Induction heating unit for heat bonding a lid having a metallic layer to a container

This relates to an apparatus for heat bonding a lid having a metallic layer to a plastic container. The container, filled with a product, is seated in a nest and a lid is seated in place thereon. There is at least one corner on the lid and projecting from that corner is a pull tab. An induction heating unit is associated with the lid and presses it tightly against the container while inducing electrical energy under controlled conditions into the metal layer. The induction heating unit is provided with a specific arrangement of ferrite members for controlling the induction of current into the metallic layer. The ferrite parts in conjunction with the induction coil serve to concentrate the induced electrical energy into substantial alignment with the induction coil notwithstanding the fact that there is a corner and there is projecting from the corner of the lid a pull tab.

This invention relates in general to new and useful improvements in the 
application of closures to containers, and more particularly the 
application of a primarily plastic lid to a plastic container. 
In accordance with this invention there is provided a container, which is 
preferably box-like, formed of a suitable plastic material and having an 
exposed surface formed of a heat bondable plastic material. The container 
is closed by way of a lid which is also primarily formed of plastic but 
which has incorporated therein a metallic layer into which electrical 
energy may be induced. The lid has an exposed undersurface which is also 
formed of a heat bondable plastic material, which plastic material of the 
lid is heat bondable to the plastic material of the container. 
It is known that one my induce electrical current into metal for the 
purpose of heating the metal. The heat pattern induced into the metal is 
generally in accordance with the configuration of an induction coil. It is 
also known to utilize ferrite as a means for controlling the introduction 
of current into the metallic material. This invention relates to a 
specific heating unit including a specific relationship of the induction 
coil to ferrite current concentrators. It is the purpose of this invention 
to uniformly concentrate the introduction of electrical current into the 
metallic layer of the lid so as to provide for a concentration of the 
heating of the lid and container opposed surfaces along a narrow pattern 
with such heating and thus bonding being uniform throughout the length of 
the heating pattern. By concentrating the heat, less energy is expended in 
the heat bonding of the lid to the container, and a more uniform bond is 
obtainable. This, in turn, provides not only for a better package, but 
also for a lower power source and a shorter time of operation. 
Other problems are involved. Most particularly, since the lid has rounded 
corners, the concentration of induced electrical current must be 
specifically controlled in the corners. 
Next, not all corners of the lid are identical. In order to minimize the 
force required to effect peeling of the lid from the container during the 
opening of the container, at least that corner where peeling is initiated 
is provided with a very small radius. 
In addition, the lid, in order to facilitate removal, is provided with a 
projecting pull tab. The pull tab is formed of the same material as the 
lid with the result that it includes the metallic layer which absorbs 
certain of the electrical current and also certain of the heat from the 
metallic layer of the lid. Special efforts must be taken to compensate for 
the existence of the pull tab.

Referring now to the drawings in detail, it will be seen that there is 
illustrated in FIG. 2 a typical environment of the invention wherein a 
lid, generally identified by the numeral 20, is to be heat bonded to a 
container 22 utilizing an induction heating unit which is generally 
illustrated in FIG. 1 and is identified by the numeral 24. In the 
illustrated embodiment of the container 22 and the lid 20, there are four 
sides joined by four corners with three of the corners being identical and 
the fourth corner being of a smaller radius. The three corners are 
identified by the numeral 26 while the fourth corner is identified by the 
numeral 28 and has projecting therefrom a pull tab 30 which is connected 
to the remainder of the panel by way of a narrow neck 32. 
Referring now to FIGS. 3, 4 and 5, it will be seen that the container 22 is 
of a stepped wall construction including an upper wall part 34 which 
terminates in an outwardly directed flange 36. The flange 36, in turn, 
terminates in a depending reinforcing flange 38. 
The lid 20 is to be heat bonded to the upper surface of the flange 36. In 
order that the lid may be easily and accurately positioned relative to the 
flange 36, the flange 36 has formed therefrom an upwardly directed rib 40 
which is of an inverted channel shaped cross section and which extends 
entirely about the periphery of the flange 36 except at the corner 28. It 
will be seen that when the rib 40 is formed from the flange 36, the 
thickness of the flange is diminished as opposed to its thickness where 
there is no rib. This reduction in thickness is best illustrated in FIG. 5 
and will be discussed more hereinafter. 
Reference is now made to FIG. 7 wherein it will be seen that both the lid 
20 and the container 22 are of a multilayered construction. The lid is 
preferably, but not limited to an outer layer 42 formed of a polypropylene 
copolymer. The outer layer 42 is directly bonded to an intermediate layer 
44 formed of a homopolymer with the layer 44 having bonded thereto a very, 
very thin layer 46 of a plastic adhesive which will bond to the 
homopolymer layer 44 and a metal foil layer 48 which is preferably formed 
of aluminum. There is a final layer 50 which is similar to the layer 46. 
