Slot die and method of operating same

Abstract

A slot die and related methods of use are provided. The slot die includes an applicator slot extending across the width of the slot die and having opposing first and second slot die surfaces, the applicator slot being in fluid communication with a fluid flow path through the slot die. A flexible die lip provides the first slot die surface and is capable of independently adjusting the cross-sectional height of the fluid flow path. A plurality of actuators are spaced along the width of the first slot die surface, each actuator operatively coupled to the flexible die lip and adjusting the cross-sectional height at a respective location to provide localized adjustment of fluid flow through the applicator slot, the applicator slot having a neutral slot height profile that is negative along at least a portion of the width of the slot die.

Description

[Technical Field]

[0001] A slot die and associated method for producing a continuous web using an extrusion process is provided. [Background technology]

[0002] In the field of extrusion, slot dies are used for the large-scale production of a wide variety of products. These slot dies include opposing die lips that form an applicator slot that extends along the width of a moving web or roller that receives an extrudate such as a film. As used herein, the term "width" as used with respect to slot dies and slot die components refers to the lateral, or cross-web, dimension of the slot die or slot die component.

[0003] Slot dies are particularly useful for producing extruded films, coatings, and other extrusion-formed products. For example, slot dies can be used in slot die coating to apply fluid materials to chill rollers, release liners, other extruded webs, or other continuous substrates. The coating material can be at ambient or controlled temperature. At ambient temperature, the extruded composition can be a reactive composition that cures at some point after being coated onto the substrate. When the temperature of the coating material is elevated to ensure that the coating material is melted or liquefied for processing, this is often referred to as hot melt coating or extrusion coating.

[0004] Alternative configurations are possible. For example, depending on various process considerations, the extruded film may be fed directly into the nip or biased to contact one or the other roller just prior to the nip. The slot die may be oriented vertically, horizontally, or at other angles. The nip orientation is also adjustable. The rollers forming the nip may be of different diameters and compositions. They may be metal, release-coated, rubber-covered, embossed or smooth, chilled, or use a heated temperature controller.

[0005] The extrusion coating composition may contain a diluent, such as a solvent. Useful solvents for this purpose include water, organic solvents, and any suitable fluid that dissolves or disperses the components of the coating. The solvent is usually removed by subsequent processing, such as drying. The coating may include a single layer or multiple layers, and some slot dies may be used to apply multiple layers simultaneously. The coating may be a continuous coating across the entire width of the die, or alternatively, may include multiple strips, each extending across only a portion of the width of the die and separated from adjacent strips. The extruded film may then be processed by longitudinal orientation or tentering operations.

[0006] The thickness of the extruded film or coating is highly dependent on the extrudate flow rate through the slot die. As mentioned above, slot dies contain flexible die lips that can be used to adjust the local height of the applicator slot, or "slot height," to control the extrudate flow rate from the applicator slot and provide a desired web thickness profile.

[0007] The slot die may include multiple actuators spaced along the width of the applicator slot to manipulate the caliper profile. For example, each actuator may be configured to provide localized position adjustment of a flexible die lip. During the extrusion process through the slot die, the cross-web profile of the extrudate is systematically measured. The actuators may then be adjusted collectively or individually to provide a desired caliper profile, typically a uniform caliper, for the extrudate across the width of the applicator slot.

[0008] A significant technical problem encountered in extrusion is draw resonance, which is defined as a persistent periodic non-uniformity of the web gauge or weight in the machine direction. In manufacturing, this typically manifests as excessive oscillations in the width and thickness of the extruded web between the slot die and the moving substrate. Draw resonance can occur in any melt drawing process, such as spinning, melt embossing, or extrusion coating. Summary of the Invention

[0009] The provided slot die and method represent a novel solution to the problem of drag resonance based on the concept of negative neutral slot height and / or negative zero-pressure slot height. The use of slot dies with negative neutral slot height has been dismissed as impossible by extrusion technology experts. However, the provided slot die and method have proven effective in eliminating drag resonance, increasing line speeds, and reducing extruded film thickness, allowing for significant reductions in overall manufacturing costs.

[0010] It should be noted that while the term "negative slot height" is sometimes used herein, the actual operating slot height is never actually negative. As molten extrudate flows through the slot die, internal fluid pressure forces the closed slot open to become a pressure-deformed applicator slot. When flow stops, the die lips contact each other with a compressive spring force, and the slot can physically close to a zero gap. In the "neutral" (or relaxed) state, there is spatial interference between the die lips.

[0011] Switching from a conventional positive neutral die slot to a negative neutral die slot has the technical advantage of recycling the "spring force" of the die lip, allowing the operating die slot to be reduced even further than would otherwise be possible. Due to physical constraints, the actuators used to adjust the shape of the flexible die lip can only exert a limited force, individually or collectively. Because the system is effectively constrained by a limited force budget, it is desirable to incorporate these forces into the slot die rather than wasting them simply closing the lip itself.

[0012] Reducing slot height helps address the issue of drag resonance, a major problem in many different manufacturing operations using a variety of materials. This includes any operation that uses a drop die, such as film extrusion, extrusion coating, extrusion replication, and hot melt drop dies. Drag resonance directly impacts product profitability for several reasons. First, drag resonance limits the maximum speed of the production line, reducing productivity. Second, drag resonance reduces web thickness uniformity, potentially resulting in waste and inferior product. Third, drag resonance limits the minimum web thickness, impacting product costs associated with material use, secondary costs for processing and handling additional materials, and increased energy costs for heating and melting the polymer. Finally, drag resonance reduces a product's market viability and profitability.

