Patent Application
20240240362
Spunbond nonwoven fabrics comprise bonded webs of continuous filaments formed by extruding a molten thermoplastic polymer from a plurality of fine capillaries as molten filaments. The molten filaments are quenched to at least partially solidify them and then they are attenuated by one or more high velocity air streams which reduce their diameter. In addition to generating relatively fine filaments, the pneumatic drawing of the filaments in the spunbond process also acts to increase the crystallinity of certain polymers, such as propylene polymers, which provides the formed filaments and fabrics with increased tensile strength. By way of example, spunbond filament nonwoven fabrics and processes for making the same are disclosed in U.S. Pat. No. 4,340,563 to Appel et al, U.S. Pat. No. 8,246,898 to Conrad et al. and U.S. Pat. No. 8,333,918 to Lennon et al.
Spunbond filament nonwoven fabrics are commonly used in a wide range of products. The reason for this extensive and varied use in part relates to the ability of spunbond filament nonwoven fabrics to provide a desirable combination of properties including strength, opacity (coverage) and a pleasing hand-feel. Further, the cost of manufacture of spunbond filament fabrics is relatively low as compared to other materials with like properties such as traditional knitted or woven fabrics. As a result, spunbond filament nonwoven fabrics have been found to be particularly useful in relation to the manufacture of single-use or limited-use products; e.g. absorbent personal care products, wipes, protective apparel, geotextiles, tarpaulins, etc.
In order to further improve various properties of the nonwoven fabrics it is often desirable to reduce the average fiber diameter of the spunbond filaments forming the nonwoven fabric. Various measures have been taken to influence and reduce filament diameter. However, forming spunbond filaments having diameters significantly less than about 20 microns has proven difficult without also reducing the overall through-put of the polymer through the system. In this regard, lower polymer through-put rates allows the pneumatic drawing forces to more extensively act upon the extruded filaments and reduce their overall diameter. However, reducing the overall through-put of the system increases the overall cost of the nonwoven fabric. Prior attempts to produce small diameter spunbond filament nonwoven fabrics at high production rates often resulted in fiber breaks, hard spots or other issues that negatively impacted process stability, yields and/or overall web quality. Thus, manufacturers were essentially forced to choose between low filament diameter and high process efficiency.
Therefore, in order to address the continued and unmet needs, the present invention provides an improved process for the production of spunbond filament nonwoven fabrics comprising small diameter filaments at high rates of production and with high process stability.
Throughout the specification and claims, discussion of the articles and/or individual components thereof is with the understanding set forth below.
The term “comprising” or “including” or “having” are inclusive or open-ended and do not exclude additional unrecited elements, compositional components, or method steps. Accordingly, the terms “comprising” or “including” or “having” encompass the more restrictive terms “consisting essentially of” and “consisting of.”
As used herein “continuous filaments” means filaments formed in a substantially continuous, uninterrupted manner having indefinite length and having a high aspect ratio (length to diameter) in excess of about 10,000:1.
As used herein, unless expressly indicated otherwise, when used in relation to material compositions, the terms “percent” or “%” refer to the quantity by weight of a component as a percentage of the total.
As used herein, the term “polymer” generally includes but is not limited to, homopolymers, copolymers, such as for example, block, graft, random and alternating copolymers, terpolymers, etc. and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term “polymer” shall include all possible geometrical configurations of the molecule. These configurations include, but are not limited to isotactic, syndiotactic and random symmetries.
As used herein “ethylene polymer” or “polyethylene” means a polymer having greater than 50 mol. % units derived from ethylene.
As used herein “olefin polymer” or “polyolefin polymer” means a polymer having greater than 50 mol. % units derived from an alkene, including linear, branched or cyclic alkenes.
As used herein “propylene polymer” or “polypropylene” means a polymer having greater than 50 mol. % units derived from propylene.
As used herein, the term “nonwoven” web or fabric means a structure or a web of material that has been formed without use of traditional fabric forming processes such as weaving or knitting, to produce a structure of individual filaments or threads that are entangled or intermeshed, but not in an identifiable, repeating manner.
