Fiber forming device and method of using the same

Abstract

Disclosed is a fiber forming device, which is highly suitable for producing a nonwoven web with excellent barrier properties. In one aspect, the fiber forming device can be used to produce a meltblown web or a co-formed web. The fiber forming device includes a die having multiple rows of polymer nozzles for forming fibers. An air flow path is positioned on either side of the multiple rows of polymer nozzles. Additionally, the air flow path is positioned between the multiple rows of polymer nozzles. The air flow path produces a refined air flow, which refines the fibers produced by the polymer nozzles and guides the fibers onto a forming surface for forming a nonwoven web.

Description

BACKGROUND OF THE INVENTION

[0001] One type of web formed from a molten thermoplastic polymer is known as a meltblown web. Fibers are formed by extruding a molten thermoplastic polymer material through a plurality of small holes. The resulting molten filaments or fibrils enter a converging high velocity air stream, which refines or draws the filaments of the molten polymer to reduce their diameter. Thereafter, the meltblown fibers are carried by the high velocity air stream and deposited on a collecting surface or a forming screen to form a nonwoven web of randomly dispersed meltblown fibers.

[0002] Generally speaking, meltblowing utilizes specialized equipment to form a meltblown web from a polymer. Typically, the polymer flows from a die through a narrow cylindrical outlet and forms meltblown fibers. The narrow cylindrical outlet may be arranged to be substantially straight and located in a plane that is the bisector of the apex of a V-shaped die. Typically, a pair of air plates are positioned near the die apex to form two air flow paths between the air plates and the die apex along each face of the die apex. Thus, air can flow through these air flow paths to impinge on the fibers leaving the die apex, thereby refining the fibers.

[0003] Exemplary meltblown systems are discussed or described, for example, in U.S. Patent No. 4,663,220, U.S. Patent No. 6,074,597, U.S. Patent No. 5,902,540, U.S. Patent No. 6,336,801, U.S. Patent No. 6,972,104, and U.S. Patent No. 7,316,552, which are hereby incorporated by reference.

[0004] Meltblown webs can be formed to have many highly desirable properties. For example, because meltblown webs can be made from relatively small fibers, the webs have excellent barrier properties against various different types of fluids, such as liquids and gases. Thus, meltblown webs are commonly used in the production of all different types of medical protective products, including surgical gowns, wound dressings, face masks, and the like. A system and method for manufacturing a meltblown web having enhanced barrier and / or filtration properties is highly desirable.

[0005] Specifically, an improved process and method for producing a meltblown web having excellent barrier and / or filtration properties are needed. More specifically, a method and system for producing a meltblown web having a greater fiber density and / or producing ultrafine fibers in an efficient manner are needed. SUMMARY OF THE INVENTION

[0006] The present disclosure generally relates to a fiber forming device that is particularly suitable for producing a nonwoven web having ultrafine fibers. The nonwoven web made of fibers has excellent barrier and / or filtration properties. The present disclosure also generally relates to a method for producing a nonwoven web by a fiber forming device.

[0007] For example, in one aspect, the present disclosure relates to a fiber forming apparatus that includes a die having a length and a width. The die includes a first row of polymer nozzles spaced apart from and parallel or substantially parallel to a second row of polymer nozzles. For example, the first row of polymer nozzles can be within ten degrees, five degrees, or two degrees of parallel to the second row of polymer nozzles. The first row of polymer nozzles and the second row of polymer nozzles are configured to receive a stream of molten polymer material for ejecting polymer fibers from the die. The first row of polymer nozzles and the second row of polymer nozzles extend along the length of the die.

[0008] The die further includes a first air flow path, a second air flow path, and a third air flow path that are spaced apart and extend along the length of the die in a parallel or substantially parallel relationship. For example, the air flow paths can be within ten degrees, five degrees, or two degrees of parallel to each other. The first air flow path is positioned between a first outer edge of the die and the first row of polymer nozzles. The second air flow path is positioned between a second outer edge of the die and the second row of polymer nozzles. The third air flow path is positioned between the first row of polymer nozzles and the second row of polymer nozzles. The first air flow path includes an outlet that is positioned such that the air flow exiting the outlet converges with the air flow exiting the third air flow path. Similarly, the second air flow path can include an outlet that is positioned such that the air flow exiting the outlet converges with the air flow exiting the third air flow path. The first air flow path, the second air flow path, and the third air flow path are configured to direct a stream of refining air against the molten polymer fibers exiting the first row of polymer nozzles and the second row of polymer nozzles. The third air flow path is in communication with a gas flow path that is configured to control the fluid flow to the third air flow path independently of the fluid flow to the first air flow path and the second air flow path such that gas can be supplied to the third air flow path at a different pressure than the gas supplied to the first air flow path and the second air flow path. The first air flow path can also be controlled independently of the second air flow path.

