a nonwoven web. Nonwoven webs can be used in filtration media, adsorbents, various textiles for clothing, hygiene products, and even drug delivery and / or other medical systems (e.g., to form stents and bandages).

[0004] Conventional meltblown systems include a polymer supply section, which contains an extruder that supplies one or more polymer materials (e.g., in solid form) to a melter. The polymer is melted in the melter and then sent to a metering section. The metering section contains one or more metering pumps that control the polymer throughput. Downstream from the metering section is a die assembly, which contains a polymer supply and distribution configuration (e.g., a coat hanger type, or other suitable configuration) to ensure a uniform polymer flow and desired residence time across the entire die width. The end of the die outlet is typically equipped with a nose tip with an orifice and a hot air manifold that supplies an airflow of a predetermined temperature and velocity, stretching the molten polymer, which then begins to solidify and form fibers as it exits the orifice. The fibers formed from the solidifying polymer are blown into a collection device, where they are aggregated to form a nonwoven web.

[0005] In conventional melt-blown systems, the hot air manifold supplies heated air considerably upstream of the die tip. As a result, the die is primarily heated by this heated air. The temperature of the heated air is adjusted to achieve a predetermined die tip temperature necessary to obtain the filament stretching rate required for good spinning and melt-blown. Due to air loss (e.g., adiabatic expansion as it exits the die tip), the air entering the die must be much hotter than the optimal die tip temperature (e.g., 30°C or more higher). This causes the polymer temperature in the polymer pool within the die to rise to a temperature equal to or close to the heated air temperature in the manifold. This is particularly noticeable when the polymer residence time is 1 minute or longer. For example, when forming microfibers (e.g., fibers with a diameter of 0.75–1.5 μm) using a conventional melt-blown system, the polymer residence time becomes very long due to the large polymer channels and orifices inside the die, causing the polymer inside the die to rise to almost the same temperature as the heated air. A similar phenomenon can occur, for example, when forming composite fibers (two-component or multi-component fibers). This is particularly problematic when the flow rate of one polymer component is less than 50% of the total.

[0006] Polymers commonly used to form meltblown fibers (e.g., polypropylene) can withstand the high temperatures in the die. However, newer polymeric materials (e.g., biodegradable polymers, thermally degradable polymers, and thermally degradable additives) currently being used or considered for use in textiles and other fibrous materials may degrade when exposed to the high temperatures in the die.

[0007] Therefore, what is desired is a meltblown system that can more effectively control the temperature of the molten polymer within the die to efficiently form nonwoven webs composed of fibers with appropriate dimensions (e.g., micro- or nanofibers) and desired shapes, and that can utilize a wide range of polymers and other materials. Summary of the Invention

[0008] The meltblown system of the present invention includes a die having a die inlet end that receives molten polymer from a polymer source, a cavity located downstream from the die inlet end through which the molten polymer flows, and a die outlet end that receives the molten polymer from the cavity and delivers it to an orifice at the die outlet end. A fluid supply includes a fluid inlet and a fluid channel connected to the fluid inlet and extending to the die outlet end, and supplies fluid to the die outlet end for drawing a fiber formed from the molten polymer emerging from the die outlet end. The fluid supply supplies fluid at a temperature T2 that is different from the molten polymer temperature T1 in the cavity, and the system is configured to independently maintain the molten polymer in the cavity at temperature T1 during operation.

[0009] Additionally, a method of forming a meltblown product includes directing molten polymer through a plurality of orifices at a die outlet in a meltblown system, the molten polymer being maintained at a temperature T1, and forming fibers by contacting the molten polymer emerging from the die outlet with a fluid at a temperature T2, different from temperature T1. The molten polymer in the die is maintained at temperature T1 when it emerges from the die outlet and contacts the fluid.

[0010] The meltblown systems of the present invention can efficiently form nanofibers with diameters less than 1 micrometer (eg, 100 nanometers or less), as well as larger fibers (eg, about 1-10 micrometers in diameter).

[0011] Further features and advantages of the present invention will become apparent from consideration of the following detailed description of specific embodiments. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of a conventional meltblown system.

[0013] [Figure 2] FIG. 1 is a cross-sectional view of a portion of a die for a conventional meltblown system, taken along the longitudinal direction of the die.

[0014] [Figure 3] 3 is a cross-sectional view of the conventional die shown in FIG. 2, taken along a direction intersecting the longitudinal direction of the die.

[0015] [Figure 4] FIG. 1 is a perspective view of a die for a meltblown system according to an embodiment of the present invention.

[0016] [Figure 5] 5 is a cross-sectional view of a portion of the die of FIG. 4, taken along the longitudinal direction of the die.

[0017] [Figure 6] 5 is an enlarged cross-sectional view of the spin pack in the die of FIG. 4, showing a cross section along the longitudinal direction of the spin pack and die.

[0018] [Figure 7] 5 is a cross-sectional view of the die of FIG. 4 taken along a direction perpendicular to the longitudinal dimension of the die (ie, perpendicular to the cross-section of FIG. 5).

[0019] [Figure 8] Figure 7 is an enlarged view of a portion of the cross-section, showing the point at the tip of the spin pack where the polymer exits the discharge port and comes into contact with heated air.

[0020] Throughout this specification, the same elements are denoted by the same reference numeral. DETAILED DESCRIPTION OF THE INVENTION

[0021] As described herein, the meltblown spinning system and method of synthetic fibers achieve and maintain independent and isolated temperature control between the molten polymer in the meltblown die and the gas (e.g., air) used to stretch the polymer emerging from the die for fiber formation.