The container 22, on the other hand, is generally of a thermoformed 
construction and includes the base layer 52 which is formed of a suitable 
polypropylene. A barrier layer 54, such as SARAN, EVAL and the like, is 
bonded to the base layer 52 by a very thin plastic adhesive layer 56. A 
similar layer 58 bonds the barrier layer 54 to a special layer 60 which is 
of a construction wherein when subject to a peeling action will internally 
fracture or separate. In accordance with this invention, the lid 20 is to 
be applied to the container 22 by way of a heat bond between the layers 50 
and 60 with the heat bond being of a very controlled nature and being 
formed by induction heating through the inducing of a current into the 
metal layer 48 under controlled conditions. 
Referring now to FIG. 8, it will be seen that the induction heating unit 24 
includes a support 62 formed of a suitable plastic material so as to have 
insulating characteristics. The support 62 has a face 64 from which a 
solid induction coil 66 depends. The induction coil 66 has an exposed face 
68 which is intended to engage the outer surface of the lid 20 and a 
tubular base 70 to which the solid induction coil 66 is preferably secured 
such as by silver soldering. The face 64 of the support 62 is provided 
with a peripheral recess or groove 72 in which the tubular base 70 is 
seated. 
As is customary, the induction coil 66 is provided with twin leads 74, 76 
which, in turn, will be coupled to a suitable source of high frequency 
electrical energy (not shown). 
At this time, it is pointed out that when the induction heating unit 24 
performs satisfactorily, substantially only that portion of the lid 20 and 
the container 22 aligned with the face 68 of the induction coil 66 will be 
heated. When proper bonding occurs, the layers 50 and 60 will be heat 
bonded together as previously described. 
When the lid 20 is peeled from the container, the layer 60 will internally 
rupture and that part of the layer 60 bonded to the layer 50 will remain 
bonded to the layer 50, thus providing a clear indication of the extent 
and quality of the heat bond between the layers 50, 60. Further, by 
permitting the layer 50 to be natural in color, i. e. generally 
transparent, and by coloring the layer 60 white or a similar color, it 
will be immediately apparent as to the extent of the heat bond between the 
layers 50, 60. 
On the other hand, the layer 50 will discolor in the areas where it is 
heated. In order to obtain maximum efficiency and maximum concentration of 
the induced current, it is desired that the induced current into the lid, 
as well as into the container, be substantially in alignment with the face 
68 of the induction coil 66. On the other hand, there is illustrated in 
FIG. 6 a lid 20 which was bonded to a container 22 and then peeled 
therefrom, which lid was heat bonded to the container during an early 
phase of the development of the induction heating unit. It will be seen 
that within the ruptured band of the layer 60 the layer 50 is discolored 
to define heated areas 77 well within the confines of the bond between the 
layers 50, 60. The net result was that while from time to time 
satisfactory bonds between the layers 50 and 60 could be obtained, there 
was a certain degree of overheating and most particularly a large waste of 
energy. This large of waste of energy required not only a heating unit 
with greater capacity, but also more operational time. In a properly 
heated lid, the heat zones 77 would be substantially nonexistent. 
It will be seen from the heat pattern 77 of FIG. 6 that conditions along 
the straight sides of the lid were quite different from those at the 
corners of the lid and that much greater control of the induced current 
was required along the corners. 
At this time it is pointed out that subsequent to the heat bonding of the 
lid illustrated in FIG. 6 to a container, the configuration of the heat 
bond between the lid and the container has been changed so as to provide 
for the relatively sharp corner 28 adjacent the pull tab 30. 
Returning once again to FIG. 8, as well as FIG. 1, it will be seen that 
disposed radially inwardly of the induction coil 66 is a first ferrite 
member identified by the numeral 78. The ferrite member 78 is generally 
L-shaped and includes a vertical leg 80 which is disposed closely adjacent 
to and parallel to the lower part of the induction coil 66. The ferrite 
member 78 also includes a horizontal leg 82 disposed at the upper end of 
the leg 80 and extending generally radially inwardly away from the 
induction coil 66. It is to be noted that the leg 82 is seated on a spacer 
84, which in turn, is seated on the face 64 of the support 62. The spacer 
84 is provided with a peripheral notch 86 in which the leg 82 seats. 
The leg 82 is clamped against the spacer 84 by a current director 88 which 
engages the underside of the leg 82. The current director 88 is secured to 
the spacer 84 by means of suitable fasteners 90. It is to be understood 
that the current director 88 is preferably formed of a sheet of aluminum. 
While the ferrite member 78 does adequately function to concentrate the 
induced heat in the lid 20 to that portion generally aligned with the face 
68 of the induction coil 66 along the straight edges of the lid 20, 
special current concentration must be effected at the corners. 
