Patent Publication Number: US-2010107568-A1

Title: Method and apparatus for heat-sealing container

Description:
TECHNICAL FIELD  
     This invention relates to a method and an apparatus for heat-sealing a container and, more particularly, to a method and an apparatus capable of carrying out heat-heating at a high speed and in a stable manner in a case where a cap in the form of a film should be heat-sealed to a container main body made of paper or synthetic resin and formed in the shape of a cup. 
     BACKGROUND ART  
     A container in which a cap in the form of a film is heat-sealed on a container main body made of paper or synthetic resin and formed in the shape of a cup is used broadly as a container for food etc., as, for example, a container for jelly, baby food, viscous food such as soup or miso or cooked food. 
     For sealing a container main body and a cap in such a container, heat-sealing which carries out sealing by heating using a seal head is generally used. 
     As such heat-sealing method, Japanese Patent Application Laid-open Publication No. 2004-250027 discloses a method in which a cap is conveyed and placed on a container by cap pressing and conveying means disposed above container conveying means and, while the state in which the cap is in close contact with the container is maintained, induction heating is carried out by a high frequency seal head which is disposed above the cap without contacting the cap. According to this method, sealing can be achieved at a high speed without vertically moving the seal head or container. 
     Japanese Patent Application Laid-open Publication No. 11-20801 discloses high speed adhesion between a cap and a container by using of both heating with a heater cartridge and high frequency induction heating or supersonic vibration heating. 
     Japanese Patent Application Laid-open Publication No. 58-19536 discloses that, as shown in its FIG. 4, a pressing and heating belt 4 in which a metal member 2 is sandwiched between a heat resisting member 3 is provided above a container conveying belt conveyer 1 in a manner to move synchronously in parallel with the conveyer 1 and that a high frequency induction heating coil 5 is disposed in the belt 4 to high frequency induction heating the pressing and heating belt 4 so that a cap 7 placed on a container 6 may be sealed. 
     SUMMARY OF THE INVENTION 
     In carrying out sealing at a high speed by using one of the above described heat-sealing methods, if capacity of a heat receiving and imparting portion of a seal head, i.e., heat capacity, is small, temperature of the seal head tends to drop during sealing when the seal head is pressed against the cap and heating of the cap is made in a peripheral portion of the cap and, therefore, a seal head having a more or less lump shape and having a large heat capacity must be used. 
     If, however, one attempts to carry out sealing at a high speed by using a large seal head, not only the peripheral portion of the cap but also the central portion of the cap tend to be heated and therefore temperature of the central portion tends to rise and, as a result, gas in a head space of the container is inflated in a stage before the welded portion is completely solidified and wrinkles are produced in the cap thereby causing difficulty in sealing. 
     Moreover, if one attempts to carry out sealing at a high speed i.e., in a short period of time, by elevating temperature of the seal head, the cap tends to adhere to the seal head thereby causing difficulty in sealing and, in this case, limitation is posed on the type of material which can be used as the cap. 
     Further, in the case of Japanese Patent Application Laid-open Publication No. 2004-250027 in which the cap is heated by high frequency induction heating, the cap must be heated directly and, therefore, sealing by heating can be made only in the case that the cap is made of metal. 
     Furthermore, in all of the above described methods, the entire surface of the cap is heated and, as a result, gas in the head space of the container is inflated thereby causing difficulty in sealing. 
     The present invention has been made in view of these problems of the prior art methods. It is an object of the invention to provide a method and an apparatus for heat-sealing a container capable of carrying out sealing at a high speed and in a stable manner regardless of material of a cap. 
     For achieving the above described object of the present invention, in the first aspect of the invention, there is provided a method for heat-sealing a container by sealing the container by heat welding a cap on a flange portion provided in an opening portion of the container comprising a step of high frequency induction heating a seal head formed in the shape of the flange portion of the container and pressing the cap with the heated seal head to weld the cap to the container. 
     According to this method for heat-sealing a container, since the seal head formed in the shape of the flange portion of the container is high frequency induction heated and the heated seal head is pressed on the cap to weld the cap, by using a seal head having a shape necessary for sealing the cap, influence by dropping in the temperature and inflation of gas in the head space can be prevented and sealing at a high speed in a stable manner can be achieved. 
     In the second aspect of the invention, there is provided a method for heat-sealing a container as defined in the first aspect further comprising a step of cooling the seal head while the heated seal head is pressing the cap. 
     According to this method for heat-sealing a container, the seal head is cooled while the heated seal head is pressing the cap. Since pressing is finished after the seal head is cooled, even if sealing temperature is raised, adhering of the cap to the seal head can be prevented and sealing at a high speed and in a stable manner can be achieved even in a higher degree. 
     In the third aspect of the invention, there is provided a method for heat-sealing a container as defined in the second aspect wherein cooling of the seal head is made by supplying a cooling medium into the seal head. 
     According to this method for heat-sealing a container, since cooling of the seal head is made by supplying a cooling medium into the seal head, cooling of the seal head can be made easily. 
     In the fourth aspect of the invention, there is provided a method for heat-sealing a container by sealing the container by heat welding a cap on a flange portion provided in an opening portion of the container with a seal head comprising a heating ring formed along the shape of the flange portion and a high frequency induction heating coil provided on the inside of the heating ring via magnetic shielding plates, said method comprising a step of high frequency induction heating the heating ring with the high frequency induction heating coil and pressing the cap with the heating ring to weld the cap to the container. 
