Method and device for the tape-sealing of panels of paper, cardboard, plastic, or wood, and adhesive tape therefor

A method and device for applying heat-activatable adhesive tape to boxes and the like, using sealing tape with adhesive that can be activated through radiant heat or hot air prior to its application to the box surface, where, in contact with a cold surface, the adhesive is instantaneously cured. The device includes a suction-type conveying device for the adhesive tape, either a belt conveyor cooperating with an infra-red heater, or a suction drum with a hot air supply.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the box making art, and more particularly 
to methods and devices for the tape-sealing of box panels of paper, 
cardboard, plastic, wood, and the like, as well as to adhesive tapes that 
are suitable for this purpose. 
2. Description of the Prior Art 
The manufacture of box containers for commercial goods involves in general 
the cutting of a box blank of predetermined configuration from a 
continuous web of cardboard, corrugated board, pasteboard, and the like, 
in an automatic blank cutting operation, whereupon the blank is creased 
along its fold edges, and the flaps are bent into place and permanently 
connected together. These flap connections, which are made in the process 
of mechanized box production, are commonly referred to as "factory seals" 
or "manufacturer's seals". 
The oldest version of commonly employed factory seals is the one using wire 
staples of round or flat wire. This design, however, necessitates an 
overlap between the flaps which are to be so connected, meaning that the 
boxes require larger blanks and additional folding operations. The 
overlapping box portions also make stacking of the finished boxes more 
difficult. A further problem of this design relates to the mechanical 
resistance of the stapled connections, especially in the case of 
light-weight cardboard boxes. Furthermore, the stapling operation is slow 
and therefore generally not very satisfactory, because it requires a 
stapler anvil, in order to hold the flaps together and to correctly close 
the staple. A still further shortcoming of this type of flap connection 
comes to the fore, when coated box materials are used, where the staples 
create breaks in the otherwise humidity-proof surface of the box, so that 
humidity may penetrate through these breaks along the staples, for 
example. 
Similar shortcomings are characteristic of a second mode of box flap 
connection, where overlapping flaps are directly bonded against one 
another. This kind of connection has the additional disadvantage that the 
mechanical resistance of the connection is determined by the tear 
resistance of the inner and outer webs that constitute the connection. 
This tear resistance, i.e. the resistance of the material against 
separation into different layers, is frequently inadequate for the 
specified purpose. 
It has further been suggested to employ adhesive tape, in order to produce 
factory seals on boxes of the above-mentioned type, such tapes being of 
the non-reinforced or bias-reinforced adhesive tape variety. This type of 
flap connection does not require the previously necessary overlap at the 
factory seal, thus simplifying the configuration of the box blank and the 
folding operation, as well as reducing the size of the blank. However, the 
known adhesive tapes of the humidity-activatable type have the 
disadvantage that they cannot be applied to coated surfaces. Consequently, 
it was impossible in the past to use such tapes for moisture-proof and 
water-proof plastic coated cardboard boxes. Until now, therefore, there 
has not been in existence a tape-sealing method which could be used 
economically for coated box containers. 
In general, the method of tape-sealing factory seals on boxes has been 
hampered by the problem of correct adhesive activation, the latter 
requiring a precisely controlled moisturization of the tape. But, since 
the optical degree of moisturization differs from adhesive to adhesive, 
and in some cases is even influenced by the conditions and duration of 
storage of the adhesive tape, problems of downtime and spoilage are 
common. A still further problem encountered with regular adhesive tapes is 
that the latter, after moisturization and application to the box surface, 
require a certain time for the adhesive to set and cure, which means that 
an automatic folding machine requires a special pressing station through 
which the boxes have to travel until the tape is securely glued to the 
substrate. This requirement constitutes an upper limit for the production 
rates of mechanized box making machinery where such a tape-sealing method 
is used. Ancillary problems encountered with this method are the 
well-known tendency of water-activatable adhesive tapes to curl, as a 
result of fluctuations in the ambient temperature and/or humidity 
conditions, and problems of adhesion encountered when the box panels are 
not entirely clean, as when their flaps carry dust on the outer surfaces. 
