Patent Publication Number: US-6341719-B2

Title: Dispensing/metering device for two-component or one-component adhesive

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a dispensing/metering device for two-component or one-component adhesive, which is designed for use particularly, but not solely with film bonding machines. 
     In accordance with one aspect of the invention, two tanks are fitted to contain the component(s), namely resin and hardener in the case of two-component adhesive, whereas a single tank can be used in the case of one-component adhesive. 
     These tanks are fitted to a heated support in such a way that they can easily be removed, so that heat is transmitted to the products through the base of the containers. 
     In accordance with another aspect of the invention, the level of the components in the tanks is monitored by an ultrasound sensor, thus avoiding the use of mechanical devices, which would be difficult to clean when the type of adhesive is changed. 
     The result is a much simpler device than those already known, which is functional and eliminates practically all the down time required for cleaning of tanks when changing from one type of adhesive to another. 
     The known devices used to measure out and dispense adhesive are equipped with fixed tanks for the products that constitute the adhesive, the tanks being heated by a resistor fitted inside a jacket which surrounds the side wall of each tank. 
     Each tank is connected to a pump which conveys the required amount of product to a mixer, where the two components are mixed before use. 
     These machines are completed by various accessories, including float devices which monitor the product level in the tanks. 
     A metering device of this kind is known from the Italian patent application N° PC 98A 028 of the same inventor. However, these machines present a considerable drawback when the time comes to change over from one type of adhesive to another; the machine has to be shut down for a considerable time to allow thorough cleaning of the tanks and the devices inside them, so as not to contaminate the new products with residues of the previous ones. This is a fairly long, inconvenient and difficult operation which, as mentioned, requires the machine to be shut down for several hours in order to perform sufficiently thorough cleaning. The same problem also applies to cleaning of other parts of the machine, especially the dispensing nozzles, which have a complex shape and are therefore difficult to clean as thoroughly as necessary, with the result that when the type of adhesive is changed, the operators often replace the dispensing head as well as cleaning the machine because of the difficulty of cleaning the head properly. This drawback is now solved by the present invention, which offers a metering device for both two-component and one-component adhesive, in which the tank or tanks that contain the adhesive are fitted removably on a heated plate so that they can easily be removed or replaced with other tanks containing the new product, and can be thoroughly washed at a distance from the machine. 
     The machine in accordance with the invention also has an innovative dispensing head which can be used with either two-component or one-component adhesives, and can easily be cleaned thoroughly. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This invention will now be described in detail, by way of example but not of limitation, with reference to the annexed figures in which: 
     FIG. 1 is a view of a device in accordance with the invention 
     FIG. 2 is a side view of the device shown in FIG. 1 
     FIG. 3 is a plan view of the device in accordance with the invention 
     FIG. 4 is a cross-section of the dispensing head in a device in accordance with the invention 
     FIG. 5 is a vertical cross-section of the device in accordance with the invention 
     FIG. 6 is a schematic plan view of the device in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the annexed figures, the device basically comprises a base  1 , which also constitutes the adhesive heating plate, on which a pair of tanks  2  and  2 ′ are mounted. Each of the said tanks contains one of the components of the mixture in the case of two-component adhesive, and the said components are pumped out and metered by devices which will be described below. 
     In the case of one-component adhesive, one of the tanks could be bypassed, and the corresponding pump with associated control electronics and heating devices could also be bypassed with a selector switch. 
     The said selector switch could also select the tank from which the adhesive is pumped. 
     A control unit  3 , containing a PLC or an analog computer, controls the functions of the machine and the various units of which it is composed. 
     In particular, there is a hole  4  in heated base  1  in correspondence with each tank  2  and  2 ′ into which is inserted a connector with a suitable gasket such as an O-ring or the like, the said connector being fitted to the base of the tank. 
     Hole  4  leads on the opposite side to a pipe  7  which is connected to the inlet of a motorised metering pump  8 , in particular a gear pump, the outlet of which is connected to a product dispensing head  10 . 
     Each tank can be secured to baseplate  1  with a set of snap hooks  14  of known type or the like, and a cap  15  with an O-ring  16  is fitted to close the bottom of the tank. 
     Tank  2  is closed by a lid  17  to which a pipe  18  leads from a container  19  filled with moisture-absorbing material such as silica gel; the air which penetrates into the tank passes through the said moisture-absorbing material as the level of the product in the tank falls. 