     According to this method for heat-sealing a container, the seal head with which the cap is heat welded on the flange portion provided in the opening portion of the container comprises the heating ring formed along the shape of the flange portion and the high frequency induction heating coil provided on the inside of the heating ring via magnetic shielding plates and the heating ring is high frequency induction heated with this high frequency induction heating coil and pressed on the cap to weld the cap. Therefore, by using a seal head having a heating ring having a shape necessary for sealing the cap and concentrically heating the heating ring shielded by the magnetic shielding plates, influence by dropping in the temperature and inflation of gas in the head space can be prevented and sealing at a high speed in a stable manner can be achieved. 
     In the fifth aspect of the invention, there is provided a method for heat-treating a container as defined in the fourth aspect wherein supply of electricity to the high frequency induction heating coil is stopped after the heating ring has been heated to a predetermined temperature and then pressing with the heating ring is continued for a predetermined period of time. 
     According to this method for heat-sealing a container, since supply of electricity to the high frequency induction heating coil is stopped after the heating ring has been heated to a predetermined temperature and then pressing with the heating ring is continued for a predetermined period of time, heating with the heating ring which has been heated to a predetermined temperature is continued for a predetermined period of time necessary for heat welding and, therefore, sealing can be made in a sealing state which becomes stable and proper in a short period of time. 
     In the sixth aspect of the invention, there is provided a method for heat-treating a container as defined in the fourth or fifth aspect wherein the heating ring is cooled while pressing with the heating ring is continued. 
     According to this method for heat-sealing of a container, since the heating ring is cooled while pressing with the heating ring is continued, even if the temperature is raised, pressing is finished after the heating ring is cooled and, therefore, adhering of the cap to the heating ring can be prevented and sealing at a high speed and in a stable manner can be achieved even in a higher degree. 
     In the seventh aspect of the invention, there is provided a method for heat-sealing a container as defined in the sixth aspect wherein the heating ring has a hollow portion and cooling of the heating ring is made by supplying a cooling medium into the hollow portion. 
     According to this method for heat-sealing a container, since the heating ring has a hollow portion and cooling of the heating ring is made by supplying a cooling medium into the hollow portion, cooling of the heating ring at a high temperature can be made easily in a short period of time. 
     In the eighth aspect of the invention, there is provided a method for heat-sealing a container as defined in the seventh aspect wherein cooling of the heating ring with the cooling medium and supplying of the cooling medium are made by providing a plurality of cooling medium supplying and exhausting openings in the hollow portion of the heating ring and supplying and exhausting the cooling medium from a different one of the supplying and exhausting openings in a predetermined order or at random. 
     According to this method for heat-sealing a container, cooling of the heating ring with the cooling medium and supplying of the cooling medium are made by providing a plurality of cooling medium supplying and exhausting openings in the hollow portion of the heating ring and supplying and exhausting the cooling medium from a different one of the supplying and exhausting openings in a predetermined order or at random. By supplying and exhausting the cooling medium from a different one of the supplying and exhausting openings in a predetermined order or at random, the heating ring can be cooled to a uniform temperature whereby heating temperature for next heating can be made uniform and heat-sealing can be made in a stable manner. 
     In the ninth aspect of the invention, there is provided an apparatus for heat-sealing a container comprising a seal head for sealing the container by heat welding a cap on a flange portion provided in an opening portion of the container, said seal head comprising a seal head main body, a heat welding member provided in the seal head main body and formed in the shape of the flange portion, and a high frequency induction heating coil provided in the seal head main body for high frequency induction heating the heat welding member. 
     According to this apparatus for heat-sealing a container, since the apparatus comprises the heat welding member provided in the seal head main body and formed in the shape of the flange portion, and the high frequency induction heating coil provided in the seal head main body for high frequency induction heating the heat welding member, by heating the heat welding member in the form of the flange portion with the high frequency induction heating coil, the heat welding member can be heated to a necessary temperature for sealing in a short period of time and, therefore, influence of dropping in the temperature and inflation of gas in the head space can be prevented and high-speed and stable sealing can be achieved with a seal head having a shape necessary for sealing of the cap. 
     In the tenth aspect of the invention, there is provided an apparatus for heat-sealing a container as defined in the ninth aspect wherein the heat welding member comprises a cooling medium flow-path which enables the heat welding member to cool while pressing of the heat welding member on the cap is maintained. 
     According to this apparatus for heat-sealing a container, since the heat welding member comprises a cooling medium flow-path which enables the heat welding member to cool while pressing of the heat welding member on the cap is maintained, cooling of the seal head can be made easily and, therefore, even if the temperature is raised, by finishing pressing after the seal head is cooled, adhering of the cap to the seal head can be prevented and sealing at a high speed and in a stable manner can be achieved even in a higher degree. 
     In the eleventh aspect of the invention, there is provided an apparatus for heat-sealing a container as defined in the ninth or tenth aspect wherein the heat welding member comprises a non-welding member on a surface of the heat welding member which presses the cap. 
     According to this apparatus for heat-sealing a container, since the heat welding member comprises a non-welding member on a surface of the heat welding member which presses the cap, even if the sealing temperature is raised, adhering of the cap to the seal head can be prevented by covering of the seal head and sealing at a high speed and in a stable manner can be achieved even in a higher degree. 