Similar shortcomings apply to the use of adhesive tapes of the 
self-adherent type (e.g. so-called masking tapes) which, because of their 
curling tendency, are entirely unsuitable for mechanized application. 
Much the same conditions apply to the closing operation on filled boxes, 
when the so-called "shipper's seal" is applied. In this operation, the 
abutting outer bottom flaps, or cover flaps, as the case may be, are 
connected together by means of wire staples, glue, adhesive tape, or 
masking tape, or the like. The problems encountered with the various 
sealing methods and materials are very similar to those described earlier 
in connection with the production of the "factory seal". 
On the other hand, it has already been proposed to produce the shipper's 
seal with the help of special adhesive tape, using a heat-activatable 
adhesive. The proposed adhesive has an activating temperature between 
50.degree. C. and 70.degree. C. The great disadvantage of this type of 
adhesive, however, is that it requires between 12 and 24 hours to cure. 
Such a long curing time, in turn, requires a correspondingly extended 
storage of the sealed boxes following closing, during which time the 
sealing tape must not be subjected to stress. This means considerable 
delays in terms of storing and shipping procedures, as well as changes in 
the production timing. Still another important shortcoming resides in the 
fact that the comparatively low activating temperature of the adhesive can 
lead to re-activation of the adhesive at temperatures as low as 50.degree. 
C., on particularly hot summer days, for example, so that special 
precautions need to be taken in terms of storage and shipping conditions 
for this type of box. 
Lastly, there is known a box sealing method using heat-activatable tape, 
where the tape is applied to its substrate by means of hot jaws or hot 
plates. The simultaneous application of pressure and heat through the hot 
plates produces a welding effect at the instant of application. A 
particular disadvantage of this taping method is that it can only be then 
performed satisfactorily, when a firm counter support is available, the 
operating rate of a machine being thus largely determined by the 
resistance of the substrate under the pressure of the hot plates. Modern 
box making machinery, however, operates at production rates at which there 
is not enough time available for this kind of adhesive tape to be applied 
securely and consistently to the boxes. 
SUMMARY OF THE INVENTION 
It is a primary objective of the present invention to propose a new method 
and an improved device for the tape-sealing of boxes and panels of paper, 
cardboard, plastic, wood, and the like, by means of heat-activatable 
adhesive tape, which method and device are suitable for mechanized 
production at high production rates, producing a durable resistant seal 
between the above materials in a simple, rapid operation. 
The present invention proposes to attain the above objectives, by 
suggesting the use of a heat-activatable adhesive-coated tape of delayed 
curing action, the adhesive on the tape being activated by means of 
directly or indirectly applied heat, after which the tape is promptly 
applied to the box flaps under moderate pressure. 
The proposed novel tape-sealing method completely eliminates all the 
disadvantages and shortcomings of the prior art box sealing methods 
mentioned earlier. The proposed method, using preferably a 
heat-activatable adhesive tape whose adhesive layer has an activating 
temperature of 100.degree. C. and above, also produces a very even 
activation of the adhesive layer, as the necessary heat is applied either 
indirectly, or directly, through radiation. The result is a very uniform 
adhesive bond between the tape and the substrate which is very durable and 
unaffected by extraneous influences. The high activating temperatures of 
the proposed adhesive not only offer a practically absolute safety against 
ambient conditions during storage, they also virtually preclude any 
failure of the adhesive bond through reactivation of the tape, once it has 
been applied to the box. The proposed sealing tape with its 
heat-activatable adhesive layer is also suitable for application onto 
coated cardboard surfaces for which all previously known tape-sealing 
methods have proved to be entirely unsuitable. The very high adherence 
obtainable with the novel tape further makes it possible to utilize 
plastic coated material for the tape itself. Consequently, the proposed 
novel tape-sealing method offers the possibility, for the first time, to 
produce absolutely humidity-proof box containers, using coated cardboard 
boxes which are tape-sealed in accordance with the method of this 
invention. 
