Filament Adhesive Dispenser

Abstract

A dispensing device and method for a filament adhesive is provided. The dispensing device uses a barrel containing one or more heating elements and a rotatable screw received within the barrel, the rotatable screw optionally including at least one mixing element. An inlet extends through the side of the barrel to receive the filament adhesive, the inlet including a sloped nip point that prevents the filament adhesive from breaking as it is drawn into the barrel. An outlet at the distal end of the barrel is for dispensing the filament adhesive in molten form. Using the provided dispensing device, and optionally with computer assistance, the adhesive can be precisely applied to a predetermined location on a substrate.

Description

Technical Field

[0001] A dispenser for filament adhesives is provided along with its system and method. The dispenser provided can be useful, for example, when disposing a pressure-sensitive adhesive on a bonding surface.

Background Art

[0002] A pressure-sensitive adhesive is a material that adheres to a substrate when pressure is applied. They do not require solvents, water, or heat to effect a bond. State-of-the-art pressure-sensitive adhesives can achieve extremely high bonding performance and can replace conventional mechanical fasteners in many industrial applications. These bonding solutions are also economical and easy to use.

[0003] Conventional pressure-sensitive adhesives are thin and flat and are generally dispensed in the form of sheets or rolls. However, in certain applications, it may be advantageous to form the pressure-sensitive adhesive in situ. For example, in automotive bonding applications, by making the bonding surface of the parts non-planar, an improvement in mechanical holding force can be achieved. Some parts can have a ribbed bonding surface, and significant penetration of the pressure-sensitive adhesive into the ribbed structure is required to obtain proper bonding strength.

[0004] Furthermore, the most commonly used plastics are thermoplastic olefins (referred to as "TPO", and sometimes also as "PP / EPDM"), which are low surface energy plastics similar to polypropylene. Conventional pressure-sensitive adhesives do not achieve a high degree of "wet-out" on these plastics and similar plastics, and as a result, the surface area between the adhesive and the substrate is reduced. To improve "wet-out", primers and other surface treatments can be used, but these increase the complexity and cost of the bond. For these reasons, bonding to non-planar low surface energy substrates remains a difficult technical problem.

Summary of the Invention

[0005] Devices, kits, and assemblies for mixing and dispensing a filament adhesive are provided herein. The filament adhesives include those using a core / sheath configuration, including adhesives that are dispensed in a hot melt form and then cooled to provide a pressure sensitive adhesive. Using the provided dispensing devices, and optionally with computer assistance, these adhesives can be accurately applied to predetermined locations on a substrate. The ability to customize the size and shape of the pressure sensitive adhesive provides increased versatility to manufacturers.

[0006] Core-sheath adhesives having a pressure sensitive adhesive core (i.e., core-sheath PSA) are distinguishable from conventional filaments in several respects. For one, pressure sensitive adhesives tend to have a relatively soft viscoelastic consistency, which makes them difficult for many conventional FFF (fused filament fabrication) print heads. These materials tend to buckle and / or jam when pushed into the melt zone. Some FFF print heads have been augmented with supply tubes or guides that enable the feeding of rubber-based filaments. However, the reason these filaments can be fed successfully is mainly because they have a significantly higher Shore D durometer than typical pressure sensitive adhesive materials.

[0007] Another technical issue relates to the dimensions of the filament adhesive. To obtain an acceptable throughput for most industrial applications, the diameter of the filaments provided needs to be large enough, generally about 6 millimeters or more. This can be several times larger than the diameter of conventional filaments used in 3D printers. Larger diameter filaments are desired to accommodate the material throughput required in large-scale manufacturing processes.

[0008] Core-sheath PSA also exhibits behavior different from that of conventional hot melt adhesives. Unlike conventional hot melt materials, core-sheath PSA maintains a high melt viscosity even when heated. This is desirable for the dimensional stability of the adhesive dispensed onto a substrate. Even when melted, these materials do not drip, sag, or move in any other way from the location where they are placed.

[0009] The present disclosure describes a dispensing head that can dispense filament adhesives, such as core-sheath PSA, while being capable of weight reduction. Suitable substrates include, but are not limited to, irregular surfaces, complex geometries, and flexible media. Further uses of this pressure-sensitive adhesive include sealing, joining in narrow spaces, patterned adhesive placement, and joining of household appliances.

[0010] In a first aspect, a dispensing head for a filament adhesive is provided. The dispensing head includes a barrel containing one or more heating elements, an inlet extending through the side of the barrel for receiving the filament adhesive, the inlet including an inclined nip point that prevents the filament adhesive from breaking when the filament adhesive is drawn into the barrel, an outlet at the distal end of the barrel for dispensing the filament adhesive in a molten form, and a rotatable screw received within the barrel, the rotatable screw optionally including at least one mixing element.

[0011] In a second aspect, a dispensing system is provided that includes the dispensing head and the filament adhesive.

[0012] In a third aspect, a method for dispensing a filament adhesive from a dispensing head having a heated barrel that receives a rotating screw is provided. The method includes supplying a filament adhesive through an inlet of the heated barrel, the inlet including an angled nip point that reduces the cutting or breaking of the filament adhesive as the filament adhesive is drawn into the heated barrel, melting the filament adhesive within the heated barrel to provide a molten adhesive, optionally mixing the molten adhesive using at least one mixing element disposed on the rotating screw, and dispensing the molten adhesive through an outlet at a distal end of the heated barrel. BRIEF DESCRIPTION OF THE DRAWINGS

[0013]

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[0014] The repeated use of reference characters in the specification and drawings is intended to represent the same or similar features or elements of the present disclosure. It should be understood that many other modifications and embodiments, which are within the scope and spirit of the principles of the present disclosure, can be devised by those skilled in the art. These figures may not be drawn to exact scale.

[0015] Definitions As used herein, "Ambient conditions" means a temperature of 25 degrees Celsius and a pressure of 1 atmosphere (about 100 kilopascals).

[0016] "Ambient temperature" means a temperature of 25 degrees Celsius.

[0017] "Nominal screw length" refers to the length of the flighted portion of the extrusion screw (the portion that normally contacts the extrudate).