     In the twelfth aspect of the invention, there is provided an apparatus for heat-sealing a container as defined in the tenth or eleventh aspect wherein the heat welding member comprises cooling medium exhausting means for exhausting the cooling medium in the cooling medium flow-path after cooling of the cap. 
     According to this apparatus for heat-sealing a container, since the heat welding member comprises cooling medium exhausting means for exhausting the cooling medium in the cooling medium flow-path after cooling of the cap, heating for sealing a next cap can be made in an even shorter period of time whereby sealing can be made at a high speed and in a stable manner. 
     In the thirteenth aspect of the invention, there is provided an apparatus for heat-sealing a container as defined in any of the ninth-twelfth aspects wherein the seal head main body comprises temperature holding means for holding heating temperature of the heat welding member. 
     According to this apparatus for heat-sealing a container, since the seal head main body comprises temperature holding means for holding heating temperature of the heat welding member, a temperature which becomes a basis of temperature range of heating and cooling can be maintained and, therefore, when heating and cooling are repeated, sealing can be made at a high speed and in a stable manner in an even shorter period of time. 
     In the fourteenth aspect of the invention, there is provided an apparatus for heat-sealing a container comprising a seal head and sealing the container by heating the seal head and pressing a cap placed on a flange portion of an opening portion of the container with the heated seal head to heat-weld the cap to the container, said seal head comprising a heating ring shaped along the shape of the flange portion, and a high frequency induction heating coil wound in a plurality of windings provided on the inside of the heating ring and held between magnetic shielding plates. 
     According to this apparatus for heat-sealing a container, since apparatus for heat-sealing the container comprising the seal head and sealing the container by heating the seal head and pressing the cap placed on the flange portion of the opening portion of the container with the heated seal head to heat-weld the cap to the container, said seal head comprising the heating ring shaped along the shape of the flange portion, and the high frequency induction heating coil wound in a plurality of windings provided on the inside of the heating ring and held between magnetic shielding plates, by heating the heating ring shaped along the shape of the flange portion with the high frequency induction heating coil held between the magnetic shielding plates, the heating ring can be heated concentrically to a temperature necessary for sealing the cap in a short period of time and, therefore, influence of dropping in the temperature and inflation of gas in the head space can be prevented and high-speed and stable sealing can be achieved with a seal head having a shape necessary for sealing of the cap. 
     In the fifteenth aspect of the invention, there is provided an apparatus for heat-sealing a container as defined in the fourteenth aspect wherein the heating ring of the seal head comprises a hollow portion which is a cooling medium flow-path capable of cooling the heating ring while the heating ring is pressed on the cap and a plurality of cooling medium supplying and exhausting openings provided in the cooling medium flow-path which can change a supplying and exhausting position of the cooling medium. 
     According to this apparatus for heat-sealing a container, the heating ring of the seal head comprises the hollow portion which is the cooling medium flow-path capable of cooling the heating ring while the heating ring is pressed on the cap and a plurality of cooling medium supplying and exhausting openings provided in the cooling medium flow-path which can change a supplying and exhausting position of the cooling medium. By making the heating ring hollow and using the inside of the hollow portion as the cooling medium flow-path, and carrying out cooling while changing the supplying and exhausting position of the cooling medium among the plurality of cooling medium supplying and exhausting openings, adhering of the cap to the heating ring can be prevented and high-speed and stable sealing can be made even in a higher degree and, further, uniform cooling and uniform next heating can also be realized. 
     In the sixteenth aspect of the invention, there is provided an apparatus for heat-sealing a container as defined in the fourteenth or fifteenth aspect claim wherein the heating ring comprises a non-welding member on a surface of the heating ring which presses the cap. 
     According to this apparatus for heat-sealing a container, since the heating ring comprises a non-welding member on a surface of the heating ring which presses the cap, even if the sealing temperature is raised, adhering of the cap to the heating ring can be prevented by covering of the heating ring and sealing at a high speed and in a stable manner can be achieved even in a higher degree. 
     In the seventeenth aspect of the invention, there is provided an apparatus for heat-sealing a container as defined in the fifteenth or sixteenth aspect wherein the heating ring comprises cooling medium exhausting means for exhausting the cooling medium in the cooling medium flow-path after cooling of the cap. 
     According to this apparatus for heat-sealing a container, since the heating ring comprises cooling medium exhausting means for exhausting the cooling medium in the cooling medium flow-path after cooling of the cap, heating for sealing a next cap can be made in an even shorter period of time and sealing can be made at a high speed and in a stable manner. 
     In the eighteenth aspect of the invention, there is provided an apparatus for heat-sealing a container as defined in any of the fourteenth-seventeenth aspects wherein the seal head comprises temperature holding means for holding heating temperature of the heating ring. 
     According to this apparatus for heat-sealing a container, since the seal head comprises temperature holding means for holding heating temperature of the heating ring, a temperature which becomes a basis of temperature range of heating and cooling can be maintained and, therefore, when heating and cooling are repeated, sealing can be made at a high speed and in a stable manner in an even shorter period of time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded view showing a container used in an embodiment of the container heat-sealing method and apparatus of the present invention. 
         FIG. 2  a vertical section showing an embodiment of the container heat-sealing method and apparatus of the present invention. 
         FIG. 3  is a schematic plan view showing an embodiment in which the container heat-sealing method and apparatus of the invention are applied to a rotary type heat-sealing apparatus carrying out high speed continuous heat-sealing. 
         FIG. 4  is a schematic view of another embodiment of the container heat-sealing method and apparatus of the present invention. 