     Lid  17  also contains an ultrasound sensor  20  designed to monitor the level of the product in the tank and send a corresponding signal to control unit  3 . 
     A membrane pressure sensor  21  is connected to the outlet of each pump  8 , and is also connected to control unit  3 . 
     A temperature sensor  24  is positioned in a seating in the wall of tank  2 . 
     A plurality of heating elements are inserted in baseplate  1 ; in this specific case they are constituted by electrical resistors  25 , but they could also be constituted by any heating device of known type. 
     Preferably, as illustrated in FIG. 6, at least one pair of resistors  25  is located in the immediate proximity of hole  4  through which the product exits from the tanks, and is thus immediately heated. 
     The tanks and the various distribution pipes are enclosed in a casing  26  lagged with a suitable layer of heat insulation material which is secured around the tanks to prevent heat dispersion and maintain a suitable temperature in the tanks. 
     Finally, the pipes which convey the adhesive component to the dispensing head are also suitably provided with heat insulation means, which may include heating means such as an electrical resistor. 
     Dispensing head  10  is illustrated in detail in FIG.  4 . 
     The said head comprises a body  27  with a pair of inlets or chambers  28  and  29  fitted with connectors, not shown in the figure, for the pipes leading from tanks  2  and  2 ′ which contain the components of the adhesive. 
     A pair of inspection and cleaning pipes  30  and  31 , each closed by a cap, lead to chambers  28  and  29 . 
     Pipes or nozzles  32  and  33  lead from chambers  28  and  29  to a connector  34  on head  10 . 
     The end of connector  34  presents two consecutive lengths  35  and  36  of a different diameter. Nozzles  32  and  33  lead to the end walls of these lengths  35  and  36  respectively. 
     Connector  34  is threaded, and a closing cap  13  is screwed to it. The shape of the end wall of the said cap  13  complements that of the end of connector  34 , so that it rests against the end wall of the latter and seals nozzles  32  and  33 . 
     An outlet pipe  37 , with a thread  28  for fitting a dispensing syringe or the like  39 , leads to one of chambers  28  and  29 ; in the case illustrated in the figure it leads to chamber  28 . Chamber  28  is connected to the adhesive tank when a one-component adhesive is used. 
     The device operates as follows. 
     To prepare the device for operation, it is sufficient to fit the tanks to plate  1 , insert connector  5  into hole  4 , and secure the tanks with snap hooks  14 . When the tanks are filled with the required products, they can be closed with hermetically sealing lid  17 , and the machine is switched on. Resistors  25  heat plate  1 , from which heat is transmitted to the product through the bottom of the tanks; the temperature of the product is monitored by sensor  24 , which transmits the data to the control unit. 
     At the same time pumps  8  are activated to pump the product from the bottom of the tanks and convey it through hole  4  and pipe  7  to dispensing head  10 . The speed of the pumps can be independently regulated to allow perfect metering of the two fluids when they are discharged. 
     In the case of two-component adhesive, the two components reach chambers  28  and  29 , from which they are dispensed through nozzles  32  and  33  which lead to connector  34 , to which dispensing syringe  39  is fitted. 
     In the case of one-component adhesive, cap  13  is screwed to connector  34 , thus sealing nozzles  32  and  33  to prevent hardening of the product, and dispensing syringe  39  is fitted to connector  38  on outlet pipe  37 , from which the adhesive conveyed from the tank to chamber  28  is dispensed. 
     If cleaning operations are necessary, it is sufficient to connect to connector  38  or  34  devices able to pump a cleaning fluid such as a solvent, and to remove the closing caps from inspection pipes  30  and  31 . 
     If the fluid is pumped through nozzles  32  and  33 , thorough cleaning can be performed easily and quickly, and all debris is removed, exiting through inspection pipes  30  and  31 , which are of larger diameter. When the type of adhesive needs to be changed, it is no longer necessary to shut down the machine before a thorough tank cleaning operation can be performed; it is sufficient to loosen snap hook  14  and remove the tanks, which can thus be cleaned conveniently at a later stage. When the pipes have been washed with a suitable solvent, the tanks containing the new adhesive can be attached, and the machine started up again. 
     An expert in the field could devise numerous modifications and variations, all of which should be deemed to fall within the scope of this invention.