[0009] In one aspect, the die can include a fiber distribution surface. The first row of polymer nozzles, the second row of polymer nozzles, the first air flow path, the second air flow path, and the third air flow path can all be positioned along the fiber distribution surface. The fiber distribution surface can have a V shape and define a vertex. The first row of polymer nozzles and the second row of polymer nozzles can be configured to eject fibers adjacent to the vertex of the fiber distribution surface. In one aspect, the first row of polymer nozzles and the second row of polymer nozzles can each be positioned at an angle toward each other.

[0010] Similarly, the first air flow path and the second air flow path may each be positioned at an angle toward each other. The third air flow path may be configured to eject a fluid stream in a generally downward and vertical direction. In one embodiment, the first air flow path and the first row of polymer nozzles are symmetric with the second air flow path and the second row of polymer nozzles with respect to the vertical axis of the die.

[0011] The first air flow path, the second air flow path, and the third air flow path may have any suitable shape or configuration for ejecting pressurized gas. For example, each air flow path extends along the length of the die, where the air flow path is any structure that allows gas to flow along the path from two points, including, for example, channels, slots, orifices, passages, and chambers. In one embodiment, the first air flow path is in communication with a first air chamber, the second air flow path is in communication with a second air chamber, and the third air flow path may be in communication with a third air chamber. Each of the chambers may be isolated from the other chambers and may be used to supply pressurized gas to the air flow paths. For example, a fluid flow regulator may regulate the flow rate and / or pressure of the gas supplied to the air chambers for ejecting the gas from the air flow paths at a desired pressure and / or velocity. In one embodiment, the gas flow through the third air flow path is controlled independently of the air flows through the first air flow path and the second air flow path.

[0012] In one embodiment, the fiber forming device may include more than two rows of parallel polymer nozzles. For example, the fiber forming device may include a third row of polymer nozzles and a fourth air flow path. The fourth air flow path may be positioned between the second row of polymer nozzles and the third row of polymer nozzles. In one embodiment, the gas flow through the fourth air flow path is controlled independently of the air flows through the first air flow path, the second air flow path, and / or the third air flow path.

[0013] The fiber forming device of the present disclosure is designed to be operable to minimize turbulence, thereby producing ultrafine fibers having a small diameter. In one embodiment, the third air flow path may receive pressurized gas through a pair of air paths separated by a wedge-shaped flow control device. The wedge-shaped flow control device is used to direct the gas flow through the third air flow path while preventing turbulence.

[0014] The present disclosure also relates to a method for forming a nonwoven web. The method includes forming at least two parallel rows of fibers from a molten polymeric material. The fibers are contacted with a plurality of air streams for fiber attenuation. The air streams include a first air stream impinging on the first row of fibers from a first side, a second air stream impinging on the second row of fibers from a second side, and a third air stream directed between and impinging on the first row of fibers and the second row of fibers. The first air stream is ejected from a first air flow path at a first pressure, the second air stream is ejected from a second air flow path at a second pressure, and the third air stream is ejected from a third air flow path at a third pressure. According to the present disclosure, during the formation and attenuation of the fibers, the third pressure is greater than the first pressure and greater than the second pressure. The method further includes the step of depositing the attenuated fibers on a forming surface to form a nonwoven web.

[0015] In one embodiment, the pressure ratio of the third pressure of the third air stream ejected from the third air flow path to the first pressure of the first fluid stream and / or to the second pressure of the second fluid stream is maintained at about 1.05:1 to about 2:1, such as about 1.08:1 to about 1.5:1, such as about 1.1:1 to about 1.3:1.

[0016] Generally, any suitable thermoplastic polymer can be used to form the fibers. For example, in one embodiment, the fibers are formed from an olefin polymer (such as a polypropylene polymer). Alternatively, the fibers can be formed from a biodegradable polymer and / or a bio-based polymer. For example, the biodegradable polymer can be a polylactic acid polymer or a polyhydroxyalkanoate polymer, such as polyhydroxybutyrate.

[0017] In one embodiment, the method may further include the step of contacting the fibers in a molten state with an absorbent material (such as a pulp material) to form a co-formed web.

[0018] During the production of the fibers, the gas pressure leaving the first air flow path, the gas pressure leaving the second air flow path, and the gas pressure leaving the third air flow path can be relatively low to prevent turbulence. For example, the gas pressure can be less than about 10 psi, such as less than about 7 psi, such as less than about 5 psi, such as less than about 4 psi. The gas pressure is generally greater than about 0.5 psi. The diameter of the fibers formed during the method can be less than about 5 microns, such as less than about 4 microns, such as less than about 3 microns.