[0018] "Non-stickiness" refers to a material that passes a "self-adhesion test" in which the force required to peel the material from itself without crushing the material is below a predetermined maximum threshold amount. The self-adhesion test is described below and is typically performed on a sample of the sheath material to determine whether the sheath is non-sticky.

[0019] As used herein, the term "pressure-sensitive adhesive" refers to a material that is normally tacky at room temperature and can be adhered to a surface by applying light finger pressure, and thus can be distinguished from other types of adhesives that are not pressure-sensitive. A general description of pressure-sensitive adhesives can be found in Encyclopedia of Polymer Science and Engineering, Vol. 13, Wiley-Interscience Publishers (New York, 1988). Further description of pressure-sensitive adhesives can be found in Encyclopedia of Polymer Science and Technology, Vol. 1, Interscience Publishers (New York, 1964). As used herein, "pressure-sensitive adhesive" or "PSA" refers to a viscoelastic material having the following properties: (1) strong and permanent tack, (2) adhesion to substrates other than fluorinated thermoplastic films under finger pressure or less, and (3) sufficient cohesive strength to be cleanly peeled from the substrate. Pressure-sensitive adhesives can also meet the Dahlquist criterion as described in Handbook of Pressure-Sensitive Adhesive Technology, D. Satas, 2nd ed., page 172 (1989). This criterion defines a pressure-sensitive adhesive as an adhesive having a creep compliance of more than 1×10 -6 cm 2 / dyne for 1 second at its use temperature (e.g., at temperatures in the range of 15°C to 35°C).

BEST MODE FOR CARRYING OUT THE INVENTION

[0020] As used herein, the terms "preferred" and "preferably" refer to embodiments described herein that can provide certain advantages under certain circumstances. However, other embodiments may also be preferred in the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are not useful, nor is it intended to exclude other embodiments from the scope of the invention.

[0021] As used in this specification and the appended claims, unless the context clearly dictates otherwise, the singular forms "a", "an", and "the" are intended to include the plural referents. Thus, for example, references to a component preceded by "a" or "the" may include one or more of the components and their equivalents known to those skilled in the art. Further, the term "and / or" means any one or all of the listed elements or any combination of any two or more of the listed elements.

[0022] Note that the terms "comprise" and variations thereof do not have a limiting meaning when these terms appear in the appended description. Further, "a", "an", "the", "at least one", and "one or more" are used interchangeably herein. Relative terms such as left, right, front, rear, top, bottom, side, above, below, horizontal, vertical, etc. may be used in this specification, in which case they are from the perspective seen in a particular drawing. These terms are used only to simplify the description and are in no way intended to limit the scope of the present invention.

[0023] 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 that embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases "in one or more embodiments", "in a particular embodiment", "in one embodiment", or "in an embodiment" at various places throughout this specification are not necessarily referring to the same embodiment of the present invention. Where applicable, trade names are presented in all capital letters.

[0024] The assemblies and methods described herein are useful when dispensing an adhesive in a molten form onto a substrate. The adhesive to be dispensed is optionally a pressure-sensitive adhesive. In some embodiments, the adhesive to be dispensed has a composition that obviates the need to pre-apply a primer onto the substrate. Eliminating the primer treatment step saves time and cost and provides significant convenience to the user.

[0025] Advantageously, the assemblies and methods provided can use a filament adhesive. A filament adhesive is an adhesive provided in a continuous filamentous configuration. The filament adhesive preferably has a uniform cross-section. Advantageously, the filament adhesive can be continuously supplied from a spool into a dispensing device such as a dispensing head.

[0026] A particularly useful filament adhesive has a core-sheath filament configuration as described in co-pending U.S. Provisional Patent Application No. 62 / 633,140 (Nyaribo et al.). A core-sheath filament material has a configuration in which a first material (i.e., the core) is surrounded by a second material (i.e., the sheath). Preferably, the core and the sheath are concentric and share a common longitudinal axis. The ends of the core need not be surrounded by the sheath.

[0027] An exemplary filament adhesive is shown in FIG. 1 and will hereinafter be referred to by the numeral 100. The core-sheath filament adhesive 100 includes an adhesive core 102 and a non-tacky sheath 104. The adhesive core 102 is a pressure-sensitive adhesive at ambient temperature. As shown, the core 102 has a cylindrical outer surface 106, and the sheath 104 extends around the outer surface 106 of the core 102. It should be understood that the core-sheath filament adhesive 100 generally has a circular cross-section as shown herein, but other cross-sectional shapes (e.g., square, hexagonal, or multi-lobed) are also possible.

[0028] Advantageously, the non-stick sheath 104 prevents the filament adhesive 100 from sticking to itself, thereby enabling convenient storage and handling of the filament adhesive 100 on the spool.

[0029] The diameter of the core-sheath filament is not particularly limited. Factors affecting the selection of the filament diameter include size constraints on the adhesive dispenser, the desired adhesive throughput, and the accuracy requirements for adhesive application. The core-sheath filament can have an average diameter of from 1 millimeter to 20 millimeters, from 3 millimeters to 13 millimeters, from 6 millimeters to 12 millimeters, or in some embodiments, an average diameter less than, equal to, or greater than 1 millimeter, 2 millimeters, 3 millimeters, 4 millimeters, 5 millimeters, 6 millimeters, 7 millimeters, 8 millimeters, 9 millimeters, 10 millimeters, 11 millimeters, 12 millimeters, 13 millimeters, 14 millimeters, 15 millimeters, 16 millimeters, 17 millimeters, 18 millimeters, 19 millimeters, or 20 millimeters. The filament adhesive 100 can be a stock item and can be provided in any length suitable for the application.

[0030] The dispensing methods described herein provide many potential technical advantages, at least some of which are unexpected. These technical advantages include retention of adhesive properties after dispensing, low volatile organic compound (VOC) properties, avoidance of die cutting, design flexibility, realization of complex non-planar bonding patterns, printing onto thin and / or delicate substrates, and printing onto irregular and / or complex topologies.

[0031] The core-sheath filament adhesives according to the present disclosure can be made using any known method. In an exemplary embodiment, these filament adhesives are made by extruding a molten polymer through a coaxial die. The technical details, options, and advantages regarding the core-sheath filament adhesives described above are explained in U.S. Patent Application No. 62 / 633,140 (Nyaribo et al.).