The delayed curing action of the heat-activatable adhesive layer, in 
conjunction with the need for higher temperatures for the activation of 
the adhesive, produce operating conditions, under which the hot adhesive 
tape, contacting a cold substrate, produces an almost shock-like cooling 
effect on the adhesive upon contact with the cold box panel surface, 
resulting in a virtually instantaneous adherence of the tape to the panel 
surface. The very burdensome curing times previously required in 
connection with water-activatable adhesive tape or with thermo-adhesive 
tape are thereby entirely eliminated, as well as the special problems 
which are encountered when heat-activatable materials are applied with the 
use of hot plates and/or hot jaws. It follows from this that the immediate 
adherence of the tape to its substrate and the earlier-mentioned 
characteristic of the proposed adhesive to undergo delayed curing, in 
connection with the comparative simplicity of the operating steps 
involved, lend themselves for high production rates under this method. It 
is thus no longer necessary to consider the adherence of the tape to its 
substrate as a limiting factor in the selection of the operating speed of 
the machine. It was further found that the use of the novel 
heat-activatable adhesive tape brings with it a higher degree of 
uniformity in terms of adhesive activation, because of the higher 
temperatures employed and because of the possibility of applying the heat 
to the tape before it reaches the substrate. Lastly, because the novel 
tape is virtually unaffected by changes in ambient conditions during 
storage and use, it does not exhibit the curling tendency which is 
characteristic of prior art tapes. 
Although the proposed novel method offers a maximum of advantages, when 
applied in conjunction with the production of boxes of plastic coated 
cardboard, when producing factory seals on such blanks, it can, of course, 
also be used to great advantage for different purposes, such as the 
application of the shipper's seal to this type of plastic coated cardboard 
box, as well as for the sealing of other types of boxes and panels along 
abutting seams, including panels of such materials as corrugated board, or 
wood (veneer and plywood) used in similar applications. The adhesive may 
be activated by means of heated rollers or heated plates, or indirectly, 
by means of radiant heat. 
A preferred mode of heat-activating the adhesive tape involves the 
radiation of heat onto the tape by means of an infrared heater. Another 
convenient mode of heating the adhesive tape involves the use of a stream 
of hot air, whereby, under certain circumstances, the tape itself may 
simultaneously also be heated from its back side through heat convection, 
as when the tape is guided over a hot conveyor belt or over a hot 
conveying drum, or the like, while it moves through an activating zone in 
a box sealing machine. The simultaneous heating of the body of the tape 
has for its effect that more time may elapse between the activation of the 
adhesive and the application of the tape to its substrate, thus 
introducing a certain safety factor, without chaning the fact that the 
shock-like cooling of the adhesive upon contact with the intended 
substrate virtually immediately cures the adhesive.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1 of the drawings, there is illustrated a device for the 
tape-sealing of box containers of corrugated board, to which the so-called 
"factory seal" is being applied. The device consists essentially of a 
supply roll 1 from which a continuous length of sealing tape 2 is paid out 
over suitable guide rollers, to a cutting device 3, where the tape 2 is 
cut at certain intervals and stopped, so that successive tape lengths 4 
are fed at regular intervals to a tape conveyor belt 5 slanting downwardly 
away from the cutting device 3. The endless perforated conveyor belt 5 
runs over the perforated lower side of a vacuum box 6, thereby being 
capable of carrying a succession of tape lengths 4 on its lower side. As 
the tape lengths 4 move downwardly toward the lower end of the tape 
conveyor 5, corresponding box blanks 7 move horizontally toward the same 
point, being carried by a blank conveyor 8. 
Facing the lower side of the tape conveyor belt 5, and mounted on a machine 
frame 9, is a heater 10. The latter is preferably an infrared heater. The 
heater 10 is surrounded by a reflector housing 12 which is open toward the 
lower side of the tape conveyor belt 5, where a retractable screen 11 is 
interposed between the heater opening and the conveyor belt 5. 