[0019] Other features and aspects of the present disclosure are discussed in more detail below. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The full and enabling disclosure of the present disclosure is set forth more particularly in the remainder of the specification and in reference to the drawings, in which:

[0021] Figure 1 is a perspective view of one embodiment of a system and method for producing a nonwoven web that can be associated with a fiber forming device according to the present disclosure;

[0022] Figure 2 is a perspective view of one embodiment of a fiber forming device according to the present disclosure;

[0023] Figure 3 is as Figure 1 a perspective view of a die that is part of the fiber forming device shown;

[0024] Figure 4 is Figure 2 a cross-sectional view of the fiber forming device shown;

[0025] Figure 5 is a magnified cross-sectional view showing a polymer nozzle and an air flow path that can be incorporated into the fiber forming device as Figure 2 shown;

[0026] Figure 6 is Figure 3 a cross-sectional view of the die shown; and

[0027] Figure 7 is a cross-sectional view of another embodiment of a fiber forming device according to the present disclosure.

[0028] The repeated use of reference numerals in this specification and the drawings is intended to represent the same or analogous features or elements of the invention. DETAILED DESCRIPTION

[0029] Those of ordinary skill in the art will understand that this discussion is only a description of exemplary embodiments and is not intended to limit the broader aspects of the present disclosure.

[0030] Generally speaking, the present disclosure relates to a fiber forming device and a method of forming a nonwoven web using the device. The fiber forming device of the present disclosure is particularly suitable for producing ultrafine fibers having a diameter of less than about 5 microns, such as less than about 3 microns, for producing nonwoven webs having excellent barrier properties. For example, the fiber forming device can be used to produce meltblown fibers for producing meltblown webs.

[0031] In the past, conventional meltblown dies included a single row of capillaries positioned along the apex of the wedge-shaped die tip. The present disclosure relates to an improved meltblown apparatus that is more robust and capable of producing meltblown webs with a greater range of properties. While the meltblown apparatus of the present disclosure can be used to produce fibers with a larger diameter, the apparatus is particularly suitable for producing ultrafine fibers in order to produce products with improved barrier and / or filtration properties. To produce a nonwoven web according to the present disclosure, the fiber forming device of the present disclosure includes a greater number and greater density of capillaries or polymer nozzles for forming fibers. The higher density of polymer nozzles enables the production of finer fibers while still maintaining a relatively high production rate, such that compared to conventional meltblown apparatuses, the fiber forming device of the present disclosure can be used to manufacture a web without significantly reducing the processing speed.

[0032] As will be described in more detail below, the fiber forming device of the present disclosure does not include only a single row of polymer nozzles for producing fibers, but rather includes at least two rows of polymer nozzles separated by at least one air flow path that supplies pressurized gas between the multiple rows of fibers being produced in order to thin the fibers and also direct the fibers onto a moving forming surface. In one aspect, the pressure or velocity of the internal air flow supplied between two rows of fibers is controlled relative to the external air flow contacting the opposite sides of the fibers to minimize turbulence when at least three air flows converge. Thus, one aspect of the present disclosure is to independently control the gas pressure or velocity of the internal air flow compared to the external air flow for producing a web that not only has excellent mechanical properties but also has uniform properties.

[0033] Reference Figure 1 , shows one embodiment of a system and method for producing a nonwoven web according to the present disclosure. Figure 1 The system shown includes a fiber forming device 14 manufactured according to the present disclosure and shown in more detail in Figures 2 to 6 . As Figure 1 shown, hopper 10 supplies polymer material to extruder 12 attached to fiber forming device 14, which extends across width 16 of nonwoven web 18 to be formed by the meltblown process. Pressurized gas is supplied to the fiber forming device to thin these fibers as they are formed.

[0034] The extruded fibers 44 exit the polymer nozzles or die tip of fiber forming device 14 and form a bonded and tacky fiber nonwoven web 18 on forming surface 46, which can be removed by rolls 47, which can be designed to press web 18 together to improve the integrity of the web. Thereafter, web 18 can be conveyed to a winding roll through a conventional arrangement and further processed or incorporated into various articles.

[0035] The nonwoven webs manufactured according to the present disclosure can be used in a variety of different applications. For example, due to the excellent barrier and / or filtration properties of the webs, the webs are particularly suitable for the production of medical products such as surgical drapes, face masks, and other protective clothing. The nonwoven webs are also very suitable for absorbent articles such as diapers, training pants, feminine hygiene products, wound dressings, etc. In one aspect, the nonwoven webs of the present disclosure are incorporated into laminates and then used to manufacture various products. For example, the meltblown webs manufactured according to the present disclosure can be combined with one or more spunbond webs. In a particular application, the meltblown webs manufactured according to the present disclosure can be placed between two spunbond webs for the production of various articles.