[0032] FIG. 2 shows a dispensing head 150 having a configuration for receiving, melting, mixing, and dispensing the filament adhesive 100 of FIG. 1. The dispensing head 150 includes a barrel 152 and a rotatable screw 154 received therein. A gearbox 156 and a motor 158 are operatively connected to the screw 154, and an alignment wheel 160, which can be electric, is mounted on a side surface of the barrel 152 where the filament is guided into the dispensing head 150. Further details regarding each of these components are as follows.

[0033] The barrel 152 has a configuration of a barrel used in a single-screw extruder. The barrel 152 has a cylindrical inner surface 170 and engages with the screw 154 in an enclosing relationship. The inner surface 170 terminates at an outlet 172 at the distal end of the barrel 152. The outlet 172 is generally circular, but can also be rectangular or have any other suitable shape. The barrel 152 includes one or more (not visible) embedded heating elements for heating the inner surface 170 during the dispensing operation to melt the filament adhesive. Optionally, the inner surface 170 of the barrel 152 can be grooved or otherwise textured to increase the friction between the barrel 152 and the extruded adhesive.

[0034] Referring again to FIG. 2, an inlet 174 extends through the upper surface of the barrel to receive the filament adhesive. As further illustrated, the inlet 174 includes a front sidewall 176 that defines an inclined nip point at which the front sidewall 176 merges with the outer surface of the screw 154. Advantageously, the inclined nip point prevents the filament adhesive from breaking when the filament adhesive is drawn into the barrel 152. The inclined nip point is part of a robust supply mechanism that enables the continuous supply of the filament adhesive into the barrel 152 without the need for operator supervision.

[0035] The drive mechanism for the dispensing head 150 is provided by a gearbox 156 and a motor 158. In some embodiments, the dispensing head 150 includes a control unit that enables adjustment of the speed and / or torque of the rotatable screw 154. In some embodiments, the motor 158 is a servo motor. The servo motor is advantageous because it can provide a high degree of torque over a wide range of rotational speeds.

[0036] As shown, the inlet 174 generally has an inverted funnel shape, and the cross-sectional area of the inlet 174 increases as it approaches the screw 154. The inlet 174 has one or more sidewalls, such as the front sidewall 176 as shown. The front sidewall 176 can be planar or curved. When viewed laterally, at least a portion of the front sidewall 176 extends at an acute angle with respect to the longitudinal axis of the screw 154. This acute angle, which facilitates the supply of the filament adhesive, can be 10 degrees to 70 degrees, 18 degrees to 43 degrees, 23 degrees to 33 degrees, or, in some embodiments, less than, equal to, or greater than 10 degrees, 13 degrees, 15 degrees, 17 degrees, 20 degrees, 22 degrees, 25 degrees, 27 degrees, 30 degrees, 32 degrees, 35 degrees, 37 degrees, 40 degrees, 42 degrees, 45 degrees, 47 degrees, 50 degrees, 53 degrees, 55 degrees, 57 degrees, 60 degrees, 65 degrees, or 70 degrees.

[0037] Figure 3 shows a top view of barrel 152 showing further details regarding the shape of inlet 174. Inlet 174 includes an outer inlet 175 and a hidden surface extending from outer inlet 175 and shown in dashed lines. As can be seen from Figure 3, the front wall 176 is not planar and has a complex compound curvature. The curved surface of inlet 174, including front wall 176, defines a recess within the inner surface 170 of barrel 152 as a whole to accommodate the filament adhesive when the filament adhesive is being supplied. As a whole, inlet 174 can extend along 10 percent to 40 percent, 15 percent to 35 percent, 20 percent to 30 percent of the nominal screw length, or, in some embodiments, less than, equal to, or greater than 10 percent, 12 percent, 15 percent, 17 percent, 20 percent, 22 percent, 25 percent, 27 percent, 30 percent, 32 percent, 35 percent, 37 percent, or 40 percent of the nominal screw length.

[0038] The recess surrounded by inlet 174 can extend both axially and circumferentially with respect to screw 154 as shown here. By providing space for the filament adhesive to move within barrel 152, the recess reduces the likelihood that the flights of rotatable screw 154 will cut the filament adhesive during operation of dispensing head 150. The reason it is disadvantageous for it to be cut is that due to the breakage of the filament, the dispensing process is interrupted and the operator needs to manually reinsert the filament adhesive into dispensing head 150 before restarting the process.

[0039] Figures 4 and 5 show the features of screw 154 in more detail. Screw 154 includes, at one end, a shank 180 for connection to a drive mechanism. Shank 180 is connected to a shaft 182 having a diameter that gradually increases along its length. Spiral flights 184 extend around shaft 182 for transporting the molten material in the forward direction when screw 154 rotates within barrel 152.

[0040] Proximally to the location where the filament adhesive is supplied into dispensing head 150, as also shown in the cross-sectional view of FIG. 5, a notch 188 is provided in helical flight 184, providing gripping lug 186. Gripping lug 186 provides an additional edge that captures the continuous filament adhesive passing through inlet 174 and actively draws it into barrel 152. This is a significant advantage over supply mechanisms that require pushing the adhesive into the supply zone and risk inducing buckling and twisting of the filament adhesive. Gripping lug 186 can extend over nominally 1 percent to 30 percent, 3 percent to 25 percent, 5 percent to 20 percent of the screw length, or, in some embodiments, 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, 6 percent, 7 percent, 8 percent, 9 percent, 10 percent, 11 percent, 12 percent, 13 percent, 14 percent, 15 percent, 16 percent, 17 percent, 18 percent, 19 percent, 20 percent, 22 percent, 25 percent, 27 percent, or less than, equal to, or greater than 30 percent of the nominal screw length.

[0041] On the opposite end of the screw 154, a mixing section 190 is disposed. The mixing section 190 includes a plurality of mixing elements (here, cylindrical posts 192). However, the mixing section 190 can also be represented in other configurations not shown in FIG. 4. Other screw features that can be employed as mixing elements include grooved cylinders (such as those found in Maddock mixers), screw sections with high-density flights having cross-cuts (such as those found in Saxton mixers), or any of a variety of known post patterns including those used in pineapple mixers. Optionally, posts or pins can be disposed on the inner sidewall of the barrel 152 to assist in the mixing process, in which case cross-cuts may be present within the flights of the screw 154 to avoid interference. Also, there may be openings that serve to disperse or distribute the adhesive composition within the barrel, and these can also function as mixing elements.

