Abstract:
A hot melt dispensing system includes a container for storing solid hot melt material, a hot press melter having a loading position for receiving solid hot melt material and a melting position for applying heat and pressure to liquefy the hot melt material, a feed system for transporting solid hot melt material from the container to the hot press melter and a dispensing system for administering the liquefied hot melt material.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/556,586, filed on Nov. 7, 2011 and entitled “PRE-MELTER”. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates generally to systems for dispensing hot melt adhesive. More particularly, the present disclosure relates to a melting system for preparing liquid hot melt adhesive. 
         [0003]    Hot melt dispensing systems are typically used in manufacturing assembly lines to automatically disperse an adhesive used in the construction of packaging materials such as boxes, cartons and the like. Hot melt dispensing systems conventionally comprise a material tank, heating elements, a pump and a dispenser. Solid polymer pellets are melted in the tank using a heating element before being supplied to the dispenser by the pump. Because the melted pellets will re-solidify into solid form if permitted to cool, the melted pellets must be maintained at temperature from the tank to the dispenser. This typically requires placement of heating elements in the tank, the pump and the dispenser, as well as heating any tubing or hoses that connect those components. Furthermore, conventional hot melt dispensing systems typically utilize tanks having large volumes so that extended periods of dispensing can occur after the pellets contained therein are melted. However, the large volume of pellets within the tank requires a lengthy period of time to completely melt, which increases start-up times for the system. For example, a typical tank includes a plurality of heating elements lining the walls of a rectangular, gravity-fed tank such that melted pellets along the walls prevents the heating elements from efficiently melting pellets in the center of the container. The extended time required to melt the pellets in these tanks increases the likelihood of “charring” or darkening of the adhesive due to prolonged heat exposure. 
       SUMMARY 
       [0004]    A hot melt dispensing system includes a container for storing solid hot melt material, a hot press melter having a loading position for receiving solid hot melt material and a melting position for applying heat and pressure to liquefy the hot melt material, a feed system for transporting solid hot melt material from the container to the hot press melter and a dispensing system for administering the liquefied hot melt material. 
         [0005]    A hot press melting apparatus includes a first heated plate, a second heated plate aligned with the first heated plate and having a drain and a perforated plate located between the first heated plate and the second heated plate for allowing liquefied hot melt material to pass through the perforated plate to the drain but preventing solid hot melt material from passing through the perforated plate. The first heated plate is spaced from the perforated plate by a first distance in an accelerated melting position, and the first heated plate is spaced from the perforated plate by a second distance greater than the first distance in a loading position. 
         [0006]    Solid hot melt material is melted using a melting device having opposed first and second heated plates. A method includes heating the first plate and the second plate, feeding the solid hot melt material to a region between the first plate and the second plate, pressing the first plate and the second plate together while heating the first and second plates to press the solid hot melt material against the first plate and the second plate to increase a melting rate of the solid hot melt material, and removing liquefied hot melt material from the second plate and the region between the first plate and the second plate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a schematic view of a system for dispensing hot melt adhesive. 
           [0008]      FIG. 2  is a schematic view of a hot press melter within the system of  FIG. 1 . 
           [0009]      FIG. 3A  is a perspective view of one embodiment of the hot press melter of  FIG. 2  in a loading position. 
           [0010]      FIG. 3B  is a perspective view of one embodiment of the hot press melter of  FIG. 2  in an accelerated melting position. 
           [0011]      FIG. 4  is a perspective view of another embodiment of part of the hot press melter of  FIG. 2 . 
           [0012]      FIG. 5  is a perspective view of one embodiment of a heated plate suitable for use in the hot press melter of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Conventional hot melt dispensing systems do not typically have short startup times. The system components generally need to be “warmed up” (heated to reach operating temperatures) before dispensing can commence. Additionally, the solid hot melt material to be dispensed must be heated to form a liquid so that it can flow through the system and be dispensed. In most systems, the solid hot melt material is added to a melting vessel, often as a large solid mass. In these systems, melting the solid hot melt material takes significant time. The invention described herein provides a melting system that can quickly liquefy hot melt material. 