[0022] The meltblown system according to the present invention may include one or more extruders, a screw for generating and conveying molten polymer, a device for driving or pumping the polymer, a die for metering and guiding the molten polymer to an orifice of a die tip, a gas source (usually heated air) that comes into contact with the polymer flow out of the orifice and stretches it to form fibers, and a collection station for collecting the formed fibers to produce fabrics or other products.

[0023] Conventional meltblown systems can produce fibers from a wide variety of polymers, including polyolefins (e.g., polyethylene, polypropylene, polybutylene), polyesters (e.g., polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polytrimethylene terephthalate (PTT), polybutylene terephthalate (PBT)), polyacrylamides, polyurethanes, polylactic acid (PLA), polyamides (e.g., nylon 6, nylon 6.6, nylon 6.10), polyvinyl alcohol (PVA, e.g., ethylene vinyl alcohol), and their various grades (e.g., different grades of PLA, PP, PET), block copolymers, and combinations thereof. Furthermore, fibers with different cross-sectional shapes (e.g., bicomponent side-by-side, sheath-core, islands-in-the-sea, and segmented pie) can also be produced.

[0024] However, as mentioned above, conventional meltblown systems lack temperature separation between the polymer heated in the die and the heated gas used to draw the fiber, making it difficult to form fibers containing certain temperature-sensitive polymers or additives. Examples of temperature-sensitive polymers include certain polyolefins (polypropylene (PP), polyethylene (PE)), polyvinyl alcohol (PVA), ethylene vinyl alcohol, polylactic acid (PLA), polyamide 6 (PA-6), polyamide 11 (PA-11), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), polyurethane (PU), and even polyhydroxyalkanoates (PHAs) (e.g., PHBH from Kaneka Corporation, Tokyo). TM Examples of heat-sensitive additives include magnesium stearate, which is added to polymers used to form filtration media and, in particular, masks (e.g., M95 masks). Therefore, the use of one or more heat-sensitive polymers, along with the addition of heat-sensitive additives, can make it very difficult to manufacture nonwoven fabrics or textiles using conventional meltblown equipment and methods.

[0025] The meltblown system of the embodiment illustrated in Figure 1 comprises an extruder 2 that receives a solid polymer (e.g., pelletized polymer) from a hopper 1, and a pump or drive device 4 (e.g., a motor for a screw extruder) for the extruder 2. The extruder 2 is heated to a suitable temperature to melt the polymer material in the hopper 1, and the molten polymer is supplied to the inlet of the die 3. Figure 1 shows a configuration in which a single molten polymer flow based on polymer supplied from one hopper 1 is supplied through the extruder, but the system can also be configured to include two or more hoppers and extruders, forming multiple molten polymer streams containing different polymers to form single-component fibers, two-component fibers, three-component fibers, multi-component fibers, etc. The molten polymer that has passed through the die 3 is discharged from an opening or orifice 6 provided at the die outlet end (e.g., formed in the shape of a chip), and is stretched by heated air from hot air sources 13 and 14 to form fibers 7. The formed fibers 7 are deposited on a collection surface 8 (e.g., a conveyor belt system driven by axles 9) to form a nonwoven web or mat 10. The nonwoven mat 10 may be further compressed and / or bonded by rolls before being collected by a take-up roll or other collection device.

[0026] As shown in Figures 2 and 3, a conventional melt-blown die 3 comprises a pump 15, a pump block 18, and a spin pack 22. The pump block 18 receives molten polymer from the pump 15 and guides it through an inlet cavity 16 located within the pump block 18 to a lower cavity 20, and further to an orifice 6 in the spinneret of the spin pack 22. The channels within the pump block 18 are sized to regulate the polymer throughput within the die and, if necessary, to merge the polymer flow within the spin pack of the die. The channels within the spin pack include multiple manifold plates, through which channels formed by machining, drilling, etc., are provided. Openings and channels in vertically stacked plates communicate with each other, defining channels that extend to the orifice 6.

[0027] The spin pack inlet includes a pack filter 25, located between the upper cavity 16 and the lower cavity 20. The polymer passes through the pack filter 25 and flows into a channel leading to the orifice 6. Many conventional dies, such as die 3 shown in FIGS. 2 and 3, include a wide channel or cavity 20 below / downstream of the pack filter 25 to form a large-volume reservoir or pool of molten polymer from which it flows to the orifice 6 at the die exit end. The dimensions of cavity 20 are larger than the other polymer channels in the die and serve to control the residence time of the molten polymer within the die before fiber formation. This is found in known meltblowing die configurations, such as those described in U.S. Pat. Nos. 3,825,379; 3,825,380; 4,720,252; 6,972,104; 10,975,500; and 11,447,893, all of which are incorporated herein by reference. For example, the die 3 shown in Figure 3, which includes a cavity 16, is sometimes referred to as a "coat hanger die." This is because the cavity extends from the inlet (where the molten polymer is delivered from pump 15) along the length of the die in the cross-sectional direction (CD), resembling a coat hanger shape. As used herein, "machine direction (MD)" refers to the dimension of the die corresponding to the direction of web travel (i.e., the overall flow direction of the web formed from the fibers extruded from the die), and "cross dimension (CD)" refers to the direction perpendicular or 90° to the machine direction (MD). Such channels or cavities are easily formed (e.g., cut) with tooling during die manufacture.