         FIG. 5  is a schematic vertical section of the embodiment shown in  FIG. 4 . 
         FIG. 6A  is an explanatory view of heating and cooling processes of an embodiment of the container heat-sealing method and apparatus and  FIG. 6B  is an explanatory view of change in temperature of this embodiment. 
         FIG. 7A  is a schematic view of the prior art heat-sealing apparatus and  FIG. 7B  is a cross sectional view of this apparatus. 
         FIG. 8  is a sectional view showing another example of the heating ring of the present invention. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION  
     Description will now be made in detail about embodiments of the present invention with reference to the accompanying drawings. 
       FIGS. 1 and 2  show an embodiment of the container heat-sealing method and apparatus.  FIG. 1  is an exploded view of the container and  FIG. 2  is a vertical sectional view of the embodiment of the heat-sealing apparatus. 
     In this container heat-sealing apparatus (hereinafter referred simply to as “heat-sealing apparatus”)  20 , as shown in  FIG. 1 , a container  10  is composed of a container main body  11  and a cap  12  which covers the container main body  11 . This container main body  11  is formed in the shape of a cup and has, in the periphery of an upper end opening portion, a flange portion  11   a  which extends horizontally outwardly. The cap  12  has, in its outer peripheral portion, a heat seal portion  12   a  which extends horizontally corresponding to the flange portion  11   a.  This annular heat seal portion  12   a  is formed integrally on the inner side thereof with a recessed cap portion  12   b  which projects downwardly to be positioned in the container. As the cap  12 , a normal flat plate type cap including the heat seal portion  12   a  and is not formed in the shape of a recessed cap portion may also be used. 
     The heat-sealing apparatus  20  which heat-seals the container main body  11  and the cap  12  together has, as shown in  FIG. 2 , a seal head  21 . 
     A seal head main body  22  of the seal head  21  is provided with a heat welding member  23  having the same shape as and corresponding to the shape of the heat seal portion  12   a  of the cap  12 , for example, a hollow ring shape, in such a manner that the lower surface of the heat welding member  23  is exposed. The hollow portion  23   a  of the heat welding member  23  constitutes a flow-path of a cooling medium, e.g., cooling water and a cooling medium pipe  24  is connected to the flow-path to supply and exhaust the cooling medium. 
     This heat welding member  23  is made of a material, e.g., metal, which can be heated by high frequency induction heating. 
     A high frequency heating coil  25  is disposed above the heat welding member  23  of the seal head main body  22  of the seal head  21 . The coil  25  has windings of, e.g., three windings in a horizontal plane parallel to the upper surface of the heat welding member  23  and is connected to a high frequency power source through an electric current supply member (feeder)  26  connected to one end portion of the coil  25 . This high frequency heating coil  25  is also made hollow and a cooling medium such as cooling water can be supplied to and exhausted from this hollow portion via a cooling medium pipe  27 . 
     A ferromagnetic substance member  28  is provided in the seal head main body  22  in a manner to surround the heat welding member  23  and the high frequency heating coil  25 . The seal head  21  thus composed can be moved vertically and moved for pressing by means of an unillustrated elevating and pressing device. 
     In this heat-sealing apparatus  20 , a container support  29  is provided below the seal head  21  to support the lower surface of the flange portion  11   a  of the container main body  11 . 
     The cap  12  is placed on the container main body  11  which is supported by the container support  29  and is filled with contents and, after the heat seal portion  12   a  of the cap  12  is superposed on the flange portion  11   a  of the container main body  11 , the cap  12  is pressed between the container support  29  and the seal head  21 . 
     Description will now be made about the operation of the heat-sealing apparatus  20  having the above described structure as well as the method for heat-sealing a container. 
     This type of heat-sealing apparatus  20  is normally provided on a filling line of the container  10  and is used for high speed continuous production according to which contents are filled in the container main body  11  and then the cap  12  is placed on the container main body  11  and sealed by heat-sealing. Description will however be made with respect to an example in which a single container is heat-sealed. 
     After contents are filled in the container main body  11  of which the flange portion  11   a  is supported by the container support  29 , the cap  12  is placed on the container main body  11  and the heat seal portion  12   a  of the cap  12  is superposed on the flange portion  11   a  of the container main body  11  with the recessed cap portion  12   b  projecting into the head space of the container main body  11  thereby reducing the capacity of the head space. In a case where a normal flat type cap having no recessed cap portion is used as the cap, the cap  12  is placed on the container main body  11  in such a manner that the heat seal portion  12   a  is superposed on the flange portion  11   a.    
     In the seal head  21 , in parallel to mounting of the cap  12 , high frequency current is supplied from the high frequency current source to the high frequency heating coil  25  through the electric current supply member  26  to heat the surface of the heat welding member  23 . This heating by the high frequency heating coil  25  is high frequency induction heating according to which high frequency flux generated by high frequency current penetrates the heat welding member  23  which is the object of heating and thereby induces an eddy current having a very high density which heats the surface of the heat welding member  23 . 
     The temperature of heating of this seal head  21  will suffice if the container main body  11  and the cap  12  which constitute the container  10  to be welded by heat-sealing are welded and sealed together. Temperature control is made by determining the temperature of heating at a proper value depending upon the materials of the container main body  11  and the cap  12 . By way of example, in a case where the cap is made of polyethylene terephthalate resin or a case where the cap is made of stacked layers and polypropylene resin is used as an inner sealant material, temperature required for heat-sealing usually is within a range from 180° C. to 220° C. 