[0042] The length of the mixing section 190 is not particularly limited and can depend on various factors, including the adhesive composition being extruded and the supply rate of the filament adhesive. The mixing section 190 can be nominally 5 percent to 30 percent, 7 percent to 25 percent, 8 percent to 20 percent of the screw length, or in some embodiments, less than, equal to, or greater than 5 percent, 6 percent, 7 percent, 8 percent, 9 percent, 10 percent, 11 percent, 12 percent, 13 percent, 14 percent, 15 percent, 16 percent, 17 percent, 18 percent, 19 percent, 20 percent, 22 percent, 25 percent, 27 percent, 30 percent, or 35 percent of the nominal screw length.

[0043] For the effective melting, mixing, and dispensing of the filament adhesive within a relatively compact enclosure, the nominal ratio of screw length to screw diameter can be 8:1 to 20:1, 9:1 to 17:1, 10:1 to 14:1, or, in some embodiments, less than, equal to, or greater than 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, or 20:1.

[0044] The dispensing head 150 provided can exhibit a significant throughput. In a preferred embodiment, the dispensing head can dispense the adhesive composition at a throughput of at least 3 kg / hour, at least 4 kg / hour, at least 5 kg / hour, at least 6 kg / hour, at least 7 kg / hour, or at least 8 kg / hour.

[0045] FIG. 6 presents a schematic view of a dispensing system 228 that includes a dispensing head 250 equipped with a mount for attachment to the end of a movable arm 230. The dispensing head 250 can have features similar to those of the dispensing head 150 as described above. The movable arm 230 is mounted to a table 232 and can have any number of joints that allow the dispensing head 250 to translate and rotate with up to six degrees of freedom. The movable arm 230 enables the dispensing head 250 to dispense the adhesive composition with accuracy and reproducibility over a wide range of locations relative to the table 232.

[0046] Optionally, and as shown in the figure, the dispensing system 228 further includes a filament adhesive 234 for continuous supply within the dispensing head 250 as shown in FIG. 6. The filament adhesive 234 can be continuously unwound from a spool 236 as shown. It should be understood that the location of the spool 236 relative to the other components of the dispensing system 228 is not critical and can be mounted in a convenient location. The spool 236 can be fixed to the table 232 or to a structure on the table.

[0047] In various embodiments, the portion of the spool 236 that contacts the filament adhesive 234 can have structural features that assist in the conveyance of the filament adhesive 234. For example, that portion of the spool 236 can include a spiked region, a sticky surface, or any other feature that assists in the payout of the filament adhesive 234. Although not shown in FIG. 6, the filament adhesive 234 can also be guided along a channel or pipe that extends between the spool 236 and the dispensing head 250. This channel or pipe can include a low-friction (e.g., fluoropolymer) surface to smooth the movement of the filament adhesive 234 therein and prevent twisting.

[0048] The dispensing head 250 of FIG. 6 is shown dispensing an adhesive composition 238 in hot melt form onto the bonding surface of a substrate 240. The substrate 240 need not be limited and can be, for example, an industrial part for adhesively connecting to an assembly. Optionally, by mounting the substrate 240 on the table 232, a spatial reference point for positioning the dispensing head 250 can be provided. This can be particularly useful in an automated process that uses a computer to control the position and orientation of the dispensing head 250.

[0049] The dispensing of the adhesive composition 238 can be automated or semi-automated and thus requires little or no intervention by a human operator. One advantage of the provided method is that it is possible to dispense the adhesive composition 238 onto the substrate 240 in accordance with instructions provided by a computer and based on a predetermined pattern. The predetermined pattern can be two-dimensional (along a planar surface) or three-dimensional (along a non-planar surface). The predetermined pattern can be represented by a digitized model on a computer that allows the predetermined pattern to be customized for any of a wide variety of substrates.

[0050] Here, the adhesive composition 238 is a thermoplastic elastomer that remains flowable even after being dispensed. In certain applications, this molten adhesive conforms to the shape of the protruding or recessed features of the substrate 240 for improved mechanical retention. Optionally, the protruding or recessed features may have one or more undercuts to further enhance the strength of the bond.

[0051] In FIG. 6, the bonding surface of the substrate 240 has a ribbed configuration, allowing the adhesive composition 238 to flow into and penetrate the recessed areas between the ribs. By providing an increased surface area for bonding, this configuration results in a significantly stronger bond compared to a planar bonding configuration. When the adhesive composition 238 is cooled to ambient temperature, its cohesive forces increase and the material behaves as a pressure - sensitive adhesive.

[0052] In some embodiments, the bonded substrate 240 can be placed in direct contact with the corresponding article or assembly to complete the bond. Such an operation can be manual, semi - automated, or fully automated. If the bonded substrate 240 is not ready for bonding, its exposed dispensing adhesive surface can be covered with a release liner to maintain its tackiness. Depending on the application, the bonded substrate can then be packaged, stored, or conveyed to a subsequent manufacturing process.

[0053] Further improvements are also possible. Although not shown in the drawings, one or more additional heating elements can be provided to preheat the filament adhesive before it enters the heated barrel of the dispensing head. Preheating the adhesive may require less heat to melt it, potentially allowing for a shorter screw / barrel. The additional heating elements can be placed on peripheral components or on a portion of the dispensing head itself. In some embodiments, the alignment wheel 160 incorporates an additional heating element.

[0054] The dispensed adhesive can also be applied to another adhesive article. For example, it can be used to make a skin adhesive on a foam tape. The dispensed material can be foamed or non-foamed. Non-foamed adhesive compositions may be preferred because they can be reprocessed more easily without loss of performance. On the other hand, foamed adhesives can be cost-effective and useful for bonding to rough or other non-uniform surfaces. Optionally, the filament adhesive is foamed by incorporating glass bubbles or other foaming components into the filament adhesive composition.

[0055] The potential uses for the provided dispensing head can extend beyond those in the present disclosure, and some are described in the co-pending U.S. Provisional Patent Application No. 62 / 810,221 (Napierala et al.), filed on the same day as this application.

