CN113260743A - Spinneret block with integrated spinneret body and nozzles for making spun fibers - Google Patents

Abstract

The invention relates to a special embodiment of a die block for a spunspray process for forming fibers or filaments which may also form a spunspray web or nonwoven comprising such formed fiber webs, for example as one layer of a multilayer composite web. The die block includes a spinneret block having an integral spinneret body and nozzles.

Description

Spinneret block with integrated spinneret body and nozzles for making spun fibers

Technical Field

The present invention relates to an apparatus adapted to form a spunlaid filament for forming a high quality nonwoven material, and methods of making and operating such an apparatus.

Background

Spunmelt is a process in which fibers are spun from a molten polymer through a plurality of nozzles in a die block (also referred to as a die head, which is connected to one or more extruders) for forming a web, such as a nonwoven web or component thereof. Spunmelt processes are well known in the art and include meltblowing (see, e.g., US8017534(K-C)) and spunbonding (see, e.g., US5935512 (K-C)).

According to such techniques, a "hybrid" technique (commonly known as "spincasting") has been developed and described, for example, in US9303334 (Biax). This technology provides many benefits with respect to fiber and web properties and with respect to manufacturing equipment and processes. However, when such techniques are implemented, several obstacles are encountered. As will be discussed in more detail herein below, first, it is difficult to precisely align each nozzle relative to the others (leading to difficulties in the assembly stage), but also with respect to the blow holes, so that the annular cage air flow may be off-center and degrade the filaments and further web properties, such as by unwanted binding of adjacent filaments.

It is therefore an object of the present invention to overcome the problems of the spinspray technique.

Disclosure of Invention

In a first aspect, the invention is a die block for forming melt blown filaments, the die block comprising:

at least one supply of molten polymer;

an air supply source;

a spinneret block, the spinneret block comprising:

a spinneret body including a polymer supply source side, an

A plurality of nozzles forming a nozzle array;

an air distribution plate including an opening;

an outer air plate comprising an opening;

a cover strip;

fixing the appliance;

wherein the spinneret block, the air distribution plate, the external air plate and the cover strip are installed in this order and fixed by a fixing means so that

The nozzles protrude through corresponding openings of the air distribution plate and also through corresponding openings of the outer air plate, an

Allowing a polymer passage of molten polymer to be formed through the nozzle from a polymer supply side of the spinneret body; and

allowing an air passage for air to be formed from an air supply source through the openings of the air distribution plate and the outer air plate;

whereby the openings of the outer plate and the nozzles are adapted to allow molten polymer to exit the nozzles and the air flowing through the openings of the outer air plate is substantially parallel, wherein the spinneret body and the nozzles are integral.

The mold block may satisfy one or more of the conditions selected from the group consisting of:

an inner diameter of the nozzle of less than about 1.25mm, preferably less than about 0.8 mm;

an outer diameter of the nozzle, the outer diameter being less than about 2 mm;

a length of the nozzle less than about 50 mm;

a length of the nozzle greater than about 10 mm;

an L/d ratio of the nozzle, the L/d ratio being less than about 50;

the die block has a CD width greater than 250mm, preferably greater than 1500mm, even more preferably greater than about 2000mm, or even more preferably greater than 5000 mm. The invention also relates to a die block, which comprises an integrated spinneret body and a nozzle, and also comprises a pre-hole of the spinneret block, wherein the pre-hole comprises the following components:

extending from an upper surface toward the capillary, the upper surface positioned toward a supply of molten polymer;

in the form of a counterbore for the capillary tube of the nozzle;

preferably with a chamfer angle between 30 ° and 60 °;

preferably having a diameter of between 1.5 and 4 times the inner diameter of the capillary;

preferably having a length greater than about 2mm, preferably greater than about 4 mm;

preferably having a length of less than about 20mm, preferably less than about 14mm, more preferably less than about 8mm, and most preferably about 6 mm.

In a preferred embodiment, the transition of the nozzle to the base of the spinneret block has a radius of greater than about 0.1mm, preferably greater than about 0.3 mm.

The array of nozzles of the mold block comprises at least two sub-arrays comprising nozzles differing from nozzles of different sub-arrays in at least one dimension selected from the group consisting of:

the inner diameter of the nozzle;

the outer diameter of the nozzle;

the length of the nozzle.