     The seal head  21  which has been heated to a temperature required for heat-sealing is moved by the unillustrated elevating and pressing device to press the heat seal portion  12   a  of the cap  12  to the flange portion  11   a  of the container main body  11  which is supported by the container support  29  with the cap  12  placed thereon. 
     Since the heated heat welding member  23  of the seal had  21  has the same shape as the shape of the flange portion  11   a  and the heat seal portion  12   a,  a portion which is necessary for heat-sealing only is heated and pressed and heat-sealing is made at a predetermined temperature. 
     In the heating by this seal head  21 , the central portion (the recessed portion  12   b ) of the cap  12  is not directly heated by virtue of the shape of the heat welding member  23  and the shape of the cap  12  having the recessed portion  12   b  but the flange portion  11   a  and the heat seal portion  12   a  only are directly heated and, therefore, even heat-sealing is made at a high temperature, inflation of gas in the head space of the container main body  11  can be held to the minimum and expansion of the cap  12  can also be prevented so that failure in sealing due to these causes can be prevented. Even if the cap  12  is formed in a flat plate shape, direct heating of its central portion can be prevented. 
     Then, cooling water as the cooling medium is supplied to the hollow portion  23   a  of the heat welding member  23  of the seal head  21  through the cooling medium pipe  24  for cooling the heat welding member  23  compulsorily while the heat welding member  23  is kept pressed to the heat seal portion  12   a  of the cap  12 . The seal head  21  then is elevated by the elevating and pressing device and heat-sealing of one container  10  is thus completed. 
     Since pressing is finished after the heat welding member  23  is cooled in the above described manner, even if the heat-sealing is made at a high temperature, adhering of the cap  12  (i.e., a covering material of the cap such as a heat-sealing film) to the surface of the heat welding member  23  can be prevented and, therefore, high speed and stable heat-sealing can be achieved. Accordingly, materials which have been said to have difficulty in heat welding such as polyester resins e.g., polyethylene terephthalate and polyethylene naphthalate and polyamide resins e.g., nylon can be used for heat-sealing whereby the scope of materials to which heat-sealing is applicable can be broadened. 
     By forming a cover layer  30  made of a material which can prevent heat welding of the heat seal portion  12   a  of the cap  12 , e.g., fluorine containing resin or polyimide on the surface of the heat welding member  23  which contacts the heat seal portion  12   a  of the cap  12 , adhering of the cap  12  can be completely prevented. 
     For preparing for heat-sealing of a next container, cooling medium exhausting means  31  may be provided for exhausting the cooling medium which was supplied to the hollow portion  23   a  of the heat welding member  23  so that next heating may be made easily and in a short period of time. As this cooling medium exhausting means  31 , for example, a changeover valve  32  may be provided in the cooling medium pipe  24  to enable supply of a fluid  33 , e.g., compressed air, which has a smaller heat capacity than the cooling medium so that the cooling medium may be replaced by air simultaneously with exhaustion and recovery of the cooling medium from the hollow portion  23   a  of the heat welding member  23 . 
     By replacing the cooling medium in the hollow portion  23   a  of the heat welding member  23  by air having a smaller heat capacity than the cooling medium such as cooling water, heating time can be shortened and heat-sealing thereby can be made at a higher speed. 
     For shortening heating time until next heat-sealing after cooling of the seal head  21 , an electric heater  34  which constitutes the temperature holding means may be provided adjacent to the heat welding member  23  of the seal head  22  and temperature may be controlled so that, after temperature is lowered to a value at which adhering of the cap  12  can be prevented, the temperature will not be lowered further so that a temperature which becomes a basis of temperature range of heating and cooling, i.e., the lowest temperature in the temperature range, can be maintained. 
     By this arrangement, even when high frequency induction heating of the heat welding member  23  of the seal head  21  is made with the high frequency heating coil  25 , temperature is maintained at the lowest temperature required for heat-sealing by the electric heater  34  or the like constituting the temperature holding means and, therefore, heating may be made on the basis of this lowest temperature in the temperature range, i.e., heating starting temperature whereby the heat welding member  23  can be heated to the heat-sealing temperature in a shorter period of time. 
     In a case where high-speed continuous heat-sealing is made by using such heat-sealing apparatus  20 , a rotary type heat-sealing apparatus  40  (hereinafter referred simply to as “heat-sealing apparatus  40 ) as shown in the schematic plan view of  FIG. 3 , for example, is used. 
     In this heat-sealing apparatus  40 , a container main body supply unit A of a rotary type container main body conveying apparatus  41  which conveys the container main body  11  filled with contents conveys the container main body  11  to a cap supply position B while replacing the head space of the container main body  11  with inert gas or other gas. At this cap supply position B, the cap  12  which is conveyed from a cap stack position C by a cap conveying apparatus  42  is placed on the container main body  11  and the container main body  11  then is conveyed to a heating position D of the container main body conveying apparatus  41  by moving in a rotating locus. 
     At this heating position D, the seal head  21  which is induction heated by the high frequency induction coil  25  is lowered to press and heat the heat seal portion  12   a  of the cap  12  and conveys the container main body  11  to a cooling position E in a rotating locus while maintaining this pressing state. 