[0056] There are many advantages to dispensing pressure-sensitive adhesives using the provided dispensing head. The deployment of the dispensing head in a dispensing system makes the loading and replacement of consumables easier, especially in an automated process, by using the filament adhesive wound on a spool as a roll product. The provided screw configuration is also well-suited for using PSA filament adhesives, which have a relatively soft viscoelastic consistency and are difficult to supply into conventional dispensers. Unlike conventional dispensers, the provided dispensing head does not require a guide structure for supplying the filament adhesive.

[0057] The dispensing head provided is also modular, enabling it to be used with any of a variety of customized nozzles, providing the desired accuracy in adhesive placement. The dispensing head provided may enable the adhesive to be dispensed in a customized manner. For example, it is possible to dispense the adhesive onto the substrate in dots, stripes, or other discontinuous patterns. As described above, a suitable coating pattern need not be planar and can be disposed on a complex and irregular bonding surface. Nozzles useful for these purposes are commercially available from various suppliers, including Nordson Corporation (Westlake, OH).

[0058] In some embodiments, the dispensing head includes a nozzle that includes at least one actuator that can regulate or block the flow of the adhesive composition, typically at or near the opening through which the adhesive composition is ejected from the nozzle. Such an actuator can be actuated manually or automatically and can be located inside or outside the nozzle. When disposed externally, such an actuator can include a structure that not only regulates or blocks the flow but also serves to wipe the discharge opening of the nozzle.

[0059] For example, FIG. 7 shows an end actuator 470 that uses a rocking arm wiper blade 472 having a configuration that serves to block the flow to maintain pressure and also helps to avoid dripping from the device when the dispensing operation is stopped.

[0060] In some embodiments, the actuator has a spring mechanism that allows the flow of the adhesive composition only when the internal pressure exceeds a certain minimum value. This feature can be useful in managing pressure and avoiding long, gradual flow rate changes typically undesirable when switching the dispenser on and off.

[0061] Figure 8 shows yet another embodiment in which the dispensing head 350 has a secondary flow path 360 disposed outside the cylindrical inner wall of the barrel 352, enabling the path of the molten adhesive composition to be directed back to an upstream location along the barrel 352. The advantage derived from this is the ability to maintain a steady internal pressure within the barrel by continuing to operate the dispenser even when the flow through the nozzle is stopped. In the recirculation mode, the supply of filamentous adhesive can be tapered off according to those skilled in the art to manage a consistent flow of adhesive through the barrel.

[0062] The recirculation function can be facilitated by a manual, semi-automatic, or automatic actuator capable of assisting in the start and / or stop of recirculation within the dispensing head. Optionally, and as shown in the figure, the dispensing head can include a mechanical, electromechanical, hydraulic, or pneumatic valve that redirects the flow from the outlet of the dispensing head to the secondary flow path.

[0063] The secondary flow path need not be external to the cylindrical inner wall of the barrel. For example, the screw itself may have a configuration that enables the adhesive composition to be recirculated around the rotating flights of the screw when the adhesive composition cannot flow through the outlet. In that case, the outlet actuator can be used to switch recirculation on and off.

[0064] The provided dispensing head is highly efficient and lightweight. In some embodiments, the dispensing head has a total weight of up to 10 kg, up to 8 kg, or up to 6 kg. Practical examples of the dispensing head are lightweight and compact enough to be attached to lightweight robotic arms currently used in manufacturing facilities. Since the screw and barrel are configured to provide excellent mixing within a short residence time in the melting zone, waste is also reduced and the risk of thermal degradation of the adhesive is minimized.

[0065] Although not intended to be exhaustive, further embodiments of the provided filament adhesive dispensers, systems, and methods are shown below.

[0066] 1. A dispensing head for a filament adhesive, comprising a barrel including one or more heating elements, an inlet extending through a side surface of the barrel for receiving the filament adhesive, the inlet including an inclined nip point that prevents the filament adhesive from breaking when the filament adhesive is drawn into the barrel, an outlet at a distal end of the barrel for dispensing the filament adhesive in a molten form, and a rotatable screw received within the barrel, the rotatable screw optionally including at least one mixing element.

[0067] 2. The dispensing head of embodiment 1, wherein the inclined nip point is partially defined by a front side wall surface of the inlet that extends at an acute angle with respect to the longitudinal axis of the rotatable screw.

[0068] 3. The dispensing head of embodiment 2, wherein the acute angle is between 13 degrees and 53 degrees.

[0069] 4. The dispensing head of embodiment 3, wherein the acute angle is between 18 degrees and 43 degrees.

[0070] 5. The dispensing head of embodiment 4, wherein the acute angle is between 23 degrees and 33 degrees.

[0071] 6. The dispensing head of any one of embodiments 2 - 5, wherein the inlet extends along 10 percent to 40 percent of the nominal screw length of the rotatable screw.

[0072] 7. The dispensing head of embodiment 6, wherein the inlet extends along 15 percent to 35 percent of the nominal screw length of the rotatable screw.

[0073] 8. The dispensing head of embodiment 7, wherein the inlet extends along 20 percent to 30 percent of the nominal screw length of the rotatable screw.

[0074] 9. A dispensing head according to any one of Embodiments 1 to 8, wherein at least one mixing element includes a plurality of posts disposed on a rotatable shaft.

[0075] 10. A dispensing head according to any one of Embodiments 1 to 9, wherein the rotatable screw further includes a supply element adjacent to the inlet, and the supply element includes a plurality of gripping lugs.

[0076] 11. A dispensing head according to any one of Embodiments 1 to 10, wherein the rotatable screw has a length: diameter ratio of 8:1 to 20:1.

[0077] 12. The dispensing head of Embodiment 11, wherein the rotatable screw has a length: diameter ratio of 9:1 to 17:1.

[0078] 13. The dispensing head of Embodiment 12, wherein the rotatable screw has a length: diameter ratio of 10:1 to 14:1.

[0079] 14. A dispensing head according to any one of Embodiments 1 to 13, further comprising a drive mechanism operably connected to the rotatable screw.

[0080] 15. A dispensing head according to any one of Embodiments 1 to 14, wherein the inlet includes at least one side wall surface providing a recess for accommodating a filament adhesive, and the recess extends along both the axial direction and the circumferential direction with respect to the rotatable screw.