The nozzle array may further comprise at least two sub-arrays, each of the sub-arrays being connected to a separate polymer supply system adapted to supply molten polymer to said sub-arrays, the molten polymer differing in at least one characteristic selected from the group consisting of:

a polymer type;

a polymer flow rate;

the polymer pressure;

the temperature of the polymer.

In another aspect, the invention is a method for making a die block comprising a spinneret body and a plurality of nozzles, an air distribution plate and an external air plate, the method comprising the steps of:

providing a one-piece mold block precursor, preferably of steel;

machining from a single piece mold block precursor:

a spinneret block, the spinneret block comprising:

a nozzle;

an air inlet and a distribution chamber;

an air distribution plate;

an external air panel;

wherein the machining is a high precision CNC process.

In another aspect, the invention is a method for making a spinneret block comprising a spinneret body and a plurality of nozzles for a die block, the method comprising the steps of:

providing a single piece spinneret block precursor, preferably steel;

processing from a single piece of spinneret block material:

a nozzle;

an air flow passage;

wherein the machining is a high precision CNC process.

In yet another aspect, the invention is a process for cleaning meltblowing equipment comprising the steps of: providing a spinneret or die block as described above, burning the polymer residue; ultrasonically removing combustion residues; pressurized water/steam is blown through the nozzle.

In yet another aspect, the present invention relates to a process for forming a nonwoven web (nonwoven web) comprising meltblown fibers, the process comprising the steps of:

providing an apparatus as described above;

providing a thermoplastic polymer for forming meltblown fibers, the thermoplastic polymer having an MFI of 30 to 2000;

the filaments are formed by applying a pressure of less than 70 bar, preferably less than 50 bar, more preferably less than 45 bar at the polymer supply.

Drawings

Figure 1 shows a spinning apparatus according to the prior art.

Fig. 2A to 2H illustrate certain features of the present invention.

Fig. 3, 4A-4D and 5 illustrate other features of the present invention.

The same numbers in the drawings indicate the same or equivalent features. The figures are schematic and not drawn to scale.

Detailed Description

The invention relates to a special embodiment of a die block for a spunblowing process for forming fibers or filaments which may also form a fibrous web or nonwoven comprising such formed fibrous web, for example as one layer of a multilayer composite web. Spunmelt is a process in which fibers are spun from molten polymer through a plurality of nozzles in a die connected to one or more extruders. The spunmelt process may include meltblowing, spunbonding, and hybrid processes (also known as spunblowing) as described in more detail below.

Meltblown is a process for producing very fine fibers having a diameter of less than about 10 microns in which a plurality of molten polymer streams are attenuated with a high velocity stream of hot gases once the filaments emerge from a nozzle. The attenuated fibers are then collected on a flat belt or drum collector. A typical meltblowing die has about 35 nozzles per inch and a single row of nozzles. Typical meltblowing dies utilize angled air jet ports at each side of the nozzle row for attenuating the filaments.

Spunbond is a process that produces strong fibrous nonwoven webs directly from thermoplastic polymers by attenuating the filaments with high velocity cold air while quenching the fibers near the spinneret surface. The individual fibers are then randomly laid on a collection belt and conveyed to a bonder to impart added strength and integrity to the web. The fiber size is typically below 250pm and the average fiber size is in the range between about 10 microns to about 50 microns. Compared to meltblown fibers, fibers are extremely strong due to molecular chain alignment; this molecular chain alignment is achieved during the refinement of the crystallized (solidified) filaments. A typical spunbond tool has multiple rows of polymer holes and for conventional polymers of the polypropylene type, the polymer Melt Flow Index (MFI) is typically less than about 500g/10 min under a load of 2.16 kg.

The present invention relates to spunblowing (a hybrid process between conventional meltblowing and conventional spunbonding processes) that utilizes multiple rows of spinnerets similar to those used for spunbonding, except that the nozzles are arranged to allow parallel gas jets to spin around to refine and solidify it. Each of the extruded filaments is shrouded by a pressurized gas and may be cooler or hotter than the polymer melt in temperature. Optionally, the perimeter around all filaments may be surrounded by a curtain of pressurized gas.