As can be seen in FIGS. 2 and 3, where the infrared heater 10 and the 
retractable screen 11 are illustrated in greater detail, the screen 
assembly 11 consists essentially of two double-acting pneumatic cylinders 
13 and appropriate parallel guides carrying a flat, rectangular panel 
which, in the extended position of the cylinders 13, covers the opening of 
the infrared heater 10. The purpose of the screen 11 is to serve as a 
cover for the heater 10 against foreign objects and to protect the tape 
conveyor belt 5 against overheating during stillstand and between 
activation phases of the device. In the place of the pneumatic cylinders 
13 may also be used hydraulic cylinders, or suitable solenoids and 
springs. The intensity of heat radiation is adjustable in two ways: On the 
one hand, it is possible to adjust the distance between the infrared 
heater 10 and the tape conveyor belt 5 by means of an adjustment spindle 
16 (FIG. 3); on the other hand, one can adjust the heater output, using 
the heater output controls 17. The latter include manually adjustable 
controls as well as machine-speed-responsive automatic heater output 
controls. In a production machine, these controls may include special 
heater warm-up controls which, during an initial warm-up phase, switch the 
heater to maximum output, following which the output is automatically 
adjusted in accordance with the machine speed. 
In the movement plane of the box blanks 7 on the blank conveyor 8 are 
further arranged two opposing roller pairs 14a and 14b and a succession of 
roller pairs 15a and 15b, and a succession of roller pairs 15a and 15b, 
respectively. The rollers 14a double as guide rollers for the tape 
conveyor belt 5, the first pair 14a,b defining the point where the 
activated adhesive tape length 4 and the box panel 5 are joined. 
the device illustrated is designed for the automatic production of factory 
seals on box blanks. A regular succession of blanks 7 arrives horizontally 
between the roller pairs 14a and 14b, while a succession of tape lengths 4 
arrives in synchronous motion from above, moving through an adhesive 
activating zone between the infrared heater 10 and the tape conveyor belt 
5. As a tape length 4 enters the radiation zone of the heater 10, 
automatic controls actuate the cylinders 13 which retract the screen 11. 
The adhesive layer of the sealing tape 4, facing toward the heater 10, is 
not activated through direct heat radiation. No additional heating of the 
tape itself takes place. Before meeting with the box blank 7 between the 
roller pairs 14a,b, the activated tape length 4 leaves the activation 
zone, so that a shock-like cooling of the adhesive takes place, as it 
comes into contact with the cold surface of the box blank 7. To the extent 
that a portion of the tape conveyor belt 5 may have been heated through 
exposure to radiant heat from the heater 10, it is cooled again as it 
moves around the vacuum box 6. The controls for the screen 11 are set to 
automatically advance the latter between the heater 10 and the tape 
conveyor belt 5, should the supply of tape lengths 4 be interrupted for 
any reason. 
Referring now to FIG. 4, there is illustrated a second embodiment of the 
invention, showing a tape-sealing device which employs a modified method 
of the invention in connection with a box closing machine, applying the 
so-called "shipper's seal". This device also uses a different mode of 
heat-activating the adhesive of the sealing tape, the previously described 
infrared heater being replaced by a hot air activating system. 
The device of FIG. 4 consists essentially of a supply roll 20, holding a 
continuous length of adhesive tape 21. The latter is paid out from roll 20 
through the action of a tape feed roller 22, connected to a suitable drive 
(not shown) and cooperating with a retractable counter-roller 22a, 
controlled by a solenoid 22b. From the feed roller 22, the tape 21 travels 
to a cutting device 23, from where the cut tape length advances to a drum 
29 which will be described in more detail further below. A certain 
distance below the drum 29 is arranged a horizontal conveyor belt 24 which 
carries filled boxes 25 at regular intervals, the boxes passing just 
underneath the drum 29. 