[0028] Heated fluid or gas, typically air, is used to draw the molten polymer and form fibers of the desired cross-section, denier, and shape. Heated air is introduced into the die 3 via one or more air sources or air manifolds 30. The inlet of the air manifold 30 is typically located at the top of the die 3 and distributes the heated air along or through the pump block 18 to adjacent cavities 16, 20, and other die structures through which the molten polymer flows. Specifically, heated air enters the manifold 30 at the top of the die 3 through an inlet, flows along the pump block 18, and is then directed downward to the die tip through channels 32 on both sides of the die. Small channels or air slots 34 (e.g., adjustable air slots or air knives) on both sides of the die are then injected toward the molten polymer emerging from the orifices 6 of the die 3. The molten polymer exiting the orifices 6 forms an extruded fiber, which is drawn by contact with the surrounding heated air.

[0029] Providing the manifold 30 at the top of the die 3 facilitates die installation in a meltblown system. This configuration also has the advantage that the spin pack 22 is separated from the heated air source, allowing it to be easily removed from the die 3 and replaced. Furthermore, supplying heated air from the top of the die helps heat the die, which is useful for forming certain fibers (e.g., polypropylene fibers). Furthermore, adjusting the temperature of the heated air allows for a die tip temperature that achieves the desired spinning and filament draw rates required for meltblowing. Because of heat losses due to adiabatic expansion and other factors as the heated air exits the die, the temperature of the heated air introduced at the top of the die 3 must be significantly higher than the optimal die exit / die tip temperature. For example, the temperature should be at least 30°C higher than the molten polymer temperature, and in some cases even higher.

[0030] Residence times of the molten polymer within the die (e.g., in the large volume cavities or pools formed in the enlarged "coat hanger" portion of cavity 16 and the wide portions of cavity 20, and / or through very small channels such as those used to form microfibers) can be as long as 10 minutes or more in conventional dies, resulting in the molten polymer within the die reaching temperatures comparable to or nearly the same as the temperature of the heated air.

[0031] For example, as shown in FIG. 3 , heated air is supplied at temperature T2, while the molten polymer in the channels of die 3 is heated to temperature T1. Here, temperature T2 is typically significantly higher than temperature T1 (e.g., 30° C. or higher). As an example (e.g., when the molten polymer includes polypropylene), temperature T1 may be 230° C., and temperature T2 (the temperature of the heated air) may be 270° C. Furthermore, as can be seen from the T1 and T2 arrows in FIG. 3 , the molten polymer in the die enters pump block 18 from pump 15 at temperature T1, but heats up to approach, and possibly even reach, temperature T2 by the time it reaches widened cavity 20. This occurs because heated air surrounds the channels in pump block 18 and other parts of die 3. Specifically, air is introduced through manifold 30 and air inlet at temperature T2 and maintained at that temperature as it passes through flow passage 32 (which also extends vertically along the side of die 3) to orifice 6. Heat transfer between air channel 32 and die 3 often heats the polymer residing within and flowing through cavity 20, causing it to reach a temperature equal to or close to temperature T2 when it exits die orifice 6. Historically, this has not been a problem given the types of polymers traditionally used to form fabrics and other textile products. However, as noted above, this can be problematic for certain novel polymers (e.g., certain biodegradable polymers) or when the polymer contains heat-sensitive additives that may be degraded when heated to the temperature T2 of the heated air flowing through and / or along the die.

[0032] According to embodiments described herein, a meltblown system comprises a die in which a source of heated air or fluid, including a manifold and an inlet, is positioned to be thermally isolated (i.e., prevent or significantly limit heat exchange between the heated air and the polymer passage) from all polymer passages in the die until the polymer is ejected from the orifice of the die tip. This can be achieved by positioning the heated air flow path appropriately away from the polymer passage and / or by providing sufficient insulation between the heated air channel and the polymer passage. Furthermore, the dimensions of the polymer flow passage in the die can be appropriately set to reduce the residence time of the molten polymer in the die and prevent or minimize heat transfer between the heated air (or other heated gas or fluid) used to stretch the fibers extruded from the die and the molten polymer.

[0033] As an example, a manifold with an inlet for introducing heated air (or other heated gas / fluid) to stretch the extruded fibers discharged from the die's outlet orifice may be positioned near the spin pack (e.g., attached to the spin pack) and / or close to the die's outlet orifice, and configured to minimize the contact area between the heated air and the parts of the die, as well as the heat transfer between them. This also minimizes heat transfer between the heated air (or other heated gas / fluid) and the molten polymer flowing through the die.

[0034] Figures 4 to 8 show an example of a die that effectively separates and independently maintains the temperature of the polymer flow and airflow within and along the die. Similar to die 3, die 100 includes a pump 115 that receives molten polymer from a molten polymer source (e.g., extruder 2 shown in Figure 1) and supplies it at an appropriate flow rate to a supply passage or channel 120 in a pump block 118. Die 100 further includes a spin pack 122 that is detachably attached to a portion of die 100.