To explain the general principles of a spunspray apparatus and process for forming filaments and further webs, such as nonwoven webs or components of such webs, reference is explicitly made to US9303334 which describes such techniques in more detail. Thus, figure 1 shows a mould block for such a "hybrid" spincasting process.

In general, die block 26 includes as elements spinneret body 52, air distribution plate 70, outer plate 78 and cover strip 88. In addition, the nozzles 58 extend from the spinneret body 52 through openings of the distribution plate 70 and the outer plate 78, respectively, such that the molten material can pass through the capillaries 60 of the nozzles 58 to form filaments 86 at the tips of the nozzles 96.

Generally, the order of the elements is such that the spinneret body 52, air distribution plate 70, outer plate 78 and cover strip 88 are arranged along the force of gravity; and for the purpose of this explanation, the spinneret body 52 is positioned above and secured to the air distribution plate 70 by a securing means, not shown, the air distribution plate 70 is positioned above and secured to the outer plate 78, the outer plate 78 is positioned above and secured to the cover strip 88.

Although the present description has been explained by reference to the positioning of the mold blocks (such that the nozzles have a vertical orientation), the skilled person will readily understand that this vertical orientation is not necessary; and the mold blocks may be tilted about the CD orientation axis so that the nozzles may be oriented with respect to vertical: greater than 5 °, or greater than 15 °, or greater than 30 °, or greater than 45 ° or greater, but typically less than 90 ° (i.e., horizontal).

Fig. 1 shows a cross-sectional view of a mold block 26. When located in a manufacturing facility for forming nonwovens, this view corresponds to an x-z direction view, where the x direction 12 represents the direction of manufacture (i.e., the direction of movement of the resulting web) and the z direction 15 corresponds to the height (along gravity). In the depicted embodiment, three nozzles 58 represent one "column" of rows (here three rows) of mold blocks 26. The mold block includes a plurality of columns positioned adjacently in the y-direction 18 (i.e., perpendicular to the plane of the drawing and represented by circles) such that the columns and rows of nozzles form a nozzle array of the mold block. The spinneret body 52 can include as few as ten nozzles 58 to thousands of nozzles 58. For commercial scale production lines, the number of nozzles 58 in the spinneret body 52 can range between about 500 to about 10000. The number of rows and columns may vary. Typically, the number of rows will be greater than 1, typically greater than 5, and will be less than about 30, or even less than 15. Typically, the number of columns will be greater than 50, may be greater than about 200, and may be less than 3500.

As described in US'334, the nozzle 58 is formed by a capillary tube that is inserted through an opening in the spinneret body 52 to form a passageway for the molten polymer. Each of the nozzles 58 has a capillary inner diameter and an outer diameter. The inner diameter may range between about 0.125mm to about 1.25 mm. The outer diameter of each nozzle 58 should be at least about 0.5 mm. The outer diameter of each nozzle 58 may range between about 0.5mm to about 2.5 mm.

Typically, the length of the nozzle 58 is in the range of between about 0.5 inches to about 5 inches.

Since the molten polymer needs to pass only through the capillaries of the nozzle, US'334 describes a tube that will fit closely to, and typically be welded to, the spinneret body; the spinneret body represents an important difference when compared to the present invention, as will be described in more detail herein below.

The molten material 22, which 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 the case of propylene-based polymers, upstream of the die block 26, typically in an extruder (not shown), typically to at least about 170 ℃, typically to about 210 ℃. Optionally, different polymers may be directed to respective different sets of nozzles.

The polymer throughput through each nozzle 58 is indicated in "grams per hole per minute" ("ghm"). The throughput of polymer through each nozzle 58 may range between about 0.01ghm to about 4 ghm.

Mold block 26 further includes cavity 30 and inlet 28; the inlet 28 is connected to a cavity 30, positioned toward the polymer supply, and is generally at an upper portion of the spinneret body (i.e., against gravity). The molten material 22 is conveyed along the polymer path from the inlet 28 toward the upper portion of the spinneret body 52 and also downwardly through the nozzles. The spinneret body 52 also has one or more gas channels 32 formed therethrough for delivering pressurized gas (air) to an air chamber 54, the air chamber 54 being formed substantially between the spinneret body 52 and the air distribution plate 70. A plurality of nozzles 58 extend downwardly from the spinneret body, allowing molten material to flow through capillaries 60 for exit downwardly from the outer plate from the nozzles and die block at nozzle tips 96 in the form of filaments 86.