[0036] Reference Figures 2 to 6 , more particularly shows the fiber forming device 14 of the present disclosure. Reference Figures 2 to 4 , the fiber forming device 14 includes a die head 20 that is mounted to a flow head 22 and is specifically shown in Figure 3 . The flow head 22 is designed to supply molten polymer material to the die head 20 and to supply pressurized gas to the die head 20. For example, as shown in Figure 2 , the flow head 22 includes polymer ports 24 and 26 that are designed to be connected to an extruder. In the embodiment shown in Figure 1 , for example, the extruder 12 is connected along the top surface of the flow control device 14. In the embodiment shown in Figure 2 , however, the flow control device 14 is designed to be connected to one or more extruders along one side of the flow head 22.

[0037] As shown in Figure 2 , the flow head 22 further defines gas ports 28, 30, and 32. The gas ports 28, 30, and 32 are used to connect to a pressurized gas source such as a heated air source. The gas ports 28, 30, and 32 are used to supply gas to the die head 20 and then to refine the polymer fibers being produced and to direct the fibers onto the forming surface 46, as shown in Figure 1 .

[0038] Reference Figure 4 , shows a cross-sectional view of the fiber forming device 14. According to the present disclosure, the die head 20 includes a first row of polymer nozzles 34 that are spaced apart from a second row of polymer nozzles 36. In Figure 4 , two representative polymer nozzles 34 and 36 are shown. A row of nozzles 34 and 36 extends along the length of the die head 20. As shown more clearly in Figure 4 , the polymer port 26 includes a molten polymer flow path 40 that divides into two separate flow paths for supplying molten polymer material to the first row of polymer nozzles 34 and the second row of polymer nozzles 36.

[0039] The die head 20 may include an air plate 38 that forms a fiber distribution surface 42. The pair of air plates 38 is used to form an air flow path. In the illustrated embodiment, the fiber distribution surface 42 has a V shape including a vertex 40. The first row of polymer nozzles 34 and the second row of polymer nozzles 36 are positioned adjacent to the vertex 40 and may be parallel or substantially parallel to each other and parallel or substantially parallel to the vertex 40. In the illustrated embodiment, the polymer nozzles 34 and 36 are positioned in an angular relationship such that the polymer nozzles 34 and 36 are angled toward each other and toward the vertex 40.

[0040] In addition to the two rows of polymer nozzles 34 and 36, the die head 20 further includes a first air flow path 50 positioned on one side of the first row of polymer nozzles 34, a second air flow path 52 positioned on the opposite side of the second row of polymer nozzles 36, and a third air flow path 54 positioned between the first row of polymer nozzles 34 and the second row of polymer nozzles 36. Pressurized gas is supplied to the air flow paths 50, 52, and 54 to create three air streams that converge and contact the fibers formed by the polymer nozzles 34 and 36. The third air flow path 54 positioned between the first row of polymer nozzles 34 and the second row of polymer nozzles 36 is further used to prevent the two rows of fibers from prematurely contacting each other when the thermoplastic polymer is in a molten state and before contacting the forming surface 46.

[0041] As Figure 4 shown, the flow head 22 of the fiber forming device 14 includes separate air chambers. In this embodiment, for example, the flow head 22 includes a first air chamber 56, a second air chamber 58, and a third air chamber 60. The first air chamber 56 is designed to supply pressurized gas to the first air flow path 50 (and in some embodiments, may be part of this first air flow path). The second air chamber 58 is designed to supply pressurized gas to the second air flow path 52 (and in some embodiments, may be part of this second air flow path). Similarly, the third air chamber 60 is designed to supply pressurized gas to the third air flow path 54 (and in some embodiments, may be part of this third air flow path). More specifically, as Figure 3 and Figure 4As shown, the manifold head 22 cooperates with the die head 20 for supplying pressurized gas to different air flow paths. For example, the die head 20 may include a first air path 62 in fluid communication with a first air flow path 50, a second air path 64 in fluid communication with a second air flow path 52, and a third air path 66 in fluid communication with a third air flow path 54. In this way, pressurized gas can be supplied independently to each of the air flow paths 50, 52, and 54. Thus, the fiber forming device 14 provides independent control of the gas pressure and gas velocity of the air flows exiting the three different air flow paths 50, 52, and 54. Accordingly, the air flows ejected from the die head 20 can be controlled and adjusted to ensure that the fibers are refined to a desired amount and to prevent gas turbulence from occurring when the different air flows converge. For example, turbulence can cause the fibers to agglomerate and stick together before contacting the forming surface.