[0013] Preferred embodiments of the provided slot die and method can be advantageously deployed in conjunction with systems and methods for adjusting slot dies previously described in U.S. Patent Nos. 9,044,894 (Loukusa et al.), 9,216,535 (Trice et al.), 9,579,684 (Yapel et al.), and 9,744,708 (Loukusa et al.). However, these techniques may have broader application throughout extrusion technology, particularly where drag resonance is a limitation.

[0014] In a first aspect, a slot die is provided comprising: an applicator slot extending across a width of the slot die and having opposing first and second slot die surfaces, the applicator slot being in fluid communication with a fluid flow path through the slot die; a flexible die lip providing the first slot die surface and capable of independently adjusting a cross-sectional height of the fluid flow path; and a plurality of actuators spaced apart along the width of the first slot die surface, each actuator operatively coupled to the flexible die lip and adjusting the cross-sectional height at a respective location to provide localized adjustment of fluid flow through the applicator slot, the applicator slot having a neutral slot height profile that is negative along at least a portion of the width of the slot die.

[0015] In a second aspect, a method of operating a slot die is provided, the slot die comprising: an applicator slot extending across a width of the slot die and having opposing first and second slot die surfaces, the applicator slot being in fluid communication with a fluid flow path through the slot die; a flexible die lip providing the first slot die surface and capable of independently adjusting a cross-sectional height of the fluid flow path; and a plurality of actuators spaced apart along the width of the first slot die surface, each actuator operatively coupled to the flexible die lip and adjusting the cross-sectional height at a respective location to provide localized adjustment of fluid flow through the applicator slot, the method comprising: adjusting the first slot die surface using the plurality of actuators to provide a slot height profile that is non-negative across the entire width of the slot die prior to extrusion; extruding extrudate through the applicator slot to increase the cross-sectional height along part or all of the slot height profile; and further adjusting the first slot die surface using the plurality of actuators during extrusion to achieve a target slot height profile, wherein the applicator slot has a slot height profile that is negative along at least a portion of the width of the slot die in the absence of the influence of extrudate pressure.

[0016] In a third aspect, a method of operating a slot die is provided, the slot die comprising: an applicator slot extending across a width of the slot die and having opposing first and second slot die surfaces, the applicator slot being in fluid communication with a fluid flow path through the slot die; a flexible die lip providing the first slot die surface and capable of independently adjusting a cross-sectional height of the fluid flow path; and a plurality of actuators spaced along the width of the first slot die surface, each actuator operatively coupled to the flexible die lip and adjusting the cross-sectional height at a respective location to provide localized adjustment of fluid flow through the applicator slot, the method including: adjusting the first slot die surface using the plurality of actuators to provide a slot height profile that is non-negative across the entire width of the slot die prior to extrusion; extruding extrudate through the applicator slot to increase the cross-sectional height along part or all of the slot height profile; and further adjusting the first slot die surface using the plurality of actuators during extrusion to achieve a target slot height profile, wherein the applicator slot has a neutral slot height profile that is negative along at least a portion of the width of the slot die. [Brief explanation of the drawings]

[0017] [Figure 1A] FIG. 1A is a thickness profile measured from a beta gauge showing the manifestation of the entrainment resonance. [Figure 1B] FIG. 1B is a thickness profile measured from a beta gauge, showing the manifestation of the entrainment resonance. [Figure 2] FIG. 2 is a cross-sectional view of a slot die according to an exemplary embodiment. [Figure 3] FIG. 3 is a bottom view of the slot die of FIG. 1 showing multiple actuators aligned along the width of the slot die. [Figure 4]FIG. 4 is a schematic diagram of an actuator assembly including a position sensor and a controller for selecting a position of the actuator assembly based on the output of the position sensor. [Figure 5] FIG. 5 is an enlarged fragmentary cross-sectional view of a slot die according to another embodiment, showing the die slot in both a neutral position (upper die lip shown in dashed lines) and an active position (upper die lip shown in solid lines). [Figure 6] FIG. 6 is a block diagram illustrating an exemplary process for operating a slot die. [Figure 7] FIG. 7 is a chart showing various slot height profiles for slot dies having different configurations. [Figure 8] FIG. 8 shows the coat weight profile obtained using a slot die with a negative neutral slot profile. [Figure 9] FIG. 9 shows the tensile strength curves of the extrudates at room temperature.

[0018] Repeat use of reference characters in the specification and drawings is intended to represent the same or similar features or elements in the present disclosure. It should be understood that numerous other modifications and embodiments may be devised by those skilled in the art that fall within the scope and spirit of the principles disclosed. The figures may not be drawn to scale. DETAILED DESCRIPTION OF THE INVENTION

[0019] As used herein, the terms "preferred" and "preferably" refer to the embodiments described herein that may offer certain advantages, under certain circumstances. However, other embodiments may also be preferred, under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, or is not intended to exclude other embodiments from the scope of the invention.

[0020] As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Thus, for example, reference to a component with "a" or "the" can include one or more of the component and equivalents thereof known to those skilled in the art. Furthermore, the term "and / or" means one or all of the described elements or a combination of any two or more of the listed elements.

[0021] It should be noted that the term "comprises" and variations thereof do not have a limiting meaning when these terms appear in the following description. Additionally, "a," "an," "the," "at least one," and "one or more" are used interchangeably herein. Relative terms such as left, right, front, rear, above, below, side, upper, lower, horizontal, vertical, etc. may be used herein, and when so, are from the perspective observed in a particular drawing. These terms are used only to simplify the description and are not intended to limit the scope of the invention in any way.

[0022] References throughout this specification to "one embodiment," "a particular embodiment," "one or more embodiments," or "an embodiment" mean that a particular feature, structure, material, or characteristic described in connection with an embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrases "in one or more embodiments," "a particular embodiment," "in one embodiment," or "an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment.