Additionally, a plurality of stationary pins 62 may surround the nozzle array, be attached to the spinneret body, and extend through openings of the air distribution plate into openings of the outer air plate.

Each of the stationary pins 62 is an elongated solid member having a longitudinal center axis and an outer diameter. Each of the stationary pins 62 are fixed to the spinneret body 52 and they generally have an outer diameter similar to the polymer nozzles 58. The outer diameter of each of the stationary pins 62 should remain constant throughout its length. The size of the outer diameter may vary. The outer diameter of each of the static pins 62 may be at least about 0.25mm, or at least about 0.5mm, or at least about 0.6mm, or even at least about 0.75mm, and/or less than about 5mm or less than about 2 mm.

An air distribution plate 70 is secured to the spinneret body 52, the spinneret body 52 having a plurality of openings. Each of the first openings 72 receives one of the nozzles 58. If stationary pins 62 are employed, they are received in the second openings 74, and each of the third openings 76 is positioned adjacent to the first and second openings 72, 74, respectively. When operating the process, pressurized gas (typically air) flows along the air passageway from the air chamber 54 through the opening 72 (which is a thin ring around the nozzle), the opening 74 (also a thin ring around the stationary pin, if present), and the third opening 76 (which is the primary passageway for air).

An outer air plate 78 is secured to the air distribution plate 70, remote from the spinneret body 52. The outer member 78 has a plurality of first openings 80 surrounding the nozzle 58. A second enlarged opening 82 surrounds each of the stationary pins 62, if present.

In operation, molten material 22 (polymer) is extruded through each of the nozzles 58 to form a plurality of filaments 86, the filaments 86 being intended to be shrouded from ambient air by pressurized gas (air) that is discharged at a predetermined velocity through a first enlarged opening 80 (substantially parallel to the axis of the capillary 60 and thus to the direction of flow of the filaments 86 at the nozzle tip 96), the first enlarged opening 80 being formed in the outer member 78.

The flow of pressurized gas (air) exiting the second enlarged opening 82 (formed in the outer member 78 about the stationary pin, if present) forms another cage air flow that is also oriented substantially parallel to the axis of the nozzle and thus also substantially parallel to the filaments exiting the nozzle, thereby tending to separate the filaments 86 from the ambient air, as indicated by arrows 94 in fig. 1.

While the technique of US'334 can be fully used to provide extremely useful nonwoven materials, it has been observed that it has certain limitations, primarily due to inaccuracies caused by the insertion of the nozzle tube into the spinneret body and corresponding fixture. Even when a plurality of nozzle tubes (which may be thousands) are adjusted with the highest precision, thermal expansion at least upon insertion and welding and the welding itself (if applied) tend to cause minor variations which can accumulate over the width of the spinneret block and which can then induce a deterioration in the processing capacity of the apparatus and/or the quality of the resulting product.

If the capillary tube is not accurately centered in the opening 82, the annular air passage around the nozzle will be eccentric and thus the air's cage effect is uneven, which can disrupt the smooth air flow and cause binding, i.e., adjacent filaments blow toward each other and can then stick to each other, resulting in a larger fiber size distribution.

In addition, even with precision welding and machining tools, there is a high probability of burrs being present that interfere with the smoothness of the flow into and through the capillary tube.

As a result, deposits of polymeric material may form around the inlet of the capillary, which may degrade over time and require more frequent cleaning.

Given the multiple protruding capillaries and the close fitting air distribution plate, the difficulty of proper installation increases with these changes and the number of nozzles in one installation step. Thus, there is currently a practical limit to the y-direction extension of a single spinneret body and hence a complete die block: about 500mm (about 20 inches).

Thus, when such mold blocks are employed in large scale operations, where the overall y-direction extension may well exceed 2m, typically 2.6m or even more than 5m, multiple mold blocks need to be employed which not only add to the processing complexity, but can also affect the quality of the resulting product, at least because of the y-direction edge effect of each block.