As used herein, the term “machine direction” or “MD” refers to the direction of travel of the forming surface onto which filaments are deposited during formation of a fibrous web.
As used herein, the term “cross-machine direction” or “CD” refers to the direction which is essentially perpendicular to the machine direction defined above.
As used herein “personal care articles” means any and all articles or products used for personal health or hygiene including diapers, adult incontinence garments, absorbent pants and garments, tampons, feminine pads and liners, bodily wipes (e.g. baby wipes, perineal wipes, hand wipes, etc.), bibs, changing pads, bandages, and components thereof.
As used herein “protection articles” means all articles intended to protect a user or equipment from contact with or exposure to external matter including, for example, face masks, protective gowns and aprons, gloves, caps, shoe covers, equipment covers, sterile wrap (e.g. for medical instruments), car covers, and so forth.
As used herein “melting point” means that determined by differential scanning calorimetry (DSC). For purposes herein, the maximum of the highest temperature peak is considered to be the melting point of the polymer. A “peak” in this context is defined as a change in the general slope of the DSC curve (heat flow versus temperature) from positive to negative, forming a maximum without a shift in the baseline where the DSC curve is plotted so that an endothermic reaction would be shown with a positive peak. A heating rate of 10° C./minute is used.
In reference to
As shown in reference to
Optionally, albeit highly preferred, below the distributor 21 is a filter or screen 22 and a support member 23. The screen acts to filter impurities or other unwanted debris from the molten streams in order to prevent fowling of the spinneret such as by blocking one or more of the capillaries. Suitable screens may for example comprise one or more stacked screens ranging between about 50-350 mesh. Supporting the screen(s) is a support member 23. Suitable support members may, for example, simply comprise a metal plate having a high number and frequency of apertures extending there through. The pressurized molten polymer stream may be directed from the support plate 23 into the spinneret 24. With respect to the attachment of the various components forming the spinning assembly, in order to form a seal sufficient to withstand the high pressures associated with this process the components within the spinning assembly will have seals rated for the high temperatures and pressures described herein including for example those provided by metal-to-metal seals or high performance gaskets.
As shown in
As best seen in reference to
In reference to
In addition, in certain embodiments the inner or center region of the extrusion area may have less closely spaced exit orifices as compared to regions adjacent the CD edges, proximate the quench air flow. In this regard, the pattern of exit orifices may have a CD extending segment at or proximate the center of the extrusion area that has reduced density of conduits or that is entirely lacking exit orifices. For example, the center region may have a section extending across the CD centerline having an MD width between about 10 and about 60 mm that either lacks any conduits or alternatively that has a significantly reduced capillary density (e.g. a capillary density less than 70%, 60%, 50%, 40% or 30% of the average).
The spinneret will have a relatively high density or close spacing of exit orifices such as for example those having an exit orifice or hole density at least about 3 exit orifices per cm2; the density being measured in relation to the number of exit orifices within the extrusion area. In certain embodiments the spinneret may have an exit orifice density at least about 3.5, 3.7, 4, 4.3, 4.5, 4.7, 5, 5.3, 5.5, 5.7, 6, 6.5, 6.7, 7, 7.3 or 7.5 exit orifices per cm2 and/or no more than about 20, 19.5, 19, 18.7, 18.5, 18.3, 18, 17.7, 17.5, 17.3, 17, 16.7, 16.5, 16.3, 16, 15.7, 15.5, 15.3, 15, 14.7, 14.5, 14.3 or 14 exit orifices per cm2. In a further aspect, the number of exit orifices within the spinneret will be greater than 5000 per meter of the extrusion area length (CD length) and in certain embodiments will be greater than about 6000/M, 6500/M, 7000/M, 7500/M, 8000/M or even 8500/M per meter of the extrusion area length (CD length).
