Abstract:
Various processes and relevant devices for causing polymer films, which are extensible to adhere to the edges of openings of plastic or PET or even metal containers, by releasing electrostatic charges opposite in sign to those of containers and/or the polymer films to be applied thereto. The processes derive from a single general inventive concept.

Description:
This application claims the benefit of Swiss Application No. 1059/01 filed Jun. 13, 2001 and PCT/IB02/02132 filed Jun. 11, 2002. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to the field of container closures and particularly of liquid and food container sealing. It addresses two processes to condition both the edge of the opening of the plastic or metal container and the extensible polymer film to be applied thereto with the process disclosed in Patent Application Ribi WO 98/32668 of Jan. 23, 1998. 
   Thanks to such conditioning, performed with various devices allowing to perform the processes, an effective and safe sealing effect is obtained. 
   2. Related Art 
   In prior art sealing techniques, liquid and/or food containers are typically sealed either by means of bonded screw plugs or metal plugs, or by the application of various metal disks, to be attached to the edge of the opening, or with blind seals, which are held in position by other mechanical devices, like those mentioned above. 
   A more practical, cost-effective, hence industrially advantageous arrangement is proposed by the invention disclosed in Patent Application WO 98/32688 of Jan. 23, 1998, and various implementations thereof, i.e. devices for applying extensible polymer films to the edges of the openings of glass containers. 
   Nevertheless, this arrangement cannot be used for plastic or metal containers because, as explained below, adhesion thereof is hindered by the electrostatic charges of equal polarity on the faces of the two materials to be attached or simply due to the lack of electric charges on said faces. 
   SUMMARY OF THE INVENTION 
   The processes which form the subject of this invention and the devices used for implementation thereof allow two plastic surfaces, or plastic and metal surfaces, to effectively adhere to each other, thereby assisting the application of an extensible polymer film to the opening of a plastic or metal container. 
   The invention essentially consists in charging electrostatically the adhering surfaces in opposite polarity and in possibly improving said adhesion by heating the two surfaces. 
   The tight adhesion of extensible plastic seals on plastic or metal materials not only depends on the surface condition, but also on temperature, which allows a better mutual adaptation of the two materials in contact with each other during the application. Nevertheless, as shown in various tests and specific measurements, film adhesion is mostly affected by the presence of opposite electrostatic charges on the opposed faces of the materials to be attached. 
   Typically, in normal conditions, the charges on the two materials, i.e. plastic-plastic or plastic-metal, unlike glass-plastic, have the same polarity (or are absent), hence the surfaces tend to remain separate when attempting to join them. 
   The processes of this invention, and the devices used to implement them, consist in assigning electrostatic charges of opposite polarity to the two adhering materials. 
   This simple arrangement allows even a relatively weak force, like electrostatic force, to be effective in assisting the adhesion of the deformable extensible plastic material to the edge of the container opening, so that the two boundary air layers adjacent to the two materials are removed thereby allowing atmospheric pressure to exert its full force. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1   a  and  1   b  show the device in its simplest configuration for implementing the process adhering two surfaces. 
       FIG. 2  shows the device of  FIGS. 1   a  and  1   b  including a generator and accessories thereof. 
       FIG. 3  shows the device with a single capacitor. 
       FIG. 4  shows the device applying film to a metal can. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The process consists in directing a flow  24 , or continuous or discontinuous jet of air or any appropriate dry gas on the edge of the opening  21  of the container  1  to be sealed. 
   This flow  24  is generated by any suitable compressed air or gas source, e.g. a compressor, or even directly by heating or changing the state of a suitable liquid or solid. Obviously, this process is conceived for and operates on any suitable surface composing the edge  21  of the container to be sealed, either painted, anodized, frosted or passivated. 
   The typical device for the implementation of said basic process, as shown in  FIG. 1  is described below. 
   In order to improve the efficiency of the process, the molecules composing the flow  24  are charged electrostatically by using an electrostatic charge generator  8  equal or equipollent to the so-called Van der Graaf type, with or without capacitors  9 , to increase the available charges. Then, these charges are directly released to the molecules of the flow  24 , by simple contact in the feed pipe  15 . 
   So, the plates  7  of the same sign may be licked by the flow  24  thereby suitably charging it. 
   Various capacitors may be used, either simply consisting of two plates  7  with an interposed dielectric  19 , i.e. the air or gas itself, or formed by combinations of various plates with other interposed dielectrics  19 . The plates  7  may also be made of porous materials to extend the surface thereof, such as activated carbon, which may be also used with suitable fluid dielectrics  19 . 
   The devices for implementing the above mentioned variants of the process, are described below. 
   The air or gas flow  24  is appropriately heated by electrical resistors or any suitable heat exchangers  18  disposed in the feed pipe  15  or by the pipe  15  itself, after suitably heating it, to bring the edge of the opening  21  and possibly also the film  13  of the seal to the proper temperature. 
   Obviously, heating temperature must not exceed the softening points of the materials in use. 
   Said heating assists the adhesion of the film  13  both for a better plasticity of the contacting surfaces, and for the decreased viscosity of air or gas which form the boundary layer adjacent to the surfaces. 
   Typically, the process is effective because the boundary air or gas layer of the surfaces is removed as the surfaces of the film  13  and the opening  21  are driven closer thanks to the electrostatic forces. Hence, atmospheric pressure, which is no longer counterbalanced by the pressure of residual air or gases between the two surfaces, can be fully exerted, thereby creating such a force of adhesion as to create in turn a tangential, i.e. shearing friction between the two surfaces: whose coefficient of friction, which increases with the plasticity or relative “adaptability” of the two surfaces, improves when the edge  21  of the opening and the film  13  are heated. 
   The device for implementing this variant of the process is described below. 
   As an alternative to the previously described heating arrangement, the edge of the containers  21  and/or the film  13  which forms the seal are previously suitably heated by a radiant heat energy source  22 . 