In addition, given that the cleaning process (the correlation of which is exacerbated by the increase in deposits around the capillary inlet), it can only be performed in one direction, i.e., along the normal process flow direction. Typically, the cleaning process involves a pyrolysis treatment, followed by treatment with pressurized steam or water. In addition, ultrasonic cleaning, a commonly desired process for removing such residues, is not properly employed because it can extremely adversely affect the connection of the capillary to the spinneret body (i.e., welding or close fitting).

Thus, having described the principles of the spinspray process as known from US'334, figures 2A to 2F illustrate the principles of the present invention by showing the die block 126, the die block 126 comprising a spinneret block 152, an air distribution plate 170, an external air plate 178 and a cover strip 188 arranged in the same manner as described above and below in figure 1. Also shown is a row of five nozzles 158, the five nozzles 158 also being arranged in columns and rows forming a nozzle array as described above. As described herein, the nozzles are oriented vertically along the force of gravity. However, the orientation of the system may be such that the orientation of the nozzle is angled with respect to gravity, and the skilled person will readily adjust the relative positioning terms, such as "above" or "below", accordingly.

Optionally, the nozzle array may comprise sub-arrays. Such sub-arrays may comprise at least one row of nozzles, preferably but not necessarily extending over the full width of the mould block.

In a first embodiment of a mold block comprising one or more sub-arrays, as shown in fig. 2G, the nozzles of at least one of the sub-arrays are substantially different from the nozzles of a different sub-array in at least one dimension selected from the group consisting of: the inner diameter of the nozzle, the outer diameter of the nozzle, and the length of the nozzle. Within the present context, the term "substantially different" refers to a difference in their respective dimensions of at least 5%, typically more than 10%.

In another embodiment as shown in fig. 2H (without excluding other embodiments), the nozzles of one sub-array may be connected to a first separate polymer supply system adapted to supply molten polymer to said sub-array that differs from molten polymer supplied to a different sub-array in at least one characteristic selected from the group consisting of: polymer type, polymer flow rate, polymer pressure, and polymer temperature. Optionally, the nozzle may be implemented with co-axially positioned sub-capillaries to form bicomponent or multicomponent fibers, wherein such sub-capillaries are supplied with different respective immiscible polymer types.

Although fig. 2A shows the elements in an assembled state (with the fixture omitted), fig. 2B shows the spinneret block 152, the air distribution plate 170, and the external air plate 178 in an exploded view, and fig. 2C-2F show these individual elements.

A key feature of the present invention is that the nozzles 158 are not formed separately as capillaries and are inserted into holes in the spinneret body, as described in US' 334. Rather, spinneret body 153 and nozzles 158 are "integral" so as to form, for example, a spinneret block 152 made from a single piece of material. The integration may be conveniently achieved by modern CNC machining techniques such as laser cutting, flame and plasma cutting, punching, drilling, milling, turning, pick and place, sawing, and other such techniques as are known in the CNC processing art.

Referring to fig. 2C, a piece of material (preferably of uniform composition, preferably metal, and more preferably steel) is selected as a spinneret block precursor 210, the spinneret block precursor 210 being shown in phantom lines circumscribing the spinneret body and nozzles integrally formed therewith. The spinneret block precursor 210 may be prepared in sizes that generally correspond to the overall size of the post-spinneret block, or its external dimensions may be formed in situ.

Then, in parallel or in succession (but not necessarily in the order listed), the various features of the spinneret block are formed, in particular but not limited to:

an inlet cavity 130 for molten polymer 122;

an air inlet and distribution chamber 132 (air supply means, not shown);

an array of nozzles 158, each nozzle 158 having an inner diameter 157 and an outer diameter 159, the inner diameter 157 corresponding to the diameter of a capillary of the molten fluid stream;

optionally other fixing holes (199).

These elements can be machined with extreme precision, particularly with respect to the size, positioning and orientation of the nozzle 158. In addition, once programmed, it is a well known manufacturing process, only the spinneret block precursor is installed into the CNC machining tool and the machining program is started.

Each of the nozzles 158 has an inner diameter 157 and an outer diameter 159. The inner diameter may be greater than about 0.125mm and/or less than about 1.25 mm. The outer diameter of each nozzle 158 is preferably greater than about 0.5mm, or greater than 1mm, and/or less than about 2.5 mm. Typically, the length of the nozzle 158 is greater than about 20mm and/or less than about 150 mm.