[0023] The technical problem of drag resonance is observed as a web thickness oscillation using a scanning web thickness gauge. This is because high-frequency periodic surges (waves) in the machine direction manifest as an artifact represented by waves in the cross direction. Figures 1A and 1B illustrate the absence and presence of drag resonance, respectively. The provided slot die and method offer a unique technological advancement that can reduce or eliminate the undesirable effects of drag resonance.

[0024] 2 and 3 illustrate the operation of an exemplary slot die, hereinafter designated 50. The slot die 50 is shown in cross section for clarity and includes an upper die block 52 and a lower die block 54. The upper die block 52 and the mating lower die block 54 constitute mating halves that form a fluid flow path through the slot die 50. An inlet 56, a die cavity 58, and an applicator slot 60 are in fluid communication with one another. The applicator slot 60 is bounded by a fixed upper die lip 61 and a flexible lower die lip 62 and extends longitudinally across the width of the die. In this embodiment, the upper die lip 61 is integral with the upper die block 52, and the flexible die lip 62 is integral with the lower die block 54. However, it should be understood that either or both of the die lips 61, 62 may be modular and replaceable.

[0025] The die lips 61, 62 extend across the width of the applicator slot 60. Multiple actuator assemblies 70 are mounted to a common mounting bracket 72 and aligned along the width of the slot die 50, as shown in FIG. 2. In some cases, the mounting bracket 72 may be segmented and include individual structures for each of the actuator assemblies 70. Each actuator assembly 70 is operable to adjust the height of the fluid flow passage at a respective location along the width of the slot die 50, providing localized adjustment of fluid flow through the applicator slot 60. This adjustment is achieved by changing the shape and / or position of the flexible die lip 62 within the extrudate fluid flow passage within the slot die 50.

[0026] During operation of the slot die 50, extrudate enters the slot die 50 through fluid flow path inlet 56 (indicated by an arrow), passes through the slot die 50's fluid flow path, including die cavity 58, and is extruded through applicator slot 60 into the nip region between counter-rotating rollers 98, 99. Depending on process considerations, the extrudate may be fed directly into the nip or biased to contact one or the other roller just prior to the nip. Although not shown here, a continuous substrate may be conveyed into the nip region to provide a carrier for the extruded web.

[0027] If desired, the extrudate may be passed over and under a series of rollers to cool it. Additionally, additional processes may be performed on the extrudate downstream of rollers 98, 99. These processes are not directly related to this disclosure but may include, but are not limited to, stretching, coating, texturing, printing, cutting, winding, laminating, and the like. In some processes, a manufacturing release liner may be removed, a release liner may be added, or one or more additional layers (e.g., laminated transfer tape) may be added. Any necessary curing steps, such as exposure to an electron beam, a heated oven, or a UV chamber, may also be performed.

[0028] The extrudate is not particularly limited and can include any conventional extrudable thermoplastic or curable composition. Useful extrudable thermoplastic compositions include, for example, polyolefins (polypropylene (PP), high density polyethylene (HDPE), low density polyethylene (LDPE), linear low density polyethylene (LLDPE)), various known hot melt adhesives, styrenic block copolymers, and mixtures thereof.

[0029] 3 illustrates a slot die 50 with five actuator assemblies 70. It should be understood that there may be more or fewer actuator assemblies depending on the width of the slot die 50. Each actuator assembly 70 is attached to or engaged with a flexible die lip 62, as shown, and the actuator assemblies 70 are evenly spaced along its width. Each actuator is operable to provide local adjustment of the position of the flexible die lip 62 within the applicator slot 60 of the slot die 50, thereby controlling the height of the fluid flow path at that location.

[0030] As described in further detail with respect to FIG. 4 , each actuator assembly 70 may be motorized and may include precision sensors, such as a linear variable differential transformer (LVDT) or linear encoder, to quantify the movement of its output shaft. The output shafts of the linear actuator assemblies 70 are spaced along the width of the flexible die lip 62, and each linear actuator assembly 70 is operable to adjust the local position of the die lip. The position of each linear actuator is independently controllable to provide a desired cross-web profile of the extrudate. Furthermore, the position of the linear actuator assembly 70 may be precisely adjusted during operation of the slot die 50 to provide a desired die cavity pressure within the die cavity 58 based on the cross-sectional area of ​​the fluid flow path adjacent to the flexible die lip 62 within the slot die 50. In other examples, the position of each actuator assembly 70 may be actively controlled to create extrudates with patterned features, such as repeating or random features. References herein to the position of an actuator or actuator assembly are intended to more specifically refer to the relative positions of the actuator output shafts.

[0031] FIG. 4 shows an assembly including an actuator assembly 70, a zero-backlash coupler 74, and a controller 76. The actuator assembly 70 includes a motor 78, a linear actuator 82 coupled to the motor 78, and a position sensor 80. The motor 78 rotates a shaft mechanically coupled to the linear actuator 82. The sensor 80 measures the position of the linear actuator 82. For example, the sensor 80 may be an LVDT sensor or a linear encoder. The sensor 80 is secured to the output shaft 84 of the linear actuator 82 with a clamp 86 and accurately measures the relative position of the output shaft 84 of the linear actuator 82. In other examples, the sensor 80 may measure the position of the coupler 74, the die actuator linkage 88, or the flexible die lip itself.

[0032] The controller 76 receives position input from both the motor 78 and the sensor 80. For example, the motor 78 may be a stepper motor, providing an indication of the number of "steps" the stepper motor has taken from a known reference position. The sensor 80 may provide the controller 76 with more accurate position information than that provided by the motor 78. The controller 76 provides instructions to the motor 78 to drive the output shaft 84 of the actuator assembly 70 to a predetermined position. In some examples, the controller 76 may control a set of actuator assemblies 70 simultaneously or sequentially. Here, the controller 76 may be used to control each of the actuator assemblies 70 in the slot die 50 shown in FIGS. 2 and 3 .

