Patent Application
20210310156
The present invention relates to an equipment adapted to create filaments of the spun-blown type for forming nonwoven materials of superior quality as well as to a process for operating such equipment.
Spunmelt is a process where fibers are spun from molten polymer through a plurality of nozzles in a die head connected to one or more extruders for being formed into web, such as nonwoven webs or as components thereof. The spunmelt processes are well known in the art, and may include melt-blowing, see e.g. U.S. Pat. No. 8,017,534 (K-C, Harvey), spun-bonding, see e.g. U.S. Pat. No. 5,935,512 (K-C, Haynes).
From such technologies, a “hybrid” technology, often referred to as “spun-blowing” has been developed and described in e.g. WO2015/171707/U.S. Pat. No. 9,303,334 (Biax, 2014). This technology provides a number of benefits with regard to the fiber and web properties, but also with regard to the equipment and process for the manufacturing. However, the equipment is quite inflexible with regard to replacement of individual nozzles, as in case of uneven wear of the nozzles over time, or if varying filament diameter were to be executed.
Thus, from U.S. Pat. No. 6,364,647 it is known to construct a similar spun-blowing apparatus wherein the nozzles are removable. Whilst this provides certain improvements with regard to operation but also with regard to product flexibility, such a design carries a disadvantage of sharp transition from the polymer supply system into the nozzle capillary, which results in turbulences of the polymer flow, not only reducing smoothness of the flow through the capillary, but also increasing the propensity for polymer depositions around the nozzle opening that may require more frequent cleaning.
Henceforth, it is an object of the present invention to overcome problems of the spun-blowing technology.
The present invention is a die block for forming spun-blown filaments comprising
The spinneret block, the air distribution plate, the exterior air plate, and the cover strip are mounted in this order and secured by the securing means such that
The openings in the exterior plate and the nozzles are adapted so as to allow molten polymer exiting the nozzles and air flowing through the openings of the exterior air plate are at an angle of less than 30°, preferably less than about 10° and more preferably essentially parallel.
Further, the spinneret body comprises
The nozzles comprise
Further, the upper sections of the nozzles fit removably into the upper portions of the lower plate, preferably without protruding therefrom, wherein further the upper plate opening diameter and the lower plate opening diameter or the chamfering exhibit a difference of less than 50 μm, preferably less than 20 μm.
The die block may further satisfy one or more of the conditions selected from the group consisting of
Optionally, the openings in the upper plate of the die block satisfy one or more of the conditions selected from the group consisting of
The nozzles of the die block may form an array and further comprise stationary pins, preferably exhibiting the same outer diameters and lengths as a nozzle, the stationary pins being positioned at the periphery of the array.
The upper plate of a die block may further comprise
wherein
The sealant compound may be adapted to prevent in an assembled state of the die block the flow of the molten polymer
The grooves may exhibit a rounded cross-sectional shape or at least a rounded base, preferably a cross-sectional shape of a partial oval with a half-circular base and straight sides above.
The grooves may exhibit one or more of the dimensions selected from the group consisting of
The grooves may comprise a sealant which may be selected from the group consisting of acrylic resins, adhesive sealants, butyl rubber, elastic sealants, epoxy thermosets, latex sealants, plastic sealants, polysulfide sealants, polyurethane sealants, rubber sealants, silicone sealants, preferably polysiloxanes, or fluorocarbon polymers, such as PTFE, or urethane sealants, more preferably of the silicon or PTFE type.
The array of nozzles of a die block may comprises at least two sub-arrays comprising nozzles differing from nozzles of a different sub-array in at least one of the dimensions selected from the group consisting of
Optionally, the array of nozzles of the die block comprises at least two sub-arrays, each of the sub-arrays being connected to a separate polymer supply system adapted to supply molten polymer to the sub-array differing in at least one of the features selected from the group consisting of
In another aspect, the present invention is a process for forming a nonwoven web comprising spun-blown fibers, comprising the steps of
Same numerals in the figures depict same or equivalent features. Figures are schematic and not to scale.
The present invention relates to a particular execution for a die block for spun-blowing process for forming fibers or filaments that may further form a fibrous spun-blown web or nonwoven comprising such a formed spun-blown web, e.g. as a layer in a multi-layer composite web.