The activation of each tape length takes place as it travels around the 
periphery of the vacuum drum 29 which, as the word implies, has a 
perforated peripheral surface 29a against which the adhesive tape 21 is 
held under suction, as it travels around the drum 29. The latter is 
rotatably supported on a hollow stationary shaft 28. Radial bores 28a in 
the wall of the shaft 28 transmit suction from the shaft to the inside of 
the drum. The effect of the vacuum is angularly limited, however, by means 
of two vacuum baffles 30 extending from the shaft 28 to near-contact with 
the inside of the vacuum drum 29. The vacuum baffles 30 thus subdivide the 
interior of the drum 29 into a vacuum chamber 31a, to which corresponds a 
suction range on the periphery of the drum 29, and an atmospheric chamber 
31b, to which corresponds a similar peripheral space of the drum 29 where 
no suction takes place. The cut tape length 21, arriving on the clockwise 
rotating drum periphery at about 9 o'clock, leaves that periphery at about 
4 o'clock. In this angular range, the drum periphery is substantially 
enclosed within a housing 38 to which is connected a tabular air nozzle 
26. Inside the latter is disposed a heater cartridge 27 by means of which 
air passing through the nozzle 26 into the housing 38 is heated. The 
blower (not shown) which supplies that air to the nozzle 26, via an air 
supply line 32, is preferably the same blower which also creates the 
suction for the vacuum chamber 31a of drum 29. While the latter may be 
operating on a continuous basis, the supply of heated air to the drum 
housing 38 is interruptable by means of a control clappet 33 arranged near 
the junction between the nozzle 26 and the housing 38. This control 
clappet is shown in enlarged detail in FIG. 5. An aperture 34 in the 
clappet is designed to supply a reduced amount of hot air to the drum 
surface, even when no tape, length 21 is present, so that the heated drum, 
in turn, will transfer heat to the body of the tape through heat 
convection. Where such heating of the tape itself is not desirable, the 
clappet aperture 34 is simply omitted, so that the supply of hot air to 
the drum surface is interrupted, as soon as the adhesive layer of the tape 
21 has been activated and the tape is leaving the suction range on the 
drum circumference. 
In FIG. 4 is further illustrated a known double-pendulum tape rolling 
device consisting of two tape rollers 36 and 36a mounted on pivotably 
supported pendulum arms 35 and 35a, respectively, which are operatively 
linked together by means of a linkage 37. 
The device of FIGS. 4 and 5, operates as follows: As a full box container 
25 approaches the adhesive activating drum 29, it operates, at a certain 
distance from the latter, a control switch for the drive solenoid 22b, 
thereby causing the counter-roller 22a to engage the adhesive tape 21 
against the drive roller 22 and to advance the tape against the drum 29. 
Simultaneously, the air control clappet 33 is switched from its bypass 
position (shown by dotted lines in FIG. 5) to its activating position 
(solid lines in FIG. 5), thereby opening the housing 38 of the drum to the 
hot air nozzle 26. The adhesive tape 21 reaches the drum 29 at its 
peripheral suction range so that the drum will now continue to advance the 
adhesive tape 21, and the drive solenoid 22b can be de-energized. 
While the tape length 21 moves past the air nozzle 26, hot air is blown 
against the upwardly facing adhesive layer of the tape 21. This causes the 
adhesive material to be activated, while heat is also transferred from the 
drum surface to the tape itself, which snugly contacts the drum under the 
effect of the vacuum. This supply of supplemental heat into the body of 
the tape itself assures a sufficiently long maintenance of the activation 
of the adhesive layer following movement of the latter out of the 
activation zone. At about 4 o'clock on the periphery of the drum, where a 
vacuum baffle 30 separates the vacuum chamber 31a from the atmospheric 
chamber 31b, the adhesive strip 21 leaves the periphery of the drum 29, 
being guided vertically downwardly by means of a guide bracket. 
