MELTBLOWN SPINNING WITH SEPARATE AND INDEPENDENT AIR AND POLYMER TEMPERATURE CONTROL

FIELD

The present invention relates to meltblown processes and related equipment for such processes.

BACKGROUND

A meltblown process, as used herein, refers to a process in which synthetic fibers, such as microfibers and nanofibers (i.e., fibers having cross-sectional geometries on the micrometer or nanometer sizes, e.g., fibers having a diameter or cross-sectional dimension(s) of no greater than 0.5 micrometers, or from about 50 nanometers to about 300 nanometers), are formed by extruding a polymer melt through small nozzles or orifices surrounded by a high speed blowing gas (e.g., air). The fibers formed and emerging from the orifices of the meltblown equipment can be deposited randomly to form a nonwoven textile web. Nonwoven fibrous webs formed from a meltblown process can be used in applications including, without limitation, filtration media, in sorbent materials, in various types of fabrics for apparel, hygiene products, and in drug delivery and/or other medical systems (e.g., in forming stents, bandages, etc.).

Conventional meltblown systems include a polymer feed section comprising an extruder to deliver one or more polymer materials (e.g., in solid form) to a melter, where melted or molten polymer material is then delivered from the melter to a metering section comprising one or more metering pumps that facilitate control of polymer throughput through the system. Downstream from the metering section is provided a die assembly that comprises a polymer feed distribution configuration (e.g., a coat-hanger configuration, or any other suitable configuration) that provides an even polymer flow and desired residence time across the width of the die. An outlet end of the polymer die typically includes a nose tip with orifices and a hot air manifold that provides air streams at set temperatures and velocities to attenuate the molten polymer where the polymer begins to solidify forming fibers near to where the polymer emerges from the die orifices. The fibers formed from the solidifying polymer emerging from the die orifices are blown toward a collection device for collecting the fibers and forming a nonwoven web.

The hot air manifold for conventional meltblown systems typically provides heated air at a location well above the die tip. This results in the die being heated primarily by the air from the hot air manifold. The temperature of the heated air is typically adjusted to achieve a particular die tip temperature required to achieve good spinning and filament attenuation velocities required in the meltblowing process. Due to air heat losses (e.g., adiabatic expansion as the air exits the die tip), the air entering the die must be much hotter than the optimum die tip temperature (e.g., greater than 30° C.). This causes polymer in the polymer pool within the die to also rise to a temperature that is at or near the heated air temperature in the manifold. This is particularly true when the polymer residence time within the die is 1 minute or greater. For example, when forming microfibers (e.g., fibers having diameters or transverse cross-sections of 0.75-1.5 micron) via a conventional meltblown system, the polymer residence time within the die (due to the large size of the polymer channels and orifices within the die) can be very long, resulting in the polymer being heated within the die to about the same temperature as the heated air. The same situation can occur, e.g., when bicomponent (or multi-component) fibers are formed in which one polymer component of the fibers has a flow rate of ≤50% of the total polymer flow rate.

Typical polymers (e.g., polypropylene) used to form meltblown fibers can tolerate the higher temperatures within the die. However, newer types of polymer materials that are being used or considered for use in fabrics and other fibrous materials (e.g., biodegradable polymers, thermally degradable polymers, thermally degradable additives, etc.) might degrade if subjected to the higher temperatures within the die.

Accordingly, it would be desirable to provide a meltblown system that is effective in forming nonwoven webs with fibers of suitable dimensions (e.g., micro or nanofibers) and/or having suitable geometries and that facilitate the use of a wide variety of polymer and/or other materials forming the fibers by more effectively controlling the temperature of the molten polymer material within the die.

SUMMARY

A meltblown system comprises a die comprising a die inlet end to receive 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 to receive the molten polymer from the cavity and deliver to outlet orifices at the die outlet end. A fluid supply comprises a fluid inlet and a fluid channel connected with the fluid inlet and extending to the die outlet end so as to deliver fluid to the die outlet end to attenuate fibers formed from molten polymer emerging from the die outlet end. The fluid supply provides fluid at a temperature T2 that differs from a temperature T1 of the molten polymer within the cavity, and the meltblown system is configured to independently maintain the molten polymer within the cavity at the temperature T1 during operation of the meltblown system.

In addition, a method of forming a meltblown product comprises directing molten polymer within a die of a meltblown system through a plurality of orifices at a die outlet, the molten polymer having a temperature T1, and directing a fluid to contact the molten polymer emerging from the die outlet to form fibers from the polymer emerging from the die outlet, the fluid having a temperature T2 that differs from the temperature T1. The molten polymer within the die is maintained at the temperature T1 when the polymer emerges from the die outlet and contacts the fluid.

Meltblown systems as described herein can effectively form nano fibers (e.g., fibers having diameters less than 1 micrometer, e.g., no greater than 100 nanometers) as well as larger sized fibers (e.g., fibers having diameters of about 1-10 micrometers).

The above and still further features and advantages of the present invention will become apparent upon consideration of the following detailed description of specific embodiments thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a conventional meltblown system.

FIG. 2 is a cross-sectional view of a portion of a conventional die for a meltblown system, where the cross-section is taken along a lengthwise dimension of the die.

FIG. 3 is a cross-sectional view of the conventional die of FIG. 2, where the cross-section is taken along a direction that is transverse the lengthwise dimension of the die (i.e., transverse the cross-sectional view of FIG. 2).