   The device for implementing this variant of the process is described below. 
   The gas of the flow  24  is replaced by dry steam  27  produced by any appropriate dry steam generator  25 . This variant has the advantage that the edge of the container opening  21  is heated directly. In practice, the edge  21  is preferably pre-heated to a certain temperature, anyway below the material softening point by a heat source  22 , to prevent any condensation of dry steam  27 . 
   A suitable monitored system for integrating and controlling flow rate, pressure, temperature and time of exposure to flow  27  allows a drawback-free optimized use of the device. Moreover, the dry steam jet  27  will have the advantage of sterilizing the edge of the opening  21  of the container  1 . 
   The device for implementing the above process, shown in  FIG. 1   b  is described below. 
   The process consists in releasing by contact opposite electrostatic charges to the edge of the opening  1  and to the film  13  to be applied thereto. 
   This contact occurs before and during the step of applying the sealing film  13 , whereas the charges of one sign are released by the container support  11  to the container  1  itself and the charges of the opposite sign are released by the film driving rollers  12  to the film  13 . Charges are usually provided by a special generator  8 , possibly including capacitors  9  and rheostats  10 . 
   The device for implementing this variant of the process, shown in  FIG. 1   b  is described below. 
   The device as shown in  FIG. 1   a,  consists in a compressed air or gas generating system, in which compressed air or gas is generated by any suitable pump  2 , equipped with a motor  3 . The system includes one or more storage tanks, pipes  15  having opening and closing valves, flow control valves and one or more nozzles  5  which may be oriented relative to the opening of the container  21  to be sealed. Therefore, air or gas flow is controlled by manometers P and manostats PS, for controlling outlet pressure, hence flow rate. This air or gas flow may also be pulsating and coincide with the passage of the container edge before the nozzle/s. 
   The jet has the function of removing and pushing away the electrostatic charges of the container  1 , or appropriate new electric charges, in such a manner that a difference of electrostatic potential is established between the container  1  and the film  13  acting as a seal. 
   The force exerted by the electrostatic charges will allow air or gases to be expelled from between the two surfaces, thereby allowing atmospheric pressure to exert its full force. 
   The device as shown in  FIG. 2 , consists of a system including an electrostatic charge generating system. This system comprises a charge generator  8  of the “Van der Graaf” or equivalent type, one or more appropriate capacitors  9  and at least one rheostat  10 . 
   The equal sign plates of these capacitors  9 , may be either connected to appropriately insulated surfaces in contact with the air or gas flow or be themselves immersed in the gas carrying pipe  15 . This sign shall be opposite to the one of the charges at the surface of the film  13 . 
   The device as shown in  FIG. 1 , consists in a system which has scattering tips  17  both on the surfaces in contact with the flow in the feed pipe  15  and on the equal-sign plate/s of the capacitors  9 , immersed in the flow. 
   These tips have the function of quickly releasing the capacitor charges to air or gas. The concentration of charges on projections of charged surfaces is a well-known physical phenomenon. 
   In the device shown in  FIG. 2 , the plates  7  of the capacitors  9  are connected to one or more additional homologous plates  7  of capacitors  9 , even outside the feed pipe  15 , and to one or more rheostats  10  which have the function to control the flow of electric charges to be released. 
   In the device shown in  FIG. 2 , the systems are equipped with a heating system. 
   This system will be preferably inserted in a special widened portion of the feed pipe  15 , i.e. a muffler  4  containing one or more heaters  18  of any type, e.g. electric resistors or heat exchangers. 
   This system will obviously be monitored by appropriate thermostats TS and suitably insulated. An alternative to this solution consists in heating the feed pipe  15  by the same means. 
   The device shown in  FIG. 1   b,  consists in a system wherein the air or gas jet is replaced by a dry steam generating system. This system consists of a dry steam generator  25 , with measuring and controlling equipment as well as with an adequately insulated feed pipe  15 . The control equipment consists of automated thermostats TS and manostats PS and a flow controller R. Water may be advantageously heated electrically but also by other sources of heat energy. 
   This device will be preferably used in association with a preheater  22  for preliminarily heating the surfaces to be blown to prevent condensation. Moreover, dry steam  27  will have the function of sterilizing the edge of the opening  21 . 
   The device identical to the one provided for air or gas, supplements the device described above. Here, the dry steam blowing system integrates a system for generating electrostatic charges and releasing them to water molecules. 
   The inflow pipe  26  will have inner insulated surfaces connected to the equal-sign plates  7  of one or more capacitors, which are in turn fed by an electrostatic charge generator  8 . The inner surfaces or plates  7  of the inflow pipe  26  may in turn have scattering tips  17 , as in the case of air or gas. 
   The charge flow will be controlled as needed by an appropriate rheostat  10 . 
   In the device shown in  FIG. 3 , a radiant heat source is used for any type of device as described and claimed herein. This infrared ray generating source may be either simply an electrically heated surface or any other heated mass in any other appropriate manner. Both parts, i.e. the container  1  and the film  13  will be placed in the proximity of the surfaces to be headed in such a manner that radiant heat brings the container opening  21  and the film  13  to the desired temperatures. 
   In the device which is not shown, a corona-type charge generator is used. An adequately insulated high voltage generator for charging suitable bodies disposed in the proximity of the edge of the opening  21  and of the film  13 , will release charges of the appropriate sign to the surfaces. Then, the generator will typically consist of an electric generator, one or more high voltage transformers, appropriate control and adjustment instruments, like capacitors  9 , rheostats  10 , fuses and insulated wires. 
   The device shown in  FIGS. 3 and 4  consists of an electrostatic charge generating system which will supply both the container  1  and the film with electrostatic charges of opposite signs. The “Van der Graaf” or equivalent generator  8 , equipped with rheostats  10  and one or more capacitors, will feed, by the plates of opposite sign  7  of its capacitor/s, the support  11  of the container on the one hand and the driving rollers  12  for the film band  13 . Hence, the opposite sign charges will cause the film  13  and the edge of the container opening  21  to adhere against each other and will expel the residual air or gas between the two surfaces. 
   LIST AND KEY OF FIGURES 
   