[0035] A feed channel 120 delivers molten polymer from a pump 115 to a pack filter of a spin pack, located partially within the die 100. The pack filter defines a cavity 124 within the spin pack 122 (best seen in FIGS. 5 and 6 ), which extends along the longitudinal machine direction (MD) of the spin pack 122 or is formed along its cross section. A plurality of feed channels 126 extend vertically downward from the pack filter cavity 124 toward smaller sub-channels 128. Specifically, each feed channel 126 tapers outward in the longitudinal machine direction (MD) cross section of the spin pack 122. Thus, the outlet end of each feed channel 126 is wider than its inlet end. Furthermore, a plurality of sub-channels 128 extend from the outlet end of each feed channel 126. The subchannels 128 may be formed, for example, as grooves or etchings along a flat surface or plate portion of the spin pack 122 located at the widened outlet of each feed channel 126. The subchannels 128 lead to smaller diameter exit orifices 130 through which the molten polymer is extruded from the die 100. The cavity 124 has much larger dimensions compared to the channels 126, 128. Therefore, the residence time of the molten polymer within the cavity 124 is significantly longer than the residence time of the molten polymer flowing within the channels 126, 128. However, because the dimensions of the cavity 124 are much smaller than the dimensions of the cavity 20 of the conventional meltblowing die 3 (FIGS. 2 and 3), the overall residence time and throughput of the molten polymer through the die 100 of FIGS. 4-8 is still lower than that of the conventional die 3 (FIGS. 2 and 3).

[0036] The spin pack 122 is detachably connected to a part of the die 100 (e.g., the pump block 118), allowing for easy replacement with a different spin pack. This allows for modification of the polymer flow / network channel within the spin pack of the die, thereby controlling the type, shape, etc., of polymer fibers that can be formed. For example, by providing and installing different spin packs for the same die, fibers with one or more types of polymer (mono-component / homo-component fibers, two-component, three-component, multi-component fibers) and fibers of different sizes, deniers, and geometric shapes (circular, irregular, sea-core, side-by-side, sea-island, trefoil, or multi-lobed, etc.) can be formed. Therefore, the inlet for the molten polymer in the die (including at least a portion of the channel 122) is located in a part of the die that is not within the spin pack, and the spin pack, including the die outlet orifice 130, is separable or removable from the part of the die containing the molten polymer inlet (e.g., the pump block 118 or other parts of the die).

[0037] As mentioned above, in conventional meltblown dies (e.g., die 3 shown in Figures 2 and 3), the manifold 30 and air inlet are fixed to a suitable position considerably upstream of the spin pack (e.g., spin pack 22), for example, on the pump block 18. This configuration makes it easier to remove the spin pack from the die (because it is less necessary to detach components other than the spin pack from the pump block). Furthermore, as mentioned above, it is sometimes desirable to have some heat transfer between the heating airflow and the die, which results in heat transfer with the molten polymer and can increase thermal efficiency (especially when the temperatures of the polymer and air may be equivalent or similar in the meltblown process).

[0038] In contrast, the meltblowing die 100 described herein includes a source of heated air (or other heated fluid), along with an inlet and channel, located well downstream of the molten polymer pool or cavity within the pump block and die, and closer to the spin pack and its exit orifice. Specifically, a pair of heated air supply units or manifolds 140 are attached to the spin packs 122, located on opposite sides of the die 100, below the pump block 118. As shown in Figures 7 and 8, each manifold 140 is attached to opposite sides of the spin pack 122 and includes an air inlet 142 that leads to a channel 146 within the spin pack 122 and supplies heated air (or other fluid) to a narrow channel 152 in a corresponding air knife 150. Each air inlet 142 and channel 146 is positioned well below the pack filter cavity 124. In other words, each air inlet 142 and air channel 146 (as well as all other air channels supplying decelerating flow to the exit orifice 130) is positioned downstream (i.e., in the MD direction) of the cavity 124 and is located between the cavity 124 and the exit orifice 130. The air inlet 142 of each manifold 140 is at least partially, and preferably substantially, surrounded or sealed by an insulating member 144, which limits or prevents heat transfer between the air inlet 142 and the spin pack 122, as well as the pump block 118 and / or other portions of the die 100. The insulating member 144 may be composed of, for example, fiberglass, mineral wool, or other material with sufficiently low thermal conductivity to adequately insulate the air inlet.

[0039] Each air knife 150 is positioned adjacent to the end of the spin pack 122, including the corresponding manifold 140 and outlet orifice 130, such that a portion of the channel 146 and narrow channel 152 are defined between the surface of the spin pack, the manifold, and the air knife. Specifically, the outlet end of the spin pack 122 has a tapered (e.g., V-shaped) shape, and the outlet orifices 130 are located at the end or tip of the spin pack. The air knives 150 are positioned to surround the tapered outlet end of the spin pack 122, forming narrow channels 152 between the opposing exterior surfaces of the spin pack outlet end and each air knife. As best shown in Figure 8, the narrow air channels 152, located on either side of the spin pack outlet, extend downward and converge toward each other, allowing heated airflow to exit each channel 152 and meet with polymer exiting each outlet orifice 130 of the spin pack, thereby drawing the extruding fiber.

[0040] Thus, the heated air from manifold 140 is physically and thermally isolated from the molten polymer flowing through pump block 118 and most of die 100. This is because manifold 140 is located well below pump block 118 and does not come into contact with it at all. Furthermore, heated air channels 146 and 152 are located below and sufficiently isolated (both physically and thermally) from pack filter cavity 124 (i.e., the location of the molten polymer's longest residence time within the die and spin pack). This minimizes or prevents heat transfer between the molten polymer in the die (particularly within the spin pack) and the heated air and corresponding air inlets 142 and channels 146, 152 in manifold 140. As a result, the molten polymer is effectively isolated and separated from the heated air (or other fluid) through the die and to the exit orifice, maintaining a nearly constant temperature from the die entrance at the pump and pump block to the die exit orifice. In particular, the molten polymer flowing through the die 100 is maintained at a temperature T1 that is significantly different from the temperature T2 of the heated air (or other fluid source). For example, the difference between the temperature T1 of the molten polymer and the temperature T2 of the heated air can be maintained by at least about 20°C, or at least about 30°C, at least about 40°C, or at least about 50°C or more. By way of further example, in a scenario where the temperature T1 of the molten polymer is set to 230°C throughout the die and at the discharge port, and the heated air is set to 270°C, the polymer temperature can be maintained at 230°C throughout the molten polymer's residence time within the die 100, and the polymer will exit the discharge orifice 130 at the set temperature T1.