FIG. 4 is a view in perspective of a meltblown die for a meltblown system in accordance with embodiments described herein.

FIG. 5 is a cross-sectional view of a portion of the die of FIG. 4, where the cross-section is taken along a lengthwise dimension of the die.

FIG. 6 is an enlarged view of the spin pack for the die of FIG. 4, taken in cross-section along the lengthwise dimension of the spin pack and die.

FIG. 7 is a cross-sectional view of the die of FIG. 4, where the cross-section is taken along a direction that is transverse the lengthwise dimension of the die (i.e., transverse the cross-sectional view of FIG. 5).

FIG. 8 is an enlarged view of a portion of the cross-sectional view of FIG. 7 at a location of the spin pack tip where polymer emerges from an outlet orifice and contacts heated air.

Like reference numerals have been used to identify like elements throughout this disclosure.

DETAILED DESCRIPTION

As described herein, systems and methods of meltblown spinning of synthetic fibers are described that achieve and maintain separate and independent temperature control between the molten polymer within the meltblown die and the gas (e.g., air) used to attenuate the polymer material emerging from the die to form the fibers.

Meltblown systems as described herein can include one or more extruders, conveying screw that forms molten polymer and drives or pumps for the polymer, a die that meters and channels molten polymer to orifices at the die tip, a source of gas (typically heated air) that contacts and attenuates the polymer flow exiting the orifices at the die tip to form fibers, and a collection station that collects the formed fibers to form a fabric or other article from the fibers.

Conventional meltblown systems can form fibers from a variety of different types of polymers including, without limitation, polyolefins (for example, polyethylene, polypropylene, polybutylene, etc.), polyesters (for example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polytrimethylene terephthalate (PTT) and polybutylene terephthalate (PBT), polyacrylamides, polyurethanes, polylactic acids (PLA); polyamides (for example, Nylon 6, Nylon 6,6 and Nylon 6,10), polyvinyl alcohol (PVA, for example, ethylene vinyl alcohol) and/or any variety of grades (for example, different grades of PLA, different grades of polypropylene, different grades of PET, etc.) and/or block copolymers or any other combinations of such polymer types. Fibers having different cross-sectional geometries (e.g., side-by-side bicomponent, sheath-core, islands-in-the-sea, segmented pic, etc.) can also be formed using meltblown systems.

However, as previously noted, and as further noted herein, due (at least in part) to the non-segregation between the polymer heated within the die of a conventional meltblown system and the heated gas used to attenuate the fibers, it can be difficult to form fibers in conventional meltblown systems when using certain types of temperature sensitive polymers and/or additives provided in the fibers. Some examples of temperature sensitive polymers include, without limitation, certain polyolefins such as polypropylene (PP) and 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 biodegradable polymers such as polyhydroxyalkanoates (PHAs) (e.g., PHBH™ biodegradable PHA commercially available from Kaneka Corporation, Tokyo Japan), polybutylene adipate terephthalate (PBAT), and polyhydroxyalkanoates such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). An example of a heat sensitive additive that is provided in polymers that form certain types of textiles such as filtration materials and, in particular, for forming face masks (e.g., M95 face masks), is magnesium stearate. It can be quite difficult, particularly when using one or more heat sensitive polymers for forming fibers, and further still when a heat sensitive additive is required for addition with the polymers to form such fibers, to manufacture fabrics or textiles from meltblown fibers using conventional meltblown equipment and methods.

An example embodiment of a meltblown system is depicted in FIG. 1. The meltblown system comprises an extruder 2 that receives solid polymer (e.g., solid polymer pellets) from a hopper 1, and a pump or drive system 4 for the extruder 2 (e.g., motor for the screw extruder). The extruder 2 is heated to a suitable temperature to melt the polymer material from the hopper 1, forming a molten polymer that is delivered to the inlet of a die 3. While the example embodiment of FIG. 1 depicts a single flow of molten polymer from an extruder based upon polymer fed from a single hopper 1, it is noted that the meltblown system can include any selected number of polymer feeds, including two or more hoppers and/or two or more extruders, to facilitate formation of a plurality of molten polymer streams comprising different polymers so as to form fibers that include one or more different types of polymers (e.g., mono component fibers, bicomponent fibers, tricomponent fibers, multi-component fibers, etc.). Molten polymer flowing through the die 3 emerges from openings or orifices 6 at the die outlet end (e.g., formed as a tip), where the heated air from hot air sources 13, 14 attenuate the polymer to form fibers 7. The formed fibers 7 are collected on a collection surface 8 (e.g., a conveyor belt system driven by axles 9), where a nonwoven web or mat 10 of fibers is formed. The fibrous nonwoven mat 10 can further be compressed and/or bonded by rolls and then collected (e.g., on a winder roll or other collection device, not shown).

Referring to FIGS. 2 and 3, a conventional meltblown die 3 includes a pump 15, a pump block 18 and a spin pack 22. The pump block 18 that receives molten polymer from the pump 15 and directs the molten polymer through an inlet cavity 16 disposed within the pump block 18, to a lower cavity 20, and then to outlet orifices 6 within a spinneret of a spin pack 22 at the lower outlet end of the die 3. The channels within the pump block 18 are suitably dimensioned to meter polymer throughput within the die as well as combine polymer flows as needed within the spin pack of the die. The channels within the spin pack can comprise any number of manifold plates including channels formed within (e.g., via, machining, boring, etc.) and extending through the manifold plates, where the plates are vertically aligned such that the openings/channels of adjacent plates communicate with each other to define one or more channels extending through the plates to the outlet orifices 6.