Spunmelting is a process where fibers are spun from molten polymer through a plurality of nozzles of a die head connected to one or more extruders. The spunmelt process may include melt-blowing, spun-bonding and the hybrid process as described hereinafter in more detail, also referred to as spun-blowing.
Melt-blowing is a process for producing very fine fibers typically having a diameter of less than about 10 microns, where a plurality of molten polymer streams are attenuated using a hot, high speed gas stream once the filaments emerge from the nozzles. The attenuated fibers are then collected on a collector, e.g. a flat belt or drum collector. A typical melt-blowing die has around 35 nozzles per inch and a single row of nozzles. The typical melt-blowing die uses inclined air jets at each side of the row of nozzles for attenuating the filaments.
Spun-bonding is a process for producing strong fibrous nonwoven webs directly from thermoplastics polymers by attenuating the spun filaments using cold, high speed air while quenching the fibers near the spinneret face. Individual fibers are then laid down randomly on a collection belt and conveyed to a bonder to give the web added strength and integrity. Fiber size is usually below 250 μm and the average fiber size is in the range of more than about 10 microns and/or less than about 50 microns. The fibers are very strong compared to melt-blown fibers because of the molecular chain alignment that is achieved during the attenuation of the crystallizing (solidifying) filaments. A typical spun-bond die has multiple rows of polymer holes and for a conventional polymer of the polypropylene type the polymer melt flow index (MFI) is usually below about 500 grams/10 minutes at 2.16 kg load.
The present invention is related to a hybrid process between a conventional melt-blown process and a conventional spun-bond process, using a multi-row spinneret similar to the spinneret used in spun-bonding except the nozzles are arranged to allow parallel gas jets surrounding the spun filaments in order to attenuate and solidify them. Each of the extruded filaments is shrouded by pressurized gas and its temperature can be colder or hotter than the polymer melt. Optionally, the periphery around the array with the filaments may be surrounded by a curtain of pressurized gas.
In order to explain the general principles of the spun-blowing equipment and process for forming filaments and further webs, such as nonwoven webs or components of such webs, express reference is made to U.S. Pat. No. 9,303,334 describing such a technology in greater detail. Thus,
Overall, a die block 26 comprises as elements a spinneret body 52, an air distribution plate 70, an exterior plate 78, and a cover strip 88. Further, nozzles 58 extend from the spinneret body 52 through openings of the distribution plate 70 and exterior plate 78, respectively, such that molten material can pass through the capillary 60 of the nozzle 58 to form filaments 86 at the tip of the nozzle 96.
For ease of explanation, the order of the elements referred to in the following is such that the spinneret body 52, the air distribution plate 70, the exterior plate 78, and the cover strip 88 are arranged along gravity, such that the spinneret body 52 is positioned above and secured to the air distribution plate 70, which is positioned above and secured to the exterior plate 78, which is positioned above and secured to the cover strip 88, with securing means not shown.
The number of rows can vary as well as the number of columns. Typically, the number of rows will be more than 1, often more than 5, and will be less than about 30, or even less than 15. Typically, the number of columns will be more than 50, but can be more than about 200, and may be less than 3500.
As described in US'334, the nozzles 58 are formed of capillary tubes that are inserted through openings in the spinneret body 52 to form a passageway for the molten polymer.
Each of the nozzles 58 has an inside capillary diameter and an outside diameter. The inside diameter can range from between about 0.125 mm to about 1.25 mm. The outside diameter of each nozzle 58 should be at least about 0.5 mm. The outside diameter of each nozzle 58 may range from between about 0.5 mm to about 2.5 mm.
Typically, the length of a nozzle 58 ranges from between about 0.5 to about 6 inches.
As the molten polymer needs to pass only through the capillaries of the nozzles, US'334 describes the tubes to be tightly fitted and typically welded to the spinneret body, which represents an important difference, when compared to the present invention, as will be described in more detail herein below.
The molten material 22, as may be a thermoplastic polymer of the homopolymer type or a mixture of different polymers, is heated to a temperature well above its melting point, in case of propylene based polymers typically to at least about 170° C., often to about 210° C., upstream of the die block 26, usually in an extruder (not shown). Optionally, different polymers may be directed to respectively different groups of nozzles.
The polymer throughput through each nozzle 58 is stated in “gram per hole per minute” (“ghm”). The polymer throughput through each nozzle 58 can range from between about 0.01 ghm to about 4 ghm.