[0042] To supply gas to the fiber forming device 14, the gas ports 28, 30, and 32 can be placed in communication with a single pressurized gas source or multiple pressurized gas sources. For example, each of the gas ports 28, 30, and 32 can be connected to a separate pressurized gas source. Then, fluid flow regulators can be placed in the system for controlling the gas pressure within the air flow paths 50, 52, and 54. In one embodiment, each air flow path can be in communication with a separate fluid flow regulator. Alternatively, the outer air flow paths 50 and 54 can be in communication with a single fluid flow regulator, while the intermediate air flow path 52 can be in communication with a separate fluid flow regulator. For example, the fluid flow regulator can be a pressure regulator that can control pressure. Alternatively, the fluid flow regulator can be any suitable flow meter.

[0043] The gas supplied through the air flow paths 56, 58, and 60 can be air or any other suitable non-reactive gas. In one embodiment, the refining gas can be heated. For example, the gas can be heated to a temperature greater than about 80°C, such as greater than about 100°C, such as greater than about 125°C, such as greater than about 150°C, and generally less than about 400°C, such as less than about 300°C, such as less than about 200°C. The refining gas can be supplied through each of the air flow paths 50, 52, and 54 at any suitable pressure, such as at a pressure of about 1 psig to about 30 psig. In one embodiment, the pressure of the refining gas can be relatively low, such as less than about 20 psig, such as less than about 15 psig, such as less than about 10 psig, such as less than about 7 psig, such as less than about 5 psig, such as less than about 4 psig. The gas pressure is generally greater than about 1 psig, such as greater than about 2 psig.

[0044] When producing fibers using the fiber forming device 14 as shown in the figure, it is generally preferred to avoid gas turbulence. In this regard, in one embodiment, the gas pressure or velocity of the gas leaving the second air flow path 52 is generally greater than the gas pressure or velocity of the gas leaving the air flow paths 50 and 54. It has been found that maintaining a greater gas pressure in the intermediate air flow path 54 significantly reduces gas turbulence when different gas flows converge. In one embodiment, the ratio of the gas pressure in the third air flow path 54 to the gas pressure in the first air flow path 50 and / or the second air flow path 52 is from about 1.05:1 to about 2:1, such as from about 1.08:1 to about 1.5:1, such as from about 1.1:1 to about 1.3:1. In some embodiments, it has been found that the above gas pressure ratio is optimal when operating at a pressure of about 2 psig to about 4 psig.

[0045] As Figure 4 shown, the third air flow path 54 may also include a wedge-shaped flow control device 68 further for minimizing turbulence. The flow control device 68 is positioned at the top of the gas nozzle where the gas nozzle intersects the air path 66. The wedge-shaped flow control device 68 is designed to direct the gas flow towards the outlet of the air flow path 54 with minimal turbulence.

[0046] Referring Figure 5 , a magnified partial cross-sectional view of the vertex 40 of the die 20 is shown. More specifically, Figure 5 the relationship between the first row of polymer nozzles 34 and the second row of polymer nozzles 36 and the air flow paths 50, 52, and 54 is shown. It should be understood that Figure 5 the embodiments shown are exemplary and other arrangements of the nozzles and air flow paths are possible. In Figure 5 the embodiments shown, the air flow path 50 and the polymer nozzle 34 are symmetric with respect to the polymer nozzle 36 and the air flow path 52 along the vertical axis. As shown, the polymer nozzles 34 and 36 include capillary tips through which the polymer fibers are formed. In the embodiments shown, the outlets of the polymer nozzles 34 and 36 are recessed from the vertex 40 of the die 20 and the fiber distribution surface. The polymer nozzles 34 and 36 are connected to the air flow path 54. The air flow paths 50 and 52 are connected to the vertex 40.

[0047] The openings of the air flow paths 50 and 52 are approximately the same distance from the recesses of the polymer nozzles 34 and 36. In one embodiment, the width or diameter of the outlet of the air flow path 54 is generally less than the outlets of the air flow paths 50 and 52. The fiber distribution surface also defines an opening 70 through which the fibers are guided.

[0048] The air flow paths 50, 52, and 54 can define an opening having any suitable shape sufficient to deliver the attenuating gas to the fibers being formed. In one embodiment, for example, the air flow paths 50, 52, and 54 can include slots or channels extending along the length of the die 20. Alternatively, the air flow paths can mimic the flow paths 62, 64, and 66 as Figure 3 shown, and include a row of orifices aligned with multiple rows of polymer nozzles. The orifices can be circular as Figure 3 shown, or can have different shapes. For example, the orifices can be slits and can have a length extending to surround one or more polymer nozzles.