A pack filter 25 is provided at the inlet to the spin pack and is located between the upper cavity 16 and the lower cavity 20. The polymer flows from the pack filter 25 to a channel leading to outlet orifices 6. In most conventional dies, such as the die 3 depicted in FIGS. 2 and 3, a wide channel or cavity 20 disposed beneath/downstream from the pack filter 25 provides a large volume, reservoir or pool for the molten polymer, and the molten polymer flows within the cavity 20 to the orifices 6 at the die outlet end. The dimensions of the cavity 20 tend to be much greater than other polymer channel dimensions within the die so as to control the residence time of the molten polymer within the die prior to emerging from the die outlet orifices and forming fibers. This can be seen, e.g., in known meltblown 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, each of which is incorporated herein by reference in its entirety. For example, the die 3 including cavity 16 shown in FIG. 3 is also referred to as a “coat hanger” die, since the open cavity initially expands or widens in a cross direction (CD) of the die 3 from its inlet (where molten polymer is fed from the pump 15) to widened dimensions along a length of the die 3, where the widened portion of the cavity 16 resembles a coat hanger shape. As used herein, machine direction (MD) refers to a dimension of the die that corresponds with overall direction of flow of the web travel (i.e., movement of the web formed from fibers extruded from the die), while cross direction (CD) refers to the direction that is orthogonal or 90° to the machine direction (MD). Such channels or cavities are much easier to form in a die (e.g., easily cut with a tool) when manufacturing the die.

A heated fluid or gas, typically air, is used to attenuate the molten polymer and form fibers of suitable cross-sections, deniers and shapes. The heated air can be provided via one or more air sources or air manifolds 30 to the die 3 via inlet locations or air inlets. The air manifolds 30 with air inlets are typically located at the top end of the die 3 along and/or within the pump block 18, where the heated air flows downward from the air manifolds 30 and air inlets in close proximity distribution with cavity 16, cavity 20 and/or other die structure through which molten polymer also flows. In particular, the heated air is directed from the air inlets of the manifolds 30 at the top of the die 3, along the pump block 18, and through channels 32 extending along opposing sides and downward along portions of the die 3 to the die outlet end (die tip). The outlet air is then directed from the opposing sides of the die through smaller channels or air slots 34 (e.g., adjustable air slots or air knives) toward the molten polymer material emerging from the outlet orifices 6 of the die 3. The molten polymer emerging from the outlet orifices 6 forms extruded polymer fibers which are attenuated by contact with the heated air flowing downward around and contacting the extruded fibers.

Providing the manifolds 30 with heated air inlets at the top of the die 3 facilitates case of die installation in a meltblown system. This configuration further facilitates case at which a spin pack 22 of the die can be removed from the die 3 and replaced with another spin pack (since the source of heated air is separated from the spin pack). Providing the heated air at the top of the die can further assist in heating the die, which may be desirable for the formation of certain types of fibers (e.g., polypropylene fibers). In addition, the air temperature can be adjusted to achieve a particular die tip temperature required to obtain good spinning and filament attenuation velocities for the meltblowing process. Due to air heat losses (e.g., adiabatic expansion as the air exits the die outlet end), the temperature of the heated air entering at the top of the die 3 must be much greater than the optimum die outlet/die tip temperature. For example, the air temperature is typically greater than the molten polymer temperature by at least 30° C. or (in certain embodiments) even greater.

Due to the residence time of the molten polymer within the die (e.g., at the large volume cavity or pool defined at the widened, “coat hanger” portion of the cavity 16 and also the wide portion of cavity 20) and/or in scenarios in which microfibers are formed (and thus very small channels are used to form the microfibers), the residence time in conventional dies can be 10 minutes or greater. This often results in the molten polymer material within the die heating up so as to be at or near the temperature of the heated air.

As can be seen, e.g., in FIG. 3, the heated air is supplied at a temperature T2, while the molten polymer within channels of the die 3 has been heated to a temperature of T1, where temperature T2 is typically much greater than temperature T1 (e.g., 30° C. or greater). In an example embodiment (e.g., in which the molten polymer comprises polypropylene), temperature T1 might be 230° C., while temperature T2 (temperature of the heated air) might be 270° C. As can further be seen by the T1 and T2 arrows shown in FIG. 3, the molten polymer within the die enters from the pump 15 into the pump block 18 having a temperature T1 but then heats up, approaching or even equaling temperature T2, by the time the molten polymer is present within the widened cavity 20. This occurs due to the heated air surrounding the channel(s) within the pump block 18 and other portions of the die 3. In particular, the air enters from manifolds 30 and the air inlets at the temperature T2, and are maintained at this temperature while flowing through airflow channels 32 (which also extend vertically along sides of the die 3) to the outlet orifices 6. Heat transfer between the air channels 32 and the die 3 often results in polymer residing within and flowing through the cavity 20 to heat up, often heating up to the same or similar as temperature T2 when emerging from the outlet orifices 6. Historically this has not been an issue, given the types of polymers that have been conventionally used to form fabrics and other textiles. However, as noted previously herein, this can present a problem when utilizing certain new types of polymers (e.g., certain biodegradable polymers) and/or certain types of additives in the polymers that are heat sensitive and can degrade if heated up to the heated air temperature T2 flowing along and/or within the die.