         [0014]      FIG. 1  is a schematic view of system  10 , which is a system for dispensing hot melt adhesive. System  10  includes cold section  12 , hot section  14 , air source  16 , air control valve  17 , and controller  18 . In the embodiment shown in  FIG. 1 , cold section  12  includes container  20  and feed assembly  22 , which includes vacuum assembly  24 , feed hose  26 , and inlet  28 . In the embodiment shown in  FIG. 1 , hot section  14  includes melt system  30 , pump  32 , and dispenser  34 . Air source  16  is a source of compressed air supplied to components of system  10  in both cold section  12  and hot section  14 . Air control valve  17  is connected to air source  16  via air hose  35 A, and selectively controls air flow from air source  16  through air hose  35 B to vacuum assembly  24  and through air hose  35 C to motor  36  of pump  32 . Air hose  35 D connects air source  16  to dispenser  34 , bypassing air control valve  17 . Controller  18  is connected in communication with various components of system  10 , such as air control valve  17 , melt system  30 , pump  32 , and/or dispenser  34 , for controlling operation of system  10 . 
         [0015]    Components of cold section  12  can be operated at room temperature, without being heated. Container  20  can be a hopper for containing a quantity of solid adhesive pellets (solid hot melt material) for use by system  10 . Suitable adhesives can include, for example, a thermoplastic polymer glue such as ethylene vinyl acetate (EVA) or metallocene-based hot melt adhesives. Feed assembly  22  connects container  20  to hot section  14  for delivering the solid adhesive pellets from container  20  to hot section  14 . Feed assembly  22  includes vacuum assembly  24  and feed hose  26 . Vacuum assembly  24  is positioned in container  20 . Compressed air from air source  16  and air control valve  17  is delivered to vacuum assembly  24  to create a vacuum, inducing flow of solid adhesive pellets into inlet  28  of vacuum assembly  24  and then through feed hose  26  to hot section  14 . Feed hose  26  is a tube or other passage sized with a diameter substantially larger than that of the solid adhesive pellets to allow the solid adhesive pellets to flow freely through feed hose  26 . Feed hose  26  connects vacuum assembly  24  to hot section  14 . 
         [0016]    Solid adhesive pellets are delivered from feed hose  26  to melt system  30 . Melt system  30  can include a container (melter  46 , shown in  FIG. 2 ) and resistive heating elements (not shown) for melting the solid adhesive pellets to form a hot melt adhesive in liquid form (liquefied hot melt material). Melt system  30  can be sized to have a relatively small adhesive volume, for example about 0.5 liters, and configured to melt solid adhesive pellets in a relatively short period of time. Pump  32  is driven by motor  36  to pump hot melt adhesive from melt system  30  to dispenser  34  through supply hose  38 . Motor  36  can be an air motor driven by pulses of compressed air from air source  16  and air control valve  17 . Pump  32  can be a linear displacement pump driven by motor  36 . In the illustrated embodiment, dispenser  34  includes manifold  40  and module  42 . Hot melt adhesive from pump  32  is received in manifold  40  and dispensed via module  42 . Dispenser  34  can selectively discharge hot melt adhesive whereby the hot melt adhesive is sprayed out outlet  44  of module  42  onto an object, such as a package, a case, or another object benefiting from hot melt adhesive dispensed by system  10 . Module  42  can be one of multiple modules that are part of dispenser  34 . In an alternative embodiment, dispenser  34  can have a different configuration, such as a handheld gun-type dispenser. Some or all of the components in hot section  14 , including melt system  30 , pump  32 , supply hose  38 , and dispenser  34 , can be heated to keep the hot melt adhesive in a liquid state throughout hot section  14  during the dispensing process. 
         [0017]    System  10  can be part of an industrial process, for example, for packaging and sealing cardboard packages and/or cases of packages. In alternative embodiments, system  10  can be modified as necessary for a particular industrial process application. For example, in one embodiment (not shown), pump  32  can be separated from melt system  30  and instead attached to dispenser  34 . Supply hose  38  can then connect melt system  30  to pump  32 . 