[0033] Referring again to FIG. 4 , the zero-backlash coupler 74 comprises two halves—a lower half 90 and an upper half 92—fastened together. The lower half 90 is attached directly to the die actuator linkage 88 using screws or bolts. Additionally, the zero-backlash coupler 74 includes a stacked protrusion assembly that is bolted to the end of the output shaft 84 of the actuator assembly 70. The stacked protrusion assembly includes two metal discs 94 that surround an insulating disc 96. The insulating disc 96 may comprise a ceramic material. The lower half 90 and the upper half 92 are joined together to enclose the stacked protrusion assembly, which includes the metal discs 94 and the insulating disc 96 and is bolted to the end of the output shaft 84. When the upper half 92 is securely fastened to the lower half 90, the output shaft 84 is effectively aligned with the zero-backlash coupler 74 and the die actuator linkage 88.

[0034] The zero-backlash coupler 74 functions to thermally isolate the actuator assembly 70 from the slot die. Within this assembly, a thermal insulating disk 96 significantly limits the metal-to-metal contact path between the output shaft 84 of the actuator assembly 70 and the die actuator linkage 88, protecting the actuator assembly 70 from harmful heat emanating from the slot die 50. While slot dies typically operate at temperatures in excess of 300°F (149°C), actuator assembly 70 components, including the motor 78 and sensor 80, can experience limited functionality or even permanent damage if exposed to temperatures above 130°F (54°C). For this reason, the zero-backlash coupler 74 preferably helps maintain the actuator assembly 70 at or below 130°F (54°C).

[0035] In an alternative embodiment, the metal disk 94 may be replaced with a disk of a non-metallic material to avoid metal-to-metal contact between the output shaft 84 and the die actuator linkage 88. Such a configuration further thermally isolates the actuator assembly 70 from the slot die housing. As a further example, a surface portion of the coupler 74 may be configured as a passive heat spreader to maintain the temperature of the actuator assembly 70 at or below 130°F (54°C). This may be used independently of or in combination with the insulating disk 96. In a further example, active thermal control may be used to cool the zero-backlash coupler 74, the output shaft 84, or the actuator assembly 70.

[0036] In contrast to slot die designs that utilize a differential bolt as the actuation mechanism, the zero-backlash coupler 74 couples the output shaft 84 of the actuator assembly 70 to the die actuator linkage 88 with little or no backlash. While differential bolt mechanisms can exhibit backlash of over 100 micrometers, the zero-backlash coupler 74 may have very little backlash, for example, less than 10 micrometers, or even less than 5 micrometers, such as about 3 micrometers.

[0037] In slot dies that use a set of differential bolts to control the width of the applicator slot, the relatively large backlash of each differential bolt means that adjusting the position of one differential bolt can change the height of the fluid flow path in the other bolts. In slot die 50, the position of output shaft 84 of actuator assembly 70 directly corresponds to the local position of flexible die lip 62. As such, slot die 50 facilitates repeatable and precise positioning that is not available in slot dies that utilize differential bolts as the actuation mechanism.

[0038] Other actuation mechanisms are possible. For example, the actuation mechanism may include one or more of a thermally adjustable bolt, a differential bolt, a piezoelectric actuator, a pneumatic actuator, and a hydraulic actuator. In some embodiments, the applicator slot may be adjusted by applying a compressive or tensile load to the flexible die lip using a lever supported by a rotating shaft as a support, with the actuation rod being axially displaced by the body of the slot die. The rotational force of the lever is converted into an axial force on the actuation rod, which becomes a compressive or tensile load applied to the flexible die lip. The lever may also apply a force directly to the actuation rod at the point of application of the lever.

[0039] In another example, a thermally adjustable bolt automatically adjusts the applicator slot using multiple adjustment pins coupled to respective thermal elements positioned on the flexible die lip. In such a configuration, the applicator slot can be adjusted through the action of the corresponding adjustment pins applying mechanical force to the flexible die lip due to the expansion or contraction of the thermal elements. Furthermore, the actuation mechanism may include providing at least two adjustment pins and / or thermal elements that are adjusted simultaneously. The foregoing aspects and other variations are described in U.S. Pat. No. 9,700,911 (Nakano) and International Patent Publication No. WO 2019 / 219724 (Colell et al.). Each of these actuation mechanisms is capable of controlling the flexible die lip by applying a push or pull force at precise, spaced locations along the flexible die lip.

[0040] 5 shows a fragmentary view of a slot die 100 having upper and lower die blocks 102, 104 and an applicator slot defined as the space between a fixed upper die lip 111 and a flexible lower die lip 112. In this view, the remaining components of the slot die 100, including the actuator assembly and control system, have been omitted for simplicity.

[0041] In reality, many forces simultaneously act on the upper and lower die lips 111', 112 and contribute to the resulting actual slot height profile. In addition to the bite forces that prevent the upper and lower die lips 111', 112 from overlapping, there are also forces generated by the flow of melt fluid through the slot die 100 (i.e., the effect of extrudate pressure) that tend to widen the applicator slot. Finally, there are active forces applied by multiple actuators used to adjust the web thickness, such as the actuator assembly 70 of Figures 2 and 3.

[0042] As used herein, slot height reflects the spatial separation between the slot die surfaces on opposing die lips that define the applicator slot and can be physical and / or theoretical. In Figure 5, slot die 100 is shown in two different applicator slot configurations. The first configuration, shown in solid lines, is represented by upper die lip 111 and flexible die lip 112, resulting in a positive slot height h. The second configuration, shown in dashed lines, is represented by a fixed upper die lip 111' and flexible die lip 112, resulting in a negative slot height h'.