Furthermore, the current concentration at the corners 26 will be different 
from that at the corner 28 because of the influence of the pull tab 30. 
Referring now to FIGS. 9 and 10, which is a typical construction of the 
induction heating unit 24 for a corner 26, it will be seen that there is 
formed in the upper surface of the support 62 centered on the induction 
coil 66 at the center of the curvature of the corner 26 a square end bore 
92 which is of a depth to leave only a shallow strip of the material of 
the support 62 at the top of the groove 72, the strip being identified by 
the numeral 94. 
In addition to the bore 92, whose position is best shown in FIG. 10, at 
each corner 26 there is also a pair of small diameter bores 96 whose 
positions are best illustrated in FIG. 10. 
An inverted U-shaped ferrite member 98 has a cross bar portion 100 thereof 
seated in the bore 92 and depending legs 102 extending through the bores 
96. 
Overlying the cross bar portion 100 is another ferrite member 104 which is 
similar to the cross bar portion 100. 
A silicone sponge member 106 is pressed into the upper portion of the bore 
92 and serves to hold the ferrite members 98 and 104 clamped in position. 
It is to be understood that the ferrite members 98 and 104, together with 
the ferrite member 78, serve to control the flow of induced current into 
the metallic layer 48 so as to concentrate the heating of the layers 50 
and 60 to an area aligned with a corner portion of the induction coil face 
68. 
At the corner 28, not because of the change in configuration, but because 
of the existence of the pull tab 30, the flow of induced current at the 
corner 28 is different from that at the corner 24. Accordingly, there are 
provided additional ferrite members. The additional ferrite members 
include a generally triangular ferrite member 108 which is positioned 
adjacent the base of the induction coil 66 radially inwardly thereof and 
between the ferrite member 98 and the ferrite member 78, as is best shown 
in Figures 11 and 12. In order to receive the ferrite member 108, the 
spacer 84 is cut away at the corner 28 as will be obvious from a 
comparison of FIGS. 9 and 11. 
There is also provided a ferrite member 110 which is arcuate in plan and 
angular in elevation. The ferrite member 110 has a base 112 which is 
seated against the lower portion of the induction coil 66, as is shown in 
FIG. 11, while extending around the corner 28 with the induction coil as 
shown in FIG. 12. The ferrite member 110 also includes an upstanding leg 
114 which abuts against the end of the associated leg 102 of the ferrite 
member 98. It has been found that the ferrite members 108 and 110 
compensate for the existence of the pull tab 30 and more particularly with 
respect to the metallic layer thereof so that the heating of the layers 50 
and 60 at the corner 28 is substantially maintained in alignment with the 
face 68 of the induction coil 66. 
Reference is now made to FIG. 8 wherein it is illustrated that when the lid 
20 is being applied to the container 22, the flange or rim 40 of the 
container is supported by a nest generally identified by the numeral 116. 
The nest 116 is a hollow member including a base 118 and an upstanding 
side wall 120. The upper end of the side wall 120 carries a plastic member 
122 which forms the direct support for the flange 40. In order that a 
vacuum may be drawn within the nest 116 surrounding the container 22, 
suitable openings 124 are formed in the upstanding wall 120. 
It is to be understood that the support 122 not only has insulating 
characteristics, both electrical and heat, but also that it have a certain 
degree of resiliency so that when the lid 20 is forced against the flange 
36 by the heating unit 24, there will be a certain degree of compensation 
for the difference in thickness of the flange 36 at the corner 28 as 
opposed along the straight line portions of the lid. 
It is to be understood that a vacuum is to be drawn within the container 
prior to the application of the lid 20. It is further desirable that the 
lids 20 be heat bonded to the containers 22 on an automatic basis. 
Accordingly, there is provided a suitable automatic apparatus which is 
illustrated in FIGS. 13, 14 and 15 and is generally identified by the 
numeral 126. 
First of all, there is a conveyor 128 for delivering a filled container 26 
having a lid 20 loosely seated thereon to the apparatus 126. The conveyor 
128 may be in the form of a plurality of interconnected plates 130 which 
have central openings 132 for receiving the containers 22 while supporting 
the containers by engaging the flanges 38 thereof. It is to be understood 
that the conveyor 128 will move normal to the FIG. 13 illustration. 
The nest 116 is carried by an upwardly movable support 134 which is mounted 
for straight line movement on a plurality of pins 136 which, in turn, are 
carried by a base member 138. The base member is carried by brackets 140 
which, in turn, are carried by a support member 142. 