         [0018]      FIG. 2  is a schematic view of one embodiment of melt system  30 . Melt system  30  includes hot press melter  46  and liquid adhesive reservoir  48 . Hot press melter  46  receives solid adhesive pellets from feed assembly  22  and melts the pellets to form liquid hot melt adhesive, which exits melter  46  and enters liquid adhesive reservoir  48 . 
         [0019]    As shown in  FIG. 2 , hot press melter  46  includes housing  50 , first heated plate  52 , second heated plate  54  and press drive  56 . Housing  50  encloses first and second heated plates  52  and  54  and also includes opening  58 , where solid adhesive pellets from feed assembly  22  (or some other source) are introduced into hot press melter  46 . First heated plate  52  is a plate capable of transferring heat to hot press melter  46 . In some embodiments, first heated plate  52  contains a heating element (heating element  53  shown in  FIG. 3A ). Exemplary heating elements include, but are not limited to, resistive heating elements, heaters cast within the plate and cartridge heaters. In other embodiments, first heated plate  52  conducts heat from a separate heat source to hot press melter  46 . During operation, first heated plate  52  generally has a temperature between 200° F. (93° C.) and 450° F. (232° C.), depending on the type of hot melt material being melted. Second heated plate  54  is similar to first heated plate  52 . Second heated plate  54  is a plate capable of transferring heat to hot press melter  46 . In some embodiments, second heated plate  54  contains a heating element. Exemplary heating elements include, but are not limited to, resistive heating elements, heaters cast within the plate and cartridge heaters. In other embodiments, second heated plate  54  conducts heat from a separate heat source to hot press melter  46 . During operation, second heated plate  54  generally has a temperature between 200° F. (93° C.) and 450° F. (232° C.), depending on the type of hot melt material being melted. In exemplary embodiments, first and second heated plates  52  and  54  are metallic. Solid adhesive pellets are melted in melter  46  by transferring heat from first and second heated plates  52  to the pellets. During operation, first and second heated plates  52  are pressed together to increase the contact surface area between the adhesive pellets and plates  52  and  54 , thereby increasing the melting rate of the adhesive pellets. 
         [0020]    Press drive  56  controls the position(s) of one or more of the first and second heated plates  52  and  54 . In the embodiment illustrated in  FIG. 2 , press drive  56  controls the position of first heated plate  52  within housing  50  and with respect to second heated plate  54 . Press drive  56  can include a rod (as shown) or a similar structure having one end attached to first heated plate  52  and the other end attached to a device capable of motion. In some embodiments, the position of first heated plate  52  is controlled using a motor, an actuator, pneumatics and the like. In  FIG. 2 , hot press melter  46  is shown in an open or loading position with first heated plate  52  spaced from second heated plate  54 . First heated plate  52  is located above opening  58  while second heated plate  54  is located below opening  58 . Solid adhesive pellets are able to enter melter  46  through opening  58  while hot press melter  46  is in the loading position. Solid adhesive pellets enter melter  46  between first heated plate  52  and second heated plate  54 . Once a sufficient amount of solid adhesive pellets has entered hot press melter  46 , press drive  56  moves first heated plate  52  towards second heated plate  54 . Reducing the distance between first heated plate  52  and second heated plate  54  increases the surface area of first and second heated plates  52  and  54  exposed to the solid adhesive pellets, allowing more heat to be transferred to the adhesive and increasing the rate of melting. More specifically, first and second heated plates  52  and  54  press the solid adhesive pellets, thereby thinning the mass of pellets so that the pellets contact more of the surface area of first and second heated plates  52  and  54 . 