Accordingly, the textile block includes a polymer pathway that passes through the capillary of the nozzle 158 from the inlet cavity 130 toward the nozzle tip 196, where the filaments are formed.

In addition, due to this high precision, the nozzles 158 fit accurately through the respective nozzle openings 172 of the air distribution plate 170, and the nozzle openings 172 in the air distribution plate can be made only slightly larger than the outer diameter of the nozzles, down to an annular gap of less than 0.1 mm.

Thus, the air flow of the air chamber 132 (which is defined by the spinneret block 152 and the air distribution plate 170) may pass through the plurality of air flow openings 176, such as may be in different rows (i.e., not visible in the particular cross-sectional plane shown in fig. 2), see dashed lines in fig. 2E, optionally staggered rows (see dashed lines in fig. 2A). In addition, the nozzle will also fit very precisely into the nozzle opening 180 of the outer air plate and provide a very accurate and concentrically formed annulus around the nozzle 158. In operation, this results in a very uniform annular air shroud around filaments 186 as they exit nozzle tips 196 substantially parallel to the filaments, thereby significantly reducing, if not preventing, filament binding.

Fig. 2A also shows two options (alternatively or collectively) for forming an outer perimeter curtain as described in US' 334. In a first option, the air passage openings 183 in the outer air plate are located around the nozzle array. In a second option, stationary and solid pins 162, also machined from the same spinneret block precursor, extend from the spinneret body through openings 174 of the air distribution plate into openings 182 of the external air plate 178, thereby also allowing for annular air flow around these pins (similar to the manner described in US' 334).

In addition, by eliminating the practical limitation of the y-direction dimension of the die block, the present approach allows for much easier manufacturing (when assembling the die block), which can now completely exceed the typical 500mm die block made according to the teachings of US'334, and can now be greater than 1000mm, even greater than 2600mm (as a typical dimension of a nonwoven manufacturing unit, such a die block can be included in the nonwoven manufacturing unit), and can even reach above 5000 mm.

Since the present invention allows for the use of one-piece and one-piece mold blocks over much larger widths, fiber formation and fiber settling will be more uniform in the cross direction than if several mold blocks of smaller widths were assembled together.

As shown in fig. 3, this mode provides another advantage in that the transition from the capillary to the spinneret body can be implemented with a radius 310, the radius 310 preferably being greater than 0.1mm, more preferably greater than 0.3 mm. This transition will increase the stability compared to the embodiment according to US'334 and thus also the positioning of the nozzle.

Fig. 4A and 4C illustrate an exemplary embodiment to reduce, if not avoid, these adverse effects of sharp edges around the opening of the capillary tube of the nozzle.

In fig. 4A, as a first embodiment of a nozzle according to the present invention, the nozzle 158 may be a nozzle as generally described above with reference to US' 647 having an inner capillary diameter 157 of a capillary 160 for a molten fluid stream. The capillary inner diameter may range between about 0.125mm to about 1.25 mm. At its upper end, the capillary 160 is chamfered at a chamfer section 333, preferably at a chamfer angle between 30 ° and 60 °, allowing a transition from the capillary to a chamfered opening diameter 337. The present chamfer opening diameter may range from greater than about 2mm or 4mm to less than about 20mm or 14mm, or less than 8 mm. The outer diameter 159 of the lower section 335 of the nozzle 158 should be at least about 0.5mm, and may range between about 0.5mm to about 2.5 mm.

Typically, the overall length 330 of the nozzle 158 is in a range between about 20mm to about 150 mm. The length 334 of the lower section 335 may be about 10mm to about 140 mm. The length of the chamfered section from the first diameter to the second diameter may range from about 2mm to about 4mm or more.

Optionally, and as shown in fig. 4B and 4C, the transition from the capillary diameter to the chamfer opening diameter may be implemented as a radius or as another gradual transition curve (such as an elliptical or parabolic shape). In the present description, the term "chamfer" is intended to include such embodiments by comparison, and the chamfer angle is intended to correspond to the end point of a radius or smooth curve. Another embodiment according to the present invention is shown in fig. 4D, which also shows a nozzle 158 having a capillary 160, the capillary 160 having an inner capillary diameter 157 at the tip of the nozzle. In addition, the nozzle has a chamfered opening diameter 337 towards the polymer supply, the chamfered opening diameter 337 being chamfered towards the pre-hole diameter 341 to indicate the pre-hole of the capillary over the pre-hole length 344 to be further chamfered towards the capillary inner diameter 157. In this embodiment, the length of the nozzle is defined by the length of the capillary tube, the length of the pre-hole (if present) plus the length of the chamfered section.

