Patent Application
20220010458
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 methods to manufacture and operate such an equipment.
Spunmelting is a process where fibers are spun from molten polymer through a plurality of nozzles in a die block, also referred to as 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 include meltblowing, see e.g. U.S. Pat. No. 8,017,534 (K-C), and spunbonding, see e.g. U.S. Pat. No. 5,935,512 (K-C).
From such technologies, a “hybrid” technology, often referred to as “spun-blowing” has been developed and described in e.g. U.S. Pat. No. 9,303,334 (Biax). 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, when implementing such technology, several hurdles have been encountered. As will be discussed in more detail herein below, it is difficult to precisely align the individual nozzles, first, relative to other nozzles, which results in difficulties at the assembly stage, but also with regard to air blowing holes, such that an annular shrouding air flow may become eccentric and deteriorate filament and further web properties, such as by undesired bundling of adjacent filaments.
Henceforth, it is an object of the present invention to overcome problems of the spun-blowing technology.
In a first aspect, the present invention is a die block for forming meltblown filaments, this die block comprising
The die block may satisfy one or more of the conditions selected from the group consisting of
The present invention also relates to a die block comprising a unitary spinneret body and nozzles, further comprising pre-holes in the spinneret block, the pre-holes
In a preferred embodiment, the transition of the nozzles to the base of the spinneret block exhibits a radius of more than about 0.1 mm, preferably more than about 0.3 mm.
The array of nozzles in the die block may comprise 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
The array of nozzles may further comprise at least two sub-arrays, each of the sub-arrays are connected to a separate polymer supply system adapted to supply molten polymer to said sub-arrays differing in at least one of the features selected from the group consisting of
In another aspect, the present invention is a method for the manufacture of a die block comprising a spinneret block comprising a spinneret body and a plurality of nozzles, an air distribution plate, and an exterior air plate, comprising the steps of
In another aspect, the present invention is a method for the manufacturing of a spinneret block comprising a spinneret body and a plurality of nozzles for being used in a die block, comprising the steps of
In yet a further aspect, the present invention is a process for cleaning a melt blowing apparatus, comprising the steps of providing a spinneret or a die clock as described, burning of polymer residues, ultrasonically removing burnt residues, blowing pressurized water/steam through the nozzles.
In yet a further aspect, the present invention relates to a process for forming a nonwoven web comprising meltblown fibers, comprising the steps of
4A to D and 5 depict further features of the present invention.
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 of a die block for a spun-blowing process for forming a fibers or filaments that may further form a fibrous web or nonwoven comprising such a formed fibrous web, e.g. as a layer in a multi-layer composite web. 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. The spunmelt process may include meltblowing, spunbonding and the hybrid process as described hereinafter in more detail, also referred to as spun-blowing.
Meltblown 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 flat belt or drum collector. A typical meltblowing die has around 35 nozzles per inch and a single row of nozzles. The typical meltblowing die uses inclined air jets at each side of the row of nozzles for attenuating the filaments. Spunbond 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 from between about 10 microns to about 50 microns. The fibers are very strong compared to meltblown fibers because of the molecular chain alignment that is achieved during the attenuation of the crystallizing (solidifying) filaments. A typical spunbond 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 spun-blowing, a hybrid process between a conventional meltblown process and a conventional spunbond process, using a multi-row spinneret similar to the spinneret used in spunbonding 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 all of 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.
Typically the order of the elements 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, and for the purpose of the present explanation, 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.
Whilst the present description has been explained by referring to a positioning of the die block such that the nozzle exhibits a vertical orientation, the skilled person will readily realize that this is not essential, but the die block may be tilted around a CD oriented axis such that nozzles may be oriented relative to the vertical at more than 5°, or more than 15°, or more than 30°, or more than 45° or even more, though typically less than 90° (i.e. horizontal).
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.
The die block 26 further comprises a cavity 30 and an inlet 28 connected to the cavity 30, positioned towards the polymer supply, and typically at the upper part of the spinneret body (i.e. against gravity). 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 each of the stationary pins 62 may be at least about 0.25 mm, or at least about 0.5 mm, or at least about 0.6 mm, or even at least about 0.75 mm, and/or less than about 5 mm, or less than about 2 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 material 22 (polymer) 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 (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
Whilst the technology of US'334 can be employed well to provide very useful nonwoven materials, it has been observed that it carries certain limitations, mainly due to the inaccuracies induced by the insertion of the nozzle tubes into the spinneret body and the respective fixation. Even when adjusting the plurality of nozzle tubes, as may be several thousands, with utmost precision, at least the thermal dilatation upon inserting and welding, as well as the welding itself, if applied, tend to cause minute variations that can accumulate over the width of the spinneret block and then induce deterioration in handling of the equipment and/or quality of the resulting product:
If the capillaries are not exactly centered in the openings 82, the annular air passage way around the nozzles will be eccentric and hence the shrouding effect of the air is uneven which may disrupt the smooth airflow and result in bundling, i.e. adjacent filaments are blown towards each other and then may stick to each other, resulting in a larger fiber size distribution.
Further, even with sophisticated welding and machining tools, there is a high probability of burrs that disturb the smoothness of the flow into and through the capillaries.
As a consequence thereof, deposits of polymeric material may form around the inlet of the capillaries, which may degrade over time and require more frequent cleaning.