In accordance with the embodiments described herein, a meltblown system includes a die in which the heated air or fluid supply source including manifolds and inlets are positioned so as to thermally isolate (i.e., prevent or significantly limit heat exchange between) the heated air from all polymer passages within the die prior to the polymer exiting the die tip orifices. This can be achieved via suitable placement of the heated air passages away from the polymer passages and/or providing sufficient insulation between the heated air channel(s) and the polymer passages. In addition, the polymer flow passages within the die can be suitably dimensioned to reduce the residence time of molten polymer within the die, thus preventing or minimizing heat transfer between molten polymer and heated air (or other heated gas or heated fluid) used to attenuate fibers being extruded from the die.

In example embodiments, the manifolds with inlets that direct heated air (or other heated gas or heated fluid) to attenuate extruded fibers emerging from the die outlet orifices can be provided at or near the spin pack (e.g., secured to the spin pack) and/or in close proximity to the die outlet orifices so as to minimize surface area contact with and also heat transfer between the heated air and portions of the die. This in turn also minimizes heat transfer between the heated air (or other heated gas or heated fluid) and molten polymer flowing within the die.

An example embodiment of a die which effectively separates and independently maintains temperatures of the polymer flow and airflow within and along the die is depicted in FIGS. 4-8. Similar to the die 3, die 100 includes a pump 115 that receives molten polymer from a molten polymer source (e.g., extruder 2 as shown in FIG. 1) and delivers the molten polymer at a suitable flow rate into feed passage or channel 120 within the pump block 118. The die 100 further includes a spin pack 122 that is securable to (and removable from) a portion of the die 100.

A feed channel 120 delivers molten polymer within a portion of the die 100 from the pump 115 to a pack filter. The pack filter defines a cavity 124 (as best viewed in FIGS. 5 and 6) within the spin pack 122 is elongated in a lengthwise dimension or taken along a cross-section in the machine direction (MD) of the spin pack 122. A plurality of feed channels 126 extend vertically from the pack filter cavity 124 toward smaller, sub-channels 128. In particular, each feed channel 126 expands outward in an angled manner in the lengthwise dimension or taking along a cross-section in the machine direction (MD) of the spin pack 122. Thus the outlet end of each feed channel 126 is wider in dimension in relation to its inlet end. In addition, each feed channel 126 extends at its outlet end to a plurality of sub-channels 128. The sub-channels 128 can be formed, e.g., as grooves or etches along a flat surface or plate portion of the spin pack 122 at the widened outlet of each feed channel 126. The sub-channels 128 feed to even smaller dimensioned outlet orifices 130 from which molten polymer is extruded from the die 100. The cavity 124 is much greater in dimensions in comparison to channels 126, 128. Thus, the residence time of molten or melt polymer within the cavity 124 is significantly greater than the residence times of the molten polymer flowing through the channels 126, 128. However, since the dimensions of the cavity 124 are much smaller than the dimensions of the cavity 20 for a conventional meltblown die 3 (FIGS. 2 and 3), the overall residence time and throughput of molten polymer through the die 100 of FIGS. 4-8 is still much lower than that of the conventional die 3 (FIGS. 2 and 3).

The spin pack 122 is removably connected with a portion (e.g., the pump block 118) of the die 100 to facilitate easy replacement with another spin pack, e.g., so as to change polymer flows/network channels flowing through the spin pack of the die, which in turn controls types, shapes, etc. of polymer fibers that can be formed. For example, different spin packs can be provided and installed with the same die to facilitate the formation of different polymer fibers or different groups of polymer fibers including, without limitation, fibers with one or more polymers (e.g., single or homo component fibers, bicomponent, tri component, or multicomponent fibers), as well as the formation of fibers having different sizes, deniers and/or geometries (e.g., round, irregular, sheath-core, side-by-side, island-in-the-sea, trilobal or multi-lobal, etc.). Thus, the inlet for molten polymer within the die (including at least a portion of channel 122) is located in a portion of the die that is not within the spin pack, and the spin pack including outlet orifices 130 for the die is therefore separable or removable from the portion of the die including the molten polymer inlet (e.g., the pump block 118 and/or another portion of the die).

As previously noted, for conventional meltblown dies (e.g., the die 3 depicted in FIGS. 2 and 3), the manifolds 30 and air inlets are secured to the die at a suitable location well above the spin pack (e.g., spin pack 22), such as at the pump block 18. This configuration facilitates case of removal of the spin pack from the die (having fewer components to disconnect from the pump block other than just the spin pack). As further previously noted, it is often desirable to provide some degree of heat transfer between the heated airflow and the die, which in turn provides heat transfer with the molten polymer and can render the process more heat efficient (particularly when the polymer and air can be at the same or similar temperatures for a meltblown process).