[0049] Reference Figure 6 shows the relationship of the polymer nozzles 34 and 36 to the vertical axis of the die 20. As described above, the polymer nozzles 34 and 36 can be positioned at an angle such that the nozzles face each other and also point to the apex 40 of the fiber dispensing surface 42. Similar to the polymer nozzles 34 and 36, the first air flow path 50 and the second air flow path 52 are also aligned with each other at an angle relative to the horizontal axis of the die 20. The air flow paths 50 and 52 are angled to face each other and eject an air stream through an opening positioned at the apex 40.

[0050] In the above-described embodiment, the die 20 includes a first row of polymer nozzles and a second row of polymer nozzles. In an alternative embodiment, the die 20 can include more than two rows of polymer nozzles in combination with one or more additional air flow paths.

[0051] For example, reference Figure 7 shows another embodiment of the die 20 according to the present disclosure. Like reference numerals are used to denote like elements. As Figure 7 shown, the die 20 includes three rows of polymer nozzles, namely a first row of polymer nozzles 34, a second row of polymer nozzles 36, and a third row of polymer nozzles 90. The first row of polymer nozzles 34 is positioned adjacent to the first air flow path 50. The third row of polymer nozzles 90 is positioned adjacent to the second air flow path 52. The third air flow path 54 is positioned between the first row of polymer nozzles 34 and the second row of polymer nozzles 36. In the Figure 7 shown embodiment, the die 20 further includes a fourth air flow path 92, which is positioned between the second row of polymer nozzles 36 and the third row of polymer nozzles 90.

[0052] The polymer material used to form the fibers and nonwoven web according to the present disclosure can vary. Generally, any suitable thermoplastic polymer can be used. In one embodiment, the polymer material can be a polyolefin polymer, such as a polypropylene polymer or a polyethylene polymer.

[0053] In alternative embodiments, a polyester polymer may be used. For example, the polyester polymer may be bio-based and / or biodegradable. Generally, any of a variety of polyesters may be employed, such as aliphatic polyesters, such as polycaprolactone, polyamide esters, polylactic acid (PLA) and its copolymers, polyglycolic acid, polyalkylene carbonates (e.g., polyethylene carbonate), poly-3-hydroxybutyrate (PHB), poly-3-hydroxyvalerate (PHV), copolymers of 3-hydroxybutyrate and 4-hydroxybutyrate, copolymers of 3-hydroxybutyrate and 3-hydroxyvalerate (PHBV), copolymers of 3-hydroxybutyrate and 3-hydroxyhexanoate, copolymers of 3-hydroxybutyrate and 3-hydroxyoctanoate, copolymers of 3-hydroxybutyrate and 3-hydroxydecanoate, copolymers of 3-hydroxybutyrate and 3-hydroxyoctadecanoate, and succinate-based aliphatic polymers (e.g., polybutylene succinate, polybutylene adipate succinate, polyethylene glycol succinate, etc.); aliphatic-aromatic copolyesters (e.g., polybutylene adipate terephthalate, polyethylene glycol adipate terephthalate, polyethylene glycol isophthalate adipate, polybutylene isophthalate adipate, etc.); aromatic polyesters (e.g., polyethylene terephthalate, polybutylene terephthalate, etc.); and so on.

[0054] A particularly suitable polyester is polylactic acid, which generally may be derived from monomer units of any isomer of lactic acid, such as L-lactic acid (“L-lactate”), D-lactic acid (“D-lactate”), meso-lactic acid, or mixtures thereof. The monomer units also may be formed from the anhydrides of any isomer of lactic acid, including L-lactide, D-lactide, meso-lactide, or mixtures thereof. Such cyclic dimers of lactic acid and / or lactide also may be employed. Any known polymerization method, such as polycondensation or ring-opening polymerization, may be used to polymerize lactic acid. A small amount of a chain extender (e.g., a diisocyanate compound, an epoxide compound, or an anhydride) may be employed. Polylactic acid may be a homopolymer or a copolymer, such as those containing monomer units derived from L-lactic acid and monomer units derived from D-lactic acid. Although not required, the content of one of the monomer units derived from L-lactic acid and the monomer units derived from D-lactic acid is preferably about 85 mole % or higher, about 90 mole % or higher in some embodiments, and about 95 mole % or higher in some embodiments. A variety of polylactic acids may be blended in any percentage, each having a different ratio of monomer units derived from L-lactic acid to monomer units derived from D-lactic acid. Of course, polylactic acid also may be blended with other types of polymers (e.g., polyolefins, polyesters, etc.).