     At the cooling position E, cooling water is supplied as the cooling medium from the cooling medium pipe  24  to the hollow portion  23   a  of the heat welding member  23  to start cooling. Then, at a container discharge position F, the seal head  21  is elevated and the sealed container  10  is discharged. 
     Thus, heat-sealing of one container is completed in the rotary conveying of the container from the cap supply position B to the container discharge position F. Then, in the course of return movement from the container discharge position F to the heating position D, discharge of the cooling medium and high frequency induction heating necessary for next heat-sealing are made at a position such as position G. 
     According to the heat-sealing apparatus  40  combined with the rotary type conveying apparatus, heat-sealing can be finished by cooling while the seal head is maintained in a pressing state and, therefore, heat-sealing can be made continuously at a high speed. For example, according to this heat-sealing apparatus  40 , high speed sealing of 600 containers per minute can be realized in contrast to the prior art apparatus in which heat-sealing speed is 20 to 30 containers per minute. 
       FIG. 4  is a schematic view of another embodiment of the invention and  FIG. 5  is a schematic vertical section of the embodiment of  FIG. 4 . 
     A heat-sealing apparatus  20  for carrying out heat-sealing comprises, as shown in  FIGS. 4 and 5 , a seal head  122  which is mounted on the lower surface of an upper portion of an apparatus frame  121 . 
     This seal head  122  comprises a seal head main body  123  which is composed of a cylindrical central member  123   a  and an outer annular member  123   b.  The central member  123   a  and the annular member  123   b  are attached concentrically to the apparatus frame  121  and an annular opening  123   c  between the central member  123   a  and the annular member  123   b  constitutes an annular opening corresponding to the shape of the heat seal portion  12   a  of the cap  12  which has the same shape as the flange portion  11   a  of the container  10 . 
     In the annular opening  12   c  of the seal head  123 , there is provided a heating ring  124  shaped along the heat seal portion  12   a  which is the same as shape of the flange portion  11   a  of the container main body  11 . 
     The heating ring  124  is shaped in the form of a ring having a generally U-shaped section which opens upwardly and having outwardly extending flange portions  124   a  at both inner and outer circumferences in the upper portion. The flange portions  124   a  are in abutting engagement with stepped portions formed in the lower portions of the seal head main body  123 . A bottom portion  124   b  of the heating ring  124  is exposed in the lower surface thereof to the space below and held between a support plate  123   d  in the shape of a disk and a support plate  123   e  in the shape of a ring. By this arrangement, an annular space is formed with the apparatus frame  121 , the seal head main body  123  and the heating ring  124 . 
     The bottom portion  124   b  of the heating ring  124  is made hollow to form a hollow portion  124   c  which constitutes a flow-path of a cooling medium such as cooling water. A plurality of cooling medium supplying and exhausting openings  124   d  are formed to communicate with the flow-path. In the illustrated example, two opening  124   d  are formed at diagonal positions and these openings  124   d  are respectively connected to cooling medium pipes  125  so hat the cooling medium can be supplied and exhausted from either of these pipes  125 . 
     The heating ring  124  is made of a material, e.g., metal, which can be heated by high frequency induction heating. 
     In the annular space between the seal head main body  123  and the heating ring  124  of the seal head  122 , a high frequency induction heating coil  126  is disposed in such a manner that it is held on both sides thereof between magnetic shielding plates  127 . This high frequency induction heating coil  126  is wound, for example, in plural windings in both horizontal and vertical directions and is connected to a high frequency oscillator  128  via an electricity supply member (feeder)  128   a  provided at the end of the coil  126 . This high frequency induction heating coil  126  is made hollow to form a hollow portion and the cooling medium such as cooling water can be supplied to and exhausted from this hollow portion through an unillustrated cooling medium pipe. 
     Opposing the seal head  122 , a container support  129  is provided in the lower portion of the apparatus frame  121  to support the lower surface of the flange portion  11   a  of the container main body  11  of the container  10 . 
     In this heat-sealing apparatus  20 , an elevating and pressing device  130  is provided so that, after the cap  12  is placed on the container main body  11  which is supported by the container support  129  and filled with contents in such a manner that the heat seal portion  12   a  of the cap  12  is superposed on the flange portion  11   a  of the container main body  11 , these portions can be pressed between the container support  129  and the seal head  122 . 
     To this elevating and pressing device  130  is attached the container support through an air cylinder  131 . By elevating the container support  129  and further stretching the rod, the heat seal portion  12   a  of the cap  12  superposed on the flange portion  11   a  of the container main body  11  is pressed between the container support  129  and the seal head  122 . 
     Pressing of the heat-sealing portion  12   a  of the cap  12  superposed on the flange portion  11   a  of the container  11  may be made not only by vertically moving the container support  129  but also by vertically moving the seal head  122 . 
     Description will now be made about the operation of the heat-sealing apparatus  20  constructed in the above described manner as well as the method for heat-sealing the container. 
     This type of heat-sealing apparatus  20  is normally provided on a filling line of the container  10  and is used for high speed continuous production according to which contents are filled in the container main body  11  and then the cap  12  is placed on the container main body  11  and sealed by heat-sealing. Description will however be made with respect to an example in which a single container is heat-sealed. 
     After contents are filled in the container main body  11  of which the flange portion  11   a  is supported by the container support  129 , the cap  12  is placed on the container main body  11  and the heat seal portion  12   a  of the cap  12  is superposed on the flange portion  11   a  of the container main body  11  with the recessed cap portion  12   b  projecting into the head space of the container main body  11  thereby reducing the capacity of the head space. In a case where a normal flat type cap having no recessed cap portion is used as the cap, the cap  12  is placed on the container main body  11  in such a manner that the heat seal portion  12   a  is superposed on the flange portion  11   a  as shown in  FIGS. 4 and 5 . 