[0043] While the negative slot height h' is theoretical and not physical, it is still a useful mathematical construct that can be defined and calculated under certain assumptions. For example, h' can represent the degree to which the fixed upper die lip 111' and the flexible die lip 112 overlap along the slot height dimension, assuming they are able to slide into each other in the absence of external forces. This defines the neutral slot height, and the neutral slot height values ​​across the width of the slot die 100 collectively define the neutral slot height profile.

[0044] Alternatively, h′ may represent the degree to which the fixed upper die lip 111′ and the flexible die lip 112 overlap along the slot height dimension, assuming they are able to enter each other without the influence of internal extrudate pressure but with the force applied to the flexible die lip 112 by the multiple actuator assemblies 70. This measurement is referred to as the zero-pressure slot height, and the zero-pressure slot height values ​​across the width of the slot die 100 collectively define the zero-pressure slot height profile. The effect of extrudate pressure may be modeled or empirically calculated, as described in International Patent Publication No. WO 2022 / 123355 (Secor et al.).

[0045] Regardless of whether the slot height h' represents a neutral slot height or a zero pressure slot height, the slot height h' can be less than, equal to, or greater than -2500 micrometers to 3500 micrometers, -1300 micrometers to 1650 micrometers, -1300 micrometers to 500 micrometers, or in some embodiments, -2500 micrometers, -2000, -1500, -1300, -1000, -500, 0, 500, 1000, 1500, 1650, 2000, 2500, 3000, or 3500 micrometers.

[0046] As the extrudate flows through the slot die, the pressure exerts an outward force, opening the closed slot into a pressure-deformed die lip configuration. When flow stops, the applicator slot physically closes, resulting in a zero gap where the die lips contact each other. In this case, the flexible die lips are in a stressed (i.e., unrelaxed) state, reflecting an equilibrium where the compressive spring forces from the die lips repel each other.

[0047] Advantageously, changing from a conventional positive neutral die slot to a negative neutral die slot reclaims the available spring force of the flexible die lip, which can result in a further reduction in the operating die slot. This is technically important because the actuator forces are already limited and these forces are not wasted simply bending the flexible die lip to a closed (i.e., zero slot height) position.

[0048] The use of an applicator slot having a negative neutral slot profile along at least a portion of the width of the slot die can provide substantial technical advantages over conventional slot dies, particularly in the suppression of undesirable drag resonance. Drag resonance is reflected in persistent periodic non-uniformity of gauge or weight in the machine direction and can cause significant technical problems in many manufacturing processes and many extrudate compositions. Manufacturing processes adversely affected by drag resonance include, but are not limited to, film extrusion, extrusion coating, extrusion replication, and operations using drop dies, such as hot melt drop dies. Reduction or elimination of drag resonance allows for increased line speeds, reduced extruded web thickness, and an overall reduction in web production costs.

[0049] Direct contact between the upper and lower die lips 111', 112 can cause Brinell damage or permanent surface deformation of the slot die 100. It is generally desirable that the extrudate pressure influence and / or actuator force be sufficient at all times to avoid such contact. This may require special considerations and deviations compared to techniques used to operate conventional slot dies. These modes of operation are described in more detail below.

[0050] Other die configurations are possible. For example, although not shown, both opposing die lips may be independently adjustable by separate adjustment mechanisms. Such configurations, and related options and advantages, are described in International Patent Publication No. WO 2022 / 123294 (Yapel et al.).

[0051] 6 illustrates an exemplary workflow 150 using a control loop to achieve slot height adjustment in a provided slot die, such as slot die 50. Based on the desired actuator position (and by inference the slot height profile), the target thickness profile of the extrudate, and the measured current web thickness profile, a computational prediction of the slot die adjustment is possible. Under certain assumptions, the relationship between the slot height profile and the web thickness profile can be calculated, allowing prediction of a slot height profile suitable for achieving the target web thickness profile.

[0052] Initially, the manufacturing process employs initial actuator setting profiles (block 151). These actuator settings may or may not be predetermined. These initial profiles may be stored based on historical data under similar process conditions, or, in the absence of such data, may be set to default values ​​based on user input. Thus, the actuators assume initial positions according to these presets at the start of the control loop. Advantageously, the initial actuator settings may result in an applicator slot having a non-negative slot height profile across the entire width of the slot die. As discussed above, this configuration helps avoid die lip damage caused by collisions between these components. In a preferred embodiment, the actuator presets are constant or flat across most or the entire width of the slot die.

[0053] During the extrusion process, block 152 indicates the first step of providing a profile measurement of the web extruded from the applicator slot of the slot die. As previously mentioned, known measurement techniques may be used. The profile measurement may be performed in the as-cast state or after the extrudate has been somewhat oriented or otherwise modified. In the former case, the web thickness profile measurement is performed immediately adjacent to where the extruded web exits the applicator slot (the "as-cast state"). The thickness measurement may also be performed shortly after the molten web solidifies, or at a location after the cast web has been post-processed (the "transformed state").

[0054] Some gaging devices scan back and forth along the width of a moving web to collect data on web thickness. Often, these measurements can include numerous individual measurements, which may be scattered across the width of the web as well as taken at different times. To manage this, a controller can process the raw individual measurements and convert them into a small number of data values ​​that, using a form of cross-web and down-web averaging, capture a virtual snapshot of the cross-web thickness profile at a specific location along the continuous web.

[0055] The provided method can be used for both continuous full-web coated extrudates and stripe-coated extrudates. In the case of full-web coating, the multiple measured values ​​represent the entire coated width. In the case of stripe coating, the measured thickness values ​​correspond to multiple coated areas spaced apart from one another along the cross-web direction, and the measurements cover only the coated stripes, not the uncoated lanes between them.