         [0021]      FIGS. 3A and 3B  illustrate one embodiment of hot press melter  46 . Housing  50  has been removed from  FIGS. 3A and 3B  to better illustrate first and second heated plates  52  and  54 . First heated plate  52  includes first side  60  and second heated plate  54  includes second side  62  that faces first side  60 .  FIG. 3A  illustrates first and second heated plates  52  and  54  in the open or loading position while  FIG. 3B  illustrates first and second heated plates  52  and  54  in the closed or accelerated melting position. In the loading position, first side  60  of first heated plate  52  is spaced from second side  62  of second heated plate  54  by distance d 1 . In the accelerated melting position, first side  60  of first heated plate  52  is spaced from second side  62  of second heated plate  54  by distance d 2  which is smaller than d 1 . 
         [0022]    In addition to first and second heated plates  52  and  54 , hot press melter  46  shown in  FIGS. 3A and 3B  also includes perforated plate  64 . Perforated plate  64  is positioned atop second heated plate  54  along second side  62 . When solid adhesive pellets enter hot press melter  46 , the pellets are initially located between first heated plate  52  and perforated plate  64 . Perforated plate  64  contains perforations  66 . Perforations  66  can be circular, oval, rectangular or irregularly shaped. Perforations  66  are sized to be smaller than the solid adhesive pellets added to hot press melter  46 . For example, in the case of generally circular perforations and pellets, perforations  66  generally have a diameter larger than the diameter of the solid adhesive pellets added to hot press melter  46 . Liquefied hot melt adhesive is able to flow through perforations  66 , but the solid adhesive pellets are unable to pass through perforated plate  64  because the pellets are too large to pass through perforations  66 . Thus, perforated plate  64  prevents the passage of hot melt material until the material has begun melting. In some embodiments, perforated plate  64  includes a heating element, such as those described with respect to first and second heated plates  52  and  54 . Alternatively, perforated plate  64  can simply be heated conductively by second heated plate  54 . 
         [0023]    Second heated plate  54  includes drain  68 . In the embodiment illustrated in  FIG. 3A , drain  68  is located between the body of second heated plate  54  and perforated plate  64 . Gravity and the pressure created by moving first heated plate  52  toward second heated plate  54  causes liquefied (melted) hot melt adhesive to pass through perforations  66  of perforated plate  34 . The liquid hot melt adhesive is routed to drain  68  where it flows out of hot press melter  46 . In the embodiment shown in  FIGS. 3A and 3B , drain  68  is located on one side of second heated plate  54 . Liquid hot melt adhesive that has passed through perforated plate  64  exits melter  46  through drain  68  and flows to liquid adhesive reservoir  48  (shown in  FIG. 2 ). In alternate embodiments, drain  68  is a conical or funnel-like drain that has a drain opening in the bottom of second heated plate  34  (see  FIG. 4 , shown without perforated plate  64 ). 
         [0024]    In some embodiments, perforations  66  all have roughly the same size. In other embodiments, perforated plate  64  contains perforations  66  of different sizes. As shown in  FIG. 3A , perforations  66 A are smaller than perforations  66 B. Perforations  66 A and  66 B both prevent solid adhesive pellets of a size larger than perforations  66 B from passing through perforated plate  64 . The smaller perforations (perforations  66 A) further restrict the passage of solid adhesive pellets. Additionally, the smaller perforations also mean that more surface area of perforated plate  64  is available to contact the solid adhesive pellets, providing additional opportunity for heat transfer from perforated plate  64  to the solid adhesive pellets. In some embodiments, perforations  66 A have an average diameter of about 2 millimeters to prevent solid adhesive pellets having a diameter of about 5 millimeters from passing through perforated plate  64 , while perforations  66 B have an average diameter of about 4 millimeters to prevent solid adhesive pellets having a diameter of about 8 millimeters from passing through perforated plate  64 . For non-circular perforations  66 , the above average diameter values apply to the average lengths and/or widths of the perforations. 