At its top, i.e. on the upper spinneret body side oriented towards the polymer supply, the die block 26 has a cavity 30 and an inlet 28 connected to the cavity 30. The molten material 22 is conveyed along the polymer passageway from inlet 28 towards the upper portion of the spinneret body 52, and further via the nozzles downwardly. The spinneret body 52 also has one or more gas passages 32 formed therethrough for conveying pressurized gas (air) to an air chamber 54, which is essentially formed between the spinneret body 52 and the air distribution plate 70. The plurality of nozzles 58 extend downwardly from the spinneret body allowing molten material to flow through the capillaries 60 for exiting the nozzles and the die block downward of the exterior plate at nozzle tip 96 in the form of filaments 86.
Further, a plurality of stationary pins 62 may surround the array of nozzles, affixed to the spinneret body and extending through openings of the air distribution plate into the openings of the exterior air plate.
Each of the stationary pins 62 is an elongated, solid member having a longitudinal central axis and an outside diameter. Each of the stationary pins 62 is secured to the spinneret body 52 and usually they have a similar outside diameter to the polymer nozzles 58. The outside diameter of each of the stationary pins 62 should remain constant throughout its length. The dimension of the outside diameter can vary. The outside diameter of the stationary pins 62 may be more than about 0.25 mm, or more than about 0.5 mm, or more than about 0.6 mm, or even more than about 0.75 mm.
An air distribution plate 70 is secured to the spinneret body 52 having a plurality of openings. Each one of first openings 72 accommodates one of the nozzles 58. If stationary pins 62 are employed, they are accommodated in second openings 74, and each of the third openings 76 is located adjacent to the first and second openings, 72 and 74 respectively. When operating the process, pressurized gas, typically air, is flowing along air passageways from the air chamber 54 through openings 72, which are a thin annulus around the nozzles, openings 74, also a small annulus around the stationary pins, if present, and third openings 76 as a main passageway for the air.
An exterior air plate 78 is secured to the air distribution plate 70, away from the spinneret body 52. The exterior member 78 has a plurality of first openings 80 surrounding the nozzle 58. Second enlarged openings 82 surround each of the stationary pins 62, if present.
In operation, the molten polymeric material 22 is extruded through each of the nozzles 58 to form multiple filaments 86 which are intended to be shrouded from the ambient air by the pressurized gas, typically though not necessarily air, emitted through the first enlarged openings 80, formed in the exterior member 78, at a predetermined velocity essentially parallel to the axis of the capillaries 60 and hence the flow direction of the filaments 86 at the nozzle tip 96
The pressurized gas (air) flow exiting the second enlarged openings 82 formed in the exterior member 78 around the stationary pins, if present, forms a further shrouding air flow, which is also oriented essentially parallel to the axis of the nozzles, and hence also essentially parallel to the filaments exiting the nozzles, aiming at isolating the filaments 86 from surrounding ambient air, as indicated in
In U.S. Pat. No. 6,364,647 (hereinafter referred to as US'647) a system is described (see
During operation, the nozzles are pressed into the respective openings by the pressure of the molten polymer.
However, this system still carries a disadvantage of sharp transition from the polymer supply chamber 22 into the plurality of nozzle openings.
As a consequence, deposits of polymeric material may form around the inlet of the capillaries, which may degrade over time and require more frequent cleaning.
A plurality of nozzles 158, in
Typically, the overall length 330 of a nozzle 158 may be more than about 20 mm and/or less than about 150 mm. The length 332 of the upper section 331 may be more than about 1 mm and/or less than about 50 mm, and the length 334 of the lower section 335 may be more than about 10 mm and/or less than about 140 mm.
Each nozzle 158 is fitted into an opening 360 of the lower plate 155 that has an upper portion 361 and a lower portion 365.
The upper portion 361 is adapted to receive the upper section 331 of the nozzle 158 and exhibits a diameter 362, which is not more than 2 mm wider than the outer diameter 161 of the upper section of nozzle 158. For a good fit, the diameter 362 is less than 50 μm or even less than 10 μm more than the outer diameter 161 of the upper section of the nozzle, and it may even be slightly smaller, such as less than 10 μm smaller, such as when the nozzle is fitted with force or at lower temperature.