Following payout of the required length of the adhesive tape 21 past the 
cutting device 23, through a corresponding angular motion of the vacuum 
drum 29, the cutting device 23 is activated through an appropriate switch 
in the path of the box 25. Due to the prior de-energization of the drive 
solenoid 22b, the leading edge of the uncut tape stops at the cutting 
device 23, while the cut tape length is fed around the vacuum drum 29, 
through the adhesive activating zone under the housing 38. 
The leading edge of the adhesive tape 21, leaving the surface of the drum 
29 at about 4 o'clock, moves downwardly in front of the tape roller 36, 
just before the front face of the box 25 reaches the downwardly extended 
roller. The movement of the box against the tape and the tape roller 36 
causes the latter to execute a clockwise pivoting motion around the upper 
leading edge of the box 25, as the latter advances under the drum 29. This 
pivoting motion of the roller 36 on its pendulum arm 35 produces a similar 
counterclockwise pivoting motion of the roller 36a and pendulum 35a, due 
to the connecting linkage 37, so that the two pendulum arms wind up 
extending toward each other, allowing the advancing box 25 to pass under 
the second tape roller 36a, as the first tape roller 36 applies pressure 
against the sealing tape on the box 25. The passage of the trailing edge 
of the box past the tape roller 36 frees the latter, at which point the 
tape roller 36a takes over the application of the tape against the box. 
Thus, as the trailing edge of the box moves past the roller 36a, the 
latter follows the box in a clockwise descending motion, thereby pressing 
the trailing portion of the adhesive tape against the back face of the box 
25. 
As soon as the activated adhesive tape 21 leaves the housing 38, the air 
controlled clappet 33 is returned to its bypass position (FIG. 5), thereby 
reducing the amount of air passing through the drum 29, through the now 
result of the uncovered perforations, to a value which is sufficient to 
maintain the desired drum temperature. 
The device illustrated and described hereinabove represents an embodiment 
of the inveniton which is designed to seal filled boxes on their upper 
closure seam, following prior sealing of the bottom seam. It should be 
understood, however, that both a bottom seal and a top seal could be 
applied in a modified device of the invention, a similar, inverted and 
perhaps slightly longitudinally offset second tape activating and applying 
unit being in this case arranged below the horizontal box conveyor. 
In FIGS. 6a, 6b, and 6c, are schematically illustrated cross sections of 
three different sealing tapes with heat-activatable adhesive layers, 
composed in accordance with the present invention. The three tape 
configurations have the following characteristics: 
The tape of FIG. 6a consists of two separate carrier layers 40 and 41 of 
paper, film, or some other suitable material, the two layers holding 
between them an intermediate layer with reinforcing fibers 42, the layers 
being glued together in a conventional manner. This multi-layer carrier 
tape carries on one of its outer faces a heat-activatable adhesive layer 
44, based on a thermoplastic or thermo-setting polymerisate, 
polycondensate, or polyadduct, or on an appropriately transformed natural 
plastic material. 
The tape version of FIG. 6b features a single-layer carrier tape 45 of any 
suitable material, to which a heat-activatable adhesive layer 46 is 
applied, reinforcing fibers 47 being embedded in the adhesive layer. The 
possibility of incorporating the reinforcing fibers directly in the 
heat-activatable adhesive layer has the additional advantage of assuring 
that the reinforcing fibers become intimately bonded to the substrate 
itself, thereby reinforcing the box flaps at the abutting joint, rather 
than reinforcing only the sealing tape, which then only indirectly 
represents a reinforcement of the box, through the intermediate of a 
carrier layer, e.g. layer 41 in FIG. 6a. 
The third tape version, shown in FIG. 6c, features a non-reinforced sealing 
tape consisting of a carrier web 48 of any suitable material and of a 
heat-activatable adhesive layer 49. 
It should be understood, of course, that the foregoing disclosure describes 
only preferred embodiments of the invention and that it is intended to 
cover all changes and modifications of these examples of the invention 
which fall within the scope of the appended claims.