The molten polymer is pumped into and through the spinning assembly and spinneret at high-pressures to achieve the throughputs and exit velocities discussed herein below. The molten polymer is extruded out of the exit orifices 89 at rates of at least about 0.3 g/hole/minute or “g/h/m.” To calculate g/h/m, the mass of the extrudate composition pumped through the spinneret over a selected period of time is divided by the number of exit orifices and the selected time. The extrusion rate, in certain embodiments, may be at least about 0.3 g/h/m, 0.33 g/h/m, 0.35 g/h/m, 0.37 g/h/m, 0.4 g/h/m, 0.43 g/h/m or 0.45 g/h/m and/or not more than about 0.6 g/h/m, 0.57 g/h/m, 0.55 g/h/m, 0.53 g/h/m or 0.5 g/h/m. In a further aspect, the molten extrudate is pumped through and out of the spinneret having an exit velocity greater than about 10 feet/minute and in certain embodiments may be at least about 10.3, 10.5, 10.7, 11, 11.3, 11.5, 11.7, 12, 12.3 or 12.5 feet/minute and/or may be not more than about 45, 43, 40, 38, 35, 33, 30, 28, 25 or 23 feet/minute. The exit velocity (Ve) of the extrudate at the exit orifices is calculated according to the formula below:
In a further aspect, the temperature of the polymer can be regionally controlled either as it enters the spinning assembly or as it moves through the spinning assembly such that the temperature of the molten polymer extrudate exiting the exit openings proximate the quench air is at a higher temperature relative to the molten polymer extrudate exiting the exit openings within the interior of the spinneret and extrusion region. In reference to the embodiments described herein, molten polymer at a first temperature would be extruded out of the rows of exit openings proximate the CD edge and molten polymer at a second temperature (lower than the first temperature) would be extruded out of rows of exit openings proximate the center of the spinneret and spinning area. In this regard, the quench air will first impact and pass through the outer portions of the bundle and as it does so and cools the molten filaments the quench air will warm prior to striking the inner or centrally located filaments within the bundle. When the outer extruded filaments are at a slightly elevated temperature relative to the inner extruded filaments, this will help improve processing at the conditions described herein and create a more uniform frost line across the total filament bundle.
In reference to
As may be seen in
Additional high speed air or ‘draw air’ may also directed into the fiber draw unit such as being directed into the upper narrow channel 53 via conduits and blowers in fluid communication therewith. In addition, the draw air introduced into the channel(s) of the drawing unit may be introduced at speeds greater than about 50 M/second or 75 M/second. The draw air may be directed into the channel(s) from either one or more sides of the draw unit and at one or more locations vertically within the draw unit. The angle of introduction may be either perpendicular to the direction of the filament flow or at a downward angle.
The fiber draw unit may have additional channels below the initial constricting opening and associated channel. The additional channels below the initial constricted opening and associated channel may be sequentially smaller, wider than the constricted opening or have sections of varying MD width. In reference to the embodiment depicted in
The pneumatic forces acting upon the filaments are configured to achieve a draw ratio of not more than about 1100 and in certain embodiments may be at least about 250, 280, 300, 330, 350, 380, 400, 430, 450, 480, 500, 530, 550, 580, 600, 630 or 650 and/or not more than about 1100, 1080, 1050, 1030, 1000, 980 or 950. The draw ratio is calculated by dividing the terminal velocity (VT) by the exit velocity (VE discussed above) as follows:
The terminal velocity is calculated as follows:
The entraining air forming the pneumatic forces upon the filaments enters the system from the openings or gaps located between the various components above the drawing unit and the various blowers as noted. However, the filament draw unit will typically employ additional air blowers or other air feeds as is known in the art. The walls 54 of the draw unit 50 may optionally be manipulated inwardly or outwardly in order to modify the size of the channel at different locations within the draw unit. In certain embodiments, the walls 54 may be moved inwardly or outwardly in discrete sections so as to form a channel having varying dimension or widths in order to adjust the drawings forces and spreading of the filaments within the bundle. Still further, in order to improve the uniform spreading and coverage of the formed nonwoven fabric, as is known in the art a deflector plate 56 may be used to spread the filaments. Optionally, electrostatic charge bars (not shown) or other components may further be employed to aid with spreading of filaments, web formation and laydown. While the drawings depict an open air melt-spinning system, it will be readily appreciated that the process of the present invention will also work with closed-air systems as are known in the art. Examples of various quench and drawings systems suitable for use in the present invention include, but are not limited to, those described in U.S. Pat. No. 4,340,563 to Appel et al, U.S. Pat. No. 5,935,512 to Haynes et al., U.S. Pat. No. 6,692,601 Najour et al., U.S. Pat. No. 6,783,722 to Taylor, U.S. Pat. No. 7,037,097 Wilkie et al., U.S. Pat. No. 7,762,800 to Geus et al., U.S. Pat. No. 8,246,898 to Conrad et al., U.S. Pat. No. 8,333,918 to Lennon et al. and US2017/0211217 Nitschke et al.