[0041] Thermal separation and isolation between polymer temperature and heated air can be further enhanced by effectively minimizing the residence time of the molten polymer within the die. For example, the network of polymer flow channels (including the pack filter cavity 124, supply channel 126, subchannel 128, and discharge orifice 130) through the supply channel 120 and spin pack 122 of the pump block 118 can be appropriately sized to achieve a desired residence time (i.e., the time from when the polymer enters the spin pack from the supply channel 120 to when it exits the spin pack through the discharge orifice 130). This residence time minimizes heat transfer between the internal channel surface of the die and the polymer flowing through it. In particular, the residence time is controlled in combination with the appropriate arrangement of heated air supply and airflow channels described herein to effectively maintain the molten polymer at a desired temperature until it passes through the die and is discharged.

[0042] For example, the polymer supply channel 126 of die 100 has a much smaller cross-sectional dimension and a larger length-to-diameter (L / D) ratio compared to the pack filter cavity 124 and the wide die channel 20 of a conventional meltblown beam 3. Conventional dies include a wide die pool or cavity, for example, having a width or cross-sectional dimension of about 0.5 to 0.75 inches (about 1.27 to 1.91 cm) in the machine direction (MD) of the die and a continuous dimension along the cross direction (CD). The volume of the wide channel or cavity 20 in a conventional meltblown die is typically about 645 cm³ per meter in the CD direction of the cavity. 3 From approximately 1450cm 3 In addition, providing such a large width or cross-sectional dimension within the die reduces the pressure within the die. However, the large volume of cavity 20 in this conventional die increases the residence time of the molten polymer within the die.

[0043] In contrast, the pack channels 126 in the spin pack 122 of the die 100 have a much smaller width / cross-sectional dimension than the passages or cavities in conventional dies. For example, each pack channel 126 in the meltblown die 100 has a width in the machine direction (MD) of about 0.020 inches to about 0.040 inches (about 0.05 cm to about 0.10 cm), e.g., about 0.03 inches (about 0.08 cm), and a discrete (varying) dimension in the cross direction (CD). The volume of the channel 126 is significantly smaller than that of conventional meltblown dies, approximately 50 cm per meter of cavity in the CD. 3 For example, the volume defined by the channel 126 of the melt blown die 100 is approximately 15 cm per meter in the CD direction of the cavity. 3 ~about 35cm 3 (For example, about 25 cm 3 ) can be.

[0044] Furthermore, while the cross-sectional dimension or diameter of a die outlet orifice is typically limited to about 0.007 inches (about 0.0178 cm), the cross-sectional dimension or diameter of the outlet orifice 130 of the die 100 can be as small as about 0.004-0.005 inches (about 0.010-0.013 cm). As a result, the L / D ratio of the outlet orifice 130 in the die 100 can be at least 50:1, at least 75:1, at least 100:1, at least 125:1, or even 150:1 or greater. In contrast, the L / D ratio of the channels in a conventional meltblown die is limited to a maximum of 10:1. This is because in conventional dies, there is no small channel leading from the cavity 20 to the orifice 6; instead, the cavity 20 feeds the orifice 6 directly.

[0045] The manufacture of die 100 requires high-precision machining (extremely precise machining) inside the die to achieve the small dimensions of channels 126 and 128. However, these small channel dimensions result in a smaller channel volume and a shorter residence time for the polymer within the die. Consequently, due to these differences in die channel / cavity dimensions, the residence time for polymer in conventional meltblonde dies is approximately 20 to 50 seconds under a maximum flow rate of 80 kg / m / hour, while in meltblonde die 100 it is approximately 0.3 to 1.2 seconds (e.g., approximately 0.6 seconds) under the same flow rate conditions.

[0046] During operation, die 100 can be implemented in the system shown in Figure 1 (i.e., die 3 is replaced by die 100). One or more types of polymer (e.g., monocomponent or homocomponent fibers, binary fibers, multicomponent fibers, etc.) are supplied from at least one hopper 1 to the inlet of die 100 via at least one extruder 2. Pump 115 of die 100 delivers the molten polymer to the supply channel 120. From the supply channel 120, the molten polymer is led to the pack filter cavity 124 and then to the channel 126 of the spin pack 122. From the cavity 124, the polymer flows further into multiple supply channels 126, from which it is further led into multiple subchannels 128, and finally to the discharge orifice 130.

[0047] Heated air is introduced from the manifold 140 through the air inlet 142 into channel 146 in the spin pack 122. This channel 146 is positioned at an appropriate distance below the filter cavity 124. This thermally isolates the molten polymer remaining in the cavity 124 from the heated air flowing through the spin pack 122. The heated air then flows from channel 146 into channel 152 of the air knife 150, where it is ejected to converge from the outlet end of the spin pack 122, flowing towards the polymer being pushed out from the discharge orifice 130, forming polymer fibers 7. The formed fibers 7 are gathered on the surface 8 and further processed.