In contrast with conventional meltblown dies, the meltblown die 100 as described herein includes the heated air (or other heated fluid) supply source with inlets and channels well below the pump block and the molten polymer pool or cavity within the die, and also closer in proximity to the spin pack and outlet orifices of the spin pack. In particular, a pair of heated air supply units or manifolds 140 are secured to the spin pack 122 below the pump block 118 and on opposing sides of the die 100. As shown in FIGS. 7 and 8, each manifold 140 secures to an opposing side of the spin pack 122 and includes an air inlet 142 that extends to a channel 146 within the spin pack 122 for delivering heated air (or other fluid) to a narrow channel 152 of a corresponding air knife 150. Each air inlet 142 and channel 146 are further disposed a suitable distance below the pack filter cavity 124. In other words, each air inlet 142 and air channel 142 (as well as all other air channels providing attenuating airflow to the outlet orifices 130) are disposed downstream (i.e., in the MD direction) of the cavity 124 and thus located between the cavity 124 and the outlet orifices 130. The air inlet 142 of each manifold 140 is at least partially surrounded, and preferably substantially encased or enclosed, by a suitable insulation member 144 that limits or prevents heat transfer between the air inlet 142 and spin pack 122 as well as the pump block 118 and/or other portions of the die 100. The insulation member 144 can comprise, e.g., fiberglass, mineral wool and/or any other material having a suitably low thermal conductivity that sufficiently insulates the air inlets.

Each air knife 150 is disposed adjacent the corresponding manifold 140 and the end of the spin pack 122 including outlet orifices 130 such that portions of the channel 146 and the narrow channel 152 are defined between surface portions of the spin pack, the manifold and the air knife. In particular, the outlet end of the spin pack 122 can have a tapered (e.g., V-shaped) configuration with the outlet orifices 130 being disposed at the end portion or tip of the spin pack. The air knives 150 surround the tapered outlet end of the spin pack 122 so as to define the narrow channels 152 between opposing exterior surfaces of the spin pack outlet end and each air knife. As best viewed in FIG. 8, the narrow air channels 152 disposed at opposing sides of the spin pack outlet extend downward in a converging manner toward each other such that heated airflow exits each channel 152 and converges with polymer flowing from each outlet orifice 130 of the spin pack (thus attenuating extruded fibers emerging from the outlet orifices).

Thus, the heated air from manifolds 140 is isolated, both physically and thermally, from molten polymer flowing through the pump block 118 and most of the die 100. This is due to the manifolds 140 being located well below and not in any contact with the pump block 118. Further, the heated air channels 146 and 152 are provided below and sufficiently isolated (both physically and thermally separated) from the pack filter cavity 124 (i.e., the location within the die and spin pack in which molten polymer has the greatest residence time). This minimizes or prevents thermal transfer between the molten polymer within the die (and, in particular, in the spin pack) and heated air in the manifolds 140 and corresponding airflow inlets 142 and channels 146, 152. The result is that molten polymer can be safely and effectively isolated and separated from the heated air (or other fluid) flowing through the die to the outlet orifices so as to substantially maintain the same temperature of the molten polymer from inlet to the die (at the pump and pump block) to the outlet orifices of the die. In particular, molten polymer flowing within the die 100 can be maintained at a temperature T1 which is significantly different from a temperature T2 of the heated air (or other fluid source). For example, a temperature difference of a least about 20° C., or at least about 30° C., or at least about 40° C., or at least about 50° C. or greater, between the temperature T1 of the molten polymer and the temperature T2 of the heated air can be maintained throughout the die and at the outlet orifices 130. In a further example, in a scenario in which the molten polymer temperature T1 should be set at 230° C. through the die and to the outlet orifices where the fibers are extruded, and in which the heated air is set at 270° C., the molten polymer temperature can be maintained at 230° C. during the entire residence time of the molten polymer in the die 100 such that the polymer emerges from the outlet orifices 130 at the set temperature T1.

The thermal separation and isolation between polymer temperature and heated air for the die can also be enhanced by effectively minimizing residence time of the molten polymer within the die. For example, the feed channel 120 of the pump block 118, and the network of polymer flow channels through the spin pack 122 (including the pack filter cavity 124, the feed channels 126, the sub-channels 128, and the outlet orifices 130) can be suitably dimensioned so as to achieve a desired residence time within the spin pack 122 (i.e., time between entry of polymer into the spin pack from feed channel 120 and exit of polymer from the spin pack via outlet orifices 130) that minimizes any thermal transfer between internal channel surfaces of the die and the polymer flowing through the die. In particular, the residence time can be controlled, in combination with suitable placement of the heated air supply and airflow channels as described herein, such that a desired temperature of the molten polymer is effectively maintained as it flows through and exits the die.

In example embodiments, polymer feed channels 126 of the die 100 are much smaller in cross-sectional dimension and have much greater length-to-diameter (L/D) ratios in comparison to the pack filter cavity 124 and also the wide die channel 20 of a conventional meltblown beam 3. Conventional dies include a die pool or cavity that is wide and varies, e.g., from about 0.5-0.75 inch (about 1.27-1.91 cm) in width or cross-sectional dimension in the machine direction (MD) of the die and a continuous dimension in the cross direction (CD) of the die. The volume of the wide channel or cavity 20 for a conventional meltblown die typically ranges from about 645 cm³to about 1450 cm³per meter of cross direction CD dimension of the cavity. In addition, providing such a large width or cross-sectional dimension for these channels in the die reduces pressure within the die. However, this large volume defined by the cavity 20 in the conventional die also increases residence time of molten polymer within the die.