[0081] 16. A dispensing head according to any one of Embodiments 1 to 15, wherein the total weight of the dispensing head is 10 kg or less.

[0082] 17. A dispensing system comprising a dispensing head according to any one of Embodiments 1 to 16 and a filament adhesive.

[0083] 18. The dispensing system of embodiment 17, wherein the filament adhesive comprises a core-sheath adhesive.

[0084] 19. The dispensing system of embodiment 18, wherein the core-sheath adhesive has a pressure-sensitive adhesive core that is viscoelastic at ambient temperature.

[0085] 20. The dispensing system of embodiment 18 or 19, wherein the core-sheath adhesive has a sheath that is non-tacky at ambient temperature.

[0086] 21. The dispensing system of any one of embodiments 18 to 20, wherein the core-sheath adhesive has a diameter of 1 millimeter to 20 millimeters.

[0087] 22. The dispensing system of embodiment 21, wherein the core-sheath adhesive has a diameter of 3 millimeters to 13 millimeters.

[0088] 23. The dispensing system of embodiment 22, wherein the core-sheath adhesive has a diameter of 6 millimeters to 12 millimeters.

[0089] 24. The dispensing system of any one of embodiments 17 to 23, wherein the dispensing head is connected to a table, and either the dispensing head or the table is movable relative to the other.

[0090] 25. The dispensing system of embodiment 24, further comprising a movable arm connected to the table, and the dispensing head is connected to the distal end of the movable arm.

[0091] 26. The dispensing system of embodiment 24 or 25, wherein the movement of the dispensing head or the table is controllable by a computer.

[0092] 27. The dispensing system of any one of embodiments 17 to 26, further comprising one or more external heating elements for preheating the filament adhesive before it is received into the inlet.

[0093] 28. The dispensing system according to any one of Embodiments 17 to 27, further comprising a molding die removably connected to the pouring outlet.

[0094] 29. The dispensing system according to any one of Embodiments 17 to 28, further comprising a nozzle actuator capable of adjusting the flow of the molten filament adhesive from the pouring outlet.

[0095] 30. A method of dispensing a filament adhesive from a dispensing head comprising a heated barrel for receiving a rotating screw, the method comprising supplying the filament adhesive through an inlet of the heated barrel, the inlet including an inclined nip point that avoids breakage of the filament adhesive as the filament adhesive is drawn into the heated barrel, melting the filament adhesive in the heated barrel to provide a molten adhesive, optionally mixing the molten adhesive using at least one mixing element disposed on the rotating screw, and dispensing the molten adhesive through an outlet at a distal end of the heated barrel.

[0096] 31. The method of Embodiment 30, wherein the filament adhesive is a core-sheath filament adhesive.

[0097] 32. The method of Embodiment 30 or 31, wherein the molten adhesive is a pressure-sensitive adhesive at ambient temperature.

[0098] 33. The method according to any one of Embodiments 30 to 32, further comprising preheating the filament adhesive before the filament adhesive enters the heated barrel.

[0099] 34. The method according to any one of Embodiments 30 to 33, further comprising using a nozzle actuator connected to the outlet to adjust the flow of the molten adhesive from the outlet.

[0100] 35. A method according to any one of embodiments 30 to 34, wherein the molten adhesive is dispensed onto a substrate.

[0101] 36. A method according to embodiment 35, wherein the molten adhesive can be dispensed at a predetermined location on the substrate by either the dispensing head being movable relative to the substrate and / or the substrate being movable relative to the dispensing head.

[0102] 37. A method according to embodiment 35 or 36, wherein the movement of the dispensing head or the substrate is controlled by a computer.

[0103] 38. A method according to any one of embodiments 35 to 37, wherein the dispensing head is connected to the distal end of a movable arm that is directly or indirectly connected to the substrate.

[0104] 39. A method according to any one of embodiments 30 to 38, wherein the molten adhesive is dispensed at a rate of at least 2 kg per hour.

[0105] 40. A method according to embodiment 39, wherein the molten adhesive is dispensed at a rate of at least 3 kg per hour.

[0106] 41. A method according to embodiment 40, wherein the molten adhesive is dispensed at a rate of at least 4 kg per hour.

Examples

[0107] The objects and advantages of the present disclosure are further illustrated by the following non-limiting examples, but it should be understood that the specific materials cited in these examples and their amounts, as well as other conditions and details, do not unduly limit the present disclosure.

[0108] Unless otherwise specified, all parts, percentages, ratios, etc. in the examples and other parts of this specification are by weight.

Table 1

[0109] Test method: 90° Peel Strength Test: A strip of the sample adhesive, 12.5 mm wide × 1.5 mm thick × 125 mm long, was dispensed directly onto the substrate. The sample adhesive was allowed to cool to room temperature (25 °C) for 10 minutes. Next, an aluminum foil was manually laminated onto the exposed surface of the sample adhesive by passing a 6.8 kg steel roller twice in each direction. The bonded sample was left at 25 °C and 50% humidity for 4 hours. Using a tensile testing machine equipped with a 50 kN load cell, a peel test was carried out at room temperature at a separation speed of 30.5 cm / min. The average peel force was recorded and used to calculate the average peel adhesion strength in units of Newton / cm.

[0110] Static Shear Strength Test: A strip of the sample adhesive, 12.5 mm wide × 1.5 mm thick × 25.4 mm long, was dispensed directly onto an aluminum coupon in a state where the length of the strip spanned the width of the aluminum coupon. The aluminum coupon was fabricated by cutting an anodized aluminum 5005 - H34 Code990MX (thickness 1.6 mm, width 101.6 mm, length 304.8 mm, obtained from Lawrence&Frederic Inc (Streamwood, Illinois, United States)) into small pieces, 25.4 mm wide × 50 mm long, and a 6 - mm hole was provided at the center of the short edge for hanging the bonded sample on the test hook. After cooling to room temperature for 10 minutes, an aluminum foil strip, 25.4 mm wide × 120 mm long, was attached to the exposed surface of the sample adhesive by manually passing a 6.8 kg steel roller twice in each direction. The tail of the foil was looped and stapled. The bonded sample was subjected to a standing time of 4 hours at 25 °C and 50% humidity. The test panel was vertically attached to the hook at room temperature, and a 250 - gram weight was attached to the loop portion of the aluminum foil. The hanging time until the sample dropped from the plastic substrate was recorded. If no breakage occurred, the test was stopped after 72 hours.