[0056] Block 154 represents the next step, which is to perform a web-to-die mapping of these profile measurements. Several simplifying assumptions may be made when mapping gauge measurements to the die. First, it may be assumed that the data received from the profile measurements is taken edge-to-edge, which is generally true for modern gauge systems with edge detection. Second, it may be assumed that the gauge data corresponds directly to the actual extrudate weight / thickness. If the web is placed on a release liner, the weight of the underlying release liner may be subtracted, so that the data represents only the coating weight. Finally, it may be assumed that neck-in from both ends of the extruded web occurs symmetrically.

[0057] Because the number and locations of coarse-grained measurements often differ from those of the die lip actuators, a generalized method of mapping measurements to actuator locations is preferred. Film neck-in calculations can account for the effects of different flow rates, retraction distances, and web speeds. In one embodiment, coated web coordinates in physical units (inches or millimeters) are mapped to actuator unit coordinates (i.e., a die coordinate system based on sequential actuator numbers). This process allows for mapping from the coating measurement array to physical coated web locations and, through a web-to-die mapping function, to physical die locations. Here, the coating measurement array can represent, for example, an array of recent thickness measurements generated each time the scanner traverses a moving web.

[0058] Once a die-to-web or web-to-die mapping function is in place, it may be advantageous to utilize that function in other parts of the profile control scheme. For example, mapping can incorporate cross-web variations into control parameters such as controller gains and actuator interactions through the coating flow field. This can be done ad hoc based on production experience, or in a more scientific way using a fluid dynamics model of the coating flow field.

[0059] Any suitable model that characterizes fluid rheology can be used to model the flow. For example, the flow modeling can include finite element analysis or can rely directly on one or more equations. Exemplary mathematical models are described, for example, in pending International Patent Application No. WO 2022 / 123355 (Secor et al.).

[0060] In some embodiments, mapping this relationship is facilitated by a scan position to die bolt position mapping that is pre-built into the measurement system. Various commercial systems can perform web to die mapping, such as the Profile Control Solution from NDC Infrared Engineering Inc. of Irwindale, California.

[0061] Proceeding next to block 156, the web thickness profile deviation is determined, which is provided by a residual array (i.e., vector) of values ​​representing how much the current web thickness profile deviates from the target web thickness profile for each of the control zones (block 158). A control zone, as referred to herein, represents a segment of the slot die that corresponds to a particular actuator.

[0062] The initial target profile in block 158 may be defined near the location where the extrudate exits the slot die (e.g., near applicator slot 60 in FIG. 2), or alternatively, downstream of the location where the web has been partially or fully converted. Deviations between the desired and actual web caliper profiles can result from different causes for a given production line, and incorporating both types of measurements to fully understand and correct such deviations can provide significant technical advantages.

[0063] In subsequent iterations of workflow 150, the profile deviation determined in block 156 may be based on the initial target web caliper profile established in block 158, or may be based on a modified target web caliper profile, if desired. The modification of the target web caliper profile need not be particularly limited and may be predetermined using a computer algorithm or may be done manually with input from an operator.

[0064] The first time workflow 150 is run, a target web thickness profile is assigned. This profile may be based on a stored web thickness profile, such as an array of web thicknesses used in a previous iteration of workflow 150 or in other workflows run under similar conditions. For example, a target web thickness profile previously used when the same or similar slot die and similar flow conditions through the slot die were used. While a flat extrudate profile is generally desired, there are situations in which other profiles are preferred. For example, a "dogbone" shaped target profile may be desired to control edge instabilities in the extrusion process, such as those associated with drag resonance and edge scalloping.

[0065] In block 156, a profile deviation is determined based on the difference between the initial target web thickness profile from block 158 and the measured web thickness profile, if available. The initial iteration of the control loop of workflow 150 may be performed before a complete set of web thickness measurements is obtained. If a measured web thickness profile is not yet available, adjustment of the slot die may be delayed until a sufficient number of web thickness measurements are obtained. If partial profile measurements (block 152) are obtained, workflow 150 may be used to adjust the slot die for some of the applicator slots and not for others.

[0066] Once the profile deviation has been determined in this manner, an appropriate slot height adjustment can be calculated (block 160). In predicting the appropriate actuator adjustment for the flexible die lip to achieve the initial target profile from block 158, it is advantageous to apply a pressure die deformation model that allows for separation of the mechanical effects associated with the slot die in the absence of fluid flow from the effects of fluid flow through the die. A suitable model can predict the pressure profile across the applicator slot and the corresponding pressure deformation at the flexible die lip. In some cases, this pressure-based deformation may be measured empirically.

[0067] The pressure deformation may be accounted for by adding it to the calculated slot height to obtain a target slot height profile. This target slot height profile may be compared to the current slot height profile (block 162) and appropriate adjustments may be determined. In particular, the current slot height includes the pressure deformation (D) due to the flow of the extrudate composition through the applicator slot. By subtracting the deformation D due solely to the fluid from the pressure-compensated slot height profile H+D, a zero-pressure slot height profile (H) can be obtained, which can be used to calculate the target actuator position.

[0068] Mathematical models describing the fluid dynamics and pressure effects within a slot die are described in detail, such as in pending International Patent Application Nos. WO2022 / 123296 (Secor et al.) and WO2022 / 123355 (Secor et al.).

[0069] The target actuator position may result in an applicator slot having a zero-pressure slot height profile that is negative along at least a portion of the width of the slot die (i.e., the slot height profile in the absence of the influence of extrudate pressure). In some embodiments, the target actuator position may result in an applicator slot having a zero-pressure slot height profile that is negative along the entire width of the slot die (i.e., the slot height profile in the absence of the influence of extrudate pressure). In some embodiments, the resulting slot die configuration may include a negative neutral slot height profile along at least a portion of the width of the slot die. Optionally, the resulting slot die configuration may include a negative neutral slot height profile along the entire width of the slot die.