The lower portion 365 is adapted to receive the lower section 335 of the nozzle 158 and exhibits a diameter 366, which is not more than 2 mm wider than the outer diameter 159 of the lower section of nozzle 158. For a good fit, the diameter 366 is less than 50 μm or even less than 10 μm more than the outer diameter 159 of the lower section of the nozzle, and it may even be slightly smaller, such as less than 10 μm smaller, such as when the nozzle is fitted with force or at lower temperature.
The transition from the upper portion 361 of the opening 360 to the lower portion 365 is preferably a sharp one, though a small radius or chamfering is acceptable. However, this transition should be matched with the transition from the upper section 331 of the nozzle to its lower section 335.
Most preferably, the length 332 of the upper section 331 of the nozzle 158 may be the same as the length 364 of the upper portion 361 of the opening 360, such that the differential 369 is zero, though the differential may be less than 10 μm, or less than about 2 μm. A negative differential (i.e. the nozzle protruding out of the hole) is not preferred.
The length 368 of the lower portion 365 of the opening 360 may be more than about 2 mm and/or less than about 100 mm.
The upper plate 151 of the spinneret body 153 comprises openings 370 that are aligned with the axis 339 of the capillary 160 of the nozzle 158, and hence with the openings in the lower plate 155. The opening 370 exhibits at its lower end a diameter 372 that matches as much as possible the diameter of the capillary 160 or—if present—of the chamfering 333.
Preferably, the difference between these diameters is less than about 20 μm more preferably less than about 10 μm. Also, the offset of the axis of the opening 370 from the axis of the capillary is most preferably essentially zero, but preferably less than 5 μm or less than 50 μm. Optionally and often preferably, the opening 370 has a chamfering 375 at its upper end, preferably at an angle of at least 1°, or 10°, or 30°, or 60° and/or less than 90° or any angle among these values. Thus, in the extreme the chamfering may extend over the full length of the upper plate, such that the cross-sectional view of the opening may correspond to a trapeze, as indicated by dotted lines 376 in
During operation, the openings 370 function as pre-holes for the capillaries and preferably exhibit a diameter of more than about 1.5 and/or less than about 4 times the diameter of the capillary and a length corresponding to the thickness of the upper plate of more than about 2 mm and/or less than about 20 mm.
Such a pre-hole provides a smoother flow from the cavity with the molten material into the capillary 160, which in turn will widen the opportunity for a wider process window for the process.
Also, it is also with the scope of the present invention that the die block may—in addition to the nozzles as described in the above—comprise stationary pins, as described in the context of US'334 in the above.
In yet a further variant of the present invention allowing to broaden the operating range of the equipment, the chamfering may be executed as grooves. To this end, the spinneret body is executed non-unitary in two parts, namely a first plate, also referred to as taper plate, comprising a polymer supply side, and a second plate positioned opposite of the polymer supply side. The second plate comprises grooves on the surface towards the first plate, which are oriented parallel to the row of nozzles.
Generally, each row groove may belong to at least one row of nozzles, preferably two rows of nozzles belong to one row groove, as depicted in the figure. Preferably, though not necessarily, all row grooves comprise nozzle holes 156, more preferably each row grove comprises two rows of nozzle holes 156. Thus, for the exemplary execution in
Preferably, the second plate 155 of the spinneret block further comprises closed circumferential groove 145, parallel to the row grooves as well as perpendicular thereto to circumscribe the nozzle array. Preferably, the x-y-directional corners of the circumferential groove 145 are rounded. Preferably, though not necessarily, the circumferential groove exhibits the same cross-sectional shape as the row grooves.
The holes in the second plate are adapted to receive nozzles in the variant of removable nozzles, and the wider opening of the row grooves provides the chamfering effect as described in the above allowing a smooth flow of the molten polymer.