The pack channels 126 of the spin pack 122 of the die 100 have much smaller width/cross-sectional dimensions in comparison to the passages or cavities within conventional dies. For example, each pack channel 126 of the meltblown die 100 can have a machine direction (MD) width of about 0.020 inch to about 0.040 inch (about 0.05 cm to about 0.10 cm), such as about 0.03 inch (about 0.08 cm), and a cross direction (CD) dimension that is discontinuous (varies). The volume of the pack channels 126 is much smaller in comparison to conventional meltblown dies and is no greater than about 50 cm³per meter of CD dimension of the cavity. For example, the volume defined by the channels 126 of the meltblown die 100 can be about 15 cm³to about 35 cm³(e.g., about 25 cm³) per meter of CD dimension of the cavity.

Further, the cross-sectional dimensions or diameters of the outlet orifices of the die are typically limited to about 0.007 inch (about 0.0178 cm), while the cross-sectional dimensions or diameters of the outlet orifices 130 of the die 100 can be as small as about 0.004-0.005 inch (about 0.010-0.013 cm). This results in L/D ratios for outlet orifices (130) within the die 100 that can be at least 50:1, or at least 75:1, or at least 100:1, or at least 125:1, or 150:1 or greater. In contrast, the L/D ratios for channels in conventional meltblown dies is limited to no greater than 10:1 particularly since there are no smaller channels leading from the cavity 20 to the outlet orifices 6 in a conventional die (the cavity 20 feeds directly to the outlet orifices 6).

While the manufacture of the die 100 requires a higher precision cut within the die (very precise machining) to achieve such small dimensions for the channels 126 and 128, the small channel dimensions result in a smaller channel volume and corresponding smaller residence time of polymer within the die. Accordingly, with these differences in die channel/cavity dimensions, the residence time of polymer within a conventional meltblown die at a maximum flow rate of 80 kg/m/hour is about 20 seconds to about 50 seconds, while the residence time for the meltblown die 100 at the same flow rate is about 0.3 second to about 1.2 seconds (e.g., about 0.6 second).

In operation, the die 100 can be implemented in the system of FIG. 1 (i.e., replacing die 3 with die 100). One or more types of polymer (e.g., for forming single or homo component fibers, bicomponent fibers, multi component fibers, etc.) can be fed from at least one hopper 1 to at least one extruder 2 and to the inlet of the die 100. A pump 115 of the die 100 delivers molten polymer into feed channel 120. From the feed channel 120, the molten polymer is directed into the pack filter cavity 124, and then into the channels 126 of the spin pack 122. From the cavity 124, polymer continues to flow into the plurality of feed channels 126 of the spin pack 122, which lead to a further plurality of sub-channels 128 and then to the outlet orifices 130.

Heated air enters from the manifolds 140, via the air inlets 142, into the channels 146 located within the spin pack 122 a suitable distance below the filter cavity 124. This ensures molten polymer residing within the cavity 124 is thermally isolated from the heated air flowing within the spin pack 122. The heated air continues to from the channels 146 into the channels 152 of the air knives 150, and emerge from the outlet end of the spin pack 122 in a converging manner toward polymer being extruded from the outlet orifices 130 to form the polymer fibers 7. The fibers 7 are collected on a surface 8 for further processing.

Maintaining the airflow thermally isolated from the molten polymer flowing within the die 100, including the spin pack 122, combined with reducing the residence time of polymer flow within the die, allows for a significantly large temperature difference between the temperature T1 of the molten polymer and the temperature T2 of the heated air during operation, where the temperature T1 is maintained relatively constant for the molten polymer throughout the die 100 and until the polymer reaches and is extruded from the outlet orifices 130 of the die. This holds true regardless of whether the molten polymer temperature T1 is less than or greater than the heated air temperature T2.

Thus, the embodiments described herein and depicted in FIGS. 4-8 facilitate production of meltblown fibers in which precise temperature control of the polymer within the die can be achieved regardless of difference between molten polymer temperature and attenuation airflow temperature. Separation of heated air inlets and heated air channels from the polymer channel(s) within the die achieves the desired thermal isolation and temperature independence of the polymer within the die. In other words, the much greater air temperature does not influence the temperature of polymer within the die prior to polymer exiting the die to form the fibers.

With the configuration of die 100 shown in FIGS. 4-8, the temperature T1 of the polymer can be maintained throughout the die such that the much greater temperature T2 of the heated air does not alter the polymer temperature. Further, the lower volume die cavity 124 also enhances maintaining of the polymer at the desired temperature T1, since the residence time of polymer within the die is minimized (e.g., in the event there is any slight increase in die temperature due to the higher temperature T2 of the heated air).

The meltblown system as described herein is further very effective in forming fibers with high temperature and/or temperature resistant polymers having very high melting points, such that the temperature T1 of the molten polymer within the die is greater than the temperature T2 of the air or gas used to attenuate the polymer emerging from the die outlet to form the fibers.

Thus, the embodiments herein describe a meltblown die and meltblown system utilizing a meltblown die that are configured to receive the process air at a point closest to the die tip/spin pack outlet end and away from polymer passages to allow the polymer to be thermally isolated from the air heat. By providing independent temperature control of the polymer within the meltblown die (by separating and thermally insulating heated air manifolds, inlets and channels from the die), and further decreasing residence time/increasing throughput of polymer within the die, a number of enhancements in meltblown fiber production can be realized. Some non-limiting examples of the benefits of the temperature separation meltblown die and system as described herein and depicted in the example embodiment of FIGS. 4-8 are now described.