[0070] When making adjustments during an extrusion operation, the controller may predict a set of discrete actuator settings suitable for reaching a desired slot height profile. In a preferred embodiment, this set of discrete actuator settings is based on a plurality of actuator settings corresponding to a preselected cross-web profile. As described below, the plurality of discrete actuator settings may be obtained by using a predictive model to determine appropriate actuator adjustments (block 164).

[0071] In a preferred embodiment, the prediction of an individual setting from a zero-pressure current slot height derived from multiple individual settings and / or current slot heights (block 162) can be obtained through a mathematical structure called a stiffness matrix. The stiffness matrix converts actuator settings to a corresponding slot height profile in the absence of flow field physical effects. While not discussed in detail here, International Patent Publication No. WO 2012 / 170713 (Secor et al.) describes in more detail an example of how empirical test data can be used to construct a stiffness matrix for a particular slot die.

[0072] Overview: The stiffness matrix and inverse stiffness matrix are used to convert changes in actuator position to changes in slot height, and vice versa. The stiffness matrix is ​​expressed in Equations 1 and 2 below.

[0073]

number

[0074] The stiffness matrix K generally has N×N elements (N is the total number of active actuators), and the jth actuator setting A jrepresents the change in slot height at the measurement point due to a change in actuator position. The stiffness matrix may reflect significant mechanical interactions between the actuators. In general, a change in actuator position may cause a change in slot height at positions several actuators away. In some embodiments, this is represented by a banded stiffness matrix. In many cases, the banded stiffness matrix can be assumed to be symmetric. For example, the matrix may have significant non-zero components only along five diagonals: the main diagonal and the two diagonals on either side of it.

[0075] Once the stiffness matrix is ​​determined, the slot height measurements can be used in two ways. First, for any set of actuator settings, the resulting slot height profile can be calculated by multiplying the actuator displacements by the stiffness matrix according to Equations 1 and 2. Second, the actuator settings that result in a specified slot height profile are calculated by multiplying the desired slot height change by the inverse of the stiffness matrix. To determine the appropriate set of actuator adjustments, Equation 3 is used:

[0076]

number

[0077] Once the actuator adjustments are complete, workflow 150 returns to block 152, where a new profile measurement is taken and the process begins again. The steps of workflow 150 can incrementally refine the actuator settings / positions based on real-time web thickness measurements. Over time, through these incremental adjustments, the desired target web thickness profile can be achieved.

[0078] Table 1 reports the properties of the extruded web under various extrusion conditions, comparing (i) a first slot die (EX-1) with a neutral slot height of 4 mils and (ii) a second slot die (EX-2) with a neutral slot height of -10 mils. Web thickness calculations are based on the density of polypropylene, 0.9 g / cm. 3 It is assumed that:

[0079] As shown, the latter allows for a very significant reduction in the pressure-adjusted slot height, from 1020 micrometers (40 mils) to 560 micrometers (22 mils). This is also reflected in the thickness of the web produced using EX-2 (19 gsm vs. 32 gsm) and the lower draw ratio (26.5 vs. 28.6). The two EX-2 runs in Table 1 represent webs made at two different extruder flow rates. Compared to the EX-1 run, the draw ratio was reduced by 45% to achieve the same thickness, and even when producing a thinner (19 gsm) web, the draw ratio was 7% lower. In both cases, the lower draw ratio was found to significantly suppress draw resonance.

[0080] [Table 1] Figure 7 shows both the pressure-adjusted slot height profile and the zero-pressure slot height profile for the above-described dies EX-1 and EX-2. As can be seen in this chart, the zero-pressure slot height profiles for both EX-1 and EX-2 extended to negative values ​​along at least a portion of the width of the slot die. However, EX-2 provides a much larger useful operating window for producing thin webs at potentially lower draw ratios to reduce or eliminate draw resonance.

[0081] Figure 8 shows the thickness consistency of an extruded web cast onto a uniformly thick polypropylene backing. This is captured through basis weight measurements plotted against the Control Zone Index. Good web thickness uniformity was achieved when producing webs from the EX-2 slot die, with an average total weight of 61 gsm at start-up. This is evidenced by a well-controlled extrudate weight profile of 32 gsm, with only minor variations in total material weight, and a 3σ parameter of 2.16.

[0082] Furthermore, it has been discovered that the pull-in resonance can be further reduced by appropriate selection of the extrudate composition. For example, where possible, it can be beneficial to select an extrudate with a higher melt flow rate and a tensile strength curve that is less favorable to resonance. The critical deformation energy E lim represents the maximum deformation energy that a polymer sample can withstand before yielding or breaking, and corresponds to the area under the tensile strength curve from zero elongation to the point where the material yields or breaks.

[0083] Figure 9 shows the room temperature tensile strength curves for various extrudates and how they correlate with the likelihood of pull-in resonance. As shown, curve A indicates the critical tensile stress σ at which there is break in the tensile strength curve. crt Curve B shows the yield stress σ, which represents a more severe fracture in the tensile curve where irreversible deformation occurs.yield The tensile strength curve was obtained at the process temperature, and the critical deformation energy E lim Since it is impractical to calculate E, instead, a sample of the extrudate material can be tested at room temperature. lim The higher the value of E, the less likely the entrainment resonance is. In this hypothetical diagram, curve A tends to be favorable for entrainment resonance. lim Curve C shows a relatively high E lim Indicates the value of

[0084] As shown, W A , W B , and W C are E for curves A, B, and C, respectively. lim It refers to the triangular area that approximates the value of E. lim The value of can be material specific. For example, a useful polyolefin extrudate composition has a thermal conductivity of 0.65 MJ / m at 25°C. 3 to 1.87MJ / m 3 E lim while styrene-based block copolymers used in the formulation of hot melt adhesives may have a viscosity of 12 MJ / m at 25°C. 3 to 206MJ / m 3 E lim and preferably 139 MJ / m 3 Greater than.