[0055] In a specific embodiment, polylactic acid has the following general formula structure:

[0056]

[0057] The polylactic acid may have a number average molecular weight (“M n n”) in the range of from about 40,000 to about 180,000 grams per mole, in some embodiments from about 50,000 to about 160,000 grams per mole and in some embodiments from about 80,000 to about 120,000 grams per mole. Similarly, the polymer also typically has a weight average molecular weight (“M w w”) in the range of from about 80,000 to about 250,000 grams per mole, in some embodiments from about 100,000 to about 200,000 grams per mole and in some embodiments from about 110,000 to about 160,000 grams per mole. The ratio of the weight average molecular weight to the number average molecular weight (“M w w / M n n”), i.e., the “polydispersity index” is also relatively low. For example, the polydispersity index is typically in the range from about 1.0 to about 3.0, in some embodiments from about 1.1 to about 2.0 and in some embodiments from about 1.2 to about 1.8. The weight average molecular weight and the number average molecular weight can be determined by methods known to those skilled in the art.

[0058] The above polymers can be used to form single-component fibers, bicomponent fibers or multicomponent fibers. To form bicomponent fibers, for example, two different molten polymer streams can be fed to each polymer nozzle to form fibers. The two different polymers can be in a side-by-side arrangement or a core-sheath arrangement.

[0059] As described above, the fiber forming apparatus 14 of the present disclosure is particularly suitable for producing a meltblown web. In one embodiment, during web formation, when the molten fibers are deposited on the forming surface, an absorbent material can be blown into the molten fibers. For example, the absorbent material can be superabsorbent particles, a cellulose material, etc. Cellulose materials that can be used include pulp fibers such as softwood fibers and / or hardwood fibers. Contacting the absorbent material with the fibers during formation produces a web having liquid absorbent properties.

[0060] The nonwoven web manufactured according to the present disclosure can have any suitable basis weight. For example, the web can have a basis weight of from about 3 gsm to about 40 gsm. In one embodiment, a relatively lightweight web is formed, having a basis weight of less than about 15 gsm, such as less than about 10 gsm, such as less than about 8 gsm.

[0061] These and other modifications and variations of the present invention can be practiced by those of ordinary skill in the art without departing from the spirit and scope of the invention more particularly described in the appended claims. In addition, it should be understood that aspects of the various embodiments can be interchanged, in whole or in part. Further, those of ordinary skill in the art will understand that the foregoing description is merely illustrative and is not intended to limit the invention further described in such appended claims.

Claims

1. A fiber forming device, the fiber forming device comprising: A die head having a length and a width, the die head including a first row of polymer nozzles spaced apart from and substantially parallel to at least a second row of polymer nozzles, the first row of polymer nozzles and the second row of polymer nozzles being configured to receive a stream of molten polymer material for ejecting polymer fibers from the die head, the first row of polymer nozzles and the second row of polymer nozzles extending along the length of the die head; A first air flow path, a second air flow path, and a third air flow path, the first air flow path, the second air flow path, and the third air flow path being spaced apart and extending along the length of the die head in a parallel relationship, the first air flow path being located between a first outer edge of the die head and the first row of polymer nozzles, the second air flow path being located between a second outer edge of the die head and the second row of polymer nozzles, the third air flow path being located between the first row of polymer nozzles and the second row of polymer nozzles, the first air flow path including a first outlet positioned such that an air stream flowing out of the first outlet converges with an air stream leaving the third air flow path, the second air flow path including a second outlet positioned such that an air stream flowing out of the second outlet converges with an air stream leaving the third air flow path, the first air flow path, the second air flow path, and the third air flow path all being configured to direct a refining air stream against the molten polymer fibers leaving the first row of polymer nozzles and the second row of polymer nozzles; and Wherein the third air flow path is in communication with a gas flow path configured to control the fluid flow to the third air flow path independently of the fluid flow to the first air flow path and to the second air flow path, such that gas can be supplied to the third air flow path at a different pressure than the gas supplied to the first air flow path and the second air flow path, Wherein the fiber forming device further includes a fluid flow regulator in communication with the gas flow path leading to the third air flow path, the fluid flow regulator being configured to maintain the gas pressure through the third air flow path higher than the pressure of the gas leaving the first air flow path and the pressure of the gas leaving the second air flow path.

2. The fiber forming device according to claim 1, wherein the first row of polymer nozzles and the second row of polymer nozzles are each positioned at an angle toward each other.