         [0025]    During operation, solid adhesive pellets (or pillows) are added to melter  46  between first heated plate  52  and perforated plate  64  through opening  58  while melter  46  is in a loading position. Once the pellets have been added to hot press melter  46 , the pellets begin melting due to the heat transferred from first and second heated plates  52  and  54  and perforated plate  64  to the pellets. When hot press melter  46  is in the open position, heat is transferred to the pellets conductively by perforated plate  64  and/or second heated plate  54  and convectively by first heated plate  52 . The rate of melting is increased by moving first heated plate  52  towards perforated plate  64  and second heated plate  54  in an accelerated melting position. By reducing the distance between first side  60  of first heated plate  52  and second side  62  of second heated plate  54 , the pellets are pressed and brought into contact with additional heated surfaces (first side  60 , perforated plate  64  and second side  62 ). The pressed pellets are spread out over a greater surface area of first side  60  of first heated plate  52  and second side  62  of second heated plate  54  to provide greater area for heat transfer. Pressing the pellets eliminates “dead space” on the heating surfaces of first and second plates  52  and  54 . Heat is conductively transferred from these surfaces to the now partly compressed pellets. When hot press melter  46  is in the accelerated melting position, heat is transferred to the pellets conductively by first heated plate  52 , perforated plate  64  and/or second heated plate  54 , leading to an increased rate of melting. 
         [0026]    Liquefied hot melt adhesive passes through perforated plate  64  and exits hot press melter  46  through drain  68  in second heated plate  54  and enters liquid adhesive reservoir  48 . Liquid adhesive reservoir  48  communicates with pump  32  so that the liquid hot melt adhesive can be pumped from liquid adhesive reservoir  48  to dispenser  34  where it is dispensed. Liquid adhesive reservoir  48  is a vessel that maintains the hot melt adhesive in a liquid state. In some embodiments, liquid adhesive reservoir  48  is large enough to hold a surplus of liquid hot melt adhesive to ensure that pump  32  has a sufficient supply to operate continuously for a predetermined amount of time, such as between cycles of the loading position and the accelerated melting position for hot press melter  46 . In other embodiments, liquid adhesive reservoir  48  is smaller and functions merely as a conduit between hot press melter  46  and pump  32 . In either case, liquid adhesive reservoir  48  can be actively heated by heating elements to ensure that the hot melt adhesive remains in a liquid state. In some embodiments, liquid adhesive reservoir  48  is a secondary melter that transfers heat to the hot melt adhesive within the reservoir to further melt any partially solid adhesive that exited hot press melter  46 . 
         [0027]    Once the solid adhesive pellets have been melted in hot press melter  46 , hot press melter  46  transitions from the accelerated melting position to the open position to allow additional solid adhesive pellets to enter melter  46 . Press drive  56  causes first heated plate  52  to move away from perforated plate  64  and second heated plate  54  until hot press melter  46  is again in the open position. The cycle begins anew and solid adhesive pellets are added to hot press melter  46  through opening  58 . In some embodiments, melter  46  cycles between the open position and the accelerated melting position between once every five seconds and once every five minutes. The cycle time depends on factors that include the size of hot press melter  46 , the size of the solid adhesive pellets, the melting temperature of the solid adhesive pellets and the temperature of hot press melter  46 . Generally, the cycle time and the quantity of solid adhesive pellets delivered to hot press melter  46  are sufficient to permit pump  32  to run continuously. 
         [0028]      FIG. 5  illustrates another embodiment of a heated plate suitable for use in hot press melter  46 . While  FIGS. 3A ,  3 B and  4  illustrate perforated plate  64  atop second heated plate  54 , the embodiment shown in  FIG. 5  does not possess a perforated plate. Instead, second heated plate  54 A contains surface features that increase the surface area of second heated plate  54 A that can be exposed to the hot melt adhesive. Surface features include, but are not limited to, ribs, channels, dimples, indentations and combinations thereof. Second heated plate  54 A shown in  FIG. 5  includes ribs  70  that form channels  72  on second side  62 . Solid adhesive pellets entering hot press melter  46  are fed by gravity into channels  72 . Channels  72  are sloped to one side of second heated plate  54 A to direct liquid hot melt adhesive to drains  68  where it exits melter  46 . In some embodiments, first heated plate  52  (not shown) can have complimentary surface features. For example, ribs on first heated plate  52  can fit into channels  72  on second heated plate  54 A and vice versa. 
         [0029]    While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.