[0085] The techniques described in this disclosure can be implemented in hardware, software, firmware, or any combination thereof. For example, various examples of the provided methods can be implemented in one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other equivalent integrated or discrete logic circuitry, as well as any combination of these components embodied in a controller, user interface, or other device. The term "controller" can generally refer to any of the foregoing logic circuitry, either alone or in combination with other logic circuitry, or other equivalent circuitry.

[0086] When implemented in software, the functionality attributed to the systems and controllers described in this disclosure may be embodied as random access memory (RAM), read-only memory (ROM), non-volatile random access memory (NVRAM), electrically erasable programmable read-only memory (EEPROM), flash memory, magnetic media, optical media, or similar computer-readable storage media. These instructions may be executed by one or more processors to support one or more examples of the functionality described in this disclosure. Various examples are described in the preceding text.

[0087] All references, patents, and patent applications cited in the above patent application are incorporated herein in their entirety in a consistent manner. In the event of any inconsistency or contradiction between any of the incorporated references and this application, the information in the above description shall prevail. The above description is provided to enable one skilled in the art to practice the claimed disclosure and should not be construed as limiting the scope of the disclosure, which is defined by the claims and all equivalents thereto.

Claims

1. an applicator slot extending across the width of the slot die and having opposing first and second slot die surfaces, the applicator slot being in fluid communication with a fluid flow path through the slot die; a flexible die lip providing the first slot die surface and capable of independently adjusting the cross-sectional height of the fluid flow passages; a plurality of actuators spaced apart along a width of the first slot die surface, each actuator operatively coupled to the flexible die lip and adapted to adjust the cross-sectional height at a respective location to provide local adjustment of fluid flow through the applicator slot; the applicator slot having a neutral slot height profile that is negative along at least a portion of the width of the slot die; Slot die.

2. The slot die of claim 1 , wherein the neutral slot height profile is negative along the entire width of the slot die.

3. The slot die of claim 1 or 2, wherein the neutral slot height profile has a neutral slot height in the range of -2500 micrometers to 3500 micrometers.

4. The slot die of claim 3, wherein the neutral slot height profile has a neutral slot height in the range of -1300 micrometers to 1650 micrometers.

5. The slot die of claim 4, wherein the neutral slot height profile has a neutral slot height within the range of -1300 micrometers to 500 micrometers.

6. 1. A method of operating a slot die, comprising: an applicator slot extending across the width of the slot die and having opposing first and second slot die surfaces, the applicator slot being in fluid communication with a fluid flow path through the slot die; a flexible die lip providing the first slot die surface and capable of independently adjusting the cross-sectional height of the fluid flow passages; a plurality of actuators spaced apart along a width of the first slot die surface, each actuator operatively coupled to the flexible die lip and adapted to adjust the cross-sectional height at a respective location to provide local adjustment of fluid flow through the applicator slot; The method is using the plurality of actuators to adjust the first slot die surface to provide a slot height profile that is non-negative across the width of the slot die prior to extrusion; extruding extrudate through the applicator slot to increase the cross-sectional height along a portion or all of the slot height profile; and using the plurality of actuators to further adjust the first slot die surface during extrusion to achieve a target slot height profile; the applicator slot having a slot height profile that is negative along at least a portion of the width of the slot die in the absence of an extrudate pressure influence; method.

7. The method of claim 6 , wherein the applicator slot has a neutral slot height profile that is negative along at least a portion of the width of the slot die.

8. 1. A method of operating a slot die, comprising: an applicator slot extending across the width of the slot die and having opposing first and second slot die surfaces, the applicator slot being in fluid communication with a fluid flow path through the slot die; a flexible die lip providing the first slot die surface and capable of independently adjusting the cross-sectional height of the fluid flow passages; a plurality of actuators spaced apart along a width of the first slot die surface, each actuator operatively coupled to the flexible die lip and adapted to adjust the cross-sectional height at a respective location to provide local adjustment of fluid flow through the applicator slot; The method is using the plurality of actuators to adjust the first slot die surface to provide a slot height profile that is non-negative across the width of the slot die prior to extrusion; extruding extrudate through the applicator slot to increase the cross-sectional height along a portion or all of the slot height profile; and using the plurality of actuators to further adjust the first slot die surface during extrusion to achieve a target slot height profile; The method wherein the applicator slot has a neutral slot height profile that is negative along at least a portion of the width of the slot die.

9. 9. The method of claim 8, wherein the applicator slot has a slot height profile that is negative along at least a portion of the width of the slot die in the absence of the influence of extrudate pressure.

10. The method of any one of claims 6 to 9, wherein the extrudate comprises recycled or degraded polymer.

11. The method of any one of claims 6 to 10, wherein the extrudate comprises a mixture of compatible polymers.

12. The method of any one of claims 6 to 11, wherein the extrudate comprises one or more of polypropylene, high density polyethylene, low density polyethylene, linear low density polyethylene, and a hot melt adhesive.

13. The extrudate comprises a polyolefin and has a viscosity of 0.65 MJ / m ３ to 1.87 MJ / m ３ The method according to any one of claims 6 to 12, wherein the limiting deformation energy is

14. The extrudate contains a styrene-based block copolymer and has an extrudate strength of 12 MJ / m ３ to 206 MJ / m ３ The method according to any one of claims 6 to 12, wherein the limiting deformation energy is

15. The extrudate has a viscosity of 139 MJ / m ３ to 206 MJ / m ３ 15. The method of claim 14, wherein the critical deformation energy is

16. A slot die or method according to any preceding claim, wherein both the first and second slot die surfaces are independently adjustable by separate adjustment mechanisms.

Images