     In the seal head  122 , in parallel to mounting of the cap  12 , high frequency current is supplied from the high frequency oscillator  128  to the high frequency induction heating coil  126  through the electric current supply member  128   a  to heat the surface of the bottom portion  124   b  of the heating ring  124 . This heating by the high frequency induction heating coil  126  is high frequency induction heating according to which high frequency flux generated by high frequency current penetrates the heating ring  124  which is the object of heating and thereby induces an eddy current having a very high density which heats the surface of the bottom portion  124   b  of the heating ring  124 . 
     The temperature of heating of this heating ring  124  of the seal head  122  will suffice if the container main body  11  and the cap  12  which constitute the container  10  to be welded by heat-sealing are welded and sealed together. Temperature control is made by determining the temperature of heating at a proper value depending upon the materials of the container main body  11  and the cap  12 . By way of example, in a case where the cap is made of polyethylene terephthalate resin or a case where the cap is made of stacked layers and polypropylene resin is used as an inner sealant material, temperature required for heat-sealing usually is within a range from 180° C. to 220° C. 
     Then, by operating the air cylinder  131  of the elevating and pressing device  130 , the container main body  11  which is supported by the container support and is covered with the cap  12  with the heat seal portion  12   a  of the cap  12  being superposed on the flange portion  11   a  of the container main body  11  is elevated and pressed to the seal head  122  in which the heating ring  124  has been heated to a temperature necessary for heat-sealing. 
     Since the heating ring  124  of the seal head  122  is formed along (i.e., in the same shape as) the shape of the flange portion  11   a  and the heat seal portion  12   a,  heat-sealing is performed at a predetermined temperature with the portion necessary for heat-sealing only being heated and pressed. 
     The heating and cooling processes by the heat-sealing apparatus  20  and temperature change in these processes are shown in  FIGS. 6A and 6B . As shown in these figures, the heating ring  124  is heated to a predetermined temperature, e.g., 180° C. and then heating by the high frequency oscillator  128  is stopped and pressing by the elevating and pressing device  120  only is maintained. 
     In the heating by this seal head  122 , the central portion (the recessed portion  12   b ) of the cap  12  is not directly heated by virtue of the shape of the heating ring  124  and the shape of the cap  12  having the recessed portion  12   b  but the flange portion  11   a  and the heat seal portion  12   a  only are directly heated and, therefore, even if heat-sealing is made at a high temperature, inflation of gas in the head space of the container main body  11  can be held to the minimum and expansion of the cap  12  can also be prevented so that failure in sealing due to these causes can be prevented. Even if the cap  12  is formed in a flat plate shape as shown in  FIGS. 4 and 5 , direct heating of its central portion can be prevented. 
     Since the heating ring  124  is formed in the annular shape having the U-shaped section, the heating ring  124  is thin and has a small heat capacity and therefore can be heated to a high temperature in a short-period of time with the high frequency induction coil  126  having plural windings in the horizontal and vertical directions. Moreover, drop in the temperature after stopping supply of electric current is relatively small and a predetermined temperature can be maintained whereby sealing can be achieved by maintaining pressing with the heating ring  124  for a period of time necessary for heat-sealing. 
     After heat welding by the heating ring  124  of the seal head  122  is made by maintaining pressing of the heating ring  124 , cooling water as the cooling medium is supplied through the cooling medium pipe  125  to the cooling medium flow-path formed by the hollow portion  124   c  of the heating ring  124  with one of the cooling medium supplying and exhausting openings  124   d  being used as a supplying opening and another of the openings  124   d  being used as an exhausting opening to compulsorily cool the heating ring  124 . After the heating ring  124  is cooled to a predetermined temperature, the container support  129  is lowered by the elevating and pressing device  130  to complete heat-sealing of one container  10 . Cooling of the heating ring  124  to a predetermined temperature is continued even after lowering of the container  10  and discharge of water (see  FIG. 6A ) to be described later is performed. 
     By this arrangement, since pressing is finished while the heating ring  124  of the seal head  122  is cooled, even if heating time is shortened by elevating the heating temperature, adhering of the cap  12  (i.e., the covering material of the cap such as a heat-sealing film) to the surface of the heating ring  124  of the seal head  122  can be prevented whereby high-speed and stable heat-sealing can be achieved. Besides, since the heating ring  124  is formed annularly and thin, it has a small heat capacity and therefore can be cooled in a short period of time. 
       FIG. 8  shows a modified example of the heating ring. 
     In the heating ring  224  of  FIG. 8 , the same component elements as those of the heating ring shown in  FIG. 5  are designated by the same reference characters and description thereof will be omitted. 
     This heating ring  224  is divided in two portions of the upper portion and the lower portion. The upper portion  224   a  is formed integrally with a central portion  123   a  and is made of a synthetic resin, e.g., polyether ether ketone resin and the lower portion  224   b  is made of metal. A cooling medium is supplied to an opening portion  226  between the upper portion  224   a  and the lower portion  224   b.  A gap between the upper portion  224   a  and the lower portion  224   b  is sealed with an O-ring  227 . Reference character  228  designates a blank plug and reference character  229  designates a heating ring holder. 