The fully drawn filaments 34 exit the bottom of the filament drawing unit 50 through the exit opening 57 and are deposited onto a forming surface 60 such as a fabric or wire. As is known in the art, one or more vacuums 62 are positioned beneath the forming surface 60 to draw the filaments on to the forming surface 60 and form a relatively loose matt or web 36 of filaments 34. The vacuums also remove the draw air in order to prevent deflected air from interfering with filament lay-down and/or from disturbing the matt 36 once laid on the wire. The suctioning of the air from underneath the drawing unit can also assist in driving the movement of both the air and fibers through the drawing unit and onto the forming wire.
Optionally, the matt of filaments can be treated in order to impart some minimal degree of integrity required for additional handling. Such treatment may, for example, include consolidating the matt with a compaction roll (not shown) or through the use of a high velocity through-air bonder 64. Such through-air bonders impart only minimal filament-to-filament bonding sufficient for additional handling and processing and without significantly melting the filaments. Such bonders and methods are described in U.S. Pat. No. 5,707,468 to Arnold et al. In addition, in order to achieve relatively higher basis weight fabrics, multiple banks of spinnerets and drawing units may be located sequential over the foraminous forming surface upstream of the consolidating and/or bonding apparatus.
After formation, the nonwoven matt is desirably bonded in order to increase the overall integrity and strength of the same. In one aspect, the matt may be mechanically bonded such as by entanglement. In this regard, the filaments may be entangled by hydroentangling which includes subjecting the matt to one or more rows of fine high-pressure jets of water so that the filaments become sufficiently entangled with one another to form a coherent nonwoven fabric. In other embodiments, the matt may be bonded by one or more techniques known in the art such as by the application of adhesive, pressure, heat and/or ultrasonic energy. In certain aspects, the matt may be pattern bonded, as is known in the art, using a pair of bonding rolls 66, 68, wherein at least one of the rolls has a pattern of protuberances or “pins” corresponding to the desired pattern of bond points to be imparted to the matt and form a bonded nonwoven fabric 38. The two cooperative rolls form a nip through which the matt is passed with the application of pressure and, optionally, heat. While suitable bond elements may be formed without the application of heat, use of heat together with pressure is preferred. The bonding can be conducted as is known in the art employing a nip formed by patterned roll and a smooth anvil roll (“pin-to-flat”) or by two coordinated patterned rolls (“pin-to-pin”). With respect to the use of a smooth anvil roll, the roll may be a steel roll or alternatively may be coated with a resilient material. By way of example only, various pattern bonding methods are shown and described in U.S. Pat. No. 3,855,046 to Hansen et al., U.S. Pat. No. 4,333,979 to Sciaraffa et al., U.S. Pat. No. 4,374,888 to Bornslaeger, U.S. Pat. No. 5,110,403 to Ehlert, U.S. Pat. No. 5,858,515 to Stokes et al., U.S. Pat. No. 6,165,298 to Samida et al. and so forth. As is known in the art, the pressures, temperatures, residence time, base sheet composition, basis weight, and other parameters will impact the selection of the desired degree of pressure and/or heat applied to the base sheet to form the bond points. Alternatively, the matt of filaments can be adhesively bonded such by spray, gravure roll or other means for the application of adhesive in the desired pattern as is known in the art.