[0048] By thermally isolating the airflow from the molten polymer flowing through die 100 (including spin pack 122) and reducing the residence time of the polymer flow within the die, a large temperature difference between the temperature of the molten polymer, T1, and the temperature of the heated air, T2, can be achieved during operation, where temperature T1 remains constant relative to the molten polymer throughout the die 100 until it reaches the die exit orifice 130 and is extruded. This is true whether the temperature of the molten polymer, T1, is lower or higher than the heated air temperature, T2.

[0049] Thus, the embodiments described herein and illustrated in Figures 4-8 allow for precise temperature control of the polymer within the die, regardless of differences between the polymer temperature and the drawing air temperature, facilitating the production of meltblown fibers. By separating the heated air inlet and heated air channel from the polymer channel within the die, the desired thermal isolation and temperature independence of the polymer is achieved. In other words, higher air temperatures do not affect the polymer temperature within the die before it exits the die for fiber formation.

[0050] 4-8, the polymer temperature T1 can be maintained throughout the die without the higher heated air temperature T2 altering the polymer temperature. Additionally, the low volume design of the die cavity 124 minimizes polymer residence time, helping to maintain the polymer at the desired temperature T1 (e.g., even if the die temperature increases slightly due to the higher heated air temperature T2).

[0051] The meltblown systems described herein are also highly effective in forming fibers using high-temperature, heat-resistant polymers with very high melting points, where the temperature T1 of the molten polymer in the die is greater than the temperature T2 of the air or gas that stretches the polymer as it emerges from the die exit to form a fiber.

[0052] Thus, embodiments of the present invention provide a meltblown die and system configured to receive process air proximate the die tip / spin pack exit end, away from the polymer path. This thermally isolates the polymer from the air heat. Isolating and insulating the heated air manifold, inlet, and channel from the die allows for independent temperature control of the polymer within the die, further reducing residence time within the die and increasing throughput, thereby achieving many improvements in meltblown fiber production. The following provides an exemplary description of some of the advantages of the temperature-isolated meltblown die and system described herein and illustrated in the embodiments of Figures 4-8.

[0053] For example, embodiments described herein enable the production of meltblown fabrics and textiles using heat-sensitive polymeric materials and heat-sensitive additive materials that are added to the polymeric materials to form the meltblown fibers without the risk of overheating or degrading the heat-sensitive materials during the manufacturing process. Non-limiting examples of heat-sensitive polymers are described below. As described herein, the molten polymer flowing through the meltblown die can maintain the heat-sensitive polymer and heat-sensitive additive below their decomposition or degradation temperatures, even when the temperature of the heated air (or heated fluid) used to draw the fibers exceeds their decomposition temperatures.

[0054] Furthermore, the embodiments described herein facilitate the manufacture of meltblown fabrics and textile products using high-temperature, heat-resistant polymers without changing the molten polymer temperature inside the die, even while using a low-temperature airflow.

[0055] By using the embodiments described herein, it is possible to reduce spinning defects (e.g., shots and flies) in meltblown fibers compared to conventional meltblown systems.

[0056] Additionally, the present embodiments enable optimal production of fabrics and other textile products containing thermally decomposable materials, including fibers formed from temperature-sensitive polymers, fibers formed from biodegradable polymers, and fibers containing temperature-sensitive additives, because the die configuration allows for more precise and independent control of the melting temperatures of different polymer components within the die (e.g., when making bicomponent or multicomponent fibers, especially when one or more polymers are heat-sensitive and have a melting point much lower than the heated gas / air temperature). Examples of polymers that can be used to form fibers using the die configurations described herein and maintain the desired molten polymer temperature within the die include polyolefins (polypropylene (PP), polyethylene (PE)), polyvinyl alcohol (PVA), ethylene vinyl alcohol (EVOH), polylactic acid (PLA), polyamide 6 (PA-6), polyamide 11 (PA-11), polyethylene terephthalate (PET), polytetrafluoroethylene (PTFE), polyurethane (PU), and biodegradable polymers (such as PHBH™ biodegradable PHA, available from Kaneka Corporation, Tokyo), polybutylene adipate terephthalate (PBAT), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). Examples of heat-sensitive additives include magnesium stearate and starch for textile applications. In particular, thermosensitive polymers and additives having degradation or decomposition temperatures below 270°C, e.g., 260°C or less, 250°C or less, or even 245°C or less, can be used to effectively form monocomponent, bicomponent, and multicomponent fibers and incorporate them into fabrics. An example of a thermosensitive additive contained in the polymer forming the filter material, particularly a mask (e.g., M95 mask), is magnesium stearate (e.g., Techmer's PPM13774 as an additive to polypropylene). The temperature of the heated air (or heated fluid) effective for drawing the fibers is typically at least about 250°C, at least about 260°C, or even at least about 270°C. Therefore, meltblown systems using the die configurations described herein are particularly suited to forming masks containing magnesium stearate.

[0057] This embodiment enables the formation of meltblown fabrics and textile products containing a higher proportion of nanofibers (e.g., fabrics and textile products containing more than 25% nanofibers). In particular, the meltblown system of the present invention facilitates the formation of meltblown microfibers and nanofibers (i.e., fibers with a diameter or cross-sectional dimension of 0.5 micrometers or less, or in the range of about 50 nanometers to about 300 nanometers). The meltblown die described herein provides a wide operating window that allows the use of heated air or heated gas at a temperature much higher than the polymer melting temperature. This makes it possible to form finer meltblown fibers without degrading the polymer in the die. The low flow rate (and therefore high residence time) associated with forming microfibers and nanofibers makes the present invention far more advantageous than conventional meltblown systems.