3. The fiber forming device according to claim 2, wherein the die head includes a vertical axis extending from the top to the bottom of the die head, and includes a horizontal axis perpendicular to the vertical axis, and wherein the first row of polymer nozzles is positioned at an acute angle with respect to the vertical axis, and the second row of polymer nozzles is positioned at an acute angle with respect to the vertical axis.

4. The fiber forming device according to any one of claims 1 to 3, wherein the die head includes a fiber distribution surface, the first row of polymer nozzles and the second row of polymer nozzles are arranged along the fiber distribution surface, similarly, the first air flow path, the second air flow path and the third air flow path are also arranged along the fiber distribution surface, the fiber distribution surface has a V shape defining a vertex, and wherein the first row of polymer nozzles and the second row of polymer nozzles are positioned to eject polymer fibers adjacent to the vertex of the fiber distribution surface.

5. The fiber forming device according to any one of claims 1 to 3, wherein the first air flow path and the second air flow path are each positioned at an angle towards each other.

6. The fiber forming device according to claim 5, wherein the die head includes a vertical axis extending from the top to the bottom of the die head, and includes a horizontal axis perpendicular to the vertical axis, and wherein the first air flow path is positioned at an acute angle with respect to the horizontal axis, and the second air flow path is positioned at an acute angle with respect to the horizontal axis.

7. The fiber forming device according to any one of claims 1 to 3, wherein the third air flow path is positioned to eject gas in a downward vertical direction.

8. The fiber forming device according to any one of claims 1 to 3, wherein the first air flow path and the first row of polymer nozzles are symmetric with respect to the vertical axis of the die head to the second air flow path and the second row of polymer nozzles.

9. The fiber forming device according to any one of claims 1 to 3, wherein the first air flow path and the second air flow path include slots extending along the length of the die head, or include a row of orifices extending along the length of the die head.

10. The fiber forming device according to any one of claims 1 to 3, wherein the first air flow path is in fluid communication with a first air chamber, the second air flow path is in fluid communication with a second air chamber, and the third air flow path is in fluid communication with a third air chamber, the first air chamber, the second air chamber and the third air chamber are isolated from each other, and each of the first air chamber, the second air chamber and the third air chamber is in communication with a pressurized gas source for supplying pressurized gas to each of the first air flow path, the second air flow path and the third air flow path.

11. The fiber forming apparatus according to any one of claims 1 to 3, wherein the third air flow path is in fluid communication with the wedge-shaped flow control device for guiding gas flow through the third air flow path while preventing turbulence.

12. The fiber forming apparatus according to any one of claims 1 to 3, further comprising a third row of polymer nozzles and a fourth air flow path positioned between the second row of polymer nozzles and the third row of polymer nozzles.

13. A method for forming a nonwoven web, the method comprising: forming two rows of fibers from a molten polymer material; contacting the fibers with a plurality of air flows for attenuating the fibers, the air flows including a first air flow impinging on the first row of fibers from a first side, a second air flow impinging on the second row of fibers from a second side, and a third air flow guided between and impinging on the first row of fibers and the second row of fibers, the first air flow being ejected from a first air flow path at a first pressure, the second air flow being ejected from a second air flow path at a second pressure, and the third air flow being ejected from a third air flow path at a third pressure, and wherein the third pressure is greater than the first pressure and the second pressure; and depositing the attenuated fibers on a forming surface for forming a nonwoven web.

14. The method according to claim 13, wherein the pressure ratio of the third pressure of the third air flow to the first pressure of the first air flow is in the range of 1.05:1 to 2:

1.

15. The method according to claim 14, wherein the pressure ratio of the third pressure of the third air flow to the second pressure of the second air flow is in the range of 1.05:1 to 2:

1.

16. The method according to any one of claims 13, 14 or 15, wherein the polymer material comprises a polyolefin polymer.

17. The method according to any one of claims 13, 14 or 15, wherein the polymer material comprises a biodegradable polymer.

18. The method according to any one of claims 13, 14 or 15, further comprising the step of contacting two rows of parallel fibers with a liquid absorbent material before depositing the fibers on the forming surface for forming a co-formed web.

19. The method according to any one of claims 13, 14 or 15, wherein the first row of fibers is ejected from a first row of polymer nozzles, and the second row of fibers is ejected from a second row of polymer nozzles, and wherein the first row of polymer nozzles and the second row of polymer nozzles are each positioned at an angle towards each other.

20. The method according to any one of claims 13, 14 or 15, wherein the first pressure, the second pressure and the third pressure are all maintained below 10 psi and above 0.5 psi.

21. The method according to any one of claims 13, 14 or 15, wherein the fiber diameter of the attenuated fibers deposited on the forming surface is less than 5 microns.

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