The support 142 has mounted therein a first linear fluid motor 144 having a 
piston rod 146 which is provided at its free end with a guide rod 148. The 
piston rod 146 has its free end connected to a base 150 of a second 
extensible motor 152. The motor 152 has a piston rod 154 which is coupled 
to the support 134 for the nest 116. 
The support 134 has mounted in spring loaded relation thereabove and 
surrounding the base of the nest 116 a peripheral sealing member 156 which 
carries an upwardly facing sealing ring 158. The base of the nest 116 is 
provided with a sealing ring 160 about the periphery thereof with the 
sealing ring 160 contacting the inner surface of the sealing member 156 to 
maintain a sealed sliding relationship with respect thereto. 
Mounted above the base 142 is a suitable support 162 which carries in 
depending relation an extensible fluid motor 164. The motor 164 has a 
piston rod 166 which is connected to an upper part of a housing 168. The 
housing 168 has a sealing face 170 which opposes the sealing member or 
ring 156 and carries a sealing element or ring 172. 
There is mounted within the housing 168 a fixed support 174 which is 
carried by a suitable hanger type support 176 that extends through a slot 
178 in the housing 168. The support 174 has mounted thereon on the 
underside thereof the induction heating unit 24. 
The interior of the housing 168 carries a sealing ring 180 which engages 
the outer periphery of an upper part of the support 174 so as to maintain 
in the lower portion of the housing 168 a sealable compartment 182. 
At this time, with reference to FIGS. 1 and 8, it is to be noted that the 
underside of the current director 88 there is provided a machined central 
surface portion 184. An annular groove 186 is machined in this surface 
portion and has seated therein an O-ring 188. The O-ring 188 projects down 
below the lower surface of the director 88 and is adapted to come into 
sealing engagement with the upper surface of the lid 20. 
Within the area defined by the sealing ring 188 there is a plurality of 
vacuum ports 190 which are connected to a vacuum manifold 192. 
Returning to FIG. 13, it will be seen that the vacuum manifold 192 is 
connected to a vacuum passage 194 formed in the support 174 which in turn, 
is connected to a vacuum line 196. A further vacuum passage 198 is formed 
in the support 174 and opens through the periphery of the support 174 
within the housing 168. The vacuum passage 198 is connected to a second 
vacuum line 200. 
OPERATION 
It is to be understood that a container 22, filled with a product and 
having the lid 20 loosely seated thereon will be delivered by the conveyor 
128 into the space between the nest 116 and the induction heating unit 124 
and in alignment therewith. At this time the fluid motors 144 and 166 will 
be actuated so as to move the support 134 and the nest 116 upwardly while 
the body 168 moves downwardly. The nest 116 will pick the filled container 
22 up off of the plate 130 of the conveyor 128 and move the container 22 
and lid 20 to a position closely adjacent to the induction heating unit 
24. At that time the ring member will be moved to a position wherein the 
sealing ring 158 thereof will engage the underside of the conveyor plate 
130 and form a seal therewith. At the same time the lower face 170 of the 
housing 168 will approach the upper surface of the plate 130 and the 
sealing ring 172 carried thereby will form a seal with the upper surface 
of the plate 130. Vacuum is now drawn through the vacuum lines 196 and 200 
with preferably the vacuum being drawn through the line 196 shortly in 
advance of the vacuum being drawn through the line 200. The net result is 
that the lid 20 will be lifted minutely off of the container 22 and held 
against the underside of the O-ring 188. A vacuum will be drawn within the 
sealed off chamber defined in part by the housing 168, in part by the 
plate 130 and in part by the nest 116. Since the lid 20 has been lifted 
off of the container 22, the vacuum through the vacuum line 200 will be 
drawn within the container. After this occurs, the extensible fluid motor 
152 will be actuated to further move the nest 116 upwardly so that the lid 
20 engages the face 68 of the induction coil 66 at the preselected 
pressure. 
Then when the lid 20 is tightly clamped against the flange 36 of the 
container 22, the induction coil 66 will be temporarily energized so as to 
induce current into the metallic layer 48 for a sufficient time to effect 
the heating of the layers 50 and 60 to a self bonding temperature 
substantially only in alignment with the face 68 of the induction coil 66. 
As soon as the energization of the induction coil 66 has been completed, 
the extensible motors 144, 152 and 164 will be actuated in the opposite 
direction to open the apparatus 126 and to permit the conveyor plate 130 
to move out from between the induction heating unit 24 and the nest 116 
carrying the sealed container. The removal of the one conveyor plate 130 
will be followed by the movement of a next following conveyor plate and 
container and lid assembly to move into position for heat bonding of that 
lid to that container. 
Although only a preferred embodiment of the induction heating unit and the 
utilization thereof have been specifically illustrated and described 
herein, it is to be understood that minor variations may be made therein 
without departing from the spirit and scope of the invention as defined by 
the appended claims.