[0058] This embodiment allows for the formation of meltblown fabrics and textiles with smaller fibers, even when operating at the same grams / holes / minute or kg / m / hr die width conditions as conventional meltblown systems.

[0059] This embodiment allows for the formation of meltblown fabrics and textiles with a narrower fiber diameter distribution, even when operating at the same grams / holes / minute or kg / m / hr die width conditions as conventional meltblown systems.

[0060] This embodiment further enables the formation of fibers containing high-temperature polymers and / or high-performance polymers, and fabrics incorporating them. These include, but are not limited to, polyamides (polyamide 6 (PA-6), polyamide 66 (PA-66)), polyethylene terephthalate (PET), polyurethane (PU), polyetherimide (e.g., polyetherimide commercially available under the trademark ULTEM), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), and ether-based polyurethane foams including melamine foam (e.g., POLYDAMP® sound-absorbing foam (PAF) from Polymer Technologies). Such high-viscosity polymers have a melt flow rate (MFI) of at least about 8 g / 10 min, or at least about 10 g / 10 min, where the MFI is measured according to the ASTMD1238 or ISO1133 standard. These types of polymers are usually unusable for fiber formation in conventional melt-blown systems due to their high viscosity. However, the meltblown dies and systems described herein can process these polymers, even if the fiber diameter is at least 3 micrometers, at least 5 micrometers, or in the range of 5 to 10 micrometers. This is made possible by operating the system with very hot heated air (e.g., superheated air at a temperature about 20 to 80°C higher than the molten polymer temperature, and at least 30°C higher than the die tip / die exit end). Using superheated air, the polymer is heated after being extruded from the die exit end, making high-viscosity polymers, which are difficult to apply in conventional meltblown systems, available.

[0061] This embodiment allows for the production of meltblown fabrics and textiles at higher production rates (kg / m / hr or kg / hr) with properties equivalent or similar to those of conventional meltblown systems.

[0062] Example

[0063] The advantages of a meltblown system including the die configuration described herein and shown in Figures 4-8 were demonstrated by comparing it with a conventional meltblown system of the type shown in Figures 2 and 3. Both systems used the same polymer, the same molten polymer temperature T1 (the temperature of the molten polymer at the die inlet), and the same heated air temperature T2. The polymer used was polypropylene, and the ideal or desired molten polymer temperature T1 to be maintained in the die was 240°C. The air inlet temperature T2 was set at 270°C, and the desired die tip outlet temperature was 240°C. The polypropylene fibers were 2 μm in diameter and formed into a meltblown nonwoven fabric for an N95 mask.

[0064] The systems shown in Figures 4-8 were found to exhibit at least a 55% increase in throughput (70 kg / m / hr vs. 45 kg / m / hr) over conventional systems for producing the same nonwoven fabric. Conventional dies could not be operated beyond 45 kg / m / hr without degradation of the resulting fibers due to inadequate heating of the molten polymer within the die caused by the heated air. In contrast, the systems shown in Figures 4-8 were capable of much longer operation without degradation of the resulting polymer fibers, even at throughputs approaching 80 kg / m / hr. Furthermore, the systems shown in Figures 4-8 maintained the desired polymer temperature throughout the polymer residence time within the die, despite the large temperature difference between the heated air temperature T2 used to draw the fiber and the molten polymer temperature T1. This contrasts with the conventional systems shown in Figures 2 and 3, where the molten polymer temperature T1 within the die varied (approaching temperature T2 upon exiting the die) and was therefore unable to maintain the desired temperature.

[0065] Thus, the present invention provides the following:

[0066] A meltblown system comprising: a die including a die inlet end that receives molten polymer from a polymer source; a cavity located downstream of the die inlet end through which the molten polymer flows; a die outlet end that receives the molten polymer from the cavity and delivers it to an outlet orifice at the die outlet end; and a fluid supply comprising a fluid inlet and a fluid channel connected to the fluid inlet and extending to the die outlet end, for delivering fluid to the die outlet end to draw a fiber formed from the molten polymer exiting the die outlet end, wherein the fluid supply delivers fluid at a temperature T2 that is different from a temperature T1 of the molten polymer in the cavity, and the meltblown system is configured to independently maintain the molten polymer in the cavity at temperature T1 during operation.

[0067] The temperature T2 may be higher than the temperature T1.

[0068] The meltblown system may further include a plurality of channels extending from the cavity to a discharge orifice at the die exit end, each channel of the plurality of channels having an L / D ratio of at least 50:1.

[0069] The system's gas inlet and fluid channels may be spaced apart from the cavity and positioned between the cavity and the die outlet end.

[0070] The die outlet end may be disposed within a spin pack separable from a portion of the die including the die inlet end, the spin pack including the die outlet end. The fluid supply may also include at least one manifold attachable to the spin pack and supplying fluid at temperature T2 to the gas inlet. The manifold may be spaced from the cavity and positioned between the cavity and the die outlet end.