[0111] Self - adhesion test: During storage, it is desirable that the core sheath filaments do not fuse or adhere together integrally. The sheath material provides a non - adhesive surface that coats the core adhesive. To determine whether a candidate sheath material meets the requirement of being "non - sticky", a self - adhesion test was performed on a film of the pure sheath material. Coupons (25 millimeters × 75 millimeters × 0.8 millimeters) were cut out. For each material, two coupons were stacked on top of each other and placed on a flat surface in an oven. On top of the two coupons, a 750 - gram weight (43 - millimeter diameter, flat bottom) was placed such that the weight was centered on the film. The oven was heated to 50 degrees Celsius, and the samples were left under those conditions for 4 hours and then cooled to room temperature. A static T - peel test was used to evaluate pass / fail. One end of one coupon was fixed to a stationary frame, and a 250 - gram weight was attached to the corresponding end of the other coupon. If the film was flexible and began to peel, they formed a T - shape. If it was possible to separate the two coupons with this static 250 - gram load within 3 minutes after applying the weight to the second coupon, the sample was considered a pass and was considered non - sticky. Otherwise, if the two coupons remained adhered, it was considered a fail.

[0112] Example 1 (EX1): Step 1: Preparation of acrylic resin Two sheets of ethylene / vinyl acetate film (obtained from Consolidated Thermoplastics Co. (Schaumburg, IL, United States)) having a vinyl acetate content of 6% and a thickness of 0.0635 millimeters (0.0025 inches) were heat-sealed at their side edges and bottom using a liquid bag-making and filling machine to form a rectangular tube 5 cm (1.97 inches) wide. This tube was then filled with a monomer mixture of 89.8% EHA, 10% AA, 0.05% IOTG, and 0.15% Irg651. The filled tube was then heat-sealed at the top and at regular intervals across the direction along the length of the tube to form individual pouches 18 cm × 5 cm in size, each containing 26 grams of the composition. These pouches were placed in a water bath maintained at about 21°C to 32°C and the composition was cured by exposing first one side and then the opposite side to ultraviolet radiation at an intensity of about 4.5 milliwatts per square centimeter for 8.3 minutes. This radiation was supplied from a lamp with about 90% of the emitted light having a wavelength of 300 to 400 nanometers (nm).

[0113] Step 2: Preparation of the sample adhesive composition A core-sheath filament was formed by coextruding the acrylic resin (produced in Step 1) and Nucrel coaxially. Nucrel was the outer sheath material and was 6.5% by mass of the total adhesive composition. The filament diameter was 8 millimeters. The acrylic resin was fed into the coaxial die at 163 degrees Celsius through a 40-millimeter twin-screw rotating at 200 RPM. Nucrel was fed into the die at 193 degrees Celsius from a 19-millimeter twin-screw rotating at 9 RPM. This filament adhesive was wound onto a roll and stored for dispensing. Nucrel was subjected to a self-adhesion test and passed.

[0114] Step 3: Dispensing of the sample adhesive The dispensing temperature was set at 180 degrees Celsius. The screw speed regarding the test sample was set at 300 RPM for the preparation of test pieces, and was changed as shown in Table 3 for throughput measurement.

Table 2

[0115] The throughput of the dispenser was measured by collecting the material for 60 seconds and weighing the dispensed material.

[0116] In addition to throughput measurement, the bonding performance of the adhesive was evaluated using Adhesive EX1. The substrate was coated by manually moving it at 25 millimeters per second under the dispensing head. The gap between the substrate and the nozzle during dispensing was set at 1 millimeter. For substrates of aluminum (anodized aluminum 5005 - H34 Code990MX with a thickness of 1.6 mm, a width of 101.6 mm, and a length of 304.8 mm, obtained from Lawrence&Frederic Inc (Streamwood, Illinois, United States)) and wood (S4S poplar with a thickness of 12.7, a width of 76.2 mm, and a length of 300 mm), the peel strength test was carried out as received without any additional cleaning process or primer treatment process. Then, the bonded test pieces were evaluated for 90° peel strength and static shear strength. The results are shown in Table 3.

[0117] Comparative Example 1 (CE1) For comparison with EX1, an acrylic foam tape having an equivalent composition was selected. As substrates representative of both the recommended and non-recommended substrates for acrylic foam tapes, aluminum and wood were selected. Porous and irregular wood substrates are generally not recommended for bonding acrylic foam tapes because of their limited bonding performance. Acrylic foam tape 5665 obtained from 3M Company (St. Paul, MN, United States) was cut to the sizes described below and subjected to the 90° peel strength and static shear strength tests as described above. With some modifications to the test method regarding sample preparation, it was defined as follows: A strip 12.5 millimeters wide × 125 millimeters long was adhered to an aluminum foil strip with the non-liner side attached to the aluminum strip. The release liner was removed and the liner side was attached to the target substrate by manually passing a 6.8-kilogram steel roller twice in each direction. Peel strength tests were performed on substrates of aluminum (anodized aluminum 5005-H34 Code 990MX, 1.6 mm thick, 101.6 mm wide, 304.8 mm long, obtained from Lawrence & Frederic Inc (Streamwood, Illinois, United States)) and wood (S4S poplar, 12.7 thick, 76.2 mm wide, 300 mm long) as received without any additional cleaning or primer treatment steps. The results are presented in Table 3.

Table 3

[0118] Manufacture of screws: A 25.4 cm (10.0 inch) head screw 154 with a diameter of 1.91 cm (0.75 inch), as shown in Figure 4, was machined within a computer numerical controlled (CNC) three-axis vertical end mill. The machining process was to be carried out on a solid block of aluminum using two operations. In the first step, the upper half of the screw was machined looking down the screw axis. The partially milled block was inverted, and then the remaining half of the screw was machined.

[0119] Production of the barrel: A barrel 152 of 22.9 cm (9.0 inch) × 5.08 cm (2.0 inch) × 5.08 cm (2.0 inch), as shown in Figure 2, was machined within a CNC three-axis vertical end mill. The machining process was to be carried out on a solid block of aluminum. The central cavity was first drilled with a drill bit and then reamed to 1.92 cm (0.7574 inch). The inclined inlet 174 was first milled perpendicular to the barrel axis, and then a second milling operation was performed at an angle offset 28 degrees from parallel to the barrel axis.