The resulting nonwoven fabric desirably has high tensile strength, uniform opacity (coverage) and/or pleasing hand. For many applications the bonded nonwoven fabric can have a basis weight less than about 175 g/m2. In certain embodiments, the nonwoven fabrics can have a basis weight less than about 150 g/m2, 120 g/m2, 90 g/m2, 60 g/m2, 45 g/m2, 35 g/m2, 30 g/m2, 25 g/m2, 20 g/m2, or even 18 g/m2 and further, in certain embodiments, can have a basis weight in excess of about 5 g/m2, 8 g/m2, 10 g/m2 or 12 g/m2. Further, the filaments as formed by this process and as provided in the corresponding nonwoven fabric can have an average denier (g/9000M) of less than about 1.5 or less and in certain embodiments may have an average fiber denier equal to or less than about 1.4, 1.3 or 1.2 and/or at least about 0.7, 0.73, 0.75, 0.77, 0.8, 0.83, 0.85, 0.87 or 0.9. Similarly, the filaments as formed by this process and as provided in the corresponding nonwoven fabric can have an average fiber size less than or equal to about 16 microns and in certain embodiments may have an average fiber size equal to or less than about 16, 15.8, 15.5, 15.3, 15, 14.8 or 14.5 u and/or at least about 10, 10.3, 10.5, 10.8, 11, 11.3, 11.5, 11.8 or 12 p.
The extrudate composition, namely that used to make and form the fibers herein, will predominantly comprise one or more thermoplastic olefin polymers. Suitable polyolefins include, but are not limited to, homopolymers, copolymers and terpolymers of ethylene (e.g., low density polyethylene, high density polyethylene, linear low density polyethylene, etc.), propylene (e.g., syndiotactic, atactic, isotactic, etc.), butylene and so forth. In addition, blends and combinations of the foregoing are also suitable for use in connection with the present invention. In one embodiment, for instance, the polymeric portion of the extrudate composition will include greater than about 65 weight percent olyolefin polymer(s) and in certain embodiments the polymer may comprise at least about 65, 70, 75, 80, 85, 90, 95% by wt. olefin polymer and/or less than about 100, 99, 98 or 97 wt. % olefin polymer. By way of non-limiting example, the polymeric portion of the extrudate and formed filaments may comprise between about 65 to about 100 weight percent, between about 70 to about 99 weight percent, between about 80 to about 99 weight percent, between about 70 to 98 weight percent, between about 80 to 98 weight percent or between about 90 to about 99 weight percent. Further, in a particular embodiment, the polymeric portion of the extrudate composition may comprise entirely of olefin polymers such as for example, comprising entirely of polymers selected from the group of propylene, ethylene and butylene polymers. The extrudate composition will have a melt-flow rate (MFR) less than about 60 dg/minute, and in certain embodiments will have an MFR greater than about 5, 8, 10, 12 or 15 dg/minute and/or less than about 55, 53, 50, 48 or 45 dg/minute. Further, as is known in the art, the extrudate composition may optionally include one or more fillers, colorants (e.g. TiO2, pigments), antioxidants, softening agents, surfactants, slip agents and so forth. In particular, as is well known in the art, one or more slip agents, such as fatty acid amides, may be added to the extrudate composition for melt spinning.
In certain embodiments the spunbond filament matts and/or fabrics may, optionally, be treated by various other known techniques such as, for example, stretching, necking, needling, creping, printing, and so forth. In still further embodiments, the coherent nonwoven matts or fabrics may optionally be applied with one or more topical treatments or applications in order to enhance the surface properties of the nonwoven. For example, the nonwoven fabric may be treated with surfactants, detergents, anti-static, sequestrants, plasma fields (e.g. to improve wettability), electric fields (e.g. to form electrets), solvents, anti-microbial agents, pH modifiers, binders, fragrances, inks and so forth.