Considering the plurality of protruding capillaries and the tightly fitting air distribution plate, the difficulty of proper mounting increases with these variations, but also the number of nozzles in one mounting step. Thus there is presently a practical limitation of the y-directional extension of a single spinneret body and consequently of the complete die block of about 500 mm (approx. 20 in).
Thus, when employing such die blocks in large scale operations, where an overall y-directional extension may be well over 2 m, often 2.6 m, or even more 5 meter, multiple die blocks need to be employed, which not only increase handling complexity but that also can impact on the quality of the resulting product, at least because of y-directional edge effects of each block.
Further, considering the cleaning process, the relevance of which is aggravated by the increase in deposits around the capillary inlets, it only can be executed in one direction, namely along the normal process flow direction. Typically, the cleaning process comprises a pyrolytic treatment followed by treatment with pressurized steam or water. Also, ultrasonic cleaning, a generally desirable process for removing such residues, cannot be properly employed as it may very negatively interact with the connecting of the capillary tubes to the spinneret body, i.e. the welding or tight fitting.
Having thusly described the principle of the spun-blowing process as known from US'334,
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.
In a first execution of a die block comprising one or more sub-arrays as shown in
In a further execution as shown in
Whilst
It is a key feature of the present invention that the nozzles 158 are not formed separately as capillary tubes and inserted into holes of the spinneret body, as described in US'334. Rather, the spinneret body 153 and the nozzles 158 are “unitary” forming the spinneret block 152 as made from a single piece of material. This can conveniently achieved by modern CNC machining technology, such as employing laser cutting, flame and plasma cutting, hole-punching, drilling, milling, lathing, picking and placing, sawing, and other such technologies as known in the art for CNC treatments.
Referring to
Then, parallel or consecutively, though not necessarily in the listed order, the various features of the spinneret block are formed, especially though not limiting
These elements may be machined with extreme precision, in particular with regard to the size, positioning and orientation of the nozzles 158. Further, once programmed, it is a well-known manufacturing process, just mounting the spinneret block precursor into the CNC machining tool and starting the machining program.
Each of the nozzles 158 has an inside diameter 157 and an outside diameter 159. The inside diameter may be more than about 0.125 mm and/or less than about 1.25 mm. The outside diameter of each nozzle 158 is preferably more than about 0.5 mm, or more than 1 mm and/or less than about 2.5 mm. Typically, the length of a nozzle 158 is more than about 20 mm and/or less than about 150 mm.
Thus, the spin block comprises a polymer passageway that goes from the inlet cavity 130 through the capillaries of the nozzles 158 towards the nozzle tip 196, where the filaments are formed.
Further, because of this high precision, the nozzles 158 fit accurately though the respective nozzle openings 172 of the air distribution plate 170, and the nozzle openings in the 172 in the air distribution plate can be made only slightly larger than the outer diameter of the nozzle, down to an annular gap of less than 0.1 mm.
Thus, the air flow from the air chamber 132, which is delimited by the spinneret block 152 and the air distribution plate 170, may be through the plurality of air flow openings 176, as may be in a different row (i.e. not visible in the particular cross-sectional plane shown in
Further, the present approach allows much easier manufacturing when assembling the die block, by eliminating a practical restriction for the y-directional size of a die block, which now may well exceed the typical 500 mm of die block made according to the teaching of US'334, and may now be more than 1000 mm, even more than 2600 mm (as a typical size of a non-woven manufacturing unit into which such die block may be included) and even more than 5000 mm can be reached.
With the present invention allowing to employ single piece and unitary die blocks over much larger width, the fiber formation and fiber laydown will be cross-directionally more homogeneous as compared to having several less wide die blocks assembled together. As depicted in
In
Typically, the overall length 330 of a nozzle 158 ranges from between about 20 mm to about 150 mm. The length 334 of the lower section 335 may be from about 10 mm to about 140 mm. The length of the chamfering section from the first diameter to the second diameter may range from about 2 mm to about 4 mm or more.
Optionally, and as depicted in
For one or both of the chamfering it may be executed as described for
Optionally, and often preferably, the spinneret block 152 may comprise pre-holes 340, see
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.
Thus, in a second aspect, the present invention relates to operating the equipment as described in the above in a process with a wide process window, which is primarily dictated by
As a comparative example, the equipment and the process as described in US'334 may exhibit
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 340, 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.
In a further, and often highly preferred execution of the present invention, as depicted in
In a further aspect, the present invention allows simpler maintenance of the equipment. First, as the spinneret block (152) is now unitary and of the same material, it can readily withstand ultrasonic treatment without risking damaging the connection of the nozzles 158 and the spinneret body 153.
Second, as the nozzles and the spinneret body are much sturdier than e.g. a design as described in US'334, the equipment can also be cleaned with water and/or steam at a higher pressure and also not only along manufacturing direction, but also in the reverse direction (back-flushing).
Thus the cleaning of a spinneret block according to the present invention may comprise the steps of
| Number | Date | Country | Kind |
|---|---|---|---|
| 1818689.0 | Nov 2018 | GB | national |
| 1905253.9 | Apr 2019 | GB | national |
| 1911165.7 | Aug 2019 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/080293 | 11/5/2019 | WO | 00 |