For one or both of the chamfers, the chamfers may be implemented as described for fig. 4A, or may be implemented as radii, as described for fig. 4B and 4C.

Optionally and generally preferably, the spinneret block 152 may include pre-holes 340, see fig. 4D showing only one nozzle. These pre-holes are located upward and precisely aligned with the axis of the capillary 160 of the nozzle 158. The pre-holes may have a diameter of 1.5 to 4 times the diameter of the capillary tube and a length of about 2mm to about 20 mm. Preferably, the transition from the pre-hole 310 to the capillary 160 is implemented in a gradual manner, for example with a chamfer angle between 30 ° and 60 ° at the inlet and at the transition towards the capillary.

The pre-orifice provides a smoother flow from the cavity with molten material to the capillary 160, which in turn will widen the wider process window of the process.

Thus, in a second aspect, the present invention relates to operating an apparatus as described above in a process having a wide process window, the process being mainly indicated by:

the pressure of the molten polymer in the cavity;

the temperature of the molten polymer;

the diameter of the capillary;

the length of the capillary;

the material properties of the molten polymer, as expressed by the Melt Flow Index (MFI), as can be determined by ASTM D1238 and ISO1133, and for polypropylene as polymer, can suitably be treated in existing equipment and processes, suitably expressed in units of grams per 10 minutes at 210 ℃ and under a load of 2.16 kg.

As a comparative example, the apparatus and process as described in US'334 may have:

an inner diameter of the capillary of 0.46 mm;

a capillary length of 24 mm;

and thus an L/d ratio of about 52;

and preferably at a temperature of about 210 c, wherein the back pressure of the molten polymer is from 50 bar to 70 bar, the molten polymer having an MFI of less than about 500[ g/l0min @2.16kg load ]. To achieve comparable fiber size and shape, the apparatus of the present invention illustratively has:

a capillary diameter of 0.46 mm;

a capillary length of about 18 mm;

a pre-hole diameter of about 1.2 mm;

a pre-hole length of about 6mm (including a 60 ° chamfer at the inlet and at the transition to the capillary);

and thus a capillary L/d ratio of about 39, which would also allow the use of a polypropylene polymer having an MFI of about 500[ g/L0min @2.16kg load ] at a back pressure significantly below 50 bar.

One benefit of subjecting the polymer to lower back pressure is that the reduction in mechanical stress allows for the production of tougher nonwovens.

In other words, the present invention provides an apparatus that can have a lower L/d ratio, which is indicative of flow resistance for a given MFI, and thus allows operation with a wider process window of MFI and backpressure.

Furthermore, the smoother flow from the cavity of the molten polymer 130 to the pre-holes 340 (preferably, an even smoother flow of the polymer in the chamfer) significantly reduces the turbulence of the polymer around the inlet and thus also reduces polymer residue deposition, allowing longer operating times without interrupting cleaning.

In another generally highly preferred embodiment of the present invention, as shown in FIG. 5, all three components (the spinneret block 126, the air distribution plate 170, and the external air plate 178) are fabricated from a single piece of material (indicated by dashed line 510); whereby in a first step the slabs are separated from which the respective elements are formed by CNC machining, as described above.

In another aspect, the invention allows for simpler maintenance of the device. First, because the spinneret block (152) is now integral and of the same material, it can readily withstand sonication without risk of damaging the connection of the nozzles 158 and the spinneret body 153.

Secondly, since the nozzle and spinneret body are much more robust than the design described in, for example, US'334, the apparatus can also be cleaned with water and/or steam at higher pressures and not only in the manufacturing direction but also in the opposite direction (back-flushing).

Thus, the cleaning of the spinneret block according to the present invention may comprise the steps of:

separately burning the pyrolysis residues;

loosening the pyrolysis residue by ultrasonic means;

the ultrasonically loosened pyrolysis residue is washed along the flow direction of the molten polymer and/or optionally washed in the opposite flow direction with pressurized water or steam.