For example, the embodiments described herein facilitate the manufacture of meltblown fabrics and textiles using heat sensitive polymer materials and/or heat sensitive additive materials added to the polymer materials to form the meltblown fibers without risk of overheating and/or degrading such heat sensitive materials during the meltblown manufacturing process. Some non-limiting examples of heat sensitive polymers are described later herein. The molten or melt polymer flowing within the meltblown die as described herein effectively maintains such heat sensitive polymers and/or heat sensitive additives within the melt polymer below their degradation or decomposition temperatures despite the heated air (or heated fluid) temperature used to attenuate the fibers being greater than such decomposition temperatures.

The embodiments described herein further facilitate the manufacture of meltblown fabrics and textiles using high temperature/heat resistant polymers with airflows at lower temperatures without risk of modifying the molten polymer temperature within the die.

Fewer spinning defects (e.g., shot and fly) in the meltblown fibers can be achieved utilizing the embodiments described herein in relation to conventional meltblown systems.

The embodiments described herein further facilitate optimal production of fabrics and other textiles comprising thermally degradable materials, including fibers formed from temperature sensitive polymers, fibers formed from biodegradable polymers, and fibers formed including temperature sensitive additive. This is due to the die configuration providing more precise and independent control of melt temperatures for different polymer components within the die (e.g., when making bicomponent or multi-component fibers), particularly polymers in which one or more different polymers are heat sensitive (e.g., heated gas/heated air temperature much greater than melt temperatures of such polymers). Non-limiting examples of temperature sensitive polymers that can be used to form fibers in the die configuration described herein, in which the temperature of the molten or melt polymer within the die can be maintained at a desired temperature (separate and independent from heated air temperature for the air used to attenuate the fibers) include certain polyolefins such as polypropylene (PP) and 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 polyhydroxyalkanoates (PHAs) (e.g., PHBH™ biodegradable PHA commercially available from Kaneka Corporation, Tokyo Japan), polybutylene adipate terephthalate (PBAT), and polyhydroxyalkanoates such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). Some non-limiting examples of heat sensitive additives include magnesium stearate additives for fabrics and starch. In particular, heat sensitive polymers and/or additives can be used to effectively form fibers (e.g., mono component, bicomponent or multicomponent fibers) as well as such fibers effectively incorporated into fabrics, where such heat sensitive polymers and additives have a degradation temperature or decomposition temperature that is less than 270° C., such as no greater than 260° C., or no greater than 250° C., or no greater than 245° C. An example of a heat sensitive additive that is provided in polymers that form certain types of textiles such as filtration materials and, in particular, for forming face masks (e.g., M95 face masks), is magnesium stearate (e.g., Techmer PPM13774 as an additive to polypropylene). Effective heated air (or heated fluid) temperatures for attenuating fibers is typically at least about 250° C., or at least about 260° C., or even at least about 270° C. Thus, a meltblown system utilizing the die configuration as described herein is particularly suitable for forming face masks which include magnesium stearate.

The embodiments described herein facilitate the forming of meltblown fabrics or other textiles with a larger number of nano-fibers (e.g., fabric or textile includes 25% or more nano-fibers). In particular, the meltblown system of the present invention facilitates easier formation of meltblown micro or nanofibers (i.e., fibers having cross-sectional geometries on the micrometer or nanometer sizes, e.g., fibers having a diameter or cross-sectional dimension(s) of no greater than 0.5 micrometers, or from about 50 nanometers to about 300 nanometers). Meltblown dies as described herein provide a larger operating window allowing heated air or heated gas to be much greater in temperature than the polymer melt temperature(s), which in turn allows for the formation of finer meltblown fibers without degrading polymer within the die. The low flow rates (and thus higher residence times) associated with forming micro or nano fibers makes utilizing the present invention much more advantageous over using conventional meltblown systems.

The embodiments described herein facilitate the formation of meltblown fabrics or textiles with smaller fibers in comparison to conventional meltblown systems while operating using the same grams/hole/minute and/or the same kilograms/meter/hour of die width.

The embodiments described herein also facilitate the formation of meltblown fabrics or textiles having smaller fiber size distribution in comparison to conventional meltblown systems while operating using the same grams/hole/minute and/or the same kilograms/meter/hour of die width.

The embodiments described herein also facilitate the formation of fibers and fabrics incorporating such fibers that comprise high temperature and/or high performance polymers including, without limitation, polyamides such as polyamide-6 (PA-6) and polyamide-66 (PA-66), polyethylene terephthalate (PET), polyurethane (PU), polyetherimides (e.g., polyetherimides commercially available under the trademark ULTEM), polyether ether ketones (PEEKs), polyether ketone ketones (PEKKs), and ether-based polyurethane foams including melamine foams such as POLYDAMP® Acoustical Foam (PAF) (Polymer Technologies, Inc.), or any other polymers having a high viscosity, where a melt flow index (MFI) of such polymers is at least about 8 grams/10 minutes, or at least about 10 grams/10 minutes, where the MFI is measured based upon ASTM D1238 or ISO 1133 standards. These types of polymers typically cannot be used to form fibers in a conventional meltblown system due to their high viscosity levels. The meltblown die and system as described herein can process these types of polymers, even at larger sizes, such as fiber diameters of at least 3 micrometers, or at least 5 micrometers, or even in the 5-10 micrometer size range. This is achievable by operating the system with the heated air being at a very high temperature (e.g., from about 20° C. to about 80° C. over the molten polymer temperature), such as superheated air in which the heated air is much greater than the die tip/die outlet end (at least 30° C. or greater) without degrading the polymer processed within the meltblown die. Utilizing superheated air can heat a polymer after exiting the die outlet end, which facilitates the use of higher viscosity polymers that otherwise might not be suitable for use in conventional meltblown systems.