[0120] Production of the robot mounting bracket: A robot mounting bracket with a thickness of 1.27 cm (0.5 inch) was machined from aluminum. The robot mounting bracket was characterized by tapped holes for mounting the alignment wheel motor. Two sets of through holes were arranged for connection to the gearbox 156 mounting bracket and the barrel mounting bracket. Further, holes and circular recesses were made for attachment to a UR-10 robot arm manufactured by Brass Corp (Eden Prairie, MN, United States).

[0121] Production of the gearbox mounting bracket: The gearbox 156 mounting bracket with a thickness of 1.27 cm (0.5 inches) was machined from aluminum. The gearbox 156 mounting bracket was characterized by holes for connection to the outer surface of the gearbox.

[0122] Fabrication of the barrel mounting bracket: The barrel 152 mounting bracket with a thickness of 1.27 cm (0.50 inches) was machined from aluminum. The barrel 152 mounting bracket was characterized by holes for connection to the outer surface of the gearbox 156.

[0123] Fabrication of the dispensing nozzle: The dispensing nozzle 172 with a threaded end was machined. The threaded end was assumed to have a hole of 0.64 cm (0.25 inches) that is connected to a slot opening of 0.1 cm (3.94E - 2 inches) × 1.27 cm (0.5 inches).

[0124] Fabrication of the alignment wheel: The alignment wheel 160 with a thickness of 2.54 cm (1.00 inches) having a connecting shaft was machined from aluminum. The outer radius of curvature of the alignment wheel was 0.5 cm (0.196 inches).

[0125] Fabrication of the alignment wheel heating block: The alignment wheel 160 heating block with a thickness of 1.20 cm was machined from aluminum. This block was assumed to have two slots for attaching an insertion heating cartridge obtained from McMaster - Carr (Elmhurst, IL. United States), Elmhurst, IL. United States.

[0126] Fabrication of the heat shield: Four thermal shields (left, right, top, and bottom) with a thickness of 0.16 cm were machined from a glass mica ceramic plate obtained from McMaster-Carr (Elmhurst, IL, United States).

[0127] Assembly of the dispensing head: Servo motor 158 of model SVL-204 obtained from Automation Direct (Cumming, GA, United States) was connected to a 10:1 gearbox. Screw 154 was inserted into barrel 152, and thrust bearings with washers on each side were placed on the screw shaft. Then, the assembly of the barrel and the screw was inserted through the barrel 152 mounting bracket with the thrust bearings and washers placed inside the barrel mounting bracket. Gearbox 156 was mounted on the gearbox bracket. The shaft of gearbox 156 and screw 154 were connected with a motor shaft coupler. Both the barrel 152 bracket and the gearbox 156 bracket were connected to the motor mounting bracket. The dispensing head was mounted on the robot arm. The nozzle was screwed into the barrel. All electrical connections were made. The barrel was heated with three 100-watt heating cartridges embedded in the barrel. The temperature was monitored with a J-type thermocouple. The barrel was insulated with a ceramic plate fastened to the outside of the barrel.

[0128] All reference documents, patent documents, or patent applications cited in the above patent application are hereby incorporated by reference in their entirety in a consistent manner. In case of any inconsistency or contradiction between a part of the incorporated reference documents and this application, the information in the foregoing description shall prevail. The foregoing description is for enabling those skilled in the art to practice the disclosure described in the claims and should not be construed as limiting the scope of the present disclosure, which is defined by the claims and all their equivalents.

Claims

1. A dispensing head for a filament adhesive, comprising: a barrel including one or more heating elements; an inlet extending through a side surface of the barrel for receiving the filament adhesive, the inlet including an inclined nip point that prevents the filament adhesive from breaking when the filament adhesive is drawn into the barrel; an outlet at a distal end of the barrel for dispensing the filament adhesive in a molten form; a rotatable screw received within the barrel; and the inlet has a plurality of side walls including a front side wall; the inclined nip point is partially defined by a front side wall surface of the inlet that extends at an acute angle with respect to a longitudinal axis of the rotatable screw; the front side wall merges with an outer surface of the rotatable screw, and a cross-sectional area of the inlet increases as it approaches the rotatable screw; a dispensing head.

2. The dispensing head according to claim 1, wherein the acute angle is between 13 degrees and 53 degrees.

3. The dispensing head according to any one of claims 1 to 2, wherein the rotatable screw includes helical flights, and the inlet extends along 10 percent to 40 percent of a nominal screw length of the rotatable screw.

4. The dispensing head according to claim 3, wherein the rotatable screw further includes a supply element adjacent to the inlet, the supply element includes a plurality of gripping lugs, and the gripping lugs include notches provided in the helical flights.

5. The dispensing head according to any one of claims 1 to 4, wherein at least one mixing element is disposed on a rotatable shaft.

6. The dispensing head according to any one of claims 1 to 5, wherein the rotatable screw has a length: diameter ratio of 8:1 to 20:

1.

7. The dispensing head according to any one of claims 1 to 6, further comprising a drive mechanism operably coupled to the rotatable screw.

8. A dispensing system comprising the dispensing head according to any one of claims 1 to 7 and the filament adhesive.

9. The dispensing system according to claim 8, wherein the filament adhesive includes a core-sheath adhesive.

10. A method of dispensing a filament adhesive from a dispensing head comprising a heated barrel receiving a rotatable screw, Supplying the filament adhesive through an inlet of the heated barrel, the inlet including an inclined nip point that reduces shearing of the filament adhesive as the filament adhesive is drawn into the heated barrel; Melting the filament adhesive within the heated barrel to provide a molten adhesive; Mixing the molten adhesive; Dispensing the molten adhesive through an outlet at a distal end of the heated barrel, and The inlet has a plurality of sidewalls including a front sidewall; The inclined nip point is partially defined by a front sidewall surface of the inlet that extends at an acute angle to a longitudinal axis of the rotatable screw; The front sidewall merges with an outer surface of the rotatable screw, and a cross-sectional area of the inlet increases as it approaches the rotatable screw. Method.

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