[0071] The die cavity of the system is approximately 50 cm per meter in the cross direction (CD) of the cavity. 3 The following volumes may be used:

[0072] In another embodiment, a method for forming a meltblown product includes directing molten polymer (at temperature T1) in a die of a meltblown system through multiple orifices at a die outlet, contacting the polymer emerging from the die outlet with a fluid at a temperature T2 different from temperature T1 to form fibers from the polymer emerging from the die outlet, wherein the molten polymer in the die is maintained at temperature T1 as the polymer emerges from the die outlet and contacts the fluid.

[0073] The temperature T2 may be higher than the temperature T1.

[0074] The fluid may include heated air.

[0075] The difference between temperature T1 and temperature T2 may be at least about 30°C, or at least about 50°C.

[0076] The die may include a cavity and a plurality of channels disposed below the cavity and extending to a discharge port at the die outlet, and fluid may be directed to the fluid channels within the die from a fluid source attachable to a portion of the die, the fluid source and the fluid channels being spaced from the cavity and positioned between the cavity and the discharge port.

[0077] The molten polymer may have a decomposition temperature of 245° C. or less, and the temperature T2 of the fluid may be at least about 260° C. Additionally, the molten polymer may include an additive having a decomposition temperature of 245° C. or less, and the temperature T2 of the fluid may be at least about 260° C.

[0078] The molten polymer may include additives, the additives including magnesium stearate.

[0079] The molten polymer may have a melt flow rate (MFI) of at least about 8 g / 10 min. Additionally, the molten polymer may further comprise one or more of polyamide, polyethylene terephthalate, polyurethane, polyetherimide, polyetheretherketone, polyetherketoneketone, and ether-based polyurethane foam.

[0080] Although the present invention has been described in detail with reference to specific embodiments, it will be obvious to those skilled in the art that various changes and modifications are possible without departing from the spirit and scope of the invention. Accordingly, the present invention is intended to encompass such changes and modifications as long as they fall within the scope of the appended claims and their equivalents.

Claims

1. 1. A meltblown system comprising: a die including a die inlet end for receiving molten polymer from a polymer source, a cavity downstream from said die inlet end through which the molten polymer flows, and a die outlet end for receiving the molten polymer from said cavity and delivering it to an outlet orifice at the die outlet end; and a fluid supply section comprising a fluid inlet and a fluid channel connected to the fluid inlet and extending to the die outlet end for supplying fluid to the die outlet end for drawing a fiber formed from molten polymer emerging from the die outlet end; wherein the fluid supply supplies a fluid at a temperature T2 that is different from a temperature T1 of the molten polymer in the cavity, and the meltblown system is configured to independently maintain the molten polymer in the cavity at temperature T1 during operation.

2. The meltblown system of claim 1 , wherein temperature T2 is higher than temperature T1.

3. The meltblown system of claim 1 further comprising a plurality of channels extending from the cavity to a discharge orifice at the die exit end.

4. The meltblown system of claim 3 , wherein each channel of the plurality of channels has an L / D ratio of at least 50:

1.

5. The meltblown system of claim 4 , wherein the fluid inlet and the fluid channel are spaced apart from the cavity and disposed between the cavity and the die outlet end.

6. 2. The meltblown system of claim 1, wherein the die outlet end is disposed within a spin pack separable from a portion of the die that includes the die inlet end, the spin pack including the die outlet end.

7. 7. The meltblown system of claim 6, wherein the fluid supply further comprises at least one manifold attachable to the spin pack that supplies fluid at a temperature T2 to the fluid inlet.

8. The meltblown system of claim 7 , wherein the manifold is spaced from the cavity and disposed between the cavity and the die outlet end.

9. The cavity of the die has a cross-direction (CD) of about 50 cm per meter of the cavity. ３ 2. The meltblown system of claim 1, having a volume of:

10. A method for producing a meltblown product, comprising: directing molten polymer in a die of a meltblown system through a plurality of orifices at a die exit, the molten polymer having a temperature T1; and contacting the molten polymer emerging from the die outlet with a fluid at a temperature T2 different from the temperature T1 to form a fiber from the molten polymer emerging from the die outlet; wherein the molten polymer in the die is maintained at a temperature T1 when the molten polymer emerges from the die exit and contacts the fluid.

11. The method of claim 10, wherein the temperature T2 is higher than the temperature T1.

12. The method of claim 10 , wherein the fluid comprises heated air.

13. 11. The method of claim 10, wherein the difference between temperature T1 and temperature T2 is at least about 30°C.

14. 11. The method of claim 10, wherein the difference between temperature T1 and temperature T2 is at least about 50°C.

15. 11. The method of claim 10, wherein the die includes a cavity and a plurality of channels disposed below the cavity and extending to a discharge orifice at the die outlet, the fluid being conducted to the fluid channels within the die from a fluid source attachable to a portion of the die, the fluid source and the fluid channels being spaced from the cavity and disposed between the cavity and the discharge orifice.

16. 11. The method of claim 10, wherein the molten polymer has a decomposition temperature of 245°C or less and the temperature T2 of the fluid is at least about 260°C.

17. 11. The method of claim 10, wherein the molten polymer comprises an additive having a decomposition temperature of 245°C or less, and the temperature T2 of the fluid is at least about 260°C.

18. 11. The method of claim 10, wherein the molten polymer comprises an additive, the additive comprising magnesium stearate.

19. 11. The method of claim 10, wherein the melt flow rate (MFI) of the molten polymer is at least about 8 g / 10 min.

20. 11. The method of claim 10, wherein the molten polymer comprises one or more of polyamide, polyethylene terephthalate, polyurethane, polyetherimide, polyetheretherketone, polyetherketoneketone, and ether-based polyurethane foam.

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