Meltblown fabrics or textiles can be formed utilizing the embodiments described herein at a higher production rate (kilograms/meter/hour or kg/m/hour) but with the same or similar properties as that which may be formed from conventional meltblown systems.

EXAMPLE

The benefits of utilizing a meltblown system including a die configuration as described herein and depicted in FIGS. 4-8 as described herein has been demonstrated by comparison with a conventional meltblown system such as the type depicted in FIGS. 2 and 3. The same polymers were used with a molten polymer temperature T1 (molten polymer temperature at the inlet to the die) as well as the heated air temperature T2 being the same for both systems. Polypropylene was the polymer used, where the ideal or desired molten polymer temperature T1 to be maintained within the die was 240° C. The air inlet temperature T2 was set at 270° C., and the desired die tip outlet end was 240° C. The polypropylene fibers had a 2 micron diameter to form a meltblown fabric for N95 masks.

It was determined that the system of FIGS. 4-8 provided at least a 55% increase in throughput capacity vs. the conventional system (70 kg/m/hr vs. 45 kg/m/hr) producing the same fabric. Due to the undesirable heating of the molten polymer within the die caused by the heated air, the conventional die could not operate above 45 kg/m/hr without degradation of the fibers formed. In contrast, the system of FIGS. 4-8 was operable for much greater periods of time and even at throughput approaching 80 kg/m/hr without a degradation in the polymer fibers formed. In addition, desired polymer temperature for the system of FIGS. 4-8 was maintained throughout the residence time of the polymer within the die despite a large temperature between the molten polymer temperature T1 and the heated air temperature T2 used to attenuate the fibers. This is in contrast to the conventional system of FIGS. 2 and 3, where the molten polymer temperature T1 changed for the molten polymer within the die (approaching temperature T2 as the molten polymer emerged from the die).

Thus, the present invention provides the following:

A meltblown system comprises a die including a die inlet end to receive 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 to receive the molten polymer from the cavity and deliver to outlet orifices at the die outlet end, and a fluid supply comprising a fluid inlet and a fluid channel connected with the fluid inlet and extending to the die outlet end so as to deliver fluid to the die outlet end to attenuate fibers formed from molten polymer emerging from the die outlet end. The fluid supply provides fluid at a temperature T2 that differs from a temperature T1 of the molten polymer within the cavity, and the meltblown system is configured to independently maintain the molten polymer within the cavity at the temperature T1 during operation of the meltblown system.

The temperature T2 can be greater than the temperature T1.

The meltblown system can further comprise a plurality of channels extending from the cavity to outlet orifices at the die outlet end. Each channel of the plurality of channels can have a L/D ratio of at least 50:1.

The gas inlet and fluid channel of the system can be disposed a distance from the cavity and located between the cavity and the die outlet end.

The die outlet end can be disposed in a spin pack that is separable from a portion of the die including the die inlet end, and the spin pack includes the die outlet end. In addition, the fluid supply can comprise at least one manifold securable to the spin pack that delivers fluid at the temperature T2 to the gas inlet. The manifold can be located a distance from the cavity and located between the cavity and the die outlet end.

The die cavity of the system can have a volume no greater than about 50 cm³per meter of cross dimension (CD) of the cavity.

In other embodiments, a method of forming a meltblown product comprises directing molten polymer within a die of a meltblown system through a plurality of orifices at a die outlet, the molten polymer having a temperature T1, and directing a fluid to contact the molten polymer emerging from the die outlet to form fibers from the polymer emerging from the die outlet, the fluid having a temperature T2 that differs from the temperature T1. The molten polymer within the die is maintained at the temperature T1 when the polymer emerges from the die outlet and contacts the fluid.

The temperature T2 can be greater than temperature T1.

The fluid can comprise heated air.

A difference between temperature T1 and temperature T2 can be at least about 30° C. or at least about 50° C.

The die can include a cavity and a plurality of channels disposed below the cavity that extend to outlet orifices of the die outlet, the fluid can be directed from a fluid source securable with a portion of the die into a fluid channel within the die, and the fluid source and fluid channel can be distanced from the cavity and disposed between the cavity and the outlet orifices.

The molten polymer can have a decomposition temperature of no greater than 245° C., and the temperature T2 of the fluid can be at least about 260° C. In addition, the molten polymer can include an additive having a decomposition temperature of no greater than 245° C., and the temperature T2 of the fluid can be at least about 260° C.

The molten polymer can comprise an additive, the additive comprising magnesium stearate.

The molten polymer can have a melt flow index (MFI) at least about 8 grams/10 minutes. In addition, the molten polymer can further comprise one or more of a polyamide, a polyethylene terephthalate, a polyurethane, a polyetherimide, a polyether ether ketone, a polyether ketone ketone, and an ether-based polyurethane foam.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.

MELTBLOWN SPINNING WITH SEPARATE AND INDEPENDENT AIR AND POLYMER TEMPERATURE CONTROL

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