In addition, spunbond filament nonwoven fabrics of the present invention may be used alone or in connection with a multi-layer laminate. By way of example, the spunbond filament nonwoven fabric (S) may be used in combination with a film (F) to form a S/F, S/F/S, S/S/F/S or other multi-layer laminates. As a further example, the spunbond filament nonwoven fabric (S) may be used in connection with other nonwoven fabrics such as meltblown fiber fabrics (M) to form S/M, S/M/S, S/M/M/S, S/S/M/S or other multi-layer laminates. Various techniques may be utilized to bond the spunbond filament nonwoven fabric together with other layers including hydroentangling, adhesive, thermal, ultrasonic and other forms of bonding. Exemplary composite and/or laminate materials, and various end uses for the spunbond filament nonwoven fabrics include, but are not limited to, those described in U.S. Pat. No. 4,720,415 Vander Wielen, U.S. Pat. No. 5,226,992 Morman, U.S. Pat. No. 5,492,751 to Butt et al., U.S. Pat. No. 5,688,476 Bourne et al., U.S. Pat. No. 5,843,057 McCormack, U.S. Pat. No. 6,115,839 to Covington et al., U.S. Pat. No. 6,534,149 to Daley et al., U.S. Pat. No. 6,811,638 to Close et al., U.S. Pat. No. 7,022,201 Anderson et al., U.S. Pat. No. 7,803,244 Siqueira et al., U.S. Pat. No. 8,603,281 to Welch et al., U.S. Pat. No. 8,914,936 Jemsby et al. and WO98/53896 to Reader.
In one aspect, the nonwoven fabrics may be used as a component of a personal care article either alone or together with other layers or materials. In this regard, the spunbond filament nonwoven fabrics are well suited to serving as a layer intended to come into contact with the skin and/or for layers used for liquid handling. For example, the spunbond filament nonwoven fabrics may comprise part of the liquid intake structure such as comprising a top-sheet, surge material or core wrap. In a further aspect, the spunbond filament nonwoven fabrics may comprise an outer layer of a breathable baffle layer such as is commonly provided by microporous film/spunbond fabric laminates. In still further aspects, the spunbond filament nonwoven fabrics may comprise the outer facing of an elastic component. In this regard, elastic materials, while desirable for their ability to enhance the fit of an article, often have a tacky or otherwise undesirable hand-feel. In a further aspect, the nonwoven fabrics may also be employed as a component of a protection fabric including, for example, use as an outer facing material for elastics or barrier materials. Still further, the spunbond filament nonwoven fabrics may be used as or within a wiper, mop head, wash cloth, geotextile material, filter, housewrap, sound insulation and still other end uses.
It will be appreciated that while the invention has been described in detail with respect to specific embodiments and/or examples thereof, it will be apparent to those skilled in the art that various alterations, modifications and other changes may be made to the invention without departing from the spirit and scope of the same. It is therefore intended that the claims cover or encompass all such modifications, alterations and/or changes.
Tensile Strength: As used herein “tensile strength” or “strip tensile”, is the peak load value, i.e. the maximum force produced by a specimen, when it is pulled to rupture. Samples for tensile strength testing are prepared by drying and then die cutting test specimens to a width of 25 mm and length of approximately 152 mm. The instrument used for measuring tensile strengths is an MTS Criterian 42 and MTS TestWorks™ for Windows Ver. 4 (MTS Systems Corp., Research Triangle Park, NC). The load cell is selected, depending on the strength of the sample being tested, such that the peak load values fall between 10 and 90 percent of the load cell's full scale load. The gauge length is 76 mm and jaw length is 76 mm. The crosshead speed is 305 mm/minute, and the break sensitivity is set at 70% and the slope preset points at 70 and 157 g. The sample is placed in the jaws of the instrument and centered with the longer dimension parallel to the direction of the load application. The test is then started and ends when the specimen breaks. The peak load is determined, for purposes herein, based upon the CD tensile strength. Six (6) representative specimens are tested, and the arithmetic average of all individual specimen tested is the tensile strength for the product.
The average fiber size of the spunbond filaments is determined optically using a calibrated digital microscope with on-screen measurement. The filaments widths (diameter) are selected manually and the digital microscope provides the associated dimension.
The melt flow rate (“MFR”) as used herein means that measured in accordance with ASTM D1238-13 using a melt indexer, utilizing condition 230° C./2.16 kg for compositions predominantly comprising propylene polymer(s) and 190° C./2.16 kg for compositions predominantly comprising ethylene polymer(s).
This application claims priority from U.S. provisional Patent Application Ser. No. 62/756,313 filed on 6 Nov. 2018, the entire contents of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62756313 | Nov 2018 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 17291338 | May 2021 | US |
| Child | 18621989 | US |