     FIG. 1 
     a  
   
   Shows the device in its simplest configuration for implementing the process as claimed and comprises the following:
       1 . Plastic or metal container to be sealed.     2 . Gas pump (for air or other suitable gas).     3 . Motor.     4 . Storage tank.     5 . Nozzle.     11 . Container support (possibly movable, e.g. conveyor belt).     12 . Roller for driving the extensible polymer film (possibly armor-plated).     13 . Extensible polymer film (possibly armor-plated).     14 . Device for applying the extensible polymer film (as per Patent application WO 98/32668 of Jan. 23, 1998).     15 . Gas pipe.     21 . Opening edge.   P. Manometer.   S. Condensation drain.   M. Flow control.   PS. Manostat   

   
     FIG. 1 
     b  
       
         24 . Gas flow pipe. 
         25 . Dry steam generator. 
         26 . Insulated pipe. 
         27 . Dry steam jet. 
       TS. Thermostat. 
       R. Flow control. 
       M. Additional flow control. 
     
  
   
     FIG. 2 
   
   Shows the device in the configuration that includes a generator and accessories thereof for implementing the process as claimed and comprises the following:
       1 . Plastic or metal container.     2 . Gas (air) pump.     3 . Motor.     4 . Storage tank.     5 . Nozzle.     6 . Muffler containing capacitor plates immersed in the air flow.     7 . Plates of the internal capacitor.     8 . Generator.     9 . External parallel capacitor.     10 . Rheostat.     11 . Insulated support.     12 . Film driving roller.     13 . Polymer film.     14 . “RIBI” film application device.     15 . Gas pipe.     16 . Manostat electric contactor.     17 . Scattering tips.     18 . Heater.     21 . Opening edge.     24 . Gas flow pipe.   P. Manometer.   T. Thermometer.   TS. Thermostat.   M. Flow control.   PS. Manostat.   

   
     FIG. 3 
   
   Shows the device with a single capacitor  9  for implementing the process as claimed and comprises the following:
       1 . Plastic (or metal) container.     7 / 11 . Container support.     8 . Generator.     9 . Capacitor.     10 . Rheostat.     7 / 11 . Container support (and plate).     12 . Film driving guide roller.     12   bis.  Film driving guide roller (and plate having a charge opposite to the container support).     13 . Extensible polymer film.     14 . “RIBI” film application device.     20 . Insulator.     21 . Opening edge.   

   
     FIG. 4 
   
   Shows a device for applying the film  13  to a metal can  1 , wherein both the film driving roller/s  12  or  12   bis  and the container support are themselves capacitor plates, and consist of at least two plates, having a dielectric  19  interposed therebetween, and whose charges, of opposite sign, are released to the film  13  and to the container  1 . The drawing comprises the following:
       1 . Container.     8 . Generator.     9 . Capacitor.     10 . Rheostat.     7 ./ 11 . Support-plates.     12 . Driving roller.     12   bis.  Electrostatically charged driving roller.     13 . Film.     14 . “RIBI” film application device.     19 . Dielectric.     20 . Insulator.     21 . Opening edge.