Claims (10)

1. A die block for forming meltblown filaments, comprising:

at least one supply of molten polymer;

an air supply source;

a spinneret block, the spinneret block comprising:

a spinneret body including a polymer supply side, an

A plurality of nozzles forming a nozzle array;

an air distribution plate comprising an opening;

an outer air plate comprising an opening;

a cover strip; and

fixing the appliance;

wherein the spinneret block, the air distribution plate, the external air plate and the cover tape are installed in this order and fixed by the fixing means so that

The nozzles protrude through corresponding openings in the air distribution plate and also through corresponding openings in the outer air plate, an

Causing a polymer passage of molten polymer to be formed through the nozzle from the polymer supply side of the spinneret body; and

causing an air passage for air to be formed from the air supply through the air distribution plate and the openings in the outer air plate;

whereby the openings in the outer plate and the nozzles are adapted to allow molten polymer to exit the nozzles and the air flowing through the openings of the outer air plate is substantially parallel;

the mould block is characterized in that:

the spinneret body and the nozzle are integrated.

2. The mold block of claim 1, the mold block satisfying one or more of the conditions selected from the group consisting of:

the inner diameter of the nozzle is less than about 1.25mm, preferably less than about 0.8 mm;

the outer diameter of the nozzle is less than about 2 mm;

the nozzle has a length of less than about 50 mm;

the nozzle has a length greater than about 10 mm;

the L/d ratio of the nozzle is less than about 50;

the CD width of the die block is greater than 250mm, preferably greater than 1500mm, even more preferably greater than about 2000mm or even greater than 5000 mm.

3. The mold block of claim 1 or 2, further comprising a pre-hole in the block, the pre-hole:

extending from an upper surface, in the form of a counterbore, toward the capillary, the upper surface positioned toward a supply of the molten polymer;

preferably with a chamfer angle between 30 ° and 60 °;

preferably a diameter of between 1.5 and 4 times the inner diameter of the capillary;

preferably having a length greater than about 2mm, preferably greater than about 4 mm;

preferably having a length of less than about 20mm, preferably less than about 14mm, more preferably less than about 8mm, and most preferably about 6 mm.

4. A mould block according to any one of claims 1 to 3 wherein the transition of the nozzle to the base of the block has a radius greater than about 0.1mm, preferably greater than about 0.3 mm.

5. The mold block of any of the preceding claims, wherein the array of nozzles comprises at least two sub-arrays comprising nozzles that differ from different sub-array nozzles in at least one dimension selected from the group consisting of:

an inner diameter of the nozzle;

the outer diameter of the nozzle;

the length of the nozzle.

6. A mould block according to any preceding claim wherein

The nozzle array further 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-arrays, the molten polymer differing in at least one characteristic selected from the group consisting of:

a polymer type;

a polymer flow rate;

the polymer pressure;

the temperature of the polymer.

7. A method for manufacturing a spinneret block comprising a spinneret body and a plurality of nozzles for a die block, the method comprising the steps of:

providing a single piece spinneret block precursor, preferably steel;

processing from the single piece of spinneret block material:

a nozzle;

an air flow passage;

wherein the machining is a high precision CNC process.

8. A method for manufacturing a die block comprising a spinneret block, an air distribution plate, and an external air plate, the spinneret block comprising a spinneret body and a plurality of nozzles, the method comprising the steps of:

providing a one-piece mold block precursor, preferably of steel;

processing from the single piece mold block precursor:

a spinneret block, the spinneret block comprising:

a nozzle;

an air inlet and a distribution chamber; an air distribution plate; an external air panel;

wherein the machining is a high precision CNC process.

9. A process for cleaning meltblowing equipment comprising the steps of:

providing an apparatus according to any one of claims 1 or 2;

burning the polymer residue;

ultrasonically removing combustion residues;

blowing pressurized water or steam through the nozzle.

10. A process for forming a nonwoven web comprising meltblown fibers, the process comprising the steps of:

providing an apparatus according to any one of claims 1 to 6;

providing a thermoplastic polymer for forming MB fibers, the thermoplastic polymer having an MFI of 30 to 2000;

the filaments are formed by applying a pressure of less than 70 bar, preferably less than 50 bar, more preferably less than 45 bar at the polymer supply.

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