Further, the grooves 140 and 145 are adapted to receive a sealant, allowing to fill selected grooves but also any gap that may be formed between the first and the second plate of the spinneret block. For the row grooves, this allows to block the polymer flow into the nozzle holes and further into the capillaries of the nozzles connected to this row groove. Even further, it allows to prevent the flow from one groove to the neighbouring one, as otherwise might occur through a gap between the first and the second plate. Thus, by application of the sealant, rows of nozzles can be “switched off”, as depicted in
For the sealant material the key requirement is that it withstands the operating temperatures, i.e. it does not flow into the capillaries or into the gap at the elevated temperatures, and thus should not be fluid up to temperatures of about 100° C., preferably 180° C., more preferably more than 230° C. or even more than 500° C. or more. Thus, the sealant may be selected from the group consisting of acrylic resins, adhesive sealants, butyl rubber, elastic sealants, epoxy thermosets, latex sealants, plastic sealants, polysulfide sealants, polyurethane sealants, rubber sealants, silicone sealants, e.g. polysiloxanes, fluorocarbon polymers, such as PTFE, or urethane sealants, with silicones and PTFE being preferred, and PTFE being most preferred. An exemplary sealant may be “PTFE wire 3.2 mm”, as commercially available from ATAG Spa, Italy.
Preferably, though not necessarily, a fluid or pasty sealant undergoes curing after being applied and the spinneret block is assembled, though pre-cured materials may be used as well, such as O-rings of appropriate size.
Preferably, and in particular for fluid or pasty sealants, the amount of sealant is selected so as to slightly overfill the groove, so as to enable squeezing of small amounts of the sealant into the gaps between the first and the second plate. This feature is particularly beneficial for relatively thin second plate, as may be less than about 20 mm, more preferably less than about 10 mm, or even less than about 8 mm. During assembly or operation, such relatively thin plates may slightly deform such that without any sealant molten polymer may ooze outwardly or into a neighbouring groove.
Further, the sealant is adapted to be removed from the grooves and from the holes or capillaries, if penetrated there into, when the spinneret block is disassembled. This removal can be made pure mechanically, or by blowing air or liquid though the holes or capillaries, or by any other means not damaging the structure.
The benefit of grooves filled with grooves is essentially to allow to widen the operating range of the die block.
It is known that it is preferred from an operational perspective, but also for good product quality to maintain the polymer flow through a capillary within a relatively narrow range. However, for different products or product types, different web basis weights are desired. However, when switching from, e.g. a lower basis weight, e.g. 35 g/m2, to a higher one, e.g. 60 g/m2, the flow rate through the capillaries may be increased, which requires higher operating pressures, hence cost, but also may deteriorate the quality of the resulting fibers, e.g. by increased stress applied to the polymer molecules. Henceforth, a conventional approach is to replace the complete spinneret block by another one with a different number of nozzle rows. This implies a high effort both with regard to work for this change over, but also with regard to maintaining a stock of replacement part. As to the latter, the nozzles represent a significant part of the costs. Henceforth it is beneficial to keep a minimum of replacement part—as enabled by this aspect of the present invention. To this end, a die block is designed for the upper range of throughput, as exemplarily and for explanatory purposes only with twelve rows of nozzles, with which a high basis weight product can satisfactorily be produced. When a lower basis weight product is to be made, the outermost row grooves, each connected to two nozzles, may be filled with sealant, such that only 8 nozzles are operational, and lower basis weights may be made without product quality deterioration. For even lower basis weight, two more row grooves may be filled, only 4 nozzle rows will now be operational.
In order to avoid deadspace, which may lead to deterioration of the polymer, it is preferred to adapt the holes in the first plate 151 of the spinneret body to the number of non-filled grooves, as depicted in
Optionally, the array of nozzles may comprise sub-arrays. Such a sub-array may include at least one row of nozzles, preferably, though not necessarily extending over the full width of a die block.
Referring to
In a further execution as depicted in
This process window is primarily dictated by
As a comparative example, the equipment and the process as described in US'334 exhibiting
In order to achieve comparable fiber dimensions and properties, the equipment of the present invention present invention exemplarily exhibited
One benefit of subjecting the polymer to a lower backpressure is that the reduction of the mechanical stress results in allowing to produce stronger nonwovens.
In other terms, the present invention provides an equipment that can exhibit a lower L/d ratio, which is—for a given MFI—indicative of the flow resistance, and thusly allows to operate at a wider process window for MFI and backpressure.
Further, the smoother flow from the cavity for the molten polymer 130 to the pre-hole 370, preferably even more smoothed flow of polymer in the chamfering, significantly reduces the turbulence of polymer around the inlet and hence also polymer residue deposition, allowing longer operating times without interruption for cleaning.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1819098.3 | Nov 2018 | GB | national |
| 1905253.9 | Apr 2019 | GB | national |
| 1911165.7 | Aug 2019 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/080291 | 11/5/2019 | WO | 00 |