     According to such heat-sealing apparatus  20 , materials which have been said to have difficulty in heat welding such as polyester resins e.g., polyethylene terephthalate and polyethylene naphthalate and polyamide resins e.g., nylon which have a relatively high melting point can be used as the cap for heat-sealing whereby the scope of materials to which heat-sealing is applicable can be broadened. Additionally, thickness of the cap can be increased to such a degree that the invention is applicable to a cap formed by injection molding. Even in a case where the material of the cap is changed in the above described manner, by maintaining pressing of the heating ring  124  for a period of time after heating the heating ring  124  to a predetermined temperature until start of the cooling process with supply of electric current being stopped, temperature and time necessary for heat welding the material can be secured. 
     By forming, as shown in the enlarged view of  FIG. 5 , a cover layer  124   e  which is made of a material such as fluoride resin or polyimide which can prevent heat welding of the heat seal portion  12   a  of the cap  12  at least on the surface of heating ring  124  which contacts the heat seal portion  12   a  of the cap  12 , adhering of the cap  12  can be completely prevented. 
     For preparing for next heat-sealing of a container, the cooling medium which has been supplied to the hollow portion  124   c  of the heating ring  124  may be discharged by providing an unillustrated cooling medium exhausting means whereby discharge of water can be made in a simple manner so that heating of the cooling water in the hollow portion  124   c  in next heat-sealing will be obviated and heating of the heating ring  124  can be made easily and in a short period of time. 
     As this cooling medium exhausting means, for example, a changeover valve may be provided in the cooling medium pipe  125  to enable supply of a fluid such as compressed air which has a smaller heat capacity than the cooling medium so that air can replace the cooling medium while the cooling medium is discharged and recovered from the hollow portion  124   c  of the heating ring  124 . 
     According to this arrangement, by replacing the cooling medium in the hollow portion  123   a  of the heat welding member  123  with air which has a smaller heat capacity than the cooling water used as the cooling medium, heating time can be shortened and high speed heat-sealing thereby can be realized. 
     For further shortening heating time until next heat-sealing after cooling of the seal head  122 , an electric heater which constitutes the temperature holding means may be provided adjacent to the heat welding member  124  of the seal head  122  and temperature may be controlled so that, after temperature is lowered to a value at which adhering of the cap  12  can be prevented, the temperature will not be lowered further so that a temperature which becomes a basis of temperature range of heating and cooling, i.e., the lowest temperature in the temperature range, can be maintained. 
     By this arrangement, even when high frequency induction heating of the heat welding member  124  of the seal head  122  is made with the high frequency induction heating coil  126 , temperature is maintained at the lowest temperature required for heat-sealing by the electric heater or the like constituting the temperature holding means and, therefore, heating may be made on the basis of this lowest temperature in the temperature range, i.e., heating starting time whereby the heat welding member  124  can be heated to the heat-sealing temperature in a shorter period of time. 
     Further, by supplying and exhausting the cooling medium through different ones of cooling medium supplying and exhausting openings  124   d  when the heating ring  124  is cooled after finishing heat-sealing of a next container, drop of temperature in the portion of the heating ring  124  where the cooling medium enters and elevation of temperature in the portion of the heating ring  124  where the cooling medium exits can be prevented whereby uniform cooling can be ensured notwithstanding repeated heating and cooling. By this arrangement, temperature of the heating ring  124  by subsequent heating can be made uniform whereby heat-sealing can be made with a stable quality. 
     In the above described embodiment, two cooling medium supplying and exhausting openings  124   d  are diagonally provided and cooling is made by changing the cooling medium supplying opening and the cooling medium exhausting opening alternately each time the container  10  is changed. Alternatively, more than two cooling medium supplying and exhausting openings may be provided and cooling may be made by changing the cooling medium supplying opening and the cooling medium exhausting opening in a predetermined order, or detecting temperature in some portions of the heating ring  124  and supplying and exhausting the cooling medium at a suitable position randomly so that distribution in the temperature will not be produced. Further alternatively, the cooling medium may be supplied simultaneously from plural positions and exhausted from plural positions or a single position or the cooling medium may be supplied from a single position and exhausted from plural positions. 
     In the above described embodiments, description has been made with respect to a case where the cap having a recessed cap portion or a flat cap portion is placed on the container main body having the shape of a cup. The shapes of the cap and the container main body are not limited to these shapes but other shapes such as a tray may be used as the shapes of the cap and the container main body. 
     In the above described embodiments, either the seal head or the container support is moved vertically to heat-seal a container during the heat-sealing process of the container. In these embodiments, the other of the seal head and the container support which has been described as moveing vertically in these embodiments may be moved vertically for heat-sealing. 
     Supply of the cooling medium may be omitted depending upon the material of the cap or the conditions of heating. In this case, time for the entire heat-sealing process may be shortened or heating time may be lengthened. 
     Since heat-sealing at a high speed can be made, drinks which have in the past been filled in a metal can or a PET bottle may be filled in the container used in the present invention and the container may be sealed at a high speed. Prepared food containing a solid food or viscous food may also be filled in the container used in the present invention and the container may be sealed at a high speed. 
     INDUSTRIAL APPLICABILITY  
     The present invention is applicable to a method and an apparatus for heat-sealing a container. Particularly, in the case of heat-sealing a cap in the form of a film on a container main body in the form of a cup made of paper or a synthetic resin, heat-sealing can be made at a high speed in a stable manner.